94 articles found
Similarity Solutions of Two Dimensional Turbulent Boundary Layers
Bohua Sun
Subject: Physical Sciences, Fluids & Plasmas Keywords: Turbulent boundary layers; laminar boundary layers; similarity transformation; similarity solution; Prandtl mixing length; Reynolds number
The exact similarity solutions (also called as special exact solutions) of two dimensional laminar boundary layer were obtained by Blasius in 1908, however, no similarity solutions for two dimensional turbulent boundary layers have been reported in the literature. With the help of dimensional analysis and invariance principle, Prandtl mixing length $\ell=\kappa y$ for one dimensional turbulent boundary layer is extended to $\ell(x,y)=\kappa y (1-\frac{y}{\delta})\sqrt{\frac{\nu}{U\delta}} $ for the two dimensional turbulent boundary layers, furthermore, with a similarity transformation, we successfully transform the two dimensional turbulent boundary layers partial differential equations into a single ordinary differential equation $f'''+ ff''+\beta(1-f'^2)+\kappa^2[\eta^2(1-\eta)^2f''|f''|]'=0$. As an application, similarity solutions of the two dimensional turbulent boundary layer on a flat plate at zero incidence have been studied in detail. To solve the ordinary differential equation numerically, a complete Maple code is provided.
Similarity Solutions of Two Dimensional Turbulent Boundary Layers by Prandtl Mixing Length Modelling
The exact similarity solutions of two dimensional laminar boundary layer were obtained by Blasius in 1908, however, for two dimensional turbulent boundary layers, no similarity solutions (special exact solutions) have ever been found. In the light of Blasius' pioneer works, we extend Blasius similarity transformation to the two dimensional turbulent boundary layers, and successfully transform the two dimensional turbulent boundary layers partial differential equations into a single ordinary differential equation. By author's Maple code, we numerically solve the ordinary differential equation and produce some useful quantities.
Higher Order Wave Equation with Logarithmic Source Term
Sh. Hajrulla, L. Bezati, F. Hoxha
Subject: Mathematics & Computer Science, Applied Mathematics Keywords: global existence; damping; boundary source; logarithmic wave equation; initial boundary value problem; decay estimate
Online: 30 December 2017 (14:58:51 CET)
In this paper we study the initial boundary value problem for logarithmic Higher Order Wave equation. Introducing the Logarithmic Sobolev inequality and using the combination of Galerkin method, we consider the theorem of existence of a global weak solution to problem for the initial boundary value problem of the logarithmic wave equation. By constructing an appropriate Lyapunov function, we obtain the decay estimates of energy for logarithmic Higher Order Wave equation. The proof of the main theorem is given.
Coupling of the Earth's Surfaces to the Lower Atmospheres
David Roy Fitzjarrald
Subject: Earth Sciences, Atmospheric Science Keywords: turbulence and thermals; atmospheric boundary layer
Online: 19 July 2022 (10:49:15 CEST)
This brief review introduces some general properties of lower atmospheric motions that may be exploited by birds, linking historical findings and current knowledge from both observational and modeling perspectives. The relative importance of turbulent mixing resulting from wind shear and that from buoyant thermals is emphasized as well as the determinants of the geometry of the resulting vertical motions.
Flexibility Versus Certainty in Planning: A Critical Review of Cross-Boundary Spatial Planning Systems and Practices
Anutosh Das, Mohammad Shahriyar Parvez
Subject: Social Sciences, Accounting Keywords: Cross-Boundary Spatial Planning Systems and Practices
This research has critically argued that a vigilant combination of flexibility and certainty in spatial planning can bring about the most optimum planning outcomes. Therefore, to reproachfully evaluate the core argument, this research has tried to empirically respond to the research question of which balance of government intervention and market freedom produces the optimal economic, social and spatial outcomes. This research question has been further translated into an associated central hypothesis i.e., a hybrid planning system with an optimal balance between discretionary and regulatory planning approach can bring about the desired economic, social, and spatial outcomes.
An Approximate Solution to Prandtl's Equations for a Laminar Flow over an Infinite Horizontal Flat Plate
John Venetis
Subject: Physical Sciences, Mathematical Physics Keywords: boundary layer flow; flat plate; Prandtl's equations
Online: 10 October 2019 (07:45:58 CEST)
In this paper, a further mathematical analysis of some previous results of the author's ongoing investigation regarding Prandtl's equations is accomplished. In particular, the objective of the present work is the performance of an approximate explicit solution to Prandtl's system of equations for a laminar, isothermal, incompressible and steady boundary layer flow of a Newtonian fluid, over an infinite horizontal flat plate.
Effects of Unstable Stratification on Ventilation in Hong Kong
Tobias Gronemeier, Siegfried Raasch, Edward Ng
Subject: Keywords: convective boundary layer; LES; street-level ventilation
Online: 4 August 2017 (16:00:16 CEST)
Ventilation in cities is crucial for the well being of their inhabitants. Therefore, local governments require air ventilation assessments (AVAs) prior to the construction of new buildings. In a standard AVA, however, only neutral stratification is considered, although diabatic and particularly unstable conditions may be observed more frequently in nature. The results presented here indicate significant changes in ventilation within most of the area of Kowloon City, Hong Kong, included in the study. A new definition for calculating ventilation was introduced, and used to compare the influence of buildings on ventilation under conditions of neutral and unstable stratification. The overall ventilation increased due to enhanced vertical mixing. In the vicinity of exposed buildings, however, ventilation was weaker for unstable stratification than for neutral stratification. The influence on ventilation by building parameters, such as the plan area index, was altered when unstable stratification was considered. Consequently, differences in stratification were shown to have marked effects on ventilation estimates, which should be taken into consideration in future AVAs.
Decentralization and Transboundary Pollution: Evidence from the Change of Water Pollution Levels in China
Yongliang Yang, Manhong Shen
Subject: Social Sciences, Economics Keywords: Boundary effect; Transboundary pollution; Propensity Score Matching
Online: 20 March 2017 (17:33:38 CET)
Pollution spillover is an important issue to improve the water environment of transboundary rivers, which has been aggravated by the decentralization of China's pollution control and promotion system.This paper analyzes the evolution of the pollution reduction mandates and the possible change of water environment in China which are tested with the water quality data of state key monitoring sections in 2004-2014 .In terms of research methods, this paper mainly uses Propensity Score Matching reference with group difference test and OLS. Empirical findings support the association between decentralization and pollution levels. The pollution levels of the monitoring points located at the boundary are significantly higher than that of interior counties. The pollution of tributary is more serious than trunk stream,which quickly reversed after the system changed. Water pollution levels rapidly changes when we compare the monitoring site in front of jurisdictional boundaries with that after the jurisdictional boundaries. We draw the following conclusions that local goverments may manipulate pollution within their jurisdictions and total pollutant control system will exacerbate border pollution, while water quality inspection can reduce marginal pollution.
Black Hole Entropy from Non-Dirichlet Sectors, and Bounce Solution
Inyong Park
Subject: Physical Sciences, Acoustics Keywords: black hole entropy; non-Dirichlet boundary condition; bounce
Online: 23 September 2022 (02:06:59 CEST)
In a series of recent works the relevance of gravitational boundary degrees of freedom and their dynamics in gravity quantization and black hole information has been explored. In this work we further the progress by keenly focusing on the boundary degrees of freedom as the origin of black hole entropy. Wald's entropy formula is scrutinized, and the reason that the Wald's formula correctly captures the entropy of a black hole is examined. Afterwards, limitations of the Wald's method are discussed; a coherent view of entropy based on boundary dynamics is presented. The discrepancy observed in the literature between holographic and Wald's entropies is addressed. We generalize the entropy definition so as to handle a time-dependent black hole. Large gauge symmetry plays a pivotal role. Non-Dirichlet boundary conditions and gravitational analogues of Coleman-De Luccia bounce solutions are central in identifying the microstates and differentiating the origins of entropies associated with different classes of solutions. The result in the present work leads to a view that black hole entropy is entanglement entropy in a thermodynamic setup.
Gravitational, Electromagnetic and Quantum Interaction: From String to Cloud Theory
Mohammed B. Al-Fadhli
Subject: Physical Sciences, General & Theoretical Physics Keywords: Conformal Einstein Field Equations; Boundary Terms; Brane-World
Considerable efforts have been devoted to modifying gravity, which aim to elucidate the possible existence or nature of dark matter and dark energy, achieve a better description of observation data, verify theoretical restrictions in the strong curvature regime and to formulate quantum gravity. In addition, despite the enormous success of the quantum field theory, the framework requires the so-called renormalization techniques and breaks down at high energies. Recently, the Planck Legacy 2018 release has confirmed the presence of an enhanced lensing amplitude in the cosmic microwave background power spectra, which prefers a positively curved early Universe with a confidence level greater than 99%. This study considers the implied positive curvature of the early Universe as the curvature of 'the background or the 4D conformal bulk' and distinguishes it from the localized curvature that is induced into the bulk by the presence of comparably smaller celestial objects that are regarded as '4D relativistic cloud-worlds'. To consider the interaction between the bulk and cloud-worlds, this paper presents interaction field equations in terms of the brane-world modified gravity counting for the bulk conformal curvature and the boundary terms, which could remove the singularities and satisfy a conformal invariance theory. Similarly, the quantum fields and clouds are regarded as '4D relativistic branes' embedded in vacuum energy of a field strength reliant on the background curvature due to gravity. A visualization of the evolution of the 4D relativistic cloud-worlds over the conformal space-time of the 4D bulk is presented.
Parity Dependent Quantum Phase Transition in the Quantum Ising Chain in a Transverse Field
Daniel Sacco Shaikh, Maura Sassetti, Niccolò Traverso Ziani
Subject: Physical Sciences, Condensed Matter Physics Keywords: Ising model; quantum phase transitions; frustrated boundary conditions
Phase transitions- both in the classical and in the quantum version- are the perfect playground for appreciating universality at work. Indeed, the fine details become unimportant and a classification in very few universality classes is possible. Very recently, a striking deviation from this picture has been discovered: some antiferromagnetic spin chains with competing interactions show a different set of phase transitions depending on the parity of number of spins in the chain. The aim of this article is to demonstrate that the same behavior also characterizes the most simple quantum spin chain: the Ising model in a transverse field. By means of an exact solution based on a Wigner-Jordan transformation, we show that a first order quantum phase transition appears at zero applied field in the odd spin case, while it is not present in the even case. A hint of a possible physical interpretation is given by the combination of two fact: at the point of the phase transition, the degeneracy of the ground state in the even and the odd case substantially differ, being respectively 2 and 2N, with N the number of spins; the spin of the most favorable kink states changes at that point.
An Explanation and Understanding of Aerodynamic Lift by Triple Deck Theory
Alois Schaffarczyk
Subject: Engineering, Mechanical Engineering Keywords: Aerodynamic Lift; Boundary Layer Theory; Triple Deck Theory
Online: 9 November 2021 (14:52:31 CET)
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An explanation of aerodynamic lift still is under controversial discussion as can be seen, for example, in a recent published article in Scientific American [1]. In contrast to an approach via integral conservation laws we here review an approach via the classical Kutta-Condition and its relation to boundary layer theory. Thereby we summarize known results for viscous correction to the lift coefficient for thin aerodynamic profiles and try to remember the work on triple-deck or higher order Boundary Layer theory, its connection to interactive boundary layer theory, viscous/inviscid coupling as implemented to well-known engineering code Xfoil. Finally we compare its findings to simple 2D numerical solution of full Navier Stokes equations (CFD)models. As a conclusion, a clearer definition of terms like understanding and explanation applied to the phenomenon of aerodynamic lift will be given.
STEP-NC Based Squashing Slicing Algorithm for Multi-Material and Multi-Directional Additive Process
Jumyung Um, Joung min Park, Ian Anthony Stroud
Subject: Engineering, Automotive Engineering Keywords: Additive manufacturing, STEP-NC, Boundary representation, Multi-materials
The paper describes problems with the current additive manufacturing chain before considering additive manufacturing as part of a modern manufacturing chain. Additive manufacturing can be used for near net-shape for finishing, for repair or for adding special features which cannot be made with traditional manufacturing. This paper describes how STEP-NC deals with these different scenarios in terms of accuracy, multi-material and variation of slice direction. The possibilities of multi-material objects also raises questions about the design of such objects and how these need to be handled by an advanced controller. The paper also describes non-planar slicing. Curved direction and cylindrical direction are shown to improve the accuracy of curved structure additive manufacturing. STEP-NC using boundary representation has better capability of depicting complex internal structures for additive processes. By using exact model of the final product represented by STEP-NC, the paper demonstrates improvements in data size reduction, slicing accuracy, and precise manipulation of internal structure.
Preprint TECHNICAL NOTE | doi:10.20944/preprints202012.0179.v1
Practical Implementation of Molecular Dynamics Code for Beginners Using Python
Sumith Yesudasan
Subject: Engineering, Automotive Engineering Keywords: Python; Molecular Dynamics; Scientific Computing; Periodic Boundary Condition
Online: 8 December 2020 (06:47:59 CET)
In this paper, we introduce a simple yet powerful and working version of the molecular dynamics code using the Python 3.9 language. The code contents are published in the link given in the appendix 1. The structure and components of the program is given in detail using flowcharts and code snippets. The program consists of major features like velocity verlet integrator, thermostats, COM removal, input and output modules, virial, pressure, and other thermodynamic quantities estimation etc. The author believes that this program will be helpful to graduate students who perform research in molecular dynamics simulations who intend to write their own code instead of the sophisticated open source packages.
Investigation of Laminar-Turbulent Transition on a Rotating Wind Turbine Blade of Multi Megawatt Class with Thermography and a Microphone Array
Torben Reichstein, Alois Peter Schaffarczyk, Christoph Dollinger, Nicolas Balaresque, Erich Schuelein, Clemens Jauch, Andreas Fischer
Subject: Engineering, Energy & Fuel Technology Keywords: boundary layer transition; wind turbine; thermography; aerodynamic glove
Knowledge about laminar-turbulent transition on operating multi-megawatt wind turbine blades needs sophisticated equipment like hot-films or microphone arrays. Contrarily thermographic pictures can easily be taken from the ground and temperature differences indicate different states of the boundary layer. The accuracy however, still is an open question, so that an aerodynamic glove known from experimental research on aero-planes was used to classify the boundary-layer state of a 2 megawatt wind turbine blade operating in the orthern part of Schleswig-Holstein, Germany. State-of-the-art equipment for measurering static surface pressure was used for monitoring the lift distribution. To distinguish laminar and turbulent parts of the boundary layer (suction side only) 48 microphones were applied together with ground-based thermographic cameras from two teams. Additionally, an optical camera mounted on the hub was used to survey vibrations. During start-up (from 0 to 9 rpm) extended, but irregularly shaped regions of a laminar boundary layer were observed which had the same extension measured both with microphones and Thermography. When an approximately constant rotor rotation (9 rpm corresponding to approximately 6 m/s wind-speed) was achieved, a flow transition was visible at the expected position of 40 % chord length on the rotor blade, which was fouled with dense turbulent wedges and an almost complete turbulent state on the glove was detected. In all observations, quantitative determination of the flow transition positions from thermography and microphones agree well within their accuracy.
Using Non-Fourier's Heat Flux and Non-Fick's Mass Flux Theory in the Radiative and Chemically Reactive Flow of Powell-Eyring Fluid
Hina Firdous, Syed Tauseef Saeed, Hijaz Ahmed, Syed Muhammad Husnine
Subject: Mathematics & Computer Science, Computational Mathematics Keywords: Eyring-Powell fluid; Non-Fourier's heat flux and non-Fick's mass flux theory; Boundary layer flow; Radiation; Convective boundary conditions.
Online: 8 September 2021 (16:29:03 CEST)
The behavior of convective boundary conditions is studied to delineate their role in heat and mass relegation in the presence of radiation, chemical reaction, and hydromagnetic forces in three-dimensional Powell-Eyring nanofluids. Implications concerning non-Fourier's heat flux and non-Fick's mass flux with respect to temperature nanoparticle concentration were examined to discuss the graphical attributes of the principal parameters. An efficient optimal homotopy analysis method is used to solve the transformed partial differential equations. Tables and graphs are physically interpreted for significant parameters
An Entropic Approach for Pair Trading in PSX
Tanweer Ul Islam, Laiba Amer
Subject: Social Sciences, Business And Administrative Sciences Keywords: Pair Trading; Model uncertainty; Model risk; Optimal boundary; PSX
The perception in pair trading is to recognize two stocks that move together, and their prices will converge to a mean value in future. However, finding the mean-reverted point at which the value of the pair will converge, and optimal boundaries of the trade is not easy. As uncertainty and model misspecifications may lead to losses. To cater for the problems, this study employs the novel entropic approach that utilizes entropy as penalty function for the misspecification of the model. The use of entropy as a measure of risk in pair trading is a nascent idea and this study utilizes daily data for 64 companies listed on PSX for the years 2017, 2018, and 2019, respectively to compute the returns based on the entropic approach. These companies cover the major sectors including Cement, Chemical, Automobile Assembler, Food and Personal Care Products, Oil and Gas Marketing Companies, Oil and Gas Exploration Companies Ltd, Power Generation and Distribution, Refinery and Pharmaceuticals. The returns to these stocks are then evaluated and compared with the Buy and Hold strategy. The results show positive and significant returns from pair trading using an entropic approach.
Closed Form Solution of Plane-Parallel Turbulent Flow Along an Unbounded Plane Surface
Subject: Physical Sciences, Fluids & Plasmas Keywords: turbulent flow; Prandtl mixing length; Reynolds number; boundary layer
A century-old scientific conundrum is solved in this paper. The Prandtl mixing length modelled plane boundary turbulent flow is described by: $\frac{du^+}{d{y^+} }+\kappa^2{y^+} ^2\left( \frac{du^+}{d{y^+} }\right)^2=1$, together with boundary condition $ {y^+} =0:\, u^+=0$. Only an approximate solution to this nonlinear ordinary differential equation (ODE) has been sought so far, however, the exact solution to this ODE has not been obtained. By introducing a transformation, $2\kappa y^+=\sinh \xi$, I successfully find the exact solution of the ODE as follows: $u^+=\frac{1}{\kappa}\ln(2\kappa {y^+} +\sqrt{1+4\kappa^2{y^+} ^2})-\frac{2{y^+} }{1+\sqrt{1+4\kappa^2{y^+} ^2}}$.
The System of Differential Equations Associated With Involutions
Farrukh Nuriddin ugli Dekhkonov
Subject: Mathematics & Computer Science, General Mathematics Keywords: Involution; linear differential equation; fixed point; boundary value problem
In this paper, we consider with a class of system of differential equations whose argument transforms are involution. In this an initial value problem for a differential equation with involution is reduced to an initial value problem for a higher order ordinary differential equation. Than either two initial conditions are necessary for a solution, the equation is then reduced to a boundary value problem for a higher order ODE.
A Method of Solving Compressible Navier Stokes Equations in Cylindrical Coordinates Using Geometric Algebra
Terry E. Moschandreou
Subject: Mathematics & Computer Science, Applied Mathematics Keywords: cylindrical; geometric algebra; boundary layer; compressible flow; Hunter-Saxton
A method of solution to solve the compressible unsteady 3D Navier-Stokes Equations in cylindrical co-ordinates coupled to the continuity equation in cylindrical coordinates is presented in terms of an additive solution of the three principle directions in the radial, azimuthal and z directions of flow. A dimensionless parameter is introduced whereby in the large limit case a method of solution is sought for in the boundary layer of the tube. A reduction to a single partial differential equation is possible and integral calculus methods are applied for the case of a body force directed to the centre of the tube to obtain an integral form of the Hunter-Saxton equation. Also an extension for a more general body force is shown where in addition there is a rotational force applied.
Mechanical Modelling of Interfacial Phase in Coatings
Ri Xia, Mingchen Huo, Jinquan Xu
Subject: Materials Science, Surfaces, Coatings & Films Keywords: interfacial phase; interface model; displacement jump; boundary element method
Interface between matrix/coating or coating/coating in fact represents a very complicate thin interfacial layer. So interface model is necessary to avoid the difficulty on considering such a complicate thin layer in analysis. Classic interface model and cohesive model have been widely used in stress analysis of coating materials, though they cannot represent the effect of very thin interfacial layer accurately. A complete interface model has been deduced from the equivalent constitutive of interfacial layer in this paper. It is found that both classic interface model and cohesive model sometimes cannot give correct analysis results, while the complete interface model can always give a correct result. Moreover, the stress parallel to interface within the interfacial layer can also be analyzed by the new model. Besides, this model can also be used to describe the equivalent properties of interfacial layer, thereby, can provide a quantitative characterizing method for interfacial layer itself.
The Stable Operation Analysis of the DC Converter System into a Microgrid System, Taking into Account the Parameters of the Energy Source and the Own Parameters of the DC Converter
Denis Kotin, Ilya Ivanov
Subject: Engineering, Electrical & Electronic Engineering Keywords: DC Microgrid; DC-DC converter; stability analysis; stability boundary; CPL
In this paper, the authors consider the influence of the type of power supply and the internal parameters of the DC-DC converter on the stability of the system at constant power load. The stability of the system under consideration is important in the design and development of the power supply system for an autonomous consumer. Such a typical system can be a DC microgrid. In the work, when analyzing the stability of the system, the power source is not considered an ideal voltage source, but the active-inductive nature of the voltage source is taken into account, which is equivalent to using a synchronous machine with permanent magnets. The Rauss-Hurwitz algebraic criterion was used as a criterion for analyzing the stability of the system. This will make it possible to build and analyze the areas and boundaries of the system's stability. As a result, the areas and boundaries of the stability of the system were presented. The general trend towards the behavior of the zone of instability of the system was given. At the same time, dependences describing the boundaries of instability are presented, which are combinations of parameters of the DC-DC converter, beyond which the system becomes unstable. The presented definitions of the instability limits can be used as a corrective device of the control system to ensure the stability of the system in the upper limits of the power consumption.
Application of Local Gauge Theory to Fluid Mechanics - Part 2 Example: Basic Model of Tollmien-Schlichting Waves and Analytical Solution
Thomas Merz
Subject: Physical Sciences, Condensed Matter Physics Keywords: boundary layers; transition to turbulence; Navier–Stokes equations; local gauge
The gauge field equation for fluid mechanics established in Part 1 is developed into a first-order scattering theory in the simplified case of a two-dimensional incompressible flow over a flat plate. This is used to present a model for the origin of Tollmien-Schlichting (TS) waves based on scattering between fluid particles. As a result, analytical formulae for the maximum amplification factor and the transition point from laminar to turbulent flow in the boundary layer are obtained. The mathematical transformations from the stationary field equations in Part 1 to a scattering theory with time evolution along the flow axis using Wick rotation are elaborated in detail.
The Global Forest Transition is a Human Affair
Claude A. Garcia, Sini Savilaakso, René W. Verburg, Victoria Gutierrez, Sarah Jane Wilson, Cornelia B. Krug, Marieke Sassen, Brian E. Robinson, Hannah Moersberger, Babak Naimi, Jeanine M. Rhemtulla, Hélène Dessard, Valéry Gond, Cédric Vermeulen, Franck Trolliet, Johan Oszwald, Fabien Quétier, Stephan A Pietsch, Jean-Francois Bastin, Anne Dray, Jaboury Ghazoul, Patrick O. Waeber
Subject: Earth Sciences, Environmental Sciences Keywords: Forest transition, sustainable transformation, boundary objects, games, decision-making, agency
Online: 5 March 2020 (11:58:55 CET)
Forests across the world stand at the crossroad with climate and land use changes shaping their future. Despite the demonstration of political will and global efforts, forest loss, fragmentation and land degradation continue unabated. No clear evidence exists that these initiatives are working. Why are policies designed to halt deforestation and increase restoration of forest landscapes failing? A key reason for this apparent ineffectiveness lies in the failure to recognize the agency of the stakeholders involved and the adaptive capacities of the systems we seek to steer. Landscapes do not happen. We make them. They are the result of the sum of individual actions and decisions made by all stakeholders, and the interactions between these and biophysical processes. Likewise, forest transitions are not ecological, but social and behavioral. They are a product of the way humans manage ecosystems. Decision-makers need to integrate better representations of people's agency in their mental models. We suggest possible solution pathways to overcome this key current barrier. These involve eliciting mental models behind policy decision, changing perspectives to better understand divergent points of view and refining strategies through explicit theories of change. Games designed to represent the constraints and opportunities that exist in the landscapes can help decision makers in these task.
A Three Phase Model Charactering Low-Velocity Impact Response of SMA Reinforced Composites under Vibrating Boundary Condition
Mengzhou Chang, Fangyun Kong, Min Sun, Jian He
Subject: Materials Science, Polymers & Plastics Keywords: SMA reinforced composite; low-velocity impact; vibrating boundary; numerical analysis
Structural vibration induced by dynamic load or natural vibration is a nonnegligible factor in failure analysis. Based on vibrating boundary condition, impact resistance of shape memory alloy reinforced composites is investigated. In this investigation, modified Hashin's failure criterion, Brinson's model and visco-hyperelastic model are implemented into the numerical model to charactering the mechanical behavior of glass fiber/epoxy resin laminates, SMAs and interphase, respectively. First, fixed boundary condition is maintained in simulation to verify the accuracy of material parameters and procedures by comparing with experimental data. Then, a series of vibrating boundaries with different frequencies and amplitudes are applied during the simulation process to reveals the effect on impact resistances. The statistics of absorbed energy and contact force indicate that impact resistance of the composite under high frequency and large amplitude is lower than that under low frequency and small amplitude, and summarized by a mathematical expression.
Boundary-Element Analysis of Magnetic Polarization Tensor for Metallic Cylinder
Zhongwei Jin, ganghua qin, haidong fan, ruochen huang, ziqi chen, qian zhao, mingyang lu, zhijie zhang, anthony peyton, wuliang yin
Subject: Keywords: Boundary element method (BEM); magnetic polarization tensor; magnetic induction; dipole approximation
The magnetic polarization tensor has a promising capability of determining the geometry and material properties of metallic samples. In this paper, a novel computation method is proposed to estimate the magnetic polarization tensors for the metallic samples using the boundary element method. In this method, the metallic sample is placed in a uniformly distributed magnetic field. Based on assumptions that the excitation frequency and/or the conductivity of the sample is very high, the metallic sample is regarded as a perfect electrical conductor (PEC). Therefore, the scattered field at a certain distance can be simulated. By utilising the boundary element method, the magnetic polarization tensor can be derived from the simulated scattered field. The theoretical calculation is presented and simulations and experiments have been carried out to validate the proposed method. The results from the simulation are matched with the analytical solution for the case of sphere samples. Moreover, there is a good agreement between the simulation results and the experimental results for the copper cylindrical samples.
Stability and Stabilization of Ecosystem for Epidemic Virus Transmission Under Neumann Boundary Value Via Impulse Control
Ruofeng Rao
Subject: Mathematics & Computer Science, Algebra & Number Theory Keywords: Neumann boundary value; Laplacian semigroup; Poincare inequality lemma; impulse control; Lyapunov-Razumikhin method
In this paper, by using the variational method, a sufficient condition for the unique existence of the stationary solution of the reaction-diffusion ecosystem is obtained, which directly leads to the global asymptotic stability of the unique equilibrium point. Moreover, delayed feedback ecosystem with reaction-diffusion item is considered, and utilizing impulse control results in the globally exponential stability criterion of the delayed ecosystem. It is worth mentioning that the Neumann zero-boundary value that the infected and the susceptible people or animals should be controlled in the epidemic prevention area and not allowed to cross the border, which is a good simulation of the actual situation of epidemic prevention. And numerical examples illuminate the effectiveness of impulse control, which has a certain enlightening effect on the actual epidemic prevention work . That is, in the face of the epidemic situation, taking a certain frequency of positive and effective epidemic prevention measures is conducive to the stability and control of the epidemic situation. Particularly, the newly-obtained theorems quantifies this feasible step. Besides, utilizing Laplacian semigroup derives the $p$th moment stability criterion for the impulsive ecosystem.
Working Paper ARTICLE
Group Analysis of the Boundary Layer Equations in the Models of Polymer Solutions
Sergey V. Meleshko, Vladislav V. Pukhnachev
Subject: Mathematics & Computer Science, Applied Mathematics Keywords: symmetry; admitted Lie group; invariant solution; boundary layer equations; polymer solution
The famous Toms effect (1948) consists of a substantial increase of the critical Reynolds number when a small amount of soluble polymer is introduced into water. The most noticeable influence of polymer additives is manifested in the boundary layer near solid surfaces. The goal of the present paper is a group analysis of the boundary layer equations in two mathematical models of the flow of aqueous polymer solutions: the second grade fluid (Rivlin and Ericksen, 1955) and the model derived by Pavlovskii (1971). The equations of the unsteady two-dimensional boundary layer in the Pavlovskii and Rivlin-Ericksen models are analyzed for the first time here. These equations have no definite type so that finding their exact solutions is very important in order to understand the mathematical nature of the above mentioned models. The problem of group classification with respect to the arbitrary function of the longitudinal coordinate and time present in the equations, which sets the pressure gradient of the external flow, arises. All functions for which an extension of the admitted Lie group occurs are found. The task includes the ratio of two characteristic length scales. One of them is the Prandtl scale, and another is defined as the square root of the normalized coefficient of relaxation viscosity (Frolovskaya and Pukhnachev, 2018) and does not depend on the characteristics of the motion. The paper contains a number of exact solutions in the Pavlovskii model including a solution describing the flow near a critical point. Among the solutions of the new model of the boundary layer, a special place is taken by the solution of the stationary problem of flow around a rectilinear plate. Within the framework of the Prandtl theory of the boundary layer, such a solution was constructed by Blasius (1908). As is well-known, this solution has a non-removable defect: the transverse velocity near the edge of the plate increases without bound. The introduction of a relaxation term into the model makes it possible to eliminate this singularity.
Sodar Observation of the ABL Structure and Waves over the Black Sea Offshore Site
Vasily S. Lyulyukin, Margarita Kallistratova, Daria Zaitseva, Dmitry Kuznetsov, Arseniy Artamonov, Irina Repina, Igor Petenko, Rostislav Kouznetsov, Artem Pashkin
Subject: Earth Sciences, Atmospheric Science Keywords: breeze; sodar; atmospheric boundary layer; internal gravity waves; Kelvin-Helmholtz billows
The three-axes Doppler sodar Latan-3 operated on an oceanographic stationary platform in the coastal zone of the Black Sea in June 2015. The platform is located 450 meters offshore from the southern coast of the Crimea Peninsula in the region of Katsiveli (44.39°N, 33.99°E). The water depth at the site is about 30 meters. The atmospheric boundary layer (ABL) typical for the mediterranean seas was observed when the wind is from the sea. The physical processes typical for the coastal mountain terrain was observed when the wind was from the shore. Complex measurements of the ABL parameters were performed using a sodar. Auxiliary measurements of the ABL parameters were performed using a temperature profiler and an ultrasonic thermometer-anemometer. Observations were made mostly during a fair weather with a pronounced diurnal course of meteorological parameters. Sodar data analysis revealed a strong wave activity in the ABL. Internal gravity waves with amplitudes of up to one hundred meters were regularly observed in a layered turbulence structure under stable conditions. Various forms of Kelvin-Helmholtz billows were observed at the interface between the sea breeze and the return flow aloft and in the low level jets.
Comparison of Smallest Eigenvalues for Nabla Fractional Boundary Value Problems
Jagan Mohan Jonnalagadda
Subject: Mathematics & Computer Science, Analysis Keywords: nabla fractional difference; boundary value problem; cone; u0- positive operator; eigenvalue
In this article, we establish the existence of and then compare smallest eigenvalues for nabla fractional boundary value problems involving a fractional difference boundary condition, using the theory of u0-positive operators with respect to a cone in a Banach space.
Scaling Group Analysis of Mixed Bioconvective Flow in Nanofluid with Presence of Slips, MHD and Chemical Reactions
Mohd Faisal Mohd Basir, M. Jashim Uddin, Ahmad Izani Md. Ismail
Subject: Physical Sciences, Mathematical Physics Keywords: Bioconvection, Magnetohydrodynamics, Scaling group of transformations, Slip boundary conditions, Chemical reaction
Online: 5 October 2018 (11:39:39 CEST)
Bioconvective flows have attracted attention in recent years due to actual and potential applications. In this paper, we consider a steady and laminar convective MHD flow of a nanofluid with heat, mass and microorganism transfer with a heat source/sink present. In addition, we assume there exists a first order chemical reaction. The governing partial differential equations (PDEs) are reduced to ordinary differential equations (ODEs) using the scaling group transformation and the associated boundary value problem is then solved. The influences of selected governing parameters on the dimensionless velocity, temperature, nanoparticle concentration, density of motile microorganisms, skin friction, heat transfer, mass transfer, and motile microorganism density rates are computed and discussed
Ab Initio Molecular Dynamics Simulation of Tribochemical Reactions Involving Phosphorus Additives at Sliding Iron Interfaces
Sophie Loehlé, M. C. Righi
Subject: Materials Science, Surfaces, Coatings & Films Keywords: lubricant additives; boundary lubrication; ab initio molecular dynamics; tribochemistry; organophosphorus additives
We performed for the first time to our knowledge fully ab initio molecular dynamics simulations of additive tribochemistry in boundary lubrication conditions. We consider an organophosphourus additive that has been experimentally shown to reduce friction in steel-on-steel sliding contacts thanks to the tribologically-induced formation of an iron phosphide tribofilm. The simulations allow us to observe in real time the molecular dissociation at the sliding iron interface under pressure and to understand the mechanism of iron phosphide formation. We discuss the role played by the mechanical stress by comparing the activation times for molecular dissociation observed in the tribological simulations at different applied loads with that expected on the basis of the dissociation barrier.
Incompatibility Stresses and Lattice Rotations Due to Grain Boundary Sliding in Heterogeneous Anisotropic Elasticity
Thiebaud Richeton
Subject: Materials Science, Metallurgy Keywords: grain boundary sliding; incompatibility stresses; anisotropic elasticity; heterogeneous elasticity; lattice rotations
Online: 1 May 2017 (09:06:32 CEST)
Non-uniform grain boundary sliding can induce strain and rotation incompatibilities at perfectly planar interfaces. Explicit analytic expressions of stress and lattice rotation jumps are thus derived at a planar interface in the general framework of heterogeneous anisotropic thermo-elasticity with plasticity and grain boundary sliding. Both elastic fields are directly dependent on in-plane gradients of grain boundary sliding. It is also shown that grain boundary sliding is a mechanism that may relax incompatibility stresses of elastic, plastic and thermal origin although the latter are not resolved on the grain boundary plane. This relaxation may be a driving force for grain boundary sliding in addition to the traditionally considered local shears on the grain boundary plane. Moreover, the obtained analytic expressions are checked by different kinds of bicrystal shearing finite element simulations allowing grain boundary sliding and where a pinned line in the interface plane aims at representing the effect of a triple junction. A very good agreement is found between the analytic solutions and the finite element results. The performed simulations particularly emphasize the role of grain boundary sliding as a possible strong stress generator around the grain boundary close to the triple line because of the presence of pronounced gradients of sliding.
Elastodynamic Behaviour of Laminate Structures with Soft Thin Interlayers: Theory and Experiment
Maria V. Wilde, Mikhail V. Golub, Artem A. Eremin
Subject: Engineering, Mechanical Engineering Keywords: laminate; soft material; thin interlayer; guided waves; edge waves; effective boundary conditions
Online: 13 January 2022 (18:45:28 CET)
Laminate structures composed of stiff plates and thin soft interlayers are widely used in aerospace, automotive and civil engineering encouraging the development of reliable non-destructive strategies for their condition assessment. In the paper, elastodynamic behaviour of such laminate structures is investigated with emphasis on its application in ultrasonic based NDT and SHM for the identification of interlayer mechanical and interfacial contact properties. A particular attention is given to the practically important frequency range, in which the wavelength considerably exceeds the thickness of the film. Three layer model with spring-type boundary conditions employed for imperfect contact simulation is used for numerical investigation. Novel effective boundary conditions are derived via asymptotic expansion technique and used for analysis of the peculiar properties of elastic guided waves in considered laminates. It is revealed that the thin and soft film influences the behaviour of the laminate mainly via the effective stiffnesses being a combination of the elastic moduli of the film, its thickness and interface stiffnesses. To evaluate each of these parameters separately (or to figure out that the available experimental data are insufficient), a step-wise procedure employing the effective boundary conditions is proposed and tested versus the laser Doppler vibrometry data for Lamb waves in Aluminium/Polymer film/Alumunium structure. The possibility of using film-related thickness resonance frequencies to estimate the film properties and contact quality is also demonstrated. Additionally, the rich family of edge waves is also investigated, and the splitting of fundamental edge waves into pairs is revealed.
Solving Prandtl-Blasius Boundary Layer Equation Using Maple
Subject: Physical Sciences, Fluids & Plasmas Keywords: Prandtl boundary layer; Prandtl-Blasius equation; numerical solution; Runge-Kutta method; Maple
A solution for the Prandtl-Blasius equation is essential to all kinds of boundary layer problems. This paper revisits this classic problem and presents a general Maple code as its numerical solution. The solutions were obtained from the Maple code, using the Runge-Kutta method. The study also considers convergence radius expanding and an approximate analytic solution is proposed by curve fitting. Similarly, the study resolves some boundary layer related problems and provide relevant Maple codes for these.
Taming the Natural Boundary of Centered Polygonal Lacunary Functions: Restriction to the Symmetry Angle Space
L.K. Mork, Keith Sullivan, Darin J. Ulness
Subject: Mathematics & Computer Science, Analysis Keywords: lacunary function; gap function; centered polygonal numbers; Natural boundary; singularities; broom topology
Online: 19 February 2020 (11:43:50 CET)
This work investigates centered polygonal lacunary functions restricted from the unit disk onto symmetry angle space which is defined by the symmetry angles of a given centered polygonal lacunary function. This restriction allows for one to consider only the p-sequences of the centered polygonal lacunary functions which are bounded, but not convergent, at the natural boundary. The periodicity of the $p$-sequences naturally gives rise to a convergent subsequence, which can be used as a grounds for decomposition of the restricted centered polygonal lacunary functions. A mapping of the unit disk to the sphere allows for the study of the line integrals of restricted centered polygonal that includes analytic progress towards closed form representations. Obvious closures of the domain obtained from the spherical map lead to four distinct topological spaces of the "broom topology'' type.
Navigation Algorithm Based on the Boundary Line of New and Old Soil Combined Using Guided Filtering and Improved Anti-noise Morphology
Wei LU, Mengjie Zeng, Ling WANG, Hui LUO, Subrata Mukherjee, Xuhui Huang, Yiming DENG
Subject: Engineering, Other Keywords: intelligent tractor; vision navigation; improved anti-noise morphology; boundary line; Guided Filtering
An improved anti-noise morphology vision navigation algorithm is proposed for intelligent tractor tillage in a complex agricultural field environment. At first the two key steps, Guided Filtering and improved anti-noise morphology navigation line extraction were addressed in detail. Then the experiments were carried out in order to verify the effectiveness and advancement of the presented algorithm. Finally, the optimal template and it's application condition were studied for improving the image processing speed. The comparison experiment results show that the YCbCr color space has minimum time consumption of 0.094 s in comparison with HSV, HIS and 2R-G-B color spaces. The Guided Filtering method can effectively distinguish the boundary between the new and old soil than other competing vanilla methods such as Tarel, Multi-scale Retinex, Wavelet-based Retinex and Homomorphic Filtering inspite of having the fastest processing speed of 0.113 s. The extracted soil boundary line of the improved anti-noise morphology algorithm has best precision and speed compared with other operators such as Sobel, Roberts, Prewitt and Log. After comparing different size of image template, the optimal template with the size of 140×260 pixels can meet high precision vision navigation while the course deviation angle is not more than 7.5°. The maximum tractor speed of the optimal template and global template are 51.41 km/h and 27.47 km/h respectively which can meet real-time vision navigation requirement of the smart tractor tillage operation in the field. The experimental vision navigation results demonstrated the feasibility of the autonomous vision navigation for tractor tillage operation in the field using the new and old soil boundary line extracted by the proposed improved anti-noise morphology algorithm which has broad application prospect.
Navigation Algorithm Based on the Boundary Line of New & Old Soil Using Improved Anti-Noise Morphology
Wei Lu, Mengjie Zeng, Ling Wang, Hui Luo, Yiming Deng
Subject: Engineering, Control & Systems Engineering Keywords: intelligent tractor; vision navigation; improved anti-noise morphology; boundary line; Guided Filtering
An improved anti-noise morphology vision navigation algorithm is proposed for intelligent tractor tillage in a complex agricultural field environment. Firstly, the two key steps, Guided Filtering and improved anti-noise morphology navigation line extraction, were addressed in detail. Then the experiments were carried out in order to verify the effectiveness and advancement of the presented algorithm. Finally, the optimal template and its application condition were studied for improving the image processing speed. The comparison experiment results show that the YCbCr color space has minimum time consumption, 0.094 s, compared with HSV, HIS and 2R-G-B color spaces. The Guided Filtering method can enhance the new & old soil boundary effectively than any other methods such as Tarel, Multi-scale Retinex, Wavelet-based Retinex and Homomorphic Filtering, meanwhile, has the fastest processing speed of 0.113 s. The extracted soil boundary line of the improved anti-noise morphology algorithm has best precision and speed compared with other operators such as Sobel, Roberts, Prewitt and Log. After comparing different size of image template, the optimal template with the size of 140×260 pixels can meet high precision vision navigation while the course deviation angle is not more than 7.5°. The maximum tractor speed of the optimal template and global template are 51.41 km/h and 27.47 km/h respectively which can meet real-time vision navigation requirement of the smart tractor tillage operation in the field. The experimental vision navigation results demonstrated the feasibility of the autonomous vision navigation for tractor tillage operation in the field using the new & old soil boundary line extracted by the proposed improved anti-noise morphology algorithm which has broad application prospect.
Three-Dimensional Cloud Volume Reconstruction from the Multi-Angle Imaging SpectroRadiometer
Byungsuk Lee, Larry Di Girolamo, Guangyu Zhao, Yizhe Zhan
Subject: Earth Sciences, Atmospheric Science Keywords: MISR; cloud volume; cloud geometry; cloud shape; cloud boundary; cloud volume reconstruction.
Abstract: Characterization the 3-D structure of clouds is needed for a more complete understanding of the Earth's radiative and latent heat fluxes. Here we develop and explore a "ray casting" algorithm applied to the Multi-angle Imaging SpectroRadiometer (MISR) on board the Terra satellite, to reconstruct 3-D cloud volumes for observed clouds. The ray casting algorithm is first applied to geometrically simple synthetic clouds to show that, under the assumption of perfect, clear-conservative cloud masks, the reconstruction method yields overestimation whose magnitude depends on the cloud geometry and the resolution of the reconstruction grid relative to the image pixel resolution. The method is then applied to two select MISR scenes, fully accounting for MISR's viewing geometry for reconstructions over the Earth's ellipsoidal surface. The MISR Radiometric Camera-by-camera Cloud Masks at 1.1 km resolution and custom cloud masks at 275 m resolution independently derived from MISR RGB channels are used as input cloud masks. A wind correction method, termed "cloud spreading", is devised and applied to the cloud masks to offset potential cloud movements over short time intervals (around 7 minutes at maximum) between the cameras. The MISR cloud top height product is used as a constraint to reduce the overestimation at the cloud top. The reconstruction results show that their uncertainty is significant when the wind correction is applied, and that they have more refined structures when the input cloud mask has a higher resolution. Recommendations for improving the presented cloud volume reconstructions as well as for future passive remote sensing satellite missions are discussed.
Chebfun Solutions to a Class of 1D Singular and Nonlinear Boundary Value Problems
Călin-Ioan Gheorghiu
Subject: Mathematics & Computer Science, Computational Mathematics Keywords: Chebfun; differential equation; non-linearity; singularity; convergence; Bernstein growth; improper integrals; boundary layer
The Chebyshev collocation method (ChC) implemented as Chebfun is used in order to solve a class of second order one-dimensional singular and genuinely nonlinear boundary value problems. Efforts to solve these problems with conventional ChC have generally failed, and the outcomes obtained by finite differences or finite elements are seldom satisfactory. We try to fix this situation using the new Chebfun programming environment. However, for toughest problems we have to loosen the default Chebfun tolerance in Newton's solver as the ChC runs into trouble with ill-conditioning of the spectral differentiation matrices. Although in such cases the convergence is not quadratic the Newton updates decrease monotonically. This fact, along with the decreasing behaviour of Chebyshev coefficients of solutions, suggests that the outcomes are trustworthy, i.e., the collocation method has exponential (geometric) rate of convergence or at least an algebraic rate. We consider first a set of problems that have exact solutions or prime integrals and then another set of benchmark problems that do not possess these properties. Actually, for each test problem carried out we have determined how Chebfun solution converges, its length, the accuracy of the Newton method and especially how well the numerical results overlap with the analytical ones (existence and uniqueness).
The Effect of Open Boundaries on the Buoyant Viscoelastic Flow in a Vertical Porous Layer
Stefano Lazzari, Michele Celli, Antonio Barletta
Subject: Engineering, Mechanical Engineering Keywords: Buoyant convection; Porous medium; Oldroyd–B viscoelastic fluid; Linear stability analysis; Open boundary
The Oldroyd–B model for a linear viscoelastic fluid is employed to investigate the buoyant flow in a vertical porous layer with permeable boundaries kept at different uniform temperatures. Seepage flow in the viscoelastic fluid saturated porous layer is modelled through an extended version of Darcy's law taking into account the Oldroyd–B rheology. The basic stationary flow is parallel to the vertical axis and describes a single–cell vertical pattern where the cell has an infinite vertical height. A linear stability analysis of such a basic flow is carried out to determine the onset conditions for a multicellular pattern. The neutral stability curves and the values of the critical Rayleigh number are evaluated numerically for different retardation time and relaxation time characteristics of the fluid.
Computational Analysis of Haemodynamic Indices in Synthetic Atherosclerotic Coronary Netwroks
Sergey Simakov, Timur Gamilov, Philipp Kopylov, Fuyou Liang
Subject: Mathematics & Computer Science, Algebra & Number Theory Keywords: 1D haemodynamics, stenosis, systole variations, coronary circulation, tachycardia, boundary conditions, FFR, CFR, iFR.
Haemodynamic indices are widely used in clinical practice for deciding on a particular type of treatment. Low quality of the CT data and tachycardia complicate interpretation of the measured or simulated values. In this work, we present a novel approach for evaluating resistances in terminal coronary arteries. Using 14 measurements from 10 patients, we show that this algorithm retains the accuracy of 1D haemodynamic simulations in less detailed (truncated) geometric models of coronary networks. We also apply the variable systole fraction model to study the effect of elevated heart rate on the values of FFR, CFR and iFR. We conclude that tachycardia may produce both overestimation or underestimation of coronary stenosis significance.
A Polygonal Scaled Boundary Finite Element Method for Solving Heat Conduction Problems
Yang Yang, Zongliang Zhang, Yelin Feng, Yuzhen Yu, Kun Wang, Lihui Liang
Subject: Engineering, Automotive Engineering Keywords: Scaled boundary finite element method; Heat conduction; Abaqus UEL; Polygon; Quadtree; Semi-analytic
This paper presents a steady-state and transient heat conduction analysis framework using the polygonal scaled boundary finite element method (PSBFEM) with polygon/quadtree meshes. The PSBFEM is implemented with commercial finite element code Abaqus by the User Element Subroutine (UEL) feature. The detailed implementation of the framework, defining the UEL element, and solving the stiffness/mass matrix by the eigenvalue decomposition are presented. Several benchmark problems from heat conduction are solved to validate the proposed implementation. Results show that the PSBFEM is reliable and accurate for solving heat conduction problems. Not only can the proposed implementation help engineering practitioners analyze the heat conduction problem using polygonal mesh in Abaqus, but it also provides a reference for developing the UEL to solve other problems using the scaled boundary finite element method.
A Major Impact of WRF Planetary Boundary Layer Schemes on Simulation Accuracy of Vertical Wind Structure by 3D Doppler Wind Lidar
Lei Zhang, Jinyuan Xin, Yan Yin, Wenyuan Chang, Min Xue, Danjie Jia, Yongjing Ma
Subject: Earth Sciences, Atmospheric Science Keywords: 3D Doppler Wind Lidar; planetary boundary layer; vertical wind; wind speed; wind direction
The accuracy of wind field simulation and prediction is one of the most significant parameters in the field of atmospheric science and wind energy. Limited by the observation data, there are few researches on wind energy development. A 3D Doppler wind lidar (DWL) providing the high-vertical-resolution wind data over the urban complex underlying surface in February 2018 was employed to evaluated the accuracy of vertical wind field simulation systematically for the first time. 11 PBL schemes of the Weather Research and Forecasting Model (WRF) were employed in simulation. The model results were evaluated in groups separated by weather (sunny days, haze days and windy days), observation height layers, and various observation wind speeds. The test results presented that the vertical layer altitude of the observation point position was the most important factor. The simulation is fairly well at a height of 1000-2000m, as most of the relative mean bias of wind speed and wind direction are less than 20% and 6% respectively. Below 1000 m, the wind speed and direction biases are about 30%-150% m.s-1 and 6%-30% respectively. Moreover, when the observed wind speed was lower than 5 m.s-1, the bias were usually large, and the wind speed relative mean bias is up to 50-300%. In addition, the accuracy of simulated wind profile is better in 10-15m.s-1 than other speed ranges, and is better up 1000m than below 1000m in the boundary layer. We see that the WRF boundary layer schemes have different applicability to different weather conditions. The WRF boundary layer schemes have significant differences in wind field simulation with larger error under the complex topography. A PBL scheme is not likely to maintain its advantages in the long term under different conditions including altitude and weather conditions.
Measurement Problem in Quantum Mechanics\\ and the Surjection Hypothesis
Fritz W. Bopp
Subject: Physical Sciences, General & Theoretical Physics Keywords: quantum measurements; two boundary interpretation of quantum mechanics; surjection interpretation of quantum mechanics
Starting with unitary quantum dynamics, we investigate how to add quantum measurements. Quantum measurements have four essential components: the furcation, the witness production, an alignment projection, and the actual choice decision. The first two components still lie in the domain of unitary quantum dynamics. The decoherence concept explains the third contribution. It can be based on the requirement that witnesses reaching the end of time on the wave function side and the conjugate one have to be identical. In this way, it also stays within the quantum dynamics domain. The surjection hypothesis explains the actual choice decision. It is based on a two boundary interpretation applied to the complete quantum universe. It offers a simple way to reduce these seemingly random projections to purely deterministic unitary quantum dynamics, eliminating the measurement problem.
Spatiotemporal Dynamics of the Kinetic Energy in the Atmospheric Boundary Layer from Minisodar Measurements
Alexander Potekaev, Liudmila Shamanaeva, Valentina Kulagina
Subject: Earth Sciences, Atmospheric Science Keywords: atmospheric boundary layer; spatiotemporal dynamics of the atmospheric kinetic energy; turbulence; minisodar measurements
Spatiotemporal dynamics of the atmospheric kinetic energy and its components caused by the ordered and turbulent motions of air masses are estimated from minisodar measurements of three velocity vector components and their variances within the lowest 5–200 m layer of the atmosphere, with a particular emphasis on the turbulent kinetic energy. The layered structure of the total atmospheric kinetic energy has been established. From the diurnal hourly dynamics of the altitude profiles of the turbulent kinetic energy (TKE) retrieved from minisodar data, four layers are established by the character of the altitude TKE dependence, namely, the near-ground layer, the surface layer, the layer with a linear TKE increase, and the transitive layer above. In the first layer, the most significant changes of the ТКЕ were observed in the evening hours. In the second layer, no significant changes in the TKE values were observed. A linear increase in the TKE values with altitude was observed in the third layer. In the fourth layer, the TKE slightly increased with altitude and exhibited variations during the entire observation period. The altitudes of the upper boundaries of these layers depended on the time of day. The MKE values were much less than the corresponding TKE values, they did not exceed 50 m2/s2. From two to four MKE layers were distinguished based on the character of its altitude dependence. The two-layer structures were observed in the evening and at night (under conditions of the stable atmospheric boundary layer). In the morning and daytime, the four-layer MKE structures with intermediate layers of linear increase and subsequent decrease in the MKE values were observed. Our estimates demonstrated that the ТКЕ contribution to the total atmospheric kinetic energy considerably (by a factor of 2.5–3) exceeded the corresponding МКЕ contribution.
Using Dielectric Relaxation Spectroscopy to Characterize the Glass Transition and Onset of Crystallinity of Skim-Milk Powder
Martin G. Buehler
Subject: Chemistry, Food Chemistry Keywords: DRS dielectric relaxation; DSC differential scanning calorimetry; SMP skim milk powder; boundary curves
Online: 9 April 2018 (10:22:24 CEST)
This paper describes the dielectric relaxation spectroscopy (DRS) method for obtaining glass transition temperature and the onset of crystallinity of skim milk powder (SMP). The methodology consists of exposing SMP samples to numerous constant temperatures, T, and water activities, aw, and measuring the relaxation time. Measurements are based on changes in the loss-tangent height at its peak frequency. Glass transition times are identified at peaks in the loss-tangent height versus time curve and the onset of crystallinity times are identified when the loss-tangent height collapses. The analysis leads to two boundary curves: glass transition Tg, aw curve and the onset of crystallinity Tc, aw curve. They separate the SMP stable (long shelf life) and unstable (short shelf life) regions. Two curve fitting algorithms were developed for (a) aw2, tg curve where tg is the time to glass transition and aw2, tc curve where time tc is the time to onset of crystallinity and (b) Tg, aw and Tc, aw boundary curves. Finally, the DRS data are compared to differential scanning calorimetry (DSC) results.
Marine Turbine Hydrodynamics by a Boundary Element Method with Viscous Flow Correction
Francesco Salvatore, Zohreh Sarichloo, Danilo Calcagni
Subject: Engineering, Marine Engineering Keywords: marine current turbines; hydrodynamics; boundary element methods; trailing wake models; viscous flow correction
A computational methodology for the hydrodynamic analysis of horizontal axis marine current turbines is presented. The approach is based on a boundary integral equation method for inviscid flows originally developed for marine propellers and adapted here to describe the flow features that characterize hydrokinetic turbines. To this purpose, semi-analytical trailing wake and viscous-flow correction models are introduced. A validation study is performed by comparing hydrodynamic performance predictions with two experimental test cases and with results from other numerical models in the literature. The capability of the proposed methodology to correctly describe turbine thrust and power over a wide range of operating conditions is discussed. Viscosity effects associated to blade flow separation and stall are taken into account and predicted thrust and power are comparable with results of blade element methods that are largely used in the design of marine current turbines. The accuracy of numerical predictions tend to reduce in cases where turbine blades operate in off-design conditions.
About the Ultimate Efficiency of Interference Binary Codes
Artem Sergeevich Adzhemov, Nicolay Yurievich Albov
Subject: Engineering, Electrical & Electronic Engineering Keywords: Code construction; minimum code distance; noise immunity; coding efficiency; theoretically achievable boundary; correction codes
The digital representation of various signals allows, at the subsequent stages of their transmission, to apply correction codes that provide protection against possible errors arising from the action of interference in the communication channel. At the same time, it is important that, with the required correcting ability, these codes have the maximum possible speed. The article presents the results of calculations for linear codes, showing their really achievable limiting capabilities.
Functionally Graded Plate Fracture by Field Boundary Element
Simone Palladino, Luca Esposito, Paolo Ferla, Renato Zona, Vincenzo Minutolo
Subject: Engineering, Automotive Engineering Keywords: Functionally Graded Materials; FGM; Field Boundary Element Method; FBEM; Interface; Stress intensity factor; SIF
The paper describes the Field Boundary Element Method applied to the fracture analysis of a 2D rectangular plate made of Functionally Graded Material to calculate Mode I Stress Intensity Factor. The object of the Field Boundary Element Method is the transversely isotropic plane plate. Its material presents an exponential variation of the elasticity tensor depending on a scalar function of position, i.e., the elastic tensor results from multiplying a scalar function by a constant taken as a reference. Several examples using a parametric representation of the structural response show the suitability of the method that constitutes a sight of Stress Intensity Factor evaluation of Functionally Graded Materials plane plates even in the case of more complex geometries.
THz Properties of Long YBaCuO Bicrystal Josephson Junction Studied with a Cold-Electron Bolometer
Andrey Pankratov, Leonid Revin, Anna Gordeeva, Dmytry Masterov, Alexey Parafin, Viktor Zbrozhek, Leonid Kuzmin
Subject: Physical Sciences, Condensed Matter Physics Keywords: anisotropic high-$T_c$ grain-boundary; YBCO Josephson oscillator; cold-electron bolometer; sine-Gordon equation
The response of the Cold-Electron Bolometers (CEBs), integrated into a 2-D array of dipole antennas, has been measured by irradiation from YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) 50 $\mu$m long Josephson junction into the THz region at frequencies from 0.1 to 0.8 THz. The possibility of controlling the amplitude-frequency characteristic is demonstrated by the external magnetic field in the traveling wave regime of a long Josephson junction. YBCO junction has been formed on the bicrystal Zr$_{1-x}$Y$_x$O$_2$ (YSZ) substrate by magnetron sputtering and etching of the film. CEBs have been fabricated using an Al multilayer structure by a self-aligned shadow evaporation technique on Si substrate. Both receiver and oscillator have been located inside the same cryostat at 0.3K and 2.7K plates, respectively.
Existence Results for Nonlinear Fractional Problems with Non-Homogeneous Integral Boundary Conditions
Alberto Cabada, Om Kalthoum Wanassi
Subject: Mathematics & Computer Science, Analysis Keywords: Fractional Equations; Green's Functions; Integral Boundary Conditions; Fixed Point Index; Existence and Non-existence
This paper deals with the study of the existence and non existence of solutions of a three parameter's family of nonlinear fractional differential equation with mixed-integral boundary value conditions. We consider the $\alpha$-Riemann-Liouville fractional derivative, with $\alpha \in (1,2]$. In order to deduce the existence and non existence results, we first study the linear equation, by deducing the main properties of the related Green's functions. We obtain the optimal set of parameters where the Green's function has constant sign. After that, by means of the index theory, the nonlinear boundary value problem is studied. Some examples, at the end of the paper, are showed to illustrate the applicability of the obtained results.
Thermal Convection Forecast using a Theoretical Model Calibrated with Statistical Data from Soaring Flights
Cristian V. Vraciu, Bogdan Antonescu, Dorinel Visoiu
Subject: Earth Sciences, Atmospheric Science Keywords: Thermal updraft velocity; Thermal convection; Soaring; Atmospheric Boundary Layer; Soaring birds; Sailplane; Aviation safety.
Online: 29 October 2018 (13:10:05 CET)
A forecasting scheme of the thermal updraft velocity based on a theoretical model and data collected from flights records at gliding competitions, is presented. The forecasting scheme was based on the hypothesis that there is linear relationship between the overheat function at ground surface and the temperature difference between soil and air. The proportionality factor of this relationship was determined experimentally using observations recorded during gliding flights. The results showed that based on this simple scheme forecasting thermal convection is possible at any geographical location.
Measurements of high-frequency Atmospheric Turbulence and its Impact on the Boundary Layer of Wind Turbine Blades
Alois Peter Schaffarczyk, Andreas Jeromin
Subject: Engineering, Energy & Fuel Technology Keywords: Advanced turbulence statistics, piezo-electric flow sensor, atmospheric boundary layer16 stability, laminar-turbulent transition
To gain insight into the differences between onshore and offshore atmospheric turbulence, 2 pressure fluctuations were measured for offshore wind under different environmental conditions. 3 A durable piezo-electric sensor was used to sample turbulent pressure data at 50 kHz. Offshore 4 measurements were performed at 100 m height on Germany's FINO3 offshore platform in the 5 German Bight together with additional meteorological data provided by Deutscher Wetterdienst 6 (DWD). The statistical evaluation revealed that the stability state in the atmospheric boundary has a 7 large impact on turbulent fluctuations. Therefore, we used higher statistical properties (described 8 by so-called shape factors) to the stability state. Data was classified to be either within the unstable, 9 neutral or stable stratification. We found that in case of stable stratification, the shape factor is 10 mostly close to zero, indicating that a thermally stable environment produces closer-to Gaussian 11 distributions. Non-Gaussian distributions were found in unstable and neutral boundary layer states 12 and an occurrence probability was estimated. Possible impact on laminar-turbulent transition on the 13 blade is discussed with application of so-called laminar aerofoils on wind turbine blades. Use of a 14 cut-off frequency to separate load and aerodynamic turbulence is proposed.
Application of Initial Boundary Value Problem on Logarithmic Wave Equation in Dynamics
Shkelqim Hajrulla, Leonard Bezati, Fatmir Hoxha
Subject: Mathematics & Computer Science, Applied Mathematics Keywords: initial boundary value problem; Gross-Sobolev inequality; logarithmic wave equation; global existence of solution
We introduce a class of logarithmic wave equation. We study the global existence of week solution for this class of equation. We deal with the initial boundary value problem of this class. Using the Galerkin method and the Gross logarithmic Sobolev inequality we establish the main theorem of existence of week solution for this class of equation arising from Q-Ball Dynamic in particular.
Relative Lagrangian Formulation of Finite Thermoelasticity
I-Shih Liu, Marcello G. Teixeira
Subject: Physical Sciences, Mathematical Physics Keywords: relative Lagrangian formulation; thermoelastic solid; small on large; successive linear approximation; boundary value problem
Besides the Lagrangian and the Eulerian descriptions, the motion of a body can also be expressed relative to the present configuration of the body, known as the relative motion description. It is interesting to consider such a relative motion description in general to formulate the basic system of field equations for solid bodies. In doing so, when the time increment from the present state is small enough, the nonlinear constitutive equations can be linearized relative to the present state so that the resulting system becomes linear. This will be done for thermoelastic materials with a brief comment on the exploitation of entropy principle in general. Relative Lagrangian formulation is based on the well-known ``small-on-large'' idea, and can be implemented for solving problems with large deformation in successive incremental manner. Some applications of such a formulation in numerical simulations are briefly reviewed.
Design and Characterizing of Blower Wind Tunnel Using CFD
Itimad Azzawi
Subject: Engineering, Mechanical Engineering Keywords: Blower wind tunnel design; CFD; Boundary layer controller; Turbulent intensity Validation; Power spectral density (PSD)
new subsonic blower wind tunnel design has been studied both numerically and experimentally, it is also referred to as "blower" wind tunnel. This paper, is initially aimed to address each sequential stage of the wind tunnel design process. Rather than applying the standard method of modelling solely the flow in the test section, a large-scale CFD model of the whole wind tunnel was employed. The loss of every constituent element was calculated and then all the losses are added up to determine the power needed for the wind tunnel operation which is used as "intake fan" boundary conditions in the CFD model. Then, flow uniformity and turbulent intensity measurements in an empty test section using a Pitot-static tube and hot wire anemometer (HWA) were introduced to validate the CFD results. The results showed that flow quality was significantly affected by boundary layer controllers (honeycomb and mesh screens) in the settling chamber and wide-angle diffuser. Investigations were also conducted to evaluate the flow deficit in the wake area behind a convex hump model using HWA. This was additional experimental tests carried out to validate the suitability of the wind tunnel flow aerodynamic research.
Segmentation of Agricultural Parcels in Satellite Images Based on Historical Vegetation Index Data
Maria Pavlova, Valerii Timofeev, Dmitry Bocharov, Irina Kunina, Anna Smagina, Mikhail Zagarev
Subject: Mathematics & Computer Science, Artificial Intelligence & Robotics Keywords: digital farming; remote sensing; land management; multispectral image processing; land cover mapping; agricultural field boundary
This paper considered the issue of agricultural fields boundary recognition in satellite images. A novel algorithm based on the aggregated history of vegetation index data obtained via open satellite data, Sentinel-2, was proposed. The proposed algorithm included several basic steps, namely the detection of parcel regions on aggregated index data; the calculation of aggregated edge maps; the segmentation of parcel regions using the edges obtained; the computation of connected components and their contour extraction. In this paper, we showed that the use of aggregated vegetation index data and boundary maps allow for much more accurate agricultural field segmentation compared to the instant vegetation index approach. The quality of segmentation within regions of Russia and the Ukraine was estimated. The dataset that was used and Python implementation of the proposed algorithm were provided.
Existence and Local Stability of Stationary Solutions for Nonlinear Gilpin Ayala Competition Model with Dirichlet Boundary Value
Subject: Mathematics & Computer Science, Applied Mathematics Keywords: Gilpin Ayala competition model; Lyapunov function; Mountain Pass Lemma; Palais Smale condition; Dirichlet boundary value
In this paper, the existence of two nontrivial stationary solutions for the nonlinear Gilpin Ayala two species competition model is given by using the mountain pass lemma, and the local stability criterion of the trivial solution is given by using Lyapunov function method. Based on the local stability criterion, we give some suggestions on how to avoid the population extinction. This is, when the population is on the verge of extinction, we should try our best to avoid the diffusion behavior and reduce the diffusion coefficient, otherwise the species are easy to go extinct. Numerical example shows the effectiveness of the proposed method.
Chemical Spill Encircling using a Quadrotor and Autonomous Surface Vehicles: a Distributed Cooperative Approach
Marcelo Jacinto, Antonio Pascoal, Rita Cunha
Subject: Engineering, Control & Systems Engineering Keywords: Quadrotor control; Autonomous Surface Vehicle control; Cooperative Path Following; Online Path Planning; Chemical Spill Boundary Encircling
This article addresses the problem of formation control of a quadrotor and one (or more) marine vehicles operating at the surface of the water with the end goal of encircling the boundary of a chemical spill, enabling such vehicles to carry and release chemical dispersants used during ocean cleanup missions to break-up oil molecules. Firstly, the mathematical models of the Medusa class of marine robots and quadrotor aircrafts are introduced, followed by the design of single vehicle motion controllers that allow these vehicles to follow a parameterized path individually using Lyapunov based techniques. At a second stage, a distributed controller using event triggered communications is introduced, enabling the vehicles to perform cooperative path following missions according to a pre-defined geometric formation. In the next step, a real time path planning algorithm is developed that makes use of a camera sensor, installed on-board the quadrotor. This sensor enables the detection in the image of which pixels encode parts of a chemical spill boundary and use them to generate and update in real time a set of smooth B-spline based paths for all the vehicles to follow cooperatively. The performance of the complete system is evaluated by resorting to 3-D simulation software, making it possible to simulate visually a chemical spill. Results from real water trials are also provided for parts of the system, where two Medusa vehicles are required to perform a static lawn-mowing path following mission cooperatively at the surface of the water.
The Expansion Theorems for Sturm-Liouville Operators with an Involution Perturbation
Abdizhahan Sarsenbi
Subject: Mathematics & Computer Science, General Mathematics Keywords: differential equations; involution; boundary value problems; Green's function; eigen6 function expansions; equiconvergence; Riesz basis; spectral properties
In this work, we studied the Green's functions of the second order differential operators with involution. Uniform equiconvergence of spectral expansions related to the second-order differential operators with involution is obtained. Basicity of eigenfunctions of the second-order differential operator operator with complex-valued coefficient is established.
Entropy Optimized Flow of Hybrid Nanomaterial over a Porous Stretchable Surface
T. Hayat, Zobia Kainat, Sohail A. Khan, A. Alsaedi
Subject: Materials Science, Biomaterials Keywords: Darcy-Forchheimer; Surface stretch; Unsteady boundary layer; MHD flow; Nanofluid; Heat generation / absorption and entropy analysis
The aim of this articles is to investigate the entropy optimization in unsteady MHD flow Darcy-Forchheimer nanofluids towards a stretchable sheet. The surface we tend to think about is porous and stretchy under acceleration. Flow occurs due to the stretching of the surface. Four distinct types of aqueous nanostructures are taken in this examination where copper oxide ( ), copper ( ), titanium dioxide ( ) and aluminum oxide ( ) are the nanoparticles. Irreversibility analysis are discussed through second law of thermodynamics. The expression of energy is mathematically designed and discussed according to heat generation / absorption, dissipation, thermal radiation, and joule heating. The nonlinear PDE (partial differential conditions) is first changed to ODE (normal differential conditions) through appropriate similarity variables. Here we used the numerically embedded solution technique to develop a numerical result for the obtained nonlinear flow expression. Influence of various flow parameter velocity temperature distribution and entropy generation are discussed. Reduction occurs in velocity profile for larger porosity and magnetic parameters. An enhancement in entropy generation and temperature distribution is seen for Brinkman number. An opposite effect is noticed in velocity and temperature through solid volume friction.
Existence and Uniqueness of BVPs Defined on Semi-Infinite Intervals: Insight from the Iterative Transformation Method
Riccardo Fazio
Subject: Mathematics & Computer Science, Algebra & Number Theory Keywords: Boundary value problems; semi-in nite intervals; existence and 22 uniqueness; iterative transformation method; numerical test
This work is concerned with the existence and uniqueness of boundary value problems defined on semi-infinite intervals. These kinds of problems seldom admit exactly known solutions and, therefore, the theoretical information on their well-posedness is essential before attempting to derive an approximate solution by analytical or numerical means. Our utmost contribution in this context is the definition of a numerical test for investigating the existence and uniqueness of solutions of boundary problems defined on semi-infinite intervals. The main result is given by a theorem relating the existence and uniqueness question to the number of real zeros of a function implicitly defined within the formulation of the iterative transformation method. As a consequence, we can investigate the existence and uniqueness of solutions by studying the behaviour of that function. Within such a context the numerical test is illustrated by two examples where we find meaningful numerical results.
Investigating Primary Cilia during Peripheral Nervous System Formation
Elkhan Yusifov, Alexandre Dumoulin, Esther T. Stoeckli
Subject: Life Sciences, Biochemistry Keywords: primary cilium; ciliogenesis; neural circuits formation; neural crest cells; DRG; boundary cap cells; sympathetic ganglia; PNS
The primary cilium plays a pivotal role during embryonic development of vertebrates. It acts as a somatic signaling hub for specific pathways, such as sonic hedgehog signaling. In humans, mutations in genes that cause dysregulation of ciliogenesis or ciliary function lead to severe developmental disorders called ciliopathies. Beyond its obvious role in early morphogenesis, growing evidence points towards an essential function of the primary cilium in neural circuit formation in the central nervous system. However, very little is known about a potential role in the formation of the peripheral nervous system. Here, we investigated the presence of the primary cilium in neural crest cells and their derivatives in the trunk of the developing chicken embryo in vivo. We found that neural crest cells, sensory neurons, and boundary cap cells all bear a primary cilium during key stages of early peripheral nervous system formation. Moreover, we described differences in the ciliation of neuronal cultures of different populations from the peripheral and central nervous system. Our results offer a framework for further in vivo and in vitro investigations on specific roles that the primary cilium might play during peripheral nervous system formation.
Marine Boundary Layer Height Obtained by New Numerical Regularization Method Based on GPS Radio Occultation Data
Jianyin Zhou, Jie Xiang, Sixun Huang
Subject: Earth Sciences, Atmospheric Science Keywords: Marine boundary layer height; Numerical regulation method; Double-parameter model function method; COSMIC data; Climate characteristics
Online: 7 July 2020 (16:56:28 CEST)
The boundary layer height (BLH) distinguishes the interface between the lower and free atmosphere, which is a key variable in numerical simulation, aerosol, and environmental pollution studies. Thus, the goal of this work is to propose a novel method conjuncting with numerical regularization to analyze climate characteristics of the marine boundary layer height (MBLH) using 2007-2011 GPS-RO data from the COSMIC mission. While traditionally, the difference method has been used to achieve this aim, herein, we propose an innovative method, in which the bending angle profile gradient was calculated using the numerical regulation method where the regulation parameters are determined by the double-parameter model function method. Then, the MBLH was determined by employing the maximum gradient method to ascertain the height corresponding to the smallest gradient. The results show a correlation between currents and the MBLH—a relationship that has not been previously demonstrated. A low MBLH is associated with seasons and regions where cold ocean currents are prevailing; whereas a high MBLH is observed in the seasons and places where warm currents are prevailing. This correlation was validated by comparing the obtained results with different occultation data—i.e., atmprf and echprf—which also established that atmprf is more sensitive to convective cloud top capture. In seas with active convection, the armprf calculated bending angle is higher than that from echprf. Subsequently, the standard deviation was used to express the MBLH confidence level. The results show that the MBLH standard deviation is highest in low latitudes and lowest in the middle and high latitudes. Furthermore, we analyzed the interannual MBLH variation trend, which displayed a seasonal variation and spatial distribution corresponding with the current and subsolar point. Finally, we conducted a case study in the South China Sea, and identified a distinctive seasonal change and downward trend.
A 2D Electrostatic Non-Linear Second-Order Differential Model for Electrostatic Circular Membrane MEMS Devices: A Result of Existence and Uniqueness
Paolo Di Barba, Luisa Fattorusso, Mario Versaci
Subject: Engineering, Electrical & Electronic Engineering Keywords: circular membrane mems devices; electrostatic actuator; boundary non-linear second-order differential problems; singularities; mean curvature
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In the framework of 2D circular membrane Micro-Electric-Mechanical-Systems (MEMS), a new non-linear second-order differential model with singularity in the steady-state case is presented in this paper. In particular, starting from the fact that the electric field magnitude is locally proportional to the curvature of the membrane, the problem is formalized in terms of the mean curvature. Then, a result of existence of at least one solution is achieved. Finally, two different approaches prove that the uniqueness of the solutions is not ensured.
Three-Dimensional Modeling Interaction of Shock Wave with Fin at Mach 5
Amjad A. Pasha
Subject: Engineering, Other Keywords: high speed flows; shock wave; turbulent boundary layer; shock-unsteadiness; separation bubble; turbulence modeling; single fin
The three-dimensional single fin configuration finds application in an intake geometry where the cowl-shock wave interacts with the side-wall boundary-layer. Accurate numerical simulation of such three-dimensional shock/turbulent boundary-layer interaction flows, which are characterized by the appearance of strong crossflow separation, is a challenging task. Reynolds-averaged Navier-Stokes computations using the shock-unsteadiness modified Spalart-Allmaras model is carried out at Mach of 5 at large fin angle of 23◦. The computed results using the modified model are compared to the standard Spalart-Allmaras model and validated against the experimental data. The focus of work is to implement the modified model and to study the flow physics in detail in the complex region of swept-shock-wave turbulent boundary-layer interaction in terms of the shock structure, expansion fan, shear layer and the surface streamlines. The flow structure is correlated to the wall pressure and skin friction in detail. It is observed that the standard model predicts an initial pressure location downstream of the experiments. The modified model reduces the eddy viscosity at the shock and predicts close to the experiments. Overall, the surface pressure using modified model is predicted accurately at all the locations. The skin friction is under predicted by both the models in the reattachment region and is attributed to the poor performance of turbulence models due to flow laminarization.
Analytical Modeling of Fluid Flow in Hydrophobic, Rectangular Microchannels with General Navier-Slip Boundary Conditions
Navid Kashaninejad
Subject: Engineering, Mechanical Engineering Keywords: slip flow; navier-slip boundary condition; hydrophobic microchannels; analytical solutions; poiseuille number; velocity profile of poiseuille flow
Fluid mechanics of flow in hydrophobic, rectangular microchannels with finite aspect ratios is of paramount importance. In such microchannels, not only the effect of the side walls should be taken into account, but also the classical assumption of no-slip boundary condition (BC) is no longer valid at the solid-liquid interface. Accordingly, slip flow can occur in microchannels fabricated from surfaces with low wetting conditions, hydrophobic surfaces. Determining the interactions of liquid molecules adjacent to solid surface is still a challenging issue, and it is especially important in small scale domains. Herein, the fluid mechanics of flow through rectangular hydrophobic microchannels has been reconsidered by taking into account the general Navier-slip BCs at the solid-liquid interface. For fully developed incompressible flow in microchannels at low Reynolds number, partial differential equation (PDE) of the momentum equation simplifies to the classical Poisson equation. Accordingly, by analytically solving the Poisson equations with general Navier-slip BCs, the most general forms of velocity distributions, flow rate, friction factor and Poiseuille number have been obtained.
Multi-Relaxation Time Lattice Boltzmann Simulations of oOscillatory Instability in Lid-Driven Flows of 2D Semi-Elliptical Cavity
Zhe FENG, HeeChang LIM
Subject: Engineering, Mechanical Engineering Keywords: lattice Boltzmann method; mass-conserved wall treatment; non-equilibrium extrapolation boundary condition; mass leakage; parallel computation; CFD
In this study, the multi-relaxation-time lattice Boltzmann method is applied to investigate the oscillatory instability of lid-driven flows in two-dimensional semi-elliptical cavities with different vertical to horizontal aspect ratios K in the range of 1.0--3.0. The program implemented in this study is parallelized using CUDA (compute unified device architecture), a parallel computing platform, and computations are carried out on NVIDIA Tesla K40c GPU. To carry out precise calculations, the CUDA algorithm is extensively investigated, and its parallel efficiency indicates that the maximum speedup is 47.6 times faster. Furthermore, the steady--oscillatory Reynolds numbers are predicted by implementing the CUDA-based programs. The amplitude coefficient is defined to quantify the time-dependent oscillation of the velocity magnitude at the monitoring point. The simulation results indicate that the transition Reynolds numbers correlate negatively with the aspect ratio of the semi-elliptical cavity, and are smaller than those of the rectangular cavity at the same aspect ratio. In addition, the detailed vortex structures of the semi-elliptical cavity within a single period are also investigated when the Reynolds number is larger than the steady--oscillatory value to determine the effects of periodic oscillation of the velocity magnitude.
Moving Surface Boundary Layer Control Analysis and the Influence of the Magnus Effect on an Aerofoil with a Leading-Edge Rotating Cylinder
Md. Abdus Salam, Bhuiyan Shameem Mahmood Ebna Hai, M. A. Taher Ali, Debanan Bhadra, Nafiz Ahmed Khan
Subject: Engineering, Mechanical Engineering Keywords: Moving surface boundary layer control; symmetric aerofoil; asymmetric aerofoil; velocity ratio; Magnus effect; lift coefficient; drag coefficient
A number of experimental and numerical studies point out that incorporating a rotating cylinder can superiorly enhance the aerofoil performance, especially for higher velocity ratios. Yet, there have been less or no studies exploring the effects of lower velocity ratio at a higher Reynolds number. In the present study, we investigated the effects of Moving Surface Boundary-layer Control (MSBC) at lower velocity ratios (i.e. cylinder tangential velocity to free stream velocity) and higher Reynolds number on a symmetric aerofoil (e.g. NACA 0021) and an asymmetric aerofoil (e.g. NACA 23018). In particular, the aerodynamic performance with and without rotating cylinder at the leading edge of the NACA 0021 and NACA 23018 aerofoil was studied on the wind tunnel installed at Aerodynamics Laboratory. The aerofoil section was tested in the low subsonic wind tunnel, and the lift coefficient and the drag coefficient were studied for different angles of attack. The experiments were conducted for two Reynolds numbers: 200000 and 250000 corresponding to two free stream velocities: 20 m/s and 25 m/s, respectively, for six different angle of attacks (-5°, 0°, 5°, 10°, 15° and 20°). This study demonstrates that the incorporation of a leading edge rotating cylinder results in an increase of lift coefficient at lower angle of attacks (maximum around 33%) and delay in stall angle (from 10° to 15°) relative to the aerofoil without rotating cylinder.
An Exploration of a Balanced Up-downwind Scheme for Solving Heston Volatility Model Equations on Variable Grids
Chong Sun, Qin Sheng
Subject: Mathematics & Computer Science, Computational Mathematics Keywords: Heston volatility model; initial-boundary value problems; finite difference approximations; up-downwind scheme; order of convergence; stability
This paper studies an effective finite difference scheme for solving two-dimensional Heston stochastic volatility option pricing model problems. A dynamically balanced up-downwind strategy for approximating the cross-derivative is implemented and analyzed. Semi-discretized and spatially nonuniform platforms are utilized. The numerical method comprised is simple, straightforward with reliable first order overall approximations. The spectral norm is used throughout the investigation and numerical stability is proven. Simulation experiments are given to illustrate our results.
MISR-GOES 3D Winds: Implications for Future LEO-GEO and LEO-LEO Winds
James Carr, Dong Wu, Michael Kelly, Jie Gong
Subject: Earth Sciences, Atmospheric Science Keywords: 3D-Winds, atmospheric motion vectors (AMVs), MISR, GOES-R, planetary boundary layer (PBL), stereo imaging, parallax, CubeSats
Global wind observations are fundamental for studying weather and climate dynamics. Most wind measurements come from atmospheric motion vectors (AMVs) by tracking the displacement of cloud or water vapor features. These AMVs generally rely on thermal infrared (IR) techniques for their height assignments, which are subject to large uncertainties in the presence of weak or reversed vertical temperature gradients around the planetary boundary layer (PBL) and with tropopause folding. Stereo imaging can overcome the height assignment problem using geometric parallax for feature height determination. In this study we develop a stereo 3D-Wind algorithm to simultaneously retrieve AMV and height from geostationary (GEO) and low Earth orbit (LEO) satellite imagery and apply it to collocated Geostationary Operational Environmental Satellite (GOES) and Multi-angle Imaging SpectroRadiometer (MISR) imagery. The new algorithm improves AMV and height relative to products from GOES or MISR alone, with an estimated accuracy of <0.5 m/s in AMV and <200 m in height with 2.2 km sampling. The algorithm can be generalized to other LEO-GEO or GEO-GEO combinations for greater spatiotemporal coverage. The technique demonstrated with MISR and GOES has important implications for future high-quality AMV observations, for which a low-cost constellation of CubeSats can play a vital role.
Lagrangian Meshfree Particle-based Computational Acoustics for Two-dimensional Sound Propagation and Scattering Problems
Yong Ou Zhang, Xu Li, Tao Zhang
Subject: Physical Sciences, Acoustics Keywords: meshfree method; particle-based computational acoustics; smoothed particle hydrodynamics; corrective smoothed particle method; boundary conditions; Lagrangian approach
Meshfree particle method, which is always regarded as a pure Lagrangian approach, is easily represented complicated domain topologies, moving boundaries, and multiphase media. Solving acoustic problems with the mesfree particle method forms a branch of the acoustic wave modeling field, namely, particle-based computational acoustics (PCA). The aim of this paper is to improve the accuracy of using the PCA method to solve two-dimensional acoustic problems, and realize the particle representation with a hybrid meshfree and finite-difference time-domain (FDTD) method for acoustic boundary conditions at both the plane and curved surface. As a widely used Lagrangian meshfree method, the smoothed particle hydrodynamics (SPH) based on the support domain and the kernel function has developed rapidly in recent years. The traditional SPH method is easily implements parallel processing and has been applied in sound wave simulation. As a corrective method with higher accuracy than SPH, the acoustic propagation and scattering in the time domain is simulated with the corrective smoothed particle method (CSPM). Moreover, a hybrid meshfree-FDTD boundary treatment technique is utilized to represent different acoustic boundaries in the Lagrangian approach. In this boundary treatment technique, the parameter value of virtual particles is obtained with the FDTD method, which concerns truncation errors based on the Tayler series expansion. Soft, rigid, and Mur's absorbing boundary conditions are developed to simulate sound waves in finite and infinite domain. Results of modeling acoustic propagation and scattering show that CSPM is accurate and convergence with exact solutions, and different acoustic boundaries are validated to be effective in the computation.
Modeling Sound Propagation Using the Corrective Smoothed Particle Method with an Acoustic Boundary Treatment Technique
YongOu Zhang, Xu Li, Tao Zhang
Subject: Engineering, General Engineering Keywords: computational acoustics; meshfree method; Lagrangian approach; smoothed particle hydrodynamics; corrective smoothed particle method; boundary conditions; numerical method
The development of computational acoustics allows simulation of sound generation and propagation in complex environment. In particular, meshfree methods are widely used to solve acoustics problems through arbitrarily distributed field points and approximation smoothness flexibility. As a Lagrangian meshfree method, smoothed particle hydrodynamics (SPH) method reduce the difficulty in solving problems with deformable boundaries, complex topologies, or multiphase medium. The traditional SPH method has been applied in acoustic simulation. This study presents the corrective smoothed particle method (CSPM), which is a combination of SPH kernel estimate and Taylor series expansion. The CSPM is introduced as a Lagrangian approach to improve accuracy in solving acoustic wave equations in the time domain. Moreover, a boundary treatment technique based on the hybrid meshfree and finite difference time domain (FDTD) method is proposed to represent different acoustic boundaries with particles. To model sound propagation in pipes with different boundaries, soft, rigid, and absorbing boundary conditions are built with this technique. Numerical results show that the CSPM algorithm is consistent and demonstrates convergence with exact solutions. Main computational parameters are discussed, and different boundary conditions are validated to be effective for benchmark problems in computational acoustics.
Effects of Domain Boundaries on the Diffraction Patterns of One Dimensional Structures
Frederic Timmer, Joachim Wollschläger
Subject: Physical Sciences, Condensed Matter Physics Keywords: spot-profile analysis; one dimensional physics; low energy electron diffraction; binary surface technique; supercell model; domain boundary
Online: 10 November 2016 (15:50:29 CET)
Motivated by diffraction experiments on the 23×3R30∘ reconstructed Si(111) due to deposition of rare earth elements (Dy, Tb) and silicide formation we analyse the splitting and non-splitting of superstructure spots. For this purpose, we model diffraction patterns for one dimensional structures generated by the binary surface technique and use supercell models to keep the analysis simple. Diffraction pattern are calculated in the framework of the kinematical diffraction theory and they are analyzed as a function of the domains and domain boundaries. Basic properties of the diffraction pattern are analyzed for model systems of a two-fold and a three-fold periodicity. The rules derived from these calculations are applied to the "real-world" system of Si(111)-(23×3R30∘)-RESi2 (RE = Dy or Tb). Depending on the combination of domains and domain boundaries of different types a plethora of different features are observed in the diffraction patterns. These are analyzed to determine the sizes of both domain boundaries and domains from experimentally observed splitting of specific superstructure spots.
Formation of Sawtooth Wavesfor Cylindrical and Sphericalkortweg-de Vries-Burgers Equations
Alexey Samokhin
Subject: Physical Sciences, Acoustics Keywords: Korteweg-de Vries-Burgers equation; cylindrical and spherical waves; saw-tooth solutions; periodic boundary conditions; head shock wave
For the KdV-Burgers equations on cylindrical and spherical waves the development of a regular profile starting from an equilibrium under a periodic perturbation at the boundary is studied. The equations describe a medium which is both dissipative and dispersive. Symmetries, invariant solutions and conservation laws are investigated. For an appropriate combination of dispersion and dissipation the asymptotic profile looks like a periodical chain of shock fronts with a decreasing amplitude (sawtooth waves). The development of such a profile is preceded by a head shock of a constant height and equal velocity which depends on spatial dimension as well as on integral characteristics of boundary condition; an explicit asymptotic for this head shock and a median of the oscillating part is found.
Discontinuous Boundary Elements for Fluid Flow Problems in Discrete Fracture Networks
Bin Wang, Yin Feng, Xu Zhou, Sandra Pieraccini, Stefano Scialò, Corrado Fidelibus
Subject: Engineering, Energy & Fuel Technology Keywords: Discrete Fracture Network (DFN); fractured rock hydrology; Boundary Element Method (BEM); Domain Decomposition Method (DDM); subsurface fluid flow
Modeling fluid flow in three-dimensional (3D) Discrete Fracture Networks (DFNs) is of relevance in many engineering applications, such as hydraulic fracturing, oil/gas production, geothermal energy extraction, nuclear waste disposal and CO2 sequestration. A new Boundary Element Method (BEM) technique with discontinuous quadratic elements and a parallel Domain Decomposition Method (DDM) is presented herein for the simulation of the steady-state fluid flow in 3D DFN systems with wellbores, consisting of planar fractures having arbitrary properties and wellbore trajectories. Numerical examples characterized by DFNs of increasing complexity are investigated to evaluate the accuracy and efficiency of the presented technique. The results show that accurate solutions can be obtained with less nodes than with mesh-based methods (e.g. Finite Element Method). In addition, the DDM algorithm used provides a quite fast convergence. The simulation results of the fluid flow around intersections among traces (linear intersections between fractures), intersections between traces and a fracture boundaries, and wellbore intersections is accurate. Source code is available at : https://github.com/BinWang0213/PyDFN3D.
Analysis and Computation of Solutions for a Class of Nonlinear SBVPs Arising in Epitaxial Growth
Amit K Verma, Biswajit Panditt, Ravi P Agarwal
Subject: Mathematics & Computer Science, Algebra & Number Theory Keywords: Radial solutions; singular boundary value problems; non-self-adjoint operator; Green's function; lower solution; upper solution; iterative numerical approximations.
In this work the existence and nonexistence of stationary radial solutions to the elliptic partial differential equation arising in the molecular beam epitaxy are studied. Since we are interested in radial solutions we arrive at the following fourth-order differential equation
A Non-Standard Finite Difference Scheme for Magneto-Hydro Dynamics Boundary Layer Flows of an Incompressible Fluid Past a Flat Plate
Riccardo Fazio, Alessandra Jannelli
Subject: Mathematics & Computer Science, Algebra & Number Theory Keywords: MHD model problem; boundary problem on semi-infinite interval; non-standard finite difference scheme; quasi-uniform mesh; error estimation
This paper deals with a non-standard finite difference scheme defined on a quasi-uniform mesh for approximate solutions of the Magneto-Hydro Dynamics (MHD) boundary layer flow of an incompressible fluid past a flat plate for a wide range of the magnetic parameter. We show how to improve the obtained numerical results via a mesh refinement and a Richardson extrapolation. The obtained numerical results are favourably compared with those available in the literature.
Extended Dynamical Equations of the Period Vectors of Crystals under Constant External Stress to Many-body Interactions
Gang Liu
Subject: Physical Sciences, Condensed Matter Physics Keywords: dynamical equation; crystal; period vectors; periodic structure; period dynamics; pressure; stress; many-body interaction; molecular dynamics; periodic boundary conditions
Since crystals are made of periodic structures in space, predicting their three period vectors starting from any values based on the inside interactions is a basic theoretical physics problem. For the general situation where crystals are under constant external stress, we derived dynamical equations of the period vectors in the framework of Newtonian dynamics, for pair potentials recently (doi:/10.1139/cjp-2014-0518). The derived dynamical equations show that the period vectors are driven by the imbalance between the internal and external stresses. This presents a physical process where when the external stress changes, the crystal structure changes accordingly, since the original internal stress can not balance the external stress. The internal stress has both a full kinetic energy term and a full interaction term. It is extended to many-body interactions in this paper. As a result, all conclusions in the pair-potential case also apply for many-body potentials.
Time-Correlated Vortex Tunneling in Layered Superconductors
John H. Miller Jr., Martha Y. S. Villagrán
Subject: Physical Sciences, Condensed Matter Physics Keywords: layered superconductor; thin film; superconducting properties; flux vortex; Josephson vortex; Abrikosov vortex; Josephson junction; quantum tunneling; soliton; grain boundary
The nucleation and dynamics of Josephson and Abrikosov vortices determine the critical currents of layered high-Tc superconducting (HTS) thin films, grain boundaries, and coated conductors, so understanding their mechanisms is of crucial importance. Here we treat pair creation of Josephson and Abrikosov vortices in layered superconductors as a secondary Josephson effect, in which each full vortex is viewed as a composite fluid of micro-vortices, such as pancake vortices, which tunnel coherently via a tunneling matrix element. We introduce a two-terminal magnetic (Weber) blockade effect that blocks tunneling below a threshold current, and simulate time-correlated vortex tunneling above threshold. The model shows nearly precise agreement with voltage-current (V-I) characteristics of HTS cuprate grain boundary junctions, which becomes more concave rounded as temperature decreases, and also explains the piecewise linear V-I behavior observed in iron-pnictide bicrystal junctions and other HTS devices. When applied to either Abrikosov or Josephson pair creation, the model explains a plateau seen in plots of critical current vs. thickness of HTS coated conductors. The observed correlation between theory and experiment strongly supports the proposed quantum picture of vortex nucleation and dynamics in layered superconductors.
Vertical Boundary Mixing Events during Stratification Govern Heat and Nutrient Dynamics in Windy Tropical Lakes with High Water-Level Fluctuations: A Long-Term (2001-2018) Study
Martín Merino Ibarra, Jorge A. Ramírez-Zierold, Patricia M. Valdespino-Castillo, Fermin S. Castillo-Sandoval, Andrea P. Guzmán-Arias, Mariel Barjau-Aguilar, Emiliano Monroy-Ríos, Luz M. López- Gómez, Arantxa Sacristán-Ramírez, José G. Quintanilla-Terminel, Roberto González–De Zayas, Jorge Jimenez-Contreras, María E. Valeriano-Riveros, Gloria Vilaclara-Fatjó, Salvador Sánchez-Carrillo
Subject: Earth Sciences, Environmental Sciences Keywords: eutrophication; water management; hypolimnetic warming; boundary mixing; mixing events; internal waves; long-term series; Valle de Bravo; biogeochemistry; nutrient flux
Physical processes play important roles in controlling eutrophication and oligotrophication. In stratified lakes, internal waves can cause vertical transport of heat and nutrients without breaking the stratification, through boundary mixing events. Such is the case in tropical Valle de Bravo (VB) lake, where strong diurnal winds drive internal waves, boundary mixing and hypolimnetic warming during stratification periods. We monitored VB during 18 years (2001-2018) when important water-level fluctuations (WLF) occurred, affecting mixing and nutrient flux. Mean hypolimnetic temperature increase (0.06–1.04°C month-1) occurred in all the stratifications monitored. We analyzed temperature distributions and modeled the hypolimnion heat budget to assess vertical mixing between layers (26,618–140,526 m-3h-1), vertical diffusivity coefficient KZ (6.2x10-7–3.3x10-6 m2s-1) and vertical nutrient entrainment to epilimnion on monthly scale. Stability also varied as a function of WLF. Nutrient flux to the epilimnion ranged 0.36–5.99 mg m-2d-1 for soluble reactive phosphorus (SRP) and 5.8–97.1 mg m-2d-1 for dissolved inorganic nitrogen (DIN). During low water-level years, vertical nutrient fluxes increase and can account for up to &gt;40% of the total external nutrients load to the lake. Vertical mixing changes related to WLF affect nutrient recycling, their flux to sediments, ecosystemic metabolic balance and planktonic composition of VB.
Change Point Estimation in Panel Data without Boundary Issue
Barbora Peštová, Michal Pešta
Subject: Mathematics & Computer Science, Applied Mathematics Keywords: change point; estimation; consistency; panel data; short panels; boundary issue; structural change; bootstrap; non-life insurance; change in claim amounts
Panel data of our interest consist of a moderate number of panels, while the panels contain a small number of observations. An estimator of common breaks in panel means without a boundary issue for this kind of scenario is proposed. In particular, the novel estimator is able to detect a common break point even when the change happens immediately after the first time point or just before the last observation period. Another advantage of the elaborated change point estimator is that it results in the last observation in situations with no structural breaks. The consistency of the change point estimator in panel data is established. The results are illustrated through a simulation study. As a by-product of the developed estimation technique, a theoretical utilization for correlation structure estimation, hypothesis testing, and bootstrapping in panel data is demonstrated. A practical application to non-life insurance is presented as well.
Corrosion Resistance of the Welded Joints From the Ultrafine-Grained Near-α Titanium Alloys Ti-5Al-2V Obtained by Spark Plasma Sintering
V. N. Chuvil'deev, A. V. Nokhrin, C. V. Likhnitskii, V. I. Kopylov, P. V. Andreev, M. S. Boldin, N. Yu. Tabachkova, A. I. Malkin
Subject: Materials Science, Metallurgy Keywords: titanium alloy; ultrafine-grained microstructure; equal channel angular pressing; spark plasma sintering; diffusion welding; corrosion; hat salt corrosion; diffusion; grain boundary.
A diffusion welding of coarse-grained and ultrafine-grained (UFG) specimens of titanium near-α alloy Ti-5Al-2V used in nuclear power engineering was made by Spark Plasma Sintering. The failure of the welded specimens in the conditions of hot salt corrosion and of electrochemical corrosion were shown to have preferentially intercrystalline character. In the case of presence of macrodefects, crevice corrosion of the welded joints was observed. The resistance of the alloys against the intercrystalline corrosion was found to be determined by the concentration of vanadium at the titanium grain boundaries, by the size and volume fraction of the β-phase particles and by the presence of micro- and macropores in the welded joints. The specimens of the welded joints of the UFG alloy have higher hardness, hot salt corrosion resistance and the electrochemical corrosion.
Study of Planetary Boundary Layer and Aerosol Transport Using Ceilometer and Air Quality Modelling in New South Wales (NSW), Australia
Hiep Nguyen Duc, Md Mahmudur Raman, Toan Trieu, Merched Azzi, Matthew Riley, Thomas Koh, Shaohua Liu, Kasun Bandara, Vishall Krishnan, Yujing Yang, Jeremy Silver, Michael Kerley, Stephen White, Jordan Capnerhurst, John Kirkwood
Subject: Earth Sciences, Atmospheric Science Keywords: Planetary boundary layer height (PBLH); Mixing level height (MLH); Vaisala CL51 ceilometer; CCAM-CTM; WRF-CMAQ; HYSPLIT trajectory analysis; MODIS satellite
The planetary boundary layer height (PBLH) is one of the key factors in influencing the dispersion of the air pollutants in the troposphere and hence the air pollutant concentration on ground level. For this reason, accurate air pollutant concentration depends on the performance of PBLH prediction. Recently, ceilometer, a lidar instrument to measure cloud base height, has been used by atmospheric scientists and air pollution control authorities to determine the mixing level height (MLH) in improving forecasting and understanding the evolution of aerosol layers above ground at a site. In this study, ceilometer data at an urban (Lidcombe) and a rural (Merriwa) location in the New South Wales, Australia was used to validate the PBLH prediction from two air quality models (CCAM-CTM and WRF-CMAQ) as well as to understand the aerosol transport from sources to receptor point at Merriwa for the three case studies where high PM10 concentration was detected in each of the three days. The results show that the PBLH prediction by the two air quality models corresponds reasonably well with observed ceilometer data and the cause and source of high PM10 concentration at Merriwa can be found by using ceilometer MLH data to corroborate with back trajectory analysis of transport of aerosols to the receptor point at Merriwa. Of the three case studies, one had aerosol source from north and north west of Merriwa in remote NSW where windblown dust is the main source, and the other two had sources from south and south east of Merriwa where anthropogenic sources dominate,
Fundamentals of Climatology for Engineers
Shiblu Sarker
Subject: Engineering, Other Keywords: Climate and Weather; Climate Model; Heat Transport; Radiation Balance; Atmospheric circulation; sea surface temperature; Planetary boundary layer; El Niño-Southern Oscillation (ENSO)
The study of long-term average weather patterns is known as climatology. It is a distinct field of study from meteorology and can be broken down into several subdivision. In order to predict the future, the knowledge of climatology is essential. In other words, with the help of climatology, we can figure out how likely it is that snow and hail will fall to the ground, and how much solar thermal radiation can reach a certain location etc. Climatology often focuses on how the climate has changed over time and how it has affected people and events. Both meteorology and climatology fall under the general term "meteorology", in particular, they are subdivision of research in the same field. In case of predicting the weather, meteorologists use variables such as humidity, air pressure, and temperature. This article's primary objective is to familiarize engineers with the fundamentals of climate and its processes so that they can effectively apply this knowledge to comprehend the climatic impact on water resources systems.
Wave and Hydrodynamic Processes in the Vicinity of a Rubble-mound, Permeable, Zero-freeboard Breakwater
Theofano Koutrouveli, Athanassios Dimas
Subject: Engineering, Civil Engineering Keywords: rubble-mound; zero-freeboard; porous-media; immersed-boundary; level-set; Smagorinsky subgrid scale model; wave reflection; wave transmission; wave overtopping; wave setup
A numerical study for the effect of crest width, breaking parameter and trunk permeability on hydrodynamics and flow behavior in the vicinity of rubble-mound, permeable, zero-freeboard breakwaters (ZFBs) is presented. The modified two dimensional Navier-Stokes equations for two-phase flows in porous media with a Smagorinsky model for the subgrid scale stresses were solved numerically. An immersed-boundary/level-set method was used. The numerical model was validated for the cases of wave propagation over a submerged impermeable trapezoidal bar and over a low-crested permeable breakwater. Five cases of breakwaters were examined, and the main results are: (a) The size of the crest width, B, does not notably affect the wave reflection, vorticity and currents in the seaward region of ZFBs, while wave transmission, currents in the leeward side, and mean overtopping discharge, all decrease with increasing B. A non-monotonic behavior of the wave setup is also observed. (b) As the breaking parameter decreases, wave reflection, transmission, currents, mean overtopping discharge, and wave setup decrease. This observation is also verified by relevant empirical formulas. (c) As the ZFB trunk permeability decreases, an increase of the wave reflection, currents, wave setup, and a decrease of wave transmission and mean overtopping discharge is observed.
An Extremely Efficient Boundary Element Method for Wave Interaction with Long Cylindrical Structures Based on Free-Surface Green's Function
Yingyi Liu, Ying Gou, Bin Teng
Subject: Engineering, Marine Engineering Keywords: long cylindrical structure; free-surface Green function; higher-order boundary element method; multipole expansion; singularity elimination; Gauss-Kronrod; numerical quadrature; OpenMP parallelization
The present study aims to develop an efficient numerical method for computing the diffraction and radiation of water waves with horizontal long cylindrical structures, such as floating breakwaters. A higher-order scheme is used to discretize geometry of the structure as well as the relevant physical quantities. As the kernel of this method, Wehausen's free-surface Green function is calculated by a newly-developed Gauss-Kronrod adaptive quadrature algorithm after elimination of its Cauchy-type singularities. To improve computational efficiency, a Chebyshev approximation approach is applied to a fast calculation of the Green function that needs evaluation thousands of times. In addition, OpenMP parallel technique is used to the formation of influence coefficient matrix, which significantly reduces CPU time. Finally, computations are performed on wave exciting forces and hydrodynamic coefficients for the long cylindrical structures, either floating or submerged. Comparison with other numerical and analytical methods demonstrates good performance of the present method.
Effect of Layer Thickness and Heat Treatment on Microstructure and Mechanical Properties of Alloy 625 Manufactured by Electron Beam Powder Bed Fusion
Julio Cesar Diaz, Kurtis I. Watanabe, Aldo Rubio, Alex De La Cruz, Dana Godinez, Lawrence E. Murr, Ryan B. Wicker, Edel Arrieta, Francisco Medina
Subject: Materials Science, Metallurgy Keywords: electron beam powder bed fusion (EBPBF); Inconel 625; microstructure and mechanical properties; layer-thickness effects; heat treatment; duplex grain structure; grain boundary carbides
This research program investigated the effects of layer thickness (50 and 100 microns) on the microstructure and mechanical properties of electron beam powder bed fusion (EBPBF) additive manufacturing of Inconel 625 alloy. The as-built 50 and 100 micron layer thickness components were also heat treated at temperatures above 1100 oC, which produced a recrystallized grain structure containing annealing twins in the 50 micron layer thickness components, and a duplex grain structure consisting of islands of very small equiaxed grains dispersed in a recrystallized, large-grain structure containing annealing twins. The heat treated component microstructures and mechanical properties were compared with the as-built components in both the build direction (vertical) and perpendicular (horizontal) to the build direction. Vickers microindentation hardness (HV) values for the vertical and horizontal geometries averaged 227 and 220 for the as-built 50 and 100 micron layer components, and 185 and 282 for the corresponding heat treated components. The yield stress values were 387 MPa and 365 MPa for the as-built layer horizontal and vertical 50 micron layer geometries, and 330 MPa and 340 MPa for the as-built 100 micron layer components. For the heat treated 50 micron components, the yield stress values were 340 and 321 MPa for the horizontal and vertical geometries, and 581 and 489 MPa for the 100 micron layer components, respectively. The elongation for the 100 micron layer as-built horizontal components was 28% in contrast to 65% for the corresponding 100 micron heat treated layer components, an increase of 132% for the duplex grain structure. However, the coarse grains containing annealing twins and the equiaxed small grain islands in the duplex structure for the heat treated components contained continuous carbides in the grain boundaries, and this may indicate sensitization and a reduction in corrosion resistance. These findings point to the potential mechanical property advantage for heat treatment of Inconel 625 alloy 100 micron layer thickness components fabricated by EBPBF.
GEO-GEO Stereo-Tracking of Atmospheric Motion Vectors (AMVs) from the Geostationary Ring
James L. Carr, Dong L. Wu, Jaime Daniels, Mariel D. Friberg, Wayne Bresky, Houria Madani
Subject: Earth Sciences, Atmospheric Science Keywords: 3D-winds; atmospheric motion vectors (AMVs); GOES-R; ABI; Himawari; AHI; planetary boundary layer (PBL); stereo imaging; parallax; Image Navigation and Registration (INR)
Height assignment is an important problem for satellite measurements of Atmospheric Motion Vectors (AMVs) that are interpreted as winds by forecast and assimilation systems. Stereo methods assign heights to AMVs from the parallax observed between observations from different vantage points in orbit while tracking cloud or moisture features. In this paper, we fully develop the stereo method to jointly retrieve wind vectors with their geometric heights from geostationary satellite pairs. Synchronization of observations between observing systems is not required. NASA and NOAA stereo-winds codes have implemented this method and we have processed large datasets from GOES-16, -17, and Himawari-8. Our retrievals are validated against rawinsonde observations and demonstrate the potential to improve forecast skill. Stereo winds also offer an important mitigation for the loop heat pipe anomaly on GOES-17 during times when warm focal plane temperatures cause infra-red channels that are needed for operational height assignments to fail. We also examine several application areas, including deep convection in tropical cyclones, planetary boundary layer dynamics, and fire smoke plumes, where stereo methods provide insights into atmospheric processes. The stereo method is broadly applicable across the geostationary ring where systems offering similar Image Navigation and Registration (INR) performance as GOES-R are deployed.
Influence of Temperature on Contact Pressures and Resource of Metal-Polymer Plain Bearings with the Filled Polyamide PA6 Bushing
Myron Chernets, Mykhaylo Pashechko, Anatolii Kornienko, Andrei Buketov
Subject: Engineering, Automotive Engineering Keywords: metal-polymer plain bearings; PA6 based polyamide composites; dispersed glass and carbon fibers; temperature; Young's modulus; maximum contact pressures and resource; boundary and dry friction
It is known that the elastic characteristics of polyamides change with increasing temperature, in particular, the Young's modulus decreases significantly. This fact is practically not taken into account in design calculations of metal-polymer plain (MP) bearings, operating under conditions of the boundary and dry friction. The purpose of the study is the analysis of the effect of temperature on the change of the Young's modulus and, accordingly, the contact strength and triboresource according to the developed method of calculating MP bearings. MP bearings with a bushing made of polyamide PA6 reinforced with glass or carbon dispersed fibers were investi-gated. Quantitative and qualitative regularities of change of the maximum contact pressures and resource of the bearings at temperature increase under conditions of boundary and dry friction are established. The pressures in the bearing bushing made of PA6+30GF will be lower than for the bushing made of PA6+30CF. The resource of the bushing made of PA6+30CF will be significantly greater than for PA6+30GF. For thermoplastic polymers, the increase in temperature will have a useful practical effect due to the decrease in the rigidity of the polymer composites of the bearing bushing.
The Stele - A Developmental Perspective on the Diversity and Evolution of Primary Vascular Architecture
Alexandru Tomescu
Subject: Biology, Plant Sciences Keywords: stele; stelar architecture; plant development; plant anatomy; procambium; endodermis; boundary layer; developmental domain; protostele; siphonostele; eustele; vascular tissue; xylem, phloem; pith; evo-devo; evolution; fossil
The stele concept is one of the oldest enduring concepts in plant biology. This paper reviews the concept and its foundations, and builds an argument for an updated view of steles and their evolution. The history of studies of stelar organization has generated a widely ranging array of definitions of the stele that determine the way we classify steles and construct scenarios about the evolution of stelar architecture. Because at the level of the organism biological evolution proceeds by, and is reflected in, changes in development, concepts of structure need to be grounded in development in order to be relevant in an evolutionary perspective. For the stele, most of the traditional definitions that incorporate development have viewed it as the totality of tissues that either originate from procambium – currently the prevailing view – or are bordered by a boundary layer (e.g., endodermis). A definition of the stele that would bring consensus between these perspectives recasts the stele as a structural entity of dual nature. Here, I review briefly the history of the stele concept, basic terminology related to stelar organization, and traditional classifications of the steles. I then revisit boundary layers from the perspective of histogenesis as a dynamic mosaic of developmental domains. I use classic and recent anatomical and molecular data to reaffirm and explore the importance of boundary layers for stelar organization. Drawing on data from comparative anatomy, developmental regulation, and the fossil record, I offer a model for a stele concept that integrates both the boundary layer and the procambial perspective, consistent with a dual nature of the stele. The dual stele model posits that stelar architecture is determined in the apical meristem by two major cell fate specification events: a first one that specifies a provascular domain and its boundaries, and a second event that specifies a procambial domain (which will mature into conducting tissues) from cell subpopulations of the provascular domain. If the position and extent of the developmental domains defined by the two events are determined by different concentrations of the same morphogen (most likely auxin), then the distribution of this organizer factor in the shoot apical meristem, as modulated by changes in axis size and the effect of lateral organs, can explain the different stelar configurations documented among tracheophytes. This model provides a set of working hypotheses that incorporate assumptions and generate implications that can be tested empirically. The model also offers criteria for an updated classification of steles that is in line with current understanding of plant development. In this classification, steles fall into two major categories determined by the configuration of boundary layers – boundary protosteles and boundary siphonosteles, each with subtypes defined by the architecture of the vascular tissues. Validation the dual stele model and, more generally, in-depth understanding of the regulation of stelar architecture, will necessitate targeted efforts in two areas: (i) the regulation of procambium, vascular tissue, and boundary layer specification in all extant vascular plants, considering that most of the diversity in stelar architecture is hosted by seed-free plants, which are the least explored in terms of developmental regulation; (ii) the configuration of vascular tissues and, especially, boundary layers, in as many extinct species and lineages as possible.
A Method Framework for Automatic Airspace Reconfiguration-Monte Carlo Method for Eliminating Irregular Sector Shapes Generated by Region Growth Method
ZhiJian Ye, FanHe Kong, BaoCheng Zhang, Wei Gao, JianFeng Mao
Subject: Earth Sciences, Geoinformatics Keywords: Airspace Reconfiguration; irregular boundary smoothing; dynamic Monte Carlo method by changing location of flexible vertices; Monte Carlo method by radius changing; Voronoi diagram; graph cutting; multi-objective optimization
With the growth of air traffic demand in busy airspace, there is an urgent need for airspace sectorization to increase air traffic throughput and ease the pressure on controllers. The purpose of this paper is to develop a method framework that can perform airspace sectorization automatically, reasonably, which can be used as an advisory tool for controllers as an automatic system, especially for eliminating irregular sector shapes generated by simulated annealing algorithm (SAA) based on region growth method. Two graph cutting method, dynamic Monte Carlo method by changing location of flexible vertices (MC-CLFV) and Monte Carlo method by radius changing (MC-RC) were developed to eliminating irregular sector shapes generated by SAA in post-processing. The experimental results show that the proposed method framework of AS can automatically and reasonably generate sector design schemes that meet the design criteria. Our methodology framework and software can provide assistant design and analysis tools for airspace planners to design airspace, improve the reliability and efficiency of airspace design, and reduce the burden of airspace planners. In addition, this lays the foundation for reconstructing airspace with more intelligent method.
The Coronavirus Disease 2019 Spatial Care Path: Home, Community, and Emergency Diagnostic Portals
Gerald J. Kost
Subject: Medicine & Pharmacology, Pathology & Pathobiology Keywords: Emergency Use Authorization; endemic; false omission; false omission rate; home testing; point-of-care testing (POCT); positive predictive value geometric mean-squared; prevalence boundary; recursive protocol; tier; visual logistics
Goals: To use visual logistics for interpreting COVID-19 molecular and rapid antigen test (RAgT) performance, determine prevalence boundaries where risk exceeds expectations, and evaluate benefits of recursive testing along home, community, and emergency spatial care paths. Methods: Mathematica/open access software helped graph relationships, compare performance patterns, and perform recursive computations. Results: Tiered sensitivity/specificity comprise: T1) 90%/95%; T2) 95%/97.5%; and T3) 100%/≥99%, respectively. In emergency medicine, median RAgT performance peaks at 13.2% prevalence, then falls below T1, generating risky prevalence boundaries. RAgTs in pediatric ERs/EDs parallel this pattern with asymptomatic worse than symptomatic performance. In communities, RAgTs display large uncertainty with median prevalence boundary of 14.8% for 1/20 missed diagnoses, and at prevalence >33.3-36.9% risk 10% false omissions for symptomatic subjects. Recursive testing improves home RAgT performance. Home molecular tests elevate performance above T1, but lack adequate validation. Conclusions: Widespread RAgT availability encourages self-testing. Asymptomatic RAgT and PCR-based saliva testing present the highest chance of missed diagnoses. Home testing twice, once just before mingling, and molecular-based self-testing help avoid false omissions. Community and ER/ED RAgTs can identify contagiousness in low prevalence (<22%). Real-world trials of performance, cost-effectiveness, and public health impact could identify home molecular diagnostics as the optimal diagnostic portal.