text: Not sure exactly what you mean by "model."  If you are good with math and are looking for a computer model, I would try out a program called "Extend 5LT."  \n\nThis program is used by manufacturers, industrial engineers and others who need to simulate stuff.  It is a little difficult to learn in the beginning but it is a very valuable tool.  I believe they still have a free version available at the web site below.\n\nGood luck.