the acc will impose the boundary conditions by solving a system of linear equations. in a rigid model-problem, it will build a unique matrix of coefficients, generate the lu decomposition, and reuse that same matrices to find the circulation in the rings at every time step. for aeroelastic simulations, however, because the relative position of the rings is permanently changing due to the deformation of the lattices, the cc will recalculate the influence matrix and lu decomposition at each time step.