Coupled simulation of multibody and finite element systems: an efficient and robust semi-implicit coupling approach

Standard coupling approaches for simulating coupled MBS/FEM systems may entail enormous CPU times in order to achieve a stable and accurate solution. To stabilize and speed up the solution process, semi-implicit coupling approaches can be applied successfully. In literature, semi-implicit coupling approaches have been introduced, where Jacobian information is exchanged between the subsystems using partial derivatives with respect to the state vectors of the subsystems. The drawback of these methods is that the numerical calculation of the Jacobians with respect to the whole state vector of the subsystems is very time-consuming. The key idea of the semi-implicit coupling technique presented here is to reduce the computational effort by using Jacobian information only with respect to the coupling variables. The semi-implicit coupling technique introduced here is exemplarily applied for coupling a commercial MBS code with a commercial FEM code. As a practical example, we consider a hybrid nonlinear rotor/bearing model of a high-speed turbine. The rotor is modeled as a flexible multibody system. For calculating the bearing reactions, a finite element discretization of Reynolds fluid film equation is applied which yields the pressure distribution in the fluid films of the hydrodynamic bearings. Both codes are coupled via interprocess communication (IPC). A very time-efficient implementation of the semi-implicit coupling approach can be accomplished by a parallelization on multiple CPUs.