Hi

I'm doing 2-way FSI simulation with hyper elastic materials, i'm trying to use Mooney Rivlin 5 parameter model for hyper elastic behavior. I borrowed all 5 parameters from an article with the same concept, but i'm having a serious converging problem. I have tried to run the simulation with different mesh size and different elements, also with different time step size (increasing and decreasing the step size) but each time Solution information gives me the same Error below:

*Distributed sparse solver minimum pivot in absolute value= ** 3.737065875E-02 at node 281725 UZ. ** DISP CONVERGENCE VALUE = 0.7277 CRITERION= 0.3713E-01** EQUIL ITER 1 COMPLETED. NEW TRIANG MATRIX. MAX DOF INC= 0.7277 ** FORCE CONVERGENCE VALUE = 5.978 CRITERION= 0.7782E-03** DISP CONVERGENCE VALUE = 7.648 CRITERION= 0.3987 ** EQUIL ITER 2 COMPLETED. NEW TRIANG MATRIX. MAX DOF INC= 7.648 ** *** ERROR *** CP = 619.418 TIME= 221:22** Element 152312 (type = 6, SOLID186) (and maybe other elements) has ** become highly distorted. Excessive distortion of elements is usually ** a symptom indicating the need for corrective action elsewhere. Try ** ramping the load up instead of step applying the load (KBC,1). You ** may need to improve your mesh to obtain elements with better aspect ** ratios. Also consider the behavior of materials, contact pairs, ** and/or constraint equations. Please rule out other root causes of ** this failure before attempting rezoning or nonlinear adaptive ** solutions. If this message appears in the first iteration of first ** substep, be sure to run shape checking of elements.*

I have already run the same model with elastic materials and it converged with little changes in mesh size. But for the hyper elastic material, nothing seems to effect the converging process. I'm attaching a picture of what happens to the model after the element distortion.

Could anyone help me?