I'm having the same problem as pretty much everyone who tried using infinite elements with transient tructural analysis. At or a bit after the application of the load, I'm getting the rigid body movement error. I've tried to constraint my model in many ways. Now, as you will be able to see from my code, I've applied symmetric boundary conditions to some faces, and completely block the bottom face of the infinite elements. Normally, without the infinite elements, it should be completely restrained. However, now, no matter what I change, I'm still getting the same error. my time size is very small as well.
One thing to note is that I'm using Rayleigh damping coefficients, and the only way I did obtain some results (and they did not make sense at all for me), is by increasing the beta damping coefficient to unrealistic values, as for the alfa damping coefficient, I'm leaving it at zero.
Should I maybe use non linear controls to obtain some results ?
Or there are some dynamic analysis control options I could apply in order for my analysis to work ?
Any help would be appreciated
P.S: I've already checked the other two discussions concerning infinite elements + transient analysis