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Guest posted a topic in Altair OptiStructHello, I am a member of Ka RaceIng, the formula student team from Karlsruhe. I make a size optimization of a tubular rear frame. The objective is "minimize weighted compliance" and the constraint consists of a maximum mass. Unfortunately, I often get this error message: Messages for the job: *** ERROR # 153 *** Exactly zero pivoting encountered during Numerical Factorization; the model may have rigid body mode. Solver error no. = -514 spc set id = 2 index = 1 Possible reasons are: 1) insufficiently constrained model, 2) having rigid body mechanisms within the model, 3) extremely ill-conditioned rigid element sets, 4) extremely thin shells (as used for skinning) that have MID2/MID3, 5) gap elements with extremely high stiffness (KA, especially KT or MU). Check the model and rerun the problem. (MECHCHECK may be used to find the rigid body modes. To do so, change the input to be an eigenvalue analysis and add MECHCHECK.) (WARNING: results obtained with MECHCHECK cannot be used because the model is changed internally.) This error was detected in subroutine bcsmtxfct. All 1D elements are connected and the frame is constraint at 6 points, so I don't think that there are not enough boundary conditions. At the moment, I have no idea how to solve this problem. Please find attached the simulation model. Could you please help me? Thank you very much . Kind regards, Kilian Kiesel
Guest posted a topic in Altair RADIOSSHi, I am trying a simple impact analysis like radioss example 26 ruptured plate ( I am not interested in the rupture, just want to try an impact problem). I am using a soft non linear material M36_PLAS_TAB with a stress strain curve (E=8Mpa,nu=0.42,rho=1.412e-6Mg) and fixing the whole bottom surface. I used the volume tetra mesh to mesh my disk. ( I am using solid elements instead of shells as a basis for a more complex problem I am working on) The model was working fine with linear elastic materials... I read a few posts about this problem. There it was suggested to use a really thin linear elastic surface on top. And to change the element formulation. Could you please elaborate more in detail the steps to overcome this problem? Thanks!