Error 179: Circular dependency

Altair Forum User

I have a variety of 3D solid components that I wanted to connect together in an assembly. I've done this with RBE2 elements, and the spotweld feature. However, since the original rigids had non-zero length and were attached to a 3D solid element (no rotational DOF), when the assembly comes under tension, the RBE2s rotate, which skews my total displacement results in the assembly.

 

In order to get around this, I've used the 'face' tool to generate 2D PSHELL faces around all connected components, and then re-defined the spotwelds to reference the 2D elements, which do have rotational DOFs. Since they have rotational DOFs, this means that the rotation of the RBE2 elements should be maintained, and the faces will not separate. However, when I run my model, I get a message indicating

 

*** ERROR # 179 ***

 The dependent d.o.f.s of multi-point constraints produces a singular matrix. This may be caused by a circular dependency in which a d.o.f. is indirectly dependent upon itself.

 

I don't actually have any MPCs in my model, so I assumed this was associated with the SPC I have applied to a rigid element in my model. However, when I use Tool > check elems > 1-d > rigid loops or dependency, then I get that 0 rigid elements are inter-dependent. Tool > dependency > elems > all also fails to identify any nodes with multiple dependency. Any suggestions on further troubleshooting?

 

Thanks,

Brad

tinh

Hello

Could you show a screenshot of your model?

did you check on 'include independent nodes' in panel 'check elems'?

here in your model, MPCs are RBE2.

what kind of spotweld did you use?

take caution that rotation dof #6 is pseudo for PSHELL (by auto-SPC)

Altair Forum User

The client I'm working with won't let me disclose screenshots of the model, but I have definitely checked the 'include independent nodes' box when doing my dependency check. The spotweld I used was through 1D > spotweld > using nodes > nodes-nodes, connected with rigid elements. I'm not sure what you mean by pseudo for rotation DOF #6 though. I had all RBE2 elements constrained in all 6 DOF, since I didn't want them moving at all. Will this cause problems?

 

Thanks,

Brad

tinh

Hi

so, did you connect the RBAR(spotweld) with RBE2?

in such case then panel F10 check dependency should show problem

If it does not show a problem then anyway you should not connect RBAR with RBE2