CMASS2 warning

[kowalski98]

hi all, i'm running a sim in Simcenter for a test for a dummy spacecraft. The test is set up such that there is a mass offload to simulate the spacecraft panels being weightless in space. There are some components on the panel I don't want to model/mesh, so I simulated this with a cmass2 element tied with RBE3s to various points on the panel. When I run the sim, I get the following message on the dashboard:
WARNING
There are mass elements in the part, but no gravity or centrifugal loads.
The mass elements will be ignored in the analysis.
SUGGESTION: Apply a gravity or centrifugal load.
I don't want to apply gravity, because that would place stress on components that don't see gravitational force, and a centrifugal load doesn't seem appropriate here.
Any tips?
Thanks in advance!

 

[GVDR]

Hello,
I am not completely sure about your mass offload setup. As soon as you do not define gravity load you should have your expected conditions ?
Coming back to the mass and RBE3, RBE3 is a connection designed to transmit loads, so if you apply a load to your mass it will be transmitted properly. This connection does not rigidly connect the mass to your structure, as its DOF become slave and its movement will be the average of your connection points so if no load is present on the mass there will be no effect.
You may want to use RBE2 elements to connect your mass so that the mass displacement becomes master and forces the panel connection points to move accordingly. This way the mass and possible inertia will have the desired effect on the structure.

 

[BlasMolero]

Dear Kowalski,
Strange the warning message: in a modal/eigenvalue analysis (SOL103) not need to apply any loading to run the NASTRAN solver, and in fact, real eigenvalue analysis is the basis for many types of dynamic response analyses, like modal frequency dynamic response (SOL111) or Transient Time History Modal Analysis (SOL112). What type of analysis are you trying to run?.
Best regards,
Blas.