Learning Forum

[Vishalyadav08]

I am trying to perform Modal Analysis on a two-wheeler frame structure assembly. The assembly earlier had penetration and gaps. I have attached different components via bonded type contact and tried to adjust the closure of contact via pinball radius and eliminated penetrations by editing geometry via Spaceclaim. The geometry now only has gaps (which I cannot eliminate). While running the Modal Analysis for un-constrained geometry, I am getting first three natural frequencies as zero but 4th to 6th as non-zero values. Also, the first six mode shapes are normal (first three displacements and the later three as rotation about the three axis). What should I do to make all six natural frequencies as zeron

[Aniket]

Have you applied any boundary condition except bonded contact? Are the nonzero frequencies near zero?n-AniketnHow to access Ansys help linksnGuidelines for Posting on Ansys Learning Forumn

[Vishalyadav08]

No I have not applied any other boundary condition. And the non zero frequencies are between 20 to 40 Hz.n

[BenjaminStarling]

nThis is a known issue/limitation with penalty based contacts and rotational modes. It occurs when the two surface contacting are not parallel/normal to each other. To fix this you can change the formulation to MPC, or try and control the mesh such that all surfaces have equal elements that are normal for each pair of elements.nUnfortunately there currently is no other solution, and sometimes MPC contact is not an acceptable formulation, which means you can be stuck with defeaturing your model to ensure the contact faces are normal to each other. n

[Vishalyadav08]

Hi ArraynI'm trying both MPC and Beam Formulation for whole assembly. Before that I've tried both MPC and beam formulation for a simplified version of assembly (having only few components) just for checking the contact. Both formulations are working and showing similar trend in natural frequencies. For the whole chassis however, beam formulation is converging and giving result. MPC formulation is unable to converge and showing an unknown error. I think this is happening because of improper selection of contact and target bodies.n