Hello Aiswarya,
When we have an assembly of parts of different sizes made from different materials, all interacting with each other, we need to check our contacts thoroughly. Generally zero mode frequenices tell us that body is not properly constrained. There's another domain called free-free modal analysis (for example modal analysis of an airplane, where zero frequency mode shapes are expected). To eliminate the issue in your model, check if it's sufficiently constrained, Have a look at this Ansys Innovation Course on evaluating rigid body modes in modal analysis.
Modal Analysis in Ansys Mechanical | Ansys Courses
Regards,
Nanda.
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