Erik Kostson
Ansys Employee

No worries - I would take away the LUMPM, but perhaps that will not do it. Most likely if material dimensions are OK, it is the Boundary conditions.

Use springs on all the nodes/points with boundary conditions – one spring (COMBIN14) for each direction so you need 3 springs (X,Y,Z) for each node/point where you apply your constraint/displacement boundary conditions. Then you will need to probably tune the spring stiffness to get better agreement between tests and FEA. Finally make sure you measure the mode shapes experimentally.