Converges of Eigen period

[Anonymous]

Converges of Eigen period

Hey! I have modeled a beam (450X450mm ) length 4500mm in robot using beam elements. And got convergence of the Eigen period when I used 20 elements. I have solved the same problem using the differential equation for the beam without shear def.  Inn the result I get some differences and I have concluded that it must be the shear deformation. When I tried to model the same beam with length 200 m. I got some difftenses and the Eigen period got even bigger than the analytical solution.

I tough that the FEM solution always gave a stiffer construction than the analytical tough you impose a fictitious stiffness upon the construction.?????? The mass of the systems are the same.

[Artur.Kosakowski]

If I remember correctly that depends on the mass matrix type and the convergence is from 'above' or from 'bottom' respectively.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.