The natural frequency (modal) with nonlinear materials processor is very similar to the Natural Frequency -Modal processor. However, it can handle nonlinear material models. It is useful when a hyperelastic or curve material model is needed. Actuator, contact, coupling, dashpot, general contact, pulley, slider, 2D kinematic and 3D kinematic element parts must be deactivated to perform this analysis.
Notes:
- The shell element formulations available for other nonlinear analyses (MES, Static Stress with Nonlinear Material Models, and MES Riks) are also available for nonlinear modal analyses. All of the considerations for using nonlinear shell elements are applicable to nonlinear modal analyses too. In particular, the slenderness of the elements must be considered when choosing the appropriate element formulation and advanced options. See the
How to Determine Whether Shell Elements are Thick or Thin
section of the Shell Elements help page for more information.
- Undesirable nonlinear modal results may occur for perfectly flat shell element structures when using the Thin element formulation. You can resolve this problem by switching to the General shell element formulation and activating the Reduced integration for transverse shear terms option.
- Although the results from a Natural Frequency (Modal) with Nonlinear Material Models analysis include displacements, use these displacements only to visualize the mode shape. The magnitude of the displacements is relative to each other. The natural frequency is a theoretical result due to unspecified dynamic loads, so the results cannot contain absolute displacements.
- Since there are no absolute displacements in the analysis, there are no absolute strains or stresses. Therefore, the nonlinear material properties are not used. The stiffness of the parts in the position modeled are used in the modal analysis.