If a portion of a model is not constrained by restraints or connections, one or more rigid body modes in the model are calculated. A rigid body mode represents the possibility of unrestricted motion for a model or component in a particular direction. For example, a completely unconstrained part has six rigid body modes: one for each of the three coordinate directions and one for each of the three coordinate rotations. Rigid body modes have a natural frequency value of zero (or very nearly zero). If the requested frequency range starts at zero, rigid body modes are the first modes calculated. If your results include only rigid body modes, the simulation might fail. Therefore, you should request more modes than the number of rigid body modes in the model. If the number of requested modes is insufficient, the number of rigid body modes in the model is estimated so you can adjust the number of requested modes accordingly. You can also adjust the frequency range to screen out zero-valued frequencies in your results. | |||||||||