You use modal analysis to determine the natural frequencies and mode shapes of a structure. Both are important parameters in the design of a structure for dynamic loading conditions, and are required for a spectrum analysis, or a mode-superposition harmonic or transient analysis.

You can perform a modal analysis on a prestressed structure, such as a spinning turbine blade. Another useful feature is modal cyclic symmetry, which enables you to review the mode shapes of a cyclically symmetric structure by modeling just a sector of it.

Modal analysis in the Ansys, Inc. family of products is a linear analysis. Any nonlinearities, such as plasticity and contact (gap) elements, are ignored even if they are defined. You can select from among several mode-extraction methods: Block Lanczos, Supernode, Subspace, PCG Lanczos, unsymmetric, damped, and QR damped. The damped and QR damped methods allow you to include damping in the structure. The QR damped method also accommodates unsymmetrical damping and stiffness matrices. Details about mode-extraction methods are covered later in this section.