Modal Structural Simulations

Modal analysis enables you to model the undamped, free vibration characteristics of a structure by determining natural frequencies and mode shapes. You can then design your structure to avoid resonant frequencies or to vibrate at a specific frequency. Note that, although the results of a modal analysis include displacement results, you should only use these displacements to visualize the mode shape. The natural frequency and mode shape results are based on unspecified dynamic loads, so the results do not include absolute displacement values.

You can also include the pre-stress effects of a static analysis in your modal analysis. A typical example is the large tensile stress induced in a turbine blade under a centrifugal load that can be captured by a static structural analysis. Because this causes significant stiffening of the blade, including this pre-stress effect will result in much higher, realistic natural frequencies in a modal analysis.

Note: Discovery assumes a linear pre-stress condition for pre-stressed modal analysis. All non-linear behavior is treated as linear for the pre-stress condition. For the purpose of computing the pre-stress condition, sliding frictional contacts are assumed to be bonded, and sliding frictionless contacts are assumed to be idealized sliding.

Note: Modal (Natural Frequency) analysis is also used as the basis for several of the Topology Optimization goals (Maximize Natural Frequency, Balance Stiffness and Frequency, and Target Natural Frequency).

To specify a modal analysis:

Select the Natural Frequency in the ribbon of the Simulation tab.
Specify the Number of Modes in the physics tree. You can specify up to 12 modes.
Set up any constraints, including forces, supports, displacements, and mass conditions.

The specified number of mode shapes are calculated, with Von Mises Stress and Displacement Magnitude results calculated for each mode. Each is shown as a separate result. The results for mode 1 are displayed by default, but you can select a different mode from the legend. You can calculate results for each frequency of a selected mode shape or for all modes at once.