Cyclic symmetric normal modes solutions

You can include a Cyclic Modes step in your Simcenter 3D Multiphysics Structural and Coupled solutions to perform cyclic modes analysis. The Cyclic Modes step supports a cyclic symmetric solution for normal modes at higher harmonic indices. The software computes the modes about the nonlinear stress or displacement state at the end of a previous static step in the solution. The Cyclic Modes step allows you to specify the harmonics for which to solve or choose a set of harmonics you define using the Harmonics Set modeling object.

Note:

Cyclic modes analysis is supported in NX Nastran version 11 or later, or any version of Simcenter Nastran.

Cyclic boundary coupling

When you include a Cyclic Modes step in a solution, you must define the boundary coupling using the Cyclic Symmetry simulation object at the global level.

For more information, see Cyclic symmetric boundary coupling.

Default cyclic analysis coordinate system (CSYS)

You must also define a default cylindrical coordinate system for the coupling in the FEM. The origin of the cylindrical system must be at the center of the revolution, and the Z-axis must be consistent with the axial direction. The default cylindrical coordinate system can be part of the FEM file template and, therefore, automatically created.

For more information about the global cyclic analysis coordinate system, see Simulation coordinate systems.

Specifying the harmonics to compute and output

In a Cyclic Modes step, you must specify:

• The harmonic numbers for which the software should compute a cyclic modes solution.

• The harmonic numbers for modal output.

You use the Harmonics Set modeling object to specify the harmonic numbers. For example, if you request a modal solution for the 0th, the 1st, and the 2nd harmonic, a discrete cyclic modal solution occurs for each of these harmonics. The options in the Harmonics Set dialog box correspond to the Simcenter Nastran HARMONICS case control command.

For each harmonic number, the software computes the following:

• Grid point displacements

• Stress

• Strain

• Grid point forces

• SPC forces

• Multipoint forces

• Element strain energy

• Element kinetic energy

• Grid point kinetic energy

The modal solution for each harmonic term is discrete and independent of other harmonic terms. Additionally, the software does not couple the modal results between the different harmonic numbers.

For more information, see Specifying harmonic index numbers.

Post-processing results from a cyclic modes analysis

After you solve a cyclic modes analysis, you can use Post-processing to display the results on either a 3D segment of the model or on a full 360° model display.

When you load results from a cyclic modes analysis into the Post Processing Navigator, the software organizes the results according to their harmonic index value.

For more information, see Cyclic symmetric post-processing options.

You can also filter orthogonal mode pairs in harmonic results using an option in the Post Preference dialog box. When selected, only one mode in an orthogonal pair of cyclic results is shown in the Post Processing Navigator and other dialog boxes that display results. In addition, a result probe calculates its values accordingly and uses only one mode from the orthogonal pair.

For more information, see Post view preferences.

Where do I find it?

Application

Pre/Post

Prerequisite

A Simulation file as the work part and the displayed partSimcenter Nastran or Simcenter 3D Multiphysics as the specified solverStructural or Coupled as the specified analysis typeSOL 401 Multi-Step Nonlinear (Simcenter Nastran), SOL 402 Multi-Step Nonlinear Kinematics (Simcenter Nastran), or Multi-Step Nonlinear (Multiphysics) as the specified solutionDefault cyclic analysis cylindrical coordinate system defined in the FEMCyclic Symmetry simulation objectStep - Cyclic Modes as the step type

Learn more

Specifying harmonic index numbers

Cyclic symmetric post-processing options

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Cyclic symmetric normal modes solutions, Simcenter 3D 2021.1 Series

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