Fourier harmonics analysis

You can include an Axisymmetric Fourier Modes step in your solution to perform axisymmetric Fourier harmonics analyses. The software computes the modes about the nonlinear stress or displacement state at the end of a previous static step in the solution.

Note:

Axisymmetric Fourier analysis is supported in NX Nastran version 11 or later, or any version of Simcenter Nastran.

In a standard axisymmetric analysis, the software calculates a subset of the 3D modes. The calculated modes are pure axial or radial modes and do not have any theta variation. These modes correspond to the 0th harmonic modes in an axisymmetric Fourier analysis. In an axisymmetric Fourier analysis, the software computes all the modes for a 3D structure. These modes include axial and radial modes with a theta variation as well as torsional modes. These modes have harmonic index numbers >0.

For more information, see Fourier harmonic solution in the Multi-Step Nonlinear User's Guide.

Supported element types

You can use the following types of elements in an Axisymmetric Fourier Modes step:

• Axisymmetric

• Plane stress

• Chocking

In an axisymmetric Fourier analysis, both axisymmetric and chocking elements:

• Have radial, axial, and theta degrees of freedom.

• Have those degrees of freedom represented as harmonic terms in a Fourier series.

Chocking element Gauss locations use the axisymmetric Fourier formulation if the software considers the location to be chocked. For the software to consider a location to be chocked, the following must be true:

• The loads in a previous static step result in the chocked condition.

• The axisymmetric Fourier step is sequentially dependent on the previous static subcase.

By default, the software considers all Gauss locations on the chocking elements to be unchocked in an axisymmetric Fourier step. For more information on chocking elements, see Chocking elements.

Specifying the harmonics to compute and output

In an Axisymmetric Fourier Modes step, you must specify:

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

• The harmonic numbers for modal output.

You can use the Harmonics Set dialog box to specify these harmonic numbers. For example, you can specify 0, 5, 7 if you want to compute modal results for the zeroth, fifth, and seventh harmonic. The options in the Harmonics Set dialog box correspond to the Simcenter Nastran HARMONICS case control command.

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

• Symmetric and antisymmetric displacements

• Stress

• Strain

• Single-point constraint (SPC) forces

• Nodal forces

For more information, see HARMONICS and HOUTPUT in the Simcenter Nastran Quick Reference Guide.

Post-processing results from an axisymmetric Fourier analysis

After you solve an axisymmetric Fourier 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 an axisymmetric Fourier normal modes analysis into the Post Processing Navigator, the software organizes the results according to their harmonic index value. For more information on displaying results for an axisymmetric Fourier normal modes analysis, see Axisymmetric Fourier harmonics post-processing options.

Where do I find it?

Application

Pre/Post

Prerequisite

A Simulation file as the work part and displayed partSimcenter Nastran or Simcenter 3D Multiphysics as the specified solverStructural as the specified analysis type2D Solid Option set to either ZX Plane, Z Axis or XY Plane, X AxisSOL 401 Multi-Step Nonlinear (Simcenter Nastran), SOL 402 Multi-Step Nonlinear Kinematics (Simcenter Nastran), or Multi-Step Nonlinear (Multiphysics) as the specified solutionStep - Axisymmetric Fourier Modes as the step type

Harmonics Set

Application	Pre/Post
Prerequisite	A Simulation file as the work part and displayed partSimcenter Nastran or Simcenter 3D Multiphysics as the specified solverStructural as the specified analysis type2D Solid Option set to either ZX Plane, Z Axis or XY Plane, X AxisSOL 401 Multi-Step Nonlinear (Simcenter Nastran), SOL 402 Multi-Step Nonlinear Kinematics (Simcenter Nastran), or Multi-Step Nonlinear (Multiphysics) as the specified solutionStep - Axisymmetric Fourier Modes as the step type
Command Finder	Modeling Objects

Learn more

Specifying harmonic index numbers

Axisymmetric Fourier harmonics post-processing options

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Fourier harmonics analysis, Simcenter 3D 2021.1 Series

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