2D axisymmetric and 3D cyclic symmetry analysis (SOL 402)

Note:

The capabilities described here are not officially supported for this release. This information is presented here to encourage you to test the capabilities. Please contact Customer Support if you would like to provide us with any feedback.

These capabilities are disabled by default. To test them, you must set system cell 755 to 1 in Simcenter Nastran. For more information, see The NASTRAN Statement and NASTRAN.

SOL 402 Multi-Step Nonlinear Kinematics provides you with several options for analyzing models that contain both 2D axisymmetric and 3D cyclic symmetry components. This capability lets you solve models, such as turbomachinery, that consist of rotors.

Note:

You can use both SOL 402 and SOL 414 to analyze models with rotors. In general, SOL 402 lets you focus on stress analysis, contact, nonlinear materials, and the dynamics of the entire system. SOL 414 lets you focus on the vibrations of the system and generate Campbell diagrams and harmonic response. Both solutions can consider rotors in rotation, but SOL 402 takes large displacements into account, and this is not optimal for considering vibrations because of the long computation time required. SOL 414, on the other hand, assesses the effect of the rotational speeds directly in the internal force of elements, and can therefore compute the vibrations much more quickly. For information on SOL 414, see Rotor dynamic analysis (SOL 414).

You can set up your 2D-3D analysis using both of the following methods:

• To automatically couple the 2D axisymmetric portion of your model to a 3D cyclic symmetry sector or a full 360-degree representation, use the Fourier Multi Harmonic and 3D Coupling simulation object.

• To couple the 2D axisymmetric portion of your model to the 3D portion so that you can apply forces or moments and monitor results, use the FOU3 element.

For the 2D axisymmetric analysis, you can request the harmonic numbers of the harmonic behavior for the Fourier axisymmetric elements using the Harmonic Set and Harmonics to Constrain modeling objects.

After you solve the 2D axisymmetric-3D cyclic symmetry model, in post-processing, you can recombine the axisymmetric and cyclic symmetry sectors to view the full model.

Fourier Multi Harmonic and 3D Coupling simulation object

The Fourier Multi Harmonic and 3D Coupling simulation object automatically couples a 2D axisymmetric portion of your model with a 3D cyclic symmetry sector or full 360-degree representation by connecting the edge of the 2D axisymmetric mesh (also called the Fourier mesh) to an element face on the 3D cyclic symmetric mesh.

To create the Fourier Multi Harmonic and 3D Coupling simulation object, you identify the source region (edge of the 2D axisymmetric portion of your model) and the target region (element face on the 3D cyclic symmetry sector or on the full 3D portion of your model). You then set options for the software to generate virtual nodes that establish the connection between the 2D and 3D portions of your model. The virtual nodes are copies of the nodes in the 2D edge region. The software glues the virtual nodes to the nodes on the 3D face and connects the virtual nodes to the nodes on the 2D edge using constraint conditions. You can control the number of virtual nodes and their location using the options in the Connection Nodes group of the Fourier Multi Harmonic and 3D Coupling dialog box. The goal is to generate enough nodes for a good connection but not so many nodes that the model becomes over constrained.

(1) 3D cyclic symmetry sector; (2) 2D axisymmetric component; (3) Fourier Multi Harmonic and 3D Coupling simulation object connecting the 3D and 2D portions of the model

FOU3 element

The FOU3 element (also called Fourier-3D connection element or FOU3 coupling element) is a specialized RBE3 element that couples a source node on the 3D portion of your model (3D cyclic symmetry sector or full 3D model) to a target node on the 2D Fourier axisymmetric portion of your model. You can use the FOU3 element to distribute boundary conditions or add bushing and bearing connections that you could not otherwise add to a Fourier mesh.

Because the FOU3 element supports multi-harmonics, you can simulate bending. To consider bending, you must request harmonic 1 (harmonic 0 is axisymmetric deformation).

When you create the FOU3 element, you can specify its coupling behavior by editing its mesh associated data. The behavior you select determines the source and target nodes that you need to select. On the Mesh Associated Data dialog box:

• To couple radial, tangential, and axial displacements, select 3 Kinematic Constraints.For this option, the 3D source node must have six degrees of freedom, and the 3D source node and 2D target node must be coincident (that is, they must share the same axial and radial location).

• To link the 3D node at R=0.0 to the mean displacement of a disk, where the radius of the disk is determined by the coordinate of the Fourier node, select 3D Node Linked to Mean Displacement.For this option, the 3D source node must lie on the axis of symmetry and the 2D target node must have the same axial coordinate.

Requesting harmonic output for the 2D axisymmetric analysis

To request the harmonic numbers for the 2D axisymmetric analysis, use the following modeling objects:

• To request the harmonic numbers of the harmonic behavior for the Fourier axisymmetric elements, create the Harmonic Set modeling object.

• To omit harmonic numbers from the output, create the Harmonics to Constrain modeling object.

You define both the Harmonics Set and the Harmonics to Constrain modeling objects at the solution level. The Harmonics Set requests the harmonic numbers for all of the subcases. The Harmonics to Constrain, however, limits the harmonic numbers by the following subcase types:

• Modal subcases:Subcase - Complex ModesSubcase - Cyclic ModesSubcase - Normal Modes

• Nonlinear and preload subcases:Subcase - Nonlinear StaticsSubcase - Nonlinear DynamicsSubcase - Preload

Harmonics Set corresponds to the FHAR bulk entry, and Harmonics to Constrain corresponds to the FHAC bulk entry.

Requesting harmonic output for cyclic symmetry

For Subcase - Cyclic Modes, you can request the harmonics to compute by creating or specifying a Harmonics Set. This Harmonics Set is created at the subcase level and corresponds to the HARMONICS case control command. It represents the wave number for the cyclic symmetric mesh.

Note:

When your solution contains both Harmonics Set (FHAR) at the solution level and Harmonics Set (HARMONICS) at the Subcase - Cyclic Modes level, the solver handles the sets as follows:

• The solution-level Harmonics Set (FHAR) requests the harmonic terms to apply to the circumferential shape functions used by the axisymmetric harmonic elements.

• The subcase-level Harmonics Set (HARMONICS) defines the wave numbers.

Post-processing results

To generate the results necessary for viewing the full 2D axisymmetric structure in post-processing, set the following options in the Solution dialog box, Parameters page:

• To specify how you want the 2D axisymmetric results to be displayed, select the Fourier Harmonic Post-Processing Recombination Mode (FHPOST) check box and then select an option from the list.

• To specify the number of angle increments in a 90-degree quadrant in which the software computes the 3D harmonic results for the axisymmetric Fourier elements, select the Number of Recombined Elements per 90 Degrees (FHPNST) check box and type the number of angle increments.

Where do I find it?

Creating the Fourier Multi Harmonic and 3D Coupling simulation object

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partSimcenter Nastran as the specified solverStructural as the specified analysis typeSOL 402 Multi-Step Nonlinear Kinematics as the specified solution type
Command Finder	Fourier Multi Harmonic and 3D Coupling
Simulation Navigator	Under the active solution, right-click the Simulation Objects node→New Simulation Object→Fourier Multi Harmonic and 3D Coupling

Creating the FOU3 coupling element

Application	Pre/Post
Prerequisites	A FEM file as the work part and displayed partSimcenter Nastran as the specified solverStructural as the specified analysis typeSOL 402 Multi-Step Nonlinear Kinematics as the specified solution type
Command Finder	1D Connection
Location in dialog box	1D Connection dialog box→Type list set to Node to Node→Connection Element group→Type list→FOU3

Creating Harmonic Set or Harmonics to Constrain modeling objects

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partSimcenter Nastran as the specified solverStructural as the specified analysis typeSOL 402 Multi-Step Nonlinear Kinematics as the specified solution type
Simulation Navigator	Right-click the active solution→Edit
Location in dialog box	Solution dialog box→Case Control page→Create Modeling Object (next to Fourier Harmonics or Fourier Harmonics to Constrain)

Displaying 2D axisymmetric and 3D cyclic symmetry results in post-processing

Application	Pre/Post
Prerequisites	Results from a cyclic symmetric, axisymmetric, or multi-stage cyclic symmetric solution Contour plot color display in a post view
Command Finder	Set Result
Location in dialog box	Edit Result dialog box→Symmetric Display Options

2D axisymmetric and 3D cyclic symmetry analysis (SOL 402), Simcenter 3D 2021.1 Series

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