Coupling 2D and 3D portions of a model (SOL 414)

You can create and analyze a rotor that consists of a 2D axisymmetric portion and a 3D model or a 3D sector of cyclic symmetry. For example, you can:

• Model the shaft of a rotor with 2D Fourier multi-harmonic elements.

• Model the rotor using cyclic symmetry.

• Couple the mesh of the 2D shaft with the mesh of the 3D part that models a sector of the rotor.

• Apply cyclic symmetry boundary conditions to describe the complete 3D model.

To connect a 2D axisymmetric portion of your model to a 3D model or a sector of a 3D cyclic symmetry model, such as connecting a shaft and a rotor, you can use the following options:

• FOU3 coupling element, which is a manual method for connecting a node on the axis of a 3D rotor to a node in the 2D axisymmetric portion of the model.

• Fourier Multi Harmonic and 3D Coupling simulation object, which automatically couples a 2D axisymmetric model and a full 3D rotor model or a 3D sector of cyclic symmetry.

Fourier-3D connection element

The Fourier-3D connection element (also called FOU3 coupling element) connects the source node on the axis of a rotor in the 3D portion of your model to a target node in the connectivity of a Fourier axisymmetric element. The 3D portion can include elements with six degrees-of-freedom such as solid elements, beam elements, and bushing elements.

You can include the source node in the connectivity of other elements, use it to apply forces or moments, or use it to monitor results. The FOU3 coupling element is a special type of RBE3 that distributes the forces and moments between the 3D node and the Fourier elements with harmonic-dependent degrees-of-freedom.

You create FOU3 coupling elements using the 1D Connection command.

After you create an FOU3 coupling element, you can specify its coupling behavior in the Mesh Associated Data dialog box:

• From the Fourier Connection Option list, select 3 Kinematic Constraints to couple the radial, tangential, and axial displacements.For this option, the source and target nodes must be coincident.

• From the Fourier Connection Option list, select 3D Node Linked to Mean Displacement 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.For this option, the source node must lie on the symmetry axis and the target node must have the same axial coordinate.(1) FOU3 element using 3D Node Linked to Mean Displacement connection option to connect (2) CBEAR2 and (3) 2D axisymmetric node(1) FOU3 element using 3D Node Linked to Mean Displacement connection option to connect (2) 2D axisymmetric node to (3) axis of rotor

For more information and examples using the Fourier-3D connection element, see Creating connection elements on a rotor model (SOL 414).

Automatic 2D-3D coupling

You can optionally model a portion of the geometry as axisymmetric and model the remainder of the geometry without axisymmetry. To do so, use automatic 2D-3D coupling to connect an axisymmetric mesh edge to an element mesh face in the non-axisymmetric portion of the model. The non-axisymmetric portion of the model can be a full 360-degree representation or a cyclic symmetric sector.

You request the automatic 2D-3D coupling with the Fourier Multi Harmonic and 3D Coupling simulation object. You create an element edge region on the Fourier mesh and a surface region on the 3D mesh. The software creates virtual nodes during the solution along a face that is parallel to the 3D face region. The virtual nodes are copies of the nodes in the 2D edge region. It 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.

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

Best practices

Following are some best practices when you use the Fourier Multi Harmonic and 3D Coupling simulation object to connect a 2D axisymmetric portion of a model with a 3D cyclic symmetry sector.

• Avoid coincident nodes between the 2D Fourier model and the face on the 3D faces cyclic symmetry sector.

• If you manually set the angle computation for determining where to locate the virtual nodes, set initial and variation angle values that omit the border edges of the 3D sector.For more information, see Automatic Angles Computation in Fourier Multi Harmonic and 3D Coupling dialog box.

• Set an adequate number of virtual nodes but not so many that the model is overconstrained. For example, if the face of the 3D sector has 5 circumferentially equidistant nodes, a good number of virtual nodes is 4.

• If the 2D part is modeled with parabolic Fourier elements, the solver displays messages about fixations, such as the following:============================================================== == WARNING  FIXATION OF D.O.F. CORRESPONDING TO NULL PIVOTS == == IF NOT EXPECTED, CHECK THE CONSISTENCY OF YOUR RESULTS   == ============================================================== You can ignore these messages because they do not affect the results of the analysis. To eliminate the messages, you must remove the midside nodes (BEDGE region) of the edges from the coupling definition. To remove them, you must edit the input file. These midside nodes cannot be removed in Pre/Post.

Where do I find it?

Manually connecting 2D and 3D using FOU3 coupling elements

Application	Pre/Post
Prerequisites	A FEM file as the work and displayed partSimcenter Nastran as the specified solverRotor Dynamics as the specified analysis typeAny solution type except SOL 414,103 Eigenvalues and Superelement Reduction
Command Finder	1D Connection
Location in dialog box	Connection Element group→Type list→FOU3

Automatically coupling Fourier elements to 3D elements

Application	Pre/Post
Prerequisites	A Simulation file as the work and displayed partSimcenter Nastran as the specified solverRotor Dynamics as the specified analysis typeAny solution as the specified solution typeFor SOL 414,103 Eigenvalues and Superelement Reduction, Computation Options must be set to Eigenvalues
Command Finder	Fourier Multi Harmonic and 3D Coupling
Simulation Navigator	Right-click Simulation Objects→New Simulation Object→Fourier Multi Harmonic and 3D Coupling

Coupling 2D and 3D portions of a model (SOL 414), Simcenter 3D 2021.1 Series

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