Creating connection elements on a rotor model (SOL 414)

Typically, you define concentrated masses, bearings, forces, and boundary conditions on the rotor axis. Your options to do this are different depending on whether you are modeling a 3D rotor or a 2D axisymmetric rotor.

Connection elements on a 3D rotor model

For 3D rotor models, you define a bearing on the rotor axis and link it to the 3D model using an RBE2 (spider) element.

(1) 3D rotor; (2) RBE2 element; (3) bearing element

Connection elements on a 2D axisymmetric rotor model

For 2D axisymmetric rotor models, you can create a connection similar to the bearing on the rotor axis for the 3D model by using either of the following:

• Fourier-3D connection elements (FOU3)Creating FOU3 elements is a manual process in which you must create one element for each node on the 2D axisymmetric mesh that needs to be connected to a bearing connection on the rotor axis. If you also have retained nodes for applying an Unbalance Mass load or a boundary condition, you must then create an RBE3 to link the nodes of the FOU3 elements that are located on the rotor axis to the retained nodes.(1) FOU3 element connecting (2) CBEAR2 and (3) 2D axisymmetric node

• Bearing (CBEAR2) and bushing (CBUSH and CBUSH2) universal connectionsCreating universal connections is a more automated process. When you create the bearing or bushing universal connection, you select the source and target nodes, specify how you want them to be connected (for example, connecting a source node to the target nodes using a spider connection), and set the axis. When you realize (mesh) the universal connection, the CBEAR2, CBUSH, CBUSH2, FOU3, and RBE3 elements are automatically created for you.(1) Bearing universal connection; (2) spider elements linking to a high-pressure rotor; (3) spider elements linking to a low-pressure rotor****Bearing universal connection (realized) with (1) CBEAR2 element; (2) RBE3 element; (3) FOU3 elements

You can use both FOU3 connection elements and universal connections in your model. In general, use the universal connections to create bearing and bushing connections. Use the FOU3 connection elements when you need to add the following on the rotor axis:

• Boundary conditions, such as Force or Unbalance Mass

• 0D meshes to create Lumped Mass (concentrated mass)

• CLINK element for adding Geometric Misalignment loads

• Retained node to monitor output

For information on bearing or bushing universal connections, see Universal connections, Bearing universal connection for rotor dynamics (SOL 414), and Using bushing universal connections in rotor dynamics (SOL 414). For information on manually creating FOU3 elements, see Creating FOU3 elements below.

Creating FOU3 elements

The FOU3 element links a node on the 2D axisymmetric portion of the model to a node on the rotor axis, and then links the node on the rotor axis to a bearing connection. You select a 3D node on the rotor axis first and then a 2D node on the axisymmetric mesh of rotor shaft.

If a larger portion of the 2D axisymmetric model acts on the bearing, you can create as many FOU3 element connections as necessary between the 3D nodes on the rotor axis and the 2D model nodes, with all of the FOU3 connections using the same axial coordinates. The 3D nodes are projected onto the rotor axis, and the FOU3 elements are perpendicular to the rotor axis.

(1) FOU3 elements perpendicular to rotor axis

The following example shows the FOU3 elements connected with RBE3 elements, a bushing element, and a single-point constraint (SPC).

(1) FOU3 elements perpendicular to rotor axis; (2) RBE3 element between nodes 1948, 1946, 1947, and 1970; (3) CBUSH2 element between nodes 1970 and 1999, with an SPC connection on node 1999; (4) Grounded bushing element

In this example, you link the 3D nodes on the rotor axis using an RBE3 element to connect the 3D nodes to the bearing node. Use 3D-Fourier connections like this for bearings, concentrated mass (on 0D elements), or boundary conditions that are defined on the rotor axis.

Setting degrees of freedom in an RBE3 element

When you use an RBE3 element, the translational degrees of freedom (DOFs 1, 2, and 3) are transmitted by default. If you also want the rotational degrees of freedom (DOFs 4, 5, and 6) to be taken into account, you must change the default. To do so, right-click the RBE3 element and choose Edit Mesh Associated Data. In the Leg Node Degrees of Freedom group, set the all of the DOFs to On.

Connecting a single node on a 2D rotor to a concentrated mass

This example workflow uses a single FOU3 element to link a single node on a 2D rotor to a concentrated mass.

1. Create a node for the concentrated mass (1) on the rotor axis.

2. Identify a node on the 2D rotor (2) that has the same axial position as the node for concentrated mass (1).

3. Create a 1D Connection FOU3 element (3) between the source node (1) and target node (2).

Connecting a concentrated mass on the edge of a 2D rotor

This example workflow uses multiple FOU3 elements to link nodes on a 2D rotor to paired nodes on the rotor axis and a concentrated mass.

1. Identify the nodes on the top edge of the 2D rotor (1).

2. For each node identified on the 2D rotor (1), create a node on the rotor axis (2)

3. Create an FOU3 1D connection for each pair of nodes (3).The source nodes (2) are on the rotor axis.The target nodes (1) are on the 2D rotor edge.

4. On the rotor axis, create a node at the location of the concentrated mass (3).Note: In this example, the actual concentrated mass is not shown.

5. Create an RBE3 (5) 1D connection between the concentrated mass (5) and the nodes on the rotor axis (2).

Where do I find it?

Creating FOU3 elements

Application	Pre/Post
Prerequisites	A FEM file as the work and displayed partSimcenter Nastran as the specified solverRotor Dynamics as the specified analysis type
Command Finder	1D Connection
Location in dialog box	Connection Element group→Type list→FOU3

Creating bearing or bushing universal connections

Application	Pre/Post
Prerequisite	A FEM or assembly FEM file as the work part and displayed partSimcenter Nastran as the specified solverRotor Dynamics as the specified analysis typeTo realize a bearing universal connection as CBEAR2 + FOU3 + RBE3 spider(s), 2D Solid Option is set to a plane and axis
Command Finder	Bearing Connection Bushing Connection

How do I

Create connection elements between coincident nodes with CBEAR2 elements

Define rotor bearing or bushing properties

Create a rotor region

Define a rotor

Define the rotor dynamics solution parameters

Create an unbalance mass

Define forcing frequencies

Define nonlinear transient parameters

Set the duration of the simulation

Create a modeling object

Assign a modeling object to a solution or solution subcase

Learn more

Rotor dynamic analysis (SOL 414)

Modeling axisymmetry (SOL 414)

Modeling cyclic symmetry (SOL 414)

Damping (SOL 414)

Quick links

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Pre/Post video examples

Bulk Entry Descriptions

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Creating connection elements on a rotor model (SOL 414), Simcenter 3D 2021.1 Series

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