17.6.2.32. Rotating Force

The Rotating Force boundary condition is available for a Full Harmonic Response analysis when the Coriolis Effect property in the Rotodynamics Controls category of the Analysis Setting is set to On, Stationary Reference Frame. The default setting is Off. If the analysis does not specify the Solution Method as Full and the Coriolis Effect property is not turned on, the boundary condition is not valid.

You specify a Rotating Force as a force rotating synchronously or asynchronously.

When you set the Calculated From property to Unbalanced Mass, the force is a specific synchronous force due to Mass Unbalance. The application calculates the actual unbalanced rotating force as show here:

FUnb = m * r * Ω2 = Unb * Ω2

Where:

FUnb = Actual Unbalanced Force due to Unbalanced Mass.

m = Magnitude of mass unbalance (input value from Mass field).

r = Distance from the mass unbalance to the spin axis (input value from Rotating Radius field).

Unb = Unbalanced Force or Mass Unbalance = m * r (computed value shown in Unbalanced Force field).

Ω = Rotational velocity of the structure.

When you set the Calculated From property to Direct Input, the force is a general harmonic rotating forces and it can be applied synchronously or asynchronously based on the value of the Synchronous Ratio property.

For specific technical information, see the General Asynchronous Rotating Force and Specific Synchronous Forces: Mass Unbalance topics of the Harmonic Analysis with Rotating Forces on Rotating Structures section in the Mechanical APDL Theory Reference.

Tips and Hints

Note the following:

  • The axis of the Rotating Force should coincide with or be parallel to one of the Global Coordinate (X, Y, or Z) axes.

  • You can create either a specific synchronous configuration or a general rotating asynchronous configuration, but not a combination of the two. A combination would require that two SYNCHRO commands be issued on two different components. The Mechanical Ansys Parametric Design Language (MAPDL) Solver does not support the use of multiple SYNCHRO commands. The solver overwrites any existing SYNCHRO definitions when the command is issued.

Important:  The Rotating Force boundary condition does not support multiple spool or rotor/stator problems.

This page includes the following sections:

Analysis Types

Rotating Force is only available for Harmonic Response analyses using the Full Solution Method.

Dimensional Types

The supported dimensional types for the Rotating Force boundary condition include:

  • 3D Simulation

Geometry Types and Topology Selection Options

Rotating Force is always applied to all bodies of a model.

Magnitude Options

The Rotating Force boundary condition is defined as a constant.

Applying a Rotating Force Boundary Condition

To apply a Rotating Force:

  1. Specify the Analysis Settings of the Harmonic Response analysis accordingly.

  2. On the Environment Context tab, open the Loads drop-down menu and select Rotating Force. Alternatively, right-click the Environment tree object or within the Geometry window and select Insert>Rotating Force.

    Note:  By default, the application scopes the Rotating Force boundary condition to All Bodies. This includes connections (that is, bearings, springs, beams, etc.).

  3. Select a desired geometry selection filter, Body, Face, or Edge and then select the Click to Define field of the Axis property. Select the desired entity to define as the axis of rotation, and then click Apply.

    Note:

    • For a Face selection, the axis of rotation is normal to the selected face.

    • For an Edge selection, the axis of rotation is along the selected edge.

    • This axis should coincide with or be parallel to one of the Global Coordinate (X, Y, or Z) axes.

  4. Specify the Define By property. The options specify where the force is applied on your model.

    Tip:  The properties of the Location category define the point where the Rotating Force is applied on the model. Ansys recommends that you do not use a Remote Point to specify this point.

  5. Specify the Calculated From property. Options include Unbalanced Mass (default) and Direct Input. This property defines how the force is generated, either based on the mass of the structure or a Magnitude entry.

  6. Using the options of the Hit Point Selection property, specify whether the application selects a node or a Remote Point as the point on the axis where the Rotating Force (F Command) is applied. Options include Mesh Node (default) and Remote Point. Ansys recommends that you use a Remote Point for this property's definition.

Details Pane Properties

The properties available in the Details pane are described below.

CategoryProperties/Options/Description

Scope

Define By: A read-only field displaying how the object is scoped - Geometry Selection.

Geometry: A read-only field displaying the geometries that the object is scoped to - All Bodies.

Axis: This property defines the axis of rotation of the scoped geometry and its direction of rotation.

Location

Define By: This property specifies how the force is applied on your model.

The Define By property options, listed below, specify where the force is applied on your model:

Coordinates

You use this default setting to either:

  • Select a user-defined coordinate system from the Coordinate System property. For all other Define By options, the Coordinate System property is read-only.

  • Manually define coordinates using the X/Y/Z Coordinate properties.

This is the only option that provides the Location property.

Geometry Selection

The Geometry property becomes visible when the Define By property is set to Geometry Selection. Select the Geometry property field and select the desired geometry. Displays the type of geometry and the number of geometric entities (for example: 1 Face, 2 Edges) based on specified Location.

Named Selection

The Named Selection property becomes visible when the Define By property is set to Named Selection. This field provides a drop-down list of available user-defined Named Selections.

Remote Point

The Remote Points property becomes visible when the Define By property is set to Remote Point. This field provides a drop-down list of available user-defined Remote Points. In order for this property to be an available option of the Define By property, you need an existing Remote Point to be defined.

Note:  Selecting a Remote Point on the rotational axis disables the Unbalanced Force property because the Rotating Radius is zero.

X Coordinate/Y Coordinate/Z Coordinate: These properties are only available for as input properties when the Define By property is set to Coordinates. Otherwise these properties are read-only.

Location: Specify a geometric entity on your model to apply the Rotating Force. Body, Face, and Edge selections are supported.

Definition

Type: Read-only field that describes the object - Rotating Force.

Calculated From: Options include Unbalanced Mass (default) and Direct Input.

Mass: Entry field when the Calculated From property is set to Unbalanced Mass. Enter a desired mass value.

Rotating Radius: This property displays when you set the Calculated From property to Unbalanced Mass. The application automatically updates the value of this property if you make a change to the selection of the Location property. This field becomes read-only when the Define By property is set to Remote Point.

Unbalanced Force: Visible and read-only when the Calculated From property is set to Unbalanced Mass. Unbalanced Force = Mass * Rotating Radius.

Synchronous Ratio: Entry field when the Calculated From property is set to Direct Input. The default value is 1.

Magnitude: Entry field when the Calculated From property is set to Direct Input.

Phase Angle: Specify a phase shift angle that defines how the load can be out of phase with another load. Boundary conditions supported with the Phase Angle property enable you to specify a phase shift that defines how the loads can be out of phase with one another. You can specify the preferred unit for phase angle (in fact all angular inputs) to be degrees or radians using the Units menu on the Home tab.

Hit Point Selection: This property specifies whether the application selects a node or a Remote Point as the point on the axis where the Rotating Force (F Command) is applied. Options include Mesh Node (default) and Remote Point. Ansys recommends that you use a Remote Point for this property's definition.

Remote Point for Hit Point: Visible when the Hit Point Selection property is set to Remote Point. This field provides a drop-down list of available Remote Points.

Suppressed: Include (No - default) or exclude (Yes) the boundary condition form the solution.

Information

The Information category provides read-only information for the following properties:

Hit Points

  • Hit Point: Node Id: this information property displays the node identifier at the Hit Point location. It has certain requirements and conditions, including:

    • The Hit Point Selection property must be set to Mesh Node

    • A valid mesh must be generated.

    • A valid node needs to exist at the Hit Point location. If no node is found, then no information is displayed.

    • When the Hit Point Selection property is set to the Remote Point option, this property requires a valid Remote Point and then displays the Named Selection created in ds.dat file.

  • Hit Point: Location X

  • Hit Point: Location Y

  • Hit Point: Location Z

Axis Locations

Axis Location coordinates are always with respect to Global Coordinate System.

  • Axis Location X

  • Axis Location Y

  • Axis Location Z

Axis Components

Axis coordinates and Components gives information of where and how the axis is oriented. Axis Components are always unit vectors with respect to Global Coordinate System.

  • Axis Component X

  • Axis Component Y

  • Axis Component Z

Mechanical APDL References and Notes

The following Mechanical APDL commands, element types, and considerations are applicable for this boundary condition.

  • The CORIOLIS command is issued to account for gyroscopic damping effect resulted from rotational velocity defined via CMOMEGA.

  • The SYNCHRO command is issued based on specific synchronous/general asynchronous definition of all of the Rotating Forces.

  • The CMOMEGA command is issued based on axis definition of all of the Rotating Forces.

  • The F command is applied at Hit Point location based on specific synchronous/general asynchronous definition of Rotating Force.

API Reference

For specific scripting information, see the Rotating Force section of the ACT API Reference Guide.