Prescribing Rigid Motion

In transient simulations, you can model rigid motions of the solid structure by prescribing corresponding mesh motions. You can define rigid rotations, translations, or the trajectory of the structure in space. When computing the solid displacements, Simcenter STAR-CCM+ accounts for the elastic deformation due to the inertia forces that arise from acceleration of the solid structure.

To define rigid motion:

Right-click the Tools > Motions node and add one of the following motions. Depending on the selected motion type, specify the relevant motion settings, such as the rotation rate and axis, or the object trajectory.

Motion Type	Motion Settings
Rotation	To model a rigid rotation about a fixed axis, specify the axis of rotation and either the rotation rate or rotation angle. When the solid stress model is active, any expressions that define the rotation axis direction and origin must be time-independent. See Prescribing Rotations and Translations.
Translation	To model a rigid translation along a fixed direction, specify the translation velocity and the direction along which the solid translates. See Prescribing Rotations and Translations.
Rotation and Translation	To model a combination of rotation and translation, define the details for both motions.
Trajectory	To define the trajectory of the solid structure in space, use a field function. Solid stress regions do not support table-based trajectories. See Prescribing Motion along a Specified Trajectory.

For more information on the available settings, see Rigid Motion Models Reference.

If required, define any superposing motions. For example, you can define a rotation motion relative to another rotation motion.

For istructions, see Superposing Additional Rigid Motions and Superposing Motions on a Trajectory Motion.

For superposing motions, Simcenter STAR-CCM+ calculates the total mesh velocity and acceleration according to Eqn. (4874) and Eqn. (4876).

To assign a motion to the solid region:

Select the Regions > [Solid Region] > Physics Values > Motion Specification node and choose the relevant motion using the Motion property.

When defining loads and constraints on moving solids, the following apply:

You always define constraints with respect to a coordinate system that follows the prescribed solid motion.
You can define body, surface, curve, and point loads in either the laboratory coordinate system (appropriate, for example, for gravity loads) or in a coordinate system that follows the solid motion.

To define a coordinate system that follows the solid motion:

Create a local coordinate system. Choose either Cartesian, Spherical, or Cylindrical, as appropriate to your load, or constraint. For instructions, see Creating a Local Coordinate System.
Select the relevant Tools > Motions > [Rigid Motion] node and set Managed Coordinate Systems to the local coordinate system that you created.

To define loads and constraints in this coordinate system:

Depending on the type of load, or constraint, use one of the following methods:

Load Type	Method
Body Load	Define the body load as described in Applying Mechanical Loads. Select the [Solid Region] > Physics Values > Body Load node and set Coordinate System to the moving local coordinate system.
Surface, Curve, or Point Load	Define the surface, curve, or point load as described in Applying Mechanical Loads. Select the Regions > [Segments] > [Segment] > Physics Conditions > Solid Stress Loads node and set Method as appropriate. Expand the [Segment] > Physics Values node. For Traction, Force, or Line Load values, set Coordinate System to the moving coordinate system. Loads specified using the Pressure method are always defined in the coordinate system that follows the solid motion.
Surface, Curve, or Point Constraint	Define the surface, curve, or point constraint as described in Applying Constraints. Select the Regions > [Segments] > [Segment] > Physics Conditions > Solid Stress Constraints node and set Method as required. Constraints specified using the Fixed or Normal Displacement methods are automatically defined in the coordinate system that follows the solid motion. When using the Displacement method: Select the [Segment] > Physics Values > Displacement node and set Coordinate System to the moving local coordinate system.

Simcenter STAR-CCM+ also allows you to define rotations and translations with respect to the motion of a 6-DOF body. This type of motion is described in the context of Fluid-Structure Interaction applications (see Fluid-Structure Interaction General Workflow). You can use a similar setup for solid-only simulations. However, you can only define 6-DOF bodies when the simulation contains a region with DFBI motion (see Dynamic Fluid Body Interaction).

Note	If you are running a quasi-static analysis (that is, you activated the Static Analysis mode for the Solid Stress solver), the inertia terms caused by the deformation are neglected, while rigid accelerations contribute to the structure loading.