Motion Models

Simcenter STAR-CCM+ provides several motion models that move the mesh vertices using different methods.

Stationary

The stationary model sets the grid velocity to zero, $v_{g} = 0$ , which means that no mesh motion is applied. In this case, the mesh vertices remain static during the simulation.

You can define the mesh as stationary with respect to the laboratory frame or a rigidly moving reference frame. Defining the mesh as stationary with respect to a moving frame allows you to model the rotations and translations of a region as a steady-state problem in the moving frame. This approach provides a time-averaged solution and is not appropriate for cases that require a time-accurate description.

Rigid Motions: Rotation, Translation, Rotation and Translation, Trajectory

Rigid motion models move the mesh vertices according to user-specified rotations, translations, or trajectories. Rigid motions can only be defined with respect to the laboratory reference frame.

The mesh velocity

v_{g}

is defined as follows:

For rotation, $v_{g} = ω_{g} \times r$ , where $ω_{g}$ is the prescribed angular velocity and $r$ is the position vector of a mesh vertex.
For translation, $v_{g} = v_{g, t}$ , where $v_{g, t}$ is the prescribed translation velocity.
For rotation and translation, $v_{g} = v_{g, t} + ω_{g} \times r$ .
For trajectory-driven motions, you specify the mesh trajectory using imported table values, which specify the coordinates ${(x, y, z)}_{i}$ that define the trajectory.
Simcenter STAR-CCM+ determines the grid velocity based on the specified input data: you can either include time data in the table, ${(t, x, y, z)}_{i}$ , or provide a field function that defines either the velocity or displacement as a function of time.

Morphing

For morphing motion, Simcenter STAR-CCM+ deforms the mesh according to the displacement of a set of control points. In this case, $v_{g}$ can be interpreted as the rate of change of the mesh vertices displacement in response to the control points displacement. Morphing motion can be defined in either a stationary or a moving reference frame.

For more information on the morphing method, see Morphing.

DFBI Motions: DFBI Rotation and Translation, DFBI Embedded Rotation, DFBI Morphing

When these motions are assigned to a region, the region is coupled with a 6-DOF body. When defining the 6-DOF body, you specify the region boundary that represents the surface of the rigid body. In this case, Simcenter STAR-CCM+ calculates the motion of the body in response to the fluid forces and moments at the coupled boundary (see 6-DOF Rigid Body Motion).

The effect of the motion of the rigid body on the coupled region is accounted for by morphing the fluid boundary (DFBI Morphing), or by moving the entire fluid mesh rigidly (DFBI Rotation and Translation and DFBI Embedded Rotation).

Solid Displacement Motion

The Solid Displacement motion moves the vertices of a solid mesh according to the non-rigid displacements $u$ computed by the solid stress solver (see Eqn. (4877)). This motion model is intended for two-way coupled Fluid-Structure Interaction analyses, where the motion of the solid mesh drives the morphing motion of the fluid mesh.

If the solid mesh is rigidly rotating and translating, but the effect of non-rigid deformations on the fluid flow are still important, the fluid mesh must morph according to the total displacement $u_{T}$ (see Eqn. (4878)). For this purpose, the Solid Displacement motion can be superposed onto rotation and translation motions.