Motion

In general, motion can be defined as the change in position of a body with respect to a certain reference frame.

Motion has different connotations in solid mechanics and fluid mechanics. In solid mechanics, a portion of solid region represents a portion of the solid body. Therefore, motion of the solid region corresponds to motion of the solid body. In fluid mechanics, a portion of fluid region represents a portion of space through which material flows. In this context, you move the fluid region to account for changes in the shape and position of the boundaries, for example due to the motion of adjacent bodies. Some examples of motion-induced flows are:

  • Mixing vessels, where mixer blades drive the flow
  • Turbomachinery
  • Flexible diaphragms in medical applications
  • Ship and propeller motion
  • Fluid structure interaction

There are four broad categories for defining motion in Simcenter STAR-CCM+: mesh displacement in real time, stationary mesh in a moving reference frame, harmonic balance flutter, and morphing in steady-state.

Mesh Motion in Transient Simulations

In transient simulations, mesh motion models allow you to move the vertices of the computational domain during the simulation:
  • In fluid mechanics applications, you can move the mesh rigidly according to prescribed rotations and translations (Rotation, Translation, Rotation and Translation, Trajectory motions), or use the Morphing method that accounts for non-rigid deformations. Simcenter STAR-CCM+ also provides the User-Defined Vertex Motion, which allows you to define the displacement of the mesh vertices, when the default models do not provide the required control.

    Fluid regions can also be coupled with 6-DOF rigid bodies in Dynamic Fluid-Body Interaction (DFBI) analyses. In this case, Simcenter STAR-CCM+ calculates the motion of the 6-DOF rigid body in response to applied forces. The fluid mesh is then either rigidly moved (DFBI Rotation and Translation, DFBI Embedded Rotation or Superposing Motion on a [body]-Motion), or morphed (DFBI Morphing motion), based on the calculated rigid body motion. For more information, see Dynamic Fluid Body Interaction.

  • In solid mechanics applications, you can move the solid mesh rigidly according to prescribed rotations and translations (Rotation, Translation, and Rotation and Translation motions).
  • In Fluid-Structure Interaction (FSI) simulations, you can move the solid mesh according to the displacements calculated by the solid stress solver (Solid Displacement motion). In solid-only simulations, it is not necessary nor convenient to move the mesh vertices with the Solid Displacement motion, as you can visualize the computed deformations using appropriate post-processing techniques, for example, using displacement vector warp surfaces. The Solid Displacement motion is intended for two-way coupled Fluid-Structure Interaction simulations, where the solid displacement motion of the solid drives the morphing motion of the fluid. If the solid mesh is also 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. For this purpose, the Solid Displacement motion can be superposed onto rotation and translation motions. See Modeling Fluid-Structure Interaction.
Rigid Motions
  • Rotation
  • Translation
  • Rotation and Translation
  • Trajectory

See Prescribing Rigid Rotations and Translations and Prescribing Motion along a Specified Trajectory.

Morphing
Morphing (deforming mesh)
Motion driven by 6-DOF Bodies:

See: DFBI Motion

  • DFBI Rotation and Translation
  • DFBI Embedded Rotation
  • DFBI Morphing
User-Defined Vertex Motion
User-Defined Vertex Motion
Solid Displacement
See Modeling Fluid-Structure Interaction.

Stationary Mesh in Moving Reference Frame

In steady simulations, or in transient simulations that do not require a time-accurate solution, moving reference frames provide a way of modeling rigid rotations and translations as a steady-state problem, while leaving the mesh stationary. Moving reference frames can rigidly rotate, or rotate and translate, relative to the laboratory frame. For more information, see Reference Frames and Moving Reference Frame.

For flow around rotating machinery, Simcenter STAR-CCM+ also provides simplified approaches that approximate the effect of a rotating structure on the surrounding flow field, without the need of mesh motion, moving reference frames, or detailed modeling of the structure geometry. For more information, see Rotating Flow.

Harmonic Balance Flutter

This category of motion is a corollary of the real-time displacement and applies only to harmonic balance flutter. The imposed modal displacement of the flutter boundary is applied to the frequency domain solver. There is only one option for this approach.

Morphing in Steady-State

This morphing motion is performed in steady-state for cases where the shape of the solution domain is part of the solution. This type of motion applies, for example, to fluid-structure-interaction simulations where you calculate the steady-state flow around a static deformation of the structure under the action of the steady-state fluid loads (aeroelastic or hydroelastic equilibrium). Since the velocity of the structure is zero (or almost zero), the grid flux is zero. For this motion type, the morpher is used to deform the mesh at the boundaries. Another use case for this morphing motion in steady-state is the simulation of die extrusion of non-Newtonian fluids. The extrudate is modeled as a free surface using the Arbitrary Lagrangian-Eulerian (ALE) method to track the shape of the free surface boundary.

For more information, see Setting up Extrusion and Free Surface Flow.

Morphing (deforming mesh)