Fluid-Structure Interaction Reference

Fluid Region > Interface Boundary > Physics Conditions

FSI Coupling Specification

Allows you to check the coupling between the solid and fluid domains. This property is read-only and depends on the motion settings for the solid region.

For problems where the solid is Stationary or subject to rigid body or superposed rigid body motions, this property is set to Solid Motion.
For problems where the solid is subject to Solid Displacement, this property is set to Solid Displacement.

Solid Region > Interface Boundary > Physics Conditions

FSI Dynamic Stabilization

Available when you set the Stabilization Method for the Fluid Structure Coupling solver to Dynamic (see Stabilization Method), and you set the FSI Coupling Specification to either Fluid load - Pressure & Wall Shear Stress or Fluid Load - Pressure (see FSI Coupling Specification).

Allows you to select the calculation method for the displaced fluid per unit area. The solver uses this value as a preconditioner for the implicit algorithm in achieving stability. The solver adds a force correction which is proportional to the product of the displaced fluid per unit area and the change in the structure acceleration. This preconditioner is particularly important in strongly coupled FSI applications.


Method	Corresponding Value Nodes
Auto Simcenter STAR-CCM+ automatically estimates the volume of displaced fluid per unit area.	None
Manual Allows you to manually specify the volume of displaced fluid per unit area.	FSI Dynamic Stabilization Coefficient Allows you to set the Displaced Fluid Volume/Surface Area

FSI Coupling Specification

Specifies the coupling between the fluid and solid.


Method	Corresponding Physics Values
Uncoupled Neglects the effects of the fluid load on the solid body.	None
Fluid Load - Pressure & Wall Shear Stress Accounts for the effect of both the fluid pressure and wall shear stress on the solid. See Eqn. (343).	FSI Mapped Traction Allows you to specify the Coordinate System in which the Mapped FSI Traction vector is defined. See Mapped FSI Traction.
Fluid Load - Pressure Accounts for the effect of the fluid pressure on the solid, while neglecting the wall shear stress. Pressure is the normal component of the fluid load, as defined in Eqn. (343).
Fluid Load - Wall Shear Stress Accounts for the effect of the fluid wall shear stress on the solid, while neglecting pressure. Wall shear stress is the tangential component of the fluid load, as defined in Eqn. (343).

FSI Fluid Load Clipping

Allows you to set the limit values for both Pressure and Shear when either are active.


Properties	Corresponding Value Nodes
Pressure When activated, allows you to set limit values for the fluid pressure that is applied to the solid.	FSI Pressure Clipping Specifies the Maximum and Minimum values of the fluid pressure. Only the values within the specified range are applied to the solid.
Shear When activated, allows you to specify an upper limit for the wall shear stress that is applied to the solid.	FSI Shear Clipping Specifies the Maximum value of wall shear stress. Only the values below the specified maximum value are applied to the solid.

FSI Fluid Load Ramping

Simcenter STAR-CCM+ ramps the fluid load from zero to the actual value, in a specified time.

Option

Corresponding Value Nodes

None: The full fluid load is applied at the start of the simulation.

None

Linear: The fluid load will be linearly increased between the times specified.

FSI Traction Linear Ramping

Allows you to specify the Starting Time and the Stopping Time for which the fluid load will be applied.

注	Ensure that the Stopping Time is set before the Starting Time.

Surface Load Linearization

Available when the Nonlinear Geometry model is active in the solid physics continuum. See Nonlinear Geometry Model Reference.

Fluid Structure Coupling Solver

The fluid structure coupling solver manages the mapping of the coupled fields between the fluid and solid. Within the properties of the solver, you can specify the stabilization method across the solid-fluid interface.

Solver Properties

Stabilization Method

Allows you to choose the method of stabilization for two-way coupled FSI simulations. As well as stabilizing the solution, the stabilization method accelerates the convergence of the coupled system. One-way coupled problems do not require stabilization.


Method	Corresponding Node
None (default) Suitable for one-way coupled FSI setups. No stabilization is applied to the FSI problem.	None.
Constant Displacement Under-relaxation Applies a constant, specified under-relaxation factor to the deformation of the fluid-structure interface. Suitable for two-way coupled FSI setups.	Solvers > Fluid Structure Coupling > Constant Displacement Under-relaxation Allows you to set the Under-Relaxation Factor.
Dynamic Specifies the method for calculating the displaced volume per unit area. Recommended for transient, two-way coupled simulations in which the displaced fluid volume is relatively large.	Regions > [Solid Region] > Boundaries > [Interface Boundary] > Physics Conditions > FSI Dynamic Stabilization For properties, see FSI Dynamic Stabilization.

Model Compatibility

Allows you to select whether the model compatibility is enforced. The options for this are:

Enforce—prevents the simulation from running if the simulation contains any of the following incompatible settings:
- Morph At Inner Iterations is deactivated.
- Boundary-mode fluid-structure interfaces.
- 2nd order temporal discretization with the Newmark or Generalized-α time integration method selected.
Ignore—allows the simulation to run to completion when it contains incompatible settings. However, results may be inaccurate if this option is selected.

Solver Controls

Displacement Convergence Tolerance

Convergence Tolerance —sets the tolerance by which to assess convergence of the coupled FSI solution. When the Solid Stress Displacement residual is less than the specified tolerance, the solid stress computation stops for the remainder of the time-step. The default value of 1E-10 is determined as the Multiplier times the Minimum Limit of the Displacement Criterion.
Use Reference Minimum Value—when activated, the Convergence Tolerance is equal to the Minimum Value of the Displacement Criterion times the Multiplier. When deactivated, you specify the tolerance directly using the Convergence Tolerance property. Specifying a value for the Convergence Tolerance automatically deactivates Use Reference Minimum Value. You can activate Use Reference Minimum Value only when the Criterion Option of the Displacement Criterion is set to Minimum.
Multiplier—the value of the multiplicative factor applied to the Minimum Value of the Displacement Criterion to determine the Convergence Tolerance. The default value is 1E-4. See 使用监视器作为停止条件.

Constant Displacement Under-relaxation

See Stabilization Methods.

Field Functions

FSI Traction

Vector field function that represents the fluid traction on the fluid side of the FSI interface. The FSI traction

T_{f}

is the sum of the shear force

T_{s}

and the pressure component in the normal direction

T_{N}

after FSI Fluid Load Clipping and/or Ramping have been applied such that:

T_{f} = T_{s} + T_{N} = T_{s} - p N

(343)

and

N \cdot T_{s} \equiv 0

where

p

is the fluid pressure on the interface and

N

is the normal vector to the interface.

If $T_{f}$ on the fluid side of the FSI interface changes in the laboratory coordinate system $O$ , Simcenter STAR-CCM+ calculates the pressure and shear component.

Mapped FSI Traction

Vector field function that represents the fluid traction mapped onto the solid side of the FSI interface.

The mapped FSI traction is stored as the combination of $T_{s}$ and $p$ and represents a load that follows the motion of the solid, for example, from time $t_{0}$ to time $t_{1}$ .

Mapped FSI Traction (pressure component)

Scalar field function which represents the pressure component of the Mapped FSI Traction on the solid side of the FSI interface. Only available if Temporary Storage Retained is activated under the Fluid Structure Coupling solver.

Mapped FSI Traction (shear component)

Vector field function which represents the shear component of the Mapped FSI Traction on the solid side of the FSI interface. Only available if Temporary Storage Retained is activated under the Fluid Structure Coupling solver.