One-way fluid-structure interface coupling

One-way, weak coupling analysis considers the effect of vibration of the structure on the fluid, but ignores the effect of the fluid pressure on the structure. One-way, weak coupling solves faster than the default two-way, strong coupling method, and can be used when the vibration results are already available or when you know that the fluid loading and acoustic pressure do not affect the structural response significantly. A good use of weak coupling is for the acoustic radiation of a vibrating structure.

Two-way, strong coupling is recommended for panel-like vibrations, in which the acoustic pressure and fluid loading are important. Example uses for two-way coupling include coupling of interior fluid volume with the car body, a submarine underwater, or a thin, lightweight loudspeaker membrane coupled to the air in front of it and to the air in the loudspeaker cabinet.

One-way, weak coupling is relevant only for vibro-acoustic analysis.

You can select the coupling type on the Fluid-Structure Interface Modeling Parameters modeling object, defined on the Solution dialog box on the Bulk Data page in the Simcenter Nastran FEM solver environment, and on the Vibro-Acoustic Coupling group in the Simcenter 3D Acoustics BEM solver environment.

Coupling for Simcenter Nastran FEM

One-way, weak coupling ignores the effect of fluid on the structure, so Simcenter Nastran performs two frequency response solutions in the following order within a given instance of a solve:

1. The structural frequency response equations are solved. Once computed, the structural vibrations at the elements in the fluid structure interaction are projected onto the boundary of the acoustic model using the coupling matrix to form the loading condition for the fluid.

2. The frequency response equations are solved for the fluid degrees of freedom, using the loading due to the projected structural velocity results from the previous step (in addition to any acoustic sources) as boundary conditions.

This method of solving two sets of equations with fewer degrees of freedom is faster than the two-way, strongly coupled solution, which contains all the structural and fluid degrees of freedom.

In a weakly coupled vibro-acoustic scenario, you can use one of the following approaches to set up your model.

• The first approach defines both the fluid and a full structural model, including one-way coupling, and applies force loads (or enforced displacements) in a few degrees of freedom at which the structure is excited. Simcenter Nastran first computes the structural vibration response, followed by the acoustic response. Both steps are part of a single Nastran solution.

• The second approach computes the vibrations on the structure first as a separate Nastran solution for the structure-only model. In a second Nastran solution, which includes both structure and fluid, you can apply the known surface vibrations from the first solution as enforced vibrations. You can do this using a load recipe.

To prevent calculations for any remaining structural degrees of freedom, set the Skip Solving the Structural DOFs (SPCSTR) parameter to YES on the Bulk Data page in the Solution dialog box. This option constrains all of the structural degrees of freedom.

For more information, see Enforced vibration loading at fluid-structure interface.

Coupling for Simcenter 3D Acoustics BEM

The Acoustics BEM indirect vibro-acoustic solver environment supports only one-way, weak coupling.

In an indirect BEM vibro-acoustic solution, you can define predefined enforced vibration loads using an enforced vibration constraint or using a load recipe.

Coupling for Simcenter 3D Noise and Vibration

The Noise and Vibration solver environment supports only one-way, weak coupling.

In an Acoustic Transfer Vector (ATV) Response or Modal Acoustic Transfer Vector (MATV) Response solution, you use a boundary condition to reference an external file that contains modal participation factors. The software uses this external file to apply the modal participation factors to target nodes in your model.

Post-processing coupling quality results

With both Simcenter Nastran FEM and Simcenter 3D Acoustics BEM, you can use post-processing plots to verify the quality of the fluid-structure coupling. The coupling quality results display coupled and/or uncoupled structural or acoustic faces or nodes that are selected for coupling. It displays the following results:

• Coupling quality results for Simcenter Nastran FEMFluid coupled faces: closest distance to structural faces - Element-FaceFluid uncoupled faces: search distance - Element-FaceFluid coupled and uncoupled faces: distance - Element-FaceStructural coupled (0) and uncoupled (1) faces - Element-Face

• Coupling quality results for Simcenter 3D Acoustic BEMStructural coupled and uncoupled faces: distance- ElementalFluid coupled (0) and uncoupled (1) nodes- Nodal

For more information, see Plot coupling quality results.

Where do I find it?

Creating a fluid-structure interface in Simcenter Nastran FEM

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partSimcenter Nastran as the specified solverVibro-Acoustic as the specified analysis typeSOL 108 Direct Frequency Response or SOL 111 Modal Frequency Response as the solution type
Simulation Navigator	Right-click the Modeling Objects node→Modeling Objects
Location in dialog box	Modeling Objects Manager dialog box→Type list→Fluid-Structure Interface Modeling Parameters or Fluid-Structure Interaction Control Parameters

Creating a fluid-structure interface in Acoustics BEM

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partSimcenter 3D Acoustics BEM as the specified solverIndirect Vibro-Acoustic as the specified analysis typeVibro-Acoustic Response as the solution type
Simulation Navigator	Right-click the Modeling Objects node→Modeling Objects
Location in dialog box	Modeling Objects Manager dialog box→Type list→Fluid-Structure Interface Modeling Parameters

Creating a fluid-structure interface in Noise and Vibration

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partSimcenter 3D Noise and Vibration as the specified solverVibro-Acoustic as the specified analysis typeAcoustic Transfer Vector (ATV) Response or Modal Acoustic Transfer Vector (MATV) Response as the solution type
Simulation Navigator	Right-click the Modeling Objects node→Modeling Objects
Location in dialog box	Modeling Objects Manager dialog box→Type list→Fluid-Structure Interface Modeling Parameters

Checking model quality results in Acoustics BEM

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partSimcenter 3D Acoustics BEM as the specified solverDirect Acoustic, Indirect Acoustic, or Indirect Vibro-Acoustic as the specified analysis typeAcoustic or Vibro-Acoustic Response as the solution type
Command Finder	Solve
Simulation Navigator	Right-click the Simulation file→New Solution
Location in dialog box	Solve dialog box→Submit list→Solve Model Quality Results

Checking coupling quality results in Simcenter Nastran FEM and Simcenter 3D Acoustics BEM

Application	Pre/Post
Prerequisites	A Simulation file as the work part and displayed partSimcenter Nastran or Simcenter 3D Acoustics BEM as the specified solverAcoustic or Vibro-Acoustic as the specified analysis typeFor Simcenter Nastran FEM, SOL 108 Direct Frequency Response or SOL 111 Modal Frequency Response as the solution type
Post Processing Navigator	Expand the Acoustic or Vibro-Acoustic result node →Expand the Coupling Quality Results node→right-click the required result node→Plot

How do I

Define fluid-structure interface modeling parameters

Plot coupling quality results

Define fluid-structure interaction control parameters (Simcenter Nastran FEM acoustics)

Define fluid-structure interface modeling parameters (Acoustics BEM)

Look up more details

Fluid-Structure Interface Modeling Parameters dialog box (Acoustics BEM)

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Pre/Post video examples

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Related Topics

Overview of acoustic capabilities

One-way fluid-structure interface coupling, Simcenter 3D 2021.1 Series

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