Acoustic-Structure Boundary
The Acoustic-Structure Boundary coupling () is used to couple a Pressure Acoustics model to any structural component. This includes both the FEM based acoustics interfaces and the BEM based acoustics interface. The feature couples to Solid Mechanics, Poroelastic Waves, Shell, Membrane, and Multibody Dynamics interfaces.
The coupling includes the fluid load on the structure and the structural acceleration as experienced by the fluid. For thin interior structures like shells or membranes with fluid on both sides, a slit is added to the pressure variable and care is taken to couple the up and down sides.
Mathematically the condition on exterior boundaries reads
where utt is the structural acceleration, n is the surface normal, pt is the total acoustic pressure and FA is the load (force per unit area) experienced by the structure. On interior boundaries the condition reads
such that the acoustic load is given by the pressure drop across the thin structure. The up and down subscripts refer to the two sides of the interior boundary.
In 2D components it is possible to define the out-of-plane thickness for the structural interfaces while in acoustics this thickness effectively is unity (set to 1 m). A rescaling is automatically performed for the pressure load to account for this difference in interpretation in 2D.
In models with large deformations of the structure, for example, if a membrane is prestressed and deforms, the resulting area change is automatically included when using the multiphysics coupling between the structure and the acoustic domain.
Settings
The Label is the default multiphysics coupling feature name.
The Name is used primarily as a scope prefix for variables defined by the coupling node. Refer to such variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different coupling nodes or physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.
The default Name (for the first multiphysics coupling feature in the model) is asb1.
Coupled Interfaces
This section defines the physics involved in the multiphysics coupling. The Acoustics and Structure lists include all applicable physics interfaces.
The default values depend on how this node is created.
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If it is added from the Physics ribbon (Windows users), Physics contextual toolbar (Mac and Linux users), or context menu (all users), then the first physics interface of each type in the component is selected as the default.
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If it is added automatically when a multiphysics interface is selected in the Model Wizard or Add Physics window, then the two participating interfaces are selected.
You can also select None from either list to uncouple this node from a physics interface. If the physics interface is removed from the Model Builder, for example Pressure Acoustics, Frequency Domain is deleted, then the Acoustics list defaults to None as there is nothing to couple to.
If a physics interface is deleted and then added to the model again, then in order to re-establish the coupling, you need to choose the physics interface again from the Acoustics or Structure lists. See Multiphysics Modeling Approaches in the COMSOL Multiphysics Reference Manual.