Prestressed Acoustic–Structure Interaction
When modeling transducers like microphones or ultrasound horns there are often parts of the structure, like the diaphragm or a bolt, that are under tension or prestressed. In these cases, it is essential to include this effect when modeling the transducer. A prestressed part will shift the resonance frequency of the mechanical system and thus the overall vibroacoustic behavior will change.
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Piezoelectric Tonpilz Transducer with a Prestressed Bolt: Application Library path Acoustics_Module/Piezoelectric_Devices/tonpilz_transducer_prestressed.
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The Brüel & Kjær 4134 Condenser Microphone: Application Library path Acoustics_Module/Electroacoustic_Transducers/bk_4134_microphone.
Such prestressed acoustic–structure interaction models can be set up and solved fully coupled including all effects. The procedure is as follows:
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Set up the model including all relevant physics.
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Couple the physics using the required multiphysics couplings.
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All acoustic sources, structural loads, and any forcing that are nonstatic, should be defined using the linper() operator. This will ensure that they are used only in the frequency-domain part of the study (that one is set to linear perturbation).
4
Add a Prestressed Analysis, Frequency Domain study.
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Note that in the Stationary step the acoustics physics interfaces have an orange warning triangle under the Physics and Variables Selection. This simply means that they will not be used in the stationary study since acoustics is not supporting the study type. Therefore the Solve for this field will automatically not be marked under the Dependent Variables in the Solver Configurations.
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Note also that the Include geometric nonlinearity check box is selected in the Frequency-Domain, Perturbation step. If it is not checked, the prestress effect is lost.
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Solve the model for the desired frequencies.
A prestressed type of analysis can also be done on pure structural problems in the frequency domain and when searching for eigenfrequencies of structures.
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 Harmonic Perturbation, Prestressed Analysis, and Small-Signal Analysis in the COMSOL Multiphysics Reference Manual.
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 Prestressed Structures, Modeling Pretensioned Bolts, and Mechanical Damping and Losses in the Structural Mechanics Module User’s Guide