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 traducer. A prestressed part will shift the resonance frequency of the mechanical system and thus the overall vibroacoustic behavior will change.
Piezoelectric Tonpilz Transducer with a Prestressed Bolt: Application Library path Acoustics_Module/Piezoelectric_Devices/tonpilz_transducer_prestressed.
The Brüel & Kjær 4134 Condenser Microphone: Application Library path Acoustics_Module/Electroacoustic_Transducers/bk_4134_microphone.
Such prestressed acoustic-structure iteration models can be set up and solved fully coupled including all effects. The procedure is as follows:
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All acoustic sources, structural loads, and any forcing that are non-static, for example, any acoustic source 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).
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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 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 box is checked in the Frequency-Domain, Perturbation step. If it is not checked the prestress effect is lost.
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A prestressed type of analysis can also be done on pure structural problems in the frequency domain and when searching for eigenfrequencies of structures.
See also Prestressed Structures, Pretensioned Bolts, and Mechanical Damping and Losses in the Structural Mechanics Module User’s Guide