QUESTION:
Is it possible to perform an acoustic analysis and impose complex impedance as a boundary condition? The impedance is set with material property MU, however ANSYS only allows a real value for this property. Does ANSYS have any plans to extend the functionality to allow complex impedance? Alternatively, is there a workaround for achieving the same result?
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ANSWER:
One method of applying complex impedance is to use SURF153/154 on the boundary. Since impedance (SF,,IMPD) is "damping at the surface," the user could put SURF153/154 with appropriate values for added mass per unit area (real constant 6) and viscosity (MP,VISC) for the real and imaginary portions of impedance:
VISC = Re[impedance]
ADMSUA = Im[impedance]/w (for z > 0)
EFS = -w*Im[impedance] (for z < 0)
If the imaginary part of impedance is negative, elastic foundation stiffness EFS (real constant 4) can be used instead of added mass per unit area ADMSUA, as ANSYS will not accept "negative" mass or stiffness.
The user should keep in mind the following:
1) The values of ADMSUA (or EFS) need to be modified between substeps since these would otherwise be frequency-dependent
2) The unsymmetric option (FSI) needs to be used between the FLUID29/30 and SURF153/154 interface
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QUESTION: Is it possible to perform an acoustic analysis and impose complex impedance as a boundary condition? The impedance is set with material property MU, however ANSYS only allows a real value for this property. Does ANSYS have any plans to extend the functionality to allow complex impedance? Alternatively, is there a workaround for achieving the same result? -------------------------------------------------------------- ANSWER: One method of applying complex impedance is to use SURF153/154 on the boundary. Since impedance (SF,,IMPD) is "damping at the surface," the user could put SURF153/154 with appropriate values for added mass per unit area (real constant 6) and viscosity (MP,VISC) for the real and imaginary portions of impedance: VISC = Re[impedance] ADMSUA = Im[impedance]/w (for z > 0) EFS = -w*Im[impedance] (for z < 0) If the imaginary part of impedance is negative, elastic foundation stiffness EFS (real constant 4) can be used instead of added mass per unit area ADMSUA, as ANSYS will not accept "negative" mass or stiffness. The user should keep in mind the following: 1) The values of ADMSUA (or EFS) need to be modified between substeps since these would otherwise be frequency-dependent 2) The unsymmetric option (FSI) needs to be used between the FLUID29/30 and SURF153/154 interface |
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