I am studying the attenuation of ultrasonic wave in viscoelastic solid (using transient study). However, when adding a viscous damping subnode, I don't know how to get the viscosity parameter: bulk viscosity ηb and shear viscosity ηv. And loss factor damping can't be used in transient study.
Although I have found some formulas to calculate the value of ηb and ηv in StructuralMechanicsModuleUsersGuide (p152) :
ηb=Kη/ω
ηv=Gη/ω
K is bulk modulus, G is shear modulus, η is loss factor, ω is excitation frequecy
I can't figure out the meaning of the parameters in the formulas above. What's more, the attenuation coefficient calculated using these formulas in COMSOL was quite different from the experimental result. So I don't know how to proceed with the calculation.
I hope somebody could provide me with some advice. I want to know how to get the parameters of the viscosity or some formulas to calculate the parameters. I also hope to know some other methods or models to simulate the propagation of ultrasonic wave in viscoelastic solid material.
Thanks for your help.
Xiangwei Geng