Hello,
I am currently working on the sound radiation of a vibrating structure and I am trying to use the equivalent radiated power (ERP) value of the outer surface of the structure as an indicator of the radiated sound power.
However, I have noticed an important disagreement between the Hyperworks Help documentation on how the ERP value is computed and the engineering literature.
How the ERP computation is described in the HyperWorks documentation:
In the literature (Norton, M.P. : Fundamentals of noise and vibration analysis for engineers), the radiated sound power is described using the radiation ratio, not the radiation loss factor:
The difference is that there is no factor 1/2 and the radiation ratio (sigma) is used instead of the radiation loss factor. This radiation ratio has the following formula for infinite flat plates:
and more complicated formulas for other geometries, but it is clearly frequency-dependant, as it can be seen as well on the following plot:
.
However, in the PARAM control card of OPTISTRUCT, one can only set a fixed value for the ERPRLF, so they clearly do not refer to the same physical quantity. In the book of Norton, the radiation loss factor (RLF) is defined as follows:
.
It is obvious that, if one introduces this formula in the formula for the ERP in the Hyperworks Documentation, one does obtain the radiated sound power as defined in the handbook, but multiplied with a factor (1/2)*rho_0*c /(omega*rho_S).
I kindly ask you to explain to me this difference and to which extent one can use the ERP (as defined in the documentation) as an indicator of sound vibration of a structure.
Best regards,
Matteo