General Mechanical

Acoustic – Physics behind the Analysis

• PrabhuManickam
Subscriber

Hi,

I seen many videos they doing acoustic harmonic analysis.

1st they do Modal Analysis

2nd Harmonic response analysis

3rd Harmonic Acoustics

Modal analysis results is given to Harmonic response. Then harmonic response result is given as an input to harmonic acoustic.

(Harmonic Response results gives Imported velocity to harmonic acoustic)

Now how they find the dB levels using the velocity values? What is the equation behind it to calculate it?

General Formula for dB = log (pressure difference)

In ansys how they calculate the dB using the Velocity one? Please say the physics and calculation behind of that analysis.

• Erik Kostson
Ansys Employee
Hi

So when you transfer the velocities to the harmonic acoustic system, we will then solve there for the acoustic pressures (generated by this velocity excitation).
Thus pressure is the main variable we solve for in an acoustic analysis ( just as displacements are in a structural analysis).
(See the acoustic theory in our help for more info on the equation solved)
Finally with the pressures (P_ansys) calculated in the the acoustic domain, we can calculate the sound pressure levels in dB using the equation: 20*Log10(P_ansys/sqrt(2)/P_ref), where P_ref (reference pressure) is equal to 20 microPa. See chapter 8.6 in the ansys theory reference for details.

All the best

Erik