Engineering | Finite Element Analysis | Stress
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Noise in the acoustic sense is usually produced by vibration of a body or is caused
by instabilities in fluid flow (such as turbulence). An acoustic analysis enables
the prediction of the way sound radiates inside and outside of a product, simultaneously
or separately. The problem is oftentimes viewed from three different viewpoints,
sound generation, sound propagation and structural interaction. It is usual to perform
the analysis in the frequency domain.
In an analysis, boundary conditions include
velocities, pressures, impedances (relationship between pressure & velocity), and
acoustic monopole and plane wave sources. Velocity and impedance can usually be combined
into a simultaneous velocity and impedance type boundary conditions. Velocities are
usually obtained from a dynamic structural analysis.
The acoustic investigations
usually determine pressure, intensity, acoustic velocity, and radiated power for
the domain of interest. In addition, more specialized analyses calculate structural/acoustic
coupling, embedded frequency response, acoustic sensitivities, effects of multiple
acoustic properties, and reverberant field effects.
Solution Approaches.
From a formal point of view, acoustic behaviour is governed the linear wave equation.
This formulation is a function of the acoustic pressure and the velocity of propagation
of the wave. Numerical methods are applicable to very general problem types, but
are difficult to compute and usually involve relatively large models.
In uncoupled
analyses, the acoustic medium is not considered to have any effect on the vibration
of the structure. Therefore, the structural frequency response analysis is performed
first, and the computed vibration is used to define the velocity boundary conditions
for the acoustic analysis.
In coupled analysis, the structural vibration is considered
to be effected by the surrounding acoustic medium. In this case, both the structural
vibration and the acoustic response are computed within the same analysis model.
The structural normal modes are computed first.
Acoustics
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