PAFEC VibroAcoustics 聲音分析軟體

PAFEC-VibroAcoustics - Application Areas
Audio
Air is a light medium and hence will generally have a lesser effect on a vibrating structure than in underwater acoustics. However the cone, dustcap and surround of a loudspeaker drive unit are also light, and hence to obtain accurate results a fully coupled analysis is necessary.
Application Areas
cone breakup
cabinet cavity modes
radiation from drive unit
diffraction from edges
placement of speakers in a small room
radiation from panels
horn design
load/displacement computation for spiders and surrounds compression
   driver design

Underwater Acoustics
For structures vibrating underwater a fully coupled vibroacoustic solution is almost always essential. The density of fluid ensures that the pressure field generated by the vibrating surface applies significant loading to the structure and it vibrates differently in fluid from in vacuo. Generally speaking modes/resonances will occur at lower frequencies due to an added mass effect. Radiation damping generally reduces the amplitude at resonance.
Application Areas
SONAR transducer design
array design
SONAR domes
radiation from submerged structures
scattering from submerged structures
tile design

Medical Ultrasonics
Physiotherapy transducer based on the model created by Martin Hughes, during his PhD at the University of Bath under the supervision of Professor Victor Humphrey, assisted by funding from the National Physical Laboratory.

A more complete description of the transducer can be found in "Finite Element and Boundary Element Modelling of a Medical Ultrasound Transducer and its Generated Near-Field" , University of Bath 2001.

Architectural
Acoustic finite and boundary elements solve the Helmholtz equations exactly, within the discretization error. Thus effects such as defraction are naturally modelled. It is also possible to model interactions with structural objects such as windows. However, the element size required is proportional to the wavelength, therefore as the number of elements increases the problem becomes computationally larger. Thus FE and BE techniques can be used to analyse 'small rooms'

Areas of localised design, such as diffusers or apertures can benefit from finite and boundary element analyses.

Axisymmetic analysis of a cylindrical aperature in a rigid baffle connecting two half spaces. Each half space is bounded by an infinite rigid baffle, with the aperature at the centre. A plane wave is incident on the baffle in the right hand space. A combination of acoustic finite and boundary elements are used to model this problem.

Barriers
Finite and boundary element techniques can be used to analyse barriers. It is relatively straightforward to predict results for 'ideal conditions'. However the effectiveness of the barrier will change with wind conditions, and variations in temperature in the surrounding air space will also be difficult to incorporate into the model. A boundary element approach could be used to compare between a number of different designs under 'ideal conditions', with the assumption that the best design might also be best in other circumstances.

Automotive
In automotive acoustics it is usually possible to use uncoupled acoustic analysis. Surface vibration data may be taken from a previous structural FE analysis or from experimental measurement.

For interior cavity problems the sound field is set up by a number of vibrating panels. For a particular point of interest, e.g. the driver's outside ear, a contribution to the pressure at this point can be computed from each panel. These sum in the complex plane to give the resultant pressure. Panels which have a positive(negative) contribution relative to the resultant pressure are sources(sinks). Reducing vibration at a sink will actually make the problem worse!

Application Areas
interior cavity resonances
panel contributions
source/sink identification
drive-by noise
air intake/exhaust analysis

Ultrasonic Cleaning
The example below illustrates the action of an ultrasonic cleaning device. A cermic block is attached to a steel plate at the base of the tank containing water. The ceramic is excited by a voltage applied across the electrodes on the upper/lower surfaces. The vibration of the plate radiates acoustic energy into the water. The surface at the top of the tank is defined as free. Cavitation affects the properties of the acoustic medium, and in particular the fluid becomes becomes lossy. The example is a simple plain strain model.