simulation of low frequency sonar devices - pzflex.com of low frequency sonar devices. o at...
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Simulation of Low Frequency Sonar Devices
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o At frequencies below 20 kHz housing resonances can significantly affect deviceperformance
o This is particularly true for wideband hydrophones, and parametric array
o These resonances can be difficult to predict, and may be detected late in thedesign cycle
Parasitic bending modes can
significantly affect device
performance
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o PZFlex behaves like a virtual experiment, offering all the outputs which a designer may measure experimentally
o Large models can be constructed, totalling hundreds of millions of elements, allowing entire array assemblies to be simulated
o Fast solver – axisymmetric results available in a matter of minutes
o Wideband results from single run
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o Electrical Impedance
o Mode Shapes
o Pressure and displacement levels
o Beam patterns
o Directivity Index
o Efficiency
o Pulse-echo response
o Crosstalk
o Bandwidth
o New materials, including single crystal
o Shocking
o Bondline effectsExperimental measurements can
be easily duplicated in simulation
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o The following example analyses the performance of a circular ceramic device between 1 and 20 kHz
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o Axisymmetric model
o Spherical absorbing water load:
o High performance boundary condition allows the size of the load to be minimised reducing model size
o Performance requirements are high due to large dynamic range of TVR
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o A number of parasitic resonances exist
o Of particular interest is the large null at 10.8kHz
o Conductance increases while TVR reduces
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o The 10.8 kHz modal displacement shows a bending mode thatresults in poor surface dilation quality
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o The 10.8 kHz modaldisplacement shows abending mode that results inpoor surface dilation quality
o The 10.8 kHz beam patternconfirms that this mode hasdistorted the beam, reducingTVR
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1-3 Piezocomposite device
polymer encapsulant not shown
PZT Pillar
Polymer filler
Backing
Aluminium
housing
o For more complex devices a 3D model can be used
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116 mm
76 mm
Wavelength in
water at 10kHz
is 150 mm
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o The device is simulated in a water load, and absorbing boundaries are applied to the surface to remove reflections
o Boundary performance can be improved by creating a spherical water load
o This increases the boundary performance, improving the dynamic range of the simulation
o To allow fine geometric features such as PZT pillars to be meshed the grid is refined in the transducer region
o This allows fewer elements to be used in the boundary, reducing the size of the model
o Overall reduction on model size and run time can be significant
Spherical Boundary and Refined Grid
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Water
load
Fine
transducer
mesh
Coarse
water
mesh
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o Pressures, displacements, stresses etc. can all be visualised while the model is running
o Model meshed to look at performance from 1 – 20 kHz
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o The following outputs provide insight into the device’s performance
o Electrical conductance
o Transmit Voltage Response (TVR)
o Modal displacements
o Beam patterns
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Bending
modes in
housing
Lateral modes in
composite / backing
assembly
Further
overtones
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Bending
modes in
housing
Hydrostatic
mode
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3.6kHz length
bending mode
5.8kHz width
bending mode
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3.6 kHz 5.8 kHz
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o Modal displacement at 7.6kHz is complex and is reflected in the beam pattern
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o Analysis at 10kHz shows a lateral mode in the piezocomposite
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o Virtual experiments in PZFlex can give insight into the performance of LF sonar devices
o A single model provides information over a wide bandwidth
o Spherical absorbing boundaries allow a combination of:
o Sub wavelength model dimensions
o High dynamic range >70dB
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Simulation Metrics
Model2D
Axisymmetric3D
Piezocomposite
Elements 17,200 1,370,000
Runtime 1 min 15 s* 23 min 30 s**
Memory (RAM) 8.6 MB 230 MB
* Run on dual core i7 laptop
** Run on dual quad core Intel Xeon E5520