现代汽车使用Actran计算汽车风噪声benchmark
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1) Impact excitation (hammer) at specific locations of each window to validate the vibro-acoustics modelling 2) Flow excitation with different configurations (flow speed, yaw angle )
Microphones, Accelerometers & Impact location
• Two microphones are set inside the cavity :
•
Accelerometers are set at the same location as the hammer impact:
– Micro-Model developed by Allard-Johnson
•
Local & global indicators:
– Displacement, pressure… – Dissipated energy in each layer or each material or any specific area defined by the user
Tortuosity Thermal Length (m) Viscous Length (m)
0.879
3.31 0.00012174 0.0009483
PROPERTIES
HEAVY LAYER
1 2000 0.04 0.45
ALUMINIUM
12 2700 69 0.33
GLASS
4 2500 70 0.22
– Consider a simplified model of cavity and compare vibro-acoustic simulation
results to experimental measurements – This simplified model includes:
• Structure with 3 windows • Multi-layer trim component • Acoustic cavity
•
Different models can be used depending on the number of material properties available
Vibro-Acoustic Model
• Meshing criterion guided by:
– 4-6 quadratic elements per bending wavelength: bend
cbend
f
– 3-4 quadratic elements per acoustic wavelength:
cf
•
Two meshes have been generated to decrease the CPU requirements for the lower part of the frequency range (<1600Hz).
Context, Objective & Strategy
• Context: HMC is looking for a technology to predict the sound generated by A-Pillar vortex inside the car cavity Objective and Strategy:
Actran Model 1/2
•
CUT
All the different parts (cavity, foam, glass, aluminium…) are represented
Actran Model 2/2
CUT VIEW ZOOM FOAM
Thickness
CUT
MATERIALS
IMPACT EXCITATION
•
Experimental data up to 1600Hz provided by HMC for results comparison
Automation of the process (including creation of plots) using scripting possibilities available in Actran for fast handling of a large amounts of results
•
Results are very good
Accelerometer result : front window impact
IMPACT
PT3
Front Window
ACCELEROMETER
PT3
Front Window
•
Results of window acceleration at impact points :
•
POST_PROCESSING
Actran Model : Windows clamping
• Windows are now connected to the structure using a glue material
•
The connection is 3mm thick as the sealer on the schema
• How to import those data in Actran ?
Computation sequence strategy
•
• •
Compressible CFD transient simulation around the cabin with PowerFlow
– Actran is also compatible with Fluent, Star-CCM+, CFX, Ensight Gold…
Coarser mesh
Thinner mesh
Impact Excitation
Actran MODEL
CoБайду номын сангаасputational sequence
• • Local force applied at the locations of all hammer shocks Results outputed for the accelerometers and microphones for each hammer shock positions independently
AIR
Speed Of Sound(m/s) Density (kg/m3) 340 1.225
Thickness (mm) Density (kg/m3) Young’s Modulus (GPa) Poisson's ratio
Porous Materials used inside the cavity
•
All results are based on the same Actran model, only the boundary
condition at the windows changes
Actran Model Impact Excitation
Flow Excitation
Actran Model
•
Acceleration at a point other than the impact point :
– Good match at low frequency – Correctly captures the trend at higher frequency
Flow Excitation
• • Model foam, rock wool, fibers... Porous elements: All based on Biot model
– Vibrating skeleton surrounded by a fluid – Thus 3 + 1 = 4 degrees of freedom per node – Material properties (frequency dependent):
– Good match with the experimental results on the whole frequency range
Accelerometer result : side window impact
IMPACT
PT2
Side Window
ACCELEROMETER
PT4
Side Window
Configuration description
FOAM 20mm
GLASS
HEAVY LAYER 4mm
FOAM 40mm
ALUMINIUM 12mm Total Geometry Trimmed body Geometry
Trimmed Body Section
• • • •
Aluminium cabin 3 windows (1 front window, 2 side windows) Cavity filled with a trimmed body (porous material + heavy layer) All properties are provided by HMC
Computational Sequence
Aerodynamic excitation
• • 2 cruising speed : 110 and 130 km/h 2 Yaw angles: – 0° orientation (symmetric) – -10° orientation FLOW 0°
Bench Mark Test
Aero-Acoustics Transmission through a Hyundai Simplified Model
Project Presentation
Outline
• Context, Objective & Strategy • Actran model • Impact Excitation • Flow Excitation – Computational Sequence – Results • Conclusion & Perspectives
• Foam skeleton properties : Young modulus, density, Poisson ratio • Fluid properties : fluid density • Foam properties : tortuosity, resistivity, porosity, imperviosity…
20 and 40mm 1.225 734.9 10000 68300 0.35
Air Density (kg/m3) Solid Density (kg/m3) Tensile Modulus (Pa) Flow Resistivity (MKS Rayls/m) Poisson’s Ratio
Porosity
•
Hyundai Simplified Model
– Predict the noise at the driver’s ears location when the windows are excited
by an exterior flow (vortex).
Methodology
• Two steps are considered for this study :
4 configurations
FLOW -10°
• •
Compressible Unsteady CFD results with PowerFlow Outputs: the wall pressure fluctuation loaded on the windows at each CFD time steps (time domain)
Mapping and Fourier transform of the CFD pressure results (time domain) on structure surface mesh (frequency domain) Vibro-acoustic computation of the coupled structure and cavity
Microphones, Accelerometers & Impact location
• Two microphones are set inside the cavity :
•
Accelerometers are set at the same location as the hammer impact:
– Micro-Model developed by Allard-Johnson
•
Local & global indicators:
– Displacement, pressure… – Dissipated energy in each layer or each material or any specific area defined by the user
Tortuosity Thermal Length (m) Viscous Length (m)
0.879
3.31 0.00012174 0.0009483
PROPERTIES
HEAVY LAYER
1 2000 0.04 0.45
ALUMINIUM
12 2700 69 0.33
GLASS
4 2500 70 0.22
– Consider a simplified model of cavity and compare vibro-acoustic simulation
results to experimental measurements – This simplified model includes:
• Structure with 3 windows • Multi-layer trim component • Acoustic cavity
•
Different models can be used depending on the number of material properties available
Vibro-Acoustic Model
• Meshing criterion guided by:
– 4-6 quadratic elements per bending wavelength: bend
cbend
f
– 3-4 quadratic elements per acoustic wavelength:
cf
•
Two meshes have been generated to decrease the CPU requirements for the lower part of the frequency range (<1600Hz).
Context, Objective & Strategy
• Context: HMC is looking for a technology to predict the sound generated by A-Pillar vortex inside the car cavity Objective and Strategy:
Actran Model 1/2
•
CUT
All the different parts (cavity, foam, glass, aluminium…) are represented
Actran Model 2/2
CUT VIEW ZOOM FOAM
Thickness
CUT
MATERIALS
IMPACT EXCITATION
•
Experimental data up to 1600Hz provided by HMC for results comparison
Automation of the process (including creation of plots) using scripting possibilities available in Actran for fast handling of a large amounts of results
•
Results are very good
Accelerometer result : front window impact
IMPACT
PT3
Front Window
ACCELEROMETER
PT3
Front Window
•
Results of window acceleration at impact points :
•
POST_PROCESSING
Actran Model : Windows clamping
• Windows are now connected to the structure using a glue material
•
The connection is 3mm thick as the sealer on the schema
• How to import those data in Actran ?
Computation sequence strategy
•
• •
Compressible CFD transient simulation around the cabin with PowerFlow
– Actran is also compatible with Fluent, Star-CCM+, CFX, Ensight Gold…
Coarser mesh
Thinner mesh
Impact Excitation
Actran MODEL
CoБайду номын сангаасputational sequence
• • Local force applied at the locations of all hammer shocks Results outputed for the accelerometers and microphones for each hammer shock positions independently
AIR
Speed Of Sound(m/s) Density (kg/m3) 340 1.225
Thickness (mm) Density (kg/m3) Young’s Modulus (GPa) Poisson's ratio
Porous Materials used inside the cavity
•
All results are based on the same Actran model, only the boundary
condition at the windows changes
Actran Model Impact Excitation
Flow Excitation
Actran Model
•
Acceleration at a point other than the impact point :
– Good match at low frequency – Correctly captures the trend at higher frequency
Flow Excitation
• • Model foam, rock wool, fibers... Porous elements: All based on Biot model
– Vibrating skeleton surrounded by a fluid – Thus 3 + 1 = 4 degrees of freedom per node – Material properties (frequency dependent):
– Good match with the experimental results on the whole frequency range
Accelerometer result : side window impact
IMPACT
PT2
Side Window
ACCELEROMETER
PT4
Side Window
Configuration description
FOAM 20mm
GLASS
HEAVY LAYER 4mm
FOAM 40mm
ALUMINIUM 12mm Total Geometry Trimmed body Geometry
Trimmed Body Section
• • • •
Aluminium cabin 3 windows (1 front window, 2 side windows) Cavity filled with a trimmed body (porous material + heavy layer) All properties are provided by HMC
Computational Sequence
Aerodynamic excitation
• • 2 cruising speed : 110 and 130 km/h 2 Yaw angles: – 0° orientation (symmetric) – -10° orientation FLOW 0°
Bench Mark Test
Aero-Acoustics Transmission through a Hyundai Simplified Model
Project Presentation
Outline
• Context, Objective & Strategy • Actran model • Impact Excitation • Flow Excitation – Computational Sequence – Results • Conclusion & Perspectives
• Foam skeleton properties : Young modulus, density, Poisson ratio • Fluid properties : fluid density • Foam properties : tortuosity, resistivity, porosity, imperviosity…
20 and 40mm 1.225 734.9 10000 68300 0.35
Air Density (kg/m3) Solid Density (kg/m3) Tensile Modulus (Pa) Flow Resistivity (MKS Rayls/m) Poisson’s Ratio
Porosity
•
Hyundai Simplified Model
– Predict the noise at the driver’s ears location when the windows are excited
by an exterior flow (vortex).
Methodology
• Two steps are considered for this study :
4 configurations
FLOW -10°
• •
Compressible Unsteady CFD results with PowerFlow Outputs: the wall pressure fluctuation loaded on the windows at each CFD time steps (time domain)
Mapping and Fourier transform of the CFD pressure results (time domain) on structure surface mesh (frequency domain) Vibro-acoustic computation of the coupled structure and cavity