Mecanum. Acoustic Materials: Characterization. We build silence. Mecanum Inc.

Transcription

1 ecanum We build silence Acoustic aterials: Characterization ecanum Inc.

2 otivation Sound quality in vehicles starts at the design stage odels are used to simulate the acoustics of vehicles odels are used to develop and optimize sound packages aterial properties and cell morphology are the input parameters to models 2

3 What about sound packages? Sound packages are made of a combination of materials, including: Carpet Fabric Felt Fiber Foam Porous film 3

4 What is a porous material? Porous material Two phases: solid and fluid Elastic coupling Visco-inertial coupling What does it do? Transforms acoustic energy into heat How does it dissipate energy? Viscous effect Thermal effect Structural damping 4

5 What about their frame? Elastic frame Rigid frame Limp frame Granular 5

6 Types of Porous aterials Polymeric foam etallic foam Recycled Glass wool / glass fiber Felt ultilayer, carpet and fabric 6

7 How are they modeled? They are modeled at a homogeneous macroscopic scale. H 2 acroscopic scale h << H h << H 1 << H H 1 << H 2 u x u x h u z u z H 1 u y u y Porous material acroscopic scale Homogeneous solid Homogeneous fluid 7

8 How are they modeled? At a local scale: heterogeneous At a macroscopic scale: homogeneous Example: Chipped foam 8

9 How are they modeled? BIOT (u,p) formulation worked out by ATALLA and PANNETON governs the propagation of the coupled elastic waves (compression and shear) and acoustic wave (compression). μu ~ i,jj ~ λ + 1 ω 2~ ρ f μ ~ + u j,ij + ω 2~ ρ s p, ii + p γ ~ ~ 1 = K f u i u i,i = γ ~ p, i Elasto-dynamic equation Helmholtz equation [J. Acoust. Soc. Am. 104(3),p ] Biot's macroscopic parameters u : p : Solid phase macroscopic displacement vectors Fluid phase macroscopic pressure ~: Denotes a complex and frequency dependent quantity λ,µ : Effective solid phase Lamé coefficients K f : Effective fluid phase bulk modulus ρ s : Effective solid phase density ρ f : γ : Effective fluid phase density Fluid-solid coupling coefficient 9

10 Rigid and Limp limits (P) Rigid frame formulation - Helmholtz equation with effective density and bulk modulus : Laplacian operator (P) Limp frame formulation - Helmholtz equation with effective density and bulk modulus - Added inertia of the solid phase For heavy frame, ρ, the limp limit tends to the rigid limit 10

11 Porous aterials: odeling (cont d) Accuracy echanical Admittance Empirical Limp Rigid Poroelastic Hypotheses Computation time 11

12 12 What are the basic parameters? The Biot s parameters are obtained from macroscopically averaged geometrical, physical and elastic properties. loss factor structural ) ( Poisson ratio s modulus Young' ) ( the foam density of 1 characteristic length thermal ' viscous characteristic length tortuosity static flow resistivity porosity ~ ~ ~ ~ ~ ~ η ω ν ω ρ Λ Λ α σ φ E λ μ ρ s γ f ρ f K α Λ Λ ) ( ) ( Λ = s ds s r v v dv r v = Λ s ds v dv

13 What are the input parameters? Compatible with: NOVA FOA-X Difficult to measure Source: GUI from NOVA 13

14 easuring input parameters? Impedance tube Resistance meter echanical analyzer Porosity and density meter Tortuosity meter FOA-X NOVA 14

15 Impedance and Transmission Tube Properties: - Absorption coefficient - Reflection coefficient - Surface impedance AST E1050, ISO Correction for temperature, barometric pressure, and attenuation. Acquisition System 15

16 Impedance and Transmission Tube Fully automated High accuracy Correction for: - Temperature - Barometric pressure - Tube attenuation Compatible with FOA-X characterization module TUBE-X Software 16

17 SIGA - Airflow Resistance eter Properties: - Static airflow resistivity - Static air permeability Direct method based on AST C522 Comparative method based on standardized resistance. Foams, fibers, felts, fabrics, and films Acquisition System 17

18 SIGA - Airflow Resistance eter ay be used for quality control SIGA-X Software 18

19 QA - Quasi-static echanical Analyzer Properties: - Young s modulus - Poisson s ratio - Damping loss factor Based on standard ISO Novel direct method gives the true elastic properties. Frequency: Hz Acquisition System 19

20 QA - Quasi-static echanical Analyzer Check how elastic properties vary with frequency QA-X Software 20

21 Porosity and Density eter Properties: - Open porosity - True bulk density Perfect gas law Acquisition System and PHI-X Software 21

22 Tortuosity eter Properties: - Tortuosity - Two characteristic lengths Ultrasound techniques - Transmission - Reflection (60 to 1000 khz) Hardware and TOR-X Software 22

23 FOA-X Properties: - Static airflow resistivity - Tortuosity - Viscous length - Thermal length - Open porosity - Thermal static permeability - Young s modulus - Poisson s ratio - Damping loss factor Unique analytical characterization method based on impedance tube measurements. FOA-X Software 23

24 FOA-X Classic easurements (optional) ρ 1, σ, φ ~ φσ ρ( ω) = ρ 0α 1 j 1+ ωρoα ~ γ 1 β ( ω) = γ H ω 1 j 1+ j 2ω Η ω j H Acoustic odel FOA-X Characterization odule FOA-X and Impedance Tube Configuration Sample and Holder icrophones Enviro Weather Station Atmospheric Pressure Temperature Relative Humidity Standard AST Impedance Tube Test Noise Source 24

25 FOA-X Verifying the quality of results The final stage of the characterization is to verify if the characterized properties can be used as input parameters in models to predict correctly the material acoustical indicator. The acoustical indicators of a material are measured with the impedance tube. - Normal sound absorption coefficient - Complex reflection coefficient - Surface impedance coefficient 25

26 FOA-X Verifying the quality of results Once verified, save properties in a material database 26

27 ecanum s Hardware & Software Integration NOVA Simulation Software FOA-X Tortuosity eter Porosity/Density eter Resistivity eter Acquisition System QA Database Impedance Tube TUBE-X Software 27

28 Validation examples... 28

29 FOA-X versus Classic Characterization (1/6) Porosity Resistivity Tortuosity Classical FOA-X Porosity 0.96 ± ± 0.00 Resistivity (Ns/m 4 ) 5111 ± ± 984 Tortuosity 1.14 ± ± 0.03 Viscous length (µm) 147 ± 10 Thermal length (µm) 274 ± 14 Classic characterization uses: Porosity / density meter Resistivity meter Ultrasound tortuosity meter Thermoformable Sheet Foam Absorption coefficient Absorption coefficient (45,62 mm) (22.81mm) Prediction (RIGID ODEL) 0.1 easure Frequency (Hz) Frequency (Hz) 29

30 FOA-X versus Classic Characterization (2/6) Porosity Resistivity Tortuosity Classical FOA-X Porosity 0.87 ± ± 0.07 Resistivity (Ns/m 4 ) ± ± 2500 Tortuosity 2.12 ± ± 0.43 Viscous length (µm) 29.1 ± 10.4 Thermal length (µm) 85.5 ± 13.6 Classic characterization uses: Porosity / density meter Resistivity meter Ultrasound tortuosity meter Absorption coefficient Absorption coefficient Sheet Foam Carpenter Co ,00 mm 12,56 Prediction (RIGID ODEL) easure Frequency (Hz) Frequency (Hz) 30

31 FOA-X versus Classic Characterization (3/6) Porosity Resistivity Tortuosity Classical FOA-X Porosity ± ± 0.07 Resistivity (Ns/m 4 ) ± ± 1838 Tortuosity 1.04 ± ± 0.00 Viscous length (µm) 109 ± 11 Thermal length (µm) 128 ± 21 Classic characterization uses: Porosity / density meter Resistivity meter Ultrasound tortuosity meter Absorption coefficient elamine Foam , Frame resonance , Prediction (RIGID ODEL) 0.1 easure Frequency Frequency(Hz) (Hz) 31

32 FOA-X versus Classic Characterization (4/6) Tortuosity Viscous length Thermal length Classical FOA-X Porosity 0.89 ± 0.02 Resistivity (Ns/m 4 ) ± 1257 Tortuosity 1.13 ± ± 0.02 Rigid Frame - etallic Foam GRNI-35-A (150 C) Viscous length (µm) 17.4 ± ± 3 Thermal length (µm) ± ± 5 Direct characterization uses: Porosity / density meter Resistivity meter Ultrasound tortuosity meter Absorption coefficient NOVA prediction with FOA-X foam parameters easure Frequency (Hz) 32

33 NOVA versus Impedance Tube easurements (5/6) Single Layer - Elastic Frame NOVA is fed by the foam parameters measured with FOA-X Frame resonance 33

34 Quasi-static echanical Analyzer (QA) Validation (simulation with NOVA) Sound absorption coefficient Rigid-frame model Biot poroelastic model Experimental AST E Frequency (Hz) 34

35 Experimental Validation for ultilayer System with Impervious Film Plane wave Absorption coefficient Fibrous Septum Foam 2 Rigid wall Frequency (Hz) 35

36 Experimental Validation for ultilayer System with a Perforated Screen 1 (25.06 mm) Absorption coefficient 1 Perforated screen 3 Rigid frame Perforated screen (0.79 mm) Prediction easure 3 (12.57 mm) Frequency (Hz) 36

37 Transmission Loss of an Aluminium Panel elamine Configuration 37

38 Transmission Loss of an Aluminium Panel + Felt All 5 acoustic material properties of the tested felt are computed using FOA-X and used in NOVA for prediction. Test NOVA prediction 38

39 Transmission Loss of Car Laminated Glass 6,00E+01 NOVA Predictions vs Test TL (db) 5,00E+01 4,00E+01 3,00E+01 2,00E+01 1,00E+01 Glass (Nova) Laminate (Nova) Glass (Test) Laminate (Test) 0,00E Frequency (Hz) The frequency dependencies of the core material of the laminated glass are accounted for in NOVA 39

40 Can we use NOVA for complex 3D problems? Yes. For complex configurations NOVA s formulations and FOA-X s measured parameters are used within a ecanum 3D version. They are also used within a novel substruturing method to handle independently several trim components (Implementation in Straco s PE software). aster-structure Acoustic Cavities Air Gap aster-structure Component atrix Complex Porous Components Y ss Y sc aster Structure dof s Y t sc Y cc Acoustic Cavity dof s 40