Modeling of multilayer sound material (TRIM) LMS Virtual ...oss.jishulink.com/caenet/forums/upload/2012/05/17/368/... · 08.03.2007 · Modeling of multilayer sound material (TRIM)

Dr. Koen De LangheIndia - December 2006

Modeling of multilayer sound material (TRIM)LMS Virtual.Lab Fast TRIM

2 copyright LMS International - 2006

Outline

2 Existing LMS Trim Modeling Practice

1 What is a Multi-Layer Trim Material ?

3 Trim Substructuring

4 Some Validation Examples

5 Virtual.Lab Fast TRIM

6 Summary and Conclusion


What is a Multi-Layer Trim Material ?

Widely used in the automotive and aerospace industry (firewall, door trim panels, floor carpets, roof liner…)

Made of a superposition of• Visco-elastic layers• Poro-elastic layers• Fluid layers

Typical set-up for automotive trim consists of four layers :• Heavy visco-elastic covering layer• Thick porous material layer• Damping layer• Metal panel (car body)

Physics = double mass-spring system


What is a Multi-Layer Trim Material ?

Porous materials consist of a solid phase (skeleton or frame) and a fluid phase (air in pores)

Noise and vibration reduction mechanisms• Viscous flow in porous channels

=> energy dissipation due to friction between fluid and skeleton• Temperature fluctuation of air due to acoustic wave

=> energy dissipation due to contact with skeleton at ambient temperature• Vibration of skeleton excited by base plate or fluid vibration

=> energy dissipation due to visco-elastic losses


Outline








Existing LMS Vibro-Acoustic Trim Modeling Practice[Virtual.Lab Rev 5B or SYSNOISE Rev 5.6]

Added mass on structural plate to model effect of trim mass on the structural dynamicsApply simple surface impedance on the acoustic boundary to model the acoustic absorption effect of the trim(impedance function is measured or computed e.g. with LMS VIOLINS)

Structural Modes

+ Added massAcoustic BCsStructural

loading Surface impedance

Vibro-acoustic case

Not satisfactory, more accurate method is needed !


Improved Trim Modeling : Full Biot modeling

3D FEM coupled poro-elastic modelNeed to mesh the entire porous material domain Solves simultaneously for the pore acoustic pressure and the skeleton structural displacementBig system with un-symmetric, frequency-dependent mass and stiffness matrices

Very detailed and precise modeling, but based on roughly estimated materialpropertiesVery costly in terms of CPU time

Call for a more simple and realistic approach !


Outline








Improved Trim Modeling: Wave-Based Transfer Admittance

Biot-Allard model:Homogeneous isotropic trim materialsConsider cavity-trim-plate system infinitely extended in x1 directionAllows to compute transfer admittances for a plane wave hitting the trim layer with incidence angle θTransfer admittance defines relation between acoustic pressure and velocity on two sets of faces

Flexible plate

Trim layer

Cavityθ

x1

x3

(pa ,va)

(ps ,vs)

⎥⎦

⎤⎢⎣

⎡⎥⎦

⎤⎢⎣

⎡=⎥

⎦

⎤⎢⎣

⎡

a

s

a

s

pp

vv

54

21

αααα



⎥⎦

⎤⎢⎣

⎡⎥⎦

⎤⎢⎣

⎡′′′′

=⎥⎦

⎤⎢⎣

⎡

a

s

a

s

pv

vp

54

21

αααα

Normal plate velocity

Acoustic pressure at the trim-cavity interface

Pressure loading on flexible plate

Fluid velocity at the trim-cavity interface

{ }⎮⌡⌠ ′

iS

dSi nn NN1αω

Structural Impedance

{ }⎮⌡⌠ ′

jS

dSi NN5αω

Acoustic Admittance

{ }⎮⌡⌠ ′

iS

dSNNn2α

{ }⎮⌡⌠ ′

jS

dSNNn42 αω

Coupling Term

Coupling Term


Transfer Admittance Coefficient

Alpha Prime One

-40000

-20000

0

20000

40000

60000

80000

100000

1.25

E+0

1

4.38

E+0

1

7.50

E+0

1

1.06

E+0

2

1.38

E+0

2

1.69

E+0

2

2.00

E+0

2

2.31

E+0

2

2.63

E+0

2

2.94

E+0

2

3.25

E+0

2

3.56

E+0

2

3.88

E+0

2

4.19

E+0

2

4.50

E+0

2

4.81

E+0

2

5.13

E+0

2

5.44

E+0

2

5.75

E+0

2

6.06

E+0

2

6.38

E+0

2

6.69

E+0

2

7.00

E+0

2

7.31

E+0

2

7.63

E+0

2

7.94

E+0

2

8.25

E+0

2

8.56

E+0

2

8.88

E+0

2

9.19

E+0

2

9.50

E+0

2

9.81

E+0

2

Frequency (Hz)

Alp

ha P

rim

e

RealImag

Pure Added Mass at low frequencyDamping effect between 300Hz and 500Hz


Alpha Prime 2

-8

-6

-4

-2

0

2

4

6

1.25

E+0

1

4.22

E+0

1

7.19

E+0

1

1.02

E+0

2

1.31

E+0

2

1.61

E+0

2

1.91

E+0

2

2.20

E+0

2

2.50

E+0

2

2.80

E+0

2

3.09

E+0

2

3.39

E+0

2

3.69

E+0

2

3.98

E+0

2

4.28

E+0

2

4.58

E+0

2

4.88

E+0

2

5.17

E+0

2

5.47

E+0

2

5.77

E+0

2

6.06

E+0

2

6.36

E+0

2

6.66

E+0

2

6.95

E+0

2

7.25

E+0

2

7.55

E+0

2

7.84

E+0

2

8.14

E+0

2

8.44

E+0

2

8.73

E+0

2

9.03

E+0

2

9.33

E+0

2

9.63

E+0

2

9.92

E+0

2

Frequency

Alp

ha P

rime

2

RealImag


Standard Coupling at low frequencyComplex coupling at 400Hz (phase effect)Almost de-coupled at higher frequencies



Alpha Prime 5

-6.E-04

-4.E-04

-2.E-04

0.E+00

2.E-04

4.E-04

6.E-04

8.E-04

1.25

E+0

1

4.38

E+0

1

7.50

E+0

1

1.06

E+0

2

1.38

E+0

2

1.69

E+0

2

2.00

E+0

2

2.31

E+0

2

2.63

E+0

2

2.94

E+0

2

3.25

E+0

2

3.56

E+0

2

3.88

E+0

2

4.19

E+0

2

4.50

E+0

2

4.81

E+0

2

5.13

E+0

2

5.44

E+0

2

5.75

E+0

2

6.06

E+0

2

6.38

E+0

2

6.69

E+0

2

7.00

E+0

2

7.31

E+0

2

7.63

E+0

2

7.94

E+0

2

8.25

E+0

2

8.56

E+0

2

8.88

E+0

2

9.19

E+0

2

9.50

E+0

2

9.81

E+0

2

Frequency (Hz)

Alph

a Pr

ime

5

RealImag.

Pure Added Mass at low frequency Damping effect between 300Hz and 500Hz



Transfer Admittance Coefficients (alpha)Computed for any combination of Fluid / Poro-elastic / Visco-elastic layersFrequency-dependentAccount for all physical effects :

• Added structural impedance• Added acoustic admittance• Modified coupling between acoustic cavity and structural plate

Various layers are characterized by :Fluid properties : sound speed(freq) ; mass density(freq)Elastic properties : Young’s modulus(freq) ; Poisson ratio(freq) ; mass densityBiot parameters : porosity ; tortuosity ; flow resistivity ; characteristic viscous length ; characteristic thermal length


Porous Material Characterization (1)

Tortuosity :Measure of the “straightness” of the pore channelsImportant parameter : defines mass coupling between fluid and frame (α∞ = 1 : no mass coupling – straight pores) Measured by ultra-sonic method (directly proportional to the sound speed at very high frequencies)Typical values : from 1 to 2

Porosity :φ = Volume of open pores / Total volumeMeasured by compressing sample to eliminate air or by filling it with water and measuring the volume of the water drained out Typical values for foams : 0.95 to 0.99



Flow Resistivity :

Pressure difference that needs to be applied across a porous sample in order to obtain a given airflowCrucial parameter : determines viscous losses due to frame-fluid friction Typical value for foams : 5 000 to 100 000 N.s.m-4

QDPS

..∆

=σ

SampleDifferential manometer

Flow meterAir Flow

S

D∆P

Q



Characteristic viscous length :Characterizes the viscous energy exchange between fluid and frame Λv ≈ cross-section of the intersections between the poresMeasured by ultra-sonic methodTypical value for foams : 50 µm

Characteristic thermal length :Characterizes the thermal energy exchange between fluid and frame Λt ≈ pore sizeMeasured by ultra-sonic methodTypical value for foams : 100 µm

Λt Λv


Outline








Validation case 1: Cavity backed plateSimple Felt layer


Result: Pressure inside cavity

Bare Plate

Fast TRIM

Full Biot


Validation case 1: Cavity backed platemulti-layer


Result: Pressure inside cavity

Fast TRIM

Full Biot


Cavity Backed plate: Test versus Simulation

Bare Plate Treated Plate

Simulation

Test


Outline








Material Definition

Available in FEM Acousticsworkbench only !

Do not mesh the trim material volume => Only define grids connected by the relation

First, define Material Properties for multi-layer trim

Fluid MaterialVisco-elastic MaterialPoro-elastic Material


Multi-Layer Trim Property Definition

Trim Property is used to define the multi-layer trim set-upStructure Grid and Acoustic Grid for the TA relationIndividual definition of layers

• Thickness• Assign material

Ordering of the different layers (closer to structure/closer to cavity)

Do not include trim property elements in Wetted Surface definition !


Known Transfer Admittance functions

If Transfer Admittance coeff are known Transfer Relation Admittance:

E.g. based on measurementsWith todays measurement techniques, direct measurement of Transfer Admittance is possible


Apply to treated surfaces

Comparison

Full Detailed Run X hours

Fast TRIM X + ∆ hours

Create groups (or panels) of treated surfaces

Apply multilayer properties to panels

Dr. Koen De LangheIndia - December 2006

Thank you

Documents

Modeling of multilayer sound material (TRIM) LMS Virtual ...oss.jishulink.com/caenet/forums/upload/2012/05/17/368/... · 08.03.2007 · Modeling of multilayer sound material (TRIM)