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2013 SAE NVC Structure Borne Noise Workshop 2013 Automotive Analytics LLC A.E.Duncan Slide 1 SAE 2013 NVH Conference Structure Borne NVH Workshop Alan Duncan Alan Duncan Altair Engineering @ Honda NVH Specialist Greg Greg Goetchius Goetchius Tesla Motors NVH Specialist Jianmin Jianmin Guan Guan Altair Engineering NVH Manager Contact Email: [email protected]

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Page 1: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 1

SAE 2013 NVH ConferenceStructure Borne NVH Workshop

Alan DuncanAlan Duncan Altair Engineering @ HondaNVH Specialist

Greg Greg GoetchiusGoetchius Tesla MotorsNVH Specialist

JianminJianmin GuanGuan Altair Engineering NVH Manager

Contact Email: [email protected]

Page 2: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 2

Structure Borne NVH WorkshopWorkshop Objectives -1. Review Basic Concepts of Automotive Structure Borne Noise.

2. Propose Generic Targets.

3. Present New Technology Example.

Intended Audience �• New NVH Engineers.

• �Acoustics� Engineers seeking new perspective.

• �Seasoned Veterans� seeking to brush up skills.

Page 3: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 3

Structure Borne NVH Workshop• Introduction• Low Frequency Basics• Mid Frequency Basics• Live Noise Attenuation Demo• New Technology

Uncertainty and NVH Scatter • Closing Remarks

Page 4: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 4

Structure Borne NVH Workshop• Introduction• Low Frequency Basics• Mid Frequency Basics• Live Noise Attenuation Demo• New Technology

Uncertainty and NVH Scatter• Closing Remarks

Page 5: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 5

Rideand

Handling

NVH Durability

ImpactCrashWorthiness

Competing Vehicle Design Disciplines

Page 6: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 6

Automotive Engineering Objectives are Timeless

Page 7: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 7

Structure Borne NVH Workshop• Introduction• Low Frequency Basics• Mid Frequency Basics• Live Noise Attenuation Demo• New Technology

Uncertainty and NVH Scatter• Closing Remarks

Alan Duncan

Page 8: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 8

Structure Borne Noise and Vibration

VibratingSource

Frequency Range: up to 1000 HzSystem Characterization

• Source of Excitation• Transmission through Structural Paths • “Felt” as Vibration• “Heard” as Noise

Page 9: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 9

Structure Borne NoiseAirborne Noise

Res

pons

e

Log Frequency

�Low�Global Stiffness

�Mid�

Local Stiffness+

Damping

�High�

Absorption+

Mass+

Sealing+

Damping

~ 150 Hz ~ 1000 Hz ~ 10,000 Hz

Automotive NVH Frequency Range

Page 10: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 10

Low Frequency Basics• Source-Path-Receiver Concept• Single DOF System Vibration• NVH Source Considerations• Receiver Considerations• Vibration Attenuation Strategies

Provide Improved IsolationMode ManagementNodal Point MountingDynamic Absorbers

Page 11: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 11

Low Frequency Basics• Source-Path-Receiver Concept• Single DOF System Vibration• NVH Source Considerations• Receiver Considerations• Vibration Attenuation Strategies

Provide Improved IsolationMode ManagementNodal Point MountingDynamic Absorbers

Page 12: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 12

RECEIVER

PATH

SOURCE

Structure Borne NVH Basics

Page 13: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 13

Low Frequency Basics• Source-Path-Receiver Concept• Single DOF System Vibration• NVH Source Considerations• Receiver Considerations• Vibration Attenuation Strategies

Provide Improved IsolationMode ManagementNodal Point MountingDynamic Absorbers

Page 14: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 14

m

APPLIED FORCE

F = FO sin 2 π f t

k c FT

TR = FT / F

TransmittedForce

Single Degree of Freedom Vibration

= fraction of critical damping

fn = natural frequency

f = operating frequency

( )2n

22n

2

2n

ff2)ff(1)ff(21ζ

ζ+−

+=

ζmk

Page 15: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 15

0 1 2 3 4 50

1

2

3

4Tr

ansm

issi

bilit

y R

atio

1.414Frequency Ratio (f / fn)

Vibration Isolation Principle

m

APPLIED FORCEF = FO sin 2 π f t

k c FT

TR = FT / F

TransmittedForce

Isolation RegionIsolation Region

1.00.5

0.375

0.25

0.15

0.1

Page 16: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 16

Low Frequency Basics• Source-Path-Receiver Concept• Single DOF System Vibration• NVH Source Considerations• Receiver Considerations• Vibration Attenuation Strategies

Provide Improved IsolationMode ManagementNodal Point MountingDynamic Absorbers

Page 17: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 17

Two Main Sources

NVH Source Considerations

Suspension Powertrain

Page 18: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 18

Typical NVH Pathways to the Passenger

PATHS FOR

STRUCTURE BORNE

NVH

Page 19: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 19

Structure Borne NVH Sources

Page 20: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 20

Structure Borne NVH Sources

Primary Consideration:

Reduce the Source first as much as possible because whatever enters the structure is transmitted through multiple paths to the receiver.

Transmission through multiple paths is more subject to variability.

Page 21: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 21

Low Frequency Basics• Source-Path-Receiver Concept• Single DOF System Vibration• NVH Source Considerations• Receiver Considerations• Vibration Attenuation Strategies

Provide Improved IsolationMode ManagementNodal Point MountingDynamic Absorbers

Page 22: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 22

Receiver ConsiderationsSubjective to Objective Conversions

Subjective NVH Ratings are typically based on a 10 Point Scale resulting from Ride Testing

A 2 ≈≈≈≈ 1/2 A 1Represents 1.0 Rating Change

TACTILE: 50% reduction in motion

SOUND : 6.dB reduction in sound pressure level ( long standing rule of thumb )

Receiver Sensitivity is a Key Consideration

Page 23: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 23

Low Frequency Basics• Source-Path-Receiver Concept• Single DOF System Vibration• NVH Source Considerations• Receiver Considerations• Vibration Attenuation Strategies

Provide Improved IsolationMode ManagementNodal Point MountingDynamic Absorbers

Page 24: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 24

Total 2178.2 Kg (4800LBS)Mass Sprung 1996.7 Kg

Unsprung 181.5 Kg (8.33% of Total)Powertrain 181.5 Kg

Tires 350.3 N/mmKF 43.8 N/mmKR 63.1 N /mmBeam mass lumped on grids like a beam M2,3,4 =2 * M1,5

Symbolic Model of Unibody Passenger Car8 Degrees of Freedom

From Reference 6

318

2

6

4

75

Page 25: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 25

1 2 4 5

6 7

8

3

TiresWheels

SuspensionSprings

Engine Mass

EngineIsolator

Flexible Beam for Body

8 Degree of Freedom Vehicle NVH Model

Page 26: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 26

8 Degree of Freedom Vehicle NVH ModelForce Applied to Powertrain Assembly

Forces at Powertrain could represent a First OrderRotating Imbalance

Feng

1 2 4 5

6 7

8

3

Page 27: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 27

Engine Isolation Example

Response at Mid Car

0.0001

0.0010

0.0100

0.1000

1.0000

5.0 10.0 15.0 20.0Frequency Hz

Velo

city

(mm

/sec

)

Constant Force Load; F ~ A 15.9 Hz8.5 Hz7.0 Hz

700 Min. RPM First Order UnbalanceOperation Range of Interest

318

2

6

4

753311

8822

66

44

7755

Page 28: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 28

Engine Isolation Example

Response at Mid Car

0.0001

0.0010

0.0100

0.1000

1.0000

5.0 10.0 15.0 20.0Frequency Hz

Velo

city

(mm

/sec

)

Constant Force Load; F ~ A

700 Min. RPM First Order UnbalanceOperation Range of Interest

318

2

6

4

753311

8822

66

44

7755

15.9 Hz

8.5 Hz

7.0 Hz

Engine Idle Speed Operating Shapes

at 700 RPM

Lowest Body Movement

Page 29: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 29

Concepts for Increased Isolation�Double� isolation is the typical strategy for further improving isolation of a given vehicle design.

Subframe is Intermediate Structure

Suspension Bushing is first level

Second Level of Isolation is at Subframe

to Body Mount

Page 30: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 30

8 Degree of Freedom Vehicle NVH ModelRemoved Double Isolation Effect

WheelMass

Removed

1 2 4 5

6 7

8

3

Page 31: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 31

Double Isolation ExampleVertical Response at DOF3

0.0E+00

1.0E+00

2.0E+00

3.0E+00

4.0E+00

5.0E+00

6.0E+00

5.0 10.0 15.0 20.0Frequency Hz

Velo

city

(m

m/s

ec)

Base Model

Without Double_ISO

1.414*fn

318

2

6

4

753311

8822

66

44

7755

Page 32: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 32

Low Frequency Basics• Source-Path-Receiver Concept• Single DOF System Vibration• NVH Source Considerations• Receiver Considerations• Vibration Attenuation Strategies

Provide Improved IsolationMode ManagementNodal Point MountingDynamic Absorbers

Page 33: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 33

Mode Management Chart

0 5 10 15 20 25 30 35 40 45 50HzFirst Order Wheel/Tire Unbalance V8 Idle

Hot - Cold

EXCITATION SOURCESInherent Excitations (General Road Spectrum, Reciprocating Unbalance, Gas Torque, etc.)Process Variation Excitations (Engine, Driveline, Accessory, Wheel/Tire Unbalances)

Hz

Hz0 5 10 15 20 25 30 35 40 45 50

0 5 10 15 20 25 30 35 40 45 50

CHASSIS/POWERTRAIN MODES

Ride ModesPowertrain Modes

Suspension Hop and Tramp ModesSuspension Longitudinal Modes

Exhaust Modes

BODY/ACOUSTIC MODES

Body First Bending First Acoustic Mode

Steering Column First Vertical BendingBody First Torsion

(See Ref. 1)

Page 34: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 34

8 Degree of Freedom Vehicle NVH ModelBending Mode Frequency Separation

Beam Stiffness was adjusted to align Bending

Frequency with Suspension Modes and then

progressively separated back to Baseline.

1 2 4 5

6 7

8

3

Page 35: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 35

Response at Mid Car

0.10

1.00

10.00

100.00

5 10 15 20Frequency Hz

Velo

city

(mm

/sec

)

18.2 Hz Bending13.Hz Bending10.6 Bending

8 DOF Mode Separation Example

18.2 Hz13.0 Hz

10.6 Hz318

2

6

4

753311

8822

66

44

7755

Page 36: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 36

Response at Mid Car

0.10

1.00

10.00

100.00

5 10 15 20Frequency Hz

Velo

city

(mm

/sec

)

18.2 Hz Bending13.Hz Bending10.6 Bending

8 DOF Mode Separation Example

All Operating Shapes at 10.6 Hz

318

2

6

4

753311

8822

66

44

7755 Highest Body Bending

Page 37: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 37

Low Frequency Basics• Source-Path-Receiver Concept• Single DOF System Vibration• NVH Source Considerations• Receiver Considerations• Vibration Attenuation Strategies

Provide Improved IsolationMode ManagementNodal Point MountingDynamic Absorbers

Page 38: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 38

Front input forces Rear input forces

First Bending: Nodal Point Mounting ExampleMount at Nodal Point

Locate wheel centers at node points of the first bending modeshapeto prevent excitation coming from suspension input motion.

Page 39: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 39

Passenger sits at node point for First Torsion.

Side View

First Torsion: Nodal Point Mounting ExamplesMount at Nodal Point

Transmission Mount of a3 Mount N-S P/T is nearthe Torsion Node.

Rear View

Engine

Page 40: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 40

Powertrain Bending Mode Nodal Mounting

Mount system is placed to support Powertrain at the Nodal Locations of the First order Bending Mode. Best compromise with Plan View nodes should also be considered.

1 2 4 5

6 7

3

Page 41: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 41

1 2 4 5

6 7

8

3

8 Degree of Freedom Vehicle NVH ModelBending Node Alignment with Wheel Centers

Redistribute Beam Masses to move Node Points to

Align with points 2 and 4

Page 42: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 42

Response at Mid-Car

0.0E+00

1.0E+00

2.0E+00

3.0E+00

4.0E+00

5.0 10.0 15.0 20.0Frequency Hz

Velo

city

(m

m/s

ec)

Node ShiftedBase Model

First Bending Nodal Point Alignment

318

2

6

4

753311

8822

66

44

7755

Page 43: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 43

Response at Mid-Car

0.0E+00

1.0E+00

2.0E+00

3.0E+00

4.0E+00

5.0 10.0 15.0 20.0Frequency Hz

Velo

city

(m

m/s

ec)

Node ShiftedBase Model

First Bending Nodal Point Alignment

318

2

6

4

753311

8822

66

44

7755

Operating Shapes at

18.2 Hz

Node Shifted Model

No Residual Body Bending

Page 44: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 44

Diagnosis: Increase at 10.2 Hz

Body Bends up at Downward Position of Cycle

Page 45: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 45

Diagnosis: Increase at 10.2 Hz

Motion Experienced when Bending is Present

Motion Experienced when Bending is Removed

Diagnosis: Increase at 10.2 Hz

Center - Undeformed Position

Up Position

Down Position

CONCLUSION:Response Increases when a Beneficial mode is Removed.

Page 46: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 46

Low Frequency Basics• Source-Path-Receiver Concept• Single DOF System Vibration• NVH Source Considerations• Receiver Considerations• Vibration Attenuation Strategies

Provide Improved IsolationMode ManagementNodal Point MountingDynamic Absorbers

Page 47: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 47

YO

xSDOF

Dynamic Absorber Concept

MYO

x

Auxiliary Spring-Mass-Damperm = M / 10

2DOFM

Page 48: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 48

Powertrain Example of Dynamic Absorber

Anti-Node Identifiedat end of Powerplant

k c

Absorber attached at anti-node acting in the Vertical and Lateral plane.

Tuning Frequency = √√√√ k/m

m

[Figure Courtesy of DaimlerChrysler Corporation]

Page 49: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 49

Baseline Sound Level63 Hz Dynamic Absorber63 + 110 Hz Absorbers

Baseline Sound Level63 Hz Dynamic Absorber63 + 110 Hz Absorbers

[Figure Courtesy of DaimlerChrysler Corporation]

10 dB

Page 50: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 50

Low Frequency Basics - Review• Source-Path-Receiver Concept• Single DOF System Vibration• NVH Source Considerations• Receiver Considerations• Vibration Attenuation Strategies

Provide Improved IsolationMode ManagementNodal Point MountingDynamic Absorbers

Page 51: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 51

Structure Borne NVH Workshop• Introduction• Low Frequency Basics• Mid Frequency Basics• Live Noise Attenuation Demo• New Technology

Uncertainty and NVH Scatter• Closing Remarks

Jianmin Guan

Page 52: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 52

Mid Frequency NVH Fundamentals

This looks familiar!Frequency Range of Interest has changed to

150 Hz to 1000 Hz

Page 53: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 53

Typical NVH Pathways to the Passenger

PATHS FOR

STRUCTURE BORNE

NVHNoise Paths are the

same as LowFrequency Region

Noise Paths are thesame as Low

Frequency Region

Page 54: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 54

Mid-Frequency Analysis CharacterStructure Borne Noise

Airborne Noise

Res

pons

e

Log Frequency�Low�

Global Stiffness�Mid�

Local Stiffness+

Damping

�High�

Absorption+

Mass+

Sealing

~ 150 Hz ~ 1000 Hz ~ 10,000 Hz

High modal densityand coupling in

source, path andreceiver

• Mode separation is less practical inmid-frequency

• New Strategy is Effective Isolation:Achieved by reducing energy transferlocally between source and receiver atkey paths.

•• Mode separation is less practical inMode separation is less practical inmidmid--frequencyfrequency

•• New Strategy is Effective Isolation:New Strategy is Effective Isolation:Achieved by reducing energy transferAchieved by reducing energy transferlocally between source and receiver atlocally between source and receiver atkey paths.key paths.

Page 55: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 55

Mid-Frequency Analysis Character

Control Measures for Mid Frequency Concerns

Effective Isolation

Attenuation along Key Noise Paths

Page 56: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 56

Mid-Frequency Analysis Character

Control Measures for Mid Frequency Concerns

Effective Isolation

Attenuation along Key Noise Paths

Page 57: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 57

Classical SDOF: Rigid Source and Receiver

Tra n

smis

sibi

l ity

Ra t

io

1.0 1.414 10.0

f / f n

�Real Structure�Flexible (Mobile)Source and Receiver

Isolation Effectiveness

Effectiveness deviates from the classical development as resonances occur in the receiver structure and in the foundation of the source.

Isolation RegionIsolation Region

1.0

Page 58: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 58

Mobility• Mobility is the ratio of velocity response at the excitation point on structure

where point force is applied

Mobility =Velocity

Force

• Mobility, related to Admittance, characterizes Dynamic Stiffness of the structure at load application point

Mobility =Frequency * Displacement

Force

=Frequency

Dynamic Stiffness

Page 59: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 59

• The isolation effectiveness can be quantified by a theoretical model based on analysis of mobilities of receiver, isolator and source

• Transmissibility ratio is used to objectively define measure of isolation

TR =Force from source without isolator

Force from source with isolator

Isolation

V r

V ir

V is

F r

F ir

Receiver

Source

F is

Fs V s

Isolator

VF s=

Y i + Y r + Y s

V r

F r

Receiver

Source

F s V s

VF s=

Y r + Y s

VV

Page 60: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 60

TR = ( Y r + Y s ) //// ( Y i + Y r + Y s )

• For Effective Isolation (Low TR) the Isolator Mobility must exceed the sum of the Source and Receiver Mobilities.

Y r : Receiver mobility

Y s : Source mobility

Y i : Isolator mobility

V m

V im

V if

F m

F im

Receiver

Source

F if

F f V f

Isolator

TR = Force from source without an isolator Force from source with an isolator

Isolation

Recall that K 1Y ∝

Page 61: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 61

TR = ( ) //// ( ) K body

1K source

1+ K body

1 + K iso

1K source

1+

K iso

K sourceK body

K iso1.0 5.0 20.0

1.0

5.0

20.0

0.67 0.55 0.51

0.55 0.29 0.20

0.51 0.20 0.09

Generic targets:body to bushing stiffness ratio of at least 5.0source to bushing stiffness ratio of at least 20.0

Designing Noise Paths

Page 62: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 62

Body-to-Bushing Stiffness RatioRelationship to Transmissibility

Stiffness Ratio; K body / K iso

Tran

smis

sibi

lity

Rat

io T

R

0

0.1

0.2

0.3

0.4

0.5

0.6

1 2 3 4 5 6 7 8 9 10

Target Min. = 5 gives TR = .20

For a source ratio of 20

Page 63: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 63

Mid-Frequency Analysis Character

Control Measures for Mid Frequency Concerns

Effective Isolation

Attenuation along Key Noise Paths

Page 64: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 64

Identifying Key NVH PathsKey NVH paths are identified by Transfer Path Analysis (TPA)

Fi

TactileTransferTactile

TransferAcousticTransfer

AcousticTransfer

Operating loads Operating loads

Break the system at the points where the forces enter the body (Receiver)

Total Acoustic Response is summation of partial responses over all noise paths

Pt = ΣΣΣΣ paths [Pi ] = ΣΣΣΣ paths [ (P/F) i * Fi ]

Page 65: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 65

Identifying Key NVH PathsTPA Example: Contribution at One Transfer Path

Partial response from a particular path: Pi = (P/F) i * Fi

P/T LoadCrank torque

91 Hz

FiTFi

Page 66: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 66

Identifying Key NVH PathsTPA Example: Sum of Key Transfer Paths at One Peak

P/T LoadCrank torque

P/T LoadCrank torque

Total Response: Pt = ΣΣΣΣ paths [Pi ] = ΣΣΣΣ paths [ (P/F) i * Fi ]

Page 67: 2013 nvh str_borne_workshop_web

2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 67

Attenuating Key NVH PathsTPA Example: Identifying Root Cause of Dominant Paths

P/T LoadCrank torque

PMiFi

TFi

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 68

Attenuating Key NVH PathsTPA Example: Dominant Paths over Frequencies

P/T LoadCrank torque

Fi

TFi

PMi

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 69

Designing Noise PathsTPA Example: Cascading Vehicle Targets to Subsystems

Limit TF to a 55 dB target

See changes in response

P/T LoadCrank torque

TFi

Once the dominant noise paths and root cause have been identified, the task is reduced to solving problems of:

1. High Force2. High Transfer Function3. High Point Mobility

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Designing Noise Paths

Fi

Acoustic Transfer (P/F)iAcoustic Transfer (P/F)i

Operating loads createForces (Fi) into body atAll noise paths

F FF F

FF F

Pt = ΣΣΣΣ paths [Pi ] = ΣΣΣΣ paths [ Fi * (P/F) i ] = ΣΣΣΣ paths [ Fi * (P/V) i * (V/F)i]

P/V

P/F(Kbody)

V/F

Measurement Parameters Generic Targets

P/F Acoustic Sensitivity 50 - 60 dBL/N

V/F Structural Point Mobility (Receiver Side)

0.2 to 0.3 mm/sec/N

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 71

Recall for Acoustic Response Pt

Pt = ΣΣΣΣ paths [Pi ] = ΣΣΣΣ paths [ Fi * (P/V) i * (V/F)i]

“Downstream” Effects: Body Panels

(P/V)i !!!! �Downstream� (Body Panel) System Dynamics: Three Main Effects:

Increased Damping

Increased Stiffness

1. Panel Damping

2. Panel Stiffness

3. Panel Acoustic Contribution

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 72

Generic Noise Path Targets

K iso

K body> 5.0

K iso

K source

> 20.0

AcousticSensitivity < 50 - 60

dBL/N

StructuralMobility < 0.2 to 0.3 mm/sec/N

Panel Damping Loss Factor> .10

Primary: Minimize the Source Force< 1.0 N

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 73

Final Remarks on Mid Frequency Analysis

• Effective isolation at dominant noise paths is critical• Effective isolation at dominant noise paths is critical

• Reduced mobilities at body & source and softenedbushing are key for effective isolation

• Reduced mobilities at body & source and softenedbushing are key for effective isolation

• Other means of dealing with high levels of response(Tuned dampers, damping treatments, isolatorplacement at nodal locations) are also effective

• Other means of dealing with high levels of response(Tuned dampers, damping treatments, isolatorplacement at nodal locations) are also effective

• Mode Separation remains a valid strategy as modesin the source structure start to participate

• Mode Separation remains a valid strategy as modesin the source structure start to participate

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 74

Structure Borne NVH: Concepts Summary

• Source-Path-Receiver as a system1. Reduce Source

2. Rank and Manage Paths

3. Consider Subjective Response

• Effective Isolation

• Mode Management

• Nodal Point Placement

• Attachment Stiffness

• �Downstream� (Body Panel) Considerations

• Source-Path-Receiver as a system1. Reduce Source

2. Rank and Manage Paths

3. Consider Subjective Response

• Effective Isolation

• Mode Management

• Nodal Point Placement

• Attachment Stiffness

• �Downstream� (Body Panel) Considerations

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 75

Structure Borne NVH Workshop• Introduction• Low Frequency Basics• Mid Frequency Basics• Live Noise Attenuation Demo• New Technology

Uncertainty and NVH Scatter• Closing Remarks

Greg Goetchius

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Toolbox Demo Noise Test Results

85

61

68

63

55

47

39

30

40

50

60

70

80

90

1) Baseline:Imbalance, No

Isolation

2) Imbalance +Isolation

3) No Imbalance,No Isolation

4) No Imbalance,No Isolation +

Damping

5) No Imbalance +Isolation +Damping

6) #5 + Absorption 7) #6 + InsulatorMat

SPL

(dB

A)

Tool Box Demo Test Results

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 77

Structure Borne NVH Workshop• Introduction• Low Frequency Basics• Mid Frequency Basics• Live Noise Attenuation Demo• New Technology

NVH Scatter and UncertaintyClosing Remarks Alan Duncan

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NVH Scatter and Uncertainty

• Scatter 20 Years Ago

• Scatter 10 Years Ago

• New Technology to Address Scatter

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 79

NVH Scatter and Uncertainty

• Scatter 20 Years Ago

• Scatter 10 Years Ago

• New Technology to Address Scatter

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 80

Frequency ( Hz )

Mag

. of F

RF

Magnitude of 99 Structure Borne Noise Transfer Functions for Rodeo�s at the Driver MicrophoneMeasurements from Kompella and Bernhard ( Ref. 8 ) 1993 Society of Automotive Engineers, Inc.

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 81

Soun

d Pr

essu

re [

dB( l

in)]

Frequency ( Hz )

Acoustic Scatter from Simulation of the vibroacoustic behavior of a vehicle due to possible tolerances in the component area and in the production process.

© 2000 Society of Automotive Engineers, Inc.Reproduced with permission from paperby Freymann, et. Al. (Ref. 9)

12 dB Variation

Experimentally detected Scatter in low frequency vibroacoustic behavior of production vehicles.

Freymann, BMW NVH Scatter Results

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 82

CONCLUSIONs: From K/B and BMW StudiesIt is not highly probable:

1. that a Single Test will represent the Mean response2. that a CAE Simulation will match a Single Test

Variability observed from multiple tests of �identical� vehicles is important in understanding the degree to which the Test (or Simulation) of a Design is representative of the Mean response.How many Tests (or Simulations) of a Design would be required for the result to be considered statistically significant?

Scatter Implications for Test (or Simulation) NVH Development

Scatter is the �Physics�

Test Simulation

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 83

NVH Scatter and Uncertainty

• Scatter 20 Years Ago

• Scatter 10 Years Ago

• New Technology to Address Scatter

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Test Variation Band10. dB; 50-150 Hz20. dB; 150-500 Hz

Reference Baseline Confidence CriterionFor Operating Response Simulations

Test Upper BoundTest Band AverageTest Lower Bound

REF. 8

Confidence Criterion:Simulation result mustfall within the band oftest variation.

Simulation Prediction

FUDGEFACTORS

Soun

d FR

F

Frequency Hz2003 Workshop Confidence Criterion Lecture with Voice Track available at www.AutoAnalytics.com on DOWNLOAD page.

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FlashBack: 1995 Paper on Root Cause of Scatter

(Ref. 15)

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 86

Root Cause of Scatter : Conditions

Total Response

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 87

NVH Scatter and Uncertainty

• Scatter 20 Years Ago

• Scatter 10 Years Ago

• New Technology to Address Scatter

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 88(Ref. 12)

Non-Parametric Probabilistic Simulation; Soize, Durand, Gagliardini

Goal: Define a Modeling Methodology that:1. Accounts for NVH Scatter2. Quantifies Uncertainty with Statistical

Significance using a Stochastic Model3. Accounts for the Combined Effect of Modeling

and Manufacturing Uncertainty

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(See Ref. 11 for Model Details)

Non-Parametric Probabilistic Simulation; Soize, Durand, Gagliardini

Tactile Responses

POWERTRAIN LOADS

NTF @ DRIVER EAR

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 90

Non-Parametric Probabilistic Simulation; Soize, Durand, Gagliardini

Standard Eqn. forStructural-Acoustic Coupling Modal Model

Typical Derivation for creating the randomized Dynamic Matrix with Gaussian Distribution.Non-Parametric: Direct Changes in Modal Matrices.

The scatter created is a function of:Dispersion Parameter: δOnce determined, δ is a constant controlling the amplitude level of scatter.

7 Dispersion Constants are needed:

3 for Structure: M, D, K

3 for Acoustics: M, D, K

1 for Coupling: Cn,m

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 91

Non-Parametric Probabilistic Simulation; Soize, Durand, Gagliardini

Proof of Process ConvergenceCONCLUSIONS: Converged at 200 REALIZATIONS

and with Struct to 400 and Fluid to 350 Hz

Monte Carlo Randomization

Converges at 200 Realizations of the Random Matrices.

Increasing No. of Modes

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 92

Structural Uncertainty

Coupling Uncertainty

Acoustic Uncertainty

95% Upper Confidence BandNominal / Original Model Response50% Confidence Band (Mean Stochastic Model)95% Lower Confidence Band

Non-Parametric Probabilistic Simulation; Soize, Durand, Gagliardini

CONCLUSION: � The Model shows 95% Confidence Bands with increasing Scatter at higher frequency similar to K-B Study.

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 93(Ref. 13)

Non-Parametric Probabilistic Simulation; Soize, Durand, Gagliardini

Main Paper - Development is ExtensiveIncludes Test Data Comparison

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 94

FIG. 10. Finite element mesh of the computational structural acoustic model.

(See Ref. 11 for Model Details)

Non-Parametric Probabilistic Simulation; Soize, Durand, Gagliardini

Full Vehicle System � Body and ChassisStructural-Acoustic ModelSimilar Detail Level as first paper

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 95

FIG. 16. Comparisons of the stochastic computational model results with the experiments. Graphs of the root mean square of the acoustic pressures averaged in the cavity in dB scale: experiments for the 30 configurations (gray lines); Mean computational model (dashed line); mean value of the random response (mid thin solid line); 95% confidence region: the upper and lower envelopes are the upper and lower thick solid lines.

Non-Parametric Probabilistic Simulation; Soize, Durand, Gagliardini

95% UPRNominal 50% Mean95% LWR

NOTE: Acoustic Dispersion Parameters are determined here with Mean Structure held Invariant.

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 96

FIG. 19. Comparisons of the stochastic computational model results with the experiments for observation Obs6. Graphs of the moduli of the FRFs in dB scale: experiments for the 20 cars (gray lines); Mean computational model (dashed line); mean value of the random response (mid thin solid line); confidence region: the upper and lower envelopes are the upper and lower thick solid lines.

OBS # 6

Non-Parametric Probabilistic Simulation; Soize, Durand, Gagliardini

P/T Load2nd Order

95% UPRNominal 50% Mean95% LWR

NOTE: Structure Dispersion Parameters are determined here with Mean Acoustic held Invariant.

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 97

FIG. 20. Comparisons of the stochastic computational model results with the experiments for the booming noise. Graphs of the moduli of the FRFs in dB(A) scale: experiments for the 20 cars (thin gray lines); mean value of the experiments (thick gray line); Mean computational model (dashed line); Mean value of the random response (mid thin solid line); 95% confidence region: the upper and lower envelopes are the upper and lower thick solid lines.

P/T Load2nd Order

95% UprNominal 50% Mean95% Lwr

Non-Parametric Probabilistic Simulation; Soize, Durand, Gagliardini

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 98

FIG. 20. Comparisons of the stochastic computational model results with the experiments for the booming noise. Graphs of the moduli of the FRFs in dB(A) scale: experiments for the 20 cars (thin gray lines); mean value of the experiments (thick gray line); Mean computational model (dashed line); Mean value of the random response (mid thin solid line); 95% confidence region: the upper and lower envelopes are the upper and lower thick solid lines.

P/T Load2nd Order

95% UprNominal 50% Mean95% Lwr

Non-Parametric Probabilistic Simulation; Soize, Durand, Gagliardini

CONCLUSIONS:. The 95% Confidence Bands encapsulate the Measured Scatter of 20 Vehicles.. Half-Bandwidth Scatter (between Mean and Upr 95%) is similar to K-B Half-Bands.

NOTE: The Method has Quantified the Model and Manufacturing Combined Uncertainty.

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(Ref. 14)

Non-Parametric Probabilistic Simulation; Jund, Guillaume, Gagliardini

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 100

FIG. 4: Computed booming noise inside a car vs. rpm, using only structure-borne excitation compared with the measured value (brown bold). Thin dotted black: deterministic computation; green: median value; thin dotted blue: lower bound with a 95% probability; dotted red: upper bound with a 95% probability.

P/T Load2nd Order

Non-Parametric Probabilistic Simulation; Jund, Guillaume, Gagliardini

95% UprNominal 50% Mean95% Lwr

TestMeasurement

Author:Focus of Correlation Effort

All Test Peaks in Band: Results imply a Countermeasure is needed.

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 101

FIG. 7: Booming noise inside a car vs rpm. Stochastic modelling. Comparison of the median value of a baseline configuration (green) with a modification set (blue bold)

P/T Load2nd Order

Non-Parametric Probabilistic Simulation; Jund, Guillaume, Gagliardini

FIG. 6: Booming noise inside a car vs rpm. Deterministic models. Comparison of a baseline configuration (green) with a modification set (blue bold).

DETERMISTIC MODEL STOCHASTIC MODEL - Mean Level

. Amplitude Range = 30 dB

. Need Tradeoff Judgment

. Amplitude Range = 15 dB

. Decision is Clearer that both Designs are Equal Performers

Blue: New DesignGreen: Base

A-B Design Decision using Deterministic Model - vs - Mean Stochastic Model

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 102

Conclusions:

Kompella and Bernhard Test Observations are still relevant after 20 Years.

Scatter-like NVH Variation exists even in Best-in-Class vehicles.

Observations about Scatter:

Observations from Soize, Durand, Gagliardini, et. al. PapersThe Non-Parametric stochastic computational model with dispersion

parameters derived from a test database accounts for NVH Scatter due to combined Modeling and Manufacturing Uncertainties.

The Upper, Lower, and Mean Confidence Probabilities lead to moreprecise assessment of the effects of NVH scatter.

A database of dispersion parameters enables a virtual product development process assuring robust NVH performance.

The model configuration lends itself to an automated computational methodology driving a robust virtual product development process.

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 103

Structure Borne NVH Workshop• Introduction• Low Frequency Basics• Mid Frequency Basics• Live Noise Attenuation Demo• New Technology

Uncertainty and NVH Scatter• Closing Remarks: Q & A

Alan-Greg-Jimi

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2013 SAE NVC Structure Borne Noise Workshop2013 Automotive Analytics LLC A.E.DuncanSlide 104

SAE 2013 NVH ConferenceStructure Borne NVH Workshop

Thank You for Your Time!

Q & AQ & A

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Primary References (Workshop Basis: 4 Papers)

1. A. E. Duncan, et. al., “Understanding NVH Basics”, IBEC, 1996

2. A. E. Duncan, et. al., “MSC/NVH_Manager Helps Chrysler Make Quieter Vibration-free Vehicles”, Chrysler PR Article, March 1998.

3. B. Dong, et. al., “Process to Achieve NVH Goals: Subsystem Targets via ‘Digital Prototype’ Simulations”, SAE 1999-01-1692, NVH Conference Proceedings, May 1999.

4. S. D. Gogate, et. al., “’Digital Prototype’ Simulations to Achieve Vehicle Level NVH Targets in the Presence of Uncertainties’”,

SAE 2001-01-1529, NVH Conference Proceedings, May 2001

Structure Borne NVH References

WS + Refs. at www.AutoAnalytics.com at download link

Structure Borne NVH Workshop - on InternetAt SAE www.sae.org/events/nvc/specialevents.htm

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Supplemental Reference Recommendations5. T.D. Gillespie, Fundamentals of Vehicle Dynamics, SAE 1992

(Also see SAE Video Lectures Series, same topic and author)6. D. E. Cole, Elementary Vehicle Dynamics, Dept. of Mechanical

Engineering, University of Michigan, Ann Arbor, Michigan, Sept. 1972

7. J. Y. Wong, Theory of Ground Vehicles, John Wiley & Sons, New York, 1978

8. N. Takata, et.al. (1986), “An Analysis of Ride Harshness” Int. Journal of Vehicle Design, Special Issue on Vehicle Safety, pp. 291-303.

9. T. Ushijima, et.al. “Objective Harshness Evaluation” SAE Paper No. 951374, (1995).

10. G. Goetchius; �The Seven Immutable Laws of CAE/Test Correlation� Sound and Vibration Mag. Editorial June 2007, online at SandV.com

Structure Borne NVH References

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New Technology References (2013 NVH Workshop)

11. Sol, A.; Van Herpe, F.; “Numerical Prediction of a Whole Car Vibro-Acoustic Behavior at Low Frequencies”; SAE # 2001-01-1521

12. Durand, J.; Gagliardini, L.; Soize, C.; “Nonparametric Modeling of the Variability of Vehicle Vibroacoustic Behavior”; SAE # 2005-01-2385; SAE 2005 Noise and Vibration Conference Proceedings.

13. Durand, J.; Gagliardini, L.; Soize, C.; “Structural-acoustic modeling of automotive vehicles in presence of uncertainties and experimental identification and validation”; Journal of the Acoustical Society of America 24, p 1513-1525

14. Jund, A.; Gagliardini, L.; et.al.; “AN INDUSTRIAL IMPLEMENTATION OF NON-PARAMETRIC STOCHASTIC MODELLING OF VEHICLE VIBROACOUSTIC RESPONSE” CONVEBONOV Workshop, University of Sussex, Brighton, UK, March 27-28 2012

15. Gardhagen, B. and Plunt, J., “Variation of Vehicle NVH Properties due to Component Eigenfrequency Shifting - Basic Limits of Predictability” SAE 951302 May 1995 NVH Conference

Structure Borne NVH References