NVH CAE Concept Modelling and Optimization at BMW

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VECOM-CLEPADr. L. Cremers06.06.2011Page 1

VECOM Suppliers Workshop:Vehicle Concept Modeling in the Automotive Sector.

NVH CAE concept modeling and optimization at BMW.

06.06.2011 VLEVA, Brussels

Dr. L. Cremers


- Introduction to the BMW Group and the structural dynamics and vibrations team.

NVH CAE concept modeling and optimization.Overview.

- Global static car body stiffness modeling and optimization with Beams and Shells concept models.

- Full vehicle vibro-acoustic comfort modeling.

- Structural intensity modeling.

- Full vehicle vibration comfort simulation using multi-- Full vehicle vibration comfort simulation using multi-body simulation models

- Aero-acoustic modeling.

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NVH CAE concept modeling at BMW.Introduction to the BMW Group.

BMW Group brands

Mi i BMW R ll R

BMWMotor-cycles

Husqvarna

FIZ R&D centre in MunichProduction & assemblyHeadquartersMunich

Mini BMW Rolls-Royce


Vehicle architecture and integrationAcoustics and vibrationsStructural dynamics and vibrations

Introduction to the team.Structural dynamics and vibrations.

Structural dynamics and vibrations

Targeting, analyzing and monitoring static and dynamic car body stiffness and vibration levels for optimal full vehicle NVH performance throughout the complete development phase.

Early-phase FE car body concept modeling and optimization.

Static car body testing, modal analysis and vibration comfort measurements of complete vehicles, car bodies and components.

• local and global car body static stiffness.• natural frequencies and mode shapes.• Local dynamic stiffness at car body connection points• sensitivity analysis based on modal data.• FE optimization of the car body structure.• analysis of panel vibrations (ERP).• …

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Project phase/tools:

Concept phase Series production

Structural dynamics and vibrations.Activities throughout the development phase.

Development phase

Plant quality monitoring

MB/FEMSimulation

Concept phase Series production

Prototypes

Hybrid modelling(Assembly and substructuring)

Development phase

Testing(Modal analysis, holography,

4-poster ...)

Prototypes and

concept cars


original beam cross section

equivalent standard

Structural dynamics and vibrations.FE concept modelling and optimization.

Beams and shells FE concept models

optimized equivalent cross section

cross section

B

H

t 1

t 2

B

H

t 1

t 2

Goal of the optimisation is to reach a minimal car body weight

First functional assessments of car body concepts

Goal of the optimisation is to reach a minimal car body weight...• considering functional design targets for the complete car

... by varying the constructed space...• using the beam cross section dimensions height, width and plate thickness as design variables

... while respecting design constraintse.g. package constraints

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Structural dynamics and vibrations.FE concept modelling and optimization.

In the past: Cross Section substituted with equivalent Beam Library propertydim1

dim2

dim4 dim3 Desvars: dim1…dim4

wState of the art: Exact geometrical description with Nastran PBxSECT

h

t(1)

t(2)

t(3)

Desvars: w, h, t(1)…t(3)


Structural dynamics and vibrations. Beams and shells FE concept models.Example with ABCS-modelling.

original beam cross section geometry!

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Structural dynamics and vibrations. FE concept modelling and optimization.

Beams & shells FE concept model

Optimization

statics dynamicscrash

roll-oversteeringwheel

Nastran .f06-file

Optimization, Nastran sol200 (10 load cases, well over

1500 design variables)

Nastran f06 results

file

freq.separation

statics dynamics freq. sep. crash roll-over steering weightwheel

Optimization history

Optimization results

statics dynamics freq. sep. crash roll-over steering weightwheel


Design model: creation of large number of desvars, geometrical responses and constraints with OptiCenter


Applicationregion

Desvars forouterdimensions and

ll thi kwall thicknesses

Geometricalresponses and constraints

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Design model: Creation of functional responses, constraintsand objective function with OptiCenter


Responses and constraints fordynamicstiffnesses

Responses and constraints forstatictiffstiffnesses

Weightingfactors


Post Processing: Visualization of optimization resultsChanges in construction space


Changes in wall thickness

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‚Material switch‘

Steel

Structural dynamics and vibrations. FE concept modelling and optimization.Application case: BMW 3-Series with Al car body

Al



Change in weight and functional performance after one-to-one material switch

‐64,4

‐11,9

Masse [kg] Statik [%] Dynamik [Hz]

E90 Alu

‐235,1

E90 Alu optimiert

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Aluminum car body optimization

Target: Equal global static and dynamic car body stiffness in comparisson with


Equal global static and dynamic car body stiffness in comparisson with steel body.

Design space: full car body beam structure (red)

Geometric constraints:construction space max. +50%



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Rocker panel Roof carier


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Masse [kg] Statik [%] Dynamik [Hz]Masse [kg] Statik [%] Dynamik [Hz]


‐64,4

‐11,9

E90 Alu

E90 Alu optimiert

‐64,4

‐11,9‐1,2

7,2

E90 Alu

E90 Alu optimiert

‐235,1‐235,1

‐168,6

At the cost of constructionspace!

in what areas is it usefull tointroduce light weightmaterials?


Wind excitation Wind excitation

Target of NVH engineering:optimal vibro-acoustic comfort for driverand passengers.

Full vehicle vibro-acoustic comfort.Sound sources.

Engine

Drive shaft and

Exhaust

Gearbox

Engine

Drive shaft and

Exhaust

Gearboxdifferential

Road excitation

differential

Road excitation

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Full vehicle vibro-acoustic comfort.Vibro-acoustic car body transmission paths.

Important aspects:• local dynamic stiffness at excitation

points.

Car body excitation

Panel radiation

SPL at driver‘s ear

p• panel radiation• acoustic field• vibro-acoustic coupling


Full vehicle vibro-acoustic comfort.Local dynamic stiffness FE modeling.

Local vibration due to harmonic load at engine mounts (225 Hz)

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Localresonance problem


x-direction: Red

Point mobilityengine mount

problem

z-direction: Blue

Target: Black


+7+18

100200

100200

-2

100200

+8+7+4+90+12Frontal Strut Tower

200400

50100

200400

50100

200400

50100

z-Richtungy-Richtungx-Richtung


+6

+17

+12

+11

+2

+2

+6

-3

-4

-3

-2

+7

+11

+12

+3

-1

+8-6

+5+120

+12+11+12+5-100Gear-box Bridge

+3+7+8+8+7+8Rear Axle Mount, Front Screw

+8+22+12+10-8+2Drve Shaft Mount

+12+8+6+4-4-3Engine Mounts

+2+6-5+10-4-2Front Axle Mount, Rear Screw

+2+8+8+8-6-4Front Axle Mount, Middle Screw

-4+15+12+120-1Front Axle Mount, Front Screw

Strong target-violation

Target violation

Target violation in dB

+6+6+10+4+1+2-9-4-22Tunnel bridge screw

+5

+2

+7

+4

-2

+8

+2

+8

+4

0+9+100+7Rear Strut Tower

0+6+17+7-7-2Rear Shock Absorber

+10+10+3+4+1+9Rear Axle Mount, Rear ScrewTarget violation, check significance

OK.

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Example of Panel Vibration at 60 Hz

Full vehicle vibro-acoustic comfort.Panel vibration FE modeling – Radiated power.


Example for “weak point” in floor panel (excitation at gear-box bridge)

Sum

Full vehicle vibro-acoustic comfort.Panel vibration FE modeling – Radiated power.

Floor Panel

Mag

nitu

de

Frequency

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Full vehicle vibro-acoustic comfort.Vibrational energy flow through the car body.

How does the energy flow through the car body from excitation point towards the

Car body excitation

Panel radiation

SPL at driver‘s ear

excitation point towards the radiating panels?

?


Structural intensity analysis.Time Domain Measurements.

High Resolution Measurement:Example: Tube Frame

Excitation

1

2 3 4

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Structural Intensity Calculation.Time Domain Calculation.

Simulation Vibration Energy Flow.


Structural Intensity Calculation. Example Frequency Domain: Vehicle Underbody.

Initial configuration, real STI, detailed view.

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car body (rigid)car body (flexible)

Full vehicle vibration comfort simulation.Multi body simulation toolbox.

h t t (fl ibl )

drive train

engine / gearbox

exhaust system (flexible)

Hinterachse

Vorderachse Tires


Full vehicle vibration comfort simulation.4-poster test simulation.

rigid bodyflexible body

Torsion load case

Frequency (Hz)

Displ

aceme

nt (m

m)

rigid bodyflexible body

Bending load case

Vibration response at customer relevant car body positions

Frequency (Hz)

Accel

eratio

n (m/

s2 )

y

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Full vehicle vibration comfort simulation.Engine idle comfort simulation.

[Hz]16

14 Engine roll13-15 Hz

0 200 400 600 800 [1/min]

12

10

8

6

4

2

0

Vehicle rollon tire springs

Vehicle lateralEngine lateral / roll

Engine roll

engine idle rpm550 700

5-7 Hz

9-11 Hz

13 15 Hz

0,5. MO

1. MO

1,5. MO


Aero-acoustic modelling.Isosurface of constant velocity (BMW 3series).

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Aero-acoustic modelling.Streamlines of the airflow around the car body.


Aero-acoustic modelling.Streamlines of the airflow around the car body.

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Aero-acoustic modelling.Sound pressure level on the car body surface.


Aero-acoustic modelling.Sound pressure level on the car body surface.

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Thank you for your attention.


MTargets for statics

D l

Optimization resultGlobal static and dynamic stiffness

not specified

Modell A DeltaTarget

Modell B DeltaTarget

DeltaA-B

Tunnel

Rocker panel

Tail center

Tail longitudinal carrier

Wheel house torsion

Engine mount torsion

Front vehicle cross bending

1. bending

1. torsion

front vehicle torsion

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Optimization historyGlobal dynamic stiffness

target frequency

target frequency and feasibility region indicator

final frequency and mode number

initial frequency

frequency history

weighting factor


target stiffness

Optimization historyGlobal static stiffness

target stiffness and feasibility region indicator

initial stiffness

final stiffness and FE node number

stiffness history

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Optimization historyWeight

weight history

reference weight


Optimization historyPseudo-Crash

stress level reached in maximum loaded element and element number

max. allowable stress level (steel: 400 N/mm²) and feasibility region indicator

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Optimization historyMode separation

final frequency separation in Hz with mode-numbers of modes involved

minimal frequency separation in Hz between two selected modes

and feasibility region indicator


Optimization historySteering wheel impedance

normalized steering wheel FRF amplitude by excitation between

10 and 40 Hz

maximum normalized amplitude of steering wheel FRF

Documents

NVH CAE Concept Modelling and Optimization at BMW