full vehicle early-phase concept optimization for premium ... · condensed flexible car body models...

MSC Software Confidential MSC Software Confidential

Full vehicle early-phase concept optimization for

premium NVH comfort at BMW 2012 Regional User Conference

Presented By: Dr. L. Cremers - BMW AG, Naji El Masri – Noesis Solutions

Tommaso Tamarozzi, Laurens Coox - KU Leuven,

Maximilien Landrain, Bram Vanderheggen - Noesis Solutions.

May 7-8, 2013

MSC Software Confidential MSC Software 2013 Users Conference Americas., May 7-8, 2013.

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FULL VEHICLE NVH COMFORT OPTIMIZATION.

OUTLINE.

The BMW Structural Dynamic Analysis Group.

Beams and shells modeling for early-phase car body concept optimization.

Overview of current process and Optimus integration.

• Application case 1: Car body ‘material switch’.

• Application case 2: Car body stiffness vs. wheel base.

Full vehicle NVH concept optimization.

• Application case 3: Design exploration and optimization using an NVH

full vehicle model.

Conclusions.


.

Seite 3

FULL VEHICLE NVH DEVELOPMENT & OPTIMIZATION.

STRUCTURAL DYNAMIC ANALYSIS GROUP.

Integral 4

~ 560 Parameter

Doppelquerlenker

~ 320 Parameter

Allrad

~ 230 Parameter

M 57D30 / 6HP26

~ 160 Parameter

GFZG

~ 1500 Parameter

Integral 4

~ 560 Parameter

Doppelquerlenker

~ 320 Parameter

Allrad

~ 230 Parameter

M 57D30 / 6HP26

~ 160 Parameter

GFZG

~ 1500 Parameter

Structure borne

noise

Vibration comfort.

Structural dynamic

analysis

Test & Integration Concept development

SAS4_DV.wmv

wie_vor_von_hinten.avi


.

FULL VEHICLE NVH DEVELOPMENT & OPTIMIZATION. ROLE OF STRUCTURAL DYNAMICS.

Road induced vibrations in secondary Ride

& Comfort: noticeable vibrations of the car

body at the floor panel, seat, door etc. after

crossing minor road bumps


.

EARLY-PHASE CAR BODY OPTIMIZATION.

BEAMS & SHELLS CONCEPT MODELLING.

condensed flexible car body

models for full vehicle multi-

body vibration comfort

simulation.

Static and dynamic car body stiffness: - global static load cases. - local dyn. stiffness at connection points. - car body eigenfrequencies.

Structural dynamic car body development through numerical beam structure optimization.

NVH car body target setting. Early-phase functional development, evaluation and optimization of the car body regarding acoustic

and vibration comfort requirements. Beam & Shell FEM with simplified beam connection methods. Parametric beam barrier structure.


.

Seite 6



1500 design variables

MSC Nastran SOL200

optimization.

Functional targets

Minimum weight

25 load cases

Roll-over

Crash

Steering

wheel

vibrations

Static stiffness Dynamic

stiffness


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

OptiCenter.

Application region

Desvars for outer

dimensions and wall

thicknesses

Geometrical

responses and

constraints


.



Responses and

constraints for

dynamic stiffnesses

Responses and

constraints for static

stiffnesses

Weighting factors

Design model: creation of functional responses, constraints and objective

function with OptiCenter.


.


OPTIMIZATION PROCESS USING OPTIMUS

FE concept model

Nastran DESVARs

Interfacing design variables from

MSC.Nastran using Optimus Interfacing Outputs from

MSC.Nastran using Optimus

w

h

t(1)

t(2)

t(3)

MSC.Nastran

PBxSECT design var


.



changes in wall thickness

Post-processing: visualization of optimization results.

change in construction space.

Optimization history (global static stiffness).


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APPLICATION CASE 1: ‚MATERIAL SWITCH‘.

Steel

Al

Change in weight and functional performance after

one-to-one material switch.


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Seite 12



Change in construction space.

Change in wall thickness

Aluminum car body optimization

Target:

Equal global static and dynamic car body stiffness in

comparison with steel body.

Design space:

full car body beam structure (red)

Geometric constraints:

construction space max. +50%


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Seite 13



Rocker panel

Roof carrier

-235,1

-64,4

-11,9

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

E90 Alu

E90 Alu optimiert

-235,1

-64,4

-11,9

-168,6

-1,2

7,2

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

E90 Alu

E90 Alu optimiert

At the cost of construction

space!

in what areas is it useful to introduce light

weight materials?

Aluminum

Opt. Aluminum


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Question:

How does the global car body stiffness change with increasing wheel base?

Parameter study using MSC.Nastran & Optimus, monitoring both global

static and dynamic stiffness (eigenfrequencies)!

Seite 14


APPLICATION CASE 2: STIFFNESS VS WHEEL BASE.


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Optimus workflow including mode tracking based on mode correlation.


.



incre

asin

g w

he

el b

ase

change in

weight (kg)

change in static

torsion stiffness (%) change in global

torsion mode (Hz)

MAC

value

de

cre

asin

g g

lob

al

stiff

ne

ss

? ?


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FULL VEHICLE NVH OPTIMIZATION.

APPLICATION CASE 3: MOUNT STIFFNESS OPTIMIZATION.

BMW 3Series full-vehicle NVH multi-body simulation model. ‘simplified’ model without doors, lids, roof, front and rear windows!

NVH Design exploration and

optimization by varying engine and

gearbox mount stiffnesses.


.

Competing NVH-requirements for engine and gearbox mount stiffness.

Low stiffness for maximum structure-borne noise isolation.

low frequency vibrations of car body and power train for optimal vibration comfort.

e.g. engine idle vibrations, start/stop vibrations, engine judder…



Local dynamic

car body stiffness


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Engine idle vibration comfort.


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Full vehicle 4-poster simulation: sine sweep torsion excitation 0-60Hz.


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Optimus work flow


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Methodology for design exploration and optimization:

•DOE: 3 Level Full Factorial.

•RSM: Quadratic Least Squares.

•DOE: Verification Latin-Hypercube.

•Optimizations:

Evolutionary Multi-Objective on RSM and validation of optimal points.

Evolutionary Multi-Objective on analysis.

Target based Single Objective on RSM.

Objective:

Minimize car body and steering wheel vibrations (RMS), while constraining relative motion

between engine and car body.


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Correlations based on 3-level full factorial DOE

Inputs - Outputs Outputs - Outputs

Stiffness in X and Z are dominant.

All output have to be considered.


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RSM: Quadratic Least Squares

Least Squares Quadratic is

accurate enough.

Error prediction is below 6% for

worst case scenario.

Acc

Engine

Z (RMS)

Acc

Body

Z

(RMS)

Mount

Stiffness Z

Mount

Stiffness

X

Mount

Stiffness

X

Mount

Stiffness

Z

Ste

eri

ng

wh

eel acc Z

(RM

S)


.



Multi objective optimization results

Conflicting

objectives

Acc

Body

Z

(RMS)

Acc

Engine

Z

(RMS)

Acc

Steering

wheel

Z (RMS)

Acc

Steering

wheel

Z (RMS) Acc

Engine

Z (RMS)

Acc Body Z (RMS) Acc Body Z (RMS)

Acc S

teeri

ng

wh

eel

Z

(RM

S)

Acc

Engine

Z (RMS)

Acc

Body

Z (RMS)


.



Multi objective optimization results

Mount stiffness X

Mount stiffness X

Mo

un

t sti

ffn

ess Z

Acc

Body

X (RMS)

Acc

Body

Z

(RMS)

Acc

Body

X

(RMS)

Eigenfrequency shifts are evaluated based on full vehicle

vibration comfort ‚finger print‘!

Engineering task is to find the best compromise amongst all

functional requirements!


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FULL VEHICLE NVH COMFORT OPTIMIZATION.

SUMMARY.

multi-objective concept optimization has become a very important task

in automotive NVH development.

Advanced optimization processes are used on both component an

system level to explore the design space in search of optimal designs.

MSC.Nastran & Optimus software play herein an important role to

capture the simulation process and accelerate the optimization

schemes (SOL 200, Global Optimizer, Multi-Objective Optimizer with

Pareto fronts). The wide range of post-processing capabilities

facilitates the exploration of the design space of complex systems in a

multi-objective and even multi-disciplinary context.


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THANK YOU VERY MUCH FOR YOUR ATTENTION!

Dr. L. Cremers

[email protected]

BMW AG

80788 München

full vehicle early-phase concept optimization for premium ... · condensed flexible car body models...

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