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.

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

~ 1500 Parameter

Integral 4

~ 560 Parameter

Doppelquerlenker

~ 320 Parameter

Allrad

~ 230 Parameter

M 57D30 / 6HP26

~ 160 Parameter

~ 1500 Parameter

Structure borne

Vibration comfort.

Structural dynamic

analysis

Test & Integration Concept development

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

Steering

vibrations

Static stiffness Dynamic

stiffness

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

MSC.Nastran

PBxSECT design var

changes in wall thickness

Post-processing: visualization of optimization results.

change in construction space.

Optimization history (global static stiffness).

APPLICATION CASE 1: ‚MATERIAL SWITCH‘.

Change in weight and functional performance after

one-to-one material switch.

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%

Seite 13

Rocker panel

Roof carrier

-235,1

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

E90 Alu

E90 Alu optimiert

-235,1

-168,6

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

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.

Optimus workflow including mode tracking based on mode correlation.

change in

weight (kg)

change in static

torsion stiffness (%) change in global

torsion mode (Hz)

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

Engine idle vibration comfort.

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

Optimus work flow

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.

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.

RSM: Quadratic Least Squares

Least Squares Quadratic is

accurate enough.

Error prediction is below 6% for

worst case scenario.

Engine

Z (RMS)

Stiffness Z

Stiffness

eel acc Z

Multi objective optimization results

Conflicting

objectives

Engine

Steering

Z (RMS)

Steering

Z (RMS) Acc

Engine

Z (RMS)

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

Engine

Z (RMS)

Multi objective optimization results

Mount stiffness X

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!

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.

THANK YOU VERY MUCH FOR YOUR ATTENTION!

Dr. L. Cremers

Luc.Cremers@bmw.de

BMW AG

80788 München

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