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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
VECOM-CLEPADr. L. Cremers09.05.2011Page 2
- 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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VECOM-CLEPADr. L. Cremers09.05.2011Page 3
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
VECOM-CLEPADr. L. Cremers09.05.2011Page 4
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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VECOM-CLEPADr. L. Cremers09.05.2011Page 5
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
VECOM-CLEPADr. L. Cremers09.05.2011Page 6
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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VECOM-CLEPADr. L. Cremers09.05.2011Page 7
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)
VECOM-CLEPADr. L. Cremers09.05.2011Page 8
Structural dynamics and vibrations. Beams and shells FE concept models.Example with ABCS-modelling.
original beam cross section geometry!
5
VECOM-CLEPADr. L. Cremers09.05.2011Page 9
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
VECOM-CLEPADr. L. Cremers09.05.2011Page 10
Design model: creation of large number of desvars, geometrical responses and constraints with OptiCenter
Structural dynamics and vibrations. FE concept modelling and optimization.
Applicationregion
Desvars forouterdimensions and
ll thi kwall thicknesses
Geometricalresponses and constraints
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VECOM-CLEPADr. L. Cremers09.05.2011Page 11
Design model: Creation of functional responses, constraintsand objective function with OptiCenter
Structural dynamics and vibrations. FE concept modelling and optimization.
Responses and constraints fordynamicstiffnesses
Responses and constraints forstatictiffstiffnesses
Weightingfactors
VECOM-CLEPADr. L. Cremers09.05.2011Page 12
Post Processing: Visualization of optimization resultsChanges in construction space
Structural dynamics and vibrations. FE concept modelling and optimization.
Changes in wall thickness
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VECOM-CLEPADr. L. Cremers09.05.2011Page 13
‚Material switch‘
Steel
Structural dynamics and vibrations. FE concept modelling and optimization.Application case: BMW 3-Series with Al car body
Al
VECOM-CLEPADr. L. Cremers09.05.2011Page 14
Structural dynamics and vibrations. FE concept modelling and optimization.Application case: BMW 3-Series with Al car body
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
8
VECOM-CLEPADr. L. Cremers09.05.2011Page 15
Aluminum car body optimization
Target: Equal global static and dynamic car body stiffness in comparisson with
Structural dynamics and vibrations. FE concept modelling and optimization.Application case: BMW 3-Series with Al car body
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%
VECOM-CLEPADr. L. Cremers09.05.2011Page 16
Structural dynamics and vibrations. FE concept modelling and optimization.Application case: BMW 3-Series with Al car body
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VECOM-CLEPADr. L. Cremers09.05.2011Page 17
Structural dynamics and vibrations. FE concept modelling and optimization.Application case: BMW 3-Series with Al car body
VECOM-CLEPADr. L. Cremers09.05.2011Page 18
Rocker panel Roof carier
Structural dynamics and vibrations. FE concept modelling and optimization.Application case: BMW 3-Series with Al car body
10
VECOM-CLEPADr. L. Cremers09.05.2011Page 19
Masse [kg] Statik [%] Dynamik [Hz]Masse [kg] Statik [%] Dynamik [Hz]
Structural dynamics and vibrations. FE concept modelling and optimization.Application case: BMW 3-Series with Al car body
‐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?
VECOM-CLEPADr. L. Cremers09.05.2011Page 20
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
11
VECOM-CLEPADr. L. Cremers09.05.2011Page 21
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
VECOM-CLEPADr. L. Cremers09.05.2011Page 22
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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VECOM-CLEPADr. L. Cremers09.05.2011Page 23
Localresonance problem
Full vehicle vibro-acoustic comfort.Local dynamic stiffness FE modeling.
x-direction: Red
Point mobilityengine mount
problem
z-direction: Blue
Target: Black
VECOM-CLEPADr. L. Cremers09.05.2011Page 24
+7+18
100200
100200
-2
100200
+8+7+4+90+12Frontal Strut Tower
200400
50100
200400
50100
200400
50100
z-Richtungy-Richtungx-Richtung
Full vehicle vibro-acoustic comfort.Local dynamic stiffness FE modeling.
+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.
13
VECOM-CLEPADr. L. Cremers09.05.2011Page 25
Example of Panel Vibration at 60 Hz
Full vehicle vibro-acoustic comfort.Panel vibration FE modeling – Radiated power.
VECOM-CLEPADr. L. Cremers09.05.2011Page 26
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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VECOM-CLEPADr. L. Cremers09.05.2011Page 27
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?
?
VECOM-CLEPADr. L. Cremers09.05.2011Page 28
Structural intensity analysis.Time Domain Measurements.
High Resolution Measurement:Example: Tube Frame
Excitation
1
2 3 4
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VECOM-CLEPADr. L. Cremers09.05.2011Page 29
Structural Intensity Calculation.Time Domain Calculation.
Simulation Vibration Energy Flow.
VECOM-CLEPADr. L. Cremers09.05.2011Page 30
Structural Intensity Calculation. Example Frequency Domain: Vehicle Underbody.
Initial configuration, real STI, detailed view.
16
VECOM-CLEPADr. L. Cremers09.05.2011Page 31
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
VECOM-CLEPADr. L. Cremers09.05.2011Page 32
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
17
VECOM-CLEPADr. L. Cremers09.05.2011Page 33
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
VECOM-CLEPADr. L. Cremers09.05.2011Page 34
Aero-acoustic modelling.Isosurface of constant velocity (BMW 3series).
18
VECOM-CLEPADr. L. Cremers09.05.2011Page 35
Aero-acoustic modelling.Streamlines of the airflow around the car body.
VECOM-CLEPADr. L. Cremers09.05.2011Page 36
Aero-acoustic modelling.Streamlines of the airflow around the car body.
19
VECOM-CLEPADr. L. Cremers09.05.2011Page 37
Aero-acoustic modelling.Sound pressure level on the car body surface.
VECOM-CLEPADr. L. Cremers09.05.2011Page 38
Aero-acoustic modelling.Sound pressure level on the car body surface.
20
VECOM-CLEPADr. L. Cremers09.05.2011Page 39
Thank you for your attention.
VECOM-CLEPADr. L. Cremers09.05.2011Page 40
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
21
VECOM-CLEPADr. L. Cremers09.05.2011Page 41
Optimization historyGlobal dynamic stiffness
target frequency
target frequency and feasibility region indicator
final frequency and mode number
initial frequency
frequency history
weighting factor
VECOM-CLEPADr. L. Cremers09.05.2011Page 42
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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VECOM-CLEPADr. L. Cremers09.05.2011Page 43
Optimization historyWeight
weight history
reference weight
VECOM-CLEPADr. L. Cremers09.05.2011Page 44
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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VECOM-CLEPADr. L. Cremers09.05.2011Page 45
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
VECOM-CLEPADr. L. Cremers09.05.2011Page 46
Optimization historySteering wheel impedance
normalized steering wheel FRF amplitude by excitation between
10 and 40 Hz
maximum normalized amplitude of steering wheel FRF