optimized design of vehicle underbody system

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OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM EATC 2013 - Turin Emanuele Santini Products and Systems Simulation Specialist Product Acoustic and Thermal Performance Autoneum Management AG, CH-8406 Winterthur [email protected] . www.autoneum.com

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Page 1: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

OPTIMIZED DESIGN OF VEHICLE

UNDERBODY SYSTEM

EATC 2013 - Turin

Emanuele Santini

Products and Systems Simulation Specialist

Product Acoustic and Thermal Performance

Autoneum Management AG, CH-8406 Winterthur

[email protected] . www.autoneum.com

Page 2: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

AGENDA

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1. Introduction – Autoneum

2. Problem definition

3. Analysis – Design Guidelines CAE based

4. Test case 1 – Design Optimization (Guidelines VS

Optistruct)

5. Test case 2 – Design Optimization = f(packaging space)

6. Test case 3 – Stress reduction possibilities

7. Conclusion

Page 3: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

3

Leading partner for the major light vehicle and heavy truck manufacturers around the

world. Unique combination of core competences:

Leading acoustics and thermal management

Product excellence

Global presence with a broad customer portfolio

Innovative and cost effective solutions for noise reduction and thermal management

to increase vehicle confort value

Focus on underbody as exterior acoustic and structural parts; fiber consolidated

parts (glass fiber free).

Introduction – Who is Autoneum?

EATC - E. Santini - 23/04/2013

Page 4: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

Problem Definition

4

Optimise the design of underbody panels, in order to fulfil OEMs structural requirements with the minimal

material / part layout, in a very short timeline.

Define general design guidelines

taking into account:

- Aerodynamic load

- Standstill deflection

- Water absorption

- Free-Free flexural behaviour

- Number of fixation points

- Stone chips

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A

A

Page 5: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

CAE Pre-Development/Development

Underbody Design Process

5

Underbody System

Final CAD design model

Optimize beadings design

Maximize part stiffness

Reduce part weight

Optimize material layout,

tailored thickness distribution

Aerodynamics pressure

distribution

Thermal characterization

and temperature distribution

CFD lift and drag

Mechanical Simulation

Aero-Thermal Simulation

EATC - E. Santini - 23/04/2013

Page 6: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

Preliminary Analysis

6

Deflection reduced of 37%

Deformation shape totally changed

Fixation points influence Not all design modifications bring real benefits to the

stiffness of the panel, depending on the configuration

of the fixation points, and on the load case

considered.

Design modifications:

Exploiting the stiffness coming from the

fixation points

Connecting the weakest areas of the part,

changing the shape deformation

Deformation reduction of 12.5% with 1 bead

Max deformation increased of 20% with 1 bead

and 25% with 3

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Load case Influence

Page 7: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

7

Analysis

- Optistruct Topography Optimization -

Optimized distribution of shape reinforcements in a design region,

taking into account:

- Geometry and fixation points of the panel

- Loading case (aerodynamic load, snow load, modes…)

Optimization Targets:

- Increase the stiffness under a specific load case

- Maximize the resonant frequencies

- Decrease the strains/stresses at the fixation points

Design Variables:

- Beads height

- Beads width

- Draw angle

- Minimum distance

particular pattern constraints can be imposed

Constraints:

- Packaging space available

- Minimize the weight

- Beads dimensions (width)

- A minimum target for another load case

EATC - E. Santini - 23/04/2013

Page 8: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

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• Identification of the most important parameters

• Optimization applied on panels with variable parameters

• Best beading design for different possible configuration

Right design modifications can be applied W/O the mean of the optimization

Boundary Conditions (features) Variables Nb

Distance between fixation points 10

Offset between the plan of the fixation

points and the part’s plan 4

Design Variables (beading design) Variables Nb

Number of Beads 7

Distance between beads 20

Width 8

Height 10

Thickness of the part 4

Beads’ thickness 4

Optistruct Usage - DOE

Design Modification Variables Outcoming

of the DOE

parameters

Findings of the

DOE

Page 9: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

DOE findings – examples

Bead Width Beads Height

Beads Distance Beads Number

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Lower is

better Lower is

better

Lower is

better

Page 10: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

Test Case 1 - Initial Design

Functional Requirements:

-Maximum reversible deviations from the nominal geometry due to loads during

vehicle operation 10mm (at 250 km/h)

- Maximum deflection of 5mm between the mounting points and a maximum of

3mm of gap formation in the edges areas when the vehicle is at a standstill

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V=250 km/h

Deformation

Load Case:

Weight of the part + water absorbed during 24h

Simulated for different area weight:

(1400, 1200, 1000 gsm)

Load Case:

Aerodynamics Pressure at Vmax=250 km/h

AFR=500 Ns/m3 (simulated for different area weight)

Pmax= 1050 Pa

P140 km/h= 200 Pa

Standstill

Deflection

Page 11: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

Test Case 1 – Best practices

- 3 Proposals -

Exploiting the

fixation points

Reinforcing the

weakest areas of the

part

Outcoming of the DOE

parameters

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Page 12: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

12

DEFLECTION REDUCTION OF 46%

INITIAL DESIGN NEW DESIGN

DEFLECTION REDUCTION OF 56%

INITIAL DESIGN

DEFLECTION REDUCTION OF 41%

INITIAL DESIGN NEW DESIGN

NEW DESIGN

EATC - E. Santini - 23/04/2013

Outcoming of the DOE

parameters

Reinforcing the

weakest areas of the

part

Exploiting the

fixation points

Test Case 1 – Best practices

- 3 Proposals - Standstill

Page 13: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

13

Test Case 1 – Design Optimisation

- Optistruct Designs - Standstill

Free Opt° Pattern Opt°

Compliance

optimization

center= 0.85mm reduction of 57%

edge=0.88mm reduction of 42%

Free Opt° Pattern Opt°

Modal

frequencies

optimization

center= 1.71mm reduction of 14%

edge=0.71mm reduction of 48%

EATC - E. Santini - 23/04/2013

Page 14: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

Test Case 1

Weight Reduction - Speed max

14

Optimization made from

the aerodynamics

pressure distribution

Design proposal from

developed guidelines

Optistruct

target

Deformation map

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Lower is

better

Optimization made from an

uniform pressure distribution

Page 15: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

Test Case 2 – Optistruct Application

Design Optimization = f(packaging space)

15

Blue area: 1.7mm

Yellow area: 5.2 mm

Beads: 4.4 mm

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Matlab routine: calculating the distance at

each node from all the components to the

bottom surface of the underbody

Averaged distance at each element

PSHELL with the computed thickness

associated to the corresponding element

Each color correspond to a different

PSHELL ID

Optistruct topography optimization with

elements constrained wrt the calculated

packaging space.

Page 16: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

Test Case 2 – Optistruct Application

CAE dedicated optimization

Static deformation reduction between 25%-35% w.r.t. original design for the optimized solutions

Dynamic behavior can be considerably changed/improved : eg: more than double natural freq. -

specific vibration modes can be shifted (modal tuning)

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Optimization made according to the packaging space (calculated with an internal Matlab routine)

Each shell of the FEM constrained to a maximum bead‘s height according to the packaging space

measured on the car model

Page 17: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

Test Case 2

Design Examples

Underbody Design Examples

Today Design Design2 Design 1

Beading profile according to the packaging space

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Blue areas: material consolidated (e.g. 2mm at 1000gsm)

Yellow areas: material unconsolidated (e.g. 4mm at 1000gsm)

Brown areas: material unconsolidated, beading profile (e.g. 4mm at 1000gsm)

Beading profile with different height

across the part

Page 18: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

Vehicle operation

at 250 km/h

Standstill

condition

Deformation comparison= f (Designs)

Vehicle operation (250 km/h), and at a standstill

0%

20%

40%

60%

80%

100%

120%

Aerodynamique Pressure

(250 km/h)

Standstill at the center of the

part

Standstill at the edges

defo

rmati

on

(%

)

for

each

fu

ncti

on

al

req

uir

em

en

t

Original Design

Design 1

Design 2

Design 2 performs better than the design 1

particularly during vehicle operation

(transversal beading design)

Modal frequencies improved of 40% for

design 1 and 50% for design 2

Test Case 2

Design Proposals - Deformation

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Page 19: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

19

Design modifications can reduce the

strain rate, and consequently any

possible failure issue.

Modifying locally the geometry

around the fixation area, the strain

rate decreases from 6% to 3-4%

depending on the modification.

Initial configuration Circular bead Transversal bead

7 mm

10 mm

Fixation

point

Test Case 3 - Design modification

Maximum strain reduction – Fatigue Analysis

EATC - E. Santini - 23/04/2013

Page 20: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

Conclusions

- Design optimization allows even at low material density to achieve the functional requirements of

the customers in terms of stiffness (Also multiparameter optimization)

- Specific material mechanical properties can be further exploited by dedicated CAE shape

optimization

- Design optimization used to find the best generalized design features

definition of underbody design guidelines, which can be used to:

a) identify lightest solutions fulfilling functional requirements,

b) reduce number of fixation points.

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Page 21: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

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Q&A

THANK YOU FOR YOUR ATTENTION

Emanuele Santini

Products and Systems Simulation Specialist

Product Acoustic and Thermal Performance

Autoneum Management AG, CH-8406 Winterthur

[email protected] . www.autoneum.com

Page 22: OPTIMIZED DESIGN OF VEHICLE UNDERBODY SYSTEM

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Underbody systems are defined as parts, which are added below the body of a car, with aerodynamic functions and with the aim of

improving its protection and acoustic performances. Underbody parts are subject to a variety of loads during vehicle operation, which

degrade their original performances. Thus, an accurate design of the underbody shape is needed, in order to preserve its correct

functioning and optimize its performances. In particular, it would be desirable to reduce the deflection of the underbody part under

operating loads, while preserving the same bill of material (cost) or even reducing it.

In this work, we study the best possible part profiles by making use of CAE optimization. Our study aims at defining design guidelines,

which can be used by the product engineers in order to design parts with an optimal solution since the beginning of the development.

Simulations have been carried out by using Altair optimization software “Optistruct”, with the objective of increasing the stiffness of the

panels, while reducing the compliance under aerodynamic load and increasing the resonance frequencies. For this purpose, a

topography optimization has been performed for some shape patterns. More precisely, the different areas of the panels are

constrained to a different level of maximum dislocation, depending on the packaging space available. In this way, some “special”

shapes have been found, which are applicable in a large variety of configuration panels.

Finally, the optimization results allow us to propose different modification solutions (some of them have been prototyped), with the

objective to increase the flexural stiffness of our panels. A 20% weight reduction of the parts is achievable by these modifications, thus

fulfilling the functional requirements with a minimal material part layout.

Emanuele Santini

Products and Systems Simulation Specialist

Product Acoustic and Thermal Performance

Autoneum Management AG, CH-8406 Winterthur

[email protected] . www.autoneum.com

OPTIMIZED DESIGN OF VEHICLE

UNDERBODY SYSTEM

EATC - E. Santini - 23/04/2013