Download - 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
AGENDA
2 EATC - E. Santini - 23/04/2013
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
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
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
EATC - E. Santini - 23/04/2013
A
A
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
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
EATC - E. Santini - 23/04/2013
Load case Influence
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
8 EATC - E. Santini - 23/04/2013
• 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
DOE findings – examples
Bead Width Beads Height
Beads Distance Beads Number
9 EATC - E. Santini - 23/04/2013
Lower is
better Lower is
better
Lower is
better
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
10 EATC - E. Santini - 23/04/2013
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
Test Case 1 – Best practices
- 3 Proposals -
Exploiting the
fixation points
Reinforcing the
weakest areas of the
part
Outcoming of the DOE
parameters
11 EATC - E. Santini - 23/04/2013
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
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
Test Case 1
Weight Reduction - Speed max
14
Optimization made from
the aerodynamics
pressure distribution
Design proposal from
developed guidelines
Optistruct
target
Deformation map
EATC - E. Santini - 23/04/2013
Lower is
better
Optimization made from an
uniform pressure distribution
Test Case 2 – Optistruct Application
Design Optimization = f(packaging space)
15
Blue area: 1.7mm
Yellow area: 5.2 mm
Beads: 4.4 mm
EATC - E. Santini - 23/04/2013
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.
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)
16 EATC - E. Santini - 23/04/2013
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
Test Case 2
Design Examples
Underbody Design Examples
Today Design Design2 Design 1
Beading profile according to the packaging space
17 EATC - E. Santini - 23/04/2013
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
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
18 EATC - E. Santini - 23/04/2013
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
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.
20 EATC - E. Santini - 23/04/2013
21 EATC - E. Santini - 23/04/2013
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
22
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