O. Grimes*, A. Appella*, C. Bastien*, J. Christensen

EHTC 2013 - Turin

* Coventry University, Department of Engineering and Computing, Priory Street, Coventry, CV1 5FB

1. Previous Work & Research

2. Vehicle Design Volume Definition

3. BIW Load Path Identification

4. BIW Member Sizing

5. BIW Member Shape and Gauge

6. Automation of the Process

7. Conclusion

Audi A6

Mazda CX5

Typical Body in White (BIW) architectures have evolved over many years to

achieve legal and consumer safety test performance, but the underlying

architecture has remained very much the same.

Is this now the most efficient architecture

looking forward to electric vehicles (EV’s)??

Inertia Relief was demonstrated a reasonable method

of applying inertial crash loading during topology

optimisation to extract ideal structural load paths. This

presented the opportunity to develop a method of

proposing new vehicle architectures.

*(Towards the Lightweighting of Low Carbon Vehicle Architectures using Topology Optimisation, 2012)

IR

add

k 0F k u u

0 k

F k u

Finds optimal material distribution throughout a design volume

Improvements:

• Separated Door (Rigid Hinges)

• Windows

• Removal Non-Design Areas

• Allocation of AUX Components

• IR Stability (Compliance Control)

Limitations:

• Solid beam members

• No beam Sizing or Shape

• No buckling consideration

• Final mass still > 2 tonnes

• Unfeasible manufacture

Forces Applied onto Barriers

• Shell Element Barriers

• Non Design Areas

• Contact Surfaces or

equivalence attachment to

the non-design volume

Rear Impact: 707kN

(0,5o,10 o,-5 o,-10 o)

Roof Crush: 30kN

Front Impact: 707kN

(0,5o,10o,-5o,-10o)

Pole Impact: 300kN

Side Impact: 300kN

Inclusion of all Auxiliary

Components

• All components of significant

mass included.

• Rigid elements to centre of

mass locations.

• Rigid elements attached to non-

design elements.

• Additional masses for large

components at mounting points.

• Rigid suspension modelled with

damper and lower arm points.

• First Order Tetrahedral Elements

• Use of Optimisation Controls – DISCRETE

– MINDIM

• Inertial Relief

• Concentrated Point Masses

• Nodal Displacement Responses

2 – 3mm

• Volume Reduction Objective

25mm

Mesh

15mm

Mesh

Using the wireframe meshed with beam elements

• Tube profile chosen

• Outer diameter and thickness (DEQATN)

• Shear Panels

• Per member/Per element

• Symmetrical properties

• Displacement constraints (10mm-20mm)

• Loads applied directly to beam elements

• Buckling Consideration

Per Beam

Member

Method

Per Element Method

Buckling Equations

• Euler Equation

• Applied in critical areas

• Response to max element force within a member

• Only considers static buckling

OD = 60 mm OD = 51 mm

𝐵𝐿𝑜𝑐𝑎𝑙 𝐹𝑎𝑐𝑡 =64𝐹𝑚𝑎𝑥𝐿

𝐸𝜋3(𝐷𝑜4 − 𝐷𝑖

4)

OptiStruct provided all round best optimisation package:

• Fully integrated into HyperMesh and FE solver.

• Considerably Lower Run Times

• Converged solution, every time

• Instant post processing using .prop import

• Variable sizing through members

Starting from 35mm Radius

Starting from 70mm Radius

Full Shape Morphing

Cross Section Morphing

Final Mass: 0.118kg

Final Mass: 0.112kg

Requirements:

•Discrete Design Variable

•Function: Sum of Thickness

•Function Constraint

•Dependencies

Reinforcement Selection Results

Local Morphing Ability

Reinforcement Integration to Shape Selection Results

Final Beam

Design

Optimisation Example Set Up:

•Objective: Minimise Mass

•Constraints: Displacement (4mm)

Reinforcements

•Design Variable: Morphing Shapes

•Vehicle must be able to

withstand Loads on both

sides.

•Applying Loads to both

sides increases Load

Cases.

•Increased Load Cases

Increases response

numbers increasing solver

time.

•Implementing Symmetry

plane causes both sides to

be optimised for the

maximum force.

Initial

Morphing

Beam

Diameter

• Average diameter taken of all

beam elements within 1D member.

• Diameter applied to 2D beam

diameter.

• Shape variation becomes a

function of 1D beam optimisation.

• Initial diameter should be closed to

optimised diameter.

• Design Volume from Styling

– Removal of Aux Comps

– Removal of Cabin Volume

• Topology Stage

– CONM’s for Aux Comps

– Combine Opti Controls

– Separation of Apertures

• Wireframe

– Shrink Wrap Topology

– User Interpretation/No Auto

• Beam Model

– Per member/Per Element Opt

• Morphing

– With Initial Sizing

– Map Morph to Wireframe

– For each Beam

– Replace Forces

LABOUR INTENSIVE,

NEEDS AUTOMATION!!

Scripting the Process

Using TCL in HyperWorks

The optimisation process and accompanying scripts present a method of

examining varying vehicle architectures and extracting realistic BIW sections

in less than a day. Enabling fast design and effect studies.

Thank you for your attention.

...any questions?