Parametric study of rear-end impacts using FEM and CFDhani/pdf_files/Master_Thesis_Presentation.pdf · Chalmers University of Technology Modelling of Whiplash Trauma Parametric study

Chalmers University of Technology

Modelling of Whiplash TraumaParametric study of rear-end impacts using FEM and CFD

Andreu Oliver González

Mourya Vanama

Applied Mechanics

07 June 2010

Chalmers University of TechnologyApplied Mechanics

Outline

• Introduction

• Objective

• Methodology

• Results

• Conclusions

• Future Scope

2


Introduction

3Introduction Objective Methodology Results Conclusions Future Scope



$4.5 billion/year€ 10 billion/year

Statistics – Whiplash Injuries

High cost to the society



Statistics – Whiplash Injuries


Whiplash Injury

• Hyper extension of the neck

• Low speed rear-end impacts (16-24 km/h)

Applied Mechanics



Anatomy - Human Vertebral Column


Ventral root

Spinal nerve

Dorsal root

Dura mater

Extradural (epidural) space

Arachnoid mater

Spinal ganglion mater

Subdural space

Pia mater

Subarachnoid space

Ramus communicans

Ventral primary ramus

Dorsal primary ramus


Injury Mechanisms

Facet Joint Capsule Strain

• Impingement of the capsule

• Strain due to deformation

Applied Mechanics




Injury Mechanisms

Pressure Gradients in Spinal Canal

Volume change

Pressure gradient



Injury Criterion

Neck Injury Criteria (NIC)

Calculated at maximum retraction phase

Critical limit of 15 m2/s2

211 )()·(2.0 dtHeadTHeadTNIC CgAccelAccelCgAccelAccel


Objective


Investigate the effect of different parameters on:

• Facet joint loadings and NIC FE simulations (LS-DYNA)

• Pressure gradients CFD simulations (OpenFOAM)


Methodology

12Objective Results Conclusions Future ScopeIntroduction Methodology



Parametric Study FEM

Facet Joint Capsule Strain

NIC

Output

Output

InputCFD

Pressure

gradients

Procedure



Parametric Study



0 50 100 150 2000

2

4

6

8

Time (ms)

Acc

eler

atio

n (

g)

Square Crash Pulses at Delta V of 15 kmph

2.5g

5g

7.5g

Parametric Study

Crash pulses

Square Crash Pulses at delta-V of 15 km/h



FE modelling


CFD

Theoretical model


Whiplash

motion

Cervical spinal

canal length

change

Blood

transportation

Pressure

gradients

Model of the

spinal venous

plexus


Geometrical model

Spinal venous plexus modelled with respect to the THUMS



Geometrical model

Different zone heights and top view



Geometrical model

The mesh


C1_Occ

T1

Inner patch

Outer patch

Side pipe patch

Side pipe

extreme patch


Kinematic model


Representative

point

Inter-

polation

Input

data

Reading and saving

input data

Cylinder motion

Rigid

Deformable


a) Rigid cylinders

Extrapolation of the motion

in two steps

b) Deformable cylinders

Interpolation of the

rigid cylinders

motion


Upper rigid cylinder

Lower rigid cylinder

Deformable cylinder

Premotion Motion


Fluid dynamic properties

• Blood

• Newtonian

• Laminar flow

Boundary conditions

• Extremes of side pipes and main pipe Inlet/Outlet

• The rest of the model Wall

Solver

• For incompressible fluid based on PISO and SIMPLE


Properties Value

Density, [kg/m3] 1050

Dynamic viscosity, [kg/ms] 0.0035

Kinematic viscosity, [m2/s] 3.33·10-6


Results

24Objective Methodology Conclusions Future ScopeIntroduction Results


MotionWith head restraint

Without head restraint

Applied Mechanics


2.5

g2

.5g

5g

5g

7.5

g7.5

g


0 0.05 0.1 0.15 0.2 0.25-300

-250

-200

-150

-100

-50

0

50

100

150

200

Time [s]

Accele

ration [m

/s2]

C1

C2

C3

C4

C5

C6

C7

T1

Applied Mechanics

Motion


Rotational displacement

around Y axis

Longitudinal acceleration

0 0.05 0.1 0.15 0.2 0.25-20

-10

0

10

20

30

40

50

Time [s]

Rota

tional D

ispla

cem

ent [d

eg]

C1

C2

C3

C4

C5

C6

C7

T1

Max. Extension at 0.115 s


Motion verification



Motion verification

Longitudinal velocity

Vertical velocity


0 0.05 0.1 0.15 0.20

2

4

6

8

10

Time [s]

Lo

ng

itu

din

al ve

locity [m

/s]

C1

C2

C3

C4

C5

C6

C7

T1

0 0.05 0.1 0.15 0.20

2

4

6

8

10

Time [s]

Ve

locity [m

/s]

C1

C2

C3

C4

C5

C6

C7

T1

0 0.05 0.1 0.15 0.2-1.5

-1

-0.5

0

0.5

1

Time [s]

Ve

locity [

m/s

]

C1

C2

C3

C4

C5

C6

C7

T1

0 0.05 0.1 0.15 0.2-1.5

-1

-0.5

0

0.5

1

Time [s]

Ve

locity [

m/s

]

C1

C2

C3

C4

C5

C6

C7

T1

C

F

D

F

E

M

0 0.05 0.1 0.15 0.2-1.5

-1

-0.5

0

0.5

1

Time [s]

Ve

locity [

m/s

]

C1

C2

C3

C4

C5

C6

C7

T1


FE simulationsFacet Joint Strains

Applied Mechanics


Acceleration

Pulses

Strains (With Head Restraint)

C2 - C3 C3 - C4 C4 - C5 C5 - C6 C6 - C7 C7 -T1

2.5g 0.0342 0.0368 0.1309 0.2062 0.1883 0.2151

5g 0.2265 0.2037 0.2759 0.2612 0.2076 0.2944

7.5g 0.2893 0.2633 0.3482 0.3290 0.2843 0.3763

Strains (Without Head Restraint)

2.5g 0.1715 0.1712 0.4301 0.7561 0.5989 0.5792

5g 0.4814 0.3383 0.5117 0.9172 0.6456 0.5791

7.5g 0.4029 0.3088 0.5132 0.9236 0.6067 0.9326


Facet Joint Strains - 5g

Applied Mechanics


With

he

ad

restr

ain

t

With

ou

t h

ea

d

restr

ain

t

0 50 100 150 200 2500

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Time [ms]

Str

ain

C2-C3

C3-C4

C4-C5

C5-C6

C6-C7

C7-T1

0 50 100 150 200 2500

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Time [ms]

Str

ain

C2-C3

C3-C4

C4-C5

C5-C6

C6-C7

C7-T1


Neck Injury Criterion (NIC)

Applied Mechanics


NIC

max

[m2/s

2]

Acceleration

0

5

10

15

20

25

30

35

40

45

2.5g 5g 7.5g

With Head Restraint

Without Head Restraint

Non-upright posture with head restraint


CFD simulations

Convergence

- All time steps should fully converge


10-3

10-2

10-1

25

30

35

40

45

50

Time [s]

Num

ber

of itera

tions


Behaviour of Pressure



Behaviour of Pressure


0 0.05 0.1 0.15 0.2-300

-200

-100

0

100

200

300

Time [s]

Mean p

ressure

[P

a]

Mean pressure of the different solid cylinders

C1

C2

C3

C4

C5

C6

C7

T1


Behaviour of Velocity


0 0.05 0.1 0.15 0.2-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

Time [s]

Vert

ical re

lative v

elo

city o

f th

e b

lood flo

w [m

/s]

Vertical relative velocity of the blood flow for the different solid cylinders

C1

C2

C3

C4

C5

C6

C7

T1


Behaviour of Velocity


t = 0.1897 s

t = 0.1209 s


• Head restraint

• Ford Taurus Seat – Underperforms for 7.5g

• The CFD solver should be based on SIMPLE

algorithm

Applied Mechanics

Conclusions


NIC

Facet joint strains


Future Scope

• FEM simulations

• Broader parametric study

• Physiological factors for male and female

• Analysis of Nkm

• CFD simulations

• Consider blood compressibility and vein flexibility

• Use geometry without hole

• Include flow resistance when exiting the model

• Deformation in radial and axial direction



THANK YOU FOR YOUR ATTENTION

Questions?

39

Documents

Parametric study of rear-end impacts using FEM and CFDhani/pdf_files/Master_Thesis_Presentation.pdf · Chalmers University of Technology Modelling of Whiplash Trauma Parametric study