Simulations v1

8/19/2019 Simulations v1

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Why do simulations?&

Different tools for

simulationsA Chawla


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Contents

• (The need of simulations)

• Two types of simulations and their uses

– Inputs needed in them

– Their advantages and limitations – Case studies

• ….


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Two types of simulations• Multi-body simulations

– Each body is modeled as a rigid body

with – Forces applied when bodies interact /collide

– Are quick to run as well as develop

– Suitable for gross simulations, longduration simulations

– Possible tools – Madymo, PC Crashand case studies

• Finite Element Simulations – For modeling flexibility in bodies

– Are much more time expensive

– Take much more time during the run as

well as in developing – Much more complex

– Typically suitable for short durationsimulations (100-400 msecs)

– Possible tools - Pam Crash, LS Dynaand case studies

BACK


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What we need to develop

simulations in PCcrash

• Detailed data from accident site

– Location of vehicles

– Vehicle damage data

– Road site data, road marks etc – Vehicle data (dimensions, body weight, MOIs)

– Estimates on vehicle speeds

– Coefficients of restitutions, coefficients offriction


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Accident photographshere are some main pictures of Dwarka accident

rest position of wagonR Right wheel partially brocked rest position of Truck rest position of Truck

Skidding marks of vehicles

After collision

Skidding marks of vehicles

After collisionSkidding marks of vehicles

After collision


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A Sample animation


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3) point of impact position at 0.225 s

view 1


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Sequential positions of both vehicles during the crash (view1)


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9) Here truck position while hitting the pavement &

unbalance there


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Madymo simulations• Typically used to assess injury

parameters for occupants / pedestrians

in accidents• What we need

– Vehicle data (geometry, mass, MOIs ..)

– Vehicle force deformation characteristics• Obtained by conducting tests

– Human body / Dummy models

BACK


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• Kinematics of passenger and driver as a

result of a moving three wheeler impactingupon rigid wall is observed.

Three wheeler - Front impact

simulation

•OCC_SID

E.MPV


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Kinematics

T = 0 ms T = 20ms T = 40ms

T = 60ms T = 80ms T = 100ms

T = 120ms T = 140ms T = 160ms


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Kinematics (contd)

T = 180ms T = 200ms T = 220ms

T = 240ms T = 260ms T = 280ms

T = 300ms


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• Kinematics of initially stationary pedestrian

observed as result of impact with movingthree wheeler.

Three wheeler Pedestrian

impact simulation

FRONT.MPV

BACK


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RTV with the Driver

Tyres

Driver’s DummyModelRTV Seats


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RTV model with driver and passengers


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J-Turn Simulation at RTV Entrance Speed of 7.5m/s

Roll Angle at 7.5 m/s

0 667 1333 2000 2667 3333 4000 4667 5333 6000 6667 7333 8000 8667 9333 10000

-0.060

-0.052

-0.044

-0.036

-0.028

-0.020

-0.012

-0.004

0.004

0.012

0.020

Time (ms)

red

Roll Angle

Z-comp. displacement (m)

0 667 1333 2000 2667 3333 4000 4667 5333 6000 6667 7333 8000 8667 9333 10000

0.450

0.440

0.430

0.420

0.410

0.400

0.390

0.380

0.370

0.360

0.350

Time (ms)

Vertical Displacement (m)

R-front-wheel / Z-comp. displacement (m) R-rear-wheel / Z-comp. displacement (m)Roll Angle at 7.5 m/s

Vertical displacement at7.5m/s


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Comparison of RTV rollover maneuvers results

with other vehicles results reported by

Frokenbrock etal (2002) and Gawade (2004)

From this comparison it is evident that in RTV increased

rollover propensity is expected *** BACK

Vehicle J-Turn Road Edge Recovery

2001 Chevrolet Blazer 17.29 m/s 16.09 m/s

2001 Toyota 4 Runner 20.5 m/s 17.06 m/s

1999 Mercedes ML320 20.04 m/s ….

2001 Ford Escape … 21.51 m/s

RTV 7.5 m/s 8.75 m/s

Three wheeler 7.98 m/s 9.00 m/s


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• Detailed geometry of the bodies is modeled

• Material properties have to be known

• Contacts, initial conditions have to be modeled

• Development takes much more time – and

• Simulations are also very consuming

• Hence used for only short duration simulations• Case studies – Model development

– Motor cycle wall simulation

– Car – MC simulation• (Details and history of MC standards)

– Airbags for MC

– Human Body Modeling

Finite Element Simulations

BACK


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o e eve opmen

methodology - ComponentTests


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FE Car Model• Component models

verified as per ISO(13232) compatible

tests

• FE models validatedagainst the same F-

δ curves

BACK


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Motorcycle Model• Components modeled

• Validated against

tests

• Suspension modeledas spring + damper


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MC-Wall crash validation


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MC Model validation

Comparison of w all forces

-20000

0

20000

40000

60000

80000

100000

120000

140000

0 20 40 60 80 100 120

Time (sec.)

Experimental

FE Simulation

BACK


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Car – MC simulations


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A sample simulation


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90o side Impact with car

stationary

40 ms

120 ms

With gripDummy without

(handle) grip

BACK


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A sample airbag simulation


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AIRBAGS for MCs

• Some Important Issues

– Need of a backing surface

– Size of airbag

– Out of position rider – Role of helmet


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Possible Initial Positions


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Out of position rider simulations


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Issues in airbag simulations• The gas dynamics behaviour in the first

few msecs becomes important• Gas dynamics is captured using Arbitrary

Lagrangian Euler Simulations (ALE)

• …. Complexity increases further

• … Simulations take upto 10 hrs for 10

msecs of run


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The model developed


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X-acceleration

• Peak accelerations

upto about 120g

• Duration about 4-6

msecs

• Change in peak

acceleration with AB

volume is small

BACK


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Simulations v1

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