6. Frontal Crash Simulation

AIM:

• To perform frontal crash analysis of the neon car model and obtain the simulation results and plot the required graphs.

OBJECTIVES OF THE PROJECT:

• To set up the car model for frontal crash analysis.
• To create appropriate interface for the model.
• To check the model for intersections and penetrations.
• To create a rigid wall for the model to crash.
• To assign mass to the model upto 700kg.
• To perform mass balancing and bring the COG of the model to the desired region.
• To assign initial velocity of 35mph.
• To procure the desired output results.

PROCEDURE:

• The first step is to import the model in the Radioss profile.
• Go to FILE > IMPORT > SOLVER DECK > BROWSE > OPEN.
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• Unit System -
• Now, we have to check the unit system for the solver.
• Go to MODEL > CARDS > BEGIN CARD to check the unit system. For this model we are following the kg, mm, ms unit system.
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• Time step -
• Go to MODEL > CARDS > ENG_DT_NODA > TMIN = 0.0001. This will set the time step for the analysis.
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• Intersections and Penetration check -
• Next, we will check the interfaces and penetrations. Go to TOOLS > PENETRATION CHECK > COMPONENTS > ALL > CHECK.
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• We can see that there are no intersections and penetrations in the model.

• Interface contact -
• Now, go to SOLVER > INTER and delete the predefined interfaces. Now, CREATE > INTERFACE > TYPE 7 with the recommended parameters. We define the interface for all the components.
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Istf=4, Igap=2, Idel=2, Fscale_gap=0.8, Stmin=1KN, Fric=0.2, Gapmin=0.5, Iform=2 and Inacti=6.

• 
• The interface type7 is used because this is used for self intersection node to surface type contact.

• Rwall Plane - 
• Now, we have to create a rigid wall. Go to SOLVER > CREATE > RWALL > PLANE. Select the outermost elemental node on the bumper for the Rwall plane. The plane will be in X-axis, hence give the normal in X-axis as -1. Give a gap of 5 mm in the X-axis such that the plane does not intersect the bumper. Provide search distance as 1000mm and Friction=0.1.
• 
• The rigid wall will be created.
• 

• Initial Velocity - 
• Now, we have to provide initial velocity for the model. Go to SOLVER > CREATE > INIVEL > TYPE: TRANSLATIONAL IN X > GRND_ID= COMPONENTS=ALL. The conversion of 35mph in mm/ms is 15.6464.
• 

• Mass balancing - 
• Now, we have to balance the mass and obtain the COG in the desired region. The initial mass is observed to be 188kg. The COG of the vehicle is as shown in the black circle.
• 
• We have to bring the mass to 700kg approx for the whole model and the COG should be below the driver’s seat. So to obtain the required CG location, we have to do mass balancing by adding mass at the rear and at the front.
• Go to SOLVER > CREATE > ADMASS > MASS TYPE = 0 > GRND_ID > SELECT NODES > MASS.
•   
• 
• In, this way the mass balancing is performed to get the required COG. The total mass of the model is brought approximately to 700kg. The added mass location is as shown in the black circles.
• 
• The COG of the model is as defined by the black cirle.
• 
• 

• Accelerometer - 
• Now, we have to define accelerometer below the B-pillar. Go to SOLVER > CREATE > ACCELEROMETER > NODE_ID > FCUT=1.64. Create accelerometer at both right and left side.
• 
• 

• Sections -
• Next, we have to obtain the results for the defined cross sections. For that first we have to create moving frames. Go to SOLVER > CREATE > FRAMES > MOVING > CREATE BY NODE REFERENCE > ORIGIN > X-AXIS > XY PLANE > CREATE.
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• Then go to SOLVER > CREATE > SECT > FRAME_ID > DELTA T=0.1 > ALPHA = 1.94 > IFRAME = 12.
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• Similarly, we will create the moving frames and sections at the desired areas on the left and right side of the model. Totally, there will be 10 sections.
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• Intrusions - 
• Next, we have to create intrusions. To find the results we have to create moving frames at seat parts. Then, go to MODEL > OUTPUT BLOCKS > CREATE > INTRUSIONS > NODE_ID > I_SKEW. This will give the output result for the intrusions.
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• 

• Output blocks - 
• Next, we have to define the outputs. Go to MODEL > OUTPUT BLOCKS > CREATE > ACCELEROMETER and SECTIONS and RWALL CARDS.
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• This will define Radioss that these output results should be provided after simulation.

• Model Checker -
• At last, go to TOOLS > MODEL CHECKER > RADIOSS BLOCK > RIGHT CLICK ON ERROR > RUN. This will run the model checker for any errors if any.
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• We have no errors in the model and hence we can proceed to run the simulation.

• Analysis tool -
• Go to ANALYSIS > RADIOSS > INPUT FILE > INCLUDE CONNECTOR > OPTIONS = -NT 4 > RADIOSS.
• 
• This will run the Radioss simulation.
• Open .out engine file from saved folder and check final value of Energy error, Mass error, Simulation time and Total no of cycles.
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• Here, the energy error is shown in the red box and mass error in the blue box.

• 
• We can see that Radioss took 6hrs and 21 minutes to run the simulation file.
• Click on view Results, which will open Hyperview window.

• Hyperview - 
• In Hyperview go to CONTOUR > RESULT TYPE > VON MISES > AVERAGING METHOD > SIMPLE > APPLY.
• 
• In the above crash simulation the neon car model is seen to be impacting the rigid wall, the vehicle body is seen to bending around the COG point. Hence, the location of the COG of the vehicle is the most important and is kept under the driver seat for safety of the driver. Also, the deformation seems unrealistic as the model is a reduced scale model due to software constraints. The maximum stress concentrations in the vehicle are few and the impact energy is fairly distributed along the body.
• The maximum von-misses stress obtained is 0.3629. 
• In Hyperview go to CONTOUR > RESULT TYPE > PLASTIC STRAIN > AVERAGING METHOD > SIMPLE > APPLY.
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• The plastic strain is observed in the front bumper region where the kinetic energy is absorbed in the front region safeguarding the passenger region.
• Maximum plastic strain obtained is 0.703.

• Hypergraph 2D -
• Open Hypergraph 2D and load T01 file.
• Go to GLOBAL VARIABLES > INTERNAL ENEGRY, KINETIC ENERGY and TOTAL ENERGY > MAG > APPLY. This will plot the energy graph.
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• From the above plot, we see that at the strat the kinetic energy is about 85000kgmm2/ms2 and as the simulation progresses the kinetic energy at 80 ms is 46000kgmm2/ms2. This kinetic energy reduces and it is transformed into internal energy, hence the total energy is being constant at 85000kgmm2/ms2. There is very less contact energy and Hourglass energy deviation, which means the simulation is stable.

• Go to NODE INTRUSION > DISP- RESULTANT DISPLACEMENT > APPLY. This will plot the intrusion graph.
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• For node 66695, the distance between the node and the skew is 767mm and the resultant displacement is about 800mm. Hence, the intrusion is 840 - 767 = 73mm.
• Similarly the intrusion for the node 66244 is 840 - 793 = 47mm.

• Go to GLOBAL VARIABLES > RWALL > NORMAL RESULTANT, TANGENT AND TOTAL FORCES > APPLY. This will plot the rigid wall forces.
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• From the above graph we can say that, the peak value of the total resultant forcce is about 130KN. There is variation between the tangent resultant force and hence the total resultant force curve is below the normal resultant force.

• Go to SECTION > TOTAL RESULTANT FORCE > APPLY. This will plot the section forces.
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• The peak value at A_pillar_left is 1.9KN observed at the end.

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• The peak value at A_pillar_right is 0.0065KN, whivh is very much less than the left pillar.The force is high at the start and eventually reduces to an average force of 0.001KN.

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• The peak value at the A_pillar_left_hindge is 5.9KN at 40ms.

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• The peak value at A_pillar_right_hindge is 12KN at 73ms. The force at 34ms reduces to zero and then increases rapidly.

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• The peak value at left_fender is 15.5KN at 14ms. After 20 ms the force value shows very less variation and stays average.

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• The peak value at right_fender is 12KN at 12ms.

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• The peak value at left_rail is 13KN at 50ms.

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• The peak value at right_rail is 1.7KN at 27ms.

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• The peak value at left_shotgun is 6KN at 34ms.

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• The peak value at right_shotgun is 12.5KN at 9ms.

• Go to ACCELEROMETER > RESULTANT ACCELERATION > APPLY. This will plot the acceleration graph.
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• From this acceleration graph we can see that the acceleration at the left point is much greater than the acceleration at the right point. The value of the acceleration of left point at 1ms reaches upto 245mm/ms2, then it reduces largely. This is because the point pivots around the COG.

LEARNING OUTCOMES:

• To define INIVEL for the model.
• To define ACCELEROMETER for the model.
• To adjust the mass balance to get the desired COG location.
• To check for the COG location.
• To create Moving Frames.
• To create sections to obtain the results.
• To use model checker for checking errors.
• To provide the output results in the output blocks.

CONCLUSION:

• Hence, by performing this project we conclude that during the crash analysis of the neon car model, the location of the COG acts as the bending point for deformation of the model in certain way. The energy error in the simulation is observed to be -1.8%, which is pretty fine for the simulation.