BIW Frontal crash simulation using RADIOSS SOLVER.

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The instructions for this assignment were as follows:

1. Check the unit system and either follow[Mg mm s] or [Kg mm ms].
2. Create an appropriate interface, friction 0.2, and recommended parameters.
3. Make sure of no penetrations and intersection.
4. Correct rigid bodies if any issues.
5. Create a rigid wall with friction 0.1.
6. Compare the model weight with the full-scale 300k nodes model and use added masses to reach target weight 700kg while getting COG about the required range.
7. Initial velocity 35 mph.
8. Use model checker to ensure good quality.
9. Time-step :0.5 to 0.1 microseconds.
10. Run 80 ms.
11. Request for the following results:
    1. Sectional force in the rails at the location of indicated node 174247.
    2. The axial force received on the rails from the bumper.
    3. Shotgun cross-sectional forces.
    4. A pillar cross-section.
    5. Acceleration curve received on the accelerometer at base of B pillar (on B pillar rocker).
    6. Intrusions on the dash wall 66695,66244

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OBJECTIVE: To set up the frontal crash simulation of a Neon car model, in the RADIOSS solver deck and analyze the results as per the instructions given.

PROCEDURE:

1. Solver deck set-up
   1. Import the .rad file provided. Kg mm ms kN is taken as the units for this model. The .rad file contains the solver deck set-up for a reduced model of the Neon car. The Model has been reduced to only some essential parts in order to make it possible for the students to edit the deck in Hyperworks student edition which has node limitations.

      Fig 1. The reduced Neon car model

   2. We need to set up the deck as per the instructions.
   3. The deck already has some interfaces defined. We can delete these interfaces and create a single interface for the whole model using the type 7 contact interface. Since we are also asked to find the force transfer from the bumper to the rail, we will define a second type 7 contact interface keeping the bumper as the master segment and the rest of the front part of the car as its slaves. Note: We need to make sure to enable the Time history option for the defined contacts to have the results recorded in the .T01 file during the simulation. We can either enable it while defining the contacts or by going into the Time History tab and adding the necessary requests separately.

      Fig 2. Interface type 7 defined for the whole model	Fig 3. Interface type 7 defined for Bumper-rail

   4. Now we need to apply an initial velocity of 15.64mps which is equal to 35mph. The initial velocity was applied to all the parts of the model.

      Fig 4. Initial velocity defined for the model

   5. A rigid wall with a friction coefficient of 0.1 was created perpendicular to the global X-direction for the collision.

      Fig 5. Rigid barrier created

   6. A gravity load of 0.00981mm/ms^2 in the - Z direction was applied on all the parts for making the simulation more realistic.

      Fig 6. Gravity load applied to the model

   7. Aditional mass was added to the model at necessary locations for bringing the COG to an acceptable location on the model.

      Fig 7. COG after Mass balancing

   8. Circular sections were created on the required regions as per the assignment instructions.

      Fig 8. Sections created

   9. Accelerometers were created on the rockers near the bottom part of the B-pillars for recording the accelerations during the crash.

      Fig 9. Accelerometers created in the model

   10. The Dtmin values were defined by going into the DT_eltype_keyword_flag present under the engine tab in the Control cards.

       Fig 10. DTmin values for the analysis

   11. The run time was set as 80ms by editing the RUN option under the engine tab in the Control cards.
   12. We need to find intrusions at two nodes on the Floor of the car. We will be creating two type-4 springs with very negligible stiffnesses in the x-direction in order to measure the intrusions. One end of the spring will be on the nodes where intrusions are to be measured and the other end will be on a node that is free from any deformation during the crash. Here we have been instructed to keep the reference nodes as 121739 and 122048 for the intrusion nodes, 66695 and 66244 respectively.
   13. Intersection and penetration checks were conducted. No intersections or penetrations were detected by the model checker.

       Fig 11. Intersection/ penetration check

2. Result requests
   1. Go to the Time history menu and create the required TH requests. Make sure to include the accelerometers, the intrusion springs, the Rwall, the Interfaces, and the Sections.

      Fig 12. TH requests created

   2. In order to request for contour animations, we have to go to the anim_vect option under the engine tab in the control cards.

      Fig 13. Contours requests created

3. Model checker
   
   1. Now that we have completed the solver deck set-up, we need to check the model for any error by using the model checker in Hypercrash.
   2. The connectivity of the model was checked to see if there are any free parts. Two free spherical joints were detected. After confirming that these joints are nod being used anywhere in the model, they were deleted.

      Fig 14. Connectivity check

   3. The model checker came up with 2 errors and 9 warnings. Most of the warnings were created due to presence of node groups, surface groups that are not being used. These were suppressed to remove those warnings. Some free nodes, joints springs were also detected by the model checker. These were deleted. The completed model now shows a warning for possible hourglass elements. This can be ignored.

      Fig 15. Model checker

   4. Export the completed solver deck to the target folder and run the analysis using the engine starter file in the Radioss solver manager.
   5. The engine input file shows the engine parameters set.

      Fig 16. Engine input file(0001.rad file)

   6. The run completed successfully with no errors and 4 warnings as shown in the Starter listing file.

      Fig 17. Starter listing file(0000.out file)

   7. The energy error and mass errors need to be checked in the Engine out file. An energy error of -1.2% and a mass error of ~2.9% were found which are acceptable.

      Fig 18. Energy error(1.2%) and mass error(2.9%)

   8. The run seems acceptable as the errors are within limits. So we can move on to Post-processing the results. Open the Results in Hyperview and Hypergraph and generate the necessary contours and plots respectively.

RESULTS:

1. Crash animation: The deformation on the left side of the car is more than the right side. The front of the car seems to rise during the crash. This might be the result of mass balancing that we have done on the model.

   Fig 19. Crash animation

2. Energy plots: The plots show a decrease in KE and an Increase in internal station energy after the occurrence of the impact. The total energy has stayed nearly constant throughout the run. The choice of Hourglass free shell element formulations have helped in keeping the hourglass energy to a very negligible value. The contact energy can be seen to have increased across the run time with the increasing amount of deformations imparted on the model and the resulting increase in contact between different parts.

   Fig 20. Energy vs time plots

3. The intrusion of nodes 66695 and 66244 into the occupant space: The resultant elongation of the intrusion measuring springs were plotted against time. The values of elongation at the end of the simulation will give the intrusion measurements for both the nodes during the run time. An intrusion of 144.95mm and 150.83mm was measured for nodes 66695 and 66244 towards the end of the simulation.

   Fig 21. Intrusions of nodes 66695 and 66244

4. Vonmisses stress contour: A maximum of 0.4Gpa was recorded during the run time.
   

   Fig 22. Vonmisses stress contour

5. Accelerations measured by the accelerometers: The plot shows the acceleration values recorded by the accelerometers placed at the rocker arms at the bottom of the B-pillars. Accelerations become non-zero after the impact. The accelerometer on the Left rocker has recorded more variations and peaks as a result of more deformations on the left side. The right side accelerometer has recorded lower acceleration variations.

   Fig 23. Acceleration vs time plots

6. Rigid wall forces: The rigid wall experienced a maximum force of 142kN at 2.1ms. A peak is observed at 0.4ms which is when the car bumper impacted the wall. After that, a dip can be observed while the front part of the car is getting crushed. At about 10ms, a part of the rail bends and hits the wall which is why a second peak can be seen on the plot at this point in the simulation. Every time a component begins to deform, the resultant forces experienced by the wall can be seen as decreasing.

   Fig 24. Rwall forces(kN)

7. Axial forces on the bumper-rail interface: The forces are high at the beginning of the impact and decreases as the run progresses. In the end, the forces can be seen to rise again, this might be due to self impact. A maximum of 12.42kN was recorded during the run time.

   Fig 25. Axial forces on the bumper to rail interface(kN)

8. Sectional forces on A-pillar: The forces are higher on the left side A-pillar. The peak values were recorded as 2.93 kN and 2.39 kN for the Left and right sides respectively.

   Fig 26. Sectional forces on A-pillar(kN)

9. Sectional forces on A-pillar-btm: A peak force of 7.73 kN was recorded on the right side compared to 4.24 kN recorded in the left side section. The higher value of force on the right side is due to the impact of the bent region onto the section.

   Fig 27. Sectional forces on A-pillar-btm(kN)

10. Sectional forces on Shotgun: Similar to the A-pillar sectional forces, the shotgun sectional forces also indicate a larger force transfer through the left side section with a peak value of 13.73kN. The right side section recorded a peak force of 7.76 kN.

    Fig 28. Sectional forces on Shotgun(kN)

11. Sectional forces on headlight bracket: In both the sides, the forces are larger in the beginning and getting reduced as the run progresses. Similar to the previous sections we analyzed, the peak value of force is greater in the left side section(7.51 kN). The peak force on the right side was recorded as 7.08 kN.

    Fig 29. Sectional forces on headlight bracket(kN)

12. Sectional forces on the rail: The forces on both sides increase as the impact takes place and reaches the peak values of 31.81 kN and 35.14 kN for the left and right side sections respectively. Thereafter, the forces are decreasing until the end of the simulation.

    Fig 30. Sectional forces on the rail(kN)

CONCLUSION:

1. The solver deck was set-up as per the instructions.
2. All necessary output requests were placed.
3. The simulation was run successfully with acceptable amounts of energy error(1.2%) and mass error(2.9%).
4. The left side of the car BIW had more deformations compared to the right side.
5. All the sectional forces were plotted. The maximum sectional forces were recorded on the Rail and shotgun sections and low forces were recorded on the A-pillar. Thus more force transfer occurs along the rails and shotgun parts.
6. Intrusions were measured using nodes 66695 and 66244. The intrusions were calculated as 144.95mm and 150.83mm respectively. Acceleration was measured using accelerometers created on the rockers at the bottom of the b-pillar.

Find the simulation files and results here.