Side Crash Analysis of a car ( BIW )

Objective :

Side crash analysis - To import a given model and analyze its behaviour in various aspects by feeding required inputs , and requesting required outputs using tools in hyperworks , through which the analysis of the model during side crash could be determined

Procedure :

1. Open hypermesh and choose RADIOSS interface
   
   
2. Then import the 0000.rad file
   
   
   
   
3. Check for correct unit system --> Kg mm ms ( As per requirement )
   
   
4. Open model in browser tab and select cards --> Begin card
   
   
5. Check for the units of mass , length , time
   
   
6. After importing , check for the penetrations in the model , since penetration leads to simulation errors and timestep issues
   
   
7. In this process, hypercrash was more convenient in checking for penetrations issues , thus hypercrash application was opened
   
   
8. Go to Applications in menu bar and select Hypercrash
   
   
9. Once Hypercrash was opened , contact interface from browser tab selected
   
   
10. Select all the interfaces created and click the check penetration for selected objects option
    
    
11. The quality window appears showing all the penetrations and intersctions of the model
    
    
12. There where no penetrations found in this case
    
    
13. Then, hypermesh window is again opened to assign the simulation run time
    
    
14. In the browser tab open cards under which select ENG_RUN
    
    
15. To assign the simulation run time in ms , enter required values in Tstop ( In this case 80ms assigned )
    
    
    
    
16. Then , to assign Timestep open solver browser
    
    
17. In solver browser , right click --> create --> engine keywords --> DT --> DT
    
    
18. In which assign the required timestep in Tmin ( In this case 0.5 was assigned )
    
    
19. After which initial velocity to be assigned for which solver browser is opened
    
    
20. Right click --> create --> boundary conditions --> INIVEL
    
    
21. In which as per the direction of global axis and required velocity to be mentioned accordingly
    
    
22. In this case as per global axis , y-direction is mentioned with required velocity ( To be mentioned in mm/ms )
    Requirement velocity 35mph
    1 mm/ms = 2.23 mph
    35mph = 15.6 mm/ms
    
    
23. After which Grnod_id to be selected , Right click on Grnod_id and select create
    
    
24. Under Entity IDs select all the nodes of the model
    
    
25. Click proceed and initial velocity is assigned as per requirement
    
    
26. After which rigid wall is created
    
    
27. To create rigid wall , in the model browser , right click --> create --> rigid wall
    
    
28. The Engineering data , Normals ( these denotes distance from origin and normal from axes ) were entered and select Geometry type as Cylinder
    
    
29. Slide value, diameter , Dsearch values were entered
    
    
30. Rigid wall has been created
    
    
31. Next interfaces were to be created for the model
    
    
32. In the model browser , right click --> create --> contact
    
33. In the contact window , enter ther recommended parameters like Type of contact , Istf , Igap , Idel , Stmin , Fric , Gapmin , Inacti , Iform
    
    
34. Then for selecting Masters and slaves right click the Surf_id(M) and Grnod_id(S) respectively and under Entity IDs select the components for master and slaves
    
    
    
    
35. As per requirement , the given model's mass has to reach a target mass of 700kg from its initial mass by adding mass to it and bring the CG ( Centre of Gravity ) to required position ( near centre cross beam )
    
    
36. To know the initial mass and CG of the model
    Tools --> Mass details --> Mass , Cog and Inertia
    
    
37. Select mass tab to view total mass ( Initially ) - Initial mass = 166kg (approx)
    
    
    
    
38. Using the COG tab and the node ID , initial COG of the model is found by creating a node
    
    
    
    
39. To add mass to the components , in the model browser , right click --> solver mass
    
    
40. Under which select the required mass type , mass and grnd_ID( Right click --> create and under Entity_IDs select the Nodes for which mass to be added )
    
    
    
41. After adding masses over the components , check the total mass again so as to reach the target mass
    
    
    
    
42. Also check the COG of the model to reach the required position
    
    
    
    
43. Thus the target mass and COG position reached
    
    
44. Then as per output requests , ( Over TH )
    
    Intrusions on the B-pillar , Hinge pillar , Fuel Tank region to be determined after simulation
    
    
45. To request TH for these intrusion positions , from solver browser , right click --> create --> TH --> node
    
    
46. Select the nodes from Entity IDs - Select nodes in each area seperately
    
    B-pillar selection :
    
    
    
    Hinge pillar selection :
    
    
    
    Fuel tank region selection :
    
    
    
    
    
47. After which Skew to be created directly opposite to these positions of intrusions to determine its intrusion during crash
48. To create skew , in the solver tab , right click --> create --> skew --> Mov
    
    
49. Three skews were created opposite to three intrusion points
    
    
    
    
50. After which , these three skews to be linked with the intrusion nodes of the TH
    
    
51. Open the TH card and the intrusion node and then specify the Iskew by selecting under system
    
    
    
    
52. Similarly select the Skews for respective intrusion points that were present directly opposite
    
    
53. Then , to analyze the peak velocity at a given position ( Node ID = 337773 )
    
    
54. To request TH for this position , from solver browser , right click --> create --> TH --> node
    
    
55. Select the node from Entity IDs - Select node 337773 - As per requirement
    
    
    
56. After which cross sections were to be selected
    
    
57. To create section open solver browser right click --> create --> SECT --> SECT
    
    
58. Enter N1, N2 , N3 to specify directions
    
    
59. Right click on grnod_id to enter Entity_ID ( where 2 rows of nodes selected )
    
    
    
    Similarly on the other area were cross section to be studied
    
    
    
    
60. After selecting nodes ,
    
    
61. Right click on grshel_id to enter Entity_ID ( where elements covering the 2 rows of nodes were selected to specify sectional force )
    
    
62. Assign deltaT , alpha , Iframe as per requirement
    
    
    
    
    
    
63. These were to be plotted in TH during analysis , thus these cross sections were to be defined under TH card
    
    
64. Open TH card in solver and under node select cross section and right click to select all the cross sections created under Entity IDs
    
    
    
    
65. All the inputs were specified as per requirements
    
    
66. Before simulation run , model checker performed to check the model for better result during simulation run and to avoid errors
    
    
67. To check , Tools --> Model checker --> Radioss Block
    
    
68. Model checker tab appears
    
    
    
    
69. Right click on Error and select Run to determine the errors and the Errors tab opened to view the errors
    
    
    
    
70. If no errors , proceed for the simulation run else solve the errors and then run the simulation
    
    

SIMULATION RUN :

1. After which Simulation RUN could be performed using Analysis panel in main menu
   
   
2. Choose RADIOSS option and select the required parameters , input file to save the generated files
   
   
   
   
3. Click RADIOSS to run the simulation and files will be generated in input file location
   
   
4. After simulation run , a dialog box shows the total number of cycles and simulation time
   
   
   
   
   
5. After which open the 0001.out file that was generated during simulation run and check the energy error & mass error
   
   
6. Energy error to very maximum level of +5% is acceptable model , -5% represents a good model and better to be close to 0%
   At ideal conditions -15%
   
   
7. Using page window layout , split the window for convenienece
   
   
8. Select Hyperview option in toolbar and click load model to upload .h3d file from the generated files during simulation run
   
   
9. Click Apply
   
   
10. The simulation runs for a period of 80ms for 17 frames
    
    Frame - 8
    
    
    
    Frame - 15
    
    
    
    
11. Observe the animation RUN and analyse the changes occuring in the elements and their reaction for a period of 80ms
    
    
12. Similarly analyse using contour ( select contour icon on toolbar )
    
    
13. Select result type as Displacement or Vonmises , averaging method as simple
    
    Also use maximum and minimum measurement plotiing using measures icon in the toolbar
    
    
14. Click Apply
    
    Contour frame - 8
    
    
    
    Contour frame - 15
    
    
    
    
15. Next open Hypergraph , import T01 file using data file option to plot graphs
    
    
16. Plot ,
    Y Type - Global variables
    Y request - Hourglass energy , Total energy , Internal energy , Kinetic energy , Contact energy
    Y component - MAG
    
    
    
    
17. Then select - for plotting intrusions due to displacement during deformation
    Y Type - Intrusion B-pillar , Intrusion Hinge pillar , Intrusion Fuel tank
    Y request - 123347 , 123254 , 123428
    Y component - DISP - Resultant displacement
    
    
    
    
18. Then select - for plotting peak velocity during deformation
    Y Type - Peak velocity
    Y request - 337773
    Y component - VEL - Resultant Velocity
    
    
    
    
19. Then select - for plotting sectional forces over the 2 cross sectional areas
    Y Type - Cross section
    Y request - cross section 1 - cross section 2
    Y component - Total resultant forces
    
    
    
    
    
    
20. These graphs define the plotted details and variations over a period of 80ms
    
    
21. Thus the model have been fed with inputs and required outputs were derived after simulation , and analyzed for the changes in its nature over a defined period of 80ms

Observations over outputs after simulation :

Animation:

The car model was analyzed for its side crash over a cylindrical pole type rigid body , were the deformation starts almost in the middle of the car ( near B pillar )

This impact at a velocity of 15.6ms ( 35mph ) , makes the car deform in such a way that , it folds right way when the pole of diameter 200mm was made as an impactor

The impact leads to deformation of the car starting from the side region of the car

The stresses gets transferred from the pole to the components of the car due to contact

Majorly the stresses gets transferred near the bottom rail near the rocker , since it gets deformed and bend the most by absorbing more stresses

With reference to the contour plots, the maximum stress was observed near the B pillar rocker (bottom) region on frame 16 for a total frame of 17 at a value of 0.34



Global forces :

• Hour glass energy :
  
  The hourglass energy in this case seems to be NIL and shows that there were less energy errors and contributes for a good simulation of the model ( Ishell = 24 - QEPH used in the property contributes reduction in hourglassing )
  
  
• Kinetic energy and Internal energy :
  
  Initially when car with its mass and velocity impacts with the rigid pole, higher amount of kinetic energy was generated .
  
  This kinetic energy once created at the initial stage of impact , gets transmitted to the inner parts/components of the car during deformation .
  
  Due to this transmission of energy , kinetic energy drops down gradually and at the same time internal energy gets created within the components of the car
  
  This internal energy increases with time period of 80ms during this collision and simultaneously kinetic energy decreases
  
  
• Contact energy :
  
  This energy on the whole seems to be low and at the start of 40ms to end of 80ms , there was a small raise in this energy
  
  This was probably due to friction between the components during deformation at the time period of 40ms to 80ms
  
  
• Total energy :
  
  On the whole the total energy for the side crash for about 80ms stays at its peak and maintained at same level through out simulation with a very minor drop

Sectional forces :

These are forces that are analyzed over a particular region to determine amount forces passing through it

As per requirement , 2 sections on the bottom cross beams were analyzed

• These sections differ in their forces passing through them
  
  
• Both the sections differ by their geometry and material , property leads to difference in their sectional forces ( also their location during the impact )
  
  
• The first section shows that very minimum of the forces pass through their cross section since this part/component compared to the other one stays away from the point of contact ( pole - rigid body )
  
  
• Due to which the stresses transferred to this cross section was minimum and resulting in less deformation
  
  
• Only at the end of simulation it touches its peak due to collision and other frictional contact forces, thus the stresses got increased
  
  
• The second section shows more forces passing through its cross section , since the impact was almost direct from the pole
  
  
• Due to this impact , the deformation were too high due to the stresses passing through the region
  
  
• More the stresses more the deformation caused
  
  
• Initially at the cross sectional area , the stresses were observed to be low since the forces where yet to vome from the other components lying before them
  
  
• The forces go very high during the time period of 40-50ms shows that during that time the deformations were high and after which the forces were transmitted
  
  
  
  Overall view on sectional forces :
  
  These forces were plotted to analyze the amount of forces received and passing through them over a period of time during deformation. ( 80 ms )
  
  The amount for forces transferred and received depends on the position of the components
  
  If the component was present at very beginning or front of the model were deformation or collision starts , thats the point where the stresses were maximum
  
  And gradually as time passes, deformation increases and forces get transferred to other components
  
  These forces gets transferred only after that particular component has received enough stresses and the remaining stresses gets passed to next component
  
  Also the stress depends on the area of cross-section ( Higher the area more the total stress observed in that particular area )
  
  And finally when the stresses pass through component by component , the stresses received by the component present at the end of the sequence , expected to be minimum
  
  Also when the component was expected to get the impact so much in direct form , experiences more of the stress ( B-pillar cross beam - second section as per explanation above )

Intrusion of B-pillar , Hinge pillar and fuel tank region :

• 123428 - Fuel tank region ( represented in Blue )
  
  
• 123254 - Hinge pillar ( represented in red )
  
  
• 123347 - B-pillar ( represented in green )
  
  
• The graph represents that , fuel tank region and B-pillar seems to have similar and very less displacement reading
  
  
• The Hinge pillar shows more displacement reading compared to other two
  
  
• These as they were plotted within the TH , each region have a frame of reference created using skew
  
  
• These displacement values shows the gap between the frame of reference and the region respectiively
  
  
• Since the fuel tank region and B pillar have similar gap between their own frame of reference , they show similar displacement
  
  
• And they are low because their intrusion was higher due to higher deformation and stress
  
  
• The Hinge pillar shows less deformation as compared to other two region , thus resulting is less intrusion
  
  
• Due to less intrusion , the gap is more wider and the displacement values with respect to thier frame of reference was shown higher

To reduce fuel tank intrusion :

Other regions had beams connecting the pillars across both sides . these beams carry the seat of the car . Cross beams covering the fuel tank region would probably reduce fuel tank intrusion . If seats were arranged , the intrusion levels could decreases comparatively .C pillar component and structural strengthening could reduce intrusion over fuel tank region .

Peak velocity :

Peak velocity was about 17mm/ms (approx) for the time 4-5ms (approx) for a time period of 80ms

The velocity at the initail stage of impact seems to be high as the kinetic energy shoots high at initail stage of impact

And then sudden drops near 10ms and gradually maintained within 2 - 6 mm/ms for a period of 80ms

Output file 0001.out observation :

Time step :

Time step was observed to be constant throughout the simulation for a period of 80ms ( No fluctuation or change in timestep )

Energy error :

As far as the energy error , it was well maintained to its limit

Initially starts at 0.0% and decreases gradually from to -0.1% --> -2.5% ( shows dissipation of energy )

But overall the energy error was maintained under / near to 0% which was a good sign

Mass error :

Generally this error occurs when timestep decreases and to manage or to increase the timestep the masses are added to the model which in turn reflects in the mass error

In this case the mass error increases gradually with increase in time due to additional masses added to nodes , to balance the COG and attain the target mass of 700kg

Rectify :

Avoid adding mass through nodes over a particular region , mass to be distributed evenly throughout during component preprocessing

Normal termination :

Finally after checking for outputs in the engine output file , to check whether the simulation have been considered good

At the end of the simulation , " NORMAL TERMINATION " would be printed in the engine output file

Thus the output file observation have been done using 0001.out file

Result and Conclusion :

Thus for a given model , side crash simulation have been carried out using Hyperworks ( Hypermesh ) , under recommended inputs and required outputs

Analysis for the simulation have been studied