Frontal crash analysis of a car ( BIW )

Objective :

Frontal 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 frontal 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 , x-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 are entered with reference to the 300K model
29. Silde value and Dsearch values are entered
    
    
    
    
30. Rigid wall has been created
    
    
31. Next interfaces are 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 )
    
    
    
    
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 dash wall to be determined after simulation
    
    
45. As per requirement node ID 66695 and 66244 intrusions are to be determined using TH plots
    
    To request TH for these intrusion nodes position , from solver browser , right click --> create --> TH --> node
    
    
46. Select the nodes from Entity IDs
    
    
    
    
47. Accelerometer to be mounted over base of B pillar ( B pillar rocker ) to analyze acceleration curve
    
    
48. In Solver browser , right click --> create --> TH --> ACCEL
    
    
49. On the accelerometer window , right click on Entity ID's and the in node_ID select the node over the rocker ( similarly other side )
    
    
    
    
50. Thus to create acceleration curve in output TH graph, accelerometer was created over B pillar ( on rocker )
    
    
51. Similarly as per requirements , sectional forces were to be studied using the outputs from TH data
    
    
52. For this the position with node ID's were specified
    
    
53. Over these positions Sectional area were to be selected
    
    
54. Using the given node IDs , the nodes and the position to create sections were determined ( this was done using find options and node ID entered )
    
    
55. All the required positions were identified
    
    
    
    
56. Similarly on the appropriate positions on the other side of the model have to be specified
    
    
57. In each position , section selection were made ( Similar procedure for all position )
    
    
58. To create section open solver browser right click --> create --> SECT --> SECT
    
59. Enter N1, N2 , N3 to specify directions
    
    
60. Right click on grnod_id to enter Entity_ID ( where 2 rows of nodes selected )
    
    
    
    
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. Similarly as per requirement , 10 sectional positions were created under SECT in solver
    
    
    
    
64. These were to be plotted in TH during analysis , thus these cross sections were to be defined under TH card
    
    
65. Open TH card in solver and under node select cross section and right click to select all the cross sections created under Entity IDs
    
    
    
    
66. All the inputs were specified as per requirements
    
    
67. Before simulation run , model checker performed to check the model for better result during simulation run and to avoid errors
    
    
68. To check , Tools --> Model checker --> Radioss Block
    
    
69. Model checker tab appears
    
    
70. Right click on Error and select Run to determine the errors and the Errors tab opened to view the errors
    
    
    
    
71. 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
    
    
15. Contour frame - 8
    
    
    
    Contour frame - 15
    
    
    
    
16. Next open Hypergraph , import T01 file using data file option to plot graphs
    
    
17. Plot ,
    Y Type - Global variables
    Y request - Hourglass energy , Total Translational energy , Internal energy , Kinetic energy , Contact energy , Mass
    Y component - MAG
    
    
    
    
18. Then select - for plotting acceleration curve
    Y Type - Accelerometer 1 , Accelerometer 2
    Y request - 1 accelerometer 1 , 2 accelerometer 2
    Y component - ACC - Resultant acceleration
    
    
    
    
19. Then select - for plotting intrusions due to displacement during deformation
    Y Type - Intrusion 1 , Intrusion 2
    Y request - 66695 , 66244 ( As per requirement )
    Y component - Resultant displacement
    
    
    
    
20. Then select - for plotting sectional forces over the 10 cross sectional areas
    Y Type - Cross section
    Y request - cross section 1 - cross section 10
    Y component - Total resultant forces
    
    
    
    
21. These graphs define the plotted details and variations over a period of 80ms
    
    
22. Thus the model have been fed with inputs and required outputs were drawn after simulation , and analysed for the changes in its nature over a defined period of 80ms
    
    
    

Observations over outputs after simulation :

Animation :

The car model is allowed to crash in the front region , where the deformation starts from the bumper and travel through the interior parts of the car

Initially the stress were maximum at the bumper and slowly passes through the inner components

With reference to the contour plots, the maximum stress was observed near the dash board region on frame 15 for a total frame of 17 at a value of 0.399

The stresses reach its maximum value when the component absorption of forces over the region were high

Sectional forces :

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

As per requirement , 5 sections on each side of the car model were to be created and analyzed for sectional forces ( Totally 10 sections )

1. A pillar cross-sections
   
   
   By observing this , the forces across both the A pillar were not similar
   
   This was perhaps due to difference in selection of nodes and elements over those cross-sections
   
   Or the transmission of forces through the region would differ due to material , property nature
   
   If there were softer material in the deformation , maximum of the forces would be absorbed by that material and less forces would be transmitted
   
   Similarly in case of harder material present , then maximum forces would have been transferred across it to the next component
   
   Both the cross-sections in A pillar , seems to raise the forces , over a period of time ( As time increases )
   
   Since A pillar deformation starts increasing over a period of time , increase in this stresses were observed ( Since A pillar is located behind few components that first gets deformed and then comes to A pillar )
   
   
   
   
2. Rail component
   
   
   
   By observing this , the stresses over both the rails were almost similar shows both the rails have undergone similar deformation
   
   Since the Rails were obviously present in the front of the car model , as the crash starts to deform , the stresses starts initially at the bumper and then passes through the rails
   
   So initially the stresses were high on the raiils and then the stresses passes though the rails to other components
   
   Then over a period of time , again the stresses seems to increase in the rails due to friction with other components coming in contact ( End of the simulation 70ms - frame 15 )
   
   
   
3. Shot gun
   
   
   
   
   By observing this, there seems to be difference in shotgun stresses , might be due to sectional selection and also due to deformation pattern
   
   Absorbing more forces during deformation results in increase in its stresses
   
   This absorption of stresses differ due to nature of material and property , also the forces received by that component/part from the previous components
   
   Thus there would be differences in the stresses of every component
   
   Since the shotgun positioned after the rails , the forces received by the shotgun were after the rails
   
   In TH , for a time of 80ms , it could be seen that the forces initailly were low and then increases ( This is due to , once the rails receive the forces initailly , it then passes remaining forces )
   
   Thus for a period of 80ms , the forces received by the shotgun were at the period of 20ms to 45ms approx.
   
   
   
4. Hinge pillar
   
   
   
   Similar to other components , there were differences observed in the hinge pillars due to several reasons like explained before ( depends on absorption of forces with nature of material and property )
   
   Initailly the forces received by the hinge pillars were low due to its positioning , gradually increases as time increases
   
   Forces seems to be received less compared to bumper rails and shot gun , since the hinge pillar located behind those components and obviously the stress would have been absorbed by them and remaining reaches the hinge
   
   
5. Inner pillar
   
   
   
   After bumper rail, these were the components to receive more forces and results in higher stresses
   
   Due to position of this component right next to rails and the area of cross section was much more than shot gun , hinge pillar and A pillar , ( the stress concentration were seems to be more )
   
   Inner pillar , initially at low stresses due to time . Since initially the rails were only components receiving forces and as time passes the inner pillar receives the forces
   
   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.
   
   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 ( Bumper rail )
   
   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
   
   
   

Intrusion of dash :

1. To determine the intrusion of a particular position ( as per requirement ) TH were plotted with time against displacement
   
   
2. There were 2 nodes ( 66695 & 66244 ) given to find its intrusion , which were plotted for displacements over a period of simulation time 80ms
   
   
3. And found to have displacements almost similar for a period of 80ms
   
   
4. There seems to be very gradual increase in the displacement due to deformation
   
   
5. Displacement of about 900mm for a period of 80ms was observed

Acceleration curve :

1. To determine the acceleraion over a particular position , accelerometer mounted and plotted to TH to determine acceleration over a period of time
   
   
   
   
2. Acceleration generally is change in velocity with time
   
   
3. By observing the graph , it shows that the acceleration has increased at the time period of 50ms to its maximum position
   
   
4. This was due to the velocity at that time period would have been maximum
   
   

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 increases to 0.1% --> 0.8% ( shows absorption of energy )

Then decreases to 0.0% --> -1.8% ( Shows dissipation of energy )

But overall the energy error was maintained 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 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 , frontal crash simulation have been carried out using Hyperworks ( Hypermesh ) , under recommended inputs and required outputs

Analysis for the simulation have been studied

Model and files :

.h3d - https://drive.google.com/file/d/1tACn02UDFI4QnLGCwWibtYl1kkA1iS5X/view?usp=sharing

T01 - https://drive.google.com/file/d/1-m1v8XDD3u-EYpLIpsDVl8fl42SDmh0S/view?usp=sharing

Model - https://drive.google.com/file/d/1T-wTNHeI1KZjPXDxQQ9ya18cXaHvDeE8/view?usp=sharing