Assignment 6-Frontal Crash Simulation Challenge
Frontal Crash Simulation
Objective:- To perform frontal crash analysis in the neon model with the recommended parameters and output requests.
Problem Specification:-
Frontal crash-BIW
- Check unit system and either follow[Mg mm s] or [Kg mm ms].
- Create appropriate interface ,friction 0.2 and recommended parameters.
- Make sure of no penetrations and intersections.
- Correct rigid bodies if any issues.
- Create rigid wall with friction 0.1.
- Compare the model weight with the full scale 300k nodes model and use added masses to reach target weight 700kg while getting CG about the required range.
- Initial velocity 35 mph.
- Use model checker to ensure good quality.
- Time-step :0.5 to 0.1 microseconds.
- Run 80 ms.
Output requests:
- Sectional force in the rails at location of indicated node 174247.
- Axial force received on the rails from bumper.
- Shotgun cross sectional forces.
- A pillar cross section.
- Acceleration curve received on the accelerometer at base of B pillar (on B pillar rocker).
- Intrusions on the dash wall 66695,66244.
Procedure
1) Check the unit system
Open the given starter file to check the unit system.
2) Check the intersections and penetrations
Go to Tools>Penetrations Check> Select the components
( There were no penetrations and intersections found in the model)
3) Interface creation
Create a type 7 interface for all the components of the model. Go to Solver>Create>Inter>Type7. Set the recommended parameters.
Select all the components in the master surface and slave nodes.
4) Rigid wall creation:
Create the outermost node on the bumper of the car using the temp node option
Right-click on the solver browser and go to Create>Rwall>Plane.
For the location of the rigid wall select the created temp node and provide a 10 mm translation on the x-axis so that wall cannot touch the model. Define the normal in the negative x direction.
5) Mass Balancing
Go to Tools>Mass Details> Mass ,Cog and Inertia
Initially mass of the model is 188 Kg, in order to represent scaled model into full car model, the mass should be converted to 700 Kg.
Right click on the Solver deck and create ADmas card to add mass to the model.
An additional mass of 51.2 kg is added to each node so that the full car model is represented.
(Here COG is located exactly near the driver's seat)
6) Initial Velocity
To create initial velocity right click on the solver browser and then navigate to Create>BOUNDARY CONDITION>INIVEL.
Under INIVEL card select all the components as the entity for grnd_ID.
Specify the velocity of 15.6464 mm/ms in the x-direction.
Run Time and Time step:
Go to Cards under Model browser, To check the run time open the ENG RUN card and set the Tstop as 80 ms. For the time step, open the ENG_DT_NODA card and change the Tmin value to 0.5 microseconds or 0.0005 ms.
Output requests:
Cross-sections:-
The results which we want on required cross-sectional parts will be calculated based on the frame of reference. So before creating cross-sections create the moving frame on a particular node of that section.
To create the moving frames right-click in the Solver browser and navigate to Create > FRAME> MOV. Select the nodes for the x-axis and XY plane and then click on create.
Thus a moving frame will be created. Now create the cross section for this frame. To create a cross-section, right-click on the Solver browser and navigate to Create > SECT> SECT. In the section, the panel specify the Frame_ID as the moving frame, delta value as 0.1, and specify alpha as 0.628 Then select the elements for cross-sectional results
Similarly, create the cross-sections at required parts namely A-pillar, Shotgun or Fender, Bracket, and Rail. These cross-sections will be created on both sides i.e. left side and right side of the vehicle.
After creating the cross-sections, to request the results in TH or time history go to Output Blocks under the Model browser. Then right click and create a new output block. Under the Entity IDs option, select the cross-section created and thus we will be able to plot graphs of the cross-sectional forces in HyperGraph.
In the same way, create the output blocks for the remaining cross-sections.
Accelerometer
To create an accelerometer, right-click in the Solver browser and navigate to Create > ACCEL Then in node_ID_ select the node on the B-pillar and specify F_cut.
Create the output block of the accelerometer.
Intrusion -
To find the intrusions on the dash wall at nodes 66695 and 66244 respectively create skews at the Seat reinforcement part
Then create the output blocks for the nodes.
The axial force received on the rails from bumper
To calculate the Axial force received on the rails from the bumper create another type 7 interface for the component behind the bumper. Then create the output block for it.
Model Checker:
Before starting to run the simulation, it is necessary to check for errors in the model. For this use Tools > Model Checker > Radioss Blocks.
After running the checks, click on the Autocorrect command through which the software will automatically perform the possible corrections and give a green tick in the status bar From the above figure, we can ensure that the quality of the model is good for simulation. The error which says the nodes NI, N2, and N3 are badly defined, can be ignored as the sections are assigned to moving frames that are created separately. Other errors and warnings can also be ignored.
Simulation and Results
Now run the simulation Go to Analysis>Input file>Include connector>Options= -nt 4
Open. out engine file from the saved folder and check the final value of energy error, mass error, simulation time, and total no of cycles.
( In this case, the energy error is -0.9% and the mass error is 0.11% which are in the acceptable range)
Now Plot the required curves using Hypergraph 2D and the required animation using the Hyperview.
In the above crash simulation of the vehicle, we can see the vehicle's body is impacting the rigid wall. As this model is a reduced model and not a complete model, the deformation is unrealistic.
From the Von Mises stress plot, we can say that the stress distribution is quite good in the vehicle after the crash. There are very few areas where we can see stress concentration. Generally, the stress is more in the bumper region as it is the first point of impact.
Energy curve
Observations:-
- The total energy is constant throughout the simulation.
- The kinetic energy is very high at the beginning of the simulation then after it gets converted into internal energy.
- Contact energy is generated because of the type 7 contact.
Cross-Sectional Forces
- A-Pillar:-
- The resultant force experienced on the left A-pillar is more than that of the right A-pillar.
- Shotgun:-
- The maximum resultant force experienced on the shotgun component is close to 1KN
- Rail:-
- The maximum resultant force experienced on the rail component is close to 4.5 KN
- The resultant force experienced on the left rail is less than that of the right rail component.
The axial force received on the rails from bumper
- The maximum axial force received on the rails from the bumper is close to 2.3 kN.
Accelerometer:-
- The maximum acceleration experienced is 0.16 mm/ms2.
Intrusion:-
The displacement at node 66244 is 1000 mm and the distance between the node 66244 and the node of its respective skew is 791.545 mm. Thus the intrusion at the node with ID 66244 is 1000-791.545=208.455 mm. Similarly, the distance between the node ID 662695 and the node of its respective skew is 770.360 mm and the resulting intrusion is 900-770.360=129.64
Conclusion:-
Thus, the model was simulated for a frontal crash test and the results were discussed. From the output file, the energy error and mass error are in the acceptable range so it concludes that the simulation is pretty stable. Results are not the most accurate even though the mass is balanced & COG is located at its exact position for more accurate results, it is advised to use a full-scale neon model for the simulation.