Side Crash Analysis - BIW of Neon Car

Aim:

To set up the case for SIDE CRASH - BIW OF NEON car and successfully running the simulation while also observing the errors and energy changes.

SOFTWARE:

HYPERWORKS 2020

USER PROFILE:

RADIOSS

OBJECTIVE:

The objective of the challenge is to follow the below-given steps:

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 penetration and intersections.
4. Create a rigid wall with friction 0.1 as per the reference model.
5. Compare the model weight with the reference model and use added masses to reach the target weight of 700kg while getting CG about the required range.
6. Initial velocity as shown in the picture.
7. Use a model checker to ensure good quality.
8. Timestep :0.5 to 0.1 microseconds.
9. Run 80ms.

PROCEDURE:

Importing the model:

First import the starter file (.rad) in HYPERMESH by going to menu bar > file > import > solver deck. Browse the file from the system and import it.

Checking for the units:

After importing the model, check for the units. In this project, we are following the [Kg mm ms] unit system. In order to change the unit system Go to Tab bar > Cards > Begin card.

Creating the interface:

Now in order to create the interface, Go to Tab bar > Groups > right-click on it and create. In this project, we are creating a Type 7 interface. Set the below-recommended properties to create a Type 7 interface.

Note: Delete all the previous interfaces which are present under the groups.

Card image: Type 7

Gmod_id (S) (slave entities) : select all the components

Surf_id (M) (Master entities) : select all the components

Istf: 4 - It is the gap for stiffness definition, it is the interface stiffness which is the minimum of the master and slave stiffness.

Igap: 2 - It is the gap option flag. Igap = 2 is Variable gap + gap scale correction of the computed gap.

Idel: 2 - It is the node and segment deletion flag. When a 4-node shell, a 3-node shell, or a solid element is deleted, the corresponding segment is removed from the master side of the interface. It is also removed in case of explicit deletion using Radioss Engine keyword /DEL in the Engine file.

Additionally, non-connected nodes are removed from the slave side of the interface.

Stmin: 1 - It is the minimum stiffness value that can be used only if Istf value is not equal to 1.

Irem_gap: 1 - The option Irem_gap is used to deactivate slave nodes that are close to elements. But in this case, since we put the value as 1 that means there is no deactivation of slave nodes.

Stfac: 2 - Stiffness scale factor applied to the master side of the interface (if Istf is not equal to 1).

Fric: 0.2 - Coulomb friction

inacti: 6 - Deactivation flag of stiffness in case of initial penetrations. But in this case, the value is set to 6 which means the gap is variable with time but initial penetration is computed.

Gapmin: 0.5 - Minimum gap for impact activation.

Iform: 2 - Stiffness (incremental) formulation.

Creating a rigid wall:

To create a rigid wall Go to Tab bar > right-click > create > rigid wall.

Now under the rigid wall properties give the below-mentioned values and click on the arrow to select the base node (M).

Refer to the below images to create a Rigid wall/pole.

Geometry type: cylinder

XM, YM, ZM: select the base node at which we want to create the rigid wall

Normal : 0, 0, 1 - In order to give a normal direction, put 1 in z coordinate (since we are creating a pole to act as a rigid wall whose plane will be normal to z-axis)

Slide: 2 - sliding with friction

Dsearch : 1000 - Distance for slave search / Search distance

Fric : 0.1 - Friction

Diameter: 254 - Diameter of the rigid wall/pole.

Creating a COG point and balancing the mass:

The center of gravity should be exactly right below the driver’s seat (at the center of the body). To have COG at that position we need to balance the mass of the entire component/body.

First, check the current COG point and total mass of the body so that based on the requirements we can add the mass. In order to check the current mass and COG of the body Go to the menu bar > Tools > Mass details > Mass, Cog, and Inertia.

To view the COG point on the graphical screen we need to create a node by giving Cogx, y and z values. Go to the main menu page > Geom > nodes. Give the above COG values in x,y, and z respectively, and click on create to view the COG point.

Since the COG point is not at the center of the body, add some mass in such a way that the COG point is shifted at the center.

Always try to add mass at the lower portion of the body because in crash analysis the height of the COG also matters a lot.

To add mass Go to Tab bar > right click on the tab area > Create > Solver Mass. Select Mass type as 0 (it will add mass value on each node) and Mass value as 2.5.

Right-click on the gmd_id and click on create to select the nodes where we want to add the mass.

Still, the COG point is not at the center of the body and also the current total mass of the body is 366 kg approx. To reach the required mass of 700kg, create another solver mass (Solver Mass2) to add the remaining mass (i.e 334 kg approx). Select the nodes under gmd_id where we want to add the mass, give Mass type as 0 and Mass value as 4.2.

Now the COG point and total mass of the component/body have reached the required range.

Applying initial velocity:

To create initial velocity, Go to Tab bar > right click on the solver browser > create > BOUNDARY CONDITIONS > INIVEL.

Right-click on the gmd_id and click on create to select all the nodes of the components and click on proceed. Give the velocity value as 15.65 in the y-direction. (since the car is moving in the y-direction).

Note: Initial velocity is given as 35mph. We need to convert this mph value to the current unit system i.e, mm/ms. So 35mph will be equal to 15.65 mm/ms.

Penetration and intersection check:

To check the penetrations, Go to menu bar > Tools > Penetration check.

In the entity editor, click on the selection, and under groups, select the type 7 contact that we have created. In the Tab bar, we can view if there are any penetration and intersection in the model. After running the check, we can see that there is no penetration and intersection in the model.

Checking for errors:

To avoid any kind of problems during simulation, we need to perform a check for errors. To perform this operation Go to menu bar > Tools > Model Checker > RadiossBlock. In the tab bar, a new browser will open, right-click on ERROR and run it.

If there will be any errors present in the model then it will be highlighted with a cross mark. Clear the errors if there are any (currently there are no errors in the model).

Applying Time-step and run-time value:

To apply the time step value, Go to Tab bar > cards > ENG_ANIM_DT. Change the Tfreq value to 0.5.

To apply the run-time value, Go to Tab bar > cards > ENG_RUN. Change the Tstop value to 80.

Output requests:

• Sectional force in the cross member.
• The intrusion at B pillar, hinge pillar, and fuel tank region. Provide recommendations on what can help to reduce Fuel tank intrusion.
• Peak velocity of an inner node of the door.

Creating CROSS-SECTIONS:

To create a cross-section, we also need to create a frame in order to define the local coordinates of the cross-section. Go to Tab bar > under solver browser > right click and create > Frame > MOV.

select three nodes N1,N2 and N3 and click on proceed to create a movable frame.

Now create a section, Go to Tab bar > under solver browser > right click and create > SECT > SECT.

Under entity editor Select the origin node (N1), Axis node (N2), and plane node (N3) and this will create a skew.

Now under Frame ID, select the frame which we have created to define the local coordinates for the cross-section and also set the iframe value as 12. Give deltaT value as 0.1 and alpha value as 1.67.

Frame: It is a type of reference coordinate system where the quantities defined follow their own origin.

Skew: It is a type of reference coordinate system that helps in defining local quantities with respect to the global coordinate system.

deltaT: It is a time step value for saving the data.

alpha: Coefficient for filtering.

Right-click on grshell_id and create to select the elements for creating a section.

A cross-section has been created at RAIL 1. Similarly, we need to create a CROSS-SECTION for another RAIL (i.e RAIL 2).

After creating all the cross-sections, we need to call these sections in the “Output Block”. To perform this operation Go to Tab bar > under model browser > right-click on output block and create > name the new card as cross-sections > under Entity IDs select all the cross-sections which we have created and click on ok.

Creating Intrusions:

We need to create the intrusions at the given regions ( i.e, at B pillar, hinge pillar, and fuel tank region). But to create an intrusion we also need a skew to define the local coordinate system, so first create a skew. To perform this operation Go to Tab bar > under solver browser > right click and create > SKEW > MOV. select the origin node (N1), Axis node (N2), and plane node (N3) and this will create the coordinates (system) for the intrusion.

The coordinates for all the intrusions (i.e for B pillar, hinge pillar, and fuel tank) have been created. Now we need to call these intrusions in the output block and define the respective skew in the respective intrusion. To perform this operation Go to Tab bar > under Model Browser > Output Blocks > create > intrusion for B pillar, hinge pillar, and fuel tank (create separately) > under Entity IDs select the node where we want to create the intrusion and under Iskew select the skew system which we have created to define the local coordinates.

Note:

Fuel tank intrusion is at 125375 (node id).

B pillar intrusion is at 123409 (node id).

Hinge pillar intrusion is at 123368 (node id).

Applying Peak Velocity:

Peak velocity needs to be applied in the inner node of the door. To apply the peak velocity we first need to create a SKEW in the inner node of the door. To perform this operation Go to Tab bar > under solver browser > right click and create > SKEW > MOV. select the origin node (N1), Axis node (N2), and plane node (N3) and this will create the coordinates (system) for the peak velocity.

Now Go to Tab bar > under Model Browser > Output Blocks > create > Peak velocity. Under Entity IDs select the inner node of the door where we want to create the peak velocity and under Iskew select the skew system which we have created to define the local coordinates for peak velocity.

Note:

Peak velocity is created at 338467 (node id) i.e is the inner node of the door. The skew coordinate origin and the peak velocity node will be located at the same node.

Errors faced and the steps to solve them:

The final part of any simulation is checks and bug fixes during and after simulation. The only errors which we faced after setting up the case for simulation were empty sets. While creating the Center of gravity (COG) point these sets may get created and it can be deleted. Though while checking the errors through the model checker in Hypermesh it won’t show the error of empty sets but while checking for errors in HyperCrash these errors can be found and deleted easily.

To run the model checker in HyperCrash, first, export the setup case file and open it in HyperCrash. To open HyperCrash from the HyperMesh window, Go to menu bar > Applications > HyperCrash (select the unit system and run). This will open the HyperCrash window. Import the rad file (exported file from HM). Now to run the model checker in HyperCrash Go to menu bar > Quality > Model Checker > Run. Delete the empty sets and again export it. Now to run the simulation, open this file in Hypermesh and make sure to delete the unsupported cards. These unsupported cards are created by HyperCrash while exporting the file and it doesn’t make any change in the model.

Note: It is recommended to check for errors in HyperCrash before running the simulation in HyperMesh because it gives more minute and important information regarding the errors which we can face during the simulation.

Running the simulation:

After completion of all the tasks on the model, run the simulation and save it in a separate folder. To run the simulation, Go to the main menu page > Analysis > Radioss. Click on "save as" to change the file directory. Tick the box of include connectors and under the options tab, type the value as -nt 4, and click on Radioss to run the simulation.

Once the simulation is started, HYPERMESH will popup a box in which it will show the simulation process.

After the simulation run is completed, a message will show on the popup screen as the job is completed.

All the files which were generated during the simulation run such as the .h3d file, T01 file, starter file, engine file, etc will be stored in the input file directory.

Viewing Animation:

To view the animation, open HyperView. To perform this operation, Go to the Tool bar and from the client selector open HyperView, and update the animation file (.h3d) in it. Select this file from the directory folder (the new folder which we created for the input file directory). After updating it click on apply to view the animation.

Now click on the play button to view the animation.

Plotting the Graphs:

To plot the graphs, open HyperGraph 2D. To perform this operation, Go to the Tool bar and from the client selector open HyperGraph 2D, and update the time history file (TO1) in it. Select this file from the directory folder (the new folder which we created for the input file directory).

After updating it, select the cross-sections, intrusions, and peak velocity which we need to plot and click on apply.

The above graphs show all the CROSS-SECTIONS, INTRUSIONS, and PEAK VELOCITY that were applied to the SIDE CRASH-BIW.

The graphs for Internal energy, Kinetic energy, Contact energy, Hourglass energy, and Total energy vs Time are plotted below.

ENERGIES:

CROSS-SECTIONS:

RAIL 1:

RAIL 2:

INTRUSIONS:

Fuel tank :

B pillar :

Hinge pillar :

PEAK VELOCITY:

OBSERVATIONS:

A few important points have been mentioned below after observing all the graphs for cross-sections, intrusions, and energies.

From the cross-sections graph, it can be observed that the deformation of rail 1 and rail 2 is not similar. This is because the stresses develop in rail 1 are higher compared to rail 2. Due to this reason, there are a lot of fluctuations in the rail 1 graph while the rail 2 graph has lesser fluctuations.

Contact energy started to increase after 40ms, this is because the body is changing its shape very drastically during the crash which results in the elements getting penetrated causing the contact energy to rise.

From the animation, it can be observed that the side body of the car is getting deformed very quickly when it crashes to the pole (which is considered a rigid wall). The amount of deformation after the impact is not acceptable as it can result in risking the life of the occupant.

From the graphs of intrusions, it can be observed that the deformation at the B pillar is high due to the sudden impact of the pole on it. The deformation can be reduced by changing the material, which may help in increasing the stiffness of the component.

The peak velocity is having the highest frequency at the point of impact and later reducing it to a constant value. This is because the vehicle at the point of impact has a higher speed and due to collision, the speed of the car reduces which results in less deformation taking place after a certain point.

PHRASES USED:

Below we have briefly discussed the important phrases which we have been used in the above procedure.

BIW:

Body in white simply called BIW is a manufacturing stage in automotive industries where all the components of a car body (before painting), barring moving parts (e.g., hoods, fenders, etc.), trims (e.g., glass, seats, etc.), or chassis subassemblies, have been welded together. All these sheet metal components are welded together to form a vehicle structure.

INTERFACES:

Interfaces are defined to model how parts interact when they come into contact with each other. In this project, we are creating a Type 7 interface.

Type 7 interface:

Type 7 interface is a node to surface type of contact. It is a general-purpose contact and is used to simulate all conditions. It provides a cylindrical gap area around the edges which makes it more accurate. The main advantage of interface type 7 is that the stiffness is not constant and increases with the penetration preventing the node from going through the shell mid-surface.

RIGID WALL:

Rigid walls allow for an easy way to define an interface between a rigid surface and nodes of a deformable body. A rigid wall is defined by a surface type and a group of slave nodes. It is a concrete wall which will be fixed in one place. It is plotted in this case to perform a crash analysis on the body. It can sustain enough load to perform a crash analysis.

Center of gravity (COG):

The Center of gravity simply called COG is a point from which the weight of a body or system may be considered to act. It is very important that the COG should be at the center of the body during crash analysis so that the animation of the crash looks like a real-time scenario.

Initial velocity:

Initial velocity is the velocity of the object before the effect of acceleration which causes the change. It is the velocity of the body at which motion starts where time interval = 0

Penetration and Intersection:

Penetration and intersection play an important role in simulations. If any solver faces these issues then most of the time the solver may stop or it produces unrealistic results with unrealistic deformations of the component. Penetrations are defined as the material thickness of shell elements passing through one another while intersections are defined as individual elements passing through one another.

CROSS-SECTIONS:

A section is a set of nodes and a set of elements. More the sections in the body, better the force distribution, and less the pointed load. Less the pointed load we have, the less the load will be in a particular region which results in fewer injuries to the occupant.

Intrusion:

Intrusion results when the energy of the crash exceeds the strength of the vehicle frame, resulting in a violation of the occupant compartment. Injury may then occur either from direct contact with the vehicle structure, or passenger movement as a result of the acceleration imparted to the occupant from the vehicle.

Peak Velocity:

The peak velocity is the highest velocity received during the impact of an object at a given time. We have applied peak velocity at the inner node of the door to calculate the impact an occupant can receive once the car crashes.

RESULT & CONCLUSION:

Below mentioned values were noted at the end of the simulation.

ENERGY ERROR: -12.8%

MASS ERROR : 0.1205E-01

TOTAL NUMBER OF CYCLES: 80001

TOTAL SIMULATION TIME: 3282.89s

The case for SIDE CRASH - BIW was set up successfully and the simulation for the same was run in HyperMesh without any errors.