Assignment 6-Frontal Crash Simulation Challenge

Aim-

Frontal crash analysis, deck setup using hyper mesh and hyper crash.

Objective-

• To check the unit system and either follow [Mg mm s] or [Kg mm ms].
• To create the appropriate interface, friction 0.2 and recommended parameters.
• To make sure of no penetrations and intersections.
• To correct rigid bodies if any issues.
• To create a rigid wall with friction 0.1.
• To 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.
• To create an initial velocity of 35 mph.
• To input Time-step:0.5 to 0.1 microseconds and Run 80 ms.

Steps to follow-

• Check for UNIT SYSTEM
• Import model in HYPER WORKS
• Check for penetration and intersection
• Add masses to reach a target weight of 700kg 
• Export changes file and import in HYPER MESH
• Create Interface contact's
• Create interface contact between component and bumper
• Create a rigid wall
• Add velocity to the nodes
• Create cross-section's
• Create acceleration nodes
• Create MOV sckew/frames for intrusion O/P results.
• Create TH for section forces, intrusion springs, interface contacts 
• Create cards
• Model checker

Procedure-

CHECK FOR UNIT SYSTEM-

In the data, we have two files 

 The starter file stores information about:

• To check unit Go to Neon_front_0000.rad file >> Open >> check the unit system.

• Here some setup is done by Hypercrash and the remaining setups are done in Hypermesh.
• To open 0000.rad file we have to first open hypermesh.
• After Importing, we get the model, then go to Model Browser>Cards>BEGIN_CARD.

CHECK FOR PENETRATION AND INTERSECTION-

• Penetration is defined as the overlap of the material thickness of shell elements, while Intersection is defined as elements that actually pass completely through one another. All models and especially impact models should be checked for penetrations and intersections and De penetrated to ensure the integrity of the model. Penetrations adversely affect results and should be removed.
• To check penetration and intersection.
• To open hypercrash we have to first open hypermesh 

• Selecting Proper UNIT SYSTEM
• Select Neon starter file and drag it to hypercrash application to open the model.

• Got to Quality>> Check Intersection on tree >> Select parts > Click on check penetration.

• No intersection and penetrations present
• We can clearly see from the above figure there are no penetrations and intersections are present in the model.

• A vehicle’s center of gravity, or CG, is the theoretical point where the sum of all of the masses of each of its individual components effectively acts. In other words, from a physics perspective, a vehicle behaves as its entire weight resides at this one point. Carrying weight up high, such as a panoramic sunroof will raise a vehicle’s CG while placing heavy subsystems low in a vehicle, such as a battery pack, will work to lower it. Lower is better from a handling standpoint, as it reduces weight transfer during cornering and braking, and it also reduces the propensity to roll over.

ADD MASSES:

Mass balancing: In order to maintain the CG of a car we have to add mass for the given components, In the given model here are so many parts are missing because of the node limits in the student version

• To check the CG Go to menu >> Mass >> Balancing >> Show CG point 
• Before adding mass check the CG.

Current weight: 188 kg

Target weight: 700 Kg

• We have to add the mass in such a way that the Centre of gravity is exactly in the middle of the Cross Beam to simulate the real-time model.
• We are only worried about the position of the COG (X and Y axis) and not the height (Z-axis).
• We use Type 1 Mass, where mass is distributed on each node of the selected group.
• Added Mass > Create New >> Type =1 >> Enter the Value (ex. 85kg) >>right click to pick nodes >> Select the group node by selecting in the graphics >> Select Add/Remove nodes by picking selection >> After selected hit YES >> Save.

• Mass type selected is 0, where each node is given the specified mass.

• Then the nodes where the mass to be given is selected.

• Similarly, 25 nodes for 20kg each, 11 nodes with 1kg each and a node with 0.5kg is selected each under different ADMAS collector.

• Then, the mass and COG is checked in Hypermesh. To view the COG position, a point is created with the obtained COG cordinates,

EXPORT HYPERCRASH FILE-

• Export the changes made in hypercrash and import the same file in hypermesh to make other changes
• For that Go to File >> Export >> RADIOSS

• Now import the same file in hypermesh to do other changes 
• For that open hypermesh Go to file >> Import solver deck >> Select Neon_0000.rad file >> Import.

CREATE SELF CONTACT-

• In this case, the Type 7 Contact Interface is defined. Interface TYPE7 is a multi-usage impact interface, modeling contact between a master surface and a group of slave nodes. It is also possible to consider heat transfer and heat friction.

TYPE 7: NODE TO SURFACE

The recommended properties are as following:

1.Igap = 2 (Variable Gap took into account.)
2.Gapmin ≥ 0.5mm (minimum thickness to avoid the numerical issue.)
3.Inacti = 6 (remove initial penetrations wherever possible, else reduce to less than 30% of the defined gap)
4.Istf = 4 (Stiffness based on softer Segment)
5.Stmin = 1 kN/mm (Minimum stiffness in contact to avoid too soft contact.)
6.Idel = 2 (remove slave nodes from contact because of element deletion)
7.Iform = 2 (Frictional Forces are calculated on the basis of Stiffness parameter.)

• Creating new self contact(type_7).
• Then after this step, we simply need to give in the Slave nodes and the master segment. Since we are defining a Self-Impact in the model, the Slave and Master segments for this contact will be the entire given model. So, we then select the slave and master in the graphics area.

• Recommended properties

CREATE RIGIT WALL:

• A rigid wall is a nodal constraint applied to a set of slave nodes in order to avoid the node penetration to the wall. If contact is detected, then the slave node acceleration and velocity are modified. Mainly to constrain the movement of a moving body after impact, we will be using a plane wall. An infinite plane wall is a plane that extends to infinity. It is defined with two points.
• Rigid wall entities provide a method for treating a contact between a rigid surface and nodal points of a deformable body. In the Radioss user profiles, rigid walls can be created in the Model and Solver browsers. 
• To create an RWALL Go to Slover browser >> Create >> Rwall >> Plane.

• We need a reference node to create an RWALL so for that we are creating a temp node in the mid of bumper.
• Now translate this node to some distance with the reference of this translate node we have to create an R-wall with respect to that CO-ORDINATES.

• Now select the translated node and note down the X, Y, and Z coordinates.
• It is a Shell element with no thickness (gap) and infinite thickness.
• A search tolerance is given (optional) so that the nodes within the range will be taken as slaves.
• We are going to create an Infinite plane-type Rigid wall.
• Enter the coordinates of the Temp node [XM, YM, ZM] >> Enter the Direction of the Normal [-1, 0, 0] >> Dsearch : 1000 >> ok

The rigid wall is facing opposite to the car so the normal is on the negative X-axis.

1. We have to provide frictional parameters for the rigid wall when the slave nodes come in contact
2. Friction type [Slide] = 2: Sliding with friction
3. Frictional Coefficient [FRIC] = 0.1
4. The D-search distance we can use around the range of 1000 mm. All the Nodes within this distance will be considered as salve nodes for the contact between the car and the Rigid Wall.

CREATE VELOCITY-

Initial velocity 35 mph.

Converting 35mph into ms 

1mph = 0.447 ms

So, 35mph = 15.6464 ms

• The initial velocity (Vi) is the velocity of the object before acceleration causes a change. After accelerating for some amount of time, the new velocity is the final velocity (Vf). 
• Initial velocity = [Final velocity - (acceleration×time)]
• v_i = v_f - at.
• v_i = initial velocity (m/s).
• To create a velocity Go to solver browser >> Create >> Boundry conditions (BC) >> Inivel.

•  Go to grnd_ID and right click on it and hit Create.

•  Set the entity selector to components and select all the components.

• Select the type as TRA. In the velocity component, enter Vx = 15.65 since we want the velocity in the global X direction and Vy and Vz = 0.

CREATE SECTIONAL FORCES-

• Creation of Sections at A-Pillar, Shot Gun, rails, and the Bumper in order to Study the sectional forces.
• We have to know how the forces are transmitted from the Bumper to the Dashboard and the rate of deformation. It is done in order to ensure the safety of the passenger.
• Certain components have to crash (deform) more than the other so that the forces are distributed correctly leaving very little force left to transmit inside the cabin.

We are creating sections for the following parts:

• To create a section and Frame Go to Slover browser >> Create >> Section >> SEC >> Rename as LEFT RAIL

• Now when we create a section a new tab will display their we have to select N1, N2, and N3 nodes
• We then need to select the three nodes on which we need the Frame system.
• In this case setup, we need to define around 8 sections.
• We need to make sure that the normal of all the sections defined need be in one particular direction. All the normal can be facing either the wall or even away from the wall. We need to make sure that they are in a single direction. 
• We can create a Section just in the same way as we created a section system.
• We need to right-click in the solver browser and select frame.

•     Selecting frame nodes.

• Assigning Th history plot of selected sections for getting the forces.
• Also we will define the TH history for accelerometer as well.

• Now as per requirement we will create moving sckews for the nodes 66695 & 66244.
• For that we have to go to radioss tools>>sckews and frames and there by we have to create the MOV frame for instruction calculations.

CREATE REQUIRED CARDS-

TIMESTEP CONTROL

• Enter T stop as 80ms and T freq as 5
• Go to ENG_RUN enter T stop as 80ms 
• For T freq 
• Go to ENG_ANIM_DT enter T freq as 5 

MODEL CHECKER-

• This is the last and final check before giving it for simulation.
• The Model checker will give us any warnings and Errors regarding the model definition and, the boundary and Kinematic conditions, etc.
• For example:

1. Boundary Condition is not defined properly
2. Incompatible Kinematic Condition
3. The Part Property or material is not defined properly, etc.
4. We can avoid the Warnings as the solver will take care of them.
5. But we must fix every Error in order to get a successful simulation free of problems.

 Tools > Model checker > Radioss block > Check Runs

 Run For Check Errors

• After running the model the we got to know that there are some errors in the model which we will clear by auto fix option.

• Running auto correct will take some time and try to clear the errors.

• Errors are removed we only left with some warnings which is acceptable.

RUN THE ANALYSIS-

• Analysis >> Radioss >> Input File: (File Location) >> Hit Radioss
• The input file is the same Started file (contains model information) that we had just imported.
• The animation video along with the frames will be saved in the same folder where the starter file exists.

Conclusion-

Frontal crash analysis was carried out on the given front half of a BIW model of the Dodge Neon as per the given requirements. The output requests were also generated after the creation of cross-sections in each of those regions. Acceleration and intrusion values were also measured at certain points of the model. The analysis also proves the importance of the crumple zone - which is the front portion of the BIW in this case. It absorbs most of the forces generated during a frontal crash and therefore, protects the occupant(s).