Assignment 6-Frontal Crash Simulation Challenge

Assignment 6-Frontal Crash Simulation Challenge

AIM:

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 intersection.
• 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:

The model is imported using the import option hypermesh or hypercrash.

The unit system is checked in the rad file and it is found to be kg mm ms or if you are using latest version of hypercrash starting only it will show the units.check for the pentrtions in tool>penetration check.

Open hyper crash and make the cg near to the driver seat (target weight is 700kg).

CREATE SELF CONTACT:

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

CREATE RIGID WALL:

Go to Slover browser >Create > Rwall > Plane

CREATE VELOCITY:

Initial velocity 35 mph.Converting 35mph into ms 1mph = 0.447 ms. So, 35mph = 15.6464 msTo create a velocity Go to solver browser > Create >Boundry conditions (BC) > Inivel .

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 >

CREATE ACCELERATION NODES:

Creating Accelerometer at both sides of the B pillar.An accelerometer is a basic technology that converts mechanical motion into an electrical signal. It is an electromechanical device that measures acceleration forces, whether caused by gravity or motion.To create accelerometer Go to Model browser > Create > Accelerometer > Select Node_ID > Select node > Proceed

CREATE SPRINGS:

We are setting two Spring elements to study the intrusions.Create 2 parallel spring elements from the indicated nodes (66695,66244) till the Crossbeam.Springs can be created from the 1D Panel > Springs To create a spring first as temp node at that particular node id then select another node on other to see deflection after crash.

CREATE PROPERTIES TO SPRINGS:

To create spring property Go to Components > RigidBody > Property > P4 spring type is selected, mass and stiffness value is assigned.

REQUESTING TH FOR INTRUSION SPRINGS, ACCELEROMETER, SECTION FORCE:

Delete existing TH and create new.There are some Output files that are requested in the Starter File.We can create the Output requests from within the Solver Browser:

Solver Browser > Right Click > Create > TH > Select the Output Request

Output Requests	Boundary Conditions
INTER	i. Self Impact ii. Left Bumper and headlight iii. Right Bumper & headlight
ACCEL	i. On Left B Pillar ii. On Right B Pillar
SPRING	i. Intrusion on node 66244 ii. Intrusion on node 66695
RWALL	i. Rigid Wall
SECTION	i. Left Rail ii. Right Rail iii. Left A-Pillar iv. Right A-Pillar v. Right Shotgun vi. Left Shotgun

CREATE REQUIRED CARDS:

TIMESTEP CONTROL

Engine Card	TSCALE [Scale factor]	Tmin [Critical Timestep]	Description
ENG_DT_NODA	0.67	0.001	Mass is added to the node when the computed timestep becomes smaller than the critical timestep.
ENG_DT_BRICK	0.9	0.0001	Controls the timestep by small strain formulation on the elements if they cause the timestep to drop.
ENG_DT_INTER	0.9	0.0005	Uses the default constant timestep method.

Then using model checker option errors were checked and in that the unused cards are deleted.

The warnings can be ignored.

RUN THE ANALYSIS:

Analysis > Radioss > Input File: (File Location) >Radioss open the results in hyperview

HyperView > Frontal_crash.h3d > Apply

Displacement:

VonMises:

From the simulation, we can see that, Initially, the bumper starts crushing then the bumper forces are transferred to the left and right rail from the rail forces are transferred to A-Pillar left and right. In each stage, the forces are going to reduce because energy is absorbed in each stage. Because of no engine blocks, suspension system etc the car BIW is going to go down at the end of the simulation.

Results after simulation:

1) Energy and Mass error:

Check for energy and mass errors at the simulation's conclusion to see whether the findings are acceptable. To check for the Energy error and Mass error, open the save location file and click on the simulation output file. A negative mistake indicates that some energy has been lost. The Hourglass Energy can explain a negative Energy Error in the case of underintegrated components (Belytschko shells, solids with one integration point), as it is not included in the energy balance. 10% to 15% is the typical quantity of Hourglass energy.If the error is positive, there is an energy creation.In the case of using QEPH shell formulation or fully integrated elements, the Energy Error can be slightly positive since there is no Hourglass energy and the computation is much more accurate. An error of 1% or 2% will be acceptable.In the case of a larger positive energy, the source of this energy has to be identified. Incompatible kinematic conditions can lead to such a situation.If the error reaches ±99%, the computation has diverged; except in the first cycle of a run for which the initial energy of the system was null so that a relatively false energy balance often introduces large relative error.

After simulation run

Check the Starter Output File for Errors:

1. A starter Output file of .out format is generated after analysis.
2. The Output file contains the data during simulation, such as Cycle, Timestep, Energies, and Errors.
3. We have to check for energy and Mass error which means that the solver did not need to add mass onto the nodes to reduce the timestep to further avoid the Hourglass Error.

OBSERVATION:

• The Energy Error is Negative and it is in the range -3.0% which is acceptable.
• Mass error is 0.3898E-03 which is acceptable.
• We can conclude that there are no errors in the analysis.

PLOT THE GRAPH AND COMPARE RESULTS:

The tools to plot the graph are available on Hypergraph.

Hypergraph 2D > Data File > Frontal_CrashT01 > Apply

A hypergraph is a data analysis and plotting tool that represents the FEA from the simulation in graphs with respect to the selected unit system.

INTERNAL ENERGY AND KINETIC ENERGY:

Energy distortion is what internal energy is. We all know that energy cannot be generated or destroyed, thus as the kinetic energy decreases, more energy is absorbed by the system. The initial kinetic energy will be high once the vehicle has reached a specific speed, let's say 15.646 mm/s for the model. Once the stiff wall strikes the automobile, the car begins to deform, collecting the surrounding energy and storing it. Internal Energy begins to rise as a result. At the point of maximum deformation, the velocity will zero out and the kinetic energy will likewise zero out, leaving the system with no energy to absorb. Internal Energy remains constant as a result moving forward.

CONTACT ENERGY AND HOURGLASS ENERGY:

From the above graph, we can see that the Hourglass energy is almost negligible since we have used Improved integrated element formulation (QEPH).

Ideally, all of KE should be converted into IE and the Total Energy must remain constant, but in our case, since we have Hourglass Energy error, our Total Energy is decreasing. We can rectify this hourglass energy by further reducing the Timestep of the simulation and giving the Ideal Properties wherever we can. Our Requirement from an Ideal Simulation is that we have minimal Contact energy and maximum Energy absorption/Deformation in the elements. We can check the Energy error in the Engine output file, which has maxed out at -1.4% to 0.8% which is within the limits. Our Mass error is also very minimal which means that the solver did not need to add mass onto the nodes to reduce the timestep to further avoid the Hourglass Error.

Contact Energy is nothing but the opposite energy generated from the System to Avoid Penetration. To avoid penetration, we have determined the Gap min value to 0.5. When the car is moving with a velocity of 35mph and hits the rigid wall, it starts deformation at the bumper section and hence the penetration of the elements occurs and thus the opposite reaction force also exerted in order to avoid the penetration. Hence the contact energy increasing gradually from zero.

SECTIONAL FORCES:

1. On RAILS:

The maximum cross-sectional force at Left Rail is 32.5 kN/mm at t= 20ms whereas the maximum cross-sectional force at the Right rail is 33 kN/mm at t=20 ms. The force acting on the rail is the force transmitted by the bumper during the crash. The force transmitted by the bumper to the rail can be unequal due to which the force received at the LH rail may differ from the RH rail. During a crash, the rail will get into direct contact with the rigid wall which will increase the compressive force and then deform. Therefore, the compressive force drops down.

2. On Shotguns:

The maximum cross-sectional force at Left Shotgun is 8 kN/mm at t=49 ms whereas the maximum cross-sectional force at Right Shotgun is 5 kN/mm at t=49ms. The Force that occurred at the shotgun is the force transmitted from the rail section. The force propagation is not the same at both the rails and hence the amount of deformation at both the shotgun sections are different. Once the Compressive force reaches its maximum value it starts to deform rapidly. Therefore, the Compressive force is decreasing as referred from the graph. As the crash happen continuously, the shotgun will come into contact with the Rigid wall as found in Animation, the rigid wall also exerts the force directly on to the shotguns and hence there is an increase in the Sectional force as seen in the graph.

3. On A-Pillars:

The maximum cross-sectional force at Left A-Pillar is 0.6 kN/mm at t= 25 ms whereas the maximum cross-sectional force at Right A-Pillar is 1.5 kN/mm at t=50 ms when the car hits the rigid wall, there will be some amount of force coming into the A-pillar at both sides. These forces coming to the A-pillar are nothing but the force transmitted from the rail and the shotgun. The force flowing into the LH and RH of the A-pillars will not be equal and hence the deformation of the elements will differ accordingly. During a frontal crash, the sectional force reaching the A-pillars are coming in from the rails and shotgun, hence the force at the A-pillars will be less when compared to the front sections. When the compressive force between the wall and car is maximum, the rail and shotgun get in contact with the rigid wall which causes the shotgun and rail to exert more force. This force then propagates to the A-pillars and hence the force reaching the A-pillar increases again.

INTRUSION SPRINGS:

To check the Intrusion at the dash wall at the particularly given node, we have created the spring over the place. The intrusion at this particular node is calculated in order to check whether the crash will result in the safety of the driver due to the deformation that occurred at the front portion of the vehicle. From the above graph, we can see that the maximum intrusion occurred in the spring (Node 66695,121754) during a crash is 100mm above and the maximum intrusion occurred in the spring (Node 66244,121868) during a crash is 110 mm above. Practically this elongation referred to which extent the foot pedal or the passenger's legs will move once the crash is happening. From the animation, we can notice that there is not much deformation that occurred at this location and the elongation is also low. Hence, we can conclude that there are fewer injuries will happen to the Passenger/driver.

ACCELEROMETER:

As we all know that an Acceleration is the rate of change of velocity. To measure the acceleration, we have placed the accelerometer near the Rocker of B-Pillar on both sides. From the above graph, we can see that initially, the acceleration is constant before the vehicle hitting the rigid wall. Once the Car hits the rigid wall with the initial velocity, The acceleration of the vehicle during the crash is not constant across the structure. The front of the vehicle slows down immediately as it hits the rigid wall, while the rest of the structure decelerates at a slower rate as seen in the graph. As seen from the graph there is a sudden increase in the acceleration, this might be because of some vibration that occurs during the crash with respect to the point where the accelerometer is placed.

Maximum acceleration at LH = 17 mm/ms2 at t=20 ms

Maximum acceleration at RH = 14 mm/ms2 at t=25 ms

Learning Outcome

1. Learned how to set up a frontal crash test.
2. Learned how the Rigid wall interface works and can lead to incompatible Kinematic conditions.
3. Learned how Sectional forces are generated.
4. Learned how the distribution of forces among the components during a frontal crash.
5. Learned how some components are designed to deform in such a way to ensure the safety of the passengers inside the cabin.
6. Learned how to check for Energy, mass, and momentum balance.
7. Learned how to Debugging errors in order to get the right results.

CONCLUSION:

The given model was simulated for the frontal crash using Radioss and the results obtained were validated. The graphical results were plotted for all the test cases. From the simulation, it can be observed that there was minimum deformation in the cabin, and also minimum intrusion was found in the driver’s seat area.