Neon frontal crash Analysis on BIW model using Hypermesh RADIOSS

OBJECTIVE

In this challenge, we check and create the properties for a Neon frontal crash-BIW model and run the simulation & observe results.

Question:

Frontal crash-BIW

  • Check the unit system and either follow[Mg mm s] or [Kg mm ms].
  • Create an appropriate interface, friction 0.2 and recommended parameters.
  • Make sure of no penetrations and intersection.
  • Correct rigid bodies if any issues.
  • Create a 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.
  • Timestep :0.5 to 0.1 microseconds.
  • Run 80ms.

Output requests:

  • Sectional force in the rails at a location of indicated node 174247.
  • The axial force received on the rails from the 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. We keep the unit system is [kg mm ms]. We can go to the starter RAD file and check the unit system is given.

2. Create Type 7 Interface contact in which we give recommended properties.

  • Igap=3: To avoid initial penetrations, the solver considers the variable gap with the gap scale correction factor, and also the size of the mesh is taken into account.
  • Fscalegap = 0.8. Gap scale correction factor. The gap nodes and segments keep on changing because of constant vibration generate while calculating the force.
  • Gapmin=0.5
  • Friction = 0.2
  • Idel= 2 i.e. when one element is deleted, the master segment is removed from the contact and slave nodes became free are also removed.
  • Inacti=6,  It adjusts the master segment to remove the initial penetration and it increases stability and gives space to nodes for vibration.
  • Istf= 4, By this we calculate Initial contact stiffness Ko= min. (Km, Ks)
    km= master segment stiffness
    and Ks= equivalent nodal stiffness
  • Iform= 2, Friction based on stiffness formulation: sliding forces are computed using stiffness parameters of the interface
  • Stmin=1 kN/mm, Minimum stiffness to avoid too soft contact

We make two interface contact card:

a) One is of self contact in between the nodes and elements of the car itself. All nodes are the slave and all elements are master.
b) Another is in between Bumper and rails only. Bumper as master and rail as a slave. This we make because we need to know the Axial forces and sectional forces received on the rails from bumper

3. For checking Interference and penetration, we can check into Hypermesh and Hypercrash both.

while checking into Hypercrash some errors I got we can fix into Hypercrash itself but there is a problem, we cant export the file and open into Hypermesh because in the student version of Hypercrash node limit is 10,000 for exporting. so, it shows this command "please reduce the no. of nodes below 10,000"

So, we check the error in Hypercrash and fix it into Hypermesh.
we can see errors in Hypermesh also can fix it into Hypermesh itself and sometimes we did this too.

But if nodes are under the limit then it is preferable that we fix errors in the Hypercrash itself because in Hypermesh we can see the Node id and can directly reach that node by search option.

4. Create a Rigid wall with a friction value of 0.1 and give search distance Dsearch = 1000.

5. Masses are added to reach target weight 700kg while getting CG about the required range. Near to the seat Reinforcement.
The position of C.G in both vertical and horizontal directions influences acceleration to a very large extent. So it should be in the proper place.

6. Initial velocity 35 mph which is equal to 15.64 m/s or mm/ms.

7. Timestep 0.5 microseconds and Run for 80ms and frequency of animation file are 5. so, by this we get 16 animation files.

After doing all this work, again we run model checker & ensure good quality by checking errors and warning.

After that, we run the simulation.

 

RESULTS

1. For getting sectional force in the rail at a location of indicated node 174247, we make TH card with the cross-section over that node.

The highlighted part in the gif shows the areas on which take crosssection.

In the rail section, we get the max. value of total resultant force is 22.5 KN at around 15 ms (4th frame). Again it fluctuates.
Force decreases because at that time the rail of the front part of BIW crumples so the back part of the rail gets space to move further and little force decreases and increases.

2. The axial force received on the rails from the bumper.

  • The axial force can be checked by resultant normal force on the rail.
  • The peak value of force is around 42 KN at around 15 ms. after that it again decreases suddenly and keeps on decreases.

3. Shotgun cross-sectional forces.

  • The left side shotgun having more forces at the beginning but around after 30-35 ms the right side shotgun experience more force.
  • The sudden hikes in force value around 32 ms on the right side shotgun up to 14-15 KN and fluctuates and decreases.

4. A pillar cross-section.

  • Right side A-Pillar experiences more force as compares to Ls A-pillar, value of force fluctuates between 0-7 KN. 
  • Both Fluctuates at the beginning and increases in value around 5-8 ms and again fluctuates.
  • The left-side A-pillar experience around 5 KN force maximum. 

5. Acceleration curve received on the accelerometer at base of B pillar (on B pillar rocker)

  • Max. Acceleration on the right side (by accelerometer-1) is 19 mm/ms^2 and after is keeps on decreasing with fluctuation.
  • Max. Acceleration on the left side (by accelerometer-2) is 34 mm/ms^2 and after is keeps on decreasing with fluctuation.
  • We know, the change in acceleration w.r.t. time is called Jerk. So by the graph, we get to know that BIW experiences some jerk while crashing.

6. Intrusions on the dash wall of node 66695 & node 66244.

                                                                    Before Crash

 

                                                                  After Crash

  • The relative displacement of node 66244 is 881.356 mm and node 66244 is 896.632 mm w.r.t global coordinates in the x-direction.

7. Energy curves plots 

  • We all know that kinetic energy is converted into internal energy while crash, as element gets deforms it absorbs energy.
  • The decrement we observe in total energy is due to some energy gets converted into contact energy.

  • The contact energy is increased to avoiding penetration between the elements by increasing the stiffness.
  • Contact energy keeps on increasing. As the simulation stops at 80 ms if it keeps on running we get more value of contact energy.
  • In beginning Hourglass energy increases after that, it became nearly constant.

8. Energy error & Mass error 

  • The max. energy error is -2.7%, we can check in the Engine OUT file. It is within considerable limits.
  • Energy error is negative so it means -2.7% energy dissipates during the simulation.
  • There is zero mass error. As we know if time steps are decreasing then the mass is added to maintain the imposed time step.

CONCLUSION

Successfully performed the Neon Frontal Crash simulation and the following observations are analyzed.

  • Increase mass according to the requirement and change center of gravity keep it on proper position.
  • Create a Rigid wall at the required position.
  • Create a TYPE-7 interface contact with the recommended parameters.
  • The max. value of sectional force in the rail is 22.5 KN.
  • Acceleration curve received with the help of an accelerometer. Max. acceleration value is 34 mm/ms^2.
  • Understood, how to rectify and fix errors via model checker in Hypermesh and Hypercrash also.

 

Neon frontal crash Analysis on BIW model using Hypermesh RADIOSS

Google drive link of files-

https://drive.google.com/open?id=1xOQSnV9Lifgq5mTiGmUmlZzOtKPwRawB

 

 

 


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