Assignment 7-Side Pole Crash Simulation Challenge

Question:

Neon side 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 penetration and intersections.
• Create a rigid pole with a friction of 0.1 as per the FMVSS 214 standards.
• 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.
• Initial velocity - 20mph, as per the standards.
• Use a model checker to ensure good quality.
• Timestep:0.5 to 0.1 microseconds.
• Run 80ms.

Output requests:

• Sectional force in the cross member.
• 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.

Solution :-

 

Step 1 :- Intersection and penetration checking :-

1. Before opening the model check units for further results from the starter input file.

 2.Import the given model "neon_side_reduced_0000" into Hypermesh GUI.

3.To check for penetrations in the model, we will go to Toolsmenu on the Menu bar and click on the Penetration Check option. In the Penetration check panel, we will select all the components and click on Check command. The software will check for penetrations and then display the results 

There are no penetration or intersection errors found.

Step 2: - Balancing COG: -

1.The BIW model doesn't consist of the exact weight of the vehicle so Additional mass should be added to the BIW model considering the weight of the Body after manufactures e.g. with the weight of the seats, the weight of the persons and all other weights in realistic condition.

2.The targeted weight is given 700kg where the actual mass before adding external weight is 166kg.

3.To Add the mass, Click on added mass, and to create a new object Select Type0 - Mass is distributed to each node of the node group, and click save

4.Check COG, simultaneously after giving the mass in the balancing menu.

5.Add mass according to the needs till the point reaches the centre and till the mass attains the target value. Below, image show that COG is present on required location i.e. under the driver seat.

Current weight: 166 kg

Target weight: 700 Kg

Inorder to bring CG to our required position, the masses should be added to the nodes.

For adding the masses, "Addded mass" option in the Loadcase is choosed 

 

COG location after balancing.

Step 3: - Creating contact surfaces.

1. A contact interface should be defined to view the contact energy. Here the type-7 Contact is used (Node to Surface), because of its high accuracy and correct physical representation. The self-impact is defined in the Contact interface as the body acts as both master and Slave.

1. 2. Interface properties Changed to recommended conditions as mentioned in the problem statement and create another interface for bumper and rail contacts.

Step 4 : -  Rigid wall

To create a cylindrical rigid wall at the left side of the car, we will need the outermost node at the front left door of the car. So we will create the outermost node on the element edge using temp nodes option. Then we will right click in solver browser and navigate to Create > RWALL > CYL. In the RWALL panel, under Engineering data we will specify the coordinates of the pole which will be at some distance from the outermost node on side door. Then we will give the normal direction to the pole in Z-axis and diameter of the pole to be 254 mm. The FRIC value will be 0.1 and Dsearch value will be 1000 

Step 5 :- Initial velocity :-

• In this simulation, the initial velocity given to the model is 35Mph or 15.6464 mm/ms.
• To set the initial velocity of the model LoadCase>Initial Velocity>Set the value of the velocity in Y-Direction>Select all nodes>Yes>Save

Step 6 :- Section creation. :-

• 1. The results which we want on required cross sectional parts will be calculated based on a frame of reference. So before creating cross section, we will create moving frames on a particular node of that section. Now as we have to create the moving frames which are also called as local axis, we have to perfectly align our local axis to the global axis.
• 2. Now we can create moving frame using these nodes. In Solver browser, we will right click and navigate to Create > FRAME > MOV. So here, we will create frame by node reference and select the nodes for x-axis and xy plane and then click on create.
• 3. Thus a moving frame will be created. Now we will create cross section for this frame. To create a cross section, we will right click on the Solver browser and navigate to Create > SECT > SECT. In section panel, we will specify the Frame_ID as the moving frame which we created and delta value as 0.1. From Hyperworks help menu, we get that the general value of alpha is taken as 2π10">2π102π10 . Thus we will specify alpha as 0.628. We will right click and create grshel_id, then we will select the elements where we want the cross sectional results. Thus the cross section will be created as follows.

Step 7 :- Run model checker to ensure good quality

To check the quality of the model in Hypermesh, in Menu Bar we will navigate to Tools > Model Checker > RadiossBlock. This will open a new Model Checker browser.

In this browser, we will click on Run checks command which is at the top right side in the above figure, indicated in red box. After running the checks, we get zero errors only warning are shown we can ignore these warnings and move further. 

Step 8 :- Set time step and runtime

To check these parameters in Hypermesh, we will navigate to Cards under Model browser. To check the run time, we will open ENG_RUN card where we will see that the model already have the run time in Tstop as 80 ms. For the time step, we will open ENG_DT_NODA card and we will change the Tmin value to 0.5 ms.

 

Step 9 :- Output request

1. Peak velocity of inner node of the door.

To find peak velocity at the inner node of the door, we will create a moving frame at the node location by using the same procedure as we used in cross section creation. Then we will create output block for the peak velocity by specifying the node and the frame or skew based on which the peak velocity is calculated

2. Intrusions at B-pillar, hinge pillar and fuel tank :-

Here, we need to find the intrusions at B-pillar, hinge pillar and fuel tank. So to find the results at the specified parts, we need to have a frame of reference. Thus we will create moving frames at the opposite side which are at right B-pillar, hinge pillar right side and fuel tank opposite side

3. Sectional forces in cross-members

For this we will go to Output Blocks under Model browser. Then we will right click and create a new output block. Under Entity IDs option, we will select the cross section that we created and thus we will be able to plot graphs of the cross-sectional forces in Hypergraph.

REQUESTING TH (Time History files ) FOR INTRUSION SPRINGS, PEAK VELOCITY NODE, SECTION FORCE:

output files requested are as shown in table below

Output Requests	Boundary Conditions
INTER	i. Self-Impact
SPRING	i. Intrusion on the Fuel tank ii. Intrusion on the B-Pillar iii. Intrusion on the Hinge pillar
RWALL	i. Rigid Wall
SECTION	i. Driver Rail ii. B-Pillar Rail

RUN THE SIMULATION:

1. Click on the analysis panel in the Hyper mesh.
2. Save the model in the local directory.
3. Type -nt 4 in option and click on Radioss.

The energy error is -1

% which is in acceptable limit. The mass error is 0.02% which also less than 5% it is acceptable. The run was “normal terminated’ which implies the processor successfully completed. There was no sudden changed in energy as well as in error

In the above crash simulation of the vehicle, we can see the vehicle body is impacting on a Pole. After the impact, the frame of the vehicle deforms and the vehicle body gets contracted around the pole with left B-Pillar as the pivot point. The CG of the vehicle is in the same axis or direction of the pole, so we can see even deformation of the frame around the pole.

Plots in Hyperview 2D :

                The plots like energy differences, displacements, velocity and normal forces are analyzed.

From the above plot, we can see that there is high amount of Kinetic energy at the start of the simulation but as the simulation progresses, the kinetic energy in the vehicle decreases and gets converted into internal energy, so the internal energy increases in the same proportion. Thus the total energy in the system is almost constant at 85000 kg*mm2/ms2 and due to some energy loss which we can see in energy error, there is some decrease in total energy. We can also see some amount of contact energy in the model as we have defined the value of friction in Type 7 interface due to which contact energy is generated.

As it can be seen in the starting, the rigid wall force generated is zero till 3 ms of simulation because of no contact, but at the 6 ms there is peak rise in the wall forces to a value of 95KN which is the point of first impact, Then rigid wall force decreases and stabilizes to a constant value between 25 to 35 kN.

As we all know when the car hits the pole first impact will be the door and due to the deformation, the inner portion of the door might hit the passengers inside the car and lead to injuries. Hence it is important that the Peak velocity at the door region is to be calculated.

From the Graph, the peak velocity of the node on the door is 9 mm/s at 45 s. The velocity of the node is almost constant before hitting the rigid cylindrical wall (up to 2 ms). After impact, there is a steep drop and then a small rise, probably due to the folding deformation created as the crash progresses (due to inertia). As time passes, we can see the velocity gradually decreasing.

 

From the above graphs, we can observe the resultant forces on the hinge, B-Pillar, and the fuel tank parts. It can be observed that the change in

resultant forces as time progresses and the model makes an impact with the rigidwall. The forces on the fueltank,BPillar and Hinge support is seen to be increasing with impact.

Section forces on the rails can also be observed.

 CONCLUSION :

Thus, the model was simulated for a side pole crash test and the results were discussed. From the output file the energy error and mass error is in an acceptable range so I can conclude that the simulation is pretty stable. Cross-members A and B are playing important role in the Impact force absorption. So, improving the cross-member material or adding some extra support element near the cross member can improve their performance, also for the Fuel tank side as we discuss earlier need some reinforcement. We can also work on the B-pillar property improvement as it's the closest part which is comes in the contact with the force during the side crash.

 RECOMMENDATION TO REDUCE FUEL TANK INTRUSION:

1. By adding anti intrusion bars in the door strengthens the assembly, there causing less deformation during side crash.

2. By adding cross members near the fuel tank reduces the intrusions.

3. By changing the material of the fuel tank or B-Pillar helps us to get a lower intrusion value. For example, high quality steel with considerable strength avoids the problem but the drawback is that it increases the mass.