Assignment 7-Side Pole Crash Simulation Challenge

OBJECTIVE:

• Perform the side crash simulation on the neon car model.
• In this project, we are going to make sure that there is no penetration and intersection in the model. Create the rigid wall with the friction of 0.1. We have to add the mass in the car to make the total mass of the car to be 700 kg. We have to create sections and check the sectional forces there. We have to check the intrusion in the given part of the body. We have to check the peak velocity at the inner node of the door.

PROCEDURE:

• The model is imported using the import option in the hypercrash.

• The unit system is checked in the rad file and it is found to be kg mm ms.

• Initially, the penetrations are check using the check all solver contact interfaces option.

• Using added mass option in the hypercrash additional mass is added for the passenger, driver and trunk portion of the car and the total mass of about 700kg is achieved and the COG point is placed properly.

• Apply velocity to the model using the initial velocity option in the load case menu tab. 
• The given velocity is 35mph and that is equal to 15.6464 m/s.
• The velocity is applied in the y-direction.

•  Then the model is exported to the hypermesh using the export option.
• Then the model is imported in the hypermesh using the import option in the hypermesh.

 

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.

All limitations that were encountered with interfaces TYPE3, TYPE4 and TYPE5 are solved with this interface:

• A node can be at the same time act as a slave and a master node.
• Each slave node can impact each master segment; except if it is connected to this segment.
• A node can impact more than one segment.
• A node can impact on the two sides, on the edges and on the corners of each segment.
• It is a fast search algorithm without limitations.

The main limitations of this interface are:

• Time step is reduced in case of high impact speed or contacts with a small gap.
• It does not work properly if used with a rigid body at high impact speed or a rigid body with a small gap.

It does not solve edge to edge contact (to solve this, /INTER/TYPE11 should be used along with TYPE7).

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.)

Delete existing contacts and create new contacts with recommended properties.

 

CREATE RWALL CYLINDER:

• 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.
•  In the Radioss user profiles, a rigid cylinder is created in the Model and Solver browsers. 
• To create an RWALL Cylinder ,Go to Slover browser >> Create >> Rwall >> Cylinder 

• We need a reference node to create an RWALL Cylinder so, we are creating a temp node in the mid of B-Pillar
• Now translate this node to some distance with the reference of this translate node we have to create an R-wall Cylinder with respect to that CO-ORDINATES.
• The given friction value 0.1 is entered and the D-search is the approx value of around 400 is given.

 

CREATE SECTIONAL FORCES:

• Creation of Sections at B-Pillar and Driver rail in order to Study the sectional forces
• We have to know how the forces are transmitted from the B-Pillar to the rails 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:

Sl. no	1
Rocker Beam SECTION	Driver rail
Cross Member SECTION	B-Pillar rail

• Create a moving frame: Use the Systems panel to create rectangular, cylindrical, and spherical coordinate systems. Use this function when you want to define nodes, loads, and constraints in a different coordinate system to create a section and Frame 
• Go to Slover browser >> Create >> Section >> SEC 
• Initially, the section was created and the fixed frame is created and it is assigned to the respective section.
• For both cases, it is created separately.

 

CREATE SPRINGS:

• We are planting Spring elements to study the intrusions (forces inside the cabin causing deformation/rupture).
• Create 3 parallel spring elements.
• Springs can be created from the 1D Panel > Springs 
• To create a spring first as temp node at that particular selected node then select another node on other to see deflection after crash simulation
• After adding nodes now 
• Go to 1D page >> Springs >> Select first and Second node >> Create spring.
• After spring is created the property is assigned in the model tab as spring type and minimal mass and stiffness value is entered.

 

 

REQUESTING TH FOR INTRUSION SPRINGS, PEAK VELOCITY NODE, SECTION FORCE:

• Delete existing TH and create new.
• All the Global variables (Internal energy, Kinetic energy, Contact Energy, Hourglass Energy, etc.) are already requested by default.
• We have to call for additional Time History files for the boundary conditions that we have created for the frontal crash model.
• We can create the Output requests in the Solver Browser for peak velocity as follows:

• Solver Browser > Right Click > Create > TH > Select the Output Request
• To create TH ,Go to Slover browser >> Right-click >> Create >> TH >> Select element >> ok

 

 

CREATE REQUIRED CARDS:

TIMESTEP CONTROL

Engine Card	T SCALE  [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.

• 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.
• Tools > Model checker > Radioss block > Check Run
• The warnings can be ignored and it is confirmed that there is no error in the model.
  
  

 

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.

Review the Simulation

We have to import the animation file in HyperView first:

HyperView >> FIRST_RUN. h3d >> Apply

1. The tools to review the simulation are available on HyperView.
2. HyperView is a post-processing and visualization environment for FEA that gives the output of the analysis in a simulations format that is user friendly to understand.
3. From the simulation, we can review how the impact force acts and causes deformations and point of rupture on the model.

 

Von Mises:

• From the simulation, we can see that initially, the car is hitting the R-wall cylinder with a velocity of 15.64m/s while hitting the first impact is with B-Pillar then the forces going to transferred to the left and right and front direction in the roof rail and cross member in the bottom as shown in below figure here In each stage the forces going to reduce because of energy observed.

 

Results after simulation:

1) Energy and Mass error:

• At the end of the simulation, do the energy error and mass error checks and determine whether results would be acceptable
• Open the save location file and click on the output file of the simulation to check for the Energy error and Mass error.
• If the error is negative, it means that some energy has been dissipated.
• In the case of under-integrated elements (Belytschko shells, solids with 1 integration point), the Hourglass Energy can explain a negative Energy Error since it is not counted in the energy balance. The normal amount of Hourglass energy is about 10% to 15%.
• 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 has been linearly increasing up to -1.4% only, which is acceptable.
• Mass error is zero 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 >> FIRST_RUNT01 >> 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:

Internal energy is nothing but distortion energy. When the Kinetic Energy is Decreases, the Energy absorbed by the system increases i.e we all know that Energy neither be created nor be destroyed. Once the vehicle is moving with a certain velocity (Say 15.646mm/ms for the Model), the initial kinetic Energy will be High (Refer to Above Graph). Once the car is hit by the rigid wall, the vehicle starts deforming results in absorbing the Surrounding Energy and Stored it. Thus, internal Energy starts increasing. At the Maximum deformation, the Velocity will become Zero and thus the kinetic energy will also be dropping down to zero resulting there is no energy to absorb in the system. Thus, Internal Energy Remains Constant thereafter.

 

CONTACT ENERGY AND HOURGLASS ENERGY:

• From the above graph, we can see that the hourglass energy is minimum throughout the analysis since we have used Improved integrated element formulation (QEPH).
• The contact energy is increasing as the car approaches the side rigid pole.

 

PEAK VELOCITY :

 

• As we all know that 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 17.0m/s. As we have seen from the above graph there are fluctuations in the shock waves this is because of vibration that occurred during the crash of the vehicle.

 

INTRUSION SPRINGS:

 

• Intrusions are one of the important parameters while checking passenger safety in crashes. To know the intrusions at B-Pillar, Fuel tank, and Hinge Pillar we have placed a spring in these particular regions of B-Pillar, Fuel Tank and Hinge pillar from this we can see the intrusion at that particular region and we can also understand how much intrusion is happened in these regions. Here in this graph, we can see that the B pillar(brown) has the maximum intrusion, then come to the fuel tank(Blue) and the least intrusion is seen at the hinge pillar(Green). 
• Here at the B-Pillar, the spring elongation of 767mm. The B-pillar touches the rigid pole and the other side is crushed towards it, so its intrusion is so high. For the Fuel tank, the spring elongation is 750 mm and for the Hinge Pillar, it shows an elongation of 393 mm.
• Since due to the Node limitation in the software, we don’t have the full-scale model and many missed components like the rear axle, Fuel tank, etc. But in real condition, the rear axle, wheels, and the fuel tank give much more stiffness to the car and this might help to reduce the intrusion in a good manner. To reduce the intrusion in this model we can add one cross member near to the Fuel tank region.

 

SECTIONAL FORCES:

• From the graph, it is evident that cross member has the maximum force and then the force on the rocker beam is increased and then it deforms.
• This indicates that the force is initially transmitted much in the cross member as compared to the rocker beam.

 

Learning Outcome

1. Learned how to set up a side 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 side 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.
8. Learned how to place a node to see his peak velocity.

CONCLUSION:

• The given model was simulated for the side 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 maximum deformation in the cabin, and also maximum intrusion was found in the cabin area. This is due to the limited number of nodes in the student version some of the BIW, engine blocks, suspension system, etc are removed, so the results are not as in real condition. After understanding these we will get to know what all things we should do on this car to make it safer. For example to decrease the amount of intrusion in the Fuel tank region we can introduce a cross member there.