Assignment 6-Frontal Crash Simulation Challenge

OBJECTIVE:

To perform frontal crash simulation on the given model with given conditions and observe simulation results.

PROCEDURE:

Import:

Checking Unit system:

From neon_front_0000.rad file:

Model Browser>Cards>BEGIN_CARD 

It is observed that, the unit system followed is Kg mm ms which is as given in the required unit system.

Creating Interface:

The interface described in the model is deleted and a new interface is created under the solver browser 

Create>INTER>Type7

Type 7 recommended porperties are defined aong with the given properties.

Penetration Check:

The given file is importrd to hypercrash. Under Contact Inerface browser, Check Penetrations for selected objects is selected after slecting the components.

Hence checked that there is no penetrations in the model.

Creating RIGID Wall:

Rigid wall is created under solver browser by using

Create>RWALL>Plane.

Inorder to select a postion, outermost and centre node on the bumper part is selected. 

A small gap of 20mm is added to the x cordinate to create wall a little away from the model. Since normal of the wall is on negative X-direction, -1,0,0 is defined in the Normal tab.

Dsearch is defined till 2000mm.

Slide is set to 2 to incorporate a friction of 0.1 as specified.

Hence Rigid Wall is created with specified properties.

Mass Balancing:

To compare the model mass and to make the model weight equivalent to the full scale model weight, Hypercrash application is used.

To view CoG and mass, Mass>Balancing option is used.

It is observed that the scaled frontal model only weighs 188kg.

Also the position of COG is currenlty closer to the dashboard region whereas it should be near to the driver seat region.

Now to shift the COG to the desired area, some masses are added to the rear part.

The added mass will account for fuel tank, passengers weight , additional luggage load etc.

To Add mass, ADMAS option is used under solver browser

Create>ADMAS.

A new mass collector is created, 

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,

Hence the mass is corrected to 700kg to represent a real-life mass of a vehicle, and also the position of COG is now relocated to the desired position.

Defining Initial Velocity:

To define an initial velocity of 35mph (15.6464 mm/ms) under solver browser:

Create>Boundary Conditions>INIVEL

Now before moving into simmulation, inorder to observe the outputs required, we have to create cross sections on Rail, Shotgun, A-Pillar, Create an accelerometer and an intrusion on dash wall specified nodes.

To view cross sectional force on the moving model, a frame which is movable should be created which act as reference to the cross section at which forces is to be computed.

To create a movable frame under solver browser using,

Create>Frame>MOV

In the frame creation window, we should select origin nodes and also the global axis directional nodes which can be created by translate tool and translating the duplicate of origin node to X and Y direction. Clicking on create after selecting nodes, creates a new frame with specific ID.

After Frame is created, now a section should be created for this frame which is created under the solver browser:

Create >SECT>SECT

In the newly created section, the elements are selected under grshel_id and the reference frame created is define by the Frame ID.

Similarly the frame and sections are created at all positions as recommended; Rails, Shotgun, Bumper -Rail, A-Pillar.

Accelerometer:

At the base of B-Pillar, an accelerometer is created under the solver browser by:

Create>ACCEL

The node at which the accelerometer is to be placed is also selected.

Intrusions:

To find the intrusion on the dash wall at nodes,  66695 and 66244, a frame for reference is created. Then under timehistory block, the node is selected as Entity ID and frame is selected as iskew.

Model Checker:

To check for any error in the model, 

Tools>Model Checker>RadiossBlock 

After the model checker tab opens, Run Checks option is clicked, and then auto correct option is clicked, which will rectify the errors and warnings.

One warning obtained on accelerometer is corrected by adding an outputblock of accelerometer under solver browser,

All the error and warnings are displayed which is partially corrected using auto correct option. The error shown is due to not selecting N1, N2 and N3 to the newly created sections for A-Pillar, Rails, Bumper and shotgun which can be neglected. Rest of the warnings are also neglected.

Run Time & Time Step:

The run time of the simulation is checked under ENG_RUN tab under model browser>cards

The time step is set to 0.00025ms under DT_NODA tab

After all the above formulaions are done, we can now perform simulation of the model to review the crash results.

Simulation:

The simulation is run using Radioss Tool under Analysis tab.

 Once the analysis is done, frontcrash_0001.out file is observed to check the stability of the  model.

From the .OUT file,

Energy error : 0% to -1.7%

Mass Error : 0 Throughout the simulation.

Hence Energy and mass error are within the stable limits.

Now the time for simulation and number of cycles taken to complete the simulation is also noted from the OUT file.

Plotting the energy curves using Hypergraph 2-D with the help of T01 File:

Internal energy, Kinetic energy and Total energy curve is plotted. It is observed that there is an increase in the internal energy in the model with the progress in simulation. With the increase in Internal energy, there is a proportional decrease in kinetic energy in the model.

Hourglass energy remains negligible throughout the simulation and a slight increase in contact energy. 

Hence Total energy remains constant roughly due to compensation between kinetic and internal energy. Total energy shows a slight decrease due to slight increase in contact energy as shown in the above graph.

Plotting the Cross-Sectional forces using Hypergraph 2-D with the help of T01 File:

1) Sectional force in the rails at location of indicated node 174247.

From the graph, it is observed that, at the start of the crash where bumper absorbs the forces, there is no increase in cross sectional force in the rails. Then force suddenly rises till there is maximum deformation and then increases slighlty till end of simulation due to forces acting on the model.

 2) Axial force received on the rails from bumper:

Normal force acting on the Rails from bumper is plotted. Since the force acts directly on the bumper intially, compared to other curves, there is a steep increase in normal force acting at the start of the crash and then continues in a non-linear pattern rising and falling throughout the simulation.

3) Shotgun cross sectional forces:

Cross sectional force at this area is observed rising from the start towards end of the simulation with a slight decrease towards the end of the simulation.

It is also observed that, when the Normal forces at rails from bumper decreases, there is an increase in cross sectional forces at shotgun region.

4) A-pillar cross section:

Cross sectional foeces on the A-Pillar is plotted. It is observed that rather than having steep rise in cross sectional froces as in other cases, the rise in cross sectional forces in the A-Pillar region is more smooth which is a good characteristic as in case of a crash.

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

Accelerometer readings at the base of the B-Pillar is plotted. Accelerometer is used to measure the acceleration forces at the base of B-Pillar.

It can be seen that there are many spikes in the graph which shows sudden movement at the specified region. The highest imopact is recorded at around 18ms of the simulation.

6) Intrusions on the dash wall 66695,66244:

It is observed that, there is a maximum displacement of about 2300mm on 66244 node and 2255mm on 6695 node.

Animation and Contour plot of the simulation is obtained under Hyperview using the h3d file saved in the directory:

At the start, it is observed that the bumper absorbs most of the energy during the crash. 

Further simulation shows that the forces due to crash is distributed throughout the model components with very less stress concentration at specific locations. 

Being a scaled model, the rear part of the model under simulation is found to bend inwards which is not desirable.

Initially bumper deforms, then the forces are transmitted through rails to rest of the model components. The front part of the model gets lifted due to the crash which shows the real life scenario to a certain extent. But since there is no tyres, engine and associated parts in the  in the model it cannot be compared fully with a real life crash. Also the rear passenger seat part bends inwards which will be due to the load applued to correct the mass and might be due to the position of Centre of Gravity.

CONCLUSION:

The given frontal crash model is analysed for a frontal crash scenario and the requested output aspects are observed.

The forces and energy curves at the specified locations are observed.