Assignment 7-Side Pole Crash Simulation Challenge

 

Aim-Side Pole Crash Simulation of Dodge Neon BIW using RADIOSS solver and Preprocessing using HyperMesh / HyperCrash.

Objective- To perform a crash analysis on the left side of a Dodge Neon BIW, also known as a side crash. The analysis is to be carried on the deformation and the forces created as a result of the crash at a speed of 35 mph. Along with the analysis, certain output requests were to be generated and they are as follows:

• Sectional force in the cross members.
• Intrusion at B pillar, hinge pillar, and fuel tank region(Also provide recommendations on what can be done to help reduce fuel tank intrusion)
• Peak velocity of a node on the inner door panel.

Procedure-

• Check for Unit system
• Import model in HYPERCRASH
• Check for penetration and intersection
• Add masses to reach a target weight of 700kg 
• Export changes file and import in HYPERMESH
• Create Self Interface contact
• Create a rigid wall
• Add Initial velocity to the model
• Create cross-section's to find sectional forces on the cross members
• Create springs to check intrusion in different positions
• Assign property to springs
• Create TH for section forces, intrusion springs, interface contacts 
• Create cards
• Run Model checker and correct errors if any
• Run the Analysis

Import the Model

First, we will import the .rad starter file of the model which is named as neon_side_reduced_0000.rad in Radioss using Import Solver Deck option.

Reduced Model for Side Crash Analaysis

CHECK FOR UNIT SYSTEM:

Now inorder to check the unit system of the model. we can go Model browser, and in Cards, check BEGIN_CARD.

or we can just open the Neon_front_0000.rad in a notepad ,where we will be able to check the units.

So for this model, we will see that the unit system followed is [kg mm ms].

We will be using Hypercrash and Hypermesh to set up the model. Some checks will be done in Hypercrash and some in Hypermesh. First, we will import the model into Hypercrash

Now go to Application >> Hypercrash>> Select the unit system >> open

Select Neon starter file and drag it to hypercrash application to open the model

CHECK FOR PENETRATION AND INTERSECTION:

Penetration is defined as the overlap of the material thickness of shell elements, while Intersection is defined as elements that actually pass completely through one another. All models and especially impact models should be checked for penetrations and intersections and De penetrated to ensure the integrity of the model. Penetrations adversely affect results and should be removed.

To check penetration and intersection

Got to Quality>> Check all solver contact interfaces >> Select parts > Click on check penetration

As you can see in the image below there are no penetrations or intersections present in the model

Compare the model weight with the full-scale 300k nodes model and use added masses to reach a target weight of 700kg while getting CG about the required range.

A vehicle’s center of gravity, or CG, is the theoretical point where the sum of all of the masses of each of its individual components effectively acts. In other words, from a physics perspective, a vehicle behaves as its entire weight resides at this one point. Carrying weight up high, such as a panoramic sunroof will raise a vehicle’s CG while placing heavy subsystems low in a vehicle, such as a battery pack, will work to lower it. Lower is better from a handling standpoint, as it reduces weight transfer during cornering and braking, and it also reduces the propensity to roll over.

Add Masses

Mass balancing: In order to maintain the CG of a car we have to add mass for the given components, In the given model here are so many parts are missing because of the node limits in the student version

To check the CG

Go to Menu >> Mass >> Balancing >> Show CG point 

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 as shown in fig

After selecting that, by right clicking on Mass browser select Create New. In that,Type 1 is selected.

In order to distribute the given mass to each node of the node group selected. 

then we added mass to different components as shown in table below in the BIW structure in order to obtain the required mass of 700 kg and to place CG at required location

MASS in KG	DESCRIPTION
40	Left side part which supports the fuel tank
40	Right side part which supports the fuel tank
80	B-Pillar beam
90	Seat cross reinforcement
60	Driver and his seat
60	Passenger and his seat
50	Left side legs place
50	Right side legs place
64.567	Dashboard

After balancing the mass, we achieve our target mass that is 700kg as shown in the figure below and CG at the desired location

  

 Applying Initial Velocity

To add initial velocity to the system in Hypercrash, we need to go to LoadCase > Initial Velocity.

For [Gnod_id] Support, we shall be selecting all the nodes in the model. The required velocity is 35 mph but the units are in mm/ms, which would be 15.6464 mm/ms. and vehicle is moving is along the y-axis, so this value will be entered in [Vy] Y Velocity. All other velocity values would be 0.

After entering the values, we can click save at the bottom of the panel.

now we will export the radios file from Hypercrash and import in to HyperMesh to do rest of the case setup

Create Contact Interfaces

• Creating self contact

For this model, we will create Type 7 interface for all the components of the model as it is self-impacting or the nodes and elements of the model will have contact between them. Interface TYPE7 is a multi-usage impact interface, modeling contact between a master surface and a group of slave nodes. It is also possible to consider heat transfer and heat friction.

 We will go to Solver browser and we will delete all the existing interfaces.

Now create a new contact 

Goto model browser >> Right-click >> Create >> Contact >> Rename as Self contact >> Select slave node and master components >> Enter Type 7 recommended properties

 

Self contact Type 7 card                                                 After creating self contact

                                                                                      check whether master and slave nodes selected proper 

                                                                                      For that, right-click on self-contact >> Review 

     

CREATE RIGID WALL CYLINDER:

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 as shown below.

     

The cylindrical rigid wall or the Pole will then be created as shown below.

     

Creating Cross Section –

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. So for this, we will extract the node location or coordinates of a particular node on the section in nodes panel. Then we will offset the node in X-axis by 10 units and create a new node. Similarly, we will offset and create a node in Y-axis as shown below.

     

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.

     

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 $\frac{2\pi }{10}$. 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.

Similarly, we will create the cross sections at both the cross members as shown below.

Requesting Output file for Cross-sections created

After creating the cross sections, we will request the results in TH or time history. 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 which we created and thus we will be able to measure sectional force passing through the cross members by creating plots in HyperGrapgh.

To Measure Intrusions –

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 create spring between left and right parts of B-piller, Hinge-piller and fuel tank, for creating spring go to 1D -> SPRINGS -> SPRING2 and select 2 nodes as shown in figure below.

Spring created as shown in the figure below

Now we have to create property card for spring and assign it to the spring element created

Go to model Browser >> Create >> Property >> Rename as Intrusion springs 

After creating a property, a new tab will open there we have to select CARD image as P4 SPRING and Mass as 0.001, and Stiffness as 0.001

Requesting output (Time History files) for spring

Inorder to measure intrusions on the spring, we have to request /TH/SPRING files, go to solver browser -> right-click create ->TH -> Spring

then select the entity ID is spring element created at each position as shown in figure below.

• Now for B-Pillar we will create the moving Scew and we will directly request the instrustion output using TH_Node.

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 right-click on solver browser -> create -> skew -> MOV

select the required node as origin node then select node to define x-axis and XY-plane.as shown in figure below

Output request for peak velocity on Inner door

The next step is to create a Time History (TH) output specifically for this. For that, we can switch to the model browser and create a new output block, this time for peak velocity (right-click > create > output blocks). The entity ID is going to be just the one node - node 337773 and for lskew, we shall be selecting the skew created previously.

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
SECTION	i. Driver Rail ii. B-Pillar Rail
NODE	i. Peak velocity node on (NODE ID 335875)

• Now before setting runtime we will check for the connectivity.
• After checking the connectivity, there are total 3 part in assembly which are not connected tp other bodies, so, we will connect them using rigid bodies and we will do the time stepping addition.

Time Step and Run time –

To check these parameters in Hypermesh, we will navigate to Cards under Model browser. To check the run time,  For the time step, we will input timestep value as shown in table below

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	0.67	0.0005	Uses the default constant timestep method.

we will open ENG_RUN card and input run time in Tstop as 80 ms.

Go to ENG_ANIM_DT card enter T freq as 5 

      

MODEL CHECKER:

Finally, before carrying out the RADIOSS analysis, an error check was run on the file through Hypermesh. The model check tool can be accessed through Tools>>model Checker>> Radioss Block.

• We will try to clear the errors and then we will run the analysis.

RUNNING THE ANALYSIS IN RADIOSS-

Switching to Hypermesh, moving to Analysis > radioss, we can click 'save as' to save the file if it hasn't been saved yet. Care must be taken to include '_0000.rad' in the file name since it's the starter file. After that, we can check the connectors option and input '-nt 4' in the options bar before clicking 'Radioss'. This starts the Radioss simulation.

 

ANALYSING THE OUTPUT FILE

The next step is to carry out energy error and mass error checks and this is done by analyzing the RADIOSS engine output file. This can be accessed from the same directory as the starter and engine files and is denoted by the '.out' extension. The file in question contains '_0001.out' and can be accessed using any text editor - such as Notepad++.

 

• As we can see, the energy error is -1.8%. It is definitely acceptable due to its proximity to 0% error. In addition to that, the mass error is 0.9311E-5, there is negligible mass error.

Total Simulation Time: 7629.78 s
Total Number of cycles: 340733

 

Results & Animations-

To view the simulation, we can switch to Hyperview through the client selector.

In Hyperview, we will need to import the h3d variant of the file. After importing, we can then select the 'contour' tool to switch to the Von Mises contour so we can analyze the stresses that form within the BIW in the simulation. This is what the simulation looks like:

Displacement contour plot

• In the above crash simulation of the vehicle, we can see the vehicle BIW 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.

Von Mises stress contour plot

 

From the Von Mises stress plot, we can say that the stress distribution is quite good in the vehicle after the crash. There are very few areas where we can see stress concentration. Generally the stress is more in B-pillar and cross members as B-pillar takes the initial impact and then the impact is transferred to the cross members.

From the simulation, we can see that initially, the car is hitting the R-wall cylinder with a velocity of 35mph, while 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 members in the bottom as shown in below figure. In each stage, transfer of force is going to reduce because energy absorbed by the components

 

GENERATING OUTPUT PLOTS

After generating the simulation, we can then go ahead and generate the plots. Using the same client selector, we can switch to Hypergraph. In the Hypergraph client, we need to import time history file T01 file

On importing, we can build the plots using different variables. We shall first look at general plots of energies and rigid wall forces generated in and by the entire BIW respectively.

Global Variable - Energies

• The changes in kinetic and internal energies occur at the exact moment the BIW makes contact with the rigid cylindrical wall. Understandably, the BIW loses kinetic energy throughout the simulation due to the obvious decrease in velocity. At the same time, it absorbs the forces, and this results in an increase in internal energies, and as a result, the deformations also occur.

Sectional force on Cross-member:

Cross-members are very crucial in the side-impact analysis as these components prevent the body to shrink or deform inward. When the car hits the rigid body maximum amount of forces will pass through the cross member of the base and roof. This component along with door bar and support, door outer, B pillar, and rocker are also involved in the majority to prevent deforming. But the forces acting on every other component eventually pass from the cross member.

The max sectional force at the B-pillar cross member is 5.67 KN at 75.5 ms and for the driver seat cross member it is 2.78 KN at 39.5 ms.

 

Peak velocity at Inner Door-

• 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 16.41 mm/ms at 4.0 ms. 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 progressed (due to inertia). As time passes, we can see the velocity gradually decreasing.

Intrusion inside the car at B pillar, hinge pillar, and fuel tank-

• The intrusion or deformation of the component can harm the occupants and the inner part of the car like a fuel tank. From the above plot, it is obvious that intrusion near the fuel tank is 578.5 mm and near the B pillar is 207.5 mm which are substantial.
• The fuel tank region received the least displacement, followed closely by the B-Pillar, then the Hinge Pillar. Admirably, the B-Pillar was able to absorb a lot of the impact due to multiple reinforcement members attached to it and in its vicinity, despite being one of the first regions of impact in the crash. The hinge pillar did not have any reinforcements and hence suffered the most displacement.
• This intrusion must be avoided by using some alternative method or by using any composite material which can withstand load near the fuel tank.

 

Conclusion-

Side crash analysis was carried out on the given BIW model of the Dodge Neon as per requirements. The output requests were also generated after the creation of cross-sections in each of those regions. Peak velocity and intrusion values were also measured at certain points of the model.

Fuel tank intrusion and intrusions, in general, could be reduced by using anti-intrusion beams (or side-impact beams) between the pillars. They increase the rigidity of the doors and distribute the energy in the event of a side-on crash. The model already does have such beams as shown:

There may be stronger options for anti-intrusion bars but there is the weight-to-cost factor that might be a major factor. There are multiple materials other than steel such as aluminium and composites being tested that are lightweight but effectiveness is more or less comparable. If more bars can be used, that could be an option as well.

Otherwise, another option is to simply add an extra cross member next to the fuel tank to reinforce that region.