Assignment 6-Frontal Crash Simulation Challenge

Crashworthiness Analysis using HyperMesh and Radioss

#Project 1 - Frontal Crash Simulation Challenge
AIM: To perform the crash on the frontal section of the car with wall and analysis where stresses are working on it.

OBJECTIVES:
Frontal crash-BIW
1. Checking the unit system and either following [Mg mm s] or [Kg mm ms].
2. Creating appropriate interface, friction 0.2 and recommended parameters.
3. There should be no penetrations and intersections.
4. Creating a rigid wall with friction 0.1.
5. Adding masses to reach target weight 700kg while getting CG about the required range.
6. Adding Initial velocity 35 mph.
7. Running a model checker to ensure good quality.
8. Time-step: 0.5 to 0.1 microseconds.
9. Running 80 ms.

Output requests:
1. Adding a sectional force in the rails at the location of indicated node 174247.
2. Adding Axial force received on the rails from the bumper.
3. Adding Shotgun cross sectional forces.
4. Adding a cross section to a pillar.
5. Acceleration curve received on the accelerometer at base of B pillar (on B pillar rocker).
6. Adding Intrusions on the dash wall at node 66695 and 66244.

PROCEDURE OF OBJECTIVE 1: Checking the unit system and either following [Mg mm s] or [Kg mm ms].

STEP 1: Open the starter file neon_front_000.rad file, go to-
 *Menu bar>file>import>solver desk>select .rad file>import

STEP 2: Checking unit system of the model
 *Model browser>cards>begin card

PROCEDURE OF OBJECTIVE 2: Creating appropriate interface, friction 0.2 and recommended parameters.

CREATE SELF CONTACT:

• In this case, the Type 7 Contact Interface is defined. 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.

TYPE 7: NODE TO SURFACE

                                Type 7 contact

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

• 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
• We can select slave and master as a component and as well as node selection 
• For that, we just have to right-clicked where selecting nodes are components there is one option called create/Edit select and proceed with nodes or components

•   Creating new self contact(type_7)
• Then after this step, we simply need to give in the Slave nodes and the master segment. Since we are defining a Self-Impact in the model, the Slave and Master segments for this contact will be the entire given model. So, we then select the slave and master in the graphics area.

• Recommended properties

check whether master and slave nodes selected proper 

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

                                                        Slave and Master components

CREATE INTERFACE CONTACT BETWEEN BUMPER AND HEADLIGHT BRACKETS:

Now create a new contact's 

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

                                                              Selecting slaves nodes

                                                            Master component selected

                                          Review of left headlight and bumper contact

Here BLUE indicates MASTER component and RED indicates SLAVE nodes

                                             Review of right headlight and bumper contact

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

                                              Checking for intersection and penetrations

                                                 No intersection and penetrations present

We can clearly see from the above figure there are no penetrations and intersections are 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 centre 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 

                                                      Total mass when we imported 

It is showing that the total mass of the body is 188.2 kg which is 700-188.2 = 511.8 kg less than our target mass. 

Before adding mass check the CG, To check the COG of the body we have to click on the specs icon.

                                  Checking for CG

                                                                 CG before adding mass

Current weight: 188 kg

Target weight: 700 Kg

1. We have to add the mass in such a way that the Centre of gravity is exactly in the middle of the Cross Beam to simulate the real-time model.
2. We are only worried about the position of the COG (X and Y axis) and not the height (Z-axis).
3. We use Type 1 Mass, where mass is distributed on each node of the selected group.

Added Mass > Create New >> Type =1 >> Enter the Value (ex. 85kg) >>right click to pick nodes >> Select the group node by selecting in the graphics >> Select Add/Remove nodes by picking selection >> After selected hit YES >> Save

                                                                      Adding mass

                                                              Selecting mass type as 1

                                                              selecting nodes by graphics

                                                 Mass added for particular selected nodes

MASS in KG	DESCRIPTION
85	Driver and his seat
85	Passenger and his seat
170.7875	The rear seat, spare wheel and fuel tank
170.7875	The rear seat, spare wheel and fuel tank

After balancing the mass we achieve our target mass that is 700kg as shown in the figure below

After adding the mass:-

And CG of the model:-

EXPORT HYPERCRASH FILE:

Export the rad file changes made in hypercrash and import the same file in hypermesh to make other changes

For that

Go to File >> Export >> RADIOSS

                                                                

Now import the same "runname_0000.rad" file in hypermesh to do other changes 

For that open hypermesh 

Go to file >> Import solver deck >> Select Neon_0000.rad file >> Import

            Selected starter file from the folder

                                                                  Model imported

CREATE RIGID WALL:

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.

Rigid wall entities provide a method for treating a contact between a rigid surface and nodal points of a deformable body. In the Radioss user profiles, rigid walls can be created in the Model and Solver browsers. 

To create an RWALL 

Go to Slover browser >> Create >> Rwall >> Plane 

                                                                Creating an RWALL

We need a reference node to create an RWALL so for that we are creating a temp node in the mid of bumper

                                                             Temp node creating

                                                              TEMP node created

Now translate this node to some distance with the reference of this translate node we have to create an R-wall with respect to that CO-ORDINATES

                                                                       Translate node

                                                                    Node Translated

Now select the translated node and note down the X, Y and Z coordinates

                                                             Co-ordinates X, Y and Z values 

• It is a Shell element with no thickness (gap) and infinite thickness.
• A search tolerance is given (optional) so that the nodes within the range will be taken as slaves.
• We are going to create an Infinite plane type Rigid wall.

Enter the coordinates of the Temp node [XM, YM, ZM] >> Enter the Direction of the Normal [-1, 0, 0] >> Slect GRNOD_ID 1: set of displayed nodes >> Dsearch : 1000/1500 >> ok

The rigid wall is facing opposite to the car so the normal is on the negative X-axis.

1. We have to provide frictional parameters for the rigid wall when the slave nodes come in contact
2. Friction type [Slide] = 2: Sliding with friction
3. Frictional Coefficient [FRIC] = 0.1
4. The D-search distance we can use around the range of 1000 mm. All the Nodes within this distance will be considered as salve nodes for the contact between the car and the Rigid Wall.
5. We can add a separate set of nodes to this Rigid wall that the system should consider for Slave nodes in the option of [grnod_ID1] as shown below figure. We can use this option and add all the nodes in the model to the Slave nodes. 

                                                                   Selected Slave nodes 

                       RWALL tab

                                         Rigid wall with infinite plane created

To create a velocity 

Go to solver browser >> Create >> Boundry conditions (BC) >> Inivel 

                                                                        Creating velocity

Define the Node group on which specified initial velocities are applied(grnd_ID1).

                                               Selecting GRNOD_ ID 1 slave nodes

Define the Type of Velocity (Translational /Rotational).

Since we need to apply the velocity in translational X Direction, define the velocity 15.646m/s

                                        INIVEL Tab

                                                                  Review of inivel nodes 

CREATE SECTIONAL FORCES:

Creation of Sections at A-Pillar, Shot Gun, rails and the Bumper in order to Study the sectional forces

We have to know how the forces are transmitted from the Bumper to the Dashboard 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	2	3
LEFT SIDE SECTION	RAIL	SHOTGUN	A-PILLAR
RIGHT SIDE SECTION	RAIL	SHOTGUN	A-PILLAR

To create a section and Frame 

Go to Slover browser >> Create >> Section >> SECT

 

                                                                   Creating section

Now when we create a section a new tab will display their we have to select N1, N2 and N3 nodes 

                                                             Selecting N1, N2 and N3 

• We then need to select the three nodes on which we need the Frame system.
• In this case setup, we need to define around 6 sections.
• We need to make sure that the normal of all the sections defined need be in one particular direction. All the normal can be facing either the wall or even away from the wall. We need to make sure that they are in a single direction. 
• We can create a Section just in the same way as we created a section system.
• We need to right-click in the solver browser and select frame.

                                                                        Section created

                                                                Selecting frame nodes 

                                                                  Frame created

Now assign this frame system in section

Define the Nodes with reference to the Axis of the Frame.
• Enter the values of Delta T and Alpha Value as 0.1 and 0.67 respectively.
• Define the cutting plane by a group of elements and its orientation by a group of nodes(grshell_ID)
• Hence, the sections will be created.

                                                            Assigning frame system

                                                  Selected elements for section forces

                     Section Tab

                                                           All 6 Section Created

 CREATE ACCELERATION NODES:

Creating Accelerometer at both sides of the B pillar.

An accelerometer is a basic technology that converts mechanical motion into an electrical signal. It is an electromechanical device that measures acceleration forces, whether caused by gravity or motion.

To create accelerometer 

Go to Model browser >> Create >> Accelerometer >> Select Node_ID >> Select node >> Proceed

                                                             Creating accelerometer

This is done to get the Acceleration output of the Crash i.e., rate of deformation.

                                                  Accelerometer node selected

                                                            Accelerometer created

 CREATE SPRINGS:

• We are planting Spring elements to study the intrusions (forces inside the cabin causing deformation/rupture).
• Create 2 parallel spring elements from the indicated nodes (66695,66244) till the Crossbeam.
• Springs can be created from the 1D Panel > Springs 

To create a spring first as temp node at that particular node id then select another node on other to see deflection after crash 

After adding nodes now 

Go to 1D page >> Springs >> Select first and Second node >> Create spring

                                                                          Spring tab

                                                                         Springs created

CREATE PROPERTIES TO SPRINGS:

To create spring property

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

                                                    Creating new property for spring

After creating property a new tab will open there we have to select CARD image as P4 SPRING and Mass as 0.1 and Stiffness as 0.001

             Changes CARD IMAGE

REQUESTING TH FOR INTRUSION SPRINGS, ACCELEROMETER, SECTION FORCE:

Delete existing TH and create new 

                                                                      Delete existing TH

They are Output files that are requested in the Starter File.

• 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 from within the Solver Browser:

Solver Browser > Right Click > Create > TH > Select the Output Request

Output Requests	Boundary Conditions
INTER	i. Self Impact ii. Left Bumper and headlight iii. Right Bumper & headlight
ACCEL	i. On Left B Pillar ii. On Right B Pillar
SPRING	i. Intrusion on node 66244 ii. Intrusion on node 66695
RWALL	i. Rigid Wall
SECTION	i. Left Rail ii. Right Rail  iii. Left A-Pillar iv. Right A-Pillar  v. Right Shotgun vi. Left Shotgun

To create TH 

Go to Slover browser >> Right click >> Create >> TH >> Select section for Sectional forces >> ok

                                                           Creating TH for sectional forces

                                                           Assign left rail section 

Do the same for others 

                          Output Requests

CREATE REQUIRED CARDS:

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.

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 

                       ENG_ANIM_DT card

                       ENG_RUN card

                                                          Final SET-UP

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.

For example:

1. Boundary Condition is not defined properly
2. Incompatible Kinematic Condition
3. The Part Property or material is not defined properly, etc.
4. We can avoid the Warnings as the solver will take care of them.
5. But we must fix every Error in order to get a successful simulation free of problems.

we export the rad file and execute the Model check in Hypercrash

Quality > Model checker > Runs

As shown in the figure below errors and warnings will show in the model checker tab

Upon inspection we found that there were two unnecessary translational joint present in the model, we delete those two translational joint and run the model checker again

                     

Now as you can see in the model checker tab all errors are rectified and rest of the warnings we can ignore.

RUN 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.

     

After completion of simulation a pop-up window appears showing Normal Termination without any errors as in figure below.

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 -1.2%. It is definitely with in the acceptable range of -10% to +5% error. In addition to that, the mass error is 0.0302, which means that a negligible quantity of mass of was added during the simulation, possibly for the sake of time step control/stabilization. It is a rather low amount so it's still acceptable.

Total Simulation Time:  4048.41s
No. of cycles               :  80001

SIMULATION ANIMATION

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.

Then the contour panel is opened, which appears as shown in fig below. In which the parameters to view the simulation are selected. Such as: result type:In terms of Displacement, von misses stress etc. then  selecting the components & apply.

  

From the simulation, we can see that. Initially, the bumper starts crushing then the bumper forces are transferred to the left and right rail then from the rail forces are transferred to A-Pillar LH and RH. In each stage, the forces are going to reduce because energy is absorbed in each stage. Because of no engine blocks, suspension system and tyre etc the car BIW is going to go down at the end of the simulation

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 bumper region as it is the first point of impact.

GENERATING THE PLOTS

After generating the simulation, we can then go ahead and generate the plots. Using the same client selector, we can switch to Hypergraph2D . In the Hypergraph client, we are asked to import the required file, which is the T01 (Time history file ) variant of the 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. 

Some basic definitions of energies: 

• Energy: Energy, in physics, the capacity for doing work. It may exist in potential, kinetic, thermal, electrical, chemical, nuclear, or other various forms. In FEA we have Total Energy, Internal Energy, Kinetic energy, Contact energy and hourglass energy
• Total Energy (TE): Total Energy is the sum of Internal Energy, Kinetic energy & External Work
• Internal Energy (IE): The internal energy of a thermodynamic system is the energy contained within it. It is the energy necessary to create or prepare the system in any given internal state. It does not include the kinetic energy of motion of the system as a whole, nor the potential energy of the system as a whole due to external force fields, including the energy of displacement of the surroundings of the system. It keeps account of the gains and losses of energy of the system that are due to changes in its internal state
• Kinetic energy (KE): In physics, the kinetic energy (KE) of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity.
• Contact Energy (CE): Contact energy is the energy acting opposite to the system to prevent the penetration acting on the system due to the applied load case.
• Hourglass energy (HE): This is usually done by adding extra stiffness or viscosity across the diagonal which adds extra strain energy into the system and we call this Hourglass Energy. 

 GLOBAL VARIABLE GRAPHS: ENERGIES