Assignment 6-Frontal Crash Simulation Challenge

OBJECTIVE :

1.To Run the crash simulation for the given car model with the following case set up

• unit system of [Kg mm ms].
• Creating appropriate interface ,friction 0.2 with recommended parameters.
• Making sure of no penetrations and intersections.
• Correcting rigid bodies if any issues.
• Creating rigid wall with friction of 0.1.
• Comparing the model weight with the full scale 300k nodes model and use added masses to reach target weight 700kg while getting CG about the required range.
• Applying an initial velocity 35 mph.
• Using model checker to ensure good quality.
• Input the Time-step Value between 0.5 microseconds to 0.1 microseconds.
• Run the simulation for 80 ms.

2. To Plot the fillowing output results

• Sectional force in the rails at location of indicated node 174247.
• Axial force received on the rails from bumper.
• Shotgun cross sectional forces.
• A pillar cross section.
• Acceleration curve received on the accelerometer at base of B pillar (on B pillar rocker).
• Intrusions on the dash wall 66695,66244.

Fig 1 Given Crash model

CASE SET UP AND EXECUTION :

1. Unit System

In the Begin card of the imported model, the units are set for Mass , Length and Time as Kg, mm & ms respectively.

Fig 2 Units for the Input

2. Creating appropriate interface ,friction 0.2 with recommended parameters.

The intreface card is created in the solver for the Interface type-7 . All the nodes are selected for the Master and slave groupings and the following values are given in the card :

1. Istaf = 4 (for Stiffness scale factor determined based on main and secondary characteristics)
2. Igap = 2 ( Variable gap + gap scale correction after being computed)
3. Idel = 2 ( When an element is deleted the corresponding segment form the main segment gets deleted)
4. Friction = 0.1 (Prescribed value)
5. Stmin = 1
6. Gapmin = 0.5
7. Inacti = 6 ( gap is variable with time but intail penetration is computed)

Fig 3 Interface type 7 card

3.Applying the Intial velocity of 35 mph

The INVEL card is created in the solver and the intial velocity of 15.6 mm/ms (35 mph) is assigned by selecting all the nodes.

Fig 4 Assigning the Intial velocity

4.Creating the Rigid wall

The Rigid wall is created in the model by creating the Rigid wall card in the model browser. The Coordinate for the node at which rigid wall is to be created is entered and the Dsearch value of 1000 is given. The Normal to the Rigid wall is also entered.

Fig 5 Rigid wall Creation

5. Creating the Accelerometer

The accelerometer is created below the A & B Pillars. The Accelerometer card is created in the solver and the Node is selected where the accelerometer and the cut off frequency is entered as well.

Fig 6 Accelerometer Creation

6. Creating the Cross section across Pillar, Shotgun, Rail & Crashbox

Step 1 : Creating the Moving Frame

The Moving Frame is created in the component where the cross section is to be created by creating the frame card in the solver. The nodes from the component where the sections are to be created are selected as N1,N2 and N3 in the card.

Fig 7 Creating the frame

Step 2 : Creating the Section in the selected component

The Component where the section is to be created is isolated and the section card is created in the solver. In the section card the N1, N2 & N3 are chosen and the frame created for that particular component is chosen with delta t and alpha value of 0.1 and 1.69 respectively. The Rows of shell elements are chosen on the component for the creaation of the section. The Iframe is assigned the value 12 i.e, the cog of the section .

Fig 8 Creating the Section

Step 3 : Adding the sections in the Output blocks

The Sections block is created in the Time history blocks of the output. The newly created sections in the solver are added in the time history blocks.

Fig 9 Adding the sections in the Output blocks

7. Creating the intrusions in the output blocks

The Intrusions are created in the output blocks. The Mentioned nodes are selected for the inrusion by Id.

Fig 10 Creating the Intrusion in the Output block

8. Mass Balancing to shift the COG

Masses are added to the selective nodes to shift the COG to the required range and increase the overall weight of the model to 700 kg by creating the Solver mass card in the model browser. The COG is checked in the mass Details of the tool.

Fig 11 Adding mass ot nodes through the solver mass

Fig 12 Total mass and COG

9. Checking the model using the model checker.

The model is checked using the model checker in the tool and any error or warning is corrected before running the simulation.

RESULTS :

1. Sectional Forces on the rails, shotguns, pillars and the Crashbox

Fig 12 Sectional Forces

Observation :

The Sectional forces are maximum across the Right rail section where as it is found to be the least across the left side pillar.

2 . Accelerometer curves

Observation :

The acceleration peaks across the left pillar more and at higher values as compared to the Right Pillar.

3. Intrusion on the dash walls

Fig 15 Intrusions for Node 66695 & 66244

Observation :

It can be seen that the intrusion for both Nodes i.e, 66695 & 66244 is increasing in the similar way with respect to time.

CONCLUSION :

The given crash model was succesfully run and all the results were tabulated succesfully.

Fig 16 Crashed Model