Crash Analysis of Rail model.

Comparison of results with base simulation and improved shell element properties

1.Using the crash beam file from the previous assignment, change the run time to 55 ms.

2. Change the number of animation steps during simulation to a minimum of 25 and maximum of 60.

3. Run the base simulation without any modification to element properties.

4. At the end of the simulation, do the energy error and mass error checks and determine whether results would be acceptable.

5. If acceptable, Plot rigid wall forces, internal energy, hourglass energy, contact energy, total energy of the simulations.

6. Change all the shell elements properties to recommended properties, save this as separate, rad files and run the simulation.

7. Follow steps 5 and 6.

8. Create a brief report comparing all the results from steps 5 and 6 for both simulations.

9. Comment whether there is any change in the results and why there is any change in the result.

WITHOUT RECOMMENDED PARAMETERS :

• Importing File into Radioss,

• Select Radioss > 0000.Rad > Import, which contains model details

• The shell model will be visible on the screen, Run Time is been set as 55ms

Frequency Calculation:

Frequency = Termination End Time/ Steps Required

Frequency =55/50

F=1.1

RUNNING SIMULATION WITHOUT ANY MODIFICATION TO ELEMENT PROPERTIES:

• To perform analysis, Analysis > Radioss

• Run Radioss

• Hyperworks solver file gets displayed.

• We able to find Energy Error = -10.30% and Mass Error =0.1659E-03
• Click on Resullts, to view animated view of the model

• Click on 1 - Which segements the display.
• Click on the split part and select Hypergraph 2D
• Click on File icon and select T01 File, Which stores the graph datas.

• Select the Required parameter to be plotted.
• Energies to be displayed in an graph sheet, in which.

Global Variables > Internal Energy > Mag > Apply

> Kinetic Energy > Mag > Apply

> Total Energy > Mag > Apply

> Hourglass Energy > Mag > Apply

> Contact Energy > Mag > Apply

Rigid Walls > 4 Rigid wall 1 > FNXX-NORMAL FORCE > Apply

• Datas are plotted on the graph.

GRAPH PLOTS :

1

2

3

4

5

RIGID WALL RESULTANT :

GRAPH DESCRIPTION:

• Using Hypergraph 2D, we plot Energy Characteristics (Internal, Kinetic, Hourglass, Contact,Total Energy)and Rigid wall characteristics (Resultant Force)
• The Internal energy was 0 initially, later it increases change in work done, approximated 2.0E+07
• kinetic energy is maximum at the initial condition, after crashing in rigid wall, it slows down and 4.0E+04
• Total energy is the sum of KE+PE+IE, which should be a flat line, decreases due to hourglass energy deflection approximated to 5.5E+07
• Contact energy is found be 0 Throughout the process.

RECOMMENDED PARAMETER :

Recommended Parameters are to be given as input, for the same components, in which input datas are,

Parameters	Comment
Ishell =24	QEPH 4 nodes shells are best combination of cost and accuracy.
Ismstr=2	Full geometric nonlinearities (default)with possible small strain formulation activation in RADIOSS Engine.
Ish3n=2	Standard 3 noded shell (C0)with modification for large rotation(default)
N=5	Number of integration points set to 5 for accuracy bending.
Ithick=1	Thickness change is taken into account for accuracy.
Iplas=1	Iterative plasticity for good accuracy.

• Same properties is used for both Hat Section and closed out panel.

• And same procedure is to be followed on analysis done on previous model.

• We able to find Energy Error = -0.1% and Mass Error =0.1659E-03
• Click on Resullts, to view animated view of the model

1

2

3

4

5

GRAPH DESCRIPTION:

• Using Hypergraph 2D, we plot Energy Characteristics (Internal, Kinetic, Hourglass, Contact,Total Energy)and Rigid wall characteristics (Resultant Force)
• The Internal energy was 0 initially, later it increases change in work done, approximated 1.7E+07
• kinetic energy is maximum at the initial condition, after crashing in rigid wall, it slows down and 4.4E+04
• Total energy is the sum of KE+PE+IE, which is a flat line, due to optimization of hourglass energy in modified element property found to be stable.
• Contact energy is found be 0 Throughout the process.

RIGID WALL RESULTANT :

ENERGY ERROR AND MASS ERROR :

ENERGY ERROR : When the elements are subjected to deformation, there will be multiple forces acting on the elements, the elements will undergo change in shape, which is unrealistic, without proper shape, in which system induces some opposite forces to rectify the deformation that is induced by hour glass energy, is known as Energy error.

• "If the error is negative, it means that some energy has been dissipated.

  In case of under integrated elements (Belytschko shells, solids with 1 integration point), the Hourglass energy can also 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 case of using QEPH shell formulation (I_shell=24) 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% is acceptable

  If the positive energy error is greater than 2%, the source of this energy has to be identified. Incompatible kinematic conditions can lead to such a situation".

MASS ERROR: When there is an energy error affecting the elements, the solver usually add up or removes mass according to the requirement involuntarily, that caused mass error. Usually mass error upt 2-3% is considered to be acceptable.

Comparing both models , we arrive for the conclusion is that,

Energy Error = -10.3% (Without Modification) & -0.1% (With Modification)

Mass Error =0.1659E-03 (Without Modification) & 0.1659E-03(With Modification) i.e, 0.0001659 < 2-3% and is neglible

Falls under limit of acceptance.

HOUR GLASS COMPARISON:

The imagine shows the comparison of elemental deformation between Q4(1 to 4) Vs QEPH(24) way of processing the deformation that occurs. We can find QEPH retains its structure, that by processing the data by using stiffness method. The QEPH is also known as Improved Under Integrated method. Whereas, on other hand Q4 is an default way of hypermesh to process the data, which is quicker and less accurate, and we can see the elemental structures getting broken, which is not ideal.

COMPARISON OF DATAs PROCESSED WITHOUT AND AFTER MODIFICATION:

• The Internal energy on default conditions is approx 2.0E+07, whereas on Modifying the properites we get 1.7E+07
• kinetic energy on default conditions is approx 4.0E+04, whereas on Modifying the properites we get 4.4E+04
• Total energy is the sum of KE+PE+IE, which should be a flat line is not achieved, on modified model, due to optimization of hourglass energy in modified element property found to be stable.
• Contact energy is found be 0 Throughout the process on both the simulations.

These comparisons are projecting that the integration conditions , by means of which data is been processed and manages. QEPH is better in processing the data than Q4.Strain formulation method induced.Continous thickness data taken into account are the factors that created better impact.