Assignment 3

RADIOSS ELEMENT FORMULATION

OBJECTIVES :

To Compare 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.

Recommended properties:

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.

PROCEDURE :

• CASE1

1. Change the run time and animation steps in the engine file Element_Formulation-Shell_assignment_0001.RAD file.

FIG 1 : ENGINE FILE

2. Import Starter file Element_Formulation-Shell_assignment_0000.RAD in Hypermesh under Radioss profile.

FIG 2 : FE COMPONENT SETUP case1

3. View the shaded elements and hide unnecessary surfaces. Do not use recommended element properties for case1.

4. Under Analysis > Radioss select the destination folder CASE1 to save the simulation.

FIG 3 : RADIOSS ANALYSIS WITHOUT RECOMMENDED ELEMENT PROPERTIES

5. Switch to Hyperview choose Element_Formulation-Shell-3_assignment.h3d file from CASE1 folder to run the simulation. The way elements deform is not acceptable. It could lead to Hourglass and contact energy errors.

FIG 4 : CRASH SIMULATION

6. Open Element_Formulation_Shell3_assignment_0001.out file in notepad.

7. Check the %energy error and mass error. The maximum energy error is -10.3% and mass error is 0.1659E-03.

• CASE 2 :

1. Import starter file Element_Formulation-Shell_assignment_0000.RAD in Hypermesh under Radioss profile.

FIG 5 : FE COMPONENT SETUP case2

3. View the shaded elements and hide unnecessary surfaces. Use recommended element properties for case2.

4. Under Analysis > Radioss select the destination folder CASE2 to save the simulation.

5. After Radioss job is done, open the Hyperview and select Element_Formulation-Shell-3_assignment.h3d file from CASE2 folder to run simulation. The deformation is acceptable so that the elements have negligible or no Hourglass energy error nor contact error.

HOURGLASS ERROR OVERVIEW

In the case of these Reduced Integration elements, while post processing results, we can see a false or fake deformation mode (zig zag lines). Such a thing is the Hour Glass phenomenon.

The above is an example of a Single Integration point shell element. The values captured at the single integration point at the centre remains same as the dotted lines have not changed in magnitude or in angle. However, the element as a whole has shown a change in configuration. This is because elements with lesser integration points are less stiffer and as there is no stiffness in this mode, these elements have shown this kind of change in Configuration.

In actual physical scenario or in Experiments, this does not happen. But in FEA this happens. This is just a non physical zero energy mode which leads to excessive element distortions. The more structured and less distorted your elements are, the better the results.

6. Switch to Hypergraph by splitting the graphic area and select Element_Formulation-Shell-3_assignmentTO1 file.

7. Under Build Plot, select

• X Type : Time
• Y Type : Global Variables
• Y Request : Internal Energy, Hourglass Energy, Contact Energy, Total Energy
• Y Component : MAG and click apply.

FIG 6 : HYPERGRAPH PLOTTING

8. Similarly,After creating New plot, Go to Build Plot and select,

• X Type : Time
• Y Type : Rigid wall/Rwall-Force
• Y Request : 4 RIGID WALL 1
• Y Component : total resultant force and apply.

FIG 7 : PLOTTING RIGID WALL FORCES

COMPARISON OF CASE 1 AND CASE 2 :

1. The Animation captured for CASE1 is not natural since elements distort with observable hourglass error while CASE 2 is natural because of using recommended Element properties.

2. There is Hourglass energy error and contact energy error in CASE 1 but negligible or zero error in CASE 2.

<- CASE 1

<- CASE 2

FIG 8 : VISIBLE HOURGLASS ENERGY ERROR IN CASE 1 BUT NO HOURGLASS ERROR IN CASE 2

3. The %Energy error exceeds -10.3 % for CASE 1 whereas it is just 0.1% for CASE 2. For a simple component the error of -10.3% is not acceptable.

4. The mass error is constant 1.1659E-03 for both cases.

LINK FOR CASE 1 FILES: https://drive.google.com/drive/folders/1JMgyWSqS7f8YMOUOPMcWJxDQLlggjdEW?usp=sharing

LINK FOR CASE 2 FILES: https://drive.google.com/drive/folders/10YDZlzrmlpeYCyTDsFdl-CEKa5k9CUxq?usp=sharing

CONCLUSION :

1. The Engine file is edited as specified.

2. The component is subjected to crash simulation with and without recommended element properties.

3. The Seperate .out files are checked for energy error and mass error and acceptable case is judged.

4. The Hypergraph plotting is done for acceptable case(case 2) for Internal Energy, Hourglass energy, contact energy , Total energy and Rigid wall forces.