COMPARING THE SIMULATION RESULTS OF THE BASE SETUP AND IMPROVED SHELL ELEMENT PROPERTIES

Comparison of results with base simulation & improved shell element properties

Objective:

To be able to compare the results with base simulation and improved shell element properties which are required for crash applications by following the below procedure,

1.Using the crash beam file from given 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 element properties for crash applications:

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.

Case set up and Execution with images:

As per given questions:

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

Sol:Import the starter file into the hyper works and change the run time in (T_stop) the ENG_RUN to 55ms in solver browser.

Importing the starter file into radioss

Changing the run time to 55ms through

Solver browser>ENGINE_KEYWORDS>RUN>ENG_RUN>Change T_stop to 55

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

Sol: Change the animation steps through

Solver Browser>ENGINE_KEYWORDS>ANIM>ANIM/DT>ENG_ANIM_DT>change T_start as minimum 25 and T_freq as maximum 60.

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

Sol: Properties before editing the element properties

Run the base simulation by changing the Geom to Analysis in menu page, select the file location from save as. Put the export options to all, run options to analysis, run number 1, give -nt 4 (number of threads to run simulation) in options as shown in the below picture and finally hit radioss to run simulation.

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

Sol: These energy error and mass error we should look at by opening the FIRST_RUN_0001.Out file.

Energy error:

The error must be negative and decreasing. The error must be less than 15% at the end of computation. If the error increases a little, then decrease my be normal. If the error, increases this means that a problem has occurred. Then, the error may grow to 99.9% with computation failure message.

So ideally error should be at most -15% and better to have -5%. The closer to 0% error the better. For QEPH shell formulation or fully integrated elements, the energy error may slightly positive since there is no hour glass energy and the computation is much more accurate. An error of 1 or 2% will be acceptable. Otherwise any positive error means energy has been created which indicates model issue.

Mass Error:

This error is acceptable up to 0.5%.

Review the starter output file FIRST_RUN_0001.out with a text editor.

Check the % (Energy) Error and Mass addition at the end of the computation.

The results mass error -10.3% (Less then 15% is acceptable) and mass addition 0.1659E-03 (Not more then 0.5) are under the given crash application margin. So, the results are acceptable.

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

Sol:

Plotting the Rigid Wall force as a function of time:

Before plotting the graphs load the h3d model file in the hyper view and apart from that all 1D elements are represented by dot through Preferences>Visualization>All 1D elements are represented by Dot>Size of the mark 0.15>Click apply>Press ok (all 1D weld elements are appear).

Observe the animation and plot the rigid wall forces by splitting the screen through page layout window on top of the menu bar. Change the 2_sd Graphical user interface to hypergraph 2d in tool bar.

Open the time history file into the hyper graph 2d (Element_Formulation-Shell-3_assignmentT01). Select Y-type, Y-request, and Y-component as Rigid wall>RIGID WALL 1>Resultant and click apply.

Graph

Therefore, the minimum and maximum rsultant forces are 20367.257813 and 113439.453125 N.

Plotting the Internal Energy as a function of time:

Open the T01 model file in to the hyper graph 2d. Select Y-type, Y-request, and Y-component as Global Variables>Internal Energy>MAG and click apply.

Graph

Therefore, the internal energy with respect to time is raised from 0.00 to 19312604.000 J.

Plotting the Hourglass energy as a function of time:

Open the T01 model file in to the hyper graph 2d. Select Y-type, Y-request, and Y-component as Global Variables>Hourglass Energy>MAG and click apply.

Graph

Therefore, the Hourglass energy with respect to time is raised from 0.000 to 6301777.500 J.

Plotting the Contact energy as a function of time:

Open the T01 model file in to the hyper graph 2d. Select Y-type, Y-request, and Y-component as Global Variables>Contact Energy>MAG and click apply.

Graph

Therefore, the contact energy reaches maximum 25460.953125 J.

Plotting the Total energy as a function of time:

Open the T01 model file in to the hyper graph 2d. Select Y-type, Y-request, and Y-component as Global Variables>Total Energy>MAG and click apply.

Graph

Therefore, the total energy fall down from 61314900 J to 549830 J.

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

Sol: Changing the shell element properties which are recommended for crash applications

Run the simulation by changing the Geom to Analysis in menu page, select the file location from save as. Put the export options to all, run options to analysis, run number 1, give -nt 4 (number of threads to run simulation) in options as shown in the below picture and finally hit radioss to run simulation as done in the base simulation.

7. Follow steps 5 and 6.

Sol:Checking the % (Energy) Error and Mass addition after changing the element properties which are applicable for crash applications.

Hence the energy error is decreased from -10.3% to -0.1% and mass addition remains constant (does not change before and after changing the properties).

Plotting the Rigid Wall force as a function of time:

Therefore, the minimum and maximum resultant forces are 8659.816406 and 114153.796875 N.

Plotting the Internal Energy as a function of time:

Therefore, the internal energy with respect to time is raised from 0.00 to 19750490.000 J.

Plotting the Hourglass energy as a function of time:

Therefore, the Hourglass energy constant entire simulation.

Plotting the Contact energy as a function of time:

Therefore, the contact energy reaches maximum 6137.749023 J.

Plotting the Total energy as a function of time:

Therefore, the total energy fall down from 61258280 J to 61314900 J.

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

Comparison of results with base simulation and improved shell element properties
Sl.no	Parameter	Base simulation	Improved shell element properties
Minimum	Maximum	Minimum	Maximum
1	Total resultant forces	20367.257813 N	113439.453125 N	8659.816406 N	114153.796878 N
2	Internal Energy	0	19312604.000 J	0	19750490.00 J
3	Hourglass Energy	0	6301777.5000 J	0	0
4	Contact Energy	0	25460.953125 J	0	6137.749023 J
5	Total Energy	54983028 J	61314900.00 J	61258280 J	61314900 J

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

Sol: After running these two simulations we observe major difference in two results that are decreasing of energy error % and controlling the formation of hour glassing by physical stabilization (QEPH Elements).

The energy error is decreased from -10.3% to 0.1% and the mass error remains constant for both two simulations.

Concept of hourglass energy:

Hour glass modes are non-physical modes of deformation that occur in under integrated elements and produce no stress. Reduced integration can lead to non-physical zero energy modes, called hourglass modes. There are two methods to control formation of hour glassing i.e., Perturbation and Physical Stabilization.

The controlling of the hour glassing by stabilization are counter plotted below. That shows the hour glass energy entire chash remains zero i.e., the quality of element formation and shell properties which are applied are exactly matched to component.

Therefore, all the results are changed due to the editing of shell elements properties which are recommended for the crash applications.

Result:

Comparison of results with base simulation and improved shell element properties which are recommended for crash application are done successfully. Apart from this the energy error reduced from (base simulation) -10.3% to (improved shell element properties) -0.1% and the mass addition for both simulations are same. This indicates the component under good quality.

Conclusion:

By this assignment I am able to learn about how to compare the results with base simulation and improved shell element properties, how to check the energy and mass errors from engine files, and also how to plot the graphs in hyper graph.

Google drive link:

https://drive.google.com/open?id=1461cxXSrVwFtgKb-HgW4YB5uPP52ZahJ