Assignment 3-2D Element Formulation Challenge

Aim

Comparison of results with base simulation and improved shell element properties.

Procedure

Import the .rad file.

1. CASE 1

As per the requirement run time changed to 55.

• Further To have 40 animation steps, the frequency should be Run time/Animation steps = 55/40 = 1.375
• In model tree, under CARDS collector, ENG_ANIM_DT card have a Tfreq of 1.0, which is changed to 1.375.

The base simulation is run without any modification to element properties using Radioss option under Analysis tab.
Create a folder to save the rad files in local directory.edit options providing number of threads as " -nt 4 ".
After analysis, the .OUT file is viewed to check whether the Energy error and mass error fall within the aceptable range

The energy error starts from 0% to 10% which is within acceptable range.Mass error stays constant throughout the simulation at 0.1659e-04 which is also within the acceptable range.Since the error values are acceptable, rigid wall forces, internal energy, hourglass energy, contact energy, total energy of the simulation are plotted with the help of hypergraph 2-Dhyperview is opened to view the simulation (deformation of the crush tube).model and results (h3d file) are loaded from the newly created folder.

Contour plot of Hourglass energy and Von Mises is obtained using contour option under hyperview.

Since the error values are acceptable, rigid wall forces, internal energy, hourglass energy, contact energy, total energy of the simulation are plotted with the help of hypergraph 2-D.File named Element_Formulation-Shell-3_assignmentT01 is opened.Specified energies are plotted against time on the same plot as shown below:

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.

As per the recommendation property criteria changed and repeated the procedure as it performed for above default .

CASE 2 OUT FILE given below

Contour plot of Hourglass energy and Von Mises is obtained using contour option under hyperview.

Specified energies are plotted against time on the same plot as shown below:

When recomended properties are changed from the base values, simulation results shows that

• Total Energy remains constant rather than decreasing which is clear from the energy error which went till-10% now changed to -0.1%.
• Hourglass energy which was increasing changed to zero throughout the simulation.
• Contact energy characteristics are same in both cases.
• Internal energy is having a gradual increasing characateristics in both the cases.
• Rigid wall forces also decreased to a lower value than that of default value rigid wall force value.
• Contour plots shows that there is a slight increase in maximum displacement of element with recommended property values.

Hourglass energy:

In FEA, the hourglass mode is also known as the "zero energy mode" because deformation energy of elements under hourglassing mode is zero. But the hourglass energy is not equal to zero.In a shell element which have a number of integration points, for reduced computation effort, a reduced integration which uses a single integration point is used. In such cases, the deformation mode from the analysis results will be false. This is called hourglass phenomenon.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.

Conclusion

Learned how to carry out simulation using hypergraph and the property card how it gives changes in the simulation results.