Hypermesh Report on - Performing a comparison of the simulation results of the base setup and improved 2D shell element properties

Hypermesh Report on: -

Performing a comparison of the simulation results of the base setup and improved 2D shell element properties.

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• Introduction:

In the standard 4-node 2D shell element, full integration and reduced integration schemes have been used to compute the stiffness matrices and force vectors:
- The full integration scheme is often used in programs for static or dynamic problems with implicit time integration. It presents no problem for stability, but sometimes involves “locking” and computations are often more expensive.
- The reduced integration scheme, especially with one-point quadrature (in the mid-surface), is widely used in programs with explicit time integration such as RADIOSS and other programs applied essentially in crashworthiness studies. These elements dramatically decrease the computation time and are very competitive if the hourglass modes (which result from the reduced integration scheme) are “well” stabilized.

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Hourglass due to reduced itegration: -

• Hourglass modes are nonphysical modes of deformation that occurs in under-integrated elements and produce no stress. By under-integrated, we mean...
  • solid elements with a single integration point.
  • shell or T-shell elements with a single in-plane integration point.
• Reduced integration can lead to non-physical zero-energy modes, called an hourglass mode.
• Two models used to control formulation of hourglassing:
  • perturbation (Q4 elements)
  • physical stabilization (QEPH elements)

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Hourglass pertubration control method:

• Perturbation (viscous) method Ishell = 1,2,3 or 4 (Q4).
  • The hourglass is detected with the relative motion (velocity) of the nodes.
  • when hourglassing is detected, a force is applied on the node to stabilize the deformation.
  • The force is defined according to the element stiffness (young,s modulus, yield stress, plastic tangent, etc.)
  • This force introduced artificial energy (named hourglass energy).
• Perturbation method Ishell = 24 (QEPH) = stiffness method.
  • Hourglass yield depends on natural yield.
  • Hourglass loading stiffness depends on natural tangent modulus.
  • The hourglass treatment is done at the material level.

Hourglass control methods comparison:

• The Q4 (Belytshko & tsay) elements may have lead behavior in case of large rotation and distortion and in case of elastic load-unloading cycles.
  • Inhibits additional hourglassing deformation (can\'t recover from previously accumulated HG deformation)
  • Viscous forms recommended for high velocity/high strain rate problems, e.g., those involving high explosives.
• The QEPH elements give accurate results in case of loading and unloading even if there is an hourglass mode deformation.
  • Able to reduce the total accumulated hourglassing deformation.
  • Preferred for the lower rate problems, including crash stimulation.
  • Stiffness forms may artificially stiffen response. Therefore, reduce the hourglass coefficient, say form 0.10 to 0.03, to minimize stiffness effect.

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

This image shows that the run time has been changed to 55ms in text file and after reading that text file we can see the ENG_RUN properties have also changed the Tstop = 55.

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

This image shows that as we changed the values in text file and after reading that file in hypermesh we have got the Changed the number of animation steps during simulation to a minimum of 25 and maximum of 60 in ENG_ANIM_DT properties.

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Here we have to perform two stimulations and compare them with generated results:

• Procedure for Default values of hourglass control parameters: -

Step 1: Import the geometry

1. Go to the files/import sub-panel.
2. Select the \'.rad\' import translator.
3. In the filename field, enter [Element_Formulation-Shell-3_assignment_0000.rad] or use the browser to find the file.
4. Click import.

Step 2: Export file to Hyperview

This image shows step by step procedure of exporting the file so that we can see the stimulation in hyperview.

Process:

• Goto analysis page
• then click on > Radioss command
• then select and type > -nt 4 in options
• then select input file > Element_Formulation-Shell-3_assignment_0000.rad
• then click on > Radioss.

Step 3: load file in Hyperview

This image shows an image that got loaded in the hyperview window with a hat_section body and a rigid wall.

Process:

• Goto load file
• then select and browse > Element_Formulation-Shell-3_assignment_0000.h3d in options
• then select and browse > Element_Formulation-Shell-3_assignment_0000.h3d in options
• then click on > Apply to load the file in hyperview.

Step 4: Perform stimulation for default hourglass values.

This image shows the hat_section body before stimulation and after stimulation. As we can able to see that the body structure is getting unstable as the elements are unable to resist this type of deformation since it has no stiffness in this mode.

Process:

This highlighted is an important command named contour. By this command, we can assign different types of stimulation like - Displacement, von-mises stress, etc.

• Goto Contour option which is on the command line.
• then click and select any of the mentioned types of stimulations like > Displacement stimulation option.
• then click on > Apply. (Then we will see that body is ready for stimulation.)
• but to play stimulation we have to click on > Play command. (Then we will see stimulation of the body.)

Step 4: Generate graphs for the default hourglass values.

This image shows the plot of global variable vs. time by showing results values for - Internal energy, Kinetic energy, Hourglass energy, Total energy & Contact energy (MAG).

This image shows the plot of the rigid wall/RIGID WALLS vs. time by showing results values for - Resultant Normal Force (NF), Resultant Tangent Force (NF) & Total Resultant Force.

This image shows the plot of the global variable vs. time by showing results values for - Time Step (MAG).

Process:

If we select this command it will open show the relevant graphs data which have been generated during stimulation.

This image shows graph content entities that have been imported.

• Goto hypergraph page
• then select and browse > Element_Formulation-Shell-3_assignmentT01 file.
• then click on and select > Y-type option.
• then click on and select > Y-request option
• then click on and select > Y-component option.
• Here we will have an X-axis fix as time.
• then click on > Apply.

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• Procedure for Recommended properties of hourglass control parameters: -

Step 1: Import the geometry

1. Go to the files/import sub-panel.
2. Select the \'.rad\' import translator.
3. In the filename field, enter [Element_Formulation-Shell-3_assignment_0000.rad] or use the browser to find the file.
4. Click import.

Step 2: Changing Default properties to Recommended properties.

This above image shows the recommended values that should be exported before generating the engine file and importing it to hyperview.

Process:

This image shows that we have to apply recommended values in the properties of the hat_section & close-out panel.

Now as we can see that the recommended properties have been applied so we are ready to generate and export the Element_Formulation-Shell 3_assignment_0000 .rad file to hyperview.

Step 3: Export file to Hyperview

This image shows step by step procedure of exporting the file so that we can see the stimulation in hyperview.

Process:

• Goto analysis page
• then click on > Radioss command
• then select and type > -nt 4 in options
• then select input file > Element_Formulation-Shell-3_assignment_0000.rad
• then click on > Radioss.

Step 4: load file in Hyperview

This image shows an image that got loaded in the hyperview window with a hat_section body and a rigid wall.

Process:

• Goto load file
• then select and browse > Element_Formulation-Shell-3_assignment_0000.h3d in options
• then select and browse > Element_Formulation-Shell-3_assignment_0000.h3d in options
• then click on > Apply to load the file in hyperview.

Step 5: Perform stimulation for default hourglass values.

This image shows the hat_section body before stimulation and after stimulation. Now we can see the difference as we have applied the QEPH element method. As we can see 1 integration point on the surface => Hourglass modes with null strain energy must be stabilized. In previous stimulation, it was producing meaningless results but as we can see it has produced meaningful data.

Step 6: Generate graphs for the default hourglass values.

This image shows the plot of global variable vs. time by showing results values for - Internal energy, Kinetic energy, Hourglass energy, Total energy & Contact energy (MAG).

This image shows the plot of the rigid wall/RIGID WALLS vs. time by showing results values for - Resultant Normal Force (NF), Resultant Tangent Force (NF) & Total Resultant Force.

This image shows the plot of the global variable vs. time by showing results values for - Time Step (MAG).

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Conclusion: -

Comparing Both the results:

This image shows the comparion between default values and recommended values of hourglass control parameters.

We can see that the hourglass energy is gradually increasing while running default properties and it\'s nearly zero while running the recommended properties.

We have got the energy error results that there has been reduced value from -10.3% to -0.1% after changeing the default properties to recommended properties.

We can also notice that there is no change in the mass error values in both stimulations.

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