Assignment 3

Assignment 3

Objective

1. To change the run time to 55 ms in the given crash beam.
2. To change the number of animation steps during simulation to a minimum of 25 and maximum of 60.
3. To run the base simulation without any modification to element properties.
4. At the end of the simulation, to do the energy error and mass error checks and determine whether results would be acceptable.
5. If acceptable, to plot rigid wall forces, internal energy, hourglass energy, contact energy, total energy of the simulations.
6. To change all the shell elements properties to recommended properties and run the simulation.
7. To do the energy error and mass error checks and to plot rigid wall forces, internal energy, hourglass energy, contact energy, total energy of the simulations after changing properties to recommended properties.
8. To compare all the results.
9. To comment whether there is any change in the results and why there is any change in the result.

Procedure

1. To change the run time to 55 ms in the given crash beam.

Import the starter file. (Open hypermesh. Import Solver Deck > Import _0000.rad File)

Go to solver browser. Open the tree ENGINE_KEYWORDS > RUN > RUN > ENG_RUN. Click on ENG_RUN.

Change the value of Tstop to 55.

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

Open the tree ENGINE_KEYWORDS > ANIM > ANIM/DT > ENGINE_ANIM_DT. Click on ENGINE_ANIM_DT.

Change the value of Tstart to 25.

3. To run the base simulation without any modification to element properties.

• In panels go to Anslysis > Radioss.
• Select the input file destination.
• Select export option as All. It will select all hidden files also (If any).
• Run option as Analysis.
• Run number as 1.
• Options as -nt 4 (-nt 4 means 4 CPU solves the problem at a time).
• Now click Radioss.

After the run of the simulation the following window will pop up.

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

Go to files and open the file 0001.out file. Check the energy error and mass error.

Energy error : The energy must be negative and decreasing. The error must be less than -15% at the end of the simulation.

In this problem at the end of simulation energy error is -10.3% and mass error is 0.1659E-03. Eneegy error is less than -15% in this problem therefore results are acceptable.

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

To see the deformations in the crash beam change the client selector to Hyperview. Browse Altair Hyperviw Player (.h3d file) file and click apply. Play the animation to see the deformation in the crash beam. The deformation time starts from 25ms as we have given Tstart as 25.

To change the visualization of different elements go to Preferences > Options > (New window popups) Visualization.

Change All 1D elements to Dot. Size of mark can also be changed. Change it 0.15.

To plot various graphs

Click Page window layout and select two window layout. Click on second window and switch to Hypergraph 2D. Click Expand/reduce window.

Import T01 file and plot the required files.

Rigid wall forces

Select Y type as Rigid wall/Rwall-forces, Y Request as 4 Rigid wall 1, Y component as Total Resultant Force > Apply.

Now Y Component as Resultant Normal Force > Apply and Again Y Component as Resultant Tangent Force > Apply.

Internal Energy and Kinetic Energy

Open the new plot. Select Y Type as Global Viables, Y request as Internal Energy and Kinetic enegy, Y Component as MAG > Apply

Hourglass Energy

Open new plot. Select Global Variables > Hourglass Energy > MAG > Apply.

Contact Energy

Open new plot. Select Global Variables > Contact Energy > MAG > Apply

Total Energy

Open new plot. Select Global Variables > Total Energy > MAG > Apply

To see the results of various contour switch to hyperview and click contour.

Select result type as Displacement and click apply

Select result type as Von mises, Average method as simple and click apply

Select Result Type as Hourglass and click apply

6. To change all the shell elements properties to recommended properties and run the simulation.

Change the run time to 55 ms and Tstart to 25 by same procedure followed as above.

Change all the shell elements properties to recommended properties.

Go to Model browser > Properties > Select Hat section and Close out panel and change the properties.

Now run the file as earlier without changing any options (Analysis > Radioss)

7. To do the energy error and mass error checks and to plot rigid wall forces, internal energy, hourglass energy, contact energy, total energy of the simulations after changing properties to recommended properties.

Go to files and open the file 0001.out file. Check the energy error and mass error.

To plot rigid wall forces, internal energy, hourglass energy, contact energy, total energy of the simulations.

To see the deformations in the crash beam change the client selector to Hyperview. Browse Altair Hyperviw Player (.h3d file) file and click apply. Play the animation to see the deformation in the crash beam. The deformation time starts from 25ms as we have given Tstart as 25.

To plot various the graphs

Click Page window layout and select two window layout. Click on second window and switch to Hypergraph 2D. Click Expand/reduce window.

Import T01 file and plot the required files.

Rigid wall forces

Select Y type as Rigid wall/Rwall-forces, Y Request as 4 Rigid wall 1, Y component as Total Resultant Force > Apply.

Now Y Component as Resultant Normal Force > Apply and Again Y Component as Resultant Tangent Force > Apply.

Internal Energy and Kinetic Energy

Open the new plot. Select Y Type as Global Viables, Y request as Internal Energy and Kinetic enegy, Y Component as MAG > Apply

Hourglass Energy

Open new plot. Select Global Variables > Hourglass Energy > MAG > Apply.

Contact Energy

Open new plot. Select Global Variables > Contact Energy > MAG > Apply

Total Energy

Open new plot. Select Global Variables > Total Energy > MAG > Apply

Countour plots

Displacement

Von mises

Hourglass

8. To compare all the results.

To compare the graphs before and after the recommended properties

Rigid wall Forces

Internal Energy and Kinetic Energy

Hourglass Energy

Contact Energy

Total Energy

Displacement contour

Von Mises contour

Hourglass contour

To compare Results

Without recomended properties With recomended properties

Max Value Min Value Max Value Min Value

1. Rigid Wall

i. Total Resultant Force 113357 52885.3 113638 21032.9

ii. Resultant Normal Force 113357 52552.8 113638 11670.8

iii. Resultant Tangent Force 5921.82 196.394 17497.9 154.759

2. Internal Energy 19285676 0 17465234 0

3. Kinetic Energy 61314900 35680184 61314900 43792244

4. Hourglass Energy 6.31597e06 0 0 0

5. Contact Energy 25411.5 0 7598.86 0

6. Total Energy 61314900 54965860 61314900 612574807

7. Dispacement 7.611e02 9.759e-03 7.810e02 6.203e-01

8. Von Mises 3.499e02 0 3.497e02 0

9. Hourglass 2.283e04 -2.693e01 0 0

Conclusion

By using recommended element properties

• Energy error reduces (reduced from -10.3% to -0.1%)
• There is no change in mass error.
• There is improvement in the results.
• The hourglass reduced to zero.

Details on Hourglass

Hourglass modes are nonphysical modes of deformation that occur in underintegrated elements and produce no stress.

By underintegrated, we mean

• Solid elements with a single integration point.
• Shell or Tshell elements with a single in-plane integration point.

Hourglassing Due To Reduced Integration : Reduced integration can lead to non-physical zero energy modes, called hourglass modes.

Hourglassing modes

Underintegrated solids have 12 HG modes (4 such modes are shown below).
Underintegrated shells have 5 HG modes.

Hourglass Modes in Shells

Avoiding or Minimizing Hourglass Modes

Fully integrated solids and shells do not hourglass

• Full integration is more expensive.
• Fully integrated elements can be less robust for large deformations.

Tetrahedrons and triangles do not hourglass

• Generally not recommended due to locking tendencies.

For elements that are susceptible to hourglass modes, internal hourglass forces are applied to resist the hourglass mode deformation

• There are several algorithms (hourglass formulations) available for computing these forces.

Two methods used to control formation of hourglassing

1. Perturbation (Q4 Elements)
2. Physical Stabilization (QEPH Elements)

Hourglass Perturbation Control Method

Perturbation method Ishell=1,2,3 or 4 (Q4)

• The hourglass deformation 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.
• This force is defined according the element stiffness (Young modulus, yield stress, plastic tangent,..)
• This force introduces an artificial energy (named hourglass energy)

Perturbation method Ishell= 24 (QEPH)

• Hourglass yield depends on natural yield
• Hourglass loading stiffness depends on natural tangent modulus
• The hourglass treatment is done at the material level.