How-to : COMSOL for Crystal Plasticity on hoffman2

0. Make sure XQuartz is installed locally (Mac OS). You may need to restart your computer prior to full installation. More information can be found here - https://www.hoffman2.idre.ucla.edu/access/x11_forwarding/. If using a different OS, follow the similar instructions at the previous link to enable local GUI operation.

1. ssh into hoffman2 terminal and enable X11 forwarding for GUI appications with the -Y command.

ssh -Y login_id@hoffman2.idre.ucla.edu

2. Request an interactive session. An example of a 4-hour interactive session can be found below. More information can be found here: https://www.hoffman2.idre.ucla.edu/computing/interactive-session/.

qrsh -l h_rt=4:00:00,h_data=12G

For access to COMSOL 5.5 if you have high-performance nodes, use

qrsh -l rh7,h_data=20G

3. Load COMSOL into the workspace

module load comsol

4. Run COMSOL

comsol

If this GUI crashes, try

comsol -3Drend sw

Or

comsol &

5. Given a minute or two, the COMSOL GUI should open. From here, you can use File -> Load File -> select the poly_cp.mph file. The simulation parameters can be altered by selecting the desired varaible tab. Once all desired parameters have been updated, you can hit "compute" to start the simulation.

6. Alternatively to running COMSOL during an interactive session, the job .mph file can be submitted through hoffman2. To run in a multi-thread capacity use:

comsol.q.multithread

Alternatively, to run in parallel use

comsol.q.parallel

In both cases, follow to menu to build the command file (as you would with the job.q menu), and submit the job. The hoffman2 description for job submission can be found here - https://www.hoffman2.idre.ucla.edu/comsol/.

If accessing the comsol.q menu fails, use the qsub approach of:

qsub -N MYCOMSOLMPHFILE /u/local/apps/submit_scripts/submit_comsol_multithreaded.sh

where MYCOMSOLMPHFILE is the name or path to your comsol file without the trailing .mph.

How-to : Basic Post-Processing of COMSOL Data

Once the .mph file finishes being run through the COMSOL software, several different avenues can be taken to analyze the initial microstructure and resulting structural propoerty evolution.

Plotting Grain Structure

This step could take place prior to running the .mph file, so long as the grain orientations have been pre-loaded into COMSOL. Follow the steps of:

1. Click on Interpolation 1/2/3, under global definitions
2. "Create Plot" (makes a new "3D plot group")
3. Click on "Volume", which appears to be a filled in 3D cube in the toolbar
4. Under Dataset, select "From Parent"
5. For expressions, use the drop down selection menu to select Global Def->Functions-> qi1
6. Finally, click "plot". Then delete the plane data one tab above for easier viewing. The structure should appeear as something similar to the image shown below:

Plotting Spatially distributed variables

If dislocation density were of interst, for example, follow the steps below. The same procedure would be possible for any other spatially distributed variable or derived value.

1. Click on the "Derived Values" tab
2. Click on "Volume", which appears to be a filled in 3D cube in the toolbar
3. Select the specific point in time from the "Time" dropdown menu that you are interested in plotting
4. Click on the "Volume 1" tab which appears below the newly created 3D plot group
5. Under "Dataset" select "From Parent"
6. Under the expressions tab, use the drop down red and green arrows to select the variable of interest. For derived values follow the path of Component 1 -> Definitions -> Variables -> (Dislocation Density)
7. Finally, click plot and the 3D volume should populate with an image similar to the one below.

Plotting the Stress-Strain Curve

The default loading conditions of the poly_cp.mph file is in the xx direction, but the process can easily be converted to whatever reference frame is used.

1. Right click on the "Derived Values" tab
2. Navigate to the "Line Average" selection
3. Select the 4 edges that lie in the x-y plane and are perpendicular to the xx direction
4. Under the list of expressions to compute, add in the expressions for F11, F12, F13, F21, F22, F23, F31, F32, F33, W11.
5. Click "Evaluate" so COMSOL can compute the averaged values across the areas selected.
6. In the new table that is created in the lower right-hand corner of the screen, click the "copy headers and table to clipboard" selection. Paste the data into an empty text file.
7. Calculate the total strain tensor as E = (F'F -I)/2 where F' is the transpose of the deformation tensor F. Where F = [F11, F12, F13; F21, F22, F23; F31, F32, F33]. Then plot the xx component of the E tensor against the intermediate stress value W11.
8. Alternatively, the data can be loaded into MATLB and the stress_plotter.m script can be used.

Plotting Geometrically Necessary Dislocations

1. Go to the results section of the output file and click the "Volume" button (filled-in cube in the upper toolbar)
2. In box for the expression, specify the following for the norm of the G tensor:

sqrt(G11^2 + G12^2 + G13^2 + G21^2 + G22^2 + G23^2 + G31^2 + G32^2 + G33^2)

3. Hit plot! The result should look similar to the image below:

Note: process meant to link with code found here: https://github.com/admal002/Diffuse-interface-polycrystal-plasticity