Contact Information Processing

[Mohammad Wasfi]

Hi, 

This is a DEME-related question. It possible might be helpful to other people who use Chrono GPU as well.

I am pretty new to DEM simulations so excuse my ignorance on this topic. I have used the DEME solver to obtain the particle contact information file that includes information such as interacting particles, forces, and contact locations. I have some questions regarding these that I hoped you could help me with. 

1- For DEM users, what are some of the most important parameters that can be extracted using the particles' contact information?

2- I have done some reading and have found that particle stresses can be calculated using the contact information as 1/V*sum(x_i*F_i) where x is the contact location and F is the contact force. This is pretty easy to do when you have one file. However, since contact files are outputted at every frame, I was wondering if there is a program that DEM users use to process this data. I realize that ParView is one popular option. I would appreciate it if someone had a good example to share.

3- Visualization. what would be the best way to use/combine the contact data files with the sphere data files (Outputted using WriteSphereFile ) to better visualize the calculated data? In other words, if I were to process the contact information file in ParaView, what is the best way to render the results along with the sphere data files? 

Thank you so much for your help in advance, I realize that these might be some basic things that DEM users know how to do. However, I have been reading a lot about this and could not find very good resources regarding these questions. Any good examples with pictures will be so much appreciated. Hope this helps other users who are new to DEM modeling as well. 

Thank you again, 

[Ruochun Zhang]

Hi,

The questions look quite general. Here is what I think.

In terms of some essential properties that you may want to extract from a simulation, well, it depends on your needs. As you noted, the normal and shear stress can be important, and then maybe the strain rate, etc. People may have different ways of deriving them in the case of granular material.

As for processing and visualizing the data, in my case I always write my own scripts to do that, because the way I need them to be massaged tends to be specific. Granted, ParaView can visualize both point data and volumetric data, but I tend to finish all the post-processing work before shipping the data to ParaView, instead of attempting to combine them in ParaView, or any other specialized visualization tool, for that matter.

Writing scripts for post-processing is simple, you can use Matlab or Python. For example, if you have force data as a point cloud, then you can use scipy to subsample them at the locations of your granular particles and associate the result with each particle, then output these data-infused particles to a CSV file, then visualize it in ParaView. That is the easiest way for me. 

We can get more creative. An example in DEME is the Indentation demo, where in the simulation script, we directly calculate the particle strain based on the difference of particle locations between 2 frames, and ask the solver to stream that information into the output file directly (I was too lazy to bother post-processing there). It might be more difficult to pull off, but what I want to say is that what you do to the data obtained from the simulation is up to you, and it is easier and more explicit to use scripts to do that.

Thank you,

Ruochun