Sample density

Submitted by mdvalencia on Wed, 05/27/2020 - 04:28

Hello everyone.

I am running a model for a geotechnical test known as Direct Shear, I have defined the box were the particles must be inserted, and the number of particles I have to inserts for the density I want to reach, when I run the software it seems that the particles are greater than the software can put into the geometry I defined, however, when I put the particles in a wider section of insertion the problem persists, one of the things I have performed is to reduce the number of particles, but for that solution, the sample would not reach the density I need after the application of confining pressure. I would like to know if the method I am using to define the number of particles is correct or if I have to improve my methodology. I am attaching the equations I am using for the N particles definition.

I hope you can help me

Thank you so much for your attention.

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Image icon npart.png6.11 KB
richti83's picture

richti83 | Fri, 05/29/2020 - 13:21

Shouldn't the formula for sphere volume be 4/3 Pi r^3 ? But that's maybe a typo ..

With the available insert methods you can only reach 33% voidfraction in liggghts bc. overlapping of spheres is not allowed in particle insert phase.
To overcome this, have a look at examples\LIGGGHTS\Tutorials_public\packing. The idea is to insert the number of desired particles but with less diameter and than blow them up slightly to the needed volume while the boundaries are fixed.

Best, Christian.

mdvalencia | Tue, 06/02/2020 - 03:11

Hi Chistian

Thank you again for recommending me the example. I would like to understand the syntax used in the packing code. I see there is an alpha start and an alpha target. I would like to understand more about those factors. If I want to grow my particles to the double of the size I defined, is it ok to set alphastart = 1 and alphatarget=2?.

Thanks

Miguel

mdvalencia | Sat, 05/30/2020 - 02:51

Thanks I will follow that tutorial

Best regards, Miguel