problem with cylinder model

[Chiny Lan]

Hi, I try to using a cylinder as wheel to do single wheel test based on the demo_FSI_SingleWheelTest. But the cylinder interact with the particles as if the radius of the cylinder becomes larger. There is always a gap between the cylinder and the particle.

Then I test the demo_FSI_CylinderDrop using WCSPH json. It shows similar behaviors.

[Radu Serban]

This is because the actual representation of the cylinder as far as interaction with the soil phase is concerned is a collection of so-called BCE markers (of the same “radius” as the SPH particles) that are arranged in several layers *on* and below the cylinder surface.  To get a visualization that corresponds to the actual simulation, you could either:

• Change the visual appearance of the cylinder to that collection of BCE markers.
• Inflate the radius of the visualization cylinder by the radius of an SPH particle.

--Radu

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[Chiny Lan]

Oh, I really works. Thanks!

Can I change the size of BCE markers so that they are not the same size as SPH particles?

Moreover, If there is some method to fill the SPH granular terrain with particles of random radius and positon? 

[Radu Serban]

You may want to read a bit more on SPH.  The particles in SPH are *NOT* the same as particles in granular material.  The problem is solved as a continuum with a meshless methos (SPH here) with is a Lagrangian particle-based method.

As such:

• it makes no sense to have particles “of random radius and position”
• for a proper coupling of the two phases, the BCE markers must be similar to the SPH particles (read up on phase coupling with such Boundary Constraint Enforcing markers).  You can reduce initial spacing for SPH particles and BCE markers simultaneously.

 

But maybe you are interested in doing actual granular dynamics?  In that case, you should look at the Chrono::Multicore and Chrono::GPU modules. For those, there are indeed functions that allow initialization of the granular materials with different statistics for mixtures and various space samplers (including a Poisson disk sampler) to provide the initial particle positions.

 

--Radu

 

From: projec...@googlegroups.com <projec...@googlegroups.com> On Behalf Of Chiny Lan
Sent: Friday, 30 December 2022 12:29
To: ProjectChrono <projec...@googlegroups.com>
Subject: Re: [chrono] problem with cylinder model

 

Oh, I really works. Thanks!

Can I change the size of BCE markers so that they are not the same size as SPH particles?

Moreover, If there is some method to fill the SPH granular terrain with particles of random radius and positon? 

 

在2022年12月30日星期五 UTC+8 16:33:31<Radu Serban> 写道：

This is because the actual representation of the cylinder as far as interaction with the soil phase is concerned is a collection of so-called BCE markers (of the same “radius” as the SPH particles) that are arranged in several layers *on* and below the cylinder surface.  To get a visualization that corresponds to the actual simulation, you could either:

• Change the visual appearance of the cylinder to that collection of BCE markers.
• Inflate the radius of the visualization cylinder by the radius of an SPH particle.

--Radu

 

From: projec...@googlegroups.com <projec...@googlegroups.com> On Behalf Of Chiny Lan
Sent: Friday, 30 December 2022 09:22
To: ProjectChrono <projec...@googlegroups.com>
Subject: [chrono] problem with cylinder model

 

Hi, I try to using a cylinder as wheel to do single wheel test based on the demo_FSI_SingleWheelTest. But the cylinder interact with the particles as if the radius of the cylinder becomes larger. There is always a gap between the cylinder and the particle.

Then I test the demo_FSI_CylinderDrop using WCSPH json. It shows similar behaviors.

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[Chiny Lan]

Thanks for your answer!

I previously used the DEM method to simulate granular material. Now I try to use SPH to simulate it since the continuum representation method is more efficient. But the technical reference of SPH in Chrono seems not too much. Please forgive me for asking such a simple question.

[Radu Serban]

No need for excuses 😊!
I just wanted to point out that there are some fundamental differences between granular dynamics and the continuum representation using SPH.  Take a look at  https://sbel.wisc.edu/journal-papers/ where you will find some papers that give details about the SPH-based continuum representation of terramechanics in Chrono.

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[Chiny Lan]

Hi, I just checked the demo_FSI_CylinderDrop. The SPH particles actually interacted with BCE markers.

And I then checked the single wheel test simulation that using a cylinder as wheel. The BCE markders seems not to interact with SPH particles and exist gap. Moreover, the output of sinkage of cylinder is too small as I used the default json file of demo_FSI_SingleWheelTest.

[Wei Hu]

SPH is not like DEM, even though two SPH particles do not directly touch each other, they still have interaction since there is kernel support which is a few times larger than the radius of the particles you see here. Please let the cylinder move on the terrain a bit and look at it again, I think the gap should be smaller than this one. I suspect that the cylinder might already touch the terrain and bounced up a bit now, so let it run a bit longer to see if you still see a large gap.

Thank you,

Wei

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