# resonant column test

Hello everyone

I am a new user on Yade and I am new modelling in DEM.

I want to model a resonant column test, which consist on apply an isotropic stress on a cylindrical soil sample and then apply torsion to different strain levels. I have seen the triaxial test examples and there the soil sample used is a cube in a rigid wall, the isotropic consolidation there is applied through servo-controled system and then the deviatoric stress is applied. I have several questions about that topic.

1. I would like to know if the servocontrol system could be used in a cylindrical sample or if the sample response will be different if I use a cubic sample, I haven't found any reference about the topic, but I have seen in several references and in other examples that explain the consolidation could be achieved increasing the particle sizes. That takes me to the next question.

2. If I perform the isotropic consolidation increasing the particle sizes I have a change in the PSD, in some forums and some references I have seen that size doesn't matter in Yade, at least in models where high frequencies effects are not important. But in a resonant column test, the frequencies are foundamental to define the material behavior. And also if I change the particles and I consider the gravity there could be a change...

3. My last question is about the initial particle sizes I should use. I have seen that O'Sullivan (2011) recomends to use the representative volume element, but if I have a distribution of particles sizes, the number of contacts changes, Does that matter?

Thanks

## Question information

- Language:
- English Edit question

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- Answered

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- Yade Edit question

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- Last query:
- 2019-07-18

- Last reply:
- 2019-07-18

Robert Caulk (rcaulk) said : | #1 |

> if the servocontrol system could be used in a cylindrical sample

If you are referring to triax-script1.py (?), TriaxialStressC

[1]https:/

Jan Stránský (honzik) said : | #2 |

If I did the example now, I would use boxes instead of facets..

Jan

Thank you for your help Robert. I am going to try with that example. I have seen that the model runs very slow with the real PSD. Do you have some recommendations about this topic having into account the test I want to perform?.

Thanks

Miguel

Jan Stránský (honzik) said : | #4 |

Hi Miguel,

> the model runs very slow with the real PSD

could you post the values you use?

The critical time step depends on particle size, its density/mass and stiffness

t_cr = R * sqrt(density/young) [1]

the smaller particles, the smaller critical time step, the smaller simulation. Real PSD could contain very small particles.

some options:

- artificially "cut" the PSD, not including the smallest particles

- increase mass of the smallest particles to increase critical time step (google selective mass scaling, advanced mass scaling or such).

cheers

Jan

PS: as it is quite different question than the original one, next time please open a new question [2]

[1] https:/

[2] https:/

Thanks Jan. next time I will open a new question.

My I have defined my PDS as follows:

psdSizes,

And the time step I have used is

O.dt=.5*

I understand this calculates the time steep in function the particles' array

Thanks for your answer

Miguel

## Can you help with this problem?

Provide an answer of your own, or ask Miguel David Valencia Galindo for more information if necessary.