Yade

resonant column test

Asked by Miguel David Valencia Galindo

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
Status:
Answered
For:
Yade Edit question
Assignee:
No assignee Edit question
Last query:
Last reply:
Revision history for this message
Robert Caulk (rcaulk) said : 		#1

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

If you are referring to triax-script1.py (?), TriaxialStressController, the answer is no since it is designed to let the user control 6 walls of a cube. However, there is a hidden triaxial example showing one creative way to apply isotropic stress to a cylindrical specimen in Yade [1]. In that example, Jan controls hundreds of individual facets around a cylindrical cohesive specimen. Such a method might be problematic if you have wide PSD and a non-cohesive packing, since particles will almost certainly "leak out". A good starting point, nonetheless.

[1]https://gitlab.com/yade-dev/trunk/blob/master/examples/concrete/triax.py

Revision history for this message
Jan Stránský (honzik) said : 		#2

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

Revision history for this message
Miguel David Valencia Galindo (ingmdvg) said : 		#3

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

Revision history for this message
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://yade-dem.org/doc/formulation.html#stability-considerations
[2] https://www.yade-dem.org/wiki/Howtoask

Revision history for this message
Miguel David Valencia Galindo (ingmdvg) said : 		#5

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

My I have defined my PDS as follows:

psdSizes,psdCumm=[0.000075,0.00015,0.0003,0.000425,0.0006,0.00085,0.00118,0.00236,0.00475],[0.2,0.26,0.42,0.52,0.6,0.69,0.77,0.92,1.]

And the time step I have used is

O.dt=.5*PWaveTimeStep()

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.

To post a message you must log in.