# How to get P-wave and S-wave velocity

Hi,

I'd like to ask that how to get the P-wave velocity and Shear wave velocity in Yade for a DEM soil model?

According to [1], in which it gets timestep accoring to the velocity of P-Wave propagation, so I guess there is already an function that can directly get the P-Wave velocity, but I didn't find it.

For the Shear wave velocity, do you have any suggestions to get it?

Thanks!

Leonard

## Question information

Language:
English Edit question
Status:
Solved
For:
Assignee:
No assignee Edit question
Solved by:
Leonard
Solved:
Last query:
 Revision history for this message Jérôme Duriez (jduriez) said on 2021-04-26: #1

I think what is usually coined in the doc as P-Wave velocity is
(b.mat.young / b.mat.density)**0.5 # b a body with a material having these young and density attributes -- most of them.

Whether (b.mat.young / b.mat.density)**0.5 actually is a elastic wave velocity in a packing including bodies with these velocities is another question, in my opinion (and the answer would be no), but this is part of the classical confusion about these "young" parameter..

As for the S-wave velocity, it's kind of the same: the only way I see to measure it is to actually simulate a S wave and to measure its speed.

(Note that in the particular case of your link, the doc is even more unfortunate in my opinion -- on my TODO list by the way.. -- since PolyhedraMat.young may not be a stress-like quantity in Pa)

 Revision history for this message Jérôme Duriez (jduriez) said on 2021-04-26: #2

> in a packing including bodies with these *parameters*

Sorry

 Revision history for this message Bruno Chareyre (bruno-chareyre) said on 2021-04-28: #3

Hi,

PWave velocity is (bulk modulus /density)**0.5 with "modulus" and "density" defined at the macroscale.

For density it is simply mat.density * (1-porosity). For the modulus, you can evaluate it with a static loading (uniaxial compression).
I would discourage trying to actually simulate a wave propagation, it is particularly complex and error-prone.
Bruno

 Revision history for this message Leonard (z2521899293) said on 2021-05-09: #4

Thanks Jérôme and Bruno!