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[Jan Stránský <question218111@xxxxxxxxxxxxxxxxxxxxx>]

Question #218111 on Yade changed:
https://answers.launchpad.net/yade/+question/218111

Jan Stránský proposed the following answer:
Where does this script come from? Anyway let me explain how Yade works in
this script and why the results are correct:


O.materials.append(FrictMat(young=3e8,poisson=0.3,frictionAngle=radians(20),density=2600,label='spheres'))
>

material with density=2600 is created


> c0=utils.sphere([0,0,0],.5,material='spheres')
>

body with material 'spheres' is created. At this moment, mass of the
particle is computed from density (2600) and its volume


> O.bodies[0].material.density=260000
>

now you set density of the material to 260000, but actual particle's mass
remains unchanged. If you created new particle of the same size with
material 'spheres', it would have different mass than the original particle
c0


> O.dt=utils.PWaveTimeStep()
>

PWaveTimeStep computes time step from particles' mass, not their material
densities. That's why changing material.density has no effect.

If you do

c0.state.mass *= 100

than the time step computed with PWaveTimeStep would be different.

cheers
Jan

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