About Clump's Velocity Initialization

Hi,

I think you have two problems:

1. Your bodies (including the clump) are dynamic, ie they can not have in general (unless they do not sustain any force/interaction) a constant velocity, equal to the one you defined.

Then, the velocity you defined is only an initial velocity, and what happens afterwards depends on interaction possibilities (there are some, here), and kinetic energy might turn into interaction energy (velocity may vanish)

See https://yade-dem.org/doc/user.html#motion-constraints

(this is not clump-specific)

2. In the specific case of clump, it seems you need to (logically ?) deal with dynamic and velocity attributes at the clump body level.
Hence, adding
O.bodies[clumpId].dynamic = False

and replacing
O.bodies[clumpId[1][0]].state.vel
with
O.bodies[clumpId].state.vel

should do what you want

Note that I'm not really a clump user, so better check yourself.

PS: note that in general, looking at the 3D view to know whether bodies move or not is generally misleading because displacements upon the DEM cycles get usually unnoticed to the eye. Better check bodies state.vel (which confirms the GUI impression here)

Thank you so much, Duriez.

Thank you for answering so carefully, But I still have problems to this question. :(

->1:
    I went back to inspect to check the initial speed (not yet started the iteration) and found it was still zero. In order to avoid confusion, I did a comparative experiment. If it was not clump, I used this method to assign the initial speed and check the initial speed as my desired value.

->2:
    I tried what you said again. If you assign a function clumpId directly, it will make an error (parameter mismatch). If you assign a function clumpId [0], although it does not make an error, the detection speed is still zero.

->ps:
   Thank you very much for reminding me of this. I have always ignored this. Sometimes we don't necessarily see reality. :)

Hello,

> clumpId=O.bodies.appendClumped([sphereBig,sphereSmall])

O.bodies.appendClumped returns (id of clump, list of id of members). So it is usually used like this (it is more readable):
#
clumpId, memberIds = O.bodies.appendClumped(...)
#
this will also solve your problem 2

> I want ... give one of them initial speed

You can assign a velocity to a clump member. However, the value is overwritten from the values of the clump. This is why your approach does not work.
Alternatively, you can assign velocity and angular velocity to the clump.

> If you assign a function clumpId [0], although it does not make an error, the detection speed is still zero.

what is "detection speed"?

cheers
Jan

Thank you so much Jan :)

I used the wrong word, actually "detection speed" refers to the initial velocity observed from the "inspect button" after I press F12.

->#
->clumpId, memberIds = O.bodies.appendClumped(...)
->#

When I write in this way, and I use "O.bodies[clumpId].state.vel=(...)", the initial velocity I get is still zero.

Best regards

Yingnan

Thanks Jan Stránský, that solved my question.