yade-dev team mailing list archive

[sega <sj2001@xxxxxxxxx>]

Hi,

> 1. Factets have normals - what is their meaning? Is it the normal from
> the edge towards the center of mass of the facet?

> 2. What happens if vertices of facet are not in-plane?

InteractingFacet:normal is the normal to a plane in which the facet lies 
(see n_f on fig. distance-to-facet.pdf attached to this mail)

InteractingFacet:edgeNormals is the perpendiculars to the edges. They lies in 
the facet's plane and directed in the facet (see again distance-to-facet.pdf)

on distance-to-facet.pdf: 
x'_0 is Facet se3.position (it is the facet origin);
x'_1 is Facet::vertices[0] (it from x'_0, e.q. from origin); 
x'_2 is Facet::vertices[1] (it from x'_0 also, not from x'_1); 
etc...

n_f = x'_2 UnitCross x'_1

E.q.
edge e_0 = x'_1 - x'_0 = x'_1
edge e_1 = x'_2 - x'_1
edge e_2 = x'_3 - x'_2
etc...

d = n_f Dot ( x - x'_0 ), 
x is the sphere center.

d is distance from x to facet if the projection of x to a facet plane lies in 
facet perimetre.



> 3. Why should I want to have not only facets, but also edges and
> vertices? Does it avoid some singularities at facet boundary?

Edge is the intersection of two faces.
Since the facets are distinct objects, and they are not connected to any 
combinatorial structure (such as, for example, triangulation), the scope of 
interaction with an edge will be the scope of interaction with two faces 
simultaneously. To exclude such a dual interaction imposed edges as separate 
body. (Similarly for vertices as the intersection of two or more edges).

> 4. What subclass of PhysicalParameters for facet is needed so that
> spheres can bump into facets etc (I can look into the code here)?

Any.... For geometry need only se3. See examples/STLImporterTest.py...
(Although I am not sure that I understood correctly this question).

>
> 4. Could you give some rudiementary working example of say 1 sphere
> falling into cone from 4 facets (or something like that)?

Try the other day.

> I tried running your model but didn't succeed (will investigate shortly).
What happened?

> (Preferably you could do the whole thing in python; I added methods for
> raw attribute access to make vector<Vector3r> Facet::vertices (and
> similar) accessible in a way, but didn't figure out the normals. 

> They > are calculated in postProcessAttributes, is that why in your example,
> you save the simulation and load it again? 

Yes.

==
Best regards, Sergei D.

Attachment: distance-to-facet.pdf
Description: Adobe PDF document

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