Andrew Coppin wrote:
> 
> *WE ARE IMPRESSED*
> 

Speak only for yourself. But thanks anyway. :-)

Christoph

-- 
POV-Ray tutorials, IsoWood include,                 
TransSkin and more: http://www.tu-bs.de/~y0013390/  
Last updated 13 Aug. 2002 _____./\/^>_*_<^\/\.______

Post a reply to this message

Alex wrote:
> 
> Is brittle fracture one of them? :)

I'm not sure what you would expect in that concern, but accurately
modelling fracture would not be possible with such a system, neither with
a FEM system BTW, it requires calculations on the microscopic and
crystallographic level which is a totally different matter.

> Can anyone help you with documentation and/or sample scenes?
> 

I doubt so, unless you have some special clairvoyant abilities ;-) It's
somehow like the chicken and egg problem...

Christoph

-- 
POV-Ray tutorials, IsoWood include,                 
TransSkin and more: http://www.tu-bs.de/~y0013390/  
Last updated 13 Aug. 2002 _____./\/^>_*_<^\/\.______

Post a reply to this message

On Thu, 26 Sep 2002 13:06:18 +0200, Christoph Hormann
<chr### [at] gmxde> wrote:

>accurately modelling fracture would not be possible with such 
>a system, neither with a FEM system BTW, it requires calculations
>on the microscopic and crystallographic level which is a totally
>different matter.

This is an interesting FEM-based solution:

O'Brien, J. F., Hodgins, J. K. Graphical Modeling and Animation of
Brittle Fracture. SIGGRAPH 99 Conference Proceedings, 137-146, 1999

Further work of O'Brien et. al. can be found in more recent
proceedings of the SIGGRAPH conferences.

Actually brittle fracture is not the worst problem - try getting the
hang of plastically tipped crack propagation :)


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

Post a reply to this message

Peter Popov wrote:
> 
> This is an interesting FEM-based solution:
> 
> O'Brien, J. F., Hodgins, J. K. Graphical Modeling and Animation of
> Brittle Fracture. SIGGRAPH 99 Conference Proceedings, 137-146, 1999
> 
> Further work of O'Brien et. al. can be found in more recent
> proceedings of the SIGGRAPH conferences.

Thanks, i already knew about these, very interesting but some of the
methods used are hardly physically accurate, the FEM is used to determine
the stress field to conclude where fractures occur, but initiation and
propagation of cracks in brittle material is strongly influenced by
microscopic defects in the material and the crystallographic structure
(just imagine a pane of amorphous glass will break totally different than
one made of crystalline material).  Anyway despite the lot of guessing
probably involved the results look fairly good.  Sadly the calculations
seem quite complicated (refining the FEM grid during calculations etc.)
and calculation speed is accordingly slow.

For those interested in the material:

http://www.cs.berkeley.edu/~job/Papers/

> Actually brittle fracture is not the worst problem - try getting the
> hang of plastically tipped crack propagation :)

I know, everything has it's pros and cons, while ductile fracture is much
more deterministic the effects to take into consideration are much more
diverse...

Christoph

-- 
POV-Ray tutorials, IsoWood include,                 
TransSkin and more: http://www.tu-bs.de/~y0013390/  
Last updated 13 Aug. 2002 _____./\/^>_*_<^\/\.______

Post a reply to this message

Peter Popov wrote:
> 
> Actually brittle fracture is not the worst problem - try getting the
> hang of plastically tipped crack propagation :)

BTW, i already thought about adding support for plastic deformation in my
system, it would be fairly simply to introduce by adding a threshold to
the extension of each connection and when this is reached the unextended
length is modified.  I don't know if that would be of practical use
though, and fracture is something totally different of course.

Christoph

-- 
POV-Ray tutorials, IsoWood include,                 
TransSkin and more: http://www.tu-bs.de/~y0013390/  
Last updated 13 Aug. 2002 _____./\/^>_*_<^\/\.______

Post a reply to this message

On Tue, 24 Sep 2002 23:23:15 +0200, Christoph Hormann <chr### [at] gmxde>
wrote:
> The first uses newly implemented face-mass collision tests (thanks to ABX
> for the triangle distance function, i used a modified version of it for
> this)

Is there any interesting addition to my function ? I'm currently joining all
available patches and bugfixes into one release. Can you share your addition
to be included in ?

ABX

Post a reply to this message

ABX wrote:
> 
> Is there any interesting addition to my function ? I'm currently joining all
> available patches and bugfixes into one release. Can you share your addition
> to be included in ?

My variation returns several in between values like the index of the
'cylinder' the function value is calculated from (if it isn't calculated
from the face) and the gradient vector.  

But the modified code would not be useful on it's own, it's just a local
function in my patch wich is called by the collision detection function.

Christoph

-- 
POV-Ray tutorials, IsoWood include,                 
TransSkin and more: http://www.tu-bs.de/~y0013390/  
Last updated 13 Aug. 2002 _____./\/^>_*_<^\/\.______

Post a reply to this message

Great simulation. Universities may be intrested in stuff like this !

Does it only work with a ball or does your formula work with any geometry in
the middle of the film ? :-)



--Theo

----------------------------------------------------------------------------
---------------------------------------------------------------------
Distributed Network-Rendering or Local SMP-Rendering on all CPU's you have.
With SMPOV und POV-Ray 3.5. * Download free at:
http://www.it-berater.org/smpov.htm


"Christoph Hormann" <chr### [at] gmxde> schrieb im Newsbeitrag
news:3D90D7C3.C148673B@gmx.de...
>
> I made some more progress with the mechanics simulation patch, here are
> two test animations.
>
> The first uses newly implemented face-mass collision tests (thanks to ABX
> for the triangle distance function, i used a modified version of it for
> this) as well as grouping of masses for optimizing the collision tests
> (the two balls and the nodes of the box are in different groups, only
> collisions between them and not between the individual nodes of the box
> are tested).  The collision test itself is not yet well optimized.  For
> self collision tests of cloth etc. where the nodes have no radius this
> could be much improved.
>
> The second animation shows a new gradient descent calculation method.
> This means inertia is not taken into account, therefore there is much less
> tendency for instability because oscillations can't occur.  Also there are
> no dissipative forces (friction and damping) so the sheet is sliding on
> the sphere.  All this is of course not physically accurate, but it is much
> faster than methods based on integration of the movement equations and it
> can be useful for example for 'relaxing' a designed geometry before
> starting a real simulation or for generating a static result for a still.
>
> As visible in the end there are no self collision tests, but the
> calculation is really fast, about 12-15 seconds parsing per frame for a
> 50x50 nodes grid.
>
> Christoph
>
> --
> POV-Ray tutorials, IsoWood include,
> TransSkin and more: http://www.tu-bs.de/~y0013390/
> Last updated 13 Aug. 2002 _____./\/^>_*_<^\/\.______

Post a reply to this message