[Sidefx-houdini-list] Smorganic

Ozgur Yılmaz eoyilmaz at gmail.com
Sun Apr 18 13:23:14 EDT 2010


sorry I was wrong about vorticity. It is the divergence and curl of the
velocity field that you use as parameters while modelling a fluid flow.
Vorticity is another concept that happens in boundaries of viscous fluids
when the fluid is in touch with a solid material.

E.Ozgur Yilmaz
Lead Technical Director
www.ozgurfx.com


On Sun, Apr 18, 2010 at 11:02 AM, Ozgur Yılmaz <eoyilmaz at gmail.com> wrote:

> Pablo, if you can download the videos in their site, you can actually see
> the thin layer of particles that they are talking about. So it doesn't seem
> to me like that they are doing some trick in surfacing phase, but instead
> they are filling new particles in specific places, specifically the places
> where the holes are going to form.
>
> As they have explained in the interview, this places where a hole is going
> to form actually can be found by calculating the divergences of the
> particles. I haven't tested this idea though, so I'm sure there are some
> other things that they keep as a secret.
>
> I've generated particles where the density gets lower a threshold, but as
> the Fusion CI guys said there are sudden explosions when you do something
> like that. So you also need to keep track of the inner pressure to prevent
> explosions in the simulation.
>
> So the whole idea should be something like that, calculate each particles
> divergence, and if the divergence goes below a threshold (may be negative
> divergence is enough, I need to check it), then check the pressure at that
> position and if the pressure goes also below a threshold emit a new particle
> at this position, and may inherit the attributes from the neighbour
> particles ( again I haven't tested anything). Though, these are bare ideas,
> this Monday I'm going to look at these ideas, when I get back to work.
>
>
> Cheers.
>
> E.Ozgur Yilmaz
> Lead Technical Director
> www.ozgurfx.com
>
>
> 2010/4/18 Pablo Giménez <pablogipi at gmail.com>
>
> I remembered this article about Smorganic.
>> After reading it and having done some similar work before in Houdini, the
>> main thing the people from Fusion CI is doing is just slving the lack of
>> deontrol in the RF mesher, basically doing stuff you can do in SOPs.
>> Fluid solvers can get nice results at mid scales but not a so small
>> scales,
>> that´s truth, but you can get the overall motion sing SPH or grid solvers,
>> the trick is the look. Their main achieve is to get a smooth thin layer of
>> geometry from the particles created in RF. This is perfectly doable in SOP
>> using particles created from DOPS or even RF. I remember doing simialr
>> stuff
>> some years ago in the H8 times using RF particles in Houdini to get a
>> decent
>> mesh.
>> Then you have a plethora of tools like Particle surfacer, Smooth, Preak,
>> magnet, Convert, etc ... to get a nice mesh in Houdini.
>> Finally to get the finest and high frequency details you have displacement
>> shaders on your arsenal.
>> Voila Smorganic!
>> I have seen lots of amazing sims from these guys but the stuff  around
>> smorganinc is just marketing around some techniques to fix and massage
>> meshes created from particles simulated using SPH. Stuf that Houdini TDs
>> have been done for years.
>> We have been living with Smorganics and we didn´t know, Oh my godness!
>> My 2 cents.
>>
>> 2010/4/17 Ozgur Yılmaz <eoyilmaz at gmail.com>
>>
>> > first of all, David Johnson; you were write about being not specific,
>> sorry
>> > about that, as you correctly guessed the thing I want to achieve was to
>> > have
>> > a continuous thin sheet of water.
>> >
>> > Alex and Szymon, thank you for your links, those were very helpful...
>> >
>> > After reading the article about smorganic, I remembered that the fluid
>> > motion is estimated as vorticities and divergences about a point, so the
>> > motion of moving away or moving towards a point called the divergence,
>> and
>> > moving or spinning around a point is called vorticity. I had a book
>> > (probably left at the studio) where it was explaining the whole idea
>> behind
>> > the fluid dynamics, I need to look at that book again (need to wait till
>> > Monday :) ).
>> >
>> > As Szymon suggested, I need to add my own nodes to the particle fluid
>> > solver, nodes that searches for low divergent areas and creates new
>> > particles.
>> >
>> > So thank you guys again, you enlightened me.
>> >
>> > Cheers...
>> >
>> > E.Ozgur Yilmaz
>> > Lead Technical Director
>> > www.ozgurfx.com
>> >
>> >
>> > On Sat, Apr 17, 2010 at 9:09 PM, Szymon Kapeniak
>> > <szymon.kapeniak at gmail.com>wrote:
>> >
>> > > Go it. Thanks!:
>> > >
>> > >
>> >
>> http://www.cgw.com/Publications/CGW/2009/Volume-32-Issue-12-Dec-2009-/Viewpoint.aspx
>> > >
>> > > 2010/4/17 Alex Czetwertynski <alex at franktheplumber.com>:
>> > > > If you can find it, get the CGW (Computer Graphics World) issue from
>> > > > december 09 (the one with Avatar on the cover).  The Fusion CS
>> people
>> > > > wrote an article on smorganics and how it works within realflow
>> > > >
>> > > >
>> > > > On Apr 17, 2010, at 7:12 AM, François Duchesneau wrote:
>> > > >
>> > > >> And with a Vop Pop you can have lots of control on the behavior of
>> the
>> > > >> global force and letting the sph make the particles stick together.
>> > > >>
>> > > >> François
>> > > >>
>> > > >> Szymon Kapeniak wrote:
>> > > >>>>> I've looked at the orbit node but it seems like it orbits a
>> bunch
>> > > >>>>> of
>> > > >>>>> particles around another particle, my problem is to fill new
>> > > >>>>> particles
>> > > >>>>> (probably to a position where the density is below a threshold)
>> > > >>>>> into a
>> > > >>>>> fluid
>> > > >>>>> simulation...
>> > > >>>>>
>> > > >>>>> I'm quite new in DOPs/POPs in houdini (although I'm much more
>> > > >>>>> experienced
>> > > >>>>> with SOPs), so I don't know how to setup a system that adds new
>> > > >>>>> particles
>> > > >>>>> to
>> > > >>>>> an ongoing simulation...
>> > > >>>>>
>> > > >>>>> Thank you...
>> > > >>>>>
>> > > >>>
>> > > >>> How close you can come to Fusion demos this is another story of
>> > > >>> course, but my suggestion would be to dive into sph solver in DOPs
>> > > >>> and
>> > > >>> look around. Basically it consists with a series of microsolvers
>> > > >>> computing different qualities of fluids. You can turn on / turn
>> off
>> > > >>> any of them (open asset and start play with it) - I think only
>> > > >>> density
>> > > >>> is mandatory for other solvers to work properly. You can for
>> example
>> > > >>> turn off all external forces and pipe a pop solver instead to a
>> > > >>> chain.
>> > > >>> If you point it to a pop network (like the one created for you by
>> a
>> > > >>> shelf tool "Particle Fluid from Object", you can control fluids
>> like
>> > > >>> they were particles, but they look rather like computed by sph. I
>> > > >>> suspect this is what is happening in Fusion demos inside RF.
>> > > >>>
>> > > >>>
>> > > >>>> 2010/4/17 Alex Czetwertynski <alex at franktheplumber.com>:
>> > > >>>> I was at a presentation at DMALA where the Fusion guy was showing
>> > > >>>> this.  He made a big point about it being a Realflow solution
>> only.
>> > > >>>>
>> > > >>>
>> > > >>> Perhaps in terms of amount of particles which practically can be
>> > > >>> computed, this can be done by RF only.
>> > > >>>
>> > > >>>
>> > > >>>> I think you should have been more specific in what about the
>> > > >>>> example you
>> > > >>>> were looking to recreate. François' suggestion of the orbit pop
>> > > >>>> would be for
>> > > >>>> making the particles move in the vortex, but my guess is that
>> > > >>>> you're trying
>> > > >>>> to make the water stay in a nice thin sheet as it moves. That is
>> a
>> > > >>>> much
>> > > >>>> harder task. Maybe you could contact the guy from Fusion CIS to
>> > > >>>> see if you
>> > > >>>> could license his solver and use it in DOPs. Just a thought.
>> > > >>>>
>> > > >>>>
>> > > >>>
>> > > >>> Aren't they using vanilla Realflow with custom scripting?
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>>
>>
>> --
>> Un saludo
>> Best Regards
>> Pablo Giménez
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>
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