[Sidefx-houdini-list] Smorganic

Ozgur Yılmaz eoyilmaz at gmail.com
Mon Apr 19 06:59:13 EDT 2010


allright guys, I need help...

I've been struggling all the weekend. Basically I want to calculate the
divergence of the velocity vector field of the particles, there is a node
called "Gas Analysis" in micro solvers which actually does that. The Gas
Analysis node wants a source and destination fields, where it will calculate
the divergence of the source field and store the data in destination field.

So I need first to create divergence scalar field. At this stage I can use
"Gas Match Field" node to create the divergence field. It needs a reference
field like density to create another one with the same size and length. But
whenever I enter divergence to field and density to reference field and
connect the "Gas Match Field" to the final_solver as the final input it
gives me an error saying: "Required data density not found or the wrong
type". I've also tried "vel" as the reference field and have the same kind
of error. So what could be wrong, any idea?

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


On Mon, Apr 19, 2010 at 10:11 AM, Ozgur Yılmaz <eoyilmaz at gmail.com> wrote:

> Actually Pablo, you are right, a solution that works, at the end of the
> day, is a solution, no matter what have been used to reach the goal. I
> support your point of view. I was just saying that the guys haven't used a
> technique that can be done by using SOPs.
>
>
> Cheers....
>
> E.Ozgur Yilmaz
> Lead Technical Director
> www.ozgurfx.com
>
>
> 2010/4/18 Pablo Giménez <pablogipi at gmail.com>
>
>> 2010/4/18 Ozgur Yılmaz <eoyilmaz at gmail.com>
>>
>> > 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.
>> >
>> I got your point. And I am pretty sure their system is better than some
>> massage in surfacing, more complex and probably more exact in terms of
>> maths.
>> But I have to deal with this kind of problems with fluids several times,
>> and
>> sometimes the more complex solution is not the best.
>> I have worked with several RF artists I have used it a lot indeed, and
>> many
>> problems they can´t solve just because RF is basically a fluid solver can
>> be
>> solved with SOPs.
>> At the end of the day you have to get the proper look. I remember one time
>> trying to getting a very thin layer of fluid, from some RF particles, as
>> they point in their article it was really difficult due to resolution
>> limitations, basically due to limitation in the SPH workflow, you need to.
>> Solution, just get a more thick surface wich fills all the holes and then
>> use a custom peak done in VOPs which make the layer thinner using some
>> atributes. job done.
>> Is just an example and I don´t want to say the stuff they are doing is
>> bad,
>> just recall that sometimes you don´t need rocket science to solve a
>> problem,
>> just be smart and notice the details that makes something work, and have
>> in
>> your hands the tool to modify your geometry/data to make it.
>> And BTW, the problem they want to solve is at small scales, grid solvers
>> work really well at this scales and you can create an isosurface from it,
>> and have all the data at your hands from the DOP operators, even
>> divergence,
>> and use these data in any other context in Houdini.
>> Probably I am wrong, but as I have said before sometimes effects TD
>> solutions are better than engineers solutions.
>> Appart from this RF is an excellent tool and I have several friends at
>> NextLimit so no worries here :)
>>
>>
>> > 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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>>
>>
>> --
>> Un saludo
>> Best Regards
>> Pablo Giménez
>> _______________________________________________
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