Why Realflow doesn't have a container?

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Vitor Teixeira
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Why Realflow doesn't have a container?

Postby Vitor Teixeira » Fri Jan 08, 2010 3:39 am

All the fluids simulation, if I'm not wrong, have to be emitted inside a container. The reason for this to happen is it because in physics, a fluid is generally regarded as a continuum, rather than a bunch of individual molecules?! Where by doing this we can manipulate them by adding values to different sections of the containers. I mean where a combustion and different parameters can take place, interacting with each other - manipulating the simulation. Is this idea right?
But why Realflow doesn't need a container is something that I'm trying to understand. Is it because each particle represents an element of liquid mass? I'm getting a little confuse.
Thanks


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Why Realflow doesn't have a container?

Postby tmdag » Fri Jan 08, 2010 3:57 am

It's matter of algorithm used.
Eulerian grid-based fluids are defined in a container,
RF's SPH (Smoothed-particle hydrodynamics) do not need one (and any other software as well).


As Calibrix said In this topic, You will see such container soon :)

NEW Hybrid Based Fluids Solver
This NEW solver will allow you to simulate medium- to large-scale fluids. In the core is a grid-based solver that automatically detects those areas where more resolution is needed, and creates particles that will then be simulated using our standard particle-based solver. Additional details like foam or mist, and even displacement maps, can be created as well.
"Do not feed the trolls"
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Why Realflow doesn't have a container?

Postby lukeiamyourfather » Fri Jan 08, 2010 4:03 am

Fluid simulations that require a "container" are usually grid based solvers like Navier-Stokes for fire and smoke. RealFlow uses smoothed particle hydrodynamics (SPH) which is not the same thing and is not based on a grid. There's quite a lot of information out there about SPH, but this is a good place to start.

http://en.wikipedia.org/wiki/Smoothed-particle_hydrodynamics

SPH is not the only method to simulate liquids but it is probably one of the best methods to simulate liquids for CG and visual effects because of its relative flexibility compared to other methods. Cheers!

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Why Realflow doesn't have a container?

Postby Vitor Teixeira » Fri Jan 08, 2010 5:19 pm

So Reaflow uses an Lagrangian approach right?
What other SPH are out there?
ICE from softimage?

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Why Realflow doesn't have a container?

Postby lukeiamyourfather » Fri Jan 08, 2010 6:35 pm

Vitor Teixeira wrote: So Reaflow uses an Lagrangian approach right?
What other SPH are out there?
ICE from softimage?

There's glu3D for Max, the ICE SPH stuff from Thiago and Grant for Softimage XSI, Houdini has an SPH solver out of the box, and then there's a lot of solvers out there not related to CG.

This isn't out yet but its wroth looking into if you're interested in other simulators. Knowing the work of the individuals leads me to believe its not SPH though.

http://www.exoticmatter.com/overview/

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Why Realflow doesn't have a container?

Postby Vitor Teixeira » Fri Jan 08, 2010 11:35 pm

As they are particle based it's correct to say they use an Lagrangian approach.
Inside particle based we have SPH are there any others?
And inside the grid based?

I'm not understanding well where the Navier Stokes fills in

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Why Realflow doesn't have a container?

Postby tmdag » Sat Jan 09, 2010 3:35 am

After little google digging I've collected some more informations for You:

Navier-Stokes Equasions, describe the motion of fluid it can be adapted in many techniques


Heightfield Fluids(for e.g. Realwave)
Represent fluid surface as 2D function (and problem is that it can have one value per (x, y) = no breaking waves)


Lagrangian methods
Lagrangian specification of the flow field is a way of looking at fluid motion where the observer follows an individual fluid parcel as it moves through space and time


Particle based, Meshfree method
Meshfree methods eliminate some or all of the traditional mesh-based view of the computational domain and rely on a particle (either Lagrangian or Eulerian) view of the field problem.
- SPH (1977) (smoothed Particle Hydrodynamics) invented for simulation of stars, used for simulating fluid flows.
The smoothed-particle hydrodynamics (SPH) method works by dividing the fluid into a set of discrete elements, referred to as particles

The following numerical methods are generally considered to fall within the general class of "meshfree" methods. Acronyms are provided in parentheses.
â–ª Smoothed particle hydrodynamics (SPH) (1977)
â–ª Diffuse element method (DEM) (1992)
â–ª Element-free Galerkin method (EFG / EFGM) (1994)
â–ª Reproducing kernel particle method (RKPM) (1995)
â–ª hp-clouds
â–ª Natural element method (NEM)
â–ª Material Point Method (MPM)
â–ª Meshless local Petrov Galerkin (MLPG)
â–ª Moving particle semi-implicit (MPS)
â–ª Generalized finite difference method (GFDM)
â–ª Particle-in-cell (PIC)
â–ª Moving particle finite element method (MPFEM)
â–ª Finite cloud method (FCM)
â–ª Boundary node method (BNM)
â–ª Boundary cloud method (BCM)
â–ª Method of fundamental solution(MFS)
â–ª Method of particular solution (MPS)
â–ª Method of Finite Spheres (MFS)
â–ª Discrete Vortex Method (DVM)
Related methods:
â–ª Moving least squares (MLS) - provide general approximation method for arbitrary set of nodes
â–ª Partition of unity methods (PoUM) - provide general approximation formulation used in some meshfree methods
▪ Continuous blending method (enrichment and coupling of finite elements and meshless methods) - see Huerta & Fernández-Méndez (2000)
â–ª eXtended FEM, Generalized FEM (XFEM, GFEM) - variants of FEM (finite element method) combining some meshless aspects
â–ª Local Maximum-Entropy (LME) - see Arroyo & Ortiz (2006)
â–ª Space-Time Meshfree Collocation Method (STMCM) - see Netuzhylov (2008), Netuzhylov & Zilian (2009)
â–ª Mesh-free radial point interpolation method (RPIM)





Eulerian grid-based methods
The Eulerian specification of the flow field is a way of looking at fluid motion that focuses on specific locations in the space through which the fluid flows

- volume of fluid method (VOF)

- Lattice Boltzmann methods (LBM)
BGK (Bhatnagar-Gross-Krook) model
MRT (Multiple-Relaxation-Time) model
Regularized model
Entropic model

"Instead of solving the Navier–Stokes equations, the discrete Boltzmann equation is solved to simulate the flow of a Newtonian fluid with collision models such as Bhatnagar-Gross-Krook (BGK). By simulating streaming and collision processes across a limited number of particles, the intrinsic particle interactions evince a microcosm of viscous flow behavior applicable across the greater mass."
Blender 3d uses Lattice Boltzmann method
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Vitor Teixeira
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Why Realflow doesn't have a container?

Postby Vitor Teixeira » Sat Jan 09, 2010 3:47 am

This is huge. Fantastic quite impressive.
I'm going to take a look.
I'll ask anything later if I need to.

Can you give me some links of this information. It's mainly because I'll need to prove where I got this information. For reasons connected to the bibliography in the dissertation. I'm sorry if I'm asking a lot.
It's ok if you don't have the time.
Really thank you

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Why Realflow doesn't have a container?

Postby tmdag » Sun Jan 10, 2010 6:25 pm

About different mesh free methods:
http://en.wikipedia.org/wiki/Meshfree_methods
http://www.springerlink.com/content/f505n82805687324/

about Lattice Boltzmann:
http://en.wikipedia.org/wiki/Lattice_Boltzmann_Method
http://www.lbmethod.org/
"Do not feed the trolls"
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FX Technical Director
Weta Digital

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Vitor Teixeira
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Why Realflow doesn't have a container?

Postby Vitor Teixeira » Mon Jan 11, 2010 1:40 am

Thanks a lot Albert for having the time to give that.
I really appreciate your help.

Luke I talked with Robert Bridson he told that the product will probably will be available to buy in the next summer to Mac and Linus, with support focused on Fedora versions similar to Maya. Is Fedora a lot different from Ubuntu?
Cheers


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