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Hi!
You are on the right track! Moving the data at 2 nodes per step, stops the
height from adding up unrealistically? Fine! I wonder though.. Do your
system works so that all horisontal movements has a steady speed? Imagine
the wind direction is -1*x and you have a rock somewhere that blocks that
movement. This will cause waves to bounce off in different directions, and
some waves will go directly the opposite way ( 1*x )... In your system,
will they continue in that direction with the same speed and fade out? In
real life, I suppose they will fade and change speed, to eventually end up
going at -1*x again.
This may not be necessary to simulate, though, as the effect might be
subtle?
> To work, the simulation requires some rain
> or lots of wave-emitters, which looks rather
> irregular, but it might do for some scenes
Fortunately, your system does not slow down with the use of many wave
emitters.
> still pondering about another set of macros
> designed to just model the basic flows of the
> stream, and then superimpose some irregular
> waves on that later...
Sounds very interesting!
> Regards,
> Tim
Hugo
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I looks better, however I think the effect is lost until the closing seconds
of the anim (when the water appears to slow down/smooth out)
--
Rick
Kitty5 NewMedia http://Kitty5.co.uk
POV-Ray News & Resources http://Povray.co.uk
TEL : +44 (01270) 501101 - FAX : +44 (01270) 251105 - ICQ : 15776037
PGP Public Key
http://pgpkeys.mit.edu:11371/pks/lookup?op=get&search=0x231E1CEA
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The interaction you describe is more or less a
very physical one: water hits against a rock and
thus, water masses tumble before it, creating the
waves. The water will then be washed away by
the current, but new water also washes against the
rock. Its an ongoing difficult process which isn't
handled by my simulation at all.
In my simulation, the waves caused by wave-emitters
all move at steady speed: 1 node per step. Still, its
not too unrealistic to just move them downstream. Ever
observed raindrops hitting a river? Its the same
effect taking place. But the interaction at the rocks
lacks some physical precision, which is why I am
thinking about some other means which are just
meant to build some basis for a near-realistic still-
frame, and some animated turbulence on the surface
should give a visually acceptable river. Here's a
link to a nice program which is what I'm after:
http://john.deweese.com/StableFluids/
Regards,
Tim
--
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights
Email: Tim### [at] gmx de
> Hi!
>
> You are on the right track! Moving the data at 2 nodes per step, stops the
> height from adding up unrealistically? Fine! I wonder though.. Do your
> system works so that all horisontal movements has a steady speed? Imagine
> the wind direction is -1*x and you have a rock somewhere that blocks that
> movement. This will cause waves to bounce off in different directions, and
> some waves will go directly the opposite way ( 1*x )... In your system,
> will they continue in that direction with the same speed and fade out? In
> real life, I suppose they will fade and change speed, to eventually end up
> going at -1*x again.
>
> This may not be necessary to simulate, though, as the effect might be
> subtle?
>
> > To work, the simulation requires some rain
> > or lots of wave-emitters, which looks rather
> > irregular, but it might do for some scenes
>
> Fortunately, your system does not slow down with the use of many wave
> emitters.
>
> > still pondering about another set of macros
> > designed to just model the basic flows of the
> > stream, and then superimpose some irregular
> > waves on that later...
>
> Sounds very interesting!
>
> > Regards,
> > Tim
>
> Hugo
>
>
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I know, that's what I wanted: first, show it in action,
and then what happens when you stop "raining". I
wanted to see if that would perhaps give at some point
a nice basis for a still, because I think the animated
river works for the animation, but would look rather
unrealistic for a still. Its showing the good and bad
sides of the algorithm.
--
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights
Email: Tim### [at] gmxde
> I looks better, however I think the effect is lost until the closing
seconds
> of the anim (when the water appears to slow down/smooth out)
>
> --
> Rick
>
> Kitty5 NewMedia http://Kitty5.co.uk
> POV-Ray News & Resources http://Povray.co.uk
> TEL : +44 (01270) 501101 - FAX : +44 (01270) 251105 - ICQ : 15776037
>
> PGP Public Key
> http://pgpkeys.mit.edu:11371/pks/lookup?op=get&search=0x231E1CEA
>
>
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For more complex fluid flow simulations, Nick Foster and Ronald Fedkiw's
SIGGRAPH 2001 paper 'Practical Animation of Liquids'
(http://www.cis.upenn.edu/~fostern/pdfs/foster_siggraph01.pdf) is excellent,
if somewhat advanced for my own maths skills...
You mention that what you're looking for is more like Jos Stam's 'Stable
Fluids' paper. I've just had a go at modifying his algorithm to apply to
fluids with a height-field for the air/water boundry, such as the ones
you're simulating. Instead of treating the fluid as incompressibly as he
does, I am using a scalar 'height' field as well as a 2d vector velocity
field to describe the fluid as a 2D compressible one, with the density of
fluid at each point being represented by the height (i.e. depth) of water at
that point.
In my algorithm, first the both height and velocity fields are advected by
the velocity field as Stam describes in his paper
(http://www.dgp.toronto.edu/people/stam/reality/Research/pdf/ns.pdf). The
next stages of the algorithm describe how the height and the velocity of the
fluid interact. Firstly, if the velocities of the fluid around a certain
point are such that more fluid is flowing towards that point than away from
it, the height of that point increases to accomodate the extra water.
Secondly, the velocity field is modified so that at places where there is a
'slope' in the height field, the water tends to run down the slope -
equivalent to very dense areas of a compressed fluid expanding outwards to
equalise the pressure.
This algorithm produces some interesting effects, such as realistic wakes
behind objects. There are still a few bugs to iron out: I suspect that my
algorithm could be improved, and the advection technique introduces
significant blurring due to antialiasing if small time steps are used.
Hopefully I'll get the time to render and post an animation soon to show
what I mean?
Has anyone else tried a "ground-up" approach to fluid flow in Pov-Ray (i.e.
looking at the physics first, then writing the code, rather than basing the
code on what looks best)? I'd be most interested to hear from anyone who
has.
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All that sounds very neat, and from what you're
saying I'm really impatient to see some first tests
and results. For my part, I was just fumbling with
the idea of trying something which crudely models
the behaviour of water, in a much less precise way
than described in all those papers, but which would
be sufficient for a POV-Ray render, taking the long
parsing times into account...
All those difficult equations appear to me like
the system should better be implemented with
C++ or JAVA (JAVA for portability) than
with POV-Script, just because of the speed.
--
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights
Email: Tim### [at] gmxde
> For more complex fluid flow simulations, Nick Foster and Ronald Fedkiw's
> SIGGRAPH 2001 paper 'Practical Animation of Liquids'
> (http://www.cis.upenn.edu/~fostern/pdfs/foster_siggraph01.pdf) is
excellent,
> if somewhat advanced for my own maths skills...
>
> You mention that what you're looking for is more like Jos Stam's 'Stable
> Fluids' paper. I've just had a go at modifying his algorithm to apply to
> fluids with a height-field for the air/water boundry, such as the ones
> you're simulating. Instead of treating the fluid as incompressibly as he
> does, I am using a scalar 'height' field as well as a 2d vector velocity
> field to describe the fluid as a 2D compressible one, with the density of
> fluid at each point being represented by the height (i.e. depth) of water
at
> that point.
>
> In my algorithm, first the both height and velocity fields are advected by
> the velocity field as Stam describes in his paper
> (http://www.dgp.toronto.edu/people/stam/reality/Research/pdf/ns.pdf). The
> next stages of the algorithm describe how the height and the velocity of
the
> fluid interact. Firstly, if the velocities of the fluid around a certain
> point are such that more fluid is flowing towards that point than away
from
> it, the height of that point increases to accomodate the extra water.
> Secondly, the velocity field is modified so that at places where there is
a
> 'slope' in the height field, the water tends to run down the slope -
> equivalent to very dense areas of a compressed fluid expanding outwards to
> equalise the pressure.
>
> This algorithm produces some interesting effects, such as realistic wakes
> behind objects. There are still a few bugs to iron out: I suspect that my
> algorithm could be improved, and the advection technique introduces
> significant blurring due to antialiasing if small time steps are used.
> Hopefully I'll get the time to render and post an animation soon to show
> what I mean?
>
> Has anyone else tried a "ground-up" approach to fluid flow in Pov-Ray
(i.e.
> looking at the physics first, then writing the code, rather than basing
the
> code on what looks best)? I'd be most interested to hear from anyone who
> has.
>
>
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If the blocks are underwater completely (but near the surface), i imaging
there is no interaction with the water to create waves, right? it would be
cool if it did. although, i'm already drooling all over my keyboard watching
this. i love water simulations =)
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Thanks! Yes, you're right. Water interaction
only takes place where the nodes are
intersected with objects. Right now, the
system only checks the calm position of
the nodes, not the displaced ones. So far,
I haven't noticed the need to check the displaced
ones, after all, the waves aren't meant to be
that high.
--
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights
Email: Tim### [at] gmxde
> If the blocks are underwater completely (but near the surface), i imaging
> there is no interaction with the water to create waves, right? it would be
> cool if it did. although, i'm already drooling all over my keyboard
watching
> this. i love water simulations =)
>
>
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