HI,

I have been using realflow for past 2 years
after looking at houdini its never going back to realflow
The approach and quality is just crazy and jaw drop

But ofcourse the software being new,am not able to solver lot of issue
I have been constantly watching and working looking at the water fall tutorial from go procedure

For the current project we have to do a water rafting sequence
Now the problems, i was able to get nice water flowing after adding small and big stones ,but how do we get more volume the river is very thin in volume
i wanted my simulation more thick and Fat so that its higher from ground
and gives more volume .

I hope i haven't missed out any point
Waiting for a early response
Thanks

Can you make the emitter bigger?!

Cheers

HI,

Even when i make the emitter big ,after it travels some distance the
volume reduces.
i was thinking some vop node or may be some way it maintains volume
and it has some thickness

there is Particle Motion/Separation/Apply Particle Separation parameter on FLIP solver, maybe that can help preserve some volume

I would also try adding extra emitters along the way…

You could try several things:

- Decreasing the grid scale in your flip object (default is 2, try something like 1)
- Increasing velocity, this should emit more particles if im correct
- Inside your FLIP Object node stead of using a surface sop as a input geometry you could try using a particle field, then go to some and use point from volume with low particle distance so you should have more particles per frame

Just play around with these stuff and see for yourself what they do..

Ok ,so basically what eveyone is saying is i need to generate more particles to get more volume.

Does reseeding and separation help u get more volume or its not recomended ?

Yeah reseed particle should give you more particles if you set particles per voxel to a higher value you should have more particles, I usually use this when I want to increase my particle count just a little bit instead of subdividing my grid (lowering my particle seperation).

Im not sure if you are talking about the seperation tab in the flipsolver node –> particle motion –> seperation, when you enable this and set the scale lower than 1, you wel seperate your fluid is smaller groups.. for example 0.5 shoulg give you small droplet groups.

If you want to have more distance between your particle you might want to look at divergence perhaps, values lower that 1 should attract the particles to eachother and higher than 1 push them away from eachother.

There might also be a collision seperation somewhere for particles, dont have houdini on this computer at this moment..

Hi Vidit,

I hope by now you might have found solution for your problem. While going thru this post I notice, you are trying to follow waterfall tutorial and as you mentioned that you are doing a water rafting shot.
My simple question is that why you are trying to fill the river in first place? Do you need to show the river ending in a fall? If not I would suggest you might take the approcah of a filled tank or area and create basic motion of river and let the character interact with it.
I might be wrong but if you can post ur scene file or a picture of what you are trying to do then you might get more accurate answer, provided you have not solved your problem yet. But it is a good case study to learn some more.

Well the solution is still pending ,i have a work around to get volume
basically i have low ress base simulation and on top of that another simulation which is detailed and has lower density(lighter than the base fluids,referred to peter quint tutorial for flip)
But its going to be really heavy

I have been working in realflow for few years and have encountered same problem,but with hybrido similar to flip it gives you volume but detail is lost

I need to show the river hitting the edge and turns of whole set.
So am not sure talk would help because it will have rectangle boundries.
I may be wrong also as am still new to houdini

I would really wish to share the file and image ,but due to Client agreement and NDA i can't share anything.
I am really happy with the forum and the fact someone actually replied back asking if this problem was solved .


I wish there were more tutorial for flip

Thanks again

I made this in photoshop just for the visual purpose.let me know if this helps

Gravity has accelerating effect on the sloped water to the point where it thins out and hits a terminal velocity which can be due to faster water colliding against slower water, friction against the collision surface, internal viscosity forces when the water essentially turns in to a violent mix of air and water and in extreme cases such as a waterfall, air resistance itself.

Flip doesn't have built-in checks to acceleration and velocity by default.

The fluid will thin out as the simulation progresses as your fluid accelerates just like in reality. If you clamp velocity you will get unrealistic motion for the fluid affected by the velocity as you described. It will look like muddy water with low acceleration/velocity thresholding to sludge with high acceleration/velocity thresholding.


Your reference image shows a nice calm flat river babbling over a small shelf in to a tiny pool and then slowly carrying forward and you want your fast moving water down a steep slope to have a similar feel. Two competing looks.

Ok.

The recommendations regarding bulking the sim by simply reducing the volume resolution wrt the particle scale size is fine but it will definitely change the look and not really counter the thinning of the fluid. In fact with more accurate velocities present at higher grid values may allow for even greater acceleration and velocities to be supported. Yes you can carry more particles but in the end it will thin out pretty fast and just delay the effect until further down the steep river.

I recommend you stay away from divergence as it requires a divergence field and a divergence pass in the flip solver. This will cause increased memory requirements and decreased sim speed for not much gain. FLIP can do decent water sims without divergence these days.


So here's the scenario: you need to add a terrific amount of fluid down a steep set of rapids which will create a simulation with an incredible amount of energy then send a raft down in to what will be an extraordinary set of class 6 rapids which no raft could navigate with occupants remaining in said vessel at the end of the ride.

http://www.youtube.com/watch?v=hFEQJ9ZuBfk [youtube.com]
Check out the 1:14 mark and that is pretty much the scenario in reality. Notice how thin the water gets and adding more fluid at the top will just create more of a frothy mess and not a nice thick fast moving sheet of water. The steeper the slope, the thinner the water gets given that the same amount of water is entering the falls at the top.

What to do to keep things real yet look exciting?
- Add flatish shelves with deep catch basins along the path of the river to try to create pools of slower water to impede the progress of the water moving over the thinner parts of the river bed. This is a plausible scenario if the river bed consists of very hard and very soft layers of rock that was eroded over time.
- Make your river bed less steep. Use a different camera location and lens focal length to make the river look steeper than what it really is.


So what cheats can you employ to give you some control back?
- Use Pumps to emit net new water in strategic places along the waterway with creative velocities mostly with the velocity in Y magnitude determinging fluid emission rate. Make sure the net new water has counter velocities to push back the water but not so much as to create too much turbulence.
- Add counter velocities in strategic locations along the river bed in the body of the fluid to keep the fluid in check without affecting the look. This can be done by adding/sculpting collision velocities to the river bed for example. Add velocities to the river bed in an upward direction of course but tilted back a bit in the direction of the water flow to kinda simulate a wee bit of drag between the river bottom and the fluid interacting in that localized region.
- Parent constrain pumps and sinks (with or without velocity sculpting) before and after the raft and in strategic parts of the river to get the raft to the height you want it to and to plow a path through the water churn so that it can at least look plausible.

Good luck!

Hi Vidit,

Look what I said, a picture tells a lot then words. And see who came to rescue you.

Thanks Jeff for the great explaination and ideas to achieve the effects.

From your pics, I notice that you are reducing the Particle Radius Scale when you are reducing Particle Sepration to get more volume. In my opinion you should not do that as you will loose particles.

Don't take my words, just put a flip tank in a new scene and playblast. And then without changing anything else, just reduce Particle Radius Scale to 0.5 from 1.2 (Default). Do you got what I mean to say. Now try doing same with 0.95. I am not saying don't touch this, experiment with it. In my tests, I have notice there is a value for this parameter, if you go below that you start lossing them.

Infact in one of my test, I was able to actually increase Particle Separation while retaining the details. I did few other changes in my setup to get almost same level of details and guess what I got some more voulme too. But those changes will not work for you as your reference/ target water is very calm.

Wow ..that was some great help,i learned a lot
Thanks JEff ,you were a great help
thanks 3d gang for those tips

3d gang i think the image was just for a reference ,my requirement is like this
http://www.youtube.com/watch?v=YyhpyCJZI4k [youtube.com]
1:00 mark

as jeff sugested i have done those modification to the set,made more slopy or gave it a slant with patched of ups and downs

i even tried playing with the particle radius scale it works great

3d gang can u please share the houdini file for the tank flow ..it very interesting and would like to see how u got so much detail in the mesh
what was ur particle seperation ..what u used fore rendering
how to get more detail on the mesh to define the scale of the set


thanks a lot again to all you guys

And special thanks to jeff ..you rock !!!!

Glad to know, water flowing at ur end. Vidit you changed your reference, not a good practice on shot production but I understand while working on something there might be new findings or change of course.

Particle separation for first part in movie for my early post, was 0.025 but for the later part it is 0.05. Huge saving on calculation and disk space. I used subsurface shader for the rendering water body with an env light using PBR. Please note that sim was not done using tank flow, I am still working on that method to get same kind of motion and detail. Although I managed to get permission to put test render on forum, but didn't got it for hip file. I am afraid at moment I can't share the same hip file.

But no worries, just to prove what I said in my early post and give you the exact method that changed my sim a lot with detail and volume, I am attaching another movie file. I used Jeff's scene to demonstrate the difference when you change particle radius scale and what happen when you tweak just one parameter on ur setup, check it out. Nothing fancy and if you have seen waterfall tutorial as well as Peter's video, they have explained the same, I just picked it.

Thanks 3D-gang for more help.
some more questions.(please)

1.At what scale should i sim with respect to world scale
like my sets are huge and the sim will never happen .ever..so how much should i scale it down ?
because i notice ur particles separation is .025 and with the scale i am working on highress sim is around coming to .05 and for far shot .1
with low ress i can sim around 500 frames in 12 hours (24 gb Hp zeon )
and highress takes twice or some times 3 times .

2.Do u actually use reseeding,i notice it takes a lot of space

3. how do i get small detail that i can see in ur render.

4.can u also share some of ur stats.

5.Will my base model on which am running the sim only can give more splashes flying

6.How do you really start your shot ? do's and don't

i know i have asked a lot of question .so far this the only forum which has really helped me so far.

Thanks a ton again

Sorry for delay, was busy breaking things at work. I am able to tweak further Jeff's scene to get more details in sim. But let me first answer your questions.

1.At what scale should i sim with respect to world scale ….
It is a very difficult question to answer, people say do this, do that but my personal opinion, whatever works for you, gives you right scale in final render, sim at optimal level on your hardware and setup (very imp), gives you dynamics you are looking for. Actual world scale sounds good to work on but in reality we all know how hard it become to work on it, although not always but in some situation or case, specially if you are dealing with huge sets, like your case. I am not aware about your scene scale so it is not easy to give you a number.

2. Do u actually use reseeding,i notice it takes a lot of space
Reseeding is on by default and I have not touched it, so yes I am using it with default setting. I am not sure about disk space usage with it but it should not change drastically.

3. how do i get small detail that i can see in ur render.
No short cut or fix method as each scene will be setup differently and lot of factors will influence the sim. Need lot of testing, trying and failing.

4.can u also share some of ur stats.
Nothing great, sim for 240 frames took 2 hours that cost me approx 70 GB disk space and render took 26 hours with 12 GB RAM, OC i7 processor.

5.Will my base model on which am running the sim only can give more splashes flying
For sure your base model is going to help a lot, specially if you have turns and up-downs, like your reference images. Some time if I am not getting good response from floor then I add dummy geos in between for collision, same I am doing in Jeff's scene.

6.How do you really start your shot ? do's and don't
click on Houdini and jump in it

I am still learning and not sure the steps I am taking to get more details are right or not, but uploading some wip render samples from my tests. Not huge difference between these renders and I am still not satisfied with it, will work on it further. This week I faced some weird issues with my machine and while trying to fix it, I torn apart the files that I tweaked to get these renders. I will upload hip file in sometime, in case anyone want.

Thanks a lot for all those answer ,you have been great help.
I had some time to check out the new houdini 12.5 ,its too good
The sim file size per frame has also decreased .

as oh now am good with the sim detail i got and client is happy with the result
But am stuck with rendering of the water and foam

they want to render both water and foam together,so we can see the foam below and above water.
can u share ur render settings with Jeff file ..with subsurface including foam and splash render settings .

Good to know that you got what you was looking and client is happy. I am sure by now you have completed the shot, sorry was real busy past month thus not able to help/post anything.
Vidit, I have not worked on splash/foam part for my test yet but I am sure with 12.5's new tools it is easy to get them.
Although you might not need the scene file now but as I had it prepare and have render few clips too, just posting them here with subsurface shader in it that I used in my earlier test. You might still want to tweak shader further. I wanted to change few things in light, environment but just to keep same settings as Jeff's original file had, I have just tweaked shader only. Look for the yellow color coded nodes in it, those are the nodes I have tweaked for sim, compare to Jeff's setting.
Still with time and efforts, settings for sim and shader can be tweaked further for desire look and dynamics.