Method for Creating River with Variable Slopes

[hrigsby]

I'm new to Phoenix and I'm trying to find a good starting point for creating a large scale river with different slopes.

Images of my base file: https://imgur.com/a/fHeuzPW

Image 1 shows the riverbed before I add water. Essentially I need to simulate water from the auto bridge down to the pedestrian bridge and the rocks define the extents of the water (ideally). It about 1,000 linear feet from bridge to bridge.

Image 2 shows my first effort. For some reason the water seems to be piling up in certain locations and not filling in the river bed, despite generating enough water to overflow the intended extents of the river up around the auto bridge.

Image 3 shows my Liquid Source Object. I started with a single box shooting water downstream, but I found that it was creating a lot of turbulence. So I decreased the velocity, increased the source surface area, and pointed the source polys straight down so that the water would just bubble out and follow the natural terrain. This is what generated the result in Image 2.

Down towards the pedestrian bridge, there is a waterfall feature that has a steeper slope than the rest of the area. I've tried created an initial liquid fill object so that I don't have to wait for the water from the source to fill the entire river, but I haven't been successful in this effort because of the variable slopes of the riverbed. I've also started dabbling in the cascade simulations so that I can shrink the grid down to a more manageable size.

What would be the best method of approaching this project? Is there a tutorial that I should check out (I've found a lot of ocean tutorials and then a small, uniform creek bed, but nothing that demonstrates how to go about creating a more organic, larger scale river.

Thanks!

[georgi.zhekov]

Hey,

You can make different simulators for the different parts of the river and if you need those to interact with each other you can use the cascade option as you have guessed. We currently have no such a tutorial, but I'll add this in the to do list.
Also make sure that your ground geometry is shelled and has no issues (open edges, strange vertices, etc).

Cheers,

[hrigsby]

Hey,

You can make different simulators for the different parts of the river and if you need those to interact with each other you can use the cascade option as you have guessed. We currently have no such a tutorial, but I'll add this in the to do list.
Also make sure that your ground geometry is shelled and has no issues (open edges, strange vertices, etc).

Cheers,

Hey Georgi. Thanks for the response. A tutorial would be incredible as I haven't really found much similar to this. The creek/river simulation tutorial is useful, but it's old and also quite a uniform surface. The organic nature of this project is what makes it more difficult.

I'm also a bit confused about the cell size. I've gone through the documentation about it, but I still can't grasp exactly how to handle such a large scale scene. I currently have a cell size of approximately 8" and that's giving me 9 million total cells in my first liquid object. Should I be aiming for a more realistic "water droplet" size, or should I try to maintain a reasonable number of total cells in the simulation?

EDIT: I also can't figure out what is stopping the water from filling in this space (https://imgur.com/a/E0pNYWk). I shelled the terrain and it looks clean; it's also just a simple downhill slope from where the water is stopping. I put in a sphere to serve as another emitter to try and fill the space in and it just bubbles water up into a wall around this imaginary "forcefield". Any ideas as to what is going wrong here?

[Svetlin.Nikolov]

Hey, just to make sure - in order to diagnose this, export Solid Voxels from the Output into the Special channel, simulate a few frames and enable it in the Preview rollout - in case this space gets filled with voxels, then indeed some geometry is interfering with the simulation and might have some open edges or naughty normals. Are you excluding all nodes that are not related to the simulation from the scene? In such a setup it would be good to switch the Scene Interaction rollout mode to Include list and pick just the obstacles, emitters, sources and forces that should play with the sim.

[Svetlin.Nikolov]

Btw, we just redid the river scene with the Phx 3' FLIP liquid solver a month or so ago, so it's up to date and all principles in it that you can use apply: https://docs.chaosgroup.com/display/PHX3MAX/River

[Svetlin.Nikolov]

As for the voxel size - the (too) general rule is to use as few voxels as possible as long as you don't get large chunks of liquid or too think layers of liquids where the liquid should be a thin film over a surface. Intuitively - 9 million voxels for a simulator would be pretty low for this kind of simulation; 50-100 million would be the preferred resolution, but if you can work below that and still get good looking results, it's a win.

Hope this helps, cheers!

[hrigsby]

Hey, just to make sure - in order to diagnose this, export Solid Voxels from the Output into the Special channel, simulate a few frames and enable it in the Preview rollout - in case this space gets filled with voxels, then indeed some geometry is interfering with the simulation and might have some open edges or naughty normals. Are you excluding all nodes that are not related to the simulation from the scene? In such a setup it would be good to switch the Scene Interaction rollout mode to Include list and pick just the obstacles, emitters, sources and forces that should play with the sim.

Turns out it was just a rookie mistake. I thought I had everything dialed in, but it turns out the local low created by the terrain in this spot was outside of the bottom of the grid (I couldn't see that until I turned on "Graph Cells") so now I think I should be good to go.

I appreciate the link to the updated river tutorial. I'll definitely check that out and see if it's more useful than the older one I'd seen on Youtube. I still think a more organic river tutorial would be useful (maybe one that has a variable stream width, variable slope, waterfalls, etc.) but the one y'all have was definitely a great baseline for figuring out the program! Thanks again.

[Svetlin.Nikolov]

Whew, this explains it! Glad it's working now and will also add a vote to a large river tutorial with cascades. We have a list with all examples and tutorials we want to make, prioritize them and and work on them one by one.