Small boat simulation - Long Ripple life on calm water

[daniel_fisher]

Hi,
I'm pretty new to Pheonix but I've hit a brick wall in trying to simulate a particular scene, I hope someone can help. We are trying to emulate a long wake with nice patterns like you would see on a very still early morning lake where that water surface has almost mirror like / still condition. The ripples from even slow moving boats or canoes fan out quite gently for a long time. When we run the simulation the waves seem to fade away too quickly for the effect we are trying to achieve. Can anyone point me in the right direction of what I am doing wrong?
Many Thanks in advance
Daniel

[Svetlin.Nikolov]

Hey,

The jet boat is definitely moving too fast compared to your simulation, so it creates much stronger, taller waves that last longer.

The duck has a different shape than your boat so it pushes more liquid to the side, so its wake is also different.

So either make your vessel faster, or if you can't alter the speed of your boat, but you still want to get such a wave, then increase the Motion Velocity multiplier in the right click properties of the vessel geometry. Looks like you need to boost it seriously in order to get this kind of result - 5-10 times maybe.

Ah, also - how deep is your simulator? Is it very shallow or does it cover the vessel completely?

Cheers!

[daniel_fisher]

Hi Svetlin,
Thank you so much for taking the time to help!
I've noted what you have said about the shape and speed and I will try the Motion velocity multiplier now. I have attached a side view of the depth of the simulator (it's not the actual boat we are using but it basically the same shape just low poly.
Thanks again
Dan

[daniel_fisher]

Sorry, the simulator depth is more like this.

[Svetlin.Nikolov]

Ah, okay, I was going to say the simulator is too low res, but the second image looks like the proper voxel count and depth.

However, it seems the scene scale is too low - in the Grid rollout you can see the lengths corresponding to the X/Y/Z axes of the simulator and they must be like the real world size of the effect. If these are people in the boat, then definitely the simulator must be taller than just 1.6 meters along Z. If it's too late to change the model, you can cheat the solver into thinking its world size is larger than it actually is by using the Scene Scale parameter at the top of the Grid rollout. Increase it until the lengths you see for X/Y/Z start corresponding to the real world size of the effect.

Also, if you haven't gone through the Ship tutorial, give it a run: https://docs.chaosgroup.com/display/...p+in+the+Ocean. It mentions all the important things to look out for in such sims.

Cheers!

[daniel_fisher]

Again, thank you! I will adjust that all now, already the velocity object multiplier is having a positive effect.

I did follow the ship tutorial, it was really useful I think I just lost along the way when creating this scene.

Thanks again Svetlin!

Dan

[Svetlin.Nikolov]

already the velocity object multiplier is having a positive effect.

Sweet! Hope this will do the job - there is no direct way to control the height, the shape and the length of these waves, so it's all about the speed and shape of the vessel, and if they are already fixed and can't be changed, then only the velocity multiplier can be controlled and some other indirect influences can be the depth of the liquid, the grid resolution of the simulator, and the Steps per Frame, though their effect can't really be generalized and predicted - if you still have a lot of time to iterate, try altering any of them too.

[daniel_fisher]

Great! We have some time so I will try simulating adjusting the depth, grid res and steps per frame to see what happens.
Thanks Svetlin!

[daniel_fisher]

Hi Svetlin, that for all of your help. We have the wake as we were hoping now but after the high res simulation we get these lines running across the simulation? Any ideas what this may be?

Many Thanks

[Svetlin.Nikolov]

Hey, unfortunately these are an effect of the fluid solver. If you are not going to use displacement over the liquid surface that would hide these, you could reduce or remove them using various smoothing methods - check here for more info: https://docs.chaosgroup.com/display/...+and+smoothing

[daniel_fisher]

Thanks Svetlin, at least it wasn't me this time. I will have a look through that, thank you.

[daniel_fisher]

We got to a compromise a while ago with this and have rendered various animations out at lower HD resolution but when we render out at say 4K the liquid solver has so much more noise - why is there is a difference when the render size is adjusted? I'm not sure what we are doing wrong here. Many Thanks
Dan

[Svetlin.Nikolov]

Huh, is this the same frame from the same simulation? It looks like even the ocean level is changed, which does not add up...

[daniel_fisher]

Exactly the same frame - just render straight after with a different resolution. It's as if there is a setting based on pixel size rather than world space if that makes sense? Here is another example while we were playing with the render settings last night, we had it looking as we wanted on the interactive renderer but when we test it in 4k it looks awful. It seems like we can get close to the results again by changing the isosurface level and ocean sampling but there is no way of previewing this on the interactive renderer which is making it very time consuming. Any help would be great Svetlin.

[Svetlin.Nikolov]

There is certainly something more going on because see how the container's borders are subsided in the 2nd image....

One thing that would definitely be different is the foam if you are rendering in Points mode - note that Points mode renders particles with a pixel size by default, so increasing the image resolution will make the particles look smaller. You have to adjust the Point Radius from the Particle Shader - check more info here: https://docs.chaosgroup.com/display/...am-PointPoints

Also, is there any displacement applied to the container?