Holding object shape while animated?

Discussions about the use of Realflow
wyoder
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Holding object shape while animated?

Postby wyoder » Thu Dec 21, 2017 3:22 pm

I'm extremely new to RealFlow, in fact i'm still using the demo version to see if I can figure out how to do this before I commit to the purchase, and i'm having trouble finding tutorials for what I need. I have an animated object that, if possible, I need to make completely out of water. Currently i'm just trying to figure out how to do it on the model itself without any animation, but I can't figure out how to get it to retain its shape completely. For this scene in particular, it's a water dragon that flies in and lands, but i'll need to apply the same effect to a few other scenes as well.

So far i've just sort of thrown together some things i've seen across various tutorials. I made a Fill Object emitter using the model as a reference with high Density, and "fill volume" checked, int pressure at 2, ext pressure at 1, viscosity at 1, and surface tension at 2, but when I hit simulate the particles just gradually clump together and some start dripping down, so his wings end up with a lot of holes in them. I found another tutorial that mentioned using the Magic daemon, but it was referring to having the particles switch from forming one shape to another and the settings (escape and approach both set to 50) just caused my model to explode before reforming in a very, very loose outline of the model.

Basically, i'm almost completely in the dark on how to do this, so any help would be greatly appreciated!


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Oldcode
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Re: Holding object shape while animated?

Postby Oldcode » Thu Dec 21, 2017 8:55 pm

Actually, you want to load the object twice.

The first object will be used by the fill emitter to generate the particles in the proper place.

The second object will be set to "Solid Outside". This is the object that will interact with the particles and make them move inside as the object animates and moves.

Read this page about Fluid Object Interaction.

http://support.nextlimit.com/display/rf ... nteraction

Good Luck,
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wyoder
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Re: Holding object shape while animated?

Postby wyoder » Thu Dec 21, 2017 10:06 pm

Thank you for your response!

Do I need to use a still model of the first frame of the animation, like an obj? I probably should have clarified more initially, but i'm importing an alembic file animated in Lightwave, not animating the object in RealFlow itself. When I import the alembic twice, it doesn't give me the option to use either of them as the reference object for the fill emitter, and it doesn't seem like I can use a multibody as a solid outside as you suggested.

Also, totally irrelevant, but I thoroughly appreciate your username and signature. Dragonheart is one of my favorite movies!

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Oldcode
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Re: Holding object shape while animated?

Postby Oldcode » Fri Dec 22, 2017 12:37 pm

Yes, sorry I forgot to mention that. Having the object you use with the Fill Emitter should be a still object, and make sure the domain is not connected to this object so the particles do not interact with it. You only need it to do the fill.

Good Luck,
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wyoder
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Re: Holding object shape while animated?

Postby wyoder » Thu Dec 28, 2017 5:19 pm

I've got it set up as you suggested, but somewhere along the way, RealFlow decided my computer isn't strong enough to even try the simulation. Any time I try to change the density of the Fill Object emitter, RealFlow crashes saying the application ran out of system memory. It does it sometimes with the resolution, too. I have 32 gb of RAM so I should be okay overall. It's got the max particles set to 200 million by default, but lowering that doesn't seem to make a difference.

I'm trying to make it with a resolution of 15 and a Density of 500. When I try to simulate it with the default emitter settings, nothing shows up. The model is around 18,000 polygons, if that could be an issue, but in my experience that's relatively low-res for a character model.

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ChristianZ
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Re: Holding object shape while animated?

Postby ChristianZ » Fri Dec 29, 2017 8:26 am

Yeah, the fill object emitter can cause a lot of problems of this kind. I just did a project recently with a snow flake and had to adjust the object shape and size several times until it was filled properly.

Regarding the memory and particles number: something like 200 Mio is way to much to handle with Realflow. You have to consider that the software is doing fluid simulation calculations with all of these particles in contrast to a standard 3D software that is simply emitting the particles. So, a number of like 100'000 particles for testing and a final resolution of 1-2 Mio is more realistic.

If you don't see particles when filling then the object might be too small in relation to the emitters resolution. Changing the "geometry scale" of the project can help so that the object to be filled gets larger.
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ChristianZ
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Re: Holding object shape while animated?

Postby ChristianZ » Fri Dec 29, 2017 9:47 am

By the way, the density parameter does not change the space that particles are taking within the fluid. It only changes the weight of the particles. I think it is better to use the default number (1000 or more).
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wyoder
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Re: Holding object shape while animated?

Postby wyoder » Fri Dec 29, 2017 2:38 pm

I figured that was probably the case, for the max particles, but as I said changing the value doesn't seem to stop RealFlow from crashing. 200 million is the default value it gives me, but lowering it to 100,000 or even 10,000 doesn't keep it from crashing when I try to change Density, Resolution, or the Fill Ratios. Thank you for clarifying on the density setting. The tutorial I found played around with it, but didn't really explain what it was doing.

As for the object being too small for the emitter; can it also possibly be too big? For some reason, the alembic file i'm using imports into RealFlow extremely large, at least 10 times larger than the default grid size. The still object imports at the correct size, so i've been having to manually scale and reposition it to match the alembic file's starting position. As it stands now, playing with the resolution doesn't change whether or not the particles show up when simulating. I turned the geometry scale up to match what i've been resizing the still model (100.0), but it didn't make a difference so I may not be doing it correctly.

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ChristianZ
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Re: Holding object shape while animated?

Postby ChristianZ » Fri Dec 29, 2017 5:05 pm

As for the object being too small for the emitter; can it also possibly be too big? For some reason, the alembic file i'm using imports into RealFlow extremely large, at least 10 times larger than the default grid size.


That is definitely a possibility. The imported object should fit within the grid plane in the viewport or smaller. If you export an animated alembic from Cinema4D, for example, use a factor of 0.01 for export.
On the realFlow side it might be better to use a standard particle emitter for this project because it works with particle-polygon collisions which may be easier to handle than the volume-based containers with the grid-based Dyverso and Hybrido system.
Also, it might be easier to lock the timeline and let the object fill up with particles instead of filling the object with the fill object emitter.
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