How can I make this fluid?

Discussions about the use of Realflow
jyh126
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How can I make this fluid?

Postby jyh126 » Mon Sep 25, 2017 1:30 pm

http://i64.tinypic.com/2n1ygx5.jpg

Hi,

I want to make this fluid,

I've already tested many times, but I don't know how I approach this simulation.


I tried line emitter, square emitter and used imported obj file.

Noise field, sheeter, crown, drag force, gravity... I tried everything but I can't find a way


Please, help me.. thanks!!


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ChristianZ
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Re: How can I make this fluid?

Postby ChristianZ » Mon Sep 25, 2017 8:32 pm

Hi

that won't be easy...
I think you are on the right track with an imported object or more generally, by using a shape that emits liquid. I am thinking about another tutorial that creates more like a cloth-like object, but emission of fluid at the edges in addition.
Cloth like simulations like this https://vimeo.com/215163045
RF10 standard, System specs: OSX 10.11, MacPro 4.1 2xXeon, GTX980Ti, 64 GB RAM

Forester
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Re: How can I make this fluid?

Postby Forester » Wed Sep 27, 2017 11:12 am

There are several ways to make a free form liquid like those shown in your reference picture.

If I could respectfully disagree with ChristianZ by a small amount, I believe the best way is to create a helper shape object, import it into Realflow, and then use a standard emitter to push particles onto the helper object and "stream" the fluid along that object.

I've made a demonstration of the difference between using an Object Emitter and using a helper object to shape the fluid stream of a standard emitter. Here is a picture of a comparison of the two techniques that displays the problem with using an Object Emitter. http://www.expandingwave.com/wp-content/rf_help/Comparison_ObjectEmitter_ShaperEmitter.jpg. (You can download the RF10 demonstration files here - http://www.expandingwave.com/wp-content/rf_help/MakeupFreeForm.zip).

The problem with using an Object Emitter for a free-form liquid stream is that is extremely difficult to create a polygon object shape that has vertices or faces that are regularly spaced well enough to create a smooth fluid stream. For this demonstration, I created a curved shape and then attempted to make it into a flat polygon emitter using the best available tools in Maya. This is my result after several attempts to create the best set of regular vertices and faces. http://www.expandingwave.com/wp-content/rf_help/ShapeEmitterMesh.jpg. As you can see, it is not very good.

But, using the same curve shape, I extruded a solid 3d model - shape helper object as shown in the first picture. Then I created a simple rectangular emitter whose particles are pointed toward the helper object and will stream along it to create a free form fluid.

Please note that in Dyverso, you can make some additional smoothness in a streaming fluid by increasing the density of the fluid, or by adding the Sheeter Daemon to the simulation. In general, using a Sheeter Daemon with Dyverso is not recommended because the results will be unstable. But it does work sometimes, and it will work in this demonstration file set if you want to try it. You can increase the particle density, but this will give you a thicker fluid - that is not what you want. Two things you should never do when using an Object Emitter in Dyverso is to add some value to the Randomness setting or add some value to the Jitter setting. In both case, you will create a chaotic fluid, instead of a smooth fluid.

Of course, you don't have to use Dyverso. You can use the standard SPH solver, but all of the above information applies to this solver as well. Dyverso is simply faster and will let you experiment more quickly to get the fluid shape you want.

A third alternative, is to use a Spline Emitter, but this will rarely create a free form fluid of variable thickness.

So, the best technique (in my opinion only) is to think about the general shape you want for your fluid, and then create a 3D model of a shape helper object that gets you close to your desired shape. Gravity, Attractor Daemons and these kinds of things are not needed.

You can group the emitter and the helper shape, and animate their joint movement. By animating the emitter and helper object, you can create some very nice fluid shapes in free form space. Other tips are to make the helper object not visible to the renderer so that only the fluid shows. Also, to use Mesh settings to smooth and thin the fluid to a degree that you wish. And please note that a solid 3D object is not necessary - you can create and use any kind of a shaped plane or sheet object and it will work well.
Windows 7 Pro 64 - Realflow 10.1.2.0162 (Nov 2017 patched) Standard Version

jyh126
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Joined: Fri Aug 25, 2017 3:21 am

Re: How can I make this fluid?

Postby jyh126 » Thu Sep 28, 2017 1:49 am

I really appreciate for your replies :)

I tried to use helper object and my final output is this
http://i67.tinypic.com/5a2um9.png

but my client said that it is not looks like water or fluid


So I will try another helper object and adjust value of density


Thanks for you tip !

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tsn
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Re: How can I make this fluid?

Postby tsn » Thu Sep 28, 2017 7:03 am

Seems I have to give my 2 Ct. to this conversation as there are some misunderstandings:

Changing density shouldn't have any effect on the fluid simulation - it doesn't make it thicker or "heavier", or anything else. Density is only taken into account if you simulate multiple fluids and want them to interact, e.g. foam and water. If you really see differences then please let me know, because then it's a (severe) bug.

Another thing concerns the Sheeter daemon: it won't make your simulations unstable, just slower - esp. with the GPU, because it's not optimized for CUDA/OpenCL at the moment. But, the results with Liquid-PBD and the Sheeter often have a chaotic and not very believable look. But instead of going back to the old and slow standard particle emitters I'd rather use Dyverso's Liquid-SPH type. This will give you better results, also in conjunction with the Sheeter, and on the GPU it's pretty fast as well.

The standard particles and Dyverso's Liquid-SPH are based on exactly the same method: SPH.

And the Dyverso spline emitter supports variable and animatable thickness through the "Thickness" parameter. You can control the fluid stream's thickness even per control point.

Cheers,
Thomas

jyh126
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Re: How can I make this fluid?

Postby jyh126 » Thu Sep 28, 2017 9:39 am

Thanks Tomas!

It's very helpful to me!!

:)

Forester
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Re: How can I make this fluid?

Postby Forester » Thu Sep 28, 2017 3:16 pm

Thank you very much for the clarifications, and for your two cent's input Thomas. Much more valuable than just two cent's worth of information from an expert!

It is new information to me that we can control the thickness of emission at individual control points along a Spline Emitter. This is extremely valuable information - it means that the Spline Emitter is incredibly useful, and would allow much more control over the shape of a free form liquid sheet. It means that the Spline Emitter could be a better solution to JYH126's project than would be a helper object. Especially because the Spline Emitter can be animated easily. (Personally, I am going now to experiment with this - thank you again for the information!)

One of the great things about this Forum, and the participation by many people ....

It is good news to learn that the Sheeter Deamon does not create an actual instability with the Dyverso Solver. Even though it is recommend to not use it in the User Guide, I have used it often, sometimes with success and sometimes not. It is great to know that the successful results are not just a random occurance. I will have more confidence in it in the future.

As a minor clarification on my part, in the demo RF file set that I provided, increasing the density of the particles from the Object Emitter does increase the thickness of the fluid. (Partly why I provided the file set - to allow people to experiment for themselves to see the results of changing density or adding the Sheeter Daemon.) And increasing the density makes the fluid more rough, not more smooth.

But I would not regard this as a severe bug. Simply, it seems to be one of the drawbacks of using an Object Emitter with irregular vertices or faces for the purpose of creating a free form fluid sheet. The apparent thickness seems due to particles moving away from the vertices at slightly different angles, or perhaps due to small interactions among the particles close to the emission points from the Object Emitter's vertices. I suppose that I should have clarified that in ordinary circumstances, increasing the density of the emitter should have no effect on the thickness of the fluid, as you state.
Windows 7 Pro 64 - Realflow 10.1.2.0162 (Nov 2017 patched) Standard Version

Forester
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Re: How can I make this fluid?

Postby Forester » Thu Sep 28, 2017 3:56 pm

JYH126, to me it looks like you have done a very good job of making a free form liquid like that shown in your reference image. You seem to learn the RF program very quickly, and to do good work with it!
Windows 7 Pro 64 - Realflow 10.1.2.0162 (Nov 2017 patched) Standard Version

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tsn
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Re: How can I make this fluid?

Postby tsn » Thu Sep 28, 2017 4:44 pm

Hi Forester,

Thank you so much for your kind words and the additional information on the various subjects. Great to see that you really dig into RF's features and make up your mind about the concepts behind the software. With regards density I'll definitely take a look at your file, but from your description I consider this a normal behaviour and not a bug. The object emitter is something special anyway ;)

jyh126, I absolutely agree with Forester on your preview images. To me they look very good as well, and I have the impression that your client has no idea of how liquids actually behave.

jyh126
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Re: How can I make this fluid?

Postby jyh126 » Thu Sep 28, 2017 5:23 pm

Thank you guys! Forester and Thomas :)

My client want watery fluid!

So I'm trying variable ways.

I will show you when my work is done!



I'm always impressed when I visit this forum because of your help.

Thanks you so much!!
Last edited by jyh126 on Thu Sep 28, 2017 5:37 pm, edited 1 time in total.


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