Pipes & Pressure

[Quidam]

I've not yet purchased this asset, but am working on a project involving pipe and wondered if this asset would suit. Are there any examples of it moving through hollow cylinders?

Also, while I can see from the demos that it is affected by gravity, to what extent are the effects of pressure modeled? If a pipe is filling up but gets capped, does it continue to fill up as if the cap were air-permeable?

Thanks!

[josemendez]

I've not yet purchased this asset, but am working on a project involving pipe and wondered if this asset would suit. Are there any examples of it moving through hollow cylinders?

Also, while I can see from the demos that it is affected by gravity, to what extent are the effects of pressure modeled? If a pipe is filling up but gets capped, does it continue to fill up as if the cap were air-permeable?

Thanks!

Hi,

As with any realtime particle-based simulation, fluid is weakly compressible. This means that pressure is simulated and incompressibility enforced, but only up to a certain extent. Fluid can still be compressed under sufficiently high pressures, and guaranteeing a higher compressibility threshold requires more processing power. The simulation method used by Obi is position-based fluids (PBF), you can look it up if you want a more in-depth description of its capabilities. I reccomend to read up of the different methods of fluid simulation for your project, as there are a lot of them and most have very well defined strengths and weaknesses.

Fluid can collide with any geometry, including hollow cylinders.

kind regards,

[Quidam]

Thank you very much for your informative answer. I get what you mean in regards to the pressure exerted on the fluid, but can you tell me if it reacts at all to air pressure? I'm guessing since I haven't seen it mentioned that it doesn't, after poking around for a few minutes.

How does the simulation behave when filling a U pipe where the other end of the U is capped? Will it fill to level with the opening, or will there be an air bubble left on the capped side, and if so, does its size change with the amount of fluid pressure exerted on it?

While that would be great, at this point it's just gravy, as the nature of your response has already indicated to me that this is the asset for the job.

If you'll forgive an aside, do you ever bundle your assets together at a discount? I've had my eye on your rope asset, too.

[josemendez]

Thank you very much for your informative answer. I get what you mean in regards to the pressure exerted on the fluid, but can you tell me if it reacts at all to air pressure? I'm guessing since I haven't seen it mentioned that it doesn't, after poking around for a few minutes.

How does the simulation behave when filling a U pipe where the other end of the U is capped? Will it fill to level with the opening, or will there be an air bubble left on the capped side, and if so, does its size change with the amount of fluid pressure exerted on it?

While that would be great, at this point it's just gravy, as the nature of your response has already indicated to me that this is the asset for the job.

If you'll forgive an aside, do you ever bundle your assets together at a discount? I've had my eye on your rope asset, too.

Hi!

Air pressure is simulated in a simplified way. Fluid curvature is calculated at its boundaries and then a force proportional to the air density is applied in the direction of the surface's normal. In engineering-grade simulators air is usually simulated as a second, lower-density fluid phase but this is pretty much impossible to achieve in real time due to the sheer volume of fluid you'd have to simulate (though it allows for air bubble formation). You can see a list of available fluid parameters here, the one you're looking for is named "atmospheric pressure".

http://obi.virtualmethodstudio.com/tutor...rials.html

The "atmospheric drag" parameter would be also relevant as it determines the relative density of the surrounding air.

If you fill a U pipe with fluid, it would initially level out both sides of the "U". If you cap one end and keep pouring fluid trough the open end, it would eventually overflow (since it must conserve its volume). Air bubble formation is not currently supported as it would require to simulate air as a second fluid phase (as described in the above paragraph).

We've sold the asset at a discounted price before, but when to discount it is out of our control. The Asset Store notifies us when they're about to make a sale, and asks us if we want to temporarily reduce the price a certain percentage. ObiFluid will likely be included in the next sale, but unfortunately I cannot tell you when this will happen as it is not up to us.

[Belisica]

Hi!

Air pressure is simulated in a simplified way. Fluid curvature is calculated at its boundaries and then a force proportional to the air density is applied in the direction of the surface's normal. In engineering-grade simulators air is usually simulated as a second, lower-density fluid phase but this is pretty much impossible to achieve in real time due to the sheer volume of fluid you'd have to simulate (though it allows for air bubble formation). You can see a list of available fluid parameters here, the one you're looking for is named "atmospheric pressure".

http://obi.virtualmethodstudio.com/tutor...rials.html

The "atmospheric drag" parameter would be also relevant as it determines the relative density of the surrounding air.

If you fill a U pipe with fluid, it would initially level out both sides of the "U". If you cap one end and keep pouring fluid trough the open end, it would eventually overflow (since it must conserve its volume). Air bubble formation is not currently supported as it would require to simulate air as a second fluid phase (as described in the above paragraph).

We've sold the asset at a discounted price before, but when to discount it is out of our control. The Asset Store notifies us when they're about to make a sale, and asks us if we want to temporarily reduce the price a certain percentage. ObiFluid will likely be included in the next sale, but unfortunately I cannot tell you when this will happen as it is not up to us.

I consider getting the Obi Fluid asset for 2d simulations. This thread answered many of my questions. To elaborate further: Can air be simulated (volum, pressure) together with water such that a barometer can be simulated? When an air volum is under variable outside air pressure, will it change its volume?

[josemendez]

I consider getting the Obi Fluid asset for 2d simulations. This thread answered many of my questions. To elaborate further: Can air be simulated (volum, pressure) together with water such that a barometer can be simulated? When an air volum is under variable outside air pressure, will it change its volume?

Only to an extent. Atmospheric pressure is simulated as a force parallel to the fluid surface normal. Specifically, we implemented eqns. (13) and (14) in this article:
http://gamma.cs.unc.edu/SPH_GAS/sph_gas.pdf