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Fluid Simulation for Dummies (2006)

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Re: Fluid Simulation for Dummies (2006)

#11

Post by WhitneyLand »

cherryteastain wrote: post #3

Treat this as a "what do I need to do to make fluid flow that looks okayish in graphics" post rather than "how do I implement physics accurate CFD for industrial/scientific purposes" post. Lots of points in there like > "Air is an example of a compressible fluid; you squish it and it gets smaller. Water is an example of an incompressible fluid; you squish it and it pushes back, and doesn't get any smaller" (this only…

Hate it when incompressible fluids are mentioned like it’s literally true with any qualification or explanation.

Iiuc water might compress ~50% at the right place in the Earth’s mantle, maybe just not looking much like liquid.

Re: Fluid Simulation for Dummies (2006)

#12

Post by usrnm »

WhitneyLand wrote: post #11
cherryteastain wrote: post #3

Treat this as a "what do I need to do to make fluid flow that looks okayish in graphics" post rather than "how do I implement physics accurate CFD for industrial/scientific purposes" post. Lots of points in there like > "Air is an example of a compressible fluid; you squish it and it gets smaller. Water is an example of an incompressible fluid; you squish it and it pushes back, and doesn't get any smaller" (this only…

Hate it when incompressible fluids are mentioned like it’s literally true with any qualification or explanation. Iiuc water might compress ~50% at the right place in the Earth’s mantle, maybe just not looking much like liquid.

Every science including physics consists of models that are just good enough for a particular use case. It's implied

Re: Fluid Simulation for Dummies (2006)

#14

Post by jlhawn »

lacunary wrote: post #8
jlhawn wrote: post #2

The title should be updated to note this is from 2006. Has there been anything like this published in the past 20 years but for compressible fluids? I have wanted to make a simple atmospheric model for years but have been unable to because of the complexity and probably my lack of complete understanding.

I'm curious what you want to model; what's an example phenomenon you'd like to be able to demonstrate?

Atmospheric circulation. hadley cell, polar cell, and mid-latitude cells. It would also be interesting to see how new bands would occur if we increased the rotational speed of the earth, thus increasing the strength of the coriolis effect. It would also be neat to draw your own continents and orography and see how that impacts climate. which places become more wet/dry, etc. Change how much long wave radiation is absorbed by the atmosphere as the composition of the atmosphere changes. I'm not interested in actually making weather or climate predictions but using it as a tool to educate people on how the climate works.

Re: Fluid Simulation for Dummies (2006)

#15

Post by otterdude »

wiz21c wrote: post #9
otterdude wrote: post #4

This is an ok introduction to CFD in that you discretize a problem, but it is not insightful and not scientific in its approach. The author routinely admits he doens't know how certain portions of the code work. This is a much better approach to CFD / Navier-Stokes and will help you understand the various phenomenon along the way. https://lorenabarba.com/blog/cfd-python-12-steps-to-navier-s...

CFD start to become really painful when the fluid leaves the cells...

Thats why we have the courant number!

Re: Fluid Simulation for Dummies (2006)

#16

Post by dieselgate »

WhitneyLand wrote: post #11
cherryteastain wrote: post #3

Treat this as a "what do I need to do to make fluid flow that looks okayish in graphics" post rather than "how do I implement physics accurate CFD for industrial/scientific purposes" post. Lots of points in there like > "Air is an example of a compressible fluid; you squish it and it gets smaller. Water is an example of an incompressible fluid; you squish it and it pushes back, and doesn't get any smaller" (this only…

Hate it when incompressible fluids are mentioned like it’s literally true with any qualification or explanation. Iiuc water might compress ~50% at the right place in the Earth’s mantle, maybe just not looking much like liquid.

Think it was a high school physics demonstration where a glass bottle is filled to the brim with water and then dropped to show it doesn't break? Something like that, or you can hit it fairly hard with a hammer and it won't break as easily compared to an empty bottle.

That and boiling water in a paper cup over a bunsen burner (chemistry class) are some of my favorite science demonstrations!

Was literally talking to someone the other day about water being irregular in how it expands at freezing temperatures opposed to contracting.

Water/H2O is such a cool molecule/substance

Re: Fluid Simulation for Dummies (2006)

#17

Post by btrettel »

jlhawn wrote: post #2

The title should be updated to note this is from 2006. Has there been anything like this published in the past 20 years but for compressible fluids? I have wanted to make a simple atmospheric model for years but have been unable to because of the complexity and probably my lack of complete understanding.

Fluid dynamicist here. The word "compressible" has multiple meanings and this might be confusing you. You don't need compressible flows in the sense of high Mach numbers. There are other models where the flow is variable density, but thermodynamic and hydrodynamic pressure are decoupled to remove the pressure waves that make high Mach number flows hard. There's also the Boussinesq approximation for buoyancy when the density varies only a small amount. I'm not particularly familiar with atmospheric models, but I'm sure they don't use the high Mach number form. "Incompressible" methods are common for the second class of model I mentioned, though how to use them so might not be obvious.

Re: Fluid Simulation for Dummies (2006)

#18

Post by jamiejquinn »

jlhawn wrote: post #14
lacunary wrote: post #8

Earlier quoted context omitted.

I'm curious what you want to model; what's an example phenomenon you'd like to be able to demonstrate?

Atmospheric circulation. hadley cell, polar cell, and mid-latitude cells. It would also be interesting to see how new bands would occur if we increased the rotational speed of the earth, thus increasing the strength of the coriolis effect. It would also be neat to draw your own continents and orography and see how that impacts climate. which places become more wet/dry, etc. Change how much long wave radiation is abso…

Interestingly, most large-scale atmospheric models I know of use a (mostly) incompressble fluid approximation, even though air is obviously compressible at human scales. It just isn't at the flow speeds and length scales of global-scale fluid models. Where compressibility is important for those models is where density changes due to temperature. Look into the Boussinesq and anelastic approximations if you're interested!

Re: Fluid Simulation for Dummies (2006)

#19

Post by amemi »

otterdude wrote: post #4

This is an ok introduction to CFD in that you discretize a problem, but it is not insightful and not scientific in its approach. The author routinely admits he doens't know how certain portions of the code work. This is a much better approach to CFD / Navier-Stokes and will help you understand the various phenomenon along the way. https://lorenabarba.com/blog/cfd-python-12-steps-to-navier-s...

I agree; Dr. Barba's series is excellent.

In addition, replicating Jameson et al. (AIAA 1981-1259) [1], is a worthwhile, more advanced follow up, great if you want to get into serious CFD development eventually.

[1] http://aero-comlab.stanford.edu/Papers/jameson.aiaa.1981-125...

Re: Fluid Simulation for Dummies (2006)

#20

Post by rendaw »

cherryteastain wrote: post #3

Treat this as a "what do I need to do to make fluid flow that looks okayish in graphics" post rather than "how do I implement physics accurate CFD for industrial/scientific purposes" post. Lots of points in there like > "Air is an example of a compressible fluid; you squish it and it gets smaller. Water is an example of an incompressible fluid; you squish it and it pushes back, and doesn't get any smaller" (this only…

This was just posted a couple days ago too... how does it compare (also focused on visual sim)? https://news.ycombinator.com/item?id=48286745
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