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I suspect that you may've skimmed the article a bit fast. The author uses terminology a little differently while developing their explanation. For example, wi
by _Nat_ 5y ago
I suspect that you may've skimmed the article a bit fast. The author uses terminology a little differently while developing their explanation.
For example, with respect to compressibility, the author isn't saying that water isn't compressible in the physical sense, but rather that it's not compressible in the mode of its behavior in their prior example (which they refer to as a "Naïve Implementation"). Which they're correct about -- their naive implementation would be more like an ideal-gas at near-vacuum pressures, which would be pretty unrealistic for water under normal conditions. And they also explain that non-compressibility (in the physical sense) is merely an approximation.
Then as for pressure-differences, the author has stuff like a variable called "difference_in_p" and writes about the pressure-field and such. So, no worries, they're not actually confused about incompressible fluids being able to have pressure-differences.
You are right that they typo'd "Navier-Stokes equations" in two different ways: they always seem to miss the last "s" in "Stokes", and sometimes they non-idiomatically put Stokes's name before Navier's. Presumably the author should fix the spelling of Stokes's name -- the latter might be a stylistic quirk (sometimes folks may intentionally re-order a list of names, arguing that it'd be more fair that way).
All that said, I can appreciate how it might be odd to see common terms used in a conceptual-development in a manner inconsistent with their meanings in the standard literature. It might be helpful for the author to include something like a disclaimer that they're taking a constructivist approach, and that the terminology used during construction may vary from the final definitions one'd arrive at once the standard theory is constructed.
- ptero 5y agoYou perfectly hit the points that rub me the wrong way when looking at the post: redefining commonly used terminology, lack of a short dose of physics for a background, misspelling Navier-Stokes, etc. Neither of those should doom a computational project, but I think they have a bigger negative impact on readers than the author realizes. My 2c.
- bernulli 5y agoI like where the author is coming from, but maybe having started with the actual physics and/or equation and then explaining what those terms mean in a naive way would have much more impact. Giving an intuitive explanation of a physical term can be a great service to anyone learning a subject. Starting instead with "here's how I imagine diffusion" from scratch reads like an introduction to homeopathy: "why, you have a bloated belly that feels hard, then you need to drink a (properly diluted) solution of some hard substance, say granite".
- bernulli 5y agoThe problem with that is that you see all that because you already have a working knowledge of fluid mechanics. Someone reading this from the intended audience, ie someone looking for a gentle introduction, will not realize that absolute statements like “The incompressibility of fluids is the reason why those beautiful curls pop up in fluid bodies.” or “A substance that can not be compressed, can not have areas of higher and lower pressure” are simply and plainly wrong. The result simply is, as I stated, that the interested reader will not have learned anything physical about fluids, and will not even know the vocabulary to dive deeper afterwards. Note also, that the “naive” way still requires you to understand the divergence of a vectorfield, at which point the whole approach collapses and I wonder why they don’t simply give us the equations and then we can see for ourselves.