#navier-stokes

[amimmy]

look at my finite elements, boy

[stvff-talks]

Fluid Sim Failing but In Progress

[wild-moss-art]

Another thing about the cybertruck. You can tell the engineers were either instructed to ignore or just decided to not run a fluid flow simulation. That thing simply is not aerodynamic. It’s designed to LOOK aerodynamic in the silhouette but in a way that is divorced from like. Actual fluid flow. No roundedness for air to flow over. The straight edges will create sooo much turbulence and I’d love to see the dead ass wake of that thing. Aerodynamic in the same way as a fucking glacier

[musicallisto]

charles leclerc on instagram, 10.22.2024

[cpericardium]

People love inventing extremely difficult problems in the field of mathematics. They always do this. Make up problems and then go "ah man this one is too hard… I'll put a bounty on it"

[to-shards-you-say]

i'm going to annihilate myself why would someone say something so cruel about my fantasy book world

[lolmanthecat]

It doesn't happen often, but when it does, the sensation is majestic.

The important thing is that Marcille did not learn to blaspheme against the natural order to save her girlfriend. She just happened to have studied the art of spitting in God's eye for wholly unrelated reasons, and when the opportunity by chance arose to employ that skill in service of girlfriend-saving, she was ready.

[thenightlymirror]

[forgottenbones]

Navier-Stokes Equations - Numberphile

[concernedfriend]

trying to convince an animal shelter to name their new arrivals Navier and Stokes and I'm not sure they're going for it

[kris-and-the-pnictogens]

oh wow there are relativistic Navier-Stokes equations too, huh! relativistic viscosity. I should look into that ~Chara of Pnictogen

I don’t like this

can I go home now?

[snail-day]

Oh, there's such a lack of yandere nerd!gojo content out in the world. He'd be such a freaking loser dragging his poor lab partner back to his stupidly large apartment that his parents bought him (trust fund kids, am I right?) The poor son of a bitch pushes up his glasses for what has to be the fifth time in the last minute, his fingers shaking just enough to smudge the lenses. He would normally take the time to clean them. After all, this is a very special moment. However, his focus is locked entirely on you, pupils blown wide with exhilaration, his face burning hot.

He’s finally alone with you.

A free hand hovers over yours, the way a scientist might hesitate before handling a delicate, precious agar sample. But you’re not just any experiment. You’re his.

"Oh - oh, wow, you’re shaking," Gojo breathes out, voice nearly cracking from how much he’s holding back. A large, pathetic grin wobbles, too eager and lovesick. "That’s… ahhh, you probably think that’s bad, huh? But - !" Letting out a breathless, giddy laugh, barely able to contain himself. "But it’s not! It’s just your fight-or-flight response kicking in! Isn’t that amazing? It’s just pure biology - adrenaline, cortisol, your nervous system firing on all cylinders - " cutting himself off with another shaky inhale, squeezing his eyes shut for a second, he’s really trying to collect himself (and failing, he's pretty sure he came in his pants).

"You don’t actually have to be afraid, though," he continues, voice softer now, "Because I’d never, ever hurt you! Never! I mean, scientifically speaking, fear is just your body misinterpreting stimuli, and that’s kind of tragic, don’t you think?" Bright blue manic eyes flicker over you, adoringly, like you’re a rare phenomenon he’s lucky enough to witness firsthand. "Because I love you. God, I love you so much. Do you know how long I’ve been waiting for this?"

His fingers twitch, and then finally, he touches you. Just barely. A featherlight brush of his fingertips against the back of your hand, and he shudders like you’ve just sent a shock straight through him.

"Warm," he mutters, almost to himself. "Oh wow, you’re so warm." That pretty face of his is practically glowing red now, and he laughs, high, nervous, like he can’t believe this is actually happening. "I always - I always thought about this, you know? Back in class? How your skin might feel? I - I tried to calculate it once, based on average human body temperature and external environmental factors, but- but actually feeling it is so much better!"

His voice cracks at the end, and he slaps a hand over his mouth, muffling a half-sob, half-laugh. His glasses slide down again. He shoves them up with a clumsy knuckle, barely able to hold himself together.

The room is a mess of his obsessions, shelves packed with manga, figurines lined up like tiny sentinels, textbooks, and loose papers stacked in towers on his desk Complex chemical equations scrawled across a whiteboard, some of them crossing into territory you can’t even begin to understand.

One of them looks… medical. With dosages sprawled out within the Navier-Stokes equation.

Gojo’s long, pale fingers he laces over yours, and oh how his entire body shudders again, like he’s barely restraining himself from pulling you into his arms. "You - you have no idea how much I adore you," voice trembling. "I mean, did you know your hair shines under fluorescent lighting? I wrote a whole equation trying to determine the way light refracts off the strands. And the way you chew on your pen cap when you’re thinking? I- I started doing it too, just to feel closer to you - though studies show - it's like really bad for your teeth so - we should - should stop that bad habit - ah "

His other hand moves suddenly, reaching for something on the desk. A glint of silver. Your breath stutters between soft sobs.

When did he get a syringe? Wasn't he just professing his undying love for you?

Gojo blinks, as if he just remembered he was holding it. Then he lets out another one of those nervous, giddy laughs, clutching the syringe close to his chest like it’s something precious. "Oh - this? Ahaha, you - ah, you weren’t supposed to see that yet! I was gonna - " He bites his lip, gaze flickering between the syringe and you like he’s debating something. "I mean, it’s nothing bad! Just a little - just a little help! A tiny, tiny chemical nudge to help you relax! I measured everything perfectly, I promise! You can trust me! "

And oh are you starting to cry even more which causes him to freak out just a little more... "L-Let’s start over," small stammers as his manic smile widening. "I-I’ll explain it all again! In even more detail! Ohhh, you’re gonna love this!"

[omarfor-orchestra]

Vabbè

Ora gli dice "guarda che non sei gay hai solo un gemello morto"

[argumate]

So what do you want your fluid sim to *do*? Are you just after a cheap way to approximate Navier-Stokes?

I have some examples of things I'd like to do: breaking waves (I know this is challenging), pipes and U-bends and fountains, dams and the bursting thereof, but mostly it's about exploring what approximations are simple enough for me to understand, cheap enough to use, and yet feel real enough to be fun, which is to say real in the sense of sincerely authentic constructs in their own right, they don't have to perfectly match actual real water because that's kinda impossible.

[literallymechanical]

Zap Energy says that they’ve solved Z-pinch by “shear stabilization”, where they have different sections of the plasma moving at different velocities (faster outside, slower inside). Doesn’t shear like that cause instability, not suppress it? Or are plasmas not subject to that law of fluid dynamics

You’re thinking of instabilities in flowing plasma like it’s turbulence in flowing fluid. This is partially correct, but like... okay. So, the field of physics that governs the movement of plasma is called magnetohydrodynamics, where you introduce Maxwell’s equations into Navier-Stokes. It is horrible. I am but a humble mechanical engineer, and I leave the physics to physicists.

The physicists tell me that Zap Energy's science is solid.

Bit of context: Zap Energy is taking an old fusion energy concept from the 1950's called a Z-pinch, and revamping it with modern plasma physics.

A Z-pinch works on the principle that passing an electric current through a conductor generates a magnetic field, which in turn crushes (or "pinches") the conductor. The first observations of the pinch effect were in hollow metal tubes that were used as lightning rods, like this one from a factory in 1905:

Image by Brian James, CC BY-SA 3.0, Wikimedia Commons

Plasma is electrically conductive, and is subject to the same compressive pinch effect as metal. Lightning itself is a plasma pinch, actually.

When you pinch a plasma, it heats up. The fast-moving, charged plasma particles repel each other and push back against the magnetic field until the system reaches equilibrium. The stronger the plasma current, the harder the pinch, the more pressure, and the more heat. With sufficient plasma current and the right hydrogen isotopes, you can create a pinch strong enough to induce nuclear fusion.

The pinch effect was first utilized by a class of fusion machines called Z-pinches in the early 1950's. However, those Z-pinches were extremely unstable. The most common analogy is that compressing plasma with a Z-pinch is like trying to squeeze jello with rubber bands.

UK Atomic Energy Authority, Public domain, via Wikimedia Commons

Both linear and toroidal Z-pinches have been built. The toroidal Z-pinch above shows some of the characteristic kink instabilities of a pinched plasma – it goes all squiggly. Researchers started adding external magnets to Z-pinches to help reduce instabilities (which eventually led to the development of the tokamak), but could never get a truly stable plasma. Z-pinch fusion research was largely abandoned in favor of the tokamak and stellarator.

However, the external magnets of a tokamak or stellarator are massive, complex, and use incredible amounts of power. The University of Washington and Zap Energy went back to the old concept of a magnet-less linear Z-pinch, but with a more modern understanding of plasma physics. They discovered that by using a flowing plasma rather than a stationary one, with a faster flow rate on the outer layers (a "sheared-flow" Z-pinch), they were able to achieve great stability with no magnets.

Credit: Zap Energy

Rather than filling a chamber with stationary hydrogen and then pinching it, they blow a "smoke ring" of plasma around a cylinder into their chamber. An electrode at the tip of the cylinder then fires a pulse into the plasma, which creates a pinch with a complex velocity profile.

Credit: Zap Energy

Zap Energy’s physics basis is good. They’ve pretty convincingly demonstrated that sheared-flow does indeed stabilize a pinched plasma, and if they can pull off magnetic confinement fusion with no magnets, it will be massively cheaper than any other method. The uncertainty that Zap is facing comes from mechanical considerations (in particular, electrode erosion is a tricky problem to solve), and the relatively thin margins for efficiency that are inherent to any pulsed fusion technique.