The Tidal Flow of Logic
“Let’s go down. Be careful—it’s slippery.”
Chief Seo took the lead and opened the submarine’s upper hatch.
I followed him down the painfully narrow vertical ladder.
Thud.
The moment my feet hit the floor, I caught the damp, cold smell of metal.
Mixed in with it was the sharp sting of lubricant, enough to bite at the nose.
“Wow…”
I’d thought the inside of a tank was cramped, but this was on another level.
The ceiling sat so low it felt like it might scrape the top of my head, and above it, countless pipes and bundles of cable were packed in so tightly they looked knotted together by a madman.
The passage itself was barely wider than my shoulders.
“This is basically a coffin. And you’re telling me fifty people eat and sleep in here?”
“Compared to early models like the 209 class, this is a huge improvement. At this level, it’s practically a hotel. Once you’re used to it, it’s surprisingly cozy. Watch your head.”
Chief Seo bent with practiced ease and led me through the maze-like passage.
We passed the crew quarters and arrived at the aft machinery room, the submarine’s heart.
This was where the pipes were most densely tangled.
The operating table where today’s patient was lying.
“Here it is.”
Chief Seo swept his flashlight across the ceiling.
Silver titanium pipes twisted and stretched in a chaotic lattice overhead.
I pointed to the intercom mounted on the wall.
“The shore power connection is live, right? Call the duty room and have them run the cooling pump at exactly ten percent output.”
“Ten percent?”
Chief Seo blinked in confusion. “At that rate, the flow speed’ll be almost nothing. What exactly are we supposed to see with that? If you want to check vibration, you need at least rated output…”
“If it trembles at ten percent, it’ll burst at a hundred.”
At my blunt answer, Chief Seo shut his mouth for a moment, then picked up the receiver.
A little later—
Whirr—
The pump started up with the faintest of motor sounds.
Gurgle, gurgle.
I could hear coolant beginning to move through the pipes.
It was so weak that I would’ve missed it entirely if I hadn’t been listening for it.
And yet—
Tap. Tap-tap.
The thin titanium pipes hanging from the ceiling twitched intermittently.
It looked like a nest of irritated snakes writhing in place.
Shhhhhh—
There it was.
The blue fluid rushing through the pipes was violently agitated.
Once the smooth flow reached a narrowed bottleneck, it was turning into a blood-red torrent, as if enraged.
The problem was that, because of the limited space, the pipe thickness had been designed far too thin.
When the coolant was forced through the cramped passage, its speed increased, and the pressure built until the stream gained a brutal, straight-line force.
The problem became even worse in the sections where the pipes curved.
When that red stream, so determined to keep going straight, hit a bend, it slammed into the pipe wall and transferred the impact into the metal itself.
Red light was leaking from the pipes.
“See it?”
I shone my flashlight on the elbow joint where the pipe was shuddering.
“Even at only ten percent output, the pipe’s practically trying to straighten itself. Classic fire hose effect.”
“Ah…”
“What happens when you turn on a hose lying on the ground?”
I asked, without looking away from the pipe. “It can’t handle the pressure, so it starts flailing around like it’s possessed, right? That’s exactly what this pipe is doing. You’ve forced high blood pressure through a narrow artery, and now the vessel’s thrashing around under the strain.”
Chief Seo’s expression darkened with grim understanding.
“Space is limited, and we still have to meet the required cooling efficiency… I know that. But we had no choice. If we lower the flow rate, the battery overheats.”
“Then we find a choice.”
I adjusted the hard hat that was damp with sweat and said, “I’ve seen enough here. Let’s go to the design room. I need to run a simulation.”
*
The ADD detached office tucked into one corner of the shipyard.
Everyone had gone home, and the empty office was lit only by the lonely glow of a single monitor.
“Mm…”
Kim, who had been dozing on a field cot, jolted upright at the sound of someone entering.
His hair was a mess, his eyes bloodshot—the textbook appearance of a researcher being ground to dust.
“Huh? Chief? What brings you here at this hour? And this man is…”
Kim’s gaze swept over me from head to toe.
It was obvious he was wary of an outsider—especially one who’d shown up in a suit at this hour.
“Introductions later. Power up the main computer. I need to run a coolant-line simulation.”
“What? Now? It’s four in the morning. And per security regulations, outsiders can’t…”
“Take a seat, Assistant Manager. We don’t have time.”
I cut him off and nodded toward the chair.
Kim’s face darkened with disbelief.
“Who exactly are you to start ordering people around the moment you walk in—”
“He’s my guest. Do as he says.”
At Chief Seo’s stern order, Kim pouted and sat down.
“Man… unbelievable.”
Clack, tap.
Grumbling all the while, he launched the program.
I stood behind him, arms folded, and looked down at the monitor.
A complex 3D pipe model filled the screen.
“From here on, you’ll adjust the shape variables exactly as I tell you and run it.”
“Seriously… what the hell am I supposed to set?”
Kim’s annoyance was blatant.
I ignored it and gave my first instruction.
“Increase the pipe thickness by 2 millimeters.”
“There won’t be enough space. It’ll interfere with the other pipes. You’ll light up every warning in the system.”
“Run it first.”
With a hand that practically said have it your way and let it fail, Kim entered the numbers and hit Run.
Whirr—
The computer’s cooling fans spun up, and a moment later the results appeared.
Exactly as expected.
The turbulence kinetic energy graph at the bottom of the screen spiked like it was trying to punch through the ceiling, and yellow warning windows popped up around the pipe model.
Narrowing the flow path had raised the pressure, and the fluid had only grown wilder in response.
“See? Narrow the path and all you do is raise the pressure. Even undergrads know that.”
Kim snorted.
I said nothing, only glared at the monitor.
Simply making it thicker wasn’t the answer.
Then what?
“All right, then let’s stick a straight 5-millimeter pin inside. We need to calm the flow down somehow.”
“Wow. You really just throw ideas around, don’t you? That’ll only create resistance and make it worse.”
Kim clicked his tongue but still changed the input.
The simulation ran again.
The result was even more disastrous.
Thousands of white vector arrows representing the fluid flow slammed into the pin and scattered in every direction, tangling together in a chaotic mess.
It looked like a ball of thread that had been hopelessly knotted.
“See that? The vectors are all tangled. You’ve only increased resistance. I told you, a pin just makes the turbulence worse.”
Kim pointed at the monitor with the smug air of a man who thought he had me cornered.
But I was looking at something else.
At the disaster on the screen.
The monitor before me was flooded with blood-red color.
No. A straight line wasn’t the answer.
The fluid was screaming as it slammed head-on into the straight pin.
Its lost kinetic energy clumped together like dark red clots, battering the pipe wall mercilessly, and that impact spread outward as vibration.
When force collided with force, things broke.
That was when it happened.
In the middle of that chaotic red storm of turbulence—
a single faint blue line flashed into existence, sharp as lightning.
That line didn’t confront the pin head-on.
Instead, it curved smoothly along the edge of the pin and glided past the red collision, slipping forward like water down a spiral staircase.
It was a perfect rotational form—fluid clinging to the pipe wall and flowing with effortless grace.
That was my answer.
I followed the blue trajectory with my eyes and compared it to the engineering knowledge stored in my head.
Blocking it wasn’t the solution.
You had to guide it.
What if I made the water cling to the wall and spiral along it, just like that blue line?
Rifling.
The principle that makes a bullet spin in flight.
I could apply that to fluid.
“Erase it. Then draw it again.”
“And now what?” Kim asked.
“Twist the pin. Like a spiral rifling groove.”
Kim’s hands froze.
Slowly, he turned his head and looked up at me.
The expression in his eyes was the same one you’d use to look at a lunatic.
“What?! Rifling? You want me to turn a pipe into a gun barrel?”
“Two millimeters deep, thirty-degree pitch. Cut the grooves in a spiral.”
“That’ll blow up the friction coefficient and wreck the pump! You’re telling me to intentionally build an obstacle into the pipe, and not just any obstacle—a spiral one? When we’d already be better off using a smooth pipe?”
Even Chief Seo, listening from the side, looked troubled.
“Isn’t that a bit of a stretch? From a fluid dynamics perspective, deliberately increasing resistance like that…”
“I’m not making resistance. I’m making a guide.”
I cut him off firmly.
“The water has lost its path and is slamming into the wall. I’m giving it a road to follow. Just run it first. We’ll argue after we see the numbers.”
Kim looked at Chief Seo as though he couldn’t believe what he was hearing.
Chief Seo let out a long sigh and gave a small nod.
Go ahead, that gesture said.
Clack, clack-clack!
Kim grimaced and hammered at the keyboard with rough, exaggerated motions.
While the model was being revised, I glanced sideways at the predicted torsional stress values displayed in the corner of the monitor.
If the fluid were forced into rotation by the rifling, the pipe would, in reaction, be subjected to twisting forces.
The force that had once tried to straighten the fire hose was now going to squeeze the pipe as if wringing out wet laundry.
That had to be relieved too.
“Wait. Add one more variable.”
“Oh, what now?”
“Break the straight sections every meter and insert bellows. We have to absorb the torsional stress created by the rifling.”
“Sigh… you really do go all out. This is turning into a patchwork design.”
Though he kept grumbling, Kim added the bellows modeling exactly as I instructed.
And finally—
Solving…
The loading bar began to fill.
I stood with my arms folded and watched the monitor.
Already, I could see the result in my mind.
A swirling stream of water. Elegant curves sliding along the pipe wall.
Ding—!
A cheerful chime rang out, and the result screen appeared.
“...Huh?”
A stupid sound escaped Kim’s mouth.
He rubbed his eyes in disbelief and stared at the screen again.
The tangled white vector arrows that had been colliding in a mess moments before were gone without a trace.
In their place, a new set of white vectors traced an orderly spiral along the pipe wall, marking a disciplined flow.
Most astonishing of all was the graph.
The vibration displacement, which had earlier looked ready to punch through the top of the screen, had dropped all the way to the bottom and was barely crawling along.
It was as stable as a green wave could be.
“Uh…? Wha—?”
Kim looked as if he might get sucked right into the monitor.
Without thinking, he scratched his forearm hard enough to raise goosebumps.
That was proof enough that he was rattled.
“Whoa… the vortex is gone, and it’s settled into a perfect rotational flow. Pressure loss is lower than expected, too… and the pump load is within acceptable range.”
“...This actually works?”
Chief Seo also couldn’t close his mouth.
“You stabilize the fluid by adding rifling… I can’t believe you thought to apply bullet physics to fluid dynamics…”
Kim slowly turned his chair toward me, his expression vacant.
The suspicion and dismissiveness from earlier were gone without a trace.
“Chief… where on earth did you find someone like this? Even a professor specializing in fluid dynamics wouldn’t think of this.”
At that, Chief Seo let out a crooked smile.
“You know who he is, don’t you? The man we were talking about in the break room.”
“Huh? When did we—”
Kim’s eyes flicked from the employee badge pinned to my suit jacket to my face and back again.
The look of suspicion on his face gave way to dawning certainty.
“Wait… Hanseo Defense? That… the ground-systems monster guy?”
“Yeah. Executive Director Baek Gunwoo.”
“Huh— wh-what? Really? You mean it’s really him?”
Kim’s face went pale.
He must have remembered, in a rush, every time he’d dismissed me as “just some guy who makes tanks” and muttered complaints when I didn’t do things the way he liked.
I gave a faint smile.
“Sounds like you’ve been talking about me behind my back a lot. No wonder my ears were itching.”
“N-no! Absolutely not! I never said anything bad about you! Just that you were like a monster… as a compliment…!”
Kim waved his hands frantically, looking positively stricken.
I stood, straightened my clothes, and let the matter settle.
That about wrapped things up.
But there was still one thing to do.
After looking between Kim and Chief Seo for a moment, I said in an utterly calm voice, “Ah, I almost forgot.”
“Yes?”
“This rifled tube-and-bellows hybrid design.”
I pointed at the result screen on the monitor.
“All patents and intellectual property belong to Hanseo Defense. You have no objections, right?”
Chief Seo and Kim could only nod blankly.
Of course they couldn’t object.
It hadn’t been their supercomputer that brought a dying patient back to life. It had been my head.
While the shipyard remained caught in that frantic work, unwelcome news reached Republic of Korea Navy Headquarters.
A Chinese submarine had started playing hide-and-seek in the deep waters of the East Sea—a report that was enough to give anyone a headache just thinking about it.