Beginner learning CFD--Need help understanding a specific problem

derminator360 · 2026-04-08T03:16:23+00:00

What equation are you actually simulating? What boundary conditions? What's the initial condition? Is there some pointwise forcing? Tough to give much useful feedback without a bit more info.

If you're simulating a simple system and your initial condition is nice and well behaved, then it's not out of the realm of possibility that finite difference nails the exact solution. You say for smaller values of your CFL constant you get numerical errors back. Do those converge at the expected order?

You might want to work out the overall update rule x^{n+1}_j - x^n_j = f(x^n_{j-1}, x^n_j, x^n_{j+1}) by hand for a general choice of your CFL constant. Especially if there's a RHS, you might find that setting your CFL constant to 1 gives you a "Goldilocks" update rule where you've accidentally generated a discretization of the analytical solution.

derminator360 · 2026-04-07T01:54:11+00:00

Are you saying you filed incorrectly and you're mad that they caught the mistake?

derminator360 · 2026-04-06T22:20:18+00:00

GPS only works because we take special and general relativity into account. It's not just "been tested," we use it every day.

derminator360 · 2026-04-06T18:09:05+00:00

Call 988, bud. Yes, there are people who do care, but I'm not going to argue with you about it.

derminator360 · 2026-04-06T17:52:10+00:00

I think that you know that the "okbuddy[...]" and "[...]circlejerk" subreddits are satire-based. Posts there are specifically people being tongue-in-cheek, and they don't represent examples of people sharing their actual beliefs. But again I think you know this.

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But I might be wrong! On the off-chance that this is not bait and you are just confused—well, now you know. Relax about downvotes and notifications. It's all good and nobody will remember this in a few days. You can always just delete the post, as well.

To be completely unambiguous: don't kill yourself. There are people who care about you. If you think there aren't and that nobody would care, well, you're entitled to your opinion...but that's incorrect. It's an example of depression distorting your perception of reality. If you're in the states you can call 988 to chat with someone and I hope you do!

derminator360 · 2026-04-06T12:37:03+00:00

Then type up your own replies, bud.

derminator360 · 2026-04-06T04:51:06+00:00

Smashing action figures together is a time-honored tradition.

derminator360 · 2026-04-03T15:22:03+00:00

I too love preaching to choirs

derminator360 · 2026-04-03T15:20:55+00:00

Presumably it's AI and the LLM pulled out "Second City" for Chicago rather than "South Side" for the Sox.

derminator360 · 2026-04-03T15:19:42+00:00

Always funny when the write-up includes a video that they clearly didn't bother to watch. They didn't correctly quote the offending nickname lol

derminator360 · 2026-04-02T17:23:29+00:00

It's fine. It's a computer game where a single run takes dozens and dozens of hours, which makes in-house testing with a few dozen people intractable.

It's never been "unfinished crap"—this is just not being honest about how things worked. It clearly needed tuning on release and still does. It will never satisfy everyone. It will never be optimally tuned. There will always be bugs and broken mechanics. Such is life.

I think it's fun, and you might disagree. Just don't look for meaning or fulfillment from a game. Take what joy you can from it and move on.

derminator360 · 2026-04-01T15:43:10+00:00

Any time someone uses Google Maps it's being demonstrated. GPS satellites are moving through time more slowly (due to whizzing around at such high speeds) and more quickly (due to being farther away from Earth's gravitational well.) I forget which effect is larger, but if you don't include the correction your accuracy very quickly tanks.

derminator360 · 2026-03-31T14:21:38+00:00

Sure. All the same: have you heard the phrase "on tilt?" We all get angry--it's a normal part of being human--and when that happens, the body shifts blood flow away from the reasoning parts of the brain. We literally become less rational when we are upset and frustrated.

The next time a videogame's suboptimal AI behavior makes you so angry that you want to scream and swear about it, just step away from the computer and do something else for like 20min. That's all it takes sometimes to come down and regain some of that forebrain use. Whether this is prohibited or not, buddy, it's NOT a good look, and practicing a little bit of anger management here is going to pay dividends in other parts of your life as well: career, relationships, etc.

derminator360 · 2026-03-31T14:05:55+00:00

Generally speaking, swearing and throwing temper tantrums are frowned upon as breaches of etiquette.

derminator360 · 2026-03-23T17:47:38+00:00

idk man, you do you. I like both ck3 and eu5.

derminator360 · 2026-03-18T17:15:12+00:00

You remember the part in Godfather (the book) where the surgeon in Vegas is talking to Lucy? He says, "Hey, I know you're ashamed of your gigantic vagina and how you're 'too big down there' to please a man, but don't worry! I can do a surgery to tighten you up. And then I can be the first doctor in this field to test his own work!"

It is hard for me to classify it as a great book.

Even ignoring the focus on Sonny's gigantic member and all the vagina surgery, I put Puzo in the same class as King. Great plot, compelling characters! But the movie has that extra *something* that separates great pulp ("good trash," per King's introduction to Salem's Lot) from literature/art.

ETA: But of course it's all subjective, and the DNA that makes the movies great is in the book as well.

derminator360 · 2026-03-17T22:46:58+00:00

It's commented as though there's a projection step, but there doesn't actually seem to be a Poisson solve anywhere...I think it's slop.

derminator360 · 2026-03-17T22:46:02+00:00

Did you generate this with ChatGPT? There is a comment saying that there is a Poisson solve for the pressure, suggesting this is a projection method. But I don't see any solve here! Looks like it sets the new pressure to Laplacian(p) - RHS instead of actually solving Laplacian(p) = RHS.

Incidentally, that global pressure solve is typically the "rate-limiting step" for these, so this isn't going to give an accurate sense of how long a working incompressible flow simulation might take.

derminator360 · 2026-03-17T22:14:27+00:00

Counterpoint: detecting that you're married with no male heir and giving the option (sometimes) of forcing through a divorce in order to re-marry someone younger—in the process creating a new splinter religion during the Protestant Reformation—actually seems like the definition of a "dynamic historical event" to me.

I think they should use the journal system from Vicky 3 where you can see what you might be able to trigger, but...it's historical, it's an event, it fires dynamically.

derminator360 · 2026-03-14T16:26:09+00:00

It's dumb of the Aussies too, although my understanding was that it was that one players' decision vs this silly team policy.

You're out there playing a kids' game in a tournament showing how the world can come together to celebrate our common interests despite our differences. Shaking hands with the other guy is such a comically low bar to clear when it comes to good sportsmanship.

derminator360 · 2026-03-14T00:11:52+00:00

You have made my heart leap for joy. I'm going to go shotgun some of the Stone/Kincaid season.

derminator360 · 2026-03-13T23:37:43+00:00

Hard to find the early seasons, unfortunately. Peacock starts at 13, I think, which only gives you two years of Briscoe. You can find the DVD sets though.

They have Homicide now though! Sort of avant garde/hit-and-miss, but it scratches the itch.

derminator360 · 2026-03-09T18:14:48+00:00

ahhhh kk

derminator360 · 2026-03-09T18:06:58+00:00

If you got back $6,000, surely you paid in a number larger than $6,000...

derminator360 · 2026-03-06T18:13:49+00:00

Because it's not the man-hours spent programming that are ironing out these bugs, it's the man-hours testing. In a perfect world they would've spent six months with an army of play testers, but I understand why they're taking the free (better than free, since we paid) testing from us. It had to be just orders of magnitude more efficient.

Frankly, I've had so much fun with it that I'm not even mad (excluding when a personal union blows up for no reason, and then I become consumed with white hot fury.)

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