The most expensive number in engineering • Hacker News Board

Re: The most expensive number in engineering

#101

Post by robbrown451 » Mon, May 31, 2021, 10:21 PM UTC

glitchc wrote: post #67

ben_w wrote: post #58

Earlier quoted context omitted.

> For the record, Star Wars is not science fiction nor has it ever been portrayed as such. FWIW this is literally the first time I’ve encountered someone claiming that it isn’t science fiction. ( Soft SciFi, to be sure, but still: https://tvtropes.org/pmwiki/pmwiki.php/Main/MohsScaleOfScien... )

Lucas himself has stated that although science fiction inspired him to create these stories, Star Wars is indeed not science fiction but rather science fantasy: https://scifi.stackexchange.com/questions/46481/did-george-l... Because all the stories are " a long, long time ago in a galaxy far, far away," it's not even clear if Luke and the gang are humans or some other species. Of course it's easy to think of them as…

True but Lucas doesn't have final say on classifying his movies. People who make things have an incentive to claim that their work is somehow special.

I'd just say Star Wars is science fiction with lots of fantasy elements, as well as lots of influence from different genres (Earth-based war films, adventure serials, etc.)

I see the fact that humans in Star Wars seem to be the "same species" as Homo sapiens to be similar to the fact that movies that take place in ancient Greece have the characters speak modern English. We are expected to understand that humans in Star Wars evolved there, not in Africa on Earth. It would be more realistic to have the main characters look very different from us, but it probably wouldn't make for as enjoyable a movie.

Re: The most expensive number in engineering

#102

Post by aetherspawn » Mon, May 31, 2021, 10:26 PM UTC

I used to work for a place that built fast cars. We had a mate that used 5.0 or more for the factor of safety everywhere. Everything he designed was about 30% heavier than it needed to be, but we could easily adapt his parts for prototyping because it never mattered if you drilled a hole through the middle or cut them in half. They were plenty strong and reliable.

We called this the “Factor of Lloyd” and we had a few sayings about it.

Re: The most expensive number in engineering

#103

Post by UncleMeat » Mon, May 31, 2021, 10:29 PM UTC

glitchc wrote: post #49

UncleMeat wrote: post #41

Earlier quoted context omitted.

I don’t think this is science fiction doing this to connote the future in many of these cases. The cars in the “fast” franchise also survive ludicrous damage. The bodies of action heroes survive falls from ridiculous heights and blows and stab wounds that would kill somebody with ease. This is more a property of action movies (and adventure movies, to a lesser degree).

Seems disingenuous to lump a science fiction movie where the focus is future technologies to an action movie with exaggerated physics and lack of real damage. In action movies, bad guys die with one bullet while the hero finds his way to safety (and survives!) despite having 10 or more lethal bullet wounds. For the record, Star Wars is not science fiction nor has it ever been portrayed as such. It's very much an acti…

Three movies were referenced in the comment I responded to: Return of the Jedi, Star Trek: Into Darkness, and 2001: A Space Odyssey. Two of those movies are definitely not focused on future technologies.

Many people call Star Wars "science fantasy", but I'm extremely confident that this is used less frequently than "science fiction" to describe it and I am absolutely confident that I'd be able to find marketing copy by LucasFilm or distributors describing it as science fiction, even if that aggravates people who are really into more cerebral sci-fi.

Re: The most expensive number in engineering

#104

Post by Terretta » Mon, May 31, 2021, 10:41 PM UTC

I like the “most expensive number” hook, and enjoyed the read.

However, I’d hazard the most unnecessarily costly variable in engineering (over time, in aggregate; as well as on most any given substantial project) is the number of days later a project starts than it could have if it had just gone ahead and started.

Re: The most expensive number in engineering

#105

Post by vladTheInhaler » Mon, May 31, 2021, 10:43 PM UTC

cardiffspaceman wrote: post #96

05 wrote: post #50

Earlier quoted context omitted.

> For example in the JJ Abrams movie Star Trek Into Darkness we see the Enterprise operating at depth in an ocean, then dramatically zooming away into space. Subverted in Futurama: https://www.youtube.com/watch?v=7GDthiBGMz8

What about a craft like the space shuttle? You have it powered through the atmosphere by a set of powerful rocket engines. The forces on its hull while it is accelerated through the Atmosphere by rocket engines or gravity would seem to be analyzable as atmospheres of pressure. So the Enterprise and Bessie both need to be designed for more atmospheres than 1.0, due to the fact that both ships encounter gaseous environ…

What your're talking about is called the max q condition[1]. It's definitely a significant design consideration, but I believe that the loading would very different when the rocket is plowing through the air in a particular direction, compared to an "equivalent" hydrostatic stress applied uniformly over the surface, so even though the structure might be fine with the first, it wouldn't survive the second. For instance, think about corrugated or honeycomb materials - they often have a "strong" orientation and a "weak" orientation.

[1] https://en.wikipedia.org/wiki/Max_q

Re: The most expensive number in engineering

#106

Post by justincredible » Mon, May 31, 2021, 11:05 PM UTC

codeflo wrote: post #35

The article suggests using a probabilistic failure model instead of a large a safety factor, and explains how a safety factor established in the 1930s affected the cost of the Space Shuttle. But spacecraft might be a special case, where any additional weight is so expensive, and you also expect the models to be especially accurate and manufacturing to be extremely precise. For more everyday civil engineering, I think…

I don't think the probabilistic failure model is suggested, merely presented. The author concludes that departing from the stated safety factor is necessarily taking on additional risk.

Re: The most expensive number in engineering

#107

Post by msrenee » Mon, May 31, 2021, 11:07 PM UTC

boulos wrote: post #86

It’s kind of mentioned in the article, but to be more explicit: reducing safety factors has asymmetric risk vs reward. Reducing the factors “just” lowers cost or improves performance. But if your field is padding by 50%, then you need to tradeoff an “up to 50%” cost reduction (or similar) versus “had a catastrophic failure”. So, reducing the padding from 5x to 1.5x was already most of the benefit. If you were at 1.2,…

I feel like that's what was so unconvincing to me in this article. The only argument they gave against over-engineering was cost. At that point you have to decide how much risk is worth how much in savings. Is a 1% increase in the likelihood of the bridge failing in extreme conditions and killing 10 people worth a savings of $100k? What's a human life worth? What's a low increase in risk to a human's life worth? How much of an increase in the tax rate is reasonable to reduce the likelihood of someone dying due to a structure failing?

On my end, it's pretty easy. Am I personally willing to pay an extra $100 in taxes a year to measurably reduce the likelihood of another resident dying due to structure failure? If there's a quantifiable advantage to the increased cost, then absolutely. Will the increases in my taxes reduce a 4% chance of failure to 3% over 25 years? Heck yeah. Even better, how about we find some other facet of the budget that does not benefit the populace? What business is being subsidized by my taxes that does not benefit anyone who needs the help? There's lots of that here.

Trying to decide whether to cut the weight on an airplane? How much money will it save? What does that do to the price of a ticket? Is a savings of $10 per ticket worth a 1% increase in the likelihood of the plane crashing into a cornfield in the next 10 years? It sure doesn't seem worth it to me.

Honestly, those cost savings don't usually go into decreasing the price of tickets anyway. In my pessimistic view of reality, what actually ends up happening is that I pay that $10 per ticket either way and the reduced cost leading to that reduction in safety for the passengers ends up going into some executive's pocket. So even the argument that reduced costs are a good thing for the average person isn't really an argument at all. The person who might die from the decision is never going to see the benefit anyway and at that point, this starts looking like a pretty terrible deal for the average person.

Re: The most expensive number in engineering

#108

Post by mike50 » Mon, May 31, 2021, 11:18 PM UTC

Gibbon1 wrote: post #45

rossdavidh wrote: post #33

Earlier quoted context omitted.

I think the idea is that, if you calculate the load incorrectly enough, or use inappropriate enough materials, the safety factor will not save you. But, if you have done those things correctly, then the safety factor should be enough to save you from normal unknowns, unexpecteds, etc.

Yeah four things going on. Design errors Probabilistic nature of the loads applied. Material defects Fatigue Deterioration All structures have a service life and it's the service lifetime an experienced engineer is trying to hit. For the impeller in a rocket turbo pump the service life is like 5 minutes. For the impeller in a hydro electric dam it's 50 years. The other thing that one of my professors pointed out was…

In what discipline? In Electrical Engineering a fuse circuit breaker or receptacle may be used thousands of times and in dozens of redesigns.

Re: The most expensive number in engineering

#109

Post by spease » Mon, May 31, 2021, 11:29 PM UTC

snowwrestler wrote: post #34

Grossly increasing the factor of safety is a subtle way that science fiction stories connote a feeling of very advanced technology. For example in the JJ Abrams movie Star Trek Into Darkness we see the Enterprise operating at depth in an ocean, then dramatically zooming away into space. Then later another ship falls from orbital height and plows through San Francisco without losing its hull shape. In Star Wars the Mi…

I can sort of buy this.

In Gravity things are probably a lot more robust than they actually should be, but collisions with debris or other objects tend to be immediately fatal for the vehicles involved. Debris at high velocity goes straight through stuff.

Similarly, in For All Mankind, most stuff is pretty fragile and volatile, as you’d expect for Apollo-era tech. It’s only the later stuff that the show makes up which starts to show much resilience.

In the Expanse, technology is considerably more advanced, but still vastly inferior to any Star Trek or Star Wars vehicle. And in the Expanse we see the hulls of ships routinely get punctured, and a single torpedo or rail gun hit is often fairly decisive. Even the Donnager is forced to shut down its reactor due to a torpedo hit.

And even in non-Abrams Trek, in an alternate timeline Voyager still survives a hard crash on a planet reasonably intact, even if it was fatal to everybody on board. Possibly only because the inertial dampeners were offline.

Re: The most expensive number in engineering

#110

Post by antonvs » Mon, May 31, 2021, 11:35 PM UTC

snowwrestler wrote: post #34

Grossly increasing the factor of safety is a subtle way that science fiction stories connote a feeling of very advanced technology. For example in the JJ Abrams movie Star Trek Into Darkness we see the Enterprise operating at depth in an ocean, then dramatically zooming away into space. Then later another ship falls from orbital height and plows through San Francisco without losing its hull shape. In Star Wars the Mi…

> the monolith is made out of a material that humans can’t dent or cut. Why so strong? It’s basically just an automated radio.

The monoliths were supposed to be able to assess and monitor the activity and level of development of local species, possibly telepathically, catalyze evolution to develop intelligence, and encourage technology use. A monolith also transformed David Bowman into the Star Child. And of course, they had to maintain themselves over evolutionary timescales. So they were much more than just radios.

In sequels (which perhaps don't count), they became ridiculously overpowered (spoiler alert), replicating exponentially to perform Kardashev level II feats of solar system engineering, and hosting multiple uploaded intelligences like Bowman and HAL.