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The most expensive number in engineering

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Re: The most expensive number in engineering

#141

Post by tcoff91 »

snowwrestler wrote: post #136
thaumasiotes wrote: post #131

Earlier quoted context omitted.

> The idea is: this advanced civilization has such command over physical technology, that they can effortlessly engineer unnecessary strength without losing any of their designed performance. Are you sure the idea isn't just "we never thought about it"? Old cars are sturdy and robust while new cars are extremely fragile and will total themselves at the drop of a hat. That's not because the 50s possessed ancient techn…

Old cars were not sturdier or more robust than new cars. That’s a myth. You can Google “crash test old car vs new” or something like that to see examples.

90s volvos were absolute tanks . My friend had one and it got rear ended while parked and both the car that rear ended it and the car in front of the Volvo got totaled. The Volvo was pretty much fine and just needed a new bumper (which was easily done as the bumpers were distinct from the body work).

Re: The most expensive number in engineering

#142

Post by makapuf »

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…

And we're also guilty of this when we use multiple ghz/GB computers with advanced GPU firing excel to make simple computations, or a multi-ton car to drive one person half a mile.

Re: The most expensive number in engineering

#143

Post by mturmon »

WalterBright wrote: post #66
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…

Aircraft have a smallish safety factor, because of the weight. They make up for it with much more careful design, manufacture, and maintenance along with frequent inspections.

Yes. I linked below a slide set by a Lee Petersen, JPL engineer who was instrumental in setting up the uncertainty accounting for the Mars lander EDL system - both Curiosity and Perseverance. (Among other uses of UQ for engineered systems at JPL.)

In the slides he’s deliberately contrasting a “MUF” (model uncertainty factor) approach that uses safety factors, possibly stacked as indicated in the OP, versus a “BE+U” (best estimate plus uncertainty) approach.

The latter uses verified physics-based models, validation of model predictions versus experimental tests, and uncertainty quantification of sources of error, to get a best estimate of whatever quantity is critical to safe operation, and an uncertainty. A final margin can then be added onto that, see slide 13.

The mess at the system level that can result from a stack of ad hoc MUFs applied at the subsystem level is shown on slide 15.

Incidentally, many of the comments nearby seem to think the application of domain specific safety factors is still state of the art. This just isn’t true any more for high risk systems.

https://cstools.asme.org/csconnect/Filedownload.cfm?thisfile...

Re: The most expensive number in engineering

#144

Post by TeMPOraL »

thaumasiotes wrote: post #131
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 idea is: this advanced civilization has such command over physical technology, that they can effortlessly engineer unnecessary strength without losing any of their designed performance. Are you sure the idea isn't just "we never thought about it"? Old cars are sturdy and robust while new cars are extremely fragile and will total themselves at the drop of a hat. That's not because the 50s possessed ancient techn…

> Are you sure the idea isn't just "we never thought about it"?

There are two sides to it. On the one hand, the new cars are "fragile" on purpose, because they're literally a big, single-use inertial dampener, with wheels and an engine.

On the other hand, there are great many appliance categories where you can clearly tell the old models, made in 70s and earlier, are indeed sturdy and robust, and new models are just flimsy. Appliances that don't experience the kind of forces like cars have to account for. It's hard to give any other explanation here than the obvious one: the old models were made before the market optimized the quality away.

Re: The most expensive number in engineering

#146

Post by ben_w »

lupire wrote: post #133
robbrown451 wrote: post #101

Earlier quoted context omitted.

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 simi…

Why isn't Lord of the Rings "science fiction" but Star Wars is? They both have technology unknown to us.

LotR magic isn’t supposed to be technology, it’s literal-god (Eru Ilúvatar) created everything by singing, literal-devil (Morgoth) has a different and incompatible song, some legendary things happened (only in-universe they actually happened and aren’t mere tales like our myths, and the elves being immortal can remember them), and then the literal spirits of literal minor angels (Maiar) took human form and did magic as the wizards.

Re: The most expensive number in engineering

#147

Post by wiredfool »

auxym wrote: post #118
wiredfool wrote: post #2

"""A non-empirical alternative to the factor of safety has been around since the 1940s, but still doesn’t have widespread adoption. I think the image below describes the concept, called probabilistic design, best. """ This is _exactly_ LRFD (Load Factor Resistance Design) which has been in the Civil Engineering building codes since the mid 80's, and became common in use the 90's when I was an Engineer (in training).…

Did you do civil? I did mechanical and barely just heard of LRFD and probalistic design. Not very common in mechanical, maybe in aerospace.

Yep. I did Civil/Structural.

Re: The most expensive number in engineering

#148

Post by supermatt »

Any idea where I can learn some simple structural engineering?

For example, I want to build a small building. I want to be able to calculate things like the snow load of the roof, make a suitable truss, take into consideration things like the safety factor, and build with the materials to meet those requirements.

I can buy plans for similar constructions, but i don't see how they decide what size wood to use where, etc - and I want to gain an understanding of that.

Re: The most expensive number in engineering

#149

Post by nearbuy »

snowwrestler wrote: post #139
glitchc wrote: post #67

Earlier quoted context omitted.

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…

When Star Wars was released, it was understood to be science fiction. See this interview with Alec Guinness in 1977: https://youtu.be/0qxcEBI1iKI They both call it science fiction. Lucas was wary of that label because science fiction had a (well-earned) reputation at that time as a ghetto of heavy-handed allegory with hammy acting and terrible special effects. Lucas was striving for more than that. He was trying to c…

Any fantasy movie in a futuristic setting (even one that's technically in the past, like Star Wars) would be widely considered science fiction. Granted, that is a common definition of science fiction.

But science fiction can also be something like The Twilight Zone: a genre that explores "what-if" scenarios. A genre that takes some fictional premise and attempts to explore the consequences logically. An example premise could be, how might modern society have evolved if the Greek gods were real? A sci-fi story would try to approach that question in a scientific and logical way. Star Trek often followed this pattern. Star Wars doesn't.

A weakness of defining sci-fi by a futuristic setting is that you can change the genre with only superficial changes to the story. Other major genres - comedy, horror, mystery, romance, action - are defined by the feeling or thought process they try to evoke. But take Star Wars and replace the planets with kingdoms, the Jedi with wizards, and the force with.. well, that's fine as it is.. and you can create a story with the exact same plot points but without a futuristic setting. There's no actual science in Star Wars; only a futuristic setting.

Setting doesn't feel like it should be the feature that defines a genre. You should be able to have a comedy, horror or mystery take place in a futuristic setting and a sci-fi that takes place in the present (and we often do, eg, The Handmaid's Tale).

I'll note that there aren't many movies that stick to just sci-fi; most incorporate a lot of action (like The Matrix). This is probably because filmmakers feel 2+ hours of science fiction would be boring. The movie The Martian heavily cut from the science of the book and focused on the action (while the book had little action and a lot of science). You see a strong sci-fi focus more often in literature and TV.

Re: The most expensive number in engineering

#150

Post by nearbuy »

dragontamer wrote: post #85
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... )

And Vulcan are space elves, Klingon are space orcs and Borg are space undead. All of this stuff has inspiration from classical fantasy. That doesn't change whether or not something is SciFi or not. There is an intersection of SciFi and Fantasy for sure, and the line gets blurred. Artificial human stories can be cyborgs, androids, clones, golems, or chimera, or even explicit fantasy races like minotaurs. If it's an an…

I see the similarities for Klingons and Borg, but I don't see much similarity between Vulcans and elves beyond the pointy ears. Vulcans are more like androids: logical and outwardly emotionless, but not necessarily wise. The human captain (e.g. Kirk) tends to figure out a winning solution despite the resident Vulcan often complaining it isn't logical.

That doesn't detract from your point.

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