3 ms·

It's not software: it's mathematics. You don't build a bridge by successively creating bridges with more and more structural reinforcement until the bridges st

It's not software: it's mathematics. You don't build a bridge by successively creating bridges with more and more structural reinforcement until the bridges stop falling down. Instead, you calculate the appropriate size of the columns using a model and only build a single bridge. This is no different. Finite element methods are such a known quantity that we're able to design nuclear weapons without ever testing them in meatspace. If it's good enough for nuclear weapons, I am strongly convinced it's good enough for something as simple as stress analysis.

tempguy9999 7y ago
I'm neither an aero engineer nor a nuke weapons designer but I am pretty sure that nuclear weapons are a whole lot more complex than a plane. As for not testing nukes, I'm damn sure they test the relevant non-nuclear parts such as the lensing (conventional) explosives. > ...for something as simple as stress analysis Of entire wings? From the article "..such as using machines to bend the wings to extreme angles and shaking the fuselage until it cracks" Your job isn't in this area I guess. I'm sure of it. BTW the model is only as good as its inputs so if you have a defective batch of components (and wasn't there very recently a case where a bunch of deliberately below-spec aluminium parts were delivered to various aerospace companies which cost lots to rectify) then your model had better refelect that defect. But how are you going to find out? With pure maths?
- chroem- 7y ago
  > Your job isn't in this area I guess. I'm sure of it. I'm a mechanical engineer. My point is that stress analysis is the oldest, simplest, and most well understood application of finite element analysis. I can't even begin to imagine the multiphysics that goes into simulating a nuclear weapon, but if we are willing to bet our entire nuclear deterrent on it, it seems reasonable to skip some additional rounds of physical tests that are mostly a formality at this point. Also, defective materials are caught much earlier in the manufacturing process through quality assurance methods, before they become airplanes. And then you apply a factor of safety on your calculations for added assurance.
  - samcday 7y ago
    > Also, defective materials are caught much earlier in the manufacturing process through quality assurance methods, before they become airplanes. Okay so maybe this is an apple's to oranges comparison, but I thought of the story how NASA was scammed by a supplier passing off shitty aluminium as space grade [1]. Is it reasonable to assume that if it can happen to NASA, it can happen to Boeing? https://weather.com/news/news/2019-05-02-nasa-launch-failures-caused-by-faulty-aluminum-scam https://weather.com/news/news/2019-05-02-nasa-launch-failure...
    - chroem- 7y ago
      They check the airframes with nondestructive ultrasonic testing that doesn't involve oblitering entire aircraft. That would be caught at one of several different QA points. We're mostly talking about design verification, which is different.
      - tempguy9999 7y ago
        Parent post gave the example I was remembering. And the company, Sapa, didn't (AFAICT) manufacture the components, they were a third-party testing service! They provided exactly the tests you say should have picked up the problems.
  - kanaba 7y ago
    > I'm a mechanical engineer. My point is that stress analysis is the oldest, simplest, and most well understood application of finite element analysis. I am not a mechanical engineer. My understanding is that some composite materials used in modern aircraft manufacturing can fail in ways unlike classic aircraft aluminum (i.e. suddenly, without prior visible signs of stress/wear). Is that relevant here?
    - goatinaboat 7y ago
      I am a mechanical engineer, and yes it is. The composites are simply too new to have all their properties adequately modelled yet. And they are a moving target.
- noir_lord 7y ago
  > I'm neither an aero engineer nor a nuke weapons designer but I am pretty sure that nuclear weapons are a whole lot more complex than a plane. Depends on the plane I guess, Cessna 172 or F-34 or 787 and the nuke (last gen two stage fusion or Little Boy). The nuke is harder to build because of the requirement for fuel purification but the actual engineering has to be in the same order of complexity as a modern airliner surely. I mean we built little boy in the 1940's we definitely couldn't have built anything like the F-35 then.
  - deleted 7y ago
    [deleted]
  - tempguy9999 7y ago
    Sorry, a bit wasted ATM and it bled through. I meant the exact opposite, that planes are likely a boatload more complex than nukes. A fission nuke is at heart 2 lumps of metal that get squeezed together. How would one explain a plane in such terms? Sorry for the crappy mistake.
    - noir_lord 7y ago
      I did wonder. That said the engineering on a nuclear warhead is still exquisite (if such a word is accurate for such a horrible device), requiring insane tolerances and timings to ensure everything works properly. So it’s a different kind of complexity I guess.
gameswithgo 7y ago
people still spot check bridges with physical tests because we can’t perfectly simulate material properties or fluid flow
- chroem- 7y ago
  Absolutely, but NDT is a far cry from testing an aircraft to failure.
ridgeguy 7y ago
> something as simple as stress analysis. Stress analysis isn’t simple. In aircraft applications, the analysis has to model not only metals, but composite materials that have anisotropic and nonlinear responses, account for acoustic energy distribution and local concentration effects, incorporate static- low- and high-cycle fatigue mechanisms (which differ in the materials imperfections that initiate them and in how the ultimate failures play out), incorporate time varying and differential spatial temperature distributions ranging from -55°C to ~1500°C (hot section, commercial engines) and on and on. It’s not simple. I really like physical testing to validate analytical models of complex physical systems.
Bendingo 7y ago
> we're able to design nuclear weapons without ever testing them in meatspace Perhaps you are forgetting about all the nuclear weapons testing that was carried out in the 40's 50's and 60's ? (The last tests by USA and USSR, took place in the early 90's.) [0] https://en.wikipedia.org/wiki/List_of_nuclear_weapons_tests https://en.wikipedia.org/wiki/List_of_nuclear_weapons_tests

tempguy9999 7y ago

I'm neither an aero engineer nor a nuke weapons designer but I am pretty sure that nuclear weapons are a whole lot more complex than a plane. As for not testing nukes, I'm damn sure they test the relevant non-nuclear parts such as the lensing (conventional) explosives. > ...for something as simple as stress analysis Of entire wings? From the article "..such as using machines to bend the wings to extreme angles and shaking the fuselage until it cracks" Your job isn't in this area I guess. I'm sure of it. BTW the model is only as good as its inputs so if you have a defective batch of components (and wasn't there very recently a case where a bunch of deliberately below-spec aluminium parts were delivered to various aerospace companies which cost lots to rectify) then your model had better refelect that defect. But how are you going to find out? With pure maths?

chroem- 7y ago
> Your job isn't in this area I guess. I'm sure of it. I'm a mechanical engineer. My point is that stress analysis is the oldest, simplest, and most well understood application of finite element analysis. I can't even begin to imagine the multiphysics that goes into simulating a nuclear weapon, but if we are willing to bet our entire nuclear deterrent on it, it seems reasonable to skip some additional rounds of physical tests that are mostly a formality at this point. Also, defective materials are caught much earlier in the manufacturing process through quality assurance methods, before they become airplanes. And then you apply a factor of safety on your calculations for added assurance.
- samcday 7y ago
  > Also, defective materials are caught much earlier in the manufacturing process through quality assurance methods, before they become airplanes. Okay so maybe this is an apple's to oranges comparison, but I thought of the story how NASA was scammed by a supplier passing off shitty aluminium as space grade [1]. Is it reasonable to assume that if it can happen to NASA, it can happen to Boeing? https://weather.com/news/news/2019-05-02-nasa-launch-failures-caused-by-faulty-aluminum-scam https://weather.com/news/news/2019-05-02-nasa-launch-failure...
  - chroem- 7y ago
    They check the airframes with nondestructive ultrasonic testing that doesn't involve oblitering entire aircraft. That would be caught at one of several different QA points. We're mostly talking about design verification, which is different.
    - tempguy9999 7y ago
      Parent post gave the example I was remembering. And the company, Sapa, didn't (AFAICT) manufacture the components, they were a third-party testing service! They provided exactly the tests you say should have picked up the problems.
- kanaba 7y ago
  > I'm a mechanical engineer. My point is that stress analysis is the oldest, simplest, and most well understood application of finite element analysis. I am not a mechanical engineer. My understanding is that some composite materials used in modern aircraft manufacturing can fail in ways unlike classic aircraft aluminum (i.e. suddenly, without prior visible signs of stress/wear). Is that relevant here?
  - goatinaboat 7y ago
    I am a mechanical engineer, and yes it is. The composites are simply too new to have all their properties adequately modelled yet. And they are a moving target.
noir_lord 7y ago
> I'm neither an aero engineer nor a nuke weapons designer but I am pretty sure that nuclear weapons are a whole lot more complex than a plane. Depends on the plane I guess, Cessna 172 or F-34 or 787 and the nuke (last gen two stage fusion or Little Boy). The nuke is harder to build because of the requirement for fuel purification but the actual engineering has to be in the same order of complexity as a modern airliner surely. I mean we built little boy in the 1940's we definitely couldn't have built anything like the F-35 then.
- deleted 7y ago
  [deleted]
- tempguy9999 7y ago
  Sorry, a bit wasted ATM and it bled through. I meant the exact opposite, that planes are likely a boatload more complex than nukes. A fission nuke is at heart 2 lumps of metal that get squeezed together. How would one explain a plane in such terms? Sorry for the crappy mistake.
  - noir_lord 7y ago
    I did wonder. That said the engineering on a nuclear warhead is still exquisite (if such a word is accurate for such a horrible device), requiring insane tolerances and timings to ensure everything works properly. So it’s a different kind of complexity I guess.

gameswithgo 7y ago

people still spot check bridges with physical tests because we can’t perfectly simulate material properties or fluid flow

chroem- 7y ago
Absolutely, but NDT is a far cry from testing an aircraft to failure.

ridgeguy 7y ago

> something as simple as stress analysis. Stress analysis isn’t simple. In aircraft applications, the analysis has to model not only metals, but composite materials that have anisotropic and nonlinear responses, account for acoustic energy distribution and local concentration effects, incorporate static- low- and high-cycle fatigue mechanisms (which differ in the materials imperfections that initiate them and in how the ultimate failures play out), incorporate time varying and differential spatial temperature distributions ranging from -55°C to ~1500°C (hot section, commercial engines) and on and on. It’s not simple. I really like physical testing to validate analytical models of complex physical systems.

Bendingo 7y ago

> we're able to design nuclear weapons without ever testing them in meatspace Perhaps you are forgetting about all the nuclear weapons testing that was carried out in the 40's 50's and 60's ? (The last tests by USA and USSR, took place in the early 90's.) [0] https://en.wikipedia.org/wiki/List_of_nuclear_weapons_tests https://en.wikipedia.org/wiki/List_of_nuclear_weapons_tests