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Good luck designing crash resilient structures without simulating it on FEM based software though.

by antegamisou 2y ago

tightbookkeeper 2y ago
They did this just fine until without such tools for the majority of innovation in the last century.
- antegamisou 2y ago
  Except that everything's gotten abysmally complex. Vehicle crash test experiments are a good example of validating the FEM simulation (yes that's the correct order, not vice versa)
  - tightbookkeeper 2y ago
    How can you assert so confidently you know the cause and effect? Certainly computers allow more complexity, so there is interplay between what it enables and what’s driven by good engineering.
- drpossum 2y ago
  Having worked on the design of safety structures with mechanical engineers for a few projects, it is far, far cheaper to do a simulation and iterate over designs and situations than do that in a lab or work it out by hand. The type of stuff you can do on paper without FEM tends to be significantly oversimplified. It doesn't replace things like actual tests, but it makes designing and understanding testing more efficient and more effective. It is also much easier to convince reviewers you've done your job correctly with them. I'd argue computer simulation has been an important component a majority of mechanical engineering innovation in the last century. If you asked a mechanical engineer to ignore those tools in their job they'd (rightly) throw a fit. We did "just fine" without cars for the majority of humanity, but motorized vehicles significantly changed how we do things and changed the reach of what we can do.
  - tightbookkeeper 2y ago
    > It is also much easier to convince reviewers you've done your job correctly with them. In other words, the work that doesn't change the underlying reality of the product? > We did "just fine" without cars for the majority of humanity We went to the moon, invented aircraft, bridges, skyscrapers, etc, all without FEM. So that's why this is a bad comparison. > If you asked a mechanical engineer to ignore those tools in their job they'd (rightly) throw a fit. Of course. That's what they are accustomed to. 80/20 paper techniques that were replaced by SW were forgotten. When tests are cheap, you make a lot of them. When they are expensive, you do a few and maximize the information you learn from them. I'm not arguing FEM doesn't provide net benefit to the industry.
    - V_Terranova_Jr 2y ago
      What is your actual assertion? That tools like FEA are needless frippery or that they just dumb down practitioners who could have otherwise accomplished the same things with hand methods? Something else? You're replying to a practicing mechanical engineer whose experience rings true to this aerospace engineer. Things like modern automotive structural safety or passenger aircraft safety are leagues better today than even as recently as the 1980s because engineers can perform many high-fidelity simulations long before they get to integrated system test. When integrated system test is so expensive, you're not going to explore a lot of new ideas that way. The argument that computational tools are eroding deep engineering understanding is long-standing, and has aspects of both truth and falsity. Yep, they designed the SR-71 without FEA, but you would never do that today because for the same inflation-adjusted budget, we'd expect a lot more out of the design. Tools like FEA are what help engineers fulfill those expectations today.
      - tightbookkeeper 2y ago
        > What is your actual assertion? That the original comment I replied to is false: "Good luck designing crash resilient structures without simulating it on FEM based software." Now what's my opinion? FEM raises the quality floor of engineering output overall, and more rarely the ceiling. But, excessive reliance on computer simulation often incentivizes complex, fragile, and expensive designs. > passenger aircraft safety are leagues better today Yep, but that's just restating the pros. Local iteration and testing. > You're replying to a practicing mechanical engineer Oh drpossum and I are getting to know each other. I agree with his main point. It's an essential tool for combatting certifications and reviews in the world of increasing regulatory and policy based governance.
sashank_1509 2y ago
I’d guess most of the bridges in US were built before FEM existed
- double0jimb0 2y ago
  FEM runs on the same math and theories those bridges were designed on on paper.
- meindnoch 2y ago
  Anyone can design a bridge that holds up. Romans did it millenia ago. Engineering is designing a bridge that holds up to a certain load, with the least amount of material and/or cost. FEM gives you tighter bounds on that.
- drpossum 2y ago
  The average age of a bridge in the US is about 40-50 years old and the title of the article has "80 years of FEM". https://www.infrastructurereportcard.org/wp-content/uploads/2017/01/Bridges-Final.pdf https://www.infrastructurereportcard.org/wp-content/uploads/... I'd posit a large fraction were designed with FEM.
somat 2y ago
The FEM is just a model of the crash resistant structure. Hopefully it will behave like the actual structure, but that is not guaranteed. We use the FEM because it is faster and cheaper than doing the tests on the actual thing. However if you have the time and money to do your crash resiliency tests on the actual product during the development phase. I expect the results would be much better.
- formerly_proven 2y ago
  Yes, with infinite time and budget you'd get much better results. That does not sound like an interesting proposition, though.

Good luck designing crash resilient structures without simulating it on FEM based software though.

tightbookkeeper 2y ago

They did this just fine until without such tools for the majority of innovation in the last century.

antegamisou 2y ago
Except that everything's gotten abysmally complex. Vehicle crash test experiments are a good example of validating the FEM simulation (yes that's the correct order, not vice versa)
- tightbookkeeper 2y ago
  How can you assert so confidently you know the cause and effect? Certainly computers allow more complexity, so there is interplay between what it enables and what’s driven by good engineering.
drpossum 2y ago
Having worked on the design of safety structures with mechanical engineers for a few projects, it is far, far cheaper to do a simulation and iterate over designs and situations than do that in a lab or work it out by hand. The type of stuff you can do on paper without FEM tends to be significantly oversimplified. It doesn't replace things like actual tests, but it makes designing and understanding testing more efficient and more effective. It is also much easier to convince reviewers you've done your job correctly with them. I'd argue computer simulation has been an important component a majority of mechanical engineering innovation in the last century. If you asked a mechanical engineer to ignore those tools in their job they'd (rightly) throw a fit. We did "just fine" without cars for the majority of humanity, but motorized vehicles significantly changed how we do things and changed the reach of what we can do.
- tightbookkeeper 2y ago
  > It is also much easier to convince reviewers you've done your job correctly with them. In other words, the work that doesn't change the underlying reality of the product? > We did "just fine" without cars for the majority of humanity We went to the moon, invented aircraft, bridges, skyscrapers, etc, all without FEM. So that's why this is a bad comparison. > If you asked a mechanical engineer to ignore those tools in their job they'd (rightly) throw a fit. Of course. That's what they are accustomed to. 80/20 paper techniques that were replaced by SW were forgotten. When tests are cheap, you make a lot of them. When they are expensive, you do a few and maximize the information you learn from them. I'm not arguing FEM doesn't provide net benefit to the industry.
  - V_Terranova_Jr 2y ago
    What is your actual assertion? That tools like FEA are needless frippery or that they just dumb down practitioners who could have otherwise accomplished the same things with hand methods? Something else? You're replying to a practicing mechanical engineer whose experience rings true to this aerospace engineer. Things like modern automotive structural safety or passenger aircraft safety are leagues better today than even as recently as the 1980s because engineers can perform many high-fidelity simulations long before they get to integrated system test. When integrated system test is so expensive, you're not going to explore a lot of new ideas that way. The argument that computational tools are eroding deep engineering understanding is long-standing, and has aspects of both truth and falsity. Yep, they designed the SR-71 without FEA, but you would never do that today because for the same inflation-adjusted budget, we'd expect a lot more out of the design. Tools like FEA are what help engineers fulfill those expectations today.
    - tightbookkeeper 2y ago
      > What is your actual assertion? That the original comment I replied to is false: "Good luck designing crash resilient structures without simulating it on FEM based software." Now what's my opinion? FEM raises the quality floor of engineering output overall, and more rarely the ceiling. But, excessive reliance on computer simulation often incentivizes complex, fragile, and expensive designs. > passenger aircraft safety are leagues better today Yep, but that's just restating the pros. Local iteration and testing. > You're replying to a practicing mechanical engineer Oh drpossum and I are getting to know each other. I agree with his main point. It's an essential tool for combatting certifications and reviews in the world of increasing regulatory and policy based governance.

sashank_1509 2y ago

I’d guess most of the bridges in US were built before FEM existed

double0jimb0 2y ago
FEM runs on the same math and theories those bridges were designed on on paper.
meindnoch 2y ago
Anyone can design a bridge that holds up. Romans did it millenia ago. Engineering is designing a bridge that holds up to a certain load, with the least amount of material and/or cost. FEM gives you tighter bounds on that.
drpossum 2y ago
The average age of a bridge in the US is about 40-50 years old and the title of the article has "80 years of FEM". https://www.infrastructurereportcard.org/wp-content/uploads/2017/01/Bridges-Final.pdf https://www.infrastructurereportcard.org/wp-content/uploads/... I'd posit a large fraction were designed with FEM.

somat 2y ago

The FEM is just a model of the crash resistant structure. Hopefully it will behave like the actual structure, but that is not guaranteed. We use the FEM because it is faster and cheaper than doing the tests on the actual thing. However if you have the time and money to do your crash resiliency tests on the actual product during the development phase. I expect the results would be much better.

formerly_proven 2y ago
Yes, with infinite time and budget you'd get much better results. That does not sound like an interesting proposition, though.