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从业超过50年的以色列机械工程师:在工程计算上,别信学校那套!

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1#
发表于 2016-9-26 13:56:18 | 只看该作者 回帖奖励 |倒序浏览 |阅读模式
标题党了一把,其实这是个机械英语教学帖,当然,里面干货也不少。
今天这篇文章的主题是 engineering calculation。是一个资深以色列工程师对于刚入行的年轻人在工程计算上的意见和建议。
老规矩,我先把原文贴出来,大家自由翻译文章,并把译文贴在回复中,可以是文章中的一句,一段,有空的同学翻译全文也是极好的,参与学习的社友都能得到威望奖励。
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以下是作者简介。作者出生在以色列,毕业于以色列理工学院(传说中的中东MIT)机械工程专业,专注于机械设计超过50年,目前在以色列本古里安大学教授机械光学设计。
Adam Rubinstein
Born in Israel, studied Mechanical engineering in the Technion, specialized in mechanical design and particularly mechano-optics. Over 50 years experience as a design engineer, and about 24 of them as an independent consultant. lately, partially retired and teaching mechano-optical design at BGU in Beer-Sheva, Israel.

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下面是正文分隔线
———————————————————————————————————————

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1、Don't believe everything they teach you at school, real life is very different!
2、You should immediately dismiss from your head the idea that there is only one right answer to any design question. Keep your mind open to all options.
3、Design failures can have many different forms and all should be considered.
4、What came first, the chicken or the egg? The analysis of a hypothetical design will always start with a range of assumptions which can be adjusted.
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The difference between school and “real life” problem solving
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When we pass from high school to university we bring with us the idea that answers are obtained by engineering calculations. We use analytical formulas and we are educated to believe that the results are either right or wrong – there is no in between and no grey areas. We are used to having all of the relevant data associated with a problem. I even remember checking my answers by verifying that if I used all the data given in a problem – do we always need to use all of the data to get the answer?

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This is not real life. Data is never “given”, it is usually incomplete, and there is not necessarily a single “right” formula. I have seen many students ask me which of two different formulas (teeth strength and surface fatigue) to use for calculating gear wheels. It was very difficult to make them understand that both were “right” and that they should use the worst case. Always err on the side of caution.
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There are many ways to fail (but it only takes one)
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While teaching strength of bolts I once calculated a bolt for a number of different possible failure modes. I calculated for the “standard”, the pull strength of the core for the less common shaving of the threads and also for shearing of the head and a few more bizarre possible modes. I showed that, although all are possible, the standard bolts will nearly always fail at the core first. However, under certain conditions (too few mating threads, a weak mating material, etc) the threads might shave first. Confused? Let me explain….
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Forgetting the other possible failure modes may be very dangerous. As the designers of the first British jet airliner, the Comet, discovered at the high cost of lost planes and lives in the early 1950’s.
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The risks of designing for the real world
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It is always risky to design something new. High flying jets and the use of aluminium were pretty new in those days. British engineers also failed to realise the effects of repeating decompression loads and stress concentrations on the fatigue strength of the aluminium airframe. Calculating for static loads was just not enough.
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How did they calculate their airframe then? Computers were still in their infancy and FEA programs were not written yet. They had to use stress formulas and manual structural analysis tools. Even today, with our powerful computers and programs, it is not easy to analyse a structure as complex as an airframe. We have better research tools but the old problems and challenges are still there.
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Skill, common sense and patience

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What they must have done was to make simplifications, calculating parts of the structure one at a time and performing tests for real parts and assemblies. This was in fact a combination of some calculations with experimental testing to prove the design. We must admit that in spite of the crude tools they had they did a good job after all.

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We would like to think that today we do much better in our design work. Indeed our tools are far better than theirs but in principle what we do is very much the same. We build our models and test them by applying FEA programs. The fact that we can run the test on a computer model rather than on a hardware model is only a difference of time and cost. We must still have a finished design before we can test or analyse it.

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What came first, the chicken or the egg?

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It is a vicious circle: we need a complete design in order to test it, yet we cannot complete the design without calculating it. How do we break this vicious circle? By guessing our way to the design! By experience, by rules of the thumb and by rough calculations based on preliminary design ideas and sketches!

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Don’t forget that these early assumptions can be revisited and recalculated but at least they allow us to begin the process.

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2#
发表于 2016-9-26 14:10:42 | 只看该作者
抱歉,看不懂里面的内容啊~~我回去好好学学英文
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3#
发表于 2016-9-26 14:19:50 | 只看该作者
1.不要全部相信你在学校学到的东西,现实生活是完全不同的
7 d8 n3 M- S7 K2.你应该完全的摒弃大脑里对于一个设计只有一种正确方案这样的想法,保持你的思路找到所有的方案" L- x$ k9 o& ?# T
3.设计的不当之处会表现在许多方面,每个方面都应被考虑2 n  V( c& Z4 J: I: p/ a
4.先有鸡还是先有蛋,许多创新设计的研究分析开始于一系列的初步构思
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渣渣水平只有翻译些简单的,估计还有许多的错误,哈哈来个英语牛逼的大侠多译点  k) p! }" }1 X

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层主属于直译,可以在不改变意思的前提下,多做一些句式变化~  发表于 2016-9-26 14:39

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4#
发表于 2016-9-26 15:13:32 | 只看该作者
楼主,我爱你,谢谢喽,努力中

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爱我就好好学英语  发表于 2016-9-26 16:35
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5#
发表于 2016-9-26 15:14:01 | 只看该作者
When we pass from high school to university we bring with us the idea that answers are obtained by engineering calculations. We use analytical formulas and we are educated to believe that the results are either right or wrong – there is no in between and no grey areas.   @) d( N, G, `3 c5 F' q; P1 i
当我们从高中进入大学  我们带着我们自己的想法用工程计算得到答案。我们教育让我们相信我们使用公式分析的结果要么是对的要么是错的-在它们之间没有  灰色地带(我的理解就是模棱两可).

点评

第二小句的重点在IDEA,是个怎么样的IDEA呢,是个所有答案都可以由工程计算得到的IDEA。  发表于 2016-9-27 15:57

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6#
发表于 2016-9-26 16:17:29 | 只看该作者
What came first, the chicken or the egg?   先有鸡、还是先有蛋?5 C% Q: O* O8 c8 B
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It is a vicious circle: we need a complete design in order to test it, yet we cannot complete the design without calculating it. How do we break this vicious circle? By guessing our way to the design! By experience, by rules of the thumb and by rough calculations based on preliminary design ideas and sketches!% n0 `1 ?& C2 \0 r  B

: V6 }4 ^( E- H+ f: d& ~+ m这是个死循环:  我们需要完成一个完整的演算过程来验证它,然而这个是永远算不完的! 那我们如何打破这个循环呢?只能有理有据的猜了!  根据经验得,这个猜想只能靠经验法则和模糊计算来验证了!; x9 A5 K9 A7 m/ A0 r* v& v1 o

- c5 L5 w, {7 T8 b9 ^. u* NDon’t forget that these early assumptions can be revisited and recalculated but at least they allow us to begin the process.
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我们得牢记这些先人的猜想,因为先有猜想才能有验证,即使它需要反复验和算!
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感觉愧对老师和她的80分!

点评

第一句有点歧义:我们需要完整的设计方案来进行计算,然而没有计算压根就无法完成设计。  发表于 2016-9-27 16:06

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7#
发表于 2016-9-26 16:19:36 | 只看该作者
   当我们从高中步入大学之后,我们便形成了这样一种概念,即结果都是经过工程计算得来的。学习中通过方程分析计算得出的结果非对即错,答案是唯一的,这使得我们认为实际亦是如此。学生在处理问题时惯于把相关因素都考虑进去,我甚至记得自己判断答案正确与否是根据有没有把题目给定的相关数据都利用上了没有。然而我们真的需要把方方面面都考虑到才能得出结果吗?
3 x3 ~& Z% T* c& [   现实问题并非如此。通常来说,我们掌握的资料并不完善,计算过程也不是一成不变的。学生们曾经不止一次得问我,设计齿轮时应以齿的强度为准还是以齿面的疲劳强度为准。实际上两个都可以作为齿轮设计的准则,而优先选用最可能导致齿轮最先失效的强度作为设计的准则。作为学生去理解它还是非常困难的,还需谨慎区别!

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这翻译!非常牛啊!赞一个!  发表于 2016-9-28 08:41
满分十分,给你9分,用词准确,句式多变,整体连贯,大学六级对你来说应该是小菜一碟  发表于 2016-9-26 16:31

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参与人数 1威望 +50 收起 理由
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8#
发表于 2016-9-26 16:31:47 | 只看该作者
What came first, the chicken or the egg?
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It is a vicious circle: we need a complete design in order to test it, yet we cannot complete the design without calculating it. How do we break this vicious circle? By guessing our way to the design! By experience, by rules of the thumb and by rough calculations based on preliminary design ideas and sketches!
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Don’t forget that these early assumptions can be revisited and recalculated but at least they allow us to begin the process.

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# N; [+ @' {( o/ r& Y; E& L8 q4 x先有鸡还是先有蛋?/ T7 V' i: R; s4 o2 ^0 }# p; ^0 r) d2 U
       这是一个恶性循环,我们需要一个完整的设计来检验我们的理论。但没有计算之前,我们又无法完成这个设计。怎样才能打破这种恶性循环呢? 只能靠假设,靠经验以及”拇指法则“和建立在初步设计思路和草图上的粗略的计算。) u5 p& R( V  L  O* K# K' p+ t
       虽然,这些早期的假设还需要后来的重新验证和计算,但至少凭借这些资料,我们可以开始进行设计。
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7 k9 U+ |( E# T9 N   对英语比较有兴趣,但基础不好,算积极参与吧。
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参与人数 1威望 +30 收起 理由
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9#
发表于 2016-9-26 16:48:18 | 只看该作者
左次无咎 发表于 2016-9-26 15:134 x( O6 \. c2 _% S, `# c
楼主,我爱你,谢谢喽,努力中
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我要好好学英语,挣钱,养你, J  t, P. d9 T- s# q. A
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10#
发表于 2016-9-26 17:26:21 | 只看该作者
淡然 发表于 2016-9-26 16:31
) p6 y' g' p( k4 OWhat came first, the chicken or the egg?+ F1 w3 t# U$ l- `3 s' m# [) J& o& X# \- h0 r9 k7 a0 a
It is a vicious circle: we need ...

: X6 ~* {0 F% i! N7 D; L* |; o9 k据说是先有鸡,然后才有蛋。
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点评

那就肯定一点,是先有鸡,然后才有蛋。^_^。  发表于 2016-10-1 10:11
能不能肯定一点,用“据说”是啥情况?  发表于 2016-9-28 08:43
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