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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下面是正文分隔線
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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.
1 B& u' [- s4 a作者: www.zdscj.com 時(shí)間: 2016-9-26 14:10
抱歉，看不懂里面的內(nèi)容啊~~我回去好好學(xué)學(xué)英文作者: 青wings 時(shí)間: 2016-9-26 14:19
1.不要全部相信你在學(xué)校學(xué)到的東西，現(xiàn)實(shí)生活是完全不同的 3 p4 K6 q- |$ ^; W2.你應(yīng)該完全的摒棄大腦里對(duì)于一個(gè)設(shè)計(jì)只有一種正確方案這樣的想法，保持你的思路找到所有的方案 ! A* l- ?, r; b7 M, {2 d6 c% r3.設(shè)計(jì)的不當(dāng)之處會(huì)表現(xiàn)在許多方面，每個(gè)方面都應(yīng)被考慮8 n1 \ S5 k8 O! ~
4.先有雞還是先有蛋，許多創(chuàng)新設(shè)計(jì)的研究分析開始于一系列的初步構(gòu)思! q8 E/ x. w3 E# u
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渣渣水平只有翻譯些簡(jiǎn)單的，估計(jì)還有許多的錯(cuò)誤，哈哈來(lái)個(gè)英語(yǔ)牛逼的大俠多譯點(diǎn) ' T! @5 N- x9 m2 `, N* c& [2 g作者: 左次無(wú)咎 時(shí)間: 2016-9-26 15:13
樓主，我愛你，謝謝嘍，努力中作者: 掛726面 時(shí)間: 2016-9-26 15:14
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. # k8 t: _/ X T9 `# A) J/ h
當(dāng)我們從高中進(jìn)入大學(xué) 我們帶著我們自己的想法用工程計(jì)算得到答案。我們教育讓我們相信我們使用公式分析的結(jié)果要么是對(duì)的要么是錯(cuò)的-在它們之間沒有 灰色地帶（我的理解就是模棱兩可）.作者: UGAIHAOWY 時(shí)間: 2016-9-26 16:17
What came first, the chicken or the egg? 先有雞、還是先有蛋？8 l- D" g- s5 u
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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! # y( H" J, w+ W: K; ]% P$ R/ `5 p, w
這是個(gè)死循環(huán)： 我們需要完成一個(gè)完整的演算過(guò)程來(lái)驗(yàn)證它，然而這個(gè)是永遠(yuǎn)算不完的！ 那我們?nèi)绾未蚱七@個(gè)循環(huán)呢？只能有理有據(jù)的猜了！ 根據(jù)經(jīng)驗(yàn)得，這個(gè)猜想只能靠經(jīng)驗(yàn)法則和模糊計(jì)算來(lái)驗(yàn)證了！ 9 q! E* ~+ b3 S# a9 C: V, R/ I+ ^/ a* J" E# x. b
Don’t forget that these early assumptions can be revisited and recalculated but at least they allow us to begin the process./ `0 d- A$ I) `; c
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我們得牢記這些先人的猜想，因?yàn)橄扔胁孪氩拍苡序?yàn)證，即使它需要反復(fù)驗(yàn)和算！) X8 ~+ M: t5 C/ }( L
4 O: z4 @& j) }2 D9 F' W0 V4 `) c感覺愧對(duì)老師和她的80分！作者: 宋仲龍 時(shí)間: 2016-9-26 16:19
當(dāng)我們從高中步入大學(xué)之后，我們便形成了這樣一種概念，即結(jié)果都是經(jīng)過(guò)工程計(jì)算得來(lái)的。學(xué)習(xí)中通過(guò)方程分析計(jì)算得出的結(jié)果非對(duì)即錯(cuò)，答案是唯一的，這使得我們認(rèn)為實(shí)際亦是如此。學(xué)生在處理問(wèn)題時(shí)慣于把相關(guān)因素都考慮進(jìn)去，我甚至記得自己判斷答案正確與否是根據(jù)有沒有把題目給定的相關(guān)數(shù)據(jù)都利用上了沒有。然而我們真的需要把方方面面都考慮到才能得出結(jié)果嗎？ : n l+ R$ G" T' B 現(xiàn)實(shí)問(wèn)題并非如此。通常來(lái)說(shuō)，我們掌握的資料并不完善，計(jì)算過(guò)程也不是一成不變的。學(xué)生們?cè)?jīng)不止一次得問(wèn)我，設(shè)計(jì)齒輪時(shí)應(yīng)以齒的強(qiáng)度為準(zhǔn)還是以齒面的疲勞強(qiáng)度為準(zhǔn)。實(shí)際上兩個(gè)都可以作為齒輪設(shè)計(jì)的準(zhǔn)則，而優(yōu)先選用最可能導(dǎo)致齒輪最先失效的強(qiáng)度作為設(shè)計(jì)的準(zhǔn)則。作為學(xué)生去理解它還是非常困難的，還需謹(jǐn)慎區(qū)別！作者: 淡然 時(shí)間: 2016-9-26 16:31
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 F9 H: X8 q( I; K" O- [先有雞還是先有蛋？ p9 q) ~# O W3 S- j, t
這是一個(gè)惡性循環(huán)，我們需要一個(gè)完整的設(shè)計(jì)來(lái)檢驗(yàn)我們的理論。但沒有計(jì)算之前，我們又無(wú)法完成這個(gè)設(shè)計(jì)。怎樣才能打破這種惡性循環(huán)呢? 只能靠假設(shè)，靠經(jīng)驗(yàn)以及”拇指法則“和建立在初步設(shè)計(jì)思路和草圖上的粗略的計(jì)算。 2 Z0 k; r/ F1 M* D3 L( l2 R+ A 雖然，這些早期的假設(shè)還需要后來(lái)的重新驗(yàn)證和計(jì)算，但至少憑借這些資料，我們可以開始進(jìn)行設(shè)計(jì)。 $ {' [5 ~# U! ^+ F " O1 N4 F0 n* Z' P5 C9 P3 l 對(duì)英語(yǔ)比較有興趣，但基礎(chǔ)不好，算積極參與吧。 y+ I' H8 s8 ^0 n ( q& d' V7 q }+ l& o& ^- m作者: 左次無(wú)咎 時(shí)間: 2016-9-26 16:48
淡然 發(fā)表于 2016-9-26 16:31! ?/ t5 ?( }8 c8 P' V- S2 |
What came first, the chicken or the egg?+ F1 w3 t# U$ l- `3 s' m# [$ F4 `5 o+ Z8 g* X* T
It is a vicious circle: we need ...
" M- q7 m/ @; y; Z" r i, E' p% r6 C據(jù)說(shuō)是先有雞，然后才有蛋。 6 b4 Z7 ^( b1 ?+ b5 a作者: 貝XB2016 時(shí)間: 2016-9-26 18:34
么么么么么么么么噠作者: 燃溪 時(shí)間: 2016-9-26 21:00
There are many ways to fail (but it only takes one)7 s6 g5 b4 `4 ]
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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…. ; b4 N ^5 K1 {- V/ B0 B; \' z- S4 y# m) ]3 G* q' e; D
失效的形式有許多種（但總歸發(fā)生其中一種） 4 ^2 S1 }' K" e% F 當(dāng)我講解螺栓的受力的時(shí)候，曾經(jīng)對(duì)一個(gè)工作中的螺栓，從不同的失效形式上計(jì)算過(guò)。標(biāo)準(zhǔn)失效形式——螺栓桿的極限拉力拉力，螺紋的剪力（這個(gè)不太常見），螺栓頭的所受的切向力和其他一些不尋常的失效形式。我這么做，是為了讓學(xué)生了解到，雖然螺栓失效的形式多種多樣，但是大部分情況下，它總是在螺栓桿處首先出現(xiàn)問(wèn)題。然而，在某種特殊的條件下（旋入螺紋太少，被連接件強(qiáng)度太低，等等），螺紋會(huì)首先被剪短。覺得困惑了嗎？我們可以這樣來(lái)解釋：…… * m: b; N. @% k# a% j+ s% q* r作者: 掛726面 時(shí)間: 2016-9-27 16:08
掛726面 發(fā)表于 2016-9-26 15:14 J5 P# e' T3 w( o6 B$ ~
When we pass from high school to university we bring with us the idea that answers are obtained by e ...
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英語(yǔ)大渣渣，受教了 謝謝" _2 w+ G0 m/ E- m ~ 作者: zhumao6011 時(shí)間: 2016-9-28 08:30
1.不要相信他們?cè)趯W(xué)校教你的任何事，真正的生活是非常不同的 U8 B1 ^4 `4 I
2.你應(yīng)當(dāng)馬上拋棄認(rèn)為設(shè)計(jì)問(wèn)題只有一種正確解答的這種認(rèn)識(shí)，讓你的大腦對(duì)各種觀點(diǎn)敞開大門。 + b( e( Q; R' }! p n3.設(shè)計(jì)失敗會(huì)有很多不同的形式，所有這些都應(yīng)當(dāng)被考慮。 * _ s- ~: }! ]/ D' g, y& k4.什么先出現(xiàn)？先有雞還是先有蛋？一個(gè)假想設(shè)計(jì)的分析總是從可以調(diào)節(jié)的假設(shè)范圍開始的。 / B) f# g4 f6 z " o+ P3 I# H y# |! w作者: 滾刀魚 時(shí)間: 2016-9-28 15:40
這只是一篇文章？還是一本書？如果只是一篇文章，請(qǐng)問(wèn)樓主帖子里面已經(jīng)貼的完整了嗎？& o9 o- D1 Y7 ~' Q3 E" h& ?- V
如果是一本書，麻煩樓主能否告訴書名？作者: 小師妹_c937B 時(shí)間: 2016-9-28 16:32
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.
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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那么他們是如何計(jì)算機(jī)體的強(qiáng)度？當(dāng)時(shí)計(jì)算機(jī)還只是個(gè)雛形，有限元分析等計(jì)算工具尚未發(fā)明。他們只能手動(dòng)進(jìn)行受力分析計(jì)算。即便是今天，手握強(qiáng)大的計(jì)算工具和軟件，對(duì)機(jī)體這樣復(fù)雜結(jié)構(gòu)進(jìn)行（力學(xué)/結(jié)構(gòu)）分析仍然是困難重重。研發(fā)使用的計(jì)算工具有了充足的進(jìn)步但是那些老大難的問(wèn)題依然沒有解決 % t- h& R& O" K7 E; z
8 q, Y# x5 S6 f- R uengineeringclicks.com作者: 荷鋤望月 時(shí)間: 2016-9-30 20:44
1、Don't believe everything they teach you at school, real life is very different!* R# v, R# ]3 e+ k* G7 q- o
勿信學(xué)校所授，現(xiàn)實(shí)大相徑庭。 0 p, t* N1 v1 ?0 {0 N' [/ ~8 A" |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., X$ Q& \4 m' Q# g9 a5 S8 j/ S
拋卻心中執(zhí)念，設(shè)計(jì)之旨，絕非唯一。包容并蓄，方得其趣。' ^: `( M3 u* L! i
3、Design failures can have many different forms and all should be considered. : o: T3 z# `4 x設(shè)計(jì)之過(guò)，成因繁多，宜細(xì)審視，不可偏廢。 0 h8 b/ m+ `7 Q# P4、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 adjusted0 }+ N" f' Z! N1 O- |
雞生蛋乎？或否焉。假定設(shè)計(jì)分析常始于假想，亦可反矣。 ; X' r$ g) x$ g- j) q4 Q. T! v- D / d' n4 l+ t& I4 n4 N既然是從業(yè)五十余年，就翻得有些古味。剛看到文章，加班累了，權(quán)當(dāng)換換腦子。只為戲言，權(quán)當(dāng)一樂。作者: menglingtao 時(shí)間: 2016-10-1 13:51
沒學(xué)好，我回去好好學(xué)英文。作者: 天天天藍(lán)_ 時(shí)間: 2016-10-2 22:59
只能膜拜了作者: 血刃x 時(shí)間: 2016-10-3 15:34
1.別信學(xué)校的那一套，現(xiàn)實(shí)是不一樣的（學(xué)校是紙上談兵，哈哈哈哈哈）7 T! K. h. `' ]* q* }1 i- L( ]
2.你應(yīng)該做的是思考更多的方案，摒棄答案唯一論1 e \4 C- S7 ]' | 作者: 血刃x 時(shí)間: 2016-10-3 15:41
荷鋤望月 發(fā)表于 2016-9-30 20:44 5 k: ~% P- C% J" q5 }' |1、Don't believe everything they teach you at school, real life is very different!' V/ L. c+ I. y" K* A
勿信學(xué)校所授，現(xiàn) ...
