船舶工程外文翻譯---船舶結構安全性和可靠性

1、<p>　　中文3800字,2300單詞，1.3萬英文字符</p><p>　　出處：Paik J K, Frieze P A. Ship structural safety and reliability[J]. Progress in Structural Engineering and Materials, 2001, 3(2):198–204.</p><p><b

2、>　　外文翻譯</b></p><p>　　Ship structural safety and reliability</p><p>　　J K Paik 1 and P A Frieze 2</p><p>　　1 Pusan National University, South Korea</p><p>　　2 P

3、AFA Consulting Engineers, UK</p><p><b>　　Summary</b></p><p>　　Recent research and development in the area of design methodologies related to safety and reliability of ship structures

4、 is reviewed, focusing on some relevant probabilistic approaches used for the load and resistance factor design (LRFD) of ship hulls against collapse. Important insights and findings previously obtained in the literature

5、 are summarized, and recommendations are made with respect to both technologically improved design procedures and those needed for future development.</p><p>　　Key words: </p><p>　　ship structur

6、al safety; ship structural reliability; load and resistance factor design; ship hull collapse; probability-based ship structural design; hull girder load; hull girder strength; ultimate limit state; ultimate strength; ta

7、rget reliability.</p><p>　　Hull girder collapse accident</p><p>　　Overall collapse of ships’ hulls rarely occurs in still water or in waves. Fig. 1 shows a Cape size bulk carrier that recently c

8、ollapsed during discharge in port of her 126 000 t of iron ore cargo. While the 23-year-old 139 800 dwt ship has not broken in two, her mid-section is reportedly lying on the seabed, indicating that the hull girder has,

9、in fact, completely collapsed. After having emptied the bow and aft holds among five cargo holds, buckling collapse took place in the vessel’s deck whil</p><p>　　Fig. 1 A ship hull collapse during unloading

10、of cargo at port</p><p>　　(Courtesy of Lloyds List)</p><p>　　A ship hull in the intact condition will clearly sustain applied loads smaller than the design loads, and in normal sea and loading c

11、onditions it will not suffer structural failure such as buckling and collapse, except for possible localized yielding. However, the loads acting on the ship hull are uncertain, owing to rough seas or unusual loading/unlo

12、ading of cargo. In these cases, applied loads may exceed design loads and the ship hull may collapse globally. Furthermore, since aging ships may s</p><p>　　Probability-based structural design procedure</

13、p><p>　　The main steps for probability-based ship structural</p><p>　　design are normally as follows:</p><p>　　● establish a target reliability;</p><p>　　● identify all

14、unfavorable failure modes of the structure;</p><p>　　● formulate the limit state function for each failure mode identified above;</p><p>　　● identify the probabilistic characteristics (mean, v

15、ariance, distribution) of the random variables in the limit state function;</p><p>　　● calculate the reliability against the limit state with respect to each failure mode of the structure;</p><p&

16、gt;　　● assess if the predicted reliability is greater than the target reliability, and redesign the structure otherwise;</p><p>　　● evaluate the reliability analysis results with respect to parametric sens

17、itivity considerations.</p><p>　　Modelling of hull girder strength</p><p>　　Four types of limit state can be considered: namely, serviceability limit state, ultimate limit state, fatigue limit s

18、tate and accidental limit state . The serviceability limit state involves deterioration of less vital functions including:</p><p>　　● local damage which may reduce the durability of the structure or affect

19、the efficiency of structural or non-structural elements;</p><p>　　● unacceptable deformations which affect the efficient use of structural or non-structural elements, or the functioning of equipment;</p&

20、gt;<p>　　● excessive vibrations which cause discomfort to people or affect non-structural elements, or the functioning of equipment. </p><p>　　The ultimate limit state represents the collapse of the

21、structure, from factors such as:</p><p>　　● loss of equilibrium of the structure or part of the structure, considered as a rigid body (e.g. over turning or capsizing);</p><p>　　● attainment of

22、the maximum resistance capacity of sections, members or connections by gross yielding, rupture or fracture;</p><p>　　● instability of the structure or part thereof, such as by buckling of columns, plates, s

23、hells and stiffened panels.</p><p>　　The fatigue limit state results from damage accumulation under the action of cyclic loads and the accidental limit state is due to accidents such as collisions or groundi

24、ng.</p><p>　　Overall failure of ship hull girders, which rarely occurs, is normally governed by buckling and plastic collapse of the deck, bottom or sometimes the side shell stiffened panels. Failure of deck

25、, bottom or side shell stiffened panels can then lead to progressive collapse and ultimate hull girder failure. For many years, ship structural researchers have been working towards the goal of reliability-based limit st

26、ate design of ship structures. However, reliability-based design requires calculation </p><p>　　A number of studies on the ultimate collapse strength of ships’ hulls have been undertaken theoretically, numer

27、ically and experimentally . Some of the results have been reviewed by the ISSC Technical Committee III.1 on ‘Ultimate Strength’. The ultimate strength reliability of ships’ hulls, considering existing local damage relate

28、d to corrosion, fatigue and collision/grounding, has also been studied.</p><p>　　Previous studies on the development of a formulation for ultimate hull strength prediction may be classified into three groups

29、. The first is a linear approach, where the behaviour of the hull up to failure of the compression flange is assumed to be linear elastic, i.e. ignoring buckling, and the ultimate moment capacity of the hull is basically

30、 expressed as the ultimate strength of the compression flange multiplied by the elastic section modulus, with a simple correction for buckling and yieldin</p><p>　　The first approach is quite simple, but its

31、 accuracy is usually wanting because, after buckling of the compression flange, the behaviour of the hull is no longer linear, and the neutral axis changes position. Empirical formulations (the second approach) may provi

32、de reasonable solutions for conventional hulls, but one has to be careful in using empirical formulations for new and general-type hulls, since they are usually derived on the basis of limited data, or for a particular h

33、ull form, using a</p><p>　　The ship hull ultimate strength formula is eventually expressed as a function of design parameters related to geometric and material properties including plate thickness, yield str

34、ength and Young’s modulus. When time-variant structural degradation (e.g. corrosion) is considered, the value of member thickness at any particular time is a function of such damage. In probability-based design methods,

35、all the design parameters are treated as the random variables. The hull ultimate strength formula fo</p><p>　　Limit state function</p><p>　　Mathematically, the limit state function for structura

36、l failure can be given as a function of the random variables, as follows:</p><p>　　f（X）=f（，，………） （1）</p><p>　　where f (X) is the limit state function representing t

37、he margin between structural capacity and demand (i.e. loads or load effects); x i represents the design</p><p>　　parameters. The limit state function f (X) characterizes the condition of the structure and d

38、efines two domains of safety with regard to the limit surface (envelope), as follows:</p><p>　　f（X）>0 in the safe domain</p><p>　　f（X）=0 on the limit surface

39、 （2）</p><p>　　f（X）<0 in the unsafe domain</p><p>　　With two independent random variables, the ultimate limit state function f (X) for ship hull collapse is usually taken as the margin bet

40、ween ship hull ultimate strength and total bending moment , as follows:</p><p>　　f（X）=- （3）</p><p>　　whereand are functions of the design variables

41、.</p><p>　　Methods of reliability analysis</p><p>　　The methods for structural reliability analysis are usually classified into four types, namely level I, level II, level III and level IV . The

42、 level I method corresponds to the deterministic or partial safety factor method, using only one characteristic mean value for each variable. A relevant allowable usage factor for each variable that may be determined by

43、calibration of a higher level reliability method-based results is applied in the level I reliability analysis to approximately supplement </p><p>　　The ship structural reliability analysis is usually underta

44、ken by the level III method. Since the theory ofreliability analysis is discussed in many references, e.g. Mansour and Ditlevsen & Madsen , only a very brief description for the level III method is given here. Gene

45、rally the probability of failure P f can be calculated as follows:</p><p>　　=P（X）dx （4）</p><p>　　where p(X) is the joint probability density function of the r

46、andom variables X=，，………associated with loading, material properties, geometric characteristics, etc. and</p><p>　　f (X) is the limit state function, defined such that negative values imply failure. Since f (

47、X) is usually a complicated nonlinear function, it is not easy to perform the integration of eq. (4) directly. Therefore, the equation is normally solved by use of approximate procedures . </p><p>　　With the

48、se approximations, as indicated in Fig. 2, the limit state surface is usually approximated at the design (failure) point by either a tangent hyper-plane or a hyper-parabola, which simplifies the mathematics related to th

49、e calculation of the failure probability. The first type of approximation results in the use of a so-called first-order reliability method (FORM) and the second type of approximation is central to the so-called second-or

50、der reliability method (SORM). Such methods facilita</p><p>　　= （5）</p><p>　　where is the standard normal distribution function.</p><p>&

51、lt;b>　　Fig. 2</b></p><p>　　Further considerations</p><p>　　While a number of useful methodologies for analyzing the safety and reliability of ship structures have been developed over th

52、e past decades, further developments are needed. Some further considerations in probability-based design of ship structures are as follows:</p><p>　　● geometric parameters may be treated as deterministic, a

53、lthough this may need to be confirmed in the case of deck and bottom plating thickness;</p><p>　　● elastic modulus may be taken as deterministic, but yield stress needs to be treated as a random variable wi

54、th a mean value based on a fuller assessment of strain-rate effects on yield in large-scale representative ship-type structures than presented here. In the first instance, yield stress values could be based on tensile co

55、upon test results when wave-induced bending moments dominate, and similarly derived static values of yield stress for dominant still water load conditions.</p><p>　　● hull girder and stiffened panel ultimat

56、e strength models require benchmarking against realistic mechanical collapse test data so that the distribution parameters for their associated modelling errors can be evaluated;</p><p>　　● when time-varian

57、t structural degradation, e.g. due to corrosion and fatigue, is considered, the probabilistic characteristics of such damage at any particular time should be quantified. While some work continues in this area, there exis

58、t probabilistic corrosion rate estimation models for tanker structures and for bulk carrier structures;</p><p>　　● consensus is required about the preferred methodology for determining an appropriate return

59、 period of response for ship design and how this might be achieved given the current status of environmental parameters and data records;</p><p>　　● the load factor methodology promoted in the literature is

60、 extremely promising, particularly because its form is compatible with limit state (LRFD) design code formats. Consensus is required concerning its generality and any further development. Classification Society and naval

61、 experiences should be helpful in identifying load combinations to be addressed. However, in identifying a safety format, account should be taken of relevant ISO codes (e.g. ISO 2394) in this area;</p><p>　　

62、● target safety and reliability initially requires a calibration approach to determine appropriate values, followed by adjustments based on judgments concerning successful designs and target reliabilities in other indus

63、tries, whilst recognizing that floating structures probably need one order of magnitude (in probability of failure terms) more reliability than comparable bottom-founded structures, and an expectation that component and

64、system reliabilities should differ by about one order in pro</p><p>　　● partial factor determination will require some form of simplified modelling of strength, loading or the reliability process in order t

65、hat such determination can proceed efficiently. Curve- or surface- fitting can be applied in all cases.</p><p>　　船舶結構安全性和可靠性</p><p>　　J K 帕克[1] P A 普萊斯[2]</p><p>　　1.韓國釜山國家大學 2.英國

66、FAFA工程師顧問</p><p><b>　　摘 要</b></p><p>　　最近在研究和發(fā)展對該地區(qū)船舶結構的設計方法，安全性和可靠性的評估，將阻力、負荷作為因子運用概率的方法來對船體的抗損毀能力進行設計。一些重要的發(fā)現(xiàn)和見解在以前的一些文獻中有過總結，并且建議通過技術和設計的改進來達到將來發(fā)展的需要。</p><p>　　【關鍵詞】

67、船舶結構安全；船舶結構可靠性；負荷和阻力因子設計；船體損壞的幾率的結構設計；主船體梁負荷；船體梁極限狀態(tài)；極限強度；船舶可靠性。</p><p><b>　　船體梁倒塌事故</b></p><p>　　全面破損的船體很少發(fā)生在靜水或較小波浪中。圖1顯示最近一艘散貨船損毀，在港口排放出 126000噸的鐵礦石貨物。不過這艘服役23年的139800載重噸的船并未折成兩段，

68、有報道稱它的中間分段沉入海底，這表明船體梁全部損毀。清空后船艏和船艉之間有5個貨艙，屈曲發(fā)生在船的甲板上，盡管船體的中間部位還是完整的。一般都認為發(fā)生這個事故主要是因為不當?shù)貜拇闲敦?，但是毫無疑問會有關于船體極限狀態(tài)以及檢驗和維護方面的猜測。</p><p>　　確保船體的完整性顯然是要求維持所施加的載荷要小于設計載荷，在普通海域和加載條件下它將不會遭受結構失效，比如屈曲和崩潰，除了可能的局部屈服。然而，由于大

69、波浪或不當?shù)难b卸貨物作用，在船舶表面載荷是不確定的。在這種情況下，外加載荷有可能超過設計荷并且船體表面會破損。此外，由腐蝕引起的疲勞老化可能會導致結構減弱，疲勞和局部損壞會引起結構抵抗能力的減弱，船體結構在外加負荷下甚至在小于設計負載的時候可能破損。</p><p>　　圖1，一船舶在港口卸貨的時候斷裂（由勞埃德提供）</p><p><b>　　粗糙結構設計程序</b&g

70、t;</p><p>　　粗糙的船舶結構設計通常如下：</p><p>　　建立一個可靠度目標；</p><p>　　確認所有不利結構的失效模式；</p><p>　　為上文提到的每個失效模式制定極限狀態(tài)方程；</p><p>　　識別概率特征（平均方差分析、分布）隨機變量的極限狀態(tài)方程；</p><

71、;p>　　對各個結構的失效模式進行極限狀態(tài)的可靠性計算；</p><p>　　如果預測的可靠性評估大于目標可靠度，要對其他結構重新設計；</p><p>　　進行參數(shù)對可靠性分析結果敏感性的考慮；</p><p><b>　　船體梁結構強度</b></p><p>　　四種類型的極限狀態(tài)可以被分為：使用極限狀態(tài)，最

72、終極限狀態(tài)、疲勞極限狀態(tài)及意外極限狀態(tài)，使用極限狀態(tài)退化的有以下幾個方面，包括：</p><p>　　局部損壞發(fā)生在那些耐用性可能減弱，結構或非結構要素受影響的結構；</p><p>　　影響那些結構或非結構要素，或運行設備的不可接受的變形；</p><p>　　過度的振動引起人的不舒適或者影響非結構要素和運行設備。</p><p>　　極限

73、狀態(tài)表示的結構的損壞，從以下方面表示，如：</p><p>　　結構或部分結構的失衡被認為是一個剛體的（傾覆）；</p><p>　　當截面達到最大的負載能力，組織連接將達到屈服，將斷裂或破裂；</p><p>　　不穩(wěn)定的結構或部分結構，例如屈曲圓柱、板材、船殼和加強筋等。</p><p>　　疲勞極限狀態(tài)結果形成是因為長期在負載的條件下，

74、意外極限狀態(tài)是由于事故，比如碰撞或擱淺。</p><p>　　所有不經(jīng)常發(fā)生船體梁的失效，一般都是由于甲板、船底或有時舷側外板的加強筋的屈曲和塑性變形。失效的甲板、船底或舷側外板的加強筋會導致進一步的破壞并最終使船體梁完全失效。多年來，船舶結構研究人員一直朝著船舶結構可靠性極限設計的目標努力。然而，可靠性設計要求最終極限狀態(tài)的計算，不僅是船體梁，還有所有的結構面板和其他的結構。同時，這些計算必須需要大量的時間。因

75、此將這些計算應用有限元分析并不太實際，對于結構零件和完整的船體梁要有效地進行極限強度的計算必須要發(fā)展通用的表達式。</p><p>　　大量的從事人員已經(jīng)從理論上、數(shù)學上和實驗上對船體的極限的破裂強度進行了研究。有些關于極限強度的研究成果已經(jīng)通過了船舶技術委員會的審核。關于船體極限強度可靠性目前已經(jīng)研究過的有與腐蝕、疲勞和碰撞有關的局部損壞。</p><p>　　以往關于發(fā)展船體極限強度預

76、測構想的研究分為三個部分。首先是線性的方法，船體的抗壓凸緣在船體上的失效現(xiàn)象被看做是線性且具有彈性的，忽略屈曲。且最終船體的極限強度相當于抗壓凸緣的極限強度乘以彈性結構的剖面模數(shù)，加上對屈曲和屈服的簡單的修正。第二種是用實證研究方法，在通過實驗的方法和從縮放圖像或真實模型中提取出的數(shù)據(jù)資料的基礎上得到的表達式。第三是一種分析方法，從船體受載荷的瞬間的理論計算值推算出船體截面的應力分布，重點考慮抗壓凸緣的張力屈服。</p>

77、<p>　　第一種方法是很簡單的，但通常其準確性不足，因為抗壓凸緣受到彎曲后，船體并沒有表現(xiàn)出線性，并且中和軸的位置發(fā)生了變化。實證研究法（第二種方法）可以為常規(guī)船體提供合理的解決方案，但是在新型和常規(guī)船體表達式的使用中必須要很小心，因為經(jīng)驗公式通常是通過有限的數(shù)據(jù)或個別特殊的船型推算出來的。另一種分析方法（第三種方法）能應用于新型的和常規(guī)的船型因為它們包括的剖面形式更精確。</p><p>　　船體極

78、限強度的公式最終表示成一種與幾何、材料的性質(zhì)包括板厚、屈服強度、彈性模量有關的設計。當隨時間變化結構的減弱（例如腐蝕），一直都認為對于這種損害有特別研究的價值。在粗糙的設計方法中，所有的設計參數(shù)都被當做隨機變量。船體扭曲的極限強度與一般的下垂是不同的。</p><p><b>　　極限狀態(tài)方程</b></p><p>　　數(shù)學上，對于失效的結構會根據(jù)隨機變量給予極限狀

79、態(tài)方程，如下：</p><p>　　f（X）=f（，，………） （1）</p><p>　　f（X）是極限狀態(tài)方程，代表結構承載能力和需求大?。捶匣蚍闲Ч┑牟钪?，表示設計參數(shù)，極限狀態(tài)方程f(X)把與限制表面的安全性有關的結構和定義兩個方面的特征表示出來，如下：</p><p>　　f（X）>0 在安

80、全區(qū)域</p><p>　　f（X）=0 在限制表面上 （2）</p><p>　　f（X）<0 在不安全區(qū)域</p><p>　　兩個獨立的隨機變量，它的極限狀態(tài)方程f（X）通常表示船體破壞時被看作是船體極限強度和彎矩總和的差，如下</p><p>　　f（X）=-

81、 （3）</p><p>　　其中和是方程的設計變量。</p><p><b>　　可靠性分析的方法</b></p><p>　　結構可靠性分析方法通常被分成4類，就是一級、二級、三級、四級。一級水平方法相當于是確定局部安全因素的方法，對每個變量運用唯一的特征平均

82、值。有關對每個變量允許的使用因素可能取決于更高水平可靠性分析方法的校核標準，應用在一級水平的可靠性分析方法可能是與不確定因素有關的補充。二級水平方法是使用兩個標準，即均值和標準偏差，描述每個隨機變量的特征?？煽啃灾笖?shù)方法，例如一階、二階力矩法是二級水平方法中一種典型的例子。二級水平方法采用聯(lián)合概率密度函數(shù)的特征來描述隨機變量。運用三級水平的可靠性分析方法要么采用近似分析法（例如一階或二階的可靠性分析方法），要么采用數(shù)值模擬方法（例如蒙特

83、卡羅模擬或者方向取樣分析都被應用）。四級水平方法是通過工程經(jīng)濟分析比較目標結構和參考結構的完整性和前景，考慮到結構失效和維護與花費和獲利有關。四級水平方法被用在目標的可靠性上。</p><p>　　這艘船結構可靠性分析通常用三級水平方法，理論分析在很多的文獻中被研究，例如曼蘇爾和麥迪森，三級方法僅是在這里有非常簡短的描述。一般失效的概率的計算方式如下：</p><p>　　=P（X）dx

84、 （4）</p><p>　　在p(X)是聯(lián)合概率密度函數(shù)隨機變量X=，，………與加載條件、材料特性、幾何特征等有關，f(X)是極限狀態(tài)方程，定義為取到負值時即為失效。因為f(X)通常含有比較復雜的非線性的功能，它不能直接地應用公式（4）整合完成，因此方程式通常運用近似的程序來解決。</p><p>　　運用近似的方法，

85、就像圖2表明，極限狀態(tài)船體表面通常接近于設計（失效）點要么高于切線要么高于拋物線，利用簡化數(shù)學運算來計算有關的失效概率。第一種近似結果使用在所謂的一階的可靠性方法，第二種近似方法是主要用在所謂的二階的可靠性方法。這種方法通過廣泛應用的標準軟件能方便快速計算失效概率。除了一些個別的有關隨機變量的概率分布，對這種運算的聯(lián)系很容易做出解釋，還要考慮各種不相關的隨機變量?？煽啃詷藴实慕Y果是可靠性指數(shù)與失效概率的關系：</p>&l

86、t;p>　　= （5）</p><p>　　這是函數(shù)的標準正態(tài)分布。</p><p><b>　　圖2</b></p><p><b>　　將來規(guī)劃</b></p><p>　　然而船舶結構安全性和可靠性的

87、一些分析方法在過去使用了幾十年，進一步的發(fā)展是非常必要的。一些關于船舶結構可能性設計的進一步發(fā)展規(guī)劃如下：</p><p>　　幾何參數(shù)可以被看做是確定的，盡管它們可能要在甲板和船底板厚度上要進一步的</p><p><b>　　確認；</b></p><p>　　2. 彈性模量可以當作是確定的，但是屈服應力的平均值要被當作是一個隨機變量，以

88、</p><p>　　這里提出的常規(guī)船型為代表，評估屈曲對結構的影響。在這個例子中，波浪引起的彎矩在屈服應力的試驗結果中起著重要的作用，同樣在靜水中的負載狀態(tài)在屈服應力中也明顯起著重要作用；</p><p>　　3. 船體梁和加強板材的極限強度需要真實船模的機械破壞性試驗的數(shù)據(jù)作為標準，所以他們建模的誤差的參數(shù)分布是可以估算的；</p><p>　　4. 隨著使

89、用時間增加結構減弱，如由于腐蝕和疲勞，認為這些損害在特定時間的特征概率分布應該被量化，同時很多繼續(xù)從事這方面的工作，現(xiàn)在有油船和散貨船模型結構的腐蝕率的概率分布的估算；</p><p>　　5. 考慮到當前狀況的環(huán)境參數(shù)和數(shù)據(jù)記錄，一致認為選擇適當母型船來設計船舶的決定是非常正確的；</p><p>　　6. 這種負荷系數(shù)的方法對促進理論發(fā)展非常有前景，特別是因為它的形式與極限狀態(tài)（系

90、數(shù)設計法）設計規(guī)范格式相一致。普遍認為對于它的普遍性的進一步發(fā)展非常有必要。船級社和船廠的經(jīng)驗對負載組合的處理非常有幫助，不過，識別格式是否安全，還要考慮到這個地區(qū)的相關的國際標準組織有關的規(guī)定（比如國際標準組織2394）；</p><p>　　7. 目標的安全性和可靠性最初需要校核的方法來確定標準，然后通過調(diào)整有關成功的設計來判斷目標的可靠性，同時從其他方面認識到流動結構可能需要一個（按失效概率）或更多來比較