外文翻譯--垂直防波堤的概率統(tǒng)計方法

1、<p><b>　　中文1300字</b></p><p>　　Maritime Engineering 159</p><p>　　December 2006 lssue MA4</p><p>　　Pages 137-140</p><p>　　Specifying seawall crest levels

2、 using a probabilistic method</p><p>　　Probabilistic methods provise a powerful frame word for the design of coastal defenses. However, present knowledge of the behavior of these structures is insufficient t

3、o assess their safety against specific types of failure, such as excessive overtopping by wave action. However, the choice of overtopping model used to describe the failure is crucial to the outcome of the assessment. Th

4、e paper illustrates the different results obtained from two models used to describe wave overtopping. The models</p><p>　　1. INTRODUCTION</p><p>　　In the design lf seawalls, it is important to s

5、trike the correct balance between satisfying the structural and functional requirement of the project, avoiding unnecessary expense, and having undesirable impacts on the surrounding environment. one important element in

6、 such considerations is the choice of the seawall crest level(CL)which is necessary to limit to permissible valves the mean wave overtopping discharge per unit length of seawall (Q).Basic variable which are relevant to t

7、he choice of </p><p>　　Besides listing many of the wide range of consequences and potential effects of wave overtopping in urban areas, this paper provides an example of the use of a probabilistic method in

8、determining the crest level of a seawall subject to the action of a combination of wind-sea and swell (bimodal wave conditions).The purpose is to illustrate the importance in probabilistic design of the choice of model r

9、est to describe failure. The degree of confidence in the determined crest level will vary depend</p><p>　　2. SINGLE FAILURE MODE PROBABILITY ANALYSIS </p><p>　　In probabilistic methods, theoreti

10、cal expressions or empirical formulae describing single failure modes may be used to define a failure function ,Z=Z(X1,...,XN),where Xi ,i=1,...,N are the N basic variables of the problem (e.g. water level, wave conditio

11、ns, structure dimensions and material properties).positive values of Z imply the absence of failure and zero or negative values represent failure in the mode being considered, the surface defined by Z=0 is Calles the fai

12、lure surface. Variables wh</p><p>　　Since some of the resistance or load variables are random (and may even be correlated), the value of the failure function is also a random variable, and the probability of

13、 failure (Pf),during a specified reference period, can be expressed as </p><p><b>　?。?）</b></p><p>　　In which fx1....xn is the joint probability density function of the basic variab

14、le X1... Xn.</p><p>　　Expiration (10forms the mathematical basis of probabilistic analysis, with the exception of simple failure functions of just a few random variables, the multiple integrations cannot be

15、performed analytically abed have to be approximated in some way. This is the aim of the various probabilistic methods; these methods are often classified according to the types of calculations performed and the approxima

16、tions made. Three levels are commonly distinguished. They are listed here in order of decreasin</p><p>　?。╝）Level Ⅲ :the full distribution approach. This method provides an ‘exact’ probabilistic analysis, us

17、ing full joint probability density functions including the correlations among the variable. Use is made of numerical integration or, more commonly, sampling techniques.</p><p>　　（b） Level Ⅱ:the limit state a

18、pproach. Approximation methods are applied in which the generally non-normal and/or correlated variables are transformed into Normal independent variables. Reliability indices are used as measures of the reliability.<

19、/p><p>　?。╟）Level Ⅰ:the limit state approach. This level involves calculations uncharacteristic values and partial load and resistance factors. The factors represent, for example, the ratio of load at failure t

20、o a permissible working load.</p><p>　　3. PARASODE-BALI</p><p>　　PARASODE-BALI (Probabilistic Assessment of Risks Associated with Seawall Overtopping, Dune Erosion and Breakwater Aroour Layer In

21、stability)is an extended version of PQRASODE, which uses the Level Ⅱ First Order Reliability Method (FORM).As the name suggests, the program concentrates on three failure mechanisms, but the majority of the code is gene

22、ric and can be applied with minor adjustments to other types of failure.</p><p>　　PARASODE-BALI operates in two ways:</p><p>　　(a)the ‘analysis mode’ in which the failure probability is calculat

23、ed or a given value of the design parameter (e.g. the crest level of a seawall).</p><p>　　(b)the ‘design mode’ in which the value of a specific design parameter is calculated for a target probability of fail

24、ure.</p><p>　　The program incorporates routines for transforming the correlated variables to a set of independent variables and for mapping non-Normal distributions to equivalent Normal distributions. The tr

25、ansformation of non-Normal variables into Normal variables is performed following the methodology of Racdwitz and Fiessler. The transformation of correlated variables into independent variables is performed following the

26、 methodology of Racdwitz and Fiessler. The transformation of correlated variables into </p><p>　　There are ten continuous, pre-defined, statistical distributions programmed in PARASODE-BALI: Normal, logarith

27、mic Normal, umbel, uniform, Gamma, Beta, Freshet, exponential, Rayleigh and We bull. Each distribution may be truncated either on the left or on the fight side by using the method of Beaumont.4 the random variables can a

28、lso be described by empirical distributions, defined by the user, which are the result of measurements not easily fitted by a pre-defined distribution.</p><p>　　Output from PARASODE-BALI relating to wave ove

29、rtopping has been validated using the Level [] commercial software package@Risk.s,6</p><p>　　4. A PROBABILISTIC METHOD APPLIED TO WAVE OVERTOPPING OF SEAWALLS BY BIMODAL SEAS</p><p>　　4. I. Wave

30、 overtopping models </p><p>　　The failure mode of wave overtopping is implemented in PARASODE-BALI using the models of Hedges and Reis, Vander Meer and Janssen and Owen. One of the main contributions to unce

31、rtainty in probabilistic seawall design with respect to overtopping is associated with the overtopping model adopted to describe failure. In order to illustrate the importance of the choice of model to the design, the He

32、dges and Reis and the Van der Meer and Janssen models are used in the case study described in Section 5</p><p>　　Hedges and Reis </p><p>　　Vander Meer and Janssen</p><p>　　where Q i

33、s the mean permissible wave overtopping discharge per unit length of seawall; A and B are empirical coefficients ; is the surf similarity parameter or Irizarry number for random waves, ;　g is the gravitational accelerat

34、ion; r is the seawall slope roughness; is the seawall freeboard, CL-SWL; is the effective freeboard when the front slope is rough rather than smooth.</p><p>　　原文摘自Maritime Engineering（《海洋工程》159期（2006年12月）　

35、第137頁至140頁）</p><p><b>　　譯文：</b></p><p>　　垂直防波堤的概率統(tǒng)計方法</p><p>　　在防波堤工程的設計中，概率論方法無疑是一個強有力的方法。然而，有關防波堤結構在波浪的作用下的反映的知識有限，并不能對防波堤的安全做出全面的預測和評估。概率論的確可以成功的預測某種特殊形式的破壞，比如防波堤的越頂波

36、浪。然而，用來分析破壞的越頂模型對評估的結果有著十分重要的影響。這篇文章分析、說明了兩種用來描述波浪越頂的模型的區(qū)別。這些模型是在名為PARASODE-BALL的計算機軟件中完成的。這個軟件采用ROMR方法去設計和評估海岸結構的。由于巨型越頂波浪直接關系到結構的安全，這兩種模型得出了相似的結果。然而，在確保都市地區(qū)人員和財產的安全方面兩種模型確有著巨大的區(qū)別。</p><p><b>　　1、簡介<

37、;/b></p><p>　　在設計防波堤時，平衡工程的結構的適用性和經濟性是十分重要的，一方面要滿足工程結構和功能要求，另一方面又要避免不必要的支出，并且還要避免對周邊環(huán)境的不利影響。一個重要的因素就是對防波堤的垂直度（CL）的選擇，它在限制典型越頂波在單位長度防波堤上的釋放的允許臨界作用起了十分重要的作用；基本變化參數的選擇，它與防波堤的垂直度的選擇有關；防波堤的迎波面與水平面的傾斜角（a）；靜水面的選

38、擇（SWL）；</p><p>　　事件波的特性，比如巨波的高度和波峰期。在一定的程度上，概率論方法可以在特殊的波浪垂直度上正確的計算結構破壞的可能性和和結果，和處理措施。</p><p>　　這篇文章， 除了列舉了許多在城市地區(qū)越過防波堤的波浪可能出現的廣泛后果和潛在的影響。還提供了一個垂直防波堤的工程實例，該防波堤在海風和波浪的聯合作用下。其作用在于說明在用概率論方法預測結構破壞時，對

39、模型選擇的重要性。在絕對垂直的防波堤時，預測結果的可信程度取決于兩個方面，一方面可信度在越波模型的分布，另一方面在模型中所采用的隨機可變參數的選用。 </p><p>　　2 、單破壞模型的概率分析</p><p>　　用概率論方法，理論或者經驗公式去預測單個破壞模型時應當先定義破壞公式，Z＝Z（X1，X2，…，Xn）其中Xi，i=1,…,N.N該問題的表示N個基本參變量。（比如水位，波浪

40、情況，結構的尺寸和材料性質）當Z為正值時說明結構沒有破壞的危險。當Z為零或負值時說明模型可能會出現破壞。把表面定義為Z＝0，是破壞界面。那些會導致Z增大的變數定義為抵抗變數，然而那些增加Z變小趨勢的參數叫做傾覆變數。</p><p>　　盡管一些抵抗變數和傾覆變數是隨機的（甚至是相互關聯的），破壞方程的數值也是隨機變數。在一個特殊的參考時期內，結構破壞的概率可以表達為</p><p>&l

41、t;b>　?。?）</b></p><p>　　其中是基本變量的聯合概率密度函數</p><p>　　等式（1）列出了概率分析的數學基本模型。用于預測只有幾個隨機變量的簡單破壞函數。當有多個變量的多重積分不能進行解析，需要做某種程度的簡化。這些方法往往按照計算和簡化方法進行分類。這些方法往往區(qū)分為三個層次。他們按照精確程度和難易程度的順序排列在下文在；</p>

42、<p>　　(a)層次三：全部分配方法。這種方法提供了一個額外的概率分析，充分利用聯合密度函數，包括相互之間的變數。使用數值積分或更普遍的抽樣技術。</p><p>　　(b)層次二：用半概率方法。近似方法用于把一般的非正常和/或相關變量轉變?yōu)楠毩⒆兞??？尚胖笖涤脕砗饬靠煽啃浴?lt;/p><p>　　(c)層次三：用極限狀態(tài)方法。這個層次包含基于特征值和負荷與阻力因素。這些阻力

43、因素代表了，比如，在破壞時荷載同允許的工作荷載。</p><p>　　3 PARASODE-BALLS</p><p>　　PARASODE-BALL(概率風險評估波浪漫堤) 是PARASODE 的一個擴展版本，它是用一級Ⅱ階的可靠性分析方法。正如它的名字所示，這個程序致力于三種破壞模式，但是最主要的核心是通用和可以應用于微調其他形式的破壞。</p><p>　　P

44、ARASODE-BALL操作有兩種方法：</p><p>　　(a)分析模型操作，也就是對于某一給定的參數算出失敗的概率。</p><p>　　(b)設計模型操作，也就是對于某一目標失敗概率算出特定的計算參數。</p><p>　　該程序包含了改造相關變量為獨立變量,繪制非正態(tài)分布 等效正態(tài)分布. 是根據Rackwitz和Fiessler方法把非正態(tài)變數變轉化為正態(tài)

45、變數。把相關變量轉化為獨立變量是根據CIRIA的方法。注意到PARASODE-BALL 允許用戶在兩個變量之間指定一個非零相關值。 數值為零的相關系數確保兩個獨立變量。</p><p>　　在PARASODE-BALL里面有十組連續(xù)的，預定義，統(tǒng)計分布程序：正態(tài)分布、標準正態(tài)分布、均勻分布,費切特分布 ,指數分布,瑞利分布和維博分布 。</p><p>　　每一種分布都用Beaumont方

46、法在左側或右側截斷。隨機變量也可以用經驗分布來描述，被用戶定義，這樣評估的結果就會和預定義分布不相適應。</p><p>　　4 一個概率論方法應用于在雙峰海的防波堤的波浪越頂。</p><p>　　波浪越頂的破壞模型在parasode-ball 中建立。采用Hedges和Reis、Van der Meer 和Janssen和Owen的模型建立。為了說明在設計中的模型選擇的重要性。Hedg

47、es，Reis，Van der Meer，Janssen，用于同一個工程的研究。詳細過程見第五節(jié)。破壞反映方程見下:</p><p>　　Hedges和Reis模型</p><p>　　Van der Meer和Janssen模型</p><p>　　其中Q表示允許的波浪越頂在單位長度防波堤上的釋放。A和B是經驗參數。是隨機波浪的相似參數。＝其中g是重力加速度。r是