故障樹(shù)與可靠性框圖

1、故障樹(shù)與可靠性框圖 故障樹(shù)分析 (fta)的歷史故障樹(shù)分析 (fta)是可靠性和安全分析的另外一種技術(shù)。1962年美國(guó)貝爾實(shí)驗(yàn)室為美國(guó)空軍在民兵導(dǎo)彈發(fā)射控制系統(tǒng)而發(fā)展了該理論，以后被boeing公司引進(jìn)并擴(kuò)展。故障樹(shù)分析是許多建立在運(yùn)籌學(xué)和系統(tǒng)可靠性之中的符號(hào)"邏輯分析方法"的其中一種方法。其他方法包括可靠性框圖 ( rbds)。 什么是故障樹(shù)圖 (ftd)?故障樹(shù)圖 ( 或者負(fù)分析樹(shù))是一種邏輯因果關(guān)系圖，它根據(jù)元部件狀態(tài)(基本事件)來(lái)顯示系統(tǒng)的狀態(tài) (頂事件)。就像可靠性框圖 (rbds)，故障樹(shù)圖也是一種圖形化設(shè)計(jì)方法，并且作為可靠性框圖的一種可替代的方法。

2、一個(gè)故障樹(shù)圖是從上到下逐級(jí)建樹(shù)并且根據(jù)事件而聯(lián)系，它用圖形化"模型"路徑的方法，使一個(gè)系統(tǒng)能導(dǎo)致一個(gè)可預(yù)知的，不可預(yù)知的故障事件（失效），路徑的交叉處的事件和狀態(tài)，用標(biāo)準(zhǔn)的邏輯符號(hào)（與，或等等）表示。在故障樹(shù)圖中最基礎(chǔ)的構(gòu)造單元為門(mén)和事件，這些事件與在可靠性框圖中有相同的意義并且門(mén)是條件。 故障樹(shù)和可靠性框圖 ftds 和rbds最基本的區(qū)別在于rbd 工作在"成功的空間"，從而系統(tǒng)看上去是成功的集合，然而，故障樹(shù)圖工作在"故障空間"并且系統(tǒng)看起來(lái)是故障的集合。傳統(tǒng)上，故障樹(shù)已經(jīng)習(xí)慣使用固定概率(也就是，組成樹(shù)的每一個(gè)事件都有一個(gè)發(fā)生

3、的固定概率) 然而可靠性框圖對(duì)于成功(可靠度公式)來(lái)說(shuō)可以包括以時(shí)間而變化的分布，并且其他特點(diǎn)。畫(huà)故障樹(shù)：門(mén)和事件 故障樹(shù)是由門(mén)和事件(塊)建立，通常在故障樹(shù)中運(yùn)用最多的兩個(gè)門(mén)與門(mén)和或門(mén)。例如，由2個(gè)事件 (或塊or blocks)組成一個(gè)頂事件 (或一個(gè)系統(tǒng))。如果任何一個(gè)事件的發(fā)生都引起頂事件發(fā)生，那么這些事件(塊)用一個(gè)或門(mén)連接。再者，如果兩個(gè)事件同時(shí)發(fā)生才能引起頂事件的發(fā)生，那么它們用與門(mén)連接。用一個(gè)可視化的例子，假設(shè)由組件a和b組成系統(tǒng)的一個(gè)簡(jiǎn)單案例，任何一個(gè)組件發(fā)生故障都會(huì)導(dǎo)致系統(tǒng)故障。 系統(tǒng)可靠性框圖rbd是串聯(lián)結(jié)構(gòu)組成，(看 rbd結(jié)構(gòu))，如圖所示：該系統(tǒng)的故障樹(shù)圖包括兩個(gè)基本

4、事件，它們以與門(mén)("頂事件")連接。對(duì)于發(fā)生"頂事件"來(lái)說(shuō)， 不是 a發(fā)生就是 b發(fā)生，換句話(huà)說(shuō)，a發(fā)生故障或者b發(fā)生故障才能引起系統(tǒng)失效。故障樹(shù)和可靠性框圖 的關(guān)系通常來(lái)說(shuō) (一些特例除外)，一個(gè)故障樹(shù)能很容易地轉(zhuǎn)化為一個(gè) rbd，然而，把一個(gè)rbd轉(zhuǎn)化為故障樹(shù)通常很難，尤其還包含非常 復(fù)雜結(jié)構(gòu)。下列表格顯示了在故障樹(shù)圖中常用的門(mén)符號(hào)和它們和rbd的聯(lián)系。(術(shù)語(yǔ)"經(jīng)典故障樹(shù)"的定義參考由 美國(guó)核管理委員會(huì)的 故障樹(shù)手冊(cè) (nureg-0492) 。table 1: classic fault tree gates and

5、theirtraditional rbd equivalentsname of gateclassic fta symboldescriptionrbd equivalent與門(mén)與門(mén)表示僅當(dāng)所有輸入事件發(fā)生時(shí)，輸出事件才發(fā)生simple parallel configuration see example或門(mén)或門(mén)表示至少一個(gè)輸入事件發(fā)生時(shí)，輸出事件就發(fā)生series configuration see example表決門(mén) 表決門(mén)表示僅當(dāng)n個(gè)輸入事件中有r個(gè)或r個(gè)以上的事件發(fā)生時(shí)，輸出事件才發(fā)生k-out-of-n parallel configuration see example禁門(mén)禁門(mén)表

6、示僅當(dāng)事件發(fā)生，輸入事件的發(fā)生導(dǎo)致輸出事件的發(fā)生simple parallel configuration of all the events plus the condition see example順序與門(mén)順序與門(mén)表示僅當(dāng)輸入事件按規(guī)定發(fā)生時(shí)，輸出事件才發(fā)生standby parallel configuration (without a quiescent failure distribution)dependency andnot used in classic fta. gate defined by reliasoft. the output event occurs

7、if all input events occur, however the events are dependent, i.e. the occurrence of each event affects the probability of occurrence of the other events.load sharing parallel configurationxorthe output event occurs if exactly one input event occurs.  cannot be represented and does not appl

8、y in terms of system reliability. in system reliability, this would imply that a two-component system would function even if both components have failed. table 2: rbd constructs without a traditional fault tree equivalentfunctionfta equivalentdescriptionrbd equivalentdependency (load sharing)no

9、t used in classic fta.allows for modeling event dependency (or load sharing). the output event occurs if all input events occur, however the events are dependent, i.e. the occurrence of each event affects the probability of occurrence of the other events.load sharing parallel configurationtrue stand

10、by with a quiescent failure distribution a priority and gate can be used. however, this does not account for quiescent failure probabilities.standby redundancy configurations consist of items that are inactive and available to be called into service when/if the active item fails (i.e. on standb

11、y). items on standby can also fail (quiescent) while waiting to switch. standby parallel configuration table 3: traditional fault tree gates without an rbd equivalentname of gateclassic fta symboldescriptionrbd equivalentxorthe output event occurs if exactly one input event occurs. in a two com

12、ponent system the event does not occur if both or none of the inputs occur.   when modeling system reliability, this implies that the system is successful if none of the components fail or if all of the components fail. cannot be represented and does not apply in terms of system relia

13、bility. in system reliability, this would imply that a two-component system would function even if both components have failed.事件在故障樹(shù)中，門(mén)是一種把事件和狀態(tài)連接起來(lái)的邏輯符號(hào)。故障樹(shù)中一個(gè)事件(或一個(gè)狀態(tài) )塊相同于在rbd中標(biāo)準(zhǔn)塊，因?yàn)樗袀€(gè)發(fā)生概率 (或者是一個(gè)分布函數(shù))。然而，不像傳統(tǒng)rbds，一個(gè)單個(gè)圖形被用來(lái)表示塊 (或事件)，故障樹(shù)用幾個(gè)圖形來(lái)表示塊。表4論述了這些圖形的意義。table 4: traditional fault tree event

14、 symbols and their rbd equivalentsprimary event blockclassic fta symboldescriptionrbd equivalentbasic eventa basic initiating fault (or failure event).  blockexternal event (house event)an event that is normally expected to occur. in general, these events can be set to occur or not occur, i.e.

15、they have a fixed probability of 0 or 1.block that cannot fail or that is in a failed state.  undeveloped eventan event which is no further developed. it is a basic event that does not need further resolution. blockconditioning eventa specific condition or restriction that can apply to any gate

16、. block: placement of the block will vary depending on the gate applied to. table 5: additional fault tree constructs and their rbd equivalentsprimary event blockclassic fta symboldescriptionrbd equivalenttransferindicates a transfer continuation to a sub tree.   subdiagram block例 1一個(gè)

17、帶有表決門(mén)的故障樹(shù)圖和相等價(jià)的 rbd 。 例 2故障樹(shù)和復(fù)雜的 rbds：一個(gè)復(fù)雜可靠性框圖的最好的例子叫做所謂 "橋路。" 以下 rbd表示這樣的橋路。 橋路作為故障樹(shù)表示需要利用復(fù)制事件，因?yàn)殚T(mén)能表示元件以串聯(lián)和并聯(lián)的方式。檢查該系統(tǒng)發(fā)現(xiàn)任何下列發(fā)生故障，將會(huì)引起整個(gè)系統(tǒng)故障：· ·     元件1和2發(fā)生故障  · ·        元件3和4發(fā)生故障 · ·        元件1，5和4