Yuayua L, Youpeg Zhag, Rag Hu Study o Rsk Aalyss of Ralway Sgal System YUANYUAN LI, YOUPENG ZHANG, RANG HU School of Automato ad Electrcal Egeerg Lazhou Jaotog Uversty NO.88 ANg West Aeue, Lazhou, GaSu CHINA elzabeth03@63.com Abstract:-Ralway sgal system requres the hgh level of safety order to safeguard safe operato of the tra ad people s lves, so the rsk aalyss of ralway sgal system couts for much. However, due to the complete of the rsk data, t s ofte mpossble to obta a satsfactory result. Ths artcle presets a comprehesve study the rsk aalyss model of ralway sgal system o safety rsks. I ths methodology, evdetal reasog s employed to sytheszg the experts opos thus produced to determe the relatve mportace of the rsk cotrbutos. Ths allows ucerta formato the rsk aalyss process. The, weghted ad rsk factor values are coverted to the matrxes represeted umercal features va the cloud model. Fally, the rsk level s obtaed by usg the weghted average tegrated fucto. Also, a practcal case study o rsk aalyss of computer terlockg system s preseted to demostrate the applcato of the proposed rsk aalyss, ad the result shows that the method s ot oly sutable for rsk aalyss method, but also s able to fd out the weak lks ralway sgal system. What s more, t provdes a ew foudato for the rsk aalyss of ralway sgal system. Key-words:-Ralway sgal system, Rsk aalyss, Computer terlockg system, Evdetal reasog, Cloud model Itroducto Wth the rapd developmet of the ral trasportato, ad the creasg mprovemet of rug speed ad desty meas severer requremets for the safety of ralway sgal system. Thus, t s of vtal sgfcace to have the rsk aalyss of the ralway sgal system safety. Ad so ts securty assessmet possesses very mportace sgfcace. Computer terlockg system s the mportat part of the Chese tra cotrol system, whch, through aalyss o t, wll exert a certa postve fluece o securty of Cha s ralway sgal system. At preset, there are may ma methods o rsk aalyss of complcated system, such as fault tree aalyss (FTA) [,2], aalytcal herarchy process [3], bayesa etworks [4,5], fuzzy set theory [6,7], et al. The method of fault tree aalyss ad bayesa etworks are quattatve aalyss methods amog these, whch ca calculate the rsk level of the system through modelg. However, may crcumstaces, the applcato of quattatve aalyss tools may ot gve satsfactory results because the rsk data of ralway are complete or t s a great dffcult to obta the basc data ad quatfy the umber of rsk factors the actual process of evaluato, addto, the ormal operatos of the ralway sgal system s drectly related to ths stuatos that cotas equpmet falure, the chage of atural evromet, the techcal level of the operatg persoal. The other methods of aalytcal herarchy process ad fuzzy set theory ca trasfer from the qualtatve aalyss to the quattatve aalyss, whch ca tegrate the quattatve aalyss ad the qualtatve aalyss. But these methods caot systematcally cosder the ucertaty volved the rsk aalyss, whch cotas fuzzess ad radomess of rsk, as well as the complete kowledge s caused by adoptg the expert assessmet. As dscussed above, a ew method should be preseted to assess the rsk of ralway sgal system safety. As a ma tool to deal wth the ucertaty E-ISSN: 2224-266X 427 Volume 4, 205
Yuayua L, Youpeg Zhag, Rag Hu problem, the evdetal reasog has a promet advatage expresso ad sythess of ucertaty formato [8]. It s also used to deal wth assessmet problems wth ucertaty, whch has bee developed o the bass of the Dempster-Shafer theory. Meawhle, cloud model s a effectve ad smple ucerta trasto model betwee qualtatve cocept ad quattatve represetato, further more the cloud model ca realzes the trasto betwee qualty value ad precse value by combg the fuzzess ad radomess [9]. Cosderg the characterstcs of methods above ad the preset stuato Cha, a rsk aalyss of ralway sgal system s establshed o the bass of the evdetal reasog ad cloud model ths paper, whch ca produce a aalyss results objectvely ad reasoablely. The preseted method s ot oly cosderg the kds of ucertaty rsk, but also carryg out the rsk aalyss uder complete data effectvely. I ths way, the rsk assocated wth all rsk factors ca be evaluated wth a sem quattatve aalyss method based o cloud evdetal reasog. Frstly, these ucertaty evaluatos through expert remarks ca be combed by usg the evdetal reasog so as to produce weght value ad rsk assessmet value of each rsk factor. Secodly, the weght value ad the assessmet value of rsk factors are expressed correspodgly the form of cloud model. Ad the rsk of the whole system ca fally be assessed. A applcato shows that the proposed methodology s feasble the practce of rsk aalyss of ralway sgal system. 2 The rsk aalyss process based o cloud evdetal reasog Accordg to the theory above, a comprehesve rsk aalyss of ralway sgal system based o cloud evdetal reasog was preseted ad developed, whch ca calculate the fal rsk level, ad the the result was expressed the form of cloud droplets. I proceedg wth our research, frst of all, rsk aalyss begs wth problem defto whch cludes detfyg the eed for safety, e.g., the rsk factors settg, ad that of the evaluato crtera. Secodly, all of the experts judgmets of system rsk were sytheszed by applyg evdetal reasog whch s a ratoal way to atta the weght value ad rsk assessmet value. The, the weght value ad the rsk assessmet value are expressed the form of cloud model, ad we ca obta the evaluato result through the comprehesve assessmet betwee the weght value ad the rsk assessmet value, whch ca fally be expressed by a floatg cloud model, ad we would lke the floatg cloud to compare wth the stadard cloud model whe determg the fal rsk grades. The aalyss flow of system rsk based o cloud evdetal reasog s show Fgure. Determe the factor settg ad the evaluato crtero of ralway sgal system Ivte experts to judge the rsk of system Determe the weght value ad the assessmet value of rsk factors through the evdetal reasog Covert the results to the form of cloud egevalues Comprehesve evaluato based o The operato rule of cloud Compare the floatg cloud to the correspodg stadard cloud of the evaluato crtero Obta the fal aalyss result of ralway sgal system rsk Fg. The aalyss flow of system rsk based o cloud evdetal reasog 3 Rsk aalyss model of ralway sgal system 3.The rsk factors settg ad the evaluato crtero The purpose of rsk detfcato s to systematcally detfy all potetal hazardous evets assocated wth a ralway sgal system. Frst of all, the rsk factors settg of the assessmet system ca be determed by rsk detfcato. Suppose there are rsk factors, whch ca be expressed the rsk factors settg U={u,u 2,,u }. I addto, accordg to the Europea ralway safety stadards, the evaluato crtero s dvded to four levels whch cossts of eglgble, tolerable, udesrable, tolerable. The the settg V={v,v2,v3,v4}={eglgble, tolerable, udesrable, tolerable} s used to express the four levels, ad each rsk level s realzed wth the cloud model. The qualtatve remarks of each factor the assessmet E-ISSN: 2224-266X 428 Volume 4, 205
Yuayua L, Youpeg Zhag, Rag Hu system gve ths paper all have blateral costrats, for the factor remark that has blateral costrats [Cm,Cmax]. Its cloud processg ca use the termedate value of costrats as the expectato to approxmate the remark, ad the the egevalues of the cloud ca be calculated, whch s show Equato() as follows: Ex = (C m + C max ) / 2 E = (C max C m ) / 6 () He = λ where λ s a costat that ca be adjusted accordg to the fuzzess ad radomess rsk factors. 3.2 Calculate the weght factors Oce the factors settg ad the rsk level settg are establshed, the rsk aalyss moves from the rsk detfcato to the data ad formato collecto. Because the cotrbuto of each rsk factor to the system s dfferet, the weght of the cotrbuto of each rsk factor should be take to cosderato order to represet ts relatve cotrbuto to the rsk of a ralway sgal system. I ths study, fve mportat degrees are used to descrbe that how mportat about rsk factor, whch s represeted by the settg S, ad t s served as a frame of dscermet evdetal reasog. Therefore, the weght state settg of rsk factors s S={s,s 2,s 3,s 4,s 5 }={very mportat, more mportat, mportat, less mportat, ot mportat}. Cosderg the statstc data does ot exst, expert judgmets should be appled. The, we eed to ask for the experts to apply ther wealth of experece to gve the assessmet for the weght degree of each rsk factor. Suppose murs a degree of cotrbuto of rsk factor of u, whch s accordg to the expert of r, murs defed by: where mur mur( s ) = x mur( s 5) = x m = ur s referred to as a basc probablty assgmets. mur( s ) represets the extet to whch the obtaed weght evaluato by the rth expert of the rsk factor of u belogs to a weght level of S defed weght state. However, the dfferet evdeces are sytheszed by the classcal evdetal theory tool may ot gve reasoable results due to the hgh coflct betwee bodes of evdeces. I order to solve ths problem above, the dscoutg evdece combato rule s used to mprove the classcal evdetal reasog ths study. Before the formato fuso of evdece, we gve a dscout coeffcet for each evdece accordg to certa rules to reduce the degree of coflct betwee the evdece formato, the, evdetal reasog s used to sythesze the evdece formato. Suppose there are m experts to assess the weght of rsk factor, the, we ca costruct m evdeces of E, E 2 E m, the basc probablty assgmets s correspodg to each evdece s m, m 2 m m. I ths paper, the dstace of evdeces mght be take to accout to determe the dscout coeffcet. Ad the, the dstace betwee E ad E 2 s defed as follows [0]: ( ) Τ d j = m m j D ( m m j) (2) 2 where,j=,2,,m. = A D B, AB, RS ( ) A B, d [0,]. j The dstace of evdeces ca descrbe the degree of cofdece betwee bodes of evdeces whch s obtaed by the dfferece of evdece. Whe d j =0, t represets that the two peces of evdece are exactly the same, ad they have greatest smlarty. Whe d j s more large, t shows that there are larger coflct betwee the two peces of evdece, the smlarty s more lttle. Accordg to Equato (2) to calculate the dstace of evdeces, ad the smlarty of evdeces ca be defed by: s j = d (3) the, the obtaed smlarty betwee ay two evdeces ca be expressed to a smlarty matrx as follows: j E-ISSN: 2224-266X 429 Volume 4, 205
Yuayua L, Youpeg Zhag, Rag Hu S s2 s s s s s2 2 2 = (4) If the degree of a sgle pece of evdece provded by a expert s hghly supported by the other evdeces, showg that the evdece s more smlar wth other evdeces, ad so the dscout coeffcet of the evdece should be larger. O the cotrary, the lower degree of support, the lttle correspodg dscout coeffcet s. Therefore, the degree of evdece of E s supported by other evdeces ca be calculated as follows: Sup( E ) = sj, j =,2,, (5) j=, j I ths paper, we serve the hghest degree of support amog evdeces as the key evdece. We ca compare the degree of support of E to the key evdece, ad the the dscout coeffcet of E ca be defed as follows, Sup( E ) β = =, 2,, (6) max{sup( E )} r r Thus the obtaed basc probablty assgmets of each evdece above ca be ameded accordg to the obtaed dscout coeffcet as follows: m ( sk) = β ms ( k) sk S m ( S) = m ( sk ) (7) The purpose of the amedmet of the basc probablty assgmets s to reduce the degree of coflct amog evdeces, ad the the judgmets of each expert ca be sytheszed by usg the evdetal reasog algorthm. The sythess rule of evdetal reasog ca be stated as follows: m ( A) m ( B ) A ma ( ) = K 0 A = 2 j A Bj = A (8) Cosequetly, the basc probablty assgmets of rsk factors ca be calculated through the Equato (8). Ad the weght processg ca use the largest credblty value as the fal weght value of the rsk factor, whch s represeted by u w. Ad the we ca tur the each weght level to the cloud wu model (Ex wu u,e w,he ), as s show Table. At ths stage, accordg to the operatoal rule of cloud [], let the weght factors that s expressed as cloud model be the ormalzed relatve weght of rsk factors W={w,w 2,,w }. Ths ca be represeted by usg Equato (9): w wu (Ex wu, E wu u, He ) = = wu (Ex wu, E wu wu, He ) = = 2 wu wu 2 E 2 w He u w u w u w u w u Ex Ex E Ex He = = = (,, w + u w + u w u w u w u w u w u w Ex Ex Ex Ex Ex Ex Ex = = = = = = (Ex, E, He ) w w w Table Deftos of the weght cloud The weght state very mportat more mportat mportat less mportat ot mportat Ex.000 0.750 0.500 0.250 0 E 0.085 0.085 0.085 0.085 0.085 He 0.002 0.005 0.005 0.005 0.002 2 ) (9) 3.3Determe the assessmet value of rsk factors The method of determg the evaluato value of rsk factors s the same as the weght factors determato method. I a smlar way, frstly, we have vted a group of experts to gve the evaluato of each rsk factor accordg to the four rsk levels that are defed by secto 3.. The, after determg the dscout coeffcet, we ca calculate the fal assessmet result mu through E-ISSN: 2224-266X 430 Volume 4, 205
Yuayua L, Youpeg Zhag, Rag Hu sytheszg the ameded value by usg the evdetal reasog, ad the the fal result s expressed as cloud model. 3.4 The result of rsk aalyss After all rsk factors weght value ad assessmet value are calculated, the comprehesve assessmet result ca be obtaed through combg the two mportat value by usg fuzzy operato. The comprehesve result of assessmet system s F = wm =(Ex,E,He), ad the correspodg = u floatg cloud ca be obtaed through the Forward Cloud Geerator. The, we compare the floatg cloud wth the stadard cloud model to determe the fal rsk grades. I other words, the fal comprehesve result s decded by the dstace betwee the floatg cloud ad the stadard cloud model, the dstace s shorter, the greatest mpact o floatg cloud. 4. Establsh the evaluato crtero of cloud model Frstly, the qualtatve descrptors of rsk level are defed as eglgble, tolerable, udesrable ad tolerable, t s also expressed by the settg V={v,v 2,v 3,v 4 }={eglgble, tolerable, udesrable, tolerable}, ad the correspodg evaluato value rages are [0,3), [3,5), [5,7) ad [7,8). Accordg to the formula () ad the method metoed secto 3., we ca calculate the assessmet value of the rsk stadards expressed the form of the egevalues of the cloud model, ad the we ca obta the rsk evaluato crtero based o the cloud model. The evaluato crtero based o cloud model s show Table 2. Table2 Evaluato crtero based o cloud model rsk level eglgble tolerable udesrable tolerable evaluato crtero (.5,0.5,0.05) (4,0.33,0.05) (6,0.33,0.05) (7.5,0.67,0.05) 4 A case study Computer terlockg system s oe of the ew techologes of ralway sgal system, ad ts ma fucto s to guaratee the safety, relablty of the hgh-speed tra. I ths secto, a case example o rsk aalyss of computer terlockg system s used to demostrate the proposed rsk aalyss methodology. The rsk level s dvded accordg to the defto of rsk of EN5026 whch s the Europea Ralway safety stadard [2]. The, we have set up the rsks factors settg of the system through learg system structure, fucto requremets ad the actual stuato. Ad the rsk factors settg of computer terlockg system s descrbed by U={u,u 2,u 3,u 4 }={swtch operatos ad collecto fault, electrcal shock of terlockg equpmet, sgal cotrol fault, terlockg equpmet msfre}, whch volves four rsk factors resultg falure of computer terlockg system. 4.2 Calculate the weghts ad assessmet value I ths study, we should work out the weght value of each rsk factor because the cotrbuto of each rsk factor to the computer terlockg system s dfferet. The weght factors ca be obtaed accordg to the method descrbed secto 3.2. The rsk factor of u serves as a example to expla the step. The basc probablty assgmets of rsk factors of u ca be obtaed by adoptg the evaluato of fve experts who are vted to assess the weght level. The basc probablty assgmets of u s show Table 3. Table 3 the BPA of swtch operatos ad collecto fault weght state expert expert 2 expert 3 expert 4 expert 5 s 0.7 0.6 0 0.2 0.6 s 2 0.2 0.3 0.4 0.4 0.4 s 3 0. 0. 0.5 0.4 0 s 4 0 0 0. 0 0 E-ISSN: 2224-266X 43 Volume 4, 205
Yuayua L, Youpeg Zhag, Rag Hu s 5 0 0 0 0 0 The smlarty betwee evdeces ca be calculated by the precedg Equato (2) ad Equato (3), The, we ca obta a smlar matrx: 0.9000 0.4084 0.564 0.8268 0.9000 0.4804 0.6394 0.9000 S = 0.4084 0.4804 0.8268 0.4432 0.564 0.6394 0.8268 0.6000 0.8268 0.9000 0.4432 0.6000 Ad the, the dscout coeffcet ca be calculated by the Equato (5) ad Equato (6), the result s show as follows: β =(0.9245,,0.7394,0.9008,0.9487) Accordg to the dscout coeffcet above, the obtaed basc probablty assgmets of u show Table 3 be ameded by usg Equato (7). the the evaluato result of rsk factor of u ca be acqured by sytheszg the formato through the sythess rule of evdetal reasog, ad the evaluato results s show Table 4. The largest credblty of weght value of w s served as the fal evaluato result of the weght factor. I other words, the weght value of swtch operatos ad collecto fault s very mportat, ad t s expressed by cloud model as (.000,0.085,0.002). Table 4 The weght evaluato result of swtch operatos ad collecto fault rsk factor s s 2 s 3 s 4 s 5 S u 0.6888 0.3025 0.0087 0 0 0 I a smlar way, the weght value of the other rsk factors ad the correspodg cloud model ca be obtaed. The, the weght of rsk factors ca be ormalzed by usg the Equato (9), ad we also ca obta the result expressed by cloud model, the result s show Table 5. mportat u 2 more mportat (0.750,0.085,0.005) (0.230,0.023,0.00) u 3 very mportat (.000,0.085,0.002) (0.308,0.03,0.00) u 4 mportat (0.500,0.085,0.005) (0.54,0.05,0.00) We have carred out the evaluato of the rsk level of each rsk factor. The method to determe the rsk assessmet value s smlar to the method of the determato of the weght factors. The evaluato result of rsk s show Table 6. Table 6 The result of rsk aalyss rsk factor rsk level Cloud model expresso u eglgble (.5,0.5,0.05) u 2 tolerable (4,0.33,0.05) u 3 eglgble (.5,0.5,0.05) u 4 tolerable (4,0.33,0.05) 4.3 The evaluato result of rsk aalyss Accordg to the weght value of each rsk factor descrbed Table 5 ad the evaluato result of rsk factors descrbed Table 6, the fal evaluato result F = wm u =(2.460,0.269,0.026) = ca be calculated by usg the weghted average tegrated fucto. The, the correspodg floatg cloud ca be obtaed through the forward cloud geerator, ad the fal rsk grades ca be obtaed o the bass of comparg the floatg cloud wth the stadard cloud model. From the above result descrbed Fgure 2, t s obvous that the floatg cloud s located betwee the eglgble cloud ad the tolerable cloud, ad t s closer to the eglgble cloud, Therefore, the fal rsk aalyss result of computer terlockg system ca be though as eglgble. Table 5 The weght value of rsk factors based o cloud model rsk factor weght state cloud model expresso The ormalzed cloud model u very (.000,0.085,0.002) (0.308,0.03,0.00) E-ISSN: 2224-266X 432 Volume 4, 205
Yuayua L, Youpeg Zhag, Rag Hu b e e m M rsh p the floatg cloud eglgble tolerable udesrable tolerable The evaluato value Fg.2 The aalyss result of computer terlockg system rsk I geeral, the safety of computer terlockg system s coformed to the teratoal safety stadards. The assessmet result s cosstet wth the actual stuato. Meawhle, accordg to the evaluato result, we ca obta the weak lk whch cossts of two rsk factors, amely electrc shock of terlockg equpmet ad system msfre. Therefore, we have to adopt a certa measures agast the two tolerable level of the electrc shock of terlockg equpmet ad system msfre. For example, the cable sulato dstace betwee equpmet shall be desged accordace wth teratoal stadard to prevet electrc shock, ad cosderg the problem that coolg system completely, the fre accdet ca be preveted by usg the fre materals. Furthermore, we have to stregthe the securty of computer terlockg system to avod uecessary accdets. 5 Coclusos I order to solve the problem of ralway sgal system safety rsk aalyss, ad combg wth the actual stuato of Cha ralway, the paper proposes a ew sem quattatve methodology for ralway sgal system based o the evdetal reasog ad cloud model. I ths methodology, the evaluato of the rsk of a computer terlockg system s carred out by usg a evdetal reasog approach, whch provdes the rsk aalyss wth a ratoal tool to make full use of the experts judgmet, ad reduces the ucertaty rsk. The mproved evdetal reasog s well suted for hadlg the coflct problem betwee evdeces, ad makg the result more objectvely ad effectvely. The cloud model combes the fuzzess ad radomess of rsk ad realzes the trasto betwee qualty ad quatty, ad t ca make the evaluato result be reflected tutvely. The comprehesve rsk aalyss of computer terlockg system based o cloud evdetal reasog has show to be qute reasoable ad effectve practce. The proposed methodology wll provde the bass for rsk maagemet decso, furthermore, t also provdes a referece for rsk aalyss of ralway sgal system. Ackowledgemets Ths project has bee supported by Cha Ralway Corporato ad Techology Research ad Developmet Program (205X007-H). Refereces: [] J. H. Lu, X. C. Da, Z Guo ad Y. Wag, Quattatve Safety Assessmet Method Based o Rsk Ralway System, Cha Ralway Scece,Vol.30, No.5, 2009, pp. 23-28. [2] E. Jafara ad M. A. Rezwa, Applcato of fuzzy fault tree aalyss for evaluato of ralway safety rsks: a evaluato of root causes for passeger tra deralmet, Joural of Ral ad Rapd Trast.Vol.226,No., 202, pp.4-25. [3] Z. Guo, X. L. Shag ad H. L. AHP-Based Safety Assessmet Model for Ral Trast System, Cha Ralway Scece, Vol.32, No.3, 20, pp.23-25. [4] Y. L. Che ad H. S. Su, Rsk Assessmet Method o Tra Cotrol System Usg Bayesa Network, Computer Egeerg ad Applcato, Vol.49, No.24, 203, pp.238-242. [5] H. H. Zhu, Z. W. Xu, M. Me ad Y. J. Zhu, Research o Probablstc Safety Assessmet Ralway System Based o Bayes Networks, Computer Applcatos ad Software, Vol.28, No.3, 20, pp.26-3. [6] Y. D. Zhag, J. Guo, X. C. Da ad G. Z. Ba, Study o Rsk Occurrece Frequecy Aalyss Model of Tra Cotrol System, Cha Safety E-ISSN: 2224-266X 433 Volume 4, 205
Yuayua L, Youpeg Zhag, Rag Hu Scece Joural, Vol.22, No.9, 202, pp.37-42. [7] M. A, Y. Che ad C. J. Baker, A Fuzzy Reasog ad Fuzzy-aalytcal Herarchy Process Based Approach to the Process of ralway rsk formato: A Ralway Rsk Maagemet System, Iformato Sceces,Vol.8, No.8, 20, pp.3946-3966. [8] J. Wag, J. B. Yag ad P. Se, Safety Aalyss ad Sythess Usg Fuzzy Sets ad Evdetal Reasog, Relablty Egeerg ad System Safety, Vol.47, No.2, 995, pp.03-08. [9] D. Y. L, C. Y. Lu, Y. Du ad X. Ha, Artfcal Itellgece wth Ucertaty, Joural of Software, Vol.5, No., 2004, pp.583-594. [0] A. L. Jousselme, D. Greer, E. Bosse, A New Dstace Betwee Two Bodes of Evdece, Iformato Fuso, Vol.2, No., 200, pp.90-0. [] X. J. Yag, L. Zeg, F. Luo ad S. X. Wag, Cloud Herarchcal Aalyss, Joural of Iformato & Computatoal Scece, Vol.2, No.7, 200, pp.2468-2477. [2] Europea Stadard EN5026, Ralway Applcatos-The Specfcato ad Demostrato of Relablty, Avalablty, Mataablty ad Safety (RAMS), 2003. E-ISSN: 2224-266X 434 Volume 4, 205