专业外语关于横风影响探讨.doc

Study on the safety of operating high- speed railway vehiclessubjected to crosswinds姓名： 学号：班级： Abstract: A coupled vehicle-track dynamic model is put forward for use in vestigating the safety effects of crosswinds on the operation of a high-speed railway vehicle. In this model, the vehicle is modeled as an onlinear multi-body system, and the ballasted track is modeled as a three-layer discrete elastic support system. The steady aerodynamic forces caused by crosswinds are modeled as ramp-shaped external forces being exerted on the vehicle body. This model was used in a numerical analysis of the dynamic response and dynamic derailment mechanisms of high-speed vehicles subjected to strong crosswinds. The effects of the crosswind speeds, crosswind attack angle, and vehicle speed on the operational safety of the vehicle were examined. The operational safety boundaries of a high-speed vehicle subjected to crosswinds were determined. The numerical results obtained indicate that crosswinds at attack angles of 75 to 90 with respect to the forward direction of the vehicle have a great influence on the safety of operating high-speed railway vehicles. The wheelset unloading limit, which determines the position of the warning boundary dividing the safe operating area and the warning area, is the most conservative, criterion to use in assessing the high-speed operational safety of vehicles in crosswinds.Key words: High-speed railway, High-speed train, Crosswinds, Safety boundary, Derailment1 IntroductionWith the rapid development of high-speed rail-ways around the world, the operating safety ofhigh-speed trains has become one of the major con-cerns of current railway research. Fatal railway ac-cidents, which are the catastrophic consequences ofunsafe operating conditions, should be prevented(Evans, 2011; Silla and Kallberg, 2012). Strongcrosswinds are among the extreme forces of naturethat threaten the safe operation of trains. Many rail-way vehicles have been blown over by extremecrosswinds in locations around the world. As shownin Fig. 1, on the 28th of February, 2007, a train fromUrumqi to Aksu was blown off its track by strongwinds in Turpan, Xinjiang Uygur Autonomous Re-gion of China (Xinhua News Agency, 2007). Fourpeople were killed, and more than 30 were injured. Todate, more than 30 strong-crosswind-induced acci-dents have been reported in Japan (Fujii et al., 1999;Gawthorpe, 1994). Most of these accidents occurredon narrow-gauge tracks (Fujii et al., 1999). Three characteristics of high-speed trains, i.e.,their lightweight construction, high driving velocities,and distributed traction (Fujii et al., 1999), have sig-nificant influences on their operational safety whensubjected to crosswinds. In recent years, the cross-wind safety of railway vehicles has been of greatinterest to researchers and railway industries. Manyrailway vehicle safety standards, such as EN 14067-6(CEN，2010) and TSI/HS-RST-L64-7/3/2008 (OJEU,2008), have been proposed to evaluate the街namicresponse of trains to crosswind action and ensure theiroperational safety. Reviews of recent internationalwork in this field were presented by Carrarini (2006)and Baker et al. (2009). Crosswind stability analysis of railway vehiclesinvolves tvo issues. The first is the flow field arounda train in operation and the aero街namic forces actingon the car bo街.The second is the resultant街namicresponse and crosswind stability of the train-trackcoupling system and its safety assessment. Most ofthe previous studies on this subject have focused onthe first issue. A large number of full-scale windtunnel tests and computational fluid街namics (CFD)simulations have been carried out to examine theairflow around high-speed trains in crosswind sce-narios (Baker et al., 2004; Diedrichs, 2005; Cheli etal., 2010). The second issue, which was investigatedin this study, has not received much attention in pre-vious studies. Many efforts have been made to usemulti-bo街街namic models to study the characteris-tic wind curves, which represent critical crosswindspeeds, at which the selected derailment criteria reachtheir limits and vehicle overturning occurs (Orellanoand Schober, 2003; Cheli et al., 2006; Xu and Ding,2006). Typically, quasi-steady approaches are pro-posed for use in calculating the wheel loading reduc-tion caused by crosswind forces. Such approaches arebased on equilibrium of the steady aero街namicforces and the restoring forces on the railway vehicleand do not take into account the transient responsethat occurs when a vehicle is subjected to a crosswind(RSSB, 2000; Carrarini, 2006). To investigate the operating safety of high-speedrailway vehicles subjected to strong crosswinds, avehicle-track model that considers the crosswindeffect was developed and was used in a numericalanalysis carried out in a time domain. In this ap-proach, the vehicle is modeled as a nonlinear multi-bo街system, and the track is modeled as a three-layersystem. The rails are modeled as Timoshenko beamssupported by discrete sleepers. The coupling of the vehicle and the track is simulated by the track movingwith respect to the vehicle operating at a constantspeed, which permits consideration of the effects ofperiodic discrete rail supports on the vehicle-trackinteraction. The rolling contact of the wheel-rail sys-tem reflects the geometric relationship and contactforces between the wheels and rails. The wheel-railgeometric relationship is solved spatially and evalu-ated on-line using a new wheel-rail contact model(Chen and Zhai, 2004). The wheel-rail contact forcesinclude normal and tangential forces. The normalforces of the wheel-rail system are calculated usingthe Hertzian contact theory, and their tangentialforces are calculated using the nonlinear creep theoryproposed场Shen et al. (1983). In the analysis con-ducted in this stu街，the crosswind was assumed to bestea街，and the aero街namic forces due to the cross-wind were modeled as ramp shape external forcesexerted on the car bo街.The crosswind forces con-sidered included the side force, the lift forces, the rollmoment, the pitch moment, and the yaw moment. Thenumerical analysis was conducted to investigate the街namic response and derailment mechanism of ahigh-speed vehicle in a strong crosswind scenario.The effects of the crosswind speed, the crosswindattack angle, and the vehicle speed on the operationalsafety of the vehicle were examined in detail. Theoperational safety boundaries of a high-speed vehiclesubjected to crosswinds were determined from街-namic simulations of vehicle-track coupling and ex-fisting safety assessment criteria.2 Dynamic model of coupled vehicle-tracksystem in crosswindsThe causes of derailment or overturn of railwayvehicles operating in strong crosswinds are not easyto identi斤，and it is very difficult to recreate accidentsin site tests or laboratory experiments. Numericalmodeling is an effective means of stu街ing the causes3 Conclusions In this stu街，a街namic model for a coupledvehicle-track system was developed to investigate theeffect of crosswinds on the operating safety ofhigh-speed railway vehicles. The steady aero街namicforces caused by crosswinds were modeled asramp-shaped external forces exerted on the vehicle.Numerical analyses were conducted to investigate the街namic responses and the街namic derailmentmechanism of a high-speed vehicle in strong cross-wind scenarios. The effects of the crosswind speed,crosswind attack angle, and vehicle speed on theoperating safety of the vehicle were examined. Theoperational safety area, warning area, and derailmentarea and their boundaries were defined and werecalculated using the街namic coupled vehicle-trackmodel and existing criterion limits. The results ob-tamed clearly indicate the operational safety surplus of each derailment criterion for a high-speed train operating in crosswinds, namely, the gap between thecriterion limit boundary and the derailment boundary.The following conclusions can be drawn from thenumerical results. 1. The crosswind has a great influence on theride comfort and safety of railway passengers. As thecrosswind speed increases, the街namic responses ofthe car bo街and the wheel-rail forces increase line-arly. Flange climbing does not play a key role in thelikelihood of derailment of high-speed railway vehi-cles subjected to strong crosswinds. Overturningusually occurs when a vehicle enters into a crosswindscenamo. 2. The crosswind attack angle, vehicle speed,and wind speed have a great influence on the operat-ing safety and the likelihood of overturning of ahigh-speed vehicle operating in crosswinds. As thecrosswind speed and vehicle speed increase, thewheel unloading ratio and the wheel rise increaselinearly. Crosswind attack angles of 750 to 900 cor-respond to the worst-case scenarios and have thegreatest influence on the likelihood of derailment ofsuch vehicles. The crosswind direction should also betaken into account in assessing the safety ofhigh-speed railway vehicles operating in crosswinds. 3. The wheelset unloading ratio 4V/V determinesthe boundary of the common safety area, which is thesmallest area defined by the three key factors ofinfluence. This area is considered the safety area forhigh-speed trains operating in crosswinds. The threekey factors of influence are the vehicle speed, thecrosswind speed, and the attack angle. Note that the crosswind scenarios consideredinvolved constant mean wind speeds in this study. In