Tekerlek Profillerinin Raylı Taşıt Dinamiğine Etkisinin İncelenmesi

Abstract

Raylı taşıt dinamiği demiryolu mühendisliğinin temel konularından biridir. Farklı fiziksel koşullar altında aracın davranışı yapılan dinamik analizler sonucu belirlenir. Aracın dinamiğini etkileyen temel parametreler taşıtın boyutları, kütle ve atalet değerleridir. Ayrıca süspansiyon elemanlarının yay ve sönüm katsayıları ve bu elemanların bağlantı noktalarının konumları da taşıt dinamiğini etkilmektedit. Taşıtın davranışını belirleyen bir diğer önemli parametre ise tekerlek ve ray profilidir. Tekerlek profilinin yuvarlanma düzlemi aracın düz yoldaki davranışını, flanş bölgesi ise kurptaki davranışını belirlemektedir. Metro ve hafif metro sistemlerinde tekerlek profili standartlar tarafından belirlenirken tramvay hatlarında ise işletmeci tarafından hat karakteristikleri ve işletme hızı gibi parametreler göz önünde bulundurularak belirlenmektedir. Tekerlek profili tasarımında dikkat edilmesi gereken ana husus konfor-güvenlik ilişkisinin doğru bir şekilde kurulmasıdır. Bu tez kapsamında raylı taşıt dinamiğinde önemli bir etkiye sahip olan tekerlek-ray teması üzerinde durulmuştur. Öncelikle Simpack yazılımında bir tramvay aracına ait 52 serbestlik dereceli dinamik model oluşturulmuştur. Daha sonra üç farklı tekerlek profili (TTP1, TTP2 ve TTP3) modele eklenerek performansları incelenmiş ve karşılaştırılmıştır. Yapılan kararlılık, konfor ve kurp analizleri sonucunda TTP2 ve TTP3 profilleri konfor, yanal kararlılık açısından daha iyi sonuçlar verdiği gözlemlenmiştir. Kurp analizinde ise her üç profilinde güvenlik sınırlarını aşmamakla birlikte TTP1 profilinin deray oranı daha düşük çıkmıştır. Yapılan bu tez ile modellenen tramvay aracının dinamik sürüş performansı bakımından en uygun tekerlek profili belirlenmiştir. Önerilen tekerlek profili ile konfor iyileştirilirken güvenlik standartlar tarafından belirlenen sınırlar içerisinde tutulmuştur.

Metro and trams are one of the most cost effective vehicles in urban transportation. This is due to the low energy loss of metal on metal contact between wheels and rail. The advantageous characteristics in passenger carrying capacity and punctual operation make them more preferable than other urban transportation vehicles. They also offer a secure and comfortable trip for passengers. Metro and trams differ from other railway vehicles in operating conditions. Some main differences are the distance between stations, passenger capacity, braking and acceleration. Especially tram vehicles’ design inputs vary considerably since they are operated within the motorway traffic and with respect to city’s weather condition and geological specification. The selection of railway wheel and rail profiles is a challenge that has faced engineers since the dawn of the railway age. This thesis is mainly focused on rail-wheel profile contact which has a very important effect on railway vehicle dynamics. Metro and light rail vehicle wheel profiles are determined with respect to the predefined standards. However in tramways, it is determined by the operator considering the parameters such as line characteristics and operating speeds. Increasing axle loads, the presence of tight curves and light vehicles causes more complexitty for wheel/rail interface. These differing requirements are all oriented toward same targets; increased durability and comfort, reduction of maintenance costs, and increased safety. First of all, the dynamic model is created in Simpack software. The dynamic behaviour of a railway vehicle can be analysed using three types of analysis: • linear analysis, for the evaluation of the vehicle model eigenvalues; • stability analysis, used for the evaluation of the critical speed of the vehicle; • dynamic analysis, to simulate the actual behaviour of the railway system in operating conditions. The complete vehicle–track system can be split up into three subsystems: vehicle, wheel–rail contact, and track.The first step in every vehicle computer simulation is to set up a mechanical model appropriate to fulfil the desired simulation task. The multibody system (MBS) approach is a powerful and widely used method for this procedure, especially if the vehicle’s running behaviour is to be analyzed. The typical model of a railway vehicle is composed of the three sub-assemblies: the car body, the front bogie, trailer bogie and the rear bogie. Each bogie consists of the bogie frame, bolster, and two wheelsets. In this research, the car body and bogie frames, as well as the wheelsets are treated as rigid bodies and are defined by their mass–inetria characteristics (mass, moments of inertia, and the position of the centre of gravity), and by the relative position of the bogies with respect to the car body itself. Each rigid body has six degrees of freedom; three translations and three rotations. All bodies are connected by linear and non-linear springs and dampers, representing the primary and secondary suspensions. Primary and secondary suspensions are often used to support the carbody components and to provide vibration isolation. The primary suspension is connected between the wheelset and the side frame, while the secondary suspension is connected between the bolster and the side frame. The primary and secondary suspensions consist of spring, damper, bump stop and trailer arm. Difference between contact areas is presented by creating contact models for these three wheel profiles. Mode frequencies and dampings are investigated by applying the modal analysis to investigate the stability of the system. Resonance characteristics of components such as carbody, bogie and bolster are observed with the aid of their mode shapes. Stability of the system indicated by investigating the damping values and root-loci figures for a speed range of 0-70 km/h. On the other hand, after the analysis of the most critical curve area under operating conditions, equivalent conicity did not exceed the limits. Lateral irregularity is applied to the straight track to see the lateral movement of the carbody during maximum velocity of 70 km/h. Lateral movement of the carbody is absorbed in time after the analysis and stability of the vehicle is proved for these conditions. Superiority of the TTP2 and TTP3 wheel profiles is shown by the lateral stability analysis results. Comfort index from EN 12299 standard is compared between three wheel profiles by using a track irregularity which is defined in ORE B176 and also superiority of the TTP2 and TTP3 is investigated with respect to comfort for passengers. L/V ratio, creepages, creep forces and lateral forces are compared for each wheel profile by curve analysis for the most critical curve in the line. As a result, altough none of the wheel profiles exceed the safety limit, TTP1 profile yields much safer results. On the other hand, TTP2 and TTP3 generates lower lateral forces during the curve than TTP1 profile. Therefore, TTP2 and TTP3 profiles have superior characteristcs for maintenance costs and irregularites on wheel and rail profile. To sum up, TTP1 profile is safer for curve analysis and TTP2 and TTP3 profiles have superior lateral stability and comfort characteristics and less lateral forces generated acting on the rail. Basic principle for wheel profile design process is building the relation between comfort and safety in a proper way. Comfort should be improved while safety limits should not be exceeded for designed wheel profile. With respect to these informations, optimization can be done on the wheel tread and flange area to get better results for safety and comfort. Additionally, profiles can be compared for wear conditions.