Dissertations / Theses on the topic 'Wagon dynamics'

The link suspension is the most prevailing suspension system for freight wagons in central and western Europe. The system design is simple and has existed for more than 100 years. However, still its characteristics are not fully understood. This thesis emphasizes freight wagon dynamics and comprises three parts:

In the first part a review of freight wagon running gear is made. The different suspension systems are described and their advantages and disadvantages are discussed. The review covers the running gear standardized by UIC and the conventional so-called three-piece bogie. Additionally five improved three-piece bogies and twelve novel running gear designs are presented.

The second part focuses on the lateral force-displacement characteristics in the link suspension. Results from stationary measurements on freight wagons and laboratory tests of the link suspension characteristics are presented. To improve understanding of the various mechanisms and phenomena in link suspension systems a simulation model is developed. Link suspension systems have strongly nonlinear characteristics including a hysteresis loop. The loop exhibits usually three characteristic sections with different tangential stiffnesses. The actual contact geometry of the links and end bearings has a significant influence on the characteristics. By wear in ordinary service - as well as by geometric tolerances on new components - the contact geometry may deviate considerably from nominal geometry. Further, it seems that elastic deformation in the contact surfaces has considerable effects on the suspension characteristics, in particular on the initial rolling stiffness for small displacements. Also, flexibilities in links and end bearings influence the characteristics. It is also observed that new components after a short period of dynamic testing can exhibit a very low amount of energy dissipation, a phenomenon that is also indicated in some stationary measurements on wagons.

To summarize the second part, it appears that the link suspension characteristics are very sensitive to several factors being hard to control in the real world of freight wagon operations. The various stiffnesses and hysteresis loops have a considerable variation and may have a strong influence on the ride qualities of vehicles. As long as the characteristics can not be controlled within closer limits than found in this study, there is a strong need for sensitivity analysis to be made, both in predictive multibody simulations of vehicle dynamics, as well as in verification and acceptance tests.

In the third part a study on the possibility to improve ride qualities of freight wagons with link suspensions is presented. Parametric studies with multibody dynamic simulations on freight wagons equipped with link-suspension bogies are performed. The effect of supplementary friction and hydraulic damping is investigated under various running conditions: speed, loading, tangent and curved track, wheel-rail contact geometry, track gauge and track irregularities. Substantial improvements of the lateral running behaviour of wagons with link suspension bogies can be achieved - both at ordinary speeds and at increased speeds - by using a proper combination of supplementary hydraulic dampers. Speeds up to 160 km/h could be realistic.

The link suspension is the most prevailing suspension system for freight wagons in Central and Western Europe. The system design is simple and has existed for more than 100 years. However, still its characteristics are not fully understood. This thesis investigates the dynamic performance of freight wagons and comprises five parts: In the first part a review of freight wagon running gear is made. The different suspension systems are described and their advantages and disadvantages are discussed. The second part focuses on the lateral force-displacement characteristics of the link suspension. Results from stationary measurements on freight wagons and laboratory tests of the link suspension characteristics are presented. To improve the understanding of various mechanisms and phenomena in link suspension systems, a simulation model is developed. In the third part the multibody dynamic simulation model is discussed. The previous freight wagon model developed at KTH is able to explain many of the phenomena observed in tests. In some cases, however, simulated and measured running behaviour differ. Therefore, a new simulation model is presented and validated against on-track test results. The performance of standard two-axle freight wagons is investigated. The most important parameters for the running behaviour of the vehicle are the suspension characteristics. The variation in characteristics between different wagons is large due to geometrical tolerances of the components, wear, corrosion, moisture or other lubrication. The influence of the variation in suspension characteristics and other parameters on the behaviour of the wagon, on tangent track and in curves, is discussed. Finally, suggestions for improvements of the system are made. A majority of the traffic related track deterioration cost originates from freight traffic. With heavier and faster freight trains the maintenance cost is likely to increase. In the fourth part the possibility to improve ride comfort and reduce track forces on standard freight wagons with link suspension is discussed. The variation of characteristics in link suspension running gear is considerable and unfavourable conditions leading to hunting are likely to occur. Supported by on-track tests and multibody dynamic simulations, it is concluded that the running behaviour of two-axled wagons with UIC double-link suspension as well as wagons with link suspension bogies (G-type) can be improved when the running gear are equipped with supplementary hydraulic dampers. Finally in the fifth part the effects of different types of running gear and operational conditions on the track deterioration marginal cost — in terms of settlement in the ballast, component fatigue, wear and RCF — is investigated. Considerable differences in track deterioration cost per produced ton-km for the different types of running gear are observed. Axle load is an important parameter for settlement and component fatigue. Also the height of centre of gravity has significant influence on track deterioration, especially on track sections with high cant deficiency or cant excess.
QC 20100802

Hector Rail AB is a Swedish line haul provider for the European Rail Transport Market. On one of their lines, Hector Rail transports large cylinder-shaped paper rolls of different sizes from Holmsund to Skövde, and compressed recycled paper back to Holmsund, with Y25 bogie wagons. The wheels of these wagons experience surface initiated rolling contact fatigue, RCF, which is increasing the maintenance cost. In a collaboration with KTH Royal Institute of Technology a study of the risk of developing RCF cracks when comparing different track qualities, load cases, speeds, curves and wheel-rail friction coefficients as well as the consideration of wear is carried out. The difference in surface initiated RCF when applying the different input parameters is analysed. The location along the track where the wheels are likely to initiate RCF is calculated, as well as the location of RCF on the wheels. The model also provides the curve characteristics that are most likely to initiate RCF on the wheels. This tool can be used for optimising and further streamlining the operation for freight traffic on this (or any other) line with respect to wheel damages and planned maintenance.
Hector Rail AB är en Svensk linje trafik leverantör for den Europeiska transportmarknaden på spår. På en av deras sträckor transporterar Hector Rail stora cylindriska pappersrullar i olika storlekar från Holmsund till Skövde, och sammanpressat återvunnet papper tillbaka till Holmsund, med Y25 bogie vagnar. Hjulen till dessa vagnar upplever kross på löpbanan, vilket ökar underhållskostnaderna. I ett sammarbete med KTH Kungliga Tekniska Högskolan görs en studie för risken att utveckla krossprickor vid jämförelse mellan olika spårkvalitéer, lastfall, hastigheter, kurvor och hjul-räl friktion. Hänsyn tas också till effekten av nedbrytningen av hjulen. Skillnaden i kross i löpbanan vid ansättning av de olika indata parametrarna har analyserats. Positionen längs spåret där hjulen sannlolikt initierar kross har beräknats så väl som positionen av kross på hjulen. Modellen levererar även kurvfallen som högst troligen initierar kross på hjulen. Detta verktyg kan användas för att optimera och effektivisera verksamheten för godstrafik på detta (eller andra) spår med hänsyn till hjulskador och planerat underhåll.

Unlike methods such as replacing components when they fail or on a calendar time schedule, Condition Based Maintenance (CBM) consists of quantifying component degradation in real-time, allowing repairs to be made only when necessary and improving the overall efficiency of mechanical systems. An ideal CBM application for freight railway wagons would consist of a wireless self-powered electronic device installed on each vehicle, detecting and communicating parameters such as brake, bearing or wheel faults, and dynamic instabilities. Such a monitoring device has not been achieved yet, mainly because of the lack of electricity on-board the vehicles and the cost of instrumenting massive fleets. Recent advances and cost reductions in devices and technologies for the Internet of Things (IoT) open the possibility for developing a feasible on-wagon monitoring device. Wireless data transmission, acquisition, and digital signal processing are the most power demanding tasks in on-board condition monitoring sensor nodes. Traditional approaches use mostly digital signal processing and opt for reducing monitoring and communication events, limiting the types of parameters that can be measured and the associated analyses. On the other hand, the approach of the present project is to develop an innovative hardware architecture based on analogue computing for decreasing energy consumption with a reduced sensor node architecture. That is, achieving fault detection using analogue electronic circuitry which directly extracts relevant information from sensor signals, hence reducing digital system workload and complexity and thereby being able to handle higher frequency analogue signals with simple electronic components. This project develops an innovative sensor node hardware architecture and algorithms for a practical on-wagon monitoring device, with low power usage and sufficient on-board calculation capability to provide warning messages when a fault emerges. Developments regarding sensors, IoT, integrated systems and fault detection techniques were reviewed. A wheel flat defect was used as a case study to develop and investigate the proposed condition monitoring sensor node. Railway vehicle dynamic behaviour was simulated to determine operating conditions for the device and the nature of the signals to be monitored. The device concept was firstly proven by combining vehicle dynamic simulations with a physical prototype of the on-wagon fault detection analogue circuit. Subsequently, a hardware prototype version of the circuit was constructed and tested on a scaled bogie rig. The proposed sensor node hardware architecture effectively reduced power consumption and memory requirements for detecting a wheel flat defect using on-board acceleration signals.

The empty weight or tare load of railway freight wagons is significant compared to the gross load (13-43% of the gross load) which not only reduces the possibility of carrying a higher payload but also increases the energy consumption per payload tonne hauled. One way to reduce the energy consumption per tonne payload is to reduce the tare load. One possibility of lowering the tare load is to reduce the number of components such as a bolster, sideframes, and axles. A two-axle wagon compared to a bogied wagon creates a possibility to reduce tare by up to 4-5t on a two-axle configuration. The fewer components on a two-axle wagon, however, result in inferior dynamic performance such as low critical hunting speed, poor curving ability, greater vehicle response to short irregularities etc, so, in spite of having low tare, the two-axle wagons are not as popular as the bogied wagons. To take advantage of the lower tare mass of a two-axle wagon, a new concept wagon was conceptualised as a wagon with maximum axle load (~41 tonnes) and with enough load space to ensure a 80 tonne gross mass. The developed concept resulted in a wagon with a deck length of ~19.8m that allows carrying three 20’, or a 20’ and a 40’, or a 65’ container. The axle spacing (13.8m), overhang length (3m), tare mass (8t) and gross mass (80t) of the developed concept wagon is considerably different to the normal two-axle wagon. The challenge then was to design a suspension that would pass dynamics and roadworthiness tests. It was reasoned that as the developed concept wagon was a new and radical concept, a more rigorous test approach to dynamic testing should be added to the normal tests and acceptance parameters in railway standards. A more rigorous test approach was developed which included consideration of test track defect lengths based on bogie centre distance (BCD) and resonance conditions for the cyclic track defects. The consideration of resonance condition requires developing equivalent amplitudes of track defects corresponding to the wavelengths in the track which are multiples of bogie centre distance for the cyclic bounce, pitch and roll track defects. Using the more rigorous testing regime an innovative axle suspension was developed and refined to a design with three stages consisting of a conventional leaf spring, and the UIC link suspension in series with two multi-stage coil springs. It was also necessary to add longitudinal stiffness to improve axle yaw stability and hunting speed. The resulting design showed excellent stability with a critical speed of 204km/h and the multi-stage suspension allowed for negotiation of isolated lateral, vertical and long twist track defects as per AS7509 up to the defect band F of the ARTC track geometry standard. The short twist tests were however problematic. The resultant concept requires a smaller short twist track defect limit (8mm over 2m) than the defect band G of ARTC track geometry standard. The developed concept performed satisfactorily on track spectra up to FRA class 6 track. Finally, the energy consumption of the developed wagon concept was evaluated and compared with similar capacity wagons such as RQTY, sgns60 and double stack container wagons in a train simulation. The energy saving ranged from 6 to 12% across various operating scenarios.

"Braking and traction torques are not explicitly considered in most of the wagon dynamics simulation packages, as their primary focus is to provide a platform for long distance route simulations with near real-time scenarios which demands fast solution algorithms. These packages consider the braking scenarios through the definition of speed profile as a priori. It is commonly acknowledged that the speed profile is affected by tribological and geometric parameters at the wheel-rail interface as well as the characteristics of brake application. Hence it’s prudent to evaluate the speed profile based on input torque due to traction/ brake forces; this research has considered such an approach and developed the program that can simulate the longitudinal behaviour of railway wagon dynamics during braking and traction. Consequently, this program enables to simulate wheelset locking and wagon yaw, roll, pitch in a natural way."--Abstract.

"There is a large quantity of literature available on longitudinal train dynamics and risk assessment but nothing that combines these two topics. This thesis is focused at assessing derailment risks developed due to longitudinal train dynamics. A key focus of this thesis is to identify strategies that can be field implemented to correctly manage these risks. This thesis quantifies derailment risk and allows a datum for comparison. A derailment risk assessment on longitudinal train dynamics was studied for a 107 vehicle train consist travelling along the Monto and North Coast Lines in Queensland, Australia. The train consisted of 103 wagons and 4 locomotives with locomotives positioned in groups of two in lead and mid train positions. The wagons were empty hopper wagons on a track gauge of 1067mm. The scenarios studied include: the effect of longitudinal impacts on wagon dynamics in transition curves; and the effects of longitudinal steady forces on wagon dynamics on curves. Simulation software packages VAMPIRE and CRE-LTS were used. The effects of longitudinal impacts from in-train forces on wagon dynamics in curves were studied using longitudinal train simulation and detailed wagon dynamics simulation. In-train force impacts were produced using a train control action. The resulting worst-case in-train forces resulting from these simulations were applied to the coupler pin of the wagon dynamics simulation model. The wagon model was used to study the effect of these in-train forces when applied in curves and transitions at an angle to the wagon longitudinal axis. The effects of different levels of coupler impact forces resulting from different levels of coupling slack were also studied. Maximum values for wheel unloading and L/V ratio for various curve radii and coupler slack conditions were identified. The results demonstrated that the derailment criteria for wheel unloading could be exceeded for a coupler slack of 50mm and 75mm on sharper curves, up to 400m radii. A detailed study of the effect of steady in-train forces on wagon dynamics on curves also was completed. Steady in-train forces were applied to a three wagon model using VAMPIRE. Maximum and minimum values of wheel unloading and L/V ratio were identified to demonstrate the level of vehicle stability for each scenario. The results allowed the worse cases of wheel unloading and L/V ratio to be studied in detail. Probability density functions were constructed for the occurrence of longitudinal forces and coupler angles for the Monto and North Coast Lines. Data was simulated for a coupler slack of 25, 50 and 75mm and force characteristics were further classified into the occurrences of impact and non-impact forces. These probability density functions were analysed for each track section to investigate the effects of coupler slack, track topography and gradient on wagon dynamics. The possible wagon instability in each of these scenarios was then assessed to give a measure of the potential consequences of the event. Risk assessment techniques were used to categorise levels of risk based on the consequences and likelihood of each event. It was found that for the train configuration simulated, the Monto Line has a higher derailment risk than the North Coast Line for many of the scenarios studies in this thesis. For a coupler slack of 25mm no derailment risks were identified, 50mm coupler slack derailment risks were only identified on the Monto track and the majority of derailment risks were identified for a 75mm coupler slack." -- abstract

A survey of literature and existing technologies indicated that algorithms and systems for on-board monitoring devices for freight wagons are still not well developed. This was found to be primarily due to the difficulty of developing a practical on-board monitoring system due to the lack of power and electrical communications on standard freight wagons. In addition, large wagon fleet sizes make it imperative that any such system be both robust and cheap. Consequently, it was observed that traditional approaches to freight wagon health monitoring are performed from track side instruments as the wagons pass by. As it could be seen that any freight monitoring system must require only limited instrumentation, and to ensure that the research in this thesis would have practical usefulness the target design was constrained to using just two tri-axial accelerometers. Various approaches to inferring wagon dynamic behaviour and safety from just acceleration measurements were reviewed. These included model-based health monitoring methods and signal-based fault detection and isolation (FDI) methods. Model-based health monitoring methods, such as inverse modelling methods, Kalman Filter based methods, etc., utilise various estimation models to analyse sensor-collected acceleration signals for either real-time wheel-rail dynamic predications or real-time suspension parameter estimation. Conversely, signal-based FDI methods analyse sensor-collected acceleration signals directly via various signal-processing methods to detect the occurring faults directly. From the review it was discovered that linearisation of the models was required by model-based health monitoring methods which affects the accuracy of the results given the highly non-linear nature of railway vehicle suspensions and dynamic responses. The signal-based FDI methods, however, were found to be impeded by a different problem, that of requiring a large prebuilt database to cover all possible fault conditions. Such a database is time-consuming and difficult to build for the proposed wagon application. It was realised that advantage could be taken in the heavy haul train context from the fact that such trains are generally made up of near identical wagons and usually near identical service condition. It was proposed that the problem of a prebuilt database construction could be solved via a “Self-collaborate” system of sharing and comparing data between wagons via local communications. A signal-based method was therefore proposed based on the concept of cross-correlation and comparisons between adjacent heavy haul wagons. To generate data to test the proposed method, simulations were completed using a realistic and detailed MBS model of a typical 40t axle load heavy haul wagon. Simulations were undertaken using the Gensys vehicle dynamics software package. The wagon was modelled with the following detail: all vehicle components, including a carbody, two bolsters, four sideframes and four wheelsets, were given six degrees of freedom (DOFs), and all bolster springs and wedge damper springs were modelled as nonlinear stiffness elements. The track and operational conditions chosen for testing the approach were for a tight curve at prescribed curve speed and straight track at full speed. The FRA Class 4 track irregularity was assumed for the track surface. A method using cross-correlation of acceleration measurements to calculate Fault Indicators (FIs) was developed. This method was tested for various wagon suspension faults including changes to spring stiffness and damping. Two categories of cross-correlation analyses were made, including the cross-correlation analyses of acceleration signals between different directions from same sensors (Category 1) and the cross-correlation analyses of acceleration signals in the same directions between front and rear sensor (Category 2). Analysis results showed that, among all the proposed Fault Indicators, cross-correlation of vertical accelerations between the front and rear sensor was the most sensitive FI to both bolster spring faults and wedge damper faults. Though the considered faults did not cause more than 10% variations in wheel-rail dynamic parameters, namely wheel unloading and derailment index, the proposed FIs indicated over 300% variation, indicating high sensitivity. The sensitivity of these results and the robustness of the proposed method were further explored with variations in track condition and areas of further work recommended.