Colin Cole

Simulated comparisons of wagon coupler systems in heavy haul trains

Abstract Three types of wagon connection coupling systems are evaluated in a train simulation model consisting of 107 vehicles. The three wagon connection coupling systems are auto-couplers with standard draft gears, auto-couplers with draft gears with wedge unlocking features, and the traditional drawhook buffer system. The train is made up of 103 wagons and 4 locomotives. The locomotives are placed in groups of two at the head and mid-train positions. Dynamic response and fatigue damage is compared for a control disturbance on a crest and on a flat track section. The effect of coupling-free travel (slack) is also investigated.

Wagon instability in long trains

Lateral force components and impacts from couplers can adversely affect wagon stability. These issues are significant in longer and heavier trains increasing the risk of wagon rollover, wheel climb, wagon body pitch, bogie pitch and wagon lift-off. Modelling of coupler angles has been added to normal longitudinal train simulation to allow comprehensive study of lateral components of coupler forces. Lateral coupler forces are then combined with centripetal inertia calculations to determine quasi-static lateral forces, quasi-static vertical forces and quasi-static bogie lateral to vertical ratio, allowing the study of stringlining, buckling and wagon rollover risks. The approach taken allows for different rolling stock lengths, overhang and coupling lengths, and allows the study of angles occurring in transitions. Wagon body and bogie pitch are also studied with enhancements added to previous modelling to allow the study of wagon lift-off.

Creep force modelling for rail traction vehicles based on the Fastsim algorithm

The evaluation of creep forces is a complex task and their calculation is a time-consuming process for multibody simulation (MBS). A methodology of creep forces modelling at large traction creepages has been proposed by Polach [Creep forces in simulations of traction vehicles running on adhesion limit. Wear. 2005;258:992–1000; Influence of locomotive tractive effort on the forces between wheel and rail. Veh Syst Dyn. 2001(Suppl);35:7–22] adapting his previously published algorithm [Polach O. A fast wheel–rail forces calculation computer code. Veh Syst Dyn. 1999(Suppl);33:728–739]. The most common method for creep force modelling used by software packages for MBS of running dynamics is the Fastsim algorithm by Kalker [A fast algorithm for the simplified theory of rolling contact. Veh Syst Dyn. 1982;11:1–13]. However, the Fastsim code has some limitations which do not allow modelling the creep force – creep characteristic in agreement with measurements for locomotives and other high-power traction vehicles, mainly for large traction creep at low-adhesion conditions. This paper describes a newly developed methodology based on a variable contact flexibility increasing with the ratio of the slip area to the area of adhesion. This variable contact flexibility is introduced in a modification of Kalkers code Fastsim by replacing the constant Kalkers reduction factor, widely used in MBS, by a variable reduction factor together with a slip-velocity-dependent friction coefficient decreasing with increasing global creepage. The proposed methodology is presented in this work and compared with measurements for different locomotives. The modification allows use of the well recognised Fastsim code for simulation of creep forces at large creepages in agreement with measurements without modifying the proven modelling methodology at small creepages.

A review of dynamics modelling of friction draft gear

Longer and heavier trains mean larger in-train forces and more complicated force patterns. Practical experience indicates that the development of fatigue failure of coupling systems in long heavy trains may differ from conventional understanding. The friction-type draft gears are the most widely used draft gears. The ever developing heavy haul transport environment requires further or new understanding of friction draft gear behaviour and its implications for train dynamics as well as fatigue damage of rolling stock. However, modelling of friction draft gears is a highly nonlinear question. Especially the poor predictability, repeatability and the discontinuity of friction make this task more challenging. This article reviews current techniques in dynamics modelling of friction draft gears to provide a starting point that can be used to improve existing or develop new models to achieve more accurate force amplitude and pattern predictions.

Longitudinal train dynamics

Longitudinal train dynamics (LTD) simulations have played an instrumental role over many decades in the development of longer trains, especially freight trains. Modern LTD simulations with individual vehicles considered and incorporating detailed modelling of couplings started during the 1960s. Since then, LTD simulators have been reported from all around theworld. It is well known that the researchers and engineerswidely used longitudinal train dynamic simulators in their projects and studies, but are there differences in these simulators and simulation approaches? Due to the commercial aspects and/or Intellectual Property issues, simulators were developed within separate institutions using developers’ experience and limited testing data and publications. Currently, there are no standards or standard questions to assess the correct implementation of LTD analyses and the state of LTD studies. Given this situation, the Centre for Railway Engineering initiated the International Benchmarking of LTD Simulators (hereafter referred to as the benchmark). This special issue describes the benchmarking questions that have been sent to many research, commercial and government institutions and organisations across five continents and presents various papers that report on the approaches and advances in the topic of LTD. For all participants, this benchmark exercise offered a good opportunity to validate their research and access the expertise of other research institutions. More work will be necessary by researchers as this topic progresses with the analyses of all submitted results and contributions. Taking into account the current state of knowledge in this specific area and the editors’ personal experience, researchers and engineers were invited to cover topics related to numerical and experimental studieswith the application of LTD simulators and approaches for this special issue. These included issues related to locomotive/train and wagon/train interaction, train dynamics simulation, vehicle/track resistance modelling, and modelling the behaviour of air brake, coupler and draft gear systems. This list of topics can be extended because recent research activities show that this area requires implementation of multidisciplinary knowledge and approaches. Some of proposed topics have been extensively covered by this issue, but there are still a great number of topics left untouched in the special issue providing opportunities for further research and development in this field. Wewould like to thank all researchers who have participated in the benchmark andwho have published their scientific ideas and developments. We hope that readers will enjoy reading the papers included in this special issue.

An inverse railway wagon model and its applications

An inverse wagon model was developed to estimate wheel–rail contact forces using only measurements of wagon body responses as inputs. The purpose of this work was to provide mathematical modelling to embed in low-cost devices that can be mounted on each freight wagon in a large wagon fleet. To minimize cost, complication, and the maintenance inconvenience of these devices, the constraint is imposed that transducers and connections are limited to locations on the wagon body. Inputs to the inverse model developed include only vertical and lateral translational accelerations and angular accelerations of roll, pitch, and yaw of the wagon body. The model combines the integration and partial modal matrix (PMM) techniques together to form an IPMM method. Besides wheel–rail contact forces some motion quantities such as the lateral and yaw displacements of wheelset are also predicted. Results from the inverse model were compared with data from full scale laboratory suspension tests for vertical suspension excitations. The inverse model was also compared with results from simulations completed in VAMPIRE® for more complicated track input profiles. The model results and the applications of the model are discussed.

Advanced dynamic modelling for friction draft gears

A white-box friction draft gear model has been developed with all components of the draft gear and their geometries considered. The conventional two-stage (loading and unloading) working process of the friction draft gear was detailed as a four-stage process. A preliminary work called the ‘base model’ was improved with regard to force–displacement characteristics, friction modelling and transitional characteristics. A set of impact test data were analysed; five types of draft gear behaviour were identified and modelled: hysteresis, stiffening, change of stage, locked unloading and softening. Simulated comparisons of three draft gear models were presented: a look-up table model, the base model and the advanced model.

Design and Simulation of Rail Vehicles

The fields of rail vehicle design, maintenance, and modification, as well as performance issues related to these types of vehicles, are examined in this text. Rail vehicle design issues and dynamic responses are analyzed, design and features of rail vehicles are described, and methods that address the operational conditions of this complex system are introduced. Both non-powered and powered rail vehicles are a focus - passenger and freight rolling stock, locomotives, and self-powered vehicles used for public transportation. Problems involved in designing and modeling all types of rail vehicles are introduced. Applications of train operations, vehicle dynamics, and track infrastructure maintenance are explored. Fundamentals of locomotive design, longitudinal train dynamics, and multibody dynamics are introduced, and co-simulation techniques are discussed. Recent advances in rail vehicle design are highlighted, and applicable standards and acceptance tests from around the world are contained.

Co-simulation of a mechatronic system using Gensys and Simulink

The design of mechatronic systems for rail vehicles requires the implementation of modern software tools. Nowadays, it is common to use co-simulation for the creation of mechatronic models. This approach is usually based on the combination of two types of software – multi-body simulation packages for mechanical models and tools for simulation of electric, control systems, etc. The existing commercial codes (SIMPACK, VI-RAIL, VAMPIRE, UM) provide different approaches for co-simulation; however, they have a lot in common. The one thing that makes them very similar is the use of Simulink for co-simulation. In this paper, we propose a description of the client interface in Simulink for co-simulation with Gensys. The evolution of the proposed approach has been performed by means of a simulation of a simplified traction control system for a hauling locomotive running on straight track conditions.

Simulation of Curving at Low Speed Under High Traction for Passive Steering Hauling Locomotives

The traction control in modern electric and diesel electric locomotives has allowed rail operators to utilise high traction adhesion levels without undue risk of damage from uncontrolled wheel spin. At the same time, some locomotive manufacturers have developed passive steering locomotive bogies to reduce wheel rail wear and further improve locomotive adhesion performance on curves. High locomotive traction loads in curving are known to cause the loss of steering performance in passive steering bogies. At present there are few publications on the curving performance of locomotive steering with linkage bogies. The most extreme traction curving cases of low speed and high adhesion for hauling locomotives have not been fully investigated, with effects of coupler forces and cant excess being generally ignored. This paper presents a simulation study for three axle bogie locomotives in pusher and pulling train positions on tight curves. The simulation study uses moderate and high traction adhesion levels of 16.6% and 37% for various rail friction conditions. Curving performance is assessed, showing forced steering bogies to have considerable advantages over self steering bogies. Likewise it is shown that self steering bogies are significantly better than yaw relaxation bogies at improving steering under traction. As the required traction adhesion approaches the rail friction coefficient, steering performance of all bogies degrades and yaw of the bogie frame relative to the track increases. Operation with excess cant and tensile coupler forces are both found to be detrimental to the wear performance of all locomotive bogies, increasing the bogie frame yaw angles. Bogie frame pitching is also found to have significant effect on steering, causing increased performance differences between bogie designs.