How can rail transport be made safer, more efficient and environmentally friendly? How must the trains of tomorrow be designed? Rail transport researchers at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) are addressing these questions. In the 'Next Generation Train' (NGT) project, researchers from nine DLR institutes are using an interdisciplinary approach to tackle the key questions of how the trains the future can be made fast, safe, comfortable and environment-friendly.
The main objective is to raise the maximum running speed by 25 percent without breaching existing safety standards. At the same time, researchers hope to halve the specific energy consumption. In addition, noise emissions will be reduced and travellers' comfort enhanced with regard to cabin pressure variations, climate control, vibration and acoustics. Using modular designs and intelligent system integration – in a similar way to road vehicles – it will be possible to develop railway vehicles that can be constructed at a much lower cost. DLR transport researchers also see considerable potential for increasing the efficiency of development and approval processes. Their work is intended to contribute to unlocking these potential improvements, in that the possibilities offered by integrated modelling of the system as a whole will be demonstrated and concrete proposals for harmonising the requirements and processes across Europe will be introduced. This will lead to a significant shortening of development times.
Background: The requirements for railway vehicles have changed a great deal in the last 10 years. This development is being driven by the rise in energy costs, the increasing importance of the life cycle costs of a vehicle in comparison to its acquisition costs, stringent requirements on the safety of future vehicles, competition with other modes of transport and rising expectations for passenger comfort. The NGT project brings DLR's existing skills in railway vehicle engineering together; the focus is on the vehicle. Related areas, such as the design of the track and of automatic train control systems are included in this research. Above all, value is added through the whole-system treatment of design issues and through the great potential for synergy. Networking among the partners allows for integrated treatment of the various topics, from conceptual design and materials qualification through detailed design and simulation to verification based on near production-ready components.
Lightweight construction in the Next Generation Train
As part of the NGT project, DLR researchers are developing lightweight construction techniques for the carriage bodies, for the nose sections of multiple-unit trains – which are particularly vulnerable in collisions – as well as for the interior of high-speed trains. Lightweight structures and assembly technologies play a role in, among other things, complying with maximum axle weights, and saving energy during acceleration and braking. This directly influences the reduction of environmental pollution caused by emissions. For example, sandwich structures with a honeycomb core and glass fibre reinforced skins can have the same flexural stiffness as solid components (for example, aluminium), but are much lighter. Use of these materials would allow the weight of the interior of NGTs to be greatly reduced.
Aerodynamics: wind tunnel makes stability in crosswinds observable
Aerodynamic design will play a key role in the achievable performance characteristics of the new trains. Important safety issues that must be addressed to gain type approval (for example, crosswind stability), the effects of the moving train on its environment and immediate surroundings, and passenger's perception of comfort and thus their acceptance of the new trains are all largely determined by aerodynamics. For example, the shape of the train nose is significantly influenced by air displacement in tunnels and by crosswind stability. In a wind tunnel, DLR researchers simulate crosswinds by directing airflow onto a 1:100 scale model of a train at an oblique angle. The resulting flow structures are made visible by means of smoke and laser illumination. To obtain reliable results on key safety issues such as the passing of oncoming trains or behaviour in a crosswind, new test facilities are being designed and built for the study of aerodynamics in crosswinds, tunnel aerodynamics, high Reynolds number aerodynamics and aeroacoustics.
Simulation of passenger flows
How do passengers behave when they board or disembark from a double-decker high-speed train? What role does vehicle design play in optimising the processes in the train and between train and platform? DLR researchers are simulating various vehicle configurations, analysing boarding and alighting times and are modelling the movement of individual people inside the train with various arrangements of seating, steps and doors. The objective is to identify the best concept for the smooth flow of passengers and fast transfers by taking into account interchanges during long-distance travel and technical constraints. The researchers are working with TOMICS (Traffic Oriented Microscopic Simulator), simulation software for modelling individual passenger movements in the traffic space.
Life cycle cost and high-speed route evaluation
Life cycle costs play a key role in the market introduction of new railway vehicles. The NGT-LCC (Next Generation Train - Life Cycle Costing) programme, specially developed by DLR for railway vehicles, is a scenario-enabled, modular tool for analysing cost structures in the 'vehicle production – operation – infrastructure' process chain. DLR researchers have also designed a routing tool based on a geographical information system (GIS). Using geographical data, this determines the most cost-effective route between two locations. Factors such as inclines, population density and bodies of water determine the route of a high-speed line, significantly influencing construction costs. The calculated routes enable an evaluation of the feasibility of new high-speed lines.
Simulating energy flows
Due to their weight, modern railway vehicles must meet stringent requirements with regard to energy efficiency. An additional challenge with diesel-powered railway vehicles is the reduction of carbon dioxide and other pollutant emissions. Future pollutant limits can only be complied with through exhaust gas treatment systems, which generally cause a reduction in engine power. The recovery of energy during braking, combined with energy storage systems, allows the use of energy that would otherwise be wasted. This enables fuel-efficient performance with less powerful engines. DLR is developing new concepts for energy optimisation.
To evaluate these, multi-property models of railway vehicles and their components are being developed. The test facilities at DLR enable the validation of newly developed component models. The energy flow simulation compares examples of the energy flow of a conventional diesel-electric regional railway vehicle with a vehicle where reduced diesel engine power is compensated by the use of braking energy recovery and storage. The visualisation of the energy flows illustrates the differences in the operating modes of both systems. Although the diesel engine power in the hybrid vehicle is considerably lower than in a conventional vehicle, it is possible to achieve the same performance. However, the hybrid vehicle uses significantly less fuel, greatly reducing the emission of pollutants in comparison to conventional vehicles.
System dynamics of wheels and rails
The targets for NGT in relation to running speed, passenger capacity and comfort, as well as reduction of noise and wear, can only be achieved if the dynamics of the wheel-rail system are also examined and improved. DLR has already made significant contributions to the analysis of vehicle-system dynamics for railway vehicles and prepared the way for the virtual design of a railway vehicle with what is referred to as multi-body simulation. This method is used in the NGT project with realistic configuration scenarios to calculate the dynamic loads due to vehicle movement and, for example, take them into account in designing the structure of the carriage body. It is also important to ensure that the wheel-rail forces do not exceed allowable thresholds when determining the suitability of a train concept.
Mechatronic systems for active wheel guidance and bogie control offer enormous potential for improving the safety and comfort of railway vehicles. In addition to enhanced running stability, wear reduction and reduced noise, the mechatronic bogies for the NGT will allow a smooth and comfortable ride for passengers on the lower level of a double-deck vehicle. The main components of the bogie are the individually controlled driving wheels with an associated wheel mount that can be turned to follow a curved track. Individual wheel motors act as both propulsion systems and as actuators that can exert different torques on the two separate wheels of a wheelset. This allows the bogie to be aligned with the path of the track and steered into curves, making the wheels run more quietly and reducing wear.