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Improving the energy efficiency of a tram’s running gear
Get PDFThis research analyses the influence of some design features of an undercarriage of a tram on the energy efficiency in terms of mechanical energy losses during its operation. The work includes the comparison of results of the research from two main points of view, namely from a running gear design and a railway wheel design. Two variants of a tram’s bogie are investigated. A standard bogie and a bogie with a system that allows a radial adjustment of the wheelsets in curves. Two designs of a railway wheel are compared, a wheel with the traditional construction scheme and a wheel with a perspective construction scheme. The values of mechanical energy losses due to slippage in the contact between the wheels and rails are analysed. These losses are obtained with reference to a specific route and the value of the average power dissipated. Moreover, an analysis of advantages and disadvantages of bogie designs has made it possible to consider the most appropriate bogie design in terms of ensuring the energy efficiency. In this case, the bogie design with the wheels with the perspective construction scheme can be considered as the optimal option
Analysis of tunnel excavation based on linear DFN-FEM modelling
Get PDFSimulations of tunnel excavations have to take into account the natural occurrence of joints and faults in the surrounding rock mass, which dominantly control its mechanical response. In this paper, we present work in progress toward 3D finite element analysis of excavation using equivalent rock-mass properties derived from stochastically generated discrete fracture networks (DFNs). The equivalent stiffness is determined by volume averaging. Presently, we solve the problem linearly for an incremental change of the stress state. The fracture’s stiffness is assumed to depend on the initial normal stress acting in direction normal to it. However, within the solved incremental step, we assume the fracture’s stiffness to be constant. This assumption is acceptable for small stress changes. Since the fractures represented in the DFN model have preferred directions, the equivalent stiffness is anisotropic
Hygro-mechanical model for concrete pavement with long-term drying analysis
Get PDFConcrete pavements are subjected to the combination of moisture transport, heat transport and traffic loading. A hygro-mechanical 3D finite element model was created in OOFEM software in order to analyse the stress field and deformed shape from a long-term non-uniform drying. The model uses a staggered approach, solving moisture transfer weakly coupled with MPS viscoelastic model for ageing concrete creep and shrinkage. Moisture transport and mechanical sub-models are calibrated with lab experiments, long-term monitoring on D1 highway and data from 40 year old highway pavement. The slab geometry is 3.5×5.0×0.29 m, resting on elastic Winkler-Pasternak foundation. The validation covers autogenous and drying strain on the slab. The models predict drying-induced tensile stress up to 3.3 MPa, inducing additional loading on the slab, uncaptured by current design methods
Influence of Electrode Surface Evolution on the Properties of High-current Vacuum Arcs in Switching Applications
Get PDFProperties of high-current vacuum arcs in dependence on electrode surface status have been studied. The AC current pulses with 16kA (rms) at 50Hz have been applied to spiral contact system made of conventional CuCr material. Each contact pair was loaded with 20 shots. Arc diagnostics comprises arc current and voltage measurements as well as various optical diagnostics. Two high-speed cameras were used for analysis of arc dynamics. Near infrared radiation spectroscopy was applied for determination of the anode surface temperature after the arc extinguishing. The results show clear changes in arc dynamics and anode surface temperature with progressing surface ageing
Length of transfer time between connecting trains – is there an ideal value?
Get PDFQuality public transport is an essential part of global mobility. In general, there is an effort to ensure that as many transport users as possible use public transport. The public transport subsystems also include rail transport. Nowadays, traveling by train is not only a matter of overcoming longer distances in national and international transport, but also a matter of daily commuting to work, school or service. Suburban rail transport is usually part of integrated transport systems, the principle of which is the possibility to use several types of means of transport in one journey per ticket. An indicator of the proper functioning of these systems is the existence of quality and convenient transfer dates times and reliable transfer links that minimize waiting times and total time spent on transportation. Within these systems, there is no network-specific maximum transfer time, which usually depends on the technical solution of the transfer point, the distance that passengers have to cover between vehicles or check-in technology (for example, front door boarding, turnstiles, etc.). the ideal value of the transfer time in terms of the probability that the passenger will not miss the connection and at the same time represents different aspects of the view of this issue. This is on the specific route Ostrava – Prague, which is the busiest in the Czech Republic. Within it, two reference links will be selected (one for each direction), the mean value of the delay in the stations with connections and other statistical indicators will be determined. Furthermore, a simulation of train delays is created using the Monte Carlo method, from which the probability of a connection is determined and subsequently the degree of dissatisfaction with the route is determined while maintaining the current connections. From which a transfer time is subsequently identified in which the probability of passing is as low as possible, but at the same time in normal situations passengers do not have to wait too long
Cooperation of active steering control of wheelsets with subsystems of an autonomous urban rail vehicle
Get PDFThe paper presents the motivations for the application of actively controlled elements in the running gear of a rail vehicle and the challenges that need to be addressed before deploying vehicles with actively controlled elements in real operation. Furthermore, the paper presents the design of an active element concept and its control for steering the axles of an urban rail vehicle to improve the vehicle’s passage through small radius curves. The design takes into account the fundamental issues of cost and safety of the application of active elements, which are addressed in the presented control design by using data from autonomous driving subsystems such as the environmental database or the anti-collision system
Comparative study of state space averaging and PWM with extra element theorem techniques for complex cascaded DC-DC Buck converter
Get PDFUntil now, most commonly used state space averaging and PWM techniques have been applied to different converter topologies and their advantages and disadvantages were stated. However, the superiority of an analytical technique was not justified based on a parametric comparison of these techniques for the same converter topology. Hence, in this paper, first time a comparative evaluation of two commonly used modelling techniques for fourth order converter is presented. The first approach makes use of a state-space averaging of the converter and is based on analytical manipulations using different state representations of the converter. The second approach is based on PWM switch modelling with an extra element theorem and consists of topological manipulations. The two modelling techniques are applied to the same complex cascaded DC-DC Buck converter and a transfer function is obtained. These techniques are compared for different features and the study concludes that state space modelling technique is systematic and less complicated than PWM switch modelling with an extra element theorem for a higher order converter
Self-interference cancellation in underwater acoustic communications systems using orthogonal pilots in IBFD
Get PDFThis paper proposes a Self-interference (SI) cancellation system model of Underwater acoustic (UWA) communication for in-band full-duplex (IBFD) technology. The SI channel is separated from the Far channel by exploiting a concurrently orthogonal pilot channel estimation technique using two orthogonal frequency-division multiplexing (OFDM) blocks to establish orthogonality between them based on a unitary matrix. Compared to the half-duplex channel estimator, the mean squared error (MSE) and the bit error rate (BER) provided strong evidence for the efficiency of the proposed SI cancellation. Since full-duplex systems are more efficient than half-duplex ones, the proposed approach might be seen as a viable option for them. The proposed method proved effective when used with a fixed full-duplex (FD) position and FD shifting of up to 4°. Different channel lengths and distances are adopted to evaluate the proposed method. Initial findings indicate that MSE for the SI channel minimum mean-square error (MMSE) estimator at 20 dB is 0.118 · 10−3, for fixed FD. In addition, this paper presents a geometry channel model for the Far channel in the IBFD underwater communication system that describes the propagation delay of the multipath reflection. The simulation results for the multipath propagation delay spread are similar to the traditional results, with the delay spread of the suggested model reaching (79 ms), which is close to the Bellhop simulator result (78 ms)
Parametric optimisation of friction stir welding on aluminium alloy (EN AW-1100) plates
Get PDFFriction stir welding is a solid-state welding process used extensively for aluminium alloys. EN AW-1100 alloy is mostly used for its exceptional corrosion resistance, high ductility, high thermal and electrical conductivities, and cost-effectiveness. This study is focused on the optimisation of friction stir welding parameters to achieve enhanced mechanical properties of 5mm thick EN AW-1100 alloy plates welded with a single pass, using Taguchi L9 orthogonal array and ANOVA analysis. Experimental results revealed that maximum tensile strength of 79 MPa and percentage elongation of 38.87 % were achieved. The maximum Vickers hardness achieved in the stir zone was 34.15. These results were used for optimisation using Minitab and it was determined that 2000 RPM, 30 mm·min−1 traverse speed and square probe profile came out to be the best parameters for maximum tensile strength. 4000 RPM, 30 mm·min−1 traverse speed and square probe geometry were the best parameters for maximum hardness in the stir zone. ANOVA analysis showed that the most significant parameter for tensile strength was traverse speed. None of the considered parameters were influencing the hardness value in the stir zone at a 95 % confidence level
RESEARCH AND APPLICATION OF U-BIT CONSTRUCTION METHOD IN SUBWAY STATION ENGINEERING LOCATED IN SATURATED SOFT SOIL AREA
Get PDFIn order to solve the problems existing in the construction of underground structures located in the downtown of saturated soft soil area, such as insufficient construction site, complex adjacent structures and great impact on the surrounding environment, the construction method of underground bundled integrate tunnel(U-BIT) is proposed. In this method, after steel pipes jacking completed, concrete is filled into the pipes, and prestress is tensioned to make each independent pipe combined to form a whole bearing structure, so as to achieve the purpose of reducing the size of structural components, improving the structural stiffness and bearing capacity. Based on the structural mechanical properties test and the project of Wuding Road Station of Shanghai Metro Line 14, the failure mechanism of bundled integrate structure, the tension technology of prestressed tendons in narrow space and the variation rules of ground surface subsidence are systematically studied. The research shows that structural seam sections will be destroyed before pipe sections, so ensuring the mechanical performance of seam sections is very important to make sure the structural safety. Since each independent pipe is combined to form an overall stable structure under the prestress effect, the subsequent soil excavation has little influence on the tension of prestressed tendons and ground surface deformation. Therefore, the above construction method can control the ground surface subsidence effectively and reduce the influence of underground engineering construction on the surrounding environment.