This study proposes an alternative method to calculate the transient responses of multi-conductor overhead transmission lines based on ABCD representation, recursive convolutions and numerical method ...for rational approximation in the frequency-dependent curves. In the classical universal line model, the characteristic admittance matrix ${\bi Y}_{\rm c}\lpar \omega \rpar $Yc(ω) and propagation matrix ${\bi H}\lpar \omega \rpar $H(ω) are represented by rational functions. In ${\bi H}\lpar \omega \rpar $H(ω), previous and correct identification of the modal travelling times is required. However, these modal travelling times are estimated numerically, which do not offer good accuracy in some cases. This fact has a considerable effect on the rational representation of ${\bi H}\lpar \omega \rpar $H(ω) itself and consequently on the transient responses. In the alternative method, a previous estimation of the modal travel times is unnecessary because when using the ABCD representation for each propagation mode, a direct relation exists between the currents and tensions of the receiving and sending ends. These relationships are fitted by smooth rational functions, and then, using recursive convolution methods, the authors obtain the explicit equations of the currents and voltages to calculate the transient responses. The results demonstrate that the alternative method is accurate when compared with the frequency-domain solution of the transmission line transformed to the time domain using the numeric Laplace transform and with the Bergeron method.
Gröna tåget (the Green Train) is a research and development project with the aim to develop a high-speed tilting train concept for the Swedish and Nordic markets. Competition with other modes needs ...to be evaluated, especially as regards travelling times and fares, with special attention paid to domestic airlines.
For new trains, gains in travelling times and lower operational costs can be expected. Model calculations of operational costs for domestic air stages and high-speed trains, respectively, show that high-speed trains have lower costs per available seat kilometer. Train operators can meet competition with fares from coaches and air carriers provided they introduce yield management. The primary competition is about travelling times. Gröna tåget would increase the train’s attractiveness and win over some travel from airlines.
This paper describes a case study in which travelling-time implications for siting health-care facilities were examined for one of the health-care regions in the UK. The results of the study were ...produced to assist a planning consortium with a specific problem of siting a regional specialty. The accessibility of the sites was measured in terms of travelling-time distributions for the population of the county of Essex, a rural part of the North-East Thames Regional Health Authority. The results show that the optimal selection of site(s) in Essex is dependent on the service provided by centres outside Essex and the relative importance of short and long travelling-times.
This paper proposes a new method to measure the axial stress of bolt based on the combination of first trailing (T1) wave and shear (S) wave ultrasound using an electromagnetic acoustic transducer ...(EMAT). T1 wave is generated by the mode conversion of S and longitudinal (L) waves. By analyzing the formation and propagation path of the T1 wave in bolt through the finite element (FE) model, the travelling time of T1 is calculated. The analysis indicates that the axial stress of bolt can be measured combining the travelling times of T1 wave and S wave. The sensitivities of S, L and T1 waves to the changes of bolt axial stress are analyzed. The experimental results show that the method based on the combination of T1 and S waves ultrasound using an EMAT can measure the bolt axial stress accurately. Compared to the method based on the combination of L and S waves, the proposed method has lower measurement errors. The relative error is less than 1.8 %.
We consider travelling times of billiard trajectories in the exterior of an obstacle K on a two-dimensional Riemannian manifold M. We prove that given two obstacles with almost the same travelling ...times, the generalised geodesic flows on the non-trapping parts of their respective phase-spaces will have a time-preserving conjugacy. Moreover, if M has non-positive sectional curvature, we prove that if K and L are two obstacles with strictly convex boundaries and almost the same travelling times then K and L are identical.
•A MILP formulation for the inventory routing problem with time-dependent travelling times.•A novel TD-IRP benchmark based on real-life routing data.•Showing the relevance of optimising the IRP with ...time-dependent travelling times.•A matheuristic determining clients to visit and quantity to deliver first and routing second.•The matheuristic proves very efficient with small gaps to the best lower bounds found.
In this paper, we consider a variant of the Inventory Routing Problem (IRP), the Time-Dependent IRP (TD-IRP). The TD-IRP extends the routing component of the IRP by making the travelling time between two locations no longer constant but depending on the departure time. In order to investigate the relevance of considering time-dependent travelling time functions, a set of new benchmark instances based on real-data is assumed. Numerical experiments show that optimising with time-dependent travelling times is cost-efficient, but computationally challenging. Thus, we propose a matheuristic that decomposes the problem, based on the observation of the structure of optimal TD-IRP solutions. The proposed matheuristic defines the set of clients to visit and the quantity to deliver for each period first and solves the routing problem second. Numerical experiments prove it to be very efficient and yield solutions with small gaps to the best lower bounds found. Because it separates the routing problem, the proposed matheuristic opens the possibility to solve the TD-IRP very efficiently by taking advantage of the rich literature on time-dependent routing problems.
This paper studies the optimization of discretionary after-sales services with spare parts consumption and repairman travel. Discretionary service means that the service quality and spare parts ...consumption are determined by the service provider. We assume that a long service time enables the service provider to perform a thorough repair, which leads to a high repair quality and low spare parts consumption. Each service encounter comprises both repairman travel and repair service steps. We find that the dual concerns of service quality and spare parts consumption lead to a counterintuitive impact of the spare parts price: the service provider would decrease the consumption of spare parts even if selling the spare parts becomes more profitable. In addition, we show that the repairman travelling time has different impacts on the optimal service time given the maximum sojourn time constraint. In particular, as the repairman travelling time increases, the service provider increases the repair time to keep the repair quality at a high level if no sojourn time is guaranteed; however, if a maximum sojourn time is guaranteed, the service provider decreases the repair time to meet the promise.
Billiard trajectories (broken generalised geodesics) are considered in the exterior of an obstacle K with smooth boundary on an arbitrary Riemannian manifold. We prove a generalisation of the ...well-known Santalo's formula. As a consequence, it is established that if the set of trapped points has positive measure, then for all sufficiently small smooth perturbations of the boundary of K the set of trapped points for the new obstacle obtained in this way also has positive measure. More generally the measure of the set of trapped points depends continuously on perturbations of the obstacle K. Some consequences are derived in the case of scattering by an obstacle K in IRn. For example, it is shown that, for a large class of obstacles K, the volume of K is uniquely determined by the average travelling times of scattering rays in the exterior of K.
Travelling times in scattering by obstacles Noakes, Lyle; Stoyanov, Luchezar
Journal of mathematical analysis and applications,
10/2015, Letnik:
430, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The paper deals with some problems related to recovering information about an obstacle in a Euclidean space from certain measurements of lengths of generalised geodesics in the exterior of the ...obstacle. The main result is that if two obstacles satisfy some generic regularity conditions and have (almost) the same travelling times, then the generalised geodesic flows in their exteriors are conjugate on the non-trapping part of their phase spaces with a time preserving conjugacy. Apart from that a constructive procedure is described that shows how to recover an obstacle consisting of two convex domains in the plane from travelling times.
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