Abstract

The paper reports the development and application of a SPH (smoothed particle hydrodynamics) based simulation of rapid filling of pipelines, for which the rigid-column model is commonly used. In this paper the water-hammer equations with a moving boundary are used to model the pipe filling process, and a mesh-less Lagrangian particle approach is employed to solve the governing equations. To assign boundary conditions with time-dependent (upstream) and constant (downstream) pressure, the SPH pressure boundary concept proposed recently in literature is used and extended. Except for imposing boundary conditions, this concept also ensures completeness of the kernels associated with particles close to the boundaries. As a consequence, the boundary deficiency problem encountered in conventional SPH is remedied. The employed particle method with the SPH pressure boundary concept aims to predict the transients occurring during rapid pipe filling. It is validated against laboratory tests, rigid-column solutions and numerical results from literature. Results obtained with the present approach show better agreement with the test data than those from rigid-column theory and the elastic model solved by the box scheme. It is concluded that SPH is a promising tool for the simulation of rapid filling of pipelines with undulating elevation profiles. Keywords: Rapid filling of pipelines; Undulating elevation profile; SPH

Abstract

This paper presents a new approach for automated merging multiple aircraft flows in a busy Terminal Maneuvering Area (TMA). This work is motivated by the current overloaded airspace in the Beijing Capital international airport, the highlighted delay in the China air transportation and the need of more efficient methods to help air traffic controllers. Present research consists of a new approach to optimize a set of aircraft planned to land at a given airport based on multi-agents technique, which is automated generating comprehensive sequencing plan and conflicts-free trajectories.The architecture of the system is based on a Point Merge (PM) route structure to enable expediting or delaying aircraft while staying on lateral navigation mode.The whole system is designed by two main models to manage the process of arriving flows: Sequencing leg and Link. And then, 4 kinds of agents are designed to support the implementation of this automated system: aircraft agent, flow manager agent, conflict detection and resolution agent and 4D trajectory planning agent. We consider the 4D trajectory-based operation situation in TMA and apply different wake turbulence constraint in these two models. Finally, aconclusion is made and future work is outlined. Refereed/Peer-reviewed

Abstract

Under an increasing maritime transport in the Baltic Sea, and especially in the Gulf of Finland, the possibility of environmental harm and accidents due to shipping pressure is growing. To counteract increasing risks, adequate measures for accident prevention and mitigation of environmental consequences are critically important. The Gulf of Finland Mandatory Ship Reporting System (GOFREP) is a the complex socio-technical maritime transport safety management system that has been in efficient operation since 2004 and it is open to further improvement and development. However, environmental safety is not explicitly covered by the GOFREP so far. According to our working hypothesis, the Systems Theoretic Accident Models and Processes (STAMP) can be extended beyond the area of socio-technical system safety into realm of complex eco-socio-technical systems safety. This paper attempts to demonstrate the conceptual potential of STAMP based on adaptive management of the Maritime Spatial Planning processes and integrated safety management of eco-socio-technical maritime transport system.

Abstract

Software-defined networking (SDN) is a cornerstone of next-generation networks and has already led to numerous advantages for data-center networks and wide-area networks, for instance in terms of reduced management complexity and more fine-grained traffic engineering. However, the design and implementation of SDN within wireless sensor networks (WSN) have received far less attention. Unfortunately, because of the multi-hop type of communication in WSN, a direct reuse of the wired SDN architecture could lead to excessive commu- nication overhead. In this paper, we propose a cluster-based flow management approach that makes a trade-off between the granularity of monitoring by an SDN controller and the communication overhead of flow management. A network is partitioned into clusters with a minimum number of border nodes. Instead of having to handle the individual flows of all nodes, the SDN controller only manages incoming and outgoing traffic flows of clusters through border nodes. Our proof-of- concept implementations in software and hardware show that, when compared with benchmark solutions, our approach is significantly more efficient with respect to the number of nodes that must be managed and the number of control messages exchanged.

Abstract

This article presents an in-situ comparative analysis and power quality tests of a newly developed photovoltaic charging system for e-bikes. The various control methods of the inverter are modeled and a single-phase grid-connected inverter is tested under different conditions. Models are constituted for two current control methods the proportional resonance and the synchronous rotating frames. In order to determine the influence of the control parameters, the system is analyzed analytically in the time domain as well as in the frequency domain by simulation. The tests indicated the resonance instability of the photovoltaic inverter. The passivity impedance-based stability criterion is applied in order to analyze the phenomenon of resonance instability. In conclusion, the phase-locked loop (PLL) bandwidth and control parameters of the current loop have a major effect on the output admittance of the inverter, which should be adjusted to make the system stable. Document type: Article

Abstract

The electric travelling salesman problem with time windows (ETSPTW) is an extension of the well-known travelling salesman problem with time windows (TSPTW). The ETSPTW additionally considers recharging operations of the electric vehicle at identical charging stations. However, different charging technologies used at public or private stations result in different charging times of the electric vehicles. Therefore, this study extends the ETSPTW by additionally considering charging operations at customer locations with different charging rates, called hereafter the electric travelling salesman problem with time windows and mixed charging rates (ETSPTW-MCR). To the best of our knowledge, this is the first study that considers both private and public charging stations for the ETSPTW. In addition to the extended version of the ETSPTW, this paper introduces a new and effective hybrid Simulated Annealing/Tabu Search (SA/TS) algorithm to solve the ETSPTW-MCR problem efficiently. Distinct from the existing hybridization of SA and TS, the proposed hybrid SA/TS algorithm employs efficient search procedures based on the TSPTW restrictions, a modified solution acceptance criterion, and an advanced tabu list structure. Moreover, an improved dynamic programming procedure is integrated to optimally find the charging station visits in shorter computational times. The proposed hybrid SA/TS is tested on several TSPTW and ETSPTW benchmark problems and compared with well-known solution approaches. Results of these experiments show that the proposed algorithm outperforms the other considered competitor algorithms both with regard to solution quality and computational time. Furthermore, 26 new best results are obtained for the ETSPTW instances. In addition, the hybrid algorithm is applied to a new problem set generated for the ETSPTW-MCR by extending the ETSPTW problems found in the literature. Comparisons with the ETSPTW results show that significant distance savings are found for most of the instances by charging the electric vehicle at customer locations. As a result of the computational studies, it should be concluded that the proposed algorithm is capable of finding efficient and more realistic route plans for the electric vehicles. ispartof: EXPERT SYSTEMS WITH APPLICATIONS vol:134 pages:279-303 status: Published online

Abstract

Urban emergent incidents affect transportation operation and result in the rapid spread of traffic congestion in network, so it's necessary to analyze the dynamic changes of traffic flow distribution under emergent incidents. Therefore, model and algorithm for the dynamic traffic assignment problem under emergent incidents have been highly concerned by government and scholars. This paper proposes a stochastic dynamic traffic assignment (SDTA) model based user optimum considering the loss of node capacity and change of network structure under traffic and environment emergencies. The Nested Logit model is used to describe the departure time and path choice. Then, the variational inequality formulation is proposed and discrete dynamic network loading algorithm is designed and validated by a numerical example. The results show that the model and algorithm can be used to express the development trend of actual dynamic network under emergency. Document type: Article

Abstract

"jats:p"For efficiently increasing the logistic systems, the core specialists’ attention has to be directed to reducing costs and increasing supply chains reliability. A decent attention to costs reduction has already been paid, so it can be stated that in this way there is a significant progress. But the problem of reliability evaluation is still insufficiently explored, particularly, in such an important sphere as inventory management at the dependent demand."/jats:p" "jats:p"In the article there is a suggested methodical approach that allows calculating the safety stock quantity at the dependent demand in view of supply chains reliability requirements; the variants for different inventory management strategies at the dependent demand are examined; optimal strategy choice algorithm and results of total costs calculation in view of the reliability are given. Document type: Article