Developing a dynamic neighborhood structure for an adaptive hybrid simulated annealing – tabu search algorithm to solve the symmetrical traveling salesman problem

This paper applies a hybrid simulated annealing – tabu search algorithm to solve the Traveling Salesman Problem (TSP). Fully considering the characteristics of the hybrid algorithm, we develop a dynamic neighborhood structure for the hybrid algorithm to improve search efficiency by reducing the randomness of the conventional 2-opt neighborhood. A circle-directed mutation is developed to achieve this dynamic neighborhood structure. Furthermore, we propose adaptive parameters that can be automatically adjusted by the algorithm based on context specific examples. This negates the need to frequently readjust algorithm parameters. We employ benchmarks obtained from TSPLIB (a library of sample instances for the TSP) to test our algorithm, and find that the proposed algorithm can obtain satisfactory solutions within a reasonable amount of time. The experimental results demonstrate that the proposed hybrid algorithm can overcome the disadvantages of traditional simulated annealing and tabu search methods. The results also show that the dynamic neighborhood structure is more efficient and accurate than the classical 2-opt. Also, adaptive parameters are appropriate for almost all of the numerical examples tested in this paper. Finally, the experimental results are compared with those of other algorithms, to demonstrate the improved accuracy and efficiency of the proposed algorithm.     

A meta-heuristic based goal-selection strategy for mobile robot search in an unknown environment

The single-robot search problem in an unknown environment is defined as the problem of finding a stationary object in the environment whose map is not known a priori. Compared to exploration, the only difference lies in goal selection as the objectives of search and exploration are dissimilar, i.e. a trajectory that is optimal in exploration does not necessarily minimize the expected value of the time to find an object along it. For this reason, in this paper we extend the preliminary ideas presented in Kulich et al. [1] to a general framework that accounts for the particular characteristics of the search problem. Within this framework, an important decision involved in the determination of the trajectory can be formulated as an instance of the Graph Search Problem (GSP), a generalization of the well-known Traveling Deliveryman Problem (TDP) which has not received much attention in the literature. We developed a tailored Greedy Randomized Adaptive Search Procedure (GRASP) meta-heuristic for the GSP, which generates good quality solutions in very short computing times and is incorporated in the overall framework. The proposed approach produces very good results in a simulation environment, showing that it is feasible from a computational standpoint and the proposed strategy outperforms the standard approaches.     

Force exertion in awkward working postures-strength capability while twisting or working overhead

Isometric strength data have been collected for three of the awkward work situations often imposed by workplace constraints in industry, as found in jobs such as maintenance and repair. The effects of the task layout factors (location of the workpiece, reach distance and direction of force exertion) were investigated and the data has been tabulated to show the degree to which strength may be reduced in different situations. Strength measurements in the present study were found to be considerably higher than previous measurements, apparently due to differences in instructions on foot placement that were given to subjects, which indicates that even small constraints on posture within the workplace may have large effects on the ability to exert force.     

一起电动单梁起重机脱轨坠落事故的分析

本文介绍了一起电动单梁起重机运行脱轨坠落的事故案例，分析了造成事故的直接原因和间接原因，汇总了起重机运行啃轨故障的常见致因，提出了预防起重机坠落事故的管理手段和技术措施，对预防和减少同类事故具有鼍示意义。     

Effect of working position and cold environment on muscle activation level and fatigue in the upper limb during manual work tasks

Several occupational groups are exposed to periods of low ambient temperatures while performing manual work tasks outdoors. Work tasks typically include heavy lifting, tool handling, and overhead work. This study evaluated the effect of working position and cold environment on muscle activation level (%RMS_max) and fatigue in the upper limb during manual work tasks. Fourteen male participants (25 ± 3 years, 80.9 ± 6.4 kg, 182 ± 5 cm) completed a 2-h test protocol consisting of five test periods alternating with four work periods, wearing identical sets of clothing, under cold (−15 °C) and control (5 °C) conditions. The work periods consisted of manual work at the hip level, manual overhead work, and a lifting exercise. The test periods consisted of isometric maximal voluntary contractions (MVC) and seated rest. Skin temperatures decreased during cold exposure, especially in the extremities. %RMS_max in the forearm was higher in the cold condition both during overhead work and work at the hip level than that for the same work in the control condition, especially at the end of the test when the difference was approximately 25% (equating to 2–3 %RMS_max). For the middle deltoid muscle, the %RMS_max was approximately three times (or 10 %RMS_max) higher during overhead work than work at the hip level, but there was no additional cost of working in the cold. Signs of deltoid muscle fatigue (decrease in electromyography median power frequency and an increase in %RMS_max) were observed during the overhead work periods in both temperature conditions. No decrease in MVC, as a sign of overall muscle fatigue, was observed in either condition.Relevance to industryThis study demonstrated that when wearing suitable cold-weather protective clothing, the adverse effect of work posture is much higher than that of cold on muscle demand and physical strain.     

LPPTE: A lightweight privacy-preserving trust evaluation scheme for facilitating distributed data fusion in cooperative vehicular safety applications

Vehicular networks have tremendous potential to improve road safety, traffic efficiency, and driving comfort, where cooperative vehicular safety applications are a significant branch. In cooperative vehicular safety applications, through the distributed data fusion for large amounts of data from multiple nearby vehicles, each vehicle can intelligently perceive the surrounding conditions beyond the capability of its own onboard sensors. Trust evaluation and privacy preservation are two primary concerns for facilitating the distributed data fusion in cooperative vehicular safety applications. They have conflicting requirements and a good balance between them is urgently needed. Meanwhile, the computation, communication, and storage overheads will all influence the applicability of a candidate scheme. In this paper, we propose a Lightweight Privacy-Preserving Trust Evaluation (LPPTE) scheme which can primely balance the trust evaluation and privacy preservation with low overheads for facilitating the distributed data fusion in cooperative vehicular safety applications. Furthermore, we provide exhaustive theoretical analysis and simulation evaluation for the LPPTE scheme, and the results demonstrate that the LPPTE scheme can obviously improve the accuracy of fusion results and is significantly superior to the state-of-the-art schemes in multiple aspects.     

Adapting overhead lines to climate change: Are dynamic ratings the answer?

Thermal ratings of overhead lines (OHL) are determined by the current being carried and ambient climatic conditions. Higher temperatures as a result of climate change will give rise to lower ratings, and thus a reduction in current-carrying capacity across the electricity network. Coupled with demand growth and installation of renewable generation on weaker sections of the network, this could necessitate costly reinforcements and upgrades. Previous UK-based work applying a subset of data from the UK Climate Projections model (UKCP09) has indeed indicated likely reductions in the steady-state OHL ratings under worst-case temperature increases. In the present work, time series data from the full UKCP09 probabilistic climate change modelling framework, including an additional algorithm to incorporate hourly wind conditions, is applied to OHL ratings. Rather than focus purely on worst-case conditions, the potential for an increased risk of exceeding nominal ratings values on thermally constrained OHL is analysed. It is shown that whilst there is a small increase in risk under future climate change scenarios, the overall risk remains low. The model further demonstrates that widespread use of real-time dynamic rating systems are likely to represent the most cost-efficient adaptation method for lines which are frequently thermally constrained.     

基于AMESim液压冲击钻机行走液压系统建模与分析

液压冲击钻机的行走装置是整机的运行部分,也是整台设备的支承基座,其液压系统的设计合理与否,对整机的性能起着关键性的作用,因此,分析其液压系统性能对于了解机器性能十分必要。研究行走装置液压系统的工作原理,基于AMESim搭建所研究系统的仿真模型,确定仿真参数后,对模型进行仿真分析,获取冲击钻机行走装置液压系统速度特性曲线和各油口的压力特性曲线,对设计进行分析验证,以检验其准确性与合理性,为该类系统的改进设计和行走装置的优化等提供理论依据和研究方法。     

一种用于起重机起升系统的平衡阀动态特性分析与结构优化

对一种用于起重机起升系统的平衡阀进行动态特性分析,讨论了不同工况下平衡阀的工作原理,找出影响系统稳定性的各项因素,分析了不同阻尼孔直径和平衡阀阀口截面梯度对平衡阀流量特性的影响,同时提出结构优化方案。仿真和测试结果表明:所提出的优化方案可以有效改善平衡阀的动态特性,减小负载下落时系统液压波动现象,为平衡阀的研究设计提供理论支持。     

同步光分组交换网核心节点光分组长度分析

研究了同步光分组交换网中光分组长度的设计及其对一些网络性能参数的影响,分别推导了光分组中开销所占比率、时延及光纤延时线长度与光分组长度的关系,并给出各自相应的理论分析和数值解析,为光分组中分组长度的设计做了基础工作。