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Using M-integral for multi-cracked problems subjected to nonconservative and nonuniform crack surface tractions
http://ir.lib.ncu.edu.tw/handle/987654321/49841
title: Using M-integral for multi-cracked problems subjected to nonconservative and nonuniform crack surface tractions abstract: In this paper, an energy parameter based on the concept of the M-integral is proposed for describing the fracture behavior of a multi-cracked solid subjected to nonconservative and nonuniform crack surface tractions. By using the M-integral with a suitably chosen closed contour, one can evaluate the 'surface creation energy' (SCE) required for creation of the stressed cracks. Also, it is demonstrated that the property of path-independence holds even under the action of crack surface tractions. Therefore, the singular stress field in the near-tip areas is not directly involved in the calculation so that a complicated finite element model around the crack tips is not required in evaluation of the M-integral. (C) 2011 Elsevier Ltd. All rights reserved.
<br>Theory and experimental study for sliding isolators with variable curvature
http://ir.lib.ncu.edu.tw/handle/987654321/49840
title: Theory and experimental study for sliding isolators with variable curvature abstract: Because a conventional isolation system with constant isolation frequency is usually a long-period dynamic system, its seismic response is likely to be amplified in earthquakes with strong long-period wave components, such as near-fault ground motions. Seismic isolators with variable mechanical properties may provide a promising solution to alleviate this problem. To this end, in this work sliding isolators with variable curvature (SIVC) were studied experimentally. An SIVC isolator is similar to a friction pendulum system (FPS) isolator, except that its sliding surface has variable curvature rather being spherical. As a result, the SIVC's isolation stiffness that is proportional to the curvature becomes a function of the isolator displacement. By appropriately designing the geometry of the sliding surface, the SIVC is able to possess favorable hysteretic behavior. In order to prove the applicability of the SIVC concept, several prototype SIVC isolators, whose sliding surfaces are defined by a sixth-order polynomial function, were fabricated and tested in this study. A cyclic element test on the prototype SIVC isolators and a shaking table test on an SIVC isolated steel frame were all conducted. The results of both tests have verified that the prototype SIVC isolators do indeed have the hysteretic property of variable stiffness as prescribed by the derived formulas in this study. Moreover, it is also demonstrated that the proposed SIVC is able to effectively reduce the isolator drift in a near-fault earthquake with strong long-period components, as compared with that of an FPS system with the same friction coefficient. Copyright (C) 2011 John Wiley & Sons, Ltd.
<br>The Linehaul-Feeder Vehicle Routing Problem with Virtual Depots and Time Windows
http://ir.lib.ncu.edu.tw/handle/987654321/49839
title: The Linehaul-Feeder Vehicle Routing Problem with Virtual Depots and Time Windows abstract: This paper addresses the linehaul-feeder vehicle routing problem with virtual depots and time windows (LFVRPTW). Small and large vehicles deliver services to customers within time constraints; small vehicles en route may reload commodities from either the physical depot or from the larger vehicle at a virtual depot before continuing onward. A two-stage solution heuristic involving Tabu search is proposed to solve this problem. The test results show that the LFVRPTW performs better than the vehicle routing problem with time windows in terms of both objective value and the number of small vehicles dispatched.
<br>The Linehaul-Feeder Vehicle Routing Problem With Virtual Depots
http://ir.lib.ncu.edu.tw/handle/987654321/49838
title: The Linehaul-Feeder Vehicle Routing Problem With Virtual Depots abstract: The problem addressed in this paper-the linehaul- feeder vehicle routing problem with virtual depots (LFVRP-VD)-can be regarded as an extension of the vehicle routing problem. During delivery operation, one large vehicle departs from the physical depot (PD) and services all virtual depots (VDs). A set of small vehicles delivers to customers and, if necessary, reloads either from the PD or from the large vehicle at a VD before continuing work. The objective of the operation is to minimize the total travel and waiting costs for all vehicles. Two heuristics that embed the cost-sharing method and the threshold method are proposed for initial solution construction. Seventeen test problems are extensively examined. The results show that the cost-sharing method outperforms the threshold method in terms of several selected performance measures. In addition, the more candidates available a VD can choose, the better the obtained objective value. Note to Practitioners-Linehaul-feeder vehicle routing problem with virtual depots is practical to the logistics and transportation companies, especially in the urban area where local streets are too narrow or large vehicles are not allowed to enter. Note that the higher the customer demands, the better the benefit of the LFVRP-VD.
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