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181.
《Optimization methods & software》2012,27(4):573-585
Interior point (IP) algorithms for Min Cost Flow (MCF) problems have been shown to be competitive with combinatorial approaches, at least on some problem classes and for very large instances. This is in part due to availability of specialized crossover routines for MCF; these allow early termination of the IP approach, sparing it with the final iterations where the Karush Kuhn-Tucker (KKT) systems become more difficult to solve. As the crossover procedures are nothing but combinatorial approaches to MCF that are only allowed to perform few iterations, the IP algorithm can be seen as a complex ‘multiple crash start’ routine for the combinatorial ones. We report our experiments of allowing one primal-dual combinatorial algorithm to MCF to perform as many iterations as required to solve the problem after being warm-started by an IP approach. Our results show that the efficiency of the combined approach critically depends on the accurate selection of a set of parameters among very many possible ones, for which designing accurate guidelines appears not to be an easy task; however, they also show that the combined approach can be competitive with the original combinatorial algorithm, at least on some ‘difficult’ instances. 相似文献
182.
An improved bacterial foraging algorithm for combined static/dynamic environmental economic dispatch
Nicole Pandit Anshul Tripathi Shashikala Tapaswi Manjaree Pandit 《Applied Soft Computing》2012,12(11):3500-3513
Economic dispatch is carried out at the energy control center to find out the optimal output of thermal generating units such that power balance criterion is met, unit operating limits are satisfied and the fuel cost is minimized. With growing environmental awareness and strict government regulations throughout the world, it has become essential to optimize not only the total fuel cost but also the harmful emissions, both, under static as well as dynamic conditions. The static environment economic dispatch finds the optimal output of generating units for a fixed load demand at a given time, while the dynamic environmental economic dispatch schedules the output of online generators with changing power demands over a certain time period (normally one day) so as to minimize these two conflicting objectives, simultaneously. In this paper, the price penalty factor approach is employed for simultaneous minimization of cost and emission. The generator ramp rate constraints, non-convex and discontinuous nature of cost function and the large number of generators in practical power plants, make this problem very difficult to solve. Here, a fuzzy ranking approach is employed to identify the solution which offers the best compromise between cost and emission objectives. 相似文献
183.
Kalyanmoy Deb Francisco Ruiz Mariano Luque Rahul Tewari José M. Cabello José M. Cejudo 《Applied Soft Computing》2012,12(10):3300-3311
Design, implementation and operation of solar thermal electricity plants are no more an academic task, rather they have become a necessity. In this paper, we work with power industries to formulate a multi-objective optimization model and attempt to solve the resulting problem using classical as well as evolutionary optimization techniques. On a set of four objectives having complex trade-offs, our proposed procedure first finds a set of trade-off solutions showing the entire range of optimal solutions. Thereafter, the evolutionary optimization procedure is combined with a multiple criterion decision making (MCDM) approach to focus on preferred regions of the trade-off frontier. Obtained solutions are compared with a classical generating method. Eventually, a decision-maker is involved in the process and a single preferred solution is obtained in a systematic manner. Starting with generating a wide spectrum of trade-off solutions to have a global understanding of feasible solutions, then concentrating on specific preferred regions for having a more detailed understanding of preferred solutions, and then zeroing on a single preferred solution with the help of a decision-maker demonstrates the use of multi-objective optimization and decision making methodologies in practice. As a by-product, useful properties among decision variables that are common to the obtained solutions are gathered as vital knowledge for the problem. The procedures used in this paper are ready to be used to other similar real-world problem solving tasks. 相似文献
185.
提出一种带有局部空间项控制因子的图割光流估计算法,能判断和处理光流场的平移遮挡现象。文中分析了平移遮挡的形成机理,构造了遮挡判别公式,基于本次的正向和反向光流场,依靠遮挡判别结果调节局部空间项控制因子,建立下次的能量泛函,加强背景区域对遮挡区域的平滑作用,隔绝运动区域对遮挡区域的平滑作用,从而构造出新结构的网络流图。另外,该算法被证明可以阻断遮挡误判在各次图割优化过程间的传递,从而使逐次α-扩散移动图割光流算法具有自适应处理遮挡的能力。通过与Ground-truth光流场的实验对比,表明该算法能较好地判断与处理遮挡导致的光流场无效区域。 相似文献
186.
提出一种在LUV空间中基于多层次化结构Nystrm方法的自适应谱聚类算法。首先引入LUV色彩空间,避免了RGB色彩空间中色彩辨别阈对分割的影响,在纹理、边缘区域取得了更好的分割效果;其次将谱聚类算法中基于多层次化结构的方法和基于Nystrm采样的方法结合起来,有效减少了运算时间、解决了数据量较大时计算过程中内存溢出的问题;最后在K均值聚类中通过对特征间隙(eigengap)的分析,自适应地选择K值的大小,解决了自动确定聚类数目的问题。将提出的方法在LUV色彩空间中和RGB色彩空间中分别进行图像分割实验,结果表明在LUV色彩空间中取得效果更加理想。同时也将提出的算法与基于Nystrm方法的谱聚类算法(spectral clustering-Nystrm,SC-N)进行比较。实验结果表明,该算法在数据运算量、运行时间和分割结果上都优于SC-N方法。 相似文献
187.
针对未知环境中障碍物种类多样性和位置不确定性的特点,提出了基于约束点的路径规划方法。首先对机器人在未知环境中检测到的局部障碍物信息进行分类和几何特征属性描述,得其约束点信息,然后引入改进后的A*算法,将其搜索范围局限于约束点上,计算约束点的评价函数值后得到子目标点,机器人到达子目标点后,若陷入死区,则采取回溯路径策略,重新选择子目标点,否则根据该点所属的障碍物种类采取跨越或绕行避障策略,最后移动机器人在未知环境中顺利到达目标点。仿真研究说明本文提出的路径规划方法具有可行性和有效性。 相似文献
188.
A network of powerful personal computers, linked by a high-speed local area network, is being seen increasingly as an alternative to a traditional centralized time-sharing operating system. The PULSE project is investigating how such a system may be constructed to give the benefits of a self-sufficient personal computer to each user without losing the facilities for communication and sharing of data inherent in centralized systems. In particular, a distributed file system has been built which provides a single global UNIX 1 UNIX is a trademark of Bell Laboratories. -like hierarchy, with a consistent appearance when accessed from any machine. Replicated copies of files are maintained to improve reliability, increase performance, and enable each machine to run stand-alone, albeit with reduced facilities. 相似文献
189.
Dynamic light scattering is a suitable method for the investigation of transport properties such as the thermal diffusivity of optically transparent fluids. The main advantages of the method are its quickness, the fact of the thermodynamic state of equilibrium of the sample (gradients are not required), and the relatively simple evaluation of data without the necessity of calibration. However, an insufficient production of intensity of scattered light may be a limiting effect. For that reason the vicinity of the gas-liquid critical point represents the classical range of application. In this paper, it is shown that by means of an appropriate choice of experimental apparatus, measurements are also feasible in an extended range of states. Broad regions around critical points of three pure fluids (sulfur hexafluoride, SF6; ethane, C2H6; nitrous oxide, N2O) over temperature ranges ¦T-T
c¦ of 0.02 to 50 K and density ranges (/c) of 0.2 to 2 were investigated. In this region the thermal diffusivity shows great variations with temperature and density and cannot be described by means of ideal-gas behavior or relations for liquids. The measurements were carried out along the coexistence curve for both phases, along the critical isochore and along some isotherms with TT
c. The measured or calculated density, pressure, and thermal diffusivity data as well as some correlations are presented. 相似文献
190.
采用16Mn钢非承载十字焊接接头疲劳试验结果对使用Dang Van准则的疲劳评定局部方法进行了研究。结果表明,有限元分析中应力集中区单元尺寸对局部参量计算有明显影响,为获得比较合理的预测结果需对焊趾应力集中区所划分的单元尺寸限定,当接头焊趾半径在0.15-0.8mm变化时应选择最小单元尺寸0.32-0.62mm计算局部参量;在此基础上Dang Van准则可以对焊态接头做出合理的评定,但Dang Van建议的卢值偏安全。此外,通过计算发现焊趾半径只影响局部很小区域(约0.5mm内)的应力集中分布,在某一深度(约0.5mm)后存在稳定的应力集中,因而建议采用距应力集中区最大应力处某一深度的应力参数计算Dang Van局部参量可能更为合理,这将减小局部参数对焊趾半径及单元尺寸的依赖性。 相似文献