火电站多目标负荷调度及其算法的研究

对传统意义下负荷调度模型进行修正,同时考虑最小化燃料费用和污染排放量,提出了火电站多目标负荷调度模型;并将强度Pareto进化算法(SPEA2)与并行遗传算法(PGA)相结合对其求解.结果表明:该算法求得的Pareto最优解分布均匀、收敛速度快、寻优能力强,决策者可根据不同的侧重点在Pareto解集中选择最终的满意解.应用该算法对某电厂进行多目标负荷调度,验证了其可行性和有效性.     

帕累托最优在车辆底部防护结构设计中的应用研究

为了提升爆炸冲击环境下车辆的防护性能,针对其底部防护结构设计中大规模计算、强非线性和多优化目标的特点,利用多物质单元与流-固耦合算法仿真车辆的动态响应。通过灵敏度分析,筛选底部结构中钣金件的厚度、几何形状等设计参数,并利用实验设计建立该问题的数学优化模型,结合帕累托最优的多目标遗传算法,得到该优化问题的帕累托解集空间曲面和一个最优设计方案,该方案在不增加结构质量的情况下,能显著提高车辆底部防护性能。     

Transient process relaxation time research under the condition of self-similar traffic input in wireless networks

In the article, the results of measuring the traffic in wireless networks are presented. The results provide evidence of the traffic being notably self-similar. The two following models were developed in order to estimate the parameters of a wireless network operating along with the input traffic being self-similar: a model for systems with no restrictions on the quantity of the orders in the system lines and a model for systems with limited buffer volumes. The two types of incoming traffic that each system was simulated for were the Poisson and self-similar traffic.The main objective of the article is to figure out the relaxation time and dependences of the relaxation time and loss probability on different parameters of the simulated systems.     

Multi-criteria design optimization study of solvent extraction in mixer–settler units

Solvent extraction is considered as a multi-criteria optimization problem, since several chemical species with similar extraction kinetic properties are frequently present in the aqueous phase and the selective extraction is not practicable. This optimization, applied to mixer–settler units, considers the best parameters and operating conditions, as well as the best structure or process flow-sheet. Global process optimization is performed for a specific flow-sheet and a comparison of Pareto curves for different flow-sheets is made. The positive weight sum approach linked to the sequential quadratic programming method is used to obtain the Pareto set.In all investigated structures, recovery increases with hold-up, residence time and agitation speed, while the purity has an opposite behaviour. For the same treatment capacity, counter-current arrangements are shown to promote recovery without significant impairment in purity. Recycling the aqueous phase is shown to be irrelevant, but organic recycling with as many stages as economically feasible clearly improves the design criteria and reduces the most efficient organic flow-rate.     

A multi-objective selection procedure of determining a Pareto set

Ranking and selection (R&S) procedures have been widely studied and applied in determining the required sample size (i.e., the number of replications or batches) for selecting the best system or a subset containing the best system from a set of k alternatives. Most of the studies in the R&S have focused on a single measure of system performance. In many practical situations, however, we need to select systems based on multiple criteria. A solution is called Pareto optimal if there exists no other solution which is better in all criteria. This paper discusses extending a R&S procedure to select a Pareto set containing non-dominated systems. Computational results show that the proposed procedures are effective in obtaining non-dominated systems.     

Multi-objective evolutionary algorithm for SSSC-based controller design

In this paper, an evolutionary multi-objective optimization approach is employed to design a static synchronous series compensator (SSSC)-based controller. The design objective is to improve the transient performance of a power system subjected to a severe disturbance by damping the multi-modal oscillations namely; local mode, inter-area mode and inter-plant mode. A genetic algorithm (GA)-based solution technique is applied to generate a Pareto set of global optimal solutions to the given multi-objective optimization problem. Further, a fuzzy-based membership value assignment method is employed to choose the best compromise solution from the obtained Pareto solution set. Simulation results are presented and compared with a PI controller under various disturbances namely; three-phase fault, line outage, loss of load and unbalanced faults to show the effectiveness and robustness of the proposed approach.     

Bayesian approach to parameter estimation of the generalized pareto distribution

Several methods have been used for estimating the parameters of the generalized Pareto distribution (GPD), namely maximum likelihood (ML), the method of moments (MOM) and the probability-weighted moments (PWM). It is known that for these estimators to exist, certain constraints have to be imposed on the range of the shape parameter,k, of the GPD. For instance, PWM and ML estimators only exist fork>−0.5 andk≤1, respectively. Moreover, and particularly for small sample sizes, the most efficient method to apply in any practical situation highly depends on a previous knowledge of the most likely values ofk. This clearly suggests the use of Bayesian techniques as a way of using prior information onk. In the present work, we address the issue of estimating the parameters of the GPD from a Bayesian point of view. The proposed approach is compared via a simulation study with ML, PWM and also with the elemental percentile method (EPM) which was developed by Castillo and Hadi (1997). The estimation procedure is then applied to two real data sets.     

The multi-criteria minimum spanning tree problem based genetic algorithm

Minimum spanning tree (MST) problem is of high importance in network optimization and can be solved efficiently. The multi-criteria MST (mc-MST) is a more realistic representation of the practical problems in the real world, but it is difficult for traditional optimization technique to deal with. In this paper, a non-generational genetic algorithm (GA) for mc-MST is proposed. To keep the population diversity, this paper designs an efficient crossover operator by using dislocation a crossover technique and builds a niche evolution procedure, where a better offspring does not replace the whole or most individuals but replaces the worse ones of the current population. To evaluate the non-generational GA, the solution sets generated by it are compared with solution sets from an improved algorithm for enumerating all Pareto optimal spanning trees. The improved enumeration algorithm is proved to find all Pareto optimal solutions and experimental results show that the non-generational GA is efficient.     

Variable neighborhood search for multi-objective resource allocation problems

The Resource Allocation Problem (RAP) is a classical problem in the field of operations management that has been broadly applied to real problems such as product allocation, project budgeting, resource distribution, and weapon-target assignment. In addition to focusing on a single objective, the RAP may seek to simultaneously optimize several expected but conflicting goals under conditions of resources scarcity. Thus, the single-objective RAP can be intuitively extended to become a Multi-Objective Resource Allocation Problem (MORAP) that also falls in the category of NP-Hard. Due to the complexity of the problem, metaheuristics have been proposed as a practical alternative in the selection of techniques for finding a solution. This study uses Variable Neighborhood Search (VNS) algorithms, one of the extensively used metaheuristic approaches, to solve the MORAP with two important but conflicting objectives—minimization of cost and maximization of efficiency. VNS searches the solution space by systematically changing the neighborhoods. Therefore, proper design of neighborhood structures, base solution selection strategy, and perturbation operators are used to help build a well-balanced set of non-dominated solutions. Two test instances from the literature are used to compare the performance of the competing algorithms including a hybrid genetic algorithm and an ant colony optimization algorithm. Moreover, two large instances are generated to further verify the performance of the proposed VNS algorithms. The approximated Pareto front obtained from the competing algorithms is compared with a reference Pareto front by the exhaustive search method. Three measures are considered to evaluate algorithm performance: D1_R, the Accuracy Ratio, and the number of non-dominated solutions. The results demonstrate the practicability and promise of VNS for solving multi-objective resource allocation problems.     

多目标进化算法中基于聚集距离调整的分布性保持方法

在经典的非支配排序遗传算法中,基于聚集距离的种群维护策略并不能很好地保持解集的分布性。提出一种改进的基于聚集距离调整的分布性维护策略,根据邻近个体的聚集距离大小关系,保留分布较好的个体。与经典算法NSGA-Ⅱ,PESA-Ⅱ和小生境方法进行比较,实验结果表明,提出的分布性维护策略能较大程度提高分布性,并保持较好的收敛性。