不完全柔性制造系统的最优控制

考虑具有随机需求的不完全柔性制造系统的最优控制，系统在各种产品间的切换时间是不可忽略的。运用马尔可夫最优决策过程归纳方法，导出机器服务率的最优控制策略。通过分析最优值函数的性质，证明最优策略具有简单的阈值结构，从而可得到次优生产策略--阈值控制策略。     

离散排序系统中信息流量的控制方法

为了提高网络的工作性能，我们对不同服务器的服务方式进行了研究，本文讨论了离散时间系统中并行服务器信息流切换的控制问题。根据并行服务器网络系统信息流分配的特点，我们建立了一个模糊控制器来决定切换服务的最优策略，使得分组在系统中的平均逗留时间最小。     

按单装配系统中组件生产和库存分配控制策略研究

针对由两种组件、三类顾客需求组成的按单装配系统, 本文研究了其中的组件生产控制与库存分配问题. 在各类顾客需 求是泊松到达过程, 各种组件加工时间服从指数分布的假设下, 我们运用马尔科夫决策理论建立了无限期折扣总成本模型, 根据Lippman转换得到了相应归一化后的离散最优方程, 在此基础之上分析了生产和库存分配联合最优控制策略的结构性质. 本文证明了最优策略是依赖于系统状态的动态策略. 组件的最优生产策略是动态基库存策略, 其中基库存水平是关于系统中其他组件库存水平的非减函数. 而最优的分配策略是动态的阈值策略, 对于只需一种组件构成的顾客需求, 组件的分配阈值是系统中另一组件库存水平的增函数; 而对于同时需要两种组件组成的顾客需求, 其各组件的分配阈值是另一组件库存水平的减函数. 最后通过数值试验给出了各个参数对联合最优控制策略的影响, 并得到了相应的管理启示.     

输入随机的不可靠串行生产线的反馈控制

对于具有随机输入和随机需求的一类串行生产纡系统,利用转移率一致化技术和随机动态规划方法,给出了输入率和服务率分配的最优反馈控制策略,指出 最优控制具有邦一邦形式的开关结构。仿真例子验证了方法的有效性。     

全IP 4G无线网络中的关键问题

第四代移动通讯系统的特点是:多种接入网络和基于IP的传输技术.不同的接入技术使用户在选择服务时有了极大的灵活性,而服务也具有不同的QoS支持、商务类型和服务提供商.在考虑QoS和AAAC的同时,实现向最优网络进行无缝切换不仅要求无缝换手协议,而且要求智能换手决定策略.本文介绍了全IP结构的第四代移动通讯系统的特点和关键技术以及未来的问题和研究方向.     

排队系统定价控制问题的研究综述

定价作为服务系统价值因素的调控机制,在拥塞控制、收益管理和服务质量控制等领域有重要的应用.服务提供商设计定价策略使得系统性能在诱导的顾客行为下达到最优.排队模型是分析服务系统性能的重要模型.本文介绍了排队系统定价控制的基本要素,包括排队模型、顾客行为、性能指标以及定价策略类型,围绕静态定价策略、动态定价策略和优先级定价策略,详细综述了排队系统定价控制的研究现状,然后简要介绍了作者针对排队网络动态定价问题的最新研究进展,最后总结了该领域的研究现状、尚未解决的问题、当前的研究热点以及未来的发展方向.     

提高虚拟空间会议系统传输效率的分层策略研究

降低虚拟空间会议系统(VST)的混频时延和降低混频器数量是一对矛盾的问题．本文研究了VST系统的通信效率与混频器关系，提出了在保证系统通信容忍的时延情况下，选取最少的混频器数量，以及在分层结构中系统通信的最小时延策略．采用这种策略，能够有效地保证VST系统提供较高质量的服务时延和较低成本的混频．     

VOD系统在最优平均性能下的过载问题研究

由于视频点播(VOD)系统打破了以往传统影音服务的局限,可以给用户提供更多的主动性和交互性,因此近年来得到了广泛关注和应用。但在视频点播(VOD)系统中,当媒体服务器处于过载状态时,服务质量和性能都会下降。本文采用Markov决策过程(MDP)中的bias优化方法研究了VOD系统在最优平均性能下的过载问题,使用bias优化算法可在平均性能最优策略集中找到使服务器处于过载状态的稳态概率最小的策略。该策略能够使服务器在长期运行平均服务请求数达到最大的同时,处于过载状态的稳态概率最小。最后,通过一个仿真实例,说明了该算法的有效性。     

打印参数可变模式下3D打印批调度问题研究

研究打印参数可变模式下3D打印批调度问题,旨在对打印任务随机到达的3D打印服务系统进行优化建模.考虑到工作台尺寸的限制以及打印参数层高对打印质量的影响,论文以各个任务队列长度作为系统联合状态,以任务组合以及打印参数层高作为系统的联合控制变量,以提高生产率、减少打印质量损失、节约电能为综合目标,将优化问题描述为半马尔科夫决策过程(SMDP),以便采用策略迭代算法、Q学习等算法求解系统最优调度策略.仿真结果表明,与层高参数固定模式以及先到先服务(FCFS)模式相比,本文求解的批调度策略能够有效提高生产性能.     

从方具有多目标的仿射型诱导策略研究

本文讨论当从方具有多个目标，主方对从方的诱地策略设计问题，给出了最优诱导策略和可诱导域的定义，研究了仿射型诱导策略的存在条件及解的结构形式，并探讨了当主方只具有对从方决策的部分观测时的诱导问题。     

Optimal control structure of an unreliable manufacturing systemwith random demands

This paper considers an unreliable manufacturing system with random processing times and random product demands. The system can produce many part types and its total capacity is constrained by a fixed constant. The objective is to find an optimal service-rate allocation policy between different part types by minimizing the expected discounted inventory and backlog cost. Structural properties of the optimal control policy are investigated. It is shown that the optimal policy is of a switching structure. For producing a one part type case, the optimal control is a threshold policy. For producing a two part types case, the optimal control can be described by three monotone switching curves and its asymptote properties are derived. Numeric examples are given to illustrate the results     

Optimal hedging point control for a failure-prone manufacturing system

This paper considers a manufacturing system with multiple operational modes producing one part type. The part processing time at each operational mode is exponentially distributed and its rate is controllable. The demand arrival is random and described by a Poisson process. By minimizing an infinite-horizon discounted expected cost function, the optimal service rate control is derived. It is proved that the optimal policy is of a hedging point structure by examining the properties of the optimal cost function such as convexity, monotonicity and asymptotic behaviours. The hedging points at different operational modes can be ordered according to their production capacities. The relationships of the hedging points with some system parameters are presented. These structural properties of the optimal control policy are helpful in finding simple and realistic suboptimal policies for practical manufacturing systems. A numerical example is given to demonstrate our results.     

An application of modern control theory to a time-dependent queuing system for optimal operation

‘ Bang-bang ’ optimal closed-loop service policy for a time dependent M/M/l queuing system is derived using optimal control theory. The policy is based on probabilistic (and not stochastic) behaviour of the queue. Computational results are obtained for an illustrative example with non-bang-bang service policy using the conjugate gradient algorithm with bounded control variables. It is interesting to note that the optimal service policy is not sensitive to the arrival rate but to the mean service cost of a customer.     

Optimization analysis of an unreliable multi-server queue with a controllable repair policy

This article deals with an infinite-capacity multi-server queueing system, in which the servers are assumed unreliable and may fail at any time. To conserve energy while delivering reliable service, a controllable repair policy is introduced. With such a policy, the failed servers will be sent to the repair facility only when the number of failed machines in the system arrives at a preset threshold value. A quasi-birth-and-death process is used to model the complex system and the stability condition is examined. The rate matrix is calculated approximately and steady-state stationary distributions are obtained by a matrix-analytic approach. The closed-form expressions of important system characteristics are presented. A cost model is constructed to determine the optimal repair policy, the optimal value of service rate and the optimal value of repair rate. Three heuristic algorithms are employed to deal with the optimization problem. Some numerical results are provided to compare the efficiency of two methods.     

Determination of an optimal configuration of operating policies for direct-input-output manufacturing systems using the Taguchi method

Some modern manufacturing systems have workstations directly integrated with a centralized storage and handling system for work-in-process. We consider a Direct-Inlet-Output manufacturing system(DIOMS) which has a number of machine centers placed along a built-in automated storagejretrieval system(AS/RS). The storagdretrievai(S/R) machine handles parts placed on pallets for the machine centers located at either one or both sides of the AS/RS.

This paper investigates the operational aspect of DIOMS by the Taguchi method. Four operating policies including input sequencing control. dispatching rule for the S/R machine, machine center-based part type selection rule, and storage assignment policy are treated as design factors. For the performance characteristics, man flow time and throughput are adopted. The number of machine centers, the number of part types, demand rate, processing time and the rate of each part type. vertical and horizontal speed of the SIR machM and the size of a local buffer in the machine centers are considered as noise factors in generating various DIOMS environments. A robust design experiment with inner and outer orthogonal arrays are conducted by computer simulation, and an optimal configuration of operating policies is presented which consists of a combination of the level of each design factor. The validity of the optimal configuration is investigated by comparing its SN ratios with those obtained by an experiment with fiill factorial designs.     

Optimal pricing policies for services with consideration of facility maintenance costs

For survival and success, pricing is an essential issue for service firms. This article deals with the pricing strategies for services with substantial facility maintenance costs. For this purpose, a mathematical framework that incorporates service demand and facility deterioration is proposed to address the problem. The facility and customers constitute a service system driven by Poisson arrivals and exponential service times. A service demand with increasing price elasticity and a facility lifetime with strictly increasing failure rate are also adopted in modelling. By examining the bidirectional relationship between customer demand and facility deterioration in the profit model, the pricing policies of the service are investigated. Then analytical conditions of customer demand and facility lifetime are derived to achieve a unique optimal pricing policy. The comparative statics properties of the optimal policy are also explored. Finally, numerical examples are presented to illustrate the effects of parameter variations on the optimal pricing policy.     

服务率不确定的单站点传送带给料加工站系统鲁棒优化控制

研究了服务率不确定情况下的单站点传送带给料加工站(CSPS)系统的鲁棒优化控制问题。在仅知服务率区间的条件下,以CSPS系统的前视距离作为控制变量,将鲁棒优化控制问题建模成不确定参数的半马尔可夫决策过程(SMDP)的极大极小优化问题,在状态相关的情况下,给出全局优化算法进行鲁棒控制策略求解。首先,运用遗传算法求解固定策略下的最差性能值;其次,根据求解得到的最差性能值,运用模拟退火算法求解最优鲁棒控制策略。仿真结果表明,服务率不确定的CSPS系统的最优鲁棒性能代价与服务率固定为区间中值系统的最优性能代价相差不大,并且随着不确定区间的缩小,两者的差值越小,说明了全局优化算法的有效性。     

WiMAX系统中的一种最优化准入控制方法

WiMAX正逐渐成为"最后一公里"无线宽带接入的主要解决方案,在WiMAX系统中,准入控制(AC)起着很重要的作用。目前关于AC策略最优化的研究主要考虑服务提供商的利益,即收益最大化,而很少考虑用户的要求。AC策略在收益最大化的基础上增加了关系用户利益的两个约束条件,即阻断率和带宽利用率。实验结果表明,该方法在收益、阻断率、带宽利用率三方面都有良好的性能,兼顾了服务提供商和用户的利益。     

Optimal control of the service rate of an exponential queuing network using Markov decision theory

An exponential queuing network of two service stations is considered. The service rate at each station can either be fast or slow. A policy in which the service rate to be used at each station is specified as a function of the state of the system is investigated in order to minimize a given objective cost function. Howard's policy space algorithm is used to characterize the form of the optimal policy. Results show that the optimal policy is a simply connected one and of montone structure.