基于排队的两类顾客易逝品库存控制策略研究

本文采用排队理论在面向两类顾客需求的环境下讨论易逝品库存排队系统控制策略问题。首先刻画面向两类顾客服务且具有马尔科夫结构的易逝品库存系统排队模型,获得库存水平状态的稳态概率分布以及作为库存成本控制的系统稳态性能指标。接下来,构建库存控制成本函数及考虑服务水平约束的库存控制优化模型,设计了改进的遗传算法。最后,数值算例揭示出系统参数的敏感性和相应的管理启示。     

基于两类需求分布的(s,S)库存系统研究

分析了一种基于销售损失和两类需求的(s,S)库存系统.系统拥有两种消费者,每种形式的消费者需求满足相互独立且参数不同的泊松过程,补货前置期服从指数分布.由生灭过程理论推导出稳态分布方程,并得到库存水平状态的稳态概率分布以及库存控制的系统性能指标,构建出服务水平约束下的库存控制模型.结合一种改进的遗传算法,找寻最小的库存成本.最后对系统模型中各个参数进行敏感性分析并指示其库存管理意义.     

基于可用度的装备售后保障系统控制策略研究

基于客户端装备系统可用度,构建一个由备件库存和服务台组成的闭环装备保障系统,通过分析备件库存水平状态特征,推导出备件库存水平状态稳态概率分布,并计算出可用度等几个保障质量指标,建立了基于可用度目标约束的保障系统控制优化模型,采用遗传算法并通过数值仿真揭示出可用度性质和保障系统的运作管理策略.     

服务水平约束下双需求类静态配给策略

考虑一个周期盘点、无限期、缺货回补、双需求类的库存系统,其中高优先级需求的目标服务水平较高。系统采用基准库存策略补充库存,依据静态配给策略分配库存,即优先满足高优先级需求,仅当持有库存水平不低于固定配给阈值时满足低优先级需求。优化目标是在服务水平约束下最小化期望库存持有量。为提升计算效率,引入“预留库存假设”,即允许通过提高低优先级需求缺货水平的方式补充库存,使得期末持有库存水平不低于本期高优先级需求缺货水平与固定配给阈值之和。基于预留库存假设,给出两类需求服务水平和期望库存持有量的解析表达式,证明上述绩效指标关于控制参数的单调性,刻画满足服务水平约束的控制参数可行域,得到原系统最优控制参数的近似求解算法。算例分析表明,基于预留库存假设的绩效衡量方法和参数求解算法准确性好且计算效率高。     

具有两类需求服务的随机库存系统控制策略研究

研究具有两类顾客排队需求服务的随机库存系统.系统采取(s,Q)补货策略且当库存水平下降到安全库存s时,到达的第二类顾客以概率P得到服务.首先,建立库存水平状态转移方程并通过递推算法求解获得库存水平稳态概率分布和系统稳态指标;接下来,构建库存成本函数;最后,采用数值试验的方法研究该库存系统的最优控制策略并考察系统参数的敏感性.     

面向两类客户的双渠道采购库存控制策略

采用排队分析技术,构建基于利润最大化的库存控制模型来考察零售商面向两类客户需求的环境下,双渠道采购库存控制策略.首先,建立了库存水平状态稳态概率分布的平衡方程,并推导出其稳态概率分布以及作为构建系统利润函数的稳态性能指标.然后,建立系统利润最优化模型,并设计改进的遗传算法.最后,通过数值实验考察系统库存控制策略以及参数的敏感性.     

考虑合同保质期的快速失效药品的二级供应链库存策略研究

医院药品对保质期和服务水平有非常高的要求,同时,药品的库存空间在医药库存中也有重要影响。首先针对快速失效的医药药品考虑了医药库存的合同保质期以及库存空间约束,同时考虑医院库存以及制造商库存,基于经济订货批量模型和经济生产批量模型建立了二级供应链的医药库存模型,然后用MATLAB软件求解了模型最优解,并对一些重要参数进行了敏感性分析。研究发现,合同保质期对医院订购批量、制造商生产批量和总库存成本有一定的影响,其中对于制造商的生产批量以及医院的库存成本影响较大。如果不考虑合同保质期的约束,将会对总库存成本带来更大损失。     

基于顾客反馈的销售商库存控制策略仿真

销售商的实际服务水平与其目标服务水平存在差异.针对服务水平影响顾客潜在需求和销售商库存水平的复杂系统问题,运用服从特定分布的离散随机数模拟市场中受历史实际服务水平影响的顾客反馈需求,建立以总销售利润最大为目标的销售商库存系统动力学仿真模型模拟顾客-销售商间的互动反馈关系,基于STELLA软件动态模拟服务水平控制策略下库存系统中物流和信息流的传递和反馈.最后的实例仿真结果验证了模型和算法的合理有效性,指出了敏感型销售商与固执型销售商在面对不同顾客需求时的绩效差异,这也表明了提出的算法在现代商品销售中的实用性.     

需求依赖于服务水平的易变质品库存策略研究

本文研究需求依赖于上一周期服务水平、缺货时订单部分损失的两周期易变质品库存问题。分别考虑一次订货和多次订货两种情况,以平均利润最大化为目标构建库存模型,证明了模型解的存在性和唯一性,得到了最优库存服务水平和最优补货策略。最后,通过算例给出两个模型的应用,对重要参数进行了灵敏度分析,并且将两种模型的结果进行了对比分析。结果表明:订单损失率的增加会提高服务水平,但会使得利润降低;顾客期望服务水平的提高会降低第一阶段的服务水平,同时使利润减少;单位库存持有成本或变质率的增加会降低服务水平和平均利润。通常情况,企业通过多次订货能获得更大的利润,而只有当库存持有成本极小时,一次订购才能够获得更大的利润。同时,结果也表明:服务水平对库存策略有较大的影响,因此在进行库存决策时考虑服务水平具有重要的作用。     

碳限额与碳交易约束下制造商生产-库存控制策略

针对制造商订货、储存、生产过程中的碳排放问题,探讨了碳限额与碳交易约束下制造商生产-库存控制策略,在对碳限额与碳交易进行数学度量的基础上构建了碳限额与碳交易约束下制造商生产-库存成本模型,并通过模型分析得出有碳约束且成本最优生产量及原材料最大订货倍数以及碳限额与碳交易约束下制造商最优生产-库存策略。计算实验与算例分析表明:相比于无碳约束情形,碳限额与碳交易约束下制造商订货数量更高,而订货频率及生产批量更低,并得出三种交易价格之下,决策变量的变化趋势。     

Cost-effective inventory control in a value-added manufacturing system

This paper considers the cost-effective inventory control of work-in-process (WIP) and finished products in a two-stage distributed manufacturing system. The first stage produces a common WIP, and the second stage consists of several production sites that produce differentiated products with different capacity and service level requirements. The unit inventory holding cost is higher at the second stage. This paper first uses a network of inventory-queue model to evaluate the inventory cost and service level achievable for given inventory control policy, and then derives a very simple algorithm to find the optimal inventory control policy that minimizes the overall inventory holding cost and satisfies the given service level requirements. Some managerial insights are obtained through numerical examples.     

Derivation of the cost equation of a dual replenishment inventory model with two order levels

This paper investigates an inventory control system where a single product can be ordered in two separate and independent processes within an inventory cycle. The cost equation is developed by deriving the steady-state probabilities for each level of inventory and using those probabilities to define (a) the average level of inventory, (b) time between replenishments and (c) the units acquired using each replenishment. The terms of the equation are represented as a function of two order levels: the least-order level, used to determine the need for two replenishment processes, and the maximum-order level, which represents the highest level of inventory allowed.     

基于绩效保障模式的可修备件保障系统运营管理策略

基于绩效保障模式,设计了一个由备件仓库和维修车间组成的装备可修部件闭环保障系统,推导了备件库存水平状态的稳态概率分布,计算了可用度等几个保障绩效度量指标,建立了基于可用度约束的保障系统运作优化模型,并通过仿真分析探讨了保障系统运营管理策略问题。     

A queuing approach for inventory planning with batch ordering in multi-echelon supply chains

This paper presents stylized models for conducting performance analysis of the manufacturing supply chain network (SCN) in a stochastic setting for batch ordering. We use queueing models to capture the behavior of SCN. The analysis is clubbed with an inventory optimization model, which can be used for designing inventory policies . In the first case, we model one manufacturer with one warehouse, which supplies to various retailers. We determine the optimal inventory level at the warehouse that minimizes total expected cost of carrying inventory, back order cost associated with serving orders in the backlog queue, and ordering cost. In the second model we impose service level constraint in terms of fill rate (probability an order is filled from stock at warehouse), assuming that customers do not balk from the system. We present several numerical examples to illustrate the model and to illustrate its various features. In the third case, we extend the model to a three-echelon inventory model which explicitly considers the logistics process.     

Lost-sales inventory systems with a service level criterion

Competitive retail environments are characterized by service levels and lost sales in case of excess demand. We contribute to research on lost-sales models with a service level criterion in multiple ways. First, we study the optimal replenishment policy for this type of inventory system as well as base-stock policies and (R, s, S) policies. Furthermore, we derive lower and upper bounds on the order-up-to level, and we propose efficient approximation procedures to determine the order-up-to level. The procedures find values of the inventory control variables that are close to the best (R, s, S) policy and comply to the service level restriction for most of the instances, with an average cost increase of 2.3% and 1.2% for the case without and with fixed order costs, respectively.     

Perishable Inventory System at Service Facilities with N Policy

Abstract

This article presents a perishable stochastic inventory system under continuous review at a service facility in which the waiting hall for customers is of finite size M. The service starts only when the customer level reaches N (< M), once the server has become idle for want of customers. The maximum storage capacity is fixed as S. It is assumed that demand for the commodity is of unit size. The arrivals of customers to the service station form a Poisson process with parameter λ. The individual customer is issued a demanded item after a random service time, which is distributed as negative exponential. The items of inventory have exponential life times. It is also assumed that lead time for the reorders is distributed as exponential and is independent of the service time distribution. The demands that occur during stock out periods are lost.The joint probability distribution of the number of customers in the system and the inventory levels is obtained in steady state case. Some measures of system performance in the steady state are derived. The results are illustrated with numerical examples.     

An inventory control system for products with optional components under service level and budget constraints

Modularization and customization have made enterprises face the multi-item inventory problems and the interactions among those items. A powerful, affordable information technology system can make the continuous review inventory policy more convenient, efficient, and effective. In this study, a (Q, r) model is developed to find the optimal lot size and reorder point for a multi-item inventory with interactions between necessary and optional components. In order to accurately approximate costs, the service cost is introduced and defined in proportion to the service level. In addition, the service cost and purchasing cost are taken simultaneously, and are treated as a budget constraint for executives to consider because the firm’s strategy could influence the choice of service level. The proposed model is formulated as a nonlinear optimization problem, as the service level is nonlinear. Thus, some known procedures are revised to solve this problem and the results are compared with other models. The results show that the revised procedure performs better than the N–R procedure, leading to important insights about inventory control policy.