生产与销售的库存模型

本对工厂生产所需原材料的库存和生产的产品的库存问题进行了研究,给出了生产和销售速率一般意义下的库存模型和计算最佳生产周期的地,并对两种生产和销售速率的特殊情况,分析进行了讨论。     

集中式供应链的生产与库存分配联合决策

考虑一个由单一制造商和多销售点构成的二级集中式供应链,制造商采用积欠订货策略生产和销售产品,因而面临生产、运输和积欠订货型库存分配与补货的联合决策问题.综合考虑了延迟交货成本、库存持有成本、运输成本和生产成本,建立了最大化总利润的非线性混合整数规划模型,以联合优化供应链的生产、运输及库存分配方案.证明了最优的产品生产分配方案应该具有的结构性质:各个销售网点在任意销售间隔期末同时出现缺货或者库存剩余.同时,提出了基于逐级求解策略的分层求解算法,保证了解的全局最优性.最后,敏感性分析表明:单位产品的库存持有成本与延迟交货成本对最优分配次数及生产量的影响作用相反,固定运输成本也会影响制造商的分配方案及生产计划,但三者均不会影响每个间隔期末的产品分配方案(分配量).     

具有定价和开机成本的生产-库存系统的最优(s,d,S)策略

考虑一个具有有限容量和开机成本的连续盘点生产-库存系统, 其控制策略为(s,d,S)策略. 未被满足的需求都会丢失. 当机器处于关闭状态时,库存产品可以两个不同的价格进行销售. 当机器处于开机状态时,库存只能以较高的价格进行销售. 研究了如何发现该系统下的最优(s,d,S)策略,并开发了用于计算最优控制参数的有效算法.     

在中心仓库有损失销售的二级分布库存管理模型的研究

通过对一个中心仓库和N个零售商的二级分布库存系统进行分析,采用基本(S-1,S)库存策略,综合运用了排队法和M ETR IC近似法,提出了一种在中心仓库有损失销售的二级库存管理模型,该模型描述在中心仓库缺货情况下,多数零售商不等待延期付货,而直接与供应商订货,导致中心仓库就会因损失销售而产生机会成本.该模型可达到二级分布库存系统的总成本最小.     

生鲜农产品双渠道供应链库存合作策略研究

随着我国"互联网+农业"战略的不断推进,生鲜农产品的网络销售渠道呈现出快速增长的趋势,但是生鲜农产品易腐易损、贮藏周期短、流通损耗大的特点在一定程度上加大了其网络销售渠道的运作难度.为此,从生鲜农产品传统销售渠道与网络销售渠道的库存协调与合作的视角,针对生鲜农产品双渠道供应链系统的特性,运用系统动力学的理论与方法构建了双渠道供应链库存独立系统、单级库存合作系统和多级库存合作系统的动力学模型.通过系统模型的仿真模拟,结果表明零售商与网络配送点进行库存紧急调拨的单级库存合作系统在牛鞭效应、服务水平和供应链总成本三个指标上表现最优,在供应链总库存指标上表现次优,整体上是最优的,并针对模型仿真结果,有针对性的提出对策与建议.     

需求受库存影响下具有固定保质期物品的最优订货策略

带有固定保质期物品的订货是供应链终端销售系统的一个重要决策问题,假设需求依赖库存展示水平并考虑"后进先出"的销售策略而建立了相应的库存决策模型,其中物品在固定保质期内仍具有常数的变质速率.然后以系统平均利润最大化为目标讨论了模型最优解的存在性及唯一性,并提供了寻求模型整体最优解的简单方法.最后给出应用实例,并分析了模型参数变化对最优订货策略的影响.     

带有服务员休假的库存系统

研究了带有服务员多重休假、损失销售和(s,S)补货策略的库存系统,其中顾客到达为泊松过程、休假时间及系统前置补货时间都服从指数分布.利用拟生灭过程方法对系统进行稳态分析,给出了带有休假的库存系统的稳态分布、平均库存和平均损失率,并将带有休假库存系统的性能指标与经典无休假库存系统的性能指标做了比较.最后通过数值算例说明服务员休假对库存系统的影响.     

钢铁企业订货系统模型的VENSIM建模与仿真实现

订货模型存在于大多数的公司中,用以根据销售情况组织公司生产.在简单生产-分配系统模型基础上,构建了钢铁企业零售商订货模型;运用系统动力学方法分析了该订货模型,并采用了阶跃函数描述了复杂变化的零售商销售状况,通过VENSIM建模与仿真分析,找出了零售商销售-订单-库存的相互关系;结果表明,钢铁企业生产-分配系统的特征与采用阶跃函数得出的结果非常相似,对钢铁企业零售商的订货策略具有指导意义.     

ERW钢管考虑动态库存和交货期的多阶段生产计划优化方法研究北大核心

多阶段生产计划在钢管制造企业中起着重要的作用,在学术研究中也具有一定的复杂性.由于企业库存与生产及计划密切相关、订单交货期对生产和库存又具有很强的关联性,在研究中将库存的动态性和交货期纳入多阶段生产计划中,试图寻求找到优化的生产计划的方法.根据ERW直缝焊管企业的生产特点,对其生产计划的制订方式进行了优化.针对多阶段生产计划建立了考虑库存和交货期的提前/拖期惩罚数学模型,通过遗传算法对其进行求解及优化,从而得到生产计划的较优解.     

ERW钢管考虑动态库存和交货期的多阶段生产计划优化方法研究

多阶段生产计划在钢管制造企业中起着重要的作用,在学术研究中也具有一定的复杂性.由于企业库存与生产及计划密切相关、订单交货期对生产和库存又具有很强的关联性,在研究中将库存的动态性和交货期纳入多阶段生产计划中,试图寻求找到优化的生产计划的方法.根据ERW直缝焊管企业的生产特点,对其生产计划的制订方式进行了优化.针对多阶段生产计划建立了考虑库存和交货期的提前/拖期惩罚数学模型,通过遗传算法对其进行求解及优化,从而得到生产计划的较优解.     

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.     

Pricing and lot sizing for an EPQ inventory model with rework and multiple shipments

This paper deals with an economic production quantity (EPQ) inventory model with reworkable defective items when a given multi-shipment policy is used. In this work, it is assumed that in each cycle, the rework process of all defective items starts when the regular production process finishes. After the rework process, a portion of reworked items fails. This portion becomes scrap and only the perfect finished items can be delivered to customers at the end of rework process. A profit function is derived to model the inventory problem and it is shown that the profit function is concave. Due to the complexity of the optimization problem, an algorithm is developed to determine the optimal values of manufacturing lot size and price such that the long-run average profit function is maximized. Furthermore, two special cases are identified and explained. Finally, a numerical example is given to illustrate the applicability of the proposed inventory model.     

The scheduling of deliveries in a production-distribution system with multiple buyers

In a real production and distribution business environment with one supplier and multiple heterogeneous buyers, the differences in buyers’ ordering cycles have influence on production arrangements. Consequently, the average inventory level (AIL) at the supplier’s end is affected by both the production policy and the ordering policy, typically by the scheduling of deliveries. Consequently, the average inventory holding cost is most deeply affected. In this paper, it is proposed that the scheduling of deliveries be formulated as a decision problem to determine the time point at which deliveries are made to buyers in order to minimize the supplier’s average inventory. A formulation of the average inventory level (AIL) in a production cycle at the supplier’s end using a lot-for-lot policy is developed. Under the lot-for-lot policy, the scheduling of deliveries (SP) is formulated as a nonlinear programming model used to determine the first delivery point for each buyer with an objective to minimize the sum of the product of the individual demand quantity and the first delivery time for each buyer. Thus, the SP model determines not only the sequence of the first deliveries to individual buyers, but also the time when the deliveries are made. An iterative heuristic procedure (IHP) is developed to solve the SP model assuming a given sequence of buyers. Six sequence rules are considered and evaluated via simulation.     

Effects of imperfect products on lot sizing with work in process inventory

The economic production quantity (EPQ) is one of the most widely known inventory control models that can be regarded as the generalized form of the Economic Order Quantity. However, the model is built on an unrealistic assumption that all the produced items need to be of perfect quality. Also, the introduction of work in process, WIP, as part of the inventory has been of lesser concern in developing inventory models. This paper attempts to develop the economic production quantity considering work in process inventory and manufacturing imperfect products that may be either reworkable or non-reworkable. The non-reworkable imperfect products are sold at a reduced price. This paper introduces a new model for this problem.     

Fleet routing position-based model for inventory pickup under production shutdown

This paper addresses the problem of collecting inventory of production at various plants having limited storage capacity, violation of which forces plant shutdowns. The production at plants is continuous (with known rates) and a fleet of vehicles need to be scheduled to transport the commodity from plants to a central storage or depot, possibly making multiple pickups at a given plant to avoid shutdown. One operational objective is to achieve the highest possible rate of product retrieval at the depot, relative to the total travel time of the fleet. This problem is a variant (and generalization) of the inventory routing problem. The motivating application for this paper is barge scheduling for oil pickup from off-shore oil-producing platforms with limited holding capacity, where shutdowns are prohibitively expensive. We develop a new model that is fundamentally different from standard node-arc or path formulations in the literature. The proposed model is based on assigning a unique position to each vehicle visit at a node in a chronological sequence of vehicle-nodal visits. This approach leads to substantial flexibility in modeling multiple visits to a node using multiple vehicles, while controlling the number of binary decision variables. Consequently, our position-based model solves larger model instances significantly more efficiently than the node-arc counterpart. Computational experience of the proposed model with the off-shore barge scheduling application is reported.     

Zero-Inventory Conditions for a Two-Part-Type Make-to-Stock Production System

We consider the dynamic scheduling of a two-part-type make-to-stock production system using the model of Wein [12]. Exogenous demand for each part type is met from finished goods inventory; unmet demand is backordered. The control policy determines which part type, if any, to produce at each moment; complete flexibility is assumed. The objective is to minimize average holding and backorder costs. For exponentially distributed interarrival and production times, necessary and sufficient conditions are found for a zero-inventory policy to be optimal. This result indicates the economic and production conditions under which a simple make-to-order control is optimal. Weaker results are given for the case of general production times.     

Integrated inventory model with quantity discount and price-sensitive demand

Quantity discount has been a subject of study for a long time; however, little is known about its effect on integrated inventory models when price-sensitive demand is placed. The objective of this study is to find the optimal pricing and ordering strategies for an integrated inventory system when a quantity discount policy is applied. The pricing strategy discussed here is one in which the vendor offers a quantity discount to the buyer. Then, the buyer will adjust his retail price based on the purchasing cost, which will influence the customer demand as a result. Consequently, an integrated inventory model is established to find the optimal solutions for order quantity, retail price, and the number of shipments from vendor to buyer in one production run, so that the joint total profit incurred has the maximum value. Also, numerical examples and a sensitivity analysis are given to illustrate the results of the model.     

A Note on an Inventory Model with Inventory-level-dependent Demand Rate

This model discusses an infinite time-horizon deterministic inventory model without shortages, where the demand rate at any instant depends on the on-hand inventory (stock level) at that instant down to a certain stock level and then it becomes constant for the remaining period of the cycle. The decision rule for finding the optimal order quantity is also given, and three numerical examples are presented to illustrate the model developed.     

线性需求合并短缺的变质性物品的生产——库存模型

本文发展了线性需求合并短缺的变质性物品的生产——库存模型，以系统平均总费用最小为目标，提供了有限计划期内的生产调整策略以便适应市场需求的变化．同时还提供了无短缺情形的相应模型，最后出示了一些数字例子     

时变需求等量进货情形下集成供应链生产订货策略研究

构建了一个包含原料采购、生产和销售过程的集成供应链模型,研究了由原料、生产商和销售商产品构成的三层库存系统的生产订货问题。在有限的规划期内,销售商每次进货量相同,生产商按照EOQ模型采购原材料。以最小化供应链系统的总运营成本为目标,构建一个混合整数非线性规划模型,寻找销售商最优订货方案和生产商最佳生产策略。首先利用网络优化方法求解生产商的最优生产计划,其次利用定界穷举法寻求销售商最优的订货周期,给出了具体的计算方法和Matlab程序。通过算例分析验证了算法的有效性,并研究了各参数对最小费用及最优解的影响。