含模糊服务水平的可控提前期供应链库存优化

在文献"含服务水平约束的可控提前期供应链Stackelberg模型与协调机制研究"(管理学报,2008)的基础上,进一步将服务水平约束看作一个模糊数,进而探讨具有模糊服务水平约束的可控提前期供应链库存优化问题,并采用模糊非线性规划的方法进行求解。采用数值实验方法,对所建的库存优化模型进行了分析,结果表明:最优订货批量、提前期、供应链各方库存成本和获得该成本的隶属度水平均随对模糊服务水平弹性区间的不同主观估计变化而变化。但当模糊服务水平弹性区间增大到一定程度时,会出现服务水平约束无效的情形,则最优订货决策,库存总成本,及获得该成本的隶属度均不会再发生变化。     

多级库存控制的连锁经营企业配送网络设计

研究了随机需求条件下连锁经营企业配送网络设计及其库存决策的联合优化问题.详细分析了基于POT(power of two)多级库存控制策略的连锁企业多级工作库存及订货成本,给出了门店及配送中心在满足给定服务水平条件下的安全库存成本.在综合考虑运输成本和配送中心选址成本的基础上,建立了以系统总成本最小为目标的配送系统总成本优化模型,并采用遗传算法求解该优化模型,在得到最优配送网络设计方案的同时,确定了配送中心订货周期及门店配送周期.通过算例验证了模型及算法的有效性,并分析了需求、运输距离和选址成本等因素的变化对系统总成本的影响,为连锁经营企业的物流配送网络设计及库存控制提供决策支持.     

服务水平约束且安全系数可变时的库存模型

以订货批量和安全系数为变量,建立了在给定的服务水平约束条件下,安全系数变化时的最优库存决策模型.由模型的分析知,所建立的模型是一个凸规划问题,存在唯一的最优解,并且给出了模型的求解算法,最后通过一个算例说明了模型和算法的有效性.     

基于TCO模型的联合库存成本管理

针对联合库存成本管理的特点和不足,根据总拥有成本的概念建立了优化模型.该模型着力于系统地调节与分配联合库存的多个供应商之间的订单和批量,实现了降低联合库存总拥有成本的目的.通过分析钢铁企业的一个案例证明,该模型具有应用价值.     

基于Weibull函数的易逝品库存优化模型研究

研究了变质率服从Weibull分布的易逝品库存优化问题.在固定订货周期内,针对需求依赖于瞬时库存水平且允许缺货的情况,采取部分延迟订货策略,建立了以单位时间平均总成本最小为目标的易逝品库存优化模型,给出了模型存在唯一最优解的条件,并应用牛顿迭代法对该模型进行了求解.通过实例验证了该模型的有效性和可行性,对模型中的需求率、变质率和延迟订货率等参数进行了灵敏度分析.     

基于多变量的联合决策库存优化问题

以订货费用、提前期、订货量、安全系数和价格折扣为决策变量,建立了包括准备费用、订购费用、缺货费用、库存费用和提前期压缩费用等可变的联合约束下的库存数学模型.利用最大最小原则进行模型分析求解.通过实例证明,建立的库存模型与算法能够有效地从多方面优化解决此类库存问题,为生产库存控制提供理论依据,同时提高该类生产企业的反应速度和竞争能力.     

需求受相关性影响的设备备件库存优化

备件多级库存模型通常基于备件需求相互独立的假设，但随着库存系统层次的增加以及协同管理方式的应用，备件需求的相关性将显著影响库存优化决策。针对需求具有相关性的备件库存问题，以服务响应时间为约束条件，以库存成本及缺货成本最小化为目标建立备件两级库存决策模型。引入Nataf概率变换法，利用已知的备件需求边缘概率密度函数构造满足特定相关性条件的随机需求样本，并将蒙特卡洛仿真与遗传算法相结合求解最优库存分配方案。仿真算例证明，设备备件库存的最优决策随着需求相关性系数的增大而发生变化，根据需求相关性的变化适当地调整库存决策，有利于降低备件库存系统总成本，提高库存系统对顾客需求的响应能力。     

考虑缺货成本的VMI利益分配

考虑缺货成本,从库存成本角度开展研究,通过对比实施VMI前后供应链库存成本模型,指出VMI短期内供应链收益来源于库存成本变化,且存在责任利益不一致的情况。针对供需双方不同地位,应用价格契约、斯坦科尔博格博弈模型与收益共享契约分别建立了零售商占优与供需双方地位平等情况下的利益分配模型,求解出零售商激励采购价格与收益共享系数的具体值,并采用算例进行分析。     

周期可变下考虑多车型的库存路径优化研究

目的 研究基于供应商管理库存模式下，由一个供应商和多个零售商组成的二级供应链配送系统的库存路径优化问题，确定计划期内各配送周期的长度、数量，对供应链中库存策略与配送方案问题进行协调优化，使系统总成本最低。方法 考虑的成本包括库存持有成本、缺货成本和配送成本。为降低供应链系统的总成本，提出全新的周期可变策略。结果 采用遗传算法求解得出最佳方案。将不同策略的算例结果进行对比分析，结果表明周期可变策略与周期固定策略相比，系统总成本最低节约比例为1.7%，最高节约比例为42.3%。结论 通过对计划期内各配送周期的长度及数量进行划分调整可以有效地节约系统总成本，同时，采用多车型的配送方案明显优于采用同车型的配送方案。     

零件中心备件库存分类控制的研究

分析了库存ABC分类法存在的问题,提出了基于客户服务水平的库存ABC分类法,给出了相应的订货点、安全库存和订货量的计算模型,实现了提高顾客服务水平、降低库存成本的目标。     

An inventory model with emergency orders under explicit energy cost considerations

The inventory model in this paper is targeted to production systems with constant production rates but underlying possibilities for undesirable circumstances to threaten the production schedule. The inventory policy proposed explicitly considers energy cost when determining optimal size for order quantity, safety stock and inventory cycle length such that the total expected cost per unit time is minimised. The results are compared to a traditional inventory policy that does not consider the direct impact of energy cost. An analysis of the model reveals three production environment characteristics in which inventory policies are most significantly affected by changes in energy cost: heavy product weight, high regular product demand or high emergency product demand. If any one of the three key factors increases, then changes of the inventory decisions or related logistics costs become more significant. The cost effectiveness of implementing the proposed inventory policy also becomes more significant as any one of the three key factors increase with respect to energy cost.     

Weibull分布变质物品库存模型研究

研究了变质物品在考虑资金时间价值时的经济订货批量问题.假定物品的变质率服从两参数的Weibull分布,物品的需求率与库存水平有关,且为库存水平的线性函数,计划时域内进行多次订货,订货时间间隔相等,允许缺货且短缺量完全拖后,以库存系统的总费用最小为目标函数,建立了变质物品在存货依赖性需求下考虑资金时间价值时的最优订货批量模型,分析了模型存在唯一的最优解的必要条件,并且给出了在该条件下求解模型最优解的算法,最后给出了一个计算实例.     

Comments on ‘vendor-managed inventory with consignment stock agreement for single vendor–single buyer under the emission-trading scheme’

Zanoni, Mazzoldi, and Jaber [Zanoni, S., L. Mazzoldi, and M. Y., Jaber. 2014. Vendor-managed inventory with consignment stock agreement for single vendor–single buyer under the emission-trading scheme. International Journal of Production Research 52 (1): 20–31] consider a joint economic lot size problem under the vendor-managed inventory with consignment stock agreement and an emission-trading scheme. They show that the total cost of the system is a jointly convex function by simply showing that every element of the Hessian is positive. Noticing this mistake, we analyse the same problem in this technical note. We first provide a closed-form solution when the production rate is given. In order to avoid a complete search over all possible production rates, we then develop an efficient continuous approximation algorithm. Computational experiment shows that the approximation algorithm is effective and efficient.     

基于安全库存策略的提高订单及时率方法研究

电脑供应链中的各种不确定因素使得非核心零部件中间商经常需要依靠大量备货或加急生产来满足客户需求。而当非核心零部件中间商不愿为此备货时,交货延迟的发生比例不可避免地会较高。针对此问题,本文提出了一种基于安全库存策略的提高订单及时率减少交货延迟的方法。此方法首先对电脑生产商的需求量进行估计,在综合考虑影响订单及时率的各类确定性和随机性因素的条件下,推导得到最优安全库存因子;然后,根据电脑生产商需求估计量与安全库存因子,计算出安全库存,如果电脑生产商需求量小于安全库存量,则使用安全库存直接交货,否则,向供应商追加订货后一并交货;最后,给出了该方法的年平均库存衡量公式。实证计算结果表明,与传统的面向订单生产方法(MTO)相比,本文方法可以使电脑零部件中间商的库存周转速度加快5~6倍,单位库存持有成本降至原来的14%,订单交货准时率提升至80%左右。     

Safety stock determination based on parametric lead time and demand information

In many production environments where demand and lead times are variable, significant levels of safety stock inventory are required to assure timely production and delivery of the final product. Traditional models to determine the appropriate safety stock level may result in more safety stocks at sub-assembly and finished goods levels than necessary and thus lead to higher inventory carrying costs than desired. Such models generally incorrectly assume that the demand during the lead time follows a normal distribution. This paper revisits and analyses a re-ordering point inventory model developed by Estes (1973 Estes, R. 1973. The joint probability approach and reorder point determination. Journal of Production and Inventory Management, 14(2): 50–56.  [Google Scholar]) that accounts for demand and lead time variability without making any particular distributional assumptions. Instead, it focuses on historical data to determine the possible outcomes of the replenishment cycle. We compare the proposed model with the traditional model by conducting simulation analysis using three data sets obtained from an electronics manufacturer. The results indicate that the proposed model yields much closer to target service levels and lower inventory carrying costs than the traditional model, regardless of the data set used.     

The use of rush deliveries in periodic review assemble-to-order systems

We calculate optimal safety stock in a periodic review (T,S) assemble-to-order system having multiple components and multiple finished goods (FGs). Customer orders for FGs arrive according to independent Poisson processes, and cannot be neither backlogged nor lost. In case of potential component stock-out, the studied system uses rush deliveries from suppliers. For this setting, approximate expressions of the optimal safety stock that minimise the sum of inventory holding and rush ordering costs are developed. Exact optimal safety stocks are calculated using Discrete Event Simulation, and compared numerically to the approximate expressions. The model is applied to a first-tier automotive supplier and yields to a significant reduction in terms of inventory holding and rush ordering costs. A sensitivity analysis on relevant system parameters such as components demand, assembly coefficients and unit rush ordering cost is conducted.     

Shortage decision policies for a fluid production model with MAP arrivals

We consider on a continuous production/inventory process where a single machine produces a certain product into a finite buffer. The demands arrive according to a Markov Additive Process governed by a continuous-time Markov chain, and their sizes are independent and have phase-type distributions depending on the type of arrival. Two shortage policies are considered: the backorder policy, in which any demand that cannot be satisfied immediately is backlogged, and the order policy, in which any demand that cannot be satisfied immediately is supplied (alternatively, the latter policy can be considered as lost sales). We assume that the total cost includes a production loss cost, a penalty cost, a fixed cost for an order and a variable cost for the ordered amount. By applying the regenerative theory, we use tools from the exit-time theorem for fluid processes to obtain the discounted cost functionals under both policies. In addition, the models are extended to include a non-zero safety stock. Numerical examples, sensitivity analysis and comparative study are included.     

Schedule instability,service level and cost in a material requirements planning system

The primary objective of this work was to evaluate how four important system parameters (schedule frozen interval, schedule re-planning interval, safety stock and lot-sizing rules) affect material requirements planning (MRP) system performance in terms of schedule instability, total cost and service level, considering different levels of two operating factors: the lead-times of items in the product structure, and the accuracy of the demand forecast. The research design employed a simulation model in Visual Basic run on a personal computer. This study concluded that all system parameters and operating factors significantly influence the three performance measures. Frozen interval, forecast accuracy, and lead-time have the most significant impact on system instability and total cost. Forecast accuracy, safety stock, and lead-time have the most impact on service level. Due to the interactions among system parameters and operating factors, there are no win-win principles to set parameters in order to achieve better system performance under all operating conditions. However, the results help determine appropriate system parameters under particular operating conditions. For example, when the forecast is more accurate, system instability is relatively insensitive to the size of re-planning interval, but frequent re-planning helps reduce total cost and improve service level.     

Preventive maintenance and optimal buffer inventory for products sold with warranty in an imperfect production system

This paper deals with an imperfect production system with allowable shortages due to regular preventive maintenance for products sold with free minimal repair warranty. Preventive maintenance is an essential factor of the just-in-time structure that results in a shutdown of the production process for a certain period of time. During such an interruption, a buffer stock is needed to adjust the market demand. The study includes the possibility of imperfect production and determines the optimum buffer level and production run time by trading off the holding cost, shortage cost, rework cost, repair cost for warranty, labour/energy costs, material cost and cost for maintenance so that the cost per unit product is minimised.