基于中心化存储和横向转运的选址——库存联合决策模型

针对单一产品、单周期、单一供应商、多配送中心、供应商和需求点位置已知的情况,假定（Q,R）库存检查策略、给定备选地址、无容量约束、各需求点的需求完全独立且均服从正态分布、配送中心级和需求级同时采取中心化安全库存策略、允许配送中心间及同一配送线路内的需求点间通过横向转运对缺货进行瞬间补充、不计缺货成本和转运时间,构建了二层规划模型。上层规划解决选址及需求点的分配问题;下层规划确定配送中心级和需求级的中心化存储方案。发现如果考虑库存持有成本、转运成本等因素的影响,安全库存的集中存放策略并不是聚集在某一个地方,而是在多个地方进行有限、适度的集聚,其成本更低。     

Classification-based model selection in retail demand forecasting

Retailers supply a wide range of stock keeping units (SKUs), which may differ for example in terms of demand quantity, demand frequency, demand regularity, and demand variation. Given this diversity in demand patterns, it is unlikely that any single model for demand forecasting can yield the highest forecasting accuracy across all SKUs. To save costs through improved forecasting, there is thus a need to match any given demand pattern to its most appropriate prediction model. To this end, we propose an automated model selection framework for retail demand forecasting. Specifically, we consider model selection as a classification problem, where classes correspond to the different models available for forecasting. We first build labeled training data based on the models’ performances in previous demand periods with similar demand characteristics. For future data, we then automatically select the most promising model via classification based on the labeled training data. The performance is measured by economic profitability, taking into account asymmetric shortage and inventory costs. In an exploratory case study using data from an e-grocery retailer, we compare our approach to established benchmarks. We find promising results, but also that no single approach clearly outperforms its competitors, underlying the need for case-specific solutions.     

Application and research on the complex dynamics behaviour under price-discount promotion policy in inventory control system

In this paper, we study the inventory control system of the apparel industry supply chain in which the products are fast-fashion and mass-consuming goods. Retailers tend to promote by price-discount policy to regulate overstock situation caused by fluctuated demand, frequent product upgrading, etc. Here, we discuss the impact of fluctuated demand triggered by price-discount promotion policy on the comprehensive inventory control system in which the final inventory and supply line stock are considered and weighted differently according to corresponding practical operation situations. In this model, stock returns are permissible. Then we calculated the Lyapunov stable region of the decision parameters based on the state space model. These conclusions present the managers a big picture to inspect the inventory control system and serve as reliable references to make correct decisions.     

Determining optimal fuel delivery strategies under uncertainty

During the preparation before a hurricane makes landfall, affected individuals may be asked to evacuate. Large and small-scale evacuations can cause rapid increases in the demand for gasoline fuel. However, during a hurricane vessels carrying gas may be delayed and/or rerouted, adding to the difficulty of providing the necessary gas in affected areas. In this work, we determine alternate delivery locations and times for vessels carrying fuel that are scheduled to arrive and deliver fuel at ports impacted by an approaching hurricane. Motivated by Hurricane Irma in Florida, we develop a multi-period stochastic scheduling model that incorporates hurricane (weather) advisories, fuel delivery schedules, port storage capacities, and port docking capacities. Our model determines the best schedule based on two objectives: (1) minimize the total unmet demand at each port, and (2) minimize inequities in unmet demands among the ports. We also present a case study and a numerical experiment based on fuel delivery data from ports in Florida. Among our key findings is that port availability is the driving factor in determining feasible schedules for vessel gas deliveries. We also present a scheduling heuristic that dynamically adapts to weather advisories so as to minimize the impact of unmet demand in the affected areas.     

允许延期支付时的生产商—销售商一体化生产库存模型

在考虑信用期的情况下,研究了生产率为常数、需求率随价格变化情形下的变质性物品生产库存模型,通过考虑生产商、销售商双方的联合总收益,得到了一体化生产库存模型并给出了求解最优生产库存策略的算法和算例。     

A Note on EOQ Model for Items with Mixtures of Exponential Distribution Deterioration,Shortages and Time-varying Demand

An inventory model is considered in which inventory is depleted not only by demand, but also by deterioration. In this paper, we derive the EOQ model for inventory of items that deteriorates at a mixtures of exponential distributed rate, assuming the demand rate with a continuous function of time. Moreover, the proposed model cannot be solved directly in a closed form, thus we used the computer software IMSL MATH/LIBRARY (1989) to find the optimal reorder time Further, we also find that the optimal procedure is independent of the form of the demand rate. Finally, we also assume that the holding cost is a continuous, nonnegative and non-decreasing function of time in order to generalize EOQ model. Moreover, four numerical examples and sensitivity analyses are provided to assess the solution procedure.     

基于商品性质的多级分销模式选择及网络库存定位模型的研究

本文以典型的多级分销网络为研究对象,从商品的需求量、需求波动及商品价值等特性对分销网络的服务能力和成本水平的影响出发,对如何根据不同商品特性选择科学的分销模式及如何在多级网络中进行合理的库存定位问题进行了研究,并基于此提出了一个可行的定性分析模型,借助此模型,可帮助企业在设计分销网络和现有网络的优化过程中,根据所经营商品的不同特性进行合理的网络设计和运营,大大提高网络运营效率。     

Six ways to reduce inventory

The purpose of this presentation is to help you reduce the inventory in your operation. We will accomplish that task by discussing six specific methods that companies have used successfully to reduce their inventory. One common attribute of these successes is that they also build teamwork among the people. Every business operation today is concerned with methods to improve customer service. The real trick is to accomplish that task without increasing inventory. We are all concerned with improving our skills at keeping inventory low.     

Firm performance in dynamic environments: The role of operational slack and operational scope

This study examines the effects of operational scope (breadth of product offering, extent of geographical diversification, and extent to which production processes can effectively meet varying demand) and operational slack (resources in excess of what is required to fulfill expected demand) on firm performance, contingent on two components of a firm's dynamic environment, unpredictability and instability. We collate quarterly data on 3857 publicly traded firms in 19 industries from the years 1991 to 2013 (representing 99,559 firm-quarter observations). Using panel data analysis, we find that narrow product offerings, low geographical diversification, low levels of excess capacity, and low inventory slack are each positively associated with firm performance. More importantly though, we find that operational scope is associated with improved performance in unpredictable environments, whereas operational slack is associated with improved performance in unstable environments. These findings contribute to the research on operations strategy by identifying the industry-specific environmental conditions under which operational slack and operational scope are associated with firm performance.     

A general method for addressing forecasting uncertainty in inventory models

In practice, inventory decisions depend heavily on demand forecasts, but the literature typically assumes that demand distributions are known. This means that estimates are substituted directly for the unknown parameters, leading to insufficient safety stocks, stock-outs, low service, and high costs. We propose a framework for addressing this estimation uncertainty that is applicable to any inventory model, demand distribution, and parameter estimator. The estimation errors are modeled and a predictive lead time demand distribution obtained, which is then substituted into the inventory model. We illustrate this framework for several different demand models. When the estimates are based on ten observations, the relative savings are typically between 10% and 30% for mean-stationary demand. However, the savings are larger when the estimates are based on fewer observations, when backorders are costlier, or when the lead time is longer. In the presence of a trend, the savings are between 50% and 80% for several scenarios.     

Transaction costs, capital-gains taxes, and housing demand

The paper considers the effect of transaction costs—particularly in the form of capital-gains taxes—on the aggregate demand for owner-occupied housing. The framework is an overlapping-generations model, where consumers can avoid the transaction costs (taxes) by keeping the same house for both periods of life. The first part of the paper analyzes the consumer's choice problem. It distinguishes between costs that are fixed irrespective of the size of the house bought or sold, and costs such as capital-gains taxes that are related to the house value. It is shown that higher transaction costs have lock-in effects, inducing consumers to keep the same house for both periods. Also it is found that under a wide variety of circumstances the amount of housing demanded will increase as the household is being locked in. Finally, the paper looks at the effects on aggregate demand from an increase in capital-gains taxes. It is shown that an increased rate of taxation decreases demand for low tax rates. But for high tax rates, when lock-in effects become important, one generally gets the opposite effect; high tax rates tend to increase housing demand.     

随机需求下销售周期对零售商绩效影响的仿真分析

运用系统动力学方法构建了包含市场需求、企业生产、劳动力和库存管理的一级供应链运作模型。通过灵敏度和优化分析仿真技术研究了随机需求下产品销售周期对零售商成本、利润和供应链牛鞭效应的影响。结论显示,与生产成本和劳动力成本相比,库存成本对产品销售周期的变化更敏感;在不考虑生产启动成本情况下,随着销售周期增大,总利润呈线性递减;连续库存补充计划比传统的经济订货批量模式能够为企业带来更多的利润,更有利于减弱牛鞭效应的影响。     

具有模糊—随机性的易腐货品最优补货策略

结合易腐物品的变质特点,考虑不确定环境下配送中心以固定周期为连锁门店送货、连锁商单位时间需求为模糊变量的分销系统,通过利用三参数Weibull函数来描述易腐货品的变质特性,运用可信性理论的逆模糊化和随机理论,建立了模糊-随机下的每周期易腐货品的最优补货策略模型。借助MATLAB得到了求解最优补货策略的方法,并通过仿真模拟验证了方法的合理性。     

生鲜食品的二级补货系统优化研究

针对连锁超市的配送网络。建立一个两级的库存系统模型，其中包括一个中心仓库和若干门店，每个门店面对的是随机的相互独立的需求，该需求服从正态分布。该库存系统是采用基于连续检测的再订货点方法管理。本文针对超市的生鲜食品补货的特征，增加对于过剩成本的考虑，采用分散库存控制权的方法，按照从门店到配送中心的思路。优化总库存成本，从而得出最佳的订购批量，同时也得出最佳的产品供给水平、再订货点等。     

Modeling mobile health service delivery to Syrian migrant farm workers using call record data

A significant number of Syrian refugees under temporary protection in Turkey work in agriculture seasonally in various rural areas during several months a year. These migrant farm workers and their families are deprived of access to the regular health care system and preventive services due to their remote locations. The government supports the delivery of different types of mobile health care services, such as vaccination for children, reproductive health and screening services. While planning the mobile health care service delivery, it is critical to know where the refugees will work during what time frame; hence the demand for the services. By analyzing the call record data of a major mobile network operator in Turkey, we quantify the increase in the volume of calls made by Syrian refugees in various agricultural areas during the harvesting season of local crops. This information helps us to forecast spatial and temporal distribution of demand for mobile health care services at a fine granularity. Taking demand over multiple periods as input into a mathematical programming model, we optimize the routing of mobile clinics that visit locations close to where refugees are concentrated over the given planning horizon. We consider three hierarchical objectives. Given the availability of a number of mobile clinics at community health centers in the districts, the first objective aims to maximize the percentage of refugees that can benefit from each service type within pre-defined close distances. The second objective minimizes the number of clinics needed while covering the maximum percentage of refugees. The third objective minimizes the total travel distance of the clinics, while keeping the maximum coverage level using a minimum number of clinics to achieve this level. We quantify the benefits of centralized planning (by the province directorate) over decentralized planning (by each district separately). We also show the trade-off between the required number of clinics and coverage of potential patients.     

动态持有成本下的库存成本模型研究

对制造业企业来说,更大的生产能力就有机会带来更多的销量,所以在库存模型中需求率是与库存量正相关的变量,而并非在整个在库时间内都保持为常量。论文提出了一种库存成本与需求率分别和库存时间与库存量相关的模型,并针对两种成本结构各设计了一种优化算法以确定最优订购量和最优库存时间。     

A TIME SERIES ANALYSIS OF ANNUAL PASSENGER DEMAND FOR THE STATE RAILWAY OF THAILAND

This paper presents a time series regression model to estimate annual passenger demand for the State Railway of Thailand (SRT). The model was developed for a time period of 15 years (1974–1988), incorporating such variables as the country's gross domestic product (GDP), SRT passenger fares, competing intercity bus fares, and a dummy variable of the Fifth National Five Year Plan advocating a railway-favored modal shift policy. This simple but useful model analysis estimated the demand elasticities as: 0.907 with respect to real GDP; -0.970 with respect to real SRT fare; and 0.808 with respect to real bus fare. Remarkable manufacturing-oriented economic development of Thailand in recent years played an important part in recent SRT demand increases. As the relatively high own and cross fare elasticity estimates imply, the SRT is concerned about demand loss to competing intercity bus services, and has thus been keeping fare levels low. The model analysis also estimated a demand gain of 12.3% due to the modal shift policy during the Fifth Plan period, suggesting effectiveness of the policy.     

碳约束下需求离散随机的库存控制问题研究

文章站在零售商的角度,通过分析需求离散随机库存控制过程中的碳排放因素,设计出基于碳排放成本的随机库存控制模型,对低碳供应链中库存控制的要素进行了分析,并通过算例来说明该模型。模型有利于进一步提升供应链的核心竞争力,推动低碳供应链管理的深入研究。     

The effects of workforce strategies on manufacturing operations

This paper tests the effects of three workforce strategies on a multistage, multiproduct manufacturing system under various operating conditions. These three strategies are those that are predominant in today's world economics. One type is a chase strategy, often used by firms that employ low skilled workers and faced with seasonal product demands, where workforce levels fluctuate according to increases and decreases in production requirements. A level-flexible strategy, commonly called the Toyota system, keeps the aggregate workforce at a constant size but by having flexibly trained workers it can allow transfers of workers between various departments and processes as production requirements dictate. The third major type is a level-inflexible strategy, such as that used on mass-assembly lines employed by American automobile manufacturers. Under this strategy, the number of workers remains constant in each department as well as at the aggregate level regardless of short term changes in the production requirements. The manufacturing system is envisioned as a sequential planning process with interrelated decisions made at the levels of aggregate planning, master production scheduling, and departmental planning. This process is modeled as a zero-one mixed integer program. The operating conditions under which the strategies are tested are the variability of demand, the level of service, and the degree of inventory investment. The strategies are statistically tested as to their effects on five criteria: average weekly workforce size, average quarterly inventory investment, average weekly overtime, total setups and the average weekly ratio of departmental load to capacity.Using four different products and an experimental manufacturing environment described within the paper, we tested for any statistical differences between the three strategies. We found that none of the strategies had significantly different workforce sizes. Also, the chase strategy had the smallest average quarterly inventory investment. This implies that the “Japanese” level-inflexible strategy does not have the smallest workforce or lowest inventory as claimed by some.We also tested the effects of the operating conditions on the workforce strategies. The level-flexible strategy was most insulated from the seasonality, inventory restrictions, and service level. Thus again the claims made for the level-inflexible strategy about being insulated from its environment were not substantiated. It was found that the seasonality of demand had the greatest impact on the three workforce strategies. Also, the level of service greatly affected the utilization of labor resources.The major overall conclusion is that the level-flexible strategy which is associated with some Japanese manufacturing firms does not achieve the claims that some of its adherents have made for it. It does not have the smallest workforce or the lowest inventory nor is it best insulated from its environment. Furthermore, the seasonality of demand and the level of service do effect this strategy.     

基于Arena的随机需求和随机提前期二级库存仿真优化

讨论了由一个供应商和多个经销商组成的二级库存优化问题,该系统中每个经销商的客户需求以及供应商和经销商的订货提前期都是随机的,供应商和每个经销商都采用(T,s,S)混合策略进行库存管理。首先建立了该二级库存系统优化问题的数学模型,然后设计了解决该问题的仿真流程并基于仿真软件Arena建立了仿真模型,通过对由一个供应商和三个经销商所组成的二级库存系统的仿真实验表明,利用计算机仿真方法能够很好地解决随机需求和随机提前期的二级库存系统优化问题,其所得结果更贴近实际系统。