The traditional (Q,r) inventory control model assumes that the date at which the order is entered is the same as the date at which it is requested or expected to be delivered. Hence, the penalty cost is incurred when the customer places the order if inventory is unavailable. This is a reasonable assumption for retail systems and most distribution centers (DC), but not for an assemble-to-order (ATO) environment. In this scenario, there is a delivery time which is usually pre-negotiated and in addition to considering the manufacturing process time and in some cases the outbound transportation time, it also has some safety time built-in. This safety time is defined by the manufacturer and represents information related to when the penalty is incurred. The main objective of this research is to develop a modified (Q,r) policy that incorporates the safety time, and to evaluate this policy in terms of expected inventory cost and expected penalty cost / late orders. The problem is addressed following the heuristic approach discussed by Hadley and Whitin (1963). Two main models are developed based on the following assumptions: 1) early shipments are allowed by the customer, and 2) no early shipments are allowed. The behavior of both models is analyzed mathematically and by means of numerical examples. It is shown that from a manufacturer perspective, the first model is preferred over the traditional (Q,r) model. However, it poses a threat for the long term business relationship with the customer because the service level deteriorates, and for the implications that early shipments have on the customer inventory. The behavior of the second model is strictly related to the problem being addressed. Its merits with respect to the traditional and the "early shipment" model are discussed. This discussion is centered on the coefficient of variation of the lead-time demand, the ratio (IC/pi), and the location of the supplier. A final model which is a hybrid of the previous two shipping policies is developed. The models developed in the course of this research are generalizations of the traditional (Q,r) model.

In this study, the seat inventory control problem is considered for airline networks from the perspective of a risk-averse decision maker. In the revenue management literature, it is generally assumed that the decision makers are risk-neutral. Therefore, the expected revenue is maximized without taking the variability or any other risk factor into account. On the other hand, risk-sensitive approach provides us with more information about the behavior of the revenue. The risk measure we consider in this study is the probability that revenue is less than a predetermined threshold level. In the risk-neutral cases, while the expected revenue is maximized, the probability of revenue being less than such a predetermined level might be high. We propose three mathematical models to incorporate the risk measure under consideration. The optimal allocations obtained by these models are numerically evaluated in simulation studies for example problems. Expected revenue, coefficient of variation, load factor and probability of the poor performance are the performance measures in the simulation studies. According to the results of these simulations, it shown that the proposed models can decrease the variability of the revenue considerably. In other words, the probability of revenue being less than the threshold level is decreased. Moreover, expected revenue can be increased in some scenarios by using the proposed models. The approach considered in this thesis is especially proposed for small scale airlines because risk of obtaining revenue less than the threshold level is more for this type of airlines as compared to large scale airlines.

In this master thesis study, new inventory control mechanisms are developed for the repairables in Nedtrain. There is a multi-item, multi echelon system with a continuous review and one for one replenishment policy and there are different demand supply options in each control mechanism. There is an aggregate mean waiting time constraint in each local warehouse and the objective is to minimize the total system cost. The base stock levels in each warehouse are determined with an approximation method. Then different demand supply options are compared with each other.

Software development of R.O.C. military maintenance parts inventory control system¡¦s integrated requirement used to adopt data flow approach. Data flow approach not only flunks to guide users to describe their real need but also fails to provide a coalescence picture that integrates the operating personnel, materials data sources and logistic system together with completeness and consistency. Using architecture-oriented approach, structure elements, services, connections, and interaction behaviors of R.O.C. military maintenance parts inventory control system¡¦s integrated requirement are adequately documented. With this transparent document, developers and users shall obtain full integrality and consistency of technical support and requirement provision during the system development. This research embraces the structure behavior coalescence, abbreviated as SBC, approach to construct the architecture-oriented analysis-model of military maintenance parts inventory control system¡¦s integrated requirement, abbreviated as AOAMMMPICSIR. AOAMMMPICSIR shall be referred as an R.O.C. military architecture-oriented analysis tool and it shall help outsource the software development of military maintenance parts inventory control system¡¦s integrated requirement with success and quality.

The term resource is used to refer to a machine, tool-group, piece of equipment or personnel. Optimization models for resource maintenance are obtained in conjunction with other production related decisions like production planning, production scheduling, resource allocation and job inspection. Emphasis is laid on integrating the above inter-dependent decisions into a unified optimization framework. This is accomplished for large stationary resources, small non-stationary resources with high breaking rate and for resources that form a part of a network. Owing to large problem size and high uncertainty, the optimal decisions are determined by formulating and solving the above problems as Markov decision processes (MDPs). Approximate dynamic programming based algorithms are used for solving the large optimization problems at hand. The performance of resulting near optimal policies is compared with that of traditional formulations in all cases. The latter treat the resource maintenance decisions independent of other manufacturing related decisions. In certain formulations, the resource state is not completely observable. This results in a partially observable MDP (POMDP). An alternative algorithm for the solution of POMDP is developed, where several mixed integer linear programs (MILPs) are solved during each ADP iteration. This helps obtain better quality solutions for the POMDPs with very large or continuous action spaces in an efficient manner.

<p>Detta examensarbete har ägt rum vid Produktionsverkstad 1 (PV1) på Wexiödisk AB där diskmaskiner av huvtyp tillverkas. Syftet med detta examensarbete har varit att undersöka vilka lagerstyrningsmodeller som är lämpliga för att styra avdelningens materialflöden med. Arbetet har genomförts i två steg. Först behandlades artiklar unika för produkterna vid PV1, därefter artiklar gemensamma med andra produkter. Enligt modeller ur relevant litteratur utformades förslag på hur dessa kunde appliceras praktiskt. Förslagen presenterades och diskuterades med berörd personal som valde Tvåbingesystem 2. Ett test gjordes enligt principen ”den japanska sjön” vilket innebar lägre lagernivåer i lastbärarna. De problem som uppstod noterades. Resultatet blev att antalet artiklar som plockades i veckosatser minskades vilket skapat underlag för att minska administrationen av tillhörande plocklistor. Plockvagnen har kunnat tas bort vilket frigjort yta vid monteringsavdelningen. Förutsättningar finns att slå samman två plocklistor till en och därmed förenkla arbetet för förrådspersonalen.</p> / <p>This degree project has been performed at Production unit 1 (PV1) at Wexiödisk AB, where hood type washing machines is manufactured. The purpose of this project has been to investigate which inventory control models that could be suitable to control the section’s material supplies. The work has been accomplished in two steps. At first, items unique to products manufactured at PV1 were treated, followed by items common with other products. According models in relevant literature, suggestions were made to how the models could be applied practically. The suggestions was presented to and discussed with the parties concerned who chose Two-bin system 2. A trial was carried out according to the principle of “the Japanese river” which implied lowered inventory levels. The problems that occurred were noted. The result was that the number of items that was weekly picked and distributed was reduced which has created a basis to also reduce the administration of the systems picking lists. The item wagon has been removed which has cleared floor space at the assembly section. Conditions have been created to merge two picking lists into one and thereby simplify the work for the inventory staff.</p>

Thesis (Ph.D.)--Mississippi State University. Department of Industrial and Systems Engineering. / Title from title screen. Includes bibliographical references.

Thesis (Ph.D)--Industrial and Systems Engineering, Georgia Institute of Technology, 2010. / Committee Co-Chair: John H. Vande Vate; Committee Co-Chair: Shi-Jie Deng; Committee Member: Anton J. Kleywegt; Committee Member: Hayriye Ayhan; Committee Member: Mark E. Ferguson. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Sammanfattning Syfte - Syftet med denna studie är att bidra till ökad förståelse för hur lager kan styras när varierad efterfrågan förekommer. För att uppnå syftet är målet med studien att sammanställa processer som underlättar för lagerstyrning vid varierad efterfrågan. Detta möjliggörs genom att besvara följande frågeställningar: 1. Vilka metoder för säkerhetslagerberäkning och lagerstyrning är lämpliga när hänsyn bör tas till varierad efterfrågan? 2. Hur påverkas lagerförings- och ordersärkostnader av olika sätt att styra lager vid varierad efterfrågan? Metod - Teorier angående lagerstyrning vid varierad efterfrågan samlades in via litteraturstudier. En fallstudie genomfördes för att applicera det teoretiska ramverket på empiri från fallföretaget. Empiri samlades in via intervjuer och dokumentationsstudier och utgjorde en grund för beräkningar och vidare analys. Resultat - Lämplig säkerhetslagerberäkning vid varierad efterfrågan anses vara SERV2 som tar hänsyn till antalet bristtillfällen och ger ett bra mått på lagertillgängligheten över tid. De dynamiska lagerstyrningsmetoderna Silver &amp; Meal samt Wagner-Whitin kan i större utsträckning hantera stora variationer i efterfrågan gentemot beställningspunktssystem. Beräkningar resulterade i att Wagner-Whitin var den lagerstyrningsmetod som i majoriteten av fallen genererar lägst totalkostnad när hänsyn tas till lagerförings- och ordersärkostnader. En process för lagerstyrning vid varierad efterfrågan har kartlagts där indata i form av metod- och resursobjekt redogörs. Detta för att bidra till ökad förståelse för hur lager kan styras vid varierad efterfrågan. Implikationer - Inom denna studie framgår det att kostnaderna för lagerstyrningen vid varierad efterfrågan kan sänkas med hjälp av dynamiska lagerstyrningsmetoder. Det är dock viktigt med trovärdig indata för att generera tillförlitliga resultat. Begränsningar - Inom de dynamiska lagerstyrningsmetoderna vägs ordersärkostnad mot lagerföringskostnad och genererar det mest ekonomiska alternativet ur lagerstyrningens perspektiv. Det måste inte vara det bästa ur ett helhetsperspektiv då förändrade orderkvantiteter kan påverka andra delar av materialflödet. De processkartor som är upprättade utgår från den valda lösningen, detta begränsar tillämpningen till verksamheter som har liknande förutsättningar som fallföretaget. Nyckelord - Varierad efterfrågan, lagerstyrning, säkerhetslagerberäkning, lagerstyrningsmetod. / Abstract Purpose - The purpose of this thesis is to develop an understanding of how to control inventory when the demand varies. To achieve the purpose, the goal is to create a process that facilitates inventory management at varied demand. This is feasible by answering following questions: 1. Which methods of safety stock calculation and inventory control are appropriate and take varied demand in consideration? 2. How is the inventory carrying cost and ordering cost affected by different methods of controlling inventory when demand varies? Method - Information about controlling inventory at varied demand was gathered through literature studies. A case study was carried out to apply the theoretical framework on empirical data from the business case. The empirical data was collected through interviews and documentation studies, which provided a basis for calculation and further analysis. Findings - SERV2 is considered as an appropriate method for safety stock calculations since it takes the number of occasions for shortages into account and provides a good measurement of the stock availability over time. The dynamic inventory control methods Silver &amp; Meal and Wagner-Whitin can handle variations in demand better than order point systems. Calculations show that Wagner-Whitin generates the lowest total costs in the majority of cases. A process is established to facilitate inventory management at varied demand. Implications - Within this study it is shown that using dynamic inventory control methods can reduce inventory control costs when demand varies. Nonetheless it is important to have persuasive input to generate reliable results. Limitations - The dynamic inventory control methods balance order cost with inventory carrying costs to find the most economic option from an inventory control perspective. It is not always the best solution from a holistic perspective since changed order quantities can affect other parts of the material flow. The established process charts are based on chosen solution, which limits its application to businesses with similar conditions as the case study. Keywords - Varied demand, inventory control, safety stock calculation, inventory management

published_or_final_version / Mathematics / Master / Master of Philosophy