The implicit assumption in conventional inventory models is that the stored products maintain the same utility forever, i.e., they can be stored for an infinite period of time without losing their value or characteristics. However, generally speaking, almost all products experience some sort of deterioration over time. Some products have very small deterioration rates, and henceforth the effect of such deterioration can be neglected. Some products may be subject to significant rates of deterioration. Fruits, vegetables, drugs, alcohol and radioactive materials are examples that can experience significant deterioration during storage. Therefore the effect of deterioration must be explicitly taken into account in developing inventory models for such products. In most existing deteriorating inventory models, time is treated as a continuous variable, which is not exactly the case in practice. In real-life problems time factor is always measured on a discrete scale only, i.e. in terms of complete units of days, weeks, etc. In this research, we present several discrete-in-time inventory models and identify optimal ordering policies for a single deteriorating product by minimizing the expected overall costs over the planning horizon. The various conditions have been considered, e.g. periodic review, time-varying deterioration rate, waiting-time-dependent partial backlogging, time-dependent demand, stochastic demand etc. The objective of our research is two-fold: (a) To obtain optimal order quantity and useful insights for the inventory control of a single deteriorating product over a discrete time horizon with deterministic demand, variable deterioration rates and waiting-time-dependent partial backlogging ratios; (b) To identify optimal ordering policy for a single deteriorating product over a finite horizon with stochastic demand and partial backlogging. The explicit ordering policy will be developed for some special cases. Through computational experiments and sensitivity analysis, a thorough and insightful understanding of deteriorating inventory management will be achieved.

Made available in DSpace on 2015-05-08T14:53:24Z (GMT). No. of bitstreams: 1 ArquivoTotal.pdf: 2670073 bytes, checksum: b32f39ed0b53334c57b727abcef4f5cd (MD5) Previous issue date: 2014-08-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The work presented in this thesis concerns the problem of sizing and sequencing batch production, single level, skilled (CLSP), in a manufacturing plant precast concrete used in construction, where the sizing and sequencing of lots production in a given period, represent a challenge for the company, which in turn seeks to minimize the costs of production, inventory, setup and improve the level of service customers' demands. The problem consists in defining the size of lots and production sequence of several blocks precast concrete in a press line, with setup times too high. It was proposed, therefore, a mathematical model whose objective is to minimize the costs of production, setup and inventory, involved in the manufacturing process of these products through the exact method of Integer Linear Programming. The presented model aims to solve the problem was proposed and applied to the real situation of the company for the purpose of comparison of current results with the results after application of the model . / O trabalho que se apresenta nesta dissertação diz respeito ao problema de dimensionamento e sequenciamento de lotes de produção, único nível, capacitado (CLSP), em uma fábrica de produtos pré-moldados de concreto usados na construção civil, onde o dimensionamento e sequenciamento dos lotes de produção num período pré-definido, representam um desafio para a empresa; que por sua vez busca minimizar os custos de produção, estoque, setup e melhorar o nível de atendimento das demandas dos clientes. O problema consiste em definir o tamanho dos lotes e sequência de produção de diversos blocos pré-moldados de concreto em uma linha de prensagem, com tempos de setup muito altos. Será proposto, portanto, um modelo matemático cujo objetivo é minimizar os custos de produção, setup e estoque, envolvidos no processo de fabricação destes produtos através do método exato de Programação Linear Inteira. O modelo a ser apresentado visa resolver o problema proposto e será aplicado em situação real da empresa para fins de comparação dos resultados atuais com os resultados após aplicação do modelo.