Dept. of Industrial Engineering - Master's degree

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https://hdl.handle.net/11693/13885

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Open Access
Design and analysis of just-in-time production systems
(Bilkent University, 1988) Oğuz, Ceyda
Just-in-Time (JIT) production systems have initially appeared in the Japanese manufacturing environment due to the scarcity of their critical resources. The main aim in JIT production systems is to eliminate waste. To achieve this objective, setup times, lead times, in-process inventories, and defective production must all be minimized. In the design process of a JIT production system, several factors such as lot size, number of kanbans, unit load size, and buffer capacities must be taken into account. In this study, a mathematical model is developed for a single-item, single-line, multi-stage, and multi-period JIT production system. The original model is nonlinear in both objective function and constraints. To reduce the computational difficulties, the nonlinear model is then approximated by a linear model. Next, a simulation model is developed to incorporate the stochastic nature of the demand. A sensitivity analysis is performed on unit load size and on buffer capacity under different demand patterns to examine their effects on the behavior of the model. The results show that thofee unit load size values exceeding 10 percent of the maximum demand in the planning horizon have no effect on the model.
Open Access
Part family machine group formation problem in cellular manufacturing systems
(Bilkent University, 1989) Kandiller, Levent
The first and the most important stage in the design of Cellular Manufacturing (CM) systems is the Part Family Machine Group Formation (PF/MGF) problem. In this thesis, different approaches to the PF/MG-F problem are discussed. Initially, the design process of CM systems is overviewed. Heuristic techniques developed for the PF/MG-F problem are classified in a general framework. The PF/MG-F problem is defined and some efficiency indices designed to evaluate the PF/MG-F techniques are presented. One of the efficiency indices evaluates the inter-cell flows and inner-cell densities while another one measures the within-cell work-load balances. Another index measures the under-utilization levels of machines. A number of the most promising PF/MG-F techniques are selected for detailed analysis. These selected techniques are evaluated and compared in terms of the efficiency measures by employing randomly generated test problems. Finally, further research areas are addressed.
Open Access
Sensitivity analysis of distance constraints and of multifacility minimax location on tree networks
(Bilkent University, 1989) Doğan, Esra
In this thesis, the main concern is to investigate the use of consistency conditions of distance constraints in sensitivity analysis of certain network location problems. The interest is in minimax type of objective functions. A single parametric approach is adopted in the sensitivity analysis for the m-facility minimax location problem on tree networks. Apart from the traditional sensitivity analysis approach, a conceptual framework for imprecision in distance constraints is developed.
Open Access
Unit demands inventory system with acceptance sampling
(Bilkent University, 1989) Akbaş, Zeki
In this study, an extension to the unit demands inventory model with exponentially distributed interdemand times is considered. In this extension orders may arrive in two shipments due to an acceptance sampling scheme. The defective items that are detected by the plan will arrive through a second shipment. A reorder-point, order-quantity (s,Q) type control plan is adopted. The corresponding cost-rate function is constructed and numerically optimized for the best operating policy.
Open Access
A New approach in the maximum flow problem
(Bilkent University, 1989) Eren, Aysen
In this study, we tried to approach the maximum flow problem from a different point of view. This effort has led us to the development of a new maximum flow algorithm. The algorithm is based on the idea that when initial quasi-flow on each edge of the graph is equated to the upper capacity of the edge, it violates node balance equations, while satisfying capacity and non-negativity constraints. In order to obtain a feasible and optimum flow, quasi-flow on some of the edges have to be reduced. Given an initial quasi-flow, positive and negative excess, and, balanced nodes are determined. Algorithm reduces excesses of unbalanced nodes to zero by finding residual paths joining positive excess nodes to negative excess nodes and sending excesses along these paths. Minimum cut is determined first, and then maximum flow of the given cut is found. Time complexity of the algorithm is o(n^m). The application of the modified version of the Dynamic Tree structure of Sleator and Tarjan reduces it to o(nmlogn).
Open Access
Price dependent procurement decisions in one-period inventory problem
(Bilkent University, 1989) Polatoğlu, Hakan
In this work the classical newsboy model is extended by introducing a price dependent demand pattern. It is intended to obtain optimal procurement and pricing decisions for maximizing the expected profit. It is shown that, both decisions can be made simultaneously if we are able to identify the effects of price on the demand process.
Open Access
Solution of feasibility problems via non-smooth optimization
(Bilkent University, 1990) Ouveysi, Iradj
In this study we present a penalty function approach for linear feasibility problems. Our attempt is to find an eiL· coive algorithm based on an exterior method. Any given feasibility (for a set of linear inequalities) problem, is first transformed into an unconstrained minimization of a penalty function, and then the problem is reduced to minimizing a convex, non-smooth, quadratic function. Due to non-differentiability of the penalty function, the gradient type methods can not be applied directly, so a modified nonlinear programming technique will be used in order to overcome the difficulties of the break points. In this research we present a new algorithm for minimizing this non-smooth penalty function. By dropping the nonnegativity constraints and using conjugate gradient method we compute a maximum set of conjugate directions and then we perform line searches on these directions in order to minimize our penalty function. Whenever the optimality criteria is not satisfied and the improvements in all directions are not enough, we calculate the new set of conjugate directions by conjugate Gram Schmit process, but one of the directions is the element of sub differential at the present point.
Open Access
Analytical loading models and control strategies in flexible manufacturing systems: a comparative study
(Bilkent University, 1990) Kırkavak, Nureddin
There are three problem areas in designing and implementing a manufacturing line : the part family selection and grouping, system configuration and toolings and the operational control of manufacturing. The manufacturing process has to be stream-lined by considering resources and products to achieve flow lines operating around product families with acceptable levels of utilization. The stream-lined processes have to be assigned to tandem machines in the manufacturing lines. Then, interactions between production and inventory levels should be controlled at the operational level. Based on this framework, first a system configuration and tooling problem is modeled. The model turns out to be a large mLxed integer linear program, so that some alternative optimal seeking or heuristic techniques are used to solye the model for constructing a flow line structured Flexible Manufacturing System. Push systems of the Material Requirements Planning type or pull systems like the base-stock or Kanban schemes are often seen as alternatives for controlling manufacturing systems. The differentiating features of push, pull and a hybrid strategy are studied by discrete event simulation under different system and environmental characteristics for Flexible Manufacturing Systems. The impact of assignment of operations to machines on the performance of the system is also discussed.
Open Access
Two new algorithms for the linear assignment problem
(Bilkent University, 1990) Ekin, Oya
The linear assignment problem (AP) being among the first linear programming problems to be studied extensively,, is a fundamental problem in combinatorial optimization and network flow theory. AP arises in numerous applications of assigning personnel to jobs, assigning facilities to locations, sequencing jobs, scheduling flights, project planning and a variety of other practica.1 problems in logistics planning. In this thesis work, we seek for new approaches for solving the linear assignment problem. The main concern is to develop solution methods that exhibit some sort of parallelism. We present two new approaches for solving the assignment problem : A dual-feasible signature guided forest algorithm and a criss-cross like algorithm.
Open Access
Simplex Tableau based approximate projection in Karmarkar's algorithm
(Bilkent University, 1990) Günalay, Yavuz
In this thesis, our main concern is to develop a new implementation of Karmarkar’s LP Algorithm and compare it with the standard version. In the implementation, the “Simplex Tableau” information is used in the basic step of the algorithm, the projection. Instead of constructing the whole projection matrix, some of the orthogonal feasible directions are obtained by using the Simplex Tableau and to give an idea of its effectiveness, this approximation scheme is compared with the standard implementation of Karmarkar’s Algorithm, by D. Gay. The Simplex Tableau is also used to calculate a basic feasible solution at any iteration with a very modest cost.
Open Access
Some heuristics as preprocessing for 0-1 integer programming
(Bilkent University, 1991) Yılmaz, Fatih
It is well-known that 0-1 integer programming is one of the hard problems to solve other than special cases of constraint set in mathematical programming. In this thesis, some preprocessing will be done to get useful informations, such as feasible solutions, bounds for the number of Ts in feasible solutions, about the problem. A new algorithm to solve general (nonlinear) 0-1 programming with linear objective function will be devoloped. Preprocessing informations, then, are appended to original problem to show improvements in enumerative algorithms, e.g. in Branch and Bound procedures.
Open Access
The distribution of the residual lifetime and its applications
(Bilkent University, 1991) Çağlar, Mine Alp
Let T be a continuous positive random variable representing the lifetime of an entitle This entity could be a human being, an animal or a plant, or a component of a mechanical or electrical system. For nonliving objects the lifetime is defined as the total amount of time for which the entitj'^ carries out its function satisfactoriljc The concept of aging involves the adverse effects of age such as increased probability of failure due to wear. In this thesis, we consider certain characteristics of the residual lifetime distribution at age t, such as the mean, median, and variance, as descril)ing aging. The following families of statistical distributions are studied from this point of view: 1. Gamma with two parameters, 2. Weil^ull with two paxameters, .3. Lognormal with two parameters, 4. Inverse Poljmomial with one parameter. Gamma and Weil)ull distrilDutions are fitted to actual data.
Open Access
Manufacturing flexibility in the justification of advanced automation investments
(Bilkent University, 1991) Çetinkaya, Sıla
A substantial amount of literature pertaining to flexibility has accumulated over the last decade. Nevertheless, there are several strategically important issues underlying this concept which are not understood properly, Understanding flexibility is made difficult by its multidimensional nature. Based on a detailed review of the literature we classify the conceptual frameworks on formalizing flexibility as: • type based understanding • change based understanding. We suggest the change based approach can provide a greater understanding of flexibility to managers whose knowledge about technological details is limited. Thus we expand Suresh’s (1990.b) capability-ease definition to provide a basis for the understanding. There have been a prevailing discussion between researchers on how flexibility relates to system performance. In fact type based and change based approaches are two different ways of determining relevant performance measures associated with flexibility. We suggest a framework capability-ease approach for the analysis of relevant performance measures. If it is followed by a task force capability-ease approach can contribute to a greater understanding of flexibility which leads to the selection of more appropriate performance measures. It is well recognized that for the future of manufacturing, flexibility is a crucial concept. However flexibility investments have been difficult to justify because of their high initial costs and strategic implications. Over the last few years incremental implementation of flexible technology has been suggested as a remedy for the investment justification problems, because it leads to lower annual capital outlays. We develop a m ixed-zeroone, nonlinear program m ing, m ultim achine, m ultiperiod, replacem ent model for incremental implementation of flexible automation. Capability and ease notions are adapted for modeling flexibility and a reclassification of costs is considered. Thus some specific aspects of designing flexibility are modeled in contrast to machine-level equipment replacement problem.
Open Access
A comparative study of computational procedures for resource constrained project scheduling problem
(Bilkent University, 1991) Bala, Hasan
Customarily, the project sclheduling problem is thought in the context of PERT and CPM. Although widely used and powerful, these techniques do not take into account a basic feature of the problem, that is resource limitations. The problem addressed in this study is to schedule the activities of a single project in order that all resource and precedence relationships constraints are satisfied with an objective of minimizing total of activity completion times. Our purpose is to make a computational comparison of some solution procedures for the problem. Firstly, the 0 - 1 formulation of the problem is introduced together with the underlying assumptions. Then, we describe the solution procedures tested in this study. In order to evaluate them, the random activity networks are generated. Finally, we provide the results and conclusions.
Open Access
A successive algorithm for the Chinese Postman Problem
(Bilkent University, 1991) Narin, Noyan
The Chinese Postman Problem being one of the well known problems in combinatorial optimization has many applications in real life problems such as mail delivery, road maintenance and bus scheduling. In this thesis work, we present a successive algorithm for the solution of Chinese Postman Problem. Additionally, we present efficient data structures for the existing algorithms in literature and for the implementation of our successive algorithm.
Open Access
The analytic hierarchy process applied to the justification of advanced manufacturing systems
(Bilkent University, 1991) Urhan, Kubilay Ediz
In this thesis, a multi-attribute decision model for the justification of advanced manufacturing systems by use of Analytic Hierarchy Process is developed. The model constructed is a general model which can be applied to any advanced manufacturing system justification problem. In the model, cost is directly included in a single hierarchy with tlie benefits, and the final decision is given depending on the priority vector of this single hierarchy. A hypothetical cell replacement decision in a cellular manufacturing system is given to demonstrate the application of the model.
Open Access
Design and implementation of an MRP-II system in electronics industry
(Bilkent University, 1991) Cankat, A Burç
Manufacturing Resource Planning (MRP II) system is a modern production planning and control method that is relatively new in our country. In today's competitive and continuously improving industrial scene MRP II systems play an important role in increasing productivity. Electronics industry is a field that is highly suitable for MRP applications and can easily set a good example for further improvements. This work aims at applying a professional MRP II softv>^are to a relatively large electronic equipment manufacturer. In this aspect the semi-formal operating system of the company is totally reconstructed and formalized to meet the requirements of the new system. To achieve these a phased implementation plan is developed and executed and thus a successful implementation is performed. Finally, the initial results of the new system are discussed.
Open Access
A polyhedral approach to delivery man problem
(Bilkent University, 1992) Keskinocak, Pınar
In this thesis we discuss some polyhedral approaches to the Delivery Man Problem(DMP),which is a special case of the Traveling .Scvlesman Problem(TSP). First, we look at two formulations of the problem and describe a combinatorial solution procedure for the linear programming relaxation.Then we give some valid inequalities and discuss a Lagrangean Relaxation procedure and a cutting plane procedure. Finally, we propose heuristics for tree graphs and general graphs and give computational results.
Open Access
Mathematical models of evolution
(Bilkent University, 1992) Özaktaş, Hakan
Two categories of evolutionary models are analyzed. The first category is the so-called autogenesis phenomenon. The emergence of self-organization, which has been discussed previously by Csanyi and Kampis is verified. The model is extended to an interrelated multi-level autogenesis system. Similarly, self-organization is observed in a hierarchical order for ea.ch level. The second category is the optimization model ol evolution. An ongoing process of consecutive LP runs associated with random perturbation of the parameters at each step, is designed to simulate the evolutionary mechanisms (mutations, variations and selection) and the population dynamics of a hypothetical ecological system. Two diihu'ent LP ajrproaches for Lotka-Volterra systems are compared and contrastc'd. A brief history of evolution a.nd some mathematical models that have been constructed up to date are also descrilred in the beginning chapter.
Open Access
Reactive scheduling in cellular manufacturing systems
(Bilkent University, 1993) Görgülü, Elif
A real-time scheduling problem, specifically rescheduling under machine breakdowns, is considered in this thesis. A heuristic approach is developed for a manufacturing cell with a modified flow shop structure. The strategy reschedules part of the initial schedule to match up with the preschedule at some point. In contrast to other studies, the objective is to create a new schedule that is consistent with the other production planning decisions like material flow and purchasing by utilizing the time critical decision making concept. In the proposed heuristic approach, a new rescheduling strategy is developed and different match-up points are defined for each machine in order to maximize the flexibility during rescheduling. It is compared with alternative reactive scheduling methods in an experimental design and significance of some factors are tested by analysis of variance tests.