Browsing by Subject "Scheduling (Management)"

Now showing 1 - 7 of 7

Open Access
Adaptive thread and memory access schelduling in chip multiprocessors
(2013) Aktürk, İsmail
The full potential of chip multiprocessors remains unexploited due to architecture oblivious thread schedulers used in operating systems, and thread-oblivious memory access schedulers used in off-chip main memory controllers. For the thread scheduling, we introduce an adaptive cache-hierarchy-aware scheduler that tries to schedule threads in a way that inter-thread contention is minimized. A novel multi-metric scoring scheme is used that specifies the L1 cache access characteristics of a thread. The scheduling decisions are made based on multi-metric scores of threads. For the memory access scheduling, we introduce an adaptive compute-phase prediction and thread prioritization scheme that efficiently categorize threads based on execution characteristics and provides fine-grained prioritization that allows to differentiate threads and prioritize their memory access requests accordingly.
Open Access
An application of stochastic programming on robust airline scheduling
(2014) Karacaoğlu, Nil
The aim of this study is to create flight schedules which are less susceptible to unexpected flight delays. To this end, we examine the block time of the flight in two parts, cruise time and non-cruise time. The cruise time is accepted as controllable within some limit and it is taken as a decision variable in our model. The non-cruise time is open to variations. In order to consider the variability of non-cruise times in the planning stage, we propose a nonlinear mixed integer two stage stochastic programming model which takes the non-cruise time scenarios as input. The published departure times of flights are determined in the first stage and the actual schedule is decided on the second stage depending on the non-cruise times. The objective is to minimize the airline’s operating and passenger dissatisfaction cost. Fuel and CO2 emission costs are nonlinear and this nonlinearity is handled by second order conic inequalities. Two heuristics are proposed to solve the problem when the size of networks and number of scenarios increase. A computational study is conducted using the data of a major U.S. carrier. We compare the solutions of our stochastic model with the ones found by using expected values of non-cruise times and the company’s published schedule.
Open Access
Application of the critical path method to the planning of a technology transfer project using linear programming
(1993) Emirli, Elif
The main purpose of this thesis is to utilize the critical path method in the planning of a technology transfer project by using linear programming. LINDO software is practiced in establishing the linear programming formulation and a matrix generator is written in C language to input the formulation into LINDO format. In this way, the schedule of the project is created, the completion time of the project is calculated and the activities forming the critical path are determined. Also by applying a parametric analysis to the right-hand sides of the constraints (activity durations) for the noncitical activities, the times when the critical activities became critical are determined.
Open Access
Fleet type assignment and robust airline scheduling with chance constraints under environmental emission considerations
(2013) Şafak, Özge
Fleet Type Assignment and Robust Airline Scheduling is to assign optimally aircraft to paths and develop a flight schedule resilient to disruptions. In this study, a Mixed Integer Nonlinear Programming formulation was developed using controllable cruise time and idle time insertion to ensure passengers’ connection service level with the objective of minimizing the costs of fuel consumption, CO2 emissions, idle time and spilled passengers. The crucial contribution of the model is to take fuel efficiency of aircraft into considerations to compensate for the idle time insertion as well as the cost of spilled passengers due to the insufficient seat capacity. The nonlinearity in the fuel consumption function associated with controllable cruise time was handled by second order conic reformulations. In addition, the uncertainty coming from a random variable of non-cruise time arises in chance constraints to guarantee passengers’ connection service level, which was also tackled by transforming them into conic inequalities. We compared the performance of the schedule generated by the proposed model to the published schedule for a major U.S. airline. On the average, there exists a 20% total cost saving compared to the published schedule. To solve the large scale problems in a reasonable time, we also developed a two-stage algorithm, which decomposes the problem into planning stages such as fleet type assignment and robust schedule generation, and then solves them sequentially.
Open Access
Integrated machine-scheduling and inventory planning of door manufacturing operations at OYAK Renault factory
(2012) Bozkaya, Nurcan
A car passes through press, body shell, painting and assembly stages during its manufacturing process. Due to the increased competition among car manufacturers, they aim to continuously advance and improve their processes. In this study, we analyze planning operations for the production of front/back and left/right doors in body shell department of Bursa Oyak-Renault factory and propose heuristic algorithms to improve their planning processes. In this study, we present four different mathematical models and two heuristics approaches which decrease the current costs of the company particularly with respect to inventory carrying and setup perspectives. In the body shell department of the company, there are two parallel manufacturing cells which produces doors to be assembled on the consumption line. The effective planning and scheduling of the jobs on these lines requires solving the problem of integrated machine-scheduling and inventory planning subject to inclusive eligibility constraints and sequence independent setup times with job availability in flexible manufacturing cells of the body shell department. The novelty in the models lie in the integration of inventory planning and production scheduling decisions with the aim of streamlining operations of the door manufacturing cells with the consumption line. One of the proposed heuristic approaches is Rolling Horizon Algorithm (RHA) which divides the planning horizon into sub-intervals and solves the problem by rolling the solutions through sub-intervals. The other proposed algorithm is Two-Pass Algorithm which divides the planning horizon into sub-intervals and solves each sub-problem in each sub-interval to optimality for two times by maintaining the starting and ending inventory levels feasible. These approaches are implemented with Gurobi optimization software and Java programming language and applied within a decision support system that supports daily planning activities.
Open Access
Minimizing schedule length on identical parallel machines: an exact algorithm
(1991) Akyel, H. Cemal
The primary concern of this study is to investigate the combinatorial aspects of the single-stage identical parallel machine scheduling problem and to develop a computationally feasible branch and bound algorithm for its exact solution. Although there is a substantial amount of literature on this problem, most of the work in this area is on the development and performance analysis of approximation algorithms. The few optimizing algorithms proposed in the literature have major drawbacks from the computer implementation point of view. Even though the single-stage scheduling problem is known to be unary A/’P-hard, there is still a need to develop a computationally feasible optimizing algorithm that solves the problem in a reasonable time. Development of such an algorithm is necessary for solving the multi-stage parallel machine scheduling problems which are currently an almost untouched issue in the deterministic scheduling theory. In this study, a branch and bound algorithm for the single-stage identical parallel machine scheduling problem is proposed. Promising results were obtained in the empirical analysis of the performance of this algorithm. Furthermore, the procedure that is developed to determine tight bounds at a node of the enumeration tree, is an approximation algorithm that solves a special class of identical parallel machine scheduling problems of practical interest. This algorithm delivers a solution that is arbitrarily close to 4/3 times the optimum. To our knowledge this is the best result obtained for this problem so far.
Open Access
Robust airline scheduling with controllable cruise times and chance constraints
(2012) Duran, Aslıgül Serasu
This is a study on robust airline scheduling where flight block times are considered in two parts as cruise time and non-cruise time. Cruise times are controllable and non-cruise times are random variables. Cruise time controllability is used together with idle time insertion to handle uncertainty to guarantee passenger connection service levels while ensuring minimum costs. The nonlinearity of these cost functions are handled by representing them via second order conic inequalities. The uncertainty in non-cruise times are modeled through chance constraints on passenger connection service levels, which are expressed using second order conic inequalities using the closed form equations. Congestion levels of origin and destination airports are used to decide variability for each flight. Computational study shows exact solutions can be obtained by commercial solvers in seconds for a single hub schedule and in minutes for a 4-hub daily schedule of a major US carrie