Optimization Model for an Airline Crew Rostering Problem: Case of Garuda Indonesia

This paper discusses the cockpit crew rostering problem at Garuda Indonesia, taking into account a number of internal cockpit crew labor regulations. These internal labor regulations are in general more restrictive at Garuda Indonesia than at other airlines, so that modeling the cockpit crew rostering problem for Garuda Indonesia is challenging. We have derived mathematical expressions for the cockpit crew labor regulations and some technical matters. We model a non-linear integer programming for the rostering problem, using the average relative deviation of total flight time to the ideal flight time as the objective function. The optimization model have been tested for all classes of cockpit crews of Garuda Indonesia, using a simulated annealing method for solving the problem. We obtained satisfactory rosters for all crew members in a short amount of computing time. This shows that the optimization problem is well-defined

Wiener-Hopf techniques for the analysis of the time-dependent behavior of queues

In this thesis we study the time-dependent behavior of queueing systems. The study is focused on the queueing systems:\ud 1. the GI/G/1 system,\ud 2. the GI/Hm/s system,\ud 3. the Markovian Fluid Flow Model, the fluid flow model that is modulated by a Markov process,\ud 4. the Semi-Markovian Fluid Flow Model, a generalization of the Markovian Fluid Flow Model.\ud In general, the time-dependent behavior of queueing systems is much influenced by the initial server(s)’s work load. This leads us to consider the queueing systems with non-zero initial server(s)’s work load. In the GI/G/1 system and the GI/Hm/s system this means that in the beginning there exist a number of (special) customers to serve. In the last two systems, initially the buffer has non-zero content.\ud The technique that is used to analyze the behavior of the queueing systems studied in this thesis is based on the Wiener-Hopf factorization. A brief discussion on the Wiener-Hopf factorization is given in chapter 2, where we also give the conditions on the existence of uniqueness of the factorization. In this chapter we also give some preliminaries that we need for the analysis in the rest chapters

A heuristic method for solving airline crew pairing problems

The airline crew pairing problem is one of the optimization problems which classified as a NP-hard problem. Since the number of feasible pairings in flight schedules can be numerous, the exact methods will not efficient to solve the problem. We propose a heuristic method for solving crew pairing problems. Initially, we generate a feasible solution by maximizing the covered flights. Then, we improve the solution by constructing a procedure to avoid the local optimal solution. We test our method to an airline schedules. The computational results show that our method can give the optimal solution in short period of time

Towards Sustainable City: A Covering Model for Recycling Facility Location-allocation in Nilai, Malaysia

Sustainable waste management is essential for any nation. To limit the amount of waste transported to landfills, it is critical to handle waste properly, notably by segregating recyclables from discarded waste. Waste separation at the source is critical to ensure that generated waste is not completely directed to landfill. The practice of waste separation would initiate the recycling process, which is able to reduce the amount of waste sent to the landfill. Recycling is critical to the achievement of two Sustainable Development Goals (SDGs), 11 and 12, for which Malaysian government has set the goal for recycling rates to reach 40% by 2025 in 2022, the rate has reached 33.17%. In Malaysia, recyclables are either collected on-site or sent to a designated facility. The separation at source activity is essential for developing recycling practices. Despite being the largest waste generator, public engagement, particularly at the household level, has remained low, most likely due to recycling facility availability and accessibility issues. Thus, improving public access to the facility would lead to increased recycling rates. In this study, a mixed integer linear programming model is proposed to locate recycling facilities in optimal locations that cover the most amount of waste generated by households. The capacity level is induced to ensure that the dropped-off recyclables are proportionate at the designated facility locations. Several experiments were conducted for validity purposes, and the proposed model was applied in a Malaysian urban area, namely Nilai. As a result, the proposed model was able to locate the optimal locations with the requisite capacity level while ensuring coverage for most Nilai households

Optimization model for multi-products multi-periods multi-suppliers raw-material selection and composition, and order quantity problem with one-year minimum order quantity contract

This paper concerns the optimization model for a multi-product multi-period raw-material selection and composition, and order quantity problem faced by a beverage company. • There are some criteria in raw material selection, which we accommodate all the criteria in the objective function. There are several suppliers, and one of the decision criteria is a one-year minimum order quantity contract between the company and the suppliers. The actual one-year demand for raw materials may deviate significantly from the one-year minimum order quantities. • We derive a function that can be regarded as a penalty function to maintain the total order quantities in one year to fulfill the minimum one-year order quantity contracts. This penalty function is a part of the objective function and can be relaxed once the one-year minimum order quantity contracts are fulfilled. • We performed several numerical experiments to check the optimal solutions for various demands and for various objective functions. These experiments show our MILP (Mixed Integer Linear Programming) gives the desired optimal solutions and show the influence of decision criteria on the optimal solution