A reach project scheduling problem

Project scheduling is a very common problem in engineering and many companies with project based manufacturing environment have to deal with project scheduling issues on a daily basis. The goal in a project scheduling problem is to minimize the cost or the project completion time with the given precedence rules and other constraints. In this study we propose a project scheduling approach for a manufacturing company that has to manage several projects simultaneously. The scheduling problem is a multi-project, multi-mode, resource constrained problem with time-cost tradeoff decision. The objective in the problem is to minimize the aggregate cost of current and planned projects. We first developed a linear model to solve the problem. However, the total number of jobs increases with increasing number of projects, and with increasing complexity the overall problem grows exponentially. To solve the problem in a reasonable time we developed a heuristic approach which based on decomposition of the problem. Quality and time issues of the proposed model are discussed in detail. KEY WORDS: Project based manufacturing systems, resource constrained scheduling problems, time-cost tradeoff, preemptivity, multi mode systems, multiproject sheduling, mathametical programming and decomposition.