Erection scheduling at shipbuilding using constraint directed graph search

Abstract

This research develops the erection scheduling expert system for shipbuilding: DAS-ERECT. The backbone scheduling in shipbuilding plant is the erection scheduling at the main docks, because the erection schedule influences on not only the makespan at the docks, but also the utilization level of overall shipbuilding plant including preceding block assembly shops. Thus the shipbuilding scheduling system requires a multi-level hierarchical architecture by nature. So our project, DAS project, has adopted the hierarchical architecture in building the scheduling expert systems for Daewoo shipbuilding company. In the hierarchical architecture, detailed scheduling necessary at the lower level assembly plants are delegated to the individual plant``s schedulers as far as the requirements from the higher level scheduler are satisfied. However, if the lower level scheduling is impossible, the higher level scheduler attempts to adjust the original requirements. The advantages of hierarchical architecture are the reduced computational complexity and its robustness during the reactive phase. The second key issue in scheduling at the docks stems from the complexity of search. To handle this problem, we propose the constraint dir ected graph search (CDGS) which amalgamates the notion of graph expansion and constraint directed pruning into an algorithm. The CDGS is guided by constraints not only for pruning search space but also for selecting the best node for erection. In this research, the algorithm for CDGS and the representation scheme for constraints are developed to realize the system DAS-ERECT. DAS-ERECT is implemented using the expert system development tool UNIK on SUN SPARC station. To accommodate the data availability during the implementation process, the two phased implementation approach is adopted. A series of experiments are performed using the real data to evaluate the performance of two systems. In the preliminary phase, an ideal system is developed regardles...