Inter-Sop Integrated Scheduling Theory And Methodology For Shipyard

After the investigation on the manufacturing system in some typical shipyards, it is found that the manufacturing in the shops has the close procedure relationship. The feature of manufacturing in shops is that the jobs flow among fixed equipments. The manufacturing in shops for jobs of a shipyard mainly is taken in steel sheet pre-treating center, cutting center, flat subsection manufacturing center and curve subsection manufacturing center. During this period, jobs are processed in several shops hybridly. For example, after the steel sheets are pre-treated, some of them flow to the cutting center, some of them flow to the flat subsection manufacturing center, and the other flow to the curve subsection manufacturing center. On the other hand, the jobs flowing into the curve subsection manufacturing center may come from the pre-treating center, the cutting center, and the flat subsection manufacturing center. Besides, the batch size of shipmaking is usually one basing on order. And there is usually rush order jobs in the manufacturing. Because of these features in the shipmaking, the precision management may be achieved only with the tight cooperation among shops.But traditionally, the production management in a shipyard in our country is that each shop is managed by person's experience separately. The period to make scheduling for each shop is changing from about two weeks to tens of days. The manufacturing of one job in the following shop can't start until it is finished in the previous shop and sent to the following shop at the end of scheduling period in the previous shop. This is the reason that makes much longer lead time for ship building in our country than that in Korea or Japan where the production management is more advanced. It further results in the large in-process inventory and the low equipment utility.In order to improve the production management, some studies on theory and method about scheduling are conducted in this paper, which include following aspects.1) The academic idea of inter-shop integrated scheduling problem (IS-ISP) is proposed according to the production practice in the shipyard. And the inter-shop is discomposed into three layers, which are cell layer, shop layer and inter-shop layer, with hierarchy analysis method. The cell layer concerns identical parallel flow shop scheduling problem (IPFSP) and hybrid flow shop containing multi-functional machines (HFSP-MFM) that can be often found in the shipyard. In the shop layer, there often exists more than one cell layer shop. Crossed flow shop scheduling problem and multi-shop scheduling problems that are often seen in the shipyard are studied. Inter-shop layer refers to make schedule for several shops. By the industrial application in a domestic big shipyard, it was found that the makespan would be shortened by 45% with IS-ISP comparing the traditional scheduling method.2) The network theory is employed to establish multi-level disjunctive graph model for the IS-ISP. For the IS-ISP, which is analyzed by hierarchy analysis method, it is very suitable to establish a multi-level disjunctive graph model by employing the network theory. The link situation between nodes in the models will represent the constraints of the machines, jobs in the manufacturing system; The values related with the links will represent the constraints such as the precedence of jobs and machines, as well as the constraints such as ready time or due time of jobs and machines; The shortest path will represent the optimization criterion for the scheduling problem. The scheduling problem is to queue the jobs so that one or several objectives for the manufacturing system will be optimized under some constraints. Then the beginning time and completing time of each job on every processing stage will be determined. The hierarchy structure of the inter-shop scheduling problem will be described by multi-level disjunctive graph model. The multi-level disjunctive graph model not only can express all constraints that the mathematic programming is able to describe, but also is extremely suitable for the algorithms based on path searching such as ACO algorithm. The searching procedure level by level can not only reduce the number of path to be searched, but also make use of the searching methods and information renewing methods used at the lower levels. So the multi-level disjunctive graph model is helpful to shorten the time for each computation generation, and to improve the searching efficiency.3) A new hybrid ant colony optimization (HACO) algorithm is produced by introducing the crossover and mutation oparators in the genetic algorithm (GA) into the ACO algorithm. For the combined optimization problem that is described with disjunctive model, it is extremely suitable for apply ant colony optimizaiton (ACO) algorith, which is based on path searching. But the ACO has the shortage to fall in the local convergency, while the crossover, mutation operators in the GA is able to jump out of the local convergency during the optimizaiton. So crossover, mutation operators in the GA are introduced in the ACO. And the HACO is conducted. GA and ACO are both newly developped meta-heuristic algorithms that not only have good performance, but they can cooperate each other very well. The HACO algorithm makes use of the advantages of the GA which is rapid at evolution and the ACO which is good at convergency. The HACO is compared with other algorithms by applying to kinds of instances of different scales. It is found that the HACO has advantages on both optimizaiton speed and solution convengency especially for large scale instances. Then the algorithm with the best feature is apply to the real scheduling in the shop floor.4) The disturbance of rush order often occur in the real proction. When the rush order comes, some of the original jobs have already been processed in some stages. In such situation, the original schedule needs to be reworked so that the rush order would be processed as soon as possible, and the original jobs would not be delayed too much. Industrial application shows that after a rush order job is inserted into a batch of jobs, the postponed time for original jobs is less than 1%, but the ratio of makespan of the rush order job and the sum of the processing time on all stages is 1, which means it will be produced on time. Other production disturbance can also be solved by establishing the corresponding disjunctive model.