چارچوب شبیه سازی یکپارچه برای برنامه ریزی عملیات کشتی ها و سازه های دریایی

Recently, requests for accurate process planning using simulation have been increasing in many engineering fields, including the shipbuilding industry. To date, designers of shipyards have developed in-house simulation systems or used commercial systems such as the QUEST by Dassault system when requests for the simulation of process planning have occurred. However, these methods have some limitations. First, it requires a lot of time to develop a new in-house simulation system. In addition, it is hard to reuse previously developed systems when developing a new one and it is also hard for these to satisfy the various needs of shipyards effectively. To solve these limitations, an integrated simulation framework is proposed in this study. The proposed simulation framework provides an environment for developing various simulation systems for shipbuilding process planning. It consists of a simulation kernel, basic simulation component and application-specific simulation component. The simulation kernel manages both DEVS (discrete event system specification) and DTSS (discrete time system specification) to deal with various simulation requests. The basic simulation component provides commonly used simulation models and modeling strategies, which are used to make a simulation system more efficient. The application-specific simulation component implements the dynamics analysis, collision detection and realistic three-dimensional visualization. To evaluate its efficiency and applicability, the proposed simulation framework is applied to the block erection process of ships and offshore structures. The results show that the proposed simulation framework, as compared with those of existing studies and of commercial simulation systems, can provide a consistent, integrated development environment for a simulation system.

1.1. Background of this study Shipyards are constructing huge ships and offshore structures. For instance, a deadweight 300,000 ton VLCC (very large crude carrier), which can carry 300,000 ton of crude oil, can be delivered to a ship owner after a total design and production period of about 14 months. During this time, it is very important for a shipyard to deliver the ship to its owner on delivery day. Thus, the shipyard should set up accurate process planning by investigating a number of design alternatives as early as possible. However, even though process planning may be set up based on past experience, many problems which are not expected in advance may occur during production, since all ships and offshore structures to be constructed are different from each other in purpose, shape and size. To grasp these problems and to prepare design alternatives beforehand, designers of shipyards are now developing and using in-house systems themselves or are setting up process planning by using commercial simulation tools. However, for the case of developing in-house systems, it is hard to reuse simulation systems which have already been developed by various designers using different methods in different development environments. Thus, developing a new system using this approach requires a lot of time and effort when an application domain of the systems changes. In the case of using the commercial simulation tools, it is difficult for the designers to use existing design and production information, such as CAD information, process planning information, scheduling information, and so on, for simulation. Furthermore, it is difficult to reflect various requirements of the designers and to maintain the security of design and production information. Therefore, if a consistent, integrated simulation environment (‘simulation framework’) that can support the development of a new simulation system is developed, then it is possible to set up accurate process planning in the early stages of development and to provide varied, flexible design alternatives that can increase productivity. 1.2. Related works Many studies related to simulation model architecture and simulation engines have been conducted in the past. Here, the simulation model architecture represents a method for defining the simulation model according to a predefined form, and the simulation engine plays the role of operating the simulation model by progressing the simulation time. Especially, Zeigler [1] and [2] have studied a simulation model architecture of discrete event simulation called DEVS (Discrete EVent System Specification) and are now conducting many other studies related to DEVS. On the other hand, very little research related to simulation frameworks has as yet been carried out. Here, the simulation framework represents an integrated simulation environment that can support the development of a new simulation system. Praehofer and Zeigler et al. [1], [2], [3], [4] and [5] proposed a modeling and simulation method that can handle simulation models of discrete event and discrete time, and they also developed a simulation framework based on the proposed method. In the case of discrete event simulation, the operation of a simulation system is represented as a chronological sequence of events. Process or material flow simulation systems and the like are included in the category of discrete event simulation. On the other hand, in the case of discrete time simulation, the operation of a simulation system is represented as the progress of time. State changes only occur at discrete time instants. Dynamic simulation systems and the like are included in the category of discrete time simulation. However, the developed simulation framework focuses only on the material flow simulation system of a workshop. Thus, it was difficult for it to be applied to a large factory such as a shipyard, and it was also hard to use existing design and production information for simulation. Woo [6] developed a simulation framework based on a commercial simulation tool called QUEST (QUeuing Event Simulation Tool) by the Dassault System Co., Ltd. and applied it to the shipbuilding process of a shipyard. He analyzed the shipbuilding process from the viewpoints of production, process and resource (PPR), and he then defined simulation models for the shipbuilding process by using IDEF (ICAM DEFinition) and UML (unified modeling language). In addition, he tried to use the shipyard's existing scheduling information for simulation. However, because the developed simulation framework is based on a commercial simulation tool, the existing framework had to be newly developed from the beginning if the simulation tool had been changed for any reason. Furthermore, it was difficult to use the CAD information, which is one of existing design and production information sources of the shipyard, for simulation. Some studies related to the simulation framework have been made but have had some limitations, as mentioned above. To overcome these limitations, we proposed a new simulation framework for process planning in shipbuilding. The proposed simulation framework can reuse the already developed simulation systems and have various modules required for applications in shipbuilding, including a dynamic calculation module, a collision detection module, and so on. In addition, it can be applied to various application domains by introducing a similar concept to the research of Praehofer and Zeigler et al.

In this study, an integrated simulation framework which provides an environment for developing various application systems for shipbuilding process planning is proposed. To evaluate its efficiency and applicability, the proposed simulation framework is applied to the block erection simulation and the block turn-over simulation. The proposed simulation framework can deal with various simulation requests because it supports the combined discrete event and discrete time simulation, and provides various schemes to increase the reusability of the simulation models and environments to develop the application systems easily. It also supports various application-specific simulation components such as dynamics, collision detection, graphics modules, etc. Thus, it can be applied to the application fields easily. In future research, it is required to compare the simulation results with the field data to verify accuracy and efficiency. In addition, it is necessary to study wire dynamics in order to describe the behavior of the wire more accurately, and the interface between the simulation models and the dynamics models. The method to analyze the behavior of hydrostatic and hydrodynamic floating object in detail will be also studied. Finally, to increase the applicability of the proposed simulation framework, it is necessary to apply it to various application systems in shipbuilding such as the design of a torpedo tube of a submarine, the bell-mouth design, the general arrangement of submarine's compartments, and so on.