سیستم مدل سازی ساختاری بدنه اولیه برای برنامه ریزی فرآیند به کمک کامپیوتر در کشتی سازی

At the initial stage of ship design, it is difficult for designers to define all design information of a hull structure on 2D drawings. Thus, other designers must undertake the arduous task of translating such information to generate a 3D CAD model of the hull structure which is required at the following design stage such as the initial process planning stage. Since this task needs much time and effort, the 3D CAD model is not being generated at the initial design stage. For solving this problem, an initial hull structural modeling system is developed in this study. The applicability of the developed system is demonstrated by applying it to a deadweight 300,000 ton VLCC (Very Large Crude oil Carrier). The results show that the developed system can quickly generate the 3D CAD model of the hull structure and accurately extract the production material information for computer-aided process planning at the initial design stage.

1.1. Ship production process A ship is a huge structure made up of a large number of hull structural parts. Here, a hull structure represents the body of the ship, and a hull structural part represents a part that is placed on the hull structure to secure the structural strength of the ship. As for a deadweight 300,000 ton VLCC (hereafter simply referred to as the ‘300 K VLCC’), the length, breadth, and depth is about 320, 60, and 30 m, respectively. Thus, contrary to an automobile, the ship cannot be constructed all at once. The ship is first divided into a number of building blocks (block division), For example, the ship is divided into about 200 building blocks in the case of the 300 K VLCC (see Fig. 1). Here, a building block is a unit element for production of the ship. Each building block is assembled in the assembly shop near the dock. Large building blocks, which are called erection blocks, are made by joining several building blocks together. Then, the large building blocks are moved on the dock and welded to each other according to a suitable sequence, which is called the block erection, to complete the final assembly to the ship. That is, the construction process of the ship is similar to the process that a large product is made up of a number of Lego blocks. At this time, to efficiently construct the ship, it should be determined how the ship is divided into building blocks (process planning). This task is performed at the initial process planning stage in shipbuilding design. Fig. 1 gives an example of a block division drawing of the 300 K VLCC. According to this drawing, this ship is divided into about 200 building blocks and then these building blocks are finally constructed together on the dock. Full-size image (112 K) Fig. 1. Example of the block division drawing of the 300 K VLCC. Figure options At the initial process planning stage, designers of the shipbuilding company normally determine the work sequences and methods, necessary resources, work duration, etc. based on existing enterprise resources. To perform these tasks, the production material information of the ship is necessary. The production material information includes the weight, center of gravity, painting area, joint length for welding, etc. Basically, this information can be regarded as given in the building block unit at these stages. The most important resources of the shipbuilding company are the docks and cranes that are used to erect the building blocks of the ship. If the ship is divided into a number of building blocks and then constructed on the dock, the dock occupation ratio of the ship increases, and this reduces productivity of the shipbuilding company. Therefore, it is important to set an optimal number of the building blocks considering the maximum capacity of the cranes. Here, the most important factors that need to be considered are the accurate weight and center of gravity of the building blocks. The painting area of the building blocks needs to be known to calculate the amount of paint and the number of man hours required for painting the building blocks on the painting shop. The joint length between the building blocks is necessary to calculate the number of man hours required for erecting the building blocks on the dock, and the joint length in the building block is required to calculate the number of man hours required for assembling the building block in the assembly shop. 1.2. The current state of hull structural modeling in shipbuilding At the initial process planning stage, various design information of the hull structure such as the placing position of bulkheads, number of decks, frame space, placing position of equipments, etc. are obtained from 2D drawings such as the lines, general arrangement, midship section, construction profile, etc. Then, the hull structure, that is, the ship is divided into a number of building blocks using these information, taking into account the capacity of the assembly shops and cranes, and referencing the data of parent ships. Finally, the production material information of each building block is estimated and manually calculated from hull structural parts, which are included in the corresponding building block, as shown in Fig. 2. Since, currently, this calculation is manually performed based on the 2D drawings, data of parent ships, and design experiences, the accuracy and reliability of the calculated information is quite low. This calculation is possible only if the data of the parent ships are available, and it is very difficult to perform such calculation for building an entirely new ship where there is no existing data. Full-size image (40 K) Fig. 2. Existing procedure of manually generating the production material information at the initial process planning stage. Figure options If a 3D CAD model of the hull structure at the initial design stage, that is, the initial hull structural model can be generated and such model can be divided into a number of building blocks, the production material information of a building block unit which is required at the initial process planning stage can be accurately generated. Many shipbuilding companies are now attempting to perform hull structural modeling and generate the initial hull structural model at the initial design stage. However, despite the fact that there are many shipbuilding CAD systems such as the TRIBON [1], IntelliShip [2], NUPAS-CADMATIC [3], FORAN [4], etc. they do not yet have a CAD system supporting the initial design stage where design changes arise very frequently. The TRIBON system, which was developed by TRIBON Solutions (currently, AVEVA Group plc) several decades ago, is being widely used by most shipbuilding companies, and much of the design and production experiences of these shipbuilding companies have been reflected on this system. Thus, the system has been proven to be an efficient CAD system but only for the production design stage. However, it is being reported by many specialists in the shipbuilding industry that the design functions of this system are insufficient to be applied at the initial and detailed design stages due to the limitations of its geometric modeling kernel which was developed long time ago. In the TRIBON system, the production material information can be generated only after completing the production modeling of a building block unit at the production design stage where the block division of a ship is already determined. Thus, it is difficult to secure a 3D CAD model which is necessary to accurately generate the production material information for the initial process planning at the initial design stage. The IntelliShip system, which was jointly developed by Intergraph Corporation, Samsung Heavy Industries in Korea, Hitachi Shipbuilding (currently Universal Shipbuilding) in Japan, and Odense Steel Shipyard in Denmark, sets a goal of generating a 3D CAD model beginning from the initial design stage. However, it is being reported by many specialists that the size of the generated 3D CAD model is so large that it slows down the running speed due to the combination of problems that arise as a result of the conversion from a general-purpose mechanical CAD system to a shipbuilding CAD system. Thus, the IntelliShip system is currently used for the detailed modeling of a hull structure at the detailed design stage and the production modeling of a building block unit at the production design stage. Accordingly, as this system can generate the 3D CAD model only after the detailed design stage, it is difficult to secure the 3D CAD model at the initial stage, similarly to in the TRIBON system. Other systems such as the NUPAS-CADMATIC, the FORAN, etc. are being used for the production modeling of the hull structure at the production design stage in some shipbuilding companies. However, these systems also require a number of user inputs for generating the 3D CAD model of the hull structure, and thus, they are not suitable for the initial design stage. As mentioned above, many shipbuilding companies require a shipbuilding CAD system to generate the 3D CAD model through rapid modeling and to extract the production material information for the initial process planning at the initial design stage. However, the existing systems do not satisfy these requirements. Thus, so far, the production material information has been generated using 2D drawings, data of parent ships, and design experiences. In this study, an initial hull structural modeling system is developed to quickly generate the 3D CAD model of a whole hull structure at the initial design stage, that is, the initial hull structural model, and to accurately extract the production material information by using the 3D CAD model, as shown in Fig. 3. Full-size image (96 K) Fig. 3. Present hull structural design flow using the existing shipbuilding CAD systems and future flow using the developed system. Figure options 1.3. Related works In the latter 1980s, the demand for CIMS (Computer Integrated Manufacturing System) in shipbuilding increased and the importance of a 3D CAD model in the hull structural design was embossed. As a result, some projects were commenced such as ‘Computerized Ship Design and Production’ (CSDP, 1988–1994) in Korea and ‘CIMS Pilot Model Development’ (1989–1992) in Japan, and many related works were made. In the case of researches conducted at the institutes and ship building companies, KRISO (Korea Research Institute of Ships and Ocean Engineering) conducted a subproject related to the CSDP project entitled ‘Development of the Ship Structural CAD System’ [5]. In this subproject, the required specification, procedures and contents of design practice about the hull structural design were analyzed for developing a shipbuilding CAD system. With these analysis results, a data structure was proposed to represent all design information. However, the system implementation was not made based on the proposed data structure. DSME (Daewoo Shipbuilding and Marine Engineering) also commenced a subproject as part of the CSDP project entitled ‘Development of the Initial Process Planning and Scheduling Information Processing System’ [6]. In this subproject, the procedures and contents of design practice about the hull form definition, ship compartment arrangement, hull structural design, process planning and scheduling, etc. were analyzed for developing a shipbuilding CAD system. However, the system implementation was not completed, as well. Only the possibility of implementing the integrated system was examined based on the VDS (Vehicle Design System), which is a general-purpose CAD system and was developed by Intergraph Corporation. In the case of researches conducted at the universities, Min [7] proposed a data structure based on the object-oriented concept for developing a hull structural design and analysis system. He implemented the prototype system based on the proposed data structure. Using the system, he performed 2D CAD modeling of a simple panel structure and generated a finite element model for structural analysis from the 2D CAD model. However, this data structure could only represent the design information of a simple panel having a 2D shape, and thus this study was insufficient to represent a hull structure having a complex 3D shape. Kim [8] proposed a data structure which can store the geometric and topological information of a simple panel structure having a 3D shape, and implemented a prototype system. However, this data structure could only store the design information of a panel, and thus the prototype system was possible to perform 3D CAD modeling of a simple hull structure having only panels. Nomoto et al. [9] commenced a subproject as part of the ‘CIMS Pilot Model Development’ project. They proposed a data structure based on the object-oriented concept and a prototype system called ‘SODAS (System Of Design and Assembling for Shipbuilding)’. However, this data structure can only represent the limited design information of the cargo hold region of a hull structure. Furthermore, the prototype system cannot perform hull structural modeling of stiffeners which are required to secure the structural strength of a ship. Yum [10] proposed a data structure to perform hull structural modeling at the initial design stage and developed a prototype system. Using the system, it was possible to perform modeling of a unit of a hull structural part such as a panel and stiffener. However, this data structure can only store the design information of not a whole hull structure but the limited region (e.g. cargo hold region) of the whole hull structure, and moreover the prototype system was possible to perform hull structural modeling of a VLCC. Lee et al. [11] proposed a data structure to perform hull structural modeling at the initial design stage and developed a prototype system. Using the system, it was possible modeling of a structure system unit such as a web frame system, stringer system, girder system, etc. which corresponds to the modeling unit at the initial design stage, and it was possible to generate the limited production material information of a building block such as the weight, center of gravity, and painting area. However, the proposed data structure cannot represent the relationship between hull structural parts. Thus, the joint length of a building block could not be generated. 1.4. The proposed hull structural modeling in this study At the initial stage of ship design, the design concept of a ship evolves rapidly and is optimized through repetition and analysis. A designer represents the final design results on 2D drawings containing all design information of an initial hull structure of the ship. Fig. 4(a) shows an example of one of the 2D drawings of the 300 K VLCC. These 2D drawings are used to represent and communicate the design results to other designers. As shown in Fig. 4(a), the design results of hull structural parts such as a panel, stiffener, etc. are represented by points, lines, arcs, and drawing symbols, and their thickness, placing position and direction, and material property are also represented on the 2D drawings. Although the designer represents the design results on these 2D drawings, however the designer want to represent that the design results equal to a 3D CAD model shown in Fig. 4(b), through the 2D drawings. Here, the 3D CAD model is regarded to reflect design semantics, that is, shipbuilding design meaning of the designer. Full-size image (96 K) Fig. 4. Example of the hull structural information on the 2D drawings and the corresponding 3D CAD model. Figure options The hull structural modeling system developed in this study represents the design results as hull structural information such as geometric and topological information, design attributes, relationship information between hull structural parts. This hull structural information means minimal product information which is required to represent a whole hull structure at the initial design stage. Furthermore, this hull structural information can be used to generate the corresponding 3D CAD model of the hull structure, if required. To efficiently store this information at the initial design stage, a data structure for the initial hull structure is proposed in this study. Fig. 4(c) shows the hull structural information of a stiffener on a panel. A trace line, design attributes (e.g. section type, material, etc.), and relationship information between the stiffener and the panel construct the hull structural information of the stiffener. Fig. 4(d) shows the 3D CAD model of the stiffener generated from the hull structural information shown in Fig. 4(c). At the initial design stage, a function-oriented product definition process, which is focused on functions such as the arrangement, rough definition of the shape, and determination of the dimension of hull structural parts, is necessary to calculate the structural strength and estimated production cost, and to satisfy rules and regulations. In contrast, the production design stage primarily involves the generation of production drawings. A hull structural modeling unit at the initial design stage which satisfies this requirement is the structure system such as a web frame system, stringer system, girder system, etc. Thus, the initial hull structural model is generated by performing the initial modeling of a whole hull structure with bigger hull structural parts such as the structure system at the initial design stage. Then, the detailed hull structural model is generated by performing the detailed modeling of the hull structure with smaller hull structural parts. Finally, the production hull structural model of a building block unit is generated by performing the production modeling of each building block. Fig. 5 shows the hull structural modeling concept of a structure system unit, which is suitable to be used at the initial design stage. The developed system can be used to perform hull structural modeling, and then generate the initial hull structural model of the whole hull structure at this initial design stage. In addition, it can be used to perform the detailed modeling of the initial hull structure at the detailed design stage and the production modeling of a building block unit through the block division process at the production design stage. The TRIBON system, however, can be used only to perform the production modeling of a building block unit at the production design stage, and the IntelliShip system can be used to perform the detailed modeling of the whole hull structure at the detailed design stage and the production modeling of a building block unit at the production design stage. Full-size image (84 K) Fig. 5. Hull structural modeling concept of a structure system unit at the initial design stage. Figure options To quickly perform the initial hull structural modeling of a structure system unit at the initial design stage where the hull structural design is not fixed, a hull structural modeling method that can generate a new hull structural part by referencing already defined parts is required. More detailed contents about the developed system will be presented below. Outfittings, such as piping, ventilation, and electrical and miscellaneous steel structures are also component of the ship with the hull structural parts and however the developed system is only performing the modeling of the hull structural parts of the hull structure.

At the initial stage of ship design, it is difficult for designers to define all design information of a hull structure on 2D drawings. Thus, other designers must undertake the arduous task of translating such information to generate a 3D CAD model of the hull structure which is required at the following design stages. Since it needs much time and effort to perform such task for generating the 3D CAD model from the 2D drawings, the 3D CAD model is not being generated at the initial design stage. Thus, at the initial process planning stage, designers are manually generating the production material information of building blocks by using the data of parent ships and from design experiences. The generated information has low accuracy and reliability. For solving this problem, an initial hull structural modeling system was developed in this study. The developed system consists of a data structure for the initial hull structure, hull structural modeling function, generating function of the 3D CAD model, generating function of the production material information, user interface, non-manifold geometric modeling kernel, and graphic library. Using the developed system, a designer can perform hull structural modeling of a system unit at the initial design stage, define hull structural parts by referring existing hull structural parts, and generate a 3D CAD model of various level-of-details of the hull structure. The applicability of the developed system was demonstrated by applying it to hull structural modeling and generation of the production material information of a deadweight 300,000 ton VLCC. The application result showed that the developed system can be efficiently used for hull structural modeling and generation of the production material information for the initial process planning at the initial design stage. That is, by using the system, the designer can generate the 3D CAD model of the whole hull structure and then extract accurate product material information such as the weight, center of gravity, joint length for welding, painting area, etc. of building blocks in an early stage of ship design. Outfittings, such as piping, ventilation, and electrical and miscellaneous steel structures are also component of the ship with the hull structural parts and however the developed system is only performing the modeling of the hull structural parts of the hull structure. Thus, it is necessary to develop an outfitting modeling system to extract more accurate product material information considering outfittings. 2D drawings are still important communication methods among designers, classification society, and ship owners. Thus, it is necessary to develop a function to automatically generate 2D drawings from the initial hull structural model. The additional research on automatic generation of a finite element model for the global structural analysis will be required using the initial hull structural system to integrate with CAE systems. Moreover, for a perfect interface with existing shipbuilding CAD systems and classifications' software, the initial hull structural model should be transferred to the systems and software.