planning information, and simulation model would also cost a great amount of extra time, and the result would be that the confidence and efficiency of the simulation modeling could not satisfy the engineering demands of virtual ship assembly. Consequently, virtual ship assembly is not widely applied in practical conditions.

This paper proposes a modeling method of virtual ship assembly which integrates the ship three-dimensional design and construction plan, establishes a workflow  model for virtual ship assembly modeling, and develops a method of information transformation and analysis for ship three-dimensional design and ship construction  planning based on the engineering requirements. Furthermore, with the application of the software engineering design specifications and relational data model, a simulation database, which realizes the information integration of different systems involved in virtual ship assembly, is established, and a communication system is also developed in order to support the virtual assembly modeling. After that, by applying the virtual assembly in the process of a ship, the rationality of the simulation method is verified.

2 The method of virtual ship assembly modeling

Virtual ship assembly includes the virtual roam of cabins, the static interference detection of the multi-disciplinary general layout, and the dynamic interference detection of the ship assembly process (Yuan et al., 2009a, Yuan et al., 2009b). Consequently, the information of the objects which would be assembled into the ship should be considered in the modeling of the virtual ship assembly. The information of the geometry, the spatial location, the topological relationship of the structure, the assembly sequence, the assembly time, and the application type of the virtual assembly should  be contained in the modeling as examples (Zha et al., 2007; Wan et al. 2007). Fig.1 reveals the composition of the virtual ship assembly modeling.

Fig.1 The composition of the virtual ship assembly model

Nowadays, three-dimensional design is widely used in ship product design (Liu, 2003, Ma et al., 2006). First of all, it is necessary to establish the three-dimensional models of the ship. Second, the models should be transformed into the corresponding data format which can be accepted by the simulation software of the virtual ship assembly. By this way, it can provide visual information for the simulation system of the virtual ship assembly. Although some information, such as assembly sequence, assembly structure, and assembly time, is difficult to acquire by the model transformation method, designers can still obtain it by analyzing the construction plan. Consequently, the method of virtual ship assembly modeling as shown in Fig.2 can be adopted. This method requires extracting and transforming the information of the three-dimensional model and construction plan, and then creating the application files for different simulation types of the virtual assembly. By applying this method, the ship’s three-dimensional information and construction plan can be fully utilized by the simulation of the virtual ship assembly. Therefore, it can enhance the consistency of the virtual ship assembly modeling and the actual characteristics of the ship construction, thereby improving the efficiency of the simulation modeling.

Fig.2 The simulation method of virtual ship assembly modeling

Fig.2  shows  that  the  modeling  process  of  virtual   ship assembly   should   be   tightly   integrated   with   the ship’s three-dimensional modeling and the construction planning system; that is to say, the integration method should include the process integration and the information integration (Yuan et al., 2009). To this end, a new simulation modeling method is devised. The method integrates modeling of ship three-dimensional information, formulation of  a construction plan, and modeling of the  virtual assembly, and then transforms and analyzes the information concerning the three-dimensional design, the construction plan, etc. Moreover, after analyzing the data stream and applying the software engineering design specifications and the relational data model, a simulation database is established    for    virtual    ship    assembly,    realizing   the information integration mentioned above.