Design Point Generation Method from a Lightweight Model for Dimensional Quality Management in Shipbuilding

Abstract

A ship is constructed by assembling blocks and installing outfits in the assembled ship structure. The measured data of real products and the design data are analyzed to prevent the loss caused by dimensional quality errors in shipbuilding. In recent years, 3D shapes have been used for efficient dimension quality management; however, it is difficult to deal with the large-scale Computer Aided Design (CAD) data required for managing extra-large blocks. A lightweight model is widely used for visualizing and sharing large data in Product Lifecycle Management. This model is mainly composed of triangular elements to minimize the file size and increase visibility. There are no problems with visually confirming the shape based on these triangular elements, but the model has a limitation when numerically calculating the exact position on a curve or a surface. In this article, we propose a method that uses a lightweight model to improve the efficiency of dimensional quality management. Accurate boundary curves are restored from the lightweight model used for visualization. After matching the connectivity of triangular elements, boundary element edges are extracted. Boundary curves are generated by connecting these boundary element edges. In addition, the density for tessellation was evaluated and found to be suitable for the shipbuilding process. The proposed method was tested on several models to demonstrate its feasibility. A ship is designed by dividing it into several blocks, which constitute the hull, and each block is constructed separately and assembled. Blocks are usually made by assembling small parts fabricated by machining steel plates, and the ship is constructed through the assembly of large blocks from the small blocks. For this process to be performed smoothly, errors are calculated between the design dimensions and manufactured dimensions, and then, the errors are used to correct for erroneous portions after constructing each block. In addition, the dimensions for outfitting and the positions of the hull structure are modified in the case of misalignment during the outfitting process such as installing pipes, equipment, and devices on the hull structure. Dimensional quality management is an activity performed to meet the dimensional quality that is required in the shipbuilding process, including at offshore manufacturing plants.