Research On System Design And Key Technology Of Ship CAD Based On NX Platform

Different ship models need to be established at different stages of the audit process.For example,in the hull design stage,a three-dimensional model containing detailed ship structures needs to be established;in the finite element analysis stage,a finite element preprocessing model needs to be created;in the structural standard calculation stage,a special verification model needs to be established.If manual modeling is required at each stage,many duplicate designs will result,extending the production design cycle.At present,a universal 3D ship model that satisfies the audit process can not be designed by using the mainstream ship CAD design software.Therefore,in order to achieve efficient modeling and reduce repetitive design,it is necessary to develop a ship CAD system that is oriented to the audit process.According to the rapid modeling project of ship structure of China Classification Society,this paper analyzes the advantages and disadvantages of professional ship design software and the development status of ship CAD technology at home and abroad,a ship CAD modeling system for the audit process is designed and developed based on the generic 3D modeling software NX.It achieves the rapid creation of ship structures,provides common models and data for other modules of the audit process,and achieves data sharing.Both the geometry and the data of the ship model are described,with all ship structures represented by zero-thickness sheet body and the materials,profiles and other data is recorded as attributes in geometry.Through the analysis of NX parametric modeling and custom feature technology,the ship structure is expressed in the form of custom features to ensure the efficient storage of data and solve the problem of association update between components,and the parametric modeling method ensures ship structure's parametric drive and batch quick creation.In order to solve the problem of data inconsistencies among different modules,a full life cycle database system is designed based on the lightweight database SQLite,and it stores the ship general information,standard parts information and CAD model data into the underlying database to ensure the fast data query.Through the data import and export,the CAD modeling data is provided to other modules to achieve data sharing.For reducing the amount of model data,the paper deeply studies the characteristics of NX modeling and a three-laminated panel model including release model,master model and tool model is established.it avoids the parameterized association between different panels.Besides,it manages the panel and its subsidiary structures by combining the custom structure navigation tree,the custom panel navigation tree,the NX assembly tree and the NX feature tree,which is more meet the needs of the ship designers.Finally,taking the 180 000 DWT Bulk carrier as an example,the paper uses the ship CAD system to design the ship structure and verify the feasibility of the system.At the same time,it compares with NX's own ship design module to confirm the high efficiency of system modeling and its effectiveness in reducing the amount of model data.