The Study On Based Middle Platform For Ship Fem Transformation Of CAD/CAE

During the design of ship structure, hull structure generally requires the finite element analysis. The primary task of finite element analysis is to create finite element model. Because of the complexity of ship structure, creating a reasonable model is rather time-consuming. According to the statistics, during the finite element analysis, creating the FEM accounts for 50-80% of the workload[1]. Consequently, creating a fast and efficient FEM has become a critical factor to improve the efficiency of hull structure analysis.At present, creating a hull FEM mostly is carried out by hand-method. Firstly, we should take the coordinates of hull structure from the two-dimensional drawings which were completed on the preliminary design stage, we can input these data into the finite analysis software, PATRAN and ANSYS, etc, then creating nodes and elements and assigning the property to the elements. This modeling process is very cumbersome, inefficient and error-prone, greatly affected the efficiency of hull structure analysis[2]. Consequently, looking for a fast finite element modeling method has become the object to every ship designer.Considering the features of CAD and CAE system, this paper presents a method of quickly creating FEM. The guiding principle is making the middle platform as the carrier , and make full use of the existing CAD system model data, to maximize the realization of CAD and CAE models of data sharing between systems. The main method: Firstly, extracting relevant geometric model information and material characteristics from CAD system; Then on the theory of knowledge engineering, to simplify the structure of the geometric model, the details of editing, abstraction and symmetry reduction simplified maintenance; Based on component type, to rename automaticly the component ID and create and assign element properties, material properties and mesh properties and other information;Geometric information of each component, cell properties, material properties and mesh properties and other information are automatically associated with the output to the finite element analysis software for further processing and calculation.Based on the method, in accordance with object-oriented thinking, we develop the data conversion tools FEMCS system, the tool has a common format data file read, model visualization inspection, structural model processing, the output data file format commonly used functions. This paper made the following works:Above all,by analyzing the main problems of current finite element analysis, after careful analysis of data exchange technology and interface mode of existing heterogeneous CAD and CAE system, considering the characteristics of heterogeneous systems ,we determine the basic framework and ideas of model data exchange.In accordance with the requirements of software engineering, according to the output characteristics of CAD geometric model and the input requirements of CAE finite element model, the paper complete the construction of middle platform. Then the paper describes in detail the database design of middle platform.Second, by analyzing the structure of the ship,the paper proposed the data exchange mode between the mainstream CAD system and the middle platform.Around the model's rapid conversion, the paper studied several critical questions. 1) On the basis of KBE and analysis about relevant information, using the structure of language what computer can recognize to establish the knowledge base, and achieve automatically simplification of the model. 2) To facilitate later extraction of the finite element analysis of data, the paper automatically renamed and reclassified each component of the model by using the quaternary structure.3) To facilitate post-finite element analysis of data extraction and creation, the material information, the opening of information and profile type information which extracted from the CAD system is strored as the form of temporary files.Then, by a typical analysis of FEA process, around the mesh, the paper studied the mesh of the required information. The paper proposed the data exchange mode between CAE system and the middle platform, and key issues related to the research. 1) Based on the type and characteristics of the simplified mode, through human-computer interaction, we can extract and create the element properties, material properties, grid properties and other information which involved in the model,established a library element properties, material property database , grid properties and associated databases and other knowledge rule base. 2) In the knowledge base and rule base, we can compare the board frame type, component type and spatial location information of the member ID with the rule base one by one, and give each component unit properties, material properties and mesh properties and other information. 3) Extractting the geometric information of each component, element properties, material properties, mesh properties and other relevant information to the file as a carrier neutral, model data and associated attributes are associated and merged automatically.Finally, based on the above theory and AutoCAD ActiveX technology, using Visual Basic and VBA language to its second development, we develop the finite element model create system -FEMCS. Using FEMCS system, we extract one block model from TRIBON system into FEMCS system as part level, in accordance with the requirements of the finite element analysis, we can deal with the model.We can output the model data to the ANSYS system as neutral format for further processing. By applying proven, research methods is possible, the development tool has a certain practicality.