發展Aveva Marine船體資料庫與有限元素法模型之間的轉換程式

THE DEVELOPMENT OF TRANSFORMATION INTERFACE PROGRAM BETWEEN AVEVA MARINE DATA BASE AND FINITE ELEMENT METHOD

According to Structural Design Assessment Rule from Ship Classification Association, finite element method (FEM) has be-come more and more important in ship design. In addition, the design rule can govern the mesh size and element arrangement for different loading analyses. For example, in ship-hull analyses, the arrangement of plate element should follow the direction of the primary stiffener. For most cases, the meshing can only be performed semi-automatically due to geometric complexity and tremendous amount of work hour has to be devoted to correct the local mesh errors. In ship building industries, it has been estimated that about 80% of overall analysis time is usually spent on mesh generation. Therefore, the main objective of this research is to develop a tool that can speed up the process of mesh generation. The Aveva Marine (AM) is an engineering software used to manage and design ship model. In order to reduce the build-ing time of FEM model, we develop an interface program for AM and Abaqus, which is an FEM program. For this interface program, we first transform the information in the XML file from AM program and reconstruct the Non-uniform Rational Basis Spline (NURBS) function for each ship block. Then, the interface program would directly generate the initial graphics exchange specification (IGES) file and the FEM mesh for Abaqus. In order to generate the IGES file, we need to rebuild the NURBS functions and associate information including the knots and control points, For the calculation of control points and the coordinates of the attached stiffeners and holes in the parametric domain, a least square optimization algorithm is developed to perform the inverse mapping from the real domain to the parametric domain. In this study, we build an example structure with real ship block geometry to verify the applicability of our interface program. This program gives us flexibility to build FEM mesh with desired meshing orientation, element size and types, which can greatly reduce the model building time for FEM analyses. 根據船籍協會規範，有限元素法逐漸成為船體設計流程中重要的工具，設計規範中也有規定船體結構分析時，網格大小、網格方向與載重類型應該遵照一定的規格進行分析。例如船殼分析時，單元方向應該平行主要加強材。由於船體結構的形狀複雜，一般在模型建立時必須以手動的方式進行，也必須人工進行模型的局部網格除錯，這個工作必須耗費極大量的人力與工時，而船體結構分析有八成以上的時間都花費在建立模型與生成網格上。因此，本研究的主要目的為建立一個加速模型生成與分析的工具，希望能協助船廠減輕工程師的工作負擔。為了減少有限元素法模型建立的時間，我們決定直接使用船廠管理船體設計資訊的軟體Aveva Marine程式，匯出船體模型資訊（.XML檔案），並使用非均勻B樣條曲線方程式重建幾何形狀，生成電腦輔助設計常用的.IGES檔案（initial graphics exchange specification, .IGES），並在非均勻B樣條曲線方程式所特有的母空間中建立網格資訊，再寫入有限元素法Abaqus程式輸入檔中。由於非均勻B樣條曲線方程式為非線性投影方程式，在建立過程中所需要先設定節點向量（knot vector）並求解控制點資訊，本文提出使用最小平方差法結合取樣點資訊反算船板的控制點座標，在建立板的非均勻B樣條曲線方程式幾何描述後，再使用牛頓法將所有加強材反投影回母空間中，這個流程讓我們可以在母空間中進行網格布置，並使網格平行加強材方向。最後我們使用所發展出的程式對一個樣板船體結構進行分析，並驗證網格的連接與完整性，並證實程式可以協助減少大量的分析時間。