An Automatic Modeling Method For Complex CAD Models Of Tubular Structures And Isogeometric Analysis

Because tubular structures have a wide range of applications in buildings, vehicle engineering, aerospace field and bioengineering, they have gained much attention in the CAD community. Usually, CSG method are adopted to construct the CAD models of tubular structures. However, most tubular structures are composed of trimmed surfaces, they may result in overlap and gap issues, which can cause inconvenience to subsequent analysis and manufacturing. In the past, many methods were employed to construct high-order smooth surfaces. However, those methods are complicated and time-consuming. Adjusting the surfaces of the tubular structures is not easy. What is more, pipe splicing was restricted to a small amount of surfaces, engineering application requires pipeline modeling as quickly as possible at the same time. An automatic modeling technique for complex CAD models of tubular structures has been proposed to address the issues. First, we construct wire frame of the objective model. Second, the frame will be simplified into a set of CAD NURBS curves with joints, which are composed of two-way joints and bifurcations, each curve of each joint is expressed in quadratic form of NURBS curve. Third, a G0continuous CAD model can be automatically generated by using the present method.Isogeometric analysis is a new numerical computation method that is based on precise geometric representation with an aim to bridge the existing gap between CAD and CAE. it can use the CAD models directly to make CAE analysis and calculation; it also avoid the more time-consuming mesh generation of traditional finite element analysis. The high-degree continuous basis function(NURJBS,T-spline) of isogeometric analysis used to exactly model the geometry will also serve as the basis for the solution space. This method can improve the efficiency of structural analysis in practical engineering applications compared to traditional method. What’s more, it has the vital significance in improving product performance and accelerating product into the market. In the end paper introduces the basic thought of isogeometric analysis and gives formula based on Reissner-Mindlin degenerate shell of isogeometric analysis.With the help of Rhinoceros, we extracted the wire frame model of B-rep model of a tubular engineering structure; Using Visual Studio2008, the control points and weight factors of NURBS surfaces are generated by using C++programming language. The generated CAD model is displayed by MATLAB2008and ACIS. The proposed method has been successfully applied to reconstruct the car-body CAD model of an electric car. Finally, we conducted isogeometric static analysis for the generated car-body CAD model of an electric car by isogeometric shell analysis based on Reissner-Mindlin theories.