Study On Representation Of Ship-Hull Surface And Three Dimensional Modeling Design

Representation of curves and surfaces is the most kernel and important research focus in Computer-Aided Geometric Design area. The shape surfaces of shipbuilding, aircraft and automobile are very complicated and difficult to describe. The highly fairing or smoothing surfaces are demanded imperatively in shape design and manufacturing. The fairness concept, which is derived form engineering practice, includes abundant contents, and is related to Mathematics, Physics, Aesthetics and Psychology, etc.. The fairing refers mainly to the smoothing and esthetical shape of geometry. To assess the fairness of curves and surfaces or fairing level, the experience of designer is relied heavily on. The subjective sensations often play more important roles, every designer maybe draw different conclusions for estimating the same shape. So through proposing the fairing criteria and establishing curves and surfaces fairing algorithms, fairness defined in mathematical and physical methods is essential. The subjective methods must be taken place by strict and objective mathematical procedure to assess fairness of surfaces and curves. Fairing curves and surfaces is a current research hot-point in CAD/CAM field. Many scientific researchers of out-and-indoor have made huge efforts to deal with fairing curves and surfaces over the past few decades.The shape of ship-hull surface is very sophisticated. Mathematical representation of ship-hull surface is important in shipbuilding industry. The advantages, such as easily computing form-lines and accurately lofting, are offered by mathematical ship-hull surface. Hull structure modeling, engineering analyzing and manufacturing are based on mathematical ship-hull surface. Furthermore, hull structure designing in virtual reality environment and intelligent building depend heavily on the ship-hull surface model. In this thesis, Non-Uniform Rational B-Spline, i.e., named NURBS, is used to model ship-hull surface. Interpolating, fairing and representing ship-hull surfaces are the most important parts of researching task.To interpolate the given ship offset data, the ship-hull surface is represented successfully by NURBS. The boundary conditions computation and knots vector construction are detailed in NURBS curve and surface interpolation.According to properties of curve and surface, algorithms, which is based on the elastic splint and the thin plate energy models respectively, are employed to fair curve and surface. Ship-hull form and surface are faired perfectly by these algorithms respectively. TheAbstractboundary conditions of ship-hull form and surface are controlled in fairing process. Then curvatures and highlight lines are used to estimate fairness of curve and surface respectively.Based on projection principle, a method for surface/plane intersection is presented. The theory of this method is laconic. The numerical intersecting algorithm is widely used in ship-hull surface modeling in this thesis. The desired results are obtained.According to ship-hull surface modeling, new design methods in 3D can be implemented conveniently. The working procedures, such as ship-hull shell plates arrangement and expansion, hull structure lay and parametric feature-based modeling, and tank subdivision and calculation, etc., can be carried out intuitively in 3D virtual world. Comparing with the traditional design in 2D, the 3D design methods by computer aided have more beyond challenge advantages.Using Visual C++ programming language, ship-hull surface modeling and fairing are realized in ObjectARX developing environment of AutoCAD system platform. Otherwise, defining feature-based classes, constraining relationship of structures, and linking and managing database are investigated in this paper.