Application Of CAD In Vietnam Fishing Vessel-hull Design And Stability Calculation

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 thesmoothing 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 oftenplay more important roles, every designer maybe draw different conclusions for estimatingthe same shape. So through proposing the fairing criteria and establishing curves and surfacesfairing algorithms, fairness defined in mathematical and physical methods is essential. Thesubjective methods must be taken place by strict and objective mathematical procedure toassess 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 hugeefforts to deal with fairing curves and surfaces over the past few decadesThe 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 andintelligent 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 ofresearching task.To interpolate the given ship offset data, the ship-hull surface is representedsuccessfully by NURBS. The boundary conditions computation and knots vector constructionare 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. The boundary 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 in3D can be implemented conveniently. The working procedures, such as ship-hull shell plates arrangement and expansion, hull structure lay and parametric feature-based modeling, andtank subdivision and calculation, etc., can be carried out intuitively in3D virtual world. Comparing with the traditional design in2D, the3D design methods by computer aided have more beyond challenge advantages.Using VBA programming language, ship-hull surface modeling and fairing are realized in AutoLisp of AutoCAD system platform. Otherwise, defining feature-based classes, constraining relationship of structures, and linking andmanaging database are investigated in this paper.