Study Of Hull Molded Lines System In CADDS5 Based On NURBS

The ship mathematization has bring birth to a grave change in ship designing, building craft and research effort. In these days, computer has been used extensively in shipbuilding industry. Because the shape of hull is very complicated and the curves and the surfaces have second order continuity, after many years of research and discussion.the appearance of B-spline brings the ship CAD with a breakthrough, Now,NURBS (nonuniform rational B-spline) becomes the most powerful fuction in hull cuve fitting and fairing.At the present time, ther are many hull molded lines systems in world. But two theory cores must be existed in them.1, expression of hull molded line;2, static calculation. Polynomial, transcendental function, new quadratic curve,B-spline and NURBS have been used in expression of hull molded line, trapezoidal method, Simpson method have been used in static calculation. Trapezoidal method replaces curve with straightway and Simpson method replaces curve with second degree parabola.NURBS is the only mathematic method about geometric definition of industrial product in the STEP international standard.lt produces communal mathematical expression for elementary curves and free curves.So, one database can save two kind of information.More and more CAD/CAM systems adopt and develop NURBS.In fact,NURBS is thought about as the index point of a CAD software.The ship static ability is one of the most important abilities.It includes buoyancy,steady,anti-sinking,So, the static calculation plays pivotal role.How to improve the precision of integral is the target of scholars in world.This paper express the hull molded lines with cubic NURBS and does the integrating of cubic NURBS curve.