Studv On Smoothing Method Of Hull Curve And Surface Based On CATIA

As an important means of surface transportation,ships are required to have specific navigational performance,and its outer surface shape is more complex than that of aircraft and automobile,so smoothing the curve and surface of ship is the basis of its fluid performance.CATIA,as a 3D aided design software integrating manufacture and design,has been widely used in ship design and manufacture in recent years.Major ship enterprises are gradually migrating their business processes to CATIA platform.Because CATIA is a general software platform rather than a special software for ship design and manufacture,the related functions of ship design and manufacture are not perfect,especially the special module for ship lofting process is not provided.Recently,when most shipbuilding companies use CATIA to carry out production design,they usually use the hull model with other 3D design software to perform the follow-up work.This is not consistent with the design concept of a single data source.Therefore,Therefore,in order to perfect the hull fairing function of CATIA,realize the unification of data source and avoid the error brought by cross-platform data exchange.Combining with the general principles and methods of curve and surface fairing,this paper studies the fairing method of ship’s curve and surface based on CATIA V5 platform.It mainly includes the following work:1.The model of ship hull wireframe is constructed by using line drawing as input data.Using the secondary development interface provided by CATIA,the nodal point of the curve is transformed from 2D to 3D,and the shape curve of the space hull is automatically generated by spline interpolation.At the same time,by simulating the process of manually creating bow arc,the center line and tangent line are interrelated,so that the other curve can be automatically adjusted when the position of the offset point of any curve in the two is adjusted.2.Combining the local smoothing method based on circle-ratio and wavelet,the mathematical model of curve and surface local smoothing based on CATIA is proposed.The model divides the curve smoothing into two steps : coarse smoothing and fine smoothing.In the coarse smoothing stage,the smoothing method based on roundness is used to smooth nodal points sequence.The local smoothing method based on wavelet is used in the fine fairing stage.The curve is decomposed into low frequency and high frequency parts by wavelet.Then the bad points are determined according to the smoothing criterion,and the corresponding wavelet coefficients are modified.Finally,curve smoothing using wavelet reconstruction technique.For surface smoothing,the surface is discretized into a grid curve,and then the grid curve is smoothed by the method of fairing curve,and eventually the surface is smoothed.3.Construction and integration of smoothing function.Based on the fairing mathematical model built in this paper,combined with CATIA secondary development interface and third-party open source library,the integration of fairing algorithm encapsulation and curve surface fairing function is realized in CATIA platform.In order to verify the reliability of the research method,the fairing model and fairing system are verified by the example of curve and surface and the 15000 t bulk carrier respectively.In the case of combining circle-ratio and wavelet-based local smoothing method,the curve reaches smoothing while maintaining the position of key points.In addition,the surface wrinkles can be eliminated by the mesh surface after smoothing surface discretization.The fairing system can create the hull frame model through the ship’s lines,and on this basis,realize the fairing of the real ship model.The results show that,based on the fairing model combined with the circle-ratio and wavelet local fairing method,the fairing of hull curve and surface can be realized on the CATIA platform by using the secondary development technology for customized development.