基于能量优化与非均匀B样条小波的曲面光顺

提出通过非均匀B样条曲面的小波分解以及能量法的结合对曲面光顺的算法。小波分解实现了数据的压缩,提高了算法的效率;同时结合能量法对分解后曲面的细节部分进行边界约束光顺处理。最后用实例验证了算法的有效性。     

浅窄航道船舶线性位置导数估算

本文采用简化的一元流分析方法，引入非均匀流的概念对浅水中的细长体理论作了修正，计算了船舶在浅窄航道中斜航时的线性位置导数，计算中对粘性影响作了适当修正。计算结果与试验值吻合较好，且本法简便，便于在船舶设计初始阶段对浅窄航道船舶线性位置导数的估算。     

A NEW METHOD FOR REPRESENTING THE CIRCLE BY NURBS

In this paper, a new algorithm for representing conics precisely is presented using NURBS ofdegree two. The algorithm requires only four control vertices, which is the minimum number of controlvertices compared with the other algorithms using the square control vertice configuration, to representa full circle using the full circumscribing square based representation. This paper also derives a new con-dition for NURBS to precisely represent conics and shows the necessary and sufficient condition of rep-resentation of a circular arc.     

A STUDY ON NONEQUILIBRIUM TRANSPORT OF NONUNIFORM BEDLOAD IN STEADY FLOW

In the case of steady flow, an equilibrium state for an alluvial reach referring tothe input of sediment over a sufficiently long time (time interval in the order of months) is equalto the output of sediment. A nonequilibrium state exists under steady flow when the sedimenttransport rate changes with time and space, so that there is no balance between input and outputof sediment. The experiments were performed in an open circuit tilting flume with the bed slope of 0.001-0. 009, the flume length of 30m and flume width of 0. 5m. The boundary condition atupstream and in all experiments, the rate of sedimant supply was zero. The coal or sand was se-lected as the Wed material. The grain diameter of the bed material varied in the range of 0.05-20. 00ram. The equation of nonequilibrium transport of nonuniform bedload is derived. Thegrain distribution of the size distribution of bedload is calculated by modified Gessler's formula.The grain size distribution of bed material is calculated by CARICHAR mixed layer model. These equations are applied to numerical simulation of armoring of riverbeds. The results ofthe bedload transport rate and the grain size distribution of the bedload at the end of the down-stream in the process of time, as well as the grain size distribution of the bed material in the pro-cess of time and distance are all in close agreement with the measurements.     

Interactive Sculpting with Deformable Nonuniform B-splines

This paper describes an efficient method for manipulating deformable B-spline surfaces, based on minimizing an energy functional. The major benefit of the proposed new fairness norm is that it preserves the natural representation of the B-spline surface control points (a two dimensional array) which has an efficiency advantage over other methods. The designer uses forces as a main sculpting tool and is free to specify a single force, a set of isolated forces, forces situated on a line or curve or area of the deformable surface. The user is allowed to modify several parameters and in this way to change the physical properties of the object.     

An extension of Nyquist's theorem to non-uniformly sampled finite length data

This paper examines non-uniformly sampled functions on a finite interval. the aim is to investigate what conditions must be satisfied in order to recover the baseband spectrum from such data. It is shown that the concept of band limitation inherent in Nyquist's theorem must be generalized into a quantity termed primary interval bandwidth limitation. This property is explored and various algorithms are developed, including an extension of the classical band-limited interpolation formula. Measures are obtained that provide guidelines for assessing where approximate techniques can be employed and the use of these in adaptive scenarios is considered. the key results are illustrated by a set of numerical examples. the findings are presented in the context of time variables, but the approach is applicable to any type of sample domain. the treatment is one-dimensional, as are the examples discussed, but the extension to multiple dimensions is immediate and straightforward.     

Nonlinear Projection Recovery in Digital Inpainting for Color Image Restoration

This paper concerns with nonuniform sampling and interpolation methods combined with variational models for the solution of a generalized color image inpainting problem and the restoration of digital signals. In particular, we discuss the problem of reconstructing a digital signal/image from very few, sparse, and complete information and from a substantially incomplete information, which will be assumed as the result of a nonlinear distortion. Differently from well known inpainting applications for the recovery of gray images, the proposed techniques apply to color images embedding blanks where only gray level information is given. As a typical and inspiring example, we illustrate the concrete problem of the color restoration of a destroyed art fresco from its few known fragments and some gray picture taken prior to the damage. Numerical implementations are included together with several examples and numerical results to illustrate the proposed method. The numerical experience suggests furthermore that a particular system of coupled Hamilton-Jacobi equations is well-posed. Massimo Fornasier received his Ph.D. degree in Computational Mathematics on February 2003 at the University of Padova, Italy. Within the European network RTN HASSIP (Harmonic Analysis and Statistics for Signal and Image Processing) HPRN-CT-2002-00285, he cooperated as PostDoc with NuHAG (the Numerical Harmonic Analysis Group), Faculty of Mathematics of the University of Vienna, Austria and the AG Numerical/Wavelet-Analysis Group of the Department of Mathematics and Computer Science of the Philipps-University in Marburg, Germany (2003). Since June 2003 he is research assistant at the Department of Mathematical Methods and Models for the Applied Science at the University of Rome “La Sapienza”. Since May 2004 he is Individual Marie Curie Fellow (project FTFDORF-FP6-501018) at NuHAG. His research interests include applied harmonic analysis with particular emphasis on time-frequency analysis and decompositions for applications in signal and image processing. Since 1998, he developed with Domenico Toniolo the Mantegna Project (http://www.pd.infn.it/~labmante/) at the University of Padova and the local laboratory for image processing and applications in art restoration. Recently he has focused his attention on adaptive and dynamical schemes for the numerical solution of (pseudo) differential equations and inverse problems in digital signal processing.     

A simple generator for the <Emphasis Type="Italic">t</Emphasis> distribution

Summary A new algorithm for generating random variates from the t distribution is presented. It is based on a generalization of the ratio of uniforms method for the Cauchy distribution. It is simple, short and uniformly fast for all degrees of freedom.      

阵元服从正态分布的阵列DOA特性研究

在研究了零均值正态分布的简洁闭式的基础上给出了一种新的阵列列元布置方法一阵元间距服从正态分布阵列．与等距均匀阵列相比非等距阵元分布阵列具有设备量节省、阵列孔径增大、可获得更高的分辨力等优点．理论与仿真实验表明，阵元间距服从正态分布的非等距阵列能获得较好的空间谱估计性能．     

工业汽轮机调节级部分进汽瞬态数值研究

针对采用喷嘴调节的汽轮机调节级效率和安全性问题,基于时均的N-S方程,采用六面体结构化网格和有限容积法,对某机组调节级内部流动进行了数值计算。给出了不同工况下调节级内部压力和速度分布图,分析了4阀开和3阀开工况下调节级内部流动。给出了动叶旋转一周扭矩的变化,并将非定常扭矩进行了傅里叶变换,得到了频谱图。研究结果表明,部分进汽使调节级内部流动不均匀,4阀开,动叶所承受最大瞬时扭矩是进汽弧段平均扭矩的2.2倍,3阀开,动叶所承受最大瞬时扭矩是进汽弧段平均扭矩的1.8倍,这可以为调节级动叶安全性校核提供参考;频谱图显示,动叶受到与转速相关的低频激振力;3阀开工况下调节级的效率比4阀开工况下降低7%。