图像插值的改进自适应核回归方法

针对 steering 自适应核回归的插值算法中图像整体灰度值偏离较大和空洞的现象,本文提出了一种基于改进的自适应核回归函数的图像插值算法.该方法根据图像的自相似性原理,通过把图像邻域中像素间几何距离函数融入 steering 自适应核函数中,实现一种改进的自适应核函数,并采用这种核函数对图像进行回归插值.实验结果表明...     

基于小波函数的核主元特征约简方法研究

提出一种基于小波核函数的核主元特征约简方法,核函数是核主元分析的关键,将Mexican hat小波函数引核主元分析中,以增强核主元分析的非线性映射能力.用转子在正常、油膜涡动、不平衡和径向碰摩状态下的实验数据对该方法进行了检验,比较了主元分析、核主元分析与小波核主元分析的效果.结果表明,小波核主元分析方法能有效地区分转子故障模式,更适合于故障诊断中的非线性特征约简.     

基于演化非对称核函数的均值漂移跟踪算法

针对传统均值漂移跟踪算法中采用的对称核函数模板中包含了较多背景像素点,影响跟踪精确度和稳定性的缺点,在固定非对称核函数的基础上对均值漂移跟踪算法进行了改进,提出了一种基于演化非对称核函数的均值漂移目标跟踪算法。本文算法首先介绍了将非对称核函数模板引用到均值漂移算法框架的关键问题——模板中心——的计算方法;其次将非对称核函数模板的表述和演化有机结合,提出了利用区域相似度的目标轮廓水平集演化算法并阐述了非对称核函数模板的更新策略。实验结果表明,相比现有的方法,本文提出的基于演化非对称核函数模板均值漂移跟踪算法具有更高的准确性和可靠性,同时也能满足一般目标跟踪任务的实时性要求。     

核最小二乘算法检测红外点目标(英文)

对于背景呈非线性变化的复杂图像,用背景预测的方法对红外点目标进行检测时,传统的线性最小二乘法(Least Squares,LS)的效果比较差.文章使用核方法(Kernel Methods,KMs)推导了最小二乘法的非线性版本:核最小二乘算法(Kernel Least Squares,KLS);进一步推导出了更适合动态系统时序预测的指数加权形式的核最小二乘算法(Kemel Exponential wleighted Least Squares,KEWLS).提出了一种基于核方法的红外点目标检测算法,先用KEWLS非线性回归算法预测红外图像背景,再通过自适应门限检测残差图像中的目标,非线性函数回归和红外序列图像检测实验表明核方法较大地改进了算法的非线性函数估计与红外背景预测能力.     

层次型支持向量机人脸检测器

大量的数值实验表明，在非线性支持向量机中，核函数的选取对支持向量机性能的影响很大。核函数的选择一直是一个难题。本文利用遗传算法的全局优化能力比较并分析了多项式核函数和高斯核函数的检测正确率和支持向量个数两项指标，提出了一种层次型支持向量机人脸检测器。实验结果证明，本文的方法确实取得了较好的效果。     

基于全矢谱核函数主元分析的旋转机械故障诊断方法研究

结合全矢谱和核函数主元分析的各自优点,提出了一种基于全矢谱核函数主元分析的旋转机械故障诊断新方法.该方法充分利用了全矢谱提取回转信息的完整性和全面性,同时又利用了核函数主元分析具有处理非线性问题的能力.提出的方法与传统的核函数主元分析方法进行了对比,试验结果表明提出的方法是有效的,非常适合提取旋转机械故障的非线性特征,并能很好的进行旋转机械的故障模式识别.     

圆柱绕流气动噪声数值分析

为了快速预测刚性圆柱绕流的气动噪声,研究了一种将离散涡方法(DVM)和涡声理论结合起来计算低马赫数、高雷诺数流场气动噪声的方法。首先用Oseen粘性涡模型改进了离散涡方法并模拟了圆柱绕流,分析结果与实际情况相符。根据流场计算的结果,应用涡声理论进一步计算了远场的声压。测点的总声压级与实验值及其他数值计算结果都比较吻合。最后绘制了声场的指向性特性曲线,表明圆柱绕流声场明显的偶极子特性。     

马鞍屋盖表面锥形涡流动模型研究

该文基于大跨平屋盖和马鞍屋盖表面锥形涡流动显示试验,对现有的兰金涡模型进行改进,在其涡核区与势流区之间添加过渡区,从而建立了简化的二维锥形涡流动模型,给出了旋涡上部流速、旋涡内部流线曲率以及屋面涡核吸力之间的定量关系。据此流动模型,分析了旋涡强度的影响因素即为旋涡内部流线曲率和旋涡流速:旋涡内部流线曲率越大,旋涡转速越快,旋涡强度越大。基于流动显示试验和测压试验所得平屋盖以及马鞍屋盖表面各旋涡参数之比,以平屋盖表面锥形涡为基准,量化了各风向下马鞍屋盖表面的锥形涡强度。通过加入考虑旋涡效应对传统准定常理论进行修正,给出了锥形涡涡核吸力(均值、峰值)的计算公式,并将计算值与马鞍屋盖刚性模型风洞测压试验数据进行对比,验证了锥形涡流动模型对于预测马鞍表面锥形涡涡核吸力的有效性。     

海上远景小目标检测方法的研究

海水本身运动的复杂性以及海水与其它环境因素所产生的干扰物理场,往往使得海上小目标的探测尤为困难.因此,以可见光图像序列中海面小目标检测为研究对象,提出了核函数-马尔科夫随机场(Markov Random Fields,MRF)前景分割模型.该模型利用所提出的邻域相关核函数背景模型对图像序列的求解结果作为MRF的观测值,...     

组合核函数支持向量机在水中目标识别中的应用

论文研究了支持向量机核函数构成条件以及不同核函数的特性，结合水中目标识别技术特点，提出了一种组合核函数支持向量机的方法。提取了基于小波变换的舰船辐射噪声奇异性、尺度-过零、尺度-能量特征，对水中目标进行了SVM分类识别。研究表明，基于组合核函数的支持向量机分类识别效果优于单独核函数的支持向量机识别效果。     

Roll‐up of a viscous vortex sheet

Abstract

The vortex sheet roll‐up for a viscous fluid flow under an initially periodic perturbation is studied by using a core‐spreading vortex method [2]. The viscous term, usually neglected in prior studies, is considered in the present study. In order to avoid the singularity at the center of point vortices, a convolution decomposition procedure is applied to form the vortex blobs. When calculating the stream function and the velocity field, the computations for the vortex method are usually time‐consuming due to the involvement of a large number of vortex blobs. This is improved by employing an efficient algorithm based on multipole expansions [6] to perform far‐field calculations. With the help of the fast algorithm, the time complexity of the one‐step calculation is directly proportional to the number of vortex blobs.

Numerical results show that the roll‐up of a vortex sheet with the viscous effect is slower than that of an inviscid vortex sheet. During the roll‐up of the vortex sheet, the spread and the flatness of the vorticity distribution are also studied by calculating the second moments and the fourth moments, respectively. Both results indicate the roll‐up of an inviscid vortex sheet is stretched slightly longer than that of a viscous vortex sheet.     

Wind pressure features of large-span flat roof in different wind fields induced by conical vortex

The wind pressure features on a large-span flat roof in uniform flow field and turbulent field induced by conical vortex were studied, through wind tunnel tests. From the comparison of the mean and fluctuating wind pressure distributions on a flat roof in different wind fields induced by conical vortex, results indicate that the mean suction dominates in the smooth flow, whereas the fluctuating suction is more obvious in the turbulent flow. The probability density function for the pressure fluctuations under different approaching flows is analyzed. The two-peaked distribution, peculiar to turbulent flow field, is observed on the curve of probability density. The fluctuating pressures at reattachment points are larger under the turbulent flow. This indicates a more intense reattachment, which may cause overturning moment for roof-mounted items. Point vortex, RanKine vortex, and simplified Cook expression are applied to fit the pressure profiles beneath conical vortices, respectively. The results have shown that the RanKine vortex model and simplified Cook expression were applicable to forecast the wind pressure profiles beneath conical vortices, while point vortex underestimated the real wind suction. The wind pressure distributions in turbulent fields induced by different wind angles were contrasted, when the approaching flow is along the diagonal of the roof, the intensity of the vortex pairs is almost equal, with obvious reattachment. When the approaching flow deviate from the diagonal of the roof, the lateral turbulent component spins the vortex more quickly; this induces larger mean suctions beneath windward vortices. Smaller suctions are observed beneath the leeward vortex, due to less vorticity being converted to vortex motion from the freestream.     

Vortex motion in the early stages of unsteady flow around a circular cylinder

In this paper, processes in the early stages of vortex motion and the development of flow structure behind an impulsively-started circular cylinder at high Reynolds number are investigated by combining the discrete vortex model with boundary layer theory, considering the separation of incoming flow boundary layer and rear shear layer in the recirculating flow region. The development of flow structure and vortex motion, particularly the formation and development of secondary vortex and a pair of secondary vortices and their effect on the flow field are calculated. The results clearly show that the flow structure and vortices motion went through a series of complicated processes before the symmetric main vortices change into asymmetric: development of main vortices induces secondary vortices; growth of the secondary vortices causes the main vortex sheets to break off and causes the symmetric main vortices to become “free” vortices, while a pair of secondary vortices is formed; then the vortex sheets, after breaking off, gradually extend downstream and the structure of a pair of secondary vortices becomes relaxed. These features of vortex motion look very much like the observed features in some available flow field visualizations. The action of the secondary vortices causes the main vortex sheets to break off and converts the main vortices into free vortices. This should be the immediate cause leading to the instability of the motion of the symmetric main vortices. The flow field structure such as the separation position of boundary layer and rear shear layer, the unsteady pressure distributions and the drag coefficient are calculated. Comparison with other results or experiments is also made. This work was presented at the First Asian Congress of Fluid Mechanics, Bangalore in December 1980.     

Non-spherical bubble behavior in vortex flow fields

The boundary element method (BEM) is applied to solve the unsteady behavior of a bubble placed in a vortex flow field. The steady vortex field is given in terms of the viscous core radius and the circulation, both of which may vary along the vortex axis. For this study, 2DynaFS^©, an axisymmetric potential flow code which has been verified successfully for diverse type of fluid dynamic problems, is extended. The modifications to accommodate the ambient vortex flow field and to model the extreme deformations of the bubble are presented. Through the numerical simulations, the time history of the bubble geometry and the corresponding pressure signal at a fixed field point are obtained. A special effort is made to continue the numerical simulation after the bubble splits into two or more sub-bubbles. Indeed, it is found that an elongated bubble sometimes splits into smaller bubbles, which then collapse with the emission of strong pressure signals. The behavior of the axial jets after the split is also studied in more detail. This work was conducted at Dynaflow, Inc. (www.dynaflow-inc.com). The work has been supported by the Office of Naval Research under the contract No. N0014–99-C-0369 monitored by Dr. Ki-Han Kim. This support is greatly appreciated.     

水下稳态涡流场声传播的数值模拟和实验研究

声波穿过涡流场时声传播特性会发生改变,可由此判断涡流场的存在及其特征参数。文章首先推导了二维稳态涡流场的射线微分方程组,实现了声波通过涡流场的声线轨迹模拟。然后开展水池超声传感器实验,采用现代计算流体力学(Computational Fluid Dynamics,CFD)仿真方法获取涡流场参数。最后将通过涡流场声信号的时延结果,与实验测量值进行对比分析。结果表明,对于涡核半径为30 mm,最大切向速度为1.2 m·s^-1的涡流场,数值模拟误差小于10%,验证了基于射线声学的水下稳态涡流场声传播数值模拟的有效性。     

爆炸管道出口外流场的数值模拟

采用带化学反应的多组分Euler方程,数值模拟了爆炸管道出口形状对爆轰波泄出外流场结构的影响.采用高速阴影光学显示技术拍摄了外流场的照片,对数值计算方法进行了验证.在此基础上,考察了不同出口形状对爆轰波溢出后的外流场的动力学演变规律的影响,分析讨论了涡环与激波的相互作用过程.     

不同流体条件下涡街流量计的测量特性研究

本文详细阐述了涡街流量计的工作原理,先通过实验对在不同流体条件下的相对示值误差进行分析,再利用SOLIDWORKS FLOWSIMULATION流体计算软件对涡街流量计进行相应的流场分析等。     

涡流管分离模型及实验研究

通过对涡流管的热力分析和流动分析，建立其内部过程的数学模型。从速度场的变化推导内部热分离的温度方程。实验系统测量涡流管内部温度场及速度场，理论计算值与实验值吻合。     

Spatial correlation properties and correlation vortices of partially coherent vortex beams diffracted by an aperture

Taking the Gaussian–Schell model vortex beam as a typical example of partially coherent vortex beams, the spatial correlation properties and correlation vortices of partially coherent vortex beams diffracted by an aperture are studied. It is shown that the off-axis displacement and spatial coherence affects the spectral degree of coherence. The number and position of correlation vortices depend on the off-axis displacement, spatial coherence, aperture truncation and propagation distance, where the effect of aperture diffraction on the correlation vortices is stressed. The number of correlation vortices decrease as the truncation parameter increases. The correlation vortices in the diffracted field result from the vortex embedded in partially coherent beams at the source plane rather than from the aperture diffraction. The correlation vortices in the diffracted field appear even when the vortex core is stopped by the aperture.