结构化与非结构化网格融合技术研究

为了得到质量高、适用性强的有限元计算网格,将结构化网格与非结构化网格两种划分方法相融合,通过网格拓扑转化技术将交界面处的四面体网格转化成三角形网格来满足拓扑一致,实现网格无缝连接。通过算例与实验结果对比发现,该方法生成的网格数量少,计算精度高,适用范围广。     

三维精确局部加密网格划分在行波管模拟软件中的应用

通过半径与最小边之比控制网格质量,用三维分段线性结构（3D-PLC）作为网格初始数据进行自适应,用PLC进行局部加密形成Delaunay自适应网格划分方法,最后以螺旋线和电子枪为实例证明该方法的可行性。     

多层区域划分下蚁群算法研究

通过网格区域划分和分层手段可以找到一条较好的路径,蚁群算法的时间和空间计算复杂度得到有效的降低。其中,网格划分的层数多少直接影响了蚁群算法的最优解。这种新的算法提供了在连续变化空间优化情况下,方便有效地解决TSP问题的方法。     

基于网格划分策略的改进人工鱼群算法

人工鱼群算法是一种新型的随机搜索优化算法，初步研究表明该算法具有许多优良的性质。通过引入网格划分策略和禁忌搜索算法．对基本人工鱼群算法进行了改进，减少了迂回搜索的无用计算，同时也使人工鱼可以在解空间内进行更为全面的搜索，提高了搜索效率，加快了系统满意解域的确定；通过对变量空间进行网格划分，提供了获取系统最优解的方法，而且加强了对鱼群公告板信息的使用。实验表明，与基本人工鱼群算法相比，该方法具有明显的优越性。     

开关磁阻电机温度场分析中模型网格划分方法

针对开关磁阻电机温度场分析中模型网格划分对分析结果造成的影响,提出一种变密度网格划分方法。首先建立开关磁阻电机的有限元模型,然后针对其主要发热部件电机绕组采用六面体变密度网格划分,其余部件采用自动网格划分,并在此基础上进行了相应的有限元温度场分析,同时与采用传统四面体自动网格划分方法作了对比研究,最后通过实验对上述变密度网格划分方法作了进一步的实验验证,结果表明:所提出的变密度网格方法有效提高了开关磁阻电机温度场分析的准确性,因而具有较好的应用价值。     

复合网格法在电磁散射问题中的应用研究

复合网格方法采用区域分解算法的思想,将计算区域分为粗网格与细网格两个区域.在电磁散射问题中,细网格区域包含了微细结构的电磁散射信息.利用连接边界条件,将粗网格计算结果和细网格计算结果分步进行计算,从而得到包含有微细结构的电磁散射信息.该计算方法可以减少此类计算问题的计算量,所得结果与全部区域进行细网格划分的结果进行了比较,两种结果复合很好.     

基于网格部分细化的DOA估计方法

计算复杂度和估计精确度一直是波达方向(DOA)估计研究的重点。现有基于压缩感知的DOA估计算法与传统算法相比具有一定优势,但这些稀疏信号重建模型都是将角度空间等间距划分,仍存在算法计算复杂度较高和估计精确度较低的问题。针对这些问题,提出一种对角度空间网格进行部分细化的DOA估计方法。该方法包括裂变过程和学习过程,裂变过程通过产生新网格点对角度空间进行细化,学习过程通过迭代不断逼近波达方向。仿真结果表明,提出的算法耗时较少,而且在非常稀疏的初始网格划分的条件下(初始间隔为20°),仍可以获得较高的估计精确度。     

局部网格动态聚类算法

针对传统网格聚类算法聚类精度较低,处理流数据效率较低等问题进行改进。提出局部网格动态聚类算法,算法引入维度半径概念进行增量动态网格划分,通过采用新的簇边界判定方法对簇边界进行判定,依据稀疏网格与其邻接密集网格的质心距离,将稀疏网格归并到相应网格簇中,对于不能归并的稀疏网格则采用局部网格划分方法对稀疏网格再次进行划分聚类,避免簇边界的误删,在一定程度上提高了聚类精确度。通过对比实验结果表明提出的算法具有更好的聚类时效性和聚类精度。     

一种基于改进网格聚类的雷达信号预分选算法

基于网格的聚类算法是雷达信号预分选领域的一种常用方法。针对现有网格聚类算法需要人为确定网格划分、边界处理精度低的问题,提出一种改进的网格聚类算法,该算法对输入雷达信号脉冲顺序不敏感,根据网格数据压缩率自适应确定网格划分和密度阈值。仿真实验验证了算法的有效性和抗噪声能力。     

考虑枕效应的网状可展开天线电性能预测

提出了一种预测网状可展开天线电性能的数值计算方法.针对网状可展开天线采用三角形拼合的这一特点,首先从结构力学出发确定天线枕效应变形,然后采用巴斯卡图插值进行面片网格划分,给出了网格划分准则,其次通过最佳吻合抛物面确定最优馈源的位置和指向,最后考虑丝网的电磁漏射对网状天线进行电性能预测.通过仿真算例验证了该方法的可行性和有效性.     

Multi-grid interface in computational electromagnetics

An elegant and accurate technique of interfacing segments of a uniform computational mesh with different spatial resolution is described. The technique is illustrated in the time-domain for a TLM mesh. Results show that a seamless interface is achieved between different mesh areas, thus allowing multi-scale problems to be accurately mapped onto the mesh.     

Numerical study on performance of pyramidal and conical isotropic etched single emitters

A full three-dimensional model was implemented in order to investigate the electrical characteristics of conical and pyramidal isotropic etched emitters. The analysis was performed using the finite element method (FEM). The simulations of both emitters were modeled using a combination of tetrahedral and hexahedral elements that are capable of creating a mapped and regular mesh in the vacuum region and an irregular mesh near the surfaces of the emitter. The electric field strengths and electric potentials are computed and can be used to estimate the field enhancement factor as well as the current density using the Fowler-Nordheim (FN) theory. The FEM provides results at nodes located at discrete coordinates in space; therefore, the surface of the emitter can be generated through a function interpolating a set of scattered data points. The emission current is calculated through integration of the current density over the emitter tip surface. The influences of the device geometrical structure on its potential distribution, electric field and emission characteristics are discussed.     

基于多角度照片的真实感三维人脸建模的研究

为了提高重构的三维人脸的真实感,提出了以Candide-3模型作为通用的人脸模型的一种改进的利用多角度照片进行合成的方法。首先利用改进的双目立体视觉系统,将获取的二维信息映射到三维空间上,测定特征点的深度信息;然后采用自动和交互的方式对Candide-3模型进行校准,合成三维人脸模型。最后采用改进的多角度映射方法对皮肤纹理进行映射贴图,合成具有真实感的三维人脸模型。验证表明,该方法能够更好的生成一个具有较好逼真度的真实感的三维人脸模型。     

Microwave modeling and validation in food thawing applications

Developing temperature fields in frozen cheese sauce undergoing microwave heating were simulated and measured. Two scenarios were investigated: a centric and offset placement on the rotating turntable. Numerical modeling was performed using a dedicated electromagnetic Finite Difference Time Domain (FDTD) module that was two-way coupled to the PHYSICA multiphysics package. Two meshes were used: the food material and container were meshed for the heat transfer and the microwave oven cavity and waveguide were meshed for the microwave field. Power densities obtained on the structured FDTD mesh were mapped onto the unstructured finite volume method mesh for each time-step/turntable position. On heating for each specified time-step the temperature field was mapped back onto the FDTD mesh and the electromagnetic properties were updated accordingly. Changes in thermal/electric properties associated with the phase transition were fully accounted for as well as heat losses from product to cavity. Detailed comparisons were carried out for the centric and offset placements, comparing experimental temperature profiles during microwave thawing with those obtained by numerical simulation.     

基于弹性网格特征和神经网络的手写文字识别

提出一种有效的文字特征提取方法,在传统弹性网格基础上,采取与对角弹性网格相结合的方法进行特征提取,然后通过改进的BP神经网络进行文字识别.该方法集合了弹性网格特征和神经网络的优势,可有效提高手写文字的识别率、识别速度以及识别系统的泛化能力.实践证明,该方法用于文字识别准确性较高.     

Objective and subjective evaluation of static 3D mesh compression

3D mesh compression is essential in the context of network-based virtual worlds, but so are objective and subjective fidelity of the reconstructed mesh to the original one. Unfortunately, it is difficult to establish a fair way to compare objectively two textured, triangular 3D meshes meant to approximate the surface of the same 3D object. We explain why by elaborating on how the geometric distance between two meshes can be estimated, after introducing some basic concepts related to mesh shape and a brief taxonomy of static 3D mesh coding techniques. We review a selection of such coding techniques, almost all of which deal only with the shape of the surface, and then focus on surface appearance, usually described separately with a texture to be mapped onto the 3D mesh at rendering time, and we also review existing techniques specifically devised to compress textures meant for 3D models. Finally, we discuss the even larger complexity of establishing any reasonable way to compare the subjective quality of the experience produced by two versions of the same 3D object, especially if different rendering methods may be used.     

Gateway Placement for Throughput Optimization in Wireless Mesh Networks

In this paper, we address the problem of gateway placement for throughput optimization in multi-hop wireless mesh networks. Assume that each mesh node in the mesh network has a traffic demand. Given the number of gateways to be deployed (denoted by k) and the interference model in the network, we study where to place exactly k gateways in the mesh network such that the total throughput is maximized while it also ensures a certain fairness among all mesh nodes. We propose a novel grid-based gateway deployment method using a cross-layer throughput optimization, and prove that the achieved throughput by our method is a constant times of the optimal. Simulation results demonstrate that our method can effectively exploit the available resources and perform much better than random and fixed deployment methods. In addition, the proposed method can also be extended to work with multi-channel and multi-radio mesh networks under different interference models.     

A dual mesh scheme for finite element based reconstruction algorithms

The finite element (FE) method has found several applications in emerging imaging modalities, especially microwave imaging which has been shown to be potentially useful in a number of areas including thermal estimation. In monitoring temperature distributions, the biological phenomena of temperature variations of tissue dielectric properties is exploited. By imaging these properties and their changes during such therapies as hyperthermia, temperature distributions can be deduced using difference imaging techniques. The authors focus on a microwave imaging problem where the hybrid element (HE) method is used in conjunction with a dual mesh scheme in an effort to image complex wavenumbers, k(2). The dual mesh scheme is introduced to improve the reconstructed images of tissue properties and is ideally suited for systems using FE methods as their computational base. Since the electric fields typically vary rapidly over a given body when irradiated by high-frequency electromagnetic sources, a dense mesh is needed for these fields to be accurately represented. Conversely, k(2) may be fairly constant over subregions of the body which would allow for a less dense sampling of this parameter in those regions. In the dual mesh system employed, the first mesh, which is uniformly dense, is used for calculating the electric fields over the body whereas the second mesh, which is nonuniform and less dense, is used for representing the k(2) distribution within the region of interest. The authors examine the 2-D TM polarization case for a pair of dielectric distributions on both a large and small problem to demonstrate the flexibility of the dual mesh method along with some of the difficulties associated with larger imaging problems. Results demonstrate the capabilities of the dual mesh concept in comparison to a single mesh approach for a variety of test cases, suggesting that the dual mesh method is critical for FE based image reconstruction where rapidly varying physical quantities are used to recover smoother property profiles, as can occur in microwave imaging of biological bodies.     

Automatic superpixel generation algorithm based on a quadric error metric in 3D space

As a preprocessing step for computer vision tasks, research on generating superpixels of an image has been widely conducted recently. In this paper, we propose a fully automatic superpixel generation algorithm by simplifying the 3D triangle mesh modeled from a 2D input image. The simplification is performed based on a modified quadric error metric (QEM) method. The pipeline of our algorithm is simple. Given an image, we first turn it into a 2D triangle mesh and then lift the mesh to 3D based on the gray values of the image. We then simplify the 3D mesh based on the modified QEM method which encodes the features in the image intrinsically to ensure feature-aware superpixels. After obtaining the simplified mesh, we map it back to the 2D image to generate triangular-shaped superpixels. Our algorithm is fully automatic. The number of superpixels can be controlled intuitively. Experimental results demonstrate the effectiveness of our approach.