Numerical Tidal Current Modeling Using Fine Boundary-Fitted Grids for Tidal Flats

Fine grids with small spacing in boundary-fitted coordinates are normally used to treat the computation of fluid dynamics for estuarine areas and tidal flats. However, the adoption of Cartesian components of velocity vectors in this kind of non-orthogonal coordinates will definitely result in a difficulty in solving implicitly the transformed momentum equations, and also complicate the wet-dry point judgement used for flood areas. To solve this problem, equations in terms of generalized contravariant velocity vectors in curvilinear coordinates are derived in the present study, by virtue of which, an Alternative-Direction-Implicit numerical scheme in non-orthogonal grids would then be easily obtained, and wet-dry point judgement would as well be largely simplified. A comparison is made between the explicit scheme and implicit scheme, showing that the present model is accurate and numerically stable for computations of fluid dynamics for estuarine areas and tidal flats.

Modelling Three-Dimensional Winds on a NW Pacific Region of Mexico Using Boundary-Fitted Grids

In this study, the momentum equations describing an atmospheric flow over a NW Pacific region of Mexico are solved numerically. In order to capture the complex flow-topography interactions with detail, a combination of a numerical wind model in full 3D curvilinear coordinates, along with a high resolution boundary-fitted grid is used. Boundary conditions were obtained from ten years (2002-2012) of measured offshore wind data. Prevailing winds from April to September during that period of observations were selected for the simulations. For the cases analyzed, it was found that at the points of the study region (PSS, PSM, PM), wind speed increased about 10% to 20% of its offshore values, while inland they decreased about 86% to 96%. This spatial behavior agreed very well with the observed local winds. A coastal jet (CJ), 35 km long with speeds about 1.5 - 2 m/s, emanating from PSS was found for NNW winds. Modeled winds were also used to compute wind stresses, wind stress curl, and CUI fields. Wind stress values agreed very well to those reported in the literature. High values of wind stress curl, and CUI were found at the lee of the points (PSS, PSM, PM). Indirect estimations of sea surface currents were about 15 - 20 cm/s offshore and 5 - 10 cm/s at the coast.

2-D boundary-fitted coordinate grid generation for casting with complex shape

In order to overcome the zigzag grids generated by conventional finite difference method on complicated casting boundaries in the simulation of casting process, the generation program for 2-D boundary-fitted coordinate grid has been developed by solving a set of partial differential equations (PDE) numerically. The STL format files were treated as input data for 2-D physical regions. The equipartition method for boundary points was used to improve the self-adaptability of grid according to the characteristic of the STL format files. The program was demonstrated through some examples. The comparison between the conventional finite difference method and the proposed method shows that this program is effective and flexible for generation of boundary-fitted grid in any arbitrary 2-D complex domain, and the grid is in accordance with the variety of boundary curvature finely. The program also provides two types of boundary-fitted grids for double-connected region, O-type and C-type. The limitation of the step-like boundary with the rectangle grid could be avoided effectively. Therefore, the computational accuracy and efficiency would be improved and the computational time would be saved significantly by the application of boundary-fitted grids.

Feature study of body-fitted Cartesian grids used in casting numerical simulation

A type of mesh called a body-fi tted Cartesian mesh,very different from the traditional structured body-fi tted mesh,is established.At f irst,the right parallelepiped mesh is generated,then,a feature analysis is done on the cross sections.These cross sections are the intersections of the casting shape with the right parallelepiped grids(under the Cartesian coordinate system).On the basis of the feature analysis,two sorts of body-f itted boundary grids,shape-keeping grids and shape-distortion grids,are def ined.Shape-distortion grids can be removed or weaken by increasing the number of grids or moving the coordinates of the mesh generation region,so actually the body-fitted Cartesian mesh generation is to get shape-keeping grids.A shape-keeping grid mainly consists of two sorts of surfaces(I type face and II type face),and each of them is joined by two types of points(I type point and II type point).If only these two types of points were given,the shape-keeping mesh would be constructed.In this paper,the cases of the above two boundary grids being generated were discussed.An algorithm was put forward to get the shape-keeping grids.Several body-fi tted Cartesian meshes generated on castings show the validity of the algorithm.The mesh generation examples show that the body-fi tted Cartesian mesh is more excellent than the right parallelepiped mesh in aspects of decreasing grids number and being closer to the shape of the casting solid.

公共体育服务融入基层网格化管理的意义解析与路径探索

网格化管理是基层政府在科层制体系内利用信息技术实现政府管理流程再造的创新性举措,其普及程度与应用范围日益扩大,呈现出向公共服务领域倾斜的趋势。公共体育服务融入基层网格化管理有助于推动公共体育服务管理重心下移,有助于强化公共体育服务供给的多部门协同,有助于改善公共体育服务供需错位问题,有助于促进公共体育服务的“管监评分离”;然而,其实践层面也可能引发公共体育服务管理的形式化问题,呈现公共体育服务管理的新碎片化状态,挤压体育社会组织和市场组织参与公共体育服务供给的空间,弱化社区自治组织在公共体育服务供给上的作用。公共体育服务融入基层网格化管理的路径主要包括将社会体育指导员、体育场地纳入网格化管理的资源库,将全民健身工作领导协调机制嵌入网格化管理的联动中心,将体育社会组织、市场组织吸纳进网格化管理的合作框架,将社区自治与网格化管理有机衔接4个方面。

基于栅格特征的打印软件环境研究

通过对不同打印软件打印文字的栅格特征进行实验研究,分析栅格特征与打印软件的关联性,判断操作系统、打印驱动程序、文字处理软件等打印软件环境的相关信息,为打印文件机源种属鉴别提供新的思路。以中易宋体100个常用汉字为研究对象,使用兄弟、惠普、联想、佳能、富士施乐、京瓷、松下、光电通等常见品牌打印机,设置300、600 dpi分辨率或默认模式,打印八号、七号、六号、小五号、五号、小四号、四号、小三号、三号、小二号样本500份。将不同种类操作系统、不同类型打印驱动程序、不同种类文字处理软件、不同版本中易宋体字库环境下打印的文字,制作成栅格模拟图,进行栅格特征比对,总结栅格特征多样性产生的原因。结果表明,字符轮廓线的栅格适配与否、缺失像素的补偿规则、映射到设备空间的字符轮廓线大小、描述字体的曲线种类等因素会使栅格特征发生改变。横笔段厚度特征与字符轮廓线的栅格适配与否关系较大;竖笔段宽度特征与映射到设备空间的字符轮廓线横向大小关系较大;斜笔画阶梯特征与缺失像素的补偿方式、描述字体的曲线类型等关系较大;平行笔段间距特征(即平行笔段间的空白栅格多少)与映射到设备空间的字符轮廓线的纵向大小关系较大。通过栅格特征,可以分析打印文件的打印软件环境信息,如操作系统类型、打印驱动程序种类、栅格适配方式、文字处理软件种类等,可以为打印文件机源种属鉴别提供新的思路。

离子推力器栅极组件热变形测量方法

栅极组件是离子推力器的核心部件,其所包含的多层栅极结构在工作过程中会发生热变形,导致栅极间距发生改变,进而影响离子推力器的工作性能及寿命。为了实现栅极结构在实际工况下热变形的非接触测量与评估,改进和发展了基于摄像测量的栅极变形观测方法,评价了不同图像分析方法(灰度重心法、圆拟合法、灰度匹配法)对变形测量精度的影响。结果表明灰度匹配方法观测精度高,环境适应性好;同时,设计并实现了一套栅极热变形环境模拟与变形测量系统,可实现高温、通水、通气环境下变形的高精度观测。最后,对环境箱通水通气对测量精度的影响进行了评价,结果表明二者均会对测量精度造成影响,通水对实验结果的影响大于通气的影响。

基于Vector Fitting的光伏并网逆变器控制器参数频域辨识方法

光伏并网逆变器通常含有内外环、锁相环等不同带宽控制环节,且控制器参数往往并不可知,即存在“灰箱”问题。为准确辨识不同带宽控制器参数,提出一种基于端口导纳特性的光伏并网逆变器控制器参数频域辨识方法。首先,建立典型控制下光伏并网逆变器交流端口的dq理论导纳模型,得到其理论导纳标准式;然后,通过扫频手段获得光伏并网逆变器交流端口的测量导纳数据,并采用Vector Fitting算法对测量的端口导纳数据进行矢量拟合,得到拟合导纳标准式;最后,运用最小二乘原理使理论导纳标准式与拟合导纳标准式对应项系数差值的平方和最小,从而辨识得到光伏并网逆变器控制器参数的估计值。参数辨识实例表明,所提方法能够同时准确辨识出不同带宽控制器参数。

基于历史天气的区域电网负荷预测

随着社会经济的迅速发展,人们对电能的需要日益增加,但是在电网运行中,常常会出现电力产能过剩或者不足的情况,为保证电力系统安全稳定、经济运行,就必须掌握各种区域电网负荷的变化规律和发展趋势。论文对重庆市区供电分公司供电区域电网中长期负荷进行预测,提出一种预测区域电网中长期负荷的方法,即一种基于前12个月历史天气条件和区域电网负荷关联关系的多元非线性拟合的特征参数因子曲线的中长期负荷预测方法,建立基于不同算法的多种预测模型,通过归一化处理,得到的区域电网中长期负荷预测的精度高,与实际区域电网负荷之间的误差小,对于区域电网中长期负荷预测分析具有重要参考利用价值。

卡尔曼滤波改进虚拟同步机控制研究

虚拟同步发电机(VSG)通过模拟同步发电机的动态特性为电网提供惯性支持,但是VSG系统中通信传输过程的噪声会影响精度,从而造成频率抖动。针对上述问题,在传统的VSG控制系统上加入卡尔曼滤波环节,形成一种新型的抗扰控制方式。在控制中利用遗传算法将卡尔曼滤波器的协方差矩阵Q和R作为遗传算法的个体编码,设计适应度函数来评估不同参数组合下的滤波效果,以提升VSG系统的性能。仿真结果表明,所提出的控制策略能够有效提高运行稳定性,消除机端频率抖动。

森林碳储量快速估算技术探析

在陆地生态系统生产总值(Gross Ecosystem Product,GEP)核算体系中,碳储量核算是其核心内容。利用测树因子核算森林碳储量的传统方法存在外业工作量大、成本高、工时长、且不易实现等诸多缺点。本文介绍一种森林碳储量快速估算的新方法,该方法通过超光谱探测叶子组成成分和森林植被树种细致分类、分段式植被指数函数反演并经过曲面拟合获取稳定叶面积指数,由定量总叶面积密度反求测树因子、再通过优势树种分生物量比例关系用网格法直接求出森林生物量及碳储量,具备覆盖范围大、效率高、成本低的优点。

基于多正弦信号注入的大功率并网逆变器电网阻抗在线测量技术研究

文中研究基于多正弦扰动信号注入的大功率并网逆变器电网阻抗测量技术。选取多正弦信号作为电压扰动,参考空间光场理论中的Gerchberg-Saxton相位恢复算法对扰动信号进行优化设计;剪辑函数作为其中的关键要素,能够决定扰动信号时域波峰的剪辑速度和剪辑能力;为提升上述性能,提出采用反正切函数代替传统算法中的对数剪辑函数,仿真结果表明,相位恢复算法的剪辑性能得到大幅提升;随后,通过逆变器将扰动信号注入电网,采用Gauss-Newton非线性最小二乘法对采集到的扰动信号特征谐波频率点的信息进行曲线拟合,获取当前电网阻抗信息;最后,于搭建的1.5 MW并网逆变器RT-Lab平台进行多弱电网场景下的阻抗测量实验,实验结果验证了此方案的有效性和准确性。

基于s-grid的断层一体化建模方法

根据断层两盘的空间位置关系和s-grid相邻网格间的关系,提出一种网格与断层的拟合方法("构造断层面法"),依据各地层的关系将断层划分成不同高程平面的结构体,通过将断层破碎带作为网格拟合对象的一部分,最终达到一体化建立断层的效果,并给予了破碎带可被编辑的地质属性。该拟合方法可在工程中提升建模精度,防止锯齿状边界的出现,使得三维模拟情况更加贴近实际情况。同时,断层破碎带亦可根据工程需求进行属性传递,保证了断层两盘的属性连通性。

基于改进遗传退火算法的电网智慧供应链最优仓库自动定位方法

为了解决供应链下仓库物资分散、信息错乱、运行效率低下等问题,以提高仓库管理水平、保障仓库运输的供求时间为目标,提出一种基于改进电网智慧供应链最优仓库自动定位方法。建立运输时间最短的目标函数,通过改进遗传退火算法,选择染色体编码方式,设置自动定位约束条件,构建电网物资仓库之间的供需量模型,自动定位存在最优供求关系的最优仓库。实验结果证明,应用所提方法后,随惩罚成本而产生变动的各成本变化趋势整体较平缓,未及时满足需求比例与总成本呈正相关;所定位仓库符合目标影响函数;使用62次迭代即获得了最优仓库定位的目标函数。可以缓解电力物资调度矛盾,提高了电网物资供给点、周转仓、需求点的运输效率。

“数值传热学”中贴体网格与非结构化网格上的有限容积法对比教学

提出了一套贴体网格和非结构化网格有限容积法的对比教学方法。该方法基于典型案例引入以及对照式、综合式辨析策略,给出了对不规则区域有限容积法涉及贴体网格和非结构化网格内涵的差异,两者对有限容积法实施过程差异,控制方程的异同,控制方程变换的实质以及物理问题适应性5个重要内容进行综合辨析教学的要点及实施过程。该对比教学方法可为“数值传热学”或“计算流体力学”的教学或自学提供参考。

基于内壁点云切片坐标的高速公路隧道整体变形监测方法

因高速公路隧道在使用过程中容易产生横向、纵向形变,易产生高速公路隧道安全问题,为此,提出一种基于内壁点云切片坐标的高速公路隧道整体变形监测方法。采用投影平面方式将内壁实现点云信息分层,令各段点云映射到中心位置的参考平面,提取内壁点云信息,运用最小二乘法拟合隧道平面,使用格网化内插值算出各点云内插值,通过各时间点网格内插值变化情况,判断出该隧道变形相关量,根据网格平面所在位置得出变形位置,完成隧道整体变形监测。结果表明:所提方法的监测信息数量和计算时间分别为9921个和6.21s,能够敏锐感知细微隧道变形,监测效率最高,具有较高实用性与有效性,该方法可有效提高高速公路隧道交通运行的安全性。

Proof of the Monotonicity of Grid Size and Its Application in Grid-Size Selection for Mesoscale Models

Terrain characteristics can be accurately represented in spectrum space. Terrain spectra can quantitatively reflect the effect of topographic dynamic forcing on the atmosphere. In wavelength space, topographic spectral energy decreases with decreasing wavelength, in spite of several departures. This relationship is approximated by an exponential function. A power law relationship between the terrain height spectra and wavelength is fitted by the least-squares method, and the fitting slope is associated with grid-size selection for mesoscale models. The monotonicity of grid size is investigated, and it is strictly proved that grid size increases with increasing fitting exponent, indicating that the universal grid size is determined by the minimum fitting exponent. An example of landslide-prone areas in western Sichuan is given, and the universal grid spacing of 4.1 km is shown to be a requirement to resolve 90% of terrain height variance for mesoscale models, without resorting to the parameterization of subgrid-scale terrain variance. Comparison among results of different simulations shows that the simulations estimate the observed precipitation well when using a resolution of 4.1 km or finer. Although the main flow patterns are similar, finer grids produce more complex patterns that show divergence zones, convergence zones and vortices. Horizontal grid size significantly affects the vertical structure of the convective boundary layer. Stronger vertical wind components are simulated for finer grid resolutions. In particular, noticeable sinking airflows over mountains are captured for those model configurations.

Image interpolation algorithm on a triangular grid

A new method for constructing a fitting surface on a triangular grid is presented. Assuming images are obtained by sampling from the original scene. Conventional polynomial interpolation methods generally construct the fitting surface on a square grid. Different from existing methods, the new method constructs the fitting surface on a triangular grid which can divide the original surface more detailed and improve approximation accuracy. As the quality of the image edges plays a key role in visual effects of image, the new method uses image edges as constraints to get a triangle grid. The new method constructs a cubic polynomial patch locally using image data to approximate the original surface. Experimental comparison results of the new method with other methods show that the new method can produce high-quality images and remove the zigzagging artifact.

基于协方差拟合的离格气体泄漏源定位方法

针对网格划分类算法导致的量化误差影响估计性能以及相干信源下难以准确定位的问题,提出了一种基于协方差拟合的离格气体泄漏源定位方法。利用协方差拟合准则重构出泄漏源在相干信号下的协方差矩阵,使其恢复Toeplitz特性,引入以L_(2)范数作为约束条件的离格模型,将恢复出的协方差矩阵与离格模型进行联合估计。最后利用泄压阀模拟气体管道泄漏的发生,对比低信噪比及相干信源下的仿真结果。实验分析表明:该方法虽然对快拍数依赖稍显敏感但是弥补了相干信源下传统稀疏恢复类算法的失效问题,同时在低信噪比情况下依然能够准确进行角度估计,为复杂环境下的气体泄漏监测提供了新的思路。

基于正交贴体网格的黏弹介质地震波模拟

常规的有限差分地震波数值模拟采用笛卡尔坐标系的规则网格对计算区域进行网格剖分,在模拟起伏地表下的地震波场时,不仅不利于实现自由边界条件,而且由于阶梯状网格近似,在网格角点处容易产生虚假散射波,从而影响模拟精度。为此,将计算流体力学中的正交贴体网格生成技术引入起伏地表下黏弹介质的网格剖分中,采用优化的同位网格有限差分法计算曲线坐标系的一阶速度—应力方程,并通过选择性滤波法消除同位网格差分产生的格点振荡。正交贴体网格能够精确地描述起伏地表,网格的正交性也使得实施自由边界条件时无需做复杂的坐标转换和插值运算。数值算例表明:该方法得到的数值解与解析解完全吻合;与规则网格有限差分法模拟结果相比,在相同网格间距条件下,该方法能够有效消除阶梯状网格引起的虚假散射波,从而提高数值模拟精度。此外,起伏地表两层和三层黏弹介质模型模拟结果表明,该方法对复杂模型同样有较强的适用性。