协调多时次差分格式的数值试验

在一个简化气候模式的混沌态上，针对影响实际预报准确度的多种因素，将协调多时次差分 格式与提为时间演变的变分同化进行了全面的比较.结果发现协调多时次差分格式可以有效 地纠正模式误差，尤为独特之处在于其还可以有效地纠正微分方程本身不完善所造成的误差 ，而这一点正是变分同化所不及的. 关键词： 协调多时次差分格式 变分同化 全局数值试验 混沌     

自忆模式中差分格式的稳定性研究

基于大气运动是一种不可逆过程的观点，引进了忆及过去时次资料的记忆函数，导出热传导的自忆性方程，研究了方程分别取Richardson和DuFort-Frankel格式，回溯阶p取1时的稳定性.探讨了多时刻模式中数值积分有时发散的问题，揭示了由过去时次资料动态求取记忆函数，改变了原定设计的差分格式，且它是一个时间平滑因子的本质. 关键词： 回溯阶差分格式 多时次 稳定性 记忆性     

磁流体方腔槽道流整体线性稳定性数值方法研究

将Chebyshev谱配置法和基于非均匀网格的高阶FD-q差分格式运用于磁流体方腔槽道流整体线性稳定性研究,比较两类数值方法的优缺点.Chebyshev谱配置法收敛快且精度高,但需要构造非常庞大的满矩阵,存储量和计算开销巨大;高阶FD-q差分格式采用了基于Kosloff-Tal-Ezer变换的Chebyshev谱配置点作为离散网格,在保持较高网格收敛精度的同时,差分格式可以采用稀疏矩阵进行存储,显著降低了存储量和计算开销.相比传统的谱配置法,基于非均匀网格的高阶FD-q差分格式计算效率得到显著的提升,将高阶FD-q差分格式运用于非正则模线性最优瞬态增长的计算,计算效果良好.     

用最小二乘法对多峰值数据进行曲线拟合及曲线峰中心位置的精确求解

提出一种计算机自动分组的方法，使得最小二乘法可以应用于多峰值数据处理，同时，给出了计算曲线中心位置的方法。     

一种线性最小二乘法的声源目标精确定位方法

在分析了声音能量距离衰减模型的基础上,提出了一种声源发射能量未知下的声源目标位置精确定位计算方法。将声音能量定位模型转化为非约束线性最小二乘法估计问题,其定位结果直接用代数解表示。同时对非约束线性最小二乘法下的参数进一步优化,提出了约束线性最小二乘法以提高定位精度。对信标节点位置坐标存在高斯噪声下的定位计算方法进行了改进以减少定位误差。仿真验证了该定位计算方法的有效性,数值模拟了不同观测信号噪声和信标节点位置噪声对定位误差的影响。结果同时表明,约束线性最小二乘法比非约束线性最小二乘法的定位误差更小,更接近于定位误差的克拉美罗下界值。     

一种线性最小二乘法的声源目标精确定位方法

在分析了声音能量距离衰减模型的基础上,提出了一种声源发射能量未知下的声源目标位置精确定位计算方法。将声音能量定位模型转化为非约束线性最小二乘法估计问题,其定位结果直接用代数解表示。同时对非约束线性最小二乘法下的参数进一步优化,提出了约束线性最小二乘法以提高定位精度。对信标节点位置坐标存在高斯噪声下的定位计算方法进行了改进以减少定位误差。仿真验证了该定位计算方法的有效性,数值模拟了不同观测信号噪声和信标节点位置噪声对定位误差的影响。结果同时表明,约束线性最小二乘法比非约束线性最小二乘法的定位误差更小,更接近于定位误差的克拉美罗下界值。      

弹性力学的复变量无网格方法

在移动最小二乘法的基础上，提出了复变量移动最小二乘法.复变量移动最小二乘法的优点是采用一维基函数建立二维问题的逼近函数，所形成的无网格方法计算量小.然后，将复变量移动最小二乘法应用于弹性力学的无网格方法，提出了复变量无网格方法，推导了复变量无网格方法的公式.与传统的无网格方法相比，复变量无网格方法具有计算量小、精度高的优点.最后给出了数值算例. 关键词： 移动最小二乘法 复变量移动最小二乘法 无网格方法 弹性力学 复变量无网格方法     

对角加载最小二乘法的时间延迟估计

最小二乘法是一种经典而有效的时间延迟估计算法,但由于最小二乘法矩阵求逆不稳定,在低信噪比情况下将失效.本文提出了对角加载最小二乘法(DL-LS),对求逆的矩阵加上一个正定阵,可以解决矩阵求逆不稳定的问题.并从正则化的角度分析了固定加载量的缺点——提高对低信噪比容忍性的同时降低了准确性,从而进一步提出了二次加载来解决这个...     

差分吸收光谱法测量大气污染的浓度反演方法研究

介绍了差分光学吸收光谱法(DOAS)测量大气污染气体浓度的基本原理,描述了对测量光谱所作的一些必要处理,对最小二乘法作了简单介绍,并将它用在DOAS方法中的浓度反演中,通过与当地监测站的数据进行对比,证明了最小二乘法非常适用于DOAS方法中的浓度反演. 关键词： 差分光学吸收光谱法 光谱处理 最小二乘法 环境监测     

基于最小二乘支持向量机的混沌控制

利用支持向量机良好的非线性函数逼近和泛化能力，提出基于最小二乘支持向量机非线性补偿的混沌控制新方法.应用最小二乘支持向量机离线辨识混沌系统的非线性部分，并用辨识模型补偿系统的非线性，同时应用线性状态反馈控制混沌系统.对三种典型连续混沌系统的仿真研究表明，提出的控制方法可以有效的控制混沌系统到达设定的目标状态，并且由线性状态反馈控制器构成的闭环系统稳定. 关键词： 混沌控制 支持向量机 最小二乘支持向量机 状态反馈 稳定性     

紧致方法对流动换热及静态分岔的模拟

发展了基于投影法的紧致方法求解流动换热问题,对顶盖驱动流和侧壁加热的方腔内自然对流换热问题进行了数值模拟。与其它传统方法相比,紧致方法能在较少的网格结点下获得精度较高的计算结果。进一步,采用所发展的紧致方法对不同工况下的Rayleigh-Benard对流及其静态分岔现象进行了数值模拟。数值计算结果表明当长宽比变大时,底部努塞尔数会有小幅度增加。当长宽比为8时,用所发展的紧致方法不同的初场可以得出三种不同的流场和温度场。与基于QUICK格式的SIMPLE算法相比,所发展的紧致方法可以多预测一种静态分岔现象。     

Linearity preserving nine-point schemes for diffusion equation on distorted quadrilateral meshes

In this paper, we employ the so-called linearity preserving method, which requires that a difference scheme should be exact on linear solutions, to derive a nine-point difference scheme for the numerical solution of diffusion equation on the structured quadrilateral meshes. This scheme uses firstly both cell-centered unknowns and vertex unknowns, and then the vertex unknowns are treated as a linear combination of the surrounding cell-centered unknowns, which reduces the scheme to a cell-centered one. The weights in the linear combination are derived through the linearity preserving approach and can be obtained by solving a local linear system whose solvability is rigorously discussed. Moreover, the relations between our linearity preserving scheme and some existing schemes are also discussed, by which a generalized multipoint flux approximation scheme based on the linearity preserving criterion is suggested. Numerical experiments show that the linearity preserving schemes in this paper have nearly second order accuracy on many highly skewed and highly distorted structured quadrilateral meshes.     

Entangled quantum clocks for measuring proper-time difference

We report that entangled pairs of quantum clocks (non-degenerate quantum bits) can be used as a specialized detector for precisely measuring difference of proper-times that each constituent quantum clock experiences. We describe why the proposed scheme would be more precise in the measurement of proper-time difference than a scheme of two-separate-quantum-clocks. We consider possibilities that the proposed scheme can be used in precision test of the relativity theory. Received 7 November 2001     

一种具有高分辨率特性的人工粘性法

八十年代发展起来的全变差不增格式在激波计算中所显示的卓越特性使其在气体力学问题的求解中得到广泛的应用。但全变差不增格式的一个缺点是计算量较大。本文提出了一种具有高分辨率特性的人工粘性方法,既保持了全变差不增格式的激波分辨率高的优点,又具有人工粘性法计算量较少的优点。     

Evaluation of force implementation in pseudopotential-based multiphase lattice Boltzmann models

The Lattice Boltzmann method (LBM) has proven to be a promising approach in handling multiphase flow problems. In the most widely applied pseudopotential-based LBM multiphase models, multiphase effects can be added in the form of forces, which is further divided into two aspects of force incorporation scheme and force expression. However, the effect of both aspects on coexistence densities and spurious current has not been evaluated systematically. In this paper, Modified Yuan-type and Zhang-type force expressions are chosen, and then they are incorporated into the lattice Boltzmann equation by the Shan–Chen and exact difference method force incorporation scheme to recover the Carnahan–Starling equation of state (EOS) with an additional surface tension term. Based on the computational results of two phases coexisting at a steady state, it can be observed that the force incorporation scheme affects the coexistence densities implicitly with different relaxation times and does not lead to a large difference in values. Force expression is found to greatly affect the achievable highest density ratio, of which the discrete gradient operator of the pseudopotential plays a crucial role. Spurious current is observed to be related to both the force expression and force incorporation scheme, and in our simulation a different force incorporation scheme brings about a large difference. Moreover, our modification on Yuan-type force expression not only improves the accuracy in capturing coexistence densities at low temperatures, but also provides the possibility of tuning the density ratio and surface tension independently at high density ratios.     

单个守恒型方程熵耗散格式中熵耗散函数的构造

对于一维单个守恒律方程,文[8]设计了一种非线性守恒型差分格式.此格式为二阶Godunov型的,用的是分片线性重构(reconstruction),重构函数的斜率是根据熵耗散得到的.格式满足熵条件.与传统的守恒格式不同的是此格式在计算过程中不仅用到了数值解还用到了数值熵.在此格式中一个所谓的熵耗散函数起到了很重要的作用,它在每一个网格的计算中耗散熵,以保证格式满足熵条件.文[8]中设计的熵耗散函数比较复杂,并且不是很完善.故数值地分析了在格式的构造中为何应给熵以一定的耗散,及应耗散多少.并且给出了一个新的以数值解的二阶差分作为基本模块的熵耗散函数.最后给出了相应的数值算例.     

A cutback method for measuring low linear fibre birefringence using an electro-optic modulator

A new cutback method based on the use of phase discrimination is proposed for low-linear-fibre-birefringence measurement. In this destructive method, a detection scheme for determining the phase difference between two readily obtained signals is used to give the phase retardation of the test fibre directly. The detection scheme mainly consists of two wave plates, two sections of fibre and an electro-optic modulator. The features of this measurement scheme are two-fold. First, the aforementioned phase difference between two detected signals, and, accordingly, linear fibre birefringence, can be determined in a simple manner, compared with the conventional cutback method. Second, the test fibre can be short in length despite the existence of fibre cladding modes. Experiments show that the proposed method can give a reliable measurement of linear fibre birefringence.     

An adaptive scanning scheme for effective whole field stress separation in digital photoelasticity

In photoelasticity, the method of obtaining the individual values of principal stresses/normal stresses separately is referred to as stress separation. Shear difference method is one of the widely used techniques for stress separation in digital photoelasticity. Normally a simple raster scanning approach is used in shear difference method in which stress separation is carried out for all the lines within the model domain by either row-wise horizontally or column-wise vertically starting from the boundary pixels. This requires the presence of a free boundary to start the integration scheme for every row of interest, which is not always possible in most of the practical problems. In order to overcome this, in this paper, an adaptive scanning scheme is proposed so that stress separation can be carried out even if there is only one free boundary pixel available in the model. The new scanning scheme is validated using the theoretically generated data for the problem of a ring subjected to internal pressure. Later, the applicability of this scheme is demonstrated by using two other example problems.     

Quantum watermarking based on threshold segmentation using quantum informational entropy

We propose a new quantum watermarking scheme based on threshold selection using informational entropy of quantum image. The core idea of this scheme is to embed information into object and background of cover image in different ways. First, a threshold method adopting the quantum informational entropy is employed to determine a threshold value. The threshold value can then be further used for segmenting the cover image to a binary image, which is an authentication key for embedding and extraction information. By a careful analysis of the quantum circuits of the scheme, that is, translating into the basic gate sequences which show the low complexity of the scheme. One of the simulation-based experimental results is entropy difference which measures the similarity of two images by calculating the difference in quantum image informational entropy between watermarked image and cover image. Furthermore, the analyses of peak signal-to-noise ratio, histogram and capacity of the scheme are also provided.     

基于SOA和级联取样光纤光栅的多波长激光器

研究了基于半导体光放大器(SOA)和双段级联取样光纤光栅构成的新型结构多波长激光器.设 计了取样光纤光栅，计算了其反射谱，模拟了多波长激光器的输出光谱.基于自行制作的SOA 和取样光纤光栅，进行了多波长激光器的实验研究，得到了间隔为0.8nm、输出功率不平坦 度小于1.0dB的11个波长输出.理论和实验两个方面都可以验证：与基于普通取样光栅的多波 长方案相比，基于双段级联取样光栅的方案能改善输出谱平坦度，并可提高可激射波长数. 关键词： 半导体光放大器 取样光纤光栅 多波长激光器