适应性波束形成器的随机变界截尾算法

本文对适应性波束形成器给出一种递推随机变界截尾算法,并在较简单的条件下,证明了算法几乎处处具有大范围收敛性.     

回响环境下的最优波束形成器设计

目前大多数波束形成器(beamformer)的设计方法在模型建立时都是为了得到期望的波束形成响应(beamformer response),如最小方差无失真响应(minimum variance distortionless response,MVDR)方法和线性约束最小方差(linearly constrained minimum variance,LCMV)方法.为了构造人们期望的波束形成响应,最简单的方法就是采用从目标声源点到波束形成器输出点的脉冲响应(impulse response),加上一个波束形成器群延迟(group delay).然而对于波束形成器群延迟的估计却是未知的,经验地,人们将其选择为波束形成器长度的一半.可是在回响环境下,这样的波束形成响应选择往往不是最优的.为了设计最优波束形成器,本文考虑波束形成响应与波束形成器的联合设计问题.首先,引入一个新的变量来表示波束形成响应,并且将波束形成响应与波束形成器联合设计问题建模成一个结构型约束凸优化(structured constrained convex optimization,SCCO)问题.其次,利用SCCO问题的结构可分性,引入交替方向法(alternating direction method of multipliers,ADMM)来加以求解.为了文章的完整性,本文还给出ADMM算法收敛性结果的一个简单证明框架.最后,数值实验结果表明,提出的波束形成器设计方法在回响环境下是有效的,并且比LCMV方法效果更好.     

具有非平稳相关输入的自适应阵算法

在输入{X_k} 是相互独立的平稳随机序列的假定下,自适应阵算法的收敛性问题得到较好的解决.当目标信号Y(t)的某些统计特性已知时,给出了问题的解.当我们对目标信号一无所知时,用对加权阵施加约束的方法来代替,也证明了算法的期望收敛于最优解.修改了这一算法,并进一步证明了算法期望收敛、几乎处处收敛和均方收敛于最优解.则综合了上述方法,并取消了对输入协方差阵R=EX_kX_k~T和约束条件阵C~τC是非奇异的要求,而给出了一个使用范围更广的算法.也证明了算法几     

用于动态无功补偿的无功功率超短期预测方法

钢铁企业配电网中大量的非线性和冲击性负荷严重影响企业电网的电能质量及相关设备的使用寿命.充分考虑了冲击性负荷的特点,在带时变噪声统计估值器的Sage-Husa自适应滤波算的基础上,提出了一种改进Sage-Husa自适应滤波超短期预测算法.改进后的算法可以正确估计系统的输入噪声方差Q和测量噪声方差R,提高了预测准确度,同时继承了原算法的优点,计算速度快,存储量小,适合于在线应用.某钢铁企业轧钢车间部分供电母线的实际预测结果表明:该算法预测精度较高,计算速度快,可用于指导无功动态补偿,提高电压合格率和电气节能效果.     

基于限制玻尔兹曼机的极限学习机方法

针对高维数据中存在冗余以及极限学习机(ELM)存在随机给定权值导致算法性能不稳定等问题,将限制玻尔兹曼机(RBM)与ELM相结合提出了基于限制玻尔兹曼机优化的极限学习机算法(RBM-ELM).通过限制玻尔兹曼机对原始数据进行特征降维的同时,得到ELM输入层权值和隐含层偏置的优化参数.实验结果表明,相比较随机森林,逻辑回归,支持向量机和极限学习机四种机器学习算法,RBM-ELM算法能获得较高的分类精度.     

相关数据密度函数的非线性小波估计

本文考虑了严平稳随机序列密度函数的非线性小波估计,证明了在Besov空间中,非线性小波估计可达到最优收敛速度.进一步讨论了自适应非线性小波估计,证明了自适非线性小波估计可达到次最优速度即和最优速度相差in n.     

平面几何模型的EMD分解算法及其应用

经验模态分解(Empirical mode decomposition,简称EMD)算法是一种处理非线性非平稳信号的时频分析方法.该方法可以自适应地将输入信号分解成若干层本征模函数(Intrinsic mode function,简称IMF)和一层余项函数,通过对IMF的特定操作可以实现信号的滤波和去噪等功能.经典的EMD算法主要针对标量形式的函数信号,对于平面几何图形,EMD则按每一个坐标分量分别处理,其效果往往较差.文章提出一种向量形式的平面几何模型EMD算法,该算法将一个平面几何模型分解成若干层偏置向量和一个残差模型,其中偏置向量表示几何体不同尺度的特征,残差模型表示输入模型的大致形状.通过在极值点的定义中施加特征尺度的限制从而保证每次分解只分离出特定尺度的特征.实验表明,该方法可以有效地实现平面几何模型的分解,并应用在去噪、特征编辑以及特征迁移的领域.通过与经典方法以及标量函数信号EMD算法的比较,文章方法的有效性得到验证.     

一类非平稳随机传递系统的最佳非线性滤波及优化算法

运用最佳非线性滤波方法及优化算法,讨论了一类不完全数据与具有连续时间的非平稳随机过程的最佳控制问题,得到了这两种状态下的两个最佳控制数学模型,给出了这类非平稳随机传递系统的最佳编码与最佳译码的建立方法,为解决这类非平稳随机过程的最佳控制提供了一种有效可靠的解决方法.     

非对称弹性需求网络容量限制交通分配有效算法

在非对称交通网络中,针对路段容量限制下弹性需求用户均衡分配模型计算困难,提出了一种路段容量限制弹性需求用户均衡交通分配问题的有效算法.该算法在迭代时,排队延误因子、误差因子与交通需求通过自适应调节来逼近真实路段车辆行驶时间和出行者交通需求,促使各路段交通流量逐步满足限制条件,最终达到弹性需求广义用户均衡.方法克服了容量限制弹性需求用户均衡分配计算量大及随机分配法要求枚举所有路径的困难.随后证明了算法的收敛性,并对一个小型路网进行了数值试验.     

基于多模型自适应估计的姿态敏感器误差校准

提出一种基于多模型自适应估计(MMAE)的星敏感器低频误差(LFE)校准方法.星敏感器低频误差主要是由空间热环境的周期性变化造成的,会对卫星姿态确定精度造成显著影响.低频误差的影响可以通过扩维卡尔曼滤波(AKF)进行校准.但是,在星敏感器观测量中不存在低频误差的情况下,AKF的姿态估计精度往往不及传统卡尔曼滤波(KF).针对这一问题,将KF与AKF相结合,设计了基于MMAE的姿态确定滤波算法,该算法能够根据星敏感器在轨误差特性自适应的选择KF或AKF算法进行滤波.仿真结果表明,所提算法综合性能优于KF和AKF,适用于对姿态确定精度要求较高的高分辨率对地观测卫星.     

Harmonic distrotions under nonlinear periodic deformation of fluid polymers

Conclusions 1. It has been shown for a number of viscoelastic fluid systems that under nonlinear periodic deformation, the contribution of the third harmonic of the stress to the fundamental does not exceed 20% of the amplitude.2. In the case of clay soil and melt of filled polyethylene, the shape of the stress waves is essentially definable by the relative phase angle of the third harmonic of the stress and is practically independent of the deformation amplitude in a growing nonlinear range of deformation.3. In the case of the polyethylene melt, the amplitude dependence of the phase angles of the stress harmonics is in satisfactory agreement with the analysis of model I. With increasing deformation amplitude, the modulus vector of the first harmonic rotates counterclockwise and remains in the first trigonometric quadrant; the modulus vector of the third harmonic passes from the second to the third quadrant, and the modulus vector of the fifth harmonic passes from the second to the fourth quadrant via the third.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 893–898, September–October, 1978.     

Some observations on the performance of balloons from the rate of rotation of the fan in the F-Type radiosonde

If the rate of ascent of the balloon is constant, the rate of rotation of the fan in the F-Type radiosonde should decrease with height, due to the decrease in the density of the air. It was observed from the radiosonde ascents of Minicoy that the rate of rotation of the fan remained almost unchanged up to even 100 mb. It is shown that this is due to the increase in the rate of ascent of the balloon by about 2% of the value near the ground per km. ascent. Positive evidence of turbulence in the stratosphere is provided by the large fluctuations in the rate of rotation of the fan. It is also observed that the balloon whose fabric at the 50 mb. level is about 0·014 mm. thick bursts due to the turbulence.     

An investigation on the influence of slot injection/suction on the spreading of a thin film under gravity on a rotating disk

We investigate the influence of slot injection/suction on the axisymmetric spreading of a thin film under the influence of gravity and rotation. The effects of surface tension are ignored. We allow a very thin film to precede the bulk of the fluid to overcome the singularity which arises as a consequence of applying the no-slip boundary condition. We show how the width of the slot and magnitude of the injection/suction influences the height of ridges and depth of cavities on the profile of the free surface of the thin film. Rotation increases the depth of the cavities and the height of the ridges as compared to the effects of gravity alone. The presence of rotation also results in the formation of a breaking wave.     

Prediction of the deformation properties of a polymeric composite with a granular-fibrous filler

Conclusion A variant of calculation of the characteristics of the deformation properties of a hybrid composite containing a complex disperse filler in the form of granular particles and short fibers was proposed. The effect of aggregation of the granular filler, the statistical distributions of the fibers by lengths and orientation in the material, and the anisotropy of the fibers are taken into consideration in the calculation. The statistical distribution of the orientation of the fibers is given by a function proportional to the distance from the center to the surface of a triaxial ellipsoid in the corresponding direction. The uniform random distribution of the fibers in bulk and in the plane is a special case of this distribution. The results of the analysis of the effect of the parameters of the statistical distributions of the length and orientation of short fibers on the elasticity characteristics of a composite are reported. The dependence of the creep of the composite on the ratio of the concentration of the components of the complex filler was determined, and the efficiency of partial replacement of a granular filler by a short-fiber filler to inhibit creep of the composite was demonstrated. The possibilities of predicting the long-term creep were experimentally confirmed on the example of LDPE filled with ground limestone and short glass fibers.Presented at the Sixth All-Union Conference on the Mechanics of Polymer and Composite Materials (Riga, November, 1986).Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 898–909, September–October, 1987.     

The thermodynamically consistent equations of a thermoelastic saturated porous medium

A phenomenological model of a porous medium saturated with fluid is considered with in the framework of the hypothesis of interpenetrating continua. Assuming that there are no phase transitions, that the contribution of pulsations to the stress tensor and kinetic energy is small, and the components of the medium are in thermal equilibrium, mass, momentum and energy equations and a law of conservation of compatibility of the deformations and velocities are formulated. Using a representation of the force of interaction of the components in the form of the sum of equilibrium and dissipative components, a new form of inequality is obtained for the rate of entropy production. A definition of a thermoelastic saturated porous medium is given. The symmetry group of such a medium is considered as a set of two groups, corresponding to the symmetry of the skeleton and the fluid. It is shown that, in the class of thermoelastic porous media with an arbitrary type of symmetry of the skeleton, the saturating fluid can only be an ideal fluid, while the thermodynamic potentials and the porosity, stresses and entropies determined by them do not depend on the temperature gradient and the relative fluid velocity. It is found that the condition of incompressibility of only one of the components of the medium leads to the elimination of the porosity from the governing relations, rather than to kinematic limitations. The limitations imposed on the governing relations by the principle of thermodynamic consistency and the requirement of independence of the choice of the frame of reference are investigated. A form of the governing relations, necessary and sufficient to satisfy these principles, is obtained. It is shown that the Biot equations are one of the forms of thermodynamically consistent governing relations. A thermodynamic validation of the effective-stress tensor is given.     

Identification and orbit determination of a tethered satellite system

Orbital motion of a tethered satellite system, composed of two satellites and an inextensible tether, is considered by using a perturbed two-body model. This approach is adopted so that the determination of the orbit of one of the satellites can be attempted without using observations of the motion of the other satellite in the system. The identification of the tethered condition of the system using observations of only one of the satellites in the tethered satellite system is considered. The characteristics of the `tether perturbed' motion of the observed satellite are investigated. Estimation of the state of the system using near perfect data is also illustrated. Observations of one satellite provide the entire state of the system and a parameter involving the ratio of the masses of satellites and the tether length.     

State of stress and strain of brake-class parachutes

The article describes the special features of the operation of brake-class parachutes. It substantiates the possibility of replacing the solution of the dynamic problem of opening of a brake parachute by the static calculation of its state of stress and strain (SSS). The derivation of the equation of motion of a soft carcassed shell is based on the finite element method. The steady-state solution is obtained by the method of adjustment. As an example the results of calculation of the characteristics of the SSS of a cross-shaped brake parachute are presented. It is shown that in the zone of its lower edge considerable concentrations of tension arise in the tissue, the tissue gradually joins the operation of the carcass; the transverse carcass is unsubstantially loaded. The results of the calculations agree with the experimental data.Translated from Dinamicheskie Sistemy, No. 5, pp. 32–36, 1986.     

On the “genetic memory” of chaotic attractor of the barotropic ocean model

The structure of attractor of barotropic ocean model is studied in this paper. Theorems of the existence of the attractor for the finite dimensional approximation of this model are proved as well as its convergence to the attractor of the model itself. Some properties of stationary solutions of this model and their stability are discussed.The structure of the attractor is partially explained by the sequence of bifurcations the system is subjected to by variations of leading parameters. The principal feature of the studied system is the existence of two “almost invariant” basins of chaotic attractor with very rare transitions between them. This is related to the rise of a couple of non-symmetric stable stationary solutions in the model with symmetric forcing.The “memory” of chaos appears also in the presence of maxima in the spectrum of energy. These maxima correspond either to the principal frequency of the limit cycle which arose in the Hopf bifurcation, or to the frequencies of the Feigenbaum phenomenon.     

Free vibrations of a cantilevered plate with a polymer coating

The article considers some of the special characteristics of the free vibrations of a steel cantilevered plate, with the formation of a polymer coating on the plate. It compares the results of an experimental investigation of the effect of internal stresses in the coating on the vibrations and on the static bending of the plate. It demonstrates the possibility of determining the internal stresses in the coating from the change in the frequency of the natural vibrations of a plate with a coating.Institute for the Mechanics of Metal-Polymer Systems, Academy of Sciences of the Belorussian SSR, Gomel'. Translated from Mehanika Polimerov, No. 3, pp. 541–544, May–June, 1970.