换流站交流滤波器过负荷保护误动作机理及防误动策略

换流站是耦合交直流系统的关联区域,站内设备众多、运行环境复杂。交流滤波器配置的保护虽然较为齐全,但在各类异常扰动情况下,电气量特殊的暂态特征仍会引发过负荷等保护的误动作。通过分析典型过负荷和励磁涌流工况下交流滤波器电阻支路电流波形的特点,揭示涌流引起交流滤波器过负荷保护误动作的机理。从波形相似度角度考虑,结合斯皮尔曼等级相关系数,提出了基于斯皮尔曼等级相关系数的交流滤波器过负荷保护辅助判据,并利用仿真试验验证该判据识别励磁涌流工况扰动的有效性,以防止保护误动的发生,提高保护的可靠性。

公路隧道岩溶构造地质雷达正演与探测实例波形特征对比研究

公路隧道岩溶构造地质预报是地质雷达超前地质预报的重难点,而对岩溶构造的地质雷达反射波形特征识别是预报准确的重中之重。为了准确识别反射波形特征,通过对隧道围岩溶腔中不同填充介质的岩溶构造建立雷达正演模型,模拟研究雷达反射波波形特征。本次模型构建填充情况主要分为空溶腔(空气),充水的溶腔,充泥、砂的溶腔,混合填充的溶腔4类,对应得到其正演反射波形特征为2大类。将模拟结果与探测实例波形特征对比研究,其反射波波形特征作为地质雷达探测预报岩溶构造时可参考的波性特征,定性判别岩溶构造中不同的填充介质情况,以进一步提高预报结果的准确性。

远距跨越电缆线路中振荡波局部漏电检测定位

为解决因电子振荡波过强而产生的局部漏电问题,提出远距跨越电缆线路中的振荡波局部漏电检测定位方法。通过放电波形特征处理的方式,计算线路振荡波的等效时频结果,对放电脉冲进行识别提取参数的寻优处理,按照局部电子脉冲的反射原理,对电缆线路中的漏电位置进行检测与定位匹配,借助振荡波的传输特点,设计集中检测定位流程,完成局部漏电的检测定位。对比实验结果表明,与T-F特征算法相比,应用新型检测定位方法后,单行电子通行下,局部漏电检测定位精度达到90%;多行电子通行下,局部漏电检测定位精度达到80%,能够有效解决局部漏电问题。

强干扰下舰船通信网络信号传输质量检测方法

为解决舰船通信网络信号质量检测区间受限的问题,提出强干扰下的新型舰船通信网络信号传输质量检测方法。通过信号波形特征提取、干扰算子定义2个步骤,完成强干扰下舰船通信网络的信号识别。在此基础上,通过传输信号质量的抖动幅值定义、传输时间间隔误差计算、检测相位算子求解3个步骤,完成新型信号传输质量检测方法的搭建。对比实验结果表明,与传统检测方法相比,应用强干扰下舰船通信网络信号传输质量检测方法后,待检测信号质量算子的最大值超过9.50 Mb,最小值低于2.00 Mb,整个检测区间长度得到明显扩充。

Analysis of elastic anisotropy of tight sandstone and the influential factors

Tight sandstone has a certain anisotropy. Using ultrasonic measurements of samples in three different directions and related matched experiments, this study systematically analyzes the pore structure and anisotropy of tight sandstone samples obtained from oil fields and compares results with those of shale. Results firstly show that the anisotropy of tight sandstone is mainly related to the compositional layering and thin interbedding which occur in different sedimentary environments. Tight sandstone has typical transverse isotropic medium characteristics, Young’s modulus increases in different directions with increasing confining pressure, Poisson’s ratio change is not obvious, anisotropic coefficients decrease with increasing effective pressure, and a certain linear relationship exists between ε, γ, and δ. This article finally summarizes anisotropy in different areas, thereby providing a foundation for the use of suitable appraisal models in different regions. This research can be used as an experimental reference for logging evaluation, seismic data interpretation, and fracturing develop of tight sandstones.

The Evolutionary Characteristics of the Temperature in Typical Counties in Southwest China——Taking Meitan County in Guizhou Province as an Example

Based on the method of linear trending,analysis was made upon the daily temperature statistics of Meitan County from 1951 to 2009,and the results showed that the temperature in general was on the rise.With 1980 as the turning point,it was on the decline before while later the temperature increased quickly.Among these figures,the variation rates of annual average temperature,annual maximum temperature,and annual minimum temperature are 0.11 ℃/10 a,0.08 ℃/10 a,and 0.36 ℃/10 a.The variation rates of average temperature in spring,summer,fall and winter are respectively 0.12 ℃/10 a,0.07 ℃/10 a,0.12 ℃/10 a,and 0.13 ℃/10 a.Morlet wavelet was adopted to analyze the periodicity of temperature change which has periods of different scales.But since 2000,during different time scales most of the areas have been in the period of temperature rises.Besides,certain rule exists in the periodicity of maximum temperature and minimum temperature.Before 1970s,they had opposite changing rules,and the alteration of the peak value occurred.However,in the late 1980s,they had similar changing rules,and their peak values appeared at the same time.It means that against the background of global warming,the reaction of temperature evolution in Meitan County is quite remarkable.

Wave statistics for ship seakeeping in China offshore

Ocean waves are the core environmental elements affecting the movements and structure design of ships. Statistical analysis of wave parameters is the basis for the establishment of long-term ship environmental adaptability prediction model. The observations from coastal stations, buoys, altimeters and volunteer ships that cover from 1993 to 2011 were interpolated into miller Ion-lat grids by using bilinear method and the analytical fields of ocean waves were given. By using optimal interpolation, the analysis wave fields were assimilated into the WAVEWATCH III （WW3） simulation results. From the assimilated results, the wave rose statistics, the wave height of muitiyear return period and the extreme 2-D wave spectrum are related to the ship seakeeping were calculated. Finally, the wave statistics in China offshore were analyzed in detail.

Fluvial reservoir characterization and identification:A case study from Laohekou Oilfield

Finding channel sandbodies is an important task in oil and gas exploration due to the importance of fluvial reservoirs. It is difficult to describe fluvial reservoirs in detail owing to their frequent changes and serious intersections, as well as limitations of S/N ratio and seismic data resolution. Based on the Laohekou 3D data in Shengli Oilfield, we analyze the general characteristics of fluvial reservoirs in this area, from which we find that they are characterized by strong amplitudes on seismic profiles, high continuity on time slices, and low frequency in the frequency domain. In addition, a cluster of strong string-bead- like reflections was found after color processing and detailed interpretation. To understand this observation, we conduct forward modeling to explain the mechanism. This provides a new way to identify ancient channels in similar areas. By using the multi-attribute fusion and RGB display techniques, channel incision is more obvious and the characteristics of the channel structures are manifested much better. Finally, we introduce and apply multi-wavelet detection technology to identify weaker fluvial reservoir signals.

锚杆检测在地铁隧道中的应用探析

本文以国内某地铁暗挖车站围岩支护为工程背景,采用LX-10M型锚杆锚固质量检测仪,对锚杆锚固质量进行无损检测,在分析无损检测结果的基础上有效评价了岩石砂浆锚杆施工质量的注浆密实度。注浆密实度质量状况被划分为四个等级,并最终实现对隧道围岩支护质量的判别。

电力线通信噪声信号压缩与重构方法与效果评价研究

噪声是影响电力线通信质量的主要因素,对于宽带技术的信息化发展具有直观影响。本文围绕信号采集与噪声特征分析、噪声信号的压缩处理、波形数据的重构等层面,分析了电力线通信噪声信号的压缩与重构方法,并基于评价方法、评价结果阐释了对于电力线通信噪声信号压缩与重构效果的具体评价,以供参考。

Flooding Characteristics of Hydrofoil Impeller in a Two- and Three-phase Stirred Tank

The flooding characteristics of hydrofoil impeller were systematically investigated in a two-and three-phase 383 mm i.d. stirred tank operated on air, water and spherical glass beads. The volumetric solid concen-tration Cs was varied from 0 to 25%. And the superficial gas velocity Ug was at the range of 0-0.096 m·s-1. A fast and objective method for identifying flooding point NF is developed based on the statistical analysis of the pressure fluctuation signals. It is found, the effect of solid concentration on the flooding point NF depends on the gas velocity. At the lower gas velocity (Ug = 0.010 m·s-1), the solid concentration has only a minor effect. However, it displays a very significant effect on the flooding point NF at the medium and high gas velocity. The flooding point NF linearly increases with the gas velocity Ug, at lower solid concentration (Cs = 0, 10%). When Cs = 20%, the behavior of NF versus Ug becomes more complex. The correlations of the flooding characteristics in the slurry stirred tank are proposed by considering the solid concentration effect.

Influence of water saturation on propagation of elastic waves in transversely isotropic nearly saturated soil

Biot' s two-phase theory for fluid-saturated porous media was applied in a study carried out to investigate the influence of water saturation on propagation of elastic wave in transversely isotropic nearly saturated soil. The characteristic equations for wave propagation were derived and solved analytically. The results showed that there are four waves: the first and second quasi-longitudinal waves (QP1 and QP2), the quasitransverse wave (QSV) and the anti-plane transverse wave (SH) . Numerical results are given to illustrate theinfluence of saturation on the velocity, dispersion and attenuation of the four body waves. Some typical numerical results are discussed and plotted. The results can be meaningful for soil dynamics and earthquake engineering.

Gaussian particle filter based pose and motion estimation

Determination of relative three-dimensional （3D） position, orientation, and relative motion between two reference frames is an important problem in robotic guidance, manipulation, and assembly as well as in other fields such as photogrammetry. A solution to pose and motion estimation problem that uses two-dimensional （2D） intensity images from a single camera is desirable for real-time applications. The difficulty in performing this measurement is that the process of projecting 3D object features to 2D images is a nonlinear transformation. In this paper, the 3D transformation is modeled as a nonlinear stochastic system with the state estimation providing six degrees-of-freedom motion and position values, using line features in image plane as measuring inputs and dual quaternion to represent both rotation and translation in a unified notation. A filtering method called the Gaussian particle filter （GPF） based on the panicle filtering concept is presented for 3D pose and motion estimation of a moving target from monocular image sequences. The method has been implemented with simulated data, and simulation results are provided along with comparisons to the extended Kalman filter （EKF） and the unscented Kalman filter （UKF） to show the relative advantages of the GPF. Simulation results showed that GPF is a superior alternative to EKF and UKF.

Internal energy and specific antiferromagnetic heat in a ferromagnetic- double layers

The internal energy and specific heat of a Heisenberg ferro- antiferromagnetic double-layer system are studied by using spin-wave theory and the retarded Green function method at low temperatures. Numerical results show that the antiferromagnetic intralayer coupling J2 has an important influence on internal energy and specific heat for a four-sublattice system with antiferromagnetic （or ferrimagnetic） interlayer couplings.

高压开关柜超声液局放信号的液形建模研究

局部放电(Partial discharge,简称PD)信号能够直接、客观地反映高压电气设备的绝缘劣化程度,是设备绝缘状态在线检测的重要方法之一。文章运用高压开关柜超声波PD信号波形拟合得到超声波PD波形方程,并结合声波传播特性及现场环境干扰噪音建立PD波形实验模型,最后运用波形时域特征算法对所建立模型进行特征提取,将所提取的特征输入到模式识别器进行验证。验证结果表明:本文建立的高压开关柜超声波PD模型信号与实际测量的信号具有很高的相似度,对基于超声波局放信号的高压开关柜绝缘状态在线检测有一定参考价值。

Hydrodynamic Performance of Multiple-Row Slotted Breakwaters

This study examines the hydrodynamic performance of multiple-row vertical slotted breakwaters. We developed a mathematical model based on an eigenfunction expansion method and a least squares technique for Stokes second-order waves. The numerical results obtained for limiting cases of double-row and triple-row walls are in good agreement with results of previous studies and experimental results. Comparisons with experimental measurements of the reflection, transmission, and dissipation coefficients （CR, Cr, and CE） for double-row walls show that the proposed mathematical model adequately reproduces most of the important features. We found that for double-row walls, the CR increases with increasing wave number, kd, and with a decreasing permeable wall part, din. The Cr follows the opposite trend. The CE slowly increases with an increasing kd for lower kd values, reaches a maximum, and then decreases again. In addition, an increasing porosity of dm would significantly decrease the CR while increasing the Cr. At lower values of kd, a decreasing porosity increases the CE, but for high values of kd, a decreasing porosity reduces the Ce. The numerical results indicate that, for triple-row walls, the effect of the arrangement of the chamber widths on hydrodynamic characteristics is not significant, except when kd〈0.5 Double-row slotted breakwaters may exhibit a good wave-absorbing performance at kd〉0.5, where by the horizontal wave force may be smaller than that of a single wall. On the other hand, the difference between double-row and triple-row vertical slotted breakwaters is marginal.

MODELING AND SIMULATION OF COMPOUND CLUTTER FOR COASTAL ENVIRONMENT

This paper introduces a novel clutter power model of coastal compound and deduces the statistic characteristics and the arithmetics of model parameter estimation algorithm. Then, a novel coastal compound distributed model of the clutter amplitude is proposed and its statistic character- istics are studied. Subsequently, the nonlinear relation of autocorrelation function is deduced between the coastal compound clutter random sequences and the correlated Gaussian random sequences, which is the important prerequisite for the clutter simulation based on the ZMNL (Zero Memory NonLin- earity). Lastly, the advantage of the algorithm is demonstrated by a feasible simulation of the gen- eration of the random coastal compound clutter sequences.

Analytical Results of Eigenstates and Eigenenergies for Three Kinds of Models Describing N-mode Multiphoton Process

We obtain. the exact analytical results of all the eigenvalues and eigenstates for three kinds of models describing N-mode multiphoton process without using the assumption of the Bethe ansatz. The exact analytical results of all the eigenstates and eigenvalues are in terms of a parameter lambda for three kinds of models describing N-mode multiphoton process. The parameter is shown to be determined by the roots of a polynomial and is solvable analytically or numerically. Moreover, these three kinds of models can be processed with the same procedure.

Hydroelastic interaction between water waves and a thin elastic plate of arbitrary geometry

An analytical method is developed for the hydroelastic interaction between surface incident waves and a thin elastic plate of arbitrary geometry floating on an inviscid fluid of finite depth in the framework of linear potential flow.Three kinds of edge conditions are considered and the corresponding analytical representations are derived in the polar coordinate system.According to the surface boundary conditions,the fluid domain is divided into two regions,namely,an open water region and a plate-covered region.With the assumption that all the motion is time-harmonic,the series solutions for the spatial velocity potentials are derived by the method of eigenfunction expansion.The matching conditions for the continuities of the velocity and pressure are transformed by taking the inner products successively with respect to the vertical eigenfunction for the free surface and the angular eigenfunction.A system of simultaneous equations,including two edge conditions and two matching conditions,is set up for deriving the expansion coefficients.As an example,numerical computation for the expansion coefficients of truncated series is performed for an elliptic plate.The results show that the method suggested here is useful to revealing the physical features of the gravity wave scattering in the open water and the hydroelastic response in the plate.

Characteristics of nonlinear evolution of wavepackets in boundary layers

The nonlinear evolution of a finite-amplitude disturbance in a 3-D supersonic boundary layer over a cone was investigated recently by Liu et al. using direct numerical simulation （DNS）. It was found that certain small-scale 3-D disturbances amplified rapidly. These disturbances exhibit the characteristics of second modes, and the most amplified components have a well- defined spanwise wavelength, indicating a clear selectivity of the amplification. In the case of a cone, the three-dimensionality of the base flow and the disturbances themselves may be responsible for the rapid amplification. In order to ascertain which of these two effects are essential, in this study we carried out DNS of the nonlinear evolution of a spanwise localized disturbance （wavepacket） in a flat-plate boundary layer. A similar amplification of small-scale disturbances was observed, suggesting that the direct reason for the rapid amplification is the three-dimensionality of the disturbances rather than the three-dimensional nature of the base flow, even though the latter does alter the spanwise distribution of the disturbance. The rapid growth of 3-D waves may be attributed to the secondary instability mechanism. Further simulations were performed for a wavepacket of first modes in a supersonic boundary layer and of Tollmien-Schlichting （T-S） waves in an incompressible boundary layer. The re- suits show that the amplifying components are in the band centered at zero spanwise wavenumber rather than at a finite spanwise wavenumber. It is therefore concluded that the rapid growth of 3-D disturbances in a band centered at a preferred large spanwise wavenumber is the main characteristic of nonlinear evolution of second mode disturbances in supersonic boundary layers.