Impedance Analytical Method of Wave Run-up and Reflection from A Slotted-Wall Caisson Breakwater

An impedance analytical method （IAM） is developed to study the interaction of plane water wave with a slotted-wall caisson breakwater. The non-linear boundary condition at the slotted-wall is expressed in terms of flow resistance. A set of algebraic expressions are obtained for free surface elevation inside and outside chamber, and reflection coefficient. The prediction of the reflection coefficients shows that the relative widths of the chamber inducing the minimum reflection coefficient for a slotted-wall caisson breakwater are in a range of 0.10～0.20, which are smaller than that （0.15～0.25） for a perforated-wall caisson breakwater. The reflection coefficients and free surface elevation obtained by the present model are compared with that of laboratory experiments carried out by previous researchers.

Longitudinal impedance measurements and simulations of a three-metal-strip kicker

A kicker is a critical component for beam injection and accumulation in circular particle accelerators. A ceramic slat kicker plated with a TiN conductive coating was applied in the Beijing Electron Positron Collider (BEPCII). However, the ceramic slat kicker has experienced several sudden malfunctions during the operation of the BEPCII in the past. With a reliable kicker structure, a three-metal-strip kicker can substitute the original ceramic slat kicker to maintain the operational stability of the BEPCII. A comparison of the numerical simulation was conducted for three kicker models, demonstrating the comprehensive advantage of the three-metal-strip kicker. Furthermore, impedance bench measurements were conducted on a prototype of a three-metal-strip kicker. The longitudinal beam-coupling impedance was measured using a vector network analyzer via the coaxial wire method. A satisfactory agreement was obtained between the numerical simulations and measurements. Based on the numerical simulation data, the loss factor was 0.01721 V/pC, and the effective impedance was 3.59 mΩ(σ=10 mm).The simulation of the heat deposition on each part of the kicker demonstrated that 84.4%of the parasitic loss of the beam was deposited on the metal strips, and the total heat deposition power on the kicker was between 113.3 and 131.5 W. The obtained heat deposition powers can be considered as a reference for establishing the cooling system.

Seismic fluid identification using a nonlinear elastic impedance inversion method based on a fast Markov chain Monte Carlo method

Elastic impedance inversion with high efficiency and high stability has become one of the main directions of seismic pre-stack inversion. The nonlinear elastic impedance inversion method based on a fast Markov chain Monte Carlo （MCMC） method is proposed in this paper, combining conventional MCMC method based on global optimization with a preconditioned conjugate gradient （PCG） algorithm based on local optimization, so this method does not depend strongly on the initial model. It converges to the global optimum quickly and efficiently on the condition that effi- ciency and stability of inversion are both taken into consid- eration at the same time. The test data verify the feasibility and robustness of the method, and based on this method, we extract the effective pore-fluid bulk modulus, which is applied to reservoir fluid identification and detection, and consequently, a better result has been achieved.

VIRTUAL-RAY METHOD AND ITS APPLICATION IN THE PLANE WAVE SCATTERING BY AN IMPEDANCE WEDGE

The virtual-ray method for treating HF electromagnetic scattering problems is derived from the plane wave of free space, and using this the plane wave scattering by an impedance wedge is studied. In the solution process a novel concept of generalized circle is introduced so that the complete amplitude function is obtained. And a reasonable physical interpretation for the term W2, which was neglected previously, is given. The calculated results agree well with those of the analytical solution obtained by G.D. Maliuzhinets(1958).

Electrical Impedance Tomography Based on Direct Search Method

Solution to impedance distribution in electrical impedance tomography （EIT） is an ill-posed nonlinear inverse problem. It is especially difficult to reconstruct an EIT image in the center area of a measured object. Tikhonov regularization with some prior information is a sound regnlarization method for static electrical impedance tomography under the condition that some true impedance distribution information is known a priori. This paper presents a direct search method （DSM） as pretreatment of image reconstruction through which one not only can construct a regularization matrix which may locate in areas of impedance change, but also can obtain an initial impedance distribution more similar to the true impedance distribution, as well as better current modes which can better distinguish the initial distribution and the true distribution. Simulation results indicate that, by using DSM, resolution in the center area of the measured object can be improved significantly.

Transient Hydroelastic Response of VLFS by FEM with Impedance Boundary Conditions in Time Domain

A time-dependent finite element method (FEM) is developed to analyze the transient hydroelastic responses of very large floating structures (VLFS) subjected to dynamic loads. The hydrodynamic problem is formulated based on the linear theory of fluid and the structural response is analyzed based on the thin plate theory. The FEM truncates the unbounded fluid domain by introducing an artificial boundary surface, thus defining a finite computational domain. At this boundary surface an impedance boundary conditions are applied so that no wave reflections occur. In the proposed scheme, all of the procedures are processed directly in time domain, which is efficient for nonlinear analyses of structure floating on unbounded fluid. Numerical results indicate acceptable accuracy of the proposed method.

Acoustic impedance inversion of zero-offset VSP data

Highly precise acoustic impedance inversion is a key technology for pre-drilling prediction by VSP data. In this paper, based on the facts that VSP data has high resolution, high signal to noise ratio, and the downgoing and upgoing waves can be accurately separated, we propose a method of predicting the impedance below the borehole in front of the bit using VSP data. First, the method of nonlinear iterative inversion is adopted to invert for impedance using the VSP corridor stack. Then, by modifying the damping factor in the iteration and using the preconditioned conjugate gradient method to solve the equations, the stability and convergence of the inversion results can be enhanced. The results of theoretical models and actual data demonstrate that the method is effective for pre-drilling prediction using VSP data.

Electrochemical impedance spectra of V_2O_5 xerogel films with intercalation of lithium ion

Vanadium pentoxide xerogel films used for lithium rechargeable batteries were prepared from crystalline c-V2O5 by melt quenching method,then the electrochemical process of lithium intercalation into vanadium pentoxide xerogel films was simulated with an equivalent circuit model, which was derived from the mechanism of electrode reactions. Measured electrochemical impedance spectra at various electrode potentials were analyzed by using the complex non-linear least-squares fitting method. The results show that impedance spectra consist of 2 high-to- medium frequency depressed arcs and a low frequency straight line. The high frequency arc is attributed to the absorption reaction of lithium ions into the oxide film, the medium frequency arc is attributed to the charge transfer reaction at the vanadium oxide/electrolyte interface and the low frequency is characterized by a straight line with a phase angle of 45° corresponding to the diffusion of lithium ion through vanadium oxide phase. The experimental and calculated results are compared and discussed focusing on the electrochemical performance and the state of charge of the electrode. Moreover, the high consistence of the fitted values of the model to the experimental data indicates that this mathematical model does give a satisfying description of the intercalation process of vanadium pentoxide xerogel films.

AN ANALYSIS ON INPUT IMPEDANCE OF A SINGLE MICROSTRIP PATCH IN THE QUASI-OPTICAL CAVITY

The electromagnetic field integral equation in the quasi-optical cavity is obtained using the dyadic Green’s function. An expression is derived for the input impedance of a single microstrip patch cavity excited by a coaxial probe using moment method. The input impedance of a rectangular microstrip patch is discussed with this method. The result of this paper is similar to that of the microstrip antenna. This paper is of very important value for designing microstrip quasi-optical oscillator.

Improve Spatial Resolution of Electrical Impedance Tomography Image Based on Non-uniformity Fine Mesh

In electrical impedance tomography (EIT) an approximation for the internal resistivity distribution is computed based on the knowledge of the injected currents and measured voltages on the surface of the body. Several difficulties have been identified in EIT, where the main problem is the low spatial resolution. This paper presents a fining mesh method based on finite element method (FEM), by fining the sensitive element, the most actual signal is obtained in certain electrode number. Newton-Raphson reconstruction algorithm improves the spatial solution of image. The advantages of this method are the improvement of spatial resolution and ease of implementation.

Closed-form internal impedance model and characterization of mixed carbon nanotube bundles for three-dimensional integrated circuits

Based on the complex effective conductivity method, a closed-form expression for the internal impedance of mixed carbon nanotube （CNT） bundles, in which the number of CNTs for a given diameter follows a Gaussian distribution, is proposed in this paper. It can appropriately capture the skin effect as well as the temperature effect of mixed CNT bundles. The results of the closed-form expression and the numerical calculation are compared with various mean diameters, standard deviations, and temperatures. It is shown that the proposed model has very high accuracy in the whole frequency range considered, with maximum errors of 1% and 2.3% for the resistance and the internal inductance, respectively. Moreover, by using the proposed model, the high-frequency electrical characteristics of mixed CNT bundles are deeply analyzed to provide helpful design guidelines for their application in future high-performance three-dimensional integrated circuits.

Efficient Computation of Scattering from Targets with Negative Impedance Surface

Current surface integral equations used for computing scattering from targets with negative impedance boundary condition（IBC）are not efficient.A modified surface dual integral equation（M-SDIE）for targets with negative IBC is presented.A pure imaginary number is used to balance the formulations.It is proved that the M-SDIE is accurate and efficient with three numerical examples.The first numerical example shows that the M-SDIE is accurate compared with Mie.The second example shows that the presented SIE is efficient.In the third example,a missile head is selected to present the computing power of the M-SDIE.All the examples show that the M-SDIE is an efficient algorithm for negative IBC.

Boundary Estimation in Annular Two-Phase Flow Using Electrical Impedance Tomography with Particle Swarm Optimization

In this study we consider the boundary estimation of annular two-phase flow in a pipe with the potential distribution on the electrodes mounted on the outer boundary of the pipe, by taking use of electrical impedance tomography (EIT) technique with the numerical solution obtained from an improved boundary distributed source (IBDS) method. The particle swarm optimization (PSO) is used to iteratively seek the boundary configuration. The simulation results showed that PSO and EIT technique with numerical solution obtained from IBDS has been successfully applied to the monitoring of an annular two-phase flow.

光储直流微电网多运行工况稳定性分析

直流微电网的结构越来越复杂,运行工况也越来越多,而现有稳定性分析方法主要针对单一工况。因此研究适用于多工况运行系统的通用稳定性分析方法非常必要。首先,依据不同的运行工况建立光储直流微电网各单元的阻抗模型,利用稳态分析法结合劳斯判据推导得出系统稳定时负载功率及母线电容的边界条件;其次,通过重新定义系统环路增益表达式,得到更具通用性的基于母线电压控制变换器(BVCC)和母线电流控制变换器(BCCC)的稳定性判据,并利用该判据对系统多种运行工况进行稳定性分析,借助所得边界条件对稳定裕度较低的工况计算合适的系统参数,保证系统能够处于稳定运行状态;最后,搭建系统的仿真模型,通过对3种典型工况仿真分析,验证边界条件及稳定性分析结论的准确性。

基于同步压缩变换的电缆缺陷定位研究

由于采集信号为入射波与多反射波的叠加,且多分量信号之间存在耦合不服从线性叠加原理,导致以采用魏格纳分布(Wigner-Ville distribution,WVD)为核函数的传统时频域反射法(time-frequency domain reflection,TFDR)存在严重的交叉项干扰,影响对缺陷的定位和判断。针对这一问题,本文提出一种基于同步压缩变换的电缆缺陷定位方法,该方法采用同步压缩变换(synchrosqueezing transform,SST)替代WVD以消除交叉项干扰,并以高分辨率定位电缆缺陷。同时分析参考信号相关参数,针对不同长度电缆测试,提出参考信号设计原则。该方法的主要步骤包括:通过采用TFDR法获取时域定位信号;然后采用SST求取压缩和重排后的时频谱图,以获取更精确的时频表达并消除交叉项干扰。最后,搭建了10kV交联聚乙烯电缆仿真模型进行研究,并选取了长度为500 m含中间接头的XLPE电力电缆和某地约32km海底电缆对算法进行实验验证。仿真及实验结果表明:SST算法对信号进行重排后能有效消交叉相的干扰,提高了时频域反射法定位精度。

面向光伏能量收集应用的实时MPPT预估算法研究

对于环境中存在的各种类型能量源,其往往具有不同的阻抗特性以及输出功率范围。为了提高能量收集系统的能量萃取能力,合理的接口电路设计是关键。基于此,通过对环境中光伏(Photovoltaic,PV)能量源微弱直流特性以及高效率收集和转化的研究,在传统开路电压法(Open-Circuit Voltage,OCV)的基础上,结合输入电压纹波控制,提出了一种可实时最大功率点追踪(Maximum Power Point Tracking,MPPT)的预估算法。该预估算法根据能量源的输出特性,采用了分数开路电压法(Fractional Open-Circuit Voltage,FOCV),并根据纹波大小动态调节变换器的工作模式,实现阻抗匹配。为了尽可能减小因采样带来的能量损失,采用可片上全集成的较小的采样电容,并逐周期的进行开路电压采样和计算,实现了对源功率变化的高精度追踪。仿真结果表明,所提出的追踪算法能够实时监测能量源的状态,具有高的追踪速度和追踪精度,且采样时间仅需100 ns。能量源功率在1μW~10 mW范围内变化时,最短的追踪时间仅需4.37μs,追踪精度可达99.7%。

基于加权高斯混合概率模型的系统谐波阻抗估计

针对现有方法受背景谐波随机波动影响而导致系统谐波阻抗估计误差大的问题,提出一种基于概率统计的系统谐波阻抗估计方法。采用3阶加权高斯混合分布函数建立系统谐波电压概率模型,以反映背景谐波的随机波动性。构建系统谐波阻抗的对数似然方程,采用确定性退火算法对期望最大化方法进行改进,提高了隐变量的估计精度和迭代速度,实现对背景谐波随机性波动下系统谐波阻抗估计。采用KL散度和误差对该方法背景谐波概率模型的准确性和系统谐波阻抗的估计精度进行评价,并采用仿真实验分析和实测数据实验对该方法的估计效果进行分析,实验分析表明,该方法对系统谐波阻抗估计具有较强的稳健性和较高的准确性。

基于动态磁网络法大型感应电机阻抗参数及起动特性计算

为提高大型感应电机动态阻抗参数及起动特性计算的准确性及计算效率,构建了考虑电机转子转速变化引起气隙磁导变化的非线性动态磁网络模型。以一台6.5 MW大型感应电机为例,分析起动电流变化对电机内各处饱和程度的影响机理,在此基础上,根据磁力线路径及电机内饱和程度确定动态磁网络模型中的非线性磁导的计算方法。将动态磁网络模型与转子趋肤效应模型相结合,提出计及漏磁并考虑转子转速变化及饱和偏移现象的电机动态阻抗参数的计算方法。推导并建立基于转子多回路法的大型感应电机的动态数学模型,根据电机瞬态过程中的电磁耦合关系,确定动态数学模型与磁网络模型的动态耦合求解方法,提出大型电机瞬态过程中考虑电流、转速、饱和及趋肤程度变化的动态阻抗参数及起动特性的计算方法。通过与有限元计算结果及实验结果对比,验证了所提出计算方法的正确性。

透平试验件对试验台横振不平衡响应的影响

重型燃气轮机透平试验台系统由试验台和试验件两部分构成。对于已经建成的试验台,需要考虑不同试验件对试验台横振不平衡响应的影响。本文利用机械阻抗综合法的阻抗匹配原理,将未知试验件的动力学特性模化为交界面上的机械阻抗,来确定试验件对试验台横振不平衡响应的影响,得出未知试验件的设计限制范围。同时,建立了某个试验件和试验台的动力学模型,分析了该系统的横向振动不平衡响应,验证了试验件不平衡响应的设计限制范围的有效性。

压气机试验件转子对试验台转子横振不平衡响应的影响

重型燃气轮机压气机试验台系统的动力学性能由试验台转子与试验件转子共同决定。对于已经建成的试验台,在实际运转过程中,需要满足不同试验件的实验需求。因此,在设计试验件转子时,需要考虑其对试验台转子横振不平衡响应的影响。将未知试验件转子的动力学特性模化为试验台转子和试验件转子交界面上的机械阻抗,在交界面处利用机械阻抗综合法的阻抗匹配原理来确定试验件转子对试验台转子横振不平衡响应的影响,得出未知试验件转子的设计限制范围。最后,建立了某一试验台转子和试验件转子的动力学模型,分析了该系统的横向振动不平衡响应,验证了试验件转子不平衡响应的设计限制范围的有效性。研究结论为压气机试验件转子的设计提供了指导意见。