Finite element numerical simulation of 2.5D direct current method based on mesh refinement and recoarsement

To deal with the problem of low computational precision at the nodes near the source and satisfy the requirements for computational efficiency in inversion imaging and finite-element numerical simulations of the direct current method, we propose a new mesh refinement and recoarsement method for a two-dimensional point source. We introduce the mesh refinement and mesh recoarsement into the traditional structured mesh subdivision. By refining the horizontal grids, the singularity owing to the point source is minimized and the topography is simulated. By recoarsening the horizontal grids, the number of grid cells is reduced significantly and computational efficiency is improved. Model tests show that the proposed method solves the singularity problem and reduces the number of grid cells by 80% compared to the uniform grid refinement.

Multiple linear system techniques for 3D finite element method modeling of direct current resistivity

The strategies that minimize the overall solution time of multiple linear systems in 3D finite element method (FEM) modeling of direct current (DC) resistivity were discussed. A global stiff matrix is assembled and stored in two parts separately. One part is associated with the volume integral and the other is associated with the subsurface boundary integral. The equivalent multiple linear systems with closer right-hand sides than the original systems were constructed. A recycling Krylov subspace technique was employed to solve the multiple linear systems. The solution of the seed system was used as an initial guess for the subsequent systems. The results of two numerical experiments show that the improved algorithm reduces the iterations and CPU time by almost 50%, compared with the classical preconditioned conjugate gradient method.

On-line Measurement for Ohmic Resistance in Direct Methanol Fuel Cell by Current Interruption Method

Electrochemical impedance spectroscopy (EIS) is widely used in fuel cell impedance analysis. However, for ohmic resistance (R Ω), EIS has some disadvantages such as long test period and complex data analysis with equivalent circuits. Therefore, the current interruption method is explored to measure the value of RΩ in direct methanol fuel cells (DMFC) at different temperatures and current densities. It is found that RΩ decreases as temperature increase, and decreases initially and then increases as current density increases. These results are consistent with those measured by the EIS technique. In most cases, the ohmic resistances with current interruption (R iR ) are larger than those with EIS (R EIS ), but the difference is small, in the range from –0.848% to 5.337%. The errors of R iR at high current densities are less than those of R EIS . Our results show that the R iR data are reliable and easy to obtain in the measurement of ohmic resistance in DMFC.

Preparation of Sn nano-film by direct current magnetron sputtering and its performance as anode of lithium ion battery

Sn thin film on Cu foil substrate as the anode of lithium ion battery was prepared by direct current magnetron sputtering(DCMS). The surface morphology,composition and thickness and the electrochemical behaviors of the prepared Sn thin film were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),inductively coupled plasma atomic emission spectrometry(ICP),cyclic voltammetry(CV) and galvanostatic charge/ discharge(GC) measurements. It is found that the Sn film is consists of pure Sn with an average particle diameter of 100 nm. The thickness of the film is about 320 nm. The initial lithium insertion capacity of the Sn film is 771 mA·h/g. The reversible capacity of the film is 570 mA·h/g and kept at 270 mA·h/g after 20 cycles.

Clay Minerals Channels Identification in the Tindikala-Boutou Area (Eastern-Cameroon) along the Kadey River Using Direct Current (DC) Method

To achieve the current study, geoelectrical surveys along six (06) profiles of 4 km long in a 100 m × 200 m grid defined according to the triangulation principle in the Tindikala-Boutou (Eastern-Cameroon) area along the Kadey River have been made through electrical sounding and profiling following Schlumberger array. The instrument is the resistive meter Syscal Junior 48 (IRIS Instrument). The data have been processed and modelled with Res2Dinv and Winsev softwares, and then interpolated with Surfer software. Investigation method used is the Direct Current (DC) method. Interpretations and analyses of results from the investigation method highlight weak zones or conductive discontinuities. The latter has been identified as shear zones within granitic structures of the Precambrian basement, according to the geologic and tectonic background of the area. The structural trend of these shear zones is E-W approximately. The mineralization characterized by conductive zones proves the presence of clay minerals disseminated in weathered quartz vein, which cross the shear zones. The intense activities of gold washers encountered in the studied area are able to attest the presence of clay minerals concentrations.

Fabrication and Characterization of VO_2 Thin Films by Direct Current Facing Targets Magnetron Sputtering and Low Temperature Oxidation

Low valence vanadium oxide(VO2-x) thin films were prepared on SiO2/Si substrates at room temperature by direct current facing targets reactive magnetron sputtering, and then proc- essed through rapid thermal annealing. The effects of the annealing on the structure and phase transition property of VO2 were discussed. X-ray photoelectron spectroscopy, X-ray diffraction tech- nique and Fourier transform infrared spectroscopy were employed to study the phase composition and structure of the thin films. The resistance-temperature property was measured. The results show that VO2 thin film is obtained after annealed at 320 ℃ for 3 h, its phase transition tempera- ture is 56 ℃, and the resistance changes by more than 2 orders. The vanadium oxide thin films are applicable in thermochromic smart windows, and the deposition and annealing process is compatible with micro electromechanical system process.

Effects of the sputtering power on the crystalline structure and optical properties of the silver oxide films deposited using direct-current reactive magnetron sputtering

This paper reports that a series of silver oxide （AgzO） films are deposited on glass substrates by direct-current reactive magnetron sputtering at a substrate temperature of 250 ℃ and an oxygen flux ratio of 15：18 by modifying the sputtering power （SP）. The AgxO films deposited apparently show a structural evolution from cubic biphased （AgO ＋ Ag20） to cubic single-phased （Ag20）, and to biphased （Ag20 ＋ AgO） structure. Notably, the cubic single-phased Ag20 fihn is deposited at the SP = 105 W and an AgO phase with （220） orientation discerned in the Ag^O films deposited using the SP 〉 105 W. The transmissivity and refiectivity of the AgxO films in transparent region decrease with the increase the SP, whereas the absorptivity inversely increases with the increase of the SP. These results may be due to the structural evolution and the increasing film thickness. A redshift of the films＇ absorption edges determined in terms of Tauc formula clearly occurs from 3.1 eV to 2.73 eV with the increase of the SP.

Evidence of Iron Mineralization Channels in the Messondo Area (Centre-Cameroon) Using Geoelectrical (DC &IP) Methods: A Case Study

A geophysical survey was conducted in the Kelle-Bidjocka village, Messondo subdivision, in the Centre Region, Cameroon. The data acquisition was made by combining Schlumberger profiling and electrical soundings along six (06) profiles of 1500 m in length for a total of 64 geoelectrical stations’ survey conducted through a variable mesh 100 m × 200 m, or 100 m × 300 m. The equipment used is the DC resistivimeter Syscal Junior 48 (Iris Instrument). Processing and modelling of field data are made by using the Res2Dinv, Qwseln and Surfer software. The investigation methods used are electrical resistivity (DC) and induced polarization (IP) methods. The analyses and interpretations have helped to highlight areas of weakness or conductive discontinuities (fractures, faults, shear zones, etc.) in Precambrian gneiss formations, sometimes undergoing weathering processes. They identify the weathering or mineralogical accumulation horizons, the most promising is a mineralization channel identified in the NE-SW direction. The highlighted mineralization is characterized by strong gradients of chargeability or polarization. Samples and other geological evidences observed in the area are used to associate the most polarizable structures with ferriferous formations. Weakly polarizable and particularly conductive backgrounds identified by the inverse pseudo-sections are thought to be sulphate minerals or groundwater targets for future hydrogeological studies.

Gold Mineralization Channels Identification in the Tindikala-Boutou Area (Eastern-Cameroon) Using Geoelectrical (DC &IP) Methods: A Case Study

To achieve the current study, geoelectrical surveys along six (06) profiles of 4 km long in a 100 m × 200 m grid defined according to the triangulation principle in the Ngoura area (Tindikala-Boutou villages) have been made through electrical sounding and profiling following Schlumberger array. The instrument is the resistivimeter Syscal Junior 48 (IRIS Instrument) which uses the electrical current. The data have been processed and modelled with Res2Dinv and Winsev softwares then interpolated with Surfer software. Electrical methods used are the Direct current (DC) and the Induced Polarization (IP). Interpretation and analyses of results from each investigation method highlight weak zones or conductive discontinuities and mineralized zones. Conductive zones have been identified as shear zones within granitic structures of the Precambrian basement, according to the geologic and tectonic background of the area. The structural trend of these shear zones is E-W. The mineralization within it is N-S and characterized by high values of chargeability, essentially in the eastern part of the area under study. This mineralization proves the presence of metalliferous or sulphide heaps disseminated in weathered quartz veins which cross shear zones. Also, the poor mineralization and conductive structures in shear zones characterize the groundwater zones. The intense activities of gold washers encountered in the area enable to link that mineralization to gold within quartz veins. The near surface gold mineralization is eluvial or alluvial, and in depth this mineralization is primary.

Combined Geoelectrical Approach DC and IP Methods in the Identification of the Mineralized Bodies Parallel to the NE-SW Tectonic Line of Kadei River: Case of Quartz or Pegmatite Gold Bearing Veins of Ngoura Subdivision (East Cameroon)

A geophysical investigation of subsurface structures using the Syscal Junior 48 resistivity-meter was conducted in Ngoura subdivision (East Cameroon) following a combined geoelectrical direct current (DC) approach involving Resistivity and IP methods. This investigation was allowed to collect data on forty-five (45) profiling lines at three acquisition levels (AB = 100 m, MN = 10 m;AB = 200 m, MN = 20 m and AB = 500 m, MN = 50 m) and two electric panels L1 and L4, using the Schlumberger array. Processing, modeling and interpretation of data collected using the Winsev, Res2Dinv and Surfer software helped in highlighting a conductive and strongly mineralized discontinuity in granite formations, which lined up with the NE-SW Kadei tectonic line. It extends beyond 100 m depth over an average width of 600 m. The mineralization associated with this discontinuity is identified by a high concentration of disseminated metalliferous minerals in quartz or pegmatite veins. The mining reconnaissance works in the study area and those of several authors have characterized this anomaly to a lode gold quartz or large pegmatite. The results of this study correlate with geological and tectonic data for the region marked by NE-SW Kadei tectonic line. Therefore, they confirm the reliability of a geoelectrical DC investigation method combining Resistivity and IP to the identification of ore bodies.

基于七阶NR法与Broyden方法的柔性直流系统潮流新算法

目的 为了解决当前柔性直流输电系统潮流算法求解效率低的问题,方法 首先提出基于七阶NR法的潮流算法,该算法相较于传统的潮流算法具有更高的收敛阶数,可以有效减少迭代次数,提高算法效率;其次,针对七阶NR法单步迭代计算量大的问题,提出基于七阶NR法与Broyden方法的改进算法,利用七阶NR法突出的收敛特性,减少迭代次数,同时保留Broyden方法单步迭代计算成本较低的优势,避免浪费计算能力,使计算效率得到较大提升;最后提出一种经验法则,以确定改进算法中高阶NR法的迭代次数。结果 使用经典和改进算法对修改后的IEEE标准算例进行仿真测试,结果表明:与经典NR法相比,交流和直流的改进算法潮流计算结果最大误差分别为1×10^(-8)和2×10^(-8);平均计算时间方面,在IEEE-14、IEEE-30、IEEE-57、IEEE-118共4种算例系统下,改进算法的平均计算时间比经典NR法的减少了约61%;当算例系统由双端变为三端和双馈入后,改进算法的迭代次数保持不变,计算时间分别增加0.352 ms和0.636 ms;在重负荷情况下,改进算法的计算效率最高,且预设迭代次数较简单,当负荷值达到2.992时,其计算时间仅为经典NR法的60%。结论 本文的改进算法具有与经典NR法相同的精确性,但在计算速度方面更有优势,且更有利于在重负荷等极端情况下使用。

基于直流电位降法的缺陷区域多探针检测

油气管道在服役过程中由于制造过程、环境复杂等因素容易产生缺陷,造成管道破裂等事故,因此对管道的无损检测具有重要意义。通过直流电位降法研究裂纹缺陷对电位场的影响规律,建立了多探针缺陷检测方法。首先采用有限元法对含有缺陷的平板试样进行电位分析,缺陷区域的电位差明显高于无缺陷区域,通过多探针的检测范围对试样区域进行划分后,提出了多探针缺陷区域检测方法。检测到区域存在缺陷后,对缺陷影响因子k进行计算,无缺陷区域k值基本在0.8~1.2之间,而缺陷周围的k值都超过了2,根据k值的分布可以得到缺陷的大致位置和尺寸。并搭建了多探针检测试验平台进行试验,结果表明,缺陷附近的电势差显著高于其他区域,与有限元结果相符。缺陷区域电势差明显高于其他区域,无缺陷区域k值在0.75~1.2之间,缺陷区域k值基本大于1.5。通过k值分布对缺陷位置和尺寸进行分析,与实际尺寸相差在3~5 mm左右。

磁控溅射制备碳化硼薄膜的结构与成分分析

近年来国际上^(3)He资源的短缺造成了基于^(3)He的中子探测器高昂的成本,而以碳化硼薄膜作为中子转换层的硼基中子探测器逐渐成为了最有前景的替代方案。通过直流磁控溅射制备了Ti/B_(4)C多层膜,并使用透射电子显微镜(TEM)、飞行时间二次离子质谱(ToF-SIMS)、X射线光电子能谱(XPS)等手段对薄膜的结构与成分进行表征。结果表明:Ti层存在结晶情况;H、O、N元素为薄膜内部的主要杂质,且多分布于Ti层与B_(4)C-on-Ti过渡层中;更高的本底真空度能够降低碳化硼薄膜内的杂质含量,提高B含量占比;中子探测效率测试结果证明本底真空度的提高能够有效提高碳化硼中子转换层的效率。

溅射功率对直流磁控溅射TiAlN涂层组织和摩擦学性能的影响

在室温下采用直流磁控溅射技术在304L不锈钢表面制备TiAlN涂层,研究了溅射功率(80,100,120,140,160 W)对TiAlN涂层组织和摩擦学性能的影响。结果表明:TiAlN涂层由面心立方结构的TiAlN相以及少量TiN和AlN相组成。随着溅射功率的增加,TiAlN涂层变厚,表面晶粒更加致密,但溅射功率160 W下制备的涂层表面大颗粒较多,晶粒尺寸先变小后变大,结合力先增大后减小,平均摩擦因数和比磨损率均整体呈先减小后增大的趋势;溅射功率140 W下制备的涂层具有最小的晶粒尺寸、最强的结合力、最小的平均摩擦因数和比磨损率,磨痕较平整且仅有少量磨屑,磨损机制为轻微的黏着磨损。

考虑多馈入系统无功电压特性的同时换相失败评估方法

针对目前基于多馈入相互作用因子(multi-infeed interaction factor,MIIF)同时换相失败评估准确度不足的问题,首先阐明了多馈入高压直流系统中交流系统故障后暂态无功功率的作用机理,揭示了无功功率和电压之间复杂的相互作用对MIIF的显著影响。其次,提出了一种考虑到无功功率和电压相互作用的改进MIIF因子,用于衡量多馈入直流系统之间的相互作用,分别计算了交直流系统间无功功率不平衡引起的电压降和直流换流站间无功功率传输引起的电压变化。然后,基于最小关断角定理,综合考虑了暂态无功功率和电压特性的影响,提出了临界同时换相失败因子(critical simultaneous commutation failure factor,CSCFF)及其计算表达式。通过比较MIIF和CSCFF,提出了一种同时换相失败评估方法,在评估同时换相失败时具有更高的准确性。最后,利用PSCAD/EMTDC平台构建了双馈入和三馈入高压直流仿真模型,验证了所提方法在不同故障类型、耦合阻抗和故障严重程度下的有效性和适用性。

基于对称分量法的调相机定子故障特征分析

传统同步调相机定子绕组匝间短路故障机理分析方法通常认为电机定子电流接近三相对称,并以此为基础建立同步调相机故障电流的数学表征。但是,一旦发生定子绕组匝间短路故障,同步调相机三相定子电流的对称性将遭到破坏,使得传统故障机理分析方法所建立的数学表征无法准确反映电机内部电气量的变化。文中通过引入对称分量法,建立故障后同步调相机瞬时有功/无功功率的数学模型,提出利用瞬时有功/无功功率中的2次谐波进行定子绕组匝间短路故障诊断。仿真和实验的结果表明:相较于利用定子电流3次谐波与基波幅值之比诊断故障的传统方法,文中方法在轻微故障状态下能提高至少7倍的诊断灵敏度,更易完成早期故障诊断。同时,所提方法中的故障特征量不受同步调相机工况和故障位置的影响,具有强鲁棒性。

超宽工作面三维电法数据特征研究及应用

超宽工作面的构建有助于推动煤炭资源的安全、高效开采。然而,受巷道空间、施工条件的限制,常规矿井地球物理的探测深度有限,无法准确获取超宽工作面内部及顶底板一定范围内的地质信息。为了提高超宽工作面底板富水区的探测精度,给实测数据处理及解释提供依据,在总结分析当前矿井地球物理探测技术的基础上,针对可应用于超宽工作面探测的三维直流电阻率法,结合河南永城某煤矿21106工作面底板灰岩水的赋存特征,采用理论分析、数值模拟和实测数据相结合的研究方法,系统研究了三维观测和二维观测模式的数据特征和分辨能力。研究结果表明:相较于传统的同侧发射接收二维观测模式,对侧发射接收的三维观测模式对工作面底板低阻体的反应更为灵敏;对侧发射接收三维观测模式所得数据,经过常规视电阻率公式计算后,视电阻率与实际电性有时相反,因此需要采用三维反演方式进行数据处理;对河南永城某煤矿21106工作面观测到的三维模式数据进行了三维反演处理,经井下钻探资料验证了三维观测结果的可靠性。研究结果为二极装置条件的二维观测和三维观测数据解释提供了依据。

特高压直流一次设备运行状态k-means聚类监测仿真

针对特高压直流一次设备运行状态异常可能导致电网运行不稳定的问题,提出特高压直流一次设备运行状态监测方法,并进行仿真分析。首先构建基于能量均衡的动态分簇算法,控制无线传感器网络采集特高压直流一次设备运行状态数据,利用k-means算法动态分簇,通过竞争函数和能量比平衡各簇能量,并在簇中划分节点为不同等级节点,高效采集一次设备运行状态数据。采用改进的稀疏主成分分析法选择采集到的一次设备运行状态数据关键特征,最后将特征选择后运行状态数据输入至训练完成的BP神经网络中,实现特高压直流一次设备运行状态监测。实验结果表明:所提方法具有优异的数据采集能力,并且运行状态监测中的PR曲线和ROC曲线更为理想,同时AUC值更高。

担水沟煤矿特厚煤层开采底板导水破坏带深度实测研究

为了研究特厚煤层开采对工作面底板破坏深度的影响,通过在担水沟煤矿9204工作面底板2个观测钻孔,运用直流电法观测分析工作面回采过程中底板岩体视电阻率的变化特征,结合工作面与测点的空间位置关系,得出采动影响下的底板破坏深度,并将其与未考虑煤厚因素影响的统计公式和理论公式的计算值进行比较分析。结果表明,工作面实测底板破坏深度为17.3 m和18.3 m;实测底板最大破坏深度小于统计公式值7.81%~12.90%,大于理论公式值24.81%。探讨其机理认为,相对于工作面斜长、采深等因素,煤厚因素对底板破坏深度影响较低;且工作面底板下17 m赋存有一厚层隔水砂质泥岩,不易产生导水裂缝,降低了底板导水破坏深度。

瞬变电磁法在采空区积水与灰岩富水区探测中的应用

针对米山煤矿二采区15号煤层所面临的上覆水害问题,在开采前为查明上覆3号煤层采空区积水,以及顶板K 5、K 2灰岩富水区。在地质分析与地球物理特征分析基础之上,进行瞬变电磁法探测试验。优选了探测设备、回线装置与探测参数,通过地面瞬变电磁探测,初步圈定了3号煤层采空区积水、顶板K 5与K 2灰岩富水区的分布范围。针对初步圈定的老空水与灰岩水分布范围,利用不同硬件、回线装置与探测参数的瞬变电磁进行浅埋区复测,同时开展不同物探方法的直流电法复测,验证了前期探测成果,确定了7处3号煤层采空区积水与6处灰岩富水区,为下一步安全高效绿色开采提供了技术支撑,值得进一步推广应用。