Coupling of Acoustical Plane p-Wave to a Cased Borehole

Theoretical and numerical study on the coupling acoustic field of the plane p-wave to a cased borehole is carried out. The medium outside the cased borehole is modeled as the porous medium. The scattering field characteristics in the cased borehole are investigated when a plane fast p-wave is incident in tilt to the cased borehole from the porous medium. The scattering fields inside and outside the cased borehole are analyzed and deduced by Biot＇s theory under the boundary conditions on each interface, and they are numerically studied. It is found that the scattering field has strong resonant characteristics and there exists a series of resonant frequencies and peaks. The effects of the frequency, radii of each interface, incident angle, porosity, and other parameters on the resonant acoustic field have been investigated in detail in the fast and slow formations respectively. The resonant characteristics of the scattering field are also analyzed from the physical sense.     

钻孔雷达全向天线的设计与分析

根据钻孔雷达全向天线的设计要求,为减少天线的结构尺寸增加带宽,设计了一种新型电阻加载全向天线。通过理论分析和数值优化,选择了较优的结构尺寸,得到了较佳方向图和带宽。天线外径为65 mm,使用10 mm厚天线罩封装后外径为85 mm;天线的S11小于-10 dB频带为70~260 MHz,带宽约190 MHz。该天线的带宽超过100 MHz,中心频率处增益大于-3 dB,辐射电场脉冲波形拖尾小于主峰幅度1/5,方向图在H面为全向。基于矢量网络分析仪的天线特性测量结果与数值计算结果基本一致,结果表明设计的天线能够满足钻孔测井雷达系统小尺寸宽带的要求。     

Seismoelectric waves in a borehole excited by an external explosive source

The conversion of energy between seismic and electromagnetic wave fields has been described by Pride’s coupled equations in porous media. In this paper, the seismoelectric field excited by the explosive point source located at the outside of the borehole is studied. The scattering fields inside and outside a borehole are analyzed and deduced under the boundary conditions at the interface between fluid and porous media. The influences of the distance of the point source, multipole components of the eccentric explosive source, and the receiving position along the axis of vertical borehole, on the converted waves inside the borehole are all investigated. When the distance from the acoustic source to the axis of a borehole is far enough, the longitudinal and coseismic longitudinal wave packets dominate the acoustic and electric field, respectively. The three components of both electric field and magnetic field can be detected, and the radial electric field is mainly excited and converted by the dipole component. Owing to the existence of borehole, the electric fields and magnetic fields in the borehole are azimuthal. The distance from the point where the maximum amplitude of the axial components of electric field is recorded, to the origin of coordinate indicates the horizontal distance from the explosive source to the axis of vertical borehole.     

外表面应力自由的充液有限壁厚井孔中的声场及其频散曲线的“平台”特征

为了开发一种新型标准刻度井,对外表面应力自由的充液有限壁厚井孔中的声场进行了更加深入的研究,计算分析了这种圆柱形封闭声波导结构中的声场和多阶对称模式波的频散特性。结果表明:充液有限壁厚井孔中高阶对称模式波的相速度频散曲线在一定频率范围内出现“平台”现象;当声源激发主频大于5 kHz且慢度时间相关法(STC)的窗长取4到5个周期时,得到全波波形中的“首波”速度与高阶模式波相速度频散曲线上的“平台”区域速度接近,该“平台”区域的速度与有限壁厚管材的纵波速度相差百分比随管材泊松比增加呈指数型上升;通过选择合适的管材材料以及改变其几何尺寸,可在一定频率范围内控制对称模式波相速度频散曲线的“平台”宽度、位置及平稳度。这一研究可为建立行业标准的声速刻度井提供新思路。      

声测井中的声压-速度有限差分方法

为了解决薄互储层的声测井问题,提出了声压-速度有限差分方法:用声压和速度矢量做为场变量,分别描述井内流体和井外弹性固体或双相介质。这样选择场变量的优点是:处理脉冲点源(或线源)与套网格技术相比简单得多;在内边界上的差分格式稳定,精度得到了改进;人为边界上的吸收效果较好。用柱坐标分别给出了井壁上流体与弹性固体、流体与双相介质的声压-速度边界条件,并用守恒积分方法处理了井壁上的边界条件。通过用声压-速度有限差分方法模拟弹性固体和双相介质地层的声场,证明了声压-速度有限差分方法的有效性。     

Radiation properties of ICRF waveguide couplers

The radiation spectra of a dielectric-filled waveguide (DWG) and a folded waveguide (FWG) antenna in the ion cyclotron range of frequencies are evaluated for tokamaks with the waveguide codes, which model the coupling of the waveguide modes to the plasma waves with outward radiating boundary conditions. The codes provide a self-consistent calculation of the fields across the waveguide apertures for various antenna phasings taking into account a complete set of waveguide eigenmodes including the reflected modes and, in the case of DWG, an arbitrary orientation of the antenna to the plasma magnetic field. In the studied cases, the spectra are found to be well described by a model which is based on a simplified wave field pattern determined by the antenna aperture geometry. Comparison to the corresponding loop antenna is carried out     

等离子体通道天线的辐射场计算

提出了一种用于高功率微波武器的等离子体通道天线(PCA),计算了该天线的辐射方向图。推导出了一般性天线的辐射方向函数;建立了PCA的近似电磁模型;给出了圆坐标系下PCA和周围空气中的电磁场,利用边界条件得出了PCA的色散方程,求出PCA的表面波波矢。重点讨论了PCA的辐射场随等离子体密度、天线长度、半径的变化,证实了PCA方向图的可控性。     

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提出了一种用于高功率微波武器的等离子体通道天线(PCA),计算了该天线的辐射方向图。推导出了一般性天线的辐射方向函数;建立了PCA的近似电磁模型;给出了圆坐标系下PCA和周围空气中的电磁场,利用边界条件得出了PCA的色散方程,求出PCA的表面波波矢。重点讨论了PCA的辐射场随等离子体密度、天线长度、半径的变化,证实了PCA方向图的可控性。     

天线振子作为初值问题求解

根据计算实践和物理考虑,指出电磁场基本方程作为一阶双曲型偏微分方程组的初值问题,可以成为有效的天线振子数值计算方法。对于隐式差分格式,建议了一种交替方向追赶和外边界插值相结合的办法。讨论了圆柱对称振子的数值结果。     

Transmission line theory for an insulated linear antenna in a fluid- or air-filled borehole

Using a transmission line theory, expressions for the propagation constant and characteristic impedance of a borehole antenna are derived. Both air-filled and fluid-filled holes are considered. The required modal equation is solved by a rapidly convergent iterative method. Some data for the input impedance and effective dipole moment for the terminated line are then provided. It appears that the presence of conducting fluid in the hole will not seriously impair the effectiveness of the radiating structure, but the voltage gradients in the insulation will be increased markedly.     

二维圆柱坐标系中五角形共形网格算法

 时域有限差分（FDTD）算法求解电磁问题时，如果目标结构不能和传统网格体系共形，往往采用局部共形网格或非正交网格算法。详细讨论了二维圆柱坐标系中五角形共形网格算法，该算法能方便地对倾斜薄层媒质或电导率不均匀的倾斜媒质等复杂结构建模,并以锥形电磁脉冲天线为例，验证了该算法的有效性。     

Ignition of hydrocarbon films under the conditions of surface microwave discharge

In the present work, rapid plasma-stimulated ignition of liquid hydrocarbons was carried out in still air under conditions of surface microwave discharge. It was shown that, depending on the microwave input power, the breakdown time changed in a range from 5 to 30μs, ignition occurred on an antenna in the area of the surface microwave discharge at a temperature not exceeding 1000 K, and the speed of the front boundary propagation of the intense ignition region near the antenna was 300 m s^?1.     

长椭圆旋转介质球中的半波振子天线

本文从麦克斯韦方程出发,求出有损耗的长椭圆旋转介质球中一个同焦点的小的长椭圆旋转形半波振子发射天线上的电流分布和其输入阻抗,以及它在有损耗的介质球中和外部自由空间中所产生的场。     

Analysis of noncircular fluid-filled boreholes in elastic formations using a perturbation model

This paper presents a perturbation model to obtain flexural mode dispersions of noncircular fluid-filled boreholes in homogeneous elastic formations. The perturbation model is based on Hamilton's principle with a modified procedure for the reference state selection in order to handle the directional sensitivity of the flexural modes. The accuracy of the perturbation model has been confirmed by comparison to boundary integral solutions. Numerical results confirm that for a fast formation, even modes, and for a slow formation, odd modes are more sensitive to changes in the borehole elongation and azimuth. Even though the focus of this work is on elliptical boreholes and breakouts, the formulation is valid for any kind of noncircular borehole.     

Experiments on stress dependent borehole acoustic waves

In the laboratory setup, a borehole traverses a dry sandstone formation, which is subjected to a controlled uniaxial stress in the direction perpendicular to the borehole axis. Measurements are made in a single loading-unloading stress cycle from zero to 10 MPa and then back down to zero stress. The applied stress and the presence of the borehole induce anisotropy in the bulk of the material and stress concentration around the borehole, both azimuthally and radially. Acoustic waves are generated and detected in the water-filled borehole, including compressional and shear headwaves, as well as modes of monopole, dipole, quadrupole, and higher order azimuthal symmetries. The linear and non-linear elastic parameters of the formation material are independently quantified, and utilized in conjunction with elastic theories to predict the characteristics of various borehole waves at zero and finite stress conditions. For example, an analytic theory is developed which is successfully used to estimate the changes of monopole tube mode at low frequency resulted from uniaxial stress, utilizing the measured material third order elasticity parameters. Comparisons between various measurements as well as that between experiments and theories are also presented.     

双负媒质结构改善Ku波段天线辐射特性

基于负介电常数和负磁导率产生原理,采用金属细线和裂环谐振器结构,针对12.5 GHz频率开展双负媒质结构设计。通过特殊边界条件下S参数计算以及Nicolson-Ross-Weir方法,完成等效参数的提取,获得介电常数、磁导率、折射率实部均为负值,且折射率接近于0的左手材料特性。将双负媒质结构加载于Ku波段圆锥喇叭口面进行仿真优化,提高天线增益2.17 dB,在11~13 GHz频带范围内,加载天线的增益均有所改善。实验结果表明,口面加载双负媒质结构后,天线增益提高1.51 dB,后向辐射减小5.7 dB,辐射特性获得了明显改善。     

Hybrid Modes in a Square Corrugated Waveguide

By using two scalar eigenfunctions, electric and magnetic fields in the rectangular (or square) corrugated waveguide are analyzed. In a rectangular corrugated waveguide, the boundary conditions on two corrugated and two smooth walls can be satisfied to excite the hybrid mode. In a highly oversized waveguide where the wavelength of dominant mode is close to that in vacuum, two smooth walls can be exchanged with the corrugated walls because the boundary condition at those walls is satisfied approximately. The replacement is possible due to almost no penetration of the electromagnetic fields into the gap of the replaced walls when the direction of main electric field is parallel to the gap of replaced walls. This characteristic enables us to rotate the polarization of the hybrid mode in the oversized square waveguide with all four corrugated walls and is applicable to the remote steering antenna for electron cyclotron heating in the ITER.     

Numerical Simulation of a Multi-Frequency Resistivity Logging-While-Drilling Tool Using a Highly Accurate and Adaptive Higher-Order Finite Element Method

A novel, highly efficient and accurate adaptive higher-order finite element method ($hp$-FEM) is used to simulate a multi-frequency resistivity logging-while-drilling (LWD) tool response in a borehole environment. Presented in this study are the vector expression of Maxwell's equations, three kinds of boundary conditions, stability weak formulation of Maxwell's equations, and automatic $hp$-adaptivity strategy. The new $hp$-FEM can select optimal refinement and calculation strategies based on the practical formation model and error estimation. Numerical experiments show that the new $hp$-FEM has an exponential convergence rate in terms of relative error in a user-prescribed quantity of interest against the degrees of freedom, which provides more accurate results than those obtained using the adaptive $h$-FEM. The numerical results illustrate the high efficiency and accuracy of the method at a given LWD tool structure and parameters in different physical models, which further confirm the accuracy of the results using the Hermes library (http://hpfem.org/hermes) with a multi-frequency resistivity LWD tool response in a borehole environment.     

偶极子声波测井在套管井中的声场特征*

偶极子声波测井在套管井中的应用越来越多,本文重点研究了套管井不同胶结状况下偶极子声源在套管井中激发的声场特征,通过解析方法分析了水泥环第一界面和第二界面不同胶结状况下井孔模式波的频散和衰减。计算结果表明,在水泥环第一界面或第二界面胶结差时井孔声场中可观测地层弯曲波和套管弯曲波;与胶结良好时相比,地层弯曲波的频散曲线向低频偏移,水泥环第二界面胶结差时偏移较大;套管弯曲波对水泥界面存在的流体环厚度很敏感,随着流体环厚度的增加套管弯曲波的相速度逐渐增大,激发幅度也明显增强,这一特征为利用套管弯曲波的相速度估算流体环厚度提供了可能。本文的计算结果为利用套管井中越来越多的偶极子声波测井资料评价水泥胶结质量奠定了理论基础。     

有限磁场中激光等离子体通道天线的传播特性

 提出了一种用于辐射高功率微波的各向异性磁化等离子体通道天线（AMPCA），阐述了该天线的具体实现方法，给出了其工作原理，建立了AMPCA的电磁模型。推导了广义柱坐标系下各向异性磁化等离子体中纵向场满足的波动方程，并给出了纵向场与横向场的关系，利用边界条件导出了AMPCA传播模式的特征方程，并在极限条件下，将结果与已有文献进行对比，验证了所推导结果的正确性和有效性。数值计算了AMPCA传播模式的色散曲线。