Monitoring the change in horizontal stress with multi-wave time-lapse seismic response based on nonlinear elasticity theory

Monitoring the change in horizontal stress from the geophysical data is a tough challenge, and it has a crucial impact on broad practical scenarios which involve reservoir exploration and development, carbon dioxide (CO_(2)) injection and storage, shallow surface prospecting and deep-earth structure description. The change in in-situ stress induced by hydrocarbon production and localized tectonic movements causes the changes in rock mechanic properties (e.g. wave velocities, density and anisotropy) and further causes the changes in seismic amplitudes, phases and travel times. In this study, the nonlinear elasticity theory that regards the rock skeleton (solid phase) and pore fluid as an effective whole is used to characterize the effect of horizontal principal stress on rock overall elastic properties and the stress-dependent anisotropy parameters are therefore formulated. Then the approximate P-wave, SV-wave and SH-wave angle-dependent reflection coefficient equations for the horizontal-stress-induced anisotropic media are proposed. It is shown that, on the different reflectors, the stress-induced relative changes in reflectivities (i.e., relative difference) of elastic parameters (i.e., P- and S-wave velocities and density) are much less than the changes in contrasts of anisotropy parameters. Therefore, the effects of stress change on the reflectivities of three elastic parameters are reasonably neglected to further propose an AVO inversion approach incorporating P-, SH- and SV-wave information to estimate the change in horizontal principal stress from the corresponding time-lapse seismic data. Compared with the existing methods, our method eliminates the need for man-made rock-physical or fitting parameters, providing more stable predictive power. 1D test illustrates that the estimated result from time-lapse P-wave reflection data shows the most reasonable agreement with the real model, while the estimated result from SH-wave reflection data shows the largest bias. 2D test illustrates the feasibility of the proposed inversion method for estimating the change in horizontal stress from P-wave time-lapse seismic data.

STABILITY OF STEADY MULTI-WAVE CONFIGURATIONS FOR THE FULL EULER EQUATIONS OF COMPRESSIBLE FLUID FLOW

We are concerned with the stability of steady multi-wave configurations for the full Euler equations of compressible fluid flow. In this paper, we focus on the stability of steady four-wave configurations that are the solutions of the Riemann problem in the flow direction, consisting of two shocks, one vortex sheet, and one entropy wave, which is one of the core multi-wave configurations for the two-dimensional Euler equations. It is proved that such steady four-wave configurations in supersonic flow are stable in structure globally, even under the BV perturbation of the incoming flow in the flow direction. In order to achieve this, we first formulate the problem as the Cauchy problem （initial value problem） in the flow direction, and then develop a modified Glimm difference scheme and identify a Glimm-type functional to obtain the required BV estimates by tracing the interactions not only between the strong shocks and weak waves, but also between the strong vortex sheet/entropy wave and weak waves. The key feature of the Euler equations is that the reflection coefficient is always less than 1, when a weak wave of different family interacts with the strong vortex sheet/entropy wave or the shock wave, which is crucial to guarantee that the Glimm functional is decreasing. Then these estimates are employed to establish the convergence of the approximate solutions to a global entropy solution, close to the background solution of steady four-wave configuration.

Reservoir prediction using multi-wave seismic attributes

The main problems in seismic attribute technology are the redundancy of data and the uncertainty of attributes, and these problems become much more serious in multi-wave seismic exploration. Data redundancy will increase the burden on interpreters, occupy large computer memory, take much more computing time, conceal the effective information, and especially cause the ＂curse of dimension＂. Uncertainty of attributes will reduce the accuracy of rebuilding the relationship between attributes and geological significance. In order to solve these problems, we study methods of principal component analysis （PCA）, independent component analysis （ICA） for attribute optimization and support vector machine （SVM） for reservoir prediction. We propose a flow chart of multi-wave seismic attribute process and further apply it to multi-wave seismic reservoir prediction. The processing results of real seismic data demonstrate that reservoir prediction based on combination of PP- and PS-wave attributes, compared with that based on traditional PP-wave attributes, can improve the prediction accuracy.

Dressed multi-wave mixing in a V-type four-level atomic system

The dressed four- and six-wave mixings in a V-type four-level system are considered. Under two different dressed conditions, two- and three-photon resonant Autler-Townes splittings, accompanied by enhancement and suppression of wave mixing signal, are obtained analytically. Meanwhile, an electromagnetic induced transparency of multi-wave mixing is presented, which shows multiple peaks and asymmetric effects caused by one-photon, two-photon and three-photon resonances, separately. The slow light propagation multiple region of multi-wave mixing signal is also obtained.

An ultrasonic multi-wave focusing and imaging method for linear phased arrays

To overcome the inherent limits of traditional single wave imaging for nondestructive testing,the multi-wave focusing and imaging method is thoroughly studied.This method makes the compressional waves and shear waves focused in both emission and reception processes,which strengthens the focusing energy and improves the signal-to-noise ratio of received signals.A numerical model is developed to study the characteristics of a multi-wave focusing field.It is shown that the element width approaching 0.8 wavelengths of shear waves can keep a balance between the radiation energy of two waves,which can achieve a desirable multi-wave focusing performance.And an experiment using different imaging methods for a linear phased array is performed.It can be concluded that due to the combination of the propagation and reflection characteristics of two waves,the multi-wave focusing and imaging method can significantly improve the imaging distinguishability of defects and expand the available sweeping range to a sector of-650 to 65°.

Multi-Waves,Breathers,Periodic and Cross-Kink Solutions to the(2+1)-Dimensional Variable-Coefficient Caudrey-Dodd-Gibbon-Kotera-Sawada Equation

The present article deals with multi-waves and breathers solution of the(2+1)-dimensional variable-coefficient CaudreyDodd-Gibbon-Kotera-Sawada equation under the Hirota bilinear operator method.The obtained solutions for solving the current equation represent some localized waves including soliton,solitary wave solutions,periodic and cross-kink solutions in which have been investigated by the approach of the bilinear method.Mainly,by choosing specific parameter constraints in the multi-waves and breathers,all cases the periodic and cross-kink solutions can be captured from the 1-and 2-soliton.The obtained solutions are extended with numerical simulation to analyze graphically,which results in 1-and 2-soliton solutions and also periodic and cross-kink solutions profiles.That will be extensively used to report many attractive physical phenomena in the fields of acoustics,heat transfer,fluid dynamics,classical mechanics,and so on.We have shown that the assigned method is further general,efficient,straightforward,and powerful and can be exerted to establish exact solutions of diverse kinds of fractional equations originated in mathematical physics and engineering.We have depicted the figures of the evaluated solutions in order to interpret the physical phenomena.

Multi-wavelength continuous-wave Nd:YVO4 self-Raman laser under in-band pumping

Multi-wavelength continuous-wave self-Raman laser with an a-cut composite YVO4/Nd:YVO4/YVO4 crystal pumped by an 879-nm wavelength-locked laser diode is demonstrated for the first time.Multi-wavelength Raman lasers at 1168.4,1176,1178.7,and 1201.6 nm are achieved by the first Stokes shift of the multi-wavelength fundamental lasers at 1064,1066.7,1073.6,1084,and 1085.6 nm with two Raman shifts of 890 and 816 cm^-1.A maximum Raman output power of 2.56 W is achieved through the use of a 20-mm-long composite crystal,with a corresponding optical conversion efficiency of 9.8%.The polarization directions of different fundamental and Raman lasers are investigated and found to be orthogonalπandσpolarizations.These orthogonally polarized multi-wavelength lasers with small wavelength separation pave the way to the development of a potential laser source for application in spectral analysis,laser radar and THz generation.

Multi-wave forward modeling of a reservoir and AVO analysis

In the process of accurate interpretation of multi-wave seismic data,we wanted to solve the problem of multi-wave information recognition.Based on techniques of elastic wave forwarding,targeting the geological model of a reservoir of an oil field exploration area,we used a high-order staggered-grid difference technology to simulate many shots of seismic records of nonzero offset shots,implemented multi-wave seismic data processing to acquire the CMP of P waves and converted waves,NMO traces of CCP pre stacks,including AVA information and superposition profiles.Based on the AVA calculation of the model,the layer parameters of the model and the forwarding wave field relations of the P-S wave,we also compared and studied the correspondence between P waves and converted waves.The results of our analysis show that the results from simulation and from the AVO analysis are consistent.Significant wave field differences between P waves and converted waves in the same reservoir were found,which are helpful in recognizing and interpreting the multi-wave information in this area.We made use of the multi-wave data to provide the important guidelines for reservoir prediction.

Optical Multi-wave Mixing Process Based on Electromagnetically InducedTransparency

In this paper,we propose and analyze an optical multi-wave mixing scheme for the generation of coherent light in a five-level atomic system in the context of electomagneticall induced transparency.A detailed semiclassical study of the propagation of generated mixing and probe fields is demonstrated.The analytical dependence of the generated minxing field on the probe field and the respective detuning is predicted.Such a nonlinear optical process can be used for generating short-wavelength radiation at low pump intensities.

Magnetic-field-sensitive multi-wave interference

We report an experimental study of magnetic-field-sensitive multi-wave interference,realized in a three-wave RF-atom system.In the F=1 hyperfine level of the ^(87)Rb 5^(2)S_(1/2) ground state,Ramsey fringes were observed via the spin-selective Raman detection.A decrease in the fringe contrast was observed with increasing free evolution time.The maximum evolution time for observable fringe contrasts was investigated at different atom temperatures,under free-falling and trapped conditions.As the main interest of the Ramsey method,the improvement in magnetic field resolution is observed with an increase of evolution time T up to 3 ms and with the measurement resolution reaching 0.85 nT.This study paves the way for precision magnetic field measurements based on cold atoms.

A simple multi-wave algorithm for the uncapacitated facility location problem

The multi-wave algorithm(Glover, 2016)integrates tabu search and strategic oscillation utilizing repeated waves(nested iterations) of constructive search or neighborhood search. We propose a simple multi-wave algorithm for solving the Uncapacitated Facility Location Problem(UFLP) to minimize the combined costs of selecting facilities to be opened and of assigning each customer to an opened facility in order to meet the customers' demands. The objective is to minimize the overall cost including the costs of opening facilities and the costs of allocations. Our experimental tests on a standard set of benchmarks for this widely-studied class of problems show that our algorithm outperforms all previous methods.

Global Stability of Multi-wave Configurations for the Compressible Non-isentropic Euler System

This paper is contributed to the structural stability of multi-wave configurations to Cauchy problem for the compressible non-isentropic Euler system with adiabatic exponentγ∈(1,3].Given some small BV perturbations of the initial state,the author employs a modified wave front tracking method,constructs a new Glimm functional,and proves its monotone decreasing based on the possible local wave interaction estimates,then establishes the global stability of the multi-wave configurations,consisting of a strong 1-shock wave,a strong 2-contact discontinuity,and a strong 3-shock wave,without restrictions on their strengths.

Multi-wave mixing Autler-Townes splitting in the five-level atomic system

We have demonstrated the Autler-Townes (AT) splitting of the four-wave mixing (FWM) process and the six-wave mixing (SWM) process in an elec tromag netically induced transparency (EIT) window in five-level atomic vapor of 87 Rb. Moreover we discuss interactions of multi-dressed states. The experimental results agree well with the theoretical analysis.

多波地震联合技术精细雕刻隐蔽河道砂体——以四川盆地西北部ZT地区沙溪庙组为例

四川盆地陆相致密砂岩气资源丰富,是目前天然气增储上产的重要领域,但侏罗系沙溪庙组沙一段河道砂体纵向多期叠置,横向同期交汇且河道砂体类型多样,隐蔽性强,形成了复杂多变的地震反射特征,准确刻画河道砂体难度极大。为了解决四川盆地西北部(以下简称川西北)ZT地区沙溪庙组一段(以下简称沙一段)多期河道砂体及储层刻画不清晰、精度低的问题,采用新采集的三维地震三分量转换横波(PS波)资料,结合PP波叠前数据和常规叠后地震资料,在正演模拟基础上,形成了多波地震联合雕刻河道砂体关键技术,并分析了河道砂体多波地震响应特征随砂体孔隙度的变化规律。研究结果表明:(1)砂体顶界PP波地震响应随孔隙度增大由强波峰转变为强波谷,而PS波地震响应不随物性变化发生极性反转,基于横波对岩性的刻画可有效识别多期隐蔽河道砂体;(2)相较反映横波阻抗变化率的叠前P-G属性,PS波振幅能量更聚焦,雕刻的河道砂体横向展布特征更清晰,边界更清楚;(3)叠前P-G属性具有更高的纵向分辨率,有利于区分叠置砂体,并落实砂体的发育期次。结论认为,多波地震技术联合充分发挥P-G的高分辨率优势确定纵向砂体发育期次,发挥PS波横向连续性优势刻画横向边界,实现了ZT地区沙一段河道砂体的完整精细雕刻,生产应用效果显著,并为该区井位部署和储量升级提供了有力技术支撑,为四川盆地陆相致密砂岩气规模效益开发奠定了坚实的基础,同时有力推进了多波地震勘探技术的发展。

Research on model testing of a new ultrasonic multi-wav detecting method

The traditional crack exploring method with echo （reflected wave） in metals is called the ＂single-wave detecting method＂ that uses a probe of single weight. This method is not able to detect directly the size and shape of the crack and the result can only be obtained by relative comparison, that is to compare the echo amplitudes of the unknown quantity （crack） with the known quantity （regular artificial crack） to determine the equivalent size and shape of a certain crack.

一种可模态分离的高分辨率频率-波数法及其工程应用

高分辨率频率-波数法是通过计算F-K谱从能量角度获取主导表面波频散信息的一种常用方法。然而,由于高模态瑞利波的能量通常低于基阶波的能量,因此难以分离多模态频散信息。本文通过建立多模态瑞利波模型,并讨论其相速度、波数和能量特性,提出一种可模态分离的高分辨率频率-波数法。通过增强F-K谱上的高模态能量,提取其多模态能量的局部极值,进而得到相速度点,对所有相速度点进行概率分布并拟合,得到多模态频散曲线。工程应用表明,改进的高分辨率频率-波数法能够较好地还原多模态瑞利波信息,通过对提取的多模态频散曲线进行联合反演,可以得到与工程钻孔结果匹配较好的剪切波速度结构。

多自由度振荡浮子装置波浪爬升特性试验与数值模拟

增加振荡浮子式波浪能发电装置的自由度可以拓宽设备的捕获频带,从而有效地提高其捕获效率,但这也意味着浮子与波浪间的作用过程更加复杂,产生的波浪爬升等非线性现象不容忽视,严重时甚至会发生越浪从而降低浮子装置的使用寿命和效率.本文开展了规则波作用下多自由度浮子迎浪侧波浪爬升特性的物理模型试验,对单自由度运动和多自由度耦合运动的浮子上的波浪爬高进行了比较,以分析在有无动力输出装置(power take-off,PTO)阻尼条件下自由度之间的相互作用效应,并使用数值模拟分析耦合运动浮子周围的流场分布.结果显示,增加自由度可以导致没有PTO阻尼的浮子上的波浪爬高显著降低,有效降低越浪风险.对于有PTO阻尼的多自由度振荡浮子,增加垂荡方向上的PTO阻尼力对波浪爬升有很大影响.三自由度耦合运动浮子能更好地利用波浪能并具有更好的安全性.

融入多维度思政的“电磁场与电磁波”课程教学改革与实践

为深入贯彻落实习近平总书记关于全面推进高校课程思政建设的精神,在“电磁场与电磁波”课程教学改革中,通过设计多维度思政环节、多链条构建高阶性知识体系,多环节融合的科研案例教学模式,将知识传授与思政育人深度融合,培养学生家国情怀、拓展国际视野,塑造科学素养和执着的探索精神。通过合理嵌入育人要素,把思想政治工作贯穿教育教学全过程,激励学生成才,实现专业知识传授和价值引领的同频共振。

基于多层全连接神经网络的6C地震波极化向量识别研究

利用机器学习原理,提出一种基于多层全连接(multi-layer fully connected, MFC)神经网络的六分量(six-component, 6C)地震波极化向量识别方法。首先利用6C地震波各波型极化向量数学模型和一系列仿真参数得到5种波型和噪声波型各5 000个极化向量数据集,然后随机选取其中5 000个作为测试集,其余划分为训练集,进行MFC神经网络与支持向量机(support vector machine, SVM)的综合辨识性能对比实验。结果表明,MFC神经网络模型识别5种极化向量类型(SH波和Love波视为一类)和6种极化向量类型的效果均显著优于SVM模型,平均识别率分别达到99.786%和87.940%。

基于Barker码脉冲压缩技术的钢板多阵元Lamb波电磁超声换能器设计与优化

为了解决传统Barker码脉冲压缩技术受脉冲功率放大器额定参数(占空比,最大脉冲宽度等)限制而导致的脉冲压缩效果下降、检测速度降低等问题,提出一种基于Barker码脉冲压缩技术的多阵元Lamb波电磁超声换能器(EMAT)。建立了基于tone-burst信号激励-Barker码脉冲压缩技术的多阵元Lamb波EMAT检测过程的有限元模型,分析了永磁体的配置形式、阵元序列长度、激励信号周期数、曲折线圈匝数等因素对脉冲压缩后的主旁瓣比和主瓣宽度的影响,并进行了实验验证。结果表明:曲折线圈匝数为4和Barker码序列长度为13位的多阵元EMAT在配置3对外置永磁体后,其信噪比(SNR)可提高9.8 dB。综合考虑检测回波的空间分辨率和SNR,多阵元Lamb波EMAT最佳参数为:曲折线圈匝数为10、激励信号周期数为11、Barker序列为13位,并配置3对外置永磁体。