Reservoir information extraction using a fractional Fourier transform and a smooth pseudo Wigner-Ville distribution

Currently, it is difficult for people to express signal information simultaneously in the time and frequency domains when analyzing acoustic logging signals using a simple-time or frequency-domain method. It is difficult to use a single type of time-frequency analysis method, which affects the feasibility of acoustic logging signal analysis. In order to solve these problems, in this paper, a fractional Fourier transform and smooth pseudo Wigner Ville distribution （SPWD） were combined and used to analyze array acoustic logging signals. The time-frequency distribution of signals with the variation of orders of fractional Fourier transform was obtained, and the characteristics of the time-frequency distribution of different reservoirs under different orders were summarized. Because of the rotational characteristics of the fractional Fourier transform, the rotation speed of the cross terms was faster than those of primary waves, shear waves, Stoneley waves, and pseudo Rayleigh waves. By choosing different orders for different reservoirs according to the actual circumstances, the cross terms were separated from the four kinds of waves. In this manner, we could extract reservoir information by studying the characteristics of partial waves. Actual logging data showed that the method outlined in this paper greatly weakened cross-term interference and enhanced the ability to identify partial wave signals.

MSMVT:多尺度和多视图Transformer半监督医学图像分割框架

近年来,Transformer在众多监督式计算机视觉任务中取得了显著进展,然而由于高质量医学标注图像的缺乏,其在半监督图像分割领域的性能仍有待提高。为此,提出了一种基于多尺度和多视图Transformer的半监督医学图像分割框架:MSMVT(multi-scale and multi-view transformer)。鉴于对比学习在Transformer的预训练中取得的良好效果,设计了一个基于伪标签引导的多尺度原型对比学习模块。该模块利用图像金字塔数据增强技术,为无标签图像生成富有语义信息的多尺度原型表示;通过对比学习,强化了不同尺度原型之间的一致性,从而有效缓解了由标签稀缺性导致的Transformer训练不足的问题。此外,为了增强Transformer模型训练的稳定性,提出了多视图一致性学习策略。通过弱扰动视图,以校正多个强扰动视图。通过最小化不同视图之间的输出差异性,使得模型能够对不同扰动保持多层次的一致性。实验结果表明,当仅采用10%的标注比例时,提出的MSMVT框架在ACDC、LIDC和ISIC三个公共数据集上的DSC图像分割性能指标分别达到了88.93%、84.75%和85.38%,优于现有的半监督医学图像分割方法。

Hilbert-Huang变换联合平滑伪Wigner-Ville时频分布识别储层流体性质

苏里格气田致密砂岩储层具有低孔、低渗、气水关系复杂等特点,利用常规测井资料进行流体识别难度较大。以阵列声波测井资料为基础,利用希尔伯特-黄(Hilbert-Huang)变换联合平滑伪魏格纳(Wigner-Ville)时频分布分别提取阵列声波测井信号的时间边缘和频率边缘特征,并研究与储层流体分布的关系。结果表明:气层和水层在时间边缘和频率边缘分布存在明显差异。在时间边缘分布特征上,气层能量最低,水层能量最高;在频率边缘分布特征上,气层和水层均有一定的频散,且水层能量高于气层能量;储层含气越多,信号衰减越严重。因此利用信号在时间分布和频率分布上的差异可以进行流体性质识别。

基于FrFT的最优平滑伪Wigner-Ville分布

分数阶傅里叶变换具有旋转性、时移特性、频移特性等重要数学性质,将其结合广义时频带宽积准则,可设计出平滑伪Wigner-Ville分布(SPWVD)的最优时域窗函数,该窗函数能根据实际处理信号自适应地变化,从而提高SPWVD的精度。为了验证所设计窗函数的有效性,本文使用调频信号进行测试,仿真结果显示,该窗函数能有效提高传统SPWVD的精度。

平滑伪Wigner-Ville变换的地震面波到达时间提取

通过对地震面波到达时间识别方法研究,提出一种基于平滑伪Wigner-Ville变换的方法提取地震面波到达时间,主要用于目标探测方法研究。在此背景下,通过实际的振动系统进行采集数据,利用Wigner-Ville变换以及平滑伪Wigner-Ville变换分析并提取面波。通过其频率分布,能量衰减规律等特性与实际参数进行对比,从而得出所用方法的有效性。对目标检测和精准定位的方法研究具有重大的意义。

基于Wigner-Ville分布与Chrip-Z变换的高分辨时频分析方法

时频分析方法一直广泛地应用于地震数据的处理与资料解释中。针对油气勘探面临的圈闭规模小、储层薄且埋深大、烃源丰富却分布零散等复杂情形时,如果地震资料有效信号频带较窄、分辨率较低,则需高分辨时频分析方法,以提高对微型油气目标的识别精度。平滑伪Wigner-Ville分布(SPWVD)双线性时频分析方法具有良好的时频聚焦性,线性调频Chrip-Z变换(CZT)的螺旋采样插值特性可突出三维空间局部细节。结合此二者优势,形成一种可提高地震信号时频分辨率的新方法(SPWVD-CZT)。该方法通过采样的方式实现数值的插值计算,以增加有效频段的划分点数,完善时频分布的局部细节,在时频域实现频谱信息的细化处理。模拟信号试算和实际地震资料河道微相识别的应用结果表明,该方法能显著提升地震数据时频分析的频率采样率,可为微型地质体的发现及油气开发提供技术支撑。

Structural Damage Identification via Pseudo Strain Energy Density and Wavelet Packet Transform

Based on strain signals, a new time-domain methodology for detecting the beam local damage has been developed. The pseudo strain energy density （PSED） is defined and used to build two major damage indexes, the average pseudo strain energy density （APSED） and the average pseudo strain energy density rate （APSEDR）. Probability and mathematical statistics are utilized to derive a standardized damage index. Furthermore, by applying the analytic relation between the strain energy release rate and the stress intensity factor, an analytic solution of crack depth is derived. For the dynamic strain signals, the wavelet packet transform is used to pre-process measured data. Finally, a numerical simulation indicates that this method can effectively identify the damage location and its absolute severity.

The W transform and its improved methods for time-frequency analysis of seismic data

The conventional linear time-frequency analysis method cannot achieve high resolution and energy focusing in the time and frequency dimensions at the same time,especially in the low frequency region.In order to improve the resolution of the linear time-frequency analysis method in the low-frequency region,we have proposed a W transform method,in which the instantaneous frequency is introduced as a parameter into the linear transformation,and the analysis time window is constructed which matches the instantaneous frequency of the seismic data.In this paper,the W transform method is compared with the Wigner-Ville distribution(WVD),a typical nonlinear time-frequency analysis method.The WVD method that shows the energy distribution in the time-frequency domain clearly indicates the gravitational center of time and the gravitational center of frequency of a wavelet,while the time-frequency spectrum of the W transform also has a clear gravitational center of energy focusing,because the instantaneous frequency corresponding to any time position is introduced as the transformation parameter.Therefore,the W transform can be benchmarked directly by the WVD method.We summarize the development of the W transform and three improved methods in recent years,and elaborate on the evolution of the standard W transform,the chirp-modulated W transform,the fractional-order W transform,and the linear canonical W transform.Through three application examples of W transform in fluvial sand body identification and reservoir prediction,it is verified that W transform can improve the resolution and energy focusing of time-frequency spectra.

基于小波变换和拟动力法的边坡地震稳定性评价方法

结合简化Bishop法,推导了地震作用下边坡的稳定性计算公式,包括拟静力法(pseudo-static method,简称PSM)、经典拟动力法(pseudo-dynamic method,简称PDM)和修正拟动力法(modified pseudo-dynamic method,简称MPDM)。其中,修正拟动力法将土体视为Kelvin-Voigt材料,考虑了土体的黏弹特性和放大特性。在此基础上,对修正拟动力法进行了推广,使剪应力在坡顶、坡面处均为0,符合边坡应力特征。然后,基于Morlet小波分析,以El centro波为研究对象获得了地震波的频谱分布特征。通过提取峰值加速度PGA时刻的卓越频率,提出了一种考虑地震动时频特征的边坡地震稳定性评价方法。最后,将各方法与实例进行了验证。结果表明:拟动力法所需参数较少且意义明确,能够快速、准确地评价边坡地震稳定性,与时程分析方法结果接近。该研究成果可为边坡地震危险性评价、地震滑坡灾害范围分析预测、抗震应急抢险提供理论依据。

基于Swin Transformer的疟疾细胞图像识别研究

为了协助医务人员更准确、更快速地诊断疟疾,提出一种基于Swin Transformer(SwinT)的疟疾细胞图像识别方案。方案采用伪彩色图像增强算法对血片图像进行预处理,以突出图像的颜色对比度,并引入SwinT模型作为主干网络,解决下采样固定和全局信息无法交互的问题,同时引入卷积层对图像进行线性变换,构建残差网络解决梯度消失和梯度爆炸问题。实验表明,与图像量化等其他图像增强方法相比,本文方法增强了疟疾细胞图像的色彩对比度,改进后方案的准确率达到99.7%,高于现有文献方法,可以对疟疾的辅助治疗带来更有价值的支持。

一种基于Swin Transformer神经网络的低截获概率雷达信号调制类型的识别方法

本文针对低截获概率(Low Probability of Intercept,LPI)雷达信号调制类型的识别问题提出了一种基于Swin Transformer神经网络的识别方法.该方法首先用平滑伪Wigner-Ville分布对信号进行时频变换,将一维时域信号转换为二维时频图像,然后使用Swin Transformer神经网络对时频图像进行特征提取和调制类型识别.仿真结果显示该方法具有较强的抗噪声能力,在低信噪比条件下识别准确率高,且具有较强的小样本适应能力.

Radar Signal Intra-Pulse Feature Extraction Based on Improved Wavelet Transform Algorithm

With the new system radar put into practical use, the characteristics of complex radar signals are changing and developing. The traditional analysis method of one-dimensional transformation domain is no longer applicable to the modern radar signal processing, and it is necessary to seek new methods in the two-dimensional transformation domain. The time-frequency analysis method is the most widely used method in the two-dimensional transformation domain. In this paper, two typical time-frequency analysis methods of short-time Fourier transform and Wigner-Ville distribution are studied by analyzing the time-frequency transform of typical radar reconnaissance linear frequency modulation signal, aiming at the problem of low accuracy and sen-sitivity to the signal noise of common methods, the improved wavelet transform algorithm was proposed.

Fitting method of pseudo-polynomial for solving nonlinear parametric adjustment

The optimal condition and its geometrical characters of the least square adjustment were proposed. Then the relation between the transformed surface and least squares was discussed. Based on the above, a non iterative method, called the fitting method of pseudo polynomial, was derived in detail. The final least squares solution can be determined with sufficient accuracy in a single step and is not attained by moving the initial point in the view of iteration. The accuracy of the solution relys wholly on the frequency of Taylor’s series. The example verifies the correctness and validness of the method. [

SOLVING COUPLED PSEUDO-PARABOLIC EQUATION USING A MODIFIED DOUBLE LAPLACE DECOMPOSITION METHOD

In this paper, the modification of double Laplace decomposition method is pro- posed for the analytical approximation solution of a coupled system of pseudo-parabolic equation with initial conditions. Some examples are given to support our presented method. In addition, we prove the convergence of double Laplace transform decomposition method applied to our problems.

Novel Way to Suppress Reverberation Based on Fractional Fourier Transform

A novel method of anti-reverberation based on the fractional Fourier transformation is presented. By virtue of the fact that it has a good focus property in the fractional Fourier domain, the linearly frequency modulation (LFM) signal can be seperated from the reverberation through a swept-frequency filter. With the actual reverberation data and the LFM pulse for seperation, the good results are obtained: the reverbareation is largely removed, and relatively the better performance is shown under the lower signal reverberation ratio (SRR). Based on the theorical analyses and simulation results, two schemes for detecting targets are provided: one is the detection of the LFM echo from the target with a threshold by means of this method directly; the other is to detect the target by means of other methods, with this method performing pre-process to increase SRR, which need enough large SRR.

An Accurate Numerical Solution for the Modified Equal Width Wave Equation Using the Fourier Pseudo-Spectral Method

In this study, the numerical solution for the Modified Equal Width Wave (MEW) equation is presented using Fourier spectral method that use to discretize the space variable and Leap-frog method scheme for time dependence. Test problems including the single soliton wave motion, interaction of two solitary waves and interaction of three solitary waves will use to validate the proposed method. The three invariants of the motion are evaluated to determine the conservation properties of the generated scheme. Finally, a Maxwellian initial condition pulse is then studied. The L2 and L∞ error norms are computed to study the accuracy and the simplicity of the presented method.

Application of Fractional Fourier Transform in seismic data denoising

Data processing is a basic and crucial factor in seismic exploration,which can influence the effect of subsequent processing directly. Thus the selection of appropriate method for data processing is one of the most important tasks throughout the work. By simulating,the authors analyze and compare Fractional Fourier Transform( FRFT) and Wigner-Ville distribution( WVD),then summarize the similarities and advantages and disadvantages of the two methods. The results reveal that FRFT is more effective and suitable for application in seismic exploration than WVD.

STUDY OF CONSTITUTIVE RELATIONS FOR PSEUDO-ELASTICITY AND SHAPE MEMORY BEHAVIOR

Constitutive relations are given for the description of the deformation behavior of shape memory materials. The deformation is the superposition of the elastic, the thermal and the phase transformation deformation caused by the transformation from one to the other among the high temperature phase, the low temperature phase and the stress induced phase. The phase transformation is controlled by the driving force, i.e., the Gibbs energy difference between the phases.

基于频率响应与图像特征提取的动车组变压器绕组状态诊断方法研究

动车组变压器是保障高速铁路稳定运行的核心设备,频率响应法是目前检测变压器绕组状态的有效方法。为提升车载变压器绕组状态诊断的准确性,结合暂态信号与频率响应法提出基于频率响应与图像特征提取的动车组变压器绕组状态诊断方法。搭建试验车载变压器绕组故障模拟平台,获取不同故障类型和故障位置的频响曲线,利用类Gram矩阵结合幅频和相频曲线信息,再利用密度分层法转换为伪彩色图,提取对应的灰度共生矩阵和灰度差分矩阵特征值,根据鹈鹕优化支持向量机方法对绕组故障进行诊断。试验结果表明:车载变压器绕组故障发生时,伪彩色图能够反映出故障信息,有利于图像分析和特征提取,采用基于频率响应与图像特征提取的动车组变压器绕组状态诊断方法能够识别车载变压器绕组的典型故障类型和位置。

应用测井资料小波变换与伪成像技术精细划分深部隔夹层

隔夹层影响流体渗流,控制油水及剩余油分布,深层取心成本高,常规测井曲线分辨率低且薄互层信号模糊,深部隔夹层识别难度大。通过对关键井岩心研究,得出了隔夹层敏感测井曲线及其响应特征,采用小波分解和重构,对常规敏感测井曲线进行了高分辨率处理,降低了邻层平滑效应,突出了薄层界面测井响应特征,薄层识别分辨率提高了近1倍。综合利用隔夹层地层倾角矢量模式和伪成像特征,确立了深部隔夹层判识划分方法,应用实例表明,该方法可精细识别隔夹层,相比常规方法,隔夹层辨识能力显著提升,井间小层对比精度提高38%,解释了油水界面倾斜问题,得出了剩余油分布规律。