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首页> 外文期刊>Journal of Applied Geophysics >Finite difference modeling of ultrasonic propagation (coda waves) in digital porous cores with un-split convolutional PML and rotated staggered grid
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Finite difference modeling of ultrasonic propagation (coda waves) in digital porous cores with un-split convolutional PML and rotated staggered grid

机译：具有未分裂卷积PML和旋转交错网格的数字多孔核中超声传播（尾波）的有限差分建模

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Ultrasonic wave propagation in heterogeneous porous cores under laboratory studies is an extremely complex process involved with strong scattering by microscale heterogeneous structures. The resulting coda waves, as an index to measure scattering attenuation, are recorded as continuous waveforms in the tail portion of wavetrains. Because of the contamination of reflections from the side ends and reverberations between the sample surfaces, it is difficult to extract pure coda waves from ultrasonic measurements for the estimation of the P- and S-coda attenuation quality factors. Comparisons of numerical and experimental ultrasonicwave propagation in heterogeneous porous cores can give important insight into understanding the effect of boundary reflections on the P- and S-codas in the laboratory experiment. It challenges numerical modeling techniques by threemajor issues: the creation of a digital coremodel tomap heterogeneous rock properties in detail, the perfect simulation with a controllable and accurate absorbing boundary, and overcoming the numerical dispersions resulting fromhigh-frequency propagation and strong heterogeneity in material. A rotated staggered-grid finitedifference method of Biot's poroelastic equations is presented with an unsplit convolutional perfectly matched layer (CPML) absorbing boundary to simulate poroelastic wave propagation in isotropic and fluid-saturated porous media. The contamination of boundary reflections on coda waves is controlled by the CPML absorbing coefficients for the comparison between numerical and experimental ultrasonicwaveforms.Numerical examples with a digital porous core demonstrate that the boundary reflections contaminate coda waves seriously, causing much larger coda quality factors and thus underestimating scattering attenuation.
机译：在实验室研究中，超声波在异质多孔核中的传播是一个极其复杂的过程，涉及到微尺度异质结构的强散射。产生的尾波作为测量散射衰减的指标，被记录为波列尾部的连续波形。由于来自侧面末端的反射污染和样品表面之间的混响，很难从超声测量中提取纯尾波以估算P和S尾衰减质量因数。比较数值和实验超声波在异质多孔核中的传播，可以为理解实验室实验中边界反射对P和S尾气的影响提供重要见解。它通过以下三个主要问题对数值建模技术提出了挑战：创建详细映射非均质岩石特性的数字岩心模型，具有可控且精确的吸收边界的完美模拟以及克服了高频传播和材料中强烈的非均质性导致的数值离散。提出了Biot多孔弹性方程的交错交错网格有限差分方法，该方法具有未分裂的卷积完全匹配层（CPML）吸收边界，以模拟多孔弹性波在各向同性和流体饱和的多孔介质中的传播。用CPML吸收系数控制尾声对边界波的污染，以比较数值和实验超声波波形。带有数字多孔核的数值示例表明边界反射严重污染尾波，导致更大的尾声质量因数，因此低估了散射衰减。

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