Estimation of a non-stationary prior covariance from seismic data     

Rasmus Bødker Madsen  Thomas Mejer Hansen  Henning Omre 《Geophysical Prospecting》2020,68(2):393-410

Non-stationarity in statistical properties of the subsurface is often ignored. In a classical linear Bayesian inversion setting of seismic data, the prior distribution of physical parameters is often assumed to be stationary. Here we propose a new method of handling non-stationarity in the variance of physical parameters in seismic data. We propose to infer the model variance prior to inversion using maximum likelihood estimators in a sliding window approach. A traditional, and a localized shrinkage estimator is defined for inferring the prior model variance. The estimators are assessed in a synthetic base case with heterogeneous variance of the acoustic impedance in a zero-offset seismic cross section. Subsequently, this data is inverted for acoustic impedance using a non-stationary model set up with the inferred variances. Results indicate that prediction as well as posterior resolution is greatly improved using the non-stationary model compared with a common prior model with stationary variance. The localized shrinkage predictor is shown to be slightly more robust than the traditional estimator in terms of amplitude differences in the variance of acoustic impedance and size of local neighbourhood. Finally, we apply the methodology to a real data set from the North Sea basin. Inversion results show a more realistic posterior model than using a conventional approach with stationary variance.  相似文献   

The magnetotelluric impedance tensor through Clifford algebras: part II — a constrained stochastic heuristic method for recovering the magnetotelluric regional impedance tensor in 2D/3D case     

Ivan Romero-Ruiz  Jaume Pous 《Geophysical Prospecting》2019,67(3):670-695

A method for obtaining the galvanic distortion matrix is presented so that the regional impedance tensor (free of distortion) is recovered. The method is a constrained stochastic heuristic method, which consists in randomly exploring the space of the distortion parameters. Constraints are imposed on the shortest periods of the regional impedance tensor that, at these short periods, tends to be two dimensional (or one dimensional). Depending on the constraints used, two different methods to recover the regional impedance tensor in this 2D/3D case are presented. Method 1 needs to find the strike of the short periods and Method 2 applies to the measurement directions. Twist, shear and anisotropy parameters are obtained. Thus, the regional impedance tensor is recovered with the only exception being the vertical shift due to the gain, which is equal for all the components of the tensor. Examples with synthetic impedance tensors from 2D/3D models perturbed with galvanic distortion are presented to illustrate how the algorithm works. The presence of noise in data is considered and rules for proceeding are provided. The same examples perturbed by Gaussian noise together with experimental data illustrate the capabilities of the algorithm.  相似文献   

基于非静压模型的波浪空间聚焦研究     

马小舟  马建兴  马玉祥  董国海 《中国海洋大学学报(自然科学版)》2020,50(4):128-135

为研究波浪聚焦特性,分析极端波浪的产生机理,采用非静压模型通过数值模拟的方法对波浪聚焦的影响因素进行了详细研究。本文采用SWASH非静压波浪模型,模型垂向均匀分三层以保证足够的色散精度以及非线性精度来高效准确的模拟波浪在变化地形上的传播。研究发现在最大波浪未发生破碎时,波浪在半圆形凸起斜坡浅滩上传播,波浪聚焦是波高增大的最主要原因。初始kR(波数与浅滩半径乘积)值对波浪在该地形上的聚焦特性有着重要影响。初始kR越大,最大波高位置距聚焦地形坡脚的距离越远。当kR在1.4π~4.05π之间时,随着kR的减小,最大相对波高先增大后减小,当kR=2.45π时,最大相对波高达到极大值,可达2.48倍初始波高。  相似文献   

NIM陆面过程模式的研究:模式建立与对比研究     

邵海燕  陈万隆 《南京气象学院学报》2000,(4)

为了真实模拟干旱、半干旱地区以及湿润地区的陆面与大气之间的能量和物质交换 ,发展了一个具有普适性的南京气象学院 ( NIM)陆面过程 ( LSP)模式。该模式是由等温植被参数化方案和本文建立的土壤模式所组成。土壤模式又分为五层模式和两层模式两种。利用 1 979年 5～ 8月“青藏高原气象科学实验”资料作验证 ,同时将五层模式与 Deardorff( 1 978)陆面模式、两层模式作了对比 ,结果表明五层土壤模式的模拟效果较好 ,它比 Deardorff模式优越 ,也比两层土壤模式模拟效果稍好一些。  相似文献   

Measurements of sheet flow transport in acceleration-skewed oscillatory flow and comparison with practical formulations   总被引：1，自引：0，他引：1  

Dominic A. van der A  Tom O'Donoghue  Jan S. Ribberink 《Coastal Engineering》2010

Near-bed oscillatory flows with acceleration skewness are characteristic of steep and breaking waves in shallow water. In order to isolate the effects of acceleration skewness on sheet flow sand transport, new experiments are carried out in the Aberdeen Oscillatory Flow Tunnel. The experiments have produced a dataset of net transport rates for full-scale oscillatory flows with varying degrees of acceleration skewness and three sand sizes. The new data confirm previous research that net transport in acceleration-skewed flow is non-zero, is always in the direction of the largest acceleration and increases with increasing acceleration skewness. Large transport rates for the fine sand conditions suggest that phase lag effects play an important role in augmenting positive net transport. A comparison of the new experimental data with a number of practical sand transport formulations that incorporate acceleration skewness shows that none of the formulations performs well in predicting the measured net transport rates for both the fine and the coarser sands. The new experimental data can be used to further develop practical sand transport formulations to better account for acceleration skewness.  相似文献   

Numerical modelling of landslide‐generated waves with the particle finite element method (PFEM) and a non‐Newtonian flow model          下载免费PDF全文

F. Salazar  J. Irazbal  A. Larese  E. Oate 《国际地质力学数值与分析法杂志》2016,40(6):809-826

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A fiber-section model based Timoshenko beam element using shear-bending interdependent shape function     

Li Ning  Li Zhongxian  Xie Lili 《地震工程与工程振动(英文版)》2013,12(3):421-432

A fiber-section model based Timoshenko beam element is proposed in this study that is founded on the nonlinear analysis of frame elements considering axial,flexural,and shear deformations.This model is achieved using a shear-bending interdependent formulation(SBIF).The shape function of the element is derived from the exact solution of the homogeneous form of the equilibrium equation for the Timoshenko deformation hypothesis.The proposed element is free from shear-locking.The sectional fiber model is constituted with a multi-axial plasticity material model,which is used to simulate the coupled shear-axial nonlinear behavior of each fiber.By imposing deformation compatibility conditions among the fibers,the sectional and elemental resisting forces are calculated.Since the SBIF shape functions are interactive with the shear-corrector factor for different shapes of sections,an iterative procedure is introduced in the nonlinear state determination of the proposed Timoshenko element.In addition,the proposed model tackles the geometric nonlinear problem by adopting a corotational coordinate transformation approach.The derivation procedure of the corotational algorithm of the SBIF Timoshenko element for nonlinear geometrical analysis is presented.Numerical examples confirm that the SBIF Timoshenko element with a fiber-section model has the same accuracy and robustness as the flexibility-based formulation.Finally,the SBIF Timoshenko element is extended and demonstratedin a three-dimensional numerical example.  相似文献   

Viscoelastic functionally graded finite element method with recursive time integration and applications to flexible pavements     

Eshan V. Dave  William G. Buttlar 《国际地质力学数值与分析法杂志》2012,36(9):1194-1219

The finite‐element (FE) method is used for modeling geotechnical and pavement structures exhibiting significant non‐homogeneity. Property gradients generated due to non‐homogeneous distributions of moisture is one such example for geotechnical materials. Aging and temperature‐induced property gradients are common sources of non‐homogeneity for asphalt pavements. Investigation of time‐dependent behavior combined with functionally graded property gradation can be accomplished by means of the non‐homogeneous viscoelastic analysis procedure. This paper describes the development of a generalized isoparametric FE formulation to capture property gradients within elements, and a recursive formulation for solution of hereditary integral equations. The formulation is verified by comparison with analytical and numerical solutions. Two application examples are presented: the first describes stationary crack‐tip fields for viscoelastic functionally graded materials, and the second example demonstrates the application of the proposed procedures for efficient and accurate simulations of interfaces between layers of flexible pavement. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

A FIC‐based stabilized mixed finite element method with equal order interpolation for solid–pore fluid interaction problems          下载免费PDF全文

Ignasi de‐Pouplana  Eugenio Oñate 《国际地质力学数值与分析法杂志》2017,41(1):110-134

A new mixed displacement‐pressure element for solving solid–pore fluid interaction problems is presented. In the resulting coupled system of equations, the balance of momentum equation remains unaltered, while the mass balance equation for the pore fluid is stabilized with the inclusion of higher‐order terms multiplied by arbitrary dimensions in space, following the finite calculus (FIC) procedure. The stabilized FIC‐FEM formulation can be applied to any kind of interpolation for the displacements and the pressure, but in this work, we have used linear elements of equal order interpolation for both set of unknowns. Examples in 2D and 3D are presented to illustrate the accuracy of the stabilized formulation for solid–pore fluid interaction problems. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

A variational formulation for three-dimensional analysis of extensible marine riser transporting fluid   总被引：1，自引：0，他引：1  

Chainarong Athisakul 《Ocean Engineering》2011,38(4):609-620

This paper presents a model formulation for static and dynamic analysis of three-dimensional extensible marine riser transporting fluid. A variational model formulation is developed based on the principle of virtual work-energy and the extensible elastica theory. The virtual work-energy functional is composed of the virtual strain energy due to axial stretching, bending, and torsion and the virtual work done by the external and internal fluid. The governing dynamic equilibrium equations are derived in the Cartesian coordinate. The finite element method is used to obtain the numerical solutions. The numerical examples are provided to demonstrate interesting effects of fluid transportation and axial deformation on large displacements and dynamic properties of the three-dimensional extensible marine riser.  相似文献