共查询到20条相似文献，搜索用时 15 毫秒
1.
Complex-valued random fields represent a natural extension of real-valued random fields and can be useful for modeling vectorial data in two dimensions (i.e., a wind field). In such a case, some theoretical issues arise concerning generating and fitting complex covariance functions to be used for prediction purposes. In this paper, some general aspects and properties of complex-valued random fields are summarized and a procedure to fit complex stationary covariance functions is proposed. A case study for analyzing wind speed data is presented. 相似文献
2.
A geotechnical problem that involves several spatially correlated parameters can be best described using multivariate cross-correlated random fields. The joint distribution of these random variables cannot be uniquely defined using their marginal distributions and correlation coefficients alone. This paper presents a generic methodology for generating multivariate cross-correlated random fields. The joint distribution is rigorously established using a copula function that describes the dependence structure among the individual variables. The cross-correlated random fields are generated through Cholesky decomposition and conditional sampling based on the joint distribution. The random fields are verified regarding the anisotropic scales of fluctuation and copula parameters. 相似文献
3.
Gonzalo Sapriza Azuri Jorge Jódar Jesús Carrera Hoshin V. Gupta 《Mathematical Geosciences》2013,45(5):621-645
A model for generating daily spatial correlated rainfall fields suitable for evaluating the impacts of climate change on water resources is presented. The model, termed Stochastic Rainfall Generating Process, is designed to incorporate two major nonstationarities: changes in the frequencies of different precipitation generating mechanisms (frontal and convective), and spatial nonstationarities caused by interactions of mesoscale atmospheric patterns with topography (orographic effects). These nonstationarities are approximated as discrete sets of the time-stationary Stochastic Rainfall Generating Process, each of which represents the different spatial patterns of rainfall (including its variation with topography) associated with different atmospheric circulation patterns and times of the year (seasons). Each discrete Stochastic Rainfall Generating Process generates daily correlated rainfall fields as the product of two random fields. First, the amount of rainfall is generated by a transformed Gaussian process applying sequential Gaussian simulation. Second, the delimitation of rain and no-rain areas (intermittence process) is defined by a binary random function simulated by sequential indicator simulations. To explore its applicability, the model is tested in the Upper Guadiana Basin in Spain. The result suggests that the model provides accurate reproduction of the major spatiotemporal features of rainfall needed for hydrological modeling and water resource evaluations. The results were significantly improved by incorporating spatial drift related to orographic precipitation into the model. 相似文献
4.
In this paper, we introduce a novel stochastic model for the permeability tensor associated with stationary random porous media. In the light of recent works on mesoscale modeling of permeability, we first discuss the physical interpretation of the permeability tensor randomness. Subsequently, we propose a nonparametric prior probabilistic model for non‐Gaussian permeability tensor random fields, making use of the information theory and a maximum entropy procedure, and provide a physical interpretation of the model parameters. Finally, we demonstrate the capability of the considered class of random fields to generate higher levels of statistical fluctuations for selected stochastic principal permeabilities. This unique flexibility offered by the parameterization of the model opens up many new possibilities for both forward simulations (e.g. for uncertainty propagation in predictive simulations) and stochastic inverse problem solving. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
5.
Aquifer properties, for example permeability and porosity, vary in space and may be characterized by their distributions. The property distribution is not totally random but shows some correlation structure. Because most of the values are not known, some rational method is required to generate credible aquifer distribution properties for inclusion in fluid transport models. This paper presents a numerically efficient method of generating geostatistical random fields, by the source Point Method (SPM). The SPM is a very efficient method and requires little computer time and relatively small data storage, as compared to other methods of generating random fields. In addition, the SPM is modified to include any desired amount of anisotropy in the property distribution of a system. By using conditional covariances, a formula for a two-dimensional anisotropic field is derived to prespecify the desired correlation length in any direction. Results show that for an anisotropic medium the correlation length can be pre-specified in any specific direction. 相似文献
6.
Using the results of the first paper in this series, which dealt with an inverse procedure for hydrocarbon generation, this paper focuses on case histories and numerical implementation of the model. Experimental data on residual kerogen analysis have been used with the inverse procedure to examine the applicability of the model to hydrocarbon generation directly from the degradation of kerogen, and to derive the kinetic parameters for the construction of a prediction equation. Energy-dependent channeling probability distributions are used to exhibit the stability of the model in describing the processes of kerogen degradation. The numerical methods for the solution of the inverse procedure and a sensitivity analysis are also discussed. 相似文献
7.
In petroleum exploration and production, it is essential to have good estimations of the uncertainties on the reserves. Uncertainties
on the velocity model used during the data processing are of major importance in this estimation. The generation of several
velocity fields gives access to a quantified estimation of the uncertainties due to the velocity model inversion. The use
of statistical methods helps in generating several important, equiprobable velocity fields, matching all the available velocity
information. This paper presents an efficient simulation algorithm to generate instantaneous velocity fields, constrained
by the distribution of values measured at the wells, and calibrated by the stacking velocities, taken as root-mean-square
velocities. The simulations also match the covariance model given for the instantaneous velocity fields. The method is developed
in a simple one-layer case with constant velocity, and then extended to more realistic situations. Finally, a real data application
is shown, using data provided by ENI–Agip Division, and the efficiency of the proposed simulation method is discussed. 相似文献
8.
We consider point processes defined on the space–time domain which model physical processes characterized qualitatively by the gradual increase over time in some energy until a threshold is reached, after which, an event causing the loss of energy occurs. The risk function will, therefore, increase piecewise with sudden drops in correspondence to each event. This kind of behaviour is described by Reid's theory of elastic rebound in the earthquake generating process where the quantity that is accumulated is the strain energy or stress due to the relative movement of tectonic plates. The complexity and the intrinsic randomness of the phenomenon call for probabilistic models; in particular the stochastic translation of Reid's theory is given by stress release models. In this article we use such models to assess the time-dependent seismic hazard of the seismogenic zone of the Corinthos Gulf. For each event we consider the occurrence time and the magnitude, which is modelled by a probability distribution depending on the stress level present in the region at any instant. Hence we are dealing here with a marked point process. We perform the Bayesian analysis of this model by applying the stochastic simulation methods based on the generation of Markov chains, the so called Markov chain Monte Carlo (MCMC) methods, which allow one to reconcile the model's complexity with the computational burden of the inferential procedure. Stress release and Poisson models are compared on the basis of the Bayes factor. 相似文献
9.
Surendra P. Verma Lorena Díaz-González Rosalinda González-Ramírez 《Geostandards and Geoanalytical Research》2009,33(1):29-49
Numerous studies report geochemical data on reference materials (RMs) processed by outlier-based methods that use univariate discordancy tests. However, the relative efficiency of the discordancy tests is not precisely known. We used an extensive geochemical database for thirty-five RMs from four countries (Canada, Japan, South Africa and USA) to empirically evaluate the performance of nine single-outlier tests with thirteen test variants. It appears that the kurtosis test (N15) is the most powerful test for detecting discordant outliers in such geochemical RM databases and is closely followed by the Grubbs type tests (N1 and N4) and the skewness test (N14). The Dixon-type tests (N7, N8, N9 and N10) as well as the Grubbs type test (N2) depicted smaller global relative efficiency criterion values for the detection of outlying observations in this extensive database. Upper discordant outliers were more common than the lower discordant outliers, implying that positively skewed inter-laboratory geochemical datasets are more frequent than negatively skewed ones and that the median, a robust central tendency indicator, is likely to be biased especially for small-sized samples. Our outlier-based procedure should be useful for objectively identifying discordant outliers in many fields of science and engineering and for interpreting them accordingly. After processing these databases by single-outlier discordancy tests and obtaining reliable estimates of central tendency and dispersion parameters of the geochemical data for the RMs in our database, we used these statistical data to apply a weighted least-squares linear regression (WLR) model for the major element determinations by X-ray fluorescence spectrometry and compared the WLR results with an ordinary least-squares linear regression model. An advantage in using our outlier procedure and the new concentration values and uncertainty estimates for these RMs was clearly established. 相似文献
10.
11.
Stochastic fractal (fGn and fBm) porosity and permeability fields are conditioned to given variogram, static (or hard), and multiwell pressure data within a Bayesian estimation framework. Because fGn distributions are normal/second-order stationary, it is shown that the Bayesian estimation methods based on the assumption of normal/second-order stationary distributions can be directly used to generate fGn porosity/permeability fields conditional to pressure data. However, because fBm is not second-order stationary, it is shown that such Bayesian estimation methods can be used with implementation of a pseudocovariance approach to generate fBm porosity/permeability fields conditional to multiwell pressure data. In addition, we provide methods to generate unconditional realizations of fBm/fGn fields honoring all variogram parameters. These unconditional realizations can then be conditioned to hard and pressure data observed at wells by using the randomized maximum likelihood method. Synthetic examples generated from one-, two-, and three-dimensional single-phase flow simulators are used to show the applicability of our methodology for generating realizations of fBm/fGn porosity and permeability fields conditioned to well-test pressure data and evaluating the uncertainty in reservoir performance predictions appropriately using these history-matched realizations. 相似文献
12.
中西部前陆盆地天然气勘探前景 总被引：13，自引：0，他引：13
本在对中西部分布的前陆盆地天然气资源、已发现气田储量和近期天然气勘探进展等方面分析的基础上，指出前陆盆地蕴藏着丰富的天然气资源，是今后天然气勘探的重点地区。并从气源条件、生储盖组合、圈闭、运移通道等方面论述了前陆盆地具有利的天然气成藏条件。 相似文献
13.
In an effort to develop and improve potential geophysical field interpretation we suggest that the singularity method should be extended toward areal data. This procedure enables mass and fast calculation of singularities in area and stable solutions. Studying the behavior of model fields and localization of singularities in the phase planes of vector fields permits the use of findings in interpreting geopotential fields. Model and real-life cases of this procedure as applied to tectonic dislocations and local geologic features are exemplified. We show that the proposed procedure significantly enhances the application of the singularity method to interprete geopotential fields. 相似文献
14.
G K Rangarajan 《Journal of Earth System Science》1992,101(4):329-338
Wiener filters are derived from the horizontal field data of two adjacent equatorial electrojet stations, Adis Ababa and Trivandrum
from several sequences of quiet days. The time invariant property of the filter is established and the filter is applied to
conditions marked by afternoon counter electrojet events. The prediction efficiency is shown to be consistently high. Possible
uses of this technique in studies related to generating mechanisms of counter electrojet events and the day-to-day variability
in electrojet currents are indicated. Inter-relationships and day-to-day variability of different components of the fields
at the two stations are highlighted. 相似文献
15.
Flow of fluids and transport of solutes in porous media are subjects of wide interest in several fields of applications: reservoir
engineering, subsurface hydrology, chemical engineering, etc. In this paper we will study two-phase flow in a model consisting
of two different types of sediments. Here, the absolute permeability, the relative permeabilities and the capillary pressure
are discontinuous functions in space. This leads to interior boundary value problems at the interface between the sediments.
The saturation Sw will be discontinuous or experience large gradients at the interface. A new solution procedure for such problems will be
presented. The method combines the modified method of characteristics with a weak formulation where the basis functions are
discontinuous at the interior boundary. The modified method of characteristics will provide a good first approximation for
the jump in the discontinuous basis functions, which leads to a fast converging iterative solution scheme for the complete
problem.
The method has been implemented in a two-dimensional simulator, and results from numerical experiments will be presented.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
16.
The mechanisms generating the charges/potentials and abnormal electromagnetic radiation that accompany earthquakes have been discussed based on observational, theoretical and laboratory studies, in particular over the last few decades. We previously conducted stick‐slip tests using precut granite cores with a contact electrode on the sample side, and proposed that surface charges released from charge trapping centres on sheared asperities are a possible source of the above‐mentioned charges or potentials. Here we discuss seismo‐electric and magnetic fields formed by the surface charges, and derive their scaling laws with the earthquake magnitude at a distance. According to our model, detectability of these fields at a point on the ground surface depends strongly on wet/dry condition at a fault zone (sheared asperities). 相似文献
17.
为了揭示河床沉积物非均质性对潜流交换的影响,构建了沙波地形作用下的地表水-地下水耦合模型,通过生成不同的渗透系数随机场,讨论了不同地表水动力过程和河床沉积物非均质性对潜流交换通量、交换空间及平均停留时间的影响规律。结果表明,所构建的地表水-地下水耦合模型能够准确刻画水沙界面附近流场,模型具有良好的适用性;均质或非均质河床沉积物情景下,水沙界面上的平均交换通量、停留时间与雷诺数之间均呈现幂函数关系,潜流交换深度则在地表水进入完全紊流之后趋于稳定。结果还表明,较强的河床沉积物非均质性能够有效增强水沙界面上潜流交换通量和空间交换频率,但会制约潜流交换空间并缩短水流在潜流带中的停留时间。 相似文献
18.
A new approach for calculating strain for particulate media 总被引：1，自引：0，他引：1
Discrete element modelling is a viable alternative to conventional continuum‐based analysis for analysing problems involving localized deformations of particulate media. However, to aid in the interpretation of the results, it is useful to express the results of discrete element analyses in terms of the continuum parameters of stress and strain. A number of homogenization methods have been proposed to calculate strain in discrete systems; however, two significant limitations of these methods remain. First, none of these methods incorporate particle rotation effects satisfactorily, although significant particle rotation occurs in shear bands in both physical tests and numerical simulations of granular materials. Additionally, observations of the particle displacement fields in shear bands in granular materials indicate that the displacements within the localizations are erratic. Consequently, existing linear, local interpolation approaches produce substantial variations in the strain values calculated in adjacent elements in the region of localization, hindering clear visualization of the strain localization as it evolves. A new method of domain discretization for calculating strain is proposed. This method is capable of capturing particle rotation and employs a non‐local meshfree interpolation procedure capable of smoothing the erratic displacements in strain localizations, which better defines their evolution. The proposed method is validated for problems involving both two and three dimensions. A number of methods are compared with the proposed method and pertinent insights are made. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
19.
非饱和-非稳定渗流条件下的边坡临界滑动场 总被引：1，自引：0，他引：1
受季节性降雨或水库运行的影响,岸坡外水位及坡内孔隙水压力场的变化较大,不利于岸坡的稳定性。在水位变化过程中,利用非饱和-非稳定渗流有限元计算得到孔隙水压力场,基于非饱和土的渗流和抗剪强度理论,对水位变化过程中的边坡临界滑动场法进行改进,提出可考虑水位变化与岸坡非饱和-非稳定渗流过程的边坡临界滑动场数值模拟方法。将改进后的水位变化过程中的边坡临界滑动场法分别应用于黏土、粉土岸坡在水位升降过程中的稳定性分析,研究了水位升降速率及基质吸力对岸坡稳定性的影响,并揭示了边坡在水位变化过程中的稳定性变化历程。研究表明,该方法计算结果合理、可靠,更适用于涉水边坡的稳定性计算,且岸坡稳定性变化历程受水位升降速率、基质吸力等多种因素共同影响,只有在考虑非稳定渗流的基础上同时考虑基质吸力的作用才能正确得出水位变化过程中岸坡稳定性变化规律和实质。 相似文献
20.
南美洲被动大陆边缘盆地的油气地质特征 总被引：3，自引：2，他引：1
南美洲被动大陆边缘盆地是目前世界油气勘探最活跃的地区之一。南美洲被动大陆边缘盆地形成于晚侏罗世-早白垩世冈瓦纳大陆的裂解,经历了前裂谷期、同裂谷期、过渡期、后漂移期4个阶段,发育了多套生储盖组合。其中同裂谷期的湖相源岩为最重要的生油岩,过渡期发育的盐岩层对油气的成藏起着关键作用。近年来,发现的大油气田均位于盐下同裂谷期的陆相碎屑岩和湖相碳酸盐岩储层中。南美东部被动大陆边缘盆地可以按油气潜力分为3类,最有潜力区位于巴西东海岸的中南部盆地群。随着油气勘探技术的进步,在本区进行油气藏勘探具有广阔的前景。 相似文献