基于CoupModel的青藏高原多年冻土区土壤水热过程模拟

近年来, 青藏高原多年冻土区生态环境呈现出逐年恶化趋势, 从而对多年冻土活动层水热过程造成显著影响. 此外, 如何构建更加有效、 针对寒区的陆面过程模式成为寒区研究的重点、 热点之一. 作为一种有效的参数估计方法, Bayes参数估计算法具有准确估计陆面过程模式参数的能力. 因此, 基于2005-2008年观测数据, 利用CoupModel模型对青藏高原风火山流域土壤水热运移过程进行模拟; 同时, 利用Bayes参数估计方法估计部分水热运移参数. 结果显示: 模型对土壤温度(ST)的模拟效果较好, NSE系数均在0.90以上; 也能够较好模拟浅层(0~40 cm)土壤水分, NSE值均达到0.80以上, 而对40 cm以下土壤水分的模拟结果较差. 模型也能够较准确模拟活动层土壤的冻结-融化过程. 模型对温度水分极值和40 cm深度以下水分的模拟存在一些偏差. 值得一提的是, 基于重要性采样MCMC方案的Bayes参数估计算法能够有效估计水热运移参数, 模型模拟结果得到极大的改进. Bayes算法能够广泛解决陆面过程模式参数估计问题.     

Hierarchical object-based stochastic modeling of fluvial reservoirs

This paper describes a novel approach to modeling braided stream fluvial reservoirs. The approach is based on a hierarchical set of coordinate transformations involving relative straingraphic coordinates, translations, rotations, and straightening functions. The emphasis is placed on geologically sound geometric concepts and realistically-attainable conditioning statistics including areal and vertical facies proportions. Modeling proceeds in a hierarchical fashion, that is (1) a stratigraphic coordinate system is established for each reservoir layer, (2) a number of channel complexes are positioned within each layer, and then (3) channels are positioned within each channel complex. The geometric specification of each sand-filled channel within the background of floodplain shales is a marked point process. Each channel is marked with a starting location, size parameters, and sinuosity parameters. We present the hierarchy of eight coordinate transformations, introduce an analytical expression for the channel cross-section shape, describe the simulation algorithm, and demonstrate how the realizations are made to honor local conditioning data from wells and global conditioning data such as areal and vertical proportions.     

Modeling of Fluvial Reservoirs with Object Models

An object model for fluvial reservoirs that has been developed from 1985 to present is described. It uses a formal mathematical object model (marked point process) describing the distributions of four facies: channel, crevasse, barrier, and background. Realisations from the model are generated using the Metropolis-Hastings simulation algorithm with simulated annealing conditioning on the volume ratios and well observations. The main challenge has been to find a suitable parameterization of the geology of fluvial reservoirs, and to find and implement the generating function of the channels in the simulation algorithm. The model and simulation algorithm can be conditioned on arbitrary well paths including horizontal wells and paths with partly missing observations, well test data, well contacts, seismic data, and general geological knowledge.     

Well Conditioning in Object Models

This paper presents two object models with corresponding simulation algorithms, which aim to condition well data correctly while still converging in reasonable time. The first model is devoted to fluvial channels and the second one is mainly intended for smaller objects. To verify the conditioning, a method for validating well conditioning algorithms for object models is given. The purpose is to determine the extent to which the well conditioning introduces a bias in the models. To do this, we check that the double expectation of a parameter conditioned to wells is equal to the unconditional expectation. This method is applied to two different object models. Both the conditioning algorithms presented here give good results using this test.     

基于过程对象的地表覆盖变化时空过程表达模型

时空过程表达是时空数据分析、规律发掘等研究热点的基础。本文从土地利用/地表覆盖变化(land use/cover change,LUCC)时空数据分析和规律发掘应用角度出发,提出了一种基于过程对象的时空过程表达模型,阐述了该模型的时空过程判定方法和存储管理方法。该模型将地表覆盖斑块看作时空对象,将斑块自身变化和相互转化以对象时空过程的形式表达;通过时空过程的组合来表达空间范围更广的时空变化,使斑块变化与景观格局总体变化联系起来。该模型可用于面状地理实体的时空演变模拟和变化规律挖掘等。通过对黑龙江大兴安岭地区地表覆盖时空过程对象的建立、检索与分析,验证了模型的有效性。     

A Connectivity Index for Discrete Fracture Networks

Connectivity is an important measure for assessing flow transport in rock, especially through fractures. In this paper, rock fracture systems are modelled by a discrete fracture model simulated by a marked point process. A connectivity index is then introduced to quantify the connectivity between any two points in space. Monte Carlo simulation is used to evaluate the connectivity index for stationary cases and relationships between the connectivity index and the parameters of the discrete fracture model are analysed. The average number of intersections per fracture, X_f, and the fracture intensity, P12 (P32), are calculated and the relationships between these parameters and the connectivity index are investigated, concluding that X_f is the more suitable parameter for the classification of rock mass flow properties. The relationships between the connectivity index and the percolation state of the fractured medium are also discussed. An edge correction is briefly discussed and a practical example is used to demonstrate the method of computing the connectivity index.     

锦屏二级水电站岩石夹层非定常参数剪切蠕变模型及参数识别研究

通过对锦屏二级水电站岩石夹层的剪切蠕变试验结果分析,提出了非定常参数的Burgers蠕变模型。由于对部分参数考虑了其值随时间改变的特性,该模型不仅能够反映岩石夹层的加速蠕变过程,而且能比定常参数Burgers模型更好地描述初始蠕变和稳态蠕变过程。由于非定常参数Burgers模型的参数较多,参数辨识不宜采用迭代法或者最小二乘法等线性优化方法,而采用基于随机搜索的粒子群算法,并取得了较好的效果。     

岩石剪切断裂面接触算法的开发与应用

为了克服现有数值计算方法在计算复杂断裂面接触滑移过程中效率低的问题，通过吸收边界元的建模思想，提出了新的数值计算方法。在该算法中，所有网格均位于岩块的边界，利用显示差分方法计算得到岩块之间的相互作用力以及岩块的位移量。利用“小球在抛物面上滑移”、“哑铃在不同倾角的斜面上”两个模拟试验对文中的算法进行验证，同时利用文中算法与有限元算法对直剪试验进行模拟。结果表明：算法能够准确描述物体之间的相互接触，准确计算得到接触块体之间的法向位移。算法能够准确判断出接触物体的“滑移状态”和“稳定状态”，摩擦力的数值计算结果与解析解的误差小于10?10。在计算断裂面接触和剪应力变化规律时，算法与有限元算法的计算结果一致，但文中计算方法的效率显著提高。     

Influence of object concentration on finite strain and effective viscosity contrast: insights from naturally deformed packstones

Deformed conglomerates and ooidal/oncoidal packstones are commonly used to evaluate finite strain in deformed sedimentary successions. In order to obtain a correct estimate of finite strain, it is necessary to consider not only the different behaviour of matrix and objects, but also object concentration. The analysis of two-component rocks characterised by high values of packing commonly results in a substantial underestimate of bulk strain and of viscosity contrast between objects and matrix. In this study, the effects of the volumetric fraction of competent inclusions on both object and bulk measured finite strain, as well as on apparent viscosity contrast, have been investigated in naturally deformed packstones characterised by variable object concentration on the scale of the hand specimen (and hence for homogenous viscosity contrast). Object finite strain has been obtained by Rf/ analysis, whereas the Fry method provides a measure of whole-rock strain that is also a function of inclusion concentration. Therefore, the finite strain measured by the Fry method is better termed effective bulk strain. In order to investigate the role of object concentration, this parameter has been plotted against object and effective bulk strain, and also against viscosity contrast. These diagrams show that: (i) for high values of packing, measured object and effective bulk strain show values that are significantly lower with respect to the calculated maximum value (that would result in the ideal case of no particle interaction and represents therefore the real bulk strain of the samples); (ii) the viscosity contrast shows lower values with respect to the calculated maximum one (that is equal for the three principal sections of the finite strain ellipsoid), and as packing reaches the maximum value, the viscosity contrast approaches a unit value. Empirical equations have also been found that link object concentration with both object and effective bulk finite strain.     

Peridynamics simulations of geomaterial fragmentation by impulse loads

In this work, we have developed nonlinear peridynamics models of drained and saturated geomaterials, and applied them to simulations of dynamic fragmentation and ejecta formation due to impulse loads. First, we have re‐phrased and re‐interpreted the non‐local state‐based peridynamics formulation to connect the non‐local integral operator with the local differential operator. Second, we have implemented the Drucker–Prager plasticity model in state‐based peridynamics at finite strain. A peridynamics version of the Hughes and Winget algorithm is derived for the constitutive update. Third, we have developed a peridynamics U‐p formulation for saturated geomaterials. Fourth, numerical simulations have been carried out to verify the proposed peridynamics formulations in the simulation of geomaterial fragmentation induced by impulse loads. Comparisons of analytical and numerical results indicate that the peridynamics model has the ability to both match traditional continuum compression examples, as well as simulate complex geomaterial fragmentation processes resulting from impulse loads. Copyright © 2015 John Wiley & Sons, Ltd.     

Simulation Experiments of Land Surface Physical Processes and Ecological Effect over Different Underlying Surface

Based on the existing Land Surface Physical Process Models(Deardorff, Dickinson, LIU, Noilhan, Seller, ZHAO), a Comprehensive Land Surface Physical Process Model (CLSPPM) is developed by considering the different physical processes of the earth‘s surface-vegetation-atmosphere system more completely. Compared with SiB and BATS, which are famous for their detailed parameterizations of physical variables, this simplified model is more convenient and saves much more computation time. Though simple, the feas...     

Least-squares center-to-center and mean object ellipse fabric analysis

The subjectivity of ellipse fitting in many strain techniques has hindered the determination of fabric anisotropy and tectonic strain. However, many sets of x, y co-ordinates can be approximated as an ellipse using a least-squares algorithm to calculate a best-fit ellipse and associated average radial error. For instance, the two dimensional shape of many objects can be approximated as an ellipse by entering digitized co-ordinates of the object margin into the ellipse algorithm.The rim of maximum point density in a normalized Fry diagram is defined by normalized center-to-center distances between touching or nearly touching objects. The enhanced normalized Fry (ENFry) method automates ellipse fitting by entering center-to-center distances between these “touching” objects into the least-squares ellipse algorithm. For homogeneously deformed populations of 200 objects, the ENFry method gives an accurate and precise measure of whole-rock fabric anisotropy, particularly for low ellipticities. When matrix strain exceeds clast strain, manual ellipse fitting of normalized Fry plots gives more accurate matrix anisotropies.The mean object ellipse (MOE) method calculates the best-fit ellipse from the geometry of the objects. Three points from the margin of each object ellipse, centered at the origin and expanded or reduced to unit volume, are used to calculate the best-fit fabric ellipse. The MOE method is very precise for small data sets, making it a good method for mapping heterogenous object strain. However, least-squares calculations maximize the influence of distal and spurious ellipticities, causing the MOE method to overestimate the fabric ellipticity of most aggregates.     

A surrogate-based simulation–optimization approach application to parameters’ identification for the HydroGeoSphere model

A systematic approach is needed to use water more productively, because water shortages limit socio-economic development in many parts of the world. The aim of this paper is to establish a surrogate-based simulation–optimization approach to identify parameter values for a fully integrated surface water and groundwater flow coupling simulation. A surface water and groundwater flow coupling simulation model was implemented using HydroGeoSphere (HGS) model and the parameter sensitivities in the model were analyzed using local sensitivity analysis method. The parameters that exerted a large influence on the output results of the HGS model were then selected as stochastic variables, and the stochastic variable data sets were generated using the latin hypercube sampling (LHS) method, which, thereby, were used as inputs in HGS model to obtain the corresponding outputs. On the basis of input and output data sets, a kriging surrogate model of the HGS model was then established and verified, and parameter values of HGS model were identified using a surrogate-based simulation–optimization approach. The results of this study show that parameters that exert a large influence on the simulation output results include hydraulic conductivity, porosity, the van genuchten parameter (\(\alpha\)), and channel manning coefficient. The established kriging surrogate model is an ideal alternative to the HGS model for simulating and predicting, while optimal parameter values can be identified effectively and accurately using the established approach. The results of this research reveal that huge computational loads can be mitigated while using the kriging surrogate as an alternative for a simulation model in the solution process of optimization model.     

应用数值模拟研究神狐海域水合物第一次试采数据

2017年神狐海域第一次试开采成功后,许多学者应用数值模拟对试采数据进行研究,但模拟结果与实际试采数据存在偏差.为了探求原因,本研究建立了二维柱坐标系下水合物降压开采数学模型,开发了相应的程序,能够模拟渗透率等储层参数非均匀分布条件下开采过程,同时能够模拟开采井压力等动态参数对开采过程的影响.通过数值实验,得出偏差原因:（1）泥质粉砂型储层存在水敏性,水合物分解产生的淡水引起粘土膨胀,使渗透率下降;（2）须将开采井压力作为动态输入参量.据此,修正了渗透率模型,考虑了开采井压力随时间的变化,得到的模拟产气量与试采数据十分接近,使降压开采数值模拟更逼近实际情况.      

Corner points localization in electronic topographic maps with deep neural networks

Digitized topographic maps normally have to go through the geometric calibration before practical utilization. Nowadays, the reference points for the calibration are still manually assigned. Corner points (graticule intersections) in a map are usually good candidates in favor of the reference points. This paper proposes an algorithm for automatically locating the corner points in the electronic topographic maps by detecting the specific rectangle objects in the map corners. It assigns the probabilities to each row and column in the region of interests (RoIs) to provide information regarding the location of the objects. In order to facilitate the object detection with high level visual features, the deep neural networks (DNNs) are employed in the proposed algorithm. For the object proposal, the sliding window scheme is adopted. The experimental results indicate that the proposed approach outperforms the conventional bounding-box regression method in both detection and localization accuracy. For the proposed algorithm, the average F1 score in the object detection is 0.91, which is 12% higher than the conventional model. The mean Euclidean distance between the predicted corner points and the ground-truth by the proposed algorithm is 2.22 pixels, 35.8% lower compared with the regression based model.     

Generalized cross-covariances and their estimation

Generalized cross-covariances describe the linear relationships between spatial variables observed at different locations. They are invariant under translation of the locations for any intrinsic processes, they determine the cokriging predictors without additional assumptions and they are unique up to linear functions. If the model is stationary, that is if the variograms are bounded, they correspond to the stationary cross-covariances. Under some symmetry condition they are equal to minus the usual cross-variogram. We present a method to estimate these generalized cross-covariances from data observed at arbitrary sampling locations. In particular we do not require that all variables are observed at the same points. For fitting a linear coregionalization model we combine this new method with a standard algorithm which ensures positive definite coregionalization matrices. We study the behavior of the method both by computing variances exactly and by simulating from various models.     

Summary and Prospects of Numerical Simulation Research of the Atmospheric Boundary Layer

As an important bridge between the underlying surface and the free atmosphere, the atmospheric boundary layer is not only closely related to the development of various weather processes, but also plays a key role in local and regional weather and climate changes. In view of the complexity of the atmospheric boundary layer, the numerical simulation of the atmospheric boundary layer has always been a hotspot and difficulty in the numerical simulation research of the atmosphere. In this paper, the three numerical model development stages of the atmospheric boundary layer in recent decades were summarized and the important advances in arid and semi-arid areas, Tibet Plateau, urban complex underlying surface, and special typhoon boundary layer were reviewed. At present, there are still five scientific problems to be solved urgently, including cloud and boundary layer interaction, boundary layer parameterization, model resolution, boundary layer data assimilation and boundary layer development mechanism. Moreover, it was pointed out that in this field we need to strengthen the understanding of different types of atmospheric boundary layer processes, boundary layer bottom and top interface exchange, boundary layer development mechanism in special regions, improve boundary layer parameterization scheme and give full play to the advantages of LES in boundary layer simulation.     

基于遗传算法的新安江模型日模拟参数优选研究

在概念性水文模型的参数率定中,目前还没有一个传统优化方法能够提供保证足够高效和稳定性的算法。为了克服传统优化方法中局部收敛性的缺点,近年来利用遗传算法通过计算机准确稳定地进行概念性水文模型的参数优选的尝试得到越来越多的重视和发展。目前优选水文模型待定参数,大多是从次洪模型的方面去讨论,有关日模拟模型的遗传算法参数优选讨论的较少。本文系统分析了基于遗传算法的新安江模型日模拟参数的自动优选,同时针对遗传算法在模型参数众多的情况下时间效率低下问题,通过利用新安江模型参数分层原理与模型参数敏感性分析对优选结果影响,提出一套简化的日模型参数遗传算法优选方案。经过流域模拟检验,该优选方案可行,运行效率高,可以作为类似模型遗传算法参数率定快速、有效的方案。     

Soil Moisture Parameterization and Its Influences in Weather and Climate Simulation: A Review

The soil hydrological process in land surface models and its influences on weather and climate simulation have got much attention by scholars both at home and abroad. First, this paper traced the definition and determination of soil moisture, and then reviewed its parameterization in different models, including soil-water characteristic curves for different soil types and numerical methods for solving soil moisture equations. Moreover, methods of soil hydrological parameter determination and uncertainties within land surface models were specified. Also, the importance of methods in parameter sensitivity analysis and optimization was emphasized, and the new datasets of soil hydraulic parameters would play a very important role in the improvement of the land surface model and soil moisture simulation. Finally, the research progress of feedback mechanism between soil moisture and precipitation was summarized. Spatial and temporal distribution of soil moisture and its abnormal would cause a positive feedback, and on the contrary, the meso-scale characteristics of soil moisture distribution had a negative feedback. By summarizing the progresses of the uncertainties and problems in soil moisture simulation, the influences of soil moisture on simulating weather and climate were pointed out.     

基于对偶加权后验误差估计的2.5维直流电阻率自适应有限元正演

采用易于模拟复杂地形起伏和倾斜界面的非结构三角单元剖分网格,并利用对偶加权后验误差估计指导网格自动细化过程,实现了2.5维直流电阻率法自适应有限元数值模拟。在实例模型分析中,分别计算了层状模型和垂直岩脉模型的直流电阻率响应,并与其解析解进行了比较。对比结果表明,该算法所得数值解精度很高,解的相对误差小于0.5%。最后,计算了起伏地形2.5维地电模型视电阻率异常,并利用比较法进行了地形改正。地形改正结果与水平地形时的结果对比表明,比较法可以较好地消除地形影响,突出局部地质体异常。