Accurate local upscaling with variable compact multipoint transmissibility calculations

We propose a new single-phase local upscaling method that uses spatially varying multipoint transmissibility calculations. The method is demonstrated on two-dimensional Cartesian and adaptive Cartesian grids. For each cell face in the coarse upscaled grid, we create a local fine grid region surrounding the face on which we solve two generic local flow problems. The multipoint stencils used to calculate the fluxes across coarse grid cell faces involve the six neighboring pressure values. They are required to honor the two generic flow problems. The remaining degrees of freedom are used to maximize compactness and to ensure that the flux approximation is as close as possible to being two-point. The resulting multipoint flux approximations are spatially varying (a subset of the six neighbors is adaptively chosen) and reduce to two-point expressions in cases without full-tensor anisotropy. Numerical tests show that the method significantly improves upscaling accuracy as compared to commonly used local methods and also compares favorably with a local–global upscaling method.     

Micromechanical approach to unsaturated water flow in structured geomaterials by two-scale computations

This article presents a micromechanical approach to the problem of unsaturated water flow in heterogeneous porous media in transient conditions. The numerical formulation is based on the two-scale model obtained previously by periodic homogenization. It allows for a coupled solution of the non-linear flow equations at macroscopic and microscopic scales and takes into account the macroscopic anisotropy of the medium and the local non-equilibrium of the capillary pressure. The model was applied to simulate two-dimensional water infiltration at constant flux into an initially dry medium containing inclusions of square and rectangular shapes. The numerical results showed the influence of the inclusion–matrix conductivity ratio and the local geometry on the macroscopic behavior. The influence of the conductivity ratio manifested itself by the acceleration or retardation of the onset of the macroscopic water flux at the outlet, while the local geometry (anisotropy) significantly affected the macroscopic spatial distribution of the water flux. Such type of approach can be extended to simulate coupled phenomena (for example hydro-mechanical problems) with evolving local geometry.     

Reservoir description using dynamic parameterisation selection with a combined stochastic and gradient search

There is a correspondence between flow in a reservoir and large scale permeability trends. This correspondence can be derived by constraining reservoir models using observed production data. One of the challenges in deriving the permeability distribution of a field using production data involves determination of the scale of resolution of the permeability. The Adaptive Multiscale Estimation (AME) seeks to overcome the problems related to choosing the resolution of the permeability field by a dynamic parameterisation selection. The standard AME uses a gradient algorithm in solving several optimisation problems with increasing permeability resolution. This paper presents a hybrid algorithm which combines a gradient search and a stochastic algorithm to improve the robustness of the dynamic parameterisation selection. At low dimension, we use the stochastic algorithm to generate several optimised models. We use information from all these produced models to find new optimal refinements, and start out new optimisations with several unequally suggested parameterisations. At higher dimensions we change to a gradient-type optimiser, where the initial solution is chosen from the ensemble of models suggested by the stochastic algorithm. The selection is based on a predefined criterion. We demonstrate the robustness of the hybrid algorithm on sample synthetic cases, which most of them were considered insolvable using the standard AME algorithm.     

小波变换在少震、弱震区地下水位数据分析中的应用

利用小波变换和多尺度分析原理，对位于少震弱震区的湖南的具有不同变化形态的6口典型井4年的水位日均值序列进行了分析。结果显示，通过多尺度分析可以很方便地将水位日均值序列中的高频部分与低频部分分开，而且对不同井孔的含水层系统而言，分离出去的频率成分的主模是不同的，这反应出不同井孔的含水层系统对同一频率的响应存在差异，主模的频率反映了正常背景下井孔－含水层系统的优势频率。Morlet小波分析的结果对时间序列的突然变化和周期结构都有很好的反映。     

Multiscale geographically and temporally weighted regression: exploring the spatiotemporal determinants of housing prices

Understanding scale effects is important and indispensable for geography studies. However, spatial and spatiotemporal statistical tools for measuring the operational scales of different processes are rather limited. This article extends the popular geographically and temporally weighted regression (GTWR) model to consider operational scale effects by proposing multiscale GTWR (MGTWR), which offers a flexible and scalable framework for identifying and analysing multiscale processes by specifying flexible bandwidths for various covariates. Then, MGTWR is employed to explore spatiotemporal variations and how influential factors are associated with housing prices in Shenzhen. This article attempts to extend GTWR to MGTWR in consideration of scale effects, thereby highlighting the importance of different levels of spatiotemporal heterogeneity. Furthermore, the empirical results of this study can provide valuable policy implications for real estate development in areas where urban planning should address multiscale effects in both temporal and spatial dimensions.     

求解地震静校正问题的双尺度反演方法

通过对地震静校正问题的分析,综合线性反演方法的计算速度快和非线性反演方法寻找全局最优解能力强的优点,提出了求解地震静校正问题的双尺度反演方法.在大尺度下采用非线性反演方法为小尺度下的线性反演计算初始模型,利用小尺度下的线性反演方法获得精细模型.对反演参数的选取进行了讨论,使双尺度反演算法具有自适应的特点.理论模型和实际资料的计算表明该方法计算结果精度高、计算速度快.     

A practical co-simulation approach for multiscale analysis of geotechnical systems

The particulate nature of granular soils can be accurately simulated at a microscale level. However, due to the huge spatial extent of geotechnical systems, a model fully constructed at such a scale is almost impossible with current computing technologies. Hence, continuum-based approaches are considered as the practical scale for modeling the majority of problems. Combining both scales enables benefiting from the advantages of both techniques while trying to overcome their drawbacks. Although a significant number of publications have addressed coupling both scales, only a few provide information regarding implementing the proposed procedures. In this study, an efficient co-simulation framework for conducting multiscale analysis is introduced. The framework is based on integrating existing continuum and micromechanical modeling software packages and therefore benefitting from already existing codes. A computational simulation of a rigid pile in contact with granular soil demonstrating the capabilities of such technique is presented. The near-field zone surrounding the pile is modeled using DEM whereas FEM is utilized to model far-field zones that are not affected by the presence of the pile. Results of conducted simulations resemble those obtained from experimental results. The proposed approach appears to be a very effective and promising tool to model boundary value problems of geotechnical systems.     

东亚地区南北两个风暴源地中风暴的结构和动力学差异

基于欧洲中心中期天气预报再分析资料(ERA-40),使用涡旋追踪和合成技术、多尺度子空间变换以及局地多尺度能量分析方法研究了东亚地区南北两个风暴源地中风暴的差异。结果发现,南、北两个源地风暴在结构上和内部动力过程上均存在着显著不同。南支源地(40°N以南)风暴底层比高层强,与线性斜压模式中的最不稳定模态结构相似;而北支源地(40°N以北)风暴则正好相反,与下游发展理论所描述的斜压波结构相似。并且发现,南支源地风暴的非地转风场比北支源地风暴的强。能量学诊断结果显示,南支源地风暴的能量源除了斜压不稳定外,有很大一部分来自正压不稳定,而北支源地风暴中则是存在弱的动能逆尺度传输。此外,南支源地风暴的浮力转换和非绝热做功均比北支源地风暴的强,其主要原因是南支源地风暴的垂直运动更强,风暴中的水汽更加充足。      

小波变换多尺度地震波形反演

完全非线性地震波形反演问题是石油地球物理勘探领域中一个非常重要而又难度很大的问题。本文提出了多尺度地震波形反演的小波变换方法,对于一维非线性地震波形反演问题,将该方法和已有的简单迭代法及多重网格法作了比较,数值实验结果表明,本方法效果较好。     

广州气温与厄尔尼诺的多尺度相互联系

通过对广州气温距平和Ｎｉｎｏ　３、Ｎｉｎｏ　１＋２区ＳＳＴＡ序列做小波变换,研究了广州气温变化与ＥＮＳＯ振荡过程之间的多尺度联系,发现它们都存在着强的十年际振荡。年际尺度的振荡为正相关,十年际风度为负相关。由于ＳＳＴＡ的十年际变率是由强厄尔尼诺事件的韵律产生的,因此;广州气温对强烈厄尔尼诺的响应性质上不同于对普通厄尔尼诺的响应．