Applying a real‐coded multi‐population genetic algorithm to multi‐reservoir operation

The primary objective of this study is to propose a real‐coded hypercubic distributed genetic algorithm (HDGA) for optimizing reservoir operation system. A conventional genetic algorithm (GA) is often trapped into local optimums during the optimization procedure. To prevent premature convergence and to obtain near‐global optimal solutions, the HDGA is designed to have various subpopulations that are processed using separate and parallel GAs. The hypercubic topology with a small diameter spreads good solutions rapidly throughout all of the subpopulations, and a migration mechanism, which exchanges chromosomes among the subpopulations, exchanges information during the joint optimization to maintain diversity and thus avoid a systematic premature convergence toward a single local optimum. Three genetic operators, i.e. linear ranking selection, blend‐α crossover and Gaussian mutation, are applied to search for the optimal reservoir releases. First, a benchmark problem, the four‐reservoir operation system, is considered to investigate the applicability and effectiveness of the proposed approach. The results show that the known global optimal solution can be effectively and stably achieved by the HDGA. The HDGA is then applied in the planning of a multi‐reservoir system in northern Taiwan, considering a water reservoir development scenario to the year 2021. The results searched by an HDGA minimize the water deficit of this reservoir system and provide much better performance than the conventional GA in terms of obtaining lower values of the objective function and avoiding local optimal solutions. Copyright © 2006 John Wiley & Sons, Ltd.     

P–T paths in the Handöl area, central Scandinavia: record of Caledonian accretion of outboard rocks to the Baltoscandian margin

The Seve–Köli Nappe Complex is widespread in the Scandinavian Caledonides and is composed of units representing parts of the Baltoscandian margin (Seve Nappes) now overlain by magmatic–sedimentary rocks (Köli Nappes) derived from west of this margin. The metamorphic evolution of Köli and Seve units has been studied in the Handöl area, central Scandinavian Caledonides, where a fragmented ophiolite with cover sequence in the lower Köli units is thrust over the higher grade Seve units. Thermobarometry constrains metamorphic conditions to 490–570° C/950–600 MPa, with a slight downwards increase in grade, for the lower Köli (Bunnerviken lens), 520–620° C/1000–600 MPa for the upper Seve (Täljstensvalen Complex), 630–740° C/750–650 MPa for the middle Seve (Snasahögarna Nappe) and 480–600° C/1150–1000 MPa for the lower Seve (Blåhammarfjället Nappe).
P–T paths during garnet growth have been constructed for all units, except the highest grade middle Seve. These paths record heating at the base of the Köli and cooling in the underlying Seve units. Pressure increase during garnet growth is indicated for all units leading to anticlockwise P–T paths in the Seve. The results imply thermal convergence with time for all units and spatial convergence in metamorphic grade in the Köli. It is suggested that the contrasting metamorphic histories on either side of the Seve–Köli boundary resulted from the emplacement of relatively colder Köli rocks on top of relatively hotter Seve rocks and that emplacement of structurally higher units contributed to the increase in pressure.     

Analytical study of mine closure behaviour in a poro‐visco‐elastic medium

This paper is interested in the hydro‐mechanical behaviour of an underground cavity abandoned at the end of its service life. It is an extension of a previous study that accounted for a poro‐elastic behaviour of the rock mass (Int. J. Comput. Geomech. 2007; DOI: 10.1016/j.compgeo.2007.11.003 ). Deterioration of the lining support with time leads to the transfer of the loading from the exterior massif to the interior backfill. The in situ material has a poro‐visco‐elastic constitutive behaviour while the backfill is poro‐elastic, both saturated with water. This loading transfer is accompanied by an inward cavity convergence, thereby compressing the backfill, and induces an outward water flow. This leads to a complex space–time evolution of pore pressures, displacements and stresses, which is not always intuitive. In its general setting, a semi‐explicit solution to this problem is developed, using Laplace transform, the inversion being performed numerically. Analytical inversion leading to a quasi‐explicit solution in the time domain is possible by identifying the characteristic creep and relaxation times of volumetric strains with those of the deviatoric strains, on the basis of a parametric study. A few numerical examples are given to illustrate the hydro‐mechanical behaviour of the cavity and highlight the influence of key parameters (e.g. stiffness of backfill, lining deterioration rate, etc.). Further studies accounting for more general material behaviours for the backfill and external ground are ongoing. Copyright © 2008 John Wiley & Sons, Ltd.     

Developing an empirical model of canopy water flux describing the common response of transpiration to solar radiation and VPD across five contrasting woodlands and forests

A modified Jarvis–Stewart model of canopy transpiration (E_c) was tested over five ecosystems differing in climate, soil type and species composition. The aims of this study were to investigate the model's applicability over multiple ecosystems; to determine whether the number of model parameters could be reduced by assuming that site‐specific responses of E_c to solar radiation, vapour pressure deficit and soil moisture content vary little between sites; and to examine convergence of behaviour of canopy water‐use across multiple sites. This was accomplished by the following: (i) calibrating the model for each site to determine a set of site‐specific (SS) parameters, and (ii) calibrating the model for all sites simultaneously to determine a set of combined sites (CS) parameters. The performance of both models was compared with measured E_c data and a statistical benchmark using an artificial neural network (ANN). Both the CS and SS models performed well, explaining hourly and daily variation in E_c. The SS model produced slightly better model statistics [R² = 0.75–0.91; model efficiency (ME) = 0.53–0.81; root mean square error (RMSE) = 0.0015–0.0280 mm h^‐1] than the CS model (R² = 0.68–0.87; ME = 0.45–0.72; RMSE = 0.0023–0.0164 mm h^‐1). Both were highly comparable with the ANN (R² = 0.77–0.90; ME = 0.58–0.80; RMSE = 0.0007–0.0122 mm h^‐1). These results indicate that the response of canopy water‐use to abiotic drivers displayed significant convergence across sites, but the absolute magnitude of E_c was site specific. Period totals estimated with the modified Jarvis–Stewart model provided close approximations of observed totals, demonstrating the effectiveness of this model as a tool aiding water resource management. Analysis of the measured diel patterns of water use revealed significant nocturnal transpiration (9–18% of total water use by the canopy), but no Jarvis–Stewart formulations are able to capture this because of the dependence of water‐use on solar radiation, which is zero at night. Copyright © 2012 John Wiley & Sons, Ltd.     

Evaluation of the Ross fast solution of Richards’ equation in unfavourable conditions for standard finite element methods

Ross [Ross PJ. Modeling soil water and solute transport – fast, simplified numerical solutions. Agron J 2003;95:1352–61] developed a fast, simplified method for solving Richards’ equation. This non-iterative 1D approach, using Brooks and Corey [Brooks RH, Corey AT. Hydraulic properties of porous media. Hydrol. papers, Colorado St. Univ., Fort Collins; 1964] hydraulic functions, allows a significant reduction in computing time while maintaining the accuracy of the results. The first aim of this work is to confirm these results in a more extensive set of problems, including those that would lead to serious numerical difficulties for the standard numerical method. The second aim is to validate a generalisation of the Ross method to other mathematical representations of hydraulic functions.     

低纬度化极应用迭代法的技术条件分析

针对现有的磁赤道地区磁异常迭代化极方法进行了分析,重点研究了迭代计算中的关键因素———映射函数的选择对迭代收敛性的影响,通过改变映射函数将其推广到除赤道外的其它低纬度条件的化极,并进一步给出了不同磁纬度地区的收敛条件。经过模型计算和实测磁异常验证,改进后的方法既适用于磁赤道也同样适用于其它低纬度地区,并且在保证化极效果的基础上提高了迭代计算的效率。     

Geomorphic covariance structure of a confined mountain river reveals landform organization stage threshold

Significant growth in mountain rivers research since 1990 has promoted the concept that canyon-confined mountain rivers have complex topographic features nested from base- to flood-stages due to canyon structure and abundant large bed elements. Nesting means literally structures inside of structures. Mathematically, nesting means that multiple individual features and repeating patterns exist at different frequency, amplitude, and phasing, and can be added together to obtain the complete structure. Until now, subreach-scale landform structure, including nesting, has not been quantified sufficiently to understand morphodynamic mechanisms that control and respond to such organization. Geomorphic covariance structure analysis offers a systematic framework for evaluating nested topographic patterns. In this study, a threshold stage in mountain river inundation was hypothesized to exist. Above this stage landform structure is organized to be freely self-maintaining via flow convergence routing morphodynamics. A 13.2 km segment of the canyon-confined Yuba River, California, was studied using 2944 cross-sections. Geomorphic covariance structure analysis was carried out on a meter-resolution topographic model to test the hypothesis. River width and bed elevation had significantly less variability than previously reported for lower slope, partially confined gravel/cobble river reaches. A critical stage threshold governing flow convergence routing morphodynamics was evident in several metrics. Below this threshold, narrow/high “nozzle” and wide/low “oversized” were the dominant landforms (excluding “normal channel”), while above it wide/high “wide bar” and narrow/low “constricted pool” were dominant. Three-stage nesting of base-bankfull-flood landforms was dictated by canyon confinement, with nozzle–nozzle–nozzle nesting as the top permutation, excluding normal channel.     

澳洲北部强/弱越赤道气流对应的环流配置

采用1980～2004年的NCEP/NCAR再分析资料, 挑选5～8月中澳洲北部越赤道气流的极强和极弱年作为典型样本,探讨了强/弱越赤道气流对应的环流系统的配置特征。结果表明: 强越赤道气流通常对应北半球辐合带维持较强, 或南半球澳高维持较强,亦或澳洲冷空气活动频繁发生的环流形势, 同期西太平洋副高通常偏东或偏北; 弱越赤道气流通常对应西太平洋副高的偏西或偏南, 或者是西太平洋副高－辐合带共同演进过程的多次发生。     

A review of Asian-Pacific monsoon

Research on the Asian-Pacific monsoon has a long history. This paper starts by summarizing field experiments investigating the Asian-Pacific monsoon. Since the 1960s, a number of international and regional monsoon projects and field experiments have been carried out, and substantial progress regarding research on the Asian-Pacific monsoon has been made. Second, the onset and the seasonal march of the Asian summer monsoon and the annual cycle of active and break periods of the monsoon, which are characterized by precipitation maxima and minima, are studied. Since the inter-tropical convergence zone （ITCZ or TCZ） is the dominating weather system and is the major birthplace of typhoons and tropical convective systems, the monsoonal rainfall and ITCZ are analyzed after the onset of the Asian monsoon. Finally, because the ITCZ has a close relationship with tropical convective systems and rainfall events in monsoon regions, analyses of the developments of deep convection and rainfall events are briefly introduced.