Mitigating horizontal divergence “checker-board” oscillations on unstructured triangular C-grids for nonlinear hydrostatic and nonhydrostatic flows     

《Ocean Modelling》2013

A complication of finite-volume triangular C-grid methods is the numerical emergence of horizontal divergence errors that lead to grid-scale oscillations in vertical velocity. Nonlinear feedback via advection of momentum can lead to numerical instability in velocity modes via positive feedback with spurious vertical velocities induced by horizontal divergence truncation error. Existing strategies to mitigate divergence errors such as direct divergence averaging and increased diffusion do not completely mitigate horizontal vertical velocity oscillations. We present a novel elliptic filtering approach to mitigate this spurious error and more accurately represent vertical velocities via improved calculation of horizontal divergences. These results are applied to laminar curved channel flows, demonstrating the applicability of the method to reproduce secondary flow features.  相似文献   

Nonresonant generation of MHD disturbances during supernova explosions in an inhomogeneous interstellar medium     

I. N. Toptygin 《Astronomy Letters》2007,33(4):259-269

We analyze the nonresonant generation of large-scale magnetic inhomogeneities near a shock front by accelerated particles. The MHD disturbances are generated by the electric current excited by relativistic particles in the preshock medium in the presence of weak large-scale density inhomogeneities. The MHD modes considered can be amplified by other resonant and nonresonant mechanisms related to the presence of relativistic particles. We estimate the magnetic fields and the energies to which charged particles can be accelerated in different phases of the interstellar medium by taking into account the random magnetic fields generated by the mechanism considered.  相似文献   

Portable irrigation system for studying hillslope and wetland runoff generation processes     

J. M. Waddington  K. J. Devito 《水文研究》2001,15(2):281-287

The advantage of an irrigation system is that experiments of varying precipitation duration and intensity can be performed in a controlled situation. An effective portable irrigation system is described for use in experimental plot hillslope and wetland runoff studies. The system consists of four parts:(1) a water pump; (2) a tracer reservoir; (3) a chemical feed pump; and (4) distribution hoses. Relatively uniform water application is achieved by a series of manual valves controlling water flow from the main carrier hose to the distribution hoses. The irrigation system materials are inexpensive and installation and operation costs are minor. The system was used to study runoff generation from a small‐saturated area in a spring‐fed swamp for a range of precipitation intensities and durations. The irrigation system applied a maximum intensity of 14·0mm h^?1, for a maximum duration of 180 min, to a 190m² area. This range of application incorporated all storms up to a one in three year event. The variance of the tracer load was almost three times greater for natural (60%) than with the irrigation system (22%). The irrigation system reduced the uncertainty in the pre‐event water fraction (using a two‐component hydrograph separation) from 3·4% in natural events to only 0·7%. The irrigation system design, operation, calibration and cost are presented. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

汶川M_S8.0级地震成因三“层次”分析——基于深部电性结构   总被引：2，自引：1，他引：1       下载免费PDF全文

赵国泽  陈小斌  肖骑彬  王立凤  汤吉  詹艳  王继军  张继红  H. Utada  M. Uyeshima 《地球物理学报》2009,52(2):553-563

2008年5月12日汶川M_S8级地震的发生不是局部地区孤立的构造事件,研究汶川地震的孕震机制,应该把局部分析和区域分析相结合,关注地壳上地幔直至地幔过渡带的深部结构.基于近年来在东北、华北和汶川地震附近地区进行的深部结构电磁探测结果,结合地震学等其他资料,从太平洋板块的俯冲、印度板块的碰撞和松潘甘孜地块的推挤三个“层次”探讨分析汶川特大地震的成因.太平洋板块向亚洲大陆的俯冲作用,导致中国大陆东部地幔过渡带深度较普遍地存在着停滞的板片,它对汶川地震的影响不可忽视.印度板块与青藏高原的碰撞,使组成高原的各地块发生向北和向东的运动,各地块向东的运动作用于南北地震带中南段,影响到该区域的地震活动.松潘甘孜地块向四川地块的推挤,使松潘甘孜地块运动方向和龙门山断裂带形成“丁”字形结构,龙门山断裂带显示为较陡直的电性边界,加剧了汶川地震前的应力积累,可能是汶川地震发生的最直接的诱因.  相似文献   

Slope runoff study in situ using rainfall simulator in mountainous area of North China     

XU Jing-Ji  YANG Cong  LIU Chang-Meng  SONG Xian-Fang  HU Shan-Shan  LI Fa-Dong  TANG Chang-Yuan 《地理学报》2009,30(4):461-470

Simulated rainfall is a valid tool to examine the runoff generation on the slope.13 simulated rainfall experiments with different rainfall intensities and durations are completed in a 5 m ×10 m experimental plot in mountainous area of North China.Simultaneously,rainfall,surface runoff,soil-layer flow,mantel-layer flow and soil moisture are monitored respectively.From the results,it is found that the hydrographs in all layers have the characteristics of rapid rise and fall.The recessions of surface flow and soil-layer flow are much faster than that of mantel-layer flow.Surface flow,the main contributor,makes up more than 60% of the total runoff in the study area.It even exceeds 90% in the cases of high intensity rainfall events.Runoff coefficient(ratio of total runoff to rainfall amount) is mainly influenced by rainfall amount,rainfall intensity and antecedent soil moisture,and the relationship can be well expressed by a multiple linear regression function α = 0.002P + 0.182i + 4.88Wa-0.821.The relation between the rainfall intensity and the lag time of three flows(surface runoff,soil-layer flow and mantel-layer flow) is shown to be exponential.Then,the result also shows that the recession constant is 0.75 for surface runoff,is 0.94 for soil-layer and mantel-layer flow in this area.In this study area,the dominant infiltration excess runoff is simulated by Horton model.About 0.10 mm/min percolation is observed under the condition of different rainfall intensities,therefore the value is regarded as the steady infiltration rate of the study area.  相似文献   

构造应力对煤化作用的影响及其瓦斯灾害性   总被引：1，自引：0，他引：1  

陈玲霞  王志荣  李小明 《煤田地质与勘探》2009,37(5):11-14

通过对豫西滑动构造区二1煤动力变质作用特征的研究,探讨了构造煤变质成烃作用与煤化进程的应力影响因素。研究结果表明,不同性质的构造应力具有不同的煤化效应;与拉张应力相比,具各向异性的挤压应力,对煤变质程度的增加、煤基本结构单元BSU侧链和官能团的脱落,以及煤层瓦斯的生成,都具有很大的促进作用。   相似文献   

缓冲区生成的边界追踪算法优化技术     

王结臣  李利番  李丽  沈定涛 《地理与地理信息科学》2009,25(1)

利用缓冲区边界曲线上各点距缓冲目标距离相等的性质,建立一种基于矢量追踪思想的缓冲区生成方法.提出并探讨了以下优化技术:进行缓冲目标弧段重采样;扩展弧段数据结构以提高点、弧距离计算的效率;闭合边界追踪过程中采用折半逼近的追踪策略并进行动态数据压缩;对缓冲目标集合进行自适应分组和运用分治算法等.结果表明.该算法在内存占用、计算精度等方面具有优势,其计算效率亦可满足一般的GIS应用需求;此外,该算法中边界追踪的思想可以推广应用于空间分析算法设计中.  相似文献   

Generation and Accumulation of Marine Gases in the Himalayan: Taking the Tarim Basin as An Example     

SU Jin  ZHANG Shuichang  ZHU Guangyou  ZHANG Bin  WANG Yu  WANG Xiaomei 《《地质学报》英文版》2013,87(Z1):587-589

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Soil moisture states,lateral flow,and streamflow generation in a semi‐arid,snowmelt‐driven catchment     

James P. McNamara  David Chandler  Mark Seyfried  Shiva Achet 《水文研究》2005,19(20):4023-4038

Hydraulic connectivity on hillslopes and the existence of preferred soil moisture states in a catchment have important controls on runoff generation. In this study we investigate the relationships between soil moisture patterns, lateral hillslope flow, and streamflow generation in a semi‐arid, snowmelt‐driven catchment. We identify five soil moisture conditions that occur during a year and present a conceptual model based on field studies and computer simulations of how streamflow is generated with respect to the soil moisture conditions. The five soil moisture conditions are (1) a summer dry period, (2) a transitional fall wetting period, (3) a winter wet, low‐flux period, (4) a spring wet, high‐flux period, and (5) a transitional late‐spring drying period. Transitions between the periods are driven by changes in the water balance between rain, snow, snowmelt and evapotranspiration. Low rates of water input to the soil during the winter allow dry soil regions to persist at the soil–bedrock interface, which act as barriers to lateral flow. Once the dry‐soil flow barriers are wetted, whole‐slope hydraulic connectivity is established, lateral flow can occur, and upland soils are in direct connection with the near‐stream soil moisture. This whole‐slope connectivity can alter near‐stream hydraulics and modify the delivery of water, pressure, and solutes to the stream. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Groundwater assessment and management: implications and opportunities of globalization     

Karen G. Villholth 《Hydrogeology Journal》2006,14(3):330-339

The present and predicted increase in groundwater’s share of human freshwater withdrawals, its unprecedented importance for human activities globally, and the emerging threats from escalated and unplanned use and degradation, especially in the developing countries, point to the need for intensified efforts to cope with the imbalances. Despite these facts, there is little intervention by governments in developing countries. Sufficient knowledge, awareness and understanding of the groundwater resources and their proper management are missing in these countries, as well as in the international community. Links and trends are described, which highlight problem areas, such as water contamination, urbanization, and socio-economic factors related to groundwater management practices. Globalization provides novel opportunities for facilitating the process of acquiring and applying the necessary knowledge and can, and should, be further explored and developed. The likely benefits of this are: increase in convergence of understanding and approaches; the sharing of knowledge; and potentially wide-reaching, lasting, and scale-crossing networks. The international development and research community is in a particularly fortunate position to promote and facilitate such a process, which should go hand in hand with well focused and coordinated “on the ground” tasks, such as local networking, field investigations, capacity building, and advocacy activities.

Karen G. VillholthEmail: Phone: +94-11-278-7404Fax: +94-11-278-6854

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