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为研究以流体粒子描述波浪运动，以固体单元描述砾石运动的两相介质大变形运动，在港口、海岸工程科学研究中具有重要意义。本文提出砾石单元法（GEM），介绍了光滑粒子动力学方法（SPH）和GEM的基本原理，阐述了GEM与离散单元法（DEM）的异同之处，说明了采用SPH方法与GEM构建波浪砾石耦合运动数学模型的方法和过程。应用SPH方法建立数值波浪水槽，用GEM模拟波浪作用下堆积砾石的滚落、坍塌变形，构建了SPH方法与GEM耦合数学模型。模拟了水槽造波和波浪生成过程和波浪作用下砾石的滚落、坍塌变形，并与物理模型试验成果进行了比较，结果基本吻合。本文提出的GEM法具有模拟单相堆积砾石运动和堆积砾石与流体粒子耦合多相介质运动的功能，是对DEM法的补充和改善。本文提出的堆积力学球概念和拟序排列求解方法是砾石单元法的重要组成部分。 相似文献
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The jet structure of the Southern Ocean front south of Australia is studied in stream-coordinate with a new altimeter product—Absolute Dynamic Topography (ADT) from AVISO. The accuracy of the ADT data is validated with the mooring data from a two-year subantarctic-front experiment. It is demonstrated that the ADT is consistent with in-situ measurements and captures the meso-scale activity of the Antarctic Circumpolar Current (ACC). Stream-coordinate analysis of ADT surface geostrophic flows finds that ACC jets exhibit large spatio-temporal variability and do not correspond to particular streamfunction values. In the circumpolar scope ACC jets display a transient fragmented pattern controlled by topographic features. The poleward shift of jet in streamfunction space, as revealed by a streamwise correlation method, indicates the presence of meridional fluxes of zonal momentum. Such cross-stream eddy fluxes concentrate the broad ACC baroclinic flow into narrow jets. Combined with a recent discovery of gravest empirical mode (GEM) in the thermohaline fields, the study clarifies the interrelationship among front, jet and streamfunction in the Southern Ocean. 相似文献
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Snow interception is a crucial hydrological process in cold regions needleleaf forests, but is rarely measured directly. Indirect estimates of snow interception can be made by measuring the difference in the increase in snow accumulation between the forest floor and a nearby clearing over the course of a storm. Pairs of automatic weather stations with acoustic snow depth sensors provide an opportunity to estimate this, if snow density can be estimated reliably. Three approaches for estimating fresh snow density were investigated: weighted post-storm density increments from the physically based Snobal model, fresh snow density estimated empirically from air temperature (Hedstrom, N. R., et al. [1998]. Hydrological Processes, 12, 1611–1625), and fresh snow density estimated empirically from air temperature and wind speed (Jordan, R. E., et al. [1999]. Journal of Geophysical Research, 104, 7785–7806). Automated snow depth observations from adjacent forest and clearing sites and estimated snow densities were used to determine snowstorm snow interception in a subalpine forest in the Canadian Rockies, Alberta, Canada. Then the estimated snow interception and measured interception information from a weighed, suspended tree and a time-lapse camera were assimilated into a model, which was created using the Cold Regions Hydrological Modelling platform (CRHM), using Ensemble Kalman Filter or a simple rule-based direct insertion method. Interception determined using density estimates from the Hedstrom-Pomeroy fresh snow density equation agreed best with observations. Assimilating snow interception information from automatic snow depth measurements improved modelled snow interception timing by 7% and magnitude by 13%, compared to an open loop simulation driven by a numerical weather model; its accuracy was close to that simulated using locally observed meteorological data. Assimilation of tree-measured snow interception improved the snow interception simulation timing and magnitude by 18 and 19%, respectively. Time-lapse camera snow interception information assimilation improved the snow interception simulation timing by 32% and magnitude by 7%. The benefits of assimilation were greatly influenced by assimilation frequency and quality of the forcing data. 相似文献
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宽肩台堆石堤是海岸工程中的一种海堤形式，其以结构简单、施工快捷、布局灵活和造价经济的特点在工程中得到了广泛应用。宽肩台防波堤以堆积块石为主体，在海区波浪作用下达到稳定的堆积结构。进行宽肩台式防波堤稳定性的研究
是设计宽肩台防波堤的重要基础。介绍了波浪水槽的光滑粒子动力学 （SPH） 理论和建立方法，验证了造波结果。提出了一种块石单元法 （GEM） 模式，以块石单元为独立刚体来模拟宽肩台防波堤上的块石在波浪作用下的受力状态和运动过程。建立了一种垂向二维光滑粒子动力学方法 SPH 与 GEM 耦合的波浪和块石模型，采用 SPH 与 GEM 相结合，对防波堤堆石孔隙外部的波浪运动和内部的孔隙环流进行模拟计算，并根据 Forchheimer 公式确定孔隙内部的压力。用 SPH 方法模拟堆石堤外部流场的波浪破碎压力，用孔隙环流模拟堆石堤内部的孔隙压力。使用耦合模式模拟了宽肩台防波堤孔隙流场，验证了孔隙压力分布。模拟了波浪作用于块石和块石对波浪动力响应过程，给出了静态平衡到动态平衡的流固场变化，模拟结果与物理模型试验结果基本一致。耦合模型的建立为宽肩台堆石堤的稳定性研究提供了理论依据，同时也为同类型工程研究提供了新思路。 相似文献
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Lorenzo de la Fuente Yves Delage Serge Desjardins Allan MacAfee Garry Pearson Harold Ritchie 《Pure and Applied Geophysics》2007,164(6-7):1303-1325
Three cases of widespread sea fog in Lunenburg Bay, Nova Scotia were used to evaluate the suitability of operational regional
GEM forecast fields for inferring advection fog occurrences. Verification scores suggest that the objective analyses contain
significant departures from observations that will affect model accuracy, given the sensitivity of fog condensation microphysics.
Dew point depression (ES) scores show larger differences compared to temperature, with both influenced by surface characteristics.
For objective analyses and GEM forecasts ES < 2 C seems to match fog satellite images better than the physical threshold ES
≤ 0 C. In addition the GEM forecasts show a general tendency towards drier conditions near the surface, therefore reconfiguring
GEM to better represent condensation in the boundary layer is proposed. 相似文献
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Mahfooz A. Hafez Magdy A. Atya Azza M. Hassan Motoyuki Sato Thomas Wonik Abeer K EI-Kenaw 《应用地球物理》2008,5(2):136-143
Ground penetrating radar, electromagnetic terrain conductivity, and electric tomography have proven to be effective tools if they are combined together to investigate archeological sites. We have conducted a geophysical survey at the Akhmim archaeological site, the main objective of our survey is to locate additional buried structures for further excavation. Geophysical data were acquired in the area using the GEM-300 multi-frequency terrain conductivity profiler, the SIR 2000 ground penetrating radar, and the Syscal R2 resistivity meter systems. The results of the integrated interpretation show a number of buried features and a strong linear zone about 1 m wide that coincides with the suspected trend of a buried wall. There appears to be two parallel ridges of strong reflections on either side, indicating two parallel walls extended East-West and a room is identified at the bottom left comer of the site. Moreover, the interpretation results of some selected GPR and dipoledipole resistivity profiles adjacent to the open-air museum suggest the existence of a second statue of Ramses Ⅱ to the right of the previously discovered statue which could still be buried in the sand. 相似文献
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The geoid undulation on GRS80 in the Taiwan area at half‐degree grid points has been calculated using the reduced 30’ × 30’ block mean gravity anomalies and the OSU91A geopotential coefficient set up to degree and order 360. The OSU91A results have been used to compare with WGS84, CEM10C, and OSU86F geoid undulations determined in 18 first‐order triangulation stations of the Taiwan Geodetic Datum 1980 (TGD80). Comparisons have also been made between these free‐air anomalies determined from OSU91A, and terrestrial gravity anomalies. It has been found that the average difference between the OSU91A model‐derived, and 243 actual point free‐air anomalies is 16.8 ± 48.0 mgal. It has also been found that more reliable and dense terrestrial gravity data are needed, both for terrestrial observations and for the OSU91A model, to achieve the very high‐precision geoid on GRS80 in the area of study. 相似文献
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Mapping groundwater‐dependent ecosystems using remote sensing measures of vegetation and moisture dynamics 
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下载免费PDF全文 Olga V. Barron Irina Emelyanova Thomas G. Van Niel Daniel Pollock Geoff Hodgson 《水文研究》2014,28(2):372-385
Protection of groundwater‐dependent ecosystems (GDEs) is an important criterion in sustainable groundwater management, particularly when human water consumption is in competition with environmental water demands; however, the delineation of GDEs is commonly a challenging task. The Groundwater‐dependent Ecosystem Mapping (GEM) method proposed here is based on interpretation of the land surface response to the drying process derived from combined changes in two multispectral indices, the Normalised Difference Vegetation Index and the Normalised Difference Wetness Index, both derived from Landsat imagery. The GEM method predicts three land cover classes used for delineation of potential GDEs: vegetation with permanent access to groundwater; vegetation with diminishing access to groundwater; and water bodies that can persist through a prolonged dry period. The method was applied to a study site in the Ellen Brook region of Western Australia, where a number of GDEs associated with localised groundwater, diffuse discharge zones, and riparian vegetation were known. The estimated accuracy of the method indicated a good agreement between the predicted and known GDEs; Producer's accuracy was calculated as up to 91% for some areas. The method is most applicable for mapping GDEs in regions with a distinct drying period. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献