Impact of dissipation and dispersion terms on simulations of open‐channel confluence flow using two‐dimensional depth‐averaged model          下载免费PDF全文

Qing‐yuan Yang  Wei‐Zhen Lu  Su‐fen Zhou  Xie‐kang Wang 《水文研究》2014,28(8):3230-3240

The flow patterns in confluence channel and the simulation of confluence flow are more complex than that in straight channel. Additional terms in the momentum equations, i.e. dissipation terms, denoting the impact of turbulence, and dispersion terms, denoting the vertical non‐uniformity of velocity, show great impacts on the accuracy of numerical simulations. The dissipation terms, i.e. the product of eddy viscosity coefficient and velocity gradient, are much larger than those of the flow in straight channel. In this study, the zero equation model and the depth‐averaged k‐ε model are used to analyse the impact of eddy viscosity. Meanwhile, the dispersion terms in the momentum equation, depending on the vertical non‐uniformity of velocity, are usually neglected in routine simulation. With the use of detailed experimental data for verification, this study presents the distribution of parameters of vertical non‐uniformity and the intimated connection between non‐uniformity parameters and accuracy of numerical simulations of confluence flow with depth‐averaged models. The results present that simulation accuracy of confluence flow is very sensitive to the turbulence modes, which cannot be handled by normal, simple turbulence model. On the contrary, the impact of dispersion terms is both flow‐condition‐dependent and place‐dependent, and such impact is negligible when secondary circulation is weak. The results indicate the key elements in modelling confluence flow and are helpful for selecting suitable numerical model and solving engineering problems encountered in confluence channel. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Conversion of Pressure to Depth for Moored Instruments Using a Reference Bottom Mounted Pressure Sensor     

Junde Li  Weifang Jin  Guanghong Liao  Beifeng Zhou 《大气与海洋》2015,53(4):377-382

A new method is proposed to convert pressure measured by an instrument to water depth using an additional available bottom-moored pressure sensor. A perturbation analysis is used in this analysis, which leads to a simple formula for calculating water depth (defined as one from the mean sea surface to the instrument) from the pressure data. In field experiments, this method is easier to apply than existing methods. Based on the theoretical derivation, the error associated with the method comes from two sources when the instrument depth is known at the beginning of the measurement: temporal variation of deep water density at depths deeper than the instrument and variation in the gravitational acceleration with instrument displacement. These two sources contribute up to 4% of the error relative to the vertical displacement of the instrument, assuming the pressure sensor is accurate. With the vertical displacement of the instrument being on the order of 10?m, the absolute error is on the order of 0.4?m, which is expected and acceptable in oceanic measurements. The method is applied to data from a field experiment that took place along the Myanmar coast in December 2012.  相似文献   

Climate Comparisons and Change Projections for the Northwest Atlantic from Six CMIP5 Models     

John W. Loder  Augustine van der Baaren  Igor Yashayaev 《大气与海洋》2015,53(5):529-555

Abstract

Key physical variables for the Northwest Atlantic (NWA) are examined in the “historical” and two future Representative Concentration Pathway (RCP) simulations of six Earth System Models (ESMs) available through Phase 5 of the Climate Model Intercomparison Project (CMIP5). The variables are air temperature, sea-ice concentration, surface and subsurface ocean temperature and salinity, and ocean mixed-layer depth. Comparison of the historical simulations with observations indicates that the models provide a good qualitative and approximate quantitative representation of many of the large-scale climatological features in the NWA (e.g., annual cycles and spatial patterns). However, the models represent the detailed structure of some important NWA ocean and ice features poorly, such that caution is needed in the use of their projected future changes. Monthly “climate change” fields between the bidecades 1986–2005 and 2046–2065 are described, using ensemble statistics of the changes across the six ESMs. The results point to warmer air temperatures everywhere, warmer surface ocean temperatures in most areas, reduced sea-ice extent and, in most areas, reduced surface salinities and mixed-layer depths. However, the magnitudes of the inter-model differences in the projected changes are comparable to those of the ensemble-mean changes in many cases, such that robust quantitative projections are generally not possible for the NWA.  相似文献   

基于深度加权的重力梯度张量数据的3D聚焦反演   总被引：1，自引：0，他引：1  

杨娇娇  刘展  陈晓红  徐凯军 《世界地质》2015,34(1):210-218

针对重力梯度数据聚焦反演结果中存在的"上漂"现象,在经典Tikhonov正则化理论框架下,引入最小支撑泛函数对反演模型进行约束以避免反问题解的不稳定,并针对重力梯度数据聚焦反演中存在的趋肤效应,在模型目标函数中引入指数深度加权函数。通过理论模型,对部分重力梯度张量分量进行了单独以及联合聚焦反演,验证了基于深度加权的聚焦反演方法的有效性,并将该反演方法运用到涩北一号气田区的实际数据中,反演结果较好地反映出气田位置。  相似文献   

漫溃堤洪水联算全二维水动力模型及应用   总被引：1，自引：0，他引：1       下载免费PDF全文

苑希民  田福昌  王丽娜 《水科学进展》2015,26(1):83-90

为应对河道洪峰流量增大和漫溃堤长历时相伴发生的洪灾现象,借鉴全二维气相色谱理论提出全二维水动力模型概念,建立了模拟河道和灌区洪水演进的漫溃堤洪水联算全二维水动力模型,并采用Roe格式的近似Riemann解对界面通量进行数值求解。模型内通过漫溃堤堰流公式成功实现河道与灌区的耦联,考虑溃口展宽变化,加密处理河道网格,采用热启动与干湿水深理论对模型进行优化,并利用加大糙率法对村庄较为密集的地形进行优化处理,尽可能反应地面真实情况。将该模型应用于黄河宁蒙段河道与左右岸灌区的漫溃堤洪水演进模拟,计算结果合理可靠,流场分布均匀光滑,初步验证了模型的精度及可靠性,研究成果对河道溃决洪水的精细仿真模拟和该地区洪水风险分析决策具有重要意义。  相似文献   

基于WiFi探针数据的城市出行轨迹提取     

廖嘉欣  吴启用  兰小机  张红庆 《地球信息科学学报》2021,23(11):1946-1955

为了更便捷地提取城市居民的出行轨迹,从而分析个体的日常空间行为,进而为城市管理的各项措施决策提供数据支撑,本文提出基于WiFi探针数据的城市出行轨迹提取方法,主要解决WiFi探针数据的路网匹配及丢失轨迹重构问题。首先,通过对终端MAC码和时间戳进行多列排序后提取出轨迹记录序列,利用信号强度RSSI值为每条记录提取坐落在路网上的候选点集。其次,设计基于局部评价的算法,对于每一个候选点,利用其前后相邻的几条记录提取的候选点集与其之间的时空关系,先后对其进行时间一致性评价和空间一致性评价,再结合以时间反比动态构建的权函数,得到最终评分;然后将每个候选点集中评分最高的点作为最佳匹配点,至此完成轨迹记录的路网匹配。最后,先采用基于深度优先的路径搜索算法搜索出丢失轨迹上下点之间的所有可行路径,再基于TOPSIS法决策出最优的重构路径。本文以东莞市市中心区域收集的WiFi探针数据为实验数据进行测试,平均每日可提取6万多条轨迹,与其中获取的GPS数据相比较验证了方法的可行性,为城市出行轨迹挖掘提供了新的解决方案。  相似文献   

基于二分搜索的水深数据与遥感影像匹配算法     

郭剑  黄文骞  吴迪  梁志诚  魏帅 《海洋测绘》2014,34(5):42-45

研究了遥感水深反演的数据匹配方法,分析了插值加密法与最短距离法的优缺点。针对高分辨率卫星影像海量数据,传统匹配方法无法有效进行数据匹配问题,提出基于二分搜索的阈值距离法。实验表明,新算法的匹配效率与匹配精度得到了显著提高,有助于获得更好的水深反演效果。  相似文献   

一种珠江口深度基准面格网模型的建立     

俞成明  周庆冲  陈跃平 《海洋测绘》2014,(1):34-36

针对珠江口现阶段陆海高程基准不统一的事实以及由此产生的海岸带陆海数字成果无法拼接的问题,详细介绍了基于国家高程基准建立珠江口深度基准面格网模型的技术流程及构建方法。通过项目实施获取的实测数据对模型进行精度检验与方法比较,确立采用克里金内插法建立珠江口深度基准面格网模型。最后对模型的具体应用进行了阐述与展望。  相似文献   

Optimal Design of Equivalent Water Depth Truncated Mooring System Based on Baton Pattern Simulated Annealing Algorithm简   总被引：2，自引：2，他引：0  

张火明  黄赛花  管卫兵 《中国海洋工程》2014,28(1):67-80

The highest similarity degree of static characteristics including both horizontal and vertical restoring force-displacement characteristics of total mooring system, as well as the tension-displacement characteristics of the representative single mooring line between the truncated and full depth system are obtained by annealing simulation algorithm for hybrid discrete variables （ASFHDV, in short）. A“baton” optimization approach is proposed by utilizing ASFHDV. After each baton of optimization, if a few dimensional variables reach the upper or lower limit, the boundary of certain dimensional variables shall be expanded. In consideration of the experimental requirements, the length of the upper mooring line should not be smaller than 8 m, and the diameter of the anchor chain on the bottom should be larger than 0.03 m. A 100000 t turret mooring FPSO in the water depth of 304 m, with the truncated water depth being 76 m, is taken as an example of equivalent water depth truncated mooring system optimal design and calculation, and is performed to obtain the conformation parameters of the truncated mooring system. The numerical results indicate that the present truncated mooring system design is successful and effective.  相似文献   

重污染下我国中东部地区1960~2010年霾日数的时空变化特征   总被引：4，自引：1，他引：3       下载免费PDF全文

符传博  丹利 《气候与环境研究》2014,19(2):219-226

对1960~2010年我国中东部地区霾日数的时空变化特征的分析结果表明:1)霾日数大值区主要分布在人口众多的四川盆地、北京-天津-河北地区、长江中下游地区以及广东-广西中部。2)季节变化上,霾日数冬季较多,其中北京-天津-河北地区中部和西南部、四川盆地和东北地区东部和南部等地超过20 d,夏季最少。3)霾日数气候趋势系数在北京-天津-河北地区、长江三角洲地区和珠江三角洲地区趋势系数高达0.8。4)霾日数呈现明显的上升趋势[3.69 d(10 a)–1],其气候趋势系数为0.82,通过了99.9%的信度检验。5)我国中东部气溶胶光学厚度和对流层NO2的空间分布与年平均霾日数的分布基本一致,近51年来能源消耗量的稳定上升趋势也表明,人为因素导致的大气污染物排放量增加是引起霾天气出现频率上升的重要因素。  相似文献