Influence of the turbulence closure scheme on the finite-element simulation of the upwelling in the wake of a shallow-water island     

Sébastien Blaise  Eric Deleersnijder  Laurent White  Jean-François Remacle 《Continental Shelf Research》2007

A three-dimensional finite-element model is used to investigate the tidal flow around Rattray Island, Great Barrier Reef, Australia. Field measurements and visual observations show both stable eddies developing at rising and falling tide in the wake of the island. The water turbidity suggests intense upwelling able to carry bed sediments upwards. Based on previous numerical studies, it remains unclear at this point whether the most intense upwelling occurs near the centre of the eddies or off the island's tips, closer to the island. All these studies resorted to a very simple turbulence closure, with a zero-equation model whereby the coefficient of vertical viscosity is computed via an algebraic expression. In this work, we aim at studying the influence of the turbulence closure on model results, with emphasis on the prediction of vertical motions. The Mellor and Yamada level 2.5 closure scheme is used and an increase in the intensity of vertical transport is observed. This increase is partly explained by the fact that the Mellor and Yamada model takes into account the hysteresis effect in the time variation of turbulence variables. The influence of the advection of turbulence variables is estimated to be negligible. By a better representation of transient coastal phenomena, the Mellor and Yamada level 2.5 turbulence closure improves the model to a significant degree.  相似文献   

Deriving reservoir operational strategies considering water quantity and quality objectives by stochastic fuzzy neural networks     

Paulo Chaves  Toshiharu Kojiri 《Advances in water resources》2007

By taking advantage of the close relationship between quality and quantity of water, we investigated the potential improvements of the in-reservoir water quality through the optimization of reservoir operational strategies. However, the few available techniques for optimization of reservoir operational strategies present some limitations, such as restrictions on the number of state/decision variables, the impossibility considering stochastic characteristics and difficulties for considering simulation/prediction models. One technique which presents great potential for overcoming some of these limitations is applied here and investigated for the first time in such complex system. The method, named stochastic fuzzy neural network (SFNN), can be defined as a fuzzy neural network (FNN) model stochastically trained by a genetic algorithm (GA) based model to yield a quasi optimal solution. The term “stochastically trained” refers to the introduction of a new loop within the training process which accounts for the stochastic variable of the system and its probabilities of occurrence. The SFNN was successfully applied to the optimization of the monthly operational strategies considering maximum water utilization and improvements on water quality simultaneous. Results showed the potential improvements on the water quality through means of hydraulic control.  相似文献   

高精度迎风偏斜格式的比较与分析   总被引：1，自引：0，他引：1  

冯涛  李建平 《大气科学》2007,31(2):245-253

利用一种具有任意阶精度的一般显式有限差分公式构造出高精度迎风偏斜格式，并利用 Fourier分析法评估了这些迎风偏斜格式的耗散误差与频散误差。结果表明，偶阶精度格式的数值相速度快于实际相速度，而奇阶精度格式的数值相速度慢于实际相速度。并且，偶阶精度格式的耗散误差与频散误差低于相邻的奇阶精度格式。为了检验这些格式的计算性能，在一维问题上进行了应用。首先，考虑恒定风场条件下的一维平流试验。主要选择两种不同的初始条件来评价数值格式的精度，这两种试验问题分别是高斯函数、方波函数。试验结果表明，随着数值格式精度的提高，数值格式的误差逐渐减小。而对于高于六阶精度的格式来说，改进的程度并不是很大。其次，应用各阶格式到具有两种不同初始条件的无粘Burgers方程。数值结果表明，随着数值格式阶数的增加，数值结果也得到了明显改进。而对于高于六阶精度的格式来说，进一步的变化并不明显。总之，在兼顾效率与精度条件下六阶迎风偏斜格式是最好的。  相似文献   

高炮防雹作业决策指挥系统的研制     

金凤岭  张云峰  翟国辉  安英玉 《气象》2007,33(6):112-117

从黑龙江省人工影响天气工作的实际出发，利用现有的新一代天气雷达、卫星遥感等探测手段，依托先进的通讯设备和网络技术，对黑龙江省冰雹的发生、发展、演变、冰雹路径以及雷达回波特征等进行研究，研制了人工防雹作业指挥系统，实现冰雹天气预警、空域电话录音、指挥高炮科学作业、作业数据存储和作业情况宏观调控等多项功能，提高了高炮防雹作业的科学性。  相似文献   

湖南人工增雨云型的分析判别与多普勒天气雷达指挥系统的研制应用   总被引：4，自引：4，他引：4       下载免费PDF全文

唐林  魏鸣  王治平 《气象科学》2007,27(1):95-100

对湖南主要人工增雨对象——积云和积层混合云作了多普勒天气雷达回波分析与判别,发现对流云在不同发展阶段回波特征有明显差异,而积层混合云持续时间长,回波特征变化小。综合分析回波强度、回波顶高、含水量、云顶温度、回波移速、回波面积等参数,得出湖南的人工增雨指标和评分规则,并依此建立地面人工增雨多普勒天气雷达指挥系统。它可实现实时指挥,发布作业预警信息以及作业方位角、仰角、用弹量等作业参数指令,结合作业点GPS信息及GIS地理信息将指导产品通过网络分发到各作业炮点。试验表明,它能有效提高对作业时机的预判能力、对作业对象的选择能力以及对实时作业的指导能力。  相似文献   

灾害系统中GIS空间分析的应用研究     

张顺香  朱广丽 《测绘与空间地理信息》2007,30(5):62-64,69

讨论了一种地理信息系统空间分析算法——最短路径分析,然后利用最短路径结果,采用表上作业法将灾害救援物资进行优化,给出最优调运方案。  相似文献   

Afforestation of European landscapes: How do different farmer types respond to EU agri-environmental schemes?   总被引：1，自引：0，他引：1  

Søren Præstholm  Anette Reenberg  Søren Pilgaard Kristensen 《GeoJournal》2006,67(1):71-84

This paper investigates how different types of farmers manage the landscape with primary emphasis on farmland afforestation, planned landscape changes, and the extent to which EU agri-environmental schemes take farm type specific characteristics into account in information strategies. The empirical data concern landscape practices of more than 2,000 landowners in 16 European areas in eight countries who were surveyed using quantitative questionnaires. Supplementary in-depth interviews were conducted for two case areas in Denmark to further investigate the role of the policy information environment. The analysis is based on a categorization of the farmers into hobby, part-time, full-time and retired farmers. This study shows that hobby farmers constitute a high proportion of landowners and manage a large part of the rural landscape. At the same time, hobby farmers are relatively more interested in landscape changes and differ from other landowners by considering farmland afforestation more often than full-time landowners, for example. Yet, 40% of the hobby farmers who are considering farmland afforestation are not familiar with the agri-environmental scheme for farmland afforestation. One reason may be their low membership rate in traditional information networks such as farmers’ or foresters’ associations, as revealed by the in-depth analysis of the cases in Denmark. Thus, it is proposed that policy impact may be improved if farmer type specific differences are explicitly taken into account in the scheme logistics for EU agri-environmental schemes.  相似文献   

Adaptive finite element analysis of cone penetration in clay     

J. Walker  H. S. Yu 《Acta Geotechnica》2006,1(1):43-57

This paper presents a numerical technique for the analysis of the cone penetration test by means of the commercial finite element code ABAQUS. The von Mises yield criterion with its associated flow rule is assumed to model the plastic behaviour of elastoplastic undrained clays. An explicit finite element scheme is used to efficiently perform a large number of loading increments and to simplify the treatment of contact. An Arbitrary Langrangian–Eulerian (ALE) scheme is adopted to preserve the quality of mesh throughout the numerical simulation. A volumetric weighting algorithm adjusts the relative positions of nodes after each loading increment. This prevents mesh over distortion and allows the simulation to run continuously. The variation of the cone resistance is examined in relation to various parameters such as the in situ stress state, shaft and cone face roughness, and the material strength when steady state conditions have been reached. The trends of these variations are highlighted and compared with those found by other researchers. This technique can be extended to analyse the plastic behaviour of elastoplastic sands often modelled using either the Drucker–Prager yield criterion or a critical state model.  相似文献   

闪电定位系统布网方案设计的技术探讨   总被引：8，自引：0，他引：8  

吴翠红  左申正  万玉发 《气象》2002,28(6):11-15

以闪电定位系统的定位原理和误差分析方法的基础，利用系统布设客观分析软件的自动选站和误差计算功能，比较了以不同方式组成的闪电监测网在一定范围内的定位误差。结果显示，除了系统本身存在的方位和时间误差外，布设子站的数目、几何形状、站距的大小对定位精度的影响均非常明显，与系统采取的定位算法也有很大关系。同时，提出并采取“一子多主，多叉组合”的技术策略，以湖北省为例，对闪电定位系统布网方案设计进行技术探讨。  相似文献   

平均经圈环流质量流函数简化计算方案的应用   总被引：4，自引：2，他引：4  

龚振淞  王盘兴  马杰 《南京气象学院学报》2002,25(3):328-333

用一个简化计算方案，求得了1948-1999年52a逐月平均经圈环流质量流函数。用它分析了平均经圈环流的气候态及20世纪80年代和90年代最强El Nino事件的气候异常态。结果表明：它很好地给出了平均经圈环流的气候态的季节变化及气候异常态与SSTA的物理联系。上述结果与通常迭代法计算结果基本一致。  相似文献