Characteristics of Parameters for Local Scour Depth around Submarine Pipelines in Waves     

Sungduk Kim  Ju-Heum Yeon 《Marine Georesources & Geotechnology》2013,31(2):162-176

The purpose of this study is to investigate the characteristics of parameters for local scour depth around submarine pipes due to waves. Because it is impossible to consider all the factors that influence the scour, it is reasonable to investigate the correlations between parameters and scour. The experimental works about scour were performed for the conditions of 40, 60, 90 m pipe diameter, various wave periods, and wave height in the case of horizontal bed and 1/10 slope bed, respectively. Analyzing the results of experiments, the Reynolds number, Shields parameter, Keulegan-Carpenter number, Ursell number, and Modified Ursell number were estimated. The correlations between the relative scour depth, which is the maximum equilibrium local scour depth divided by the pipe diameter, and 5 parameters were analyzed. It was shown that there was hardly any correlation with the Reynolds number. In the case of a horizontal bed, the Keulegan-Carpent number had the highest correlation, but in the case of the slope bed the correlation was greatly reduced. The modified Ursell number showed a high correlation regardless of the type of bed.  相似文献   

Energy- and flux-budget (EFB) turbulence closure model for stably stratified flows. Part I: steady-state,homogeneous regimes   总被引：3，自引：3，他引：0  

S. S. Zilitinkevich  T. Elperin  N. Kleeorin  I. Rogachevskii 《Boundary-Layer Meteorology》2007,125(2):167-191

We propose a new turbulence closure model based on the budget equations for the key second moments: turbulent kinetic and potential energies: TKE and TPE (comprising the turbulent total energy: TTE = TKE + TPE) and vertical turbulent fluxes of momentum and buoyancy (proportional to potential temperature). Besides the concept of TTE, we take into account the non-gradient correction to the traditional buoyancy flux formulation. The proposed model permits the existence of turbulence at any gradient Richardson number, Ri. Instead of the critical value of Richardson number separating—as is usually assumed—the turbulent and the laminar regimes, the suggested model reveals a transitional interval, , which separates two regimes of essentially different nature but both turbulent: strong turbulence at ; and weak turbulence, capable of transporting momentum but much less efficient in transporting heat, at . Predictions from this model are consistent with available data from atmospheric and laboratory experiments, direct numerical simulation and large-eddy simulation.  相似文献   

生态环境与社会经济复合系统的协同进化   总被引：3，自引：2，他引：1       下载免费PDF全文

马向东  孙金华  胡震云 《水科学进展》2009,20(4):566-571

在系统分析水资源约束下生态环境与社会经济复合系统的竞争与合作关系的基础上,以协同学理论为基础,建立了复合系统的有序度模型和复合系统的协同进化模型,给出了相应的计算方法。论文对模型进行了相应分析,指出在不同情况下复合系统的协同进化分为3种情况:部分竞争替代、部分竞争共存、完全独立共存。以黑龙江垦区1986~2006年生态环境和社会经济复合系统的统计数据为基础,建立了相应的协同进化模型并进行分析计算,结果符合实际。  相似文献   

三角模糊数方法在水环境风险评价中的应用   总被引：1，自引：0，他引：1  

陈飞鸣  李玉强  田海龙 《地下水》2009,31(6):107-109

为了研究丁香湖再生水回用后对丁香水源地水质带来的风险,利用三角模糊法对再生水回用后丁香湖地区水质进行风险评价,得出北部污水处理厂的出水在未来可能对丁香湖周边的水源地产生污染,使此水源地无法保证出水的安全,甚至可能使之废弃的结论。建议对污水厂出水深度处理,严格控制相应指标后再进行回用,同时加强水源地保护,尽量阻止污染物进入水源地防护区。  相似文献   

太阳活动对京津冀地区旱涝的影响   总被引：3，自引：0，他引：3       下载免费PDF全文

池俊成  顾光琴 《高原气象》2009,28(5):1175-1180

利用中国气象科学院等整理的中国近五百年旱涝等级资料, 应用小波分析、 相关矩分析等方法, 详细分析了太阳黑子变化与京津冀地区旱涝的关系。在统计太阳黑子极值年附近旱涝特征时发现, 在太阳黑子峰值年附近京津冀地区容易出现偏旱的年份, 低谷年附近容易出现偏涝的年份。小波分析结果表明, 太阳黑子与旱涝指数在9.8年、 78.6年、 132.2年周期处存在对应关系, 说明太阳黑子的变化对京津冀地区的旱涝有一定影响。通过旱涝指数与太阳黑子相对数的相关矩分析, 发现两者相关关系存在阶段性的转折变化, 即由正相关转为负相关, 或者由负相关转为正相关, 相关矩发生转折的时间间隔最长为81年, 最短为23年, 平均为50年。本文还对相关矩阶段性变化的可能原因进行了初步分析。  相似文献   

影响广西的热带气旋年频数的BP神经网络预测模型   总被引：1，自引：0，他引：1  

何慧  欧艺  李艳兰 《热带气象学报》2009,25(4)

对影响广西的热带气旋(TC)年频数与大气环流的关系进行分析表明,TC年频数与全球范围大气环流异常有密切关系,特别是春季南半球中高纬度环流异常和低纬越赤道气流异常.利用相关分析从春季全球大气环流场中选择初选预报因子,然后对初选预报因子作EOF展开构造综合预报因子,运用BP神经网络方法建立TC年频数预报模型,并对所建立的模型进行独立样本试验.结果表明,该预报模型对历史样本拟合精度高,试报效果优于传统的逐步回归模型,可在汛期预测业务中应用.  相似文献   

南京北郊冬季大气气溶胶及其湿清除特征研究   总被引：18，自引：0，他引：18  

康汉青  朱彬  樊曙先 《气候与环境研究》2009,14(5):523-530

利用WPS(宽范围颗粒粒径谱仪)、雨滴潜仪和雾滴谱仪测量了2007～2008年冬季南京北郊大气气溶胶数浓度谱分布和降水强度,分析了气溶胶粒子的分布特征以及气溶胶粒径与湿清除系数的关系.结果表明:气溶胶粒子具有明显的双峰型R变化特征,数浓度主要集中在0.02～O.2μm粒径范围内,受汽车尾气排放、混合层高度变化以及颗粒物水平输送的影响较大.降雨、降雪和雾过程都对气溶胶粒子有不同程度的清除,降雨和浓雾对核模态和粗模态的气溶胶粒子的清除能力显著,降雪对粒径小于0.03μm的气溶胶粒子的清除能力较强.  相似文献   

Landslides susceptibility mapping based on geographical information system,GuiZhou, south-west China   总被引：6，自引：0，他引：6  

Wei Dong Wang  Cui Ming Xie  Xiang Gang Du 《Environmental Geology》2009,58(1):33-43

The purpose of this study is to assess the susceptibility of landslides around the area of Guizhou province, in south-west of China, using a geographical information system (GIS). The base map is prepared by visiting the field area and mapping individual landslide at a scale of 1:500,000 topographic maps. In the study, slope, lithology, landslide inventory, tectonic activity, drainage distribution and annual precipitation were taken as independent causal factors. Therefore, six causal factors maps are prepared by collecting information from various authorized sources and converting them in to GIS maps. The susceptibility assessment is based on the qualitative map combination model and trapezoidal fuzzy number weighting (TFNW) approach. Using a predicted map of probability, the study area was classified into four categories of landslide susceptibility: low, moderate, high and very high. In addition, the weighting procedure showed that the TFNW is an efficient method for landslide causal factors weighting.  相似文献   

The 27-Day and 22-Year Cycles in Solar and Geomagnetic Activity     

Mikhail G. Shnirman  Jean-Louis Le Mouël  Elena M. Blanter 《Solar physics》2009,258(1):167-179

We study the evolution of the longitudinal asymmetry in solar activity through the wave packet technique applied to the period domain of 25 – 31 days (centered at the 27-day solar rotation period) for the sunspot number and geomagnetic aa index. We observe the occurrence of alternating smaller and larger amplitudes of the 11-year cycle, resulting in a 22-year periodicity in the 27-day signal. The evolution of the 22-year cycle shows a change of regime around the year 1912 when the 22-year period disappears from the sunspot number series and appears in the aa index. Other changes, such as a change in the correlation between solar and geomagnetic activity, took place at the same time. Splitting the 27-day frequency domain of aa index shows an 11-year cycle for higher frequencies and a pure22-year cycle for lower frequencies, which we attribute to higher latitude coronal holes. This evidence is particularly clear after 1940, which is another benchmark in the evolution of the aa index. We discuss briefly the mechanisms that could account for the observed features of the 22-year cycle evolution.  相似文献   

北京市1998～2001年大气气溶胶粒子数浓度分析   总被引：13，自引：0，他引：13  

姜忠  石广玉  陈焕森 《气候与环境研究》2003,8(4):495-502

通过对北京市1998～2001年气溶胶数浓度的测量,分析了气溶胶粒子谱分布和数浓度变化,揭示了北京市气溶胶数浓度特征及其变化规律,同时还分析了沙尘与北京市气溶胶数浓度的联系.研究表明,北京市气溶胶数浓度自1998年逐年减小,2001年6月开始有所增加,气溶胶数浓度日变化特征同20世纪80年代有较大差异,北京市气溶胶变化与沙尘天气密切相关  相似文献