Analysis of interaction between ship bottom air cavity and boundary layer     

《Applied Ocean Research》2016

The successful designs of hulls for ships employing drag reduction by air bottom cavitation have been based on solutions of inverse problems of the theory of ideal incompressible fluid. However, prediction of the drag reduction ratio, the air demand by ventilated cavities and the cavity impact on the hull–propeller interaction is impossible in the framework of this theory because all mentioned characteristics depend on interaction of air cavities with the ship boundary layers. Because the known CFD tools are not fitted to ventilated cavitation at low Froude numbers, an analysis of this interaction requires a novel flow model. This model includes the incompressible air flow in the ventilated cavity, the compressible flow of a water–air mixture in the boundary layer on cavities and downstream of them and the curl-free incompressible outer water flow. The provided 2D computations employing this model allows for explanations of the earlier observed effects and for prediction of the air demand by ventilated cavities. The computed velocity profiles downstream of cavities are in the accordance with the available experimental data.  相似文献   

肥城市土地生态系统安全评价研究          下载免费PDF全文

魏宁宁  李文海  孙晓芳 《山东国土资源》2016,32(4):46-50

在分析土地生态系统安全内涵的基础上,以肥城市为研究区域,选取24个指标构建土地生态系统安全评价指标体系,采用熵值法、综合指数法和GIS相结合的方法,对肥城市2000—2013年的土地生态系统安全状况进行分析。研究结果表明:14年来,肥城市土地生态系统安全状况处于波动状态,土地生态系统安全面临着诸多压力。最后提出了提高土地生态系统安全状况的对策建议。  相似文献   

石墨、萤石等战略非金属矿产发展趋势研究     

陈军元  刘艳飞  颜玲亚  高树学  欧阳友和  龙涛 《地球学报》2021,42(2):287-296

战略性新兴产业几乎或多或少都与非金属矿及其制品有关,随着战略性新兴产业的发展,我国战略性矿产资源消费将迎来快速增长期.本文选取石墨、萤石、高纯石英、叶蜡石四种非金属矿产为战略非金属矿产,收集其产量、消费量、贸易情况等资料,对其重要性及用途、供需情况等进行研究,并对其未来需求趋势进行预测.本文认为石墨、高纯石英、萤石、叶蜡石在战略性新兴产业中有重要应用,未来需求将呈快速增长趋势,其中石墨、萤石2030年需求量分别为138.7万t、567.9万t.为国家制定勘查投入及产业发展政策提供参考.  相似文献   

谈新形势下地勘单位改革发展的现状及未来发展方向     

闫国红  王瑞丰  张成兵  翟延亮  韩立红  马双双  王海明  姚伟 《中国煤炭地质》2021,(3):79-82

新中国成立以来,地勘单位先后在计划经济和市场经济下为国家的发展做出了重要贡献,也先后经历了初步探索、属地化管理、事企分体运行等不同阶段。十九大以来,随着事业单位改革的逐步深入,地勘单位改革迫在眉睫。为了更好的适应时代发展,又快又好地进行地勘单位转型,通过研究不同历史时期地勘单位发展的问题和困难,指出现阶段面临的主要问题是改革意愿不强烈、转型工勘领域受阻、资本占有率低和人才匮乏。以此为基础,提出转变思想、学习集团化企业路线、投身地方产业结构、全面提升自然资源意识、加强自身建设和长期持续稳定转型的发展建议,供转型发展的地勘单位参考。  相似文献   

阻塞形势下内蒙古东南部地区一次冷涡暴雨过程水汽特征分析     

马素艳  伊娜娜  赵斐  张旭 《气象与环境学报》2019,(2):1-8

使用常规观测资料、FY-2G卫星及1°×1°的NCEP再分析资料,对2017年7月6—7日内蒙古东南部地区一次冷涡暴雨天气过程进行分析。结果表明:在稳定的"一槽一脊"型环流背景下,阻塞高压稳定维持,西风槽东移受阻移动缓慢,加深为涡,暴雨发生在冷涡发展加强阶段;低空急流建立,一方面形成偏南水汽输送,为暴雨提供源源不断的水汽,水汽收支主要集中在700 hPa以下,暴雨发生前水汽净收入明显增大,南、北边界水汽贡献率大;另一方面,偏南暖湿气流的输送使不稳定层结建立,能量在暴雨区积聚,偏南低空急流与高空急流耦合,又为暴雨发生提供了动力条件;暴雨发生前后湿度场变化显著,大气可降水量最大达到55—60 kg·m^-2,且暴雨发生前增幅显著,增幅近2倍。暴雨区700 hPa (850 hPa)上比湿不低于7 g·kg^-1(12 g·kg^-1),强降水出现在水汽图上白亮区断裂消失后,高层比湿峰值附近和相当黑体温度<230 K为强降水高发区。  相似文献   

Effect of connecting rain barrels on the storage size reduction     

Yongwon Seo  Nam‐Jeong Choi  Daeryong Park 《水文研究》2012,26(23):3538-3551

In this article, the possibility of sharing rain barrels and the potential benefit of reducing storage size through physical and non‐physical connections of rain barrels in a community are investigated. Using the concepts of homogeneous/heterogeneous users in rainwater harvesting systems (RWHS), two simple cases of a community composed of four prospective users are examined. The first is performed with the users who have the same mean and variance in water demands (homogeneous users), and the second is with the users with different means and variances (heterogeneous users). To take account for the rainfall characteristics in different places, historical records from six cities in the USA are used for storage–reliability–yield analysis. The result indicates that required total storage can be reduced by connecting multiple rain barrels. In addition, a significant difference is found between homogeneous and heterogeneous user groups. Homogeneous users do not achieve a substantial benefit from connecting their rain barrels; these users may even be disadvantaged by sharing. In contrast, heterogeneous users receive benefit by reducing the total required storage. Most benefit is expected between users with maximum difference in mean water demands. The reduction in storage size was as considerable as 37% in this study. The quantity of storage reduction depends on locations and target reliabilities. Knowledge of the benefits and limitations of rain barrel connections can improve RWHS performance through ability to customize a network plan for individual users. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Water flux measurement and prediction in young cashew trees using sap flow data     

Philip G. Oguntunde  Nick van de Giesen 《水文研究》2005,19(16):3235-3248

Measurements of sap flow, meteorological parameters, soil water content and tension were made for 4 months in a young cashew (Anacardium occidentale L.) plantation during the 2002 rainy season in Ejura, Ghana. This experiment was part of a sustainable water management project in West Africa. The Granier system was used to measure half‐hourly whole‐tree sap flow. Weather variables were observed with an automatic weather station, whereas soil moisture and tension were measured with a Delta‐T profile probe and tensiometers respectively. Clearness index (CI), a measure of the sky condition, was significantly correlated with tree transpiration (r² = 0·73) and potential evaporation (r² = 0·86). Both diurnal and daily stomata conductance were poorly correlated with the climatic variables. Estimated daily canopy conductance g_c ranged from 4·0 to 21·2 mm s⁻¹, with a mean value of 8·0 ± 3·3 mm s⁻¹. Water flux variation was related to a range of environmental variables: soil water content, air temperature, solar radiation, relative humidity and vapour pressure deficit. Linear and non‐linear regression models, as well as a modified Priestley–Taylor formula, were fitted with transpiration, and the well‐correlated variables, using half‐hourly measurements. Measured and predicted transpiration using these regression models were in good agreement, with r² ranging from 0·71 to 0·84. The computed measure of accuracy δ indicated that a non‐linear model is better than its corresponding linear one. Furthermore, solar radiation, CI, clouds and rain were found to influence tree water flux. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

A CASE STUDY ON SANDSTORM   总被引：5，自引：0，他引：5       下载免费PDF全文

杨东贞  徐晓斌  温玉璞 《Acta Meteorologica Sinica》1991,(2)

The favourable synoptic situation and climate background for a sandstorm process,which occurred in theperiod 9—16 April 1988,have been studied through analyzing weather maps,meteorological elements,satellitecloud pictures and sandstorm trajectories.The sand dust origin area,the directions and the paths of sanddust transport,and the extent the sand dust reached are also investigated.The results of measurments andanalysis indicate that the concentration of sand dust particles is 10 times greater than the normal.It is also shownthat the elements in the sand dust are lithophylic and come from natural source through the chemical composi-tion analysis of the sand dust,so that the sand dust has not been polluted by human activities.  相似文献   

地震系统文献资源的现状及其发展对策     

梁凯利  赵小倩 《国际地震动态》1995,(2):14-17

本文概述了地震系统文献资源的现状及其发展对策，内容包括地震文献资源概况、地震文献资源的调查分析、地震系统文献资源建设中存在的主要问题以及地震文献资源建设发展对策。  相似文献   

基于RS的新疆哈密地区生态环境需水分析     

尹小君  周可法  包安明  王涛  孙莉 《干旱区地理》2007,30(3):57-363

干旱半干旱地区水资源缺乏,准确地计算区域生态环境用水和生态环境需水,可以对稀缺水资源进行合理调配,同时起到生态保护的作用。研究过程主要分为两个步骤:(1)采用RS技术,对新疆哈密地区1990年、2000年、2005年中巴资源一号卫星(China Brazil Earth Resources Sat-ellite)数据进行解译,形成1990年、2000年、2005年哈密地区土地覆被图形数据和相应的属性数据,确定相应年份各景观类型的面积;(2)参考有关研究并结合哈密地区实际情况,确定各景观类型的单位生态用水定额和需水定额,进而计算出1990年、2000年、2005年哈密地区的生态用水量,并以2005年哈密地区生态用水量为主要依据计算出保持哈密地区生态环境现状的生态需水量。研究结果表明,为了实现哈密地区生态环境整体保持在现状水平不致恶化、局部区域生态环境(巴里坤湖区)有所改善的生态治理目标,区域内生态环境需水总量为7.526×109m3,这一庞大的需水量将对该地区水资源配置造成巨大的压力;而当结合各类景观的地物空间位置特征进行分析时,发现该区域生态用(需)水量最大的景观(低覆盖草地)可以利用山地积雪融水进行自给,区域内实际需要规划配置的生态环境需水量为2.66×108m3,仅占区域生态环境需水总量的3.53%。在区域生态用(需)水计算过程中应考虑各种景观类型的生态用(需)水量的时空差异性,以保证水资源调配的科学与合理。  相似文献