Experimental investigation of single blade and propeller loads by free running model test. Straight ahead sailing     

《Applied Ocean Research》2019

The understanding and the accurate assessment of propeller loads in realistic operative scenario, both design and off-design conditions, is of paramount importance to design low emission and comfortable ships, fulfilling the requirements of structural integrity of the propulsion system, safety and continuity of operations at sea. To this purpose, a deeper characterization of the propeller functioning, in terms of averaged and fluctuating loads, can be attained by means of the quantification of the single blade loads. In this work, a novel set up that allows to monitor the loads developed by a single blade was implemented on a free running, self propelled maneuvering model with the aim to investigate in details the hydrodynamic interactions between the spatially non-homogeneous and time-variant wake of the hull and the propeller and a complete characterization of its performance. This preliminary work introduces the experimental setup and provides a preliminary overview of the results relative to straight ahead motion.  相似文献   

Validation and comparison of Advanced Differential Interferometry Techniques: Murcia metropolitan area case study   总被引：1，自引：0，他引：1  

G. Herrera  R. Toms  J.M. Lopez-Sanchez  J. Delgado  F. Vicente  J. Mulas  G. Cooksley  M. Sanchez  J. Duro  A. Arnaud  P. Blanco  S. Duque  J.J. Mallorqui  R. De la Vega-Panizo  O. Monserrat 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(5):501-512

This paper is focused on the analysis of the performance of Stable Point Network (SPN) and Coherent Pixel Technique (CPT), which are Advanced Differential Interferometry Techniques (A-DInSAR) that estimate, among other results, mean deformation velocity maps of the ground surface and displacement time series from a SAR dataset. The test site is the metropolitan area of the city of Murcia (Spain) where a moderate slow subsidence induced by the overexploitation of aquifers is present. SAR data acquired between July 1995 and August 2005 from ERS and ENVISAT sensors have been processed by the SPN and CPT techniques and compared with in situ instrumental measurements assumed as reference. Experimental results have shown that both SPN and CPT techniques provide estimates of the deformation evolution in time with an absolute difference below 6 mm consistently in all comparisons: SPN vs extensometer, CPT vs extensometer and SPN vs CPT. The proposed validation and comparison experiment between both A-DInSAR techniques has been useful to observe their differences and complementarities.  相似文献   

A modified Becker’s split-window approach for retrieving land surface temperature from AVHRR and VIRR          下载免费PDF全文

权维俊  陈洪滨  韩秀珍  刘勇洪  叶彩华 《Acta Meteorologica Sinica》2012,26(2):229-240

In order to provide a long time-series,high spatial resolution,and high accuracy dataset of land surface temperature(LST) for climatic change research,a modified Becker and Li’s split-window approach is proposed in this paper to retrieve LST from the measurements of Advanced Very High Resolution Radiometer(AVHRR) onboard National Oceanic and Atmospheric Administration(NOAA)-7 to-18 and the Visible and InfraRed Radiometer(VIRR) onboard FY-3A.For this purpose,the Moderate Resolution Transmittance Model(MODTRAN) 4.1 was first employed to compute the spectral radiance at the top of atmosphere(TOA) under a variety of surface and atmosphere conditions.Then,a temperature dataset consists of boundary temperature T s(which is one of the input parameters to MODTRAN),and channels 4 and 5 brightness temperatures(T 4 and T 5) were constructed.Note that channels 4 and 5 brightness temperatures were simulated from the MODTRAN output spectral radiance by convolving them with the spectral response functions(SRFs) of channels 4 and 5 of AVHRRs and VIRR.The coefficients of modified Becker and Li’s split-window approach for various AVHRRs and VIRR were subsequently regressed based on this temperature dataset using the least square method.As an example of validation,one AVHRR satellite image over Beijing acquired at 0312 UTC 27 April 2008 by AVHRR onboard NOAA-17 was selected to retrieve the LST image using the modified Becker and Li’s approach.The comparison between this LST image and that from the MODIS level-2 LST product provided by the University of Tokyo in Japan indicates that the correlation coefficient is 0.88,the bias is 0.6 K,and the root mean square deviation(RMSD) is 2.1 K.Furthermore,about 70% and 37% pixels in the LST difference image,which is the result of retrieved LST image from AVHRR minus the corresponding MODIS LST image,have the values within ± 2 and ± 1 K,respectively.  相似文献   

Modern Agriculture in Advanced Placement Human Geography     

《The Journal of geography》2012,111(3-4):132-141

Abstract

This article is an overview of the agriculture section in the outline of the Advanced Placement (AP) human geography course. It is intended to provide a more detailed framework on which teachers may develop their own curriculum for the AP class. Special emphasis is given to the practice of agriculture in contemporary industrial societies. It also encourages teachers to balance the cultural and historical views of agriculture contained in many textbooks with an economic and geographic focus. Agribusiness is also given special treatment.  相似文献   

ALI 遥感数据在岩矿信息提取中的应用研究   总被引：1，自引：0，他引：1  

刘汉湖 《地质与勘探》2009,45(4):456-461

论文对研究区ALI数据进行了纯净像元提取,在此基础上,对纯净像元进行N-D散点图分析,选择出不同端元并进行归类分析,作为后期分类识别的样本.这里采用决策树方法对研究区岩矿进行识别,研究发现:样本区在MNF变换后图像上的波谱(前几个波段)可分性远远大于其在变换前图像上的波谱可分性,基于此的决策树分类方法能够识别出岩矿.  相似文献   

峡东区上震旦统陡山沱组发现宏体化石   总被引：25，自引：1，他引：25       下载免费PDF全文

陈孟莪  肖宗正 《地质科学》1991,(4):317-324

峡东区上震旦统陡山沱组顶部发现宏体化石,包括高级藻类和蠕虫类,共8属10种,其中有些分类未定的化石。这从形态学上证明了后生藻类植物的分化及第一次为后生动物在陡山沱期的存在提供了可信的证据。这是一次有突破性的发现。  相似文献   

基于ASCAT 散射计数据的2013 年南极周边海面风速特征分析     

张婷  张杰  杨俊钢 《海洋科学》2015,39(2):57-62

利用2013年1月1日~2013年12月31日的ASCAT散射计风速数据,从海面风速季平均分布特征、平均海面风速特征、海面风速大于10 m/s发生比例统计等方面,对55°S以南的南极周边海域开展了风速空间分布特性统计,得到以下结果:7月平均风速最大,为12 m/s,1月平均风速最小,为8 m/s。对于南极周边海域,区域平均风速主要在9~12 m/s,全年出现的时间大于280 d,约占全年的77%。风速大于10 m/s所占比例4~9月大于1~3月和10~12月。从全年来看,南极周边海域在4~9月风速普遍较大,且0°~60°W海域内风速明显比其他海域要小。在此基础上将2013年每日的区域平均风速与月平均风速与2012年做了对比,变化趋势与2012年基本一致。通过本项长期工作,可以了解南极风场环境基本情况,建立与更新基础资料和图件,得到南极地区风场要素时空分布、变化规律,服务于南极科学考察、全球变化等多学科研究应用。  相似文献   

云滴数浓度对超级单体龙卷影响的数值模拟研究     

王霁吟  陈宝君  郑凯琳  花少烽 《大气科学》2019,43(6):1413-1423

为了探讨云滴数浓度对于龙卷发生、发展的影响,利用ARPS（Advanced Regional Prediction System）模式,通过调整云滴数浓度（分别取高3000 cm-3、中1000 cm-3和低100 cm-3）的变化,对2003年7月8日安徽省无为县超级单体龙卷进行理想模拟试验。研究表明:三组试验都模拟出超级单体风暴的特征结构如钩状回波和V型入流缺口;云滴数浓度高的试验中上升气流更强、风暴较先发展且持续时间长,近地面涡度也较其他两组试验更大;从三组试验中找到4个龙卷涡旋,其中云滴数浓度高的试验中有两个,涡旋总持续时间接近30 min,最大近地面风速为46.93 m s-1,最大涡度值为0.42 s-1;高云滴数浓度情况下地面冷池弱,更有利于龙卷产生,并对龙卷的发生、发展有促进作用。  相似文献   

闪电河流域农牧交错带微波遥感土壤水分产品评价   总被引：1，自引：1，他引：0  

谢秋霞  贾立  陈琪婷  尹燕旻  Menenti Massimo 《遥感学报》2021,25(4):974-989

空间网格分辨率为9 km的SMAP (Soil Moisture Active and Passive)、0.1D (Degree)的ASCAT (The Advanced Scatterometer)、 25 km的FY-3B以及25 km ESA-CCI (European Space Agency-Climate Change Initiative)是较为广泛应用的卫星遥感土壤水分产品,对数据质量的评价是进一步应用于旱情监测、蒸散发估算等研究的前提。本研究基于2018年9月在闪电河流域内蒙古农牧交错带区域开展的碳、水循环与能量平衡遥感综合试验,采用近似同步的两种尺度观测数据即点尺度地面实测土壤水分数据以及面尺度(1 km×1 km)机载土壤水分数据,利用RMSE (Root Mean Square Error), MAE (Mean Absolute Error),R (Correlation Coefficient),Bias以及ubRMSE (unbiased Root Mean Square Error)等评价指标分别对SMAP, ASCAT, FY-3B, ESA-CCI土壤水分卫星遥感产品进行了评价。本研究利用机载土壤水分数据作为桥梁,实现了从点尺度地面实测土壤水分数据、至面尺度(1 km×1 km)机载土壤水分数据、再至粗格网面尺度(9 km×9 km、0.1 D×0.1 D、25 km×25 km)卫星遥感土壤水分产品的对比分析过程。利用地面观测值对机载观测土壤水分开展评价分析,发现在裸土区域,机载土壤水分数据与地面实测数据较为一致,RMSE, MAE, Bias, ubRMSE以及R值分别为0.033 cm~3/cm~3,0.030 cm~3/cm~3,-0.004 cm~3/cm~3, 0.033 cm~3/cm~3, 0.474。对卫星土壤水分产品的评价结果显示,SMAP的9 km土壤水分卫星产品与地面观测更为一致,其RMSE,MAE,Bias,ub RMSE以及R值分别为0.037 cm~3/cm~3,0.032 cm~3/cm~3,-0.008 cm~3/cm~3, 0.036 cm~3/cm~3, 0.507。SMAP, ASCAT, FY-3B以及ESA-CCI与机载土壤水分数据有更高的相关性,R值分别为0.735, 0.558, 0.558, 0.575。综上,闪电河流域实验区内的4种卫星遥感土壤水分产品中,SMAP产品与地面土壤水分、机载土壤水分数据均较为一致,其次是FY-3B与ESA-CCI。  相似文献   

AREMS/973模式系统对2004年中国汛期降水实时预报检验   总被引：1，自引：0，他引：1  

吴秋霞  史历  翁永辉 《大气科学》2007,31(2):298-310

2004年夏季5～8月，AREMS/973模式系统投入了业务运行，模式区域主要覆盖了中国大陆及周边临近地区，该模式系统基于中国气象局MICAPS/9210业务数据平台，每天2次、完全自动的实时预报24 h累积降水。作者主要对每日0000 UTC时起报的24 h累积降水预报场进行综合检验，由此对AREMS/973模式系统的24 h降水预报能力给予客观的评价。AREMS/973模式系统对于中国汛期降水具有很强的预报能力，其24 h 累积降水的月总降水分布很好地反应了汛期各时期主雨带的位置、强度及范围，同时该模式系统能够准确预报出独立降水事件的发生和发展，其中，长江中下游和东北地区预报降水与观测降水的时间位相吻合最好；除了5月和8月华北地区、5月西南东部地区、以及5月和6月长江中下游地区，AREMS/973模式系统预报的降水强度总体上弱于观测降水强度，且对于25 mm 以上量级的降水过程， 模式预报的降水范围小于观测降水范围。AREMS/973模式系统预报降水的能力随着降水量级的增大而减小，降水量级愈大，模式预报技巧愈低，对于50 mm 以上量级的降水过程，模式系统预报降水事件的发生概率类似于随机偶然事件的发生概率。5月，长江中下游地区降水预报略优于其他地区，其次是华南地区，6月雨带北移至江南和江淮地区，此时，长江中下游地区降水预报显著优于其他地区，7月末至8月华北雨季开始，降水预报最优区北移至华北地区，即AREMS/973模式系统降水预报最优区随着雨带的北移而北移，主雨带所在区域往往也是模式降水预报最优的地区。作者对此进行了初步探讨。  相似文献