Velocity profiles and bed shear stress over various bed configurations in a river bend     

John S. Bridge  Jack Jarvis 《地球表面变化过程与地形》1977,2(4):281-294

Vertical velocity profiles measured over various bed configurations (plane beds, ripples, and dunes) in. the meandering River South Esk, Glen Clova, Scotland are presented on semilogarithmic paper. Local bed shear stress and roughness height are calculated from the lowermost parts of the profiles using the Karman-Prandtl law of the wall; these parameters, and the geometrical properties of the profiles, are related to the various bed configurations. A graphical model is used to identify profiles developed on specific regions of dune geometry, in order to discriminate those profiles that define bed shear effective in transporting sediment over dunes. An assessment is made of the errors involved in estimating local mean velocity from extrapolating the law of the wall to the water surface. A Darcy-Weisbach friction coefficient is related to bed configuration and local stream power.  相似文献   

Parameter analysis for gate metal—oxide—semiconductor structures of ion-implanted 4H silicon carbide metal—semiconductor field-effect transistors     

王守国  张义门  张玉明 《海洋学报(英文版)》2010,29(9)

From the theoretical analysis of the thermionic emission model of current--voltage characteristics, this paper extracts the parameters for the gate Schottky contact of two ion-implanted 4H-SiC metal--semiconductor field-effect transistors (sample A and sample B for three and four times multiple ion-implantation channel region respectively) fabricated in the experiment, including the ideality factor, the series resistance, the zero-field barrier height, the interface oxide capacitance, the interface state density distribution, the neutral level of interface states and the fixed space charge density. The methods to improve the interface of the ion-implanted Schottky contact are given at last.  相似文献   

利用相关逼近法建立定位与姿态数据的同步模型          下载免费PDF全文

齐珺  暴景阳  周丰年  崔扬  冯金涛 《海洋测绘》2010,30(2):28-31

根据海道测量精密测量的需求,对姿态与定位数据融合的同步方法进行了研究。通过GPS大地高数据和升沉数据,建立了一种基于相关逼近原理的定位与姿态数据同步模型。该模型能够确定定位与姿态数据的相对延时,实现两类数据在同一时间基准下的同步。实例计算表明,定位与姿态数据的相对延迟时间已成为两类数据融合应用中必须考虑的因素。由同步模型解算后,GPS大地高数据与总升沉数据体现了更好的一致性,由此也验证了模型的有效性。  相似文献   

Characteristics of developing waves as a function of atmospheric conditions,water properties,fetch and duration     

J.P. Le Roux 《Coastal Engineering》2009

For any specific wind speed, waves grow in period, height and length as a function of the wind duration and fetch until maximum values are reached, at which point the waves are considered to be fully developed. Although equations and nomograms exist to predict the parameters of developing waves for shorter fetch or duration conditions at different wind speeds, these either do not incorporate important variables such as the air and water temperature, or do not consider the combined effect of fetch and duration. Here, the wind conditions required for a fully developed sea are calculated from maximum wave heights as determined from the wind speed, together with a published growth law based on the friction velocity. This allows the parameters of developing waves to be estimated for any combination of wind velocity, fetch and duration, while also taking account of atmospheric conditions and water properties.  相似文献   

Analysis of threshold and incipient conditions for sediment movement     

A.A. Beheshti  B. Ataie-Ashtiani 《Coastal Engineering》2008

Prediction of threshold conditions and incipient motion is the essential issue for the study of sediment transport. This work compares existing empirical threshold curves proposed for Shields diagram, a method based on the concept of probability of sediment movement, and an empirical method based on movability number. These methods are used to predict the incipient motion conditions for experimental runs taken from various studies. Most of the experimental data, used in this work, have not been used before in derivation of alternative formulations for Shields diagram and other methods. The empirical threshold curves based on the Shields entrainment function was the least successful at predicting the measured incipient motion conditions, while the use of the movability number gives good predictions of critical shear velocity compared with experimental data.  相似文献   

共线条件方程在建筑物比高求解中的应用     

李二森  张保明  郭海涛  郑明清  徐安建  赵建超 《海洋测绘》2008,28(1):46-48

高度信息作为人工地物的重要属性信息，在军事和民用上都具有很高的利用价值。针对人工地物高度提取的发展现状及存在的主要问题，对单张航片利用共线条件方程确定人工地物比高方法的原理和技术进行了研究，并进行了实验，验证了方法的可行性。  相似文献   

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荣敏  周巍  陈春旺 《大地测量与地球动力学》2009,29(6):123-125

?????й?854??GPS/?????????EGM2008??EGM96?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????289??GPS/??????н????????????????????????????????????????????????EGM2008???EGM96???????á?  相似文献   

Variations of Kuroshio geostrophic transport south of Japan estimated from long-term IES observations     

Koji Kakinoki  Shiro Imawaki  Hiroshi Uchida  Hirohiko Nakamura  Kaoru Ichikawa  Shin-Ichiro Umatani  Ayako Nishina  Hiroshi Ichikawa  Mark Wimbush 《Journal of Oceanography》2008,64(3):373-384

Two inverted echo sounders were maintained on coastal and offshore sides of the Kuroshio south of Japan from October 1993 to July 2004. Applying the gravest empirical mode method, we obtained a time series of geostrophic transport. Estimated transports generally agree well with geostrophic transports estimated from hydrography. Their agreement with the hydrographic transports is better than that of transports estimated from satellite altimetry data. The geostrophic transport is expressed as the surface transport per unit depth multiplied by the equivalent depth. The geostrophic transport varies mostly with the surface transport and fractionally with the equivalent depth. Seasonal variation of the geostrophic transport has a minimum in March and a maximum in September, with a range of about one fifth of the total transport.  相似文献   

Seasonality and duration in extreme value distributions of significant wave height     

Fernando J. Mndez  Melisa Menndez  Alberto Luceo  Raúl Medina  Nicholas E. Graham 《Ocean Engineering》2008,35(1):131-138

This paper presents a statistical model to characterize the long-term extreme value distribution of significant wave height, conditioning to the duration of the storm and accounting for seasonality. A time-dependent version of the peak over threshold (POT) approach is used to build the model, which is then applied to specific reanalysis time series and NOAA buoy records. The model considers the annual and semiannual cycles which are parameterized in terms of harmonic functions. The inclusion of seasonal variabilities substantially reduces the residuals of the fitted model. The information obtained in this study can be useful to design maritime works, because (a) the model improves the understanding of the variability of extreme wave climate along a year and (b) the model accounts for the duration of the storm, which is a key parameter in several formulations for rubble mound breakwater design.  相似文献   

模糊神经网络在GPS高程转换中的应用   总被引：1，自引：1，他引：0  

方毅  雒卫民 《地理空间信息》2009,7(4):108-110

介绍了T-S模糊神经网络的基本原理以及如何确定GPS高程转换的模糊神经网络模型，并采用该模型对实测数据进行了计算分析。结果表明，模糊神经网络能够对小区域GPS高程做出比较准确定的拟合，从而能够为GPS高程转换提供一种较好的方法，能够满足实际工程需要。  相似文献