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排序方式: 共有286条查询结果,搜索用时 703 毫秒
1.
重庆地面最高气温与最大风速年极值的渐近分布 总被引:3,自引:0,他引:3
利用重庆1951-1990年间地面最高气温和1956-1990年间地面最大风速年极值的记录,采用韦伯分布和耿贝尔分布分别对其渐近分布进行拟合.通过统计推断,找出重庆地面最高气温和地面最大风速年极值遵循的最佳渐近分布--韦伯分布. 相似文献
2.
This paper investigates the use of data assimilation in coastal area morphodynamic modelling using Morecambe Bay as a study site. A simple model of the bay has been enhanced with a data assimilation scheme to better predict large-scale changes in bathymetry observed in the bay over a 3-year period. The 2DH decoupled morphodynamic model developed for the work is described, as is the optimal interpolation scheme used to assimilate waterline observations into the model run. Each waterline was acquired from a SAR satellite image and is essentially a contour of the bathymetry at some level within the inter-tidal zone of the bay. For model parameters calibrated against validation observations, model performance is good, even without data assimilation. However the use of data assimilation successfully compensates for a particular failing of the model, and helps to keep the model bathymetry on track. It also improves the ability of the model to predict future bathymetry. Although the benefits of data assimilation are demonstrated using waterline observations, any observations of morphology could potentially be used. These results suggest that data assimilation should be considered for use in future coastal area morphodynamic models. 相似文献
3.
Parameter sensitivity of three Kalman filter schemes for assimilation of water levels in shelf sea models 总被引:2,自引:0,他引:2
In applications of data assimilation algorithms, a number of poorly known assimilation parameters usually need to be specified. Hence, the documented success of data assimilation methodologies must rely on a moderate sensitivity to these parameters. This contribution presents a parameter sensitivity study of three well known Kalman filter approaches for the assimilation of water levels in a three dimensional hydrodynamic modelling system. The filters considered are the ensemble Kalman filter (EnKF), the reduced rank square root Kalman filter (RRSQRT) and the steady Kalman filter. A sensitivity analysis of key parameters in the schemes is undertaken for a setup in an idealised bay. The sensitivity of the resulting root mean square error (RMSE) is shown to be low to moderate. Hence the schemes are robust within an acceptable range and their application even with misspecified parameters is to be encouraged in this perspective. However, the predicted uncertainty of the assimilation results are sensitive to the parameters and hence must be applied with care. The sensitivity study further demonstrates the effectiveness of the steady Kalman filter in the given system as well as the great impact of assimilating even very few measurements. 相似文献
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Hubert Hellmann 《洁净——土壤、空气、水》2003,31(2):85-96
A Recent Contamination Trend: Polycylic Aromatic Hydrocarbons (PAHs) in Aquatic and Terrestrial Sediments Concentrations of polycylic aromatic hydrocarbons (PAHs) measured in aquatic sediments of small, medium‐sized or very large inland lakes, of estuaries as well as in terrestrial sediments from Germany, the UK, Finland, and the USA were plotted in 10 trend curves over the period from 1800 to 1990. The segments of the bore cores were dated for their deposition age. For comparability of the results, the trend is preferentially shown by the guide parameter fluoranthene. Until the 19th century, a constant background value of CFluo = 10…50 μg/kg was observed in all regions. Then a steep increase in concentration followed, reaching in the aquatic sediments a maximum in the period 1940 to 1965, while the individual fluoranthene values ranged widely from 90 to 2400 μg/kg. In several regions, a more or less distinct decrease superseded this maximum, although this development did not appear in terrestrial sediments, in one estuary, and in remote forest lakes in Finland. The trend curves reflect the atmospheric deposition of PAHs in airborne dust and in some cases the import through runoff via rivers. Thus, the sediment profiles depict the development of air pollution by pyrogenic contaminants over more than a century. Sediment profiles from rivers can be used only with a high degree of reservation, because of the irregularity and low representativity of the sedimentation. 相似文献
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根据旋回特征可把西藏南部的中白垩纪地层分为四个等级。第一级旋回主要是大套的碎屑岩与碳酸盐岩的交替,以及生物种类的变化,表现了当时海平面周期性变化。第二级旋回代表了古生产率和氧化还原的韵律性变化,通过对CaCO3含量的AR-FFT处理得出的周期(ZMa)与Berger等人所计算的理论周期基本相符。因此,可以认为这种旋回根本原因是因轨道参数变化所引起的古环流改变所造成,如地中海型环流与河口型环流的互换,必将导致古生产率以及海洋水体性质的改变。第三级旋回表现为层偶的变化,如泥岩与灰岩互层以及黑色页岩与灰岩互层,在本区主要有三个周期:4.3、5.2和9.2万年,它们分别相当于斜率(ε)和偏心率(C)的理论周期值,旋回的周期主要是因为气候的变化引起陆源物质的稀释作用发生周期性变化,气候的周期性变化是由于轨道参数的改变而引起,因此,这种族回具有全球的可对比性。第四级旋回是由于海水里季节性变化所引起的纹层状层理。 相似文献
8.
框架结构的串联多自由度简化体系等效刚度参数的识别法 总被引:1,自引:0,他引:1
地框架结构和高耸建筑物进行地震反应分析时它常常被简化为串联多自由度体系。本文对此体系的刚度参数提出了一般的计算方法-参数识别法。 相似文献
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10.
Ian Knowles Michael Teubner Aimin Yan Paul Rasser Jong Wook Lee 《Hydrogeology Journal》2007,15(6):1107-1118
A new inverse technique for modelling groundwater flow, based on a functional minimization technique, has been used to calibrate
a groundwater flow model of a subregion of the Port Willunga aquifer within the Willunga Basin in South Australia. The Willunga
Basin is the location of extensive viticulture, irrigated primarily by groundwater, the levels and quality of which have declined
significantly over the last 40 years. The new method is able to generate estimates of transmissivity, storativity and groundwater
recharge over the whole subregion as a time-varying continuous surface; previous methods estimate local discrete parameter
values at specific times. The new method has also been shown to produce accurate head values for the subregion and very good
estimates of groundwater recharge. Its ultimate goal will be to provide a new and invaluable tool for significantly improved
groundwater resource management.
Supported in part by US National Science Foundation grants, DMS-0107492 and DMS-0079478. 相似文献