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831.
832.
833.
该文研究了海洋平台输液管道振动流的行为特性。依据振荡流体力学基本原理 ,建立了输液管道非定常、不可压缩、粘性振动流的物理模型和数学模型。推导出了关于流场速度、压力系数的微分方程组 ,得到了不同条件下流动的速度和压力分布。结果表明流体诱发的海洋平台输液管道振动流的行为特性受管道结构形状及流体性质的影响。比较等截面管道的变分解和数值解 ,说明本文所选用的方法用于研究海洋平台输液管道振动流是有效的。 相似文献
834.
利用小波包分析和混沌特征提取进行船舶辐射噪声分类 总被引:3,自引:2,他引:3
基于船舶辐射噪声信号具有非线性、非平稳的特征,提出采用提取船舶辐射噪声信号的非线性混沌特征量和多尺度小波能量特征,并将两者综合作为特征参数输入神经网络分类器进行船舶分类识别。实验结果表明,该方法能较好地区分不同类型的船舶。 相似文献
835.
836.
Predictive vegetation modeling is defined as predicting the distribution of vegetation across a landscape based upon its relationship with environmental factors. These models generally ignore or attempt to remove spatial dependence in the data. When explicitly included in the model, spatial dependence can increase model accuracy. We develop presence/absence models for 11 vegetation alliances in the Mojave Desert with classification trees and generalized linear models, and use geostatistical interpolation to calculate spatial dependence terms used in the models. Results were mixed across models and methods, but in general, the spatial dependence terms more consistently increased model accuracy for widespread alliances. GLMs had higher accuracy in general. 相似文献
837.
Estimating vertical velocity in the oceanic upper layers is a key issue for understanding ocean dynamics and the transport
of biogeochemical elements. This paper aims to identify the physical sources of vertical velocity associated with sub-mesoscale
dynamics (fronts, eddies) and mixed-layer depth (MLD) structures, using (a) an ocean adaptation of the generalized Q-vector form of the ω-equation deduced from a primitive equation system which takes into account the turbulent buoyancy and momentum fluxes and
(b) an application of this diagnostic method for an ocean simulation of the Programme Océan Multidisciplinaire Méso Echelle
(POMME) field experiment in the North-Eastern Atlantic. The approach indicates that w-sources can play a significant role in the ocean dynamics and strongly depend on the dynamical structure (anticyclonic eddy,
front, MLD, etc.). Our results stress the important contribution of the ageostrophic forcing, even under quasi-geostrophic
conditions. The turbulent w-forcing was split into two components associated with the spatial variability of (a) the buoyancy and momentum (Ekman pumping)
surface fluxes and (b) the MLD. Process (b) represents the trapping of the buoyancy and momentum surface energy into the MLD
structure and is identified as an atmosphere/oceanic mixed-layer coupling. The momentum-trapping process is 10 to 100 times
stronger than the Ekman pumping and is at least 1,000 times stronger than the buoyancy w-sources. When this decomposition is applied to a filamentary mixed-layer structure simulated during the POMME experiment,
we find that the associated vertical velocity is created by trapping the surface wind-stress energy into this structure and
not by Ekman pumping. 相似文献
838.
839.
Linear combinations of order statistics to estimate the quantiles of generalized pareto and extreme values distributions 总被引:2,自引:0,他引:2
G. Salvadori 《Stochastic Environmental Research and Risk Assessment (SERRA)》2003,17(1-2):116-140
Ad hoc techniques for estimating the quantiles of the Generalized Pareto (GP) and the Generalized Extreme Values (GEV) distributions
are introduced. The estimators proposed are based on new estimators of the position and the scale parameters recently introduced
in the Literature. They provide valuable estimates of the quantiles of interest both when the shape parameter is known and
when it is unknown (this latter case being of great relevance in practical applications). In addition, weakly-consistent estimators
are introduced, whose calculation does not require the knowledge of any parameter. The procedures are tested on simulated
data, and comparisons with other techniques are shown.
The research was partially supported by Contract n. ENV4-CT97-0529 within the project “FRAMEWORK” of the European Community – D.G. XII. Grants by “Progetto Giovani Ricercatori” are also acknowledged. 相似文献
840.
一种基于多项式外推的局部透射边界位移解(外行波为平面波情形) 总被引:3,自引:4,他引:3
基于外行波局部法向透射概念,从多项式外推的角度,结合一维和广义二维几何解释,推导建立了外行波为平面波时,人工边界节点位移解的计算公式。对该位移解的精度进行了时域分析,论证了该位移解收敛于数值精确解的必要条件和线性外推位移解的精度与数值精确解匹配的充要条件。在此基础上提出了一次“精确”透射的概念和相应的数学方法,实现了该位移解逼近于数值精确解的优化计算。 相似文献