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黄思训 《高校应用数学学报(A辑)》1988,(4)
油膜自激振动是引起机械振动的一个重要原因之一,大型发电机组由于油膜自激振动而影响机组直至破坏机组,国内外都有文献纪录。本文采用一个简单近似模拟系统说明油膜自激振动与极限环是密切相关的。且给出实例说明消除这类自激振动也就是说改变轴承的几何尺寸与各参数的关系是行之有效的办法。 相似文献
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大气中非线性波动的非频散解——Ⅰ.拟能影响函数及其应用 总被引:1,自引:0,他引:1
本文讨论大气中非线性波动的非频散解。在引入相角函数后,把大气中非线性偏微分方程组化为非线性常微分方程组。在系统的平衡点及奇异点附近讨论轨线性质,得到了非线性波动的一系列解析表达式。本文第一部分主要讨论二个问题1.拟能及拟能影响函数与非线性波解的关系,通过对拟能影响函数的讨论,可以判定周期解、孤波解、间断周期解与间断孤波解的存在条件,并且指出外界扰动若使拟能影响函数发生微小变化,则会导致孤立波的产生。2.间断周期解存在性讨论及函数逼近方法的使用。在求近似解过程中往往采用Taylor展开方法,但带来许多麻烦,本文对拟能影响曲线采用函数逼近的方法收到了良好的效果。 相似文献
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Application of Tikhonov regularization method to wind retrieval from scatterometer data Ⅱ: cyclone wind retrieval with consideration of rain 下载免费PDF全文
According to the conclusion of the simulation experiments in paper I, the Tikhonov regularization method is applied to cyclone wind retrieval with a rain-effect-considering geophysical model function (called GMF+Rain). The GMF+Rain model which is based on the NASA scatterometer-2 (NSCAT2) GMF is presented to compensate for the effects of rain on cyclone wind retrieval. With the multiple solution scheme (MSS), the noise of wind retrieval is effectively suppressed, but the influence of the background increases. It will cause a large wind direction error in ambiguity removal when the background error is large. However, this can be mitigated by the new ambiguity removal method of Tikhonov regularization as proved in the simulation experiments. A case study on an extratropical cyclone of hurricane observed with SeaWinds at 25-km resolution shows that the retrieved wind speed for areas with rain is in better agreement with that derived from the best track analysis for the GMF+Rain model, but the wind direction obtained with the two-dimensional variational (2DVAR) ambiguity removal is incorrect. The new method of Tikhonov regularization effectively improves the performance of wind direction ambiguity removal through choosing appropriate regularization parameters and the retrieved wind speed is almost the same as that obtained from the 2DVAR. 相似文献
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This paper addresses the problem of estimating lower
atmospheric refractivity under the nonstandard propagation conditions
frequently encountered in low altitude maritime radar applications.
The vertical structure of the refractive environment is modeled by
using a five-parameter model, and the horizontal structure is modeled
as range-independent. The electromagnetic propagation in the
troposphere is simulated by using a split-step fast Fourier
transform based on parabolic approximation to the wave equation. A
global search marked as a modified genetic algorithm (MGA) for the 5
environmental parameters is performed by using a genetic algorithm
(GA) integrated with a simulated annealing technique. The retrieved
results from simulated runs demonstrate the ability of this method
to make atmospheric refractivity estimations. A comparison with the classical GA
and the Bayesian Markov Chain Monte Carlo (Bayesian-MCMC) technique
shows that the MGA can not only shorten the inverse time but also
improve the inverse precision. For real data cases, the inversion
values do not match the reference data very well. The
inverted profile, however, can be used to synoptically describe
the real refractive structure. 相似文献
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本文提出了一个不含科氏力但包括频散效应和耗散效应的二层模式,证明了在一定参数条件下,该模式中除包含有非线性周期解和孤波解外,还包含有单调和振荡型的行波解。文中给出了它们存在的条件。特别指出:振荡型的行波解的波形与一类飑线过境时气压涌升的波形很类似。 相似文献
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把赤道东太平洋地区大气对流层,海洋混合层看作是在定常热源(太阳辐射)驱动下的动力系统,利用一个局域平均的热力学气候模式,建立了海气耦合自激振荡模型,得到了一个封闭的自治的二次系统,对系统进行了线性和非线性分析.结合系统稳定的极限环解,对海气耦合的物理机制进行了探讨.和观测事实的比较表明,在赤道东太平洋区域平均的以500 hPa为代表的大气对流层的温度距平和海表温度距平,在相平面上和极限环解定性上很一致.这为研究热带海气相互作用的年际变化提供了一个理论模型. 相似文献
30.
Theoretical aspects of variational data assimilation (VDA) for a simple model with both global and local observational data are discussed. For the VDA problems with global observational data, the initial conditions and parameters for the model are revisited and the model itself is modified. The estimates of both error and convergence rate are theoretically made and the validity of the method is proved. For VDA problem with local observation data, the conventional VDA method are out of use due to the ill-posedness of the problem. In order to overcome the difficulties caused by the ill-posedness, the initial conditions and parameters of the model are modified by using the improved VDA method, and the estimates of both error and convergence rate are also made. Finally, the validity of the improved VDA method is proved through theoretical analysis and illustrated with an example, and a theoretical criterion of the regularization parameters is proposed. 相似文献