低频大气声重波的非线性Schrdinger方程

本文采用多重时空尺度展开的方法,对于不可压缩等温大气,导出了二维情况下低频声重波的非线性Schrdinger方程,讨论了声重波的非线性性质.在垂直方向上,声重波具有可传播性和幅度随高度增长的特性;在水平方向上,声重波能表现为孤子包络调制的波列.     

垂直切变风场中声重波的Burgers-KdV方程研究

本文从可压缩流体的原始动力学方程出发,利用二维约化摄动方法推导出垂直切变风场中考虑曳引效应的二维声重波的Burgers-KdV方程,并对其非线性性态作了一些研究.主要结果:1.声重波在远场处能激发起孤波和多周期波列等非线性波动;2.给出上述非线性波动与大气背景风场、密度等的制约关系;3.进一步推测大气风剪切是E_s形成的可能机制.从本文推导出的方程出发,可进一步研究声重波远场处的相互作用、能量转换、不稳定性和定源等问题.     

低频大气声重波的非线性Schr?dinger方程

本文采用多重时空尺度展开的方法,对于不可压缩等温大气,导出了二维情况下低频声重波的非线性Schr?dinger方程,讨论了声重波的非线性性质.在垂直方向上,声重波具有可传播性和幅度随高度增长的特性;在水平方向上,声重波能表现为孤子包络调制的波列.     

Locally-induced nonlinear modes and multiple equilibria in planetary fluids

It is demonstrated that nonlinear Rossby modes, such as modons and IG eddies, can be excited in planetary fluids by a sufficiently strong forcing of potential vorticity. When a weak forcing is balanced with a weak dissipation, two (linear and nonlinear) equilibrium states can be produced, depending on the initial condition. When the fluid is inviscid, a sufficiently strong steady forcing may generate a sequence of propagating nonlinear eddies. A weak forcing, by contrast, only generates linear Rossby waves. The criterion which divides the high amplitude nonlinear state and the low amplitude linear state may be interpreted in terms of a ratio of a time necessary to force the eddy to a time for a fluid particle to circulate about the nonlinear eddy once.     

A multiple distribution Markovian model for annual hydrologic time series

Nonlinear serial dependence and skewness of annual hydrologic time series {X _t } have been challenging the classical theory of Gaussian stochastic processes, particularly if the study of extremes (dry or wet years) is required as it is often the case. In this paper, a new and general model is proposed assuming that the geophysical system which is responsible forX _t can take different states and that this state process is modeled by a Markov chain. At each time,X _t is generated from a statistical distribution which depends on the state that has occurred. This model can preserve non-linear structures of serial dependence and it can produce a skewed marginal distribution ofX _t without any transformation. A successful application of this model to the study of annual rainfall at Fortaleza (Northeast of Brazil) is also presented.     

非线性大气Ekman层三维动力学特征

本文采用Ｂｏｕｓｓｉｎｅｓｑ近似，利用地转动量近似（ＧＭＡ）方法，研究了大气Ｅｋｍａｎ层的三维非线性动力学特征，得到了Ｅｋｍａｎ层中三维风速分布的解析解，着重讨论了热成风对Ｅｋｍａｎ层水平风速分布的影响，对传统的求垂直速度的方法进行了改进。     

Evidence of nonlinear site response in horizontal-to-vertical spectral ratio from near-field earthquakes

The issue is addressed as to whether the horizontal-to-vertical spectral ratio (HVSR) method is sensitive to the amplitude of ground motion from near-field earthquakes. Twenty-one three-component accelerograms from two closely located similar soil sites in the town of Lefkas are used. The recordings represent 17 earthquakes covering a wide range of magnitudes, epicentral distances and azimuths. Peak horizontal accelerations (PGA) and velocities (PGV) lie in the ranges 20–540 cm/s² and 1.4–55.2 cm/s. For each HVS ratio, the site's fundamental-resonance frequency, f_res, is determined visually. Linear correlation analysis shows that f_res is strongly (negatively) correlated to PGA and PGV (r between −0.7 and −0.8); no correlation is found with resonance amplitude or epicentral distance. We show that the observed correlation is attributable to soil nonlinearity and indicate how weak-motion estimates of f_res can be corrected for use in assessing site response during strong shaking.     

Nonlinear response of surface soil and NTT building due to soil–structure interaction during the 1995 Hyogo-ken Nanbu (Kobe) earthquake

The 1995 Hyogo-ken Nanbu (Kobe) earthquake brought about enormous damage to structures in the Hanshin and Awaji areas. In this paper the importance of investigating the relationship between ground motion and structural damage is pointed out.

Strong seismic motion was observed at the NTT (Nippon Telegraph and Telephone) Building during this earthquake. The structural damage to this building was relatively slight. In order to evaluate the relationship between ground motion and structural damage, it is necessary to assess the effects of the soil–structure interaction. In this study, the seismic response of the building and of the surface soil were evaluated by means of a nonlinear soil–structure interaction analysis using FEM.

It was found that, the nonlinearity of surface soil near the building had a great effect on the soil–structure interaction, especially the rocking of the building.