Measure of the exponential splitting of the homoclinic tangle in four-dimensional symplectic mappings     

Elena Lega  Massimiliano Guzzo  Claude Froeschlé 《Celestial Mechanics and Dynamical Astronomy》2009,104(1-2):191-204

Using four-dimensional symplectic maps as a model problem, we numerically compute the unstable manifolds of the hyperbolic manifolds of the phase space related to the single resonances. We measure an exponential dependence of the size of the lobes of these manifolds through many orders of magnitude of the perturbing parameter. This is an indirect numerical verification of the exponential decay of the normal form, as predicted by the Nekhoroshev theorem. The variation of the size of the lobes turns out to be correlated to the diffusion coefficient.  相似文献   

旋转扰动流体中壁面湍流不稳定及其拟序结构研究Ⅰ:实验     

Enrico Ferrero  张瑛  全利红  Luca Mortarini  Renato Forza 《气象与减灾研究》2009,32(3)

重点介绍和讨论了中性条件下旋转扰动流体中边界层强迫不稳定及其相关的一些问题,阐述了旋转体系中切变驱动边界层不稳定的动力学特征.这些不稳定状态的研究在大气物理学、流体动力学、海洋学等多个领域中引起科学家极大的兴趣,近年来在实验和理论研究中都得到了不断的发展.意大利都灵大学基础物理系地球科学实验组通过水槽旋转实验方法,不断改变水槽启动或结束时的旋转运动速度,以及底部壁面粗糙度等要素,所得到的实验结果与SDBL理论非常一致.  相似文献   

A numerical study of the hyperbolic manifolds in a priori unstable systems. A comparison with Melnikov approximations     

Elena Lega  Massimiliano Guzzo  Claude Froeschlé 《Celestial Mechanics and Dynamical Astronomy》2010,107(1-2):115-127

Using numerical methods we study the hyperbolic manifolds in a model of a priori unstable dynamical system. We compare the numerically computed manifolds with their analytic expression obtained with the Melnikov approximation. We find that, at small values of the perturbing parameter, the topology of the numerically computed stable and unstable manifolds is the same as in their Melnikov approximation. Increasing the value of the perturbing parameter, we find that the stable and unstable manifolds have a peculiar topological transition. We find that this transition occurs near those values of the perturbing parameter for which the error terms of Melnikov approximations have a sharp increment. The transition value is also correlated with a change in the behaviour of dynamical quantities, such as the largest Lyapunov exponent and the diffusion coefficient.  相似文献   

Low-T thermochronometric evidence for post-thrusting (< 11 Ma) exhumation in the Western Outer Carpathians,Poland     

Stefano Mazzoli  Leszek Jankowski  Rafal Szaniawski  Massimiliano Zattin 《Comptes Rendus Geoscience》2010,342(2):162-169

Thermal indicators record exhumation of sedimentary units from depths in excess of 6 km over most of the Outer Carpathian fold and thrust belt in Poland. Apatite fission track data, showing cooling ages ranging between 32.1 ± 4.8 and 7.0 ± 0.8 Ma, indicate that exhumation was partially coeval with shortening. However, new thermochronometric information obtained as part of this study allowed us to unravel a previously undetected, post-thrusting exhumation stage. The integration of new field data and structural analysis with low-T thermochronometry suggests that termination of thrusting – at ca. 11 Ma in the area of the present study – was followed by gravity disequilibria within the orogenic wedge. The related extension and denudation phenomena appear to have played a primary role in the recent (< 10 Ma) tectonic evolution of the Western Outer Carpathians, exerting a major control on exhumation processes in this key area of the Alpine–Carpathian mountain system.  相似文献   

The role of preconditioning in the solution to FE coupled consolidation equations by Krylov subspace methods     

Massimiliano Ferronato  Giorgio Pini  Giuseppe Gambolati 《国际地质力学数值与分析法杂志》2009,33(3):405-423

The repeated solution in time of the linear system arising from the finite element integration of coupled consolidation equations is a major computational effort. This system can be written in either a symmetric or an unsymmetric form, thus calling for the implementation of different preconditioners and Krylov subspace solvers. The present paper aims at investigating when either a symmetric or an unsymmetric approach should be better used. The results from a number of representative numerical experiments indicate that a major role in selecting either form is played by the preconditioner rather than by the Krylov subspace method itself. Two other important issues addressed are the size of the time integration step and the possible lumping of the flow capacity matrix. It appears that ad hoc block constrained preconditioners provide the most robust algorithm independently of the time step size, lumping, and symmetry. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

The seismic response to overpressure: a modelling study based on laboratory, well and seismic data   总被引：1，自引：0，他引：1  

José M. Carcione  Umberta Tinivella 《Geophysical Prospecting》2001,49(5):523-539

We investigate the seismic detectability of an overpressured reservoir in the North Sea by computing synthetic seismograms for different pore-pressure conditions. The modelling procedure requires the construction of a geological model from seismic, well and laboratory data. Seismic inversion and AVO techniques are used to obtain the P-wave velocity with higher reliability than conventional velocity analysis. From laboratory experiments, we obtain the wave velocities of the reservoir units versus confining and pore pressures. Laboratory experiments yield an estimate of the relationship between wave velocities and effective pressure under in situ conditions. These measurements provide the basis for calibrating the pressure model. Overpressures are caused by different mechanisms. We do not consider processes such as gas generation and diagenesis, which imply changes in phase composition, but focus on the effects of pure pore-pressure variations. The results indicate that changes in pore pressure can be detected with seismic methods under circumstances such as those of moderately deep North Sea reservoirs.  相似文献   

A rheological model for anelastic anisotropic media with applications to seismic wave propagation     

José M. Carcione  Fabio Cavallini 《Geophysical Journal International》1994,119(1):338-348

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致密砂岩衰减岩石物理图板分析:储层微裂隙预测          下载免费PDF全文

庞孟强  巴晶  J. M. Carcione  A. Vesnaver  马汝鹏  陈天胜 《地球物理学报》1954,63(11):4205-4219

致密砂岩储层普遍具有孔隙度低、微裂隙发育的特点,岩石内部常含有强烈的结构非均质性.致密砂岩发育的微裂隙使储层具有良好的连通性,促成高饱和气的天然气成藏.针对川西某探区须家河组高含气饱和度致密砂岩,本文选取致密砂岩岩心样本,进行了不同围压下的超声波实验测量.考虑储层完全饱气情况下的粒间孔隙、微裂隙双重孔隙结构,采用Biot-Rayleigh双重孔隙方程,构建致密砂岩岩石物理模型,进而分析了裂隙含量对纵波频散和衰减的影响.基于地震波衰减,构建了致密砂岩多尺度岩石物理图板.采用谱比法和改进频移法估算致密砂岩样本及储层衰减,对超声和地震频带下的图板进行校正.将校正后的图板应用到研究工区,选取二维测线和三维区块,进行储层孔隙度和裂隙含量的定量预测.对比实际资料进行分析,结果显示,本文预测的孔隙度和裂隙含量与三口测井的孔隙度曲线和实际产气情况基本吻合,基于孔隙-裂隙衰减岩石物理模型有效地预测了优质储层的分布区域.  相似文献   

Allozyme genotypes and tolerance to copper stress in Hediste diversicolor (Polychaeta: Nereididae)     

Virgilio M  Abbiati M 《Marine pollution bulletin》2004,49(11-12):978-985

This study analysed the occurrence of genotypic shifts in laboratory populations of Hediste diversicolor (Polychaeta: Nereididae) exposed to copper stress. Specimens of H. diversicolor were collected at three sites, up to 10 km apart, in the estuarine area of the Pialassa lagoons (North Adriatic Sea, Italy) and were used in acute toxicity tests. Specimens were assigned to copper exposure (0.34 mg/l Cu2+) or control conditions. Each combination of Treatment and Site was replicated in two tanks containing 35 specimens of H. diversicolor. The genotypic structure of both dead and survived specimens was analysed by allozyme electrophoresis at six loci (ALD, FH, HBDH LDH, PGI, SDH). Under copper exposure, specimens with the genotypes ALD100/100 and PGI102/102 had significantly lower mortalities than other genotypes Results were consistent across the three sites, suggesting that, under laboratory conditions, effects of copper stress on H. diversicolor is related to individual genotypes at ALD and PGI loci.  相似文献   

Velocity and attenuation in partially saturated rocks: poroelastic numerical experiments     

Hans B. Helle  Nam H. Pham  José M. Carcione 《Geophysical Prospecting》2003,51(6):551-566

We use a poroelastic modelling algorithm to compute numerical experiments on wave propagation in a rock sample with partial saturation using realistic fluid distribution patterns from tomography scans. Frequencies are in the range 10 to 500 kHz. The rock is a homogeneous isotropic sandstone partially filled with gas and water, which are defined by their characteristic values of viscosity, compressibility and density. We assume no mixing and that the two different pore-fills occupy different macroscopic regions. The von Kármán self-similar correlation function is used, employing different fractal parameters to model uniform and patchy fluid distributions, respectively, where effective saturation is varied in steps from full gas to full water saturation. Without resorting to additional matrix–fluid interaction mechanisms, we are able to reproduce the main features of the variation in wave velocity and attenuation with effective saturation and frequency, as those of published laboratory experiments. Furthermore, the behaviour of the attenuation peaks versus water saturation and frequency is similar to that of White's model. The conversion of primary P-wave energy into dissipating slow waves at the heterogeneities is shown to be the main mechanism for attenuating the primary wavefield. Fluid/gas patches are shown to affect attenuation more than equivalent patches in the permeability or solid-grain properties.  相似文献