共查询到20条相似文献，搜索用时 218 毫秒
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采用弱非线性近似得出中层耗散大气连续谱Ｒｏｓｓｂｙ波包的非线性时空演化方程，讨论了Ｒｏｓｓｂｙ波包的三波相互作用问题．数值计算表明，耗散和非线性的共同效应决定了Ｒｏｓｓｂｙ波包的演变．当一个Ｒｏｓｓｂｙ波包通过大气传播时，它的振幅若超过某个阈值，空间尺度分别比它大和比它小的两个次级Ｒｏｓｓｂｙ波包的振幅会随时间增长．特别当这两个次级波包同时随时空变化时，仅当主波的振幅超过一个更大的阈值，且其群速度介于两次级波包的群速度之间时，两次级波包的振幅才会随时空同时增长，即出现绝对不稳定现象，耗散和３个波包的频率失配都会增大不稳定的阈值． 相似文献
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本文将太阳风涨落传输能量产生磁层亚暴的机制推广到无碰撞等离子体过程。太阳风的涨落在磁层顶激发压缩阿尔文波,并在磁尾的无碰撞等离子体中传播。尾瓣中满足条件β?1,而等离子体片中β≥1,其中β为等离子体压力与磁压之比。这样,快磁声波在尾瓣中几乎不衰减,而在等离子体片中很快衰减,将波动能量耗散在等离子体片中使等离子体加热或者粒子加速。这种机制还表明,磁尾等离子体片中的高能粒子可以由太阳风涨落动能耗散而被加速,不一定是直接源于太阳。 相似文献
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采用二维全隐欧拉（FICE）格式对具有高斯分布的重力波波包在可压大气中传播时的饱和过程进行数值模拟和分析．数值计算结果表明,波振幅首先随高度增加而增加,但当波振幅接近于线性不稳定性给出的阈值时,不再增加,重力波波包达到饱和进而破碎．破碎出现的高度（86．50km）比线性理论预言的结果（84．59km）要高一些,并且一般都在波包的下游出现．波破碎过程能使波能量在空间重新分配,并对重力波能量有明显的耗散作用．并且波破碎会使波相关能量传输方向偏离线性射线理论的射线路径． 相似文献
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声波在岩石材料中传播时会发生差异衰减现象.由于岩石强度、完整性不同，造成其频率响应不同，声波通过不同强度的岩石时，对不同频率的声波信号滤除状况也就有所不同.通过力学强度高的岩石时，声波基本能够保持其原有频率成分，相反，当通过低强度岩石时，高频分量会迅速衰减而缺失，主要保留低频分量.通过实例研究，分析了声谱衰减特征与岩样矿物组成、密度及结构完整性的关系，验证了声谱衰减特征与岩体强度具有很好相关性的结论.通过分析研究声波信号在不同岩体中传播的衰减变化，指出声波衰减在一定程度上能够反映出岩体的风化程度、破碎状态、强度及各向异性等特征.可以发展成为岩体工程地质勘测、试验和施工中的常规实验方法. 相似文献
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间断有限元方法(Discontinuous Galerkin method,简称DGM)在求解地震波动方程时具有低数值频散、网格剖分灵活等优点,因此,为适应数值模拟对模拟精度和复杂地质结构的要求,本文提出一种新的加权Runge-Kutta间断有限元(weighted Runge-Kutta discontinuous Galerkin,简称WRKDG)方法,用于求解三维D′Alembert介质中声波方程.本文不仅详细推导了其数值格式,特别地,根据常微分方程理论给出了满足数值稳定性条件的一般经验公式,并首次对该方法的数值频散和耗散进行了深入分析,且考虑了耗散参数对结果的影响.同时,我们也对该方法进行了精度测试,并分析了3D情形下WRKDG方法的并行加速比,结果表明3D WRKDG方法具有良好的并行性.最后,我们给出了包含均匀模型、非规则几何模型以及非均匀Marmousi模型在内的数值模拟算例.结果表明,该方法不仅计算准确,能与解析解很好地吻合,且能有效模拟包含球体在内的非规则模型及非均匀Marmousi模型中的衰减声波波场.数值模拟实验进一步验证了WRKDG方法在求解三维D′Alembert介质中声波方程时的正确性和有效性,并获得了对这种强衰减介质中波传播特征的规律性新认识. 相似文献
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利用含气非饱和Biot-Stoll模型研究了声波在海底表层沉积物介质中的传播,讨论了骨架耗散、含气饱和度对快纵波、慢纵波和横波速度和衰减的影响,并与Biot模型的结果进行了对比.研究结果表明:孔隙流体黏滞耗散与骨架耗散共同影响声波传播速度和衰减,低频情况下骨架耗散引起的衰减占主要地位,高频情况下骨架耗散引起的衰减较小;少量气体(<1%)的引入显著改变了快纵波速度,气体含量的变化对快纵波衰减影响很大,低频情况下气体对慢纵波速度的影响不大,而对横波速度的影响较大,气体含量的变化对慢纵波和横波衰减影响较小.利用超声波测量系统测量了一例杭州湾海底沉积物样品的纵波速度和衰减,当含气量趋近0%时,Biot-Stoll模型预测的纵波速度和实验测量结果较为一致. 相似文献
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Acoustic wave dispersion and attenuation in marine sediment based on partially gas-saturated Biot-Stoil model 总被引：1，自引：0，他引：1 
下载免费PDF全文
下载免费PDF全文 利用含气非饱和Biot-Stoll模型研究了声波在海底表层沉积物介质中的传播,讨论了骨架耗散、含气饱和度对快纵波、慢纵波和横波速度和衰减的影响,并与Biot模型的结果进行了对比.研究结果表明:孔隙流体黏滞耗散与骨架耗散共同影响声波传播速度和衰减,低频情况下骨架耗散引起的衰减占主要地位,高频情况下骨架耗散引起的衰减较小;少量气体(＜1％)的引入显著改变了快纵波速度,气体含量的变化对快纵波衰减影响很大,低频情况下气体对慢纵波速度的影响不大,而对横波速度的影响较大,气体含量的变化对慢纵波和横波衰减影响较小.利用超声波测量系统测量了一例杭州湾海底沉积物样品的纵波速度和衰减,当含气量趋近0％时,Biot-Stoll模型预测的纵波速度和实验测量结果较为一致. 相似文献
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Michiya Uryu 《Pure and Applied Geophysics》1980,118(1):661-693
The mechanism of acceleration of the mean zonal flow by a planetary wave is explained intuitively by considering the wave drag which a corrugated bottom feels when it excites the wave. The explanation is justified by solving the problem of vertical propagation of a planetary wave packet and the second order mean motion induced around it. The discussion is slightly extended to the case of small damping, to illustrate in a compact form the fact that the mean zonal acceleration is determined by a forcing due to wave transience plus that due to wave dissipation.The mean flow induced by a steady, dissipating planetary wave is discussed, and it is shown that it depends largely on the dissipation scale-height of the wave whether the northern region is heated or cooled. For example, if the wave velocity-amplitude increases upward in spite of dissipation, the induced easterly flow increases with height and the temperature of the northern region increases relative to that in the southern region. A similar point has been made byDunkerton (1979) in connection with westerly flows induced by Kelvin waves.The Lagrangian-mean motion induced by a planetary wave is briefly discussed in connection with the mechanism of acceleration of the mean zonal flow, in the case of a slowly varying wave packet. Further, in order el elucidate the effects of wave dissipation and time dependence of wave amplitude, the results obtained for a steady, dissipating wave and for a growing baroclinic wave are mentioned. 相似文献
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When treating the forward full waveform case, a fast and accurate algorithm for modelling seismic wave propagation in anisotropic inhomogeneous media is of considerable value in current exploration seismology. Synthetic seismograms were computed for P-SV wave propagation in transversely isotropic media. Among the various techniques available for seismic modelling, the finite-difference method possesses both the power and flexibility to model wave propagation accurately in anisotropic inhomogeneous media bounded by irregular interfaces. We have developed a fast high-order vectorized finite-difference algorithm adapted for the vector supercomputer. The algorithm is based on the fourth-order accurate MacCormack-type splitting scheme. Solving the equivalent first-order hyperbolic system of equations, instead of the second-order wave equation, avoids computation of the spatial derivatives of the medium's anisotropic elastic parameters. Examples indicate that anisotropy plays an important role in modelling the kinematic and the dynamic properties of the wave propagation and should be taken into account when necessary. 相似文献
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模拟弹性波在孔隙介质中传播，需要稳定有效的吸收边界来消除或尽可能的减小由人工边界引起的虚假反射. 本文在前人工作基础上，首次建立了弹性孔隙介质情况下完全匹配层吸收边界的高阶速度-应力交错网格有限差分算法，并详细讨论了完全匹配层的构建及其有限差分算法实现. 首先，本文通过均匀孔隙模型的数值解与解析解的对比，验证所提出的数值方法的正确性；然后，本文考察了完全匹配层对不同入射角度入射波和自由表面上的瑞利波的吸收性能，将完全匹配层与廖氏和阻尼吸收边界进行了对比，研究了这三种吸收边界在不同吸收厚度情况下对弹性波吸收能力. 数值结果表明，在孔隙介质中，完全匹配层作为吸收边界能十分有效地吸收衰减外行波，无论对体波还是面波，是一种高效边界吸收算法. 相似文献
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《Journal of Atmospheric and Solar》2007,69(12):1357-1365
In the framework of solving the problem of acoustic energy transfer from near-surface sources through the upper atmosphere, the propagation of sinusoidal signals of different origin is studied. All calculations are made by means of a model that takes into account the inhomogeneity of the atmosphere, nonlinear effects, absorption, divergence of wave front due to long-range acoustic wave propagation, etc., but does not include the effect of gravity. Infrasonic waves of various periods and their absorption at various heights of the atmosphere are investigated. The calculations show that a sinusoidal signal is destroyed by nonlinear processes during its upward propagation; it transforms into two, initial and final, impulses. The location of the “transformation zone” depends on frequency; its height increases with decreasing frequency. The acoustic waves can heat the upper atmosphere, for example, waves with a period of 3 min generated by thunderstorms can heat the atmosphere by up to ΔTa=13.08 K/day in the region of 323–431 km. The efficiency of a point artificial emitter is too weak to heat the atmosphere significantly. 相似文献
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Modelling the wave phenomena in acoustic and elastic media with sharp variations of physical properties using the grid‐characteristic method 下载免费PDF全文
下载免费PDF全文 Alena V. Favorskaya Michael S. Zhdanov Nikolay I. Khokhlov Igor B. Petrov 《Geophysical Prospecting》2018,66(8):1485-1502
This paper introduces a novel method of modelling acoustic and elastic wave propagation in inhomogeneous media with sharp variations of physical properties based on the recently developed grid‐characteristic method which considers different types of waves generated in inhomogeneous linear‐elastic media (e.g., longitudinal, transverse, Stoneley, Rayleigh, scattered PP‐, SS‐waves, and converted PS‐ and SP‐waves). In the framework of this method, the problem of solving acoustic or elastic wave equations is reduced to the interpolation of the solutions, determined at earlier time, thus avoiding a direct solution of the large systems of linear equations required by the FD or FE methods. We apply the grid‐characteristic method to compare wave phenomena computed using the acoustic and elastic wave equations in geological medium containing a hydrocarbon reservoir or a fracture zone. The results of this study demonstrate that the developed algorithm can be used as an effective technique for modelling wave phenomena in the models containing hydrocarbon reservoir and/or the fracture zones, which are important targets of seismic exploration. 相似文献
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Elastic wave propagation in inhomogeneous anisotropic media 总被引：1，自引：0，他引：1
XIU CHENG WEI ) MIN YU DONG ) YUN YAI CHEN ) ) Geoscience Department University of Petroleum Beijing China ) Institute of Geophysics China Seismological Bureau Beijing China 《地震学报(英文版)》1998,11(6):655-667
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