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1.
《中国海洋湖沼学报》2017,(5)
Elastic waves in the seabed generated by low-frequency noise radiating from ships are known as ship seismic waves and can be used to detect and identify ships.To obtain the propagation characteristics of ship seismic waves,an algorithm for calculating seismic waves at the seafl oor is presented based on the staggered-grid fi nite diff erence method.The accuracy of the algorithm was tested by comparison with analytical solutions.Numerical simulation of seismic waves generated by a low-frequency point sound source in a typical shallow sea environment was carried out.Using various source frequencies and locations in the numerical simulation,we show that the seismic waves in the near fi eld are composed mostly of transmitted S-waves and interface waves while transmitted P-waves are weak near the seafl oor.However,in the far fi eld,the wave components of the seismic wave are mainly normal modes and interface waves,with the latter being relatively strong in the waveforms.As the source frequency decreases,the normal modes become smaller and the interface waves dominate the time series of the seismic waves. 相似文献
2.
A continuously stratified nonlinear model is set up to study the impact of topographical character on the generation of internal solitary waves over a sill by tidal flow. One of the reasons why almost all of the generated internal solitary waves propagate westward in the northern South China Sea is explained. The model simulations describe the generation and propagation of internal waves well. When the strength of imposed barotropic tides and the water stratification stay unchanged, the steepness of the sill slope can control both (a) whether or not the waves induced over a sill by tidal flow are linear internal waves or nonlinear internal solitary waves, and (b) the amplitude of the internal solitary waves generated. If the steepness of the sill is asymmetric, the nonlinear internal solitary waves may be induced on the steeper side of the sill. These conclusions are supported by a numerical experiment with a monthly-mean stratification and an actual seafloor topography from the Luzon Strait. 相似文献
3.
瑞雷波法已在研究地球内部结构、近地表地球物理工程和超声无损检测等领域中获得了广泛应用,尤其是近年来瑞雷波法作为近地表场地表征新兴领域的前沿技术已成为国际学术研究与应用的热点。对国内外近地表弹性介质瑞雷波勘探的主要研究成果与进展进行了综述,通过对瑞雷波勘探现有的研究成果和进展密切追踪发现当前近地表瑞雷波勘探主要基于水平地表弹性水平层状介质模型,利用单分量瑞雷波相速度频散曲线单目标反演获得一维横波速度剖面和相关岩土力学参数。但是,该方法也存在着现有瑞雷波频散曲线反演极易出现模式误识别、现有单分量单目标瑞雷波反演未充分利用多分量信息、现有瑞雷波相速度反演未充分利用群速度传播特性、现有瑞雷波反演未充分利用质点椭圆极化振动特性等挑战性学术难题和不足。基于上述问题,建议未来近地表弹性介质瑞雷波勘探重点研究方向应集中在进行多模式表面波全速度谱反演研究、多站多分量表面波相速度多目标全速度谱反演研究、单站多分量表面波群速度多目标全速度谱反演研究和单站多分量表面波椭圆极化振动特性多目标反演研究。由此构建新的近地表多分量瑞雷波多目标全速度谱反演理论,引领多分量瑞雷波多目标反演学科前沿,拓展现有单分量瑞雷波单目标反演理论范畴,推动多分量瑞雷波高精度实用勘探技术的发展。 相似文献
4.
The wind waves generated by cold waves are some of the most dangerous waves in Bohai Bay. In this paper records of the wind
waves under the influence of cold waves in November, 1968, are discussed. It is shown that the north wind is very strong in
spring and winter. The frequency spectrum of the development and decline of wind waves depends mainly on the wind speed. The
change of shape and scale parameters of the spectrum are discussed and the calculation equations are shown.
This paper was published in Chinese inOceanologia et Limnologia Sinica.16(2): 147–155, 1985. 相似文献
5.
Ocean internal waves appear as irregular bright and dark stripes on synthetic aperture radar(SAR) remote sensing images. Ocean internal waves detection in SAR images consequently constituted a difficult and popular research topic. In this paper, ocean internal waves are detected in SAR images by employing the faster regions with convolutional neural network features(Faster R-CNN) framework; for this purpose, 888 internal wave samples are utilized to train the convolutional network and identify internal waves. The experimental results demonstrate a 94.78% recognition rate for internal waves, and the average detection speed is 0.22 s/image. In addition, the detection results of internal wave samples under dif ferent conditions are analyzed. This paper lays a foundation for detecting ocean internal waves using convolutional neural networks. 相似文献
6.
Rossby waves with linear topography in barotropic fluids 总被引：1，自引：0，他引：1
Rossby waves are the most important waves in the atmosphere and ocean, and are parts of a large-scale system in fluid. The theory and observation show that, they satisfy quasi-geostrophic and quasi-static equilibrium approximations. In this paper, solitary Rossby waves induced by linear topography in barotropic fluids with a shear flow are studied. In order to simplify the problem, the topography is taken as a linear function of latitude variable y, then employing a weakly nonlinear method and a perturbation method, a KdV （Korteweg-de Vries） equation describing evolution of the amplitude of solitary Rossby waves induced by linear topography is derived. The results show that the variation of linear topography can induce the solitary Rossby waves in barotropic fluids with a shear flow, and extend the classical geophysical theory of fluid dynamics. 相似文献
7.
Long waves such as tsunamis can be trapped by islands due to wave refraction, and these trapped waves will cause huge damage even in the sheltered shoreline of the island. That all waves propagating into the topography and finally reaching the coastline are called perfect trapped modes, while any waves escaping from the topography are called leaky modes. Whether these long waves can be trapped is dependent on the depth profile of the island. This paper presents analytic solutions of the ray path for waves propagating into the circular island with power function profiles. Wave height distributions over the island are further investigated based on the principia that crowded rays correspond to large wave height and sparse rays correspond to small wave height. The trapped mechanism for water waves over the island is revealed based on their ray paths. Furthermore, the perfectly trapped criterion is derived, that is, when the slope gradient at the topography toe is greater than twice the ratio of the water depth to the radial distances, all wave rays propagating on the island will finally reach the coastline, and the waves are perfectly trapped. 相似文献
8.
从正压涡度方程出发,在弱非线性和弱基流切变条件下,导得了描述非线性大气长波活动的推广的Ｋｄｖ方程,并得到了方程的孤立波解及其色散关系。取近似于实际大气运动的物理参数作数值计算,得到了振荡型Ｒｏｓｂｙ孤立波的水平结构和移动特征,其结果较之寻常的Ｋｄｖ孤立波更接近于实际大气中的阻塞流型。 相似文献
9.
李志坚 《地球科学与环境学报》1988,(3)
本文研究了SV波在自由面上全反射的一些特殊现象。首先,从波动方程出发讨论了散射P、SV波的相移和反射场中P波的质点运动;然后,应用功能原理,计算了自由面上非均匀P波的能流密度,得出非均匀P波平均能流为零的一般结论。本文所得到的结论,对于各种地震波、弹性波和电磁波在两种均匀介质界面上发生的全反射,均可适用。 相似文献
10.
An investigation of the properties of low-frequency internal waves in the northeastern China Seas 总被引：1，自引：0，他引：1
A simple and practical method for separating low-frequency internal waves from low-frequency barotropic waves was employed
to analyze the observation data. Analysis of some data gathered in the northestern China Seas revealed strong semidiurnal
internal tides and near-inertial internal waves at the stations in the East China Sea and near-inertial waves but no semidiurnal
internal tides at the station in the centre of the Yellow Sea. The geographic properties of low-frequency internal waves in
the region are discussed primarily on the basis of the mechanism of internal tide generation on the continental shelfbreak,
and the mechanisms of local generation and global generation.
Project supported by the National Natural Science Foundation of China. 相似文献
11.
Various aspects of studies on internal tides are reviewed .Both beam-like structure and modal structure of internal tides may exist in the ocean . Bottom intensifications are caused by many factors .e.g. upstream blocking , which is the result of nonlinear interaction among waves . The energy may decay very fast so that internal tides are mostly locally generated .Internal tides may have considerable residual currents.In a 3-D frame, numerical study revealed that internal waves may interfere with each other to cause strong motions fer from the generation sources.The mechanism that determines how the lee waves break to form various nonlinear waves such as solitary waves, hydraulic jumps and internal surges or bores remains unclear. Analytic study is difficult , so numerical method may be effective . A radiation condition on the open boundary must be employed. A complete 3-D model may gain interesting result.Study on internal tides in China is limited to field observations and data analysis . 相似文献
12.
STATISTICAL PROPERTIES OF HIGH-FREQUENCY INTERNAL WAVES IN QINGDAO OFFSHORE AREA OF THE YELLOW SEA 总被引：1，自引：0，他引：1
Densely-sampled thermistor chain data obtained from a shallow-water acoustics experiment in the Yellow Sea off the coast of Qingdao were analyzed to examine the statistical properties of the 6 to 520 cpd frequency band internal waves observed. The negative skewness coefficients and the greaterthan-3 kurtosis coefficients indicated non-Gaussianity of the internal waves. The probability distributions were negatively skewed and abnormally high peaks. Nonlinear properties, as exemplified by the asymmetric waveshapes of the internal waves in the offshore area are described quantitatively. 相似文献
13.
We derived the dispersion relation (correct to the second order in wave slope) of nonlinear waves in a developing process, proved that there are mainly three time scales in a developing process of nonlinear waves governed by coupling mechanisms. The three time scales are oscillation, evolution and developing time scales. We also proved that even in the developing process of nonlinear waves, there is no term in dispersion relation in proportion to the first order of wave slope. In a stationary case our results agreed with the discrete form obtained by Weber in 1977. Our computed results of wave speed in the wallops spectrum were in good agreement with the laboratory measurements made by Ramamonjiarisoa (1976) in energy-containing range. 相似文献
14.
Internal waves play a crucial role in ocean mixing, and density perturbation and energy flux are essential quantities to investigate the generation and propagation of internal waves. This paper presents a methodology for calculating density perturbation and energy flux of internal waves only using a velocity field that is based on linearized equations for internal waves. The method was tested by numerical simulations of internal waves generated by tidal flowing over a Gaussian topography in a stratified fluid. The density perturbations and energy fluxes determined using our method that only used velocity data agreed with density perturbations and energy fluxes determined by the equation of state based on temperature data. The mean relative error (MRE) and root mean square error (RMSE) between the two methods were lower than 5% and 10% respectively. In addition, an experiment was performed to exam our method using the velocity field measured by Particle Image Velocimetry (PIV), and the setup of the experiment is consistent with the numerical model. The results of the experiments calculated by the methods using PIV data were also generally equal to those of the numerical model. 相似文献
15.
Capillary and capillary-gravity waves possess a random character, and the slope wavenumber spectra of them can be used to
represent mean distributions of wave energy with respect to spatial scale of variability. But simple and practical models
of the slope wavenumber spectra have not been put forward so far. In this article, we address the accurate definition of the
slope wavenumber spectra of water surface capillary and capillary-gravity waves. By combining the existing slope wavenumber
models and using the dispersion relation of water surface waves, we derive the slope wavenumber spectrum models of capillary
and capillary-gravity waves. Simultaneously, by using the slope wavenumber models, the dependence of the slope wavenumber
spectrum on wind speed is analyzed using data obtained in an experiment which was performed in a laboratory wind wave tank.
Generally speaking, the slope wavenumber spectra are influenced profoundly by the wind speed above water surface. The slope
wavenumber spectrum increases with wind speed obviously and do not cross each other for different wind speeds. But, for the
same wind speed, the slope wavenumber spectra are essentially identical, even though the capillary and capillary-gravity waves
are excited at different times and locations. Furthermore, the slope wavenumber spectra obtained from the models agree quite
well with experimental results as regards both the values and the shape of the curve. 相似文献
16.
青岛台站重力固体潮和海潮负荷特征研究 总被引：1，自引：0，他引：1
选取青岛台站2012-01~2013-02 gPhone重力仪连续观测资料进行预处理和调和分析,获得其重力潮汐参数,并选取8个全球海潮模型对O1、K1和M2潮波进行海潮负荷改正。结果表明：1）8个主要潮波调和分析的振幅因子标准差均在2.6%之内,与理论潮汐模型值的差异也在3.0%之内;2）利用海潮模型对O1、K1和M2潮波进行改正能有效地降低残差矢量,观测残差负荷改正的有效性大致分布在30%~75%,全球海潮模型对青岛台站主要潮波的海潮负荷改正差别不大。 相似文献
17.
三峡数字地震台网中心记录典型波形初步分析 总被引：10，自引：6，他引：4
狄莉莎 《大地测量与地球动力学》2004,24(2):52-57
对三峡地区数字地震台网中心记录的典型的天然地震、疑炮、一次爆破及一次滑坡等波形进行初步分析后认为：①数字地震仪器与模拟地震仪器所记录的地震波形特征基本一致；②三峡地区数字地震台网中心2003年5月19日至2004年1月所记录的多数天然地震事件是非构造型(由溶洞塌陷引起的陷落型)地震事件。 相似文献
18.
A proposal, an analysis and an experiment are presented for extracting the normal direction data of random sea waves by reconstructing
the reflected light rays from sea surface with an airborne image of the sun’s glitter. The slope distribution of the random
sea waves can be determind quantitatively, simply and directly by means of this method. 相似文献
19.
INTRODUCTIONEquatorialKelvinwavesareofspecialsignificanceinthedynamicsoftheequatorialocean ,duetotheirhighpropagationspeedandequatoriallytrappednature.NumericalandobservationalstudiesstronglysuggestedthatKelvinwavesplayamajorroleinElNi no SouthernOscillationandotheroceanphenomena.Themainthermoclinevariabilityinthetropicaloceanswasstudiedextensivelybyvariousre searchers (LongandChang ,1 990 ;YangandYu ,1 992 ) .Animportantfeatureoftheequatorialoceanthermalstructureistheeastwardshoaling… 相似文献
20.
Surface waves comprise an important aspect of the interaction between the atmosphere and the ocean, so a dynamically consistent framework for modelling atmosphere-ocean interaction must take account of surface waves, either implicitly or explicitly. In order to calculate the effect of wind forcing on waves and currents, and vice versa, it is necessary to employ a consistent formula- tion of the energy and momentum balance within the airflow, wave field, and water column. It is very advantageous to apply sur- face-following coordinate systems, whereby the steep gradients in mean flow properties near the air-water interface in the cross-interface direction may be resolved over distances which are much smaller than the height of the waves themselves. We may account for the waves explicitly by employing a numerical spectral wave model, and applying a suitable theory of wave–mean flow interaction. If the mean flow is small compared with the wave phase speed, perturbation expansions of the hydrodynamic equations in a Lagrangian or generalized Lagrangian mean framework are useful: for stronger flows, such as for wind blowing over waves, the presence of critical levels where the mean flow velocity is equal to the wave phase speed necessitates the application of more general types of surface-following coordinate system. The interaction of the flow of air and water and associated differences in temperature and the concentration of various substances (such as gas species) gives rise to a complex boundary-layer structure at a wide range of vertical scales, from the sub-millimetre scales of gaseous diffusion, to several tens of metres for the turbulent Ekman layer. The bal- ance of momentum, heat, and mass is also affected significantly by breaking waves, which act to increase the effective area of the surface for mass transfer, and increase turbulent diffusive fluxes via the conversion of wave energy to turbulent kinetic energy. 相似文献