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31.
Dong-Sheng Jeng 《Ocean Engineering》1998,25(1):49-67
To simplify the complicated mathematical process, most previous investigations for the water waves-seabed interaction problem have assumed a porous seabed with isotropic soil behavior, even though strong evidence of anisotropic soil behavior has been reported in soil-mechanics literature. This paper proposes an analytical solution of the short-crested wave-induced soil response in a cross-anisotropic seabed. As shown in the numerical results presented, the wave-induced seabed response, including pore pressure, effective stresses and soil displacements, is affected significantly by the cross-anisotropic elastic constants. A parametric study is performed to clarify the relative differences in pore pressure between isotropic and cross-anisotropic solutions. 相似文献
32.
This paper seeks to reconstruct the parameters of elastic layered media such as P-wave velocity, S-wave velocity, density and thickness from the multioffset seismic reflection data. Since the data are highly non-linear to the low-wavenumber components, the non-linear waveform inversion method, with the aid of generalized ray theory, is proposed to solve this problem in space–time domain. As opposed to the layer-stripping method, the present method attempts to invert all layer parameters simultaneously, thus reducing the cumulative errors resulting from the upper layers. The parameters are inverted by minimizing the weighted square error between the observed data and the calculated data of the layered model, the optimization of which is based on the quasi-Newton method. In synthetic tests, we find that the inverted results are good when the variation of parameters between layers is not too large. The modified method for large variation of parameters is first to fix those of deeper layers and neglect the signals reflected from them, then recover some other parameters simultaneously until those of upper layers attain a stable value, and finally, invert all parameters simultaneously. The results so obtained show a significant improvement. This method was tested to be stable in the presence of noise in seismograms. 相似文献
33.
In the past few decades, considerable efforts have been devoted to the phenomenon of wave-seabed interaction. However, conventional investigations for determining wave characteristics have been focused on the wave nonlinearity. On the other hand, most previous works have been only concerned with the seabed response under the wave pressure, which was obtained from the assumption of a rigid seabed. In this paper, the inertia forces and employing a complex wave number are considered in the whole problem. Based on Biot’s poro-elastic theory, the problem of wave-seabed interaction is first treated analytically for a homogeneous bed of finite thickness and a new wave dispersion relationship is also obtained, in which the soil characteristics are included. The numerical results indicate that the effects of soil parameters significantly affect the wave characteristics (such as the damping of water wave, wave length and wave pressure). Furthermore, the effects of inertia forces on the wave-induced seabed response cannot always be ignored under certain combination of wave and soil conditions. 相似文献
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35.
Higher plant n-alkane average chain length as an indicator of petrogenic hydrocarbon contamination in marine sediments 总被引：1，自引：0，他引：1
The n-alkane average chain length (ACL) is the weight-averaged number of carbon atoms of the higher plant C25–C33 n-alkanes. The abundance of individual n-alkanes from higher plant sources generally increases with increasing carbon number in coastal marine sediments around Taiwan, but this trend is reversed for petrogenic hydrocarbons. The ACL would potentially be lowered if petrogenic hydrocarbons were added to sediments containing biogenic hydrocarbons alone. To test this idea, a marine environment off southwestern Taiwan known to contain both biogenic and petrogenic hydrocarbons and two nearby rivers were selected for investigating possible difference in ACL values between their sediments. The average CPI of C25–C33 n-alkanes was 4.08 ± 2.04 (range 1.90–8.96, n = 15) for the river sediments and 1.70 ± 0.16 (range 1.43–1.97, n = 15) for the marine sediments. The ACL of C25–C33 n-alkanes for river sediments ranged from 29.2 to 30.5 (average 29.9 ± 0.4), and for marine sediments from 28.4 to 29.3 (average 28.9 ± 0.3). The ACL difference between marine and river sediments was significant (Student's t test at 99% confidence) although it appeared small. It is suggested that the ACL can be an additional indicator for detection of petrogenic hydrocarbons in coastal marine sediments. 相似文献
36.
The determination of the characteristics of a standing wave boundary layer, such as water particle velocities and shear stresses, is a vital issue in the prediction of sediment transport rate. Thus, an accurate measure of boundary layer characteristics is a key factor in the study of the wave boundary layer. In this study, a fiber-optic laser Doppler velocimeter (FLDV) is applied to directly measure the velocity profile in the standing wave boundary layer. As the experimental data presented in this paper, the antinode points of standing waves are found to move in the temporal domain. The previous second-order solution for a standing wave boundary layer is insufficient for the prediction of larger Ursell numbers. 相似文献
37.
A theoretical model for the decay of progressive interfacial gravity waves propagating above a porous bed is developed assuming potential flow in a two-layer system with a free surface and a sharp interface. A new wave dispersion relation for two-layer flow above a quasi-static porous seabed is derived and investigated. The solutions for the nonlinear wave profile are derived using a perturbation method and the effects of geometric and flow parameters including bed characteristics, depth ratios and the densities of the two fluids are studied and discussed. Comparisons with existing analytical solutions for viscous interfacial wave attenuation over a rigid bed demonstrate the relative importance of the porous bed as a mechanism for wave decay. It is shown that the influence of a porous seabed on wave propagation is significant when the depth of the lower layer, normalised by the wavenumber, is less than π. 相似文献
38.
The wave dispersion equation has played a very important role in the development of ocean surface wave theories. The evaluation of the length of a water wave is an essential example of solving the dispersion relation. Conventional ocean wave theories have been based on an assumption of a rigid impermeable seabed. Thus, the conventional wave dispersion equation can only be used in the case of a wave propagating over a rigid impermeable seabed. For waves propagating over a porous seabed (such as a sandy bed), the conventional dispersion relation is no longer valid because of the absence of the characteristics of the porous seabed. The objective of this study is to establish a new wave dispersion equation for waves propagating over a porous seabed. Based on the new relation, the effects of a porous seabed on wave characteristics (such as the wavelength and wave profile) are discussed in detail. 相似文献
39.
A third-order perturbation approximation for the partial reflection from a vertical wall is presented in this paper. The wave parameters are expressed in terms of the amplitude of incident waves. The reflection coefficient is defined as the ratio of the height of reflected waves to incident waves. The numerical results demonstrate the significant influences of reflected coefficient on the wave profile and wave frequency bifurcation. For example, the critical angle of wave frequency bifurcation with partial reflection is about 7.5 degrees, not 21 degrees as reported previously for fully reflection. 相似文献
40.
Analytical solutions for wave velocities and wave vectors are yielded for a continuously inhomogeneous cross‐anisotropic medium, in which Young's moduli (E, E′) and shear modulus (G′) varied exponentially as depth increased. However, for the rest moduli in cross‐anisotropic materials, ν and ν′ remained constant regardless of depth. We assume that cross‐anisotropy planes are parallel to the horizontal surface. The generalized Hooke's law, strain–displacement relationships, and equilibrium equations are integrated to constitute governing equations. In these equations, displacement components are fundamental variables and, hence, the solutions of three quasi‐wave velocities, VP, VSV, and VSH, and the wave vectors, $\mathop{\mathop{l}\limits^{\rightharpoonup}}\nolimits_{P}$ $\mathop{\mathop{l}\limits^{\rightharpoonup}}\nolimits_{\mathit{SV}}$, and $\mathop{\mathop{l}\limits^{\rightharpoonup}}\nolimits_{{\mathit{SH}}}$, can be generated for the inhomogeneous cross‐anisotropic media. The proposed solutions and those obtained by Daley and Hron, and Levin correlate well with each other when the inhomogeneity parameter, k, is 0. Additionally, parametric study results indicate that the magnitudes and directions of wave velocity are markedly affected by (1) the inhomogeneous parameter, k; (2) the type and degree of geomaterial anisotropy (E/E′, G′/E′, and ν/ν′); and (3) the phase angle, θ. Consequently, one must consider the influence of inhomogeneous characteristic when investigating the behaviors of wave propagation in a cross‐anisotropic medium. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献