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1.
The strong coupling between hydrodynamics and seafloors on shallow muddy shelves, and resulting bed reworking, have been extensively documented. On these shelves, spectral wave transformation is driven by a complex combination of forcing mechanisms that include nonlinear wave interactions and wave energy dissipation induced by fluid-mud at a range of frequencies. Wave-mud interaction is investigated herein by using a previously validated nonlinear spectral wave model and observations of waves and near-bed conditions on a mildly-sloping seafloor off the muddy central chenier-plain coast, western Louisiana Shelf, United States. Measurements were made along a cross-shelf transect spanning 1 km between 4 and 3 m water depths. The high-resolution observations of waves and near-bed conditions suggest presence of a fluid mud layer with thickness sometimes exceeding 10 cm under strong long wave action (1 meter wave height with 7 s peak period at 4 meter depth). Spectral wave transformation is modeled using the stochastic formulation of the nonlinear Mild Slope Equation, modified to account for wave-breaking and mud-induced dissipation. The model is used in an inverse manner in order to estimate the viscosity of the fluid mud layer, which is a key parameter controlling mud-induced wave dissipation but complicated to measure in the field during major wave events. Estimated kinematic viscosities vary between 10−4-10−3 m2/s. Combining these results of the wave model simulations with in-depth analysis of near-bed conditions and boundary layer modeling allows for a detailed investigation of the interaction of nonlinear wave propagation and mud characteristics. The results indicate that mud-induced dissipation is most efficient when the wave-induced resuspensions of concentrations > 10 g/L settle due to relatively small bottom stresses to form a fluid mud layer that is not as thin and viscous as a consolidated seafloor in absence of wave action but also not as thick and soft as a near-bed high concentration layer that forms during strong wave action. 相似文献
2.
The Guyana coastal system is characterized by very thick deposits of Amazon mud and high mud concentrations in its coastal waters. The mud deposits can be quite soft and may liquefy under incoming waves. Subsequently, the liquefied mud damps the incoming waves effectively. This paper presents a simple model to predict wave attenuation over soft (fluid) mud beds. This model is based on the two-layer approach by Gade [Gade, H.G., 1958, Effects of a non-rigid, impermeable bottom on plane surface waves in shallow water, Journal of Marine Research, 16 (2) 61–82.] which is implemented in the standard version of the state-of-the-art wave-prediction model SWAN. Input to the mud wave damping module consists of the extension, thickness, density and viscosity of the liquefied (fluid) mud layer. 相似文献
3.
V. Lykousis S. Alexandri J. Woodside G. de Lange A. Dählmann C. Perissoratis K. Heeschen Chr. Ioakim D. Sakellariou P. Nomikou G. Rousakis D. Casas D. Ballas G. Ercilla 《Marine and Petroleum Geology》2009
Detailed multibeam, sedimentological, and geophysical surveys provide ample new data to confirm that the Anaximander Mountains (Eastern Mediterranean) are an important area for active mud volcanism and gas hydrate formation. More than 3000 km of multibeam track length was acquired during two recent missions and 80 gravity and box cores were recovered. Morphology and backscatter data of the study area have better resolution than previous surveys, and very detailed morphology maps have been made of the known targeted mud volcanoes (Amsterdam, Kazan and Kula), especially the Amsterdam “crater” and the related mud breccia flows. Gas hydrates collected repeatedly from a large area of Amsterdam mud volcano at a sub-bottom depth of around 0.3–1.5 m resemble compacted snow and have a rather flaky form. New gas hydrate sites were found at Amsterdam mud volcano, including the mud flow sloping off to the south. Gas hydrates sampled for the first time at Kazan mud volcano are dispersed throughout the core samples deeper than 0.3 m and display a ‘rice’-like appearance. Relative chronology and AMS dating of interbedded pelagic sediments (Late Holocene hemipelagic, sapropel layer S1 and ash layers) within the mud flows indicate that successive eruptions of Kula mud volcano have a periodicity of about 5–10 kyrs. New mud volcanoes identified on the basis of multibeam backscatter intensity were sampled, documented as active and named “Athina” and “Thessaloniki”. Gas hydrates were sampled also in Thessaloniki mud volcano, the shallowest (1264 m) among all the active Mediterranean sites, at the boundary of the gas hydrate stability zone. Biostratigraphical analyses of mud breccia clasts indicated that the source of the subsurface sedimentary sequences consists of Late Cretaceous limestones, Paleocene siliciclastic rocks, Eocene biogenic limestones and Miocene mudstones. Rough estimations of the total capacity of the Anaximander mud volcanoes in methane gas are 2.56–6.40 km3. 相似文献
4.
Owing to the interactions among the complex terrain, bottom materials, and the complicate hydrodynamics, typhoon waves show special characteristics as big waves appeared at the high water level(HWL) and small waves emerged at low and middle water levels(LWL and MWL) in radial sand ridges(RSR). It is assumed that the mud damping, sandy bed friction and wave breaking effects have a great influence on the typhoon wave propagation in this area. Under the low wave energy, a mud layer will form and transport into the shallow area, thus the mud damping effects dominate at the LWL and the MWL. And high Collins coefficient(c around 1) can be applied to computing the damping effects at the LWL and the MWL. But under the high wave energy, the bottom sediment will be stirred and suspended, and then the damping effects disappear at the HWL. Thus the varying Collins coefficient with the water level method(VCWL) is implemented into the SWAN to model the typhoon wave process in the Lanshayang Channel(LSYC) of the RSR, the observed wave data under "Winnie"("9711") typhoon was used as validation. The results show that the typhoon wave in the RSR area is able to be simulated by the VCWL method concisely, and a constant wave breaking coefficient(γ) equaling 0.78 is better for the RSR where wide tidal flats and gentle bed slopes exist. 相似文献
5.
6.
Modelling of multi-bodies in close proximity under water waves—Fluid forces on floating bodies 总被引：1，自引：0，他引：1
This work presents two-dimensional numerical results of the dependence of wave forces of multiple floating bodies in close proximity on the incident wave frequency, gap width, body draft, body breadth and body number based on both viscous fluid and potential flow models. The numerical models were validated by the available experimental data of fluid oscillation in narrow gaps. Numerical investigations show that the large amplitude responses of horizontal and vertical wave forces appear around the fluid resonant frequencies. The convectional potential flow model is observed to un-physically overestimate the magnitudes of wave forces as the fluid resonance takes place. By introducing artificial damping term with appropriate damping coefficients μ∈[0.4, 0.5], the potential flow model may work as well as the viscous fluid model, which agree with the damping coefficients used in our previous work for the predication of wave height under gap resonance. In addition, the numerical results of viscous fluid model suggest that the horizontal wave force is highly dependent on the water level difference between the opposite sides of an individual body and the overall horizontal wave force on the floating system is generally smaller than the summation of wave force on each body. 相似文献
7.
1 .Introduction The dynamics of soft mud under surface water waves is of great importance to the sedimentationprocesses in approach channels and harbors ,and has long been drawing attention. Advancements innumerous engineering applications inthe shallowco… 相似文献
8.
Drilling at the site UBGH1-9, offshore Korea in 2007, revealed varied gas-hydrate saturation with depth and a wide variety of core litholgies, demonstrating how the variations in the lithology are linked with those in gas-hydrate saturation and morphology. Discrete excursions to low chlorinity values from in situ background chlorinity level occur between 63 and 151 mbsf. In this occurrence zone, gas-hydrate saturations estimated from the low chlorinity anomalies range up to 63.5% of pore volume with an average of 9.9% and do not show a clear depth-dependent trend. Sedimentary facies analysis based on grain-size distribution and sedimentary structures revealed nine sediment facies which mainly represent hemipelagic muds and fine- to medium-grained turbidites. According to the sedimentary facies distribution, the core sediments are divided into three facies associations (FA): FA I (0–98 mbsf) consisting mainly of alternating thin- to medium-bedded hemipelagic mud and turbidite sand or mud beds, FA II (98–126 mbsf) dominated by medium- to very thick-bedded turbidite sand or sandy debris flow beds, and FA III (126–178 mbsf) characterized by thick hemipelagic mud without intervening discrete turbidite sand layers. Thermal anomalies from IR scan, mousse-like and soupy structures on split-core surfaces, non-destructive measurements of pressure cores, and comparison of gas-hydrate saturations with sand contents of corresponding pore-water squeeze cakes, collectively suggest that the gas hydrate at the site UBGH1-9 generally occurs in two different types: “pore-filling” type preferentially associated with thin- to medium-turbidite sand beds in the FA I and “fracture-filling” type which occurs as hydrate veins or nodules in hemipelagic mud of the FA III. Gas-hydrate saturation in the FA II is generally anomalously low despite the dominance of turbidite sand or sandy debris flow beds, suggesting insufficient methane supply. 相似文献
9.
At high bed shear stress sheet flows often occur in coastal waters in which high-concentration bedload sediments are transported in a thin layer near the bed. This paper firstly constructs a theoretical model (partial differential equations, PDEs) for the intense transport of non-cohesive bedload sediments by unidirectional currents and then seeks a special solution to the PDEs to determine the thickness of the bedload particle–water mixture, which could serve as the “reference height” that is often invoked in numerical computation and simulation of suspended sediment transport in turbulent flows. Moreover, a modified formula is presented to determine the “reference concentration”. Using a “uch” approach the present study derives a 1D formula for predicting bedload transport rate in sheet flows driven by asymmetric waves, with the help of a novel formula for evaluating wave friction factor. The new bedload formula can generically take into account slope angle (positive and negative), wash load concentration in the driving water flow and other factors that affect bedload transport rate. It compares well with measured data in a large-scale wave flume [Dohmen-Janssen, C.M., Hanes, D.M., 2002. Sheet flow dynamics under monochromatic non-breaking waves. Journal of Geophysical Research, 107(C10), 1301–1321], a large-scale oscillatory water tunnel [ Hassan, W.N., Ribberink, J.S., 2005. Transport processes of uniform and mixed sands in oscillatory sheet flow. Coastal Engineering, 52, 745–770] and in a swash zone of natural beach [Masselink, G., Hughes, M.G., 1998. Field investigation of sediment transport in the swash zone. Continental Shelf Research, 18, 1179–1199]. 相似文献
10.
波浪与带窄缝方箱作用共振现象的数值模拟 总被引：1，自引：1，他引：0
By introducing a source term into the Laplace equation, a two-dimensional fully nonlinear time-domain numerical wave flume (NWF) is developed to investigate the resonance induced by the interaction bet... 相似文献
11.
M. V. Kosnik V. A. Dulov V. N. Kudryavtsev 《Izvestiya Atmospheric and Oceanic Physics》2010,46(3):369-378
We investigate the role of different physical mechanisms in the generation of the capillary-gravity wind wave spectrum. This
spectrum is calculated by integrating a nonstationary kinetic equation until the solution becomes stready. The mechanisms
of spectrum generation under consideration include three-wave interactions, viscous dissipation, energy influx from wind,
nonlinear dissipation, and the generation of a parasitic capillary ripple. The three-wave interactions are taken into account
as an integral of collisions without additional simplifications. It is shown that the three-wave interactions lead to solution
instability if the kinetic equation takes into account only linear sources. To stabilize the solution, the kinetic equation
should incorporate a nonlinear dissipation term, which in the range of short gravity waves corresponds to energy losses during
wave breaking and microscale wave breaking. In the range of capillary waves, the account of nonlinear dissipation is also
needed to ensure a realistic level of the spectrum for large wind velocities. For the steady-state spectrum, the role of three-wave
interactions remains essential merely in the range of the minimum of phase velocity, where a trough on the curvature spectrum
is formed. At the remaining intervals of the spectrum, the main contribution into the spectral energy balance is provided
by the mechanisms of wave injection, nonlinear dissipation, and the generation of parasitic capillaries. 相似文献
12.
In this note we investigated the effects of a thin visco-elastic mud layer on wave propagation. Within the framework of linear water-wave theory, analytical solutions are obtained for damping rate, dispersion relation between wave frequency and wave number, and velocity components in the water column and mud layer. The wave attenuation rate reaches a maximum value when the mud layer thickness is about the same as the mud boundary layer thickness. Heavier mud has a weaker effect on the wave damping. However, the wave attenuation rate does not always decrease as the elastic shear modulus increases. In the range of small values for elastic shear modulus, the wave attenuation can be amplified quite significantly. The current solutions are compared with experimental data with different wave conditions and mud properties. In general, good agreements are observed. 相似文献
13.
Validation of the three-wave quasi-kinetic approximation for the spectral evolution in shallow water
This paper aims at validating the three-wave quasi-kinetic approximation for the spectral evolution of weakly nonlinear gravity waves in shallow water. The problem is investigated using a one-dimensional numerical wave propagation model, formulated in the spectral representation. This model includes both a nonlinear triad interactions term and a wave breaking dissipation term. Some numerical tests were carried out in order to show the importance of using the triad nonlinear term in wave propagation spectral models, particularly to describe both behavior of the spectral integral parameters and of the spectral shape evolution in shallow water depth. Furthermore; a comparison against different set of experimental observations was carried out. Comparing the numerical results with the experimental observations made it possible to show the modeling efficiency of the three-wave quasi-kinetic approximation. 相似文献
14.
Water waves propagating over a layer of soft mud or submerged aquatic vegetation can drastically attenuate over distances comparable to several wave lengths. The attenuation in the case of mud has been found previously to be reasonably described by an exponential decay. Waves reflect from beaches and any structures that they impact. The reflected waves affect wave heights measured in the field or laboratory wave basins.Decomposition of small amplitude waves into incident and reflected waves is a linear problem. However, the presence of the exponential damping introduces nonlinearity to the decomposition problem and requires an iterative process for solving the problem. Despite considerable experimental research on attenuation of waves over mud, none of the existing methods for decomposition of incident and reflected waves have accounted for this case.Here, the Newton Algorithm was used to account for the effect of wave decay over mud by quasi-linearizing the nonlinear equations. Also, a second method using a new error function and a commercial nonlinear solver was proposed in both time and frequency domain. The performance of both methods has been verified using artificial as well as laboratory data. 相似文献
15.
Solitary wave evolution over a shelf including porous damping is investigated using Volume-Averaged Reynolds Averaged Navier–Stokes equations. Porous media induced damping is determined based on empirical formulations for relevant parameters, and numerical results are compared with experimental information available in the literature. The aim of this work is to investigate the effect of wave damping on soliton disintegration and evolution along the step for both breaking and non-breaking solitary waves. The influence of several parameters such as geometrical configuration (step height and still water level), porous media properties (porosity and nominal diameter) or solitary wave characteristics (wave height) is analyzed. Numerical simulations show the porous bed induced wave damping is able to modify wave evolution along the step. Step height is observed as a relevant parameter to influence wave evolution. Depth ratio upstream and downstream of the edge appears to be the more relevant parameter in the transmission and reflection coefficients than porosity or the ratio of wave height–water depth. Porous step also modifies the fission and the solitary wave disintegration process although the number of solitons is observed to be the same in both porous and impermeable steps. In the absence of breaking, porous bed triggers a faster fission of the incident wave into a second and a third soliton, and the leading and the second soliton reduces their amplitude while propagating. This decrement is observed to increase with porosity. Moreover, the second soliton is released before on an impermeable step. Breaking process is observed to dominate over the wave dissipation at the porous bottom. Fission is first produced on a porous bed revealing a clear influence of the bottom characteristics on the soliton generation. The amplitude of the second and third solitons is very similar in both impermeable and porous steps but they evolved differently due to the effect of bed damping. 相似文献
16.
针对波浪能转换装置(WEC)研究重点主要集中在能量捕获效率方面,而忽略其附带的消波功能的问题。基于Open FOAM程序,建立垂荡浮子式波浪能发电装置与桩式约束的浮式防波堤的集成系统(OBC-FB)。主要研究WEC中的重要组件动力输出系统(PTO)对集成系统波能捕获效率及消波性能的影响。分析流体黏性影响下线性PTO系统的最优PTO阻尼特性。开发非线性电磁阻尼模型与线性PTO系统性能进行比较。结果显示,考虑黏性影响下线性的最优PTO阻尼系数略大于无黏的理论值;适当增大PTO阻尼系数可以获得更大的波能捕获宽度比(CWR),从而可以保证装置单位特征尺寸的波能转换效率更高,同时可以在更宽波况范围保证消波性能;相较于线性PTO阻尼系统,非线性电磁PTO阻尼系统可以更好地兼顾波能捕获效率和消波性能。因此,在OBC-FB集成系统的优化设计中,PTO阻尼系统是一个重要的优化参数。 相似文献
17.
Application of desingularized approach to water wave propagation over three-dimensional topography 总被引：1，自引：0，他引：1
A numerical approach based on desingularized boundary element method and mixed Eulerian–Lagrangian formulation [Zhang et al., 2006. Wave propagation in a fully nonlinear numerical wave tank: a desingularized method. Ocean Engineering 33, 2310–2331] is extended to solve the water wave propagation over arbitrary topography in a three-dimensional wave tank. A robust damping layer applicable for regular and irregular incident waves is employed to minimize the outgoing wave reflection back into the wave tank. Numerical results on the propagation of regular and irregular incident waves over the flat bottom and linear incident waves over an elliptical shoal show good concurrence with the corresponding analytical solutions and experimental data. 相似文献
18.
As known, the rolling motion characteristics, amplitudes and accelerations, greatly influence the ability of a ship to operate and survive in bad weather. On the other hand, traditional computer codes for seakeeping calculations fail the forecasting of large amplitude rolling. There is a great need of using semi-empirical damping models and coefficients. This stresses the importance of campaigns of measurements as described in the paper, to get a deeper insight into the physical-mathematical modelling of the different contributions to rolling equation.Experimental tests on nonlinear rolling in a regular beam sea of a Ro-Ro ship model have been conducted by varying both the wave steepness and the wave frequency. The use of a parameter estimation technique, based on the least squares fitting of the stationary numerical solution of the nonlinear rolling motion differential equation, allowed to obtain informations on the damping model and on the linear and nonlinear damping coefficients. These exhibit a quite strong dependence on frequency that reduces the efficiency of constant coefficients rolling equation to simulate large amplitude nonlinear rolling. The results indicate that a good quality prediction model of nonlinear rolling cannot be based on constant coefficients time domain simulations. These can infact lead to incorrect estimates of rolling amplitudes even when the parameters have been obtained through high level parameter estimation procedures based on experimental data. The analysis indicates also a marked dependence of the effective wave slope coefficient on wave amplitude. The introduction of both these dependences on the rolling equation allows to reproduce the experimental results with great accuracy even at large amplitudes. 相似文献
19.
Open boundaries are important when simulating water waves. In this study, a transparent boundary condition at an open boundary was developed for simulating nonlinear water waves propagating to a distant area using the Moving Particle Semi-implicit method. The novelty of this study is that the technique of wave analysis used in the experiment was introduced into the particle simulation to absorb incident waves; the simulation cost was reduced by employing inflow and outflow regions instead of a long dissipation region. Incident waves in front of the boundary were evaluated using Fourier analysis, and the particles on the transparent boundary were forced to move at the velocity of the analytical solution for Stokes waves in order to absorb the incident waves. The analysis was restricted to periodic waves. Wave propagation was simulated for two wave periods using the developed transparent boundary condition. The results showed that this transparent boundary transmitted the incident waves with small reflection and the simulation cost was lower than that for wave damping by a conventional highly viscous region. 相似文献
20.
A technique is developed for including the effects of dissipation due to wave breaking in two-dimensional elliptic models based on the mild-slope wave equation. This involves exploration of convergence properties pertaining to iteration due to presence of the nonlinear wave breaking parameter in the governing equations as well as new boundary conditions that include wave-breaking effects. Five wave-breaking formulations are examined in conjunction with the resulting model, which is applied to tests involving a sloping beach, a bar-trough bottom configuration, shore-connected and shore-parallel breakwaters on a sloping beach, and two real-world cases. Model results show that three of the formulations, when used within the context of the modeling scheme presented here, provide excellent results compared to data. 相似文献