Mathematical analysis of long-wave breaking on open channels with bottom friction     

Yong Hong Wu  Ji-Wei Tian 《Ocean Engineering》2000,27(2)

In this paper we study the breaking of long waves propagating along an open channel with linear friction on the bottom. The equations governing the wave propagation consist of a pair of first-order nonlinear hyperbolic partial differential equations (PDEs). We first transformed the PDEs into a pair of ordinary differential equations (ODEs) along the characteristic directions by means of a pair of Riemann invariants. By analyzing the ODEs, we found that the breaking of waves can be identified by the singularity of the derivative of the Riemann invariants. Thus, we derived an analytical solution for the derivative of the Riemann invariants. Then, a breaking criterion and an analytical formula for the estimation of breaking time were developed and validated through numerical experiments. It is also shown in the paper that the present model includes the previous model neglecting bottom friction as a special case.  相似文献   

Distinguishing Developing Versus Non-Developing African Easterly Waves Using Adaptive Observational Strategies     

Mrinal K. Biswas  T. N. Krishnamurti 《Marine Geodesy》2013,36(4):356-377

The impacts of dust loaded, Saharan Air Layer (SAL) during the life cycle of African Easterly Waves (AEWs) is a many-faceted scientific problem. It entails possible radiative effects of dust aerosols, impacts of dust on cloud physics, and the cloud nuclei of condensation, advective effects, that is, intrusions of dry dusty air versus humid air into the interior of storms. This paper addresses several such AEWs of the eastern Atlantic Ocean, where we have made use of special aircraft reconnaissance data sets that include wind and humidity profiles in the vertical. Using what are called adaptive observational strategies within a mesoscale model, we show the impacts of adding such observations in the analysis and in short-range forecasts of several AEWs. We do not have the direct and indirect effects of aerosols, but we do include the advective component. Our results show that the inclusion of humidity profiling distinguishes between developing versus nondeveloping AEWs from the use of these additional data sets via the adaptive observational strategies.  相似文献   

Nonlinear wave Packets of Equatorial Kelvin Waves     

Guan-yu Chen  John P. Boyd 《地球物理与天体物理流体动力学》2013,107(5):357-379

The weakly nonlinear dynamics of packets of equatorial Kelvin waves is studied using singular perturbation theory applied to the shallow water wave equations. Within the limits of the perturbation theory, which is formally restricted to weak mean shear and weak nonlinearity, we derive a Nonlinear Schroedinger equation to describe the envelope of the wave packet. We find that nonlinearity has a defocusing effect so that coherent wave packets must owe their existence entirely to the generation mechanism rather than to nonlinear focusing of a broad initial disturbance.  相似文献   

Modelling the influence of currents on wave propagation at the entrance of the Tagus estuary   总被引：1，自引：0，他引：1  

L. Rusu 《Ocean Engineering》2011,38(10):1174-1183

A study of the wave propagation and of the consequences of the influence of currents on waves in the Tagus estuary is performed in the present work. For this purpose a high-resolution SWAN domain was coupled to a wave prediction system based on the two state of the art phase averaged wave models, WAM for wave generation and SWAN for nearshore wave transformation. The most important factors affecting the incoming waves are the local currents and the wind. These influences were evaluated by performing SWAN simulations in the target area with and respectively without considering the tide level and tide induced currents. The model results were compared with wave measurements, validating in this way the results of the wave prediction system developed herewith.  相似文献   

Stability of submerged rock berms exposed to motion of liquefied soil in waves     

B. Mutlu Sumer  Figen Hatipoglu Dixen  Jørgen Fredsøe 《Ocean Engineering》2011,38(7):849-859

The paper describes the results of an experimental study on the behaviour of a submerged rock berm in liquefied backfill soil. The soil is liquefied by waves, and the rock berm is subject to the orbital motion of the liquefied soil. The soil used in the experiments was silt with d₅₀=0.075 mm. Various berm materials were used, stones of size 0.74-2.5 cm, plastic balls of size 3.6 cm, brass of size 2.5 cm and steel of size 1.0 cm. The experiments show that rock berms that are stable under very large waves can be unstable when they are exposed to the motion of liquefied soil. The limited data obtained in the study were plotted as a function of the mobility number versus the Keulegan-Carpenter number for the range of the Reynolds number of the tests. The critical mobility number corresponding to the incipient motion of the berm stones is determined. Recommendations are made as to how the present findings can be implemented in practice.  相似文献   

Standing shocks around black holes and estimation of outflow rates     

Santabrata Das  Sandip K. Chakrabarti 《Journal of Astrophysics and Astronomy》2002,23(1-2):143-147

We self-consistently obtain shock locations in an accretion flow by using an analytical method. One can obtain the spectral properties, quasi-periodic oscillation frequencies and the outflow rates when the inflow parameters are known. Since temperature of the CENBOL decides the spectral states of the black hole, and also the outflow rate, the outflow rate is directly related to the spectral states.  相似文献   

Ships with ventilated cavitation in seaways and active flow control     

《Applied Ocean Research》2015

Bottom ventilated cavitation has been proven as a very effective drag reduction technology for river ships and planning boats. The ability of this technology to withstand the sea wave impact usual for seagoing ships depends on the ship bottom shape and could be enhanced by some active flow control devices. Therefore, there is the need in numerical tools to estimate the effects of bottom changes and to design such devices. The fundamentals of active flow control for the ship bottom ventilated cavitation are considered here on the basis of a special model of cavitating flows. This model takes into account the air compressibility in the cavity, as well as the multi-frequency nature of the incoming flow in wavy seas and of the cavity response on perturbations by incoming flow. The numerical method corresponding to this model was developed and widely manifested with an example of a ship model tested in a towing tank at Froude numbers between 0.4 and 0.7.The impact of waves in head seas and following seas on cavities has been studied in the range of wavelengths from 0.45 to 1.2 of the model (or ship) length. An oscillating cavitator-spoiler was considered as the flow controlling devices in this study. The oscillation magnitude and the phase shift between cavitator oscillation and the incoming waves have been varied to determine the best flow control parameters. The main results of the provided computational analysis include oscillations of cavity surface, of the pressure in cavity and of the moment of hydrodynamic load on the cavitator. The major part of computations has been carried out for the flap oscillating at the frequency coinciding with the wave frequency, but the effect of a frequency shift is also analyzed.  相似文献   

Effects of Dispersion of Wave Packets in the Determination of Lifetimes of High-Degree Solar <Emphasis Type="Italic">p</Emphasis> Modes from Time – Distance Analysis: MDI Data     

Dean-Yi Chou  Oleg Ladenkov 《Solar physics》2007,241(1):7-15

The cross-correlation function of solar p modes in a time – distance analysis changes with travel distance (or travel time). The exponential decrease in the amplitude of the cross-correlation function with travel distance has been interpreted as the dissipation of solar p-mode power and used to determine the lifetimes of high-degree p modes. It is found that the width of the cross-correlation function increases with travel distance. We interpret the increase in width as the dispersion of the wave packet in a time – distance analysis. The dispersion would also cause a decrease in amplitude and affect the determination of lifetimes. We include the dispersion effect in the determination of lifetimes of high-degree p modes in a time – distance analysis and find that the derived lifetime increases significantly compared with the previous study for degree less than 400.  相似文献   

A numerical model for onset of scour below offshore pipelines     

Zhipeng Zang  Liang Cheng  Ming Zhao  Dongfang Liang  Bin Teng 《Coastal Engineering》2009

A numerical model is developed to predict the onset of local scour below offshore pipelines in steady currents and waves. The scour is assumed to start when the pressure gradient underneath the pipeline exceeds the floatation gradient of the sediments. In this model, the water flow field above the bed is determined by solving the two-dimensional (2-D) Reynolds-averaged Navier–Stokes equations with a k-ω turbulence closure. The seepage flow below the seabed is calculated by solving the Darcy's law (Laplace's equation) with known pressure distribution along the common boundaries of the flow domains-seabed. The numerical method used for both the turbulent flow around the pipeline and Darcy's flow in the seabed is a fractional finite element method. The average pressure gradient along the buried pipe surface is employed in the evaluation of onset condition with a calibration coefficient. The numerical model is validated against experimental data available in literature. A unified onset condition for steady currents and waves is proposed. Influences of flow parameters, including water depth, embedment depth, boundary layer thickness, Reynolds number (Re) and Keuleagan–Carpenter (KC) number, on the pressure drop coefficient over the pipeline are studied systematically.  相似文献   

A Formal Theory for Vortex Rossby Waves and Vortex Evolution     

James C. McWilliams  Lee P. Graves  Michael T. Montgomery 《地球物理与天体物理流体动力学》2013,107(4):275-309

A formal theory is presented for the balanced evolution of a small-amplitude, small-scale wave field in the presence of an axisymmetric vortex initially in gradient-wind balance and the accompanying changes induced in the vortex by the azimuthally averaged wave fluxes. The theory is a multi-parameter, asymptotic perturbation expansion for the conservative, rotating, f-plane, shallow-water equations. It extends previous work on Rossby-wave dynamics in vortices and more generally provides a new perspective on wave/mean-flow interaction in finite Rossby-number regimes. Some illustrative solutions are presented for a perturbed vortex undergoing axisymmetrization.  相似文献