Breaking wave forces and velocity fields

A new technique for measuring velocities under breaking wave crests using laser-doppler anemometry has been developed. Results may be obtained at positions up to 4 millimeters from the crest.A wave field is presented for a vertically fronted wave and comparison is made with an appropriate numerical study. The velocities obtained are far in excess of the predictions of linear theory.Measurements have also been made of the forces produced by this wave on a horizontal cylinder. Comparisons with large regular waves indicate that forces due to breaking waves can be up to five times greater for similar wave heights.     

Wave orbital velocity, fade, and SAR response to azimuth waves

Orbital motion of azimuth waves imposes differential Doppler shifts on wave imagery as seen by a SAR. This paper shows that these Doppler shifts are a function only of the wave and sensor geometry, and are not a function of SAR parameters. The azimuth wave reflectivity so modulated is equivalent to a redistributed scatterer density which can be used as an input with the SAR modulation transfer function for general distributed scenes to derive the azimuth wave image. The static scatterer density is calculated for a variety of sea states. Wave accelerations are not of first-order importance. Scatterer fade (decorrelation) is of central importance, as it impacts the SAR transfer function that is effective in wave imaging.     

A practical surface panel method to predict velocity distribution around a three-dimensional hydrofoil including boundary layer effects

A practical, low order and potential-based surface panel method is presented to predict the flow around a three-dimensional rectangular foil section including the effect of boundary layer. The method is based on a boundary-integral formulation, known as the “Morino formulation” and the boundary layer effect is taken into account through a complementary thin boundary layer model. The numerical approach used in the method presents a strongly convergent solution based on the iterative wake roll-up and contraction model including the boundary layer effect. The method is applied to a three-dimensional foil section for which the velocity distribution around the foil was measured using a 2D Laser Doppler Velocimetry system in a large cavitation tunnel. Comparison of the predicted velocity distributions both inside and outside of the boundary layer of the foil as well as the boundary layer shapes obtained from the numerical model show fairly good correlation with the measurements, indicating the robustness and practical worthiness of the proposed method.     

A model for the response of wave directions in slowly turning wind fields

On the basis of the wave energy balance equation, the response model of mean directions of locally wind-generated waves in slowly turning wind fields has been derived. The results show that in a homogeneous field, the time scale of the response is not only related to the rate of wave growth, but also to the directional energy distribution and the angle between the wind direction and the mean wave direction. Furthermore, the law of change in the mean wave direction has been derived. The numerical computations show that the response of wave directions to slowly turning wind directions can be treated as the superposition of the responses of wave directions to a series of sudden small-angle changes of wind directions and the turning rate of the mean wave direction depends on the turning rate and the total turning angles of the wind direction. The response of wave directions is in agreement with the response for a sudden change of wind directions if the change in wind directions is very fast. Based on the no     

基于GPS单点测速的海浪测量方法初探

首先分析比对了已有的测波方法,阐述了将GPS单点测速应用到测波中的优点.然后讨论了基于多普勒频移的测速方法,并分析了各类误差对测速精度的影响.最后利用静态数据进行动态测速模拟试验和实测动态数据测速与RTK (Real Time Kinematic,实时动态测量系统)位置差分测速进行—致性检验.结果表明,使用静态数据采用...     

Tone generation on a hydrofoil of a high-speed ship

Experimental results of hydrofoil singing on a full-scale passenger ship are reported. It is proposed that hydrodynamic generation of a tone is caused by self-excited oscillation of a foil trailing edge. The natural frequency of the vibrating structure as well as the frequency of the external force are estimated. A lift-oscillator model is applied for modeling purposes. One effective method of eliminating the hydrofoil singing is discussed.     

Analysis of a jet-controlled high-lift hydrofoil with a flap

A jet-controlled high-lift hydrofoil with a flap is investigated using both experimental and computational methods. Experiments were carried out in a cavitation tunnel to measure forces and moment acting on the hydrofoil, and surface pressure distribution. The measured data show the feasibility of such a device for marine applications. Computational studies have also been carried out in parallel with the measurements. The computational results are analyzed in terms of global and local quantities using available experimental data. The present computational results compare well with the well-known experimental data for circulation control flows. The results for flow around a hydrofoil with a blown flap further validate the concept behind the proposed device. The results of the study demonstrate the applicability of the technology to the design of practical control surfaces.     

Theoretical and experimental investigation of a vertical wall response to wave impact

The laboratory and field experiments so far have shown that when a wave breaks directly on a vertical faced coastal structure, the resulting impact pressures may become very severe in magnitude and short in duration. Some experimental evidence in the literature suggests that the structural response to the extremely high magnitude impact forces is only limited. This study is mainly concerned with the comparison of the theoretical and experimental results of a vertical wall response under the wave impact loading. In the dynamic analysis of the wall the classical elastic plate theory is used and the numerical results for the dynamic values of the transverse displacement are obtained by employing the method of finite elements. In the theoretical analyses the experimental pressure histories are used and the theoretical wall deflection histories are compared with the experimental results. The computational and experimental deflection histories exhibit similar patterns. The theoretical maximum wall deflections are mostly found to be slightly smaller than the experimental values.     

An experimental investigation of a vertical wall response to breaking wave impact

Laboratory experiments are conducted to measure the impact pressures and resulting deflections from breaking oscillatory waves on a vertical wall with 1/10 foreshore slope. The maximum impact pressure data on the wall are statistically analysed and the relationships between the magnitudes of impact pressures and forces, and their durations, are investigated. The maximum impact pressures, among the 90 wave impacts, are found to vary between 1.37 × 10⁴and 28.3 × 10⁴Pa. The maximum impact pressures are shown to reasonably satisfy the log-normal probability distribution and they occur most frequently slightly below the still-water level. The greatest wall deflection at the point of measurement is caused by an impact which has a maximum pressure of 3.6 × 10⁴Pa, corresponding to 50% probability in the log-normal distribution. It is found that the longer-lasting low impact forces are more effective in producing the larger wall deflections. In this respect, the maximum impact pressures in the range between 2.5 × 10⁴and 5 × 10⁴Pa obtained in this study are found to be the most effective. The upper limit of this range (when non-dimensionalised by the specific weight of water and deep-water wave steepness) is suggested as a design value for vertical walls.     

基于地震速度构建的低频响应在波阻抗反演中的应用

以V工区北部为例,应用井数据、速度数据和地震属性共同恢复低频响应数据,同时使用层速度、层位信息（层的深度和厚度）以及反射振幅的信息进行反演,结果显示可以改善预测纵波阻抗的结果,同时与通常情况下的孔隙度预测作了对比,结果表明孔隙度预测的可信度得到了一定程度的改善。     

Sensitivity of wave model predictions to wind fields in the Western Mediterranean sea

The paper compares the wave hindcast in the Western Mediterranean sea using the reanalysis wind fields from HIPOCAS and ERA-40 from ECMWF for November 2001. The study has concentrated on the Mediterranean coast of Spain where there are known difficulties with the wind and wave modelling. Two winter storms have been compared. The main differences between the significant wave heights using the ERA-40 reanalysis (ECMWF) and HIPOCAS reanalysis winds were observed to increase when moving southwards in the geographical domain at the offshore locations. Systematic negative biases of Hs were obtained with the ERA-40 data at all the coastal locations analyzed, whereas positive biases are typical for the HIPOCAS reanalysis. For offshore and coastal locations when using the ERA-40 data the Hs biases increased moving to South, while this pattern was not so clear for the HIPOCAS data. The inconsistencies in the comparisons of modelled waves against measurements seem to be associated with the quality of the wind fields.     

Numerical simulation for hydrodynamic characteristics of a bionic flapping hydrofoil

In order to study the propulsion mechanism of the bionic flapping hydrofoil (BFH), a 2-DoF (heave and pitch) motion model is formulated. The hydrodynamic performance of BFH with a series of kinematical parameters is explored via numerical simulation based on FLUENT. The calculated result is compared with the experimental value of MIT and that by the panel method. Moreover, the effect of inlet velocity, the angle of attack, the heave amplitude, the pitch amplitude , the phase difference, the heave biased angle, the pitch biased angle and the oscillating frequency are investigated. The study is useful for guiding the design of bionic underwater vehicle based on flapping propulsion. It is indicated that the optimal parameters combination is v=0.5m/s, θ0=40°.θ0=30°,Ψ=90°,Фbias=0°,θbias=0°and f=0.5Hz .     

Dynamic and diffusive growth of microbubbles near a two-dimensional hydrofoil

A technique for predicting the bubble growth along a two-dimensional hydrofoil with traveling bubble cavitation is presented. The method is based on the dynamic response of ambient microbubbles to the flow field and the subsequent diffusion of dissolved air into the flow field cavities. The bubble growth model is divided into three components, including the prediction of 1) the hydrofoil surface pressure distribution, 2) the ambient microbubble response to the pressure distribution, and 3) the diffusive mass flow rate. The hydrofoil velocity and pressure field is determined by two-dimensional thin airfoil theory. The microbubble response to the pressure field is given by the Rayleigh-Plesset equation with the addition of a mass diffusion term. The diffusion of dissolved gasses into the cavitation bubbles is determined by a solution to the steady-state diffusion equation under spherically symmetric convective flow. Results are given for the bubble wake of a NACA 66-006 (a = 0.8meanline) hydrofoil with traveling bubble cavitation. The effect of the relative velocity of the cavitation bubbles with respect to the surrounding water is investigated as well as the significance of the mass diffusion term in the Rayleigh-Plesset equation.     

The application of wave induced forces to a two-dimensional finite element long wave hydrodynamic model

This paper describes the modification of a two-dimensional finite element long wave hydrodynamic model in order to predict the net current and water levels attributable to the influences of waves. Tests examine the effects of the application of wave induced forces, including comparisons to a physical experiment. An example of a real river system is presented with comparisons to measured data, which demonstrate the importance of simulating the combined effects of tides and waves upon hydrodynamic behavior.     

Analysis of directional wave fields using X-band navigation radar

The aim of this work is to present an approach to describe complex sea states including the ones consisting of superpositions of swell and wind sea components, using a nautical radar in X-band as a remote sensing technique. In the present article, the inversion method to obtain the spectral representation of the wave fields is described. The method is applied to analyse data obtained from simulation techniques, as well as from measurements obtained during oceanographic campaigns in the Bay of Biscay and North Sea.     

Extraction of coastal ocean wave fields from SAR images

Wave spectra derived from synthetic aperture radar (SAR) images acquired by ENVISATs are compared to in situ measurements by seven sensors, deployed in a field experiment carried out on the French coast of La Manche (English Channel). The wave spectra inversion scheme is adapted for shallow water from the European Space Agency (ESA)'s operational processing techniques used for level 2 ocean wave products. Under the low to moderate wind speed observed conditions, overall good agreement is found between in situ and SAR observations over a wide range of wave heights and directions, including waves propagating in the radar azimuth direction and incidence angles different from the standard imagette products.     

The impact of stratification on the wave velocity field generated by a barotropic tide impinging upon an oceanic ridge

The horizontal wave velocity field generated by a barotropic tide impinging upon a subwater ridge is considered in the linear theory assumptions for long waves. The ocean is assumed to be twolayered, with the tidal wave on-running at an arbitrary angle to the ridge axis. The dependence of the horizontal velocity amplitudes on stratification, the angle of barotropic tide impinging, and the bottom feature geometry is studied.Translated by V. Puchkin.     

Marine pipeline dynamic response to waves from directional wave spectra

A methodology has been developed to calculate the dynamic probabilistic movement and resulting stresses for marine pipelines subjected to storm waves. A directional wave spectrum is used with a Fourier series expansion to simulate short-crested waves and calculate their loads on the pipeline. The pipeline displacements resulting from these loads are solutions to the time-dependent beam-column equation which also includes the soil resistance as external loading. The statistics of the displacements for individual waves are combined with the wave statistics for a given period of time, e.g. pipeline lifetime, to generate probabilistic estimates for net pipeline movement. On the basis of displacements for specified probability levels the pipeline configuration is obtained from which pipeline stresses can be estimated using structural considerations, e.g. pipeline stiffness, end restraints, etc.     

A new concept of a hull form to improve wave response characteristics for marine construction barges

The object of the new hull form is to provide a single hull which possesses long natural periods of roll and heave and has substantially reduced motion response amplitudes in very high sea states. Model tests and preliminary estimates indicated that the new hull form can be designed for roll and heave motions nearly equivalent to those of much larger semisubmersible units.All existing conventional marine construction barges have rectangular cross section hull. The new hull form consists of a system of upper side tanks and lower side tanks added onto a rectangular cross section hull. The upper tanks and lower tanks form longitudinal troughs on the port and starboard sides. Structural grillage of any open type is to connect the upper and lower tanks at the side of the vessel. Figure 1 indicates a profile and a typical transverse section of the new hull form. The new hull comprises the concept of reduced water plane area which is turn results in low transverse metacentric height and low tons per in. immersion. The novel features of combining low GM_T and low TPI with extremely heavy damping and added mass of the entrained water characteristics result in very long natural periods of roll and heave and considerably small rolling and heaving amplitudes in high sea states. The open side shell plating on the side of the vessel functions to dissipate wave energy at the side of the vessel which would have otherwise been transmitted to the vessel and caused the vessel to respond. This paper presents the conceptual foundation and outline of the new hull form. Model test results are presented and implemented. Also presented is the design philosophy.