Effect Of Regular Waves Research Articles

Smoothed-Particle Hydrodynamics Simulation of Ship Motion and Tank Sloshing under the Effect of Regular Waves

Smoothed-Particle Hydrodynamics Simulation of Ship Motion and Tank Sloshing under the Effect of Regular Waves

Investigation of Submergence Depth and Wave-Induced Effects on the Performance of a Fully Passive Energy Harvesting Flapping Foil Operating Beneath the Free Surface

This paper investigates the performance of a fully passive flapping foil device for energy harvesting in a free surface flow. The study uses numerical simulations to examine the effects of varying submergence depths and the impact of monochromatic waves on the foil’s performance. For the numerical simulations, a in-house artificial compressibility two-phase solver is employed and coupled with a rigid body dynamic solver. The results show that the fully passive flapping foil device can achieve high efficiency for submergence depths between 4 and 9 chords, with an “optimum” submergence depth where the flapping foil performance is maximised. The effects of regular waves on the foil’s performance were also investigated, showing that waves with a frequency close to that of the natural frequency of the flapping foil-aided energy harvesting. Overall, this study provides insights that could be useful for future design improvements for fully passive flapping foil devices for energy harvesting operating near the free surface.

Hydrodynamic assessment of artificial shell blocks for coastal protection

As a novel type of composite breakwater, hollow artificial shells based on rubble mound bases are proposed. The main concept is using shapes from nature to overcome a nature phenomenon (waves). This type of shells is distinguished from other species. Its length and width are almost twice the height, which increases the stability of every individual shell. Additionally, the out-layer grooves and the semicircular shape smoothly dissipate incident waves. The new composite breakwater was investigated physically in a wide wave flume under the effect of regular waves. The breakwater performance was introduced through wave reflection, wave transmission, and wave dissipation coefficients. Several varying wave actions (wave height, wave period) were applied to the breakwater in four states: emergent, partially submerged, submerged and fully submerged. The partially submerged case showed the best efficiency compared with other states. The reflection coefficient ranges from 0.16 to 0.46, the transmission coefficient ranges from 0.3 to 0.48, and the dissipation coefficient ranges from 0.75 to 0.92. The Partially submerged breakwaters have been compared with some of the most commonly used types of breakwaters, and have shown to have better efficiency, particularly in areas with short coastal waves. Also, the crest width of a submerged breakwater can be reduced dramatically to less than half, by deploying artificial shell blocks on the crest.

An experimental study on the evolution of a submerged berm under the effects of regular waves in low-energy conditions

Reduced-scale mobile-bed flume tests are conducted on the evolution of a submerged berm under the effects of regular waves in low-energy conditions. Twenty-three flume tests are performed on a profile model of a submerged berm under different combinations of wave heights and wave periods. The profile shapes and water elevations along the profile are recorded during the tests. Comprehensive analyses are conducted on the profile evolution and the wave parameters along the profile of the submerged berm model. In all cases the crest of the submerged berm moves onshore and the profile shape become asymmetrical. Overall analyses are conducted on the evolution-related parameters such as the moving distance of the centroid ( D lc ), the change of skewness of the profile shape ( C sk ), the change of the crest elevation of the submerged berm ( C cl ) and the irregularity parameter of the profile shape ( K rms ). The effects of wave height and wave period on these parameters are discussed. An Empirical Orthogonal Function (EOF) analysis of the test results indicates two major evolution patterns of the submerged berm, onshore migration and onshore inclining of the crest, both of which are controlled by wave height. The velocity skewness, wave height and local water depth are the major factors that impact the onshore sediment transport under low energy conditions. No obvious connections can be found between acceleration skewness and sediment transport in this experimental study. However, large acceleration skewness would reduce the values of velocity skewness and impact the sediment transport indirectly. This paper proposes new insights on the morphodynamics of submerged berms under low-energy conditions and provide validation data for numerical models. • The evolution of a submerged berm under low-energy conditions are studied via a series of flume tests. • A general portrait on the feature of the evolution of a submerged berm under low energy conditions is given. • The effects of wave height and wave period on the shape-changing of the submerged berm are analyzed quantitatively. • Two major evolution patterns of the submerged berm in this case are onshore migration and onshore inclining of the crest. • The velocity skewness, wave height and local water depth dominate the onshore sediment transport under low energy conditions.

Study on flow structure of tandem multiple jets under the effect of regular waves

The effect of regular waves on the flow structure of tandem multiple jets is investigated experimentally in this study. The tandem multiple jets are discharged vertically into the wave flow. The particle image velocimetry (PIV) technique is employed to measure the flow field of tandem multiple jets. The movement of tandem multiple jets in regular waves is defined starting from the orifices as the separated region, the mixing region and the mixed region. These three regions are distinguished by the mixing point and the mixed point, respectively. The results show that the wave-to-jet velocity ratio Rwj is the most important parameter to characterize the effect of regular waves on multiple jets, affecting the mixing point location, the vertical velocity decay and the cross-sectional distribution of vertical velocity. Using curve-fitting, the formulas estimating the effects of wave-to-jet velocity ratio (Rwj) on the mixing point location and the vertical velocity decay are derived. This study reveals that the regular wave has a positive effect on the mixing and dilution of tandem multiple jets.

Effects of Regular Waves on Propulsion Performance of Flexible Flapping Foil

The objective of the present study is to analyze the effects of waves on the propulsive performance and flow field evolution of flexible flapping foil, and then offer a way to take advantage of wave energy. The effects of regular waves on the propulsive performance of a two-dimensional flexible flapping foil, which imitated the motion and deformation process of a fish caudal fin, were numerically studied. Based on computational fluid dynamic theory, the commercial software Fluent was used to solve the Reynolds-averaged Navier–Stokes equations in the computational domain. Several numerical models were employed in the simulations, which included user-defined function (UDF), numerical wave tank (NWT), dynamic mesh, volume of fluid (VOF), post-processing, and analysis of the wake field. The numerical tank was also deep enough, such that the tank bottom had no influence on the surface wave profile. First, the numerical method was validated by comparing it with experimental results of rigid foil, flapping under waves. The effects of three key wave parameters on the propulsive performance of flexible and rigid foils were then investigated; the results show that higher performance can only be obtained when the motion frequency of the foil was equal to its encounter frequency with the wave. With this precondition, foils were able to generate higher thrust force at larger wave amplitudes or smaller wavelengths. Similarly, the percentage of wave energy recovery by foils was higher at smaller wave amplitudes or wavelengths. From a perspective of wake field evolution, increasing foil velocity (relative to water particles of surrounding waves), could improve its propulsive performance. In addition, flexible deformation of foil was beneficial in not only enhancing vortex intensity but also reducing the dissipation of vortices’ energy in the flow field. Therefore, flexible foils were able obtain a better propulsive performance and higher wave energy recovery ability.

On the Effect of Regular Waves on Inclined Negatively Buoyant Jets

The target of this paper is to measure the modifications that regular waves induce on the geometrical features and dilution of inclined negatively buoyant jets. In order to achieve this aim, we have carried out a set of experiments in a wavemaker-equipped flume, by measuring the concentration fields via light-induced fluorescence, a non-intrusive and full-field image analysis technique. The wave and jet parameters were selected in order to simulate the case of a typical discharge of brine, from a desalination plant, into the Mediterranean Sea, and compare it to a reference case, i.e., the same jet discharging into a stagnant water body. The mean concentration fields were obtained, as well as the geometrical features and dilution of the jets. The three main effects of waves on inclined negatively buoyant jets are the bifurcation (i.e., the separation in two branches), the rotation of the point of maximum height and the oscillation of the impact point around a fixed position different from the stationary one, and the reduction in size of the sea region interested by the discharge; this last effect increases with the wave period. As a consequence, under waves with high period and amplitude, the dilution of inclined negatively buoyant jets tends to decrease.

Near-field dilution of a turbulent jet discharged into coastal waters: Effect of regular waves

The effect of regular waves on three-dimensional scalar structures of a vertical round jet in the wave-following-current environment is investigated. The wave effect is represented by two dimensionless parameters, i.e. the wave-to-current velocity ratio Rwc and Strouhal number St. The jet concentration distribution, including 13 cases in the wave-following-current environment and 1 case in the current-only environment, is obtained using the large eddy simulation method and validated by experimental data. The results show that the characteristics of the distinctive ‘effluent clouds’ phenomenon, namely the effluent cloud size and the distance between adjacent effluent clouds, are strongly dependent on Rwc and St. As a result, different structures of the time-averaged concentration distribution are found in the transverse planes, and they are classified into three types: one-peak type, two-peak type, and three-peak type. The area of the concentration contour of C =0.25Cm, where Cm is the time-averaged cross-sectional maximum concentration, is defined as the jet visual area that represents the jet dilution characteristic. It highlights the existence of an optimal wave-to-current velocity ratio (approximately 0.6 here) for the highest dilution of a jet in the wave-following-current environment, which provides useful guidelines for selecting the sites of wastewater or brine discharge projects.

Numerical Simulations of Regular Wave Impact on Horizontal Plate Based on SPH Methods

The numerical wave flume was established for simulating the impact effects of regular waves on horizontal plate by adopting the method of Smoothed Particle Hydrodynamics (SPH).The impact process of regular waves on horizontal plate was analyzed, and the impact pressure-time curves were gotten using a new estimation method. The comparison of numerical results and experimental results shows that the new estimation method can predict the peak impact pressure more accurately.

Modeling and calculation of bed score around large-diameter vertical cylinder under wave action

The results of studying the scour of bed composed of fine and coarse sand around models of large-diameter vertical cylinder under the effect of regular waves are presented. Comparison of the results of experiments with fine and coarse sand showed essential qualitative and quantitative distinctions between the two cases. The results of experiments with coarse sand were used to derive, for the first time, a formula for the estimation of the score depth, including two similarity criteria—the sediment motion factor (SM-factor), and Keulegan-Carpenter number. This formula is applicable to both the engineering analysis of the scour depth of gravel bed or protective riprap by crashed rock or fine stone and the approximate prediction of the scour depth of sand bed around structures under real storm conditions. The conditions for correct modeling of wave scour around structures with large horizontal dimensions are considered and the irrelevance of modeling such scour with the use of fine-sand models is demonstrated.

A Theoretical Study on the Second-Order Wave Forces for Two-Dimensional Bodies

Nonlinear wave forces on fixed or floating offshore structures have attracted much attention recently. This paper deals with the nonlinear effects of regular waves on fixed two-dimensional bodies up to second-order terms. The second-order diffraction potential is solved consistently and the second-order steady wave forces and the biharmonic wave forces with frequency corresponding to the double of the incident wave frequency are obtained.