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1.
A lift based wave energy converter, namely, a cycloidal turbine, is investigated. This type of wave energy converter consists of a shaft with one or more hydrofoils attached eccentrically at a radius. The main shaft is aligned parallel to the wave crests and submerged at a fixed depth. In the two-dimensional limit, i.e. for large spans of the hydrofoil (or an array of these), the geometry of the converter is suitable for wave termination of straight crested Airy waves. Results from two-dimensional potential flow simulations, with thin hydrofoils modeled as either a point vortex or discrete vortex panel, are presented. The operation of the cycloidal turbine both as a wave generator as well as a wave-to-shaft energy converter interacting with a linear Airy wave is demonstrated. The impact on the performance of the converter for design parameters such as device size, submergence depth, and number of hydrofoils is shown. For optimal parameter choices, simulation results demonstrate inviscid energy conversion efficiencies of more than 99% of the incoming wave energy to shaft energy. This is achieved using feedback control to synchronize the rotational rate, blade pitch angle, and phase of the cycloidal wave energy converter to the incoming wave. While complete termination of the incoming wave is shown, the remainder of the energy is lost to harmonic waves traveling in the up-wave and down-wave directions.  相似文献   

2.
A renewable energy harvester using the piezoelectric effect is developed for the ocean tidal and wind flow. The harvester is made of connected driving blades to an octo-generator, which has a rotator with n blades and a stator attached by eight mass-spring-piston-cylinder-piezoelectricity devices. The resonance and force magnification are utilized to increase the power output of the harvester. A corresponding mathematical model is developed to calculate the root mean square of the generated electric power. The simulation results indicate that the generated power is largely enhanced when the near-resonant condition is established. The power increases with increases in the magnetic flux density, the large-to-small diameter ratio of the cylinder, the size of magnetic bar face, and decreases in the gap between two magnetic faces and the size of the piezoelectric bar face. A generated power of 5 kW is realized by the harvester working under an ocean tidal speed, V = 1.75 m/s, and its geometric and material properties of driving length L = 7.5 m, spring constant kv = 65000 N/m, gap between the two magnets s = 0.0015 m, large to small diameter ratio of the cylinder z = 6, and magnetic flux density Br = 1.45 T.  相似文献   

3.
Based on the linear potential flow theory and matching eigen-function expansion technique, an analytical model is developed to investigate the hydrodynamics of two-dimensional dual-pontoon floating breakwaters that also work as oscillating buoy wave energy converters (referred to as the integrated system hereafter). The pontoons are constrained to heave motion independently and the linear power take-off damping is used to calculate the absorbed power. The proposed model is verified by using the energy conservation principle. The effects of the geometrical parameters on the hydrodynamic properties of the integrated system, including the reflection and transmission coefficients and CWR (capture width ratio, which is defined as the ratio of absorbed wave power to the incident wave power in the device width). It is found that the natural frequency of the heave motion and the spacing of the two pontoons are the critical factors affecting the performance of the integrated system. The comparison between the results of the dual-pontoon breakwater and those of the single-pontoon breakwater shows that the effective frequency range (for condition of transmission coefficient KT < 0.5 and the total capture width ratio ηtotal > 20%) of the dual-pontoon system is broader than that of the single-pontoon system with the same total volume. For the two-pontoon system, the effective frequency range can be broadened by decreasing the draft of the front pontoon within certain range.  相似文献   

4.
Wave–current flow is a phenomenon that is present in many practical engineering situations. Over the past several decades, this type of flow has been increasingly investigated under controlled laboratory conditions. This paper presents a numerical study of wave–current flow in the ocean basin of the LabOceano (COPPE/UFRJ). A homogeneous multiphase model based on the RANS equations and the k–ɛ turbulence model implemented in ANSYS-CFX code were used. A cross section of the ocean basin was represented. A regular wave with a height of 0.08 m and a period of 1.80 s (i.e., a wave steepness of H/L = 0.016), propagating on favourable currents, was simulated. The behaviour of the free surface elevation over time and the streamlines along the basin for wave and wave–current flows were presented. The numerical results were compared to the non-viscous theory given by the Rayleigh equation applied to the problem of wave–current interaction. Good agreement was found between the wave length estimated by the numerical results and the analytical solutions, with a deviation of less than 2%.  相似文献   

5.
In this paper, wave farms composed of two either surging or heaving wave energy converters are considered. Using a numerical model which takes into account wave interactions, the impact on the absorbed wave power of the separating distance between the two systems and the wave direction is studied. In regular waves, a modified qmod factor is introduced and it is found to be more relevant than the usual q factor for identifying this impact. Then, it is shown that, asymptotically, the alteration of the energy absorption due to wave interaction effects decreases with the square root of the distance. This is a slow decay, which leads to a still significant modification of the wave energy absorption at long distance (up to 15% at a distance of 2000 m). In irregular waves, it is shown that constructive and destructive effects compensate each other, particularly when considering the mean annual power. It leads to a smaller impact of the wave interactions on the absorbed energy and shorter distances (smaller than 10% for distances greater than 400 m). Finally, conclusions on if wave interactions should be taken into account or not when designing a wave farm are drawn in function of the distance.  相似文献   

6.
The effect of water depth on the performance of a small surging wave energy converter (WEC) is investigated analytically, numerically and experimentally. It is shown that although the average annual incident wave power is significantly reduced by water depth, a large proportion of this reduction is due to the dissipation of highly energetic, but largely unexploitable seas. It is also shown that the power capture is related more closely to incident wave force than incident wave power. Experimental results demonstrate that both the surge wave force and power capture of a flap-type WEC increase in shallow water.  相似文献   

7.
Ocean surface gravity waves play a major role in many engineering and environmental problems, both in the open ocean and in coastal zones. Therefore, it is essential to improve our knowledge on spatial and temporal variability of wave climate. This study aims at investigating this variability in the North-East Atlantic Ocean (25°W–0°W and 30°N–60° N), using a 57-year hindcast (1953–2009) obtained with a spectral wave model forced with reanalysis wind fields. The hindcast analysis reveals firstly strong seasonal fluctuations of wave climate, with winters characterized by large and long-period waves of mean direction spreading from south-west to north-west, and summers characterized by smaller and shorter-period waves originating from norther directions. From northern (55°N) to southern (35°N) latitudes, the significant wave height (Hs) decreases by roughly 40%, the mean wave direction (Mwd) rotates clockwise by about 25% while the peak period (Tp) only grows by 5%. These three parameters also exhibit a strong inter-annual variability, particularly when winter-means (from 1st of December to 1st of April) are considered. Linear trend analysis over the studied period shows spatially variable long-term trends, with a significant increase of Hs (up to 0.02 m yr?1) and a counterclockwise shift of Mwd (up to ?0.1° yr?1) at northern latitude, contrasting with a fairly constant trend for Hs and a clockwise shift of Mwd (up to +0.15° yr?1) at southern latitudes. Long-term trends of Tp are less significant, with still a slight increase in the north-eastern part of the study area (up to +0.01 s yr?1). Eventually, a comparison between the inter-annual variability of the winter-means of the three selected wave parameters and the North Atlantic Oscillation (NAO) reveals: (1) a strong positive correlation between Hs and the NAO index at northern latitudes (correlation coefficient up to R = 0.91) and a significant negative correlation at southern latitudes (up to R = ?0.6); (2) no significant correlation for Mwd north of 40°N and a clear positive correlation southward of 40°N (up to R = 0.8) and (3) a northward increasing correlation for Tp (up to R = 0.8). Long-term trends for Hs, Mwd and Tp are finally explained by a significant increase in the NAO index over the studied period.  相似文献   

8.
An autonomous upwardly-moving microstructure profiler was used to collect measurements of the rate of dissipation of turbulent kinetic energy (ε) in the tropical Indian Ocean during a single diurnal cycle, from about 50 m depth to the sea surface. This dataset is one of only a few to resolve upper ocean ε over a diurnal cycle from below the active mixing layer up to the air–sea interface. Wind speed was weak with an average value of ~5 m s−1 and the wave field was swell-dominated. Within the wind and wave affected surface layer (WWSL), ε values were on the order of 10−7–10−6 W kg−1 at a depth of 0.75 m and when averaged, were almost a factor of two above classical law of the wall theory, possibly indicative of an additional source of energy from the wave field. Below this depth, ε values were closer to wall layer scaling, suggesting that the work of the Reynolds stress on the wind-induced vertical shear was the major source of turbulence within this layer. No evidence of persistent elevated near-surface ε characteristic of wave-breaking conditions was found. Profiles collected during night-time displayed relatively constant ε values at depths between the WWSL and the base of the mixing layer, characteristic of mixing by convective overturning. Within the remnant layer, depth-averaged values of ε started decaying exponentially with an e-folding time of 47 min, about 30 min after the reversal of the total surface net heat flux from oceanic loss to gain.  相似文献   

9.
The moored three-float line absorber WEC M4 has been developed to optimise power capture through experiments and linear diffraction modelling. With the progression down wave from small to medium to large floats, the device heads naturally into the wave direction. The bow and mid floats are rigidly connected by a beam and a beam from the stern float is connected to the hinge point above the mid float for power take off (PTO). Increasing the bow to mid float spacing to be more than 50% greater than the mid to stern float spacing has been found to improve power capture. To increase power capture further and potentially reduce electricity generation cost the number of mid floats and stern floats is increased while maintaining a single bow float for mooring connection. The bow and mid floats still form a rigid body while the stern floats may respond independently. A time domain linear diffraction model based on Cummins method has been applied to configurations of 121, 123, 132, 133, and 134 floats where the numbers indicate the number of floats: bow, mid, stern. This shows how power capture is increased while response remains similar. We only consider uni-directional (long-crested) waves with narrow band width typical of swell. By considering scatter diagrams for various offshore sites capacities may range from 3.7 MW to 17.3 MW for the eight float system with a capacity factor of 1/3 while the cost of electricity assuming capital cost to be a fixed multiple of steel cost is reduced from that for the three-float system.  相似文献   

10.
This paper investigates the performance of a small axisymmetric buoy under wave-by-wave near optimal control in surge, heave, and pitch modes in long-crested irregular waves. Wave prediction is obtained using a deterministic propagation model. The paper describes the overall formulation leading up to the derivation of the feedforward control forces in surge and heave, and the control moment in pitch. The radiation coupling between surge and pitch modes is accounted for in the model. Actuation is relative to deeply submerged reaction masses. Heave oscillations are constrained by the swept-volume limit. Oscillation constraints are also applied on the surge and pitch oscillations. The paper discusses time-domain simulations for an irregular wave input with and without the present control. Also discussed are results obtained over a range of irregular wave conditions derived for energy periods from 7 s to 17 s, and a significant wave height of 1 m. It is found that, while the gains in power capture enabled by the present control are significant, the actuation forces are also very large, given the small size of the buoy. Further, due to the small size, heave is found to be the dominant contributor to power capture, with relatively modest contributions from surge and pitch.  相似文献   

11.
The short-term wave characteristics are required for design and operation of industrial facilities within the coastal areas. Water surface displacement measured using waverider buoy moored at 13 m water depth in the eastern Arabian Sea off the west coast of India have been analyzed to study the short-term statistics of waves covering full one year period. The study indicates that the values of the observed maximum wave height as a function of duration are not consistent with the theoretical expected value. There is significant variation (1.29–2.19) in the ratio between highest 1% wave and significant wave height compared to the theoretical value of 1.67. The data recorded at 13 m water depth indicates that the significant wave height is ∼8% lower than that predicted by the conventional Rayleigh distribution. The theoretical bivariate log-normal distribution represents the joint distributions of wave heights and periods for the study area.  相似文献   

12.
The wave transmission, reflection, and energy dissipation of the double rows of vertical piles suspending horizontal steel C shaped bars are experimentally and theoretically studied under normal regular waves. Different wave and structural parameters are investigated e.g. the wave length, the C shaped bars draft and spacing, the supporting piles diameter and spacing, and the space between the double rows. Also, the theoretical model based on an eigenfunction expansion method is developed to study the hydrodynamic breakwater performance. In order to examine the validity of the theoretical model, the theoretical results are compared with the experimental and theoretical results obtained by different authors. Comparison between experiments and predictions showed that theoretical model provides a good estimate to the different hydrodynamic coefficients when the friction factors of the upper and the lower parts are fU = 1.5 and fL = 0.75. The present breakwater physical model gives efficiency near other similar systems of different shapes.  相似文献   

13.
The possibility of using wave farms for coastal defence warrants investigation because wave energy is poised to become a major renewable in many countries over the next decades. The fundamental question in this regard is whether a wave farm can be used to reduce beach erosion under storm conditions. If the answer to this question is positive, then a wave farm can have coastal defence as a subsidiary function, in addition to its primary role of producing carbon-free energy. The objective of this work is to address this question by comparing the response of a beach in the face of a storm in two scenarios: with and without the wave farm. For this comparison a set of ad hoc impact indicators is developed: the bed level impact (BLI), beach face eroded area (FEA), non-dimensional erosion reduction (NER), and mean cumulative eroded area (CEA); and their values are determined by means of two coupled models: a high-resolution wave propagation model (SWAN) and a coastal processes model (XBeach). The study is conducted through a case study: Perranporth Beach (UK). Backed by a well-developed dune system, Perranporth has a bar between − 5 m and − 10 m. The results show that the wave farm reduces the eroded volume by as much as 50% and thus contributes effectively to coastal protection. This synergy between marine renewable energy and coastal defence may well contribute to improving the viability of wave farms through savings in conventional coastal protection.  相似文献   

14.
Investigation of the bottom slope effects on the nonlinear transformation of irregular waves, which are generated based on JONSWAP spectra, is carried out in a physical wave flume with three slopes (β = 1/15, 1/30, 1/45). The slope effects on the estimation of representative wave height are examined first. To obtain a better estimation of wave height, the slope effect should be considered when slope is larger than 1/30. The nonlinear parameters (bicoherence, skewness and asymmetry) are estimated by using the wavelet-based bispectrum, and the empirical formulae regarding these nonlinear parameters as a function of the local Ursell number are derived based on the present data measured on each slope. The results indicate that the slopes have a negligible effect on the variations of the skewness. The fitted coefficients of the formulae for the other parameters on slope β = 1/15 are clearly different from the results on the slopes β = 1/30 and 1/45, indicating that slope influence on the parameterization cannot be ignored when β > 1/30. Hence, new formulae considering the slope effect are presented. Furthermore, the empirical formulae for the data in surf zone are recommended.  相似文献   

15.
An expedient piezoelectric coupled buoy energy harvester from ocean waves is developed. The harvester is made of several piezoelectric coupled cantilevers attached to a floating buoy structure, which can be easily suspended in the intermediate and deep ocean for energy harvesting. In the buoy structure, a slender cylindrical floater is attached on a large sinker. The energy harvesting process is realized by converting the transverse ocean wave energy to the electrical energy via the piezoelectric patches mounted on the cantilevers fixed on the buoy. A smart design of the buoy structure is developed to increase the energy harvesting efficiency by investigation of the effects of the sizes of the floater and the sinker. A numerical model is presented to calculate the generated electric power from buoy energy harvester. The research findings show that up to 24 W electric power can be generated by the proposed expedient buoy harvester with the length of the piezoelectric cantilevers of 1 m and the length of the buoy of 20 m. The technique proposed in this research can provide an expedient, feasible and stable energy supply from the floating buoy structure.  相似文献   

16.
A high resolution modeling study is undertaken, with a 2.5-dimensional nonhydrostatic model, of the generation of internal waves induced by tidal motion over the ridges in Luzon Strait. The model is forced by the barotropic tidal components K1, M2, and O1. These tidal components, along with the initial density field, were extracted from data and models. As the barotropic tide moves over the Luzon Strait sills, there is a conversion of barotropic tidal energy into baroclinic tidal energy. Depressions are generated that propagate towards the Asian Seas International Acoustics Experiment (ASIAEX) test site on the Chinese continental shelf. Nonlinear effects steepen the depressions, frequency and amplitude dispersion set in, and disintegration into large amplitude solitary waves occurs. The effects of varying the initial density field, tidal component magnitudes, as well as adding a steady background current to represent the occasional excursions of the Kuroshio Current into the strait, are considered.Depressions are generated at each of the two sills in Luzon Strait which radiate away, steepening and evolving into internal solitary wave trains. Baroclinic fluxes of available potential energy, kinetic energy and linear are calculated for various parameter combinations. The solitary wave trains produced in the simulations generally consist of large amplitude wave trains alternating with small amplitude wave trains. During strong tidal flow, Kelvin–Helmholtz type instabilities can develop over the taller double-humped sill. The solitary waves propagating towards the ASIAEX test site have been observed to reach amplitudes of 120–250 m, depending on the tidal strength. ASIAEX observations indicate amplitudes up to 150 m and the Windy Island Experiment (WISE) measurements contain magnitudes over 200 m. The model results yield solitary wave amplitudes of 70–300 m and half widths of 0.60–3.25 km, depending on parameter values. These are in the range of observations. Measurements by Klymak et al. (2006), in the South China Sea, exhibit amplitudes of 170 m, half widths of 3 km and phase speeds of 2.9 m s?1. Model predictions indicate that the solitary waves making up the wave packet each experience different background currents with strong near surface shear.The energy in the leading soliton of the large amplitude wave trains ranges between 1.8 and 9.0 GJ m?1. The smaller value, produced using barotropic tidal currents based on the Oregon State University data base, is the same as the energy estimated to be in a solitary wave observed by Klymak et al. (2006). Estimates of the conversion of barotropic tidal energy into radiating internal wave energy yield conversion rates ranging between 3.6% and 8.3%.  相似文献   

17.
We describe experiments with multi-directional focused waves interacted with a vertical circular cylinder in a 3D wave basin. The focus of this study is on the run-up of multi-directional focused waves, wave forces, and wave pressures on the cylinder. Part I, the study on wave run-up, has already been presented by Li et al. (2012). In this paper, the analysis of the wave force on the vertical cylinder is presented.In this experiment, a cylinder with 0.25 m in diameter was adopted and different wave parameters, such as focused wave amplitude, peak frequency, frequency bandwidth and directional spreading index, are considered. The model scale kpa (kp is the wave number corresponding to peak frequency, a is the radium of the cylinder) varies from 0.32 to 0.65. The maximum forces of multi-directional focused wave on cylinder were measured and investigated. The results showed that the wave parameters have a significant influence on the wave force, and that the spatial profile of the surface of multi-directional focused wave can also affect its force on the cylinder, which is different from two-dimensional wave. In addition, the ‘secondary loading cycle’ phenomenon was also observed and discussed. In our experiments, the ‘secondary loading cycles’ occur when kA > 0.36 for all cases. While in some referred small scale experiments, the secondary load cycles are observed even for kA = 0.2, when the waves are longer enough. To larger model scale, the pronounced secondary load cycle occurs with larger wave steepness waves.  相似文献   

18.
Investigations of biomass, production, and anthropogenic impact require knowledge of the spatial distribution of the species concerned. Studies of the spatial distribution of soft-sediment infauna are inherently difficult, because the organisms are generally not readily visible, necessitating painstaking excavation. Although the large-scale (tens of km) distribution patterns of infaunal bivalves have been studied previously, the fine-scale (1 to tens of meters) has received much less attention. We investigated the fine-scale spatial distribution of the edible cockle Cerastoderma edule at a fishing-impacted site and a non-impacted site on an intertidal mudflat in Bourgneuf Bay, France, in 2009–2010. A preliminary study using a 1 m spatial lag was performed to determine the optimum lags for a nested sampling design. Cohorts were identified using Bhattacharya-resolved size-frequency distributions and verification of isotropy, and the spatial characteristics of each cohort were determined using Moran's I auto-correlation coefficient. The non-impacted site presented one strongly-aggregated main cohort, C3, (Moran's I = 0.67 to − 0.34, spatial range 16 to 20 m, inter-patch distance 41 to 51 m). The impacted site presented two main cohorts, C2 (1.31 cm mean shell length, SL) and C3 (2.11 cm SL) both of which also showed a patchy spatial distribution (C2: Moran's I = 0.7 to − 0.72, spatial range 22 to 35 m; inter-patch distance 63 to 90 m; C3: Moran's I = 0.41 to − 0.63, spatial range 36 to 58 m, inter-patch distance not defined). The C3 cohort was less aggregated than the C2; possibly due to the homogenizing effect of fishing, which typically proceeds via a Lévy walk foraging model.Our results show that the spatial distributions of C. edule retained a strongly aggregated character over the 8 months of the study, suggesting that these characteristics are powerfully maintained by recruitment/post-recruitment processes, despite intense fishing pressure throughout the sampling period, and indeed for decades, prior to this study. These data also show that we cannot assume a random or a regular spatial distribution for this species in studies of biomass, production, trophic relations, or anthropogenic impact; rather, close attention must be paid to the spatial characteristics of studied populations in order to reduce the confounding effects of auto-correlation.  相似文献   

19.
《Marine Chemistry》2007,103(1-2):30-45
The chemistry of dissolved Fe(III) was studied in the Scheldt estuary (The Netherlands). Two discrete size fractions of the dissolved bulk (< 0.2 μm and < 1 kDa) were considered at three salinities (S = 26, 10 and 0.3).Within the upper estuary, where fresh river water meets seawater, the dissolved Fe concentration decreases steeply with increasing salinity, for the fraction < 0.2 μm from 536 nM at S = 0.3 to 104 nM at S = 10 and for the fraction < 1 kDa from 102 nM to 36 nM Fe. Further downstream, in the middle and lower estuary, this decrease in the Fe concentration continues, but is far less pronounced. For all samples, the traditionally recognised dissolved strong organic Fe-binding ligand concentrations are lower than the dissolved Fe concentrations.Characteristics of dissolved Fe-binding ligands were determined by observing kinetic interactions with adsorptive cathodic stripping voltammetry. From these kinetic experiments we concluded that apart from the well-known strong Fe-binding organic ligands (L, logK′ = 19–22) also weak Fe-binding ligands (P) existed with an α value (binding potential = K′ · [P]) varying between 1011.1 and 1011.9. The presence of this relatively weak ligand explained the high concentrations of labile Fe present in both size fractions in the estuary. This weak ligand can retard or prevent a direct precipitation after an extra input of Fe.The dissociation rate constants of the weak ligand varied between 0.5 × 10− 4 and 4.3 × 10− 4 s− 1. The rate constants of the strong organic ligand varied between kd = 1.5 × 10− 3–17 × 10− 2 s− 1 and kf = 2.2 × 108–2.7 × 109 M− 1 s− 1. The dissociation rate constant of freshly amorphous Fe-hydroxide was found to be between 4.3 × 10− 4 and 3.7 × 10− 3 s− 1, more labile or equal to the values found by Rose and Waite [Rose, A.L., Waite, T.D., 2003a. Kinetics of hydrolysis and precipitation of ferric iron in seawater. Environ. Sci. Technol., 37, 3897–3903.] for freshly precipitated Fe in seawater.Kinetic rate constants of Fe with the ligand TAC (2-(2-Thiazolylazo)-p-cresol) were also determined. The formation rate constant of Fe(TAC)2 varied between 0.1 × 108 and 3.6 × 108 M− 1 s− 1, the dissociation rate constant between 0.2 × 10− 5 and 17 × 10− 5 s− 1 for both S = 26 and S = 10. The conditional stability constant of Fe(TAC)2 (βFe(TAC)2′) varied between 22 and 23.4 for S = 10 and S = 26 more or less equal to that known from the literature (logβFe(TAC)2′ = 22.4; [Croot, P.L., Johansson, M., 2000. Determination of iron speciation by cathodic stripping voltammetry in seawater using the competing ligand 2-(2-Thiazolylazo)-p-cresol (TAC). Electroanalysis, 12, 565–576.]). However, at S = 0.3 the logβFe(TAC)2′ was 25.3, three orders of magnitude higher. Apparently the application of TAC to samples of low salinity can only be done when the correct βFe(TAC)2′ is known.  相似文献   

20.
We have employed laboratory and numerical experiments in order to investigate propagation of waves in both long and short-crested wave fields in deep water. For long-crested waves with steepness, ϵ = kcac = 0.1 (a fairly extreme case), reliable prediction can be performed with the modified nonlinear Schrödinger equation up to about 40 characteristic wavelengths. For short-crested waves the accuracy of prediction is strongly reduced with increasing directional spread.  相似文献   

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