Showing papers on "Wave power published in 2002"

Optimum Control of Oscillation of Wave-Energy Converters

Abstract: The power output from wave energy converters (WECs) may be increased by controlling the oscillation in order to approach an optimum interaction between the WEC and the incident wave. Optimally controlled WECs, designed to operate at full capacity a rather large fraction of their lifetime, may improve the economic prospects for wave power significantly. Most of the WECs discussed here, utilise just one mode of oscillation. An upper bound is given to the ratio between the converted power from a given wave, and the geometrical volume of the converter. One control strategy for maximising the converted power is based on measuring the incident wave, whereas another strategy utilises measurement of the WEC's own oscillation as input to the controller. In either case the measured quantity has to be predicted some seconds into the future because of noncausal control functions.

Electrical generators for direct drive wave energy converters

Abstract: Wave power devices traditionally use conventional rotary electrical machines for power conversion. However hydraulic systems or air turbines are required to convert the low reciprocating motion of the wave device to rotation at 1500 rpm. The concept of a direct drive system is introduced, in which a reciprocating electrical machine is driven at the same speed as the device. A linear permanent magnet synchronous machine is compared to the transverse flux machine in a basic design study for this application. The latter machine is identified as offering the best potential. Electromagnetic and electric circuit models are developed to investigate the performance of the transverse flux machine in a wave energy converter. Measures are suggested to optimise the performance of the machine.

Apparatus and methods for energy conversion in an ocean environment

Abstract: A wave power generator comprises an air bellows that is longitudinally expandible and contractible in response to the rise and fall of a flotation member subjected to wave action and to which the air bellows is attached. Expansion and contraction of the air bellows causes air to flow into and out of the air bellows, and the flow of air rotates a turbine generator to generate electrical power. Other wave power generators utilize wave action to effect relative linear movement between a coil and magnet to generate electrical power. The wave power generators may be used to supply electrical power to deep water hydrogen generators in which water is electrolyzed at great depths underwater to generate compressed hydrogen gas.

The Offshore Floating Type Wave Power Device ”Mighty Whale” Open Sea TestsPerformance of The Prototype –

Abstract: Mighty Whale is a floating wave power device based on the Oscillating Water Column (OWC) principle. It converts wave energy into electric energy, and produces a relatively calm sea area behind. The open sea tests were begun in September 1998 in Gokasho Bay, Nansei Town, Mie Prefecture. Measurements collected since then include performance data in typhoon seasons. This paper presents the measurements of wave energy absorption, floating body motion, and wave height dissipation. It is expected that these results will be useful in the design of offshore wave power devices in the future.

On the self-consistent modeling of a traveling wave sustained nitrogen discharge

Abstract: We present a self-consistent formulation to study low-pressure traveling wave (azimuthally symmetric surface transverse magnetic mode) driven discharges in nitrogen. The theoretical model is based on a self-consistent treatment of the electron and heavy particle kinetics, wave electrodynamics, gas thermal balance, and plasma–wall interactions. The solution provides the axial variation (as a result of nonlinear wave power dissipation along the wave path) of all discharge quantities and properties of interest, such as the electron energy distribution function and its moments, population densities of all relevant excited and charged species [N2(X 1Σg+,ν),N2(A 3Σu+,a′ 1Σu−,B 3Πg,C 3Πu,a 1Πg,w 1Δu), N2+, N4+, e], gas temperature, degree of dissociation [N(4S)]/N, mean absorbed power per electron, and wave attenuation. A detailed analysis of the energy exchange channels among the degrees of freedom of the heavy particles is presented. Particular attention is paid to the axial variation of the gas and wall tempe...

Microseismic measurement of wave-energy delivery to a rocky coast

Abstract: Rocky coasts are attacked by waves that drive sea-cliff retreat and etch promontories and embayments into the coastline. Understanding the evolution of such coastlines requires knowledge of the energy supplied by waves, which should depend upon both the deep-water waves and the coastal bathymetry they cross. We employ microseismic measurements of the wave-induced shaking of sea cliffs near Santa Cruz, California, as a proxy for the temporal pattern of wave-energy delivery to the coast during much of the winter 2001 storm season. Visual inspection of the time series suggests that both deep-water wave heights and tide levels exert considerable control on the energy delivered. We test this concept quantitatively with two models in which synthetic time series of wave power at the coast are compared with the shaking data. In the first model, deep-water wave power is linearly scaled by a fitting parameter; because this model fails to account for the strong tidal signal, it fits poorly. In the second model, the wave transformation associated with shoaling and refraction diminishes the nearshore wave power, and dissipation associated with bottom drag and wave breaking is parameterized by exponential dependencies on two length scales; this model reduces the variance by 32%-45% and captures the essence of the full signal. Shoaling and refraction greatly modulate the wave power delivered to the coast. Energy dissipated by bottom drag across the shelf is relatively small; the dissipation length scale is many times the path length across the shelf. In contrast, much energy is dissipated in the surf zone; the tidal-dissipation depth scale is of the same order as the tidal range (1-2 m), which accounts for the strong dependence of the cliff shaking on the tide.

Hysteretic Characteristics of Wells Turbine For Wave Power Conversion

Abstract: A Wells turbine blade for wave power conversion has hysteretic characteristics in a reciprocating flow. The hysteretic loop is opposite to the well-known dynamic stall of an airfoil. In this paper, the mechanism of the hysteretic behavior was elucidated by an unsteady 3-dimensional Navier-Stokes numerical simulation. It was found that the hysteretic behavior was associated with a streamwise vortical flow appearing near the blade suction surface. And also the effects of solidity, setting angle and blade thickness on the hysteretic characteristics of the Wells turbine have been discussed.

Analysis of Wave Directional Spreading Using Neural Networks

Abstract: The short-term directional spreading of wave energy at a given location is popularly modeled with the help of the Cosine Power model. This model is oriented mainly around value of the spreading parameter involved in its expression. This paper describes how a representative spreading parameter could be arrived at from easily available wave parameters such as significant wave height and average zero-cross wave period, using the technique of neural networks. It is shown that training of the network with the help of observed directional wave (e.g., heave-pith-roll buoy) data could be used to establish dependency of the spreading parameter on more commonly available unidirectional wave parameters derived from, for example, pressure gauge data. It is found that such a procedure involving neural networks is much more accurate and reliable than the conventional approach based on statistical linear regression.

The Open Sea Tests of the Offshore Floating Type Wave Power Device “Mighty Whale”: Performance of the Prototype

Abstract: This paper presents the characteristics of wave conditions, wave energy absorption, response of hull-motion and wave height dissipation based on the results of the open sea tests. 0.5–1.0m of significant wave height and 6–7 seconds of significant wave period appear the most predominant, and average wave energy is estimated 4.88kW/m around the test site. Average power output for the test is approximately 6kWh and the maximum total energy efficiency is around 15% that is ranging from 6–7 seconds of significant wave period. Slow drift oscillation of hull was observed motion in surge, sway and yaw and the value of its amplitude almost equal to estimated values in design stage. Then the mean value of transmission coefficient is about 0.8 under 8.0 seconds of significant wave period. We are considering that the results of the tests should be useful for optimum design of an offshore floating type wave power device.Copyright © 2002 by ASME

Energy Dissipation in Surface Layer Due to Vertically Propagating SH Wave

Abstract: Vertical array data recorded during the 1995 Kobe earthquake are used to calculate the upward and downward energy flow based on one-dimensional SH-wave multireflection theory, from which the energy dissipation in a surface layer is evaluated as their residual. The dissipated energy thus evaluated in a liquefied site is found to reach about 70% of the upward input energy, which indicates that soil nonlinearity and liquefaction serve as effective energy absorbers. In contrast, more energy returns to deeper ground in sites without strong nonlinear behavior. Furthermore, the dissipated energy in the surface layer tends to increase nonlinearly in a convex shape with increasing equivalent damping ratio of the soil there. A simplified two-layer system indicates that the energy dissipation is influenced not only by the soil damping in the surface layer but also by the impedance ratio between the base and surface layers and the input frequency. The same convex relationship is also obtained in the two-layer system, indicating that the simplified system may reflect some important aspects of the energy dissipation mechanisms in the ground.

Wind- and wave-power driven buoy, has Darrieus wind wheel mounted on upper face of buoy

Abstract: A powered buoy (1) which simultaneously utilizes wave- and solar energy in a device for generating renewable energy and through which the economy is increased relative to separate units. On the top surface of the powered buoy is located a wind wheel, which is specifically designed as a conventional Darrieus wind wheel (2).

Productivity of Ocean-Wave-Energy Converters: Turbine Design

Abstract: A study was undertaken to identify which of a range of advanced Wells turbine configurations would maximize wave power productivity. The productivity is estimated of a monoplane with fixed guide vanes, a monoplane with variable-pitch blades, and a high- and low-solidity biplane with counterrotating rotors. Two control mechanisms are investigated for the variable pitch configuration. Raleigh distributions based on a mean annual pneumatic power rating of 500 kW are utilized to generate the short and long-term variations of input power to be matched with experimental turbine performance data obtained from a steady-state test rig. It was found that productivity was relatively insensitive to turbine configuration but that a low-solidity counterrotating turbine had the best performance characteristic providing high peak efficiency and gradual onset of stall.

Investigation on the Oscillating Buoy Wave Power Device

Abstract: An oscillating buoy wave power device (OD) is a device extracting wave power by an oscillating buoy Being excited by waves, the buoy heaves up and down to convert wave energy into electricity by means of a mechanical or hydraulic device Compared with an Oscillating Water Column (OWC) wave power device, the OD has the same capture vvidth ratio as the OWC does, but much higher secondary conversion efficiency Moreover, the chamber of the OWC, which is the most expensive and difficult part to be built, is not necessary for the OD, so it is easier to construct an OD In this paper, a nu-merical calculation is conducted for an optimal design of the OD firstly, then a model of the device is built and, a model test is carried out in a wave tank The results show that the total efficiency of the OD is much higher than that of the OWC and that the OD is a promising wave power device

Investigation on the oscillating buoy wave power device

Abstract: An oscillating buoy wave power device (OD) is a device extracting wave power by an oscillating buoy Being excited by waves, the buoy heaves up and down to convert wave energy into electricity by means of a mechanical or hydraulic device Compared with an Oscillating Water Column (OWC) wave power device, the OD has the same capture width ratio as the OWC does, but much higher secondary conversion efficiency Moreover, the chamber of the OWC, which is the most expensive and difficult part to be built, is not necessary for the OD, so it is easier to construct an OD In this paper, a numerical calculation is conducted for an optimal design of the OD firstly, then a model of the device is built and, a model test is carried out in a wave tank The results show that the total efficiency of the OD is much higher than that of the OWC and that the OD is a promising wave power device

Wave power generator

Abstract: A method and device (10) for extracting useful energy from wave motion (12) in a body of water (11). The method involves providing the energy extraction device (10) having an energy collection surface (23) responsive to variations in hydrostatic pressure generated by wave motion; and positioning the energy extraction device in the body of water at a location where the body of water is at a depth D and a wave length λ. The ratio of water depth to wave length (D/λ) is in a range of about 0.1 to 0.5. Useful energy is delivered by the energy extraction device (10). With the ratio of water depth to wave length (D/λ) within the range prescribed above, the water may be considered to be in a regime intermediate between a deep water regime and a shallow water regime for the prescribed wave length. The energy extraction device (10) has a rigid surface (25) extending downwardly from the energy collection surface (23) for intercepting water disturbances generated by the wave motion (12) and deflecting the water disturbances to the region above the energy collection surface (23).

Desired wave power to interference wave power ratio measuring apparatus, desired wave power to interference wave power ratio measuring method and desired wave power to interference wave power measuring program

Abstract: PROBLEM TO BE SOLVED: To improve accuracy in SIR without performing RAKE synthesis SOLUTION: In a desired wave power to interference wave power ratio measuring apparatus, desired wave power measuring circuits 104-1 through 104-N measure the desired power of multi-path reception signals for each path, and interference wave power measuring circuits 105-1 through 1-5-N measure interference power of the multi-path reception signals for each path A synthesizing section 111 applies weight synthesis to at least one of the desired wave power for each path measured by the circuits 104-1 through 104-N or the interference wave power for each path measured by the circuit 105-1 through 105-N An SIR calculating circuit 109 calculates a desired wave power to interference wave power ratio on the basis of the output value from the section 111

Investigation on the Oscillating Buoy Wave Power Device

Abstract: An oscillating buoy wave power device (OD) is a device extracting wave power by an oscillating buoy. Being excitedby waves, the buoy heaves up and down to convert wave energy into electricity by means of a mechanical or hydraulic de-vice. Compared with an Oscillating Water Column (OWC) wave power device, the OD has the same capture width ratio as the OWC does, but much higher secondary conversion efficiency. Moreover, the chamber of the OWC, which is the mostexpensive and difficult part to be built, is not necessary for the OD, so it is easier to construct an OD. In this paper, a nu-merical calculation is conducted for an optimal design of the OD firstly, then a model of the device is built and, a model testis carded out in a wave tank. The results show that the total efficiency of the OD is much higher than that of the OWC andthat the OD is a promising wave power device.

Movable object type wave power energy converter

Abstract: A movable object type wave power energy converter, wherein a generator and a power extracting means having power extracting pulleys engaged with wires and a reversible unit are mounted on a movable object, and at least a pair of wire mechanisms having fixed objects such as anchors installed at a sea bottom, weights, and wires having one ends connected to the fixed objects and the other ends connected to the weights are installed along a major wave advancing direction and generally symmetrically in longitudinal direction, and the wire mechanisms are installed additionally in the direction perpendicular to the major wave advancing direction so that the energies caused by the vertical movement, horizontal movement, and rotating swing of the movable object by wave can be extracted effectively.

Design Method of Wave Power Generating System With Wells Turbine

Abstract: This is a report of a fundamental study on the design method that takes into account the interaction between the air chamber and the turbine, using the rule of similarity in the nondimensional form of the governing equations. We present how to analyze the power absorbed in irregular waves by using both their spectrum and probability. It is shown that the linear theory of water wave is applicable to the evaluation of the absorbed power in air chambers. Turbine performances in irregular waves are easily shown with the probability density distribution, that is, Gaussian distribution. This paper also presents a design method that will lead to minimum construction cost. Cost is now a very important factor in the construction of wave power generating systems.

Air Turbine With Staggered Blad Es For Wave Power Conversion

Abstract: In a self-rectifying air turbine for wave energy conversion, it is reported that the rotor encountered different maximum velocities between the inhalation and exhalation processes of the oscillating water column. This paper describes the development of an efficient turbine suitable for such actual asymmetric flow conditions. The air turbine with staggered blades has been presented and investigated experimentally by model testing under steady flow conditions. The running and starting characteristics under pseudo-sinusoidal oscillating flow conditions were then clarified by using a quasi-steady analysis. As a result, it is found that the air turbine with staggered blades is superior to the Wells turbine, and a suitable choice of design factor has been suggested for the preset angle of the rotor.

Built-in hydraulic wave power float

Abstract: A built-in hydraulic wave power float is provided. The structure comprises a float main body, a center pipe, a bobber, a built-in oil cylinder, a piston, a driving oil pipe, a hydraulic motor, a generator, a storage battery, etc. With the energy acquisition and transfer conversion system in the bobber-piston-oil cylinder-hydraulic motor-generator-storage battery mode formed by the hydraulic motor, the generator and the storage battery which are arranged in the float main body as well as the bobber, the built-in oil cylinder, the piston and other components arranged in the center pipe, compared with the prior air turbine wave power float, the utility model is good in waterproof performance, low in failure rate, easy to start and high in energy transfer as well as conversion efficiency.

Wave power generator using height differential between wave crests and troughs to generate energy consists of floating pontoon connected hinge-like to floating blade to drive energy generator

Abstract: A pontoon (1) floating on or near a water surface is connected hinge-like via joint (3) to a similar floating blade (2). The blade follows the wave motion, while the pontoon is connected to a substructure, which is located lower in the water and acts against up and down movements of the pontoon. The pivot movement of the blade is used to drive an energy generator. The blade is coupled to hydraulic cylinders (10), and the fluid in the cylinders operates an energy generator.

External hydraulic wave power generating buoy

Abstract: The utility model discloses an external hydraulic wave power venerating buoy which comprises a buoy body, a central tube, an external fuel tank, a piston, an under-water suspender, a driving tube, a hydraulic motor, a generator, an accumulator and so on. Elements such as the external fuel tank, the piston and the under-water suspender that pass through the buoy body, and the hydraulic motor, the generator and the accumulator that are installed in the buoy body form an energy acquisition and conversion system in the piston-fuel tank-hydraulic motor-generator form. Compared with the traditional air-turbine power generating buoy, the utility model has good waterproof performance, low failure rate, easy start-up, and high energy transmission and conversion efficiency.