Showing papers on "Wave power published in 2009"

A review of wave energy converter technology

Abstract: Ocean waves are a huge, largely untapped energy resource, and the potential for extracting energy from waves is considerable. Research in this area is driven by the need to meet renewable energy targets, but is relatively immature compared to other renewable energy technologies. This review introduces the general status of wave energy and evaluates the device types that represent current wave energy converter (WEC) technology, particularly focusing on work being undertaken within the United Kingdom. The possible power take-off systems are identified, followed by a consideration of some of the control strategies to enhance the efficiency of point absorber-type WECs. There is a lack of convergence on the best method of extracting energy from the waves and, although previous innovation has generally focused on the concept and design of the primary interface, questions arise concerning how best to optimize the powertrain. This article concludes with some suggestions of future developments.

Wave power extraction from an oscillating water column at the tip of a breakwater

Abstract: To reduce the costs of construction, operation, maintenance, energy storage and grid connection, some devices for extracting energy from sea waves are likely to be installed on the coast. We study theoretically a single oscillating water column (OWC) installed at the tip of a long and thin breakwater. The linearized problems of radiation and scattering for a hollow cylinder with an open bottom are then solved by the usual method of eigenfunction expansions and integral equations. Since a thin breakwater is the limit of a wedge, an exact solution for the diffraction by a solid cylinder at the tip of a wedge is derived to facilitate the analysis. Following Sarmento & Falcao (J. Fluid Mech., vol. 150, 1985, pp. 467–485), power takeoff by Wells turbines is modelled by including air compressibility in the chamber above the water surface. The effects of air compressibility on the extraction efficiency is studied. It is shown that for this simple geometry the angle of incidence affects the waves outside the structure but not the extracted power.

Wave energy assessments in the Black Sea

Abstract: The present work aims to evaluate the wave energy resources in the Black Sea basin. The study is focused on the western part of the sea, which is traditionally considered as being more energetic. In order to give a first perspective of the wave climate, a medium-term wave analysis was carried out using in situ measured data. As a further step, a wave prediction system was implemented for the Black Sea. This was based on the simulating waves near-shore model, which is used for both wave generation and near-shore transformation. This methodology has the advantage that a single model covers the full scale of the modelling process. Various tests were performed considering data measured at three different locations. Special attention was paid to the whitecapping process, which is still widely considered to be the weak link in deep water wave modelling. Comparisons carried out against measured data show that the wave prediction system generally provides reliable results, especially in terms of significant wave heights and mean periods. By increasing the resolution in geographical space, the field distributions of wave energy were analysed for both high and average wave conditions. The analysis and the wave prediction system developed are a prerequisite for further investigations extended in time and with increased resolution in the near-shore direction.

Wave-power extraction by a compact array of buoys

Abstract: The majority of existing single-unit devices for extracting power from sea waves relies on resonance at the peak frequency of the incident wave spectrum. Such designs usually call for structural dimensions not too small compared to a typical wavelength and yield high efficiency only within a limited frequency band. A recent innovation in Norway departs from this norm by gathering many small buoys in a compact array. Each buoy is too small to be resonated in typical sea conditions. In this article a theoretical study is performed to evaluate this new design. Within the framework of linearization, we consider a periodic array of small buoys with similarly small separation compared to the typical wavelength. The method of homogenization (multiple scales) is used to derive the equations governing the macroscale behaviour of the entire array. These equations are then applied to energy extraction by an infinite strip of buoys, and by a circular array. In the latter case, advantages are found when compared to a single buoy of equal volume.

Vertical motion wave power generator

Abstract: A vertical motion wave power generator having a flotation device, a vertical support structure fixed to the ocean bottom, and a single power shaft attached rotatably to the flotation device. By the use of a pair of one-way clutches the single power shaft converts the up and down motion of ocean waves into continuous unidirectional rotational force to drive an electric generator. The power shaft, transmission, and generator are all attached to the flotation device and move up and down in unison with the flotation device.

ISWEC: Design of a prototype model with gyroscope

Abstract: The extraction of energy from ocean waves has been investigated in Europe since the 1970s. Hundreds of devices have been proposed, many have been tested in some form or other and a few of these have been commercialized. In this paper a gyroscopic wave energy converter is studied and a procedure to design a prototype model to be tested at the wave tank at the University of Edinburgh is outlined. A linearized model of the device is extrapolated and used as a mathematical tool in the design process. The final version of the prototype model is verified using the complete nonlinear model.

Wave-based defect detection and interwire friction modeling for overhead transmission lines

Abstract: In this study, the feasibility of continuous, online monitoring of power lines using ultrasonic waves is considered. Local and global wave-based approaches for wire break detection in overhead transmission lines are presented. Both methods use a sending/receiving transducer to generate an ultrasonic, longitudinal, elastic wave in the cable. Defects in the cable cause a portion of the incident ultrasonic wave to be reflected back to the transducer, which when received, can be used to identify the presence of the defect. Although the transducers can only be attached to the surface of the cable, subsurface wires can also be interrogated since elastic energy spreads to these wires through friction contact. This study also explores how the elastic energy of a propagating wave becomes distributed among contacting rods via friction contact. This work focuses specifically on a two-rod system in which the wave energy from an excited “active” rod is transmitted to a neighboring “passive” rod through friction contact. An energy-based model is used to approximate the time average elastic wave power in the two rods as a function of propagation distance. Power predictions from the energy-based model compare well with experimental measurements and finite element simulations.

Advanced wave energy converter control

Abstract: A wave energy converter (WEC) system includes first and second bodies which can move relative to each other in response to waves and a power-take-off (PTO) device coupled between the two bodies to convert their relative motion into energy. A sensor is used to sense selected characteristics of an incoming wave and produce signals which are applied to a control computer for predicting the impact of the incoming waves on the WEC. Simultaneously, signals indicative of the actual conditions (e.g. the velocity) of the WEC are also supplied to the control computer which is programmed to process the predicted and actual information in order to generate appropriate signals (forces) to the components of the WEC such that the average wave power captured by the PTO is maximized.

Apparatus for converting wave energy into electrical energy

Abstract: An apparatus for converting wave energy into electrical energy includes a wave power generation unit including a frame and float guides. A wave power generation float is joined to the float guides for vertical motion in response to the wave energy. The wave power generation float includes at least one wave power conversion module. The wave power conversion module includes a module case and an air sealing tube formed in the module case for generally preventing fluids from entering the module case. A power transmission cable transmits electrical energy where one end of the power transmission cable passes through the air sealing tube and is joined to the frame. A cable reel winds and unwinds the power transmission cable. A power transmission drive translates a bidirectional rotation of an input shaft into a unidirectional rotation. A generator generates electrical energy in response to the unidirectional rotation.

GREMO: A GIS-based generic model for estimating relative wave exposure

Abstract: Wave exposure plays a major role in shaping the ecological structure of nearshore communities, with different community types able to survive and/or thrive when typically exposed to different levels of wave energy. This can be quantified by taking direct field measurements with wave buoys over time and then manipulating the data to derive typical conditions. However, taking these measurements is only feasible for very limited areas due to logistical constraints, and generating them with numerical wave models can also be expensive to run and may require data inputs that are either lacking or are highly uncertain. Instead, the relative differences in wave exposure between places (relative wave exposure) may be sufficient to distinguish between different community types. It is possible to approximate relative wave exposure using a cartographic approach. Typically this involves measuring the relative shelter or openness of a particular location based on the distances from it to the nearest potential wave blocking obstacle in all directions with provides an approximation of fetch. Given that dominant wind speed and direction data is available for a particular site, these fetch distances can be manipulated to estimate the potential wave climate at that site, with some models going as far as to link this to linear wave theory in order to calculate wave power. This works because the extent to which large waves can form, and to which seas are ‘fully developed’, is constrained by wind velocity, time and fetch. Mapping relative wave exposure in this relatively simple way could be used to predict the spatial distribution of broad categories of ecological community types, especially where this information is difficult to collect using more direct methods. Despite its relative efficiency and simplicity, running a cartographic-based relative exposure model for more than a local study area quickly becomes computationally intensive, which drives the need to set up the model to run as quickly as possible while minimizing the risk of not detecting potential wave blocking obstacles, and thus underestimating the wave exposure. Yet surprisingly, no studies have tested the sensitivity of the relative wave exposure estimates that these models produce to variation in how key factors, such as the density of points from which fetch distances are measured (point spacing), the angle increment at which the fetch lines are drawn around each point (fetch angle spacing), and the adjustment of fetch line lengths based on bathymetry, are set in the model. This paper presents a preliminary analysis that shows the extent to which estimated relative wave exposure changed when the above model settings were varied for four case study areas within the Great Barrier Reef selected for their characteristic spatial arrangement (number and density) of obstacles. This was done using a new GIS-based generic model for estimating relative wave exposure (GREMO) which integrates many existing techniques into a single modeling platform.

Optimization of the lay-out of a farm of wave energy converters in the North Sea: analysis of wave power resources, wake effects, production and cost

Abstract: Wave energy holds a lot of possibilities, as oceans contain an infinite amount of energy. In the past many concepts for wave power conversion were invented and tested. A Wave Energy Converter (WEC) converts the kinetic and/or potential energy of waves into electricity. Thus far, none of the concepts for wave power conversion has reached a maturity that makes it economic exploitable due to several technological and non-technological barriers. As the rated power of a single WEC is rather small, several WECs need to be arranged in a geometric configuration or in a `farm'. WECs in a farm are partly absorbing and partly redistributing the incident wave power. The power produced by each individual WEC in the farm is affected by the presence of its neighbouring WECs. The current knowledge about the redistribution of energy inside and behind a farm of WECs is rather limited. Both the power production and cost of a farm are dependent on the lay-out of the farm. So far, most studies concentrate on the optimization of a single WEC, rather than optimizing a complete farm. To develop a commercial technology, the impact of arranging WECs in a farm has to be investigated as well. The optimization of the lay-out of a farm of WECs in the North Sea is the focus of this PhD research. The wave power resources and possible locations for the deployment of a farm of WECs in the North Sea are quantified in a first part of this PhD research. In this PhD work an optimal balance between power production and cost of a farm of WECs is aimed at. Therefore in a second part the wake effects behind a farm of WECs are studied in a time-dependent mild-slope wave propagation model MILDwave, developed at Ghent University. Finally the cost of a farm is discussed in a third part of this PhD work. Moreover an investment analysis of the deployment of a farm of WECs in the southern North Sea is presented.

Wave power generator using two buoys

Abstract: PURPOSE: A wave power generator using two buoys is provided to make an energy converting process simple by preventing the influence by the difference between the rise and fall of the tide. CONSTITUTION: A wave power generator comprises a first buoy(10), a second buoy(20) and a linear generator(40). The first buoy moves up and down on seaware surface by the wave. The second buoy is inserted into the first buoy. The second buoy has relative motion to the first buoy since the second buoy has different dynamic reaction characteristic about the wave with the first buoy. The linear generator includes a generator outer tube(41), a field magnet(45) and an armature(47). The field magnet and the armature are connected to the generator outer tube or the second buoy.

Research on wave power application by the information system for ocean wave resources evaluation

Abstract: A computer software system was established,which can manage,calculate and analyze the data from the ocean wave observing recordsUsing this system,wave energy resource of Shengshan sea area,Zhejiang Province was evaluated in detailWave power density typically ranges from 05 to 88 kW/m,the frequency of 2 kW/m is about 60%,and as a result wave power still makes a substantial contribution to these locations energy supplyThe analysis of the wave direction frequency distribution of wave power density,has the instruction significance regarding the design of the wave power generation deviceDuring the summer,the southerly direction frequency distribution of wave power density is above 55% ;However during the autumn and winter,the northern direction frequency distribution is above 60%Wave period in the sea area focuses on the distribution of 4～5 s,wave height focuses on 12～15 mThose terms are significant properties for the design of wave power generation device and the effective use of wave energy

Parametric decay instability during high harmonic fast wave heating experiments on the TST-2 spherical tokamak

Abstract: A degradation of heating efficiency was observed during high harmonic fast wave (HHFW) heating of spherical tokamak plasmas when parametric decay instability (PDI) occurred. Suppression of PDI is necessary to make HHFW a reliable heating and current drive tool in high ? plasmas. In order to understand PDI, measurements were made using a radially movable electrostatic probe (ion saturation current and floating potential), arrays of RF magnetic probes distributed both toroidally and poloidally, microwave reflectometry and fast optical diagnostics in TST-2. The frequency spectrum usually exhibits ion-cyclotron harmonic sidebands f0 ? nfci and low-frequency ion-cyclotron quasi-modes (ICQMs) nfci. PDI becomes stronger at lower densities, and much weaker when the plasma is far away from the antenna. The lower sideband power was found to increase quadratically with the local pump wave power. The lower sideband power relative to the local pump wave power was larger for reflectometer compared with either electrostatic or magnetic probes. The radial decay of the pump wave amplitude in the SOL was much faster for the ion saturation current than for the floating potential. These results are consistent with the HHFW pump wave decaying into the HHFW or ion Bernstein wave (IBW) sideband and the low-frequency (ICQM). Two additional peaks were discovered between the fundamental lower sideband and the pump wave in hydrogen plasmas. The frequency differences of these peaks from the pump wave increase with the magnetic field. These decay modes may involve molecular ions or partially ionized impurity ions.

POSITION MOORING OF WAVE ENERGY CONVERTERS - An engineering study into the mooring of structures in a highly exposed shallow ocean regime, within the context of the economics of renewable energy conversion

Abstract: The principles of systems engineering are applied in order to establish the requirements for mooring wave energy conversion devices. These requirements capture both the function of maintaining position in energetic wave climates as well as the need to enable an economic lifecycle for the development of a viable wave energy conversion industry. As such, material costs, marine operations costs and concerns captured by existing industry regulatory bodies gain relative importance in the supporting discussion, though technical concerns remain central to the presented scientific methods. Requirements that would be unique to a particular method of wave energy conversion are avoided as the aim is to contribute to a general body of knowledge to support the wide variety of proposed solutions in this area. Engineering and scientific methods are applied to investigate which kind of mooring systems are most likely to fulfil these holistic requirements. Cable mooring solutions are studied in some detail. In addition the relative merits of fixed and articulated tower structures are assessed. Consideration is given to different scales of structures and different water depths. Previously established analytical methods are applied in conjunction with experimental work carried out at 1:60 scale. The overall conclusions show that mooring system design should be an integral part of wave power system designs and not a postscript to the design process. There are significant challenges to the positioning of structures in this exposed, shallow-water regime, especially structures that must fundamentally have a wave absorbing wet surface. The choice of mooring design can significantly influence how wave power is extracted and how such systems are operated and maintained. The results and supporting discussion establish that technological breakthroughs in vertically loaded anchors will be required before point absorbing arrays can be viably used to generate electricity for the grid. Such anchors, in conjunction with articulated towers or elastic tendons are the most promising line of investigation. Such solutions could theoretically satisfy low material costs and enable acceptable seabed footprints. However, the lack of a versatile and inexpensive vertically loaded anchor or elastic cables with acceptable fatigue life, mean that these solutions are not yet commercially available.

RAYTEC: a new code for electron cyclotron radiative transport modelling of fusion plasmas

Abstract: As it was recognized that local electron cyclotron (EC) wave power losses can be a competitive contribution to the 1D electron power balance for reactor-grade tokamak plasmas in regimes as anticipated for steady-state operation, a systematic effort is ongoing to improve the modelling capability for the radial profile of EC wave emission. This effort aims at generating a hierarchy of codes that cover the non-local behaviour of EC wave transport for inhomogeneous plasmas and in the presence of reflecting walls with increasingly improved accuracy and also provide sufficient computational efficiency for being usable in 1D transport studies. The recently developed code RAYTEC, which explicitly addresses the geometrical effects present in toroidal plasmas with arbitrary cross-section, is described and used to investigate the impact of elongation of the plasma cross-section and of toroidicity on the angular dependence of the EC radiation field, on the profile of the net EC wave power density lost from the plasma and on the total EC power loss for ITER-like plasma conditions. Furthermore, a comparison is made with the results of simpler models in use to describe both local and total EC power losses as well as with ones obtained from analytical formulae that are introduced on the basis of Trubnikov's formula for EC power emission.

Integrated design of direct-drive linear generators for wave energy converters

Abstract: Linear permanent magnet generators are a potentially useful technology for wave power applications. Typically, optimisation and comparison of these generators is based on an electromagnetic analysis with limited regard for the structural and thermal analysis. This paper presents a comparison of an air-cored synchronous machine and a double-sided iron-cored synchronous machine which includes the structural and bearing requirements for a more accurate cost comparison, and a discussion of the thermal issues. It is shown that both cost and feasibility depend heavily on these issues.

Offshore combined power generation system

Abstract: A combined offshore system for generating electricity includes of an offshore windmill unit with a generator for extracting power from wind and transferring it into electricity, a electricity export cable connected to the windmill for exporting produced electricity to offshore or onshore consumers, and at least one offshore wave power unit for extracting power from waves. This offshore wave power unit is characterized in that electricity produced by the wave power unit is transferred via the same electricity export cable as the electricity generated by the windmill unit.

Wave power plant

Abstract: The wave power plant is intended for converting the energy of a disturbed water surface into electrical energy by means of a displacement-type body (2) which floats on a water surface (1) and in which an electrical generator (10) is accommodated and spontaneously rotated by means of the tension force of a cable (5) that connects the body (2) to a diving, floating anchor (6). The tension force occurs every time the body, floating to the surface as a result of buoyant force, moves upwards in the Earth's gravitational field. The free (i.e. not connected to the sea bed) orientation of the anchor (6) under the body (2) makes it possible to use the plant in deep waters where wave energy is highest.