Showing papers on "Wave power published in 1997"

Design synthesis of oscillating water column wave energy converters: Performance matching:

Abstract: The matching of a Wells air turbine to an oscillating water column (OWC) is addressed, with particular reference to design synthesis at the Islay prototype wave power converter. The level o...

The islay wave power project: an engineering perspective.

Abstract: The design, construction and subsequent operation of the 75kW oscillating water column wave power plant on the Isle of Islay has provided a significant insight into the practicality of wave power conversion. The development of wave power plant poses a significant design and construction challenge for not only civil but also mechanical and electrical engineers. The plant mus withstand the immense forces imposed during storms, yet efficiently convert the slow cyclic motion of waves into a useful energy source such as electricity and so so at a price competitive with other forms of generation. In addition, the hostile marine environment hampers the construction process and the variability of the wave resource poses problems for electrical control and grid integration. Many sceptics consider wave power conversion to be too difficult, too expensive and too variable to justify the effort and expense necessary to develop this technology. However, the authors contend that with modular wave power systems developed from the practical experience gained with the Islay plant, wave power is a viable technology is still at the early stages of development and will require the construction of number of different prototypes before there is extensive commercial exploitation.

Cost effectiveness of wave power extraction at erosive coasts

Abstract: Cost of wave power extraction is investigated for the coasts where erosion has been continuing without suitable countermeasures. By a wave power extraction, a shoreline accretion is expected due to the mean sea level drop. Cost effectiveness is discussed with the concept of total cost instead of the generation cost only.

Use of numerical wind-wave models for assessment of the offshore wave energy resource

Abstract: In the last two decades the performance of numerical wind-wave models has improved considerably. Several models have been routinely producing good quality wave estimates globally since the mid-1980s. The verifications of wind-wave models have mainly focused on the evaluation of the error of the significant wave height H{sub s} estimates. However, for wave energy purposes, the main parameters to be assessed are the wave power P{sub w} and the mean (energy) period T{sub e}. Since P{sub w} is proportional to H{sub s}{sup 2}T{sub e}, its expected error is much larger than for the single-wave parameters. This paper summarizes the intercomparison of two wind-wave models against buoy data in the North Atlantic and the Mediterranean Sea to select the most suitable one for the construction of an Atlas of the wave energy resource in European waters. A full verification in the two basins of the selected model--the WAM model, implemented in the routine operation of the European Centre for Medium-Range Weather Forecasts--was then performed against buoy and satellite altimeter data. It was found that the WAM model accuracy is very good for offshore locations in the North Atlantic; but for the Mediterranean Sea the results are much less accurate, probably duemore » to a lower quality of the input wind fields.« less

Wave-powered ocean profiler

Abstract: An ocean profiler that utilizes ocean wave energy to provide power for repeated ascent and descent of an oceanographic instrument. In one embodiment the instrument assembly is provided with either positive or negative buoyancy such that the instrument can traverse one half of the travel cycle rapidly utilizing the buoyancy force. Utilizing wave power for instrument traversing greatly reduces the power requirement of the apparatus allowing extended unattended operation.

Wave energy conversion in a random sea.

Abstract: The response of a three-dimensional oscillating water column (OWC) wave energy converter in monochromatic and random seas was investigated to determine the potential power available. Probabilistic models of available average wave power in a random sea state were formulated through the development of probability density functions transformed from theoretical distributions of wave heights and periods in a random wave field and a functional relationship describing the wave power. The computed available average wave power in a random sea state was in good agreement with measured wave spectra data. A hybrid-finite element method was used to numerically model the fluid-device interaction and to establish the radiation diffraction hydrodynamic force coefficients for the device. Six OWC devices with varying wall configurations, modelled in finite depth and monochromatic seas, showed considerable variation in peak performance and frequency response bandwidth with a consistent variation in performance between devices for obliquely incident wave directions. The numerical model for monochromatic seas was verified using the results of wave tank experiments. Based on a transformation of random variables using a functional relationship developed for wave power extraction in monochromatic seas, a probabilistic density function of wave power extraction was derived. Based on a linear superposition principle, overall device performance in random seas with narrow and broad banded wave spectra characteristics was determined. In random seas, the performance of the device is influenced by the frequency bandwidth of the wave spectra such that an increase in the spectral bandwidth parameter causes a reduction in peak performance, but effectively broadens the frequency response of the device. Predicted overall device performance in random seas were in agreement with experimental tests.

Transmission power control circuit for radio equipment

Abstract: PROBLEM TO BE SOLVED: To obtain a stable transmission output regardlessly of the magnitude of the input electric power of a wave detector by providing a high frequency amplifier capable of switching gain between a directional coupler and the wave detector SOLUTION: A part of transmission wave power is taken out by the directional coupler 3 and inputted to the high frequency amplifier 6 provided with a gain changing-over function The high frequency amplifier 6 provided with the gain change-over function can change gain, for example, 0 and 20dB by a gain change-over signal which is inputted from a gain control input terminal 8 In a state where transmission power is large, for example, from 1W to 10W, the amplifying degree of the high frequency amplifier 6 is adopted as 0dB by the change-over signal from the gain control input terminal 8, a part of power of transmission wave which is branched in a grain oriental coupler 3 is added to the wave detector as is and it is wave-detected so as to be a D C voltage In a state where a transmission power value is small, for example, from 10mW to 01mW, the stable transmission output is obtained even if a wave detector input is small by the change-over signal from the gain control input terminal 8

Introduction to wave power

Abstract: Wave power, resulting from the transfer of energy from wind into water, represents a large potential source of energy for the UK, Europe and some other parts of the World. The wave power around the UK and Eire has an estimated annual average of 120 GW. When factors such as the need to avoid heavy shipping areas, the need to leave space between devices and the inability of devices to capture all of the incident energy are taken into consideration, the technical resource may be of the order of 25 GW. The technically achievable total world potential might be around 2000 GW.

Learning form the Islay wave power plant

Abstract: In 1985, the wave power team at the Queen's University of Belfast commenced work on the prototype shoreline wave power plant on the Isle of Islay. A natural rock gully 4 m wide was selected in the south facing side of a headland to reduce the amount of construction and provide a partially sheltered environment in which to gain `sea experience' and conduct fundamental research, During 1988, a concrete plenum chamber 4 m wide, 9 m long and 9.7 m high was constructed and the pneumatic power output monitored for two years using a simple orifice. Finally, in May 1991, the plant was fully commissioned with the installation of the mechanical electrical plant and connection to the electrical distribution grid. The plant comprised a 1.2 m diameter biplane Wells turbine direct coupled to a 75 kW wound rotor induction motor operating as a generator above its synchronous speed of 1500 RPM. The design, construction and subsequent operation of the wave power plant has provided a significant insight into the feasibility of wave power conversion. The development of wave power plant poses a significant design challenge for civil, mechanical and electrical engineers. The plant must withstand the immense forces imposed during storms yet efficiently convert the slow cyclic motion of waves into a useful energy source such as electricity and do so at a mice competitive with other forms of generation. The step from the laboratory to prototype installations is considerable and was undoubtedly underestimated at the outset of the project. (5 pages)

Modeling and simulation of the Islay wave power conversion system

Abstract: This paper describes the modeling and simulation of the Islay wave power conversion system which is located on the Island of Islay off the western coast of Scotland. A hybrid model of a wave-driven turbine and a grid-connected wound-rotor induction generator is constructed. The generator is modeled such that it retains the actual rotor phase variables but transforms the stator variables only. The model, implemented in Matlab, can be used to investigate under both transient and steady states the behaviors of system variables such as the stator current, the rotor current, and the generated power and torque. Some of the simulation results are presented.

Floating wave-power station for electricity generation

Abstract: With reduced association of the mechanism and economical/ecological operation of the mechanism, water turbines (2,7) with nozzles (7) instead of vanes are placed on floating bodies of different types (52,30) in water flow (12) and even in the sea, either intermittently or permanently, to obtain current. Anchoring the turbine in the water flow (12) causes adjustment of the hydraulic power mechanism (1,2,7). The wave power (11) of the nozzle rotor (2,7) is emitted into the water flow and also to pressure tubes or hoses as a free turbine with the additional use of pontoons as other floating bodies or ships. In connection with a current inducing device the rotation of the turbine can be achieved near the surface of the water. Thus the electric generator is mounted on the turbine shaft (4) clear of the water. The water turbines (2,7) have a nozzle jet buffer device (21) to amplify the wave power. The buffer device (21) does not prevent rotation of the turbine and is fastened parallel to the shaft (4) outside the support (23). The buffer device (21) parallel to the shaft (4) has comparatively wide gaps (21a) for energetically required waste water (40) from the water nozzle jets (7,7a).

Observations of Wave Transformation near Breaking

Abstract: Analysis of the change in the spectrum of wind waves over a 5-km reach just prior to the surf zone during a major extratropical storm indicates that significant shifts in the spectral distribution of wave energy occur. For both onshore and offshore winds, the midrange of the spectrum loses up to 40% of the energy content, while the low- and high-frequency ranges have an energy gain. In the onshore case, gain in the high-frequency range dominates, and in the offshore wind case (predominant wave energy propagation is still shoreward), gain in the low-frequency region dominates.

Vertically moving wave-power generator

Abstract: A wave-power generator has a floating body (6) whose vertical movement is used to generate electricity. Water enters through holes (4) in the side of the hollow chamber(3) at the top of a post-shaped body (2). The outer dimensions of this body are the same as those of conventional stakes used for coastal protection and this generator forms part of such an array. The floating body is joined to the generator (7) through a bulkhead. The generator is coupled to a spring which stores some of the energy of the upward movement and when the wave decays, the spring gives its energy to the generator as the floating body falls through gravity.

Standing Waves: Transmission Line Failure Caused by Reflected Energy

Abstract: The creation of standing waves in systems vulnerable to harmonics is of interest in both mechanical and electrical contexts. There are cases of harmonics in electrical oscillating systems as well as mechanical ones. Common characteristics of these wave phenomena are transport energy, reflection, and resonance, to list a few. Failures of systems that transport this wave energy, either in the form of sound (longitudinal) waves or electromagnetic (transverse) waves have significant similarities. This paper examines the failure of an energy transport system for electromagnetic waves, a television transmission system, and interprets the investigation of the failure in terms common to both mechanical and electrical systems. Investigating failures that sometimes have an obscure cause-effect relationship, especially if they are rare occurrences, often leads to enhanced design parameters that will prevent future occurrences. The paper concludes that if the cause of the failure cannot be significantly reduced, it can be minimized by closer attention to methods that diminish the effects.

Onset of spatial instability in parametric four-wave in a medium with a diagonally bipolar response

Abstract: A method of analyzing equations on the phase plane is used to solve a system of equations describing four-wave mixing in media with diagonally bipolar nonlinearity. It is shown theoretically that for certain parameters of the interacting waves, parametric instabilities may occur. It is established that the conversion of the mixed wave power depends strongly on their initial phase shift.

Evaluation of Wave Transmission Characteristics of OSPREY Wave Power Plant for Noyo Bay, California.

Abstract: : This report discusses wave flume tests of a newly designed ocean swell powered renewable energy (OSPREY) wave power generating caisson to assess its suitability and efficiency. Tests were carried out in a new wave flume commissioned by Applied Research and Technology (ART), of Inverness, Scotland. Data from both regular and irregular wave tests are shown. Wave transmission test results are plotted and compared with previous tests of a proposed rubble-mound alternative. Test results indicate that three-unit and four-unit OSPREY arrays allow significantly more wave energy transmission than the rubble-mound breakwater. In order to satisfy the basic requirements for wave sheltering at this site, it would appear that the OSPREY units must be placed closer together, integrated within the rubble mound, or spaced using integrated inactive caissons.