Vengatesan Venugopal

Wave Spectral Bandwidth as a Measure of Available Wave Power

A key requirement in the description of the performance of a wave energy converter is how the efficiency of power capture changes with the properties of the sea. This paper examines the effect of two generic power transfer functions (PTF) on power production from six simulated wave spectra. These were chosen to represent a series of wind, wind-swell mixed and swell dominated seas. The spread in energy within the sea state as defined by a variety of bandwidth parameters was examined to determine if there was a correlation between the width of the transfer function and the sea bandwidth. It was found that, for the ‘constant’ height PTF, the bandwidth parameter Bb (calculated using zeroth, minus-one and minus-two spectral moments) provided the best correlation. Customary bandwidths e and ν performed poorly. When the PTF was allowed to vary in height as well as width there was little improvement in correlation from the un-scaled results.Copyright

Marine Energy Resource Assessment for Orkney and Pentland Waters With a Coupled Wave and Tidal Flow Model

Some preliminary results obtained from a coupled wave and 3D tidal flow numerical model, applied to the Orkney and Pentland waters in the Scottish region of the United Kingdom, are reported in this paper. The coupled wave and flow model was applied to the Orkney Islands comprising a domain of 1.25°W – 5°W and 58.25° N – 59.75°N. The model was run by boundary inputs of wind and water level extracted from European Centre for Medium Range Weather Forecasts (ECMWF) and Danish Hydraulic Institute’s (DHI) global tidal model respectively. The model has been calibrated and validated with wave buoy and ADCP (Acoustic Doppler and Current Profiler) measurements. The depth-wise current velocity components predicted by the model were compared with ADCP measurements for three sites in the Pentland Firth. The results indicated that the coupled model worked well and the tidal current velocities from the model correlated well with ADCP measurements at different depths.Copyright

Hebridean Marine Energy Resources: Wave-Power Characterisation Using a Buoy Network

The Outer Hebrides of Scotland were identified as an area with a high wave power resource of 42.4kW/m. The Outer Hebrides of Scotland are currently targeted by a range of developers for demonstration and commercial developments of wave energy converters and current planning efforts are based on initial deployments by 2014. Technology providers with well advanced plans to develop the Hebridean wave resource include Aquamarine Power (Oyster) [1], Pelamis (P2) [2] and Voith Wavegen (OWC) [3]; all of these companies are partners in the Hebridean Marine Energy Futures project [4] to help move the industry into the commercialisation stage.As part of the Hebridean Marine Energy Futures project, a three year programme aimed at developing a high resolution wave energy resource map to support the site selection process of marine energy developers, a network of three wave measuring buoys was deployed 15km offshore in a depth of 60m and at distances of 11km between buoys. Measured wind and wave data from this buoy network for autumn 2011 are analysed and presented in this paper along with estimated wave power for the same duration.Copyright

A 5MW direct-drive generator for floating spar-buoy wind turbine: Development and analysis of a fully coupled Mechanical model

This work forms the first of a two-part investigation aimed at identifying the challenges and opportunities of implementing a direct-drive generator for a spar-buoy type floating wind turbine. Preliminary specifications are presented for a fully coupled aero-hydro-servo-elastic model of a floating wind turbine with a 5 MW direct-drive generator. The drive-train model uses a low-speed, high-torque radial flux permanent magnet generator supported by two main-shaft bearings. The mechanical properties of the drive-train, including the main dimensions, mass of major nacelle equipment and details for the hub/nacelle assembly are presented. The rationale behind the adjustments to the tower and platform properties and the motivation to selection of best arrangement that is appropriate for supporting the developed system is explained. A discussion on the development of the variable speed-variable pitch control system suitable for the direct-drive system including modifications to avoid negative damping and blade-pitch instability are presented. Fully coupled simulations for the developed aero-hydro-servo elastic model were carried out in HAWC2 for the normal operating conditions of the wind turbine. The aerodynamic response of the model was verified and compared with that of a geared floating wind turbine system. Some initial results comparing the main shaft loads of the land-based and floating versions of the direct-drive wind turbine suggest satisfactory dynamic behaviour of the drive-train. The results prompt further research using a detailed drive-train model to verify the internal response, loading and durability of the components to assess their compatibility with a floating wind turbine system.

Performance Analysis of a Semicircular Free Surface Breakwater

In the present study, the hydrodynamic performance of a semicircular free surface breakwater (SCB) has been investigated through a systematic experimental programme. Three semicircular breakwater models were tested: one with impermeable front and rear walls; a second with perforated front wall and impermeable rear wall; and a third with perforated front and rear walls. The models were tested for three submergence depths with reference to the still water level in a wave flume under irregular seas with different significant wave heights and peak periods. The performance of the breakwaters was evaluated in the form of coefficients of transmission (CT ), reflection (CR ) and energy dissipation (CL ). The measured wave modification in front of the structure and in the breakwater’s chamber were quantified and presented in the form of a ratio relative to the incident wave height, respectively. Also, the measured horizontal wave forces acting on the SCB were analysed and reported in a dimensionless form. Empirical equations were then developed using nonlinear multiple regression models to estimate the hydrodynamic characteristics of the SCB models.Copyright

Characterising the wave power potential of the Scottish coastal environment

ABSTRACT The study focuses around the energetic waters of Scotland that has expressed high interest in the development of wave energy farms. There are only a few long-term suitable studies characterising coastal locations. A detail coastal resource assessment is provided, focusing on wave energy and site characterisation. Mean nearshore energy content in the Western coasts is ≥50 kW/m and on the East ≈10 kW/m. Monthly and seasonal analyses outline available resource and annual variations. Availability of production is also examined, West coastlines present higher levels, however, depending on resource and wave converters operational range significant differences are shown. Availability levels on the East coastline are low ≈40% due to lower wave heights, while Western locations record consistently over 80% at both scenarios examined. Results discuss the potential applicability of favourable wave converters, and characteristics which achieve maximum utilisation based on the local environment.

A 5 MW direct-drive generator for floating spar-buoy wind turbine: Drive-train dynamics

This article proceeds with investigations on a 5 MW direct-drive floating wind turbine system (FWTDD) that was developed in a previous study. A fully integrated land-based direct-drive wind turbine system (WTDD) was created using SIMPACK, a multi-body simulation tool, to model the necessary response variables. The comparison of blade pitch control action and torque behaviour with a similar land-based direct-drive model in HAWC2 (an aero-elastic simulation tool) confirmed that the dynamic feedback effects can be ignored. The main shaft displacements, air-gap eccentricity, forces due to unbalanced magnetic pull (UMP) and the main bearing loads were identified as the main response variables. The investigations then proceed with a two-step de-coupled approach for the detailed drive-train analysis in WTDD and FWTDD systems. The global motion responses and drive-train loads were extracted from HAWC2 and fed to stand-alone direct-drive generator models in SIMPACK. The main response variables of WTDD and FWTDD system were compared. The FWTDD drive-train was observed to endure additional excitations at wave and platform pitch frequencies, thereby increasing the axial components of loads and displacements. If secondary deflections are not considered, the FWTDD system did not result in any exceptional increases to eccentricity and UMP with the generator design tolerances being fairly preserved. The bearing loading behaviour was comparable between both the systems, with the exception of axial loads and tilting moments attributed to additional excitations in the FWTDD system.

Optimization of Spacing for Oscillating Wave Surge Converter Arrays Using Genetic Algorithm

AbstractThe oscillating wave surge converter (OWSC) is a type of ocean wave power device typically consisting of a flap, or arm, hinged at the bottom to allow forward and backward movement by surging waves, and is efficient in generating electricity from waves due to its capability in operating at a wide range of wave spectra. The power generated from the OWSC could be further maximized by arranging the devices in an array at their optimal spacing. This paper addresses the optimization of device configuration within an array by using the genetic algorithm (GA) scheme, for which the spacings between devices are taken as the optimization variables, and the maximum q-factor is chosen as the objective function. The q-factor is a performance assessment parameter that quantifies the average total power produced by an array compared to an individual device. Three array layouts—namely, the single-, double-, and triple-array, each comprising 12 OWSCs—were considered. The pitch response amplitude operator (RAO) of ...

Observations on Shallow Water Wave Distributions at an Ocean Energy Site

The paper analyses the changes in wave conditions during wave propagation between intermediate and shallow water depths at a potential wave energy deployment location.The Outer Hebrides of Scotland in the United Kingdom are home to the world’s largest fully consented wave power project and hence a detailed understanding of the local resource is important to the developer to inform annual yield forecasting, technology refinements, and installation and operational plans. To support wave power projects and to reduce uncertainty and risk associated with yield production and performance estimates of energy developments, a sensor network was installed in the area from 2011–2013. Consisting of three floating buoys in intermediate depth and two combined acoustic and pressure sensors in the nearshore region, the data obtained from the different sensors at different locations in close proximity to each other have given a valuable insight in the hydrodynamic wave processes in the area.Data of the two acoustic sensors and one wave buoy are analysed in this paper for a period covering the full range of sea states to be expected throughout a calendar year. Distributions of maximum and significant wave heights, wave steepness and wave direction during a range of different meteorological conditions are examined and a comparison between the different sensor locations is included. The analysis also considers different distributions of both wave power and period observed during the measurement campaign.Copyright

WAVE ENERGY ASSESSMENT AND WIND CORRELATION FOR THE NORTH REGION OF SCOTLAND, HINDCAST RESOURCE AND CALIBRATION, INVESTIGATING FOR IMPROVEMENTS OF PHYSICAL MODEL FOR ADAPTATION TO TEMPORAL CORRELATION.

Wave energy sites around Scotland, are considered one of the most energetic waters, as they are exposed to the Atlantic Ocean. The amount of energy reaching the shoreline provides an opportunity for wave energy deployments. Currently, considerations on wave devices expect them to be installed at nearshore locations. That means that the potential wave resource has to be investigated, since deep to shallow water interactions alter the shape of propagated waves. Resource assessment for these regions is essential in order to estimate the available and extractable energy resource. Although several numerical models exist for wave modelling, not all are suitable for nearshore applications. For the present work, the nearshore wave model SWAN has been used to simulate waves for the Hebridean region. The set-up, calibration and validation of the model are discussed. The resulting wave conditions are compared with buoy measurements. Results indicate that the modelling technique performed well.