Monthly Archives: October 2012

High-Wire Act: HVdc Technology: The State of the Art


R. Adapa – Power and Energy Magazine, IEEE, November, 2012

Abstract

Developed to meet a combination of technical and economic considerations, high-voltage dc (HV dc) was launched in 1954 with the first commercial transmission link between the island of Gotland and the Swedish mainland. Since then, HV dc technology has advanced dramatically, and more than 100 HV dc transmission systems have been installed around the world.

Link

Leave a comment

Filed under Grid

RANS Simulation of the Heave Performance of a Two-Body Floating-Point Absorber Wave Energy System


Y-H. Yu and Y. Li, Computers & Fluids, October, 2012

Abstract

This paper presents our recent numerical study on a point absorber wave energy conversion (WEC) system using a Reynolds-averaged Navier-Stokes (RANS)-based computational fluid dynamics (CFD) method. The device we studied is a two-body floating-point absorber (FPA), which operates in heave and generates energy from the relative motion between the two bodies. A series of numerical simulation was performed to analyze the hydrodynamic response and the power absorption performance of the system in regular waves. Overall, it was successful to use the RANS method to model the complex hydrodynamics interaction of the FPA system. We demonstrated the significance of the nonlinear effects, including viscous damping and wave overtopping. The study showed that the nonlinear effects could significantly influence the power output and the motion of the FPA system, particularly in larger waves.

Link

Leave a comment

Filed under Modeling

Flow control for VATT by fixed and oscillating flap


Q. Xiao, W. Liu, and A. Incecik – Renewable Energy, March, 2013

Abstract

The present study is aimed to explore the potential to improve Vertical Axis Tidal Turbine (VATT) energy harnessing efficiency by using modified blades with fixed and oscillating flap. The fixed flap concept is borrowed from its application in aerodynamics area for reaching a high lift force at low flying speed. Oscillating flap is motivated by our relevant biomimetic studies on the flapping wing propulsion or energy extraction. Present investigation is concentrated on a VATT with NACA 0018 profile blade as its baseline turbine. Numerical simulations are carried out by solving incompressible Unsteady Navier–Stokes equations at turbulence flow condition. Computed results show that under certain optimal flap geometry and flow conditions, turbine power coefficient reaches 28% enhancement as compared to the conventional blade turbine. Detailed analysis on the flow structure demonstrates that this is related to the effective flow separation suppression and vortex control by applying a fixed and oscillating flap.

Link

Leave a comment

Filed under Modeling

Ship to Grid: Medium-Voltage DC Concepts in Theory and Practice


G.F. Reed, B.M. Grainger, A.R. Sparacino, Z-H. Mao – Power and Energy Magazine, IEEE, November, 2012

Abstract

Corporate research centers, universities, power equipment vendors, end users, and other market participants around the world are beginning to explore and consider the use of dc in future transmission and distribution system applications. Recent developments and trends in electric power consumption indicate an increasing use of DC-based power and constant power loads. In addition, growth in renewable energy resources requires dc interfaces for optimal integration. A strong case is being made for intermeshed AC and DC networks, with new concepts emerging at the medium-voltage (MV) level for MV DC infrastructure developments.

Link

 

 

Leave a comment

Filed under Grid

System Perspectives on Hydro-Kinetic Energy Conversion


K. Yuen – Uppsala University, 2012

Abstract

Free-flowing water currents such as tides and unregulated water courses could contribute to world electricity production given the emergence of robust technical solutions for extracting the energy. At Uppsala University, a concept for converting the energy in water currents to electricity using a vertical axis turbine with fixed blade-pitch and a direct-drive permanent magnet generator is studied. Continue reading

Leave a comment

Filed under System Development

Tidal stream energy site assessment via three-dimensional model and measurements


P.A. Work, K.A. Haas, Z. Defne, and T. Gay – Applied Energy, 2012

Abstract

A methodology for assessment of the potential impacts of extraction of energy associated with astronomical tides is described and applied to a site on the Beaufort River in coastal South Carolina, USA. Despite its name, the site features negligible freshwater inputs; like many in the region, it is a tidal estuary that resembles a river. A three-dimensional, numerical, hydrodynamic model was applied for a period exceeding a lunar month, allowing quantification of harmonic constituents of water level and velocity, and comparison to values derived from measurements, recorded at a location within the model domain. The measurement campaign included surveys of bathymetry and velocity fields during ebb and flood portions of a tidal cycle for model validation. Potential far-field impacts of a generic tidal energy conversion device were simulated by introducing an additional drag force in the model to enhance dissipation, resulting in 10–60% dissipation of the pre-existing kinetic power within a flow cross-section. The model reveals effects of the dissipation on water levels and velocities in adjacent areas, which are relatively small even at the 60% dissipation level. A method is presented to estimate the optimal vertical location for the energy conversion device and the potential power sacrificed by moving to a different altitude.

Link

Leave a comment

Filed under Resource Assessment

Pitch Angle Effect for Horizontal Axis River Current Turbine


R. Balaka and A. Rachman – Procedia Engineering, 2012

Abstract

The horizontal hydro-kinetic river current turbine power technology is one of the renewable decentralized power services potential in delivering energy for the communities in remote regions inaccessible by electricity connection. The utilization of the kinetic mechanism makes the application of the turbine less environmentally detrimental and more extensively available than the conventional hydro-energy which uses the level differences. However, the only kinetic mechanism of the turbine possibly brings the application to be less economically attractive since the low typical river velocity. This highly possibly results in the low turbine performance. Thus to make the turbine application economically feasible, in the design turbine stage, a preliminary figure on an efficient design is paramount. In order to contribute in satisfying this requirement, this study investigates the effect of the variation of the pitch angle, one of the design turbine parameters, on the horizontal axis river turbine performance. The investigation is conducted by a parametric study with the mathematical model of the Blade Element Momentum theory. The results indicate that the increasing of the pitch angle initially enhances the performance. However, too much pitch angle enhancement results in low performance and reduces the rotation operation which in turn it requires a high gearing ratio of the transmission system. This study also attempts to discuss the philosophy behind the results of the investigation, relating the phenomena to the hydrodynamic behaviour.

Link

Leave a comment

Filed under Modeling

Constrained optimization of the shape of a wave energy collector by genetic algorithm


A.P. McCabe – Renewable Energy, March, 2013

Abstract

Wave energy extraction requires the conversion of the energy within the waves to drive the power take off system, often by means of a principal interface, or collector. This paper describes part of the development of a robust, systematic method of optimizing the collector shape to improve energy extraction using a genetic algorithm. The collector geometry uses a parametric description based upon bi-cubic B-spline surfaces, generated from a relatively small number of control points to reduce the dimensionality of the search space. The collector shapes that are optimized have one plane of symmetry and move in one degree of freedom (surge). Each candidate shape is assessed in a wave climate based upon data from a site in the North-East Atlantic Ocean. Three cost functions, distinguished by the severity of the penalty put on the size of the candidate collectors, and four constraint regimes, defined by two displacement and two power rating limits, are the governing influences on the twelve optimization procedures described. The selected collector shapes from each optimization run are appraised in terms of size, complexity and their performance compared to that of ‘benchmark’ box-shaped collectors.

Link

Leave a comment

Filed under Modeling

Testing of a ducted axial flow tidal turbine


T.A. Lokocz – Masters thesis, University of Maine, 2012

Abstract

This research analyzes the performance of a ducted axial flow tidal turbine and compares the result to an unducted turbine. While the focus of this research is on experimental results obtained in tow tank tests, the turbine and duct were designed using the open source software code, OpenProp. OpenProp was used because of the suitability of the design approach for the optimization of a turbine design and its modeling capability for ducted propellers. While OpenProp has the capability to analyze ducted turbines, this capability has been added only recently and has not been validated. Thus, the duct used in the experimental work could not be optimized and was intended to provide data which could be used as a part of the validation of the ducted portion of the code. Literature reviews indicate that limited experimental data exists for the performance of comparable ducted and unducted turbines. The design used is a three-bladed, ducted turbine with blade shapes optimized in OpenProp. For the unducted case, an optimal Cp of 0.44 was measured at a tip speed ratio of 4.43. The duct was shown to have a detrimental effect on the performance of the turbine with a maximum Cp = 0.4 at a tip speed ratio of 4.4. This result demonstrates the challenges associated with the design of an efficient ducted turbine.

Link

Leave a comment

Filed under Testing Infrastructure

Spatial variability of ocean waves, from in-situ measurements


I.C.G. Ashton, J-B. Saulnier, G.H. Smith – Ocean Engineering, January, 2013

Abstract

This paper describes the analysis of the spatial properties of ocean waves using measurements from an array of four directional wave buoys installed in a square formation, with side 500 m, in the Celtic Sea, UK. Wave measurements in this area have been installed to support resource assessment and design for wave energy devices at the Wave Hub site off the North Cornwall coast. This unique deployment of multiple directional sensors provides high quality direct measurements of the spatial properties of the wave field. Spectral parameters measured simultaneously by all four buoys within the array are compared and it is demonstrated that wave conditions cannot be considered stationary across the measurement area. Differences in the measured wave fields were observed primarily in the low frequencies and are observed to be of a level sufficient to impact the assessment of site characteristics. Theoretical estimations of refraction and bottom friction indicate that these physical processes contribute to the observed measurements. The results demonstrate the potential effect of spatial variability in wave fields on the monitoring of wave energy sites, and highlight the requirement for accurate evaluation of physical processes.

Link

 

Leave a comment

Filed under Resource Characterization