Category Archives: Analytics

Offshore wind structure weight algorithms


Mark J. Kaiser and Brian F. Snyder – Ships and Offshore Structures, February 2014

Abstract

Decommissioning requirements for offshore renewable energy facilities in US federal waters requires that all facilities be removed and the seafloor be cleared of all obstructions at the end of the life of the lease. Before construction activities are permitted, developers are required to post a bond based on the estimated cost of decommissioning to ensure that the federal government is protected in case of company default. The purpose of this note is to provide weight algorithms of offshore wind farm components to estimate the lift requirements in decommissioning, the scrap value of material, and disposal cost. Weight algorithms are calibrated and compared with North Sea project data and examples illustrate the procedures. The component weights at the Cape Wind farm offshore Massachusetts are estimated.

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Filed under Analytics, Economics, Installation

Equations used to predict the velocity distribution within a wake from a horizontal-axis tidal-current turbine


Wei-Haur Lam and Long Chen – Ocean Engineering, March 2014

Abstract

The investigation of the wake from a tidal-current turbine becomes important when considering a tidal farm. Each single turbine wake in a turbine farm would significantly affect the performance of another turbine located adjacent or downstream. In this study, two novel analytical equations are developed to predict the mean velocity within the wake of a tidal-current turbine. The equations are proposed to predict the initial velocity close to the turbine and the lateral distributions at various sections downstream, respectively. The first equation for the initial flow prediction is derived based on the axial momentum theory and dimensional analysis, while the second equation for lateral velocity distribution prediction is derived based on Gaussian probability distribution. The derivation of the proposed equations is presented and their predictions are compared with the existing experimental and numerical results. Validation of these novel equations gives a variation of 6% at the initial flow and 8% at the lateral sections compared to the experimental and numerical results. These equations are potentially the foundation of the analytical method for wake prediction of a tidal turbine.

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Wave-power absorption from a finite array of oscillating wave surge converters


E. Renzi, A. Abdolali, G. Bellotti, and F. Dias – Renewable Energy, March 2014

Abstract

Semi-analytical and fully numerical modelling is developed in the framework of the inviscid potential flow theory to investigate the dynamics of a wave farm made by flap-type wave energy converters in the nearshore. The hydrodynamic parameters and the efficiency of the system in typical layouts are calculated with both models. Good agreement is shown between the two approaches. Parametric analysis undertaken with the semi-analytical model allows to identify a near-resonant phenomenon which is responsible for increasing the absorbed power by the single elements of the array. Such result could be used as a preliminary design criterion. The numerical model is then applied to analyse a configuration of practical engineering interest, i.e. an array of two staggered converters. The dynamics arising in this more complex system is explained, showing that non-symmetric layouts can be less effective.

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Filed under Analytics, Modeling, System Development