Sea wave energy is being increasingly regarded in many countries as a major and promising resource. The paper deals with the development of wave energy utilization since the 1970s. Several topics are addressed: the characterization of the wave energy resource; theoretical background, with especial relevance to hydrodynamics of wave energy absorption and control; how a large range of devices kept being proposed and studied, and how such devices can be organized into classes; the conception, design, model-testing, construction and deployment into real sea of prototypes; and the development of specific equipment (air and water turbines, high-pressure hydraulics, linear electrical generators) and mooring systems.

Wave energy utilization: A review of the technologies

Gait Analysis. An Introduction

Wave energy is arguably one of the most promising renewables. Less developed at present than other renewables, the existing models to estimate the costs of a wave energy project are often oversimplified, and the resulting scatter in the economic assessments weighs on the confidence of potential investors and constitutes therefore an impediment to the development of wave energy. Indeed, understanding the costs of wave energy is one of the main fields of research in marine renewable energy. In this context, the main objective of this paper is to review all the factors that must be considered in an economic analysis of wave energy, including a number of elements that are usually overlooked. In the process we characterise the direct and indirect costs of a wave farm – preliminary costs, construction, operation and maintenance and decommissioning cost – as well as its prospective incomes. For each of them a reference value is presented, together with a generic formula for its calculation. Moreover, the levelised cost, i.e., the production cost of an energy unit (1 kW h), is compared between various energy sources, and on these grounds conclusions on the profitability and competitiveness of wave energy are drawn. In sum, this work reviews the state of the art and sets the basis for a thorough economic analysis of wave energy.

The economics of wave energy: A review

Loads for use in the design of ships and offshore structures

Wave-height distributions and nonlinear effects

Magnetic levitation has been used to implement low-cost and maintenance-free electromagnetic energy harvesting. The ability of levitation-based harvesting systems to operate autonomously for long periods of time makes them well-suited for self-powering a broad range of technologies. In this paper, a combined theoretical and experimental study is presented of a harvester configuration that utilizes the motion of a levitated hard-magnetic element to generate electrical power. A semi-analytical, non-linear model is introduced that enables accurate and efficient analysis of energy transduction. The model predicts the transient and steady-state response of the harvester a function of its motion (amplitude and frequency) and load impedance. Very good agreement is obtained between simulation and experiment with energy errors lower than 14.15% (mean absolute percentage error of 6.02%) and cross-correlations higher than 86%. The model provides unique insight into fundamental mechanisms of energy transduction and enables the geometric optimization of harvesters prior to fabrication and the rational design of intelligent energy harvesters.

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Magnetic levitation-based electromagnetic energy harvesting: a semi-analytical non-linear model for energy transduction.

Wave spectra are estimated from wave frequency motions of a vessel at zero or low advance speed. Minimization of a cost functional that indicates how well the estimated spectrum results in the measured motion spectra was based on sequential quadratic programming and a genetic algorithm. Two procedures have been developed and applied to numerically simulated motions of a 59 m length offshore supply vessel.

Ocean Wave Spectral Estimation Using Vessel Wave Frequency Motions

Kalman filtering of vessel motions for ocean wave directional spectrum estimation

The paper presents an approach to determine the global load effects induced on ship structures by abnormal, freak, or episodic waves. It refers to the present procedure of determining extreme values of wave-induced responses, including the recent advances of adopting time series of wave elevation as reference design conditions to calculate the wave-induced structural loads on ships in heavy weather. It is shown how this procedure can be extended to account for abnormal or episodic waves. Reference is made to what is presently known about abnormal or freak waves, showing that although it is possible to determine the loads induced by these waves in floating and fixed structures, the present knowledge about the probability of occurrence of these waves is not enough to allow a wave design criterion to be defined in a way consistent with the present probabilistic approaches. However, it is suggested that at the present stage of knowledge it is possible to determine the loads induced by abnormal waves similar to ones that have been measured at various ocean locations and that are thus realistic; a method is described to perform such calculations. Although this information cannot replace the wave-induced loads calculated with the presently established procedures, it can serve as guidance for the design. An application example is presented of a containership subjected to a wave trace that includes an episodic wave that was measured during a severe storm in Central North Sea. The measured wave time history is modified in order to investigate the influence of the wave steepness on the induced vertical motions and loads. The loads induced by the abnormal wave are compared for the first time with extreme values from long-term distributions.

R. Pascoal

Papers

Magnetic levitation-based electromagnetic energy harvesting: a semi-analytical non-linear model for energy transduction.

Ocean Wave Spectral Estimation Using Vessel Wave Frequency Motions

Kalman filtering of vessel motions for ocean wave directional spectrum estimation

Abnormal Wave-Induced Load Effects in Ship Structures

Mooring system influence on the efficiency of wave energy converters