Alessandro Antonini

Wave energy production in Italian offshore: Preliminary design of a point absorber with tubular linear generator

The paper presents the preliminary design and modelling of a point absorber wave energy converter consisting of a floating buoy connected to a tubular linear generator fixed at the seabed. The behaviour of the device is described by the equation of motion of a single body system restricted to vertical motion. The model of the coupled buoy-generator system is used to simulate the behaviour of the wave energy converter under regular waves of different heights and periods. Then the electricity production of an hypothetical installation off the Alghero coast is estimated. The results show that the device capacity factor at the study site is around 15%. This is a very promising value considering that the studied device has not been specifically optimized for the Alghero wave climate. The work suggests that the presented technology could be very attractive for the Italian offshore.

Assessment of the surge effects in a heaving point absorber in the Mediterranean Sea

In the present paper, the feasibility of wave electricity production in Italian seas is investigated through the implementation of a variant of the Seabased point absorber WEC. A numerical model of the coupled buoy-generator system is presented, which simulates the behavior of the WEC under different significant wave heights and periods. The WEC scheme is an improvement of the modeling of a three-body device, taking into account several aspects (independence among the bodies, heave and surge) ignored in previous studies for simplification of the scheme.One WEC composed by three bodies is simulated, with two different hydrodynamic numerical model schemes: a floating buoy and a submerged sphere placed at 25 meters below the water surface. The third body is the translator of the linear generator, which is located at the sea bottom and attached to the submerged sphere by a steel wire.For the hydrodynamic numerical model, the two bodies are allowed to move independently; heave and surge modes have been taken into account. The first scheme consists in the modeling with only three degrees of freedom, one per body only in the vertical direction (heave) and the other with five degrees of freedom, adding the horizontal component of movement for the buoy and the submerged body (surge). The results are compared with previous results of a WEC modeled as a single body system, with only one degree of freedom along the vertical axis. Preliminary results show that the produced energy in a simplified 1 DoF scheme is higher than results produced by the 3 DoF scheme, and is then approximately equal for the 5 DoF. The power matrixes present similar shapes. So the simplification made by neglecting the surge mode, in order to have a simpler dynamic model, doesn’t give a significant improvement in the capture width and energy production assessment.Copyright

Finite Element Modelling and Limit Analysis of Fastnet Lighthouse Under Impulsive Ocean Waves

Being exposed to strong ocean waves for more than a century, the Fastnet lighthouse is assessed for its structural response to the intense lateral loading. The Finite Element Method (FEM) was implemented for the structural analysis using the commercial software Abaqus. The lighthouse is built with large and meticulously dovetailed granite blocks which make it a very unique structural system. Three different finite element model configurations were tested, modelling the lighthouse as continuous homogeneous (elastic and nonlinear), and as discontinuous with contact interfaces between each course of blocks allowing uplift and sliding. The applicability and efficacy of these approaches is discussed. The impact load of the wave was applied as a time-history sequence, assuming that the wave breaks just in front of the structure surface corresponding to the least favourable scenario. Different intensities and heights were considered for the impact load. Finally, the FEM results are also compared with the results of the limit analysis method which calculates the minimum intensity of lateral static load that is necessary for causing uplift and overturning of rigid bodies. This comparison demonstrates the usefulness of the limit analysis method as a tool for quick preliminary assessment of the lateral load bearing capacity of this particular structural typology. This work is part of the STORMLAMP project (STructural behaviour Of Rock Mounted Lighthouses At the Mercy of imPulsive waves) funded by the UK Engineering and Physical Sciences Research Council, which is gratefully acknowledged.