Experimental investigation of the mooring system of a wave energy converter in operating and extreme wave conditions

A proper design of the mooring systems for Wave Energy Converters (WECs) requires an accurate investigation of both operating and extreme wave conditions. A careful analysis of these systems is required to design a mooring configuration that ensures station keeping, reliability, maintainability, and low costs, without affecting the WEC dynamics. In this context, an experimental campaign on a 1:20 scaled prototype of the ISWEC (Inertial Sea Wave Energy Converter), focusing on the influence of the mooring layout on loads in extreme wave conditions, is presented and discussed. Two mooring configurations composed of multiple slack catenaries with sub-surface buoys, with or without clump-weights, have been designed and investigated experimentally. Tests in regular, irregular, and extreme waves for a moored model of the ISWEC device have been performed at the University of Naples Federico II. The aim is to identify a mooring solution that could guarantee both correct operation of the device and load carrying in extreme sea conditions. Pitch motion and loads in the rotational joint have been considered as indicators of the device hydrodynamic behavior and mooring configuration impact on the WEC

Excitation forces estimation for non-linear wave energy converters: A neural network approach

Investigating optimal control algorithms is a continuing concern within the Wave Energy field. A considerable amount of literature has been published on optimal control architectures applied to Wave Energy Converter (WEC) devices. However, most of them requires the knowledge of the wave excitation forces acting on the WEC body. In practice such forces are unknown and an estimate must be used. In this work a methodology to estimate the wave excitation forces of a non-linear WEC along with the achievable accuracy, is discussed. A feedforward Neural Network (NN) is applied to address the estimation problem. Such a method aims to map the WEC dynamics to the wave excitation forces by training the network through a supervised learning algorithm. The most challenging aspects of these techniques are the ability of the network to estimate data not considered in the training process and their accuracy in presence of model uncertanities. Numerical simulations under different irregular sea conditions demonstrate accurate estimation results of the NN approach as well as a small sensitivity to changes in the plant parameters relative to the case study presented

Monolithic Pixel Sensors in Deep-Submicron SOI Technology

Monolithic pixel sensors for charged particle detection and imaging applications have been designed and fabricated using commercially available, deep-submicron Silicon-On-Insulator (SOI) processes, which insulate a thin layer of integrated full CMOS electronics from a high-resistivity substrate by means of a buried oxide. The substrate is contacted from the electronics layer through vias etched in the buried oxide, allowing pixel implanting and reverse biasing. This paper summarizes the performances achieved with a first prototype manufactured in the OKI 0.15 micrometer FD-SOI process, featuring analog and digital pixels on a 10 micrometer pitch. The design and preliminary results on the analog section of a second prototype manufactured in the OKI 0.20 micrometer FD-SOI process are briefly discussed.Comment: Proceedings of the PIXEL 2008 International Workshop, FNAL, Batavia, IL, 23-26 September 2008. Submitted to JINST - Journal of Instrumentatio

Fast nonlinear Froude–Krylov force calculation for prismatic floating platforms: a wave energy conversion application case

Computationally fast and accurate mathematical models are essential for effective design, optimization, and control of wave energy converters. However, the energy-maximising control strategy, essential for reaching economic viability, inevitably leads to the violation of linearising assumptions, so the common linear models become unreliable and potentially unrealistic. Partially nonlinear models based on the computation of Froude–Krylov forces with respect to the instantaneous wetted surface are promising and popular alternatives, but they are still too slow when floaters of arbitrary complexity are considered; in fact, mesh-based spatial discretisation, required by such geometries, becomes the computational bottle-neck, leading to simulations 2 orders of magnitude slower than real-time, unaffordable for extensive iterative optimizations. This paper proposes an alternative analytical approach for the subset of prismatic floating platforms, common in the wave energy field, ensuring computations 2 orders of magnitude faster than real-time, hence 4 orders of magnitude faster than state-of-the-art mesh-based approaches. The nonlinear Froude–Krylov model is used to investigate the nonlinear hydrodynamics of the floater of a pitching wave energy converter, extracting energy either from pitch or from an inertially coupled internal degree of freedom, especially highlighting the impact of state constraints, controlled/uncontrolled conditions, and impact on control parameters’ optimization, sensitivity and effectiveness

Data-based control synthesis and performance assessment for moored wave energy conversion systems: the PeWEC case

With a model-based control strategy, the effectiveness of the associated control action depends on the availability of a representative control-oriented model. In the case of floating offshore wave energy converters (WECs), the device response depends upon the interaction between mooring system, any mechanical parts, and the hydrodynamics of the floating body. This study proposes an approach to synthesise WEC controllers under the effect of mooring forces building a representative data-based linear model able to include any relevant dynamics. Moreover, the procedure is tested on the moored pendulum wave energy converter (PeWEC) by means of a high-fidelity mooring solver, OrcaFlex (OF). In particular, the control action is computed with and without knowledge of the mooring influence, in order to analyse and elucidate the effect of the station-keeping system on the harvested energy. The performance assessment of the device is achieved by evaluating device power on the resource scatter characterising Pantelleria, Italy. The results show the relevance of the mooring dynamics on the device response and final set of control parameters and, hence, a significant influence of the station-keeping system on control synthesis and extracted mechanical power

Real-time wave excitation forces estimation: An application on the ISWEC device

Optimal control strategies represent a widespread solution to increase the extracted energy of a Wave Energy Converter (WEC). The aim is to bring the WEC into resonance enhancing the produced power without compromising its reliability and durability. Most of the control algorithms proposed in literature require for the knowledge of the Wave Excitation Force (WEF) generated from the incoming wave field. In practice, WEFs are unknown, and an estimate must be used. This paper investigates the WEF estimation of a non-linear WEC. A model-based and a model-free approach are proposed. First, a Kalman Filter (KF) is implemented considering the WEC linear model and the WEF modelled as an unknown state to be estimated. Second, a feedforward Neural Network (NN) is applied to map the WEC dynamics to the WEF by training the network through a supervised learning algorithm. Both methods are tested for a wide range of irregular sea-states showing promising results in terms of estimation accuracy. Sensitivity and robustness analyses are performed to investigate the estimation error in presence of un-modelled phenomena, model errors and measurement noise

LNL irradiation facilities for radiation damage studies on electronic devices

In this paper we will review the wide range of irradiation facilities installed at the INFN Legnaro National Laboratories and routinely used for radiation damage studies on silicon detectors, electronic components and systems. The SIRAD irradiation facility, dedicated to Single Event Effect (SEE) and bulk damage studies, is installed at the 14MV Tandem XTU accelerator and can deliver ion beams from H up to Au in the energy range from 28MeV to 300 MeV. An Ion Electron Emission Microscope, also installed at SIRAD, allows SEE testing with micrometric sensitivity. For total dose tests, two facilities are presently available: an X-rays source and a 60Co γ-ray source. The 7MV Van de Graaff CN accelerator provides 1H beams in the energy range 2–7MeV and currents up to few μA for both total dose and bulk damage studies. At this facility, very high dose rates (up to ∼100 krad/s (SiO2)) can be achieved. Finally, also neutron beams are available, produced at the CN accelerator, by the reaction d + Be ⇒ n+B

Analysis of a gyroscopic-stabilized floating offshore hybrid wind-wave platform

The energy innovation scenario sees hybrid wind-wave platforms as a promising technology for reducing the variability of the power output and for the minimization of the cost of offshore marine renewable installations. This article presents a model that describes the installation of a 5 MW wind turbine on a floating platform designed by Fincantieri and equipped with gyroscopic stabilization. The use of gyros allows for the delivery of platform stabilization by damping the wave and wind induced motion on the floater and at the same time producing extra power. Shetland Island was chosen as the reference site because of its particularly harsh weather. Final results show that the total production of power in moderate and medium climate conditions is considerable thanks to the installation of the gyro, together with a significant stabilization of the platform in terms of pitching angle and nacelle acceleration

Total dose effects on deep-submicron SOI technology for Monolithic Pixel Sensor development

We developed and characterized Monolithic pixel detectors in deep-submicron Fully Depleted (FD) Silicon On Insulator (SOI) technology. This paper presents the first studies of total dose effects from ionizing radiation performed on single transistor test structures. This work shows how the substrate bias condition during irradiation heavily affects the resulting radiation damage

Ácidos orgânicos como extratores de metais pesados fitodisponíveis em solos tratados com lodo de esgoto.

Ainda não foi desenvolvido um método de extração eficiente para estimar teores fitodisponíveis de metais pesados, porque os extratores utilizados não simulam reações semelhantes às que ocorrem próximo às raízes. O objetivo deste trabalho foi avaliar uma solução de ácidos orgânicos rizosféricos como extratora de teores fitodisponíveis de metais pesados presentes em solos tratados com lodo de esgoto. Os solos utilizados foram: Latossolo Amarelo distrófico, Neossolo Quartzarênico e Latossolo Vermelho distrófico, cultivados com plantas de banana, pupunha e café, respectivamente. A avaliação do extrator (solução composta por ácido acético, cítrico, lático e oxálico em concentrações de 1,00, 0,72, 0,49 e 0,12 mol L-1, respectivamente) foi feita a partir da análise da correlação entre teores de metais pesados (Cd, Cr, Cu, Ni, Pb e Zn) extraídos do solo e os teores nas plantas. As correlações foram significativas, indicando a eficiência do extrator para todos os casos estudados. Entre os metais avaliados, as quantidades extraídas de Pb correlacionaram-se melhor com teor fitodisponível nas três situações investigadas