Francesco Paparella

Up-Wave and Autoregressive Methods for Short-Term Wave Forecasting for an Oscillating Water Column

The real-time control of wave energy converters (WECs) requires the prediction of the wave elevation at the location of the device in order to maximize the power extracted from the waves. One possibility is to predict the future wave elevation by combining its past history with the spatial information coming from a sensor which measures the free surface elevation up-wave of the WEC. As an application example, this paper focuses on the prediction of the wave elevation inside the chamber of the oscillating water column (OWC) for the Pico OWC plant in the Azores, and two different sensors for the measurement of the free surface elevation up-wave of the OWC were tested. The study showed that the use of the additional information coming from the up-wave sensor does not significantly improve the linear prediction of the chamber wave elevation given by a forecasting model based only on the past values of the chamber wave elevation.

Multibody Modelling of Wave Energy Converters Using Pseudo-Spectral Methods With Application to a Three-Body Hinge-Barge Device

Multibody wave energy converters are composed of several bodies interconnected by joints. Two different formulations are adopted to describe the dynamics of multibody systems: the differential and algebraic equations (DAEs) formulation, and the ordinary differential equations (ODEs) formulation. While the number of variables required for the description of the dynamics of a multibody system is greater in the DAE formulation than in the ODE formulation, the ODE formulation involves an extra computational effort in order to describe the dynamics of the system with a smaller number of variables. In this paper, pseudo-spectral (PS) methods are applied in order to solve the dynamics of multibody wave energy converters using both DAE and ODE formulations. Apart from providing a solution to the dynamics of multibody systems, pseudo-spectral methods provide an accurate and efficient formulation for the control of multibody wave energy converters. As an application example, this paper focuses on the dynamic modeling of a three-body hinge-barge device, where wave-tank tests are carried out in order to validate the DAE and ODE models against experimental data. Comparison of the ODE and DAE PS methods against a reference model based on the straightforward (Runge-Kutta) integration of the equations of motion shows that pseudo-spectral methods are computationally more stable and require less computational effort for short time steps.

Benefits of up-wave measurements in linear short-term wave forecasting for wave energy applications

The real-time control of wave energy converters requires the prediction of the wave elevation at the location of the device in order to maximize the power extracted from the waves. One possibility is to predict the future wave elevation by combining its past history with the spatial information coming from a sensor which measures the free surface elevation up-wave of the wave energy converter. As an application example, the paper focuses on the prediction of the wave elevation inside the chamber of the oscillating water column (OWC) for the PICO OWC plant in the Azores, and two different sensors for the measurement of the free surface elevation up-wave of the oscillating water column were tested. The study showed that the use of the additional information coming from the up-wave sensor does not significantly improve the linear prediction of the chamber wave elevation given by a forecasting model based only on the past values of the chamber wave elevation.

Ocean forecasting for wave energy production

There are a variety of requirements for future forecasts in relation to optimizing the production of wave energy. Daily forecasts are required to plan maintenance activities and allow power producers to accurately bid on wholesale energy markets, hourly forecasts are needed to warn of impending inclement conditions, possibly placing devices in survival mode, while wave-by-wave forecasts are required to optimize the real-time loading of the device so that maximum power is extracted from the waves over all sea conditions. In addition, related hindcasts over a long time scale may be performed to assess the power production capability of a specific wave site. This paper addresses the full spectrum of the aforementioned wave modeling activities, covering the variety of time scales and detailing modeling methods appropriate to the various time scales, and the causal inputs, where appropriate, which drive these models. Some models are based on a physical description of the system, including bathymetry, for example (e.g., in assessing power production capability), while others simply use measured data to form time series models (e.g., in wave-to-wave forecasting). The paper describes each of the wave forecasting problem domains, details appropriate model structures and how those models are parameterized, and also offers a number of case studies to illustrate each modeling methodology.

Optimal Control of a Three-Body Hinge-Barge Wave Energy Device Using Pseudospectral Methods

This paper shows the potential of optimal control for enhancing the power capture for a three-body hinge-barge wave energy converter (WEC). It is the first documented application of a coordinated control strategy for a hinge-barge WEC, where power is converted at the joints between both the fore and aft pontoons, and the central barge section. Two separate optimal control formulations, based on different model representations, are evaluated and are shown to considerably outperform an optimal constant damping control strategy.

A low-cost motion capture system for small-scale wave energy device tank testing

The measurement of the motion of a small-scale wave energy device during wave tank tests is important for the evaluation of its response to waves and the assessment of power production. Usually, the motion of a small-scale wave energy converter (WEC) is measured using an optical motion tracking system with high precision and sampling rate. However, the cost for an optical motion tracking system can be considerably high and, therefore, the overall cost for tank testing is increased. This paper proposes a low-cost capture system composed of an inertial measurement unit and ultrasound sensors. The measurements from the ultrasound sensors are combined optimally with the measurements from the inertial measurement unit through an extended Kalman filter (EKF) in order to obtain an accurate estimation of the motion of a WEC. [DOI: 10.1115/1.4041608]

Enhancement of the wave energy conversion characteristics of a hinge-barge using pseudospectral control

This paper shows the benefits of using pseudo-spectral (PS) methods for the optimal control of a three-body hinge-barge device. Two different control formulations are derived based on different representations of the dynamic model of the device: the differential and algebraic equations (DAE) formulation, and the ordinary differential equations (ODE) formulation. Wave-tank tests are carried out in order to validate the DAE and ODE models against experimental data. For control design, PS methods show significant improvements in terms of absorbed power with respect to an optimal damping strategy.

Erratum to “Up-Wave and Autoregressive Methods for Short-Term Wave Forecasting for an Oscillating Water Column” [Jan 15 171-178]

In the above paper (ibid., vol. 6, no. 1, pp. 171-178, Jan. 2015), the acknowledgement of financial support was not included, due to a publication error. It is presented here.