scholarly journals Experimental and Numerical Collaborative Latching Control of Wave Energy Converter Arrays

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 3036 ◽  
Author(s):  
Simon Thomas ◽  
Mikael Eriksson ◽  
Malin Göteman ◽  
Martyn Hann ◽  
Jan Isberg ◽  
...  
Keyword(s):  
Wave Energy ◽  
Learning Algorithm ◽  
Wave Energy Converter ◽  
Irregular Waves ◽  
Scale Model ◽  
Energy Converter ◽  
Ideal Behavior ◽  
Model Free ◽  
Physical Scale ◽  
Latching Control

A challenge while applying latching control on a wave energy converter (WEC) is to find a reliable and robust control strategy working in irregular waves and handling the non-ideal behavior of real WECs. In this paper, a robust and model-free collaborative learning approach for latchable WECs in an array is presented. A machine learning algorithm with a shallow artificial neural network (ANN) is used to find optimal latching times. The applied strategy is compared to a latching time that is linearly correlated with the mean wave period: It is remarkable that the ANN-based WEC achieved a similar power absorption as the WEC applying a linear latching time, by applying only two different latching times. The strategy was tested in a numerical simulation, where for some sea states it absorbed more than twice the power compared to the uncontrolled WEC and over 30% more power than a WEC with constant latching. In wave tank tests with a 1:10 physical scale model the advantage decreased to +3% compared to the best tested constant latching WEC, which is explained by the lower advantage of the latching strategy caused by the non-ideal latching of the physical power take-off model.

Numerical and Experimental Analysis of a Novel Wave Energy Converter

2010 ◽  
Author(s):  
Ken Rhinefrank ◽  
Al Schacher ◽  
Joe Prudell ◽  
Joao Cruz ◽  
Nuno Jorge ◽  
...  
Keyword(s):  
Wave Energy ◽  
Wave Energy Converter ◽  
Irregular Waves ◽  
Numerical Code ◽  
Scale Model ◽  
Energy Converter ◽  
Modeling Tools ◽  
Physical Experiments ◽  
Wave Basin ◽  
Wave Research

A novel point absorber wave energy converter (WEC) is being developed by Columbia Power Technologies, LLC (CPT). Numerical and physical experiments have been performed by Columbia Power, Garrad Hassan and Partners (GH) and Oregon State University (OSU). Three hydrodynamic modeling tools including WAMIT, GH WaveFarmer, and OrcaFlex are used to evaluate the performance of the WEC. GH WaveFarmer is a specialized numerical code being developed specifically for the wave energy industry. Performance and mooring estimates at full scale were initially evaluated and optimized, which were then followed by the development of a 1/33rd scale physical model to obtain comparable datasets, aiming to validate the predictions and reduce the uncertainty associated with other numerical model results. The tests of the 1/33rd scale model of the CPT WEC were recently carried out at the multi-directional wave basin of the O.H. Hinsdale Wave Research Laboratory (HWRL), in conjunction with the Northwest National Marine Renewable Energy Center (NNMREC) at OSU. This paper presents details of the modeling program and progress to date. Emphasis is given to the coupling of WAMIT with GH WaveFarmer for performance estimates and the coupling of WAMIT with the OrcaFlex model for mooring load estimates. An overview of the novel 3-body WEC, including operation and mooring system, is also presented. The 1/33rd scale model functionality is described including an overview of the experimental setup at the basin. Comparisons between the numerical and experimental results are shown for both regular and irregular waves and for several wave headings and dominant directions using a number of spreading functions. The paper concludes with an overview of the next steps for the modeling program and future experimental test plans.

scholarly journals Experimental Analysis of a Novel Adaptively Counter-Rotating Wave Energy Converter for Powering Drifters

2019 ◽  
Vol 7 (6) ◽  
pp. 171 ◽  
Author(s):  
Guoheng Wu ◽  
Zhongyue Lu ◽  
Zirong Luo ◽  
Jianzhong Shang ◽  
Chongfei Sun ◽  
...  
Keyword(s):  
Wave Energy ◽  
Wave Energy Converter ◽  
Irregular Waves ◽  
Surface Velocity ◽  
Small Scale ◽  
Power Constraint ◽  
Energy Converter ◽  
Wave Tank ◽  
Wide Range ◽  
Rotating Wave

Nowadays, drifters are used for a wide range of applications for researching and exploring the sea. However, the power constraint makes it difficult for their sampling intervals to be smaller, meaning that drifters cannot transmit more accurate measurement data to satellites. Furthermore, due to the power constraint, a modern Surface Velocity Program (SVP) drifter lives an average of 400 days before ceasing transmission. To overcome the power constraint of SVP drifters, this article proposes an adaptively counter-rotating wave energy converter (ACWEC) to supply power for drifters. The ACWEC has the advantages of convenient modular integration, simple conversion process, and minimal affection by the crucial sea environment. This article details the design concept and working principle, and the interaction between the wave energy converter (WEC) and wave is presented based on plane wave theory. To verify the feasibility of the WEC, the research team carried out a series of experiments in a wave tank with regular and irregular waves. Through experiments, it was found that the power and efficiency of the ACWEC are greatly influenced by parameters such as wave height and wave frequency. The maximum output power of the small scale WEC in a wave tank is 6.36 W, which allows drifters to detect ocean data more frequently and continuously.

scholarly journals Numerical and Experimental Investigation on a Moonpool-Buoy Wave Energy Converter

Energies ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2364 ◽  
Author(s):  
Hengxu Liu ◽  
Feng Yan ◽  
Fengmei Jing ◽  
Jingtao Ao ◽  
Zhaoliang Han ◽  
...  
Keyword(s):  
Numerical Model ◽  
Wave Energy ◽  
Wave Energy Converter ◽  
Scale Model ◽  
Energy Converter ◽  
Point Absorber ◽  
Motion Responses ◽  
Computational Fluid Dynamics Cfd ◽  
The Time Domain ◽  
Good Agreement

This paper introduces a new point-absorber wave energy converter (WEC) with a moonpool buoy—the moonpool platform wave energy converter (MPWEC). The MPWEC structure includes a cylinder buoy and a moonpool buoy and a Power Take-off (PTO) system, where the relative movement between the cylindrical buoy and the moonpool buoy is exploited by the PTO system to generate energy. A 1:10 scale model was physically tested to validate the numerical model and further prove the feasibility of the proposed system. The motion responses of and the power absorbed by the MPWEC studied in the wave tank experiments were also numerically analyzed, with a potential approach in the frequency domain, and a computational fluid dynamics (CFD) code in the time domain. The good agreement between the experimental and the numerical results showed that the present numerical model is accurate enough, and therefore considering only the heave degree of freedom is acceptable to estimate the motion responses and power absorption. The study shows that the MPWEC optimum power extractions is realized over a range of wave frequencies between 1.7 and 2.5 rad/s.

scholarly journals Hydro-Elastic Modelling of an Electro-Active Wave Energy Converter

2013 ◽  
Author(s):  
Aurélien Babarit ◽  
Benjamin Gendron ◽  
Jitendra Singh ◽  
Cécile Mélis ◽  
Philippe Jean
Keyword(s):  
Numerical Model ◽  
Wave Energy ◽  
Ocean Basin ◽  
Wave Energy Converter ◽  
Scale Model ◽  
Linear Potential ◽  
Energy Converter ◽  
Outer Flow ◽  
Modal Expansion ◽  
Linear Potential Theory

Since 2009, SBM Offshore has been developing the S3 Wave Energy Converter (S3 WEC). It consists in a long flexible tube made of an Electro-Active Polymer (EAP). Thus, the structural material is also the Power Take Off (PTO). In order to optimize the S3 WEC, a hydro-elastic numerical model able to predict the device dynamic response has been developed. The inner flow, elastic wall deformations and outer flow are taken into account in the model under the following assumptions: Euler equation is used for the inner flow. The flow is also assumed to be uniform. Elastic deformation of the wall tube is linearized. The outer flow is modeled using linear potential theory. These equations have been combined in order to build the numerical model. First, they are solved in the absence of the outer fluid in order to obtain the modes of response of the device. Secondly, the outer fluid is taken into account and the equation of motion is solved by making use of modal expansion. Meanwhile, experimental validation tests were conducted in the ocean basin at Ecole Centrale De Nantes. The scale model is 10m long tube made of EAP. The tube deformations were measured using the electro-active polymer. The model was also equipped with sensors in order to measure the inner pressure. Comparisons of the deformation rate between the numerical model and experimental results show good agreement, provided that the wall damping is calibrated. Eventually, results of a technico-economical parametric study of the dimensions of the device are presented.

Latching Control of a Floating Oscillating Water Column Wave Energy Converter in Irregular Waves

2014 ◽  
Author(s):  
João C. C. Henriques ◽  
Juan C. Chong ◽  
António F. O. Falcão ◽  
Rui P. F. Gomes
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Rotational Speed ◽  
Phase Control ◽  
Wave Energy Converter ◽  
Irregular Waves ◽  
Oscillating Water Column ◽  
Random Waves ◽  
Energy Converter ◽  
Excitation Force

The paper concerns the phase control by latching of a floating oscillating-water-column (OWC) wave energy converter of spar-buoy type in irregular random waves. The device is equipped with a two-position fast-acting valve in series with the turbine. The instantaneous rotational speed of the turbine is controlled through the power electronics according to a power law relating the electromagnetic torque on the generator rotor to the rotational speed, an algorithm whose adequacy had been numerically tested in earlier papers. Two alternative strategies (1 and 2) for the latching/unlatching timings are investigated. Strategy 1 is based on the knowledge of the zero-crossings of the excitation force on the floater-tube set. This is difficult to implement in practice, since the excitation force can neither be measured directly nor predicted. Strategy 2 uses as input easily measurable physical variables: air pressure in the chamber and turbine rotational speed. Both strategies are investigated by numerical simulation based on a time-domain analysis of a spar-buoy OWC equipped with a self-rectifying radial-flow air turbine of biradial type. Air compressibility in the chamber plays an important role and was modelled as isentropic in a fully non-linear way. Numerical results show that significant gains up to about 28% are achievable through strategy 1, as compared with no phase control. Strategy 2, while being much easier to implement in practice, was found to yield more modest gains (up to about 15%).

Latching Control of an OWC Spar-Buoy Wave Energy Converter in Regular Waves

2012 ◽  
Author(s):  
J. C. C. Henriques ◽  
A. F. O. Falcão ◽  
R. P. F. Gomes ◽  
L. M. C. Gato
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Phase Control ◽  
Wave Energy Converter ◽  
Irregular Waves ◽  
Wave Direction ◽  
Regular Waves ◽  
Energy Converter ◽  
Chamber Volume ◽  
The Time Domain

The present paper concerns an OWC spar-buoy, possibly the simplest concept for a floating oscillating-water-column (OWC) wave energy converter. It is an axisymmetric device (and so insensitive to wave direction) consisting basically of a (relatively long) submerged vertical tail tube open at both ends, fixed to a floater that moves essentially in heave. The length of the tube determines the resonance frequency of the inner water column. The oscillating motion of the internal free surface relative to the buoy, produced by the incident waves, makes the air flow through a turbine that drives an electrical generator. It is well known that the frequency response of point absorbers like the spar buoy is relatively narrow, which implies that their performance in irregular waves is relatively poor. Phase control has been proposed to improve this situation. The present paper presents a theoretical investigation of phase control by latching of an OWC spar-buoy in which the compressibility of air in the chamber plays an important role (the latching is performed by fast closing and opening an air valve in series with the turbine). In particular such compressibility may remove the constraint of latching threshold having to coincide with an instant of zero relative velocity between the two bodies (in the case under consideration, between the floater and the OWC). The modelling is performed in the time domain for a given device geometry, and includes the numerical optimization of the air turbine rotational speed, chamber volume and latching parameters. Results are obtained for regular waves.

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