scholarly journals Mathematical Framework for Hydromechanical Time-Domain Simulation of Wave Energy Converters

2018 ◽  
Vol 2018 ◽  
pp. 1-15
Author(s):  
J. Seixas de Medeiros ◽  
S. Brizzolara
Keyword(s):  
Dynamic Model ◽  
Wave Energy ◽  
Time Domain ◽  
Time Integration ◽  
Average Power ◽  
Panel Method ◽  
Mathematical Framework ◽  
Power Extraction ◽  
Wave Energy Converters ◽  
Energy Converters

Efficient design of wave energy converters based on floating body motion heavily depends on the capacity of the designer to accurately predict the device’s dynamics, which ultimately leads to the power extraction. We present a (quasi-nonlinear) time-domain hydromechanical dynamic model to simulate a particular type of pitch-resonant WEC which uses gyroscopes for power extraction. The dynamic model consists of a time-domain three-dimensional Rankine panel method coupled, during time integration, with a MATLAB algorithm that solves for the equations of the gyroscope and Power Take-Off (PTO). The former acts as a force block, calculating the forces due to the waves on the hull, which is then sent to the latter through TCP/IP, which couples the external dynamics and performs the time integration using a 4th-order Runge-Kutta method. The panel method, accounting for the gyroscope and PTO dynamics, is then used for the calculation of the optimal flywheel spin, PTO damping, and average power extracted, completing the basic design cycle of the WEC. The proposed numerical method framework is capable of considering virtually any type of nonlinear force (e.g., nonlinear wave loads) and it is applied and verified in the paper against the traditional frequency domain linear model. It proved to be a versatile tool to verify performance in resonant conditions.

scholarly journals Hardware-in-the-Loop Validation of Model Predictive Control of a Discrete Fluid Power Power Take-Off System for Wave Energy Converters

Energies ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3668
Author(s):  
Anders H. Hansen ◽  
Magnus F. Asmussen ◽  
Michael M. Bech
Keyword(s):  
Model Predictive Control ◽  
Predictive Control ◽  
Wave Energy ◽  
Fluid Power ◽  
Wave Power ◽  
Reactive Control ◽  
Power Extraction ◽  
Wave Energy Converters ◽  
Extraction Algorithm ◽  
Energy Converters

Model predictive control based wave power extraction algorithms have been developed and found promising for wave energy converters. Although mostly proven by simulation studies, model predictive control based algorithms have shown to outperform classical wave power extraction algorithms such as linear damping and reactive control. Prediction models and objective functions have, however, often been simplified a lot by for example, excluding power take-off system losses. Furthermore, discrete fluid power forces systems has never been validated experimentally in published research. In this paper a model predictive control based wave power extraction algorithm is designed for a discrete fluid power power take-off system. The loss models included in the objective function are based on physical models of the losses associated with discrete force shifts and throttling. The developed wave power extraction algorithm directly includes the quantized force output and the losses models of the discrete fluid power system. The experimental validation of the wave power extraction algorithm developed in the paper shown an increase of 14.6% in yearly harvested energy when compared to a reactive control algorithm.

Genetic Optimization of Shape and Control of Non-Linear Wave Energy Converters

2020 ◽  
Author(s):  
Jiajun Song ◽  
Ossama Abdelkhalik ◽  
Shangyan Zou
Keyword(s):  
Wave Energy ◽  
Time Domain ◽  
Optimization Approach ◽  
Linear Wave ◽  
Variable Size ◽  
Wave Energy Converters ◽  
Hydrostatic Force ◽  
Non Linear ◽  
The Time Domain ◽  
Energy Converters

Abstract This paper presents an optimization approach to design ax-isymmetric wave energy converters (WECs) based on a nonlinear hydrodynamic model. This paper shows optimal nonlinear shapes of buoy can be generated by combing basic shapes in an optimal sense. The time domain non-linear Froude-Krylov force can be computed for a complex buoy shape, by adopting analytical formulas of its basic shape components. The time domain Forude-Krylov force is decomposed into its dynamic and static components, and then contribute to the calculation of the excitation force and the hydrostatic force. A non-linear control is assumed in the form of the combination of linear and nonlinear damping terms. A variable size genetic algorithm (GA) optimization tool is developed to search for the optimal buoy shape along with the optimal control coefficients simultaneously. Chromosome of the GA tool is designed to improve computational efficiency and to leverage variable size genes to search for the optimal non-linear buoy shape. Different criteria of wave energy conversion can be implemented by the variable size GA tool. Simulation results presented in this paper show that it is possible to find non-linear buoy shapes and non-linear controllers that take advantage of non-linear hydrodynamics to improve energy harvesting efficiency with out adding reactive terms to the system.

A Comparison of Selected Strategies for Adaptive Control of Wave Energy Converters

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Jørgen Hals ◽  
Johannes Falnes ◽  
Torgeir Moan
Keyword(s):  
Wave Energy ◽  
Reactive Power ◽  
Average Power ◽  
Volume Ratio ◽  
External Input ◽  
Irregular Waves ◽  
Optimal Velocity ◽  
Wave Energy Converters ◽  
Absorbed Power ◽  
Energy Converters

Wave-energy converters of the point-absorbing type (i.e., having small extension compared with the wavelength) are promising for achieving cost reductions and design improvements because of a high power-to-volume ratio and better possibilities for mass production of components and devices as compared with larger converter units. However, their frequency response tends to be narrow banded, which means that the performance in real seas (irregular waves) will be poor unless their motion is actively controlled. Only then the invested equipment can be fully exploited, bringing down the overall energy cost. In this work various control methods for point-absorbing devices are reviewed, and a representative selection of methods is investigated by numerical simulation in irregular waves, based on an idealized example of a heaving semisubmerged sphere. Methods include velocity-proportional control, approximate complex conjugated control, approximate optimal velocity tracking, phase control by latching and clutching, and model-predictive control, all assuming a wave pressure measurement as the only external input to the controller. The methods are applied for a single-degree-of-freedom heaving buoy. Suggestions are given on how to implement the controllers, including how to tune control parameters and handle amplitude constraints. Based on simulation results, comparisons are made on absorbed power, reactive power flow, peak-to-average power ratios, and implementation complexity. Identified strengths and weaknesses of each method are highlighted and explored. It is found that overall improvements in average absorbed power of about 100–330% are achieved for the investigated controllers as compared with a control strategy with velocity-proportional machinery force. One interesting finding is the low peak-to-average ratios resulting from clutching control for wave periods about 1.5 times the resonance period and above.

The dynamics and power extraction of bottom-hinged plate wave energy converters in regular and irregular waves

2015 ◽  
Vol 96 ◽  
pp. 86-99 ◽  
Author(s):  
R.P.F. Gomes ◽  
M.F.P. Lopes ◽  
J.C.C. Henriques ◽  
L.M.C. Gato ◽  
A.F.O. Falcão
Keyword(s):  
Wave Energy ◽  
Irregular Waves ◽  
Plate Wave ◽  
Power Extraction ◽  
Wave Energy Converters ◽  
Hinged Plate ◽  
Energy Converters

scholarly journals Array modeling and testing of fixed OWC type Wave Energy Converters

2020 ◽  
Vol 3 (3) ◽  
pp. 137-143
Author(s):  
Bret Bosma ◽  
Ted Brekken ◽  
Pedro Lomonaco ◽  
Bryony DuPont ◽  
Chris Sharp ◽  
...  
Keyword(s):  
Numerical Model ◽  
Wave Energy ◽  
Average Power ◽  
Irregular Waves ◽  
Regular Waves ◽  
Wave Energy Converters ◽  
Phase Errors ◽  
Array Optimization ◽  
Tank Test ◽  
Energy Converters

If wave energy technology is to mature to commercial success, array optimization could play a key role in that process. This paper outlines physical and numerical modeling of an array of five oscillating water column wave energy converters. Numerical model simulations are compared with experimental tank test data for a non-optimal and optimal array layout. Results show a max increase of 12% in average power for regular waves, and 7% for irregular waves between the non-optimized and optimized layouts. The numerical model matches well under many conditions; however, improvement is needed to adjust for phase errors. This paper outlines the process of numerical and physical array testing, providing methodology and results helpful for researchers and developers working with wave energy converter arrays.

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