Numerical Wave Tank Simulation of a Variable Geometry Wave Energy Converter

2020 ◽  
Author(s):  
Shangyan Zou ◽  
Ossama Abdelkhalik
Keyword(s):  
Wave Energy ◽  
Reactive Power ◽  
Irregular Waves ◽  
Variable Geometry ◽  
Numerical Wave Tank ◽  
Wave Tank ◽  
Wave Energy Converters ◽  
Highly Nonlinear ◽  
Numerical Wave ◽  
Energy Converters

Abstract This paper presents a high-fidelity numerical wave tank simulation for Variable Geometry Wave Energy Converters (VG-WECs). Typically, wave energy converters require reactive power to optimize the energy conversion, which significantly jeopardizes the economic index of the system. The proposed VGWECs allows comprehensive shape-changing not only in response to ocean climate but also to reduce the reactive power requirements on the power take-off (PTO) unit. This design aims at eliminating reactive power with minimal impact on optimality in terms of energy production. To investigate the dynamic behavior of the VGWEC, this model is simulated in a Computational Fluid Dynamics (CFD) based Numerical Wave Tank (CNWT) using ANSYS 2-way Fluid Structure Interaction (FSI) tool. The interaction between irregular waves and the VGWEC is simulated. The numerical results show that the proposed VGWEC has large deformation and motion in response to the incoming wave. This highly nonlinear interaction between waves and VGWEC can be leveraged to eliminate reactive power.

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.

scholarly journals Validation of a CFD-based numerical wave tank model for the power production assessment of the wavestar ocean wave energy converter

2020 ◽  
Vol 146 ◽  
pp. 2499-2516 ◽  
Author(s):  
Christian Windt ◽  
Josh Davidson ◽  
Edward J. Ransley ◽  
Deborah Greaves ◽  
Morten Jakobsen ◽  
...  
Keyword(s):  
Wave Energy ◽  
Power Production ◽  
Wave Energy Converter ◽  
Ocean Wave ◽  
Numerical Wave Tank ◽  
Energy Converter ◽  
Tank Model ◽  
Wave Tank ◽  
Ocean Wave Energy ◽  
Numerical Wave

An Efficient Convex Formulation for Model-Predictive Control on Wave-Energy Converters

2017 ◽  
Author(s):  
Qian Zhong ◽  
Ronald W. Yeung
Keyword(s):  
Model Predictive Control ◽  
Predictive Control ◽  
Wave Energy ◽  
Optimization Problem ◽  
Reactive Power ◽  
Tuning Parameter ◽  
Primary Concern ◽  
Penalty Term ◽  
Wave Energy Converters ◽  
Energy Converters

Model-Predictive Control (MPC) has shown its strong potential in maximizing energy extraction for Wave-Energy Converters (WECs) while handling hard constraints. As MPC can solve the optimization problem on-line, it can better account for state changes and reject disturbances from the harsh sea environment. Interests have arisen in applying MPC to an array of WECs, since researchers found that multiple small-size WECs are more economically viable than a single large-size WEC. However, the computational demand is known to be a primary concern for applying MPC in real-time, which can determine the feasibility of such a controller, particularly when it comes to controlling an array of absorbers. In this paper, we construct a cost function and cast the problem into a Quadratic Programming (QP) with the machinery force being the “optimizer,” for which the convexity can be guaranteed by introducing a penalty term on the slew rate of the machinery force. The optimization problem can then be solved efficiently, and a feasible solution will be assured as the global optima. Constraints on the motion of the WEC and the machinery force will be taken into account. The current MPC will be compared to others existing in literature, including a nonlinear MPC [1] which has been applied in wave-tank tests. The effects of constraints on the control law and the absorbed power are investigated. Performances of the WEC are shown for both regular and irregular wave conditions. The current MPC is found to have good energy-capture capability and is able to broaden the band-width for capturing wave energy. The reactive power required by the PTO system is presented. The additional penalty term provides a tuning parameter, of which the effects on the MPC performance and the reactive power requirement are discussed.

Nonlinear Time-Domain Simulation of the Heaving-Buoy Type Wave Energy Converter by Using Three-Dimensional Potential Numerical Wave Tank Under Irregular Wave Conditions

2020 ◽  
Author(s):  
Sung-Jae Kim ◽  
Weoncheol Koo ◽  
Moo-Hyun Kim
Keyword(s):  
Wave Energy ◽  
Time Domain ◽  
Three Dimensional ◽  
Wave Energy Converter ◽  
Hydrodynamic Performance ◽  
Numerical Wave Tank ◽  
Energy Converter ◽  
Wave Tank ◽  
Type Wave ◽  
Numerical Wave

Abstract The aim of this paper is to evaluate the hydrodynamic performance of a heaving buoy type wave energy converter (WEC) and power take-off (PTO) system. To simulate the nonlinear behavior of the WEC with PTO system, a three-dimensional potential numerical wave tank (PNWT) was developed. The PNWT is a numerical analysis tool that can accurately reproduce experiments in physical wave tanks. The developed time-domain PNWT utilized the previously developed NWT technique and newly adopted the side wall damping area. The PNWT is based on boundary element method with constant panels. The mixed Eulerian-Lagrangian method (MEL) and acceleration potential approach were adopted to simulate the nonlinear behaviors of free-surface nodes associated with body motions. The PM spectrum as an irregular incident wave condition was applied to the input boundary. A floating or fixed type WEC structure was placed in the center of the computational domain. A hydraulic PTO system composed of a hydraulic cylinder, hydraulic motor and generator was modeled with approximate Coulomb damping force and applied to the WEC system. Using the integrated numerical model of the WEC with PTO system, nonlinear interaction of irregular waves, the WEC structure, and the PTO system were simulated in the time domain. The optimal hydraulic pressure of the PTO condition was predicted. The hydrodynamic performance of the WEC was evaluated by comparing the linear and nonlinear analytical results and highlighted the importance accounting for nonlinear free surfaces.

Development of 3-D Numerical Wave Tank and Applications on Comb-Type Breakwater

2010 ◽  
Author(s):  
Zhuo Fang ◽  
Liang Cheng ◽  
Ningchuan Zhang
Keyword(s):  
Offshore Structures ◽  
Wave Generation ◽  
Irregular Waves ◽  
Secondary Wave ◽  
Wave Forces ◽  
Numerical Wave Tank ◽  
Wave Reflections ◽  
Wave Tank ◽  
Numerical Wave ◽  
Source Wave

In this study, a 3-D numerical wave tank is developed, based on a commercial computational fluid dynamics (CFD) package (FLUENT) to predict wave forces on coastal and offshore structures. A source wave-generation method is introduced to FLUENT through user-defined functions to generate incident waves. Spongy layers are used on both upstream and downstream sides of the wave tank to reduce the effects of wave reflections and secondary wave reflections. Various wave trains, such as linear monochromatic waves, second order Stokes waves and irregular waves were generated by using different source functions. It is demonstrated through numerical examples that the source wave-generation method can accurately generate not only small amplitude waves but also nonlinear waves. The present numerical wave tank is validated against standing waves in front of a vertical breakwater. Interactions between waves and a comb-type breakwater are simulated using the present model. The numerical results are compared with physical experimental results. It is found that the present numerical wave tank simulated the wave and breakwater interactions well.

scholarly journals Extending Complex Conjugate Control to Nonlinear Wave Energy Converters

2020 ◽  
Vol 8 (2) ◽  
pp. 84
Author(s):  
David G. Wilson ◽  
Rush D. Robinett ◽  
Giorgio Bacelli ◽  
Ossama Abdelkhalik ◽  
Ryan G. Coe
Keyword(s):  
Energy Harvesting ◽  
Limit Cycle ◽  
Wave Energy ◽  
Limit Cycles ◽  
Reactive Power ◽  
Complex Conjugate ◽  
Linear Wave ◽  
Wave Energy Converters ◽  
Linear Limit ◽  
Energy Converters

This paper extends the concept of Complex Conjugate Control (CCC) of linear wave energy converters (WECs) to nonlinear WECs by designing optimal limit cycles with Hamiltonian Surface Shaping and Power Flow Control (HSSPFC). It will be shown that CCC for a regular wave is equivalent to a power factor of one in electrical power networks, equivalent to mechanical resonance in a mass-spring-damper (MSD) system, and equivalent to a linear limit cycle constrained to a Hamiltonian surface defined in HSSPFC. Specifically, the optimal linear limit cycle is defined as a second-order center in the phase plane projection of the constant energy orbit across the Hamiltonian surface. This concept of CCC described by a linear limit cycle constrained to a Hamiltonian surface will be extended to nonlinear limit cycles constrained to a Hamiltonian surface for maximum energy harvesting by the nonlinear WEC. The case studies presented confirm increased energy harvesting which utilizes nonlinear geometry realization for reactive power generation.

A Study on Performance Evaluation of Non-Reflective Boundary for Progressive Waves Reproduction Introduced in Numerical Wave Tank With MPS Method

2021 ◽  
Author(s):  
Yasuhiro Aida ◽  
Tomotaka Takeo ◽  
Tomoki Ikoma ◽  
Koichi Masuda
Keyword(s):  
Position Control ◽  
Wave Spectrum ◽  
Irregular Waves ◽  
Finite Width ◽  
Water Tank ◽  
Numerical Wave Tank ◽  
Wave Tank ◽  
Reflected Waves ◽  
Mps Method ◽  
Numerical Wave

Abstract Numerical simulation based on the moving particle semi-implicit (MPS) method is effective for the analysis of floating motion in stormy waves in both coastal and offshore areas. However, when the outer circumference of the calculation area is composed of wall boundaries, superimposed waves are generated by the reflected waves, which makes it difficult to reproduce wave fields in offshore areas. Therefore, in this study, we developed two types of non-reflective boundary that can be applied to a numerical wave tank with the MPS method. One type is an attenuation zone in which a high-viscosity region with a finite width is set from the end of the water tank. The other type is a wave absorption control boundary that detects the amount of water surface fluctuation in front of the boundary and prevents reflection via position control. Regular and irregular waves were created in a numerical wave tank with these boundaries and the wave dissipation performance was quantitatively evaluated by comparing the estimates for incident and reflected waves, the time-series waveform, and the wave spectrum.

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