scholarly journals The performance of the Mocean M100 wave energy converter described through numerical and physical modelling

2020 ◽  
Vol 3 (1) ◽  
pp. 11-19
Author(s):  
J. Cameron McNatt ◽  
Christopher H. Retzler
Keyword(s):  
Frequency Domain ◽  
Wave Energy ◽  
Time Domain ◽  
Numerical Models ◽  
Average Power ◽  
Physical Modelling ◽  
Wave Energy Converter ◽  
Domain Model ◽  
Energy Converter ◽  
Cost Of Energy

Mocean Energy has designed a 100-kW hinged-raft wave energy converter (WEC), the M100, which has a novel geometry that reduces the cost of energy by improving the ratios of power per size and power per torque. The performance of the M100 is shown through the outputs of frequency-domain and time-domain numerical models, which are compared with those from 1/20th scale wave-tank testing. Results show that for the undamped, frequency-domain model, there are resonant peaks in the response at 6.6 and 9.6 s, corresponding to wavelengths that are 1.9 and 3.7 times longer than the machine. With the inclusion of power-take-off and viscous damping, the power response as a function of frequency shows a broad bandwidth and a hinge flex amplitude of 12-20 degrees per meter of wave amplitude. Comparison between the time-domain model and physical data in a variety of sea states, up to a significant wave height of 4.5 m, show agreements within 10% for average power absorption, which is notable because only simple, nonlinear, numerical models were used. The M100 geometry results in a broad-banded, large amplitude response due to its asymmetric shape, which induces coupling between modes of motion.

scholarly journals A New Bi-Level Optimisation Framework for Optimising a Multi-Mode Wave Energy Converter Design: A Case Study for the Marettimo Island, Mediterranean Sea

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5498 ◽  
Author(s):  
Mehdi Neshat ◽  
Nataliia Y. Sergiienko ◽  
Erfan Amini ◽  
Meysam Majidi Nezhad ◽  
Davide Astiaso Garcia ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Wave Energy ◽  
Average Power ◽  
Wave Energy Converter ◽  
Domain Model ◽  
Energy Converter ◽  
Mode Wave ◽  
Prototype Development ◽  
Cost Of Energy ◽  
Multi Mode

To advance commercialisation of ocean wave energy and for the technology to become competitive with other sources of renewable energy, the cost of wave energy harvesting should be significantly reduced. The Mediterranean Sea is a region with a relatively low wave energy potential, but due to the absence of extreme waves, can be considered at the initial stage of the prototype development as a proof of concept. In this study, we focus on the optimisation of a multi-mode wave energy converter inspired by the CETO system to be tested in the west of Sicily, Italy. We develop a computationally efficient spectral-domain model that fully captures the nonlinear dynamics of a wave energy converter (WEC). We consider two different objective functions for the purpose of optimising a WEC: (1) maximise the annual average power output (with no concern for WEC cost), and (2) minimise the levelised cost of energy (LCoE). We develop a new bi-level optimisation framework to simultaneously optimise the WEC geometry, tether angles and power take-off (PTO) parameters. In the upper-level of this bi-level process, all WEC parameters are optimised using a state-of-the-art self-adaptive differential evolution method as a global optimisation technique. At the lower-level, we apply a local downhill search method to optimise the geometry and tether angles settings in two independent steps. We evaluate and compare the performance of the new bi-level optimisation framework with seven well-known evolutionary and swarm optimisation methods using the same computational budget. The simulation results demonstrate that the bi-level method converges faster than other methods to a better configuration in terms of both absorbed power and the levelised cost of energy. The optimisation results confirm that if we focus on minimising the produced energy cost at the given location, the best-found WEC dimension is that of a small WEC with a radius of 5 m and height of 2 m.

scholarly journals Influence of a Taut Cable on the Performance of a Point-Absorber Wave Energy Converter

2018 ◽  
Author(s):  
R. Wang ◽  
Y. Wei ◽  
M. van Rooij ◽  
B. Jayawardhana ◽  
A. I. Vakis
Keyword(s):  
Frequency Domain ◽  
Wave Energy ◽  
Alternative Energy ◽  
Frequency Domain Analysis ◽  
Wave Energy Converter ◽  
Domain Model ◽  
Energy Harvest ◽  
Energy Converter ◽  
Point Absorber ◽  
Improved Model

In recent years, wave energy converters (WECs) have received considerable attention as an efficient way to harvest alternative energy sources. Within this class of systems, point-absorbers are popular and have become one of the most widely used renewable energy harvest designs all over the world, at least in the preliminary R&D stage, with many relevant research works having been published as well. However, unlike the single buoy and PTO systems which already have a comprehensive research basis, the connection cable has received little attention. The traditional taut cable analysis approach, initiated from the needs of the oil&gas industry, has been applied for WEC investigations. However, this approach utilizes an essential assumption that the oscillating term (PTO force) is much smaller than the static term of the cable force (pre-tension) and could be neglected, which may not be proper for WEC applications. In this work, a conventional frequency domain model is utilized to test and verify the validity of the previously mentioned assumption by presenting the ratio between two force terms. Then the ratio could be applied in combination with sea state contours to reveal the critical state of the cable. Then, a fully nonlinear time domain method of a numerical solution of the point-absorber wave energy converter is presented. According to the critical states obtained from the frequency domain analysis, an improved model of a slack cable is proposed. Its influence on the energy extraction performance is investigated using the open source code — WEC-Sim. This work provides insight into simulating a proper model of the cable and how the design of the cable influences the WEC performance.

Power Take-Off Selection for a U-Shaped OWC Wave Energy Converter

2019 ◽  
Author(s):  
Alessandra Romolo ◽  
João C. C. Henriques ◽  
Luís M. C. Gato ◽  
Giovanni Malara ◽  
Valentina Laface ◽  
...  
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Time Domain ◽  
Wave Energy Converter ◽  
Domain Model ◽  
Ocean Engineering ◽  
Energy Converter ◽  
Natural Period ◽  
Air Pocket ◽  
Air Turbine

Abstract The REWEC3 (Resonant Wave Energy Converter) is a fixed oscillating water column (OWC) wave energy converter (WEC) incorporated in upright breakwaters. The device is composed by a chamber containing a water column in its lower part and an air pocket in its upper part. The air pocket is connected to the atmosphere via a duct hosting a self-rectifying air turbine. In addition, a REWEC3 includes a vertical U-shaped duct for connecting the water column to the open sea (for this reason it is known also as U-OWC). The working principle of the system is quite simple: by the action of the incident waves, the water inside the U-shaped duct is subject to a reciprocating motion, which induces alternately a compression and an expansion of the air pocket. The pressure difference between the air pocket and the atmosphere is used to drive an air turbine coupled to an off-the-shelf electrical generator connected to the grid. The main feature of the REWEC3 is the possibility of tuning the natural period of the water column in order to match a desired wave period through the size of the U-duct. The REWEC3 technology has been theoretically developed by Boccotti, later tested at the natural basin of the Natural Ocean Engineering Laboratory (NOEL, Italy), and finally proved at full scale with REWEC3 prototype built in the Port of Civitavecchia (Rome, Italy). The objective of this paper is to select and optimize a turbine/generator set of a U-shaped OWC installed in breakwaters located in the Mediterranean Sea, such as the Port of Civitavecchia, where the first prototype of REWEC3 has been realized, or the Port of Salerno or Marina delle Grazie of Roccella (Italy). The computations were performed using a time domain model based on the unsteady Bernoulli equation. Based on the time-domain model of the power plant, the following data is computed for the turbines: i) the ideal turbine diameter; ii) the generator feedback control law aiming to maximize the turbine power output for turbine coupled to the REWEC3 device for Mediterranean applications.

scholarly journals Design and Simulation of a Novel Mechanical Power Take-Off for a Two-Body Wave Energy Point Absorber

2018 ◽  
Author(s):  
Xiaofan Li ◽  
Chien-An Chen ◽  
Qiuchi Xiong ◽  
Robert Parker ◽  
Lei Zuo
Keyword(s):  
Frequency Domain ◽  
Output Power ◽  
Wave Energy ◽  
Time Domain ◽  
Wave Energy Converter ◽  
Mechanical Power ◽  
Total Output ◽  
Test Machine ◽  
Mechanical Motion ◽  
Energy Converter

In this paper, a two-body self-react wave energy converter with a novel mechanical Power Take-off (PTO) is introduced. The PTO rectifies the mechanical motion and regulates the flow with a mechanism called Mechanical Motion Rectifier (MMR), which converts the reciprocating motion of the ocean wave into unidirectional rotation of the generator. The overall system is analyzed in both time and frequency domain. In time domain, the piecewise non-linear dynamic model of the MMR PTO is derived, and parameters that could significantly influence the MMR property is extracted. By building the model into WEC-Sim, a time domain wave energy converter (WEC) simulation tool, to simulate and evaluate the performance of the PTO. In addition, the system is modelled as a two-body vibration system for frequency domain analysis in order to further investigate and optimize the proposed wave energy converter. The tunable parameters within the system, including the equivalent mass, the equivalent damping coefficient, and the PTO stiffness, are discussed based on the criteria of maximization of the total output power. To verify the theoretical analysis, a bench test prototype is developed and tested on a hydraulic test machine. The experimental results in line with the derived model and can be used for reasonable estimation on the output power of the proposed system in real ocean conditions.

Development of Control Strategies for Interconnected Pneumatic Wave Energy Converters

2017 ◽  
Author(s):  
Eric Thacher ◽  
Helen Bailey ◽  
Bryson Robertson ◽  
Scott Beatty ◽  
Jason Goldsworthy ◽  
...  
Keyword(s):  
Wave Energy ◽  
Time Domain ◽  
Power Output ◽  
Numerical Models ◽  
Control Strategies ◽  
Low Cost ◽  
Optimization Procedure ◽  
Wave Energy Converter ◽  
Energy Converter ◽  
Sea State

In the field of wave energy converter control, high fidelity numerical models have become the predominant tool for the development of accurate and comprehensive control strategies. In this study, a numerical model of a novel wave energy converter, employing a pneumatic power take-off, is created to provide a low-cost method for the development of a power-maximizing control strategy. Device components and associated architectures are developed in the time domain solvers Proteus DS and MATLAB/Simulink. These two codes are dynamically coupled at run time to produce a complete six degree of freedom, time domain simulation of the converter. Utilizing this numerical framework, a genetic algorithm optimization procedure is implemented to optimally select eight independent parameters governing the PTO geometry. Optimality is measured in terms of estimated annual energy production at a specific deployment location off the West Coast of Canada. The optimization exercise is one layer of PTO force control — the parameters selected are seen to provide significant improvements in the annual power output, while also smoothing the WEC power output on both a sea-state by sea-state and wave-by-wave basis.

Methodology for Performance Assessment of a Two-Body Heave Wave Energy Converter

2013 ◽  
Author(s):  
Adrian de Andrés ◽  
Raúl Guanche ◽  
José A. Armesto ◽  
Fernando del Jésus ◽  
César Vidal ◽  
...  
Keyword(s):  
Time Series ◽  
State Space ◽  
Wave Energy ◽  
Time Domain ◽  
Classical Method ◽  
Power Production ◽  
Wave Energy Converter ◽  
Domain Model ◽  
Energy Converter

A wave energy farm composed by several two-body heaving wave energy converters is being developed by IH Cantabria. This study presents a methodology to obtain the power performance of an isolated two-body heaving wave energy converter, previously presented and analyzed by [1]. The methodology relies on a numerical model which represents the motion of the two bodies in the time domain. This time domain model has been built substituting the entire Cummins equation system with a state-space system, thereby avoiding the convolution integral of the radiation force term with a state-space subsystem, previously used in [2] and [3]. The performance of the device along its life cycle has been estimated based on a proposed new methodology. The new method is proposed in order to obtain the long term power production of a device with the same computational effort than the classical method based on the power matrix. The proposed method is able to estimate long term power production time series. This long time series is obtained using the MaxDiss selection technique from [4] in order to compute only the power of the most representative sea states and the Radial Basis Function interpolation technique (RBF) to obtain the complete power series.

Time Domain Modeling and Power Output for a Heaving Point Absorber Wave Energy Converter

2014 ◽  
Author(s):  
Jeremiah Pastor ◽  
Yucheng Liu
Keyword(s):  
Frequency Domain ◽  
Wave Energy ◽  
Time Domain ◽  
Power Output ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Wave Energy Converter ◽  
Energy Converter ◽  
Power Absorption ◽  
Point Absorber

This paper presents, assesses, and optimizes a point absorber wave energy converter (WEC) through numerical modeling, simulation, and analysis in time domain. Wave energy conversion is a technology especially suited for assisting in power generation in the offshore oil and gas platforms. A linear frequency domain model is created to predict the behavior of the heaving point absorber WEC system. The hydrodynamic parameters are obtained with AQWA, a software package based on boundary element methods. A linear external damping coefficient is applied to enable power absorption and an external spring force is introduced to tune the point absorber to the incoming wave conditions. The external damping coefficient and external spring forces are the control parameters, which need to be optimized to maximize the power absorption. Two buoy shapes are tested and a variety of diameters and drafts are compared. Optimal shape, draft, and diameter of the model are then determined to maximize its power absorption capacity. Based on the results generated from the frequency domain analysis, a time domain analysis was also conducted to derive the responses of the WEC in the hydrodynamic time response domain. The time domain analysis results allowed us to estimate the power output of this WEC system.

scholarly journals Sensitivity of a Wave Energy Converter Dynamics Model to Nonlinear Hydrostatic Models

2015 ◽  
Author(s):  
Ryan G. Coe ◽  
Diana L. Bull
Keyword(s):  
Linear Model ◽  
Wave Energy ◽  
Three Dimensional ◽  
Wave Energy Converter ◽  
Domain Model ◽  
Interpolation Model ◽  
Surface Integral ◽  
Energy Converter ◽  
Motion Constraints ◽  
Large Improvement

A three dimensional time-domain model, based on Cummins equation, has been developed for an axisymmetric point absorbing wave energy converter (WEC) with an irregular cross section. This model incorporates a number of nonlinearities to accurately account for the dynamics of the device: hydrostatic restoring, motion constraints, saturation of the power-take-off force, and kinematic nonlinearities. Here, an interpolation model of the hydrostatic restoring reaction is developed and compared with a surface integral based method. The effects of these nonlinear hydrostatic models on device dynamics are explored by comparing predictions against those of a linear model. For the studied WEC, the interpolation model offers a large improvement over a linear model and is roughly two orders-of-magnitude less computationally expensive than the surface integral based method.

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