On the Numerical Modelling of the Non Linear Behaviour of a Wave Energy Converter

2009 ◽  
Author(s):  
Aure´lien Babarit ◽  
Hakim Mouslim ◽  
Alain Cle´ment ◽  
Pauline Laporte-Weywada
Keyword(s):  
Wave Energy ◽  
Numerical Models ◽  
Computation Time ◽  
Wave Energy Converter ◽  
Linear Potential ◽  
Energy Converter ◽  
Wave Energy Converters ◽  
Cfd Models ◽  
Linear Potential Theory ◽  
Energy Converters

Wave energy converters of the wave activated body class are designed to have large amplitudes of motion, even in moderate sea states, because their efficiency is directly related with the amplitude of their motion. Hence, classical seakeeping numerical tools based on linear potential theory, which are widely used in the design process of offshore structures, are not accurate enough in the case of wave energy conversion. So, large differences between numerical predictions and wave tank experiments are often observed. On the other hand, the use of CFD models theoretically able to provide more accurate results is still difficult for wave energy applications, mainly because this requires a huge computation time. Moreover, it is well known that viscous solver have difficulties in propagatating gravity waves accurately. In this paper, we assess the potential of two advanced hydro-dynamic numerical models in the numerical modelling of wave energy converters. These numerical models are expected to provide more accurate results than classical linear theory based numerical models and faster results than CFD models. Particularly, these tools are expected to be able to deal efficiently with large motions of wave energy converters. In the first one, the hydrostatic forces and the Froude-Krylov forces are computed on the exact wetted surface of the wave energy converter, whereas radiation and diffraction forces are computed using the standard linear potential theory. Using this model, it is shown that we were able to predict the parametric roll phenomenon in the case of the SEAREV wave energy converter. In the second one, a Navier Stokes solver, based on RANS equations, is used. Comparisons are made with experiments and it is showed that this tool is able to model quite accurately viscous effects such as slamming. However, computation time is found to be long with this last tool.

Optimization of Mooring Configuration Parameters of Floating Wave Energy Converters

2011 ◽  
Author(s):  
Pedro C. Vicente ◽  
Anto´nio F. O. Falca˜o ◽  
Paulo A. P. Justino
Keyword(s):  
Wave Energy ◽  
Oil And Gas ◽  
Wave Energy Converter ◽  
Domain Model ◽  
Floating Point ◽  
Mooring System ◽  
Energy Converter ◽  
Energy Devices ◽  
Wave Energy Converters ◽  
Energy Converters

Floating point absorbers devices are a large class of wave energy converters for deployment offshore, typically in water depths between 40 and 100m. As floating oil and gas platforms, the devices are subject to drift forces due to waves, currents and wind, and therefore have to be kept in place by a proper mooring system. Although similarities can be found between the energy converting systems and floating platforms, the mooring design requirements will have some important differences between them, one of them associated to the fact that, in the case of a wave energy converter, the mooring connections may significantly modify its energy absorption properties by interacting with its oscillations. It is therefore important to examine what might be the more suitable mooring design for wave energy devices, according to the converters specifications. When defining a mooring system for a device, several initial parameters have to be established, such as cable material and thickness, distance to the mooring point on the bottom, and which can influence the device performance in terms of motion, power output and survivability. Different parameters, for which acceptable intervals can be established, will represent different power absorptions, displacements from equilibrium position, load demands on the moorings and of course also different costs. The work presented here analyzes what might be, for wave energy converter floating point absorber, the optimal mooring configuration parameters, respecting certain pre-established acceptable intervals and using a time-domain model that takes into account the non-linearities introduced by the mooring system. Numerical results for the mooring forces demands and also motions and absorbed power, are presented for two different mooring configurations for a system consisting of a hemispherical buoy in regular waves and assuming a liner PTO.

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.

scholarly journals Initial conceptual demonstration of control co-design for WEC optimization

2020 ◽  
Author(s):  
Ryan G. Coe ◽  
Giorgio Bacelli ◽  
Sterling Olson ◽  
Vincent S. Neary ◽  
Mathew B. R. Topper
Keyword(s):  
Design Optimization ◽  
Wave Energy ◽  
Wave Energy Converter ◽  
Short Paper ◽  
Energy Converter ◽  
Matlab Toolbox ◽  
Wave Energy Converters ◽  
Practical Engineering ◽  
Converter Design ◽  
Energy Converters

While some engineering fields have benefited from systematic design optimization studies, wave energy converters have yet to successfully incorporate such analyses into practical engineering workflows. The current iterative approach to wave energy converter design leads to suboptimal solutions. This short paper presents an open-source MATLAB toolbox for performing design optimization studies on wave energy converters where power take-off behavior and realistic constraints can be easily included. This tool incorporates an adaptable control co-design approach, in that a constrained optimal controller is used to simulate device dynamics and populate an arbitrary objective function of the user's choosing. A brief explanation of the tool's structure and underlying theory is presented. In order to demonstrate the capabilities of the tool, verify its functionality, and begin to explore some basic wave energy converter design relationships, three conceptual case studies are presented. In particular, the importance of considering (and constraining) the magnitudes of device motion and forces is shown.<br>

The Economics of Multi-Axis Point Absorber Wave Energy Converters

2013 ◽  
Author(s):  
Daniel S. Richardson ◽  
George A. Aggidis
Keyword(s):  
Wave Energy ◽  
Performance Comparison ◽  
Linear Potential ◽  
Advantages And Disadvantages ◽  
Point Absorber ◽  
Wave Energy Converters ◽  
Point Absorbers ◽  
Linear Potential Theory ◽  
Economic Comparison ◽  
Energy Converters

This paper examines the economic advantages and disadvantages of multi-axis point absorber wave energy converters in comparison to conventional heave-only point absorbers. A multi-axis point absorber wave energy converter (MA-PAWEC) is classified as a point absorber device that has a power take off (PTO) system extracting energy from more than one mode of motion (e.g. heave and surge). The majority of existing point absorber devices operate in heave mode alone. Therefore the forces exerted along other axes must be resisted by the mooring system, any reciprocal component of which constitutes a wasted opportunity to extract energy. The economics of PAWECs are governed by the available resource, energy generated by the device, capital cost and operational cost. These factors are examined for MA-PAWECs and compared to a generic heave-PAWEC. For a performance comparison, a simple generic body PAWEC is examined under heave mode operation and multi-axis operation in a representative spectrum. The modelling is based on linear potential theory. The potential advantages of MA-PAWECS are identified as greater energy absorption, fewer installed devices for a given capacity, and greater array control. Disadvantages include higher capex, higher maintenance costs and sensitivity to PTO costs. The performance and costs are assigned an estimated economic scaling factor and are applied to a generic heave-PAWEC for an economic comparison of the two devices. This indicates that a multi-axis approach to point absorbers could offer a 21% lower cost of electricity than the incumbent heave-response devices.

Preliminary Cross-Validation of Wave Energy Converter Array Interactions

2013 ◽  
Author(s):  
Matt Folley ◽  
Trevor Whittaker
Keyword(s):  
Numerical Model ◽  
Wave Energy ◽  
Cross Validation ◽  
Wave Energy Converter ◽  
Energy Yield ◽  
Energy Converter ◽  
Wave Energy Converters ◽  
The Cost ◽  
Wave Farm ◽  
Energy Converters

The development of wave energy for utility-scale electricity production requires an understanding of how wave energy converters will interact with each other when part of a wave farm. Without this understanding it is difficult to calculate the energy yield from a wave farm and consequently the optimal wave farm layout and configuration cannot be determined. In addition, the uncertainty in a wave farm’s energy yield will increase the cost of finance for the project, which ultimately increases the cost of energy. Numerical modelling of wave energy converter arrays, based on potential flow, has provided some initial indications of the strength of array interactions and optimal array configurations; however, there has been limited validation of these numerical models. Moreover, the cross-validation that has been completed has been for relatively small arrays of wave energy converters. To provide some validation for large array interactions wave basin testing of three different configurations of up to 24 wave energy converters has been completed. All tests used polychromatic (irregular) sea-states, with a range of long-crested and short-crested seas, to provide validation in realistic conditions. The physical model array interactions are compared to those predicted by a numerical model and the suitability of the numerical and physical models analysed. The results are analysed at three different levels and all provide support for the cross-validation of the two models. The differences between the physical and numerical model are also identified and the implications for improving the modelling discussed.

Constrained Optimal Control of a Heaving Buoy Wave-Energy Converter

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Jørgen Hals ◽  
Johannes Falnes ◽  
Torgeir Moan
Keyword(s):  
Energy Absorption ◽  
Wave Energy ◽  
Optimal Operation ◽  
Wave Energy Converter ◽  
Irregular Waves ◽  
Energy Converter ◽  
Model Predictive Controller ◽  
Wave Energy Converters ◽  
Predictive Controller ◽  
Energy Converters

The question of optimal operation of wave-energy converters has been a key issue since modern research on the topic emerged in the early 1970s, and criteria for maximum wave-energy absorption soon emerged from frequency domain analysis. However, constraints on motions and forces give the need for time-domain modeling, where numerical optimization must be used to exploit the full absorption potential of an installed converter. A heaving, semisubmerged sphere is used to study optimal constrained motion of wave-energy converters. Based on a linear model of the wave-body interactions, a procedure for the optimization of the machinery force is developed and demonstrated. Moreover, a model-predictive controller is defined and tested for irregular sea. It repeatedly solves the optimization problem online in order to compute the optimal constrained machinery force on a receding horizon. The wave excitation force is predicted by use of an augmented Kalman filter based on a damped harmonic oscillator model of the wave process. It is shown how constraints influence the optimal motion of the heaving wave-energy converter, and also how close it is possible to approach previously published theoretical upper bounds. The model-predictive controller is found to perform close to optimum in irregular waves, depending on the quality of the wave force predictions. An absorbed power equal to or larger than 90% of the ideal constrained optimum is achieved for a chosen range of realistic sea states. Under certain circumstances, the optimal wave-energy absorption may be better in irregular waves than for a corresponding regular wave having the same energy period and wave-power level. An argument is presented to explain this observation.

Towards a Definition and Metric for the Survivability of Ocean Wave Energy Converters

2010 ◽  
Author(s):  
Adam Brown ◽  
Robert Paasch ◽  
Irem Y. Tumer ◽  
Pukha Lenee-Bluhm ◽  
Justin Hovland ◽  
...  
Keyword(s):  
Wave Energy ◽  
Energy Content ◽  
Ocean Waves ◽  
Wave Energy Converter ◽  
Ocean Wave ◽  
Energy Converter ◽  
Term Survival ◽  
Wave Energy Converters ◽  
Ocean Wave Energy ◽  
Energy Converters

Survivability is a term that is widely used in the ocean wave energy industry, but the term has never been defined in that context. The word itself seems to have an intrinsic meaning that people understand; this fact often leads to the term’s misuse and its confusion with “reliability”. In order to design systems that are capable of long term survival in the ocean environment, it must be clear what “survivability” means and how it affects the design process and ultimately the device being deployed. Ocean energy is relatively predictable over the span of months, days, and even hours, which makes it very promising as a form of renewable energy. However, the variation of the energy content of ocean waves in a given location is likely high due to the effect of storms and the seasons. Wave energy converters must be built to be reliable while operating and survivable during severe conditions. Therefore, probabilistic design practices must be used to insure reliability and survivability in conditions that are constantly changing. Reliability is used to numerically express the failures of a device that occur while the system is operational, and it is usually expressed in terms of the mean time between failure (MTBF). However, in the context of ocean wave energy converters, the devices are likely to be continuously deployed in conditions that push them beyond their operating limits. During these times it is likely that wave energy converters will be placed in some sort of “survival mode” where the device sheds excess power, reducing system loading. Survivability is focused specifically on failures that occur during these times, when the device is experiencing conditions that surpass its operational limits. Developing a highly survivable wave energy converter is an outstanding goal, but without a standard definition of the term survivability, progress towards that goal cannot be measured. The purpose of this paper is to provide an initial definition for survivability, and to introduce a simple metric that provides an objective comparison of the survivability of varying wave energy converter technologies.

scholarly journals A Study on Electrical Power for Multiple Linear Wave Energy Converter Considering the Interaction Effect

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2964 ◽  
Author(s):  
Qiao Li ◽  
Motohiko Murai ◽  
Syu Kuwada
Keyword(s):  
Wave Energy ◽  
Interference Effect ◽  
Electrical Power ◽  
Wave Energy Converter ◽  
Energy Converter ◽  
Multiple Wave ◽  
Floating Structures ◽  
Wave Energy Converters ◽  
Electrical Generator ◽  
Energy Converters

A linear electrical generator can be used on wave energy converter for converting the kinetic energy of a floating structure to the electricity. A wave farm consists of multiple wave energy converters which equipped in a sea area. In the present paper, a numerical model is proposed considering not only the interference effect in the multiple floating structures, but also the controlling force of each linear electrical generator. In particular, the copper losses in the electrical generator is taken into account, when the electrical power is computed. In a case study, the heaving motions and electrical powers of the multiple wave energy converters are estimated in the straight arrangement and triangle arrangement. In addition, the average electrical power is analyzed in different distances of the floating structures. The aim of this paper is to clear the relationship between the interference effect and electric powers from wave energy converters. This will be useful for deciding the arrangement of multiple wave energy converters.

scholarly journals Initial conceptual demonstration of control co-design for WEC optimization

2020 ◽  
Vol 6 (4) ◽  
pp. 441-449
Author(s):  
Ryan G. Coe ◽  
Giorgio Bacelli ◽  
Sterling Olson ◽  
Vincent S. Neary ◽  
Mathew B. R. Topper
Keyword(s):  
Design Optimization ◽  
Wave Energy ◽  
Wave Energy Converter ◽  
Short Paper ◽  
Energy Converter ◽  
Matlab Toolbox ◽  
Wave Energy Converters ◽  
Practical Engineering ◽  
Converter Design ◽  
Energy Converters

AbstractWhile some engineering fields have benefited from systematic design optimization studies, wave energy converters have yet to successfully incorporate such analyses into practical engineering workflows. The current iterative approach to wave energy converter design leads to sub-optimal solutions. This short paper presents an open-source MATLAB toolbox for performing design optimization studies on wave energy converters where power take-off behavior and realistic constraints can be easily included. This tool incorporates an adaptable control co-design approach, in that a constrained optimal controller is used to simulate device dynamics and populate an arbitrary objective function of the user’s choosing. A brief explanation of the tool’s structure and underlying theory is presented. To demonstrate the capabilities of the tool, verify its functionality, and begin to explore some basic wave energy converter design relationships, three conceptual case studies are presented. In particular, the importance of considering (and constraining) the magnitudes of device motion and forces in design optimization is shown.

scholarly journals Initial conceptual demonstration of control co-design for WEC optimization

2020 ◽  
Author(s):  
Ryan G. Coe ◽  
Giorgio Bacelli ◽  
Sterling Olson ◽  
Vincent S. Neary ◽  
Mathew B. R. Topper
Keyword(s):  
Design Optimization ◽  
Wave Energy ◽  
Wave Energy Converter ◽  
Short Paper ◽  
Energy Converter ◽  
Matlab Toolbox ◽  
Wave Energy Converters ◽  
Practical Engineering ◽  
Converter Design ◽  
Energy Converters

While some engineering fields have benefited from systematic design optimization studies, wave energy converters have yet to successfully incorporate such analyses into practical engineering workflows. The current iterative approach to wave energy converter design leads to suboptimal solutions. This short paper presents an open-source MATLAB toolbox for performing design optimization studies on wave energy converters where power take-off behavior and realistic constraints can be easily included. This tool incorporates an adaptable control co-design approach, in that a constrained optimal controller is used to simulate device dynamics and populate an arbitrary objective function of the user's choosing. A brief explanation of the tool's structure and underlying theory is presented. In order to demonstrate the capabilities of the tool, verify its functionality, and begin to explore some basic wave energy converter design relationships, three conceptual case studies are presented. In particular, the importance of considering (and constraining) the magnitudes of device motion and forces is shown.<br>

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