Wave Prediction and Robust Control of Heaving Wave Energy Devices for Irregular Waves

2011 ◽  
Vol 26 (2) ◽  
pp. 627-638 ◽  
Author(s):  
Marco P. Schoen ◽  
Jørgen Hals ◽  
Torgeir Moan
Keyword(s):  
Robust Control ◽  
Wave Energy ◽  
Irregular Waves ◽  
Energy Devices ◽  
Wave Prediction

scholarly journals Discrete control of resonant wave energy devices

2012 ◽  
Vol 370 (1959) ◽  
pp. 288-314 ◽  
Author(s):  
A. H. Clément ◽  
A. Babarit
Keyword(s):  
Wave Energy ◽  
Control Strategies ◽  
Optimal Operation ◽  
Irregular Waves ◽  
Discrete Control ◽  
Continuous Control ◽  
Sea Waves ◽  
Energy Devices ◽  
Resonant Wave ◽  
Marginal Improvement

Aiming at amplifying the energy productive motion of wave energy converters (WECs) in response to irregular sea waves, the strategies of discrete control presented here feature some major advantages over continuous control, which is known to require, for optimal operation, a bidirectional power take-off able to re-inject energy into the WEC system during parts of the oscillation cycles. Three different discrete control strategies are described: latching control, declutching control and the combination of both, which we term latched–operating–declutched control. It is shown that any of these methods can be applied with great benefit, not only to mono-resonant WEC oscillators, but also to bi-resonant and multi-resonant systems. For some of these applications, it is shown how these three discrete control strategies can be optimally defined, either by analytical solution for regular waves, or numerically, by applying the optimal command theory in irregular waves. Applied to a model of a seven degree-of-freedom system (the SEAREV WEC) to estimate its annual production on several production sites, the most efficient of these discrete control strategies was shown to double the energy production, regardless of the resource level of the site, which may be considered as a real breakthrough, rather than a marginal improvement.

Experimental Studies of a Floating Cylindrical OWC WEC

2012 ◽  
Author(s):  
Wanan Sheng ◽  
Brian Flannery ◽  
Anthony Lewis ◽  
Raymond Alcorn
Keyword(s):  
Model Test ◽  
Wave Energy ◽  
Water Surface ◽  
Sea Water ◽  
Experimental Studies ◽  
Irregular Waves ◽  
Surface Measurement ◽  
Impulse Turbine ◽  
High Rotational Speed ◽  
Energy Devices

Oscillating water column (OWC) wave energy converters (WECs) are a popular type of wave energy devices, due to their advantages over many other WECs. For example, OWC WECs normally have no moving components in sea water, and have a small torque and a high rotational speed for a certain power take-off. Practically, some foundation-type pioneer plants of OWC WECs have been very successful in generating electricity to grids continuously. In order to obtain higher yields of wave energy production, it is proposed to move the OWC WECs to open and deep water regions, and for the purposes of economics and reliability, the OWC WECs are designed to be floating devices, with a potential of utilizing the device motions to improve wave energy conversion capacity. To further understand the OWC WEC performances in waves, a floating cylindrical OWC has been designed and tested in an ocean wave tank. In the model test, five different size orifices are designed to represent different damping levels of the air flow. In the experimental study, a systematic series of tests in both regular and irregular waves has been conducted to help understand the hydrodynamics and aerodynamics of the generic OWC device. In the model test, the interior water surface motion and the pressure in the air chamber are measured and based on them the primary power take-off by the device can be calculated. Alternatively, the power take-off can be calculated by the pressure measurement only or by the interior water surface measurement only due to the unique relation of the pressure drop and the airflow passing through the orifices. In addition, in the experiment, the motions of the floating structure have also been measured, from which it is possible to correlate the motions and the wave energy extraction. As expected, the orifices exhibit a quadratic non-linear relation between pressure and the flowrate. Though simple, the orifice power take-off system may exhibit a similar flow feature to that of an impulse turbine, thus an appropriate model to the impulse turbine.

scholarly journals Dynamic Response of Coupled Mooring Lines and Floating Wave Energy Devices in Waves / Currents

2019 ◽  
Vol 8 (12) ◽  
pp. 5539-5545
Keyword(s):  
Renewable Energy ◽  
Dynamic Response ◽  
Wave Energy ◽  
Degrees Of Freedom ◽  
Ocean Waves ◽  
Irregular Waves ◽  
Mooring Lines ◽  
Energy Devices ◽  
Six Degrees Of Freedom ◽  
The Government

Various global studies have shown that ocean waves energy have large potential in renewable energy sector. Their role within renewable energy gets high priority in the future by the government of United Kingdom. The principle concept of wave energy is when wave energy is converted into potential energy by the wave energy devices to generate electricity. An understanding of the dynamic response of the devices and mooring lines is important for this paper. This paper deals with the analysis of the various effects that influence the different design of wave energy converter devices. The mooring design idea is also analyzed to show which mooring layout is suitable to fulfill the requirement. The design of mooring configuration also influence how wave power is extracted and how such system are operated and maintained. The effects investigated in this paper are regular and irregular waves, motion @ six degrees of freedom, maximum and minimum mooring tension, different waves direction, wave current, energy and power take off.

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.

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