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.

A Comparison of Self-Rectifying Turbines for OWC Based Wave Energy Power Extracting Device Using Numerical Simulation

2002 ◽  
Author(s):  
A. R. Ansari ◽  
H. B. Khaleeq ◽  
A. Thakker
Keyword(s):  
Numerical Simulation ◽  
Wave Energy ◽  
Sea Water ◽  
Time History ◽  
Flow Conditions ◽  
Wells Turbine ◽  
Impulse Turbine ◽  
Simulation Techniques ◽  
Simple Geometry ◽  
Wide Range

This paper presents a comparison of self-rectifying turbines for the Oscillating Water Column (OWC) based Wave Energy power extracting device using numerical simulation. The two most commonly used turbines for OWC based devices, the Impulse and the Wells turbines were evaluated under real sea simulated conditions. Assuming the quasi-steady condition, experimental data for both 0.6m turbines with 0.6 hub to tip ratio was used to predict their behavior under real sea conditions. The real sea water surface elevation time history data was used to simulate the flow conditions using standard numerical simulation techniques. A simple geometry of the OWC was considered for the simulation. The results show that the overall mean performance of an Impulse turbine is better than the Wells turbine under unsteady, irregular real sea conditions. The Impulse turbine was observed to be more stable over a wide range of flow conditions. This paper reports the comparison of performance characteristics of both these turbines under simulated real sea conditions.

Numerical Studies of a Floating Cylindrical OWC WEC

2012 ◽  
Author(s):  
Wanan Sheng ◽  
Anthony Lewis ◽  
Raymond Alcorn
Keyword(s):  
Numerical Simulation ◽  
Water Column ◽  
Wave Energy ◽  
Water Surface ◽  
Mechanical Energy ◽  
Hydrodynamic Performance ◽  
Coupling Effects ◽  
Energy Devices ◽  
Power Extraction ◽  
Device Development

Oscillating water column (OWC) wave energy converters (WECs) are a popular type of wave energy devices. Generally, the OWC WECs have a simple structure and working principle, but with a high conversion efficiency, and a high reliability in power take-off due to a small torque and a high rotation speed for a certain power extraction. The OWC devices convert wave energy into pneumatic energy primarily by producing the pressured and de-pressured air (pneumatic energy) in the air chamber through the motions of the interior water surface in the water column. Conventionally, the pneumatic energy is converted into mechanical energy through an air turbine (in small scaled model, an orifice or porous membrane material is used for non-linear or linear power take-off modelling). However, these processes are very limitedly understood due to the complexities of the hydrodynamics, aerodynamics, and thermodynamics and their coupling effects. Theoretical and numerical attempts are very limited, especially when the coupling effects are included. As a result of the difficulties, in the device development, the most popular and acceptable approach may be the model tests, with different scaling factors in their corresponding development stages, as recommended by the relevant wave energy development protocols. To reduce the dependencies on the physical modelling in the OWC device development, numerical methods are very desirable to accommodate the simulation and assessment of the hydrodynamic and aerodynamic/thermodynamic performances of the OWC WECs. This is the main target of this investigation. In this numerical simulation, the hydrodynamic performances (including the motions of the structure and the interior water surface in waves) are carried out by employing a conventional boundary element method (i.e., WAMIT in this case) in frequency domain. To include the effects of the airflow passing through an orifice, its aerodynamic performance is much simplified by assuming its effects on the hydrodynamic performance through some extra damping coefficients to the motions of the floating structure and to the motion of the interior water surface. In this way, the interior water surface response can be obtained for the coupling effects of the hydrodynamics and aerodynamics of the OWC WEC. In this regard, an important issue in the numerical simulation is to seek an appropriate representation of the damping levels.

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.

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.

scholarly journals Performance Analysis of Surface Reconstruction Algorithms in Vertical Scanning Interferometry Based on Coherence Envelope Detection

Micromachines ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 164
Author(s):  
Dongxu Wu ◽  
Fusheng Liang ◽  
Chengwei Kang ◽  
Fengzhou Fang
Keyword(s):  
Surface Reconstruction ◽  
Measurement Accuracy ◽  
Experimental Studies ◽  
Reconstruction Algorithm ◽  
Low Noise ◽  
Surface Measurement ◽  
Reconstruction Algorithms ◽  
Centroid Method ◽  
Envelope Detection ◽  
Vertical Scanning Interferometry

Optical interferometry plays an important role in the topographical surface measurement and characterization in precision/ultra-precision manufacturing. An appropriate surface reconstruction algorithm is essential in obtaining accurate topography information from the digitized interferograms. However, the performance of a surface reconstruction algorithm in interferometric measurements is influenced by environmental disturbances and system noise. This paper presents a comparative analysis of three algorithms commonly used for coherence envelope detection in vertical scanning interferometry, including the centroid method, fast Fourier transform (FFT), and Hilbert transform (HT). Numerical analysis and experimental studies were carried out to evaluate the performance of different envelope detection algorithms in terms of measurement accuracy, speed, and noise resistance. Step height standards were measured using a developed interferometer and the step profiles were reconstructed by different algorithms. The results show that the centroid method has a higher measurement speed than the FFT and HT methods, but it can only provide acceptable measurement accuracy at a low noise level. The FFT and HT methods outperform the centroid method in terms of noise immunity and measurement accuracy. Even if the FFT and HT methods provide similar measurement accuracy, the HT method has a superior measurement speed compared to the FFT method.

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