Oscillating-water-column wave energy converters and air turbines: A review

Wave energy is substantial as a resource, and its potential to significantly contribute to the existing energy mix has been identified. However, the commercial utilization of wave energy is still very low. This paper reviewed the background of wave energy harvesting technology, its evolution, and the present status of the industry. By covering the theoretical formulations, wave resource characterization methods, hydrodynamics of wave interaction with the wave energy converter, and the power take-off and electrical systems, different challenges were identified and discussed. Solutions were suggested while discussing the challenges in order to increase awareness and investment in wave energy industry as a whole.

https://www.mdpi.com/1996-1073/11/5/1250/pdf

Ocean Wave Energy Converters: Status and Challenges

The level of awareness about ocean wave energy as a viable source of useful energy has been increasing recently. Different concepts and methods have been suggested by many researchers to harvest ocean wave energy. This paper reviews and compares the efficiencies and power performance of different wave energy converters. The types of analyses used in deriving the reported efficiencies are identified, and the stage of the power conversion processes at which the efficiencies were determined is also identified. In order to find a common way to compare the efficiencies of different technologies, the hydrodynamic efficiency in relation to the characteristic width of the wave energy converters and the wave resource potential are chosen in this paper. The results show that the oscillating body systems have the highest ratio in terms of the efficiency per characteristic width, and overtopping devices have the lowest. In addition, with better understanding of the devices’ dynamics, the efficiencies of the newer oscillating water column and body systems would increase as the potential wave energy level increases, which shows that those newer designs could be suitable for more potential locations with large variations in wave energy potentials. At last, discussion about the cost of ocean wave energy is presented as well.

https://www.mdpi.com/1996-1073/12/22/4329/pdf

Review on Power Performance and Efficiency of Wave Energy Converters

In the past twenty years, the use of wave energy systems has significantly increased, generally depending on the oscillating water column (OWC) concept. Wells turbine is one of the most efficient OWC technologies. This article provides an updated and a comprehensive account of the state of the art research on Wells turbine. Hence, it draws a roadmap for the contemporary challenges which may hinder future reliance on such systems in the renewable energy sector. In particular, the article is concerned with the research directions and methodologies which aim at enhancing the performance and efficiency of Wells turbine. The article also provides a thorough discussion of the use of computational fluid dynamics (CFD) for performance modeling and design optimization of Wells turbine. It is found that a numerical model using the CFD code can be employed successfully to calculate the performance characteristics of W-T as well as other experimental and analytical methods. The increase of research papers about CFD, especially in the last five years, indicates that there is a trend that considerably depends on the CFD method.

/pdf/wells-turbine-for-wave-energy-conversion-a-review-3rjmhrk92o.pdf

Wells turbine for wave energy conversion: a review

Hydrodynamic performance of a pile-supported OWC breakwater: An analytical study

This paper presents the characteristics of wave conditions, wave energy absorption, response of hull-motion and wave height dissipation based on the results of the open sea tests. 0.5–1.0m of significant wave height and 6–7 seconds of significant wave period appear the most predominant, and average wave energy is estimated 4.88kW/m around the test site. Average power output for the test is approximately 6kWh and the maximum total energy efficiency is around 15% that is ranging from 6–7 seconds of significant wave period. Slow drift oscillation of hull was observed motion in surge, sway and yaw and the value of its amplitude almost equal to estimated values in design stage. Then the mean value of transmission coefficient is about 0.8 under 8.0 seconds of significant wave period. We are considering that the results of the tests should be useful for optimum design of an offshore floating type wave power device.Copyright © 2002 by ASME

The Open Sea Tests of the Offshore Floating Type Wave Power Device “Mighty Whale”: Performance of the Prototype

The Offshore Floating Type Wave Power Device ”Mighty Whale” Open Sea Tests – Environmental Conditions –

PROBLEM TO BE SOLVED: To quickly restrain shake of a suspension frame of a floating crane at the time of waving SOLUTION: A damper 17 is installed on a suspension frame 12 suspended from the extreme end of a jib 10 of a floating crane 16 The damper 17 is constituted so that a weight 24 is reciprocated in the horizontal direction by drive of an actuator A first accelerometer 18 is fitted to the extreme end of the jib 10, and a second accelerometer 19 is fitted to the suspension frame 12 A control device 20 sending a drive command to the actuator of the damper 17 based on the detected signals of the first accelerometer 18 and the second accelerometer 19 is provided A constant setter adding a signal based on the phase difference between the displacement of the extreme end of the jib 10 and the displacement of the suspension frame 12 to a drive command is provided

Suspension frame shake preventing device for floating crane

PROBLEM TO BE SOLVED: To enable small force to suppress a rolling generated in a float struc ture. SOLUTION: A horizontal stage 14 is installed in a top part of a tower 13 vertically provided on a main hull 1. A solid mass is set up on the stage 14 capable of performing a reciprocating motion in the horizontal direction. A shake generated in the main hull 1 is transmitted to the solid mass through a tower 13, kinetic energy of the solid mass, generated in a high lift position, is transmitted to the main hull 1 through the tower 13, so as to suppress the shake of the main hull 1 by small force.

Antirolling device for float structure

PURPOSE:To improve the safety and efficiency of operation by reducing the heaving of a hull in which the operation is carried out under the stopped condition on the ocean. CONSTITUTION:Antiheaving tanks 2 are provided on the bow and stern of a hull 1. A duct 6 provided on the sidewall of the antiheaving tank 2 is opened to the lower portion of a side shell plate 3 so that the sea water can freely come in and out of the tank 2. Also, the antiheaving tank 2 is provided on the upper portion with an opening 7 through which air comes in and out. When the hull 1 heaves, the phase of the pitch of the sea water in the tank 2 is adapted to deviate from that of the hull 1, so that large damping force is generated and thereby an opening area A0 of the duct 6 in the pitch of the hull 1 is adjusted by a slide type regulator 8.

Seiya Yamashita

Papers

The Open Sea Tests of the Offshore Floating Type Wave Power Device “Mighty Whale”: Performance of the Prototype

The Offshore Floating Type Wave Power Device ”Mighty Whale” Open Sea Tests – Environmental Conditions –

Suspension frame shake preventing device for floating crane

Antirolling device for float structure

Hull heaving reducing device