The Spring-Like Air Compressibility Effect in OWC Wave Energy Converters: Hydro-, Thermo- and Aerodynamic Analyses

2018 ◽  
Author(s):  
António F. O. Falcão ◽  
João C. C. Henriques
Keyword(s):  
Wave Energy ◽  
Process Model ◽  
Wave Theory ◽  
Theoretical Models ◽  
Irregular Waves ◽  
Power Performance ◽  
Floating Structure ◽  
Wells Turbine ◽  
Compressibility Effect ◽  
Linear Water Wave Theory

The oscillating-water-column (OWC) wave energy converter consists of a hollow (fixed or floating) structure, open to the sea below the water surface. Wave action alternately compresses and decompresses the air trapped above the inner water free-surface, which forces air to flow through a turbine coupled to a generator. The spring-like effect of air compressibility in the chamber is related to the density-pressure relationship. It is known to significantly affect the power performance of the full-sized converter, and is normally not accounted for in model testing at reduced scale. Three theoretical models of increasing complexity are analysed and compared: (i) the incompressible air model; (ii) the isentropic process model; (iii) and the (more difficult and rarely adopted) adiabatic non-isentropic process model in which losses due to the imperfectly efficient turbine are accounted for. The air is assumed as a perfect gas. The hydrodynamic modelling of wave energy absorption is based on linear water wave theory. The validity of the various simplifying assumptions, especially in the aero-thermodynamic domain, is examined and discussed. The validity of the three models is illustrated by a case study with numerical results for a fixed-structure OWC equipped with a Wells turbine subject to irregular waves.

scholarly journals BREAKWATER ARMOR DISPLACEMENT THRESHOLDS: A POSSIBLE CORRELATION WITH CUMULATIVE WAVE ENERGY

1984 ◽  
Vol 1 (19) ◽  
pp. 186
Author(s):  
Daniel L. Behnke ◽  
Frederic Raichlen
Keyword(s):  
Wave Energy ◽  
Wave Train ◽  
Wave Length ◽  
Simple Wave ◽  
Wave Theory ◽  
Irregular Waves ◽  
Reconstruction Technique ◽  
Regular Wave ◽  
Regular Waves ◽  
Three Dimensional Model

An extensive program of stability experiments in a highly detailed three-dimensional model has recently been completed to define a reconstruction technique for a damaged breakwater (Lillevang, Raichlen, Cox, and Behnke, 1984). Tests were conducted with both regular waves and irregular waves from various directions incident upon the breakwater. In comparison of the results of the regular wave tests to those of the irregular wave tests, a relation appeared to exist between breakwater damage and the accumulated energy to which the structure had been exposed. The energy delivered per wave is defined, as an approximation, as relating to the product of H2 and L, where H is the significant height of a train of irregular waves and L is the wave length at a selected depth, calculated according to small amplitude wave theory using a wave period corresponding to the peak energy of the spectrum. As applied in regular wave testing, H is the uniform wave height and L is that associated with the period of the simple wave train. The damage in the model due to regular waves and that caused by irregular waves has been related through the use of the cumulative wave energy contained in those waves which have an energy greater than a threshold value for the breakwater.

Analysis of Wave Action Through Multiple Submerged Porous Structures

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Mohamin B. M. Khan ◽  
Harekrushna Behera
Keyword(s):  
Wave Energy ◽  
Structural Parameters ◽  
Wave Interaction ◽  
Expansion Method ◽  
Wave Theory ◽  
Rigid Wall ◽  
Porous Structures ◽  
Wave Trapping ◽  
Linear Water Wave Theory ◽  
Multiple Structures

Abstract Wave interaction with multiple bottom-standing rectangular porous structures of different structural parameters is numerically modeled using the multidomain boundary element method and the matched eigenfunction expansion method, while assuming linear water wave theory. The sensitivity of wave reflection and transmission to the wave and structural parameters is analyzed with the objective to maximize wave energy attenuation. Different configurations of multiple structures are tested for maximizing the efficiency of dissipation. Furthermore, wave trapping by multiple porous structures near a sloping rigid wall is studied. Bragg resonance is observed in the case of wave scattering by multiple structures irrespective of wave and structural parameters and is found as proportional to the number of structures deployed. In addition, the study reveals that in the presence of multiple structures, due to more wave energy dissipation, wave transmission in the lee side of the structures is reduced significantly when compared with that observed for a single structure.

scholarly journals Evaluation of the energy extraction of a small-scale wave energy converter

RBRH ◽  
2019 ◽  
Vol 24 ◽  
Author(s):  
Carla de Abreu D’Aquino ◽  
Cesar Cataldo Scharlau ◽  
Leonardo Casagrande Dalla Vecchia
Keyword(s):  
Wave Energy ◽  
Electric Energy ◽  
Wave Theory ◽  
Small Scale ◽  
Linear Wave ◽  
Energy Extraction ◽  
Wells Turbine ◽  
Global Challenge ◽  
Integrated Devices ◽  
Main Components

ABSTRACT This work aims to focus on proposals that could stimulate the development of small scale integrated devices for the global challenge to provide electric energy from renewable alternative resources without major interventions. It presents an evaluation of a small-scale wave energy extraction system that can be installed in marine near shore structures, such as fishing piers. The system is characterized by a small oscillating-water-column (OWC) converter composed by tubes tied to the pillars of the structure. A mathematical model of the OWC device was developed. The model relies on two main components. The first uses linear wave theory to describe the water level variation inside the tube as a result of a wave passing by. The second considers the air flux converted to mechanical torque using Wells turbine equations. The simulations were carried out for different water depths and wave parameters, to evaluate the ratio between the input and output energy throughout the year. For the case study presented in this paper, the performance would be better as long as the device is placed in a position where the waves are less influenced by the bottom friction, but it still has the necessary increment of the wave height.

Experimental Study of the WEPTOS Wave Energy Converter

2012 ◽  
Author(s):  
Arthur Pecher ◽  
Jens Peter Kofoed ◽  
Tommy Larsen ◽  
Tanguy Marchalot
Keyword(s):  
Experimental Study ◽  
Wave Energy ◽  
Wave Energy Converter ◽  
Power Performance ◽  
Energy Converter ◽  
Floating Structure ◽  
Incoming Wave ◽  
Novel Device ◽  
The North ◽  
Energy Absorbing

This paper presents the power performance results of the experimental study of the WEPTOS wave energy converter (WEC). This novel device combines an established and efficient wave energy absorbing mechanism with an adjustable structure that can regulate the amount of incoming wave energy and reduce loads in extreme wave conditions. This A-shaped floating structure absorbs the energy in the waves through a multitude of rotors, the shape of which is based on the renowned Salter’s Duck. These rotors pivot around a common axle, one for each leg of the structure, to which the rotors transfer the absorbed wave energy and which is connected to a common power take off system (one for each leg). The study investigates the performance of the device in a large range of wave states and estimates the performance in terms of mechanical power available to the power take off system of the WEPTOS WEC for two locations of interest. These are a generic offshore location in the Danish part of the North Sea (Point 3) and the location of the Danish wave energy centre (DanWEC) in front of Hanstholm harbour.

scholarly journals A Literature Review of Wave-Induced Heave Motion of Floating Structures

2018 ◽  
Vol 2 (1) ◽  
Author(s):  
Jia qi Xue
Keyword(s):  
Wave Theory ◽  
Body Motion ◽  
Irregular Waves ◽  
Floating Body ◽  
Superposition Method ◽  
Regular Waves ◽  
Floating Structure ◽  
Floating Structures ◽  
Heave Motion ◽  
Wave Induced

This paper provides comprehensive review on heave motion of rigid floating structure due to wave impacts. To specify and explain the structure response, this review firstly provides a brief introduction on ocean sea wave theory, floating structure motion interpretation. Then the floating body motion in regular waves was demonstrated using a superposition method of the oscillated motion in still water and the restrained motion in waves. Meanwhile, added mass and damping coefficient, these two frequency-dependent terms are brought into discussion to generate the motion response with given wave amplitude, which is known for response amplitude operator( RAO). Based on the study in regular waves, RAO of floating structure in irregular waves is introduced while no longer in time domain but in frequency domain. The whole review covers the literatures from the early 1980s up to nowadays, based on the review, it is recommended that more experimental work regarding to frequency characteristic and relative response of larger floating body should be carried out to improve the accuracy of this method.

Experimental Investigation vs Numerical Simulation of the Dynamic Response of a Moored Floating Structure to Waves

2014 ◽  
Author(s):  
Daniele Dessi ◽  
Sara Siniscalchi Minna
Keyword(s):  
Dynamical Behavior ◽  
Irregular Waves ◽  
Mooring Line ◽  
Floating Structure ◽  
Mooring Lines ◽  
Wave Energy Converters ◽  
Time Histories ◽  
Actual Configuration ◽  
Proper Orthogonal ◽  
Dynamic Wave

A combined numerical/theoretical investigation of a moored floating structure response to incoming waves is presented. The floating structure consists of three bodies, equipped with fenders, joined by elastic cables. The system is also moored to the seabed with eight mooring lines. This corresponds to an actual configuration of a floating structure used as a multipurpose platform for hosting wind-turbines, aquaculture farms or wave-energy converters. The dynamic wave response is investigated with numerical simulations in regular and irregular waves, showing a good agreement with experiments in terms of time histories of pitch, heave and surge motions as well as of the mooring line forces. To highlight the dynamical behavior of this complex configuration, the proper orthogonal decomposition is used for extracting the principal modes by which the moored structure oscillates in waves giving further insights about the way waves excites the structure.

Comparisons of Simulation Methods for Motions of a Moored Body in Waves

1985 ◽  
Vol 107 (1) ◽  
pp. 34-41
Author(s):  
M. Takagi ◽  
K. Saito ◽  
S. Nakamura
Keyword(s):  
Wave Theory ◽  
Simulation Methods ◽  
Convolution Integral ◽  
Linear Water Wave Theory ◽  
Initial Stage ◽  
Constant Coefficients ◽  
Exciting Forces ◽  
Linear Differential ◽  
Experimental Values ◽  
The Time Domain

Based on the linear water wave theory, numerical simulations are carried out for motions in waves of a body moored by a nonlinear-type mooring system. Numerical results obtained by using the equation of motion described in the time domain with a convolution integral (C.I. method) are compared with those of the second-order linear differential equation with constant coefficients (C. C. method). These results are also compared with experimental values measured from the initial stage when the action of exciting forces starts and the validity of C.I. method is discussed.

A modified Wells turbine for wave energy conversion

2003 ◽  
Vol 28 (1) ◽  
pp. 79-91 ◽  
Author(s):  
T. Setoguchi ◽  
S. Santhakumar ◽  
M. Takao ◽  
T.H. Kim ◽  
K. Kaneko
Keyword(s):  
Energy Conversion ◽  
Wave Energy ◽  
Wave Energy Conversion ◽  
Wells Turbine
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