Floating Wave Energy Device With Two Oscillating Water Columns

2007 ◽  
Author(s):  
D. C. Hong ◽  
S. Y. Hong
Keyword(s):  
Green Function ◽  
Wave Energy ◽  
Numerical Results ◽  
The Body ◽  
Energy Device ◽  
Energy Devices ◽  
Damping Parameter ◽  
Absorbed Power ◽  
Linear Damping ◽  
Drift Force

The absorbed power, motion and drift force of a floating wave energy device with two oscillating water column (OWC) chambers are studied taking account of the interaction between two chambers within the scope of the linear wave theory. The oscillating surface-pressure in the OWC chamber is represented by a product of the air-flow velocity and an equivalent linear damping parameter. The two-dimensional potential problem is formulated as a hybrid Green integral equation using the Rankine Green function inside the chamber and the finite-depth free-surface Green function outside respectively. The present numerical method makes it possible to tune the OWC and the floating body motions to the incident waves that is essential to maximize the absorbed power. The absorbed powers are calculated by both the near-field and far-field methods for various values of the linear damping parameter in two chambers. The reflection and transmission coefficients of the body are also presented. The numerical results for one OWC devices where the OWC is placed in a backward and forward bent duct buoys (BBDB and FBDB) are also presented for comparison of the performance. The present floating wave energy devices can also be served as a good floating breakwater having small drift force. The present numerical results show that the existence of reverse time-mean horizontal wave drift force is not contradictory to the principle of wave energy conservation.

scholarly journals Wave energy devices with compressible volumes

2014 ◽  
Vol 470 (2172) ◽  
pp. 20140559 ◽  
Author(s):  
Adi Kurniawan ◽  
Deborah Greaves ◽  
John Chaplin
Keyword(s):  
Wave Energy ◽  
The Body ◽  
Period Range ◽  
Energy Devices ◽  
Positive Effects ◽  
Advantages And Disadvantages ◽  
Air Turbine ◽  
Absorbed Power ◽  
The First Variation ◽  
The Second Variation

We present an analysis of wave energy devices with air-filled compressible submerged volumes, where variability of volume is achieved by means of a horizontal surface free to move up and down relative to the body. An analysis of bodies without power take-off (PTO) systems is first presented to demonstrate the positive effects a compressible volume could have on the body response. Subsequently, two compressible device variations are analysed. In the first variation, the compressible volume is connected to a fixed volume via an air turbine for PTO. In the second variation, a water column separates the compressible volume from another volume, which is fitted with an air turbine open to the atmosphere. Both floating and bottom-fixed, axisymmetric, configurations are considered, and linear analysis is employed throughout. Advantages and disadvantages of each device are examined in detail. Some configurations with displaced volumes less than 2000 m 3 and with constant turbine coefficients are shown to be capable of achieving 80% of the theoretical maximum absorbed power over a wave period range of about 4 s.

Life cycle comparison of a wave and tidal energy device

2011 ◽  
Vol 225 (4) ◽  
pp. 325-337 ◽  
Author(s):  
S Walker ◽  
R Howell
Keyword(s):  
Life Cycle ◽  
Wave Energy ◽  
Tidal Energy ◽  
Development Stage ◽  
Payback Period ◽  
Energy Device ◽  
Energy Mix ◽  
Energy Devices ◽  
Marine Energy ◽  
Marine Current

Tidal and wave energy devices are often discussed as a future contributor to the UK’s energy mix. Indeed, marine energy resources are said to have the potential to supply up to 20 per cent of the nation’s electricity demand. However, these technologies are currently at the development stage and make no meaningful contribution to the national grid. A number of devices have been developed, but no single method has emerged as the leading technology. This paper aims to compare two promising devices, one wave device and one tidal device, and assess the life cycle properties of each. A life cycle assessment of the Oyster wave energy device was conducted as part of this study, and a comparison of this and the SeaGen marine current turbine was undertaken. In both cases a ‘cradle-to-grave’ assessment was carried out, calculating emissions from materials, fabrication, transport, installation, lifetime maintenance, and decommissioning (including recycling). The SeaGen tidal device was calculated to have an energy payback period of 14 months, and a CO2 payback period of 8 months. The equivalent figures for the Oyster device were 12 and 8 months, respectively. The respective energy and carbon intensities for the two devices were 214 kJ/kWh and 15 gCO2/kWh for the SeaGen and 236 kJ/kWh and 25 gCO2/kWh for the Oyster. The calculated intensities and payback periods are close to those of established wind turbine technologies, and low relative to the 400–1000 g CO2/kWh of typical fossil fuel generation. With further developments in construction and deployment efficiency these intensities are expected to fall, so the devices appear to have the potential to offer a viable contribution to the UK’s future energy mix.

scholarly journals Fluid-Structure-Soil Interaction of a Moored Wave Energy Device

2019 ◽  
Author(s):  
Joe G. Tom ◽  
Dirk P. Rijnsdorp ◽  
Raffaele Ragni ◽  
David J. White
Keyword(s):  
Cyclic Loading ◽  
Wave Energy ◽  
Significant Proportion ◽  
Interdisciplinary Approach ◽  
Cost Effective ◽  
Wave Flow ◽  
Energy Device ◽  
Subsequent Increase ◽  
Operational Conditions ◽  
Energy Devices

Abstract This paper explores the response of a wave energy device during extreme and operational conditions and the effect of this response on the geotechnical stability of the associated taut moorings. The non-hydrostatic wave-flow model SWASH is used to simulate the response of a taut-moored wave energy converter. The predicted forces acting on the mooring system are used to compute the build-up of excess pore pressures in the soil around the mooring anchor and the resulting changes in strength and capacity. An initial loss of strength is followed by a subsequent increase in capacity, associated with long-term cyclic loading and hardening due to consolidation. The analyses show how cyclic loading may actually benefit and reduce anchoring requirements for wave energy devices. It demonstrates the viability of a close interdisciplinary approach towards an optimized and cost-effective design of mooring systems, which form a significant proportion of expected capital expenditures.

scholarly journals On Wave-Induced Elastic Deformations of a Submerged Wave Energy Device

2020 ◽  
Vol 19 (3) ◽  
pp. 317-338
Author(s):  
Shuijin Li ◽  
Masoud Hayatdavoodi ◽  
R. Cengiz Ertekin
Keyword(s):  
Nonlinear Wave ◽  
Wave Energy ◽  
Structural Integrity ◽  
Accurate Determination ◽  
Elastic Response ◽  
Wave Loads ◽  
Extreme Wave ◽  
Energy Device ◽  
Energy Devices ◽  
Wave Induced

Abstract Structural integrity has remained a challenge for design and analysis of wave energy devices. A difficulty in assessment of the structural integrity is often laid in the accurate determination of the wave-induced loads on the wave energy devices and the repones of the structure. Decoupled hydroelastic response of a submerged, oscillating wave energy device to extreme nonlinear wave loads is studied here. The submerged wave energy device consists of an oscillating horizontal disc attached to a direct-drive power take-off system. The structural frame of the wave energy device is fixed on the seafloor in shallow water. Several extreme wave conditions are considered in this study. The nonlinear wave loads on members of the submerged structure are obtained by use of the level I Green-Naghdi equations and Morison’s equation for cylindrical members. Distribution of Von Mises stresses and the elastic response of the structure to the extreme wave loads are determined by use of a finite element method. The decoupled hydroelastic analysis of the structure is carried out for devices built by four different materials, namely stainless steel, concrete, aluminium alloy, and titanium alloy. The elastic response of these devices is studied and results are compared with each other. Points of maximum stress and deformations are determined and the structural integrity under the extreme conditions is assessed. It is shown that the proposed approaches provide invaluable information about the structural integrity of wave energy devices.

scholarly journals Analysis of a Two-Body Floating Wave Energy Converter With Particular Focus on the Effects of Power Take Off and Mooring Systems on Energy Capture

2011 ◽  
Author(s):  
Made Jaya Muliawan ◽  
Zhen Gao ◽  
Torgeir Moan ◽  
Aurelien Babarit
Keyword(s):  
Wave Energy ◽  
The Body ◽  
Wave Energy Converter ◽  
Energy Converter ◽  
Operational Conditions ◽  
Energy Capture ◽  
Irregular Wave ◽  
Actual Operation ◽  
Linear Damping ◽  
Multi Body

The present paper summarizes analyses of a two-body floating wave energy converter (WEC) including the mooring system. An axi-symmetric Wavebob type WEC is chosen as the object of investigation here. However, the PTO system is modeled in a simplified manner as ideal linear damping and spring terms that couples the body 1 and the body 2 motions. The analysis is done using SIMO, a time domain simulation tool which accommodates simulation of multi-body systems with hydrodynamic interactions. In SIMO, docking cone features have been introduced between the two bodies to let them move as per actual operation and fenders are applied to represent end stops. Six alternative mooring configurations are applied to investigate the effect of mooring on power capture. In this paper, the software HydroD using WAMIT for hydrodynamic is used to determine hydrodynamic loads. The analysis is carried out for several regular and irregular wave conditions as representative of operational conditions. Simulations are performed with the purpose to study the effects of power take off (PTO) system, end stops setting and several mooring configurations on power captured by the WEC.

scholarly journals A practical design procedure for initial sizing of heaving point absorber wave energy converters

2021 ◽  
Vol 1201 (1) ◽  
pp. 012018
Author(s):  
M B Jouybari ◽  
Y Xing
Keyword(s):  
Wave Energy ◽  
Design Procedure ◽  
The Body ◽  
Wave Energy Converter ◽  
Body Volume ◽  
Energy Converter ◽  
Point Absorber ◽  
Wave Energy Converters ◽  
Practical Design ◽  
Absorbed Power

Abstract Designing a wave energy converter with the proper size has always been challenging since it is a trade-off between many factors including cost, practicality, and energy output. In this paper a practical design procedure for sizing of heaving point absorbers wave energy converters is presented. Size can be represented by the body volume. Budal power bounds are deployed to obtain the body volume and annual mean absorbed power of the wave energy converter. Budal power bounds are determined for each sea state. Aiming a specific power capture ratio, several sets of design sea states with related design volume and annual mean absorbed power are defined. With the design objective of maximizing the ratio of mean power to submerged volume, and considering suitable design constraints, the best size is obtained. The proposed procedure will be then deployed for a case study and the design will be compared with an existing similar point absorber. The results show that the mean absorbed power does not depend on the size but is a function of selected sea states. Furthermore, the comparison study reveals that the proposed design procedure yields reasonable power characteristics.

scholarly journals A novel wave-energy device with enhanced wave amplification and induction actuator

2020 ◽  
Vol 3 (1) ◽  
pp. 37-44
Author(s):  
Onno Bokhove ◽  
Anna Kalogirou ◽  
David Henry ◽  
Gareth P. Thomas
Keyword(s):  
Variational Principle ◽  
Numerical Model ◽  
Energy Conversion ◽  
Wave Energy ◽  
Electrical Power ◽  
Rogue Waves ◽  
Energy Device ◽  
Wave Amplification ◽  
Energy Devices ◽  
New Device

A novel wave-energy device is presented. Both a preliminary proof-of-principle of a working, scaled laboratory version of the energy device is shown as well as the derivation and analysis of a comprehensive mathematical and numerical model of the new device. The wave-energy device includes a convergence in which the waves are amplified, a constrained wave buoy with a (curved) mast and direct energy conversion of the buoy motion into electrical power via an electro-magnetic generator. The device is designed for use in breakwaters and it is possible to be taken out of action during severe weather. The new design is a deconstruction of elements of existing wave-energy devices, such as the TapChan, IP wave-buoy and the Berkeley Wedge, put together in a different manner to enhance energy conversion and, hence, efficiency. The idea of wave-focusing in a contraction emerged from our work on creating and simulating rogue waves in crossing seas, including a "bore-soliton-splash". Such crossing seas have been recreated and modelled in the laboratory and in simulations by using a geometric channel convergence. The mathematical and numerical modelling is also novel. One monolithic variational principle governs the dynamics including the combined (potential-flow) hydrodynamics, the buoy motion and the power generation, to which the dissipative elements such as the electrical resistance of the circuits, coils and loads have been added a posteriori. The numerical model is a direct and consistent discretisation of this comprehensive variational principle. Preliminary numerical calculations are shown for the case of linearised dynamics; optimisation of efficiency is a target of future work.

Conceptual Design of OWC Wave Energy Converters Combined With Breakwater Structures

2010 ◽  
Author(s):  
Vallam Sundar ◽  
Torgeir Moan ◽  
Jo̸rgen Hals
Keyword(s):  
Wave Energy ◽  
Ocean Waves ◽  
Floating Bodies ◽  
Energy Device ◽  
Energy Devices ◽  
Wave Energy Converters ◽  
Ocean Wave Energy ◽  
Caisson Breakwater ◽  
Perforated Caisson ◽  
Energy Converters

Ocean wave energy is one of several renewable sources of energy found in the ocean. The energy in the oscillatory ocean waves can be used to drive a machinery that converts the energy to other forms. Depending on the type and their location with respect the coast and offshore, a number of devices have been and are being developed to extract the wave energy for conversion into electricity. The most common devices are referred to as the oscillating water column (OWC), hinged contour device, buoyant moored device, hinged flap and overtopping device. Particularly popular are OWCs and moored floating bodies. The idea of integrating breakwater and wave energy converters emerged in the Indian wave energy program. Graw (1996) discussed this idea and pointed out the advantage of shared costs between the breakwater and the wave energy device. Because long waves are usually experience stronger reflection at coasts and breakwaters, they provide good conditions for the operation wave energy devices which work efficiently when the reflection is high. There are examples that OWC devices have been installed in water as shallow as 3 m. This paper reviews the options of integrating OWCs with different kinds of breakwaters like the perforated or non-perforated caisson breakwater, and non-gravity piled and floating types. The purpose of each of the concepts will also be highlighted.

scholarly journals Analytical Formulation of Nonlinear Froude-Krylov Forces for Surging-Heaving-Pitching Point Absorbers

2018 ◽  
Author(s):  
Giuseppe Giorgi ◽  
John V. Ringwood
Keyword(s):  
Wave Energy ◽  
Axisymmetric Body ◽  
The Body ◽  
Model Complexity ◽  
Computational Time ◽  
Algebraic Solution ◽  
Nonlinear Behaviour ◽  
Energy Devices ◽  
Small Pitch ◽  
Point Absorbers

Accurate and computationally efficient mathematical models are fundamental for designing, optimizing, and controlling wave energy converters. Wave energy devices are likely to exhibit significant nonlinear behaviour, over their full operational envelope, so that nonlinear models may become indispensable. Froude-Krylov nonlinearities are of great importance in point absorbers but, in general, their calculation requires an often unacceptable increase in model complexity and computational time. However, if the body is assumed to be axisymmetric, it is possible to describe the whole geometry analytically, thereby allowing faster calculation of nonlinear Froude-Krylov forces. In this paper, a convenient parametrization of axisymmetric body geometries is proposed, applicable to devices moving in surge, heave, and pitch. In general, the Froude-Krylov integrals must be solved numerically. Assuming small pitch angles, it is possible to further simplify the problem, and achieve an algebraic solution, which is considerably faster than numerical integration.

scholarly journals A Nonlinear Extension for Linear Boundary Element Methods in Wave Energy Device Modelling

2012 ◽  
Author(s):  
Alexis Merigaud ◽  
Jean-Christophe Gilloteaux ◽  
John V. Ringwood
Keyword(s):  
Boundary Element ◽  
Wave Energy ◽  
Linear Models ◽  
Boundary Element Methods ◽  
Hydrodynamic Models ◽  
Energy Device ◽  
Energy Capture ◽  
Energy Devices ◽  
Higher Order Terms ◽  
Device Modelling

To date, mathematical models for wave energy devices typically follow Cummins equation, with hydrodynamic parameters determined using boundary element methods. The resulting models are, for the vast majority of cases, linear, which has advantages for ease of computation and a basis for control design to maximise energy capture. While these linear models have attractive properties, the assumptions under which linearity is valid are restrictive. In particular, the assumption of small movements about an equilibrium point, so that higher order terms are not significant, needs some scrutiny. While this assumption is reasonable in many applications, in wave energy the main objective is to exaggerate the movement of the device through resonance, so that energy capture can be maximised. This paper examines the value of adding specific nonlinear terms to hydrodynamic models for wave energy devices, to improve the validity of such models across the full operational spectrum.

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