Characteristics of OWC Type WEC Dampers Installed on a Very Large Floating Structure

2020 ◽  
Author(s):  
Tomoki Ikoma ◽  
Shoichiro Furuya ◽  
Yasuhiro Aida ◽  
Koichi Masuda ◽  
Hiroaki Eto
Keyword(s):  
Wave Energy ◽  
Sea Water ◽  
Prediction Method ◽  
Hydrodynamic Performance ◽  
Floating Body ◽  
Hydrodynamic Characteristics ◽  
Linear Potential ◽  
Floating Structure ◽  
Combined System ◽  
Floating System

Abstract Oscillating water column (OWC) type wave energy converters (WECs) have been researched and developed. OWC WECs are relatively friendly to maintain them in operation because all of mechanical units are set above a sea water surface. In addition, a feature of an OWC device is similar to an air dumper system. Thus, it should be possible not only to harvest wave energy but also to reduce motion of a floating system at the same time. As well as WEC system should be used with other ocean renewable energies as a combined system. This paper describes hydrodynamic characteristics of OWC devices and wave fields around them of multi-OWC devices equipped large floating structures. For this research, the linear potential theory based in-house programme code was applied to calculate hydrodynamic performance of OWC regions and elastic motion behaviours of the structures. Besides, calculation results were compared with some experimental results of characteristics of OWC devices on reference papers published. Then we proved validity of the calculation method. We have quantitatively summarized how much the reduction effect can be seen according to the aircushion placement and the number of aircushions on the floating body. the paper investigated arrangement of OWC devices on the floating structure with several variations. Using the prediction method, effects of arrangement of OWC devices on the performances are investigated.

Primary Conversion Efficiency of OWC Type WECs Installed on a Large Floating Structure

2012 ◽  
Author(s):  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Chang-Kyu Rheem ◽  
Hisaaki Maeda ◽  
Yuka Watanabe
Keyword(s):  
Boundary Condition ◽  
Wave Energy ◽  
Large Scale ◽  
Prediction Method ◽  
Free Water ◽  
Wave Power ◽  
Linear Potential ◽  
Floating Structure ◽  
Distribution Method ◽  
Point Distribution

This paper describes the performance of wave power conversion. A large scale floating system on which oscillating water column type wave energy convertors installed is proposed and the efficiency of primary conversion of wave power is estimated. In this paper, a boundary condition due to OWC is theoretically modeled in order to consider influence of wave energy absorption to hydrodynamic forces on the floating structure into the three-dimensional singular point distribution method based on the linear potential theory. In the modeling, a boundary condition on a free water surface and an equation of state within an air-chamber above OWC are mathematically and linearly formulated. Air-pressures and variation of water elevation within OWC areas can be simultaneously and directly solved by setting both the variables and by solving the simultaneously equations of the air-pressure and the vertical displacement. The damper effect of OWC devices is taken into account. The validity of the prediction method proposed is proven by comparing with experimental results. There are three types of large scale wave energy platform which is a pontoon type in the paper. Each performance of the efficiency of primary conversion of wave power is estimated. It is shown that the performance is very good.

Power Generation Potential of a VLFS Equipped With OWC Type WECs and Damper Effects on Elastic Motion

2015 ◽  
Author(s):  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Yuka Watanabe ◽  
Hiroaki Eto ◽  
Chang-kyu Rheem ◽  
...  
Keyword(s):  
Power Generation ◽  
Boundary Condition ◽  
Wave Energy ◽  
Water Surface ◽  
Free Water ◽  
Vertical Displacement ◽  
Air Pressure ◽  
Linear Potential ◽  
Floating Structure ◽  
Free Water Surface

This paper describes potential of PTO (Power Take-Off) and the damper effect of motion in a large scale pontoon type floating structure on which lots of oscillating water column (OWC) type wave energy convertors (WEC) are installed. It is enable to use upper space for utilizing marine renewable energy such as wind power, tidal power, wave power generation farm using large pontoon structure. Due to the concept, it should reduce cost of maintenance as well. For investigation of PTO and elastic motion behaviours of large floating structures, we calculated three types of models on which OWC devices were installed differently. We examined how much reduction was possible when including elastic motion effects and the fixed type which radiation wave was not taken into account. In this paper, a boundary condition in order to give effect of a free water surface with air pressure is theoretically modeled. We can directly consider influence of wave energy absorption to hydrodynamic forces and wave exciting forces on the floating structure with the Green’s function method based on the linear potential theory. In the modeling, a boundary condition on a free water surface and an equation of state within an air-chamber above OWC are mathematically and linearly formulated. Air-pressures and vertical displacement within OWC areas can be simultaneously and directly solved by setting both the variables and by solving the simultaneously equations of the air-pressure and the vertical displacement. As a result, performance of PTO and hydroelastic motion of the floating structure increased when including elastic motion effect. In addition, expected value of annual PTO was about 4.4MW with 146 OWCs.

scholarly journals Wave Power Absorption by Arrays of Wave Energy Converters in Front of a Vertical Breakwater: A Theoretical Study

Energies ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 1985 ◽  
Author(s):  
Dimitrios N. Konispoliatis ◽  
Spyridon A. Mavrakos
Keyword(s):  
Wave Energy ◽  
Cylindrical Wave ◽  
Hydrodynamic Characteristics ◽  
Linear Potential ◽  
Theoretical Evaluation ◽  
Power Absorption ◽  
Array Configuration ◽  
Wave Energy Converters ◽  
Vertical Breakwater ◽  
Energy Converters

The present paper deals with the theoretical evaluation of the efficiency of an array of cylindrical Wave Energy Converters (WECs) having a vertical symmetry axis and placed in front of a reflecting vertical breakwater. Linear potential theory is assumed, and the associated diffraction and motion radiation problems are solved in the frequency domain. Axisymmetric eigenfunction expansions of the velocity potential are introduced into properly defined ring-shaped fluid regions surrounding each body of the array. The potential solutions are matched at the boundaries of adjacent fluid regions by enforcing continuity of the hydrodynamic pressures and redial velocities. A theoretical model for the evaluation of the WECs’ performance is developed. The model properly accounts for the effect of the breakwater on each body’s hydrodynamic characteristics and the coupling between the bodies’ motions and the power take-off mechanism. Numerical results are presented and discussed in terms of the expected power absorption. The results show how the efficiency of the array is affected by (a) the distance between the devices and the wall, (b) the shape of the WEC array configuration, as well as (c) the angle of the incoming incident wave.

scholarly journals Optimal Configurations of Wave Energy Converter Arrays with a Floating Body

2016 ◽  
Vol 23 (s1) ◽  
pp. 71-77 ◽  
Author(s):  
Wanchao Zhang ◽  
Hengxu Liu ◽  
Xuewei Zhang ◽  
Liang Zhang ◽  
Muhammad Aqeel Ashraf
Keyword(s):  
Wave Energy ◽  
Water Environment ◽  
Floating Body ◽  
Energy Device ◽  
Coupled Equations ◽  
Wave Energy Converters ◽  
Ocean Wave Energy ◽  
Floating System ◽  
Interaction Factors ◽  
Optimal Configurations

Abstract An array of floating point-absorbing wave energy converters (WECs) is usually employed for extracting efficiently ocean wave energy. For deep water environment, it is more feasible and convenient to connect the absorbers array with a floating body, such as a semi-submersible bottom-moored disk, whose function is to act as the virtual seabed. In the present work, an array of identical floating symmetrically distributed cylinders in a coaxial moored disk as a wave energy device is proposed The power take-off (PTO) system in the wave energy device is assumed to be composed of a linear/nonlinear damper activated by the buoys heaving motion. Hydrodynamic analysis of the examined floating system is implemented in frequency domain. Hydrodynamic interferences between the oscillating bodies are accounted for in the corresponding coupled equations. The array layouts under the constraint of the disk, incidence wave directions, separating distance between the absorbers and the PTO damping are considered to optimize this kind of WECs. Numerical results with regular waves are presented and discussed for the axisymmetric system utilizing heave mode with these interaction factors, in terms of a specific numbers of cylinders and expected power production.

scholarly journals Analytical Study on an Oscillating Buoy Wave Energy Converter Integrated into a Fixed Box-Type Breakwater

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
Xuanlie Zhao ◽  
Dezhi Ning ◽  
Chongwei Zhang ◽  
Yingyi Liu ◽  
Haigui Kang
Keyword(s):  
Wave Energy ◽  
Wave Energy Converter ◽  
Hydrodynamic Performance ◽  
Maximum Efficiency ◽  
Width Ratio ◽  
Geometrical Parameters ◽  
Linear Potential ◽  
Energy Converter ◽  
Transmission Coefficients ◽  
Incident Waves

An oscillating buoy wave energy converter (WEC) integrated to an existing box-type breakwater is introduced in this study. The buoy is installed on the existing breakwater and designed to be much smaller than the breakwater in scale, aiming to reduce the construction cost of the WEC. The oscillating buoy works as a heave-type WEC in front of the breakwater towards the incident waves. A power take-off (PTO) system is installed on the topside of the breakwater to harvest the kinetic energy (in heave mode) of the floating buoy. The hydrodynamic performance of this system is studied analytically based on linear potential-flow theory. Effects of the geometrical parameters on the reflection and transmission coefficients and the capture width ratio (CWR) of the system are investigated. Results show that the maximum efficiency of the energy extraction can reach 80% or even higher. Compared with the isolated box-type breakwater, the reflection coefficient can be effectively decreased by using this oscillating buoy WEC, with unchanged transmission coefficient. Thus, the possibility of capturing the wave energy with the oscillating buoy WEC integrated into breakwaters is shown.

The Design and Calculation of the Mooring System in Floating Body with Rope Wheel Device

2013 ◽  
Vol 361-363 ◽  
pp. 378-381
Author(s):  
Yan Gang Wang ◽  
Xing Hua Tong ◽  
Lin Sen Zhu ◽  
Yong Liu
Keyword(s):  
Potential Energy ◽  
Wave Energy ◽  
Low Cost ◽  
Floating Body ◽  
Mooring System ◽  
New Wave ◽  
Floating Structure ◽  
Energy Device ◽  
Key Technology ◽  
Energy Theory

Floating body with rope wheel structure is a new wave energy device, which is simple and low cost. Mooring system is the key technology of this device, which is use to limit the horizontal motion of the floating structure in the designated area. In this paper, potential energy theory has been used in the process of design and calculation of mooring system. Using the result of calculation, the motion of the floating body has been simulated numerically.

scholarly journals Hydrodynamic Analysis of a Modular Floating Structure with Tension-Leg Platforms and Wave Energy Converters

2021 ◽  
Vol 9 (4) ◽  
pp. 424
Author(s):  
Nianxin Ren ◽  
Hongbo Wu ◽  
Kun Liu ◽  
Daocheng Zhou ◽  
Jinping Ou
Keyword(s):  
Wave Energy ◽  
Coupling Effect ◽  
Bending Moment ◽  
Large Degree ◽  
Hydrodynamic Performance ◽  
Floating Structure ◽  
Mechanical Coupling ◽  
Wave Energy Converters ◽  
Energy Converters ◽  
Inner Tension

This work presents a modular floating structure, which consists of five inner tension-leg platforms and two outermost wave energy converters (denoted as MTLPW). The hydrodynamic interaction effect and the mechanical coupling effect between the five inner tension-leg platforms (TLP) and the two outermost wave energy converters (WEC) are taken into consideration. The effects of the connection modes and power take-off (PTO) parameters of the WECs on the hydrodynamic performance of the MTLPW system are investigated under both operational and extreme sea conditions. The results indicate that the hydrodynamic responses of the MTLPW system are sensitive to the connection type of the outermost WECs. The extreme responses of the bending moment of connectors depend on the number of continuously fixed modules. By properly utilizing hinge-type connectors to optimize the connection mode for the MTLPW system, the effect of more inner TLP modules on the hydrodynamic responses of the MTLPW system can be limited to be acceptable. Therefore, the MTLPW system can be potentially expanded to a large degree.

Study of Motion Performance of a Floating System With Four Moonpools and a VAWT

2021 ◽  
Author(s):  
Lei Tan ◽  
Satsuya Moritsu ◽  
Tomoki Ikoma ◽  
Yasuhiro Aida ◽  
Koichi Masuda
Keyword(s):  
Potential Theory ◽  
Theoretical Calculations ◽  
Model Tests ◽  
Hydrodynamic Performance ◽  
Linear Potential ◽  
Gyroscopic Effect ◽  
Floating Foundation ◽  
Motion Responses ◽  
Floating System ◽  
Linear Potential Theory

Abstract In this paper the hydrodynamic performance of a barge-type floating foundation installed with four moonpools and a VAWT was investigated through model tests and theoretical calculations. The characteristics of wave-induced motion responses and tether tensions and the effects of turbine rotations were examined. Physical model tests were conducted in a wave tank using regular waves with the wave period ranging from 0.6 to 1.6 seconds and 0.01 or 0.02 meters in amplitude. A 2-MW-class VAWT was modelled with a scale ratio of 1/100 in the experiments. By varying the mass and the rotational speed of the turbine, gyroscopic moment effects were studied. In addition, numerical calculations based on the linear potential theory and Green function method were carried out to estimate motion responses and tether tensions. The present results indicate that the gyroscopic effect due to turbine rotations can be profound. It was found that the first-order motions of the floating system were substantially reduced by the gyroscopic effect, while the second-order motions and tether tensions may be significantly increased. Moreover, the viscous damping of water motions in moonpools was found not negligible. As a result, theoretical models based on linear potential theory should be used with care in hydrodynamic analysis with regard to the floating systems with VAWT rotations. In addition, the present in-house program code was validated against WAMIT through comparing hydrodynamic predictions of a floating foundation with four moonpools, with reasonable agreement.

Using the Floating Body Symmetries to Speed Up the Numerical Computation of Hydrodynamics Coefficients With Nemoh

2018 ◽  
Author(s):  
Matthieu Ancellin ◽  
Frederic Dias
Keyword(s):  
Wave Energy ◽  
Potential Flow ◽  
Dynamic Properties ◽  
Rotational Symmetry ◽  
Floating Body ◽  
Translation Invariance ◽  
Linear Potential ◽  
Wave Energy Converters ◽  
Speed Up ◽  
Hydrodynamics Coefficients

The open source potential flow BEM solver Nemoh (developed at École Centrale de Nantes) is widely used today, notably for the development of wave energy converters. The use of a linear potential flow theory allows quick estimations of the hydro-dynamic properties of the device, such as its added mass or its radiation damping. Nonetheless, their computation with Nemoh can still be time consuming and could be optimized to facilitate the R&D process. Many wave energy converter concepts present symmetric shapes: for instance rotational symmetry for point absorbers or translation invariance for cylindrical shapes. These symmetries can be exploited in the BEM solver to significantly speed up the computations. In this paper, the mathematical effect of symmetries on the BEM resolution will be discussed and some results of its implementation in Nemoh will be presented.

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