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Numerical Modelling of Double Slit Caisson Breakwater Integrated oscillating water column Wave Energy Converter with Modal Superposition Method

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Open Journal of Fluid Dynamics 2023年第2期13卷 92-103页

作者： Mitsumasa Iino Hisashi Endo Faculty of Engineering Ashikaga University Tochigi Japan

oscillating water column wave energy converter is a power generation device in which ocean waves excite the oscillation of the water surface in an air chamber, which generates fluctuations in air pressure and rotate air turbine generator(s). The oscillation of the fluid in the air chamber is a fluid oscillation phenomenon with a natural period, similar to fluid oscillation in a container such as sloshing. Previous research has shown that for an oscillating water column with a single air chamber submerged in water, the oscillation characteristics can be modeled as a one-degree-of-freedom oscillation system that takes only a single oscillation mode into account. However, a double-slit breakwater integrated oscillating water column wave energy converter using two water columns of the breakwater separated by slit walls, has been verified to have two resonance periods. In this study, the free oscillating motion of the oscillating water column wave energy converter using the double-slit breakwater is modeled by modal superposition method including the first-order and second-order modes of vertical motion of the two water surfaces. The result from the simulation is similar to the result of the free vibration experiment.

关键词： Fluid Oscillation Wave Energy oscillating water column Modal Analysis

Effect of Fluidic Diode on Performance of Unidirectional Impulse Turbine

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Journal of Thermal Science 2024年第3期33卷 807-814页

作者： DODDAMANI Hithaish ABDUS Samad MANABU Takao SHINYA Okuhara M M ASHRAFUL Alam Department of Ocean Engineering Indian Institute of Technology MadrasChennai600036India Department of Mechanical Engineering National Institute of TechnologyMatsue CollegeShimane6908518Japan Center of Support Practical Education National Institute of TechnologyMatsue CollegeShimane6908518Japan Department of Transportation Engineering Osaka Sangyo UniversityDaito5748530Japan

A pair of unidirectional turbines(UT)can operate in oscillatory airflow without additional units.However,this arrangement suffers from poor flow rectification.A fluidic diode(FD)offers variable hydrodynamic resistance based on the flow direction,and this can be coupled with UT to improve flow rectification.In this work,a numerical investigation on the effect of FD with UT is presented using the commercial fluid dynamics software ANSYS Fluent 16.1 with k-ωSST turbulence closure model.Periodic domains of UT and FD are numerically validated individually with experimental results.Later,both are coupled to obtain the combined effect,and these results are compared with the analytical approach.It was observed that coupling FD with UT improved the unit's performance at the lower flow coefficient(<1),but its performance decreased as the flow coefficient increased.Due to the diode's presence,fluid leaving the turbine experiences higher resistance at a higher flow coefficient,which decreases the overall performance of the combined unit.

关键词： wave energy oscillating water column unidirectional impulse turbine fluidic diode flow rectification

Experimental Investigation on a Fixed oscillating water column with an Impulse Turbine for Wave Energy Conversion

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Journal of Energy and Power Engineering 2020年第1期14卷 16-25页

作者： Tengen Murakami Yasutaka Imai Shuichi Nagata Manabu Takao Institute of Ocean Energy Saga University1HonjoSaga 840-8502Japan Department of Mechanical Engineering National Institute of TechnologyMatsue College14-4NishiikumaMatsueShimane 690-8518Japan

A fixed oscillating water column(OWC)-type wave energy converter consists of an air chamber,an air turbine and a generator.The energy conversion processes are the primary conversion in an air chamber and the secondary conversion of the turbine.For the practical use,it is necessary to develop a design method which can consider the incident wave motion,the motion of the internal free surface affected in the structure such as a partly submerged wall,the fluctuation of air pressure in an air chamber,and the rotation of the air turbine.At here,the authors carried out the wave tank tests using the model OWC equipped with the impulse turbine and a generator to obtain the experimental data needed to make this design method.As the result,the efficiencies of the three cases with different speed ratio between generator and turbine,and the effects of the curtain wall depth and the wave length on the energy conversion performance were clarified.

关键词： Impulse turbine oscillating water column primary conversion secondary conversion wave energy

Hydrodynamic Performance of A Dual-Floater Integrated System Com-bining Hybrid WECs and Floating Breakwaters

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China Ocean Engineering 2022年第6期36卷 969-979页

作者： FU Lei CHENG Yong School of Naval Architecture and Ocean Engineering Jiangsu University of Science and TechnologyZhenjiang 212100China

The high investment and low return of wave energy converters(WECs)seriously hamper their large-scale commercial application.The integration of WECs and floating breakwaters is conducive to enhance the competitiveness of wave energy conversion.The objective of this paper is to investigate the hydrodynamic performance of a WEC-breakwater integrated system combining an upstream oscillating water column(OWC)and a downstream oscillating buoy(OB)via numerical simulations and physical experiments.A nonlinear numerical wave flume using Star-CCM+software is employed to obtain calculated results,where a tiny transverse gap is set between the flume wall and the block surface to simulate a similar two-dimensional(2D)model.The corresponding physical experiments are also carried out in a practical wave flume to verified the numerical results.The comparison of the isolated and hybrid system shows that the hybrid design leads to the decreased conversion efficiency of each WEC,but improves the transmission performance of the hybrid system.The wave resonance between two devices causes the abrupt reduction of OWC efficiency and a positive correlation exists with the OB efficiency.The total efficiency of the hybrid system is raised by an optimal opening ratio,a shallow OWC draft and a short spacing distance.Except for the OWC draft,other design parameters have weak effect on the wave attenuation of the hybrid system.This paper can help understand hydrodynamics of the hybrid WECs integrated with breakwaters and improve their performances.

关键词： wave energy converters floating breakwater oscillating buoy oscillating water column numerical wave flume physical experiment

超大浮体与OWC集成系统的水动力性能:半解析研究

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哈尔滨工程大学学报（英文版） 2023年第2期22卷 232-246页

作者：周加春赵玄烈臧军耿敬邝庆文 College of Shipbuilding Engineering Harbin Engineering UniversityHarbin 150001China Department of Architecture and Civil Engineering University of BathBathBA27AYUnited Kingdom PowerChina ZhongNan Engineering Corporation Limited Changsha 410000China

Responses of the very large floating Structures(VLFS)can be mitigated by implementing oscillating water columns(OWCs).This paper explores the fundamental mechanism of present wave interactions with both structures and examines the hydrodynamic performance of VLFS equipped with OWCs(VLFS-OWCs).Under the linear potential flow theory framework,the semi-analytical model of wave interaction with VLFS-OWCs is developed using the eigenfunction matching method.The semi-analytical model is verified using the Haskind relationship and wave energy conservation law.Results show that the system with dual-chamber OWCs has a wider frequency bandwidth in wave power extraction and hydroelastic response mitigation of VLFS.It is worth noting that the presence of Bragg resonance can be trigged due to wave interaction with the chamber walls and the VLFS,which is not beneficial for the wave power extraction performance and the protection of VLFS.

关键词： Semi-analytical investigation Very large floating structures oscillating water column Bragg resonance Hydroelastic response

A RANS-VoF Numerical Model to Analyze the Output Power of An OWC-WEC Equipped with Wells and Impulse Turbines in A Hypothetical Sea-State

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China Ocean Engineering 2020年第6期34卷 760-771页

作者： Paulo R.F.Teixeira Rafael A.A.C.Gonçalves Eric Didier Engineering School Universidade Federal do Rio Grande-FURGRio GrandeRS 96203-900Brazil Harbours and Maritime Structures Division Hydraulics and Environment DepartmentLaboratório Nacional de Engenharia Civil-LNECLisbon 1700-066Portugal

Wave energy is a renewable source with significant amount in relation to the global demand. A good concept of a device applied to extract this type of energy is the onshore oscillating water column wave energy converter(OWC-WEC). This study shows a numerical analysis of the diameter determination of two types of turbines, Wells and Impulse, installed in an onshore OWC device subjected to a hypothetical sea state. Commercial software FLUENT?,which is based on RANS-VoF(Reynolds-Averaged Navier-Stokes equations and Volume of Fluid technique), is employed. A methodology that imposes air pressure on the chamber, considering the air compressibility effect, is used. The mathematical domain consists of a 10 m deep flume with a 10 m long and 10 m wide OWC chamber at its end(geometry is similar to that of the Pico's plant installed in Azores islands, Portugal). On the top of the chamber, a turbine works with air exhalation and inhalation induced by the water free surface which oscillates due to the incident wave. The hypothetical sea state, represented by a group of regular waves with periods from 6 to 12 s and heights from 1.00 to 2.00 m(each wave with an occurrence frequency), is considered to show the potential of the presented methodology. Maximum efficiency(relation between the average output and incident wave powers) of46% was obtained by using a Wells turbine with the diameter of 2.25 m, whereas the efficiency was 44% by an Impulse turbine with the diameter of 1.70 m.

关键词： wave energy oscillating water column Wells turbine Impulse turbine RANS-VoF compressible air

Design and Experimental Study of A Pile-Based Breakwater Integrated with OWC Chamber

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China Ocean Engineering 2021年第3期35卷 443-453页

作者： QU Ming YU Ding-yong DOU Zhi-hao WANG Shi-lin College of Engineering Ocean University of ChinaQingdao 266100China

A structure scheme of a pile-based breakwater with integrated oscillating water column(OWC)energy conversion chamber was proposed,and four structure forms had been designed.Based on the physical test,the variations of the reflected wave height,the transmitted wave height,the air velocity at the outlet of the chamber,the air pressure and the wave height in the air chamber were studied under the conditions of different wave heights,periods,with or without elliptical front wall and the baffles on both sides of the chamber.Moreover,based on the results,the changes and relationship between the wave-eliminating effect and energy conversion effect of the scheme were analyzed.In general,it turns out,the transmission coefficients of the four structure forms are kept below 0.5.Furthermore,the transmission coefficients of the structural forms G2,G3,and G4 were all smaller than 0.4,and it is only 0.1 at its smallest.Thereinto,in general,the structure form G4 has the best wave-eliminating and energy conversion performance.At the same time,when the wave steepness is 0.066,the energy conversion and wave dissipation effect of the four structure forms is the best.The research results could be provided as the reference for the design structure selection of pile-based breakwater with integrated OWC energy conversion chamber.

关键词： wave energy conversion breakwaters energy efficiency power transmission pile-based breakwaters oscillating water column

Experimental Investigation of the Small-scale Fixed Multi-chamber OWC Device

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Chinese Journal of Mechanical Engineering 2021年第5期34卷 408-421页

作者： Mohammad Shalby Ahmed Elhanafi Paul Walker David G.Dorrell Ahmad Salah Mohamed R.Gomaa Mohamed Behiri Mechanical Engineering Department Faculty of EngineeringAl-Hussein Bin Talal UniversityMa’an 71111Jordan National Centre for Maritime Engineering and Hydrodynamics Australian Maritime CollegeUniversity of TasmaniaLauncestonTAS 7250Australia School of Mechanical and Mechatronic Systems University of Technology SydneySydneyNSW 2007Australia School of Electrical and Information Engineering University of the WitwatersrandDurban 2000South Africa Electrical Engineering Department Faculty of EngineeringAl Hussein Bin Talal UniversityMa’an 71111Jordan Mechanical Engineering Department Benha Faculty of EngineeringBenha UniversityBenha 13518Egypt 不详

Sea wave energy generators or converters(WECs)have the potential to become a viable technology for clean,renewable energy production.Among the WEC technologies,the oscillating water columns(OWCs)are the most common WEC devices studied.These have been studied and developed over many years.Multi-chamber oscillating water columns(MC-OWC)have the potential to have a higher energy conversion when extracting energy in mixed sea states than single-chamber devices.In the work reported in this paper,physical experiments are carried under regular wave conditions to test the wave power extraction of a fixed MC-OWC small-scale model.The Power Take-Off(PTO)of the device is simulated using orifice plates.The flow characteristics through these orifices are pre-calibrated such that the extracted power can be obtained only using the pressure measurement.Wave condition effects on the damping of the PTO of the device power extraction are addressed.The test results illustrate that the PTO system damping is critical and affects device performance.

关键词： cean wave energy Energy conversion oscillating water column Multi-chamber OWC

Experimental studies on the flow characteristics in an inclined bend-free OWC device

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Journal of Ocean Engineering and Science 2016年第1期1卷 77-83页

作者： Krishnil Ravinesh Ram Mohammed Rafiuddin Ahmed Mohammed Asid Zullah Young-Ho Lee Division of Mechanical Engineering The University of the South PacificSuvaFiji Division of Mechanical and Energy System Engineering Korean Maritime and Ocean UniversityBusanRepublic of Korea

A bend-free rectangular cross-section OWC device was designed and constructed for studying the effect of inclination on the flow characteristics inside the device.The inclination is meant to reduce reflection of waves and induce higher velocities in the turbine section.Experimental measurements were made in a wave channel where the OWC device was tested.An S-type Pitot tube was used to measure dynamic pressure of air in the turbine section at several inclinations.Particle Image Velocimetry(PIV)was also done to study the flow of both air and water in the OWC device.In order to focus solely on primary energy capture,no turbine was installed in the OWC device.The dynamic pressure readings were analysed for suction and compression stages.water volume fluctuations inside the capture chamber were also recorded and compared for different inclinations.The result was an increase in the velocity of air flowing in the capture chamber and hence a rise in the kinetic energy available to the turbine.It was found from experimental studies that as the angle of inclination reduced,the velocity of air in the turbine section increased.The lower angles also caused higher run-up and larger volume of water into the capture chamber.

关键词： oscillating water column Particle Image Velocimetry Wave energy.