• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.6
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• pp.1195-1204
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• 2021

In this paper, we present an optimal design method for wave power generators using the response surface analysis. Especially, in our method, we reduce the mechanical loss by selecting the linear generator whose linear movement can be converted to the electrical energy directly with the vertical movement of waves. Therefore, we calculate the exciting force acting on the drive device in a slow-wave condition and determine the winding process with a ratio of the slots and poles for the improvement of energy conversion efficiency. In addition, we employ the regression analysis for deriving the shape factors of the stator and the translator, which have a significant effect on the performance of a generator. We choose the best design variables through the response surface analysis, and then we study the optimization method for designing the efficient experiment using the analysis results. Finally, we show the validity of the proposed method through the simulation results.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.2
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• pp.111-117
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• 2012

Oscillating water column is the most widely used ocean energy converting systems all over the world. The operating performance is influenced by the efficiencies of the two converting stages in the OWC chamber-turbine integrated system. In order to consider the effects of the turbine, the orifice model are carried out. The VOF based Numerical Wave Tank (NWT) is utilized to simulate the water column oscillation inside the chamber and the results are compared with corresponding experimental data. This paper reviews the state of the art in interaction among wave elevation inside the chamber and air flow rate in the duct, which are considered the turbine effects. Effects of incident wave conditions and several shape parameters on the operating performance of OWC chamber are investigated numerically. The effects of the impulse turbine on the integrated system and interaction among the wave elevation, pressure and air flow velocities variations are investigated.

• Journal of Ocean Engineering and Technology
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• v.31 no.2
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• pp.81-90
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• 2017

The 1MW OTEC (Ocean Thermal Energy Conversion) platform was designed for application in equatorial seas. In this study, the OTEC platform was investigated using numerical and experimental methods. An octagon-shaped OTEC platform was investigated using the Ocean Engineering Basin of KRISO. These experiments included various tests of regular waves, irregular waves and irregular waves with current (wave+current). The responses of the platform in regular waves showed good agreement between the numerical and experimental results, including the motion RAO, wave run up, and mean drift force. The peak period of heave and pitch motions were observed around 0.5 rad/s, and the effect of the total reflection was found under short wave conditions. The standard deviation (STD) of the platform motion was checked in irregular waves of equatorial and Hawaiian seas. The STD of the pitch was less than $4^{\circ}$ different from the operability requirement under equatorial conditions and the surge STD of the wave frequency showed good agreement between the numerical and experimental results. The STD values of the surge and pitch were increased 66.6% and 92.8% by the current effects in irregular waves, but the pitch STD was less than $4^{\circ}$ under equatorial conditions. This study showed that the STD of the surge was affected by spring effects. Thus, the watch circle of the platform and tension of the mooring lines must be evaluated for a specific design in the future.

• Smart Structures and Systems
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• v.32 no.4
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• pp.253-266
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• 2023

The time-reversal method is employed to improve the ability of pipeline defect detection, and a new approach of identifying the pipeline defect depth is proposed in this research. When the L(0,2) mode ultrasonic guided wave excited through a lead zirconate titinate (PZT) transduce array propagates along the pipeline with a defect, it will interact with the defect and be partially converted to flexural F(n, m) modes and longitudinal L(0,1) mode. Using a receiving PZT array attached axisymmetrically around the pipeline, the L(0,2) reflection signal as well as the mode conversion signals at the defect are obtained. An appropriate rectangle window is used to intercept the L(0,2) reflection signal and the mode conversion signals from the obtained direct detection signals. The intercepted signals are time reversed and re-excited in the pipeline again, result in the guided wave energy focusing on the pipeline defect, the L(0,2) reflection and the L(0,1) mode conversion signals being enhanced to a higher level, especially for the small defect in the early crack stage. Besides the L(0,2) reflection signal, the L(0,1) mode conversion signal also contains useful pipeline defect information. It is possible to identify the pipeline defect depth by monitoring the variation trend of L(0,2) and L(0,1) reflection coefficients. The finite element method (FEM) simulation and experiment results are given in the paper, the enhancement of pipeline defect reflection signals by time-reversal method is obvious, and the way to identify pipeline defect depth is demonstrated to be effective.

• International Journal of Fluid Machinery and Systems
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• v.1 no.1
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• pp.33-37
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• 2008

EquiMar (Equitable Testing and Evaluation of Marine Energy Extraction Devices in terms of Performance, Cost and Environmental Impact) is one of the first round of energy projects under the European Commissions 7th Framework Programme (FP7). The three year EquiMar project aims to deliver a suite of protocols for the evaluation of both wave and tidal converters, harmonizing testing and evaluation procedures across the wide range of available devices, accelerating adoption through technology matching and improving the understanding of both environmental and economic impacts associated with the deployment of devices. The EquiMar protocols will cover site selection, initial design, scaling up of designs, the deployment of arrays and environmental impact assessment as well as economic issues. EquiMar will build on existing protocols, e.g. UK DTI Marine Renewables Development Fund (MRDF) protocols for wave and tidal energy, and engage with international standards setting activities, e.g. IEC TC114.

• Journal of the Korean Society for Marine Environment & Energy
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• v.17 no.3
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• pp.182-188
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• 2014

In an oscillating water column (OWC)-type wave energy conversion system, the performance of the OWC chamber depends on the chamber shape, as well as the incident wave direction and pressure drop produced by the turbine. Although the previous studies on OWC chambers have focused on wave absorbing performance in ideal operating conditions, incident waves do not always arrive normally to the OWC chamber in real sea conditions, especially in fixed devices. The present study deals with experiments and numerical calculations to investigate the effects of wave direction on the performance of the OWC chamber. The experiments were carried out in a three-dimensional wave basin for five different wave directions, including the effect of turbine using the corresponding orifice. The wave elevation inside the chamber was measured at the center point under various incident wave conditions. The numerical study was conducted by using a numerical wave tank-based volume-of-fluid model to compare the results with experimental data and to reveal the detailed flows around the chamber.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.470-475
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• 2019

This paper deals with a 30kW grid-connected PCS (Power Conversion System) for an Oscillating Water Column (OWC) wave-power generation system. Wave power generation in marine energy is suitable for Korea with the characteristics of a peninsula with three sides facing the sea. In the case of coastal disasters, wave generators can act as a breakwater to reduce damage, and can be integrated with other marine power generation systems to increase efficiency. Wave power generation systems are classified into various types, such as oscillating bodies, OWC, and overtopping according to the operation principle, and they can also be classified into two types according to the installation method: a fixed structure and floating structure. This paper proposes a 30kW grid-connected PCS topology and model for OWC wave power generation that is structurally stable with a turbine and generator that are relatively easy to maintain, and then provide a control method required for grid connection, including DC link voltage control. Simulation verification was performed to verify the proposed PCS.

• Proceedings of the KIPE Conference
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• 2006.06a
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• pp.203-205
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• 2006

This paper presents a novel soft-switching PWM utility frequency AC to high frequency AC power conversion circuit incorporating boost-half-bridge inverter topology, which is more suitable and acceptable for cost effective consumer induction heating applications. The operating principle and the operation modes are presented using the switching mode and the operating voltage and current waveforms. The performances of this high-frequency inverter using the latest IGBTs are illustrated, which includes high frequency power regulation and actual efficiency characteristics based on zero voltage soft switching (ZVS) operation ranges and the power dissipation as compared with those of the previously developed high-frequency inverter. In addition, a dual mode control scheme of this high frequency inverter based on asymmetrical pulse width modulation (PWM) and pulse density modulation (PDM) control scheme is discussed in this paper in order to extend the soft switching operation ranges and to improve the power conversion efficiency at the low power settings. The power converter practical effectiveness is substantially proved based on experimental results from practical design example.

• Journal of Navigation and Port Research
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• v.36 no.9
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• pp.729-735
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• 2012

The primary wave energy conversion by a three-dimensional bottom-mounted oscillating water column (OWC) wave power device in regular waves has been studied. The linear potential boundary value problem has been solved following the boundary matching method. The optimum shape parameters such as the chamber length and the depth of the front skirt of the OWC chamber obtained through two-dimensional numerical tests in the frequency domain have been applied in the design of the present OWC chamber. Time-mean wave power converted by the OWC device and the time-mean second-order wave forces on the OWC chamber structure have been presented for different wave incidence angles in the frequency-domain. It has been shown that the peak period of $P_m$ for the optimum damping parameter coincides with the peak period of the time.mean wave drift force when ${\gamma}=0$.

• Journal of Ocean Engineering and Technology
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• v.19 no.3
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• pp.18-24
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• 2005

Wave overtopping is one of the most important processes for the design of seawalls. The term "wave overtopping" is used here to refer to the processes where waves hit a sloping structure run up the slope and, if the crest level of the slope is lower than the highest run up level, overtop the structure. Wave overtopping is dependent on the processes associated with breaking wave. A numerical model based on Navier-Stokes equation and the Marker-density function for predicting wave overtopping of coastal structures is developed in this paper. In order to evaluate the present model, two simulations are tested. One is overflow without waves at vertical seawall, and the other is wave overtopping at sloping seawalls.