• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.4
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• pp.254-262
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• 2015

Parametric study on submerged body shape of an oscillating hemisphere point absorber was conducted to predict the optimal relation between radius and draft of the body. As an additional damping due to power takeoff system, the optimal damping same as wave radiation damping was applied to the PTO system to produce the maximum wave power. Body response spectrum and power spectrum were obtained for various peak frequencies on wave spectra. It was found that the maximum power can be generated when the peak frequency of available wave power was 20% greater than that of wave spectrum.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.3
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• pp.249-257
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• 2013

This study newly presents a synthetic phase tuning technique to suppress the unwanted torsional mode while enhancing the desired torsional mode in a pipe. Specifically, we aim at the enhancement of the first torsional mode and the suppression of the undesired, second torsional mode. Earlier efforts were to enhance the desired wave mode only in the hope that the enhancement results in the suppression of the unwanted wave mode. Unlike these efforts, the suggested technique makes the complete cancellation of the unwanted wave mode but it is shown to enhance the desired first mode for torsional wave problems. In the present study, the synthetic phase tuning is developed for the cancellation of the unwanted wave mode, meaning that the number of necessary experimental equipments is reduced. Simulation and experiment were carried out to check the effectiveness of the proposed method. As an application of the suggested technique, we investigated the reflection and mode conversion characteristics of the first torsional mode according to the step thickness variation in a stepped pipe.

• Journal of Ocean Engineering and Technology
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• v.29 no.2
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• pp.191-198
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• 2015

In this study, we proposed a new type of dual-buoy wave energy converter (WEC) exploiting multi-resonance and analyzed the experimental results from a model test in a 2-D wave flume. A dual-buoy WEC using multi-resonance has two advantages: high efficiency at the resonant frequencies and the potential to extend the frequency range available to extract wave power from the WEC. The suggested WEC was composed of an outer buoy and an inner buoy sliding vertically inside the outer buoy. As the power take-off device, a linear electric generator (LEG) consisting of permanent magnets and coils fixed at each buoy was adopted. Electricity was produced by the relative heave motion between the two buoys. To search for the optimal shape of a dual-buoy WEC, we conducted experiments on the heave motion of a two-body system in regular waves without an LEG installed. Model tests with six combinations of experimental models were conducted in order to find the motion characteristics of a dual-buoy WEC. It was found that model 2, which included a ring-shaped appendage to move the resonant frequency of the outer buoy toward a high value, showed a higher relative heave response amplitude operator (RAO) curve than model 1. In addition, the double-peak shape of the heave RAO curve shown for model 2 indicated the extension of the frequency range for extracting wave power in irregular waves.

• Journal of the Korean Institute of Gas
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• v.19 no.5
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• pp.29-35
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• 2015

Pipes, commonly used in energy and petrochemical facilities, have various types of defects induced by diverse factors and this is often issued in NDE society. Ultrasonic guided wave inspection method are normally adopted to insure the healthiness of industry pipes. Recently, ultrasonic guided wave inspection is shifted to adopt arrayed probes and system. And here we developed an array guided wave ultrasonic testing system can adapt arrayed probes and focusing methods. In this paper, an array guided wave ultrasonic testing system is presented including a transmitting focusing technique and flaw signal level enhancement.

• Korean Journal of Oriental Medicine
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• v.17 no.3
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• pp.87-96
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• 2011

Objectives : The study on the affected factor of the pulse wave is important in the pulse wave part. The purpose of this study is to secure the objective data of pulse-wave parameter on the food intakes affected the radial pulse-wave. Methods : The study was carried out healthy adult men. We researched the blood circulation index and the changes of the pulse factor according to 'before meal', 'right after meal', '30 minute after meal', '1 hour after meal' and '2 hours after meal'. We analyzed the changes according the time schedule. And analyzed the difference between 'before meal' and 'after meal'on the pulse-wave parameter. Results : The results were as follows. 1. HR, ECO and ECI were showed the highest increase 'after meal' and the significant decrease in '2 hours after meal' with 'before meal' degree. 2. In the pulse energy, 'left hand average pulse energy' was showed the highest increase 'after meal', and 'right hand average pulse energy' and 'right Quan(關)' were showed the highest increase in '30 minute after meal'. 3. h1 of '6 part of left and right hand'(Chon-Quan-Chuk, 寸關尺) was showed the significant difference statistically in 'left Chuk' and 'right Quan'. 4. T was showed the highest 'before meal' and the lowest after meal in '6 part of left and right' (Chon-Quan-Chuk, 寸關尺). 5. RAI was showed the highest 'before meal' in '6 part of left and right'(Chon-Quan-Chuk 寸關尺). Conclusions : From the about results, the food intakes was considered important factor of pulse formation. On the factor affected the pulse, we considered that continuous study needs for the future.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.1
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• pp.8-18
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• 2002

In this paper, wave energy absorption of OWC(oscillating water column) device is analyzed. The analytic model consists of a partially immersed circular vertical cylinder open at its end and an air turbine connected with the air chamber. The boundary value problem is decomposed into scattering problem related to scattering by an incident wave in the absence of a pressure variation and radiation problem describing the flow due to an oscillating pressure in the absence of an incident wave. By invoking the continuity of an air flow inside the chamber, the oscillating pressure in a chamber is derived. With oscillating pressure, the mean power absorbed by OWC device and the capture width are obtained. In numerical calculation, the induced volume flux across the internal free surface of the chamber in the scattering and radiation problem and the maximum capture width are compared with various design parameters such as radius and submergence depth of chamber and wave conditions. The maximum capture width obtained by choosing the optimal value of turbine constant occurs at the first resonant mode (Helmholtz mode) among the natural frequencies of a circular cylinder chamber.

• Journal of Navigation and Port Research
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• v.37 no.6
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• pp.597-601
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• 2013

Recently, many studies about the wave power generation system for the marine structure as the hybrid form in linked with the original features have been made of. Of these, the wave power generation system using oscillating water column(OWC) has function to convert wave energy to electrical energy with original function of the break water structure. In this type of generation system, it is important to make the flow of sea water as much as possible without loss. Output characteristics of wave power generation system depending on entrance section were described in the paper. Also, flow quantity changing with entrance section, velocity of sea water and output of wells turbine were measured by simulating OWC wells turbine model in break water, one of the general marine structure. Finally, entrance section was suggested to enhance the energy conversion efficiency based on the results of simulation.

• Journal of Ocean Engineering and Technology
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• v.36 no.5
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• pp.326-339
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• 2022

Recently, not only Korea but also the world has been suffering from problems related to coastal erosion. The hard defense method has been primarily used as a countermeasure against erosion. However, this method is expensive and has environmental implications. Hence, interest in other alternative methods, such as the eco-friendly vegetation method, is increasing. In this study, we aim to analyze the hydraulic characteristic of submerged rigid vegetation according to the cross-sectional change through a hydraulic experiment and numerical simulation. From the hydraulic experiment, the reflection coefficient, transmission coefficient, and energy dissipation coefficient were analyzed according to the density, width, and multi-row arrangement of the vegetation zone. From numerical simulations, the flow field, vorticity distribution, turbulence distribution, and wave distribution around the vegetation zone were analyzed according to the crest depth, width, density, and multi-row arrangement distance of the vegetation zone. The hydraulic experiment results suggest that the transmission coefficient decreased as the density and width of the vegetation zone increased, and the multi-row arrangement condition did not affect the hydraulic characteristics significantly. Moreover, the numerical simulations showed that as the crest depth decreased, the width and density of vegetation increased along with vorticity and turbulence intensity, resulting in increased wave height attenuation performance. Additionally, there was no significant difference in vorticity, turbulence intensity, and wave height attenuation performance based on the multi-row arrangement distance. Overall, in the case of submerged rigid vegetation, the wave energy attenuation performance increased as the density and width of the vegetation zone increased and crest depth decreased. However, the multi-row arrangement condition did not affect the wave energy attenuation performance significantly.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.5
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• pp.285-290
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• 2013

Both full linear and shallow water edge waves are compared to get a better understanding of edge wave behavior. By using method of separation of variables, we are able to get solution of full linear edge wave presented by Ursell (1952) without derivation. The shallow water edge waves show dispersive features despite being derived from shallow water equations. When bottom slope is mild enough, shallow water edge wave tends to linear edge wave and has some advantages of manipulation. Solution of edge wave generated by a moving landslide of Gaussian shape is constructed by an expansion of shallow water normal modes. Numerical results are presented and discussed on their main features.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.1
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• pp.60-73
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• 2014

The seaward reverse wave, occurring on the submerged dual porous horizontal plate, can contribute to the reduction of the transmitted wave as it reflects the propagating wave. However, the collision between the propagating and seaward reverse waves increases the water level and acts as a weight on the horizontal plate. This study investigated the characteristics of the wave pressure created by the seaward reverse wave through the analysis of experimental data. The analysis confirmed the following results: 1) the time series of the wave pressure showed reverse phase phenomena due to the collision, and the wave pressures acted simultaneously on both upper and lower surfaces of the horizontal plate; 2) the horizontal plate became repeatedly compressed and tensile before and after the occurrence of the seaward reverse wave; and 3) the seaward reverse wave created the total wave pressure to the maximum towards the direction of gravity, primarily on the upper plate. It was also confirmed that the wave distributions showed a similar trend to the wave steepness. Such outcome of the analysis will provide basic information to the structural analysis of the horizontal plate as a wave dissipater of the steel-type breakwater (STB).