• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2001.10a
• /
• pp.324-329
• /
• 2001

The destructive method is reliable and widely used for the estimation of material degradation but, it have time-consuming and a great difficulty in preparing specimens from in-service industrial facilities. Therefore, the estimation of degraded structural materials by nondestructive evaluation is strongly desired. In this paper, the use of guided wave was suggested for the evaluation of thermally damaged 2.25 Cr-lMo steel as an alternative way to compensate for limitations of fracture tests. The observation of microstructure variations of the material including carbide precipitation increase and spheroidization near grain boundary was conducted and the correlation with the guided wave features such as energy loss ratio and group velocity changes was investigated. Through this study, the feasibility of ultrasonic guided wave evaluation for thermally damaged materials was explored.

• Journal of Industrial Technology
• /
• v.16
• /
• pp.83-95
• /
• 1996

The equilibrium beach profiles with the effects of random waves and nonuniform grain size in the surf zone are derived from the Thornton and Guza(1983)'s energy dissipation model. The derived beach profiles are the functions of the breaking wave strength, the frequency of the incident wave, and the wave induced-energy dissipation at breaking point. It is not confirmed that the equilibrium beach profiles are better agreement with the measured profiles than the classical profiles. However, the characteristic of the changes of the beach profiles with respect to the breaking wave stgrngth and the frequency of the incident wave can be analyzed which has not been studied by the classical model.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2006.11a
• /
• pp.453-456
• /
• 2006

To examine the effect of shape and crest width variation of a permeable submerged breakwater on the wave energy dissipation, Two-Dimensional numerical model with Large Eddy Simulation, which is able to simulate directly WAve Structure Seabed interaction (hereafter, LES-WASS-2D) has been newly developed. A good agreement has been obtained by the comparison between the existing experimental results and LES-WASS-2D model's results for the permeable submerged breakwater. Moreover, based on the LES-WASS-2D model, the wave energy dissipation due to a permeable submerged breakwater are discussed for regular and irregular waves with relation to its crest width and shape.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 1997.10a
• /
• pp.126-131
• /
• 1997

Recently, the ground motion occurred by vehicles or trains has been recognized one of the major factors of damage of structures nearly the motion source. To isolate the environments from ground motions, it is necessary to understand the wave propagation in half spaces. Especially, Rayleigh wave is the primary concern because it transmits a major portion of the total source energy and decays the energy more slowly with response to distance than the other waves. In this study, the preliminary data(wave length and damping effect) to design the isolating system are obtained. For this, a field dynamic test is performed, using the exciter which can generate the 100kN vertical cyclic load in the range of 1-60 Hz is used. The fifteen accelerometers to measure the ground response are set up in 3 radial direction at intervals of 10 meters in each row. The wave lengths are calculated using the distance and the phase between the measuring points. The damping effects of the Rayleigh-wave are also observed from the experiments.

• Journal of Korean Port Research
• /
• v.8 no.2
• /
• pp.67-77
• /
• 1994

A time-domain numerical model is developed to examine the performance of a wave energy focusing structure in combined waves and a current. With the current assumed to be slow and the structure fully submerged, the wave-current interaction problem is reduced to a wave scattering problem in a uniform current. The diffraction of incident waves around a narrow berm is considered. The shape of the berm is defined by a parabola, imitating that of an optical reflector. The energy focus is achieved by reflecting the incident waves through a predetermined focal point. Through the numerical simulations, the numerical model is shown to be effective in modeling the wave-current interaction problem, and the current speed and direction are shown to affect significantly the location, amplitude and sharpness of the focus.

• The Journal of the Acoustical Society of Korea
• /
• v.41 no.5
• /
• pp.589-600
• /
• 2022

In order to verify the reliability of Dry Test Bench (DTB) used for testing the output energy from ballistic extracorporeal shock wave therapeutic devices, the measurements with DTB were compared with the acoustic energy measured with a Laser Doppler Vibrometer (LDV) for a commercial ballistic ESWT device. It was shown that the mechanical energy detected with DTB had variability maintained within 5 % at the same output power setting and also had a linear correlation (adj. R² = 0.991) with the acoustic energy measured with the LDV for the entire output power settings. Using the correlation between the two methods and the correlation on the acoustic energy measured in between air and water with the LDV, the DTB measurement can be used to estimate the energy flux density in water with an average error of 7.85 % for the entire output power settings of the ballistic shock wave generator considered in the experiment. DTB provides information limited to the output mechanical energy and therefore it is not suitable for testing the various acoustic output parameters required in IEC61846 and IEC63045. However, DTB that is simple in measurement principles and easy to use is expected for manufacturers and clinical users to monitor the performance of ballistic Extracorporeal Shock Wave Therapy (ESWT) devices.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.18 no.3
• /
• pp.223-232
• /
• 2015

The present paper considers the conceptual design of floating wave-offshore wind hybrid power generation system. The worldwide demand for ocean renewable energy is increasing rapidly. Wave and offshore wind energy have been attractive among the various ocean renewable energy sources, and the site to generate electricity from wave and offshore wind accords well together. This means that a hybrid power generation system, which uses wave and offshore wind energy simultaneously has many advantages and several systems have been already developed in Western Europe. A R&D project for a 10 MW class floating wave-offshore wind hybrid power generation system has been also launched in Korea. A semi-submersible platform, which has four vertical columns at each corner of the platform to be connected with horizontal pontoons, was designed for this system considering arrangements of multiple wind turbines and wave energy converters. A mooring system and power cable were also designed based on the metocean data of installation site. In the present paper, those results are presented, and the difficulties and design method in the design of hybrid power generation system are presented.

• Bulletin of the Korean Space Science Society
• /
• 2003.10a
• /
• pp.40-40
• /
• 2003

When the magnetotail is disturbed by an impulsive input such as the substorm onset, compressional magnetohydrodynamic (MHD) waves play an important role in delivering perturbed energy and exciting various wave modes and currents. The plasmasheet, in which relatively hot plasmas exist, is surrounded by relatively cold plasmas at the plasma sheet boundary layer (PSBL) and the equatorial plasmasphere. Since the Alfven speed significantly varies near these regions, the compressional waves are expected to undergo mode conversion by inhomogeneity at the boundary between cold and hot plasma regions. We investigate how the initial compressional MHD wave energy is reflected, transmitted, and absorbed across that boundary by adopting the invariant imbedding method (IIM) which gives the exact reflection, transmission, and absorption coefficients without any theoretical approximations for given frequencies and wave numbers. The IIM method is very useful in quantifying the reflection and transmission of compressional waves in the sense that we can calculate how much fast mode wave energy is delievered into shear Alfven waves or field-aligned currents. Our results show that strongly localized absorption occurs at the boundary region. This feature suggests that localized field-aligned currents can be impulsively excited at such boundary regions by any compressional disturbances, which is highly associated with impulsive auroral brightening at the substorm onset. We compare our results with previous studies in cold inhomogeneous plasmas.

• Journal of Advanced Research in Ocean Engineering
• /
• v.4 no.2
• /
• pp.66-77
• /
• 2018

This paper presents a parametric study on an oscillating water column (OWC) wave energy converter (WEC). This OWC has been planned for installation in the breakwaters on isolated islands located away from the mainland. Both a numerical analysis and a model experiment are utilized for determining a proper conceptual design for this purpose. Various design parameters, including the configurations and dimensions, are evaluated through the numerical analysis, which is based on a potential flow theory, and several design concepts are then selected as candidates. The model experiment using a 2D wave flume is conducted to evaluate the effects of the design parameters and compare the performances of the candidates. Based on the overall results of the numerical analysis and model experiment, a conceptual design of the OWC WEC applicable to a breakwater is selected.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.65 no.5
• /
• pp.811-818
• /
• 2016

This paper suggests a structure of power control system in floating wave-offshore wind hybrid power generation system. We have developed an unified SCADA(Supervisory Control and Data Acquisition) system which can be used to monitor and control PCS(Power Conversion System) based on IEC61850. The SCADA system is essential to perform the algorithm like proportional distribution and data acquisition, monitoring, active power, reactive power control in hybrid power generation system. IEC61850 is an international standard for electrical substation automation systems. It was made to compensate the limitations of the legacy industrial protocols such as Modbus. In order to test the proposed SCADA system and algorithm, we have developed the wind-wave simulator based Modbus. We have designed a protocol conversion device based on real-time Linux for the communication between Modbus and IEC61850. In this study, SCADA system consists of four 3MW class wind turbines and twenty-four 100kW class wave force generator.