• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.1
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• pp.45-52
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• 2009

In this paper, a guideline for designing breakwater in wave loads and in seismic loads is proposed. A simple model structure in breaking wave zone is examined using Morison equation in consideration with the effect of an impact load, for evaluation of the wave loads. As the impact load effect is not significant, pressure distributions according to Goda are applied for evaluation of wave loads on breakwater. Structural behavior of breakwater in wave loads can be obtained using the Goda method, as well. For seismic analysis, Ofunato and Hachinohe models, as well as an artificial seismic acceleration loads model, are adopted. Soil-structure interaction analysis is carried out to find the seismic load effect. It is found that, in certain cases, structural deformation in wave loads is in the same level as deformation that in seismic loads. Thus, it is our recommendation that these two loads are considered at the same level in breakwater design.

• Journal of Navigation and Port Research
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• v.29 no.8 s.104
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• pp.661-666
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• 2005

Recent warnings indicate that there is a potential risk of massive earthquake. These earthquakes could produce large-scale tsunamis. Consideration of the effect of Tsunami to the moored ship is very important bemuse it brings the loss of life and vast property damage in a viewpoint of ship operations within a harbor. If a tsunami occurs, a ship in a harbor may begin drifting in case of ship entering and departing harbor, and breakage of mooring rope and drifting of moored ship are happened. And extremely serious accident, such as stranding and collision to a quay, might occur. On the other hand, since the tsunami consists of approximately component waves of several minutes, there is a possibility of resonance with the long period motion of mooring vessel. As the speed of Tsunami is much faster than tidal current in a harbor, a strong resisting force might act on the moored ships. In this paper, the numerical simulation procedure in the matter of ship motions due to the attack of large-scale tsunamis are investigated and the effects on the ship motions and mooring loads are evaluated by numerical simulation.

• The Journal of the Korea Contents Association
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• v.11 no.9
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• pp.166-173
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• 2011

Asia has shown a tendency that a certain country's culture leads the fashion in turn every 10 years. The trend of Hong Kong movies in 1980's was called 'Hong Kong Wave', the trend of Japanese animation and games in 1990's was called 'Japanese Wave', and then the 'Korean Wave' began in the late 1990's. This term '~Wave(流)' is a Japanese-style term meaning '~way', '~style', '~group', and so on. In the same manner, recent popularity of Taiwanese TV dramas and a particular star that is in fashion in Japan are called 'Taiwanese Wave', and Chinese movies, broadcast, tourism, and etc. are called 'Chinese Wave'. Thus, the term 'Korean Wave' is a part of expression '~wave' used in Japan and it started to be used in the mean time, and was officially used in <韓流-Song from Korea>, a promotion record of Korean pop music, produced by Ministry of Culture and Tourism in Korea. In this paper I propose to correct the error of the term 'Korean Wave', and furthermore, to define a term expressing Korean culture and study for its usage.

• Journal of the Korean Magnetics Society
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• v.14 no.3
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• pp.109-113
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• 2004

GMR isolator was modeled using a Wheatstone bridge which is profitable for transmitting rectangular wave digital data, and the output voltage characteristics in relation to the input current were investigated in time domain. GMR isolator modeling was divided into two parts, namely magnetic and electric parts. The flow chart of the modeling was drawn in which measured MR curve of the spin valves were incorporated to obtain the electrical voltage output. For magnetic modeling, 3-dimensional model of planar coil was analyzed by FEM method to obtain the magnetic field strength corresponding to the input current. For electric modeling, resistance, inductance and capacitance of the planar coil were calculated and magnetic field waveform was obtained corresponding to the coil current waveform in time domain. Finally, MR-H curves of spin valves and the magnetic field waveform at the spin valves were composited to obtain the output voltage waveform of the isolator. Even though the amplitude of the coil current waveform was increased by 100％, decreased by 90％, or delayed by 10％ of the period compared with the input current, similar transmitted output voltage waveform to the input current waveform was obtained due to hysteretic characteristics of the spin valves at the transmission speed of over 400 Mbit/s.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.3
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• pp.23-32
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• 2004

The local geologic and dynamic site characteristics, which include soil profiles, shear wave velocity profiles and depths to the bed rock were gathered from 148 sites all over the Korean peninsula and those values are compared to those in the western USA. Site response analyses were performed based on equivalent linear scheme using design rock-outcrop acceleration of 0.154g which corresponds to the collapse level of earthquake for seismic category I structure. The results show that the amplification factor based on Korean seismic design guideline underestimates the motion in short-period range and overestimates the motion in mid-period range. It is suggested that the existing Korean seismic guideline based on UBC is required to be modified considering dynamic site characteristics in Korea for the reliable estimation of site amplification.

• Korean Journal of Optics and Photonics
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• v.19 no.3
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• pp.175-181
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• 2008

We develop a fiber optic acceleration sensor with LED, PD, POF, and a cantilever beam, having film grating at the edge of the beam. Light is transmitted from LED to PD through the film grating. When the cantilever beam moves by external vibration, output light is modulated as sinusoidal signals. The characteristics of output signals are dominated by the spacing of the film grating and also by the size and the elasticity of the beam. Two output signals, having constant initial phase difference, are obtained by two gratings with 90 degree phase difference. Those two signals are used to determine phase angle, which is proportional to the displacement of the beam. Finally, the acceleration is determined from conversion equation between displacement and acceleration. This sensor is designed for monitoring the vibration of large and complex building in the low frequency range of below 7 Hz, and is particularly suitable to measure acceleration in electromagnetic environments.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.247-247
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• 2019

수력발전 사업에 있어 Desander 구조물은 주로 고산지대 수력발전댐의 Run-of-river 형식의 발전방식에서 유사로 인한 터빈의 손상을 방지하기 위한 목적으로 설치된다. Desander의 적정 규모는 터빈의 손상을 일으킬 수 있는 유사 입경에 대해 안정적으로 침전을 시킬 수 있는 폭/길이/깊이로 평가할 수 있으며 상대적으로 Desander의 규모가 크게 설계된 경우 초기 공사비 증가하고 반대로 규모가 작게 설계된 경우 터빈의 교체 주기 단축으로 인한 유지관리비가 증가된다. 현재까지 일반적인 Desander 구조물의 설계 방식은 제거 입경의 침전 속도, 유입유량 및 깊이를 변수로 사용하여 경험식(L. Sudry method, Guicciardis method 및 Rouse method)을 통해 규모를 결정해 왔다. 하지만, 3-D 전산유체해석을 통해 유속 흐름 분석으로 직 간접적 Desander 규모의 적정성을 평가할 수 있는 현 시점에서 경험식으로부터 도출된 결과의 신뢰성과 객관성을 검증할 필요가 있다고 판단된다. 본 연구에서는 노르웨이 NSTU에서 개발한 유사의 이송 및 확산해석 기능이 내장된 범용 소프트웨어인 SSIIM을 이용하였다. SSIIM(Simulation of Sediment movements In water Intakes with Multiblock)은 개수로 흐름 상태에서 유사 이동 및 하상 변동을 분석할 수 있도록 개발된 3-D 해석 프로그램이다. SSIIM은 수치해석 방법으로 유한체적법(Finite Volume Method)를 채택하였으며 Navier-Stokes equations을 통해 유체의 흐름을 해석한다. 입력 자료는 유입 유량($m^3/sec$), 유입 유사량(kg/sec), 유출부 수위 및 해당 Desander Structure grid 자료가 사용되며 해석 결과로 Desander 내 grid 별 유속, 수위, 유사 농도 변화 등을 제공한다. 본 연구에서는 SSIIM을 이용하여 제거 목표 유사 입경의 차집 효율(Trap efficiency)로 Desander의 적정 규모를 평가 할 수 있는 설계법을 제안하며 설계 단계에서 결정되는 최소 제거유사 입자와 차집 효율에 의한 Desander의 적정 규모 평가 분석을 파키스탄 A 프로젝트를 대상으로 수행하였다. 연구 성과로 (1)SSIIM을 통해 해석된 차집 효율을 기초로 Desander의 적정 규모를 계획할 경우 경험적 방식에 비해 설계의 객관성과 신뢰성을 제고할 수 있으며 (2)3-D 수치해석을 통해 grid 별 유사농도를 확인 할 수 있어 Desander 형상과 규모에 대한 평가가 가능하다.

• Journal of the Korean Geotechnical Society
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• v.34 no.1
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• pp.5-16
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• 2018

In this study, seismic performance of geotechnical seismic isolation system capable of primary seismic isolation in the ground was evaluated. 1-G shaking table test was used to assess the performance of Teflon or steel slag as geotechnical seismic isolation systems installed beneath superstructure foundation. Response acceleration and response spectra were analyzed considering different input motions. The results were compared with those of fixed foundation structure without seismic isolation system. The steel slag-type seismic isolation system showed significant reduction in acceleration. The teflon-type seismic isolation system did not show significant effects on acceleration reduction in low-to-moderate seismicity condition, but it did show better effects in case of strong seismic condition. As input motion was transferred to the upper mass, the response spectrum of the fixed foundation structure was amplified in the short period range. In contrast, the response spectrum of the structure with seismic isolation using teflon or steel slag amplified in the long period range. It is found that the change of periodicity and the friction characteristics between isolation materials and foundations affected acceleration reduction.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.145-152
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• 2010

This study evaluated the fatigue degradation in a SUS316L specimen using the nonlinear ultrasonic method. The nonlinearity of the ultrasonic wave was estimated by a relative nonlinear parameter defined as the ratio of the amplitudes for the fundamental wave to the second harmonic wave. In the experiment, a measurement system with contact transducers was constructed; reliable measurements were assured by keeping measurement conditions consistent and reducing extra harmonics generated in the measurement system. Two types of SUS316L specimen were used in experiments; a rotating bar fatigue specimen and a tensile fatigue specimen. The fatigue condition used was high cycle fatigue. The former specimen had a cylindrical shape and was used to observe the change in the nonlinear parameter after fatigue accumulation in a specimen. The latter was a plate-shaped specimen and was used to confirm the change in the nonlinear parameter at the position where the fatigue stress was concentrated. The measured nonlinear parameter showed a strong correlation to the damage level in both fatigue tests.

• Journal of the Korean Geosynthetics Society
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• v.21 no.4
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• pp.41-53
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• 2022

In the excavation work like blasting/excavator work bordering on the urban railway, the dynamic safety of railway structures like tunnel, open-cut box structure and elevated bridge was investigated by numerical analysis in this study. The practically presented criteria on influential zones at the blasting work in the construction industry was numerically checked in cases of the precise vibration-controlled blasting (type II) and the small scale vibration-controlled blasting (type III) and it was shown that the criteria on blasting work methods needed to be supplemented through continuous field tests and numerical analyses. The influence of excavation vibration by mechanical excavators was especially investigated in case of earth auger and breaker. The numerical analysis of tunnel shows that the criteria on vibration velocities from the regression analysis of field test values was conservative. The amplification phenomenon of excavating vibration velocity was shown passing through the backfilling soil between the earth auger and the open-cut box structure. It was shown that the added-vibration on the superstructure of elevated bridge was occurred at the bottom of pile like earthquake when the excavator vibration was arriving at the pile toe. The systematic and continuous research on the vibration effect from excavating works was needed for the safety of urban railway structures and nearby facilities.