• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume II
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• pp.535-538
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• 2006

The coastline of the Choa Phraya Rivermouth in the Upper Gulf of Thailand has been changed drastically. The western side especially at Ban Laem Sing was eroded for 400 meter in 26 years or with the rate of 15 meter per year on the average. The Metropolitan Electricity Authority has granted five years research project to us to study the efficiency of the electric pole fence as a mean to reduce the wave force and increase sedimentation rate inside for mangrove replantation. If the method works efficiently, it will be used to reclaim the coastal land loss in other areas in Thailand. The project was done since 2005 after the fence was constructed completely in October 2005. The oceanographic surveys were conducted before and after the construction in northeast monsoon season to study the impact of physical oceanographic forces on the coastline change. The sedimentation rates were measured each month. It is rather low about 2 cm/month. The subsiding rate from the load of deltaic sediment and groundwater withdraw using boring data is about 30 mm/year. The cumulative sinking rate is 55.8 cm from 1978 to 1995. We have tried to design the method of mangrove plantation in this area. The remote sensing data such as LANDSAT and aerial photos from 1987 to 2002 for 15 years were used to compute the rate of coastline change at each 50 m section along the western side of the rivermouth.

• Structural Engineering and Mechanics
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• 제59권4호
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• pp.653-669
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• 2016

Recent earthquakes worldwide show that a significant portion of the earthquake shaking happens in the vertical direction. This phenomenon has raised significant interests to consider the vertical ground motion during the seismic design and assessment of the structures. Strong vertical ground motions can alter the axial forces in the columns, which might affect the shear capacity of reinforced concrete (RC) members. This is particularly important for non-ductile RC frames, which are very vulnerable to earthquake-induced collapse. This paper presents the detailed nonlinear dynamic analysis to quantify the collapse risk of non-ductile RC frame structures with varying heights. An array of non-ductile RC frame architype buildings located in Los Angeles, California were designed according to the 1967 uniform building code. The seismic responses of the architype buildings subjected to concurrent horizontal and vertical ground motions were analyzed. A comprehensive array of ground motions was selected from the PEER NGA-WEST2 and Iran Strong Motions Network database. Detailed nonlinear dynamic analyses were performed to quantify the collapse fragility curves and collapse margin ratios (CMRs) of the architype buildings. The results show that the vertical ground motions have significant impact on both the local and global responses of non-ductile RC moment frames. Hence, it is crucial to include the combined vertical and horizontal shaking during the seismic design and assessment of non-ductile RC moment frames.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2006년도 전기학술대회논문집
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• pp.39-40
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• 2006

Diesel power plant(DPP) with the medium speed diesel engine is operated under the very severe condition in aspect of load and operating time as compared with the marine diesel generator set. So, minimized vibration level have to be insured for the more stable operation of engine and generator. The vibration of generator set mainly comes from the resonance between the rigid modes by resilient mount or distortion modes by structural stiffness and the excitation forces of engine. Then, avoidance of resonance with structural modification is generally well known. In this paper, the first order vibration in non-resonance range and local vibration modes were investigated by impact test, response/ODS(operational deflection shape) measurement and 3D finite element analysis for the additional reduction of vibration. The proposed countermeasures were actually applied and their final effects were verified through the in-situ measurement.

• Wind and Structures
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• 제25권4호
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• pp.397-413
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• 2017

When bridges are constructed with lower heights from the ground, the formed channel between the deck and the ground will inevitably hinder or accelerate the air flow. This in turn will have an impact on the aerodynamic forces on the deck, which may result in unexpected wind-induced responses of bridges. This phenomenon can be referred to "ground effects." So far, no systematic studies into ground effects on the wind-induced responses of closed box girders have been performed. In this paper, wind tunnel tests have been adopted to study the ground effects on the aerodynamic force coefficients and the wind-induced responses of a closed box girder. In correlation with the heights from the ground in two ground roughness, the aerodynamic force coefficients, the Strouhal number ($S_t$), the vortex-induced vibration (VIV) lock-in phenomena over a range of wind velocities, the VIV maximum amplitudes, the system torsional damping ratio, the flutter derivatives, the critical flutter wind speeds and their variation laws correlated with the heights from the ground of a closed box girder have been presented through wind tunnel tests. The outcomes show that the ground effects make the vortex-induced phenomena occur in advance and adversely affect the flutter stability.

• 비파괴검사학회지
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• 제33권2호
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• pp.154-159
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• 2013

본 논문은 마운트의 형상 정밀도와 볼트의 체결력에 따라 마운트에 고정되는 반사경에 발생되는 응력과 변형량에 대해 연구하였다. 일반적인 반사광학계에 사용되는 고정밀 반사경은 볼트나 접착제로 마운트에 조립되는데 이러한 경우 볼트의 체결력과 접착제의 접착력으로 인해 발생하는 장력이 반사경면을 뒤틀리게 한다. 또한 반사경과 마운트를 조립한 후 반사경에 접촉되는 마운트의 표면 형상 정밀도에 따라 반사경면이 뒤틀려서 형상 정밀도가 변한다. 본 논문에서는 유한요소법을 이용한 구조 해석을 통해 반사경과 접촉되는 마운트의 형상 정밀도와 볼트의 체결력에 의해 고정밀 반사경의 반사경면에 발생되는 응력분포와 뒤틀림 변형량에 대해 연구하였다.

• 유통과학연구
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• 제15권11호
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• pp.49-57
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• 2017

Purpose - In Korea, general super markets have a great impact on the market performance of traditional markets. We propose a modified two stage DEA model for evaluating the performance of traditional markets in Incheon, Korea by identifying the influence of external environmental factors including the presence of general super markets as non-discretionary variables in DEA. Research design, data, and methodology - After obtaining bias-corrected estimates of original DEA efficiency scores using the input and output data of 49 traditional markets, we regress them on several external environmental factors by bootstrap-truncated regression. Results - We obtain bias-corrected efficiency scores from the original DEA efficiency scores by bootstrap and among the five environmental factors, the residential population and the presence of general super markets or SSMs can be considered as the driving forces influencing bias-corrected efficiency scores, positively and negatively, respectively. Conclusions - When DEA efficiency scores tend to be overestimated, we need to use a biased-corrected efficiency score by bootstrap. It is important to note that the efficiency of traditional markets can be largely influenced by external environmental factors such as the presence of general super markets or SSMs that traditional markets can not control. Therefore, it is desirable to consider such environmental factors appropriately for a reasonable performance evaluation.

• 한국해양환경ㆍ에너지학회지
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• 제6권3호
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• pp.26-36
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• 2003

낙동강 하구의 사주 발달 과정을 과거 관측 자료를 토대로 분석하고, 수치해석기법을 도입하여 파랑의 변화와 이로 인한 해빈류를 계산하여 낙동강 하구역 및 그 인접해역에서의 3차원적인 지형변화를 예측, 하구의 해안선 변화와 사주의 발달과정을 관련시켜 보았다. 실제 지형변화와 수치 실험의 결과를 분석해 본 결과, 이들 해역에서의 해안선 변화 및 사주의 발달은 하구둑의 건설과 같은 인위적인 요소 외에 해빈류의 영향이 크게 작용하며, 장래에는 진우등 하단부와 다대포 해수욕장 전면에서 사주의 발달과 이동이 예상된다.

• International Journal of Aeronautical and Space Sciences
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• 제16권3호
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• pp.394-406
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• 2015

In this work, an efficient aircraft landing simulation strategy is proposed to develop an efficient and reliable hard-landing monitoring procedure. Landing stage is the most dangerous moment during operation cycle of aircraft and it may cause structural damage when hard-landing occurs. Therefore, the occurrence of hard-landing should be reported accurately to guarantee the structural integrity of aircraft. In order to accurately determine whether hard-landing occurs or not from given landing conditions, full nonlinear structural dynamic simulation can be performed, but this approach is highly time-consuming. Thus, a more efficient approach for aircraft landing simulation which uses a hierarchical aircraft landing model and an extended inertia relief technique is proposed. The proposed aircraft landing model is composed of a multi-body dynamics model equipped with landing gear and tire models to extract the impact force and inertia force at touch-down and a linear dynamic structural model with an extended inertia relief method to analyze the structural response subject to the prescribed rigid body motion and the forces extracted from the multi-body dynamics model. The numerical examples show the efficiency and practical advantages of the proposed landing model as an essential component of aircraft hard-landing monitoring procedure.

• 대한기계학회논문집A
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• 제31권5호
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• pp.578-585
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• 2007

A vacuum circuit breaker (VCB) with permanent magnet actuator (PMA) has been studied in this study. Electromagnetic field analysis and dynamic simulations have been carried out for optimal design of VCB by using commercial software Maxwell and ADAMS. This simulation model can be an effective method for the VCB, which has non-linear output force of PMA, friction, and impact for operations. An experiment has been conducted to evaluate correctness of the simulated model. By using this evaluated model, the displacement and velocity characteristics of the VCB have been simulated with following conditions : (1) The different output forces of PMA have been applied, (2) The friction conditions in follow lever shaft and moving part have been changed, (3) The mass conditions of moving part have been changed. The simulated results shows that the velocity characteristics are mainly determined by the output force of PMA. The effects due to the changes of friction conditions against the dynamic characteristics was small, and the mass conditions of the moving parts affect the velocity and a bouncing phenomenon of VCB. From these results, the optimal design conditions for the VCB have been derived.

• 한국정밀공학회지
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• 제26권10호
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• pp.116-121
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• 2009

It is important to consider lumbar lordotic angle for setup of training program in field of sports and rehabilitaton to prevent unexpected posture deviation and back pain. The purpose of this study was to analyze the biomechanical impact of the level of lumbar lordosis angle during isokinetic exercise through dynamic analysis using a 3-dimensional musculoskeletal model. We made each models for normal lordosis, excessive lordosis, lumbar kyphosis, and hypo-lordosis according to lordotic angle and inputted experimental data as initial values to perform inverse dynamic analysis. Comparing the joint torques, the largest torque of excessive lordosis was 16.6% larger and lumbar kyphosis was 11.7% less than normal lordosis. There existed no significant difference in the compressive intervertebral forces of each lumbar joint (p>0.05), but statistically significant difference in the anterioposterior shear force (p<0.05). For system energy lumbar kyphosis required the least and most energy during flexion and extension respectively. Therefore during the rehabilitation process, more efficient training will be possible by taking into consideration not simply weight and height but biomechanical effects on the skeletal muscle system according to lumbar lordosis angles.