• 대한원격탐사학회지
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• 제35권1호
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• pp.29-37
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• 2019

Synthetic Aperture Radar (SAR) observations are powerful tools to monitor surface's displacement very accurately, induced by earthquake, volcano, ground subsidence, glacier movement, etc. Especially, radar interferometry (InSAR) which utilizes phase information related to distance from sensor to target, can generate displacement map in line-of-sight direction with accuracy of a few cm or mm. Due to decorrelation effect, however, degradation of coherence in the InSAR application often prohibit from construction of differential interferogram. Offset tracking method is an alternative approach to make a two-dimensional displacement map using intensity information instead of the phase. However, there is limitation in that the offset tracking requires very intensive computation power and time. In this paper, efficiency of parallel computing has been investigated using high performance computer for estimation of glacier velocity. Two TanDEM-X SAR observations which were acquired on September 15, 2013 and September 26, 2013 over the Narsap Sermia in Southwestern Greenland were collected. Atotal of 56 of 2.4 GHz Intel Xeon processors(28 physical processors with hyperthreading) by operating with linux environment were utilized. The Gamma software was used for application of offset tracking by adjustment of the number of processors for the OpenMP parallel computing. The processing times of the offset tracking at the 256 by 256 pixels of window patch size at single and 56 cores are; 26,344 sec and 2,055 sec, respectively. It is impressive that the processing time could be reduced significantly about thirteen times (12.81) at the 56 cores usage. However, the parallel computing using all the processors prevent other background operations or functions. Except the offset tracking processing, optimum number of processors need to be evaluated for computing efficiency.

• 콘크리트학회논문집
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• 제25권1호
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• pp.99-106
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• 2013

고속 비상체에 의한 충격을 받는 콘크리트는 그 충격력에 의해 관통, 표면관입 및 배면박리뿐만 아니라 균열의 확산에 의해 나타나는 국부적인 파괴 등 정하중을 받을 때와 다른 파괴거동을 보인다. 이러한 콘크리트의 파괴거동은 비상체의 재료적 특성, 충돌속도, 질량 및 기하학적 구조뿐만 아니라 콘크리트의 재료적 특성, 시험체의 크기 및 두께, 보강재료 및 방법 등 다양한 요인에 의해 영향을 받는다. 이 연구에서는 콘크리트 재료의 압축강도에 따른 표면관입깊이 및 배면박리성상에 대하여 평가하고, 섬유보강에 의한 배면박리억제효과에 대하여 검토하고자 하였다. 그 결과 압축강도의 증가로 인하여 표면관입깊이는 감소하였으며, 이 연구 범위의 결과는 수정 NDRC식 및 US ACE식과 유사한 경향을 나타냈다. 반면, 배면박리억제에 있어 압축강도 증가에 의한 영향은 확인할 수 없었으며, 섬유보강에 의한 인성의 향상을 통하여 배면박리를 억제할 수 있었다.

• 전자공학회논문지
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• 제51권8호
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• pp.97-103
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• 2014

최근 선형 주파수 변조-주파수 편이(Linear Frequency Modulation-Frequency Shift Keying: LFM-FSK) 신호를 사용한 후방 감시용 차량용 레이더 신호 처리 기법이 고안 되었다. 두 개의 계단 주파수(stepped frequency)신호를 순차적으로 연결한 LFM-FSK 신호의 특성을 이용 할 경우 후방 관측을 통해 차량에 대한 inverse synthetic aperture radar(ISAR) 영상을 형성할 수 있다. 이 때 관측 차량에 대한 ISAR 영상의 형성 시 펄스 간 위상 오차(inter-pulse phase error)로 인해 영상의 초점이 흐려지게 된다. 이를 해결하기 위해 본 논문에서는 particle swarm optimization(PSO)를 활용한 high resolution range profile(HRRP)의 엔트로피(entropy) 최소화를 통해 펄스 간 위상 오차의 보상을 시행하였다. 여기서 LFM-FSK 신호를 이용하여 추정 한 관측 차량의 상대속도는 비용함수의 탐색구간(searching space)을 적절히 설정하는데 도움을 준다. 시뮬레이션 결과는 제시 된 기법을 적용하여 펄스 간 위상오차의 보상을 수행함으로써 초점이 맞는 ISAR 영상이 형성됨을 보여준다.

• 한국멀티미디어학회논문지
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• 제19권4호
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• pp.725-735
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• 2016

High-resolution satellite images are used in the fields of mapping, natural disaster forecasting, agriculture, ocean-based industries, infrastructure, and environment, and there is a progressive increase in the development and demand for the applications of high-resolution satellite images. Users of the satellite images desire accurate quality of the provided satellite images. Moreover, the distinguishability of each image captured by an actual satellite varies according to the atmospheric environment and solar angle at the captured region, the satellite velocity and capture angle, and the system noise. Hence , NIIRS must be measured for all captured images. There is a significant deficiency in professional human resources and time resources available to measure the NIIRS of few hundred images that are transmitted daily. Currently, NIIRS is measured every few months or even few years to assess the aging of the satellite as well as to verify and calibrate it [3]. Therefore, we develop an algorithm that can measure the national image interpretability rating scales (NIIRS) of a typical satellite image rather than an artificial target satellite image, in order to automatically assess its quality. In this study, the criteria for automatic edge region extraction are derived based on the previous works on manual edge region extraction [4][5], and consequently, we propose an algorithm that can extract the edge region. Moreover, RER and H are calculated from the extracted edge region for automatic edge region extraction. The average NIIRS value was measured to be 3.6342±0.15321 (2 standard deviations) from the automatic measurement experiment on a typical satellite image, which is similar to the result extracted from the artificial target.

• 한국지반공학회논문집
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• 제27권7호
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• pp.5-16
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• 2011

고체 역학 및 유체 역학 분야에서 대상 물체의 변형, 변위 및 속도를 측정하기 위하여 디지털 이미지 해석 기법이 개발, 사용되고 있다. 지반 공학에서도 흙을 포함한 지반 구조물의 변형을 관측하기 위하여 Particle Image Velocimetry (PIV)와 Digital Image Correlation (DIC) 기법이 실내 시험 및 모형 시험 등에 적용되기 시작하는 추세이다. 이미지 해석은 시료의 종류 및 크기, 카메라 해상도, 해석 범위, 이미지 해석 조건에 영향을 받으므로, 다양한 조건에서의 정밀도를 평가하여 합리적으로 최적 조건을 결정할 필요가 있다. 본 연구에서는 디지털 이미지 해석 결과에 영향을 미치는 다양한 요소를 정리하였다. 그리고 높은 정확도의 해석 결과를 얻을 수 있는 최적의 이미지 해석 조건을 결정하는 절차를 제안하였으며 최종적으로 제안된 절차의 적용성을 점성토 시료에 대하여 검증하였다.

• Wind and Structures
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• 제13권6호
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• pp.557-580
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• 2010

A new inflow turbulence generation method and a combined dynamic SGS model recently developed by the authors were applied to evaluate the wind effects on 508 m high Taipei 101 Tower. Unlike the majority of the past studies on large eddy simulation (LES) of wind effects on tall buildings, the present numerical simulations were conducted for the full-scale tall building with Reynolds number greater than $10^8$. The inflow turbulent flow field was generated based on the new method called discretizing and synthesizing of random flow generation technique (DSRFG) with a prominent feature that the generated wind velocity fluctuations satisfy any target spectrum and target profiles of turbulence intensity and turbulence integral length scale. The new dynamic SGS model takes both advantages of one-equation SGS model and a dynamic production term without test-filtering operation, which is particular suitable to relative coarse grid situations and high Reynolds number flows. The results of comparative investigations with and without generation of inflow turbulence show that: (1) proper simulation of an inflow turbulent field is essential in accurate evaluation of dynamic wind loads on a tall building and the prescribed inflow turbulence characteristics can be adequately imposed on the inflow boundary by the DSRFG method; (2) the DSRFG can generate a large number of random vortex-like patterns in oncoming flow, leading to good agreements of both mean and dynamic forces with wind tunnel test results; (3) The dynamic mechanism of the adopted SGS model behaves adequately in the present LES and its integration with the DSRFG technique can provide satisfactory predictions of the wind effects on the super-tall building.

• 한국정밀공학회지
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• 제25권10호
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• pp.122-129
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• 2008

This paper deals with precise positioning of a high-speed positioning stage without inducing residual vibration by using an input shaping technique. Input shaping is well known to be a very effective tool for suppressing the residual vibration of flexible structures. However, the ordinary input shaping for positioning stages is designated mostly for velocity regulation, not for the residual vibration at the target position. The main difficulties in implementing input shaping along with precise positioning are the time delay caused by the servo system characteristics and the s-curve feature often employed in some motor controllers. This paper analyzes the dynamic responses of a single-mode-dominate stage system subjected to input shaping. A theoretical model is developed io investigate the nature of system. In order to overcome the difficulty, this paper proposes an improved input shaper based on modified command profile generation. The proposed method is proved effective through experiments and simulations.

• Asian Journal of Atmospheric Environment
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• 제5권2호
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• pp.113-120
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• 2011

Adsorbent combination studies have been carried out to remove nitrogen dioxide ($NO_2$) and volatile organic compounds (VOCs: BTEX) out of a subway environment characterized by high flow and low concentration. Optimal conditions for the high removal efficiency of the concerned target compounds were obtained through testing a series of control factors such as adsorbent sorts, thicknesses, and superficial velocity. It was found that the efficiencies increased as the specific surface area of activated carbon and its thickness increased, and external void fraction decreased. Furthermore, mixed activated carbon with granular and constructed contents was extensively tested to reduce pressure drop through the carbon bed. It was found that the performance of higher contents of granular activated carbon was better than that of higher contents of the constructed carbon. When the mixed carbon was applied to the subway ventilation system in order to eliminate $NO_2$ and VOC simultaneously, the removal efficiencies were found to be 75% and 85%, respectively.

• 한국자동차공학회논문집
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• 제22권7호
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• pp.31-39
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• 2014

Recently, as Intelligent Transportation System (ITS) and self-driving system become influential in the ground transportation system, automotive radar systems have been actively studied among the various radar systems to implement the vehicle collision detection system and distance measurement system between vehicles. Most of the automotive radars are Frequency Modulated Continuous Wave (FMCW) radar type which can calculate distance and velocity of target by estimating the frequency difference between the transmitted signal and received signal. Therefore, accurate frequency estimation is very important in the FMCW radar system. For this reason, to improve the measurement accuracy of the FMCW radar, Reverse Directional FRI (RD-FRI) Super-Resolution technique which has high frequency estimation accuracy is applied to the FMCW radar system. The feasibility of the proposed technique is evaluated with simulation results and compared with FFT and conventional Super-Resolution techniques. The simulation results show that the proposed technique estimates the frequency with high accuracy and the distance with centimeter accuracy.

• 설비공학논문집
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• 제21권7호
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• pp.409-416
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• 2009

On 21st century, global warming is the most serious environmental problem threatening the existence of lives on the earth. One of the serious reasons of this nature phenomena was due to the greenhouse effect by carbon dioxide mainly produced with the combustion process of hydro-carbon fuel. and it is mostly produced. In the high oil prices age, intensification of energy efficiency promotion in the building sector is required. Windows are dominating large percentage whole building loads, and are regarding as the primary target of energy efficiency. The purpose of this research is on the obtaining of the renewable energy source in the skyscrape buildings in the metropolitan area. The air movement is happens due to the atmospheric pressure differences in the air. Due to this simple physical theory, it is easily expected to obtain the useful renewable nature energy through the high -raised vertical air stack installed in a tall building. However, there is one problem that should be resolved which is called air-hole effect in the sky -scrape buildings.