• Wind and Structures
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• 제16권2호
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• pp.137-156
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• 2013

A wind tunnel test of a scaled-down model and field measurement were effective methods for elucidating the aerodynamic behavior of a chimney under a wind load. Therefore, the relationship between the results of the wind tunnel test and the field measurement had to be determined. Accordingly, the set-up and testing method in the wind tunnel had to be modified from the field measurement to simulate the real behavior of a chimney under the wind flow with a larger Reynolds number. It enabled the results of the wind tunnel tests to be correlated with the field measurement. The model surface roughness and different turbulence intensity flows were added to the test. The simulated results of the wind tunnel test agreed with the full-scale measurements in the mean surface pressure distribution behavior.

• Journal of the Optical Society of Korea
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• 제16권4호
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• pp.457-461
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• 2012

A real-time method to measure full field retardation near quarter wavelength is proposed. The circularly polarized beam passes through a sample with a large aperture. The measuring beam then goes through a quarter-wave plate and is then split by a Wollaston prism. An image with two sub-images is then detected by a high-speed image sensor. The full field retardation near quarter wavelength can be obtained in real time by processing the image. The measured retardation is independent of the fast axis angle of the sample and the fluctuation of the initial intensity. In experiments, a wedge waveplate is measured with different fast axis angle and initial intensity, and the full field retardations are acquired. The maximum and standard deviation of the full field retardation is $1.5^{\circ}$ and $0.4^{\circ}$. The validity of the method is verified.

• 한국전자파학회논문지
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• 제27권7호
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• pp.625-634
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• 2016

소자 단위에서 디지털로 신호를 수신하는 완전 디지털 수신 능동위상배열안테나는 최종적인 수신 빔을 디지털 빔형성 방법으로 합성하므로 일반적인 근접전계 시험 방법을 적용하기 어렵다. 따라서 본 논문에서는 완전 디지털 수신 능동위상배열안테나를 시험하기 위한 근접전계 수신 시험 구성과 방법을 제시하였다. 또한, 디지털 빔 합성 과정과 잡음 합성 과정을 토대로 근접전계 수신 시험을 통해 수신 빔 패턴 뿐 아니라, 수신 성능을 대표하는 안테나의 이득 대비시스템 잡음 온도의 비(G/T)를 측정하는 방법을 제시하고, 실제 개발된 L-밴드 장거리레이다용 완전 디지털 수신 능동위상배열안테나를 이용하여 검증한 결과를 제시하였다.

• Wind and Structures
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• 제20권6호
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• pp.719-737
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• 2015

Full scale measurement on the structural dynamic characteristics and Vortex-induced Vibrations (VIV) of a long-span suspension bridge with a central span of 1650 m were conducted. Different Finite Element (FE) modeling principles for the separated twin-box girder were compared and evaluated with the field vibration test results, and the double-spine model was determined to be the best simulation model, but certain modification still needs to be made which will affect the basic modeling parameters and the dynamic response prediction values of corresponding wind tunnel tests. Based on the FE modal analysis results, small-scaled and large-scaled sectional model tests were both carried out to investigate the VIV responses, and probable Reynolds Number effects or scale effect on VIV responses were presented. Based on the observed VIV modes in the field measurement, the VIV results obtained from sectional model tests were converted into those of the three-dimensional (3D) full-scale bridge and subsequently compared with field measurement results. It is indicated that the large-scaled sectional model test can probably provide a reasonable and effective prediction on VIV response.

• Composites Research
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• 제31권3호
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• pp.99-103
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• 2018

본 연구에서는 스캐닝 자유공간 측정 시스템을 이용하여 전자기적 특성을 가지는 표준 시편에 대한 전영역 유전율 분포를 가시화한다. 먼저 테플론 두께 차이에 따라, 유전율 측정 결과, 유전율 실수와 손실정접 측정결과가 두께변화에도 타측정과 이론치와 비교하여 신뢰할 수 있는 결과를 획득하였고 이어 Glass/epoxy 시편에 적용하여 재료에 따라 다른 유전율 분포가 나타나는 것을 제시하였다. 스캔영역을 통해, 시편 전영역에 대한 유전율 분포를 가시화 할 수 있었으며, 재료 물성 평가를 넘어 레이돔 혹은 스텔스 구조 규모의 대상체에도 적용할 수 있음을 확인하였다.

• 한국광학회지
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• 제30권6호
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• pp.237-242
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• 2019

가상현실 기기의 렌즈는 사용자의 편의성을 위한 적은 부피와 높은 현실감을 위한 넓은 시야각을 동시에 만족시켜야 하기 때문에 왜곡 수차가 필연적으로 발생하는데, 일반적인 렌즈보다 시야각이 넓고 왜곡 수차가 크기 때문에 측정이 어렵다. 본 논문에서는 가상현실 기기의 특성을 고려한 두 가지 왜곡 측정 방법을 제안하였다. 하나는 카메라 교정 방법 기반의 다중 이미지를 이용한 왜곡 측정법이며, 또 다른 하나는 카메라를 포함한 측정부를 직접 회전시켜 왜곡을 측정하는 다중 측정점을 이용한 왜곡 측정법이다. 제안된 방법들의 검증을 위해 시판된 가상현실 기기인 Google Cardboard 제품의 왜곡을 측정하고 설계 데이터를 통한 시뮬레이션 결과와 비교하였으며, 두 방법으로 측정된 왜곡 값은 시뮬레이션 결과와 비교했을 때 잘 부합하는 것으로 나타났다.

• Wind and Structures
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• 제29권6호
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• pp.471-488
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• 2019

Wind pressure is a critical argument for the wind-resistant design of structures. The attempt, however, to explore the wind pressure field on buildings still encounters challenges though a large body of researches utilizing wind tunnel tests and wind field simulations were carried out, due to the difficulty in logical treatments on the scale effect and the modeling error. The full-scale measurement has not yet received sufficient attention. By performing a field measurement, the present paper systematically addresses wind pressures on the rectangular attic of a double-tower building. The spatial and temporal correlations among wind speed and wind pressures at measured points are discussed. In order to better understand the wind pressure distribution on the attic facades and its relationship against the approaching flow, a full-scale CFD simulation on the similar rectangular attic is conducted as well. Comparative studies between wind pressure coefficients and those provided in wind-load codes are carried out. It is revealed that in the case of wind attack angle being zero, the wind pressure coefficient of the cross-wind facades exposes remarkable variations along both horizontal and vertical directions; while the wind pressure coefficient of the windward facade remains stable along horizontal direction but exposes remarkable variations along vertical direction. The pattern of wind pressure coefficients, however, is not properly described in the existing wind-load codes.

• Wind and Structures
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• 제32권2호
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• pp.143-159
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• 2021

The 246.8-m-tall Beijing Olympic Tower (BOT) is a new landmark in Beijing City, China. Its unique architectural style with five sub-towers and a large tower crown gives rise to complex dynamic characteristics. Thus, it is wind-sensitive, and a double-stage pendulum tuned mass damper (DPTMD) has been installed for vibration mitigation. In this study, a finite-element analysis of the wind-induced responses of the tower based on full-scale measurement results was performed. First, the structure of the BOT and the full-scale measurement are introduced. According to the measured dynamic characteristics of the BOT, such as the natural frequencies, modal shapes, and damping ratios, an accurate finite-element model (FEM) was established and updated. On the basis of wind measurements, as well as wind-tunnel test results, the wind load on the model was calculated. Then, the wind-induced responses of the BOT with the DPTMD were obtained and compared with the measured responses to assess the numerical wind-induced response analysis method. Finally, the wind-induced serviceability of the BOT was evaluated according to the field measurement results for the wind-induced response and was found to be satisfactory for human comfort.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2001년도 Proceedings of 2001 Korea-Japan Joint Seminar on Particle Image Velocimetry
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• pp.23-35
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• 2001

Due to advances in digital image processing, computer and optical hardware, it is possible to extract full flow information from visualized flow images. Recently, the PIV/PTV methods have been accepted as a reliable velocity field measurement technique. In my laboratory, several velocity field measurement techniques have been developed and they were applied to various thermo-fluid flow problems. In this paper, some of the industrial applications will be discussed. As a result, the PIV/PTV technique was proved to be a powerful tool for industrial fluid flow diagnosis.

• International Journal of Aeronautical and Space Sciences
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• 제18권2호
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• pp.206-214
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• 2017

In this study, measurement of thermophysical properties of materials at high temperatures was performed. This experiment employed a heater device to heat the material to a high temperature. The images of the specimen surface due to thermal load at various temperatures were recorded using charge-coupled device (CCD) cameras. Afterwards, the full-field thermal deformation of the specimen was determined using the digital image correlation (DIC) method. The capability and accuracy of the proposed technique are verified by two experiments: (1) thermal deformation and strain measurement of a stainless steel specimen that was heated to $590^{\circ}C$ and (2) thermal expansion and thermal contraction measurements of specimen in the process of heating and cooling. This research focused on two goals: first, obtaining the temperature dependence of the coefficient of thermal expansion, which can be used as data input for finite element simulation; and second, investigating the capability of the DIC method in measuring full-field thermal deformation and strain. The results of the measured coefficient of thermal expansion were close to the values available in the handbook. The measurement results were in good agreement with finite element method simulation results. The results reveal that DIC is an effective and accurate technique for measuring full-field high-temperature thermal strain in engineering fields such as aerospace engineering.