• 한국항공우주학회지
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• 제45권3호
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• pp.173-179
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• 2017

본 논문에서는 모션캡쳐 카메라를 사용한 실험을 통해 날갯짓 비행체의 주 날개, 꼬리날개 구동기 특성 분석에 대하여 기술하였다. 실험은 빛이 차단된 실내에서 진행되었고 지그에 기체를 고정하여 날갯짓으로 인한 영향을 줄였다. 주 날개와 꼬리날개 끝단에 마커를 부착하였고 모션캡쳐 카메라는 입력 신호에 대한 각각의 반응을 측정한다. 실험 결과 주 날개는 날갯짓의 주파수에 따라 진폭이 변하는 경향을 보였고, Modified Strip Theory에 실험 결과와 비행체 제원을 적용하여 양력 및 추력 발생 시뮬레이션을 구현 하였다. 꼬리날개는 종 횡축별로 스텝 신호를 인가하여 이에 따른 결과를 2차 전달함수 형태로 정의하였고, 각 축별로 구동기의 구조 차이로 인하여 최종 응답시간, 오버슈트, 최대값 등에서 차이를 나타내는 것을 확인하였다.

• 방송공학회논문지
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• 제16권5호
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• pp.846-860
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• 2011

인간의 청각기관은 소리의 방향과 거리인지에 있어서 양 귀에 들어오는 소리세기의 차이, 위상의 차이, 그리고 주파수 스펙트럼의 차이 등의 정보들을 복합적으로 이용한다. 이런 정보를 종합적으로 포함하고 있는 것을 머리전달함수라 하며, 이를 이용하여 실질적으로 존재하지 않는 음원을 근사적으로 생성할 수 있는 입체음향 시스템을 구현할 수 있다. 그러나 비개인화 된 머리전달함수는 음상정위 성능을 떨어뜨리는 주된 원인이 된다. 이에 본 논문에서는 이 머리전달함수를 이용한 3차원 음상정위를 위해 사람의 청각 특성을 이용한 알고리즘을 제안한다. 청자가 정확한 방향을 인지하기 위해 1차로 측정된 머리전달함수의 청각 자극 에너지를, 2차로 전역 마스킹 임계치와 라우드니스를 이용하여 방향감을 강조하였다. 제안된 알고리즘의 성능 평가를 위해 청감 테스트를 수행하였으며 실험결과 기존의 알고리즘에 비해 입체음향의 전체적인 인지도가 50% 이상 증가하였음을 확인할 수 있었다.

• 한국소음진동공학회논문집
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• 제24권12호
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• pp.935-942
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• 2014

The ride quality investigation is on-going topic in the car industry since its global standard has not evaluated and it is difficult to point out one part that hinders the ride quality. Since the traditional transfer path analysis that is widely used in car industry to investigate the ride quality requires a lot of test time to process the full data so that there are problems to conduct in industry. Based on these disadvantages, new approaches have developed such as OPAX(operational path analysis with eXogeneous inputs) and OTPA(operational transfer path analysis) for last decades. The OTPA only requires the operational data for evaluate the contribution of vibration sources and the OPAX has advantage of using parametric model to estimate the operating load and needs a minimum set of extra tests with excitation. In this paper, for evaluating the hindrance of ride quality two methods are used and the result is compared with another result of a car having higher ride quality.

• 한국공간구조학회논문집
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• 제10권3호
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• pp.49-56
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• 2010

본 연구에서는 스마트 최상층 면진시스템을 적용한 고층건물의 풍응답 제어성능을 검토해보았다. 이를 위하여 77층 초고층 건물을 예제구조물로 선택하였고 풍동실험을 통해서 얻은 풍하중을 사용하여 수치해석을 수행하였다. 예제구조물의 최상층은 FPS 및 MR 감쇠기로 구성된 스마트 면진시스템을 이용하여 주구조물과 분리된다. 주구조물의 동적응답을 저감시키는 것이 스마트 최상층 면진시스템의 가장 중요한 목표이지만 면진된 최상층의 과도한 응답은 구조물을 불안정하게 만들 수 있다. 따라서, 본 연구에서는 면진된 최상층과 주구조물을 효과적으로 제어하기 위하여 스카이훅제어기를 제어알고리즘으로 사용하였다. 제안된 스마트 최상층 면진시스템의 제어성능을 검토하기 위하여 일반적인 수동 최상층 면진시스템의 제어성능과 비교하였다. 수치해석결과 제안된 스마트 최상층 면진시스템을 이용하면 일반적인 수동 최상층 면진시스템에 비해서 면진층의 변위를 효과적으로 줄이면서도 구조물의 응답을 저감시킬 수 있음을 확인할 수 있었다.

• 토지주택연구
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• 제3권1호
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• pp.79-82
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• 2012

While there exists a relatively large body of technical information for the engineered design of wood-frame buildings to resist seismic ground motions, the quantitative assessment of seismic resistance of conventional houses built by prescriptive requirements is less well understood. Forintek Canada Corp., in collaboration with other research and industry partners, has embarked on a research project to address this topic. This paper will report on the seismic shake table tests of a full-scale wood-frame building. The two-story specimen, $6m{\times}6m$ in plan, was built on the seismic shake table at Tongji University in Shanghai, China, according to Part 9 of the 1995 National Building Code of Canada and shaken uni-directionally in each of the two principal directions. Three different seismic table motions were applied at increasing peak ground motion amplitudes up to 0.40 and 0.50 g. The specimen was repaired after the above sets of seismic table motions, and successive runs were conducted for increased door openings. Measurements included specimen accelerations, displacements and anchorage forces. Static stiffness of the specimen was measured at low force levels, and natural frequencies were measured after each seismic loading stage by applying low-level random excitation. The results presented consist of the capacity spectra of the shake table tests, changes in specimen stiffness and natural frequencies with increasing seismic loading. These results and those from other recent shake table tests elsewhere will be compared with simplified engineering calculations based on codified values of strength, and on that basis preliminary conclusions will be drawn on the adequacy of the current code provisions and design guides in Canada and the USA for conventional wood-frame construction.

• 전기학회논문지P
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• 제66권2호
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• pp.69-75
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• 2017

The gas turbine static starter rotates the stationary synchronous machine by the interaction of the rotor and the stator. The detection from the initial position of the rotor has been an important issue to drive with optimum torque. Previously, the gas turbine starter was used by attaching the encoder to the synchronous machine, but the position and velocity of the rotor have been estimated by sensor-less method until recently due to the difficulty in attaching and detaching and damage caused by the shaft voltage noise. In this paper, Rotor initial(stationary state) position estimation, forced commutation control(speed less than 10%), and natural commutation control(speed more than 10%) method using magnetic flux with integrated terminal voltage were presented and the sensor-less speed control performance was verified. As a result of making and evaluating the 29 kVA synchronous machine and the starting device, the performance of each control mode was satisfactory. Furthermore, the applied technology is expected to be used for the development of the gas turbine starter of tens of MW class and the field application.

• Ocean Systems Engineering
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• 제7권2호
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• pp.121-141
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• 2017

The purpose of this paper is to understand and model the slow current (~2 m/s) effects on the global response of a floating offshore platform in waves. A time-domain numerical simulation of full wave-current-body interaction by a quadratic boundary element method (QBEM) is applied to compute the hydrodynamic loads and motions of a floating body under the combined influence of waves and current. The study is performed in the context of linearized potential flow theory that is sufficient in understanding the leading-order current effect on the body motion. The numerical simulations are validated by quantitative comparisons of the hydrodynamic coefficients with the WAMIT prediction for a truncated vertical circular cylinder in the absence of current. It is found from the simulation results that the presence of current leads to a loss of symmetry in flow dynamics for a tension-leg platform (TLP) with symmetric geometry, resulting in the coupling of the heave motion with the surge and pitch motions. Moreover, the presence of current largely affects the wave excitation force and moment as well as the motion of the platform while it has a negligible influence on the added mass and damping coefficients. It is also found that the current effect is strongly correlated with the wavelength but not frequency of the wave field. The global motion of a floating body in the presence of a slow current at relatively small encounter wave frequencies can be satisfactorily approximated by the response of the body in the absence of current at the intrinsic frequency corresponding to the same wavelength as in the presence of current. This finding has a significant implication in the model test of global motions of offshore structures in ocean waves and currents.

• 한국물환경학회지
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• 제23권2호
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• pp.236-243
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• 2007

Fluorescence measurements of dissolved organic matter (DOM) have the superior advantages over other analysis tools for the applications to water quality management due to their rapid analysis. It is known that protein-like fluorescence characteristics are well corelated with microbial activities and biodegradable organic matter. In this study, potential biochemical oxygen demand (BOD) predictor were explored using the fluorescence peak intensities and/or the integrated fluorescence intensities derived from synchronous fluorescence spectra and the first derivative spectra of river samples. A preliminary study was conducted using a mixture of a river and a treated sewage to test the feasibility of the approach. It was demonstrated that the better BOD predictor can be derived from synchronous fluorescence spectra and the derivatives when the difference between the emission and the excitation wavelengths (${\Delta}{\gamma}$) was large. The efficacy of several selected fluorescence parameters was rivers in Seoul. The fluorescence parameters exhibited relatively good correlation coefficients with the BOD values, ranging from 0.59 to 0.90. Two parameters were suggested to be the optimum BOD predictors, which were a fluorescence peak at a wavelength of 283 nm from the synchronous spectrum at the ${\Delta}{\gamma}$ value of 75 nm, and the integrated fluorescence intensity of the first derivatives of the spectra at the wavelength range between 245 nm and 280 nm. Each BOD predictor showed the correlation coefficients of 0.89 and 0.90, respectively. It is expected that the results of this study will provide important information to develop a real-time efficient sensor for river BOD in the future.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.723-726
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• 2005

The two major obstacles in the application of IPMC to flapping actuators operated in the air are solvent loss and actuation force. In this paper, solvent loss of various IPMCs made of Nafion$^{TM}$117(183$\mu$m thickness) has been experimentally investigated to find out the best combination of cation and solvent for minimal solvent loss in IPMCs and higher actuation force. For this purpose. experiments for the internal solvent loss measurement of IMPCs have been conducted for various combinations of cation and solvent. From the experiments, it was found that heavy water showed improvement in the operating time up to more than two minutes. in the tip force measurement of IPMCs, it was found that smaller and thicker IPMCs produced larger tip forces. However, the shorter IPMCs generated reduced actuation displacements and created flapping motion with decreased natural frequency. For the design of flapping device actuated by 5mm wide, 10mm long, 0.2mm thick IPMCs were used in the stacked form. Since the actuation force is a few gram-force, we stacked five IPMCs to improve actuation force. To amply the actuation force, rack-and-pin ion type hinge was used for the flapping device and insect (Cicadidae) wing was attached to the stacked IPMC actuator. In the flapping test, the device could generate flapping angle of 15$^{\circ}$ at 6Hz excitation by 2.5 voltage square wave input.

• 비파괴검사학회지
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• 제18권6호
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• pp.445-454
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• 1998

본 연구는 박판 용접부 결함 검출 기법의 확립을 위해서 실시된 기초 연구로서, 전기강판 소재의 모재에 인위적인 결함을 작성하고, 이론 및 시험적 결과를 이용하여 결함을 검출하기 위한 최적의 조건과 임계 검출 결함 크기를 조사한 것이다. 이를 위해서 소재의 dispersion curve를 구하고, 두께 2.4mm의 박판에 대해서 tone burst방식에 의한 초음파 탐상을 실시하였다. 실험적 검토를 행한 결과 840kHz의 가진 주파수와 30도 그리고 85도의 입사각이 최적의 탐상 조건임을 알았다. 한편, 초음파의 속도와 dispersion커브를 비교 검토하여 본 바, 30도의 입사각에서 발생하여 전파하는 초음파는 symmetic mode이고 85도의 입사각에서는 antisymmetric mode의 파가 전파하고 있었다. 결함의 위치와 형상에 따라 반사파의 특성이 다르게 나타나고 있었으며, 특히 표면 결함의 경우에는 antisymmetric 모드의 초음파가 symmetric 모드 보다 높은 반사파 에너지를 나타내고 있었다. 또한 이러한 초음파 모드의 종류와 결함 검출과의 관계에 대해서는 유도파의 구조에 의해서 설명이 가능했다.