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고속 디지털 카메라를 이용한 알루미늄 하니콤 샌드위치 보의 고유 진동수 계측
구남서(Nam Seo Goo),방호앙미(Hoang My Vang),레빈퉁(Vinh Tung Le),김태렬(Tailie Jin) 한국항공우주학회 2017 韓國航空宇宙學會誌 Vol.45 No.1
본 연구에서는 디지털 영상 상관 기법을 이용하여 알루미늄 하니콤 샌드위치 보의 고유진동수를 계측하였다. 고속 디지털 카메라를 이용하여 보의 진동 영상을 획득하고 디지털 영상 상관 기법을 이용하여 변위를 계산하였다. 시간 영역에서의 변위 데이터를 고속 퓨리에 변환하여 주파수 영역의 응답으로 변환하였다. 랜덤 가진에 따른 주파수 영역에서의 잡음을 줄이기 위하여 스펙트럼 평균화 기법과 Savitsky-Golay 디지털 필터를 사용하였다. 가속도계를 이용한 기존의 방법 및 유한요소 해석 결과와의 비교를 통하여 방법의 정확성을 확인하였다. 결론적으로 고속 디지털 카메라와 디지털 영상 상관 기법을 이용하는 새로운 방법은 구조물의 진동을 잘 측정할 수 있음을 보였고, 센서를 부착하기 어려운 바이오 구조 등의 진동 계측에 적용할 수 있을 것이다. In this study, we measured the natural frequencies of aluminum honeycomb sandwich beams using digital image correlation technique. The vibration images were captured using two high speed digital cameras and the images were converted to displacements by the digital image correlation technique. Displacement data in time domain were tranformed to frequency domain data by fast Fourier transform software. To reduce noise invoked by random exitation, a spectrum averaging technique and Savitsky-Golay digital filter were adopted. A conventional vibration measurement using an accelerometer and a finite element analysis were performed to compare the results by high speed digital camera measurement method. In conclusion, new method using high speed digital cameras and digital image correlation technique can measure the vibration of beam structures and can be applied to bio-structures where sensors cannot be attached.
디지털 영상 보정 기법을 이용한 장수풍뎅이 모방 날개의 모달특성 계측
구남서(Nam Seo Goo),하넉산(Ngoc San Ha),김태렬(Tailie Jin) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
In this study, the dynamic characteristic of an artificial wing mimicking an Allomyrina Dichotoma beetle’s hind wing was investigated using a non-contact measurement method. The natural frequency, mode shape, and damping ratio of first two basic vibration modes in the operating frequency range were determined using a Bruel & Kjaer (B&K) fast Fourier transform analyzer along with a laser sensor. To confirm the results, a three-dimensional digital image correlation (3D-DIC) method along with high speed digital cameras was employed to construct the mode shapes of the wing when it was vibrated at pre-determined natural frequency. The mode shapes by DIC method showed a good agreement with those by laser displacement sensor. These results provide a method to investigate the modal analysis of a light weight structure like insect wing as well as construct the mode shape using DIC.
구남서(Nam Seo Goo),문영규(Young Kyu Moon),우경식(Kyeong Sik Woo) 한국복합재료학회 2002 Composites research Vol.15 No.5
본 연구의 목적은 ㈜한국화이바의 CF3327 평직 복합재료의 열전도도를 실험적으로 계측하고 이를 이론적인 예측과 비교하는데 있다. 열전도도 계측을 위하여 비교계측법의 원리를 이용한 실험 장치를 제작하였으며 열전도도가 잘 알려진 그라파이트를 실험함으로써 장비의 정확성을 확인하였다. 미시역학적인 방법은 섬유 및 기지의 물성, 섬유체적비, 직조 형태 등의 변수들이 복합재료의 유효물성치에 미치는 영향을 평가하는데 유용하다. 본 연구에서는 3차원 직-병렬 열저항 개념을 주기적으로 반복되는 평직의 단위구조에 적용하여 열전도도를 예측하였다. 해석 결과를 실험 결과와 비교한 결과 잘 일치함을 확인하였고 섬유체적비가 에폭시 수지 복합재료의 열전도도에 미치는 영향을 고찰하였다. The purpose of this study is to measure and predict the thermal conductivity of CF3327 plain-weave fabric composite made by Hankuk Fiber, Co. An experiment apparatus based on the comparative method has been made to measure the thermal conductivities of the composite material. Its accuracy was proved by measuring the thermal conductivity of graphite which is well-known. Micro-mechanical approaches are useful to assess the effect of parameters such as fiber and matrix material properties, fiber volume fraction and fabric geometric parameters on the effective material properties of composites. In this study, prediction was based on the concept of three dimensional series-parallel thermal resistance network. Thermal resistance network was applied to unit cell model that characterized the periodically repeated pattern of a plain weave. The numerical results were compared with experimental one and good agreement was observed. Also, the effects of fiber volume fraction on the thermal conductivity of several composites has been investigated.
구남서(Nam Seo Goo),김태렬(TAILIE JIN) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
Thermal output is a big source of errors on measuring the thermal deformation of specimen when a strain gage is used. Although several methods have been developed and used to solve this problem, in the range of measuring temperature is limited. In this work, we introduce digital image correlation (DIC) technique to measure a full-field the thermal deformation of a aluminum plate. We compared the deformation results of DIC and strain gage to judge the capability of the DIC. Additionally, we measured the thermal deformation of a ring structure using DIC and the result was quite matched with theoretical solutions.
구남서(Nam Seo Goo),박훈철(Hoon Cheol Park),윤광준(Kwang Joon Yoon),이열화(Yeol-Hwa Lee) 한국항공우주학회 2004 韓國航空宇宙學會誌 Vol.32 No.3
테이프래핑 구조물은 유도무기의 노즐 구조에 많이 사용되고 있는데 주로 주자직 복합재료를 띠모양으로 이은 다음 이를 맨드럴에 경사각을 가지게 감는 방법으로 제작된다. 적층된 구조물은 고압의 오토클레이브나 하이드로 클레이브에서 성형된다. 테이프래핑 구조물은 적층 형태가 일방향 복합재료의 경우와는 다르며, 제작 시 주어진 경사각을 고려한 해석이 필요하다. 본 연구에서는 테이프래핑 구조물에 대한 해석 기법을 고찰하였다. 먼저 4점 굽힘 실험에 대한 유한요소 해석 결과와 실험 결과를 비교함으로써 테이프래핑 구조물의 모델링 기법의 타당성을 검증하였다. 4점 굽힘 실험의 파단 하중과 이방성 파단 판정식의 결과를 비교함으로써 최적의 이방성 파단 판정식을 확인하였다. Tape-wrapped structures have been generally used in nozzle parts of guided missiles. A continuous band of woven composite material is wrapped around a mandrel that is designed to produce real products. After going through a vacuum bagging process, this woven composite material is cured in a high-pressure autoclave or hydroclave. However, tape-wrapped structures are difficult to analyze because of its large thickness and inclined lay-up. The present study investigates the method of analysis and failure prediction of tape-wrapped structures. The four-point bending test and its finite element analysis were performed to study how to model tape-wrapped structures and investigate their failure characteristics.
구남서(Nam Seo Goo),띠앵민드리(Cam Minh Tri Tien) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
Energy can be reclaimed and stored for later use to recharge a battery or power a device through a process called energy harvesting. Piezoelectric is being widely investigated for use in harvesting energy from motion such as body movement and machine vibration. This paper presents a simple analytical model to describe output voltage effectiveness of a Piezo-Composite Generating Element (PCGE) from vibration and its experimental verification. PCGE is composed of layers of carbon/epoxy, PZT ceramic and glass/epoxy. During the manufacturing process, the stacked layers were cured at an elevated temperature of 177℃ in an autoclave, which made the PCGE pre-stressed due to a mismatch in the coefficients of thermal expansion between the constituent layers. For the experiments, three kinds of lay-up configurations of PCGE were utilized to verify the model and to approve its ability to convert oscillatory mechanical energy into electrical energy. The predicted performances are much in agreement with experimental ones.