• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.85-85
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• 2017

무동력 복합작업기는 치즐쟁기와 디스크의 배열에 따라 작업성능이 좌우된다. 프레임과 디스크, 치즐쟁기에 가해지는 기본적인 힘의 상태를 확인하기 위한 정적 구조해석을 수행하였다. 복합작업기는 디스크는 $18^{\circ}$가 경사진 형태로 전면9개 후면9로 총 18개, 치즐쟁기(Chiselplow)는 4개로, 디스크는 모두 18개이다. 정적인 상태에서 끄는 견인력은 100마력, 150마력, 200마력으로 하였으며 Inventor의 해석 시스템은 힘을 N으로 사용하기 때문에 각 마력에 부가되는 하중을 N으로 치환하여 사용하였다. 구속조건은 frame과, disc, chisel plow에 맞닿는 면을 구속하고, 힘의 방향은 프레임과 트랙터의 연결면, 디스크 날과 땅의 접촉면에 적용했다. front /rear 디스크는 이론상으로는 양 디스크가 쌍으로 마주하고 있어서 스캔데이타를 중심으로 모델링한 결과를 바탕으로, 전후면 디스크해로우의 해석을 수행하였다. 조립 또는 사용상의 문제점이나 자연적인 유격에 의해 어느 정도 대칭이 되지 않을수 있으나 그 정도에 따라 진동과 내구성에 문제가 될 수도 있기에 한쌍에 대해 모델링을 통한 해석을 수행하였다. 해석결과에 따르면 디스크에 작용하는 폰미세스 응력은 극한강도에 미치지 않은 것으로 나타났으며 Frame의 최대 폰 미세스 응력을 제외하면, 대부분의 응력은 항복강도에 현저히 미치지 못하는 수치이고, 프레임의 경우는 150마력, 200마력으로 힘을 가할 때 항복강도는 넘는 수치이지만 극한인장강도에는 미치지 못하는 수치인 것을 알 수 있었다. 100마력에 폰 미세스 응력의 최대값은 0.161918 MPa이고 프레임 강의 항복강도인 207MPa와 디스크의 항복강도인 250MPa에 못 미치는 수치이다. 150마력과 200마력의 힘으로 회전할 때의 폰 미세스 응력의 최대값은 0.286425MPa과 0.381921 MPa로 항복강도인 250MPa에 크게 못 미치는 수치이다. 그 이유는 디스크해로우 방식의 복합작업기는 견인저항력이 작게 설계되고 작업속도를 개선하기 위한 목적으로 사용되기 때문으로 사료된다. 벤치마킹 기대의 Rear 디스크도 마찬가지로 각도는 $18^{\circ}$이며, 동일한 구속조건을 적용하여 시뮬레이션을 수행하였으며 해석결과는 모두 항복강도 이내로 예측 되었다. 디스크에 최대로 응력이 미치는 부분은 디스크와 프레임이 연결되는 허브 부분이다. 각도가 커짐에 따라 응력이 증가하므로 이를 감안한 설계인자 도출이 가능하다. 마력과 각도가 증가함에 따라 디스크 해로우에 작용하는 폰미세스 응력과, 접촉압력이 증가하므로 이에 대한 검토와 동적하중인 로드프로파일을 적용한 해석을 수행하여 내구수명 특성에 대한 연구를 수행할 계획이다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.208-208
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• 2009

최근 광섬유 센서기술의 수요는 전 산업분야에 걸쳐 높아지고 있으며, 이에 비례하여 기업 간, 국가 간 경쟁이 첨예화되고 있다. 또한 소형화, 경량화, 고성능화 센서에 대한 요구도 높아지고 있어 종래의 각종 센서들의 형태와 개선을 위한 연구개발이 매우 활발하게 전개되고 있으므로 이를 대체할 수 있는 광섬유 센서의 수요가 급격히 늘어날 전망이다. 기존 침입자 감지 시스템은 태풍, 낙뢰, 폭설, 폭우 등의 기상변화나 지반 흔들림, 통행차량 진동 및 전자기 간섭 등에 영향을 받아 오작동, 오경보가 빈번히 발생된다. 이러한 문제의 해결책으로 광섬유 센서 케이블을 이용한 시스템이 대안으로 부각되고 있다. 현재 국내에서 군부대, 공항을 중심으로 펜스와 휴전선 철책에 힘입자 감지를 위하여 도입되고 있다. 광섬유 센서 케이블을 사용하는 광망경비시스템은 광섬유 센서 케이블을 그물망 형태(광망)로 만들어 경계 지역에 설치된다. 광망경비시스템의 원리는 광섬유에 광펄스를 입사시켜 순환시키는데 침입자가 광망을 절단하거나 외력을 가할 경우 발생되는 레일리 산란에 기인하는 후방산란과 접속점과 파단점에서 생기는 반사광을 OTDR(Optical Time Domain Reflectometer)로 검출하여 침입상황 및 침입위치를 탐지한다. 그러나 이러한 침입자 감지를 위한 광망경비시스템의 핵심부품인 광섬유 센서 케이블은 기존에 전량 해외수입에 의존하고 있는 실정이며, 지금까지 국내에서 생산하기 위한 제작 기술과 노하우가 초보단계에 머물러 있다. 이러한 광섬유 센서 케이블 제작에 있어서 중요한 부분이 패키징 기술이라 할 수 있다. 이는 광섬유 센서를 일반적인 피복 구조로 패키징하게 되면, 센서 고유의 특성이 패키징 과정과 운반과정, 포설과정에서 변하게 되고 센서로써의 신뢰성이 크게 저하된다. 본 연구에서는 힘입자 감지용 광섬유 센서 케이블의 설계와 제작을 위한 제조공법을 확립하고, 이를 이용해 제작된 광섬유 센서 케이블의 신뢰성 특성을 평가하였다. 설계 제작된 광섬유 센서 케이블의 구조는 멀티모드광섬유(MMF) 에 0.9 mm Tight buffer를 코팅하고, 광심선 주위에 아라미드 얀을 삽입시킨 후 고문자 수지를 적용하여 외부 피복 (jacket)을 하였다. 제작된 광섬유 센서 케이블의 외경 측정결과 기준치 ($2.95\;{\pm}\;0.03$ mm)를 모두 만족하였고, 850 nm 파장에서의 광 손실 측정 결과 4.0 dB/km 이하였다. 또한 주요 항목의 신뢰성 특성 시험결과, 인장강도는 8~10 kg의 인장력을 갖으며 온도순환시험 ($-30^{\circ}C\;{\sim}\;+75^{\circ}C$)에서의 광 손실은 0.6 dB 이하로 나타나 침입자 감지용 광섬유 센서 케이블로 적합함을 확인할 수 있었다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.5
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• pp.593-604
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• 2007

Although composite construction has more mechanical advantages compared to noncomposite construction, the design of noncomposite construction for skew bridges with large skew angels has been often checked because composite construction may cause large stresses in the bridge deck. In this study, the analytical model considered dynamic behaviors for noncomposite skew bridges was proposed. Using the proposed analytical model, the validity of the application of noncomposite construction to skew bridges was checked. Also, the effects of interactions between the concrete deck and steel girders such as composite construction, partial composite construction, and noncomposite construction on the dynamic characteristics and dynamic behaviors of simply supported skew bridges were investigated. A series of parametric studies for the total 27 skew bridges was conducted with respect to parameters such as girder spacing, skew angle, and deck aspect ratio. Although the slip at the interfaces between the concrete deck and steel girders results in the reduction of seismic total base shear in the transverse direction due to period elongation, it causes an undesirable behavior of skew bridges by the modification in mode shapes and distributions of stiffness. Shear connectors placed by minimum requirements for partial composite action have an effect on reducing the girder stresses and deck stresses; except case of some skew bridges, the magnitude of the girder stresses and deck stresses obtained from partial composite skew bridges is similar to or slightly more than those acquired from composite skew bridges.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.1
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• pp.93-101
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• 1987

Residual stresses have remained around welding areas of a steel structure member after welding operation. The major causes to occur these residual stresses are the local heat due to a welding, the heat stresses due to a irregular and rapid cooling condition, the material and rigidity of a steel structure. Ultimatly, these residual stresses have been known to decrease a brittle fracture strength, a fatigue strength, a buckling strength, dynamic properties, and the corrosion resistance of the material. This paper deals with the residual stresses on a steel structure member through experimental studies. SWS 58 plates were welded by the method of X-groove type. These plates were layed on the heat treatment at four different temperatures; $350^{\circ}C$, $500^{\circ}C$, $650^{\circ}C$ and $800^{\circ}C$. The resulting residual Stresses were measured by hole drilling method, and the followings were obtained. The residual stresses on the vicinity of a welding point were relieved most effectively at the temperature of $650^{\circ}C$, and these stresses relieved completly when the ratio of a hole diamerter to a hole depth became unity. Hardness test shows that the higher value of hardness at the heat affected zone dropped to belower as the temperature went up from $350^{\circ}C$ to $800^{\circ}C$. The Welding input heats have not influenced the magnitude of residual stresses at the input heat range between above and below one forth than standard.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.1
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• pp.17-27
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• 2014

Numerical model became one of most important tools for identifying the state of an existing structure in accordance with development of numerical analysis techniques. A numerical model should be updated based on the measured responses from the existing structure to accurately use the model for identifying the state of the bridge and executing numerical experiments. In this study, a new model updating method based on repetition method without a differential function is introduced and applicability for high speed railway bridge is verified with dynamic stability analysis. A fine measurement based on measurement points roaming method was executed with an wireless measurement system for precise dynamic characteristic analysis. The natural frequencies and mode shapes were estimated by correlation analysis and a mode decomposition technique. An initial numerical model was constructed based on design drawings and the model have been updated in accordance with the introduced model updating method. The results from numerical experiment and field test have been compared for verifying the applicability of the model updating method. And the dynamic stability analysis has been executed to verify the usability of the updated numerical model and the model updating method. It seems that the model updating method can be used for various bridges after evaluation of applicability for other type bridges in further studies.

• The Journal of Engineering Geology
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• v.19 no.1
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• pp.15-23
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• 2009

The site effects relating to the amplification of ground motion under earthquake loading are strongly influenced by both the subsurface soil condition and geologic structure. In this study, the site effects at the Hongseong area in Korea were examined by both the site investigation including borehole drilling and in-situ seismic tests and the site visit for acquiring geologic information of ground surface. Subsurface of Hongseong area with a major instrumental earthquake event in 1978 is composed of weathered layers of a maximum of 45 m thickness overlying bedrock. A geotechnical information system based on GIS framework was implemented to effectively find out spatial geologic structure of study area and it indicated Hongseong is a shallow and wide shaped basin. Two-dimensional finite element (FE) analyses for a representative cross-section of the Hongseong area were performed to evaluate seismic site responses. From the results of seismic responses, it was observed that the ground motions were amplified during the propagation of shear waves through the soil layer overlying the bedrock and the duration of shaking near the basin edges was prolonged due to the surface waves generated by interactions of shear waves with basin geometry. Furthermore, one-dimensional FE seismic response analyses were additionally conducted for soil sites selected in the basin, and it gives similar results to the two-dimensional seismic responses at most locations in the basin with the exception of the locations near the basin edges, because the basin in this study is very shallow and wide.

• Korean Journal of Materials Research
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• v.4 no.1
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• pp.3-8
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• 1994

Recently, sound and mechanical vibration are becoming important problems in our life. In the present study, the measurement of vibration absorption characteristics of barium titanate ceramics and the investigation of its relationship to microstructures were carried out. The barium titanate ceramics is expected to be better vibration absorption material owing to its chemical and physical stability than other conventional vibration absorbers like glasswool board. Barium titanate ceramics were prepared by sintering fiberous $BaTiO_{3}$ crystallites in order to enhance the vibration absorption characteristics. The fiberous $BaTiO_{3}$ ceramics were prepared through the ionic exchange after the preparation of fiberous $K_2Ti_4O_9$ with 0.2$\mu\textrm{m}$, 1.2$\mu\textrm{m}$, 2.0$\mu\textrm{m}$, diameter length by KDC method. The fiberous crystallites were oriented in a plane perpendicular to the press direction and sintered. The investigation of the grain diameters of the sintered ceramics, equivalent factor, electromechanical coupling factor($k_1$), and the generated voltage(V) shows that the grain's diameter decreases with the increase of the diameter of the used fiberous crystallites. The vibration absorption increases the crystallites' diameter. That means that the vibration absorption increases with the internal friction of grain boundary. Which was identified by the investigation of the equivallent circuit.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.2
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• pp.159-166
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• 2018

In this study, the internal structural design, dynamic characteristics and load analyses of the small scaled rotor blade required for LCH(Light Civil Helicopter) main rotor wind tunnel test were carried out. The test is performed to evaluate the aerodynamic performance and noise characteristics of the LCH main rotor system. Therefore, the Mach-scale technique was appled to design the small scaled blade to simulate the equivalent aerodynamic characteristics as the full scale rotor system. It is necessary to increase the rotor speed to maintain the same blade tip speed as the full scale blade. In addition, the blade weight, section stiffness, and natural frequency were scaled according to the Mach-type scaling factor(${\lambda}$). For the design of skin, spar, torsion box, which are the main components of the blade, carbon and glass fiber composite materials were adopted, and composite materials are prepreg types that can be supplied domestically. The KSec2D program was used to evaluate the section stiffness of the blade. Also, structural loads and dynamic characteristics of the Mach scale blade were investigated through the comprehensive rotorcraft analysis program CAMRADII.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.82-88
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• 2018

This study investigated the structure of an 8-pole 8-slot linear generator, which acts as an electromagnetic damper by combining the structure of an electromagnetic suspension device capable of generating electrical energy through energy harvesting by absorbing the vibration energy from the road surface while driving. To compare the energy harvesting effect of the electromagnetic suspension according to the actual road surface, a driving road test was simulated for two actual road conditions, an asphalt road surface and unpacked road surface condition, using a civilian combined vehicle model in conjunction with a vehicle simulation program, Carsim and Simulink. As a result, the relative displacements of the suspensions on the asphalt road surface and the unpaved road were 8 mm and 13 mm, respectively. By applying the suspension displacement value derived by modeling the linear generator coupled to the electromagnetic suspension, the simulation was then performed for an analysis time of 0.3s by applying the same analytical conditions using the commercial electromagnetic analysis program, ANSYS MAXWELL, The average power generation on the unpacked roads and asphalt roads was 198.6W and 98.7W respectively, which was 103.7% higher for unpackaged roads. Finally, to compare the sensitivity of the road surface frequency and the suspension input displacement to the power generation output, the sensitivity of the two variables was 1.725 and 1.283, respectively, and the road surface frequency had a 34.5% higher effect on the average power generation.

• Journal of the Korean Magnetics Society
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• v.14 no.1
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• pp.33-37
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• 2004

Cu$_{0.1}$Fe$_{0.9}$Cr$_2$S$_4$ has been studied with Mossbauer spectroscopy, x-ray diffraction, vibrating sample magnetometer (VSM), and magnetoresistance (MR) measurement. The crystal structure was determined to be a cubic spinel with lattice parameter a$_{0}$=9.9880 $\AA$. The MR measurements show a semiconductor behavior below 110 K and metal behaved above 100 K. The temperature dependence of magnetization of Cu$_{0.1}$Fe$_{0.9}$Cr$_2$S$_4$ was reported. In addition to a large irreversibility between the zero-field-cooling (ZFC) and the field-cooling (FC) magnetization at applied field H=100 Oe, a cusp-like anomaly was observed in both the FC and ZFC curves. It shifted toward the lower temperature region with increasing magnetic field, and then showed convex type maximum at 110 K, under the applied field of 5 kOe. The Mossbauer spectra were measured from 15 K to room temperature. The asymmetric line broadening was observed for the sample Cu$_{0.1}$Fe$_{0.9}$Cr$_2$S$_4$, and it was considered to be dynamic Jahn-Teller relaxation. The charge state of Fe ions was ferrous in character. The unusual reduction of magnetic hyperfine field below 110 K was interpreted in terms of cancellation effect between the mutually opposite orbital current field (H$_{L}$) and Fermi contact field (H$_{C}$).