• 소음진동
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• 제7권6호
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• pp.959-966
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• 1997

In general, the booming noise intensity at tunnel exit is strongly related to the gradient of the compression wave front created by high speed train entering the tunnel. This paper presents some results in relation with the compression wave front produced when the high speed train enters a tunnel. Four kinds of tunnel entrance shape with real dimensions were studied to investigate the formation of compression wave front inside tunnel by train entering tunnel. Computations were carried out using three-dimensional compressible Euler equation with vanishing viscosity and conductivity of fluid. According to the results, the flow disturbances occured at tunnel entrance were eliminated by tunnel hood with same cross sectional area. The compression wave front is formed completely at 30-40m from tunnel entrance. The maximum pressure gradient of compression wave front is reduced by 29.8% for the inclined tunnel hood and reduced by 21.5% for the tunnel hood with holes at the top face with tunnel without hood. The length of the inclined hood is 15m and the length of the hood with holes is 20m.

• 한국멀티미디어학회논문지
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• 제23권11호
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• pp.1372-1382
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• 2020

This paper proposes a core technology for a micro river monitoring terminal device suitable for flood monitoring in small rivers and valleys. Our proposed device is basically equipped with a 77GHz radar, gyro and accelerometer sensors. To measure the flow velocity and water level, we proposed a signal processing technique that extracts pure water energy components from the observed Doppler velocity and reflection intensity from the radar. And to determine the stability of the river structure equipped with our device, we constantly monitor the displacement of the measured values of the gyro and accelerometer sensors. Experimental result verified that our method detects pure water energy in various river environments and distinguishes between flow velocity and water level well. And we verified that vibration and position change of structures can be determined through a gyro sensor. In future research, we will work to build a secure digital twin river network by lowering the cost of supplying RF-WAV devices. Also we expect our device to contribute to securing a preventive golden time in rivers.

• The Journal of the Acoustical Society of Korea
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• 제25권2E호
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• pp.79-84
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• 2006

Acoustic characteristics of a sound absorbing material can be identified, if the characteristic impedance and propagation constants are known, which have generally been determined experimentally. One easy method determining these two essential parameters is to measure the one dimensional wave characteristics in the impedance tube. In th udy, the effects of backing conditions on the impedance tube measurement have been examined using several pairs of generally used end conditions. The results showed that the measured values are similar for most pairs of end conditions: however, it was observed that the measured characteristic impedance for different thickness did not agree well for some pairs. In this work, the multi termination method, using three or more known backing con ns, was suggested to reduce such random errors, which are mostly caused by the test procedure. Employing three terminations as a set, comprised of a rigid end, an end with porous material, and an end with a backing cavity, it was demonstrated that improved measured results could be obtained for an open cell PU foam varying widely with three different thicknesses.

• 제어로봇시스템학회논문지
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• 제13권9호
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• pp.883-895
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• 2007

In this work, we present the development of a patrol robot which is intended to navigate outdoor rough terrain. Proposed mechanism consists of six legs for overcoming an obstacle, and six wheels for traveling. Also, in order to absorb vibration in rough terrain effectively, the slide-spring system and tubed type tire are adopted to each leg and each wheel. The control system of robot consists of several imbedded boards for management of lots of diverse devices such as sensors designed for rough terrain, motor controllers, camera, micro controller and so on. And the base system of the robot is designed to operate in real time and to surveille in the vicinity of the robot, and the robot system is controlled by wireless LAN connected to GUI-based remote control system, while CAN communication connects the control board and the device controllers for sensors and motor controllers. For operating this robot system efficiently, we propose the control algorithms for autonomous navigation using GPS, stabilization maintenance by posture control, obstacle-avoidance by impedance control, and obstacle-overcoming with interference-avoidance between wheels. The performance of the robot and the proposed algorithms are tested and proved by a set of experiments in outdoor rough terrain.

• 항공우주시스템공학회지
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• 제10권1호
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• pp.86-94
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• 2016

In this paper, position control of focal plane compensation device using piezoelectric actuator is conducted. The forcal plane compensation device installed on earth observation satellite camera compensates micro-vibration from reaction wheels. In this study, four experimental models of the open-loop compensation device are derived using MATLAB system identification toolbox in the input range of 0~50Hz. Subsequently, the PID controller for each model is designed and the performance test of each controller is conducted through MATLAB/Simulink. According to frequency response analysis of the closed-loop compensation device system, the PID controller designed for 38~50Hz input range has enough tracking performance for the whole 0~50Hz input range. The maximum output error is about $1{\mu}m$ for the input range. The simulation results has been verified by the experimental method.

• 열처리공학회지
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• 제25권5호
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• pp.227-232
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• 2012

Magnesium alloy have good physical properties such as good castability, good vibration absorption, high strength/weight ratios. Despite the desirable properties, the poor resistance of Mg alloy impedes their use in many various applications. Therefore, magnesium alloy require surface treatment to improve hardness, corrosion and wear resistance. Plasma Electrolytic Oxidation (PEO) is one the surface treatment methods to form oxide layer on Mg alloy in alkali electrolyte. In comparison with Anodizing, there is environmental process having higher hardness and faster deposition rate. In this study, the characteristics of oxide film were examined after coating the AZ31 Mg alloy through the PEO process. We changed concentration of sodium aluminate into $K_2ZrF_6$, KF base electrolyte. The morphologies of the coating layer were characterized by using scanning electron microscopy (SEM). Corrosion resistance also investigated by potentiodynamic polarization analysis. As a result, propertiy of oxide layer were changed by concentration of sodium aluminate. Increasing with concentration of sodium aluminate in electrolyte, the oxidation layer was denser and the pore size was smaller on the surface.

• 비파괴검사학회지
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• 제13권4호
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• pp.32-41
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• 1994

탄성파에 의한 미소 동적 변위를 측정하기 위하여 안정화 회로가 부착된 Michelson 간섭계를 개발하였다. 안정화 회로는 외부 진동신호에 따른 광로차의 교란을 보상하기 위하여 압전구동기가 부착된 기준거울을 사용하였다. 안정화 회로를 사용함으로써, 간섭계는 외부 진동신호의 영향을 줄일 수 있었고, 항상 직각조건(quadrature condition)을 만족하여 광검출기의 출력신호가 최대의 감도와 선형성을 유지할 수 있었다. 검출가능한 최소 변위는 10MHz 대역에서 0.3nm 이었다. 개발된 간섭계를 사용하여 유리관 파괴 및 강철구 충격에 의한 진앙점에서의 변위를 검출하여 이론적으로 계산된 값과 비교하였다.

• 한국ITS학회 논문지
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• 제9권5호
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• pp.87-95
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• 2010

도시의 많은 교량 구조물은 내구연한 및 노후 상태에 따라 외형적 변형이 발생하고, 지진과 태풍 등은 노후 시설물의 변형을 더욱 악화시키고 있다. 불규칙하고 미세한 점진적 외형 변형은 육안으로 확인하기 어렵고, 시설물의 성능을 저하시키게 된다. 따라서 최근에 교량 구조물의 이상 거동을 실시간의 무선 방식으로 검지하는 기술이 연구되고 있다. 본 연구는 자이로스코프를 이용하여 구조물의 미소한 물리적 변화량을 실시간으로 측정하는 변위측정모듈을 개발하였다. 개발된 계측 모듈의 성능은 시뮬레이션 실험을 통해 검증하였다.

• Smart Structures and Systems
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• 제13권4호
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• pp.501-515
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• 2014

This paper presents a linear computational homogenization framework to evaluate the effective (or generalized) electromechanical coupling coefficient (EMCC) of adaptive structures with piezoelectric structural fiber (PSF) composite elements. The PSF consists of a silicon carbide (SiC) or carbon core fiber as reinforcement to a fragile piezo-ceramic shell. For the micro-scale analysis, a micromechanics model based on the variational asymptotic method for unit cell homogenization (VAMUCH) is used to evaluate the overall electromechanical properties of the PSF composites. At the macro-scale, a finite element (FE) analysis with the commercial FE code ABAQUS is performed to evaluate the effective EMCC for structures with the PSF composite patches. The EMCC is postprocessed from free-vibrations analysis under short-circuit (SC) and open-circuit (OC) electrodes of the patches. This linear two-scale computational framework may be useful for the optimal design of active structure multi-functional composites which can be used for multi-functional applications such as structural health monitoring, power harvest, vibration sensing and control, damping, and shape control through anisotropic actuation.

• Tribology and Lubricants
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• 제24권6호
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• pp.285-290
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• 2008

The purpose of this paper is to present the case study of tribological failure analysis on the gear damages, oil leakage, and sealant sealing in a manual transmission of front engine and front wheel drive vehicle. The manual transmission is to change the speed range and direction of the engines depending on the driving conditions by friction driving forces with input and output gear system. The material property and surface roughness of the gears are strongly related to the gear noise and micro-vibration, oil leakage and wear, which may decrease the real contact area of the gear and the strength of the oil film thickness between the driving gear and driven one. The O-ring damage of speedometer driven gear and bad sealant sealing of oil pan may produce oil leakage through the contact surfaces, which cause the oil shortage and seizure on the sliding surfaces of the transaxle gears. In the failure case study, the proper repair working and good lubrication are very important for the long life of the transaxle without any tribological failures and oil leakage.