• 대한기계학회논문집
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• 제16권10호
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• pp.1900-1907
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• 1992

본 연구에서는 원형평판의 경계조건을 일부분은 고정단으로 일부분은 자유단 으로 구성하여 자유단각 .alpha.(Fig.4 참조)를 0˚, 30˚, 60˚, 90˚, 120˚, 150˚, 180˚로 변화시킴에 따른 진동모드를 시간평균 홀로그래픽 간섭계(time-average holographic interferometry)를 이용해 분석하고 자유단의 변화에 따른 고유진동수의 비를 비교하였고, 레이저 도플러 유속계(LDV)를 변형한 레이저 도플러 진동계(laser doppler vibrometer)로 원형평판의 진동변위와 시간평균 홀로그래픽 간섭계로 구한 진 동변위를 비교하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.1044-1048
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• 2002

The experimental modal testing has been carried out for the stator of a generator to confirm the vibrational mode shapes and the corresponding natural frequencies. The model of the stator for the vibration analysis was developed and a series of vibration analyses was carried out. And the properties of the solid element were updated to reduce the differences of the natural frequencies between the measured and the analysed. In the vibration anlyses, the axial, radial and circumferential properties of the solid element were separately varied to take into account the orthotropic effect of the laminated structure and to match the primary modes of the stator core which were extracted from the modal testing. After several attempts to match the measured natural frequencies and model shapes, the properties of the stator model were determined. Comparison of the vibration analyses results based on the determined properties showed fairly good coincidence with the measured data.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.421-426
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• 2003

Recently, mixers are being widely used in the water purification plant in order to increase the filtration efficiency. The mixer normally consists of impeller, shaft, hub, reduction gear, and the driving motor. It is one of the key design issues to confirm that the vibration caused by the rotation of the shaft should not coincide with the natural vibration frequency of the shaft itself. The vibration characteristics of the hydrofoil type mixer, which is the most widely used in real plants are evaluated through the finite element modeling and verified by experiment using the mock-up facility. The fundamental natural frequency of the mixer's shaft is found to be around 1.8 Hz which showed in good agreement with the experiment. The higher natural frequencies to the 2nd, 3rd, and 4th modes are also verified by the experiment. Thus the developed model is to be utilized for the structural design of the real mixer system.

• 대한토목학회논문집
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• 제28권5A호
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• pp.641-647
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• 2008

본 논문은 상시진동데이터로부터 구조물의 고유진동수 및 감쇠비를 추정하는 기법을 소개한다. 제안된 기법은 TDD기법에서 추출된 모드형상과 상호상관신호로부터 직교 잡음이 제거된 자유진동함수를 추출하고 시스템 인식기술을 적용하여서 각 모드별 고유진동수와 감쇠비를 추정한다. 제안 알고리즘의 정확도는 수치적으로 기존의 기법과 비교분석 되었다. 제안 알고리즘의 현장 적용성 검토는 서해대교 보강형의 수직방향 가속도에 대한 상시진동데이터를 통하여 검증되었으며, 총 24개의 저차모드가 추출되었다.

• 대한기계학회논문집
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• 제15권2호
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• pp.455-462
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• 1991

This paper present an analysis method of crankshaft of four cylinder internal combustion engine for studying dynamic characteristics of the shaft. For simple analysis, uniform sections of journal, pin and arm parts were assumed. Transfer Matrix Method was used, considering branched part and coordinate transformation part. Natural frequencies, natural modes and transfer functions of crank shaft were investigated based upon the Timosenko beam theory: It was shown that the calculated natural frequencies, modeshapes agree well with the experimental results.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.900-903
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• 2002

This study dealt with the experimental modal analysis of the perforated rectangular plate coupled with fluid. The natural frequencies of the perforated plate and solid plate in air were obtained by the analytical method based on the relation between the reference kinetic and maximum potential energy and compared with the experimental results. Good agreement between the results was found for the natural frequencies of the perforated plate in air. It was empirically found the natural frequencies of the perforated plate coupled with fluid. The transverse vibration modes, in-phase and out-of-phase, were observed alternately in the fluid-coupled system. Additionally, the effect of distance between perforated plate and solid plate on the fluid-coupled natural frequency was investigated.

• 한국산학기술학회논문지
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• 제15권5호
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• pp.2617-2622
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• 2014

본 연구에서는 카메라 생산 시스템의 모터가 Z축 방향으로 작업할 때 시스템에 발생하는 위험진동수를 해석하였다. 모달해석을 통하여 얻어진 결과를 보면 두 가지 모델에 발생한 고유진동들에 있어서의 각 모드의 형상을 조사할 수 있다. 본 연구 시스템에서 고유진동수 범위는 100Hz부터 500Hz로 나왔다. 모터의 무게가 20kg인 경우에 모델의 최대 등가응력이 6.2335MPa로 발생하는 것을 확인할 수 있고 이 값은 모터가 10kg인 경우의 최대 등가응력 값보다 50배 큰 것으로 나타났다. 본 카메라 생산 시스템의 고유진동과 하모닉 응답해석을 통하여 시스템의 작업 안전성을 고찰할 수 있었다.

• Structural Engineering and Mechanics
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• 제25권4호
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• pp.481-500
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• 2007

The dynamic instability of doubly curved panels, subjected to non-uniform tensile in-plane harmonic edge loading $P(t)=P_s+P_d\;{\cos}{\Omega}t$ is investigated. The present work deals with the problem of the occurrence of combination resonances in contrast to simple resonances in parametrically excited doubly curved panels. Analytical expressions for the instability regions are obtained at ${\Omega}={\omega}_m+{\omega}_n$, (${\Omega}$ is the excitation frequency and ${\omega}_m$ and ${\omega}_n$ are the natural frequencies of the system) by using the method of multiple scales. It is shown that, besides the principal instability region at ${\Omega}=2{\omega}_1$, where ${\omega}_1$ is the fundamental frequency, other cases of ${\Omega}={\omega}_m+{\omega}_n$, related to other modes, can be of major importance and yield a significantly enlarged instability region. The effects of edge loading, curvature, damping and the static load factor on dynamic instability behavior of simply supported doubly curved panels are studied. The results show that under localized edge loading, combination resonance zones are as important as simple resonance zones. The effects of damping show that there is a finite critical value of the dynamic load factor for each instability region below which the curved panels cannot become dynamically unstable. This example of simultaneous excitation of two modes, each oscillating steadily at its own natural frequency, may be of considerable interest in vibration testing of actual structures.

• Structural Engineering and Mechanics
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• 제76권3호
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• pp.293-310
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• 2020

This study derives the differential equations of free vertical bending and torsional vibrations for two- and three-pylon suspension bridges using d'Alembert's principle. The respective algorithms for natural vibration frequency and vibration mode are established through the separation of variables. In the case of the three-pylon suspension bridge, the effect of the along-bridge bending vibration of the middle pylon on the vertical bending vibration of the entire bridge is considered. The impact of torsional vibration of the middle pylon about the vertical axis on the torsional vibration of the entire bridge is also analyzed in detail. The feasibility of the proposed method is verified by two engineering examples. A comparative analysis of the results obtained via the proposed and more intricate finite element methods confirmed the former feasibility. Finally, the middle pylon stiffness effect on the vibration frequency of the three-pylon suspension bridge is discussed. It is found that the vibration frequencies of the first- and third-order vertical bending and torsional modes both increase with the middle pylon stiffness. However, the increase amplitudes of third-order bending and torsional modes are relatively small with the middle pylon stiffness increase. Moreover, the second-order bending and torsional frequencies do not change with the middle pylon stiffness.

• International Journal of Aeronautical and Space Sciences
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• 제8권1호
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• pp.21-31
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• 2007

Relaxed Static Stability (RSS) concept has been applied to improve aerodynamic performance of modern version supersonic jet fighter aircraft. The T-50 advanced supersonic trainer employs the RSS concept in order to improve the aerodynamic performance. And the flight control system stabilizes the unstable aircraft and provides adequate handling qualities. The T-50 longitudinal control laws employ a proportional-plus-integral type controller based on a dynamic inversion method. The longitudinal dynamic modes consist of short period with high frequency and phugoid mode with low frequency. The design goal of longitudinal control law is optimization of short period damping ratio and frequency using Lower Order Equivalent System (LOES) complying the requirement of MIL-F-8785C. This paper addresses phugoid mode characteristics such as damping ratio and natural frequency that is affected by the nonlinear control laws such as angle of attack limiter, auto pitch attitude command system and autopilot of pitch attitude hold.