• 한국구조물진단유지관리공학회 논문집
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• 제6권3호
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• pp.119-128
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• 2002

This study discusses the issues related to the accuracy of deflection measurement and unstable energy in the testing of FRC. Some deflection methods may include large extraneous deformations. A faulty load-deflection curve will be obtained if an unstable deflection measuring system is used, and inaccurate toughness evaluation can result from this faulty curve. Some load-deflection curve of FRC may be attributed to unstable region of the load-deflection curve. If the unstable region is not correctly evaluated toughness indices from the curve would inappropriately represent true indices. In this paper, the discussion will focus on the effects of the deflection measuring system both on the measurement of the load-deflection response of FRC and the evaluation of FRC toughness and the effects of the unstable region and the management method of unstable region on toughness evaluation of FRC. It is observed that ASTM toughness indices which is based on measured deflection at first cracking is influenced significantly by extraneous deformation of deflection measurement. Extraneous deformation in deflection measurement, however result in negligible errors in toughness evaluation if JSCE and JCI definitions are used.

• 수산해양기술연구
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• 제17권1호
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• pp.35-40
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• 1981

회전축계의 모델로서 구동원과 상호작용을 고려한 2개원판이 부착된 비대칭축계의 안정성을 연명하기 위해 안정오을 유도하고 수치계기을 행하여 제일, 이공진검성의 불안정구간을 구하였다. 비대칭축계의 위험속도 초과시의 불안정은 축의 비대칭도에 의한 불안정과 Torque 특성에 발생하는 불안정의 2종류로 분류된다. 편심의 위상용이 불안정에 미치는 영향은 매우크며, 이는 후자에 의한 불안정에 기인한다. 감양는 전자에 의해 생기는 불안정을 감소 시키나, 후자에 의한 불안정은 오히려 증가시켜서 자려진동을 유발하므로 주의를 요한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 추계학술대회 논문집 학회본부
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• pp.254-257
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• 1989

In general, unstable phenomena of induction motor are oftenly appeared at low speed and light load. This paper discribes eigenic unstable regions of I.M. itself by computer simulations and the results are compared to experimental ones. And also the optimal design parameters of I.M. which the unstable reg ion can be minimized are determined.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권2호
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• pp.688-698
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• 2019

If heave motion in the platform causes horizontal parametric vibration of a Compliant Vertical Access Riser (CVAR), the riser may become unstable. A combination of riser parameters lies in the unstable region aggravates vibrational damage to the riser. Change of axial tensile stress in the riser combined with its natural frequency and mode shape change results in mode coupling. In accordance with the state transition matrices of the riser in the coupled and uncoupled states, the stable and unstable regions were obtained by Floquet theory, and the vibration response under different conditions was obtained. The parametric excitation of the CVAR is shown to occur mainly in first-order unstable regions. Mode coupling may cause parametric excitation in the least stable regions. Damping reduces the extent of unstable regions to a certain extent.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 D
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• pp.2687-2689
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• 2000

In many cases the systems are so complex that it is not possible to obtain reasonable models using physical insight. Also a model based on physical insight contains a number of unknown parameters even if the structure is derived from physical laws. These problems can be solved by system identification. In this paper, Arago's disk system which has both stable and unstable regions is selected as an example for identification and a state-space model is identified using tailor-made model structure of this system. In stable region, a state-space model of Arago's disk system is identified through open loop experiment and a state-space model of unstable region is identified through closed loop experiment after using fuzzy controller to stabilize unstable system.

• 한국통신학회논문지
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• 제12권1호
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• pp.19-26
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• 1987

Potentially unstable한 GaAs FET를 사용하여 3~4GHz에서 평탄한 이득특성을 갖는 광대역 초고주파 증폭기를 설계하였다. 입력정합회로는 유용전력이득이 14dB인 원을 사용하여 안정한 영역에 존재하도록 설계하였다. 출력정합회로는 최대전력이 전달되고 또한 안정한 영역에 존재하도록 Fano의 대역통과 정합이론을 사용하여 설계하였다. 전송 전력이득 및 $S_11$과 $S_22$의 실험치는 이론치와 거의 유사한 특성을 나타내었다.

• 한국해양공학회지
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• 제6권1호
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• pp.62-68
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• 1992

In this study, a system coupled with the nonlinear dynamic vibration absorber was modelled, and its equation of motion was analized by the harmonic balance method to obtain the amplitude ratio. And also, the stability analysis was done by the Routh Hurwitz method. In the vibration systems coupled with the nonlinear dynamic vibration absorber, the unstable region and the jump phenomenon can be ramarkably affected by the damping ratio. The stable and unstable region that obtained to differential method excellently agreed to the result of the stability analysis of Routh Hurwitz.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1998년도 유체기계 연구개발 발표회 논문집
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• pp.123-128
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• 1998

This study presents the measurement techniques on the periodic fluctuating flow such as the discharge flow of a centrifugal impeller in unstable operating region. During rotating stall, the flow at the exit of a centrifugal compressor impeller fluctuates periodically with lower frequency than that of the blade passing. To observe the blade-to-blade flow characteristics during rotating stall, the phases of all the sampled data sets should be adjusted to those of the reference signals with two processes, in these processes, DPLEAT (Double Phase-Locked Ensemble Averaging Technique) can be used. From these measurement and data processing techniques, the characteristics not only on the blade-to-blade flow with high frequency, but also on the periodic rotating stall flow with low frequency at the centrifugal impeller exit can be clearly observed.

• 한국수산과학회지
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• 제47권2호
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• pp.168-173
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• 2014

The effect of critical minimum depth in the coastal region on storm surges was examined using a three-dimensional primitive equation model (POM). Case studies using numerical experiments in a small coastal bay in the southern sea of Korea (Hanam Bay) have examined the 'critical depth' (CD) that stabilizes the numerical calculations. Dependence of the CD of typhoon tracks and tidal components such as M2, S2, O1, and K1 were examined. The model results clearly demonstrated that the numerically unstable state of the calculation was caused by the coarse resolution of sea surface elevation.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.277-283
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• 2003

It is well known that the natural frequencies of the pipe come to be lower as internal fluid velocity and pressure increase, and the pipe will be unstable if the fluid velocity is higher than critical velocity. But even if the velocity of the fluid below the critical velocity, resonance will be caused by pulsation of the fluid. So it should be also taken into consideration that the effect of pulsating fluid in pipe design. The research of the piping system vibration due to a fluid pulsation has been studied by many people. But almost is dealt with determining the boundary between stable and unstable region without analyzing forced response in the stable region. In this study, not only stability analysis but also forced response analysis, which is caused by harmonically excited fluid especially, is conducted.