• Journal of KSNVE
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• v.3 no.4
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• pp.313-324
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• 1993

• Journal of Korean Society of Steel Construction
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• v.13 no.3
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• pp.301-311
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• 2001

For a rectangular-highrise building with aspect ratio about six, the resonant wind speed of wind-induced vibration or galloping start wing speed can be within the design wind speed. The wind-induced vibration and galloping of highrise building with aspect ratio $H/\sqrt{DB}=6$, side ratio D/B=1 to 2 at intervals of 1/4 D/B were investigated in smooth flow. For the reducing effect of wind-induced vibration of highrise building, rectangular-highrise building with corners cutting about side ratio D/B=2 were investigated. Experimental results show that in the smooth flow non corners-cutting cases have tendency of increasing wind-induced vibration and galloping vibration then corner-cutting section. Therefore, the wind-induced vibrations on rectangular-highrise buildings were reduced effectively by using corner cut method.

• Journal of Ocean Engineering and Technology
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• v.7 no.1
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• pp.73-80
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• 1993

본 연구에서는 장주형 해양구조물의 횡방향 진동에 대한 파라메트릭 가진 효과를 고찰하였다. 먼저, 장주형 해양구조물의 횡방향 운동에 대한 4계 편미방지배방정식을 비선형 Mathieu 방정식으로 유도하였다. 비선형 mathieu 방정식의 해를 구하여 장주형 해양구조물의 동적 반응 특성을 해석하였다. 유체 비선형 감쇠력은 불안정 조건하에 있는 파라메트릭 진동의 반응크기를 제한 하는데 중요한 역활을 한다. 파라메트릭 진동의 경우 가장 큰 반응크기는 Mathieu 안정차트의 첫번째 불안정 구간에서 일어난다. 반면에, 파라메트릭 진동과 강제진동의 결합 진동인 경우, 가장 큰 반응 크기는 두번째 불안정 구간에서 발생된다. 파라메트릭 가진으로 인한 장주형 해양구조물의 횡방향 운동은 동적조건에 따라 subharmonic, superharmonic 또는 chaotic 운동이 되기도 한다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.469-473
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• 2010

In this study, combustion tests using liquefying fuels with fast regression rate were performed. The chamber pressure oscillation was analyzed and hazards of combustion instabilities were examined. In case of Liquefying fuel with fast regression rate, the amplitude of chamber pressure oscillation was increased compared to the polymeric fuels. However, the critical combustion instability can hardly occur in liquefying fuel. This is because the rapid change of inner chamber diameter limits the amplification of chamber pressure oscillation. The chamber pressure oscillation due to the large increase of fuel production and the vortex shedding in pre-chamber violently occurs during combustion using single-port axial injector.

• Journal of KSNVE
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• v.9 no.5
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• pp.936-942
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• 1999

Unstable torsional vibration on the marine ship's propulsion shafting system with diesel engine occurred due to a slippage of multi-friction clutch which was installed between increasing gear and shaft generator. In this paper, the mechanism of this vibration was verified via torsional, whirling, axial and structural vibration measurements of shafting system and noise measurement of gear box. And it was also identified by the theoretical analysis method.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.12
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• pp.1021-1027
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• 2018

Experimental studies have been conducted to verify that the positive coupling between pressure oscillation (p') and combustion oscillation (q') of high frequency range is a prerequisite for the initiation of low frequency instability in hybrid rocket combustion. The post-chamber length and combustion equivalence ratio were selected as critical parameters to control the phase difference between p' and q', and p' amplitude in relation to the suppression of LFI. In the results, even if the post-chamber length increases, the phase difference between p' and q' maintains below pi/2, which is a necessary condition for the LFI development, but the amplification of RI (Rayleigh index) was substantially decreased leading to a stable combustion. In addition, results confirmed that combustion stability is achieved by changing the momentary equivalence ratio and/or by suppressing the positive coupling status of p' and q'. Thus, the periodic amplification of RI was identified as the middle path of the mechanism of occurrence of LFI.

• Journal of the Korean Society for Railway
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• v.16 no.4
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• pp.253-261
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• 2013

According to the measured results of KTX brake squeal noise in this study, high level brake noise occurred in a wide frequency range, 100~18,000Hz. To identify the sources of the brake squeal noise, unstable vibration modes due to brake disc/pad interaction were analyzed under various conditions by the finite element method. Complex eigenvalues for a brake unit with a disc and four pads were obtained. It was found that the real parts of the complex eigenvalues, that is, unstable vibration modes, were closely related to friction coefficients, pressure on the brake cylinders, elastic moduli of the components, and other conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.720-727
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• 2019

Resonating thermal lags of solid fuel with heat transfer oscillations generated by boundary layer oscillation is the primary mechanism of the occurrence of the LFI (Low Frequency Combustion Instability) in hybrid rocket combustion. This study was experimentally attempted to confirm that how the boundary layer was perturbed and led to the LFI. Special attention was also made on oxidizer swirl injection to investigate the contribution to combustion stabilization. Also the overall behavior of fluctuating boundary layer flow and the occurrence of the LFI was monitored as swirl intensity increased. Fluctuating boundary layer was successfully monitored by the captured image and POD (Proper Orthogonal Decomposition) analysis. In the results, oscillating boundary layer became stabilized as the swirl intensity increases. And the coupling strength between high frequency p', q' diminished and periodical amplification of RI (Rayleigh Index) with similar frequency band of thermal lag was also decreased. Thus, results confirmed that oscillating axial boundary layer triggered by periodic coupling of high frequency p', q' is the primary mechanism to excite thermal resonance with thermal lag characteristics of solid fuel.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.6
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• pp.463-469
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• 2004

In order to improve the instability of journal bearings, the leaf spring dampers (LSD) are introduced. The effects of LSD on the stability of journal bearings are investigated theoretically The stability of the journal bearing with LSD are compared with the results of the journal bearing without LSD. And the effects of the asymmetry of the stiffness of the leaf spring damper on the stability of rotors are also investigated.

• 전기의세계
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• v.9
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• pp.4-10
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• 1962

Relay Servo제어계의 특이한 성질의 하나로, 다른 비선형계에섣 그렇지만 외부의 동작에 의한 것이 아니고, 제어계 자체내의 조건에서 계속적으로 주기적운동, 즉 자려주기진동(Sustained Oscillation)이 발생하는 경우가 있다. 제어계가 자려진동의 상태에 있을 때 그 진폭 및 각주파수는 각 부분의 요소에 의하여 결정되고 고유한 값을 가지게 된다. 이러한 상태는 선형제어계의 입장에서 보며는 불안정상태이나, Relay제어계에서는 이 주기진동이 제어량의 일정목표치에 대한 비율이 미리 규정지은 요구조건에 비하여 실제상 허용할 수 있는 정도면 제어계는 안정하다고 할 수 있다. Relay Servo계의 안정, 불안정은 Describing함수의 방법에 의하여 Nyquist, Attnuation-phase Margin Criteria를 사용하여 Kochenburger, Johnson의 연구에서 규정지었다. Relay-Servo자려진동상태는 제어계의 Gain정수 중에서도 그 종류에 따라 각주파수 및 진폭에 미치는 영향이 달라진다. 본문은 위에 설명한 상태를 알아내기 위하여 간단한 Raly위치제어계를 구성하고 Gain정수를 변화시키면서 자려진동의 각주파수 및 진폭의 변화를 계산하고 기록계의 측정치와 비교검토하고자 한다.