• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.98-105
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• 2005

This paper presents the result of the aeroelastic stability test of the small-scaled hingeless hub system with composite paddle blades in hover and forward flight conditions. Excitation tests of hingeless hub system installed in GSRTS(General Small-scale Rotor Test System) at KARI(Korea Aerospace Research Institute) were carried out to get lead-lag damping ratio of blades with flexures as hub flexure. MBA(Moving Block Analysis) technique was used for the estimation of lead-lag damping ratio. First, blades with metal flexures, then with composite flexures of the same dynamic properties of rotor system as metal one were tested. Tests were done on the ground and in the wind tunnel according to the test conditions of hover and forward flight, respectively. Composite flexures were found to have better damping characteristics over metal ones in the non-rotating vibration test, and it was confirmed that the use of composite flexures would give observable improvement in aeroelastic stability compared to metal ones in all test conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.966-972
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• 2010

Damping characteristics of a Helmholtz resonator to passively control the combustion instability were investigated by linear acoustic analysis and atmospheric acoustic tests. Its orifice length and diameter were selected as the design parameters and supplied SPL(sound pressure level) effect on damping characteristics were investigated. Damping capacity is improved by decreasing the orifice length as well as by increasing the orifice diameter. Also, the results showed that the damping capacity of the resonator decreased nonlinearly about above 110 dB and instabilities in the nonlinear region were more effectively suppressed by increasing the orifice diameter.

• Computational Structural Engineering
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• v.11 no.1
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• pp.171-178
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• 1998

The added viscoelastic dampers increase damping and stiffness of buildings and results in so called non-classical or non-proportional damping problem. In this system the eigenvectors of the undamped system may not diagonalize the damping matrix, and the system is generally analyzed by converting the equation of motion into a 2n first order state-space form. As this approach is complex and time-consuming compared to the classically damped problem, the system is often analyzed by neglecting the off-diagonal terms in the damping matrix. In this paper the theoretical background of the approximate approach is studied, and the vibration characteristics of a three-story shear building with a viscoelastic damper are investigated using the exact and approximate method. It is found that the approximate method may produce good result when the additional damping is small, but as the damping increases the error also increase.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.4
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• pp.25-32
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• 2006

An advanced method of Relaxed Static Stability (RSS) is utilized for improving the aerodynamic performance of modern version supersonic jet fighter aircraft. The flight control system utilize RSS criteria in both longitudinal and lateral-directional axes to achieve performance enhancements and improve stability. The T-50 advanced trainer employs the RSS concept in order to improve the aerodynamic performance and the flight control law in order to guarantee aircraft stability. The longitudinal two modes are the short period with high frequency and the phugoid mode with low frequency. The design goals of longitudinal control laws is concerned with the short period damping and frequency optimization using lower order equivalent system and utilizing the requirement of MIL-F-8785C. Analysis of short period mode has been and continues to be performed This paper addresses the analysis of aircraft phugoid node characteristics such as damping, natural frequency, and analysis of aircraft pitch motion that impacted by angle of attack limiter and auto pitch attitude control law.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.04b
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• pp.131-136
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• 1993

일반적으로 공작기계 주축계에 대해서 요구되는 기본적인 항목들로는 고강성, 고감쇠, 고회전정밀도, 저발열, 장수명 등이 있다. 최근에는 이러한 기능들과 함께 가공능률과 가공정밀도의 향상을 도모하기 위해서 고속절삭을 실현햐ㄹ 수 있는 공작기계 주축계의 고속화, 즉 고속 주축계에 대한 연구가 활발히 진행되고 있다. 본 연구에서는 고속주축계의 동특성을 체계적으로해석하기 위해서 주축회전수의 영향을 고려한 유한요소모델(finite element model)을 도입하였다. 특히 주축은 세장비가 비교적 자기 때문에 Timoshenko보 이론으로, 베어링은 유한한 폭을 가지고 있기 때문에 반경방향 외에도 모멘트방향의 강성 및 감쇠특성을 가지고 있는 것으로 모델화 하였다. 그리고 고속주축계의 설계조건들을 도출하기 위해서 동특성 해석결과들로 부터 고속주축계의 모드매개변수들인 고유진동수와 감쇠비에 대한 주축 회전수, 베어링의 지지특성, 베어 링의 간격, 주축재료의 내부감쇠율 등의 영향을 고찰하였다.

• The Korean Journal of Nuclear Medicine Technology
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• v.18 no.2
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• pp.3-7
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• 2014

Purpose SPECT/CT scan to be performed attenuation correction on the basis of CT induce an overestimation of the site due to the beam hardening artifact by metal cover and reduce the images quality. Therefore, this study using a phantom that has been inserted artificial hip joint investigated that effect on the SPECT/CT image causing by metal artifact for varying the parameters of the Attenuation Map. Materials and Methods Siemens Symbia T16 SPECT/CT equipment was used. Artificial hip joint was inserted to SPECT/PET phantom, 17 mm sphere of Bright Streak area in CT image was filled with Tc-99m so that the radiation activity was 8 times compared to background. And then Hot and Background was measured in varying Wide Beam Coefficient on Attenuation Map and RBR (Region to Background Ratio) of Metal and Non-Metal was calculated and analyzed depending on the presence or absence of the hip joint. Results It tended to hot count of Non-Metal and Metal to increase as the value of the manual mode is increased, hot count ratio with the group of both manual mode 0.5 and 0.4 is the best match. Also, in automatic mode, the ratio of RBRNon-Metal and RBRMetal was 1.135, statistically significant difference was not observed in the manual mode 0.5 and 0.4. Conclusion In the automatic mode of Wide Beam Coefficient in attenuation correction map, it was found that it is over-correction by 13.52%, it was possible to minimize the over-correction by the artifact in 0.5 and 0.4 of manual mode. Further studies should be performed in order to apply to a patient with the help of this and it is considered possible to reduce the over-correction by the metal artifact of an artificial hip joint for Hip-Resurfacing Arthroplasty patients, and to improve the diagnostic performance.

• Journal of Convergence for Information Technology
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• v.12 no.3
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• pp.151-157
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• 2022

The purpose of this study was to investigate the frequency characteristics of forced vibration considering the vehicle progress. And the vibration characteristics in frequency domain that occur, when vehicle passes the bump, were analyzed. The responses such as displacement, velocity and acceleration were obtained through numerical analysis, and FFT processing was performed to analyze the frequency response function(FRF) characteristics. In particular, the location of vehicle eigenmodes and external excitation modes was clearly shown and analyzed. In the forced vibration model by external force, the behavior of the eigenmode in power spectrum and real and imaginary parts were also analyzed. The mode characteristics were also analyzed in each FRF. It was approximated by assuming total excitation force by considering the exciting frequency using impulse and sine wave forces, which can give the amplitude and frequencies. The response characteristics of forced oscillations having different mass, damping and stiffness have been systematically discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.04a
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• pp.370-375
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• 1996

부분구조합성법의 하나인 구분모드합성법을 이용하여, 비선형 진동해석을 행하는 새로운 방법을 제안하였다. 제안하는 방법은 비선형 운동방정식에 섭동법을 이용하여 미소변동량에 관하여 정리한 각 차수의 운동방정식에 구분모드합성법을 적용하였다. 여기서 1차의 운동방정식의 외력항은 0차의 변위로 표현하는 것에 의해 각차의 운동방정식을 풀었다. 또한, 제안한 방법을 이용하여 문형구조모델의 비선형 강제진동 시각역응답을 구하고, 그 계산결과에 관해서 검토했다. 그 결과, 본 해석방법을 특히 감쇠가 없는 경우에 있어서 비선형이 실현되고 있는 것이 확인되었다.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.4
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• pp.1-8
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• 2001

In this paper, a hybrid mass damper using AC-servomotor was designed and developed in order to reduce vibration levels of a 5-story test structure under base excitation. Control performances of the HMD under random and earthquakes excitations are compared with those of TMD through experimental test. It is confirmed that the HMD is more effective to reduce the vibration levels of the test structure especially for the earthquake excitation which excites more than 2 vibration modes of the structure simultaneously.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.3
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• pp.1-7
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• 2003

Excitation and system identification are carried out for a full-scale five-story structure to obtain fundamental data which will be used for the design of viscoelastic dampers, The hybrid mass driver(HMD) installed on the fifth floor was employed as external exciter to provide excitation for the building, Each floor response was measured and processed to find out where and how the viscoelastic dampers are located and designed. The sine-sweep and white noise loadings were applied to the structure by the HMD to obtain dynamic characteristics such as natural frequencies, damping ratios, and modes, The identified building was experimentally investigated again with the designed viscoelastic dampers installed at inter-stories to obtain the response behavior in the companion paper.