• 소음진동
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• 제7권5호
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• pp.819-826
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• 1997

The finite element analyses of a composite hingeless rotor blade in forward flight have been performed to investigate the influence of blade design parameters on the blade stability. The blade structure is represented by a single cell composite box-beam and its nonclassical effects such as transverse shear and torsion-related warping are considered. The nonlinear periodic differential equations of motion are obtained by moderate deflection beam theory and finite element method based on Hamilton principle. Aerodynamic forces are calculated using the quasi-steady strip theiry with compressibility and reverse flow effects. The coupling effects between the rotor blade and the fuselage are included in a free flight propulsive trim analysis. Damping values are calculated by using the Floquet transition matrix theory from the linearized equations perturbed at equilibrium position of the blade. The aeroelastic results were compared with an alternative analytic approch, and they showed good correlation with each other. Some parametric investigations for the helicopter design variables, such as pretwist and precone angles are carried out to know the aeroelastic behavior of the rotor.

• Smart Structures and Systems
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• 제18권1호
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• pp.1-16
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• 2016

Model Order Reduction (MOR) denotes the theory by which one tries to catch a model of order lower than that of the real model. This is conveniently pursued in view of the design of an efficient structural control scheme, just passive within this paper. When the nonlinear response of the reference structural system affects the nature of the reduced model, making it dependent on the visited subset of the input-output space, standard MOR techniques do not apply. The mathematical theory offers some specific alternatives, which however involve a degree of sophistication unjustified in the presence of a few localized nonlinearities. This paper suggests applying standard MOR to the linear parts of the structural system, the interface remaining the original unreduced nonlinear components. A case study focused on the effects of a helicopter land crash is used to exemplify the proposal.

• 항공우주기술
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• 제4권2호
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• pp.50-59
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• 2005

본 연구에서는 개발된 테일팬 1차 시제품의 성능시험에 대한 것이다. 한국항공우주연구원에서는 헬리콥터용 반 토오크 시스템으로 테일팬 시스템을 개발하였으며, 제작된 1차 시제품의 성능시험을 위해 테일팬 성능시험장치를 제작하였다. 테일팬 성능시험을 위해 먼저 시험장치에 대한 제작 검증용 시험을 수행하였고, 다음으로 팬블레이드와 시험장치의 고유진동수를 확인하였다. 성능 시험용 시험장치 운용회전수를 결정하기 위한 운용시험을 수행하였다. 테일기어박스(TGB)에 가속도계를 부착하여 단계적으로 회전수와 부착물들을 변화시켜가며 고유진동수와 진동 레벨을 확인하였다. 운용시험 결과로부터 테일팬 성능시험용 시험장치 운용회전수를 결정하였고, 무풍조건과 비행 조건에 따른 성능시험을 수행하였다. 측정된 데이터는 무차원화하여 분석하였고, 이 결과로 개발 시제품이 성능 요구조건을 만족시킴을 확인할 수 있었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.680-685
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• 2006

This paper describes the aeroelastic stability test of the small-scaled 'Next-Generation Blade(NRSB)' with NRSH (Next-Generation Hub System) and HCTH hingeless hub system in hover and forward flight conditions. Excitation tests of rotor system installed in GSRTS(General Small-scale Rotor Test System) at KARI(Korea Aerospace Research Institute) were tarried 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, NRSB-1F blades with HCTH hub system, Then NRSB-1F with NRSH hub system were tested. Second, NRSB-2F blades with NRSH hub system were tested. Tests were done on the ground and in the wind tunnel according to the test conditions of hover and forward flight, respectively. Non-rotating natural frequencies, non-rotating damping ratios and rotating natural frequencies were showed similar level fir each cases. Estimated damping ratios of NRSB-1F, NRSB-2F with HCTH and NRSH were above 0.5%, and damping ratio increased by collective pitch angle increasement. Furthermore damping ratios of NRSB-2F were higher than damping ratios of NRSB-1F in high pitch angle. It was confirmed that the blade design for noise reduction would give observable improvement in aeroelastic stability compared to paddle blade and NRSB-1F design.

• 한국소음진동공학회논문집
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• 제16권8호
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• pp.848-856
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• 2006

This paper describes the aeroelastic stability test of the small-scaled 'Next-generation Blade(NRSB)' with NRSH (next-generation hub system) and HCTH hingeless hub system in hover and forward flight conditions. Excitation tests of rotor 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, NRSB-1F blades with HCTH hub system, then NRSB- 1F with NRSH hub system were tested. Second, NRSB-2F blades with NRSH hub system were tested. Tests were done on the ground and in the wind tunnel according to the test conditions of hover and forward flight, respectively. Non-rotating natural frequencies, non-rotating damping ratios and rotating natural frequencies were showed similar level for each cases. Estimated damping ratios of NRSB-1F, NRSB-2F with HCTH and NRSH were above 0.5%, and damping ratio increased by collective pitch angle increasement. Furthermore damping ratios of NRSB-2F were higher than damping ratios of NRSB-1F in high Pitch angle. It was confirmed that the blade design for noise reduction would give observable improvement in aeroelastic stability compared to paddle blade and NRSB-1F design.

• 대한기계학회논문집
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• 제19권2호
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• pp.348-353
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• 1995

When cantilever beams rotate, their bending stiffnesses change due to the stretching caused by centrifugal inertia forces. Such phenomena result in variations of natural frequencies and mode shapes associated with constant speed rotational motions of the beams. These variations are important in many practical applications such as helicopter blades, turbomachines, and space structures. This paper presents the formulation of a set of linear equations governing the flapwise bending vibration of rotating cantilever beams. These equations can be used to provide accurate predictions of the variations of natural frequencies and mode shapes due to rotation.

• 한국항공운항학회지
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• 제15권3호
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• pp.6-14
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• 2007

In this research, vibration reduction and aeroelastic stability of a composite hingeless rotor hub flexure with viscoelastic constrained layer damping treatment(CLDT) were investigated. The composite flexures with viscoelastic CLDT were applied to hingeless rotor system to improve the in-plane stability of the lead-lag motion causing resonance. The modal test was performed and dynamic properties(natural frequency and loss factor) were acquired. Also, complex eigenvalue analysis(SOLlO7) in the NASTRAN structural analysis module was performed and compared with results of the modal test. To insure aeroelastic stability, damping ratio analyses of the hingeless rotor system with CLDT were accomplished at hovering condition due to collective pitch angle changes. Satisfactory results of increasing structural damping and stability were obtained.

• 한국항공우주학회지
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• 제39권12호
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• pp.1160-1165
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• 2011

본 연구는 무인항공기 및 헬리콥터 등에 장착되어 운용되는 고정밀 관측 다축 구동 EO/IR 카메라의 진동해석에 관한 것이며, 카메라에 적용된 볼 베어링을 모델링 하는데 있어서 3축 스프링요소를 적용하는 방법을 제시하였고, 이것에 의한 유한요소모델의 진동 응답 결과를 얻었다. 볼 베어링을 3축 스프링 요소로 모델링한 진동해석결과는 시험결과와 비교 되었으며, 잘 일치함을 알 수 있었다. 또한, 랜덤진동 시간이력해석을 통하여 다축 구동 EO/IR 카메라의 진동 응답 특성을 해석하고 분석하였다. 이의 연구결과는 우주용 카메라들에 사용되는 볼 베어링의 유한요소모델링 기법에 응용될 수 있다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.256-263
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• 2008

The assumed modes method is developed to derive a set of linear differential equations describing the motion of a flexible wind turbine blade and to propose an approach to investigate the forced responses result from various wind excitations. In this work, we have adopted Euler beam theory and considered that the root of the blade is clamped at the rigid hub. And the aerodynamic parameters and forces are determined based on Blade Element Momentum (BEM) theory and quasi-steady airfoil aerodynamics. Numerical calculations show that this method gives good results and it can be used fur modeling and the forced vibration analysis including the coupling effect of wind-turbine blades, as well as turbo-machinery blades, aircraft propellers or helicopter rotor blades which may be considered as straight non-uniform beams with built-in pre-twist.

• 한국항공운항학회지
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• 제15권4호
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• pp.24-32
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• 2007

In this study, computational structural vibration analyses of a smart unmanned aerial vehicle (SUAV) with tilt-rotors due to dynamic hub loads have been conducted considering detailed supporting structures of installed equipments. Three-dimensional dynamic finite element model has been constructed for different fuel conditions and tilting angles corresponding to helicopter, transition and airplane flight modes. Practical computational procedure for modal transient response analysis is successfully established. Also, dynamic loads generated by rotating blades and wakes in the transient and forward flight conditions are calculated by unsteady computational fluid dynamics technique with sliding mesh concept. As the results of present study, transient structural displacements and accelerations of the vibration sensitive equipments are presented in detail. In addition, vibration characteristics of structures and installed equipments of which safe operation is normally limited by the vibration environment specifications are physically investigated for different flight conditions.