• Journal of Ocean Engineering and Technology
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• v.15 no.3
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• pp.9-19
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• 2001

In this paper we present the aspect of inertial oscillation typically observed in the spin-up of fluids at low Rossby numbers in a circular cylinder. Numerical computations for the quasi three-dimensional equation as well as one-dimensional equation are performed to estimate the predictability of the one-dimensional equation with Ekman pumping/suction models. It is assumed that the discrepancy between the two results may be attributed to the inertial oscillation The detailed analysis to the numerical results reveals that the axial plane is dominated by a comparatively strong oscillatory flows caused by the inertial oscillation. In view of the fact that the time-averaged flow field however agrees to the Taylor-Proudman theorem, it is recommended that further analysis is needed to obtain an improved one-dimensional model like the Reynolds-averaged Navier-Stokes equation for turbulent flows.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.04a
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• pp.354-359
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• 1995

회전익의 소재로 복합재료를 선택하게 됨에 따라 헬리콥터의 유지, 보수 및 성능에서 유리하게 되었지만 허브 형태의 간소화로 인하여 해석상의 어려움은 확대 되었다고 할 수 있을 것이다. 따라서 회전익의 단면특성은 더욱 중요한 의미를 갖게 되었다. 회전익의 단면특성을 결정하기 위해서 우선적으로 각 방향운동의 연성항을 소거하는 것이 계산상 유리하고 따라서 관성주축방향을 결정하는 것이 중요하다. 그러나 회전익의 익형이 대칭형이 아니고 복합한 재료로 구성되어 있을 뿐 아니라 효율의 극대화를 위하여 축방향을 따라 비틀림을 부여하고 있기 때문에 관성주축의 방향을 결정하는데 많은 어려움이 존재한다. 따라서 본 연구에서는 실제 회전익을 그 연구 대상으로 회전익 단면의 등가강성행렬을 추출하고 외팔보의 공학이론과 회전행렬을 이용하는 방법으로 관성주축방향을 결정하는 방법을 제시하였다. 해석방법의 타당성을 확보하기 위하여 엄밀해를 알고 있는 간단해 단면을 갖는 외팔보를 이용하여 검증하였다. 이러한 방법은 관성주축방향을 결정하는 새로운 프로그램의 개발이라는 부담을 최소화 하였을 뿐 아니라, 해석방법 자체가 가지는 간편성으로 인하여 많은 시간과 노력을 줄일수 있을 것으로 기대된다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.6
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• pp.545-550
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• 2009

Generally, the smoothing pre-filter of sensor's raw measurement(accelerometer and gyroscope) is used for INS's fast alignment. When the pre-filter is abruptly removed at Navigation-mode entry in vibration environment, INS's initial attitude error can be largely generated. So that we propose initial attitude error reducing methods(monotone increasing of cutoff-frequency, real-time attitude estimation), these are proved by simulation.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.4
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• pp.36-44
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• 2003

In the industrial motor drive system which is composed of a motor and load connected with a flexible shaft, a torsional vibration is often generated because of the elastic elements in torque transmission. To solve this problem, the two degrees of freedom H$_{\infty}$ controller was designed. But it is difficult to realize that controller. In this paper, H$_{\infty}$ control of 2-mass system using partial state feedback and resonance ratio control is proposed. Proposed controller has simple structure but satisfies the attenuation of disturbances and vibrations.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.3A
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• pp.181-187
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• 2011

This paper deals with free vibrations of the Timoshenko beam supported by two elastomeric bearings at two far ends. The ordinary differential equation governing free vibrations of such beam is derived, in which both effects of rotatory inertia and shear deformation are included as the Timoshenko beam theory. Also, boundary conditions of the free end are derived based on the Timoshenko beam theory. The ordinary differential equation is solved by the numerical methods for calculating natural frequencies and mode shapes. Both effects of the rotatory inertia and shear deformation on natural frequencies are extensively discussed. Also, relationships between natural frequencies and slenderness ratio, foundation modulus and bearing length are presented. Typical mode shapes of bending moment and shear force as well as deflection are given in figures which show the positions of maximum amplitudes and nodal points.

• Transactions of the Korean Society of Mechanical Engineers
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• v.1 no.2
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• pp.82-88
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• 1977

1장이 축방향으로 자유로이 움직일 수 있는 단선지시보의 진동에 있어서 그 진폭이 크고, 축방향의 관성력과 전단변형을 고려할때 의 진동을 살폈다. 운동방정식을 처짐을 독립변수로 하는 비선형편미분방정식으로 표시하고, model expansion과 Galerkin 방법에 의해서 비정형연립상미분방정식으로 변형한 다음에 Perturbation method of muthod of multiple scale로 유사해를 구하였다. 또한 보의 진동수-진폭의 관계에 대한 일반적 표현을 구하고, 간단한 구체적 해에 대하여 1차근사해와 진동수-진폭관계를 계산하여 이미 이루어진 연구결과와 비교하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.994-999
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• 2003

A modeling method for the modal analysis of a rotating cross-ply composite beam based on Timoshenko beam theory is presented. To analyze the composite beam exactly, the effects of shear deformation and rotary inertia are included. Linear differential equations of motion are derived using the assumed mode method. For the modeling, hybrid deformation variables are employed and approximated to derive the equations of motion. The effects of the dimensionless angular velocity and the slenderness ratio parameter on the variations of modal characteristics are investigated

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.846-851
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• 2003

The differential equations governing free, in-plane vibrations of non-circular arches with non-uniform cross-section, including the effects of rotatory inertia, shear deformation and axial deformation, are derived and solved numerically to obtain frequencies. The lowest four natural frequencies are calculated for the prime parabolic arches with hinged-hinged, hinged-clamped, and clamped-clamped end constraints. Three general taper types for rectangular section are considered. A wide range of arch rise to span length ratios, slenderness ratios, and section ratios are considered. The agreement with results determined by means of a finite element method is good from an engineering viewpoint.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1991.04a
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• pp.139-144
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• 1991

4WD자동차의 엔진마운트 설계기법의 정리 및 실제차량의 실험적 mode 해 석을 통해 다음과 같은 결론을 얻었다. 1. 4WD자동차의 엔진마운트 설계 개념을 체계화시키고, 이를 실제차량에 대 해서 실험적 mode해석을 해본 결과 잘 일치함을 확인하였다. 2. power transmission system에 부가되는 장치(front propeller shaft)의 영 향을 검토한바, frequency shift현상이 발생함을 확인하였다. 이러한 영향은 이들 부가장치들의 질량증가 및 관성모멘트의 변화로 기인되며, 질량의 증가 보다는 관성모멘트의 영향이 상대적으로 크리라 판단된다.

• Journal of Korean Society of Steel Construction
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• v.13 no.6
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• pp.651-659
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• 2001

The main purpose of this paper is to present an analytical method for free vibration of stepped horizontally curved members on two-parameter elastic foundation. The ordinary differential equations governing the free vibration of such beams are derived as non-dimensional forms including the effects of rotatory inertia and shear deformation. The governing equations are solved numerically for the circular, parabolic, sinusoidal and elliptic curved beams with hinged-hinged, hinged-clamped and clamped-clamped end constraints. As the numerical results, the lowest four natural frequency parameters are presented as the functions of various non-dimensional system parameters. Also the typical mode shapes are presented.