• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.1185-1190
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• 2007

In this paper the vibration system is consisted of a rotating cantilever pipe conveying fluid. The equation of motion is derived by using the Lagrange's equation. Also, the equation of motion is derived applying a modeling method that employs hybrid deformation variables. Generally, the system of pipe conveying fluid becomes unstable by flutter. So, we studied about the influences of the rotating angular velocity, mass ratio and the velocity of fluid flow on the stability of a cantilever pipe by the numerical method. The influences of mass ratio, the velocity of fluid, the angular velocity of a cantilever pipe and the coupling of these factors on the stability of a cantilever pipe are analytically clarified. The critical fluid velocity$(u_{cr})$ is proportional to the angular velocity of the cantilever pipe. In this paper Flutter(instability) always occur in the second mode of the system.

• 한국정밀공학회지
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• 제30권8호
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• pp.854-863
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• 2013

High-speed spindle systems typically employ angular contact ball bearings, which can resist both axial and radial loading, and exhibit high precision and durability. We investigated the effects of the arrangement of the angular contact ball bearings on the dynamics of high-speed spindle systems. The spindle dynamics were studied with a number of spindle-bearing models, and the location of the bearings was varied, along with the rotational speed and the preload. A finite element spindle model and a bearing model were used, and simulated data showed that the bearing arrangement significantly affected the spindle dynamics. Furthermore, the main effects were due to the cross coupling terms between the transverse and rotational motions of the ball bearings. The coupling stiffness terms were found to influence the spindle dynamics, depending on the mode shapes. An extensive discussion is provided on the effects of the bearing arrangement on the dynamics of the spindle.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2001년도 ICCAS
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• pp.99.2-99
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• 2001

An electronically tunable current-mode second-order multifunctional filter is described in this paper. The proposed filter consists of two four-terminal floating nullors (FTFNs), two dual-output OTAs and two grounded capacitors. The circuit can simultaneously realize the lowpass, bandpass and highpass current transfer functions from the same configuration without changing the circuit configuration and elements. The natural angular frequency we and the parameter wo/Q can be orthogonally controlled through adjusting the transconductance gain of OTA. PSPICE simulation results are employed to confirm the circuit performance.

• 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.

• Journal of Biosystems Engineering
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• 제36권6호
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• pp.476-483
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• 2011

The aerial application using an unmanned helicopter has been already utilized and an attitude controller would be developed to enhance the operational convenience and safety of the operator. For a preliminary study of designing flight controller, a state space model for an RC helicopter would be identified. Frequency sweep flight tests were performed and time history data were acquired in the previous study. In this study, frequency response of the flight test data of a small unmanned helicopter was analyzed by using the CIFER software. The time history flight data consisted of three replications each for collective pitch, aileron, elevator and rudder sweep inputs. A total of 36 frequency responses were obtained for the four control stick inputs and nine outputs including linear velocities and accelerations and angular velocities in 3-axis. The results showed coherence values higher than 0.6 for every primary control inputs and corresponding on-axis outputs for the frequency range from 0.07 to 4 Hz. Also the analysis of conditioned frequency response showed its effectiveness in evaluating cross coupling effects. Based on the results, the dynamic characteristics of the model helicopter can further be analyzed in terms of transfer functions and the undamped natural frequency and damping ratio of each critical mode.

• 소음진동
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• 제8권6호
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• pp.1130-1136
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• 1998

A modelling method for the vibration analysis of rotating cantilever plates with a concentrated mass is presented. The equations of motion for the rotating plates with a concentrated mass located in an arbitrary position are derived and transformed into a dimensionless form. For the mathematical modelling of the concentrated mass. a mass density Dirac delta function is used. The effects of concentrated mass and its location. angular speed. plate aspect ratio. and hub radius of the rotating plate on the natural frequencies are studied. Particularly. mode shape variations due to some parameter variations are investigated.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.609-616
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• 2001

The vibrational characteristics of nonuniform circular rods have been studied theoretically and experimentally in this paper. The differential equation of torsional motion expressed in terms of the angular displacement has been solved exactly and approximately for a stepped circular rod and for a conically-tapered rod. Solutions of the boundary-value problem have yielded the natural frequencies, mode shapes and forced responses of the rods. The theoretical solutions of forced response have been verified by comparing them with experimental ones.

• 한국소음진동공학회논문집
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• 제23권8호
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• pp.742-751
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• 2013

The vibration analysis of a rotating cantilever beam made-up of functionally graded materials is presented based on Timoshenko beam theory. The material properties of the beams are assumed to be varied through the thickness direction following a simple power-law form. The frequency equations, which are coupled through gyroscopic coupling terms, are calculated using hybrid deformation variable modeling along with the Rayleigh-Ritz assumed mode methods. In this study, resulting system of ordinary differential equations shows the effects of power-law exponent, angular speed, length to height ratio and Young's modulus ratio. It is believed that the results will be a reference with which other researchers and commercial FE analysis program, ANSYS can compare their results.

• 소음진동
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• 제10권5호
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• pp.880-885
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• 2000

In a verical type, vibratory gyroscope, the coupled motion between the reference and sensing vibrations causes the zero-point output which means non-zero sensing vibration without angular velocity. This structural coupling leaks to an inherent discrepancy between the natural frequencies of the reference and sensing oscillations, causing the degradation of the sensing performance and dynamic stability. In this paper, the dynamic characteristics associated the coupling phenomenon are theoretically analyzed. Effects of reference frequency and coupling factor on the rotational direction and amplitude of elliptic oscillation are studied. A technique to predict the existence of curve veering of crossing in frequency trajectories is introduced to apply the design of micro gyroscopes with decoupled structures.

• Steel and Composite Structures
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• 제14권5호
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• pp.511-521
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• 2013

In this study we have considered the governing nonlinear equation of an eccentrically reinforced cylindrical shell. A new analytical method called He's Variational Approach (VA) is used to obtain the natural frequency of the nonlinear equation. This analytical representation gives excellent approximations to the numerical solution for the whole range of the oscillation amplitude, reducing the respective error of angular frequency in comparison with the variation approach method. It has been proved that the variational approach is very effective, convenient and does not require any linearization or small perturbation. Additionally it has been demonstrated that the variational approach is adequately accurate to nonlinear problems in physics and engineering.