• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.32.6-32
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• 2002

The damage localization of the structural system using the natural frequency measurement only is proposed. The existing methods use the changes of mode shape, strain mode shape or curvature mode shape before and after the damage occurrence as these shapes carry the geometric information of the structure. Basically, the change of natural frequencies of the structure can be used as the indicator of the damage occurrence but not as the indicator of the damage location as the natural frequency changes does not carry the geometric information of the structure. In this research, the feedback scope method that measures the natural frequency changes of the structure with and without the feedback Ioo...

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.2 no.2
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• pp.60-66
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• 2003

For the estimation of chatter lobe boundary it is very important to calculate the natural mode of cutting process. There are many time series algorithms for getting the natural mode of structural endmilling dynamics considering the cutting process. In this study, we have compared several time series methods such as AR algorithm, ARX, ARMAX, ARMA, Box Jenkins, Output Error, Recursive ARX, Recursive ARMAX considering the sampling frequency. As a results, the ARX, ARMAX and IV 4 are more desirable algorithms for the calculation of modal parameters such as natural frequency and damping ratio In endmilling operation. Also these algorithms may be adopted for the natural mode estimation of endmilling operation for chatter lobe prediction.

• Journal of KSNVE
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• v.8 no.3
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• pp.494-503
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• 1998

In this paper, in order to analyze dynamic characteristics of an automobile steering system consisting of many components, natural frequencies and transfer functions of each component and the total system are found on a FFT analyzer by experiments. Then, the data are transmitted to a commercial package program, CADA-PC. By analyzing the data, the mode shape of each natural frequency and damping values are obtained. Also, the function of a rubber coupling in column and telescoping effects on system are considered. C.A.E commercial programs are used to compare with the results of experiments. For the finite element modeling, I-DEAS is used. Data processing and post processing are operated on NASTRAN and XL, respectively. The ball-bearing and the linkage of shaft with column are modeled by spring element. Stiffness is modified from the results of experiments. The results of those show close agreement. In the mode shape of total system, wheel mode is dominant at lower frequency, while the column mode is main mode at higher. The role of rubber coupling in vibration isolation is clear on mode shape. Telescoping function makes natural frequency of column changed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.975-979
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• 1994

The experimental and finite element studies of a coaxial cylindrical shell filled with liquid in the annular gap were performed to understand its vibration characteristics. Finite element analysis was achieved by using ANSYS code. Form the investigation of the changing trend of natural frequencies for the change of annular gap we know that the natural frequency of the coaxial cylindrical shell varies according to the mode shape. that is, in case of in-phase mode the natural frequency decrease as annular gap increase, but in case of out-of-phase mode the natural frequency increase. Finite element analysis results show the excellent agreement with the experimental results both in air and in water case, so that analysis on other cases with be possible without experiment.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.11
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• pp.840-846
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• 2002

The vibrational system of this study is consisted of a cantilever pipe conveying fluid, the moving masses upon it and an attached tip mass. The equation of motion is derived by using Lagrange equation. The influences of the velocity and the number of moving masses and the velocities of fluid flow in the pipe have been studied on the natural frequency of a cantilever pipe by numerical method. As the size and number of a moving mass increases, the natural frequency of cantilever pipe conveying fluid is decreased. When the first a moving mass Is located at the end of cantilever pipe, the increasing of the distance of moving masses make the natural frequency increase at first and third mode, but the frequency of second mode is decreased. The variation of natural frequency of the system is decreased due to increase of the number of a moving mass. The number and distance of moving masses effect more on the frequency of higher mode of vibration.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.3
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• pp.227-236
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• 2002

We have performed two kinds of experimental modal analyses fur a radial tire for passenger car under free-suspension. One is the modal analysis to obtain three-dimensional modes of tire using accelerometers and the other is the one to identify cavity resonance frequency using a pressure sensor. From the first analysis, we have obtained the three-dimensional natural modes, which makes it possible to grasp the features of the modes and to classify the vibrational modes into symmetric, non-symmetric, and antisymmetric modes in a simple way by using the experimental results. From the first and the second experimental analyses we have identified the cavity resonance frequency and its three-dimensional mode shape.

• Journal of KSNVE
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• v.5 no.2
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• pp.215-224
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• 1995

In this paper, the three-dimensional finite element model is established to investigate the structural dynamic characteristics of rotor blade using a finite element analysis. Six natural frequencies and mode shapes are calculated by computer simulation. The first three flapping modal frequencies, the first two lead-lag modal frequencies, and the first feathering modal frequency are validated through comparison with the modal test results of the fixed rotor blade. The computer simulation results are found in good agreement with experimentally measured natural frequencies. The important results are obtained as follows: (1) Natural frequencies are changed due to the variation of rotational speed and fiber angle of rotor blade, (2) Weak coupling between flapping mode shape and lead-lag mode shape are detected, (3) Centrifugal force has more effect on flapping modal frequency than lead-lag modal frequency.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.10
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• pp.667-676
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• 2015

Working displacement variation by elastic deformation of active Gurney flap which was operated on high frequency was observed. Flap-wise natural frequency was lower than mode analysis result and hinge boundary condition was identified to be the cause through the simple modal test. Design modification for increasing natural frequency was conducted for minimizing the elastic deformation at maximum 35 Hz operating condition which was design requirement condition. Brass bushing was applied instead of rotating bearing for gap minimization and Gurney flap design modification was conducted to increase of the flap-wise natural frequency. Design modification effect was validated by natural frequency comparison with mode analysis result and modal test result of design modification model.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.8
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• pp.702-710
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• 2007

Direct numerical simulation (DNS) is performed to investigate suppressed wake transition and occurrence of lock-on in the wake of a circular cylinder disturbed by sinusoidal perturbation at the Reynolds number of 220 (A-mode instability regime). The sinusoidal perturbation, of which the frequency is near twice the natural shedding frequency, is superimposed on the free stream velocity. It is shown that the wake transition behind the circular cylinder can be suppressed due to the perturbation of the free stream velocity. This change causes a jump in the Strouhal number from the value corresponding to A-mode instability regime to the value corresponding to retarded wake transition regime (extrapolated from laminar shedding regime) in the Strouhal-Reynolds number relationship. As a result, vortex shedding frequency is locked on the perturbation frequency depending not on the natural shedding frequency but on the modified shedding frequency.

• Structural Engineering and Mechanics
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• v.22 no.6
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• pp.719-739
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• 2006

An analytical method for the free vibration of two circular plates coupled with an inviscid and compressible fluid is developed by the Rayleigh-Ritz method. The fluid is bounded by a rigid cylindrical vessel and two circular plates with an unequal thickness and diameter. It was found that the theoretical results could predict well the fluid-coupled natural frequencies with an excellent accuracy when compared with the finite element analysis results. As the fluid thickness increases or the plate thickness difference increases, an abrupt curve veering in the natural frequency loci of the neighboring modes and drastic changes in the corresponding mode shapes are observed. The mode localization frequently appears in the higher modes and in the wide gap between the plates because of a decrease in the fluid coupling owing to the fluid dispersion effect.