• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.3
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• pp.274-281
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• 2009

The carbon fiber epoxy composite material and aluminum have many advantages over other materials because of their high specific stiffness and good fatigue characteristics. Basically, the propeller shaft of automobile requires bending frequency of higher than 2,700 Nm and high natural frequency of higher than 9,200 rpm occurred by fast revolution. For this reason, natural frequency and torsion torque characteristics of hybrid shaft was studied in variation of its outer-diameter and thickness. Vibration and torque characteristics of hybrid shaft were compared by torsion tester, natural frequency experiments and FE analysis. Designed hybrid shaft satisfied its vibration and torque characteristics when its outer-diameter was 60 mm and thickness was 5 mm. Therefore, hybrid material enables to manufacture one piece structure hybrid propeller shaft rather than current two piece structure.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.608-613
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• 2003

In this paper, the variability of modal properties caused by temperature effects is assessed to adjust modal data used for frequency-based damage detection in plate-girder bridges. First, experiments on model plate-girder bridges are described. Next, the relationship between temperature and natural frequencies is assessed and a set of empirical frequency-correction formula are analyzed for the test structure. Finally, a frequency-eased method is used to locate and estimate severity of damage in the test structure using experimental modal data which are adjusted by the frequency-correction formula. Here, local damage in beam-type structures is detected by using measured frequencies and analytical mode shapes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.283-288
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• 2006

This study developes the vibration model to estimate the vibration energy of damper/spring assembly(mainbase assembly) for car CD player, and this model is verified by experiment. From frequency response, response, we investigate the natural frequency and mode shape in the up/down direction. In order to determine the analysis frequency band, we investigate the excitation frequency from the vehicle test. As the characteristics of damper and spring is changed, we carry out the vibration test(transmissibility) and investigate the change of transmissibility.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1040-1043
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• 2006

Every mechanical system has a series of natural frequencies at which it will vibrate and to which it will respond if an external stimulus or excitation at this frequency is applied. Vibration is not of itself dangerous, and is always anticipated in an operating unit. However, if the frequency of operation is coincidental with one of the natural frequency of the blade system or the blade has a natural frequency near coincide with the exciting stimulus, then the amplitude of vibration of the blade may increase to the destructive damage can result. In this paper We investigated damage of blade when turbine operated.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.4
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• pp.165-172
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• 2003

This study aims to find frequency weighting curves for the evaluation of drivers' discomfort by vertical and rotational steering wheel vibration. Equal sensation curves, inverse of frequency weighting curves, were determined for the two kinds of vibrations respectively by using the sinusoidal signals with reference amplitudes from 0.2 to 0.4 m/s2 in the frequency range from 5 to 100 ㎐. Twelve subjects joined at the tests, and median values of the twelve judgments were used to determine the equal sensation curves. An experiment was followed to compare the relative sensation magnitude between the two kinds of equal sensation curves, which showed discomfort by the rotational vibration was 1.5 times of that by the vertical vibration at 50 ㎐.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.6
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• pp.163-168
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• 2001

Vibration problems occurred in an air cooled heat exchanger with axial flow fan for a petrochemical plant were investigated. Experimental field test and theoretical verification were performed. To find the main cause of the high vibration of the fan at the air inlet of the axial fan, the frequency spectrum was measured. The natural frequency of the driving support of the heat exchanger was numerically calculated. Both of the measured and the natural frequency were approximately equal to the blade passing frequency. Because it was difficult to modify the structure of the driving support during the normal operation of the plant, the blade number of the fan was increased, which greatly reduced the vibration level of the heat exchanger.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.10
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• pp.164-169
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• 1997

The aim of this paper is to present some results of sensitivity analysis in frequency domain. The sensitivity fonctions in frequency domain is not depend on the external excitation but depend on the frequency of the system's resonance. The sensitivity functions are determined as function of partial derivatives of system transfer functions taken with respect to system design parameters. The logarithmic sensitivity function is the dimensionless sensitivity funciton available, making it useful to compare the influence of various parameters on system variables. Two degree of fredom system is used to illustrate the procedure for sensitivity analysis proposed in this paper.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.2
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• pp.17-22
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• 2009

Estimate method of cable tension forces can be classified into direct method and indirect method. Direct method is not accuracy and it has many restrictions. Therefore, in generally Indirect method, vibration method using natural frequency, has been applied to estimate the tension forces. In this study, cable tensions of recently constructed cable-stayed bridge are measured using string vibration method and this result comparing with result of multiple mode method. To put it brief, the error of string vibration method is not exceeding 2% under 7th mode. Specially third and 4th mode error is not exceeding 1%. safety.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.366-375
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• 1991

In this study, vibrational behavior of uniform pipe carrying a moving medium is studied by using a transfer matrix and the displacement function derived from the conventional beam theory. In various boundary conditions, flow velocity and mechanical property change of the variation of natural frequency are investigated. The Coriolis term in the original differential equation of motion has been ignored in the investigation. This method is used to study the variation of natural frequency with flow velocity for clamped-clamped, cantilevered, clamped-pinned, pinned-pinned, free-free straight pipe element. It is shown that clamped-clamped, free-free pipe have the highest natural frequency and critical velocity values while cantilevered pipe have the smallest natural frequency for the same mechanical properties. From the vibration effects of mechanical property variation, it is shown that bending stiffness and pipe length variation has large influence on natural frequency and critical velocity. Since the order of transfer matrix is not changed with boundary conditions of pipe element, this method proposed can be easily applied to personal-computer for vibration analysis of pipe element. Furthermore, this method can be extended to three-dimensional system by using a coordinate transformation for the analysis of piping systems.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.5
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• pp.445-452
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• 2009

In this paper, damage detection procedure using the finite element model updating was formulated and applied to a small-scale frame structure. FE model updating is the analytical method which finds the mathematical model that generates the measured dynamic properties similarly, and can be effectively used for the damage detection and SHM. For model updating, several kinds of dynamic properties, such as the natural frequencies, mode shapes, and frequency response functions, can be used as the inputs. In this paper, two kinds of model updating procedures using the natrual frequency and the frequency response function, and the natrual frequency and the mode shapes, respectively, were applied to identify the location and the severity of damage of the test structure, which is a four-story two bay steel structure. Results from the damage detection showed that more accurate identification results was obtained when the natrual frequency and the frequency response function were used than when the natrual frequency and the mode shapes were used.