• 한국소음진동공학회논문집
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• 제12권3호
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• pp.228-235
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• 2002

Two kinds of experimental modal analyses have been performed on a radial tire for passenger car under fixed axle. 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 three-dimensional natural modes and their decomposed 3-D modes in each direction, which make it possible to grasp the features of the modes that cannot be identified in the conventional 2-D modes and to classify the vibrationall modes into symmetric, non-symmetric, and antisymmetric modes in a simple way by using the experimental results. From the second experimental analysis, the cavity resonance frequency is found. Coomparing the results of the two analyses, we have Identified the three-dimensional mode of the cavity resonance. We also haute shown that natural frequencies of structural vibration depends on inflation Pressure while the cavity resonance does not.

• 한국철도학회논문집
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• 제12권4호
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• pp.465-471
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• 2009

본 논분에서는 보다 적은 실험으로 고속철도차량의 윤축에서 발생하는 소음과 진동의 동적 특성을 알기 위해 불규칙 신호처리와 시간-주파수 해석을 이용하여 분석하였다. 윤축의 소음과 진동은 대부분 차륜과 궤도의 비정상상호작용이 원인이다. 이를 분석하기 위해 마이크로폰과 가속도계를 이용하여 데이터를 수집하고 붙규칙 신호처리와 시간-주파수 분석을 이용하여 분석하였다. 분석한 결과, 이 방법들은 고속철도차량의 윤축에서 발생하는 소음과 진동의 동적특성을 분석하는데 유용함을 확인하였다.

• 한국소음진동공학회논문집
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• 제22권3호
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• pp.291-297
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• 2012

Conventional Fourier analysis can give only limited information about the dynamic characteristics of nonstationary signals. Instead, time-frequency analysis is widely used to investigate the nonstationary signal in detail. Several time-frequency analysis methods are compared for a typical acoustic emission burst generated during the impact between a ferrite ceramic and aluminum plate. This AE burst is inherently nonstationary and random containing many frequency contents, which leads to severe interference between cross terms in bilinear convolution type distributions. The smoothing and reassignment processes can improve the readability and resolution of the results. Spectrogram and scalogram of the AE burst are obtained and compared to get the characteristics information. Renyi entropies are computed for various bilinear time-frequency transforms to evaluate the randomness. These bilinear transforms are reassigned by using the improved algorithm in discrete computation.

• 한국기계가공학회지
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• 제10권4호
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• pp.22-30
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• 2011

This study analyzes harmonic vibration with natural frequency according to the configuration of damper clutch. In the case of double spring, equivalent stress at same direction of the revolution at inner and outer coil spring is over 30% as compared with at its opposite direction. Natural frequency or harmonic response with maximum deformation in case of the less coil pitch is below 3Hz as compared with in case of the more coil pitch. As the coil pitch of damper spring as the case 2 or 4 becomes smaller, its mass and deformation can be large. In these cases, spring constant and natural frequency become smaller. In the case 5 or 6 of double spring at natural vibration or harmonic response, the frequency becomes over 300Hz. As the result of this study is applied by the design of damper spring, the damage at its connected part is prevented and the durability can be predicted.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 I
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• pp.203-206
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• 2001

The reduction of chopping noise generated from inverter compressor and the piping design reducing vibration are the most important items in the quality of air conditioner. The chopping noise is identified by the study of the relationship between carrier frequency and natural frequency of the compressor shell. The high carrier frequency is the key factor in reduction of carrier noise. To keep the natural frequencies of the system as far as away from the operating frequencies appears to be the most important factor in the design of piping system.

• 한국소음진동공학회논문집
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• 제19권3호
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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.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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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.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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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.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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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.

• 한국자동차공학회논문집
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• 제11권4호
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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 ㎐.