• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.12
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• pp.929-934
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• 2002

This paper considers the vibration Problem of vehicle driveline which consists of two propeller shafts and the center bearing. The excessive vibration occurs at the center bearing when the vehicle starts to run. Using the kinematic constraints at the universal joint between two propeller shafts, we developed an one d.o.f model which describes the radial motion of the center bearing. We found out that the vibration occurs at the specific vehicle speed corresponding to the natural frequency of the model. Comparing the simulation results with test results we also show that the vibration at low vehicle speed is caused primarily by the feint angle and secondarily by the mis-aligned yoke flange rather than by the unbalance.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.297-300
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• 2005

This paper presents vibration control of an engine mount for a passenger vehicle utilizing ER fluid and piezoelectric actuator. The proposed engine mount can be isolated the vibration of wide frequency range with many types of amplitude. The main function of ER fluid is to attenuate vibration for low frequency with large amplitude, while the piezoelectric actuator is activated in hish frequency range with small amplitude. A mathematical model of the engine mount is derived using Hydraulic model and mechanical model. After formulating the governing equation of motion, then field-dependent dynamic stiffness of the engine mount is evaluated for various engine speed and excitation amplitude conditions. Then robust controller is designed to attenuate vibration of wide range frequency component. Computer simulation is undertaken in order to evaluate the vibration control performance such as transmissibility magnitude in frequency domains.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.1
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• pp.35-46
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• 2008

Harmonic vibration characteristics for the general rotor model having a breathing crack are analyzed. Analyses are performed at the half critical speed ranges. The vibration characteristics are explained by using the additional slope and bending moment at the crack position and the influence coefficient showing the structural dynamic characteristics of the rotor. With the low crack depth the magnitude of the additional slope is kept constant even at the speed range at which the orbit magnitude is very sensitive to the rotational speed change. At this speed range the vibration is affected by the influence coefficient only. As the dynamic bending moment exceeds the static bending moment with the increase of crack depth. the additional slope affects the vibration amplitude of cracked rotor and the crack propagation rate increases.

• Steel and Composite Structures
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• v.30 no.6
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• pp.577-589
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• 2019

In this study, on-site testing was carried out to investigate the vibration performance of a composite steel-bar truss slab with steel girder system. Ambient vibration was performed to capture the primary vibration parameters (natural frequencies, damping ratios, and mode shapes). The composite floor possesses low frequency (< 10 Hz) and damping (< 2%). Based on experimental, theoretical, and numerical analyses on natural frequencies and mode shapes, the boundary condition of SCSC (i.e., two opposite edges simply-supported and the other two edges clamped) is deemed more reasonable for the composite floor. Walking excitations by one person (single excitation), two persons (dual excitation), and three persons (triple excitation) were considered to evaluate the vibration serviceability of the composite floor. The measured acceleration results show a satisfactory vibration perceptibility. For design convenience and safety, a crest factor ${\beta}_{rp}$ describing the ratio of peak acceleration to root-mean-square acceleration induced from the walking excitations is proposed. The comparisons of the modal parameters determined by ambient vibration and walking tests reveal the interaction effect between the human excitation and the composite floor.

• Journal of the Korean Wood Science and Technology
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• v.19 no.1
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• pp.71-80
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• 1991

This study was carried out to investigate replaceable species with the conventional sounding board sitka spruce. by comparing the dynamic properties such as density, dynamic Young's modulus and internal friction Dynamic Young's modulus. internal friction of longitudinal and radial direction measured in free mass-free boundary condition for facile vibration analysis and measured by forced vibration method. Dynamical properties of four species were measured on squared plate specimen that the four edges were hung vertically by threads and driven magnetically through an iron piece glued on the specimen, by the use of condenser microphone as vibration transducer, and analyzed by FFT analyzer. The results obtained were as follows: 1. Chaldni method using aluminum powder was proper to identify the vibration mode in the plate vibration and it was possible to verify the resornance mode. 2. It was considered that it was necessary to investigate the influence of adhesive part on the plate vibration when the sounding board was made by two or three small board adhesion. 3. It was considered that plate vibration method, which was a superior to the vibration test of beam, was suitable for selecting suounding board because dynamic Young's modulus and internal friction show different order according to longitudinal and radial direction. 4. Paulownia tomentosa Thunb.) Steudel has been considered to be replaceable species with sitka spruce because it has high dynamic Young's modulus compared with low density, low internal friction, and K value of Paulownia tomentosa (Thunb.) Steudel is greater than that of sitka spruce.

• The Journal of Korean Physical Therapy
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• v.14 no.4
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• pp.398-411
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• 2002

Objectives: The purpose of present study was to investigate the experience and point prevalence rate and factors related with Low Back Pain (LBP) in train egineers. Methods: Questionnaires were completed by 324 train engineers in Daejeon railroad administration from May 2002. The information was used to estimate odds ratio (OR) and 95$\%$ confidence intervals (CI) for factors relation to LBP. A retrospective study design was used. Results: The experience rate for LBP was 67.9$\%$, 54$\%$ in one year interval prevalence, 53.4$\%$ in 6 months interval prevalence, and 47.8$\%$ in a point prevalence rate. Variables significantly associated with LBP experience were age (p=0.0327), train vibration(p=0.0015), labour hour(p=0.0034), and pay(p=0.0534). As subjects got older, the higher experience for LBP was (OR=1.1, 95$\%$ CI 1.0-1.2). LBP experience rate for people who had felt train vibration was a higher than those who did not (OR=2.5, 95$\%$ CI 1.4-4.4, OR=2.3 95$\%$ CI 1.3-4.0 in a point prevalence). The people who worked for long hour was a higher than those who did not (OR=2.8, 95$\%$ CI 1.4-5.6, OR=2.2, 95$\%$ CI 1.1-4.5 in a point prevalence). The people who were not satisfied with pay was a higher than those who were (OR=1.7, 95$\%$ CI 1.0-3.0). Factors related to a point prevalence rate were train vibration(p=0.0027), chair vibration (p=0.0444), and labour hour(p=0.0340). LBP a point prevalence rate for people who had felt the vibration of train chair was a higher than those who did not (OR=1.8 95$\%$ CI 0.7-2.0). Conclusions: Results from present study indicated that a statistically significant factors associated with LBP experience were age, train vibration, labour hour, and pay, Factors related to a point prevalence rate were also train vibration, the vibration of train chair, and labour hour.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.2
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• pp.131-143
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• 2013

Vibration condition monitoring of low-speed rotational slewing bearings is essential ever since it became necessary for a proper maintenance schedule that replaces the slewing bearings installed in massive machinery in the steel industry, among other applications. So far, acoustic emission(AE) is still the primary technique used for dealing with low-speed bearing cases. Few studies employed vibration analysis because the signal generated as a result of the impact between the rolling element and the natural defect spots at low rotational speeds is generally weak and sometimes buried in noise and other interference frequencies. In order to increase the impact energy, some researchers generate artificial defects with a predetermined length, width, and depth of crack on the inner or outer race surfaces. Consequently, the fault frequency of a particular fault is easy to identify. This paper presents the applications of empirical mode decomposition(EMD) and ensemble empirical mode decomposition(EEMD) for measuring vibration signals slewing bearings running at a low rotational speed of 15 rpm. The natural vibration damage data used in this paper are obtained from a Korean industrial company. In this study, EEMD is used to support and clarify the results of the fast Fourier transform(FFT) in identifying bearing fault frequencies.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.3
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• pp.566-572
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• 2009

This paper has studied breakage possibility of glass insulators by resonance and accelerated deterioration through the comparison of the natural vibration and on site vibration. The natural frequencies of the strut tube glass insulator was measured within a range of less than 1kHz. In the on site vibration, the largest frequency that was imposed on strut tube glass insulators was 80Hz with 1.13g of vertical vibration in the viaduct section, the largest vertical vibration (0.38g) was detected at 103Hz in the open route section. When site vibration and natural vibration of strut tube glass insulators were compared in terms of characteristics, the resonance frequency was not the same. In both the viaduct and open route sections, it seems that the impact by vertical vibration in strut tube glass insulators is large. It's very unlikely that glass insulators were damaged by fatigue accumulation of vibration since the possibility of damage by resonance was very low in consideration of the characteristics of natural vibration and site vibration of glass insulators. In addition, no damage was detected in the accelerated deterioration test.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.609-615
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• 2001

A turbo-fan is easily exposed to noise and vibration as against other industrial machines and the majority of them is subject to be damaged by vibration. The most usual problem of vibration in a turbo-fan is resonance so the case of being composed of iron sheet structure with low strength like a turbo-fan should be taken seriously. In this paper, FFT(Fast Fourier Transform) and Order tracking method were used to analyze factors of vibration in a turbo-fan and hereby with proper selection of vibration isolator, we wanted to reduce vibration of base. After Order tracking, we knew resonance occurred in rotational frequency 23 Hz(1400 rpm) at the casing and the bearing. After the test of base vibration using vibration isolators, the spring isolator was more effective than the robber isolator in the base vibration and the vibration isolating is more effective in the case that the isolating pad is adhered to the bottom of the isolating spring.

• Wind and Structures
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• v.36 no.6
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• pp.393-404
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• 2023

Skewness and kurtosis are important higher-order statistics for simulating non-Gaussian wind pressure series on low-rise buildings, but their predictions are less studied in comparison with those of the low order statistics as mean and rms. The distribution gradients of skewness and kurtosis on roofs are evidently higher than those of mean and rms, which increases their prediction difficulty. The conventional artificial neural networks (ANNs) used for predicting mean and rms show unsatisfactory accuracy in predicting skewness and kurtosis owing to the limited capacity of shallow learning of ANNs. In this work, the deep neural networks (DNNs) model with the ability of deep learning is introduced to predict the skewness and kurtosis on a low-rise building. For obtaining the optimal generalization of the DNNs model, the hyper parameters are automatically determined by Bayesian Optimization (BO). Moreover, for providing a benchmark for future studies on predicting higher order statistics, the data sets for training and testing the DNNs model are extracted from the internationally open NIST-UWO database, and the prediction errors of all taps are comprehensively quantified by various error metrices. The results show that the prediction accuracy in this study is apparently better than that in the literature, since the correlation coefficient between the predicted and experimental results is 0.99 and 0.75 in this paper and the literature respectively. In the untrained cornering wind direction, the distributions of skewness and kurtosis are well captured by DNNs on the whole building including the roof corner with strong non-normality, and the correlation coefficients between the predicted and experimental results are 0.99 and 0.95 for skewness and kurtosis respectively.