• Structural Engineering and Mechanics
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• v.44 no.3
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• pp.339-361
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• 2012

Large amplitude free vibration and thermal post-buckling of shear flexible Functionally Graded Material (FGM) beams is studied using finite element formulation based on first order Timoshenko beam theory. Classical boundary conditions are considered. The ends are assumed to be axially immovable. The von-Karman type strain-displacement relations are used to account for geometric non-linearity. For all the boundary conditions considered, hardening type of non-linearity is observed. For large amplitude vibration of FGM beams, a comprehensive study has been carried out with various lengths to height ratios, maximum lateral amplitude to radius of gyration ratios, volume fraction exponents and boundary conditions. It is observed that, for FGM beams, the non-linear frequencies are dependent on the sign of the vibration amplitudes. For thermal post-buckling of FGM beams, the effect of shear flexibility on the structural response is discussed in detail for different volume fraction exponents, length to height ratios and boundary conditions. The effect of shear flexibility is observed to be predominant for clamped beam as compared to simply supported beam.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.1057-1063
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• 1994

An instantaneous frequency analysis is a technique to examine a signature for the rotating machinery if the signal has several transitions within a cycle. This paper discusses the conditions of existing negative frequency components in the instantaneous frequency. By using a signal consisted of two frequency components, the instantaneous frequency analysis is conducted while the amplitude ratio between two frequency components has been changed. The analysis shows that, depending on the amplitude ratio, the instantaneous frequencies have averaged, zero-valued, or negative components. It turns out that the negative-valued instantaneous frequencies, which have been regarded as the noise effect, are the consequence of the calculation process for the multisignal components. The criteria of existing the negative values in instantaneous frequencies is given in terms of the relative amplitude ratio and the frequency difference. Especially when the amplitude ratio approaches to 1, the instantaneous frequency fluctuates ${\pm}\infty$ in theory, which implies that instantaneous frequency has unstable region around the amplitude ratio, 1.Also, as the frequency difference between major signal components is increased, the region of existing negative instantaneous becomes broader. In an instantaneous frequency analysis, therefore, a narrow band analysis is suggested, with extreme care if the amplitude ratio approaches to 1. In this paper, a vibration signal monitored from a rotating machinery is also examined as an application example in order to show the existence of negative instantaneous frequencies components.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.1
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• pp.81-88
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• 2016

Recently, high-efficiency machining in the production of high-value products with complex shapes has constantly been required along with the need for hybrid machining. In this study, in addition to wire-cut Electric Discharge Machining (EDM) and vibration, we present the possibility of a hybrid process by carrying out an experiment with aluminum alloy, and the hybrid process determines the nature of the surface. The selected experimental parameters are waveform, amplitude, peak current, and two-dimensional (2D) vibration. The experimental results give the guideline for selecting reasonable machining parameters. The surface roughness was improved about 20% with increases in the amplitude of the vibration.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.1
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• pp.92-99
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• 1997

Nowadays, Electronic Speckle Pattern Interferometry is a well-established measuring technique with a wide range of industrial applications, particularly in the fields of deformation measurement and vibration analysis. Comparing with holographic interferometry, it has some attractive features, which are rapid recording and reconstruction, satisfiable automation etc. The Time-Average ESPI is used to provide vibration mode shape of an object whose vibration amplitude is given as a fringe pattern. Its merit is rapid and simple measurement for vibrating object. However, it is not possible to determine the direction of motions of a point on the object at any given time, because it does not give any information about the phase of vibration. But, Stroboscopic ESPI can measure the amplitude and phase of vibrating surface. In this paper, loudspeakers were tested by these two methods. As a result, we can assume that these techniques will be applied directly in the loudspeaker industry.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1-4
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• 2005

This paper describes work on isolation of vibration related engine by a hydraulic engine mount with controllable area of inertia track. Automotive engine mounts are required to constrain motion of engine shake resulting from low-frequency road input of shock excitation and also to isolate noise and vibration generated by the engine with unbalanced disturbance at the high frequency range. The property of the mount depends on vibration amplitude and excitation frequency, which means that the excitation amplitude is large in low excitation frequency range and small in high frequency range. In this paper, theoretical works with model of the mount to reduce vibrations related engine were conducted. The volumetric stiffness of the mount is greatly changed according to the switching the area of the inertia track. Therefore, when the area of the inertia track is tuned, the transmissibility of the mount is effectively reduced.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.457-462
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• 2006

This paper is concerned with the active vibration control experiment on cylindrical shell equipped with Macro Fiber Composite(MFC) actuators. The MFC actuators were glued to the cylindrical shell in circumferential directions. To verify the theoretical result, vibration test using impact hammer and accelerometer was carried out. It was found from experiments that theoretical result predicts experimental result to some extent. The positive position feedback controllers were designed and applied to the test article. It was observed that the resonant amplitude of the fundamental mode was reduced by 20dB thus achieving active vibration control. The active vibration control of the response subject to non resonant excitation has been of interest. We developed the combination of the positive position feedback controller which can cope with the fundamental mode and the positive position feedback controller which can counteract the external disturbance with non resonant frequency. It was found from experiments that the hybrid controller can suppress the vibration amplitude successfully.

• Journal of the Korean Society for Advanced Composite Structures
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• v.6 no.2
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• pp.97-104
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• 2015

Compared with a strong axial rigidity due to large intial tension, cable has a weak laterally flexural rigidity. A variety of dynamic loads such as traffic loads and wind loads etc. cause the cables to vibrate significantly and affect the mechanical properties and the performance of cables. Therefore, vibration reduction design is an urgent task to control the vibration of cable-supported bridges. Because a various kind of dampers have shown to reduce the amplitude and duration time of vibration of cable from measured date in field test, damper can be considered that it is effective device significantly to reduce the amplitude and duration time in vibration of cable. Vibration characteristics of cable can change according to manufacturing method and type of established form, and damper has been designed according to distribution of natural frequencies and vibration modes. In this study, numerical analysis is used to show the reduction effects of vibrations and present the design of damper for vibration reduction of cable.

• Wind and Structures
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• v.12 no.4
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• pp.333-347
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• 2009

Many tower-supported steel stacks have been constructed in Japan, primarily for economic reasons. However the dynamic behavior of these stacks under a strong wind is not well known and the wind load design standard for this type of a stack has not yet been formulated. In light of this situation, we carried out wind response observation of an operating tower-supported steel stack with and without a tuned-mass damper. The observation revealed the performance of the tuned-mass damper installed on the stack in order to control the wind-induced vibration. Based on the observed data, we performed a wind tunnel test of a specimen of the stack. In this paper we report the results of the wind tunnel test and some comparisons with the results of observation. Our findings are as follows: 1) the tuned-mass damper installed on the specimen in the wind tunnel test worked as well as the one on the observed stack, 2) the amplitude of the vortex-induced vibration of the specimen corresponded approximately to that of the observed stack, and 3) correlation between Scruton number and reduced amplitude, y/d, (y is amplitude, d is diameter) was confirmed by both the wind tunnel test and the observed results.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.32 no.4
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• pp.421-431
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• 1996

From comparing the impact dynamic absorber with the impact damper in the auxiliary vibration system with the conventional dynamic absorber, the following conclusions are obtained as follows ; 1. Recognizing that the amplitude restraining effect of the impact dynamic absorber become resonable in a comparison of conventional one development of an improved dynamic absorber may be probable. 2. With increasing the frequency ratio, the 1st resonance peak is higher but the 2nd one gets lower. In addition, the frequency ratio is peak located at the same resonance. 3. The optimum impact clearance is smaller and the vibration constraining effect becomes better with and increase in the mass of impact ball. And it is recognizable that the optimum tuning frequency ratio and impact clearance in an accordance with the mass ratio are varied. 4. The optimum tuning condition becomes gradually lower than the case of r=1 and maximum amplitude becomes lower with an increment in the mass ratio. However, the impulse clearance is larger and the working range of restraining vibration amplitude become smaller with a decrement in the mass of impact ball.

• Structural Engineering and Mechanics
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• v.90 no.1
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• pp.27-40
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• 2024

The prediction of VIV amplitude is essential for the design and fatigue life estimation of steel tubes in tubular transmission towers. Limited to costly and time-consuming traditional experimental and computational fluid dynamics (CFD) methods, a machine learning (ML)-based method is proposed to efficiently predict the VIV amplitude of steel tubes in transmission towers. Firstly, by introducing the first-order mode shape to the two-dimensional CFD method, a simplified response analysis method (SRAM) is presented to calculate the VIV amplitude of steel tubes in transmission towers, which enables to build a dataset for training ML models. Then, by taking mass ratio M^*, damping ratio ξ, and reduced velocity U^* as the input variables, a Kriging-based prediction method (KPM) is further proposed to estimate the VIV amplitude of steel tubes in transmission towers by combining the SRAM with the Kriging-based ML model. Finally, the feasibility and effectiveness of the proposed methods are demonstrated by using three full-scale steel tubes with C-shaped, Cross-shaped, and Flange-plate joints, respectively. The results show that the SRAM can reasonably calculate the VIV amplitude, in which the relative errors of VIV maximum amplitude in three examples are less than 6%. Meanwhile, the KPM can well predict the VIV amplitude of steel tubes in transmission towers within the studied range of M^*, ξ and U^*. Particularly, the KPM presents an excellent capability in estimating the VIV maximum amplitude by using the reduced damping parameter S_G.