• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.923-928
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• 2012

In this paper, static and oscillatory instability of a nanotube conveying fluid and modelled as a thin-walled beam is investigated. Analytically nonlocal effect, effects of boundary conditions, transverse shear and rotary inertia are incorporated in this study. The governing equations and the two different boundary conditions are derived through Hamilton's principle. Numerical analysis is performed by using extend Galerkin method which enables us to obtain more exact solutions compared with conventional Galerkin method. Variations of critical flow velocity for different boundary conditions of a nanotube with analytically nonlocal effect, partially nonlocal effect and local effect of a nanotube are investigated and pertinent conclusion is outlined.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.373-378
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• 2007

On the homodyne interferometers, high pass filter(HPF) is usually used to remove the electrical noise in the interferent signal. Heterodyne interferometer has modulating frequency is shifted in the frequency region where the electrical noise effect is minimized by HPF effect. However, on the homodyne interferometer, the interferent DC-component of homodyne interferometer is unfortunately eliminated by using a HPF because its shifted frequency does not exist. Moreover, this effect is more serious the vibration amplitude is smaller. So, when unstable interferent signals via HPF are demodulated, a velocity is distorted. In this work, the mathematical explanation for the distortion of the homodyne interferent signal using the HPF is given. New synthetic heterodyne LDV based on the homodyne interferometer by exciting the reference mirror is proposed for the cancellation of the distortion. The optimum excitation condition of the mirror to compensate the distortion is discussed. The numerical simulation using the commercial MATLAB code is provided to show the effect of the proposed synthetic heterodyne LDV. The experimental results are also given and the effect of the proposed LDV is discussed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.2
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• pp.217-224
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• 2016

In this study, a transfer matrix method (TMM) for a twisted uniform beam considering the effect of rotary inertia is developed, and the differential equation and the displacements and forces are derived from Hamilton's principle. The particular transfer matrix is derived by applying the distributed mass and transcendental function while using a local coordinate system. In addition, the results obtained from this method are independent for a number of subdivided elements, and this method can determine the exact solutions for the free vibration characteristics of a twisted uniform Rayleigh beam. To validate the accuracy of the proposed TMM, the computed results are compared with those reported in the existing literature, and the comparison results indicate notably good agreement. In addition, the method is used to investigate the effects of rotary inertia for a twisted beam.

• Tunnel and Underground Space
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• v.13 no.4
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• pp.316-320
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• 2003

This study is to evaluate an irregular drill-hole depth having an effect on the blast vibration. The relationship between a peak particle velocity and a cube root scaled distance with respect to three drill-hole depths with 2.1m, 2.3m and 2.4m are compared and analyzed using a numerical regression analysis. According to the results, the deeper a drill-hole depth is the larger a peak particle velocity is. It is suggested that a drill-hole depth is proportional to a peak particle velocity at the same scaled distance. Therefore, a regular drill-hole should be carried out in order that the blast vibration velocity of a fixed range under a allowable vibration velocity is maintained.

• Tunnel and Underground Space
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• v.16 no.4 s.63
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• pp.326-333
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• 2006

In this study, the vibration waveform of the single hole which is not interfered from the different blasting holes is separated, the each dominant frequency which is determinated through the Fast Fourier Transform(FFT) is measured. Also the separation waveform executed a superposition modeling which changes to delay time from 1ms to 80 ms in 1ms interval and controls the number of blasting holes from 2 holes to 15 holes in order to investigate the effect of PPV according to the duration time of the vibration and the number of blasting holes. As a result of analysis, the longer the duration time of the vibration, the longer the delay time which is not interfered from the different blasting holes and the effect regarding the number of blasting holes from inside identical delay time did not appear a lot.

• Tribology and Lubricants
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• v.34 no.4
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• pp.132-137
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• 2018

Ultrasonic waves are used in various applications in multiple devices, sensors, and high-power machinery, such as processing machines, welders, and cleaners, because the acoustic vibration frequencies are above the human audible frequency range. In ultrasonic machining, electrical energy at a high frequency of 20 kHz or more is converted into mechanical vibration by a vibrator and an amplifier. This technique allows instantaneous separation between a tool and a workpiece during machining, machining by pulse impulse force at the time of re-contact and minimizes the minute elastic deformations of the workpiece and machine tools due to the cutting effect. The Al7075 alloy used in this study is a typical aluminum alloy with superior strength that is mainly used in aircrafts, automobiles, and sporting goods. To investigate the optimal conditions for machining aluminum alloy using ultrasonic vibration, the present experiment utilized the Taguchi orthogonal array method, and the coefficient of friction was analyzed using the characteristics of the Taguchi technique. In ultrasonic friction and abrasion tests, the changes in the friction coefficient were measured in the absence of ultrasonic vibrations and at 28 kHz and 40 kHz. As a result, the most considerable influence on the friction coefficient was found to be the normal load, and the frequency of ultrasonic vibrations increases, the coefficient of friction increases. It was thus confirmed that the amount of wear increases when ultrasonic vibration is applied.

• Earthquakes and Structures
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• v.12 no.6
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• pp.629-641
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• 2017

Foundation plays a significant role in safe and efficient turbo machinery operation. Turbo machineries generate harmonic load on the foundation due to their high speed rotating motion which causes vibration in the machinery, foundation and soil beneath the foundation. The problems caused by vibration get multiplied if the soil is poor. An improperly designed machine foundation increases the vibration and reduces machinery health leading to frequent maintenance. Hence it is very important to study the soil structure interaction and effect of machine vibration on the foundation during turbo machinery operation in the design stage itself. The present work studies the effect of harmonic load due to machine operation along with earthquake loading on the frame foundation for poor soil conditions. Various alternative foundations like rafts, barrette, batter pile and combinations of barrettes with batter pile are analyzed to study the improvements in the vibration patterns. Detailed computational analysis was carried out in SAP 2000 software; the numerical model was analyzed and compared with the shaking table experiment results. The numerical results are found to be closely matching with the experimental data which confirms the accuracy of the numerical model predictions. Both shake table and SAP 2000 results reveal that combination of barrette and batter piles with raft are best suitable for poor soil conditions because it reduces the displacement at top deck, bending moment and horizontal displacement of pile and thereby making the foundation more stable under seismic loading.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.267-278
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• 2010

To improve the grout penetration characteristics, vibration method was adopted in this study. The grout material perturbed by cyclic vibration is injected into the ground. By applying the vibrating flow system, cement particles will become less adhesive and the clogging tendency will be decreased. A series of pilot-scale chamber tests were performed to verify the enhancement of the groutability by applying the vibratory grout injection; assessment on change of the lumped parameter $\theta$ which represents a barometer of clogging phenomenon was made. Moreover, the effect of vibratory grout injection through the joint was also investigated using artificially made rock joints. Experimental results as well as analytical results show that the grout penetration depth can be substantially improved by vibration grouting. Moreover, it was found that enhancement of the permeation grouting due to vibratory injection is more dominant at low grouting pressure of less than 400kPa.

• Interaction and multiscale mechanics
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• v.2 no.3
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• pp.223-233
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• 2009

This paper presents a new nonlocal stress variational principle approach for the transverse free vibration of an Euler-Bernoulli cantilever nanobeam with an initial axial tension at its free end. The effects of a nanoscale at molecular level unavailable in classical mechanics are investigated and discussed. A sixth-order partial differential governing equation for transverse free vibration is derived via variational principle with nonlocal elastic stress field theory. Analytical solutions for natural frequencies and transverse vibration modes are determined by applying a numerical analysis. Examples conclude that nonlocal stress effect tends to significantly increase stiffness and natural frequencies of a nanobeam. The relationship between natural frequency and nanoscale is also presented and its significance on stiffness enhancement with respect to the classical elasticity theory is discussed in detail. The effect of an initial axial tension, which also tends to enhance the nanobeam stiffness, is also concluded. The model and approach show potential extension to studies in carbon nanotube and the new result is useful for future comparison.

• Smart Structures and Systems
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• v.19 no.3
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• pp.243-257
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• 2017

In this paper, free vibration of functionally graded (FG) size-dependent nanobeams is studied within the framework of nonlocal Timoshenko beam model. It is assumed that material properties of the FG nanobeam, vary continuously through the thickness according to a power-law form. The small scale effect is taken into consideration based on nonlocal elasticity theory of Eringen. The non-classical governing differential equations of motion are derived through Hamilton's principle and they are solved utilizing both Navier-based analytical method and an efficient and semi-analytical technique called differential transformation method (DTM). Various types of boundary conditions such as simply-supported, clamped-clamped, clamped-simply and clamped-free are assumed for edge supports. The good agreement between the presented DTM and analytical results of this article and those available in the literature validated the presented approach. It is demonstrated that the DTM has high precision and computational efficiency in the vibration analysis of FG nanobeams. The obtained results show the significance of the material graduation, nonlocal effect, slenderness ratio and boundary conditions on the vibration characteristics of FG nanobeams.