• Proceedings of the KSME Conference
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• 2002.08a
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• pp.655-658
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• 2002

The present paper investigated the effect of ultrasonic vibrations on the melting process of a phase-change material (PCM). Furthermore, the present study considered constant heat-flux boundary conditions unlike many of the previous researches, which had adopted constant wall-temperature conditions. Therefore in the study, modified dimensionless numbers such as Stefan and Rayleigh were adopted to represent heat transfer results. The experimental results revealed that ultrasonic vibrations accompanied the effects like agitation, acoustic streaming, cavitation, and oscillating fluid motion, accelerating the melting process as much as 2.5 times, compared with the result of natural melting (i. e., the case without ultrasonic vibration). Such effects are believed to be a prime mechanism in the overall melting process when ultrasonic vibrations were applied. Subsequently, energy could be saved by applying the ultrasonic vibrations to the natural melting In addition, various time-wise dimensionless numbers provided a conclusive evidence of the important role of the ultrasonic vibrations on the melting phenomena of the PCM.

• Wind and Structures
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• v.4 no.2
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• pp.85-100
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• 2001

The mechanism of wind-induced ovalling vibrations of cylindrical shells is numerically investigated by using a vortex method. The subject of this paper is limited to a two-dimensional structure in the subcritical regime. The aerodynamic stability of the ovalling vibrations in the second to fourth circumferential modes is discussed, based on the results of a forced-vibration test. In the analysis, two modal configurations are considered; one is symmetric and the other is anti-symmetric with respect to a diameter parallel to the flow direction. The unsteady pressures acting on a vibrating cylinder are simulated and the work done by them for one cycle of a harmonic motion is computed. The effects of a splitter plate on the flow around the cylinder as well as on the aerodynamic stability of the ovalling vibrations are also discussed. The consideration on the mechanism of ovalling vibrations is verified by the results of a free-vibration test.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.4
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• pp.325-332
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• 2011

This paper is concerned with the active control experiments on elevator vibrations by means of the active roller guide. To this end, a roller guide was designed using a voice-coil actuator and linear guide. A simple proportional control algorithm combined with the band-pass filter was implemented using the DSP. Based on the initial experiments, a new control system which can handle lateral and front-back vibrations of elevator was built and tested using the elevator test tower. The experimental results show that the elevator vibrations are reduced by the active control technique.

• Structural Engineering and Mechanics
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• v.12 no.3
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• pp.267-281
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• 2001

Transient and quasi-steady-state vertical vibrations of a multi-span beam steel bridge located on a single-track railway line are considered, induced by a superfast passenger train, moving at speed 120-360 km/h. Matrix dynamic equations of motion of a simplified model of the system are formulated partly in the implicit form. A recurrent-iterative algorithm for solving these equations is presented. Excessive vibrations of the system in the resonant zones are reduced effectively with passive dynamic absorbers, tuned to the first mode of a single bridge span. The dynamic analysis has been performed for a series of types of bridges with span lengths of 10 to 30 m, and with parameters closed to multi-span beam railway bridges erected in the second half of the $20^{th}$ century.

• Wind and Structures
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• v.17 no.1
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• pp.21-41
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• 2013

Wind-induced vibrations of mast arms of cantilever traffic signal structures can lead to fatigue failure. Two such structures were instrumented each with a sonic anemometer and a camera that records the motions of the tip of the arm. It was observed throughout this experiment that large amplitude vertical vibrations of mast arms with signals with backplates occur for the most part at low wind speed ranges, between 2 to 7 m/s, and as the wind speed increases the amplitude of the vertical vibrations decreases. The results of these experiments contradict the generally accepted belief that vortex shedding does not cause significant vibrations of mast arms that could lead to fatigue failure, which have been attributed to galloping in the past. Two damping devices were tested with mixed results.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.6
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• pp.109-116
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• 2013

Vibrations are generally recognized as the biggest concern in maintaining part' longevity of an All-in-one PC. The vibrations in PCs originate from excitation sources such as the HDD and the cooling fan. In this study, the vibrations from these sources were investigated in order to analyze the individual effects of the parameters on the structural vibrations of the PC; further, we attempted to establish design alterations that could successfully suppress vibrations, in order to achieve improved stability and part' longevity. The results show that relatively simple design alterations can substantially improve the stability of PCs.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.300-306
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• 2004

This paper is concerned with the application of perturbation method to the dynamic analysis of free-free beam. In general, the rigid-body motions and elastic vibrations are analyzed separately. However, the rigid-body motions cause vibrations and elastic vibrations also affect rigid-body motions in turn, which indicates that the rigid-body motions and elastic vibrations are coupled in nature. The resulting equations of motion are hybrid and nonlinear. We can discretize the equations of motion by means of admissible functions but still we have to cope with nonlinear equations. In this paper, we propose the use of .perturbation method to the coupled equations of motion. The resulting equations consist of zero-order equations of motion which depict the rigid-body motions and first-order equations of motion which depict the perturbed rigid-body motions and elastic vibrations. Numerical results show the efficacy of the proposed method.

• Journal of the Korean Society of Industry Convergence
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• v.13 no.2
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• pp.63-68
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• 2010

Structural vibrations are among the biggest concerns in developing high resolution DVR(Digital Video Recorder) monitors. The vibrations in DVR monitors are mostly originated from the excitation sources such as the HDD and the cooling fan. In this study, the vibrations generated from the excitation sources were investigated in order to analyze the individual effect on the structural vibrations of the monitors and further to establish the design alteration to suppress the vibrations for the stability of the structure and for the better quality of the screen. The result shows that relatively simple design alterations can improve the stability of the structure substantially.

• Structural Engineering and Mechanics
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• v.85 no.1
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• pp.81-88
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• 2023

This paper begins by analyzing cable vibrations due to external excitations and their effects on the overall dynamic behavior of cable-stayed bridges. It is concluded that if the natural frequency of a cable approaches any natural frequency of the bridge, the cable loses its rigidity and functionality. The results of this analysis explain the phenomenon that occurred on the Dubrovnik Bridge in Croatia during a storm and measures for its retrofit. A field test was conducted before the bridge was opened to traffic. It was concluded: "The Bridge excited unpleasant transverse superstructure vibration with the frequency of approximately 0.470 Hz. Hence, it seems possible that a pair of stays vibrating in phase may excite deck vibrations". Soon after this Bridge opened, a storm dumped heavy damp snow in the area, causing the six longest cable stay pairs of the main span to undergo large-amplitude vibrations, and the superstructure underwent considerable displacements in combined torsion-sway and bending modes. This necessitated rehabilitation measures for the Bridge including devices to suppress the large-amplitude vibrations of cables. The rehabilitation and monitoring of the Bridge are also presented here.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.324-329
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• 2010

Vibrations caused by automobile engine are absorbed mostly by a passive-type engine mount. However, user specifications for automobile vibrations require more stringent conditions and higher standard. Hence, active-type engine mount have been developed to cope with such specifications. The active-type engine mount consists of sensor, actuator and controller where a control algorithm is implemented. The performance of the active engine mount depends on the control algorithm if the sensor and actuator satisfies the specification. The control algorithm should be able to suppress persistent vibrations caused by the engine which are related to engine revolution. In this study, three control algorithms are considered for suppressing persistent vibrations, which are the positive position feedback control algorithm, the strain-rate feedback control algorithm, and the modified higher harmonic control algorithm. Experimental results show that all the control algorithms considered in this study are effective in suppressing resonant vibrations but the modified higher harmonic controller is the most effective controller for non-resonant vibrations.