• Structural Engineering and Mechanics
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• v.58 no.1
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• pp.181-197
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• 2016

In this paper, we investigated the propagation of surface waves in a nonhomogeneous rotating fibre-reinforced viscoelastic anisotropic media of higher order of nth order including time rate of strain. The general surface wave speed is derived to study the effect of rotation on surface waves. Particular cases for Stoneley, Love and Rayleigh waves are discussed. The results obtained in this investigation are more general in the sense that some earlier published results are obtained from our result as special cases. Also results for homogeneous media can be deduced from this investigation. For order zero our results are well agreed to fibre-reinforced materials. Also by neglecting the reinforced elastic parameters, the results reduce to well known isotropic medium. It is also observed that, surface waves cannot propagate in a fast rotating medium. Comparison was made with the results obtained in the presence and absence of rotation and parameters for fibre-reinforced of the material medium Numerical results are given and illustrated graphically. The results indicate that the effect of rotation and parameters for fibre-reinforced of the material are very pronounced.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1987.06a
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• pp.50-56
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• 1987

A mechanical face seal is most commonly used to seal liquids and gases at various speeds, pressures and temperatures. The primary seal ring is in sliding contact with the seal seat and as a result heat in the vicinity of the interface is generated. Local temperatures at points along the circumferential direction will fluctuate as asperities on the surfaces pass. This kind of fluctuation of temperature has been investigated to take place. This may lead to the hot spots phenomenon between the contacting asperities. Sibley and Allen showed photographic evidence of systemically moving hot spots in the contact zone. The appearance of such a temperature disturbance has been attributed to a kind of thermoelastic instabilities between two surfaces: This involves a feedback loop which comprises localized elevation of frictional heating, resultant localized thermal bulding, localized pressure increase as the result of the bulging and futher elevation of frictional heating as the result of the pressure increase. The heating of hot spots will be continued until the expanded material due to the frictional heating is worn off. Therefore to predict the speed of temperature propagation into the body is essential to the analysis of heat transfer on the edge of the seal.

• Journal of Mechanical Science and Technology
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• v.14 no.7
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• pp.752-763
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• 2000

The stress field around the dynamically propagating interface crack tip under a remote mixed mode loading condition has been studied with the aid of dynamic photoelastic method. The variation of stress field around the dynamic interface crack tip is photographed by using the Cranz-Shardin type camera having $10^6$ fps rate. The dynamically propagating crack velocities and the shapes of isochromatic fringe loops are characterized for varying mixed load conditions in double cantilever beam (DCB) specimens. The dynamic interface crack tip complex stress intensity factors, $K_1\;and\;K_2$, determined by a hybrid-experimental method are found to increase as the load mixture ratio of y/x (vertical/horizontal) values. Furthermore, it is found that the dynamically propagating interface crack velocities are highly dependent upon the varying mixed mode loading conditions and that the velocities are significantly small compared to those under the mode I impact loading conditions obtained by Shukla (Singh & Shukla, 1996a, b) and Rosakis (Rosakis et al., 1998) in the USA.

• Laser Solutions
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• v.8 no.1
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• pp.9-18
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• 2005

The laser direct writing method using a UV Argon-ion laser is studied for fabrication of waveguide. The laser direct writing system is constructed with a vision camera, a xy-stage, a motion controller and the delivery components of a laser beam. The UV Argon-ion laser has wavelength range of $333.6\~363.8$ nm. A photo-active UV curable polymer for a planar light-wave circuit(PLC) of single mode is used. This polymer is irradiated by Argon-ion laser and developed by a solvent after a post-baking. The optimum laser direct writing condition is obtained experimentally by changing various process parameters such as laser power, writing speed and focal length. The propagation and coupling loss of a optical waveguide was measured as 1dB/cm and 0.6dB/cm, respectively. Also, the minimum width of waveguide of $100{\mu}m$(ZPLW-207) is obtained. Finally, the waveguides of line, bend and branch type are successfully fabricated.

• Proceedings of the Korean Geotechical Society Conference
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• 1995.10a
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• pp.15.2-22
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• 1995

Evaluating stiffness of near-surface materials has been one of the critically important tasks in many civil engineering works. It is the main goal of geotechnical characterization. The so-called deflection-response method evaluates the stiffness by measuring stress-strain behavior of the materials caused by static or dynamic load. This method, however, evaluates the overall stiffness and the stiffness variation with depth cannot be obtained. Furthermore, evaluation of a large-area geotechnical site by this method can be time-consuming, expensive, and damaging to many surface points of the site. Wave-propagation method, on the other hand, measures seismic velocities at different depths and stiffness profile (stiffness change with depth) can be obtained from the measured velocity data. The stiffness profile is often expressed by shear-wave (S-wave) velocity change with depth because S-wave velocity is proportional to the shear modulus. that is a direct indicator of stiffiiess. The crosshole and downhole method measures the seismic velocity by placing sources and receivers (geophones) at different depths in a borehole. Requirement of borehole installation makes this method also time-consuming, expensive, and damaging to the sites. Spectral-Analysis-of-Surface-Waves (SASW) method places both source and receivers at the surface, and records horizontally-propagating surface waves. Based upon the theory of surfacewave dispersion, the seismic velocities at different depths are calculated by analyzing the recorded surface-wave data. This method can be nondestructive to the sites. However, because only two receivers are used, the method requires multiple measurements with different field setups and, therefore, the method often becomes time-consuming and labor-intensive. Furthermore. the inclusion of noise wavefields cannot be handled properly, and this may cause the results by this method inaccurate. When multi-channel recording method is employed during the measurement of surface-waves, there are several benefits. First, usually single measurement is enough because multiple number (twelve or more) of receivers are used. Second, noise inclusion can be detected by coherency checking on the multi-channel data and handled properly so that it does not decrease the accuracy of the result. Third, various kinds of multi-channel processing techniques can be applied to f1lter unwanted noise wavefields and also to analyze the surface-wavefields more accurately and efficiently. In this way, the accuracy of the result by the method can be significantly improved. Fourth, the entire system of source, receivers, and recording-processing device can be tied into one unit, and the unit can be pulled by a small vehicle, making the survey speed very fast. In all these senses, multi-channel recording of surface waves is best suited for a routine method for geotechnical characterization in most of civil engineering works.

• Journal of Mechanical Science and Technology
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• v.17 no.10
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• pp.1423-1430
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• 2003

In this paper, we develop a real time monitoring system to detect third-party damage on natural gas pipeline. When the damage due to third-party incidents causes an immediate rupture, the developed on-line monitoring system can help reducing the sequences of event at once. Moreover, since many third-party incidents cause damage that does not lead to immediate rupture but can grow with time, the developed on-line monitoring system can execute a significant role in reducing many third-party damage incidents. Also, when the damage is given at a point on natural gas pipeline, the acoustic wave is propagated very fast about 421.3 m/s. Therefore, the data processing time should be very short in order to detect precisely the impact position. Generally, the pipeline is laid under ground or sea and the length is very long. So a wireless data communication method is recommendable and the sensing positions are limited by laid circumstance and setting cost of sensors. The calculation and monitoring software is developed by an algorithm using the propagation speed of acoustic wave and data base system based on wireless communication and DSP systems. The developed monitoring system is examined by field testing at Balan pilot plant, KOGAS being done in order to demonstrate its validity through reactive detection of third-party contact with pipelines. Furthermore, the development system was set at the practical pipelines such as an offshore pipeline between two islands Yul-Do and Youngjong-Do, and a land branch of Pyoungtaek, Korea and it has been operating in real time.

• Journal of Energy Engineering
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• v.8 no.4
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• pp.540-545
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• 1999

The classical Fourier heat conduction equation is invalid at temperatures near absolute zero or at very early times in highly transient heat transfer processes. In such situations, a hyperbolic equation model for heat conduction based on the modified Fourier law is introduced because the wave nature of heat propagation becomes dominant. The Fourier model and the hyperbolic model for heat conduction are analyzed by using the Green's function technique together with the integral transform. Analytical expressions for the heat flux and temperature distributions in a finite slab subjected to a periodic surface heating at one of its surfaces are presented and the results obtained from each model are compared with each other. The thermal wave implied b the hyperbolic model is shown to travel through a medium and to reflect back toward the origin at the other insulated surface. On the other hand, the heat by the Fourier model propagates at an infinite speed instantaneously after a thermal disturbance is felt throughout the medium.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.3
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• pp.227-236
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• 2003

Leaks in underground pipelines can cause social, environmental and economical problems. One of relevant countermeasures against leaks is to find and repair of leak points of the pipes. Leak noise is a good source to identify the location of leak points of the pipelines. Although there have been several methods to detect the leak location with leak noise, such as listening rods, hydrophones or ground microphones, they have not been so efficient tools. In this paper, acoustic emission (AE) sensors and accelermeters are used to detect leak locations which could provide all easier and move efficient method. Filtering, signal processing and algorithm of raw input data from sensors for the detection of leak location are described. A 120m-long pipeline system for experiment is installed and the results with the system show that the algorithm with the AE sensors and accelerometers offers accurate pinpointing of leaks. Theoretical analysis of sound wave propagation speed of water in underground pipes, which is critically important in leak locating, is also described.

• Journal of computational fluids engineering
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• v.17 no.4
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• pp.49-55
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• 2012

Research has importance in proposing the design of a tunnel with a vertical vent to secure passengers in a comfortable environment and safe against pressure. Using several analysis methods, the magnitude of the pressure induced by the vertical vent in the tunnel can be analyzed. In addition to the 3-dimensional method, the 2-dimensional method and the 2-dimensional axis-symmetric method are also used to analyze the strong and weak points of each so that the optimum analysis method can be obtained. As a result, it appears that the 2-dimensional axis-symmetric method is the most suitable in analyzing tunnel pressure consider to accuracy and time effective aspect. Also, the 3-dimensional method is disadvantageous in that it takes longer in calculating results, but is more effective in predicting phenomena around the vertical vent in the tunnel.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.53.2-53.2
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• 2019

$H{\alpha}$ surges (i.e. cool/dense collimated plasma ejections) may act as a guide for a propagation of magnetohydrodynamic waves. We report a high-resolution observation of a surge observed with 1.6m Goody Solar Telescope (GST) on 2009 August 26, from 18:20~UT to 18:45UT. Characteristics of plasma motions in the surge are determined with the normalizing radial gradient filter and the Fourier motion filter. The shape of the surge is found to change from a 'C' shape to an inverse 'C' shape after a formation of a cusp, a signature of reconnection. There are apparent upflows seen above the cusp top and downflows below it. The upflows show rising and rotational motions in the right-hand direction, with the rotational speed decreasing with height. Near the cusp top, we find a transverse oscillation of the surge, with the period of ~2 min. There is no change of the oscillation phase below the cusp top, but above the top a phase change is identified, giving a vertical phase speed about 86kms-1. As the height increases, the initial amplitude of the oscillation increases, and the oscillation damping time decreases from 5.13 to 1.18min. We conclude that the oscillation is a propagating kink wave that is possibly excited by an x-point oscillation.