• 대한기계학회논문집
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• 제17권12호
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• pp.3028-3044
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• 1993

A metallic bond of great strength for the same or dissimilar metals can be produced by the explosive welding. The formation of a metallic jet at the interface between the two impacting plates has been simulated using the numerical hydrocode DYNA2D. The mechanism of explosive welding for the wave formation is also analyzed by the computer simulation technique. The microscopic with the experimentally observed behaviour of the explosive welding. The computer simulations of the explosive welding process have proven especially useful for analyzing the mechanism of metallic bones.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.647-650
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• 2002

A thermoacoustic refrigerator, using a resonant standing acoustic wave, has been built. It employs a loudspeaker to sustain a standing wave in a resonance tube. The stack of plates is 0.075mm-thick plastic sheet(Mylar), spirally wound to make a 40mm-diameter assembly 80mm long. and two heat exchanger are installed. The refrigerant is Helium gas. The description of thermoacoustic refrigerator are presented. The directly measured performance of the resonator. Tc/Th ( temperature ratio ) and $COP/COP_{c}$, (normalized by carnot's COP ) are plotted versus the thermal load Q applied to the cold end, for various speaker power.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2005년도 학술발표회 논문집
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• pp.331-342
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• 2005

This paper presents a non-destructive evaluation (NDE) technique for detecting damages on a jointed steel plate on the basis of the time of flight and wavelet coefficient, obtained from wavelet transforms of Lamb wave signals. Support vector machines (SVMs), which is a tool for pattern classification problems, was applied to the damage estimation. Two kinds of damages were artificially introduced by loosening bolts located in the path of the Lamb waves and those out of the path. The damage cases were used for the establishment of the optimal decision boundaries which divide each damage class's region from the intact class. In this study, the applicability of the SVMs was investigated for the damages in and out of the Lamb wave path. It has been found that the present methods are very efficient in detecting the damages simulated by loose bolts on the jointed steel plate.

• Journal of Information Display
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• 제10권2호
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• pp.72-75
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• 2009

The Brillouin spectrum of 4'-n-pentyl-4-cyano-biphenyl (5CB) liquid crystals homogeneously confined in a planar liquid crystal (LC) cell was measured using a 6-pass tandem Fabry-Perot interferometer. By adopting a special right-angle scattering geometry, the sound velocity of 5CB was estimated from the Brillouin shift without knowing the refractive index. The sound velocity of the longitudinal wave propagating along the direction of the directors aligned parallel to the glass plates of the LC cell was 1784${\pm}$7 m/s at 300 K. The attenuation coefficient $\alpha$ was estimated to be approximately $1.9{\times}10^6m^{-1}$, which is about twice as large as that of the longitudinal sound wave propagating along the direction perpendicular to the directors. The present method may be very useful in the evaluation of the elastic properties of the materials used in display devices, whose refractive indices are not known.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권2호
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• pp.828-834
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• 2019

Researchers have previously proven that the flapping motion of the hydrofoil can convert wave energy into propulsive energy. However, the estimation of thrust forces generated by the flapping foil placed in waves remains a challenging task for ocean engineers owing to the complex dynamics and uncertainties involved. In this study, the flapping foil system consists of a rigid NACA0015 section undergoing harmonic flapping motion and a passively actuated elastic flat plate attached to the leading edge of the rigid foil. We have experimentally measured the thrust force generated due to the flapping motion of a rigid foil attached to an elastic plate in a wave flume, and the effects of the elastic plates have been discussed in detail. Furthermore, an empirical formula was introduced to predict the thrust force of a flapping foil based on our experimental results using multiple regression analysis.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2009년도 춘계학술대회 논문집
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• pp.606-611
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• 2009

MiStrut is a new method to establish structural stability in designing braced excavations by making a rigid connection between top-level steel beams and soldier beams. MiStrut has a function of working as a strut as well as supporting cover plates of top-level steel beams. The structural mechanism of MiStrut is supposed to reduce flexural deformation of soldier beams, which may lead to reduced lateral earth pressures behind excavation. In this research, for verification of the performance of MiStrut, shear-wave velocities of subsurface soil before and after excavation was compared. The rigid connection of main girder beams with soldir beams reduced shear-wave velocity by 67% and lateral earth pressures by 90%, which indicates that MiStrut is effective development in reducing lateral earth pressures on braced excavation.

• Smart Structures and Systems
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• 제1권2호
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• pp.121-140
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• 2005

This paper presents a systematic investigation of the effect of sensor location on the data quality and subsequently, on the effectiveness of machine health monitoring. Based on an analysis of the signal propagation process from the defect location to the sensor, numerical simulations using finite element modeling were conducted on a bearing test bed to determine the signal strength at several representative sensor locations. The results showed that placing sensors closely to the machine component being monitored is critical to achieving high signal-to-noise ratio, thus improving the data quality. Using millimeter-sized piezoceramic plates, the obtained results were evaluated experimentally. A comparison with a set of commercial vibration sensors verified the developed structural dynamics-based sensor placement strategy. It further demonstrated that the proposed shock wave-based sensing technique provided an effective alternative to vibration measurement, while requiring less space for sensor installation.

• 대한기계학회논문집B
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• 제28권11호
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• pp.1440-1448
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• 2004

Multiple solutions in natural convection of air (Pr=0.7) between two horizontal walls with mean temperature difference and the same periodic nob-uniformities are investigated. An analytical solution is found for small Rayleigh number, and the general solution is investigated by using a numerical method. In the conduction-dominated regime, two upright cells are formed between two walls over one wave length. When the wave number is small, the flow becomes unstable with increase of the Rayleigh number, and multicellular convection occurs above a critical Rayleigh number. The multicellular flows at high Rayleigh numbers consist of approximately square-shape cells. And several kinds of multiple flows classified by the number of cells are found.

• 한국공작기계학회논문집
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• 제10권6호
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• pp.95-101
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• 2001

This work is concerned with construction of the intelligence stress predictor far compression strength evaluation using neural network-ultrasonic waves. The contact pressure in jointed plates was measured by using ultrasonic technique. Neural network is used to evaluate and predict contact pressure from the results of the calibration curves. The organized neural system was leaned with the accuracy of 99%, as a result of learning the ultrasonic echo ratio to the contact pressure measurement between SM45C and STS410 materials. And it could be evaluated and predicted with the accuracy of 90% in the evaluation of ultrasonic echo ratio difference in the same surface roughness and contact pressure, and 85% in the prediction of virtual ultrasonic echo ratio. Thus the proposed stress predictor is very useful for the evaluation and prediction of the contact pressure between SM45C and STS410 materials.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.240-243
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• 2005

A design procedure using spatial Fourier transform is presented for a structural-acoustic coupled radiator that can emit sound in the desired direction with high power and low side lobe level. The design procedure consists of three steps. Firstly, the structural-acoustic coupled radiator is chosen to obtain strong coupling between structural vibration and acoustic pressure. The radiator is composed by two spaces which are separated by a wall. Spaces can be categorized as reverberant finite space and unbounded semi-infinite space, and the wall are composed of two plates and an opening. The velocities on the wall are predicted. Secondly, directivity and energy distribution of radiator are predicted in wave number domain using spatial Fourier transform. Finally, optimal design variables are calculated using a dual optimal algorithm. Its computational example is presented including the directivity and resulting pressure distribution using proposed procedure.