• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1997.04a
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• pp.152-159
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• 1997

An analytical method is developed to study the propagation of surface waves across infilled trenches. The Green's function technique is used to estimate the reflection and transmission coefficients of Rayleigh waves across a semi-infinite plate inserted between two homogeneous quarter-spaces. After validating the method against experimental data, influence of the material contrast and the angle of incidence on the screening effectiveness of an infilled trench is examined.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.10
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• pp.751-759
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• 2003

The theoretical method is developed to investigate the vibration characteristics of the sloshing and bulging mode for the circular cylindrical storage tank with an annular plate on free surface. The cylindrical tank is filled with an inviscid and incompressible liquid. The liquid domain is limited by a rigid cylindrical surface and a rigid flat bottom. As the effect of free surface waves Is taken into account in the analysis, the bulging and sloshing modes are studied. The solution for the velocity potential of liquid movement is assumed as a suitable harmonic function that satisfies Laplace equation and the relevant boundary conditions. The Rayleigh-Ritz method is used to derive the frequency equation of the cylindrical tank. The effect of Inner-to-outer radius ratio and thickness of annular plate and liquid volume on vibration characteristics of storage tank is studied. The finite element analysis is performed to demonstrate the validity of present theoretical method.

• 한국가시화정보학회:학술대회논문집
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• 2002.11a
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• pp.35-38
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• 2002

Variations of temperature and velocity fields in a Hele-Shaw Convection Cell (HSC) were measured using a holographic interferometry and PIV technique with varying Rayleigh number. Experimental results show a steady flow pattern at low Rayleigh numbers and a time-dependent periodic flow at high Rayleigh numbers. Two different measurement methods of holographic interferometry, double-exposure method and real-time method, were employed to measure the temperature field variations of HSC convective flow. In the double-exposure method, unwanted waves can be eliminated and reconstruction images are clear, but transient flow structure cannot be observed clearly. On the other hand, transient flow can be observed and reconstructed well using the real-time method. PIV results show that flow inside the HSC is periodic and the oscillating state is well matched with the temperature field results. The holographic interferometry and PIV techniques employed in this study are useful for analyzing the unsteady convective thermal fluid flows.

• Geophysics and Geophysical Exploration
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• v.21 no.1
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• pp.33-40
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• 2018

We investigate the crustal and uppermost mantle SV- and SH-wave velocity structure and radial anisotropy beneath East Asia including Korea, China and Japan. Rayleigh waves and Love waves were extracted from the seismic data recorded at broadband seismic stations in East Asia. Using the MFT (Multiple Filter Technique), we obtained group velocity dispersion curves of Rayleigh and Love waves with a period range of 3 to 200 s. We obtained 62466 Rayleigh-waves dispersion-curve measurements in vertical components and 54141 Love-waves dispersion-curve measurements in transverse components, respectively. The inverted models using these data sets provide SV- and SH-wave velocity structure of crust and uppermost mantle down to 100 km depth. In both cases of the S-wave velocity structures, strong high-velocity anomalies are observed down to 30 km depth beneath the East Sea, and deeper than 30 km depth, strong low-velocity anomalies are found beneath the Tibetan plateau. In the case of the SH-wave velocity structure, strong low-velocity anomalies are observed beneath the East Sea deeper than 30 km depth, leading to negative anisotropy. On the other hand, positive anisotropy is usually observed beneath the Tibetan plateau.

• 한국연소학회:학술대회논문집
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• 2001.11a
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• pp.125-135
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• 2001

Aiming at a direct, also more realistic, prediction of unstable waves evolving in the combustion chamber, present paper introduces a new analytical method. Instability equations are freshly formulated, and solve the time-integrated ODEs for amplification factors to find the transients of pressure and velocity fluctuations. Present numerical approach requires no separate treatments for nonlinearities. Preliminary numerical experiments for unstable waves in quasi-one-dimensional rocket combustor, show validity and applicability of present model, and promise for its practical use. Study for the complex models for physics, especially velocity- and pressure-coupled responses, and inclusion of multi dimensionality remains as future tasks.

• Journal of the Korean Society for Marine Environment & Energy
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• v.12 no.2
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• pp.61-67
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• 2009

In this paper time series wave data which contain a freak wave is investigated. Various wave characteristics are compared between wave data with a freak wave and without. Among 24 hour wave data measured in the Yura Sea, two adjacent 30 min wave data with and without a freak wave are examined intensively. It is seen that the highest waves do not have the longest wave period. The wave period of the longest period waves is a little longer than the average wave period and much shorter than the significant wave period. Although the sea state is quite high, the Rayleigh distribution fits well to the probability of wave height. The characteristics of the wave spectra do not change much, but the nonlinearity increases for the wave data with a freak wave. The significant wave height without a freak wave is larger than that with a freak wave. Hence, the higher significant wave height does not always increase the probability of the occurrence of the freak waves.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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• pp.493-499
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• 2004

Variations of temperature and velocity fields in a Hele-Shaw convection cell (HSC) were investigated using a holographic interferometry and 2-D PIV system with varying Rayleigh number. To measure quasi-steady variation of temperature field, two different measurement methods of holographic interferometry, double-exposure method and real-time method, were employed. In the double-exposure method, unwanted waves were eliminated effectively using a digital image processing technique. The reconstructed images are clear, but transient flow cannot be reconstructed clearly. On the other hand, transient convective flow can be reconstructed well using the real-time method. However, the fringe patterns reconstructed by the real-time method contain more noises, compared with the double-exposure method. Experimental results show a steady flow pattern at low Rayleigh numbers and a time-dependent periodic flow structure at high Rayleigh numbers. The periodic flow pattern at high Rayleigh numbers obtained by the real-time holographic interferometer method is in a good agreement with the PIV results.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.1
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• pp.47-52
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• 2011

It is well known that stiffness of composites depends on layup sequence of CFRP(carbon fiber reinforced plastics) laminates because the layup of composite laminates influences their properties. Ultrasonic NDE of composite laminates is often based on the backwall echoes of the sample. A pair of such transducers was mounted in a holder in a nose-to-nose fashion to be used as a scanning probe on composites. Miniature potted angle beam transducers were used (Rayleigh waves in steel) on solid laminates of composites. Experiments were performed to understand the behavior of the transducers and the nature of the waves generated in the composite (mode, wave speed, angle of refraction). C-scan images of flaws and impact damage were then produced by combining the pitch-catch probe with a portable manual scanner known as the Generic Scanner ("GenScan"). The pitch-catch signal was found to be more sensitive than normal incidence backwall echo of longitudinal wave to fiber orientation of the CFRP composites, including low level porosity, ply waviness, and cracks. Therefore, it is found that the experimentally Rayleigh wave variation of pitch-catch ultrasonic signal was consistent with numerical results and one-side ultrasonic measurement might be very useful to detect the defects.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.3
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• pp.224-230
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• 2007

This work is aimed to explore a possibility of using the generalized Lamb waves for nondestructive evaluation of the bonding quality of layered substrates. For this purpose, we prepared two sets of specimens with imperfect bonding at their interfaces; 1) TiN-coated specimens with various wear conditions, and 2) CVD diamond specimens with various cleaning conditions. A dispersion simulation performed for layered substrates with imperfect interfaces are carried out to get the characteristics of dispersion curves that can be used for bonding quality evaluation. Then the characteristics of dispersion curves of the fabricated specimens are experimentally determined by use of an ultrasonic backward radiation measurement technique. The results obtained in the present study show that the lowest velocity mode (Rayleigh-like) of the generalized Lamb waves are sensitively affected by the bonding quality. Therefore, the generalized Lamb waves can be applied for nondestructive evaluation of imperfect bonding quality in various layered substrates.

• Journal of the Korean Institute of Navigation
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• v.11 no.1
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• pp.67-91
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• 1987

In this paper, a synthetic method for evaluating the seakeeping performance of a ship in waves is studied. For the prediction and evaluation of irregular phenomena to be correlated each other, the multi-dimensional Rayleigh's joint probability density function and the cumulative distribution function are approximated. According to this approximated function, it is able to calculate easily the occurrence probability of the factors on seakeeping performance. We proposed an evaluation method and an index to be defined by the seakeeping performance reliability, that is considered as the dangerousness and the relative dangerousness of the factors on seakeeping performance in waves. The use of this method aid index will be effective to install the sensors which are necessary to evaluate the states of ships at sea. Some example of the calculations by this method for 175m length single screw container ship equipped with diesel engine are also presented.