• Journal of Ocean Engineering and Technology
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• v.16 no.4
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• pp.7-12
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• 2002

This study is aimed to find the scouring mechanism at the toe of rubble mound structures. To investigate the characteristics of scouring in front of the structure, experiments were performed with regular waves in a 2-D flume. The results of this study are as follows. 1) It can be said the characteristics of incident wave causes rolling and sliding of armour block. The difference of wave pressure on the slope, internal flow as well as settlement of armour block due to the weight cause scouring. 2) It is observed that scouring depth at the toe increased when wave height or period increased. The location of ultimate scouring and deposition depth moved seaward when wave period increased. 3) The failure of rubble mound structure was caused by waves or scouring. Failure by erosion increased with high waves and long waves. 4) Using surf-similarity parameter including characteristics of incident waves and structure, scouring and deposition pattern were found and their limit was formulated.

• Interaction and multiscale mechanics
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• v.6 no.1
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• pp.1-14
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• 2013

The aim of this paper is to study the propagation of torsional surface waves in non-homogeneous isotropic layer of finite thickness placed over a homogeneous viscoelastic half-space, when both density and rigidity of the non-homogeneous medium are assumed to vary exponentially with depth. The frequency equations are obtained by using simple method of separation of variables. Further, it is seen that when viscoelastic parameter and non-homogeneity parameter is neglected, the dispersion equation gives the dispersion equations of Love waves in homogeneous, elastic and isotropic layer placed over homogeneous viscoelastic medium. The problem has been solved numerically and the effects of various inhomogeneities of the medium on torsional waves have been illustrated graphically.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.231-234
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• 2008

This paper is concerned with the analysis of elasto-plastic stress waves by a time discontinuous variational integrator based on Hamiltonian in order to more accurate results in one dimensional dynamic problem. The proposed algorithm adopts both time-discontinuous variational integrator and space-continuous Hamiltonian so as to capture discontinuities of stress waves. This study enables to preserve total mechanical energy such as internal energy, kinetic energy and dissipative energy due to plastic deformation for long integration time. Finite element analysis of elasto-plastic stress waves is carried out in order to demonstrate the accuracy of the proposed algorithm.

• The Journal of the Acoustical Society of Korea
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• v.18 no.3E
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• pp.9-20
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• 1999

To investigate the characteristics of internal waves (IWs) and their effects on acoustic wave propagation, a series of sea experiment were performed in the east coast of Donghae city, Korea in 1997 and 1998 where the water depth varies between 130 and 140 m. Thermistor strings were deployed to measure water temperatures simultaneously at 9 depths. CW source signals with the frequencies of 250,670 and 1000 Hz were received by an array of 15 hydrophones. Through the Wavelet transform analysis, the IWs are characterized as having typical periods of 2-17 min and duration of 1-2 hours. The IWs exist in a group of periods rather than in one period. Underwater acoustic signals also show obvious energy peaks in the periods of less than 12 min. Consistency in the periods of the two physical processes implies that acoustic waves react to the IWs through some mechanisms like mode interference and travel time fluctuation. Based on the thermistor string data, mode arriving structures are analyzed. As thermocline depth varies with time, it may cause travel time difference as much as 4-10 ms between mode 1 and 2 over 10 km range. This travel time difference causes interference among modes and thus fluctuation from range-independent stratified ocean structure. In real situations, however, there exist additional spatial variation of IWs. Model simulations with all modes and simple IWs show clear responses of acoustic signals to the IWs, i.e., fluctuations of amplitude and phase.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.3
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• pp.31-40
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• 2020

The structure and dynamics of multiple shock waves are studied numerically using a finite volume solver for a model with nozzle exit Mach number of 1.75. At first, the shock variation based on images were analyzed using a Matlab program then later to the wall static pressure variation. The amplitude and frequency variation for multiple shock waves are analyzed. The cross-correlation between the shock location suggests that the first and the second shocks are well correlated while the other shocks show a phase lag in the oscillation characteristics. The rms values of pressure fluctuations are maximum at the shock locations while the other parts in the flow exhibit a lower value os standard deviation.

• Journal of Korea Water Resources Association
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• v.45 no.6
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• pp.545-555
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• 2012

A numerical modeling has become increasingly popular and more important to the study of water waves with a rapid advancement of computer technology. However, different types of problems are induced during simulating wave motion. One of the key problems is re-reflection to a computation domain at the incident boundary. The internal wave generating-absorbing boundary conditions have been commonly used in numerical wave models to prevent re-reflection. For the Navier-Stokes equations model, the internal wave maker using a mass source function of the continuity equation has been used to generate various types of waves. Nonetheless, almost every numerical experiment is performed in two dimensions and only a few tests have been expanded to three dimensions. More recently, a momentum source function of the Boussinesq equations is applied to generate essentially directional waves in the three dimensional Navier-Stokes equations model. In this study, the internal wave maker using a momentum source function is employed to generate targeted linear waves in the three-dimensional LES model.

• The Journal of Internal Korean Medicine
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• v.25 no.4
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• pp.158-166
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• 2004

Background & Object : The aim of this study was to investigate the usefulness of electrogastrography in the diagnosis field of traditional medicine through a study of the relationship between gastric motility and health condition based on oriental medicine diagnostic theory in functional dyspepsia. Method : 86 patients (male 27, female 59) with functional dyspepsia and 10 healthy control subjects (male 5, female 5) were involved in the investigation. The disease information of functional dyspepsia (based on Rome criteria II) was used for dyspeptic index and scores were obtained from the comprehensive diagnosis of Qui, Xue, Shui was applied as index for health condition, those were all investigated by questionnaire. Gastric motility were recorded and analyzed using electrogastrography in fasting and postprandial period. Results : The total score of comprehensive diagnosis of Qui Xue Shui was influenced by the number of functional dyspepsia symptoms (p=0.026). In terms of electrogastrographical parameters, both postpranial normal slow waves regularity(p=0.003) and power ratio (p=0.001) in the patients had the statistical significance and they showed an incremental inverse correlation with the number of symptoms. Dominant frequency and fasting normal slow waves regularity ratio had no statistical significance. Conclusion : Results suggest that electrogastrography is useful in evaluating the health condition of patient by comprehensive diagnosis of Qui Xue Sui.

• International Journal of Safety
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• v.7 no.2
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• pp.17-22
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• 2008

Recent developments in contactless, air-coupled sensing of seismic and ultrasonic waves in concrete structures are presented. Contactless sensing allows for rapid, efficient and consistent data collection over a large volume of material. Two inspection applications are discussed: air-coupled impact-echo scanning of concrete structures using seismically generated waves, and air-coupled imaging of internal damages in concrete using ultrasonic tomography. The first application aims to locate and characterize shallow delamination defects within concrete bridge decks. Impact-echo method is applied to scan defected concrete slabs using air coupled sensors. Next, efforts to apply air-coupled ultrasonic tomography to concrete damage imaging are discussed. Preliminary results are presented for air-coupled ultrasonic tomography applied to solid elements to locate internal defects. The results demonstrate that, with continued development, air-coupled ultrasonic tomography may provide improved evaluation of unseen material defects within structures.

• Journal of Biomedical Engineering Research
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• v.7 no.2
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• pp.117-118
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• 1986

It is well known that nonlinear propagation characteristics of the wave in the tissue may give very useful information for the medical diagnoisis. In this paper, a new method to detect nonlinear propagation characteristics of the internal vibration in the tissue for the low frequency mechanical vibration by using bispectral analysis is proposed. In the method, low frequency vibration of f0( = 100Hz) is applied on the surface of the object, and the waveform of the internal vibration x (t) is measured from Doppler frequency modulation of silmultaneously transmitted probing ultrasonic waves. Then, the bispectra of the signal x (t) at the frequencies (f0, f0) and (f0, 2f0) are calculated to estimate the nonlinear propagation characteristics as their magnitude ratio, w here since bispectrum is free from the gaussian additive noise we can get the value with high S/N. Basic experimental system is constructed by using 3.0 MHz probing ultrasonic waves and the several experiments are carried out for some phantoms. Results show the superiority of the proposed method to the conventional method using power spectrum and also its usefulness for the tissue characterization.

• Journal of the Optical Society of Korea
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• v.14 no.4
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• pp.403-408
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• 2010

The acoustic properties of anti-inflammatory egonol were investigated by using micro-Brillouin scattering spectroscopy, by use of a 6-pass tandem Fabry-Perot interferometer and an optical microscope specially modified for spectroscopic purposes. The measured Brillouin spectrum was composed of a central peak centered at zero and a Brillouin doublet arising from the longitudinal acoustic waves, i.e. propagating density fluctuations. For the first time, the glass transition of egonol was identified to be about $5^{\circ}C$ at which the Brillouin peak position and the half width showed abrupt changes. The substantial damping of acoustic phonons of egonol near the glass transition temperature indicated that the contribution of internal relaxation processes such as small-amplitude librations of side chains to the damping of acoustic phonons may be substantial depending on the internal structure of molecules.