• Journal of Ocean Engineering and Technology
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• v.20 no.2 s.69
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• pp.36-40
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• 2006

As large waves enter a harbor, during their propagation, the motions a floating body are large and if may even be damaged by waves. This phenomenon may be caused by harbor resonance, resulting from large motion at low wave frequency, which is close to the natural frequency of a vessel. In order to calculate the motion of a floating body in a harbor, it is necessary to use the wave forces containing the body-harbor interference. The simulation program to predict the motions of a floating body by waves in a harbor is developed, and this program is based on the method of velocity potential contiuation method proposed by Ijima and Yoshida The calculated results are shown by the variation of wave frequency, wave angle, and the position of a floating body.

• Journal of the Korean Magnetics Society
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• v.23 no.4
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• pp.135-143
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• 2013

The clip-type pulsimeter equipped with a Hall sensor has a permanent magnet attached in the "Chwan" position to the center of a radial artery. The clip-type pulsimeter is composed of a hardware system measuring voltage signals. These electrical bio-signals display pulse rate, non-invasive blood pressure, respiratory rate, pulse wave velocity (PWV), and spatial pulse wave velocity (SPWV) simultaneously measured by using the radial artery pulsimeter, the electrocardiograph (ECG), and the photoplethysmograph (PPG). The findings of this research may be useful for developing a oriental-western biomedical signal storage device, that is, the new and fusion patient monitor, for a U-health-care system.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.12a
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• pp.43-51
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• 2007

In order to investigate the velocity structure of the southern part of the Korean peninsula, exploded seismic signals were recorded for 120 s along a 294-km WNW-ESE line and 150 s along a 335-km NNW-SSE line in 2002 and 2004, respectively. Velocity tomograms were derived from inverting P-wave and S-wave first arrival times. The raypaths indicate several midcrust interfaces. The shallowest one is at the approximate depth of $2{\sim}3\;km$ with refraction velocities of approximately Vp=6.0 and Vs=3.5 km/s, respectively. The second one of $15{\sim}17\;km$ depth has refraction velocities of approximately Vp=7.1 and Vs=3.7 km/s, respectively. The deepest significant interface varies in depth from 30.8 km to 36.1 km. The critically refracting Vp of $7.8{\sim}8.1\;km/s$ and Vs of $4.2{\sim}4.6\;km/s$ along this interface which may correspond to the Moho discontinuity. The velocity tomograms show (1) existence of a low-velocity zone centered at $6{\sim}7\;km$ depth under the Okchon fold belt and the Yeongnam massif, (2) extension of the Yeongdon fault down to greater than 10 km, and (3) existence of high-velocity materials under the Gyeongsan basin less than 4.2 km thick.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.11a
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• pp.96-101
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• 2004

When the wind blows hard, most waves are breaking in sea. Breaking waves occur, exceeding limitation of wave steepness(wave height/wave length=l/7). Because a wave of single angular frequency couldn't generate the breaking phenomena at two dimensional ocean engineering basin, the breaking wave can be generated by the superposition of waves with various angular frequencies. We research how are the particle kinematics in the breaking wave and the magnitude of the breaking wave exciting force. We compare the force in a regular wave which has same specifications(wave height, period and length) as the breaking wave. Also the experimental results of wave exciting force and particle velocity are investigated by comparison on the analytic results using the potential theory.

• Tunnel and Underground Space
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• v.14 no.4
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• pp.261-268
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• 2004

The main objectives of this study are to investigate the anisotropic characteristics of rocks and to evaluate the relationships between physical properties. A series of experiments were performed in three mutually perpendicular directions for three rock types, which are granite, granitic gneiss and limestone. The relationships of measured physical properties were evaluated. The results of ultrasonic wave velocity measurement show that granite of three rock types gives the largest directional difference, and that the wave velocity in a plane parallel to a transversely isotropic one is dominantly faster than that in a subvertical or vertical plane. It implies that ultrasonic wave velocity for rock could be used as a useful tool for estimating the degree of anisotropy. The ratio of uniaxial compressive strength to Brazilian tensile strength ranges approximately from 13 to 16 for granite. from 8 to 9 for granite gneiss, and from 9 to 18 for limestone. The directional differences for granite and granitic gneiss are very small, and on the other hand, is relatively large for limestone. It is suggested that strength of rock makes quite difference depending on the rock types and loading directions, especially for the anisotropic rocks such as transversely isotropic or orthotropic rocks. The ratio of uniaxial compressive strength to point load strength index ranges from 18 to 20 for granite, from 17 to 19 for granitic gneiss, and from 21 to 24 for limestone. These results show that point load strength index makes also a difference depending on rock types and directions. Therefore. it should be noted that the ratio of uniaxial compressive strength to point load strength index could be applied to all rock types. Uniaxial compressive strength shows relatively good relationship with point load strength index, Schmidt hammer rebound value, and tensile strength. In particulat, point load strength index is shown to be the best comparative relationship. It is indicated that point load test is the most useful tool to estimate an uniaxial compressive strength indirectly.

• Journal of the Korean earth science society
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• v.25 no.8
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• pp.774-783
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• 2004

The S wave velocity and Q$s^{-1}$ structure of the uppermost part of the soil in Nakdong Delta area have been obtained to determine the characteristics of the forementioned soil. The phase and attenuation coefficients of multichannel seismic records were inverted to obtain the S wave velocity and Q$s^{-1}$ structure of the soil. The inversion results have been compared with the borehole measurements of the area. The seismic signal of the nearest geophone from a seismic source was used as the source signal to obtain the attenuation coefficients. Amplitude ratios of the signal at each geophone to the source signal wave plotted as a function of distance for the frequency range between 10 Hz and 45 Hz. The slope of a linear regression line which fits amplitude ratio-distance relationship best for a given frequency was used as the attenuation coefficients for the frequency. The dispersion curve of Rayleigh waves and the attenuation coefficients were inverted to obtain the S-wave velocity and Q$s^{-1}$, respectively, in the uppermost 8 meter of soil layer. The borehole measurements of the area show that are two distinct layers; the upper 4 meter of silty-sand and the lower 4 meter of silty-clay. The inversion results indicate that the shear wave velocity of the upper layer is 80 m/sec and 40m/sec in the lower silty-clay layer. The spacial resolution of the shear wave velocity structure is very good down to a depth of 8 meter. The Q$s^{-1}$ in the upper silty-sand layer is 0.02 and increase to 0.03 in the lower silty-sand layer. The spacial resolution of quality factor is relatively good down to a depth of 5 meter, but very poor below the depth. In this study, the S-wave velocity is higher in the silty-clay and the Q$s^{-1}$ is smaller silty-sand than in the silty-clay. However, much more data should be analyzed and accumulated before making any generalization on the shear wave velocity and Q$s^{-1}$ of the sediments.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.1
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• pp.9-19
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• 1989

The impact stress and wave propagation of graphite/epoxy and glass/epoxy laminates subjected to the transverse low-velocity impact of steel balls are investigated theoretically. A plate finite element model based on Whitney and Pagano's theory for the analysis of heterogeneous and anisotropic plates taking into account of the transverse shear deformation is used for the theoretical investigation. This model is in conjuction with static contact laws. The basic element is a four-node quadrilateral with the five degrees-of-freedom per node. The reduced integration technique is used for shear locking associated with low-order function in application to thin plates. These two materials are composed of [0.deg./45.deg./0.deg./-45.deg./0.deg.]$_{2S}$ and [90.deg./45.deg./90.deg./-45.deg./90.deg.]$_{2S}$ stacking sequences and have clamped-clamped boundary conditions. Finally, the present results are compared with an existing solution and wave propagation theory and then impact stress and wave propagation phenomena are investigated.gated.

• Geophysics and Geophysical Exploration
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• v.8 no.1
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• pp.26-33
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• 2005

Inversion of multi-mode surface-wave phase velocity for shallow engineering site investigation has received much attention in recent years. A sensitivity analysis and inversion of both synthetic and field data demonstrates the greater effectiveness of this method over employing the fundamental mode alone. Perturbation of thickness and shear-wave velocity parameters in multi-modal Rayleigh wave phase velocities revealed that the sensitivities of higher modes: (a) concentrate in different frequency bands, and (b) are greater than the fundamental mode for deeper parameters. These observations suggest that multi-mode phase velocity inversion can provide better parameter discrimination and imaging of deep structure, especially with a velocity reversal, than can inversion of fundamental mode data alone. An inversion of the theoretical phase velocities in a model with a low velocity layer at 20 m depth can only image the soft layer when the first higher mode is incorporated. This is especially important when the lowest measurable frequency is only 6 Hz. Field tests were conducted at sites surveyed by borehole and PS logging. At the first site, an array microtremor survey, often used for deep geological surveying in Japan, was used to survey the soil down to 35 m depth. At the second site, linear multichannel spreads with a sledgehammer source were recorded, for an investigation down to 12 m depth. The f-k power spectrum method was applied for dispersion analysis, and velocities up to the second higher mode were observed in each test. The multi-mode inversion results agree well with PS logs, but models estimated from the fundamental mode alone show f large underestimation of the depth to shallow soft layers below artificial fill.

• Transactions on Electrical and Electronic Materials
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• v.9 no.5
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• pp.213-219
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• 2008

Pulse waves continuously change with respect to the characteristics and status of the cardiovascular system and in relation to the blood pressure (BP) and the pulse wave velocity (PWV). Monitoring the vascular condition by analyzing the variations in pulse waveforms has been used to diagnose vascular disorders and in drug treatment of arteriosclerosis and peripheral circulatory obstruction. In this paper, we investigated the vascular characteristic index with regard to the BP and classified by pulse wave signals. The pressure pulse wave and photoplethysmography (PPG) were measured simultaneously while subjects exercised, producing changes in the BP, to analyze the variation in the vascular characteristic index. We investigated the correlation between the BP and vascular characteristic index with regard to the classification methods of the pulse wave. The reflection index (RI) and vascular stiffness index were correlated with the diastolic BP, but no correlation was found between these parameters and the systolic BP. These results suggest the possibility of estimating BP through simple measurements of pulse waves.

• The Journal of the Acoustical Society of Korea
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• v.25 no.2E
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• pp.49-55
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• 2006

Compressional wave velocity (Vp), shear wave velocity (Vs), elastic and physical properties, and electrical resistivity for two core sediments obtained from Southeastern Yellow Sea Mud (SEYSM) were measured and computed. The sediments consist of homogeneous mud (mostly silt and clay) with shells and shell fragments. As a result, the mean grain size is uniform ($7.5-8.5{\Phi}$ throughout the core sediments. However, physical properties such as wet bulk density and porosity show slightly increasing and decreasing patterns with depth, compared to the mean grain size. The compressional (about 1475 m/s in average) and shear wave (about 60 m/s in average) velocities with depth accurately reflect the pattern of wet bulk density and porosity. Electrical resistivity is more closely correlated with compressional wave velocity than physical properties. The computed Vp/Vs and Poisson's ratios are relatively higher (more than 10) and lower (approximately 0.002) than Hamilton's (1979) data, respectively, suggesting the typical characteristics of soft and fully water-saturated marine sediments. Thus, the Vp/Vs ratio in soft and unconsolidated sediments is not likely sufficient to examine lithology and sediment properties. Relationships between the elastic constant and physical properties are correlated well. The elastic constants (Poisson's ratio, bulk modulus, shear modulus) given in this paper can be used to characterize soft marine sediments saturated with seawater.