• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.5
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• pp.315-323
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• 2015

Damage level of coastal structures has been scaled up according to increase of wave height and duration of the storm due to the abnormal global climate change. So, the design criteria for new breakwaters is being intensified and structural strengthening is also conducted for the existing breakwaters. Recently, interlocking concept has been much attention to enhance the structural stability of the conventional caisson structure designed individually to resist waves. The interlocking caisson breakwater may be survival even if unusual high wave occurs because the maximum wave force may be reduced by phase lags among the wave forces acting on each caisson. In this study, the dispersion characteristics of wave forces using interlocking system that connect the upper part of caisson with cable in the normal direction of breakwater was investigated. A simplified linear model was developed for computational efficiency, in which the foundation and connection cables were modelled as linear springs, and caisson structures were assumed to be rigid. From numerical experiments, it can be found that the higher wave forces are transmitted through the cable as the angle of incident wave is larger, and the larger the stiffness of the interlocking cable makes larger wave dispersion effect.

• Geophysics and Geophysical Exploration
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• v.22 no.4
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• pp.210-224
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• 2019

Surface wave (SW) surveys, which have been applied to numerous application fields ranging from micro-scale ultrasonic analysis to geological scale analysis, are widely used to monitor near-surface stability. The survey method is basically made through analysis on dispersion of SW propagating along the earth surface, in order to delineate shear velocity structure of subsurface. SW survey data are inverted with assuming one-dimensional (1D) layered-earth in order to recover shear wave velocities of each layer, after being analyzed to make the dispersion curve that shows phase velocity of SW with respect to frequency. This study reviews surface wave surveys with explaining the basic theory including the characteristics of dispersion and the procedure of general data processing. Even though surface wave surveys can be categorized into active and passive methods, this paper focuses only on active surface wave methods which includes continuous SW (CSW), spectral analysis of SW (SASW) and multichannel analysis of SW (MASW). Passive method will be reviewed in the subsequent paper.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.41-50
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• 2006

The crustal structure of Korean Peninsula have been investigated by analyzing group velocity dispersion data of surface wave. Cross.correlation of seismic background motions (Campillo and Paul, 2003; Shapiro et al., 2005) has been applied to estimate the short.period Rayleigh. and Love.wave group velocity dispersion characteristics of the region. Standard processing procedures were applied to the cross.correlation, except that signal whitening was used in place of one.bit sampling equalize power in signals from different times. Multiple.filter analysis was used to extract the group velocities from the estimate Green's functions, which were then use to image the spatially varying dispersion at periods between 0.5 and 20 seconds. The tomographic inversion technique used inverted all periods simultaneously to provide a smooth dispersion curve as a function of period in addition to the usual smooth spatial image for a given period. The Gyeongsang Basin in the southeastern part of the peninsula is clearly resolved with lower group velocities.

• Journal of the Korean Geotechnical Society
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• v.25 no.4
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• pp.5-17
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• 2009

In HWAW method, experimental dispersion curve is obtained through time-frequency analysis, and inversion procedure is based on the forward modeling which considers full wavefield. Therefore, it enables us to use relatively short testing setup and has advantage for two dimensional subsurface imaging compared with another surface wave methods. Numerical study was performed to verify that the HWAW method can be applied to non-horizontally layerd soil structure. The experimental dispersion curves obtained from HWAW method agreed with the theoretical dispersion curves based on full wavefield. Experimental dispersion curves are mainly more affected by the region between two receivers than by the region from source to the first receiver. Fluctuation phenomena of dispersion curve can be reduced by adequate receiver spacing setup. From numerical study, it was thought that reliable Vs distribution map can be constructed by HWAW method and finally subsurface imaging was tried in the real field.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3033-3038
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• 2007

In this research, Rayleigh instability of gas-liquid flow in annular pipe is studied in film boiling using viscous potential flow. Viscous potential flow is a kind of approximation of gas-liquid interface considering velocity field as potential including viscosity. A dispersion relation is obtained including the effect of heat and mass transfer and viscosity. New expression for dispersion relation in film boiling and critical wave number is obtained. Viscosity and heat and mass transfer have a stabilizing effect on instability and its effect appears in maximum growth rate and critical wave number. And the existence of marginal stability region is shown.

• The Journal of the Acoustical Society of Korea
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• v.15 no.6
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• pp.47-51
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• 1996

The Cylindrical Shell Equation is one of the fundamental tools in the study of the noise analysis in the cylindrical shell. Therefore, lot of the acousticians induced many cylindrical shell motion equations.[1] In the Reference[6], we introduced the newly induced cylindrical Shell Equation and Junger and Feit's shell equation[5], and computed the free wave number with the linear Equation with the supposed solution, in the case of the free motion of the shell. In this paper, we compared above cylindrical shell equations by using dispersion curve of free wave number and we describe the physical mean for the dispersion curve with ring-frequency and ring-extention-frequency. With this result, we proves the useful of a newly induced cylindrical shell equation and we can analyse the Structure-Borne Sound of the shell with this equation in the application.

• Smart Structures and Systems
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• v.1 no.3
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• pp.257-266
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• 2005

In Lamb wave detection of damages in smart structures, the excitation pulse is usually designed as a narrow band burst wave for the convenience of analysis and recognition. However, the wideband excitation can excite more modes in plate/shell structure and thus provides extra information for changes of the structure. This paper presents a method that can extract information in wideband Lamb wave signals. By transforming the detected signals into various sub-frequency band, the measured signal can be converted to its equivalences of narrow band excitations, therefore, the information in different frequency bands can be acquired from a single test and in the same time the complicity of wideband signal can be simplified. Some test results are provided to verify this method.

• Journal of the Korean Geophysical Society
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• v.6 no.2
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• pp.99-105
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• 2003

Rayleigh waves which has more than 70% of the total seismic energy is the principal component of ground roll. Frequency component of a surface wave has a different propagation velocity, that is, phase velocity, which results in a different wavelength called dispersion. Rayleigh wave is one of the most common ways to use the dispersive properties of surface waves. MASW is a seismic method to evaluate shear-wave velocity information of the ground.

• Korean Journal of Radiology
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• v.23 no.2
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• pp.237-245
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• 2022

Objective: Viscoelasticity is an essential feature of nerves, although little is known about their viscous properties. The discovery of shear wave dispersion (SWD) imaging has presented a new approach for the non-invasive evaluation of tissue viscosity. The present study investigated the feasibility of using SWD imaging to evaluate diabetic neuropathy using the sciatic nerve in a diabetic rat model. Materials and Methods: This study included 11 diabetic rats in the diabetic group and 12 healthy rats in the control group. Bilateral sciatic nerves were evaluated 3 months after treatment with streptozotocin. We measured the nerve cross-sectional area (CSA), nerve stiffness using shear wave elastography (SWE), and nerve viscosity using SWD imaging. The motor nerve conduction velocity (MNCV) was also measured. These four indicators and the histology of the sciatic nerves were then compared between the two groups. The performance of CSA, SWE, and SWD imaging in distinguishing the two groups was assessed using receiver operating characteristic (ROC) analysis. Results: Nerve CSA, stiffness, and viscosity in the diabetic group was significantly higher than those in the control group (all p < 0.05). The results also revealed a significantly lower MNCV in the diabetic group (p = 0.005). Additionally, the density of myelinated fibers was significantly lower in the diabetic group (p = 0.004). The average thickness of the myelin sheath was also lower in the diabetic group (p = 0.012). The area under the ROC curve for distinguishing the diabetic neuropathy group from the control group was 0.876 for SWD imaging, which was significantly greater than 0.677 for CSA (p = 0.030) and 0.705 for SWE (p = 0.035). Conclusion: Sciatic nerve viscosity measured using SWD imaging was significantly higher in diabetic rats. The viscosity measured using SWD imaging performed well in distinguishing the diabetic neuropathy group from the control group. Therefore, SWD imaging may be a promising method for the evaluation of diabetic neuropathy.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.25-30
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• 2006

When wet soil overlies dry soil, which can be found in the infiltration test, the radar wave is not attenuated and guided within wet soil layer. This phenomenon is known to be the dispersive guided wave and happens when the thickness of upper wet layer is less than or comparable to the wavelength of radar wave. In this study, we have conducted the FDTD modeling and obtained the velocity dispersion curve to identify the dispersive guided wave through F-K analysis. This guided wave can be explained by modal propagation theory and a simple inversion code was developed to obtain the two layer's dielectric constants as well as layer thickness. By inverting the dispersion curve from synthetic modeling data, we could obtain the accurate dielectric constants and layer thickness. Moreover, we could enhance the accuracy by including the higher mode data. We expect this method will be very useful to get the quantitative property of subsurface when the condition is similar.