• 한국지구물리탐사학회:학술대회논문집
• /
• 2007.06a
• /
• pp.237-240
• /
• 2007

The evaluation of shear modulus (or shear wave velocity) profile of site is very important in the various fields of geotechnical engineering. To obtain shear wave velocity profile, various in-situ seismic methods using surface waves have been developed. These surface wave based in-situ seismic methods have their own strength and weakness. In this study, new seismic site characterization method using the harmonic wavelet analysis of wave (HWAW) was proposed to overcome some of weaknesses in the existing surface wave based seismic site characterization methods. HWAW method which is based on time-frequency analysis using harmonic wavelet transform have been developed to determine phase and group velocities of waves. In order to estimate the applicability of HWAW method, field tests were performed. Through field applications and comparison with other test results, the applicability of the proposed method were verified.

• Journal of applied mathematics & informatics
• /
• v.20 no.1_2
• /
• pp.197-208
• /
• 2006

This paper deals with the exact solution of surface gravity waves in an ocean with irregular bed topography. In order to obtain water surface elevation and run-up of infra-gravity waves when the bed is either wavy or exponential, closed form solutions are obtained. Numerical computations indicate that when solitary wave or sinusoidal wave conditions are applied at the boundary, water surface elevation attains near Gaussian profile.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.36 no.5
• /
• pp.819-830
• /
• 2016

Hydrodynamic characteristics of wave propagation through density stratification have not been identified in details. So this study conducted a numerical simulation using LES-WASS-3D ver. 2.0 for analysis of density current due to water temperature and salinity in order to analyze hydraulic characteristics under wave action in a two-layer density stratified fluid. For the validity and effectiveness of numerical wave tank used, it was compared and analyzed with the experiment to show waveform based on $3^{rd}$-order Stoke wave theory at the internal of a density stratification. Using the results obtained from numerical simulation, the surface and internal wave heights are reduced as the wave propagates in a two-layer density stratified water. And the surface or internal wave attenuation became more serious as the vorticities were increased by the velocity difference of wave propagation due to the upper-lower density difference around the interface of a density stratification. As well, the surface and internal wave attenuations became more serious with higher density difference and depth ratio between upper and lower layers when the wave propagates through a density stratification.

• Proceedings of the KSME Conference
• /
• 2000.11a
• /
• pp.280-285
• /
• 2000

It is very important to evaluate the surface or subsurface microstructure because of their influences on mechanical properties of materials. Surface SH-wave which is horizontally polarized shear wave traveling along near surface and subsurface layer is an attractive technique for material evaluation. The destructive method is widely used for the estimation of material degradation but it has a great difficulty in preparing specimens from in-service industrial facilities. In this study, nondestructive evaluation for degraded structural materials used at high temperature though surface SH-wave method is discussed. 2.25Cr-1Mo steel specimens which were prepared by the isothermal aging heat treatment at $650^{\circ}$ were evaluated though ultrasonic nondestructive evaluation techniques investigating the change of sound velocity, attenuation coefficient and amplitude spectra. In addition, it has verified experimentally the frequency-dependence of attenuation coefficient though wavelet analysis method.

• Journal of Advanced Research in Ocean Engineering
• /
• v.2 no.2
• /
• pp.48-60
• /
• 2016

Accurate simulation of free-surface wave flows around a ship is very important for better hull-form design. In this paper, a computational fluid dynamics (CFD) code which is based on the open source libraries, OpenFOAM, was developed to predict the wave patterns around a ship. Additional anti-diffusion source term for minimizing a numerical diffusion, which was caused by convection differencing scheme, was considered in the volume-fraction transport equation. The influence of the anti-diffusion source term was tested by applying it to free-surface wave flow around the Wigley and KCS model ships. In results, the wave patterns and hull wave profiles of the Wigley and KCS model ships for various anti-diffusion coefficients showed quite close patterns. While, the band width of the water volume-fraction values between 0.1 to 0.9 at the Wigley and KCS model hull surfaces was narrowed by considering the anti-diffusion term. From the results, anti-diffusion source term decreased free-surface smearing.

• Journal of Navigation and Port Research
• /
• v.38 no.5
• /
• pp.443-450
• /
• 2014

The objective of this study is to examine the nonlinear fluid characteristics near and inside a moonpool in various sea conditions. We estimate the flow of the free surface in a moonpool taking into account the viscosity effect and the hydrodynamic forces that affects a moonpool and hull through CFD calculations. The comparison of horizontal forces per wave length shows that the hydrodynamic force is greater for the long wave length than short wave length, and the greatest hydrodynamic force acts on the moonpool when the wave length is equal to the ship's length. The horizontal force decreases as the wave amplitude decreases, and the hydrodynamic force acting on the moonpool in ${\lambda}=LBP$ is 10 times that in ${\lambda}=LBP/3$. The free surface demonstrates the piston mode, in which it oscillates up and down while remaining essentially flat, and the rise of the free surface level increases as the wave length increases. We can assume that the hydrodynamic force acting on the moonpool increases owing to the effect of a strong vortex for ${\lambda}=LBP$ and owing to the rise of the free surface level for ${\lambda}=LBP{\times}2$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2009.11a
• /
• pp.111-111
• /
• 2009

In this work, we discuss simulation of surface acoustic wave device using Comsol Multiphysics. The structure SAW device based on piezoelectric thin film aluminum-nitride (AlN) on silicon was simulated. Some parameters of SAW device such as surface velocity, displacement of piezoelectric thin film were evaluated by software. Many modes and shapes of wave are also discussed in this paper. For evaluation physical parameters of AlN piezoelectric layer, the SAW resonator was modeled and simulation results were also compared with experiment results. we simulated arid evaluated the surface Rayleigh wave of AlN thin film on silicon substrate. Results simulation and experiment showed the surface velocity of AlN thin film was about 5200 m/s and shape of surface wave was also displayed. This paper has also proposed as method to study SAW characteristic of piezoelectric thin film and found out measurement values accurately of film such as stiffness matrix, piezoelectric matrix. These values are very important in calculation and design SAW device or MEMS device based on AlN piezoelectric layer.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2022.11a
• /
• pp.113-114
• /
• 2022

This study demonstrates the performance of flexible surface wave resonators in spaces on a ship to overcome environmental limits like non-metallic walls where conventional surface wave resonators cannot installable. Although test results in plane structures show that the performance of conventional surface wave resonators are better than the flexible ones, the results are reversed in curved structures. Flexible surface wave resonators can be installed on metal-pipes that connects all spaces in a ship, and this will allow to build ultimate communication network all over the ship including the rooms like cabins or bridges that are enclosed in non-metallic walls.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.26 no.10
• /
• pp.869-875
• /
• 2015

In this paper, the surface wave that caused the isolation problem when the design of the array antenna is studied. The grounded dielectric slab model is used in order to simulate in the similar environment with the surface wave of the microstrip patch antenna. The propagation of the surface wave on the various types of grounds which are defected ground structure(DGS), perfect magnetic conductor(PMC), Soft-surface, and Hard-surface is simulated. As a result, 25 % power is blocked by the DGS when the TM-wave incident. Also, 95 % power is blocked by the PMC and Soft-surface. This study will be very useful to increase the gain of an array antenna by improving the isolation between the antenna elements.

• Journal of Ocean Engineering and Technology
• /
• v.9 no.2
• /
• pp.75-82
• /
• 1995

The free surface effects on the aerodynamic performance of 2-D wings are investigated based on the potential flow approximation. The wing is represented b source and vortex distributions on the wing surface. The steady free surface effect is taken into account by source distribution on the free surface and the velocity potentials of air and water flows are obtained. Using three different techniques, namely, positive image method, inverse image method and source distribution method, numerical results are obtained for wave elevation, pressure distribution and lift coefficient with various foil sections. The wave elevation calculated by the inverse image method is shown to be very small even at higher speeds so that the free surface effect on the performance of wings is regraded negligible. However, the wave elevations by the positive image method and source distribution method are relatively high at higher speeds and accordingly the free surface effects on wings can not be neglected.