• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• v.6 no.1
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• pp.7-14
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• 2003

The interaction of monochromatic incident waves with a submerged horizontal porous membrane is investigated in the context of two-dimensional linear hydro-elastic theory. It is assumed that the membrane is made of material with very fine pores so that the normal velocity of the fluid passing through the porous membrane is linearly proportional to the pressure difference between two sides of the membrane (e.g. Darcy's law). Using the Eigen-function expansion method, the wave-blocking performance of a submerged horizontal porous membrane is tested with various membrane tensions, porosities, lengths, and submerged depths. It is found that an optimal combination of design parameters exists for given water depth and wave characteristics.

• Water for future
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• v.9 no.1
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• pp.70-80
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• 1976

The efficient breakwater design requires a knowledge of the behaviour of the waves passing the breakwater. Wave Diffraction is an important factor and phenomeon in this behaviour. The diffraction ocean waves entering a gap in a breakwater normal to the incident wave direction in water of uniform depth has been investigated, applying a solution previously given in the author's paper, based on the theory of light diffraction by Sommerfeld. The wave profiles and heights on both the leeward side of the breakwater and the gap side have been studied and summarized in the form of diagrams with diffraction coefficients in range of x/L, y/L 0∼100, b/L=0.5∼12, with some extension of the diagrams made previously. The results of the theoretical approaches have not been experimentally verified. The theory ad computation methods with computer program in Fortran IV developed in this study make an efficient use for estimating the diffraction about a breakwater gap.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.311-318
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• 1998

In this paper, the power flow analysis(PFA) method is applied to the prediction of the vibrational energy density and intensity of coupled co-planar plates. To cover the energy transmission and reflection at the joint of the plates, the wave transmission approach is introduced with the assumption that all the incident waves are normal to the joint. By changing the frequency ranges and internal loss factors, we have obtained the PFA results, and compared them with the analytical exact solutions.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.9
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• pp.840-846
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• 2011

In this paper, reflection and RCS characteristic of the EGS(Electromagnetic Gradient Surface) due to incident angle and polarization is analyzed. Incident angle, ${\theta}_i$, is rotated from $0^{\circ}$ to $50^{\circ}$ with $10^{\circ}$ steps and perpendicular and parallel polarization of incident wave are also considered each incident angle. Reflection and RCS characteristic is not much affected by variation of polarization for normal incidence(${\theta}_i=0^{\circ}$). Reflection pattern has different characteristic due to variation of incident angle and polarization but the EGS has about 2 dB of RCS difference due to polarization in RCS characteristic.

• Journal of electromagnetic engineering and science
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• v.8 no.2
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• pp.70-75
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• 2008

In this paper, the EM wave absorber was designed and fabricated for countermeasure against EMI from a ceiling of a tollgate in ETC system. We fabricated several samples in different composition ratios of MnZn-ferrite, Carbon, and CPE(Chlorinated Polyethylene). Absorption abilities were simulated in accordance with different thicknesses of the prepared absorbers and changed complex relative permittivity and permeability according to composition ratio. The optimized mixing ratio of MnZn-ferrite, Carbon, and CPE was found as 40:15:45 wt.% by experiments and simulation. Then the EM wave absorber was fabricated and tested using the simulated data. As a result, the developed EM wave absorber has the thickness of 3.3 mm and absorption ability was more than 20 dB in the case of normal incidence and more than 11 dB for the incident angle from 15 to 45 degrees at 5.8 GHz. Therefore, it was confirmed that the newly developed absorber can be used for ETC system.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1455-1462
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• 2013

This study examines the reflection of a partially perforated wall with single chamber by 2D and 3D hydraulic experiments. The effects of slit shape on the front wall, relative chamber width and wave steepness were discussed. For the normal incident wave condition, the reflections of horizontal slit case were lower than that of the vertical slit with the similar porosity, but the differences are not significant. When the wave steepness is relatively small, the reflection coefficients are large. In the oblique incidence, the normalized wave heights along a perforated wall with similar porosity are almost same for the vertical and horizontal slit walls and therefore the difference by slit shape can be ignored.

• Geomechanics and Engineering
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• v.18 no.6
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• pp.605-614
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• 2019

The present paper seeks to investigate propagation and reflection of waves at free surfaces of homogeneous, anisotropic and rotating micropolar fibre-reinforced medium with voids. It has been observed that, in particular when P-wave is incident on the free surface, there exist four coupled reflected plane waves traveling in the medium; quasi-longitudinal displacement (qLD) wave, quasi-transverse displacement (qTD) wave, quasi-transverse microrotational wave and a wave due to voids. Normal mode Analysis usually called harmonic solution method is adopted in concomitant with Snell's laws and appropriate boundary conditions in determination of solution to the micropolar fibre reinforced modelled problem. Amplitude ratios which correspond to reflected waves in vertical and horizontal components are presented analytically. Also, the Reflection Coefficients are presented using numerical simulated results in graphical form for a particular chosen material by the help of Mathematica software. We observed that the micropolar fibre-reinforced, voids and rotational parameters have various degrees of effects to the modulation, propagation and reflection of waves in the medium. The study would have impact to micropolar fibre-reinforecd rotational-acoustic machination fields and future works about behavior of seismic waves.

• Journal of KSNVE
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• v.8 no.6
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• pp.1053-1061
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• 1998

In this paper. the power flow analysis(PFA) method is applied to the prediction of the vibrational energy density and intensity of coupled co-planar plates. To cover the energy transmission and reflection at the joint of the plates. the wave transmission approach is Introduced with the assumption that all the incident waves are normal to the joint. By changing the frequency ranges and internal loss factors. we have obtained the reliable PFA results. and compared them with the analytical exact solutions.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.11a
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• pp.233-239
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• 1999

The feasibility of an ultrasonic technique using a pulse-echo method of normal-incident compressional waves was evaluated for its sensitivity to the worn surface and near surface damage due to wear. Worn surfaces were generated at various oscillation frequency under a given load and amplitude and these surface were in situ monitored using a ultrasonic wave detection system. Analysis of the ultrasonic waves received from the worn surface revealed a close relationship between the surface and near-surface damage and the maximum echo-amplitude of the compressional waves. The ultrasonic technique was successful in assessing the level of severity of the worn surface in real time during the wear process. It is also shown that the wear depth can be easily measured by the calculation of change of the specimen thickness based on the wave speed measured for the specimen medium.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.9
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• pp.856-862
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• 2010

In this paper, the power flow analysis(PFA) method was developed to predict the vibrational responses of coupled co-planar orthotropic plates in frequencies ranging from medium to high. To cover the power transmission and reflection at the joint of the orthotropic plates, the wave transmission approach is applied with the assumption that all the incident waves are normal to the joint. Through numerical analyses, the power flow energy density and intensity fields of coupled co-planar orthotropic plates were compared with those of classical modal solutions by changing the frequency and internal loss factor, and they show good agreement in terms of the global decay and the attenuation patterns of the energy density.