• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.1
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• pp.28-31
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• 2018

This paper investigates the ground reflection effect on the channel capacity of an orbital angular momentum (OAM) multi-mode transmission system that uses uniform circular array (UCA) antennas. The ground-reflected signals cause inter-mode interferences between the OAM modes, and lead to system performance degradation. The OAM multi-mode channel capacity severely degrades owing to the ground reflection as the transmission distance increases. Increasing the UCA height above the ground and using highly directive array elements can mitigate the ground reflection effect and increase the channel capacity.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.6
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• pp.471-476
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• 2010

This paper has studied dissymmetrical light distribution design using the secondary optics in the simulation. fundamental Lambertian radiation distribution based on LED has been cut off by the secondary optics, and the first surface slope of lens and second surface slope of total reflection area have been calculated through formula. PMMA (the index of refraction: 1.49361) which is material of lens has been selected. critical angle($42.02993^{\circ}$) between Air and PMMA has been calulated by snell's law, and total reflection angle slope has been selected about $16.67^{\circ}$ to occur the total reflection. when the first surface slope and the second surface slope has been set up, Rays of all total reflection area have generated the total reflection. finally, designed LED Module has been estimated by Korean Industrial Standards for LED safety street lighting. dissymmetrical light distribution have been analyzed with reached effect of road illuminance, and average road illuminance which are each 70.6 lx, 40.35 lx, and 25.88 lx have been satisfied with Korean Industrial Standards for LED safety street lighting.

• Journal of Mechanical Science and Technology
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• v.16 no.10
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• pp.1346-1354
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• 2002

The purpose of this work is to study the effects of specularly reflecting wall under the combined radiative and laminar free convective heat transfer in an infinite square duct. An absorbing and emitting gray medium is enclosed by the opaque and diffusely emitting walls. The walls may reflect diffusely or specularly. Boussinesq approximation is used for the buoyancy term. The radiative heat transfer is evaluated using the direct discrete ordinates method. The parameters under considerations are Rayleigh number, conduction to radiation parameter, optical thickness, wall emissivity and reflection mode. The differences caused by the reflection mode on the stream line, and temperature distribution and wall heat fluxes are studied. Some differences are observed for the categories mentioned above if the order of the conduction to radiation parameter is less than order of 10$\^$-3/ fer the range of Rayleigh number studied. The differences at the side wall heat flux distributions are observed as long as the medium is optically thin. As the top wall emissivity decreases, the differences between these two modes are increased. As the optical thickness decreases at the fixed wall emissivity, the differences also increase. The difference of the streamlines or the temperature contours is not as distinct as the side wall heat flux distributions. The specular reflection may alter the fluid motion.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.3
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• pp.143-150
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• 2003

Based on the eigenfunction expansion method, the interaction between monochromatic waves and a partially immersed slotted plate with a back wall has been investigated. Analytical results show that the reflection coefficients by a partially immersed slotted plate depend on the porosity, immersed depth, chamber width, incidence angle and wave frequency. It is found that the reflection coefficient has minimum value within entire frequency range when the porosity has optimal value 0.1. Comparison between the analytical results and the experimental results(Zhu,2001) of reflection coefficients is made for various chamber widths, immersed depths and wave periods with good agreement. The present analytic method can account adequately for energy dissipation caused by flow separation behind a slotted plate and provide the design informations for the construction of slit caisson breakwater.

• The Journal of Engineering Geology
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• v.27 no.4
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• pp.513-518
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• 2017

Groundroll is a coherent noise showing dispersive behavior in land seismic-reflection records and its rejection has been a stubborn problem in data processing because they severely degrade the continuities and resolution of reflection signals. Conventional processing schemes of attenuating noises are the kind of frequency filtering (i.e., bandpass and f-k) that uses the Fourier transform (FT) along the entire trace in the time domain. To suppress them in this study, 1D wavelet filtering (WT) that can control time-varying frequency properties is tested and performed in the land-based synthetic and field seismic data. The results are compared to the ones from conventional filtering techniques in terms of continuities and resolution of reflection events. This filtering technique enhanced the reflection events by effectively eliminating the dispersive groundroll and random noises with control of time-scale function on wavelet domain.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.12
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• pp.38-43
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• 2013

In this paper, the location measurement method for the reliable location data using ultrasonic sensors is proposed for the dimming control of the LED flat lamp. The measurement errors depending on the reflection angle of the object have to be considered to obtain the reliable location data in the ultrasonic sensors. In the experiment, the cause of the measurement errors depending on reflection angle is analyzed and velocity change of ultrasonic wave depending on reflection angle is measured. And the location measurement method depending on velocity change of ultrasonic wave is proposed. From the results, the average absolute deviation of the x-coordinates was 1.47cm when the location measurement method was considered, and it was closer to the true values than the average absolute deviation of the x-coordinates which was 5.89cm without regard to the reflection angle.

• Journal of Industrial Technology
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• v.22 no.B
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• pp.35-44
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• 2002

To find the optimal solution as rapidly and exactly as possible with Nelder-Mead simplex algorithm, the present values of the reflection, expansion, contraction and/or shrink parameters of this algorithm are needed to be changed at appropriate time during the search process. The reflection parameter is selected in this study in order to be changed because reflection, expansion and contraction process can be simultaneously effected by only this parameter. Two independent indices for determining whether the present value of the reflection parameter of this algorithm should be changed or not during the search process are suggested in this study. Those indices were made of the equations of Nelder-Mead simplex algorithm's convergence criterion and Dennis-Wood's convergence criterion, respectively. It is appeared that the optimal solution can be find with smaller numbers of objective function evaluation than the original Nelder-Mead's one with fixed parameter when the those indices are used during the search process. and the more remarkable reduction effect of the number of an objective function evaluation can be obtained when the latter index is used.

• Journal of Ocean Engineering and Technology
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• v.24 no.6
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• pp.34-40
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• 2010

Bragg reflection of nonlinear waves is simulated by a 2D fully nonlinear numerical wave tank (NWT). The developed NWT was based on the Boundary Element Method (BEM) with potential theory and the mixed Eulerian-Lagrangian (MEL) time marching scheme with Runge-Kutta 4th-order time integration. A spatial variation of wave elevations and their Fourier amplitudes of each component are compared to investigate the effect of sea bottom ripples and their relative heights. The incident waves over an undulated sea bottom are partially reflected and changed to partial standing waves due to Bragg reflection. The present results are verified with linear calculations and experimental data. It is found that the 1st-order wave component is mainly affected by Bragg reflection and its spatial modulation is significant in front of the bottom ripples.

• Journal of the Korean Solar Energy Society
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• v.36 no.5
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• pp.1-8
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• 2016

In this paper, we evaluated the effect of a silica-based Anti-Reflection(AR) coating for PV modules. The coating technique can be easily applied to large-scale PV modules at room temperature with improvements of the optical properties that is qualified by the optical transmission measurements on the coated cover glass of the modules. The power improvement of the large-scale PV modules shows the increasing about 2.4% at standard condition of the coating technique on average. To improve the AR coating effect of the PV modules, we have characterized the individual PV modules by the measurements of DC power output, modified performance ratio(PRm) and the regression. The results show that the significant improvements of the AR coating effect are 6.4%, 5.5% and 4.5% of increasing of the performances by using the measurements of DC power output, modified performance ratio(PRm) and the regression, respectively.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.4
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• pp.334-344
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• 2009

In the present paper, analytic solutions are derived for scattering of obliquely incident waves by a semi-infinite breakwater or a breakwater gap of partial reflection. In order to examine the appropriateness of the derived solutions, they are compared with the solutions derived by McIver in 1999 and Bowen and McIver in 2002 for a semi-infinite breakwater and a breakwater gap, respectively, in the case of perfect reflection. The derived analytic solutions are used to investigate the effect of reflection coefficient of the breakwater and wave incident angle upon the tranquility at harbor entrance. The tranquility is deteriorated by the reflected waves as the reflection coefficient increases and as the waves are incident more obliquely.