• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.6
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• pp.7-14
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• 2014

We proposed a new algorithm to improve the calculation speed of forward ray tracing method which was quite a problem in conventional Monte Carlo algorithm. To verify the accuracy and the effect of improving calculation speed, we directly compared integrating sphere characteristics with conventional ray tracing algorithm under the same condition which was referred in a reference paper. By applying new algorithm to an absolute reflectometer, we calculated the degree of errors which were caused by baffle and port characteristics to find optimal system design condition.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.173-178
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• 2011

Nowadays, SELENE-2 is under development for the moon explorer rover in Japan. AXS(Active X-ray Spectrometer) sensor development among the candidated payloads will be on going by the world-wide co-operation. The thermal design, analysis and test will be specially performed by Korean institutes. CFD techniques are used for the conceptual design and analysis. Thin-shell plate meshes being applied by Monte-Carlo Ray Tracing Method are generated for the thermal radiation analysis. Lumped capacity model is employed for the thermal conduction simulation of the AXS payload itself. Various shapes of the payload configuration with thermal boundary conditions are proposed and selected on the purpose of the analysis of the initial design. The results of the analysis are supposed to be used as the baseline for the further detailed design of the AXS payload in the future.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.5A
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• pp.397-401
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• 2005

A different alternative method for simulating bit error rate(BER) performance of Satellite Digital Multimedia Broadcasting(DMB) in tunnel environments is presented. The method based on a channel model obtained by ray-tracing is able to support BER estimation over the channel presents arbitrary statistics that are difficult to fit to an analytic expression. The BER performance for System E over the tunnel fading channel that obtained by ray-tracing is predicted by the monte-carlo method. It can be observed that the BER performance for a straight tunnel channel is better than that for a line-of-sight(LOS) area in curved tunnel. Also, the BER performance for LOS areas in a curved tunnel outperforms that for non-line-of-sight(NLOS) areas in a curved tunnel. The BER performances for straight, curved LOS and curved NLOS tunnel channels are better than that for a Rayleigh channel(K=0) and less than that for a Rician channel with K=3. Moreover, for BER=10-3, it can be seen that there is approximately a $1{\sim}1.5\;dB$ difference between those three types of tunnel channels and a Rayleigh channel.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.989-996
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• 2011

An understanding of the concentrated solar flux is critical for the analysis and design of solar-energy-utilization systems. The current work focuses on the development of an algorithm that uses the Monte Carlo ray-tracing method with excellent flexibility and expandability; this method considers both solar limb darkening and the surface slope error of reflectors, thereby analyzing the solar flux. A comparison of the modeling results with measurements at the solar furnace in Korea Institute of Energy Research (KIER) show good agreement within a measurement uncertainty of 10%. The model evaluates the concentration performance of the KIER solar furnace with a tracking accuracy of 2 mrad and a maximum attainable concentration ratio of 4400 sun. Flux variations according to measurement position and flux distributions depending on acceptance angles provide detailed information for the design of chemical reactors or secondary concentrators.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.8
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• pp.759-764
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• 2004

This paper proposes a method that estimates MIMO channel characteristics analytically using a 3D ray tracing propagation model. We calculate the discrete spatial correlation between sub-channels by considering phase differences of paths, and using this, estimate the mean capacity upper bound of MIMO channel by Jensen's inequality. This analysis model is a deterministic model that do not approach stochastically through measurement nor approach statistically through Monte-Carlo simulations, so this model has high efficiency for time and cost. And based on the electromagnetic theory, this model may analyze quantitatively the parameters which can affect the channel capacity - antenna pattern, polarization mutual coupling, antenna structure and etc. This model may be used for the development of an optimal antenna structure for MIMO systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.1 s.104
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• pp.39-44
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• 2006

This paper proposes a method of moments(MoM)/Monte-Carlo simulation and Physical Optics(PO) model to determine Bistatic Coherent Reflectivity of sea surfaces at various wind speeds. For the MoM simulation, a Gaussian random rough sea surface was generated based on the data of Tae-An ocean at various wind speeds and sea surface heights. The numerical results of the MoM/Monte Carlo simulations were used to verify the validity region of the PO model. It was found that the numerical result for a flat surface agrees quite well with the Fresnel reflection coefficient. The validity of the PO model on the rough sea surface is shown by using ray tracing method.

• Korean Journal of Optics and Photonics
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• v.22 no.2
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• pp.83-89
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• 2011

In order to improve the calculation speed of an integrating-sphere simulator based on a ray-tracing method, parallel processing with OpenMP directive was implemented into the simulator and the randomness of Monte Carlo method was guaranteed by utilizing a parallel random number generator. It was confirmed that simulation results obtained with more than $10^7$ rays showed good agreement with theoretical results within the error range of 0.5%, and that the calculation speed improved as the number of threads increased. Finally, the spatial response distribution functions of a real integrating sphere were simulated and compared with previous results.

• Journal of computational fluids engineering
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• v.12 no.3
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• pp.62-68
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• 2007

A conceptual thermal design is performed for the optical payload system of a geostationary satellite. The optical payload considered in this paper is GOCI(Geostationary Ocean Color Imager) of COMS of Korea. The radiative thermal control system is employed in order to expect a small thermal gradient in the telescope structure of GOCl. Two design margins are applied to the dedicated radiator dimensioning, and three kinds of configuration to the heater power sizing. A Monte-Carlo ray tracing method and a network analysis method are utilized to calculate radiative couplings and thermal responses respectively. At the level of conceptual design, sizing thresholds are presented for the radiator and heater on the purpose of determining the mass and power budget of the spacecraft.

• Journal of KIISE
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• v.43 no.8
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• pp.835-840
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• 2016

Monte Carlo ray tracing has been widely used for simulating a diverse set of photo-realistic effects. However, this technique typically produces noise when insufficient numbers of samples are used. As the number of samples allocated per pixel is increased, the rendered images converge. However, this approach of generating sufficient numbers of samples, requires prohibitive rendering time. To solve this problem, image filtering can be applied to rendered images, by filtering the noisy image rendered using low sample counts and acquiring smoothed images, instead of naively generating additional rays. In this paper, we proposed a Stein's Unbiased Risk Estimator (SURE) based $\grave{A}$-Trous wavelet to filter the noise in rendered images in a near-interactive rate. Based on SURE, we can estimate filtering errors associated with $\grave{A}$-Trous wavelet, and identify wavelet coefficients reducing filtering errors. Our approach showed improvement, up to 6:1, over the original $\grave{A}$-Trous filter on various regions in the image, while maintaining a minor computational overhead. We have integrated our propsed filtering method with the recent interactive ray tracing system, Embree, and demonstrated its benefits.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.578-581
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• 1999

Dot pattern print methods composed of a diffusion film and two prism sheets, have been generally used for backlighting systems of LCDs. However, this methods require complex structures and show high power consumption and optical loss. To improve these disadvantages of conventional backlight units, light guides using highly scattering optical transmissions (HSOT) polymer as scatters, have been introduced. In this study we analyzed multiple scattering effect in light guide by means of Monte carlo simulation based on Mie scattering theory and ray tracing method. As a result it was revealed that scattering intensity depends on the size of scatters. On the other hands, it was shown that scattering efficiency depends on the wavelength of fluorescent lamp as well as the size of scatters.