• Title/Summary/Keyword: numerical methods

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Spatially Adaptive Color Demosaicing of Noisy Bayer Data (잡음을 고려한 공간적응적 색상 보간)

  • Kim, Chang-Won;Yoo, Du-Sic;Kang, Moon-Gi
    • Journal of the Institute of Electronics Engineers of Korea SP
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    • v.47 no.2
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    • pp.86-94
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    • 2010
  • In this paper, we propose spatially adaptive color demosaicing of noisy Bayer data. When sensor noises are not considered in demosaicing, they may degrade result image. In order to obtain high resolution image, sensor noises are considered in the color demosaicing step. We identify flat, edge and pattern regions at each pixel location to improve the performance of the algorithm and to reduce complexity. Based on the pre-classified regions, the demosaicing of the G channel is performed using the local statistics to reduce the interpolation error. The sensor noise is simultaneously removed by a modified version of non-local mean filter in the green and in the color difference domain. The R and B channels are interpolated easily using fully interpolated and denoised G and color difference values. Experimental results show that the proposed method achieves a significant improvement in terms of visual and numerical criteria, when compared to conventional methods.

MLFMA for Computation of TM Scattering from Near Resonant Object (유사 공진형 물체에 대한 TM 전자파의 산란계산을 위한 MLFMA방법)

  • ;W. C. Chew
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.9 no.6
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    • pp.735-745
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    • 1998
  • The method of moments has been widely used in the analysis of TM scattering problems. Recently, significant advances in the development of fast and efficient techniques for solving large problems have been reported. In such methods, iterative matrix solvers are preferred by virtue of their speed and low memory requirements. But for near resonant and strong multiple scattering problems, e.g., involving an aircraft engine inlet, a large number of iterations is required for convergence. In this paper, an efficient approximate inverse based preconditioner is used to reduce this number of iterations. By using the matrix partitioning method, the computational is used to reduce this number of iterations. By using the matrix partitioning method, the computational cost for obtaining the approximate inverse is reduced to O(N). We apply this preconditioner to an O(NlogN) algorithm, the multilevel fast multipole algorithm, for the aircraft engine inlet problem. The numerical results show the efficiency of this preconditioner.

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A Study on the Control of Asymmetric Sidelobe Levels and Multiple Nulling in Linear Phased Array Antennas (선형 위상 배열 안테나의 비대칭 Sidelobe 레벨 제어 및 다중 Nulling에 관한 연구)

  • Park, Eui-Joon
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.20 no.11
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    • pp.1217-1224
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    • 2009
  • This paper newly proposes a methodology towards computing antenna element weights which are satisfying asymmetric sidelobe levels(SLLs) specified arbitrarily on both sides of the main beam pattern, in the linear phased array antenna pattern synthesis problem. Opposite to the conventional methods in which the element weights are directly optimized from the array factor, this method is based on the optimum perturbations of complex roots inherent to the Schelkunoff's polynomial form which is described for the array factor. From the proposed methodology, the capability of nulling the directions of multiple jammers is also possible by independently perturbing only the complex roots corresponding to each jamming direction, hence allowing an enhancement of the simplicity of the numerical procedure by means of a proper reduction of the dimension of the solution space. The complex weights over the array are then easily computed by substituting the optimally perturbed complex roots to the Schelkunoff's polynomial. Some examples are examined and numerically verified by substituting the extracted weights into the array factor equation.

Permittivity Measurement of Thin Film Using a Waveguide-type Resonator with a Slot (슬랏을 갖는 도파관형 공진기를 이용한 박막 필름의 유전율 측정)

  • Cho, Chihyun;Kang, Jin-Seob;Kim, Jeng-Hwan
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.24 no.2
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    • pp.214-217
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    • 2013
  • In this paper, a waveguide-type resonator with a slot is proposed to measure permittivity of thin film from resonant frequency shifting by an attached MUT(Material Under Test). The MUT on the slot shifts resonant frequency by perturbation of electromagnetic field. Amount of shifting resonance frequency is dependent on the permittivity of MUT, and that relation is obtained from numerical simulation. The measured relative permittivity of a thin film with thickness of $65{\mu}m$ is 3.3492 with standard error of ${\pm}0.0605$ in the frequency range of 2 GHz to 3 GHz. Also the proposed method is compared with other measuring methods such as dielectric resonator and waveguide probe systems.

Coupled Effect of Soil Nail/Slope Systems (쏘일네일-사면의 상호작용 효과)

  • Jeong Sang Seom;Lee Jin Hyung;Lee Sun Keun
    • Journal of the Korean Geotechnical Society
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    • v.21 no.2
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    • pp.127-135
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    • 2005
  • In this paper, a numerical comparison of predictions by limit equilibrium analysis and finite difference analysis is presented for slope/soil-nail system. Special attention is given to the coupled analysis based on the explicit-finite-difference code, FLAC 2D. To this end, an internal routine (FISH) was developed to calculate a factor of safety for a soil nail slope according to shear strength reduction method. The case of coupled analyses was performed for soil nails in slope in which the soil nails response and slope stability are considered simultaneously. In this study, by using these methods, the failure surfaces and factors of safety were compared and analyzed in several cases, such as toe, middle and top of the slope, respectively. Furthermore, the coupled method based on shear strength reduction method was verified by the comparison with other analysis results.

Evaporation Theory for Reclaimed Clay (준설 점토 지반에서의 증발 이론 개발)

  • 이형주;이인모;이영남;성상규
    • Journal of the Korean Geotechnical Society
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    • v.19 no.4
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    • pp.55-64
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    • 2003
  • Desiccation of a soil is basically the removal of water by evaporation, which is controlled by evaporativity and evaporability. Surface evaporation improves the trafficability which is essential for the access of construction equipment in the area reclaimed with soft clay. The existing traditional methods for evaluating evaporation can not account for the deformation of reclaimed soft soils during evaporation. Therefore, a theoretical model for predicting the rate of evaporation from the surface of a deformable material is proposed. The model is based on a system of equations for coupled heat and mass transfer in unsaturated soils. The modified pressure plate extractor test and glass desiccator test were carried out to obtain the soil-water characteristic curve for a deformable soil. The column drying test was conducted to investigate one dimensional water flow, heat flow and evaporation in the surface. A finite difference program was developed to solve the coupled nonlinear partial differential equations, which permit the study of water, vapor and heat flows in the deformable soil. Comparison between measured and simulated values shows a reasonably good matching between the two.

Analysis of Diameter Effects on Skin Friction of Drilled Shafts in Sand (사질토 지반에 설치된 현장타설말뚝의 말뚝지름에 따른 주면마찰력 분석)

  • Lee, Sung-June
    • Journal of the Korean Geotechnical Society
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    • v.29 no.1
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    • pp.161-170
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    • 2013
  • In this paper, numerical pile segment analysis is conducted with an advanced soil elastoplastic model to investigate the diameter effects on skin friction behaviour of a drilled shaft in sand. Ultimate skin friction and 't-z' behavior from the pile segment analyses for drilled shafts show good agreement with those from design methods. Higher ultimate skin friction for the smaller diameter pile is related to the greater increase in the effective radial stress at the interface due to the localized dilation at and near the pile interface. Stiffer t-z curve for the smaller diameter pile is related to the early occurrence of three shear stages (early, dilation, constant volume shear stages). The diameter effects on ultimate skin friction of drilled shafts are more prominent for denser sand and lower confining pressure.

Numerical Investigation of Low-pollution Combustion with applying Flue Gas Recirculation in Counterflow Flames: Part I. Combustion Characteristics of Low NOx (대향류 화염에서 FGR이 적용된 저공해 연소의 수치적 해석: Part I. 저 NOx 연소특성)

  • Cho, Seo-Hee;Lee, Kee-Man
    • Journal of the Korean Institute of Gas
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    • v.23 no.6
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    • pp.8-16
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    • 2019
  • One of the methods for low-pollution combustion, flue gas recirculation(FGR) is effective to reduce nitrogen oxides and it was applied in CH4/air premixed counterflow flames to identify the change of flame characteristics and NOx mechanisms. Considering that the mole fraction of the products varied depending on the strain rates, the major products: CO2, H2O, O2 and N2 were recirculated as a diluent to reflect the actual combustion system. With the application of the FGR technique, a turning point of maximum flame temperature under certain strain rate condition was found. Furthermore as the recirculation ratio increased, the tendency of NO was changed before and after the turning point and the analysis on thermal NO and Fenimore NO production was conducted.

Optimal Design of Permanent Magnetic Actuator for Permanent Magnet Reduction and Dynamic Characteristic Improvement using Response Surface Methodology

  • Ahn, Hyun-Mo;Chung, Tae-Kyung;Oh, Yeon-Ho;Song, Ki-Dong;Kim, Young-Il;Kho, Heung-Ryeol;Choi, Myeong-Seob;Hahn, Sung-Chin
    • Journal of Electrical Engineering and Technology
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    • v.10 no.3
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    • pp.935-943
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    • 2015
  • Permanent magnetic actuators (P.M.A.s) are widely used to drive medium-voltage-class vacuum circuit breakers (V.C.B.s). In this paper, a method for design optimization of a P.M.A. for V.C.B.s is discussed. An optimal design process employing the response surface method (R.S.M.) is proposed. In order to calculate electromagnetic and mechanical dynamic characteristics, an initial P.M.A. model is subjected to numerical analysis using finite element analysis (F.E.A.), which is validated by comparing the calculated dynamic characteristics of the initial P.M.A. model with no-load test results. Using tables of mixed orthogonal arrays and the R.S.M., the initial P.M.A. model is optimized to minimize the weight of the permanent magnet (P.M.) and to improve the dynamic characteristics. Finally, the dynamic characteristics of the optimally designed P.M.A. are compared to those of the initially designed P.M.A.

A Numerical Study on Coughed Particle Dispersion and Deposition in Negative Pressure Isolation Room according to Particle Size (음압격리병실에서의 기침 토출입자의 입경에 따른 확산 및 침적에 대한 수치해석 연구)

  • Jung, Minji;Hong, Jin Kwan
    • Journal of The Korea Institute of Healthcare Architecture
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    • v.24 no.2
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    • pp.37-44
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    • 2018
  • Purpose: This study investigates the influences of coughing direction and healthcare worker's location on the transport characteristics of coughed particles in airborne infection isolation room (AIIR), which is commonly called negative pressure isolation room, with a downward ventilation system. Methods: Computational Fluid Dynamics (CFD) was used to simulate the airflow and for tracing the behavior of particles. Results: The results show that the airflow pattern and coughing direction have a significant influence on the characteristics of particle dispersion and deposition. When healthcare workers are in the isolation room with the patient who is lying on the bed, it is recommended to be located far from the anteroom to reduce the exposures from infectious particles. And when the patient is lying, it is more effective in removing particles than when the patient is in Fowler's position. Although it is an isolation room that produces unidirectional flow, coughing particles can spread to the whole room and a large number of particles can be deposited onto patient, bed, side rails, healthcare worker, ceiling, floor, and sidewall. Implications: Following the patients' discharge or transfer, terminal cleaning of the vacated room, furniture, and all clinical equipment is essential. Also, it is necessary to establish detailed standard operating procedure (SOP) in order to reduce the risk of cross-contamination.