• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.10
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• pp.185-190
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• 2007

In this paper, minimum sampling rates and method of nonlinear characterization were suggested for low power, quasi-memoryless PAs. So far, the Nyquist rate of the input signal has been used for nonlinear PA modeling, and it is burdening Analog-to-digital converters for wideband signals. This paper shows that the input Nyquist rate sampling is not a necessary condition for successful modeling of quasi-memoryless PAs. Since this sampling requirement relives the bandwidth requirements for Analog-to-digital converters (ADCs) for feedback paths in digital pre-distortion systems, relatively low-cost ADcs can be used to identify nonlinear PAs for wideband signal transmission, even at severe aliasing conditions. Simulation results show that a generic memoryless nonlinear RF power amplifier with AMAM and AMPM distortion can be successfully identified at any sampling rates. Measurement results show the modeling error variation is less than 0.8dB over any sampling rates.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.9 no.2
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• pp.73-80
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• 1991

Identifying linear form of the parts of precision machine, precise monitoring is indispensable. Therefore, in this study, close-range photogrammetry being tried to screw one of the parts of precision machine, using non-metric camera that is calibrated by plumb line method. Also, it is analyzed three dimensional values of tortien, offset, section and thickness. From results of this study, monitoring of the parts of precision machine was conducted efficiently using non-metric camera and possibility of this application was proved.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.3 s.333
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• pp.39-44
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• 2005

The OFDM modulation and transmission block have been modeled in order to analyse the relationship between the 2.4GHz power amplifier distortion and output ACPR for the IEEE 802.11g wireless LAN. The nonlinear characteristic of the power amplifier has been modeled as AM-to-AM and AM-to-PM using the behavioral model, and the output spectrum is analysed with the phase distortion variation. Also, amplifier back-off value from P1dB to satisfy the required IEEE 802.11g standard spectrum mask s been simulated with modeled phase distortion, and the simulation data have been compared to the measured result by using the pre-distortion technique.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.10
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• pp.809-815
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• 2014

The co-bonded dissimilar composite under a wide range of temperature change shows thermal distortion due to the differences in thermal expansion characteristics of the composite materials. Analysis of the thermal expansion characteristics of each composite is required for the design of co-bonded dissimilar composite structure with considering the shape distortion during the manufacturing process. In this work, digital image correlation (DIC) technique is introduced for measuring the thermal distortion characteristics of co-bonded dissimilar composite specimen, carbon/epoxy and silica/phenolic. The thermal distortion of co-bonded dissimilar composite specimen is numerically estimated and compared with the experiments. The estimated results is successfully validated using the measured results.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.6
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• pp.594-601
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• 2011

In this paper, a new current controller with the compensation of an unbalance and distorted grid voltages has been proposed. Generally, in the three-phase power system, single phase or nonlinear loads can be connected with the 3 phase linear load simultaneously on the same point of common coupling. Therefore, The source voltage unbalance and distortion problem can be occurred. Under these unbalance and distorted grid voltage conditions, the input current of 3 phase PWM rectifiers also have unbalance and distortion. In this paper, a current controller with the simple Model Reference Adaptive System based unbalance and distorted voltages observer is proposed to get a sinusoidal input current. The performance of the proposed algorithm is verified through the simulation and the experiment.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.464-464
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• 2012

수문분야에 있어서 빈도해석의 목적은 특정 재현기간에 대한 발생 가능한 수문량의 규모를 파악하는데 있으며, 빈도해석의 정확도는 적합한 확률분포모형의 선택과 매개변수 추정방법에 의존하게 된다. 일반적으로 각 확률분포모형의 특성을 대표하는 매개변수를 추정하기 위해서는 모멘트 방법, 확률가중 모멘트 방법, 최대우도법 등을 이용하게 된다. 모멘트 방법에 의한 매개변수 추정은 해를 구하기 위한 과정이 단순한 반면, 비대칭형의 왜곡된 분포를 갖는 자료들에 대해서는 부정확한 결과를 나타내게 된다. 확률가중 모멘트 방법은 표본의 크기가 작거나 왜곡된 자료일 경우에도 비교적 안정적인 결과를 제공하는 반면, 확률 가중치가 정수로만 제한되는 단점을 갖고 있다. 그리고 대수 우도함수를 이용하여 매개변수를 추정하게 되는 최우도법은 가장 효율적인 매개변수 추정치를 얻을 수 있는 것으로 알려져 있으나, 비선형 연립방정식으로 표현되는 해를 구하기 위해서는 Newton-Raphson 방법을 사용하는 등 절차가 복잡하며, 때로는 수렴이 되지 않아 해룰 구하지 못하는 경우가 발생되게 된다. 이에 반해, 최근의 Genetic Algorithm, Ant Colony Optimization 및 Simulated Annealing과 같은 Meta-Heuristic Algorithm들은 복잡합 공학적 최적화 문제 있어서 효율적인 대안으로 주목받고 있으며, Hassanzadeh et al.(2011)에 의해 수문학적 빈도해석을 위한 매개변수 추정에 있어서도 그 적용성이 검증된바 있다. 본 연구의 목적은 연 최대강수 자료의 빈도해석에 적용되는 확률분포모형들의 매개변수 추정을 위해 Meta-Heuristic Algorithm을 적용하고자 함에 있다. 따라서 본 연구에서는 매개변수 추정을 위한 방법으로 Genetic Algorithm 및 Harmony Search를 적용하였고, 그 결과를 최우도법에 의한 결과와 비교하였다. GEV 분포를 이용하여 Simulation Test를 수행한 결과 Genetic Algorithm을 이용하여 추정된 매개변수들은 최우도법에 의한 결과들과 비교적 유사한 분포를 나타내었으나 과도한 계산시간이 요구되는 것으로 나타났다. 하지만 Harmony Search를 이용하여 추정된 매개변수들은 최우도법에 의한 결과들과 유사한 분포를 나타내었을 뿐만 아니라 계산시간 또한 매우 짧은 것으로 나타났다. 또한 국내 74개소의 강우관측소 자료와 Gamma, Log-normal, GEV 및 Gumbel 분포를 이용한 실증연구에 있어서도 Harmony Search를 이용한 매개변수 추정은 효율적인 매개 변수 추정치를 제공하는 것으로 나타났다.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.45 no.4
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• pp.71-77
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• 2008

This paper presents a methodology for recovering the industrial radiographic images from the effects of nonlinear distortion. Analytical approach based on the inverse square law and Beer's law is developed in order to improve a mathematic model of nonlinear type. The geometric effect due to dimensions of the radioactive source appeals on the digitized images. The relation that expresses parameters values(angle, position, absorption coefficient, length, width and pixel account) is defined in this model, matching with the sample image. To perform the search for image recovery most similar to the model, a correction procedure is designed. The application of this method on the radiographic images of steel tubes is shown and recovered results are discussed.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.6
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• pp.35-42
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• 2006

Large steel industries have nonlinear loads including electric arc furnaces. These nonlinear loads generate harmonic currents and create distortions on the sinusoidal voltage of the power system. This paper provides an in depth analysis on harmonics field measurement of the electric arc furnace loads, adding a single-tuned filter at the customer bus for reducing harmonic distortion and harmonics assessment by the international harmonic standards IEC 61000-3-6 and IEEE Std. 519. The EDSA program was used as a simulation tool for the case study.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.3
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• pp.107-116
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• 1990

The liquid sloshing in an elastic tank is a fluid-structure interaction problem. It requires nonlinear analysis to solve the complicated physics involved in the large interaction of fluid-structure, the variation of dynamic characteristics of structure due to hydrodynamic loading, and the distorsion of fluid flow due to structural vibration. In this paper a Lagrangian FEM is introduced to analyze the liquid sloshing in an elastic tank assuming that the elastic wall is one degree of freedom rigid wall. Numerical integration is performed using an implicit-explicit algorithm, which is formed by mixing the predictor-corrector method and the Runge-Kutta 4th order method. The influence of dynamic characteristics of the sloshing tank on the fluid flow is discussed. The numerical method is also applied for the simulation of the wall generated wave in the tank.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.4
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• pp.313-325
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• 2011

Finite element grid system using h-refinement on the Yellow Sea was constructed based on previous study (Suh, 1999b) from 14 K to 210 K and special attention was concentrated on refining the coastal zone. In grid generation, depth change between adjacent points and non-dimensional tidal wave length ratio were considered. As a result approximately a quarter of the total nodes are located nearby 5 m of shallow area. Accurate bathymetry data using 30's and ETOPO1 with open boundary conditions of 8 major tidal constituents extracted automatically from FES2004 have been applied. In tidal simulation a 3-dimensional nonlinear harmonic model was setup and tidal amplification due to changes in vertical turbulent and bottom friction were simulated. In this study not only 8 major tidal constituents but also nonlinear shallow tides $M_4,$, $MS_4$ and long period $M_f,$, $M_{sf}$ were reproduced. It is found that implication of spatial variation of friction coefficient plays a very important role in reproduction of astronomical and shallow tides which are computed by iterative computation of nonlinear terms. Also it should be considered differently with respect to tidal periods. To understand the distribution of tidal asymmetry, amplitude ratio of $M_4/M_2$ and phase differences $2g(M_2)-g(M_4)$ were calculated. Tidal distortion ratio marks up to 0.2 on the west coast showing shallow coastal characteristics and somewhat wide range of ebb-dominances in front of Mokpo area are reproduced.