• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.6
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• pp.526-534
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• 2022

The modular multilevel converter (MMC) has been widely applied to various industrial areas because of its various advantages and structural characteristics. Therefore, many methods for synthesizing the output voltage of MMC have been studied. Among these methods, phase-shifted pulse width modulation (PSPWM) is frequently used in MMC systems because it has diverse merits, such as excellent output qualities even with a small number of cells and uniform power distribution among cells. In this study, the total harmonic distortion (THD) of the output voltage is analyzed in accordance with the number of cells in one arm of a single-delta bridge cell MMC in order to compare PSPWM methods in terms of the THD of the output voltage. The physical characteristics of the triangle and sawtooth carrier waves used for the PSPWM and the mathematical modeling of output voltage are introduced. Then, the obtained results are verified through real-time simulation of a 1 MW single-delta bridge cell MMC system.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.1
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• pp.121-127
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• 2010

This paper relates with the improved CMA blind adaptive equalization algorithm which uses the constellation matching method that improve the inverse modelling efficiency of a communication channel compared to the present CMA blind adaptive equalizer. The amplitude distortion can be compensated in the present CMA blind adaptive equalizer which is used for the reduction of intersymbol interference by distortion that generate such as a band limited wireless mobile channel, but in the improved adaptive alogorithm operates with the minimize the amplitude phase distortion in the output of equalizer by applying the cost function that is composition of additional signal constellation matching error terms. In order to evaluation of the inverse modeling efficiency of improved algorithm, the residual intersymbol interference and recovered signal constellation were compared by computer simulation. As a result of comparion of computer simulation, the improved algorithm has a good stability in the residual intersymbol interference in the steady state, but it has a slow convergence rate in the adaptation state in initial state.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.3
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• pp.315-325
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• 2017

The design dimension may not be satisfactory at the final stage due to the welding during the assembly stage, leading to cutting or adding the components in large structure constructions. The productivity is depend on accuracy of the welding quality especially at assembly stage. Therefore, it is of utmost importance to decide the component dimension during each assembly stage considering the above situations during the designing stage by exactly predicting welding deformation before the welding is done. Further, if the system that predicts whether welding deformation is equipped, it is possible to take measures to reduce deformation through FE analysis, helping in saving time for correcting work by arresting the parts which are prone to having welding deformation. For the FE analysis to predict the deformation of a large steel structure, calculation time, modeling, constraints in each assembly stage and critical welding length have to be considered. In case of fillet welding deformation, around 300 mm is sufficient as a critical welding length of the specimen as proposed by the existing researches. However, the critical length in case of butt welding is around 1000 mm, which is far longer than that suggested in the existing researches. For the external constraint, which occurs as the geometry of structure is changed according to the assembly stage, constraint factor is drawn from the elastic FE analysis and test results, and the magnitude of equivalent force according to constraint is decided. The comparison study for the elastic FE analysis result and measurement for the large steel structure based on the above results reveals that the analysis results are in the range of 80-118% against measurement values, both matching each other well. Further, the deformation of fillet welding in the main plate among the total block occupies 66-89%, making welding deformation in the main plate far larger than the welding deformation in the longitudinal and transverse girders.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.1
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• pp.47-52
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• 2012

A power amplifier is one of important factors for basestation's efficiency and the researches for efficency enhancement focus Doherty amplifier structure with GaN power devices in these days. A memory effect of Doherty amplifier affect operation characteristics for linearity and efficiency. This paper reports on electrothermal nonlinearity modeling and compensation for GaN Doherty amplifier's distortion. Also this paper reports on the dynamic expression of the instantaneous junction temperature as a function of the instantaneous dissipated power. We design distortion model for GaN Doherty amplifier and predistortion compensator for electrothermal memory effect from the proposed behavior model parameters. The simulations was evaluated by ADS Tools and GaN Doherty amplifier with 37dBm. The GaN Doherty amplifier with compensator enhanced about 16dB than without electrothemal memory effect compensator in 2-tone output spectrum.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.2
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• pp.177-182
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• 2015

General method for correcting the distortion caused by the characteristic of the fish-eye lens may be classified in two ways. The first method is a calibration method using a mathematical model taking into account the characteristics of the lens, the second method is a method using only the distortion correction image, regardless of the lens. When considering the characteristics of the lens, calibration equation can be calculated geometrically from the relationship between the three-dimensional real-world coordinates and two-dimensional image coordinates and the parameters of lens. However, it is not suitable for ellipsoid type lens, because of existing research papers have been corrected on the spherical-type fisheye lens. In this paper, we propose a method for correcting geometrically using fish-eye lens as an ellipsoid model. Through a calibration picture, it can be seen that the proposed method is valid.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.26 no.1
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• pp.93-100
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• 2008

The parameters of lens such as focal length, focus, and aperture stop changes while shooting the scenes with zoom lens. Especially, zooming action dramatically changes the geometry of lens system that causes significant change of lens model. We investigated how the lens model changes while zooming in general shooting condition. Each parameters of lens model was estimated and checked whether they can be modeled well in the condition of auto-controlling focus, aperture and vibration reduction. In order to do this, calibration images were taken, modeled in different fecal length setting. And changing patterns of models were inspected to find out if there is some elements that have some particular pattern in changing with respect to focal length. The result showed us that although we didn't control the focus and aperture setting, there's specific changing patterns in radial and do-centering distortion. Especially, the strong linear correlation was found between coefficient of $r^2$ and focal length. It is expected that many parts of distortion can be eliminated without additional self calibration even if zoom operation is done when shooting the scenes if we know its fecal length and model of this coefficient.

• Magazine of the Korea Concrete Institute
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• v.3 no.4
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• pp.133-142
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• 1991

When the behavior of a prototype concrete structure is studied through small-scale model experiments, it is necessary to reproduce all significant physical characteristics on either an one-to-one basis or a specific similitude relationship. Any distortion of similitude must be understood and its effect must be predictable. This paper focuses on improved physical modeling techniques for small-scale reinforced concrete structures. Particular emphasis is placed on the development of a model concrete mix to accurately model the important properties of full-scale prototype concrete. Four types of model reinforcement with different bond characteristics are also studied by testing twenty simple beams. The information obtained will be of immediate use to engineers contemplating small-scale modeling of reinforced concrete structures.

• Journal of KIBIM
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• v.5 no.3
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• pp.1-10
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• 2015

We have researched a character of BIM(Building Information Modeling) and GIS(Geographic Information System) data for integrated utilization of urban spatial data and building data for $CO_2$ reduction. We consider literature on integrated utilization of BIM and GIS and measure method of $CO_2$ in urban spatial unit. Among them without distortion of standard data structure, derive method how to install between BIM and GIS standard data. Rhino & Grasshopper is utilization tools of DB platform. The compatibility with existing BIM and GIS data format, graphic and numeric results can be output at the same time. And using the existing ARCHSIM, it can be easily combined for building energy analysis program. Based on BIM and GIS data to run an energy analysis target on Majang-dong, it could be poly synthetically derived the value information and graphic information.

• Journal of KSNVE
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• v.8 no.1
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• pp.180-186
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• 1998

Vibration test fixture is used in random vibration control testing. The specified reference spectrum should be transmitted equally to the specimen attachment points on the fixture. In most practical cases, however, spectrum at each of specimen attachment points may be quite different from the specified reference spectrum because of the dynamic characteristics of vibration test fixture. This paper proposes the method of experimental dynamic modification of fixture system for vibration test so that the reference spectrum can be transmitted to the specimen attachment points without distortion. The stiffness of mounts of specimen and the thickness of fixture are considered as design variables. The frequency response functions of specimen used for input data are obtained from vibration testing, and the frequency response functions of fixture are obtained from finite element modeling. The sensitivities of frequency response functions at specimen attachment points to the mount stiffness are derived from synthesis method of transfer function. And the sensitivities to the thickness of fixture are also derived from finite element modeling. The presented method is verified by computer simulation and vibration testing.

• Journal of KIISE:Computer Systems and Theory
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• v.33 no.8
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• pp.547-553
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• 2006

We present a new geometry coding method for 3D meshes, an adaptive subdivision. Previous localized geometry coding methods have demonstrated better compression ratios than the global approach but they are considered hard to use in practice partly due to time - consuming quantization. Our new localized scheme replaces this quantization with an adaptive subdivision of the localized range. The deeper level a user chooses, the closer to the original the mesh will be restored. We also present an improved connectivity coder upon the current leading Angle-Analyzer's by applying a context-modeling. As a result, our new coder provides reliable and intuitive controls between bit-rate and distortion without losing efficiency.