• 한국통신학회논문지
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• 제22권3호
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• pp.469-480
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• 1997

For moving image coding, the variable size of region coding based on local motion is more efficient than fixed size of region coding. It can be applied well to complex motions and is more stable for wide motions because images are segmented according to local motions. In this paper, new image coding method using the segmentation of motion vectors is proposed. First, motion vector field is smoothed by filtering and segmented by smoothed motion vectors. The region growing method is used for decomposition of regions, and merging of regions is decided by motion vector and prediction errors of the region. Edge of regions is excluded because of the correlation of image, and neighbor motion vectors are used evaluation of current block and construction of region. The results of computer simulation show the proposed method is superior than the existing methods in aspect of coding efficiency.

• 전기학회논문지
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• 제58권2호
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• pp.285-291
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• 2009

In this paper, comparative analysis of offset voltage PWM method and $V_{max}-V_{mid}$ PWM method for three-phase matrix converter is addressed by using a simple analytical and graphical method. Offset voltage PWM method calculates PWM patterns in terms of offset voltage and variable slope of carrier, and it simplifies matrix converter modulation algorithm significantly. $V_{max}-V_{mid}$ PWM method generates patterns by using two phases and maintaining a remaining phase to base phase, and it is implemented in the industrial products. The most important performance criterion of modulation method is a magnitude of current ripples and it is analytically modelled. The graphical illustration of theses complex multivariable functions make per-carrier cycle and per fundamental cycle behavior of two PWM methods understood. Two modulation methods are analysed with the analytical formulas and graphics, and the analysis shows offset voltage PWM method is superior to $V_{max}-V_{mid}$ PWM method with respect to input current ripples and output voltage ripples.

• 한국자동차공학회논문집
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• 제1권1호
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• pp.1-13
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• 1993

The three-dimensional numerical analysis for in-cylinder flow of four-valve engine without intake port has been successfully computed. These computations have been performed using technique of the general coordinate transformation based on the finite-volume method and body-fitted non-orthogenal grids using staggered control volume and covariant variable as dependent one. Computations are started at intake valve opening and are carried through top-dead-center of compression. A k-$\varepsilon$model is used to represent turbulent transport of momentum. The principal study is the evolution of interaction between mean flow and turbulence and of the role of swirl and tumble in generating near TDC turbulence. Results for three different inlet flow configuration are presented. From these results, complex flow pattern may be effective for promoting combustion in spark-ignition engines and kinetic energy of mean flow near TDC is well converted into turbulent kinetic energy.

• 전기학회논문지
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• 제59권10호
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• pp.1894-1899
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• 2010

This note is concerned with a robust sliding mode control(SMC) for a class of unmatched uncertain system with severe commensurate state time delay. The suggested method is extended to the control of severe state time delay systems with unmatched uncertainties except the matched input matrix uncertainty. A transformed sliding surface is proposed and a stabilizing control input is suggested. The closed loop stability together with the existence condition of the sliding mode on the proposed sliding surface is investigated through one Lemma and two Theorems by using the Lyapunov direct method with the concept of the control Lyapunov function instead of complex Lyapunov-Kravoskii functionals. Through an illustrative example and simulation study, the usefulness of the main results is verified.

• 한국군사과학기술학회지
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• 제15권5호
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• pp.705-711
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• 2012

The purpose of this study is to develop the model to estimate the penetration rate of metal under a high power continuous wave laser irradiation. To estimate it, an empirical modeling is more practical when the penetration phenomena of metal by laser irradiation is too complex to be analyzed by the numerical simulation. When several methods published earlier were applied to our results, we found out that their methods were not appropriate as the model. Therefore, we suggested the new empirical method considering effective intensity as a key variable. As a result, we confirmed that the new method was effective to model the penetration rate of SUS304 metal and expected that it could be available to other metals.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 B
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• pp.571-573
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• 1995

This paper presents a method for optimal dispatch which minimizes transmission losses and improves voltage profile of power systems using genetic algorithm based on the mechanism of natural genetics and natural selection. The constraints are VAR sources(transformer tap, generator voltage magnitude and shunt capacitor/reactor), load bus voltages and generator reactive power. Real variable-based genetic algorithms which can save coding times and maintain the accuracy are applied for optimal dispatch of reactive power. The genes of genetic algorithm consisted of integers for considering discrete VAR sources. A efficient operator for crossover is proposed to consider the effect of close genes. The algorithm proposed can apply to problems for large scale power systems with multi-variables and complex nonlinear functions efficiently. The proposed method is applied to IEEE 30 buses model system to show its effectiveness.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2000년도 가을 학술발표회논문집
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• pp.238-245
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• 2000

A general formulation for shape design sensitivity analysis over a plane arch structure is developed based on a variational formulation of curved beam in linear elasticity. Sensitivity formula is derived using the material derivative concept and adjoint variable method for the stress defined at a local segment. Obtained sensitivity expression, which can be computed by simple algebraic manipulation of the solution variables, is well suited for numerical implementation since it does not involve numerical differentiation. Due to the complete description for the shape and its variation of the arch, the formulation can manage more complex design problems with ease and gives better optimum design than before. Several examples are taken to show the advantage of the method, in which the accuracy of the sensitivity is evaluated. Shape optimization is also conducted with two design problems to illustrate the excellent applicability.

• Journal of Welding and Joining
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• 제20권1호
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• pp.83-90
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• 2002

Metal Transfer in gas metal arc (GMA) welding is a complex phenomenon affected by many parameters of the welding conditions and material properties. In this research, the correlation equation between the welding condition and detaching droplet size and detaching velocity in GMA welding was studied via recession analysis on the results of numerical analysis using the volume-of-fluid (VOF) method. Welding parameters and material properties were grouped into three dimensionless numbers and detaching droplet size was expressed as the function of them. Second order and exponential multi-variable correlation forms were assumed, and the coefficients of these equations were calculated for globular and spray modes as well as entire transfer modes. Applying correlation equation into available experimental data, it shows good agreement.

• Smart Structures and Systems
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• 제24권2호
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• pp.193-207
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• 2019

This study concerns with morphing structures, e.g. as applied in the aerospace industry. A morphing aerofoil structure capable of variable geometry was developed, which was shown to be able to cater for the different aerodynamic requirements at different stages of flight. In this work, the useful and relatively simple method has been applied, which provides a direct method for calculating required morphing shape displacements via finding the most effective bar through calculating bar sensitivity to displacement and calculating set of length actuations for bar assembly to control/adjust shape imperfection of prestressable structural assemblies including complex elements ("macro-elements", e.g., the pantographic element), involving Matrix Condensation. The technique has been verified by experiments on the physical model of an aerofoil shaped morphing pantographic structure. Overall, experimental results agree well with theoretical prediction. Furthermore, the technique of multi-iteration adjustment was presented that effective in eliminating errors that occur in the practical adjustment process itself. It has been demonstrated by the experiments on the physical model of pantographic morphing structure. Finally, the study discusses identification of the most effective bars with the objective of minimal number of actuators or minimum actuation.

• 대한기계학회논문집A
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• 제31권1호
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• pp.26-35
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• 2007

The vehicle of urban transit is a complex system that consists of various electric, electronic, and mechanical equipments, and the maintenance cost of this complex and large-scale system generally occupies sixty percent of the LCC (Life Cycle Cost). For reasonable establishing of maintenance strategies, safety security and cost limitation must be considered at the same time. The concept of system reliability has been introduced and optimized as the key of reasonable maintenance strategies. For optimization, three preceding studies were accomplished; standardizing a maintenance classification, constructing RBD (Reliability Block Diagram) of VVVF (Variable Voltage Variable Frequency) urban transit, and developing a web based reliability evaluation system. Historical maintenance data in terms of reliability index can be derived from the web based reliability evaluation system. In this paper, we propose applying inverse problem analysis method and hybrid neuro-genetic algorithm to system reliability optimization for using historical maintenance data in database of web based system. Feed-forward multi-layer neural networks trained by back propagation are used to find out the relationship between several component reliability (input) and system reliability (output) of structural system. The inverse problem can be formulated by using neural network. One of the neural network training algorithms, the back propagation algorithm, can attain stable and quick convergence during training process. Genetic algorithm is used to find the minimum square error.