• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.2
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• pp.143-150
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• 2000

In this paper, an optimum size for the inset cut feed of microstrip antennas has been determined by using the finite-difference time domain method. At first, the return losses of microstrip antennas having various shapes and types of the inset cut feeds have been computed numerically for a given frequency and a substrate. Then an optimum size of the inset cut feed has been determined by iterative computation procedure for a given condition. It was found that the optimum width of the inset cut feed is about 0.42 times of the width of 50Ω feed line and the optimum length of the inset cut feed is about 0.36 times of the length of the antenna patch. These results are proved by the experimental data obtained from the measurements of many fabricated antennas. It was also found that the optimum size of the inset cut feed is independent on the frequency, the height and the dielectric constant of the antennal substrate.

• Journal of Korean Society of Steel Construction
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• v.13 no.6
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• pp.673-681
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• 2001

The objective of this study is the development of size, shape and topology discrete optimum design algorithm which is based on the genetic algorithm. The algorithm can perform both shape and topology optimum designs of trusses. The developed algorithm was implemented in a computer program. For the optimum design, the objective function is the weight of trusses and the constraints are stress and displacement. The basic search method for the optimum design is the genetic algorithm. The algorithm is known to be very efficient for the discrete optimization. The genetic algorithm consists of genetic process and evolutionary process. The genetic process selects the next design points based on the survivability of the design points selected form the genetic process. The evolutionary process evaluates the survivability of the design points. The evolutionary process evaluates the survivability of the design points selected form the genetic process. The efficiency and validity of the developed size, shape and topology discrete optimum design algorithm was verified by applying the algorithm to optimum design examples.

• Structural Engineering and Mechanics
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• v.76 no.6
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• pp.799-821
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• 2020

The optimum design of truss structures is one of the significant categories in structural optimization that has widely been applied by researchers. In the present study, new mathematical programming called Consistent Approximation (CONAP) method is utilized for the simultaneous optimization of the size and shape of truss structures. The CONAP algorithm has already been introduced to optimize some structures and functions. In the CONAP algorithm, some important parameters are designed by employing design sensitivities to enhance the capability of the method and its consistency in various optimum design problems, especially structural optimization. The cross-sectional area of the bar elements and the nodal coordinates of the truss are assumed to be the size and shape design variables, respectively. The displacement, allowable stress and the Euler buckling stress are taken as the design constraints for the problem. In the proposed method, the primary optimization problem is replaced with a sequence of explicit sub-problems. Each sub-problem is efficiently solved using the sequential quadratic programming (SQP) algorithm. Several truss structures are designed by employing the CONAP method to illustrate the efficiency of the algorithm for simultaneous shape and size optimization. The optimal solutions are compared with some of the mathematical programming algorithms, the approximation methods and metaheuristic algorithms those reported in the literature. Results demonstrate that the accuracy of the optimization is improved and the convergence rate speeds up.

• 한국기계연구소 소보
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• s.20
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• pp.71-78
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• 1990

This investigation was undertaken to establish the technologies of grain refinement and modification, and to characterize material properties, essential for high quality aluminum alloy castings. Grain refinement seldom changed DAS and eutectic Si size, but largely decrease grain size. The variations of grain size induced by grain refinement had a great influence on the elongation without changes in the tensile strength or yield strength. The optimum Ti level lies between 0.1% and 0.16% to achieve the best possible mechanical properties. DAS and grain size were little affected, but eutectic Si size was greatly refined by modification. The variation of eutectic Si size had a great effect on the elongation, impact value, fracture toughness and fatigue crack propagation rate without changes in the tensile strength or yield strength. The Sr content of 0.015% is optimum to modification.

• Proceedings of the IEEK Conference
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• 2000.11a
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• pp.121-124
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• 2000

In IMT-2000 systems, the outer loop dynamically adjusts the target SIR so that adequate performance in terms of the frame error rate(FER) and the true quality measure is achieved. This paper utilizes an analytic model lot outer loop power control(OLPC) adjusting the target SIR in IMT-2000. The analytic model is based on the discrete-time Markov chain as voice traffic SIR. It is described that the model can be used to find the optimum step size in voice traffic for fast fading environments. The optimum step size influences the performance of OLPC： As the step size decreases, the average target SIR increases and average FER decreases.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.29 no.1
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• pp.11-20
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• 1993

The purpose of this paper is to study the subject of economic evaluation in respect of optimum ship size and basic design spiral for fishing vessels. The main ta나 is developed the methodology of engineering economic system in order to apply various methods and tools which may be utilized by the designer in his efforts to arrive at principal design characteristics of fishing vessels with optimum size. The design procedure has been modeled in mathematical form with CBR as an criteria and applied to the optimization method. The contents of the study are as follows (the special treatises).

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.193-194
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• 2006

This study describes the optimum size of a reef set in Korean coastal waters. Data were analyzed in relation to the weight and variety of fish species caught with a three-layer gill net. The results did not indicate a significant difference in the mean catch and mean number of fish species among the three different reef sets, 800, 1,600 and 2400 $m^3$.

• Magazine of the Korean Society of Agricultural Engineers
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• v.45 no.3
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• pp.50-58
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• 2003

Due to the economic growth and the improvement of life standards in the country, the quantities of waste glasses have been yearly increased. About 65% of them are recycled and the rest are reclaimed. The reclaimed waste glasses can cause some problems such as the environmental pollution as well as the processing cost of them. Thus, the purpose of this experimental research is to investigate the properties of mortar using powdered waste glasses(PWG) as a cementitious materials in mortar to recycle the reclaimed waste glasses For this purpose, the workability and strength of mortar specimens using PWG have been tested and analyzed in various grain size of them by changing the replacement ratio. As a result, considering the workability and strength of mortar specimens using PWG, it is concluded that the optimum grain size and replacement ratio of them will be existing.

• Transactions of Materials Processing
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• v.8 no.4
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• pp.356-363
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• 1999

This paper discusses some techniques for the determination of optimum blank size and pre-form design for multi-stepped deep drawing of oval shell. The deep drawing process of oval shape has been regarded as more difficult than that of cylindrical shell because of its complicated behavior of plastic deformation. But there is insufficient information in this area to carry out successful deep drawing work of irregular products such as oval, rectangular, and square shapes. In order to find the optimum conditions, the drawing apparatus for two kinds of pre-form design are built, a series of drawing experiments performed, and thickness stain distributions measured. From the results of thess suggested experiments, various optimum process variables are observed and discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.11
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• pp.1950-1956
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• 1997

An engineering goal in vibration and noise professionals is to develope quiet machines at the preliminary design stage, and various numerical techniques such as FEM, SEA or BEM are one of the schemes toward the goal. In this paper, the research has been focused on the sensitivity effect of mesh sizes for FEM application so that the optimum size of the mesh that leads to engineering solution within acceptable computing time could be generated. In order to evaluate the mesh size effect, three important parameters have been examined : natural frequencies, number of modes and driving point mobility. First, several lower modes including the fundamental frequency of a 2-D plate structure have been calculated as mesh size changes. Since theoretical values of natural frequencies for a simple structure are known, the deviation between the numerical and theoretical values is obtained as a function of mesh size. The result shows that the error is no longer decreased if the mesh size becomes a quarter wavelength or smaller than that. Second, the mesh size effect is also investigated for the number of modes. For the frequency band up to 1.4 kHz, the structure should have 38 modes in total. As the mesh size reaches to the quarter wavelength, the total count in modes approaches to the same values. Third, a mobility function at the driving point is compared between SEA and FEM result. In SEA application, the mobility function is determined by the modal density and the mass of the structure. It is independent of excitation frequencies. When the mobility function is calculated from a wavelength to one-tenth of it, the mobility becomes constant if the mesh becomes a quarter wavelength or smaller. We can conclude that dynamic parameters, such as eigenvalues, mode count, and mobility function, can be correctly estimated, while saving the computing burden, if a quarter wavelength (.lambda./4) mesh is used. Therefore, (.lambda./4) mesh is recommended in structural vibration analysis.