• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.9
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• pp.720-725
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• 2001

In this study, Pb(La,Ce)Ti $O_3$ ceramics were manufactured for 20 MHz resonator application. Electromechanical coupling factor( $k_{t}$, $k_{t3}$, mechanical quality factor( $Q_{mt}$ , $Q_{mt3}$ and dydnamic range (D.R) of thickness vibration mode were measured as the variations of $\ell$/t(length/thickness) ratio of ceramic substrates. Mechanical quality factor( $Q_{mt3}$) and dynamic range of third overtone thickness vibration mode showed the highest value of 2,773 and 52.22dB at specimen S4($\ell$/t=12), respectively. The excellent temperature stability of resonant frequency suitable for resonator application was shown, regardless of thermal shock.k.ock.k.

• International Journal of Aerospace System Engineering
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• v.2 no.2
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• pp.10-14
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• 2015

To design airfoils for novel airplanes, new knowledge of aerodynamics is required. In this study, modified Parametric SECtion (PARSEC) which is a airfoil representation is applied to airfoil design using a multi-objective genetic algorithm to obtain an optimal airfoil for consideration in the development of a Martian airplane. In this study, an airfoil that can obtain a sufficient lift and glide ratio under lower thrust is considered. The objective functions are to maximize maximum lift-to-drag ratio and to maximize the trailing edge thickness. In this way, information on the low Reynolds number airfoil could be extracted efficiently. The optimization results suggest that the airfoil with a sharper thickness at the leading edge and higher camber at the trailing edge is more suitable for a Martian airplane. In addition, several solutions which has thicker trailing edge thickness were found.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.5
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• pp.39-51
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• 2014

This paper deals with design of a direct-coupled, small-scaled permanent magnet generator (PMG) for wind power application. First, this paper determines rated power and speed of the PMG from measured characteristics of wind turbines. Second, we derive analytical solutions for the open-circuit field in order to determine optimum magnet thickness and pole pitch/arc ratio. Third, on the basis of open circuit field solutions, stator magnetic circuit including slot opening, teeth width and yoke thickness is designed. And then, a diameter of stator coil which agree with a required current density is calculated, and its turns are determined from the area of slot considering winding packing factor. Finally, finite element (FE) method is employed in analyzing the details of the designed PMG and, test results such as back-emf measurements are given to confirm the design.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 1999.10a
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• pp.265-272
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• 1999

This stability of a plate structure is very crucial problem which results in wrinkle and bucking. In this study, the effect of the pattern of spot-welding points of the two rectangular plates on the compressive and shear bucking load is studied with respect to the thickness, aspect ratio of plates and number of welding spots. Buckling coefficient of the plate not welded was compared with that of two plates with various thickness to extract the effect of thickness. The effect of number of welding spots are studied in two directions, longitudinal and transverse directions. The conclusions obtained were that the reinforcement effect was maximized when the aspect ratio was close to 1.75 at compressive load condition and that the effect of number of welding spots in transverse direction was larger than that in longitudinal direction at shearing load condition.

• Proceedings of the KWS Conference
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• 2001.10a
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• pp.81-84
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• 2001

This study introduces the new way for the evaluation criteria of the Mash-Seam Tailored Blank weldability, The materials used are low carbon automotive galvanized and high strength steels and the evaluation of weldability are examined with various thickness. Welding tests were conducted for both similar thickness and dissimilar thickness cases. The criteria developed for optimum welding conditions were based on the relationship among results of die press forming test, forming limit diagram, Erichsen test and microhardness measurements. The application of the developed criteria(fracture ratio, strength ratio, etc) in obtaining optimum welding condition revealed that a weld which satisfied ant of the criteria did not fracture during actual die press test and FLD dome test.

• Structural Engineering and Mechanics
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• v.11 no.1
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• pp.49-70
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• 2001

This paper is concerned with a study on thermo-elastoplastic characteristics of functionally graded composite. Compared to the classical layered composites, it shows a wide range of thermo-elastoplastic characteristics according to the choice of two major parameters, the thickness-wise volume fraction of constituents and the relative thickness ratio of the graded layer. Therefore, by selecting an appropriate combination of the two parameters, one is expected to design the most suitable heat-resisting composite for a given thermal circumstance. Here, we address the parametric investigation on its characteristics together with theoretical study on thermo-elastoplasticity and numerical techniques for its finite element approximations. Through the numerical experiments, we examine the influence of two parameters on the thermo-elastoplastic characteristics.

• Structural Engineering and Mechanics
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• v.27 no.3
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• pp.365-391
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• 2007

The vibration and stability analysis is investigated for composite cylindrical shells that composed of ceramic, FGM, and metal layers subjected to various loads. Material properties of FG layer are varied continuously in thickness direction according to a simple power distribution in terms of the ceramic and metal volume fractions. The modified Donnell type stability and compatibility equations are obtained. Applying Galerkin's method analytic solutions are obtained for the critical parameters. The detailed parametric studies are carried out to study the influences of thickness variations of the FG layer, radius-to-thickness ratio, lengths-to-radius ratio, material composition and material profile index on the critical parameters of three-layered cylindrical shells. Comparing results with those in the literature validates the present analysis.

• Steel and Composite Structures
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• v.30 no.4
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• pp.315-325
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• 2019

Double skin composite walls offer structural and economic merits over conventional reinforced concrete counterparts in terms of higher capacity, greater stiffness, and better ductility. This paper investigated the axial behavior of double skin composite walls with steel truss connectors. Full-scaled tests were conducted on three specimens with different height-to-thickness ratios. Test results were evaluated in terms of failure mode, load-axial displacement response, buckling loading, axial stiffness, ductility, strength index, load-lateral deflection, and strain distribution. The test data were compared with AISC 360 and Eurocode 4 and it was found that both codes provided conservative predictions on the safe side.

• Steel and Composite Structures
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• v.42 no.5
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• pp.711-722
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• 2022

In this paper, hyperbolic shear deformation plate theory is developed for thermal buckling of functionally graded plates with porosity by dividing transverse displacement into bending and shear parts. The present theory is variationally consistent, and accounts for a quadratic variation of the transverse shearstrains across the thickness and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. Three different patterns of porosity distributions (including even and uneven distribution patterns, and the logarithmic-uneven pattern) are considered. The logarithmic-uneven porosities for first time is mentioned. Equilibrium and stability equations are derived based on the present theory. The non-linear governing equations are solved for plates subjected to simply supported boundary conditions. The thermal loads are assumed to be uniform, linear and non-linear distribution through-the-thickness. A comprehensive parametric study is carried out to assess the effects of volume fraction index, porosity fraction index, aspect ratio and side-to-thickness ratio on the buckling temperature difference of imperfect FG plates.

• The korean journal of orthodontics
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• v.41 no.3
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• pp.184-190
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• 2011

Objective: The purpose of this study was to investigate the relationship between the enamel thickness of proximal surfaces and the morphologic features of mandibular incisors. Methods: Mesiodistal/faciolingual (MD/FL) index, MD width, and height of contour width/cervical width ratio were measured in 40 incisors extracted from Koreans. For determining the height of contour width/cervical width ratio, the cervical width was measured as the distance between proximal cementoenamel junctions. Then, the labial surface was ground to the height of the contour level to measure enamel thickness. Pearson correlation analysis was used to investigate the correlation between enamel thickness and morphologic features. Results: Enamel thickness was $0.75{\pm}0.07mm$ per side, and MD width was $5.56{\pm}0.40mm$. Enamel thickness and MD width were significantly correlated. However, a significant relationship was not observed between enamel thickness and MD/FL index or the height of contour width/cervical width ratio. Conclusions: The results suggest that enamel thickness is affected only by MD width. Therefore, if the MD width is the same for mandibular incisors with a large MD/FL index or triangular shape and mandibular incisors with normal shape, then the limit of enamel reduction for reproximation will be the same.