• International Journal of Aeronautical and Space Sciences
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• v.16 no.1
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• pp.19-27
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• 2015

In the present study, an effort was made to numerically investigate rectangular cavity aeroacoustics with and without doors. The simulation was performed on an open cavity with an aspect ratio of 5:1:1 at Mach 0.85 using the delayed detached eddy simulation (DDES) approach based on the Spalart-Allmaras model. Two cavity configurations, a clean cavity and a cavity with doors, were modeled. The results obtained from the clean cavity were compared with the experimental sound pressure levels (SPL) and the root mean square for the pressures applied. Furthermore, comparisons of frequencies were made using a modified semi-empirical Rossiter formula. The simulation using DDES precisely predicted the pressure fluctuation and the results matched the experiment quite well. The SPLs at the rear of the cavity were much higher than those in the front due to the instability of the shear layer impinging on the rear wall. Comparisons of DDES for the clean cavity and the doors-on cavity revealed that the SPLs inside the cavity as well as the magnitude of tones are amplified by the side doors. The main focus of this investigation was to obtain a better understanding of the open cavity acoustic resonance phenomenon and investigate the effects of cavity doors on the SPL.

• Structural Engineering and Mechanics
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• v.1 no.1
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• pp.87-102
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• 1993

A $C^{\circ}$ continuous finite element formulation of a higher order displacement theory is presented for predicting linear and geometrically non-linear in the sense of von Karman transient responses of composite and sandwich plates. The displacement model accounts for non-linear cubic variation of tangential displacement components through the thickness of the laminate and the theory requires no shear correction coefficients. In the time domain, the explicit central difference integrator is used in conjunction with the special mass matrix diagonalization scheme which conserves the total mass of the element and included effects due to rotary inertia terms. The parametric effects of the time step, finite element mesh, lamination scheme and orthotropy on the linear and geometrically non-linear responses are investigated. Numerical results for central transverse deflection, stresses and stress resultants are presented for square/rectangular composite and sandwich plates under various boundary conditions and loadings and these are compared with the results from other sources. Some new results are also tabulated for future reference.

• Journal of the Korean Home Economics Association
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• v.43 no.3 s.205
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• pp.131-145
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• 2005

The purpose of the study was to determine ae forms, patterns and structures of Huipils as traditional clothes in Guatemala and Mexico, and to cite possibilities of applying the findings of the study, acquired by comparing the differences of the two countries' Huipils, to textile or costume design. There are two types of Huipils. One is for everyday wear and another one is for special occasion. The latter is bigger in size, more colorful and is worn on top of the daily use Huipil. Huipils consist of 1 to 3 panels, and are usually made by weaving rectangular cloth which has 4 selvedges. There are various neckline such as - type, T type, 1 type, round type and square type. The types of the neckline depends on how many panels are used. The Mexican Huipils are worn usually over skirts, whereas the Huipils of Guatemalans are practically designed with white cotton that doesn't have any patterns so as to be easily put into skirts. Different from Mexicans' Huipils which mainly show big botanical patterns, the patterns of Guatemalans' Huipils combine animals, plants and abstract concepts display mixed aspects, and it seems to me that that expressed their emotions and dearest wishes.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.9
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• pp.418-423
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• 2003

This paper describes an electronic compass using micromachined X- and Y-axis micro fluxgate sensors which were perpendicularly aligned each other to measure X- and Y-axis magnetic fields respectively. The fluxgate sensor was composed of rectangular-ring shaped magnetic core and solenoid excitation(49 turns) and pick-up(46 turns) coils. Excitation and pick-up coil patterns which were formed opposite to each other wound the magnetic core alternatively to improve the sensitivity and to excite the magnetic core in an optimal condition with reduced excitation current. The magnetic core has DC effective permeability of ~1000 and coercive field of ~0.1 Oe. The magnetic core is easily saturated due to the low coercive field and closed magnetic path for the excitation field. To decrease the difference of induced second harmonic voltages from X- and Y-axis, excitation condition of 2.8 $V_{P-P}$ and 1.2 MHz square wave was selected. Excellent linear response over the range of -100 $\mu$T to +100 $\mu$T was obtained with 210 V/T sensitivity. The size of each micro fluxgate sensor excluding pad region was about 2.6${\times}$1.7 $mm^2$ and the power consumption was estimated to be 14 mW.W.

• Journal of the Korean Ceramic Society
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• v.43 no.9 s.292
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• pp.519-526
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• 2006

A full-factorial design of experiments with three input factors and two levels for each factor including center points was utilized for the preparation and characterization of twelve types of $BaTiO_3$ slips for tape casting. Ceramic powders with different particle sizes, different milling methods such as high energy milling and conventional ball milling, and two types of dispersant with different polymeric species were chosen as input factors in order to investigate their effects on slip and on green tape properties. Tape casting, a small rectangular-shaped K-square preparation, characterization and quantitative data analysis using statistical software were followed. Ceramic powder was the most significant among three input factors for the output responses of slip viscosity and green tape density, showing more favorable results with large particles than with very fine ones. In addition, high energy milling for only 30 min was more efficient than 24h of conventional ball milling in terms of powder dispersion and milling. The optimum condition based on the experimental results was a slip exposed to high energy milling with large ceramic particles along with a methylethyl acetate dispersant.

• Journal of the Korean Society of Clothing and Textiles
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• v.48 no.3
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• pp.467-484
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• 2024

This study aimed to enhance the design of cropped t-shirts to improve fit satisfaction among women in their 20s by tailoring the t-shirts to diverse body types. Body types were categorized using Size Korea's 8th Human Body Measurement Data, and statistical analysis was conducted based on the Statistical Package for the Social Sciences (version 26.0). This study also reviewed the literature on t-shirts and fit, the application of pattern and design improvements for different body types, verifying fit and size for each body type, and applying virtual fit effects using geometric forms. Frequency analysis and non-parametric verification were conducted using the Friedman test. The results showed that t-shirts with a horizontal rectangular shape was an effective design and that t-shirts with an inverted triangular structure also had a positive effect. In contrast, square t-shirts exhibited minimal effectiveness. These findings are expected to contribute to the consideration of customized shapes according to body type in t-shirt design. Research on customized virtual cropped t-shirts reflecting various body types can expand fit satisfaction studies, particularly amid the increasing trend of online shopping.

• Journal of IKEEE
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• v.28 no.1
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• pp.20-25
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• 2024

This paper presents a new dualband shared-aperture microstrip antenna to operate in the S-Band of 2 GHz and X-Band of 8 GHz, for a Low Earth Orbit satellite antenna system. The proposed antenna incorporates two types of patches those are a rectangular loop-shaped for the S-Band and a square patch for the X-Band. Each patch are optimized for its respective operating band with minimal interference. The proposed antenna achieves a bandwidth of 16 MHz in the S-Band and 572 MHz in the X-Band. The highest gain is measured 7.14 dBi at 1.99 GHz and 7.95 dBi at 7.88 GHz. The proposed antenna exhibits half power beamwidths of 85 degree and 80 degree at 1.99 GHz and 7.88 GHz, respectively. The proposed dualband shared-aperture microstrip antenna may be a good candidate for as a feeding system of a dualband reflectarray antenna With its unidirectional radiation pattern from excellent agreement between simulation and measurement results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.445-454
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• 1991

In this thesis, Mindlin plate element with nine nodes and three degrees-of-freedom at each node is formulated and is employed in eigen-analysis of a rectangular plates in order to alleviate locking phenomenon of eigenvalues. Eigenvalues and their modes may be locked if conventional $C_{0}$-isoparametric element is used. In order to reduce stiffness locking phenomenon, two methods (1, the general reduced and selective integration, 2, the new element that use of modified shape function) are studied. Additionally in order to reduce the error due to mass matrix, two mass matrixes (1, Gauss-Legendre mass matrix, 2, Gauss-Lobatto mass matrix) are considered. The results of eigen-analysis for two models (the square plate with all edges simply-supported and all edges built-in), computed by two methods for stiffness matrix and by two mass matrixes are compared with theoretical solutions and conventional numerical solutions. These comparisons show that the performance of the two methods with Gauss-Lobatto mass matrix is better than that of the conventional plate element. But, by considering the spurious rigid body motions, the element which employs modified shape function with full integration and Gauss-Lobatto mass matrix can elevate the accuracy and convergence of numerical solutions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.10
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• pp.520-526
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• 2015

The characteristics of gas-liquid Taylor (Slug) flow in a square micro-channel of $600{\sim}600{{\mu}m}$ were investigated experimentally in this paper. The test fluids were nitrogen and water. The liquid and gas superficial velocities were 0.01~3 m/s and 0.1~3 m/s, respectively. Bubble and liquid slug length, bubble velocity, and frequency were measured by analyzing optical images using a high speed camera. Bubble length decreased with higher liquid flow rate, which increased dramatically with higher gas flow rate. However, slug length did not vary with changes in inlet liquid conditions. Additionally, bubble velocities and frequencies increased with higher liquid and gas flow rates. It was found that measured bubble lengths were in good agreement with the empirical models in the existing literature, but slug lengths were not.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.3
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• pp.313-321
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• 2012

Vibration analysis of a thin-walled structure can be performed with a consistent mass matrix determined by the shape functions of all degrees of freedom (d.o.f.) used for construction of conventional stiffness matrix, or with a lumped mass matrix. In similar way stability of a structure can be analysed with consistent geometric stiffness matrix or geometric stiffness matrix with lumped buckling load, related only to the rotational d.o.f. Recently, the simplified mass matrix is constructed employing shape functions of in-plane displacements for plate deflection. In this paper the same approach is used for construction of simplified geometric stiffness matrix. Beam element, and triangular and rectangular plate element are considered. Application of the new geometric stiffness is illustrated in the case of simply supported beam and square plate. The same problems are solved with consistent and lumped geometric stiffness matrix, and the obtained results are compared with the analytical solution. Also, a combination of simplified and lumped geometric stiffness matrix is analysed in order to increase accuracy of stability analysis.