• Magazine of the Korean Society of Agricultural Engineers
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• v.34 no.1
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• pp.78-86
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• 1992

This paper aims at investigating the effect of steel ratio and the magnitude of edge-ratio on the mechanical characteristics of reinforced concrete ring sector plate. The influence of steel bars was taken into account by coupling stiffness matrix of the steel bar element with that of the concrete plate element without dealing with separate element of steel bar and by establishing the composite stiffness matrix, which leads to the desirable result which does not increase th number of element could be obtained. Through case studies with 6 cases various steel ratios in ring sector plate supported at four edges and 4 cases with different open angles, the influence of the steel ratio was examined. A numerical analysis to find out the effect of the steel ratio d ue to above mentioned cases was carried out by 4 boundary conditions ; all edges clamped (B.C-1), all edges simply supported (B.C-2), curvilinear two edges clamped and other edges free (B.C-3) and curvilinear two edges simply supported and other edges free(B.C-4). The main results obtained are summarized as follows : 1. The effect of steel ratio on the magnitude of lateral deflection and x-directional bending moment at the center of sector plate and the midpoint of outer and inner curvilinear edges is almost the same up to $30^{\circ}$ of open angle. Beyond $30^{\circ}$ of the angle, the larger the angle, the greater the effect of ratio. 2. In design works using balanced steel ratio, the effect of steel bar can be ignored. But for larger open angles, especially greater than $90^{\circ}$, it proves desirable to consider the effect of steel bar. 3. The effect of the arc length of center circle/straight edge on lateral deflection and bending moment is remarkable in B.C-2. For larger open angle, the effect is also noted except for B.C-3 which turn out hardly affected. 4. The effect of the radius of curvature/straight side length on lateral deflection and x-directional bending moment is noted in B.C-2. As open angle increases, B.C-1 and B.C-3 almost agree and B.C-2 approaches B.C-4.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.3
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• pp.289-294
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• 2012

There are several indicators to represent characteristics of chemical mechanical planarization (CMP) such as material removal rate (MRR), surface quality and removal uniformity on a wafer surface. Especially, the removal uniformity on the wafer edge is one of the most important issues since it gives a significant impact on the yield of chip production on a wafer. Non-uniform removal rate at the wafer edge (edge effect) is mainly induced by a non-uniform pressure from nonuniform pad curvature during CMP process, resulting in edge exclusion which means the region that cannot be made to a chip. For this reason, authors tried to minimize the edge exclusion by using an edge profile control (EPC) ring. The EPC ring is equipped on the polishing head with the wafer to protect a wafer from the edge effect. Experimental results showed that the EPC ring could dramatically minimize the edge exclusion of the wafer. This study shows a possibility to improve the yield of chip production without special design changes of the CMP equipment.

• Journal of Sensor Science and Technology
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• v.25 no.1
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• pp.57-64
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• 2016

To understand a two-phase flow, a liquid film thickness is one of the important factors. A lot of researches have been performed to measure liquid film thickness with various approaches. Recently, an electrical conductance method which uses the conductivity of the liquid film has been widely applied on measuring the liquid film thickness. Though the electrical method has an advantage in high spatial resolution, as the conductivity of liquid can be affected by its temperature variation, the conventional electrical conductance methods have a limitation in being applied on varying temperature conditions where a heat transfer is involved. The purpose of this study is to develop a three-ring liquid film sensor that overcomes the limitation of the conventional method. The three-ring conductance method can measure the film thickness regardless of temperature variation by compensating the change of liquid conductivity. Considering its application on a wide range of conditions such as high temperature or curved surfaces, the sensor was fabricated on flexible printed circuit board (FPCB) in this study. This paper presents the concept of the measurement method, design procedure, prototype sensor fabrication and calibration results.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.11
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• pp.2526-2533
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• 2015

In this paper, a design method for a compact dual-band coplanar waveguide-fed slot antenna using SRR(split-ring resonator) conductor is studied. The SRR conductor is loaded inside a rectangular slot of the proposed antenna for dual-band operation. When the SRR conductor is inserted into the slot, the original rectangular slot is divided into a rectangular loop region and a rectangular slot region, and frequency bands are created by the loop and slot, separately. A prototype of the proposed dual-band slot antenna operating at 2.45 GHz WLAN band and 3.40-5.35 GHz band is fabricated on an FR4 substrate with a dimension of 30 mm by 30 mm. Experiment results show that the antenna has a desired impedance characteristic with a frequency band of 2.38-2.51 GHz and 3.32-5.38 GHz for a voltage standing wave < 2, and measured gain is 1.7 dBi at 2.45 GHz, and it ranges 2.4-3.2 dBi in the second band.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.8
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• pp.1745-1751
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• 2010

In this paper, a small broadband dipole antenna that simultaneously satisfies DCS1800/PCS/WCDMA/WLAN is designed and fabricated. To reduce the size and to improve the bandwidth of planar microstrip dipole antenna, a new symmetric double-ring radiator structure is used. An antenna can be reduced with increasing effective current length of dipole, and can be obtained a wide band impedance characteristic with decreasing reactance component by using a novel symmetrical double-ring structure. The proposed antenna shows broadband characteristic of 1.07GHz(52%) from 1.5GHz to 2.57GHz with VSWR < 2 (${\leq}-10dB$).

• Structural Monitoring and Maintenance
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• v.8 no.4
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• pp.345-360
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• 2021

This paper presents an analytical approach to calculate the buckling load of the cylindrical ring structures subjected to both hydrostatic and hydrodynamic pressures. Based on the conservative law of energy and Timoshenko beam theory, a theoretical formula, which can be used to evaluate the critical pressure of buckling, is first derived for the simplified cylindrical ring structures. It is assumed that the hydrodynamic pressure can be treated as an equivalent hydrostatic pressure as a cosine function along the perimeter while the thickness ratio is limited to 0.2. Note that this paper limits the deformed shape of the cylindrical ring structures to an elliptical shape. The proposed analytical solutions are then compared with the numerical simulations. The critical pressure is evaluated in this study considering two possible failure modes: ultimate failure and buckling failure. The results show that the proposed analytical solutions can correctly predict the critical pressure for both failure modes. However, it is not recommended to be used when the hydrostatic pressure is low or medium (less than 80% of the critical pressure) as the analytical solutions underestimate the critical pressure especially when the ultimate failure mode occurs. This implies that the proposed solutions can still be used properly when the subsea vehicles are located in the deep parts of the ocean where the hydrostatic pressure is high. The finding will further help improve the geometric design of subsea vehicles against both hydrostatic and hydrodynamic pressures to enhance its strength and stability when it moves underwater. It will also help to control the speed of the subsea vehicles especially they move close to the sea bottom to prevent a catastrophic failure.

• Journal of Aerospace System Engineering
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• v.16 no.4
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• pp.68-76
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• 2022

The purpose of this paper was to design the cable networks for mesh reflector antennas, considering the flexibility of structures. An effective form-find methodology is proposed. The whole parts of the cable networks are described by the absolute nodal coordinate formulation. Additionally, nonlinear deformation of the cable can be obtained. The form-finding analysis of the reflector with standard configuration is performed, to validate the proposed methodology. The truss ring structure is numerically modeled using the frame elements. To consider the flexibility of the truss ring as well as the cable net structure, an iteration analysis between the truss ring and the cable net under tensional forces is also performed in the form-finding process. The finial configuration of the reflector with tensioned cable networks is demonstrated.

• Journal of Aerospace System Engineering
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• v.1 no.1
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• pp.36-44
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• 2007

This study was performed on preliminary structural design of a small scale WIG craft which has been developed as a next generation high speed maritime transportation system in Korea. A composite structure design using the foam-sandwich for main wing and tail fins and the honeycomb sandwich and skin-stringer-ring frame for fuselage was applied for weight reduction as well as structural stability. A commercial FEM code, NASTRAN for was utilized to confirm the structural safety for the reiterate design modifications to meet design requirements including the target weight. Each main wing was jointed with the fuselage by eight high strength insert bolts for easy assembling and disassembling as well as for assuring the required 20 years service life. For control surface structural design, the channel type spar, the foam sandwich skin and the lug joint were adopted.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.631-636
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• 2008

The cylindrical shells are mainly used in the nuclear energy structure, pressure vessel, boiler and so on. When designing of shell structures, predicting the structure change under variety boundary conditions are necessary for estimating the safety. Design variables for the design engineer include multiple material systems and boundary conditions, in addition to overall structural design parameters. Since the vibration of stiffened cylindrical shell is an important consideration for structures design, the reliable prediction method and design methodology should be required. In this study, the optimum design of stiffened cylindrical shell for maximum natural frequency was studied by analytic and numerical method.

• Clean Technology
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• v.26 no.2
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• pp.102-108
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• 2020

In recent years, packed column has been widely used in separation processes, such as absorption, desorption, distillation, and extraction, in the petrochemical, fine chemistry, and environmental industries. Packed column is used as a contacting facility for gas-liquid and liquid-liquid systems filled with random packed materials in the column. Packed column has various advantages such as low pressure drop, economical efficiency, thermally sensitive liquids, easy repairing restoration, and noxious gas treatment. The performance of a packed column is highly dependent on the maintenance of good gas and liquid distribution throughout a packed bed; thus, this is an important consideration in a design of packed column. In this study, hydraulic pressure drop, hold-up as a function of liquid load, and mass transfer in the air, air/water, and air-NH₃/water systems were studied to find the geometrical characteristic for raschig super-ring experiment dry pressure drop. Based on the results, design factors and operating conditions to handle noxious gases were obtained. The dry pressure drop of the random packing raschig super-ring was linearly increased as a function of gas capacity factor with various liquid loads in the Air/Water system. This result is lower than that of 35 mm Pall-ring, which is most commonly used in the industrial field. Also, it can be found that the hydraulic pressure drop of raschig super-ring is consistently increased by gas capacity factor with various liquid loads. When gas capacity factor with various liquid loads is increased from 1.855 to 2.323 kg^-1/2 m^-1/2 S^-1, hydraulic pressure drop increases around 17%. Finally, the liquid hold-up related to packing volume, which is a parameter of specific liquid load depending on gas capacity factor, shows consistent increase by around 3.84 kg^-1/2 m^-1/2 S^-1 of the gas capacity factor. However, liquid hold-up significantly increases above it.