• 수산해양기술연구
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• 제55권1호
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• pp.62-73
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• 2019

Recently, copper alloy netting has been proposed as a material for aquaculture facilities that can be set in harsh offshore environments. To design a cage made of copper alloy netting, it is necessary to calculate the flow of water through the netting and force of external sources on the netting. Therefore, this study measured and analyzed the current velocity reduction after passing through the netting and the hydrodynamic forces acting on the netting using copper alloy netting with nine solidity ratios. As a result of the reduction rate of the flow velocity through the netting, the flow reduction rate was increased as the solidity ratio of netting was increased. The flow reduction rate was also increased as the attack angle on the netting was decreased. In analyzing the resistance on the netting, we also discovered that resistance was increased with increase in the flow velocity and solidity ratio. An analysis of the hydrodynamic coefficient acting on the netting is shown that the drag coefficient tends to increase as the attack angle increases. We also analyzed the hydrodynamic coefficient according to the variation of the Reynolds number. When the drag coefficients acting on the netting were analyzed with the different Reynolds numbers, the Reynolds number increased from over 0.3 m/s to a relative constant. Finally, the copper alloy nettings had a smaller velocity reduction rate when comparing the flow velocity reduction rate between copper alloy nettings and nylon nettings.

• 대한물리의학회지
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• 제8권4호
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• pp.567-571
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• 2013

PURPOSE: This study find out the effect of torque and power through various solidity of mouth guard on shoulder flexion and extension. METHODS: This study was conducted with healthy adults in their 20s Korean. Cybex system was used to measure the torque and power fo shoulder joint flexion/extension during isokinetic contraction when the various solidity mouth guard was used and no mouth guard was used. RESULT: The results of this study were summarized as follows: relative torque and average power was showed significantly difference between non applying mouth guard and applying hard type mouth guard during shoulder flexion and extension at isokinetic contraction. CONCLUSION: The application of hard type mouth guard was increased torque and power in joint of body. which may be clinically useful.

• Steel and Composite Structures
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• 제21권4호
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• pp.775-789
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• 2016

This paper presents the flexural behavior & ultimate strength performance of innovative light weight sandwich panels of size $3{\times}1.2m$ with two different solidity ratios viz. 0.5 and 0.33 under out of plane bending load. From the experimental studies, it is observed that the flexural strength and the stiffness are increased by about 46% and five folds for lesser solidity ratio case. From the measured strains of the shear connectors, full shear transfer between the concrete wythes is observed. The yielding occurred approximately at 4% and 0.55% of the ultimate deformation for 100 mm & 150 mm thick panels, which shows the large ductility characteristics of the panels. From the study, it is inferred that the light weight sandwich panels behave structurally in a very similar manner to reinforced concrete panels. Further from the numerical study, it is observed that the numerical values obtained by FE analysis are in good agreement with the experimental observations.

• International journal of advanced smart convergence
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• 제9권2호
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• pp.157-163
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• 2020

Recently the blockchain technology has been actively studied due to its great potentiality. The smart contract is a key mechanism of the blockchain system. Due to the short history of the smart contract, many issues have not been solved yet. One main issue is vulnerability and another main issue is cost optimization. While the vulnerability of smart contract has been actively studied, the cost optimization has been rarely studied. In this paper, we propose two cost optimization methods for smart contracts running on the blockchain system. Triggering a function in a smart contract program code may require costs and it is repeated continuously. So the minimization of costs required to trigger a function of smart contract while maintaining the performance equally is very important. The proposed two methods minimize the usage of expensive permanent variables deployed on the blockchain system. We apply the proposed two methods to three prevalent blockchain platforms: Ethereum, Klaytn and Tron. Evaluation experiments verify that the proposed scheme significantly reduces the costs of functions in the smart contract written with Solidity.

• Wind and Structures
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• 제14권1호
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• pp.1-14
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• 2011

Open frame structures, such as those commonly found in industrial process facilities, are often densely occupied with process related equipment. This paper presents a method for estimating wind loads for high-solidity open frame structures that differs from current approaches, which accumulate wind load contributions from various individual structure components. The method considers the structure as a porous block of arbitrary plan dimension that is subject to wind from any direction. The proposed method compares favorably with wind tunnel test results for similar structures. The possibility of defining an upper bound force coefficient is also discussed.

• 한국강구조학회 논문집
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• 제23권1호
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• pp.73-81
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• 2011

골조로 구성된 철탑의 풍력계수는 구성부재의 단면형상, 충실율 등에 의해 변하며 풍향각에 의해서도 여러 가지 특성이 나타난다. 본 연구에서는 이러한 철탑골조에 대하여 충실율과 풍향각을 변화시키면서 풍동실험을 수행하여 철탑골조에 작용하는 풍력특성을 평가한다. 실험은 먼저 철탑을 구성하고 있는 부재의 특성을 파악하기 위한 기본형상 부재에 대한 실험을 수행하였다. 그리고 철탑 사각골조는 2D와 3D 형태로 기본형에 철탑부재를 추가하는 방법과, 부재크기를 증가시키는 방법으로 충실율을 변화시킨 모형을 제작하였으며, 2D 형상은 풍향각을 0도에서 90도까지, 3D 형상은 풍향각을 0도에서 45도까지 변화시키면서 풍동실험을 수행하였다. 본 연구의 결과인 철탑 사각골조의 풍력계수 특성은 향후 철탑 풍하중 설계의 기초자료로 사용될 것이다.

• 대한기계학회논문집B
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• 제25권5호
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• pp.722-730
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• 2001

The local heat transfer of an axisymmetric submerged air jet impinging on a heated flat plate is investigated experimentally with the variation of mesh-screen solidity. The screen installed in front of the nozzle exit modifies the flow structure and local heat transfer characteristics. The mean velocity and turbulence intensity profiles of streamwise velocity component are measured using a hot-wire anemometry. The temperature distribution on the heated flat surface is measured with thermocouples. The smoke-wire flow visualization technique was employed to understand the near-field flow structure qualitatively for different mesh screens. Large-scale toroidal vortices and high turbulence intensity enhance the heat transfer rate in the stagnation region. For a higher solidity, turbulence intensity become higher which increases the local heat transfer at small nozzle-to-plate spacings such as L/D<6. The local and average Nusselt numbers of impinging jet from the $\sigma$(sub)s=0.83 screen at L/D=2 are about 5.6∼7.5% and 7.1% larger than those for the case of no screen, respectively. For the nozzle-to-plate spacings larger than 6, however, the turbulence intensities for all tested screens approach to an asymptotic curve and the mean velocity along the jet centerline decreases monotonically. As the nozzle-to-plat spacing increases for high solidity screens, the heat transfer rate decreases due to the reduction in turbulence intensity and jet momentum.

• Wind and Structures
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• 제36권2호
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• pp.91-103
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• 2023

Tuned liquid dampers (TLDs) are increasingly being used as efficient dynamic vibration absorbers to mitigate wind-induced vibration in super high-rise buildings. However, the damping characteristics of screens and the control effectiveness of actual structures must be investigated to improve the reliability of TLDs in engineering applications. In this study, a numerical TLD model is developed using computational fluid dynamics (CFD) and a simulation method for achieving the coupled vibration of the structure and TLD is proposed. The numerical results are verified using shaking table tests, and the effects of the solidity ratio and screen position on the TLD damping ratios are investigated. The TLD control effectiveness is obtained by simulating the wind-induced vibration response of a full-scale structure-TLD system to determine the optimal screen solidity ratio. The effects of the structural frequency, damping ratio, and wind load amplitude on the TLD performance are further analyzed. The TLD damping ratio increases nonlinearly with the solidity ratio, and it increases with the screens towards the tank center and then decreases slightly owing to the hydrodynamic interaction between screens. Full-scale coupled simulations demonstrated that the optimal TLD control effectiveness was achieved when the solidity ratio was 0.46. In addition, structural frequency shifts can significantly weaken the TLD performance. The control effectiveness decreases with an increase in the structural damping ratio, and is insensitive to the wind load amplitude within a certain range, implying that the TLD has a stable damping performance over a range of wind speed variations.

• 말소리와 음성과학
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• 제4권3호
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• pp.3-12
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• 2012

The primary goal of the current study was to examine category solidity of Korean alveolar fricatives in the Busan and Seoul dialects of Korean. Considering the common belief of $/s^h/-/s^*/$ neutralization in Kyungsang speech, plain $/s^h/$ and fortis $/s^*/$ fricatives of Busan speakers were examined against the same fricatives of Seoul speakers. Perceptual distance between Korean $/s^h/$ and $/s^*/$ on the one hand and English /s/ on the other was investigated by use of across-linguistic mapping method. Two experiments of a perceptual mapping task of English /s/ to Korean $/s^h/$ and $/s^*/$ and a $/s^*/$-production task were conducted on users of the Busan and Seoul dialects of Korean. The results from the perception and production experiments suggested that at a micro-level, younger Busan speakers have less solid category stability for Korean $/s^*/$ compared with Seoul speakers, although their production of $/s^h/$ and $/s^*/$ was as highly distinctive from each other as that of Seoul speakers.

• International Journal of Fluid Machinery and Systems
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• 제3권3호
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• pp.260-270
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• 2010

Reducing the losses of the tip clearance flow is one of the keys in an unshrouded centrifugal compressor design and development because tip clearances are large in relation to the span of the blades and also centrifugal compressors produce a sufficiently large pressure rise in single stage. This problem is more acute for a low flow high-pressure ratio impeller design. The large tip clearance would cause flow separations, and as a result it would drop both the efficiency and surge margin. Thus a design of a high efficiency and wide operation range low flow coefficient centrifugal compressor is a great challenge. This paper describes a recent development of high efficiency and wide surge margin low flow coefficient centrifugal compressor. A viscous turbomachinery optimal design method developed by the authors for axial flow machine was further extended and used in the centrifugal compressor design. The compressor has three main parts: impeller, a low solidity diffuser and volute. The tip clearance is under a special consideration in this design to allow impeller insensitiveness to the clearance. A patented three-dimensional low solidity diffuser design method is used and applied to this design. The compressor test results demonstrated to be successful to extend the low solidity diffusers to high-pressure ratio compressor. The compressor stage performance showed the total to static efficiency of the compressor being about 85% and stability range over 35%. The test results are in good agreement with the design.