• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.70-77
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• 2004

Comprehensive investigation on the outlet's geometric shapes of a centrifugal blower with higher inlet resistance than an atmospheric pressure is carried out for improvements of its performance. Most unwanted behaviors of such blower are pulsating flows because of unbalance between inflows and outflows in a scroll casing. In order to reduce this undesirable phenomenon a triump is made for both the shape of outlet duct and an accessory structure inserted in the outlet port of the blower. The modification on the shape is concerned with the contraction of cross sectional area and the attached structure is for an intentional obstruction to cause a flow resistance. The details of the modification are examined for different cases and results. The methodologies for the work are performance evaluations including noise level and velocity measurements with PIV Consequently, the performance of improved system is close to that of the system operating with atmospheric pressure at the inlet.

• Current Optics and Photonics
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• v.1 no.2
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• pp.113-117
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• 2017

With the increasing use of high-power laser diode bars (LDBs) and stacked LDBs, the issue of thermal control has become critical, as temperature is related to device efficiency and lifetime, as well as to beam quality. To improve the thermal resistance of an LDB set, we propose and analyze a bypass heat sink with a top canopy structure for an LDB set, instead of adopting a thick submount. The thermal bypassing in the top-canopy structure is efficient, as it avoids the cross-sectional thermal saturation that may exist in a thick submount. The efficient thickness range of the submount in a typical LDB set is guided by the thermal resistance as a function of thickness, and the simulated bypassing efficiency of a canopy is higher than a simple analytical prediction, especially for thinner canopies.

• Journal of Power System Engineering
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• v.14 no.5
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• pp.48-55
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• 2010

When a large ship is advancing in waves, ship undergoes the hydroelastic response, which has influences on structural stability and the fatigue destruction etc. of the ship. Therefore, to predict accurate hydroelastic response, it is necessary to analyze hydroelastic response including fluid-structure interaction. In this research, a ship is divided into many hull elements to calculate the fluid forces and wave exciting forces on each elements using three-dimensional source distribution method. The calculated fluid forces and wave exciting forces are assigned to nodes of hull elements. The neighbor nodes are connected with elastic beam elements. We analyzed hydroelastic responses, and those are formulated by using finite element method. Particularly, to estimate the influence of forward speed on the hydroelastic responses, we use two different methods : Full Hull Rotation Method(FHRM) and Sectional Hull Rotation Method(SHRM).

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.75-78
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• 2004

Traditionally aluminum alloy have been used in manufacturing of aircraft structures, and semi-monocoque structural concept have been mainly applied in structural design of fuselage and wing. However, recently monocoque structural concept is applied in many small-size aircraft structures manufactured with composite materials. In such case appling monocoque structural concept, in initial conceptual design stage on wing, it is not easy to analyze shear flow using classical shear flow analytical method because composite skin structure can support span-wise tension/compression stress as well as sectional shear stress. In this study, an extended shear-flow analytical method to apply to composite monocoque structural concept was developed through extending the classical shear-flow analytical method.

• Steel and Composite Structures
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• v.13 no.3
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• pp.225-238
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• 2012

Steel structural elements with web-tapered I cross section, are usually made of welded thin plates. Due to the nonrectangular shape of the element, thin web section may be obtained at the maximum cross section height. The buckling strength is directly influenced by lateral restraining, end support and initial imperfections. If no lateral restraints, or when they are not effective enough, the global behaviour of the members is characterized by the lateral torsional mode and interaction with sectional buckling modes may occur. Actual design codes do not provide a practical design approach for this kind of elements. The paper summarizes an experimental study performed by the authors on a relevant number of elements of this type. The purpose of the work was to evaluate the actual behaviour of the web tapered beam-columns when applying different types of lateral restraints and different web thickness.

• Wind and Structures
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• v.16 no.5
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• pp.457-476
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• 2013

This paper presents theoretical background for a semi-empirical, mathematical model of critical vortex excitation of slender structures of compact cross-sections. The model can be applied to slender tower-like structures (chimneys, towers), and to slender elements of structures (masts, pylons, cables). Many empirical formulas describing across-wind load at vortex excitation depending on several flow parameters, Reynolds number range, structure geometry and lock-in phenomenon can be found in literature. The aim of this paper is to demonstrate mathematical background of the vortex excitation model for a theoretical case of the structure section. Extrapolation of the mathematical model for the application to real structures is also presented. Considerations are devoted to various cases of wind flow (steady and unsteady), ranges of Reynolds number and lateral vibrations of structures or their absence. Numerical implementation of the model with application to real structures is also proposed.

• Journal of Navigation and Port Research
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• v.31 no.9
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• pp.785-791
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• 2007

In this paper we proposed a model that the deformation of the submerged rubble mound breakwaters composed with materials of various size, induced by wave action, can be computed. The water particle kinematics by waves in porous mound structure are computed by CADMAS-SURF, then the deformation of structure is computed using DEM module. To investigate the interaction of wave and sectional deformation of structures, analysis is accomplished by two steps. Analysis at the first step is executed with incipient mound. And analysis at the second step is executed with deformed mound by wave action. Furthermore, behaviors of materials are influenced by various properties such as the contact stiffness and the friction angle. Therefore, in order to present the behavior of the element caused by various properties, computations are accomplished with random coefficients by using the Monte Carlo simulation.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.10
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• pp.670-675
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• 2015

Degradation diagnosis of cable is one of major issues for operation and maintenance in overhead distribution power lines. The diagnostic system for overhead power lines is composed of three parts in functional aspect - a travelling unit, a sensing unit and a communication unit. Among them, sensor detects the defects such as corrosion and disconnecting of power lines. Performance of sensor is very important, and besides, the size and structure of sensor is restricted for installation to small and lightweight diagnostic system. This paper suggests an optimal eddy current sensor best suit for small and lightweight diagnostic system in consideration of detecting performance, size and ease of installation and so on. Proposed sensor has been designed by Drum core structure and can be applied to the all domestic overhead power lines regardless of the cross-sectional areas. Also, it is showed that results of mock environmental test are satisfied.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.4
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• pp.64-72
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• 1995

Sizing design sensitivity analysis of structures subjected to the harmonic vibration is performed using adjoint variable method. Constraint is the stress and sizing design variables are thickness, bending moment of inertia, and cross-sectional area of structures. Accurate sensitivities are computed and plotted sensitivity can be used as a design guidance tool. The accuracy of sensitivities is verified by the finite difference values. Also, optimal design of three-bar structure is performed using the computed sensitivity and feasible direction method while satisfying constraints and obtaining the minimum weight.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.5
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• pp.472-481
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• 2008

In this study hydraulic experiment was carried out to investigate the flow characteristics in the submerged outlet structure of Boryeong power plant and the efficiency of bubble reduction by installing horizontal porous plate in the outlet structure. The cross-sectional mean velocity in the submerged outlet structure was smaller than 1 m/s, the target value at the design stage to prevent bubble outflow to the open sea area. In addition, it was found that the maximum depth of bubble penetration is reduced 30 to 50% by installing the horizontal porous plate at the second falling location in the submerged outlet structure. It is expected that the total bubble amount entrained in the water will be most efficiently reduced by installing square-hole-shape porous plate of 20 cm hole size and making its central section as non-porous structure to dissipate the energy of falling water.