• Journal of Power Electronics
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• v.18 no.3
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• pp.841-852
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• 2018

This paper presents a dual-algorithm search method (GWO-GSO) combining grey wolf optimization (GWO) and golden-section optimization (GSO) to realize maximum power point tracking (MPPT) for photovoltaic (PV) systems. First, a modified grey wolf optimization (MGWO) is activated for the global search. In conventional GWO, wolf leaders possess the same impact on decision-making. In this paper, the decision weights of wolf leaders are automatically adjusted with hunting progression, which is conducive to accelerating hunting. At the later stage, the algorithm is switched to GSO for the local search, which play a critical role in avoiding unnecessary search and reducing the tracking time. Additionally, a novel restart judgment based on the quasi-slope of the power-voltage curve is introduced to enhance the reliability of MPPT systems. Simulation and experiment results demonstrate that the proposed algorithm can track the global maximum power point (MPP) swiftly and reliably with higher accuracy under various conditions.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.911-922
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• 2005

A theoretical study was performed to investigate the behavioral chracteristics and shear strength of fiber reinforced concrete slender beams. In the fiber reinforced concrete beam, the shear force applied to a cross section of the beam was resisted by both compressive zone and tensile zone. The shear capacity of the compressive zone was defined addressing the interaction with the normal stresses developed by the flexural moment in the cross section. The shear capacity of the tensile zone was defined addressing the post-cracking tensile strength of fiber reinforced concrete. Since the magnitude and distribution of the normal stresses vary according to the flexural deformation of the beam, the shear capacity of the beam was defined as a function of the flexural deformation of the beam. The shear strength of the beam and the location of the critical section were determined at the intersection between the shear capacity and shear demand curves. The proposed method was developed as a unified shear design method which is applicable to conventional reinforced concrete as well as fiber reinforced concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.201-204
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• 2008

The Sectional Design Model(AASHTO LRFD) is appropriate for the design of typical bridge girders, slabs, and other regions of components where the assumptions of traditional engineering beam theory are valid. The shear resistance of a concrete member may be separated into a component, $V_c$, that relies on tensile stresses in the concrete, $V_s$, that relies on tensile stresses in the transverse reinforcement. The expressions for $V_c$ and $V_s$ apply to both prestressed and nonprestressed section, with the terms ${\beta}$ and ${\theta}$ depending on the applied loading(M, V, N, and T) and the properties of the section. With ${\beta}$ taken as 2.0 and ${\theta}$ as 45$^{\circ}$, the expressions for shear strength become essentially identical to those traditionally used for evaluating shear resistance. Recent large-scale experiments, however, have demonstrated that these traditional expression can be seriously unconservative for large members not containing transverse reinforcement. And This paper can present only a brief introduction to shear design of AASHTO LRFD and is to review of the technical difficulty.

• Advanced Composite Materials
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• v.17 no.1
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• pp.1-23
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• 2008

Robotized filament winding technology involves a robot that winds a roving impregnated by resin on a die along the directions of stresses to which the work-piece is submitted in applications. The robot moves a deposition head along a winding trajectory in order to deposit roving. The trajectory planning is a very critical aspect of robotized filament winding technology, since it is responsible for both the tension constancy and the winding time. The present work shows two original rules to plan the winding trajectory of structural parts, whose shape is obtained by sweeping a full section around a 3D curve that must be closed and not crossing in order to assure a continuous winding. The first rule plans the winding trajectory by approximating the part 3D shape with straight lines; it is called the discretized rule. The second rule defines the winding trajectory simply by offsetting a 3D curve that reproduces the part 3D shape, of a defined distance; it is called the offset rule. The two rules have been compared in terms of roving tension and winding time. The present work shows how the offset rule enables achievement of both the required aims: to manufacture parts of high structural performances by keeping the tension on the roving near to the nominal value and to markedly decrease the winding time. This is the first step towards the optimization of the robotized filament winding technology.

• Steel and Composite Structures
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• v.34 no.1
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• pp.123-139
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• 2020

The tube outward local buckling of Concrete-Filled Steel Tube (CFST) beam under high compression stress is still considered a critical problem, especially for steel tubes with a slender section compared to semi-compact and compact sections. In this study, the flexural performance of stiffened slender cold-formed square tube beams filled with normal concrete was investigated. Fourteen (14) simply supported CFST specimens were tested under static bending loads, stiffened with different shapes and numbers of steel stiffeners that were provided at the inner sides of the tubes. Additional finite element (FE) CFST models were developed to further investigate the influence of using internal stiffeners with varied thickness. The results of tests and FE analyses indicated that the onset of local buckling, that occurs at the top half of the stiffened CFST beam's cross-section at mid-span was substantially restricted to a smaller region. Generally, it was also observed that, due to increased steel area provided by the stiffeners, the bending capacity, flexural stiffness and energy absorption index of the stiffened beams were significantly improved. The average bending capacity and the initial flexural stiffness of the stiffened specimens for the various shapes, single stiffener situations have increased of about 25% and 39%, respectively. These improvements went up to 45% and 60%, for the double stiffeners situations. Moreover, the bending capacity and the flexural stiffness values obtained from the experimental tests and FE analyses validated well with the values computed from equations of the existing standards.

• Journal of Institute of Control, Robotics and Systems
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• v.15 no.9
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• pp.877-880
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• 2009

A curing process in post-printing section of R2R process is required for an electrical property of the printed pattern when devices such as RFID, Solar cell are printed. PEN as well as heat-stabilized PET which is used as a plastic substrate would be deformed at high temperature due to change of its elastic modulus. And crack in the printed pattern, which is on the plastic substrate is occurred due to the deformation of the substrate. The occurrence of crack causes electrical resistance to increase and the quality of the device to deteriorate. In case of RFID antenna, the range of reading distance is shortened as the electrical resistance of the antenna is increased. Therefore, the deformation of the plastic substrate, which causes the occurrence of crack, should be minimized by setting up low operating tension in R2R process. In low tension, slippage between a moving substrate and a roller would be generated when the operating speed is increased. And scratch would be occurred when slippage is generated due to an air entrainment, which is related to the thickness of the air film. The thickness of the air film is increased when operating speed is increased as shown by simulation based on mathematical model. The occurrence of scratch in conductive pattern printed by roll to roll process is a critical damage because it causes degradation or failure of electrical property of it.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.457-464
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• 2006

Fiber-reinforced composite materials due to their high specific strength, high stiffness and light weight are becoming increasingly used in many engineering industry, especially in the aerospace, marin and civil, etc. In this paper, the buckling load and mode shapes of composite laminates with elliptical cross-section including transverse shear deformations are analyzed. For solving this problems, a versatile flat shell element has been developed by combining a membrane element with drilling degree-of-freedom and a plate bending element. Also, an improved shell element has been established by the combined use of the addition of enhanced assumed strain and the substitute shear strain fields. The combined influence of shell geometry and elliptical cross-sectional parameter, fiber angle, and lay-up on the buckling loads of elliptical cylinder is examined. The critical buckling loads and mode shapes analyzed here may serve as a benchmark for future investigations.

• Journal of the Korea Society of Computer and Information
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• v.25 no.9
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• pp.193-201
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• 2020

In this study, we developed a simulation app that performs the Test-and-Set algorithm. The test-and-set algorithm is a highly difficult algorithm, so this simulation app was created for learners who have difficulty understanding it. Learners who want to understand the Test-and-Set algorithm gather to form a team, and use this simulation app to discuss and practice, and these teams can practice at the same time. The test-and-set, which is assumed to be a machine language, is not interrupted by using a queue, and it can be seen that the configured simulation app performs well in all three conditions of 'mutual exclusion', 'progress', and 'bounded waiting' that must be solved in the critical area problem.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.375-375
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• 2009

For many large-scale applications of high-temperature superconducting materials, large critical current density($J_c$) in high applied magnetic fields are required. A number of methods have been reported to introduce artificial pinning centers(APCs) in $YBa_2Cu_3O_{7-\delta}$(YBCO) films for enhancement of their $J_c$. We report measurements of critical current in $YBa_2Cu_3O_{7-\delta}$ films deposited by PLD on $SrTiO_3$ substrates decorated with Au nanoparticles. Au nanoparticles were synthesized on STO substrates with self assembled monolayer. Microstructural analysis of the obtained YBCO films was performed by using cross-section transmission electron microscopy(TEM). Phase and textural analysis was done using X-ray diffraction. The surface morphology and surface roughness(Ra) of the layers was measured by atomic force microscopy(AFM).

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.3
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• pp.251-258
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• 2014

Sunroof tracks are manufactured by press-forming extruded aluminum sheets. During press forming, cracking occurs along the sharply bent edge. The final positions of the punch and die were measured on the section, and their relation to cracking was investigated. Finite element simulation of bending to the final position was done to find the critical strains. Three-point bending tests with different material orientations, hardnesses, bending edge lengths, and bending radii were carried out in the laboratory, and finite element simulation of the three-point bending tests was performed to find the critical strains.