• Steel and Composite Structures
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• v.44 no.4
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• pp.503-517
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• 2022

This paper presents the mechanical buckling of bi-directional functionally graded sandwich beams (BFGSW) with various boundary conditions employing a quasi-3D beam theory, including an integral term in the displacement field, which reduces the number of unknowns and governing equations. The beams are composed of three layers. The core is made from two constituents and varies across the thickness; however, the covering layers of the beams are made of bidirectional functionally graded material (BFGSW) and vary smoothly along the beam length and thickness directions. The power gradation model is considered to estimate the variation of material properties. The used formulation reflects the transverse shear effect and uses only three variables without including the correction factor used in the first shear deformation theory (FSDT) proposed by Timoshenko. The principle of virtual forces is used to obtain stability equations. Moreover, the impacts of the control of the power-law index, layer thickness ratio, length-to-depth ratio, and boundary conditions on buckling response are demonstrated. Our contribution in the present work is applying an analytical solution to investigate the stability behavior of bidirectional FG sandwich beams under various boundary conditions.

• Steel and Composite Structures
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• v.44 no.4
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• pp.451-471
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• 2022

In the present paper, the static bending and buckling responses of functionally graded carbon nanotubes-reinforced composite (FG-CNTRC) beam under various boundary conditions are investigated within the framework of higher shear deformation theory. The significant feature of the proposed theory is that it provides an accurate parabolic distribution of transverse shear stress through the thickness satisfying the traction-free boundary conditions needless of any shear correction factor. Uniform (UD) and four graded distributions of CNTs which are FG-O, FG-X, FG- and FG-V are selected here for the analysis. The effective material properties of FG-CNTRC beams are estimated according to the rule of mixture. To model the FG-CNTRC beam realistically, an efficient Hermite-Lagrangian finite element formulation is successfully developed. The accuracy and efficiency of the present model are demonstrated by comparison with published benchmark results. Moreover, comprehensive numerical results are presented and discussed in detail to investigate the effects of CNTs volume fraction, distribution patterns of CNTs, boundary conditions, and length-to-thickness ratio on the bending and buckling responses of FG-CNTRC beam. Several new referential results are also reported for the first time which will serve as a benchmark for future studies in a similar direction. It is concluded that the FG-X-CNTRC beam is the strongest beam that carries the lowest central deflection and is followed by the UD, V, Λ, and FG-O-CNTRC beam. Besides, the critical buckling load belonging to the FG-X-CNTRC beam is the highest, followed by UD and FG-O.

• Journal of KIISE:Software and Applications
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• v.37 no.6
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• pp.455-463
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• 2010

In this paper, we present an approach to sentence boundary detection for web documents that builds on statistical-based methods and uses rule-based correction. The proposed system uses the classification model learned offline using a training set of human-labeled web documents. The web documents have many word-spacing errors and frequently no punctuation mark that indicates the end of sentence boundary. As sentence boundary candidates, the proposed method considers every Ending Eomis as well as punctuation marks. We optimize engine performance by selecting the best feature, the best training data, and the best classification algorithm. For evaluation, we made two test sets; Set1 consisting of articles and blog documents and Set2 of web community documents. We use F-measure to compare results on a large variety of tasks, Detecting only periods as sentence boundary, our basis engine showed 96.5% in Set1 and 56.7% in Set2. We improved our basis engine by adapting features and the boundary search algorithm. For the final evaluation, we compared our adaptation engine with our basis engine in Set2. As a result, the adaptation engine obtained improvements over the basis engine by 39.6%. We proved the effectiveness of the proposed method in sentence boundary detection.

• International Journal of Aerospace System Engineering
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• v.3 no.1
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• pp.10-16
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• 2016

A trigonometric Layerwise higher order shear deformation theory (TLHSDT) is developed and implemented for free vibration and buckling analysis of laminated composite and sandwich plates by analytical and finite element formulation. The present model assumes parabolic variation of out-plane stresses through the depth of the plate and also accomplish the zero transverse shear stresses over the surface of the plate. Thus a need of shear correction factor is obviated. The present zigzag model able to meet the transverse shear stress continuity and zigzag form of in-plane displacement continuity at the plate interfaces. Hence, botheration of shear correction coefficient is neglected. In the case of analytical method, the governing differential equation and boundary conditions are obtained from the principle of virtual work. For the finite element formulation, an efficient eight noded $C^0$ continuous isoparametric serendipity element is established and employed to examine the dynamic analysis. Like FSDT, the considered mathematical model possesses similar number of variables and which decides the present models computationally more effective. Several numerical predictions are carried out and results are compared with those of other existing numerical approaches.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.1
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• pp.19-26
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• 1996

An experimental and computational study of the pressure fluctuation induced by a propeller on a hull surface was carried out with three ship models and seven model propellers. The fluctuation of pressure on a flat plate was measured at KRISO cavitation tunnel and calculated by a panel and lifting surface method(XForShip code). To extend the measurement data on the flat plate into that on complex hull forms, the correction factor was determined as a ratio of the solid boundary factor(SBF). The computation of pressure fluctuation around complex hull forms was also performed to make the full scale prediction and compared with the corrected experimental data. The calculated values agreed well with the compensated experimental data and it was found that the correction factor was about 0.65-0.7.

• Progress in Medical Physics
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• v.10 no.2
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• pp.103-114
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• 1999

In this study, as a preliminary study for developing a full 3D photon dose calculation algorithm, We developed 2.5D photon dose calculation algorithm by extending 2D calculation algorithm to allow non-coplanar configurations of photon beams. For this purpose, we defined the 3d patient coordinate system and the 3d beam coordinate system, which are appropriate to 3d treatment planning and dose calculation. and then, calculate a transformation matrix between them. For dose calculation, we extended 2d "Clarkson-Cunningham" model to 3d one, which can calculate wedge fields as well as regular and irregular fields on arbitrary plane. The simple Batho's power-law method was implemented as an inhomogeneity correction. We evaluated the accuracy of our dose model following procedures of AAPM TG#23; radiation treatment planning dosimetry verifications for 4MV of Varian Clinac-4. As results, PDDs (percent depth dose) of cubic fields, the accuracy of calculation are within 1% except buildup region, and $\pm$3% for irregular fields and wedge fields. And for 45$^{\circ}$ oblique incident beam, the deviations between measurements and calculations are within $\pm$4%. In the case of inhomogeneity correction, the calculation underestimate 7% at the lung/water boundary and overestimate 3% at the bone/water boundary. At the conclusions, we found out our model can predict dose with 5% accuracy at the general condition. we expect our model can be used as a tool for educational and research purpose.. purpose..

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.41 no.5
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• pp.23-34
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• 2004

In this paper we propose a feature point tracking algorithm using optical flow under non-prior taming active feature model (NPT-AFM). The proposed algorithm mainly focuses on analysis non-rigid objects[1], and provides real-time, robust tracking by NPT-AFM. NPT-AFM algorithm can be divided into two steps: (i) localization of an object-of-interest and (ii) prediction and correction of the object position by utilizing the inter-frame information. The localization step was realized by using a modified Shi-Tomasi's feature tracking algoriam[2] after motion-based segmentation. In the prediction-correction step, given feature points are continuously tracked by using optical flow method[3] and if a feature point cannot be properly tracked, temporal and spatial prediction schemes can be employed for that point until it becomes uncovered again. Feature points inside an object are estimated instead of its shape boundary, and are updated an element of the training set for AFH Experimental results, show that the proposed NPT-AFM-based algerian can robustly track non-rigid objects in real-time.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.1
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• pp.91-97
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• 2014

Recently, the LED(Light Emitting Diode) is expected to replace conventional lamps including incandescent, halogen and fluorescent lamps for some general illumination application, due to some obvious features such as high luminous efficiency, safety, long life, environment-friendly characteristics and so on. To drive the LED, a single stage PFC(Power Factor Correction) flyback converter has been adopted to satisfy the isolation, PFC and low cost. The conventional flyback LED driver has the serious disadvantage of high 120Hz output current ripple caused by the PFC operation. To overcome this drawback, a new PFC flyback with low 120Hz output current ripple is proposed in this paper. It is composed of 2 power stages, the DCM(Discontinuous Conduction Mode) flyback converter for PFC and BCM(Boundary Conduction Mode) boost converter for tightly regulated LED current. Since the link capacitor is located in the secondary side, its voltage stress is small. Moreover, since the driver is composed of 2 power stages, small output filter and link capacitor can be used. Especially, since the flyback is operated at DCM, the PFC can be automatically obtained and thus, an additional PFC IC is not necessary. Therefore, only one control IC for BCM boost converter is required. To confirm the validity of the proposed converter, theoretical analysis and experimental results from a prototype of 24W LED driver are presented.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.4
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• pp.257-263
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• 2019

Multilayered structures include lamination by relatively thick plies and thin interlayers. For efficient peridynamic analysis of dynamic fracturing multilayered structures, the interlayer is modeled using ghost peridynamic particles while the ply is formulated via real peridynamics. With the nonlocal ghost interlayer, one may keep the discretization resolution low for the ply. In this study, the characteristics of dynamic wave propagation through the nonlocal ghost interlayer in peridynamic analysis are investigated. It is observed that the interlayer not only binds adjacent plies, but also significantly influences energy transfer between plies, and thereby their deformation and motion. In addition, near a surface or boundary, peridynamic particles do not have a full nonlocal neighborhoods. This causes the effective material properties near the surface to be different from those in the bulk. Surface correction based on neighborhood volumes is employed. The impact of surface correction on wave propagation in multilayered structures is investigated.

• Advances in materials Research
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• v.6 no.1
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• pp.13-26
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• 2017

In this work we introduce a higher-order hyperbolic shear deformation model for bending and frees vibration analysis of functionally graded beams. In this theory and by making a further supposition, the axial displacement accounts for a refined hyperbolic distribution, and the transverse shear stress satisfies the traction-free boundary conditions on the beam boundary surfaces, so no need of any shear correction factors (SCFs). The material properties are continuously varied through the beam thickness by the power-law distribution of the volume fraction of the constituents. Based on the present refined hyperbolic shear deformation beam model, the governing equations of motion are obtained from the Hamilton's principle. Analytical solutions for simply-supported beams are developed to solve the problem. To verify the precision and validity of the present theory some numerical results are compared with the existing ones in the literature and a good agreement is showed.