• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.05b
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• pp.125-129
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• 2004

The mold transformers have been widely used in underground substations in large building and have some advantages in comparison to oil-transformer, that is low fire risk, excellent environmental compatibility, compact size and high reliability. In addition, the application of mold transformer for outdoor is possible due to development of epoxy resin. The mold transformer generally has cooling duct between low voltage coil and high voltage coil. A mold transformer made by one body molding method has been developed for small size and low loss, but it needs some cooling method because heat radiation between each winding is difficult. The life of transformer is significantly dependent on the thermal behavior in windings. Many transformer designers have calculated temperature distribution and hot spot point by FEM(finite element method) to analyze winding temperature rise. In this paper, the temperature distribution and thermal stress analysis of 100kVA pole cast resin transformer for power distribution are investigated by FEM program.

• Advances in nano research
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• v.10 no.1
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• pp.25-42
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• 2021

In this article, the vibration behavior of embedded Functionally Graded Nanoplate (FGNP) employing nonlocal Kirchhoff's plate theory has been investigated under hygrothermal environment. The FGNP is considered to be supported by Winkler-Pasternak foundation. The Eringen's differential theory is used for size effect on the vibration of the FGNP. Rayleigh-Ritz method with orthogonal polynomials are employed for the governing equations and edge constraints. The advantage of this method is that it overcomes all the drawbacks of edge constraints and can easily handle any combinations of mixed edge constraints. The coefficients viz. moisture expansion, thermal expansion and elastic coefficients are considered to be transversely graded across the FGNP. The similarity of the calculated natural frequencies is examined with the previous research, and a good concurrency is seen. The objective of this article is to analyze the parameters' effect on the nondimensionalized frequency of embedded FGNP under hygrothermal environment subjected to all possible edge constraints. For this, uniform and linear rise of temperature and moisture concentration are considered. The study highlights that the nonlocal effect is pronounced for higher modes. Moreover, the effect of the Pasternak modulus is seen to be prominent compared to the Winkler modulus on non dimensionalized frequencies of FGNP.

• Journal of Korean Society of Water and Wastewater
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• v.10 no.1
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• pp.85-95
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• 1996

Although the specific resistance to filtration is the most frequently employed means for characterizing dewaterability of a sludge, it presently is not possible to design nor to prediet performance of dewatering facilities using traditional linearized parabolic filtration equation, that is, the specific resistance model because of theoretical and practical inadequacies of the concept. Limitations of the specific resistance model reflect the need to examine fundamental sludge properties and filtration behaviors affecting dewaterability. From this study, two major limitations of the specific resistance model were noted. First, specific resistance values are very dependent on the sludge concentration because of the variations of particle size distribution and cake clogging to occur when surface area mean diameter is less than $25{\mu}m$ for activated sludge, $18{\mu}m$ for water treatment plant sludge. Second, nonparabolic filtration behavior can result from cake clogging, caused by the migration of fine particles into the cake pores, accelated by skin effect with highly compressible sludges.

• Proceedings of the Korea Concrete Institute Conference
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• 1991.04a
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• pp.65-68
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• 1991

Finite element analysis is used to study the role of interfacial properties on the bond strength of reinforcing steel to concrete. Specifically, the role played by epoxy coatings on the failure of standard beam-end specimens is explored. Experimental results show that epoxy coatings reduce bond strength, but that the effect is dependent on the bar size and the deformation pattern. The finite element model for the beam-end specimen includes representations for the deformed steel bar, the concrete, and the interfacial material. The interface elements can be varied to match the stiffness and friction properties of the interfacial material. Cracking within the concrete is represented using Hillerborg's ficticious crack model. The model is used to study important aspects or behavior observed in the tests and to provide an explanation for the effect of the various test parameters.

• Steel and Composite Structures
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• v.36 no.2
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• pp.179-186
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• 2020

In this paper, the forced resonance vibration of porous functionally graded (FG) curved nanobeam is examined. In order to capture the hardening and softening mechanisms of nanostructure, the nonlocal strain gradient theory is employed to build the size-dependent model. Using the Timoshenko beam theory together with the Hamilton principle, the equations of motion for the curved nanobeam are derived. Then, Navier series are used in order to obtain the dynamical deflections of the porous FG curved nanobeam with simply-supported ends. It is found that the resonance position of the nanobeam is very sensitive to the nonlocal and strain gradient parameters, material variation, porosity coefficient, as well as geometrical conditions. The results indicate that the resonance position is postponed by increasing the strain gradient parameter, while the nonlocal parameter has the opposite effect on the results. Furthermore, increasing the opening angle or length-to-thickness ratio will result in resonance position moves to lower-load frequency.

• Steel and Composite Structures
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• v.23 no.3
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• pp.339-350
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• 2017

In this paper, various nonlocal higher-order shear deformation beam theories that consider the size dependent effects in Functionally Graded Material (FGM) beam are examined. The presented theories fulfill the zero traction boundary conditions on the top and bottom surface of the beam and a shear correction factor is not required. Hamilton's principle is used to derive equation of motion as well as related boundary condition. The Navier solution is applied to solve the simply supported boundary conditions and exact formulas are proposed for the bending and static buckling. A parametric study is also included to investigate the effect of gradient index, length scale parameter and length-to-thickness ratio (aspect ratio) on the bending and the static buckling characteristics of FG nanobeams.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.818-821
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• 2003

Sn-doped $In_{2}O_{3}$ (ITO) thin film is one of the materials widely on research not only in the academic fields but also in industrial fields because of their transparency, high conductivity and good adhesion characteristics on substrate. ITO thin films are usually preferred oriented to one of the (222), (400), and (440) planes during crystallization process, which is dependent on processing variables. The preferred orientation affects electrical, optical and etching properties of the films. In this study, thin films of preferred oriented in different orientation were fabricated by controlling processing variables. The crystallization behavior, grain size, surface roughness, transparency and electrical properties of the thin films in different orientation were examined.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.3
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• pp.434-440
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• 2004

The electro-rheological fluids for semi-active suspension system are a class of colloidal dispersion which exhibit large reversible changes in their rheological behavior when they are subjected to external electrical fields. This paper presents Bingham properties of ER fluids subjected to temperature variations. In addition, an appropriate size of the ER damper for a passenger car is proposed to investigate the effects of Bingham characteristics on the damping performance. The filed-dependent damping forces are evaluated according to the temperature variation and sedimentation ratio.

• Steel and Composite Structures
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• v.20 no.5
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• pp.963-981
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• 2016

A nonlocal trigonometric shear deformation beam theory based on neutral surface position is developed for bending, buckling, and vibration of functionally graded (FG) nanobeams using the nonlocal differential constitutive relations of Eringen. The present model is capable of capturing both small scale effect and transverse shear deformation effects of FG nanobeams, and does not require shear correction factors. The material properties of the FG nanobeam are assumed to vary in the thickness direction. The equations of motion are derived by employing Hamilton's principle, and the physical neutral surface concept. Analytical solutions are presented for a simply supported FG nanobeam, and the obtained results compare well with those predicted by the nonlocal Timoshenko beam theory.

• Geomechanics and Engineering
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• v.19 no.5
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• pp.369-381
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• 2019

The objective of this paper is to study the two dimensional deformation in transversely isotropic thermoelastic medium without energy dissipation due to time harmonic sources using new modified couple stress theory, a continuum theory capable to predict the size effects at micro/nano scale. The couple stress constitutive relationships have been introduced for transversely isotropic thermoelastic medium, in which the curvature tensor is asymmetric and the couple stress moment tensor is symmetric. Fourier transform technique is applied to obtain the solutions of the governing equations. Assuming the deformation to be harmonically time-dependent, the transformed solution is obtained in the frequency domain. The application of a time harmonic concentrated and distributed sources have been considered to show the utility of the solution obtained. The displacement components, stress components, temperature change and couple stress are obtained in the transformed domain. A numerical inversion technique has been used to obtain the solutions in the physical domain. The effects of angular frequency are depicted graphically on the resulted quantities.