• Structural Engineering and Mechanics
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• v.61 no.5
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• pp.563-576
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• 2017

This paper is a continuation of the investigations started in the paper by Akbarov, S.D., Guliyev, H.H and Yahnioglu, N. (2016) "Natural vibration of the three-layered solid sphere with middle layer made of FGM: three-dimensional approach", Structural Engineering and Mechanics, 57(2), 239-263, to the case where the three-layered sphere is a hollow one. Three-dimensional exact field equations of elastodynamics are employed for investigation and the discrete-analytical method is employed for solution of the corresponding eigenvalue problem. The FGM is modelled as inhomogeneous for which the modulus of elasticity, Poison's ratio and density vary continuously through the inward radial direction according to power law distribution. Numerical results on the natural frequencies are presented and discussed. These results are also compared with the corresponding ones obtained in the previous paper by the authors. In particular, it is established that for certain harmonics and for roots of certain order, the values of the natural frequency obtained for the hollow sphere can be greater (or less) than those obtained for the solid sphere.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.11
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• pp.1193-1201
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• 2013

Improved far field type(improved type) megasonic applicable to the cleaning equipment of single wafer processing type has been developed. In this study, to improve the uniformity of acoustic pressure distribution(APD), we utilize far field with relatively uniform APD, piezoelectric ceramic with a triangle hole in its center to prevent standing wave resulted from radial mode, and reflected wave from the wall of waveguide. On the basis of these methods, two analysis models of improved type were designed to which piezoelectric ceramic of different shape of electrode attached, and APD were analyzed by means of finite element method, and then one of them was selected by analysis results, finally, the selected model was fabricated. Test results show that the fabricated is better in the uniformity of APD than the imported and the conventional, also the fabricated shows high particle removal efficiency of 92.3% using DI water alone as a cleaning solution.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1992.10a
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• pp.117-123
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• 1992

In recent years, the finite element method has become one of the most popular numerical technique for obtaining solutions of engineering science problems. However, there exist various uncertainties in modeling the problems, such as the dimensions(geometry shape), the material properties, boundary conditions, etc. The consideration for the uncertainties inherent in the problems can be made by understanding the influences of uncertain parameters[1]. Determining the influences of uncertainties as statistical quantities using the standard finite element method requires enormous computing time, while the probabilistic finite element method is realized as an efficient scheme[2,3] yielding statistical solution with just a few direct computations. In this paper, a formulation of the probabilistic fluid-structure interaction problem accounting for the first order perturbation of geometric shape is derived, and especially probabilistical acoustic pressure scattering from the structure with surrounding fluid is focused on. In Section 2, governing equations for the fluid-structure problems are given. In Section 3, a finite element formulation, based on the functional, is presented. First order perturbation of geometric shape with randomness is incorporated into the finite element formulation in conjunction with discretization of the random fields in Section 4 and 5. Finally, the proposed formulation is applied to a acoustic pressure scattering problem from an infinitely long cylindrical shell structure with randomness of radial perturbation.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.78.2-78.2
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• 2010

We report the detection of a low-amplitude 380.8-day radial velocity (RV) variations in oscillating K2 III star ${\alpha}$ Ari (HD 12929). We do not found the correlation between RV variations and equivalent widths of chromospheric activity indicators ($H{\alpha}$ and CaII 8662 ${\AA}line$). The bisector analysis shows that bisector velocity span (BVS) and RV variations are not strongly correlated with each other. These result suggest that the RV variations could have been produced either by planetary companion or by the surface spots. If this RV variation is indeed caused by a planetary companion, an orbital solution with a period of P = 381 days, a semi-amplitude of K = 41 m/s, and an eccentricity of e = 0.25 fits the data best. Assuming a possible stellar mass of $M_{\bigstar} = 1.4-5.6 M\odot$, we estimate the minimum mass for the companion of m sini = 1.8-4.5 $M_{Jup}$ with an orbital semi-major axis of 1.2-1.9 AU. If confirmed, our finding gives a support to search for exoplanets around giant stars with multi-periodic oscillations.

• Journal of Mechanical Science and Technology
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• v.14 no.10
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• pp.1143-1150
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• 2000

The effects of ambient conditions on vaporizing sprays from a high-pressure swirl injector were investigated by an exciplex fluorescence method. Dopants used were 2% fluorobenzene and 9% DEMA (diethyl-methyl-amine) in 89% solution of hexane by volume. In order to examine the behavior of liquid and vapor phases inside of vaporizing sprays, ambient temperatures and pressures similar to engine atmospheres were set. It was found that the ambient pressure had a significant effect on the axial growth of spray, while ambient temperature had a great influence on the radial growth. The spatial distribution of vapor phase at temperatures above 473K became wider than that of liquid phase after half of injection duration. From the analysis of the area ratio for each phase, the middle part (region II) in the divided region was the region which liquid and vapor phases intersect. For liquid phase, fluorescence-intensity ratio was greatly changed at lms after the start of injection. However, the ratio of vapor phase was nearly uniform in each divided region throughout the injection.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.2
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• pp.298-305
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• 2010

In this paper, a new algorithm of optimal Volt/Var Control is proposed using Volt/Var control for the Distribution Automation System (DAS) with Distributed Generation (DG) based on the modeling of the distributed load and the distributed current. In the proposed, algorithm based on the modeling of the distributed load and the distributed current are estimated from constants of four terminals using the measurement of the current and power factor from a Feeder Remote Terminal Unit (FRTU) and DG data from RTU for DG. For the optimal Volt/Var Control, the gradient method is applied to find optimal solution for tap, capacity and power control of OLTC (On-Load Tap Changers), SVR (Step Voltage Regulator), PC (Power Condenser) and DG (Distributed Generation). In the case studies, the estimation and control of the voltages have been testified in a radial distribution system with DG using matlab program.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.05a
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• pp.252-253
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• 2019

Corrosion of rebars in reinforced concrete structures is a major factor that shortens the life of the structure. As corrosion progresses, the adhesion between the concrete tissues and the rebar decreases and the cracks in the concrete due to the expansion of the oxide intensify. Although it is necessary to measure corrosion behavior of rebars inside the concrete to measure degradation of structures due to rebar corrosion, no studies have been conducted to measure corrosion of rebars in In-situ state. In this study, corrosion of rebars in reinforced concrete specimens was attempted to be quantified using micro-computer tomography. Since corrosion of concrete takes several months per 10mm of cover, accelerated corrosion techniques were applied. Accelerated corrosion on the specimen was conducted by applying a 10 V magnetic field to the buried rebar and external electrodes with the specimen submerged in a 10% calcium chloride solution. The experiment found that within two weeks, more than 40% of rebar reduction occurred, and the cracks in the radial cracks occurred through the concrete structure, leading to the transfer of the oxide produced through the cracks to the surface of the specimen.

• Geomechanics and Engineering
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• v.7 no.1
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• pp.105-131
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• 2014

In this paper, the effects of variability of smear zone characteristics induced by installation of prefabricated vertical drains on the preloading design are investigated employing analytical and numerical approaches. Conventional radial consolidation theory has been adopted to conduct analytical parametric studies considering variations of smear zone permeability and extent. FLAC 2D finite difference software has been employed to conduct the numerical simulations. The finite difference analyses have been verified using three case studies including two embankments and a large-scale laboratory consolidometer with a central geosynthetic vertical drain. A comprehensive numerical parametric study is conducted to investigate the influence of smear zone permeability and extent on the model predictions. Furthermore, the construction of the trial embankment is recommended as a reliable solution to estimate accurate smear zone properties and minimise the post construction settlement. A back-calculation procedure is employed to determine the minimum required waiting time after construction of the trial embankment to predict the smear zone characteristics precisely. Results of this study indicate that the accurate smear zone permeability and extent can be back-calculated when 30% degree of consolidation is obtained after construction of the trial embankment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1005-1012
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• 2011

The purpose of this study was to investigate the internal nozzle flow and cavitation characteristics numerically in both circular and elliptical nozzles. The program FLUENT 6.2 was used to perform the numerical simulation of the cavitating flow in the nozzles. A comparison was made between the cavitation shapes predicted numerically and those found experimentally in order to validate the numerical solution. This study showed that the cavitation in the circular nozzle had a cylindrical shape that was symmetrical with the nozzle axis. However, the cavitation in the elliptical nozzles had a horseshoe-like shape. In addition, the radial velocity distribution varied between the major and the minor axis planes when the working fluid was flowing into the inlet.

• Bulletin of the Society of Naval Architects of Korea
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• v.9 no.2
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• pp.21-32
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• 1972

The problems of thermal stress and residual stress in resistance spot welding are studied from two standpoint namely, effect of temperature distributions and effect of the radius of free boundary. The radius of the region where the temperature distributions are occured is taken as a function of time after welding and as a finite size, 6 times of heated zone. The region of the radial stress distribution is treated as a function of time under Saint-Venant's principle and 6 or 12 times of originally heated zone. Thermal stresses and strains are obtained by analytic solution under constant mechanical properties and by the finite difference method for varing properties under temperature variation. From the computed results following conclusions are derived (1) For the engineering purpose, the region of temperature distribution and stress distribution can be treated as a finite region, $R=r_o=6r_e$ (2) If the maximum temperature of the aluminum alloy plate is less than $500^{\circ}F$, thermal stresses and strains can be obtained with constant mechanical properties. (3) The residual stresses and strains will be remained in welds and its vicinity.