• Advances in nano research
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• 제14권4호
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• pp.375-389
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• 2023

In this study, free vibration analysis of functionally graded (FG) porous truncated conical shell panels reinforced by graphene platelets (GPLs) has been investigated for the first time. Additionally, the effect of three different types of porosity distribution and five different types of GPLs patterns on dynamic response of the shell are also studied. Halpin-Tsai micromechanical model and Voigt's rule are used to determine Young modulus, shear modulus and Poisson's ratio with mass densities of the shell, respectively. The main novelties of present study are: applying 3D elasticity theory and the finite element method in conjunction with Rayleigh-Ritz method to give more accurate results unlike other simplified shell theories, and also presenting a general 3D solution in cylindrical coordinate system that can be used for analyses of different structures such as circular, annular and annular sector plates, cylindrical shells and panels, and conical shells and panels. A convergence study is performed to justify the correctness of the obtained solution and numerical results. The impact of porosity and GPLs patterns, the volume of voids, the weight fraction of graphene nanofillers, semi vertex and span angles of the cone, and various boundary conditions on natural frequencies of the functionally graded panel have been comprehensively studied and discussed. The results show that the most important parameter on dynamic response of FG porous truncated conical panel is the weight fraction of nanofiller and adding 1% weight fraction of nanofiller could increase 57% approximately the amounts of natural frequencies of the shell. Moreover, the porosity distribution has great effect on the value of natural frequency of structure rather than the porosity coefficient.

• 분석과학
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• 제21권2호
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• pp.117-122
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• 2008

표면오염도 측정용 검출소재로 주로 이용되고 있는 알파와 베타선의 동시 측정용 이중섬광체 검출소재를 개발하였다. 본 연구에서는 기존의 열용융 공정이 아닌, 고분자 소재를 용매로 녹여서 검출소재를 제조하는 용매법을 이용함으로써 제조공정을 단순화하였다. 베타선 측정용 플라스틱 섬광체는 유기섬광체, 고분자, 그리고 용매가 혼합된 용액을 도말한 후에 고형화하여 제조하였다. ZnS(Ag) 섬광체는 플라스틱 섬광체 위에 ZnS(Ag), 접착소재, 그리고 용매가 혼합된 용액을 스크린 프린팅 방법으로 도포하여 제조하였다. 제조한 이중섬광체의 알파선과 베타선에 대한 방사능 검출 성능을 평가한 결과 우수한 검출 성능을 확인하였으며, 표염오염도 측정용 소재로 적용이 가능함을 확인하였다.

• Journal of Electrochemical Science and Technology
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• 제14권4호
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• pp.311-319
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• 2023

This work was performed to characterize the electrochemical behavior of AZ31 Mg alloy in neutral aqueous solutions where Cl^-, SO₄^2-, PO₄^3-, and F^- ions were present and pH was adjusted to 6 to exclude the contribution of H⁺ and OH^- ions. Open-circuit potential (OCP) transient, electrochemical impedance spectroscopy (EIS) and potnetiodynamic polarization curves were employed. The OCP value appeared to decrease in the order of F^- > Cl^- > SO₄^2- > PO₄^3- ions while corrosion current density increased in the same order. Electrochemical impedance spectroscopy (EIS) data showed two capacitive arcs in all the solutions and one more inductive arc appeared in PO₄^3--containing solution. By fitting of two capacitive arcs, capacitance of dense film (C_df), resistance of porous film (R_pf) and double layer capacitance (C_dl) and charge transfer resistance (R_ct) beneath the porous films were obtained. A simplified model in which various thicknesses and coverages of dense and porous films are assumed to be present on the AZ31 Mg alloy surface, is suggested to explain the effects of four different anions on the electrochemical behavior of AZ31 Mg alloy.

• Structural Engineering and Mechanics
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• 제16권6호
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• pp.675-693
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• 2003

In order to consider the modified seismic response of framed structures in the presence of masonry infills, proper models have to be formulated. Because of the complexity of the problem, a careful definition of a diagonal pin-jointed strut, able to represent the horizontal force-interstorey displacement cyclic law of the actual infill, may be a solution. In this connection the present paper shows a generalized criterion for the determination of the ideal cross-section of the strut mentioned before. The procedure is based on the equivalence between the lateral stiffness of the actual infilled frame scheme during the conventional elastic stage of the response and the lateral stiffness of the same frame stiffened by a strut at the same stage. Unlike the usual empirical approaches available in the literature, the proposed technique involves the axial stiffness of the columns of the frame more than their flexural stiffness. Further, the influence of the bidimensional behaviour of the infill is stressed and, consequently, the dependence of the dimensions of the equivalent pin-jointed strut on the Poisson ratio of the material constituting the infill is also shown. The proposed approach is extended to the case of infills with openings, which is very common in practical applications.

• Journal of Electrical Engineering and Technology
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• 제10권1호
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• pp.109-117
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• 2015

This paper proposes the comparison results of various optimal power flow algorithms (OPF) to calculate the locational marginal prices (LMP) of the unreduced full scale Korean transmission system. Five different types of optimal power flow models are employed: Full AC OPF, Cubic AC OPF, Quadratic AC OPF, Linear AC OPF and DC OPF. As the results, full AC OPF and cubic AC OPF model provides LMP calculation results very similar to each other while the calculation time of cubic AC OPF model is faster than that of the Full AC OPF. Other simplified OPF models, quadratic AC OPF, linear AC OPF and DC OPF offer erroneous results even though the calculation times are much faster than the Full AC OPF and the Cubic AC OPF. Given the condition that the OPF models sometimes fail to find the optimal solution due to the severe complexity of the Korean transmission power system, the Full AC OPF should be used as the primary OPF model while the Cubic AC OPF can be a promising backup OPF model for the LMP calculations and/or real-time operation.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.691-694
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• 2003

This paper describes how to use Profibus networks to support real-time industrial communications, that is, how to ensure the transmission of real-time messages within a maximum bound time. Profibus is based on a simplified timed token protocol, which is a well-proved solution for the real-time communication systems. However, Profibus differs from the timed token protocol, thus the usual timed token protocol has to be modified in order to be applied in Profibus. In fact, the real-time solutions for networks based on the timed token protocol rely on the possibility of allocating specific bandwidth for the real-time traffic. This means that a minimum amount of time to transmit the real-time messages is always guaranteed whenever each token is arrived. In other words, with the Profibus protocol, at least, one real-time message should be transmitted per every token visit in the worst case. It is required to control medium access properly to satisfy the message deadlines. In this paper, we have presented how to obtain the optimal network parameter for the Profibus protocol. The selected network parameter is valid regardless of the behavior of asynchronous messages.

• Structural Engineering and Mechanics
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• 제55권3호
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• pp.655-674
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• 2015

In this paper, a new and simplified method is presented in which the natural frequencies of the uniform and non-uniform beams are calculated through simple mathematical relationships. The various vibration problems such as: Rayleigh beam under variable axial force, axial vibration of a bar with and without end discrete spring, torsional vibration of a bar with an attached mass moment of inertia, flexural vibration of the beam with laterally distributed elastic springs and also flexural vibration of the beam with effects of viscose damping are investigated. The governing differential equations are first obtained and then; according to a harmonic vibration, are converted into single variable equations in terms of location. Through repetitive integrations, the governing equations are converted into weak form integral equations. The mode shape functions of the vibration are approximated using a power series. Substitution of the power series into the integral equations results in a system of linear algebraic equations. The natural frequencies are determined by calculation of a non-trivial solution for system of equations. The efficiency and convergence rate of the current approach are investigated through comparison of the numerical results obtained with those obtained from other published references and results of available finite element software.

• 한국소음진동공학회논문집
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• 제20권1호
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• pp.22-28
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• 2010

Approximate analysis for a building installed with a friction damper is performed to get insight of its dynamic behavior. Energy balance equation is used to have a closed analytical form solution of dynamic magnification factor(DMF). It is found out that DMF is dependent on friction force ratio and resonance frequency. Approximation of DMF and equivalent damping ratio of a friction damper is proposed with such assumption that the building with a friction damper shows harmonic steady-state response and narrow banded response behavior near resonance frequency. Linear transfer function from input external force to output building displacement is suggested from the simplified DMF equation. Root mean square of a building displacement is derived under earthquake-like random excitation. Finally, design procedure of a friction damper is proposed by finding friction force corresponding to target control ratio. Numerical analysis is carried out to verify the proposed design procedure.

• 한국컴퓨터정보학회논문지
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• 제10권6호
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• pp.253-260
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• 2005

액티브 네트워크는 네트워크 노드인 스위치나 라우터가 패킷들의 단순한 경로 배정이나 전달만이 아닌 사용자에 의해 노드에 장착된 프로그램이나 프로그램 코드를 담은 패킷에 의해 데이터를 처리할 수 있도록 한 것이다. 본 논문에서는 기존의 중앙 집중적인 관리 시스템의 문제점을 해결할 수 있는, 액티브 네트워크 기술을 활용한 새로운 네트워크 관리 시스템을 제안하였다. 핵심은 라우터들에게 관리 패킷들을 간소화된 패턴으로 만들어 처리하게 함으로서 트래픽을 줄일 수 있는 The Smart Router 모델을 제시한 것이다. 중앙 집중적인 기존 관리 시스템의 문제점을 분석하였고 제시된 분산 관리 시스템의 장점도 검토하였다. 제시한 구조가 제공하는 성능 개선을 실험을 통해서 보여주었다.

• Composites Research
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• 제14권1호
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• pp.8-14
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• 2001

복합재 적층판의 자유단 층간분리의 모드별 변형률 에너지 해방률을 구하는 간이 계산법을 제안하였다. 층간응력은 층간에서의 평형식으로부터 층간의멘트와 층간전단력으로 평가하였다. 적층판 자유단 층간분리의 변형은 일반화된 준3차원 고전적층이론에 의하여 계산하였다. 이 간이 계산법은 변형균 에너지 해방률의 세성분을 구하는 간편한 식으로 나타내었다 복합재 적층판이 일축인장을 받는 경우에 대하여 적층판 중앙면에 대칭과 비대칭인 층간분리가 발생한 경우에 대하여 해석을 행하였다. 해석결과는 가상분리진전법에 의한 유한요소해석결과와 잘 일치하였다.