• Structural Engineering and Mechanics
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• 제54권3호
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• pp.597-605
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• 2015

In this study, linear vibrations of an axially moving beam under non-ideal support conditions have been investigated. The main difference of this study from the other studies; the non-ideal clamped support allow minimal rotations and non-ideal simple support carry moment in minimal orders. Axially moving Euler-Bernoulli beam has simple and clamped support conditions that are discussed as combination of ideal and non-ideal boundary with weighting factor (k). Equations of the motion and boundary conditions have been obtained using Hamilton's Principle. Method of Multiple Scales, a perturbation technique, has been employed for solving the linear equations of motion. Linear equations of motion are solved and effects of different parameters on natural frequencies are investigated.

• Structural Engineering and Mechanics
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• 제11권4호
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• pp.373-392
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• 2001

The main idea behind the paper is to present two alternative methods of homogenization of the heat conduction problem in composite materials, where the heat conductivity coefficients are assumed to be random variables. These two methods are the Monte-Carlo simulation (MCS) technique and the second order perturbation second probabilistic moment method, with its computational implementation known as the Stochastic Finite Element Method (SFEM). From the mathematical point of view, the deterministic homogenization method, being extended to probabilistic spaces, is based on the effective modules approach. Numerical results obtained in the paper allow to compare MCS against the SFEM and, on the other hand, to verify the sensitivity of effective heat conductivity probabilistic moments to the reinforcement ratio. These computational studies are provided in the range of up to fourth order probabilistic moments of effective conductivity coefficient and compared with probabilistic characteristics of the Voigt-Reuss bounds.

• Structural Engineering and Mechanics
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• 제40권5호
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• pp.705-718
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• 2011

The aim of the investigation described in this paper is to study the nonlinear parametric vibrations and stability of a simply-supported viscoelastic beam with an intra-span spring. Taking into account a time-dependent tension inside the beam as the main source of parametric excitations, as well as employing a two-parameter rheological model, the equations of motion are derived using Newton's second law of motion. These equations are then solved via a perturbation technique which yields approximate analytical expressions for the frequency-response curves. Regarding the main parametric resonance case, the local stability of limit cycles is analyzed. Moreover, some numerical examples are provided in the last section.

• Structural Engineering and Mechanics
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• 제43권1호
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• pp.105-126
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• 2012

Based on the first-order shear deformation theory (FSDT), and the virtual work principle, an elastic analysis for axisymmetric clamped-clamped Pressurized thick truncated conical shells made of functionally graded materials have been performed. The governing equations are a system of nonhomogeneous ordinary differential equations with variable coefficients. Using the matched asymptotic method (MAM) of the perturbation theory, these equations could be converted into a system of algebraic equations with variable coefficients and two systems of differential equations with constant coefficients. For different FGM conical angles, displacements and stresses along the radius and length have been calculated and plotted.

• 대한전기학회논문지
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• 제45권4호
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• pp.582-589
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• 1996

In this paper, an adaptive control problem of a hydraulic actuator for vehicle active suspension controller is divided into two parts: the inner loop controller and the outer loop controller. Inner loop controller, which is a nonlinear adaptive controller, is designed to control the force generated by the nonlinear hydraulic actuator acting under the effects of Coulomb friction. For simplicity of designing a nonlinear controller, the spool valve dynamics of a hydraulic actuator is reduced using a singular perturbation technique. The estimation error signal used to an indirect parameter adaptation is calculated without a regressor filtering. The absolute velocity of a sprung mass will be damped down by its negatively proportional term(sky-hook damper) adopted as an outer loop controller. Simulation results are presented to show the importance of controlling the actuator force and the validity of the proposed adaptive controller. (author). refs., figs. tab.

• Bulletin of the Korean Chemical Society
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• 제7권5호
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• pp.399-402
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• 1986

The critical micelle concentration (CMC) of sodium deoxycholate (NaDC) and the effects of amides on the micellization processes have been studied by fluorometric technique using pyrene as a probe. The addition of amides as cosolvent destabilized the NaDC micelle and increased the CMC. The order of effectiveness for the perturbation of NaDC micelle was N-methylacetamide ${\ge}$ DMF > acetamide > formamide, which is the order of hydrophobicity of the amines. This indicated that the effect of amides on the micellization processes of NaDC arises from diminution of the hydrophobic effect. The electrostatic repulsion between ionic head groups in the NaDC micelle appeared to be much less than that in aliphatic ionic micelle. This was also revealed in the weaker dependence of the CMC on ionic strength. The premicellar association of NaDC was not significantly involved in the micellization processes of the bile salt.

• International Journal of Aerospace System Engineering
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• 제7권2호
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• pp.6-12
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• 2020

The precise prediction of future position of satellite depends on the accurate determination of orbit, which is also helpful in performing orbit maneuvers and trajectory correction maneuvers. For estimating the orbit of satellite many methods are being used. Some of the conventional methods are based on (i) Differential Correction (DC) (ii) Extended Kalman Filter (EKF). In this paper, Differential Evolution (DE) is used to determine the orbit. Orbit Determination using DC and EKF requires some initial guess of the state vector to initiate the algorithm, whereas DE does not require an initial guess since a wide range of bounds for the design unknown variables (orbital elements) is sufficient. This technique is uniformly valid for all orbits viz. circular, elliptic or hyperbolic. Simulated observations have been used to demonstrate the performance of the method. The observations are generated by including random noise. The simulation model that generates the observations includes the perturbation due to non-spherical earth up to second zonal harmonic term.

• Steel and Composite Structures
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• 제38권4호
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• pp.447-462
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• 2021

In this work, we consider a problem in the context of thermoelectric materials with memory-dependent derivative for a half space which is assumed to have variable thermal conductivity depending on the temperature. The Lamé's modulii of the half space material is taken as a function of the vertical distance from the surface of the medium. The surface is traction free and subjected to a time dependent thermal shock. The problem was solved by using the Laplace transform method together with the perturbation technique. The obtained results are discussed and compared with the solution when Lamé's modulii are constants. Numerical results are computed and represented graphically for the temperature, displacement and stress distributions. Affectability investigation is performed to explore the thermal impacts of a kernel function and a time-delay parameter that are characteristic of memory dependent derivative heat transfer in the behavior of tissue temperature. The correlations are made with the results obtained in the case of the absence of memory-dependent derivative parameters.

• 비파괴검사학회지
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• 제28권1호
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• pp.16-24
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• 2008

섭동이론인 형태 섭동과 물질 섭동을 적용하여 도파관 공진기를 사용한 마이크로파 근접장 현미경의 특성에 대해 연구하였다. 먼저, Ansoft사의 HFSS (high frequency structure simulator)를 사용하여 공진기 내부의 모드해석과 함께 공진기에서 선형 및 고리형 탐침에 대해 전력전달이 최대가 되고 탐침의 감도 향상을 기대할 수 있는 위치를 확인하였다. 더불어, 유전율이 서로 다른 유전체 시료 (teflon, glass, $Al_2Q_3,\;LaAlO_3,\;SrTiO_3$)에 대해 마이크로파 반사계수$(S_{11})$를 측정하였다. 측정결과로부터 유전율이 증가함에 따라 마이크로파 반사계수$(S_{11})$는 증가하고 공진주파수는 감소하였다. 이를 통해, 도파관 공진기를 이용한 마이크로파 근접장 현미경에서 선형 및 고리형 탐침의 위치에 따른 공진기의 감도 및 공진특성에 대해 알아보았다.

• 대한수학회논문집
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• 제24권4호
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• pp.605-615
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• 2009

In this paper, we develop a reliable algorithm which is called the variation of parameters method for solving sixth-order boundary value problems. The proposed technique is quite efficient and is practically well suited for use in these problems. The suggested iterative scheme finds the solution without any perturbation, discritization, linearization or restrictive assumptions. Moreover, the method is free from the identification of Lagrange multipliers. The fact that the proposed technique solves nonlinear problems without using the Adomian's polynomials can be considered as a clear advantage of this technique over the decomposition method. Several examples are given to verify the reliability and efficiency of the proposed method. Comparisons are made to reconfirm the efficiency and accuracy of the suggested technique.