• Structural Engineering and Mechanics
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• 제70권2호
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• pp.179-197
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• 2019

In this article, the effect of different geometrical, materials and load parameters on the transient response of axisymmetric viscoelastic functionally graded annular plates with different boundary conditions are studied. The behavior of the plate is assumed the elastic in bulk and viscoelastic in shear with the standard linear solid model. Also, the graded properties vary through the thickness according to a power law function. Three types of mostly applied transient loading, i.e., step, impulse, and harmonic with different load distribution respect to radius coordinate are examined. The motion equations and the corresponding boundary conditions are extracted by applying the first order shear deformation theory which are three coupled partial differential equations with variable coefficients. The resulting motion equations are solved analytically using the perturbation technique and the generalized Fourier series. The sensitivity of the response to the graded indexes, different transverse loads, aspect ratios, boundary conditions and the material properties are investigated too. The results are compared with the finite element analysis.

• Transactions on Electrical and Electronic Materials
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• 제18권2호
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• pp.97-102
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• 2017

A current transformer (CT) is a type of sensor that consists of a combination of electric and magnetic circuits, and it measures large ac currents. When a large amount of current flows into the primary winding, the alternating magnetic flux in the iron core induces an electromotive force in the secondary winding. The characteristics of a CT are determined by the iron core design because the iron core is saturated above a certain magnetic flux density. In particular, when a large current, such as a current surge, is input into a CT, the iron core becomes saturated and the induced electromotive force in the secondary winding fluctuates severely. Under these conditions, the CT no longer functions as a sensor. In this study, the characteristics of the secondary winding were investigated using the time-difference finite element method when a current surge was provided as an input. The CT was modeled as a two-dimensional analysis object using constraints, and the saturation characteristics of the iron core were evaluated using the Newton-Rhapson method. The results of the calculation were compared with the experimental data. The results of this study will prove useful in the designs of the iron core and the windings of CTs.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제19권1호
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• pp.69-81
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• 2015

The present paper deals with the determination of temperature, displacement and thermal stresses in a semi-infinite hollow circular disk due to internal heat generation within it. Initially the disk is kept at arbitrary temperature F(r, z). For times t > 0 heat is generated within the circular disk at a rate of g(r, z, t) $Btu/hr.ft^3$. The heat flux is applied on the inner circular boundary (r = a) and the outer circular boundary (r = b). Also, the lower surface (z = 0) is kept at temperature $Q_3(r,t)$ and the upper surface ($Z={\infty}$) is kept at zero temperature. Hollow circular disk extends in the z-direction from z = 0 to infinity. The governing heat conduction equation has been solved by using finite Hankel transform and the generalized finite Fourier transform. As a special case mathematical model is constructed for different metallic disk have been considered. The results are obtained in series form in terms of Bessel's functions. These have been computed numerically and illustrated graphically.

• 한국소음진동공학회논문집
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• 제18권1호
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• pp.123-130
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• 2008

An analytical method for the free vibration of a flexible rectangular plate in contact with water is developed by the Rayleigh-Ritz method. The plate clamped along the edges is partially contacted with water at both sides. It is assumed that the contained water is incompressible and inviscid. The wet mode shape of the plate is assumed as a combination of the dry mode shapes of a clamped beam. The liquid motion is described by using the liquid displacement potential and determined by using the compatibility conditions along the liquid interface with the plate. Minimizing the Rayleigh quotient based on the energy conservation gives an eigenvalue problem. It is found that the theoretical results can predict excellently the fluid-coupled natural frequencies comparing with the finite element analysis result.

• 한국전산구조공학회논문집
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• 제28권2호
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• pp.123-130
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• 2015

본 논문에서는 전자기파에 대한 수치적 파동흡수 경계모델인 Perfectly-Matched-Layer(PML)를 개발하고 PML을 연동시킨 유한요소법에 의해 콘크리트 구조물을 통과하는 마이크로파의 전파거동을 해석하는 수치적 기법을 제시한다. 콘크리트 부재와 공기로 구성된 무한매질을 PML을 경계로 하는 유한영역으로 치환하고, 이 유한영역에서 평면 전자기파에 대한 시간 영역 맥스웰방정식의 수치 해를 혼합유한요소법에 의해 계산하였다. 공기로만 이루어진 균일매질의 경우와 콘크리트 구조물이 존재하는 비균일 매질의 경우에 대하여 단일주파수 및 복합주파수를 갖는 마이크로파의 전기장을 계산하였고, 오차분석을 위해 $L^2$-놈 형태로 표현되는 정해와 수치 해의 상대오차를 정의하여 수치 해의 정확도를 평가하였다. 이 연구는 마이크로파를 이용한 철근콘크리트 구조물의 건전도평가 및 손상평가에 적용될 수 있다.

• 대한조선학회지
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• 제13권1호
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• pp.17-23
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• 1976

Some methods of analysis of rectangular plates under distributed load of various intensity with interior supports are presented herein. Analysis of many structures such as bottom, side shell, and deck plate of ship hull and flat slab, with or without internal supports, Floor systems of bridges, included crthotropic bridges is a problem of plate with elastic supports or continuous edges. When the four edges of rectangular plate is simply supported, the double Fourier series solution developed by Navier can represent an exact result of this problem. If two opposite edges are simply supported, Levy's method is available to give an "exact" solution. When the loading condition and supporting condition of a plate does not fall into these cases, no simple analytic method seems to be feasible. Analysis of a simply supported rectangular plate under irregularly distributed loads of various intensity with internal supports is carried out by applying Navier solution well as the "Principle of Superposition." Finite difference technique is used to solve plates under irregularly distributed loads of various intensity with internal supports and with various boundary conditions. When finite difference technique is applied to the Lagrange's plate bending equation, any of fourth order derivative term in this equation produces at least five pivotal points leading to some troubles when the resulting linear algebraic equations are to be solved. This problem was solved by reducing the order of the derivatives to two: the fourth order partial differential equation with one dependent variable, namely deflection, is changed to an equivalent pair of second order partial differential equations with two dependent variables. Finite difference technique is then applied to transform these equations to a set of simultaneous linear algebraic equations. Principle of Superposition is then applied to handle the problems caused by concentrated loads and interior supports. This method can be used for the cases of plates under irregularly distributed loads of various intensity with arbitrary conditions such as elastic supports, or continuous edges with or without interior supports, and this method can also be solve the influence values of deflection, moment and etc. at arbitrary position of plates under the live load.

• 한국지진공학회논문집
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• 제13권6호
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• pp.67-86
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• 2009

이 연구에서는 u-w 정식화에 근거하여 일반적인 3차원 문제에 적용할 수 있는 지하수로 포화된 가로등방성 층상지반에서의 3차원 전달경계를 개발하였다. 지반 원역에서의 동적거동을 Fourier 급수로 전개하고, 각 항에 대한 동적강성을 u-w 정식화에 근거하여 유도하였다. 그리고 이를 Cartesian 좌표계에서 표현된 지반 근역의 3차원 유한요소와 결합할 수 있도록 변형하여 일반적인 3차원문제에도 적용할 수 있는 방법을 개발하였다. 개발된 방법을 강체 원형 기초의 동적거동 해석에 적용하고 기존의 해석 결과와 비교하여, 이 연구에서 개발된 전달경계가 정확함을 확인하였다. 또한 다양한 형태의 강체 기초 동적거동 해석에 개발된 전달경계를 적용하였고, 지하수로 포화된 가로등방성 층상지반에서 지하수위에 따라 강체 기초 동적거동의 변화 양상을 조사하여, 이 연구에서 개발된 방법의 활용성을 입증하였다.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 1996년도 학술대회
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• pp.223-227
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• 1996

In this paper we propose an adaptive fast image restoration filter, which is suitable for reducing the blocking artifacts in the compressed image in real-time. The proposed restoration filter is based on the observation that quantization operation in a series of coding process is a nonlinear and many-to-one mapping operator. And then we propose an approximated version of constrained optimization technique as a restoration process for removing the nonlinear and space varying degradation operator. We also propose a novel block classification method for adaptively choosing the direction of a highpass filter, which serves as a constraint in the optimization process. The proposed classification method adopts the bias-corrected maximized likelihood, which is used to determine the number of regions in the image for the unsupervised segmentation. The proposed restoration filter can be realized either in the discrete Fourier transform domain or in the spatial domain in the form of a truncated finite impulse response (FIR) filter structure for real-time processing. In order to demonstrate the validity of the proposed restoration filter experimental results will be shown.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.834-839
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• 2007

This paper investigates the distortion of magnetic field of a brushless DC (BLDC) motor due to deformed rubber magnet. Global or local deformation of rubber magnet in the BLDC motor is mathematically modeled by using the Fourier series. Distorted magnetic field is calculated by using the finite element method, and unbalanced magnetic force are calculated by using the Maxwell stress tensor. The first harmonic deformation in the global deformation of rubber magnet generates the first harmonic driving frequency of the unbalanced magnetic force, and the rest harmonic deformations of rubber magnet except the harmonic deformation with multiple of common divisor of pole and slot introduces the driving frequencies with multiple of slot number ${\pm}1$ to the unbalanced magnetic force. However, the harmonic deformation with multiple of common divisor of pole and slot does not generate unbalanced magnetic force due to the rotational symmetry. When the rubber magnet is locally deformed, the unbalanced magnetic force has the first harmonic driving frequency and the driving frequencies with multiples of slot number ${\pm}1$.

• 한국정밀공학회지
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• 제19권5호
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• pp.110-117
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• 2002

This paper proposes a optimization of the design variables of linear motor for the improvement of thrust. Especially, this paper treats the shoe, which can be good to flow of a magnetic flux in linear motor. Firstly, this paper uses a space harmonic analysis method(SHAM) based on Fourier series, for analyzing the characteristics of core type linear motor, including slot structure and shoe. And compare the magnetic flux densities of linear motor at air gap with the results of the SHAM and the Finite Element Method(FEM). Secondly, this paper uses a genetic algorithm, which is good to find the global solutions. The design variables are the pole pitch of magnet, the pitch of slot, the height of slot, the width of shoe and the width of magnet. The maximum thrust with optimum design variables is about 247 N which is improved about 16%.