• 한국항행학회논문지
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• 제15권4호
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• pp.543-548
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• 2011

본 논문에서는 스트립 폭과 격자주기, 유전체 층의 비유전율과 두께, 그리고 TE(transverse electric) 평면파의 입사각에 따른 접지된 유전체 평면위의 변하는 저항율을 갖는 저항띠 격자구조에 의한 H-분극 전자파 산란문제를 FGMM(Fourier-Galerkin Moment Method)를 이용하여 해석하였다. 저항띠의 변하는 저항율은 한쪽 모서리에서는 유한하고 다른쪽 모서리에서 0 저항율을 가지며, 이때 저항띠 위에서 유도되는 표면 전류밀도는 직교다항식의 일종인 차수가 ${\alpha}=1$, ${\beta}=0$인 Jacobi 다항식의 급수로 전개하였다. 정규화된 반사전력의 수치결과는 기존의 수치결과와 매우 일치하였다.

• Structural Engineering and Mechanics
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• 제85권1호
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• pp.105-118
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• 2023

The present work is an attempt to develop a simple and accurate finite element formulation for the assessment of thermal shock/thermally induced vibrations in pretwisted and tapered functionally graded material thin (FGM) blades obtained from Voigt and local representative volume elements (LRVE) homogenization models, based on neutral surface approach. The neutral surface of the FGM blade does not coincide with its mid-surface. A finite element model (FEM) is developed using first-order shear deformation theory (FSDT) and the FGM turbine blade is modelled according to the shallow shell theory. The top and the bottom layers of the FGM blade are made of pure ceramic and pure metal, respectively and temperature-dependent material properties are functionally graded in the thickness direction, the position of the neutral surface also depends on the temperature. The material properties are estimated according to two different homogenization models viz., Voigt or LRVE. The top layer of the FGM blade is subjected to high temperature and the bottom surface is either thermally insulated or kept at room temperature. The solution of the nonlinear profile of the temperature in the thickness direction is obtained from the Fourier law of heat conduction in the unsteady state. The results obtained from the present FEM are compared with the benchmark examples. Next, the effect of angle of twist, intensity of thermal shock, variable chord and span and volume fraction index on the transient response due to thermal shock obtained from the two homogenization models viz., Voigt and LRVE scheme is investigated. It is shown that there can be a significant difference in the transient response calculated by the two homogenization models for a particular set of material and geometric parameters.

• 대한기계학회논문집A
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• 제21권1호
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• pp.180-187
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• 1997

A formula for estimating the elastic stiffness of TW-HDS with a uniformly tapered width from w$_{0}$ to w$_{1}$ over the length, has been analytically derived based on Euler beam theory and Castigliano's theorem. Elastic stiffnesses of the TW-HDSs designed in the same dimensional design spaces as the KOFA HDSs have been estimated from the derived formula, in addition, a sensitivity study on the elastic stiffness of the TW-HDSs has been carried out. Analysis results show that elastic stiffnesses of the TW-HDSs have been by far higher than those of the KOFA HDSs, and that, as the effects of axial and shear force on the elastic stiffness have been 0.15-0.21%, most of the elastic stiffness is attributed to the bending moment. As a result of sensitivity analysis, the elastic stiffness sensitivity at each design variable is quantified and design variables having remarkable sensitivity are identified. Among the design variables, leaf thickness is identified as that of having the most remarkable sensitivity of the elastic stiffness.

• 정보학연구
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• 제8권2호
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• pp.77-84
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• 2005

In this paper, electromagnetic scattering problems by a resistive strip grating with tapered resistivity on a grounded dielectric plane according to strip width and spacing, relative permittivity and thickness of dielectric layers, and incident angles of a electric wave are analyzed by applying the Fourier-Galerkin Moment Method known as a numerical procedure. The boundary conditions are applied to obtain the unknown field coefficients and the resistive boundary condition is used for the relationship between the tangential electric field and the electric current density on the strip. The resistivity of resistive strips in this paper varies from zeroes at one edge to infinite at the other edge, then the induced surface current density on the resistive strip is expanded in a series of Jacobi polynomials of the order ${\alpha}=0.2,\;{\beta}=-0.2$ as a orthogonal polynomials. The numerical results of the geometrically normalized reflected power in this paper are compared with those for the existing perfectly conducting strip. The numerical results of the normalized reflected power for conductive strips case with zero resistivity in this paper show in good agreement with those of existing papers.

• Steel and Composite Structures
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• 제11권6호
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• pp.435-454
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• 2011

Bonding composite materials to structural members for strengthening purpose has received a considerable attention in recent years. The major problem when using bonded FRP or steel plates to strengthen existing structures is the high interfacial stresses that may be built up near the plate ends which lead to premature failure of the structure. As a result, many researchers have developed several analytical methods to predict the interface performance of bonded repairs. In this paper, a numerical solution using finite - difference method is used to calculate the interfacial stress distribution in beams strengthened with FRP plate having a tapered ends with different thinning profiles. These latter, can significantly reduce the stress concentration. In the present theoretical analysis, the adherend shear deformations are taken into account by assuming a parabolic shear stress through the thickness of both beam and bonded plate. Numerical results from the present analysis are presented to demonstrate the advantages of use the tapers in design of strengthened beams.

• Advances in Computational Design
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• 제3권2호
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• pp.165-190
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• 2018

In this article, the static behavior of non-prismatic sandwich beams composed of functionally graded (FG) materials is investigated for the first time. Two types of beams in which the variation of elastic modulus follows a power-law form are studied. The principle of minimum total potential energy is applied along with the Ritz method to derive and solve the governing equations. Considering conventional boundary conditions, Chebyshev polynomials of the first kind are used as auxiliary shape functions. The formulation is developed within the framework of well-known Timoshenko and Reddy beam theories (TBT, RBT). Since the beams are simultaneously tapered and functionally graded, bending and shear stress pushover curves are presented to get a profound insight into the variation of stresses along the beam. The proposed formulations and solution scheme are verified through benchmark problems. In this context, excellent agreement is observed. Numerical results are included considering beams with various cross sectional types to inspect the effects of taper ratio and gradient index on deflections and stresses. It is observed that the boundary conditions, taper ratio, gradient index value and core to the thickness ratio significantly influence the stress and deflection responses.

• Tribology and Lubricants
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• 제29권6호
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• pp.353-359
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• 2013

The rollers and/or races in cylindrical and tapered roller bearings should be profiled to relieve high edge stress concentrations caused by their finite lengths and misalignment. In this study, a numerical analysis was performed to investigate the elastohydrodynamic lubrication (EHL) of a Lundberg profile-type cylindrical roller. A finite difference method with fully nonuniform grids and the Newton-Raphson method were used to present detailed EHL pressure distributions and film shapes, as well as the variations in the minimum and central film thicknesses with the profile modification coefficient. In the Lundberg profile, the maximum pressure and minimum film thickness always occurred near the edges. Proper modification of the Lundberg profile considerably increased the minimum film thickness.

• 마이크로전자및패키징학회지
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• 제11권2호
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• pp.59-66
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• 2004

본 연구에서는 유리기판을 통한 SU-8의 이중층을 후면 노광을 통하여 테이퍼지고 속이 빈 형태의 마이크로니들 배열구조물을 만드는 새로운 방법을 제안하였으며 테이퍼지고 속이 빈 형태의 원형축의 Buckling현상에 관한 해석해를 구하였다. Pyrex 7740을 유리기판으로 사용하고 이중층 구조의 SU-8 막을 후면 노광으로 금형 구조물을 제작하는 공정을 개발하였다. $200\;{\mu}m$ 높이의 SU-8기둥들에서 $4.37{\sim}5^{\circ}$범위의 테이퍼 각도를 $400\;{\mu}m$ 높이의 SU-8기둥에서는 $3.08{\sim}4.48^{\circ}$범위 내의 테이퍼 각을 보여주고 있다. 후면 유체저장소와 가로세로 각각 10개의 테이퍼 형태로 전기도금된 니켈 마이크로니들 어레이를 유리 기판을 통해 이중층 구조의 SU-8막을 후면 노광하고. 니켈을 전기도금 함으로서 실현시켰다. $200\;{\mu}m$와 $400\;{\mu}m$ 높이의 벽두께 $10{\mu}m-20{\mu}m$ 및 내경 $33.6{\mu}m-101{\mu}m$인 마이크로니들 어레이를 제작하였다. 또한 $400\;{\mu}m$ 높이의 벽두께 $20\;{\mu}m$ 및 내경 $33.6\;{\mu}m$인 $3.08^{\circ}$의 테이퍼 각 마이크로니들의 임계 버클링힘은 1.8N이었다. 이 해는 차후의 테이퍼 형태의 마이크로니들의 설계시 많은 도움을 주리라 생각한다.

• Steel and Composite Structures
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• 제51권6호
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• pp.601-617
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• 2024

This work aims to explore the static behaviour of a tapered functionally graded porous plate (FGPP) with even and uneven porosity distributions resting on two parametric elastic foundations. The plate under investigation is subjected to bi-sinusoidal loading and the edges of the plate are exposed to different combinations of edge restrictions. In order to examin the static behaviour, bending factors (BF) related to bending and normal stresses have been evaluated using classical plate theory. To achieve this, the governing equations have been derived employing the energy concept. And to solve it, the Rayleigh-Ritz method with an algebraic function has been utilised; it is simple, precise, and computationally intensive. After convergence and validation analyses, new findings are made available. The BF of the plate have been exhaustively examined to explain the influence of aspect ratios, material property index, porosity factor, taper factor, and Winkler and Pasternak stiffness. It is observed that the BF of an elastically supported FGPP are influenced by the index of material propery and the aspect ratio. Findings also indicate that the impact of porosity is more when it is spread evenly, as opposed to when it is unevenly distributed. Further, the deformed plate's structure is significantly influenced by the different thickness variations. Examination of bending characteristics of FGPP having different new cases of thickness variations with different types of porosity distribution under fifteen different mixed edge constraints is the prime novality of this work. Results presented are reliable enough to be taken into account for future studies.

• 한국음향학회지
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• 제27권6호
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• pp.271-278
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• 2008

압전판의 길이나 폭에 따라 두께가 변화하는 압전 세라믹을 사용하여 광대역 특성을 구현하는 초음파 트랜스듀서에 대하여 압전진동자의 측면에서 본 형태에 따른 전기-음향적 특성해석을 이론적으로 수행하였다. 압전진동자의 길이방향에 따른 두께 변화를 지수함수의 조합으로 표현하고 이 함수를 이용하여 압전진동자의 전기단자에서 본 자유 어드미턴스 및 파워전달함수에 대한 식을 도출하였다. 대표적인 PZT압전 세라믹을 예로 들어 압전 진동자의 측면 형태변화에 따른 비 대역폭을 고찰해본 결과 넓은 대역폭를 얻기 위한 최적의 형태가 존재함을 알 수 있었으며, 압전진동자의 최대두께에 대한 최소두께 비가 자아짐에 따라 대역폭은 100%이상까지도 넓어질 수 있으나 파워전달함수는 반대로 감소하는 경향을 확인할 수 있었다. 또 압전진동자의 길이가 길어질수록 전달함수의 크기는 증가하나 광대역 특성을 갖는 압전진동자의 형태는 매우 한정적이 됨을 확인할 수 있었으며 이는 고효율의 광대역 초음파 트렌스듀서 제작에 있어서는 정밀한 가공이 요구됨을 확인할 수 있었다.