• Structural Engineering and Mechanics
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• 제66권6호
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• pp.737-748
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• 2018

The current study presents a new technique in the framework of the nonlocal elasticity theory for a comprehensive buckling analysis of Euler-Bernoulli nano-beams made up of bidirectional functionally graded material (BDFGM). The mechanical properties are considered by exponential and arbitrary variations for axial and transverse directions, respectively. The various circumstances including tapering, resting on two-parameter elastic foundation, step-wise or continuous variations of axial loading, various shapes of sections with various distribution laws of mechanical properties and various boundary conditions like the multi-span beams are taken into account. As far as we know, for the first time in the current work, the buckling analyses of BDFGM nano-beams are carried out under mentioned circumstances. The critical buckling loads and mode shapes are calculated by using energy method and a new technique based on calculus of variations and collocation method. Fast convergence and excellent agreement with the known data in literature, wherever possible, presents the efficiency of proposed technique. The effects of boundary conditions, material and taper constants, foundation moduli, variable axial compression and small-scale of nano-beam on the buckling loads and mode shapes are investigated. Moreover the analytical solutions, for the simpler cases are provided in appendices.

• 한국전자파학회논문지
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• 제13권10호
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• pp.1005-1016
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• 2002

본 논문에서는 2 GHz 대역에서 하나의 입력과 다수의 출력을 가지는 [10]에서 제시 한 평면 Taper 혈의 전력 분배/결합기의 수정한 구조와 접지평면에 PBG(Photonic Band Cap) 구조를 적용한 형태의 전력 분배/결합 회로를 제안한다. 제안하는 구조의 전기적 특성을 걱정하는 파라메터들을 HFSS 시뮬레이션을 이용하여 분석하였다. 입력 정한 그리고 각 출력 판에서 출력 신호의 균형과 위상의 선형성을 위해 회로의 중앙에 하나의 원형 모양을 에칭 제거하였다. 또 본 논문에서 제안한 구조의 1:2와 1:3 전력 분배 / 결합기와 [10]의 구조와 5-Parameter를 비교ㆍ분석하였다. 결과적으로 본 연구에서 제시하는 수정된 형태를 적용할 경우 기존의 전력 분배/결합기의 반사손실 특성이 2 GHz에서 20 dB 이상 개선되었고. 이에 추가하여 PBG 구조를 적용하면 또 18 dB 이상 개선된 특성을 보였다. 대역폭 또한 증가되는 것을 확인하였다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 춘계학술대회 논문집
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• pp.585-590
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• 2002

Abrasive water-jet(AWJ) machining is a new cutting technology. The AWJ can cut various materials touch as metal, glass and stone. However, the AWJ machining makes troubles including kerf, rounding and side taper. In this study, we investigated the correlation between parameters of abrasive water-jet machining arid cutting characteristics. The machining parameter were the material thickness and the traverse speed. The experiment was conducted to cut the stainless steel(STS41) and the mild steel(SS41) specimens. The results of the experiment weirs presented as the relation between cutting conditions and trouble of a dimension error, a conner error, an uncut width and a kerf.

• Structural Engineering and Mechanics
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• 제45권1호
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• pp.69-93
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• 2013

The present study deals with the dynamics of the flapwise (out-of-plane) vibrations of a rotating, internally damped (Kelvin-Voigt model) tapered Bernoulli-Euler beam carrying a heavy tip mass. The centroid of the tip mass is offset from the free end of the beam and is located along its extended axis. The equation of motion and the corresponding boundary conditions are derived via the Hamilton's Principle, leading to a differential eigenvalue problem. Afterwards, this eigenvalue problem is solved by using Frobenius Method of solution in power series. The resulting characteristic equation is then solved numerically. The numerical results are tabulated for a variety of nondimensional rotational speed, tip mass, tip mass offset, mass moment of inertia, internal damping parameter, hub radius and taper ratio. These are compared with the results of a conventional finite element modeling as well, and excellent agreement is obtained.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 봄 학술발표회 논문집
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• pp.137-144
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• 1999

The finite element method was adopted to find out the natural frequencies of a sinusoidally tapered beam with simply supported boundary conditions. The parameters considered in the numerical analysis are the taper parameter, $\alpha$ ($\alpha$=0.0, 0.1, ~ , 2.0) and the sectional property parameters, m and n [(m, n):(0, 2), (1, 3), (2, 4)]. It is generally known that the results of the numerical analysis corresponding to each pair of sectional property parameters, (m, n) are represented by second order polynominals of $\alpha$ . The coefficients of a in the polynominals are determined by using the regression technique, which reveals small m in most cases of given sectional property parameters (m, n).

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.315-320
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• 2000

The optimal design for the shape of metal ring obturator under the high pressure using parameter study on the stress analysis considering effects of design variable is presented and is compared to experimental results. The design variables are such as thickness, taper, radius of shape of the obturation ring. For optimization of the obturation ring, the weight is maximized subject to maximum stress of the obturator within allowable stress. The design constraints are geometric elements of design variables. The trends of parametric study are in good agreement with the experimental results.

• 대한기계학회논문집A
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• 제34권7호
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• pp.919-928
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• 2010

연속주조 시에 폭변경 속도를 향상시키기 위해 폭조정의 4 가지 패턴에 대해 연구하였다. 주요 사항은 폭변경 장치의 구동력을 최소화하고, 몰드 내의 응고막의 변형해석 모델을 개발하고, 폭변경 속도 상승을 제한하는 주요인자를 도출하는 것이다. 폭변경 실험을 근간으로 4 개 패턴의 주요 특징을 도출하였고, 각 패턴에 대한 힘을 비교하였다. 실험은 각 패턴의 구동력 비교를 위해 동일한 주조속도에서 수행하였다. 응고막변형 해석모델의 변수를 조정하기 위해 실험결과를 모델에 적용하였다. 폭변경 속도를 상승시키고, 구동력을 저감시키기 위해 패턴의 변수를 제어하였다. 가장 효율적인 패턴은 고속패턴이었으며, 구동력을 저감하기 위한 주요인자는 구동장치가 이동할 때의 기울기였다.

• 유공압시스템학회논문집
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• 제2권3호
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• pp.1-5
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• 2005

There are two types of solenoid actuator for force and position control of the fluid power system. One is an on-off solenoid actuator and the other is an electro-magnetic proportional actuator. They have some different characteristics for attraction force according to solenoid shape. Attraction force of the on-off solenoid actuator only depends on flux density. And the stroke-force characteristics of the proportional solenoid actuator are determined by the shape of the control cone. In this paper, steady state characteristics of the solenoid actuator for electro-hydraulic proportional valve determined by the shape of control cone are analyzed using finite element method and it is confirmed that the proportional solenoid actuator has a constant attractive force in the control region independently on the stroke position. And the shape of control cone is optimized using 1+1 evolution strategy to get a constant force. In the optimization algorithm, control cone length, thickness and taper length are used as a design parameter.

• 소성∙가공
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• 제30권6호
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• pp.275-283
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• 2021

A parametric study was conducted on the effects of five fundamental design parameters on springback, including die clearance, step height, step width, punch radius, and taper relief in an L-bending process, controlled by the compression force. The experiment was also conducted to verify the usefulness of the parametric study procedure for process design, as well as the finite element predictions. The elastoplastic finite element method was utilized. The L-bending process of the york product, which is a key part of the breaker mechanism, was employed. The deformation of the material was assumed to be due to plane strain. Five samples of each design parameter were selected based on experiences in terms of process design. The finite element predictions were analyzed in detail to show a shortcut towards the process design improvement which can replace the traditional process design procedure relying on trial-and-errors. The improved process design was verified to meet all the requirements and the predictions and experiments were in good agreement.

• 한국전자파학회논문지
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• 제27권12호
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• pp.1059-1068
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• 2016

본 논문에서는 프린트 다이폴의 지향성 증가와 동시에 부엽 레벨을 억제하는 기능을 가진 저속파 구조를 제안하고 구성 설계변수의 변화에 따른 전기적 특성의 변화를 알아보고자 한다. 유전체 기판과 도체 막대의 배열로 구성된 프린트 형태의 저속파 구조는 프린트 다이폴 안테나의 여기 방향에 위치하며 안테나의 방사 패턴 및 세기에 영향을 미친다. 이 도체 막대로 된 기생소자는 좁은 간격을 가지고 일정하게 배열되며 소자의 길이는 점차 줄어드는 형상을 가진다. 따라서 본 연구에서는 저속파 구조에서 방사 성능에 영향을 줄 수 있는 변수로 기생소자 배열 간격, 소자 길이, 소자 길이의 테이퍼 각도가 고려되며, 변수들의 변화에 따른 전기장 세기 및 위상 분포가 관찰 및 분석된다. 이를 기반으로 방사패턴이 분석이 되며, 고지향성 특성을 위한 저속파 구조의 기생소자 배열 방안이 제공된다. 제안된 안테나는 Wifi 대역(5.15~5.85 GHz)에서 동작하도록 설계되며, 안테나의 이득을 극대화하고 부엽을 억제하도록 저속파 기생소자의 설계변수가 최적화된다. 제작된 안테나의 시뮬레이션 및 측정 결과 넓은 대역폭 특성을 나타내며, 높은 효율과 이득, 낮은 부엽 레벨을 갖는 것을 확인할 수 있다.