• 한국항공우주학회지
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• 제32권8호
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• pp.91-100
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• 2004

경사기능재료 판에 대한 열탄성 변형과 응력 해석을 위해 Green 함수 방법이 채택되었다. 3 차원 비정상 온도분포에 대한 해는 적층판 이론에 의해 얻어진다. 열탄성 문제에 대한 기본 방정식은 각각 평면외 (out-plane) 변형과 평면내 (in-plane) 힘에 의해 유도되었다. 굽힘과 평면내 힘에 의한 열탄성 변형과 응력분포는 Galerkin 방법에 근거한 Green 함수를 이용하여 해석하였다. 열탄성 변형과 응력분포 해석을 위한 Galerkin Green 함수의 특성함수들은 사각판의 제차 경계조건을 만족시키는 허용함수들의 급수 형태로 근사화되었다. 단수지시된 사각 판에 대한 수치해석이 수행되었으며, 정사기능재료의 물성치가 판의 비정상 열탄성 거동에 미치는 영향이 검토되었다.

• 한국광학회지
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• 제21권5호
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• pp.214-223
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• 2010

30 cm 급 항공용 반사 망원경계에서 외부 환경 및 내부 진동에 의해 발생하는 주 반사경의 광학적인 성능 저하를 최소화하기 위하여 주 반사경의 광기계 설계를 수행 하였다. 플렉셔를 포함한 주 반사경의 해석을 위한 경계조건으로는 광학면의 수직과 수평 방향의 중력에 의한 변형과 온도 변화 ${\pm}1^{\circ}C$에 의한 열 변형을 고려하였다. 반사경의 기계적인 변형은 NX 5 I-DEAS를 사용하여 해석 하였다. 최적화된 경량화 반사경과 플렉셔의 중력에 의한 광학면의 형상 변형은 RMS surface error 16 nm 이하로 초기 설계 목표값을 만족하였다. 온도 변화 ${\pm}1^{\circ}C$에 의한 광학면의 형상 변형과 assembly load에 의한 광학면의 형상 변형은 매우 작은 값으로 주 반사경의 변형에 영향을 주지 않음을 확인하였다.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 1997년도 추계학술강연 및 발표대회 강연 및 발표논문 초록집
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• pp.7-7
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• 1997

During sintering of very porous green bodies, as obtained by compaction of hard powders - such as tungsten carbide or ceramics - or by injection moulding, important shrinkage occurs. Due to heterogeneous green density field, gravity effects, friction on the support, thermal gradients, etc., this shrinkage is often non-uniform, which' may induce significant shape changes. As the ratio of compact dimension to powder size is very high, the mechanics of continuum is relevant to model such phenomena. Thus numerical techniques, such as the finite element method can be used to simulate the sintering process and predict the final shape of the sintered part. Such type of simulation has much been developed in the last decade firstly for hot isostatic pressing and next for die compaction. Finite element modelling has been recently applied to free sintering. The simulation of sintering should be based on constitutive equations describing the thermo-mechanical behaviour of the material under any state of stress and any temperature which may arise within the sintering body. These equations can be drawn either from experimental data or from micromechanical models. The experiments usually consist in free sintering and sinter-forging tests. Indeed applying more complex loading conditions at high temperature under controlled atmosphere is delicate. Micromechanical models describe the constitutive behaviour of aggregates of spheres from the deformation of two-sphere contact either by viscous flow or grain boundary diffusion. Such models are not able to describe complex microstructure and mechanisms as observed in real materials but they can give some basic information on the formulation of constitutive equations. Practically both experimental and theoretical approaches can be coupled to identify the constitutive equations. Such procedure has been performed for modelling the sintering of compacts obtained by die pressing of a mixture of tungsten carbide and cobalt powders. The constitutive behaviour of this material during sintering has been described by a linear viscous constitutive model, whose functions have been fitted from results of free sintering and sinter-forging experiments. This model has next been introduced in ABAQUS finite element code to simulate the sintering of heterogeneous green compacts of various geometries at constant temperature. Examples of simulations are shown and compared with experiments.

• Geomechanics and Engineering
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• 제22권4호
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• pp.361-374
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• 2020

This paper is concerned with the thermoelastic bending of FG beams resting on two-layer elastic foundations. One of these layers is Winkler springs with a variable modulus while the other is considered as a shear layer with a constant modulus. The beams are considered simply supported and subjected to thermo-mechanical loading. Temperature-dependent material properties are considered for the FG beams, which are assumed to be graded continuously across the panel thickness. The used theories contain undetermined integral terms which lead to a reduction of unknowns functions. Several micromechanical models are used to estimate the effective two-phase FG material properties as a function of the particles' volume fraction considering thermal effects. Analytical solutions for the thermo-mechanical bending analysis are obtained based on Navier's method that satisfies the boundary conditions. Finally, the numerical results are provided to reveal the effect of explicit micromechanical models, geometric parameters, temperature distribution and elastic foundation parameters on the thermoelastic response of FG beams.

• Steel and Composite Structures
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• 제26권6호
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• pp.673-691
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• 2018

The main goal of this research is to examine the in-plane and out-of-plane forced vibration of a curved nanocomposite microbeam. The in-plane and out-of-plane displacements of the structure are considered based on the first order shear deformation theory (FSDT). The curved microbeam is reinforced by functionally graded carbon nanotubes (FG-CNTs) and thus the extended rule of mixture is employed to estimate the effective material properties of the structure. Also, the small scale effect is captured using the strain gradient theory. The structure is rested on a nonlinear orthotropic viscoelastic foundation and is subjected to concentrated transverse harmonic external force, thermal and magnetic loads. The derivation of the governing equations is performed using energy method and Hamilton's principle. Differential quadrature (DQ) method along with integral quadrature (IQ) and Newmark methods are employed to solve the problem. The effect of various parameters such as volume fraction and distribution type of CNTs, boundary conditions, elastic foundation, temperature changes, material length scale parameters, magnetic field, central angle and width to thickness ratio are studied on the frequency and force responses of the structure. The results indicate that the highest frequency and lowest vibration amplitude belongs to FGX distribution type while the inverse condition is observed for FGO distribution type. In addition, the hardening-type response of the structure with FGX distribution type is more intense with respect to the other distribution types.

• 대한기계학회논문집A
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• 제25권10호
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• pp.1514-1519
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• 2001

This paper is concerned with design, manufacturing and performance test of LIPCA ( Lightweight Piezo- composite Curved Actuator) using a top carbon fiber composite layer with near -zero CTE(coefficient of thermal expansion), a middle PZT ceramic wafer and a bottom glass/epoxy layer with high CTE. The main point of this design is to replace the heavy metal layers of THUNDER by thigh tweight fiber reinforced plastic layers without losing capabilities to generate high force and large displacement. It is possible to save weight up to about 30% if we replace the metallic backing material by the light fiber composite layer. We can also have design flexibility by selecting the fiber direction and the size of prepreg layers. In addition to the lightweight advantage and design flexibility, the proposed device can be manufactured without adhesive layers when we use epoxy resin prepreg system. Glass/epoxy prepregs, a ceramic wafer with electrode surfaces, and a graphite/epoxy prepreg were simply stacked and cured at an elevated temperature (177 $^{circ}C$ after following an autoclave bagging process. It was found that the manufactured composite laminate device had a sufficient curvature after detached from a flat mold. The analysis method of the cure curvature of LIPCA using the classical lamination theory is presented. The predicted curvatures are fairly in agreement with the experimental ones. In order to investigate the merits of LIPCA, a performance test of both LIPCA and THUNDE$^{TM}$ were conducted under the same boundary conditions. From the experimental actuation tests, it was observed that the developed actuator could generate larger actuation displacement than THUNDERT$^{TM}$.

• 대한기계학회논문집B
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• 제37권1호
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• pp.75-79
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• 2013

반도체 수요의 폭발적인 증가와 기술의 진보로 단위면적당 소자수가 늘어나고 있다. 그에 따라 단위면적당 발열량이 더욱 높아져서 반도체의 수명과 신뢰성 보장을 위한 냉각문제의 해결이 점점 중요해지고 있다. 특히, 집적도를 높이기 위해 소자를 기판에 매립하는 chip-in-board (CIB) 패키지에서는 방열이 더욱 심각한 문제가 된다. 본 논문에서는 각기 다른 재질의 층으로 구성된 열 전달모형을 설정하고, 3 차원 열 전달 해석으로 적절한 경계 조건에 맞추어 계산하였다. 이를 토대로 발열량을 정량적으로 예측하여 실제모델에 적용 될 수 있는 설계자료로 이용하고자 한다.

• 공업화학
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• 제7권3호
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• pp.518-529
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• 1996

본 연구는 폐열 및 태양에너지를 유용하게 이용하기위한 화학열펌프 개발 목적으로 고온영역 히트펌프에서의 원주형 반응기 충진층내 핀을 주입 전열촉진한 경우의 전열 및 반응촉진효과의 이론적 평가를 행하였다. CaO 반응층의 열 및 물질 이동에 관해서 반경방향, 원주방향에 대해 2차원 편미분방정식을 수치 적분하여 핀 주입형 반응층내 반응 및 전열 특성을 조사하였으며, 반응층내 온도분포변화, 반응완결시간, 방열량에 대한 수치해석 결과는 다음과 같다. -. 전열 핀주입에 따른 반응완결 시간이 절반이하로 줄일 수 있다고 한 실험결과와 잘 일치됨을 알 수 있었다. -. 해석결과 열화학 반응은 온도 및 농도에 주로 의존하였고, 경계 조건과 입자 충전층의 열전도도에 의해 크게 좌우되었음을 알 수 있었다.

• 공업화학
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• 제7권6호
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• pp.1181-1191
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• 1996

본 연구는 고온용 열구동형 화학열펌프에 있어서 폐열 및 태양에너지를 유용하게 이용하기위한 목적으로 $Ca(OH)_2$ 탈수반응시 원주형 반응기 충진층내 핀을 주입 전열촉진한 경우의 전열 및 반응촉진효과에 대해 이론적 평가를 행하였다. 그 결과 탈수흡열 반응시 반응층내 온도분포변화, 반응완결시간, 방열량에 대한 수치해석 결과 구리판 전열핀을 설치한 경우 입자 충전층의 탈수반응 소요시간을 크게 단축시킬 수 있었으며, 본 실험조건 하에서는 전열핀을 주입하지 않았을 때보다 탈수반응 소요시간이 1/2정도 단축됨을 알 수 있었다. 또한 해석결과 열화학반응은 온도 및 농도에 주로 의존하였고, 경계조건과 입자충전층의 열전도도에 의해 크게 좌우되었음을 알 수 있었다.

• Nuclear Engineering and Technology
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• 제45권5호
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• pp.613-624
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• 2013

Multi-dimensional two-phase phenomena occur in many industrial applications, particularly in a nuclear reactor during steady operation or a transient period. Appropriate modeling of complicated behavior induced by a multi-dimensional flow is important for the reactor safety analysis results. SPACE, a safety analysis code for thermal hydraulic systems which is currently being developed, was designed to have the capacity of multi-dimensional two-phase thermo-dynamic phenomena induced in the various phases of a nuclear system. To validate the performance of SPACE, a two-dimensional two-phase flow test was performed with slab geometry of the test section having a scale of $1.43m{\times}1.43m{\times}0.11m$. The test section has three inlet and three outlet nozzles on the bottom and top gap walls, respectively, and two outlet nozzles installed directly on the surface of the slab. Various kinds of two-dimensional air/water flows were simulated by selecting combinations of the inlet and outlet nozzles. In this study, two-dimensional two-phase void fraction profiles were quantified by measuring the local gap impedance at 225 points. The flow conditions cover various flow regimes by controlling the flow rate at the inlet boundary. For each selected inlet and outlet nozzle combination, the water flow rate ranged from 2 to 20 kg/s, and the air flow rate ranged from 2.0 to 20 g/s, which corresponds to 0.4 to 4 m/s and 0.2 to 2.3 m/s of the superficial liquid and gas velocities based on the inlet port area, respectively.