• 한국압력기기공학회 논문집
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• 제12권1호
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• pp.41-48
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• 2016

To investigate the effect of long-term thermal aging on the microstructural and mechanical characteristics of weldment made of nickel base alloy and its weld metal, an accelerated heat treatment was applied to simulate the process of long-term thermal aging in the operating condition of nuclear power plant. A representative nickel-based weldment with Alloy 600 and Alloy 182 was fabricated and heat-treated at $400^{\circ}C$ for 1,713 h and 3,427 h to simulate the thermal aging for the period equivalent to 15 and 30 years in operating pressurized water reactors, respectively. The microstructural and mechanical characteristics were analyzed by using optical microscopy, scanning electron microscopy and Vickers microhardness measurement. Changes were observed in precipitation behavior and microhardness of each specimen, and these changes were mainly attributed to the change in precipitated morphology and residual stress across the weld during the thermal aging process.

• Structural Engineering and Mechanics
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• 제53권3호
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• pp.497-517
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• 2015

In this study, nonlocal nonlinear buckling analysis of embedded polymeric temperature-dependent microplates resting on an elastic matrix as orthotropic temperature-dependent elastomeric medium is investigated. The microplate is reinforced by single-walled carbon nanotubes (SWCNTs) in which the equivalent material properties nanocomposite are estimated based on the rule of mixture. For the carbon-nanotube reinforced composite (CNTRC) plate, both cases of uniform distribution (UD) and functionally graded (FG) distribution patterns of SWCNT reinforcements are considered. The small size effects of microplate are considered based on Eringen's nonlocal theory. Based on orthotropic Mindlin plate theory along with von K$\acute{a}$rm$\acute{a}$n geometric nonlinearity and Hamilton's principle, the governing equations are derived. Generalized differential quadrature method (GDQM) is applied for obtaining the buckling load of system. The effects of different parameters such as nonlocal parameters, volume fractions of SWCNTs, distribution type of SWCNTs in polymer, elastomeric medium, aspect ratio, boundary condition, orientation of foundation orthtotropy direction and temperature are considered on the nonlinear buckling of the microplate. Results indicate that CNT distribution close to top and bottom are more efficient than those distributed nearby the mid-plane for increasing the buckling load.

• Korean Chemical Engineering Research
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• 제46권3호
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• pp.604-609
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• 2008

본 연구에서는 세계보건기구의 기준을 만족시키기 위한 포장재 개발을 목적으로 백신 수송용 장방형 포장재 내부열 전달에 대한 모델링 및 시뮬레이션을 수행하고 이를 실험결과와 비교하였다. 장방형의 박스를 구형 박스로 전환하여 구상한 1차원 모델은 냉각공정의 경우에는 실험 결과와 비교적 잘 일치하는 결과를 보였으나, 가열공정에서는 실험결과와 상당한 차이를 보여주었다. 이는 가열공정을 계산할 때, 포장재 외부에서의 경계조건을 적절히 고려해주지 못한 결과로 사료된다. 그러나, 본 연구를 통하여 상전이 물질을 함유한 다층 벽을 통한 열 전달의 문제를 전산 모사할 수 있는 기본적인 알고리즘을 성공적으로 개발할 수 있었다.

• 한국정밀공학회지
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• 제27권12호
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• pp.99-106
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• 2010

Gas turbines operation for power generation increased rapidly since 1990 due to the high efficiency in combined cycle, relatively low construction cost and low emission. But the operation and maintenance cost for gas turbine is high because the expensive superalloy hot gas path parts should be repaired and replaced periodically This study analyzed the initiation and propagation of the crack at the gas turbine blades which are coated with MCrAIY as a bond coat and TBC as a top coat. The sample blades had been serviced at the actual gas turbines for power generation. Total 7 sets of blades were analyzed and they have different EOH(equivalent operation hour). Blades were sectioned and the cracking distribution were measured and analyzed utilizing SEM(scanning electron microscope) and optical microscope. The blades which had 52,000 EOH of operation had cracks at the substrate and the maximum depth was 0.2 mm. Most of the cracks initiated at the boundary layer between TBC and bond coat and propagated down to the bond coat. Once bond coat is cracked, the base metal is exposed to the oxidation condition and undergoes notch effect. Under this environment, the crack branched at the inter-diffusion layer and propagated to the substrate. Critical cracks affecting the blade life were analyzed as those on suction side and platform.

• Structural Engineering and Mechanics
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• 제90권4호
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• pp.357-370
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• 2024

Due to the fact that the mechanism of the effects of temperature and initial geometric imperfection on low-velocity impact problem of axially moving plates is not yet clear, the present paper is to fill the gap. In the present paper, the nonlinear dynamic behavior of axially moving imperfect graphene platelet reinforced metal foams (GPLRMF) plates subjected to lowvelocity impact in thermal environment is analyzed. The equivalent physical parameters of GPLRMF plates are estimated based on the Halpin-Tsai equation and the mixing rule. Combining Kirchhoff plate theory and the modified nonlinear Hertz contact theory, the nonlinear governing equations of GPLRMF plates are derived. Under the condition of simply supported boundary, the nonlinear control equation is discretized with the help of Gallekin method. The correctness of the proposed model is verified by comparison with the existing results. Finally, the time history curves of contact force and transverse center displacement are obtained by using the fourth order Runge-Kutta method. Through detailed parameter research, the effects of graphene platelet (GPL) distribution mode, foam distribution mode, GPL weight fraction, foam coefficient, axial moving speed, prestressing force, temperature changes, damping coefficient, initial geometric defect, radius and initial velocity of the impactor on the nonlinear impact problem are explored. The results indicate that temperature changes and initial geometric imperfections have significant impacts.

• 문화기술의 융합
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• 제7권2호
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• pp.405-410
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• 2021

본 연구에서는 레일체결장치용 방진패드의 사용수명 및 스프링강성을 평가하고자 비선형 재료모델 및 피로하중조건을 적용한 유한요소해석을 수행하였다. 피로해석 결과, 초기조건 대비 스프링강성의 변화율은 약 16%로 나타나 피로경화가 발생된 것으로 분석되었다. 방진패드의 길이방향으로 발생되는 응력은 중앙부와 외곽부(Edge)의 발생응력의 차이가 약 10배 이상 발생되었다. 또한 중앙부 보다 외곽 경계부의 등가응력이 2배 이상 크게 발생하는 것으로 분석되었다. 따라서 실제 사용조건에서 방진패드의 손상 및 변형 취약부는 방진패드의 모서리부분인 것으로 분석되었다. 피로해석을 통해 산출된 반복횟수에 따른 방진패드의 등가응력을 이용하여 방진패드의 피로수명선도를 도출하였다. 본 연구에서 도출한 방진패드의 피로수명선도를 이용하여 향후 다양한 하중조건에서 방진패드의 등가응력을 산출하여 해당조건에서의 피로수명을 예측하는 데에 활용이 가능할 것으로 판단된다.

• 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.

• 대한의용생체공학회:의공학회지
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• 제43권5호
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• pp.308-318
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• 2022

The purpose of this study is to evaluate the biomechanical properties of fractured adjacent soft tissue during closed reduction after forearm fracture using the finite element method. To accomplish this, a finite element (FE) model of the forearm including soft tissue was constructed, and the material properties reported in previous studies were implemented. Based on this, nine finite element models with different fracture types and fracture positions, which are the main parameters, were subjected to finite element analysis under the same load and boundary conditions. The load condition simulated the traction of increasing the fracture site spacing from 0.4 mm to 1.6 mm at intervals of 0.4 mm at the distal end of the radioulnar bone. Through the finite element analysis, the fracture type, fracture location, and displacement were compared and analyzed for the fracture site spacing of the fractured portion and the maximum equivalent stress of the soft tissues adjacent to the fracture(interosseous membrane, muscle, fat, and skin). The results of this study are as follows. The effect of the major parameters on the fracture site spacing of the fractured part is negligible. Also, from the displacement of 1.2 mm, the maximum equivalent stress of the interosseous membrane and muscle adjacent to the fractured bone exceeds the ultimate tensile strength of the material. In addition, it was confirmed that the maximum equivalent stresses of soft tissues(fat, skin) were different in size but similar in trend. As a result, this study was able to numerically confirm the damage to the adjacent soft tissue due to the fracture site spacing during closed reduction of forearm fracture.

• 터널과지하공간
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• 제31권4호
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• pp.270-288
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• 2021

본 연구에서는 입자기반 개별요소모델(grain-based distinct element model, GBDEM)을 이용하여 암석 균열의 역학적, 수리적 거동을 평가할 수 있는 수치해석기법을 제시하고 해석해와의 비교를 통해 검증하였다. 이는 DECOVALEX-2023 프로젝트 Task G의 일환으로 수행된 벤치마크 모델링 연구로, Task G는 결정질 암반 내 균열의 열-수리-역학적 복합거동을 해석하기 위한 수치해석기법을 개발하는 데에 목표가 있다. 본 연구에서는 사면체 개별 입자들을 이용하여 해석모델을 생성하고 3DEC을 이용하여 입자와 접촉에서의 거동을 해석하였다. 이 과정에서 등가연속체 개념을 적용해 입자기반모델의 미시물성을 산정할 수 있는 새로운 기법을 제시하였다. 한편, 균열 경사각과 거칠기, 경계응력조건 및 압력 조건에 따른 해석을 실시하여 각 해석조건이 균열의 수직, 전단방향 거동에 미치는 영향을 살펴보았다. 해석 결과, 제안된 수치모델은 경계응력에 따른 균열의 미끄러짐(fracture slip)과 유체 압력에 따른 균열의 개방(fracture opening), 균열 경사에 따른 응력 분포, 거칠기로 인한 전단변위의 구속 등을 합리적으로 재현하고 있음을 확인하였다. 수치해석을 통해 계산된 균열의 수직방향, 전단방향 변위는 모두 해석해를 통해 계산된 값과 거의 일치하는 결과를 보였다. 본 연구의 해석모델은 Task G에 참여하는 국외 연구팀들과의 의견 교류와 워크숍을 통해 지속적으로 개선하는 한편, 향후 다양한 조건의 실내시험에 적용하여 타당성을 검증할 예정이다.

• 한국전자파학회논문지
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• 제18권7호
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• pp.819-827
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• 2007

본 논문은 논에 대한 전파 산란 특성을 측정하고, 수치적 계산 결과와 비교함으로써 벼의 수치적 모델링에 대한 전파 산란 알고리즘을 제시하고자 한다. 임피던스 경계 조건과 dyadic 그린함수로부터 임피던스 표면 위(수면)의 손실 있는 유전체(벼)에 대한 적분 방정식을 유도하였고, 모멘트 법을 이용하여 유전체의 체적 전류를 계산하였다. 또한, 몬테 카를로 방법을 적용하여 입사 각도 및 편파에 따른 후방 산란 계수를 수치적으로 계산하였다. 1.85 GHz의 측정 시스템을 이용하여 논의 후방 산란 계수를 측정하였으며, 본 논문에서 제시한 알고리즘의 계산 결과와 비교, 검증하였다.