• 폴리머
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• 제24권5호
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• pp.690-700
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• 2000

본 연구에서는 온도의 상승에 의하여 부피가 팽창하는 열팽창 고무 치공구의 팽창 특성을 이용하여 열경화성 복합재료를 경화하고 압축하는 과정을 실험과 모델링을 통하여 해석하였다. 열팽창 고무치공구가 사용되는 닫힌계 (fixed-volume process)와 열린계 (variable-volume process)에서 예상되는 압력을 이론적으로 유도하였고, 경화가 수반되는 과정에 있어서는 실험을 통하여 열팽창 치공구와 프리프레그가 나타내는 압력을 측정하였다. 온도가 상승하고 경화가 수반되는 경우에 등속도 압축실험에 의하여 얻어진 응력-변형율 곡선은 비선형 점탄성 특성을 보여주었는데, 본 연구에서는 Maxwell모델을 KWW (Kohlrausch-Williame-Watts)식으로 변형시킨 모델식을 이용하여 이를 매우 정확하게 표현할 수 있었다. 이 모델을 이용하여 몰드의 부피를 고정시킨 상태에서 경화시키는 닫힌계 공정에서 예상되는 압력을 예측하였으며 따라서 열팽창 치공구를 열경화성 복합재료의 경화압축 공정에 성공적으로 적용하였고 이를 해석하였다.

• 폴리머
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• 제37권2호
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• pp.135-140
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• 2013

Poly(methyl acrylate)-poly(acrylonitrile) 공중합체의 응력완화 실험은 용매기를 부착한 인장 시험기를 사용하여 여러 온도의 공기 중, 증류수, pH 3, 7, 11 용액에서 실행하였다. Ree-Eyring and Maxwell 모델로부터 얻은 완화스펙트럼 식에 실험적인 응력완화 곡선을 대입하여 poly(methyl acrylate)-poly(acrylonitrile) 공중합체의 완화스펙트럼을 얻었다. 완화스펙트럼의 계산은 Laplace 변환법을 사용한 컴퓨터 프로그램을 이용하였다. 이들 시료의 완화스펙트럼은 유동단위의 분자량과 자체확산 분포와 밀접한 관계가 있음을 알 수 있었다.

• 한국광학회지
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• 제19권1호
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• pp.80-83
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• 2008

광집게는 매질보다 큰 굴절률을 가지는 마이크로 크기의 구형 유전체를 강하게 집속되는 레이저를 이용해서 포획하고 움직이는 도구이다. 본 논문에서는 FDTD 방법을 이용해서 포획 힘을 계산하고, 그 방법을 설명하였다. 강하게 집속되는 레이저는 nonparaxial Gaussian beam을 이용해서 표현하였으며, 레이저가 대상물체와 매질에서 진행하는 것은 FDTD 방법을 이용해서 시뮬레이션 하였다. 레이저를 계산공간 전체에서 해석적으로 표현하기 위해서 scattered field formulation을 이용하였다. FDTD 방법을 이용해서 대상물체의 안팎의 전자기장을 시뮬레이션하고, 그 결과를 이용해서 Maxwell's stress tensor에 기반하여 포획 힘을 계산하였다.

• 한국자기학회지
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• 제21권5호
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• pp.174-179
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• 2011

지금까지 자성체에 미치는 전자기력을 계산하기 위해서는, 맥스웰 응력법, 가상변위법, 자하법, 자화전류법등이 널리 사용되어 왔으며, 이들은 자성체 덩어리 전체에 미치는 전자기력을 계산하는 데 있어 모두 정당한 결과를 가져온다고 보고 있다. 그러나 전자기력 밀도식의 완전한 형태에 대해서는 아직 까지도 논란이 있으며, 각 방법에 의한 표면 전자기력 밀도는 식과 수치해석 모두 다른 결과를 보인다. 본 연구는 전자기력밀도를 체적력으로 국한하여 가상공극법을 적용하였을 때, 모두 같은 형태의 식으로 도출이 됨을 해석식이 존재하는 모델을 통하여 보여준다. 즉, 가상공극 개념을 적용할 경우, 체적력 전자기력 밀도식의 통일 가능성을 보여 주는 것이다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.73-76
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• 2007

Electro-Active paper (EAPap) is a new smart material that has a potential to be used in biomimetic actuator and sensor. It is made by cellulose that is abundant material in nature. EAPap is fascinating with its biodegradability, lightweight, large displacement, high mechanical strength and low actuation voltage. Actuating mechanism of EAPap is known to be the combined effects of ion migration and piezoelectricity. However, the electromechanical actuation mechanisms are not yet to be established. This paper presents the modeling of the actuation behavior of water infused cellulose samples and their composite dielectric constants calculated by Maxwell-Wagner theory. Electro-mechanical forces were calculated using Maxwell stress tensor method. Bending deflection was evaluated from simple beam model and compared with experimental observation, which result good correlation with each other.

• 한국소음진동공학회논문집
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• 제17권12호
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• pp.1179-1183
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• 2007

Electro-Active paper(EAPap) is a new smart material that has a potential to be used in biomimetic actuator and sensor. It is made by cellulose that is abundant material in nature. EAPap is fascinating with its biodegradability, lightweight, large displacement, high mechanical strength and low actuation voltage. Actuating mechanism of EAPap is known to be the combined effects of ion migration and piezoelectricity. However, the electromechanical actuation mechanisms are not yet to be established. This paper presents the modeling of the actuation behavior of water infused cellulose samples and their composite dielectric constants calculated by Maxwell-Wagner theory. Electro-mechanical forces were calculated using Maxwell stress tensor method. Bending deflection was evaluated from simple beam model and compared with experimental observation, and which result in good correlation with each other.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제51권9호
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• pp.499-508
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• 2002

This paper presents a finite element analysis of the electromechanical field in the spindle motor of a computer hard disk drive considering the speed control and mechanical flexibility. The driving circuit equation is modified by considering the switching action of PWM inverter, and is coupled with the Maxwell equation to obtain the nonlinear time-stepping finite element equation for the analysis of magnetic field. Magnetic force and torque are calculated by the Maxwell stress tensor. Mechanical motion of a rotor is determined by a time-stopping finite element method considering the flexibility of shaft, rotor and bearing. Both magnetic and mechanical finite element equations are combined in the closed loop to control the speed using PWM. Simulation results are verified by the experiments, and they are in food agreement with the experimental results.

• Steel and Composite Structures
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• 제46권6호
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• pp.805-821
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• 2023

This study developed an evaluation system to explore the effect of the environmental temperature on the stress redistribution produced by cable stress relaxation of structural members in a steel cable-stayed bridge. The generalized Maxwell model is used to estimate stress relaxation at different temperatures. The environmental temperature is represented using the thermal coefficients and temperature loads. The fmincon optimization function is used to determine the set of stress relaxation parameters at different temperatures for all cables. The ABAQUS software is employed to investigate the stress redistribution of the steel cable-stayed bridge caused by the cable stress relaxation and the environmental temperature. All of these steps are set up as an evaluation system to save time and ensure the accuracy of the study results. The developed evaluation system is then employed to investigate the effect of environmental temperature and cable type on stress redistribution. These studies' findings show that as environmental temperatures increased up to 40 ℃, the redistribution rate increased by up to 34.9% in some girders. The results also show that the cable type with low relaxation rates should be used in high environmental temperature areas to minimize the effect of cable stress relaxation.

• Steel and Composite Structures
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• 제44권6호
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• pp.753-768
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• 2022

In this study, a graphical automatic system is developed in order to investigate the stress redistribution of structural members in a steel cable-stayed bridge. The generalized Maxwell model is selected for stress relaxation estimation, and it is carefully verified and applied to all the cable members of a steel cable-stayed bridge to investigate its stress relaxation. A set of stress relaxation parameters in all cables is determined using the fmincon optimization function. The stress redistribution of the steel cable-stayed bridge is then analyzed using ABAQUS. To shorten the investigation time, all the aforementioned phases are built up to be an automatic system. The automatic system is then employed to investigate the effect of cable cross-section areas and girder spans on stress redistribution. The findings from these studies show that the initial tension in the cables of a steel cable-stayed bridge should be kept to less than 55% of the cable's ultimate strength to reduce the effect of cable stress relaxation. The cable space in a steel cable-stayed bridge should be limited to 15,000 mm to minimize the effect of cable stress relaxation. In comparison to other structural members of a steel cable-stayed bridge, the girders experience a significant stress redistribution.

• 대한기계학회논문집
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• 제15권2호
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• pp.396-403
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• 1991

A solution is presented for the computation of the elastic-creep stresses in a hollow cylinder subjected to nonaxisymmetric temperature distribution. The creep problem is treated by the Maxwell creep model. Laplace transformation is used for reformation of the governing equation of elastic problem and Hooke's law in a function of .gamma. , .theta. , and creep constant. The governing equation is set up using the Airy stress function which leads to the biharmonic equation. The solution is obtained by using Fourer series method and Laplace inverse method used to obtain the stress components which include the variation of time. This solution shows excellent agreement with Lamkin's and Boley & Weiner's solution. The viscoelastic stresses are also obtained for the fuel rob tube subjecting nonaxisymmetric thermal load.