• 한국구조물진단유지관리공학회 논문집
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• 제18권1호
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• pp.19-30
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• 2014

본 연구에서는 강주탑 기부와 기초콘크리트 연결 구조에 대해서 국내에서 특수교량의 강주탑 기부 설계에 보편적으로 적용하고 있는 명석해협대교(明石海峽大橋) 시방기준과 비선형 FEM 해석결과를 비교하였다. 명석해협대교(明石海峽大橋) 시방기준은 1970년도에 만들어진 일본 기준으로 주탑 기부와 PS 강봉 및 기초콘크리트를 스프링으로 선형 모델링하여 설계하는 방법으로서 43년이 지난 지금까지도 간편성을 이유로 이 기준을 적용하고 있다. 그러나 비선형 FEM 해석결과의 비교를 통해 특수 장대교의 강주탑 기부의 해석 및 설계에 이 기준을 적용하는 것은 여러 가지 문제점이 있음을 알 수 있었으며, 풍하중, 지진하중에 주요하게 저항하면서도 다양한 부재들로 복잡하게 연결된 강주탑 기부에 대해서는 한계상태설계법으로 발전하려는 현 시대에 맞추어 실제 거동을 반영하는 비선형 FEM해석을 적용해야 할 것이다.

• Computers and Concrete
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• 제1권1호
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• pp.15-30
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• 2004

In this study, a design process for reinforced concrete structures using the nonlinear FEM analysis is developed. Instead of using the nonlinear analysis to evaluate the required performance after design process, the nonlinear analysis is applied before designing the reinforcement arrangement inside the RC structures. An automatic reinforcement generator for computer aided reinforcement agreement is developed for this purpose. Based on a nonlinear FEM program for analyzing the reinforced concrete structure, a smart fictitious material model of steel, is proposed which can self-adjust the reinforcement to the required amount at the cracking location according to the load increment. Using this tool, the reinforcement ratio required at design load level can be decided automatically. In this paper, an example of RC beam with opening is used to verify the proposed process. Finally, a trial design process for a real size underground RC LNG tank is introduced.

• International Journal of Aeronautical and Space Sciences
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• 제18권1호
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• pp.63-69
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• 2017

In this paper, composite laminate pull-through resistance was analyzed using the FEM method and compared with test results. 2D and 3D simplified FEM models, a nonlinear analysis, and a progressive failure analysis utilizing three composite laminate failure theories Maximum Stress, Maximum Strain, and Tsai-Wu were used to predict the FEM results with the test results. The load and boundary conditions of the test were applied to the FEM to simulate the test. A composite laminate pull-through test (ASTM D7332 Proc. B) was designed with a special fixture to collect more precise data. The test results were compared with the FEM analysis results.

• Structural Engineering and Mechanics
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• 제71권5호
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• pp.485-502
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• 2019

In this research, the nonlinear static, buckling and vibration analysis of viscoelastic micro-composite beam reinforced by various distributions of boron nitrid nanotube (BNNT) with initial geometrical imperfection by modified strain gradient theory (MSGT) using finite element method (FEM) are presented. The various distributions of BNNT are considered as UD, FG-V and FG-X and also, the extended rule of mixture is used to estimate the properties of micro-composite beam. The components of stress are dependent to mechanical, electrical and thermal terms and calculated using piezoelasticity theory. Then, the kinematic equations of micro-composite beam using the displacement fields are obtained. The governing equations of motion are derived using energy method and Hamilton's principle based on MSGT. Then, using FEM, these equations are solved. Finally the effects of different parameters such as initial geometrical imperfection, various distributions of nanotube, damping coefficient, piezoelectric constant, slenderness ratio, Winkler spring constant, Pasternak shear constant, various boundary conditions and three material length scale parameters on the behavior of nonlinear static, buckling and vibration of micro-composite beam are investigated. The results indicate that with an increase in the geometrical imperfection parameter, the stiffness of micro-composite beam increases and thus the non-dimensional nonlinear frequency of the micro structure reduces gradually.

• Structural Engineering and Mechanics
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• 제59권3호
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• pp.431-454
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• 2016

In this paper, the nonlinear static and free vibration analysis of Euler-Bernoulli composite beam model reinforced by functionally graded single-walled carbon nanotubes (FG-SWCNTs) with initial geometrical imperfection under uniformly distributed load using finite element method (FEM) is investigated. The governing equations of equilibrium are derived by the Hamilton's principle and von Karman type nonlinear strain-displacement relationships are employed. Also the influences of various loadings, amplitude of the waviness, UD, USFG, and SFG distributions of carbon nanotube (CNT) and different boundary conditions on the dimensionless transverse displacements and nonlinear frequency ratio are presented. It is seen that with increasing load, the displacement of USFG beam under force loads is more than for the other states. Moreover it can be seen that the nonlinear to linear natural frequency ratio decreases with increasing aspect ratio (h/L) for UD, USFG and SFG beam. Also, it is shown that at the specified value of (h/L), the natural frequency ratio increases with the increasing the values amplitude of waviness while the dimensionless nonlinear to linear maximum deflection decreases. Moreover, with considering the amplitude of waviness, the stiffness of Euler-Bernoulli beam model reinforced by FG-CNT increases. It is concluded that the R parameter increases with increasing of volume fraction while the rate of this parameter decreases. Thus one can be obtained the optimum value of FG-CNT volume fraction to prevent from resonance phenomenon.

• Structural Engineering and Mechanics
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• 제68권1호
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• pp.81-94
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• 2018

This paper uses the finite element method (FEM) considering geometrically nonlinear strains to study the first ply failure of laminated composite skewed hypar shell roofs through well-established failure criteria along with the serviceability criterion of deflection. Apart from validating the approach through solution of benchmark problems, skewed hypars with different practical parametric variations are studied for failure loads and tendencies. First ply failure zones are also identified to suggest design and non-destructive monitoring guidelines to the practising engineers. Recommendation tables regarding the design approaches to be adopted in specific cases and factor of safety values needed to be imposed on first ply failure load values for varying shell curvatures are also suggested in this paper. Providing practical inputs to design engineers is the main achievement of the present study.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 A
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• pp.47-50
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• 1997

The FEM(Finite Element Method) can be used to analysis SRM(Switched Reluctance Motor) as it can account for the salient pole geometry of the stator and rotor and the nonlinear properties of the magnetic materials. However, FEM requirers a lot of computer memory and computing time because, the kind of SRM drivers is verity and the switching strategies are various for one SRM driver. In this paper we proposed the method of analysis of a SRM which results are similar to FEM and has very short computing time. The Inductance and torque for each phase current at each rotor position are calculated by using two-dimensional nonlinear FEM analysis. Using the look-up table of inductance and torque and the voltage equations of SRM we obtained the phase current and torque. To verify proposed algorithm, 3 phase 6/4 SRM is analysed and found a good agreement with FEM results. And computing time is about 1/1600 of the FEM analysis.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권1호
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• pp.52-58
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• 2000

Signal propagation in nonlinear optical fiber is analyzed numerically by using SS-FEM (Split-Step Finite Element Method). By adopting cubic element function in FEM, soliton equation of which exact solution was well known, has been solved. Also, accuracy of numerical results and computing times are compared with those of Fourier method, and we have found that solution obtained from using FEM was very relatively accurate. Especially, to reduce CPU time in matrix computation in each step, the matrix imposed by the boundary condition is approximated as a sparse matrix. As a result, computation time was shortened even with the same or better accuracy when compared to those of the conventional FEM and Fourier method.

• EDISON SW 활용 경진대회 논문집
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• 제4회(2015년)
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• pp.239-245
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• 2015

In this paper, to examine the difference between the linear and non-linear static, dynamic analysis for a structure, a cantilevered beam was used. Then, an external transverse static and dynamic loads were applied at the free end of the beam. Classical theories were used for the linear analysis and the EDISON CSD solver, co-rotational dynamic FEM program, was used for nonlinear analysis. In the static analysis, effects of the load for the beam deflection were observed in the linear and nonlinear analysis. Then, normalized displacement of tip of the beam was predicted for different frequency ration and a significant difference was obtained in the vicinity of the resonant frequency. In addition, effects of frequency and time for the beam deflection were investigated to find the frequency delay.

• Nuclear Engineering and Technology
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• 제53권8호
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• pp.2696-2707
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• 2021

The purpose of this study is to investigate the efficiency of various structural modeling schemes for evaluating seismic performances and fragility of the reactor containment building (RCB) structure in the advanced power reactor 1400 (APR1400) nuclear power plant (NPP). Four structural modeling schemes, i.e. lumped-mass stick model (LMSM), solid-based finite element model (Solid FEM), multi-layer shell model (MLSM), and beam-truss model (BTM), are developed to simulate the seismic behaviors of the containment structure. A full three-dimensional finite element model (full 3D FEM) is additionally constructed to verify the previous numerical models. A set of input ground motions with response spectra matching to the US NRC 1.60 design spectrum is generated to perform linear and nonlinear time-history analyses. Floor response spectra (FRS) and floor displacements are obtained at the different elevations of the structure since they are critical outputs for evaluating the seismic vulnerability of RCB and secondary components. The results show that the difference in seismic responses between linear and nonlinear analyses gets larger as an earthquake intensity increases. It is observed that the linear analysis underestimates floor displacements while it overestimates floor accelerations. Moreover, a systematic assessment of the capability and efficiency of each structural model is presented thoroughly. MLSM can be an alternative approach to a full 3D FEM, which is complicated in modeling and extremely time-consuming in dynamic analyses. Specifically, BTM is recommended as the optimal model for evaluating the nonlinear seismic performance of NPP structures. Thereafter, linear and nonlinear BTM are employed in a series of time-history analyses to develop fragility curves of RCB for different damage states. It is shown that the linear analysis underestimates the probability of damage of RCB at a given earthquake intensity when compared to the nonlinear analysis. The nonlinear analysis approach is highly suggested for assessing the vulnerability of NPP structures.