• 한국지진공학회논문집
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• 제19권1호
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• pp.37-43
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• 2015

This paper presents a detailed procedure for a nonlinear soil-structure interaction of a seismically isolated NPP(Nuclear Power Plant) structure using the boundary reaction method (BRM). The BRM offers a two-step method as follows: (1) the calculation of boundary reaction forces in the frequency domain on an interface of linear and nonlinear regions, (2) solving the wave radiation problem subjected to the boundary reaction forces in the time domain. For the purpose of calculating the boundary reaction forces at the base of the isolator, the KIESSI-3D program is employed in this study to solve soil-foundation interaction problem subjected to vertically incident seismic waves. Wave radiation analysis is also employed, in which the nonlinear structure and the linear soil region are modeled by finite elements and energy absorbing elements on the outer model boundary using a general purpose nonlinear FE program. In this study, the MIDAS/Civil program is employed for modeling the wave radiation problem. In order to absorb the outgoing elastic waves to the unbounded soil region, spring and viscous-damper elements are used at the outer FE boundary. The BRM technique utilizing KIESSI-3D and MIDAS/Civil programs is verified using a linear soil-structure analysis problem. Finally the method is applied to nonlinear seismic analysis of a base-isolated NPP structure. The results show that BRM can effectively be applied to nonlinear soil-structure interaction problems.

• Structural Engineering and Mechanics
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• 제64권5호
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• pp.671-681
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• 2017

This study investigates the structural performance of 3D steel pipe rack suspended scaffolding systems. For the purpose, a standard full scale 3D steel pipe rack suspended scaffolding system considering two frames, two plane trusses, purlins and wooden floor is constructed in the laboratory. A developed load transmission system was placed in these experimental systems to distribute single loads to the center of a specific area in a step-by-step manner using a load jack. After each load increment, the displacements are measured by means of linear variable differential transducers placed in several critical points of the system. The tests are repeated for five different system conditions to determine the structural performance. The means of system conditions is the numbers of the tie bars which are used to connect plane trusses under level. Finite elements models of the 3D steel pipe rack suspended scaffolding systems considering different systems conditions are constituted using SAP2000 software to support the experimental tests and to use the models in future studies. Each of models including load transmission platform is analyzed under a single loading and the displacements are obtained. In addition, to calibrate the numerical models some uncertain parameters such as elasticity modulus of wooden floor and connection rigidity of purlins to plane trusses are assessed experimentally. The results of this work demonstrate that when increasing numbers of tie bars the displacement values are decreased. Also the results obtained from developed numerical models have harmony with those of experimental. In addition, the scaffolding system with two tie bars at the beginning and at the end of the plane truss has the optimum structural performance compared the results obtained for other scaffolding system conditions.

• Geomechanics and Engineering
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• 제17권2호
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• pp.119-131
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• 2019

Time dependent creep settlements are one of the most important causes of material deteriorations for the huge water structures such as concrete faced rockfill dams (CFRDs). For this reason, performing creep analyses of CFRDs is vital important for monitoring and evaluating of the future and safety of such dams. In this study, it is observed how changes viscoplastic behaviour of a CFR dam depending the time. Ilısu dam that is the longest concrete faced rockfill dam (1775 m) in the world is selected for the three dimensional (3D) analyses. 3D finite difference model of Ilısu dam is modelled using FLAC3D software based on the finite difference method. Two different special creep material models are considered in the numerical analyses. Wipp-creep viscoplastic material model and burger-creep viscoplastic material model were rarely used for the creep analyses of CFRDs in the last are taken into account for the concrete slab and rockfill materials-foundation, respectively. Moreover, interface elements are defined between the concrete slab-rockfill materials and rockfill materials-foundation to provide interaction condition for 3D model. Firstly, dam and foundation are collapsed under its self-weight and static behaviour of the dam is evaluated for the empty reservoir conditions. Then, reservoir water is modelled considering maximum water level of the dam and time-dependent creep analyses are performed for maximum reservoir condition. In this paper, maximum principal stresses, vertical-horizontal displacements and pore pressures that may occur on the dam body surface during 30 years (from 2017 to 2047) are evaluated in detail. According to numerical analyses, empty and maximum reservoir conditions of Ilısu dam are compared with each other in detail. 4 various nodal points are selected under the concrete slab to better seen viscoplastic behaviour changes of the dam and viscoplastic behaviour differences of these points during 30 years are graphically presented. It is clearly seen that horizontal-vertical displacements and principal stresses for maximum reservoir condition are more than the empty reservoir condition of the dam and significant pore pressures are observed during 30 years for maximum reservoir condition. In addition, horizontal-vertical displacements, principal stresses and pore pressures for 4 nodal points obviously increased until a certain time and changes decreased after this time.

• Steel and Composite Structures
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• 제13권1호
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• pp.15-33
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• 2012

For an axially loaded box-shaped member, the width-to-thickness ratio of the plate elements preferably should not be greater than 40 for Q235 steel grades in accordance with the Chinese code GB50017-2003. However, in practical engineering the plate width-to-thickness ratio is up to 120, much more than the limiting value. In this paper, a 3D nonlinear finite element model is developed that accounts for both geometrical imperfections and residual stresses and the ultimate capacity of welded built-up box columns, with larger width-to-thickness ratios of 60, 70, 80, and 100, is simulated. At the same time, the interaction buckling strength of these members is determined using the effective width method recommended in the Chinese code GB50018-2002, Eurocode 3 EN1993-1 and American standard ANSI/AISC 360-10 and the direct strength method developed in recent years. The studies show that the finite element model proposed can simulate the behavior of nonlinear buckling of axially loaded box-shaped members very well. The width-to-thickness ratio of the plate elements in welded box section columns can be enlarged up to 100 for Q235 steel grades. Good agreements are observed between the results obtained from the FEM and direct strength method. The modified direct strength method provides a better estimation of the column strength compared to the direct strength method over the full range of plate width-to-thickness ratio. The Chinese code and Eurocode 3 are overly conservative prediction of column capacity while the American standard provides a better prediction and is slightly conservative for b/t = 60. Therefore, it is suggested that the modified direct strength method should be adopted when revising the Chinese code.

• Transactions on Electrical and Electronic Materials
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• 제15권4호
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• pp.175-181
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• 2014

In this paper, the simulation and modeling of a polyethylene/clay nanocomposite were undertaken to predict the nanocomposite's dielectric behavior and to help design a nanocomposite material with optimum electrical properties for electrotechnical or electronic applications. A 3-D simulation model using the finite elements method was employed in order to study the effective permittivity and electric field distribution of two-phase nanocomposite materials for ordered and random distributions of inclusions in a low-loss host matrix such as polyethylene. The influence of the dispersion of reinforcing particles, and of the permittivity and radius of the inclusions, was analysed. The simulation results were compared with alternative, known theoretical solutions obtained from classical models, and were found to be in good agreement. The numerical results also indicate that for fixed volume fractions of nanoparticles the effective permittivity of the mixture, for ordered and random distributions, does not vary with the degree of dispersion. The variation of the effective permittivity with the particle radius is shown, using numerical data, to agree with the analytical modules.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 추계 학술발표회논문집
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• pp.481-488
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• 2003

A fluid-structure-isolator interaction program was developed in this study. The behavior of liquid regions are simulated by the boundary element method, and then the technique of analyzing the free surface motion in time domain is developed by using the nonlinear free surface boundary condition(NFBC) and the condition of interface between the structure and the fluid. Structure regions are modeled by the finite element method. In order to construct the governing equation of the fluid structure interaction(FSI)problem in time domain, the finite elements for a structure and boundary elements for liquid are coupled using the equilibrium condition, the compatibility condition and NFBC. The isolator is simulated by equation proposedin 3D Basis Me. In order to verify the validity and the applicability of the developed fluid- structure -Isolator interaction program, The horizontal forced vibration analysis was performed. The applicability of the developed method is verified through the artificial seismic analysis of real size liquid storage tank.

• 한국자기학회지
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• 제22권3호
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• pp.97-102
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• 2012

본 논문은 전선을 통하여 전력을 전달하는 일반적인 전력전송방식이 사용될 수 없는 환경에서 무선으로 전력을 전송하는 비접촉 전력전송기기 개발에 관한 것이다. 전력전송 방식은 자기공명방식보다 큰 전력을 전송하기에 적합한 전자기유도방식을 이용 하였다. 전력전송기기의 설계 방법은 전기장하(Electirc loading)와 자기장하(Magnetic loading)의 비율로 코어와 코일을 설계하는 장하분배법(Loading Distribution Method)으로 설계 하였고 유한요소법(Finite Elements Method)으로 기기에 발생하는 전자기장을 해석하여 설계한 전력전송기기의 적합성을 판단하고 적정한 설계치를 보정하였다. 본 연구를 통하여 개발된 전력전송방식은 비접촉식으로 수 mm 거리를 가지는 근거리에서 무선으로 전력을 전송하기에 적합함을 보였다.

• 대한기계학회논문집A
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• 제21권12호
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• pp.2121-2133
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• 1997

A finite element code is developed for 3-D self-contact problems, using continuum elements with a SRI(Selective Reduced Integration) scheme to prevent locking phenomenon by the incompressibility of rubber. Contact treatment is carried out in two ways : using the displacement constraints in case of rigid contact ; and imposing the same contact forces on two contact boundaries in case of self-contact. The finite element code developed is applied to the deformation analysis of C.V.joint boots which maintain lubrication conditions and protect the C.V.joint assembly from impact and dust. The boot accompanies large rotation depending on the rotation of the wheel axis and leading to the self-contact phenomena of the boot bellows. Since this contact phenomenon causes wear of the product and has great influence on the endurance life of the product, it is indispensable to carry out stress analysis of the rubber boots. In case of self-contact, various methods for determining contact forces have been suggested with an appropriate contact formulation. Especially, the types of penetration in self-contact are modularized to accelerate conputation with a contact algorithm.

• 한국지반공학회논문집
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• 제32권8호
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• pp.35-46
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• 2016

본 연구에서는 지반조건에 따른 실제 piled raft 기초의 거동을 실규모 시험을 통해 분석하기가 어려운 점을 감안하여 수치해석을 이용한 민감도분석을 수행하고자 하였다. 수치해석에 사용한 프로그램은 유한차분법 기반의 FLAC 3D이다. 말뚝의 수치해석 모델링은 FLAC의 구조요소 중 하나인 말뚝요소를 사용하여 모델링하였고, 지반과 래프트는 연속체 요소를 이용하여 모사하였다. 말뚝의 배열은 $3{\times}3$으로 고정하고 말뚝직경, 말뚝길이, 말뚝간격 그리고 지반조건을 민감도 매개변수로 선정하고 상관관계를 규명하였다. 그 결과, 말뚝직경이 크고 말뚝의 길이가 길수록, 그리고 말뚝의 간격이 넓을수록 piled raft 기초의 전체 지지력은 증가하는 것으로 나타났다. 그러나 지반조건에 따라 말뚝간격이 일정 간격 이상이 될 경우, piled raft 기초의 거동이 래프트만으로 지지되는 얕은기초와 유사한 거동을 보였다. 또한 지반조건이 좋아질수록, piled raft 기초의 전체 지지력은 증가함을 확인할 수 있었다.

• 한국지능시스템학회논문지
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• 제18권1호
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• pp.122-126
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• 2008

상용화된 FEM 코드와 3차원 솔리드 모델러를 통합하여 3차원 균열에 대한 자동 응력확대계수 해석 시스템을 개발하였다. 하나 또는 몇 개의 3차원 균열을 포함하는 기하학적 모델을 정의한다. 시스템에 저장된 몇 개의 절점패턴을 선택하면 자동적으로 퍼지지식 처리기법을 이용한 기하학적 모델 전 영역에 절점들이 중첩되어진다. 절점들은 생성되어지고 데로우니삼각화 법에 의한 사면체 솔리드요소가 생성되어진다. 최종적으로 완전한 유한요소 모델이 생성되어져 응력해석을 수행하게 된다. 본 논문은 몇몇 함수들을 실현시키기 위한 방법론에 대해 묘사하고 있으며 시스템의 타당성을 제시하였다.