• 대한기계학회논문집
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• 제15권1호
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• pp.190-200
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• 1991

본 연구에서는 고온에 노출되는 열-점소성 거동의 해석을 위해 소성유동, 크 리프, 응력풀림(stress relaxation)등의 거동을 동시에 다룰 수 있는 통일구성방정식 모델에 대해 논하고 적절한 모델을 선정한다. 이 모델은 미소변형이론에 근거한 것 이므로 구조물의 거동을 소변형률(small strain)과 소회전(small rotation)의 범위내 로 가정하여 해석한다.선정된 모델에 대해서 시간변화율 형태의 방정식으로부터 유 한요소법을 통한 수치화와 사용된 구성방정식을 효율적으로 처리할 수 있는 수치해석 법상의 알고리듬을 제안한다. 제안된 알고리즘을 사용하여 유한요소법 전산코드를 적상하고, 작성된 코드를 이용하여 고온에서 하중을 받는 단순보와 국부적으로 심한 가열을 받는 구조물에 적용하여 고전적인 구성방정식으로 복합적인 해석이 어려웠던 열-점소성 거동을 효과적으로 해석할 수 있음을 보인다. 본 논문은 응력해석에 주안 점을 두었으므로 열해석에 관한 상세한 논의는 가급적 생략하기로 한다.

• 대한조선학회논문집
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• 제47권3호
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• pp.430-437
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• 2010

In this paper, we develop a shape design optimization method for thermo-elastoplasticity problems that is applicable to the welding or thermal deformation problems of ship structures. Shell elements and a programming language APDL in a commercial finite element analysis code, ANSYS, are employed in the shape optimization. The point of developed method is to determine the design parameters such that the deformed shape after welding fits very well to a desired design. The geometric parameters of surfaces are selected as the design parameters. The modified method of feasible direction (MMFD) and finite difference sensitivity are used for the optimization algorithm. Two numerical examples demonstrate that the developed shape design method is applicable to existing hull structures and effective for the structural design of ships.

• 한국산업융합학회 논문집
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• 제25권6_3호
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• pp.1127-1133
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• 2022

Recently, the use of aircraft structures using Ti alloy (Ti-6Al-4V), a lightweight high-strength alloy material, is rapidly increasing due to the weight reduction of aircraft. However, high-strength materials such as Ti alloys require high energy for cutting and are classified as difficult-to-cut materials. Also, research on Laser Assisted Machining (hereinafter referred to as LAM), a cutting processing technology that utilizes improved machinability, is being actively researched. Therefore, in this paper, in order to confirm the proper temperature distribution using a laser, the finite element method is used to determine the temperature distribution according to the calorific value condition to derive the appropriate condition, and the thermal load generated at this time is used as a structural analysis. It is intended to be used as basic data for LAM processing conditions by measuring the amount of residual stress and thermal deformation caused by heat.

• Structural Engineering and Mechanics
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• 제89권3호
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• pp.265-281
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• 2024

The sound radiation responses of multi-layer composite plates subjected to harmonic mechanical excitation in hygrothermal environment is numerically investigated. A homogenized micromechanical finite element (FE) based on the higher-order mid-plane kinematics replicating quadratic function as well as the through the thickness stretching effect together with the indirect boundary element (IBE) scheme has been first time employed. The isoparametric Lagrangian element (ten degrees of freedom per node) is used for discretization to attain the hygro-thermo-elastic natural frequencies and the modes of the plate via Hamilton's principle. The effective material properties under combined hygrothermal loading are considered via a micromechanical model. An IBE method is then implemented to attain structure-surrounding coupling and the Helmholtz wave equation is solved to compute the sound radiation responses. The effectiveness of the model is tested by converging it with the similar analytical/numerical results as well as the experimentally acquired data. The present scheme is further hold out for solving diverse numerical illustrations. The results revealed the relevance of the current higher-order FE-IBE micromechanical model in realistic estimation of hygro-thermo-acoustic responses. The geometrical parameters, volume fraction of fiber, layup, and support conditions alongside the hygrothermal load is found to have significant influence on the vibroacoustic characteristics.

• Structural Engineering and Mechanics
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• 제28권6호
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• pp.695-713
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• 2008

The aim of this contribution is to present a new link/beam finite element suitable for electrothermo-structural analysis of uni-axially graded materials. Continuous polynomial variation of geometry and material properties will be considered. The element matrix and relations for solution of Joule's heat (and its distribution to the element nodes) have been established in the sense of a sequence method of a coupled problem solution. The expression for the solution of nodal forces caused by a continuously distributed temperature field has also been derived. The theoretical part of this contribution is completed by numerical validation, which proves the high accuracy and effectiveness of the proposed element. The results of the performed experiments are compared with those obtained using the more expensive multiphysical link element and solid element of the FEM program Ansys. The proposed finite element could be used not only in the multiphysical analysis of the current paths and actuators but also in analysis of other 1D construction parts made of composite or uni-axially graded materials.

• 전산구조공학
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• 제6권4호
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• pp.89-98
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• 1993

최근 원자력의 사용이 증가함에 따라 핵폐기물을 효과적으로 처리하는 문제에 관심이 집중되고 있다. 이러한 핵폐기물을 지층내에 저장할 경우 고온의 열에 의해 핵폐기물 구조체에 지대한 영향을 미치므로 지반의 열력학적 거동을 분석할 필요성이 요구된다. 본 연구는 지반내에 처분된 고온의 사용후 핵연료에 의한 열역학적인 응력이 집중되어 비선형 거동이 예상되는 저장구조체 주변에는 비선형 유한요소를 적용하고 선형거동이 예상되는 무한영역에는 선형경계요소를 사용하여, 일반적인 역학적 계와 동일한 방법으로 비선형 유한요소와 경계요소를 조합한 프로그램을 개발하였다. 사용후 핵연료 폐기구조체와 같이 국부적인 비선형거동이 예상되는 구조물에서는 조합방법이 전 영역을 비선형 유한요소로 모형화하여 해석하는 것보다 효율적임을 알 수 있었다. 또한, 지층내 지반에 영향 미치는 주요 지반계수를 변화시킨 경우, 터널경계의 변위에 이러한 계수들이 어떠한 영향을 미치는가를 개발된 방법을 사용하여 검토하였다. 검토결과, 다른 계수들의 변화보다 열팽창계수의 변화가 터널주위의 변위에 상당한 영향을 미침을 알 수 있었다.

• Computers and Concrete
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• 제2권3호
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• pp.203-214
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• 2005

In the Part 1 paper (Gawin, et al. 2005) some experimental results concerning micro-structural tests, permeability measurements and stress-strain tests of four types of High Performance Concrete, exposed to elevated temperatures (up to $700^{\circ}C$) are presented and discussed. On the basis of these experimental results parameters of the constitutive relationships describing influence of damage and temperature upon material intrinsic permeability at high temperature were determined. In this paper the effects of various formulations of damage-permeability coupling on results of computer simulations are analysed and compared with the results obtained by means of the previously proposed approach, that does not take into account the thermo-chemical concrete damage directly. Numerical solutions are obtained using the recently developed fully coupled model of hygro-thermal and damage phenomena in concrete at elevated temperatures. High temperature effects are considered by means of temperature and pressure dependence of several material parameters. Based on the mathematical model, the computer code HITECOSP was developed. Material parameters of the model were measured by several European laboratories, which participated in the "HITECO" research project. A model problem, concerning hygro-thermal behaviour and degradation of a HPC structure during fire, is solved. The influence of two different constitutive descriptions of the concrete permeability changes at high temperature, including thermo-chemical and mechanical damage effects, upon the results of computer simulations is analysed and discussed.

• 한국구조물진단유지관리공학회 논문집
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• 제11권6호
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• pp.193-200
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• 2007

고온을 받는 고강도 콘크리트의 폭렬현상을 해석하기 위하여 온도해석, 열응력해석 및 수분이동 해석과 더불어 콘크리트 피복의 박리여부까지 고려하여야 하는 매우 복잡하고 어려운 해석과정이 요구되나 아직 이에 대한 연구가 거의 없는 실정이다. 본 연구에서는 수증기 압력을 온도와 피복두께의 함수로서 정의하고 또한 적합조건을 이용함으로써 피복콘크리트의 박리여부를 예측할 수 있는 실용적인 폭렬해석 알고리즘을 개발하였다. 폭렬해석결과 콘크리트 강도가 증가 할수록 PP섬유량이 적을수록 폭렬현상이 심하게 발생하였으며, 이는 기존의 실험결과와 유사한 경향을 나타내어 향후 고강도 콘크리트 내화설계를 위한 폭렬해석 시 유용하게 활용될 수 있을 것으로 기대된다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2005년도 춘계 학술발표회 논문집
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• pp.217-224
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• 2005

A higher order zig-zag shell theory is developed to refine the predictions of the mechanical and thermal behaviors partially coupled. The in-plane displacement fields are constructed by superimposing linear zig-zag field to the smooth globally cubic varying field through the thickness. Smooth parabolic distribution through the thickness is assumed in the out-of-plane displacement in order to consider transverse normal deformation and stress. The layer-dependent degrees of freedom of displacement fields are expressed in terms of reference primary degrees of freedom by applying interface continuity conditions as well as bounding surface conditions of transverse shear stresses. Thus the proposed theory has only seven primary unknowns and they do not depend upon the number of layers. In the description of geometry and deformation of shell surface, all rigorous exact expressions are used. Through the numerical examples of partially coupled analysis, the accuracy and efficiency of the present theory are demonstrated. The present theory is suitable in the predictions of deformation and stresses of thick composite shell under mechanical and thermal loads combined.

• 한국압력기기공학회 논문집
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• 제4권2호
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• pp.1-6
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• 2008

Very High Temperature Gas Cooled Reactor (VHTR) has been selected as a high energy heat source for nuclear hydrogen generation. The VHTR can produce hydrogen from heat and water by using a thermo-chemical process or from heat, water, and natural gas by steam reformer technology. A co-axial double-tube primary hot gas duct (HGD) is a key component connecting the reactor pressure vessel and the intermediate heat exchanger (IHX) for the VHTR. In this study, a preliminary design analysis for the primary HGD of the nuclear hydrogen system was carried out. These preliminary design activities include a determination of the size, a strength evaluation and an appropriate material selection. The determination of the size was undertaken based on various engineering concepts, such as a constant flow velocity model, a constant flow rate model, a constant hydraulic head model, and finally a heat balanced model.