• Coupled systems mechanics
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• 제9권2호
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• pp.163-182
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• 2020

Coupled thermo-mechanical analysis of reinforced concrete slab at elevated temperatures from a fire accounting for nonlinear thermal parameters is carried out. The main focus of the paper is put on a one-way continuous reinforced concrete slab exposed to fire from the single (bottom) side as the most typical working condition under fire loading. Although contemporary techniques alongside the fire protection measures are in constant development, in most cases it is not possible to avoid the material deterioration particularly nearby the exposed surface from a fire. Thereby the structural fire resistance of reinforced concrete slabs is mostly influenced by a relative distance between reinforcement and the exposed surface. A parametric study with variable concrete cover ranging from 15 mm to 35 mm is performed. As the first part of a one-way coupled thermo-mechanical analysis, transient nonlinear heat transfer analysis is performed by applying the net heat flux on the exposed surface. The solution of proposed heat analysis is obtained at certain time steps of interest by α-method using the explicit Euler time-integration scheme. Spatial discretization is done by the finite element method using a 1D 2-noded truss element with the temperature nodal values as unknowns. The obtained results in terms of temperature field inside the element are compared with available numerical and experimental results. A high level of agreement can be observed, implying the proposed model capable of describing the temperature field during a fire. Accompanying thermal analysis, mechanical analysis is performed in two ways. Firstly, using the guidelines given in Eurocode 2 - Part 1-2 resulting in the fire resistance rating for the aforementioned concrete cover values. The second way is a fully numerical coupled analysis carried out in general-purpose finite element software DIANA FEA. Both approaches indicate structural fire behavior similar to those observed in large-scale fire tests.

• Nuclear Engineering and Technology
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• 제53권10호
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• pp.3379-3397
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• 2021

In this study, a multi-physics modeling method was developed to analyze a nuclear fuel rod's thermo-mechanical behavior especially for high temperature anisotropic creep deformation during ballooning and burst occurring in Loss of Coolant Accident (LOCA). Based on transient heat transfer and nonlinear mechanical analysis, the present work newly incorporated the nuclear fuel rod's special characteristics which include gap heat transfer, temperature and burnup dependent material properties, and especially for high temperature creep with material anisotropy. The proposed method was tested through various benchmark analyses and showed good agreements with analytical solutions. From the validation study with a cladding burst experiment which postulates the LOCA scenario, it was shown that the present development could predict the ballooning and burst behaviors accurately and showed the capability to predict anisotropic creep behavior during the LOCA. Moreover, in order to verify the anisotropic creep methodology proposed in this study, the comparison between modeling and experiment was made with isotropic material assumption. It was found that the present methodology with anisotropic creep could predict ballooning and burst more accurately and showed more realistic behavior of the cladding.

• 한국전산유체공학회지
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• 제21권3호
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• pp.8-14
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• 2016

A numerical analysis is conducted to estimate the core expansion and the energy behaviors induced by a core disruptive accident in a sodium-cooled fast reactor. The numerical formulation based on underwater explosion theory is carried out to simulate the core explosion inside the reactor vessel. The transient pressure, temperature and expansion of the core are examined by solving the equation of state and nonlinear governing equation of momentum conservation in one-dimensional spherical coordinates. The energy balance inside the computation domain is examined during the core expansion process. Heat transfer between the core and the sodium coolant, and the bubble rise during the expansion process are briefly investigated.

• Computers and Concrete
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• 제18권6호
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• pp.1097-1112
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• 2016

Fire loading causes a critical collapse of RC (Reinforced Concrete) Structures since the embedded steels inside are relative week against high elevated temperature. Several numerical frameworks for fire resistance have been proposed, however they have limitations such as unstable convergence and long calculation period. In the work, 2-D nonlinear FE technique is proposed using Galerkin method for RC structures under fire loading. Closed-form element stiffness with a triangular element is adopted and verified with fire test on three RC slabs with different fire loading conditions. Several simulations are also performed considering fire loading conditions, water contents, and cover depth. The proposed numerical technique can handle time-dependent fire loading, convection, radiation, and material properties. The proposed technique can be improved through early-aged concrete behavior like moisture transport which varies with external temperature.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2005년도 동계학술발표대회 논문집
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• pp.335-340
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• 2005

Nonlinear and forced oscillations of supported viscous droplet were focused in the present study. The droplet has a free contact line with solid plate and inviscid fluid. Natural frequencies of a pendant droplet have been investigated experimentally by imposing the acoustic wave while the frequency is being increased at a fixed amplitude. The evaporation was observed at atmosphere pressure. The droplet was recorded throughout the entire evaporation process and transient variations of the volume was measured. The evaporation process of oscillating droplet with thermofoil has been also observed to investigate analyzing the resonance effect on the thermal characteristics of droplet. It is found that a pendant droplet shows the resonant behaviors at each mode similar to the theoretical analysis. During imposing the acoustic wave, the pendant droplet makes a rotating motion in its longitudinal axis which is a new shape oscillation mode. The evaporation rate of a pendant droplet at resonant frequency is significantly enhanced.

• 한국정밀공학회지
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• 제16권8호
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• pp.138-148
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• 1999

Thermal deformations of tension mask under localized heating are analyzed using finite element method and electron beam landing shifts are predicted by the analysis results. In CRT, electron beam landing shifts due to thermal deformations of the tension mask make the color purity of screen worse. In order to get the final results of thermal deformations, firstly the tension processes of the mask and following welding processes between the tensional mask and rail must be analyzed sequentially. And then, nonlinear transient thermo-elastic finite element analysis is performed on every part inside CRT including tension mask, wherein thermal radiation is a main heat transfer mechanism. Because the tension mask has numerous slits, the effective thermal conductivity and effective and effective elastic modulus is calculated, and the tension mask is modeled as a shell without slits. From the displacement results of tension mask, electron beam landing shifts is calculated directly. Experiments are performed to confirm our analysis results. Temperature distributions and beam landing shifts of tension mask are measured and the results are in good agreement with those of analyses.

• Journal of Welding and Joining
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• 제17권1호
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• pp.104-115
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• 1999

판재의 비드 용접과정에서 열응력과 각변형의 발생기구 및 크기를 판재 단면에 대한 2차원 유한 요소해석을 통해 규명하고자 할 때 판재의 3차원 특성을 판재 길이의 크기효과로 간주하여, 구속경계조 건으로 설정함으로써 2차원 해석으로도 더욱 실제에 근접한 현상해석이 가능함을 제안하고자 하였다. 먼저 용접 입열에 의한 판재 내부의 천이 온도분포를 해석하였고, 이를 열응력 해석에 활용하였다. 2차 원 열응력 해석에 있어, 용접도중에 단면 전체가 길이 방향으로 동일한 크기의 변위를 한다고 가정하여 일정 변위를 길이 방향 경계조건으로 설정하고, 판재의 길이에 따라 각변형의 발생이 구속된다고 가정 하여, 판재의 길이에 의한 구속효과를 상당 구속력으로 간주하여 이를 단면 부재의 회전방향에 대한 경 계조건으로 설정함으로써 판재의 3차원 특성을 고려하고자 하였다. 제안된 방법에 의한 응력 분포 형태, 각변형 크기 등의 해석 결과가 기존의 2차원 해석 결과에 비해 실제에 더 근접함을 보여 주었다.

• 콘크리트학회논문집
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• 제24권5호
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• pp.567-575
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• 2012

이 연구는 실험과 병행 화재에 노출된 철근콘크리트 구조물의 갤러킨 유한요소해석 방법을 제시하였다. 이 방법은 비선형 비정상 온도분포해석에 관한 것으로 2차원 삼각형 요소에 대한 해석기법을 구축하였다. 해석기법의 검증을 위하여 실규모 철근콘크리트 슬래브에 대한 내화실험을 실시하였으며, 실험 결과와의 비교를 통해 해석기법의 유효성을 확인하였다. 또한 콘크리트 부재의 내화성능에 대한 실험 결과를 분석하였다. 변수분석에서는 화재규모, 콘크리트의 온도의존성 열적특성값, 콘크리트의 함수율이 콘크리트의 내화성능에 미치는 영향을 평가하였다. 이 연구에서 구축된 수치해석모델은 다양한 화재규모와 대류, 복사 경계조건, 재료의 온도의존성 열적특성값을 자유롭게 고려할 수 있다. 또한 이 논문에서는 콘크리트 슬래브를 대상으로 표준화재곡선을 대상으로만 분석하였지만 관련된 철근콘크리트 기둥 골조 해석에 용이하게 사용될 수 있을 것으로 판단되었다.