• 대한기계학회논문집
• /
• 제7권4호
• /
• pp.417-424
• /
• 1983

This paper presents two methods of obtaining approximate analytic solutions for the temperature distributions and heat flow to two-dimensional transient heat conduction problems in a finite strip with constant thermal properties using the Heat Balance Integral. The methods introduced in this study are as follows; one using the Heat Balance Integral only, and the other successively using the Heat Balance Integral and an exact analytic method. Both methods are applicable to a large number of the two-dimensional unsteady conduction problems in finite regions such as extended surfaces with uniform thickness, but in this paper only solutions for the unsteady problems in a finite strip with boundary condition at the base expressed in terms of step function are provided as an illustration. Results obtained by both methods are compared with those by the exact two-dimensional transient analysis. It is found that both approximate methods generate small time solutions, which can not be obtained easily by any exact analytic method for small values of Fourier numbers. In the case of applying the successive use of the Heat Balance Integral and Laplace transforms, the analysis shows good agreement with the exact solutions for any Fourier number in the range of Biot numbers less than 0.5.

• Structural Engineering and Mechanics
• /
• 제66권1호
• /
• pp.85-96
• /
• 2018

This study investigates the response of functionally graded (FG) gas pipe under unsteady internal pressure and temperature. The pipe is proposed to be manufactured from FGMs rather than custom carbon steel, to reduce the erosion, corrosion, pressure surge and temperature variation effects caused by conveying of gases. The distribution of material graduations are obeying power and sigmoidal functions varying with the pipe thickness. The sigmoidal distribution is proposed for the 1st time in analysis of FG pipe structure. A Two-dimensional (2D) plane strain problem is proposed to model the pipe cross-section. The Fourier law is applied to describe the heat flux and temperature variation through the pipe thickness. The time variation of internal pressure is described by using exponential-harmonic function. The proposed problem is solved numerically by a two-dimensional (2D) plane strain finite element ABAQUS software. Nine-node isoparametric element is selected. The proposed model is verified with published results. The effects of material graduation, material function, temperature and internal pressures on the response of FG gas pipe are investigated. The coupled temperature and displacement FEM solution is used to find a solution for the stress displacement and temperature fields simultaneously because the thermal and mechanical solutions affected greatly by each other. The obtained results present the applicability of alternative FGM materials rather than classical A106Gr.B steel. According to proposed model and numerical results, the FGM pipe is more effective in natural gas application, especially in eliminating the corrosion, erosion and reduction of stresses.

• 한국전산유체공학회지
• /
• 제10권4호통권31호
• /
• pp.12-17
• /
• 2005

A computational study of evaluation of current turbulence models is performed for a better prediction of thermal stratification in an upper plenum of a liquid metal reactor. The turbulence models tested in the present study are the two-layer model, the shear stress transport (SST) model, the v2-f model and the elliptic blending mode(EBM). The performances of the turbulence models are evaluated by applying them to the thermal stratification experiment conducted at JNC (Japan Nuclear Corporation). The algebraic flux model is used for treating the turbulent heat flux for the two-layer model and the SST model, and there exist little differences between the two turbulence models in predicting the temporal variation of temperature. The v2-f model and the elliptic blending model better predict the steep gradient of temperature at the interface of thermal stratification, and the v2-f model and elliptic blending model predict properly the oscillation of the ensemble-averaged temperature. In general the overall performance of the elliptic blending model is better than the v2-f model in the prediction of the amplitude and frequency of the temperature oscillation.

• 대한기계학회논문집B
• /
• 제21권3호
• /
• pp.457-472
• /
• 1997

We studied the temperature distribution and heat transfer characteristics of TEFC induction motor with thermal network program for more efficient design and better cooling performance of it. We knew the characteristics and the windage loss of outer cooling fan from fan test experiments. Frame axial and peripheral heat transfer coefficients and endwinding heat transfer coefficient were measured by various model experiments and then, compared with other experimental results. Frame was the main heat transfer surface, load-side and fan-side surface were not thermally symmetric from the heat flux distribution analysis. Steady and unsteady temperature distributions were measured by real motor experiments. From the results, we knew that rotor surface temperature was higher than coil temperature and the hottest spot in the coil was loadside endwinding outside surface. We compared the simulation results with those of real motor test and the two results showed a good agreement.

• 항공우주시스템공학회지
• /
• 제4권4호
• /
• pp.28-36
• /
• 2010

Current tanks have been developed to increase mobility and firepower, and its maximum range and destructive power are improved. This great change causes remained vibration of a gun barrel after firing. For this reason, people are trying to control vibration of gun barrel effectively. This thesis presents a modeling method and analysis results for gun barrel by using a thermal shroud as an absorber mass. DTS(Dynamically Tuned Shroud) is a vibration damping system using a thermal shroud as an added mass for decreasing remained vibration. The model has an advantage that the gun barrel's vibration can be decreased by dissipating a kinetic energy of thermal shroud without install an additional dynamic absorber to tip of the gun barrel. For analyzing the damping performance of the DTS, We derived an equation of motion of the barrel after setting a mathematical modeling, and found out the frequency analysis and tendency according to stiffness ratio between barrel and shroud.

• 한국화재소방학회논문지
• /
• 제28권1호
• /
• pp.52-57
• /
• 2014

본 논문에서는 에너지방정식과 비정상 비압축성 Navier-Stokes 방적식을 사용하여 동절기 소방배관의 동파방지를 위한 최적의 열선위치를 확인하였다. 물의 자연대류와 소방 배관의 전도 열방정식이 결합된 복합열전달을 해석하였다. 혼합 열전달 배관 내 물의 비정상적인 유동과 온도분포를 확인하기 위하여 SIMPLE 형태의 알고리즘을 기반으로 한 상용코드(ANSYS-FLUENT)가 사용되었다. 수치해석을 수행하여 등온선과 벡터장을 살펴보았다. 물의 열팽창계수를 일정하다고 가정할 때 소방 배관 단면의 하부에 열선을 설치하는 것이 다른 위치에 설치하는 것보다 시간에 따른 물의 최저온도가 가장 높아서 동파방지에 가장 효과적인 것을 확인할 수 있었다.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2011년 춘계학술대회논문집
• /
• pp.156-160
• /
• 2011

As building becomes larger, taller and more complex due to industrialization and urbanization, it tends to be vulnerable to fire and establishment of effective measures for fire safety is demanded. Especially the fact that the smoke hinders evacuation and fire-fighting activities as well as becomes the major cause of life casualty emphasizes the importance of smoke control system. To design and operate the smoke control system success folly, it is necessary to analyze and predict precisely the thermoflow induced by fire in building. The unsteady three-dimensional analysis of thermoflow induced by fire with diverse variables such as building structure, fire conditions and smoke control facilities can be effectively carried out with numerical method In this study, using the FDS(Fire Dynamics Simulation) program that spreads widely as the analysis tool for thermoflow of fire, the analysis of thermoflow in partition of building induced by fire and comparison with the experimental results for assessment of numerical analysis are presented.

• 설비공학논문집
• /
• 제16권11호
• /
• pp.1077-1083
• /
• 2004

This study is to systematically analyze the effect of various kinds of design factors on the performance of stratified thermal storage tank. Taguchi method, known as a very reasonable tool in the parametric study, is employed in the present work. Three dimensional unsteady numerical experiment is conducted for 4 design parameters of stratified thermal storage tank: inlet Reynolds number, Froude number, diffuser size d with 3 levels (Re=400, 800, 1200, Fr=0.5, 1.0, 2.0 and d=150 mm, 200mm, 300 mm) and diffuser shape with 2 levels. Orthogonal array $L_{18}(2{\times}3^7)$ is adopted for the analysis of variance. The result gives quantitative estimation of the various design parameters affecting the performance and helps to select the main factors for the optimum design of stratified thermal storage tank. Reynolds number is found to be the most dominant parameter and the diffuser shape plays significant role on the performance of stratified thermal storage tank. Based on this finding, the prior questions on the contribution of the diffuser shape proposed by the authors become clear. The optimum condition for the performance is a set of d=300mm, Re=800, and radial regulated plate diffuser. Conformation test shows the repeatability in the analysis and $1.3\%$ difference between the estimated thermocline thickness and that of numerical result.

• International Journal of Aeronautical and Space Sciences
• /
• 제18권2호
• /
• pp.279-289
• /
• 2017

In this study, a series of conjugate heat transfer (CHT) analyses are conducted for a stage of a fully cooled high-pressure turbine (HPT) at elevated levels of free stream turbulence (Tu = 5% and 25.7%). The goal of the analyses is to investigate the influence of high turbulence intensity on the fluid-thermal characteristics of a nozzle guide vane (NGV). The turbine inlet temperature is defined by considering a typical radial temperature distribution factor (RTDF). The Unsteady Reynolds Average Navier-Stokes (URANS) CHT simulations are carried out using CFX 15.0, a commercial CFD package. The presented CFD modeling approach for high turbulence intensity is verified with the experimental data from two types of NASA C3X NGVs with films. The computation grid is generated for both the fluid and solid domains. The fluid domain grid is created using a tetrahedral grid system with prism layers because of its complex geometry, and the solid domain grid is composed of only tetrahedral elements. The analytical results are compared to understand the effect of turbulence on flow characteristics and metal temperature distributions. The results obtained in this study provide useful insights on the effects of high free stream turbulence and unsteadiness. The results also lead to the proposal of meaningful turbine design guidelines.

• 한국수자원학회논문집
• /
• 제30권6호
• /
• pp.769-776
• /
• 1997

윤성범과 이기혁(1977)의 수치모형을 이용하여 열발전소의 펌프 비상중단시 냉각수 계통에서 발생하는 서어지거동을 해석하였다. 종래에 무시되었던 기계내부계통으로 부터의 유량, 폐정공기실, 및 공기유출입구, 맨홀, 개수로 및 바다의 영향을 고려하였으며, 이들이 서어지 거동에 미치는 영향을 체계적으로 분석하였다. 특히 공기유출입구의 면적에 따른 서어지 제어효과와 공기실의 공기압 변화를 제시하여 실무에의 적용이 용이하도록 하였다.