• Title/Summary/Keyword: Thermal Boundary Conditions

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Performance of Tilting Pad Journal Bearings with Different Thermal Boundary Conditions (열 경계 조건이 다른 틸팅패드저널베어링의 성능)

  • Suh, Junho;Hwang, Cheolho
    • Tribology and Lubricants
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    • v.37 no.1
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    • pp.14-24
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    • 2021
  • This study shows the effect of the thermal boundary condition around the tilting pad journal bearing on the static and dynamic characteristics of the bearing through a high-precision numerical model. In many cases, it is very difficult to predict or measure the exact thermal boundary conditions around bearings at the operating site of a turbomachine, not even in a laboratory. The purpose of this study is not to predict the thermal boundary conditions around the bearing, but to find out how the performance of the bearing changes under different thermal boundary conditions. Lubricating oil, bearing pads and shafts were modeled in three dimensions using the finite element method, and the heat transfer between these three elements and the resulting thermal deformation were considered. The Generalized Reynolds equation and three-dimensional energy equation that can take into account the viscosity change in the direction of the film thickness are connected and analyzed by the relationship between viscosity and temperature. The numerical model was written in in-house code using MATLAB, and a parallel processing algorithm was used to improve the analysis speed. Constant temperature and convection temperature conditions are used as the thermal boundary conditions. Notably, the conditions around the bearing pad, rather than the temperature boundary conditions around the shaft, have a greater influence on the performance changes of the bearing.

Boundary Element Analysis of Thermal Stress Intensity Factor for Interface Crack under Vertical Uniform Heat Flow (경계요소법을 이용한 수직열유동을 받는 접합경계면 커스프균열의 열응력세기계수 결정)

  • Lee, Kang-Yong;Baik, Woon-Cheon
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.7 s.94
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    • pp.1794-1804
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    • 1993
  • The thermal stress intensity factors for interface cracks of Griffith and symmetric lip cusp types under vertical uniform heat flow in a finite body are calculated by boundary element method. The boundary conditions on the crack surfaces are insulated or fixed to constant temperature. The relationship between the stress intensity factors and the displacements on the nodal point of a crack tip element is derived. The numerical values of the thermal stress intensity factors for interface Griffith crack in an infinite body and for symmetric lip cusp crack in a finite and homogeneous body are compared with the previous solutions. The thermal stress intensity factors for symmetric lip cusp interface crack in a finite body are calculated with respect to various effective crack lengths, configuration parameters, material property ratios and the thermal boundary conditions on the crack surfaces. Under the same outer boundary conditions, there are no appreciable differences in the distribution of thermal stress intensity factors with respect to each material properties. But the effect of crack surface thermal boundary conditions on the thermal stress intensity factors is considerable.

Thermal effects on nonlocal vibrational characteristics of nanobeams with non-ideal boundary conditions

  • Ebrahimi, Farzad;Shaghaghi, Gholam Reza
    • Smart Structures and Systems
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    • v.18 no.6
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    • pp.1087-1109
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    • 2016
  • In this manuscript, the small scale and thermal effects on vibration behavior of preloaded nanobeams with non-ideal boundary conditions are investigated. The boundary conditions are assumed to allow small deflections and moments and the concept of non-ideal boundary conditions is applied to the nonlocal beam problem. Governing equations are derived through Hamilton's principle and then are solved applying Lindstedt-Poincare technique to derive fundamental natural frequencies. The good agreement between the results of this research and those available in literature validated the presented approach. The influence of various parameters including nonlocal parameter, thermal effect, perturbation parameter, aspect ratio and pre-stress load on free vibration behavior of the nanobeams are discussed in details.

Critical thermal buckling analysis of porous FGP sandwich plates under various boundary conditions

  • Abdelhak Zohra;Benferhat Rabia;Hassaine Daouadji Tahar
    • Structural Engineering and Mechanics
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    • v.87 no.1
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    • pp.29-46
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    • 2023
  • Critical thermal buckling of functionally graded porous (FGP) sandwich plates under various types of thermal loading is considered. It is assumed that the mechanical and thermal nonhomogeneous properties of FGP sandwich plate vary smoothly by distribution of power law across the thickness of sandwich plate. In this paper, porosity defects are modeled as stiffness reduction criteria and included in the rule of mixture. The thermal environments are considered as uniform, linear and nonlinear temperature rises. The critical buckling temperature response of FGM sandwich plates has been analyzed under various boundary conditions. By comparing several numerical examples with the reference solutions, the results indicate that the present analysis has good accuracy and rapid convergence. Further, the effects of various parameters like distribution shape of porosity, sandwich combinations, aspect ratio, thickness ratio, boundary conditions on critical buckling temperature of FGP sandwich plate have been studied in this paper.

Thermal post-buckling analysis of porous functionally graded pipes with initial geometric imperfection

  • Xu, Jia-Qin;She, Gui-Lin
    • Geomechanics and Engineering
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    • v.31 no.3
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    • pp.329-337
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    • 2022
  • In this paper, the thermal post-buckling characteristics of functionally graded (FG) pipes with initial geometric imperfection are studied. Considering the influence of initial geometric defects, temperature and geometric nonlinearity, Euler-Lagrange principle is used to derive the nonlinear governing equations of the FG pipes. Considering three different boundary conditions, the two-step perturbation method is used to solve the nonlinear governing equations, and the expressions of thermal post-buckling responses are also obtained. Finally, the correctness of this paper is verified by numerical analyses, and the effects of initial geometric defects, functional graded index, elastic foundation, porosity, thickness of pipe and boundary conditions on thermal post-buckling response are analyzed. It is found that, bifurcation buckling exists for the pipes without initial geometric imperfection. In contrast, there is no bifurcation buckling phenomenon for the pipes with initial geometric imperfection. Meanwhile, the elastic stiffness can significantly improve thermal post-buckling load and thermal post-buckling strength. The larger the porosity, the greater the thermal buckling load and the thermal buckling strength.

A Study on Boundary Conditions of Piston Thermal Loading Analysis in Internal Combustion Engines (내연기관 피스톤의 열부하 해석을 위한 경제조건 설정에 관한 연구)

  • 정동수;조용석;최헌오;이진형
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.3
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    • pp.528-533
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    • 1988
  • The assignment of boundary conditions for the piston thermal loading analysis in internal combustion engine has been tested using the thermal circuit method with an engine simulation program. In an attempt to examine the accuracy of the employed boundary condition, another thermal boundary condition has been sought for through the electrolytic tank analogue method. Comparison of calculated temperature distributions obtained from these two boundary conditions with measured temperature values reveals that the electrolytic tank analogue method gives excellent agreement. However, the thermal circuit method has been found to be reasonable for practical applications, if modified partially.

THERMAL IGNITION OF A REACTION DIFFUSION SYSTEMS IN SOME CLASS A GEOMETRIES WITH DIFFERENT THERMAL BOUNDARY CONDITIONS

  • Ajadi, S.O.
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.11 no.3
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    • pp.7-20
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    • 2007
  • We examined the steady state solution for a strongly exothermic mixtures in some class A geometries subjected to different boundary conditions under Arrhenius, Bimolecular and Sensitised reactions. The solution of the governing nonlinear reaction diffusion equation was obtained using the variational method formulation executed in Mathematica package. The paper elucidates the influence of geometry, boundary conditions and types of reaction on the thermal ignition of the reactive mixture. Apart from validating known results in literature, the solution gave further insight into the influence of material properties and conditions on the occurrence of thermal ignition.

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THERMAL INSTABILITY IN REACTIVE VISCOUS PLANE POISEUILLE / COUETTE FLOWS FOR TWO EXTREME THERMAL BOUNDARY CONDITIONS

  • Ajadi, Suraju Olusegun
    • Journal of the Korean Society for Industrial and Applied Mathematics
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    • v.13 no.2
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    • pp.73-86
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    • 2009
  • The problem of thermal stability of an exothermic reactive viscous fluid between two parallel walls in the plane Poiseuille and Couette flow configurations is investigated for different thermal boundary conditions. Neglecting reactant consumption, the closed-form solutions obtained from the momentum equation was inserted into the energy equation due to dissipative effect of viscosity. The resulting energy equation was analyzed for criticality using the variational method technique. The problem is characterized by two parameters: the Nusselt number(N) and the dynamic parameter($\Lambda$). We observed that the thermal and dynamical boundary conditions of the wall have led to a significant departure from known results. The influence of the variable pre-exponential factor, due to the numerical exponent m, also give further insight into the behavior of the system and the results expressed graphically and in tabular forms.

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On the Thermal Boundary Conditions at the Interface Between the Porous Medium and the Impermeable Wall (다공성 매질과 비투과성 벽면 사이의 경계면에 대한 열적 경계 조건)

  • Kim, Deok-Jong;Kim, Seong-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.12
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    • pp.1635-1643
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    • 2000
  • The present work investigates a heat transfer phenomenon at the interface between a porous medium and an impermeable wall. In an effort to appropriately describe the heat transfer phenomenon at the interface, the heat transfer at the interface between the microchannel heat sink, which is an ideally organized porous medium, and the finite-thickness substrate is examined. From the examination, it is clarified that the he heat flux distribution at the interface is not uniform for the impermeable wall with finite thickness. On the other hand, the first approach, based on the energy balance for the representative elementary volume in the porous medium, is physically reason able. When the first approach is applied to the thermal boundary condition, and additional boundary condition based on the local thermal equilibrium assumption at the interface is used. This additional boundary condition is applicable except for the very th in impermeable wall. Hence, for practical situations, the first approach in combination with the local thermal equilibrium assumption at the interface is suggested as an appropriate thermal boundary condition. In order to confirm our suggestion, convective flows both in a microchannel heat sink and in a sintered porous channel subject to a constant heat flux condition are analyzed. The analytically obtained thermal resistance of the microchannel heat sink and the numerically obtained overall Nusselt number for the sintered porous channel are shown to be in close agreement with available experimental results when our suggestion for the thermal boundary conditions is applied.

Thermal buckling response of functionally graded sandwich plates with clamped boundary conditions

  • Abdelhak, Zohra;Hadji, Lazreg;Daouadji, T. Hassaine;Adda Bedia, E.A.
    • Smart Structures and Systems
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    • v.18 no.2
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    • pp.267-291
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    • 2016
  • In this research work, an exact analytical solution for thermal buckling analysis of functionally graded material (FGM) sandwich plates with clamped boundary condition subjected to uniform, linear, and non-linear temperature rises across the thickness direction is developed. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory accounts for parabolic distribution of the transverse shear strains, and satisfies the zero traction boundary conditions on the surfaces of the plate without using shear correction factor. A power law distribution is used to describe the variation of volume fraction of material compositions. Equilibrium and stability equations are derived based on the present refined theory. The non-linear governing equations are solved for plates subjected to simply supported and clamped boundary conditions. The thermal loads are assumed to be uniform, linear and non-linear distribution through-the-thickness. The effects of aspect and thickness ratios, gradient index, on the critical buckling are all discussed.