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Jose Carlos Bellido Alberto Donoso Pablo Pedregal 《Archive for Rational Mechanics and Analysis》2010,195(1):333-351
This paper addresses the relaxation of an optimal design problem in conductivity under a point-wise constraint on the heat flux. By using a variational approach, developed by the authors in a previous work, we obtained a complete relaxation, involving the explicit computation of constrained quasiconvex envelopes. This relaxed formulation turns out to be very simple in the remarkable compliance case, for which numerical simulations are performed. Those simulations show that our approach and results are interesting from a theoretical point of view as well as from a practical perspective. The emphasis of our work is placed on the local constraint on the heat flux, which seems to be a new ingredient for this kind of optimal design problems. 相似文献
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The purpose of this work was to study both theoretically and experimentally the process of moisture redistribution and heat transfer due to phase changes during the tests of thermal conductivity in aerated autoclaved concrete (AAC) moist specimens. The different moisture contents of the test samples were obtained in climatic chamber at equilibrium conditions reached with constant air temperature and variable relative humidity. The moist specimens were sealed inside highly impermeable polyethylene bag, as required by UNI 10051, and placed in a heat flow meter apparatus. During the experimental thermal conductivity measurements, the temperature and heat flow rate were measured under transient and steady state conditions. A theoretical analysis of the heat and mass transfer process was performed and then a suitable numerical model was used to predict the moisture redistribution and heat transfer due to the phase changes. The theoretical model has been compared against the experimental data. Substantial agreement between numerical results and experimental data was found. Then several numerical simulations have been performed to study the influence of the errors due to phase changes and non-uniform moisture distribution during the test of thermal conductivity of moist AAC specimens. 相似文献
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金属薄膜/聚合物基底(尤其是温度敏感型的聚合物)结构在外力和加热影响下的力学性能变化直接影响到器件的功能和使用寿命。通过光学显微镜原位观察钛膜/有机玻璃基底结构在力-热(20~44℃)耦合作用下的薄膜表、界面响应。在外部轴向压力作用下,薄膜会发生垂直于加载方向的屈曲。保持试件的加载端边界位移不变,对其进行加热,薄膜会出现垂直于屈曲方向的横向裂纹。通过分析发现薄膜产生横向裂纹的原因为:力-热耦合作用促使聚合物基底在非加载端方向的拉应变增大。在不同长度的薄膜裂纹段上,较长裂纹段中心部位上受到基底传递的拉应力较大,产生再次断裂的可能性较高。 相似文献
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缸套-活塞系统润滑行为与动力学行为耦合分析 总被引:12,自引:0,他引:12
建立了缸套-活塞系统油膜润滑与动力学行为耦合分析模型,并用数值方法进行了仿真计算,用有限元法计算了缸体的结构动力响应;通过采用有限差分法求解平均雷诺方程计算了缸套和活塞间的流体润滑特性,并探讨了活塞二阶振动的影响;采用顺序耦合的方法计算了考虑缸套-活塞摩擦、润滑与缸体结构振动、活塞二阶振动耦合作用的缸套-活塞间最小油膜厚度变化、摩擦力及摩擦功耗等.同不考虑缸体振动时的相应分析和计算结果对比发现,缸体结构振动对油膜润滑特性具有重要影响. 相似文献
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Residual Displacements in a Hollow Viscoplastic Cylinder Under rhe Action of a Mobile Thermal Source
A prescribed distribution of residual radial displacements on the inside surface of a hollow cylinder is considered to be formed with the help of a mobile ring heat source. It is established that this goal can be achieved if the source velocity is variable and the source power is constant. The problem is subdivided into three subproblems. The dependence of the total displacement on the source velocity is determined in the first subproblem. The second subproblem is to determine a law for velocity control depending on the prescribed distribution of residual displacements. The third subproblem consists in homogenization of their end distributions. Approaches to the solution of each of these problems are developed 相似文献
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Semiconductor-based electronic devices usually work under multiphysics fields rendering complex electromagnetic-thermo-mechanical coupling.In this work,we devel... 相似文献
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Interfacial transition zones(ITZs) between aggregates and mortar are the weakest parts in concrete. The random aggregate generation and packing algorithm was utilized to create a two-phase concrete model, and the zero-thickness cohesive elements with different normal distribution parameters were used to model the ITZs with random mechanical properties. A number of uniaxial tension-induced fracture simulations were carried out, and the effects of the random parameters on the fracture behavior of concrete were statistically analyzed. The results show that, different from the dissipated fracture energy, the peak load of concrete does not always obey a normal distribution, when the elastic stiffness, tensile strength, or fracture energy of ITZs is normally distributed. The tensile strength of the ITZs has a significant effect on the fracture behavior of concrete, and its large standard deviation leads to obvious diversity of the fracture path in both location and shape. 相似文献
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Steady and pulsatile flow and heat transfer in a channel lined with two porous layers subject to constant wall heat flux under
local thermal non-equilibrium (LTNE) condition is numerically investigated. To do this, a physical boundary condition in the
interface of porous media and clear region of the channel is derived. The objective of this work is, first, to assess the
effects of local solid-to-fluid heat transfer (a criterion indicating on departure from local thermal equilibrium (LTE) condition),
solid-to-fluid thermal conductivity ratio and porous layer thickness on convective heat transfer in steady condition inside
a channel partially filled with porous media; second, to examine the impact of pulsatile flow on heat transfer in the same
channel. The effects of LTNE condition and thermal conductivity ratio in pulsatile flow are also briefly discussed. It is
observed that Nusselt number inside the channel increases when the problem is tending to LTE condition. Therefore, careless
consideration of LTE may lead to overestimation of heat transfer. Solid-to-fluid thermal conductivity ratio is also shown
to enhance heat transfer in constant porous media thickness. It is also revealed that an increase in the amplitude of pulsation
may result in enhancement of Nusselt number, while Nusselt number has a minimum in a certain frequency for each value of amplitude. 相似文献
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International Applied Mechanics - Differential equations of thermomagnetoelasticity for flexible axisymmetric conical shells made of isotropic and orthotropic materials taking into account Joule... 相似文献
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The two-equation model in porous media can describe the local thermal non-equilibrium (LTNE) effects between fluid and solid at REV scale, with the temperature differences in a solid particle neglected. A multi-scale model has been proposed in this study. In the model, the temperature differences in a solid particle are considered by the coupling of the fluid energy equation at REV scale with the heat conduction equation of a solid particle at pore scale. The experiments were conducted to verify the model and numerical strategy. The multi-scale model is more suitable than the two-equation model to predict the LTNE effects in porous media with small thermal conductivity. The effects of particle diameter, mass flow rate, and solid material on the LTNE effects have been investigated numerically when cryogenic nitrogen flows through the porous bed with small thermal conductivity. The results indicate that the temperature difference between solid center and fluid has the same trend at different particle diameters and mass flow rates, while the time to reach the local thermal equilibrium is affected by solid diameter dramatically. The results also show that the temperature difference between solid center and surface is much greater than that between solid surface and fluid. The values of \( \rho {\text{c}} \) for different materials have important influence on the time to reach the local thermal equilibrium between solid and fluid. 相似文献
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Thickness Effect of Pulse Shaper on Dynamic Stress Equilibrium and Dynamic Deformation Behavior in the Polycarbonate Using SHPB Technique 总被引:1,自引:0,他引:1
0Introduction Thehighstrainratestress strainresponsesofpolymersandpolymericcompositematerialshave receivedincreasedscientificandindustrialattentioninrecentyears.Polymericmaterialsaresubjected todynamicloadingandhighstrainratedeformationinavarietyofimporta… 相似文献
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A two-dimensional analysis of the onset of thermal convective instability in a horizontal porous layer with open upper boundary is carried out. The saturating fluid is non-Newtonian of power-law behaviour, and its flow is represented through a suitable extension of Darcy’s law. A model of temperature-dependent viscosity is employed where the consistency index is considered as variable, while the power-law index is assumed to be constant. Numerical data for the neutral stability and for the critical values of a modified Darcy–Rayleigh number have been obtained. The feasibility of an experimental validation of the theoretical results predicted by the stability analysis is discussed in detail. An experimental set-up based on a Hele-Shaw cell is described, and preliminary results relative to the onset of convective cells are described. Observed hysteretic effects and deviations from the rheological model are identified as potential sources of uncertainty. 相似文献
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Transport in Porous Media - The present work investigates the thermal radiation transport inside porous media under local thermal non-equilibrium conditions. Two different geometrical situations, a... 相似文献
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含热传导的冲击动力学有限元程序的研究与应用 总被引:2,自引:0,他引:2
从有限变形的基本框架出发 ,建立了含热传导的冲击动力学基本控制方程和合适的初边条件。应用变分原理和伽辽金方法得出了控制方程相应的有限元列式 ,并探讨了数值计算中的几个关键算法 ,主要包括构型转换、旋转张量的算法、本构算法以及计算流程和程序框图等。利用自行研制的程序 ,对长脉冲激光辐照下靶目标的变形和破坏、冲击压缩变形及变形局部化等问题进行了数值模拟和研究 ,所得结果与实验和理论分析相吻合。 相似文献
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This paper analyzes the effect of the time-dependent shape of a load pulse on the spall strength of materials. Within the framework of a classical one-dimensional scheme, triangular pulses with signal rise and decay portions and with no signal rise portions considered. Calculation results for the threshold characteristics of fracture for rail steel are given. The possibility of optimization of fracture by selecting a loading time with the use of an introduced characteristic of dynamic strength (pulse fracture capacity) is demonstrated. The study is carried out using a structure–time fracture criterion. 相似文献