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We develop analytical and numerical conditions to determine whether limit cycle oscillations synchronize in diffusively coupled systems. We examine two classes of systems: reaction–diffusion PDEs with Neumann boundary conditions, and compartmental ODEs, where compartments are interconnected through diffusion terms with adjacent compartments. In both cases the uncoupled dynamics are governed by a nonlinear system that admits an asymptotically stable limit cycle. We provide two-time scale averaging methods for certifying stability of spatially homogeneous time-periodic trajectories in the presence of sufficiently small or large diffusion and develop methods using the structured singular value for the case of intermediate diffusion. We highlight cases where diffusion stabilizes or destabilizes such trajectories. 相似文献
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The present paper deals with the dimensional variations of limestone aggregates, cement paste, mortar, and High Performance Concrete (HPC) made with these constituents, when subjected to temperature changes in drying and sealed conditions. Variable water contents are studied for each material. The overall experimental results were obtained using strain gauges and Digital Image Correlation technique (DIC) is also applied for one configuration test. A significant difference between coefficients of Thermal Expansion (CTE) of cement paste and aggregate is observed, which leads to a large differential thermal deformation, able to explain thermal damage for temperatures between 50 °C and 100 °C. Water content has a great influence on material thermal dilation, causing delayed deformations especially for temperatures above 60 °C and for initially saturated samples. These experimental data may allow Thermo-Hydro-Mechanical models to be improved so that the in-situ long term behaviour of concrete can finally be predicted. The results confirm the dilation coefficient contrast between paste and aggregate, and also show that this contrast is markedly affected by the drying conditions and the initial state of saturation. 相似文献
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The optimal performance of a universal endoreversible steady-flow refrigerator cycle consisting of a constant thermal-capacity heating branch, a constant thermal-capacity cooling branch and two adiabatic branches with heat transfer loss was analysed using finite-time thermodynamics. The analytical formulae about cooling load, coefficient of performance, exergy loss rate, exergy output rate and ecological criterion of the endoreversible steady-flow refrigerator cycle are derived. Moreover, analysis and optimisation of the model were carried out in order to investigate the effect of the cycle process on the performance of the cycles using numerical examples. The results obtained include the performance characteristics of endoreversible steady-flow Carnot, Diesel, Otto, Atkinson and Brayton refrigeration cycles. The results can provide some theoretical guidance for the design of practical refrigerators. 相似文献
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冻融循环作用下饱和砂岩损伤扩展模型研究 总被引:2,自引:1,他引:1
首先分析饱和砂岩所经历的冻融作用的特点,认为冻融作用是一种低周疲劳荷载,且砂岩冻融循环作用下的受力状态可简化为单向拉伸荷载的循环作用。基于以上分析,在疲劳损伤理论的基础上,建立砂岩在冻融循环作用下的损伤演化方程。同时,通过对饱和砂岩冻融循环过程中的物理性质的观测,及对砂岩自身结构特点的分析,选取砂岩的开孔隙率作为损伤变量。之后通过试验数据对所建立的损伤模型进行验证,并探讨损伤方程中各参数的确定方法。经过验证,该损伤模型能较好地反映饱和砂岩在冻融循环作用下的损伤扩展规律,可以为相关的研究提供参考。 相似文献
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