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Abstract: This paper is concerned with the characteristics of wave propagation in double-walled carbon nanotubes (DWCNTs). The DWCNTs is simulated with a Timoshenko beam model based on the nonlocal continuum elasticity theory, referred to as an analytically nonlocal Timoshenko-beam (ANT) model. The governing equations of the DWCNTs beam consist of a set of four equations that are derived from the variational principle of the beam with high-order boundary conditions at the both ends, in which the effects of the nano-scale nonlocality and the van der Waals interaction between inner and outer tubes are inclusive. The characteristics of the wave propagation in the DWCNTs beam were analyzed with the new ANT model proposed and the comparisons with the partially nonlocal Timoshenko-beam (PNT) models in publication were made in details. The results show that the nonlocal effects of the ANT model proposed in the present study on the wave propagations are more significant because it is in stronger stiffness enhancement to the DWCNTs beam. [Copyright &y& Elsevier]

Abstract: In this paper, the porous NiTi shape memory alloy (SMA) fabricated by self-propagating high-temperature synthesis (SHS) has been investigated experimentally and numerically. The mathematical models about the ignition and the sintering were constructed to investigate the effect of the preheating temperature and the coil temperature on the combustion. The results showed that the temperature difference between the ignition face and the bottom face was large due to low heat transfer conductivity. The ignition time would increase with the decrease of the coil temperature and the preheating temperature. The temperatures for different locations showed a strong dependence on the combustion time for lower preheating temperature, for the preheating temperature 1173K, this mode of the combustion has transferred from SHS to thermal explosion. The transient partial molten phenomenon occurred during the process of combustion, which was more homogenous for preheating temperature 873K. The mean velocity of the combustion wave was investigated systematically. An experiment was also carried out to investigate the ignition and SHS reaction for porous NiTi alloy in this paper. It was found that the results of experiment and numerical simulation were shown in good consistence. [Copyright &y& Elsevier]

Results from combined laboratory experimental and turbulent numerical modeling studies are presented to investigate the effects of bed roughness (discrete square strips) and slope on the flow over a free overfall in a rectangular channel. A broad range of model parameters such as the bed roughness, channel slope, and incoming upstream Froude number is investigated. The water surface profiles upstream of the brink of the channel, the velocity fields in cavity between two strips, and end depth (water depth at the brink of the channel) are simulated, measured, and discussed for various input conditions. The results show that for a given dimension of bed roughness the relative spacing of roughness (defined as the ratio of the center to center distance to the height of the strip) has a significant effect on the flow. The computational results are in good agreement with the experimental measurements. [ABSTRACT FROM AUTHOR]

Highlights: [•] We improve a 2D RNG k–ε sediment model including the effect of secondary currents. [•] We develop an efficient semi-coupled scheme to solve sediment models numerically. [•] Bed deformation induced by transport of non-uniform suspended and non-uniform bedload sediments is investigated. [•] The variation of effective bed material granularity has been examined. [ABSTRACT FROM AUTHOR]