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In this paper, a modified level set method is proposed for simulation of multiphase flows with large density ratio and high Reynolds number. The present method simply introduces a source or sink term into the level set equation to compensate the mass loss or offset the mass increase. The source or sink term is derived analytically by applying the mass conservation principle with the level set equation and the continuity equation of flow field. Since only a source term is introduced, the application of the present method is as simple as the original level set method, but it can guarantee the overall mass conservation. To validate the present method, the vortex flow problem is first considered. The simulation results are compared with those from the original level set method, which demonstrates that the modified level set method has the capability of accurately capturing the interface and keeping the mass conservation. Then, the proposed method is further validated by simulating the Laplace law, the merging of two bubbles, a bubble rising with high density ratio, and Rayleigh-Taylor instability with high Reynolds number. Numerical results show that the mass is a well-conserved by the present method. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive mesh refinement-multiphase lattice Boltzmann flux solver (AMRMLBFS) for effective simulation of complex binary fluid flows at large density ratios. In this method, an AMR algorithm is proposed by introducing a simple indicator on the root block for grid refinement and two possible statuses for each block. Unlike available block-structured AMR methods, which refine their mesh by spawning or removing four child blocks simultaneously, the present method is able to refine its mesh locally by spawning or removing one to four child blocks independently when the refinement indicator is triggered. As a result, the AMR mesh used in this work can be more focused on the flow region near the phase interface and its size is further reduced. In each block of mesh, the recently proposed MLBFS is applied for the solution of the flow field and the level-set method is used for capturing the fluid interface. As compared with existing AMR-lattice Boltzmann models, the present method avoids both spatial and temporal interpolations of density distribution functions so that converged solutions on different AMR meshes and uniform grids can be obtained. The proposed method has been successfully validated by simulating a static bubble immersed in another fluid, a falling droplet, instabilities of two-layered fluids, a bubble rising in a box, and a droplet splashing on a thin film with large density ratios and high Reynolds numbers. Good agreement with the theoretical solution, the uniform-grid result, and/or the published data has been achieved. Numerical results also show its effectiveness in saving computational time and virtual memory as compared with computations on uniform meshes. [ABSTRACT FROM AUTHOR]

The fragmentation of Cu75Zr25 amorphous films with varying film thickness on polyimide substrates has been investigated by uniaxial tensile testing, in combination with in situ electrical resistivity measurements, optical microscopy and atomic force microscopy. It is revealed that the cracking strain monotonically increases as decreases, which can be attributed to the constraint effect of film thickness on shear band formation and the columnar structures in the thicker films. Similarly, the buckling strain also increases with decreasing , with the delamination of Cu75Zr25 amorphous films following the strain energy criterion. The adhesion energy between Cu75Zr25 film and polyimide is estimated to be of ∼ 6.5 J m−2 based on the buckle geometry. [ABSTRACT FROM AUTHOR]

Changes in land use are likely to affect the abundance and functioning of microorganisms in the soil. In China many paddy fields are being converted for vegetable growing. We wished to determine how these changes affected the microbial populations in one particular region in Hunan province, where the climate is subtropical monsoon, as an example. We sampled the soil down to 1 m in several fields: three that were still growing paddy rice, three that had been converted for vegetable growing 2 years earlier and three that had been growing vegetables for 25 years. Quantitative polymerase chain reaction ( qPCR) and terminal-restriction fragment length polymorphism ( T-RFLP) were used to determine the abundance and community composition of nxrA-containing nitrifiers and narG-containing denitrifiers in the soil. The abundances of these organisms depended largely on the amount of organic matter in the soil and decreased with increasing depth, as did the potential nitrification rate ( PNR) and nitrate reductase activity ( NRA). Enzyme activity was significantly correlated with the abundance of nitrogen-cycling bacteria. The change from rice to vegetable growing resulted in more residual nitrate- N in the soil, which correlated more strongly with the abundance of nxrA-containing nitrifiers in the topsoil (0-20 cm) and narG-containing denitrifiers in the deeper soil (80-100 cm). In general, the numbers of nitrogen-cycling microorganisms decreased markedly with increasing depth, but were less affected by the change from rice to vegetable cultivation in the fields investigated. Our results suggest that the abundances of nitrogen-cycling microbial communities are affected more by depth in the soil than by change of land use in these circumstances. Highlights The abundance and function of soil microorganisms change when paddy fields are converted to vegetable growing., Residual nitrate- N in the soil is affected by nitrifiers in topsoil and denitrifiers in the deeper soil., Their abundances depend largely on the amount of organic matter in soil and decrease with increasing depth., The genetic structures of the microorganisms depend more on depth in the soil than on change from rice to vegetable growing. [ABSTRACT FROM AUTHOR]