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Liquid break up is an important phenomenon in many practical applications including combustion engines and paint sprays. The fundamental mechanisms which lead to this break up are not well understood. In this paper, the lattice Boltzmann method is employed to assess its potential for investigating these mechanisms. To do this, an axisymmetric, multiple relaxation time (MRT) lattice Boltzmann method, which allows for higher Reynolds numbers to be achieved than with the standard Bhatnagar-Gross-Krook (BGK) lattice Boltzmann model, is employed to simulate liquid break up. To assess the accuracy of the model, it is employed to simulate Rayleigh break up. The computational results for Rayleigh break up are compared to experimental and theoretical predictions and shown to have agreement within several percent. Then, the model is employed to carry out initial studies of transient liquid jets to investigate the influence of surface tension, injection velocity, and liquid viscosity.

Multi-relaxation time (MRT) for Lattice Boltzmann method is gaining renewed attention among researchers in the field. The advantage of such formulation over the widely popular single-time relaxation version, is twofold: better numerical stability and wider span of physical applications, extending to non-isotropic flows. In this work, the numerical advantages of the MRT model versus single-relaxation time (BGK) operator are quantitatively assessed through direct numerical simulations of droplet formation and capillary wave propagation on interphase boundaries. The results show that by proper tuning of the collision operator, and particularly of the higher-order kinetic modes (ghosts), appreciable improvements in stability limits, of the order of 20%, and viscosity limits, of the order of 80%, can be achieved. Moreover, a theoretical analysis accounting for the reasons behind such stability improvement, is also presented.

In this paper, we propose an efficient active contour model for multiphase image segmentation in a variational level set formulation. By incorporating the globally convex segmentation idea and the split Bregman method into the multiphase formulation of the local and global intensity fitting energy model, our new model improved the original local and global intensity fitting energy model in the following aspects. First, we propose a new energy functional using the globally convex segmentation method to guarantee fast convergence. Second, we incorporate information from the edge into the energy functional by using a non-negative edge detector function to detect boundaries more easily. Third, instead of a constant value to control the influence of the local and global intensity fitting terms, we use a weight function varying with the locations of the image to balance the weights between the local and the global fitting terms dynamically. Lastly, the special structure of our energy functional enables us to apply the split Bregman method to minimize the energy much more efficiently. We have applied our model to synthetic images and real brain MR images with promising results. Experimental results demonstrate the efficiency and superiority of our model.

A closed-loop scheme of 2-stage multiphase switched-capacitor (MPSC) converter is proposed by combining variable-phase control (VPC) and pulse-width-modulation (PWM) technique for low-power DC-DC step-up conversion and high-efficiency output regulation. In this MPSC, there are 2 voltage doublers in series for boosting voltage gain up to 4 at most. Here, VPC is suggested to improve power efficiency, especially for the lower output voltage. It realizes a variable multiphase operation by changing MPSC topological path for more suitable level of voltage gain (4x/3x/2x/1x) according to the desired output. Besides, PWM is adopted for better output regulation not only to compensate dynamic error, but also to reinforce robustness against source/loading variation. Further, the theoretical analysis and design include: MPSC model, steady-state analysis, power efficiency, conversion ratio, ripple percentage, capacitance selection, stability, and control design. Finally, the closed-loop MPSC is simulated, and the hardware implementation is realized and tested. All the results are illustrated to show the efficacy of the proposed scheme.

We prove the global existence and uniqueness of strong solutions for a compressible multifluid described by the barotropic Navier–Stokes equations in dim = 1. The result holds when the diffusion coefficient depends on the pressure. It relies on a global control in time of the L² norm of the space derivative of the density, via a new kind of entropy.

The effect of sand therapy on the hemodynamics of the popliteal artery (POA) was investigated to elucidate its mechanism in atherosclerosis physiotherapy. The hemodynamic parameters of the POA before and after sand therapy were obtained from 58 subjects and statistically analyzed. A three-dimensional finite element model of POA bifurcation was established. Blood was regarded as a triple-phase flow composed of plasma, red blood cells (RBCs), and white blood cells (WBCs). Using computational fluid dynamics (CFD), blood flow velocity, wall shear stress (WSS), and blood cell volume distribution before and after sand therapy were calculated. Sand therapy could reduce the vortex and reflux in blood vessels. The maximum increase in blood axial velocity was 34.38%. The maximum WSS increased by 22.82 Pa and the blood cells gradually moved away from the vessel wall and toward the axis of the blood vessel. The reduction in vortex and reflux, and the increase in blood axial velocity after sand therapy are beneficial in reducing the accumulation of cholesterol and other substances, thereby alleviating the formation of atherosclerotic plaques and lipid streaks. The rise in WSS slows the tendency of arterial vascular thickening in regions of low WSS. The movement of blood cells to the axis of blood vessels can reduce the possibility of thrombosis caused by blood cells squeezing on the blood vessel walls. These findings suggest that sand therapy may slow atherosclerosis progression.

The application of the lubricant in the temper rolling process of tinplate manufacturing improves the mechanical properties and surface quality of the steel sheet. The removal of the residual lubricant deserves and has rarely been studied via numerical simulation. A simplified model of a single stand temper mill was established and was discretized into cells of block-structured grids. The criterion whether the lubricant could be removed was decided via multiphase simulation of a smaller model. Three parameters, the gap between the deflector and the rolls, the length of an additional baffle and the velocity of the purging air, were considered and scores of different working conditions were performed. The shapes of the steel sheet between the temper rolls and the bridle roll were also studied to screen out the conditions that the sheet could move steadily.

A continuum theory for multiphase particulate suspensions in liquid media was formulated. The generalized fundamental balance laws for the particulate phases and the continuous fluid phase were presented. The thermodynamics of the multiphase system was studied, and the method of Lagrangian multipliers was employed to include the incompressibility of materials constraint and the criterion for fully saturated media. Constitutive equations were developed, which included micro-rotational and micro-dilatational effects. The basic equations of motion of different phases were derived and discussed. Special considerations were given to the case of incompressible constituents. Applications of this theory to nanofluids, dilute suspension flows, and multiphase sedimentations were also described.

Two separate types of multiphase flow models have been developed theoretically in this paper. Fourth-grade fluid model of non-Newtonian in nature is considered the main carrier. Silver and gold metallic particles of spherical shape suspend to form highly viscous multiphase flows which drift through an inclined channel. Effects of magnetic fields acting across the channel are applied as the body force. An approximate solution for the nonlinear flow dynamics of the two-phase suspensions. A comprehensive parametric study is performed to graphs against the pertinent parameters. Further, the obtained mathematical results and visual evidence are validated through computational data and found to be in completer agreement. It is inferred that gold multiphase suspensions can effectively be used in chemical and coating processes.