Compound droplets are usually taken as microcontainers for biomedical and material encapsulation applications in which a good understanding of the free oscillatory deformation and breakup behavior is essential. In this work, the dynamics of free oscillatory deformation and breakup of a single-core compound droplet with an initial ellipsoidal shell was investigated numerically using the volume-of-fluid method. The effects of droplet diameter and the outer droplet initial deformation parameter are considered. Four outcomes are identified: oscillatory deformation, separation, separation breakup, and breakup. The evolution of the kinetic energy and pressure field of the compound droplet for the four typical outcomes is also analyzed in detail. A clear boundary exists between the first and the latter three outcomes (initial deformation parameters of 0.600–0.773), while the critical factor for the latter three outcomes is the inner and outer droplet diameter ratio. The oscillatory deformation is characterized by the inner and outer droplet undergoing a finite deformation and subsequent oscillatory behavior, with the maximum deformation of the inner and outer droplets being related to the energy transfer between the two, and the outer droplet being a periodic decaying oscillation, while the inner droplet is a large deformation oscillation interspersed with a small deformation oscillation. Separation, separation breakup, and breakup are characterized by breakup at the inner or outer interface during deformation; separation and breakup times are largely dependent on droplet diameter and the initial deformation parameter of the outer droplet; and the neck width at separation is also analyzed in detail.

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The discrete element method (DEM) often uses the angle of repose to study the microscopic parameters of particles. This paper proposes a multi-objective optimization method combining realistic modeling of particles and image analysis to calibrate gravel parameters, after obtaining the actual static angle of repose (αAoR_S) and dynamic angle of repose (βAoR_D) of the particles by physical tests. The design variables were obtained by Latin hypercube sampling (LHS), and the radial basis function (RBF) surrogate model was used to establish the relationship between the objective function and the design variables. The optimized design of the non-dominated sorting genetic algorithm II (NSGA-II) with the actual angle of repose measurements was used to optimize the design to obtain the best combination of parameters. Finally, the parameter set was validated by a hollow cylinder test, and the relative error between the validation test and the optimized simulation results was only 3.26%. The validation result indicates that the method can be reliably applied to the calibration process of the flow parameters of irregular gravel particles. The development of solid–liquid two-phase flow and the wear behavior of centrifugal pumps were investigated using the parameter set. The results show that the increase in cumulative tangential contact forces inside the volute of centrifugal pumps makes it the component most likely to develop wear behavior. The results also illustrate the significant meaning of the accurate application of the discrete element method for improving the efficient production of industrial scenarios.

In this work, the self-excited oscillating pulsating circular pipe is the object of study. Based on the flow evolution characteristics of boundary layer and vortex, the mechanism of enhanced heat transfer by self-excited oscillating pulsating flow is investigated. Moreover, a vital flow structure, the boundary vortex ring (BVR for short), is proposed. The study results show that the vortex evolution within the shear layer inside the self-excited oscillating pulsating chamber has an important influence on the formation of the downstream boundary vortex ring. Both have the same period but different phases. The boundary vortex group formed by the BVR is distributed at intervals in the pipe, and its role in promoting fluid flow increases first and then decreases. At the same time, the strength of the central mainstream area is gradually strengthened. The boundary vortex group's flow state determines the downstream pipe's heat transfer characteristics. The low-velocity zone on both sides determines the position of the heat transfer coefficient enhancement, and the central vorticity determines the amplitude of the enhancement. The boundary vortex group with a complete structure can effectively promote heat transfer, while the boundary vortex group with an incomplete structure can suppress heat transfer. The time-averaged boundary layer thickness increase ratio δ' and the time-averaged equal diameter circular tube performance evaluation index ηT provide the fundamental indexes for designing and optimizing variable cross-section heat transfer circular tubes. Furthermore, the heat transfer coefficient of the tube wall varies synchronously with the thickness of the boundary layer.

To improve the strain homogeneity and damage homogeneity of radial forging hollow shaft. Proposed radial forging die with a cycloid as a generatrix entrance surface. The effects of the structural parameters of the die forging surface, such as the radius of cycloid base circle (R), the length of sizing zone (L) and the radius of sizing zone (r) on the strain homogeneity and damage homogeneity of the machined shaft were investigated. Numerical simulations were performed according to the orthogonal design L25, and an artificial neural network approach was used to develop a mathematical prediction model and apply it to the optimization process of the genetic algorithm. The results show that the optimized structural parameters of the compromise solution are R = 68.27mm, L = 49.36mm, r = 11.01mm, εσ and Cσ are 0.2113 and 0.02562, respectively. Compared with the original structural scheme, εσ is reduced by 21.83% and Cσ is reduced by 31.58%, which indicates that the plastic deformation is more uniform and the machining damage is less during the hollow shaft forging process.