Abstract The dynamic characteristics of the stable formation of a single droplet in a gas-liquid co-flow device are studied experimentally. The scaling laws of the dimensionless necking radius R of a droplet with dimensionless remaining time τ for different parameters are analyzed, and the reasons for the transformation between these scaling laws are discussed. The results show that the change in the main pressure has little effect on the scaling law. In the earlier necking, R follows a 1/5 power law with respect to τ . In the later collapse, a 2/3 power law is matched. When the auxiliary pressure changes, the pneumatic shear force has a large impact on the earlier necking, causing the scaling law to change, but only a slight effect on the later collapse. Simultaneously, the droplet size and jet limit length decrease significantly with an increase in auxiliary pressure. The results are of great significance for revealing the mechanism of droplet formation and reducing droplet formation size in gas-liquid co-flow devices and provide a theoretical reference for further study of stable droplet formation.
This study presents analytical and numerical investigations of Marangoni interfacial instability in a two-liquid-layer system with constant solute transfer across the liquid interface. Previous research has demonstrated that both viscosity ratio and diffusivity ratio can influence the system's hydrodynamic stability via the Marangoni effect, but the distinctions in process and mechanisms are not yet fully understood. To gain insights, we developed a numerical model based on the phase-field method, rigorously validated against linear stability analysis. The parameter space explored encompasses Schmidt number ($Sc \in [0.2, 200]$), Marangoni number ($Ma_c \in [10, 2000]$), Capillary number ($Ca \in [0.01, 1]$), viscosity ratio ($\zeta_\mu \in [0.1, 10]$), and diffusivity ratio ($\zeta_D \in [0.1, 10]$). We identified two key characteristics of Marangoni instability: the self-amplification of triggered Marangoni flows in flow-intensity-unstable case and the oscillation of flow patterns during flow decay in flow-intensity-stable case. Direct numerical simulations incorporating interfacial deformation and nonlinearity confirm that specific conditions, including solute transfer out of a higher viscous or less diffusive layer, amplify and sustain Marangoni interfacial flows. Furthermore, the study highlights the role of interfacial deformation and unequal solute variation in system instability, proposing corresponding instability mechanisms. Notably, traveling waves are observed in the flow-intensity-stable case, correlating with the morphological evolution of convection rolls. These insights contribute to a comprehensive understanding of Marangoni interfacial instability in multicomponent fluids systems, elucidating the mechanisms underlying variations in viscosity and diffusivity ratios across liquid layers.
The coupling between the multilayer interfaces in compound jets has notable effects on the structure and generation sequence of the formed double emulsions. These effects are important for the performance of double emulsions, such as the capacity, release rate, and controlled release threshold in medical and chemical applications. In this work, the influence of the inner droplet on the necking of compound jets is investigated in a horizontally placed capillary flow-focusing device based on microfluidics. Three types of interface coupling modes are explored. Scaling laws that describe the time evolution of the neck radius for these different coupling modes are analyzed, and the reasons for transitions between such scaling laws are discussed. The results show that the motion and deformation of the droplet have a large impact on the neck breakup in the inertial regime, causing the scaling law to change, but only a slight effect in the viscous regime. Moreover, the inner droplet can prevent the jet from breaking up owing to interface coupling. These findings could help us to understand the role of interface coupling in compound jets and provide a reference for controlling the generation of compound droplets.
The sustainable development of Hainan's port construction has resulted in a sharp increase in ship traffic density in Qiongzhou Strait, which is impacted by strong wind and waves. Thus navigation safety of ships under different wind scales becomes critical. This paper made an analysis of shipwrecks and the number of various types of ships in service in the research area. Meanwhile, based on meteorological conditions in Hainan, the waves were simulated by using the nested SWAN wave model. After that, combining ALARP with wave height and using risk analysis theory, a risk evaluation for ship navigation security was established. Finally, the risk evaluation model was applied to two directional routes in Qiongzhou Strait. The model could provide the risk situation that ships may encounter when they are sailing intuitively and provide a reference to water traffic safety early warning. The study may reduce the numbers of shipwrecks in Qiongzhou Strait.
Analysis and optimization of steering column load under dynamic conditions is one of measures to solve the contradiction between dynamic properties requirements of vehicle steering system and great safety factor. In this paper taking C-EPS steering column with complicated load as study object, force equilibrium and dynamics conditions which meet the relationship between definite boosting torque and steering wheel load is analyzed, followed by load analysis and creation of load-optimized model based on load positions, then calculation is done with algorithm of PSO (Particle Swarm Optimization), and load optimization is realized with practical EPS product. The load optimization provide design basis for the optimization of EPS system.
Strength optimization is important method to save material and improve the dynamic performance of parts. With the research object of the output shaft, the paper has established strength optimization model and used genetic algorithm method to solve the difference strength safely coefficients in each position of the output shaft. The results show that when the shaft, with maximum loading, has been optimized, the quality reduce 6.7 percent, the maximum deformation reduce 35%, the maximum strain decrease 1%, and the biggest stress decrease 1%.
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