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Droplets oscillating on vibrating substrates are very interesting scientifically, with applications such as anti-icing, droplet transportation, and measuring dynamic surface tension. Reported here are the dynamics of droplets with different volumes on a vibrating smooth surface infused with liquid of different viscosities. The movement of the three-phase droplet contact line is used to quantify the droplet dynamics, and it is found that this movement is linearly proportional to the amplitude of the substrate and inversely proportional to the viscosity of the liquid infused therein. When the substrate viscosity is relatively low, the droplet volume also affects the contact-line movement. Scaling laws for the contact-line movement are derived involving the Ohnesorge number and the reciprocal of the capillary number. Also elucidated is the relationship between the resonance frequency and the substrate viscosity, and the characteristic droplet morphology under different substrate viscosities is extracted to describe the contact-line movement. Interestingly, the substrate viscosity is controlled in an innovative way to achieve almost the same contact-line movement on the present surface as on superhydrophobic and hydrophilic surfaces. [ABSTRACT FROM AUTHOR]

The swift advancement of underwater weaponry has thrust deep water explosions into the spotlight as a strategic asset. This study endeavors to delve into the load dynamics of deep water explosions in proximity to curved boundaries, elucidating the behaviors of shock waves, bubble movement, and jet load transmission. Employing the structured arbitrary Lagrangian–Eulerian method, we construct a coupled fluid–structure interaction model to replicate the propagation of loads during deep water explosions. Subsequently, we examine the dynamic behavior of bubbles generated by deep-water explosions near curved boundaries, elucidating the impact of water depth and detonation distance on their non-spherical motion. Finally, we consolidate the load patterns of bubble jets near curved boundaries across diverse scenarios. Our findings reveal that deep-water explosion loads are affected by variables including water depth, detonation distance, and boundary conditions, displaying a discernible pattern and complexity. The presence of curved boundaries amplifies the intensity of shock waves, leading to a reduction in bubble radius, a shortened cycle, and alterations in bubble collapse dynamics. [ABSTRACT FROM AUTHOR]

Adding a small amount of polymers can achieve significant drag reduction effects. However, for external flows, the common homogeneous mixing and diffusing injection methods are not feasible. As an alternative, the present work developed a novel water-soluble polymer composite coating. The coating made use of the film-forming property of polyvinyl alcohol with polyethyleneoxide (PEO, a well-known drag reduction polymer) incorporated into it. When the coating dissolved, PEO continuously dispersed into the external flow. The surface characteristics of the water-soluble polymer coating were characterized. Drag reduction tests were conducted using a gravity circulation system. The coating exhibited a maximum drag reduction rate (DR) of 7% in the coating section and 27% in the downstream section. The larger percentage and the greater molecular weight of PEO not only promoted polymer drag reduction but also increased the surface roughness. Competition between effects of drag reduction and surface roughness led to complex effects in the coating section. It was also found that partial coating could induce significant drag reduction effects. The optimal length ratio of coated to total surface was related to the polymer characteristics and the speed of the main flow. The 1/4 and 1/2 coating resulted in a maximum DR of approximately 7% (Re = 27 523) in the test plate section for coatings with 10 000 wppm PEO, while the 1/4 coating had a maximum DR of approximately 9% (Re = 11 468) for coatings with 20 000 wppm PEO. These results indicated that such drag-reducing composite polymer coatings have great potential to be applied in underwater equipment. [ABSTRACT FROM AUTHOR]

The secreting drag reduction mucus in fish epiderm inspires the manufacturing of five gelatin–polysaccharide drag reduction coatings. First, a mixed solution composed of the gelatin and bio-polysaccharides [guar gum, xanthan gum, locust bean gum, tragacanth gum, or acacia gum] was poured into rectangular grooved polymethyl methacrylate (PMMA) plates, and bionic coatings were obtained after curing. Then, the surface characteristics of the coatings were characterized, and the internal micro-/nanoscale three dimensional (3D) net structures provided releasing access for the polysaccharide molecules. Importantly, a parametric study focusing on the gelatin and polysaccharide proportion affected the drag reduction of the coatings in a turbulent channel flow. Based on a smooth PMMA plate without a coating as a reference, the five developed coatings exhibited considerable drag-reducing effects with the corresponding maximum drag reduction rates that all exceeded 20%. There are three drag reduction mechanisms (polymer drag reduction, slip phenomenon, and wall flexibility) and one drag increase mechanism (surface roughness). Increasing the gelatin proportion affects the release rate of the drag-reducing agents, surface flexibility, and surface slip properties. Meanwhile, increasing the polysaccharide proportion promotes the release of polysaccharides, but increases the surface roughness. Thus, the effects of gelatin and polysaccharide are complicated due to competition between these mechanisms. Future works should focus on clarifying the complex mechanisms to improve the drag reduction efficiency of the gelatin-based bio-polysaccharide coatings. These biomimetic drag-reducing coatings could be further applied to underwater equipment. [ABSTRACT FROM AUTHOR]