Rising nanoscale technologies arouse interest in investigating the impact dynamics of nanodroplets. In this work, the impact of nanodroplets on solid spheres is investigated by the molecular dynamics simulation method, to comprehensively report outcome regimes and reveal the curvature effect, in wide ranges of Weber numbers (We) from 1.5 to 235.8, diameter ratios (λ) of nanodroplets to solid spheres from 0.3 to 5, and contact angles (θ) from 105° to 135°. Five outcomes are identified, including deposition, bouncing, splash, covering, and dripping. The former three outcomes are found in the high diameter ratio range (λ > 1), showing similar dynamic behaviors with impacts on flat surfaces, whereas in the low diameter ratio range (λ ≤)1, splash disappears, and covering and dripping take place additionally. At each contact angle, the outcomes are recorded in λ-We phase diagrams. It is found that the bouncing, splash, covering, and dripping are all promoted by decreasing diameter ratios; in addition, the critical Weber numbers for trigging bouncing and splash increase with decreasing θ. However, the critical We of the boundary between the bouncing to other regimes in the low diameter ratio range is not sensitive to wettability owing to the relatively small diameter of solid spheres. For quantitatively describing the curvature effect, the boundaries between the deposition and bouncing regimes in the high diameter ratio range and between the bouncing and other regimes in the low diameter ratio range are established. Both the established models show satisfactory agreement with the boundaries in the phase diagrams.

The good indoor light environment and comfort of the teaching space are very important for students’ physical and mental health. Meanwhile, China advocates energy conservation and emission reduction policies. However, in order to obtain lower building energy consumption, higher thermal comfort, and daylighting, architects use performance simulation software to repeatedly simulate and refine, which is time-consuming and difficult to obtain the best results from three performances. Given this problem, we constructed the design framework in the early stage of the architectural design of the teaching building. In the first stage of the framework, architects optimized the performance objectives of lighting, thermal comfort, and energy consumption, and performed a cluster analysis on the optimized non-dominated solution to provide a reference for the architect. In the second stage of the framework, architects used the data generated in the optimization process to train the BP neural network and use the trained BP neural network to predict the performance of the building. In this paper, we selected Nanjing Donglu Middle School as a case study. The optimization of the building performance was assessed by a genetic algorithm, generating 3000 sets of sample data during the optimization iteration. Then, we analyzed the non-dominated solution of the sample data through the method of cluster analysis and trained the BP neural network with the sample data as a data set. The prediction model with R-values of 0.998 in the training set and test set was obtained by repeatedly debugging the number of neurons in the BP neural network. Finally, five groups of design parameters were randomly selected and brought into the trained BP neural network, and the predictive value was close to the simulated value. The construction of the framework provides design ideas for architects in the early teaching of building design and helps designers to make better decisions.

On a rectangular-ridged superhydrophobic surface, the contact time of the rebounding-coalescing droplet is for the first time investigated via lattice Boltzmann method simulations, where the rebounding-coalescing droplet is caused by an impinging droplet coalescing with an adhesive droplet. The simulation results show that at constant initial radii of impinging droplets, R₀, and various initial radii of adhesive droplets, R₁, the contact time of rebounding–coalescing droplets depends not only on the impact condition but also on the surface condition. Under various impact conditions, that is, with increased Weber numbers of We = 1–30, the contact time is gradually reduced, and then nearly constant, and eventually constant after slightly reduced at R₀ = 35 and R₁ = 25. However, at R₀ = 35 and R₁ = 10, it is gradually reduced, then increased, and eventually constant. It indicates that the contact time of rebounding-coalescing droplets is affected by the initial radii of adhesive droplets. Under different surface conditions, that is, with increased spacing distances between adhesive droplets and ridges of L = 3–17, the contact time is reduced at the low Weber number of We = 3, constant at the moderate Weber number of We = 12, and increased at the high Weber number of We = 28 at R₀ = 35 and R₁ = 25. However, at R₀ = 35 and R₁ = 10, it is reduced at both low and moderate Weber numbers of We = 3 and 12, and constant at the high Weber number of We = 28. It indicates that under different surface conditions, the contact time of rebounding-coalescing droplets is also affected by the initial radii of adhesive droplets.

Efficient droplet shedding from surfaces is fundamentally interesting and important due to its promising potential in numerous applications, such as anti-erosion, anti-icing, and self-cleaning. In this work, the bouncing dynamics of the head-on impact of two nanodroplets on superhydrophobic surfaces are investigated through molecular dynamics simulations. Three bouncing patterns, including regular-coalescence-bouncing, coalescence-hole-bouncing, and ring-bouncing, are identified at a wide range of impacting Weber numbers. For three bouncing patterns, the time evolutions of the spreading factors and the vertical velocity components are employed to analyze the particular dynamic behaviors and elucidate the underlying physics. As a counter-intuitive bouncing pattern, the ring-bouncing that two impact nanodroplets coalesce, spread, and then leave the surface in a ring shape without retracting exhibits a remarkable reduction in contact time by up to 60%. Considering four typical states for the ring-bouncing pattern, the comparison of the velocity distribution within the droplet clearly reveals that the ring-shaped droplet reshapes interfaces, which leads to a special hydrodynamics distribution. As a result, the internal flows at the inner and outer edges along the opposite direction collide with each other, leading to a sudden increase in the upward velocity. Combining the largely decreased contact area between solid and liquid with the small surface adhesion, the ring-shaped droplet rapidly bounces off the surface at the maximum spreading state. Finally, it is significantly highlighted that the ring-bouncing pattern offers a new avenue to break the contact time limit for efficient droplet shedding.

To provide beneficial reference to the assessment of the ship pollution risk of Weihai bay sea area and pollution prevention ability. Adopting the "oil particle" model, the drift and diffusion process of oil spill from a certain shipyard in Weihai bay is simulated. By using Lagrange method, the oil film center movement locus and the oil film distribution at each time is visualized. By considering the effect of environmental factors on the behavior of marine oil spill in the three-dimension flow field, turbulence, wind guide, transport and wave breaking, the oil spill prediction model predicted the oil film drift path under the combined effect of the wind and currents, oil film affected range of the sea area and coast. The expert review meeting organized by maritime agencies recognized the oil spill prediction result analysis by using this oil spill model.