The impact of a single liquid drop on a flowing liquid film is experimentally and theoretically studied. The drop impact produces a crownlike rising liquid sheet, which radially expands. Small droplets can be formed from the crown sheet, resulting in splash. The present study results in three major contributions. (1) A theoretical model is developed to predict the expansion of the crown base. The model with an introduced energy loss factor is shown to be in satisfactory agreement with our experimental observations of drop impact on both stationary and flowing films. The energy loss factor is correlated to the properties of the film and drop. (2) Analysis is conducted to derive an equation for evaluating the stretching rate of the rising crown sheet, which is the local gradient of the rising velocity at the top edge of the crown sheet. It shows that the highest stretching rate appears where the drop spreading flow is right opposite to the film flow, which helps explain why the same location is most probable for splash to take place. (3) A parameter as a function of modified Weber and Reynolds numbers is defined to predict splash and nonsplash of drop impact on flowing films. The two nondimensional numbers evaluate the competition of the two flows (drop and film) against viscosity and surface tension effects. A threshold value of the parameter is found for the occurrence of splash impact on flowing films.
The Honghe Hani Rice Terraces (China) is an ancient world heritage agricultural landscape that has been evolved in centuries as a result of farmers' indigenous practices and knowledge. The area, however, is prone to landslides that can burden the conservation of these landscapes including their social, cultural, economic and aesthetic value. In June 2018, a landslide threatened the villages of Duosha and Mengpin affecting 138 inhabitants and the terraces structure. This event marked the need to understand how farmers coexist with these natural hazards and which are the behaviours people adopt to conserve their environment and safeguard their livelihood. Results from 125 in-person interviews showed that farmers feel threaten by landslide events derived by their personal experience, but their poor perceived preparedness and the inefficient disaster information make them more vulnerable to those events. Nevertheless, they demonstrated a desire to increase their knowledge on terraces restoration and conservation practices. This is an important signal for public authorities and practitioners that need to underpin training activities and create momentum for discussion. The demonstrated high trust in authorities' decisions is a crucial element to pursue the objective and sustain the conservation of the terraces and the tourism economy.
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