The architecture of real dandelion seeds is diverse. Previous studies have primarily focused on the flow patterns and drag coefficients of dandelion seeds with a pappus angle no greater than 180°, but have paid less attention to the cases of the pappus angle larger than 180°. This work therefore numerically investigated the flow patterns and drag coefficients of dandelion seeds with the pappus angle larger than 180° when the speed of incident flow is 0.2 m/s, using double-layered models consisting of two oppositely oriented filament layers. The simulated results were then compared to those obtained from single-layered models consisting of identical number of but leeward-oriented filaments (the pappus angle lower than 180°). It reveals that, either single-layered or double-layered models, the length (L) and width (W) of separated vortex rings increase, drag coefficients (CD) increase, but the shape index (L/W) and the relative location of separated vortex rings (zu) decrease, as the number of filaments increases. At a given filament number, L, W, and zu in double-layered models are smaller than those in single-layered models, but L/W and CD in double-layered models are larger than those in single-layered models, attributed to the windward-oriented filaments. In double-layered models, thanks to small difference in the drag force but significant difference in the projected area, CD is significantly higher when both windward-oriented and leeward-oriented filaments are installed at identical locations on the central disk's perimeter compared to cases where windward-oriented and leeward-oriented filaments are installed at different locations.

Geophysical mass flows, which could endanger our health, lives, and property safety, commonly occur in mountain regions. Although many efforts have been made, transport of granular flows consisting of polydisperse grains, which is influenced by multiple factors, is still not well understood. This work focused on the effect of small spherical grains on the movement of large stones in granular flows of different grain compositions (quartz gravel, glass bead and angular stone), through experimentally measuring mass frequency distributions of granular materials deposited on flat surface. Three characteristic deposition distances (X₂₀, X₅₀ and X₈₀) and one extreme mobility probability (P_s) were extracted from cumulative frequency distributions. It reveals that, in most of cases, the inclusion of glass beads reduced X₂₀, X₅₀, and X₈₀ but increased P_s for total mass. For angular stone mass, the inclusion of glass beads increased the occurrence frequency of that X₂₀, X₅₀ and X₈₀ increase, apart from increasing P_s. These results indicated small spherical grains could effectively enhance the extreme mobility of large angular stones in mixtures. We hope these results could be helpful for improving our understanding of the transport of geophysical mass flow as well as the grain segregation in different natural environment.

Temporary works are necessary to ensure the construction and operation of railways. These works are characterized by their large scale, numerous locations, and long construction periods. However, suitable land resources for such purposes are extremely limited in mountainous railway areas. Additionally, the selection of sites for these works often overlaps with areas affected by debris flow, leading to high potential risks from geological disasters. Taking the Jinjia Gully watershed as an example, this paper explores a method for assessing debris flow risks in single gullies, including the zoning of debris flow danger areas, vulnerability analysis, and risk assessment. Based on the data obtained from field surveys, they utilize ArcGIS and the Analytic Hierarchy Process (AHP), combined with numerical simulations and indoor experiments, to establish a quantitative risk assessment method for large-scale temporary works. The results indicate that (1) the area of debris flow hazard zones decreases with increasing rainfall frequency, and (2) the vulnerability assessment model can not only reflect the types of individual work, structural materials, and construction quality but also the shielding effect of building clusters. In the direction of flow, the shielding effect range of buildings on debris flow accumulation fans is approximately 37.5 times the size of the buildings. In the direction of extension, when the angle between current and rear buildings exceeds 0.674 radians, the shielding effect can be neglected. (3) At a rainfall frequency of p = 5%, more than 80% of large-scale temporary works are in extremely low or low-risk zones, indicating that the study area is at a low risk level.

Wind turbines operating in wind-blown sand environments are subjected to severe particle adhesion driven by electrostatic effects, which significantly degrades aerodynamic performance and increases operational risks. However, the mechanisms of particle–blade collision charging and the resulting spatial distribution of surface charge remain poorly understood. To address this gap, the present study develops a numerical modeling framework that integrates the discrete phase model with a custom user-defined collision–charging model. Key parameters, including impact velocity and rebound probability coefficient, are incorporated to quantify energy transfer, particle rebound, and charge generation during collisions. These results show that particle collision and deposition are predominantly concentrated near the blade leading edge. Wind speed governs the transition from gravity-dominated, dispersed deposition at low speeds to flow-dominated impact patterns at higher speeds. Particle deposition exhibits a non-monotonic dependence on wind speed due to the competing effects of increased collision frequency and enhanced rebound. In addition, larger particle sizes and higher wind speeds lead to markedly increased charge accumulation and broader high-charge-accumulation regions on the blade surface. Simulated high-charge-accumulation regions are shown to coincide with actual lightning strike locations on in-service blades, demonstrating that enhanced charge accumulation may increase the likelihood of electrostatic discharge and lightning attachment. Scaled to a 24 h sandstorm, the accumulated surface charge can produce electric fields approaching corona inception thresholds. The proposed framework provides practical guidance for the design of anti-static coatings and lightning protection strategies for wind turbines operating in arid environments.