Search for: All records

Large deployable mesh reflectors play a critical role in satellite communications, Earth observation, and deep-space exploration, offering high-gain antenna performance through precisely shaped reflective surfaces. Traditional dynamic modeling approaches—such as wave-based and finite element methods—often struggle to accurately capture the complex behavior of three-dimensional reflectors due to oversimplifications of cable members. To address these challenges, this paper proposes a novel spatial discretization framework that systematically decomposes cable member displacements into boundary-induced and internal components in a global Cartesian coordinate system. The framework derives a system of ordinary differential equations for each cable member by enforcing the Lagrange’s equations, capturing both longitudinal and transverse internal displacement of the cable member. Numerical simulations of a two-dimensional cable-network structure and a center-feed parabolic deployable mesh reflector with 101 nodes illustrate the improved accuracy of the proposed method in predicting vibration characteristics across a broad frequency range. Compared to standard finite element analysis, the proposed method more effectively identifies both low- and high-frequency modes and offers robust convergence and accurate prediction for both frequency and transient responses of the structure. This enhanced predictive capability underscores the significance of incorporating internal cable member displacements for reliable dynamic modeling of large deployable mesh reflectors, ultimately informing better design, control, and on-orbit performance of future space-based reflector systems. 

Abstract As the largest terrestrial planet in the solar system, Earth experienced a prolonged major accretion, ending with the Moon-forming giant impact (MFGI), whereas the direct evidence and origin of the impactor Theia remain elusive. Recent computational studies indicate that parts of the impactor Theia mantle may persist above Earth’s core–mantle boundary as the large low-velocity provinces (LLVPs), yet it remains unclear how these results were affected by the initial size of Theia fragments after the MFGI. Here I explore such influence in whole-mantle convection simulations, assuming that the Theia debris size follows the size distribution of the main-belt asteroids, which provides a natural estimation of collision debris for the ill-constrained parameter during extreme impacts. The results demonstrate that the asteroid-sized Theia debris can survive Earth’s 4.5-billion-year convective history as large-scale thermochemical structures resembling the seismically observed LLVPs. The results also demonstrate that rheologically strong Theia fragments are more capable of long-term preservation compared to those with weaker compositions. The inferred viscosity of Theia fragments aligns with that proposed for LLVPs from noble gas isotope evidence for a dry plume mantle source and agrees with global mantle attenuation constraints from seismic normal modes. These findings provide insight into the physical mechanism of preserving ancient geochemical signatures in Earth’s mantle, support an inner solar system provenance for the impactor Theia, and further help explain the isotopic homogeneity between Earth and the Moon. 

Abstract Harmful algal blooms (HABs) pose significant threats to aquatic ecosystems and human health, necessitating efficient mitigation strategies. Although clay-algae aggregation has been widely used for controlling HABs, the slow sedimentation of clay-algae aggregates hampers its effectiveness. We examine how turbulence dynamics affect the formation and settling of clay-algae aggregates. Using a custom-designed plankton tower equipped with an oscillating grid and an in-situ imaging system, we investigated how varying dissipation rates of turbulent kinetic energy (ε = 8 × 10⁻⁹to 9 × 10⁻⁵m²/s³) affected the removal efficiency ofMicrocystis aeruginosaby laponite clay. In addition, we directly measured the settling velocity and size of clay-algae aggregates over time. The results demonstrate that turbulent mixing, on a time scale typical of the diurnal mixed layer of lakes, can enhance the removal efficiency of HABs by up to threefold. Higher turbulence dissipation rate,ε, leads to an increase in the settling velocity and size of clay-algae aggregates. We demonstrate that the maximum removal efficiency ofMicrocystis aeruginosais achieved when the ratio of the diameter of clay-algae aggregates is half the Kolmogorov length scale. Our findings highlight the importance of turbulence in enhancing clay-based HAB mitigation and provide actionable insights for field applications, such as leveraging natural wind-driven mixing or implementing mechanical agitation in the lakes’ surface mixed layer. This study bridges the gap between well-controlled laboratory experiments and real-world HAB implementation.