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The cross-media water entry problem widely exists in fields such as ocean engineering and aerospace. The highly non-stationary characteristics of the cross-media water entry process significantly influence the structural strength and ballistic stability of vehicles. This paper selects air-dropped torpedoes, supercavitating vehicles, and high-speed projectiles as three typical types of cross-media vehicles for study. Based on their unique structural characteristics and typical water entry conditions, this paper focuses on the current status of their respective impact load and load reduction challenges, as well as water entry ballistic stability issues. At the research methodological level, this paper systematically reviews the progress of current research in three directions: theory, experiments, and numerical simulations, and introduces the application of artificial intelligence in solving cross-media problems. Finally, this paper looks forward to future development trends in cross-media water entry research, aiming to provide a reference for structural optimization design, motion stability control, and other related studies of cross-media vehicles.

Wind energy is essential for sustainable energy development, providing a clean and reliable energy source through the wind turbine. However, the vortices and turbulence generated as wind passes through turbines reduce wind speed and increase turbulence, leading to significant power losses for downstream turbines in wind farms. This study investigates wake characteristics in wind turbines by examining the effects of different scale ratios on wake dynamics, using both experimental and numerical approaches, utilizing scaled-down models of the Aeolos H-20 kW turbine at scales of 1:33, 1:50, and 1:67. The experimental component involved wind tunnel tests in an open-circuit tunnel with adjustable wind speeds and controlled turbulence intensity. Additionally, Computational Fluid Dynamics (CFD) simulations were conducted using STAR-CCM+ (Version 15.06.02) to numerically analyze the wake characteristics. Prior to the simulation, a convergence test was performed by varying grid density and y+ values to establish optimized simulation settings essential for accurately capturing wake dynamics. The results were validated against experimental data, reinforcing the reliability of the simulations. Despite minor inconsistencies in areas affected by tower and nacelle interference, the overall results strongly support the methodology’s effectiveness. The discrepancies between the experimental results and CFD simulations underscore the limitations of the rigid body assumption, which does not fully account for the deformation observed in the experiment.

A flexible chitin nanofiber (ChNF) film with a thin fiber morphology, named, scaled-down (SD)-ChNF film, was previously found to be formed via successive partial deacetylation of the parent self-assembled ChNFs, cationization/dispersion via electrostatic repulsion in aqueous acetic acid, and suction filtration/drying. In this study, acetylation of a SD-ChNF film using acetic anhydride in pyridine was carried out to improve the mechanical properties. The FT-IR spectra of the acetylated SD-ChNF films suggested that acetylation progressed from the surface to the interior of the films with the increasing amounts of pyridine and elevating temperatures. The degrees of acetylation (DA) strongly affected the chitin crystallinity and surface morphology of the acetylated SD-ChNF films. Tensile testing of the acetylated SD-ChNF films indicated that the mechanical properties were improved by adjusting the DA values of the films. For example, the acetylated SD-ChNF film with an 1.84 DA value on surface showed values of 44.1 MPa and 24.9% for tensile strength and elongation at break, respectively.

The present study aims to develop and validate the dynamic similitude requirements for scaled-down models of large-scale complex structures for studying their vibration characteristics. Field investigations of large complex structures is a highly difficult task, which necessitates the representation of the field structure (prototype) by scaling down the geometry of such structure (model) in order to have similar similitude conditions for both static and dynamic parameters of the prototype. In this study of dynamic similitude analysis, a standard prestressed concrete I-girder largely adopted for highway bridges is considered as the prototype structure. The main objective of this paper is to establish a reliable scaling method for dissimilar systems using two similitude methods such as dimensional analysis and energy-based method. To verify the proposed method of scaling, an eigenvalue analysis was formulated considering the prestress effect and is compared with the numerical simulations of the prototype and the model by evaluating the system properties such as natural frequency and mode shape for the maximum prestress level and without prestress level. After confirming the efficacy and feasibility of the proposed method using both the similitude methods, experimental investigations are performed on the scaled-down model and validated for a similar structure. Based on the frequencies obtained from the scaled-down model, the frequencies of the prototype structure are predicted by using the dynamic similitude methods. The results indicate that, by employing the dynamic similitude theorems, the established scale models are able to predict acceptable results to estimate the vibration characteristics of the prototype bridge. The success of the proposed method is that the scaling laws derived for both the similitude methods were identical and could be performed for any dissimilar model of complex structure without involving any other similitude techniques for arriving the scale model. The proposed methodology of scaling down the prototype bridge structure is very much useful for evaluating the dynamic properties of the prototype structure as well as to estimate the existing prestress in the age-old prestressed concrete bridges.