This work studies the water-exit problems of slender cylinders under various conditions through experimental investigation. An experimental platform was equipped with high-speed photography. A total of 13 experimental cases with varying head shapes (conical, spherical, and truncated cone designs), length-to-diameter ratios (5:1–7:1), ejection velocities (7.24–17.93 m/s), and elastic moduli (227.36–279.14 MPa) were conducted to capture water-exit characteristics. The investigation identified ejection velocity as the predominant parameter governing cavity morphology and stability, with higher velocities correlating to increased cavity dimensions and reduced drag coefficients by 54%. Conical head shape resulted in superior drag reduction characteristics, forming a typical cigar-shaped cavity with clear and regular boundaries. Additionally, an increased length-to-diameter ratio substantially improved drag reduction performance by 33%. Material elastic moduli proved crucial for water-exit stability, as cylinders with lower moduli experienced severe bending deformation and even trajectory changes, while higher moduli cylinders maintained their form with minimal deformation. This study illuminates the physical mechanisms of slender body water-exit under multi-factor coupling conditions, providing experimental evidence and theoretical guidance for cross-media vehicle design and underwater equipment optimization.

Hydraulic jumps are widely used to dissipate excess energy in civil, ocean, and hydro-power engineering, particularly in high dams with large reservoirs. Different inflow and tailwater conditions lead to the occurrence of various types of hydraulic jumps. Among them, A-jumps are often preferred for stilling basin design, due to their high energy dissipation efficiency and favorable outflow patterns. This study numerically investigated the hydraulic characteristics of 75 critical A-jumps by adjusting tailwater levels, considering varying inflow conditions (flow depth, velocity, discharge, and Froude number) and stilling basin parameters (negative step height and incident angle), covering key parameter ranges from existing practical applications in high dam projects. Based on theoretical analysis and numerical simulations, estimation methods are proposed for the key hydraulic parameters of A-jumps, including the sequent depth ratio, roller length, reattachment length, and energy dissipation rate. A correction for the sequent depth ratio, incorporating the influence of the incident angle, is proposed for the first time. These estimation methods offer valuable insights for designing and optimizing negative step stilling basins in various practical engineering scenarios. To validate their applicability, a case study was conducted, showcasing the superior energy dissipation and stable outflow performance of the designed stilling basin, with the basin length shortened by 1.8% and the near-bottom velocity reduced by 42.4%, based on the proposed estimations, compared to the classical stilling basin.

This work investigates the water exit problems of slender cylinders under various con-ditions by experiment. The experimental platform is designed with a high-speed pho-tography. 13 experimental cases with varying head shapes, length-to-diameter ratios, ejection velocities, and elastic moduli was conducted to capture water-exit character-istics. The investigation identified ejection velocity as the predominant parameter governing cavity morphology and stability, with higher velocities correlating to in-creased cavity dimensions and reduced drag coefficients. Conical head shape resulted in superior drag reduction characteristics, forming a typical cigar-shaped cavity with clear and regular boundaries. Additionally, an increased length-to-diameter ratio sub-stantially improved drag reduction performance. Material elastic moduli proved cru-cial for water-exit stability, as cylinders with lower moduli experienced severe bending deformation and even trajectory changes, while higher moduli cylinders maintained their form with minimal deformation. This study illuminates the physical mechanisms of slender body water-exit under multi-factor coupling conditions, providing experi-mental evidence and theoretical guidance for cross-media vehicle design and under-water equipment optimization.