Impact acceleration reduction and trajectory deviation of a cylindrical body with a re-entrant lattice buffer during water entry

Excessive impact acceleration and trajectory deviation remain critical challenges for cylindrical bodies during water entry. This study investigates the water-entry response of a cylindrical body equipped with a re-entrant lattice structure (RLS) through experiments and coupled Eulerian-Lagrangian (CEL) simulations. A three-dimensional fluid-structure interaction model considering the elastic-plastic damage behavior of the RLS is established, experimentally validated, and used for mechanism analysis. The effects of water-entry velocity, angle, cylindrical body mass, and flat-disk radius are further analyzed. The results show that the axial compression of the RLS decouples the motion between the head and the main body, enabling staged impact-response transmission, peak acceleration reduction, impact-pulse broadening, and deformation-induced energy dissipation. The peak acceleration is reduced by up to 36.5% compared with the rigid-control configuration. Further parametric analyses show that the acceleration-reduction performance is governed by the matching between the external impact input and the compressive deformation capacity of the RLS. The RLS reduces the center-of-mass radial offset under the investigated conditions by weakening the abrupt and eccentric transmission of the initial impact response. These findings clarify the deformation-driven buffering mechanism of the RLS and provide guidance for the application and design of internal lattice buffers during water entry.