Multiphase fluid–structure interaction and shock response of a segmented vehicle during high-speed oblique water entry

The high-speed oblique water entry of a segmented vehicle presents a complex multiphase fluid–structure interaction (FSI) problem, characterized by the evolution of the vapor–liquid cavity and the transient impact loads transmission. This study constructs a high-fidelity numerical model that integrates a multiphase flow solver with a FSI solver to investigate the underlying fluid physics and shock response during initial water entry for a segmented vehicle connected by bolts. The effects of key parameters such as entry velocity and angle on the spatiotemporal evolution of cavity, impact loads transmission, and shock response spectrum (SRS) are systematically investigated. Results show that multiphase FSI during cavity evolution notably amplifies high-frequency fluctuations in acceleration and induces asymmetry stress wave propagation. Segments with longer propagation distances exhibit higher peak axial forces, while connection interfaces experience negative normal contact forces and lateral contact moments. SRS analysis reveals resonant amplification peaks at 600 and 1500 Hz across the segments, with amplitudes reaching 100 g, and higher peaks at the monitoring points. Stress concentration and wave asymmetry generate elevated local stresses at connections and bolts, necessitating protective measures targeting segment-specific load peaks, critical frequency bands, and interface/bolt reinforcement. This study provides an effective multiphase FSI simulation framework and insights into the flow and shock characteristics of a segmented vehicle during high-speed water entry.