On applicability of von Karman's momentum theory in predicting the water entry load of V-shaped structures with varying initial velocity

TL;DR

This study evaluates the applicability of von Karman's momentum theory in predicting water entry loads of V-shaped structures, combining theoretical analysis with numerical simulations and experiments to establish relationships between initial velocity and impact forces.

Contribution

It demonstrates the validity of von Karman's momentum theory for predicting water entry loads across different V-shaped structures and initial velocities, supported by numerical and experimental validation.

Findings

Maximal acceleration is linearly related to the square of initial velocity.

The velocity ratio approaches 5/6 at high initial velocities.

Theoretical and numerical results are consistent across cases.

Abstract

The water landing of an amphibious aircraft is a complicated problem that can lead to uncomfortable riding situation and structural damage due to large vertical accelerations and the consequent dynamic responses. The problem herein is investigated by solving unsteady incompressible Reynolds-averaged Navier-Stokes equations with a standard k-omega turbulence closure model. The theoretical solutions established by the von Karman's momentum theory are also employed. In order to validate the relationships between the initial vertical velocity and the peak value of vertical acceleration, free fall test cases of 2D symmetric wedge oblique entry and 3D cabin section vertical entry are presented first. The other parameters at which the maximum acceleration occurs, such as time, penetration depth, velocity, are also evaluated. Hence, the quantitative relations are investigated to water landing event for amphibious aircraft. Detailed results in terms of free surface shape and pressure distribution are provided to show the slamming effects. The results show that a linear dependence of the maximal acceleration from the square of initial vertical velocity can be derived for two-dimensional wedge, three-dimensional cabin section and seaplane with V-shaped hull. Moreover, the ratio between the corresponding velocity and the initial vertical velocity tends to a constant threshold value, 5/6, derived from the theoretical solution, when increasing the initial vertical velocity in all three cases.