Asymmetric Hydrodynamic Impact and Dynamic Response of Vessels

Abstract

Theoretical simulations are compared with drop test experiments of vessel free-fall impact on calm water, with zero and nonzero initial heel angles. The impact force and moment are predicted by using a theory described in Xu et al. (1998). The resulting motions of vessels at asymmetric impact include vertical water entry and transverse rolling. The downward deceleration equation combines the hydrostatic and hydrodynamic forces and the weight of hull, while the rolling equation takes into account the restoring moments due to asymmetry. Another simplified approach of a water entry dynamics and injury model (Gollwitzer and Peterson, 1996) is also applied to evaluate the impact acceleration for symmetric cases. The experiments were conducted at the Coastal Systems Station, Panama City, Florida, using a 2 ft × 8 ft (0.61 m × 2.44 m) prismatic hull model with 20 deg deadrise. The comparisons between the asymmetric impact theory and experiment shows varying degrees of qualitative and quantitative agreement.

Two-dimensional SPH simulations of wedge water entries

“…Concerning the angular acceleration time evolution, some oscillations can be noticed on the experimental data. These oscillations are produced by structure vibrations which cannot be captured in the context of rigid body simulations [8]. In the SPH computation, oscillations can be explained by temporal fluctuations of values used to obtain efforts on the wedge which may be due to the explicit nature of the third order Runge-Kutta ODE integrator used in this simulation, but further work is still needed to determine the exact origin of this phenomenon.…”

“…For this case, the slamming force time history of the impact obtained using our enhanced SPH method is compared with experimental and analytical results. The second test case studied then consists in the impact of a free-falling asymmetric wedge with a 20°deadrise angle [8] and three degrees of freedom, namely the vertical and horizontal linear motions (this last will not be discussed), and the angular motion in the vertical plane.…”

Review of water entry with applications to aerospace structures

“…Also in 1999, Xu et al [65] investigated the slamming response of a prismatic hull due to freefall. A two-dimensional asymmetric impact theory was applied in order to predict the impact forces and moments for both zero and non-zero heel angles.…”

Experiments on the water entry of asymmetric wedges using particle image velocimetry

“…Xu et al 27 have elucidated the role of the heel angle on the acceleration of a wedge that is asymmetrically impacting the water surface. Judge et al 18 have experimentally studied the more general case of asymmetric water entry with a nonzero heel angle and an oblique entry velocity.…”