Experimental and numerical investigation of hydrodynamic characteristics of Hall anchors during water entry

Throughout the process of water entry and deployment, the hydrodynamic behavior of anchors is governed by multiple factors including orientation, drag characteristics and geometric parameters, which strikingly affect their penetration depth and final position. This paper presents an experimental and numerical investigation of the hydrodynamic characteristics of Hall anchors during the water entry stage. A sequence of small-scale tests on the anchor dropping process were conducted by taking into account the effects of dropping heights, and horizontal initial velocities. Subsequently, a coupled finite element model was developed to simulate the fluid–structure interaction during anchor water entry. The analysis yielded several pivotal conclusions. Above all, the anchor dropping process can be divided into four stages grounded in the acceleration curve: air bubble formation, expansion, contraction, and annihilation, while the water drag coefficient stabilizes following a gradual increase during this phase. The distance covered by the Hall anchor during its variable-speed descent into the water is primarily influenced by the drop height. The anchoring trajectory is affected by initial horizontal velocity and anchoring height, etc. In this paper, a solution for the drop anchor bottoming out velocity and the anchor trajectory prediction formula are presented rooted in the experimental data and theoretical derivation. The predictions showed strong agreement with experimental results, with relative errors of 4.5% for bottoming velocity and 5.0% for the anchor dropping point location. This phenomenon imparted a certain degree of precision and scientific coherence to the prediction results, thereby furnishing a theoretical foundation for emergency anchoring procedures.