Dynamics of a towed cable crossing the air–water interface: Modeling and experimental validation

The air–water cross-medium towing system serves as an effective tool for ocean exploration and search-and-rescue operations. However, the motions of the helicopter and towed body are tightly coupled with the configuration variations of the towing cable; meanwhile, the air–water cross-medium process is subjected to nonlinear and strongly disturbed loads, resulting in complex cable configuration changes. To address this challenge, this paper proposes a computational framework based on flexible multibody dynamics. Specifically, a cable element model for the air–water cross-medium process is established using the Absolute Nodal Coordinate Formulation (ANCF) cable element, and a dedicated experimental setup for cross-medium towing and measurement is designed to validate the proposed model. Furthermore, typical working conditions are constructed to analyze the steady-state motion characteristics and formation mechanisms of the system, as well as to discuss factors influencing the steady-state configuration. Results demonstrate that the proposed cross-medium cable model exhibits good applicability to air–water towing. The air–water medium variation exerts a more significant impact on the configuration of low-stiffness cables; an increase in towing speed notably amplifies this medium effect, causing a distinct upward drift of the towed body. Additionally, high-speed near-surface air–water towing poses a risk of the towed body emerging from water. The established dynamic model can provide a valuable reference for the design and motion control of air–water cross-medium towed systems.