Operability analysis for collaborative caisson towing using multiple towlines in shallow waters with complex seabed topography

Caissons, typically transported via towing, face significant challenges in shallow waters, including limited passability, grounding risk, and restricted maneuverability. Conventional wet- and dry-towing methods have proven inadequate due to vessel constraints and depth limitations. Instead, the present study proposes a multi-towline collaborative towing method based on a framework of cable-driven parallel robots to enhance operational flexibility.

Conventional towing methods, including wet-towing by tugboats and dry-towing by semi-submersible vessels, are inadequate for shallow waters due to vessel constraints and depth limitations. Historical data from 2000 to 2020 indicate that grounding incidents accounted for 7% of maritime accidents in China, with a high frequency for structures like caissons. The inability of traditional methods to avoid obstacles efficiently necessitates the development of a new towing system that can operate in complex environments, reducing risks and improving efficiency.

To consider complex shallow-water seabed topography and prevent caissons from hitting the seabed, an operability analysis framework can be used to evaluate environmental conditions (ECs) through a discretized bathymetry map, converting elevation data into seabed wedge modules.

This probabilistic methodology integrates potential flow theory results validated by computational fluid dynamics with time-domain multi-body simulations for extreme value analysis. A distance-based criterion is employed to assess caisson passability under specific ECs. Parametric analysis across varying water depths, slopes, and aspects is used to establish characteristic distances and a data-driven approach employed to explore any nonlinear relationships, enabling passable region determination. The results demonstrate that seabed slope and aspect significantly influence caisson hydrodynamics, with water depth, slope, and aspect collectively determining passable regions.

Simulation results demonstrate that seabed slope and aspect significantly influence caisson hydrodynamics, affecting motion responses such as heave and pitch. The characteristic distance, derived from extreme value analysis with a non-exceedance probability of 10^{-2}, effectively assesses passability under specific environmental conditions. The BP neural network achieves a regression coefficient of 0.998 and a mean squared error of 9.58×10^{-4}, enabling accurate identification of passable regions. Overall, water depth, slope, and aspect collectively determine operability, with the framework providing a practical tool for safe caisson towing in shallow waters.

Ref: Yang, Z. and Ren, Z., 2025. Operability analysis for collaborative caisson towing using multiple towlines in shallow waters with complex seabed topography. Ocean Engineering, 323,120581.

https://www.sciencedirect.com/science/article/abs/pii/S0029801825002963

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