Effects of Voided Navigation Tunnel (VNT) configuration on the hydrodynamic characteristics of ships

In terrain-constrained inland navigation projects, conventional enclosed tunnels provide limited flow area, intensifying vessel-induced blockage and impairing navigation performance. To improve cross-sectional utilisation without enlarging excavation, this study proposes a Voided Navigation Tunnel (VNT). Physical model tests and Computational Fluid Dynamics (CFD) simulations were used to compare four configurations: Rectangular Navigation Tunnel (RNT), U-shaped Navigation Tunnel (UNT), Cylindrical-Strut Voided Navigation Tunnel (R-VNT), and Streamlined-Strut Voided Navigation Tunnel (S-VNT). The experiments quantified vessel responses, while CFD explained the underlying flow mechanisms. The numerical method was assessed by comparing the predicted resistance of a model-scale towed hull with open-water experimental data. Results show that VNT performance depends strongly on support shape. Relative to the UNT, cylindrical struts in the R-VNT disturb the near-hull flow and reduce effective flow capacity, decreasing vessel speed by 7.62 %. Conversely, inclined streamlined struts in the S-VNT increase vessel speed by 7.08 % and reduce sinkage by 15.31 %. Thus, a voided configuration does not inherently improve vessel performance; streamlined support design is essential for realizing its hydrodynamic benefits. These findings provide guidance for optimizing navigation-tunnel configurations under constrained excavation conditions.