Confined Water Effects on the Resistance Performance of the Immersed Tunnel Towed by a Catamaran

To fill up the research gap on immersed tunnel towing in restricted waters, towing tank experiments are conducted in this study to investigate the hydrodynamic resistance of a novel catamaran-assisted tunnel towing system under combined shallow-water and bank-confined conditions. The influences of the multi-body hydrodynamic interactions on the resistance performance of the towing system are highlighted. The results reveal that the shallow-water effect aggravates the total resistance by 44.2% for the integrated towing system and the bank effect introduces an additional 14.2% rise. The catamaran–tunnel system exhibits stronger sensitivity to the shallow water than the standalone catamaran, reaching 15.57-fold and 6.73-fold of those of the isolated catamaran across the entire test range. Furthermore, the confined water effects contribute to a high residual resistance share in total resistance, attaining 80.9% for the single catamaran and 96.0% for the coupled system in confined waterways.