Hydrodynamic analysis of floating tunnel with submerged rubble mound breakwater

Abstract

The wave interaction with a Submerged Floating Tunnel (SFT) of two different shapes (rectangular and circular) in the presence of a submerged rubble mound breakwater (SRMB) is analyzed using Multi-Domain Boundary Element Method (MDBEM). Furthermore, three typical SFT cross-sections (rectangular, trapezoidal, and circular) of equal area and structural height in the presence of SRMB under similar operating conditions are investigated as comparative study to analyse the influence of SFT shape on hydrodynamic performance. The performance of the tunnel configurations is analyzed as a (a) measurement in terms of hydrodynamic efficiency and (b) criterion for tunnel structure safety. In both shallow and intermediate water depth regions, the critical wave number and the critical angle of incidence followed by resonant wave reflection are identified, and suitable structural parameters of SRMB such as structural porosity in the armour layer, relative crest width, relative gap width between the SFT and the SRMB, structural width and position (relative draft of tunnel structure measured from the free water surface) of SFT are investigated. The present parametric investigation of SFT with SRMB reveals an improved wave transformation properties for a specific range of water depth. The coupling of SRMB has resulted not only in a reduction of wave-induced force acting on SFTs, but also in improved performance in wave transformation characteristics as a coastal protection structure, which is substantially determined by SRMB structural properties. Due to the presence of SRMB, the SFT's safety is improved, which may also add stability to the SFT. A comparative study of different distinct cross-sections of SFTs indicates that, due to its shape, the circular SFT has a reduced reflection capability and lower wave-induced force with nearly the same wave transmission as the rectangular and trapezoidal SFT. The study performed on the coupled SFT and rubble mound breakwater may be useful in determining the suitability of breakwaters not only for maintaining shore dynamics but also for protecting important floating structures for underwater transit.