ABSTRACT

Marine biofouling is a major concern in the operational performance of submerged floating tunnels (SFTs). Experiments have been performed in a wave-current flume with a narrow range of hydrodynamic conditions, to compare the SFTs' behavior with different roughness characteristics (Zou et al. 2023a). The objective of this research is to extend hydrodynamic conditions in the experiments and numerically investigate the effects of marine fouling on the hydrodynamic behavior of SFTs, including flow characteristics and forces on the SFT subject to waves. A sensitivity analysis of roughness parameters including different roughness heights and roughness coverage ratios (CR) is carried out. In addition, the hydrodynamic force of a roughened SFT with a circular shape and a newly designed parametric shape are compared. The numerical models within the framework of the CFD toolbox OpenFOAM are applied. The Morison coefficients that are found can be used for marine-fouled SFTs under waves for circular and parametric cross-sections and are recommended for engineering practice.

INTRODUCTION

For wide and deep sea crossings, the submerged floating tunnel (SFT) is one of the alternatives to underwater tunnels and sea bridges. An SFT will, however, be colonized by marine species in the weeks to years after installation, which will be one of the major challenges to the SFT's operating performance.

The marine fouling effects on the hydrodynamic forces on an SFT are firstly analyzed by the authors. The pressure distribution along the SFT, flow separation and wake characteristics are numerally examined with respect to roughness parameters under steady currents (Zou et al. 2023b). Furthermore, an experimental study of surface roughness effects on the dynamic response of an SFT has been performed at Delft University of Technology (TU Delft) and the hydrodynamic forces on the SFT subject to currents, waves, and combined current-wave flows are evaluated (Zou et al. 2023a). However, due to the limited experimental test conditions, the Keulegan-Carpenter number (KC) is rather low in the experiments. The effects of wave properties in a wider range of KC should be investigated as a further extension to the prior studies. In addition, the wake topology and vortex shedding characteristics of the SFT under waves should be further discussed, which were not properly measured in the experiments. Therefore, the current research numerically deals with the effects of marine fouling on the hydrodynamic behavior of SFTs under waves.

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