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Marine biofouling is a major concern in the operational performance of submerged floating tunnels (SFTs). The objective of this research is to investigate the effects of marine fouling (represented by surface roughness) on the hydrodynamic behavior of SFTs, including the hydrodynamic forces on the SFT subject to current-only, wave-only, and combined current-wave flow conditions. The effects of increased surface roughness induced by marine fouling on the dynamic response of an SFT are characterized by hydrodynamic force coefficients, including drag and inertia coefficients. At the Water Lab of Delft University of Technology (TU Delft), experiments have been performed in a wave-current flume to compare the SFTs’ behaviors as affected by different roughness characteristics. In addition, a parametric cross-section for an SFT is presented, and the hydrodynamic performance associated with surface roughness effects on the parametric shape and circular SFT cross-section shape are compared. The results show that the parametric shape can effectively reduce the drag coefficient (Cd) under current-only conditions and lower the inertia coefficient (Cm) when waves are present. As roughness height and coverage ratio increase, Cd generally increases while Cm decreases. However, small differences in Cd and Cm can be observed with regard to roughness parameters for wave-only conditions. The Morison coefficients adapted for a marine-fouled SFT measured in the experiments are compared to predictions from engineering standards and are recommended for engineering practice., Rivers, Ports, Waterways and Dredging Engineering, Environmental Fluid Mechanics, Hydraulic Structures and Flood Risk

The effects of surface roughness as induced by marine fouling on the hydrodynamic forces on a submerged floating tunnel (SFT) are experimentally and numerically investigated in detail at Reynolds numbers Re = 8.125 × 103–5.25 × 104. A sensitivity analysis to different roughness parameters including roughness height, skewness, coverage ratio, and spatial arrangement is performed. In addition, an optimized parametric cross-section for an SFT is proposed, and the hydrodynamic performance of the parametric shape and circular SFT cross-section shape with roughness elements is compared. The pressure distribution along the SFT, flow separation and wake characteristics are analyzed to provide a systematic insight into the fundamental mechanism relating the roughness parameters and flow around an SFT. In order to better understand the nonlinear relationships among structural geometry, roughness parameters, flow states, and structural response, an artificial intelligence method using Random Forest (RF) for feature importance ranking is applied. The results show that with the parametric shape, the hydrodynamic forces on the fouled SFT can be effectively mitigated. The roughness height and coverage ratio affect the equivalent blockage and hence, change flow separation and recirculation length in the wake. Lower skewness of the roughness elements can increase the critical Re by changing the relative roughness parameter. Horizontal arrangement of the roughness elements on an SFT generally results in the largest hydrodynamic forces, compared to staggered and vertical distributions. Throughout the feature importance ranking, the flow regime is found to be the most important feature of the hydrodynamics of the SFT. In addition, the SFT cross-section shape and roughness coverage ratio play a dominant role., Rivers, Ports, Waterways and Dredging Engineering, Hydraulic Structures and Flood Risk, Environmental Fluid Mechanics

In order to assess the dynamic performance of a submerged floating tunnel (SFT) subject to flow-induced vibration (FIV) conditions in a practical engineering application, a one-way fluid–structure interaction (FSI) model consisting of multi-scale hydrodynamic solvers combined with the finite element method (FEM) is established. A typical long, large aspect ratio SFT is modeled by coupling tube, joint, and mooring components. The SFT is simulated in the time domain under currents, waves, and extreme events. FIV of SFTs with different cross-section shapes is investigated by analyzing each structure's natural frequencies, hydraulic loading frequency, and dominant modes. The results show that FIV of the SFT tube is dominated by wave conditions. The excitation of the SFT's first dominant mode by a large wave height and period should be avoided. Standing and traveling wave patterns and multi-mode response are observed during extreme events. The hydrodynamic forcing and structural dynamic response of the SFT can be effectively reduced by adopting a parametric cross-section., Hydraulic Structures and Flood Risk, Environmental Fluid Mechanics, Wind Energy

The submerged floating tunnel (SFT), also called an Archimedes Bridge, is a new type of infrastructure for wide and deep sea-crossings, regarded as one of the alternatives to bored and immersed tunnels and bridges. It is afloat in water employing its buoyancy and a support system to balance its self-weight. However, no prototype SFT has yet been built anywhere due to the immaturity of scientific research and engineering technology. The dynamic response of the SFT subject to operating and extreme environmental conditions, which determines structural safety and reliability, is a crucial issue that needs to be better understood. In order to better comprehend the response of the SFT to hydrodynamic forces, key points including hydrodynamic loads acting on the SFT and the structural dynamic response for various structural configurations, as well as the relations and interactions among these factors must be quantified. In this study, hydrodynamic loads on various SFT cross-sectional geometries were computed. The parametric cross-section shape described by a Bezier-PARSEC curve was optimized using a hybrid Artificial Neural Network (ANN) and Genetic Algorithm (GA). The practical range of aspect ratios of the SFT cross-section was determined by conducting a sensitivity analysis under tidal current conditions. It was found that an SFT cross-section with an aspect ratio of 0.47 using a leading-edge BP curve under the given clearance is optimal for a balanced consideration of hydrodynamic performance and construction cost. Furthermore, the machine learning method used is shown to be a reliable and effective tool for the SFT cross section optimization design. The hydrodynamic loads acting on the optimal cross-section shape were compared with simpler shapes under various environmental conditions of currents and waves, including the extreme environmental conditions of internal waves, tsunamis, and super typhoons. An internal solitary wave (ISW), described by t, Hydraulic Structures and Flood Risk

The submerged floating tunnel (SFT), also called an Archimedes Bridge, is a new type of infrastructure for wide and deep sea-crossings, regarded as one of the alternatives to bored and immersed tunnels and bridges. It is afloat in water employing its buoyancy and a support system to balance its self-weight. However, no prototype SFT has yet been built anywhere due to the immaturity of scientific research and engineering technology. The dynamic response of the SFT subject to operating and extreme environmental conditions, which determines structural safety and reliability, is a crucial issue that needs to be better understood. In order to better comprehend the response of the SFT to hydrodynamic forces, key points including hydrodynamic loads acting on the SFT and the structural dynamic response for various structural configurations, as well as the relations and interactions among these factors must be quantified. In this study, hydrodynamic loads on various SFT cross-sectional geometries were computed. The parametric cross-section shape described by a Bezier-PARSEC curve was optimized using a hybrid Artificial Neural Network (ANN) and Genetic Algorithm (GA). The practical range of aspect ratios of the SFT cross-section was determined by conducting a sensitivity analysis under tidal current conditions. It was found that an SFT cross-section with an aspect ratio of 0.47 using a leading-edge BP curve under the given clearance is optimal for a balanced consideration of hydrodynamic performance and construction cost. Furthermore, the machine learning method used is shown to be a reliable and effective tool for the SFT cross section optimization design. The hydrodynamic loads acting on the optimal cross-section shape were compared with simpler shapes under various environmental conditions of currents and waves, including the extreme environmental conditions of internal waves, tsunamis, and super typhoons. An internal solitary wave (ISW), described by t, Hydraulic Structures and Flood Risk

In order to assess the dynamic performance of a submerged floating tunnel (SFT) subject to flow-induced vibration (FIV) conditions in a practical engineering application, a one-way fluid–structure interaction (FSI) model consisting of multi-scale hydrodynamic solvers combined with the finite element method (FEM) is established. A typical long, large aspect ratio SFT is modeled by coupling tube, joint, and mooring components. The SFT is simulated in the time domain under currents, waves, and extreme events. FIV of SFTs with different cross-section shapes is investigated by analyzing each structure's natural frequencies, hydraulic loading frequency, and dominant modes. The results show that FIV of the SFT tube is dominated by wave conditions. The excitation of the SFT's first dominant mode by a large wave height and period should be avoided. Standing and traveling wave patterns and multi-mode response are observed during extreme events. The hydrodynamic forcing and structural dynamic response of the SFT can be effectively reduced by adopting a parametric cross-section., Hydraulic Structures and Flood Risk, Environmental Fluid Mechanics, Wind Energy

Concepts of a submerged floating tunnel (SFT) for novel sea-crossings have been researched in recent years. An SFT tube should be moored afloat by tensioned mooring systems to maintain the tube position under complex hydrodynamic loads. In-line force is amongst the dominant hydrodynamic parameters in the SFT cross-section design and the mooring system reliability evaluation. Selecting a suitable in-line force computation method is crucial to successful and accurate SFT cross-section optimization. The transition SST model is an effective turbulence transition prediction tool in the boundary layer computation subjected to tidal flow at both low and high Reynolds numbers. Two types of parametric Bézier curves applied in airfoil optimization are used to describe the SFT cross-section. We show that an SFT cross-section described by a leading-edge Bézier-PARSEC (BP) curve has better hydrodynamic performance than a trailing-edge BP curve of equal aspect ratio (AR). To avoid large flow separation, an AR not exceeding 0.47 is recommended. An SFT cross-section design should balance hydrodynamic performance and construction cost. The SFT cross-section with AR = 0.47 using the leading-edge BP curve with fixed clearance has a comparatively small in-line force and a minimum material cost., Hydraulic Structures and Flood Risk, Environmental Fluid Mechanics

The interaction between an oceanic internal solitary wave (ISW) and a prototype submerged floating tunnel (SFT) is numerically investigated. Effect of oceanic internal solitary wave amplitude, the relative distance of the SFT to the pycnocline, cross-sectional geometry of the SFT, and the density ratio of the two fluid layers are analyzed. At a potential application site, the dynamic response of an SFT composed of a tube-joint-mooring system forced by an oceanic ISW is studied using Finite Element Method (FEM) modeling. The numerical results show that the ISW-induced force can be effectively reduced by adopting a parametric SFT cross section instead of a circle or ellipse. The influence of the relative distance of the SFT to the ISW pycnocline is crucial, and can remarkably alter the vertical force and buoyancy-weight ratio (BWR) of the SFT during ISW propagation. Large shear forces and bending moments on the SFT can occur, affecting the tension in the mooring lines, and threatening the safety and reliability of the SFT system. However, the deflections and accelerations of the SFT under the applied ISW are within structural serviceability requirements due to the low frequency of the ISW compared to the natural frequency of the SFT tube., Hydraulic Structures and Flood Risk, Environmental Fluid Mechanics

Concepts of a submerged floating tunnel (SFT) for novel sea-crossings have been researched in recent years. An SFT tube should be moored afloat by tensioned mooring systems to maintain the tube position under complex hydrodynamic loads. In-line force is amongst the dominant hydrodynamic parameters in the SFT cross-section design and the mooring system reliability evaluation. Selecting a suitable in-line force computation method is crucial to successful and accurate SFT cross-section optimization. The transition SST model is an effective turbulence transition prediction tool in the boundary layer computation subjected to tidal flow at both low and high Reynolds numbers. Two types of parametric Bézier curves applied in airfoil optimization are used to describe the SFT cross-section. We show that an SFT cross-section described by a leading-edge Bézier-PARSEC (BP) curve has better hydrodynamic performance than a trailing-edge BP curve of equal aspect ratio (AR). To avoid large flow separation, an AR not exceeding 0.47 is recommended. An SFT cross-section design should balance hydrodynamic performance and construction cost. The SFT cross-section with AR = 0.47 using the leading-edge BP curve with fixed clearance has a comparatively small in-line force and a minimum material cost., Hydraulic Structures and Flood Risk, Environmental Fluid Mechanics

The interaction between an oceanic internal solitary wave (ISW) and a prototype submerged floating tunnel (SFT) is numerically investigated. Effect of oceanic internal solitary wave amplitude, the relative distance of the SFT to the pycnocline, cross-sectional geometry of the SFT, and the density ratio of the two fluid layers are analyzed. At a potential application site, the dynamic response of an SFT composed of a tube-joint-mooring system forced by an oceanic ISW is studied using Finite Element Method (FEM) modeling. The numerical results show that the ISW-induced force can be effectively reduced by adopting a parametric SFT cross section instead of a circle or ellipse. The influence of the relative distance of the SFT to the ISW pycnocline is crucial, and can remarkably alter the vertical force and buoyancy-weight ratio (BWR) of the SFT during ISW propagation. Large shear forces and bending moments on the SFT can occur, affecting the tension in the mooring lines, and threatening the safety and reliability of the SFT system. However, the deflections and accelerations of the SFT under the applied ISW are within structural serviceability requirements due to the low frequency of the ISW compared to the natural frequency of the SFT tube., Hydraulic Structures and Flood Risk, Environmental Fluid Mechanics

A submerged floating tunnel (SFT) is a promising alternative to conventional bridges and tunnels, and can be potentially built in the Qiongzhou Strait in China. However, this area is under the threat of disasters including mega tsunamis and severe storm surges. To evaluate the hydrodynamic loads of the SFT in this hazardous zone subject to severe tsunami and typhoon impacts, the Delft3D-FLOW hydrodynamic model and SWAN wave model are coupled, and a Computational Fluid Dynamics (CFD) method is adopted. The maximum probable tsunami and typhoon Rammasun (July 2014) are selected as hazard assessment conditions in the Qiongzhou Strait. Whether the tsunami and hindcast storm surge cause extreme forcing and bring challenges to the SFT engineering design, operation, and maintenance in the Qiongzhou Strait are discussed in this study. We reveal that the typhoon impacts are more devastating than tsunami for an SFT in the Qiongzhou Strait. In order to determine the optimal SFT cross-section under extreme events, we use a parametric Bezier curve profile compared with two simpler shapes including circular and elliptical cross sections. In-line force and lift are respectively applied to evaluate the SFT's hydrodynamic behaviour. Our results reveal that the gross horizontal force on the parametric Bezier curve shape is more sensitive to flow acceleration, while the circular cross-section is dominated by current speed. The parametric Bezier curve cross-section shape has the preferable property of reducing the in-line force and postponing serious vortex shedding compared with the two simpler shapes., Hydraulic Structures and Flood Risk, Environmental Fluid Mechanics

The cross-section geometry of a submerged floating tunnel (SFT) has a large effect on hydrodynamic characteristics, structural behavior and service level, making the tunnel cross section the primary factor in optimizing efficiency. Minimizing the mean drag and the dynamic variability in the lift of the SFT cross section under bi-directional (i.e., tidal) flow has a dramatic impact on the reduction of structural displacements and mooring loads. Based on a parametric Bézier curve dynamically comprising the leading-edge radius, tunnel height and width to define the SFT geometry, a sensitivity analysis of the Bézier curve parameters for a fixed aspect ratio with prototype dimensions under uniform flow conditions was conducted by applying Computational Fluid Dynamics (CFD), and the pressure distribution around the SFT cross-section surface was analyzed. A theoretical method comprising the Kármán vortex street parameters was employed to verify the CFD simulation results. In order to determine the SFT cross section with optimal hydrodynamic properties, the mean drag and Root Mean Square (RMS) lift coefficients were selected as optimization objectives, and four Bézier curve parameters were the input variables, in a neural network and genetic algorithm optimization process (a hybrid BP-GA structure), which is less likely to become trapped in local minima. The results show the optimal tunnel cross section has a mean drag and a RMS lift coefficient reduced by 0.9% and 6.3%, respectively, compared to the original CFD dataset., Hydraulic Structures and Flood Risk, Environmental Fluid Mechanics

A submerged floating tunnel (SFT) is a promising alternative to conventional bridges and tunnels, and can be potentially built in the Qiongzhou Strait in China. However, this area is under the threat of disasters including mega tsunamis and severe storm surges. To evaluate the hydrodynamic loads of the SFT in this hazardous zone subject to severe tsunami and typhoon impacts, the Delft3D-FLOW hydrodynamic model and SWAN wave model are coupled, and a Computational Fluid Dynamics (CFD) method is adopted. The maximum probable tsunami and typhoon Rammasun (July 2014) are selected as hazard assessment conditions in the Qiongzhou Strait. Whether the tsunami and hindcast storm surge cause extreme forcing and bring challenges to the SFT engineering design, operation, and maintenance in the Qiongzhou Strait are discussed in this study. We reveal that the typhoon impacts are more devastating than tsunami for an SFT in the Qiongzhou Strait. In order to determine the optimal SFT cross-section under extreme events, we use a parametric Bezier curve profile compared with two simpler shapes including circular and elliptical cross sections. In-line force and lift are respectively applied to evaluate the SFT's hydrodynamic behaviour. Our results reveal that the gross horizontal force on the parametric Bezier curve shape is more sensitive to flow acceleration, while the circular cross-section is dominated by current speed. The parametric Bezier curve cross-section shape has the preferable property of reducing the in-line force and postponing serious vortex shedding compared with the two simpler shapes., Hydraulic Structures and Flood Risk, Environmental Fluid Mechanics

The cross-section geometry of a submerged floating tunnel (SFT) has a large effect on hydrodynamic characteristics, structural behavior and service level, making the tunnel cross section the primary factor in optimizing efficiency. Minimizing the mean drag and the dynamic variability in the lift of the SFT cross section under bi-directional (i.e., tidal) flow has a dramatic impact on the reduction of structural displacements and mooring loads. Based on a parametric Bézier curve dynamically comprising the leading-edge radius, tunnel height and width to define the SFT geometry, a sensitivity analysis of the Bézier curve parameters for a fixed aspect ratio with prototype dimensions under uniform flow conditions was conducted by applying Computational Fluid Dynamics (CFD), and the pressure distribution around the SFT cross-section surface was analyzed. A theoretical method comprising the Kármán vortex street parameters was employed to verify the CFD simulation results. In order to determine the SFT cross section with optimal hydrodynamic properties, the mean drag and Root Mean Square (RMS) lift coefficients were selected as optimization objectives, and four Bézier curve parameters were the input variables, in a neural network and genetic algorithm optimization process (a hybrid BP-GA structure), which is less likely to become trapped in local minima. The results show the optimal tunnel cross section has a mean drag and a RMS lift coefficient reduced by 0.9% and 6.3%, respectively, compared to the original CFD dataset., Hydraulic Structures and Flood Risk, Environmental Fluid Mechanics

A submerged floating tunnel’s (SFT) cross-sectional geometry is one of the main factors influencing its hydrodynamic characteristics. Minimizing the drag and lift is important for reducing the displacement of the structure and load on the mooring system. In this study, a parametric cross-section design method based on the Bézier curve is used to define the geometry of the SFT cross-section. A sensitivity analysis of the Bézier curve parameters is conducted with Computational Fluid Dynamics (CFD), and compared with simpler common cross-sections. The results show the parametric design method noticeably reduces the mean drag and RMS lift coefficient, compared with simpler common sections., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Hydraulic Structures and Flood Risk, Environmental Fluid Mechanics