Search Results (23)

A case study is conducted for a submerged floating tunnel module (SFTM) in wet tow conditions. Inspired by the successful wet tow operations of spar platforms, a wet tow scenario is examined where a tunnel module, floating horizontally with a half-diameter draft, is towed by tugboats using towlines. To evaluate the static stability of the SFTM during wet tow, numerical static offset tests are performed at varying tow speeds to determine the equivalent system stiffness. These static offset tests consider surge, sway, roll, and yaw motions. Statistical analyses are subsequently performed based on the encounter-frequency approximation with varying equivalent stiffnesses. The most probable extreme motion analysis for 3 h under sea state 4 ($H_S=2.44\mathrm{m}$ and $T_P=8.1\mathrm{s}$) shows that the beam sea condition causes the largest heave (0.6 m), and the stern sea (30 deg.) leads to the largest yaw response (0.85 deg.), which is likely to cause an instantaneous decrease in towing stability. Full article

To investigate the applicability and differences in wave loads and the dynamic response calculation principles for SFT on an entire-length scale, two numerical models of entire-length SFT with identical dimensions and parameters were established. These models are employed by a 3D diffraction method based on rigid-body assumptions, the potential flow theory and the Dummy-Connection-Mass (DCM) method based on the lumped mass method and Morison equation while considering hydroelasticity effects. The applicability of the potential flow theory and Morison equation for wave load calculation of SFT is presented along with the differences in their dynamic response calculation, which aim to explore the impact on SFT dynamic responses considering hydroelasticity by comparing the numerical calculation results. Furthermore, a comparison between free-end boundary and fixed-end boundary models, established using the DCM method, is conducted to examine the reasonableness of the commonly adopted free-end boundary condition. Full article

The submerged floating tunnel is a marine transportation infrastructure that links two shorelines. The tunnel tube body’s buoyancy exceeds gravity, with anchoring ensuring equilibrium. Anchoring reliability is crucial. This study presents a three-way coupled kinematic model for the mooring structure, formulated on Hamilton’s principle and Kirchhoff’s assumption. It explores the impact of the tube body’s buoyancy-to-weight ratio and the sea current’s angle of incidence on mooring motion response. By solving the motion analysis model, Hill’s equation system is derived to assess the parameter instability of the anchor cable structure. The coefficient of excitation instability intervals for the submerged floating tunnel is determined and validated. The findings indicate the following: (1) Increasing the float-weight ratio reduces displacement response amplitudes in all directions, bringing downstream and transverse currents closer to their initial positions; (2) Changes in current direction angles result in decreased downstream excitation strength and increased transverse displacement response with the same excitation direction; (3) The instability interval visualization effectively predicts anchor cable structure instability under parametric excitation. Structures within the instability region are deemed unstable, while those outside are considered stable. Full article

Infrastructure expansion considerably contributes to greenhouse gas emissions causing the critical global issue of climate change. In recent years, submerged floating tunnels (SFTs) have thus been developed as a sustainable and efficient solution for crossing large water bodies instead of resource-demanding superstructures (e.g., cable stayed bridges). This research delves into a comparative analysis of two SFT design alternatives: SFTs with pontoons and SFTs with tethers centered on environmental sustainability and long-term viability. By incorporating life-cycle assessments and quantitative risk analysis methodologies, our study aims to ascertain the optimal SFT design for real-world application. Our study embarks on detailed investigations into SFTs and then gathers data on material quantities and LCA studies, identifying potential hazards and comparing life cycle performance. Our new findings highlight the significant advantage of the SFT with a tethered design, which has a lower dependency on materials, particularly steels, resulting in lower CO₂ emissions. Additionally, in terms of risk, the SFT with tethers has a lower risk profile in general, especially in situations, including environmental elements, like rising water levels, potential tsunamis, and storms. This design is a promising solution for sustainable and resilient infrastructure development, coinciding with global objectives to cut down carbon emissions and enrich potential benefits in the face of increasing climatic uncertainties. Not only does this study scrutinize the risk and environmental aspects of both SFT designs, but it also opens the path for future infrastructure projects that emphasize engineering robustness and environmental sustainability. Full article

A comprehensive two-dimensional (2D) time-domain numerical model is established to investigate the interaction of irregular waves and submerged structures with different sections. The model specifically focuses on the dual-lane submerged floating tunnel (SFT) designs, encompassing elliptical, twin-circular, and round rectangular sections. For the hydrodynamic analysis, we adopt the second-order potential flow theory, while for the mooring line simulations, we employ the slender rod theory, taking into account the entire hydrodynamic load acting on it. In the coupled dynamic analysis, the fourth-order Adams–Bashforth–Moulton method, Newmark-β method, and Newton–Raphson iteration scheme are utilized for the coupled motion equation of the floating body and the dynamic equation of the mooring riser system. Experimental free decay tests are conducted to determine the damping coefficients of various section shapes in different directions. Our analysis delves into the detailed motion responses and mooring tensions of the SFTs with different section forms under irregular waves. We compare and contrast these responses in both time and frequency domains, particularly focusing on movement trends. The elliptical section structure emerges as the most stable design based on our comparisons. These findings provide valuable insights for the selection of optimal section shapes for dual-lane SFTs. Full article

The motion responses, mooring tensions, and submergence depth are the dominant factors for the arrangement of the Submerged Floating Tunnel (SFT) subjected to waves. Generally, the maximum values of motion responses, mooring tensions, and absolute submergence depth are mainly focused on. In the present study, experiments are implemented to measure the motion responses and mooring tensions of the SFT with different mooring patterns and submergence depths under waves with different characteristic wave heights and periods. In order to evaluate the arrangement of the SFT more effectively and comprehensively, besides the maximum values, several new characteristic parameters are introduced. Such parameters account for the motion responses in the frequency domain, the uniformity of the tension distribution, the length of time during which the cable reaches a relaxed condition during wave action, the KC number, the dimensionless period, the wave height, and the submergence depth. The results from the optimization analysis show the following: according to the characteristic values of motion responses and mooring tensions, the pattern of diagonal cables is better than that of diagonal cables + vertical cables; and within the range of the present experiments, there are optimal dimensionless parameters—the dimensionless submergence depth d₀/L_P ≥ 0.15, the KC number ≤ 0.8, or the dimensionless wave height Hs/d₀ ≤ 0.10—for the condition of which the dynamic responses and mooring tensions vary slightly. Full article

The submerged floating tunnel (SFT) is a novel form of transportation infrastructure for crossing deeper and wider seas. One of the primary challenges in designing SFTs is understanding their hydrodynamic response to complex environmental loads. In order to investigate the two-degree-of-freedom (2-DOF) flow-induced vibration (FIV) response of SFTs under current, a two-dimensional (2D) numerical model was developed using the Reynolds-averaged Navier–Stokes (RANS) method combined with the fourth-order Runge–Kutta method. The numerical results were validated by comparing them with the existing literature. The study then addressed the effects of coupled vibration and structural parameters, i.e., the mass ratio and natural frequency ratio, on the response and wake pattern of SFTs, numerically. The results indicated that coupled vibration had a significant impact on the SFT response at reduced velocities of Ur_wx ≥ 4.4. A decrease in mass ratio (m* < 1) notably amplified the 2-DOF vibration amplitudes of SFTs at Ur_wx ≥ 4.4, particularly for in-line vibration. Similarly, a decrease in natural frequency ratio (R_f < 1) significantly suppressed the in-line vibration of SFTs at Ur_wx ≥ 2.5. Therefore, for the design of SFTs, careful consideration should be given to the effect of mass ratio and natural frequency ratio on in-line vibration. Full article

Submerged floating tunnels (SFTs), also known as the Archimedes Bridge, are new transportation structures designed for crossing deep waters. Compared with cross-sea bridges and subsea tunnels, SFTs offer superior environmental adaptability, reduced construction costs, and an enhanced spanning capacity, highlighting their significant development potential and research value. This paper introduces a new type of SFT scale model for hydrodynamic experiments, adhering to the criteria for geometric similarity, motion similarity, and dynamic similarity principles, including the Froude and Cauchy similarity principles. This model enables the accurate simulation of the elastic deformation of the tunnel body and complex hydrodynamic phenomena, such as fluid–structure interactions and vortex–induced vibrations. Moreover, this paper details the design methodology, fabrication process, and method for similarity evaluation, covering the mass, deflection under load, natural frequency in air, and the natural frequency of the various underwater motion freedoms of the model. The results of our experiments and numerical simulations demonstrate a close alignment, proving the reliability of the new SFT scale model. The frequency distribution observed in the white noise wave tests indicates that the SFT equipped with inclined mooring cables experiences a coupled interaction between horizontal motion, vertical motion, and rotation. Furthermore, the design methodology of this model can be applied to other types of SFTs, potentially advancing technical progress in scale modeling of SFTs and enhancing the depth of SFT research through hydrodynamic experiments. Full article

The dynamic response analysis of submerged floating tunnels (SFTs) under seismic action is a complex two-way fluid–structure coupling problem that requires expertise in structural dynamics, fluid mechanics, and advanced computational methods. The coupled Eulerian–Lagrangian (CEL) method is a promising method for solving fluid–structure interaction problems, but its application to SFTs is not well established. Therefore, it is crucial to verify the accuracy and reliability of the CEL method in fluid–structure coupling simulations. This study verified the applicability of the CEL method for simulating one-way and two-way fluid–structure coupling cylindrical flow problems, and then applied the CEL method for the analysis of a shaking table test of a model SFT. A comparison of results obtained with the CEL method with those obtained in a previous indoor model test of an SFT demonstrates the agreement between the results of the CEL method and the overall trend of the experimental results, indicating the reliability of the method for the seismic analysis of SFTs. Moreover, the analysis of the dynamic response characteristics of SFTs under seismic conditions provides data support and a technological means for the seismic design of SFTs. Full article

This study investigates the vertical-type submerged floating tunnel with anchor cables. Based on the characteristics of the anchor cables, the anchor cables are simplified as a nonlinear beam model with hinged ends. Disregarding the axial displacement of the tunnel body, the loads will cause displacements in the x and z directions of the tunnel body. The vibrations of the anchor cables are decomposed into three directions, and the parameter excitation at the connection point between the anchor cables and the tunnel body is taken into account. The equations of motion for the three degrees of freedom of the anchor cables are established using Hamilton’s principle, and then the three equations are solved using the Galerkin method and the fourth-order Runge–Kutta method. The basic characteristics of an internal wave stratified flow acting on the anchor cables are considered, as well as the influence of the incident angle of the ocean currents on the three degrees of freedom of the anchor cables. The results indicate that (1) stratified flow weakens the first- and third-order vortex-induced vibrations of the anchor cables while enhancing the second-order vortex-induced vibrations. When considering the parameter excitation of the anchor cables, the first- and third-order vibrations are weakened, while the second-order vibration remains significant; (2) the first-order vibration of the anchor cables reaches its maximum value when the transverse oscillation frequency of the tunnel body is twice its natural frequency, and the second-order vibration of the anchor cables reaches its maximum value when the transverse oscillation frequency of the tunnel body is twice its natural frequency; (3) the downstream vibration of the anchor cables increases with the increase in the incident angle of the ocean currents, the cross-flow vibration of the anchor cables decreases with the increase in the incident angle of the ocean currents, and the axial vibration of the anchor cables reaches its maximum value when the incident angle of the ocean currents is 60 degrees; (4) stratified flow weakens the lock-in phenomenon of the anchor cables, and the influence of the 1/2 stratified flow on the vibrations of the anchor cables is greater than the influence of the 1/2 stratified flow. Full article

This study proposes a mooring design strategy for a submerged floating tunnel (SFT) subject to extreme waves and earthquakes. Several critical design parameters, such as submerged depth and mooring station interval, are taken into account. As a target structure, a 700 m long SFT system with permanent stations at both ends, representing the fixed–fixed-end boundary condition, is established. To consider coupled dynamics between the tunnel and the mooring system with structural elasticity, an efficient time-domain simulation model is established. Three combinations of environmental conditions are considered: extreme wave only, extreme earthquake only, and both extreme earthquake and operating wave. First, to check the submerged-depth effect on the dynamic response of the SFT system, including mooring tension, two different submerged-depth (deep and shallow) types are simulated and analyzed. It is confirmed that the deep submerged-depth model (A-type) has an advantage under extreme wave conditions, whereas the shallow submerged-depth model (B-type) is equipped with better resistance when subject to an earthquake. Thus, the compromise submerged-depth model (C-type) is newly devised to enhance structural integrity under various environmental circumstances. Furthermore, a mooring station interval sensitivity test with the C-type is performed and demonstrates the integrity of the C-type. Full article

The Submerged Floating Tunnel (SFT) is a highly promising cross-sea transportation structure. Due to its body being suspended in water, waves and flows are the primary environmental loads it encounters. Existing numerical simulations have been based on potential flow theory, which fails to fully consider shear forces and the nonlinear characteristics of the flow field. To overcome this limitation, the Computational Fluid Dynamics (CFD) approach, relying on solving the Navier-Stokes equations, can be employed. In this study, we establish a CFD model for the SFT and analyze the impact mechanisms of wave-flow coupling on its dynamic response, considering parameters such as wave height, flow velocity, wave direction, and flow direction. With increasing wave height, the acceleration, mooring tension, and heave amplitude of the SFT significantly increase, and the nonlinear characteristics of its dynamic response become more pronounced. For example, when wave height, H_i, increases from 0.046 m to 0.138 m, the maximum value of dimensionless heave, δ_z/H_i, increases from 0.075 to 0.284, nearly quadrupling in magnitude. When waves and flows propagate in the same direction, the heave amplitude of the SFT increases compared to the case with waves acting alone, while sway and roll amplitudes decrease. Under conditions of higher flow velocity, the SFT displaces significantly along the direction of flow and water depth, deviating significantly from its original equilibrium position. At this point, the tunnel primarily experiences periodic forces due to vortex shedding, and the anchor chain on the downstream side remains slack. In scenarios where waves and flows propagate in opposite directions, both the maximum acceleration and mooring tension of the SFT increase significantly. For instance, the onshore tension of the cable, F_on, increases by 36%, while the offshore tension, F_off, increases by 89%. Full article

The dynamic response characteristics of a two-dimensional submerged floating tunnel (SFT) under random and freak waves were investigated in the present study. The results demonstrate that (1) the dynamic responses of the SFT under the freak wave are significantly larger than those under the largest wave in the wave train excluding the freak wave, particularly for the motion response. The maximum values of the motion responses induced by the freak wave were several times larger than those induced by the largest wave in the wave train excluding the freak wave, far exceeding the proportion of the corresponding wave height. (2) The freak wave parameter α₁ has a significant effect on the amplification coefficients of surge, heave and pitch; all increase nonlinearly as α₁ increases. Within α₁ = 1.90~2.59, the amplification coefficients of the surge, heave and pitch vary in the ranges of 1.91~6.46, 1.53~3.87 and 1.73~5.32, respectively. (3) Amplification coefficients of tension increase almost linearly as α₁ increases. Additionally, the amplification effect of the freak wave on the mooring tension is much smaller than that on motion responses. Within α₁ = 1.90~2.59, the amplification coefficients of tension vary from 1.15 to 1.35. (4) Generalised amplification coefficients of motion responses increase as α₁ increases and are all greater than 1.0, indicating that growth rates for motion responses under the freak wave exceed the growth rates for maximum wave height. Moreover, motion responses show a significantly nonlinear growth as maximum wave height increases. The generalised amplification coefficients of the mooring tension decrease as α₁ increases, and are all less than 1.0, indicating that the dynamic amplification effect of the freak wave on the mooring tension is much smaller than that on motions. On the other hand, growth rates of the mooring tension under freak waves are smaller than the linear growth rate of the height of freak waves. Full article

A freak wave is a spike in a random wave series and hence the local characteristics in the time-domain are of key importance. When freak waves act on moored floating structures, the dynamic responses of the structures in the time and frequency domains change interdependently in a short period of time. It is difficult to comprehensively and accurately describe this physical process using a single-dimensional analysis method, such as time-domain statistical analysis or frequency-domain spectral analysis. The wavelet analysis method, which can simultaneously provide the time-domain and frequency-domain joint information of the physical process, is used to discuss the time-frequency joint variation characteristics of the dynamic responses of a two-dimensional submerged floating tunnel under a freak wave. The time-frequency characteristics of the dynamic responses induced by the freak wave and the differences from the action under random waves are investigated, with a particular emphasis on the ‘convex variation’ characteristics of the dynamic responses under a freak wave. The results show that: (1) The wavelet analysis method can effectively describe the basic characteristics of the dynamic responses of the SFT under a freak wave and clearly distinguish the differences in dynamic responses under freak and random waves. (2) Freak waves have dynamic amplification effects, which are related to the freak wave parameter α₁, on a two-dimensional SFT. Following the action of freak waves on a two-dimensional SFT, significant energy concentration occurs in the time-frequency spectrum of the dynamic response in a certain time and frequency range. The degree of energy concentration increases nonlinearly with an increase in α₁, and a certain high-frequency energy appears in the time-frequency spectrum of the motion response. The maximum values of the time-frequency spectra of the dynamic responses under a freak wave are much larger than those under a random wave with the identical wave spectrum. (3) Following the action of a freak wave on a two-dimensional SFT, the generalised energy spectra of surge, heave, pitch, and mooring tensions have convex peak values, which occur simultaneous with the occurrence of the freak wave, and the convex parts significantly increase as α₁. (4) The time lengths of the influence of a freak wave on the dynamic responses exceeded the freak wave period. With an increase in α₁, the time ranges of the large values of the time-frequency spectra of surge, heave, pitch, and mooring tensions increase nearly linearly. Full article

Submerged floating tunnels (SFTs) are an innovative traffic structure for transportation in deep and long-distance ocean environments. SFTs have the risk of being subjected to wave action in the complex ocean environment. Therefore, in order to ensure the safety and stability of SFTs during their service, the dynamic behavior of an SFT subjected to the action of waves is experimentally investigated in this study. Based on the wave–current flume, a physical scale-model experiment of an SFT for studying the dynamic behavior of an SFT subjected to regular waves interactions is deeply and thoroughly explored. The results show that the wave outputs from the wave-making system are verified to be reliable. The influence of major load parameters on the dynamic behavior of the SFT are deeply and thoroughly explored. The effects of wave height and wave period on acceleration, wave pressure, anchor cable force and displacement in an SFT are discussed. This experimental study has theoretical and practical significant for SFT design and safety. Full article