Submerged Floating Tunnel Research Articles

Numerical Investigation of Vortex Induced Vibration for Submerged Floating Tunnel under Different Reynolds Numbers

A 2D numerical model was established to investigate vortex induced vibration (VIV) for submerged floating tunnel (SFT) by solving incompressible viscous Reynolds average Navier-Stokes equations in the frame of Abitrary Lagrangian Eulerian (ALE). The numerical model was closed by solving SST k-ω turbulence model. The present numerical model was firstly validated by comparing with published experimental data, and the comparison shows that good achievement is obtained. Then, the numerical model is used to investigate VIV for SFT under current. In the simulation, the SFT was allowed to oscillate in cross flow direction only under the constraint of spring and damping. The force coefficients and motion of SFT were obtained under different reduced velocity. Further research showed that Reynolds number has not only a great influence on the vibration amplitude and ‘lock-in’ region, but also on the force coefficients on of the SFT. A large Reynolds number results in a relatively small ‘lock-in’ region and force coefficient.

水下爆炸冲击作用下悬浮隧道响应参数分析

To investigate the dynamic responses of submerged floating tunnels (SFTs) subjected to near-field non-contact explosions, the SFT was simplified as a constant-section-and-stiffness Bernoulli-Euler elastic-support beam to establish the SFT dynamic model under underwater shock load. The differential equation for the vibration was resolved with the Galerkin method. The displacement, velocity and acceleration were analyzed for the SFT, the influences of the explosive quantity, the blasting distance and the vertical stiffness of anchor cables were discussed, and the results were also used to analyze the damage of tunnels and human bodies. The results show that, the impact of the blasting distance on the kinematic parameters of the SFT is significant. Moreover, the maximum displacement of the tunnel decreases in inverse proportion to the blasting distance. Compared with those of the blasting distance of 10 m, the displacements of the tunnel body of 20m and 30 m decrease by 50.7% and 66.6%, respectively. The impact of the explosive quantity on the kinematic parameters of the SFT is significant. Also, the maximum displacement of the tunnel decreases approximately in a low-order power function with the explosive quantity. Compared with those of the explosive of 20 kg, the displacements of the tunnel body of 40 kg and 60 kg increase by 29.8% and 51.3%, respectively. The impact of the vertical stiffness of anchor cables on the kinematic parameters of the SFT is significant. Besides, the maximum displacement of the tunnel decreases approximately in a step-like form with the vertical stiffness of anchor cables. Compared with those of the vertical anchor stiffness of 5×105 N/m, the maximum displacement of the tunnel body of 5×10⁶ N/m and 5×10⁷ N/m decrease by 53.0% and 86.2%, respectively. However, there is an efficiently acting interval for the anchor cable stiffness. The stiffness has significant influence on the displacement of the tunnel body within the interval, but has little influence outside the interval (large or small).

Preliminary study on the ground behavior at shore connection of submerged floating tunnel using numerical analysis

Submerged floating tunnel (SFT) is a type of tunnel which causes the tunnel segments to float in the water. When the SFTs are connected to the ground, the connection between the SFT and the subsea bored tunnel is fragile due to the difference in behavioral characteristics between the two types of tunnels. Therefore, special design and construction methods are needed to ensure the stability of the area around the connection. However, since previous research on the stability of the connection site has not been undertaken enough, the basic step necessitates the evaluation of ground behavior at the shore connection. In this study, the numerical analysis targeting the shore connection between the subsea bored tunnel and the SFT was simulated. The strain concentration at the shore connection was analyzed by numerical simulation and the effects of several factors were examined. The results showed the instability in the ground close to the shore connection due to the imbalance in the behavior of the two types of tunnels; the location of the strain concentration varies with different environmental and structural conditions. It is expected that the results from this study can be utilized in future studies to determine weak points in the shore connection between the submerged floating tunnel and the subsea bored tunnel, and devise methods to mitigate the risks.

Dynamic Characteristics of submerged floating tunnel under irregular waves

submerged floating tunnel (SFT) is an innovative structural solution for waterway crossings and is based on the idea of Archimedes Buoyancy. The main structure is kept at a certain depth underwater and is placed in position by anchor/mooring cables. SFT becomes a more economical alternative for waterways compared to classical solutions such as cable-supported bridge, immersed tunnel or underground tunnel when the width and depth of the waterway are large enough. As SFT is completely submerged in water and is subjected to extreme environmental conditions such as waves, earthquakes, and hurricanes, therefore, the evaluation the dynamic characteristics of an SFT under irregular waves is a key demand from the design point of view. In this study, the responses of an SFT that is to be built in Qindao Lake of China are investigated under irregular waves. A 3D FEM model for SFT was established, the tunnel was modeled by 3D beam elements and cables were modeled by elastic catenary elements. The irregular waves were modeled by JONSWAP spectrum. The time history analysis was performed under irregular waves and currents. The time-domain simulations were transformed to the frequency domain by Fast Fourier Transform (FFT). The spectra were smoothed using Savitzky-Golay smoothing filters. The transfer functions of SFT horizontal and vertical displacements; and cable tensions were obtained for 30 realizations. Two major peaks have been observed in each transfer function (response spectrum). One of the peaks was associated with the peak wave frequency; the second peak was associated with the translational natural frequency of the SFT.

Dynamic Characteristics of submerged floating tunnel under irregular waves

submerged floating tunnel (SFT) is an innovative structural solution for waterway crossings and is based on the idea of Archimedes buoyancy. The main structure is kept at a certain depth underwater and is placed in position by anchor/mooring cables. As SFT is completely submerged in water and is subjected to extreme environmental conditions, therefore, the evaluation of the dynamic characteristics of an SFT under irregular waves is a key demand from the design point of view. In this study, the responses of an SFT that is to be built in Qindao Lake of China is investigated under irregular waves. The irregular waves were modeled by the JONSWAP spectrum. The time-domain simulations were transformed to the frequency domain by Fast Fourier Transform (FFT). The spectrum was smoothed using Savitzky-Golay smoothing filters. The transfer functions of SFT horizontal and vertical displacements; and cable tensions were obtained for 30 realizations. Some useful conclusions are drawn from the numerical results of the present study.

Dynamic Characteristics of submerged floating tunnel under irregular waves

submerged floating tunnel (SFT) is an innovative structural solution for waterway crossings and is based on the idea of Archimedes buoyancy. The main structure is kept at a certain depth underwater and is placed in position by anchor/mooring cables. As SFT is completely submerged in water and is subjected to extreme environmental conditions, therefore, the evaluation of the dynamic characteristics of an SFT under irregular waves is a key demand from the design point of view. In this study, the responses of an SFT that is to be built in Qindao Lake of China is investigated under irregular waves. The irregular waves were modeled by the JONSWAP spectrum. The time-domain simulations were transformed to the frequency domain by Fast Fourier Transform (FFT). The spectrum was smoothed using Savitzky-Golay smoothing filters. The transfer functions of SFT horizontal and vertical displacements; and cable tensions were obtained for 30 realizations. Some useful conclusions are drawn from the numerical results of the present study.

Hydrodynamic Behavior of Submerged Floating Tunnels with Suspension Cables and Towers under Irregular Waves

In this paper, case studies were carried out to analyze the feasibility of submerged floating tunnels (SFTs) with suspension cables. In order to apply an SFT in a field site, the deformation of the system should be controlled, even under extreme wave conditions, if vehicles or trains operate inside the SFT. Two types of suspended SFTs were proposed to analyze their hydrodynamic behavior. The main variables were the wave conditions, cross-sectional diameters, buoyancy weight ratios, inclination angles of the main cables, and installation depth of the SFT. Overall, it was found that the SFT with a mid-anchor was superior from a hydrodynamic point of view. However, a detailed hydrodynamic analysis must be performed to avoid the conditions that previously produced slack. In addition, in a case where acceleration is generated by motion, the design should be reviewed to ensure safe conditions, according to the traffic passage.

ASSESSMENT OF SEISMIC PERFORMANCE OF SUBMERGED FLOATING TUNNEL UNDER MULTI-SUPPORT SEISMIC EXCITATIONS

Submerged floating tunnel (SFT) is an innovative structural solution for the transportation infrastructure through sea straits, fjords, and inland waters and is an economical alternative to the long-span cable-supported bridge, immersed tunnel, or underground tunnel. An SFT is a massive cylindrical structure that floats at a certain depth below the water surface and subjected to extreme environmental conditions, such as waves, tsunamis and earthquakes. The seismic assessment of SFT supported by mooring cables, under multi-support seismic excitations needs to be evaluated in more detail. The time domain dynamic problem of SFT moored by inclined mooring cables/anchors is formulated and the geometric non-linear dynamic analysis of SFT subjected to hydrodynamic and seismic excitations is performed in this paper. The prototype of SFT to be constructed in Qindao Lake of China is analysed under multi-support seismic excitations. It was found that due to the fluid environment and flexible cables the effective seismic forces are dissipated well and SFT is stable under the spectrum compatible ground motions. However, the lateral component of seismic excitations produce larger responses compared to longitudinal one and may be critical for other case studies.

Tunnel-mooring-train coupled dynamic analysis for submerged floating tunnel under wave excitations

A submerged floating tunnel (SFT) is considered as an effective alternative to conventional bridges and underground/immersed tunnels for passing through deep water. In this study, a time-domain coupled hydroelastic dynamics model has been developed to solve the tunnel-mooring-train interaction under wave excitations. The equations of motion for a tunnel and mooring lines are based on the FE (finite element) rod theory with the Galerkin formulations. The tunnel is coupled with mooring lines through a specially devised connection method with linear and rotational springs. Wave-induced hydrodynamic loads are estimated by the Morison equation for a moving object. The train is modeled by using the multi-rigid-body dynamic method, in which a train element is composed of seven constituent rigid sub-bodies. The interaction between the tunnel and the train is taken into consideration based on the correspondence assumption and the simplified Kalker linear creep theory. Accordingly, the train-tunnel coupled dynamics formulas are derived. In the simple case of moving mass inside SFT in calm water, SFT's dynamic responses and mooring tensions agree well with those by a commercial program, OrcaFlex. For more complex coupling of SFT dynamics with multi-car trains in random waves, the presently developed simulation program is applied. It is seen that the influences of moving trains on the dynamic responses of the SFT are small. Under the given moderately rough wave conditions and track irregularity, the moving train also meets the safety and passenger-comfort criteria at high (80 m/s) train speed.

P.243 Experimental evaluation of the atomoxetine influence on the cognitive functions in rats

The Norwegian Public Road Administration is planning to upgrade Coastal Highway E39 by replacing ferry connections with floating bridges or submerged floating tunnels (SFTs). This study considers a potential pontoon-supported curved SFT designed for crossing Sognefjorden at a submergence of 12 m. It consists of two identical tubes with a diameter of 12.6 m each in a tandem configuration and with a length of approximately 4 km. The natural frequencies of the low-order modes are well within the energy content in the spectra of the second-order difference-frequency wave excitation forces and the vortex shedding-induced forces. In this paper, numerical simulation of wave-induced hydroelastic response and flow-induced vibrations of the twin-tube SFT is performed. Long- and short-crested waves, the first and second order wave loads, are considered. A time-domain approach to simulate crossflow vortex-induced vibration (VIV) and VIV-amplified inline drag forces, partly based on the coefficients obtained experimentally, is established and applied. The focus is on extreme conditions – relating to ultimate strength limit states. The second-order wave load substantially affects the lateral motion and lateral bending moment, as expected. The short-crested waves influence the response in both the lateral and vertical directions by exciting asymmetric eigenmodes. In strong flow conditions, once VIV is excited, the standard deviation of the vertical motion (of about 30% of the diameter) and the bending moment about the horizontal axis is more that an order of magnitude larger than that induced by the wave loads. The simulation of the wave- and flow-induced load effects provides a good reference for the design of SFTs.

A study on response analysis of submerged floating tunnel with linear and nonlinear cables

This paper presents the comparison between SFT response with linear and nonlinear cables. The dynamic response analysis of submerged floating tunnel (SFT) is presented computationally with linear and nonlinear tension legs cables. The analysis is performed computationally for two wave directions one at 90 degrees (perpendicular) to tunnel and other at 45 degrees to the tunnel. The tension legs or cables are assumed as linear and non- linear and the analysis is also performed by assuming one tension leg or cable is failed. The Response Amplitude Operators (RAO\'s) are computed for first order waves, second order waves for both failure and non-failure case of cables. For first order waves- the SFT response is higher for sway and heave degree of freedom with nonlinear cables as compared with linear cables. For second order waves the SFT response in sway degree of freedom is bit higher response with linear cables as compared with nonlinear cables and the SFT in heave degree of freedom has higher response at low time periods with nonlinear cables as compared with linear cables. For irregular waves the power spectral densities (PSD\'s) has been computed for sway and heave degrees of freedom, at 450 wave direction PSD\'s are higher with linear cables as compared with nonlinear cables and at 900 wave direction the PSD\'s are higher with non-linear cables. The mooring force responses are also computed in y and z directions for linear and nonlinear cables.

Assessment of the Dynamic Behaviors of Submerged Floating Tunnel Under a High-Speed Train Loading

Submerged floating tunnels (SFTs) are innovative structural solutions to waterway crossings and are more economical compared to the conventional structures such as cable-supported bridges, underground tunnels or immersed tunnels. The dynamic behaviors of SFT under real train loads is the primary design requirement of an SFT, However, it is not investigated using realistic train models. In this study, the China-star high-speed train is used to evaluate the dynamic displacements, internal forces and cable tensions of SFT. The tunnel is modeled by FEM, the cables are modeled by elastic catenary cables, and ocean waves and currents are modeled by Airy’s wave theory. The SFT displacements, bending moments and cable tensions were significantly influenced by moving trains. The SFT experienced extreme vertical displacements and there was a large drop in the minimum cable tensions. The mooring cables were slacked both by magnitudes and speed of the moving trains, which should be avoided for the safety of SFT. This study recommends the additional buoyancies for the stability of SFT subjected to high speed trains.

Vehicle-tunnel coupled vibration analysis of submerged floating tunnel due to tether parametric excitation

Submerged floating tunnel (SFT) is a novel type traffic structure for crossing the long straits. To analyze the vehicle-tunnel coupled vibration of SFT due to tether parametric excitation, Hamilton principle and D'Alembert's principle are applied to establish the theoretical model. The fourth order Runge-Kutta method is carried out to calculate the responses of the system. The proposed model is verified by the beam on the elastic foundation (BOEF) model without considering tether parametric excitation, and the relative difference is less than 2%. If the initial excitation can be controlled in a small range, the influence of the tether vibration on the vehicle-coupled vibration can be efficiently reduced. Meantime, the effects of some factors, such as the gravity-buoyance ratio (GBR), the inclined angle of the tether (IAT), and the vehicle velocity on the dynamic response are discussed. The results show that the dynamic amplification factors (DAFs) of the deflection and the bending moment decrease with the GBR increasing. Besides, the larger IAT results in larger tether tension fluctuation when the vehicle-tunnel coupled vibration of the SFT subjected to tether parametric excitation. And the slower vehicle is more affected by the tether vibration when the vehicle drives in the tunnel.

On the internal blast loading of submerged floating tunnels in concrete with circular and rectangular cross-sections

The Norwegian Public Roads Administration has initiated a large research project on a potential ferry-free coastal highway route E39 on the west coast of Norway. For the wide and deep fjords, a submerged floating tunnel (SFT) in reinforced concrete has been suggested as a possible solution. A potential hazard for such a structure is internal blast loading, which can be devastating to its structural integrity. To assess the blast performance of concrete structures, a shock tube has been used to generate blast loading against concrete slabs with and without reinforcement. The shock tube tests were filmed with high-speed cameras, and digital image correlation was used to measure the out-of-plane deformations. A finite element model using input from material tests was set up in ABAQUS/Explicit to recreate the slab experiments. Based on the models validated by the shock tube experiments, full-scale numerical simulations of blast loaded SFTs with circular and rectangular cross-sections were run. The results were used to assess the qualitative performance of each cross-section geometry with respect to blast loading, where the circular cross-section indicated a superiour behaviour.

Effect of Cable Stiffness and Waves Parameters on the Dynamic Responses of Submerged Floating Tunnel

Submerged floating tunnel (SFT) is a new structural solution for waterway crossings compared to the classical solutions such as cable supported bridge, immersed tunnel or underground tunnel. An SFT is subjected to extreme waves, currents, earthquakes and other environmental loadings. The effect of key structural and waves parameters are important from the design perspective for an SFT. This study, the dynamic responses of SFT are evaluated using truss and catenary cables to check the effect of cable stiffness. The second part of this study deals with the effect of wave height and wave period on the dynamic responses of SFT. 3D truss and 3D catenary cables give very similar dynamic responses under waves and vertical ground motions. The wave height and wave period mainly control the dynamic behavior of SFT.

Effect of Cable Stiffness and Waves Parameters on the Dynamic Responses of Submerged Floating Tunnel

Submerged floating tunnel (SFT) is a new structural solution for waterway crossings compared to the classical solutions such as cable supported bridge, immersed tunnel or underground tunnel. An SFT is subjected to extreme waves, currents, earthquakes and other environmental loadings. The effect of key structural and waves parameters are important from the design perspective for an SFT. This study, the dynamic responses of SFT are evaluated using truss and catenary cables to check the effect of cable stiffness. The second part of this study deals with the effect of wave height and wave period on the dynamic responses of SFT. 3D truss and 3D catenary cables give very similar dynamic responses under waves and vertical ground motions. The wave height and wave period mainly control the dynamic behavior of SFT.

Effects of marine sediment on the response of a submerged floating tunnel to P-wave incidence

Submerged floating tunnels (SFTs) are a novel type of traffic structure for crossing long straits or deep lakes. To investigate the dynamic pressure acting on an SFT under compression (P) wave incidence, a theoretical analysis model considering the effect of marine sediment is proposed. Based on displacement potential functions, the reflection and refraction coefficients of P-waves in different media are derived. Numerical examples are employed to illustrate the effects of the thickness of the sediment layer, the incident P-wave angle, the tether stiffness and spacing, and the permeability of the sediment on the dynamic pressure loading on the SFT. The results show that the dynamic pressure is related to the saturation of the sediment and affected by its thickness. Partially saturated sediment will amplify the dynamic pressure loading on the SFT, and the resonance frequency increases slightly with fully saturated sediment. Besides, increasing the tether stiffness or decreasing the tether spacing will decrease the dynamic pressure. Locating the SFT at greater depth and reducing the permeability of the sediment are effective measures to reduce the dynamic pressure acting on the SFT.

Cross-flow and torsion coupled dynamic response of submerged floating tunnel under the action of ocean current

Submerged floating tunnel (SFT) is a kind of long distance flexible sea structure. The dynamic behavior of SFT is bound to be affected by the action of ocean current. According to the typical cross-section of the structure, the two-dimensional plane coupled vibration equations are derived based on Lagrange equations to analyze the cross-flow and torsion coupled dynamic response of SFT in ocean current environment. Meantime, the fourth-order Runge-Kutta method is used to solve the vibration equations. Finally, the effect of some key parameters, such as the height-width ratio, eccentric throw and the current velocity are investigated. The results show that the eccentric throw and the current velocity have obvious effects on the coupled structure vibration. With the increase of the eccentric throw and current velocity, the amplitude of the coupled vibration increases. Moreover, it can guarantee the relatively small vibration amplitude in cross-flow direction and torsion, when the height-width ratio is between 0.5 and 0.6.

Response Analysis of Submerged Floating Tunnel Hit by Submarine Based on Smoothed‐Particle Hydrodynamics

This paper presents the theoretical investigation on the damage of the submerged floating tunnel (SFT) under extreme loads. Water was modeled by smoothed‐particle hydrodynamics (SPH). Anchor cables, SFT, and submarine were modeled by the finite element method (FEM). Penetrating phenomenon in the calculation process was achieved by the penalty function, and the fluid‐solid coupling effect was also considered in the simulation. The process of a submarine striking on the SFT was studied based on the commercial software. The relationships between the energy of the water, submarine, and SFT were studied. The structural and human damages were evaluated using the kinematics and kinetic parameters of the SFT according to the relevant criterion. The results indicate that the SPH‐FEM coupling method is suitable to investigate the impact of the SFT in the water. The initial kinetic energy of the submarine is mainly converted into kinetic energy of the water and internal energy of the tunnel. The kinematic parameters at the impact point reach a peak value. The kinematic parameters at the anchor cables reach the minimum value, so the anchor cables can inhibit the development of disaster significantly. The SPH‐FEM coupling method can be helpful for collision and explosion analysis of the SFT.

Time-Domain Hydro-Elastic Analysis of a SFT (Submerged Floating Tunnel) with Mooring Lines under Extreme Wave and Seismic Excitations

Global dynamic analysis of a 700-m-long SFT section considered in the South Sea of Korea is carried out for survival random wave and seismic excitations. To solve the tunnel-mooring coupled hydro-elastic responses, in-house time-domain-simulation computer program is developed. The hydro-elastic equation of motion for the tunnel and mooring is based on rod-theory-based finite element formulation with Galerkin method with fully coupled full matrix. The dummy-connection-mass method is devised to conveniently connect objects and mooring lines with linear and rotational springs. Hydrodynamic forces on a submerged floating tunnel (SFT) are evaluated by the modified Morison equation for a moving object so that the hydrodynamic forces by wave or seismic excitations can be computed at its instantaneous positions at every time step. In the case of seabed earthquake, both the dynamic effect transferred through mooring lines and the seawater-fluctuation-induced seaquake effect are considered. For validation purposes, the hydro-elastic analysis results by the developed numerical simulation code is compared with those by a commercial program, OrcaFlex, which shows excellent agreement between them. For the given design condition, extreme storm waves cause higher hydro-elastic responses and mooring tensions than those of the severe seismic case.