Crossing waterways is crucial to improve transport connections. In particular, new crossing methods are needed when the distance to be covered increases. Submerged Floating Tunnels (SFT) have been recently emerging as a cost-effective feasible crossing technique to connect fjords in Norway. However, only very little research has addressed the vehicle-structure interaction, with attention to the passengers, so far. In the current thesis, an algorithm was developed to study the Fluid-Structure-Vehicle-Interaction (FSVI), where the tunnel has been modelled as a Euler Bernoulli beam, the train car as a 6DOFs system, the supporting cables as linear springs, and the fluid by the Morison's hydrodynamic force expression. The Sperling ride quality and comfort indices were used to address human comfort while crossing the tunnel. It is found that, due to the low-frequency hydrodynamic environment, the influence of the FSVI on the Sperling's indices is limited, i.e. "just noticeable" from the classification table. Low-frequency flow field may cause motion sickness rather than cause comfort/discomfort during the ride. The illness rating, which is the indicator of the motion sickness, gave positive outcomes due to the small amplitude of the accelerations, and therefore no illness is expected to be felt by passengers. This study shows that displacement and acceleration can be controlled and kept inside the proposed boundaries under storm sea states, and the comfort while crossing can be guaranteed. The approach here used can be applied to other sea states with higher frequency content to address the comfort in a storm with smaller return period, which may also be important to address the fatigue resistance of the structure.

This study presents the results of small scale flume experiments on a submerged rectangular cylinder subjected to a current, regular wave and combined wave-current environment. The objective of the study is to gain more knowledge about the hydrodynamics around and the kinematics of a submerged structure, to give a contribute to the research field of the submerged floating tunnel. For this study a rectangular cylinder with an aspect ratio (breadth-depth) of 2.5 is used. Two relative submergence depths (flume depth/model submergence) of 2.75 and 1.63 are tested. For all tests a still water depth of 0.7 m is applied. Waves resulting in very low KC numbers of <1 for regular waves and KC[1+U_c/U_m ]<2 for combined waves-current are generated. To create a combined wave-current environment, a current is created in the flume, to which waves are added by the wave generator. The water velocity is measured in front of the model. To approximate the water velocity at the model, a time/phase shift is added to the velocity signal. Linear wave theory is applied to approximate the amplitudes of the orbital velocities at the depth of the model. For the first part of the study, on the hydrodynamic forces, the cylinder is rigidly fixed in the flume. Due to the inertia dominance for low KC numbers, the relationship between the wave parameters and the hydrodynamic forces is well described by the relationship between the wave parameters and the water particle accelerations. The vertical hydrodynamic forces are found to be larger than the horizontal hydrodynamic forces. The force coefficients from this study are compared to coefficient found in previous studies. The drag coefficients for the only current tests agree well with the results from (Courchesne & Laneville, 1979), (Bearman & Trueman, 1972), (Nakaguchi, 1968) and (Venugopal, 2006). For the regular wave and combined wave-current conditions comparable results are found to those by Venugopal for a rectangular cylinder towed through a wave field (Venugopal, 2008). The drag coefficients in the present study show a similar trend in magnitude as in the study by Venugopal. However, the magnitudes have an opposite sign due to the velocity phase shift method applied in the present study. Nevertheless, the effect of this difference on the total force prediction is insignificant, because of inertia dominance. In general, the Morison equation predicts the measured horizontal force well for regular waves. Adding a current component to the waves results in a larger error between the computed Morison forces and the measured force. However, an increase in the magnitude of the added velocity does not lead to a significant increase of this error. The second part of the study focuses on the same cylinder, only not fixed but held in place by 4 tethers. For these tests a buoyancy to weight ratio of 1.5 is applied. The used tested angles between the tethers and the flume bottom are 30˚ and 70 ̊. The water depth, the wave types and model submergence depths are remained equal to the first part of the study. By comparing the kinematics found in three different configurations, a 30˚ tether angle combined with the largest submergence depth of ds=035 m are found to gives the smallest displacements and accelerations. To reduce the kinematics more, it is recommended to add vertical tethers to limit the vertical movement. In general, dynamic features are seen in the tethered model, influencing the magnitude of the kinematics. To predict the magnitude of the tether forces it is recommended to integrated these features in a structural dynamic model.

The submerged floating tunnel (SFT), also known as the Archimedes bridge or suspended tunnel, is a conceptual idea for a tunnel that floats in the water, supported by its buoyancy. The tunnel would be placed underwater, not too deep in order to avoid high water pressures, but deep enough for it not to be exposed to extreme weather conditions or obstruct shipping traffic. The tunnel is kept in position with tethers that are anchored to the sea bed or floating pontoons at the water surface. This thesis focuses on the tether supported SFT. The dynamic response of a tether supported SFT, in a hydrodynamic environment, is different from the tunnels that are widely used nowadays. The SFT is always in contact with open water in which it is moving due to the hydrodynamic environment. The dynamic response of the tether supported SFT is still a gap in our engineering knowledge and this contributes to the fact that world-wide no tether supported SFT has ever been constructed. Many research has been performed in the last years. A broad range of models has been used to study the dynamic behavior of the tether supported SFT. The key in all these models is to capture the fluid structure interaction. Waves and current exert forces on the tunnel body but at the same time, the presence and motion of the tunnel body affects the wave-current environment. To model the dynamic response of a tethered SFT incorporating fluid-structure interaction, a new model has been developed. The dynamic SFT model describes the cross sectional motion and tether forces of a rectangular tubular tunnel which is pinned down by two inclined tethers, excluding longitudinal effects. The tunnel is forced by waves and current only. When assuming the SFT system to be linear, the motion of the SFT can be seen as a superposition of the motion of the tunnel body in still water and the forces on the restrained tunnel body in waves and current. The tunnel motion in still water is modelled with a dynamic module while the hydrodynamic forces on a restrained tunnel body are computed with a wave force module. The two independent modules are combined in a coupling module which makes it possible to describe the dynamic response of a tether supported SFT in a wave-current environment. The advantages of this model choice are the fast computational time and the convenience of physical interpretation. The wave force module computes the wave-current forces on the restrained tunnel body with a modified Morison formulation. This formulation is capable of computing, besides vertical and horizontal wave-current forces, the rotational wave force. Rotational wave forces are essential in the determination of tunnel roll motion and cannot be determined with the classical Morison theory. Just like the classical Morison theory, the modified Morison formulation does not take into account wave field deformation due to the presence of the tunnel structure. Therefore, for waves that are short compared with the dimensions of the SFT, diffraction effects cannot be taken into account. The absence of the diffraction effect is corrected for by integrating the dynamic pressures, water accelerations and water velocities with respect to the tunnel height and width. It should be noted that the applicability for short waves is only valid in case of structures that are submerged at a depth of at least 1.5-2 times the structure height. For shallowed submergence depths, the diffraction effects in combination with wave deformation become too large which cause prediction errors in the force determination. The force on the restrained SFT due to a uniform current can be modelled with the drag force expression from the classical Morison equation. To correct for the wave current interaction, the hydrodynamic mass coefficients are adapted as function of the Keulegan-Carpenter number. The dynamic module describes the oscillation of the SFT, in still water, with a dynamic system. A free floating tunnel has three degrees of freedom which are roll, sway and heave. This dynamic system assumes the tunnel is connected with two in-extensible tethers. Adding two rigid constrains to the free floating tunnel reduces the SFT to a single degree of freedom system. This single degree of freedom system describes a coupled translational (sway) and rotational (roll) motion around an instantaneous rotational point which can be found at the intersections of the tether axes. When assuming small vibrations, the instantaneous rotational point remains fixed at the intersection of the tether axes when the tunnel is at rest. The moment of inertia of the SFT is obtained by using the Lagrangian approach which is based on energy conservation. Because the structure is submerged in water, added damping and mass terms are used in the equation of motion. The magnitude of these damping and mass terms is calibrated with physical model experiments. The coupling module combines the wave force module and the dynamic module, which makes it possible to formulate a full equation of motion, describing the oscillation of the SFT in a wave current environment. From the equation of motion the sway and roll motions, containing accelerations, velocities and displacements, can be obtained. Apart from the motions, the tether forces can be predicted. The dynamic SFT model is validated with physical model experiments. With this dynamic SFT model, a parametric study has been performed. The first part of the parametric study focuses on the motion of the SFT. The second part examines the tether forces. Furthermore, the slack-taut transition and the safety against fatigue have been investigated. The parametric study does not take into account current. The most important findings and implications are in summary: • Each SFT configuration has a different response to the wave environment. Hence, every configuration has a different critical wave length for which the dynamic response is maximum. This critical wave length is independent of the wave height. It should be noted that the dynamic response is a comprehensive term which consists of many variables. These are; tether forces, sway motions and roll motions of which both motions contain accelerations, velocities and displacements. The most dominant parameters to influence the dynamic response are the buoyance to weight ratio (BWR), tether angle and submergence depth. • The BWR increases the stiffness of the dynamic SFT system which causes a decrease in the roll motions and sway displacement. Due to the stiffness increase, sway accelerations and velocities become larger. The natural frequency of the SFT is increased by increasing the BWR, which makes it more sensitive to shorter waves. • Configurations with large tether angles have the character to be very flexible and sway dominant, while configurations with small tether angles are stiffer and roll dominant. Tether forces for configurations with large tether angles are more sensitive to long waves, while tether forces for configurations with small tether angles are more sensitive to short waves. • A decrease in submergence depth increases all tunnel motions and tether forces, as the tunnel becomes more exposed to the wave environment. The dynamic response of the SFT becomes more sensitive to short waves. • An increase in anchorage depth results in larger tunnel motions. The increase in tether forces is negligible. • Placing the tether connection sideways of the tunnel body results in smaller roll motions and larger sway motions. Lowering the tether connection with respect to the tunnel bottom is favourable for all tunnel motions. The manner of how the tether connection is orientated, with respect to the tunnel body, has small influence on the tether forces. • Increasing the BWR, submergence depth or both reduces the risk of snapping lines and tether fatigue. Configurations with small tether angles have a smaller risk of having line snapping and tether fatigue compared to configurations with large tether angles. This study gives a supplement to the classical Morison theory. Morison’s theory is modified which makes it possible to compute rotational moments due to wave loading. Also the applicability to short waves is enlarged. A new dynamic schematization is developed which makes it possible to describe the dynamic response of a SFT as a single degree of freedom (SDOF) system. The advantages of this dynamic schematization are the fast computational time and the convenience of physical interpretation. The results obtained from this research study can be used as a preliminary design tool. In an early design stage, motions and tether forces can be predicted. Also measures to reduce these motions and tether forces can be investigated using the dynamic SFT model. Design graphs to estimate the snap-taut transition and for safety against tether fatigue are provided. It should be noted that this dynamic SFT model should not be used for detailed computations in later design stages.

This thesis aims to gain insight into the global dynamic fluid-structure interaction response of a submerged floating tunnel (SFT) under the wave and current loading to enhance the design. To this end, the tunnel tube is modelled as a Euler-Bernoulli beam deformed in three directions (horizontal displacement, vertical displacement, rotational angle), the discrete anchoring system as a continuous elastic foundation considering geometrical nonlinearity. Then, the Morison equation is used to model the combined current and wave loading and the oblique wave loading. A simplified wake oscillator and a non-simplified wake oscillator are used to model the vortex-induced vibration (VIV) under current loading. Subsequently, the modal superposition method and Runge-Kutta method are applied to obtain the response of the SFT in the time domain. The Fourier transform and the wavelet transform are applied to the time domain signal to perform a frequency domain analysis. Finally, a test on a scaled SFT model is used for a case study. A parametric study is carried out based on the results to study the influence of the geometrical and structural design parameters. The results show that the motions in the horizontal direction and the rotational direction are significantly coupled together. Geometrical nonlinearity introduces the second-order effect to the system leading to a complicated vertical motion with a considerably larger displacement compared with the linear case. The amplitude of the VIV on the tunnel tube of the scaled model is very small based on the non-simplified wake oscillator. Moreover, it is found that, basically, increase of the BWR, increase of the stiffness in the cables, increase of the distribution of the net buoyancy in inclined cable, decrease of the tunnel length or decrease of the inclination of the inclined cables can reduce the maximum response of the SFT. Based on the above findings, it is concluded that a global dynamic analysis is suggested when a SFT is expected to be subjected to oblique wave loadings. Geometrical nonlinearity is necessary to be considered for an accurate analysis especially for the response in the vertical direction. It is also necessary to be considered when the influence of the BWR is of interest. The VIV on the tunnel tube is negligible base on the scaled model.

The influence of surface roughness and shape on the submerged floating tunnel is investigated in wave and current conditions. The hydraulic forces caused by varying tunnel shapes and roughness designs are measured and analyzed.

Low-lying countries such as Belgium and the Netherlands are naturally susceptible to overtopping wave attacks. Coastal regions are therefore facing the threat of such events causing damage to dike-positioned structures and buildings. Research in this filed is often conducted using scaled-down 2D hydraulic physical models, which introduces so called scale effects that can bias the results with regard to measured wave-structure impact forces. This thesis therefore attempts to determine the effects of scaling for post-overtopping wave impacts. To achieve this, large scale physical modelling tests were conducted at Deltares’ Delta flume and compared with a small scale model of similar configuration. A second thesis aim stems from the application of measurement devices in an innovative manner while conducting the large scale tests, and their applicability is assessed here. The model comparison shows that in general the small scale test performs very similarly to its large scale counterpart, and scaling effects did not appear to bias the impact events considerably. This was also observed for the pre-impact flow evolution, where the wave interference mechanisms and resulting bore characteristics were also largely similar. The force-time signal for the largest impacts also is related to the pre-impact mechanisms observed. Classification of the extreme bore impacts according to their impact peak ratio did outline a discrepancy between the two models, which was also linked to the difference in entrapped air pocket impacts. The four measurement instruments assessed are a Terrestrial Laser Scanner (TLS), waterproof action camera(s), optical phase detection probe (OPDP) and a high speed camera mounted behind an opening in the impacted wall. Data from the former two was also used in this analysis and their performance was determined to be good.

The submerged floating crossing (SFC) considered in this study has demonstrated significant sustainability based on provided assumptions. the SFC has appeared to be a sheltered and sound idea appropriate to satisfy its expected capacities and to tackle given environmental conditions. The structure of the proposed SFC is intended to withstand all functional and environmental loads. The results of worst-case scenarios showed the base SFC design have a sufficient robustness to withstand the presumed significant loads. Some major uncertainties were faced throughout the study, which are manageable by means of modern technologies in civil engineering or some organizational arrangements.