Hydrodynamic Response Research Articles

Hydrodynamic Response Analysis of a Fixed Aquaculture Platform with a Horizontal Cylindrical Cage in Combined Waves and Currents

Biofouling on net cages adversely affects structural safety and the growth of aquacultural fish. Therefore, a novel fixed aquaculture platform with a rotatable horizontal cylindrical cage is proposed in this study, which is convenient for the cleaning of biofouling. Based on ANSYS, the numerical model of the fixed aquaculture platform was established. The response results of the strain, acceleration, and displacement of the structure under the combined action of waves and currents at three typical attack angles were calculated. The effects of water depth and cage rotation on the hydrodynamic response of the structure are discussed. The results show that the strain, acceleration, and displacement of the cage increase with the increase in wave height; however, the change with the wave period is not obvious. The direction perpendicular to the long axis of the cage is the most unfavorable load direction. The acceleration of each position increases with the increase in water depth; however, the strain response has the opposite trend. When the rotation constraint of the horizontal cylindrical cage is released, the acceleration of the cage is larger than that when the cage is fixed. The rotation of the cage has a tiny effect on the structural strain and load acting on the structure.

Scientific Investigation of Antifouling Activity from Biological Agents and Distribution of Marine Foulers-Coastal Areas of Tamil Nadu.

Biofouling is the result of a biological process that is the accumulation of micro- and macro-organisms on the surfaces of the ship which causes serious environmental problems. The consequence of biofouling includes modifying the hydrodynamic response, affecting heat exchange, can make structures heavier, accelerate or generating corrosion, biodegradation, increasing the fatigue of certain materials, and blocking mechanical functions. It causes severe problems for the objects in the water such as ships and buoys. Also, its impact on shellfish and other aquaculture was sometimes devastating. The main scope of this study is to review the currently available biocides from biological agents for marine submerged foulants and marine foulers that are present around the coastal areas of Tamil Nadu. Biological anti-fouling methods are preferred than that of the chemical and physical anti-fouling methods as it have some toxic effects on the non targeted marine biodiversity. This study focuses on the marine foulers that are present around the coastal areas of Tamil Nadu which will be helpful for the researchers to discover the suitable anti-foulers from a biological source, which will be very useful to protect the marine ecosystem and marine economy. A total of 182 antifouling compounds from marine biological sources were discovered. The marine microbes, Penicillium sp. and Pseudoalteromonas issachenkonii, were reported to possess EC50. The survey results obtained from this study show that Chennai coastal region has a lot of barnacles, and 8 different species were present in Pondicherry region.

Numerical study on dynamic analysis of a nine-module floating aquaculture platform under irregular waves

A numerical study of the dynamics of a nine-module floating aquaculture platform in irregular waves is proposed, to examine the effect of the connector type between net cages and incident wave direction on the hydrodynamic response. A numerical model based on the coupled boundary element method and lumped-mass model was used to simulate the dynamic behavior of the aquaculture platform. Time-domain statistical analysis, and time-frequency analysis based on Hilbert-Huang transform on the motion responses of net cages and the mooring force responses of the platform were then carried out. The results indicate that the mooring system has a decisive influence on the frequency-domain characteristics of surge motion, while the influence of connector can be ignored. The surge motion under flexible hawser connector is less sensitive to wave incident direction, while the wave direction has a greater impact on surge motion under spherical joint connector. The amplitudes of pitch motion under two different connectors decrease significantly under oblique incident waves, compared with perpendicular incident wave condition. The wave incident direction has little effect on the overall mooring force response of the platform. The mooring force responses at different positions show completely different frequency characteristics when the cages are connected by spherical joints. The larger the pitch response of the cage, the smaller the mooring force response of the mooring chain connected to the net cage. There is a positive correlation between the gravity frequency of the mooring force response and the gravity frequency of the pitch response of the net cage.

Future Change Projections of Extreme Floods at Catchment Scale and Hydrodynamic Response of Its Downstream Lake Based on Catchment‐Waterbody Relationship Simulation

AbstractExtreme riverine floods and hydrodynamic response of downstream lakes are the main focus of catchment flood control, especially under climate change. In this study, future changes in the extreme floods and their hydrodynamic responses are projected by driving the external coupling of the hydrological and hydrodynamic models using the precipitation and temperature outputs of the general circulation models (GCMs) in seven emission scenarios, and the impact of climate change is evaluated. The Baiyangdian Lake and its controlled catchment are selected as our study area. Results show that: (a) both the daily runoff and the lake water levels are well simulated, (b) compared with the baseline scenario, extreme riverine floods are projected to increase evidently throughout the catchment with mean rates of 33.2%, 14.1% and 10.9% in the RCP2.6, 4.5 and 8.5 scenarios, respectively because of increasing precipitation; consequently, the total lake inflow also increases by 13.5%–150.9%, most of which are from Zhulong, Xiaoyi, Tanghe, and Fuhe Rivers, and (c) the water level of the Baiyangdian Lake increases temporally during the flood seasons in all the scenarios, and the increase in water level is 0.27–1.29 m greater than that in the baseline scenario; consequently, the water depth in 55.8% and 73.4% of lake area increases over 1.0 m in the future short‐term and long‐term scenarios, respectively; the inundation area also increases by 23.4%–26.7% in the future scenarios, except in the long‐term RCP4.5 scenario. The northeastern and south‐central regions of Baiyangdian, which are near Xiong'an New Area, have a relatively high inundation risk.

Vortex-induced vibration and hydrodynamic characteristics of a round-ended cylinder

A round-ended section possesses the advantages of both circular and square sections, i.e. a large span and smooth transition at both ends. Therefore, the two-degree-of-freedom VIV response of a round-ended cylinder is numerically investigated in this paper in the reduced velocity (Ur) range of 2–16, comparing with the response of a circular cylinder of the same mass-damping ratio. The numerical results indicate that the development and separation of boundary layers determine the appearance of the minimum pressure coefficient, the vortex shedding mode and the characteristic sizes of wake structure. The reattachment and second separation of boundary layers are observed in the round-ended cylinder when Ur ≥ 6, contributing to a much downstream final separation point as compared to the circular cylinder. Both the hydrodynamic forces and the VIV response are closely associated with the vortex shedding mode, which is further illustrated by the variations of the added mass coefficient, the phase difference and the transferred energy coefficient. The turning points of the curves of hydrodynamic coefficients and response amplitudes correspond to the transition of vortex shedding mode as well as the switching of VIV branch. Compared to the circular cylinder, the oscillation of the round-ended cylinder presents an elongated lower branch and much smaller vibration amplitudes.

Kinematic and hydrodynamic modeling of a wire-driven robotic fishtail: An experimental study

Robotic fish have been extensively developed for scientific research and engineering applications, with the robotic fishtail serving as a crucial component. Due to the complex deformation mechanism and hydrodynamic interaction, it remains a significant challenge to establish a real-time precise kinematic and hydrodynamic model for flapping robotic fishtails. This paper presents a kinematic and hydrodynamic model for a wire-driven robotic fishtail, incorporating experimental investigation. The wire-driven mechanism featuring a continuously compliant backbone and position-variable vertebrae is developed, enabling more flexible fishtail flapping and adjustable fish morphology. The kinematic and hydrodynamic models are established through the quasi-static method with proposed corrections accounting for flapping velocity and nonlinear backbone deformation during a flapping stroke, precisely assessing real-time hydrodynamic responses. The proposed models have been validated through physical tests in an open-water environment, and exhibit superior response predictive ability compared to traditional methods. A significant force peak is observed at the beginning of a flapping stroke, while small amount of reversed thrust occurs at its end. In a high-frequency flapping motion, the soft caudal fin generates greater thrust than a hard fin. Comprehensively, this study presents a systematic research methodology for modeling and experimental investigation of novel robotic fishtails and biomimetic propellers.

A mathematical study of a two-layer fluid flow system in the presence of a floating breakwater in front of VLFS

The present study deals with the usefulness of a surface-piercing porous structure of definite width in a two-layer fluid placed at a finite distance from a floating elastic plate to mitigate the hydrodynamic response of the elastic plate. We use linear water wave theory with the eigenfunction expansion approach to develop analytical solutions to the model problem in finite water depth. Here, we identify and explore the complete parameter space associated with the problem by examining the hydrodynamic coefficients for waves in surface and internal modes, plate elevation, shear force, bending moment, wave loads on the elastic plate, flow amplitude in the plate-covered region and wave attenuation. We investigate the effectiveness of structures of various configurations and geometries on wave scattering. This study demonstrates an oscillatory pattern of wave reflection in the confined region between the plate and the breakwater. Moreover, optima in the oscillatory pattern can be observed due to the resonating interaction of waves and the breakwater-plate system. Furthermore, the research shows that an ideal width and distance between the breakwater and floating plate can be calculated while assuming an appropriate configuration of the porous structure to create a breakwater-plate system with a reasonable efficiency that possesses both reflection and dissipation properties. The design of various types of coastal structures employed in the marine environment for the reflection and dissipation of wave energy at continental shelves dominated by stratified fluid, described here as a two-layer fluid, will significantly benefit from the findings of the current study.

Wave effects on the hydroelastic response of a surface-piercing hydrofoil. Part 2. Cavitating and ventilating flows

The objective of this paper is to understand the effects of waves and vaporous cavitation upon the hydrodynamic and hydroelastic responses of a flexible surface-piercing hydrofoil, adding to the subcavitating results presented in Part 1. In general, the presence of a sufficiently large vaporous cavitation bubble facilitated the formation of a ventilated cavity, substantially reducing the angle of attack or speed required to induce fully ventilated flow, relative to subcavitating conditions. A new co-analysis procedure was used to isolate synchronous hydrodynamic modes and structural operating deflection shapes. Significant dynamic load amplification occurred when the resonant frequencies of the first twisting and second bending modes coalesced in both fully wetted and partially cavitating flows. The presence of waves did not diminish the effect of frequency coalescence, but did encourage intermittent lock-in with both leading edge cavity shedding and trailing edge vortex shedding at certain speeds. Partial cavity shedding typically had a negligible impact on the power spectral densities of structural motions because of incoherent cavity shedding. However, lock-in between the cavity shedding frequency and modal coalescence frequency led to shifting of the primary frequency peak, as well as amplified harmonics and interactions between the cavity shedding frequency and vortex shedding frequency. The transition from partially cavitating to fully ventilated flow caused sudden and large drops in the mean hydrodynamic loads and deformations, as well as substantial reductions in the intensity of the fluctuations.

Hydrodynamic response of a loam soil after wetting with different methods

Different points in a field can be wetted with different natural or artificial rainfall amounts and intensities. Therefore, a non-uniform soil wetting could occur during short-term monitoring of soil hydrodynamic parameters and its global effect on soil characterization is not easily predictable. For an initially dry loam soil, a sequence of three beerkan infiltration runs was performed at fixed sampling points in a period of two weeks. Immediately after the first beerkan run, the soil was perturbed by adding an additional water volume differing with the sampling point by the amount of water (0, 100 or 227 mm) and the application methodology (rainfall simulation, another beerkan run). As compared with the initial conditions, the soil infiltration parameters (mean, initial and final infiltration rates; constant of the Horton’s infiltration model) decreased by 2.9–4.3 times after wetting. A decrease of these parameters by 1.6–2.3 times remained detectable at the end of the sampling period, even if the soil likely returned to wetness conditions close to the initial ones. Relative variability decreased too (coefficients of variation = 52–135%, depending on the parameter, for the initial runs and 36–95% for the final ones). Nevertheless, a link was recognized between the infiltration parameters determined in the subsequent runs of the sequence. The correlation was stronger when the initial runs were compared with the last runs (coefficients of determination, R2 = 0.104–0.749, depending on the parameter; R >0 at P = 0.05 in all cases) than with those performed immediately after the intermediate wetting (R2 varying from a non-significant value of 0.059 to significant 0.196–0.211 values). The hydrodynamic response of a disturbed soil appears overall related to that of the initially undisturbed soil even if the disturbing agent is not exactly the same over the sampled area. Performing other investigations by characterizing the antecedent soil conditions in more detail could help to improve interpretation and modelling of hydrological processes by a more realistic description of temporal variability of soil infiltration parameters.

Hydro-structural response of complex elevated pile cap substructures to strom surge impact by smoothed particle hydrodynamics: Part 2: Model results

Extreme waves, i.e., tsunamis and storm surges, can generate tremendous hydraulic bores capable of inflicting considerable damage to near-shore bridge infrastructure, often leading to structural failure. The conventional numerical approach to studying hydrodynamic impact is based on Eulerian grid-based, e.g., finite volume or diffused element algorithms. These perform well with perfectly defined simulation domains. However, in case of severe surface deformation, these grids must be continually reconstructed, which is time-intensive and introduces cumulative system errors. As Smoothed Particle Hydrodynamic (SPH) integrates the hydrodynamic equations of motion on each particle in Lagrangian formalism, it can handle complex wave non-linearity without mesh constraints. In this study opensource DualSPHysics model is applied to study the hydrodynamic response and group effect of elevated pile cap substructures to impulsive surge impact. Two conventional grids (2 × 2, 2 × 3 array-layout) and a hexagonal pile arrangement under three submersion levels are considered in studying the pile group effect on hydrodynamic forcing mechanism, flow characteristics, and factors governing pressure variability. The uplift thrust on the pile cap was found to be dependent on the surge fluid mass, incident velocity, and vertical distance between the surge breaking point and cap bottom. At impulsive impact, gridded pile arrangement offered greater resistance to incident surge flow. In reference to free flow condition, hexagonal layout can reduce the average flow velocity by 8.22–19.76%, while for a gridded system, it is between 14.00% and 23.52% depending on the submersion level. However, in a quasi-steady state, the flow resistance of the hexagonal system was greater. The study also compared the numerical results to accepted offshore design standards, which were found to underestimate the pile's group effect, specifically for complex hexagonal layouts. Later, it proposes rationalized force diagrams to be applied in design of complex elevated structures. The paper's finding is expected to contribute to formulating new guidelines for resilient hydraulic design of coastal and deep-water elevated structures.

Dynamic analysis of the umbilical cable pull-in operation through J-tube under different wave directions

Pipelines and cables are widely used for transporting oil resources in offshore oil exploitation. J-tubes are a well-known means of placing small-diameter pipeline risers and umbilical connections on offshore platforms. In this paper, OrcaFlex develops a model of an umbilical cable J-tube pull-in installation based on an umbilical cable cross section design. The hydrodynamic response to various wave directions is studied using the lumped mass method. The results show that the longitudinal waves have little effect on the maximum effective tension of the section under water. The transverse waves will cause the cable to vibrate violently in the transverse direction. The mean shear force under the wave direction of 120° is the largest, followed by 60° and 75°, and finally 90° and 105°. In addition to the hydrodynamic response data, the mechanical characteristics of the umbilical cable and the factors that should be considered in the pull-in installation of the J-tube are provided with significance for practical application of engineering.

Structural dynamic performance of floating continuous beam bridge under wave and current loadings: An experimental study

Very large floating bridges supported by pontoons are thought to have a promising prospect in crossing the wide and deep water areas, especially for those with weak foundation. The floating bridges are directly subjected to the wave and current actions, and remains in the state of stochastic vibration during their whole service life; thus, the dynamic behavior is an important issue in the structural design process of such type of structure. However, limited experimental researches on the floating bridge structures have been reported in literature. This paper presents a scaled model test regarding to a floating continuous beam bridge with mooring system, where the actions of wave, current, and their combinations are considered. The hydrodynamic responses of the structure, including the displacements, internal forces and support reactions, have been finely measured by the established data collection system. The recorded data have been processed based on statistical and spectral analyses, so as to comprehensively investigate the hydrodynamic characteristics of the tested floating bridge, and further to identify the influences of wave and current loads on the structural performance. The presented research work gives an insight on the hydrodynamic performance of the deep-water floating continuous beam bridge with mooring system, and also extends the experience on the design and implementation of the experimental study of floating bridge structures. The presented test data can also provide a reference for the calibration of numerical investigations.

Wave power extraction by Multi-Salter's duck WECs arrayed on the floating offshore wind turbine platform

Integrating a floating offshore wind turbine (FOWT) and an array of wave energy converters (WECs) can be suggested as a proper new hybrid concept with the aim of more energy harvesting and lower total energy cost. This paper proposes the new composition of a floating braceless semi-submersible platform and an array of Salter's duck (SD) WECs. First, a comparison of the numerical results and experimental data of the hydrodynamics response of FOWT and the single SD WEC response are presented and discussed. Then, the performance of three-hybrid FOWT-Multi-Salter's Duck (FOWT-MSD) systems with 12SD, 15SD, and 18SD WECs has been investigated under different wave periods and wave heights. In the wave period of 6–9 s, 12SD absorbs more power than 15SD and 18SD. From T = 9–11 s, all three systems have the same absorbed power. For wave periods above 12 s, 15SD and 18SD have higher absorbed power than 12SD. No clear trend was observed for wave periods below 6 s. The effect of wave direction shows that at lower wave heights, maximum absorber power belongs to FOWT-12SD under zero wave direction. In contrast, increasing wave heights leads to a smaller difference between the three-hybrid systems at different wave directions.

Experimental investigation of a Multi-OWC wind turbine floating platform

The worldwide energy supply needs to be enhanced following the expanding of electrical energy request. Marine renewable energies have the potential to partially cover the incoming energy growth but the economic unfeasibility slows down their exploitation. Specifically, the viability and technological development of Wave Energy Converters could be improved through the integration into already existing offshore structures. Against this background, this work proposes a novel concept of hybrid platform composed of a spar buoy wind turbine integrated with three Oscillating Water Columns (OWCs). An experimental investigation is carried out in the wave basin of Marine Technology Research Institute (CNR-INM, Rome, Italy) aiming to analyze of the performance of the hybrid system prototype. The scaling procedure and the experimental setup are described. The focus of the analysis is on the hydrodynamic behavior of the OWCs’ air chambers considering both wave and wind loads. The influence of the wind action and the effect of air chambers damping variation on the dynamic behavior of the floating platform are deepened towards the resulted power extraction performances of the OWCs. Different wind and wave conditions are considered to test the scaled model. As result, the OWCs hydrodynamic response is positively affected by angular motion of the platform, due to the influence of the wind loads. The increasing in the damping affects the air pressure and the relative water level inside the OWCs, hence the mean extracted power.

The Effect of a Linear Free Surface Boundary Condition on the Steady-State Wave-Making of Shallowly Submerged Underwater Vehicles

Near-surface simulation methods for shallowly submerged underwater vehicles are necessary for the population of a variety of free-surface-affected, coefficient-based maneuvering and seakeeping models. Simulations vary in complexity and computational costs, often sacrificing accuracy for simplicity and speed. One particular simplifying assumption, the linearization of the free surface boundary conditions, is explored in this study by comparing the steady-state wave-making characteristics of a shallowly submerged prolate spheroid using two different simulation methods at several submergence depths and forward speeds. Hydrodynamic responses are compared between a time-domain boundary element method that makes use of a linearized free surface boundary condition and an inviscid, volume of fluid Reynolds-Averaged Navier–Stokes computational fluid dynamics code that imposes no explicit free surface boundary condition. Differences of up to 22.6%, 32.5%, and 33.3% are found in the prediction of steady state surge force, heave force, and pitch moment, respectively. The largest differences between the two simulation methods arise for motions occurring at small submergences and large wave-making velocities where linear free-surface assumptions become less valid. Nonlinearities that occur in such cases are revealed through physical artifacts such as wave steepening, wave breaking, and high-energy waves. A further examination of near-surface viscous forces reveals that the viscous drag on the vessel is depth dependent due to the changing velocity profile around the body.

Field Observation and Quasi-3D Numerical Modeling of Coastal Hydrodynamic Response to Submerged Structures

Even though submerged breakwater reduces incident wave energy, it redistributes the coastal area's wave-induced current, sediment transport, and morphological change. This study examines the coastal hydrodynamics and the morphological response of a wave-dominated beach with submerged breakwaters installed through field observation and quasi-3D numerical modeling. The pre-and post-storm bathymetry, water level, and offshore wave under storm forcing were collected in Bongpo Beach on the East coast of Korea and used to analyze the coastal hydrodynamic response. Four vertically equidistant layers were used in the numerical simulation, and the wave-induced current was examined using quasi-3D numerical modeling. The shore normal incident wave (east-northeast) generated strong cross-shore and longshore currents toward the hinterland of the submerged breakwater. However, the oblique incident wave (east-southeast) induced the southeastward longshore current and the sedimentation in the northeast area of the beach. The results suggested that the incident wave direction is a significant factor in determining the current and sediment transport patterns in the presence of the submerged breakwaters. Moreover, the quasi-3D numerical modeling is more appropriate for estimating the wave transformation, current, and sediment transport pattern in the coastal area with the submerged breakwater.

Stress Distribution on the Preliminary Structural Design of the CENTEC-TLP under Still Water and Wave-Induced Loads

An assessment is made of the stress distribution and the hydrodynamic response of the preliminary structural design of the tension leg platform of a 10 MW wind turbine. The platform supporting a 10 MW turbine is modelled and analysed by the finite element method. The stress distribution of the platform is determined in still water with the turbine at above-rated conditions, and the response of the tension leg platform is estimated in the time domain. The results of the time domain analysis show reasonable agreement between the present results and the available data. To check the design stiffener dimensions, span, and spacing against stress distribution, classification societies’ recommendations are used. The results of the stress distribution analysis indicate that the critical locations of the platform are the interaction of the lower columns with the upper columns and the connection of the tower of the turbine.

Numerical developments on the E-Motions wave energy converter: Hull design, power take-off tuning and mooring system configuration

This paper addresses a recently conducted numerical study on the E-Motions wave energy converter, aimed at improving its energy performance and efficiency. The Potential Flow Theory-based ANSYS® Aqwa™ software was used, being a robust industry-standard code that has been successfully applied to the E-Motions case study, in the past. Data from a preceding physical modelling campaign was applied towards calibration procedures for three platform variants – half-cylinder, half-sphere and trapezoidal prism, with and without the power take-off and subjected to regular waves. A non-dimensional root mean square error minimization approach was employed. Afterwards, the focus shifted towards defining and comparing the performance of sixteen E-Motions sub-variants, which included a new hull shape: enclosed frustum. Two additional stages were carried out: one oriented towards assessing ten power take-off mass-damping combinations and another to the study of four mooring system configurations. Results point towards a very significant hydrodynamic response, particularly within the resonance range and for the half-cylinder and half-sphere sub-variants, and maximum average power outputs of nearly 40 kW. For the best half-cylinder, half-sphere, trapezoidal prism and enclosed frustum sub-variants, the annual energy production estimates, per device, were 141, 110, 106 and 91 MWh/yr, respectively.

A locally corrected multiblob method with hydrodynamically matched grids for the Stokes mobility problem

Inexpensive numerical methods are key to enabling simulations of systems of a large number of particles of different shapes in Stokes flow and several approximate methods have been introduced for this purpose. We study the accuracy of the multiblob method for solving the Stokes mobility problem in free space, where the 3D geometry of a particle surface is discretised with spherical blobs and the pair-wise interaction between blobs is described by the RPY-tensor. The paper aims to investigate and improve on the magnitude of the error in the solution velocities of the Stokes mobility problem using a combination of two different techniques: an optimally chosen grid of blobs and a pair-correction inspired by Stokesian dynamics. Different optimisation strategies to determine a grid with a given number of blobs are presented with the aim of matching the hydrodynamic response of a single accurately described ideal particle, alone in the fluid. It is essential to obtain small errors in this self-interaction, as they determine the basic error level in a system of well-separated particles. With an optimised grid, reasonable accuracy can be obtained even with coarse blob-resolutions of the particle surfaces. The error in the self-interaction is however sensitive to the exact choice of grid parameters and simply hand-picking a suitable geometry of blobs can lead to errors several orders of magnitude larger in size. The pair-correction is local and cheap to apply, and reduces the error for moderately separated particles and particles in close proximity. Two different types of geometries are considered: spheres and axisymmetric rods with smooth caps. The error in solutions to mobility problems is quantified for particles of varying inter-particle distances for systems containing a few particles, comparing to an accurate solution based on a second kind BIE-formulation where the quadrature error is controlled by employing quadrature by expansion (QBX).

Effect of cable layout on hydrodynamic response of submerged floating tunnel under wave action

A submerged floating tunnel (SFT) is a new type of traffic-crossing scheme in relatively deep waters that realizes suspension fixation through gravity, buoyancy, and cable force. The cable mainly constrains the SFT, and its layout has a critical impact on the dynamic characteristics of the SFT. In this study, hydrodynamic experiments are conducted on a reduced-scale model of the SFT under regular waves. The acceleration of the SFT tunnel, cable force, wave height, and other data are collected. The dynamic response of the SFT with three cable layouts (parallel, inclined, and mixed) is analyzed. Results show that the dynamic response of the SFT with a parallel cable layout is considerably less than that of the other two cable layouts under the action of regular waves. The amplitude of cable force at the upstream side is generally less than that at the downstream side for the inclined cable of the SFT with inclined and mixed cable layouts. The cable slack phenomenon reduces the overall constraint stiffness of the SFT, and the dynamic response considerably exceeds that under non-slack conditions. Resonance zone and long-period waves are the main excitations causing the motion of SFTs when the submerged depth is at safe level.