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An analytical model of an array of moored floating flexible net cage systems is developed to study the dynamics and wave loads on the net cages under the linear water wave theory and small-amplitude wave response assumption. The Fourier–Bessel series expansion of the velocity potential is derived for the regions enclosed under the open-water and cage systems and their proximity. The theoretical solution is obtained by employing the least squares approximation method along with matching the velocity and pressure at the fluid-structure interfaces. The present result of horizontal displacement and horizontal wave load are compared with a published finite element analysis and with experimental data sets, respectively. Further, the results of cage displacements, cage accelerations, and wave loads on the different arrangements for mooring stiffness, cage radius, cage heights, and current speeds are compared and analysed. Moreover, the present analysis will be helpful to understand designing further a multiple floating fish cage system with flexible floaters application to offshore aquaculture. • A semi-analytical model for wave interaction with an array of moored flexible cylindrical net cage is developed. • The analytical solution is obtained using Fourier Bessel series solution and least squares approximation method. • The obtained results of the cage displacement compared well with the numerical FEA simulation in the literature. • The cage displacements and wave loads for different design parameters and cage arrangements are analysed in detail. [ABSTRACT FROM AUTHOR]

The wave-powered boat is a kind of mobile marine platform that can convert wave energy into thrust through the rotation of the hydrofoils. The rotation control method of the hydrofoil has a significant impact on the propulsion performance of wave powered-boats when considering ocean currents. In this paper, by establishing an equivalent instantaneous optimization model for the motion of the hydrofoil, the rotation angle that can obtain the maximum thrust is analyzed, and the relationship between the rotation angle, hydrofoil motion velocity as well as the current velocity is obtained. Subsequently, the propulsion performance of the hydrofoil under the active control method is compared with that under the passive control method through the fluid-multibody coupled analysis, and the motion parameters of the hydrofoil are explored, thus the feasibility of active control when considering the ocean currents is verified. It can be seen that the active control method based on the optimal rotation angle equation can significantly improve the propulsion performance of the wave-powered boat in the presence of currents. Under the passive control method, either increasing the stiffness or increasing the co-current velocity will make the rotation process of the hydrofoil fluctuate and disorderly. In contrast, the active control method can stabilize the rotation process of the hydrofoil, and the hydrofoil is always in a position where the maximum thrust can be obtained during rotation, thus making the propulsion performance better. The relevant research in this paper can provide a reference for similar research of the wave-powered boat. • An instantaneous optimization analysis model of the hydrofoil motion is established. • The relationship between the optimal rotation angle, hydrofoil motion velocity as well as the current velocity is obtained. • The propulsion performance of the hydrofoil under different control methods is compared. [ABSTRACT FROM AUTHOR]

Dynamically installed anchor is an innovative and cost-effective technology in marine foundation engineering. However, most of the existing researches on the hydrodynamic characteristics of dynamically installed anchors are limited to their free-fall installation performance in water without considering the action of marine environmental loads such as current. Therefore, this study aims to investigate the hydrodynamic performance of dynamically installed anchors subjected to current in a systematical manner. A complete three-dimensional CFD model is firstly established using "dynamic model analysis" method. Then, the effects of anchor geometric characteristics on the installation efficiency (i.e., penetration velocity and drag coefficient) and installation positioning accuracy (i.e., lateral velocity and displacement, and inclination angle) of the anchors subjected to current are systematically studied using the established CFD model. The influences of current velocity, current direction and geometric characteristics including anchor shaft geometry and anchor fin geometry on the hydrodynamic characteristics of anchor are discussed. Based on the obtained findings, some practical design recommendations are given, and a simple semi-empirical method for estimating the falling velocity and inclination angle of dynamically installed anchor subjected to current considering anchor geometric effects is finally proposed, which may benefit the engineering design of dynamically installed anchors. • Effects of anchor geometry characteristics on hydrodynamic performance of DIAs under current action were investigated. • Practical significance of geometric design and recommended configuration of DIAs under current action were provided. • A semi-empirical method for estimating the falling velocity and inclination angle of DIAs under current action was proposed. [ABSTRACT FROM AUTHOR]

During the launch operation of subsea equipment in the offshore industry, several factors are important for a safe and economical installation within an operating window. One of these factors is the hydrodynamic coefficients of the equipment to be installed. The coefficients can be obtained, experimentally or numerically, by applying an oscillatory motion that represents the effects of sea conditions and vessel motion, but these applications simplify conditions during a real operation and disregard important effects such as ocean currents. This paper investigates numerically the effect of current together with forced oscillation on the hydrodynamic coefficients of disks by analyzing two influence parameters, the Keulegan-Carpenter number (K C) and the reduced current velocity (V r). A numerical model validation process was carried out in stages to overcome the lack of references on the subject. The model was compared with Direct Numerical Simulation (DNS) results for low Reynolds number (R e), up to 600, in qualitative and quantitative analysis, and then applied to broader conditions found in real operations, with K C up to 3 , V r up to 0.3 , and for high R e , up to 240,000. On the model scale, higher V r generates an increase in the drag coefficient (C d) and a decrease in the additional mass coefficient (C a). Under real scale conditions, the results are similar, with variations of C d up to 300% and of C a up to 36% for low K C. Analysis of the flow topology indicates that K C and V r influenced vortex shedding and convection. Correlations for the hydrodynamic coefficients as functions of K C and V r are proposed, with a R 2 higher than 93%. • Selected RANS turbulent models presented results similar to DNS simulations for cases of forced oscillation with current for low R e. • The analysis was carried out at a higher R e , similar to a real scale, indicating an increase in drag coefficient and reduction in added mass for high currents. • The flow topology due to oscillatory movement and current shows an influence on vortex shedding. • For the first time, the influence of higher K C and current on the hydrodynamic coefficients was established. • Correlations are proposed for the hydrodynamic coefficients as functions of K C and V r , with a R 2 > 93 %. [ABSTRACT FROM AUTHOR]

Current is a key ocean-environmental factor and exhibits strong non-stationary random characteristics. The complexities of current modeling present significant challenges for deep sea oil exploitation. The multiyear return period extreme current model is one of the key factors for the reliable design of marine structures. Recently, due to limitations of design specifications and guidelines, improved methods to predict extreme values for the South China Sea based on prototype monitoring are required. In contrast to the traditional extreme value analytical method, the newly developed Average Conditional Exceedance Rate (ACER) method is robust and shows good accuracy for estimations of ocean environmental loading. The method offers good reliability for short-term prototype monitoring data. This study performs multiyear return period extreme value prediction of the current profile based on prototype monitoring data collected in the Liuhua (LH11-1) oil field that was recorded by an in-situ monitoring system. The 1-year and 10-year return period current velocity design indexes were obtained using the ACER method. The present current velocity profiles of multi-year return periods were compared with two design current load indexes of two floating platforms in Liuhua area. The consistency with comparison to TLP platform design indexes shows that the ACER method provides the accuracy and flexibility of the results needed in the construction of current load models in the South China Sea. These results could provide the basis and reference for the design of offshore structure. [ABSTRACT FROM AUTHOR]

The role of wave blocking on flexural gravity wave motion with oblique incidence and current is discussed. The oblique wave incidence due to a finite floating elastic plate is investigated using the eigenfunction expansion method. The role of different wave propagating modes on reflection coefficient is discussed. The reflection and transmission coefficients, the surface elevation, and plate deflection in the presence of current are derived. The effects of flexural rigidity and the uniform current speed on reflection and transmission coefficients are analyzed. The resonating nature of reflection coefficient for some fixed values of plate length is observed. Significant effects of different combinations of wave propagating modes of plate covered regions and open water regions on the reflection and transmission coefficients are observed. The wave energy propagation from reflection coefficient decreases whenever the Froude number increases. It has been found that the amplitude of the plate deflection increases as the value of the Froude number increases. The amplitude and wavelength of the reflection coefficient are higher for the combination of the first propagating mode of the plate covered region and the second propagating mode of the open water region. Moreover, it is found that zero reflection and full transmission occurs periodically. Co-propagating waves are found to transmit more energy while counter-propagating waves reflect more energy. Higher values of flexural rigidity result in reduced wave energy transmission. • The effect of current on wave scattering problem is analyzed • The reflection and transmission coefficients are derived in the presence of current. • The role of blocking dynamics on reflection coefficients is discussed • Nature of different combinations of wave propagating modes is discussed • The impact of current on surface elevation and plate deflection is analyzed. [ABSTRACT FROM AUTHOR]

Wave nonlinearity can drive the near-bed sediment transport and nutrient delivery on coral reefs. Previous studies have primarily concentrated on the wave nonlinearity evolution for a specific cross-shore profile and have scarcely taken the effects of currents into consideration. To better understand the nonlinear wave transformation on reef coasts, the wave height distribution and wave nonlinearity evolution are analyzed based on 3D reef-lagoon-channel experiments in a wave basin. By taking the current velocity into consideration, the Glukhovskiy distribution function is improved in calculating the probability of large wave height in the sequence. Wave skewness and asymmetry on the reef and in the channel are parameterized with the Ursell number considering the Doppler effect induced by opposing or following currents. The accuracies for estimating wave skewness and asymmetry are improved by 39% and 66%, respectively. The influence of Doppler effect on wave shapes on the reef flat and in the channel varies significantly with the incident wave heights and reef submergences. Furthermore, it is also noticed that the reduction of local water depth caused by the propagation of infragravity wave troughs increases short-wave skewness at individual wave scale on the middle of reef flat, while its effect on short-wave asymmetry is not significant. • Nonlinear waves are analyzed on a 3D reef-lagoon-channel system. • By taking currents into consideration, the Glukhovskiy distribution function is improved. • Wave nonlinearities are parameterized with the Ursell number considering the Doppler effect. [ABSTRACT FROM AUTHOR]

A set of three-dimensional numerical models is established to investigate the mechanisms of local scour around three adjacent piles with different arrangements under steady currents. The RANS equations, closed with a R N G k − ε turbulence model, are established for simulating the flow field around pile groups. A sediment scour model is adopted to estimate the motion of the sediment by predicting the erosion, advection, and deposition of the sediment. The simulation results of the bed elevation contours and the time evolution of scour depth around a single pile model are verified with the previous experimental results and show good agreement. Then, the effects of pile spacing for three adjacent piles with different arrangements on the flow field, bed elevation contours, and scour depth are discussed in detail. The results reveal that the dimensionless pile spacing has a significant effect on the flow field and local scour around the three adjacent piles. The scour hole patterns and scour depth around each pile with different arrangements are totally different. [ABSTRACT FROM AUTHOR]

Accurate characterisation of flows at tidal sites can enable the developers of tidal stream energy projects to design and model the loads on, and the performance of, tidal energy converters. Acoustic Doppler technology is versatile in the measurement of sea conditions; however, this technology can be limited in its effectiveness at measuring the small-scale kinematic fluctuations caused by waves and turbulence. A Virtual Doppler Current Profiler (VDCP) is used to sample a simulated tidal flow to understand the limitations of this type of measurement instrument whilst recording the small timescale kinematics of waves and turbulence in tidal currents. Results demonstrate the phase dependency of velocity measurements averaged between two acoustic beams and provide a theoretical error for wave and turbulence characteristics sampled under a range of conditions. Spectral moments of the subsurface longitudinal wave orbital velocities recorded by the VDCP can be between 0.1 and 9 times those measured at a point for certain turbulent current conditions, turbulence intensity measurements may vary between 0.2 and 1.5 times the inputted value in low wave conditions and turbulence length scale calculation can also vary hugely dependent on both current and wave conditions. The continuation of this work will enable effective comparison of a linear model for tidal flow kinematics against field measurements from UK tidal site data, and subsequently validate numerical models for the testing of tidal turbines. [ABSTRACT FROM AUTHOR]

A novel integrated offshore design, JOWT-SC, which combines a jacket-supported offshore wind turbine structure (JOWT) with an aquaculture steel cage (SC), is proposed in this paper. The enclosed steel cage in the integrated design can adjust to changes in water depth, preventing the fish from escaping. The jacket structure is equipped with two decks and a 10 MW reference wind turbine that provide steady electricity for the offshore fish farm. The numerical modeling and time-domain simulations were conducted in software SACS, and the dynamic responses of the JOWT-SC were also compared with the baseline JOWT, that is without a steel cage. The considered environmental conditions include waves measured from the southeast open sea area of Fujian in China, several wind speeds that represent normal operating conditions for the reference wind turbine, and a constant current flow. The results of the study demonstrate that the aquaculture steel cage significantly influences the dynamic responses of the integrated JOWT-SC substructure, and the pile-foundation shear responses are more sensitive to the wave frequency. In particular, the cage increases the hydrodynamic responses of the JOWT-SC at the mudline under the combined action of winds, waves, and currents, compared with the case where the JOWT-SC is only subjected to wind loads. Overall, the results of this study can be used as a reference for the realization of novel designs in practical engineering. • A new design concept integrating a jacket offshore wind turbine with a steel cage (JOWT-SC) is proposed. • The fishing nets of JOWT-SC are simplified as rigid member elements, ignoring their deformation. • The dynamic responses of JOWT-SC are influenced due to the existence of the cage. • Compared with the JOWT, the influence of wave frequency on the pile-foundation shear of JOWT-SC increases. [ABSTRACT FROM AUTHOR]

Interactions between solitary waves and structures in a steady current are studied based on a fully nonlinear wave potential theory, and a higher order finite element method (FEM) with a mesh of 8-node quadrilateral isoperimetric elements is employed to simulate the interaction in two-dimensions. Numerical examples are given by solitary waves propagating over an underwater rectangular cylinder in a steady current in a tank and solitary waves acting on single- and twin-rectangular cylinders in a steady current on free surface. Waves and hydrodynamic forces are obtained at different current speeds. It is found that the peak of diffracted wave due to the first and second reflections by an underwater cylinder clearly increase in following current. Furthermore, a packet of periodic waves with constant peak and trough are found to appear when the absolute value of the Froude number becomes large enough in single- and twin-cylinder cases. For the twin-cylinder cases, the maximum wave and horizontal force are clearly affected by the current especially in larger incident wave amplitudes and smaller spacings. In addition, the nonlinearity of wave or force becomes stronger at larger Froude numbers and larger incident wave amplitudes. • The interaction between a solitary wave and an underwater structure in a steady current is studied. • The intersection between a solitary wave and a single- and twin- floating cylinder in a steady current are analyzed. • The wave elevation and hydrodynamic forces on the structures under co-action of waves and currents are investigated. • The nonlinear features of wave and the hydrodynamic force at different current speeds are clear. [ABSTRACT FROM AUTHOR]

Whilst the concept of the current drag and lift forces on ship-like vessels is widely used, the hydrodynamic inertial forces due to time-varying current are usually not considered and not captured in the calculation methods. The objective of this article is to examine such forces on a weathervaning vessel by applying classical formulations of fluid mechanics. Based on the general expressions for the inertial forces on a body moving in an accelerating flow of an ideal fluid, the formulation applicable for a single-point moored vessel is presented and illustrated by examples. The effect of an oscillatory current is considered further and two limiting scenarios are examined: a periodically oscillating current acting on a vessel with a fixed mooring point (turret) and oscillatory motion of the vessel in a stationary fluid; the two scenarios corresponding to a relatively stiff and soft mooring system, respectively. Both problems are solved by the direct separation of motions, a perturbation method known in vibrational mechanics, and expressions for the mean drift forces are obtained. In both cases, the mean surge force is found to be positive, acting towards the mooring point, and the mean sway force produces a restoring moment which tends to stabilize the vessel in the direction of the current flow. A calculation example is presented and results are discussed. This study concludes that, depending on the current regime, the inertial forces due to time-varying current may be of the same order of magnitude as the quasi-steady forces, their importance increasing for lower mean current speeds. • Hydrodynamic inertial forces on a single-point moored vessel due to time-varying current. • Mean drift forces due to fluctuating current or oscillatory vessel motions. • Comparison of the inertial current forces with quasi-steady forces. [ABSTRACT FROM AUTHOR]

The development of a novel type of hybrid underwater glider (HUG) that combines the advantages of buoyancy-driven underwater glider and propeller-driven autonomous underwater vehicle (AUV) has recently received considerable interest. HUG is designed with a rotatable thruster to ensure the enough maneuverability of the vehicle for underwater docking. Unlike the fixed funnel-type dock, the dock proposed here can rotate actively to allow the vehicle to approach the docking station from most range of directions providing better accessibility for the vehicle. Considering that the ocean current may have a significant impact on the HUG, a pursuit guidance algorithm with current compensation is presented. The performance of the guidance algorithm is compared with other existing guidance algorithms, such as pure pursuit guidance and proportional navigation guidance by simulation based on the dynamic model of HUG. Moreover, underwater docking experiments are conducted to validate the feasibility of the docking system and the effectiveness of the proposed guidance algorithm. The experimental results indicate that the proposed algorithm compensates well for the current disturbances on HUG docking mission and the HUG can dock with the rotatable dock entrance successfully. [ABSTRACT FROM AUTHOR]

In recent years, local scour has received attention because it may have a negative effect on coastal structures. Because of the large-scale arc transition and other special constructs, flow patterns around composite bucket foundation are complicated, and the local scour around composite bucket foundation has rarely been reported in the literature. In the present study, a detailed laboratory testing program on model with diameters of 150 cm and 75 cm embedded in silty sand was conducted in a flume. The scouring process and equilibrium scour hole geometry under steady and bidirectional current were investigated in detail. A procedure was suggested to predict the ultimate scour depth based on the observed variation of the scour depth over a limited time period. The equilibrium scour depth under a bidirectional current was approximately 16% less than that under a steady current, and there were two spoon-shaped scour holes in the steady current scour, whereas four saddle-shaped scour holes were discovered in bidirectional current scour. Based on these results, a functional relationship was suggested between the scour depth and other parameters, such as the diameter of the foundation, Shields parameter and median diameter of the soil bed. [ABSTRACT FROM AUTHOR]

One means of producing a 3D current in a circular tank is by using groups of conditioned axial flow impellers arranged around the perimeter to collectively create a sea representative bulk flow in a laboratory setting. Unfortunately to achieve the required bulk flow neighbouring impellers have to operate at different speeds resulting in steps in the plan view velocity profile. Therefore the underlying situation that governs tank behaviour is that of two fluid streams at different speeds combining, leading to a turbulent mixing layer which then dissipates and develops. Here a simulation of this flow is created using a 2D Reynolds Averaged Navier–Stokes method and then validated with physical experiments. The implications for accuracy and computational costs of various turbulence models, boundary conditions setups, and geometry representations are assessed. These findings are then used to produce a simplified 2D numerical model of the plan view flows in a 3D test tank which is then employed to demonstrate how a satisfactory device test zone might be generated from groups of stepped inputs. This finding helps prove that a combined current and wave tank can be created using the described configuration with the model providing a useful means of testing control scenarios. [ABSTRACT FROM AUTHOR]

The manoeuvring behaviour of a vessel in currents differs remarkably from its behaviour in water without a current, stemming from hydrodynamic effects caused by the presence of the current. Given that vessels operating in open seas and coastal waters are mostly exposed to ocean currents, it is important to have an understanding of the influence of currents on ship manoeuvrability. In the present paper, by means of an unsteady Reynolds-Averaged Naiver-Stokes solver, a numerical study of ship manoeuvrability in different currents was performed. Firstly, a model-scale container ship (the KRISO Container Ship) was used to develop the Computational Fluid Dynamics (CFD) model capable of performing a self-propelled free manoeuvre. Then, a validation study was carried out to assess the validity of the CFD model by comparison with the available experimental results from a free-running test. Following this, a series of manoeuvring simulations (i.e., standard turning manoeuvres) in deep waters with current speed to ship speed ratios varying between −0.552 and −0.138/+0.138 and + 0.552 were conducted using the present CFD model. The numerical results demonstrated that the inclusion of the current has a remarkable influence on the turning performance of the ship, leading to significant changes in the ship trajectory and its turning parameters when compared to the inherent ship manoeuvrability in deep water without a current. • Free-running CFD simulations were performed to evaluate the turning performance of the KCS in currents. • A validation study was carried out to assess the validity of the CFD model. • The inclusion of the current has a remarkable influence on the turning performance of the ship. • It is highly believed to offer a deeper understanding of the ship manoeuvrability in currents. [ABSTRACT FROM AUTHOR]

Abstract: It is necessary to build a new generation of current and wave testing tanks to simulate more realistic sea conditions. Methods for wave generation and absorption are well established but those for current generation in this context are less established. One means of producing a current is by using an axial flow impeller. Unfortunately an impeller introduces into the flow unsteady velocities with high shear, strong turbulent fluctuations and hub effects, alongwith the useful thrust. In the experiment presented here honeycomb flow conditioning placed immediately downstream of the impeller is used to reduce the turbulence present in the flow. An Acoustic-Doppler Velocimeter (ADV) is used to measure three velocity components at a rate sufficient to characterise turbulence. A novel experimental arrangement using brush seals allows the ADV to penetrate the duct without compromising the integrity of the duct. A large number of point measurements were used to construct velocity profiles at various positions downstream of the honeycomb. Three different impeller speed settings were tested to investigate wake evolution. The results presented will aid the development of numerical models and increase understanding of the flow downstream of a conditioned impeller. [Copyright &y& Elsevier]

Abstract: This paper assesses the current speed data measured during different sorties across the Bosphorus on the southern coastal areas. The spatial model works on stochastic methodology for the purpose of current speed prediction at different depths within the target area. Current power generation formulation in accord with the current speed probability distribution in the Bosphorus has been developed and a simple numerical sample is presented. The current speed probability distribution function (pdf) accords theoretically with the Gamma pdf. Necessary current power estimation formulation is developed parametrically and by considering the cut-in lower current speed as 1.0m/s. The application of the methodology for more than 1.0m/s current speed yields to 0.736kW power per unit m2 turbine area and per second. [Copyright &y& Elsevier]

Abstract: Experiments on three types of soil (d 50=0.287, 0.057 and 0.034mm) with pipeline(D=4cm) either half buried or resting on the seabed under regular wave or combined with current actions were conducted in a large wave flume to investigate characteristics of soil responses. The pore pressures were measured through the soil depth and across the pipeline. When pipeline is present the measured pore pressures in sandy soil nearby the pipeline deviate considerably from that predicted by the poro-elasticity theory. The buried pipeline seems to provide a degree of resistance to soil liquefaction in the two finer soil seabeds. In the silt bed, a negative power relationship was found between maximum values of excess pore pressure p max and test intervals under the same wave conditions due to soil densification and dissipation of the pore pressure. In the case of wave combined with current, pore pressures in sandy soil show slightly decrease with time, whereas in silt soil, the current causes an increase in the excess pore pressure build-up, especially at the deeper depth. Comparing liquefaction depth with scour depth underneath the pipeline indicates that the occurrence of liquefaction is accompanied with larger scour depth under the same pipeline-bed configuration. [ABSTRACT FROM AUTHOR]

Abstract: It was necessary to obtain a more practical interactive precise model of the three-dimensional (3-D) geometry during purse seine operations considering movements of fishing vessel and details of the sea condition. The changes in the shape of a purse seine from shooting to pursing during pelagic skipjack fishing was recorded in the Southwest Pacific Ocean by photographs of the scanning sonar with in situ measurements of water flow by a current meter. The modeling of 3-D geometry during purse seining was established using finite element methods, as resultant force vector from flow drag, buoyancy, sinking force, tension of pulling or pursing acting on net panels in connection with drift of fishing vessel with time elapsed from the start of shooting to the end of pursing. The simulation results were matched closely by field measurements as a heart-like shape in upper net near floatline and a water-drop shape in purse line following drift of ship towards inside net circle during pursing. This model of a purse seine can be extended to almost any kind of purse seine generating real fishing parameters and to modeling fish capture process. [Copyright &y& Elsevier]

Abstract: This paper provides a method by which the scour depth below pipelines and around single vertical piles for combined random waves plus current including effects of second-order wave asymmetry can be derived. Here the empirical formulas proposed by Sumer and Fredsøe [1996. Scour below pipelines in combined waves and current. In: Proceedings of the 15th OMAE Conference, Florence, Italy. Vol. 5, ASME, New York, pp. 595–602] for pipelines, and by Sumer and Fredsøe [2002. The mechanics of scour in the marine environment. World Scientific, Singapore] for vertical piles are used together with Stokes second-order wave theory by assuming the basic harmonic wave motion to be a stationary Gaussian narrow-band random process. Comparisons are made with the Sumer and Fredsøe [1996. Scour below pipelines in combined waves and current. In: Proceedings of the 15th OMAE Conference, Florence, Italy. Vol. 5, ASME, New York, pp. 595–602; 2001. Scour around pile in combined waves and current. Journal of Hydraulic Engineering, 127(5), 403–411] data for linear random waves plus current. An example of calculation is also presented. [Copyright &y& Elsevier]

The prediction of wave run-up is a major issue when designing offshore structures, such as offshore wind turbine foundation. In this study M5ʹ model tree algorithm was used to predict the wave run-up for CBF due to regular wave and current. This study investigated wave-only and wave–current run-up on a CBF via model tests. The influences of the relative wave height, wave steepness, and Froude number on the relative run-up were investigated. Based on different combinations of non-dimensional parameters, the performance of novel formulae developed using the M5ʹ model tree (M5MT) algorithm was analysed in terms of statistical error indexes. The relative wave run-up was found to increase with the wave steepness, and under low water depth increase with the Froude number for low wave steepness. Based on the scatter parameter, relative water depth, the prediction formulae developed exhibited optimal performance when predicting run-up under wave-only conditions. New formulae with a reliable precision were developed for wave–current conditions based on the scatter parameter, wave steepness, relative wave height, and Froude number. The experimental results and proposed run-up formulae will assist engineers in the design of CBFs. • Run-up on composite bucket foundation is investigated under wave-current conditions. • M5' model tree algorithm was implemented to develop new formulae in run-up prediction. • Different combinations of parameters are selected to construct M5' model trees. • Scatter parameter plays the key role in prediction for composite bucket foundation. [ABSTRACT FROM AUTHOR]

Abstract: The interaction between current and flexural gravity waves generated due to a floating elastic plate is analyzed in two dimensions under the assumptions of linearized theory. For plane flexural gravity waves, explicit expressions for the water particle dynamics and trajectory are derived. The effect of current on the wavelength, phase velocity and group velocity of the flexural gravity waves is analyzed. Variations in wavelength and wave height due to the changes in current speed and direction are analyzed. Effects of structural rigidity and water depth on wavelength are discussed in brief. Simple numerical computations are performed and presented graphically to explain most of the theoretical findings in a lucid manner. [Copyright &y& Elsevier]

Abstract: Based on the second-order solutions obtained for the three-dimensional weakly nonlinear random waves propagating over a steady uniform current in finite water depth, the joint statistical distribution of the velocity and acceleration of the fluid particle in the current direction is derived using the characteristic function expansion method. From the joint distribution and the Morison equation, the theoretical distributions of drag forces, inertia forces and total random forces caused by waves propagating over a steady uniform current are determined. The distribution of inertia forces is Gaussian as that derived using the linear wave model, whereas the distributions of drag forces and total random forces deviate slightly from those derived utilizing the linear wave model. The distributions presented can be determined by the wave number spectrum of ocean waves, current speed and the second order wave–wave and wave–current interactions. As an illustrative example, for fully developed deep ocean waves, the parameters appeared in the distributions near still water level are calculated for various wind speeds and current speeds by using Donelan–Pierson–Banner spectrum and the effects of the current and the nonlinearity of ocean waves on the distribution are studied. [Copyright &y& Elsevier]

Abstract: The straits connect two large water bodies show highly strong and stratified currents related to meteorological, morphological and hydrodynamic conditions. In some cases, spatial and temporal changes of the stratified currents and their thickness, direction and magnitude are so complex. This complexity directly affects the circulation pattern in the region, water exchange between both ends of the straits and migration of fish species. In order to understand general characteristics of this kind of straits and identifying the complexity of the hydrodynamics of the region and evaluate the secondary currents and recirculation need long term, intensive, field work and measurement studies. As an example of this kind of hydrodynamically complex straits, Bosphorus strait is selected for a field study. The Bosphorus strait has a strongly stratified two-layer system and a unique case of the maximal exchange regime typical of strait flows, which is largely determined by conditions at the Black Sea. Although the Bosphorus strait has distinct two-layer stratification with an associated two-layer system exchange, no continuous current measurements have been made so far, previous measurements all having been random sampling. In this paper, a detailed measurement program has been applied to Bosphorus strait. In the measurement program, a short-term current profile measurement at selected locations at southern part of the strait has been conveyed. Additionally a long-term measurement of current profile has been performed at a selected critical location (in front of the Dolmabahçe Palace) where a recirculation flow exists in the strait. The scope of this paper is to present the techniques and the results of analysis of measurement data. In the measurements the current profile (magnitude and direction) has been determined at every 1m depth intervals from the surface to the sea bottom at 3min duration at every hour. Measurements provide that lower-layer flows in northward direction from the Sea of Marmara towards the Black Sea, whereas the upper-layer flow comes from the Black Sea and flows towards the Sea of Marmara in the opposite direction of lower layer. The Bosphorus strait exhibits distinctive features associated with variations in its width and depth. The meandering features of Bosphorus also cause recirculation flows. These results of measurements are presented, discussed and compared with previous studies. [Copyright &y& Elsevier]

Abstract: As the capability of polar plots becomes better understood, improved dynamic positioning (DP) systems are possible since the control algorithms greatly depend on the accuracy of the aerodynamic and hydrodynamic models. The measurements and estimation of the environmental disturbances have an important role in the optimal design and selection of a DP system for a marine vessel. The main objective of this work is to present a new software program capable of estimating the environmental forces, thrusters capability calculations, and capability polar plots for marine vessels. A flowchart illustrating the logic and data flow of a developed software program, the Capability Polar Plot Program (CPPP), and the estimated results for two case studies for a scientific drilling vessel and a survey vessel are presented. It is obvious from the obtained results that the developed program has a future potential for the estimation of the Capability Polar Plots for marine vessels. Moreover, the developed software program would be considered as a marine tool for the thrusters'' selection and their configuration for marine vessels and floating production units for the Oil and Gas industries. [Copyright &y& Elsevier]

This paper investigates dynamic responses and buckling of a 10 MW monopile offshore wind turbine (OWT) subjected to multiple environmental loadings including earthquake, wind, wave and current. The finite element model (FEM) of the support structure is developed in ANSYS to obtain relatively accurate and reliable structural responses. The soil structure interaction (SSI) effects are represented using a set of lateral nonlinear springs and a vertical nonlinear spring. The SSI effects on the eigenmodes of the support structure are examined. The time series of wind and wave loads are, respectively, calculated using FAST and AQWA and then fed into ANSYS as external loads to perform the seismic analysis. The structural responses and local damage characteristics of the 10 MW OWT have been studied. The results indicate that the wind, wave and current loads in the fore-aft direction have a significant effect on the seismic responses of the OWT. It is therefore the turbulent wind, wave and current loadings cannot be ignored when performing a seismic analysis of OWTs. As a result of buckling, the change of environmental load will lead to a transition between buckling modes. These findings provide useful insights for the design of monopile offshore wind turbines. • The finite element shell model of the support structure is developed to obtain relatively accurate and reliable dynamic responses. • The Control variable of environmental loads is used to investigate the effects of various environmental loads on dynamic responses of the 10 MW OWT, and verify the necessity of considering each environmental load in dynamic research. • The transient analysis results obtained in the previous section are applied as the boundary condition in the buckling analysis to closely analyze the high-risk areas. [ABSTRACT FROM AUTHOR]

The purpose of this discussion is to demonstrate how the formula for the wave-induced pipeline scour presented by Cheng et al. (2020) can be extended to random wave-induced pipeline scour. Favorable results are obtained by comparing the stochastic method predictions with the Sumer and Fredsøe (1996) data for pipeline scour beneath random waves plus current. [ABSTRACT FROM AUTHOR]

This study proposes a new length scale that measures the size of the wave-induced vortex street on one side of a pipeline. By conducting dimensional analysis, we show that the equilibrium scour depth under a pipeline, when normalized by the vortex street size, is generally dependent on the densimetric Froude number. However, by analyzing the published data, the dependence is found to be insignificant if the current velocity is smaller than the maximum orbital velocity of water particles at the bed. This result suggests that the normalized scour depth can be simply taken to be a constant for both wave-alone and wave-plus-current conditions. • Wave-induced scour depth below a pipeline scales well with the size of wave-induced vortex street. • The scour depth normalized with the vortex street size can be taken to be a constant for both wave-alone and wave-plus-current conditions. • The size of the wave-induced vortex can be quantified as the squrare root of the pipe diameter and the amplitude of the orbital motion of the wate particles at the bed. [ABSTRACT FROM AUTHOR]

Pile group effect is crucial for correct estimation of the hydrodynamic force on a pile within a pile-group foundation of sea-crossing bridge during earthquakes unlike the case of single isolated pile. A numerical calculation model considering fluid-structure interaction under the combined loads of earthquakes, waves and currents is established, based on the second development on ANSYS software. A detailed analysis of pile group effect in the earthquake-induced oscillatory flow field, is carried out by the presented method that is validated in advance. Pile group effect in the earthquake-current combined flow field, as well as in the earthquake-wave combined flow field are further discussed. Pile group effect has almost disappeared when relative spacing S / D = 4.5 and all piles behave like a single isolated pile in terms of earthquake-induced hydrodynamic forces, yet, in the coexistence field, the range of S / D influencing pile group effect has been expanded due to the presence of current and wave. For a sea-crossing bridge foundation, Pile group effect coefficient K is equal to 0.69, implying noticeable interference effects, and results show the hydrodynamic force on corner pile is greater than that on centre pile, strengthening section reinforcement pertinently so as to improve overall seismic performance. [ABSTRACT FROM AUTHOR]

Wave resonance by forced motions of two bodies in a steady current is investigated in this paper. The work is based on second order theory of potential flow and the simulation is through a higher order finite element method with 12-node elements in time domain. Boundary conditions are imposed on mean positions of all boundaries. The i -th (i = 1,2) order potentials in the fluid domain at each time step are obtained by solving the finite element system and the spatial derivatives of the potential are calculated by differencing the shape functions directly. Numerical cases are given for two rectangular cylinders undergoing in specified oscillations in a steady current. The first and second order resonances have been captured at their resonant frequencies at different current speeds, which does not seem to have been studied yet. The numerical result shows that the current speed has important influence on the wave and force at both first and second order resonances. • A higher order finite element method has been employed to analyze wave-current-body interaction. • Both linear and resultant waves & forces have been affected by the current including amplitude, phase or nonlinearity. • Larger Froude number generally causes linear or second order wave and force to be smaller at its resonant frequency. • Second order wave and force increase as Froude number increases at in vertical motion and at in horizontal motion [ABSTRACT FROM AUTHOR]

This paper describes the results of a survey performed by the authors to assess how hydro/meteo conditions are presently modelled in ship manoeuvring simulators. While mathematical models for the manoeuvring behaviour of ships are well documented in literature, an overview concerning hydro/meteo modelling did not exist yet, despite the crucial role of this aspect on the global level of realism which could be achieved in manoeuvring simulations. A questionnaire regarding current, waves, wind and water levels was therefore sent to a large list of simulator developers and users, with the explicit aim to compile the results in a research paper. The received answers were thoroughly analysed and are summarized in this paper as an overview of the state of the art in hydro/meteo data for ship simulators at the time of writing. All the results are published in an anonymous form to guarantee a high discretion level to all parties who answered the survey. The information which is publicly summarized in this paper could benefit the whole community of ship simulator users and developers by making everyone more aware of the present common practices, while also fixing a starting point for future research and improvements. • A survey about hydro/meteo data in ship simulators was sent to 30 institutes. • Twelve full replies were collected, organized and summarized in the paper. • The received results outline common approaches as well as relevant differences. • The paper summarizes information not yet available in scientific literature. [ABSTRACT FROM AUTHOR]