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Pile foundations have been widely used in offshore engineering. In this study, a three-dimensional numerical model was used to investigate the seabed response around a mono-pile under wave-current loading. Reynolds-averaged Navier-Stokes equations were used to simulate the flow field, and Biot's consolidation equations were used for simulating the response of a porous seabed. The pore water pressure within soil and the effective stress along the depth of the seabed were simulated for various current velocities, with currents traveling either along or against the wave. Results indicate that the current has a significant effect on the effective stress and the pore water pressure distributions, which increases with the current velocity, and that the current traveling against the wave increases the liquefaction depth of the porous seabed.

In nearshore regions, bidirectional tidal flow is the main hydrodynamic factor, which induces local scour around submarine pipelines. So far, most studies on scour around submarine pipelines only consider the action of unidirectional, steady currents and little attention has been paid to the situation of bidirectional tidal currents. To deeply understand scour characteristics and produce a more accurate prediction method in bidirectional tidal currents for engineering application, a series of laboratory scale experiments were conducted in a bidirectional current flume. The experiments were carried out at a length scale of 1:20 and the tidal currents were scaled with field measurements from Cezhen pipeline in Hangzhou Bay, China. The experimental results showed that under bidirectional tidal currents, the scour depth increased significantly during the first half of the tidal cycle and it only increased slightly when the flow of the tidal velocity was near maximum flood or ebb in the following tidal cycle. Compared with scour under a unidirectional steady current, the scour profile under a bidirectional tidal current was more symmetrical, and the scour depth in a bidirectional tidal current was on average 80% of that under a unidirectional, steady current based on maximum peak velocity. Based on previous research and the present experimental data, a more accurate fitted equation to predict the tidally induced live-bed scour depth around submarine pipelines was proposed and has been verified using field data from the Cezhen pipeline.

Waves and currents coexist widely in the ocean, and the interaction of waves and currents plays an important role in the instability of submarine pipelines. So far, most studies have concentrated on discussing the dynamic reaction within the seabed around a pipeline under pure wave action, monotypic sediment, and an exposed or fully buried condition. In this study, the effect of current characteristics (e.g., current velocity and propagation direction) and backfilling conditions (e.g., backfill depth and sand property) on the dynamic response around the submarine pipeline is investigated by conducting laboratory experiments. Pipeline was buried in the excavated trench using three types of sand with the median size of 0.150 mm, 0.300 mm and 0.045 mm, respectively. Five relative backfilled depths, with the ratios of backfill depth over the pipeline diameter being 0, 1/2, 1, 3/2 and 2, were tested. The excess pore pressure was measured simultaneously by using the pore pressure sensors installed around the pipeline surface and beneath the pipeline. Results show that both the pore pressure amplitude and its descent rate gradually decrease with an increasing backfill depth, which decreases the soil liquefaction potential. Under the co-current actions, the decrease rate of the pore pressure along the vertical direction increases with an increasing current velocity. However, the increased current velocity leads to a decrease of the attenuation rate under the counter-current actions compared with the pure wave actions, and the counter-current effect on the pore pressure within the seabed is greater than the co-current. The results indicate that the dynamic response around the pipeline in coarse sand is close to that without the backfill scenario, even if the backfill depth reaches up to two times that of the pipeline diameter. It is found that the larger the median particle size of backfill sand, the smaller the impact on pore pressure within the seabed beneath the pipeline.

In this paper, an analytical model that represents the streamwise velocity distribution for open channel flow with submerged flexible vegetation is studied. In the present vegetated flow modelling, the whole flow field has been separated into two layers vertically: a vegetated layer and a non-vegetated free-water layer. Within the vegetated layer, an analysis of the mechanisms affecting water flow through flexible vegetation has been conducted. In the non-vegetated layer, a modified log-law equation that represents the velocity profile varying with vegetation height has been investigated. Based on the studied analytical model, a sensitivity analysis has been conducted to assess the influences of the drag ( C D ) and friction ( C f ) coefficients on the flow velocity. The investigated ranges of C D and C f have also been compared to published values. The findings suggest that the C D and C f values are non-constant at different depths and vegetation densities, unlike the constant values commonly suggested in literature. This phenomenon is particularly clear for flows with flexible vegetation, which is characterised by large deflection.

A depth-averaged two-dimensional (2D) numerical model was developed to investigate hydrodynamics in estuaries. The Qiantang estuary is taken as a demonstrative case study. The Qiantang estuary is famous for its macro tide during the spring tide and the Qiantang bore, which poses a challenging task for accurate simulation. In this study, the model was setup to simulate the tidal elevations and the tidal velocity field in the Qiantang estuary. A mesh sensitivity analysis was carried out to optimise the mesh arrangement to achieve computational efficiency while retaining computational accuracy. The simulation results showed that, in general, the numerical simulation agreed well with the field observations, indicating that the developed 2D model can be applied to calculate hydrodynamics in a macro tidal estuary. Some deviation between the simulation and measurements at some locations exists and this discrepancy is analysed and discussed.

Laboratory experiments are presented to investigate the effect of different piggyback pipeline configurations on the morphology of local scour under wave conditions. Scour depth and width around the pipelines under regular and irregular waves are measured and analyzed for a range of pipeline and wave conditions; such as the spacing between two pipes (G), gap between the main pipe and seabed (e), pipe diameter (D), wave height (H) and period (T). Experimental results reveal that both the scour depth and width around piggyback pipeline is much larger than those around single pipe under the same wave conditions. Scour depth increases with the increase of the Keulegan-Carpenter (KC) number and decreases with increase of G and e. When e exceeds 0.5D, scour depth tends to approach 0. When spacing G is greater than 0.4D, the destabilization from small pipe to large one is greatly reduced, resulting in scour depth around piggyback pipeline being close to that around single pipe. Similar to scour depth, scour width broadens with the increase of KC number increasing and decreases with the increase of G. Experiments also show that the effect of e on scour depth is greater than that of G under the same test conditions, while their impact on scour width is opposite. Furthermore, scour width under irregular waves is extended slightly compared with regular wave for otherwise the identical conditions.

This paper presents the results of laboratory experiments and numerical simulations to investigate the effect of different piggyback pipeline configuration on the morphology of local seabed scour subject to steady currents. Piggyback pipeline configuration investigated includes the commonly used piggyback pipeline, namely a small pipe attached on the top of large pipe and new form of piggyback pipeline proposed in this study in which a small pipe is attached to the large pipe on the upstream and downstream side, respectively. Pressure gradient, drag coefficient, lift coefficient and scour extent around pipelines are measured and analyzed for a range of pipelines and current conditions. Results show that the vortex strength downstream of the commonly used piggyback pipeline is larger than that for a single as well as the new piggyback pipeline under the same condition. This new type piggyback pipeline can effectively reduce the depth and width of the scour hole. In particular, when the ratio of the small pipe diameter over the large pipe diameter is greater than 0.3, little scour under this new type piggyback pipeline occurs for the test conditions. The bed topography downstream of the pipe has also been altered to favor the backfill.

Seabed instability around a pipeline is one of the primary concerns in offshore pipeline projects. To date, most studies focus on investigating the wave/current-induced response within a porous seabed around either a fully buried pipeline or a thoroughly exposed one. In this study, unlike previous investigations, a series of comprehensive laboratory experiments are carried out in a wave flume to investigate the wave-induced pore pressures around a partially embedded pipeline in a trench layer. Measurements show that the presence of the partially buried pipeline can significantly affect the excess pore pressure in a partially backfilled trench layer, which deviates considerably from that predicted by the theoretical approach. The morphology of the trench layer accompanied with the backfill sediments, especially the deeper trench and thicker backfill (i.e., b ≥ 1 D , e ≥ 0.5 D ), provides a certain degree of resistance to seabed instability. The amplitude of excess pore pressure around the trench layer roughly exhibits a left-right asymmetric distribution along the periphery of the pipeline, and decays sharply from the upper layer of the trench to the lower region. Deeper trench depth and thicker buried layer significantly weaken the pore-water pressures in the whole trench area, thus sheltering and protecting the submarine pipeline against the transient seabed liquefaction.

Horizontal-axis tidal turbines (HATTs) have an acknowledged potential to extract a considerable amount of clean renewable energy from ocean tides. Among these, bidirectional HATTs (BHATTs) with bidirectional hydrofoils are thought to have higher economy than general HATTs. To improve the BHATTs, this study systemically investigated the influence of swept blades on the performance and hydrodynamics of the BHATT. A three-dimensional (3D) numerical model based on OpenFOAM was adopted to simulate a full-scale BHATT. The numerical framework was validated using two well-known experiments, and the mesh convergence was taken into consideration. The results indicate that the forward and backward swept blades have a limited impact on the performance and hydrodynamics of the BHATT. The upstream swept blade leads to a 4.3% decrease in the load on the rotor at design tip speed ratio (TSR) with a 2.0% decrease in the power. The BHATT with a downstream swept blade can produce 3.2% more energy at TSR = 6. Moreover, the swept blades have the opposite effect on the power of the BHATT at TSR = 6 and TSR = 9.

The near-trapping effects on wave-induced dynamic seabed response and liquefaction close to a multi-cylinder foundation in storm wave conditions are examined. Momentary liquefaction near multi-cylinder structures is simulated using an integrated wave-structure-seabed interaction model. The proposed model is firstly validated for the case of interaction of wave and a four-cylinder structure, with a good agreement with available experimental measurements. The validated model is then applied to investigate the seabed response around a four-cylinder structure at 0° and 45° incident angles. The comparison of liquefaction potential around individual cylinders in an array shows that downstream cylinder is well protected from liquefaction by upstream cylinders. For a range of incident wave parameters, the comparison with the results for a single pile shows the amplification of pressure within the seabed induced by progressive wave. This phenomenon is similar to the near-trapping phenomenon of free surface elevation within a cylinder array.

When ocean waves propagate over porous seabed, they cause variations of the pore pressure within seabed, leading to the possible wave attenuation and soil liquefaction. In order to advance and improve our understanding of the process of wave-induced seabed liquefaction and its impact on wave propagation, systematical experiments are carried out in a wave flume with a soil basin filled with silt. Both the pore pressures and water surface elevations are measured simultaneously, while the seabed liquefaction is videotaped using a high-speed camera. Laboratory measurements show that the pore pressure in surface layer mainly oscillates over time, while the wave period averaged pore pressure has little change. In the deep layer, however, the wave period averaged value of the pore pressure builds up dramatically. The results show that the wave height decreases rapidly along the direction of wave propagation when seabed liquefaction occurs. Such a wave attenuation is greatly enhanced when the liquefaction depth further increases. The experiments also demonstrate that the conditions (wave height and wave period) of incident waves have significant impacts on the wave-induced pore pressures, liquefaction depth and wave attenuation in a silt bed.

This paper presents the results from a numerical simulation study to investigate the effect of the position angle (α) of small pipeline on the local scour and the hydrodynamic force around the piggyback pipeline in steady current conditions. Results show that the local scour depth around the piggyback pipeline increases first and then decreases with the increase of α. The scour depth and width reach the maximum values as the small pipe locates at the top of the large pipeline (i.e. α = 90°). The scour around the piggyback pipeline is accelerated when α ranges between 30° and 165°, while for α = 0°–30° and 165°–180°, the local scour around the piggyback pipeline is inhibited. Furthermore, the small pipe placed in front of the large pipe has slightly larger effect on the scour hole morphology than that when it is placed behind the large pipe. The drag force coefficient increases first and reaches the maximum value at α = 75°, and then decreases with the increase of α. Eventually the drag force coefficient approaches roughly a constant. The lift force coefficient is approximately a V-shaped with the variation of α and has the maximum value at α = 90°.

Stability and safety of offshore wind turbines with mono-pile foundations, affected by nonlinear wave effect and dynamic seabed response, are the primary concerns in offshore foundation design. In order to address these problems, the effects of wave nonlinearity on dynamic seabed response in the vicinity of mono-pile foundation is investigated using an integrated model, developed using OpenFOAM, which incorporates both wave model (waves2Foam) and Biot's poro-elastic model. The present model was validated against several laboratory experiments and promising agreements were obtained. Special attention was paid to the systematic analysis of pore water pressure as well as the momentary liquefaction in the proximity of mono-pile induced by nonlinear wave effects. Various embedded depths of mono-pile relevant for practical engineering design were studied in order to attain the insights into nonlinear wave effect around and underneath the mono-pile foundation. By comparing time-series of water surface elevation, inline force, and wave-induced pore water pressure at the front, lateral, and lee side of mono-pile, the distinct nonlinear wave effect on pore water pressure was shown. Simulated results confirmed that the presence of mono-pile foundation in a porous seabed had evident blocking effect on the vertical and horizontal development of pore water pressure. Increasing embedded depth enhances the blockage of vertical pore pressure development and hence results in somewhat reduced momentary liquefaction depth of the soil around the mono-pile foundation.

Seabed consolidation state is one of important factors for evaluating the foundation stability of the marine structures. Most previous studies focused on the seabed consolidation around breakwaters standing on the seabed surface. In this study, a numerical model, based on Biot's poro-elasticity theory, is developed to investigate the unsaturated seabed consolidation around a nearshore pile foundation, in which the pile inserted depth leads to a different stress distribution. Seabed instabilities of shear failure by the pile self-weight and the potential liquefaction under the dynamic wave loading are also examined. Results indicate that (1) the presence of the inserted pile foundation increases the effective stresses below the foundation, while increases and decreases the effective stresses around the pile foundation for small (de/R 3.3) inserted depths, respectively, after seabed consolidation, (2) the aforementioned effects are relatively more significant for small inserted depth, large external loading, and small Young's modulus, (3) the shear failure mainly occurs around the inserted pile foundation, rather than below the foundation as previously found for the located marine structures, and (4) wave-induced momentary liquefaction near the inserted pile foundation significantly increases with the increase of inserted depth, due to the change of seabed consolidation state.

Local scour around seabed oil, gas or water pipelines can critically affect their stability. Accurate estimation of scour around pipelines is therefore a key topic of research for marine engineers. This paper presents results from a numerical study of clear-water scour depth below a submarine pipeline for a range of steady flow conditions. The flow field around a pipeline under scour equilibrium conditions was numerically simulated by solving the Reynolds-averaged Navier–Stokes equations with the standard k–ε turbulence closure. The flow discharge through the scour hole for various flow conditions was then investigated, and the results were used to establish the relationship between the flow discharge and the maximum scour depth. By incorporating the Colebrook–White equation, the bed shear stress was obtained and an iterative method was developed to predict the scour depth around the pipeline. The calculated scour depths using the proposed method agreed well with laboratory measurements, with the average absolute relative error being smaller than that obtained by using previous methods. Therefore, this proposed method can be used to predict the clear-water scour around submarine pipelines with improved accuracy.

Wave-induced seabed instability caused by the residual liquefaction of seabed may threaten the safety of an offshore foundation. Most previous studies have focused on the structure that sits on the seabed surface (e.g., breakwater and pipeline), a few studies investigate the structure embedded into the seabed (e.g. a mono-pile). In this study, by considering the inertial terms of pore fluid and soil skeleton, a three-dimensional (3D) integrated model for the wave-induced seabed residual response around a mono-pile is developed. The model is validated with five experimental tests available in the literature. The proposed model is then applied to investigate the spatial and temporal pattern of pore pressure accumulation as well as the 3D liquefaction zone around a mono-pile. The numerical simulation shows that the residual pore pressure in front of a pile is larger than that at the rear, and the seabed residual response would be underestimated if the inertial terms of pore fluid and soil skeleton are neglected. The result also shows that the maximum residual liquefaction depth will increase with the increase of the embedded depth of the pile.

This paper presents the results from laboratory experiments and theoretical analysis to investigate the development of scour around submarine pipeline under steady current conditions. Experiments show that the scour process takes place in two stages: the initial rapid scour and the subsequent gradual scour development stage. An empirical formula for calculating the equilibrium scour depth (the maximum scour depth) is developed by using the regression method. This formula together with the maximum entropy theory can be applied to establish a formula to predict the scour process for given water depth, diameter of pipeline and flow velocity. Good agreement between the predicted and measured scour depth is obtained.

The power output characteristics of the hydro turbine is one of the core contents for transient calculation of the hydro turbine generating sets. In particular, the hydro turbine operates far beyond the given parameters region during the load rejection transient. As such, obtaining the complete characteristics of the hydro turbine becomes one of the key issues in calculating the transient process. In this study, methods for calculating the energy losses are proposed by analyzing the general characteristics of the inner energy losses within the hydro turbine. Characteristic parameters in the hydro turbine power model are calculated from the synthetical characteristics of the model hydro turbine. The transient power model of the hydro turbine has been established and applied to calculate and reconstruct the complete characteristics of the hydro turbine. Furthermore, the relationship curve between the mechanical friction loss power and the rotation speed under different head can be established by combing the runaway curve with the proposed turbine power model. This relationship is applied to construct the complete characteristics of the mechanical friction loss. Combining the proposed two complete characteristics, the power model of the hydro turbine is suitable for simulation with a wide range of fluctuations as well as the load rejection transient. Details of the computational procedures are presented and demonstrated using a case study.

An integrated Finite Element Method (FEM) model is proposed to investigate the dynamic seabed response for several specific pipeline layouts and to simulate the pipeline stability under waves loading. In the present model, the Reynolds-Averaged Navier–Stokes (RANS) equations are used to describe the wave motion in a fluid domain, while the seabed domain is described using Biot's poro-elastic theory. The interface between water and air is tracked by conservative Level Set Method (LSM). The FEM and backward differentiation formula (BDF) are applied for spatial and temporal discretization respectively in the present model. One-way coupling is used to integrate flow and seabed models. The present model is firstly validated using several available laboratory experiments. It is then further extended to practical engineering applications, including the dynamic seabed response for the pipeline mounted on a flat seabed or inside a trench. The results show that the pipeline buried to a certain depth is better protected than that under partially buried in terms of transient liquefaction.

Laboratory experiments have been carried out to investigate wave damping over the seabed, in which the excess pore pressure and free surface elevations are synchronously measured for examining the wave-induced soil dynamics and wave kinematics. Two types of soil, namely fine sand and silt, are tested to examine the role of soil in the wave damping. Observation of experiments shows that (i) soil liquefaction takes place for some tests with silty bed and soil particles suspend into the water layer when the bed is made of silt; (ii) sand ripples can be generated for experiments with sand bed. Measurements reveal that the wave damping greatly depends on the soil dynamic responses to wave loading and the wave damping mechanism over the silty seabed differs from that over the sand bed. On the one hand, the wave damping rate is greatly increased, when soil liquefaction occurs in the silty bed. On the other hand, the presence of sand ripples generated by oscillatory flow in the sand bed experiments also increases the wave damping to some extent. Furthermore, experimental results show that soil particle suspension in the silt bed test contributes to the wave damping. Theoretical analysis is presented to enhance discussions on the wave damping. The theoretical calculations demonstrate that the wave damping is mainly induced by the shear stress in the boundary layer for the cases when no liquefaction occurs. While for the cases when soil liquefaction takes place, the viscous flow in the liquefied layer contributes most towards to the wave damping.

A two-dimensional model based on OpenTidalFarm is applied to simulate tidal stream flow around turbines. The model is governed by shallow water equations and is able to optimize the layout of the deployed turbine array in terms of maximizing the energy outputs. Three turbine array layouts including two structured layouts (regular and staggered) and one unstructured layout (optimized) are simulated to investigate the effect of turbine layouts on energy extraction. The present study shows that more energy could be extracted when lateral spacing decreases and longitudinal spacing increases within the same domain, namely the effective turbine layout is to deploy more turbines in the first row to extract energy from undisturbed tidal stream, while larger longitudinal spacing will make it possible for tidal stream to recover more before reaching the next turbines row. Taking the tidal stream turbines array around Zhoushan Islands as a case study, results show that the optimized layout can extract 106.8% energy of that extracted by the regular and staggered layout for a full tide in the same marine area. Additionally, the turbine array has a great influence on tidal stream velocities immediately behind the array and has little effect on far-field wake flow.

In this study, a new three-dimensional model was developed to provide a better understanding of the mechanism for wave-induced seabed response around the mono-pile. Based on the poro-elastic theory, the fully dynamic formulations were adopted in the present model to simulate the pore pressure, soil stresses and the displacements of both soil and mono-pile. Good agreement between the numerical simulation and experimental results was obtained. Based on the parametric study, the numerical results concluded that (1) the wave diffraction and reflection have significant effects on the pore pressure and soil displacements around the mono-pile; (2) the largest discrepancy of pore pressure due to the variation in seabed parameters appears in front of mono-pile, while the smallest discrepancy is at the position of angle 3π/4 with respect to the incident wave direction and (3) the increase in the mono-pile horizontal displacement corresponds to the increase in the wave height and the decrease in the seabed Young's m...

This paper presents the results from laboratory experiments to investigate the protection of scour around submarine pipelines under unidirectional flow using a rubber plate placed underneath the pipes. The pressure difference on the two sides of the pipeline is the driving force to initiate the movement of sediment particles and can be obtained by force balance analysis. Experiments covering a wide range of incoming flow velocity, pipe diameter and plate length show that there exists a critical pressure difference over which the movement of sediment and, thus, scour takes place. Analysis of the experimental results demonstrates that this critical pressure difference is related to the pressure difference of the axial points between upstream and downstream of the pipe, which can be easily determined. This critical pressure difference is used to develop an empirical formula for estimating the critical length of the rubber plate, over which the sediment movement and scour will not take place. Good agreement between the experiments and calculated critical plate length using the proposed formula is obtained.

Traditional rotor dynamics mainly focuses on the steady- state behavior of the rotor and shafting. However, for systems such as hydro turbine generating sets (HTGS) where the control and regulation is frequently applied, the shafting safety and stabilization in transient state is then a key factor. The shafting transient state inevitably involves multiparameter domain, multifield coupling, and coupling dynamics. In this paper, the relative value form of the Lagrange function and its equations have been established by defining the base value system of the shafting. Taking the rotation angle and the angular speed of the shafting as a link, the shafting lateral vibration and generator equations are integrated into the framework of generalized Hamiltonian system. The generalized Hamiltonian control model is thus established. To make the model more general, additional forces of the shafting are taken as the input excitation in proposed model. The control system of the HTGS can be easily connected with the shafting model to form the whole simulation system of the HTGS. It is expected that this study will build a foundation for the coupling dynamics theory using the generalized Hamiltonian theory to investigate coupling dynamic mechanism among the shafting vibration, transient of hydro turbine generating sets, and additional forces of the shafting.

Seabed scouring presents severe safety issues for subsea pipelines. It is crucial to be able to predict scour depths for various flow conditions. In this paper, the effects of flow velocity and spoiler on scour depth are investigated using laboratory experiments. It is found that both the fluid Reynolds number and the spoiler height have strong effects on scour depth. Mechanistic formulas for scour depth are proposed and validated using laboratory test data. The formulas consider the fluid velocity profile beneath the pipeline, which greatly affects scour depth. The formulas produced good match with tests data.

This paper presents results from laboratory experimental model studies investigating scour by waves around a pipeline attached to a flexible rubber plate or rigid spoiler. The rubber plate was placed between the submarine pipeline and bed, while the rigid spoiler is attached to the top of the pipe. The scour around pipelines with and without a rubber plate or a rigid spoiler under regular and irregular waves was observed and measured for a range of pipe sizes, wave amplitudes and frequencies, and the length of the plate/height of the spoiler. The experiments reveal that although the rigid spoilers can enhance the scour depth and extent (thus accelerating the self-burial of the pipe), they also have significant influence on both the upstream and downstream bed topography as sand ripples and dunes are formed. On the other hand, the rubber plates cannot only significantly increase the scour depth but also have little effect on the upstream and downstream bed. The experiments show that when the length of the plate is about 1.5 times the pipe size, it provides the optimum performance in terms of the largest scour depth while restricting the impact on nearby beds for the parameters investigated in this study.

Results from a numerical modeling study are presented to investigate the tidal elevations, tidal current velocity, bed deformation, and suspended sediment concentration in the Qiantang Estuary, China. The Qiantang Estuary is well-known for its macrotide, which generates a hydrodynamically complex environment. This presents challenges for numerical modelers to accurately simulate the flow field and sediment transport in the region. This paper presents a mathematical model using finite volume method with unstructured mesh to simulate the tide-induced water elevation, current velocity, bed deformation, and suspended sediment transport in the Qiantang Estuary. The parameters in the model were determined using the long-term observed field data of the Qiantang Estuary. The simulated tidal elevations and current velocities agree well with the field observations. The numerical prediction of the bed deformation in 5 months is reasonably compared with the field measurements carried out in the same period. H...

The interaction between wave and offshore deposits is of great importance for the foundation design of marine installations. However, most previous investigations have been limited to connecting separated wave and seabed sub-models with an individual interface program that transfers loads from the wave model to the seabed model. This research presents a two-dimensional coupled approach to study both wave and seabed processes simultaneously in the same FEM (finite element method) program (COMSOL Multiphysics). In the present model, the progressive wave is generated using a momentum source maker combined with a steady current, while the seabed response is applied with the poro-elastoplastic theory. The information between the flow domain and soil deposits is strongly shared, leading to a comprehensive investigation of wave-seabed interaction. Several cases have been simulated to test the wave generation capability and to validate the soil model. The numerical results present fairly good predictions of wave generation and pore pressure within the seabed, indicating that the present coupled model is a sufficient numerical tool for estimation of wave-induced pore pressure.

This paper investigates the complex interaction between turbulent flow and a deep-water marine structure (overlapping circular cylinders) using a commercial computational fluid dynamics code applying the large eddy simulation approach. A number of three-dimensional large eddy simulations of wake flow around overlapping cylinders of finite heights are carried out for incoming flow Reynolds number in the range 1·0 × 104 to 1·0 × 105. The effect of the height of a circular mud mat having a fixed diameter and its effect on the turbulent flow and pressure fields around this kind of bluff body is investigated. The numerically computed results show some features of the complex separated flow structures and wake properties behind the cylinder. The simulated flow velocity field together with the bed material data can be used to evaluate and estimate the scour around the overlapping cylinder and assess its stability.

This study extends previous two-dimensional research [Wang, S.D., Shen, Y.M., Zheng, Y.H., 2005. Two-dimensional numerical simulation for transport and fate of oil spills in seas. Ocean Engineering 32, 1556–1571] to three dimensions in order to investigate the vertical dispersion/motion of the spilled oil slick, which is a more realistic model of the motion of the spilled oil. To this end, a three-dimensional (3-D) model, based on the particle approach, is developed for simulating oil spill transport and fate in seas. The amount of oil released at sea is distributed among a large number of particles tracked individually. These particles are driven by a combination of water current, wave- and wind-induced speed and move in a 3-D space. Horizontal and vertical diffusion are taken into account using a random walk technique. The model simulates the most significant processes which affect the motion of oil particles, such as advection, surface spreading, evaporation, dissolution, emulsification, turbulent diffusion, the interaction of the oil particles with the shoreline, sedimentation and the temporal variations of oil viscosity, density and surface tension. In addition, the processes of hydrolysis, photo-oxidation and biodegradation are also considered in this model. The model has been applied to simulate the oil spill accident in the Bohai Sea.

A two-dimensional numerical model is developed to study the propagation of a solitary wave in the presence of a steady current flow. The numerical model is based on the Reynolds-averaged Navier-Stokes (RANS) equations with a k-e turbulence closure scheme and an internal wave-maker method. To capture the air-water interface, the volume of fluid (VOF) method is used in the numerical simulation. The current flow is initialized by imposing a steady inlet velocity on one computational domain end and a constant pressure outlet on the other end. The desired wave is generated by an internal wave maker. The propagation of a solitary wave traveling with a following/opposing current is simulated. The effects of the current velocity on the solitary-wave motion are investigated. The results show that the solitary wave has a smaller wave height, larger wave width, and higher traveling speed after interacting with a following current. Contrariwise, the solitary wave becomes higher with a smaller wave width and l...

The wave–seabed interaction issue is of great importance for the design of foundation around marine infrastructures. Most previous investigations for such a problem have been limited to uncoupled or one-way coupled methods connecting two separated wave and seabed sub models with the continuity of pressures at the seabed surface. In this study, a strongly coupled model was proposed to realize both wave and seabed processes in a same program and to calculate the wave fields and seabed response simultaneously. The information between wave fields and seabed fields were strongly shared and thus results in a more profound investigation of the mechanism of the wave–seabed interaction. In this letter, the wave and seabed models were validated with previous experimental tests. Then, a set of application of present model were discussed in prediction of the wave-induced seabed response. Numerical results show the wave-induced liquefaction area of coupled model is smaller than that of uncoupled model.