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Abstract Two dimensional wave-current-structure interaction problems are investigated in a sea environment with a flat or sloping seabed using linear boundary conditions. This problem is separated into steady and unsteady potential components. The former accounts for the current flowing over the seabed or fixed body whereas the latter describes the wave interaction with the current through modification of the free surface boundary conditions. Both steady and unsteady problems are solved using a boundary element model incorporating a continuous Rankine source method. The developed numerical model is validated by comparison with published data, where possible, and the investigation extended to examine the hydrodynamic responses of a forced oscillating body subject to the combined interactions arising from the wave, current and seabed. Highlights This paper aims to simulate hydrodynamic responses of a forced oscillating body subject to interactions between wave, current and seabed. The highlights are as followings: • The interaction of forced oscillatory body-wave-current-seabed is investigated. • Two boundary integral equations are developed. • Boundary integral is analytically evaluated. • The relationships between wave damping and wave elevation in deep and finite water depths with current effect included and excluded are numerically and mathematically examined. [ABSTRACT FROM AUTHOR]

Abstract 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. Highlights • First comprehensive experimental data for wave-induced pore pressure around buried pipeline in a trench layer. • Investigate effect of wave characteristics on transient pore-water response near the partial-buried pipeline. • Examine effect of trench depth and backfill thickness on oscillatory pore-water pressure around the partial-buried pipeline. [ABSTRACT FROM AUTHOR]

Abstract 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. Highlights • 3D model for wave-induced seabed residual response by considering the inertial terms of pore fluid & soil skeleton. • Effects of pile embedded depth on the seabed residual response and liquefaction around the vicinity of mono-pile. • Effects of wave reflection and diffraction on seabed residual response with various wave and seabed parameters. [ABSTRACT FROM AUTHOR]

Abstract This study proposed and applied a three-dimensional (3-D) numerical model based on existing 1-D and 2-D numerical models to investigate residual soil response in a homogeneous sandy seabed with a rocking mono-pile subjected to a cyclic lateral load and waves. The wave motion is governed by the Reynolds-averaged Navier-Stokes (RANS) equations. Compared to previous studies in the literature, this research analyzed the pore pressure accumulation due to wave-pile-seabed interaction considering the pile rocking effect. The proposed 3-D model is validated against existing experimental and numerical data. Subsequently, the 3-D model is used to investigate the residual response of a seabed with a mono-pile, in which pile rocking caused by a lateral cyclic load is considered. The results indicate that the existence of a rocking mono-pile greatly affects the residual response of the seabed due to pile-seabed interaction. The rate of residual pore pressure buildup was significantly faster near the mono-pile surface due to the impermeable interface and stiffness difference of the pile and seabed soil. In addition, the effect of pile rocking leads to the variation in shear stress in various parts of the seabed, resulting in different residual pore pressure variations at various positions around the mono-pile. [ABSTRACT FROM AUTHOR]

This paper considers three types of method for calculating return periods of individual wave and crest heights. The methods considered differ in the assumptions made about serial correlation in wave conditions. The long-term distribution of individual waves is formed under the assumption that either (1) individual waves, (2) the maximum wave height in each sea state or (3) the maximum wave height in each storm are independent events. The three types of method are compared using long time series of synthesised storms, where the return periods of individual wave heights are known. The methods which neglect serial correlation in sea states are shown to produce a positive bias in predicted return values of wave heights. The size of the bias is dependent on the shape of the tail of the distribution of storm peak significant wave height, with longer-tailed distributions resulting in larger biases. It is shown that storm-based methods give accurate predictions of return periods of individual wave heights. In particular, a Monte Carlo storm-based method is recommend for calculating return periods of individual wave and crest heights. Of all the models considered, the Monte Carlo method requires the fewest assumptions about the data, the fewest subjective judgements from the user and is simplest to implement. [ABSTRACT FROM AUTHOR]

The real state of ocean waves is random in nature with various monochromatic components. Transient pore pressures in a sandy seabed under the action of the random-waves with JONSWAP spectrum and the regular-waves were physically modeled, respectively. The surface elevations and the corresponding transient pore pressures in the fine-sand were measured simultaneously in a wave flume. The frequency-filtering phenomenon was observed by Fourier analysis for random-wave induced pore pressure responses. In the Fourier energy spectra, both a primary-peak (high-frequency) and a secondary-peak (low-frequency) were identified within the relatively shallow soil layer. But the primary-peak kept declining rapidly, meanwhile the secondary-peak attenuated much more slowly with increasing soil depth, which can eventually lead to a shift between the high-frequency peak and the low-frequency one. As a consequence, the upgraded primary-peak frequencies of the dual-peaked spectra at the deeper soil layer would become smaller than the original significant frequencies, indicating that the pore pressure induced by long-wave components is of vital significance there. Furthermore, a filtering-depth parameter is introduced to characterize the frequency-filtering effect. Given the pore pressure at a certain soil depth, the quantitative relationship between the primary-peak and the secondary-peak can be predicted for an arbitrary soil depth. • Physical modelling of pore pressures in a sandy seabed under random-waves with JONSWAP spectrum. • Pore pressures under random waves are profoundly distinctive from those under regular waves. • Frequency-filtering phenomenon of random-wave induced pore pressures was observed with Fourier analyses. • A filtering-depth parameter is introduced to characterize the frequency-filtering effect. • Relationship is established between the primary-peak and the secondary-peak for an arbitrary soil depth. [ABSTRACT FROM AUTHOR]

This paper proposes a two-dimensional (2D) coupled model for wave and current-seabed-pipeline interactions to examine oscillatory non-cohesive soil liquefaction around a partially buried pipeline in a trench. Unlike previous studies, two new features are included in this model: (1) wave-current interactions around the pipeline; and (2) fully coupled processes for the wave and current-seabed-pipeline system. In this study, the Reynolds Averaged Navier-Stokes (RANS) equations are applied to simulate the flow field around the pipeline, and Biot's poro-elastic theory for porous media is imposed to govern the soil response due to the wave-current loading. After being validated using data available in the literature, the 2D model is used to investigate the effects of the current velocity, the soil properties, and the wave characteristics on oscillatory non-cohesive soil liquefaction. Using the model, a function for the critical backfill thickness and the wave steepness under various flow and soil conditions is proposed to facilitate engineering practice. [ABSTRACT FROM AUTHOR]

Based on the launch & recovery system of a seafloor drill, the nonlinear coupling mechanism among the movement of the ship, the umbilical cable, and the seafloor drill caused by irregular waves is investigated, and the dynamic model that considers the influence of the seawater resistance for launch & recovery system of seafloor drill is established in this paper. Under different sea state conditions, the movement of the seafloor drill and the tension of the umbilical cable are calculated and analyzed for the seafloor drill before entering water and at different water depths. The research results showed that there are significant differences in the movement of the seafloor drill and the tension of the umbilical cable for different stages. The seawater resistance has obvious inhibition effect on reducing the erratic fluctuation of the movement of the seafloor drill and the tension of the umbilical cable. The analysis results can provide theoretical guidance for the studying of heave compensation and the constant tension automatic control of the umbilical cable. [ABSTRACT FROM AUTHOR]

While ocean waves propagating over a porous seabed, the amplitude of excess pore pressure would attenuate into the seabed (termed as "amplitude-attenuation"), which is always accompanied by "phase-lag". In this study, the amplitude-attenuation and the phase-lag phenomena in a fine-sand bed and a medium-sand bed were physically modeled in a large wave flume. A relative rigidity of soil-skeleton to pore-fluid is introduced to evaluate the seabed compressibility. Explicit expressions of the amplitude-attenuation and the phase-lag are derived and then validated with the experimental results. Parametric analyses indicate that, for the relative rigidity of the seabed much larger than 1.0, the amplitude-attenuation and the phase-lag along the non-dimensional soil depth would become more significant for larger wave period, but for smaller values of the combined rigidity-permeability parameter of the soil. A non-dimensional parameter (I c) is further derived to characterize the combined effects of wave parameters and soil properties. Simplified spatio-temporal correlation of transient pore pressure is finally established for I c ≫ 1.0, indicating the more rapidly the pore pressure amplitude attenuates within the seabed, the more significant the phase-lag becomes, correspondingly. • Amplitude-attenuation and phase-lag of wave-induced pore pressures were observed in a flume. • Explicit expressions for both the amplitude-attenuation and the phase-lag are obtained. • A key parameter is derived to characterize the combined effect of wave and soil parameters. • Spatiotemporal correlation for the transient pore pressure within a sandy seabed is established. [ABSTRACT FROM AUTHOR]

This paper presents a fully coupled flow deformation model to characterize the nonlinear seismic site response of liquefiable marine sediments, considering the ocean wave environment. Emphasis is placed on extending a simplified soil hysteresis model for the effective stress analysis of nonlinear site seismic response. The proposed model addresses the limitations of existing one-dimensional (1D) hyperbolic soil models to simultaneously capture the 3D hysteretic stress–strain behavior and the accumulated volumetric deformation of soil skeleton. The volume strain formulation of soil skeleton is included in the Biot's volumetric compatibility equation as the source term for excess pore water pressure buildup. The proposed method is implemented into an explicit time matching finite difference analysis platform, and validated against the recordings of the KSRH10 site for North–South (NS) direction of KiK-net borehole arrays in Japan. Finally, the influences of ocean wave loading upon the seismic wave propagation behavior in liquefiable marine sediments are examined with reference to the Bohai Strait site condition, China. The obtained results indicate that the ocean wave environment has significant effect on the nonlinear seismic site response of liquefiable seabed at shallow depth. • A fully coupled flow deformation model is presented for the simulation of seabed liquefaction. • A simplified soil hysteresis model is extended for the fully coupled seismic site response analysis. • Model calibrations are carried out against the recordings of the KSRH10 site from the KiK-net. • Influences of ocean wave on the seismic response of liquefiable marine sediments are investigated. [ABSTRACT FROM AUTHOR]

Abstract: Analysis of the wave–seabed–structure interaction is of great importance for the design and construction of marine structures. In this paper, a three-dimensional porous model, based on Reynolds-Averaged Navier–Stokes equations and Biot׳s poro-elastic theory, is developed by integrating 3D wave and seabed models to simulate the wave–seabed–structure interaction around the high-rising structure foundation used in the Donghai offshore wind farm. Then parametric studies for wave and seabed characteristics on soil response around the wind turbine foundation are conducted. Liquefaction potential and seabed protection methodology are investigated in the last section. The main results concluded from the numerical analysis are as follows: (i) both larger wave height and longer wave period will result in higher wave pressure on the structure and seabed; (ii) the existence of the structure has a significant effect on the wave transformation and the distribution of wave-induced pore pressure; (iii) wave height, wave period, soil permeability and degree of saturation play critical roles on dynamic soil behavior; and (iv) original seabed can be protected from liquefaction by replacing the existing layers. [Copyright &y& Elsevier]

Abstract: The subject of the wave–seabed–structure interaction is important for geotechnical and coastal engineering regarding stability analysis of foundations for offshore structures. Most previous theoretical investigations available concerned only with such a pipeline in a uniform single layer seabed. In this paper, a wave–seabed–pipeline system is modeled using finite elements. The seabed is treated as porous medium and characterized by Biot's dynamic equations. To explore the mechanism of the seabed instability, the two possible formulations: partly dynamic (u–p model) and fully dynamic (u–w model) for the wave-induced seabed response are considered. Verification of the proposed model is performed against the previous analytical result and experimental data. Based on the numerical results, the effects of wave and seabed characteristics, such as water depth, permeability, shear modulus, degree of saturation, and pipeline buried depth, on the wave-induced excess pore pressure and vertical effective stress will be examined. Finally, a parametric study will be conducted to examine the effects of wave and soil characteristics on the liquefaction potential. It is worth noting that soil permeability has a very significant influence on the pore pressure generation and liquefaction. [Copyright &y& Elsevier]

In this paper, a 3D model is developed to investigate the foundation stability around breakwaters at a river mouth, where both ocean waves and river currents are considered. The present model consists of flow and seabed sub-models. In the flow sub-model, the VARANS equations is used to describe hydrodynamic process, while the dynamic u − p approximation is employed in the seabed sub-model. Based on the integrated model, both oscillatory and residual liquefaction phenomenon is investigated by adopting the poro-elastic and poro-elastoplastic seabed models, respectively. The numerical results reveal that the breakwaters at the river mouth with the river current significantly alter the hydrodynamic properties around breakwater heads. Furthermore, the dynamic soil responses and liquefaction zones predicted by the poro-elastic and poro-elastoplastic seabed models show the completely different development trend, which the latter seabed has more intense and severe reactions. The parametric study indicates that the breakwater foundation is more likely to be liquefied in a loosely deposited soil under larger waves. The river currents can exacerbate the liquefaction condition in the region near breakwater heads. In addition, the pore pressure is smaller in front of a milder slope of breakwater flank and a round breakwater head with a smooth slope. • 3D poro-elastoplastic model for stability analysis around breakwater heads at a river mouth. • The soil liquefaction is more serious in a poro-elastoplastic seabed than a poro-elastic seabed. • The breakwater foundation is likely to be liquefied in loosely seabed with poor drainage condition. • The river currents can exacerbate the liquefaction around breakwater heads. • A milder slope of breakwater flank can prevent liquefaction around it to some extent. [ABSTRACT FROM AUTHOR]

The interaction between internal solitary waves (ISWs) and the seabed has been extensively studied, so do the energy loss, sediment resuspension, parameterization criterion and near-bed pressure variation. However, the horizontal and vertical shearing stresses of ISWs have not been directly measured. In this paper, flume experiments were designed to examine the near-bed pressure variation of shoaling ISWs over the slope with a novel device possessing four pressure sensors in different directions. Then the vertical and horizontal shearing stresses of ISWs were analyzed, with the shearing stress of ISWs in the South China Sea predicted based on field observation. The results showed that the maximum pressure variation of shoaling ISWs approximated 20 Pa, with the ISWs' horizontal shearing stress, about 3–6 Pa and the vertical one, about 10 Pa. It was predicted that the horizontal and vertical shearing stresses of ISWs in the open ocean were 5–100 kPa, larger than the maximum critical shearing stress of the sediment. This paper could promote the understanding of the seabed damage caused by ISWs and is expected to provide a reference for future field experiment design for the direct interaction measurement between ISWs and seabed sediments. • The horizontal and vertical shearing stresses of internal solitary waves were directly measured in the flume. • The horizontal and vertical shearing stresses of internal solitary waves in the open ocean are predicted 5–100 kPa. • The horizontal and vertical shearing stresses of internal solitary waves in open ocean were larger than the maximum critical shearing stress of sediment. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the results of an experimental study in which the occurrence and evolution of inhomogeneity in the strength of a uniform-originated silty seabed were investigated. The pore pressure and penetration strength at different depths inside the seabed were observed during the experimental process under the weight of the soil and under the action of waves of different heights (H=5cm, 10cm, 15cm). We found that a well-mixed silty seabed consolidates under the stress of its own weight, and its strength gradually increases as a result. Small wave action consolidates and strengthens the seabed and sediment. When the seabed is exposed to progressively higher waves, a fluidised response characterised by an arc-shaped boundary surface occurs on the seabed, and this response further controls the occurrence and evolution of the strength inhomogeneity of a uniform-origin seabed. The analyses clearly illustrate that features of seabed erosion and mass-transportation activity previously ascribed to increasing wave-current bed shear stress are controlled primarily by the process of wave-induced inhomogeneity in the strength of seabed sediments originating in the preceding period. In addition, the implications of the mechanism are explored. [Copyright &y& Elsevier]

Abstract: In this paper, an analytical approximation for the evaluation of the pore pressure and effective stresses in marine sediments under combined wave and current loadings is derived. Unlike previous investigations, non-linear interactions between waves and currents are considered in this study. An analytical solution for the wave–current induced oscillatory soil response in marine sediment is presented first. Based on the proposed analytical solution, a parametric study for the liquefaction potential will be carried out. Parametric study results indicate that the influence of current and non-linear waves on the maximum liquefaction depth is significant. [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: Wave-induced soil liquefaction can cause serious damages to coastlines and coastal infrastructures. Although liquefaction caused by regular waves over flat sea beds has been extensively investigated, studies of tsunami-induced liquefaction of coastal sandy slopes have been relatively rare. In this work, parametric studies are conducted to investigate the liquefaction potential of coastal sandy slopes caused by breaking solitary waves. The dependence of the maximum liquefaction depth on soil permeability is studied at different cross-shore locations and for different offshore wave heights. The results suggest that tsunami can induce liquefaction failure of coastal sand slopes, and that the soil responses can be characterized by the ratio of the pore pressure diffusion time scale to the wave loading time scale. Under the same wave loading condition, an offshore soil column may experience the largest liquefaction depth, while the longest duration of liquefaction (which may physically correlate to the largest liquefaction volume) occurs in the seepage zone, because of the wave loading and unloading pattern above the seepagezone. [ABSTRACT FROM AUTHOR]

Abstract: Stratified mixing is observed in a wave flume on an internal solitary wave (ISW) of depression or elevation type propagating over a submarine ridge. The submarine ridges, which comprise the seabed topography, are either semicircular or triangular. Tests are performed in a series of combinations of submarine ridges with different heights and ISW in different amplitudes within a two-layer fluid system. When the thickness of the top layer is less than that of the lower layer (i.e., H 1

Abstract: In this technical note, the phenomena of non-linear water-wave propagation above a seabed with variable depth is re-examined. The conventional Korteweg-de Vries (KdV) equation is re-derived for the general case of variable water depth. In the new form of KdV equation, the seabed bottom function is included. Two different bottom profiles are considered in this study; case 1: and case 2: . The effects of three bottom profile parameters, c, λ and ε on the wave profile are examined. Numerical results indicate that both ε and λ affect the wave profile significantly in case 1, while ε significantly affects the wave profile in case 2. [Copyright &y& Elsevier]

Abstract: Numerical analyses for the Bragg resonant reflection of carrier waves associated long waves due to sinusoidally varying seabeds are performed by using a set of coupled ordinary differential equations derived from the Boussinesq equations. The Boussinesq equations are firstly approximated with the Fourier decomposition. The coupled governing equations are then derived and used to simulate evolution of both short and long wave components. It is also found that wave groups are generated by two carrier waves with slightly different frequencies. The wave energy of the initial wave components is transferred to other harmonic components during propagation over a long distance. Evolution and reflection of both short and long waves were largely affected by nonlinearity. [Copyright &y& Elsevier]

Abstract: In this note, the interaction between water waves, a submerged breakwater, a vertical wall and a sandy seabed is studied experimentally. Laboratory experiments were conducted to record the water surface elevation and the pore pressures inside the seabed foundations. The previous analytical solution without submerged breakwater proposed by the first author [Jeng, D.-S. (1997). Wave-Induced Seabed Response in Front of a Breakwater, PhD Thesis, The University of Western Australia] was only valid in the region near the seabed surface. The strong interaction of surface waves between a submerged breakwater and a vertical wall causes the significant change in the wave-induced pore pressure within the seabed. The experimental results indicate that the wave-induced pore pressure beneath the submerged breakwater is greater than that at the toe. [Copyright &y& Elsevier]

Abstract: The wave pressure and uplift force due to random waves on a submarine pipeline (resting on bed, partially buried and fully buried) in clayey soil are measured. The influence of various parameters viz., wave period, wave height, water depth, burial depth and consistency index of the soil on wave pressures around and uplift force on the submarine pipeline was investigated. The wave pressures were measured at three locations around the submarine pipeline (each at 120° to the adjacent one). It is found that the wave pressure and uplift force spectrum at high consistency index of the soil is smaller compared to that of low consistency index. Just burying the pipeline (e/D=1.0) in clayey soil reduces the uplift force to less than 60% of the force experienced by a pipeline resting on the seabed (e/D=0.0) for I c=0.33. [Copyright &y& Elsevier]

Abstract: In this paper, an integrated model for the wave-induced seabed response in a porous seabed is proposed. Most previous studies have considered two-dimensional cases and a flat seabed. In this study, a full three-dimensional case is considered as well as a sloping seabed. The wave model (SWAN) and soil model (PORO-WSI) is coupled into one model. With the new model, the effects of wave and soil characteristics on the ocean waves-induced seabed response (including pore pressure and stresses) are investigated. Based on numerical results, the following conclusions can be drawn: (1) the magnitude of the wave-induced soil response in a sloping seabed is much smaller than that in a flat seabed (2) the wave-induced pore pressure decreases as the slope of the seabed increases. [Copyright &y& Elsevier]

The evaluation of the wave-induced seabed instability in the vicinity of a breakwater is particularly important for coastal and geotechnical engineers involved in the design of coastal structures. In this paper, an analytical solution for three-dimensional short-crested wave-induced seabed instability in a Coulomb-damping porous seabed is derived. The partial wave reflection and self-weight of breakwater are also considered in the new solution. Based on the analytical solution, we examine (1) the wave-induced soil response at different location; (2) the maximum liquefaction and shear failure depth in coarse and fine sand; (3) the effects of reflection coefficients; and (4) the added stresses due to the self-weight of the breakwater. [Copyright &y& Elsevier]

The problem of coherent reflection of an acoustic plane wave from a seabed consisting of a randomly inhomogeneous sediment layer overlying a uniform elastic sea floor is considered in this analysis. The random perturbation in the sediment layer is attributable to the sound-speed variations, resulting in volume scattering due to medium inhomogeneities. An approach based upon perturbation theory, combining with a derived Green''s function for a slab bounded above and below, respectively, by a fluid and an elastic half-space, is employed to obtain an analytic solution for the coherent field in the sediment layer. A linear system is then constructed to facilitate the computation of the coherent reflection field. The results of the coherent reflection coefficient for various sediment randomness, frequency, sediment thickness, and sea floor elasticity have been numerically generated and analyzed. It is found that the higher/larger the randomness, frequency, thickness, and shear-wave speed, the lower is the coherent reflection. Physical interpretations for the characteristics of the various results are provided. [Copyright &y& Elsevier]

In the past few decades, considerable efforts have been devoted to the phenomenon of wave-seabed interaction. However, conventional investigations for determining wave characteristics have been focused on the wave nonlinearity. On the other hand, most previous works have been only concerned with the seabed response under the wave pressure, which was obtained from the assumption of a rigid seabed. In this paper, the inertia forces and employing a complex wave number are considered in the whole problem. Based on Biot’s poro-elastic theory, the problem of wave-seabed interaction is first treated analytically for a homogeneous bed of finite thickness and a new wave dispersion relationship is also obtained, in which the soil characteristics are included. The numerical results indicate that the effects of soil parameters significantly affect the wave characteristics (such as the damping of water wave, wave length and wave pressure). Furthermore, the effects of inertia forces on the wave-induced seabed response cannot always be ignored under certain combination of wave and soil conditions. [Copyright &y& Elsevier]

Submarine pipeline is a type of important infrastructure in petroleum industry, used for transporting crude oil or natural gas. Understanding of the dynamics characteristics under hydrodynamic loading is crucial for engineers when assessing the stability of offshore pipelines in their designed service period. In this study, taking the integrated numerical model FSSI-CAS 2D as the tool, the nonlinear ocean wave & current-induced dynamics of a shallowly buried submarine steel pipeline and its surrounding loosely deposited seabed soil is numerically investigated. The excellent soil model Pastor-Zienkiewicz-Mark III (PZIII) is adopted to describe the complicated mechanical behaviour of loose seabed soil under cyclic loading. Computational results indicate that the shallowly buried submarine pipeline eventually significantly float up, and extrude the seabed soil over the pipeline driven by the gradually increased buoyancy on the pipeline caused by the accumulation of pore pressure around the pipeline, making the seabed over the pipeline hunch significantly. As a result, considerable deformation occurs in the seabed soil surrounding the pipeline. Two effective stress-based criterion are proposed to judge the occurrence of soil liquefaction. Adopting the two criterion. it is found that the surrounding seabed soil around the pipeline does not become liquefied; only stiffness softening has occurred in it. However, the soil in the upper seabed with shallow depth away from the pipeline becomes liquefied with a liquefaction depth 1.2–1.5 m. Comparative analysis indicates that the pipeline transporting natural gas floats upward with a much greater displacement than that if crude oil is transported. The computational results show that the integrated mode FSSI-CAS 2D has successfully and subtly captured a series of nonlinear physical phenomena of the intensive interaction between pipeline and its surrounding seabed soil. Finally, it is indicated that the integrated model FSSI-CAS 2D has an advantage to investigate the complicated interaction between fluid-structure-seabed foundation. • Wave & current-induced dynamics of a pipeline buried in loose seabed is studied. • The integrated model FSSI-CAS 2D is validated for pipeline-dense seabed interaction. • The third-order formulation is used to apply wave & current induced cyclic loading. • The sinking and floatation of pipeline have been successfully captured. • The soil surrounding pipeline is difficult to become liquefied under hydrodynamic loading. [ABSTRACT FROM AUTHOR]

In this paper, an elastoplastic modeling method is presented for dynamic consolidation of liquefiable seabed around a pipeline subjected to ocean environmental loadings (i.e. wave and current). Special attention is given to the cyclic plasticity modeling of liquefiable marine sediments and the evolving soil-pipeline interactions, in association with the Biot's dynamic consolidation theory. Motivated by the experimental findings, this paper extends a Masing-type model to the liquefaction-induced deformation regime of marine sediments within the cyclic plasticity framework. A novel plastic flow rule is developed to capture the cyclic-shearing-induced volumetric strain and hence exercise direct control over the response pattern of excessive pore water pressure (EPWP). Then, a model calibration procedure is outlined, with respect to cyclic laboratory sample tests under various loading paths. Finally, the combined actions of current on the wave-induced dynamics of liquefiable seabed around a buried pipeline are studied by numerical examples. The results demonstrate that the propagation of ocean current has major consequences for the wave-induced soil-structure interactions such as EPWP response, liquefaction pattern of seabed over the contact areas and uplift of pipeline. The liquefaction triggering of seabed and the consequence for the dynamic response of pipeline in the wave and current environment are also investigated. • The cyclic plasticity of liquefiable seabed around pipeline under wave and current is modeled. • A newly-observed cyclic shear-volume coupling model is incorporated into the plastic flow rule. • Model calibrations are carried out by element simulation of liquefaction against laboratory tests. • Influences of current on the wave-induced liquefaction and uplift of pipeline are investigated. [ABSTRACT FROM AUTHOR]

Wave breaking occurs when waves reach a critical level of amplitude, which results in releasing a significant amount of energy. Predicting the wave heights, locations and other characteristics of breaking waves in shallow water is an important area of research. The breaking wave height, which is the most important characteristic, depends on various parameters such as deepwater wavelength, breaking water depth and seabed slope. In this study, new formulae are proposed for predicting the breaking wave height focusing on two types of breaking waves, namely spilling and plunging. The breaking wave types can be classified by using the Iribarren number. A comprehensive set of laboratory and field observations is utilized to develop new formulae based on the Gene Expression Programming (GEP) numerical method. The datapoints representing individual waves whose breaking types have been determined to be different according to different wave breaking classification criteria have been ignored. In comparison with previous formulae, the new formulae proposed based on different breaking types have almost higher accuracy, especially in the plunging case. Therefore, it might be concluded that developing different formulae based on different breaking types, rather than a general one for all types, would lead to more accurate results. • New wave breaker prediction formulae are proposed using the gene expression programming. • Different formulae are proposed depending on the wave breaking type. • A wide range of laboratory, field and numerical data has been applied. • Comparisons are made between the proposed formulae and the previous ones. [ABSTRACT FROM AUTHOR]

With the increasing development and utilization of offshore oil and gas resources, seabed instability around pipelines subjected to combined ocean wave and current loadings and protection of the pipelines are becoming increasingly important. As a general practice, it is recommended to use trenching in shallow water region for the protection of submarine pipelines from the danger caused by storm waves and ocean currents changing level of the seabed. For a better understanding of the physical process involved in wave–current–seabed–pipeline interactions (WCSPI), a workable Finite Volume Model (FVM) is proposed to simulate wave–current induced soil responses around offshore pipelines. Based on the established FVM model, this study investigates the momentary soil liquefaction induced by various environmental loadings in ocean environments. In the present model, data exchange is taken place on the seabed surface to couple the flow and seabed sub-models. Unlike most previous studies, ocean currents are included in the present model, in which the Volume-Averaged Reynolds-Averaged Navier–Stokes (VARANS) equation is employed to govern non-linear fluid motions, while Biot's consolidation equation is used to link solid-pore fluid interactions in porous mediums. Numerical examples demonstrate the significant influence of ocean currents, trench geometry, and self-weight of the pipe on the wave-induced pore pressures and on the resultant seabed liquefaction around the pipeline. • OpenFOAM model for wave(current)-seabed interactions in a trench layer. • Significant changes of flow field and seabed liquefaction with a trench layer. • Simplified engineering design of pipeline protection with a trench layer. [ABSTRACT FROM AUTHOR]

Behavior of underwater unexploded ordnance located on the sea bed is poorly understood. Different types of munitions were tested in the swash and breaker zones of a large-scale flume containing medium sand on two initial foreshore slopes (1:16 and 1:10) with regular and irregular wave forcing (Hs = 0.3–1.1 m; T p = 2.6–9 s). Migration and burial were measured via pre- and post-run surveys and internal munition sensors. Water depths, flow velocities, wave runup and beach morphology changes were also measured. Munition sensors consist of an inertial motion unit for roll and heading and optical photocells for burial. Munition migration distances in the swash zone were greatest for the steeper slope and lower density munitions. Munition migration mimicked wave runup with net offshore transport. Breaker zone munitions experienced episodes of onshore- and offshore-directed motion without preferred direction. Denser munitions were observed to bury deeper, up to 2 munition diameters. Moderate correlation was observed between burial (r 2 = 0.48) or migration (r 2 = 0.37) with dimensionless parameters (such as Shields parameter, Keulegan-Carpenter number, object mobility number, munition density and Iribarren number), attributed to the high variability in munition response even under similar offshore forcing conditions. • Swash zone UXO migrated mostly offshore (69% of cases). • Breaker zone UXO were mobilized for 33% of cases with no preferential direction. • Roughly 40% of migration variability was related to dimensionless forcing parameters. • UXO can scour bury during erosional foreshore events. • Roughly 50% of burial variability was related to dimensionless forcing parameters. [ABSTRACT FROM AUTHOR]

When focusing on mooring system numerical modelling, the efforts are focused on validating models that increase the accuracy and maintain the computation time under reasonable limits. In this paper an approach for modelling the interaction among supporting structure and mooring system is introduced through kinematic relations. The proposed approach has been validated with the experimental wave tank 1:13.6 scaled data of the HarshLab 2.0 platform, a CALM type buoy moored with a three-line catenary system and used as a floating laboratory for materials and corrosion testing, to be installed at BiMEP. The drag forces of the buoy as well as the Morison coefficients of the heave-pitch coupling, induced by the attached structure for ships boat landing, have been identified. Results of the mooring line tensions are validated with imposed displacements of the structure and, subsequently, with coupled simulations of the moored buoy in a set of realistic sea states. Sources of differences on the estimation of line tensions are found to be mainly due to uncertainties of seabed friction forces, a high sensitivity of line tensions to small swaying and a poor pitching performance of the numerical model, very likely due to a very non-linear pitching of the physical model. • A fully coupled numerical model of a floating structure with a lumped mass mooring system. • A 1:13.6 scaled model of a moored CALM buoy, with a bow landing structure attached, physical testing. • Numerical model validation, with viscous drag force and heave-pitch cross coupled Morison force in a set of 12 sea states. [ABSTRACT FROM AUTHOR]