Current Wave Action Research Articles

Bridge pier under coupled earthquake and wave - Current actions: Numerical model establishing, optimization and structural response analysis

Bridges located in earthquake-prone areas may be subjected to earthquake, wave and current actions simultaneously. Current investigations on bridge piers under these complex loading conditions were generally performed through underwater shaking table (UST) tests, which required advanced test setups and great expenses. With the aim of eliminating these limits and developing a comprehensive understanding of the performance of deep-water bridge piers under coupled earthquake and wave-current actions, the present study carried out systematic numerical investigations. Wave generation and propagation were first simulated, for which thorough sensitivity analysis was conducted to obtain the optimal parameters, including mesh size, time step intervals, damping zone length and damping coefficients. Numerical models which are able to simulate nonlinear wave-current interactions were then established and validated. Following this, structural responses of bridge piers under wave, wave-current and coupled earthquake and wave-current actions were numerically simulated and validated by test results. Finally, parametric analysis was conducted on a pile of a practical deep-water bridge in China using the validated model with consideration of various water depth levels, diverse wave heights, different current velocities, varied earthquakes and different peak ground accelerations to reveal the influence of different excitation parameters on structural responses.

Numerical and experimental study of oil boom motion response and oil-stopping effect under wave-current action

Little research has been done on the failure of oil booms when wave-current coupling is present. This study investigates the motion response and oil-stopping failure of the oil containment boom experimentally and numerically. The oil containment effect under wave-current and the motion response of the oil containment boom were investigated through experiments. Using CFD software FLUENT for simulation, the study established a multiphase flow analysis model to simulate the oil containment of an oil containment boom and used the volume of fluid method (VOF) to track the oil-water interface. The study compares the experimental and numerical results, which are coincident with each other, and validates the validity of the numerical model. Numerical methods are used to analyze the effects of various working conditions (water flow rate, wave parameter, wave reversal, skirt height, and initial oil spill volume) on the oil containment effect of the oil containment boom. The results show that the presence of waves accelerates the oil containment failure; compared to the wave-current flowing in the same direction, wave-current reversal is better for oil containment, and the initial oil spill volume primarily affects the thickening of the oil layer, which provides an important reference for the design of an effective oil containment boom.

Numerical and experimental investigations on shape optimization of submerged floating tunnels with a discrete adjoint method

The shape of the tube in submerged floating tunnels (SFTs) plays a critical role in determining their performance and safety in marine environments. In this study, a gradient optimization procedure based on the discrete adjoint method is performed to minimize the drag force under uniform currents action. The free form deformation approach is employed to parameterize the design variables. The physical mechanisms of the optimization process are revealed via unsteady numerical simulations and experimental tests. Moreover, the hydrodynamic performance of the tube with the optimal shapes subjected to a wave–current combination is also evaluated. The results show that the drag coefficient is significantly reduced through optimization by reducing the pressure amplitude in the negative-pressure area. Additionally, the lift oscillation is also suppressed to delay structural fatigue, owing to the strength reduction and increased distance of the wake vortex. The experimental analysis indicates the advantage of the optimal shape in reducing the loads under wave–current actions, accompanied by changes in the frequency distribution of the force and vortex structure. The elliptical shape of the SFT's tube provides significant advantages in drag reduction at high Reynold number. Suggestions on the shape design of the section of SFT are given according to different types of constraints.

Analytical solution for seepage pressure of multilayered sand seabed considering interaction between wave-current action and shield tunnel

Existing theoretical studies of the seepage field around subsea shield tunnels under wave action take less account of the tunnel lining permeability, especially the effect of wave and current action on tunnel. Moreover, the solutions generally treat the sand as homogeneous and isotropic, ignoring the influence of multilayered seabed. In this paper, the analytical solutions are presented for the seepage pressure and liquefaction evaluation of sand around tunnel in multilayered seabed under wave and current action. The pore pressure response of pure seabed is obtained by the transmission and reflection matrix method. The mirror image method is introduced to establish governing equation of excess pore pressure reflected by tunnel, and the analytical solution of equation is obtained by Fourier series expansion under the condition of continuous seepage between sand and lining. Based on the superposition principle, the seepage pressure and liquefaction evaluation of sand around tunnel in multilayered seabed are obtained. Then the analytical solutions are compared with numerical and experimental results, and good agreement is obtained. In addition, the influencing factors of wave parameters (wavelength, period, current), seabed parameters (permeability, shear modulus, saturation) and tunnel parameters (lining thickness, lining permeability) are analyzed.

Strategy of scaled modeling for underwater shaking table tests on cylindrical marine structures under coupled earthquake and wave–current action: A review

AbstractMarine structures located in earthquake‐prone areas may be subjected to coupled earthquake and wave–current action and the underwater shaking table (UST) model test is one of the most effective methods to investigate the dynamic responses of them. However, the strategy of scaled modeling, including the selection of similitude criterion and the implementation of it, plays an important role in the test design, and hence influences the accuracy of response predictions of the prototype. This paper presents a comprehensive review of the strategy of scaled modeling utilized in UST model tests on marine structures subjected to coupled earthquake and wave–current action. The key performance parameters of USTs in service and being built in the world are first introduced. Then, the strategies of scaled modeling adopted in existing UST model tests of bridges, offshore wind turbines, submarine pipelines, and submerged floating tunnels are summarized. Following this, the applicability of current similitude criteria for UST model tests for different research focuses is fully discussed and the specific measure to realize the similitude criteria is concluded. Finally, recommendations for future work on similitude criteria are set out, providing insights into the improvements of the applicability and accuracy of the similitude criteria for UST model tests.

Wave-Current Loads on a Super-Large-Diameter Pile in Deep Water: An Experimental Study

Recently, the diameters and construction water depths of the pile foundations of planned and newly built sea-crossing bridges have been increasing greatly. Hydrodynamic loads are the key control factors in the design of super-large-diameter piles. However, most of the previous studies focused on the inline force on the pile with a small diameter, and there were few cases to consider the impact of the transverse force on the hydrodynamic load of the pile under wave-current actions. In this study, to understand the hydrodynamic loads on such deep-water super-large-diameter piles, the prototype was one of the 6.3-m piles used in the Xihoumen Rail-cum-Road Bridge, and 1:60-scale model tests were carried out in an experimental tank, with the actions of regular waves and waves combined with currents used as loads. The influence of the current velocity and static wave height on the inline and transverse forces on the pile was measured and analyzed. The experimental results indicate that with increasing current velocity, the fluctuation characteristics of the wave-current-induced inline and transverse forces change significantly, and their peak values increase obviously compared to those induced by only waves. In particular, the peak transverse force increases tens of times and can become equivalent to the inline force. The modified Morison formula and Kutta–Joukowski formula are used to derive the correlations between the drag coefficient CD, inertia coefficient CM, lift coefficient CL, and redefined Keulegan–Carpenter number KC*. Under wave-current action, the transverse force contributes quite significantly to the hydrodynamic load on a super-large-diameter pile, making it easier to trigger extreme structural loads. The results presented herein are an important reference for the engineering designs of such super-large-diameter piles.

Experimental study of local scour around inclined piles in combined waves and current

Compared to vertical piles, the position relationship between the inclined pile and seabed has some extra effects on the surrounding wave-current interaction and sediment transporting mechanism. A series of local scour experiments with wave-current flume are conducted for investigating scour characteristics and influencing factors around inclined piles and vertical piles at a certain inclination angles range. The experimental results indicates that there are substantial differences in scouring variation patterns between upstream inclined piles, downstream inclined piles and vertical piles, and the suppression impact of pile inclination angle on scouring was closely related to the wave-current conditions. The magnitude relationship of relative scour depth (S/D) between the inclined and vertical piles will change visibly when the sand transporting capacity under wave-current action reaches a certain level. The obtained multiple regression equation based on mixing training datasets could provide reasonable estimation for scour depth around inclined and vertical piles under wave-current and only current action.

Dynamic response of cable-stayed bridge under wind-wave-current action considering pile-soil interaction

Sea-crossing bridges are generally subjected to the combined wind, wave and current action, making it worthwhile investigating the dynamic response of cable-stayed bridges under wind-wave-current action. In this study, the numerical wave flume is utilised to obtain wave-current action, where a measured spectrum is applied to generate random waves. The stochastic wind field is calculated through the spectral representation model. These actions are validated by comparing experimental and theoretical results. A comparative analysis under different loads provides the theoretical basis for load type determination. The influence of pile–soil interaction is also studied with the consolidation, pile–soil solid contact (PSSC), and soil spring model. The results show that the root mean square (RMS) values of girder displacement are greater under regular wave-wind-current action, while the extreme values of the girder internal force present the opposite pattern due to the statistical characteristics of random waves. It indicates that the statistical characteristics of random waves should be considered to secure the girder safety. For the bridge tower, the random wave-wind-current action has a greater effect on the lateral displacement responses. Furthermore, the model considering the pile–soil interaction gets more flexible, absorbing more energy of low-frequency wave-wind-current action.

Dynamic analysis of the wind-wave-current-bridge system considering pile-soil interaction

Coastal bridges are normally confronted with a complex marine environment including wind, wave and current. Present researches rarely take the current action and pile-soil interaction into consideration. It is thus essential to conduct the dynamic analysis of the cable-stayed bridge under wind-wave-current action considering pile-soil interaction. A coupled wind-wave-current-bridge (WWCB) system is proposed in this study to help understand the bridge dynamic performance. In the WWCB system, the bridge model is established through the finite element method, and the pile-soil interaction is considered through the pile-soil solid contact (PSSC) model. The wave-current action is obtained through a numerical wave tank, while the wind is simulated as the stochastic random process and generated with spectrums. The initial geostress, mass and density distribution are also considered in the WWCB system. To illustrate the bridge dynamic characteristics, dynamic responses under different load combinations are presented. Furthermore, the natural frequency and spectral density function comparison between the consolidation model, PSSC model and soil-spring model are provided to investigate the influence of the pile-soil interaction. The results show that different from previous conclusions, the wave-current action plays the dominant role instead of the wind action in some cases when considering the pile-soil interaction. Additionally, the consideration of the pile-soil interaction would decrease the structural stiffness, resulting in lower natural frequencies and wider frequency distribution. Consequently, the influence of the wave-current action and pile-soil interaction should be noted in the practical engineering.

Effect of wave-current interaction on a long fjord-crossing floating pontoon bridge

Fjord-crossing floating bridges are sophisticated structures subjected to complex environmental loadings including combined action of wave and current. However, the effect of wave-current action is often neglected in a conventional engineering practice. This paper presents a numerical study of the dynamic response of a floating bridge under the combined action of waves and current. The effect of wave-current interaction on the hydrodynamics associated with the bridge pontoons are first evaluated by using a three-dimensional potential flow solver. A model of the entire floating bridge is then established and analysed in the time domain. The accuracy of the model is verified by comparison with available experimental data for a 1 km long curved floating bridge. Parametric studies are subsequently carried out to investigate the effect of wave-current interaction on a 4.6 km long floating bridge model for crossing the Bjørnafjord. Results show that the wave-current interaction has a significant effect on a fjord-crossing floating bridge studied in this paper. Neglection of such an interaction could lead to substantial overestimation or underestimation of the structural responses depending on the environmental headings.

Experimental investigation for the dynamic behavior of submerged floating tunnel subjected to the combined action of earthquake, wave and current

Submerged floating tunnel (SFT) is an innovative traffic structure for transportation in long and deep-water areas. The SFT that built in earthquake-prone areas has the risk to be subjected to earthquake and wave-current action simultaneously during its whole lifetime. Therefore, to ensure the safety and stability of SFT during its service, the dynamic behavior of a SFT subjected to combined action of earthquake, wave and current are experimentally investigated in this study. Based on the wave-current flume and a specially designed underwater shaking device, a physical scaled model experiment of SFT for studying the dynamic behavior of SFT subjected to the combined action of earthquake, wave and current is presented. The earthquake wave outputs from the underwater shaking device are verified to be reliable. The experimental results are also observed to conform against the numerical results well validating the test. The influence of key load parameters such as the peak ground acceleration and type of single earthquake, the wave height, and the combination of earthquake, wave and current on the dynamic behavior of the SFT are deeply and thoroughly explored. This experiment research has theoretical and engineering importance for the prevention and control hazard of design for the SFT.

Numerical Study on Initial Laying Process of Submarine Cables for Wave Energy Booster Station in Real Sea States

Hu, J.; Li, Z., and Zhang, Y., 2020. Numerical study on initial laying process of submarine cables for wave energy booster station in real sea states. In: Zheng, C.W.; Wang, Q.; Zhan, C., and Yang, S.B. (eds.), Air-Sea Interaction and Coastal Environments of the Maritime and Polar Silk Roads. Journal of Coastal Research, Special Issue No. 99, pp. 60-66. Coconut Creek (Florida), ISSN 0749-0208.Based on real sea conditions of the national wave energy demonstration site in Wanshan sea area of Zhuhai City, China, some numerical experiments are carried out to simulate the submarine cables initial laying process of the Wave Energy Booster Station in this demonstration site. The numerical model is established with the Orcaflex software employed. The motion response of laying ship and the hydrodynamic characteristics of submarine cables are simulated here under three sea conditions, i.e. usual waves, waves with current combined and possible extreme waves. Research results show that the tension and curvature of the cable are large under the condition for wave direction perpendicular to the ship axial direction, which is a relatively bad sea condition. The current also has some influences on the submarine cable laying, and the maximum effective tension of cable produced by the combined wave-current action is 1.35 times that of cable with the wave action alone. When extreme waves appear, pitch, heave and heave acceleration of the laying ship and tension of the cable ends increases obviously. And the variation of effective tension at both cable ends can reach 1.67 times that of cable ends under usual random waves. The numerical model and research results in this paper can provide some guidance for the research and construction of the cable laying of booster stations for marine renewable energy power plants in real sea conditions.

Scour characteristics of an offshore umbrella suction anchor foundation under the combined actions of waves and currents

An umbrella suction anchor foundation (USAF) is a novel foundation for offshore wind turbines. Compared to the local scour occurring around deep foundations such as monopiles, the scour around an USAF can significantly influence the stability of wind turbine systems. Therefore, research on the local scour around an USAF induced by waves and currents is of great value to coastal engineering projects. In this study, a series of scour tests of an USAF were carried out and the authors evaluated the influences of a steady current, waves, and the combination of waves and currents. The flow field and wave field were captured by an acoustic Doppler velocimeter (ADV) current meter and wave gauge, respectively. Moreover, the equilibrium depth, scope, and shape of the scour holes are determined using an ultrasonic topographic surveying meter. The results demonstrate that the scour profiles are definitely distinctive for the three environmental conditions. A standard k-ω turbulent model is used to simulate the turbulent flow field. The volume of fluid (VOF) method is used in computational fluid dynamic (CFD) software to deal with the free water surface and moving mesh to explore the changes in the topography over time. A dynamic three-dimensional numerical model of the local scour around the USAF is developed and validated by comparing the results with previous scour tests and other published experimental data. The scour characteristics of the USAF and the suction anchor foundation (SAF) are determined by solving the fully three-dimensional transient Navier-Stokes equations in a fixed Eulerian grid. The results indicate that compared with a conventional SAF, the USAF can significantly prevent scour; moreover, the scour depth is significantly different for the two foundations under the combined wave-current action and is approximately twice as large for the SAF than the USAF.

Dynamic climate-driven controls on the deposition of the Kimmeridge Clay Formation in the Cleveland Basin, Yorkshire, UK

Abstract. The Kimmeridge Clay Formation (KCF) is a laterally extensive, total-organic-carbon-rich succession deposited throughout northwest Europe during the Kimmeridgian–Tithonian (Late Jurassic). It has recently been postulated that an expanded Hadley cell, with an intensified but alternating hydrological cycle, heavily influenced sedimentation and total organic carbon (TOC) enrichment by promoting primary productivity and organic matter burial in the UK sectors of the Boreal Seaway. Consistent with such climate boundary conditions, petrographic observations, total organic carbon and carbonate contents, and major and trace element data presented here indicate that the KCF of the Cleveland Basin was deposited in the Laurasian Seaway under the influence of these conditions. Depositional conditions alternated between three states that produced a distinct cyclicity in the lithological and geochemical records: lower-variability mudstone intervals (LVMIs) which comprise clay-rich mudstone and higher-variability mudstone intervals (HVMIs) which comprise TOC-rich sedimentation and carbonate-rich sedimentation. The lower-variability mudstone intervals dominate the studied interval but are punctuated by three ∼ 2–4 m thick intervals of alternating TOC-rich and carbonate-rich sedimentation (HVMIs). During the lower-variability mudstone intervals, conditions were quiescent with oxic to suboxic bottom water conditions. During the higher-variability mudstone intervals, highly dynamic conditions resulted in repeated switching of the redox system in a way similar to the modern deep basins of the Baltic Sea. During carbonate-rich sedimentation, oxic conditions prevailed, most likely due to elevated depositional energies at the seafloor by current–wave action. During TOC-rich sedimentation, intermittent anoxic–euxinic conditions led to an enrichment of redox-sensitive and sulfide-forming trace metals at the seafloor and a preservation of organic matter, and an active Mn–Fe particulate shuttle delivered redox-sensitive and sulfide-forming trace metals to the seafloor. In addition, based on TOC–S–Fe relationships, organic matter sulfurization appears to have increased organic material preservation in about half of the analysed samples throughout the core, while the remaining samples were either dominated by excess Fe input into the system or experienced pyrite oxidation and sulfur loss during oxygenation events. New Hg∕TOC data do not provide evidence of increased volcanism during this time, consistent with previous work. Set in the context of recent climate modelling, our study provides a comprehensive example of the dynamic climate-driven depositional and redox conditions that can control TOC and metal accumulations in a shallow epicontinental sea, and it is therefore key to understanding the formation of similar deposits throughout Earth's history.

Dynamic Response of Bridge Pier under Combined Earthquake and Wave–Current Action

AbstractA study of the dynamic response of a circular bridge pier forced simultaneously by earthquake and wave–current actions is presented. On the basis of diffraction wave theory, the analytic so...

Hydrodynamics, erosion and accretion of intertidal mudflats in extremely shallow waters

Intertidal flats are shallow-water environments that undergo cyclical variations in water depth, leading to a frequent occurrence of extremely shallow water stages (ESWS; water depths <0.2 m). However, relatively little is known about the hydrodynamic conditions and erosion–accretion processes during ESWS, because the water depth is too shallow to measure in situ sediment dynamic processes using traditional methods. To address this gap, based on in situ measurements with four advanced instruments, we quantified the hydrodynamic conditions, erosion and accretion during ESWS in calm weather conditions on a highly turbid intertidal flat in Jiangsu coast, China. Our results revealed that marked erosion and accretion occurred during ESWS at the flood and ebb tidal stages, respectively. The resulting bed-level changes were three times greater during ESWS than relatively deep water stages (RDWS; water depths >0.2 m), and the rate of change was an order of magnitude faster than during RDWS. This larger and faster bed-level change occurred even though the ESWS duration only accounted for 10% of the entire tidal cycle. This result occurred because the bed shear stress due to combined current–wave action during ESWS, was, on average, two times higher than during RDWS at the flood stage causing more extensive erosion. Whereas during the ebb stage, this shear stress during ESWS was only half of that during RDWS resulting in greater accretion. The main implications of these results are that, because ESWS occur frequently (twice every tide) and are associated with large bed shear stress and bed-level changes, these conditions are likely to play an important role in morphological changes of intertidal flats. Our study shows that ESWS have a key influence on intertidal flat hydrodynamics and sediment dynamics. Thus our results are the basis for an improved understanding of the coastal morphodynamic processes on intertidal flats.

2-D Coastal Hydrodynamic Model to Evaluate the Performance of the Abu Dhabi Shore Protection System

The main shoreline of the Abu Dhabi City Main Island is facing the Arabian (Persian) Gulf from the north-west side and is exposed to continuous current wave action. Therefore, a shore protection system was developed on this side from the Main Island. The shore protection system consists of onshore and offshore breakwaters, huge volumes of damped sand, and an artificial island known as the Lulu Island. In this study, the performance of the current shore protection system of Abu Dhabi City Main Island was evaluated using the Costal Graphical Wave (CGWAVE) 2D-hydrodynamic model. The model can simulate the characteristics of the waves when they approach the breakwaters or the shoreline. Our study has shown that the breakwaters manage to dissipate most of the wave energy before the waves reach the Lulu Island, whereas this island protects the Abu Dhabi City shoreline by creating an elongated sea area between the island and the shoreline that is devoid of any wave action. The constructed shore protection system was also efficient in controlling beach erosion and flooding by damping the wave energy.

Wave and wave-current actions on a bridge tower: An experimental study

With a scale of 1:100, an experimental model was set up to investigate the dynamic responses of a bridge tower subjected to ocean waves and wave-currents. The bridge tower was designed for a sea-crossing bridge. Based on a pile-group foundation, it was designed to be a typical gate-type structure. Wave-induced base shear forces on the foundation and motion responses of the tower were measured and analyzed. The experimental results show that when a wave period is close to the natural period of the structure, an obvious resonance will be induced on the structure. For different wave action angles, the longitudinal incident waves induced the largest longitudinal base shear forces on the foundation and the greatest dynamic motions on the upper tower of the structure. Because of the pile-group effectiveness, the incident directions of the waves and the wave periods affect the acting forces on the foundation of the structure. For wave-current actions, forward currents increase the forward wave forces on the foundation and decrease the backward forces, but do not significantly affect the motion responses of the upper tower. The experimental results can be used as the verification data for numerical calculations. With the structural forms of the pile-group and the gate-type tower being typical, the results given in this study can be used as a reference for similar engineering designs.

Fatigue load estimation of a spar-type floating offshore wind turbine considering wave-current interactions

This paper considers the effects of current and wave-current interactions in fatigue analysis of floating offshore wind turbines (FOWTs). Surface water waves experience frequency shifts and wave shape modification when traveling on underlying currents. The wave-current interactions are known to be important for the responses of offshore structures, however, they have not been considered in FOWT fatigue analysis. To include such interactions, a nonlinear mooring hydrodynamics model is presented which is able to consider the cable geometric nonlinearity, seabed contact, and the current effect. The mooring model is then coupled with a spar-type FOWT model which simulates the structural dynamics of turbine blades and tower; aerodynamics of the wind-blade interaction and wave-current actions on the spar. Analytical wave-current interaction models based on Airy’s theory considering the current effect are applied for generating the flow field. Based on a spar-type FOWT and the wave-current interaction model, numerical simulations have been performed for three cases with only waves, wave and current without and with interactions. The comparison of the structural responses shows that the current and the wave-current interaction can have significant influences on FOWT tower and cable responses. Furthermore, cable fatigue life is estimated for two particular cases when the cable tension is decreased and increased respectively due to the presence of current. It is found that if the current tends to increase the cable tension, neglecting the current and wave-current interactions leads to overestimate of the cable fatigue life.

Dynamic Response of Multilayered Silty Seabeds under Wave-Current Action in the Yellow River Estuary

Few studies have focused on pore pressure and liquefaction in a layered silty seabed. This study investigated a silty seabed in the Yellow River Estuary. Based on Biot’s theory and further considering the influence of current, a numerical validation of two-dimensional seabeds under combined wave and current action was established with a quasi-static model. Based on this model, the dynamic response of five typical layered seabeds was explored under combined wave and current actions. The numerical results demonstrate a significant discrepancy in dynamic response. For instance, the distribution of the pore pressure versus the soil depth was found to be entirely different, especially for Seabed 1 and Seabed 4 (S1 and S4), where two peak values of the pore pressure occurred. Furthermore, considering the residual pore-pressure term in the liquefaction analysis, the liquefaction formed fastest in Seabed 5 (S5), and the maximum accumulative liquefaction depth was the greatest for Seabed 1 (S1), at slightly more than 8.5 m. In addition, the influences of waves and currents on the dynamic response of seabeds are discussed in parametric study, which indicates that waves and currents have a significant effect on the pore-pressure distribution. The relative differences in the maximum pore pressure for different currents, wave heights, and wave periods were found to be 27.8, 24.9, and 22.4%, respectively, of the maximum linear wave pressure P0 in Seabed 2 (S2).