Experimental And Numerical Studies Of Seabed Response Around Pile Foundation Under Wave And Current Loading

The marine structures played an important role in the regional economic development,effectively improved the regional transportation environment,greatly promoted the complementary advantages and regional cooperation.However,many technical challenges as well as opportunities have been brought.Ensuring the safety of marine structures in a complex marine environment had become a hot research issue.While,seabed response and stability around structures in the marine hydrodynamic environment were gradually becoming a key issue for ensuring the safety of marine structures.The theoretical method had great limitations for analyzing three-dimensional complex engineering problems due to its highly simplified assumptions.Therefore,both experimental research and numerical simulation were carried out to systematically study the hydrodynamic response and seabed response around structures under combined waves and currents.Unlike previous studies,both regular and random waves,as well as the interaction between waves and currents,are considered.The bottom of the structure was partially embedded within the seabed rather than simply treated as a fixed boundary.Then,the non-homogeneous seabed was considered,not limited to the uniform seabed.In addition,experimental research and numerical simulation complemented each other.The relevant physical quantities such as wave surface,current velocity and pore water pressure were monitored as comprehensively as possible.Not limited by the structure scale and the quantity of test points,the numerical simulation can comprehensively reflect the spatial distributions of research results.Therefore,the main research contents and results were as follows:(1)The flume experiment of wave(current)-seabed-structure interaction was planned.The influence of regular or random waves and currents interaction on the hydrodynamic response and seabed response around the structure was systematically studied.In experiments,the monopile was partially embedded within seabed.The experimental results showed that,the planned flume experiment can accurately and effectively monitor time histories and spatial distributions of wave surface,current velocity and pore water pressure around the structure.Moreover,it was suitable to study the significant difference between random waves and regular waves,and the strong disturbance of current to wave field.What?s more,it can also provide accurate and abundant verification data for the subsequent numerical simulation.(2)Under combined regular waves and currents,the hydrodynamic response and seabed response around the structure were experimentally studied.The interaction between wave and current was considered,and the influence of wave parameters and current velocity on the vertical and plane distributions of pore water pressure around the structure was analyzed in detail.The experimental results showed that,the variations of the hydrodynamic response and pore water pressure under combined waves and currents loading were obviously different from those under wave-only cases.Higher wave energy and larger current velocity can make the amplitude of pore water pressure larger and the attenuation of pore water pressure slower along the seabed depth.The current can promote the influence range and depth of wave parameters on the amplitude of pore water pressure.The influence of the variation of current velocity on pore water pressure got weakened in depth.In addition,the experimental results further illustrated the necessity and importance of considering the interaction between waves and currents as well as the local embedment of structures.(3)The hydrodynamic response and seabed response around the structure under combined random waves and currents were studied by the flume experiments.The interaction between random waves and currents was focused.The influence of random wave parameters,current velocity and random wave spectrums on the distributions of pore water pressure were emphasized.The experimental data shown that,compared with the equivalent regular waves(currents)loading,the amplitude of pore water pressure was larger and on a rising trend with the increase of random wave parameters.Besides,the current can promote the influence range and depth of random wave parameters on pore water pressure.Affected by the random characteristics of waves,the effect of current velocity on the spatial distribution of pore water pressure was more complex than that under combined regular waves and currents.Moreover,random wave spectrums had significant influence on the time history and amplitude of pore water pressure.An appropriate random wave spectrum should be selected to accurately describe the wave characteristics in engineering application,which further indicated that studying random waves and currents interaction had important engineering significance.(4)A numerical simulation model of wave(current)-seabed-structure interaction was established.The mass source function wave-generating method was introduced to simulate regular waves and random waves.The wave-current interaction was controled by solving Reynolds averaging Navier-Stokes equations.Governing equations of the non-homogeneous seabed are derived.Verified with a series of experimental results,the hydrodynamic response and seabed response around structure were accurately simulated by coupling wave(current)model with seabed model.The effect of non-homogeneous characteristics on seabed response cannot be ignored.Moreover,the numerical simulation model can be extendable to analyse the problem of large-scale complex structures in extremely complex marine environment.(5)The effect of current and non-homogeneous seabed characteristics on the hydrodynamic response and seabed response around the large-scale structure were numerically analyzed.Combined with engineering practice,taking the large-scale dumbbell structure as the research object,the effects of current,consolidation and the non-homogeneous characteristic of seabed on the seabed response were mainly studied.The numerical results show that,the direction of the current had a significant effect on the hydrodynamic response and seabed stability.The seabed consolidation caused by the self-weight of large-scale structures can not be ignored.It was necessary to carry out steady-state analysis to obtain the initial state of the numerical simulation.In addition,the characteristics of non-homogeneous seabed would affect seabed response.The depth function of shear modulus had significant influence on pore water pressure and liquefaction depth.The depth function of permeability had a certain influence on the pore water pressure of coarse seabed near the embedded depth of structure.