Yes / This study presents results from laboratory experiments to investigate the wake structure in the lee side of a scaled three-bladed horizontal axis tidal stream turbine with a mono-pile support structure. Experiments are conducted for a range of approaching flow velocity and installation height of rotor. Analysis of the results shows that bed shear stress increases with the increase of approaching velocity and decrease of installation height within 2D (D is the diameter of the rotor) downstream of the rotor. The flow field within 2D downstream of the rotor is greatly influenced by the presence of nacelle and mono-pile. Low stream-wise flow velocity and large turbulence intensity level is detected along the flume center right behind the nacelle and mono-pile from 1D to 2D downstream of the rotor. Stream-wise velocity at the blade tip height lower than the nacelle increases sharply from 1D to 2D and gradually grows afterwards. Correspondingly, the turbulence intensity decreases quickly from 1D to 2D and slowly afterwards. Large bed shear stress is measured from 1D to 2D, which is closely related to turbulence induced by the mono-pile. It is also found that the presence of the mono-pile might make the flow field more ‘disc-shaped’. / National Key Research and Development Program of China (No.2017YFC1404200), the Marine Renewable Energy Research Project of State Oceanic Administration (No.GHME2015GC01), the Fundamental Research Funds for the Central Universities of China (No.2017B696X14) and the Postgraduate Research & Practice Innovation Program of Jiangsu Province, China (No.KYCX17_0448)

Yes / In this study, a new three-dimensional (3-D) model was developed to provide better understanding of the mechanism for wave-induced seabed response around mono-pile. Based on poro-elastic theory, the fully dynamic (FD) formulations were adopted in the present model to simulate pore water pressure, soil stresses, displacements of both soil and mono-pile. Good agreement between numerical simulation and experimental results was obtained. Based on parametric study, numerical results indicated: (1) wave diffraction and reflection have significant effects on pore water pressure and soil displacements around mono-pile; (2) the most sensitive position for seabed parameter to pore water pressure around mono-pile locates in front of mono-pile while the least sensitive position is at the position of angle 3π/4 with respect to the incident wave direction; and (3) the increase of mono-pile horizontal displacement corresponds to the increase of wave height and the decrease of seabed Young's modulus. / National Science Fund for Distinguished Young Scholars (51425901), the National Natural Science Foundation of China (51209082, 51379071, 41176073), the Specialized Research Fund for the Doctoral Program of Higher Education of China (20120094120006, 20130094110014), the 111 project (B12032), the 333 project of Jiangsu Province (2013Ⅲ-1882)

Yes / 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 nonlinear wave effect 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 embedment 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 embedment 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. / Energy Technology Partnership (ETP), Wood Group Kenny, and University of Aberdeen; the National Science Fund for Distinguished Young Scholars (51425901) and the 111 project (B12032).