The Characteristics Of Breaking Wave Force Acting On Monopiles On Permeable Slope

The monopile is the most popular foundation type adopted in the field of offshore engineering,and the wave load is one of the key loads acting on monopiles.Whether it is able to make accurate predictions about the wave load acting on monopiles will influence the safety of foundation construction significantly.Previous researches related to wave loads were mainly conducted on impermeable seabed while the real seabed should be permeable.It is also rare to see the systematic analysis of characteristics of wave force on permeable seabed,not to mention under the effects of wave-current interactions.Aiming at these problems,the following work was done:(1)A test system which could calculate the moment on rigid monopiles under wave loads was designed.88 series of flume experiments were conducted to investigate the characteristics of solitary and regular wave force on the impermeable slope.The effects of not only the monopile diameter and wave parameters but also same-direction current on wave force were studied.Results indicate that the presence of the slope can accelerate the process of wave breaking,especially at a relatively low water depth.The same-direction current can increase the solitary wave force by 252.89%at most under the test conditions.The breaking process of regular waves can also be accelerated by increasing the wave height or decreasing the wave period,while the monopile just around the wave breaking point suffers the maximum wave force.The high-speed current can delay the breaking process of regular waves and decrease its wave height,reducing the wave force eventually.(2)Rigid permeable slopes with different permeability were set up using the foamed ceramics made from aluminum oxides.144 series of flume experiments were performed to investigate the characteristics of regular wave force on the permeable slope.And the wave-current interactions were also considered.Results show that the breaking process of regular waves can be speeded up through decreasing slope permeability.But the effects of slope permeability are weakening with the water depth increasing,unless the monopile is located nearby the breaking point.It is also possible for the regular wave which has broken on permeable slope to generate relatively high wave force on monopiles.(3)Based on the incompressible and viscous RANS equations,a 3-D numerical wave flume containing a permeable slope was established.The Forchheimer saturated drag model was introduced to consider the effects of seabed permeability on fluid motions.Using the validated model,195 simulations were carried out to investigate the characteristics of solitary wave force on the permeable seabed.Results show that with the slope permeability increasing,the breaking process of solitary waves is delayed and its wave force shows a general trend of decreasing.On the slope with low permeability,the monopile located at the position between the breaking point and 1D behind the breaking point will suffer the maximum wave force.But the monopile position has few effects on wave force on the high permeability slope.A secondary wave wall,developing after wave breaking,can lead to comparatively large wave force on monopiles on the specific slope.Besides,the inclination angle of slope and monopiles can also influence the wave force.