【作者】 刘振宇；

【导师】 王立忠；

【作者基本信息】 浙江大学 ， 岩土工程， 2020， 硕士

【摘要】 单桩基础是目前海洋工程中应用最广泛的基础形式,而波浪荷载又是作用于单桩基础上的主要外部荷载之—。能否对单桩基础所受波浪荷载进行准确预测,直接影响近海构筑物基础的服役安全。但现有波浪力相关研究多以不可渗透海床为研究对象,缺乏对真实工况下可渗透海床上破波力作用特征的系统分析,更鲜见考虑波流共同作用对波浪力影响的深入研究。针对这些问题,本文开展了以下工作:(1)设计了一套可测量并反算刚性桩在波浪作用下所受弯矩大小的测量系统,开展了 88组不可渗透斜坡上单桩所受孤立波和规则波作用力特征研究的室内水槽试验。在考虑桩径和波浪要素的同时,通过改变桩周流场流速,研究了同向流对单桩所受波浪力的影响。试验发现:斜坡存在会增强波浪破碎趋势,且低水深工况下表现更为显著;研究工况下同向流可增大孤立波作用力,单桩桩身弯矩最大增加252.89%;增大波高和减小周期均可增强规则波的破碎趋势,恰好位于波浪破碎点之后的单桩受力最大;同向流通过使规则波波高衰减,并抑制已破碎波浪沿桩侧的回流,延缓波浪破碎进程,导致试验工况下波浪力整体减弱。(2)使用不同PPI的氧化铝泡沫陶瓷材料搭建出不同渗透率的刚性斜坡海床,利用144组室内水槽试验研究了可渗透海床上单桩所受规则波作用力的变化特征,同时考虑了波流共同作用的影响。研究发现:减小海床渗透率会促进规则波破碎,进而影响波浪力;但海床渗透率的影响强度随水深增加而明显减弱,仅当单桩位于波浪破碎点附近时例外;可渗透海床上,已破碎的规则波仍可通过二次拍击在单桩上产生较大作用力。(3)基于不可压缩粘性流体的雷诺平均纳维—斯托克斯方程,构建了包含可渗透斜坡在内的三维数值波浪水槽,并引入Forchheimer饱和拖曳力模型模拟多孔介质对流体运动的阻碍作用。使用已有数据对数值模型准确性进行了验证,进而通过195组数值模拟研究了可渗透海床上孤立波破碎波浪力变化特征。结果显示:随海床渗透率增大,孤立波破碎进程减缓,波浪力整体下降;在低渗透率海床上,单桩在波浪破碎点至破碎点后1D处范围内受力最大,但在高渗透率海床上单桩位置对波浪力影响较小;在特定可渗透海床上,已破碎的孤立波由于形成“次生波墙”,也可通过二次拍击产生较大波浪力;海床倾角、单桩倾斜度等因素均会对波浪力产生影响。更多还原

【Abstract】 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.更多还原