针对海洋中浅水区域的单桩基础，建立了包含波浪、海床和单桩的三维数值模型，考虑浅水环境中椭圆余弦波与海洋风浪引起的桩身振动的共同作用，研究了桩-土耦合系统的动态响应问题.其中，波浪模型的椭圆余弦波采用Navier-Stokes方程控制，海床模型视为各向同性的多孔介质，并采用Biot方程模拟土体与孔隙水的动态响应，单桩视为可变形弹性体，并引入周期性的水平位移来模拟桩身振动.同时，在验证模型准确性的基础上，分析了椭圆余弦波作用下桩身位移、桩周的海床孔隙水压及海床液化等变化情况，并对波浪及海床的主要特性参数进行了分析.结果表明：桩身振动会导致桩顶区域的海床孔隙水压出现局部变化，并使孔隙水压沿海床深度方向的减小趋势变缓；波浪与海床的特性参数对孔隙水压的分布影响显著.
For research of offshore mono-pile foundation in shallow water, a 3-D model is established by combining wave, seabed and mono-pile to investigate dynamic response of coupled seabed and mono-pile interaction under cnoidal wave and pile rocking caused by wind and flow motion. The cnoidal wave model is governed by Navier-Stokes equations to generate cnodial wave motion. The seabed model is treated as an isotropic porous medium and the dynamic response of soil and pore water is simulated by Biot’s equations. The mono-pile is treated as deformable elastic body and pile rocking is simulated by cyclic horizontal displacement. Based on validation for simulation accuracy of present model, dynamic response of mono-pile displacement, pore water pressure and liquefaction in the vicinity of the mono-pile subject to cnoidal wave are analyzed. Furthermore, parametric studies are conducted to discuss the effect of wave and seabed characteristics. The results show that the pile rocking effect leads to local change of pore pressure at the top part of mono-pile, and slows down the rate of pore pressure decrease along seabed depth. In addition, the variations of wave and seabed parameters make obvious effects on pore pressure distribution.
［1］EICHER J A, GUAN H, JENG D S. Stress and deformation of offshore piles under structural and wave loading［J］. Ocean Engineering, 2003, 30(3): 369-385.
［2］LIN Z B, POKRAJAC D, GUO Y K, et al. Investigation of nonlinear wave-induced seabed response around mono-pile foundation［J］. Coastal Engineering, 2017, 121: 197-211.
［3］ISOBE M. Calculation and application of first-order cnoidal wave theory［J］. Coastal Engineering, 1985, 9(4): 309-325.
［4］肖波, 邱大洪, 俞聿修. 实验室中椭圆余弦波的产生［J］. 海洋学报, 1991, 13(1): 137-144.
XIAO Bo, QIU Dahong, YU Yuxiu. Generation of cnoidal wave in laboratory［J］. Acta Oceanologica Sinica, 1991, 13(1): 137-144.
［5］XU Y F, WANG J H, CHEN J J. Cnoidal water wave induced seepage in a permeable seabed with a defined thickness［J］. Coastal Engineering, 2013, 80(7): 95-99.
［6］ZHOU X L, ZHANG J, WANG J H, et al. Stability and liquefaction analysis of porous seabed subjected to cnoidal wave［J］. Applied Ocean Research, 2014, 48: 250-265.
［7］赵晖, 蔡袁强, 徐长节. 桩-土系统在波浪荷载下的动力响应分析［J］. 浙江大学学报(工学版), 2007, 41(7): 1143-1147.
ZHAO Hui, CAI Yuanqiang, XU Changjie. Dynamic response of pile-soil system due to wave force［J］. Journal of Zhejiang University (Engineering Science), 2007, 41(7): 1143-1147.
［8］尚守平, 余俊, 王海东, 等. 饱和土中桩水平振动分析［J］. 岩土工程学报, 2007, 29(11): 1696-1702.
SHANG Shouping, YU Jun, WANG Haidong, et al. Horizontal vibration of piles in saturated soil［J］. Chinese Journal of Geotechnical Engineering, 2007, 29(11): 1696-1702.
［9］张卫平, 孙昭晨. 波浪作用下考虑桩土相互作用的桩柱响应［J］. 水运工程, 2012(3): 55-59.
ZHANG Weiping, SUN Zhaochen. Piles response under wave action considering pile-soil interaction［J］. Port & Waterway Engineering, 2012(3): 55-59.
［10］ZHANG C, ZHANG Q Y, WU Z T, et al. Numerical study on effects of the embedded monopile foundation on local wave-induced porous seabed response［J］. Mathematical Problems in Engineering, 2015(3): 1-13.
［11］LIAO C C, TONG D G, CHEN L H. Pore pressure distribution and momentary liquefaction in vicinity of impermeable slope-type breakwater head［J］. Applied Ocean Research, 2018, 78: 290-306.
［12］LIAO C C, TONG D G, JENG D S, et al. Numerical study for wave-induced oscillatory pore pressures and liquefaction around impermeable slope breakwater heads［J］. Ocean Engineering, 2018, 157: 364-375.
［13］JENG D S, LUO X D, ZHANG J S. Numerical mo-del for rocking of mono-pile in a porous seabed［C］∥Proceedings of the COMSOL Conference 2010 Paris. Paris: COMSOL, 2011.
［14］CULLAR P. Pile foundations for offshore wind turbines: Numerical and experimental investigations on the behaviour under short-term and long-term cyclic loading［D］. Berlin: Technical University of Berlin, 2011.
［15］HANSEN N M. Interaction between seabed soil and offshore wind turbine foundations［D］. Denmark: Technical University of Denmark, 2012.
［16］BIOT M A. General theory of three-dimensional consolidation［J］. Journal of Applied Physics, 1941, 12(2): 155-164.
［17］ULKER M B C, RAHMAN M S, JENG D S. Wave-induced response of seabed: Various formulations and their applicability［J］. Applied Ocean Research, 2009, 31(1): 12-24.
［18］JENG D S, CHA D H. Effects of dynamic soil behavior and wave non-linearity on the wave-induced pore pressure and effective stresses in porous seabed［J］. Ocean Engineering, 2003, 30(16): 2065-2089.
［19］CHANG K A, HSU T J, LIU P L F. Vortex gene-ration and evolution in water waves propagating over a submerged rectangular obstacle—Part II: Cnoidal waves［J］. Coastal Engineering, 2005, 52(3): 257-283.
［20］HSU J R C, JENG D S. Wave-induced soil response in an unsaturated anisotropic seabed of finite thickness［J］. International Journal for Numerical and Analytical Methods in Geomechanics, 1994, 18(11): 785-807.
［21］JENG D S. Wave-induced seabed instability in front of a breakwater［J］. Ocean Engineering, 1997, 24(10): 887-917.
