在自然海洋环境中，波浪与海流往往同时存在。海流的叠加会显著改变波浪水体中的速度及压力分布，进而影响下方海床土体响应。准确评估波浪海流共同作用下的海床动力响应，对于保障海底工程结构安全具有重要意义。本研究通过物理模型实验、理论分析以及数值模拟相结合的手段，对波流共同作用下非粘性海床振荡孔压响应以及瞬态液化进行了研究，旨在揭示波浪-海流-非粘性海床相互作用的物理机制，探明波流共同作用下的海床响应规律。

现有关于波流诱导海床孔压响应的水槽实验多局限于相对水深参数（波数与水深乘积）较大的情况。相关的理论和数值研究通常忽略了波流耦合响应带来的波高变化，从而降低了孔压响应和瞬态液化深度的预测精度。本文利用流固土耦合水槽，对波流诱导砂质海床响应进行了系统的实验模拟，实验条件涵盖较大的波浪和流速范围，探究了不同波浪周期和波高及水深下叠加同向流或逆向流对于海床孔压响应的影响规律。实验观测发现，对于瞬态孔压随叠加海流的变化，除了前人研究中公认的同向流增强模式，还存在两种全新的变化模式，即过渡模式和逆向流增强模式，而具体模式则取决于单独波浪的相对水深这一无量纲参数。根据实验结果给出了相对水深与变化模式的对应范围。波高的变化虽然不会改变孔压随叠加单向流流速的变化模式，但对于非线性较大的波浪，波高越大则叠加流对孔压响应的影响越发显著。

基于质量通量、动量通量、能量通量守恒方程组，推导获得了波流耦合载荷下波高变化的一阶显式解，并与实验结果和高阶数值解对比验证了其有效性。进一步地，波流共同诱导海床孔压响应的理论解被提出。该理论解能够预测分析上述的同向流增强模式、过渡模式和逆向流增强模式等三种变化模式，且与实验值吻合良好。基于以上孔压响应理论解的参量分析，构建了不同工况下床面波压力幅值随叠加单向流流速变化的无量纲完整变化模式。对波流共同诱导海床孔压响应的理论解进行泰勒展开分析，证明了实验研究中无量纲参数相对水深选取的合理性，分析了不同响应模式的物理机制，即波流耦合载荷诱导孔压随流速的变化模式取决于波高变化和波长变化的综合影响。

基于上述波压力理论，并结合修正液化判别准则，本研究推导了波流共同作用下液化发生后海床内部的孔压响应理论解，提出了瞬态液化深度的解析解。与前人的研究不同，液化层的孔压分布、波流联合作用引起的波高及波长改变、以及相位滞后的耦合效应在本研究中均得到考虑。通过退化分析并与前人现场工况数据对比，验证了瞬态液化深度理论解的正确性。参量分析表明，忽略相位滞后会低估瞬态液化深度；对于波陡较大的波流联合作用工况，波浪非线性效应的影响不可忽略。与孔压响应类似，最大液化深度随叠加流的变化也相应地存在着三种模式，但不同波流组合下的最大液化深度包络面不再重合。通过对近似简化解分析发现，最大液化深度不仅与床面波压力相关，还与土体渗透性、压缩性、浮容重以及波浪波数有关。

对于自然环境恶劣或存在结构物的现场工况条件，通常需要借助数值模拟的手段进行分析。结合理论解和OpenFOAM开源平台，对波流共同作用进行了建模；同时采用瞬态液化非达西模型对海床土体进行了计算，可有效消除液化区域的不合理拉应力，避免了传统模型中的物理谬误；最终通过对偶mortar接触投影，实现了波浪-海流-非粘性海床模型的耦合。与实验结果对比分析表明，本耦合数值模型能够有效模拟波流共同作用下的海床孔压响应。利用建立的模型模拟了波流共同载荷下管道周围海床的动力响应，发现叠加同向流和逆向流的工况相比，瞬态液化深度存在显著差异。此外，管道的存在会对局部孔压响应和应力分布产生不可忽略的影响。

In the natural nearshore environments, waves often coexist with a current. The superposition of current could alter wave profiles significantly, and further affect the underlying seabed response. Accurate evaluation of seabed dynamic response under combined wave and current loading is essential to ensure marine engineering safety. In the present study, combining the physical modeling experiments, theoretical analysis, and numerical simulation, the non-cohesive seabed pore pressure response and instantaneous liquefaction induced by the coupling wave and current are investigated, aiming to provide insightful information on the wave-current-seabed interaction.

Previous flume observations on the pore pressure response in the seabed induced by the combined wave-current were mainly limited to conditions with relatively deep water depth, i.e., the product of pure wave number and water depth is relatively large. Existing theoretical and numerical research neglected the variation of wave height induced by wave-current coupling effects, limiting the accuracy and validity of the predictions on pore pressure response and instantaneous liquefaction depth. In this study, the combined wave-current induced pore pressure response within a sandy seabed is physically modeled in a water flume. A wide range of wave and current parameters are examined. The effects of wave period, water depth, and wave height with superimposed following and opposing currents on the change of pore pressure are investigated. Besides the well-recognized following-current enhancing mode, the present experiments firstly identify two new particular modes of pore pressure changing under superimposed current on waves, i.e., the transition mode and the opposing-current enhancing mode. The specific modes are determined by a dimensionless parameter: the relative water depth of pure wave. Based on the experimental results, the ranges of relative water depth corresponding to different modes are given. Although the varying wave heights would not change the variation mode, for waves with strong nonlinearity, the increasing wave height could amplify the effect of the current on the pore pressure.

Based on the conservation of mass, momentum, and energy flux, a first-order explicit solution for the wave height under the wave-current coupling effect is derived and validated by comparison with experimental results and higher-order numerical solutions. With this updated wave height, an analytical solution for combined wave-current induced pore pressure response is further proposed, which can clearly predict three variation modes and agrees well with the measured data. Through the parametric analysis, a general diagram for the current effect on the mudline pore pressure amplitude under different wave-current conditions is proposed. By the Taylor expansion analysis, the reasonability of the dimensionless parameter selection in the experimental study is proved, and the physical mechanism of different response modes is revealed, i.e., the variation of pore pressure with superimposed current depends on the combined effect of wavelength and wave height change.

Based on the above wave pressure theory and combined with the modified liquefaction criterion, the analytical solution of pore pressure in the seabed after liquefaction occurrence induced by combined wave-current is derived, and the theoretical solution of the instantaneous liquefaction depth is further proposed. Unlike previous studies, the distribution of pore pressure in liquefied layer, the wave height and wavelength change induced by the wave-current coupling, and the effect of phase lag are all considered in this research. By degradation analyses and comparisons with the existing offshore field observations, the present solution of liquefaction depth is verified. The parametric study shows that neglecting the phase lag will underestimate the liquefaction depth; for wave-current conditions with large wave steepness, the wave nonlinear effects can not be ignored. Similar to the pore pressure response, the variation of maximum liquefaction depth with superimposed current also has three modes, but envelopes for different wave-current combinations no longer overlap. Based on the approximate simplified solution, it can be concluded that the maximum liquefaction depth is not only related to the mudline pore pressure, but also depend on the soil permeability, compressibility, buoyant unit weight, and wave number.

In real ocean conditions with complex topography or marine structures, numerical simulation is usually required to evaluate cases with more complex boundary conditions. Combining the present theoretical solution and the OpenFOAM open-source platform, the wave-current interaction has been modeled in this study. The instantaneous non-Darcy model is utilized to simulate the non-cohesive seabed response, which can effectively eliminate the tensile stress in the liquefied area and avoid the physical fallacies in the traditional model. With dual mortar contact method, the integrated wave-current-seabed interaction model has been finally established. Comparison with experimental results shows that the present numerical model can accurately simulate the seabed pore pressure response under combined wave-current loading. Using the present model, the dynamic response of the seabed around the submarine pipeline is simulated numerically. Results show that the instantaneous liquefaction depth is significantly different between cases with following current and with opposing current. In addition, the presence of a pipeline will have a non-negligible impact on the pore pressure and effective stress response nearby.