考虑非线性孔隙流的近海结构物海床地基内波致渐进液化研究

There are a great number of offshore structures, such as breakwater and marine pipeline, have been constructed in the offshore area of China. Due to the unceasing wave loading in the offshore environment, the offshore structures are vulnerable to the wave-induced residual liquefaction in seabed foundation. It is significantly meaningful to investigate the wave-seabed- structures interaction mechanism, and the wave-induced liquefaction of seabed foundation for the engineering design.Actually, there are always some unavoidable drawbacks in the previous investigations. They are repectively (1)the exchange between the sea water and the pore water in porous seabed can not be considered when investigating the fluid-structures interaction; (2) the uncouped analytical models and numerical models can not describe the interaction mechanism between the wave, seabed and offshore structures; (3) the nonlinear porous flow in offshore structures or coarse sand bed is not taken into consideration. In this program, a new coupled numerical model will be developed to thoroughly overcome the drawbacks in previous investigations. Firstly, the classic Biot's equation will be modified to consider the nonlinear porous flow in large particle size porous media with large void. The finite element method (FEM) is adopted to discretize the modified Biot's equation, and the corresponding program codes will be developed; and permeation experiments is used to the verify the modified Biot's equation and the program codes developed. Secondly, adopting a kind of coupling algorithm of iteration, the modified Biot's equation and the Volume Average Reynolds Average Navier Stokes (AVRANS) equation are coupled together, to form a new coupled numerical model FSSI-CAS for the problem of wave-seabed-structures interaction.Adopting the wave flume experiments in Lab, the developed coupled numerical model FSSI-CAS will be validated. Finally, the developed coupled numerical model FSSI-CAS is applied to the large-scale engineering problems.

我国近海建有大量的海洋结构物，如防波堤、海底管线。由于受无休止的波浪作用，海洋结构物的海床地基极易发生液化导致结构物失稳。研究波-海床-结构物相互作用机理，及海床地基的液化对工程设计极具意义。由于受技术手段限制，前人的研究具有三个方面不足，表现为:(1)研究波-结构物作用时一般没有考虑海水和海床内孔隙水的交换，（2）解耦的解析或数值模型难以真实地描述波-海床-结构物之间的非线性作用机理，（3）难以考虑海工结构物或粗砂海床内的非线性孔隙流。本项目将致力于发展一个更为完善的耦合模型，弥补前人模型的不足。本研究首先修正经典的Biot方程，使之能够考虑孔隙介质内的非线性孔隙流，并采用有限元进行程序化，利用渗透实验加以验证。之后将该修正的Biot方程和VARANS方程进行耦合，形成用于波-海床-结构物相互作用的耦合模型FSSI-CAS，并采用水槽试验验证所发展的模型，最终应用于大尺度工程问题的计算。

近20年以来，包括我国在内的世界各国在近海海域新建了大量的海洋结构物用于开发海洋，包括防波堤、海底管线、采油平台、风力发电机等。由于海洋极端波浪、强烈地震的侵袭，近海结构物极易因为海床地基的失稳而发生破坏，造成巨大的经济损失。在工程设计中评价近海结构物的安全稳定性是工程师所面临的一个具有挑战性的问题。由于技术手段的缺失，当前设计工程师们还没有可靠性高的评价近海结构物稳定性的计算工具。基于此背景，本项目拟继续开发和优化用于研究波浪-结构物-海床地基相互作用、评价近海结构物波浪、地震稳定性的耦合计算模型FSSI-CAS 2D/3D；并采用该耦合模型研究波浪、地震作用下近海结构物及其多种类型地基的动力响应特征。通过4年的研究工作，系统优化了研究波浪-结构物-海床地基相互作用耦合模型FSSI-CAS 2D/3D，目前已经具备了在实际工程中予以应用的潜力；与此同时采用FSSI-CAS 2D/3D还系统深入地研究了在极端波浪、强烈地震作用下近海结构物与其密实弹性或欠密实弹-塑性地基的动力响应特征和结构物失稳过程与机制，还以我国烟台港西港区复合防波堤为工程案例，成功应用FSSI-CAS 2D/3D评价了其在设计极端波浪作用下的稳定性。系统的研究表明，所开发的研究波浪-结构物-海床地基相互作用、评价近海结构物波浪、地震稳定性的耦合计算模型FSSI-CAS 2D/3D可以成为我国近海结构物的设计和稳定性评价提供高可靠度的计算工具和平台。