考虑液舱晃荡及系泊系统影响的超大型LNG-FPSO波浪中运动性能研究

A very large LNG-FPSO is normally floating on sea. Under the action of ambient ocean waves, the hull will be excited to move with waves. As a result, the liquid cargo filled in tanks of the LNG-FPSO will be excited too. Unfortunately, the hull and the liquid cargo present quite different performances, and are coupled with each other. On the other hand, an LNG-FPSO is commonly moored. Therefore, motion responses of the LNG-FPSO are generally coupled with each other between the hull, tank sloshing and mooring system. For this engineering problem, there are two categories of study related to the motion performance of them to be carried out. One is the complex tank sloshing problem, and the other is the coupling effect of motions between the hull, tank sloshing and mooring system. Until those studies have been completed, hydrodynamic performance and the safety of a moored LNG-FPSO in waves may then be assessed. In the past a few years, in our laboratory a code for simulation of water tank sloshing has been developed and revised progressively. Based on it, firstly, this project will promote our study to the next step, serious validation of the code and then taking vaporing, compressibility and air entrapment into account to develop a more reasonable and more complete theoretical model for three dimensional violent sloshing. The code in hand will be further extended to accommodate the modified theoretical model able to simulate some complex phenomena of the violent sloshing, such as flip-through, breaking, impact, air cushion and so on with high fidelity. During the course of the development, a physical model experiment for violent sloshing will be performed. A state-of-the-art high-end particle image velocimetry (PIV) and a super high speed video camera will be employed, in order to analyze and record the instantaneous three dimensional fluid fields with extremely high resolution. A numerical simulation corresponding to those high resolution fluid fields will be conducted as well, in order to validate the code. Secondly, this project will set up a theoretical model of an LNG-FPSO in waves, which works on sea and is moored and filled in the tanks with liquid cargo. This model will be able to take the coupling effects between the hull, tank sloshing and mooring system into account. Also, in the course of the development of a code, a physical model experiment will be carried out in the state key laboratory of ocean engineering, which is located in our department. Time histories of wave height, position, attitude and motion responses of the LNG-FPSO will be measured and recorded by means of the state-of-the-art high-end on board free running test system. The developed code will be able to simulate motion responses of the floating hull - tank sloshing - mooring system with high precision. The knowledge and computer codes, obtained from this project, will be extensively applicable, even to the fields beyond shipbuilding industry and ocean engineering.

鉴于载液超大型LNG-FPSO尚缺乏评估其运动安全性理论工具的现状，针对液舱晃荡现象及其效应开展深入研究。在现有晃荡研究的基础上，计及LNG介质压缩性与蒸发效应，建立三维LNG液舱剧烈晃荡的合理数学模型，采用数值模拟与晃荡试验相结合的方法，研究开发计算程序，数值模拟晃荡过程中的液面翻卷破碎、砰击和气体卷入等复杂物理现象，并给出合理解释。实施带局部剧烈晃荡现象的模型试验，研究相似机理。采用激光图像测速仪、高速摄像仪精细测量三维瞬态晃荡流场，记录其复杂的物理现象并进行模拟分析。在此基础上，建立LNG-FPSO在海上作业过程中的浮体与液舱和系泊系统多重耦合的数学模型,采用数值模拟与水池试验相结合的方法，研究开发该系统在波浪上运动的高精度数值模拟程序。在海洋工程国家重点实验室采用国际上最先进的船载自航模测量系统，测量记录试验过程中的波高、船舶位置、姿态和运动的完整时历。研究成果具有广泛的应用前景。

本项目开发了一套液舱晃荡运动发生装置，利用该装置，应用激光粒子测速仪（PIV）测量了晃荡液舱内的精细流场，与数值模拟的晃荡流场进行了比较，初步验证了数值计算方法的可靠性[1]。在晃荡液舱液面的精确捕捉方面，引入了弱可压缩移动粒子半隐式算法，就溃坝算例进行了有效性验证[2]。在船体运动模拟方面，综合考虑船体、螺旋桨推进器和舵的相互作用，完善了MMG计算模型。为了验证其有效性，制作了船模，在海洋工程水池中开展了自航模实验，初步验证了该计算模型的有效性[3]。提出了一套模拟船舶在风浪中运动并伴有操舵的数值方法，该方法把操纵性和耐波性纳入一起考虑，前者把水动力划分为船体力、桨力和舵力三种成分，后者把波浪力区分为一阶力和二阶力。通过计算获得运动响应算子，再经傅氏变换获得脉冲响应算子，建立完整的时域运动方程。开展了相应的船模水池试验，由此确立了数值模拟方法的有效性[4][5]。把Rankine源方法应用于数值计算船舶航行兴波阻力，并制作了缩尺比为50的船模，在船舶拖曳水池中进行了实验验证[6][8]。提出了浮式制荡板的制荡设想，开展了该设想制荡机理的实验和数值模拟研究，确认了其制荡效果[7]。.　　本项目共发表研究论文7篇。培养博士研究生2名（毕业１名、即将毕业１名）、硕士2名（毕业１名、升入博士生１名）、本科毕业生7名。