粘性流体势流理论及波浪与毗连多浮体相互作用研究

Multiple floating bodies in proximity are often encountered in the uploading/offloading operations of oil and gas products, for example, from the FPSO to the oil shuttle tanker. Several resonant responses can be excited by the incident waves. It is well known that the potential flow model can lead to the over-prediction of resonant responses. This is mainly attributed to the assumption of inviscid fluid in the conventional potential flow theory. That means the mechanical energy dissipation, which plays a fairly important role in the resonance, can not be considered. As a contrast, the newly developed potential flow theory of viscous fluids is free from the restriction of inviscid fluids. It allows the mechanical energy dissipation to be taken into account. However, the present potential theory of viscous fluid is mainly developed for the wave propagation problem for ocean hydrodynamics. This project aims to extend the viscous potential flow theory to the context involving floating structures. The interaction of water wave with multiple floating bodies in close proximity will be investigated by using the novel potential flow theory of viscous fluids, together with the numerical simulations based on the Navier-Stokes equations and laboratory tests. The main concerned issues of this project include 1) the fluid resonance in the narrow gap formed by the floating bodies, 2) the internal liquid sloshing in the floating bodies and 3) the motion of the floating body itself under the wave actions. Furthermore, the coupling and interference of the resonant responses mentioned above will be also examined with special attentions, which is believed to be accounted for the most dangerous situation in the practical operations. A new numerical model of viscous potential flow will be established based on the Boundary Element Method in the frequency domain, which is expected to perform well in predicting the resonant responses involving significant mechanical energy dissipation. The investigations conducted in this project will be helpful to understand the unknown mechanism behind the wave-structure interaction, especially for the mechanical energy dissipation, and will be meaningful for the practical operations of multiple floating structure in close proximity under water waves.

海上油气产品的装/卸载需要毗连多浮体的联合作业，其中涉及到多种共振现象。而经典势流模型往往会对共振响应给出过高估计，其根本原因是传统的"理想流体势流理论"忽略了流体的粘性属性，无法考虑在共振中起重要作用的机械能损耗。新兴的"粘性流体势流理论"则抛开了这一假设，这为在统一的势流理论内考虑机械能损耗提供了可能途径。但是现有的"粘性流体势流理论"主要用于开阔水域的波浪传播和波能损耗问题。本项目将"粘性流体势流理论"引入到波浪与结构物相互作用问题中，同时结合NS方程数值求解和室内模型试验，重点研究波浪与毗连多浮体相互作用中的共振响应（包括浮体间窄缝内的流体振荡、浮体内部的液体晃荡、浮体自身的运动响应）以及这些运动形式之间的干涉和叠加效应。本项目研究工作的开展将建立新型的"粘性流体势流模型"，加深人们对波浪与多浮体相互作用规律，特别是机械能损耗机理的认识，为海上极端作业工况的安全保障提供技术支持。

在深远海油气资源开采中，大型海洋浮式结构和穿梭油轮等的多体联合作业将是主要的开采模式。在特定的波浪频率下，近距离并靠浮体间会形成大幅流体共振现象，威胁结构本身和现场作业安全。本项目主要面向海上多浮体联合作业中的窄缝流体共振问题开展理论、试验和数值研究。类似的问题也见于一般深海平台的月池共振问题，以及大型船舶在在码头前的靠泊作业等。.本项目研究工作的要点是粘性流体势流理论和窄缝流体共振问题。传统的“理想流体势流理论”往往对共振问题产生完全背离物理事实的奇异解，其根源在于经典势流理论的无粘性假设。本项目的研究工作从全新的“粘性流体势流理论”出发，明确了势流理论本身无需引入无粘性假设，同时“粘性流体势流理论”是一种耗散性的理论。基于该理论认识，在“粘性流体势流理论”的框架内，建立了耗散性的修正势流分析方法，从而在根本上解决了以往对势流模型中引入人工阻尼的长期性争议。进一步，为局部流体共振问题建立了具有坚实理论基础数值分析模型。通过近千组物理试验工作的开展，对窄缝流体共振的发生机理取得了深刻认识，并利用试验数据对上述数值分析模型的可靠性进行严格检验，证实了所提分析方法的可靠性。同时，本项目还基于Navier-Stokes方程，建立和发展了完备的流固耦合数值分析模型及粘性数值波浪水槽，对窄缝流体共振、液舱晃荡、浮体运动以及水下结构的动力响应等问题开展了大量研究。本项目研究工作是对经典势流理论和新兴“粘性流体势流理论”的有益发展，所建立的分析方法和计算工具，对更为广泛的海洋工程流固耦合问题具有借鉴价值。.在本项目的资助下，发表研究论文26篇，其中SCI国外期刊论文9篇（包括国际高水平学术期刊Physics of Fluids 1篇，Coastal Engineering 1篇，Journal of Fluids and Structures 2篇），EI收录12篇；授权软件著作权2项；获省部级科技奖励一等奖和三等奖共2项；培养博士研究生3名，硕士研究生7名，博士后1名；参加8次国际会议（12人次），承办国际会议3次，取得3项国际科技合作资助。