A Zonal CFD Approach for Fully Nonlinear Simulations of Two Vessels in Launch and Recovery Operations

从大型船舶上发射和回收小型车辆是海事部门的常见操作，例如从巡逻的研究船上发射和回收无人水下航行器，或从海上平台或船舶上发射和回收救生艇。此类作业通常在恶劣的海况下进行。在2014年7月举行的由BAE系统公司协调的关于海上发射和回收的用户启发学术挑战研讨会上，确定了在恶劣海况下航行时船舶安全发射和回收船上、水面和水下资产的各种挑战。其中之一是缺乏一种准确和有效的建模工具来预测两个浮体的水动力载荷和运动，例如在恶劣的海洋中，不同大小的船只可能通过非刚性链接耦合在一起。这种工具可以减少碰撞和不可接受运动的风险，并促进新概念和系统的早期测试。它也可以用来估计在部署较小船只（例如救生艇）和从较大船只的甲板上回收较小船只期间的水动力载荷。开发此类工具的困难在于：(1)必须模拟恶劣海况下的水波；(2)小型运载工具在发射或回收过程中的运动和其湿表面的变化可能非常大，可能从空气中完全干燥到完全淹没；(3)粘性效应可能起着不可忽视的重要作用，并将影响海浪与航行体运动的耦合。业界现有的方法和工具无法同时处理所有这些问题，而且通常需要非常高的计算资源。本项目将开发一个准确、高效的数值模型，可常规应用于分析两个物体在高海况下的运动和载荷，这些物体有或没有物理连接，当然也可用于分析小型飞行器从大型船只上发射和回收的过程，并计算过程中的水动力学。这将在项目合作伙伴最近开发的数值方法和计算机代码以及他们之间过去和正在进行的合作工作的成功的基础上实现。此外，该项目将涉及几个工业伙伴，以确保项目的交付和促进影响。

Launch and recovery of small vehicles from a large vessel is a common operation in maritime sectors, such as launching and recovering unmanned underwater vehicles from a patrol of research vessel or launching and recovering lifeboats from offshore platforms or ships. Such operations are often performed in harsh sea conditions. The recent User Inspired Academic Challenge Workshop on Maritime Launch and Recovery, held in July 2014 and coordinated by BAE systems, identified various challenges associated with safe launch and recovery of off-board, surface and sub-surface assets from vessels while underway in severe sea conditions. One of them is the lack of an accurate and efficient modelling tool for predicting the hydrodynamic loads on and the motion of two floating bodies, such as vessels of different size which may be coupled by a non-rigid link, in close proximity in harsh seas. Such a tool may be employed to minimise the risk of collisions and unacceptable motions, and to facilitate early testing of new concepts and systems. It may also be used to estimate hydrodynamic loads during the deployment of a smaller vessel (for example, a lifeboat) and during recovery of a smaller vessel from the deck of a larger vessel. The difficulties associated with development of such tools lie in the following aspects: (1) the water waves in harsh sea states have to be simulated; (2) the motion of the small vehicle and change in its wetted surface during launch or recovery can be very large, possibly moving from totally dry in air to becoming entirely submerged; (3) the viscous effects may play an important role and cannot be ignored, and will affect the coupling between ocean waves and motion of the vehicles. Existing methods and tools available to the industry cannot deal with all of these issues together and typically require very high computational resources. This project will develop an accurate and efficient numerical model that can be applied routinely for the analysis of the motion and loadings of two bodies in close proximity with or without physical connection in high sea-states, which of course can be employed to analyse the launch and recovery process of a small vehicle from a large vessel and to calculate the hydrodynamics during the process. This will be achieved building upon the recent developed numerical methods and computer codes by the project partners and also the success of the past and ongoing collaborative work between them. In addition, the project will involve several industrial partners to ensure the delivery of the project and to promote impact.