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

从大型船舶下水和回收小型航行器是海事部门的常见作业，例如从科考船巡逻队下水和回收无人水下航行器，或从近海平台或船舶下水和回收救生艇。此类作业通常是在恶劣的海况下进行的。最近由BAE系统协调、受用户启发于2014年7月举办的海上发射和回收问题学术挑战讲习班，确定了在恶劣海况下安全发射和回收船只上的离岸、水面和次水面资产所面临的各种挑战。其中之一是缺乏准确和有效的建模工具来预测两个浮体在严酷的海面上的水动力载荷和运动，例如可能由非刚性链节连接的不同大小的船只。这样的工具可以用来将碰撞和不可接受的运动的风险降到最低，并促进新概念和系统的早期测试。它还可用于估计较小船只(例如救生艇)部署期间和较小船只从较大船只甲板上回收时的水动力载荷。研制这类工具的困难在于：(1)必须模拟恶劣海况下的水波；(2)小型运载器在发射或回收过程中的运动及其湿表面的变化可能很大，可能从完全干燥的空气中移动到完全淹没；(3)粘性效应可能起到不可忽视的重要作用，并将影响海浪与运载器运动的耦合。业界现有的方法和工具无法同时处理所有这些问题，通常需要非常高的计算资源。该项目将开发一个准确和有效的数值模型，可常规用于分析在高海况下有或没有物理连接的两个物体的运动和载荷，当然，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。这将建立在项目伙伴最近开发的数值方法和计算机代码的基础上，以及它们之间过去和正在进行的协作工作取得的成功。此外，该项目将涉及几个行业合作伙伴，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.