Control of Launch and Recovery in Enhanced Sea-States: Part of the Launch and Recovery Co-Creation Initiative

目前，许多海上作业，例如从小型船只、有人驾驶和无人驾驶飞行器以及潜水器的母舰上进行的发射和回收（L&R），只能在足够平静的海况下进行安全尝试。例如，一艘来自母舰的小型船只的起降通常涉及两艘船在通过起重机/提升装置将两者主要物理连接之前一起靠近移动（通过弓形索连接）。在许多情况下，整个任务中对波浪至关重要的高风险因素，即小船与母船的连接和随后的提升，只持续几十秒。超过这个时间会增加手术的风险。一旦两艘船物理连接，操作人员就可以开始吊装过程。在这种情况下，即使是在大海况下，由于波浪活动低于平均水平而导致的船舶运动静止期的短期预测，也具有相当大的操作价值，并且可能允许在目前被认为不合适的条件下安全进行L&R。这种增强的L&R能力对现代海军非常有吸引力。在这个项目中，研究的目的是开发一种新的方法来预测启动L&R操作的合适时机，以及一个置信度措施（作为对人类操作员的建议），然后使用一种新型的模型预测控制（MPC）来控制启动后的后续升降机操作的执行。主要项目成果包括：(i)在软件模拟器中运行的决策支持系统（DSS）原型，该系统在有限的时间范围内为恢复过程的各个方面提供持续更新的短期预测模拟；实际物理提升过程的控制器。这两个元素将利用确定性海浪预测（DSWP）系统的海浪预测驱动的流体动力船舶运动预测模型，以及历史和实时船舶运动传感器数据。DSS最初将在小型艇接近母舰并拾取首缆（低风险活动）时进行，但尚未连接到提升装置上。该研究将假设在母舰上使用单一电缆的通用绞车/起重机提升系统。索张力是一个关键的控制量，最大可用提升力是一个主要的系统规格参数。DSS将：(i)确定一个适当的时刻，在预计的静息期连接起升绳并开始起升；（ii）为该特定模拟升降机的安全/成功提供信心措施。通过对两艘船的当前状态（用作初始条件）进行快照，以及对母舰运动的短期预测，以模拟是否有可能使用MPC控制器成功恢复小船，将确定适当的附加和提升时间。然后，作业者将获得包括信心指标在内的当前建议摘要。如果由于此建议而未启动连接和提升，则使用新当前数据的快照重复该过程。这个循环一直持续，直到作业者决定使用提升机（或放弃回收）。当实际开始连接/吊装时，物理吊装阶段将使用模拟中使用的相同MPC控制器，利用母船运动的预测、船的实际实时测量运动以及小船悬浮在水中时的自由体模型。

Currently many marine operations, such as the Launch and Recovery (L&R) from a mother ship of small craft, manned and unmanned air vehicles and submersibles, can only be attempted safely in sufficiently calm sea-states. As an example, the L&R of a small craft from a mothership typically involves the two vessels moving together in proximity (linked by a bow-line) before the main physical connection of the two via a crane/hoist mechanism. In many cases the wave-critical high risk elements of the overall task, i.e. the connection and subsequent hoist of the small craft to the parent vessel, only last for a few tens of seconds. Taking longer than this increases the operation at risk. Once the two craft are physically connected the operator is committed to initiate the hoisting process. In this context even the short term prediction of quiescent periods of vessel motion resulting from lower than average wave activity in otherwise large sea states, has considerable operational value and may allow L&R to be untaken safely in conditions which would currently be deemed unsuitable. Such enhanced L&R capabilities are very attractive to modern navies. In this project the research aim is to develop a novel approach to predicting a suitable time instant at which to initiate an L&R operation, together with a confidence measure (provided as advice to a human operator), and then to control the execution of the subsequent lift operation once initiated, using a novel form of Model Predictive Control (MPC). The key project deliverables are: (i) a prototype decision support system (DSS), running within a software simulator, which provides continuously updated short term predictive simulations over a finite-time horizon of all aspects of the recovery process; (ii) a controller for the actual physical hoist process. These two elements will exploit hydrodynamic vessel motion prediction models driven by wave predictions from a Deterministic Sea Wave Prediction (DSWP) system, and historical and real-time vessel motion sensor data. The DSS will initially be engaged as the small craft approaches the mothership and picks up a bow-line (a low risk activity), but is not yet attached to the hoist mechanism. The research will assume the presence on the mothership of a generic winch/crane lifting system with a single cable. The cable tension is a key controlled quantity and the maximum lifting force available is a major system specification parameter. The DSS will: (i) identify an appropriate moment to attach the hoist line and initiate hoisting during predicted quiescent periods; (ii) provide a confidence measure for the safety/success of that specific simulated lift. An appropriate time to attach and hoist will be identified by taking a snap-shot of the current state of both vessels (to use as initial conditions) together with short term predictions of the movement of the mothership to simulate whether it is possible to successfully recover the small craft using the MPC controller. The operator will then be presented with a current advice summary including confidence metrics. If as a result of this advice connection and hoisting is not initiated, the process repeats using a snapshot of the new current data. This cycle continues until the operator decides to engage the hoist (or the recovery is aborted). When connection/hoisting is actually initiated, the physical lifting phase will then employ the same MPC controller used in the simulation, exploiting predictions of the motion of the mothership, the actual real-time measured motions of both craft and a free body model of the small craft when suspended clear of the water.