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CFD analyses on the water entry process of a freefall lifeboat

机译：差价合约对自由落体救生艇的水入口过程分析

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The launch of lifeboats is commonly completed through freefall dropping from a considerable height, where the lifeboat is released from an inclined skid so that it can obtain a forward speed after being launched. The drop is followed by a water entry process that can induce high impact forces on the hull, which gives a significant risk of structural damages. Ascertaining the water entry impact is therefore a key step of lifeboat design; however, conventional methods have linear assumptions and assess the water impact following a quasi-static manner, which causes these methods to be not fully accurate and ignore some important details. To address this gap, this work developed a model based on Computational Fluid Dynamics to holistically simulate and analyse the process. An overset mesh technique was incorporated to reproduce the entire series of drop, water entry and resurfacing, in which the pressure distribution on the whole hull was obtained and recorded with a sampling frequency of 1000 Hz to ensure the peak impacts can be captured. Full-scale measurements were used to confirm the accuracy of the present computational model. Subsequently, a systematic series of simulations were performed to investigate how the water entry process is influenced by the inclined angle and height at which the lifeboat is dropped. The results show that a higher dropping angle can reduce the pressure impacts, but the dropping angle also dictates the lifeboat's motion pattern during the water entry. It was demonstrated that the best dropping angle is around 70 degrees for the investigated case, since an either too low or too high dropping angle would cause the lifeboat to appear in an undesirable after-launch status. This indicates the great importance to assess the optimal dropping angle for every potential freefall lifeboat launch, and the present work proved an effective approach to perform the task.
机译：通过从相当高的高度的自由降低，救生艇的发射通常是完整的，其中救生艇从倾斜的滑动释放，使得它可以在推出后获得前进速度。下降之后是水入口过程，可以在船体上引起高冲击力，这给出了结构损害的显着风险。因此，确定水处理的影响是救生艇设计的关键步骤;然而，常规方法具有线性假设并根据准静态方式评估水的影响，这导致这些方法不完全准确和忽略一些重要细节。为了解决这个差距，这项工作开发了一种基于计算流体动力学的模型，以全面模拟和分析该过程。纳入推广网格技术被融合为再现整个系列的下降，水入口和重新架，其中获得了整个船体的压力分布并记录了1000Hz的采样频率，以确保可以捕获峰值冲击。满量程测量用于确认本计算模型的准确性。随后，进行系统系列的模拟，以研究水进入过程的影响是如何受到救生艇掉落的倾斜角度和高度的影响。结果表明，较高的滴角可以降低压力影响，但下降角度也决定了在水处理期间的救生艇运动模式。据证明，所研究的情况下，最佳滴角约为70度，因为过低或过高的滴角会导致救生艇出现在不希望的后发射状态下。这表明评估每次潜在自由落体救生艇发射的最佳滴角的重要性，并且目前的工作证明了执行任务的有效方法。

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