Experimental and Theoretical Study of Ship Resistance with Unsteady Forward Speed

虽然有大量的文献与船舶阻力的理论预测和实验测量有关，但绝大多数是关于稳定前进速度下的阻力。相比之下，加速度对船舶阻力影响的研究相对较少。这是船舶基本水动力学中一个有趣而又具有挑战性的问题，具有许多实际应用。在船舶阻力模型试验中，为了充分利用有限长度的拖曳舱，需要迅速达到稳定状态；提高对起下钻时加速产生的非定常效应的理解，可以更有效地利用昂贵的设备。当船只在浅水区加速时，预计会产生一些特别复杂的影响。了解这些影响可能有助于改进高速渡轮运营模式的规划。在特殊类型的船只（如艇壳），推进是不稳定的，导致周期性的不稳定前进速度。有记录显示浪涌加速度高达1.5g。有人认为，非定常效应使平均阻力增加5%或更多，因此，如果希望优化划艇或独木舟的船体形式，这种现象显然是有趣的。目前的建议旨在使现有的合作能够继续进行这一领域的研究。来自澳大利亚悉尼新南威尔士大学的劳瑞博士教授于2006年6月访问英国，在格拉斯哥大学和斯特拉斯克莱德大学进行一项研究计划。建议在2007年秋季进行为期四周的访问，继续进行这项研究。在dr教授2006年访问格拉斯哥之前，已经开发了一种数值方法，可以预测船舶在有限宽度和深度的水中的任何速度历史的阻力时间历史。确定了两个感兴趣的领域。第一个区域是对拖曳箱试验中典型的非定常效应的检查，在拖曳箱试验中，在一段时间的稳定速度之前是一个相对较快的加速。第二个感兴趣的领域被选择作为一个初步的研究阻力与周期性非定常运动航行的船舶。在UGS Acre Rd设施中，可以使用所需的任何速度剖面进行牵引测试，但要受运行长度、速度和加速度的上限限制。在2006年博士教授访问格拉斯哥期间，进行了两项使用标准船体形式的创新实验研究，并将结果与理论预测进行了比较。第一项研究考察了拖曳箱试验中不同加速度对非定常阻力效应的影响。现在已经完成并写好了。实验结果与数值预测非常吻合，并发现了一些非常有趣的现象。例如，遵循Wehausen预测的非定常阻力的一般形式；然而，水槽宽度和深度对非定常变化的频率、幅度以及最重要的衰减率有显著影响。第二项研究考察了周期性变化的速度对阻力的影响，现在已经进行了分析。波浪阻力预测的结果也非常有希望，预计结果将在2007年提交发表。振荡速度情况的初步研究突出了一些额外的有趣的挑战；特别是(a)非定常波效应与非定常摩擦阻力的分离，以及(b)接近临界深度弗劳德数的非定常效应的预测。更多的实验将创造一个更完整的数据集，从而对这些有趣的现象有更全面的了解。这些实验是2007年计划访问的原因。

Whilst there is a huge body of literature related to the theoretical prediction and experimental measurement of ship resistance, the vast majority if it relates to resistance at steady forward speed. In contrast, relatively few studies have been made of the influence of acceleration on ship resistance. This is an interesting and challenging problem of fundamental ship hydrodynamics which has several practical applications. In ship resistance model testing, it is desirable to achieve steady conditions rapidly to make best use of a limited length of towing tank; improved understanding of the unsteady effects resulting from the acceleration at the start of a run can lead to more effective use of expensive facilities. Some particularly complex effects are expected when ships accelerate in shallow water. Understanding of these effects may help to improve planning of operational patterns for high-speed ferries. In particular types of vessels (e.g. rowing shells) the propulsion is unsteady, leading to periodic unsteady forward speed. Surge accelerations as high as 1.5g have been recorded. It has been suggested that unsteady effects increase mean resistance by 5% or more, so this phenomenon is clearly of interest if it is wished to optimise the hull form of a rowing shell or canoe.The current proposal is aimed at enabling the continuation of an existing collaboration to research in this area. Prof. Lawry Doctors, from UNSW, in Sydney Australia, visited the UK in June 2006 to carry out a research programme at the Universities of Glasgow and Strathclyde (UGS). It is proposed that this research is continued through a four week visit in Autumn 2007.Prior to Prof Doctors visit to Glasgow in 2006, a numerical method was developed which allows the time history of resistance to be predicted for any velocity history for a ship in water of finite width and depth. Two areas of interest were identified. The first area was an examination of the unsteady effects typical of a towing tank test, in which a period of steady velocity is preceded by a relatively rapid acceleration. The second area of interest was chosen as a preliminary investigation of the resistance of ships travelling with a periodic unsteady motion.In the UGS Acre Rd facility it is possible to carry out a towing test with any velocity profile desired, subject to upper limits on run length, velocity and acceleration. During Prof. Doctors visit to Glasgow in 2006, two innovative experiment studies using a standard hull form, and the results compared to theoretical predictions.The first study examined the impact of different acceleration profiles on the unsteady resistance effects on a towing tank test. This has now been completed and written up. Agreement between experiment results and numerical prediction was extremely encouraging and some very interesting phenomena were discovered. For example, the general form of the unsteady resistance predicted by Wehausen was followed; however, there were significant effects of the tank width and depth on the frequency, amplitude, and most importantly, the decay rate of the unsteady variations. The second study, examining the impact of periodically varying velocity on resistance has now been analysed. The results for the wave resistance prediction are also extremely promising, and it is expected that the results will be submitted for publication in 2007. The preliminary study of the oscillatory velocity case has highlighted some additional interesting challenges; in particular (a) the separation of unsteady wave effects from unsteady frictional resistance, and (b) the prediction of unsteady effects close to critical depth Froude Number. Additional experiments would create a more complete data set allowing a fuller insight to be gained into these interesting phenomena. These experiments are the reason for the proposed visit in 2007.