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Biological implications of the hydrodynamics of swimming at or near the surface and in shallow water

机译：在浅水或浅水区或附近游泳的水动力的生物学意义

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The origins and effects of wave drag at and near the surface and in shallow water are discussed in terms of the dispersive waves generated by streamlined technical bodies of revolution and by semi-aquatic and aquatic animals with a view to bearing on issues regarding the design and function of autonomous surface and underwater vehicles. A simple two-dimensional model based on energy flux, allowing assessment of drag and its associated wave amplitude, is applied to surface swimming in Lesser Scaup ducks and is in good agreement with measured values. It is argued that hydrodynamic limitations to swimming at speeds associated with the critical Froude number (approximate to 0.5) and hull speed do not necessarily set biological limitations as most behaviours occur well below the hull speed. From a comparative standpoint, the need for studies on the hull displacement of different forms is emphasized. For forms in surface proximity, drag is a function of both Froude and Reynolds numbers. Whilst the depth dependence of wave drag is not particularly sensitive to Reynolds number, its magnitude is, with smaller and slower forms subject to relatively less drag augmentation than larger, faster forms that generate additional resistance due to ventilation and spray. A quasi-steady approach to the hydrodynamics of swimming in shallow water identifies substantial drag increases relative to the deeply submerged case at Froude numbers of about 0.9 that could limit the performance of semi-aquatic and aquatic animals and autonomous vehicles. A comparative assessment of fast-starting trout and upside down catfish shows that the energy losses of fast-starting fish are likely to be less for fish in surface proximity in deep water than for those in shallow water. Further work on unsteady swimming in both circumstances is encouraged. Finally, perspectives are offered as to how autonomous surface and underwater vehicles in surface proximity and shallow water could function to avoid prohibitive hydrodynamic resistance, thereby increasing their operational life.
机译：根据流线型的旋转技术机构以及半水生和水生动物产生的色散波，讨论了水波在地表及其附近和浅水区的起源和影响，以期应对有关设计和制造方面的问题。自动水面和水下航行器的功能。一个基于能量通量的简单二维模型可以评估阻力及其相关的波幅，该模型被应用于小斑鸭的表面游泳，并且与测量值非常吻合。有人认为，在与临界弗洛德数（约0.5）和船体速度相关的速度下游泳的水动力限制并不一定设置生物学限制，因为大多数行为都远低于船体速度。从比较的角度出发，强调需要研究不同形式的船体位移。对于表面接近的形状，阻力是弗洛德数和雷诺数的函数。尽管波浪阻力的深度依赖性对雷诺数不是特别敏感，但与较大，较快的形式相比，较小和较慢的形式受到的通风阻力相对较小，而较大，较快的形式由于通风和喷雾而产生附加阻力。在浅水中游泳的流体动力学的准稳态方法表明，相对于深度淹没的情况（约0.9的Froude数），阻力显着增加，这可能会限制半水生和水生动物及自动驾驶汽车的性能。对快速启动鳟鱼和倒置cat鱼的比较评估表明，深水表层接近的鱼类的快速启动鱼的能量损失可能比浅水域的更快。鼓励在两种情况下对不稳定游泳进行进一步的工作。最后，提供了有关在水面附近和浅水区的自动水面和水下航行器如何发挥作用来避免水动力阻力过大从而延长其使用寿命的观点。

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