THE HYDRODYNAMICS OF A DISTENSIBLE WAVE ENERGY CONVERTER

水蟒是一种新的波能转换概念。它只是大海中的一根橡皮管，充满了水，两端闭合，锚定了头对着波浪。由于波浪的作用，它被沿其长度方向的压力变化挤压或局部放大。挤压一根充满水的橡胶管，就会产生一个凸起的波。凸起波的传播速度由管子的几何形状和材料特性决定。蟒蛇的设计使其凸起的波速接近上面水波的速度。在这种情况下，当它们沿着管子移动时，凸起会增长，聚集波能。在管子内部，凸起的波伴随着周期性的反向流动。从蟒蛇中提取能量的一种方法是使用一对鸭嘴阀将其转换为通过涡轮在高压和低压储气罐之间流动的整流气流。我们已经在实验室波浪水槽中以大约1：85的比例证明了蟒蛇的概念。在这个尺度上，转换波能量的很大一部分是在加热制造管道的薄壁橡胶时损失的，并在流过阀门的湍流中损失。尽管如此，该模型还是吸收了宽度相当于其直径5倍的锋面上的所有入射波能。电力输出系统约占其中的20%，相当于一条直径7米、长150米的水蟒在2米高的海浪中超过250千瓦。在更大的规模上，能量损失将少得多，而有用电力转换的比例要高得多。一个额定功率为1兆瓦的装置将含有大约100吨橡胶，这使蟒蛇成为功率极高的光波能量转换器。说到预测，蟒蛇与其他海洋船只或结构都不同。它与Pelamis有一些共同之处，但它更加顺从，具有更多的自由度，并且不一定跟随水面的运动。我们的数学模型是相当基本的，在许多方面与实验室的测量结果并不是很好地吻合。这项研究的目的是为了更好地了解该装置的流体力学，并制定一个全面和有效的数值计算，以便对全尺寸性能做出更可靠的估计。实验将在1：28和1：14的比例下进行，管径为0.25m和0.50m，此时橡胶的滞回损失将按比例比较小的比例低得多。计划进行三种类型的实验，以提供对内部压力、管子位移、辐射波、系泊力和吸波能力的测量：(1)在静止水中测量管子一端机械产生的凸起波，另一端吸收膨胀波；(2)规则波和不规则波的测量；(3)极端波的测量。结果将为设备的力学提供深入的见解，并支持开发一个数值模型，该模型将首次包括波浪辐射和其他迄今被忽略的因素的影响。这项工作的一些特征将与波与柔顺表面相互作用的其他例子相关。

The Anaconda is a new concept for wave energy conversion. It is just a rubber tube in the sea, full of water, closed at both ends, anchored head to waves. It is squeezed or enlarged locally by pressure variations that run along its length due to the waves. Squeezing a water-filled rubber tube starts a bulge wave running. The bulge wave travels at a speed that is determined by the geometry and material properties of the tube. The Anaconda is designed so that its bulge wave speed is close to the speed of the water waves above. In these conditions the bulges grow as they travel along the tube, gathering wave energy. Inside the tube, the bulge waves are accompanied by a periodically reversing flow. One way of extracting power from the Anaconda is to use a pair of duck-bill valves to convert this into a rectified flow past a turbine between high and low pressure reservoirs. We have proved the concept of the Anaconda at a scale of about 1:85 in a laboratory wave flume. At this scale a large part of the converted wave energy is lost in heating up the thin wall rubber from which the tube is made, and in the turbulent flow through the valves. Nevertheless, the model absorbed all of the incident wave power over a front equal in width to as much as 5 times its diameter. A power take-off system accounted for about 20% of this, corresponding to more than 250kW for a 7m diameter Anaconda, 150m long, in waves 2m high. At larger scale, energy losses would be much less significant and the proportion of useful power conversion much higher. A device rated at 1MW would contain about 100 tonnes of rubber, making the Anaconda an exceptionally light wave energy converter for its power.When it comes to predictions, the Anaconda is like no other marine vessel or structure. It has some features in common with Pelamis, but it is much more compliant, has many more degrees of freedom, and does not necessarily follow the motion of the water surface. Our mathematical models of it are rather basic, and in many respects are not in very good agreement with laboratory measurements. The aim of this research is to develop a better understanding of the hydrodynamics of the device, and formulate a comprehensive and validated numerical with which to make more reliable estimates of full scale performance. Experiments will be carried out at scales of 1:28 and 1:14, with tubes of diameters 0.25m and 0.50m, at which rubber hysteresis losses will be proportionately much lower than at smaller scale. Three types of experiments are planned, to provide measurements of internal pressures, tube displacements, radiated waves, mooring forces, and absorber power:(1) measurements in still water with bulge waves generated mechanically at one end of the tube, and absorbed at the other,(2) measurements in regular and irregular waves,(3) measurements in extreme waves.The results will provide insights into the mechanics of the device and support the development of a numerical model that will for the first time include the effects of wave radiation and other factors so far neglected. Some features of the work will be relevant to other examples of wave interactions with compliant surfaces.