Wavetank Characterisation Dataset 2 - 0.4Hz

This experiment is designed to derive the performance characteristics of a small wavetank used to test the efficiency of working scale models of wave power devices and compare these against the characteristics predicted by the theory used in its design especially at its theoretical optimal operating frequency of 1 Hz. The activity also aims to show whether waves in the tank show the characteristics of deep water waves as opposed to shallow water waves. In this case shallow water is defined as the case where wave amplitude is a significant proportion of overall water depth. In shallow water the wavelength can be expected to decrease as a function of decreasing water depth. The rig consists of a 4.9 metre tank with a paddle mechanism designed to generate continuous propagating waves. The tank features an angled beach which may be overtopped by generated waves to minimise reflections at the end of the tank. Water in the tank is constantly recirculated via a pump with water depth set by a combination of beach angle and pump flow rate. The physical and electrical characteristics of the tank are covered in more depth in Dataset 5. Datasets 1-4 represent a comparison between the observed and theoretical wavelengths of waves generated at 4 different paddle frequencies 0.25Hz, 0.4Hz, 0.7Hz and 1.0Hz for a fixed paddle stroke length. The experiments were conducted with the tank set for a nominal water depth of 500mm with 2 depth measurement probes set at a distance of 1.6 metres from each other. Results suggest that the waveforms were not good quality for any of the tested frequencies but that the observed wavelength better approximates predicted wavelength as the frequency is increased with good results at 1Hz. It can be concluded that the tank should be used at a frequency of greater than 1 Hz with the caveat that available wave power decreases as frequency increases. At 1 Hz the generated waves exhibit the characteristics usually seen at intermediate depth.

本实验旨在推导小型波浪水槽（wavetank）的性能特征——该水槽用于测试波浪能装置工作比例模型的效率，并将这些特征与设计所用理论预测的特性进行对比，尤其关注其1Hz的理论最优工作频率。本研究还旨在验证水槽内波浪是否呈现深水波特征而非浅水波特征。本实验中，浅水波定义为波幅占总水深较大比例的情况；浅水波的波长随水深减小而缩短。实验装置包含一个4.9米长的水槽，配备用于生成连续传播波浪的桨叶机构（paddle mechanism）；水槽设有斜向消波滩（angled beach），生成的波浪可漫过该滩体以最小化水槽末端的反射。水槽内的水体通过泵持续循环，水深由消波滩角度与泵流量共同调节。水槽的物理与电气特性在数据集5中有更深入的阐述。数据集1-4为固定桨叶冲程长度下，4种不同桨叶频率（0.25Hz、0.4Hz、0.7Hz及1.0Hz）所生成波浪的观测波长与理论波长对比结果。实验中水槽标称水深设置为500mm，两个深度测量探头间距为1.6米。结果表明，所有测试频率下的波形质量均欠佳，但观测波长随频率升高更接近预测值，其中1Hz时结果最优。结论认为，水槽应在高于1Hz的频率下使用，但需注意可用波浪功率随频率升高而降低；1Hz时生成的波浪表现出典型的中等深度特征。