Wavetank Characterisation Dataset 5

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.本实验旨在获取一款小型波浪水槽（wavetank）的性能特性，该水槽用于测试波浪发电装置（wave power devices）工作缩尺模型（scale models）的效率，并将实测特性与该水槽设计阶段所依据的理论所预测的特性进行对比，尤其聚焦于其理论最优工作频率（optimal operating frequency）1 Hz处的表现。本实验同时旨在验证水槽内的波浪是否具备深水波（deep water waves）而非浅水波（shallow water waves）的特性。此处将浅水波定义为波幅（wave amplitude）占总水深（water depth）比例较高的工况；浅水波的波长（wavelength）会随水深减小而缩短。该实验装置包含一条长4.9米的水槽，配有可生成连续行进波浪（propagating waves）的造波板机构（paddle mechanism）。水槽设有斜向消波滩（angled beach），可通过造波产生的波浪越过消波滩，最大限度削弱水槽末端的反射波。水槽内的水体通过循环水泵（recirculated pump）持续循环，实际水深由消波滩角度与水泵流量共同调节。水槽的物理与电气特性详见数据集5。数据集1至4对比了固定造波板冲程长度（paddle stroke length）下，分别以0.25Hz、0.4Hz、0.7Hz及1.0Hz四种造波频率生成的波浪的实测波长（observed wavelength）与理论波长（theoretical wavelength）。本次实验将水槽额定水深（nominal water depth）设置为500mm，水槽内共布设两个间距1.6米的水深测量探头（depth measurement probes）。实验结果显示，所有测试频率下的波形质量均未达理想状态，但随着造波频率升高，实测波长与理论波长的吻合度逐步提升，在1Hz处取得了较好的吻合效果。综上，该水槽应在高于1Hz的频率下开展实验，但需注意：可用波浪功率会随频率升高而降低。在1Hz工况下，生成的波浪呈现出通常仅在中等水深环境中观测到的特性。