基于FUNWAVE-TVD模型的离岸养殖围网内外波浪场数值模拟研究

Numerical Study on Wave Fields Inside and Around an Offshore Pile-Net Enclosure Structure Based on FUNWAVE-TVD Model

本研究利用完全非线性Boussinesq数值模型FUNWAVE-TVD耦合多孔介质模型,建立了模拟围网波浪场的数值模型。将计算结果和实验数据进行对比分析,验证了该模型计算规则波在穿过网箱后传播过程的准确性。进一步研究了波高和周期等因素对围网内外波浪场特性的影响,探讨了围网波浪场特性与这些水动力因素的内在联系。结果显示,离岸养殖围网的存在使波浪场背浪侧出现衰减,波高衰减率受波浪周期影响较大,最大波高衰减达到93.3%。同时,较低频规则波的波高衰减区域呈辐射状趋势扩散,并随着波浪进一步传播,最大波高衰减位置开始向两侧扩散,围网背浪侧的波高衰减程度减小,波高有恢复趋势,而高频波浪的波高衰减区域则较为集中。本研究可为实际海域桩网围护的位置和构造提供分析依据。

Aquaculture in offshore structures is an effective method for developing ocean ranching and meeting the increasing demand for marine produce and is one of the most promising ecological breeding structures. The offshore pile-net enclosure structure has wide application prospects owing to its large aquaculture volume, and its aquaculture environment is very similar to that of the natural environment. However, the existence of the pile and net structure will have a certain impact on the wave fields inside and around the pile net enclosure. Owing to the large scale of the pile-net enclosure structure, the structure significantly changes the original wave field in passing waves. Because of the complexity of the wave field at sea, construction site selection will have a significant impact on the safety of the purse seine structure. The pile-net enclosure structure also has an effect on the contents of nitrogen, phosphorus, heavy metals, and other substances in the area.Study of the impact of the pile-net enclosure structure on the original wave field is also of great significance for addressing environmental problems. Previous studies on pile-net enclosure structures have focused on the stress of the structure, and few studies have examined the impact of the structure on the original wave field in passing waves. Therefore, the propagation tendency of the pile net enclosure structure on the wave field in the original area under the action of waves and the hydrodynamic characteristics of the pile net enclosure were studied. This is of great significance for the structural design and site selection of the entire pile net enclosure. Based on the fully nonlinear Boussinesq equation and the numerical model FUNWAVE-TVD with shock capture ability, the propagation tendency of regular waves through a pile-net enclosure structure was studied. First, the wave was simulated based on the fully nonlinear Boussinesq equation. For a structure with large porosity, the pile-net enclosure structure was simplified as a porous medium model, ignoring its linear force, considering only the drag force of the netting, and using a reasonable calculation formula to calculate the flow-blocking effect of the netting. The influence of the pile-net enclosure on the wave field was simulated by combining the two. The finite volume and finite difference methods were used in the numerical calculation. First, a physical model experiment based on the lander verified whether the model was accurate for the calculation of the wave field of the netting. The physical model experiment designed different wave conditions and three netting models with large differences in compactness. The square coefficient of the wave height was used to describe the change in wave energy after the wave passed through the pile-net enclosure structure. Compared to the results of the physical model experiments, the error was small. Subsequently, the numerical model was verified from the perspective of the cage using Bi’s physical model test data. The model used a net cage model to simulate the influence of the net cage on the wave field. A numerical flume similar to that of the physical model experiment was designed, and the wave-dissipation area was set before and after.The cage size was the same as that used in the physical model experiment. The results showed that the model could better simulate the influence of the cage structure on the wave field. Different working conditions were then designed, the effects of the wave period on the wave field characteristics of the pile-net enclosure were further studied, and the internal relationship between the wave field characteristics of the pile-net enclosure structure and these hydrodynamic factors were discussed. In this study, a numerical flume similar to the physical model experiment was designed.Then, different designed wave conditions were used to determine the effects of the wave period on the wave field characteristics of the pile-net enclosure. The results showed that the influence of the pile-net enclosure on the larger periodic wave field had a radial trend and a fan-shaped radiation area behind the pile-net enclosure structure, which increased with an increase in the wave period,indicating that the wave period increased and its influence area expanded. Within a certain range on the lee side of the pile-net enclosure, the wave height showed a recovery trend, and the attenuation gradually decreased, while the attenuation area of small periodic waves was more concentrated. The wave with a small period was significantly affected by the pile net enclosure, and its wave transmission coefficient was the smallest in this study. The results show that the numerical model can effectively simulate the wave field characteristics around a pile net enclosure, which has a reference value for the location and construction of a pile net enclosure in an ocean ranching environment.