人工船礁铺设模式优选方法研究

HYDRODYNAMIC SIMULATION TO THE BEST LAYOUT OF ARTIFICIAL SHIP-REEFS

以人工船礁水动力学特征及优化组合方式为主要研究内容 ,采用数值研究的方法 ,探讨了人工船礁的不同组合及其规模大小对于形成上升流与背涡流的效果、促进海水的上下混合与交换的影响 ,并在此基础上建立了人工船礁铺设方式优选模式。结果表明 ,从船礁的相对效果看 ,铺设模式以大型单体船礁为最佳 ;不同类型船礁组合产生的最大上升流流速为来流速度的 0 0 5— 0 1 5倍 ;随来流速度的增加 ,产生的上升流及背涡流影响效果显著增强 ,在不同来流速度下 ,上升流影响范围与礁宽之比为 1 1— 5 0 ,流影高度与礁高之比为 1 4— 2 0 ,背涡流流影长度与礁高之比为 4 5— 1 3 0 ;不同礁体及其组合对“冲淤”影响差异较大 ,船礁因流线型形状 ,其“冲淤”影响较小。文中建立的人工船礁铺设方式优选模式 。

In recent years, offshore aquatic resources have declined due to over-fishing and deterioration of the marine environment. Artificial reefs are an effective measure for not only improving the marine ecological environment but also constructing fishing grounds. Since the 1980s, artificial reefs have been built in many Chinese offshore areas, and tests on the hydrodynamics of artificial reefs have been carried out in tanks. Recently, with stricter controls of marine fishing in Chinese waters, a greater number of discarded ships have been utilized to build artificial reefs, dubbed, accordingly 'ship-reefs'. To date, few reports have emerged on maximizing the effectiveness of ship-reefs through appropriate arrangement of these discarded boats. This paper considers hundreds of discarded wooden fishing boats that have been laid on the sea-floor of the Zhoushan Fishing Ground where our study to get best layout of the ships was carried out. In order to discover the optimal layout pattern, and provide theoretical basis, flume test and numerical methods were used to simulate the hydrodynamics in the case of the artificial ship-reefs, to work out how various patterns and scales would affect the formation of upward flows, back eddy flows, and mixture and exchange between shallow and deep water layers. Optimization occurs under the condition that the ship-reef layout could increase the dissolved oxygen in the water and carry nutritive salt from the bottom to the shallow layers. Ideally, the condition must be able to promote as large as possible an area of upward and back eddy flow and reduce as much as possible the sedimentation that would clog the area for marine transportation route. The sedimentation effect can be assessed by calculating the ratio of the maximum vertical current speed to that of the flow-in current. Equations were established to calculate the hydrodynamic states of the upward flow and back eddy flow around the ship-reefs, and a quantitative model was made to get the best layout. The best condition is where depth is 10-20 meters with reciprocating current, and the maximum current speed is 1.58m/s. Eight types of ship-reef layout pattern were selected for research. Results show the best layout fashion is a single large ship. The maximum speed of upward flow caused by the various combination models of the ship-reef was 0.05-0.15 times to the flowing-in speed. With the increase of flowing-in speed, the effect caused by upward flow and back eddy flow was greatly strengthened. With various flowing-in speeds, the ratio of affective width of upward flow to that of the ship-reef was 1.1-5.0, affective height of upward flow to that of ship-reef was 1.4-2.0 while affective length of back eddy flow to the height of ship-reef was 4.5-13.0. Different layout pattern of the ship-reef produced significantly different sediment clogging. The ship itself had a minor contribution to the clogging because of the streamlined shape.