Numerical Study On The Effect Of Reef Settlement On The Flow Field Of Square

As a special structure artificially made and placed in the designated position of the ocean,one of the main functions of artificial reef is to improve the marine habitat by changing its surrounding flow field effect,which is an indispensable link in the construction of marine pasture.With the application of acoustic technology and equipment in the field of marine survey,some scholars have found that different reef areas have different degrees of reef settlement,and reef settlement is bound to have an impact on the flow field effect of artificial reef.In view of the lack of settlement as a necessary consideration factor in the current research on the flow field effect of artificial reefs,this paper carries out numerical simulation research on the flow field around two square artificial reefs under five settlement degrees,and compares,analyzes and summarizes the research results of other scholars in relevant fields,so as to make up for the vacancy in the research field of artificial reef flow field to a certain extent,It provides guidance for the failure discrimination of reef flow field effect and the adjustment of Reef State.The research objects of this paper are square solid artificial reef and square porous artificial reef.When studying the influence of settlement on the flow field effect of the latter,we also comprehensively consider the hot research content of artificial reef layout spacing.The main research work and related results are as follows.（1）Mesh generation and calculation method.After a large number of experiments and attempts,the reef model and flow field in the whole calculation area are carefully divided and composed of different elements to realize the establishment of hexahedral unstructured grid.The grid encryption at different locations is carried out for different models.The average grid orthogonal quality exceeds 0.996,and the number of grids is controlled between 500000 and 2 million.At the same time,the convergence of iterative calculation within 1000 times is realized on the premise that the residual accuracy meets10^-6.（2）Effect of settlement on flow field of single square solid artificial reef.As a whole,the flow field effect of square solid artificial reef decreases with the increase of settlement depth,and the maximum velocity around the reef decreases all the time,but it still plays a good flow field effect when the settlement degree is less than 40%.When the settlement degree is 20%,the maximum velocity of upward flow of reef decreases by about 0.015m/s,the maximum height of upward flow decreases by about 1.23m,and the velocity at the top of reef increases The flow field patterns in the lateral flow region and the back vortex region are basically the same as those without settlement;When the settlement degree is40%,the maximum upwelling velocity of the reef decreases by about 0.038m/s,and the ratio of the maximum height loss degree of the upwelling to the settlement degree is 0.61.The flow field around the reef is basically the same as that without settlement except the disappearance of wake flow.When the settlement reaches 60%,the flow field effect around the reef is lost obviously.（3）Effect of sedimentation on flow field of single porous square artificial reef.Some flow field characteristics of square porous artificial reef do not decrease with the increase of settlement depth.Within 40%of the settlement degree,the reef still plays a good flow field effect.Even when the settlement degree is 20%,the flow field around the reef even becomes more complex from the perspective of lateral flow and maximum upwelling velocity:the maximum velocity of upwelling increases by about 0.015m/s,The increasing area of lateral flow is about 1.5 times that without settlement.When the settlement exceeds 60%,the reef flow field effect begins to lose significantly.（4）The influence of settlement comprehensive layout spacing on the flow field of porous square artificial reef becomes more complex.The change of layout spacing has little influence on the maximum height of upward flow,lateral flow and the flow pattern of the second reef back vortex,but has a great influence on the flow pattern between reefs and inside the second reef.When the settlement degree is≤40%,the two porous square artificial reefs still maintain good flow field effect.At the same time,increasing the layout spacing to a certain extent will improve the flow field effect of artificial reefs:the maximum velocity of upwelling at the layout spacing of 4.5m and 6m is significantly higher than that at the spacing of 3M.At the same time,when the settlement degree is≤40%,it increases with the layout spacing,The flow field between reefs becomes more complex.From the simulation results,the porous square artificial reef and square solid artificial reef maintain a good flow field effect within 40%of the settlement,but the flow field effect of porous square artificial reef is better than that of square solid artificial reef with the same size.Even when the settlement is 20%,some flow field characteristics of porous square Artificial Reef have been improved to a certain extent.The increase of layout spacing has a great impact on the flow field around the two porous square artificial reefs and the internal flow field of the second reef.On the whole,the flow field characteristics of 4.5m and 6m spacing are better than those of 3M spacing.