Study On The Optimization Of Octagonal Prism Artificial Reef Structure And The Flow Field Effect Under The Condition Of Stratified Fluid

In recent years,as the country attaches great importance to marine undertakings,the construction scale of marine ranches has gradually expanded.As an important part of the construction of marine ranches,artificial reefs are directly related to the effects of marine ranches.Flow field effect is the main evaluation criterion for the role of artificial reefs.From the existing research,there are many factors that affect the flow field effect of artificial reefs,mainly including the shape and structure of the reef itself and the current environment.Among them,it is the most effective and direct way to improve the flow field effect of artificial reef by changing the shape and structure of the reef.Therefore,designing artificial reefs with better flow field effects has become the goal of many researchers.This paper first uses physical model experiments to verify the results of the numerical simulation,and then uses numerical simulation methods to optimize the structure of the octagonal prism artificial reef.It mainly discusses two types of single-layer side plates artificial reefs and two double-layer side plates artificial reef.The main results are as follows: after verification,the flow velocity of the numerical simulation and the flow velocity of the water tank experiment are not much different,and the error between the two is small,which proves the accuracy and reliability of the numerical simulation in this paper.At 0°vertical upstream,the volume of upwelling and wake vortex and upward transport flux of the type A with the single lower side plate are better than those of the type B with the single upper side plate;and compared with type B,type A have a stronger blocking effect on water flow,and the vortex movement behind the reefs is more random.At 0° vertical upstream,the increase in the number of side plates(Type C and Type D)has a significant effect on improving the artificial reef flow field effect,especially on the upwelling effect;the side plate has an obvious blocking effect,and the onward surface is projected.There is a good correlation between the area and the volume of the upwelling flow,and it also has a certain correlation with the volume of the wake vortex.In the two two-layer side plate artificial reefs,the upwelling effect and the upward water transport flux of type C with the upper vertical side plate is better than the type D with the rising inclined side plate,and the wake vortex effect is inferior to the type D;And compared with type D,type C have a greater blocking effect on water flow,and the vortex movement behind the reef is more random.Under different upstream angles,the blocking effect of the double-layer side plate reef is quite different.There is no obvious correlation between the volume of upwelling and the projected area of the onward surface of type C and D,and there is also no obvious correlation between the volume of wake vortex of the type C and D.Due to its special structure,the octagonal prism artificial reef not only has better flow field effects,but also is suitable for more complicated ocean current environments.By summarizing the research findings of artificial reefs in recent years,whether it is physical model experiments or numerical simulation studies,single-density fluids are mostly used when studying the forces and flow field effects of artificial reefs.However,in the actual ocean,temperature,salinity,and fresh water injection are affected by many factors.As the depth increases,the density will change.Therefore,the use of numerical simulation methods,large eddy simulation,user-defined functions(UDF,User define function)to achieve temperature stratification,and through the relationship between density and temperature to achieve density stratification,and then studied the mixing The flow field effects of artificial reefs under layered conditions are compared and analyzed with the flow field effects of artificial reefs under uniform density.The main conclusions are as follows: when the cline position is constant,the volume of upwelling of two stratified conditions is greater than that of the uniform density condition,the volume of wake vortex of the condition 2 is smaller than that of the uniform density condition,and the volume of wake vortex of condition 3 is larger than the uniform density condition.the change of the intensity of the cline has a small effect on the flow direction transport flux,a greater impact on the vertical transport flux,and a small impact on the density field at the cline layer.When the strength of the cline is constant,the closer the cline is to the reef,the greater the disturbance to the density of the cline;The flow field effect of the artificial reef changes greatly with different positions of the cline layer;as the position of the cline layer gradually moves downward,the volume of the upwelling stream gradually decreases and the volume of the wake vortex gradually increases;when the strength of the cline is constant,the change of the cline position has little effect on the flow direction transport flux;When the position of the cline is close to the fish reef,the common disturbance of the fish reef and the cline has the greatest impact on the water flow,and the vertical transport flux near the bottom of the water body is significantly greater than other working conditions;Comparing 4 kinds of stratified working conditions and uniform density working conditions,the corresponding flow field effect indicators such as upwelling volume and wake vortex volume are larger or smaller than uniform density working conditions,that is,when studying the effect of stratification on the flow field effect of fish reefs According to the specific density stratification of the studied area,relevant research is more conducive to better evaluation of the flow field effect of the artificial reef used.