| In recent years,with the decline of marine fishery resources and the continuous destruction of the marine ecological environment,people's awareness of marine environment protection has gradually increased.In the work of protecting and proliferating marine organism and rehabilitating the marine ecological environment,the deployment of artificial reefs and the construction of marine ranches are important protection measures.After the artificial reef is placed on the sea floor,it can not only provide shelter for fish,but also can create different flow field characteristics such as upwelling and back vortex due to its complex internal structure.The upwelling drives nutrients at the bottom to diffuse upward and attracts fish,and the back vortex forms a slow-flow area to provide a resting place for fish.Consequently,the long-term construction of artificial reefs can effectively improve the marine ecological environment.In order to ensure the long-term stability of the ecological effects of artificial reefs,the design and optimization of artificial reefs are very important.In general,the main factors to be considered in the design and optimization of artificial reefs include two aspects: the stability of the reef and the flow field effect of the reef.Based on this,this paper used the model experiment and numerical simulation as research methods to carry out the following three aspects of research work:Firstly,in this paper,the maximum static friction coefficients of six kinds of artificial reef models with different opening ratios were measured by the plane pulling method,and the effects of the sediment particle size,the sediment water content,the loading quality,and the reef bottom opening ratio,etc.on the maximum static friction coefficient were analyzed.Using SPSS software to analyze the measurement results and got the following results:(1)When water content of sediments was in the state of saturation,the maximum static friction coefficient increased with the decreasing of the sediments particle size except when the sediment was silt.The friction force on silt was smaller obviously due to soft flowing character of ground;(2)When the sediment was silt,the maximum static friction coefficient raised obviously along with the increasing of water content first and then decreased afterwards.When the water content was 35%,the maximum static friction coefficient reached the maximum value;(3)The maximum static friction coefficient under all the sediments declined with the increasing of loading quality.The ratio of bottom opening positively correlated with the static friction force,while the position of bottom opening did not affect the maximum static friction coefficient.The results of this model experiment could provide reference for the site selection of artificial reefs and the design of bottom opening ratio.Numerical simulation study has been widely used in research of artificial reefs,and this paper took the car leaf type reef as the research object.The numerical simulation method of the computational fluid dynamics and the tank test method were used to obtain the flow resistance of the reef respectively,and the resistance coefficients of the reef body obtained by two methods were compared.The results showed that the average error of the two measurement methods was 5.35%.This verified that the numerical simulation method could be used in the calculation and analysis of the hydrodynamic performance of artificial reefs.On this basis,using computational fluid dynamics(CFD)to analyzed the stability and the flow field characteristics for three kinds of hollow artificial reefs with different influent surface under five groups of water flow and offshore waves.The results showed that:(1)At the depth of 12 m,when the flow velocity was less than 1.0m/s,the anti-slipping and anti-rolling coefficients of the three types reef were all greater than 1.0;(2)When the flow velocity gradually increased and beyond 1.0m/s,the stability coefficient of each type reef gradually decreased,and A reef began to destabilize when the flow velocity increased to 1.2 m/s,while the relative stability of C reef was the best;(3)When the same type reef was under different flow velocities,the differences in upwelling volume,relative velocity of upwelling,relative height of upwelling,relative height of back vortex,and relative length of back vortex was very small;(4)At the same flow velocity,the upwelling volume produced by A reef was 2.46 times that of C reef.The back vortex formation formed by A reef and B reef was clearer than that of C reef,and the back vortex characteristics were clearly visible.The simulation results in this section showed that the design of the inflow surface of the reef should take into account both stability and flow field characteristics.Finally,this paper studied two different types reef which had been put into operation and had achieved good results in Shunliao Bay.According to the order of front and rear reefs and vertical spacing of reefs,the two types reef were designed into eight different combinations.Then the stability and flow field characteristics of each combination mode at different flow velocities were studied with computational fluid dynamics numerical method.The results showed that:(1)The spacing of reefs had little effect on the stability of reefs,but had a greater influence on the volume of upwelling and back vortex,and the upwelling volume of the eight combined modes decreased with the increasing of the spacing.The volume of the back vortex was related to the combination mode of the reefs.When the combined reefs were the same type reef or the smaller inflow surface reef was at the front,the volume of the back vortex increased with the increasing of the distance.When the reef with the larger inflow surface was at the front,the volume of the back vortex decreased with the increasing of the distance;(2)The type of the front reef was an important factor affecting the stability of the reefs.When the reef with a larger inflow surface was used as the front reef,the stability of the reefs was better than that of other combinations.When the same type reefs were combined,the stability of the front reef with smaller inflow surface was better than that of the larger inflow surface,while the stability of the rear reef was the opposite;(3)The combined upwelling index was proposed to express the effect of the reef combination mode on the upwelling volume,then took the four combinations of single reef width with better upwelling characteristics for example.There was a strong positive correlation between the upwelling volume of the reef combination and the combined upwelling index,and the correlation coefficient was 96.2%;(4)The distribution range of vortex core in each combination showed that the B-B combination mode had the widest vortex distribution range and the A-A combination mode had the smallest vortex distribution range.When A reef was used as the front reef,the number of vortex cores in the inter-reef and post-reef areas was obviously reduced compared with other combinations.The researches in this section showed that the effect of the structural characteristics of the front reef on the flow field characteristics should be considered in the reef combination design. |
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