Research On Scale Effect Of Artificial Reefs Based On The Flow Field Simulation Experiment

As a new power of transformation for offshore fishery resources and ecological environment,marine ranching has developed rapidly in recent years.It can recover and improve marine ecological environment,protect and reproduce fishery resources,by constructing ecological engineering such as artificial reefs?AR?,Stock Enhancement.With the rapid growth of marine ranching,funds for the construction of AR in Marine Ranching should exceed 70 percent according to regulations.Therefore,as an important and necessary part of marine ranching construction,AR has gradually increased in volume.The relevant departments put forward a strategy of "reducing quantity,increasing quality and improving efficiency",to improve green development of AR on the premise of it performed well.In reality,inadequate volume led to failure to achieve goals and influenced effects.And excessive volume resulted in hindering each other and economic waste.Besides,unreasonable construction model also affected expectation,causing economic waste and sea pollution.Consequently,the rational planning of volume and model for AR construction has become the key of economic and efficient construction.In this paper,as the basis of AR effect,flow field is used as a parameter to measure the construction effect of AR.And the flow field is used as an evaluation index to study AR of different construction scales.It would evaluate the effect of AR construction and the quantitative analysis of its effect evaluation also reversely supports the optimization model planning of AR construction with the flow field effect.The aim is to use the construction target and construction model of AR as the starting point to extract AR scale indicators and flow field effect evaluation indicators,provide clear entry points for AR construction and evaluation,analyze and evaluate effect of multiple construction models of AR flow field effect,establish AR scale effect model on different effect evaluation index,and further propose the optimal unit reef construction model selection process based on upwelling effect standard.And to provide scientific and feasible planning for the AR construction focusing on the flow field.First,this study used flow field simulation experiment methods as means to obtain uniform and non-uniform layout patterns of Cross artificial reefs and 5 different reef of Da-zi artificial reefs,Mi-zi artificial reefs,Hui-zi artificial reefs,Frame artificial reefs and Solid artificial reefs.Based on the basic data of the flow field and the urban air duct planning standards,the unit reef layout model conditions were proposed for the first time.Two levels of indicators representing the size of the unit reef were proposed.The first level indicators included the relative throw amount,laying distance,relative frontal length,relative mean height,relative max height,frontal angle,frontal area ratio of unit reef?UR?,relative water depth,aspect ratio of UR,and volume ratio,permeability coefficient,relative cross-sectional area of reef monocase?MR?,which represent the characteristic indexes of the reef body.The secondary indexes included target velocity ratio and volume ratio of UR,throw density of UR and enclosure degree of UR.Further extract the characteristic indexes represented the flow field effect,including the spatial range index and the intensity index.The spatial range index included relative volume,volume efficiency index of MR,relative length,relative height,relative area and the relative area of height.The intensity index included relative volume efficiency index,average relative velocity index and max relative velocity index.Secondly,based on the above index parameters,the effect of AR flow field in the Cross artificial reefs layout pattern was studied,and quantitatively analyzed the change of the flow field characteristic index under each construction mode of AR.The optimal unit reef construction mode selection method with upwelling effect as the standard was proposed,and the AR scale effect model of the flow field effect index under the uniform layout mode was established.Discussed the effect of AR under different construction environments and the optimized construction model based on different environments.The results showed that the optimal throw amount of unit reef is 432 m3 in the mode of 4×4.In all layout modes,the laying distance is 2.0 to 3.0 times,the relative volume of the upwelling was the largest.When the laying distance is 0.5 times,the volume efficiency index of MR was the largest.and the relative volume of the back eddy and the volume efficiency index of MR was the largest at 1.5 times.When the laying distance is 2.0 times,the relative area of the upwelling and the back eddy was the largest.The largest relative length of the back eddy was 1.0 times.Based on the unit reef,when the target speed ratio is greater than or less than 0.1 times,the minimum standard of the relative volume efficiency of upwelling was 45%and 78%in order,and the back eddy was 55%.Taking the relative velocity of upwelling or back eddy as the target for AR building,the laying distance between them should be 2.0 times or less and 1.5 times or more respectively.The volume effect model of upwelling was Vu=T_ra×(5.768 e-0.003 T_ra+0.025 Ld3-0.173 Ld2+0.124 Ld+181.35 R_u²-61.827 R_u-0.165 vi2+0.368 vi),and the back eddy volume model was Vb=R_u×(0.017 T_ra 2-0.85 T_ra-T_ra?0.295 Ld2-1.453 Ld?+18.809 R_u²+2.692 R_u+11.939 vi2-12.329 vi).Thirdly,based on the Cross artificial reefs,the flow field effect was the main evaluation factor for the construction effect of AR.According to the changes in the background characteristics of the actual sea area of AR,and at the same time,drawing on the characteristics of land urban housing construction models,selected five different types of unit reef construction models with height difference of UR,height ratio of UR,aspect ratio of UR,frontal angle of UR and crossed of UR types to study the characteristics of the flow field effects of the five construction models.And further established the volume effect model of the flow field.The results showed that when the AR with different heights was selected,the greater the height of the frontal surface,the stronger the upwelling effect,and the greater the relative height of the back surface,the stronger the back eddy effect.when the relative water depth of the unit reef is 1/8,the upwelling effect was stronger.When the relative water depth of the unit reef is 1/10,the back eddy effect was stronger.The greater the relative length of the unit reef's frontal surface,the stronger the upwelling effect,and the greater the relative length of the unit reef's back surface,the stronger the back eddy effect.When the frontal surface and the incoming flow direction are at 45°,the upwelling effect was stronger.When the frontal surface and the incoming flow direction are at 90°,the back eddy effect was stronger.When the unit reef are arranged in crossed mode,the upwelling effect was stronger when the arrangement interval is 1.0 times,and the back eddy effect was the strongest when the arrangement interval is 1.5 times.The analysis of the efficiency of the reef monomers including 6 different construction modes under the uniform layout model showed that the volume efficiency of the upwelling of the frontal angle of UR is the largest.The crossed of UR upwelling area efficiency and height efficiency was the largest,and the height difference of UR was the smallest.The crossed of UR and uniform-type reefs had the highest speed efficiency and the smallest was height difference of UR.The frontal angle of UR had the largest volume efficiency of the back eddy,the aspect ratio of UR and frontal angle of UR had greater area efficiency,and the height difference of UR has the smallest.The back eddy length and velocity efficiency were evenly distributed,except that the height difference of UR was the lowest.The volume effect model of upwelling was Vu=H_m×?0.247 H_m×R_u-1.772-0.012 Ah2+1.229 Ah-725.518 D2+192.204 D+50.193 VrU+77.234 DTU-116.733 EdU?,and the back eddy volume model was Vb=H_m×?407.7 R_u²-171.43 R_u+RfU?0.03 Ah2+4.448 Ah?-142.013 VrU-24.137 DTU-10.291 EdU?.Finally,we chose five types of monomers reef,which are currently widely used,including Da-zi artificial reefs,Mi-zi artificial reefs,Hui-zi artificial reefs,Frame artificial reefs and Cross artificial reefs to study the influence law of the reef body's own structural characteristics on the flow field effect under the uniform layout model.Representatively increase the analysis of Solid artificial reefs,and further established the scale effect model of structurally different unit reefs.The results showed that,based on the law of flow field effect,the indexes of reef structure characteristics were volume ratio,permeability coefficient and relative cross-sectional area of MR.The volume effect model of upwelling was Vu=0.448 R_u-1.679-C_p?29.868 C_p-6.921?+R_sa(56.18 R_sa-35.42),and the back eddy volume model was Vb=R_u?1830 R_u-128?-R_v?95 R_v-105?+C_p?138 C_p-154?-R_sa(418R_sa-180).Finally,based on the flow field volume effect model,proposed the suggestions for the selection of structural parameters of the reef body.When the upwelling is optimal,the larger the permeability coefficient,the better the recommended value.When the relative cross-sectional area of MR is less than 0.795,the larger the value was,the better.When it is greater than 0.795,the smaller the value was,the better.It was recommended to avoid choosing the structure with a relative cross-sectional area of 0.452.When the volume ratio is less than 0.452,the larger the value was,the better.When it is greater than 0.452,the smaller the value was,the better.It was recommended to prefer to choose the structure with volume ratio of 0.452.It was recommended that when the permeability coefficient is less than 0.476,the smaller the value was,the better.When it is greater than 0.476,the larger the value was,the better,and to avoid choosing structure with permeability coefficient of 0.476.The larger the relative cross-sectional area value was,the better.The results of this study provided new ideas for evaluating the flow field of AR,as well as new methods for rationally selecting the structure of marine reefs and planning the construction model of AR.