Flow Field Effect And Physical Stability Of Artificial Reefs

With the decline of marine fishery resources and destruction of marineenvironment, artificial reef technology has been developed rapidly and become animportant part of the marine ranching construction. An artificial reef is one or moreobjects of natural or human origin deployed purposefully on seafloor to improveaquatic habitat environment and provide feeding, breeding of marine life. Theultimate purpose is to protect, improve fishery resources and improve the proliferationcatch quality.The ecological effects of artificial reefs depend on the flow field effects and thephysical stability. So evaluating the artificial reef eco-efficiency, the main index is thehydrodynamic performance of artificial reefs including the flow field effects and thephysical stability. The study of artificial reef in our country start late and very fewstudies systemiclly analyze the flow field effects and physical stability of artificialreefs.Firstly, in this paper, based on the Fluent code, the flow field around fourdifferent artificial reef models was studied by three-dimensional turbulent model,including single reef, two reefs combined in different disposal spaces. Particle imagevelocimetry (PIV) technique was used to analyze the flow flied distribution in thispaper. Comparing the evaluation indexes of flow field obtained in experiment andsimulation, a good agreement was achieved and the errors were controlled within20%.It suggested that numerical simulation method could be applied topredict the flowfield.in this paper. Based on the experimental verification, three-dimensional turbulenttechnology was used to analyze single reef with different layouts andreef sizes, twocombined reefs with different disposal spaces. And the best layout, disposal space,ratio of reef height to water depth were obtained in this study. Secondly, dynamic tankmodel test method was used to measure the forces in waves and current while friction suffered on two kinds of sediments was determined. The stability checking ofartificial reefs was carried out by comparing the forces and friction, then coefficient ofanti-slide and anti-rolling was obtained. Its achievement will establish the theoreticalfoundation for the structure design of reef and artificial reef area planning.This paper mainly composed of nine chapters. The first chapter reviewed thedevelopment status of hydrodynamic researches and computational fluid dynamics(CFD). The second and third chapters introduced the basic theory of CFD, numericalmodels, laboratory instruments, test methods and evaluation indexes in detail, toprovide a theoretical basis for the subsequent writing of this paper.The fourth chapter analyzed the influences of combined number, disposal spaceto flow field effect around tube artificial reefs by PIV model test and numericalsimulation method. The results showed that the flow field effect was best when thecombined number was15at the water depth of10m, and the ratio of reef height towater depth was0.224. In parallel combination, a better artificial reef effect wasobtained when the disposal space between two parallel reefs was1.0L; In verticalcombination, when the disposal space between two vertical reefs is2.0L, the artificialreef effect is better. Through the dynamics sink experiment, the forces acted on reefsin5current velocities and8wave conditions were measured and the coefficients ofanti-slide and anti-rolling were calculated.An equilateral triangle artificial reef was improved designed based on thetriangle reef in Xiaoshidao reef project in fifth chapter. Just as the forth chapter, theflow field around single reef with different dimensions and two reefs combined withdifferent disposal spaces were analyzed and the best ratio of reef height to water depth,best disposal space were obtained. The stability results showed that the stability ofequilateral triangle artificial reef increased slightly compared with cross reef and steelprism reef.In sixth chapter, both the model texts and numerical simulation were used tostudy the flow field around hollow square reef for scallop proliferation. The bestdisplay method, ratio of reef height to water depth and disposal space were got. Theforces in wave and current conditions were calculated by empirical formula because the dimensions of this reef were too small to do experimental research. And then weanalyzed the physical stability of reefs.In seventh chapter, learned from the conclusions in the study of Liuyan, dynamicsink model tests were carried to study wave and current forces acting on hollow cubeartificial reef. The results showed that the forces increased with the increment ofcurrent velocity, wave height and wave period. And the stability of this reef in wavesand currents was good by stability checking.In eighth chapter, based on the project of "Ecological Restoration of BeidaiheDemonstration Zone in Bohai Sea", comprehensive utilization the conclusionsobtained in previous chapters, a artificial reef core demonstration area occupying57hectare was designed using four kinds of reefs. The artificial reef area consisted of10unit reefs, and the area of each unit reef was0.22hectare while volume was517cubicmeters. This would provide a complete theoretical support for the widespread use offour reef types. In addition, this paper elaborated the ecological, economic and socialbenefits brought form artificial reef core-demonstration area, providing impetus forthe construction of artificial reefs.Finally, summary, deficiencies and follow-up work were elaborated in this paper.