Hydrodynamics Experiment Of Artificial Reefs And Numerical Simulation Of Flow Field

Due to fishing intensity enhanced and environmental pollution, our offshorefishery resources is in a serious recession. Therefore, the restoring of the ecologicalenvironment of the offshore waters, the protection of fishery resources andmaintenances of the sustainable development of marine fishery are the urgent tasks atpresent. Construction of artificial reef and development of ocean pasture ranching areconsidered as effective approaches to ease recession of fishery resources anddesertification of fishing ground, to promote the construction of coastal fishingground. As the artificial reef is in marine environment, it suffered the interaction ofwaves and currents. It is also generally placed at the bottom of the sea which belongsto bottom fish reef; as a result, most of the studies on hydrodynamic performance ofartificial reefs were taken no account of the wave. The fundamental researches ofartificial reefs are about materials, structure, stability, rational layout, density placed,ecosystem, fishing technology, etc. We should consider material of reef and sea waterenvironment to design of strength and stability of artificial reef. The influence rangeand distribution of flow field of artificial reef are mainly influenced by the fish reefstructure and the scale size, and distribution of flow field directly affects the layout ofartificial fish reef. In order to improve the efficiency and reliability of artificial fishreef, we should apply engineering analysis method to study the hydrodynamicperformance of it and the effect of the flow field before the design and delivery of theartificial reef. The research methods of this kind of structure mechanics performanceusually have model experiment and numerical simulation method. With the rapiddevelopment of computer technology, numerical simulation is widely applied to allwalks of life, and more and more be taken seriously. Therefore, flume experiment andnumerical simulation are applied to study reef hydrodynamic and flow fieldcharacteristics of artificial fish reefs in this article. Basing on3m×3m×3m square fish reef as a physical body, we taken a scale20（λ_L=20）to make two kinds of15cm×15cm×15cm square fish reef model in thisarticle. We measured water resistance of reefs under different flow rates in the refluxtank, and calculated the drag coefficient (C_d) and R_eynolds number (R_e). R_esultsshowed that R_ewas over7.5×10~4, C_dwas1.64and R_ewas greater than7.5×10~4in theautomatic model area when the model reef without lid was meeting flow head-on; R_ewas over6.36×10~4, C_dwas1.30and R_ewas more than6.36×10~4in the automaticmodel area when it was meeting flow at45°direction. R_ewas over6.0×10~4, C_dwas1.69and R_ewas more than6.0×10~4in the automatic model area when the model reefwith lid was meeting flow head-on; R_ewas over8.48×10~4, C_dwas1.43and R_ewasmore than8.48×10~4in the automatic model area when it was meeting flow at45°direction. A model of the reef body suffered different flow resistance under thedifferent incident flow way. The model reef was subjected to greater flow resistance at45°direction than hand-on. In the same incident flow, the reef body with lid sufferedlarger resistance than one without lid.Based on the FLUENT and ANSYS, this paper analysis the flow changesthrough an artificial reef using the one-way coupling analysis. Geometric modelingand meshing were deal with DM Geometry and Mesh, respectively. Fluid analysis inFLUENT and structure analysis was setting in the Static Structural (ANSYS). Thevelocity contour of different sections in flow field was achieved by the FLUENTpost-processing. From the velocity contour, flow field around the artificial reef wasimpact significantly after the fluid pass through the reef. By comparison withexperimental data and simulation results analysis, we can be seen that it is feasible todo numerical modeling using ANSYS WORKBENCH for flow field of artificial reefs.Therefore through the numerical modeling we can predict the distance when the flowfield can recover after the current pass the reef, or simply, we can calculate theappropriate position of the next reef delivered. As can be seen from the velocitycontour, the external flow field recovers when the distance is17times of the reef inthe direction of flow (section A19). From the comparison of the simulated values andmeasured values, the flow rate basically stable after the section A19. If the import flow was50cm/s, and the velocity error was in0.7to2.94%when the flow stability.Also, from the velocity contour, we can see that in the section C the distance is about3.5times of the reef (section C8) the flow can be restoration.This paper studies the hydrodynamic performance of artificial reefs of theflexible structure, and artificial fish reefs of the flexible structure is mainly composedof the supporting framework and the net panel. The support framework wascylindrical structure materials and the netting was ordinary polyethylene mesh. Themonomer model of artificial reef was oval (high is175mm, maximum diameter is480mm), and the surrounding was evenly divided into eight pieces, including4partsof PE mesh (2a=20mm，d=1mm) and4parts hollow structure. R_egarded the flexiblestructure of artificial reef as a stationary in the water fishing gear components andaccording to the nature and type of the fishing gear and fishing gear hydrodynamic,the water resistance of an object depends on the velocity of the incomingflow.Combination the reef monomer in two ways, and one was that vertical combining1to4of the monomer reefs into a cylindrical structure, in all, forming four combinations;the other one was combined4monomer reef horizontal together and then verticalcombination1-4layer, in all, forming four combinations. In the circulation channel,we choose seven flow rates: V=0.12m/s,0.2m/s,0.3m/s,0.2m/s,0.5m/s,0.6m/s,and0.7m/s, and measured seven different fish reef combination structure resistancevalue(R) of the current situation. The results show that:(1) The water resistance wasbigger when it was meeting flow=45o than=0o, for the4kinds in the firstcombination (mono-reef, bi-reefs, tri-reefs, quadri-reefs), the difference with in the0.3-23.3%. For the4kinds in the second combination (4in one layer,8in two layer,12in three layer,16in four layer), the difference was between5.9%and35.4%.(2)The calculated value of water resistance was larger than measured values, and thedifference was between4.1and10.8%for the first combination, and the difference isbetween2.1and10.7%for the second combination. In order to reduce the effect ofwater for the reef, we should choose head-on flow during the actual delivery. Overall, this study on hydrodynamic of artificial reefs with square and flexiblestructure can provide theoretical basis for the design of the reef, resistance calculationand stability checking, etc. The analogy procedure of the flow field can effectivelycalculate the flow field distribution around the reef, and the results can providetheoretical reference for the arrangement of artificial reef.