As a simplified model of artificial reefs, a series of plate models punched with square or circular openings are designed to investigate the effects of openings on the hydrodynamic characteristics of artificial reefs....As a simplified model of artificial reefs, a series of plate models punched with square or circular openings are designed to investigate the effects of openings on the hydrodynamic characteristics of artificial reefs. The models are grouped by various opening numbers and opening-area ratios. They are physically tested in a water flume or used in the numerical simulation to obtain the drag force in the uniform flow with different speeds. The simulation results are found in good agreement with the experimental measurements. By the non-dimensional analysis, the drag coefficient specified to each model is achieved and the effects of openings are examined. It is found that the key factor affecting the drag coefficient is the open-area ratio. Generally, the drag coefficient is a linear function of the open area ratio with a minus slope. The empirical formulae for the square and circular openings respectively are deduced by means of the multiple regression analysis based on the measured and numerical data. They will be good references for the design of new artificial reefs. As a result of numerical simulation, the vorticity contours and pressure distribution are also presented in this work to better understand the hydrodynamic characteristics of different models.展开更多
In the present work,the hydrodynamic performance of the double deflector rectangular cambered otter board was studied using wind tunnel experiment,flume tank experiment and numerical simulation.Results showed that the...In the present work,the hydrodynamic performance of the double deflector rectangular cambered otter board was studied using wind tunnel experiment,flume tank experiment and numerical simulation.Results showed that the otter board had a good hydrodynamic performance with the maximum lift-to-drag ratio(K_(MAX) = 3.70).The flow separation occurred when the angle of attack(AOA) was at 45?,which revealed that the double deflector structure of the otter board can delay the flow separation.Numerical simulation results showed a good agreement with experiment ones,and could predict the critical AOA,which showed that it can be used to study the hydrodynamic performance of the otter board with the advantage of flow visualization.However,the drag coefficient in flume tank was much higher than that in wind tunnel,which resulted in a lower lift-to-drag ratio.These may be due to different fluid media between flume tank and wind tunnel,which result in the big difference of the vortexes around the otter board.Given the otter boards are operated in water,it was suggested to apply both flume tank experiment and numerical simulation to study the hydrodynamic performance of otter board.展开更多
Artificial reef is a man-made object that is deployed purposefully on the seafloor to restore the offshore fishery resources and the ecological environment.To secure its ecological effects,it is important to study the...Artificial reef is a man-made object that is deployed purposefully on the seafloor to restore the offshore fishery resources and the ecological environment.To secure its ecological effects,it is important to study the possible instability of artificial reefs,like drifting and reversing caused by burial and scour in different seafloor conditions.In the present study,experiments of local scour around an artificial reef are carried out in steady currents.The effect of the open-area ratios and the open-hole heights of the cubic reefs,and the bottom angles of the triangular reefs on the time-scale of the scour process and the equilibrium scour depth are investigated.The results indicate that for the cubic artificial reef,the scour depth decreases with the increasing open-area ratios,and increases with the increasing open-hole heights.In the present study,the optimal prototype of the cubic reef with an open-area ratio of 0.49 and open-height of 0.7 m produces the minimum scour depth.For the triangular reef,the scour depth increases when the bottom angle increases.Moreover,based on the experimental results,empirical equations of the effects of the cut-opening and the bottom angle on the maximum equilibrium scour depth are proposed.The formulas will provide theoretical support and practical guidance for the optimized design and construction of artificial reefs.展开更多
Long-term fishing pressure affects the biological characteristics of exploited fish stocks. The biological characteristics of hairtail(Trichiurus lepturus) in the East China Sea are unable to recover because of long-t...Long-term fishing pressure affects the biological characteristics of exploited fish stocks. The biological characteristics of hairtail(Trichiurus lepturus) in the East China Sea are unable to recover because of long-term trawling. Fishing induces evolutionary effects on the fish's biological characteristics. Evidence of these changes includes small size at age, a shift to earlier age structure, and early maturation. Natural and artificial selection usually affect the fish's life history. Selection can induce different chances of reproduction, and individual fish can give a different genetic contribution to the next generation. In this study, analysis of time-dependent probability of significance and test of sensitivity were used to explore the effects of fish exploitation rate, mesh size, and heritability with long-term trawling. Results showed that fishing parameters were important drivers to exploited fish population. However, genetic traits altered by fishing were slow, and the changes in biological characteristics were weaker than those caused by fishing selection. Exploitation rate and mesh size exhibited similar evolutionary trend tendency under long-term fishing. The time-dependent probability of significance trend showed a gradual growth and tended to be stable. Therefore, the direction of fishing-induced evolution and successful management of fish species require considerable attention to contribute to sustainable fisheries in China.展开更多
Three-stranded rope is widely used in fishing gear and mooring system. Results of numerical simulation are presented for flow around a three-stranded rope in uniform flow. The simulation was carried out to study the h...Three-stranded rope is widely used in fishing gear and mooring system. Results of numerical simulation are presented for flow around a three-stranded rope in uniform flow. The simulation was carried out to study the hydrodynamic characteristics of pressure and velocity fields of steady incompressible laminar and turbulent wakes behind a three-stranded rope. A three-cylinder configuration and single circular cylinder configuration are used to model the three-stranded rope in the two-dimensional simulation. The governing equations, Navier-Stokes equations, are solved by using two-dimensional finite volume method. The turbulence flow is simulated using Standard κ-ε model and Shear-Stress Transport κ-ω(SST) model. The drag of the three-cylinder model and single cylinder model is calculated for different Reynolds numbers by using control volume analysis method. The pressure coefficient is also calculated for the turbulent model and laminar model based on the control surface method. From the comparison of the drag coefficient and the pressure of the single cylinder and three-cylinder models, it is found that the drag coefficients of the three-cylinder model are generally 1.3–1.5 times those of the single circular cylinder for different Reynolds numbers. Comparing the numerical results with water tank test data, the results of the three-cylinder model are closer to the experiment results than the single cylinder model results.展开更多
基金supported by Shandong Provincial Oceanic and Fishery Department (Ecological Simulation Test of the Offshore Area in Shandong Peninsula)the Primary Research and Development Program of Shandong Province (Nos. 2016CYJS04A01 and 2017CXGC0107)
文摘As a simplified model of artificial reefs, a series of plate models punched with square or circular openings are designed to investigate the effects of openings on the hydrodynamic characteristics of artificial reefs. The models are grouped by various opening numbers and opening-area ratios. They are physically tested in a water flume or used in the numerical simulation to obtain the drag force in the uniform flow with different speeds. The simulation results are found in good agreement with the experimental measurements. By the non-dimensional analysis, the drag coefficient specified to each model is achieved and the effects of openings are examined. It is found that the key factor affecting the drag coefficient is the open-area ratio. Generally, the drag coefficient is a linear function of the open area ratio with a minus slope. The empirical formulae for the square and circular openings respectively are deduced by means of the multiple regression analysis based on the measured and numerical data. They will be good references for the design of new artificial reefs. As a result of numerical simulation, the vorticity contours and pressure distribution are also presented in this work to better understand the hydrodynamic characteristics of different models.
基金supported by the National Key Technology R&D Program(No.2013BAD13B03)the Key R&D Project from Science and Technology Department of Zhejiang Province(Nos.2018C02026,2018C02040)+1 种基金the National Natural Science Foundation of China(No.31072246)the Fundamental Research Funds for the Central Universities(No.201564020)
文摘In the present work,the hydrodynamic performance of the double deflector rectangular cambered otter board was studied using wind tunnel experiment,flume tank experiment and numerical simulation.Results showed that the otter board had a good hydrodynamic performance with the maximum lift-to-drag ratio(K_(MAX) = 3.70).The flow separation occurred when the angle of attack(AOA) was at 45?,which revealed that the double deflector structure of the otter board can delay the flow separation.Numerical simulation results showed a good agreement with experiment ones,and could predict the critical AOA,which showed that it can be used to study the hydrodynamic performance of the otter board with the advantage of flow visualization.However,the drag coefficient in flume tank was much higher than that in wind tunnel,which resulted in a lower lift-to-drag ratio.These may be due to different fluid media between flume tank and wind tunnel,which result in the big difference of the vortexes around the otter board.Given the otter boards are operated in water,it was suggested to apply both flume tank experiment and numerical simulation to study the hydrodynamic performance of otter board.
文摘Artificial reef is a man-made object that is deployed purposefully on the seafloor to restore the offshore fishery resources and the ecological environment.To secure its ecological effects,it is important to study the possible instability of artificial reefs,like drifting and reversing caused by burial and scour in different seafloor conditions.In the present study,experiments of local scour around an artificial reef are carried out in steady currents.The effect of the open-area ratios and the open-hole heights of the cubic reefs,and the bottom angles of the triangular reefs on the time-scale of the scour process and the equilibrium scour depth are investigated.The results indicate that for the cubic artificial reef,the scour depth decreases with the increasing open-area ratios,and increases with the increasing open-hole heights.In the present study,the optimal prototype of the cubic reef with an open-area ratio of 0.49 and open-height of 0.7 m produces the minimum scour depth.For the triangular reef,the scour depth increases when the bottom angle increases.Moreover,based on the experimental results,empirical equations of the effects of the cut-opening and the bottom angle on the maximum equilibrium scour depth are proposed.The formulas will provide theoretical support and practical guidance for the optimized design and construction of artificial reefs.
基金financial support from the National Natural Science Foundation of China(No.31402 350)Special Fund for Agro-scientific Research in the Public Interest(No.201203018)
文摘Long-term fishing pressure affects the biological characteristics of exploited fish stocks. The biological characteristics of hairtail(Trichiurus lepturus) in the East China Sea are unable to recover because of long-term trawling. Fishing induces evolutionary effects on the fish's biological characteristics. Evidence of these changes includes small size at age, a shift to earlier age structure, and early maturation. Natural and artificial selection usually affect the fish's life history. Selection can induce different chances of reproduction, and individual fish can give a different genetic contribution to the next generation. In this study, analysis of time-dependent probability of significance and test of sensitivity were used to explore the effects of fish exploitation rate, mesh size, and heritability with long-term trawling. Results showed that fishing parameters were important drivers to exploited fish population. However, genetic traits altered by fishing were slow, and the changes in biological characteristics were weaker than those caused by fishing selection. Exploitation rate and mesh size exhibited similar evolutionary trend tendency under long-term fishing. The time-dependent probability of significance trend showed a gradual growth and tended to be stable. Therefore, the direction of fishing-induced evolution and successful management of fish species require considerable attention to contribute to sustainable fisheries in China.
基金supported by the National Natural Science Foundation of China (31072246, 30972256)Special Fund for Research on high efficient techniques for Antarctic Krill (20150256)+1 种基金Agro-Scientific Research in the Public Interest (201203018, 201303050-02)the Fundamental Research Funds for Chinese Academy of Fishery Sciences (CAFS) (2012A1301)
文摘Three-stranded rope is widely used in fishing gear and mooring system. Results of numerical simulation are presented for flow around a three-stranded rope in uniform flow. The simulation was carried out to study the hydrodynamic characteristics of pressure and velocity fields of steady incompressible laminar and turbulent wakes behind a three-stranded rope. A three-cylinder configuration and single circular cylinder configuration are used to model the three-stranded rope in the two-dimensional simulation. The governing equations, Navier-Stokes equations, are solved by using two-dimensional finite volume method. The turbulence flow is simulated using Standard κ-ε model and Shear-Stress Transport κ-ω(SST) model. The drag of the three-cylinder model and single cylinder model is calculated for different Reynolds numbers by using control volume analysis method. The pressure coefficient is also calculated for the turbulent model and laminar model based on the control surface method. From the comparison of the drag coefficient and the pressure of the single cylinder and three-cylinder models, it is found that the drag coefficients of the three-cylinder model are generally 1.3–1.5 times those of the single circular cylinder for different Reynolds numbers. Comparing the numerical results with water tank test data, the results of the three-cylinder model are closer to the experiment results than the single cylinder model results.
