Artificial reefs (ARs) are one of the key man-made constructs to restore the offshore fishery resources and recover the ecological environment. However, it is found that many ARs lost their stability and function due to scour. In order to ensure the functional effect of ARs, it is of great significance to study the instability of ARs, like burying caused by scour in different flow conditions. The three-dimensional numerical model established by FLOW-3D is used to study the local scour characteristics around the AR in steady currents. The RANS equations, closed with the RNG k-ε turbulence model, are established for simulating a stable flow field around one AR. The simulation results are compared with previous experimental results and shows good agreement. Then, the effect of the opening number and the incident angles of ARs on the scour characteristics, the equilibrium scour depth and maximum scour volume are investigated. The results indicate that the scour depth and scour volume decrease with the increasing opening number. Moreover, the empirical equations of the effect of the opening number of the AR on the equilibrium scour depth and maximum scour volume are proposed based on the numerical results. The change of the incident angles will affect the change of bed shear stress at the most upstream corner of the AR. The greater bed shear stress results in a more intense scour. This study will provide theoretical support, and practical guidance for the optimized engineering design and construction of ARs.
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.
Artificial reef (AR) is one of the key methods to restore the offshore fishery resources and ecological environment. To secure its ecological effects, it is of great significance to study the possible instability of the AR, like sinking and reversing caused by change of the submarine topography, water flow and sediment movement. In the present study, the model experiments of the triangular ARs on the mechanism of the local scour are carried out. The prototype of the triangular ARs is used in Xiaoshidao National Marine Ranching in Weihai, Shandong Province. The effects of the heights, the bottom angles and the length of the bottom of the triangular ARs on the scour volume and the equilibrium scour depth are investigated. The results show that for the ARs with the same heights, the scour depth increases with the increasing bottom angles. For the ARs with the same bottom angles, the scour depth increases with the increasing heights. A generalized linear model is used to derive the effect of the bottom angle of the triangular AR on the scour depth. The research results can provide references for the design optimization and deployment of the ARs. This proposed study will provide theoretical support and practical guidance for the optimized engineering design and construction of the ARs.
The industrial integration of offshore wind power and marine ranches has been actively explored and developed in many countries. This emerging industrial synergy can significantly improve the ecological friendliness of offshore wind power and contribute to the development of the marine economy in the region. This industrial synergy is an important development direction for future offshore engineering. Artificial reefs (ARs) are critical components of marine ranches and are widely placed around offshore wind foundations (OWFs). The ARs can block the water flow and form a complex wake region behind it, which changes the original turbulence structure and reduces scour around the OWF. Therefore, determining the arrangement of ARs for scour protection around an OWF is of great engineering significance. In this study, a three-dimensional numerical model is established using a prototype of the first offshore wind power-marine ranch demonstration project in China. The turbulent change and sediment movement between the OWF and ARs are solved using the Reynolds-averaged Navier-Stokes (RANS) and sediment transport equations. Moreover, the variations in the maximum scour depth and scour volume around the OWF at different arrangements of ARs are explored. The results demonstrate that the arrangement of ARs weakens the horseshoe vortices in front of the OWF and destroys the vortex shedding behind the OWF, thereby producing a beneficial scour protection effect. Various arrangements of ARs have different effects on scour results around the OWF. Increasing the height of the AR could significantly reduce the scour results around the OWF and play an effective role in scour protection, followed by the tandem arrangement of ARs, whereas the parallel arrangement of ARs will produce negative scour effects. This study will serve a vital guiding role in the arrangement of ARs and practical significance for scouring protection around the OWF.
Artificial reefs (ARs) are one of the key anthropogenic constructs used to restore offshore fishery resources and recover the ecological environment. However, many ARs lose their stability and function due to scour. To ensure the functional effect of ARs, it is of great significance to study the factors causing AR instability, such as burying caused by scour under different flow conditions. In this work, a three-dimensional numerical model is used to study the local scour characteristics around an AR in steady currents. Reynolds-averaged Navier-Stokes (RANS) equations, closed with the renormalization group (RNG) k-e turbulence model, are established to simulate a stable flow field around one AR. The simulation results are compared with previous experimental results, exhibiting good agreement. The effects of the opening number and the incident angles of ARs on the scour characteristics, equilibrium scour depth and maximum scour volume were also investigated. The results indicate that the scour depth and scour volume decreased as the opening number increased. Furthermore, empirical equations are proposed herein based on the numerical results derived for the effects of the AR opening number on the equilibrium scour depth and maximum scour volume. A change in the incident angle affected the bed shear stress at the most-upstream corner of the AR. The greater the bed shear stress was, the more intense the scour was. In this study, we provide theoretical support and practical guidance for the optimized engineering design and construction of ARs.
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