Current and turbulence characteristics of perforated box-type artificial reefs in a constant water depth

Artificial reefs are effective measures to improve the marine ecological environment and increase fishery production. However, there are several geometries being investigated nowadays and their setup, including the spacing between groups of them, can provide dissimilar effects on hydrodynamics. To enhance the understanding of this topic, in this paper, the focus is mainly on M-Type artificial reefs that will be adopted in Juehua Island, Liaodong Bay, China. An experimental campaign was carried out in order to simulate the influence that M-Type unit reef groups may have on the local flow field and the Particle Image Velocimetry (PIV) technique has been implemented to provide velocity maps. The results showed that with the increase of velocity’s current approaching the artificial reef, the height, length and area of the upwelling and the back vortex rise with the increase of spacing between the artificial reefs. Furthermore, when comparing different geometrical configurations with similar currents approaching the artificial reef, the maximum values of both upwelling and back vortex were obtained when the spacing between unit reefs was 1.25 L. Finally, the entropy method was used to evaluate the effects on the flow field under four kinds of spacing based on the hydrodynamic characteristics and the economic cost. The comprehensive score obtained for all the configurations followed the order 1.25 L > 1.50 L > 0.75 L > 1.00 L. Therefore, it is suggested that the original design spacing should be increased by 25% when the M-type unit reef is put into practice. Additionally, after having completed a comparative analysis, it is recommended to further change the reef group into four reef monocases. By executing this adjustment, the unit reef cost was reduced by 10%, and the influence range on the flow field increased by 10%, and this result can consequently achieve greater ecological benefits with less economic input. The results of this study provide a preliminary reference for the construction of artificial reefs M-Type from the perspective of theory and practice.

The Hydrodynamic Characteristics Induced by Multiple Layouts of Typical Artificial M-Type Reefs with Sea Currents Typical of Liaodong Bay, Bohai Sea

Artificial reefs are beneficial to restore fishery resources and increase fishery production. Meanwhile, they play a significant role in improving ocean ecology and accelerating the evolution of fishery industries. Since they are generally affected by currents, waves, and other hydrological factors, the flow field around artificial reefs and their stabilities have become a research hotspot in recent years. Research on artificial reefs is a systematic process consisting of four aspects: Firstly, the significance, the definition, the mechanism, and the present research progress were introduced for artificial reefs in detail. Secondly, the development trend of the sit-bottom artificial reef and that of the floating artificial reef were summarized, respectively. Thirdly, it was found that the combination of traditional artificial reefs and emerging ocean engineering has a great development potential in practical engineering. Finally, the existing problems related to the hydrodynamic characteristics of the artificial reefs in China were summarized, and the prospects of artificial reefs were proposed. The purpose of this study is to provide a scientific reference for the ecological and sustainable development of the large-scale construction of artificial reefs in the ocean.

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Review of Structure Types and New Development Prospects of Artificial Reefs in China

An artificial floating reef is an important part of the coastal ecological corridor. The large-scale construction of floating reefs by optimizing mooring methods can effectively improve the ecological effects of coastal projects. The artificial floating reef belongs to coastal engineering, and wave resistance is fundamental to its structural design. In this paper, the method for processing coupling forces and motion, the method for judging the floating reef out of water surface, and the method for correcting velocity and acceleration of water mass points are elaborated in detail by using the finite element method and lumped-mass mooring model. By comparing and analyzing the results of physical experiment and numerical simulation, the correctness of the numerical model is verified. Finally, the diachronic variation of pitching angle of floating reef, the tension of the mooring rope, and the total tension of the fixed points of the fishing net were analyzed by the dynamic response numerical mode with a new type of mooring. The purpose of the current study was to provide a basis for the optimization of structure shape, the matching of floating body, and the counterweight of artificial floating reef.

Numerical Simulation Study on Environment-Friendly Floating Reef in Offshore Ecological Belt under Wave Action

Three-dimensional numerical simulation on flow behavior behind trapezoidal artificial reefs

Artificial reefs are considered to have the function of repairing and improving the coastal habitat and increasing the fishery production, which are mainly achieved by changing the regional hydrodynamic conditions. The characteristics of flow turbulence structure are an important part of the regional hydrodynamic characteristics. Different methods are used to evaluate the performance of artificial reefs according to their shape and the purpose for which the reef was built. For this study, the M-shaped unit reefs, which are to be put into the area of Liaodong Bay, were selected as the research object and have never been fully investigated before. Experimental tests were conducted to assess the effect of these M-shaped artificial reefs on the vertical and longitudinal turbulent intensity under different hydraulic conditions and geometries, and datasets were collected by using the Particle Image Velocimetry technique implemented within the experimental facility. The distribution and variation characteristics of the turbulence intensity were analyzed, and the main results obtained can confirm that in the artificial reef area, there was an extremely clear turbulent boundary. Furthermore, the area of influence of the longitudinal turbulence was identified to be larger than that of the vertical turbulence, and the position where the maximum turbulence intensity appeared was close to where the maximum velocity was measured. Finally, results demonstrate that low turbulence conditions are typically located in front of the unit reef, the general turbulence area is located within the upwelling zone, and the more intense turbulence area is located between the two M-shaped monocases. These results are extremely important, because they provide the local authorities with specific knowledge about what could be the effect of these M-shaped reefs within the area where they will be implemented, and therefore, specific actions can be taken in consideration with the geometrical setup suggested as an optimal solution within this study.

Le Wang

Papers

An Experimental Investigation of Turbulence Features Induced by Typical Artificial M-Shaped Unit Reefs