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

Abstract

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.

Effects of typical artificial reefs on hydrodynamic characteristics and carbon sequestration potential in the offshore of Juehua Island, Bohai Sea

“…Earlier studies suggested that the existence of artificial reefs appears to have an inhibiting effect on flow propagation (e.g., Shu et al, 2021bShu et al, , 2021cHarris et al, 2021;Gu et al, 2022). The incoming flow velocity abruptly reduced in the front of artificial reefs, and then the flow separation occurred around the top of the first reef (Figure 5).…”

“…The physical model of different layout spacing of reefs are tested under different flow velocity (i.e., 0.085 m/s, 0.130 m/s, 0.170 m/s, 0.214 m/s, and 0.257 m/ s), meanwhile, the particle image velocimetry (PIV) technology was applied to quantify the flow fields generated around artificial reefs. Detailed information about the experimental protocol and physical model of artificial reefs can be found in Shu et al (2021b;2021c).…”

“…Hydrodynamic characteristics of flow fields near artificial reefs at a given spacing and flow rate within a series of flume-based experiments are quantified by analyzing basic parameters associated with upwelling, backswirl, vortex, and turbulent flows (more details for flume experiments can be found in our earlier works, e.g., Shu et al, 2021b;2021c), the results for hydrodynamic characteristics due to the presence of both M-shaped and square artificial reefs in a laboratory flume were proportionally scaled up to prototype magnitude and detailed in Tables 1, 2. One can observe that the M-shaped reef is superior to the square reef in terms of developing more complex flows.…”

“…FIGURE 4Side view of upwelling flows produced by (A) square ARs and (B) M-shaped ARs(Shu et al, 2021b) under the same experimental condition.…”

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

“…Different marine organisms have different tendencies towards the strong or weak turbulence fields. Such turbulence intensities around artificial reefs can meet the needs of different biological characteristics (Kim et al, 2014b;Shu et al, 2021b). The affected regions of the turbulent area produced by different types of reefs are varied, which has been discussed by Howe (2003).…”