Knotless nets have been extensively used in sea cages and offshore fish farms; the explicit illustrations of local flow patterns and subjected hydrodynamic loads have practical implications for the safe operations of aquaculture pens in open oceans. However, the effects of inclination angles of knotless nets on local flow patterns have not yet been fully discussed. In this paper, the effects of inclination angles on local time-averaged and instantaneous flow fields, velocity reductions and force coefficients are investigated using a $k-\omega$ shear stress transport-improved delayed detached eddy simulation (SST-IDDES) high-fidelity turbulence model. It is demonstrated that the inclination angles have dominant effects on the time-averaged velocity magnitudes around the net meshes. Secondly, the considerable flow interactions amongst the transverse and longitudinal net meshes, as well as cross-flow effects, are observed but weakened with the inclination angles. Thirdly, the profiles of velocity decelerations behind the net panels for 0${}^{\circ }$–45${}^{\circ }$ are not as trivial as those for 45${}^{\circ }$–90${}^{\circ }$. The associations between the embedded mechanism of subjected loads and pressure fields are established to analyse the current loads on nets in small inclination angles. The inclination angles are finally elaborated into the area-averaged velocity reduction and screen force models, then the improved characteristics are validated against the experimental data.

Large-scale aquaculture pen is one of the essential modes of offshore aquaculture being explored in recent years. In contrast to cage farming, the advantages are more significant as the larger cultural space for fish swimming, the closer-to-nature environment, and the improved ecological quality of fish. As a novel offshore aquaculture structure, fully-enclosed pile-net aquaculture pens (FPAPs) are generally deployed in exposed oceans, where severe waves and currents are of great dominance. The hydrodynamic characteristics of FPAPs in offshore areas deserve further investigation. In this paper, the numerical model of a typical FPAP in waves is proposed based on the finite element method (FEM), then wave loads on and induced motion responses of the FPAP are analyzed. The results show that the maximum loads on the structure and the maximum displacement of piles are closely proportional to the wave height. Secondly, the maximum stress of nets decreases as the embedded depth increases, while the deformation of nets tends to rise with the increase of pile spacing. At last, several structural optimal patterns are given to improve the safety of pen facilities. This work has laid a solid scientific foundation for designs and optimizations of FPAPs in the future.

The cambered deflectors in aquacultural facilities are applied to enhance hydrodynamic efficiencies or enable flow fields to be fully developed. Given the anticipated improvements with the bio-inspired profiles or tandem configurations, the hydrodynamics of cambered deflectors with the above features are investigated at $Re=1\times {10}^5$. The relationship between force coefficients and local flow behaviors for both bionic and non-bionic isolated deflectors, as well as tandem deflectors, is revealed using $k-\omega$ SST simulation. The dependencies of force coefficients on gap (G), stagger (S), and inclination angles ($\theta$) in tandem deflectors are illustrated using an updated metamodeling workflow with simulated data. It is demonstrated that the variations of force coefficients over angles of attack are related to flow physics in boundary-layer regions. The non-bionic isolated deflector with the $\theta ={10}^{\circ }$ prevails as the decent performances of $C_L$ and $\gamma$ globally, which is chosen in the following studies. Regarding tandem deflectors, $\theta$ plays a more vital role in drag coefficients ($C_D$) and lift coefficients ($C_L$), while the influence of S is not quite considerable compared to G. Aiming for cost minimizations and lift improvements, an optimized tandem case is obtained and justified with the superiorities in flow fields. This study has provided novel insights into the designs and optimizations of cambered deflectors in aquacultural engineering.