The goal of this manuscript is to investigate the influence of relative distance between the twin rotors on the hydrodynamic performance of the vertical axis twin-rotor tidal current turbine. Computational fluid dynamics (CFD) simulations based on commercial software ANSYS-CFX have been performed to enhance the understanding of interactions between the twin-rotors. The interactions between the twin rotors are known to have increased the power output efficiency as a whole, and it is, therefore, of great significance to undertake deeper research. The simulation results are found to be consistent with similar research results in the literature in some aspects. The simulation results of stand-alone turbine and twin rotors are compared from three different aspects, including blade forces, power output efficiency and wake flow field. The results showed that the cyclic variations tendency of blade force coefficients of twin rotors is close to that of the stand-alone turbine. The average power output efficiency of the twin-rotors system is higher than that of the stand-alone turbine. The interactions between the turbines increase the power output of the twin turbine system as whole in a wide relative distance range. However, smaller relative distance between the twin rotors does not mean a bigger power output efficiency of such a system. The power out efficiency of such a system would decrease when the relative distance between the twin rotors exceeds the critical point. The power output of the twin rotors reaches the peak value when the ratio between the two main axis distance and diameter of the turbine is around 9/4. This research can provide a reference for the design and development of larger tidal power stations.

In this study, the effect of joint optimization of the principal dimensions and hull form on the hydrodynamic performance of a bulk carrier was studied. In the first part of the joint optimization process, fast principal-dimension optimization of the origin parent ship considering the integrated performance of ship resistance, seakeeping, and maneuverability, as well as their relationships with the principal dimensions were analyzed in detail based on the ship resistance, seakeeping qualities, and maneuverability empirical methods of Holtrop and Mennen, Bales, and K and T indices, respectively. A new parent ship was chosen from 496 sets of hulls after comprehensive consideration. In the remaining part, a further hull form optimization was performed on the new parent ship according to the minimum wave-making resistance. The obtained results demonstrate that: (a) For the case in which the principal dimension of the original parent-type ship is different from that of the owner’s target ship, within the bounds of the relevant constraints from the owner, an excellent parent ship can be obtained by principal-dimension optimization; (b) the joint optimization method considering the principal dimension and hull form optimization can further explore the optimization space and provide a better hull.

Flow reconstruction based on limited measurement data, which can be considered as a state estimation problem, constitutes a fundamental task within the realm of fluid mechanics. In recent years, the physics-informed neural networks (PINNs) have been proposed to achieve flow field reconstruction by integrating the measurements with governing equations during network training. However, the performance is compromised by the presence of high-level data noise, and the uncertainty of the reconstructed flow fields remains unattainable. In this paper, we first perform a systematic study to investigate the impact of data noise on the reconstruction result of PINNs. Subsequently, we present strategies of early stopping and loss regularization, which can suppress the overfitting issue to some extent. Ensemble learning is also employed to quantify the uncertainty of the results from vanilla PINNs. In addition, we propose to use a Bayesian framework of PINNs (BPINNs) for flow field reconstruction, which incorporates the Bayesian neural network with PINNs. It is demonstrated that BPINNs are capable of reconstructing the velocity and pressure fields from sparse and noisy velocity measurements, while providing comprehensive uncertainty quantification of the flow fields simultaneously. Compared to the vanilla PINNs, BPINNs are more accurate and robust when there is a high level of data noise. We conduct experiments on two-dimensional cavity flow and the flow past a cylinder to validate the effectiveness of the proposed methods throughout the paper.

This study employs an improved delayed detached eddy simulation method to examine the open-water performance and wake evolution of a propeller with notched blades, using an unstructured grid with 52.5 × 106 cells. The numerical method's validity was confirmed by comparing computed thrust and torque coefficients, as well as the flow field, with experimental data. The findings reveal that notched blades significantly reduce the propeller's hydrodynamic performance and accelerate wake instability. The notches introduce substantial disturbances in the surrounding flow, generating numerous small-scale vortices. These vortices interact with neighboring tip vortices, altering their topology and leading to rapid disintegration and the formation of secondary vortex structures. Increasing the number of notches further destabilizes the tip vortex system, causing tip vortices to lose coherence and become uniformly distributed in the mid-field. This study offers a detailed analysis of how notched blade configurations impact propeller performance, near-field flow characteristics, and wake evolution, providing valuable insights into the underlying mechanisms.

The effect of waves on ice sheet is critical in the marginal ice zone (MIZ). Waves break large sea ice into small pieces and cause them to collide with each other. Simultaneously, the interaction between sea ice and waves attenuates these waves. In this study, a numerical research is conducted based on a computational fluid dynamics (CFD) method to investigate the response of single ice floe to wave action. The obtained results demonstrate that the sea ice has a violent six degree of freedom (6DoF) motion in waves. Ice floes with different sizes, thicknesses, and shapes exhibit different 6DoF motions under the action of waves. The heave and surge response amplitude operator (RAO) of the sea ice are related to wavelength. Furthermore, the overwash phenomenon can be observed in the simulation. The obtained results are compared with the model test in the towing tank based on artificial ice, and they agree well with test results.