overset grid method
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2021 ◽  
Vol 9 (9) ◽  
pp. 1017
Author(s):  
Haodong Shang ◽  
Chengsheng Zhan ◽  
Zuyuan Liu

The typical maneuvering of a ship can reflect its maneuvering characteristics, which are closely related to the safety and economy of its navigation. The accurate prediction of a ship’s maneuvering characteristics is essential for its preliminary design. This paper adopts the overset grid method to deal with multibody motion and the body-force method to describe the thrust distribution of the propeller at the model scale, as well as to obtain the changes in the hydrodynamic load and the characteristic parameters in a computational fluid dynamics (CFD) maneuver simulation. Then, the paper compares the results with those of a self-propulsion experiment conducted at the China Ship Scientific Research Center. The numerical results show that the maneuverability characteristics obtained from the CFD simulation are in satisfactory agreement with the experimental values, which demonstrates the applicability and reliability of the combination of the overset grid with the body-force method in the numerical prediction of the typical maneuvering of a ship. This provides an effective pre-evaluation method for the prediction of a ship’s maneuvering through self-propulsion.


2021 ◽  
Author(s):  
Hui-li Xu ◽  
Marilena Greco ◽  
Claudio Lugni

Abstract Fishes are talented swimmers. Depending on the propulsion mechanisms many fishes can use flapping tails and/or fins to generate thrust, which seems to be connected to the formation of a reverse von Kármán wake. In the present work, the flow past a 2D flapping foil is simulated by solving the incompressible Navier-Stokes equations in the open-source OpenFOAM platform. A systematic study by varying the oscillating frequency, peak-to-peak amplitude and Reynolds number has been performed to analyze the transition of vorticity types in the wake as well as drag-thrust transition. The overset grid method is used herein to allow the pitching foil to move without restrictions. Spatial convergence tests have been carried out with respect to grid resolution and the size of overset mesh domain. Numerical results are compared with available experimental data and discussed. The results show that the adopted methodology can be well applied to simulate large amplitude motions of the flapping foil. The transitions in the types of wake are consistent with the benchmark experimental data, and the drag-thrust transition of the pitching foil does not coincide with von Kármán (vK)-reverse von Kármán (reverse-vK) wake transition and it is highly dependent on the Reynolds number.


2021 ◽  
Vol 9 (3) ◽  
pp. 249
Author(s):  
Yu Dai ◽  
Cong Xue ◽  
Qiao Su

The capability of path tracking largely determines the operational efficiency of deep-sea mining vehicles. In this paper, the relationships of vehicle–sediment mechanical interaction were obtained by sinkage and shear tests. Then, an overset grid method was used to establish the computational fluid dynamics (CFD) model of the vehicle, and the spatial hydrodynamic distribution was calculated in different motion states. Based on the above research, a multi-body dynamic (MBD) model of the mining vehicle was developed, which considered the spatial hydrodynamic effects and the mechanical interaction between vehicle and sediment. In addition, a path-tracking controller based on fuzzy logic control was proposed. A genetic algorithm optimized the fuzzy rules through co-simulation between the controller and the MBD model. Finally, the co-simulation results of the vehicle which moved along the expected path indicated that the performance of the optimized fuzzy controller was preferable to the original fuzzy controller.


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