Numerical Simulation of Ship Maneuvers through Self-Propulsion

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.

3D Flow Simulation of a Twin-Screw Pump for the Analysis of Gap Flow Characteristics

Unsteady 3D flow simulations on a twin-screw pump are performed for an assessment of the radial, circumferential and flank gap flow effect on the pump performance. By means of the overset grid technique rigid computational grids around the counter-rotating spindles yield a high cell quality and a high spatial resolution of the gap backflow down to the viscous sublayer in terms of y^+ < 1 . An optimization of the hole-cutting process is performed on a generic gap flow and transferred to the complex moving gaps in the pump. Grid independence is ensured, and conservation properties of the overset grid interpolation technique are assessed. Simulation results are validated against measured pump characteristics. Pump performance in terms of pressure build-up along the flow path through the spindles and volume flow rate is presented for a wide range of spindle speed and pump head. Flow rate fluctuations are found to depend on head but hardly on speed. By a profound assessment of the respective radial, circumferential and flank gap contribution to the total backflow, the importance of the most complex flank gap is pointed out. Backflow rate characteristics in dependence on the pump head and the pump speed are presented.

Overset Grid Assembler and Flow Solver with Adaptive Spatial Load Balancing

An overset mesh approach is useful for unsteady flow problems which involve components moving relative to each other. Since the generation of a single mesh around all components is prone to mesh stretching due to the relative motion of bodies, using the overset grid methodology, an individual mesh can be generated for each component. In this study, a parallel overset grid assembler was developed to establish connectivity across component meshes. Connectivity information was transferred to the developed parallel flow solver. The assembler uses multiple methods such as alternating digital tree and stencil walking to reduce the time spent on domain connectivity. Both the assembler and solver were partitioned spatially so that overlapping mesh blocks reside in the same partitions. Spatial partitioning was performed using a 3D space partitioning structure, namely octree, to which mesh blocks are registered. The octree was refined adaptively until bins of octree could be evenly distributed to processors. The assembler and solver were tested on a generic helicopter configuration in terms of load balance, scalability, and memory usage.