Takanori Hino

Comparative study of MPS method and level-set method for sloshing flows

This paper presents a comparative study of a meshless moving particle semi-implicit (MPS) method and a grid based level-set method in the simulation of sloshing flows. The numerical schemes of the MPS and level-set methods are outlined and two violent sloshing cases are considered. The computed results are compared with the corresponding experimental data for validation. The impact pressure and the deformations of free surface induced by sloshing are comparatively analyzed, and are in good agreement with experimental ones. Results show that both the MPS and level-set methods are good tools for simulation of violent sloshing flows. However, the second pressure peaks as well as breaking and splashing of free surface by the MPS method are captured better than by the level-set method.

Numerical Simulation of Unsteady Turbulent Flow Around Maneuvering Prolate Spheroid

A three-dimensional Reynolds averaged Navier-Stokes method for unsteady turbulent flow around a maneuvering vehicle was developed and applied to a model problem concerning an extreme case of submarine maneuvers. A body force term is added in the momentum equations to take into account the inertial motion in the body-fixed coordinate system. The Spalart and Allmaras turbulence model is employed for turbulence closure. An artificial compressibility is introduced into the continuity equation for velocity-pressure coupling. The governing equations are discretized by second-order accurate finite volume method in space and second-order accurate backward scheme in time. The computational results are analyzed with global and local quantities and validated by comparison with experimental data. Overall, the present method performs quite well in predicting the unsteady flow phenomena associated with a maneuvering prolate spheroid, and the results compare well with available experimental data

Rowing Velocity Prediction Program with Estimating Hydrodynamic Load Acting on an Oar Blade

An oar blade behaves as unsteady hydrofoil and its load strongly depends on a reduced frequency of the rowing motion. The tank test is carried out using a circulating water channel to estimate the load.

Numerical Investigation of Influence of Surging Motion on Viscous Flows Around a Wigley Hull Running in Incident Waves

This paper presents the effect of surging motion on viscous flows around a Wigley ship running in incident waves through CFD simulation. The computational method used is based on the Navier-Stokes equations in unstructured grid system with pseudo-compressibility assumption. Since a ship changes its attitude when it runs in incident waves, we have to modify the code to be able to treat the ship motion by use of a moving grid technique. In order to simulate surging motion, the ship is connected with a spring to keep its mean position. We show the influence of surging motion on wake and ship resistance using springs of different strengths. Numerical results and discussions are shown.Copyright

Numerical simulation of the free-running of a ship using the propeller model and dynamic overset grid method

ABSTRACT An unsteady Reynolds averaged Navier-Stokes (URANS) solver to estimate the trajectory on the free-running condition of a conventional ship is developed. Ship motions are obtained by solving the motion equations and accounted for by the moving grid technique. Propeller effects are accounted for by the body forces that are derived from the propeller model, which is based on the potential theory. The prescribed rudder motions of typical free-running conditions are accounted for using the dynamic overset grid method, in which the overset information is updated at each temporal step by implementing the existing overset grid method as the numerical library. The flow around the ship hull during the turning motions is analysed, and strong interactions between the ship hull and rudder in the propeller accelerated flows are observed. Through comparisons, the present method shows its applicability to compute the flow around a ship in free-running motion.

Computation of free surface flows around box-shaped ships by an unstructured navier-stokes solver

Abstract A novel ship concept which is called ultra large block coefficient ship (ULBS) to enable efficient environmentconscious sea transportation is under investigation at Yokohama National University. Since ULBS is supposed to have a very blunt hull, flow field analysis around a ship is crucial for a design of hull forms with better hydrodynamic performance. Computational Fluid Dynamics (CFD) is expected to be an efficient design tool for unconventional hull forms such as ULBS. However, it is desirable to examine applicability of the CFD method before the actual design application. Thus, free-surface flow computations of two box-shaped ships which can be considered as the extreme cases of ULBS are carried out. Grid convergence study is performed with respect to resistance for the verification of the results. Total resistance coefficients are compared with each other and also with available experimental data. The pressure and velocity distributions of the two ships are compared with each other. The flow structures with large separations are observed and the influences of the box geometry to the flow fields are discussed.

Flow Comparisons of DES, DDES and URANS for a Circular Cylinder

Abstract Detached eddy simulation (DES), delayed DES (DDES) and unsteady Reynolds averaged Navier-Stokes (URANS) simulations are numerically investigated for a circular cylinder. Both DES and DDES improve results for drag and Strouhal number for the cylinder flow compared to experiments, reproducing the complex flow structures behind the cylinder well. The pressure distributions on the cylinder are compared with measured data, demonstrating the effectiveness of DES and DDES for highly separating flows.