Search

The high efficiency of pumpjet propulsors recently favored their application to ships, different to usual high-speed vessels and submarines, to comply with the most recent regulations on efficiency, comfort onboard and noise pollution. In this context, as a part of the activity of the EU funded project SATURN, the design, and the performances of an axial pumpjet are investigated. The pumpjet of current study is designed to replace a conventional propeller of a ferry ship. To this aim a simulation-based design optimization method employing simplified RANSE analyses, synthetic wakes generated using body force distributions and a mixing-plane based coupling between rotor and stator is employed. Main geometrical characteristics (diameter, number of rotor and stator blades) as well as distributions of pitch, chord and camber are handled in the process by a parametric description of the geometry. A genetic algorithm guides towards the Pareto convergence of the designs by requiring the maximization of the propulsive efficiency at the lowest possible cavitation inception index. Fully unsteady RANSE calculations are finally employed to characterize the unsteady performances (thrust and torque) in behind conditions including the cavitation pattern and the induced pressure pulses on the ship stern, and results are discussed and compared to those of the reference conventional propeller.

One of the most important tools in today's sailing yacht design is the Velocity Prediction Program (VPP). VPPs calculate boat speed from the equilibrium of aero- and hydrodynamic flow forces. Consequently their accuracy is linked to the accuracy of the aero- and hydrodynamic data used to represent a yacht. These data are usually derived from Experimental Fluid Dynamics (EFD) or Computational Fluid Dynamics (CFD) results and processed by means of linearisation and interpolation to represent the actual sailing state of the yacht. This interpolation is a potential source of inaccuracy. Furthermore, viscosity related effects are often estimated by simplified theoretical or empirical models potentially neglecting complex physical phenomena. As an alternative, a new method is proposed and implemented, which links the hydrodynamic model directly to a RANSE flow simulation in order to avoid linearisation and interpolation errors associated with traditional VPPs. Within this method, aerodynamic sail forces are taken into account as functions of actual boat state. They are modeled using a sail force model and coupled to the hydrodynamic model via a rigid body motion solver. This way one is able to directly evaluate the hydrodynamic forces at the actual boat state of the yacht for a given wind condition. Within this work, the inherent theory and algorithms of the method are described, and the hydrodynamic model is verified and validated against experimental data from towing tank test. Based on this verification and validation of the simulation model, the functionality of the new method is illustrated by calculating VPP polars. Finally, these VPP polars are compared with results from conventional VPPs and an assessment of the method's accuracy is provided., Ship Hydrodynamics and Structures, Mechanical, Maritime and Materials Engineering

One of the most important tools in today's sailing yacht design is the Velocity Prediction Program (VPP). VPPs calculate boat speed from the equilibrium of aero- and hydrodynamic flow forces. Consequently their accuracy is linked to the accuracy of the aero- and hydrodynamic data used to represent a yacht. These data are usually derived from Experimental Fluid Dynamics (EFD) or Computational Fluid Dynamics (CFD) results and processed by means of linearisation and interpolation to represent the actual sailing state of the yacht. This interpolation is a potential source of inaccuracy. Furthermore, viscosity related effects are often estimated by simplified theoretical or empirical models potentially neglecting complex physical phenomena. As an alternative, a new method is proposed and implemented, which links the hydrodynamic model directly to a RANSE flow simulation in order to avoid linearisation and interpolation errors associated with traditional VPPs. Within this method, aerodynamic sail forces are taken into account as functions of actual boat state. They are modeled using a sail force model and coupled to the hydrodynamic model via a rigid body motion solver. This way one is able to directly evaluate the hydrodynamic forces at the actual boat state of the yacht for a given wind condition. Within this work, the inherent theory and algorithms of the method are described, and the hydrodynamic model is verified and validated against experimental data from towing tank test. Based on this verification and validation of the simulation model, the functionality of the new method is illustrated by calculating VPP polars. Finally, these VPP polars are compared with results from conventional VPPs and an assessment of the method's accuracy is provided., Ship Hydrodynamics and Structures, Mechanical, Maritime and Materials Engineering

Es wird ein Berechnungsverfahren fuer das Seegangs- und Manoevrierverhalten von Schiffen dargestellt. Das Verfahren beruht auf einer gekoppelten interativen Loesung der Bewegungsgleichung mit sechs Freiheitsgraden eines Koerpers mit RANSE, welche die turbulente Stroemung beschreibt. Die Ergebnisse zeigen eine gute Uebereinstimmung mit experimentellen Versuchen., In this work, a computation procedure for the prediction of motion of rigid bodies floating in viscous fluids and subjected to currents and waves is presented. The procedure is based on a coupled iterative solution of the 6-DOF rigid body motion equation and the RANSE, describing the turbulent fluid flow. The method is extented to more complex ship maneuvering applications and the comparison with experiments shows promising agreement.

Es wird ein Berechnungsverfahren fuer das Seegangs- und Manoevrierverhalten von Schiffen dargestellt. Das Verfahren beruht auf einer gekoppelten interativen Loesung der Bewegungsgleichung mit sechs Freiheitsgraden eines Koerpers mit RANSE, welche die turbulente Stroemung beschreibt. Die Ergebnisse zeigen eine gute Uebereinstimmung mit experimentellen Versuchen., In this work, a computation procedure for the prediction of motion of rigid bodies floating in viscous fluids and subjected to currents and waves is presented. The procedure is based on a coupled iterative solution of the 6-DOF rigid body motion equation and the RANSE, describing the turbulent fluid flow. The method is extented to more complex ship maneuvering applications and the comparison with experiments shows promising agreement.