Project description
Determination of roll damping for modern hull forms based on experimental and computational investigations of complex flow phenomena (short: Rollex)
Due to the short computation time potential flow methods are widely applied for seakeeping simulations. The accuracy of the numerical results for the roll motion is strongly influenced by the used roll damping coefficient. This coefficient is mostly dominated by viscous effects. In the majority of cases the damping coefficient is nowadays estimated with help of empirical formula.
You can download or open a short handout in german language here.
Rollex project combines an experimental and a numerical part.
Experiments
The aim of the experimental investigation is the generation of validation data for the numerical simulations. The experiments are carried out at the wind tunnel of the Institute for Fluid Dynamics and Ship Theory (FDS) , Hamburg University of Technology (TUHH). A newly developed motion manipulator with 5+1-degrees of freedom is used to perform the desired motions of a double-hull ship model (see figure). The sixth component of freedom is the inflow velocity of the air stream in the measuring section of the wind tunnel.
The motion manipulator in the wind tunnel enables short set-up time and long time measurements in comparison to conventional towing tank model tests. Also coupled motions can be investigated.
The motion manipulator is developed in cooperation with the chair of Mechatronics at Duisburg-Essen University.
In order to analyze the contribution of the different components of the hull to the roll damping, the forces on the hull, rudders, and bilge keels are measured separately with and without propeller. The visualization via particle image velocimetry (sort: PIV) allows the investigation of complex flow phenomena such as interaction of vortex structure with the ship flow.
Calculations
The numerical calculations in the Rollex project are carried out for two modern twin-propeller hull shapes of a RoPax ferry and a Cruise Liner.
Since roll damping is dominated by viscous effects a RANSE method is applied. The RANSE-solver STAR-CCM+ from CD-adapco is used in this study. The calculations will be validated by the experimental results of the model tests, which will be carried out at the wind tunnel of TUHH and the towing tank of the SVA Potsdam (see also project description SVA).
To evaluate the different contributions to roll damping, the hull and the appendages are considered separately during the post processing.
Various calculations, for example with or without bilge keels, are carried out to investigate the coupling of these effects. The generated roll damping coefficients will be used to develop a neural network.
Click here for a video showing surface fraction and wave radiation.
The following two pictures sowing scenes from a calculation. On the left the wave radiation, on the right the vorticity in the bilge area, is shown. Both effects are contributions roll damping.
