Trans RINA, Vol 153, Part B2, Intl J Small Craft Tech, 2011 Jul-Dec
Note that grid resolution is spread in radial direction around the initial water plane for a better capturing of the free surface when the boat is sailing in heeled conditions Figure 5 shows the blocking structure used to create the volume grid.
The box walls are set as velocity inlet whilst the yacht hull and appendages are treated as hydrodynamic smooth no-slip walls. The fluid properties are that of seawater according to ITTC with a dynamic viscosity of 1.219e- 3 [Pa s] and a density of 1026 kg m-3. Free stream turbulence intensity level has been set to 1%.
7. FIRST RESULTS
In the following some of the first results obtained with RVPP are shown. Boat speed has been calculated at a TWS of 5m/s. TWAs considered for the upwind sail set range from 30° - 100°, the TWAs for the downwind sail set are varying from 90° - 180°.
Table 2: Sail Plan used for the simulation
The simulation environment around the yacht body extends 1 boat length L to front and sides of the test case and 2L in the wakefield. The box extends 0.5L above the hull and 1L below. The computational domain consists of approximately 2 million grid cells, with refinements in the vicinity of the water surface and of the boundary layer on the yacht surface.
Figure 6: History Plot of Fx Figure 6 shows a history
plot of the longitudinal-
component of the force acting on the sailboat. The dotted line shows the fluid force whilst the solid line depicts the total force, including the external force from the sails.
The plot is divided into five phases, marked by the dotted lines. Phase I is a start-up phase in which the simulation is allowed to converge from its initial values to a stable solution without rigid body motion. Phase II marks the beginning of the rigid body motion, which is at first conducted with steady sail forces similar to the approach in a towing tank. Note that the solid line reaches the abscissa, marking the equilibrium of forces.
Next
unsteady sail forces are introduced (Phase III – V) and allowed to reach convergence to sailing equilibrium. When convergence is reached, the optimizer starts to change the flat factor, trying to optimize boat speed. This procedure is conducted for at least three flat factors.
Figure 5: Blocking of the computational grid
©2011: The Royal Institution of Naval Architects
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