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Trans RINA, Vol 152, Part B2, Intl J Small Craft Tech, 2010 Jul-Dec


work of Fiddes S.P. and Gaydon J. [19]. The doublicity is assumed to be constant on a panel. The control points are positioning at the middle of each panel. A full-cosine spacing of the panels


is used in the chordwise and


spanwise direction. The wake is straight and aligned with the apparent wind. The method accounts for heel and apparent wind twist and a mirror image of the sail is used to model the influence of the sea surface. 3.2 (b) Validation of the inverse process to find camber


To prove that the approach works, a sail shape was


specified and then its pressure distribution was determined using a vortex lattice method code. This pressure distribution was then used as input in the three- dimensional inverse method that has been described. The validation process is summarized in figure 7.


4% 8%


Target Inverse 0 Iteration 1 Iteration


0% -0.5 0 X [-] Figure 9 - Comparison of the cambers at the ½ span. 8%


Target Inverse 0 Iteration 1 Iteration


0.5


Analysis


4%


0% = ? Inverse


Figure 7 – Schematic diagram of the validation test method.


Figures 8, 9 and 10 show comparisons the iterative procedure at the quarter-half-three-quarter span heights obtained after 2 iterations processor).


(~12sec on a 2.4 GHz 8%


Target Inverse 0 Iteration 1 Iteration


It can be seen that these results show very good agreement. I.e. the original (blue) sail shape can be recovered using the proposed inverse method with a maximum error of 0.1% of the sail chord at mid-span. This is acceptable in sail design practice [20].


3.3 INVERSE PROCESS WITH FIXED CAMBER AND SPECIFIED PLANFORM


3.3 (a) Solution procedure to find twist


The research results presented in the previous section have been extended to include adjustment of the twist with fixed camber. Thus equation (9) becomes:


delta Cp P deltaα Δ = * (11) 4%


This is a relationship between the difference in pressure and the twist (or angle of attack). The approach is exactly the same as shown in figure 6. The camber of each slice remains the same, but the twist changes. Extrapolations are made at the extremities.


0% -0.5 0 X [-] Figure 8 - Comparison of the cambers at the ¼ span. 0.5


Figure 11 shows a comparison of the computed twist and the target twist after 2 iterations.


3.3 (b) Validation of inverse process to find twist -0.5 0 X [-] Figure 10 - Comparison of the cambers at the ¾ span. 0.5


B-112


©2010: The Royal Institution of Naval Architects


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