Trans RINA, Vol 152, Part B2, Intl J Small Craft Tech, 2010 Jul-Dec 30


Target Inverse


15


inverse method. The initial shape and the calculated shape of the inverse process are compared and should ideally be the same. For a known planform and a fixed twist, the error is less than 0.1% of the sail camber and in the case of a known planform and fixed camber the average error is 0.05° in the twist distribution.


0


00.5 Y [-]


1 Figure 11 - Results of the twist validation investigation.


As in the previous section, it can be seen that the twist agreement is very good. The average error is 0.05° in the twist distribution. The convergence is faster for the twist than the camber because, in the former case, there is only one parameter per section.


4. CONCLUSIONS


This paper describes and validates an inverse process for designing yacht


sails. The proposed approach differs


from the traditional way of designing a sail where each sail shape is analysed and then the optimum shape is chosen. In the proposed inverse process, the optimum aerodynamics characteristics are specified beforehand and then the sail shape is computed.


In the first part of the paper the two-dimensional case is investigated. Thin aerofoil theory is used first to calculate the pressure distribution around a sectional shape of a given IACC head sail. The resulting pressure distribution compares well to other potential flow methods from the literature.


In the next section of the paper, a two-dimensional


analytical inverse procedure based on thin aerofoil theory is presented.


Based on the two-dimensional theory, a three- dimensional inverse method has next been developed to find the three-dimensional sail shape which will produce a given pressure map. The developed method is iterative in nature and modifies the sail shape until it generates the desired pressure map. It is shown that the solution of the inverse process is not unique. In order to overcome this problem the planform is assumed to be known and the method used allows both the sail twist and the sail camber to be adjusted separately in order to drive the pressure distribution to the specified target pressure distribution.


Finally results of this inverse method are presented. To validate the method, a given sail


is first analysed to


generate a pressure map (analysis method) then the resulting pressure map is utilised as an input for the


©2010: The Royal Institution of Naval Architects 6. 7. 8. 9. 10. 2. 3.


This paper deals only with an isolated sail but at the Yacht Research Unit of the University of Auckland, a similar approach for two interacting sails (a headsail and a mainsail) is currently being investigated.


5. ACKNOWLEDGEMENTS


The first author would like to thanks Mr Burns Fallow for his guidance in this project, and the support of the Yacht Research Unit and North Sails (NZ) Ltd.


6. 1.


REFERENCES


JACKSON, P.S., The Analysis of Three- Dimensional Sails, Proceedings of the


tenth


Canadian Congress of Applied Mechanics, The University of Western Ontario, Canada, 59-67, 1985.


JOHNSTON, M.S., An Aeroelastic Model for the Analysis of Membrane Wings, PhD thesis, The University of Auckland, New Zealand, 1997.


RANZENBACH, R., and XU, Z., Sail Aero- Structures: Studying Primary Load Paths and Distortion, Proceedings of the 17th Chesapeake Sailing Yacht Symposium, Annapolis, USA, 193- 204, 2005.


4.


MALPEDE, S., and BARALDI, A., A fully integrated method for


optimizing fiber-


membrane sails, Proceedings of the 3th High Performance Yacht Design Conference, RINA (NZ), Auckland, New Zealand, 47-56, 2008.


5.


PILATE, J., GERHARDT, F. C., and FLAY R. G. J., Development of a three-dimensional inverse sail design method, Proceedings of the 3th High Conference,


Performance Yacht Zealand, 257-265, 2008.


BIRNBAUM, W., and ACKERMANN, W., Die tragende Wirbelfläche als Hilfsmittel zur Behandlung des ebenen Problems der Tragflügeltheorie, ZAMM, 3(4),290-297, 1923.


GLAUERT, H., The Elements of Aerofoil and Airscrew Theory, Cambridge University Press, UK, 1948.


ANDERSON, J.D. jr, Fundamentals of aerodynamics, 2nd ed., McGraw-Hill International Edition, 1991.


KATZ, J., and PLOTKIN, A., Low speed aerodynamics, 2nd Edn, Cambridge University Press, NY, USA, 2001.


JOHNSON, W., Helicopter theory, Princeton, N. J., Princeton University Press, 1980.


Design RINA (NZ), Auckland, New


B-113


Twist [deg]


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