The K2 boat of Kite Boat Project at the San Francisco Bay (5 June 2014). 104
Roland Verheul Kite Designer & Consultant
for Inflatable Structures Rolokite Lulofsstraat 55 – Unit 33 2521 AL The Hague The Netherlands roland@rolokite.com www.rolokite.com
Structural optimisation of a kite for ship propulsion
Roland Verheul Rolokite Currently, flexible traction kites are almost exclusively used for recreational activities like kite surfing. The cur-rent designs are the result of collective experience gath-ered by a large number of designers throughout the years, fuelled by a low cost for prototyping and relatively open IP culture.
With the advent of using flexible kites for extracting wind energy and propelling ships, kite design is moving out of the ”comfort zone” and certain design rules of thumb do not apply any more. Add to this the higher cost of proto-typing and more of an engineering approach seems justi-fied.
One of the big challenges is to predict the fabric stress and overall deformation of a large kitesurf kite. From tests it has become clear that the kites start to deform signifi-cantly when the total line load exceeds 5000 N. This espe-cially affects the L/D of the kite and therefore the upwind capability of the kiteboat.
The approach here described uses a combination of real-time simulation, finite element analysis (FEA) and mea-surement data. These components interact to both val-idate the design process and come to improved kite de-signs.
During boat tests a large number of sensors are mea-suring data like boat speed and course, (apparent) wind speed, line load and angle, etc. Also a number of cameras are registering kite deformation and movement. The Kite Modelling Software functions mainly as a
parametrised kite design tool but also delivers complete input files for both the real time simulator and the FEA software. A closed canopy and tube mesh, lumped mass bridle, aero forces, inflation pressure and boundary con-ditions are automatically regenerated after each design change.
A real-time simulation is built with a freely available physics toolkit and solver within the Rhino3D CAD soft-ware environment. The kite model is fully flexible and is built along the lines of the ADAMS model of Jeroen Breukels[1].
FEA analysis is done with an open source FEA package, using a dynamic explicit solving method.
References:
[1] Breukels J.: An engineering methodology for kite design. Ph.D. Thesis, Delft University of Technology (2011)