Sailing yachts have great potential to act as future long-term oceanic observing platforms, yet to date there have not been complete autonomous sailing systems robust enough to handle long term operation in the harsh and continually changing ocean environment. The basis of control system design is a mathematical model capable of describing and capturing the physics based dynamics of the sailboat. The mathematical model represents the system to be controlled, however, a sailing yacht is a very difficult system to model from a controls perspective because of its heavy reliance on the uncontrolled spatial and temporal distribution of the wind. Presented in this paper is a modified aerodynamic force model which includes the sail angle as a control input to the sailing yacht system. The new model has been incorporated into a 4 degree of freedom (DOF) rigid body dynamic yacht model, and implemented in MATLAB/Simulink. The simulations shows model exhibits similar behavior to that observed in full scale sailing yacht sea trial data. Data taken aboard a Precision 23 day-sailer is analyzed, and it is found that the model is a likely candidate for including sail input to a physics based dynamic model for identification and control system design.
Linear dynamic models are extremely useful in autonomous vehicle controller development because they are straightforward to estimate from real data and they enable advanced control system design. To date an in depth investigation of the possibility of using a linear dynamic system model to represent sailing yacht dynamics has not been made. A non-linear simulation of a 10m racer/cruiser racer and full-scale data collected aboard a 23 ft day-sailer are used in conjunction with the one-shot least squares estimation algorithm to evaluate this possibility. Using the non-linear simulation data it is found that it is possible to use a linear model to represent sailing yacht. Full-scale data collected while sailing upwind on a port tack is used to estimate 10 different linear models.
It is common for physics-based models to be the foundation of a modern computer control system. Presented here is an overall description of a project dedicated to advancing understanding of physics-based sailing yacht models validated with full scale data. A better understanding of physics-based models and how to extract them from full scale sailing data will enable better control system design for future autonomous wind powered surface vessels.
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