Study on the design method of an automatic outrigger layout control system for variable outrigger layout trimaran

Abstract

During the navigation of a trimaran, its wave resistance is influenced by both sailing speed and outrigger layout. In the case of a variable outrigger layout trimaran, due to the adjustability of its outrigger layout according to different speeds, its wave resistance will be lower than that of traditional trimarans. In this paper, an automatic outrigger layout control system is figured out for a variable outrigger layout trimaran. The system can control and regulate the position of outriggers according to the traveling speed in order to reduce the wave resistance during navigation. The slender ship theory based resistance calculation program is applied as the solver in this system to evaluate the wave resistance of the trimaran and further determine the optimal outrigger layout under a specific speed. In order to improve the calculation accuracy, NURBS (Non-Uniform Rational B-Splines) method is introduced to modeling the hull surface. Model tests for trimaran with 6 different outrigger layouts are conducted to obtain the resistance of the trimaran in order to validate the numerical method. The steepest descent method is applied to solve the problem of searching the outrigger layout with minimum wave resistance efficiently. On this basis, an open-loop control system for trimaran outrigger layout is designed based on PID (Proportional Integral Derivative) algorithm with the control objective derived by the solver. Finally, a outrigger layout adjustment simulation (when speed changes from Fr=0.4 to Fr=0.35) is conducted on the experimental trimaran model. By comparing the resistance results obtained by numerical method utilized in this paper to the results obtained by CFD (Computational Fluid Dynamics) simulations, the effectiveness of the proposed system is validated.