Evaluation of energy consumption and motion accuracy for underwater gliders based on quadrant analysis

Underwater gliders are well known as a type of enduring platform for underwater exploration; nevertheless, they have also been criticised in terms of their compromised course-keeping capability, particularly in harsh ocean environments. A motion controller that can improve motion accuracy while maintaining a low energy demand is preferred by developers and operators. In this paper, a motion controller based on a combined feedforward and Linear Quadratic Regulator (LQR) control is proposed. The controller has been evaluated in terms of energy consumption and motion accuracy with a fully coupled numerical model integrating the vehicle dynamics, the energy consumption and the control system. A energy-accuracy chart and a quadrant analysis are then introduced to support the analysis of the controller performance and the identification of the optimum operating conditions. Based on the prototype underwater glider that has been developed at Tianjin University, various case studies in different ocean environmental conditions are performed. The results show that the method proposed can quantitatively evaluate the performance of the vehicle to effectively achieve the balance between energy consumption and motion accuracy which can support the decision-making process for the best operation strategy.