Simulação e controle de profundidade e arfagem de um veículo autônomo subaquático sob controlador não linear quase-deslizante terminal

Abstract

Recent advances in technologies associated with autonomous vehicles, combined with the growing interest in underwater applications — such as ocean exploration, environmental monitoring, and inspection of submerged structures — have driven the development of advanced modeling and control techniques for Autonomous Underwater Vehicles (AUVs). These vehicles are characterized by strongly nonlinear and coupled dynamics, as well as by significant hydrodynamic uncertainties, which impose substantial challenges on the design of control strategies capable of ensuring performance, robustness, and stability under adverse operating conditions. In this work, a Discrete-Time Terminal Sliding Mode Controller (DTSMC) is developed and evaluated for the coupled control of depth and pitch of an AUV. The study is conducted based on the dynamic model of the Naval Postgraduate School Autonomous Underwater Vehicle II (NPS AUV II), which is widely referenced in the literature for realistically representing the hydrodynamic characteristics of medium-sized submerged vehicles. The modeling framework considers the complete dynamic and kinematic equations of the vehicle, including nonlinear effects, coupling between degrees of freedom, and restoring forces associated with buoyancy and weight. The proposed controller is based on the definition of sliding surfaces associated with the depth and pitch variables, incorporating a nonlinear terminal term in order to guarantee finite-time convergence of the depth error. Control action is applied exclusively through the stern planes, which reinforces the underactuated nature of the problem and highlights the robustness of the adopted control strategy. This approach reduces the reliance on local linear models and preserves stability properties even in the presence of parametric uncertainties and external disturbances. The complete system was implemented in a numerical simulation environment using the C programming language, enabling a detailed analysis of the vehicle behavior under different initial conditions, depth references, and controller parameter configurations. The obtained results demonstrate that the DTSMC is capable of achieving effective depth reference tracking while maintaining the pitch angle within acceptable operational limits, even in the presence of inherent nonlinearities and actuator physical constraints. These results highlight the effectiveness of the proposed strategy and indicate its potential applicability to real underwater platforms.