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An adaptive fuzzy nonlinear integral sliding mode control strategy based on an extended state observer (ESO) is proposed for trajectory tracking of unmanned underwater vehicles (UUVs) in the presence of unknown external disturbances and model parameter uncertainties. A nonlinear dynamics error model of the UUV is established; the estimation of the lumped disturbances are estimated using ESO, and the control variables are compensated for in real time. A nonlinear integral sliding mode controller with saturation characteristics is designed to improve the transient and steady-state performance of the system, and the switching gain of the sliding mode control is adaptively adjusted using the fuzzy logic system, such that the weight of the output changes with the sliding mode surface; thus, the chattering of the control variables is weakened. The asymptotic stability of the control system is verified using Lyapunov stability theory. The simulation and experimental results demonstrated that the designed control strategy effectively suppresses the system lumped disturbances with high tracking accuracy and robustness. • The strategy is based on the combination of a nonlinear integral sliding mode control technique with an extended state observer. • The extended state observer achieves an effective estimation of the lumped disturbances. • The nonlinear integral sliding mode controller improves the transient and steady-state performance of the system. • The adaptive fuzzy switching rate reduces the chattering phenomenon. • Asymptotic stability of the control system is verified by Lyapunov stability theory. [ABSTRACT FROM AUTHOR]

The effects of rigid emergent vegetation on wave overtopping have been studied by numerical simulation in this study. The numerical model is based on second-order fully nonlinear Boussinesq equations and solved by a combination of finite difference and finite volume methods. Physical laboratory results of wave propagation in the vegetated area and wave overtopping on a bare slope were used to validate the capability of the model, and the numerical and experimental results agreed well, which indicated that the model can well predict wave overtopping on a vegetated slope. Then, based on the model, the effects of rigid emergent vegetation on wave overtopping were investigated. The results showed that the wave overtopping volume decreases exponentially with the increase of vegetation volume per unit water volume V veg / V w , and the wave overtopping volume can be decreased by 50% when V veg / V w equals 0.01. • Influences of rigid emergent vegetation on regular wave overtopping. • Effects of plant diameter, vegetation density and volume on wave overtopping. • Effects of wave period and height on wave overtopping. [ABSTRACT FROM AUTHOR]

The mechanism that underlies the evolution of the seasonal environment and the effects of reclamation projects in the Pearl River Estuary (PRE) were studied by modeling the hydrodynamics, suspended sediment, and water quality. Due to the seasonal variation of the freshwater discharge, the residual currents in the estuary are generally larger during the summer than during the winter. Reclamation projects significantly affect the residual current fields and decrease tidal prisms across the PRE, resulting in the variation of water exchange and material transport process. During the summer, waters high in chlorophyll -a move downstream, with increased seaward residual currents, and they more widely range from the middle estuary to the estuarine mouth than during the winter; moreover, the chlorophyll -a value peaks in these areas. Reclamation projects significantly promote the expansion of waters high in chlorophyll -a towards the estuarine mouth. The distribution of suspended sediment, nitrate, ammonium, and silicate also obviously varies with altered water exchange and chlorophyll -a distribution. Average chlorophyll -a , suspended sediment, and silicate concentrations in the whole computational domain increase by 12.71%, 15.19%, and 1.91%, respectively, while the growth of algae consumes a large amount of nitrate and ammonium. • Reclamations in the Pearl River Estuary significantly affect the water quality. • Chlorophyll -a , suspended sediment, and silicate concentrations increase after reclamations. • Nitrate and ammonium concentrations decrease by 28.82% and 19.09%, respectively. [ABSTRACT FROM AUTHOR]