The hydrodynamic coefficients of Underwater manipulators constantly change during their operation. In this study, the hydrodynamic coefficients of an Underwater manipulator were calculated using the finite volume method to better explain its hydrodynamic performance. The drag, lift, and moment coefficients and the Strouhal number of an Underwater manipulator for different postures were investigated. The results indicated that in each motion range, the coefficients first increase and then decrease. Meanwhile, when the attitude of the Underwater manipulator is axis-symmetric or origin-symmetric, the hydrodynamic coefficients and the Strouhal number obtained are approximately the identical. The drag coefficient, lift coefficient and moment coefficient reach their maximum values of 3. 59, 3. 29, and 1. 78 at angles of 30°, 150°, and 150°, respectively， with minimum values at 90°, 50° and-30°. Furthermore, the leading-edge shape of the Underwater manipulator had a significant effect on the hydrodynamic coefficient. Maximum reductions of 44%, 25%, and 50. 5% were obtained in the drag, lift, and moment coefficients, respectively, by comparing the semicircular leading edge with the right-angle leading edge. A maximum Strouhal number of 0. 219 was obtained when the semicircular leading edge of the Underwater manipulator was the upstream surface. This study will provide theoretical guidance to reveal the hydrodynamic performance of the Underwater manipulators. It also serves as a reference for the structural design of the Underwater manipulators.

This paper develops an improved robust multi-surface sliding mode controller for a complicated five degrees of freedom Underwater Vehicle-manipulator System with floating base. The proposed method combines the robust controller with some corrective terms to decrease the tracking error in transient and steady state. This approach improves the performance of the nonlinear dynamic control scheme and makes the states stable even in presence of unknown effects of hydrodynamic disturbances and unmodelled dynamics. In this regard, the dynamic model of an UVMS is extracted using the Newton– Euler formulation which has been validated by using an ADAMS 3-D model. The control algorithm is based on Lyapunov technique and is able to provide the stability of the whole system during tracking of the desired trajectory with an acceptable precision. The controller parameters are also optimized utilizing the concept of Genetic Algorithm with the aim of increasing the speed of system while decreasing the tracking error which leads to bounded control inputs. Finally, the efficacy of the control scheme, is compared with other conventional methods and the simulation results show the short settling time, low and smooth control effort and asymptotic stability of the states as well as the sliding surfaces of the proposed controller.

The hydrodynamic coefficient of an Underwater manipulator varies with changes in posture and flow field, presenting significant challenges for precise control and localization. This study, conducted numerical simulations to investigate the patterns of variation in flow field and hydrodynamic coefficients. Results showed that hydrodynamic performance remained consistent when the posture of the manipulator was either axisymmetric or origin-symmetric. Upon rotation, axial flow extended across the entire downstream surface, and the Karman vortex street entirely eliminated. Pressure coefficients on the back pressure surface of the manipulator increased with the Reynolds number within the range of 6×103 ≤ Re ≤ 3×104, while the pressure coefficient on the upstream surface remained unchanged. Within this range, drag coefficients for the upper and lower arms decreased by 27.4% and 23.9%, respectively. The hydrodynamic performance of the lower arm was independent of the upper arm's posture, with a maximum drag coefficient of 1.48 achieved at α = −90°. As the posture angle of the manipulator varied from 30° to 60°, the pressure coefficient on the upstream surface decreased from 0.75 to 0.25.

With regard to the pronounced pressure pulsation and cyclic thrust oscillation observed in the tail flow field of an Underwater vehicle operating under over-expanded conditions, and drawing inspiration from flow control techniques involving porous media structures like submarine coral reefs and breakwaters, this paper presents an innovative proposition to incorporate a porous media layer on the tail wall of the nozzle in order to regulate the structure of the tail gaseous jets. To optimize the flow control of Underwater vehicles, the utilization of porous media layers with varying degrees of porosity is employed to establish a model for Underwater supersonic gaseous jets. This model scrutinizes the intricate structure of the tail gaseous jets, as well as the consequential wall pressure and thrust engendered by the nozzle. The findings eloquently demonstrate that the porous media model, boasting a porosity of 0.34, exerts a diminished influence on the morphological characteristics of the tail gaseous jets, while concurrently yielding a superior flow control effect on the pulsation of tail wall pressure and attenuating the differential thrust generated by the Underwater vehicle. Consequently, this innovative approach effectively mitigates overall thrust oscillation, thereby enhancing the stability of the Underwater vehicle throughout its submerged operations.