Thruster Dynamics Research Articles

Adaptive dynamic positioning control of an offshore wind turbine installation vessel subjected to thruster dynamics and input constraints

This paper suggests an adaptive positioning control method for a DP-equipped offshore wind turbine installation vessel. The method combines a finite-time disturbance observer (FTDO) with adaptive command filtered backstepping (CFB) to handle issues related to thruster dynamics, input saturation, model parameter uncertainties, and unknown environmental disturbances. By analyzing the environmental loads acting on the pile legs, a mathematical model for the installation vessel is established. To counteract the unknown disturbance actively, a FTDO is utilized. Additionally, an auxiliary dynamic system (ADS) is used to mitigate the thruster input saturation issue. Then an adaptive positioning controller is designed based on the FTDO and ADS, and Lyapunov stability theory is used to prove that all signals in the control system remain uniformly ultimately bounded. Numerical simulations are conducted to verify the effectiveness of the proposed control approaches.

Learning dynamics on invariant measures using PDE-constrained optimization.

We extend the methodology in Yang et al. [SIAM J. Appl. Dyn. Syst. 22, 269-310 (2023)] to learn autonomous continuous-time dynamical systems from invariant measures. The highlight of our approach is to reformulate the inverse problem of learning ODEs or SDEs from data as a PDE-constrained optimization problem. This shift in perspective allows us to learn from slowly sampled inference trajectories and perform uncertainty quantification for the forecasted dynamics. Our approach also yields a forward model with better stability than direct trajectory simulation in certain situations. We present numerical results for the Van der Pol oscillator and the Lorenz-63 system, together with real-world applications to Hall-effect thruster dynamics and temperature prediction, to demonstrate the effectiveness of the proposed approach.

Design and implementation of a hardware-in-the-loop simulation platform for a tail-sitter UAV

Purpose A high-fidelity simulation platform helps to verify the feasibility of the controller and reduce the cost of subsequent experiments. Therefore, this paper aims to design a high-fidelity hardware-in-the-loop (HIL) simulation platform for the tail-sitter vehicles. Design/methodology/approach The component breakdown approach is used to develop a more reliable model. Thruster dynamics and ground contact force are also modeled. Accurate aerodynamic coefficients are obtained through wind tunnel tests. This simulation system adopts a mode transition method to achieve continuous simulation for all flight modes. Findings Simulation results are in good agreement with the flight log and successfully predict the state of the vehicle. Originality/value First, the effects of the propeller slipstream are considered. Second, most researchers ignore the parasitic drag caused by the landing gear and other appendages, which is discussed in this study. Third, a ground contact model is implemented to allow a realistic simulation of the takeoff and landing phases. Fourth, complete wind tunnel tests are conducted to obtain more accurate aerodynamic coefficients. Finally, a mode transition method is deployed in the HIL simulation system to achieve continuous simulation for all flight modes.

Trajectory tracking control of remotely operated vehicle based on thruster dynamics

Abstract In order to reduce the impact of thruster dead zone on remotely operated vehicle (ROV) motion performance and ensure that it can complete trajectory tracking control under external interference. In this paper, the adaptive backstepping sliding mode control(ABSMC) method based on improved rapid power-to-power approximation law is proposed. Under the influence of external interference; ABSMC can quickly reduce the position error of the system, namely, shorten the approaching time. When the position error is small, the system can smoothly enter the sliding surface to eliminate chattering. A new thrust distribution method based on the pseudo-inverse method is proposed for the dead zone of a thruster. This method uses the pseudo-inverse method when the thrust is saturated. When all thruster thrusts are unsaturated, the thrust will remain outside the dead zone for a long time. Combined with the ABSMC method, the thrust output of the thruster is more smooth and more stable with small position errors. Finally, the effectiveness of the ABSMC method and the superiority of the new thrust distribution method is verified by simulation experiments.

Fuzzy adaptive trajectory tracking control of work-class ROVs considering thruster dynamics

Work-class remotely operated vehicles (ROVs) are widely used in oceanic observation and underwater operation, which are driven by hydraulic power. A fuzzy adaptive controller considering thruster dynamics is proposed to improve the trajectory tracking performance of work-class ROVs in this paper. The dynamics of the hydraulic motor driven thruster is much higher than the position and orientation tracking ability of work-class ROVs. Thus, the system is divided into two separate subsystems: out-loop position and orientation control system, and inner-loop hydraulic control system. A fuzzy adaptive algorithm is employed in the out-loop position and orientation controller, which estimates the system parameters and disturbances respectively. A disturbance observer is used in the inner-loop hydraulic controller to attenuate the uncertainties and disturbances. A second order filter is adopted to synthesize these two controllers, which generates a smooth hydraulic motor speed command with appropriate bandwidth and range. The stability of the whole control system is proved through Lyapunov theory. Simulation results demonstrate the effectiveness of the proposed trajectory tracking control strategy under parameter uncertainties and disturbances.

Robustifying Dynamic Positioning of Crane Vessels for Heavy Lifting Operation

Construction crane vessels make use of dynamic positioning (DP) systems during the installation and removal of offshore structures to maintain the vessel's position. Studies have reported cases of instability of DP systems during offshore operation caused by uncertainties, such as mooring forces. DP “robustification” for heavy lift operations, i.e., handling such uncertainties systematically and with stability guarantees, is a long-standing challenge in DP design. A new DP method, composed by an observer and a controller, is proposed to address this challenge, with stability guarantees in the presence of uncertainties. We test the proposed method on an integrated cranevessel simulation environment, where the integration of several subsystems (winch dynamics, crane forces, thruster dynamics, fuel injection system etc.) allow a realistic validation under a wide set of uncertainties.

A 3DOF Path-Following Controller for a Non-Directionally Stable Vessel with Slow Thruster Dynamics

Abstract In this paper, a 3DOF path-following controller for an electric double-ended passenger ferry prototype is presented. The controller is formulated through a 3-step backstepping approach, taking into consideration several challenging physical properties of the vessel, such as a lack of passive damping in the vessel hull, lack of directional stability, and slow thruster dynamics compared to the vessel dynamics. The controller design also features a new thrust allocation approach that allows the thrust allocation of the over-actuated thruster system to be formulated on closed form, which enables us to include the thruster dynamics in the control law. The performance of the suggested 3DOF controller is demonstrated and compared to two other controllers through simulations with a model of the electric passenger ferry.

Adaptive synchronization for surface vessels with disturbances and saturated thruster dynamics

This work investigates the adaptive synchronization for the surface vessels with disturbances and saturated thruster dynamics. The vessel movement model becomes the three-order equation with mismatched disturbances due to the inclusion of saturated thruster dynamics. The marine disturbances are described as the multiple harmonic disturbances with unknown frequencies, unknown amplitudes and unknown phases. By fusions of the nonlinear observer and the adaptive technique, the marine disturbance estimation and rejection are transformed into the adaptive problem. The auxiliary dynamic filter generates the state vectors to represent the filtered versions of the non-achievable portions of the vessel’s positions and velocities. The state vectors on-line correct the control errors for avoiding disturbance rejection performance compromise under thruster saturation. The synchronization controller is derived via the adaptive command filtered backstepping. The surface vessel closed-loop control system is guaranteed stable. The adaptive synchronization scheme is validated by simulations with comparisons in different cases.

Underactuated Coupled Nonlinear Adaptive Control Synthesis Using U-Model for Multivariable Unmanned Marine Robotics

This paper presents the control modelling and synthesis using a coupled multivariable under-actuated nonlinear adaptive U-model approach for an unmanned marine robotic platform. A nonlinear marine robotics model based on the dynamic equation using the Newtonian method and derivation with respect to the kinematics equations and rigid-body mass matrixes are explained. This nonlinear marine robotics model represents the underwater thruster dynamics, marine robotics dynamics and kinematics related to the earth-fixed frame. Coupled multivariable nonlinear adaptive control synthesis using a U-model approach for the Remotely Operated Vehicle (ROV) and Unmanned Surface Vessel (USV) represent an unmanned marine robotics application. A comparison is presented for the proposed nonlinear control approach between the U-model control approach with nonlinear Fuzzy Logic Control and Sliding Mode Control for the ROV and USV platforms. The results show minimum mean square error values and tracking performance between the plant or system model with the proposed method. Lastly, robustness and stability analysis for the proposed U-Model nonlinear control approach are presented by implementing an adaptive learning rate value.

Adaptive trajectory tracking control for remotely operated vehicles considering thruster dynamics and saturation constraints

This paper discusses the problem of adaptive trajectory tracking control for remotely operated vehicles (ROVs). Considering thruster dynamics, a third-order state space equation is used to describe the dynamic model of ROVs. For the problem of unknown dynamics and partially known input gain, an adaptive sliding mode control design scheme based on RBF neural networks is developed using a backstepping design technique. Because of the saturation constraints of the thrusters, a first-order auxiliary state system is applied, and subsequently, a saturation factor is constructed for designing adaptive laws to ensure the stability of the adaptive trajectory tracking system when the thrusters are saturated. The proposed controller guaranteed that trajectory tracking errors are uniformly ultimately bounded (UUD). Finally, the effectiveness of the proposed controller is verified by simulations.

Finite-time composite guidance law with input constraint and dynamics compensation

Guidance laws are proposed for a near space interceptor with on–off type thrust as output. The target-interceptor engagement kinematics is integrated with the first-order dynamics of thruster to design guidance laws. The bang-bang type guidance law with linear sliding mode is proposed to deal with thruster dynamics, and the sufficient condition for finite time convergence is rigorously proved based on the finite-time convergence theory. According to the sufficient condition, a sliding mode guidance law with hysteresis-band switching is introduced to reduce the switching frequency of thruster. Then two guidance laws are combined into a composite guidance law to improve the guidance performance. Simulation results show that the line-of-sight angular rate can converge to a neighborhood of the equilibrium point before the final time of the guidance process, and the composite guidance law has better performance than typical guidance laws.

Extended state observer-based finite-time guidance laws on account of thruster dynamics

Guidance laws are designed for a near space interceptor with line-of-sight angle as input and on–off type thrust as output. The dynamics of thruster is viewed as a first-order lag with on–off working style and is integrated with the target–interceptor engagement dynamics to design bang-bang type sliding mode guidance laws. An extended state observer is designed to estimate the line-of-sight angular rate and the acceleration of target with the line-of-sight angle as a measurement. It is rigorously proved that the states of guidance system converge to a neighborhood of sliding mode in finite time and the line-of-sight angular rate converges to a neighborhood of the origin along the sliding mode in finite time under the designed guidance laws. Furthermore, in order to reduce the switching frequency of thruster, a sliding mode guidance law with hysteresis-band according to the sufficient condition for finite time convergence is proposed. Then, it is integrated with the bang-bang type sliding mode guidance law to yield a composite guidance law. Simulation results show that the extended state observer can effectively estimate the line-of-sight angular rate and the target acceleration, and the proposed sliding mode guidance laws have better performance than typical proportional guidance law.

Modeling and Adaptive Control for Multirotor Subject to Thruster Dynamics

Research on high-speed flight dynamics of multirotors is in increasing demand for “quick-reach” missions such as short-distance delivery and disaster assessment. The conventional works have integrated a linear thruster model in the dynamics modeling stage and developed a corresponding control algorithm; however, the linear thruster assumption has been shown to be accurate only in a near-hover state through wind tunnel tests. This paper proposes a novel multirotor dynamics model incorporating blade element momentum theory (BEM), which can precisely predict transient thruster output in various flight states (e.g., no flow, oblique flow, and pure side flow). With the proposed dynamics model, degradation of control performance caused by disturbances and variations is noticed under typical flight state (e.g., high-speed forward flight and drastic vertical rising). Finally, an adaptive robust backstepping control algorithm is proposed to achieve guaranteed performance under the aforementioned variations and disturbances. The simulations are carried out on a small quadrotor to verify the proposed approach.

Motion and force control with a nonlinear force error filter for underwater vehicle-manipulator systems

This paper deals with a control scheme for autonomous underwater robots equipped with manipulators. Several motion and force controllers have been developed. Most of them were designed in disregard of the dynamics of marine thrusters to develop a controller with a simple structure. However, the robot body propelled by thrusters generally has a considerably slower time response than the manipulator driven by electrical motors. Therefore, it may be difficult to construct a high-gain feedback control system to achieve a good control performance, because the high gain may excite the slow thruster dynamics ignored in the controller design, and the excitation will degrade the control performance. In this paper, we develop a motion and force controller for mathematical models with the dynamics of thrusters. It includes a nonlinear force error filter which allows us to construct a stable motion and force control system. To investigate its control performance, we conducted numerical simulations for comparing the proposed control scheme with an existing control scheme designed in disregard of the thruster dynamics. Simulation results demonstrate the usefulness of the proposed controller.

A Flat Design and a Validated Model for an AUV Reconfigurable Magnetic Coupling Thruster

Reconfigurable Magnetic Coupling Thruster (RMCT) is an enabling technology for achieving vectorial thrust on AUVs. This allows us to dispose of dynamic, compliant, and secure propulsion to enhance their agility for demanding locomotion tasks. RMCT can generate and control a thrust vector by redirecting its propeller through the compliance of the magnetic coupling and therefore achieve thrust vectoring for AUVs. In this paper, a new design of RMCT is presented. This new prototype uses a flat geometry magnetic coupling for a better AUV full integrability. The new design provides some additional advantages with regard to its predecessor (spherical RMCT); namely, construction simplicity and better torque transmission. The first characteristic is derived from its flat shapes, which makes it easier to manufacture (cubic magnets) and to isolate (planar air gap between rotors). The second characteristic is due to the fact that now both parts of the magnetic coupling can store magnets (increasing the maximal transmitted torque). This paper proposes a thruster dynamics model, a magnetic coupling model, and shows the use of a dynamic parameter identification method based on algorithms used for robotic manipulators. The validity of the dynamic model and identified parameters is then analyzed by means of experimental tests.

Trajectory Tracking Control of an Underactuated Underwater Vehicle Redundant Manipulator System

AbstractThe purpose of this study is to control the position of an underactuated underwater vehicle manipulator system (U‐UVMS). It is possible to control the end‐effector using a regular 6‐DOF manipulator despite the undesired displacements of the underactuated vehicle within a certain range. However, in this study an 8‐DOF redundant manipulator is used in order to increase the positioning accuracy of the end‐effector. The redundancy is resolved according to the criterion of minimal vehicle and joint motions. The underactuated underwater vehicle redundant manipulator system is modeled including the hydrodynamic forces for the manipulator in addition to those for the autonomous underwater vehicle (AUV). The shadowing effects of the bodies on each other are also taken into account when computing the hydrodynamic forces. The Newton‐Euler formulation is used to derive the system equations of motion including the thruster dynamics. In order to establish the end‐effector trajectory tracking control of the system, an inverse dynamics control law is formulated. The effectiveness of the control law even in the presence of parameter uncertainties and disturbing ocean currents is illustrated by simulations.

Fully-tuned fuzzy neural network based robust adaptive tracking control of unmanned underwater vehicle with thruster dynamics

In this paper, a fully-tuned fuzzy neural network based robust adaptive control (FFNNBARC) scheme for trajectory and attitude tracking of Unmanned Underwater Vehicle (UUV) subject to thruster dynamics and unknown disturbances, is proposed. The FFNNBRAC consists of a fully-tuned fuzzy neural network (FFNN) controller and a robust controller, where the FFNN estimation is introduced to approximate a backstepping control law, and the robust controller is proposed to provide the finite L2-gain property which can cope with reconstruction errors and can enhance the robustness of the overall control system. As a sequence, the FFNNBRAC scheme is able to render tracking errors asymptotically converge to zero and can guarantee all signals are bounded. Simulation studies and comparisons demonstrate the effectiveness and superiority of the FFNNBRAC scheme in terms of robustness and accuracy.

Nonlinear model predictive dynamic positioning control of an underwater vehicle with an onboard USBL system

This paper presents a novel optimization-based approach for dynamic positioning (DP) of a fully actuated underwater vehicle equipped with an onboard ultrashort baseline transceiver to provide relative position information of two earth-fixed transponders near the vehicle. The DP system error is defined by the transponders’ positions compared to the desired values, which occur at the vehicle’s target pose (position and orientation). The proposed DP strategy is composed of two loops in a hierarchical structure. In the kinematic loop, the nonlinear model predictive control is used to generate the desired velocity by optimizing a cost function of the predictive trajectories under the constraints of velocity and transponder bearings over a limited time horizon. In the dynamic loop, the neural network model reference adaptive control with pseudo control hedging is utilized to ensure the asymptotical convergence of velocity tracking errors in the presence of uncertainties associated with unknown model parameters, currents and thruster dynamics. The effectiveness of the proposed control scheme is illustrated by comprehensive simulations.

Modeling and control of a novel over-actuated marine floating platform

An autonomous dynamic positioning scheme for a novel triangular floating marine platform is developed, that stabilizes its linear and angular velocities as well as its position and orientation. For this platform, the required closed-loop forces and moments are provided by three rotating pump-jets, located at the bottom of three partly submerged cylinders, located at the corners of the platform. With this control configuration, the platform is over-actuated, i.e., it has more control inputs than degrees of freedom (DOF). Design guidelines leading to balanced actuator loading are identified. A control allocation scheme is developed that allows for station keeping under realistic constraints, disturbances and hardware limitations, without violating thruster dynamics. Furthermore, a model-based controller is proposed that aims at the reduction of fuel consumption. Simulation results, in the presence of realistic environmental disturbances, are presented that demonstrate the performance of the controller and of the allocation scheme developed. Preliminary Hardware-In-the-Loop (HIL) real time experiments are conducted and presented, showing effective platform station keeping.

Robust controller with a fixed compensator for underwater vehicle-manipulator systems including thruster dynamics

This paper deals with a control scheme for underwater vehicle-manipulator systems with the dynamics of thrusters in the presence of uncertainties in its system parameters and bounded disturbances. The authors have developed a robust controller that overcomes thruster nonlinearities, which cause an uncontrollable system. However, the controller has disadvantages in its performances (e.g., steady-state errors). In this paper we develop a robust controller with a fixed compensator including an integral action. The objective of the compensator is to improve the performances of the controller. The ultimate boundedness of a tracking error is theoretically ensured in the control system. Furthermore, simulation results support the theoretical one.