Bernard Voon Ee How

Robust Adaptive Neural Network Control for a Class of Uncertain MIMO Nonlinear Systems With Input Nonlinearities

In this paper, robust adaptive neural network (NN) control is investigated for a general class of uncertain multiple-input-multiple-output (MIMO) nonlinear systems with unknown control coefficient matrices and input nonlinearities. For nonsymmetric input nonlinearities of saturation and deadzone, variable structure control (VSC) in combination with backstepping and Lyapunov synthesis is proposed for adaptive NN control design with guaranteed stability. In the proposed adaptive NN control, the usual assumption on nonsingularity of NN approximation for unknown control coefficient matrices and boundary assumption between NN approximation error and control input have been eliminated. Command filters are presented to implement physical constraints on the virtual control laws, then the tedious analytic computations of time derivatives of virtual control laws are canceled. It is proved that the proposed robust backstepping control is able to guarantee semiglobal uniform ultimate boundedness of all signals in the closed-loop system. Finally, simulation results are presented to illustrate the effectiveness of the proposed adaptive NN control.

Robust adaptive boundary control of a flexible marine riser with vessel dynamics

In this paper, boundary control of a flexible marine riser with vessel dynamics is developed to reduce the risers vibrations. To provide an accurate and concise representation of the risers dynamic behavior, the distributed parameter model of the flexible marine riser with vessel dynamics is described by a partial differential equation (PDE) coupled with ordinary differential equations (ODEs) involving functions of space and time. Boundary control is developed at the top boundary of the riser based on Lyapunovs direct method to regulate the risers vibrations. With the proposed boundary control, uniform boundedness is achieved. The boundary control is implementable with actual instrumentation since all the signals in the control can be measured by sensors or calculated by a backwards difference algorithm. Simulations are provided to illustrate the effectiveness of the proposed control.

Robust Adaptive Position Mooring Control for Marine Vessels

In this paper, robust adaptive control with dynamic control allocation is proposed for the positioning of marine vessels equipped with a thruster assisted mooring system, in the presence of parametric uncertainties, unknown disturbances and input nonlinearities. Using neural network approximation and variable structure based techniques in combination with backstepping and Lyapunov synthesis, the positioning control is developed to handle the uncertainties, input saturation and dead-zone characteristics of the mooring lines and thrusters. Full state feedback with all states measurable and output feedback using high gain observer to estimate unmeasurable states are considered. Dynamic control allocation is presented for actuation of the position mooring system. Under the proposed robust adaptive control, semi-global uniform boundedness of the closed-loop signals are guaranteed. Numerical simulations are carried out to show the effectiveness of the proposed control.

Boundary Control of a Coupled Nonlinear Flexible Marine Riser

In this paper, boundary control for a coupled nonlinear flexible marine riser with two actuators in transverse and longitudinal directions is developed to reduce the risers vibrations. The dynamic behavior of the flexible riser is represented by a distributed parameter system with partial differential equations (PDEs) and the control is applied at the top boundary of the riser based on Lyapunovs direct method to regulate the risers vibrations. With the proposed boundary control, uniform boundedness under ocean current disturbance, and exponential stability under free vibration condition can be achieved. The proposed control is independent of system parameters, which ensures the robustness of the system to variations in parameters. Numerical simulations for demonstrating the effectiveness of the proposed control are presented.

Dynamics and control of mechanical systems in offshore engineering

Preliminaries.- Dynamic Load Positioning.- Coupled Nonlinear Flexible Marine Riser.- Flexible Marine Riser with Vessel Dynamics.- Riser System with a Torque Actuator.- Marine Installation System.- Riser Installation System.- Mooring System.

Control of Coupled Vessel, Crane, Cable, and Payload Dynamics for Subsea Installation Operations

In this paper, the coupled dynamics and control of the vessel, crane, flexible cable and payload under environmental disturbances with attached thrusters for subsea installation operations is investigated. For the practical system with physical constraints, we employ Barrier Lyapunov Function in the design of positioning control for the flexible crane-cable-payload subsystem to ensure that the constraints are not violated. Uniform stability of the flexible subsystem is shown and asymptotic positioning of the boundaries is achieved. Next, we tackle the scenario where nonuniformity of the cable, uncertainties and environmental disturbances are considered. Boundary controls are formulated using the nonlinear partial differential equation of the cable. Numerical simulations are provided to illustrate the performance of the proposed controls.

Dynamic Load Positioning for Subsea Installation via Adaptive Neural Control

In this paper, positioning control is investigated for the installation of subsea systems, with attached thrusters, under time-varying irrotational ocean current. Backstepping in combination with adaptive feedback approximation techniques is employed in the design of the control, with the option of high-gain observer for output feedback control. The stability of the design is demonstrated through Lyapunov analysis where semiglobal uniform boundedness of the closed-loop signals is guaranteed. The proposed adaptive neural control is able to capture the dominant dynamic behaviors without exact information on the hydrodynamic coefficients of the structure and current measurements. Comparative simulations with linear proportional derivative (PD), PD with adaptive term, and model-based controls are carried out. The proposed technique is found to be effective and robust and reduces tracking error of the subsea module.

Leader-follower formation control of underactuated AUVs with leader position measurement

In this paper, we investigate the leader-follower formation control of underactuated Autonomous Underwater Vehicles (AUVs). By using position measurements from the leader, we design a virtual vehicle such that the trajectory of the virtual vehicle converges to the reference trajectory of the follower. A position tracking control is designed for the follower to track the virtual vehicle using Lyapunov and backstepping synthesis. Simulation results demonstrated the effectiveness of the proposed scheme.

Boundary control of a flexible marine riser with vessel dynamics

In this paper, boundary control of a flexible marine riser with vessel dynamics is developed to reduce the risers vibrations. To provide an accurate and concise representation of the risers dynamic behavior, the distributed parameter model of the flexible marine riser with vessel dynamics is described by a partial differential equation (PDE) coupled with ordinary differential equations (ODEs) involving functions of space and time. Boundary control is developed at the top boundary of the riser based on Lyapunovs direct method to regulate the risers vibrations. With the proposed boundary control, uniform boundedness is achieved. The boundary control is implementable with actual instrumentation since all the signals in the control can be measured by sensors or calculated by a backwards difference algorithm. Simulations are provided to illustrate the effectiveness of the proposed control.

Load Positioning for Subsea Installation via Approximation Based Adaptive Control

In this paper, positioning control is investigated for the installation of subsea hardware with thrusters attached under time-varying ocean current. Adaptive neural approximation techniques are employed in the design of the control law and the stability is demonstrated by means of a backstepping and Lyapunov synthesis approach. Semiglobal uniform boundedness of the closed loop signals is guaranteed. The proposed control law is able to generate the control action required for accurate positioning without exact information on the hydrodynamic coefficients of the structure and current measurements. The performance of the proposed controller is evaluated via numerical simulations. From comparative simulations, the proposed technique is found to be effective, robust and produced an improved tracking performance.