Xiaocheng Shi

GA path planning for AUV to avoid moving obstacles based on forward looking sonar

The paper proposes a framework of obstacle avoidance for AUV based on the real-time information of forward looking sonar (FLS) in an unknown environment. The whole system includes such modules as obstacle detecting by FLS, tracking obstacles, motion estimation and local path planning to avoid obstacles. Least squares methods and its amends, Kalman filter and some adaptive methods are applied to estimate the motion parameters of different obstacles. We also take advantage of the real-time data stream to track obstacles and obtain their dynamic characteristics. A method of obstacle avoidance for AUV based on genetic algorithm (GA) has been proposed in the paper. The method utilizes floating-point genes, transforms multi-restrictions into the fitness function, such as obstacle avoidance, the minimum distances between way points and trace keeping. The introduction of elitist selection guarantees the constringency of the GA algorithm. Simulations show that the method is perfect for AUV to avoid not only static obstacles but also moving obstacles.

Amphibious hovercraft course control based on support vector machines adaptive PID

Amphibious hovercraft is very different from conventional surface ships. Its mathematical model perturbs erratically as the change of sailing status and environment. For the nonlinear characteristic, adaptive PID controller based on support vector machines (SVM) is applied in the course control. The SVM is used to identify the system information, which is then linearized to extract the instantaneous linear model. The parameters of PID are turned based on the linear model. The simulation results in harsh environment show that the controller designed achieves high dynamic and steady performances, which brings a new effective method to solve the problem of hovercraft course control.

Autonomous underwater vehicle: Petri net based hybrid control of mission and motion

Terrain scanning is one of important missions of autonomous underwater vehicle. AUVs mission control covers a wide spectrum of research topics focusing on the interplay between event-driven and time-driven dynamical systems. The former is within the realm of discrete-event system theory, whereas the latter can be tackled using well-established theoretical tools from the field of continuous- and discrete-time dynamical system. The paper describes behavior arbitration hybrid software architecture of the mission control procedure which composes of mission level, task level and behavior level. The paper provides a mission control procedure model by adopting the formalism of extended Petri net theory. The task coordination algorithm based on the RW discrete event system theory has also been proposed to coordinate the pre-planned tasks and newly triggered tasks according to the inner or external events. Details are given about the autonomous underwater vehicle at the present time, together with the simulation experimental validation of terrain scanning mission in the virtual system which has shown the reasonable hardware system, the implementation of the software and the correctness of the task coordination algorithm.

Constrained control allocation using Cascading Generalized Inverse for dynamic positioning of ships

Control allocation is an important part of the dynamic positioning system, which determines the control inputs of each thruster device from the control law. Based on the Cascading Generalized Inverse algorithm, a simple and efficient control allocation scheme was proposed to improve the ability for keeping position of dynamic positioning ships. This method improved the performance of a single generalized inverse by using multiple generalized inverses, and solved the actuators saturation problem in constrained control allocation. Applying the method, an explicit solution was obtained, and achieved a greater capacity and efficiency in the implementation process. The validity and excellent performance of this algorithm was proved by the simulation results.

Optimizing adaptive thrust allocation based on group biasing method for ship dynamic positioning

Thrust allocation is an important part of the dynamic positioning system of ships, which determines the control inputs of each thruster device from the control law. In order to improve the faults of thrust allocation algorithms efficiently, the concept of group biasing is given and the adaptive strategy of group biasing method is designed. Consequently, the optimizing adaptive thrust allocation algorithm is proposed which bases on the group biasing and optimal methods, and the amplitude of bias can be adjusted adaptively according to thrust force. Applying the algorithm, the dynamic performances of dynamic positioned ships are improved availably, and the fuel consumption and maneuverability are both considered simultaneously. The validity and excellent performances of this algorithm were proved by the simulation results.

Terminal sliding mode tracking control for dynamic positioning J-lay vessel

Horizontal surface DP vessel model, ocean disturbances and J-lay pipeline model are established. Passive nonlinear observer is used to filter high frequency motions and give estimation for immeasurable states. A terminal sliding mode controller is proposed to implement tracking control task, the controller can drive the tracking error to zero rapidly and be robust to uncertain disturbances. Pipe and wind forces are counteracted by feed forward control term. The geometric and dynamic tasks are carefully designed to guide the ship carry out pipe lay operation successfully. Simulation case with a pipe lay vessel is studied to verify the performance of guidance-control system.

An Unscented Kalman Filter based wave filtering algorithm for dynamic ship positioning

A dynamic positioning (DP) system is used to maintain a ship on a specified position and at a desired heading. A ship is exposed to the wind, currents and waves in the ocean. In order to counteract these disturbances, the dynamic positioning ship uses solely active propulsion. Since the first-order wave force is too large for the ships thrust system to deal with and it only causes the high-frequency motion, which do not induce the finial position drift. A filtering algorithm is needed to separate the high frequency motions from the low frequency ones. In this paper the Unscented Kalman Filter (UKF) method is used for the wave filtering of dynamic positioning ships. Noisy position and heading measurements are used by the UKF to estimate the low-frequency motion and the high-frequency motion. A nonlinear platform supply vessel (PSV) model is employed for both the model simulation and the estimator design. An approximation method for the first and second order wave force calculation is used to produce the high frequency and low frequency ship motion. With considering of the wind, currents and waves, some illustrative results of the UKF based wave filtering algorithm are presented.

Predictive control for submergence rescue vehicle station and attitude maneuver

It is an important control process to operate motion of a submergence rescue vehicle (SRV). Seeing that the motion of the submergence rescue vehicle is special, it is necessary to employ non-linear predictive control system. For this reason, continuous dynamic performance of the system, the logical components and the operative restraints are expressed as the non-linear equations of state with the inequality restraints, and the model principle of hybrid system is introduced. It showed that the position and attitude of the SRV could be exactly controlled by means of non-linear model predictive control. The test in a model basin also proved that the above methods were efficient.

An integrated manipulating and dynamic positioning system

An integrated manipulating and dynamic positioning system for the underwater pipeline and cable detecting and repairing equipment (in short, PCDR) has been described in the paper. The paper has introduced the system from the following aspects: its control system architecture, system integration, working mode, man-machine display, control policy and pipe position keeping simulation result. The manipulation console has been assembled in PCDR equipment and finished the surface and underwater sea trial in the Bohai Sea. The trivial has shown that the system operation was stable, the man-machine display was straight forward and the manipulation was easy which alleviated the working intensions of the working staff.