Fuguang Ding

Structural Reliability Based Dynamic Positioning of Turret-Moored FPSOs in Extreme Seas

FPSO is widely used during the deep-sea oil and gas exploration operations, for which it is an effective way to keep their position by means of positioning mooring (PM) technology to ensure the long-term reliability of operations, even in extreme seas. Here, a kind of dynamic positioning (DP) controller in terms of structural reliability is presented for the single-point turret-moored FPSOs. Firstly, the mathematical model of the moored FPSO in terms of kinematics and dynamics is established. Secondly, the catenary method is applied to analyze the mooring line dynamics, and mathematical model of one single mooring line is set up based on the catenary equation. Thereafter, mathematical model for the whole turret mooring system is established. Thirdly, a structural reliability index is defined to evaluate the breaking strength of each mooring line. At the same time, control constraints are also considered to design a state feedback controller using the backstepping technique. Finally, a series of simulation tests are carried out for a certain turret-moored FPSO with eight mooring lines. It is shown in the simulation results that the moored FPSO can keep its position well in extreme seas. Besides, the FPSO mooring line tension is reduced effectively to ensure mooring lines safety to a large extent in harsh sea environment.

Based on disturbance observer of Air Cushion Vehicle course sliding backstepping control

As far as the Air Cushion Vehicle (ACV) movement is concerned, established the nonlinear motion equations of the course and propose a sliding backstepping control algorithm base on the perturbation observer, according to the idea of backstepping recursive design, a robust variable-structure control system is used in each step to stabilize the control system what is unnecessary to adopt adaptive adjustment parameters in backstepping design, which reduces the amount of system computation. The chattering problem is reduced by using the perturbation observer. Through the application of ACV course control system, it can be seen from the simulation results that the ACV under the model uncertainties and external disturbance, the system with perturbation observer use sliding backstepping controller, design of the control law guarantees the stability of the closed-loop system and can be better observed interference to reduce output of the controller, improve the performance of the system, so it is better control effect than without observer control. Of course it can be accurate for the course control at the high movement speed.

Sensor fault diagnosis of dynamic positioning ship based on finite impulse response filter

Sensors are important components of the dynamic positioning system, take compass for instance, which measures the course of a ship. Based on the Finite Impulse Response (FIR) filter, a simple and efficient sensor fault diagnosis scheme was proposed to improve the ability for judging whether sensor is out work or not. This method improved the capability of diagnosing when and what faults occur by using double criterions of fault detection method, and solved the sensor fault diagnosis problem in output mutation. The double criterions consist of state deviation and signal-to-noise ratio (SNR). Only the output signal of both state deviation and SNR changed suddenly can prove a fault of sensor has occurred. If the output signal of state deviation transforms but the SNR does not, it just indicates that the sensor is disturbed by the external environment. Applying this 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.

Adaptive Synchronization Control of Multiple Vessels with Switching Communication Topologies and Time Delay

Recently, synchronization movement control of multiple vessels has been studied broadly. In most of the studies, the communication network among vessels is considered to be fixed and the time delay is often ignored. However, the communication network among vessels maybe vary because of switching of different tasks, and the time delay is necessary to be considered when the communication network is unreliable. In this paper, the synchronization movement of multiple vessels with switching connected communication topologies is studied, and an adaptive synchronization control algorithm that is based on backstepping sliding mode control is proposed. The control algorithm is achieved by defining cross coupling error which is combination of the trajectory tracking error and velocity tracking error. And an adaptive control term is used to estimate the external disturbances, so that the unknown external disturbances can be compensated. Furthermore, the robustness of the control law to time-varying time delay is also discussed. At last, some simulations are carried out to validate the effectiveness of the proposed synchronization control algorithm.

Ensuring Mooring Line Safety for Deepwater Turret-Moored FPSO in Extreme Seas

ABSTRACT Wang, Y.; Dou, X.; Ding, F.; Tuo, Y., and Liu, Y., 2015. Ensuring mooring line safety for deepwater turret-moored FPSO in extreme seas. This study addresses dynamic positioning technology of deepwater FPSO moored to the seabed via a turret based spread mooring system, referred to as Position Mooring (PM). In normal weather conditions, the mooring system constrains the FPSO to the predefined region. In extreme seas, however, the mooring system behaves in a limited fashion to constrain the position such that the thruster force is also needed in order to avoid damage to the mooring lines. A controller based on structural reliability is presented for turret-moored FPSO. First, a mathematical model of FPSO in terms of the kinematics and dynamics and the environmental disturbance is established. Second, a mathematical model of one single mooring line is set up based on the catenary equation. Thereafter, the mathematical model for the whole turret mooring system is established. Third, a PID and a state feedback controller based on structural reliability are designed to ensure mooring lines safety. Finally, a series of simulation tests are carried out for a turret-moored FPSO. The simulation results show that the dynamic tension of the mooring line is effectively reduced due to introduction of a reliability index in terms of controller design.

Adaptive synchronization control of multiple vessels with time delays

In this paper, an adaptive synchronization control approach is presented to control multiple fully actuated vessels along desired trajectory. And the communication network among these vessels is directed strongly connected but not necessarily balanced. Meanwhile, the control strategy is to synchronize each vessel with others in position and velocity. In addition, the proposed decentralized synchronization control law is adaptive in the presence of model parameter uncertainty and the constant coupling time delays. A combination of the Lyapunov theory and the mathematical graph theory has been used to validate the stability of the whole system. Finally, simulations of the proposed adaptive synchronization control algorithm are presented and discussed.

Research on the Course and Turn-rate Coordinated Control for an Air Cushion Vehicle

The characteristics of the air cushion vehicle (ACV) show that the ACV is easy to be Broaching-to (the craft suddenly and unintentionally thrown or cause to turn, broadside to its original direction of motion). If the turning-rate is not to be controlled during ACV in the course keeping, the turning-rate and slide-angle will reach the warning or danger value that maybe led the ACV to be broaching-to or turndown. In this paper, the course and turning-rate control methods based on nonlinear back-stepping control theory are researched, and the coordinated control strategies are given. Control method and coordinated control strategy are used in the real-time ACV automatic control system. The results of the simulation show that the control method and coordinated control strategy are very effective and make the ACV moved more gently and stability and sail much more safely.