Study on Ship Dynamic Positioning with Stochastic Backstepping Nonlinear Controller

A dynamic-positioning (DP) system can be designed to stabilize and damp the motions of a vessel when moored as well as unmoored. The vessel motion dynamic characteristics are generally significantly different when the vessel is moored as opposed to unmoored and may Vary over a wide range with changes in depth, scope, pretension, mooring pattern, and offset. In the paper, a design process is described whereby the DP controller parameters and their fictionalizations are derived for smooth stable response through the operating regime of the moored vessel. Field results from a North Sea operating drill ship are compared with predicted results, and the problems that were encountered are discussed. An augmentation scheme is presented by which the DP system will automatically back up and reinforce the holding capability of the mooring system under varying weather conditions and yet remain quiescent in calm weather. A mooring system may be deployed to extend the holding capability of a dynamically-positioned offshore drilling rig in shallow and intermediate water depths when heavy seas are predicted and vice versa. When the DP system is augmenting the mooring system, the DP system improves the damping of the moored ship in addition to increasing its holding capability, and minimizes the time required to deploy and adjust the anchor system by keeping station. For the worldwide operating offshore drilling or pipe laying rig, the combined DP and mooring systems offer unmatched flexibility and redundancy by extending the operating water depth of the rig yet providing low power requirements and operating costs in shallow water. INTRODUCTION Considerable discussion has been given to both mooring and dynamic positioning (DP) systems for offshore floating vessels.l, 2,3,4 However, generally speaking, in each case the discussions were limited to one system or the other at a time. This paper considers the combination of the two systems on one vessel and the manner in which the DP system can assist the mooring system. The paper begins with a brief review of the sizing and dynamic characteristics of a mooring system. This review establishes the range of mooring system parameters which must be accounted for in the design of the DP system for effective assistance to the mooring system. Then, a design process for the DP controller is given which allows the DP system to effectively augment the mooring system in a stable fashion in all operating regimes of the mooring system. Throughout these discussions, actual data recorded on the drill ship SAIPEM Due is used to amplify points of interest and connect theoretical with actual results. The data was collected off the coast of Italy in February 1973 and in the North Sea in Norwegian waters in May 1973. A description of the SAIPEM Due and its dynamic positioning and mooring system is given in Table I. Before reaching the final conclusions, the paper contains a section describing less obvious benefits in using the DP system with a mooring system.

During heavy lift operations, staying on position using a Dynamic Positioning (DP) system offers many advantages compared with a mooring system. However, when the vessel is connected to another fixed or floating object during the lifting operation through its hoist wires it may experience instabilities in the DP-system. These DP-instabilities are caused by the inability of the DP system to handle the relatively stiff external spring of the hoist wire correctly. This phenomenon is well known and mitigating measures such as Heavy Lift Mode have been developed over the years that work well for stationary vessels. However, when two vessels are lifting a single object together (e.g. QUAD lift), existing solutions to prevent this DP-instability are insufficient, as the nature of such lift requires a synchronous move on DP. During studies to the fundamental behavior of a DP system during heavy lift operations it is found that modifications to the Kalman filter can prevent these DP-instabilities. Heerema Marine Contractors presented the DP-stability challenges to Kongsberg Maritime, and a joint effort resulted in an implementation of a modified Kalman filter in the Kongsberg Maritime DP system. Also a dedicated engineering analysis to predict risk of DP-instabilities for specific lift configurations has been developed. The modified DP-system is tested in large number of simulations (both desktop and a full mission simulator) to test the ability of the updated DP-system to deal with a wide range of specific heavy lift conditions. Results were evaluated between Heerema office, Kongsberg and offshore personnel for developing the optimum Kalman filter parameters. Finally, the system is tested during a dedicated DP-trial program onboard Thialf. As the results of all these tests were very successful, the new High Kalman filter was made available onboard Thialf as a permanent option next to the original functionalities. The paper addresses the steps followed to define the new Kalman filter settings, the simulations performed to test the new filter as well as to show results of the offshore tests that were done to validate the numerical analysis.

Oil drilling and extraction platforms are currently being used in many offshore areas around the world. Whilst those operating in shallow seas are secured to the seabed, for deeper water operations, Dynamic Positioning (DP) is essential for the platforms to maintain their position within a safe zone. Operating DP requires intelligent and reliable control systems. Nearly all DP accidents have been caused by a combination of technical and human failures; however, according to the International Marine Contractors Association (IMCA) DP Incidents Analysis, DP control and thruster system failures have been the leading causes of incidents over the last ten years. This paper will investigate potential operational improvements for DP system accuracy by adding a Predictive Neural Network (PNN) control algorithm in the thruster allocation along with a nonlinear Proportional Integral derivative (PID) motion control system. A DP system’s performance on a drilling platform in oil and gas deep-water fields and subject to real weather conditions is simulated with these advanced control methods. The techniques are developed for enhancing the safety and reliability of DP operations to improve the positioning accuracy, which may allow faster response to a critical situation during DP drilling operations. The semisubmersible drilling platform’s simulation results using the PNN strategy show improved control of the platform’s positioning.

Using dynamic positioning (DP) ship maintains its position and heading by active thrusters. Several challenges exist with regard to the DP controller design, such as uncertain system model, actuator with saturation hard limitations, state or output (ship position or orientation) constraints. A robust receding horizon dual-mode control method is introduced into the design of DP controller using the property of the invariant ellipsoid. Outside the ellipsoid, the receding horizon control is employed .Once the state enters the ellipsoid, the control is switched to a linear state feedback control, which makes the state stay in the ellipsoid forever and stabilizes the system while satisfying the input, the state and the output constraints. The DP control is obtained by using semi-definite programming (SDP) which can be easily solved by means of linear matrix inequalities (LMI). At last, the simulation study is carried out to verify the feasibility and efficiency of the application of robust receding horizon dual-mode control for dynamic positioning ship.

Following an investigation undertaken by the publisher, we have determined that this paper was accepted on the basis of a compromised peer review process. We hereby retract the paper. The corresponding author has been notified of the retraction. The retraction statement can be found here: https://doi.org/10.1520/JTE20269996. Aiming at the difficulty of the dynamic positioning process and trajectory control under the influence of complex disturbance, ship dynamic positioning control based on the nonlinear fuzzy algorithm is studied. By analyzing the composition and task of the ship dynamic positioning system, the nonlinear characteristics of the ship dynamic positioning system are obtained, and the ship dynamic pose is described by the combined coordinate system of the geodetic coordinate system, ship hull coordinate system, and multi-degree-of-freedom coordinate system. The dual fuzzy proportional, integral, derivative (PID) algorithm is applied to the point control and surface control and an approximate algorithm is adopted to calculate the target control parameters, so as to enhance the comprehensive effectiveness of ship hull nonlinear control results. The experimental results show that the control effect of this method is better and the heading angle control error is smaller. Meet the dynamic positioning ship control needs.

Position-keeping of a floating body is a very important matter in a production system in the deep sea. How a floating body can be kept stationary is a key problem in this study. Conventionally, the mooring system is adopted to position a floating body under disturbance of wind, wave, and current; but, in general, it is difficult to survive storm disturbance in the deep sea. The dynamic positioning system can solve this problem, but thrusters must be operated at all times against random drift force of wave, wind, and current, and a great deal of energy is required. So a composite system of single-point mooring system and fuzzy control dynamic positioning (FDP) system was studied in a previous paper (Inoue, 1994). However, up to now in almost all kinds of dynamic positioning systems, control strategy must be decided in advance. This is unreasonable under a random condition. In this paper, a self-tuning fuzzy control system is put forward. By this approach, the control precision of the previous fuzzy dynamic positioning is fairly improved. The main concept of this approach is that at first a feasible control strategy is decided in advance, then during the motion of the system, the control strategy is improved automatically according to the sea conditions of operation. This system is more reasonable than the previous system because, in fact, the disturbance of wave, current, and wind cannot be predicted.

This study is concerned with the robust H ∞ control problem for dynamic positioning (DP) ships based on sampled-data. Input delay approach is used to convert the sampled-data DP ship system to a system with time-varying delay. Adequate condition is derived to determine the system's asymptotical stability and establish H ∞ performance. Then sampled-data controller is obtained by means of linear matrix inequalities. Simulation results show that the proposed method and the designed controller for DP ships are effective in the existence of varying environment disturbance.

ABSTRACTModern marine dynamic positioning (DP) systems are commonly constructed on the basis of nonlinear asymptotic observers. The primary reason for the observer's employment is to restore deficient information concerning the unmeasured velocities of the vessel. Nevertheless, using a number of separate items in addition to the observers, it is also possible to achieve desirable dynamical features of the closed-loop connection. The paper is devoted to the problem of synthesis of these items for marine vessels, which are controlled by DP systems under the action of sea wave disturbances. The essence of the problem is to identify a transfer matrix of the adjustable corrective item (filter), minimising the intensity of the control action determined by high-frequency sea wave components. The correspondent dynamic of a closed-loop system realises an economical regime of vessel motion with the aim to reduce general fuel consumption and to prevent the wearing down of actuators. A specialised approach for designing the filters is proposed that provides asymptotic stability and the integral action of a control. Applicability and effectiveness of this approach are illustrated by the practical example of DP system synthesis.

In order to further improve the control ability of dynamic positioning ship or platform under complex sea conditions, the controller and thrust allocation system of dynamic positioning are designed. A simplified three-degree-of-freedom MMG mathematical model is established for the pod full-rotation propeller used in most dynamic positioning ships. On the basis of retaining the advantages of active disturbance rejection control, the sliding mode variable structure control method is adopted to design the control law. The objective function and constraints of thrust allocation are designed based on the lowest energy consumption, and the sequential quadratic programming algorithm is used to calculate the real-time thrust allocation of each propeller. The simulation results of the ship dynamic positioning system in MATLAB show that the controller can maintain the stability and robustness of the system under the condition of external environment disturbance, and the results of the thrust allocation are reasonable, which has a certain reference value for the further study of the ship dynamic positioning control system.KeywordsSliding mode controlDynamic positioning systemThrust allocationSequential quadratic programming

The authors present a rather broad state of-the-art review of offshore positioning techniques including discussion of two basic methods currently employed - dynamic positioning and anchor-mooring. Representative examples are given in tabular form along with available operational experience. Specific design details are presented for the dynamic system as envisioned for Project Mohole and the anchor-moor system as proposed for the Navy's new class of submarine rescue vessels. Photographs of 1/8-size mockups of the latter arrangement are shown. The authors conclude that both basic systems will continue to have application in the future. The final system choice will depend on the operating depth requirements, required degree of station keeping and time on station, bottom conditions, basic vessel size and configuration and economics. INTRODUCTION The authors present a rather broad state of-the-art report on offshore positioning techniques and a description in some detail of two actual designs. What began years ago as a simple means for tethering a floating vessel now forms a major supporting role in oceanographic research, drilling operations and development of undersea ordinance. Present-day operational requirements frequently demand that a mobile floating vessel remain positioned as a working platform over a rather precise spot on the sea floor despite a variety of disturbing environmental factors. As a result of this increasing need for improved operational capability in greater and greater depths, a new technology has evolved which brings together engineers from a wide variety of disciplines: oceanographers to predict surface effects at the air-sea interface; soils engineers to analyze bottom conditions; electronic engineers to develop position sensing and measuring devices; mechanical and marine engineers to design propulsive units or mooring systems; and naval architects to incorporate the desired functional requirements into a workable, seaworthy design. The designer has essentially two avenues of approach to solving his positioning requirements - either a dynamic positioning system that uses propulsive or thrust power to hold the vessel over a given location or an anchor moor system that uses a. direct mechanical connection to the ocean floor. These two basic methods will be discussed in the sections that follow. DYNAMIC POSITIONING SYSTEMS Generally speaking, a dynamic positioning system can be considered to be composed of the following basic parts:Position sensing system - a means of establishing where the vessel or platform is in relation to the bottom or other known reference point and a means of measuring deviations from this fix. Such systems currently available include-the taut wire, satellite and seafloor-mounted sonar systems.Propulsive system - a means for providing adequate thrust in the proper direction and time to maintain position. The types of power employed for this purpose can be grouped as follows. l

Dynamic Positioning simulations of a Thrust Allocation Algorithm considering Hydrodynamic Interactions

\n The Dynamic Positioning (DP) System is responsible for the station keeping of vessels in several offshore operations. The forces required by the DP System are distributed among the available thrusters by a thrust allocation algorithm which should be accurate, efficient and robust. This means that the effective forces match the required forces while power consumption is minimized. Additionally, in case of impossibility of generating the required forces the heading of the vessel is maintained to avoid increasing environmental forces. To accurately generate the required forces, the physical limitations of the thrusters and the hydrodynamic interactions must be considered. The hydrodynamic interactions are consistently modelled to accommodate the following typical effects: thruster-hull, thruster-current and thruster-thruster interaction. The result of this modeling is a nonlinear optimization problem, which is solved using the Sequential Quadratic Programming (SQP) algorithm with slack variables. The DP simulation carried out show that by considering the hydrodynamic interactions on thrust allocation the overall performance (controllability and power consumption) of the DP system is improved.\n

As the offshore industry explores the potential of nuclear power for drilling facilities, a critical challenge emerges: how to effectively integrate the validation methodologies for nuclear power systems with those of dynamic positioning (DP) systems. This paper presents a forward-looking analysis of the validation requirements for power systems in both nuclear and DP contexts, with a specific focus on offshore drilling rigs projected for development in the next decade. The study begins by examining current validation protocols for nuclear power systems and DP systems independently, highlighting the crucial role of independent validation activities in each domain. It then identifies areas of overlap, divergence, and potential synergy between these methodologies. A significant portion of the paper is dedicated to navigating the complex landscape of regulatory considerations and industry standards that will shape the development of these hybrid systems. By analyzing existing frameworks, the authors propose a conceptual merged protocol that addresses the unique challenges posed by integrating nuclear power with DP systems in an offshore environment. The paper emphasizes the importance of maintaining rigorous safety standards while fostering innovation in this emerging field. It explores how independent validation can be structured to ensure the highest levels of safety and reliability in these complex, interconnected systems. While no case studies are currently available due to the forward-looking nature of this research, the paper presents theoretical scenarios to illustrate potential validation challenges and solutions. These scenarios serve as a starting point for industry discussion and further research. By proactively addressing these validation challenges, this paper aims to contribute to the safe and efficient development of nuclear-powered offshore drilling facilities in the coming years, potentially revolutionizing the energy landscape of offshore operations.

Object and purpose of research. The object of the research is the dynamic positioning system of a vessel with electric propulsion, the purpose is to create a computer tool for debugging the algorithms for the operation of control system for the ship’s dynamic positioning. Materials and methods. The indigenous simulation environment SimInTech is used. The model of vessel’s plane-parallel motion and methods of complex technical objects computer modeling are used. Main results. The concept and computer model of the ship technical means control system in the domestic modeling environment, mathematical and circuit models of the control object for conducting computational studies of ship control modes, developing and debugging algorithms for controlling the dynamic positioning of the ship, taking into account the optimal use of electric power system resources. Conclusion. The developed computer model of ship with the dynamic positioning system is a flexible tool for creating and debugging ship control systems and control algorithms. It provides a large number of computational studies of ship control modes for the creation and debugging of algorithms for controlling ship movement during its positioning, taking into account the optimal use of the resources of the ship's electric power system, which reduces the complexity of development and debugging of control algorithms, minimizes the number of physical experiments necessary to create ship’s dynamic positioning systems.

Among most of industrial control system, the time delay generally exists due to the actuator's own mechanical properties, which will produce the problem of force response delayed. And actuators are the main elements in Dynamic Positioning (DP) ships, thus it is necessary to solve the problem about time delay. Considering of the environmental disturbances, output response could be delayed and the environmental disturbances can't be compensated in time, it will cause the bad control effect, even oscillation. This paper proposed the adaptive fuzzy control, and it is a kind of adaptive active control. This control method can solve the time delay of passive control well. Combined with the fuzzy control, the adaptive control law is designed based on the backstepping method. Thus the adaptive fuzzy control for time-delay is verified by MATLAB simulating results.