Dynamic Positioning System Research Articles

In situ calibration of observatory broadband echosounders

Abstract Today, numerous scientific echosounders are used as continuously monitoring systems in ocean observatories. These echosounders are usually calibrated in shallow water, either in laboratory tanks or at random ocean docks before deployments. If the systems are used for quantitative measurements by the observatories, they should be calibrated at the operating depths to consider the environmental effects on the calibration parameters. In this article, a simple in situ calibration method is presented, which was recently applied to one of the nodes of the Norwegian Lofoten-Vesterålen ocean observatory, when the research vessel with dynamic positioning system suspended and moved the calibration sphere between the vessel and the transducer. The calibration results of a 70-kHz split-beam echosounder demonstrate that this method can be applied to the cabled observatories.

Experimental study on the low-speed manoeuvring capability of a twin-lift decommissioning system

ABSTRACT A simple dynamic positioning (DP) system has been developed for the scaled model of a novel twin-lift decommissioning operation. Such a decommissioning solution involves the two semi-submerged vessels transporting the topside to another vessel. And it requires the synchronised motion of the two topside-carried vessels at a low speed, under the environmental disturbances. In order to ensure efficiency and safety, model tests with a scaling factor of 1:37 have been carried out in the wave tank. The DP system in the experiment consists of a 3-Degree of Freedom (3DoF) motion equation, a Proportional–Integral–Derivative (PID) controller and a thrust allocation algorithm. This paper investigates the motion response of each vessel under the random wave and constant wind of different angles, to assess the low-speed manoeuvring performance. It is found that the given control scenarios allow the twin-lift decommissioning system to yield good motion performance under operational conditions.

Dynamic multiobjective optimization for thrust allocation in ship application

Thrust allocation is a key procedure in the dynamic position system (DPS) of marine vessels. The present work aims to study the characteristics of dynamic optimization in thrust allocation. A two-phase analysis process is proposed. In phase-I, the model for thrust allocation is generated from the viewpoint of multiobjective optimization. Fuel consumption and tear-and-wear on the thrusters are chosen as objectives. Multiobjective feasibility enhanced particle swarm optimization algorithm (MOFEPSO) is applied to find the Pareto set of this problem. An additional decision-making procedure, the technique of order preference by similarity to ideal solution (TOPSIS) is utilized to choose the final compromise solution in phase-II. The self-organizing map (SOM) technique is undertaken to mine the Pareto data set. A Remote Operated Vehicle (ROV) example is provided for illustrating the above analysis process. The effects of relative importance between objectives upon characteristics of thrust allocation are studied. The trajectories of decision variables and objectives are examined through the SOM method. Results from numerical examples demonstrate that the multiobjective optimization method together with decision-making skills can extend the application of optimization in the thrust allocation field. The findings in this work add to the understanding of relationships among several aspects of DPS.

Position Loss Risk Analysis of Dynamic Positioning Systems of Semi-submersible Drilling Units by Considering Time-varying Failure

Bai, X.; Zan, Y.F.; Luo, X.F.; Huang, K., and Guo, R.N., 2020. Position loss risk analysis of dynamic positioning systems of semi-submersible drilling units by considering time-varying failure. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 160–165. Coconut Creek (Florida), ISSN 0749-0208.Position loss risk analysis of dynamic positioning (DP) systems is essential for the operation of semi-submersible drilling units. Traditional risk analysis methods ignore the probability of equipment failure with time-varying, which may result in inaccurate analysis. In this study, fault tree analysis was combined with the continuous-time Bayesian method based on the D-vine copula model to analyze loss of position (LOP). The D-vine model decomposition method was used to calculate multiple two-dimensional copula correlation measures for determining the system reliability with time and for calculating the effect on the occurrence of LOP. The key aspects of LOP were analyzed from the perspective of the variability of equipment at the time of failure. The results can provide a crucial reference for the maintenance of the DP system.

Construction mode detection for autonomous offshore heavy lift operations

Offshore platforms and windmills are constructed by assembling huge mechanical structures transported by heavy lift vessels. The construction process comprises two interconnected operations, the dynamic positioning (DP) of the vessel and the lifting of heavy loads. The DP system is commonly designed and tuned for the case that there is no load or for the case that the heavy load is free-hanging (mode 1). During the transition from the free-hanging to the case that the vessel is connected to a heavy load which is mounted to the platform (mode 2), the DP system may not be able to preserve the position stability of the vessel, jeopardizing human and system safety. The goal of this work is to design an intelligent monitoring system for the early detection of the transition between the two construction modes by adopting a nonlinear state estimation approach. Simulation results are used for illustrating the effectiveness of the proposed construction mode detection system.

Dynamic Vessel Position Reference System Based on DP3 System

Hu, Y.; Wang, H.T.; Yang, G.R.; Xiao, J.R., and Zhang, J., 2020. Dynamic vessel position reference system based on DP3 system. In: Al-Tarawneh, O. and Megahed, A. (eds.), Recent Developments of Port, Marine, and Ocean Engineering. Journal of Coastal Research, Special Issue No. 110, pp. 159–162. Coconut Creek (Florida), ISSN 0749-0208.With the continuous development of ocean trade and the exploitation of marine resources, the ocean-going vessel dynamic positioning (DP) system has become a necessary core device for ships, wherein the DP3 system is the highest-level computer dynamic positioning system. Based on it, this paper conducts a research on the vessel positioning reference system, and designs and debugs a vessel positioning computer control system. The research results show that the application of DP3 system in ship positioning has many advantages, its console is mainly composed of Industrial Personal Computer (IPC), input and output system, driver and stepper motor, etc. In the DP3 system, the steering and propelling processes occur simultaneously, but once the computer system can't satisfy the requirements of both aspects, it will prioritize the steering requirements during the positioning process. The research in this paper provides a theoretical basis for the studies of oceangoing vessel positioning computer control system.

Wave motion compensation in dynamic positioning of small autonomous vessels

Conventional dynamic positioning (DP) systems on larger ships compensate primarily for slowly time-varying environmental forces. In doing so, they use wave filtering to prevent the DP from compensating for the first-order wave motions. This reduces wear and tear of the thruster and machinery systems. In the case of smaller autonomous vessels, the oscillatory motion of the vessel in waves may be more significant, and the thrusters can be more dynamic. This motivates the use of DP to compensate for horizontal wave motions in certain operations. We study the design of DP control and filtering algorithms that employ acceleration feedback, roll damping, wave motion prediction, and optimal tuning. Six control strategies are compared in the case study, which is a small autonomous surface vessel where the critical mode of operation is launch and recovery of an ROV through the wave zone.

Dynamic Positioning System Design for A Marine Vessel with Unknown Dynamics Subject to External Disturbances Including Wave Effect

In this paper, a new control system is proposed for dynamic positioning (DP) of marine vessels with unknown dynamics and subject to external disturbances. The control system is composed of a substructure for wave filtering and state estimation together with a nonlinear PD-type controller. For wave filtering and state estimation, a cascade combination of a modified notch filter and an estimation stage is considered. In estimation stage, a modified extended-state observer (ESO) is proposed to estimate vessel velocities and unknown dynamics. The main advantage of the proposed method is its robustness to model uncertainties and external disturbances and it does not require prior knowledge of vessel model parameters. Besides, the stability of the cascade structure is analyzed and input to state stability (ISS) is guaranteed. Later on, a nonlinear PD-type controller with feedforward of filtered estimated dynamics is utilized. Detailed stability analyses are presented for the closed-loop DP control system and global uniform ultimate boundedness is proved using large scale systems method. Simulations are conducted to evaluate the performance of the proposed method for wave filtering and state estimation and comparisons are made with two conventional methods in terms of estimation accuracy and the presence of uncertainties. Besides, comparisons are made in closed-loop control system to demonstrate the performance of the proposed method compared with conventional methods. The proposed control system results in better performance in the presence of uncertainties, external disturbance and even in transients when the vessel is subjected to sudden changes in environmental disturbances.

Analysis of API S-135 steel drill pipe cutting process by blowout preventer

In offshore oil exploration, the use of a Dynamic Positioning System (DPS) to maintain the platform at a fixed point regardless of the influence of the environment has become common practice. In the event of failure, however, the drill string inside BOP (BlowOut Preventer) must be cut and safely disconnected from the platform. Therefore, it is evident the need for an accurate and realistic virtual model of this failure process. Numerical model analysis, in addition to avoiding expensive and complex experimental tests, allows, through post-processing tools, a detailed understanding of all phases of the failure process. The present work aims to characterize the API S-135 steel, as material commonly used to manufacturing drill strings. The material parameters for the Johnson-Cook model (J-C) are obtained from experimental tensile tests on dog bone and 3-point bending beams specimens with different notch radii, covering a wide range of stress triaxialities. Experimental tests and numerical simulations were compared by means of stress-strain curves, Digital Image Correlation (DIC) and Surface Electron Microscopy (SEM) to validate the model. The material model is applied to simulate the pipe cutting process and to predict the required force for the BOP to cut drill pipes with different geometries, which in comparison to experimental tests permitted to determine BOP internal frictions. Additionally, the numerical simulation also allowed a better understanding of the cutting process here presented as well, coherent to J-C model and SEM imaging of a similar cut tube in BOP.

Auto Tuning of PID Controllers for Dynamic Positioning Systems with Nonlinearity

Auto Tuning of PID Controllers for Dynamic Positioning Systems with Nonlinearity

Anti-windup reconfigurable control for dynamic positioning vessel with thruster faults

In this study, an anti-windup reconfigurable control method is developed for dynamic positioning vessel in the presence of thruster faults and input saturation. The designed reconfiguration block acting as a virtual thruster aims at hiding the faults from the nominal controller. Also, it is added into the closed-loop system between the nominal controller and the dynamic positioning system. A thruster saturation-failure fault matrix technique is proposed to regard the thruster saturation as thruster fault, meanwhile an auxiliary system is constructed to achieve extra compensation for the adverse effects induced by input saturation. Furthermore, an integral sliding mode control method is presented to accommodate the nonlinear items in the reconfiguration block. An adaptive technique is also employed to preserve robustness against the unknown uncertainties. Finally, a vessel dynamic positioning control process is adopted to evaluate the effectiveness of the proposed method.

Conceptual design of dynamic positioning system for tugboat to improve safer operation in Indonesia, case study: port of Cilacap

Due to increasing demand of the port activity it requires rapid operations of ship assisting and tug. Complex operations combined with challenging environmental disturbance often lead to ship accident that caused damaged to the jetty or the ship itself that also disrupt the overall port operation. On of the cause that lead such accidents is the limited capability of the tugboat to handle manoeuvre in extreme environment condition. Beside the safety of the operation are threatened this is also one factor that lead to decreased in tug operation effectiveness. This study intent to analyse the potential of dynamic positioning (DP) system used in the tugboat. Port of Cilacap used as study case due to special requirement as well as challenging location that lead in extreme condition of port operation. Two type of propulsion are used which is Azimuth and Void-Schneider propulsion. The conceptual system design is analysed by perform modelling simulation in Matlab software. Several condition of operation among the type of propulsion are assessed. The result is that DP system on tugboat could reduce the potential uncontrolled movement of the ship that lead to the accident. The analysis also proved that DP system of the ship can increase effectiveness of the operations by reducing the response time during manoeuvring.

Event-Triggered Dynamic Positioning for Mass-Switched Unmanned Marine Vehicles in Network Environments.

This article is concerned with event-triggered dynamic positioning for a mass-switched unmanned marine vehicle (UMV) in network environments. First, a switched dynamic positioning system (DPS) model for a mass-switched marine vehicle is established. The switched DPS model takes into consideration changes in the marine vehicle's mass and the resultant switching of the marine vehicle's parameters. Second, for a mass-switched UMV controlled through a communication network, a novel weighted event-triggering communication scheme considering switching features is proposed. The weighted error data of multiple sampling instants are utilized to avoid a long-time nontriggering phenomenon. The consideration of switching features guarantees the current sampled data to be transmitted if a switch occurs between the last sampling instant and the current sampling instant. Then, under the event-triggering scheme, an asynchronously switched DPS model for the mass-switched UMV is established in network environments. Based on this model, a mode-dependent DPS controller and event generator co-design method are proposed to attenuate the disturbance induced by wind, waves, and ocean currents. The DPS performance analysis demonstrates the effectiveness of the proposed method.

Distributed State Estimation for Dynamic Positioning Systems with Uncertain Disturbances and Transmission Time Delays

The dynamic positioning system of unmanned underwater vehicles (UUVs) is a complex and large-scale system mainly due to the nonlinear dynamics, uncertainty in model parameters, and external disturbances. With the aid of the bio-inspired computing (BIC) method, the designed three-dimensional (3D) spatial positioning system is used for enlarging communication constraints and increasing signal coordination processing. With the growing of measurement scales, the issue of the networked high-precision positioning has been developed rapidly. Then, an information fusion estimation approach is presented for the distributed networked systems with data random transmission time delays and lost and disordered packets. To reduce the communication burden, an adaptive signal selection scheme is employed to reorganize the measurement sequence, and the parameter uncertainties as well as cross-correlated noise are used to describe the uncertain disturbances. Moreover, a reoptimal weighted fusion state estimation is designed to alleviate the information redundancy and maintain higher measurement accuracy. An illustrative example obtained from the 3D spatial positioning system is given to validate the effectiveness of the proposed method.

A Deep Learning Method for Short-Term Dynamic Positioning Load Forecasting in Maritime Microgrids

The dynamic positioning (DP) system is a progressive technology, which is used in marine vessels and maritime structures. To keep the ship position from displacement in operation mode, its thrusters are used automatically to control and stabilize the position and heading of vessels. Hence, the DP load forecasting is already an essential part of DP vessels, which the DP power demand from the power management system (PMS) for thrusting depends on weather conditions. Furthermore, the PMS is used to control power generation, and prevent power failure, limitation. To perform station keeping of vessels by DPS in environmental changes such as wind, waves, capacity, and reliability of the power generators. Hence, a lack of power may lead to lower DP performance, loss of power, and position, which is called shutdown. Therefore, precise DP power demand prediction for maintaining the vessel position can provide the PMS with sufficient information for better performance in a complex decision-making process for the DP vessel. In this paper, the concept of deep learning techniques is introduced into DPS for DP load forecasting. A Levenberg–Marquardt algorithm based on a nonlinear recurrent neural network is employed in this paper for predicting thrusters’ power consumption in sea state variations due to challenges in power generation with the relative degree of accuracy by combining weather parameter dependencies as environmental disturbances. The proposed method evaluates with three traditional forecasting methods through a set of practical real-time DP load and weather parametric data. Numerical analysis has shown that with the proposed method, the future DP load behavior can be predicted more accurately than that obtained from the traditional methods, which greatly assists in operation and planning of power system to maintain system stability, security, reliability, and economics.

СУЧАСНЕ ЦИФРОВЕ СУДНОБУДУВАННЯ

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Review of Dynamic Positioning Control in Maritime Microgrid Systems

For many offshore activities, including offshore oil and gas exploration and offshore wind farm construction, it is essential to keep the position and heading of the vessel stable. The dynamic positioning system is a progressive technology, which is extensively used in shipping and other maritime structures. To maintain the vessels or platforms from displacement, its thrusters are used automatically to control and stabilize the position and heading of vessels in sea state disturbances. The theory of dynamic positioning has been studied and developed in terms of control techniques to achieve greater accuracy and reduce ship movement caused by environmental disturbance for more than 30 years. This paper reviews the control strategies and architecture of the DPS in marine vessels. In addition, it suggests possible control principles and makes a comparison between the advantages and disadvantages of existing literature. Some details for future research on DP control challenges are discussed in this paper.

Prescribed performance trajectory tracking control of dynamic positioning ship under input saturation

This paper investigates concentrates on the trajectory tracking control problem of dynamic positioning (DP) ship, in the presence of the time-varying disturbance and input saturation. Firstly, a simplified mathematical model of three degrees of freedom is established. According to the characteristics of the DP ship, an adaptive backstepping controller which combine the prescribed performance function with disturbance observer is proposed. The control scheme can guarantee the transient and steady state performance of the trajectory tracking and meet the prescribed performance criteria. In addition, an auxiliary dynamic system is introduced into the controller to deal with the input saturation problem of the actuator, so that the DP ship can accomplish the task of trajectory tracking under the condition of actuator constraint. Subsequently, in combination of barrier Lyapunov function (BLF), it is proved that the DP system can stabilize and converge rapidly to the small neighborhood of the equilibrium point, which can achieve the prescribed performance. Finally, the effectiveness of the DP control law is demonstrated by a series of simulation experiments.

Monocular vision-based gripping of objects

Optics-based systems may provide high spatial and temporal resolution for close range object detection in underwater environments. By using a monocular camera on a low cost underwater vehicle manipulator system, objects can be tracked by the vehicle and handled by the manipulator. In this paper, a monocular camera is used to detect an object of interest through object detection. Spatial features of the object are extracted, and a dynamic positioning system is designed for the underwater vehicle in order for it to maintain a desired position relative to the object. A manipulator mounted under the vehicle is used to retrieve the object through a developed kinematic control system. Experimental tests verify the proposed methodology. A stability analysis proves asymptotic stability properties for the chosen sliding mode controller and exponential stability for the task error.

Data driven approach to risk management and decision support for dynamic positioning systems

Offshore oil and gas operations are inherently associated with risk and may have catastrophic consequences to life, property, and environment. Risk management is thus performed during the design, planning, and operation phases to control risk. Operational risk models are only periodically updated and do not always reflect the available real-time data. This is also the case for dynamic positioning (DP) operation. Monitoring the risk levels of the system during the operational phase could reduce the accident risk by providing additional decision support information for operators.In this paper, a framework for the risk management of DP operation is proposed to assist operators in decision-making. The risk management output will provide operators a real time risk status and pre-warnings of possible deviations in the system. This framework is developed to support the decision-making process of the operators with providing failure probability of alternative decision scenarios, and it can be applied to any other engineering system and operation.In order to validate the effectiveness of the framework, DP drilling operations are considered as a case study. The results demonstrate the value and effectiveness of the framework, which reduces the risk level of operations by contributing to the risk-informed decision-making of operators.