Dynamic Positioning System Research Articles

Dynamic Response Analysis and Positioning Performance Evaluation of an Arctic Floating Platform Based on the Mooring-Assisted Dynamic Positioning System

The Arctic region is rich in oil and gas resources, but exploitation of resources there is always facing great challenge. Floating offshore platform is considered as a practical choice for oil and gas exploration in the Arctic deep water regions. One of the key technologies is positioning system design under harsh arctic sea loads. In this paper, a comprehensive design of the positioning system is investigated. A coupled numerical model composed of a mooring-assisted dynamic positioning system and the Kulluk platform is established. 16 different positioning combination forms are selected and investigated. The positioning capability of the coupled system is evaluated by analyzing the platform motion response under different environmental loads, including wave, level ice, and broken ice floes. Wave load is calculated using potential flow theory. Computation of ice load is compared with the finite element method (FEM) and discrete element method (DEM). The dynamic analysis of the mooring system is carried out by using the slender finite element method. The control system of dynamic positioning adopts proportional-integral-derivative (PID) control methodology. It is found that a better positioning system design can reduce the offset by more than 50%, including surge, sway and yaw motion. The results of this study will provide a good reference for the positioning system design of an arctic floating production platform.

Stabilizing tank to improve the operational window of a W2W gangway connecting a Flotel to a FPSO

Currently, offshore operations involve multibody systems composed of two or more units. Thus, these complex scenarios require highly reliable dynamic positioning systems for controlling and tracking motion of the vessels and environmental conditions to ensure safe operation with maximum operational uptime. In these operations, the use of walk-to-work (W2W) passive telescopic gangways has become the norm to facilitate crew transfer.The present work presents an experimental-analytical study to assess benefits of a roll Stabilizing Tank (ST) to enhance the operability of a multibody system composed by a Flotel connected to a FPSO by a gangway. The system was studied using reduced scale models at the wave basin laboratory (LOC) of COPPE/UFRJ considering FPSO alone, FPSO connected to the Flotel, and with and without a ST, focusing on the behavior of the FPSO and gangway.An analytical model to evaluate the ST performance was enhanced and validated with experimental results. The model considered a linear system with its parameters tuned based on FPSO properties. Analytical results showed excellent correlation with experimental data.ST performance is remarkable in reducing motions of both, FPSO and gangway. Therefore, it could reduce the risk of operational downtime and potentially lead to significant savings.

Metamodeling of structural failure: Case study of API S-135 steel tube cut in BOP

In offshore oil exploration, the use of a Dynamic Positioning System (DPS) is necessary to maintain the platform at a fixed point regardless the influence of the environment. In an event of DPS failure, however, a drill string inside BOP (BlowOut Preventer) must be cut and disconnected from the well. The required force to cut the string is traditionally determined by analytical models and commissioning tests, which can be far from the real situations. Depending on geometry and loading conditions of this tubular, the BOP may fail to cut it, which can lead to catastrophic events. Numerical analysis can not only bring more accurate and realistic results of the failure process but also it is an alternative to the expensive and complex experimental tests. Moreover, through post-processing tools, numerical models provide a more detailed understanding of the failure mechanism. However, due to the variety of geometric and loading conditions, a metamodel is proposed to predict required forces for BOP to cut API S-135 6.63″ 40.87ppf drill pipes. A calibrated and validated material model for API S-135 steel was applied to simulate the pipe cutting process in BOP at different combined conditions, including initial normal longitudinal load, torque, internal and external pressure, pipe decentralization and indenter offsetting. The predicted forces from numerical analysis were used to feed a machine learning algorithm, particularly a regression technique, providing the metamodel parameters. The conclusion is that current BOP cutting models may underestimate the required force to cut pipe in realistic conditions.

Experimental and numerical investigation on anti-rolling performance of a DP semi-submersible platform based on thruster group biasing

For semi-submersible platforms equipped with dynamic positioning (DP) system, which has a small water-plane area and low metacentric height, roll motion will be affected by the lateral control force of the thrusters, causing a larger roll amplitude. In view of this problem, present paper proposes a thrust allocation method based on thruster group biasing. The thruster axial forces in group counteract each other while the normal force directions are opposite to form an anti-rolling moment, so that the roll damping can be enhanced without affecting the positioning performance in the horizontal plane. The roll stabilization mechanism is studied experimentally and numerically. A numerical wave tank based on computational fluid dynamics (CFD) method is established, verified and validated against the experiments. Both experimental and numerical results show that the thruster group biasing strategy can increase roll damping and reduce the roll motion of the platform by approximately 16% under the given sea condition.

Adaptive generalized predictive control for dynamic positioning system of ships with model unknown parameters

This paper proposes an adaptive generalized predictive control for dynamic positioning of ships with unknown model parameters and unknown time-varying environmental disturbances. The controlled auto-regressive integrated moving average (CARIMA) model is employed to describe the movements of ships with model parameter and disturbance uncertainties. The recursive least square method with forgetting factor is utilized to design adaptive laws to estimate the CARIMA model parameters online. Considering both the positioning accuracy and the change intensity of control increments, a cost function is constructed. The optimal control increments that minimize the cost function are obtained by using Lagrange multiplier method. Then, the adaptive control law is designed to maintain ship’s position and heading at desired values. Finally, simulation studies in different cases are carried out and simulation results demonstrate the effectiveness of the proposed control scheme.

Anti-Disturbance Lyapunov-Based Model Predictive Control for Trajectory Tracking of Dynamically Positioned Ships

Trajectory tracking is a fundamental task of the dynamic positioning (DP) system. This paper studies the problem of trajectory tracking of DP ships constrained by control inputs under environmental disturbances. To solve this problem, we develop a novel anti-disturbance Lyapunov-based model predictive control (ADLMPC) scheme. Firstly, an extended state observer (ESO) is designed to estimate environmental disturbances. By combining the ESO with Lyapunov-based model predictive control, the ADLMPC scheme is devised. Secondly, a virtual controller which satisfies input constraints is developed by backstepping and the auxiliary dynamic system, and it is integrated into the Lyapunov contraction constraint in ADLMPC. We show that if the parameters for the virtual controller are appropriately determined, the recursive feasibility of ADLMPC is theoretically guaranteed, and the uniform ultimate boundedness of all signals in the trajectory tracking control system is achieved. Finally, the simulation results display the efficacy and superiorities of the ADLMPC scheme.

Comparative study of the mating process for a spar-type floating wind turbine using two alternative installation vessels

The offshore wind industry faces many challenges as the water depth of offshore sites increases. For installation of the spar floating offshore wind turbines (OWTs), cost-effective installation methods are needed to facilitate installations at moderate or deep-water depths. In this paper, a novel installation concept initially designed for installing pre-assembled wind turbines is further studied. Two alternative installation vessels (i.e., a catamaran and a small water-plane area twin hull vessel (SWATH)) equipped with a dynamic positioning (DP) system are considered for installing 10-MW OWTs. Hydrodynamic responses of the installation systems are obtained by the fully coupled nonlinear time domain method. Based on the numerical analysis in SIMO-Riflex, a comparative study of the two vessel concepts is conducted to study selected response variables of two mating points. Compared with the catamaran installation vessel, the SWATH substantially reduces dynamic motions during the critical mating phase. The findings of this paper provide references for industrial stakeholders selecting alternative installation vessels and serve as a basis for further optimizing the concept.

DP in ice environments—development of a dynamic positioning in ice validation platform (DPIVP)

This paper presents the development of a dynamic positioning in ice validation platform (DPIVP) which is part of a larger research project aimed at developing dynamic positioning (DP) system technologies for ice-rich environments. One outcome is simulation software to aid research in this area. The DPIVP software was designed to realistically simulate the dynamics of ice-structure interactions for real-time applications and to validate components common to DP in ice simulations. The software consists of many components which the DPIVP ties together as a unified system. All components have well-defined interfaces. Many of them are also distributed, allowing execution on separate computers and/or CPUs which helps ensure real-time operation. These two characteristics also decreases coupling and encourages a more modular design with the benefit of easily substituting alternative component implementations without reprogramming the DPIVP. Alternate implementations are useful for conducting research in specific DP in ice areas without substantially changing the system, such as alternative ice force models, DP control algorithms, vessel models, 3D and 2D visualization, environment models, and data acquisition systems. The integrated system was tested and evaluated using unit testing, integration testing, and system testing. The completed system was also validated using test cases that match physical model tests; the results compared favorably. Although the software has some limitations, for example, validated ice-force models being limited to two vessels, and thus lacks the generality we wish, the end result is a working prototype that satisfies the research requirements and provides an architecture and framework for future development.

Ship Dynamic Positioning Output Feedback Control with Position Constraint Considering Thruster System Dynamics

In order to simultaneously address the issues of ship operating area limitation, unknown time-varying disturbances, immeasurable ship speed, unknown dynamics, and input saturation, this paper investigates the position-constrained ship dynamic positioning output feedback control, taking thruster system dynamics into account. Firstly, a barrier Lyapunov function (BLF) is utilized to limit the ship position inside the dynamic positioning system’s acceptable working range and to limit the ship position error. Second, the set total disturbance, which is made up of unknown time-varying disturbances and unknown dynamics and is further handled by the control strategy, is estimated using a fixed-time extended state observer (FDESO). Additionally, the thruster system dynamics equations are incorporated into the controller design process so that the generated thrust signal varies gradually without abrupt fluctuations, in keeping with engineering realities. Furthermore, the thruster input saturation issue is dealt with using a finite-time auxiliary dynamic system. Finally, a robust control term is introduced to handle the errors generated in the controller design. The stability proof section demonstrates that the designed control strategy can cause the ship to arrive and maintain at the desired location and heading, as well as stay continuously inside the designated operating area with all signals of the closed-loop control system being consistently and eventually bounded. The simulation results demonstrate that the proposed system is valid.

Design and stabilization analysis of luxury cruise with dynamic positioning systems based on sampled-data control.

This paper studies the sampled-data control issue for a luxury cruise (LC) with dynamic positioning system (DPS). The design method and mathematical model of LC is given. By constructing an improved time-dependent Lyapunov-Krasovskii function (LKF) by adding new useful terms, the sampling pattern is fully captured and less conservatism of the results are obtained. Based on the constructed the LKF, the new stability criterion is obtained and the sampled-data controller for LC with DPS is designed. Finally, an example is exhibited to prove that the proposed approach is valid and applicable.

Spatio-Temporal Digraph Convolutional Network-Based Taxi Pickup Location Recommendation

The recommendation of taxi pickup locations plays an important role for drivers in carrying passengers efficiently. In addition, the emergence of the Internet of Vehicles provides technical support for it. However, existing recommendation methods do not model dynamic global positioning system information well and in real-time. In this article, we propose a spatio-temporal digraph convolutional network (STDCN) model. First, the pickup and drop-off locations are modeled into a directed spatio-temporal graph as input to the model. The correlation between each node is calculated as a unified edge weight based on the gray relational analysis. Then, the STDCN is used for dynamic spatio-temporal feature extraction. Finally, the edge-cloud collaboration framework is adopted to recommend local taxi pickup locations in real-time. The experimental results show that the proposed method is better than competing methods in terms of effectiveness and efficiency, and it shows good industrial conversion application prospects.

Dynamic response of a SWATH vessel for installing pre-assembled floating wind turbines

New and efficient installation concepts which can reduce the cost of developing an offshore wind farm are of particular interest. This paper explores a promising concept using the small water-plane area twin-hull vessel (SWATH) to install pre-assembled wind turbines (OWT) onto floating spar foundations. A focus is placed on the hydrodynamic performance of the SWATH and the response analysis of the coupled SWATH-spar system. Firstly, the numerically calculated difference-frequency wave force effect and damping forces of the original SWATH were verified with experimental data. Secondly, the original SWATH was modified to satisfy the criteria of weight-carrying capacity and hydrostatic stability. Thirdly, a multibody numerical model for the SWATH-spar system was developed, in which the hydrodynamic and mechanical couplings between the SWATH and a spar were considered. The SWATH is equipped with a dynamic positioning system to counteract the slow-drift wave force effects. The nonlinear time-domain simulations were carried out for the mating stage when a wind turbine is lifted above the spar foundation. Based on the analysis of statistics of the relative displacement and velocity of the tower bottom and the spar top, the installation concept with SWATH is found to be of decent performance. Finally, recommendations are provided for future research on this concept, which contributes to developing next-generation installation concepts for bottom-fixed and floating wind farms.

Analysis of data fusion algorithms for the vessel with the dynamic positioning system

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informujące swoich czytelników o najnowszych osiągnięciach naukowych i nowoczesnych rozwiązaniach technicznych w Polsce i na świecie, popularyzuje problemy techniczne oraz poszerza wiedzę i kulturę techniczną.

Human-automation interaction centered approach based on FRAM for systemic safety analysis of dynamic positioning operations for offshore tandem offloading

The offshore and maritime industry comprises technologically complex vessels and facilities with increasing automation. However, automation may introduce human-automation interaction problems with possibly catastrophic consequences. Dynamic positioning (DP) operations are typical of high exposure to such threats. This study develops a human-automation interaction centered approach for systemic DP operational safety analysis in offshore tandem offloading. The proposed methodology utilizes a prevailing systemic method, i.e., the functional resonance analysis method (FRAM), to resolve holistic modeling of human-automation interaction. Therein, a novel semi-quantitative framework of FRAM based on Monte Carlo simulation is integrated and improved to facilitate traditional FRAM analysis. A case application of the methodology is presented to demonstrate the usefulness for unraveling human interactions with the DP system and enhancing operational safety. An integral FRAM model is established to investigate the performance variability of human and DP automation and their various manners of aggregation in the interactive context of tandem offloading. The results reveal critical functions, couplings, and interrelated resonant paths for systemic analysis of the emergence of tanker drive-off and collision scenarios. The FRAM analysis embraces Safety-II and resilience engineering perspective to devise more proactive safety strategies through managing variability and augment DP safety management.

Network-Based Multiple Operating Points Cooperative Dynamic Positioning of Unmanned Surface Vehicles

This article investigates the network-based multiple operating points cooperative dynamic positioning of multiple unmanned surface vehicles. First, a dynamic positioning system model is established for multiple unmanned surface vehicles. Second, a network-based multiple operating points cooperative dynamic positioning control protocol and a resultant system model for multiple unmanned surface vehicles are constructed under fixed topologies. Third, a networked multiple operating points cooperative dynamic positioning control scheme, which can guarantee the multiple operating points cooperative dynamic positioning error exponentially converge to a bounded region, is proposed. The dynamic positioning control scheme design is then extended to the case of switching topologies. Finally, the multiple operating points cooperative dynamic positioning performance analysis verifies the efficiency of the proposed control schemes.

Constrained control for a class of vessel operations: Positioning under environmental and shielding effects

This paper investigates Dynamic Positioning (DP) of an vessel next to a larger vessel subject to unknown wind and wave shielding effects in time-varying ocean environments. For safe operations, the vessels need to maintain a distance from each other which can be formulated as constrained control. Under certain conditions, the larger vessel shields the smaller vessel, and when the conditions change or due to the change in heading, the shielding reduces. For the DP system, in order to detect the shielding effect, and monitor the variation of environmental forcing on the vessel, an environment condition detector is designed based on low-frequency force learning and adaptive neural network. In the detector, estimates of wind drag coefficients are used to determine whether or not the shielding effect is present when upper thresholds are crossed. In this case, the neural network is activated in the detector and control when the small vessel moves out from the shadow of the large vessel. Prescribed performance control is proposed to meet the side-by-side safe constraint leveraging the H∞ approach to guarantee the vessel can keep its position against the exogenous disturbance. Numerical simulations demonstrate the effectiveness of the proposed design.

Discrete Wavelet Transform-based Approach of Real-time Wave Filtering for Dynamic Positioning of Marine Vessels

The ongoing development of deep-sea resources has contributed toward the widespread use of dynamic positioning (DP) systems that can operate in arbitrary sea areas without the limitation of operating water depth compared to mooring systems. The second-order slowly varying forces can be compensated by DP feedback control. Wave filtering techniques are crucial for designing the DP controller, which can improve the positioning performance and service of multiple actuators. The objective of wave filtering is to separate the motion induced by the first-order high-frequency oscillatory waves from the motion caused by the second-order low-frequency (LF) slowly varying disturbances. This paper proposes a novel real-time wave filtering approach for DP systems on the basis of the discrete wavelet transform without relying on the previous knowledge of dynamics of the vessel. Meanwhile, to suppress the end effects of wavelet filtering and achieve real-time application, symmetric boundary extension and the sliding window method are investigated in order to capture the slow time-varying LF motion of DP vessels. The proposed real-time wavelet filtering approach can significantly improve the quality of the separated components by selecting the optimal decomposition level, wavelet function parameters, and threshold denoising method. The real-time and filtering performance of the proposed approach is verified using a scaled model of an offshore supply vessel as well as full-scale experiments on the EXPLOERE I scientific investigation vessel under the action of winds, currents, and waves. The experimental results confirm that the proposed wave filtering algorithm is efficient and that the LF component waveform can be effectively recovered after wavelet filtering.

Dynamic modeling and analysis of a novel offshore gangway with 3UPU/UP-RRP series-parallel hybrid structure

It is inevitable that the 6-DOF motions of ships at sea will be induced by the marine environmental disturbances. Even though some ships are equipped with mooring or dynamic positioning systems, they still have three-dimensional motions including roll, pitch and heave, which not only reduces the efficiency of people and cargo transfer but also seriously threatens the safety of offshore transshipment. Most offshore gangways use six degrees of freedom Stewart parallel platform to compensate for these ship motions, which is a bit wasteful in both mechanical structure and power consumption. A novel 3UPU/UP-RRP series-parallel hybrid structure offshore gangway is designed in this paper. It is composed of a parallel platform of 3UPU/UP structure and a series transfer gangway of RRP structure. And a compensation scheme is proposed to compensate the roll and pitch motions of the ship with the parallel platform and the heave motion of the ship with the transfer gangway. The dynamic model of the offshore gangway is built by virtual working principle and Newton-Euler method. First, the velocity and acceleration of each component of the parallel platform are derived by vector method. Next, the dynamic model of the parallel platform is obtained by the principle of virtual work. Then, the dynamic model of the serial gangway is established by Newton-Euler method. After that, the accuracy of the dynamic mathematical model was verified by the simulation model. The power consumption of the proposed compensation method is compared with another common compensation method under sinusoidal motion excitation, and it is obtained that this compensation method has lower power consumption.

Constrained fault-tolerant thrust allocation of ship DP system based on a novel quantum-behaved squirrel search algorithm

The thrust allocation (TA) of ship dynamic positioning (DP) systems is to determine the desired thrust force and direction of each thruster of a ship such that all the thrusters jointly produce the generalized control forces commanded by DP controllers. Thruster faults inevitably occur because thrusters operate in the complex ocean environment for a long time. In addition, due to physical limitations of thrusters, the desired thrust force and direction of thrusters both have magnitude and rate constraints. In the presence of loss-of-effectiveness (LOE) faults as well as magnitude and rate constraints of thrusters of ships, the TA of their DP systems can be formulated as a constrained fault-tolerant optimization problem. This paper creates a novel quantum-behaved squirrel search algorithm (QSSA) by combining the squirrel search algorithm with a quantum Delta potential well model, and whereby solves this constrained fault-tolerant TA optimization problem. Simulation studies on a scale model supply ship verify the effectiveness of the QSSA-based constrained fault-tolerant TA of the DP ship under thruster LOE faults.

Failure mode effects and criticality analysis (FMECA) using fuzzy logic for ship dynamic positioning (DP) systems

Predicting the failure modes effect and criticality analysis (FMECA) of a dynamic positioning (DP) system using fuzzy logic is the aim of this research. The identification of DP systems and subsystems, the classification of failure modes into critical and less-critical levels based on the Risk Priority Number (RPN) to depict the main root causes of failure in the DP system are some critical objectives in support of this goal. The analysis offers details on a number of issues, including the causes of failure modes and their effects on the functionality and dependability of equipment. Based on the information provided, it was determined that a number of failure modes produced identical RPN values, and that the ranking scale was erroneous. A new method was tested but could not really prioritize the failure modes with same RPN because of the few choices in the severity, occurrence and detection template. To compensate for this, excel ranking function was employed putting severity, occurrence and detection as key criteria for ranking. Due to the high severity and occurrence index, the RPN ranking results show that the faulty DP system component identified for the scenario SSTs (F1) is categorized as very critical. SSCs (F12), SSPr (F7), SSTs(F2), and SSPs(F15) are additional critical failures. In the study, data analysis and validation were done using a fuzzy rule system based on MATLAB. From the findings, it can be inferred that the failure modes F1, F2, F5, F6, F7, F8, F10, F11, and F15 have values of a similar type of RPN. According to the initial RPN risk level results; there are 19 failure modes in the medium risk level, 2 in the low risk level and 1 in the high risk level. In the final RPN-based risk level results, there are 18 failure scenarios in the low risk level and 4 in the medium risk level. In contrast, there are 5 failure modes in the fuzzy RPN low risk level and 17 failure scenarios in the medium risk level. Without fuzzy logic, the justification score on traditional FMECA can be given directly. This makes traditional FMECA ABS show greater risk than fuzzy FMECA. The failure modes with the highest RPN values were treated as critical parts, so it was recommended that the highest value of RPN be given special attention by making the necessary repairs or replacements in order to lengthen the equipment's lifespan.