FPSO Mooring Line Failure Detection Based on Predicted Motion

2021 ◽  
Author(s):  
Amir Muhammed Saad ◽  
Florian Schopp ◽  
Asdrubal N. Queiroz Filho ◽  
Rodrigo Da Silva Cunha ◽  
Ismael H. F. Santos ◽  
...  
Keyword(s):  
Detection System ◽  
Failure Detection ◽  
Mooring Line ◽  
Mooring System ◽  
System Failure ◽  
Temporal Data ◽  
Mooring Lines ◽  
Integrity Management ◽  
The Difference ◽  
Floating Platforms

Abstract A failure in the mooring line of a platform, if not detected quickly, can cause a riser system failure, extended production downtime, or even environmental damages. Therefore, integrity management and timely detection of mooring failure for floating platforms are critical. In this paper, we propose a new model for an ANN-based mooring failure detection system. The proposal’s idea is to train a Multilayer Perceptron (MLP) to estimate the platform’s future motion based on its motion’s temporal data without failure. A classifier then indicates whether or not there is a failure in the mooring system based on the difference between the predicted and the measured motion. The results with several tests of the implemented system show that our proposal can correctly predict the motion of the platform in most environmental conditions. The system shows a precision, accuracy and F1-score of 99.88%, 99.99% and 99.94%, respectively, for detecting changes in platform motion in near real-time, quickly signaling a possible breakage of mooring lines.

Sensitivity of Mooring Line Pretension in the Design Cycle for Floating Caissons

2004 ◽  
Author(s):  
Adinarayana Mukkamala ◽  
Partha Chakrabarti ◽  
Subrata K. Chakrabarti
Keyword(s):  
Reinforced Concrete ◽  
System Design ◽  
Mooring Line ◽  
Mooring System ◽  
Mooring Lines ◽  
Design Cycle ◽  
Overall Performance ◽  
The Difference ◽  
Tacoma Narrows Bridge ◽  
System Layout

The new parallel Tacoma Narrows Bridge being constructed by Tacoma Narrows Constructors will be mounted on two towers and these towers in turn will be supported by reinforced concrete caissons referred to as East Caisson (Tacoma side) and West Caisson (Gig Harbor side). Each Caisson is towed to the location and several stages of construction will take place at the actual site. During construction, the floating caissons will be moored in place to hold it against the flood and ebb currents in the Narrows. During the mooring system design, a desired pretension is established for the lines at each draft. However, due to practical limitations in the field some variations to this design pretension value may be expected. It is important to study the effect of this variation on the overall performance of the mooring system. In this paper, the sensitivity of the mooring line pretension on the overall performance of the mooring system for the above caisson is presented. During this study, all the variables that affect the mooring system design such as mooring system layout, mooring line makeup, anchor positions, fairlead departure angles, and fairlead locations are kept constant. The only variable changed is the pretension of the mooring lines. Two approaches for defining the variations in the pretension have been studied in this paper. In the first approach, the pretension is changed in a systematic way (predicted approach). In the second method the pretension is changed randomly. The latter is considered more likely to occur in the field for this type of complex mooring system. Both sets of results are presented for some selected drafts attained by the caisson during its construction. The difference in the results from the two methods is discussed.

Behaviour of Mooring Systems for Different Line Pretensions

2014 ◽  
Vol 567 ◽  
pp. 204-209 ◽  
Author(s):  
Montasir Osman Ahmed ◽  
Anurag Yenduri ◽  
V. John Kurian
Keyword(s):  
Experimental Tests ◽  
Mooring Line ◽  
Mooring System ◽  
Preliminary Design ◽  
Mooring Lines ◽  
Matlab Code ◽  
Heading Direction ◽  
Restoring Forces ◽  
Static Approach ◽  
Floating Platforms

Mooring lines are the most commonly used station-keeping systems for floating platforms as they are easy to install and relocate. The mooring lines are usually pre-tensioned so as to use their energy absorption to reduce the platform motions and thereby, to lower the forces in the lines. To decide on the preliminary design of the platforms, it is necessary to investigate the restoring behaviour of the mooring systems for various parameters. In this study, two different mooring configurations with and without mooring line in wave heading direction are considered for determining its behaviour for various pretensions in the lines. A MATLAB code named QSAML has been developed using quasi-static approach to compute the restoring forces of the mooring system. The code is validated with experimental tests and used in this study. It has been observed that with increase in pretension of the mooring line, restoring performance of the mooring system can be improved. The maximum permissible excursions by mooring system in the wave heading direction are found to be more for relatively lower pretension values.

FPSO Mooring Line Integrity Supervising System Based on Motion Data and Natural Frequency Estimation

2021 ◽  
Author(s):  
José Lucas De Melo Costa ◽  
Asdrubal N. Queiroz Filho ◽  
Ismael H. F. Santos ◽  
Rodrigo Augusto Barreira ◽  
Anna Helena Reali Costa ◽  
...  
Keyword(s):  
Frequency Estimation ◽  
Longitudinal Axis ◽  
Mooring Line ◽  
Mooring System ◽  
Mooring Lines ◽  
Natural Period ◽  
Motion Data ◽  
Initial Hypothesis ◽  
The Difference ◽  
Property Losses

Abstract Offshore production facilities play a central role in the oil industry given the growing demand for energy resources. The mooring system of these floating structures is a critical component for safety maintenance. The timely identification of mooring lines failures can prevent environmental pollution, property losses and further system failures. In this paper we propose a system to detect and classify failures of the mooring lines based on the natural period in the longitudinal axis and in the lateral axis of the long drift oscillatory motion of the platform. The proposal starts from the hypothesis that when a line break occurs, the natural period of oscillation of the platform is increased, and this difference may indicate the malfunction of the mooring system. The proof of concept developed for the proposed system demonstrates the potential of using the natural period to detect failures in mooring lines for floating vessels, validating the initial hypothesis that the difference in a natural period appears when a line breaks and that this difference may detect line break.

scholarly journals Transient Responses Evaluation of FPSO with Different Failure Scenarios of Mooring Lines

2021 ◽  
Vol 9 (2) ◽  
pp. 103
Author(s):  
Dongsheng Qiao ◽  
Binbin Li ◽  
Jun Yan ◽  
Yu Qin ◽  
Haizhi Liang ◽  
...  
Keyword(s):  
Service Condition ◽  
Mooring Line ◽  
Mooring System ◽  
Transient Effects ◽  
Floating Platform ◽  
Transient Responses ◽  
Mooring Lines ◽  
Performance Deterioration ◽  
Steady State Responses ◽  
Influence Process

During the long-term service condition, the mooring line of the deep-water floating platform may fail due to various reasons, such as overloading caused by an accidental condition or performance deterioration. Therefore, the safety performance under the transient responses process should be evaluated in advance, during the design phase. A series of time-domain numerical simulations for evaluating the performance changes of a Floating Production Storage and Offloading (FPSO) with different broken modes of mooring lines was carried out. The broken conditions include the single mooring line or two mooring lines failure under ipsilateral, opposite, and adjacent sides. The resulting transient and following steady-state responses of the vessel and the mooring line tensions were analyzed, and the corresponding influence mechanism was investigated. The accidental failure of a single or two mooring lines changes the watch circle of the vessel and the tension redistribution of the remaining mooring lines. The results indicated that the failure of mooring lines mainly influences the responses of sway, surge, and yaw, and the change rule is closely related to the stiffness and symmetry of the mooring system. The simulation results could give a profound understanding of the transient-effects influence process of mooring line failure, and the suggestions are given to account for the transient effects in the design of the mooring system.

Validation of Mooring Simulations (for Mooring Integrity Assessment) With In-Service Tension Measurements

2021 ◽  
Author(s):  
Willemijn Pauw ◽  
Remco Hageman ◽  
Joris van den Berg ◽  
Pieter Aalberts ◽  
Hironori Yamaji ◽  
...  
Keyword(s):  
Numerical Models ◽  
Weather Conditions ◽  
Mooring Line ◽  
Mooring System ◽  
Mooring Lines ◽  
Data Set ◽  
Integrity Assessment ◽  
Motion Data ◽  
Load Cells ◽  
Line Loads

Abstract Integrity of mooring system is of high importance in the offshore industry. In-service assessment of loads in the mooring lines is however very challenging. Direct monitoring of mooring line loads through load cells or inclinometers requires subsea installation work and continuous data transmission. Other solutions based on GPS and motion monitoring have been presented as solutions to overcome these limitations [1]. Monitoring solutions based on GPS and motion data provide good practical benefits, because monitoring can be conducted from accessible area. The procedure relies on accurate numerical models to model the relation between global motions and response of the mooring system. In this paper, validation of this monitoring approach for a single unit will be presented. The unit under consideration is a turret-moored unit operating in Australia. In-service measurements of motions, GPS and line tensions are available. A numerical time-domain model of the mooring system was created. This model was used to simulate mooring line tensions due to measured FPSO motions. Using the measured unit response avoids the uncertainty resulting from a prediction of the hydrodynamic response. Measurements from load cells in various mooring lines are available. These measurements were compared against the results obtained from the simulations for validation of the approach. Three different periods, comprising a total of five weeks of data, were examined in more detail. Two periods are mild weather conditions with different dominant wave directions. The third period features heavy weather conditions. In this paper, the data set and numerical model are presented. A comparison between the measured and numerically calculated mooring line forces will be presented. Differences between the calculated and measured forces are examined. This validation study has shown that in-service monitoring of mooring line loads through GPS and motion data provides a new opportunity for mooring integrity assessment with reduced monitoring system complexity.

Research on the Arrangement of the Mooring Lines of the Thruster Assisted Mooring System

2013 ◽  
Author(s):  
Gang Zou ◽  
Lei Wang ◽  
Feng Zhang
Keyword(s):  
Mooring Line ◽  
Mooring System ◽  
Main Function ◽  
Time Domain Simulation ◽  
Mooring Lines ◽  
Dynamic Positioning System ◽  
Optimum Arrangement ◽  
Line Angle ◽  
Mooring Forces ◽  
Offshore Industry

As the offshore industry is developing into deeper and deeper water, station keeping technics are becoming more and more important to the industry. Based on the dynamic positioning system, the thruster assisted mooring system (TAMS) is developed, which consisted of mooring lines and thrusters. The main function of the TAMS is to hold a structure against wind wave and current loads with its thruster and cables, which is mainly evaluated by the holding capacity of the system. The arrangement of the mooring lines (location of anchor or the mooring line angle relative to platform) will directly affect the TAMS holding capacity because of the influence of the directions of the mooring forces. So finding out an optimum arrangement of the mooring lines is essential since the performance of the TAMS depends greatly on the arrangement of the mooring lines. The TAMS of a semi-submersible platform, which is studied in this paper, consisted of eight mooring lines. By fixing the layout of the thrusters and changing the location of each mooring line for every case, the performances of the TAMS are analyzed. The platform motions, mooring line tensions and power consumptions are compared to obtain the optimum arrangement of mooring lines, and thus a thruster assisted mooring system with a better performance can be achieved. Time domain simulation is carried out in this paper to obtain the results.

A Concept for Floating Offshore Wind Mooring System Integrity Management Based on Monitoring, Digital Twin and Control Technologies

2021 ◽  
Author(s):  
Alberto Puras Trueba ◽  
Jonathan Fernández ◽  
Carlos A. Garrido-Mendoza ◽  
Alessandro La Grotta ◽  
Jon Basurko ◽  
...  
Keyword(s):  
Control Strategies ◽  
Offshore Wind ◽  
Motion Sensor ◽  
Mooring System ◽  
Mooring Lines ◽  
Efficient Operation ◽  
Digital Twin ◽  
System Integrity ◽  
Integrity Management ◽  
And Control

Abstract Efficient operation of mooring systems is of paramount importance to reduce floating offshore wind (FOW) energy costs. MooringSense is an R&D project which explores digitization to enable the implementation of more efficient integrity management strategies (IMS) for FOW mooring systems. In this work, the MooringSense concept is presented. It includes the development of several enablers such as a mooring system digital twin, a smart motion sensor, a structural health monitoring (SHM) system and control strategies at the individual turbine and farm levels. The core of the digital twin (DT) is a high-fidelity fully coupled numerical model which integrates simulation tools to allow predictive operation and maintenance (O&M). Relevant parameters of the coupled model are updated as physical properties evolve due to damages or degradation. The DT assimilates information coming from the physical asset and environmental sensors. Besides, a smart motion sensor provides feedback of the attitude, position, and velocity of the floater to allow the computation of virtual loads in the mooring lines, the detection of damages by the SHM system and the implementation of closed-loop control strategies. Finally, the IMS takes advantage of the mooring system updated condition information to optimize O&M, reduce costs and increase energy production.

Experimental Study on the Effects of Mooring System on Air Gap Response of Semi-Submersible Platform

2020 ◽  
Author(s):  
Xu Li ◽  
Longfei Xiao ◽  
Handi Wei ◽  
Mingyue Liu
Keyword(s):  
Model Tests ◽  
Air Gap ◽  
Mooring System ◽  
Complex Task ◽  
Ocean Engineering ◽  
Free Surface Elevation ◽  
Mooring Lines ◽  
Scaled Model ◽  
Air Gap Responses ◽  
Floating Platforms

Abstract The air gap response is crucial for the safe design and operation of large-volume floating platforms such as semi-submersible and tension leg platforms. It is a complex task to perform numerical simulation on the air gap response considering the wave free surface elevation and the motions of the floating vessel. Therefore, the prediction of air gap response still relies heavily on model tests. This paper attempts to investigate the effects of the mooring system, especially the effects of the length of mooring lines, on the air gap response of semi-submersible platform based on model tests results. The scaled model of the semi-submersible platform is supported by a symmetric mooring system composed of 8 mooring lines. A set of model tests with different length of mooring lines was performed in the State Key Laboratory of Ocean Engineering basin at Shanghai Jiao Tong University, and the air gap responses of 15 locations were measured using wave probes. The results indicate that the mooring system plays an important role in the air gap response of semi-submersible platform.

The Dynamic Motion of the OC4 Floating Turbine with Different Incident Wave and Wind Directions in a Mooring System Failure Condition in Numerical Model

2020 ◽  
Author(s):  
Tzu-Ching Chuang ◽  
Wen-Hsuan Yang ◽  
Yi-Hong Chen ◽  
Ray-Yeng Yang
Keyword(s):  
Steady State ◽  
Line Tension ◽  
Time Domain Analysis ◽  
Mooring Line ◽  
Second Phase ◽  
Mooring System ◽  
System Failure ◽  
Floating Platform ◽  
Initial Tension ◽  
Wave Condition

<p><span>In this paper, the commercial software Orcaflex is used to simulate the motion behavior of the OC4 floating platform, and the floater stability and mooring line tension after the mooring system failure. In the time domain analysis, the discussion is divided into three phases—the first phase (before the tether failure), the second phase (before the tether failure, before reaching the new steady-state), and the third phase (after reaching the new steady-state). The motion characteristics and tension values at different stages were observed. In this study, only a 50-year return period wave condition is used as an input condition and simulating 11 different incident wind and wave directions. The numerical results are presented in the trajectory map and the table. About the tension of the mooring line, after the mooring system fails, it is notable that the mooring line tension will first decrease and then increase slightly above the initial tension value. In other words, the mooring system may survive after the failure of one mooring line and got a new balance of it. However, the tension amplitude will be higher than the first stage in the new balance and it will likely increase the risk of mooring line fatigue.</span></p>

Contribution of the Mooring System to the Low-Frequency Motions of a Semisubmersible in Combined Wave and Current

2009 ◽  
Author(s):  
Amany M. A. Hassan ◽  
Martin J. Downie ◽  
Atilla Incecik ◽  
R. Baarholm ◽  
P. A. Berthelsen ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Damping Ratio ◽  
Low Frequency ◽  
Scale Model ◽  
Mooring Line ◽  
Mooring System ◽  
Current Field ◽  
Mooring Lines ◽  
Mean Values ◽  
Low Frequency Motion

This paper presents the results of an experiment carried out on a semi-submersible model to measure the steady drift force and low frequency surge motions. In the experiments, the influence of mooring systems was also investigated in different combinations of current and sea state. The measurements were carried out with a 1/50 scale model which was moored using horizontal springs and catenary mooring lines. A comparative study of the mean values of steady drift motions and the standard deviation of the low frequency motion amplitudes is presented. In addition, the effect of current on the damping ratio is discussed. It is found that for both horizontal and catenary moorings, the presence of a current increases the damping ratio of the system. For the catenary mooring system, as expected, the presence of mooring lines and their interaction with waves and current increases the damping compared to the damping of the horizontal mooring system. The measured mean values of the surge motions in a wave–current field are compared to the superposed values of those obtained from waves and current separately. For the horizontal mooring, it is found that there is good agreement in moderate sea states, while in higher sea states the measured motion responses are larger. In the wave-current field, the standard deviation of the surge motion amplitudes is found to be less than that obtained in waves alone. This can be explained by the increased magnitude of the damping ratio. Only in the cases of high sea states with the horizontal mooring system, was it found that the standard deviation of the surge motions is slightly larger than those obtained for waves and current separately. This may be explained by the absence of catenary mooring line damping.

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