Dropped Polyester Mooring Line Qualification for Reuse

2021 ◽  
Author(s):  
Craig R Gage ◽  
Pierre F Liagre ◽  
Caspar N Heyl ◽  
Cesar Del Vecchio
Keyword(s):  
Gulf Of Mexico ◽  
Water Depth ◽  
Cost Savings ◽  
Mooring Line ◽  
Mooring System ◽  
Potential Cost ◽  
Mooring Lines ◽  
Minimal Damage ◽  
Recovery Effort ◽  
The Impact

The Perdido platform is a spar located in a water depth of 7,825 feet in the Alaminos Canyon Block 857in the Gulf of Mexico. The mooring system consists of nine mooring lines in three groups of three, spacedapproximately 120 degrees apart between each group. Each mooring line is composed of a platform chain,a multi-segment polyester rope including a 120 feet long test insert at the top, a ground chain, a pile chainand other associated connectors. The mooring lines are connected to suction piles. The Minimum BreakStrength for the Perdido polyester mooring line is 4,000 kips. Installation of the spar hull was completed inSeptember 2008 and the topsides was set in March 2009. The spar and its mooring system were originallydesigned for a twenty (20) year life. On May 4, 2019, mooring line # 6 (ML6) was contacted by a marine vessel down line and was severed.Contact occurred along the polyester test insert. A recovery effort was planned, and the mooring line wasreplaced in early June. The original ML6 was recovered from the seafloor on June 4, 2019 as a part of thatcampaign and submitted to an initial inspection. This paper is not intended to go into either the cause of the incident or the replacement of ML6 but willlook to the inspection of the recovered mooring line and explore its suitability for reuse. Initial inspection ofthe lines suggested minimal damage to the polyester rope segments and raised questions to the impacts of 10years of use. Testing was envisioned as a learning opportunity for the impact of service on polyester mooringand was reinforced by the potential cost savings that could be attained though reuse. A methodology wasdeveloped, supported by initial inspections and a suite of testing was performed. The results of these testsare presented in the following, along with a proposed process for assessing and considering reuse of a linefollowing a drop. Additionally, conclusions will be shared for the process, the results, and the potentialramifications for the industry.

Experimental and Numerical Study on Large Truncation of Deepwater Mooring Line

2009 ◽  
Author(s):  
Yihua Su ◽  
Jianmin Yang ◽  
Longfei Xiao ◽  
Gang Chen
Keyword(s):  
Dynamic Response ◽  
Water Depth ◽  
Numerical Study ◽  
Unit Length ◽  
Low Frequency ◽  
Model Tests ◽  
Mooring Line ◽  
Mooring System ◽  
Mooring Lines ◽  
Wave Basin

Modeling the deepwater mooring system in present available basin using standard Froude scaling at an acceptable scale presents new challenges. A prospective method is to truncate the full-depth mooring lines and find an equivalent truncated mooring system that can reproduce both static and dynamic response of the full-depth mooring system, but large truncation arise if the water depth where the deepwater platform located is very deep or the available water depth of the basin is shallow. A Cell-Truss Spar operated in 1500m water depth is calibrated in a wave basin with 4m water depth. Large truncation arises even though a small model scale 1:100 is chosen. A series of truncated mooring lines are designed and investigated through numerical simulations, single line model tests and coupled wave basin model tests. It is found that dynamic response of the truncated mooring line can be enlarged by using larger diameter and mass per unit length in air. Although the truncated mooring line with clump presents a “taut” shape, its dynamic characteristics is dominated by the geometry stiffness and it underestimates dynamic response of the full-depth mooring line, even induces high-frequency dynamic response. There are still two obstacles in realizing dynamic similarity for the largely truncated mooring system: lower mean value of the top tension of upstream mooring lines, and smaller low-frequency mooring-induced damping.

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.

Qualification and Certification of Polyester Rope for Seabed Contact

2017 ◽  
Author(s):  
Øystein Gabrielsen ◽  
Kjell Larsen
Keyword(s):  
Water Flow ◽  
Water Depth ◽  
Test Method ◽  
Mooring System ◽  
Qualification Test ◽  
Mooring Lines ◽  
Norwegian Sea ◽  
Flow Through ◽  
Full Scale Tests ◽  
Certification Requirements

The Aasta Hansteen spar in the Norwegian Sea is designed to be moored with a taut polyester rope mooring system. The water depth at the field is 1300 meters, and due to the short installation season the most efficient hookup is with pre-installed mooring lines, which require the mooring lines to be laid down on the seabed. DNV certification does not allow seabed contact for polyester ropes unless proven that no soil ingress and damage takes place. To be able to certify the ropes Statoil developed a test method including contact with soil, rope movement and forced water flow through the filter construction. Full scale tests were performed with actual rope and Aasta Hansteen soil, both in laboratory and at site. This paper discusses the certification requirements and presents adequate qualification test together with results from testing.

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.

Lightweight Materials for Mooring Lines of Deepwater Tension Leg Platforms

1984 ◽  
Vol 21 (03) ◽  
pp. 234-241
Author(s):  
Mamdouh M. Salama
Keyword(s):  
Carbon Fiber ◽  
Water Depth ◽  
Hybrid Composites ◽  
Medium Size ◽  
Mooring System ◽  
Basic Design ◽  
High Modulus ◽  
Mooring Lines ◽  
Lightweight Materials ◽  
Design Requirements

The design of a mooring system for tension leg platforms (TLPs) becomes more complicated as water depth increases. The use of steel mooring lines requires complicated tensioning, handling, and flotation systems. This paper discusses the basic design requirements for the TLP mooring system and identifies several advanced fiber-reinforced lightweight materials as alternatives to steel. High-modulus carbon fiber/KevlarcircleR fiber hybrid composites and Kevlar ropes appear to offer the optimum mooring systems for TLPs used in the development of large and medium-size reservoirs, respectively.

scholarly journals Mixed methods evaluation of a hospital group model using an embedded research approach: study protocol

BMJ Open ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. e027086
Author(s):  
Cecilia Vindrola-Padros ◽  
Estela Capelas Barbosa ◽  
Angus I G Ramsay ◽  
Simon Turner ◽  
Stephen Morris ◽  
...  
Keyword(s):  
Mixed Methods ◽  
Study Protocol ◽  
Cost Savings ◽  
Ethics Committee ◽  
Research Approach ◽  
Group Model ◽  
Potential Cost ◽  
Mixed Methods Evaluation ◽  
The Impact ◽  
Hospital Group

IntroductionHospital group models represent an organisational form that aims to bring together multiple provider organisations with a central headquarters and unified leadership responsible for locally managed operating units, standardised systems and a value-set shared across the group. These models seek to improve outcomes by reducing unwarranted variations in care provision and reducing costs through economies of scale. There is limited evidence on the impact and processes of implementing these models, so this study aims to evaluate one case study of a hospital group model.Methods and analysisWe will conduct a formative, mixed-methods evaluation using an embedded research approach to analyse the implementation of the model and its impact on outcomes and costs. We will carry out a multisited ethnography to analyse the programme theory for model design and implementation, the barriers and facilitators in the implementation; and wider contextual issues that influence implementation using semi-structured interviews (n=80), non-participant observations (n=80 hours), ‘shadowing’ (n=20 hours) and documentary analysis. We will also carry out an economic evaluation composed of a cost-consequence analysis and a return on investment analysis to evaluate the costs of creating and running the model and balance these against the potential cost-savings.Ethics and disseminationThe study protocol was reviewed by the local R&D Office and University College London Ethics Committee and classified as a service evaluation, not requiring approval by a research ethics committee. We will follow guidelines for informed consent, confidentiality and information governance, and address issues of critical distance prevalent in embedded research. Findings will be shared at regular time points to inform the implementation of the model. The evaluation will also generate: an evaluation framework to evaluate future changes; recommendations for meaningful baseline data and measuring improvement; identification of implementation costs and potential cost-savings; and lessons for the National Health Service on implementing these models.

Parametric Study of Catenary Mooring System for a Semisubmersible Floating Wind Turbine in Intermediate Water Depth

2020 ◽  
Author(s):  
Jiawen Li ◽  
Qiang Zhang ◽  
Jiali Du ◽  
Yichen Jiang
Keyword(s):  
Wind Turbine ◽  
Water Depth ◽  
Offshore Wind ◽  
Design Parameters ◽  
Mooring Line ◽  
Offshore Wind Turbine ◽  
Reference Structure ◽  
Intermediate Water ◽  
Mooring System ◽  
Floating Wind Turbine

Abstract This paper presents a parametric design study of the mooring system for a floating offshore wind turbine. We selected the OC4 DeepCwind semisubmersible floating wind turbine as the reference structure. The design water depth was 50 m, which was the transition area between the shallow and deep waters. For the floating wind turbine working in this water area, the restoring forces and moments provided by the mooring lines were significantly affected by the heave motion amplitude of the platform. Thus, the mooring design for the wind turbine in this working depth was different from the deep-water catenary mooring system. In this study, the chosen design parameters were declination angle, fairlead position, mooring line length, environmental load direction, and mooring line number. We conducted fully coupled aero-hydro dynamic simulations of the floating wind turbine system in the time domain to investigate the influences of different mooring configurations on the platform motion and the mooring tension. We evaluated both survival and accidental conditions to analyze the mooring safety under typhoon and mooring fail conditions. On the basis of the simulation results, this study made several design recommendations for the mooring configuration for floating wind turbines in intermediate water depth applied in China.

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.

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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