Qualification Method for Cut Resistant Jackets for Fiber Mooring Ropes

2021 ◽  
Author(s):  
Øystein Gabrielsen ◽  
Kjell Larsen ◽  
Svein Helge Gjøsund ◽  
Karl-Johan Reite ◽  
Kurt Eide ◽  
...  
Keyword(s):  
Contact Pressure ◽  
Mooring Line ◽  
Mooring System ◽  
Test Bed ◽  
Test Rig ◽  
Exclusion Zone ◽  
Fishing Activity ◽  
Norwegian Sea ◽  
Fishing Vessels ◽  
Abrasion Testing

Abstract The Aasta Hansteen spar platform in the Norwegian Sea has a polyester rope mooring system. The anchors and large parts of the polyester ropes are outside of the safety exclusion zone granted by the Norwegian authorities. Fishing vessels cannot be denied as long as they are outside of the safety zone, and the polyester mooring ropes need to withstand abrasion loads from the possible fishing activity. A fishing activity study in 2013 defined probability for fishing, size of possible fishing vessels and type of fishing equipment. Numerical simulations of the mooring system and crossing fishing trawl equipment made it possible to establish trawl abrasion load cases, including trawl wire lengths, speed and contact pressure. No jacket design or jacket material was at the time confirmed to withstand the established abrasion loads. The jacket solution to be chosen for the project thus needed to be specially developed, designed, tested and approved to give sufficient resistance against the established abrasion loads. Several vendors developed and offered different jacket solutions, and the selection of cut resistant jacket was dependent on adequate testing. Based on input and comments from Equinor and rope vendors, DNV constructed a test rig extension to their 2500T horizontal test bed, where the required length of trawl wire was pulled over the polyester rope with the needed contact pressure. Full-size (diameter) ropes with the proposed cut resistant jackets were tested, including break strength testing after the abrasion test. This paper presents how the possible trawl activity was defined, the numerical simulation of trawl/mooring line interaction, the test rig setup and some test results of the trawl wire abrasion testing.

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.

North Sea Mooring Systems: How Reliable Are They?

2014 ◽  
Author(s):  
Will Brindley ◽  
Andrew P. Comley
Keyword(s):  
Continental Shelf ◽  
North Sea ◽  
Recent Decade ◽  
Mooring Line ◽  
Mooring System ◽  
Failure Rates ◽  
Floating Structure ◽  
Strength Capacity ◽  
Failure Statistics ◽  
Overall Reliability

In recent years a number of high profile mooring failures have emphasised the high risk nature of this element of a floating structure. Semi-submersible Mobile Offshore Drilling Units (MODUs) operating in the harsh North Sea environment have experienced approximately 3 mooring failures every 2 years, based on an average population of 34 units. In recognition of the high mooring failure rates, the HSE has introduced recommendations for more stringent mooring strength requirements for units operating on the UK Continental Shelf (UKCS) [17]. Although strength requirements are useful to assess the suitability of a mooring design, they do not provide an insight into the question: what is the reliability of the mooring system? This paper aims to answer this question by evaluating failure statistics over the most recent decade of available data. Mooring failure rates are compared between the Norwegian Continental Shelf (NCS), the UKCS, and with industry code targets to understand how overall reliability is related to the strength capacity of a mooring system. The failure statistics suggest that a typical MODU operating in the UKCS would experience a mooring line failure in heavy weather approximately every 20 operating years. This failure rate appears to be several orders of magnitude greater than industry targets used to calibrate mooring codes. Despite the increased strength requirements for the NCS, failure rates do not appear to be lower than the UKCS. This suggests that reliability does not correlate well with mooring system strength. As a result, designing to meet the more rigorous HSE requirements, which would require extensive upgrades to existing units, may not significantly increase mooring system reliability. This conclusion needs to be supported with further investigation of failure statistics in both the UKCS and NCS. In general, work remains to find practical ways to further understand past failures and so improve overall reliability.

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.

scholarly journals Experimental studies on particle emissions from cruising ship, their characteristic properties, transformation and atmospheric lifetime in the marine boundary layer

2007 ◽  
Vol 7 (5) ◽  
pp. 15105-15154 ◽  
Author(s):  
A. Petzold ◽  
J. Hasselbach ◽  
P. Lauer ◽  
R. Baumann ◽  
K. Franke ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Particle Number ◽  
Marine Boundary Layer ◽  
Experimental Studies ◽  
Test Bed ◽  
Test Rig ◽  
Particle Emissions ◽  
Airborne Measurements ◽  
Emission Studies ◽  
Transformation Processes

Abstract. Particle emissions from ship engines and their atmospheric transformation in the marine boundary layer (MBL) were investigated in engine test bed studies and in airborne measurements of expanding ship plumes. During the test rig studies, detailed aerosol microphysical and chemical properties were measured in the exhaust gas of a serial MAN B{&amp;}W seven-cylinder four-stroke marine diesel engine under various load conditions. The emission studies were complemented by airborne aerosol transformation studies in the plume of a large container ship in the English Channel using the DLR aircraft Falcon 20 E-5. Observations from emission studies and plume studies combined with a Gaussian plume dispersion model yield a consistent picture of particle transformation processes from emission to atmospheric processing during plume expansion. Particulate matter emission indices obtained from plume measurements are 8.8±1.0×1015(kg fuel)−1 by number for non-volatile particles and 174±43 mg (kg fuel)−1 by mass for Black Carbon (BC). Values determined for test rig conditions between 85 and 110% engine load are of similar magnitude. For the total particle number including volatile compounds no emission index can be derived since the volatile aerosol fraction is subject to rapid transformation processes in the plume. Ship exhaust particles occur in the size range Dp<0.3 μm, showing a bi-modal structure. The combustion particle mode is centred at modal diameters of 0.05 μm for raw emissions to 0.10 μm at a plume age of 1 h. The smaller-sized volatile particle mode is centred at Dp≤0.02 μm. From the decay of ship exhaust particle number concentrations in an expanding plume, a maximum plume life time of approx. 24 h is estimated for a well-mixed marine boundary layer.

Sensitivity Analysis of Different Parameters of Taut Mooring System of a Truss Spar

2019 ◽  
Author(s):  
Zhuang Kang ◽  
Rui Chang ◽  
Youwei Kang ◽  
Shanchuan Liu
Keyword(s):  
Design Parameters ◽  
Mooring Line ◽  
Main Body ◽  
Mooring System ◽  
Spar Platform ◽  
Truss Spar Platform ◽  
Hole Position ◽  
Line Force ◽  
Truss Spar ◽  
Nonlinear Solutions

Abstract The taut mooring system is widely used for some advantages, such as smaller mooring radius, lighter total weight and better anti-corrosion performance. In this paper, the taut mooring system of a Truss Spar platform which was taken as the research object was investigated under the condition of 2000 m water depth in South China Sea. Firstly, the main body of the platform was analyzed in frequency domain based on the 3-d potential theory, and then the nonlinear solutions of platform displacement and mooring line force were obtained by using coupling analysis method in time domain, which determined the preliminary design parameters of mooring system. The sensitivity of the taut system is studied by changing several design parameters such as the top angle of mooring line, cable hole position and method of mooring disposal. In summary, the variation of the motion and dynamic response of the platform and mooring system has been explored and summarized by studying the design process and influential parameter of dynamic characteristics of mooring system and optimizing ideas of relevant parameters, which can further provide technical support and engineering reference for the design and application of the taut mooring system of deepwater Truss Spar platforms.

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.

A Review of Mooring Analysis Methodologies for Permanent Offshore Installations

2020 ◽  
Author(s):  
Spiro J. Pahos ◽  
Georgina Maldonado ◽  
Paul C. Westlake
Keyword(s):  
Time Domain ◽  
Line Strength ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Mooring Line ◽  
System Response ◽  
Mooring System ◽  
Deterministic Approach ◽  
Safety Factors ◽  
Analytical Approaches

Abstract Traditionally mooring line strength assessment is based on a deterministic approach, where the mooring system is evaluated for a design environment defined by a return period. The mooring system response is then checked against the mooring strength to ensure a required factor of safety. Some codes adopt a deterministic approach [1], [2], [3]. Other codes like [4] adopt a partial safety factor format where uncertainties are addressed through load factors for load components and material factors for line strength. Industry practices give guidance on mooring analysis methodology together with analysis options like coupled, de-coupled, time domain, frequency domain and the associated line tension safety factors. Prior work has demonstrated that discrepancies in mooring line tensions are observed when different analytical approaches are used [5]. Namely, the mooring line tensions of a semi-submersible unit in a coupled time domain analysis, were found to be non-compliant, whereas those calculated using a decoupled time domain analysis returned compliant tensions. This work focuses on a coupled dynamic analysis where all inertial, hydrodynamic and mechanical forces are assessed to determine the subsequent motions. Despite being considered the most accurate to capture the true dynamic response, a coupled analysis is also the least efficient in terms of the required computer resources and engineering effort [1]. This paper presents further discussion on the above observation in mooring tensions and also considers differences in the installation’s excursion. All responses are evaluated in the time domain where the nonlinear dynamic behavior of the mooring lines, slowly varying wave drift forces and coupling effects are captured. Agreement is found in the present computations, carried out with two renowned hydrodynamic codes, which validate former results and reiterate the need to distinguish between time domain methods and recommended appropriate safety factors accordingly.

Time-Domain Coupled Dynamic Analysis of Mooring Systems in Extreme Sea Condition

2018 ◽  
Author(s):  
Xuliang Han ◽  
ShiSheng Wang ◽  
Bin Xie ◽  
Wenhui Xie ◽  
Weiwei Zhou
Keyword(s):  
Dynamic Analysis ◽  
Body Surface ◽  
Time Domain ◽  
Mooring Line ◽  
Mooring System ◽  
Dynamic Coupling ◽  
Spar Platform ◽  
Coupled Dynamic Analysis ◽  
Motion Responses ◽  
The Time Domain

In order to predict the coupled motion and external wave load for the design of deepwater floating structure system, based on the three-dimensional time-domain potential flow theory, this paper present the indirect time-domain dynamic coupling method and the body nonlinear dynamic coupling method. The perturbation expansion theory is adopted to evaluate hydrodynamic on the fixed mean wetted body surface for the former method. The transient free surface Green function has been extended and applied to calculate the nonlinear hydrodynamic on the instantaneous wetted exact body surface for the latter method. The finite element model is employed to solve dynamic response of mooring line. Then asynchronous coupled method is adopted to achieve the coupled dynamic analysis of platform and mooring lines. The time-domain motion responses and spectrum analysis of Spar platform are verified and compared with the traditional indirect time-domain coupling dynamic method when the mooring system is completed. Also the time-domain motion responses and statistical characteristic of Spar platform are investigated with one mooring line broken in extreme sea condition. Some conclusions are obtained, that is, dynamic coupling effects are significant and transient position hydrodynamic calculation of platform has a great influence on the low frequency motion. The results also show that the influence on the global performance of mooring system is different when the broken line is in different place. A remarkable influence occurs when the broken mooring line is in the head-wave direction.

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