Fibre Rope Moorings for Shallow Waters

2002 ◽  
Author(s):  
Arne Ulrik Bindingsbo̸
Keyword(s):  
Breaking Strength ◽  
Research Work ◽  
Mooring Line ◽  
Shallow Waters ◽  
Mooring Lines ◽  
Deep Waters ◽  
Significant Research ◽  
Small Footprint ◽  
Drilling Rigs ◽  
Water Depths

During the last decade significant research has been carried out related to use of fiber ropes as moorings lines for offshore vessels. Most of this research work has been related to use in deep waters as taut mooring systems. The advantages of using fiber ropes include better station keeping, reduced vertical load on vessel, small footprint on seabed compared with conventional chain/wire systems. Due to very congested seabed at some drilling locations Norsk Hydro decided to use polyester fiber rope inserts for crossing of pipelines instead of wire segments and uplift buoys. Fiber rope inserts were used at seven drilling locations in water depths ranging from less than 100 m to 330 m. The mobile drilling units were Scarabeo 6 and Transocean Arctic. Two to four mooring lines had polyester inserts with lengths of approximately 800 m. The corresponding breaking strength was 1000 tons. With the use of modern anchor handling vessels (AHT) there was no rig time lost using the fiber inserts. No modifications were done to any of the AHTs. The crews were briefed onboard the AHTS and no problems occurred during installations. The only precautions taken was to clean the AHTS deck before spooling/unspooling the polyester rope. In addition two 5–7 ton spring buoys were used on each mooring line to avoid seabed contact with the rope. The ropes were inspected by DNV before installation. Our experience was only positive and fiber ropes inserts are now considered a proven tool for mooring of drilling rigs in congested seabed areas.

Experiences From Handling Mooring Line Polyester Fibre Ropes During Installation and Retrieval

2002 ◽  
Author(s):  
Lars Hilmersen
Keyword(s):  
Polyester Fibre ◽  
Mooring Line ◽  
Test Program ◽  
Mooring Lines ◽  
Bottom Part ◽  
Load Bearing ◽  
Hands On ◽  
Large Fibre ◽  
Offshore Industry ◽  
Water Depths

The use of fibre ropes made by synthetic fibres have been used more frequent as the offshore industry is moving towards larger water depths. An important aspect is the effect of handling on the large, but delicate, ropes during installation offshore using tools and equipment that easily can destroy the load bearing capacities of the ropes. In order to get hands on experience in the field large polyester ropes have been used as inserts in catenary mooring lines for Mobile Offshore Units (MODU) working on depths ranging from 80 to 350 meters. The ropes have been integrated in the catenary chain mooring lines both in the suspended part and in the bottom part of the mooring leg thus having been exposed to seafloor clay. Subsea buoy have been attached to the ropes using smaller size fibre ropes in order to lift the mooring lines from the seafloor. The paper will detail how the large fibre ropes have been mobilised and demobilised repeatedly from/to storage drums to/from the installation vessel winch drum. During installation and retrieval the fibre ropes have been installed from the vessels winch drum using regular anchor handling equipment and vessels. When the MODU has been moved between locations some ropes have been retrieved to the vessels winch drums while the others have been used to tow and to keep the units station. Samples of the used ropes are taken and is subjected to a test program in the laboratory in order to document the effect of extensive use and handling and exposure to seabed clay.

scholarly journals Effect of Water Depths on the Hydrodynamic Responses of an FPSO Platform

2018 ◽  
Vol 203 ◽  
pp. 01022
Author(s):  
Matthew Guan ◽  
Montasir Osman Ahmed Ali ◽  
Cheng Yee Ng
Keyword(s):  
Oil And Gas ◽  
Response Spectrum ◽  
Low Frequency ◽  
Mooring Line ◽  
Random Wave ◽  
Statistical Parameters ◽  
Mooring Lines ◽  
Line System ◽  
Wave Condition ◽  
Water Depths

Ship-shaped Floating Production Storage Offloading platforms (FPSO) are commonly used in the production of oil and gas in offshore deepwater regions. The vessel is held in place by mooring lines anchored to the seabed during operation, either in spread or turret mooring arrangement. When designing such systems, water depth is a main factor that needs to be considered. At greater depths, the hydrodynamic properties of mooring lines become important and may not be accurately predicted through traditional experiments or numerical quasi-static models. Numerical simulation using coupled dynamic analysis is thus recommended, as the hull-mooring behaviour is analysed simultaneously, and the damping and added mass properties of the entire mooring line system is taken into account. This paper investigates the motions and mooring line tensions of a turret-moored FPSO at various water depths ranging from 1000 m to 2000 m. The analysis focuses on numerical simulations in the fully coupled dynamic time domain. The study utilizes the commercial software AQWA, with the FPSO model subjected to a unidirectional random wave condition. The hull hydrodynamics is first solved using the 3D radiation/diffraction panel method, and the hull response equation is then coupled with the mooring line equation. The dynamic motions and mooring line tensions results are presented in terms of statistical parameters as well as response spectrum. The results highlight the significance of greater water depths on low frequency responses in surge motions and mooring line tensions, and provides insight on the increasing and decreasing trend of these responses.

A Reliability-Based Comparative Study for Mooring Lines Design Criteria

2006 ◽  
Author(s):  
Alberto Omar Vazquez-Hernandez ◽  
Gilberto Bruno Ellwanger ◽  
Lui´s Volnei Sudati Sagrilo
Keyword(s):  
Return Period ◽  
Design Procedure ◽  
Mooring Line ◽  
Design Criteria ◽  
Mooring Lines ◽  
Load Effect ◽  
Extreme Response ◽  
Line Design ◽  
Water Depths

The characteristic load effect for the design of mooring systems can be defined by means of three procedures: 1) an extreme sea state with a given return period, 2) a set of sea states on a contour line associated to a return period or 3) extreme response (tension) statistics for a long-term period. This work presents the result of a reliability-based partial safety factor calibration study for a LRFD mooring line design criteria considering the three approaches mentioned above. The calibration exercise is applied to three FPSOs considering North Sea environmental conditions and different water depths: 200m, 800m and 3000m. The mooring systems investigated take into account lines made up of chains and polyester ropes. It is shown that the design procedure based on the long-term response, among all water depths investigated, is the one that presents less scattered reliability indices around the target level.

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.

Experimental Investigation vs Numerical Simulation of the Dynamic Response of a Moored Floating Structure to Waves

2014 ◽  
Author(s):  
Daniele Dessi ◽  
Sara Siniscalchi Minna
Keyword(s):  
Dynamical Behavior ◽  
Irregular Waves ◽  
Mooring Line ◽  
Floating Structure ◽  
Mooring Lines ◽  
Wave Energy Converters ◽  
Time Histories ◽  
Actual Configuration ◽  
Proper Orthogonal ◽  
Dynamic Wave

A combined numerical/theoretical investigation of a moored floating structure response to incoming waves is presented. The floating structure consists of three bodies, equipped with fenders, joined by elastic cables. The system is also moored to the seabed with eight mooring lines. This corresponds to an actual configuration of a floating structure used as a multipurpose platform for hosting wind-turbines, aquaculture farms or wave-energy converters. The dynamic wave response is investigated with numerical simulations in regular and irregular waves, showing a good agreement with experiments in terms of time histories of pitch, heave and surge motions as well as of the mooring line forces. To highlight the dynamical behavior of this complex configuration, the proper orthogonal decomposition is used for extracting the principal modes by which the moored structure oscillates in waves giving further insights about the way waves excites the structure.

Optimized Mooring Line Simulation Using a Hybrid Method Time Domain Scheme

2014 ◽  
Author(s):  
Niels Hørbye Christiansen ◽  
Per Erlend Torbergsen Voie ◽  
Jan Høgsberg ◽  
Nils Sødahl
Keyword(s):  
Hybrid Method ◽  
Time Domain ◽  
Computation Time ◽  
Mooring Line ◽  
Mooring Lines ◽  
Fem Model ◽  
Input Variables ◽  
The Time Domain ◽  
The Cost ◽  
Short Time

Dynamic analyses of slender marine structures are computationally expensive. Recently it has been shown how a hybrid method which combines FEM models and artificial neural networks (ANN) can be used to reduce the computation time spend on the time domain simulations associated with fatigue analysis of mooring lines by two orders of magnitude. The present study shows how an ANN trained to perform nonlinear dynamic response simulation can be optimized using a method known as optimal brain damage (OBD) and thereby be used to rank the importance of all analysis input. Both the training and the optimization of the ANN are based on one short time domain simulation sequence generated by a FEM model of the structure. This means that it is possible to evaluate the importance of input parameters based on this single simulation only. The method is tested on a numerical model of mooring lines on a floating off-shore installation. It is shown that it is possible to estimate the cost of ignoring one or more input variables in an analysis.

The Anchor-Last Deployment Problem for Inextensible Mooring Lines

1975 ◽  
Vol 97 (3) ◽  
pp. 1046-1052 ◽  
Author(s):  
Robert C. Rupe ◽  
Robert W. Thresher
Keyword(s):  
Numerical Model ◽  
Equations Of Motion ◽  
Simultaneous Equations ◽  
Mooring Line ◽  
Integration Scheme ◽  
Lumped Mass ◽  
Mooring Lines ◽  
Concentrated Masses ◽  
Predictor Corrector ◽  
Lagrange’S Method

A lumped mass numerical model was developed which predicts the dynamic response of an inextensible mooring line during anchor-last deployment. The mooring line was modeled as a series of concentrated masses connected by massless inextensible links. A set of angles was used for displacement coordinates, and Lagrange’s Method was used to derive the equations of motion. The resulting formulation exhibited inertia coupling, which, for the predictor-corrector integration scheme used, required the solution of a set of linear simultaneous equations to determine the acceleration of each lumped mass. For the selected cases studied the results show that the maximum tension in the cable during deployment will not exceed twice the weight of the cable and anchor in water.

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.

Dynamic Analysis for the Design of CALM System in Shallow and Deep Waters

1997 ◽  
Vol 119 (3) ◽  
pp. 151-157 ◽  
Author(s):  
Y.-L. Hwang
Keyword(s):  
Mathematical Model ◽  
Dynamic Analysis ◽  
Model Test ◽  
Time Domain ◽  
Time Domain Analysis ◽  
Mooring Lines ◽  
Deep Waters ◽  
Wave Drift ◽  
The Mathematical Model ◽  
Survival Condition

This paper presents a time domain analysis approach to evaluate the dynamic behavior of the catenary anchor leg mooring (CALM) system under the maximum operational condition when a tanker is moored to the terminal, and in the survival condition when the terminal is not occupied by a tanker. An analytical model, integrating tanker, hawser, buoy, and mooring lines, is developed to dynamically predict the extreme mooring loads and buoy orbital motions, when responding to the effect of wind, current, wave frequency, and wave drift response. Numerical results describing the dynamic behaviors of the CALM system in both shallow and deepwater situations are presented and discussed. The importance of the line dynamics and hawser coupled buoy-tanker dynamics is demonstrated by comparing the present dynamic analysis with catenary calculation approach. Results of the analysis are compared with model test data to validate the mathematical model presented.

scholarly journals Three new species of Scissurellidae (Gastropoda, Prosobranchia) from the coast of Brazil

1972 ◽  
Vol 21 (0) ◽  
pp. 01-13 ◽  
Author(s):  
Pierre Ch. Montouchet
Keyword(s):  
New Species ◽  
Sao Paulo ◽  
The State ◽  
Shallow Waters ◽  
Brazilian Coast ◽  
São Paulo ◽  
Internal Anatomy ◽  
The Third ◽  
Deep Waters ◽  
Three New Species

A consultation of the original descriptions of the genera of Scissurellidae led the author to conclude that the valid names for the genera of this family are: Scissurella d'Orbigny, 1823 (redescription by Sowerby, 1824), Anatoma Woodward, 1859, Inoisura Hedley, 1904, Scissurona Iredale, 1924, Sinezona Finlay, 1927. Scissurella and Anatoma are cosmopolites, the first generally living in shallow waters, associated to sea-weeds, while the second is found in deep waters. The three last genera are restricted to Australasia. Three new species are described from the Brazilian coast: Soissu rella alexandrei, Scissurella eleotilis and Scissurella morretesi. The internal anatomy of S. alexandrei is described. These three new species have been found in littoral shallow waters, the two first on the northeast Brazilian coast, the third on the coast of the State of São Paulo. The fourth known species of Scissurellidae from Brazil, Anatoma aedonia (Watson, 1886), was dredged by H.M.S, "Challenger", in 1873, off Pernambuco, 350 fm (640 m).

Sign in / Sign up

Export Citation Format

Share Document