Coupled Analysis of Floating Structures With a New Mooring System

2011 ◽  
Author(s):  
Zhiming Yuan ◽  
Chunyan Ji ◽  
Minglu Chen ◽  
Yun Zhang
Keyword(s):  
Water Depth ◽  
Deep Water ◽  
Coupled Analysis ◽  
Mooring System ◽  
Full Time ◽  
Analysis Method ◽  
Floating Structures ◽  
Motion Performance ◽  
Improved Performance ◽  
Hydrocarbon Reserves

As the exploitation of hydrocarbon reserves moves towards deeper waters, the floating structures are becoming more and more popular, and the catenary and taut mooring systems are two widespread mooring systems which are used for these floating structures. However, both of them have their inherent drawbacks. The aim of the present work is to develop and validate a new mooring system which will overcome these shortcomings. To this end, the motion performance of a semi-submersible platform is simulated by employing a full time domain coupled analysis method. It is shown that the new mooring system yields very good motion performance when benchmarked against the taut mooring system, and the reasons for this improved performance are discussed. Also, the new mooring system is compatible with the characteristic of catenary mooring system, which eliminates the requirement of anti-uplift capacity of the anchors. The second aim of this paper is to explore the proper water depth in employing this new mooring system. For this purpose, several typical water depths are simulated. It is found that the new mooring system works well both in deep water and ultra-deep water. But, as the water depth becomes deeper, the advantages of the new mooring system are reduced.

High Holding Power Torpedo Pile: Results for the First Long Term Application

2004 ◽  
Author(s):  
Jairo Bastos de Araujo ◽  
Roge´rio Diniz Machado ◽  
Cipriano Jose de Medeiros Junior
Keyword(s):  
Water Depth ◽  
Deep Water ◽  
Field Tests ◽  
Free Fall ◽  
Mooring System ◽  
Holding Power ◽  
Campos Basin ◽  
Anchoring System ◽  
Very High

Petrobras developed a new kind of anchoring device known as Torpedo. This is a steel pile of appropriate weight and shape that is launched in a free fall procedure to be used as fixed anchoring point by any type of floating unit. There are two Torpedoes, T-43 and T-98 weighing 43 and 98 metric tons respectively. On October 2002 T-43 was tested offshore Brazil in Campos Basin. The successful results approved and certified by Bureau Veritas, and the need for a feasible anchoring system for new Petrobras Units in deep water fields of Campos Basin led to the development of a Torpedo with High Holding Power. Petrobras FPSO P-50, a VLCC that is being converted with a spread-mooring configuration will be installed in Albacora Leste field in the second semester of 2004. Its mooring analysis showed that the required holding power for the mooring system would be very high. Drag embedment anchors option would require four big Anchor Handling Vessels for anchor tensioning operations at 1400 m water depth. For this purpose T-98 was designed and its field tests were completed in April 2003. This paper discusses T-98 design, building, tests and ABS certification for FPSO P-50.

Influence of Nonlinear Mooring Stiffness on Hydrodynamic Performance of Floating Bodies

2009 ◽  
Author(s):  
Huilong Ren ◽  
Jian Zhang ◽  
Guoqing Feng ◽  
Hui Li ◽  
Chenfeng Li
Keyword(s):  
Equilibrium Position ◽  
Equations Of Motion ◽  
Offshore Structures ◽  
Hydrodynamic Performance ◽  
Coupled Analysis ◽  
Mooring System ◽  
Main Function ◽  
Ocean Engineering ◽  
Mooring Lines ◽  
Floating Structures

Coupled dynamic analysis between floating marine structures and flexible members such as mooring lines and risers, is a challenging work in the ocean engineering field. Coupled analysis on mooring-buoy interactions has been paid more and more concern for recent years. For floating offshore structures at sea, the motions driven by environmental loads are inevitable. The movement of mooring lines occurs due to the excitation on the top by floating structures. Meanwhile the lines restrict the buoy’s motion by forces acting on the fareleads. Positioning is the main function of mooring system, its orientation effects can’t be ignored for floating structures such as semi-submersible, FPS, and TLP, especially when the buoy’s equilibrium position shifting to another place. Similar as hydrostatic restoring forces, mooring force related with the buoy’s displacement can be transformed into mooring stiffness and can be added in the differential equations of motion, which is calculated at its equilibrium point. For linear hydrodynamic analysis in frequency domain, any physical quantity should be linear or be linearized, however mooring stiffness is nonlinear in essence, so the tangent or differential stiffness is used. Steel chains are widely used in catenary mooring system. An explicit formulation of catenary mooring stiffness is derived in this article, which consists of coupled relations between horizontal and vertical mooring forces. The effects of changing stiffness due to the shift of equilibrium position on the buoy’s hydrodynamic performance are investigated.

Study on Weight Control Methods of Single Point Mooring System of FPSO in Deepwater

2015 ◽  
Author(s):  
Yuan Hongtao ◽  
Zeng Ji ◽  
Chen Gang ◽  
Mo Jian ◽  
Zhao Nan
Keyword(s):  
Weight Control ◽  
Linear Time ◽  
Single Point ◽  
Line Tension ◽  
Coupled Analysis ◽  
Mooring Line ◽  
Mooring System ◽  
Control Methods ◽  
Analysis Method ◽  
Mooring Lines

This paper applies 3D potential theory and non-linear time domain coupled analysis method to analyze motion response of FPSO and dynamic response of mooring line of single mooring system. In addition, respectively to calculate mooring line tension of tension type and composite mooring line type and added buoy in mooring line. There the paper analyze different mooring lines to affect on the weight of single point mooring system of deepwater FPSO. Which expects to provide a theoretical basis for single point mooring system design and weight control.

Wave Spreading and Wave Drift Loads for a Standard LNG Carrier in Shallow Water

2010 ◽  
Author(s):  
Emmanuel Sergent ◽  
Mamoun Naciri
Keyword(s):  
Natural Gas ◽  
Shallow Water ◽  
Natural Frequency ◽  
Water Depth ◽  
Storage Capacity ◽  
Mooring System ◽  
Spectral Densities ◽  
Floating Structures ◽  
Wave Drift ◽  
The Impact

The need for LNG export and import terminals is anticipated to grow as natural gas progressively accounts for a larger fraction of worldwide consumed energy. These terminals are preferably located nearshore i.e. in relatively shallow water. Design of floating structures is most of the time performed assuming long-crested waves. In shallow water, diffraction of waves by a variable bathymetry can result in wave spreading i.e. in short crested seas. The effect of short crested seas on the wave drift load spectral densities for a 135,000m3 storage capacity LNG Carrier in 15m water depth is investigated. It is shown that the impact of wave spreading on drift loads depends on the natural frequency of the moored vessel and thus on the stiffness of the mooring system under consideration. Although response calculations are not performed herein for reasons to be discussed, it is conceivable that wave spreading could adversely affect loading/offloading terminal availability for stiff moorings.

scholarly journals Analysis and simulation of a single buoy mooring system based on sea environment

2014 ◽  
Vol 17 (3) ◽  
pp. 146-155
Author(s):  
Quang Xuan Le ◽  
Hien Vo ◽  
Huy Huu Nguyen ◽  
Nhat Ly Minh Tran ◽  
Thang Toan Nguyen ◽  
...  
Keyword(s):  
Water Depth ◽  
Coastal Waters ◽  
Single Point ◽  
Maximum Load ◽  
Mooring System ◽  
Optimal Length ◽  
Floating Structures ◽  
Guidelines And Standards ◽  
Mooring Chain

Single Point Mooring (SPM) is of great use to offshore floating structures which are currently in use in Vietnam’s coastal waters. However, this country is facing the lack of the related guidelines and standards for analysis, simulation and design of SPM system. This fact is the rationale for this paper which is aimed to propose a procedure for computation of the effects of sea environment on a SPM system. Specifically, the procedure enables the identification of maximum load exerting on the mooring buoy. Then, such identification together with the water depth parameter enables the determination of the optimal length and diameter of the desired chain. Finally, this paper presents a primary simulation of the mooring chain system according to various water depth conditions.

Multi-mode reliability analysis of mooring system of deep-water floating structures

2019 ◽  
Vol 192 ◽  
pp. 106517 ◽  
Author(s):  
Junfeng Du ◽  
Anteng Chang ◽  
Shuqing Wang ◽  
Mingyuan Sun ◽  
Junrong Wang ◽  
...  
Keyword(s):  
Reliability Analysis ◽  
Deep Water ◽  
Mooring System ◽  
Floating Structures ◽  
Multi Mode

Dynamic Analysis of Mooring Lines for Deep Water Floating Systems

2011 ◽  
Author(s):  
K. Gurumurthy ◽  
Suhail Ahmad ◽  
A. S. Chitrapu
Keyword(s):  
Finite Element ◽  
Dynamic Analysis ◽  
Deep Water ◽  
Time Domain ◽  
Accurate Prediction ◽  
Coupled Analysis ◽  
Analysis Method ◽  
Mooring Lines ◽  
Coupled Dynamic Analysis ◽  
Floating Systems

Efficient dynamic analysis of mooring lines and risers is necessary for deepwater floating systems that typically consist of a number of mooring lines and risers. In deepwater, the interactions between the floater motions and the large number of risers and mooring lines become significant and must be considered for accurate prediction of floater motions as well as line dynamics. Time-domain coupled dynamic analysis procedures have been proposed which can account for the coupling effects and consider most of the nonlinearities present in the problem. These methods have been shown to give more accurate results compared to traditional de-coupled analysis methods although they tend to be computationally more expensive. If the system has a large number of mooring lines and risers, it becomes very difficult and impractical to perform time domain coupled analysis. A number of efficient methodologies have therefore been proposed in the past to balance the accuracy of results with computational efficiency. Such methods include the frequency domain approach, combination of frequency and time domain methods, and combination of coupled and uncoupled analysis methodologies. Enhanced de-coupled dynamic analysis is an efficient method and is similar to the traditional de-coupled dynamic analysis method except that the floater motions are computed by coupled analysis considering a coarse finite element model of the mooring lines. In this paper, dynamic analysis of mooring lines for a deep water classical spar floater under random waves is performed by using the enhanced de-coupled dynamic analysis method and the response statistics are compared with results obtained from coupled dynamic analysis. The spar is modeled as a rigid body with six degrees-of-freedom and the mooring lines are modeled as finite element assemblage of elastic rods. All major non-linearities and the dynamic interaction between spar and its mooring lines are considered while determining the tension time histories. Hinge connection is assumed at the fairleads. At every time step of the integration of equations of motion of the spar, a series of nonlinear dynamic analyses of the mooring lines is performed using a subcycling technique. From the analyses, it is found that the enhanced de-coupled dynamic analysis provides results comparable in accuracy with the results obtained from coupled dynamic analysis in terms of predicting the response statistics, but requires only one third of the computational time. Therefore, enhanced de-coupled dynamic analysis can be used for accurate prediction of mooring line dynamics for deep water floating systems.

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.

Mechanical Qualification of Dynamic Deep Water Power Cable

2011 ◽  
Author(s):  
Roger Slora ◽  
Stian Karlsen ◽  
Per Arne Osborg
Keyword(s):  
Water Depth ◽  
Deep Water ◽  
Failure Modes ◽  
Electrical Power ◽  
Oil And Gas Industry ◽  
Electrical Heating ◽  
Power Cable ◽  
Water Power ◽  
System Integrity ◽  
Water Depths

There is an increasing demand for subsea electrical power transmission in the oil- and gas industry. Electrical power is mainly required for subsea pumps, compressors and for direct electrical heating of pipelines. The majority of subsea processing equipment is installed at water depths less than 1000 meters. However, projects located offshore Africa, Brazil and in the Gulf of Mexico are reported to be in water depths down to 3000 meters. Hence, Nexans initiated a development programme to qualify a dynamic deep water power cable. The qualification programme was based on DNV-RP-A203. An overall project plan, consisting of feasibility study, concept selection and pre-engineering was outlined as defined in DNV-OSS-401. An armoured three-phase power cable concept assumed suspended from a semi-submersible vessel at 3000 m water depth was selected as qualification basis. As proven cable technology was selected, the overall qualification scope is classified as class 2 according to DNV-RP-A203. Presumed high conductor stress at 3000 m water depth made basis for the identified failure modes. An optimised prototype cable, with the aim of reducing the failure mode risks, was designed based on extensive testing and analyses of various test cables. Analyses confirmed that the prototype cable will withstand the extreme loads and fatigue damage during a service life of 30 years with good margins. The system integrity, consisting of prototype cable and end terminations, was verified by means of tension tests. The electrical integrity was intact after tensioning to 2040 kN, which corresponds to 13 000 m static water depth. A full scale flex test of the prototype cable verified the extreme and fatigue analyses. Hence, the prototype cable is qualified for 3000 m water depth.

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