Global Performance of the Perdido Spar in Waves, Wind and Current: Numerical Predictions and Comparison With Experiments

2010 ◽  
Author(s):  
Stergios Liapis ◽  
Shankar Bhat ◽  
Constantine Caracostis ◽  
Carl Webb ◽  
Curtis Lohr
Keyword(s):  
Gulf Of Mexico ◽  
Floating Body ◽  
Global Motion ◽  
Spar Platform ◽  
Mooring Lines ◽  
Numerical Predictions ◽  
Pumping Mode ◽  
Heave Plate ◽  
The Impact ◽  
Actual Geometry

In recent years, spars have become a preferred industry solution for certain offshore deepwater developments. Perdido is the first spar platform to be operated by Shell. The Perdido spar has been recently installed in the ultradeepwater Gulf of Mexico Alaminos Canyon and is scheduled for first oil in 2010. This Direct Vertical Access (DVA) spar will operate at a water depth of 7,825′ and will be the deepest spar production and drilling facility in the world. Numerical predictions of the spar global motions in waves, wind and current are presented in this paper. Motivation for this study comes from two facts: 1. Each spar platform design is unique in terms of its size, number and geometry of heave plates, riser system and mooring system. 2. Metocean design criteria have been increased in view of the recent hurricanes. Model tests of the Perdido spar were conducted at MARIN at a scale of 1:59.94. In these experiments, several Gulf of Mexico (GOM) wave, current and wind environments were considered. The six-degree-of-freedom motions, deck accelerations, air gap, as well as the loads on the heave plates, mooring lines and risers were measured. In this paper, global motion predictions of the Perdido spar are given using Shell’s in-house COSMOS/ WAMIT suite of programs. Extensive comparisons between the numerical predictions and the experimental results were undertaken. In all cases, the comparisons are very good. In order to include heave viscous loads and damping, special line members were included at the bottom of the hard tank, the bottom of the soft tank and each heave plate, in addition to standard line members used to describe the truss. These special members contribute heave viscous loads with drag coefficients selected from the Perdido experiments. Several heave plate configurations were considered to systematically study the impact of heave plates on the spar global motions. The influence of the heave plate geometry on the heave added mass and on the global motions was derived using WAMIT. The strakes’ actual geometry was also included in the WAMIT diffraction analysis. Most of the moonpool area at the bottom of the Perdido hard tank is closed. As a result, the pumping mode was not excited during the experiments. However, numerical simulations with WAMIT showed a sharp peak at the “pumping mode” resonant frequency. This peak was suppressed by introducing a second floating body that capped the moonpool at the water surface. Based on these learnings, recommendations for global motion modeling are presented in this paper.

Effects of Heave Plate on the Hydrodynamic Behaviors of Cell Spar Platform

2006 ◽  
Author(s):  
Fan Zhang ◽  
Jianmin Yang ◽  
Runpei Li ◽  
Zhiqiang Hu
Keyword(s):  
Added Mass ◽  
Wave Loading ◽  
Spar Platform ◽  
Perforated Plates ◽  
Damping Coefficients ◽  
Numerical Predictions ◽  
Different Types ◽  
A Cell ◽  
Heave Plate ◽  
Hydrodynamic Behaviors

This paper presents an experimental study on the effect of heave plates on the hydrodynamic performances of a cell spar platform. A variation of the cell spar concept, whose hard tank still consist of several cylinders (cells) with the same diameter and length, but the lower part is fitted with a truss section and several heave plates, is modeled and tested. As the effectiveness of heave plates is crucial to the heave performance, different types of heave plates are fitted to the truss structure, varying from the number and spacing to the form, such as perforated plates, to investigate various design aspects of the plates. Experimental results and numerical predictions for the responses of the spar to the wave loading, as well as loads and added mass and damping coefficients on the heave plates are presented.

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.

Study on Snap Tension in Mooring Lines of Deepwater Platform

2009 ◽  
Author(s):  
Su-xia Zhang ◽  
You-gang Tang ◽  
Hai-xiao Liu
Keyword(s):  
Floating Body ◽  
Impact Dynamics ◽  
Mooring Line ◽  
Mooring System ◽  
Body System ◽  
External Excitation ◽  
Spar Platform ◽  
Mooring Lines ◽  
Motion Equations ◽  
Maximum Tension

Based on the theory of impact dynamics, the motion equations for a mooring line-floating body system after and before impact loading are established with consideration of the viscoelastic property of mooring lines. The factors that influence the taut-slack conditions of a mooring system are analyzed through classifying the taut-slack regions, which are defined by nondimensional ratios of displacement, frequency and damping of the system. The mooring lines of Jip spar platform is analyzed, and the snap tension characteristics of mooring lines are given, the factors that influence the maximum tension in mooring lines, including the mass of floating body, length of mooring lines, frequency and amplitude of external excitation, and pretension in mooring lines, are also analyzed through computing the dynamic response of system and parametric study. It is shown that the maximum tension increases with increase of the mass of floating body, external excitation and pretension and decreases with increase of the length of mooring lines, also, it is found that the influence of the nondimensional ratio of damping increases with increase of the pretension in mooring lines.

USING FIELD DATA FOR THE EVALUATION OF THE IMPACT OF ULTRA-LOW FREQUENCY MOTIONS ON THE FATIGUE OF MOORING LINES

2019 ◽  
Author(s):  
Guilherme Borzacchiello ◽  
Carl Albrecht ◽  
Fabricio N Correa ◽  
Breno Jacob ◽  
Guilherme da Silva Leal
Keyword(s):  
Field Data ◽  
Low Frequency ◽  
Mooring Lines ◽  
The Impact

Development of a Stepped Line Tensioning Solution for Mitigating VIM Effects in Loop Eddy Currents for the Genesis Spar

2004 ◽  
Author(s):  
T. Kokkinis ◽  
R. E. Sandstro¨m ◽  
H. T. Jones ◽  
H. M. Thompson ◽  
W. L. Greiner
Keyword(s):  
Gulf Of Mexico ◽  
Eddy Current ◽  
Eddy Currents ◽  
Comprehensive Evaluation ◽  
Design Solution ◽  
Loop Current ◽  
Mooring Lines ◽  
Test Methodology ◽  
Induced Motion ◽  
High Reynolds

A number of spars are being installed in deepwater areas in the Gulf of Mexico (GoM), which are subject to loop / eddy current conditions and must be designed for Vortex-Induced Motion (VIM). This paper shows how recent advances in VIM prediction enabled an efficient and effective mooring design solution for the existing Genesis classic spar, which is installed in Green Canyon Block 205 in the GOM. The solution may also be applicable to new spar designs. During the Gulf of Mexico Millennium Eddy Current event in April 2001, the Genesis spar platform underwent vortex induced motions (VIM) which were greater than anticipated during the design of the mooring & riser systems. Analysis showed that if such large motions were to occur in higher currents in the range of the 100-year event, they could cause significant fatigue damage, and could lead to peak tensions in excess of design allowables. After a comprehensive evaluation of potential solutions, Stepped Line Tensioning (SLT) was determined to be the best approach for restoring the platform’s original mooring capacity on technical, cost and schedule grounds. SLT did not require extensive redesign of the existing mooring system of the spar. Furthermore, SLT provided a means to improve mooring integrity on an interim basis, while completing details for permanent implementation. Under SLT, the pretensions of the mooring lines are adjusted based on forecast currents in order to keep the platform below the VIM lock-in threshold at all times and for all eddy/loop current conditions up to and including the 100-year condition. High Reynolds number model tests conducted with a new test methodology were used to get a reliable prediction of the spar’s VIM response for this evaluation.

Numerical Research on FPSOs With Green Water Occurrence

2009 ◽  
Vol 53 (01) ◽  
pp. 7-18
Author(s):  
Renchuan Zhu ◽  
Guoping Miao ◽  
Zhaowei Lin
Keyword(s):  
Three Dimensional ◽  
Green Water ◽  
Floating Body ◽  
Incoming Wave ◽  
Model Case ◽  
Floating Structures ◽  
Design And Optimization ◽  
Head Waves ◽  
Wave Heights ◽  
The Impact

Green water loads on sailing ships or floating structures occur when an incoming wave significantly exceeds freeboard and water runs onto the deck. In this paper, numerical programs developed based on the platform of the commercial software Fluent were used to numerically model green water occurrence on floating structures exposed to waves. The phenomena of the fixed floating production, storage, and offloading unit (FPSO) model and oscillating vessels in head waves have been simulated and analyzed. For the oscillating floating body case, a combination idea is presented in which the motions of the FPSO are calculated by the potential theory in advance and computional fluid dynamics (CFD) tools are used to investigate the details of green water. A technique of dynamic mesh is introduced in a numerical wave tank to simulate the green water occurrence on the oscillating vessels in waves. Numerical results agree well with the corresponding experimental results regarding the wave heights on deck and green water impact loads; the two-dimensional fixed FPSO model case conducted by Greco (2001), and the three-dimensional oscillating vessel cases by Buchner (2002), respectively. The research presented here indicates that the present numerical scheme and method can be used to actually simulate the phenomenon of green water on deck, and to predict and analyze the impact forces on floating structures due to green water. This can be of great significance in further guiding ship design and optimization, especially in the strength design of ship bows.

Effects of the Mooring Line Configuration on the Dynamics of a Point Absorber

2013 ◽  
Author(s):  
Vincenzo Nava ◽  
Marin Rajic ◽  
Carlos Guedes Soares
Keyword(s):  
Case Studies ◽  
Time Instant ◽  
Floating Body ◽  
Mooring Line ◽  
Mooring Lines ◽  
Point Absorber ◽  
Line Configuration ◽  
Frequency Domains ◽  
Restoring Forces ◽  
Static Approach

The aim of this paper is to study the dynamics of a floating body with characteristics comparable to a point absorber wave energy converter with different mooring systems, in geometrical configuration or in the materials. To this purpose, the dynamics of a moored buoy is investigated. The point absorber is modeled as a spherical buoy in plane two-dimensional motion, and it is studied under the action of irregular unidirectional wind-generated waves, moored to the seabed by means of one, two or three mooring lines. Two different sets of moorings are considered, and typical wires and chains used in offshore technology are considered, leading to a total of 6 case studies. A quasi-static approach is used for modeling the restoring forces needed to keep buoy into station, using an innovative iterative procedure able to predict for each time instant and for each cable the lay down length of the cable, being each mooring line allowed to be taut or slack. Approaches in the time and frequency domains are used to obtain the system responses in intermediate waters, where these facilities are usually installed. Results for all case studies are compared both in terms of statistics of response and tensions on the top of the cable.

scholarly journals Analysis of moored ship oscillations in waves

2020 ◽  
Author(s):  
Д.П. Ковалев ◽  
П.Д. Ковалев ◽  
А.С. Борисов
Keyword(s):  
Dynamic System ◽  
Sea Level ◽  
Order Differential Equation ◽  
External Excitation ◽  
Impact Oscillator ◽  
Mooring Lines ◽  
Sea Level Fluctuations ◽  
Port Area ◽  
Sea Level Fluctuation ◽  
The Impact

В работе рассмотрены особенности колебаний пришвартованного судна для основных портов Сахалинской области, поскольку качка судна у причала может представлять опасность и приводить к повреждению судна или швартовых линий. По данным натурных измерений морского волнения в портовых бухтах рассчитаны спектры колебаний уровня и определены периоды существующих в них волн для диапазона периодов от 2 с до 30 минут. Произведен расчет периодов собственных колебаний (качки) двух типов судов, преимущественно швартующихся в портах. С учетом полученных результатов выполнено моделирование движения судов при волнении как динамической с системы внешним возбуждающим воздействием на основе дифференциального уравнения второго порядка. Показано влияние коэффициента вязкого демпфирования и жесткости швартовых на реакцию динамической системы без удара о причал и для режима ударного осциллятора. Установлено, что в случае прихода в район порта Корсаков длинноволновой зыби движения судна могут переходить в хаотические. The paper considers the peculiarities of moored vessel oscillations for the main ports of the Sakhalin region, since the pitching of the vessel at the berth can be dangerous and lead to damages of the vessel or mooring lines. Spectra of sea level fluctuations and periods of waves in port bays were calculated using sea level fluctuation measurements obtained in the range from 2 seconds to 30 minutes. Calculations of resonance periods (pitching) of two types of vessels mainly moored in ports were done. Taking into consideration these results the simulation of the vessel movement in waves as a dynamic system with an external excitation was performed on the base of second-order differential equation. The influence of viscous damping coefficient and mooring stiffness on the response of the dynamic system is shown for two cases: for system without impact and for the impact oscillator mode. It is established that in the event of a long-wave swell coming to the Korsakov port area, the vessels movements may become chaotic.

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