Validation of Spectral Fatigue Assessment of a West-Africa FPSO Using Full-Scale Measurements

2021 ◽  
Author(s):  
Alexandru Andoniu ◽  
Jérôme de Lauzon ◽  
Remco Hageman ◽  
Pieter Aalberts ◽  
Didier L'Hostis ◽  
...  
Keyword(s):  
West Africa ◽  
Fatigue Damage ◽  
Wave Energy ◽  
Fatigue Analysis ◽  
Full Scale ◽  
Fatigue Assessment ◽  
Sources Of Uncertainty ◽  
Wave Conditions ◽  
Offshore Industry ◽  
Different Sources

Abstract In order to ensure structural integrity and safe operations, fatigue assessment of structural details is a key aspect of design and verification procedures for FPSOs. Spectral fatigue analysis is widely used in the offshore industry to assess damage induced by wave loading. However, the actual fatigue accumulation endured by units in operations usually differs from predictions due to the assumptions made at the design stage. One of the sources of uncertainty is the representation of the encountered sea states. The objective of this paper is to use in-situ measurements as a reference for evaluating the accuracy of spectral fatigue analysis and to investigate the influence of wave energy description on the fatigue assessment. Structural health monitoring systems have been increasingly used in the last decade in the offshore industry as they constitute a valuable source of information regarding the actual operating conditions, structural response, or encountered environmental conditions. This data can be used to update fatigue assessment in order to determine the remaining service life, understand how the structure is aging, or support for decision making regarding inspections, maintenance, or lifetime extension. The work presented is based on such information gathered during a measurement campaign performed on a spread-moored FPSO in West Africa. Measured strain time histories at several locations on the hull have been used to derive the actual fatigue damage endured by the unit. These damages are compared to the ones determined from spectral fatigue analysis using stress transfer functions obtained from frequency domain hydro-structure computations. Multiple analyses have been performed to evaluate the impact of different sources of statistical wave data and wave energy descriptions on the fatigue assessment. The wave conditions used originate from wave buoy measurements and hindcast data. Overall, the good agreement between full-scale measurements and calculations confirms the suitability of spectral methods for determining fatigue damage. When incomplete information is available, which is often true in the case of wave statistics, assumptions have to be made regarding parameters such as spectrum shape or wave spreading. However, using the full description of wave energy spectra, if available, can be a way of reducing uncertainties and removing unnecessary assumptions in such analysis. The results of this work show how fatigue assessment can be improved by gaining insight into the different sources of uncertainty, notably the sea state representation. With increasing focus on digital solutions, these results show realistic potential for virtual hull monitoring solutions based on accurate numerical models and realistic representation of wave conditions.

Probabilistic Fatigue Assessment of a Mooring Line Based on Station-Keeping Trials in Ice

2021 ◽  
Author(s):  
Chana Sinsabvarodom ◽  
Bernt J. Leira ◽  
Wei Chai ◽  
Arvid Naess
Keyword(s):  
Fatigue Damage ◽  
Probabilistic Models ◽  
Full Scale ◽  
Mooring Line ◽  
Stress Range ◽  
Station Keeping ◽  
Probability Models ◽  
Line System ◽  
Fatigue Assessment ◽  
Rainflow Counting

Abstract The intention of this work is to perform a probabilistic fatigue assessment of a mooring line due to loads associated with the station-keeping of a ship in ice. In March 2017, the company Equinor (Statoil) conducted full-scale tests by means of station-keeping trials (SKT) in drifting ice in the Bay of Bothnia. The vessel Magne Viking was employed in order to represent a supply vessel equipped with a mooring line system, and the realtime loading during the full-scale measurement was recorded. The second vessel Tor Viking was serving as an ice breaker in order to maintain the physical ice management activities with different ice-breaking schemes, i.e. square updrift pattern, round circle pattern, circular updrift pattern and linear updrift pattern. The fatigue degradation corresponding to these different patterns were investigated. The peaks and valleys of the mooring tension are determined using the min peak prominence method. For the purpose of probabilistic fatigue assessment, the Rainflow-counting algorithm is applied to estimate the mooring stress range. Fatigue assessment based both on Rainflow counting and fitted probabilistic models were performed. For the latter, the stress range distributions from the observed data of mooring loads are fitted to various probability models in order to estimate the fatigue damage. It is found that the stress ranges represented by application of the Weibull distribution for the probabilistic fatigue approach provides results of the fatigue damage most similar to the Rainflow counting approach. Among the different scenarios of Ice management schemes, the circular updrift pattern provides the lowest magnitude of the fatigue degradation.

Effect of Wave Induced Loading and Line Loading in Fully Stochastic Fatigue Assessment for West Africa FPSO

2004 ◽  
Author(s):  
T. H. Park ◽  
J. H. Lee ◽  
J. W. Cho ◽  
H. S. Shin
Keyword(s):  
West Africa ◽  
Fatigue Damage ◽  
Bending Moment ◽  
Ship Motions ◽  
Piping System ◽  
Site Specific ◽  
Fatigue Assessment ◽  
Loading Effects ◽  
Wave Induced ◽  
Side Shell

The fatigue assessment for a caisson of the interface between a caisson and a FPSO hull has been performed based on the FMS (Fatigue Methodology Specification) [1]. Investigation is focused on the various loading effects including inertia loading due to ship motions from a site specific swell, sea and line loading from the submerged caisson connected to the side shell of FPSO. The fully stochastic method was used for estimating damage levels from wave loadings. The component-based method was used for line loading effects. The two kinds of results from each case were combined the variance and mean period combination. For the inertia loading, it is shown that a hull deforming due to vertical bending moment is the principal effect for a fatigue assessment. For the line loading, it is found that the loading effect due to the submerged piping system connected to the side shell of FPSO is not significant for the fatigue of the side shell supporting structure. In conclusion, the fatigue damage from the site-specific swell is dominant effect among overall fatigue damage components of FPSO in the specific site condition of West Africa.

Fatigue Analysis of Free Spanning Pipelines Subjected to Vortex Induced Vibrations

2013 ◽  
Author(s):  
F. Van den Abeele ◽  
F. Boël ◽  
M. Hill
Keyword(s):  
Fatigue Damage ◽  
Oil And Gas ◽  
Flow Direction ◽  
Cross Flow ◽  
Fatigue Analysis ◽  
Sensitivity Analyses ◽  
Vortex Induced Vibration ◽  
Vortex Induced Vibrations ◽  
Offshore Industry ◽  
Girth Welds

Vortex induced vibration is a major cause of fatigue failure in submarine oil and gas pipelines and steel catenary risers. Even moderate currents can induce vortex shedding, alternately at the top and bottom of the pipeline, at a rate determined by the flow velocity. Each time a vortex sheds, a force is generated in both the in-line and cross-flow direction, causing an oscillatory multi-mode vibration. This vortex induced vibration can give rise to fatigue damage of submarine pipeline spans, especially in the vicinity of the girth welds. In this paper, an integrated numerical framework is presented to predict and identify free spans that may be vulnerable to fatigue damage caused by vortex induced vibrations (VIV). An elegant and efficient algorithm is introduced to simulate offshore pipeline installation on an uneven seabed. Once the laydown simulation has been completed, the free spans can be automatically detected. When the fatigue screening for both inline and cross-flow VIV indicates that a particular span may be prone to vortex induced vibrations, a detailed fatigue analysis is required. Amplitude response models are constructed to predict the maximum steady state VIV amplitudes for a given pipeline configuration (mechanical properties) and sea state (hydrodynamic parameters). The vibration amplitudes are translated into corresponding stress ranges, which then provide an input for the fatigue analysis. A case study from the offshore industry is presented, and sensitivity analyses are performed to study the influence of the seabed conditions, where special emphasis is devoted on the selection of pipe soil interaction parameters.

scholarly journals Umbilical Fatigue Analysis for a Wave Energy Converter

2020 ◽  
Author(s):  
Billy Ballard ◽  
Yi-Hsiang Yu ◽  
Jennifer Van Rij ◽  
Frederick Driscoll
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Wave Energy ◽  
Degrees Of Freedom ◽  
Oil And Gas ◽  
Time History ◽  
Fatigue Analysis ◽  
Offshore Wind ◽  
Wave Energy Converters ◽  
Energy Technologies

Abstract Unique umbilical designs for wave energy converters (WECs), including the ability to handle significantly larger motions and loads over long deployments, are often required when conventional marine umbilical designs for offshore oil and gas and offshore wind may not meet the design and cost needs of wave energy technologies. This study details a fatigue analysis of a dynamic power umbilical attached to a two-body floating point absorber WEC system, using the sea states provided for the PacWave testing facilities. The 6 degrees of freedom motion time history for the WEC was simulated, and the motions of the attachment point for the umbilical on the WEC and respective sea states were used to analyze the dynamic motions and fatigue of the connected power umbilical to predict the fatigue life. The results show that the fatigue damage observed is more significant in shallow water, and extensive fatigue damage may occur because of the larger curvature response of the umbilical. The umbilical configurations departing at 90 deg off incoming waves were found to have the highest fatigue life attributed to less extension or compression of the umbilical. However, additional bend stiffener/limiter features may need to be incorporated into the buoyancy section and touchdown regions to minimize curvature-induced fatigue.

Fatigue Analysis of a Point Absorber Wave Energy Converter Subjected to Passive and Reactive Control

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
A. S. Zurkinden ◽  
S. H. Lambertsen ◽  
L. Damkilde ◽  
Z. Gao ◽  
T. Moan
Keyword(s):  
Fatigue Damage ◽  
Wave Energy ◽  
Stress Responses ◽  
Fatigue Analysis ◽  
Wave Energy Converter ◽  
Wave Loads ◽  
Reactive Control ◽  
Energy Converter ◽  
Set Up ◽  
Frequency Domain Approach

This paper investigates the effect of a passive and reactive control mechanism on the accumulated fatigue damage of a wave energy converter (WEC). Interest is focused on four structural details of the Wavestar arm, which is used as a case study here. The fatigue model is set up as an independent and generic toolbox, which can be applied to any other global response model of a WEC device combined with a control system. The stress responses due to the stochastic wave loads are computed by a finite element method (FEM) model using the frequency-domain approach. The fatigue damage is calculated based on the spectral-based fatigue analysis in which the fatigue is described by the given spectral moments of the stress response. The question will be discussed, which control case is more favorable regarding the tradeoff between fatigue damage reduction and increased power production.

A Comparison of Two Wave Models and Their Influence on Fatigue Damage in Ship Structures

2013 ◽  
Author(s):  
Wengang Mao ◽  
Fredhi Agung Prasetyo ◽  
Jonas W. Ringsberg ◽  
Naoki Osawa
Keyword(s):  
Fatigue Damage ◽  
Failure Modes ◽  
Maritime Industry ◽  
Ship Structures ◽  
Fatigue Assessment ◽  
Practical Applications ◽  
The North ◽  
Fatigue Design ◽  
Wave Models ◽  
Different Sources

In the maritime industry, fatigue failure is one of the most significant failure modes for ship structures. The fatigue damage in ship structures is mainly caused by the variation of wave loadings applied on ships, leading to variable structural stresses. Therefore, a reliable description of wave environments encountered during a ship’s service life is essential for accurate fatigue assessment of ship structures. Besides the wave scatter diagram provided by classification society rules, different statistical wave models have also been built up to model wave environments along arbitrary ship routes. The wave models could provide more specific wave environment for any chosen sailing routes of an individual ship. They may have the potential to be used for some practical applications, such as conceptual ship fatigue design, remaining fatigue life prediction when a ship plans to change its original trade region, and crack maintenance planning etc. Since the development of these models may be based on different sources, e.g. satellite measurements, hindcast data, buoys, etc., the reliability and consistence of wave generations from various wave models must be validated by the measured wave environments in order to be used for those practical applications. In this paper, waves generated from two different wave models, one based on hindcast data and one mainly on satellite data, are compared with measured wave environments encountered by a 2800 TEU container vessel on the North Atlantic route. These wave models are used in the calculation of the fatigue damage in the vessel. The results obtained using waves generated from the two wave models are compared with the fatigue damage calculated based on strain measurements in the ship. Recommendations for future development of the wave models and further investigation to make the applications more realistic for ship fatigue assessment are also presented.

Application of Advanced Fatigue Damage Parameters in Comparison With Fatigue Analysis Included in Codes and Standards

2014 ◽  
Author(s):  
Philipp Rettenmeier ◽  
Karl-Heinz Herter ◽  
Xaver Schuler ◽  
Thomas Markus Fesich
Keyword(s):  
Cyclic Loading ◽  
Fatigue Damage ◽  
Fatigue Loading ◽  
Fatigue Analysis ◽  
Damage Parameter ◽  
Fatigue Tests ◽  
Loading Conditions ◽  
Critical Plane ◽  
Fatigue Assessment ◽  
Fatigue Damage Parameter

Technical components are subjected to cyclic loading conditions that can be arbitrarily complex in the most general case. For analytical fatigue strength verifications in the finite life regime both the uniaxial material characteristics by means of Wöhler curves as well as a representative equivalent fatigue damage parameter (FDP) for multiaxial cyclic loadings have to be determined. For simple loading conditions, the fatigue assessment can be performed using well-known and verified strength hypotheses for quasi-static loading conditions. However, for complex non-proportional cyclic loading conditions with rotating principle stress directions the application of these hypotheses is not sufficiently verified. Hence, advanced stress, strain or energy based strength hypotheses in critical plane formulation are used. These hypotheses require considerable numerical efforts. The fatigue concept (MPA AIM-Life) enables an assessment of complex fatigue loading conditions with different advanced strength hypotheses. An interface to the finite element code ABAQUS allows the fatigue assessment of complex component geometries. Based on fatigue tests of specimens made from ferritic and austenitic materials under uniaxial and multiaxial loading conditions (tension/torsion) the accuracy of different strength hypotheses is demonstrated. Therefore the fatigue analysis assessment included in codes and standards is compared to different advanced fatigue damage parameters.

Comparison of Different Approaches for Fatigue Damage Accumulation in Steel Risers

2011 ◽  
Author(s):  
Fernanda C. M. Takafuji ◽  
Clo´vis A. Martins
Keyword(s):  
Fatigue Life ◽  
Dynamic Analysis ◽  
Fatigue Damage ◽  
Time Domain ◽  
Damage Accumulation ◽  
Maximum Stress ◽  
Fatigue Analysis ◽  
Fatigue Damage Accumulation ◽  
Stress Point ◽  
Offshore Industry

Fatigue is one of the main concerns of the offshore industry nowadays, since the failure of equipments could put not only the environment but also some people’s lives in danger. As described in DNV-RP-C203 and in DNV-RP-F204, the aim of fatigue analysis is to verify if a certain structure — in this case, a riser — will be able to operate adequately during a desired period of time, as well as to obtain information to program inspections. In a riser, the efforts vary along its length and also around its circumference. If one considers the stress around the circumference, the maximum stress point may change. To be realistic, one approach is to calculate the stress and fatigue life around the circumference. To be more conservative and also simplify the calculation, one could consider that the maximum stress always occurs at the same point. The purpose of this paper is to compare the fatigue life obtained with both approaches in order to verify the differences between them and verify how conservative that simplification can be. To perform the task, a steel riser is considered and the dynamic analysis is executed in time domain using Orcaflex 9.4. The fatigue is analyzed through the S-N Curve approach and the Miner’s rule is used to accumulate the damage.

scholarly journals Optimizing the Power Take Off of a Wave Energy Converter With Regard to the Wave Climate

2005 ◽  
Vol 128 (1) ◽  
pp. 56-64 ◽  
Author(s):  
Gaelle Duclos ◽  
Aurelien Babarit ◽  
Alain H. Clément
Keyword(s):  
Wave Energy ◽  
Simple Wave ◽  
Wave Climate ◽  
Wave Energy Converter ◽  
Optimal Parameters ◽  
Energy Converter ◽  
Wave Energy Converters ◽  
Classical Wave ◽  
Project Site ◽  
Wave Conditions

Considered as a source of renewable energy, wave is a resource featuring high variability at all time scales. Furthermore wave climate also changes significantly from place to place. Wave energy converters are very often tuned to suit the more frequent significant wave period at the project site. In this paper we show that optimizing the device necessitates accounting for all possible wave conditions weighted by their annual occurrence frequency, as generally given by the classical wave climate scatter diagrams. A generic and very simple wave energy converter is considered here. It is shown how the optimal parameters can be different considering whether all wave conditions are accounted for or not, whether the device is controlled or not, whether the productive motion is limited or not. We also show how they depend on the area where the device is to be deployed, by applying the same method to three sites with very different wave climate.

Hybrid Fatigue Analysis Method for Railway Carbody Structure

2008 ◽  
Vol 44-46 ◽  
pp. 733-738 ◽  
Author(s):  
Bing Rong Miao ◽  
Wei Hua Zhang ◽  
Shou Ne Xiao ◽  
Ding Chang Jin ◽  
Yong Xiang Zhao
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Hybrid Method ◽  
Dynamic Stress ◽  
Stress Test ◽  
Fatigue Analysis ◽  
Railway Vehicle ◽  
Analysis Method ◽  
Structure Dynamic ◽  
Multi Body

Railway vehicle structure fatigue life consumption monitoring can be used to determine fatigue damage by directly or indirectly monitoring the loads placed on critical vehicle components susceptible to failure from fatigue damage. The sample locomotive carbody structure was used for this study. Firstly, the hybrid fatigue analysis method was used with Multi-Body System (MBS) simulation and Finite Element Method (FEM) for evaluating the carbody structure dynamic stress histories. Secondly, the standard fatigue time domain method was used in fatigue analysis software FE-FATIGUE and MATLAB WAFO (Wave Analysis for Fatigue and Oceanography) tools. And carbody structure fatigue life and fatigue damage were predicted. Finally, and carbody structure dynamic stress experimental data was taken from this locomotive running between Kunming-Weishe for this analysis. The data was used to validate the simulation results based on hybrid method. The analysis results show that the hybrid method prediction error is approximately 30.7%. It also illustrates that the fatigue life and durability of the locomotive can be predicted with this hybrid method. The results of this study can be modified to be representative of the railway vehicle dynamic stress test.

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