Wave and Current Induced Cumulative Fatigue Damage Assessment for Offshore Pipeline on Free-Span

2008 ◽  
Author(s):  
Ali Valipour ◽  
Mehrdad Zoroufi ◽  
Abbas Yeganeh Bakhtiary ◽  
Reza Valipour
Keyword(s):  
Fatigue Damage ◽  
Element Model ◽  
Major Influence ◽  
Spectral Amplitude ◽  
Linear Wave ◽  
Offshore Pipelines ◽  
Drag Forces ◽  
Waves And Currents ◽  
Cumulative Fatigue Damage ◽  
Wave Induced

Suspending pipelines between two points over an uneven seafloor is called free-spanning which induces more vortices behind the pipe especially when the pipelines are exposed to the hydrodynamic effects of waves and currents. These influences cause a significant increase in the dynamic acting drag forces. In fact, the oscillatory acting drag forces, as a result of changes in the net pressure and velocity filed around the pipeline, increase the probability of fatigue damage. Since the fatigue life of offshore pipelines has a major influence on the useful life of a project, studying it for offshore pipelines laid on uneven sea beds has become very important. Both the consequence of vortex shedding as a result of wave and current interaction with the pipeline, and the selected suitable approach in assessing fatigue damage has made the design process sophisticated. In the present study, it is attempted to employ a proper finite element model with the capability of coupling the dynamic drag forces induced by wave and current conditions with estimating cumulative fatigue damage methods. The wave profile is simulated using Non-deterministic Spectral Amplitude in Gaussian sea state and using linear wave formulation to calculate wave -induced forces. Moreover, the current force is estimated by using the conventional Morison Equation as well as employing a new approach of estimating current -induced dynamic drag forces obtained by a numerical model that includes the VIV effects. Finally cumulative fatigue damage as a result of acting those forces is investigated for various conditions of laying pipeline on the seabed.

Fatigue Design and Analysis of Offshore Pipelines and Risers Subjected to Waves and Currents

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
M. Liu ◽  
C. Cross
Keyword(s):  
Fatigue Damage ◽  
Damage Accumulation ◽  
Coupling Effect ◽  
Limit State ◽  
Ultimate Limit State ◽  
Offshore Pipelines ◽  
Fatigue Design ◽  
Fatigue Damage Accumulation ◽  
Waves And Currents ◽  
Wave Induced

The industry consensus would appear that the effect of currents on wave-induced fatigue damage accumulation is assumed as insignificant and can be ignored. Only when dealing with stability, ultimate limit state design, and vortex-induced vibration (VIV), is the recommended industry practice to consider both currents and waves simultaneously, except for fatigue design. This paper presents a study on how environmental loads should be considered in terms of currents and waves for the fatigue life design of offshore pipelines and risers. The study is intended as a spur to redress the misapprehension by focusing on the coupling effect of direct waves and currents in the context of fatigue damage assessment. It is demonstrated unequivocally that waves and currents cannot be decoupled for fatigue design assessments. Wave-induced fatigue with the inclusion of currents is manifested twofold, not only the increased mean stress correction effect but also higher total damage accumulation due to elevated stress ranges. The practice of using wave histograms while ignoring currents is shown to result in an unacceptable nonconservative fatigue design. Both effects should be accounted for in the engineering assessment. A first-order correction factor involving the ratio of current and wave velocities is introduced to evaluating the environmental load coupling effect. It is recognized that fatigue associated specifically with VIV phenomena is well understood and documented elsewhere, its discussion is thus out with the aims of this paper.

Fatigue Design and Analysis of Offshore Pipelines and Risers Subjected to Waves and Currents

2016 ◽  
Author(s):  
M. Liu ◽  
C. Cross
Keyword(s):  
Fatigue Damage ◽  
Damage Accumulation ◽  
Coupling Effect ◽  
Limit State ◽  
Ultimate Limit State ◽  
Offshore Pipelines ◽  
Fatigue Design ◽  
Fatigue Damage Accumulation ◽  
Waves And Currents ◽  
Wave Induced

The industry consensus would appear that the effect of currents on wave induced fatigue damage accumulation is assumed as insignificant and can be ignored. Only when dealing with stability, ultimate limit state design and vortex induced vibration, the recommended industry practice is to consider both currents and waves simultaneously, but except for fatigue design. This paper presents a study on how environmental loads should be considered in terms of currents and waves for the fatigue life design of offshore pipelines and risers. The study is intended as a spur to redress the misapprehension by focusing on the coupling effect of direct waves and currents in the context of fatigue damage assessment. It is demonstrated unequivocally that waves and currents cannot be decoupled for fatigue design assessments. Wave induced fatigue with the inclusion of currents is manifested twofold, not only the increased mean stress correction effect but also higher total damage accumulation due to elevated stress ranges. The practice of using wave histograms while ignoring currents is shown to result in an unacceptable non-conservative fatigue design. Both effects should be accounted for in the engineering assessment. A first order correction factor involving the ratio of current and wave velocities is introduced to evaluating the environmental load coupling effect. It is recognized that fatigue associated specifically with VIV phenomena is well understood and documented elsewhere, its discussion is thus outwith the aims of this paper.

scholarly journals Representative Environmental Condition for Fatigue Analysis of Offshore Jacket Substructure

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5494
Author(s):  
Tsung-Yueh Lin ◽  
Yi-Qing Zhao ◽  
Hsin-Haou Huang
Keyword(s):  
Fatigue Damage ◽  
Environmental Conditions ◽  
Element Model ◽  
Computational Time ◽  
Wave Load ◽  
Sea State ◽  
Stress Signals ◽  
Cumulative Fatigue Damage ◽  
The Taiwan Strait

The 20-year cumulative fatigue damage of an offshore jacket substructure was estimated under the long-term local environmental conditions in the Taiwan Strait. Because of the nonlinearity of wave load for slender members of the structure, time-domain simulations of the dynamic finite element model were conducted for each sea state. By utilizing the Dirlik method to process the stress signals, the fatigue damages of joints were computed. Concerning the computational time, we propose a probability-based method of using a representative combination of environmental conditions in this study, which can considerably reduce the required number of evaluations prior to determining fatigue damage, thereby improving the process of preliminary design. The results show that only three sea states among 120 can represent 28% of the average damage ratio, and up to 17 sea states fully resolved the fatigue life.

Fatigue Analysis and Life Prediction of Dumpers with Cumulative Fatigue Damage Approach and Finite Element Model

2007 ◽  
Vol 353-358 ◽  
pp. 909-912
Author(s):  
Shou Ju Li ◽  
Ying Xi Liu
Keyword(s):  
Finite Element ◽  
Stress Distribution ◽  
Finite Element Model ◽  
Fatigue Damage ◽  
Damage Model ◽  
Element Model ◽  
Fatigue Notch Factor ◽  
Cumulative Fatigue Damage ◽  
Stress Concentration Factors ◽  
Main Components

A fatigue damage model is developed for evaluating accumulative fatigue damage of dumpers. The loading spectrums acted on dumpers are created according to measured strain data in field. The finite element model is meshed for assessing and calculating stress distribution and strength characteristics of dumpers. The stress distribution and stress concentration factors of main components of dumper at different loading cases are numerically simulated. A fatigue damage model is developed for evaluating accumulative fatigue damage of dumpers. Fatigue damage indexes and service life are calculated by a modified Palmgren-Miner rule. The investigation shows that fatigue notch factor has a significant influence on the calculation of fatigue damage of dumpers.

scholarly journals Bending Strength of Spur Gear Teeth : 1st Report, Cumulative Fatigue Damage of Normalized 0.45% Carbon Steel

1982 ◽  
Vol 25 (202) ◽  
pp. 671-678 ◽  
Author(s):  
Toshimi TOBE ◽  
Noboru MARUYAMA
Keyword(s):  
Carbon Steel ◽  
Fatigue Damage ◽  
Bending Strength ◽  
Spur Gear ◽  
Gear Teeth ◽  
Cumulative Fatigue Damage

Experimental and Full Scale Investigation of the Importance of Fatigue Damage Due to Wave-Induced Vibration Stress in A Container Vessel

2006 ◽  
Author(s):  
I Drummen ◽  
◽  
T Moan ◽  
G Storhaug ◽  
E Moe ◽  
...  
Keyword(s):  
Fatigue Damage ◽  
Full Scale ◽  
Vibration Stress ◽  
Wave Induced

First Ocean Going Ships With Springing and Whipping Included in the Ship Design

2011 ◽  
Author(s):  
Gaute Storhaug ◽  
Erlend Moe ◽  
Ricardo Barreto Portella ◽  
Tomazo Garzia Neto ◽  
Nelson Luiz Coelho Alves ◽  
...  
Keyword(s):  
Fatigue Damage ◽  
Current Model ◽  
Life Time ◽  
Model Tests ◽  
Full Scale ◽  
Development Projects ◽  
Transient Vibration ◽  
Hull Girder ◽  
Fatigue Evaluation ◽  
Wave Induced

It is well known that ships vibrate due to waves. The wave induced vibrations of the hull girder are referred to as springing (resonance) and whipping (transient vibration from impacts). These vibrations contribute to the fatigue damage of fatigue sensitive details. An Ore Carrier of 400 000 dwt is currently being built by DSME, and at time of delivery, it will be the world’s largest bulk (ore) carrier. The scantlings of large ships must be carefully designed with respect to global loading, and when extending the design beyond experience, it is also wise to consider all aspects that may affect operation and the life time costs. The vessel will also enter a long term contract and is therefore to be evaluated for 30 year Brazil-China operation. In order to minimize the risk of fatigue damage, the vessel is designed according to DNV’s class notation CSA-2 requiring direct calculations of the loading and strength. Further it has been requested to include the effect of springing and whipping in the design. Reliable numerical tools for assessing the additional fatigue effect of vibrations are non-existing. DNV has, however, developed an empirical guidance on how the additional effect may be taken into account based on previous development projects related to the effect of vibrations on large ore carriers Due to the size and route of operation of the new design, it has, however, been required by the owner to carry out model tests in both ballast and cargo condition in order to quantify the contribution from vibration. The results from this project have been used for verification and further calibration of DNV’s existing empirical guidance. A test program has been designed for the purpose of evaluating the consequence in head seas for the Brazil to China trade. Full scale measurements from previous development projects of ore carriers and model tests have been utilized to convert the current model tests results into estimated full scale results for the 400 000 dwt vessels. It is further important to carefully consider how the vibrations are to be included in the design verification, and to develop a procedure for taking into account the vibrations which results in reasonable scantlings based on in-service experience with similar designs and trades. This procedure has been developed, and a structural verification has been carried out for the design. The final outcome of the model test was in line with previous experience and in overall agreement with DNV’s empirical guidance, showing a significant contribution from vibrations to the fatigue damage. The springing/whipping vibrations more than doubled the fatigue damage compared to fatigue evaluation of the isolated wave induced loading. The cargo condition vibrated relatively more than experienced on smaller vessels. Various sources to establish the wave conditions for the Brazil to China ore trade were used, and the different sources resulted in significant differences in the predicted fatigue life of the design.

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