Influence of the internal varying density flow on the vibrations and fatigue damage of a top-tensioned riser undergoing vortex-induced vibrations

2021 ◽  
Vol 117 ◽  
pp. 102955
Author(s):  
Wude Xie ◽  
Weiyan Xin ◽  
Hongqiang Zhang
Keyword(s):  
Fatigue Damage ◽  
Vortex Induced Vibrations ◽  
Density Flow

Experimental Study on Flexible Bare Pipe Arrays Undergoing Vortex-Induced Vibrations

2018 ◽  
Author(s):  
Y. Liu ◽  
C. Shi ◽  
Z. Liu ◽  
J. Wang ◽  
X. Bao
Keyword(s):  
Fatigue Damage ◽  
Dynamic Responses ◽  
Array Configuration ◽  
Damage Rate ◽  
Flexible Pipes ◽  
Vortex Induced Vibrations ◽  
Helical Strakes ◽  
Preliminary Study ◽  
Single Pipe ◽  
Center Distance

Vortex-induced vibration (VIV) excited by current is a major contributor to the fatigue accumulation of marine risers. For deepwater operations, several risers are often arranged together in an array configuration. In this study, a set of four identical flexible pipes of a rectangular arrangement were tested in a water tunnel. By comparing the dynamic responses of a pipe in an array with that of a single isolated pipe, the effects of the current speed and the center-to-center distance between the up-stream and downstream pipes on their dynamic responses were investigated. Fatigue damages accumulated on each pipe in an array was calculated and a factor, termed “fatigue damage amplification factor”, was defined as a ratio between the fatigue damage rate of pipe in an array and the fatigue damage rate of a single pipe at a same current condition. The results showed that for bare pipes (i.e., without helical strakes), the downstream pipes in an array configuration may have larger dynamic responses and fatigue damage rates than those of a single pipe; and, it is not always conservative to assume that the fatigue damage rate estimated for a single pipe can be used to represent the fatigue damage rates of pipes in an array. This preliminary study provided some meaningful results for the design, analysis and operation of marine riser arrays.

An Assessment of EOF Current Scatter Diagrams With Respect to Riser VIV Fatigue Damage

2002 ◽  
Author(s):  
Trond Stokka Meling ◽  
Kenneth Johannessen Eik ◽  
Einar Nygaard
Keyword(s):  
Fatigue Damage ◽  
Principal Components ◽  
Empirical Orthogonal Functions ◽  
Time Varying ◽  
Scatter Diagram ◽  
Orthogonal Functions ◽  
Vortex Induced Vibrations ◽  
Deepwater Riser ◽  
Diagram Approach ◽  
Current Modelling

The accuracy of current modelling is critical when considering deepwater riser fatigue damage caused by vortex-induced vibrations (VIV). In the present study the use of empirical orthogonal functions (EOF) to extract the governing characteristics from huge amounts of current measurements has been assessed. The amplitudes of the time varying principal components (PC) have been organized into bins in scatter diagrams. The accuracy of this scatter diagram approach with different numbers of EOF modes involved has been evaluated in terms of riser VIV fatigue damage.

Methods for Reducing a Large Number of Current Profiles to a Small Subset for Riser VIV Analysis

2005 ◽  
Author(s):  
Kostas F. Lambrakos ◽  
Djoni E. Sidarta ◽  
Hugh M. Thompson ◽  
Atle Steen ◽  
Roger W. Burke
Keyword(s):  
Fatigue Damage ◽  
Average Power ◽  
Small Subset ◽  
Large Set ◽  
Computationally Efficient ◽  
Excitation Mode ◽  
Average Value ◽  
Vortex Induced Vibrations ◽  
Simplified Procedure

The paper presents two different approaches to construct subsets of current profiles from a large set of long term current profiles for the purpose of performing calculations for riser fatigue damage from vortex induced vibrations (VIV). The subsets are intended to reproduce the fatigue damage from the full set of current profiles. In the first approach, the full set of profiles is first sorted into bins based on current magnitude, direction and shear in the profile. The profiles within each bin are then reduced to a single constructed profile through one of many possible current averaging schemes. The present study includes two types of constructed profiles; one profile is generated by the average value of the currents for each bin and the other by the average value plus one standard deviation. The second approach is based on first performing a simplified and computationally efficient VIV analysis of the full set of profiles. The profiles are then sorted into bins by the dominant excitation mode, and then a single profile is chosen to represent all the profiles that excite the mode of interest. The chosen profile for the mode of interest has VIV power-in which is close to the average power-in for all the profiles that excite the mode. The number of profiles in the subset is equal to the number of modes that are excited by the full set of profiles. The VIV power-in in this paper is estimated through a simplified procedure that is consistent with the SHEAR7 methodology. Other available codes can also be used for the simplified VIV calculations.

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.

Calibration of Safety Factors for DNV RP-F105 Free Spanning Pipelines

2006 ◽  
Author(s):  
Gudfinnur Sigurdsson ◽  
Kim Mo̸rk ◽  
Olav Fyrileiv
Keyword(s):  
Fatigue Damage ◽  
Structural Reliability ◽  
Uncertainty Modeling ◽  
Submarine Pipeline ◽  
Safety Factors ◽  
Sources Of Uncertainty ◽  
Fatigue Design ◽  
Vortex Induced Vibrations ◽  
Stochastic Parameters ◽  
Pipeline Design

Free spans often become a significant challenge in pipeline design and operation due to uneven seabed or seabed scouring effects. The trend towards deeper waters, harsher environment and installation of pipelines at very uneven seabed often implies a high number of free spans. High costs related to span intervention puts focus on minimizing these costs and still ensure integrity of the pipeline with respect to vortex induced vibrations (VIV) and associated fatigue damage. On the other hand the potential costs related to fatigue failure of a pipeline (recovery costs and economical loss) are enormous. Therefore it is essential to ensure that the probability of failure for free spans is within acceptable limits, e.g. as required by DNV-OS-F101 “Submarine Pipeline Systems”. This paper describes the structural reliability analysis performed to obtain the safety factors for free span fatigue design. Accumulation of fatigue damage due to VIV of free spans is associated with various sources of uncertainty. The important stochastic parameters are described, and the basis for the uncertainty modeling given. The calibration scope defined from a set of different pipeline cases, span scenarios, and environmental conditions is presented from which calibration results and sensitivities will be discussed.

Metocean Criteria for the Fatigue Analysis of Subsea Pipelines

2019 ◽  
Author(s):  
Richard Gibson ◽  
Marios Christou
Keyword(s):  
Fatigue Damage ◽  
Clustering Algorithms ◽  
Statistical Dependence ◽  
The Caspian Sea ◽  
Vortex Induced Vibrations ◽  
Waves And Currents ◽  
Order Of Magnitude ◽  
Extreme Value Model ◽  
Current Loading ◽  
Subsea Pipelines

Abstract This paper is concerned with a methodology for defining metocean criteria for the analysis of subsea pipelines. The approach that has been developed incorporates the statistical dependence between wave and current loading. The method achieves this through a combination of the application of the conditional extreme value model of Heffernan and Tawn (2004) and clustering algorithms. This is particularly important in regions where the currents are largely wind driven as there can be a strong correlation between the two. The results can be used to assess fatigue damage from vortex-induced-vibrations and wave loading. The same model can be used to derive deterministic design events. The method is applied to a pipeline in the Caspian Sea. The results are compared to models that assume either independence or a perfect correlation between waves and currents. It is shown that simpler models that do not accurately model the dependence between the waves and the currents can provide estimates of fatigue damage that are an order of magnitude too high or too low.

The Effect of Seabottom Proximity of the Vortex-Induced Vibrations and Fatigue Life of Offshore Pipelines

1983 ◽  
Vol 105 (4) ◽  
pp. 464-468 ◽  
Author(s):  
D. T. Tsahalis
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Experimental Results ◽  
Offshore Pipelines ◽  
Vortex Induced Vibrations

The effect of the seabottom proximity on the vortex-induced vibrations of suspended spans of offshore pipelines is discussed in the light of recent relevant experimental results. It is shown that the effect of the seabottom proximity is to drastically alter the vortex-induced vibrations of supsended spans resulting into longer fatigue lives or equivalently longer safe lengths. A “generalized” fatigue damage is formulated universally applicable to all suspended spans.

Free Span Rectifications in Submarine Pipeline Projects: A Case Study

2017 ◽  
Author(s):  
Udaivir Yadav ◽  
Pawan Negi
Keyword(s):  
Fatigue Damage ◽  
Environmental Data ◽  
Western India ◽  
Subsea Pipeline ◽  
Sea Bed ◽  
Vortex Induced Vibrations ◽  
Huge Impact ◽  
Pipeline Route ◽  
Area Of Concern

Seabed features along a subsea pipeline route are highly stochastic. Free spans may be created in the pipelines due to seabed irregularities, subsequent scouring, and horizontal movements of pipeline during operation. It is quite common to encounter free spanning sections along the pipeline route from the very start till the end. Spanning of subsea pipelines is a primary area of concern not only in the detailed design and installation stage but also during the operation stage. For ensuring the pipeline safety during operation, underwater surveys must be conducted at suitable intervals. The frequency of such pipeline free spanning surveys depends on the operators’ interest and the statutory requirements. The static and dynamic characteristic of the pipeline spans should be investigated to ensure that the pipeline can be operated within acceptable safety levels. The unsupported spans that incur static as well as dynamic loads on the pipeline, may lead to vortex-induced vibrations and ultimately fatigue, and thus affecting the pipeline serviceability and design life. Vortex induced vibrations are not allowed to occur in the operation life as far as the conventional design is considered but DNV - RP - F105 allows the onset of vortex induced vibrations provided that the fatigue damage due to vortex induced vibrations doesn’t exceed the allowable values. Pipe soil interaction has a huge impact on the pipeline design as well as the pipeline service life. Analysis of the existing conditions and stress levels based on the site-specific surveys and environmental data needs to be carefully carried out for determining the acceptability of spans and the effective intervention works if required. Hydrological studies and numerical modeling may also need to be carried out for sediment transportation analysis and for proper assessment & quantification of sea bed erosion, trenching and backfilling requirements. In the present work, the acceptable criteria in terms of static and dynamic stresses and fatigue damage limits due to vortex induced vibrations as per DNV - RP - F105 have been discussed. Further comprehensive analysis philosophy and the criticalities in the design analysis for free spanning of subsea pipeline are presented. A case study based on an offshore project in western India has been presented involving the major project issues. The main areas of concerns & challenges faced are examined in detail. Further study has been conducted for the other available strategic solutions in the VIV mitigation and rectification of free spanning sections.

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