An Approach to Include Observed VIV Likelihood in Drilling Riser Fatigue Analyses

2009 ◽  
Author(s):  
Michael A. Tognarelli ◽  
Rene D. Gabbai ◽  
Mike Campbell
Keyword(s):  
Fatigue Damage ◽  
Field Measurements ◽  
Scaling Analysis ◽  
Current Profile ◽  
Vortex Induced Vibration ◽  
Probability Of Occurrence ◽  
Industry Standard ◽  
Annual Probability ◽  
Analysis Computer ◽  
Viv Suppression

Field measurements of the response of a number of drilling risers indicate that vortex-induced vibration (VIV) occurs significantly less often than predicted by the industry-standard fatigue analysis computer program SHEAR7 V4.4. Several comparisons to model tests and field data, including one published by BP and 2H in 2007 [1], demonstrate that this analysis program is generally quite conservative, given that VIV occurs. Furthermore, this conservatism does not take into account those situations in which VIV fatigue is predicted but none is observed in the field, which adds yet another layer of “hidden” conservatism to design analyses. In an effort to address this and reduce conservatism to a more appropriate level, the probability of occurrence of vortex-induced vibration (VIV) is examined using full-scale measured data. The data has been collected over the past several years from five drilling risers without VIV suppression devices. These risers are on rigs under contract to BP at high-current-susceptible sites worldwide. Collectively, the data correspond to 9,600 10-minute field measurements, equivalent to 0.18 years of continuous monitoring. The riser response is obtained from motion loggers placed at selected positions along the riser as described in [1]. Each logger measures 3D accelerations and 2D angular rates. Through-depth currents are measured via Acoustic Doppler Current Profilers (ADCP). By comparison of measurements to computer predictions based on the observed current profile, a relationship is developed between the intensity of the fatigue damage predicted and the probability that VIV is observed in the field. Subsequently, an approach is proposed for scaling analysis predictions to reflect the relative likelihood of VIV. The database of measured and SHEAR7 maximum predicted fatigue damage rates is statistically characterized to determine how it may be used to determine factors of safety (FOS) for VIV design. A worked example for a deepwater drilling riser in the GoM is used to show how the FOS methodology can be applied in the case of multiple design currents each with a different annual probability of occurrence.

VIV Safety Factors for Drilling Risers: Propagating Model Uncertainty in a Long-Term Reliability Analysis

2013 ◽  
Author(s):  
Michael A. Tognarelli ◽  
Nikhil Panicker ◽  
Mike Campbell ◽  
Steven R. Winterstein
Keyword(s):  
Field Measurements ◽  
Mathematical Approach ◽  
Deepwater Drilling ◽  
Worked Example ◽  
Industry Standard ◽  
Annual Probability ◽  
Actual Field ◽  
Viv Suppression ◽  
Future Work

Previous work [1] has given an approach to estimate vortex-induced vibration (VIV) factors of safety (FOS) for deepwater drilling risers. This work compared fatigue predictions from the industry-standard fatigue analysis software SHEAR7 with full-scale measured data. The field data have been collected over the past several years from five drilling risers without VIV suppression devices. These risers are on rigs under contract to BP worldwide, at sites susceptible to high currents. Collectively, the data correspond to 9,600 10-minute field measurements, equivalent to 0.18 years of continuous monitoring. A worked example for a deepwater drilling riser in the Gulf of Mexico was used to show how the FOS methodology can be applied in the case of multiple design currents each with a different annual probability of occurrence. However, the paper cited future work that included development of a mathematical approach that would permit a designer to calculate a modified FOS that accounts for the number of events (currents or wave seastates) analyzed. This paper documents a mathematical approach developed that can be used to calculate the riser design FOS based on multiple events of varying fatigue damage amplitude and probability. Note that the approach is not limited to VIV. It can be used for long-term wave fatigue life for example, assuming the designer has an understanding of the statistical differences between software predictions and actual field response.

Empirical Procedures for Long-Term Prediction of Fatigue Damage for an Instrumented Marine Riser

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
C. Shi ◽  
L. Manuel ◽  
M. A. Tognarelli
Keyword(s):  
Fatigue Damage ◽  
Field Measurements ◽  
Damage Estimation ◽  
Current Profile ◽  
Short Term ◽  
Response Characteristics ◽  
Damage Rate ◽  
Using Data ◽  
Analytical Approaches

Slender marine risers used in deepwater applications can experience vortex-induced vibration (VIV). It is becoming increasingly common for field monitoring campaigns to be undertaken wherein data loggers such as strain sensors and/or accelerometers are installed on such risers to aid in VIV-related fatigue damage estimation. Such damage estimation relies on the application of empirical procedures that make use of the collected data. This type of damage estimation can be undertaken for different current profiles encountered. The empirical techniques employed make direct use of the measurements and key components in the analyszes (such as participating riser modes selected for use in damage estimation) are intrinsically dependent on the actual current profiles. Fatigue damage predicted in this manner is in contrast to analytical approaches that rely on simplifying assumptions on both the flow conditions and the response characteristics. Empirical fatigue damage estimates conditional on current profile type can account explicitly even for complex response characteristics, participating riser modes, etc. With significant amounts of data, it is possible to establish “short-term” fatigue damage rate distributions conditional on current type. If the relative frequency of different current types is known from metocean studies, the short-term fatigue distributions can be combined with the current distributions to yield integrated “long-term” fatigue damage rate distributions. Such a study is carried out using data from the Norwegian Deepwater Programme (NDP) model riser subject to several sheared and uniform current profiles and with assumed probabilities for different current conditions. From this study, we seek to demonstrate the effectiveness of empirical techniques utilized in combination with field measurements to predict the long-term fatigue damage and the fatigue failure probability.

Empirical Procedures for Long-Term Prediction of Fatigue Damage for an Instrumented Marine Riser

2011 ◽  
Author(s):  
C. Shi ◽  
L. Manuel ◽  
M. A. Tognarelli
Keyword(s):  
Fatigue Damage ◽  
Field Measurements ◽  
Damage Estimation ◽  
Current Profile ◽  
Short Term ◽  
Response Characteristics ◽  
Damage Rate ◽  
Using Data ◽  
Analytical Approaches

Slender marine risers used in deepwater applications can experience vortex-induced vibration (VIV). It is becoming increasingly common for field monitoring campaigns to be undertaken wherein data loggers such as strain sensors and/or accelerometers are installed on such risers to aid in VIV-related fatigue damage estimation. Such damage estimation relies on the application of empirical procedures that make use of the collected data. This type of damage estimation can be undertaken for different current profiles encountered. The empirical techniques employed make direct use of the measurements and key components in the analyses (such as participating riser modes selected for use in damage estimation) are intrinsically dependent on the actual current profiles. Fatigue damage predicted in this manner is in contrast to analytical approaches that rely on simplifying assumptions on both the flow conditions and the response characteristics. Empirical fatigue damage estimates conditional on current profile type can account explicitly even for complex response characteristics, participating riser modes, etc. With significant amounts of data, it is possible to establish “short-term” fatigue damage rate distributions conditional on current type. If the relative frequency of different current types is known from metocean studies, the short-term fatigue distributions can be combined with the current distributions to yield integrated “long-term” fatigue damage rate distributions. Such a study is carried out using data from the Norwegian Deepwater Programme (NDP) model riser subject to several sheared and uniform current profiles and with assumed probabilities for different current conditions. From this study, we seek to demonstrate the effectiveness of empirical techniques utilized in combination with field measurements to predict long-term fatigue damage and life.

A Practical Drilling Riser and Wellhead Vortex Induced Vibration Fatigue Comparison Between Analysis and Field Measured Data

2015 ◽  
Author(s):  
Michael Long Ge ◽  
Jomon Kannala ◽  
David Cain ◽  
Elizbar B. Kebadze ◽  
Shankar Sundararaman ◽  
...  
Keyword(s):  
Fatigue Damage ◽  
Field Measurements ◽  
Current Data ◽  
Loop Current ◽  
Vortex Induced Vibration ◽  
Acceleration Data ◽  
Blowout Preventer ◽  
Vibration Fatigue ◽  
Industry Practice ◽  
Analytical Tools

In order to design a drilling riser system that meets the operational requirements, it is industry practice to use analytical tools to predict the riser and wellhead fatigue damage. This paper focuses on the comparison between the analysis and field measurements for both the drilling riser and wellhead vortex induced vibration (VIV) fatigue damage, during a recent loop current event in the Gulf of Mexico. The field data, which includes the drilling riser configuration, riser tensioner setting, and loop current data, were considered in this comparison. As one of the key contributors to VIV fatigue, the loop current, was measured from a survey vessel in the field during the blowout preventer (BOP) latched and retrieval period. The analysis utilized the VIV program SHEAR7 V4.6 to calculate the fatigue damage for both the drilling riser and wellhead system. The field measured acceleration data from the installed monitoring system was converted to the fatigue damage by transfer function methods. Key findings and conclusions are summarized to improve future analysis predictions of drilling riser and wellhead fatigue damage.

Fatigue Damage From High Mode Number Vortex-Induced Vibration

2006 ◽  
Author(s):  
J. Kim Vandiver ◽  
Susan B. Swithenbank ◽  
Vivek Jaiswal ◽  
Vikas Jhingran
Keyword(s):  
Fatigue Damage ◽  
Field Experiments ◽  
Higher Harmonics ◽  
Vortex Induced Vibration ◽  
Third Harmonic ◽  
The Third ◽  
Damage Rate ◽  
Surface Vessels ◽  
Vortex Shedding Frequency ◽  
First Time

This paper presents results from two field experiments using long flexible cylinders, suspended vertically from surface vessels. The experiments were designed to investigate vortex-induced vibration (VIV) at higher than tenth mode in uniform and sheared flows. The results of both experiments revealed significant vibration energy at the expected Strouhal frequency (referred to in this paper as the fundamental frequency) and also at two and three times the Strouhal frequency. Although higher harmonics have been reported before, this was the first time that the contribution to fatigue damage, resulting from the third harmonic, could be estimated with some certainty. This was enabled by the direct measurement of closely spaced strain gauges in one of the experiments. In some circumstances the largest RMS stress and fatigue damage due to VIV are caused by these higher harmonics. The total fatigue damage rate including the third harmonic is shown to be up to forty times greater than the damage rate due to the vibration at the fundamental vortex-shedding frequency alone. This dramatic increase in damage rate due to the third harmonic appears to be associated with a narrow range of reduced velocities in regions of the pipe associated with significant flow-induced excitation.

Practical Design Considerations for Managing Marine Growth on VIV Suppression Devices

2015 ◽  
Author(s):  
Don W. Allen ◽  
Li Lee ◽  
Dean Henning ◽  
Stergios Liapis
Keyword(s):  
Reynolds Number ◽  
Fatigue Life ◽  
Strong Influence ◽  
Low Reynolds Number ◽  
Vortex Induced Vibration ◽  
Design Considerations ◽  
Drag Forces ◽  
Practical Design ◽  
Helical Strakes ◽  
Viv Suppression

Most deepwater tubulars experiencing high currents frequently require vortex-induced vibration (VIV) suppression to maintain an acceptable fatigue life. Helical strakes and fairings are the most popular VIV suppression devices in use today. Marine growth can significantly affect the VIV of a bare riser, often within just a few weeks or months after riser installation. Marine growth can have a strong influence on the performance of helical strakes and fairings on deepwater tubulars. This influence affects both suppression effectiveness as well as the drag forces on the helical strakes and fairings. Unfortunately, many VIV analyses and suppression designs fail to account for the effects of marine growth at all, even on a bare riser. This paper utilizes results from both high and low Reynolds number VIV test programs to provide some design considerations for managing marine growth for VIV suppression devices.

Experimental Investigation on the Suppression Device of VIV of a Flexible Riser

2014 ◽  
Author(s):  
Yun Gao ◽  
Shixiao Fu ◽  
Leijian Song ◽  
Tao Peng ◽  
Runpei Lei
Keyword(s):  
Fatigue Damage ◽  
Experimental Results ◽  
Experimental Investigations ◽  
Flexible Riser ◽  
Excited Mode ◽  
Response Characteristics ◽  
Helical Strakes ◽  
Uniform Current ◽  
Viv Suppression ◽  
Synchronization Regime

Experimental investigations were conducted on a flexible riser with and without helical strakes. A uniform current was obtained by towing a riser model in a tank, and the vortex-induced vibration (VIV) suppression of strakes with different heights and pitches was studied. The results of the bare riser show that the characteristics of the synchronization of the VIV for a flexible riser have many orders, and the excited mode jumps from one to another abruptly. During the high order synchronization regime, the VIV response decreases with the increased order of the synchronization. The experimental results also indicate that the response characteristics of a bare riser can be quite distinct from those of a riser with helical strakes, and the suppression performance depends on the geometry of the helical strakes. The fatigue damage in the CF direction is of the same order as that in the IL direction for the bare riser. However, for the riser fitted with helical strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. The experimental results also confirmed that strake height has a greater influence on the VIV response than the strake pitch, and the drag exerted on the riser increases with strake pitch and height.

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.

Vortex-Induced Vibration and Drag Coefficients of Long Cables Subjected to Sheared Flows

1986 ◽  
Vol 108 (1) ◽  
pp. 77-83 ◽  
Author(s):  
Y.-H. Kim ◽  
J. K. Vandiver ◽  
R. Holler
Keyword(s):  
Field Experiments ◽  
Broad Band ◽  
Single Mode ◽  
Response Spectra ◽  
Flow Speed ◽  
Current Profile ◽  
Vortex Induced Vibration ◽  
Sheared Flow ◽  
Typical Experiment ◽  
Lock In

The vortex-induced vibration response of long cables subjected to vertically sheared flow was investigated in two field experiments. In a typical experiment, a weight was hung over the side of the research vessel by a cable that was instrumented with accelerometers. A typical experiment measured the acceleration response of the cable, the current profile, the tension, and angle of inclination at the top of the cable. Total drag force was computed from the tension and angle measurements. Two braided Kevlar cables were tested at various lengths from 100 to 9,050 ft. As a result of these experiments, several important conclusions can be drawn: (i) the wave propagation along the length of the cable was damped, and therefore, under most conditions the cable behaved like an infinite string; (ii) response spectra were quite broad-band, with center frequencies determined by the flow speed in the region of the accelerometer; (iii) single mode lock-in was not observed for long cables in the sheared current profile; (iv) the average drag coefficient of long cables subjected to sheared flow was considerably lower than observed on short cables in uniform flows; (v) the r.m.s. response was higher in regions of higher current speed. A new dimensionless parameter is proposed that incorporates the properties of the cable as well as the sheared flow. This parameter is useful in establishing the likelihood that lock-in may occur, as well as in estimating the number of modes likely to respond.

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