STREAM JIP – Insights into Steel Catenary Riser Response Using Measured Data

Deka, Dhyanjyoti; Chandra, Yenny; Campbell, Mike; Santala, Markku; Constantinides, Yiannis; Jin, Joe; Darilmaz, Ilkay; Nadathur, Raja; Yiu, Flora

doi:10.4043/29239-ms

Cited by 3 publications

References 5 publications

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Heave Motion Induced Vortex-Induced Vibrations of a Full-Scale Steel Lazy Wave Riser

Yin

2022

Journal of Offshore Mechanics and Arctic Engineering

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Deepwater steel lazy wave risers (SLWR) subject to vessel motion will be exposed to time-varying oscillatory flow, vortices could be generated and the cyclic vortex shedding force causes the structure vibrate, such fluid-structure interaction is called vortex-induced vibrations (VIV). To investigate VIV on a riser with non-linear structures under vessel motion and oscillatory flows, time domain approaches are needed. In this study, a time-domain approach is used to simulate a full-scale SLWR. Two cases with simplified riser top motions are simulated numerically. By using default input parameters to the time domain approach, the key oscillatory flow induced VIV response characteristics such as response frequency, curvature and displacements are examined and discussed. More accurate VIV prediction could be achieved by using realistic hydrodynamic inputs into the time domain model.

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Heave Motion Induced Vortex-Induced Vibrations of a Full-Scale Steel Lazy Wave Riser

Yin

2022

Journal of Offshore Mechanics and Arctic Engineering

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Review of Hydrodynamic Coefficients for Riser Design

Deka¹,

Campbell²,

Darilmaz

et al. 2022

Day 4 Thu, May 05, 2022

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A literature review of experimental and computational hydrodynamic research is presented with the objective of highlighting the parameters that affect riser added mass coefficient (Ca) and drag coefficient (Cd). Typical riser analysis is conducted assuming constant values of hydrodynamic coefficients. However, depending on the flow regime, the hydrodynamic coefficients can vary significantly, and hence using the most conservative values in all analyses can result in overly conservative riser responses. For example, the appropriate coefficients for a steady current on the straked portion of a riser near the surface may be very different from those for small oscillatory motions of the riser near the Touch Down Point (TDP). Several opportunities of reducing conservatism are presented based on using variable hydrodynamic coefficient-based analysis. Hydrodynamic coefficients are dependent on surface roughness, nature of the flow (steady vs. unsteady) and presence of Vortex Induced Vibration (VIV) suppression devices (strakes or fairings), among other factors. Relevant and important bodies of work as documented in papers, test reports or doctoral theses in the public domain are used to determine sensitivity of Cd and Ca values to Reynold's number (Re) and the Keulegan Carpenter (Kc) number. Steady and unsteady flows are treated separately, as are unstraked (bare) and straked pipes. The practice of using constant values of hydrodynamic coefficients in riser analysis is simplistic and often overly conservative. A common practice is to use Cd of 0.7 in bare pipe fatigue analysis as a lower bound. Several tests have demonstrated that Cd can in fact lie in the 1 – 2 range depending on Kc number and Re number. Higher Cd is associated with higher hydrodynamic damping and considerable improvement in TDP fatigue life prediction. Similarly, strake Cd's in low Kc flow have also been observed to be higher than what is used in typical riser analysis, sometimes by a factor of 3 or more. On the other hand, higher Ca values can lead to higher fatigue damage prediction. The correct input of Ca is thus essential to avoid being under conservative. Ca variations with respect to Kc number for both bare and straked pipes are provided in this paper. A refined approach to application of hydrodynamic coefficients in riser analysis is necessary to avoid over or under conservatism. This is especially important in life extension studies where there is little room for additional conservatism. The riser design codes typically do not provide an in-depth review of hydrodynamic coefficients based on factors such as roughness, nature of flow or pipe cross section. This review paper of fundamental experimental and computational work on hydrodynamic parameters is a useful reference to be used in design and life extension assessments.

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STREAM JIP – An In-Depth Study of SCR Response Based on Field Measurements

Chandra,

Deka,

Campbell

et al. 2024

Day 1 Mon, May 06, 2024

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The objective of the STREAM (Steel Riser Enhanced Analytics using Measurements) Joint Industry Project (JIP) is to provide a measurement-based foundation for Steel Catenary Riser (SCR) modelling to ensure that riser response is assessed with adequate but not overly conservative parameters. Insights from phase 1 of the JIP were presented in a prior OTC paper (OTC-29239-MS). In phase 2 which is the subject of this paper, the JIP has conducted a deep dive into several other aspects of SCR design uncertainty including - combined wave and Vortex Induced Vibration (VIV), Motion Induced Vibration (MIV), and extreme storm response. The paper will describe how field measured riser response events have been categorized into wave, VIV, MIV, and other non-typical response types. Subsequently, fatigue damage rates derived from field measured data (measured fatigue) are compared against global analysis-based predictions. Concurrent wave and VIV response events are assessed to determine whether the industry standard practice of adding VIV and wave fatigue damage rates is adequately conservative. Measured VIV data is utilized to benchmark SHEAR7 and determine the hidden conservatism in it that stems from non-occurrence of VIV in the field despite the presence of sufficiently high currents. MIV response events are characterized, and the impact on overall riser fatigue is evaluated. Finally, observations field measured riser response during the peak of a major hurricane is reported and examined. In an industry first, the STREAM JIP has aggregated and analyzed full scale field data from multiple catenary risers. The JIP results provide insights into riser response characterization with potential applications for life extension and more efficient new designs.

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STREAM JIP – Insights into Steel Catenary Riser Response Using Measured Data

Cited by 3 publications

References 5 publications

Heave Motion Induced Vortex-Induced Vibrations of a Full-Scale Steel Lazy Wave Riser

Heave Motion Induced Vortex-Induced Vibrations of a Full-Scale Steel Lazy Wave Riser

Review of Hydrodynamic Coefficients for Riser Design

STREAM JIP – An In-Depth Study of SCR Response Based on Field Measurements

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