Partial Strake Coverage Vortex-Induced Vibration Benchmarking Using SHEAR7v4.5

A VIV benchmarking study was undertaken using SHEAR7v4.5 against NDP high mode VIV response laboratory data. The purpose of which was to derive an improved set of modeling parameters for partial strake coverage cases whilst not comprising previous accuracy of shear flow bare riser response predictions. Fifty percent (50%) partial strake coverage experimental data was utilized from both uniform and shear flow conditions while bare data was also included in the activity for reference purposes. The results showed that such an activity can derive an improved set of modeling parameters that significantly improve the ability to match experimental results and also highlight where future improvement efforts can be targeted

OMAE2007-29562 PHENOMENA OBSERVED IN VIV BARE RISER FIELD TESTS

ABSTRACT The following paper presents the results of preliminary data analysis performed on a densely instrumented bare riser undergoing Vortex-Induced Vibration (VIV) response at high mode number. The data analysis steps are presented and show a method whereby it is possible to resolve uncertainty in the orientation of strain gauges on a riser responding to VIV. Two new phenomena are then revealed from the data analysis. The first is the occurrence of higher harmonic VIV response in directions which are not orthogonal to the cross-flow and inline directions. Secondly, evidence of riser structural response in the form of wave propagation is observed

Reliability Based Factors of Safety for VIV Fatigue Using NDP Riser High Mode VIV Tests

Understanding the level of conservatism in a riser system design for vortex-induced vibration (VIV) fatigue is an important issue for operators. This study represents a demonstration of the calibration methodology to derive consistent values for the Factor of Safety (FoS). The exercise is performed here based on medium scale VIV data and utilizing the most commonly used VIV prediction software by industry. The results emphasize the need for (i) a coherent approach to estimate the FoS to be used and (ii) monitoring/measurement of software improvements as this may increase risk of failure if the influence of such improvements on the FoS is not quantified.DeepStar (Consortium) (DeepStar Phase IX

Using Model Test Data to Assess VIV Factor of Safety for SCR and TTR in GOM

This paper presents results obtained as part of the DeepStar Phase 10 program on VIV Factors of Safety. The objective was to develop a general methodology to calibrate Factors of Safety for VIV-induced fatigue and to apply it to partially straked risers. This was achieved using reliability methods, accepted industry VIV prediction software and state-of-the-art model test experiments. Most oil companies use a Factor of Safety of 20 when predicting VIV damage using VIV software tools. There are numerous software tools currently in use in industry to predict VIV damage to straked risers and each of them will have different accuracy, and therefore an intrinsic level of conservatism. Understanding the level of conservatism in different VIV prediction software is therefore critical to determining what Factor of Safety to use. This study benchmarks the latest generation of industry accepted VIV design tools at the time of the study (2011): SHEAR7v4.6, VIVAv6.5 and VIVANAv3.7.24 against high quality VIV data from three separate straked riser experiments. A bias distribution (predicted to measured VIV damage results) is obtained for each software tool as a function of the strake coverage. A novel reliability framework approach is then developed to incorporate all uncertainties associated with VIV fatigue prediction into a limit state function, including variability in met-ocean conditions and variability in the fatigue resistance of the material characterized by a design S-N curve. The limit state function is analyzed using First Order Reliability Methods to develop Factors of Safety for target probabilities of failure. The general method is then applied on two case studies involving an SCR and TTR in Gulf of Mexico loop currents, but it can be easily extended to different locations and riser configurations. The resulting FoS range from about 1 to 15 for most software, and are lower than industry standards for VIV prediction. The FoS do not vary markedly for different riser configurations, indicating the possibility of reducing excess conservatism when predicting VIV damage on straked risers.DeepStar (Consortium)SHEAR7 JI

Multimodal vortex-induced vibration

Abstract not availabl

OMAE2007-29562 PHENOMENA OBSERVED IN VIV BARE RISER FIELD TESTS

ABSTRACT The following paper presents the results of preliminary data analysis performed on a densely instrumented bare riser undergoing Vortex-Induced Vibration (VIV) response at high mode number. The data analysis steps are presented and show a method whereby it is possible to resolve uncertainty in the orientation of strain gauges on a riser responding to VIV. Two new phenomena are then revealed from the data analysis. The first is the occurrence of higher harmonic VIV response in directions which are not orthogonal to the cross-flow and inline directions. Secondly, evidence of riser structural response in the form of wave propagation is observed

Multimodal vortex-induced vibration

Abstract not availabl