Modelling Risers With Partial Strake Coverage

This paper compares model test data for risers with partial strake coverage to predictions made with the Vortex-Induced Vibration (VIV) prediction program SHEAR7 Versions 4.5 and 4.6. It is shown that new features in Version 4.6 substantially enhance the capability for predicting the VIV response of risers with partial coverage. Experimental data is taken from two large L/D tests: the NDP 38 m long riser tests and the Deepstar-Miami, 500 foot long riser. New methods are described for modeling risers partially covered with helical strakes. Key SHEAR7 parameters are recommended, based on parametric investigations to calibrate the model against the available experimental data. Recommended modeling procedures are described so as to facilitate implementation by SHEAR7 users in their VIV modeling tasks.SHEAR7 JI

Response Variability in Flexible Cylinder VIV Model Test Data

This paper presents some results from the 2011 SHELL tests at the MARINTEK basin. The tests involved towing densely instrumented 38m long flexible cylinders at Reynolds numbers up to 220,000. The main objective it to present the experimental results in a manner that describes the response variability that exists in the measured response data. Despite the fact that VIV is known to be a stochastic process, this is rarely addressed in the literature and currently there is no framework or 'best-practice' in the VIV community that can address statistically non-stationary data. In this paper, the experimental measurements are treated like non-stationary time-series and all statistical quantities which are typically of interest are computed with the use of short duration moving windows (or time-gates). A novel way of plotting and presenting VIV response data for flexible cylinders is introduced that is capable of revealing the inherent variability that exists in the cylinder's response.SHEAR7 Joint Industry Projec

The Identification of Power-In Region in Vortex-Induced Vibration of Flexible Cylinders

This paper proposes a novel method to identify the power-in regions of long flexible cylinders subjected to vortex-induced vibration (VIV). It also attempts to address a practical problem: “Will a secondary power-in region appear after the primary power-in region is covered with suppression devices?” The source of data is a recent model test on a 38 meter long flexible cylinder, densely instrumented with fiber optic strain gauges and accelerometers. For pipes with partial coverage of suppression devices in uniform flow, the bare region would be expected to be a power-in region and the section with suppression devices is expected to be a power-out region. Experimental data from these types of tests are used to benchmark the proposed power-in zone identification method. The method is then used to identify the power-in zones on a bare cylinder in a sheared flow. This paper also explores the occurrence of secondary power-in regions that may exist, when suppression devices are placed in the primary power-in zone. Secondary power-in regions were observed. Lessons learned from the power-in region identification in sheared flows will be a useful tool for designer/engineers choosing where to place suppression devices.DeepStar (Consortium)SHEAR7 JI

Effects of Strake Coverage and Marine Growth on Flexible Cylinder Vortex-Induced Vibrations

This paper presents some results from the recent SHELL tests at the MARINTEK basin. The tests involved towing densely instrumented flexible cylinders at Reynolds numbers up to 220,000. The main objective is to present the experimental results describing the effectiveness of different amounts of strake coverage and to explore the influence of simulated marine growth. The data are presented in terms of cross-flow (CF) response amplitudes and rainflow-counted damage rates due to the combined CF and in-line (IL) bending stresses. All the results are compared with the bare cylinder cases which will be used as a reference to determine how effective the strakes are in suppressing vortex-induced vibrations (VIV) and how this effectiveness can be affected by marine growth. The results show that even small bare sections (missing strakes) can lead to significant VIV response. Finally, the tests revealed that even moderate amounts of marine growth can quickly negate any suppression coming from the strakes.SHEAR7 JI

Reynolds Number Effects on the Vortex-Induced Vibration of Flexible Marine Risers

This paper explores the Reynolds number dependence of the Vortex-Induced Vibration (VIV) of flexible marine risers. Emphasis is placed on revealing the trends that exist between the Strouhal number and the Reynolds number and between the dimensionless amplitude (A/D) and Reynolds number. Data is drawn from recent towing tank experiments which used flexible cylinders of three different diameters. The 38m long pipes were exposed to uniform and sheared currents. The Reynolds number range extended from approximately 5,000 to 220,000 — well into the critical regime — with the larger diameter pipes responding in up to the 13th mode and the smaller diameter pipe responding well above the 20th mode. The results and trends from this set of experiments are compared to previous results from laboratory and field experiments.SHEAR7 JI

Consolidation of Empirics for Calculation of VIV Response

The present paper consolidates available experimental results for both sub-critical and critical Reynolds numbers and varying surface roughness and formulates a coefficient excitation model that aims at unbiased response estimates when using semi-empirical VIV prediction programs. A simplified procedure is suggested to account for higher order effects when relevant. The paper discusses the use of a modified coefficient excitation model with the objective of capturing or correctly reflecting certain specific features that have been observed in sub-critical and supercritical VIV experiments. The first part of this paper shows how the available low Reynolds number hydrodynamic data that currently forms the basis for most semi-empirical prediction software needs to be modified to correctly reflect the available experimental observations at sub-critical Reynolds numbers. The latter part of this paper looks at the available high Reynolds experimental data and suggests ways whereby the previously identified force coefficient database might be modified to reflect what is currently known about the VIV response of smooth and rough surfaced cylinders in the critical and super-critical Reynolds regimes.Norway Deepwater Progra

Indirect Detection of a Light Higgsino Motivated by Collider Data

Kane and Wells recently argued that collider data point to a Higgsino-like lightest supersymmetric partner which would explain the dark matter in our Galactic halo. They discuss direct detection of such dark-matter particles in laboratory detectors. Here, we argue that such a particle, if it is indeed the dark matter, might alternatively be accessible in experiments which search for energetic neutrinos from dark-matter annihilation in the Sun. We provide accurate analytic estimates for the rates which take into account all relevant physical effects. Currently, the predicted signal falls roughly one to three orders of magnitude below experimental bounds, depending on the mass and coupling of the particle; however, detectors such as MACRO, super-Kamiokande, and AMANDA will continue to take data and should be able to rule out or confirm an interesting portion of the possible mass range for such a dark-matter particle within the next five years.Comment: 10 pages, RevTe

Neutrino Telescopes' Sensitivity to Dark Matter

The nature of the dark matter of the Universe is yet unknown and most likely is connected with new physics. The search for its composition is under way through direct and indirect detection. Fundamental physical aspects such as energy threshold, geometry and location are taken into account to investigate proposed neutrino telescopes of km^3 volume sensitivities to dark matter. These sensitivities are just sufficient to test a few WIMP scenarios. Telescopes of km^3 volume, such as IceCube, can definitely discover or exclude superheavy (M > 10^10 GeV) Strong Interacting Massive Particles (Simpzillas). Smaller neutrino telescopes such as ANTARES, AMANDA-II and NESTOR can probe a large region of the Simpzilla parameter space.Comment: 28 pages, 9 figure

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

Neutrino Interactions at Ultrahigh Energies

We report new calculations of the cross sections for deeply inelastic neutrino-nucleon scattering at neutrino energies between 10^{9}\ev and 10^{21}\ev. We compare with results in the literature and assess the reliability of our predictions. For completeness, we briefly review the cross sections for neutrino interactions with atomic electrons, emphasizing the role of the $W$-boson resonance in $\bar{\nu}_{e}e$ interactions for neutrino energies in the neighborhood of 6.3\pev. Adopting model predictions for extraterrestrial neutrino fluxes from active galactic nuclei, gamma-ray bursters, and the collapse of topological defects, we estimate event rates in large-volume water \v{C}erenkov detectors and large-area ground arrays.Comment: 32 pages, 11 figures, uses RevTeX and boxedep