880 research outputs found
Report on the open meeting of restricted ECFA held at the University of Athens 10 February 1983
No full textThis report summarizes the opening presentation by J. Mulvey, L. Resvanis and T. Filippas, and the main points raised during the following discussion on the situation of high-energy physics in Greece
Modelling Risers With Partial Strake Coverage
No full textThis 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
No full textThis 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
Effects of Strake Coverage and Marine Growth on Flexible Cylinder VIV
No full textIn this paper we present 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 is presented in terms of CF response amplitudes and rainflow-counted damage rates due to the combined CF and IL bending stresses. All results are compared with the bare cylinder cases which will be used as a reference to determine how effective the strakes are in suppressing 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. We also observe that moderate amounts of marine growth can quickly negate any suppression coming from the strakes.SHEAR7 JI
The Identification of Power-In Region in Vortex-Induced Vibration of Flexible Cylinders
No full textThis 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
Ramp Tests: A Novel Approach to VIV Model Testing of Flexible Cylinders Using Continuously Varying Towing Speeds
No full textIn this paper we present a small portion of the results from the 2011 SHELL tests at the MARINTEK basin. The tests involved towing densely instrumented flexible cylinders at Reynolds numbers up to 150,000 in order to study the Vortex-Induced Vibration (VIV) response in uniform current profiles. This paper presents the experimental results collected from a series of tests where the towing speed was continuously varied while the cylinder and carriage traversed the basin. As the cylinder is accelerated (or decelerated) the incident current speed is continuously changing which means that multiple modes can be excited consecutively in a single tow through the basin. These varying towing speed tests are collectively referred to as ‘ramp tests’. The response data collected in these ‘ramp tests’ are presented in terms of CF response amplitudes and strains and are carefully compared with the response data collected during conventional steady towing speed tests. The data shows that when the acceleration of the carriage is kept below a critical value the ‘ramp tests’ are then able to provide VIV response information which is equivalent to that obtained from many constant speed tests. One ramp test provides the equivalent response data of (up to) 10 constant speed tests in a single run. This paper also introduces a dimensionless parameter γ, which determines if the proposed acceleration for a ramp test is within acceptable limits and may be used as a substitute for many constant speed tests. The parameter can be used to determine the appropriate acceleration or deceleration rate in order to ensure that a ramp test will yield suitable VIV response data. The parameter also allows one to know quickly whether or not fully developed VIV is possible in a given set of unsteady flow conditions.SHEAR7 JIPSHELL International Exploration and Production Co
Effects of Strake Coverage and Marine Growth on Flexible Cylinder Vortex-Induced Vibrations
No full textThis 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
No full textThis 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
No full textThe 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
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