Comprehensive Riser VIV Model Tests in Uniform and Sheared Flow

Abstract

Despite of considerable research activity during the last decades considerable uncertainties still remain in prediction of Vortex Induced Vibrations (VIV) of risers. Model tests of risers subjected to current have been shown to be a useful method for investigation of the VIV behavior of risers with and without suppression devices.In order to get further insight on VIV of risers, an extensive hydrodynamic test program of riser models subjected to vortexinduced vibrations was undertaken during the winter 2010 by Shell Oil Company.The VIV-model test campaign was performed in the MARINTEK Offshore Basin Laboratory. A new test rig was constructed and showed to give good test conditions. Three different 38m long riser models were towed horizontally at different speeds, simulating uniform and linearly varying sheared current. Measurements were made In-Line (IL) and Cross-Flow (CF) of micro bending strains and accelerations along the risers. The test program compromised about 400 tests, which give a rich test material for further studies.In the present paper the test set-up and program are presented and selected results are reported. INTRODUCTIONThe key objectives of the riser VIV model test campaign were:

Ramp Tests: A Novel Approach to VIV Model Testing of Flexible Cylinders Using Continuously Varying Towing Speeds

“…Towing velocities ranged from 0.25m/s to 3.45m/s which correspond to a Reynolds number range from 5,000 to 220,000 in sheared flows and up to 150,00 in uniform flows. More details on the experimental set-up can be found in Lie et al (2012). The results from these tests have already been published in a series of papers over the past few years, see Resvanis et al (2012Resvanis et al ( , 2014, Rao et al (2012Rao et al ( , 2013Rao et al ( , 2014.…”

“…Figure 3 shows the CF RMS curvature (spanwise averaged) as a function of time for the same 'ramp test'. All RMS calculations are actually 'moving RMS' calculated using equation 4. The local maxima that are easily identifiable on the plotted curvature signal are indicators of VIV lock-in at different modes.…”

Effects of Strake Coverage and Marine Growth on Flexible Cylinder Vortex-Induced Vibrations1

“…The relationship between stresses and amplitude for a flexural wave on a beam is shown in Eq. (2). Here, r is a stress, E is the Young's Modulus, e is the bending related strain, A is the response amplitude at a specific time instant, OD/2 is the distance from the neutral axis at which the stresses/strains were measured (13.5 mm), and k is the wavenumber…”

Vortex-induced vibration of a flexible cylinder: Interaction of the in-line and cross-flow responses

“…Data from two VIV tests with flexible cylinders are used to extract the motion phase angle and hydrodynamic force coefficients. The first set of tests was Shell's VIV test data, which was performed in the MARINTEK Offshore Basin in March 2011 (Lie et al, 2012). Data from earlier VIV model tests with a free-span pipeline (Baarholm, 2006) are also used in this effort.…”