Cross Section VIV Model Test For Novel Riser Geometries

The global loads and fatigue life of deepwater risers or riser bundies in current are often dominated by Vortex Induced Vibrations (VIV). Semi-empirical prediction program such as Shear7 and VIVARRAY are still the most commonly used tools for analyzing the VlV response of such systems. These programs rely on large databases with experimentally determined hydrodynamic coefficients.
A new test apparatus has been developed for measuring the hydrodynamic VIV coefflcients on an oscillating model of the riser in uniform and steady current. A 3.4 m long section of the riser can be tested at full scale dimensions and real current speeds. Tests are carried out at different tow speeds, oscillation frequencies and amplitudes. Tests at full scale Reynolds numbers reveal new insights in the Reynolds scale effects and reduce uncertainties of such effects in the design process.
An efficiënt test strategy has been developed for finding the peak lift loads of a new riser geometry or configuration. About 50 tests are needed for each flow onentation. A non-ctrcular riser bundie can be tested for 8 flow angles between 0 and 360 degrees, using steps of 45 degrees. Over 400 tests can be conducted in about 2 weeks time.