Estimation of Hydrodynamic Coefficients for VIV of Slender Beam at High Mode Orders Available to Purchase

The Hano̸ytangen test program was caried out by MARINTEK for Norsk Hydro in 1997. One purpose of this research effort was to investigate VIV response of deep sea risers subjected to sheared current. A densely instrumented 90 meter long riser model was tested in shear current, and bending strains along the riser was measured. Oscillatory part of both in-line (IL) and cross-flow (CF) displacements can be obtained by applying modal analysis on the bending moment measurements. The primary results from the analysis are that the riser is vibrating at high modes in cross-flow direction (10th–30th mode). The response is dominated standing waves for the lowest speed cases and gradually is influenced by traveling waves for increasing speed. For highest speed cases, it is dominated by traveling waves. The vibration amplitude is significantly smaller than for a rigid cylinder under equivalent conditions. Inverse force analysis estimates hydrodynamic forces from measured response of a slender beam. The method has previously been applied to rotating rig test data. The response was for these cases dominated by relatively low mode orders and standing wave responses. To understand the stochastic behaviour of high mode VIV response, the method is applied to Hano̸ytangen test in the present study to provide valuable insights by estimating CF hydrodynamic forces and coefficients from displacement time series found from modal analysis of measured strains. The results from this work are presented in terms of CF hydrodynamic force coefficients, excitation region and their variations in time and space. New excitation database is extracted based on the analysis results. They are used in VIVANA to predict the displacement and stress against experiment results.