Validation of a low-cost IMU for flow-induced vibration tracking in offshore systems

It is known that field measurement of offshore structures is highly dependent on environmental conditions, external interference, availability and accuracy of the equipment applied, among other aspects. Currently, the cost to reliably predict displacements and frequencies of risers, umbilicals and mooring lines is very high. To obtain good results through low-cost hardware, the collected data require careful signal treatment and validation of the entire procedure. To create a low-cost solution for further application, this work carried out two experimental studies: decay tests on a vertically clamped cylinder in air and decay tests on a spar platform model in a water tank. To validate the inertial measurement unit (IMU) displacement results, we have tested different positions and initial excitations. The signal was treated by applying a Kalman filter to extract the angles of the IMU, and a rotation quaternion was built at each time step. The double integration of the acceleration vector to calculate the body displacement is studied, filtering out noise and drift problems with Fourier filter and final intrinsic mode function. The frequencies and displacement time histories obtained by the IMU were compared with those of an optical tracking system. The result was an average relative error of less than 2.8% for air and water decay tests, validating the use of low-cost hardware compensated with signal treatment.