Calibration of a Time-Domain Hydrodynamic Model for A 12 MW Semi-Submersible Floating Wind Turbine

Abstract

Design optimization of mooring systems is an important step towards the reduction of costs for the floating wind turbine (FWT) industry. Accurate prediction of slowly-varying horizontal motions is needed, but there are still questions regarding the most adequate models for low-frequency wave excitation, and damping, for typical FWT concepts. To fill this gap, it is fundamental to compare existing load models against model tests results. This paper describes a calibration procedure for a three-columns semi-submersible FWT, based on adjustment of a time-domain numerical model to experimental results in decay tests, and tests in waves. First, the numerical model and underlying assumptions are introduced. The model is then validated against experimental data, such that the adequate load models are chosen and adjusted. In this step, Newman’s approximation is adopted for the second-order wave loads, using wave drift coefficients obtained from the experiments. Calm-water viscous damping is represented as a linear and quadratic model, and adjusted based on decay tests. Additional damping from waves is then adjusted for each sea state, consisting of a combination of a wave drift damping component, and one component with viscous nature. Finally, a parameterization procedure is proposed for generalizing the results to sea states not considered in the tests.

Rational Simplification of High Fidelity Wind Turbine Models Used for Mooring Analysis

“…The INO WINDMOOR 12 MW wind turbine [13] is used for comparing the models . This is a 12 MW wind turbine supported by a three-column semi-submersible foundation.…”

“…This is a 12 MW wind turbine supported by a three-column semi-submersible foundation. The base case described in [13] is anchored with a semi-taut system of three lines. The platform used here includes mean wave drift loads and damping calibrated against model tests as described in [14] (additional sea-state dependent linear and quadratic surge-and sway damping coefficients are listed in Tab.…”

“…The WINDMOOR 12 MW turbine uses the PI-control from the ROSCO controller to control the torque and blade pitch, with controller gains tuned specifically for this platform to minimize negative floater pitch-motion damping. More detailed specifications of the turbine and floater can be found in [13].…”

Effect of body motion on the wave loads computed with CFD on the INO-WINDMOOR floater

“…The INO WINDMOOR structure [1] has a triangular shape composed by three vertical columns joined at the bottom by pontoons and at the top by deck beams (Figure 1). While waves are in the positive x-axis direction, there will be two columns upstream on the port and starboard side, symmetrical with respect to the centreline plane.…”

“…As part of ongoing research aiming at improving modelling of viscous forces on offshore floating structures, CFD simulations were carried out on the 1:40 model of the INO WINDMOOR floater [1] in regular waves to extract hydrodynamic loads, both on the structure, the single columns and sections from each column.…”