Session: 01-04-02 Design and Anaysis - II

Submission Number: 157395

Simplifying Damping Matrix Calibration in Coupled Offshore Systems Using
Parameter Reduction Through Modal Decomposition 

One of the challenges in automatically calibrating damping in numerical models is the large number of parameters that need to be tuned, especially when calibrating complex floater motions. Coupled motion behavior is common in systems like floating offshore wind turbines (FOWTs), where the difference between the center of buoyancy and the center of flotation introduces such coupling. This behavior is also present in side-by-side moored vessels, where limited in-between distance and mooring line interactions lead to both hydrodynamic and mechanical couplings. As a result, the damping matrix of such a system most often includes off-diagonal terms.

For an NxN system, where N is the number of degrees of freedom (e.g., 12 for a two-body system), the number of terms to tune in the damping matrix may become substantial. Each parameter influences several others, making model calibration challenging. To reduce this complexity, a method of parameter reduction is proposed: the transformation from unit body motions (surge, sway, heave, roll, pitch, yaw) to modal coordinates through linearization and modal analysis. While this approach does not reduce the number of independent variables per se, it provides a transformation matrix that connects damping coefficients for each mode, without off-diagonal terms, to those for the unit body motions, with off-diagonal terms.

This method eliminates the need to tune all individual entries of the unit body damping matrix. Instead, the tuning process becomes constrained by the a priori known relationships identified through modal analysis. The transformation matrix remains largely unaffected by typical damping modifications and offers a practical means to reduce the number of parameters required for model calibration. The linearity assumption underlying the transformation is also discussed, as well as its effectiveness in real-world applications.

Presenting Author: Maarten van der Leij Maritime Research Institute Netherlands

Presenting Author Biography: Maarten van der Leij is Project Manager at the Maritime Research Institute (MARIN) in the Netherlands. In this role, he performs model tests and numerical (frequency-domain, time-domain and CFD) simulations, specifically for offshore (renewable) structures, both moored and on dynamic positioning. He possesses a Master of Science in Maritime Technology from Delft University of Technology and is since 2019 working for MARIN.