Mitigation of Floating Platform Motions With Tuned Liquid Column Dampers: Experimental and Numerical Investigation of a Damped Barge for Offshore Wind Applications.

Author

Mitchell A. Kelley, University of MaineFollow

Date of Award

Spring 5-10-2025

Level of Access Assigned by Author

Open-Access Thesis

Language

English

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Committee Advisor

Richard Kimball

Second Committee Member

Anthony Viselli

Third Committee Member

Andrew Goupee

Abstract

Floating wind energy remains costly compared to other energy sources, largely due to the high expense of floating platforms. UMaine’s VolturnUS+ aims to reduce these costs through a lightweight, simple barge design, contrasting with heavier, more complex platforms that are challenging to construct and deploy. To achieve dynamic performance comparable to larger, more expensive platforms, the design incorporates a seawater ballast-based bidirectional tuned liquid column damper (TLCD) to stabilize the structure in extreme storm conditions. This thesis focuses on the performance of this TLCD, of substantial mass compared to traditional systems, through experimental and numerical investigations. A 1:70 scale model was tested at the Advanced Structures and Composites Center’s Wind and Wave Laboratory, while a time-domain model was developed to simulate the coupled system dynamics including nonlinear damping effects. The work aims to deepen understanding of these dynamics to guide future design improvements. Free decay tests characterized the TLCD’s damping behavior—both in its natural state and when subjected to a tunable airflow restriction device. The distinct nonlinear damping observed validated the damping model developed to account for variations across different flow regimes. Moreover, discrepancies between the assumed and measured effective mass were identified and characterized as a function of flow obstruction configuration. Platform free decay tests further elucidated the coupled dynamics of the platform–TLCD system and were instrumental in verifying the underlying equations of motion; however, they also revealed nonlinearities in the natural pitch period not captured by the model, emphasizing the challenges inherent in modeling such complex interactions. Active wave tests demonstrated the TLCD’s effectiveness in attenuating platform pitch motions regardless of incident wave direction. Systematic studies revealed that controlling TLCD damping ratio has a substantial influence on platform pitch response. These tests confirmed the TLCD’s role in reducing pitch responses near resonance at the cost of some amplification associated with TLCD and coupled pitch eigenmodes, while also highlighting some deviations in frequency response compared to numerical simulations. Tests under realistic 50-year storm conditions revealed pronounced second-order wave effects, with notable platform energy in both pitch and surge at frequencies with minimal incident wave energy. Additionally, an alternative TLCD design incorporating baffles to redirect flow was experimentally evaluated, providing additional insights into performance improvements.

Recommended Citation

Kelley, Mitchell A., "Mitigation of Floating Platform Motions With Tuned Liquid Column Dampers: Experimental and Numerical Investigation of a Damped Barge for Offshore Wind Applications." (2025). Electronic Theses and Dissertations. 4159.
https://digitalcommons.library.umaine.edu/etd/4159