Session: 01-01-01 Offshore Platforms-1

Submission Number: 179764

Experimental and Numerical Investigation of a Pontoon-Supported Multi-Modular Floating Structure in Regular Waves 

Multi-modular floating structures, which consist of interconnected modules moored to the seabed, are proposed for applications such as floating solar energy.  Simulation approaches capable of accurately and efficiently predicting the response of multi-modular floating structures under various environmental conditions are needed. The focus of this work is on a specific type of structure consisting of modules composed of a horizontal plate supporting four vertical cylindrical pontoons, interconnected with ball joints. The objective of the study is to evaluate the accuracy and limitations of conventional hydrodynamic load models, namely Morison-based and potential flow approaches, to assess the response in waves of multi-modular floating structures.

As part of this investigation, wave tank experiments were conducted using 1:20 scale model. Motions of the modules, as well as forces in the connections and mooring system, were measured for different structure configurations and across a range of regular wave conditions. The study focuses on configurations with one, two, and four modules to limit the complexity of the coupled responses and thus enabling a clear assessment of the hydrodynamic load models’ accuracy.

The experimental results are compared against results from a time-domain simulator. The structure is modelled as a set of interconnected rigid bodies, while the ball joints are represented as springs with high stiffness. Hydrodynamic loads on the pontoons are calculated using Morison’s equation, extended by incorporating hydrodynamic coefficients extracted from a potential flow solver. As a result, the simulator captures hydrodynamic interactions and wave-frequency-dependent effects that are generally neglected in a pure Morison approach.

Comparisons of the first-order responses show that the simulator correctly identifies the natural frequencies of the system. The numerical model tends to overpredict the response amplitudes, particularly at resonance and for configurations with multiple modules, with the simulator showing smaller deviations from the experimental measurements than pure Morison and potential flow approaches. The influence of friction in the experimental mooring system was evaluated and may cause part of the discrepancies, though it does not fully explain them. More accurate modelling of viscous damping of finite-length circular cylinder in wave-like flows, for example using high fidelity numerical approaches or dedicated experiments, may also be necessary to better capture the response of the modules.

Keywords: floating solar, multi-body dynamics, hydrodynamics, wave-structure interaction, model tests, time-domain analysis

Presenting Author: Benjamin Leduc NTNU

Presenting Author Biography: Benjamin Leduc is a PhD candidate at the Norwegian University of Science and Technology (NTNU). His research focuses on the dynamic behavior of multi-modular floating structures, including both structural and hydrodynamic aspects, investigated through both numerical and experimental approaches.

Authors:

Benjamin Leduc NTNU
Erin Bachynski-Polić NTNU
Trygve Kristiansen NTNU