Session: 08-06-01 Internal Flows & FIV

Paper Number: 108105

108105 - Experimental Modeling of Water-Wave Interactions With a Flexible Beam 

This research concerns wave-basin experiments of fluid-structure interactions (FSI); specifically, the dynamic response of a flexible beam impacted by water waves. The aim of the study is the generation of experimental data that can be used to validate different numerical models of FSI, i.e., linear, nonlinear and high-fidelity.

The experimental set-up includes an initially vertical flexible cylindrical beam equipped with six accelerometers, distributed evenly along its length, that record its dynamic response. A probe placed at the free surface of the water close to the beam measures the free-surface elevation of the incident and reflected water waves. The beam is fixed to a basin carriage that traverses horizontally along the wave tank at different speeds so as to control the frequency with which waves encounter the beam. The upper and lower parts of the beam are respectively in air and submerged in water. Hammer tests on the beam in air and water are performed to obtain the dry and wetted modes and the structural and hydrodynamic damping. The novelty of the experimental setup is that it allows simultaneous measurement of beam deflections and their effect on the incident and reflected waves, rendering feasible a study of the FSI problem in different, controllable conditions.

The experiments are divided into three cases, each of which aims to study the dynamic response of the flexible beam to varying wave conditions; from regular-to-irregular and moderate-to-extreme wave height and steepness. Experimental Case 1 concerns interactions with the flexible beam when the carriage is at rest; this case will help to validate the linear FSI solvers in the non-resonant regime, as the natural frequencies of the beam are higher than the wave frequencies. Experimental Case 2 concerns interactions with the flexible beam when the carriage is moving at a constant speed. Moving the carriage changes the frequency of encounter with the waves, so that the dynamic response of the beam and its interaction with water waves, particularly at the onset of resonance, can be studied. By changing the steepness of the regular wave both linear and
nonlinear FSI solvers can be validated. Experimental Case 3 concerns steep, irregular wave interactions with the flexible beam when the carriage is at rest. This is the most complex case and is designed to yield data on structural dynamics due to nonlinear wave-loading processes related to steep and breaking waves. This case will help to validate the high-fidelity FSI solvers. 

Hence, the study covers a wide range of FSI problems that can be used to establish benchmarks for FSI-code validations.

Presenting Author: Wajiha Rehman University of Leeds

Presenting Author Biography: Wajiha Rehman is a postgraduate researcher(PGR) in the School of Mathematics at the University of Leeds. She is a Marie Sklodowska-Curie Early-Stage Researcher (ESR) for the European Union European Industrial Doctorate (EID) program; Eagre/Aegir: High-seas wave-impact modelling. As an ESR, she is working on two projects; the first one is developing a numerical model of a wave tank driven by the waveflap wavemaker to generate water waves using the variational principle of potential flow theory. The second project is to perform the experimental study of an FSI problem, i.e., water-wave interactions with a flexible beam and to develop and validate the numerical FSI solver. The FSI solver performs the wave-structure interaction analysis of water waves and the flexible offshore wind-turbine mast using (dis)continuous Galerkin’s Finite Element Method. This paper is about the second project.

Authors:

Wajiha Rehman University of Leeds
Tim Bunnik Maritime Research Institute Netherlands (MARIN)
Onno Bokhove University of Leeds
Mark Kelmanson University of Leeds