University Events

Description: Topic: Experimental Study on Fluid-Structure-Surface Interactions of Streamlined Structures

Location: SENG 110 Material Science Lab

Abstract:

Flow-induced vibration (FIV) occurs when fluid interacts with a flexible body, causing oscillation due to fluctuating forces from vortex shedding. Flow-induced vibration can affect the performance, safety, and reliability of various engineering systems, such as bridges, pipelines, wind turbines, offshore structures, etc. The FIV response of these systems can be significantly influenced by asymmetry, which can be either geometric or flow-dependent. Previous studies have investigated the relationship between bluff bodies and the free surface, showing that as the submerged height of the structure decreases, the FIV response changes considerably. Despite extensive FIV studies on geometric asymmetries, such as the asymmetric boundary condition of the structure, cross-section, and various angles of attack, the influence of flow asymmetry has not been as thoroughly investigated. For a structure submerged in water, it can experience asymmetric flow when placed near the interface of water and air (free surface). The deformable free surface can act as an elastic member that can create an additional coupling between the structure and the flow, which introduces what we term "fluid-structure-surface interactions". Understanding these interactions in submerged hydrodynamic streamline bodies is crucial for a wide variety of applications, ranging from near-surface energy harvesting to the design of marine structures and tidal power generation equipment. The majority of studies exploring the influence of free surface on streamlined structures have focused on the theoretical and computational examination of two-dimensional stability conditions. Few experimental studies have examined the impact of the free surface on the response of foils and plates in prescribed motion. To our knowledge, no previous study has visually quantified the characteristics of three and two-dimensional asymmetric flow in self-excited oscillating plates or foils.

The aim of this research is to investigate how the proximity to the deformable free water surface affects the dynamic hydroelastic and hydrodynamic behavior of a flexible plate. To achieve this goal, we initially examined the flow dynamics surrounding a stationary rigid flat plate placed near a free surface, at varying angles of attack (AOA), Reynolds numbers, and submerged depths. Later on, flow structure and subsequent FIV response of the plate, with one degree of freedom (DoF) in the plunging direction in terms of amplitude and frequency of oscillation was investigated at various AOA. In the subsequent stage, we expanded our investigation to plates with both 1DoF and 2DoF for pitching and plunging oscillations, conducting experiments at various submerged heights adjacent to the free surface. These findings represent a crucial step towards achieving the ultimate objective of this research: understanding FIV in flexible films in close proximity to the air-water interface.

We conducted a series of well-controlled lab experiments using a re-circulating water tunnel tests. In these experiments, we used a rigid flat plate fabricated from transparent acrylic. To capture pitching and plunging oscillations, we used a Miniature Rotary Magnetic Encoder and a laser displacement sensor, respectively. Our analysis involved studying the structural response of the system in terms of oscillation amplitude and frequency. We also investigated the vortex dynamics using a combination of qualitative and quantitative flow visualization techniques, including Hydrogen Bubble (HB), state-of-the-art time-resolved volumetric Particle Tracking Velocimetry (TR-PTV), and two-dimensional Particle Image Velocimetry (2D-PIV) methods. We further analyzed three and two-dimensional vortex dynamics in the wake of the structure by using techniques like proper orthogonal decomposition, phaseaveraged methods, and coherent structural analysis, such as Q and lambda criteria.

ADVISOR(S):
Dr. Banafshesh Seyed-Aghazadeh, Dept of Mechanical Engineering
(b.aghazadeh@umassd.edu)

COMMITTEE MEMBERS:
Dr. Mehdi Raessi, Dept of Mechanical Engineering
Dr. Hangjian Ling, Dept of Mechanical Engineering
Dr. Geoffrey W. Cowles, Dept of Marine Science & Technology