Finite amplitude oscillations of flanged laminas in viscous flows: Vortex–structure interactions for hydrodynamic damping control

2015 ◽  
Vol 59 ◽  
pp. 297-315 ◽  
Author(s):  
Syed N. Ahsan ◽  
Matteo Aureli
Keyword(s):  
Vortex Structure ◽  
Viscous Flows ◽  
Finite Amplitude ◽  
Damping Control ◽  
Hydrodynamic Damping

Modulation of Nonlinear Hydrodynamic Damping in Finite Amplitude Underwater Oscillations of Flanged Structures

2015 ◽  
Author(s):  
Syed N. Ahsan ◽  
Matteo Aureli
Keyword(s):  
Vortex Structure ◽  
Complex Dynamics ◽  
Added Mass ◽  
Finite Amplitude ◽  
Structure Interaction ◽  
Hydrodynamic Damping ◽  
Computational Fluid Dynamics Simulations ◽  
Newtonian Viscous Fluid ◽  
Dynamics Simulations ◽  
Hydrodynamic Fields

In this paper, we study the fluid-structure interaction problem of the harmonic oscillations of a flanged lamina in a quiescent, Newtonian, viscous fluid. Here, the flanges are introduced to elicit specific vortex-structure interactions, with the ultimate goal of modulating the nonlinear hydrodynamic damping experienced by the oscillating structure. The hydrodynamic forcing, incorporating added mass and hydrodynamic damping effects, is evaluated through boundary element method and computational fluid dynamics simulations. This allows to identify a model for the hydrodynamic forces in the form of a complex-valued function of three nondimensional parameters, describing oscillation frequency and amplitude and flange size. We find that the presence of the flanges results into larger fluid entrainment during the lamina oscillation, thus affecting the added mass. Further, we highlight the existence of a minimum in the hydrodynamic damping which is governed by complex dynamics of vortex-structure interaction. This peculiar phenomenon is discussed from physical grounds by analysis of the pertinent hydrodynamic fields. Finally, we propose a tractable form for the hydrodynamic function, to be used in the study of large amplitude underwater flexural vibrations of flanged structures.

Change in wave-form and mean flow associated with wavelength variations in rotating Couette flow. Part 1

1969 ◽  
Vol 35 (2) ◽  
pp. 337-352 ◽  
Author(s):  
H. A. Snyder
Keyword(s):  
Couette Flow ◽  
Vortex Structure ◽  
Large Range ◽  
Finite Amplitude ◽  
Wave Form ◽  
End Effect ◽  
Mean Flow ◽  
Wave Numbers ◽  
Flow Part ◽  
Wide Gap

When rotating Couette flow becomes unstable a periodic vortex structure is formed. For the wide-gap case, this flow is steady for a rather large range of the Taylor number above onset. In the region of finite amplitude instability the wave-numbers of the periodic structure are not unique. It is shown empirically that the non-uniqueness is not an end effect but a bonafide property of the flow and that the wave-form is a unique function of the wavelength. Data is presented to demonstrate the interval over which the wave-numbers can be varied when the parameters of the system are fixed. The large effect on the wave-form of small changes in the wavelength is also illustrated. These conclusions are based on extensive measurements of the azimuthal drift velocity for a particular mode of secondary flow.

On the nonlinear stability of slowly varying time-dependent viscous flows

1983 ◽  
Vol 126 ◽  
pp. 357-368 ◽  
Author(s):  
P. Hall
Keyword(s):  
Equations Of Motion ◽  
Fluid Flows ◽  
Viscous Flows ◽  
Finite Amplitude ◽  
Taylor Vortex ◽  
Time Interval ◽  
Short Time Interval ◽  
Low Frequencies ◽  
Set Up ◽  
Short Time

In this paper we investigate the manner in which finite-amplitude disturbances are set up in viscous fluid flows that are changing slowly in time. It is shown that, when the appropriate Reynolds or Rayleigh number is slowly increased, then, no matter how slowly this change takes place, there is always a short time interval where a quasi-steady approach breaks down. In this time interval a finite-amplitude solution is set up which ultimately approaches that predicted by a quasi-steady theory. In order to demonstrate our ideas we discuss the Taylor-vortex problem in a situation in which the speed of the inner cylinder changes slowly in time. In particular we discuss the case when the speed of the inner cylinder is modulated slowly in time and it is found that at low frequencies the disturbances of most physical relevance are not periodic solutions of the equations of motion.

Finite Amplitude Underwater Flexural Vibrations of Cantilevers

2012 ◽  
Author(s):  
Matteo Aureli ◽  
Maurizio Porfiri
Keyword(s):  
Cross Section ◽  
Rectangular Cross Section ◽  
Finite Amplitude ◽  
Computationally Efficient ◽  
Flexible Beams ◽  
Hydrodynamic Damping ◽  
Computational Fluid Dynamics Analysis ◽  
Fluid Damping ◽  
Flexural Vibrations ◽  
Hydrodynamic Function

We study flexural vibrations of a thin rectangular cross section cantilever beam submerged in a quiescent viscous fluid. The cantilever is subject to base excitation and undergoes oscillations whose amplitude is comparable with its width. The structure is modeled as an Euler-Bernoulli beam and the fluid-structure interaction is captured through a nonlinear complex-valued hydrodynamic function which accounts for added mass and fluid damping. Results from a parametric 2D computational fluid dynamics analysis of an oscillating rigid lamina, representative of a generic beam cross section, are used to establish the dependence of the hydrodynamic function on the governing flow parameters. It is found that, as the frequency and amplitude of the vibration increase, vortex shedding and convection phenomena are enhanced, thus promoting nonlinear hydrodynamic damping. We derive a computationally efficient reduced order modal model for beam oscillations incorporating the non-linear hydrodynamic function and we validate theoretical results against experiments on underwater vibrations flexible beams.

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