Experiment on Added-Mass and Viscous-Damping Forces acting on an Oscillating Sphere with Finite Amplitude

In this work, we perform a numerical study on the flow induced by the motion of a rigid cantilever beam undergoing finite amplitude oscillations, in a viscous fluid, under a free surface. To this aim, we use a lattice Boltzmann volume of fluid (LB-VOF) integrated method, which includes the tracking of the fluid surface. The adopted approach couples the simplicity of the LB method with the possibility to track the free surface by means of a VOF strategy. Through a parametric analysis, we study the effects related to the depth of submergence, for several values of the oscillation frequency and amplitude. Results are provided in terms of a complex hydrodynamic function, whose real and imaginary parts are the added mass and the viscous damping, respectively, acting on the lamina. Validation of the results is carried out by comparing the solution, for the limit case of lamina submerged in an infinite fluid, with those from available literature studies. We find that the presence of the free surface strongly influences the flow physics around the lamina, especially at low values of the depth of submergence. In facts, when the lamina approaches to the free surface, the fluid waves, generated by the motion of the lamina, interact with the oscillating body itself, giving rise to additional effects, which we quantify in terms of added mass and viscous damping.

Download Full-text

Accurate Backbone Curves for a Modified-Duffing Equation for Vibrations of Imperfect Structures With Viscous Damping

Journal of Vibration and Acoustics ◽

10.1115/1.2930509 ◽

1990 ◽

Vol 112 (3) ◽

pp. 304-311 ◽

Cited By ~ 8

Author(s):

D. Hui

Keyword(s):

Vibration Amplitude ◽

Initial Imperfection ◽

Finite Amplitude ◽

Viscous Damping ◽

Rectangular Plates ◽

Backbone Curve ◽

Spherical Shells ◽

Small Vibration ◽

Backbone Curves ◽

Imperfect System

This paper deals with the Runge-Kutta numerical solution of the modified-Duffing ordinary differential equation with viscous damping. Accurate backbone curves for the finite-amplitude vibrations of geometrically imperfect rectangular plates and shallow spherical shells are presented. For a structure with a sufficiently large initial imperfection, the well-known soft-spring nature of the backbone curve is confirmed for small vibration amplitude. However, for large vibration amplitude, the backbone curves tend to exhibit the usual hard-spring behavior. The predominantly “inward” deflection response (as viewed from the center of curvature) of an imperfect system is found for undamped systems, but this is not necessarily true for a viscously damped structure. Both the initial-deflection and initial-velocity problems are examined.

Download Full-text

Using CFD to Assess Low Frequency Damping

Volume 5: Ocean Engineering; CFD and VIV ◽

10.1115/omae2012-83326 ◽

2012 ◽

Author(s):

Alessio Pistidda ◽

Harald Ottens ◽

Richard Zoontjes

Keyword(s):

Standard Procedure ◽

Low Frequency ◽

Added Mass ◽

Model Tests ◽

Viscous Damping ◽

Viscous Effects ◽

Floating Bodies ◽

Time Step ◽

Damping Coefficients ◽

Quadratic Component

During offshore installation operations, floating bodies are often moored using soft mooring which are designed to withstand the environmental forces. Large amplitude motions often occur due to excitation by slowly varying wind and wave drift forces. To analyze these motions the dynamic system has to be accurately described, which includes an estimation of the added mass and damping coefficients. In general, the added mass can be accurately calculated with traditional potential theory. However for the damping this method is not adequate because viscous effects play an important role. Generally these data are obtained using model tests. This paper validates the CFD methodology as an alternative to model tests to evaluate the viscous damping. The aim is to define a standard procedure to derive viscous damping coefficients for surge, sway and yaw motion of floating bodies. To estimate viscous damping in CFD, a 3D model of the launch and float-over barge H-851 was used. For this barge, model test data is available which could be compared with the results of the CFD analysis. For the simulations, the commercial package STAR-CCM+ with the implicit unsteady solver for Reynolds-Averaged Navier-Stokes (RANS) equations was used. The turbulence model implemented was the k-Omega-SST. Numerical errors have been assessed performing sensitivity analysis on time step and grid size. Damping has been investigated by performing decay simulations as in the model tests, taking the effect of coupling among all motions into account. The P-Q fitting method has been used to determine the linear and quadratic component of the damping. Numerical results are validated with those obtained from the towing tank. Results show that CFD is an adequate tool to estimate the low frequency damping in terms of equivalent damping. More investigations are required to determine the linear and quadratic component.

Download Full-text

Damping Characteristics of Heave Plates Attached to Spar Hull

Volume 1: Offshore Technology ◽

10.1115/omae2012-83290 ◽

2012 ◽

Cited By ~ 1

Author(s):

Nimmy Thankom Philip ◽

S. Nallayarasu ◽

S. K. Bhattacharyya

Keyword(s):

Damping Ratio ◽

Added Mass ◽

Offshore Structures ◽

Viscous Damping ◽

Wave Excitation ◽

Damping Characteristics ◽

Hydrodynamic Response ◽

Key Factor ◽

The Relationship ◽

Insight Into

Damping elements are used in ships and offshore structures as response reduction devices for maintaining the hydrodynamic response within acceptable limits. The use of such elements so far has been based on past experience or using empirical based design approach. An investigation of the wave excitation forces acting on these structures with and without damping elements may give an insight into the damping effects of such elements. Also understanding the flow pattern and the magnitude of flow variation around these elements may be useful to improve the design methods. In the present study, measurement of damping forces and response were carried out to establish the relationship between wave frequency amplitude and damping ratio. It was observed that the damping varies with wave period non-linearly and linearly with wave height. Also it was observed that increase in added mass combined with viscous damping is a key factor for the effectiveness of heave plates in reducing motion response of spar platforms. Of the various configurations tested, the spar with double heave plate at the bottom has higher damping compared to other configurations.

Download Full-text

Experimental and theoretical investigation of large-amplitude oscillations of liquid droplets

Journal of Fluid Mechanics ◽

10.1017/s0022112091003361 ◽

1991 ◽

Vol 231 ◽

pp. 189-210 ◽

Cited By ~ 115

Author(s):

E. Becker ◽

W. J. Hiller ◽

T. A. Kowalewski

Keyword(s):

Oscillation Frequency ◽

Oscillation Amplitude ◽

Nonlinear Effects ◽

Finite Amplitude ◽

Droplet Radius ◽

Viscous Damping ◽

Liquid Droplets ◽

Axially Symmetric ◽

Natural Oscillations ◽

Gaseous Environment

Finite-amplitude, axially symmetric oscillations of small (0.2 mm) liquid droplets in a gaseous environment are studied, both experimentally and theoretically. When the amplitude of natural oscillations of the fundamental mode exceeds approximately 10% of the droplet radius, typical nonlinear effects like the dependence of the oscillation frequency on the amplitude, the asymmetry of the oscillation amplitude, and the interaction between modes are observed. As the amplitude decreases due to viscous damping, the oscillation frequency and the amplitude decay factor reach their asymptotical values predicted by linear theory. The initial behaviour of the droplet is described quite satisfactorily by a proposed nonlinear inviscid theoretical model.

Download Full-text

A Review of the Hydrodynamic Characteristics of Heave Plates

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.773.65 ◽

2013 ◽

Vol 773 ◽

pp. 65-69

Author(s):

Ji Bin Liu ◽

Yan Jun Liu ◽

Yu Li

Keyword(s):

Influencing Factors ◽

Added Mass ◽

Experimental Results ◽

Hydrodynamic Characteristics ◽

Viscous Damping ◽

Marine Structures ◽

The Stability

Heave plates can increase the added mass and viscous damping of marine structures. It's a more economical way to improve the stability of the marine structures' heave movement by adding heave plates compared to other methods. Many scholars have studied on the influencing factors of theirs properties. This paper describes the findings of each factor, and the results are compared. Some experimental results have still not been explained, so it is needed to continue to study heave plates.

Download Full-text

Drag cancellation by added-mass pumping

Journal of Fluid Mechanics ◽

10.1017/jfm.2016.353 ◽

2016 ◽

Vol 798 ◽

Cited By ~ 11

Author(s):

F. Giorgio-Serchi ◽

G. D. Weymouth

Keyword(s):

Shape Change ◽

Stokes Number ◽

Added Mass ◽

Navier Stokes ◽

Viscous Damping ◽

Size Change ◽

Biologically Inspired ◽

Sustained Oscillations ◽

Submerged Body

A submerged body subject to a sudden shape change experiences large forces due to the variation of added-mass energy. While this phenomenon has been studied for single actuation events, application to sustained propulsion requires the study of periodic shape change. We do so in this work by investigating a spring–mass oscillator submerged in quiescent fluid subject to periodic changes in its volume. We develop an analytical model to investigate the relationship between added-mass variation and viscous damping, and demonstrate its range of application with fully coupled fluid–solid Navier–Stokes simulations at large Stokes number. Our results demonstrate that the recovery of added-mass kinetic energy can be used to completely cancel the viscous damping of the fluid, driving the onset of sustained oscillations with amplitudes as large as four times the average body radius $r_{0}$. A quasi-linear relationship is found to link the terminal amplitude of the oscillations $X$ to the extent of size change $a$, with $X/a$ peaking at values from 4 to 4.75 depending on the details of the shape-change kinematics. In addition, it is found that pumping in the frequency range of $1-a/2r_{0}<{\it\omega}^{2}/{\it\omega}_{n}^{2}<1+a/2r_{0}$, with ${\it\omega}/{\it\omega}_{n}$ being the ratio between frequency of actuation and natural frequency, is required for sustained oscillations. The results of this analysis shed light on the role of added-mass recovery in the context of shape-changing bodies and biologically inspired underwater vehicles.

Download Full-text

504 High-Speed Computation and Experiment on Added-Mass and Viscous-Damping Force Acting on Various Oscillating 3D Prisms

The Proceedings of Conference of Kansai Branch ◽

10.1299/jsmekansai.2016.91.141 ◽

2016 ◽

Vol 2016.91 (0) ◽

pp. 141-144

Author(s):

Hajime ONISHI ◽

RYUTA Tanaka ◽

Tomoya KITAMOTO ◽

Tsuyoshi MAEDA ◽

Hideki SHIMOHARA ◽

...

Keyword(s):

High Speed ◽

Added Mass ◽

Viscous Damping ◽

Damping Force

Download Full-text

Dynamic Analysis of the UVMS: Effect of Disturbances, Coupling, and Joint-Flexibility on End-Effector Positioning

Robotica ◽

10.1017/s0263574721000072 ◽

2021 ◽

pp. 1-29

Author(s):

Umer Hameed Shah ◽

Mansour Karkoub ◽

Deniz Kerimoglu ◽

Hong-Du Wang

Keyword(s):

Autonomous Underwater Vehicle ◽

Underwater Vehicle ◽

Added Mass ◽

Hydrodynamic Forces ◽

Viscous Damping ◽

End Effector ◽

Flexible Joint ◽

Lagrange Formulation ◽

System Coupling ◽

Flexible Joint Manipulator

SUMMARY This paper investigates the dynamics of an underwater vehicle-manipulator system (UVMS) consisting of a two-link flexible-joint manipulator affixed to an autonomous underwater vehicle. The quasi-Lagrange formulation is utilized in deriving a realistic mathematical model of the UVMS considering joints’ friction, hysteretic coupling between the joints and links, and the nonlinear hydrodynamic forces acting on the system, such as added mass, viscous damping, buoyancy, drag, and vortex-induced forces. Numerical simulations are performed to demonstrate the effects of hydrodynamic forces and system coupling between the vehicle and the manipulator and the joints and the links on the precise positioning of the end effector.

Download Full-text

The Added Mass and Viscous Damping of a Spar Platform With Semi-Closed Moon Pool

Volume 2: CFD and VIV ◽

10.1115/omae2015-41067 ◽

2015 ◽

Author(s):

Li-qin Liu ◽

Jin-shuang Man ◽

Yu Qiu

Keyword(s):

Three Dimensional ◽

Added Mass ◽

Viscous Damping ◽

The Moon ◽

Spar Platform ◽

Natural Period ◽

Platform Motion ◽

Static Water ◽

Three Dimensional Models ◽

Moon Pool

The CFD (Computational Fluent Dynamics) method was used to calculate the added mass and the viscous damping of the Spar platform considering the semi-closed moon pool in this paper. The three-dimensional models of the platform with water inside the semi-closed moon pool were established by the VOF (Volume of Fluid) method. The UDF (User Defined Function) was adopted to oscillate the platform. The added mass and the damping coefficients were calculated under different KC (Keulegan-Carpenter) number and flow velocity for different opening ratio of the moon pool. The viscous damping and natural period of the platform heaving were obtained by calculating the platform motion in the static water. The influences of water inside the moon pool on the Spar platform motion were analyzed.

Download Full-text