Showing papers on "Vortex-induced vibration published in 2010"

An experimental investigation of flow-induced acoustic resonance and flow field in a closed side branch system using a high time-resolved PIV technique

Abstract: Systems with closed side branches are liable to an excitation of sound known as cavity tone. It may occur in pipe branches leading to safety valves or to boiler relief valves. The outbreak mechanism of the cavity tone has been ascertained by phase-averaged pressure measurements in previous research, while the relation between sound propagation and the flow field is still unclear due to the difficulty of detecting the instantaneous velocity field. It is possible to detect the two-dimensional instantaneous velocity field using high time-resolved particle image velocimetry (PIV). In this study, flow-induced acoustic resonance in a piping system containing closed side branches was investigated experimentally. A high time-resolved PIV technique was used to measure the gas flow in a cavity. Airflow containing oil mist as tracer particles was measured using a high-frequency pulse laser and a high-speed camera. The present investigation on the coaxial closed side branches is the first rudimentary study to visualize the fluid flow two-dimensionally in a cross-section using high time-resolved PIV, and to measure the pressure at the downstream side opening of the cavity by microphone. The fluid flows at different points in the cavity interact, with some phase differences between them, and the relation between the fluid flows was clarified.

A new wake oscillator model for predicting vortex induced vibration of a circular cylinder

Abstract: This article proposes a new wake oscillator model for vortex induced vibrations of an elastically supported rigid circular cylinder in a uniform current. The near wake dynamics related with the fluctuating nature of vortex shedding is modeled based on the classical van der Pol equation, combined with the equation for the oscillatory motion of the body. An appropriate approach is developed to estimate the empirical parameters in the wake oscillator model. The present predicted results are compared to the experimental data and previous wake oscillator model results. Good agreement with experimental results is found.

Vortex-induced vibration of a rising and falling cylinder

Abstract: In this study, we investigate the dynamics of a freely rising and falling cylinder. This is, in essence, a vortex-induced vibration (VIV) system comprising both transverse (Y) and streamwise (X) degrees-of-freedom (d.o.f.), but with zero spring stiffness and zero damping. This problem represents a limiting case among studies in VIV, and is an extension of recent research of elastically mounted bodies having very low spring stiffness, as well as bodies with very low mass and damping. We find that if the mass ratio (where m* = cylinder mass/displaced fluid mass) is greater than a critical value, m*crit = 0.545, the body falls or rises with a rectilinear trajectory. As the mass ratio is reduced below m*crit = 0.545, the cylinder suddenly begins to vibrate vigorously and periodically, with a 2P mode of vortex formation, as reported in the preliminary study of Horowitz & Williamson (J. Fluids Struct. vol. 22, 2006, pp. 837–843). The similarity in critical mass between freely rising and elastically mounted bodies is unexpected, as it is known that the addition of streamwise vibration can markedly affect the response and vortex formation in elastically mounted systems, which would be expected to modify the critical mass. However, we show in this paper that the similarity in vortex formation mode (2P) between the freely rising body and the elastically mounted counterpart is consistent with a comparable phase of vortex dynamics, strength of vortices, amplitudes and frequencies of motion and effective added mass (CEA). All of these similarities result in comparable values of critical mass. The principal fact that the 2P mode is observed for the freely rising body is an interesting and consistent result; based on the previous VIV measurements, this is the only mode out of the known set {2S, 2P, 2T} to yield negative effective added mass (CEA < 0), which is a condition for vibration of a freely rising body. In this paper, we deduce that there exists only one possible two degree-of-freedom elastically mounted cylinder system, which can be used to predict the dynamics of freely rising bodies. Because of the symmetry of the vortex wake, this system is one for which the natural frequencies are fNX = 2fNY. Although this seems clear in retrospect, previous attempts to predict critical mass did not take this into account. Implementing such an elastic system, we are able to predict vibration amplitudes and critical mass (m*crit = 0.57) for a freely rising cylinder in reasonable agreement with direct measurements for such a rising body, and even to predict the Lissajous figures representing the streamwise–transverse vibrations for a rising body with very small mass ratios (down to m* = 0.06), unobtainable from our direct measurements.

Vertical Riser VIV Simulation in Uniform Current

Abstract: Recently, some riser vortex-induced vibrations (VIVs) experimental data have been made publicly available (oe.mit.edu/VIV/) including a 10 m riser VIV experiment performed by Marintek, Trondheim, Norway, and donated by ExxonMobil URC, Houston, TX, USA. This paper presents our numerical simulation results for this 10 m riser and the comparisons with the experimental results in uniform current. The riser was made of a 10 m brass pipe with an outer diameter of 0.02 m (L/D=482) and a mass ratio of 1.75. The riser was positioned vertically with top tension of 817 N and pinned at its two ends to the test rig. Rotating the rig in the wave tank would simulate the uniform current. In the present numerical simulation the riser’s ends were pinned to the ground and a uniform far field incoming current was imposed. The riser and its surrounding fluid were discretized using 1.5×106 elements. The flow field is solved using an unsteady Reynolds-averaged Navier–Stokes (RANS) numerical method in conjunction with a chimera domain decomposition approach with overset grids. The riser is also discretized into 250 segments. Its motion is predicted through a tensioned beam motion equation with external force obtained by integrating viscous and pressure loads on the riser surface. Then the critical parameters including riser VIV amplitude (a) to the riser outer diameter (D) ratio (a/D), vorticity contours, and motion trajectories were processed. The same parameters for the experimental data were also processed since these data sets are in “raw time-histories” format. Finally, comparisons are made and conclusions are drawn. The present numerical method predicts similar dominant modes and amplitudes as the experiment. It is also shown that the cross flow VIV in the riser top section is not symmetric to that of the bottom section. One end has considerably higher cross flow vibrations than the other end, which is due to the nondominant modal vibrations in both in-line and cross flow directions. The computational fluid dynamics (CFD) simulation results also agree with the experimental results very well on the riser vibrating pattern and higher harmonics response. The higher harmonics were studied and it is found that they are related to the lift coefficients, hence the vortex shedding patterns. It is concluded that the present CFD approach is able to provide reasonable results and is suitable for 3D riser VIV analysis in deepwater and complex current conditions.

A self-resonant micro flow velocity sensor based on a resonant frequency shift by flow-induced vibration

Abstract: We report the development of a self-resonant flow sensor based on a resonant frequency shift due to flow-induced vibrations. The vibration of a microcantilever beam, induced by a turbulent flow, is modulated with its own natural frequency, and the resonant frequency is shifted by a surface stress on the beam due to fluid drag force. The vibration induced by air flow is measured by using a piezoelectric PZT material on a silicon cantilever beam. The theoretical resonant frequencies of two cantilever beams (lengths: 610 µm and 2000 µm) are 12416 Hz and 1155 Hz, respectively. For the air flow velocities of 2.8 m s−1 and 9.7 m s−1, the shifted resonant frequencies of the cantilever beam whose length is 610 µm are 12 810 Hz and 15 602 Hz, respectively. Sensitivities of the two self-resonant flow sensors with the 610 and 2000 µm long beams are approximately 384 ± 15 Hz/(m/s) and 20.4 ± 0.6 Hz/(m/s), respectively.

Steady, unsteady and transient vortex-induced vibration predicted using controlled motion data

Abstract: In this study, we represent transient and unsteady dynamics of a cylinder undergoing vortex-induced vibration, by employing measurements of the fluid forces for a body controlled to vibrate sinusoidally, transverse to a free stream. We generate very high-resolution contour plots of fluid force in the plane of normalized amplitude and wavelength of controlled oscillation. These contours have been used with an equation of motion to predict the steady-state response of an elastically mounted body. The principal motivation with the present study is to extend this approach to the case where a freely vibrating cylinder exhibits transient or unsteady vibration, through the use of a simple quasi-steady model. In the model, we use equations which define how the amplitude and frequency will change in time, although the instantaneous forces are taken to be those measured under steady-state conditions (the quasi-steady approximation), employing our high-resolution contour plots.The resolution of our force contours has enabled us to define mode regime boundaries with precision, in the amplitude–wavelength plane. Across these mode boundaries, there are discontinuous changes in the fluid force measurements. Predictions of free vibration on either side of the boundaries yield distinct response branches. Using the quasi-steady model, we are able to characterize the nature of the transition which occurs between the upper and lower amplitude response branches. This regime of vibration is of practical significance as it represents conditions under which peak resonant response is found in these systems. For higher mass ratios (m* > 10), our approach predicts that there will be an intermittent switching between branches, as the vortex-formation mode switches between the classical 2P mode and a ‘2POVERLAP’ mode. Interestingly, for low mass ratios (m* ~ 1), there exists a whole regime of normalized flow velocities, where steady-state vibration cannot occur. However, if one employs the quasi-steady model, we discover that the cylinder can indeed oscillate, but only with non-periodic fluctuations in amplitude and frequency. The character of the amplitude response from the model is close to what is found in free vibration experiments. For very low mass ratios (m* < 0.36 in this study), this regime of unsteady vibration response will extend all the way to infinite normalized velocity.

Flow-Induced Vibration Analysis of Supported Pipes Conveying Pulsating Fluid Using Precise Integration Method

Abstract: Dynamic analysis of supported pipes conveying pulsating fluid is investigated in Hamiltonian system using precise integration method (PIM). First, symplectic canonical equations of supported pipes are deduced with state variable vectors composed of displacement and momentum. Then, PIM with linear interpolation formula is proposed to solve these equations. Finally, this approach's precision is testified by several numerical examples of pinned-pinned pipes with different fluid velocities and frequencies. The results show that PIM is an efficient and rapid approach for flow-induced dynamic analysis o f supported pipes.

The effect of vibration on flow rate of non-newtonian fluid

Abstract: Acoustic stimulation is a promising method for increasing drainage of non-Newtonian fluids through porous structures in various applications. In this study, a mathematical model is developed for unsteady flow of a bi-viscous incompressible fluid in a circular straight channel. Longitudinal vibrations are superimposed on the flow driven by changing pressure gradients along the channel. Simulations are carried out for a range of relevant dimensionless parameters. Effects of vibration amplitude, frequency, and fluid viscosity ratio on the enhancement of mean flow rate are discussed. Introduction Flows of non-Newtonian fluids in narrow channels and porous structures are encountered in the vast majority of chemical, biomedical and process industries. One of the practical problems encountered with high-viscosity non-Newtonian fluids is augmenting the mean flow rate in a channel at a given mean pressure gradient. It is known that by using sound or vibrations it is possible to increase the time-averaged flow of shear-thinning and viscoplastic fluids. In this study, an unsteady flow of a nonNewtonian incompressible fluid is analyzed in a circular cross section of a channel under the presence of an oscillating pressure gradient. Model Formulation We propose a model which effectively approximates shear-thinning, shear-thickening, and Bingham fluids by using a linear functions approximations. The governing equation for the fluid flow is the momentum equation, we consider an axisymmetric flow in a tube with a constant radius and assume parallel flow. The constitutive law relating the stress and strain rate of the fluid is τ = { μ1 ∂v ∂r if τ < τ1 μ2 ∂v ∂r + τ1 if τ1 ≤ τ < τ2 μ1 and μ2 – dynamic viscosities and τ1 and τ2 – yield stresses. Figure 1: Dependence of shear stress on shear rate for different types of fluids. Figure 2: Linear functions approximation of dependence of shear stress on shear rate. By assuming constant pressure gradient ∂p ∂z = G we obtain ρ ∂v ∂t = −G + μn r ∂v ∂r + μn ∂2v ∂r2 + τn r To model the effects of unsteady pressure gradient on the fluid flow inside the tube, longitudinal vibrations are applied to the channel wall parallel to the direction of the fluid flow. The displacement of the wall is given by w = beiωt b – the displacement amplitude and ω – the angular frequency of the vibration. Define the relative velocity of the fluid with respect to the wall movement: U = (v− ẇ) The governing equation for the flow takes the form ρ ∂U ∂t = ρbω2eiωt−G + μn r ( ∂U ∂r ) + μn ( ∂2U ∂r2 ) + τn r U(R, t) = 0. Instantaneous volume flow rate through the tube

Environmental fluid dynamics-jet flow

Abstract: Jet flow is a very important research subject in both fundamental fluid dynamics and engineering applications. Jet flow has the essences of fluid dynamics, such as free and wall-bounded shear flows, turbulent flow, eddy and large vortical structures and their stability and control, and so forth. This article serves as an overview of our past and ongoing research activities on various types of jet flow, with particular reference to their application in the field of environmental fluid dynamics. The research objectives, approach, results and their engineering implications of each topic will be presented.

Vortex Induced Vibration Analysis of a Complex Subsea Jumper

Abstract: Jumpers are typically short sections of curved pipe spanning production riser elements on the sea floor. When in areas of significant currents these jumpers are subject to vortex induced vibration (VIV). The complex shape of the jumper means that numerical methods are usually needed to solve for the vibration modes of the jumper. Furthermore, the fluid flow around the jumper is also complex so that traditional methods of VIV analysis used for risers are not applicable to jumpers. Here we use a CFD code in a fully coupled analysis to predict vibration response and strain of a typical subsea jumper. A separate finite element analysis is used to calculate the eigenvalues and eigenvectors of the jumper system for input into the CFD analysis. The resulting method is economical and practical for design analyses.Copyright © 2010 by ASME

Numerical Simulation of Fluid-Structural Interaction for Vortex-Induced Vibration of Risers

Abstract: A fluid-structure-interaction model is presented by solving the viscous Navier-Stokes equations,turbulence model and structural dynamic response equation.Using the dynamic mesh technique,a simulation is carried out for the vortex-induced vibration of risers with one and two degree of freedom(DOF) in low mass and small damping at Reynolds number from 3125 to 16250.The drag and lift coefficient,vibration displacement and the vortex shedding frequency under different reduced velocities are obtained.The phenomena of "lock in",the displacement's "detuning" and "phase switch" are captured.The results are compared with available experimental and simulation results and show a good agreement.The comparing results of 1DOF and 2DOF show that the influence of in-line action on the vibration can't be omitted under low mass ratio.

Nonlinear Coupled in-Line and Cross-Flow Vortex-Induced Vibration Analysis of Top Tensioned Riser

Abstract: The fluctuating forces of the fluid exerted on the top tensioned riser (TTR) in the in-line and cross-flow directions are both modeled by van del Pol wake oscillator model and the nonlinear coupled dynamics of the in-line and cross-flow vortex-induced vibrations (VIV) of the riser are analyzed in time domain in this paper. The numerical simulation results of the riser's in-line and cross-flow displacements and curvatures are compared with experimental measurements and the comparison shows the validity of this method in modeling some main features of the riser's VIV. Finally,the effects of the riser's top tensions and internal flow velocities on the coupled vibrations of the riser are investigated.

Experimental and Numerical Investigation of Flow Induced Vibration of Steam Control Valve

Abstract: Control valves of the main steam flow for power plants are operated under wide range of valve openings and pressure ratios. In the present paper, experimental and numerical investigations are described in order to clarify mechanisms of the valve head vibration. Experiments are conducted with two types of the valve head support. One is a flexible support and the other one is with an exciter. Results show that valve head vibrations with large amplitude appear with the flexibly supported valve head under certain range of valve openings and the pressure ratio. With the valve head exciter, dynamic fluid forces are measured. Results show that the added damping force becomes negative around the condition where the valve head oscillation is observed with flexible support. Numerical analyses are carried out in order to observe the flow field. In the simulations, forced vibrations of valve head are assumed. Results show that the pressure distribution on the valve head surface changes depending on the excitation frequencies, and as a result, the negative damping force occurs.Copyright © 2010 by ASME

Vortex-induced vibration on 2D circular riser using a high resolution numerical scheme

Abstract: This paper presents a high resolution numerical method for vortex induced vibration (VIV) simulation on the fluid structure interaction (FSI) of circular cylinder which represents a two dimensional marine riser. For the VIV case, the cylinder is elastically mounted and is modeled as a spring-mass oscillation system. Based on a new proposed elemental velocity vector transformation (EVVT) method, a finite-volume total variation diminishing (TVD) approach developed recently for solving unsteady Reynolds Averaged Navier-Stokes (URANS) equation with the RNG turbulence model was used to simulate the key hydrodynamic parameters such as lift coefficients. The four-stage Runge-Kutta method is used to solve the dynamic response equation of the structure. The FSI prediction results are compared with the available experimental data and showed a good agreement in a wide range of Reynolds number, which provide a good picture of real physics of phenomenon including the Karman vortex streets with different vortex modes with regard to the reduced velocities.

Non-intrusive two-phase flow measurement system

Abstract: A process for determining a fluid flow velocity and then a mass flow rate of a cryogenic fluid in which a Helmholtz resonator is used to detect a presence of a two-phase flow in a conduit. The process first measures a frequency of the fluid flow, then determines a speed of sound of the fluid from the frequency, then measures the temperature of the fluid flow, and from the speed of sound and the temperature determines a quality of the fluid flow (liquid or vapor), and from the frequency and the fluid quality determines a Strouhal Number. The fluid flow velocity is found from an equation relating the frequency and a diameter of the surface area to the Strouhal Number. The mass flow rate is found from the fluid flow velocity and the temperature.

Steady linked vortices with chaotic streamlines

Abstract: This paper contains background information for a fluid dynamics video submitted to the Gallery of Fluid Motion to be held along with the 63rd Annual Meeting of the American Physical Society's Division of Fluid Dynamics.

Out-of-Plane Vibration of a Curved Pipe due to Pulsating Flow (Nonlinear Interactions Between In-Plane and Out-of-Plane Vibrations)

Abstract: A great deal of study has been done on the dynamics of straight pipes conveying fluid. In contrast, only a few studies have been devoted to the dynamics of curved pipe conveying fluid. In this paper, a theoretical and experimental investigation was conducted into out-of-plane vibration of a curved pipe for the case that the fluid flow contains a small time-dependent harmonic component. The nonlinear out-of plane vibrations of a curved pipe, which is hanging horizontally and is supported at both ends, are examined when the frequency of the pulsating fluid flow is near twice the fundamental natural frequency of out-of-plane vibration. The main purpose of this paper is to investigate the nonlinear interactions between the in-plane and the out-of-plane vibrations analytically and experimentally. The partial differential equations of out-of-plane motions are reduced into a set of ordinary differential equations, which govern the amplitude and phase of out-of-plane vibration, using the method of Lyapnov-Schmidt reduction. It is clarified that the excitation of the in-plane vibration produces significant responses in the out-of-plane vibrations. Finally, the experiments were conducted with a silicon rubber pipe conveying water. The typical features of out-of-plane vibration are confirmed qualitatively by experiment.Copyright © 2010 by ASME