Characteristics of the Flow-Induced Vibration and Forces With 1- and 2-DOF Vibrations and Limiting Solid-to-Fluid Density Ratios

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Osama A. Marzouk
Keyword(s):  
Density Ratio ◽  
Fluid Motion ◽  
Cross Flow ◽  
Fluid Density ◽  
Flow Induced Vibration ◽  
Drag Forces ◽  
Wide Range ◽  
Low Mass ◽  
Lift And Drag ◽  
Density Ratios

We studied various characteristics of the flow-induced vibration (FIV) of a spring-mounted cylinder, and the fluctuating lift and drag forces exerted on the cylinder due to the periodic changes in the fluid motion and vortex structure. We compared two conditions, which represent the limiting cases for the solid-to-fluid density ratio: the cylinder density is negligible relative to the fluid density, and the fluid density is negligible relative to the cylinder density. For both conditions, we examined the changes in these characteristics over a wide range of nondimensional mass-damping for one degree of freedom (1-DOF, cross-flow) and 2-DOF (cross-flow and in-line) vibration. The four cases exhibit differences (especially at low mass-damping) but also have some similarities in the characteristics of the FIV, induced forces, and energy extraction from the flow. We examined these differences and similarities, the implied errors when the in-line DOF is neglected, and the feasibility of using a single mass-damping parameter to describe the FIV.

Vibration Excitation Forces in a Normal Triangular Tube Bundle Subjected to Two-Phase Cross Flow

2011 ◽  
Author(s):  
E. S. Perrot ◽  
N. W. Mureithi ◽  
M. J. Pettigrew ◽  
G. Ricciardi
Keyword(s):  
Tube Bundle ◽  
Cross Flow ◽  
Random Excitation ◽  
Two Phase ◽  
Constant Frequency ◽  
Fluid Forces ◽  
Drag Forces ◽  
Wide Range ◽  
Drag And Lift ◽  
Lift And Drag

This paper presents test results of vibration forces in a normal triangular tube bundle subjected to air-water cross-flow. The dynamic lift and drag forces were measured with strain gage instrumented cylinders. The array has a pitch-to-diameter ratio of 1.5, and the tube diameter is 38 mm. A wide range of void fraction and fluid velocities were tested. The experiments revealed significant forces in both the drag and lift directions. Constant frequency and quasi-periodic fluid forces were found in addition to random excitation. These forces were analyzed and characterized to understand their origins. The forces were found to be dependent on the position of the cylinder within the bundle. The results are compared with those obtained with flexible cylinders in the same tube bundle and to those for a rotated triangular tube bundle. These comparisons reveal the influence of quasi-periodic forces on tube motions.

Experimental Study on the Dynamics of Four Flexible Cylinders in Square Arrangement Subjected to Uniform Cross-Flow

2012 ◽  
Author(s):  
Bijan Sanaati ◽  
Naomi Kato
Keyword(s):  
Amplitude Ratio ◽  
Lift Coefficient ◽  
Cross Flow ◽  
Mass Ratio ◽  
Drag Forces ◽  
Low Mass ◽  
Drag And Lift ◽  
Low Mass Ratio ◽  
Lift And Drag ◽  
Four Cylinders

Groups of cylinders can be found in many engineering fields such as marine and civil applications. The behaviors of the group cylinders can be very complex because it undergoes the mutual effects of adjacent cylinders arranged in different positions. In this paper, we present the results of a study on the dynamics of a group of flexible cylinders in square arrangements along with a single (isolated) cylinder subjected to uniform cross-flow (CF). Four cylinders of the same size, properties, and pretensions were tested in two configurations with different centre-to-centre separations. Horizontal and vertical separations were 2.75D & 2.75D and 5.50D & 2.75D for the first and second configurations, respectively. The tandem (horizontal) separations between the downstream and upstream cylinders, i.e., 2.75D and 5.5D, correspond to the reattachment and co-shedding regimes, respectively. Vertical separation, i.e., 2.75 was chosen in a range where the side-by-side cylinders can have proximity interference. Reynolds number ranged from 1400 to 20000 (subcritical regime). The parameter of reduced velocity reached up to 19. The aspect ratio of all the cylinders was 162 (length/diameter). Mass ratio (cylinders mass/displaced water) is 1.17, a low mass ratio. The amplitude ratio of the CF vibration of the downstream cylinders, hydrodynamic force coefficients including mean and fluctuating components of the drag and lift forces, and frequency responses for both CF and inline (IL) directions were analyzed. All the cylinders excited up to the second and fourth mode of vibrations for CF and IL directions, respectively. Mean drag coefficient of the upstream cylinders are almost twice those of the downstream cylinders at high reduced velocities. The mean lift coefficient is much higher for the upstream cylinders than the downstream cylinders with a negative value. Obvious IL and CF lock-in regions exist for all four cylinders at low reduced velocities. Among the four cylinders, the upper downstream cylinder shows the least and the most fluctuating lift and drag forces, respectively. The IL and CF frequencies of the downstream cylinders are much lower than those of the upstream ones and the single cylinder.

scholarly journals Aerodynamic Performance of Biomimicry Snake-Shaped Airfoil

2019 ◽  
Vol 9 (2) ◽  
pp. 3319-3323
Keyword(s):  
Cross Section ◽  
Lift Coefficient ◽  
Design Parameters ◽  
Drag Forces ◽  
Cross Section Shape ◽  
Section Shape ◽  
Wide Range ◽  
Lift And Drag ◽  
Drag Ratio ◽  
Lift To Drag Ratio

The cross-section shape and proportionality between geometrical dimensions are the most important design parameters of any lifting surfaces. These parameters affect the amount of the aerodynamic forces that will be generated. In this study, the focus is placed on the snake-cross-section airfoil known as the S-airfoil. It is found that there is a lack of available researches on S-airfoil despite its important characteristics. A parametric study on empty model of the S-airfoil with a cross-section shape that is inspired by the Chrysopelea paradise snake is conducted through numerical simulation. Simulation using 2D-ANSYS FLUENT17 software is used to generate the lift and drag forces to determine the performance of airfoil aerodynamic. Based on the results, the S-airfoil can be improved in performance of aerodynamic by reducing the thickness at certain range, whereby changing the thickness-to-chord ratio from 0.037 to 0.011 results in the increment of lift-to-drag ratio from 2.629 to 3.257. On other hand, increasing the height-to-chord ratio of the S-airfoil will increase maximum lift coefficient but drawback is a wide range of angles of attack regarding maximum lift-to-drag ratio. Encouraging results obtained in this study draws attention to the importance of expanding the research on S-airfoil and its usage, especially in wind energy.

scholarly journals Energy and Angular Momentum Transfer in Binary Galaxies

1990 ◽  
Vol 124 ◽  
pp. 589-593
Author(s):  
P.M.S. Namboodiri ◽  
R.K. Kochhar
Keyword(s):  
Angular Momentum ◽  
Momentum Transfer ◽  
Density Ratio ◽  
Tidal Effects ◽  
Fractional Change ◽  
Satellite Galaxy ◽  
Wide Range ◽  
Density Ratios ◽  
Irregular Variation ◽  
Spherical Satellite

AbstractWe have numerically studied tidal effects of a massive perturber on a satellite galaxy. The model consists of a spherical satellite galaxy and a point mass perturber and the encounter is non-penetrating. A wide range of density ratios and eccentricities of the relative orbits have been considered. The disruption of the satellite galaxy has been observed when the numerical value of the fractional change in the energy is greater than two. The changes in the energy and angular momentum show smooth variation in the case of unbound orbits and irregular variation in the bound orbit cases. It is shown that for a constant pericentric distance, increasing the density ratio decreases the tidal effects; and for a given density ratio an increase in the eccentricity decreases the tidal effects.

Numerical Prediction of 3-D Vortex-Induced Vibration of Catenary Riser In Planar and Non-Planar Flows

2021 ◽  
Author(s):  
Bowen Ma ◽  
Narakorn Srinil
Keyword(s):  
Flow Direction ◽  
Cross Flow ◽  
Travelling Wave ◽  
Flow Angle ◽  
Fluid Structure ◽  
Vortex Induced Vibration ◽  
Drag Forces ◽  
Wake Oscillators ◽  
Lift And Drag ◽  
Planar Flows

Abstract Vortex-induced vibration (VIV) is one of the most critical issues in deepwater developments due to its resultant fatigue damage to subsea structures such as risers, pipelines and jumpers. Although VIV effects on slender bodies have been comprehensively studied over decades, very few studies have dealt with VIV modelling and prediction of catenary risers in current flows with varying directions leading to complex fluid-structure interactions. This study advances a numerical model to simulate and predict 3-D VIV responses of a catenary riser in three flow orientations, relative to the riser curvature plane, including concave/convex (planar) and perpendicular (non-planar) flows. The model is described by equations of cross-flow and in-line responses of the catenary riser coupled with the hydrodynamic forces modelled by the distributed nonlinear wake oscillators. A finite difference method is applied to solve the coupled fluid-structure dynamic system. To consider the approaching flow in different directions, the vortex-induced lift and drag forces are formulated by accounting for the effect of flow angle of attack and the riser-flow relative velocities. Results show VIV features of a long catenary riser exhibiting a standing and travelling wave response pattern. VIV response amplitudes and oscillation frequencies are predicted and compared with experimental results in the literature for both straight and catenary risers. Overall results highlight the model capability in capturing the effect of approaching flow direction on 3-D VIV of the curved inclined flexible riser.

Combined FIV and VIV Effects on a Cantilevered Pipe Discharging Fluid in Deep Waters

2015 ◽  
Author(s):  
Shuai Meng ◽  
Hiroyuki Kajiwara ◽  
Narakorn Srinil
Keyword(s):  
Carbon Capture ◽  
Experimental Studies ◽  
Carbon Capture And Storage ◽  
Cross Flow ◽  
Integration Scheme ◽  
Flow Induced Vibration ◽  
Drag Forces ◽  
Deep Waters ◽  
Cantilevered Pipe ◽  
Wake Oscillators

To avoid or mitigate global warming, several ocean carbon capture and storage concepts have been proposed. One of the recent approaches is to dispose carbon dioxide via a fixed vertical cantilevered pipe onto the seabed in deep waters. Due to a high aspect ratio and flexibility of such long pipe conveying fluid with fixed-free end conditions and external hydrodynamic loading caused by currents, the pipe may experience large-amplitude 3-D vibrations leading to structural failure. Hence, it is essential to understand and investigate the pipe nonlinear dynamic behaviors subject to combined flow-induced vibration (FIV) and vortex-induced vibration (VIV). In this study, the 3-D nonlinear equations of a cantilevered pipe discharging fluid in the sea are analyzed using a Galerkin-based multi modal approach combined with a finite difference Houbolt’s integration scheme. Particular attention is paid to the combined effects of FIV and VIV on the dynamic response of the cantilevered pipe in water. To model the fluctuating lift and drag forces associated with VIV, the two dimensional wake oscillators distributed along the pipe are adopted. Numerical simulations in the FIV case of a pipe discharging fluid in the air are first validated with experimental results in the literature to justify the mathematical models and numerical approaches. Modal convergence analysis is also performed. Results in the combined FIV and VIV cases are then highlighted in order to show the effects of cross-flow and in-line VIV when compared with the pure FIV case. The effects of geometric nonlinearities, the coupling/interaction of multi modes and the space-time modifications of pipe responses and trajectories are highlighted. It is hoped that the numerical observations and findings obtained from this study could be verified by experimental studies which are presently lacking in the literature.

Towing Tank Experiments on the Vortex-Induced Vibrations of a Long Flexible Cylinder in a Stepped Current

2013 ◽  
Author(s):  
Francisco J. Huera-Huarte ◽  
Zafar A. Bangash ◽  
Leo M. González
Keyword(s):  
Cross Flow ◽  
External Diameter ◽  
Flexible Cylinder ◽  
Towing Tank ◽  
Supporting Structure ◽  
Drag Forces ◽  
Vortex Induced Vibrations ◽  
Curvature Measurements ◽  
Low Mass ◽  
Low Mass Ratio

We describe recent results showing the dynamic response, excited by vortex shedding, of a long flexible cylinder subject to a stepped current. The experiments were conducted at the Naval Architecture Department towing tank of the Technical University of Madrid (UPM) during March 2012. The tank is 100 m long with a cross-section of 3.8 × 2.5 m, and it is able to deliver speeds over 4 m/s. A supporting structure was designed in order to provide support for a 3 m long cylinder with an external diameter of 19 mm. The cylinder was instrumented with strain gauges providing curvature measurements in the in-line and the cross-flow directions at 11 locations along its length. Tension and drag forces were also measured at both ends of the model. More than 50 runs were conducted with the cylinder being placed vertically having its lower 65% length under the water free surface, connected to the structure by means of universal joints. The supporting structure allowed to configure different top end conditions and to apply different top tensions. Tests were conducted for Reynolds numbers as high as 34000. The cylinder had a low flexural stiffness and very low mass ratio m* of 0.67. Fundamental natural frequencies were in the range from about 4 to 7.9 Hz, and the cylinder responded in modes up to the third cross-flow. In this article we will describe the experiments and the instrumentation used, the modal tests conducted and the results obtained during the experiments.

Effects of smart flap on aerodynamic performance of sinusoidal leading-edge wings at low Reynolds numbers

2020 ◽  
pp. 095441002094690
Author(s):  
AA Mehraban ◽  
MH Djavareshkian ◽  
Y Sayegh ◽  
B Forouzi Feshalami ◽  
Y Azargoon ◽  
...  
Keyword(s):  
High Performance ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Drag Forces ◽  
Wide Range ◽  
Beam Bending ◽  
Low Reynolds ◽  
Lift And Drag ◽  
Drag Ratio

Sinusoidal leading-edge wings have shown a high performance after the stall region. In this study, the role of smart flaps in the aerodynamics of smooth and sinusoidal leading-edge wings at low Reynolds numbers of 29,000, 40,000 and 58,000 is investigated. Four wings with NACA 634-021 profile are firstly designed and then manufactured by a 3 D printer. Beam bending equation is used to determine the smart flap chord deflection. Next, wind tunnel tests are carried out to measure the lift and drag forces of proposed wings for a wide range of angles of attack, from zero to 36 degrees. Results show that using trailing-edge smart flap in sinusoidal leading-edge wing delays the stall point compared to the same wing without flap. However, a combination of smooth leading-edge wing and smart flap advances the stall. Furthermore, it is found that wings with smart flap generally have a higher lift to drag ratio due to their excellent performance in producing lift.

Vibration Excitation Force Measurements in a Rotated Triangular Tube Bundle Subjected to Two-Phase Cross Flow

2005 ◽  
Author(s):  
C. Zhang ◽  
M. J. Pettigrew ◽  
N. W. Mureithi
Keyword(s):  
Tube Bundle ◽  
Cross Flow ◽  
Fretting Wear ◽  
Experimental Program ◽  
Force Measurements ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Drag Forces ◽  
Vibration Excitation ◽  
Excitation Force

Two-phase cross flow exists in many shell-and-tube heat exchangers. Flow-induced vibration excitation forces can cause tube motion that will result in long-term fretting-wear or fatigue. Detailed vibration excitation force measurements in tube bundles subjected to two-phase cross flow are required to understand the underlying vibration excitation mechanisms. An experimental program was undertaken with a rotated-triangular array of cylinders subjected to air/water flow to simulate two-phase mixtures over a broad range of void fraction and mass fluxes. Both the dynamic lift and drag forces were measured with strain gage instrumented cylinders. The experiments revealed somewhat unexpected but significant quasi-periodic forces in both the drag and lift directions. The periodic forces appeared well correlated along the cylinder with the drag force somewhat better correlated than the lift forces. The periodic forces are also dependent on the position of the cylinder within the bundle.

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