Showing papers on "Vortex-induced vibration published in 2001"

Vortex-induced vibration reduction device for fluid immersed cylinders

Abstract: A mechanism to be applied to an exterior surface of a cylindrical structure for the reduction of the effect of Vortex Induced Vibration (VIV) in the cylindrical structure when immersed in flowing fluid, wherein the mechanism includes a generally cylindrical column having a central axis, an interior surface corresponding in size and shape to the exterior surface of the cylindrical structure to which the mechanism is to be applied and an outer surface defining a wall thickness. A reduced wall thickness is formed into the outer surface in a pattern to produce a discontinuity that interrupts the lengthwise coherence of vortex shedding of moving fluid from the outer surface when the cylindrical column is attached to the exterior of the cylindrical structure in the flowing fluid. The effect of VIV on the cylindrical structure is effectively reduced. The result is a submergible cylindrical assembly for positioning in a flowing body of water and having enhanced resistance to VIV.

Flow-Induced Vibration of Power and Process Plant Components: A Practical Workbook

Abstract: Units and dimensions the kinematics of vibration and acoustics fundamentals of structural dynamics vibration of structures in quiescent fluid 1 - the hydrodynamic mass vibration of structures in quiescent fluids 2 - simplified methods vortex-induced vibration fluid-elastic instability of tube bundles turbulence-induced vibration in parallel flow turbulence-induced vibration in cross-flow axial and leakage-flow induced vibrations impact, fatigue and wear acoustically induced vibration and noise signal analysis and diagnostic techniques.

Drive level flow-field conditioning to reduce flow field turbulence

Abstract: A flow control device (120) for a data storage system to reduce flow induced vibration. The flow control device (120) includes a plurality of streamline flow passages (122) to reduce turbulent flow in a flow field along a disc surface. Thus, air flow induced by rotation of data discs is directed through the plurality of streamline flow passages (122) to reduce turbulence to limit excitation or vibration of the head (108) and suspension components.

Experiments on Flow-Induced In-Line Oscillation of a Circular Cylinder in a Water Tunnel

Abstract: The flow-induced in-line oscillation of a cantilevered circular cylinder was experimentally studied through free-oscillation tests in a water tunnel. The response displacement amplitude at a circular cylinder tip was measured at reduced velocity from 1.0 to 4.0. A cantilevered cylinder was supported by a plate spring mounted on the water tunnel wall. The cylinder aspect ratio was varied from 5 to 21 to investigate the effect of aspect ratio on the response displacement. It is found that cylinders with aspect ratios of 5 and 10 have one excitation region, while cylinders with aspect ratios of 14 and 21 have two excitation regions. The aspect ratio, therefore, affects the amplitude of the excitation regions. The influence of end-effect was also investigated using cylinders with an end plate attached to the free end. Since the cylinders with an end plate show two excitation regions, even at an aspect ratio of 5, the flow around the free end of a cantilevered cylinder causes the end-effect. The mechanism of vibration was investigated using a cylinder with a splitter plate in wake to prevent alternate vortices. The amplitude is greater than those of a normal cylinder without a splitter plate, especially at Vr=2.3 to 3.0, where a cylinder with an end plate shows the second excitation region. In other words, the alternate vortices suppress the amplitude in this range. The maximum amplitude of each excitation region decreases in proportion to Cn and the amplitude of the first excitation is more sensitive to Cn.

Vortex-induced vibration of slender structures in unsteady flow

Abstract: Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2002.

Experiments on Flow-Induced In-Line Oscillation of a Circular Cylinder in a Water Tunnel : 1st-Report, The Difference of the Response Characteristics When a Cylinder is Elastically Supported at Both Ends and Cantilevered

Abstract: Flow-induced in-line oscillation of a circular cylinder has been experimentally studied by free-oscillation tests in a water tunnel. Response amplitudes of a circular cylinder have been measured for determining the values of the reduced mass-damping parameter of less than 1.0. In the free-oscillation tests, the cylinder models were spring-mounted so as to oscillate as a two-dimensional rigid cylinder in the water tunnel. Two types of excitation phenomena appear at approximately half of the resonance flow velocity. The response amplitudes are sensitive to the reduced mass-damping parameter during the in-line oscillation of the first excitation region with a symmetric vortex street, and the alternate vortices are periodically shed, locking-in with the vibration of the cy]inder in the second excitation region. A hysteresis phenomenon is observed to appear in the in-line oscillation of the latter region. A cantilevered circular cylinder with a finite length aspect ratio of 10 was tested for fluid-elastic characteristics of the cylinder, and these characteristics are found to be quite different from those of the two-dimensional cylinder, having only one wide velocity region of excitation. The results of this study are providing important supporting data for the recent publication Guideline for Evaluation of Flow Induced Vibration of a Cylindrical Structure in a Pipe by the Japan Society of Mechanical Engineers, Standard JSME S()12 1998.

Vortex-Induced Vibration of a Cantilever Circular Cylinder in Super-Critical Reynolds Number Flow and Its Suppression by Structure Damping

Abstract: Experimental validation of the design criteria for preventing the failure of a thermometer well by vortex-induced vibration is presented, clarifying the effects of Reynolds number and structure damping. An existing avoidance criterion for the vortex-induced vibration in the flow direction, which is given in terms of the reduced velocity Vr as Vr 1.2 (or 2.5) under the condition of Vr 1.2 are reasonably applicable to a cantilever cylinder in a pipe water flow.

Method and apparatus for reducing drag and suppressing vortex-induced vibration

Abstract: A structural element comprises an elongate body having a longitudinal axis extending along the wavy path. The body is coupled to a support on at least one end. At least a portion of the body extends through an area of fluid flow such that a plane containing the wavy path lies substantially parallel to the direction of flow. In one embodiment, the longitudinal axis extends along a substantially sinusoidal path. Also disclosed is a method of reducing drag on and suppressing vortex induced vibrations in an elongate body disposed in an area of directional fluid flow, comprising the steps of coupling at least one end of the body to a support, forming a longitudinal axis of the body along a wavy path, and orienting the body such that the wavy longitudinal path lies in a plane substantially parallel to the direction of fluid flow.

Optical control of flow-induced vibration of pipeline

Abstract: We investigate self-excited lateral vibration of a pipe due to an internal flow The stability boundary of fluid velocity is expressed in terms of the system parameters, such as, pipe material density and rigidity, and fluid density, etc To maximize the fluid transport efficiency, it is necessary to maximize the flow velocity while minimizing the lateral vibration of the pipe We use the integral minimum principle of Pontryagin to find the optimum flow velocity for minimum pipe vibration The results are illustrated by numerical simulation

Evaluation of Turbulence-Induced Vibration of a Circular Cylinder in Supercritical Reynolds Number Flow

Abstract: Experiments have been conducted on turbulence-induced vibration of a circular cylinder in water flow with supercritical Reynolds number ranging from 3×105 to 3×106 Based on the power spectral density of cylinder vibrations measured at several Reynolds numbers, fluctuating force coefficients, Strouhal number and correlation length were evaluated As a result, it was clarified that the prediction method based on the random vibration theory introducing the correlation length has sufficient margin for actual turbulence-induced response

Strouhal number effect on synchronized vibration range of a circular cylinder in cross flow

Abstract: Synchronized vibrations were measured for a circular cylinder in a water cross flow at subcritical Reynolds numbers to compare the synchronization range between the subcritical and supercritical regions and clarify the effect of the Strouhal number on the range. A small vibration in the lift direction was found in only the subcritical region when the Karman vortex shedding frequency was about 1/5 of the cylinder natural frequency. The ratio of the Karman vortex shedding frequency to the natural frequency where the self-excited vibration in the drag direction by the symmetrical vortex shedding began was about 1/4 in the subcritical region, and increased to 0.32 at the Strouhal number of 0.29 in the supercritical region. The frequency ratio at the beginning of the lock-in vibration in the drag direction by the Karman vortex shedding was about 1/2, and that in the lift direction decreased from 1 to 0.8 with decreasing Strouhal number.

Suppression And Characteristics Of Flow-Induced Vibration Of Rectangular Prisms WithVarious Width-to-height Ratios

Abstract: In this study, the response characteristics and suppression of flow-induced vibrations of rectangular prisms with various width-to-height ratios were experimentally investigated. The present study focused on rotary oscillation, one of the three types of flow-induced vibration generated in a rectangular prism. The main findings were that (i) there are three types of flow-induced vibration, i.e., vortex excitation, low-speed and high-speed torsional flutter, (ii) the flow-induced vibration occurs due to change in fluctuating pressure on the surface of the prism based on the difference of rolling-up of the shear layer separating from the leading edge of the prism, (iii) the flow-induced vibration can be classified into five patterns depending on the width-to-height ratio, and (iv) the flow-induced vibrations can be most effectively suppressed by placing a normal plate upstream of the prism.

Active modal control of timoshenko pipes conveying fluid

Abstract: This paper deals with vibration control of Timoshenko pipes conveying fluid. Excessive vibration in this flow induced vibration problem is suppressed via an active feedback control scheme. The strategy of the active vibration suppression technique will be presented and system dynamics formulated. Optimal independent modal space control technique is applied for best obtainable system performance. The computation consideration, implementation of control strategy, and the effectiveness of the control scheme are addressed. A finite element method is used for both the vibration and control analyses of the problem considered. Classical analysis by solving the partial differential equation is only applicable to systems with simple boundary conditions, such as simply supported pipes. When a more complex situation occurs, a closed form expression becomes very difficult, if not impossible, to obtain. The use of a finite element approach alleviates such deficiencies and is readily applicable to pipes with i...

The experiment of flow induced vibration in PWR RCCAs

Abstract: Recently, severe wear on the shutdown rod cladding of Ulchin Nuclear Power Plant #1, #2 were observed by the Eddy Current Test (E.C.T.). In particular, the wear at the sixth card location was up to 75%. The test results indicated that the Flow Induced Vibration (F.I.V.) might be the cause of the fretting wear resulting from the contact between Rod Cluster Control Assemblies (RCCAs) and their spacing cards (guide plates) arranged in the guide tube. From reviewing RCCAs fretting wear reports and analyzing the general characteristics of F. I. V. mechanism in the reactor, geometric layout and flow conditions arround the control rod, it is concluded that the turbulence excitation is the most probable vibration mechanism of RCCA. To identify the governing mechanism of RCCA vibration, an experiment was performed for a representative rod position in which the most serious fretting wear was experienced among the six rod positions. The experimental rig was designed and set up to satisfy the governing nondimensional numbers which are Reynolds number and mass damping parameter. The vibration amplitude measurement by the non-contact laser displacement sensor showed good agreements in the frequency and the maximum wearing (vibration) location with Ulchin E. C. T. results and Framatome report, respectively. The sudden increase in the vibration amplitude was sensed around the 6th guide plate with mass flow rate variation. Comparing the similitude rod behaviour with the idealized response of a cylinder in flow induced vibration, it was found that the dominant mechanism of vibration was transferred from turbulence excitation to periodic shedding at the mass flow rate 90l/min. Also the critical velocity of the vibration in RCCAs was determined and the vibration can be prevented by reducing the bypass flow rate below the critical velocity.

Calculation of unsteady flow around circular cylinder and vortex-induced vibration

Abstract: Numerical analysis of the unsteady flow around the stationary circular cylinder with Re (the Reynolds number) ranging from 100 to 10\+5 and its vortex-induced vibration with Re from 5160 to 6300 are conducted by solving the incompressible Navier-Stokes equations of initial variables in general curvilinear coordinates and staggered mesh. The vibration of the cylinder is studied by the moving-mesh method. A second-order projection method and the multigrid technique are used for solving the N-S equations. The response of cylinder is evaluated by the Newmark-β method. The vibration of the cylinder and the fluid flow are coupled by the boundary conditions on the surface of cylinder. The computed vortex shedding frequency agrees well with the experiment, and the obtained drag coefficient is satisfactory. The ‘beat’ and ‘lock-in’phenomena are successfully predicted. The computed amplitudes of vibration surprisingly agree well the experimental results.