Influence of Finite-Length Plate Proximity on Vortex-Induced Vibrations of Elastic Cable

2021 ◽  
Author(s):  
Oleg Ivanov ◽  
Vasily Vedeneev
Keyword(s):  
Finite Length ◽  
Amplitude Ratio ◽  
Oscillation Amplitude ◽  
Maximum Amplitude ◽  
Elastic Cylinder ◽  
Cylinder Surface ◽  
Trailing Edge ◽  
Gap Ratio ◽  
Vortex Induced Vibrations ◽  
Amplitude Increase

Abstract Vortex-induced vibrations of an elastic cylinder near a finite-length plate are experimentally investigated. A rubber cylinder of diameter D was spanned in the test section of a wind tunnel near a plate of length nearly 6D. The oscillation amplitude peak for a single cylinder was 0.3D, Reynolds number for oscillating peak-amplitude regime based on the cylinder diameter was in the range 180...260. The oscillation amplitude ratio A/D appeared to decrease with the reduction of the gap ratio G/D between the cylinder surface and the plate for the cylinder located sufficiently upstream from the plate trailing edge. However, for the cylinder location at the same level or downstream from the plate trailing edge, there are regions of essentially larger oscillation amplitude compared to the isolated cylinder case. Maximum amplitude increase by 39% was obtained.

Improvement of the Static and Dynamic Characteristics of Magnetic Head Sliders by Optimum Design

1999 ◽  
Vol 122 (1) ◽  
pp. 280-287 ◽  
Author(s):  
Hiromu Hashimoto ◽  
Yasuhisa Hattori
Keyword(s):  
Objective Function ◽  
Optimum Design ◽  
Amplitude Ratio ◽  
Optimization Technique ◽  
Hard Disk Drives ◽  
Maximum Amplitude ◽  
Disk Surface ◽  
Operating Conditions ◽  
Magnetic Head ◽  
Design Variables

The aim of this paper is to develop a general methodology for the optimum design of magnetic head sliders in improving the spacing characteristics between a slider and disk surface under static and dynamic operating conditions of hard disk drives and to present an application of the methodology to the IBM 3380-type slider design. To generate the optimal design variables, the objective function is defined as the weighted sum of the minimum spacing, the maximum difference in the spacing due to variation of the radial location of the head, and the maximum amplitude ratio of the slider motion. Slider rail width, taper length, taper angle, suspension position, and preload are selected as the design variables. Before the optimization of the head, the effects of these five design variables on the objective function are examined by a parametric study, and then the optimum design variables are determined by applying the hybrid optimization technique, combining the direct search method and successive quadratic programming. From the obtained results, the effectiveness of optimum design on the spacing characteristics of magnetic heads is clarified. [S0742-4787(00)03701-2]

Influence From Helical Strakes on Vortex Induced Vibrations and Static Deflection of Drilling Risers

2005 ◽  
Author(s):  
Carl M. Larsen ◽  
Gro Sagli Baarholm ◽  
Halvor Lie
Keyword(s):  
Dynamic Response ◽  
Test Data ◽  
Oscillation Amplitude ◽  
Cross Flow ◽  
Current Profile ◽  
Dynamic Stresses ◽  
Drag Forces ◽  
Vortex Induced Vibrations ◽  
Bending Stresses ◽  
Helical Strakes

Helical strakes are known to reduce and even eliminate the oscillation amplitude of vortex induced vibrations (VIV). This reduction will increase fatigue life, and also reduce drag magnification from cross-flow vibrations. But sections with strakes will also have a larger drag coefficient than the bare riser. Hence, the extension of a section with strakes along a riser should be large enough to reduce oscillations, but not too long in order to limit drag forces from current and waves. The optimum length and position for a given riser will therefore vary with current profile. Dynamic response from waves should also be taken into account. The purpose of the present paper is to illustrate the influence from strakes on VIV, as well as on static and dynamic response for a drilling riser. Hydrodynamic coefficients for a cylinder with helical strakes are found from experiments and applied in an empirical model for the analysis of VIV. The result from the VIV analysis is used for a second calculation of drag forces that are applied in an updated static analysis. Dynamic stresses from regular waves are also presented, but VIV are not considered for these cases. A simple study of length and position of the section with strakes is carried out for some standard current profiles. Results are presented in terms of oscillation amplitudes, fatigue damage, bending stresses and riser angles at ends. The study is based on test data for one particular strake geometry, but the analysis method as such is general, and the computer programs used in the study can easily apply other test data.

Influence of Trailing-Edge Geometry on Hydraulic-Turbine-Blade Vibration Resulting From Vortex Excitation

1960 ◽  
Vol 82 (2) ◽  
pp. 103-109 ◽  
Author(s):  
Gunnar Heskestad ◽  
D. R. Olberts
Keyword(s):  
Boundary Layer ◽  
Turbine Blade ◽  
Vortex Shedding ◽  
Hydraulic Turbine ◽  
Trailing Edge ◽  
Blade Vibration ◽  
Edge Geometry ◽  
Blade Thickness ◽  
Vortex Induced Vibrations ◽  
Approach Velocity

A study was made to determine effects of trailing-edge geometry on the vortex-induced vibrations of a model blade designed to simulate the conditions at the trailing edge of a hydraulic-turbine blade. For the type of trailing-edge flow encountered, characterized by a thick boundary layer relative to the blade thickness, the vortex-shedding frequency could not be represented by any modification of the Strouhal formula. The amplitude of the induced vibrations increased with the strength of a vortex in the von Karman vortex street of the wake; one exception was provided by a grooved edge, which is discussed in some detail. For a particular approach velocity, the vortex strength is primarily a function of the ratio of distance between separation points to boundary-layer thickness, the degree of “shielding” between regions of vortex growth, and frequency of vortex shedding.

Simple Formula to Study the Large Amplitude Free Vibrations of Beams and Plates

2008 ◽  
Vol 75 (1) ◽  
Author(s):  
G. Venkateswara Rao ◽  
K. Meera Saheb ◽  
G. Ranga Janardhan
Keyword(s):  
Free Vibration ◽  
Large Amplitude ◽  
Simple Formula ◽  
Space Variable ◽  
Linear Time ◽  
Amplitude Ratio ◽  
Compressive Load ◽  
Maximum Amplitude ◽  
Free Vibrations ◽  
Structural Members

A simple formula to study the large amplitude free vibration behavior of structural members, such as beams and plates, is developed. The nonlinearity considered is of von Karman type, and after eliminating the space variable(s), the corresponding temporal equation is a homogeneous Duffing equation. The simple formula uses the tension(s) developed in the structural members due to large deflections along with the corresponding buckling load obtained when the structural members are subjected to the end axial or edge compressive load(s) and are equal in magnitude of the tension(s). The ratios of the nonlinear to the linear radian frequencies for beams and the nonlinear to linear time periods for plates are obtained as a function of the maximum amplitude ratio. The numerical results, for the first mode of free vibration obtained from the present simple formula compare very well to those available in the literature obtained by applying the standard analytical or numerical methods with relatively complex formulations.

Simulation of Low-Reynolds Number Flow Around a Circular Cylinder Following a Slender Elliptical Path

2013 ◽  
Author(s):  
László Baranyi
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Amplitude Ratio ◽  
Oscillation Amplitude ◽  
Base Pressure ◽  
Reynolds Number Flow ◽  
Two Dimensional Flow ◽  
Number Flow ◽  
Low Reynolds ◽  
Lock In

Two-dimensional flow around a circular cylinder forced to follow an elliptical path at low Reynolds numbers is investigated numerically using a thoroughly tested in-house code based on the finite difference method. Time-mean (TM) and rms values of lift, drag and base pressure coefficients are investigated within the lock-in region against the transverse oscillation amplitude for Reynolds number Re = 150 at frequency ratios of 0.8, 0.9 and 1.0 while the ratio of in-line and transverse cylinder oscillation amplitudes is kept at six different values yielding slender elliptical cylinder paths. The objective of the paper is to investigate the effect of the shape of the path, or amplitude ratio, on force coefficients. Findings show that for the cases investigated the rms of lift and TM of drag and base pressure are hardly affected by the amplitude ratio, while its effects are pronounced on the TM of lift and rms of drag and base pressure.

Selective Surface Roughness to Suppress Flow-Induced Motion of Two Circular Cylinders at 30,000 < Re < 120,000

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Hongrae Park ◽  
Michael M. Bernitsas ◽  
Eun Soo Kim
Keyword(s):  
Surface Roughness ◽  
Amplitude Ratio ◽  
Flow Direction ◽  
Circular Cylinders ◽  
University Of Michigan ◽  
Marine Renewable Energy ◽  
Vortex Induced Vibrations ◽  
Smooth Cylinder ◽  
Induced Motion ◽  
The University

In the Marine Renewable Energy Laboratory of the University of Michigan, selectively located surface roughness has been designed successfully to suppress vortex-induced vibrations (VIV) of a single cylinder by 60% compared to a smooth cylinder. In this paper, suppression of flow-induced motions of two cylinders in tandem using surface roughness is studied experimentally by varying flow velocity and cylinder center-to-center spacing. Two identical rigid cylinders suspended by springs with their axes perpendicular to the flow are allowed one degree of freedom motion transverse to the flow direction. Surface roughness is applied in the form of four roughness strips helically placed around the cylinder. Results are compared to smooth cylinders also tested in this work. Amplitude ratio A/D, frequency ratio fosc/fn,water, and range of synchronization are measured. Regardless of the center-to-center cylinder distance, the amplitude response of the upstream smooth cylinder is similar to that of an isolated smooth cylinder. The wake from the upstream cylinder with roughness is narrower and longer and has significant influence on the amplitude of the downstream cylinder. The latter is reduced in the initial and upper branches while its range of VIV-synchronization is extended. Galloping is suppressed in both cylinders. In addition, the amplitude of the upstream rough cylinder and its range of synchronization increase with respect to the isolated rough cylinder.

Hydroelastic Vibrations of Flat Plates Related to Trailing Edge Geometry

1961 ◽  
Vol 83 (4) ◽  
pp. 671-678 ◽  
Author(s):  
G. H. Toebes ◽  
P. S. Eagleson
Keyword(s):  
Leading Edge ◽  
Equation Of Motion ◽  
Thin Plates ◽  
Comprehensive Treatment ◽  
Angle Of Incidence ◽  
Flat Plates ◽  
Trailing Edge ◽  
Edge Geometry ◽  
Vortex Induced Vibrations ◽  
Hydroelastic Vibrations

Vortex-induced vibrations of thin flat plates are studied as a function of trailing edge geometry. In an effort to extend the analysis to a more comprehensive treatment than that provided by the common vortex model, the vibrations are considered as hydroelastic phenomena. An equation of motion is formulated. From a qualitative analysis of this nonlinear equation some expected features of its solution are set forth. A detailed experimental determination is made of the amplitude spectra of various thin plates mounted at zero mean angle of incidence in the test section of a water tunnel and suspended by a torsion spring through their leading edge. The effects of trailing edge geometry and elastic properties of plate support are explored. Data analysis gives interesting confirmation of the formulated equation of motion. The vibration is shown to become self-excited and the degree of two dimensionality of the wake is deduced to be determinative in regard to the severity of the vibration.

Surface pressures and their corrections for the flow past a finite-length plate in supersonic low density flow

1979 ◽  
Vol 95 (1) ◽  
pp. 177-187 ◽  
Author(s):  
S. L. Gai
Keyword(s):  
Experimental Study ◽  
Finite Length ◽  
Leading Edge ◽  
Low Density ◽  
Cold Wall ◽  
Trailing Edge ◽  
Flow Past ◽  
Density Flow ◽  
Recent Method

An experimental study of the flow past a thin finite length plate in a supersonic low density stream is reported. The paper discusses the corrections that are necessary for surface pressures measured under rarefied conditions. It is shown that the recent method of ‘orifice’ corrections due to Harbour & Bienkowski is versatile and reliable to use for both cold wall and insulated wall measurements. For the conditions of the experiment, the flow over the plate was found to be dominated by both leading-edge and trailing-edge interactions.

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