Two Tandem Cylinders With Passive Turbulence Control in Flow-Induced Vibration: Relation of Oscillation Patterns to Frequency Response

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Kai Lan ◽  
Hai Sun ◽  
Michael M. Bernitsas
Keyword(s):  
Frequency Response ◽  
Phase Difference ◽  
Volume Ratio ◽  
Flow Induced Vibration ◽  
Frequency Spectra ◽  
Turbulence Control ◽  
Instantaneous Phase ◽  
Tandem Cylinders ◽  
Flow Induced Vibrations ◽  
The University

Flow-induced vibrations (FIV) are conventionally destructive and should be suppressed. Since 2006, the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan has been studying FIV of multiple cylinders to enhance their response for harnessing hydrokinetic power from ocean, river, and tidal currents. Interactions between multiple cylinders in FIV enable high power-to-volume ratio in a converter consisting of multiple oscillators. This paper investigates experimentally the relation between oscillation patterns and frequency response of two cylinders in tandem. All experiments are conducted in the recirculating channel of the MRELab for 30,000 < Re < 120,000. Phase analysis reveals three dominant patterns of oscillation of two tandem cylinders by calculating the instantaneous phase difference between the two cylinders. This phase difference characterizes each major pattern. Pattern A is characterized by small lead or lag of one cylinder over the other. In pattern B, there is nearly 180 deg out of phase oscillations between the cylinders. In pattern C, the instantaneous phase difference changes continuously from −180 deg to +180 deg. Using frequency spectra and amplitude response, oscillation characteristics of each cylinder are revealed in vortex-induced vibration (VIV) and galloping. Pattern A occurs mostly in galloping when the first cylinder has higher stiffness. Pattern B occurs seldom and typically in the initial VIV branch and transition from VIV to galloping. Pattern C occurs in the upper and lower VIV branches; and in galloping when the lead cylinder has lower stiffness.

Two Tandem Cylinders With Passive Turbulence Control in Flow Induced Vibration: Relation of Oscillation Patterns to Frequency Response

2017 ◽  
Author(s):  
Kai Lan ◽  
Hai Sun ◽  
Michael M. Bernitsas
Keyword(s):  
Frequency Response ◽  
Phase Difference ◽  
Volume Ratio ◽  
Flow Speed ◽  
Flow Induced Vibration ◽  
Frequency Spectra ◽  
Turbulence Control ◽  
Instantaneous Phase ◽  
Tandem Cylinders ◽  
Flow Induced Vibrations

Flow Induced Vibrations (FIV) are conventionally destructive and should be suppressed. Since 2006, the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan has been studying FIV of multiple cylinders to enhance their response for harnessing hydrokinetic power from ocean, river, and tidal currents. Interactions between multiple cylinders in FIV enable high power-to-volume ratio in a converter consisting of multiple oscillators of cylinders. This paper investigates experimentally the relation between oscillation patterns and frequency response of two cylinders in tandem. All experiments are conducted in the recirculating channel of the MRELab for 30,000<Re<120,000. Phase analysis reveals three dominant patterns of oscillation of two tandem cylinders by calculating the instantaneous phase difference between the two cylinders. This phase difference characterizes each major pattern. One is characterized by nearly 180° out of phase oscillations and one by small lead or lag of one cylinder over the other. In the third pattern, the instantaneous phase difference changes continuously from −180° to +180°. Using frequency spectra, oscillation characteristics of each cylinder are revealed in each flow speed range. Comparison of oscillation patterns and frequency spectra reveals that each oscillation pattern is related to a distinctly different frequency response.

Extraction of the Mayer wave component in blood pressure from the instantaneous phase difference between electrocardiograms and photoplethysmograms

2010 ◽  
Vol 15 (4) ◽  
pp. 522-525
Author(s):  
Norihiro Sugita ◽  
Makoto Yoshizawa ◽  
Masayuki Murakoshi ◽  
Makoto Abe ◽  
Noriyasu Homma ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Phase Difference ◽  
Wave Component ◽  
Instantaneous Phase ◽  
Mayer Wave

Effects of decoupling on spectra of seismic waves

1962 ◽  
Vol 52 (1) ◽  
pp. 123-131
Author(s):  
D. E. Willis ◽  
James T. Wilson
Keyword(s):  
Seismic Waves ◽  
High Explosive ◽  
Atomic Energy Commission ◽  
University Of Michigan ◽  
Frequency Spectra ◽  
Spherical Cavities ◽  
Significant Difference ◽  
The University ◽  
Relationship Of ◽  
The Relationship

Abstract A series of controlled high explosive shots were conducted by the Atomic Energy Commission in a salt mine near Winnfield, Louisiana, to investigate seismic decoupling theories. Two recording stations were used by the University of Michigan at various distances between 1.1 and 14.7 kilometers for a majority of these shots. Frequency analyses of the magnetic tape recordings were made and the results are presented showing the relationship of the frequency spectra as a function of charge size, distance from the source, and coupled vs decoupled shots. The smaller decoupled shots detonated in the large spherical cavities were observed to have somewhat higher predominate frequencies than the equivalent size coupled shots. A change in cavity size produced no significant difference in the shape of the spectra of the large decoupled shots.

Three-Dimensional CFD Analysis of Two Circular Cylinders Arranged Perpendicular to Each Other

2005 ◽  
Author(s):  
Karl W. Schulz ◽  
Tommy Minyard ◽  
William Barth
Keyword(s):  
Structural Dynamics ◽  
Three Dimensional ◽  
Offshore Structures ◽  
Circular Cylinders ◽  
Navier Stokes ◽  
Cfd Analysis ◽  
Flow Conditions ◽  
Tandem Cylinders ◽  
Dynamics Response ◽  
The University

A three-dimensional numerical method combining solution of the incompressible Reynolds Averaged Navier-Stokes (RANS) equations with a rigid body structural dynamics response has been developed previously to aid in the prediction of the loads and motions of offshore structures. In this paper, we use the tool to compute the hydrodynamic flow around two tandem cylinders oriented perpendicularly to each other. The flow conditions and gap distances between the cylinders are chosen to match a set of water tunnel experiments carried out at the University of Queensland. Comparisons of Strouhal frequencies and example flowfield visualizations are presented between the experimental measurements and associated CFD results.

Towards Understanding Two-Phase Flow Induced Vibration of Piping Structure With a U-Bend

2019 ◽  
Author(s):  
Olufemi E. Bamidele ◽  
Wael H. Ahmed ◽  
Marwan Hassan
Keyword(s):  
Void Fraction ◽  
Vibration Amplitude ◽  
Two Phase Flow ◽  
Bubbly Flow ◽  
Phase Flow ◽  
Flow Conditions ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Void Fractions ◽  
Flow Induced Vibrations

Abstract The current work investigates two-phase flow induced vibrations in 90° U-bend. The two-phase induced vibration of the structure was investigated in the vertical, horizontal and axial directions for various flow patterns from bubbly flow to wavy and annular-dispersed flow. The void fractions at various locations along the piping including the fully developed void fraction and the void fraction at the entrance of the U-bend were fully investigated and correlated with the vibration amplitude. The results show that the excitation forces of the two-phase flow in a piping structure are highly dependent on the flow pattern and the flow conditions upstream of the bend. The fully developed void fraction and slip between phases are important in modelling of forces in U-bends and elbows.

Boundary Backstepping Control of Flow-Induced Vibrations of a Membrane at High Mach Numbers

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Aziz Sezgin ◽  
Miroslav Krstic
Keyword(s):  
Wave Equation ◽  
Original System ◽  
Target System ◽  
Spanwise Direction ◽  
Infinite Length ◽  
Flow Induced Vibration ◽  
Trailing Edge ◽  
Flow Induced Vibrations ◽  
Mach Numbers ◽  
High Mach

We design a controller for flow-induced vibrations of an infinite-band membrane, with flow running across the band and only above it, and with actuation only on the trailing edge of the membrane. Due to the infinite length of the membrane, the dynamics of the membrane in the spanwise direction are neglected, namely, we employ a one-dimensional (1D) model that focuses on streamwise vibrations. This framework is inspired by a flow along an airplane wing with actuation on the trailing edge. The model of the flow-induced vibration is given by a wave partial differential equation (PDE) with an antidamping term throughout the 1D domain. Such a model is based on linear aeroelastic theory for Mach numbers above 0.8. To design a controller, we introduce a three-stage backstepping transformation. The first stage gets the system to a critically antidamped wave equation, changing the stiffness coefficient's value but not its sign. The second stage changes the system from a critically antidamped to a critically damped equation with an arbitrary damping coefficient. The third stage adjusts stiffness arbitrarily. The controller and backstepping transformation map the original system into a target system given by a wave equation with arbitrary positive damping and stiffness.

Experimental Study on Flow-Induced Vibration of Floating Squared Section Cylinders With Low Aspect Ratio: Part II — Effects of Rounded Edges

2016 ◽  
Author(s):  
Rodolfo T. Gonçalves ◽  
Dennis M. Gambarine ◽  
Aline M. Momenti ◽  
Felipe P. Figueiredo ◽  
André L. C. Fujarra
Keyword(s):  
Aspect Ratio ◽  
Reynolds Numbers ◽  
Ocean Basin ◽  
Separation Point ◽  
Flow Induced Vibration ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Significant Difference ◽  
Flow Induced Vibrations ◽  
Elastically Supported

Experiments regarding flow-induced vibration on floating rounded squared section cylinders with low aspect ratio were carried out in an ocean basin equipped with a rotating-arm apparatus. Floating squared section cylinders with rounded edges and aspect ratios of L/D = 2.0 were elastically supported by a set of linear springs in order to provide low structural damping to the system. Two different incidence angles were tested, namely 0 and 45 degrees. The Reynolds numbers covered the range from 2,000 to 30,000. The aim was to understand the flow-induced vibrations around single columns, gathering information for further understanding the causes for the Vortex-Induced Motions in semi-submersible and TLP platforms. Experiments on circular and squared sections cylinders (without rounded edges) were also carried out to compare the results with the rounded square section cylinders (with rounded edges). The amplitude results for in-line, transverse and yaw amplitude for 0-degree models showed to be higher for squared section cylinders compared to those for the rounded square section cylinders. No significant difference between the 45-degree models was observed. The results of ratio between frequency of motion in the transverse direction and natural frequency in still water confirmed the vortex-induced vibration behavior for the squared and rounded square section cylinders for 45-degree incidence; and also the galloping characteristics for 0-degree incidence cases. The rounded effect on the square section cylinders showed to be important only for reduced velocity larger than 8, which is probably related to the position of the separation point that changes around the rounded edge, behavior that did not occurr for the squared edge that fixed the separation point for any reduced velocity.

Map of Passive Turbulence Control to Flow-Induced Motions for a Circular Cylinder at 30,000

2013 ◽  
Author(s):  
Hongrae Park ◽  
Michael M. Bernitsas ◽  
Che-Chun Chang
Keyword(s):  
Circular Cylinder ◽  
Amplitude Ratio ◽  
Damping Ratio ◽  
Water Channel ◽  
University Of Michigan ◽  
Strong Suppression ◽  
Variable Parameters ◽  
Turbulence Control ◽  
The University ◽  
Passive Turbulence Control

Passive turbulence control (PTC) in the form of two straight roughness strips with variable width, and thickness about equal to the boundary layer thickness, is used to modify the flow-induced motions (FIM) of a rigid circular cylinder. The cylinder is supported by two end-springs and the flow is in the TrSL3, high-lift, regime. The PTC-to-FIM Map, developed in previous work, revealed zones of weak suppression, strong suppression, hard galloping, and soft galloping. In this paper the sensitivity of the PTC-to-FIM Map to: (a) the width of PTC covering, (b) PTC covering a single or multiple zones, (c) PTC being straight or staggered is studied experimentally. Experiments are conducted in the Low Turbulence Free Surface Water Channel of the University of Michigan. Fixed parameters are: cylinder diameter D = 8.89cm, m* = 1.725, spring stiffness K = 763N/m, aspect ratio l/D = 10.29, and damping ratio ζ = 0.019. Variable parameters are: circumferential PTC location αPTC ∈ [0°−180°], Reynolds number Re ∈ [30,000–120,000], flow velocity U ∈ [0.36m/s–1.45m/s]. Measured quantities are: amplitude ratio A/D, frequency ratio fosc/fn,w, and synchronization range. As long as the roughness distribution is limited to remain within a zone, the width of the strips does not affect the FIM response. When multiple zones are covered, the strong suppression zone dominates the FIM.

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