Defining a Parameter of Effectiveness for the Suppression of Vortex-Induced Vibration

2011 ◽  
Author(s):  
Cesar M. Freire ◽  
Ivan Korkischko ◽  
Julio R. Meneghini
Keyword(s):  
Shear Layers ◽  
The Body ◽  
Bluff Bodies ◽  
Vortex Induced Vibration ◽  
Vibration Effect ◽  
Splitter Plates ◽  
Offshore Engineering ◽  
Flow Mechanisms ◽  
Offshore Industry ◽  
A Current

The vortex-induced vibration (VIV) phenomenon is a very important issue in ocean and offshore engineering. When bluff bodies are immersed in a current, the boundary layers separate and form shear layers that can interact causing a periodic vortex shedding. In such condition, the forces acting on the body can make it vibrate. In the offshore industry, among other engineering applications, the vibration of structures can cause fatigue problems, reducing the life span of the element. To reduce the vortex-induced vibration effect suppressors can be employed in order to avoid the body to move, or at least, reduce the amplitude of vibration. There is a great number of suppressor types, like strakes, splitter plates, shrouds, etc; and each one has its own flow mechanisms to avoid VIV. Until now there is no simple way to compare the results and effectiveness of each suppressor. The purpose of this work is to define a parameter called suppressor effectiveness, based on the amplitude of vibration and the reduced velocity range, and use the suppressor effectiveness to compare different suppressors. The data used in the comparisons was obtained from experiments by the authors and collected from the literature.

The wakes of cylindrical bluff bodies at low Reynolds number

1978 ◽  
Vol 288 (1354) ◽  
pp. 351-382 ◽  
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
The Body ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Near Wake ◽  
Cross Sectional ◽  
Molecular Diffusivity ◽  
Splitter Plates ◽  
Low Reynolds

Experiments on the near wake of a cylinder will be discribed in an attempt to present a coherent picture of the events encountered as the Reynolds number increases from small values up to values of a few thousand. Much work on this subject has already been done, but there are gaps in our description of these flows as well as more fundamental deficiencies in our understanding of them. The subject has been reviewed several times and most recently by Berger & Wille (1972) whose paper covers much of the ground that will be discussed again here. The present work may be regarded as built upon this latest review. I remember with gratitude many helpful discussions with the late Rudolph Wille who contributed so much to this subject. The investigation has concentrated on circular cylinders, but the wakes of bluff cylinders of different cross sectional shapes have also been observed. Bluff cylinders in general are considered in §§4 and 5, together with the effect of splitter plates on circular cylinders in §9. The experiments concern, almost exclusively, flow visualization of the wakes by means of dye washed from the bodies. The patterns of dye observed are, therefore, filament line representations of the flow leaving the separation lines on the body. It must be stressed that the dye does not make visible the vorticity bearing fluid because at low Reynolds number, vorticity diffuses considerably more rapidly than does dye. The ratio of the molecular diffusivity of momentum to that of mass of dye is of the order of 100.

The mechanics of the formation region of vortices behind bluff bodies

1966 ◽  
Vol 25 (2) ◽  
pp. 401-413 ◽  
Author(s):  
J. H. Gerrard
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Free Stream ◽  
Shear Layers ◽  
Bluff Bodies ◽  
Formation Region ◽  
Splitter Plates ◽  
Free Shear Layers ◽  
High Reynolds

The characteristic lengths of the oscillating wakes of bluff bodies is discussed; in particular, those used in the universal non-dimensional frequencies proposed by Roshko (1954b) and Goldburg, Washburn & Florsheim (1965). It is concluded that these are equivalent at high Reynolds number. A closer examination leads to the conclusion that there are two simultaneous characteristic lengths; the scale of the formation region, and the width to which the free shear layers diffuse. Discussion of the mechanics of the formation region results in a physical basis for the determination of the frequency by these two characteristic lengths. The ideas developed are applied to the effects of splitter plates in the wake. The possibility of a high-Reynolds-number symmetrical formation region is suggested as an explanation of the very small lift values observed in the absence of free-stream disturbances.

Galvanotropic Reactions of Polycelis nigra in Relation to Inherent Electrical Polarity

1927 ◽  
Vol 5 (1) ◽  
pp. 66-88
Author(s):  
J. ARMITAGE ROBERTSON
Keyword(s):  
Electrical Circuit ◽  
The Body ◽  
Constant Current ◽  
Forward Movement ◽  
Electrical Currents ◽  
Turning Mechanism ◽  
Electrical Polarity ◽  
Metabolic Activities ◽  
Physiological Gradients ◽  
A Current

The galvanotropic reactions of Polycelis nigra were investigated in constant and "intermittent" (that is, a current showing slight commutator ripple) electrical currents, varying in strength from one to about ten milliamperes. Galvanotropic reactions were most readily forthcoming at about 2 m.a. constant current, higher current strengths producing signs of discomfort or rigor, and intermittent current being slightly more effective in producing such disturbances than constant current. As a rule, Polycelis places itself longitudinally, with head facing the kathode, and moves thither by means of looping, its normal gliding motion being in abeyance. If facing the kathode on application of the current, it simply loops forward, but if moving parallel to the electrodes it turns its anterior end first, and then movesmore or less directly towards the kathode. If previously facing the anode, a turn in the direction of the kathode is usually accomplished only after more or less headwaving and apparent difficulty or hesitation. Decapitate animals, if facing the anode in the current, at some time or other almost invariably loop backwards to the kathode, tail foremost, for a varying number of times, before turning their anterior end to the kathode and orientating normally. This was never observed in normal animals. Decaudate animals behave like unmutilated individuals. Decapitate-and-decaudate Polycelis (middle-pieces) reactin the same manner as do decapitate specimens, i.e. show backward looping. Longitudinal halves of Polycelis are usually curved towards the injured side, and show little or no movement, either in or out of the current; it is supposed that this curvature is mechanical and the result of the injury. Higher amperages (above 2 m.a.) produce, progressively, cessation of forward movement with twisting and apparent discomfort, and, finally, flattening of the kathodic end of the body. This last reaction is often accompanied by various postures, presumably the result of arrested movement. An explanation of these reactions, in normal and unmutilated animals, is attempted, based on the supposed interaction of the experimental current with the external portion of an inherent electrical circuit. If this inherent circuit be obstructed it is suggested that the metabolic activities, with which it is apparently correlated, are to some extent upset. Further, that to avoid this derangement, and concomitant malaise, the animals orientate themselves so that the experimental current does not flow counter to the external portion of their inherent circuit; that the turning mechanism of the flanks which affects this orientation can be explained upon similar grounds; finally that backward looping can be explained as a transference of control or dominance to the tail end, due to the combined inhibitory action of mutilation and of a contrary experimental current upon the normal physiological gradients at the anterior end. A variety of points related to the theory, and some cases of galvanotropism bearing on the work, together with their theoretical explanations, are discussed.

An Investigation of the Forces on Three Dimensional Bluff Bodies in Rough Wall Turbulent Boundary Layers

1977 ◽  
Vol 99 (3) ◽  
pp. 503-509 ◽  
Author(s):  
B. E. Lee ◽  
B. F. Soliman
Keyword(s):  
Three Dimensional ◽  
The Body ◽  
Bluff Bodies ◽  
Drag Forces ◽  
Pressure Distributions ◽  
Mean Pressure ◽  
Flow Phenomena ◽  
The Mean ◽  
Building Ventilation ◽  
Group Density

A study has been made of the influence of grouping parameters on the mean pressure distributions experienced by three dimensional bluff bodies immersed in a turbulent boundary layer. The range of variable parameters has included group density, group pattern and incident flow type and direction for a simple cuboid element form. The three flow regimes associated with increasing group density are reflected in both the mean drag forces acting on the body and their associated pressure distributions. A comparison of both pressure distributions and velocity profile parameters with established work on two dimensional bodies shows close agreement in identifying these flow regime changes. It is considered that the application of these results may enhance our understanding of some common flow phenomena, including turbulent flow over rough surfaces, building ventilation studies and environmental wind around buildings.

scholarly journals Imagination der Bewegung durch Vibrationsreize – ein neuer Ansatz in der Frühmobilisation auf der Intensivstation?

2020 ◽  
Vol 26 (4) ◽  
pp. 214-218
Author(s):  
M. Lippert-Grüner ◽  
B. Bakaláø ◽  
R. Zajíèek ◽  
F. Duška
Keyword(s):  
Nervous System ◽  
Intensive Care ◽  
Pilot Study ◽  
Sensory Information ◽  
Early Mobilization ◽  
Motor Units ◽  
The Body ◽  
Entire Body ◽  
Vibration Effect ◽  
Illusory Movement

Zusammenfassung Die Optimierung der motorischen Leistung und die Einbindung und Vernetzung bisher nicht verwendeter motorischer Einheiten sowie die vermehrte Ausschüttung neurotropher Faktoren sind zentrale Mechanismen der Vibrationswirkung, die therapeutisch auf einzelne Körperteile oder den gesamten Körper angewendet werden können. Eine Möglichkeit, die Frühmobilisation bei kritisch kranken Patienten effektiver zu gestalten und immobilitätsbedingten Veränderungen vorzubeugen, könnte die Verwendung des Vibramoov™-Systems sein. Gezielt programmierte Vibrationssequenzen stimulieren hier das Nervensystem mit sensorischen Informationen, die die Empfindung einer Bewegung nachahmen (z. B. des Gehens) und somit Regenerations- und Reor-ganisationsprozesse im zentralen Nervensystem unterstützen können. Von Bedeutung ist dieser Therapieansatz vor allem bei Patienten, bei denen aufgrund ihres Zustandes konventionelle Maßnahmen nicht oder nur eingeschränkt durchgeführt werden können. Da bisher keine Erfah-rungen zur Anwendung bei intensivpflichtigen Patienten verfügbar sind, wurde eine Pilotstudie durchgeführt mit der Fragestellung, ob diese Therapieform sicher ist und im normalen Betrieb auf der Intensivstation verwendet werden kann. Die Ergebnisse der Pilotstudie mit fünf Patienten zei-gen, dass die Anwendung von Vibramoov™ zu keiner wesentlichen Veränderung kardiopulmo-naler Parameter im Sinne einer Non-Toleranz führte und im klinischen Setting gut umsetzbar war. Schlüsselwörter: Frührehabilitation, Imagination von Bewegung, Intensivstation, Vibramoov™ Imagination of movement through vibrational stimuli – a new approach to early mobilization in intensive care units? A pilot study Abstract The optimization of motor performance and the integration and networking of previously unused motor units, as well as the increased release of neurotrophic factors, are central mechanisms related to the vibration effect that can be applied therapeutically to individual parts of the body or to the entire body. One way to make early mobilization more effective in critically ill patients and to prevent changes due to immobility could be rehabilitation with functional proprioceptive stimulation, also known as “illusory movement”. Specifically programmed vibration sequences stimulate the nervous system with sensory information that mimics the sensation of movement (e. g., walking) and can thus support regeneration and reorganization processes in the central nervous system. This therapeutic approach is particularly important for patients who, due to their condition, cannot – or only to a limited extent – carry out conventional measures. Since no experience has so far been available for use in intensive care patients, we carried out a pilot study to answer the question of whether this form of therapy can be used safely and in normal operations in the intensive care unit. The results of the pilot study with 5 patients showed that the use of Vibramoov™ did not lead to any significant change in cardiopulmonary parameters in terms of non-tolerance and was easy to implement in a clinical setting. Keywords: early rehabilitation, illusory movements, ICU, functional proprio-ceptive stimulation

A versatile taxonomy of low-dimensional vortex models for unsteady aerodynamics

2018 ◽  
Vol 858 ◽  
pp. 917-948 ◽  
Author(s):  
Darwin Darakananda ◽  
Jeff D. Eldredge
Keyword(s):  
Large Scale ◽  
Bluff Body ◽  
Point Vortex ◽  
Unsteady Aerodynamics ◽  
Shear Layers ◽  
Point Vortices ◽  
The Body ◽  
Vortex Sheets ◽  
Proposed Model ◽  
Low Dimensional

Inviscid vortex models have been demonstrated to capture the essential physics of massively separated flows past aerodynamic surfaces, but they become computationally expensive as coherent vortex structures are formed and the wake is developed. In this work, we present a two-dimensional vortex model in which vortex sheets represent shear layers that separate from sharp edges of the body and point vortices represent the rolled-up cores of these shear layers and the other coherent vortices in the wake. We develop a circulation transfer procedure that enables each vortex sheet to feed its circulation into a point vortex instead of rolling up. This procedure reduces the number of computational elements required to capture the dynamics of vortex formation while eliminating the spurious force that manifests when transferring circulation between vortex elements. By tuning the rate at which the vortex sheets are siphoned into the point vortices, we can adjust the balance between the model’s dimensionality and dynamical richness, enabling it to span the entire taxonomy of inviscid vortex models. This hybrid model can capture the development and subsequent shedding of the starting vortices with insignificant wall-clock time and remain sufficiently low-dimensional to simulate long-time-horizon events such as periodic bluff-body shedding. We demonstrate the viability of the method by modelling the impulsive translation of a wing at various fixed angles of attack, pitch-up manoeuvres that linearly increase the angle of attack from $0^{\circ }$ to $90^{\circ }$, and oscillatory pitching and heaving. We show that the proposed model correctly predicts the dynamics of large-scale vortical structures in the flow by comparing the distributions of vorticity and force responses from results of the proposed model with a model using only vortex sheets and, in some cases, high-fidelity viscous simulation.

Axial Load on the Submarine Pipeline Suspended Law of Vortex Induced Vibration

2011 ◽  
Vol 94-96 ◽  
pp. 1511-1514
Author(s):  
Yi Fei Yan
Keyword(s):  
Natural Frequency ◽  
Axial Force ◽  
Scientific Basis ◽  
Oil Field ◽  
Span Length ◽  
Submarine Pipeline ◽  
Vortex Induced Vibration ◽  
Vibration Effect ◽  
Pipeline Vibration ◽  
The Impact

The study is about submarine pipeline. Considering the impact of different axial force, The reduced velocity is introduced as the pipeline vibration effect of vortex trail releasing. The vibration parameters of the span pipeline are analyzed and vibration control formula is built. The natural span length of the submarine pipeline is calculated according to the DNV-OS-F101 rule. The natural frequency of the span pipeline and the allowable span length are solved. The case study of submarine pipeline in Chengdao oil field is made and the variation law of natural frequency of span pipeline is got. The stream reduced velocity decreases as the axial force increase. The theory analysis of the vortex induced vibration can provide the scientific basis for the safety design of offshore submarine pipeline.

CFD Solution of a Two-Canopy Parachute in a Top-to-Top Formation With a Vent of Air From One of Its Canopy

2008 ◽  
Author(s):  
Mohammad J. Izadi
Keyword(s):  
Cross Sectional Area ◽  
The Body ◽  
The Other ◽  
Bluff Bodies ◽  
Variable Cross ◽  
Sectional Area ◽  
Cross Sectional ◽  
Drag Forces ◽  
Varied Form ◽  
Two Bodies

A CFD study of a 3 Dimensional flow field around two bodies (Two Canopies of a Parachutes) as two bluff bodies in an incompressible fluid (Air) is modeled here. Formations of these two bodies are top-to-top (One on the top of the other) with respect to the center of each other. One canopy with a constant cross sectional area with a vent of air at its apex, and the other with a variable cross sectional area with no vent is studied here. Vertical distances of these two bodies are varied form zero to half, equal, double and triple radius of the body with a vent on it. The flow condition is considered to be 3-D, unsteady, turbulent, and incompressible. The vertical distances between the bluff bodies, cross sectional area, and also vent ratio of bluff bodies are varied here. The drag forces with static pressures around the two bodies are calculated. From the numerical results, it can be seen that, the drag coefficient is constant on the range of zero to twenty percent of the vent ratio and it decreases for higher vent ratios for when the upper parachute is smaller than the lower one, and it increases for when the upper parachute is larger than the lower one. Both Steady and Unsteady cases gave similar results especially when the distance between the canopies is increased.

Experimental Analysis of Vortex Induced Vibration in the Bladeless Small Wind Turbine

2019 ◽  
Author(s):  
Micha Premkumar Thomai ◽  
Lasoodawanki Kharsati ◽  
Nakandhrakumar Rama Samy ◽  
Seralathan Sivamani ◽  
Hariram Venkatesan
Keyword(s):  
Energy Conversion ◽  
Wind Turbine ◽  
Natural Frequency ◽  
Cross Section ◽  
Vortex Shedding ◽  
Rectangular Cross Section ◽  
The Body ◽  
Test Facility ◽  
Vortex Induced Vibration ◽  
Small Wind Turbine

Abstract Vortex-induced vibration is one of the predominant fundamental concepts for forced oscillation which attracts considerable practical engineering application for energy conversion. In this work, an oscillation of a mast arising as a result of wind force is utilized for energy conversion. The paradigm for energy conversion from vortex-induced vibration in the mast is the bladeless wind turbine. It consists of a rigid mass known as a mast, fixed in the spring of stiffness (k) and allowed to oscillate along the direction of the flow. In this work, four different types of mast have been fabricated and tested. The first is uniform tapered hollow conical mast (MAST1), the cross-section of the second is uniform tapered plus symbol (MAST2), the third is uniform tapered inversed plus symbol (MAST3) and the fourth is uniform tapered simple rectangular cross-section (MAST4). All the masts were fabricated using fiber carbon. The experiments were conducted in a versatile small wind turbine testing facility of Hindustan Institute of Technology and Science, Chennai. This test facility contained an open jet wind tunnel with variable frequency drive and other measuring instruments. The vibration sensor was located in the mast where it experienced a large oscillation in a free stream. In this experiment, an increase in wind velocity led to a terrible change in the amplitude of vibration. A vigorous oscillation was experienced in this mast at this critical frequency, when the natural frequency of the mast was synchronized with the frequency of the vortex shedding and the frequency of the oscillation of the mast. The total force in this oscillation was a summation of the body force due to the mass of the mast and vorticity force that is mainly which was the result of the shedding of the vortices. In this work, extensive studies have been carried out for Reynolds number ranging from 2.5 × 105 to 5.0 × 105. The mast length to diameter ratio of 13 was exposed to various speeds of wind and response was measured. The occurrence of the maximum oscillation in a simple rectangular mast was seen where vortex shedding due to the bluff body was large for constant mass and spring stiffness. The frequency of the oscillation at maximum amplitude of the rectangular cross-section mast was equal to the natural frequency, due to vortices shedding at critical velocity. This demonstrated the appropriateness of the simple rectangular cross-section for harnessing the low rated wind energy and its suitability for renewable energy conversion in the small bladeless wind turbine.

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