scholarly journals Vortex-induced vibrations of a flexible cylinder at large inclination angle

2015 ◽  
Vol 373 (2033) ◽  
pp. 20140108 ◽  
Author(s):  
Rémi Bourguet ◽  
Michael S. Triantafyllou
Keyword(s):  
Inclination Angle ◽  
Normal Component ◽  
Vortex Formation ◽  
Normal Incidence ◽  
Free Vibrations ◽  
The Body ◽  
Body Motion ◽  
Flexible Cylinder ◽  
Inflow Velocity ◽  
Vortex Induced Vibrations

The free vibrations of a flexible circular cylinder inclined at 80° within a uniform current are investigated by means of direct numerical simulation, at Reynolds number 500 based on the body diameter and inflow velocity. In spite of the large inclination angle, the cylinder exhibits regular in-line and cross-flow vibrations excited by the flow through the lock-in mechanism, i.e. synchronization of body motion and vortex formation. A profound reconfiguration of the wake is observed compared with the stationary body case. The vortex-induced vibrations are found to occur under parallel, but also oblique vortex shedding where the spanwise wavenumbers of the wake and structural response coincide. The shedding angle and frequency increase with the spanwise wavenumber. The cylinder vibrations and fluid forces present a persistent spanwise asymmetry which relates to the asymmetry of the local current relative to the body axis, owing to its in-line bending. In particular, the asymmetrical trend of flow–body energy transfer results in a monotonic orientation of the structural waves. Clockwise and counter-clockwise figure eight orbits of the body alternate along the span, but the latter are found to be more favourable to structure excitation. Additional simulations at normal incidence highlight a dramatic deviation from the independence principle, which states that the system behaviour is essentially driven by the normal component of the inflow velocity.

scholarly journals The onset of vortex-induced vibrations of a flexible cylinder at large inclination angle

2016 ◽  
Vol 809 ◽  
pp. 111-134 ◽  
Author(s):  
Rémi Bourguet ◽  
Michael S. Triantafyllou
Keyword(s):  
Inclination Angle ◽  
Vortex Shedding ◽  
High Frequency ◽  
Normal Incidence ◽  
The Body ◽  
Body Motion ◽  
High Frequency Component ◽  
Flexible Cylinder ◽  
Flow Component ◽  
Lock In

The onset of the vortex-induced vibration (VIV) regime of a flexible cylinder inclined at$80^{\circ }$within a uniform current is studied by means of direct numerical simulations, at Reynolds number$500$based on the body diameter and inflow velocity magnitude. A range of values of the reduced velocity, defined as the inverse of the fundamental natural frequency, is examined in order to capture the emergence of the body responses and explore the concomitant reorganization of the flow and fluid forcing. Additional simulations at normal incidence confirm that the independence principle, which states that the system behaviour is determined by the normal inflow component, does not apply at such large inclination angle. Contrary to the normal incidence case, the free vibrations of the inclined cylinder arise far from the Strouhal frequency, i.e. the vortex shedding frequency downstream of a fixed rigid cylinder. The trace of the stationary body wake is found to persist beyond the vibration onset: the flow may still exhibit an oblique component that relates to the slanted vortex shedding pattern observed in the absence of vibration. This flow component which occurs close to the Strouhal frequency, at a high and incommensurable frequency compared to the vibration frequency, is referred to as Strouhal component; it induces a high-frequency component in fluid forcing. The vibration onset is accompanied by the appearance of novel, low-frequency components of the flow and fluid forcing which are synchronized with body motion. This second dominant flow component, referred to as lock-in component, is characterized by a parallel spatial pattern. The Strouhal and lock-in components of the flow coexist over a range of reduced velocities, with variable contributions, which results in a variety of mixed wake patterns. The transition from oblique to parallel vortex shedding that occurs during the amplification of the structural responses, is driven by the opposite trends of these two component contributions: the decrease of the Strouhal component magnitude associated with the progressive disappearance of the high-frequency force component, and simultaneously, the increase of the lock-in component magnitude, which dominates once the fully developed VIV regime is reached and the flow dynamics is entirely governed by wake–body synchronization.

scholarly journals Distributed lock-in drives broadband vortex-induced vibrations of a long flexible cylinder in shear flow

2013 ◽  
Vol 717 ◽  
pp. 361-375 ◽  
Author(s):  
Rémi Bourguet ◽  
George Em Karniadakis ◽  
Michael S. Triantafyllou
Keyword(s):  
Shear Flow ◽  
Vortex Formation ◽  
Cross Flow ◽  
Maximum Velocity ◽  
Travelling Wave ◽  
Flexible Cylinder ◽  
Inflow Velocity ◽  
Vortex Induced Vibrations ◽  
Wide Range ◽  
Lock In

AbstractA slender flexible body immersed in sheared cross-flow may exhibit vortex-induced vibrations (VIVs) involving a wide range of excited frequencies and structural wavenumbers. The mechanisms of broadband VIVs of a cylindrical tensioned beam of length-to-diameter aspect ratio 200 placed in shear flow, with an exponentially varying profile along the span, are investigated by means of direct numerical simulation. The Reynolds number is equal to 330 based on the maximum velocity, for comparison with previous work on narrowband vibrations in linear shear flow. The flow is found to excite the structure at a number of different locations under a condition of wake–body synchronization, or lock-in. Broadband responses are associated with a distributed occurrence of the lock-in condition along the span, as opposed to the localized lock-in regions limited to the high inflow velocity zone, reported for narrowband vibrations in sheared current. Despite the instantaneously multi-frequency nature of broadband responses, the lock-in phenomenon remains a locally mono-frequency event, since the vortex formation is generally synchronized with a single vibration frequency at a given location. The spanwise distribution of the excitation zones induces travelling structural waves moving in both directions; this contrasts with the narrowband case where the direction of propagation toward decreasing inflow velocity is preferred. A generalization of the mechanism of phase-locking between the in-line and cross-flow responses is proposed for broadband VIVs under the lock-in condition. A spanwise drift of the in-line/cross-flow phase difference is identified for the high-wavenumber vibration components; this drift is related to the strong travelling wave character of the corresponding structural waves.

scholarly journals Vortex-induced vibrations of a cylinder in planar shear flow

2017 ◽  
Vol 825 ◽  
pp. 353-384 ◽  
Author(s):  
Simon Gsell ◽  
Rémi Bourguet ◽  
Marianna Braza
Keyword(s):  
Steady Flow ◽  
Cross Flow ◽  
The Body ◽  
Body Motion ◽  
Inflow Velocity ◽  
Asymmetric Pattern ◽  
Planar Shear ◽  
The Cross ◽  
The Impact ◽  
Body Case

The system composed of a circular cylinder, either fixed or elastically mounted, and immersed in a current linearly sheared in the cross-flow direction, is investigated via numerical simulations. The impact of the shear and associated symmetry breaking are explored over wide ranges of values of the shear parameter (non-dimensional inflow velocity gradient, $\unicode[STIX]{x1D6FD}\in [0,0.4]$) and reduced velocity (inverse of the non-dimensional natural frequency of the oscillator, $U^{\ast }\in [2,14]$), at Reynolds number $Re=100$; $\unicode[STIX]{x1D6FD}$, $U^{\ast }$ and $Re$ are based on the inflow velocity at the centre of the body and on its diameter. In the absence of large-amplitude vibrations and in the fixed body case, three successive regimes are identified. Two unsteady flow regimes develop for $\unicode[STIX]{x1D6FD}\in [0,0.2]$ (regime L) and $\unicode[STIX]{x1D6FD}\in [0.2,0.3]$ (regime H). They differ by the relative influence of the shear, which is found to be limited in regime L. In contrast, the shear leads to a major reconfiguration of the wake (e.g. asymmetric pattern, lower vortex shedding frequency, synchronized oscillation of the saddle point) and a substantial alteration of the fluid forcing in regime H. A steady flow regime (S), characterized by a triangular wake pattern, is uncovered for $\unicode[STIX]{x1D6FD}>0.3$. Free vibrations of large amplitudes arise in a region of the parameter space that encompasses the entire range of $\unicode[STIX]{x1D6FD}$ and a range of $U^{\ast }$ that widens as $\unicode[STIX]{x1D6FD}$ increases; therefore vibrations appear beyond the limit of steady flow in the fixed body case ($\unicode[STIX]{x1D6FD}=0.3$). Three distinct regimes of the flow–structure system are encountered in this region. In all regimes, body motion and flow unsteadiness are synchronized (lock-in condition). For $\unicode[STIX]{x1D6FD}\in [0,0.2]$, in regime VL, the system behaviour remains close to that observed in uniform current. The main impact of the shear concerns the amplification of the in-line response and the transition from figure-eight to ellipsoidal orbits. For $\unicode[STIX]{x1D6FD}\in [0.2,0.4]$, the system exhibits two well-defined regimes: VH1 and VH2 in the lower and higher ranges of $U^{\ast }$, respectively. Even if the wake patterns, close to the asymmetric pattern observed in regime H, are comparable in both regimes, the properties of the vibrations and fluid forces clearly depart. The responses differ by their spectral contents, i.e. sinusoidal versus multi-harmonic, and their amplitudes are much larger in regime VH1, where the in-line responses reach $2$ diameters ($0.03$ diameters in uniform flow) and the cross-flow responses $1.3$ diameters. Aperiodic, intermittent oscillations are found to occur in the transition region between regimes VH1 and VH2; it appears that wake–body synchronization persists in this case.

Chaos in body–vortex interactions

2010 ◽  
Vol 466 (2119) ◽  
pp. 1871-1891 ◽  
Author(s):  
Johan Roenby ◽  
Hassan Aref
Keyword(s):  
Body Shape ◽  
Mass Density ◽  
Relative Equilibrium ◽  
Large Body ◽  
Point Vortex ◽  
Cylindrical Body ◽  
The Body ◽  
Body Motion ◽  
Single Vortex ◽  
Vortex Interactions

The model of body–vortex interactions, where the fluid flow is planar, ideal and unbounded, and the vortex is a point vortex, is studied. The body may have a constant circulation around it. The governing equations for the general case of a freely moving body of arbitrary shape and mass density and an arbitrary number of point vortices are presented. The case of a body and a single vortex is then investigated numerically in detail. In this paper, the body is a homogeneous, elliptical cylinder. For large body–vortex separations, the system behaves much like a vortex pair regardless of body shape. The case of a circle is integrable. As the body is made slightly elliptic, a chaotic region grows from an unstable relative equilibrium of the circle-vortex case. The case of a cylindrical body of any shape moving in fluid otherwise at rest is also integrable. A second transition to chaos arises from the limit between rocking and tumbling motion of the body known in this case. In both instances, the chaos may be detected both in the body motion and in the vortex motion. The effect of increasing body mass at a fixed body shape is to damp the chaos.

scholarly journals Self-rechargeable cardiac pacemaker system with triboelectric nanogenerators

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Hanjun Ryu ◽  
Hyun-moon Park ◽  
Moo-Kang Kim ◽  
Bosung Kim ◽  
Hyoun Seok Myoung ◽  
...  
Keyword(s):  
Medical Devices ◽  
Mechanical Energy ◽  
Cardiac Pacemaker ◽  
Operation Time ◽  
Lithium Ion ◽  
The Body ◽  
Body Motion ◽  
Triboelectric Nanogenerator ◽  
Implantable Medical Devices ◽  
Energy Harvesters

AbstractSelf-powered implantable devices have the potential to extend device operation time inside the body and reduce the necessity for high-risk repeated surgery. Without the technological innovation of in vivo energy harvesters driven by biomechanical energy, energy harvesters are insufficient and inconvenient to power titanium-packaged implantable medical devices. Here, we report on a commercial coin battery-sized high-performance inertia-driven triboelectric nanogenerator (I-TENG) based on body motion and gravity. We demonstrate that the enclosed five-stacked I-TENG converts mechanical energy into electricity at 4.9 μW/cm3 (root-mean-square output). In a preclinical test, we show that the device successfully harvests energy using real-time output voltage data monitored via Bluetooth and demonstrate the ability to charge a lithium-ion battery. Furthermore, we successfully integrate a cardiac pacemaker with the I-TENG, and confirm the ventricle pacing and sensing operation mode of the self-rechargeable cardiac pacemaker system. This proof-of-concept device may lead to the development of new self-rechargeable implantable medical devices.

A Parametric Study of Low-Frequency Damping of Mooring System

2014 ◽  
Author(s):  
Minglu Chen ◽  
Shan Huang ◽  
Nigel Baltrop ◽  
Ji Chunyan ◽  
Liangbi Li
Keyword(s):  
Low Frequency ◽  
Structure Design ◽  
The Body ◽  
Body Motion ◽  
Mooring Line ◽  
Offshore Structure ◽  
Frequency Oscillation ◽  
Low Frequency Oscillation ◽  
Line System ◽  
Irregular Wave

Mooring line damping plays an important role to the body motion of moored floating platforms. Meanwhile, it can also make contributions to optimize the mooring line system. Accurate assessment of mooring line damping is thus an essential issue for offshore structure design. However, it is difficult to determine the mooring line damping based on theoretical methods. This study considers the parameters which have impact on mooring-induced damping. In the paper, applying Morison formula to calculate the drag and initial force on the mooring line, its dynamic response is computed in the time domain. The energy dissipation of the mooring line due to the viscosity was used to calculate mooring-induced damping. A mooring line is performed with low-frequency oscillation only, the low-frequency oscillation superimposed with regular and irregular wave-frequency motions. In addition, the influences of current velocity, mooring line pretension and different water depths are taken into account.

A Semi-Autonomous Quadruped Robot for Performing Disinfection in Cluttered Environments

2021 ◽  
Author(s):  
Yiyu Chen ◽  
Abhinav Pandey ◽  
Zhiwei Deng ◽  
Anthony Nguyen ◽  
Ruiqi Wang ◽  
...  
Keyword(s):  
Vision System ◽  
Quadruped Robot ◽  
Simulation Software ◽  
The Body ◽  
Body Motion ◽  
Daily Routine ◽  
Public And Private ◽  
Cluttered Environments ◽  
Integrated Simulation ◽  
Human Labor

Abstract The global COVID-19 pandemic has inevitably made disinfection a daily routine to ensure the safety of public and private spaces. However, the existing disinfection procedures are time-consuming and require intensive human labor to apply chemical-based disinfectant onto contaminated surfaces. In this paper, a robot disinfection system is presented to increase the automation of the disinfection task to assist humans in performing routine disinfection safely and efficiently. This paper presents a semi-autonomous quadruped robot called LASER-D for performing disinfection in cluttered environments. The robot is equipped with a spray-based disinfection system and leverages the body motion to control the spray action without an extra stabilization mechanism. The spraying unit is mounted on the robot’s back and controlled by the robot computer. The control architecture is designed based on force control, resulting in navigating rough terrains and the flexibility in controlling the body motion during standing and walking for the disinfection task. The robot also uses the vision system to improve localization and maintain desired distance to the disinfection surface. The system incorporates image processing capability to evaluate disinfected regions with high accuracy. This feedback is then used to adjust the disinfection plan to guarantee that all assigned areas are disinfected properly. The system is also equipped with highly integrated simulation software to design, simulate and evaluate disinfection plans effectively. This work has allowed the robot to successfully carry out effective disinfection experiments while safely traversing through cluttered environments, climb stairs/slopes, and navigate on slippery surfaces.

The Global Motion of a Rigid Body Subject to Periodic Body-Fixed Torques

1995 ◽  
Author(s):  
X. Tong ◽  
B. Tabarrok
Keyword(s):  
Rigid Body ◽  
Equations Of Motion ◽  
Melnikov Method ◽  
The Body ◽  
Body Motion ◽  
Heteroclinic Orbits ◽  
Coordinate Frame ◽  
Global Motion ◽  
Stable And Unstable Manifolds ◽  
Body Subject

Abstract In this paper the global motion of a rigid body subject to small periodic torques, which has a fixed direction in the body-fixed coordinate frame, is investigated by means of Melnikov’s method. Deprit’s variables are introduced to transform the equations of motion into a form describing a slowly varying oscillator. Then the Melnikov method developed for the slowly varying oscillator is used to predict the transversal intersections of stable and unstable manifolds for the perturbed rigid body motion. It is shown that there exist transversal intersections of heteroclinic orbits for certain ranges of parameter values.

LIKE TRAJECTORIES OF THE BODY MOTION IN THE MEDIUM, THE RESISTANCE OF WHICH IS PROPORTIONAL TO THE SQUARE OF RELATIVE VELOCITY

2020 ◽  
pp. 77-83
Author(s):  
A.Y. Peretyatko ◽  
Keyword(s):  
Relative Velocity ◽  
The Body ◽  
Body Motion ◽  
Huge Number ◽  
History Of ◽  
Number Of Publications

For the pre-revolutionary Don historiography, complaints about the lack of a full-fledged generalizing work of the history of the Cossacks were extremely characteristic. As shown in the article, a similar situation is observed in our time: the article has again become the main genre of Cossack historiography, and the understanding of a huge number of publications on the history of various Cossack troops is extremely difficult. The author proves that in these conditions, works that claim to generalize become especially important, but it is extremely difficult to summarize all the facts, developments and research concepts on any broad topic of Cossack history. In his opinion, the search for other methods of scientific generalization and perception by historians of the developments of their colleagues looks promising. One of these ways he sees the organization of round tables on specifically Cossack topics, especially dedicated to new discoveries.

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