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 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 Vortex-induced vibrations of a long flexible cylinder in shear flow

2011 ◽  
Vol 677 ◽  
pp. 342-382 ◽  
Author(s):  
REMI BOURGUET ◽  
GEORGE E. KARNIADAKIS ◽  
MICHAEL S. TRIANTAFYLLOU
Keyword(s):  
Shear Flow ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Maximum Velocity ◽  
Travelling Wave ◽  
Transition To Turbulence ◽  
Wave Component ◽  
Flexible Cylinder ◽  
Vortex Induced Vibrations ◽  
Lock In

We investigate the in-line and cross-flow vortex-induced vibrations of a long cylindrical tensioned beam, with length to diameter ratio L/D = 200, placed within a linearly sheared oncoming flow, using three-dimensional direct numerical simulation. The study is conducted at three Reynolds numbers, from 110 to 1100 based on maximum velocity, so as to include the transition to turbulence in the wake. The selected tension and bending stiffness lead to high-wavenumber vibrations, similar to those encountered in long ocean structures. The resulting vortex-induced vibrations consist of a mixture of standing and travelling wave patterns in both the in-line and cross-flow directions; the travelling wave component is preferentially oriented from high to low velocity regions. The in-line and cross-flow vibrations have a frequency ratio approximately equal to 2. Lock-in, the phenomenon of self-excited vibrations accompanied by synchronization between the vortex shedding and cross-flow vibration frequencies, occurs in the high-velocity region, extending across 30% or more of the beam length. The occurrence of lock-in disrupts the spanwise regularity of the cellular patterns observed in the wake of stationary cylinders in shear flow. The wake exhibits an oblique vortex shedding pattern, inclined in the direction of the travelling wave component of the cylinder vibrations. Vortex splittings occur between spanwise cells of constant vortex shedding frequency. The flow excites the cylinder under the lock-in condition with a preferential in-line versus cross-flow motion phase difference corresponding to counter-clockwise, figure-eight orbits; but it damps cylinder vibrations in the non-lock-in region. Both mono-frequency and multi-frequency responses may be excited. In the case of multi-frequency response and within the lock-in region, the wake can lock in to different frequencies at various spanwise locations; however, lock-in is a locally mono-frequency event, and hence the flow supplies energy to the structure mainly at the local lock-in frequency.

scholarly journals The State of the Cardiovascular System of Qualified Table Tennis Athletes at the Stage of Competitive Activity

2021 ◽  
Vol 6 (4) ◽  
pp. 231-236
Author(s):  
Ulizko V. M. ◽  
◽  
V. R. Kryzhanivsky ◽  
T. M. Zakharkevich ◽  
I. L. Belyavsky
Keyword(s):  
Physical Activity ◽  
Heart Rate ◽  
Cardiovascular System ◽  
High Frequency ◽  
Heart Rhythm ◽  
Frequency Component ◽  
The State ◽  
Autonomic Regulation ◽  
The Body ◽  
High Frequency Component

The condition of the cardiovascular system is one of the important criteria for assessing the impact of sports training on the human body. According to the indicators characterizing the state of the cardiovascular system, it is possible to trace the changes associated with fluctuations in the level of training, as well as to identify signs of overload as early as possible. The study of adaptive reactions of the cardiovascular system in athletes under physical activity is an important indicator for sports practice. The purpose of the study was to investigate the quantitative criteria for assessing the state of the cardiovascular system and approaches to correct the functional state of qualified athletes specializing in table tennis. Materials and methods. Studies of heart rate variability, quantitative and qualitative indicators that sufficiently reflect the autonomic functions of the body were used in order to assess the state of autonomic regulation in highly qualified athletes. Systematic physical activity causes a significant restructuring of the cardiovascular system and leads to morphofunctional changes in the mechanisms of the heart. Depending on the autonomic regulation of heart rhythm, there are different ways of myocardial adaptation processes. The balance of sympathetic and parasympathetic links of autonomic rhythm regulation is reflected in the activation of the left ventricle. Results and discussion. Adaptive changes of the cardiovascular system to competitive and training loads in the competitive period in qualified athletes are characterized by a significant decrease in heart rate (from 84.75±1.74 beats / min to 74.8±0.38 beats / min). In addition, a significantly faster process of restoring heart rate was established after exercise in the group of qualified athletes, compared with athletes of the category 1 at 4 (p >0.05) and 5 (p >0.05) minutes, respectively. According to the indicators of autonomic regulation of heart rhythm, activation of the parasympathetic link prevails in athletes of the category 1 in comparison with qualified athletes activation (according to high-frequency component, p <0.05). Significantly higher rates of individual parts of the body compared to low-skilled athletes were found out: the hormonal system (the indicator responsible for the hormonal part of the body – very low-frequency component) and the nervous system (indicators of the sympathetic nervous system – low frequency component). There are significantly higher values of the magnitude of the heart rate spectrum and high-frequency component at p <0.05, which indicates a higher power of all units of the parasympathetic regulation in the category 1 in relation to masters of sports and candidates masters of sports. Conclusion. Systematic physical activity causes a significant restructuring of the cardiovascular system and leads to morphofunctional changes in the mechanisms of the heart. Depending on the autonomic regulation of heart rhythm, there are different ways of myocardial adaptation processes. The balance of sympathetic and parasympathetic links of autonomic rhythm regulation is reflected in the activation of the left ventricle. The analysis showed that the spectral characteristics of heart rate variability significantly differ between groups of athletes with different dominance that are observed only in terms of high-frequency component, which in turn led to a change in the sympathetic-vagal balance

Otolith-Canal Optimal Interaction for Estimating Body Angular Velocity and Orientation Based on Two Kalman Filters

2008 ◽  
Author(s):  
Karim A. Tahboub
Keyword(s):  
Angular Velocity ◽  
High Frequency ◽  
Kalman Filters ◽  
Estimation Error ◽  
Semicircular Canals ◽  
The Body ◽  
Body Motion ◽  
Complementary Filter ◽  
The Difference ◽  
Translational Acceleration

The human vestibular system, consisting of the otolith and semicircular canals, provides valuable information about body motion and orientation in terms of angular velocity and translational acceleration. This article discusses the dynamic characteristics of these organs and the generated signals and proposes approaches to combine these signals to infer for the body angular velocity. This is the first step towards determining the body orientation and thus the inertial acceleration. The first presented approach evolves around a complementary filter that capitalizes on the low- and high-frequency characteristics of the signals. The second approach resembles two versions of Kalman filter that allow for explicitly estimating the drift of the semicircular canal signal. The difference between the two versions is the number of states employed: the first relies on two states while the second employs innovatively four states selected to minimize the estimation error of orientation, velocity and drift.

An experimental study of pressure fluctuations on fixed and oscillating square-section cylinders

1982 ◽  
Vol 119 ◽  
pp. 297-321 ◽  
Author(s):  
P. W. Bearman ◽  
E. D. Obasaju
Keyword(s):  
Experimental Study ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Vortex Shedding ◽  
Pressure Fluctuations ◽  
The Body ◽  
Front Face ◽  
Side Face ◽  
Lock In ◽  
Fixed Cylinder

Measurements are presented of the pressure fluctuations acting on a stationary squaresection cylinder, with the front face normal to the flow, and one forced to oscillate, transverse to a flow, at amplitudes up to 25% of the length of a side. The range of reduced velocities investigated, 4–13, includes the vortex lock-in regime. At lock-in the amplification of the coefficient of fluctuating lift is found to be much less than that found for a circular cylinder. The variation of the phase angle, between lift and displacement, is also different from that measured on a circular cylinder, and vortex-induced oscillations are possible only at the high-reduced-velocity end of the lock-in range. At reduced velocities sufficiently far below lock-in the natural vortex-shedding mode is suppressed and vortices are found to form over the side faces at the body frequency. Intermittent reattachment occurs over the side faces and, for an amplitude of oscillation equal to 10% of the length of a side face, the time-mean drag coefficient can be reduced to 60% of its fixed-cylinder value.

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.

Laser-Generated Ultrasonic Technique for Inspecting Delamination in CFRP

2006 ◽  
Vol 321-323 ◽  
pp. 968-971
Author(s):  
Won Su Park ◽  
Sang Woo Choi ◽  
Joon Hyun Lee ◽  
Kyeong Cheol Seo ◽  
Joon Hyung Byun
Keyword(s):  
High Frequency ◽  
Ultrasonic Method ◽  
Piezoelectric Sensor ◽  
Frequency Component ◽  
Guided Wave ◽  
Center Frequency ◽  
High Frequency Component ◽  
Ultrasonic Technique ◽  
Non Destructive Evaluation ◽  
Non Destructive

For improving quality of a carbon fiber reinforced composite material (CFRP) by preventing defects such as delamination and void, it should be inspected in fabrication process. Novel non-contacting evaluation technique is required because the transducer should be contacted on the CFRP in conventional ultrasonic technique during the non-destructive evaluation and these conventional contact techniques can not be applied in a novel fiber placement system. For the non-destructive evaluation of delamination in CFRP, various methods for the generation and reception of laser-generated ultrasound are applied using piezoelectric transducer, air-coupled transducer, wavelet transform technique etc. The high frequency component of laser-generated guided wave received with piezoelectric sensor disappeared after propagating through delamination region. Air-coupled transducer was tried to be adopted in reception of laser-generated guided wave generated by using linear slit array in order to generate high frequency guided wave with a frequency of 1.1 MHz. Nevertheless, it was failed to receive high frequency guided wave in using air-coupled transducer and linear slit array. Transmitted laser-generated ultrasonic wave was received on back-wall and its frequency was analyzed to establish inspecting technique to detect delamination by non-contact ultrasonic method. In a frequency spectrum analysis, intensity ratio of low frequency and center frequency was approvable parameter to detect delamination.

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.

High Frequency Vibration Analysis of Automotive Body Panels with Damping Materials

2010 ◽  
Vol 36 ◽  
pp. 293-296
Author(s):  
Yoshio Kurosawa ◽  
Takao Yamaguchi
Keyword(s):  
High Frequency ◽  
Large Scale ◽  
The Body ◽  
Viscoelastic Damping ◽  
Fe Model ◽  
Test Results ◽  
Automotive Body ◽  
Modal Damping ◽  
Practical Tool ◽  
Damping Materials

We have developed a technique for estimating vibrations of an automotive body structures with viscoelastic damping materials using large-scale finite element (FE) model, which will enable us to grasp and to reduce high-frequency road noise（200～500Hz）. In the new technique, first order solutions for modal loss factors are derived applying asymptotic method. This method saves calculation time to estimate modal damping as a practical tool in the design stages of the body structures. Frequency responses were calculated using this technique and the results almost agreed with the test results. This technique can show the effect of the viscoelastic damping materials on the automotive body panels, and it enables the more efficient layout of the viscoelastic damping materials. Further, we clarified damping properties of the automotive body structures under coupled vibration between frames and panels with the viscoelastic damping materials.

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