Maximum Oscillation Amplitude Research Articles

Oscillating flames in open tubes

When a flame passes along a tube that is open at both ends a self induced fluctuating pressure/flow field is created which the flame has to traverse. Here fuel rich (1.1<ϕ<1.4) propane-air flames have been filmed travelling along a 20mm internal diameter quartz tube. Fluctuations in the flame’s progression were observed to increase as the flame propagated, achieving a maximum oscillation amplitude of ±10mm at 220Hz that decayed as the flame progressed further towards the end of the tube. The impact of the periodic pressure gradients on the flame shape could be discerned with tongues of unburned reactants pushed into the products as well as the corresponding rapid acceleration of the flame into the unburned mixture. The impact of the fluctuations on flame chemistry was monitored by capturing the CH∗ and C2 chemiluminescence using a high speed colour camera. The CH∗/C2∗ ratio was observed to decrease as the flame was pulled back towards the burned mixture; and increased when the flame was pushed forwards. This was consistent throughout the flame progress even when small oscillations in the flame position were measured. This could be a significant feature of flames in this environment.

The influence of taper ratio on vortex-induced vibration of tapered cylinders in the crossflow direction

A series of experiments were conducted to study vortex-induced vibration of tapered cylinders free to oscillate in the crossflow direction. These experiments were performed in a re-circulating water tunnel with an open-surface test section for a Reynolds number range of Re=370–2300. Three linearly tapered cylinders with taper ratios of 29:1, 17:1 and 10:1 and a cylinder with a nonlinear taper were studied. For all tests, the mass ratio was kept constant. The maximum amplitude of the crossflow oscillations stayed almost constant for all taper ratios, at a value close to the maximum amplitude of a uniform cylinder with the same mass ratio. As the taper ratio was decreased, the lock-in range started at larger reduced velocities and sustained through higher reduced velocities. Tests were conducted for cylinders placed vertically in the test-section of the water tunnel, both with their diameter increasing downward and upward to show that the results were independent from the cylinder׳s orientation. Hybrid shedding modes (both 2S and 2P shedding over the cylinder׳s length) were observed for all the linearly tapered cases for reduced velocities up to the value corresponding to the peak amplitude of oscillations. For higher reduced velocities, only 2P shedding was observed along the length.

Wave hydro massagers

Wave hydro massagers, differing from similar devices by vacuum pressing action on the human skin, are developed and experimentally examined. The vacuum level created in different operational conditions is 1–9 kPa. The maximum oscillation amplitude is observed in the frequency range 88–504 Hz depending on the circulation of the water supply and pressure at the inlet to the hydro massager being 0.2–0.6 MPa higher than atmosphere pressure. The area of application of these devices is therapeutic massage given both in clinical and home conditions.

Periodic variations of the Hα profile width in the chromosphere of coronal holes as a possible indicator of Alfvén waves

We analyze the oscillations of the Hα profile width based on our observations of the chromosphere at the base of solar coronal holes. The maximum oscillation amplitude averaged over ten time series is 64 m 0 A. Direct calculations show that this value cannot be reached through temperature oscillations, because the periodic intensity fluctuations observed during our experiment did not exceed 5%, corresponding to Hα profile broadening only by 1.5–2 m A. We hypothesize that the observed variations can result from the propagation of torsional Alfven waves in the chromosphere of coronal holes.

Design and transient behavior of magnetic gears

The torque density is a key factor for magnetic gears. To obtain maximum torque density, the design principle of magnetic gears is proposed and the maximum transmitting torque is investigated under different combinations of the inner and outer permanent magnets (PM) rotor pole pairs. The research proves that the maximum transmitting torque and the minimum torque ripple can be obtained only when the ratio of the outer and inner PM pole pair numbers is fractional. Then, the optimal selection of the span ratio and thickness of magnetic blocks in the stationary modulating ring is investigated to obtain the maximum torque. Meanwhile, analyses of the losses of various parts in the magnetic gear show that the loss of the PMs is about 70% of the total losses. Therefore, the method of dividing the PM into several pieces along the circumferential direction is employed to reduce the PM loss, which makes the PM loss reduced by 73%. Additionally, the transient behavior of the magnetic gear is analyzed, indicating that the lower torsional stiffness is the main reason for oscillations during transient changes in speed and load. To suppress oscillations due to transients, damper windings are employed and the transient time and the maximum oscillation amplitude are reduced by 25% and 20%, respectively.

Oscillatory processes in lymph microcirculation in the human skin

This study was the first to use laser Doppler flowmetry followed by wavelet analysis in order to estimate oscillations in lymph microcirculation in 30 subjects with (n = 13) or without (n = 17) edema of the distal part of the upper limb. Lymph flow in the human skin exhibited clear dominance of pacemaker phase oscillations in the frequency ranges of 0.021–0.042 and 0.016–0.035 Hz in the skin of the palm surface of the finger nail bone and in the skin of the forearm, respectively. Edema was associated with an increase in the peak frequencies and normalized maximum amplitudes (Al/Ml, where Al is the mean value of the maximum amplitude of phase oscillations, and Ml is the value of the averaged lymph flow expressed in perfusion units). Low-amplitude oscillations were recorded rarer in the myogenic, endothelial, and respiratory ranges. We did not find any cardiac pulse rhythm in the wavelet spectrum of the lymph flow. We did not find any interaction between the Al/Ml value and the skin temperature. In the group of subjects without edema, under physiological conditions only, we found a negative correlation between the Al/Ml value and the amplitudes of myogenous proper blood flow oscillations, which reflected the number of functional capillaries and activity of oxidative metabolism in the tissue. In the group with edema, we did not find any correlations between the indices of lymph flow and blood flow. The values of normalized amplitude and frequency of phase oscillations may be used as efficient diagnostic tools in the studies on lymph microcirculation.

The motion of the thread with a variable length

This paper is devoted to the peculiarities of a process of inertial tether system deployment of the great length (tens of kilometers). And one of the main practical issues of this article is the behavior of maximum oscillation amplitude.First of all the exact analytical solution of the original problem is received. Furthermore it is shown that ratio of transverse wave velocity of the tether to the velocity of deployment is one of the main parameters of the problem. In limiting case, when initial tether length equals zero, the solution is received using another method – the method of progressing waves. Also it is demonstrated that the limiting case agrees with the previously received results.Analysis of the solution has revealed that the maximum oscillation amplitude of the tether almost always rises with the time. This effect corresponds to asymptotic instability of the solution (in this article instability is regarded as rising of oscillation amplitude with the time). Only in specific degenerate conditions the solution is stable. The received results of amplitude increase have to be considered in simulation of the tether system behavior as far as small perturbative vibrations at the reel system always take place.

Vortex-induced vibrations of a flexibly-mounted inclined cylinder

The majority of studies on vortex-induced vibrations of a flexibly-mounted rigid cylinder are for the cases where the flow direction is perpendicular to the long axis of the structure. However, in many engineering applications, such as cable stays in bridges and mooring lines of floating offshore wind turbines, the flow direction may not be perpendicular to the structure. To understand the vortex shedding behind a fixed inclined cylinder, the Independence Principle (IP) has been used. The IP assumes that an inclined cylinder behaves similarly to a normal-incidence case, if only the component of the free stream velocity normal to the cylinder axis is considered. The IP neglects the effect of the axial component of the flow, which seems reasonable for small angles of inclination, but not for large angles. In the present study, a series of experiments have been conducted on a flexibly-mounted rigid cylinder placed inclined to the oncoming flow with various angles of inclination (0°<θ<75°) in a range of Reynolds numbers from 500 to 4000 to investigate how the angle of inclination affects VIV. A rigid cylinder was mounted on springs, and air bearings were used to reduce the structural damping of the system. The system was placed in the test-section of a recirculating water tunnel and the crossflow displacements were measured at each flow velocity. Even at high angles of inclination, large-amplitude oscillations were observed. As the angle of inclination was increased, the lock-in range (the range of reduced flow velocities for which the cylinder oscillates with a large amplitude) started at a higher reduced velocity. When only the normal component of the oncoming flow was considered, the onset of lock-in was observed to be at the same normalized flow velocity for all angles of inclination except for 75°. However, the width of the lock-in region, its pattern, the maximum amplitude of oscillations and its corresponding normalized reduced velocity were not following the results of a normal-incidence case entirely. Flow visualizations showed a vortex shedding parallel to the cylinder′s axis for all the angles of inclination considered. The influence of a slight change in the added mass as well as the direction of the inclined cylinder on the response was studied as well.

Evolutionary comparisons reveal a positional switch for spindle pole oscillations in Caenorhabditis embryos

During the first embryonic division in Caenorhabditis elegans, the mitotic spindle is pulled toward the posterior pole of the cell and undergoes vigorous transverse oscillations. We identified variations in spindle trajectories by analyzing the outwardly similar one-cell stage embryo of its close relative Caenorhabditis briggsae. Compared with C. elegans, C. briggsae embryos exhibit an anterior shifting of nuclei in prophase and reduced anaphase spindle oscillations. By combining physical perturbations and mutant analysis in both species, we show that differences can be explained by interspecies changes in the regulation of the cortical Gα-GPR-LIN-5 complex. However, we found that in both species (1) a conserved positional switch controls the onset of spindle oscillations, (2) GPR posterior localization may set this positional switch, and (3) the maximum amplitude of spindle oscillations is determined by the time spent in the oscillating phase. By investigating microevolution of a subcellular process, we identify new mechanisms that are instrumental to decipher spindle positioning.

Self-sustained oscillations of a torsional SQUID resonator induced by Lorentz-force back-action

For the study of nanomechanical resonators, ultra-sensitive measurement techniques are crucial. However, if the measurement sensitivity approaches quantum-mechanical limits, the back-action of the detector on the resonator cannot be neglected. If the back-action is strong enough, the corresponding instability can create self-sustained oscillators in the resonator. Here we demonstrate that a torsional mechanical resonator, which contains a direct current SQUID displacement detector, leads to this effect. We find that the Lorentz-force back-action can be so large that, in combination with complex nonlinear Josephson dynamics, it generates intrinsic self-sustained oscillations. The flux quantization limit of the maximum oscillation amplitude is exploited to calibrate the displacement resolution, which is shown to be below the standard quantum limit. The suspended torsional SQUID provides an interesting platform to study on-chip laser-like physics in an electromechanical system that can be controlled by both a flux and current bias.

Free vibrations of a cylinder: 3-D computations at Re=1000

Vortex-induced vibrations of a circular cylinder of low non-dimensional mass (m⁎=10.0) are investigated at Re=1000. A stabilized space–time finite element formulation is utilized to solve the incompressible flow equations in primitive variables in three dimensions. Computations are carried out for reduced velocities in the range 4.2≤U⁎≤6.2 for, both, increasing and, decreasing U⁎. Three branches are identified for the cylinder response: initial, upper and lower. The cylinder response and force coefficients exhibit beats in the initial branch. The initial–upper branch transition is hysteretic. The maximum amplitude of transverse oscillations is 0.7D. This value is larger than that observed in the laminar regime and smaller than that reported earlier for large Re. Intermittency is observed in the transition between upper and lower branches. During the transition, the fraction of time spent by the cylinder in lower branch increases with U⁎. Soft-lock-in is observed on the upper branch. Although the frequency of vortex shedding and the cylinder vibration match, they are different than the natural frequency of the spring-mass system. The mode of vortex shedding is 2S on the initial branch while it is 2P along the lower branch. Perhaps, for the first time, 2S mode of vortex shedding is found along the upper branch. This is confirmed via investigation of phase difference between the lift and cylinder response.

GPS Near-Real-Time Coseismic Displacements for the Great Tohoku-oki Earthquake

Here, we present the application to the great Tohoku-oki (Japan) earthquake (United States Geological Survey M = 9.0, March 11, 2011, 05:46:24 Coordinated Universal Time) of a novel approach, named Variometric Approach for Displacements Analysis Stand-Alone Engine, able to estimate accurate coseismic displacements and waveforms in real time, in the global reference frame, just using the standard broadcast products (orbits and clocks) and the high-rate (1 Hz or more) carrier phase observations continuously collected by a stand-alone global-positioning-system receiver. We processed separately the data collected at MIZU (Mizusawa, 140 km from the epicenter) and USUD (Usuda, 430 km from the epicenter) International Global Navigation Satellite System Service sites. A total horizontal displacement of about 2.4 m east-southeast was estimated for the MIZU, with a maximum horizontal oscillation amplitude of about 3.4 m along the same direction. Generally, an overall accuracy better than 10 cm for all the components (east, north, and up) and an average accuracy around 5 cm were assessed over an interval shorter than 5 min, with respect to independent solutions obtained with two different scientific software. The threshold of 5-cm accuracy has been recently indicated as sufficient for real-time fault determination for near-field tsunami forecasting for a major earthquake, like the 2011 Tohoku-oki one.

Modified higher-order wake oscillator model for vortex-induced vibration of circular cylinders

In the present study, a modified model is introduced to estimate the structural oscillation amplitude of a circular cylinder during lock-in in the vortex-induced vibration phenomenon. The modified model includes the same van der Pol term as in the classic model, while its coefficients are assumed to be variable. This modified model is utilized to bring about compliance between theoretical solution and experimental results. Then, a fifth-order aerodynamic term is added, and the coefficients are modified and optimized using a new straightforward solution method. Here, the displacement, velocity and acceleration coupling terms are used to solve the system of equations. The response of the coupled equations is assumed to be harmonic. A linear approach is adopted to simplify and derive the solutions algebraically. The results are plotted during lock-in for amplitude as a function of reduced velocity and for maximum structural oscillation amplitude versus Skop–Griffin parameter. Finally, these results are compared with those of the classic wake oscillator model. The present modified model evinces an exact compliance with experimental measurements regarding structural oscillation amplitude, lock-in range, some hysteresis and mass damping ratio attributes, and reduces sensitivity to the type of coupling term through adding the fifth-order damping term.

Spreading of periodic diseases and synchronization phenomena on networks

In this paper, we investigate numerically the Susceptible–Infected–Recovered–Susceptible (SIRS) epidemic model on an exponential network generated by a preferential attachment procedure. The discrete SIRS model considers two main parameters: the duration τ0 of the complete infection–recovery cycle and the duration τI of infection. A permanent source of infection I0 has also been introduced in order to avoid the vanishing of the disease in the SIRS model. The fraction of infected agents is found to oscillate with a period T≥τ0. Simulations reveal that the average fraction of infected agents depends on I0 and τI/τ0. A maximum of synchronization of infected agents, i.e. a maximum amplitude of periodic spreading oscillations, is found to occur when the ratio τI/τ0 is slightly smaller than 1/2. The model is in agreement with the general observation that an outbreak corresponds to high τI/τ0 values.

Built in dampers for stayed cables in bridges via SMA. The SMARTeR-ESF project: A mesoscopic and macroscopic experimental analysis with numerical simulations

Shape Memory Alloys (SMAs) are good candidates for solid-state dampers appropriate for the oscillations of bridge stay cables because of their large recoverable strain, hysteresis and reasonable fatigue-life. This work experimentally analyzes the relevant properties of NiTi SMA and conducts facility measurements, frequency analyzes and simulations of the effects of SMA on stay cables. Appropriate phenomenological SMA models were developed and included in a Finite Element (FE) simulation environment. A complete damping solution for bridge stay cables was developed from these experimental analyzes. This paper detail the required properties for a NiTi SMA and analyzes their performance. For instance, the fatigue-life and several of the thermo-mechanical effects influencing the application of NiTi SMAs are outlined. The damping effect of the SMA was studied in two facilities. The first series of measurements was performed using cable 1 of the ELSA facility (JRC-EU, Ispra, Italy). The second was completed in two campaigns at IFSTTAR (Bouguenais, near Nantes in France). The numeric analyzes and simulated results were completely coherent with these experiments: the SMA dampers also drastically reduce the maximum oscillation amplitude induced by the simulated action. The frequency evolution of the damped cable was studied using direct calculations on the signals, the windowed Fourier transform and Morlet wavelets.

Gravity modulation study on opposed flame spread over thin solid fuels

In this work a numerical investigation has been carried out to study the effect of g-jitter on zero-gravity (0ge) opposed flow spreading flame over thin solid fuels. For comparison simulations have also been carried out for normal gravity (1ge) downward spreading flames. G-jitter is emulated by gravity modulation of sinusoidal (Agesin(2πt/Tge)) gravity perturbation (g-perturbation) of a particular time-period (Tge) and amplitude (Age) over a selected base gravity level (0ge or 1ge). The response of flames at 0ge base gravity and at 1ge base gravity was different to the imposed g-perturbation. While at 0ge the mean and the amplitude of the oscillatory flame spread rate (FSR) magnified with increase in the time period of g-perturbation, interestingly for the 1ge flame a maximum mean FSR and oscillation amplitude occurs at certain perturbation time period. Further, at very small perturbation time-periods (Tge) the FSR at 1ge was lower than the steady state FSR. The amplitude of oscillatory FSR increased with increase in perturbation amplitude (Age). However, the 0ge flame which is little affected (compared to 1ge flame) at small perturbation amplitude (Age) is affected severely at large perturbation amplitude (Age). Both the gas phase and fuel pyrolysis (or fuel response) follow perturbation signal with a lag but fuel pyrolysis is more sluggish and lags behind gas phase. The phase lag between fuel pyrolysis and gas increases at smaller time-periods (Tge) and tends to enhance the effect of external perturbation whereas at larger time-periods (Tge) this lag inhibits the effect of external perturbation.

Suppression of vortex-induced vibration using moving surface boundary-layer control

Experimental results of flow around a circular cylinder with moving surface boundary-layer control (MSBC) are presented. Two small rotating cylinders strategically located inject momentum in the boundary layer of the cylinder, which delays the separation of the boundary layer. As a consequence, the wake becomes narrower and the fluctuating transverse velocity is reduced, resulting in a recirculation free region that prevents the vortex formation. The control parameter is the ratio between the tangential velocity of the moving surface and the flow velocity (Uc/U). The main advantage of the MSBC is the possibility of combining the suppression of vortex-induced vibration (VIV) and drag reduction. The experimental tests are preformed at a circulating water channel facility and the circular cylinders are mounted on a low-damping air bearing base with one degree-of-freedom in the transverse direction of the channel flow. The mass ratio is 1.8. The Reynolds number ranges from 1600 to 7500, the reduced velocity varies up to 17, and the control parameter interval is Uc/U=5–10. A significant decreasing in the maximum amplitude of oscillation for the cylinder with MSBC is observed. Drag measurements are obtained for statically mounted cylinders with and without MSBC. The use of the flow control results in a mean drag reduction at Uc/U=5 of almost 60% compared to the plain cylinder. PIV velocity fields of the wake of static cylinders are measured at Re=3000. The results show that the wake is highly organized and narrower compared to the one observed in cylinders without control. The calculation of the total variance of the fluctuating transverse velocity in the wake region allows the introduction of an active closed-loop control. The experimental results are in good agreement with the numerical simulation studies conducted by other researchers for cylinders with MSBC.

New Look to the Constant Radial Acceleration Problem

is revisited. Some closed-form analytical solutions for this problem exist: in particular, those regarding the acceleration level required for obtaining an escape condition and the value of the maximum amplitude of the radial oscillation when an escape does not occur. Other results are known to exist in terms of elliptic integrals; however, their practical use for mission design is difficult due to the lack of physical insight connected to these mathematical functions. This paper provides new theoretical results for the motion description and new accurate approximations forboththespacecrafttrajectoryandthetimeof flightusingsimpleandclosed-formrelationships.Thisispossibleby introducingasuitable regularizationofthemotion,forwhichthesolution isperiodicwithrespecttotheindependent angular variable, and therefore can be exactly expressed in terms of a Fourier series. The new results are conveniently applied to a spacecraft repositioning problem and to a sample-return mission. Nomenclature a = osculating orbit’s semimajor axis, distance unit b = dimensionless fitting coefficient c = dimensionless Fourier coefficient e = osculating orbit eccentricity h = osculating orbit’s angular momentum, � distance unit� 2 =time unit k = modulus of � N = number of complete radial oscillations n = parameter of � r = radial distance, distance unit

A numerical simulation of VIV on a flexible circular cylinder

In this paper, numerical simulations of a flexible circular cylinder subjected to a vortex-induced vibration (VIV) are conducted. The Reynolds number for simulations is fixed at 1000. The finite volume method is applied for modeling fluid flow with the moving meshes feature. The dynamic response of a flexible cylinder fixed at both ends is modeled by the Euler–Bernoulli beam theory. The comparison between two-dimensional (2D) simulations and 3D simulations for the flexible cylinder shows that the maximum response amplitude of the cross-flow oscillation is about 0.57D for 2D rigid cylinders (modeled by a spring–damper–mass model) and 1.03D for flexible cylinders, respectively. The results from 3D simulations are closer to previous experimental results. Furthermore, the results obtained with various frequency ratios show that different wake patterns exist according to the frequency ratio, such as 2S mode, 2P mode and some more complicated modes. The wake pattern is different at various sections along the cylinder length, due to the fact that the two ends of the beam are fixed. The vibration of the flexible cylinder can also greatly alter the three dimensionality in the wake, which is our research in future work, especially in the transition region for Reynolds number ranging from 170 to 300.

Kink Waves and Their Evolution of the RLW‐Burgers Equation

This paper considers the bounded travelling waves of the RLW‐Burgers equation. We prove that there only exist two types of bounded travelling waves, the monotone kink waves and the oscillatory kink waves. For the oscillatory kink wave, the regularity of its maximum oscillation amplitude changing with parameters is discussed. Exact expressions of the monotone kink waves and approximate expressions of the oscillatory ones are obtained in some special cases. Furthermore, all bounded travelling waves of the RLW‐Burgers equation under different parameter conditions are identified and the evolution of them is discussed to explain the corresponding physical phenomena.