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The building-damper system designed by a seismic code is usually considered to be able to withstand the attack of strong earthquakes. However, near-fault earthquakes, especially those with the forward-directivity effect, might cause early and unexpected failure of code-designed dampers and consequent severe structural damage. In this paper, by taking into account near-fault earthquakes, seismic performance of the building-damper system and damper failure’s influence are evaluated systematically. A 9-storey steel building is designed by the Chinese seismic code as the benchmark model, and five typical dampers, including buckling-restrained brace damper (BRB), friction damper (FD), self-centering damper (SCD), viscous damper (VD), and viscoelastic damper (VED), are adopted. It was found that the building-damper systems show a large response and possible damper failure under the near-fault earthquake excitations. Then, the influence of damper failure is investigated, which reveals that damper failure would significantly affect seismic performance of the building-damper system, especially for the building-SCD system. Subsequently, by introducing the artificial near-fault earthquake excitation, the influences of different pulse parameters, such as pulse velocity amplitude, pulse period, and the number of significant pulses, are studied. It shows that the pulse velocity amplitude and pulse period obviously affect the seismic performance, while the number of significant pulses presents little influence.

This study measures the acoustic power loss that occurs when an acoustic wave passes through a tube with an abrupt change in area. It is determined that the power loss is proportional to the third power of the velocity amplitude, and that the proportionality coefficient depends upon the area change ratio of the tube. On the other hand, the proportionality coefficient is almost independent of the acoustic impedance and frequency in the 80-250 Hz range. Furthermore, the effect of a tapered tube in reducing the coefficient is experimentally investigated. Based on these experimental results, an empirical estimation method for the acoustic power loss is proposed and validated using a high-pressure-helium-filled tube.

Velocity and amplitude are two basic characteristics of any autowave, and their relationship reflects the internal regulation of the autowave system. This study proposes an approach to approximately estimate steady velocity–amplitude (VA) relation without deriving separate formulas for V and A. The approach presumes constructing an ansatz which represents the “petal” form of phase trajectory and contains V, A, and a free parameter (parameters). After substituting this ansatz, integration of model equations leads to a VA relation analytically. A free parameter (parameters) can be determined by comparing the analytical VA relation to the numerical data. As an example, we used the simplest autowave model possessing threshold, that is, the Gray–Scott model (cubic autocatalysis with linear inhibition) in isolated conditions with an immobilized precursor and a diffusible reactant. For all values of the inhibition rate constant allowing autowave solution (i.e., except approaching zero), the free parameter of ansatz belongs to a narrow interval has little effect on VA relation and can be regarded as fixed. Assumption of precursor immobilization does not influence the results qualitatively. This approach will be useful in investigations of more complex active media systems in biochemistry, combustion, and disease control.

Common features of the flow behavior over mountains within the hydraulic jump model are identified based on an analysis of 36 episodes of severe winds in the regions of Novorossiysk, Pevek, and Novaya Zemlya. In all these episodes, the incoming flow is characterized by a strong inversion layer at altitudes of 0.5–1.5 km and, in the case of bora, by a critical level in the wind profile in the middle troposphere, which creates conditions for a weakened dynamic interaction between the low-level air flowing over mountains and the upper layers of the atmosphere. The wind-speed increase on the lee slope is caused by the transition of the incoming flow from the subcritical to supercritical state. In this case, the velocity amplitude increases with increasing inversion intensity. Model estimates of wind-speed increase are in good agreement with observations at lee-side weather stations for episodes with a strong elevated inversion.

Microsaccades occur during gaze fixation to correct for miniscule foveal motor errors. The mechanisms governing such fine oculomotor control are still not fully understood. In this study, we explored microsaccade control by analyzing the impacts of transient visual stimuli on these movements’ kinematics. We found that such kinematics can be altered in systematic ways depending on the timing and spatial geometry of visual transients relative to the movement goals. In two male rhesus macaques, we presented peripheral or foveal visual transients during an otherwise stable period of fixation. Such transients resulted in well-known reductions in microsaccade frequency, and our goal was to investigate whether microsaccade kinematics would additionally be altered. We found that both microsaccade timing and amplitude were modulated by the visual transients, and in predictable manners by these transients’ timing and geometry. Interestingly, modulations in the peak velocity of the same movements were not proportional to the observed amplitude modulations, suggesting a violation of the well-known “main sequence” relationship between microsaccade amplitude and peak velocity. We hypothesize that visual stimulation during movement preparation affects not only the saccadic “Go” system driving eye movements but also a “Pause” system inhibiting them. If the Pause system happens to be already turned off despite the new visual input, movement kinematics can be altered by the readout of additional visually evoked spikes in the Go system coding for the flash location. Our results demonstrate precise control over individual microscopic saccades and provide testable hypotheses for mechanisms of saccade control in general. NEW & NOTEWORTHY Microsaccadic eye movements play an important role in several aspects of visual perception and cognition. However, the mechanisms for microsaccade control are still not fully understood. We found that microsaccade kinematics can be altered in a systematic manner by visual transients, revealing a previously unappreciated and exquisite level of control by the oculomotor system of even the smallest saccades. Our results suggest precise temporal interaction between visual, motor, and inhibitory signals in microsaccade control.

We present results of theoretical modeling of macroscopic circulating flow induced in a drop of ferrofluid by oscillating running magnetic field. The drop is placed in a narrow flat channel filled by a nonmagnetic liquid. The aim of this work is development of a scientific basis for a progressive method of address drug delivery to thrombus clots in blood vessels with the help of the magnetically induced circulation flow. Our results show that the oscillating running field allows inducing the carrier fluid flow with velocity amplitude 1–10 cm/s. This is the range of values, presenting interest from the point of view of the drug delivery. © 2020, EDP Sciences, Springer-Verlag GmbH Germany, part of Springer Nature.

The effect of vertically imposed, low frequency oscillations on the rheology of shear-thinning non- Newtonian fluids are studied numerically by computational fluid dynamics (CFD). Both Newtonian (water) and inelastic time-independent fluids of power-law (Poly-Anionic Cellulose (PAC)) are used as test fluids. Unsteady state simulations were performed using ANSYS Fluent version 18.0 for a vertical 2-D pipe geometry (ID = 50 mm and H = 850 mm) and sinusoidal, vertical oscillations to the liquid body itself were imposed with a user-defined function (UDF). The multiphase volume of fluid (VOF) method with realizable k-å method was used to impose the turbulence nature of the flow for the cases with water while the cases with non-Newtonian fluids were simulated under the laminar condition. Oscillations of different low frequency values (0.25–5 Hz) and different velocity amplitudes (0.1–0.3 m/s) were tested numerically. The dynamic variation of velocity and shear rate within the oscillated, bulk liquid medium is demonstrated. The flow inside the vertical pipe acts plug like at higher frequencies for both Newtonian and non-Newtonian fluids. The air–liquid interface becomes unstable with small disruptive peaks for the cases with water at higher velocity amplitudes while that is very calm for the laminar cases with non-Newtonian fluids. The achieved velocity gradients and the resultant shear rate variation are low with the increased PAC concentration due to the viscous resistance. However, the instantaneous velocity profiles display a progressively more complex structure with increased frequency and velocity amplitude, revealing the presence of alternating upward/downward motion. These alternating velocity profiles confirm the varying shear field present within a drilling pipe at different frequencies and velocity amplitudes while the variation of the shear field is more dependent on the velocity amplitude.

A finite Stokes layer with a large half-width over three-dimensional wall roughness is numerically simulated by solving the perturbation equations. Simulations are conducted for different parameters that affect the shape of the wall roughness, e.g., streamwise wave number, spanwise wave number and the amplitude of the roughness. The calculations are performed at a Reynolds number of R δ = 600 , which represents the transitional Reynolds number observed in experimental cases. The onset of the transition is shown to be highly correlated with the amplitude of pre-existing two-dimensional waves. It is found that the critical amplitude of the two-dimensional wave is approximately 1% of the velocity amplitude of the external flows. Moreover, the results indicate that the appearance of the transition is also affected by the fundamental wave numbers.

The interactive influences of oscillation frequency and velocity amplitude ratio on onset of transition in pulsatile pipe flow are investigated experimentally in the ranges of time-averaged and oscillating Reynolds numbers of 1019 ± 35 ⩽ Re ta ⩽ 4817 ± 164 and 107 ± 4 ⩽ Re os ⩽ 4261 ± 145 with velocity amplitude ratio of 0.05 ± 0.0017 ⩽ A 1 ⩽ 0.96 ± 0.03 for 227 runs. Oscillation frequency is in the range of 0.1 Hz ⩽ f ⩽ 14 Hz corresponding to Womersley number range of 2.72 ⩽ ω ′ ⩽ 32.21 covering quasi-steady, intermediate and beginning of inertia dominant regimes of pulsatile laminar flow. The onset of transition in laminar pulsatile pipe flow can be retarded up to Re ta , crit = 4817 at ω ′ = 3.85 in the covered experimental range. No more effect of A 1 on Re ta , crit is seen for ω ′ > 8.61 although there is a considerable effect of A 1 on Re os , crit . The effect of ω ′ on Re ta , crit and Re os , crit is not observed for A 1 ω ′ and A 1 are also investigated on Re ta , crit as functions of Re ta , crit = Re ta , crit ( A 1 ω ′ ) and Re ta , crit = Re ta , crit ( ω ′ / A 1 ). The interactive influences of ω ′ and A 1 are not seen on Re ta , crit for ω ′ > 8.61. This shows that the time-periodicity ( ω ′ , A 1 ) does not affect significantly the onset of transition at the beginning of inertia dominant region of pulsatile laminar flow ( ω ′ > 8.61) when compared with their interactive effects in the quasi-steady and intermediate regions ( ω ′ ⩽ 8.61). For flow classification of pulsatile flow at the onset of transition, a new non-dimensional interactive oscillation number, I os = ω ′ / A 1 is proposed. According to this non-dimensional number, the pulsatile flow at the onset of transition can be subclassified such as quasi-steady for I os I os ⩽ 30 and inertia dominant regions of pulsatile pipe flows for I os > 30 considering the effects of both ω ′ and A 1 on contrary to the classifications available in the literature.

In this study, differences of signal characteristics between mine shocks and coal and gas outbursts in coal mines were examined with the micro-seismic monitoring technique and time–frequency analysis. The duration of the mine shock is short while the coal and gas outburst lasts longer. The outburst consists of three stages: the pre-shock, secondary shock and main shock stage, respectively. The velocity amplitude of the mine shock is between 10−5 and 10−3 m/s, which is higher than that of the outburst with the same energy level. In addition, in both cases, the correlation between the velocity amplitude and energy is positive while the correlation between the signal frequency band distribution and energy is negative. The signal frequency band of the high energy mine shock is distributed between 0 and 50 Hz, and the low energy mine shock is between 50 and 100 Hz. The fractal characteristics of mine shocks were studied based on a fractal theory. The box dimensions of high energy mine shocks are lower than the low energy ones, however, the box dimensions of outbursts are higher than that of mine shocks with the same energy level. The higher box dimensions indicate more dangerous dynamic events. Keywords: Mine shock, Coal and gas outburst, Micro-seismic signal, Spectrum characteristics, Fractal characteristics

Wind-velocity data obtained from in situ measurements at the Golitsyno-4 marine stationary platform have been compared with QuikSCAT scatterometer data; NCEP, MERRA, and ERA-Interim global reanalyses and MM5 regional atmospheric reanalysis. In order to adjust wind velocity measured at a height of 37 m above the sea surface to a standard height of 10 m with stratification taken into account, the Monin–Obukhov theory and regional atmospheric reanalysis data are used. Data obtained with the QuikSCAT scatterometer most adequately describe the real variability of wind over the Black Sea. Errors in reanalysis data are not high either: the regression coefficient varies from 0.98 to 1.06, the rms deviation of the velocity amplitude varies from 1.90 to 2.24 m/s, and the rms deviation of the direction angle varies from 26° to 36°. Errors in determining the velocity and direction of wind depend on its amplitude: under weak winds ( 12 m/s), its velocity is underestimated. The influence of these errors on both spatial and temporal estimates of the characteristics of wind over the Black Sea is briefly considered.

Global recurrence plots (GRPs) and windowed recurrence quantification analysis (WRQA) are two recurrence paradigms which find wide applications to detect the onset of instability in a dynamic system. The present work reports the attempt to employ these recurrence paradigms to assess the effect of frontal gust on the force patterns of an insect-sized flapping wing in the inclined-stroke plane. Horizontal and vertical forces generated by the flapping wing in the presence of gusts of the form $$ \frac{{{\text{u}}_{\text{G}} }}{{{\text{u}}_{\text{w}} }} = \frac{{{\text{u}}_{\infty } }}{{{\text{u}}_{\text{w}} }} + \left( {\frac{{{\text{u}}_{\text{g}} }}{{{\text{u}}_{\text{w}} }}} \right)\sin \left( {2\uppi\frac{{{\text{f}}_{\text{g}} }}{{{\text{f}}_{\text{w}} }}{\text{t}}} \right) $$ were numerically estimated in the 2D reference frame for Re = 150. Nine gusts with combinations of the ratio of gust frequency to wing’s flapping frequency, fg/fw = 0.1, 0.5 and 1 and ratio of gust velocity amplitude to root mean square averaged flapping velocity, ug/uw = 0.1, 0.5 and 1 were considered. Recurrence studies of the forces were carried out to find out the gusty condition, which would trigger an onset of unstable behaviour. Studies indicated a possible onset of instability in the force patterns for gust with fg/fw = 0.1 and ug/uw = 1. The onset of unstable behaviour was prominently captured by WRQA of the vertical force coefficient based on determinism (DET) and laminarity (LAM) series.

Summary Over the last decade the acoustic 3-D full-waveform inversion technique has become almost a common tool for imaging geologically complex structures in marine, as well as in land settings. However, it has been speculated that excluding the elastic effect from the waveform modeling in some cases could have a big impact and potentially result in an erroneous image of the subsurface. To examine the contribution of the elastic effect, we conduct acoustic and elastic 3-D FWI on the 3-D seismic data, collected at the East Pacific Rise (EPR) 9°50’N, deep-water environment (minimum depth ~2500 m) with high compression velocity contrast at the seafloor. We first establish a strategy for inversion within the EPR setting, which suggest simultaneous multi-parameter inversion for the frequencies

A staggered impulse turbine is proposed for asymmetric air flows in Oscillating Water Column wave energy plants, which is expected to enhance the pneumatic power output in a wave cycle. The setting angle of rotor blades is set as 5°. The 3D numerical simulations were conducted under steady conditions using MRF and Mixing Plane model based on CFD software Fluent 12.0. Its mean efficiencies under different velocity amplitude ratios are studied using quasi-steady analysis, which derive corresponding data from the numerical simulation. It is found that the staggered turbine shows better performance than the conventional one under the asymmetrical air flows. Furthermore, its mean efficiency and output-work in a wave period are compared with another unsymmetrical twin impulse turbine system. The results show that the staggered turbine shows better output-work performance than the twin turbine system over the high flow coefficient domain (φ>0.7), which provides more choices to future research on turbine’s optimization.

Non-thermal motions in the intra-cluster medium (ICM) are believed to play a non-negligible role in the pressure support to the total gravitating mass of galaxy clusters. Future high-precision X-ray missions will allow us to directly detect the signature of these motions from highly resolved spectra of the ICM. With this perspective, we will present here a study on a set of clusters extracted from a cosmological hydrodynamical simulation, for which we simulated X-ray observations and characterized them via the non-thermal velocity amplitude of the ICM. We have applied the X-ray virtual telescope PHOX to generate mock observations of the simulated clusters and estimated in an observational fashion global X-ray properties. We included ICM non-thermal motions as additional parameter to further identify non-regular clusters. In particular, the influence of internal gas motions on the location of clusters in the LX-T plane was investigated and was found that objects with the largest amount of non-thermal velocity have on average higher X-ray luminosities. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The author firstly summarized the principles, performance and theoretical resilience model of the new type electromagnetic damper. The theoretical resilience model is further improved on this basis—normalizing the impact of vibrant frequency and vibrant amplitude on resilience as the impact of single parameter velocity amplitude. The results show that improved model can give a better effect as shown in experiment. This lays a sound foundation for simulation calculation in developing products using for practical engineering and installing the structural vibration reduction system of electromagnetic damper.

The transition criterion in the improved eN method is that transition would occur whenever the velocity amplitude of disturbance reaches 1%–2% of the free stream velocity, while in the conventional eN method, the N factor is an empirical factor. In this paper the reliability of this key assumption in the improved eN method is checked by results of transition prediction by using the Parabolized Stability Equations (PSE). Transition locations of an incompressible boundary layer and a hypersonic boundary layer at Mach number 6 on a flat plate are predicted by both the improved eN method and the PSE method. Results from both methods agree fairly well with each other, implying that the transition criterion proposed in the improved eN method is reliable.

About 25 years ago, in Paper 12 of this series, the author presented a spectroscopic orbit for 6 Boo. The velocity amplitude of little more than 1 km s−1 was much smaller than for any star whose orbit had been determined up till that time. Although it was objectively demonstrated that the orbit was very secure, a few years ago subjective misgivings prompted the author to restore the star to his observing programme. New observations of much higher precision confirm not only the spectroscopic-binary nature of 6 Boo but also, with almost astonishing fidelity, the elements already given for it.

Context. Investigations of the behavior of small-scale threads can provide an alternative approach to studying prominence dynamics and understanding its origin and nature. Aims. The behavior of threads are analyzed in a quiescent prominence, including drifting and both the horizontally and vertically oscillating motions. These indicate waves in the solar prominence. Methods. We used the Ha images at a setting wavelength of +0.076 angstrom. A quiescent prominence was observed by HINODE/SOT on 2008 January 15 for about 3 h in total. Results. Consistent with previous findings, prominences show numerous thread-like structures. Some threads clearly exhibit both vertically and horizontally oscillatory motions, while others are only drifting. Complicated cases show both drifting and oscillatory motions simultaneously. In the upper part of the prominence, the threads are oscillating independently of each other. We find that three threads oscillate with the same phase for at least two periods. The oscillations seem to be strongly damped since they disappear after a few periods. The maximum number of observed periods is 8 in our observations. In the lower part of the prominence, however, the different threads have a mixed character with the individual oscillatory motions unstable for one entire period. Most oscillatory motions will disappear after a half period or less, while the new oscillatory motions are excited nearby. A 5-min period is predominant, and the oscillating amplitudes show an average value of +/- 3.5 km s(-1). We find some upflows in the spicule layer, and they appear to transport the mass from photosphere ( or spicules themselves) to the prominence. These upflows have an average velocity amplitude of 0.8 km s(-1). Conclusions. The threads exhibit three distinct behaviors. The first is only drifting, the second is typically oscillating, and the third shows both characteristics. There are no substantial differences between the periods of horizontally and vertically oscillating threads in this prominence.