Horizontal Oscillations Research Articles

Norwegian seiches from the giant 2011 Tohoku earthquake

AbstractSeismic waves of the giant 2011 Tohoku earthquake triggered seiches in western Norwegian fjords. The seiching began a half hour after the earthquake origin time. The oscillations were noted by eyewitnesses and recorded by surveillance and cell phone cameras. The observations show maximum trough‐to‐peak amplitudes of 1.0–1.5 m and periods of 67–100 s. The water waves were not triggered from the arrival of the surface waves, the timing inferred for other seiches. Instead, the seiching began during the passage of horizontal S waves. We reproduced the S wave trigger by means of a shallow‐water wave model calibrated previously to Norwegian tides and storm surges. The simulations, which used the observed earthquake motion as forcing, show water waves with periods and amplitudes similar to those in the film clips. However, the strongest horizontal ground oscillations with shorter periods (20–30 s) did not contribute much to the formation of the seiches.

Mitigating horizontal divergence “checker-board” oscillations on unstructured triangular C-grids for nonlinear hydrostatic and nonhydrostatic flows

A complication of finite-volume triangular C-grid methods is the numerical emergence of horizontal divergence errors that lead to grid-scale oscillations in vertical velocity. Nonlinear feedback via advection of momentum can lead to numerical instability in velocity modes via positive feedback with spurious vertical velocities induced by horizontal divergence truncation error. Existing strategies to mitigate divergence errors such as direct divergence averaging and increased diffusion do not completely mitigate horizontal vertical velocity oscillations. We present a novel elliptic filtering approach to mitigate this spurious error and more accurately represent vertical velocities via improved calculation of horizontal divergences. These results are applied to laminar curved channel flows, demonstrating the applicability of the method to reproduce secondary flow features.

Experimental Study of Suppressing a Parametric Resonance in a HTSC Levitation System by a Horizontal Pendulum

This research deals with the experimental investigation of reduction in the amplitude of nonlinear oscillation in a high-Tc superconducting magnetic levitation system by using a vibration absorber. High-Tc superconducting levitation systems have very low damping and stable levitation without control. In such low-damped systems, complicated phenomena of dynamics can be easily generated by nonlinearity of the magnetic force. Our previous research showed that if the frequency of vertical excitation is in the neighborhood of double the natural frequency in the horizontal direction, horizontal oscillation can occur parametrically through nonlinear coupling between vertical motion and horizontal motion. This research investigates an effect of a vibration absorber on the parametrically excited horizontal oscillation of the levitated body. We performed experiments on a symmetric rigid bar, levitated by the electromagnetic force between superconductors fixed on the base, and magnets fixed at both ends of the bar. A simple damped horizontal pendulum is attached to the main system as a vibration absorber, so that it is linearly coupled with the main system. Through these experiments, it has been confirmed that this kind of a vibration absorber is useful for reducing the amplitude of a parametric resonance in a high-Tc superconducting levitation system.

THE CROSS SPECTRAL TIME LAG EVOLUTION ALONG BRANCHES IN XTE J1701-462

We investigate the cross spectrum of XTE J1701-462 in various types of Neutron Star-Low Mass X-ray Binary subclasses, during its 2006-2007 outburst. We analyze the relation between the time lags and temporal variabilities. We find that the hard time lags accompany with the horizontal branch oscillations (HBOs) and the soft time lags dominate the noise in the low frequency range 0.1-10 Hz on HB. In the Cyg-like phase, the time lags decrease on the middle normal branch (NB) from HB/NB vertex to NB/FB vertex, whereas the time lags are roughly invariant in the Sco-like source. We discuss that the Compton upscattering by the corona introduces the soft lag in low frequency noise. We interpret that the variation of the Comptonization component from the disk emission lead to the HBOs' time lags evolution along the Z tracks. We also report the rms amplitude spectrum and phase lag spectrum for the NBO. The $\sim$ $160^{\circ}$ phase lag is found. We present that the rms amplitude of both the Cyg-like and the Sco-like NBO linearly increase with the photon energy in low energy bands, and it will drop in the highest energy band.

Pattern formation in a horizontally shaken granular submonolayer

We study the mechanism leading to the formation of stripe-like patterns in a rectangular container filled with a sub-monolayer of frictional spherical particles when it is subjected to horizontal oscillations. By means of Molecular Dynamics simulations we could reproduce the experimental results. Systematic simulations allow to identify friction to be responsible for the pattern formation, that is, the tangential interaction between contacting particles and between the particles and the floor of the container. When particles are in contact with the floor and other adjacent particles simultaneously, there emerges a frustrated situation in which the particles are prevented from rolling on the floor. This effect leads to local jamming and eventually to stripe-like pattern formation. In the long time evolution, the stripes are unstable. Stripes may merge as well as disintegrate.

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.

Intraseasonal Modulation of the Surface Cooling in the Gulf of Guinea

Abstract A regional numerical model of the tropical Atlantic Ocean and observations are analyzed to investigate the intraseasonal fluctuations of the sea surface temperature at the equator in the Gulf of Guinea. Results indicate that the seasonal cooling in this region is significantly shaped by short-duration cooling events caused by wind-forced equatorial waves: mixed Rossby–gravity waves within the 12–20-day period band, inertia–gravity waves with periods below 11 days, and equatorially trapped Kelvin waves with periods between 25 and 40 days. In these different ranges of frequencies, it is shown that the wave-induced horizontal oscillations of the northern front of the mean cold tongue dominate the variations of mixed layer temperature near the equator. But the model mixed layer heat budget also shows that the equatorial waves make a significant contribution to the mixed layer heat budget through modulation of the turbulent cooling, especially above the core of the Equatorial Undercurrent (EUC). The turbulent cooling variability is found to be mainly controlled by the intraseasonal modulation of the vertical shear in the upper ocean. This mechanism is maximum during periods of seasonal cooling, especially in boreal summer, when the surface South Equatorial Current is strongest and between 2°S and the equator, where the presence of the EUC provides a background vertical shear in the upper ocean. It applies for the three types of intraseasonal waves. Inertia–gravity waves also modulate the turbulent heat flux at the equator through vertical displacement of the core of the EUC in response to equatorial divergence and convergence.

Experimental investigation of freely falling thin disks. Part 1. The flow structures and Reynolds number effects on the zigzag motion

AbstractThis paper describes an experimental investigation of the dynamics of a freely falling thin circular disk in still water. The flow patterns of the disk zigzag motion are studied using dye visualization and particle image velocimetry. Time-resolved disk motions with six degrees of freedom are obtained with a stereoscopic vision method. The flow separation and vortex shedding are found to change with the Reynolds number, $\mathit{Re}$. At high Reynolds numbers a new dipole vortex is shed that is significantly different from Kármán-type vortices. The vortical structures are mainly composed of leading-edge vortices, a counter-rotating vortex pair and secondary trailing-edge vortices. The amplitude of the horizontal oscillation is also dependent on the Reynolds number with a critical Reynolds number ${\mathit{Re}}_{cr} \approx 2000$, where the oscillatory amplitude is proportional to $\mathit{Re}$ for $\mathit{Re}\lt {\mathit{Re}}_{cr} $, but becomes invariant for $\mathit{Re}\gt {\mathit{Re}}_{cr} $. Three-dimensional dipolar vortices were also observed experimentally.

Experimental study of planar opposed jets with acoustic excitation

Oscillation behaviors of planar opposed jets with acoustic excitation were experimentally investigated. The flow regimes of planar opposed jets at various exit air velocities, nozzle separations, excitation frequencies, and excitation amplitudes have been identified by a flow visualization technique combining with a high-speed camera. Results show that planar opposed jets exhibit horizontal instability at L/H ≤ 4 (where L is the nozzle separation and H is the slit height of the planar nozzle) and deflecting oscillation at L/H ≥ 6. The deflecting oscillation is originally started by the antisymmetric structures in the planar jets and is self-sustained by the periodic changes of the velocity field and the pressure field. At L/H ≤ 4, the acoustic excitation results in the horizontal periodic oscillation, whose frequency is equal to the excitation frequency. The acoustic excitation of oscillation amplitude less than 10% has negligible influence on the deflecting oscillation; for synchronous or asynchronous excitation with higher amplitude, the transition from the deflecting oscillation to a steady state or horizontal oscillation occurs.

Reduction in the Amplitude of the Primary Resonance Combined with the Parametrically Excited Horizontal Oscillation in a High-Tc Superconducting Levitation System

This research proposes reduction in the amplitude of the primary resonance combined with the parametrically excited horizontal oscillation in a High-Tc superconducting levitation system. High-Tc superconducting levitation systems have very low damping and stable levitation without control. However, in such low-damped systems, complicated phenomena of dynamics can be easily generated by nonlinearity of the magnetic force. Our previous research showed that, when the frequency of vertical excitation is in the neighborhood of double the natural frequency in the horizontal direction, horizontal oscillation can occur parametrically through nonlinear coupling between vertical motion and horizontal motion. This research discusses on effects of the parametrically excited horizontal resonance on the primary resonance. We discussed possible nonlinear interaction called internal resonance between the vertical motion and the horizontal motion whose natural frequency is chosen as half that of the vertical motion. The primary resonance reduction based on this mechanism was successfully verified numerically. This kind of nonlinear oscillation can be useful for reducing resonance of a high-Tc superconducting levitation system.

Modelling the embedment process during offshore pipe-laying on fine-grained soils

Subsea pipelines are becoming an increasingly significant element of offshore hydrocarbon developments as exploration moves into deep-water environments further from shore. During the lay process, pipelines are subject to small amplitude vertical and horizontal oscillations, driven by the sea state and lay vessel motions. Centrifuge model tests have been used to simulate these small-amplitude lay effects, with varying degrees of idealization relative to the real lay process. In the soft soils found in deep water, pipe embedment can exceed a diameter or more, thus significantly affecting the lateral pipe–soil interaction, axial resistance, and thermal insulation. In this paper, results from centrifuge model tests are used to calibrate a model for calculating the dynamic embedment of a subsea pipeline. The model uses elements of plasticity theory to capture the effects of combined vertical and horizontal loading, and incorporates the softening of the surrounding soil as it is remoulded due to the pipeline motions. Influences from the lay rate, lay geometry, and sea state are included in the calculation process. The model is compared with observed as-laid pipeline embedment data from field surveys at three different offshore sites. Using site-specific soil parameters obtained from in situ testing and idealized pipe loads and motions to represent the load and displacement patterns during offshore pipe-laying, respectively, the model is shown to capture well the final as-laid embedment measured in the field surveys.

Effects of Additional Visual Oscillation on Vection under Voluntary Eye Movement Conditions—Retinal Image Motion is Critical in Vection Facilitation

Horizontal oscillation introduced into a visual inducer can enhance an observer's illusory perception of vertical self-motion induced by a vertically moving optic flow pattern. To examine the effects of increased retinal image motion on the facilitation of vection, vection strength was analysed under various stimulus conditions where the oscillation of the retinal image was determined both by the motion of the visual stimulus and the observer's eye movements. The results indicated that the facilitation of vection was regulated by the oscillation of the visual stimulus on the observer's retina rather than the stimulus oscillation per se. Thus, the current experiment clearly favours the hypothesis that increased retinal image motion plays a critical role in the facilitation of vection.

An Attempt to Describe Frequency-Correlations among kHz QPOs and HBOs by Two-Armed Vertical p-Mode Oscillations: Case of No Magnetic Field

The trapping of two-armed ($ m$$ =$ 2) vertical p-mode oscillations in relativistic disks is examined. The disks are assumed to be isothermal in the vertical direction, but are truncated at a certain height by the presence of corona. The same issues were examined in a previous paper (Kato 2012a). In this paper, unlike the previous paper, however, we do not use the approximation that the oscillations are nearly vertical, but limit to a simpler case of no magnetic field. As in the previous paper, the results suggest that the two basic oscillation modes [both are the fundamental ($ n$$ =$ 1) in the vertical direction, but in the horizontal direction one is the fundamental ($ n_{\rm r}$$ =$ 0) and the other the first overtone ($ n_{\rm r}$$ =$ 1)] correspond to the twin kHz QPOs. Second, the oscillation mode, which is the first overtone ($ n$$ =$ 2) in the vertical direction and the fundamental in the horizontal direction ($ n_{\rm r}$$ =$ 0), will correspond to the horizontal branch oscillation (HBO) of Z-sources. The latter suggests that the horizontal branch of Z-sources is a sequence of temperature change in disks whose vertical thickness is strongly terminated. The temperature increases leftward along the sequence from the apex between the normal and horizontal branches.

Closure to “Seismic Behavior of Batter Piles: Elastic Response” by A. Giannakou, N. Gerolymos, G. Gazetas, T. Tazoh, and I. Anastasopoulos

Significant advances have been made on this important research topic in the last few years because of Giannakou et al., who have faced, in urgent terms, the matter of whether inclined piles have a beneficial or detrimental role. The discusser agreeswith the authors on the fact that the horizontal drift of a superstructure supported on a group of batter piles is generally smaller than with the exclusively vertical pile group; however, it could not really be generalized that this reduction is appreciable only with tall structures. The discusser has carried out work in his Ph.D. thesis about the inclined piles, studying the behavior of a couple of piles supporting a tall superstructure (hstr 5 10m) and a short superstructure (hstr 5 2m), in different geometrical conditions and seismic excitations than those of the authors, reaching quite different results. Specifically, from results obtained performing FEM three-dimensional analysis with the computer program ADINA (ADINA 2010), and using the base of the model with two real acceleration time histories (El Centro component NS 1940 [amax 5 0:318g]; Bagnoli Irpino Earthquake 1980 [amax 5 0:358g]), the following can be concluded. The reduction of horizontal drift because of inclined piles with regard to vertical piles was more important in short superstructures than tall ones (Figs. 1 and 2). To explain these results, it is useful to keep in mind that under seismic excitation, the horizontal drift of the superstructure mass, um, is made of three parts: horizontal translation of the cap, horizontal translation because of rotation cap, and horizontal deflection of the column. The discusser has found out that the cap's horizontal translation founded on vertical piles tends to be higher than the one with the inclined piles. Instead, the contribution because of the cap rotation can increase or reduce the horizontal drift depending on the sign of the rotation. In the case of the short superstructure, Fig. 3 shows the horizontal displacement of the cap on the inclined piles, uc, the vertical displacement of the pile on the left, vcl, and the vertical displacement of the pile on the right, vcr . For better understanding of the figures, the time considered was limited to the first 3 s. Once the vertical displacements are confirmed, the rotation is obtained by dividing the difference in the vertical displacement at the head of the piles by the distance between the two piles. In Fig. 3, the horizontal oscillation frequency of the cap is quite lower than the one in the vertical direction; the vertical displacement, vcl, also has the opposite sign and basically the same amplitude of vcr. The difference in frequency

Magnetic field variations and spatial configurations of long-period sunspot oscillations according to the SOHO data

The phenomenon of long-period sunspot oscillations with periods from several tens to a thousand minutes is studied using data on the magnetic field strength and sunspot coordinates obtained based on the SOHO MDI data. It has been indicated that oscillations of the sunspot magnetic field strength are related to relative and absolute horizontal oscillation modes, as a result of which certain limitations are imposed on the interpretation of the phenomenon.

Horizontal fixation point oscillation and simulated viewpoint oscillation both increase vection in depth

Previous research has shown that vection can be enhanced by adding horizontal simulated viewpoint oscillation to radial flow. Adding a horizontally oscillating fixation target to purely radial flow induces a superficially similar illusion of self-motion, where the observer's perceived heading oscillates left and right as their eyes pursue the moving target. This study directly compared the vection induced by these two conditions for the first time. Adding fixation point oscillation and simulated viewpoint oscillation to radial flow were both found to improve vection (relative to no oscillation control displays). Neither vection advantage could be explained in terms of differences in perceived scene rigidity or motion adaptation. Our findings also provided little support for the notion that pursuit eye-movements were essential for the simulated viewpoint oscillation advantage for vection (since observers successfully fixated a stationary, centrally- placed target during these conditions in the current experiments). The strongest support was found for the proposal that fixation point oscillation and simulated viewpoint oscillation both improve vection by increasing the observer's global retinal motion.

Instabilities in a nonstationary model of self-gravitating disks. IV. Generalization of the models and comparison of results

A generalized phase model of a radially nonstationary disk with an anisotropic velocity diagram is constructed which has an exact nonlinear nonstationarity law and is a nonequilibrium extension of the equilibrium disk of Bisnovatyi-Kogan and Zel’dovich. For a comparative analysis of the instabilities of the generalized model with respect to horizontal and vertical oscillatory modes, nonstationary analogs of the dispersion relations are obtained for these modes. An analysis of these results shows that the parameters characterizing the difference and degree of anisotropy of nonlinearly nonstationary models have opposite effects on the horizontal and vertical oscillations of a disk. We also compare the horizontal and vertical oscillatory modes against the background of nonstationary models with isotropic and anisotropic velocity diagrams. For small and moderate disk rotation parameters, it is found that the vertical modes dominate the horizontal modes, while the opposite picture is seen on approaching the maximum rotation.

수평진동이 있는 용기내 자성유체 액면 동요 현상에 관한 연구

본 논문에서는 수평진동이 있는 용기내 자유표면을 갖는 자성유체에 용기하부로부터 수직자장을 인가시킨 경우 유동을 실험하였다. 실험은 직사각형 및 원통형 용기에 대해 자성유체에 인가된 자기력이 공진주파수, 액면변위에 미치는 영향을 조사하였다. 인가자장의 증가는 최대 공진점 및 액면변위에 영향을 미치고 그 결과 표면파의 진폭과 슬로싱 유동의 변동주기를 변화시킨다. In this paper, fluid movement of magnetic fluid which has free surface is investigated in a container subjected to a horizontal oscillation. Here, the vertical magnetic field is applied from the bottom of this container. The experiment is performed on the magnetic fluid in a rectangular and a cylindrical container and the effects of magnetic force exerted on the magnetic fluid are investigated on the resonance frequency and liquid surface displacement. The increase of magnetic field affects on the maximum resonance point and the liquid surface displacement. In result, it changes the amplitude of the surface wave and the period of sloshing fluid movement.

Accounting for low-frequency synchrotron X-ray beam position fluctuations for dynamic visualizations

Synchrotron X-ray radiography on beamline 05B1-1 at the Canadian Light Source Inc. was employed to study dynamic liquid water transport in the porous electrode materials of polymer electrolyte membrane fuel cells. Dynamic liquid water distributions were quantified for each radiograph in a sequence, and non-physical liquid water measurements were obtained. It was determined that the position of the beam oscillated vertically with an amplitude of ~25 µm at the sample and a frequency of ~50 mHz. In addition, the mean beam position moved linearly in the vertical direction at a rate of 0.74 µm s(-1). No evidence of horizontal oscillations was detected. In this work a technique is presented to account for the temporal and spatial dependence of synchrotron beam intensity, which resulted in a significant reduction in false water thickness. This work provides valuable insight into the treatment of radiographic time-series for capturing dynamic processes from synchrotron radiation.

LOW-FREQUENCY QUASI-PERIODIC OSCILLATION FROM THE 11 Hz ACCRETING PULSAR IN TERZAN 5: NOT FRAME DRAGGING

We report on 6 RXTE observations taken during the 2010 outburst of the 11 Hz accreting pulsar IGR J17480-2446 located in the globular cluster Terzan 5. During these observations we find power spectra which resemble those seen in Z-type high-luminosity neutron star low-mass X-ray binaries, with a quasi-periodic oscillation (QPO) in the 35-50 Hz range simultaneous with a kHz QPO and broad band noise. Using well known frequency-frequency correlations, we identify the 35-50 Hz QPOs as the horizontal branch oscillations (HBO), which were previously suggested to be due to Lense-Thirring precession. As IGR J17480-2446 spins more than an order of magnitude more slowly than any of the other neutron stars where these QPOs were found, this QPO can not be explained by frame dragging. By extension, this casts doubt on the Lense-Thirring precession model for other low-frequency QPOs in neutron-star and perhaps even black-hole systems.