Evolution in the time series of vortex velocity fluctuations across different regimes of vortex flow

2010 ◽  
Vol 470 ◽  
pp. S830-S831
Author(s):  
S.S. Banerjee ◽  
Jaivardhan Sinha ◽  
Shyam Mohan ◽  
A.K. Sood ◽  
S. Ramakrishnan ◽  
...  
Keyword(s):  
Time Series ◽  
Vortex Flow ◽  
Velocity Fluctuations ◽  
Vortex Velocity

Fundamentals concerning wave loading on offshore structures

1986 ◽  
Vol 173 ◽  
pp. 667-681 ◽  
Author(s):  
James Lighthill
Keyword(s):  
Fluid Mechanics ◽  
Natural Frequency ◽  
Potential Flow ◽  
Vortex Flow ◽  
Offshore Structures ◽  
Second Order ◽  
Mechanics Of Solids ◽  
Wave Loading ◽  
Velocity Fluctuations ◽  
Substantial Body

This article is aimed at relating a certain substantial body of established material concerning wave loading on offshore structures to fundamental principles of mechanics of solids and of fluids and to important results by G. I. Taylor (1928a,b). The object is to make some key parts within a rather specialised field accessible to the general fluid-mechanics reader.The article is concerned primarily to develop the ideas which validate a separation of hydrodynamic loadings into vortex-flow forces and potential-flow forces; and to clarify, as Taylor (1928b) first did, the major role played by components of the potential-flow forces which are of the second order in the amplitude of ambient velocity fluctuations. Recent methods for calculating these forces have proved increasingly important for modes of motion of structures (such as tension-leg platforms) of very low natural frequency.

scholarly journals Controls on short-term variations in Greenland glacier dynamics

2013 ◽  
Vol 59 (217) ◽  
pp. 883-892 ◽  
Author(s):  
A.V. Sundal ◽  
A. Shepherd ◽  
M. van den Broeke ◽  
J. Van Angelen ◽  
N. Gourmelen ◽  
...  
Keyword(s):  
Time Series ◽  
Radar Data ◽  
Early Summer ◽  
Short Term ◽  
Synthetic Aperture Radar Data ◽  
Velocity Fluctuations ◽  
Speed Up ◽  
Front Advance ◽  
Enhanced Surface ◽  
Front Dynamics

AbstractShort-term ice-dynamical processes at Greenland’s Jakobshavn and Kangerdlugssuaq glaciers were studied using a 3 day time series of synthetic aperture radar data acquired during the 2011 European Remote-sensing Satellite-2 (ERS-2) 3 day repeat campaign together with modelled meteorological parameters. The time series spans the period March–July 2011 and captures the first ∼30% of the summer melting season. In both study areas, we observe velocity fluctuations at the lower ∼10 km of the glacier. At Jakobshavn Isbræ, where our dataset covers the first part of the seasonal calving-front retreat, we identify ten calving episodes, with a mean calving-front area loss of 1.29 ± 0.4 km2. Significant glacier speed-up was observed in the near-terminus area following all calving episodes. We identify changes in calving-front geometry as the dominant control on velocity fluctuations on both glaciers, apart from a <15% early-summer speed-up at Kangerdlugssuaq Glacier during a period of calving-front advance, which we attribute to enhanced surface melt-induced basal lubrication. Our 3 day velocity maps show new spatial characteristics of the ice melange flow variability in the Jakobshavn and Kangerdlugssuaq fjord systems, which are primarily controlled by calving-front dynamics and fjord geometry.

Generating controllable velocity fluctuations using twin oscillating hydrofoils

2012 ◽  
Vol 713 ◽  
pp. 150-158 ◽  
Author(s):  
S. F. Harding ◽  
I. G. Bryden
Keyword(s):  
Inverse Problem ◽  
Time Series ◽  
Flow Velocity ◽  
Two Dimensional ◽  
Velocity Fluctuations ◽  
Instantaneous Flow ◽  
Vortex Model ◽  
Flow Fluctuations ◽  
Wide Range ◽  
Oscillatory Velocity

AbstractAn experiment apparatus has been previously developed with the ability to independently control the instantaneous flow velocity in a water flume. This configuration, which uses two pitching hydrofoils to generate the flow fluctuations, allows the unsteady response of submerged structures to be studied over a wide range of driving frequencies and conditions. Linear unsteady lift theory has been used to calculate the instantaneous circulation about two pitching hydrofoils in uniform flow. A vortex model is then used to describe the circulation in the wakes that determine the velocity perturbations at the centreline between the foils. This paper introduces how the vortex model can be discretized to allow the inverse problem to be solved, such that the foil motions required to recreate a desired velocity time series can be determined. The results of this model are presented for the simplified cases of oscillatory velocity fluctuations in the vertical and stream-wise directions separately, and also simultaneously. The more general case of two-dimensional aperiodic velocity fluctuations is also presented, which demonstrates the capability of configuration between the suggested frequency limits of $0. 06\leq k\leq 1. 9$.

The nonlinear phase of wave growth leading to chaos and breakdown to turbulence in a boundary layer as an example of an open system

1990 ◽  
Vol 430 (1878) ◽  
pp. 3-24 ◽  
Keyword(s):  
Boundary Layer ◽  
Time Series ◽  
Differential Equations ◽  
Mathematical Models ◽  
Flow Regime ◽  
Open System ◽  
Broadband Noise ◽  
Periodic Component ◽  
Velocity Fluctuations ◽  
Nonlinear Phase

The spatial development of boundary-layer instabilities has been investigated experimentally in a flow régime where nonlinearities are important. Detailed measurements of the evolution of a regular periodic wavetrain into an irregular or chaotic one are reported. It was found that the broadband noise content of the motion grew very rapidly downstream when the amplitude of the periodic component was sufficiently large. The almost explosive growth of the broadband element provided velocity fluctuations with chaotic time series similar to those generated by mathematical models based on low-order differential equations.

scholarly journals A persistent quiet-Sun small-scale tornado

2020 ◽  
Vol 643 ◽  
pp. A166
Author(s):  
K. Tziotziou ◽  
G. Tsiropoula ◽  
I. Kontogiannis
Keyword(s):  
Time Series ◽  
Phase Difference ◽  
Vortex Flow ◽  
Wave Mode ◽  
Doppler Velocity ◽  
Small Scale ◽  
Time Interval ◽  
Difference Analysis ◽  
Quiet Sun ◽  
Wave Modes

Context. Vortex flows can foster a variety of wave modes. A recent oscillatory analysis of a persistent 1.7 h vortex flow with a significant substructure has suggested the existence of various types of waves within it. Aims. We investigate the nature and characteristics of waves within this quiet-Sun vortex flow, over the course of an uninterrupted 48-min observing time interval, in order to better understand its physics and dynamics. Methods. We used a cross-wavelet spectral analysis between pairs of Hα and Ca II 8542 Å intensity time series at different wavelengths and, hence, atmospheric heights, acquired with the CRisp Imaging SpectroPolarimeter at the Swedish Solar Telescope, as well as the derived Hα Doppler velocity and full width at half maximum time series. We constructed halftone frequency-phase difference plots and investigated the existence and propagation characteristics of different wave modes. Results. Our analysis suggests the existence of Alfvénic type waves within the vortex flow that propagate upwards with phase speeds of ∼20–30 km s−1. The dominant wave mode seems to be the fast kink wave mode, however, our analysis also suggests the existence of localised Alfvénic torsional waves, which are related to the dynamics of individual chromospheric swirls that characterise the substructure of the vortex flow. The Hα V–I phase difference analysis seems to imply the existence of a standing wave pattern that is possibly arising from the interference of upwards propagating kink waves with downwards propagating ones that are reflected at the transition region or the corona. Moreover, the results provide further evidence that the central chromospheric swirl drives the dynamics of the vortex flow. Conclusions. This is the first exhaustive phase difference analysis within a vortex flow that explores the nature and dynamics of different wave modes within it. The question, however, of whether, and how, the dissipation of the derived wave modes occurs remains open, and given that such structures are ubiquitous on the solar surface, it’s also important to investigate whether they might ultimately play a significant role in the energy budget of the upper layers of the solar atmosphere.

scholarly journals Surface velocity fluctuations for Glaciar Universidad, central Chile, between 1967 and 2015

2016 ◽  
Vol 62 (235) ◽  
pp. 847-860 ◽  
Author(s):  
RYAN WILSON ◽  
SEBASTIAN H. MERNILD ◽  
JEPPE K. MALMROS ◽  
CLAUDIO BRAVO ◽  
DANIELA CARRIÓN
Keyword(s):  
Time Series ◽  
Mass Balance ◽  
General Pattern ◽  
Surface Velocity ◽  
Glacier Mass Balance ◽  
Velocity Fluctuations ◽  
The Andes ◽  
Cumulative Change ◽  
Glacier Velocity ◽  
Andes Cordillera

ABSTRACTFor the Andes Cordillera, where observed mass-balance records are sparse, long-term glacier velocity measurements potentially represent a useful tool for assessing glacier health. Utilising manual and automatic feature-tracking techniques applied to Corona, Landsat and ASTER satellite imagery, this paper presents surface velocity fluctuations for Glaciar Universidad between 1967 and 1969, and 1985 and 2015, the longest such time series available for the Andes Cordillera, outside Patagonia. This time series reveals an increase in the surface velocities of the main glacier trunk between 1967 and 1987 (~90%) followed by a deceleration between 1987 and 2015 (~80%), with ice velocities observed between 2014 and 2015 possibly representing a 48 a low. In response to the surface velocity fluctuations, the glacier front advanced between 1985 and 1992 (cumulative change of 137 ± 14 m), and again to a lesser magnitude during the 1996–98 and 2004–08 periods. Although having exhibited possible surge behaviour during the 1940s, the synchrony of the glacier changes presented for Glaciar Universidad with those reported for nearby glaciers, suggests that this glacier is responding to climatic trends. If the above scenario is true, the results indicate a general pattern of increasingly negative glacier mass-balance conditions since the late 1980s.

scholarly journals Low-Altitude Atmospheric Turbulence Sounding on the Basis of Unmanned Aerial Vehicle

2020 ◽  
Author(s):  
Alexander Shelekhov ◽  
Aleksey Afanasiev ◽  
Alexey Kobzev ◽  
Evgenia Shelekhova ◽  
Alexey Tel’minov ◽  
...  
Keyword(s):  
Time Series ◽  
Wind Velocity ◽  
Unmanned Aerial Vehicle ◽  
Weather Station ◽  
Velocity Fluctuations ◽  
Turbulent Fluctuations ◽  
Station Data ◽  
Weather Station Data ◽  
Aerial Vehicle ◽  
Turbulent Spectra

Based on the theory of turbulence, equations are derived for estimations of turbulent fluctuations of the longitudinal and transverse components of the wind velocity during ideal hovering of a quadcopter in a turbulent atmosphere. We present the results of experiments which were carried out on the territory of the Geophysical Observatory of Institute of Monitoring of Climatic and Ecological Systems, Siberian Branch, Russian Academy of Sciences, located in Tomsk Akademgorodok on the territory with complex orography, in a parkland zone with buildings of research institutes and motorways. Time series of turbulent fluctuations of the longitudinal and transverse components of wind velocity fluctuations were received with the use of an automated weather station, and time series of estimates of these components, from data of a DJI Phantom 4 Pro quadcopter during hovering. According to the automated weather station data, anisotropy was observed in one experiment during measurements in the atmosphere, but this phenomenon was not observed in the other experiment: the fluctuation spectra of all components of wind speed fluctuations coincide. The spectra of fluctuations of the longitudinal and transverse wind velocity components based on the automated weather station data and UAV telemetry are presented. The fluctuation spectra of these components for the automated weather station data and quadcopter generally coincide. The behavior of the spectra coincides with the spectrum which corresponds to Kolmogorov&ndash;Obukhov &ldquo;&ndash;5/3&rdquo; law within the inertial range. The turbulent spectra of the wind velocity fluctuations obtained with the use of the automatic weather station and with the unmanned aerial vehicle differ in the high-frequency spectral region.

The LDE-Type Flare Occurrence (1969-1993)

1994 ◽  
Vol 144 ◽  
pp. 279-282
Author(s):  
A. Antalová
Keyword(s):  
Time Series ◽  
Fourier Analysis ◽  
Sunspot Cycle ◽  
List Type ◽  
Type Number ◽  
Solar Cycles ◽  
Type Iv ◽  
Long Duration ◽  
Cycle Maximum ◽  
Flare Index

AbstractThe occurrence of LDE-type flares in the last three cycles has been investigated. The Fourier analysis spectrum was calculated for the time series of the LDE-type flare occurrence during the 20-th, the 21-st and the rising part of the 22-nd cycle. LDE-type flares (Long Duration Events in SXR) are associated with the interplanetary protons (SEP and STIP as well), energized coronal archs and radio type IV emission. Generally, in all the cycles considered, LDE-type flares mainly originated during a 6-year interval of the respective cycle (2 years before and 4 years after the sunspot cycle maximum). The following significant periodicities were found:• in the 20-th cycle: 1.4, 2.1, 2.9, 4.0, 10.7 and 54.2 of month,• in the 21-st cycle: 1.2, 1.6, 2.8, 4.9, 7.8 and 44.5 of month,• in the 22-nd cycle, till March 1992: 1.4, 1.8, 2.4, 7.2, 8.7, 11.8 and 29.1 of month,• in all interval (1969-1992):a)the longer periodicities: 232.1, 121.1 (the dominant at 10.1 of year), 80.7, 61.9 and 25.6 of month,b)the shorter periodicities: 4.7, 5.0, 6.8, 7.9, 9.1, 15.8 and 20.4 of month.Fourier analysis of the LDE-type flare index (FI) yields significant peaks at 2.3 - 2.9 months and 4.2 - 4.9 months. These short periodicities correspond remarkably in the all three last solar cycles. The larger periodicities are different in respective cycles.

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