Mean Flow Velocities and Mass Transport for Equatorially-Trapped Water Waves with an Underlying Current

2016 ◽  
Vol 18 (4) ◽  
pp. 795-804 ◽  
Author(s):  
David Henry ◽  
Silvia Sastre-Gomez
Keyword(s):  
Mass Transport ◽  
Water Waves ◽  
Mean Flow ◽  
Flow Velocities

scholarly journals Interaction of linear modulated waves and unsteady dispersive hydrodynamic states with application to shallow water waves

2019 ◽  
Vol 875 ◽  
pp. 1145-1174 ◽  
Author(s):  
T. Congy ◽  
G. A. El ◽  
M. A. Hoefer
Keyword(s):  
Water Waves ◽  
Large Scale ◽  
Kdv Equation ◽  
Linear Wave ◽  
Mean Flow ◽  
Undular Bore ◽  
Expansion Waves ◽  
Flow Interaction ◽  
The Kdv Equation ◽  
New Type

A new type of wave–mean flow interaction is identified and studied in which a small-amplitude, linear, dispersive modulated wave propagates through an evolving, nonlinear, large-scale fluid state such as an expansion (rarefaction) wave or a dispersive shock wave (undular bore). The Korteweg–de Vries (KdV) equation is considered as a prototypical example of dynamic wavepacket–mean flow interaction. Modulation equations are derived for the coupling between linear wave modulations and a nonlinear mean flow. These equations admit a particular class of solutions that describe the transmission or trapping of a linear wavepacket by an unsteady hydrodynamic state. Two adiabatic invariants of motion are identified that determine the transmission, trapping conditions and show that wavepackets incident upon smooth expansion waves or compressive, rapidly oscillating dispersive shock waves exhibit so-called hydrodynamic reciprocity recently described in Maiden et al. (Phys. Rev. Lett., vol. 120, 2018, 144101) in the context of hydrodynamic soliton tunnelling. The modulation theory results are in excellent agreement with direct numerical simulations of full KdV dynamics. The integrability of the KdV equation is not invoked so these results can be extended to other nonlinear dispersive fluid mechanic models.

scholarly journals Transcranial Color Coded Duplex Sonography Findings in Stroke Patients Undergoing Rehabilitation: An Observational Study

2022 ◽  
Author(s):  
Srikant Venkatakrishnan ◽  
Meeka Khanna ◽  
Anupam Gupta
Keyword(s):  
Clinical Outcome ◽  
Duplex Sonography ◽  
Modified Rankin Scale ◽  
Mean Flow ◽  
Stroke Patients ◽  
Symmetric Flow ◽  
Rehabilitation Outcomes ◽  
Outcome Scores ◽  
Color Coded Duplex Sonography ◽  
Flow Velocities

Abstract Background Transcranial color-coded duplex sonography (TCCD) provides information on intracranial blood flow status in stroke patients and can predict rehabilitation outcomes. Objective This study aimed to assess middle cerebral artery (MCA) parameters using TCCD in MCA territory stroke patients admitted for rehabilitation and correlate with clinical outcome measures. Material and Methods Patients aged 18 to 65 years with a first MCA territory stroke, within 6 months of onset were recruited. The clinical outcome scales and TCCD parameters were assessed at both admission and discharge. The scales used were the Scandinavian stroke scale (SSS), Barthel Index (BI), modified Rankin Scale (mRS), Fugl–Meyer upper extremity scale (FMA-UE), modified motor assessment scale (mMAS) scores. TCCD parameters measured were MCA peak systolic, end diastolic, mean flow velocities (MFV), and index of symmetry (SI) and were correlated with clinical scores. Results Fourteen patients were recruited with median age of 56.5 years, median duration of stroke was 42.5 days. Mean flow velocities of affected and unaffected MCA were 46.2 and 50.7 cm/s, respectively. Flow velocities and SI did not change between the two assessments. There was significant improvement in clinical outcome scores at discharge. Significant correlation was observed for patient group with SI > 0.9 at admission with FMA-UE, SSS, and BI scores at discharge (p < 0.05). Conclusion Flow velocity parameters did not change during in-patient rehabilitation. Patients with symmetric flow at admission had improved clinical outcomes measure scores at discharge. Thus SI can predict rehabilitation outcomes in stroke survivors.

Mass transport in water waves over an elastic bed

1995 ◽  
Vol 450 (1939) ◽  
pp. 371-390 ◽  
Keyword(s):  
Boundary Layer ◽  
Free Surface ◽  
Mass Transport ◽  
Water Waves ◽  
Viscous Boundary Layer ◽  
Curvilinear Coordinate ◽  
Transport Velocity ◽  
Mass Transport Velocity ◽  
Orthogonal Curvilinear Coordinate System ◽  
Viscous Boundary

The mass transport velocity in water waves propagating over an elastic bed is investigated. Water is assumed to be incompressible and slightly viscous. The elastic bed is also incompressible and satisfies the Hooke’s law. For a small amplitude progressive wave perturbation solutions via a boundary-layer approach are obtained. Because the wave amplitude is usually larger than the viscous boundary layer thickness and because the free surface and the interface between water and the elastic bed are moving, an orthogonal curvilinear coordinate system (Longuet-Higgins 1953) is used in the analysis of free surface and interfacial boundary layers so that boundary conditions can be applied on the actual moving surfaces. Analytical solutions for the mass transport velocity inside the boundary layer adjacent to the elastic seabed and in the core region of the water column are obtained. The mass transport velocity above a soft elastic bed could be twice of that over a rigid bed in the shallow water.

An Acoustic Time-of-Flight Approach for Unsteady Temperature Measurements: Characterization of Entropy Waves in a Model Gas Turbine Combustor

2016 ◽  
Vol 139 (4) ◽  
Author(s):  
Dominik Wassmer ◽  
Bruno Schuermans ◽  
Christian Oliver Paschereit ◽  
Jonas P. Moeck
Keyword(s):  
Gas Turbine ◽  
Acoustic Waves ◽  
Fuel Injection ◽  
Acoustic Pulse ◽  
Time Of Flight ◽  
Phase Lag ◽  
Mean Flow ◽  
Unsteady Temperature ◽  
Arrival Times ◽  
Flow Velocities

Lean premixed combustion promotes the occurrence of thermoacoustic phenomena in gas turbine combustors. One mechanism that contributes to the flame–acoustic interaction is entropy noise. Fluctuations of the equivalence ratio in the mixing section cause the generation of hot spots in the flame. These so-called entropy waves are convectively transported to the first stage of the turbine and generate acoustic waves that travel back to the flame; a thermoacoustic loop is closed. However, due to the lack of experimental tools, a detailed investigation of entropy waves in gas turbine combustion systems has not been possible up to now. This work presents an acoustic time-of-flight based temperature measurement method which allows the measurement of temperature fluctuations in the relevant frequency range. A narrow acoustic pulse is generated with an electric spark discharge close to the combustor wall. The acoustic response is measured at the same axial location with an array of microphones circumferentially distributed around the combustion chamber. The delay in the pulse arrival times corresponds to the line-integrated inverse speed of sound. For the measurement of entropy waves in an atmospheric combustion test rig, fuel is periodically injected into the mixing tube of a premixed combustor. The subsequently generated entropy waves are measured for different forcing frequencies of the fuel injection and for different mean flow velocities in the combustor. The amplitude decay and phase lag of the entropy waves adhere well to a Strouhal number scaling for different mean flow velocities.

Pulsed doppler techniques for measuring instantaneous maximum and mean flow velocities in carotid arteries

1984 ◽  
Vol 10 (4) ◽  
pp. 419-426 ◽  
Author(s):  
Karl-Fredrik Lindegaard ◽  
Søren Jacob Bakke ◽  
Arne Grip ◽  
Helge Nornes
Keyword(s):  
Carotid Arteries ◽  
Pulsed Doppler ◽  
Mean Flow ◽  
Doppler Techniques ◽  
Flow Velocities

scholarly journals SPILLING BREAKERS, BORES, AND HYDRAULIC JUMPS

1978 ◽  
Vol 1 (16) ◽  
pp. 30 ◽  
Author(s):  
D.H. Peregrine ◽  
I.A. Svendsen
Keyword(s):  
Water Waves ◽  
Mean Flow ◽  
The Mean ◽  
White Water ◽  
Pass Through ◽  
Definition Of ◽  
Spilling Breakers ◽  
Almost All ◽  
Plunging Breaker ◽  
Spilling Breaker

On gently sloping beaches, almost all water waves break. After the initial breaking the water motion usually appears quite chaotic. However, for a moderate time, for example two or three times the descent time of the "plunge" in a plunging breaker, the flow can be relatively well organised despite the superficial view which is largely of spray and bubbles. If waves continue to break the breaking motion, or "white water" soon becomes fully turbulent and the mean motions become quasisteady. A reasonable definition of a quasi-steady wave is one which changes little during the time a water particle takes to pass through it. We exclude water particles which may become trapped in a surface roller and surf along with the wave. At this stage in its development a wave on a beach may be described as a spilling breaker or as a bore. In fact, there is a range of these waves from those with a little white water at the crest to examples where the whole front of the wave is fully turbulent. In investigating the properties of such waves it is desirable to start by looking at the whole range of related motions. The most obvious extension is to the hydraulic jump; since, in the simplest view, it is equivalent to a bore but in a frame of reference moving with the wave. It is also an example where the mean flow is steady rather than quasisteady.

On mass transport in deep water waves

1962 ◽  
Vol 53 (1) ◽  
pp. 65-76 ◽  
Author(s):  
J. N. Hunt ◽  
S. K. A. Massoud
Keyword(s):  
Mass Transport ◽  
Deep Water ◽  
Water Waves ◽  
Deep Water Waves

scholarly journals HOBOE (Head-of-Bed Optimization of Elevation) Study: Association of Higher Angle With Reduced Cerebral Blood Flow Velocity in Acute Ischemic Stroke

2011 ◽  
Vol 91 (10) ◽  
pp. 1503-1512 ◽  
Author(s):  
Abigail Jade Hunter ◽  
Suzanne J. Snodgrass ◽  
Debbie Quain ◽  
Mark W. Parsons ◽  
Christopher R. Levi
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Ischemic Stroke ◽  
Flow Velocity ◽  
Blood Flow Velocity ◽  
Cerebral Blood Flow Velocity ◽  
Mean Flow ◽  
Study Association ◽  
Blood Flow Velocities ◽  
Flow Velocities

BackgroundCerebral autoregulation can be impaired after ischemic stroke, with potential adverse effects on cerebral blood flow during early rehabilitation.ObjectiveThe objective of this study was to assess changes in cerebral blood flow velocity with orthostatic variation at 24 hours after stroke.DesignThis investigation was an observational study comparing mean flow velocities (MFVs) at 30, 15, and 0 degrees of elevation of the head of the bed (HOB).MethodsEight participants underwent bilateral middle cerebral artery (MCA) transcranial Doppler monitoring during orthostatic variation at 24 hours after ischemic stroke. Computed tomography angiography separated participants into recanalized (artery completely reopened) and incompletely recanalized groups. Friedman tests were used to determine MFVs at the various HOB angles. Mann-Whitney U tests were used to compare the change in MFV (from 30° to 0°) between groups and between hemispheres within groups.ResultsFor stroke-affected MCAs in the incompletely recanalized group, MFVs differed at the various HOB angles (30°: median MFV=51.5 cm/s, interquartile range [IQR]=33.0 to 103.8; 15°: median MFV=55.5 cm/s, IQR=34.0 to 117.5; 0°: median MFV=85.0 cm/s, IQR=58.8 to 127.0); there were no significant differences for other MCAs. For stroke-affected MCAs in the incompletely recanalized group, MFVs increased with a change in the HOB angle from 30 degrees to 0 degrees by a median of 26.0 cm/s (IQR=21.3 to 35.3); there were no significant changes in the recanalized group (−3.5 cm/s, IQR=−12.3 to 0.8). The changes in MFV with a change in the HOB angle from 30 degrees to 0 degrees differed between hemispheres in the incompletely recanalized group but not in the recanalized group.LimitationsGeneralizability was limited by sample size.ConclusionsThe incompletely recanalized group showed changes in MFVs at various HOB angles, suggesting that cerebral blood flow in this group may be sensitive to orthostatic variation, whereas the recanalized group maintained stable blood flow velocities.

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