On the development and control of caustics in shear flows over elastic surfaces

1992 ◽  
Vol 92 (1) ◽  
pp. 428-434 ◽  
Author(s):  
I. David Abrahams ◽  
Gregory A. Kriegsmann ◽  
Edward L. Reiss
Keyword(s):  
Shear Flows ◽  
And Control ◽  
Elastic Surfaces

scholarly journals Lower Branch Coherent States in Shear Flows: Transition and Control

2007 ◽  
Vol 98 (20) ◽  
Author(s):  
Jue Wang ◽  
John Gibson ◽  
Fabian Waleffe
Keyword(s):  
Coherent States ◽  
Shear Flows ◽  
Lower Branch ◽  
And Control

scholarly journals Vortex formation and stability analysis for shear flows over combined spatially and temporally structured walls

1999 ◽  
Vol 5 (4) ◽  
pp. 317-328
Author(s):  
D. N. Riahi
Keyword(s):  
Stability Analysis ◽  
Wave Motion ◽  
Shear Flows ◽  
Multiple Scales ◽  
Vortex Formation ◽  
Periodic Disturbance ◽  
Theory Of Evolution ◽  
Longitudinal Vortices ◽  
Vortex Stability ◽  
And Control

Benney's theory of evolution of disturbances in shear flows over smooth and flat boundary is extended to study for shear flows over combined spatially and temporally corrugated walls. Perturbation and multiple-scales analyses are employed for the case where both amplitude of the corrugations and the amplitude of wave motion are small. Analyses for instability of modulated mean shear flows with respect to spanwise-periodic disturbance rolls and for the subsequent vortex formation and vortex stability are presented, and the effects of the corrugated walls on the resulting flow and vortices are determined. It is found that particular corrugated walls can originate and control the longitudinal vortices, while some other types of corrugated walls can enhance instability of such vortices.

On management and control of turbulent shear flows

1990 ◽  
Vol 27 (4) ◽  
pp. 305-387 ◽  
Author(s):  
H.E. Fiedler ◽  
H.-H. Fernholz
Keyword(s):  
Shear Flows ◽  
Turbulent Shear ◽  
Turbulent Shear Flows ◽  
And Control

scholarly journals Localised estimation and control of linear instabilities in two-dimensional wall-bounded shear flows

2017 ◽  
Vol 824 ◽  
pp. 818-865 ◽  
Author(s):  
H. J. Tol ◽  
M. Kotsonis ◽  
C. C. de Visser ◽  
B. Bamieh
Keyword(s):  
Shear Flows ◽  
Stokes Equations ◽  
Efficient Estimation ◽  
Single Frequency ◽  
Dimensional System ◽  
Two Dimensional ◽  
Sensor Noise ◽  
Wall Shear ◽  
Estimation And Control ◽  
And Control

A new framework is presented for estimation and control of instabilities in wall-bounded shear flows described by the linearised Navier–Stokes equations. The control design considers the use of localised actuators/sensors to account for convective instabilities in an ${\mathcal{H}}_{2}$ optimal control framework. External sources of disturbances are assumed to enter the control domain through the inflow. A new inflow disturbance model is proposed for external excitation of the perturbation modes that contribute to transition. This model allows efficient estimation of the flow perturbations within the localised control region of a conceptually unbounded domain. The state-space discretisation of the infinite-dimensional system is explicitly obtained, which allows application of linear control theoretic tools. A reduced-order model is subsequently derived using exact balanced truncation that captures the input/output behaviour and the dominant perturbation dynamics. This model is used to design an ${\mathcal{H}}_{2}$ optimal controller to suppress the instability growth. The two-dimensional non-periodic channel flow is considered as an application case. Disturbances are generated upstream of the control domain and the resulting flow perturbations are estimated/controlled using point wall shear measurements and localised unsteady blowing and suction at the wall. The controller is able to cancel the perturbations and is robust to both unmodelled disturbances and sensor inaccuracies. For single-frequency and multiple-frequency disturbances with low sensor noise a nearly full cancellation is achieved. For stochastic forced disturbances and high sensor noise an energy reduction in perturbation wall shear stress of 96 % is shown.

Control of Metal Alloy Oxidation with Electric Fields

1973 ◽  
Vol 31 ◽  
pp. 164-165
Author(s):  
R. R. Dils ◽  
P. S. Follansbee
Keyword(s):  
Electric Fields ◽  
Oxidation Process ◽  
Base Alloy ◽  
Oxide Surface ◽  
Platinum Electrodes ◽  
Insulating Layer ◽  
Iron Base Alloy ◽  
Alloy Oxidation ◽  
Aluminum Oxide Layer ◽  
And Control

Electric fields have been applied across oxides growing on a high temperature alloy and control of the oxidation of the material has been demonstrated. At present, three-fold increases in the oxidation rate have been measured in accelerating fields and the oxidation process has been completely stopped in a retarding field.The experiments have been conducted with an iron-base alloy, Pe 25Cr 5A1 0.1Y, although, in principle, any alloy capable of forming an adherent aluminum oxide layer during oxidation can be used. A specimen is polished and oxidized to produce a thin, uniform insulating layer on one surface. Three platinum electrodes are sputtered on the oxide surface and the specimen is reoxidized.

Evidence for a Blood Ganglion Barrier in the Superior Cervical Ganglion of the Rat

1982 ◽  
Vol 40 ◽  
pp. 204-204
Author(s):  
D. M. DePace
Keyword(s):  
Blood Vessels ◽  
Superior Cervical Ganglion ◽  
Peripheral Nerves ◽  
Time Schedule ◽  
Transmission Electron ◽  
Cervical Ganglion ◽  
The Central Nervous System ◽  
Cervical Ganglia ◽  
Capillary Circulation ◽  
And Control

The majority of blood vessels in the superior cervical ganglion possess a continuous endothelium with tight junctions. These same features have been associated with the blood brain barrier of the central nervous system and peripheral nerves. These vessels may perform a barrier function between the capillary circulation and the superior cervical ganglion. The permeability of the blood vessels in the superior cervical ganglion of the rat was tested by intravenous injection of horseradish peroxidase (HRP). Three experimental groups of four animals each were given intravenous HRP (Sigma Type II) in a dosage of.08 to.15 mg/gm body weight in.5 ml of.85% saline. The animals were sacrificed at five, ten or 15 minutes following administration of the tracer. Superior cervical ganglia were quickly removed and fixed by immersion in 2.5% glutaraldehyde in Sorenson's.1M phosphate buffer, pH 7.4. Three control animals received,5ml of saline without HRP. These were sacrificed on the same time schedule. Tissues from experimental and control animals were reacted for peroxidase activity and then processed for routine transmission electron microscopy.

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