Theory and observations of waves on hollow-core vortices

1980 ◽  
Vol 99 (3) ◽  
pp. 495-511 ◽  
Author(s):  
Jakob J. Keller ◽  
M. P. Escudier
Keyword(s):  
Vortex Tube ◽  
Capillary Wave ◽  
Standing Waves ◽  
Wave Pattern ◽  
Interesting Case ◽  
Hollow Core ◽  
Core Size ◽  
Viscous Effects ◽  
Wave Problem ◽  
The Core

A linear non-homogeneous analysis is presented for the standing waves produced on the hollow core of an irrotational vortex by an arbitrary obstacle on the wall of the tube containing the vortex. The group-velocity criterion based upon Kelvin's corresponding dispersion relation predicts whether a certain asymptotic wave pattern appears upstream or downstream of the obstacle. The analysis leads to amplitude singularities for the standing waves at certain critical radii of the core. The particularly interesting case of a counter-helix for which the wave energy is propagating upstream appears for a first-mode angular disturbance. For this situation it seems to be possible that the helix ends in a hydraulic jump and is continued by a counter-helix downstream, as the core size gradually diminishes due to the deceleration of the flow caused by viscous effects (not included in the analysis). The capillary-wave pattern produced by surface tension is also considered. A brief outline for the analogous wave problem is given for the case where the fluid rotates like a rigid body.Photographic observations of hollow-core vortices in water flow are presented which confirm the qualitative predictions of the analysis, both for the response to an axisymmetric area contraction and also to a 90° bend at the downstream end of the vortex tube.

scholarly journals Geometrical Scaling of Antiresonant Hollow-Core Fibers for Mid-Infrared Beam Delivery

Crystals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 420
Author(s):  
Ang Deng ◽  
Wonkeun Chang
Keyword(s):  
Structural Parameters ◽  
Transmission Band ◽  
Confinement Loss ◽  
Hollow Core ◽  
Core Size ◽  
Core Diameter ◽  
Mid Infrared ◽  
The Core ◽  
Tubular Type ◽  
Beam Delivery

We numerically investigate the effect of scaling two key structural parameters in antiresonant hollow-core fibers—dielectric wall thickness of the cladding elements and core size—in view of low-loss mid-infrared beam delivery. We demonstrate that there exists an additional resonance-like loss peak in the long-wavelength limit of the first transmission band in antiresonant hollow-core fibers. We also find that the confinement loss in tubular-type hollow-core fibers depends strongly on the core size, where the degree of the dependence varies with the cladding tube size. The loss scales with the core diameter to the power of approximately −5.4 for commonly used tubular-type hollow-core fiber designs.

Nondestructive determination of the core size of a hollow-core photonic bandgap fiber using Fabry–Perot interference

2018 ◽  
Vol 43 (13) ◽  
pp. 3045 ◽  
Author(s):  
Xiaobin Xu ◽  
Xiaoyang Wang ◽  
Taotao Zhu ◽  
Fuyu Gao ◽  
Ningfang Song
Keyword(s):  
Photonic Bandgap ◽  
Hollow Core ◽  
Core Size ◽  
Photonic Bandgap Fiber ◽  
Nondestructive Determination ◽  
The Core ◽  
Fabry Perot

scholarly journals Characteristic Analysis and Structural Design of Hollow-Core Photonic Crystal Fibers with Band Gap Cladding Structures

Sensors ◽  
2021 ◽  
Vol 21 (1) ◽  
pp. 284
Author(s):  
Bowei Wan ◽  
Lianqing Zhu ◽  
Xin Ma ◽  
Tianshu Li ◽  
Jian Zhang
Keyword(s):  
Photonic Crystal ◽  
Band Gap ◽  
Photonic Crystal Fibers ◽  
Relative Sensitivity ◽  
Confinement Loss ◽  
Hollow Core ◽  
Characteristic Analysis ◽  
Element Analysis ◽  
The Core ◽  
Crystal Fibers

Due to their flexible structure and excellent optical characteristics hollow-core photonic crystal fibers (HC-PCFs) are used in many fields, such as active optical devices, communications, and optical fiber sensing. In this paper, to analyze the characteristics of HC-PCFs, we carried out finite element analysis and analyzed the design for the band gap cladding structure of HC-PCFs. First, the characteristics of HC19-1550 and HC-1550-02 in the C-band were simulated. Subsequently, the structural optimization of the seven-cell HC-1550-02 and variations in characteristics of the optimized HC-1550-02 in the wavelength range 1250–1850 nm were investigated. The simulation results revealed that the optimal number of cladding layers is eight, the optimal core radius is 1.8 times the spacing of adjacent air holes, and the optimal-relative thickness of the core quartz-ring is 2.0. In addition, the low confinement loss bandwidth of the optimized structure is 225 nm. Under the transmission bandwidth of the optimized structure, the core optical power is above 98%, the confinement loss is below 9.0 × 10−3 dB/m, the variation range of the effective mode field area does not exceed 10 μm2, and the relative sensitivity is above 0.9570. The designed sensor exhibits an ultra-high relative sensitivity and almost zero confinement loss, making it highly suitable for high-sensitivity gas or liquid sensing.

scholarly journals The hourglass effect in hierarchical dependency networks

2017 ◽  
Vol 5 (4) ◽  
pp. 490-528 ◽  
Author(s):  
KAESER M. SABRIN ◽  
CONSTANTINE DOVROLIS
Keyword(s):  
Low Complexity ◽  
Core Size ◽  
Original Network ◽  
Hierarchical Network ◽  
Modular Systems ◽  
The Core ◽  
Dependency Networks ◽  
Dependency Network ◽  
Hierarchical Dependency ◽  
Almost All

AbstractMany hierarchically modular systems are structured in a way that resembles an hourglass. This “hourglass effect” means that the system generates many outputs from many inputs through a relatively small number of intermediate modules that are critical for the operation of the entire system, referred to as the waist of the hourglass. We investigate the hourglass effect in general, not necessarily layered, hierarchical dependency networks. Our analysis focuses on the number of source-to-target dependency paths that traverse each vertex, and it identifies the core of a dependency network as the smallest set of vertices that collectively cover almost all dependency paths. We then examine if a given network exhibits the hourglass property or not, comparing its core size with a “flat” (i.e., non-hierarchical) network that preserves the source dependencies of each target in the original network. As a possible explanation for the hourglass effect, we propose the Reuse Preference model that captures the bias of new modules to reuse intermediate modules of similar complexity instead of connecting directly to sources or low complexity modules. We have applied the proposed framework in a diverse set of dependency networks from technological, natural, and information systems, showing that all these networks exhibit the general hourglass property but to a varying degree and with different waist characteristics.

scholarly journals Swirling Flows Characteristics in a Cylinder Under Effect of Buoyancy

Mechanika ◽  
2021 ◽  
Vol 27 (3) ◽  
pp. 201-208
Author(s):  
Mustafa FEKHAR ◽  
Rachid SACI ◽  
Renée GATIGNOL
Keyword(s):  
Aspect Ratio ◽  
Thermal Stratification ◽  
Flow Behavior ◽  
Flow Characteristics ◽  
Swirling Flows ◽  
Viscous Effects ◽  
Thermal Buoyancy ◽  
State Diagrams ◽  
The Core ◽  
Flow Stagnation

Thermal buoyancy, induced by injection or by differential heating of a tiny rod is explored to control breakdown in the core of a helical flow driven by the lid rotation of a cylinder. Three main parameters are required to characterize numerically the flow behavior; namely, the rotational Reynolds number Re, the cavity aspect ratio and the Richardson number Ri. Warm injection/rod, Ri > 0, is shown to prevent on-axis flow stagnation while breakdown enhancement is evidenced when Ri < 0. Results revealed that a bubble vortex evolves into a ring type structure which may remain robust, as observed in prior related experiments or, in contrast, disappear over a given range of parameters (Λh, Re, Ri > 0). Besides, the emergence of such a toroidal mode was not found to occur under thermal stratification induced by a differentially heated rod. Moreover, three state diagrams were established which provide detailed flow characteristics under the distinct and combined effects of buoyancy strength, viscous effects and cavity aspect ratio.

scholarly journals All-fiber passively Q-switched ytterbium doped double-clad fiber lasers: experiment And modeling.

2021 ◽  
Author(s):  
Yi Lu
Keyword(s):  
Pulse Energy ◽  
Traveling Wave ◽  
Pulse Width ◽  
Fiber Lasers ◽  
Peak Power ◽  
Wave Model ◽  
Core Size ◽  
The Core ◽  
Q Switching ◽  
Output Characteristics

All-fiber passively Q-switched lasers were demonstrated using ytterbium-doped double cladding fiber (YDF) as an active medium. The laser was pumped by three 25W, 975nm fiber coupled diodes and Q-switching was initiated when the amplified spontaneous emission generated in the core of the gain fiber bleached the saturable absorber (SA). A piece of samarium-doped fiber was used as SA in first configuration and pulses with 68μJ pulse energy and 210ns pulse width were obtained. In second configuration, a piece of ytterbium-doped fiber with much smaller core size was used as SA to produce pulse energy of 86μJ. The last configuration incorporated a 9m-long YDF as gain fiber. The far end from pump was acting as SA in this case and pulses with 82μJ pulse energy and 148ns pulse width were observed. The peak power was estimated at 554W. Traveling wave model was implemented to numerically simulate the output characteristics versus pump power.

The semi-analytic theory of standing waves

1987 ◽  
Vol 411 (1840) ◽  
pp. 123-137 ◽  
Keyword(s):  
Numerical Calculation ◽  
Power Series ◽  
Deep Water ◽  
Standing Waves ◽  
Affirmative Answer ◽  
Rigorous Proof ◽  
Series Solutions ◽  
Wave Problem ◽  
Power Series Solutions ◽  
Formal Power

The algorithm proposed by Schwartz & Whitney ( J. Fluid Mech . 107, 147–171 (1981)) for the numerical calculation of formal power series solutions of the classical standing-wave problem is vindicated by a rigorous proof that resonances do not occur in the calculations. A detailed account of a successful algorithm is given. The analytical question of the convergence of the power series whose coefficients have been calculated remains open. An affirmative answer would be a first demonstration of the existence of standing waves on deep water.

Solution-Responsive Particle Size Adaptivity in Lagrangian Vortex Particle Methods

2021 ◽  
Author(s):  
Mark J. Stock ◽  
Adrin Gharakhani
Keyword(s):  
Particle Size ◽  
Particle Method ◽  
Adaptive Method ◽  
Particle Methods ◽  
Core Size ◽  
Large Particle Size ◽  
The Core ◽  
Vortex Particle Method ◽  
Computational Resources ◽  
Vortex Particle

Abstract In order to minimize the computational resources necessary for a given level of accuracy in a Lagrangian Vortex Particle Method, a novel particle core size adaptivity scheme has been created. The method adapts locally to the solution while preventing large particle size gradients, and optionally adapts globally to focus effort on important regions. It is implemented in the diffusion solver, which uses the Vorticity Redistribution Method, by allowing and accounting for variations in the core radius of participating particles. We demonstrate the effectiveness of this new method on the diffusion of a δ-function and impulsively started flow over a circular cylinder at Re = 9,500. In each case, the adaptive method provides solutions with marginal loss of accuracy but with substantially fewer computational elements.

Core@shell nanostructured Au-d@NimPtm for electrochemical oxygen reduction reaction: effect of the core size and shell thickness

2019 ◽  
Vol 9 (17) ◽  
pp. 4668-4677 ◽  
Author(s):  
Min Zhang ◽  
Shu Miao ◽  
Bo-Qing Xu
Keyword(s):  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Shell Thickness ◽  
Reduction Reaction ◽  
Core Shell ◽  
Core Size ◽  
The Core ◽  
Electrocatalytic Performance ◽  
Electrochemical Oxygen

Au-d@NimPtm nanostructures are studied to address the effects of the Au-core size (d) and NiPt-shell thickness (m) on the electrocatalytic performance of Pt for the ORR.

scholarly journals Clouds, cores, and stars in the nearest molecular complexes

1991 ◽  
Vol 147 ◽  
pp. 221-228
Author(s):  
P. C. Myers
Keyword(s):  
Column Density ◽  
Velocity Dispersion ◽  
Molecular Complexes ◽  
Star Cluster ◽  
The Sun ◽  
Core Size ◽  
Core Mass ◽  
The Core ◽  
Internal Motions ◽  
Over Time

The properties and structure of six molecular complexes within 500 pc of the Sun are described and compared. They are generally organized into elongated filaments which appear connected to less elongated, more massive clouds. Their prominent star clusters tend to be located in the massive clouds rather than in the filaments. The complexes have similar structure, but big differences in scale, from a few pc to some 30 pc. They show a pattern of regional virial equilibrium, where the massive, centrally located clouds are close to virial equilibrium, while the less massive filaments and other small clouds have too little mass to bind their observed internal motions. Complexes can be ranked according to increasing size, mass, core mass, and the mass and number of the associated stars: they range from Lupus to Taurus to Ophiuchus to Perseus to Orion B to Orion A. The cores in nearby complexes tend to have maps which are elongated, rather than round. The core size, velocity dispersion, and column density of most cores are consistent with virial equilibrium. Cores in Orion tend to exceed cores in Taurus in their line width, size, temperature, mass, and in the mass of the associated star, if any. Stars in Orion tend to be more numerous and more massive than in Taurus, while those in Taurus tend to be more numerous and more massive than in Lupus. The mass of a core tends to increase with the mass of the cloud where it is found, with the mass of the star cluster with which it is associated, and with its proximity to a star cluster. These properties suggest that complexes and their constituent cores and clusters develop together over time, perhaps according to the depth of the gravitational well of the complex.

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