Coherent Structures in Shallow Water Jets

2011 ◽  
Vol 133 (1) ◽  
Author(s):  
A.-M. Shinneeb ◽  
J. D. Bugg ◽  
R. Balachandar
Keyword(s):  
Coherent Structures ◽  
Horizontal Plane ◽  
Large Scale ◽  
Solid Wall ◽  
Vertical Wall ◽  
Vertical Plane ◽  
Vertical Direction ◽  
Particle Image Velocimetry System ◽  
Identification Algorithm ◽  
Vortical Structures

This paper reports an experimental investigation of a round jet discharging horizontally from a vertical wall into an isothermal body of water confined in the vertical direction by a flat wall on the bottom and a free surface on top. Specifically, this paper focuses on the effects of vertical confinement on the characteristics of large vortical structures. The jet exit velocity was 2.5 m/s, and the exit Reynolds number was 22,500. Experiments were performed at water layer depths corresponding to 15, 10, and 5 times the jet exit diameter (9 mm). The large-scale structures were exposed by performing a proper orthogonal decomposition (POD) analysis of the velocity field obtained using a particle image velocimetry system. Measurements were made on vertical and horizontal planes—both containing the axis of the jet. All fields-of-view were positioned at an axial location in the range 10<x/D<80. The number of modes used for the POD reconstruction of the velocity fields was selected to recover ∼40% of the turbulent kinetic energy. A vortex identification algorithm was then employed to quantify the size, circulation, and direction of rotation of the exposed vortices. A statistical analysis of the distribution of number, size, and strength of the identified vortices was carried out to explore the characteristics of the coherent structures. The results clearly reveal the existence of numerous vortical structures of both rotational senses in the jet flow, and their number generally decreases in the axial direction while their size increases. The size of vortices identified in the vertical plane is restricted by the water depth, while they are allowed to increase in size in the horizontal plane. Moreover, the results show a significant decrease in the number of small vortices for the shallowest case in the horizontal plane, with a corresponding increase in the number of large vortices and a significant increase in their size. This behavior was accompanied with an increase in the vortex circulation in the horizontal plane and a reduction in the circulation in the vertical plane. This is indicative of the dominance of the pairing process due to shallowness. Moreover, the balance between the positive and negative vortices in the vertical plane changed because of the formation of negative (clockwise) vortices near the solid wall at downstream locations.

scholarly journals Dielectric anisotropy as indicator of crystal orientation fabric in Dome Fuji ice core: method and initial results

2021 ◽  
pp. 1-12
Author(s):  
Tomotaka Saruya ◽  
Shuji Fujita ◽  
Ryo Inoue
Keyword(s):  
Crystal Orientation ◽  
Horizontal Plane ◽  
Ice Core ◽  
Vertical Plane ◽  
Vertical Direction ◽  
Core Sample ◽  
Dielectric Anisotropy ◽  
Principal Axes ◽  
Polycrystalline Ice ◽  
Initial Results

Abstract Polycrystalline ice is known to exhibit macroscopic anisotropy in relative permittivity (ɛ) depending on the crystal orientation fabric (COF). Using a new system designed to measure the tensorial components of ɛ, we investigated the dielectric anisotropy (Δɛ) of a deep ice core sample obtained from Dome Fuji, East Antarctica. This technique permits the continuous nondestructive assessment of the COF in thick ice sections. Measurements of vertical prism sections along the core showed that the Δɛ values in the vertical direction increased with increasing depth, supporting previous findings of c-axis clustering around the vertical direction. Analyses of horizontal disk sections demonstrated that the magnitude of Δɛ in the horizontal plane was 10–15% of that in the vertical plane. In addition, the directions of the principal axes of tensorial ɛ in the horizontal plane corresponded to the long or short axis of the elliptically elongated single-pole maximum COF. The data confirmed that Δɛ in the vertical and horizontal planes adequately indicated the preferred orientations of the c-axes, and that Δɛ can be considered to represent a direct substitute for the normalized COF eigenvalues. This new method could be extremely useful as a means of investigating continuous and depth-dependent variations in COF.

PIV Measurements of In-Cylinder Flow in a Four-Stroke Utility Engine and Correlation With Combustion Measurements

2004 ◽  
Author(s):  
Karen E. Bevan ◽  
Jaal B. Ghandhi
Keyword(s):  
Kinetic Energy ◽  
Horizontal Plane ◽  
Large Scale ◽  
Vertical Plane ◽  
Combustion Performance ◽  
Flow Parameters ◽  
Combustion Duration ◽  
Measurement Plane ◽  
Cylinder Flow ◽  
High Pass

Large-scale flows in internal combustion engines directly affect combustion duration and emissions production. The effect of intake port geometry on combustion performance was studied in a four-stroke spark-ignition utility engine. Three intake port geometries were investigated at three port orientations. In-cylinder flows in orthogonal planes were measured using particle image velocimetry (PIV). Combustion performance data were acquired at two load conditions and three equivalence ratios. The PIV data were processed to calculate the large-scale mean vorticity and mean high-pass filtered velocity. These flow parameters were used to characterize the in-cylinder flow in a measurement plane in a physically meaningful way and correlate the flow with combustion performance. The cumulative distribution functions of the flow parameters did not show significant port-to-port differences in either measurement plane. The mean vorticity and high-pass filtered velocity did exhibit differences due to port orientation in the horizontal plane, but not in the vertical plane. The 0-degree ports consistently produced the highest values of large-scale mean vorticity and mean high-pass filtered velocity in the horizontal plane. The kinetic energy present at ignition was also calculated to characterize the flow. The ensemble average values of the mean large-scale vorticity, high-pass filtered velocity and kinetic energy were compared to the combustion duration. The vertical plane vorticity and high-pass filtered velocity did not correlate with combustion performance. The horizontal plane vorticity and high-pass filtered velocity were found to exhibit modest correlation at the fixed torque condition, and somewhat lower correlation at the WOT condition. The correlation between kinetic energy and combustion duration was poor. The best correlation of flow field structure with engine performance was achieved for ports at the 0-degree port orientation. Ports at this orientation generated coherent, large-scale swirl.

Particle Image Velocimetry Measurements of In-Cylinder Flow in a Four-Stroke Utility Engine and Correlation With Combustion Measurements

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Karen E. Bevan ◽  
Jaal B. Ghandhi
Keyword(s):  
Kinetic Energy ◽  
Horizontal Plane ◽  
Large Scale ◽  
Particle Image ◽  
Vertical Plane ◽  
Combustion Performance ◽  
Combustion Duration ◽  
Image Velocimetry ◽  
The Mean ◽  
High Pass

Large-scale flows in internal combustion engines directly affect combustion duration and emission production. The effect of intake port geometry on combustion performance was studied in a four-stroke spark-ignition utility engine. Three intake port geometries were investigated at three port orientations. In-cylinder flows in orthogonal planes were measured using particle image velocimetry (PIV). The PIV data were processed to calculate the large-scale mean vorticity and mean high-pass filtered velocity. Combustion performance data were separately acquired at two load conditions at a fixed equivalence ratio, and compared with the PIV data. The cumulative distribution functions of the flow parameters did not show significant port-to-port differences in either measurement plane. The mean vorticity and high-pass filtered velocity did exhibit differences due to port orientation in the horizontal plane, but not in the vertical plane. The 0 deg ports (tangential orientation) consistently produced the highest values of large-scale mean vorticity and mean high-pass filtered velocity in the horizontal plane. The kinetic energy present at ignition was also calculated to characterize the flow. The ensemble-averaged values of the mean large-scale vorticity, high-pass filtered velocity, and kinetic energy were compared to the combustion duration. The vertical-plane vorticity and high-pass filtered velocity did not correlate with combustion performance. The horizontal-plane vorticity and high-pass filtered velocity were found to exhibit modest correlation at the fixed torque condition, and somewhat lower correlation at the wide open throttle condition. The correlation between kinetic energy and combustion duration was poor. The best correlation of flow field structure with engine performance was achieved for ports at the 0 deg port orientation. Ports at this orientation generated coherent, large-scale swirl.

scholarly journals A Prototype Orthogonal Vertical Beamforming for Indoor Wireless Communications

2021 ◽  
pp. 516-521
Author(s):  
Paleerat Wongchampa ◽  
Keyword(s):  
Error Rate ◽  
Horizontal Plane ◽  
Indoor Environment ◽  
Vertical Plane ◽  
Vertical Direction ◽  
Signal Interference ◽  
Packet Error Rate ◽  
Indoor Wireless ◽  
Orthogonal Property ◽  
Indoor Wireless Communications

The concept of Orthogonal Vertical Beamforming (OVB) is proposed in this paper to eliminate interference when users remain at the same angle in the horizontal plane but are positioned at different distances. This orthogonal property helps systems avoid interference in the vertical direction of the mainbeam. A fully constructed prototype tested in a real indoor environment validates the proposed concept, revealing that the proposed OVB provides higher Signal Interference plus Noise Ratio (SINR) and Packet Error Rate (PER) in the vertical plane than conventional vertical beamforming and Orthogonal Beamforming.

Coherent Structures of Turbulence: Methods of Eduction and Results

2006 ◽  
Vol 59 (6) ◽  
pp. 307-323 ◽  
Author(s):  
Giancarlo Alfonsi
Keyword(s):  
Coherent Structures ◽  
Coherent Structure ◽  
Large Scale ◽  
Mathematical Framework ◽  
Vortical Structures ◽  
Detection Techniques ◽  
Flow Phenomena ◽  
Definition Of ◽  
Inner Region ◽  
Proper Orthogonal

In this paper the issue of the coherent structures of turbulence developing in wall-bounded flows is addressed. After a short historical synthesis, some basic concepts are reviewed and the idea of coherent structure is introduced. The phenomena occurring in the inner and outer regions of the turbulent boundary layer in conjunction with the most widely used event-detection techniques are considered, with reference to the large amount of mainly experimental results existing on the subject. The flow phenomena are described in terms of events occurring in the inner region, large-scale motions developing in the outer layer and dynamics of vortical structures. In the second part of the paper, methods for the eduction of the coherent structures of turbulence from the background flow and results obtained in the framework of each method are presented. The techniques involving the invariants of the velocity gradient tensor, the analysis of the Hessian of the pressure and the proper orthogonal decomposition are considered. Each procedure involves a particular definition of coherent structure that is supported by an appropriate mathematical framework and permits the analysis of a turbulent-flow database in terms of dynamics of coherent structures. This work may contribute to the dissemination of the most recent concepts and techniques now in use in turbulence research among fluid dynamicists.

scholarly journals Millimeter-wave multi-mode circular antenna array for uni-cast multi-cast and OAM communication

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Stylianos D. Assimonis ◽  
Muhammad Ali Babar Abbasi ◽  
Vincent Fusco
Keyword(s):  
Antenna Array ◽  
Radiation Pattern ◽  
Data Transmission ◽  
Electromagnetic Waves ◽  
Horizontal Plane ◽  
Impedance Matching ◽  
Vertical Plane ◽  
Vertical Direction ◽  
Low Complexity ◽  
Circular Antenna Array

AbstractThis paper investigates uni-/multi-cast and orbital angular momentum (OAM) mode data transmission in orthogonal directions by the utilization of a new circular antenna array, operating at 28 GHz. In the horizontal plane the proposed antenna array operates as multimode transmitter (i.e., it provides broad-, uni- and/or multi-cast communication), while in the vertical direction OAM transmission occurs (i.e., it is capable of generating up to 15 spatially orthogonal OAM modes). Antenna array is designed using twelve, low-complexity, electromagnetically coupled microstrip patch antennas with high radiation efficiency. Each of these can transmit power of equivalent order of magnitude in both horizontal (i.e., broadside radiation pattern) and vertical direction (i.e., endfire radiation pattern) over electromagnetic waves of orthogonal electric components. This property leads to the formation of uni-/multi-cast and OAM modes in the horizontal plane and vertical direction, respectively. Antenna was tested through full-wave electromagnetic analysis and measurements in terms of impedance matching, mutual coupling and radiation pattern: good agreement between simulated and measurement results was observed. Specifically, it presents up to 8.65 dBi and 6.48 dBi realized gain under the uni-cast (in the horizontal plane) and OAM mode (in the vertical plane), respectively. The proposed antenna array is perfect candidate for high spectral efficiency data transmission for 5G and beyond wireless applications, where orthogonality in communication links and OAM multiplexing is a requirement.

scholarly journals Lagrangian coherent structures and entrainment near the turbulent/non-turbulent interface of a gravity current

2019 ◽  
Vol 877 ◽  
pp. 824-843 ◽  
Author(s):  
Marius M. Neamtu-Halic ◽  
Dominik Krug ◽  
George Haller ◽  
Markus Holzner
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Gravity Current ◽  
Three Dimensional ◽  
Lagrangian Coherent Structures ◽  
Flow Measurements ◽  
Vortical Structures ◽  
Entrainment Velocity ◽  
Extraction Algorithm ◽  
Entrainment Process

In this paper, we employ the theory of Lagrangian coherent structures for three-dimensional vortex eduction and investigate the effect of large-scale vortical structures on the turbulent/non-turbulent interface (TNTI) and entrainment of a gravity current. The gravity current is realized experimentally and different levels of stratification are examined. For flow measurements, we use a multivolume three-dimensional particle tracking velocimetry technique. To identify vortical Lagrangian coherent structures (VLCSs), a fully automated three-dimensional extraction algorithm for multiple flow structures based on the so-called Lagrangian-averaged vorticity deviation method is implemented. The size, the orientation and the shape of the VLCSs are analysed and the results show that these characteristics depend only weakly on the strength of the stratification. Through conditional analysis, we provide evidence that VLCSs modulate the average TNTI height, consequently affecting the entrainment process. Furthermore, VLCSs influence the local entrainment velocity and organize the flow field on both the turbulent and non-turbulent sides of the gravity current boundary.

Receptive Field Properties of Human Periodontal Afferents Responding to Loading of Premolar and Molar Teeth

2003 ◽  
Vol 89 (3) ◽  
pp. 1478-1487 ◽  
Author(s):  
Skjalg E. Johnsen ◽  
Mats Trulsson
Keyword(s):  
Horizontal Plane ◽  
Vertical Plane ◽  
Inferior Alveolar Nerve ◽  
Vertical Direction ◽  
Dental Arch ◽  
Posterior Teeth ◽  
Directional Bias ◽  
Mechanical Coupling ◽  
Molar Teeth ◽  
Stimulation Of

Impulses in 45 single mechanoreceptive afferents were recorded from the human inferior alveolar nerve with permucosally inserted tungsten microelectrodes. All afferents responded to mechanical stimulation of one or more premolar or molar teeth and most likely innervated their periodontal ligaments. For each afferent, isolated “ramp-and-hold” shaped force profiles of similar magnitudes (252 ± 24 mN; mean ± SD) were applied to the lower first premolar, the second premolar, and the first molar on the recording side. The tooth loads were applied in six directions: lingual, facial, mesial, and distal in the horizontal plane and up and down in the vertical direction of the tooth. The afferents response during the static phase of the stimulus was analyzed. All afferents were slowly adapting, discharging continuously in response to static forces in at least one stimulation direction. Twenty-nine afferents (64%) were spontaneously active, exhibiting an ongoing discharge in the absence of external stimulation. Stimulation of a single tooth was found to excite each afferent most strongly. The most sensitive tooth (MST) was the first premolar for 23, the second premolar for 13, and the first molar for 9 afferents. About half of the afferent population also responded to loading of one or two more teeth. The response profiles of these afferents indicated that the multiple-teeth receptive fields were due to mechanical coupling between the teeth rather than branching of single afferents to innervate several teeth. The afferent responses to loading the mesial and distal halves of the first molars were very similar. Thus both intensive and directional aspects of the afferent response when loading one side of the tooth was preserved to a great extent when loading the other side. When loading the MST, the afferents typically showed excitatory responses in two to four of the six stimulation directions, i.e., the afferents were broadly tuned to direction of tooth loading. In the horizontal plane, the afferent populations at the premolar teeth expressed no clear directional preferences. The afferents at the molar, however, showed a strong directional bias in the distal-lingual direction. In the vertical plane, there was a preference for downward-directed forces with a gradually decreasing sensitivity distally along the dental arch. The present results demonstrate that human periodontal afferents supplying anterior and posterior teeth differ in their capacity to signal horizontal and vertical forces, respectively.

scholarly journals Interaction of Very Large Scale Motion of Coherent Structures with Sediment Particle Exposure

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 248
Author(s):  
Sencer Yücesan ◽  
Daniel Wildt ◽  
Philipp Gmeiner ◽  
Johannes Schobesberger ◽  
Christoph Hauer ◽  
...  
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Numerical Study ◽  
Local Maximum ◽  
Wave Number ◽  
Exposure Level ◽  
Sediment Particle ◽  
High Wave Number ◽  
Large Scale Motion ◽  
Scale Motion

A systematic variation of the exposure level of a spherical particle in an array of multiple spheres in a high Reynolds number turbulent open-channel flow regime was investigated while using the Large Eddy Simulation method. Our numerical study analysed hydrodynamic conditions of a sediment particle based on three different channel configurations, from full exposure to zero exposure level. Premultiplied spectrum analysis revealed that the effect of very-large-scale motion of coherent structures on the lift force on a fully exposed particle resulted in a bi-modal distribution with a weak low wave number and a local maximum of a high wave number. Lower exposure levels were found to exhibit a uni-modal distribution.

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