Wyniki wyszukiwania - BazTech

1

Coherent structures around submerged circular and square cylinders due to change of orientation angle in steady current over plane bed

Bauri Krishna Pada

Acta Geophysica

|

2022

|

Vol. 70, no 5

2223--2250

EN

The investigation of the bursting process and coherent structures around circular and square cylindrical structures for various angular alignments over a rigid plane bed are introduced. The coherent structures and shear stresses perform a substantial characteristic in bed particle entrainment and transport from the bed around these structures. Hence, bed shear stress, power spectra are determined from the measured velocity data, in addition, third-order correlation, turbulence intensity, and kinetic energy were investigated using quadrant analysis to explore the correlation between coherent structures and sediment movement. Turbulent coherent structures due to the variations of submergence depth, velocity, orientation angle of the square cylinder, and cylinder size are also investigated. Further, the measured velocity data using Acoustic Doppler Velocimeter were validated with numerical simulations using COMSOL Multiphysics 5.0 with k-ω turbulence closure model. Outcomes indicate that the wake zone length rises with the rise of submergence ratio for the square cylinder with different angular alignments than the circular and square cylindrical structures. Bed shear stress is higher for the square cylinder with different angular alignments than the circular cylinder. The wake vortex strength increases with angular alignment signifying excessive movement of bed sediments from the bed around the cylindrical structures. The interaction events predominate near the bed and middle height of the cylinder, whereas ejection and sweep events dominate far away from the bottom toward the top of the cylinders. The stress fraction is maximum for square cylinders with higher alignment angles.

2

Mixing process in opposing fow junction with diferent angles and junction radii

Mahmodinia Sharareh, Javan Mitra

Acta Geophysica

|

2020

|

Vol. 68, no. 3

795--809

EN

Opposing fow junctions are considered as important elements in thermal and hydraulic equipment. This study numerically investigates the efects of angles and junction radii on coherent fow structures at opposing fow junctions with subcritical conditions. Hence, the three-dimensional unsteady Reynolds-averaged Navier–Stokes equations are solved with the k–ε turbulence model on a non-staggered grid using the indirect addressing treatment. After the verifcation of the numerical model, several numerical simulations are conducted for angles 35°, 40°, 45°, 50°, 60°, 70°, 80°, and 90° with diferent upstream Froude numbers and junction radii. The streamwise-oriented vortical cells only elongate into the branch channel of the opposing fow junction with angle 90°. By decreasing the angle between the main channel and confuent tributary, these cells decay in the main channel width, and one of the separation zones is gradually eliminated, as that does not form in the opposing fow junctions with angle 40°. The enhancement of junction radii decreases the dimensions of the separation and stagnation zones. Numerical simulation results of a curved-edge opposing fow junction with angle 80° indicate that any of the streamwise-oriented vortical cells in the main channel and separations zones in the branch channel are not formed. In such a condition, three vortical cells formed along the branch without decay, two cells are located near the side wall, and another cell is near the free surface.

3

Efekt przepływu elektrolitu na topografię powierzchni w obróbce elektrochemicznej (ECM)

Kozak J.

Inżynieria Powierzchni

|

2016

|

Nr 4

18--22

PL

Obróbka elektrochemiczna (ECM) należy do efektywnych sposobów kształtowania elementów o skomplikowanej geometrii z materiałów trudno skrawalnych. W artykule przedstawiono badania wpływu hydrodynamiki elektrolitu na topografię powierzchni obrobionej. Omówiono problem powstawania defektów hydrodynamicznych na powierzchni anody wywołanych niestabilnością hydrodynamiczną i tworzeniem się struktur koherentnych w warstwie przyściennej, co może prowadzić do swoistego rezonansu hydro-elektrochemicznego.

EN

Electro-Chemical Machining (ECM) is one of the effective ways of shaping parts with complex geometries from difficult-to-machine materials. This article presents a study on the influence of the hydrodynamics of electrolyte on the topography of the surface finish. It discusses the problem of the formation of hydrodynamic defects on the surface of the anode induced by hydrodynamic instability and the formation of coherent structures in the boundary layer, which may lead to a specific hydro-electrochemical resonance.

4

Application of time-frequency analysis for identification of overvoltages in medium voltage cable lines

Skomudek W.

Przegląd Elektrotechniczny

|

2008

|

R. 84, nr 11

240-242

EN

In this paper presentation the result of application of time-frequency of the measured overvoltages applies short time Fourier transform and continuous wavelet transform. The analysis based on the Fourier transform renders it possible to extract the information regarding its spectrum variance in time domain from the noise. The results gained from the application of the above analysis give the grounds of the identification of overvoltages on the basis of the frequency patterns.

PL

W artykule przedstawiono wyniki zastosowania analizy czasowo-częstotliwościowej do identyfikacji i charakterystyki przepięć występujących w liniach kablowych średniego napięcia. Wyniki jakie uzyskano stosując opisane analizy pozwalają na rozpoznawanie przepięć poprzez struktury częstotliwościowe.