scholarly journals Instability of a homogeneous flow from a lumped source in the presence of special boundary conditions on a free surface

2019 ◽  
Vol 213 ◽  
pp. 02074 ◽  
Author(s):  
Anastasia Shmyrova ◽  
Andrey Shmyrov
Keyword(s):  
Boundary Conditions ◽  
Vortex Flow ◽  
Hydrodynamic Instability ◽  
Experimental Studies ◽  
Spatial Separation ◽  
Surface Flow ◽  
Water Volume ◽  
Reverse Situation ◽  
Surface Active ◽  
Upper Boundary

In this work, experimental studies were carried out to investigate the structure of a surface flow and to understand potential mechanisms leading to the formation of this type instability. The surface flow was generated by feeding water through three sources: a lumped source with free upper boundary, a slot gap, and a lumped source for inducing a capillary-driven Marangoni flow. For flow visualization, a traditional light knife technique was used. The application of a method of spatial separation of the water volume into two isolated parts whose common surface remained unchanged and the realization of a reverse situation with a divided surface made it possible to study in detail the surface flow structure and to determine the conditions for the appearance of such hydrodynamic instability. It is shown that the formation of a vortex flow is caused by the interaction between the coordinate of the flow homogeneous along the transverse flow and the layer of a surface-active substance adsorbed at the interface. The obtained experimental results demonstrate the importance of setting different boundary conditions for potential and vortex velocity components of a convective flow in the region near the interface occupied by a surfactant.

Experimental study of liquid movement in free elementary convective cells

Energetika ◽  
2015 ◽  
Vol 61 (2) ◽  
Author(s):  
Liudmyla Bozbiei ◽  
Boris Borts ◽  
Yuri Kazarinov ◽  
Andrey Kostikov ◽  
Viktor Tkachenko
Keyword(s):  
Mass Transfer ◽  
Boundary Conditions ◽  
Solid Wall ◽  
Large Diameter ◽  
Experimental Studies ◽  
Maximum Velocity ◽  
A Cell ◽  
Convective Cells ◽  
Liquid Movement ◽  
Upper Boundary

Elementary convection cells (ECC) are formed in horizontal layers of liquid heated from below, and they are experimentally investigated in this work. Results of experimental studies were adequately described by the theoretical model of ECC. It is shown that the addition of aluminum powder to oil transforms oil to a suspension, such that boundary conditions on the solid wall can be regarded as free because there is a slip through the tape of pure oil. Change in the character of boundary conditions is confirmed by the results of numerical processing of experimental results on formation of convective rings on the layer surface by other authors. Two independent methods for determining the velocity of mass transfer in cells with various diameters are described in the article. For cells with a large diameter (17 mm), the maximum velocity of mass transfer was measured at the upper boundary on a deflection angle of the probe. Measured in this way velocity was equal to V<sub>Oil</sub> ≈ 0.2 mm/sec. For cells with a smaller diameter (2 mm), the velocity of oil on the surface of a cell was measured using an optical method and constituted the value from 3.5 mm/s to 5.2 mm/s.

Analysis of Polygonal Vortex Flows in a Cylinder with a Rotating Bottom

2021 ◽  
Vol 11 (3) ◽  
pp. 1348
Author(s):  
A. Rashkovan ◽  
S.D. Amar ◽  
U. Bieder ◽  
G. Ziskind
Keyword(s):  
Experimental Studies ◽  
Free Surface Flow ◽  
Careful Analysis ◽  
Numerical Approach ◽  
Surface Flow ◽  
Initial Water ◽  
Eddy Simulation ◽  
Disk Rotation ◽  
Inner Radius ◽  
Liquid Flows

The present paper provides a physically sound numerical modeling of liquid flows experimentally observed inside a vertical circular cylinder with a stationary envelope, rotating bottom and open top. In these flows, the resulting vortex depth may be such that the rotating bottom disk becomes partially exposed, and rather peculiar polygon shapes appear. The parameters and features of this work are chosen based on a careful analysis of the literature. Accordingly, the cylinder inner radius is 145 mm and the initial water height is 60 mm. The experiments with bottom disk rotation frequencies of 3.0, 3.4, 4.0 and 4.6 Hz are simulated. The chosen frequency range encompasses the regions of ellipse and triangle shapes as observed in the experimental studies reported in the literature. The free surface flow is expected to be turbulent, with the Reynolds number of O(105). The Large Eddy Simulation (LES) is adopted as the numerical approach, with a localized dynamic Subgrid-Scale Stresses (SGS) model including an energy equation. Since the flow obviously requires a surface tracking or capturing method, a volume-of-fluid (VOF) approach has been chosen based on the findings, where this method provided stable shapes in the ranges of parameters found in the corresponding experiments. Expected ellipse and triangle shapes are revealed and analyzed. A detailed character of the numerical results allows for an in-depth discussion and analysis of the mechanisms and features which accompany the characteristic shapes and their alterations. As a result, a unique insight into the polygon flow structures is provided.

Upper Boundary Conditions for Overland Flow

1990 ◽  
Vol 116 (7) ◽  
pp. 951-957 ◽  
Author(s):  
J. L. M. P. de Lima ◽  
P. J. J. F. Torfs
Keyword(s):  
Boundary Conditions ◽  
Overland Flow ◽  
Upper Boundary

scholarly journals Development of effective methods and means of normalizing the atmosphere of working zones of open-cast mines

2020 ◽  
Vol 34 ◽  
pp. 29-40
Author(s):  
V. Nalyvaiko ◽  
V. Konovaliuk
Keyword(s):  
Experimental Studies ◽  
Negative Temperature ◽  
Water Jet ◽  
Lower Atmosphere ◽  
Water Volume ◽  
Irrigation Systems ◽  
Harmful Substances ◽  
Technical Solutions ◽  
Open Cast ◽  
Air Exchange

The search for technical solutions for effective air exchange in the space of deep open-cast mines. Since intensive air exchange is necessary to remove and disperse harmful impurities from the open-cast mines, improvement can be achieved mainly by intensifying natural air exchange based on phase transformations of liquids in the lower atmosphere of the working zones of the open-cast mines by creating a positive or negative temperature gradient. New technical solutions are considered that provide support for the sanitary-hygienic parameters of the atmosphere of the deep open-cast mines at the normative level. The formation of an ascending gas stream by a cascade explosion of a fuel-air mixture has the greatest efficiency. The proposed method allows for the implementation of a pulsed ventilation mode with a power of the outgoing air flow of more than 1010 W with a blasting fuel mass of 30 tons. It has been established by analytical and experimental studies that it is advisable to use pulsed fine irrigation systems to intensify air exchange in a deep open-cast mines, using the double effect, ventilating gaseous working zones and cleaning them from harmful substances with the help of a fine aerosol freely floating in space. It is also advisable to use such facilities to reduce peak loads on emissions of harmful substances from the open-cast mines into the environment and to normalize the composition of the atmosphere of the deep open-cast mines. Significant peak emissions of harmful impurities in open-cast mines include mass explosions and situations involving the creation of internal inversion zones. In a computational experiment, there are two water guns: big gun (the water jet range is 200 m, water volume per one cycle is 1000 dm3) and small gun(the water jet range is 100 m, water volume per one cycle is 200 dm3). The results of the experiment indicate greater efficiency in the use of a large water gun for airing the lower horizons of the deep open-cast mines. The use of pulsed fine irrigation systems will allow for carrying out internal technological work at a depth of more than 500 meters using a motorized ore delivery system to transfer points of cyclic-flow technology.

The mixed spectral finite-difference (MSFD) model: Improved upper boundary conditions

1995 ◽  
Vol 75 (4) ◽  
pp. 353-380 ◽  
Author(s):  
Stephen R. Karpik ◽  
John L. Walmsley ◽  
Wensong Weng
Keyword(s):  
Finite Difference ◽  
Boundary Conditions ◽  
Upper Boundary

A Study of the Hydroelastic Instabilities of Supercavitating Hydrofoils

1960 ◽  
Vol 4 (04) ◽  
pp. 28-38
Author(s):  
Paul Kaplan ◽  
C. J. Henry
Keyword(s):  
Dynamic Instability ◽  
Experimental Studies ◽  
Surface Flow ◽  
Small Range ◽  
Equal Importance ◽  
Static Instability ◽  
Elastically Restrained ◽  
Density Ratios ◽  
Oscillating Foil ◽  
Stream Direction

Presented herein are the results of a theoretical study of the static and dynamic hydroelastic instabilities of rigid supercavitating hydrofoils on elastic supports. A two-dimensional theory is used to define the unsteady hydrodynamic force and moment acting on the oscillating foil, which is assumed to be elastically restrained in translation normal to the free-stream direction and in rotation about a prescribed axis which is normal to the plane of flow. All other motions are neglected. The effects of variation in the elastic and inertial properties, as well as the effect of varying the position of the upper surface flow-separation point on the possibility of either form of instability, are determined. Also, the effect of cavitation number over a small range near zero is hypothesized. The theory predicts that dynamic instability (bending-torsion flutter) is possible at the density ratios typical of supercavitating operation. This is in contrast to the results for fully-wetted flow, where the occurrence of flutter is unlikely at the structural-to-fluid density ratios typical of hydrodynamic operation. The flutter possible in supercavitated operation is also more severe than that indicated for fully-wetted flow. Furthermore, it is shown that for the supercavitating hydrofoil, static instability (torsional divergence) and dynamic instability are of equal importance which again differs from the results in fully-wetted flow where static instability was shown to be the more important practical problem. Recommendations are made for experimental studies to verify these theoretical results.

The matching effect of anthropomorphized brand roles and product messaging on product attitude

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Yuanqiong He ◽  
Qi Zhou ◽  
Shuojia Guo ◽  
Jie Xiong
Keyword(s):  
Boundary Conditions ◽  
Experimental Studies ◽  
Underlying Mechanism ◽  
Mediation Effect ◽  
Processing Fluency ◽  
Mechanism Study ◽  
Matching Effect ◽  
Content Type ◽  
Construal Levels ◽  
Peripheral Locus

PurposeThis study aims to investigate the construal congruence of anthropomorphized brand roles and product messaging and its underlying mechanism on consumers' product attitude.Design/methodology/approachFour experimental studies were conducted to test the hypotheses. Study 1 investigated the framing effect of anthropomorphized brand roles (servant vs partner) in consumers' minds. Study 2 examined the matching effect of anthropomorphized brand roles and product messaging on product attitude. 132 students were randomly assigned to a 2 (anthropomorphized roles: servant vs partner) × 2 (product messaging: higher-level construal vs lower-level construal) between-subject factorial design. Study 3 tested the mediation effect of processing fluency underlying the construal congruence mechanism. Study 4 replicated the results of study 3 and further examined the boundary conditions by introducing product innovation locus as a moderator. A total of 218 students were randomly assigned to a 2 (anthropomorphized role: servant vs partner) × 2 (product messaging: higher-level construal vs lower-level construal) × 2 (innovation locus: core innovation vs peripheral locus) between-subjects design experiment.FindingsThe results demonstrate that a construal match between product messaging and anthropomorphized brand roles –anthropomorphized “servant” with higher-level construal messaging and anthropomorphized “partner” with lower-level construal messaging – can positively influence consumers' attitude via enhanced processing fluency. Furthermore, this construal matching effect on product attitude is moderated by the innovation locus of the product.Practical implicationsThis study reveals that anthropomorphized brand roles with compatible product messaging in the associated construal levels lead to more favorable product attitudes. Furthermore, the matching effect of anthropomorphized brand roles and product messaging is stronger for products with peripheral innovation than with core innovation.Originality/valueOur study contributes to the literature in two ways. First, it provides new insights into the construal matching effect of anthropomorphized brand roles and product messaging. Second, it investigates the boundary conditions of the above-mentioned construal fit mechanism.

Computation of the Surface Materials Modification by Plasma Technology

2020 ◽  
Vol 897 ◽  
pp. 106-110
Author(s):  
Alexey M. Lykov ◽  
Nataliya V. Mokrova
Keyword(s):  
Boundary Conditions ◽  
Surface Treatment ◽  
Experimental Studies ◽  
Design Parameters ◽  
Plasma Technology ◽  
Plasma Surface ◽  
Treatment Processes ◽  
Plasma Surface Treatment ◽  
Experimental Values ◽  
Thermal Influence

Experimental studies of plasma surface treatment processes of various materials are difficult since temperatures of the surface are more than 1500-3000 K, the speed of their change is high (104 K/s), the front of melting is moving. Theoretical researches of the thermal modes are necessary for conducting plasma processes in the best possible way. The use of analytical decisions at impulse thermal influence on the surface allows to calculate temperatures on the surfaces and in the mass of the material under almost any boundary conditions. The paper presents the results of calculation of various plasma processing at dielectric and steel materials (hardening, welding), as well as comparison of the obtained design parameters with experimental values.

Numerical Simulation of Nonlinear Water Wave Propagation Over Rippled Bed

2007 ◽  
Author(s):  
Gerasimos A. Kolokythas ◽  
Athanassios A. Dimas
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Water Waves ◽  
Stokes Equations ◽  
Surface Flow ◽  
Surface Boundary ◽  
Computational Domain ◽  
Time Step ◽  
Outflow Boundary ◽  
Rippled Bed

In the present study, numerical simulations of the free-surface flow, developing by the propagation of nonlinear water waves over a rippled bottom, are performed assuming that the corresponding flow is two-dimensional, incompressible and viscous. The simulations are based on the numerical solution of the Navier-Stokes equations subject to the fully-nonlinear free-surface boundary conditions and the suitable bottom, inflow and outflow boundary conditions. The equations are properly transformed so that the computational domain becomes time-independent. For the spatial discretization, a hybrid scheme with finite-differences and Chebyshev polynomials is applied, while a fractional time-step scheme is used for the temporal discretization. A wave absorption zone is placed at the outflow region in order to efficiently minimize reflection of waves by the outflow boundary. The numerical model is validated by comparison to the analytical solution for the laminar, oscillatory, current flow which develops a uniform boundary layer over a horizontal bottom. For the propagation of finite-amplitude waves over a rigid rippled bed, the case with wavelength to water depth ratio λ/d0 = 6 and wave height to wavelength ratio H0/λ = 0.05 is considered. The ripples have parabolic shape, while their dimensions — length and height — are chosen accordingly to fit laboratory and field data. Results indicate that the wall shear stress over the ripples and the form drag forces on the ripples increase with increasing ripple height, while the corresponding friction force is insensitive to this increase. Therefore, the percentage of friction in the total drag force decreases with increasing ripple height.

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