Viscosity effect on the longwave instability of a fluid interface subjected to horizontal vibrations

2017 ◽  
Vol 814 ◽  
pp. 24-41 ◽  
Author(s):  
D. V. Lyubimov ◽  
G. L. Khilko ◽  
A. O. Ivantsov ◽  
T. P. Lyubimova
Keyword(s):  
Linear Stability ◽  
High Frequency ◽  
Incompressible Fluids ◽  
Basic Flow ◽  
Fluid Interface ◽  
Helmholtz Instability ◽  
Stability Boundaries ◽  
Low Frequencies ◽  
Viscosity Effect ◽  
High Frequency Vibrations

The effect of viscosity on the longwave Kelvin–Helmholtz instability of two immiscible incompressible fluids under horizontal vibrations is considered. The linear stability boundaries are found analytically using series expansion in terms of small wavenumber. The values of parameters, at which a transition from the longwave to finite-wavelength instability takes place, are determined. It has been shown that for high-frequency vibrations a viscous dissipation has just a weak destabilizing effect. At vibrations of moderate frequencies, destabilization is more significant, especially in the systems with large viscosity contrast. In contrast to that, at low frequencies the viscosity stabilizes the basic flow by suppressing the longwave perturbations.

Kelvin-Helmholtz instability of a slowly varying flow

1974 ◽  
Vol 65 (4) ◽  
pp. 781-797 ◽  
Author(s):  
P. G. Drazin
Keyword(s):  
Differential Equation ◽  
Ordinary Differential Equation ◽  
Horizontal Plane ◽  
Normal Modes ◽  
Incompressible Fluids ◽  
Basic Flow ◽  
The Other ◽  
Helmholtz Instability ◽  
Parabolic Profile ◽  
Wide Channel

The linear stability of a basic flow of two homogeneous inviscid incompressible fluids under the action of gravity is treated mathematically. In the basic state, one fluid is at rest below a horizontal planez= 0; and the other flows above in thexdirection, its speed varying slowly with the lateral co-ordinatey. The eigenvalue problem for normal modes is derived; its equation is a partial differential one, the co-ordinatesyandznot being separable. The problem is solved approximately by taking the modeslocallyas if the basic velocity were independent ofy, though the lateral wavenumber is allowed to vary slowly withy. This leads to an ordinary differential equation inywhich is solved by the JWKB method. Detailed calculations are made for a parabolic profile, representing the blowing of air over water in a wide channel, and for other profiles.

Simulation of vibration piercing of pipe blank at press

2020 ◽  
Vol 76 (11) ◽  
pp. 1128-1138
Author(s):  
S. R. Rakhmanov
Keyword(s):  
High Frequency ◽  
Deformation Zone ◽  
Pipe Blank ◽  
Equipment Operation ◽  
Metal Deformation ◽  
Technological Tool ◽  
High Frequency Vibrations ◽  
Pipe Blanks ◽  
Wave Phenomena

In some cases, the processes of piercing or expanding pipe blanks involve the use of high-frequency active vibrations. However, due to insufficient knowledge, these processes are not widely used in the practice of seamless pipes production. In particular, the problems of increasing the efficiency of the processes of piercing or expanding a pipe blank at a piercing press using high-frequency vibrations are being solved without proper research and, as a rule, by experiments. The elaboration of modern technological processes for the production of seamless pipes using high-frequency vibrations is directly related to the choice of rational modes of metal deformation and the prediction resistance indicators of technological tools and the reliability of equipment operation. The creation of a mathematical model of the process of vibrating piercing (expansion) of an axisymmetric pipe blank at a piercing press of a pipe press facility is an actual task. A calculation scheme for the process of piercing a pipe plank has been elaborated. A dependence was obtained characterizing the speed of front of plastic deformation propagation on the speed of penetration of a vibrated axisymmetric mandrel into the pipe workpiece being pierced. The dynamic characteristics of the occurrence of wave phenomena in the metal being pierced under the influence of a vibrated tool have been determined, which significantly complements the previously known ideas about the stress-strain state of the metal in the deformation zone. The deformation fields in the zones of the disturbed region of the deformation zone were established, taking into account the high-frequency vibrations of the technological tool. It has been established that the choice of rational parameters (amplitude-frequency characteristics) of the vibration piercing process of a pipe blank results in significant increase in the efficiency of the process, the durability of the technological tool and the quality of the pierced blanks.

scholarly journals Earless toads sense low frequencies but miss the high notes

2017 ◽  
Vol 284 (1864) ◽  
pp. 20171670 ◽  
Author(s):  
Molly C. Womack ◽  
Jakob Christensen-Dalsgaard ◽  
Luis A. Coloma ◽  
Juan C. Chaparro ◽  
Kim L. Hoke
Keyword(s):  
High Frequency ◽  
Species Differences ◽  
Low Frequency ◽  
Auditory Brainstem ◽  
Low Frequencies ◽  
Hearing Sensitivity ◽  
Sensory Pathways ◽  
Airborne Sound ◽  
Vibrational Sensitivity ◽  
Species Specific

Sensory losses or reductions are frequently attributed to relaxed selection. However, anuran species have lost tympanic middle ears many times, despite anurans' use of acoustic communication and the benefit of middle ears for hearing airborne sound. Here we determine whether pre-existing alternative sensory pathways enable anurans lacking tympanic middle ears (termed earless anurans) to hear airborne sound as well as eared species or to better sense vibrations in the environment. We used auditory brainstem recordings to compare hearing and vibrational sensitivity among 10 species (six eared, four earless) within the Neotropical true toad family (Bufonidae). We found that species lacking middle ears are less sensitive to high-frequency sounds, however, low-frequency hearing and vibrational sensitivity are equivalent between eared and earless species. Furthermore, extratympanic hearing sensitivity varies among earless species, highlighting potential species differences in extratympanic hearing mechanisms. We argue that ancestral bufonids may have sufficient extratympanic hearing and vibrational sensitivity such that earless lineages tolerated the loss of high frequency hearing sensitivity by adopting species-specific behavioural strategies to detect conspecifics, predators and prey.

Analytical Solution for Rotational Rub-Impact Plate Under Thermal Shock

2016 ◽  
Vol 32 (3) ◽  
pp. 297-311
Author(s):  
T.-Y. Zhao ◽  
H.-Q. Yuan ◽  
B.-B. Li ◽  
Z.-J. Li ◽  
L.-M. Liu
Keyword(s):  
Thermal Shock ◽  
High Frequency ◽  
Equations Of Motion ◽  
Low Frequency ◽  
Cantilever Plate ◽  
Analysis Method ◽  
Multiple Frequency ◽  
Width Direction ◽  
Blade Tip ◽  
High Frequency Vibrations

AbstractThe analysis method is developed to obtain dynamic characteristics of the rotating cantilever plate with thermal shock and tip-rub. Based on the variational principle, equations of motion are derived considering the differences between rubbing forces in the width direction of the plate. The transverse deformation is decomposed into quasi-static deformation of the cantilever plate with thermal shock and dynamic deformation of the rubbing plate under thermal shock. Then deformations are obtained through the calculation of modal characteristics of rotating cantilever plate and temperature distribution function. Special attention is paid to the influence of tip-rub and thermal shock on the plate. The results show that tip-rub has the characteristics of multiple frequency vibrations, and high frequency vibrations are significant. On the contrary, thermal shock shows the low frequency vibrations. The thermal shock makes the rubbing plate gradually change into low frequency vibrations. Because rub-induced vibrations are more complicated than those caused by thermal shock, tip-rub is easier to result in the destruction of the blade. The increasing friction coefficient intensifies vibrations of the rubbing plate. Minimizing friction coefficients can be an effective way to reduce rub-induced damage through reducing the surface roughness between the blade tip and the inner surface of the casing.

Convection of a binary mixture under high-frequency vibrations

2013 ◽  
Vol 341 (4-5) ◽  
pp. 477-482 ◽  
Author(s):  
Sergey M. Ishutov ◽  
Bela I. Myznikova ◽  
Boris L. Smorodin
Keyword(s):  
Binary Mixture ◽  
High Frequency ◽  
High Frequency Vibrations

scholarly journals Erratum to: Acute and cumulative effects of focused high-frequency vibrations on the endocrine system and muscle strength

2013 ◽  
Vol 113 (11) ◽  
pp. 2871-2871 ◽  
Author(s):  
Pierpaolo Iodice ◽  
Rosa Grazia Bellomo ◽  
Glaugo Gialluca ◽  
Giorgio Fanò ◽  
Raoul Saggini
Keyword(s):  
Muscle Strength ◽  
High Frequency ◽  
Endocrine System ◽  
Cumulative Effects ◽  
High Frequency Vibrations
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