On the Instability Mechanisms of a Disk Rotating Close to a Rigid Surface

1995 ◽  
Vol 62 (3) ◽  
pp. 764-771 ◽  
Author(s):  
F. Y. Huang ◽  
C. D. Mote
Keyword(s):  
Rotation Speed ◽  
Maximum Speed ◽  
Film System ◽  
Rigid Surface ◽  
Flow Component ◽  
Flutter Speed ◽  
Disk Rotation ◽  
Viscous Shear ◽  
Air Film ◽  
Disk Rotation Speed

The instability mechanisms of a rotating disk, coupled to a rigid surface through a viscous fluid film at the interface, are investigated analytically. The fluid in the film is driven circumferentially by the viscous shear, and it flows outwards radially under centrifugal forces. The circumferential flow component creates an equivalent viscous damping rotating at one half the disk rotation speed. This film damping dissipates all backward traveling waves where the undamped wave speeds are greater than one half the disk rotation speed. The radial flow component creates a nonsymmetric stiffness in the disk-film system that energizes any wave mode at rotation speeds above its flutter speed. Instabilities in the disk-film system are of two types. A rotating damping instability is caused by the rotating film damping at rotation speeds above a critical value that is less than the flutter speed. A combination instability is caused by the combined effect of the film stiffness and damping at rotation speeds above a threshold that is greater than the flutter speed. The maximum rotation speed of stable disk vibration is bounded above by the lowest onset speed of rotating damping instability. This speed limit is predicted for two wall enclosure designs. The maximum stable rotation speed of a 5.25-inch diameter flexible, memory disk, separated from a rigid surface by a viscous air film, is shown to be more than 15 times greater than the maximum speed of the disk without the air film.

Effect of Warp on the Multiple Equilibria of a Hydrodynamically Coupled Flexible Disk

2006 ◽  
Author(s):  
Nikhit N. Nair ◽  
Grant M. Warner
Keyword(s):  
Manufacturing Process ◽  
Shooting Method ◽  
Multiple Equilibria ◽  
Rotation Speed ◽  
Coupled System ◽  
Instability Phenomenon ◽  
Disk Rotation ◽  
Hybrid Formulation ◽  
Flexible Disk ◽  
Disk Rotation Speed

In this paper, a hydrodynamically coupled flexible disk rotating in a thin housing is mathematically modeled and an attempt is made to explain the jump instability phenomenon that occurs when the disk rotation speed is varied slightly. The disk is assumed to have an initial warped profile due to slight imperfections in the manufacturing process. After non-dimensionalization of the participating variables, a hybrid formulation is carried out. Radial flows above and below the disk are taken into consideration. The deflection and pressure equations form a coupled system, and a solution is attempted using the shooting method. The deflections obtained are plotted to obtain the deflected disk profile and appropriate conclusions are drawn.

scholarly journals Design and study of seeding devices for small selection seeding machines

2019 ◽  
Vol 126 ◽  
pp. 00008
Author(s):  
Vladimir Nemtinov ◽  
Nikolai Kryuchin ◽  
Alexandr Kryuchin ◽  
Yulia Nemtinova
Keyword(s):  
Linear Dependence ◽  
Rotation Speed ◽  
Rotation Frequency ◽  
Field Studies ◽  
Disk Rotation ◽  
Seed Supply ◽  
Computer Technologies ◽  
Laboratory Results ◽  
Agricultural Plants ◽  
Disk Rotation Speed

In this paper, it is proposed to use a self-propelled pneumatic mini-seeder with replaceable mechanical sowing devices designed and manufactured using computer technologies, advanced software and threedimensional printing for seeds selection. As a result of the research, hightech operating devices for a grain-drill feed with screw and disk-pin continuous seed metering are designed and manufactured. Grain-drill feeds allow sowing of free-flowing and non-free-flowing seeds, when used as seed meters on self-propelled pneumatic mini-seeders for selection sowing of grass seeds. Analysis of laboratory results of and field studies of the proposed grain-drill feeds allowed to determine the qualitative indicators of their performance: at a disk rotation speed of up to 15 rpm a linear dependence of the seed supply on the rotation frequency is provided; in the field studies, the instability of bluegrass seeding did not exceed 8%. The highest performance of the screw is obtained at the angle of choke inclination of 30...35 degrees with the seeding instability indicator of 2.5...3.5%. The developed grain-drill feed will significantly reduce the range of seeders and expand the set of sown seeds of various agricultural plants with one brand of a grain-drill feed.

scholarly journals Results of laboratory and bench-scale studies of seed dispensers with an electric drive of working tools

2021 ◽  
Vol 34 (06) ◽  
pp. 1761-1767
Author(s):  
Anatoly Ivanovich Zavrazhnov ◽  
Aleksandr Vladimirovich Balashov ◽  
Sergey Petrovich Strygin ◽  
Nikita Yurievich Pustovarov ◽  
Andrey Anatolyevich Zavrazhnov
Keyword(s):  
Control System ◽  
Electric Drive ◽  
Rotation Speed ◽  
Soybean Seeds ◽  
Seeding Rate ◽  
Linear Speed ◽  
Bench Scale ◽  
Disk Rotation ◽  
Trajectory Length ◽  
Disk Rotation Speed

Mechanical and pneumatic seed drills of both domestic and foreign production are used in Russian farms. They are equipped with a mechanical drive of working tools and an electronic seeding control system. Due to the slipping of the wheels or the breakage of the chains, the sowing of seeds in individual seed dispensers interrupts. According to the results of laboratory and bench-scale studies in respect to soybean seeds, the required power for the electric drive of one seed dispenser was determined, which, depending on the disk rotation speed from 10 to 60 rpm, ranged from 30 to 120 W. By calculation, using the analytical expression, the power, required for the fan drive of a 12-row seed drill, was determined, which, depending on the disk rotation speed, ranged from 1.6 to 2.47 kW. A condition is formulated, which will eliminate the probability of shifting and rolling seeds along the furrow after their fall out of the sowing disc rotating in the opposite direction to the movement of the seeder unit, provided correspondence of the linear speed of the sowing disc and the speed of the seeder unit (the effect of zero overlaps). In this case, the trajectory length of the seeds falling to the furrow should be consistent with the speed of the seeder unit and the seeding rate according to the proposed expression.

scholarly journals MAGNETIC PROPERTIES AND MAGNETIC STRIP DOMAINS IN MICRO STRIPES PrDyFeCoB

2021 ◽  
pp. 86-93
Author(s):  
D.V. Korolev ◽  
◽  
Yu.V. Stolyankov ◽  
V.P. Piskorsky ◽  
R.A. Valeev ◽  
...  
Keyword(s):  
Hysteresis Loop ◽  
Coercive Field ◽  
Rotation Speed ◽  
Magnetic Phase ◽  
Hysteresis Loops ◽  
Zero Field ◽  
Phase 2 ◽  
Soft Magnetic ◽  
Disk Rotation ◽  
Disk Rotation Speed

The article provides the analysis of PrDyFeCoB magnetic microstripes prepared by extracting material from a melt on a rotating cooling disk. The phases 2-14-1, 1-4-1 and 1-2, α-FeСо were verified in the samples. The division of a hysteresis loop into two strands shows that the coercive field of the α-FeСо phase (500–700 Oe) determines the width of the hysteresis loop near the zero field, while the coercive field of the 2-14-1 phase (10 kOe) corresponds to lateral hysteresis loops. The saturation magnetization increases by 25% with an increase in the disk rotation speed by 3 times together with correspondent acceleration of the cooling rate. This is due to the increase in the proportion of the soft magnetic phase α-FeCo and the increase in the proportion of the amorphous phase with a decrease in the proportion of the main magnetic phase 2-14-1. Strip domains and their dynamics during magnetization were detected using Kerr magneto-optical microscopy.

scholarly journals Characterization of the Transverse Distribution of Fertilizer in Coffee Plantations

Agronomy ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 601
Author(s):  
Alan Delon Andrade ◽  
Gabriel Araújo e Silva Ferraz ◽  
Murilo Machado de Barros ◽  
Rafael De Oliveira Faria ◽  
Fábio Moreira da Silva ◽  
...  
Keyword(s):  
Rotation Speed ◽  
Fertilizer Application ◽  
Production Costs ◽  
Distribution Profile ◽  
Transverse Distribution ◽  
Operating Modes ◽  
Disk Rotation ◽  
Coffee Plants ◽  
The Impact ◽  
Disk Rotation Speed

Considering the impact of fertilizers on coffee production costs, the search for greater efficiency in the use of these inputs has an important role. Accordingly, the aim of the present study is to evaluate the transverse distribution of fertilizer by a centrifugal spreader in a coffee plantation and to compare two operating modes: fertilizer application on one side (FA1), or both sides (FA2) of the coffee plants. In addition, three doses (200, 300 and 400 kg ha−1) of monoammonium phosphate and three spreading disk rotation speeds (240, 375 and 750 rpm) were tested. To characterize fertilizer distribution profiles, collectors were placed under the canopy of coffee plants, and the collected fertilizer was weighed. From the data obtained, distribution profile histograms were constructed, and coefficients of variation were calculated for each treatment. Distribution profiles with higher uniformity were related to the morphologic characteristics of the coffee plants. Regarding the operating modes evaluated, FA1 presented better results with a disk rotation speed of 750 rpm (FA1-W3); FA2 produced the best results with a disk rotation speed of 240 rpm. By relating these results with information on root morphology, FA1-W3 was found to be the most appropriate application method.

scholarly journals Analysis of the dynamic characteristics of downsized aerostatic thrust bearings with different pressure equalizing grooves at high or ultra-high speed

2021 ◽  
Vol 13 (5) ◽  
pp. 168781402110180
Author(s):  
Ruzhong Yan ◽  
Haojie Zhang
Keyword(s):  
Dynamic Characteristics ◽  
High Speed ◽  
Rotation Speed ◽  
Dynamic Stiffness ◽  
Simulation Method ◽  
Perturbation Amplitude ◽  
Thrust Bearings ◽  
Supply Pressure ◽  
Ultra High Speed ◽  
Air Film

This study adopts the DMT(dynamic mesh technology) and UDF(user defined functions) co-simulation method to study the dynamic characteristics of aerostatic thrust bearings with equalizing grooves and compare with the bearing without equalizing groove under high speed or ultra high speed for the first time. The effects of air film thicness, supply pressure, rotation speed, perturbation amplitude, perturbation frequency, and cross section of the groove on performance characteristics of aerostatic thrust bearing are thoroughly investigated. The results show that the dynamic stiffiness and damping coefficient of the bearing with triangular or trapezoidal groove have obvious advantages by comparing with that of the bearing without groove or with rectangular groove for the most range of air film thickness, supply pressure, rotation speed, perturbation amplitude, especially in the case of high frequency, which may be due to the superposition of secondary throttling effect and air compressible effect. While the growth range of dynamic stiffness decreases in the case of high or ultra-high rotation speed, which may be because the Bernoulli effect started to appear. The perturbation amplitude only has little influence on the dynamic characteristic when it is small, but with the increase of perturbation amplitude, the influence becomes more obvious and complex, especially for downsized aerostatic bearing.

Influence of Peripheral on Central Stereopsis: An Induced Depth Tilt Effect

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 276-276
Author(s):  
S Müller ◽  
E R Wist
Keyword(s):  
Opposite Direction ◽  
Rotation Speed ◽  
Neutral Density ◽  
Neutral Density Filter ◽  
Disk Rotation ◽  
Optimal Rotation ◽  
Density Filter ◽  
Pulfrich Effect ◽  
Variable Errors ◽  
Tilted Disk

A large rotating black/white sectored disk (58 deg diameter) viewed with a neutral density filter over one eye is perceived as tilted in depth according to the Pulfrich phenomenon. But with fixation on a centrally located vertical bar (7 deg in length), the disk is perceived as vertical while the central bar is perceived as tilted in the opposite direction. This effect remains even if the central 38 deg portion of the disk is occluded leaving a peripheral annulus 10 deg in width. At an optimal rotation speed of 45° s−1 and a filter of 2 log units, the inter-individual perceived tilt of the bar ranges between 5° and 10° as measured by nulling out the illusory tilt by adjustment with a joystick. Variable errors were extremely small and corresponded well with central stereoscopic resolution. The amount of illusory tilt depends on the speed of disk rotation and filter density, and its direction on the relation between the direction of motion and the filter-covered eye. The effect is not limited to Pulfrich-induced stereotilt: When the disk was stationary but physically tilted in depth, the induced tilt on the central bar corresponded to about 50% of the physical tilt. This effect, in turn, could be cancelled or enhanced by rotating the tilted disk and inducing an appropriate Pulfrich effect. With monocular viewing no induced depth tilt occurs. The results are interpreted in terms of a stereoscopic induced effect operating beyond the known peripheral limits of stereopsis.

Experimental Analysis of the Unbalance Response of Rigid Rotors Supported on Aerodynamic Foil Bearings

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Franck Balducchi ◽  
Mihai Arghir ◽  
Romain Gauthier
Keyword(s):  
Vibration Spectrum ◽  
Rotation Speed ◽  
Nonlinear Behavior ◽  
Structural Damping ◽  
Foil Bearings ◽  
Unbalance Response ◽  
Theoretical Predictions ◽  
Air Film ◽  
Rigid Rotors ◽  
Cubic Stiffness

The paper presents the experimental unbalance response of two slightly different rigid rotors supported by aerodynamic foil bearings. Impulse (Pelton) turbines manufactured directly in the mass of the rotors (on the outer surface) entrain both rotors at rotation speeds comprised between 50 krpm and 100 krpm. The displacements in the two foil bearings are measured during coast down and are depicted as waterfall plots. They show typical nonlinear behavior, i.e., subsynchronous vibrations accompanying the synchronous component. The measurements clearly show that the subsynchronous components bifurcate or jump at typical rotation speeds (mostly rational fractions of the rotation speed). The nonlinear behavior of the rigid rotor supported on foil bearings is also emphasized by varying the added unbalance: with increasing unbalance the vibration spectrum becomes gradually more diverse as new subsynchronous vibrations appear. The experimental results are compared with very simplified theoretical predictions based on the assumption that the air film in the two bearings is infinitely stiff compared to the foil structure. The latter is characterized by a cubic stiffness and a structural damping coefficient. The comparisons show only a rough qualitative agreement.

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