On the spin-up and spin-down of a rotating fluid. Part 2. Measurements and stability

1976 ◽  
Vol 77 (4) ◽  
pp. 709-735 ◽  
Author(s):  
Patrick D. Weidman
Keyword(s):  
Stability Boundary ◽  
Fluid Motion ◽  
Azimuthal Velocity ◽  
Laser Doppler Velocimeter ◽  
Rotating Fluid ◽  
Constant Acceleration ◽  
Centrifugal Instability ◽  
The Stability ◽  
Theoretical Results

Measurements of the azimuthal velocity inside a cylinder which spins up or spins down at constant acceleration were obtained with a laser-Doppler velocimeter and compared with the theoretical results presented in part 1. Velocity profiles near the wave front in spin-up indicate that the velocity discontinuity given by the inviscid Wedemeyer model is smoothed out in a shear layer whose thickness varies with radius and time but scales with hE1/4Ω. The spin-down profiles are always in excellent agreement with theory when the flow is stable. Visualization studies with aluminium tracers have made possible the determination of the stability boundary for Ekman spiral waves (principally type II waves) observed on the cylinder end walls during spin-up. For spin-down to rest the flow always experienced a centrifugal instability which ultimately disrupted the interior fluid motion.

scholarly journals Research Results of the Potato Digger Technological Process

2018 ◽  
Vol 12 (5) ◽  
pp. 14-19 ◽  
Author(s):  
V. M. Alakin ◽  
G. S. Nikitin
Keyword(s):  
Design Parameters ◽  
Operating Speed ◽  
Working Process ◽  
Projectile Motion ◽  
Operating Process ◽  
Cutoff Angle ◽  
The Stability ◽  
Theoretical Results ◽  
Optimum Working

A potato digger equipped with a four­bladed beater operating in connection with rotary separating surface has low material and energy consumption, higher separating efficiency, as well as lower degree of tuber damaging. The potato digger design should include a four­bladed intake­and­feed beater to prevent potato heap transportation faults in front of the first section. (Research purpose) Increasing the technological and economic efficiency of a potato digging­and­ separating unit through the determination of the optimum values of the design parameters and operating process of the intake­and­feed beater. (Materials and methods) the authors have made an overview of general principles of ensuring the stability of the potato heap movement provided by the four­bladed intake­and­feed beater. The dependency of the minimum beater speed on the operating speed of the potato digger has been found to exclude a probability of its overloading. The methodology of calculating the potato heap velocity and the cutoff angle between the material and the beater blades has been worked out by analyzing potato heap lifting to the upper points of the working units of the rotary separator’s first section. Operating speed of the beater has been determined through the differential equation for the speed of a potato heap moving along the blade surface. (Results and discussion) Preliminary potato heap speed and cutoff angle have been found through the equation of dynamics describing the projectile motion of an object thrown at an angle. The operating values of the angles are dependent on the potato digger working speed and can be selected from the triangle of speeds. The authors have determined the dependence of the optimal beater speed on the working speed of a potato digger. Its value should exceed the minimum speed of the beater. (Conclusions) Theoretical results allow proposing the best design features and optimum working process parameters of a four­bladed beater receiving a potato heap, transporting it and lifting on the rotary separating surface.

Effiziente Ermittlung von Stabilitätsgrenzen*/Detection of stability boundaries during milling

2017 ◽  
Vol 107 (05) ◽  
pp. 313-317
Author(s):  
C. Prof. Brecher ◽  
P. Chavan ◽  
A. Epple
Keyword(s):  
Stability Boundary ◽  
Spindle Speed ◽  
Wird Eine ◽  
Chatter Detection ◽  
Speed Variation ◽  
Spindle Speed Variation ◽  
Detection Software ◽  
The Stability ◽  
Stability Limits

Um Stabilitätskarten für Fräsprozesse effizient zu erstellen, bietet sich eine kontinuierliche Variation der Drehzahl an. Jedoch kann die permanente Änderung der Drehzahl zu einer Verfälschung der tatsächlichen Stabilitätsgrenzen führen. Dieser Fachbeitrag analysiert den Einfluss der Spindeldrehzahlvariation auf die Stabilitätsgrenzen bei Fräsversuchen mit verschiedenen Drehzahlbeschleunigungen. Für das Erkennen der Stabilitätsübergänge wird eine Rattererkennungssoftware eingesetzt.   Milling with varying spindle speed allows an efficient determination of instabilities. However, spindle speed variation may also influence the actual stability boundary with constant spindle speed. This paper analyzes the influence of spindle speed variation on the stability limits by evaluating milling trials at different spindle accelerations. For the detection of instability and stability during cutting trials, a time-domain chatter detection software was enhanced, validated and implemented.

Centrifugal instability of a Stokes layer: linear theory

1976 ◽  
Vol 350 (1662) ◽  
pp. 299-316 ◽  
Keyword(s):  
Experimental Investigation ◽  
Velocity Field ◽  
Series Solution ◽  
Taylor Vortex ◽  
Mean Velocity ◽  
Stokes Layer ◽  
Centrifugal Instability ◽  
Partial Differential System ◽  
The Stability ◽  
Theoretical Results

The instability of the flow induced by a circular cylinder oscillating in an infinite viscous fluid is investigated. The flow is shown to be unstable to a Taylor vortex mode of instability. A series solution of the partial differential system governing the stability of the flow is obtained. The method used has several advantages over the numerical methods used by different authors for related problems. The instability predicted by the theory leads to a flow with no mean velocity component tangential to the cylinders. The disturbance velocity field decays exponentially at the edge of the Stokes layer. The theoretical results are qualitatively confirmed by an experimental investigation of the problem.

On the Stability of Planar Librations of a Dumb-bell Satellite in an Elliptic Orbit

1966 ◽  
Vol 70 (672) ◽  
pp. 1098-1102 ◽  
Author(s):  
R. C. Brereton ◽  
V. J. Modi
Keyword(s):  
Central Body ◽  
Stability Boundary ◽  
Elliptic Orbit ◽  
Gravity Gradient ◽  
Exact Equation ◽  
Local Gravity ◽  
Orbit Eccentricity ◽  
Librational Motion ◽  
The Stability

The planar librational motion of a dumb-bell satellite has been studied by several authors. In most cases the analysis has been restricted to circular or nearly circular orbits. In an elliptic orbit, the variation of the angular velocity of the satellite around the central body together with the change in the local gravity gradient provides the satellite with a mechanism for exchanging energy between the librational and orbital modes. In general, this imposes a limit on the orbit eccentricity for which stable (non-tumbling) librational motion is possible. This note investigates the bounds that must be placed on a disturbance applied to a slender gravity gradient stabilised satellite so that it will librate and not tumble. The determination of the stability boundary as presented here was arrived at by the numerical solution of the exact equation of motion, obtained using an IBM 7040 computer.

scholarly journals Design of Robust PI Controllers and their Application to a Nonlinear Electronic System

2010 ◽  
Vol 61 (1) ◽  
pp. 44-51 ◽  
Author(s):  
Radek Matušů ◽  
Katarína Vaneková ◽  
Roman Prokop ◽  
Monika Bakošová
Keyword(s):  
Stability Boundary ◽  
Electronic System ◽  
Laboratory Model ◽  
Final Choice ◽  
Boundary Locus ◽  
Electronic Model ◽  
Pi Controllers ◽  
The Stability ◽  
Stable Control

Design of Robust PI Controllers and their Application to a Nonlinear Electronic SystemThe principal aim of the paper is to present a possible approach to the design of simple Proportional-Integral (PI) robust controllers and subsequently to demonstrate their applicability during control of a laboratory model with uncertain parameters through the Programmable Logic Controller (PLC) SIMATIC S7-300 by Siemens Company. The proposed and utilized synthesis consists of two steps. The former one is determination of controller parameters area, which ensures the robustly stable control loop and is based on computing/plotting the stability boundary locus while the latter one lies in the final choice of the controller itself relying on algebraic techniques. The basic theoretical parts are followed by laboratory experiments in which the 3rd order nonlinear electronic model has been successfully controlled in various working points.

Stability Boundary for Haptic Rendering: Influence of Damping and Delay

2009 ◽  
Vol 9 (1) ◽  
Author(s):  
Jorge Juan Gil ◽  
Emilio Sánchez ◽  
Thomas Hulin ◽  
Carsten Preusche ◽  
Gerd Hirzinger
Keyword(s):  
Stability Boundary ◽  
Sampling Frequency ◽  
Haptic Interface ◽  
Viscous Damping ◽  
Light Weight ◽  
Stability Boundaries ◽  
Linear Condition ◽  
Virtual Stiffness ◽  
The Stability ◽  
Theoretical Results

The influence of viscous damping and delay on the stability of haptic systems is studied in this paper. The stability boundaries have been found by means of different approaches. Although the shape of these stability boundaries is quite complex, a new linear condition, which summarizes the relation between virtual stiffness, viscous damping, and delay, is proposed under certain assumptions. These assumptions include a linear system, short delays, fast sampling frequency, and relatively low physical and virtual damping. The theoretical results presented in this paper are supported by simulations and experimental data using the DLR light-weight robot and the large haptic interface for aeronautic maintainability (LHIfAM).

INFLUENCE OF HEAT TREATMENT OF MOUNTAIN MASSIVE ON TEMPERATURE MODE OF GEOTHERMAL CIRCULATION SYSTEM

2018 ◽  
pp. 44-50
Author(s):  
Yu. P. Morozov
Keyword(s):  
Heat Transfer ◽  
Operating Time ◽  
Fluid Motion ◽  
Coolant Temperature ◽  
Circulation System ◽  
Thermal Processes ◽  
Temperature Mode ◽  
Heat Influx ◽  
Stationary Heat Transfer

Based on the solution of the problem of non-stationary heat transfer during fluid motion in underground permeable layers, dependence was obtained to determine the operating time of the geothermal circulation system in the regime of constant and falling temperatures. It has been established that for a thickness of the layer H <4 m, the influence of heat influxes at = 0.99 and = 0.5 is practically the same, but for a thickness of the layer H> 5 m, the influence of heat inflows depends significantly on temperature. At a thickness of the permeable formation H> 20 m, the heat transfer at = 0.99 has virtually no effect on the thermal processes in the permeable formation, but at = 0.5 the heat influx, depending on the speed of movement, can be from 50 to 90%. Only at H> 50 m, the effect of heat influx significantly decreases and amounts, depending on the filtration rate, from 50 to 10%. The thermal effect of the rock mass with its thickness of more than 10 m, the distance between the discharge circuit and operation, as well as the speed of the coolant have almost no effect on the determination of the operating time of the GCS in constant temperature mode. During operation of the GCS at a dimensionless coolant temperature = 0.5, the velocity of the coolant is significant. With an increase in the speed of the coolant in two times, the error changes by 1.5 times.

Sign in / Sign up

Export Citation Format

Share Document