Relative Rotational Speed Research Articles

STATCOM Controls for a Self-Excited Induction Generator Feeding Random Loads

Voltage and frequency fluctuations due to random load variation are the most important power-quality problem in a self-excited induction generator (SEIG) system. Traditionally, instantaneous voltage regulation can be achieved using static synchronous compensators (STATCOMs) to condition the reactive power flow in a power distribution system. However, their widespread use might be limited by temporary loss of synchronization owing to system frequency fluctuations. In this paper, an advanced, laboratory STATCOM was constructed based on the relative rotation speed theory, which is essential in estimating the frequency deviation and assisting the STATCOM in synchronism with system frequency. As a result, the stator voltage fluctuation due to random load variations can be eliminated and effective regulations in generator speed and mechanical power are thus able to be guaranteed. Both simulation and experimental results are in agreement with the proposed controller, leading to the conclusion that simultaneous voltage and frequency control for SEIG feeding the balanced three-phase loads is feasible.

Removal rate and surface roughness in the lapping and polishing of RB-SiC optical components

Abstract Optical components made of reaction-bonded silicon carbide (RB-SiC) have aroused the interest of researchers and engineers due to their distinct properties, such as low density, high hardness and low thermal expansion coefficient. The present study focuses on efficient fabrication of RB-SiC optical components. Here, a two-stage fabrication process is proposed. Firstly, a plate fixed with solid pellet-shaped abrasives is used for rapid removal of surface error and initial smoothing. After that, fine error removal and surface polishing is performed using felt buffs and diamond abrasives. Material removal rates and surface roughness are measured based on a Form Talysurf surface profiler. The final surface roughness with an initial value of Ra = 110.8 nanometer (nm) reached 21.6 nm after 5 min of lapping by adjusting the size of abrasives continuously from 30 to 10 micrometer (μm), and then convergent to 10.7 nm after 15 min of polishing using different sized diamond pastes as the polishing abrasive. The validity of the two-stage process in terms of efficiency and surface quality has been verified by experiments. How these factors are affected by process parameters such as the relative rotation speed, abrasives grit size, etc. are also examined.

A Mixed-Lubrication Approach to Predicting CMP Fluid Pressure Modeling and Experiments

Chemical mechanical polishing (CMP) is a manufacturing process used to remove or planarize metallic, dielectric, or barrier layers on silicon wafers. During polishing, a wafer is mounted face up on a fixture and pressed against a rotating polymeric pad that is flooded with slurry. The wafer also rotates relative to the pad. The combination of load on the wafer fixture, relative speed of rotation, slurry chemistry, and pad properties influences polishing rates. Prior work has shown that an asymmetrical subambient pressure, which exceeds that expected from the applied load, can develop at the interface between the fixture and a plane pad. The spatial distribution of this pressure can be measured and then simulated using a specially designed fixture with water as the slurry. A mixed-lubrication approach to modeling the fluid pressure was developed by including the contact stress, frictional behavior, and fluid film thickness. For a given fixture/pad separation, the contact stress can be determined using a Winkler model approximation. The film thickness can be approximated as the distance from the fixture surface to the mean asperity plane. Once the fluid film thickness is known, the fluid pressure can be determined from the two-dimensional polar Reynolds equation using finite-differencing. The theoretical pressure solution was found to match the experimental pressures when the system of forces and moments were balanced. The iterative secant numerical method was employed to compute the appropriate fluid film thickness that accommodates a balanced system of forces and moments produced by the fluid/solid interactions. After the fluid pressure is determined from an initially assumed separation, all shear and normal forces are computed from the solid contact stress and hydrodynamic fluid pressure. The results agree with the experiments. © 2005 The Electrochemical Society. All rights reserved.

Proposition of Unique Pumping System with Counter‐Rotating Mechanism

Turbo‐pumps have weak points, such as when the pumping operation becomes unstable in the rising portion of the head characteristics and/or the cavitation occurs under the intolerably low suction head. To overcome both weak points simultaneously, this article proposes a unique pumping system with counter‐rotating mechanism, which consists of two stage impellers and a peculiar motor with double rotors. The front and the rear impellers are driven by the inner and the outer rotors of the motor, respectively, keeping the relative rotational speed constant and counter‐balancing the rotational torque. Such driving conditions not only smartly improve the unstable performance at lower discharge, but also suppress the cavitation at higher discharge, in the optimum cooperation with the impeller works and the rotor outputs.

Practical Strategies for Controlling Railway Wheelsets Independently Rotating Wheels

This paper presents the development of an active control strategy for railway vehicles with independently rotating wheels. The proposed control scheme is intuitively formulated with a simple control structure and adaptive to vehicle speed. It does not require basic guidance measurements (e.g., wheel-rail deflection and angle of attack) that are expensive and impractical to implement. Speed sensors are used to measure the relative rotational speed of the two wheels on a same axle and sensors are also used to measure the relative yaw velocity of the wheelset and the body it is connected. Both curving performance and passenger ride comfort of the actively controlled vehicle are compared with that of a typical passive vehicle and an optimal control scheme.

Smart Control of Axial Flow Pump Performance by Means of Counter-Rotation

Turbo pumps have weak points, such as the pumping operation becoming unstable in the rising portion of the head characteristics and/or the cavitation occurring under the intolerably low suction head. These points have been individually overcome in general, since such phenomena originate in essentially different causes. To overcome the above weak points simultaneously, however, we propose a unique pumping system with counter-rotating mechanism and discuss its advantages. This system consists of two-stage impellers and a unique motor with double rotors. The front and rear impellers are driven respectively by the inner and outer rotors of the motor, keeping the relative rotational speed constant and counter-balancing the rotational torque. Such driving conditions not only improve smartly the unstable performance at low discharge but also suppress smartly cavitation at high discharge, under the optimum cooperation with the impeller works and the rotor outputs. The model test proved that there is no rising portion of the head characteristics and that the front impeller speed is gradually decreased with increase of the discharge as if taking the place of the inducer.

An experimental study of the two-staged wind turbines

In order to improve the torque performance of the propeller type wind turbine, and to increase the relative rotational speed of the generator, two-staged wind turbines were proposed. The experimental results of a wind tunnel test showed that self-starting characteristics of two-staged co-axial type were improved by attached front wind turbines for two bladed main wind turbine, and the relative rotational speed of counter-rotating type was increased. Then, a counter-rotating type trial machine was constructed and a wind tunnel test was also conducted. The test result demonstrated the technical possibility of conterrotating type wind powered generator.

Characterization of Polishing‐Related Surface Damage in (0001) Silicon Carbide Substrates

The nature and extent of surface damage in substrates prepared by mechanical polishing have been studied using backscattering of ultraviolet light and cross‐sectional transmission electron microscopy. When the basal plane surface is prepared by lapping or polishing with large size diamond abrasives, the surface roughness is about one‐fifth the particle size, while the subsurface damage extends to a depth of about half the abrasive size. Under optimum conditions of particle size, vertical load, and relative rotation speed, the extent of subsurface damage can be minimized resulting in a nominally defect‐free specular surface exhibiting a uniform strained layer of less than 8 nm.

HEAT TRANSFER MODELLING OF A CYLINDRICAL ER CATCH

In electro-rheological (ER) devices the control of temperature is often of paramount importance. For a device through which the ER fluid is not able to flow continuously to and from a reservoir, where it may be cooled, this can be a problem. Such a situation occurs in the ER catch. The heat generated there will predominantly be dissipated from the outer surface of the drive/input. The rate of heat transfer is thus principally a function of the speed and area of that surface and the temperatures of the ER fluid and atmosphere. Since these factors reflect on the levels of electro-stress, current requirement and viscosity of the ER fluid, an opportunity exists for optimisation of catch performance. The paper shows the results of an investigation into the effects on the cooling/heating problem of varying the radii of the clutch rotors, their relative rotational speed and inter-electrode spacing. Equilibrium fluid temperatures are confirmed by experimental evidence. The effects of heat generation in run up to speed and clutch locked periods, (through electro viscous drag and dielectric loading respectively) are quantified and compared with the case of a contemporary ER fluid in a cylindrical catch on zero volts idling. At any given operating condition, uniform temperature, viscosity and constant electro stress are assumed throughout the fluid.

Perceptual linkage of multiple objects rotating in depth.

When multiple objects rotate in depth, they are frequently perceived to rotate in the same direction even when perspective information signals counterrotation. Three experiments are reported on this tendency to recover the rotation directions of multiple objects in a nonindependent fashion (termed rotational linkage). Rotational linkage was strongly affected by slant in depth of the objects, image perspective, and relative starting phase of the objects. Linkage was found not to vary as a function of the relative rotation speed of the objects or the relative alignment of their rotation axes. Rotational linkage is interpreted as a tendency of the visual system to assign signed depths to objects based on a communality of image point direction.

A Theoretical Model for Rotating Stall in the Vaneless Diffuser of a Centrifugal Compressor

A theoretical model for rotating stall in the vaneless diffuser of a centrifugal compressor is presented. It consists of a time-evolutive calculation of the strong interaction between the inviscid flow core and the unsteady boundary layers along the walls. It is shown that, depending on the diffuser geometry and the diffuser inlet flow angle, a transient perturbation of the outlet static pressure will generate a rotating flow pattern, if the periodicity of this perturbation corresponds to the experimentally observed number of cells. The relative rotational speed and the phase relation between the velocity and the flow angle variations are also in agreement with experimental data.

On hydrodynamic boundary conditions for microstructural fluids

Various types of boundary conditions used when investigating microrotation are analysed. A boundary condition for studying microstructural fluid flows, which depends on experimental parameters, is suggested. To illustrate the result, expressions are derived for the velocity and microrotation of a micropolar fluid between two coaxial cylinders with a constant relative speed of rotation.

THE SUPERCONDUCTING PADDLEWHEEL AS AN INTEGRATED PROPULSION LEVITATION MACHINE FOR HIGH SPEED GROUND TRANSPORTATION

ABSTRACT The rotary superconducting motor, RSM, is shown to provide economical propulsion as well as levitation on a thinner aluminum track than “conventional” repulsion magnetic suspension. With the RSM, thrust and braking are provided by controlling the relative speed of rotation of the motor essentially independent of lift at all forward speeds. Using thin-plate theory, the lift and drag forces on the rotary superconducting motor are evaluated as a function of the forward speed of the vehicle as well as the relative speed of rotation of the motor. Although significant power is dissipated in the track through eddy current losses, evaluation of the energy consumption of the RSM over a route profile of 750 km with 5 intermediate stops shows this propulsion levitation system to have an energy consumption of 0.76 MJ/seat-km - significantly lower than other means of propelling and levitating high speed ground transportation.

Structure and properties of welded blanks for tools of new high-speed steels

In a broad range of values of various factors (pressure during heating and forging, heating and forging time, relative speed of rotation) the torsional strength of welded samples of steels R12+45, R9K5+45, R6M5K5+45, R8M3K6S+45, and R9M4K8F+45 is constant with a confidence coefficient of 0.95 and meets the requirements. Within this region it is necessary to select friction welding conditions in conformity with the optima technicoeconomic parameters.

Signs of rotating aerodynamic breakaway in axial pit ventilator fans

1. In aerodynamic tests on fans, either in test beds with input bends simulating pit installations or in pit conditions, rotating aerodynamic breakaway may cause variations in the fan's output, which can be heard as characteristic changes in the fan noise. These variations are usually very weak, but if there is an accidental resonance in the acoustic system formed by the fan and internal test-bed cavity, they may become stronger and appear similar to “pumpage.” 2. This undesirable effect can be avoided by appropriate choice of the test-bed chamber volume or the fan rotation speed. The acoustic mass of the ventilator and the resonance frequency can be calculated from Eqs. (1) and (3). 3. Equation (4) for the relative rotation speed of the breakaway zone, derived for axial compresors at the TsAGI[Central Aerodynamics] Institute, also gives good agreement with the experimental results for mine ventilator fans. 4. By measuring the pressure in a hole in the fan casing in front of the rotor by means of an inertialess device, we found that there are warning signs of the onset of breakaway, and these can be used in the construction of automatic anti-breakaway devices.