Showing papers on "Rotational speed published in 2014"

Direct‐Current Triboelectric Generator

Abstract: The first direct-current triboelectric generator (DC-TEG) based on sliding electrification for harvesting mechanical energy from rotational motion is reported. The DC-TEG consists of two rotating wheels and one belt for connecting them, which are made of distinctly different triboelectric materials with a specific requirement. During the rotation, the contact-induced electrification and the relative sliding between the two wheels and the belt can induce a continuous increase of the accumulated positive and negative triboelectric charges at the two rotating wheels, respectively, resulting in a Corona discharge and producing the observed current through an external load. The DC-TEG can deliver an open-circuit voltage of larger than 3200 V and a maximum power of 100 μW under an external load of 60 MΩ at a rotational speed of 1000 r min–1. By designing a point metal discharge electrode near the accumulated positive charges on the metal wheel, the instantaneous short-circuit current can be up to 0.37 mA. The DC-TEG can be utilized as a direct power source to light up 1020 serially connected commercial light-emitting diodes (LEDs) and the produced energy can also be stored in a capacitor for other uses. This work presents a DC-TEG technology to harvest mechanical energy from rotational motion for self-powered electronics.

Comparison of Test Result and Design Stage Prediction of Switched Reluctance Motor Competitive With 60-kW Rare-Earth PM Motor

Abstract: A switched reluctance motor has been designed with identical outer dimensions, maximum torque, operating area, and maximum efficiency as rare-earth permanent-magnet motors used in the Toyota Prius. In this paper, a test machine has been constructed, and test results are presented over the entire speed range. The targets are torque of 207 N·m, a shaft output of 60 kW, and the maximum efficiency of 96%, as well as a speed range of 2768-13 900 r/min with an output of 60 kW and an outer diameter and an axial length of 264 and 112 mm, respectively. It is found that a shaft output of 100 kW is possible at high rotational speed under the voltage and current ratings. The possible operation area in a torque-speed plane is found to be enhanced. It is also found that the design stage prediction is close to the test results, except in two operation regions.

Analysis and Design of a 300-W 500 000-r/min Slotless Self-Bearing Permanent-Magnet Motor

Abstract: Active magnetic bearings enable contactless operation and can therefore be used for supporting rotors spinning at high speeds. However, the rotational speed in conventional reluctance-force-based magnetic bearing topologies is limited, which is mainly due to high rotor losses and limited force control bandwidths. In this paper, a prototype of a self-bearing motor is presented, which overcomes several limitations of state-of-the-art high-speed magnetically levitated electric drive systems. Due to the employed magnetic bearing, the motor can be operated in high-purity or vacuum environments. An analytical mechanical and electrical bearing model is introduced and verified by measurements. Furthermore, a bearing inverter system is designed, and its controller performance is shown. Measurements of spinning levitated rotors up to speeds of 505 000 r/min verify the functionality of the overall system. To the authors' knowledge, this is the highest speed achieved by magnetically levitated electrical drive systems so far.

Multi objective optimization of friction stir welding parameters using FEM and neural network

Abstract: In this study the inuence of rotational and traverse speed on the friction stir welding of AA5083 aluminum alloy has been investigated. For this purpose a thermo-mechanically coupled, 3D FEM analysis was used to study the effect of rotational and traverse speed on welding force, peak temperature and HAZ width. Then, an Articial Neural Network (ANN) model was employed to understand the correlation between the welding parameters (rotational and traverse speed) and peak temperature, HAZ width and welding force values in the weld zone. Performance of the ANN model was found excellent and the model can be used to predict peak temperature, HAZ width and welding force. Furthermore, in order to find optimum values of traverse and rotational speed, the multi-objective optimization was used to obtain the Pareto front. Finally, the Technique for Order Preference by Similarity to the Ideal Solution (TOPSIS) was employed to obtain the best compromised solution.

Latex micro-balloon pumping in centrifugal microfluidic platforms

Abstract: Centrifugal microfluidic platforms have emerged as point-of-care diagnostic tools. However, the unidirectional nature of the centrifugal force limits the available space for multi-step processes on a single microfluidic disc. To overcome this limitation, a passive pneumatic pumping method actuated at high rotational speeds has been previously proposed to pump liquid against the centrifugal force. In this paper, a novel micro-balloon pumping method that relies on elastic energy stored in a latex membrane is introduced. It operates at low rotational speeds and pumps a larger volume of liquid towards the centre of the disc. Two different micro-balloon pumping mechanisms have been designed to study the pump performance at a range of rotational frequencies from 0 to 1500 rpm. The behaviour of the micro-balloon pump on the centrifugal microfluidic platforms has been theoretically analysed and compared with the experimental data. The experimental data show that the developed pumping method dramatically decreases the required rotational speed to pump liquid compared to the previously developed pneumatic pumping methods. It also shows that within a range of rotational speed, a desirable volume of liquid can be stored and pumped by adjusting the size of the micro-balloon.

Wind turbine contribution in frequency drop mitigation - modified operation and estimating released supportive energy

Abstract: Wind energy high penetration levels in power systems require robust and practical operation algorithms to maintain and improve the present conventional systems performance. Thus, several studies consider the impact of wind farms installation on grid frequency, especially during frequency drops. The proposed algorithm makes the wind turbine provide promising support during frequency deviations through two operation modes, namely, normal and support. Normal mode controls wind turbine output by adjusting rotational speed and pitch angle according to the incident wind speed category. Novel normal operation secures wind turbine positive contribution in frequency deviations curtailment regardless of poor accompanying wind speed conditions. The innovative concept of merging pitch de-loading and rotational speed overproduction deceleration is implemented to avoid continuous de-loading; hence wasted wind energy is reduced. Wind turbine generator is overloaded when frequency drop occurs during high wind speed. Major algorithm parameters are tuned based on wind turbine specifications and dominant wind speed conditions at wind turbine location. The amount of supportive excess energy during frequency deviation clearance is estimated at different wind speed circumstances, including serious wind speed drop events. An islanded medium capacity hypothetical benchmark system is implemented to examine the proposed algorithm through MATLAB and Simulink simulation environments.

Rotational Speed Measurement Through Electrostatic Sensing and Correlation Signal Processing

Abstract: Rotational speed is a key parameter for the condition monitoring and control of rotating machineries, such as generators, electromotors, and centrifugal and machine tool spindles. It is essential for precision machining and early warning of faults to measure rotational speed in real time. This paper presents the principle and application of electrostatic sensors and correlation signal processing techniques to real-time measurement of rotational speed. The electrostatic sensors and signal conditioning and processing units were designed and implemented. Experimental tests were conducted on a laboratory-scale test rig under a range of conditions including different diameters of the shaft. The results obtained suggest that the distance between the electrodes and the surface of the rotating object is a key factor affecting the performance of the measurement system. The system performs better in terms of accuracy and repeatability at a higher rotational speed as more electrostatic charge is produced on the rotating surface. High and stable correlation coefficients acquired during the tests suggest that the measurement system is capable of providing reliable measurement of rotational speed under realistic industrial conditions.

A comparative study of jet formation in nozzle‐ and nozzle‐less centrifugal spinning systems

Abstract: Centrifugal spinning, a recently developed approach for ultra-fine fiber production, has attracted much attention as compared with the electrospinning, due to its high yield, no solution polarity and high-voltage electrostatic field requirements, etc. In this study, the jet formation process and spinning parameters on jet path are explored and compared in nozzle- and nozzle-less centrifugal spinning systems. For nozzle-less centrifugal spinning, fingers are formed at the front of thin liquid film due to the theory of Rayleigh–Taylor instability. We find that the lower solution concentration and higher rotational speed favor the formation of thinner and longer fingers. Then, the critical angular velocity and initial jet velocity for nozzle-/nozzle-less centrifugal spinning are obtained in accordance with the balance of centrifugal force, viscous force, and surface tension. When jet leaves the spinneret, it will undergo a series of motions including necking and whipping processes, and then, a steady spiral jet path is formed with its radius getting tighter. Finally, we experimentally study the effect of rotational speed and solution concentration on jet path, which shows that the higher rotational speed results in a larger radius of jet path while the solution concentration has little effect on it. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1547–1559

A comparative study of jet formation in nozzle‐ and nozzle‐less centrifugal spinning systems

Abstract: Centrifugal spinning, a recently developed approach for ultra‐fine fiber production, has attracted much attention as compared with the electrospinning, due to its high yield, no solution polarity and high‐voltage electrostatic field requirements, etc. In this study, the jet formation process and spinning parameters on jet path are explored and compared in nozzle‐ and nozzle‐less centrifugal spinning systems. For nozzle‐less centrifugal spinning, fingers are formed at the front of thin liquid film due to the theory of Rayleigh–Taylor instability. We find that the lower solution concentration and higher rotational speed favor the formation of thinner and longer fingers. Then, the critical angular velocity and initial jet velocity for nozzle‐/nozzle‐less centrifugal spinning are obtained in accordance with the balance of centrifugal force, viscous force, and surface tension. When jet leaves the spinneret, it will undergo a series of motions including necking and whipping processes, and then, a steady spiral jet path is formed with its radius getting tighter. Finally, we experimentally study the effect of rotational speed and solution concentration on jet path, which shows that the higher rotational speed results in a larger radius of jet path while the solution concentration has little effect on it. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1547–1559

Improved C-dump converter for switched reluctance motor drives

Abstract: This study presents a new power converter for switched reluctance motor-based drives. In comparison with the standard power systems, the proposed one allows reduction of the switching losses, especially in a low-speed range, as well as eliminates energy intake from source during the energy discharge process. As a result the efficiency of drive can be increased in the entire range of rotational speed. The computer model of the drive and a detailed study on relationships between the output power and the rotational speed for a sample two-phase motor-based drive are presented. To verify simulations results the measurements on the laboratory test-stand are carried out.

Optimization of process parameters for friction stir lap welding of carbon fibre reinforced thermoplastic composites by Taguchi method

Abstract: Friction stir welding process parameters such as welding speed, rotational speed and tilt angle affect the strength of the weld joint For maximizing the weld strength, these process parameters must therefore be properly selected and optimized This study presents an application of Taguchi method to optimize process parameters like welding speed, rotational speed and tilt angle to maximize lap weld tensile-shear strength in 4 mm thick polypropylene composite sheets with 20 wt% carbon fiber To this end, a L9 orthogonal array of Taguchi method using three factors at three levels was used Analysis of variance and confirmation tests were conducted The results indicated that welding speed, rotational speed and tilt angle are respectively the significant parameters affecting the lap weld strength Optimization results also showed that tensile-shear strength of 606 MPa was obtained when welding speed, rotational speed and tilt angle were 25 mm/min, 1250 rpm and 1 degree, respectively

Equations of motion of rotating composite beam with a nonconstant rotation speed and an arbitrary preset angle

Abstract: In the presented paper the equations of motion of a rotating composite Timoshenko beam are derived by utilising the Hamilton principle. The non-classical effects like material anisotropy, transverse shear and both primary and secondary cross-section warpings are taken into account in the analysis. As an extension of the other papers known to the authors a nonconstant rotating speed and an arbitrary beam’s preset (pitch) angle are considered. It is shown that the resulting general equations of motion are coupled together and form a nonlinear system of PDEs. Two cases of an open and closed box-beam cross-section made of symmetric laminate are analysed in details. It is shown that considering different pitch angles there is a strong effect in coupling of flapwise bending with chordwise bending motions due to a centrifugal force. Moreover, a consequence of terms related to nonconstant rotating speed is presented. Therefore it is shown that both the variable rotating speed and nonzero pitch angle have significant impact on systems dynamics and need to be considered in modelling of rotating beams.

Effects of the tool rotational speed and shoulder penetration depth on mechanical properties and failure modes of friction stir spot welds of aluminum 2024-T3 sheets

Abstract: In this work, friction stir spot welding with 1.6 mm thickness of the 2024-T3 aluminum alloy is carried out. The effects of the tool rotational speed and shoulder penetration depth on surface appearance, macrostructure, temperature profile, maximum failure load and failure modes are investigated. Results show that, the effect of the tool rotational speed on maximum tensile shear load is similar to the effect of the shoulder penetration depth, increasing tool rotational speed and shoulder penetration depth resulted in the increase of the tensile shear load. Maximum load of about 8282 N is obtained by using 1000 rpm rotational speed and 0.7 mm shoulder penetration depth. Observation of the failed specimens indicates two types of failure modes under tensile shear loading, the shear fracture that occurs in low shoulder penetration depths and tensile shear fracture that occurs in high shoulder penetration depths.

Experimental and analytical investigation of the thermal necrosis in high-speed drilling of bone.

Abstract: Bone loss due to thermo necrosis may weaken the purchase of surgically placed screws and pins, causing them to loosen postoperatively. The heat generated during the bone drilling is proportional to cutting speed and force and may be partially dissipated by the blood and tissue fluids, and somehow carried away by the chips formed. Increasing cutting speed will reduce cutting force and machining time. Therefore, it is of interest to study the effects of the increasing cutting speed on bone drilling characteristics. In this article, the effects of the increasing cutting speed ranging from 500 up to 18,000 r/min on the thrust force and the temperature rise are studied for bovine femur bone. The results of this study reveal that the high-speed drilling of 6000-7000 r/min may effectively reduce the two parameters of maximum cortical temperature and duration of exposure at temperatures above the allowable levels, which in turn reduce the probability of thermal necrosis in the drill site. This is due to the reduction of the cutting force and the increase in the chip disposal speed. However, more increases in the drill bit rotational speed result in an increase in the amount of temperature elevation, not because of sensible change in drilling force but a considerable increase in friction among the chips, drill bit and the hole walls.