Showing papers on "Rotational speed published in 2015"

3D CFD Analysis of a Vertical Axis Wind Turbine

Abstract: To analyze the complex and unsteady aerodynamic flow associated with wind turbine functioning, computational fluid dynamics (CFD) is an attractive and powerful method. In this work, the influence of different numerical aspects on the accuracy of simulating a rotating wind turbine is studied. In particular, the effects of mesh size and structure, time step and rotational velocity have been taken into account for simulation of different wind turbine geometries. The applicative goal of this study is the comparison of the performance between a straight blade vertical axis wind turbine and a helical blade one. Analyses are carried out through the use of computational fluid dynamic ANSYS® Fluent® software, solving the Reynolds averaged Navier–Stokes (RANS) equations. At first, two-dimensional simulations are used in a preliminary setup of the numerical procedure and to compute approximated performance parameters, namely the torque, power, lift and drag coefficients. Then, three-dimensional simulations are carried out with the aim of an accurate determination of the differences in the complex aerodynamic flow associated with the straight and the helical blade turbines. Static and dynamic results are then reported for different values of rotational speed.

A Self‐Powered Angle Measurement Sensor Based on Triboelectric Nanogenerator

Abstract: A self-powered, sliding electrification based quasi-static triboelectric sensor (QS-TES) for detecting angle from rotating motion is reported. This innovative, cost-effective, simply-designed QS-TES has a two-dimensional planar structure, which consists of a rotator coated with four channel coded Cu foil material and a stator with a fluorinated ethylenepropylene film. On the basis of coupling effect between triboelectrification and electrostatic induction, the sensor generates electric output signals in response to mechanical rotating motion of an object mounted with the sensor. The sensor can read and remember the absolute angular position, angular velocity, and acceleration regardless being continuously monitored or segmented monitored. Under the rotation speed of 100 r min−1, the output voltage of the sensor reaches as high as 60 V. Given a relatively low threshold voltage of ±0.5 V for data processing, the robustness of the device is guaranteed. The resolution of the sensor is 22.5° and can be further improved by increasing the number of channels. Triggered by the output voltage signal, the rotating characteristics of the steering wheel can be real-time monitored and mapped by being mounted to QS-TES. This work not only demonstrates a new principle in the field of angular measurement but also greatly expands the applicability of triboelectric nanogenerator as self-powered sensors.

Washing machine and method of controlling the same

Abstract: A washing machine including an inner tub for receiving clothes, an outer tub accommodating the inner tub, a motor for supplying rotational force to rotate the inner tub, and a hanger unit detachably coupled to an upper end of the outer tub and from which clothes are hung, whereby wrinkles of the clothes hung from the hanger unit are reduced by virtue of vibration generated during rotation of the motor. A method of controlling a washing machine including hanging clothes on a hanger unit coupled to the inner tub, rotating the inner tub at a first lower rotational speed, and rotating the inner tub at a second rotational speed higher than the first lower rotational speed.

Melt electrospinning onto cylinders: effects of rotational velocity and collector diameter on morphology of tubular structures

Abstract: Melt electrospinning writing is a direct-writing additive manufacturing process that involves depositing a continuous, viscous and electrohydrodynamically stabilised molten jet onto a collector. Here, molten threads of medical-grade polycaprolactone (PCL) are directed towards stationary/rotating cylindrical collectors (0–6600 rpm), including very slow revolutions well below the critical translation speed (approximately 600 mm min−1) of the molten jet. In this slow-rotation region, the speed of the jet is faster than the movement of the collector and buckled/coiled fibres are produced due to compressive viscoelastic forces. The results are porous PCL tubes with wall morphologies often associated with viscoelastic liquids impinging onto a surface. The curvature of the collector affects how the fibre is deposited, with preferential fibre deposition along the axis of the cylinder. When the collector rotation speed is increased to greater than the speed of the jet, then straight fibres are produced. Such tubular structures have applications in tissue engineering. © 2015 Society of Chemical Industry

Microstructural and mechanical properties of friction stir welded 5050 Al alloy and 304 stainless steel plates

Abstract: In this study, effects of different operating conditions on friction stir welding (FSW) of dissimilar sheets of 5050 aluminum (Al) alloy and 304 stainless steel have been investigated. Recently, FSW process has been used for joining of dissimilar materials due to its ability to eliminate local casting defects of the conventional fusion welding techniques. Microstructure and mechanical properties of weld nugget in FSW process mainly depend on several parameters such as tool rotational speed, feed rate, offset, and pin profile. In the present work, effects of tool rotational speed, feed rate and offset, together with annealing process on the tensile behavior and microhardness of the welding procedure were investigated and discussed. Based on the experiments, our results showed that decreasing tool rotational speed from 710 to 500 rpm besides increasing tool feed rate from 40 to 80 mm/min leads to an improved joint. Furthermore, the defect on the stirred zone was decreased by increasing the tool offset up to 1.5 mm. On the other hand, enhancements of up to 100 and 9 % in elongation and tensile strength were achieved by applying the annealing process, respectively.

Analysis of process parameters effects on dissimilar friction stir welding of AA1100 and A441 AISI steel

Abstract: A prominent benefit of friction stir welding process is to join plates with dissimilar material. In this study, an attempt is made to find effects of tool offset, plunge depth, welding traverse speed and tool rotational speed on tensile strength, microhardness and material flow in dissimilar friction stir welding of AA1100 aluminium alloy and A441 AISI steel plates. Here, one factor at a time experimental design was utilised for conducting the experiments. Results indicated the strongest joint obtained at 1·3 mm tool offset and 0·2 mm plunge depth when the tool rotational speed and linear speed were 800 rev min− 1 and 63 mm min− 1 respectively. The maximum tensile strength of welded joints with mentioned optimal parameters was 90% aluminium base metal. Fracture locations in tensile test at all samples were in aluminium sides. Owing to the formation of intermetallic compounds at high tool rotational speed, the microhardness of joint interface goes beyond that of A441 AISI steel.

Effect of welding parameters on microstructure and mechanical properties of friction stir welded joints of 2060 aluminum lithium alloy

Abstract: Two-millimeter-thick 2060 Al-Li alloy plates were friction stir welded under a welding speed of 95–150 mm/min and rotation speed of 750–1500 rpm. The effects of welding speed and rotation speed on formation quality, microstructure, secondary phase particles’ transformation, and mechanical properties of the joints were investigated. The results show that defect-free joints are produced for varying friction stir welding (FSW) parameters, and nugget size increases firstly and then decreases with increasing rotation speed or decreasing welding speed. The weld nugget zones (WNZs) have fine dynamically recrystallized grains, and the size decreases to 7.9 μm with increasing rotation speed to 1180 rpm or decreasing welding speed to 118 mm/min, while the grains are coarsened at 1500 rpm or 95 mm/min. A similar trend occurs in the transformation of secondary phase particles, whose size is the smallest in WNZ at 1180 rpm–118 mm/min. All joints exhibit softened zones where the hardness is the lowest, and the joints fracture from WNZs or heat-affected zones. The joints welded at 1180 rpm–118 mm/min perform the highest ultimate tensile strength of 495 MPa, yield strength of 380 MPa, and elongation of 10.2 %. With increasing rotation speed or decreasing welding speed, the strengths and elongation of the joints increase firstly and then decrease.

Prediction of grain size and mechanical properties in friction stir welded pure copper joints using a thermal model

Abstract: In this study, a thermal model was developed and applied to simulate the friction stir welding of pure copper plates with the thickness of 2 mm. The different traverse speeds of 100, 200, 300, and 400 mm min−1 and rotational speeds of 400, 700, 900 rev min−1 were considered as welding parameters. Microstructural characterization, hardness measurement, tensile test, and fractography were conducted experimentally. The comparison between the numerical and experimental results showed that the developed model was practically accurate. In addition, the results confirmed that the peak temperature was the dominant factor controlling the grain size and mechanical properties, where the fine grains could be achieved at low rotational speed as well as high traverse speed. Consequently, lower peak temperature leads to the high ultimate tensile strength and hardness and the low elongation values.

Elucidating of tool rotational speed in friction stir welding of 7020-T6 aluminum alloy

Abstract: The 7020-T6 aluminum alloy plates of 4 mm thickness were friction stir welded at rotational speeds of 400, 600, 800, and 1000 rpm and constant traverse speed of 100 mm/min. The peak temperatures of the joints were recorded by precise thermocouples. Microstructure, hardness, tensile properties, and fracture surfaces of the joints were analyzed. The results showed that decreasing the tool rotational speed from 1000 to 400 rpm decreased the peak temperature from 311 to 209 °C, and hence caused a lower heat input. In addition, lower rotational speeds result in higher hardness and tensile strengths. The higher hardness and ultimate tensile strength were related to the grain boundary, precipitation, and substructure strengthening mechanisms. In addition, the fracture surfaces of the joints welded at higher heat input conditions showed more ductile mode in comparison with that of welded at lower heat input condition, which confirmed the lower tensile elongation of the joints welded at lower rotational speeds.

Kinematics and trajectory of both-sides cylindrical lapping process in planetary motion type

Abstract: The both-sides lapping process in planetary motion type is proposed in this paper to lap and polish the cylindrical surface of bearing roller. The rolling speed of roller is the key kinematical parameter that affects the generation of cylindrical surface of roller. Through analysis of friction forces and pure rolling motion, it was discovered that the rolling speed of roller only depends on the rotation speed of lower plate rather than upper plate. Based on the above result, the geometry and kinematics of workpiece in this method is described, and the functions are proved valid by an experiment in which the rolling speed of roller is observed in video. By theoretical tests under different speed conditions, it is indicated that the roller's rolling speed varies with respect to time along a nonstandard cosine curve with an offset, its amplitude depends on the speeds of lower plate rotation and carrier circulation, and its offset depends on the speeds of lower plate rotation and carrier rotation. Based on geometry and kinematics, the trajectories on the cylindrical surface of roller and on the flat surface of plate are both described and simulated. The standard deviation and the range of path curve length distribution density are applied to numerically evaluate and analyze the trajectory distribution. The effect of speed parameters on the trajectory distribution, and the generation of trajectory with respect to time are investigated.

Speed Estimation of an Induction Motor Operating in the Nonstationary Mode by Using Rotor Slot Harmonics

Abstract: In this paper, an analysis of techniques of digital signal processing used for estimating the motor slip and rotational speed of an induction motor operating in stationary or nonstationary condition by using rotor slot harmonics observed in the stator current waveform is presented. The novelty of this paper is related with three topics. First, zoom short time Chirp-Z transform was used to find the fundamental supply frequency intending to improve accuracy without increasing computational complexity. Second, it presents a tool that can be used to identify whether a motor is capable or not of producing principal slot harmonics. Finally, an algorithm was developed to find an optimal window length using rotational speed maximum relative deviation. The use of this approach was analyzed when the motor was powered by a frequency converter driving a variable load and operating in strongly nonstationary conditions. The correctness of the method has been confirmed by experimental test results. Finally, the proposed method was implemented in a conventional sucker-rod pumping unit (25D-67-36-American Petroleum Institute), to estimate the rotational speed and slip when the motor is powered by a frequency converter.

Air conditioner and air speed control method thereof

Abstract: The invention discloses an air conditioner and an air speed control method thereof. Air scattering plates are arranged at the air outlet of an indoor unit so that the air outlet speed of the indoor unit can be decreased. Air guide plates are arranged so that the air outlet direction of the indoor unit can be regulated. The method includes the following steps that when the air conditioner runs in a refrigeration mode, if a non-air-feeling control instruction is received, the air conditioner is controlled to enter a non-air-feeling running mode; T1 is judged; if T1 is larger than Tw, the air scattering plates are controlled to be opened and are controlled to swing, or the air guide plates are controlled to move upwards, and the rotation speed of an indoor draught fan is controlled to be smaller than or equal to the first preset rotating speed; and if T1 is smaller than or equal to the difference between Tw and Tx, the air scattering plates are controlled to be closed, the air guide plates are controlled to be opened to the preset air outlet angle, the rotating speed of the indoor draught fan is controlled to be smaller than or equal to the second preset rotating speed, and meanwhile when phi is judged to be larger than phi w, the air conditioner is controlled to enter the dehumidification mode. By means of the air conditioner and the air speed control method of the air conditioner, the comfortable temperature environment can be provided, and meanwhile the comfortable indoor air speed environment can be provided and comfort is improved.

A hydrodynamic analysis of a rotating drum operating in the rolling regime

Abstract: An experimental and numerical investigation of the hydrodynamic behavior in a rotating drum, operated in the rolling regime, was performed in the present work For all the simulations, the Euler–Euler approach was used A high-speed video camera technique was used in order to measure, experimentally, the particle velocity distribution The CFD simulations showed good agreement with the experimental results The influence of different drag models on particle velocity profile was analyzed It was observed that, the drag force can be neglected in the case of a rotating drum operated in the rolling regime where there is no fluid entering or leaving the system From the experimental and simulated results it was possible to verify the effect of the rotation speed and filling degree on the particle velocity in the active region and on its thickness