Low Angular Speed Research Articles

Modification of the Vertical Axis with Variations in the Number of Blades of the Savonius Wind Turbine

The potential wind speed in Indonesia is generally low at 3 m/s to 7 m/s so that this type of vertical axis turbine is considered very suitable for use in wind conditions in Indonesia. There are several types of vertical axis wind turbines. One type of vertical axis wind turbine is the Savonius wind turbine. Many advantages that this type of wind turbine has, such as being able to receive wind from all directions, easy and cheap to manufacture, and can rotate at a fairly low angular speed. This test was carried out to determine the performance of conventional and modified savonius turbines with 2 and 3 blades variables in each turbine blade shape. The form of modification made is by changing the shape of the blade twisting by 45o. The turbine is carried out on a laboratory scale with a wind source using a fan that is directly opposite the turbine. The results showed that the highest turbine power occurred in a modified 2-blade turbine, namely 1.88 Watt with a torque value of 0.04 Nm and a shaft rotation of 450 rpm. The highest rotation value is also obtained by 2 modified blades at a wind speed of 6 m/s producing 896 rpm. However, the highest torque value is obtained by a conventional 2-blade turbine with a value of 0.136 Nm. The highest turbine efficiency in each turbine is obtained by a modified 2 blade turbine with an efficiency value of 36.92% while the highest turbine efficiency for a modified 3 blade turbine reaches 11.69% which is considered less efficient than other turbines.

Closed-Form Solution for the Natural Frequencies of Low-Speed Cracked Euler–Bernoulli Rotating Beams

In this study, two closed-form solutions for determining the first two natural frequencies of the flapwise bending vibration of a cracked Euler–Bernoulli beam at low rotational speed have been developed. To solve the governing differential equations of motion, the Frobenius method of solution in power series has been used. The crack has been modeled using two undamaged parts of the beam connected by a rotational spring. From the previous results, two novel polynomial expressions have been developed to obtain the first two natural frequencies as a function of angular velocity, slenderness ratio, cube radius and crack characteristics (depth and location). These expressions have been formulated using multiple regression techniques. To the knowledge of the authors, there is no similar expressions in the literature, which calculate, in a simple way, the first two natural frequencies based on beam features and crack parameters, without the need to know or solve the differential equations of motion governing the beam. In summary, the derived natural frequency expressions provide an extremely simple, practical, and accurate instrument for studying the dynamic behavior of rotating cracked Euler–Bernoulli beams at low angular speed, especially useful, in the future, to establish small-scale wind turbines’ maintenance planes.

A Novel Method for Determining Angular Speed and Acceleration Using Sin-Cos Encoders.

The performance of vehicle safety systems depends very much on the accuracy of the signals coming from vehicle sensors. Among them, the wheel speed is of vital importance. This paper describes a new method to obtain the wheel speed by using Sin-Cos encoders. The methodology is based on the use of the Savitzky–Golay filters to optimally determine the coefficients of the polynomials that best fit the measured signals and their time derivatives. The whole process requires a low computational cost, which makes it suitable for real-time applications. This way it is possible to provide the safety system with an accurate measurement of both the angular speed and acceleration of the wheels. The proposed method has been compared to other conventional approaches. The results obtained in simulations and real tests show the superior performance of the proposed method, particularly for medium and low wheel angular speeds.

Effects of Rotor-Blade Deformation onto Performance of Domestic Wind Turbines

Paper is focused on the influence that blade deformations by torsion and bending due to drag, lift, and gravitational effects has on the performance of small wind turbines. A blade model of stiff finite elements connected by rotating junctions is used. Mechanical deformations are simulated by controlled gravity and torsional forces, and their effects are measured through the response of the wind turbine. Tests have been run before and after the deformation process under different wind conditions in a wind tunnel. No centrifugal stiffening and gyroscopic moments are considered due to the low angular speed. Wind speed was controlled to determine the effect of the deformation on the performance of the wind turbine as a function of the wind power. The results have shown that in all cases, the effects of the deformation are negative, and the decrease in power has been calculated depending on wind conditions.

Robust sensorless low‐speed trajectory tracking for a permanent magnet synchronous motor: An extended state observer based backstepping control approach

This article deals with the low‐speed sensorless trajectory tracking control of a permanent magnet synchronous motor (PMSM). The rotor position and angular speed are obtained through back electromotive forces (back‐EMF), using extended state observers (ESOs) in the alpha‐beta coordinates. Additionally, the estimation of the back‐EMF is used by an algebraic module to reconstruct online the position and speed using an off‐line estimation of the back‐EMF parameter . The control law is derived using a robust recursive controller design methodology, namely; the backstepping design approach in the d‐q coordinates. Estimation schemes allow the adaptation of the angular position, angular speed, and the load torque parameters in the control law. With this adaptation, the controller achieves the necessary robustness to reduce the effects of endogenous and exogenous perturbations present in the PMSM system. The trajectory tracking task is achieved at low angular speed, with the presence of a load torque applied to the motor shaft. Experimental results at low‐speed and rated load/no‐load conditions are presented to demonstrate the effectiveness and robustness of the proposed scheme.

Medial tibial stres sendromlu sporcularda ayak bileği izokinetik kas kuvveti ve naviküler çökme miktarı

Purpose: The purpose of this study is to compare some anatomical features and ankle isokinetic muscle strength of adolescent athletes with medial tibial stress syndrome (MTSS) and healthy control group and to examine the adequacy of ‘tibial facial traction theory in the development of MTSS.Materials and Methods: Adolescent athletes who had been diagnosed with MTSS during the season and healthy control group participants were included in the study. Demographic data and training details of the athletes were recorded. The MTSS score was used to determine the severity of the injury. The navicular drop test, lower extremity length measurement, and isokinetic muscle strength measurement were performed. Results: The complaint duration of the patients with MTSS (n:21) was 1.8 ± 1.8 months and the MTSS score was 3.9 ± 2.2. The control group (n:12) and the athletes diagnosed with MTSS had similar demographic characteristics and training details. There was no difference between the groups in terms of navicular drop and lower extremity length. There was no ‘lower extremity difference’ for right and left extremities. According to the results of the isokinetic muscle strength test in plantarflexion and dorsiflexion direction, there was no difference between the groups in terms of muscle strength at both low and high angular speeds. Conclusion: ‘The tibial traction theory’ does not sufficiently explain the pathogenesis of MTSS. Studies which evaluate isokinetic muscle strength and perform real-time dynamic analysis on the track are required to make recommendations for ideal protection and rehabilitation in cases of MTSS.

The relationship between isokinetic knee strength and jumping in young male volleyball players

Volleyball is a dynamic physical game that does not have a definite match duration but is based on high tempo, quickness, strength, flexibility, endurance and jumping. The aim of this study is to research the relationship between isokinetic knee strength and jumping height in young male volleyball players. 8 male volleyball players aged between 18-22 participated in the research voluntarily. In the study, the physical characteristics of the subjects (body height, body weight, body mass index) were determined, vertical jump heights were measured and at low (60 0 /sec) and high (300 0 /sec) speeds, the right and left knee flexion/extension concentric isokinetic strength test was applied. Data was analyzed with paired sample t-test and Spearman correlation coefficient test was used to determine the relationship between vertical jump and isokinetic strength (p<0.05). The right and left knees peak torque of the athletes were compared at low and high angular speeds and no significant difference was found. A significant positive correlation was detected between the jumping height and the right knee peak torque at low angular speed (r =.817, p<0.05). This result can be explained by the fact that quadriceps femoris, which is the biggest muscle of the lower extremity, is in the foreground during the jumps that volleyball players perform frequently. It may be advisable to give importance to leg strength training to increase the jump height.

Analysis of isokinetic knee strength in soccer players in terms of selected parameters

Purpose: The aim of study is to analyse isokinetic knee strength in soccer players in terms of selected parameters. Methods: A total of 30 subjects, 15 soccer players and 15 controls, were included in the study. Isokinetic knee strength measurements at angular speeds of 60°sec-1, 180°sec-1 and 240°sec-1 and pro-agility tests were conducted on the subjects. A body analyser was used for height, weight and body mass indexes (BMI) values. The training ages of the subjects and the positions of the soccer player group were recorded on personal information forms. Results: When the agility parameters were compared between football and control groups, a statistical difference was found in favour of the soccer player group (p &lt; 0.05). When the effects of body composition and isokinetic knee strength on agility were analysed, negative significant correlation was found between weight and agility, BMI and agility and 240° right knee extension strength and agility (p &lt; 0.05). When the positions of soccer players and isokinetic knee strengths were compared, significance was found between 60° right extension strength of defenders and midfielders and 60° left extension-flexion strengths of defenders and midfielders and forwards in favour of defenders (p &gt; 0.05). Conclusions: In conclusion, it was found that isokinetic knee strength did not have an influence on agility in low angular speeds, except for 240°sec-1 right extension. According to positions, as the isokinetic knee strength of defenders decreased, they showed higher results when compared with other positions.

Stator-Free Low Angular Speed Sensor Based on a MEMS Gyroscope

This paper demonstrates the implementation and tests the performance of a low angular speed sensor for rotary machinery based on a microelectromechanical system gyroscope. First, an experimental test setup is presented that features a top-of-the-line optical absolute angle encoder as a reference for characterizing the proposed sensor in a controlled environment chamber. A prototype of the proposed sensor has been designed and implemented with its architecture and hardware design described in detail. For the experimental purposes, a wireless synchronization scheme between the reference and the gyroscopic sensor is also discussed. The experimental measurement has taken place to benchmark the performance of the realized sensor. The experimental data have been processed and analyzed, and the results have been presented. The gyroscopic sensor has shown satisfactory results. The sensor has an accuracy of 0.06 °/s, standard deviation of 0.45 °/s, and hysteresis of 0.08 °/s.

Control of Large Salient Pole Synchronous Machines using Synchronous Optimal Pulsewidth Modulation

High-power grinding mills are used in the cement and mining industries to crush clinker or copper ore and grind these materials to fine powder. The multimegawatt speed-controlled mill drives operate at a very low angular speed. Synchronous motors with a high number of pole pairs are used as the prime movers. They are traditionally fed by load-commutated thyristorized cycloconverters. These are prone to failure modes that can lead to excessive torque pulsations and high overcurrents. The huge stator, which was built as a separate ring-shaped structure around the tubular mill, may then get mechanically displaced, and the operation of the plant is interrupted. A novel and reliable direct drive uses a voltage source inverter that operates at the unity power factor for increased efficiency. Synchronous optimal pulsewidth modulation ensures a low harmonic current distortion and reduced switching losses at a very low switching frequency. The optimization of the pulse patterns takes the anisotropic magnetic properties of a separately excited synchronous motor into account. The implementation in a 23-MW semiautonomous grinding mill installed in a Zambian copper mine is intended.

Modern Direct Torque and Flux Control methods of an induction machine supplied by three-level inverter

Abstract. This paper describes two modern direct torque and flux control methods of an induction machine supplied by a three-level inverter. Additionally, it presents a comparison of the methods both in static and dynamic states. The methods, in a specific way, make use of an increased number of active vectors of the three-level inverter in order to improve control quality and reduce switching frequency. The two methods modify the DTC method by using its advantages and eliminating, at the same time its drawbacks. In static states the comparison was based on the results of investigations performed for two different load values and three set values of angular speed, whereas in dynamic states the comparison was focused on the behavior of the machine at startup. The results of the investigations have shown that both methods give very good performance. They are characterized by both sinusoidal shape of flux and low current deformations even at low angular speeds i.e. less than 10% of the nominal value. The presented methods also allow to generate nominal flux for set zero angular speed in order to achieve excitation of the induction machine. The switching frequencies for both methods are very similar in almost the whole range of control but the methods have shown some differences in control quality, particularly for higher torque values.

Temperature Distribution of Taper Rolls in Preheating Furnace of Cold Rolling Continuous Annealing Line

In this article, three-dimensional (3-D) transient temperature distributions of taper rolls in a continuous annealing line (CAL) are investigated using finite-element analysis. Since the temperature of the strip is closely related to the surface temperature of the rolls due to the effect of contact heat transfer between them, it is crucial to determine the accurate surface temperature distributions of rolls in CAL. It is found that the temperature history of a roll remains identical and exhibits a radial-dependent distribution as the Peclet number of the roll decreases to a suitable small value, corresponding to a low angular speed of the roll. The computational time for the case with low Peclet number, however, can be significantly reduced. Moreover, it is seen that the results of a two-dimensional (2-D) model are in good agreement with those of the 3-D model in the central region covered with the strip, while the computational time of the former is about one-twentieth of the latter. Consequently, a minimum computational cost can be achieved by using 2-D model with a suitable lower value of Peclet number without sacrificing the accuracy of the simulation results.

Protostellar discs formed from rigidly rotating cores

Abridged: We use three-dimensional SPH simulations to investigate the collapse of low-mass prestellar cores and the formation and early evolution of protostellar discs. The initial conditions are slightly supercritical Bonnor-Ebert spheres in rigid rotation. The core mass and initial radius are held fixed at M_O=6.1 M_sun and R_O=17,000 AU, and the only parameter that we vary is the initial angular speed \Omega_O. Protostellar discs forming from cores with \Omega_O<1.35 10d-13 1/s have radii between 100 and 300 AU and are quite centrally concentrated; due to heating by gas infall onto the disc and accretion onto the central object, they are also quite warm, T>100 K, and therefore stable against gravitational fragmentation. In contrast, more rapidly rotating cores form discs which are less concentrated and cooler, and have radii between 400 and 1000 AU; as a consequence they are prone to gravitational fragmentation and the formation of multiple systems. We derive a criterion that predicts whether a rigidly rotating core having given M_O, R_O and \Omega_O will produce a protostellar disc which fragments whilst material is still infalling from the core envelope. We then apply this criterion to core samples for which M_O, R_O and \Omega_O have been estimated observationally. We conclude that the observed cores are stable against fragmentation at this stage, due to their low angular speeds and the heat delivered at the accretion shock where the infalling material hits the disc.

Induction Heating of Aluminum Billets Subjected to a Strong Rotating Magnetic Field Produced by Superconducting Windings

This paper presents an analysis of an original structure of induction heater using superconducting coils. With the proposed structure, two operating modes are possible to heat the aluminum billet. Either the billet is at standstill and placed within a strong rotating magnetic field (around 3.5 T) of low frequency (around 1 Hz), or the billet rotates at low angular speed (around 6 rad/s) within a strong dc magnetic field (around 3.5 T). The analysis is based on the analytical solution of two-dimensional diffusion equations for the magnetic vector potential. A closed-form expression is derived for the eddy-current power loss in the billet. This analytical expression can be used as a tool for design optimization of the induction heater. The analytical results are compared with those obtained by finite-element software. The study of the temperature field in the billet shows that a homogeneous temperature profile is obtained when a strong magnetic field of low frequency (rotating speed or ac current pulsation) is used.

Superconductors to boost wind power

More powerful generators are key to growing offshore wind farms.

Electrical method to measure the dynamic behaviour and the quadrature error of a MEMS gyroscope sensor

The electronics on board of a vibrating MEMS sensor is able to compensate only for small changes in the mechanical characteristics of the device. Thus, it is of great importance to find an easy and fast way to evaluate the mechanical parameters, such as the resonance frequency and the damping coefficient, of a MEMS sensor before putting the device on the market [A. Cigada, E. Leo, M. Vanali, Optical and electrical methods to measure the dynamic behaviour of a MEMS gyroscope sensor, Proceedings of IMECE2005 ASME International Mechanical Engineering Congress and Exposition 2005, Orlando, Florida, USA [14]]. Moreover, for a vibrating MEMS gyroscope also the quadrature error, i.e. [Y.Y. Bao, C.L. Yung, Modelling and compensation of quadrature error for silicon MEMS microgyroscope], has to be kept below a given threshold in order to be able to acurately measure low angular speeds. Verification tests are usually carried out at the end of the production process, i.e. when the package is complete. Thus, only electrical measurements are possible. In the present paper, a reliable approach to determine mechanical parameters as well as the quadrature error of the MEMS device through electrical measurements is proposed and results are compared to more traditional optical measurements.

Earth rotation measurement with micromechanical yaw-rate gyro

The direct measurement of the Earth's rotation rate by means of a micromechanical yaw-rate gyroscope is difficult to achieve due to the considerable parameter variations of the current state-of-the-art sensors of this type. This paper outlines and applies a model of the external factors' effect on the sensor measurement via a method for their compensation through a mechanical change in the sensor's orientation. This allows the determination of a value such as the Earth's rotation rate, which is at the limit of the sensor's sensitivity and less than its short-term stability. A specialized information-measurement system has been developed for the implementation of the method. This system has been used for a number of measurements, presented in a graphical form. As a result, an average value of the Earth's rotation rate has been derived. This method is applicable for a subjective categorization and evaluation of micromechanical gyroscopes using a natural source of a very low angular speed.

Dynamics of a Rigid Unbalanced Rotor with Nonlinear Elastic Restoring Forces. Part I: Theoretical Analysis

In a previous paper, the dynamic behaviour of a Jeffcott rotor was studied in the presence of pure static unbalance and nonlinear elastic restoring forces. The present paper extends the analysis to a rigid rotor with an axial length such as to make the transverse moment of inertia greater than the axial one. As in the previous investigation, the elastic restoring forces are assumed to be nonlinear and the effects of couple unbalance are also included but, unlike the Jeffcott rotor, the system exhibits six degrees-of-freedom. The Lagrangian coordinates were fixed so as to coincide with the three coordinates of the centre of mass of the rotor and the three angular coordinates needed in order to express the rotor's rotations with respect to a reference frame having its origin in the centre of mass. The precession motions of such a rotor turn out to be cylindrical at low angular speeds and exhibit a conical aspect when operating at higher speeds. The motion equations of the rotor were written with reference to a system that was subsequently adopted for the experimental analysis. The particular feature of this system was the use of a steel wire (piano wire) for the rotor shaft, suitably constrained and with the possibility of regulating the tension of the wire itself, in order to increase or reduce the nonlinear character of the system. The numerical analysis performed with integration of the motion equations made it possible to point out that chaotic solutions were manifested only when the tension in the wire was given the lowest values – i.e. when the system was strongly nonlinear – in the presence of considerable damping and rotor unbalance values that were so high as to lose any practical significance. Under conditions commonly shared by analogous real systems characterised by poor damping, where the contribution to nonlinearity is almost entirely due to elastic restoring forces, the analysis pointed out that precession motions may be manifested with a periodic character, whether synchronous or not, or a quasi-periodic character, but in no case is the solution chaotic.

A novel low-cost noncontact resistive potentiometric sensor for the measurement of low speeds

A novel low-cost sensor system for the measurement of low angular or linear speed is presented. The sensing element consists of a noncontact resistive potentiometer. The applied sliding electrode does not make mechanical contact with the resistive layer. The processing circuit consists of a very linear oscillator which converts the position quantity to a period-modulated signal. This signal can be directly read out by a microcontroller. A novel algorithm is presented which can eliminate or strongly reduce the influence of the many nonidealities, and which results in a short measurement time. The resolution of the low-cost angular speed sensor system is about 8/spl times/10/sup -2/ r/min in a measurement time of only 80 ms. The angular range is limited by the potentiometer geometry and the finite size of the sliding electrode, and typically amounts to about 270/spl deg/. The sensor system also indicates the moving direction.

Simulation of self-control of an electrostatic micromotor for an intravascular echographic system

In this paper, the possibility of using an electrostatic micromotor for an intravascular echographic system is studied. For this given application, the advantage of a micromotor is the absence of a long cable between motor and mirror. This advantage is real only if the micromotor speed can be controlled. In fact, electrostatic micromotors are often used with a step-by-step power supply but, for low mean angular speed (2000 rpm), the rotation is not regular with this type of command. So, we propose herein a self-control command based on the rotor-position control carried out by a capacitance measurement.