Rotational Speed Of Rotor Research Articles

Optimal tuning of the tuned mass damper (TMD) for rotating wind turbine blades

This paper presents the explicit formulas for optimal tuning of the tuned mass damper (TMD) for damping edgewise vibrations in rotating wind turbine blades. A 2-DOF model is first established for the rotating blade-TMD system, which acts as the basis for analytically deriving the optimal frequency-tuning and the optimal damping-tuning formulas. Two optimality criteria are considered, one based on equal dynamic amplification at two neutral frequencies and the other one based on equal modal damping ratio of the free vibration modes. As a result, two slightly different optimal frequency-tuning formulas are obtained. The formula for optimal TMD damping ratio is obtained by means of dynamic amplification analysis, and the optimal damping ratio turns out to be dependent on the rotor rotational speed. Comparison of the two optimal frequency-tuning formulas are performed in terms of the dynamic amplification curves and the root loci, using the NREL 5 MW wind turbine as the numerical example. For realistic rotor rotational speeds, the two optimal frequency-tuning formulas lead to almost identical TMD parameters.

Measurement System of a Magnetic Suspension System for a Jet Engine Rotor.

This paper presents laboratory results on the measurement system of a magnetic suspension bearing system for a jet engine rotor of an unmanned aerial vehicle (UAV). Magnetic suspension technology enables continuous diagnostics of a rotary machine and eliminates of the negative properties of classical bearings. This rotor-bearing system consists of two radial magnetic bearings and one axial (thrust) magnetic bearing. The concept of the bearing system with a magnetically suspended rotor for UAV is presented in this paper. Rotor geometric and inertial characteristics were assumed according to the parameters of a TS-21 jet engine. Preliminary studies of the measurement system of rotor engines were made on a laboratory stand with homopolar active magnetic bearings. The measurement system consisted of strain gauges, accelerometers, and contactless proximity sensors. During the research, strains were registered with the use of a wireless data acquisition (DAQ) system. Measurements were performed for different operational parameters of rotational rotor speed, control system parameters, and with the presence of disturbance signals from the control system. In this paper, obtained operational characteristics are presented and discussed.

ЧИСЛЕННОЕ МОДЕЛИРОВАНИЕ ДИНАМИКИ ГИБКОГО РОТОРА С ДВУМЯ ШАРОВЫМИ АВТОБАЛАНСИРАМИ

Ball auto-balancing devices can to compensate changes of unbalance "on the move" only for rotors operating at supercritical speeds. For automatic balancing of such rotors, classified as flexible rotors, several auto-balancers located in different cross sections of the shaft are necessary. This makes it necessary to account bending fluctuations on studies of dynamics of the rotor with auto-balancers, that is especially important in the design of the real rotors. In view of the complexity of experimental studies of such rotors in the article the method of direct numerical simulation of the dynamics of the flexible rotor system – supports – auto-balances is considered. The methodological basis of this method is the use of a discrete multi-mass rotor model, which is equivalent in dynamic characteristics to a real rotor, and also the equations of dynamics of the system discrete rotor – supports – auto-balancers, obtained in the direct form of recording. For definition of discrete masses and a matrix of coefficients of influence of stiffness of rotor cross-sections it is supposed to use calculations for finite-element model of a real rotor by existing software complexes of the engineering analysis. The mathematical model of the system dynamics obtained by the Lagrange method takes into account the non-stationarity of the rotor rotation speed, the influence of gravity and the rolling friction of the balls in the auto-balancer cages. Verification of the mathematical model was performed by reproducing the published data using a computational model for a two-support single-disk three-mass rotor with a two-ball auto-balancer. For a four-mass rotor with two two-ball auto-balancers, the results of numerical simulation of dynamics for the modes of acceleration, steady-state rotation and deceleration are presented. It is shown that for the system under consideration, only partial auto-balancing takes place in the steady rotation mode, including after a stepwise increase of the imbalance.

Method for eliminating aerodynamic lift vibration of rigid rotor helicopters based on the novel sine-trim model

A novel methodology called sine-trim is proposed from the phasor superposition principle for AC voltages in electrical engineering to eliminate the aerodynamic lift vibration of rigid rotor helicopters. An advancing blade concept rotor aerodynamic analysis model is presented on the basis of free-wake method associated with the inner- and outer-trim modules. The inner-trim module transforms the blade lift distribution curve of a rigid lift-offset rotor into a similar sinusoidal one by adjusting the blade pitch in each azimuth. An acceleration algorithm that could greatly improve the inner-trim calculation efficiency is provided. The outer-trim module selects the amplitude of the lower rotor as the preset trim value, and it is reliable and effective in trimming the overall forces and moments of the helicopter by modifying the lift sinusoid curve parameters of the upper and lower rotors. In the sine-trim, the upper and lower rotors have similar sinusoidal lift distribution parameters, and their phases and amplitudes exhibit a direct inverse relationship. Calculation results show that after being sine-trimmed, the total aerodynamic lift vibration of the rigid rotors could be eliminated regardless of the change in flight and operating conditions, such as flight speed, number of blades, and rotor rotational speed. The optimal blade pitch control distribution, which is a comprehensive superposition of many higher harmonic inputs, is obtained in all azimuths. For the same lift-offset, after sine-trimming, the effective lift-to-drag ratio may have a small degree of loss compared with the conventional advancing blade concept rotor.

Effects of Radius and Length on the Nanomotor Rotors in Aqueous Solution Driven by the Rotating Electric Field

Nanomotors with ultrahigh speed that are easy to assemble, with low friction and long service life, have been actively researched in several fields recently, owing to the relentless development of nanoelectromechanical systems (NEMS). They are based on the principle that the reorientation of the water dipole moment induced by the rotating electric field can rotate the carbon nanotubes (CNTs) immersed in the aqueous solution. The dynamic behaviors of nanomotor rotors with different radii and lengths are studied. According to molecular dynamics (MD) simulations, the lag angle between the nanomotor rotor and the water molecule dipole can be reduced by increasing the radius of the nanomotor rotor or increasing the length of the nanomotor rotor. At the same time, the synchronization speed between the nanomotor rotor and the rotating electric field can also be increased by increasing the radius of the nanomotor or reducing the length of the nanomotor rotor. These studies show that the radii and lengths of the nanomotor rotor can affect the nanomotor rotor rotation angle, rotation speed and cycle time. Our findings may have potential applications in the design of nanopropellers and nanogears of complex structure.

Reliability test prototype wind turbine savonius type helical as an alternative electricity generator

The consumption of energy in the world today is still dominated by fossil fuels that will gradually run out. This period we must utilize renewable energy sources. One source of renewable energy that is environmentally friendly and we can use is wind energy. Wind turbines can be used to generate electrical energy so that it can solve one of the energy problems for people in need. A suitable wind turbine at low wind speed and medium wind speed is a type of Savonius turbine. The development of research is made prototype wind turbine. This test is carried out on a prototype of a vertical axis type wind turbine and aluminum flask. The rotor has a diameter of 350 mm and a height of 440 mm. The measured parameters were wind speed, rotation speed of rotor, voltage, and current of the generator. The performance of wind turbine savonius in this test at wind speed 4 m / s up to 6 m / s, maximum rotation of turbine shaft 35,40 rpm, electric power 6.94 watts at 6 m / s, at 6 m / s wind speeds produce wind power of 18.65 watts and produce electrical power of 6.94 watts.

Variable rotor speed strategy for coaxial compound helicopters with lift–offset rotors

ABSTRACTThe coaxial compound helicopter with lift-offset rotors has been proposed as a concept for future high-performance rotorcraft. This helicopter usually utilizes a variable-speed rotor system to improve the high-speed performance and the cruise efficiency. A flight dynamics model of this helicopter associated with rotor speed governor/engine model is used in this article to investigate the effect of the rotor speed change and to study the variable rotor speed strategy. Firstly, the power-required results at various rotor rotational speeds are calculated. This comparison indicates that choice of rotor speed can reduce the power consumption, and the rotor speed has to be reduced in high-speed flight due to the compressibility effects at the blade tip region. Furthermore, the rotor speed strategy in trim is obtained by optimizing the power required. It is demonstrated that the variable rotor speed successfully improves the performance across the flight range, but especially in the mid-speed range, where the rotor speed strategy can reduce the overall power consumption by around 15%. To investigate the impact of the rotor speed strategy on the flight dynamics properties, the trim characteristics, the bandwidth and phase delay, and eigenvalues are investigated. It is shown that the reduction of the rotor speed alters the flight dynamics characteristics as it affects the stability, damping, and control power provided by the coaxial rotor. However, the handling qualities requirements are still satisfied with different rotor speed strategies. Finally, a rotor speed strategy associated with the collective pitch is designed for maneuvering flight considering the normal load factor. Inverse simulation is used to investigate this strategy on maneuverability in the Push-up & Pull-over Mission-Task-Element (MTE). It is shown that the helicopter can achieve Level 1 ratings with this rotor speed strategy. In addition, the rotor speed strategy could further reduce the power consumption and pilot workload during the maneuver.

Studying the load jam modes within the framework of a flat model of the rotor with an auto­balancer

This paper reports the analytically investigated load jam modes (balls, rollers, pendulums) within a flat model of the balanced rotor on isotropic elastic-viscous supports carrying the auto-balancer with many identical loads. A physical-mathematical model of the rotor-auto-balancer system is described. The differential equations have been recorded for the system motion with respect to the coordinate system that rotates at constant speed. We have found all the steady modes of motion under which loads get stuck at a constant speed of rotation. In the coordinate system that rotates synchronously with loads, these movements are stationary. Our theoretical study has demonstrated that the load jam modes in the rotor-auto-balancer system are the single-parametric families of steady movements. Each jam mode is characterized by a certain load configuration and the appropriate frequency of jams. In the coordinate system that synchronously rotates with loads: – the rotor displacement is constant; – the parameter is the angle defining the direction of the rotor displacement vector; – loads take certain fixed positions relative to the rotor displacement vector; these positions depend on the rotor rotation speed. The auto-balancer with n b identical loads of different configurations has n b +1 loads. The total number of different types of load jam modes: – 2(n b +1), if n b is odd; – 2n b +1, if n b is even. The total number of different jam frequencies: – 3(n b +1)/2, if n b is odd; – 3n b /2+1, if n b is even. The total number of different characteristic speeds is n b +2. The characteristic speeds are the points of movement bifurcations because their transitions give rise to the emergence or disappearance of single-parametric families of movements that correspond to a certain jam mode. At these points, jam modes can acquire or lose stability.

The experimental research and mechanism analysis on the influence of wave rotor rotational speed on the wave system and flow losses of gas wave ejector

Gas wave ejector (GWE) is an efficient injection and supercharging device. The rotational speed of wave rotor is an important parameter affecting the equipment performance. The influence of rotational speed on device performance was intensively studied by experiments and numerical simulations. The results suggest that there is an optimal speed to optimize the equipment performance with fixed pressure ports. Redundant compression waves are generated destroying the ideal wave system when the speed deviates from the optimal value. And the performance reduction induced by these redundant waves is different since the pressure, initial pressure ratio and reversed pressure ratio in the passages of stable pressure region are different in different working conditions. In addition, increasing rotational speed to a certain extent can reduce various types of loss in the passages. However, the viscous dissipation increases sharply if the speed is high enough. The propagation speed of shock wave increases with the increase of rotational speed, which should be taken for granted when designing the geometries of pressure ports. In the experimental conditions, the highest isentropic efficiency and ejection rate GWE can reach about 60% and 80% respectively in the experiments of this paper.

Process of crushing sprouted grains of rye, wheat and triticale in combined disperser dryer

One of promising products for obtaining natural food additives can be germinated grain of various cereals crushed to powder. Selection of mechanical impact method on germinated grain directly depends on physical-and-mechanical properties of the material. The most promising are drying and grinding installations of combined type based on interaction of suspended layer and grinding devices with blade rotor. It allows to ensure efficient use of shear and cut deformations to obtain the final product of the required particle size distribution. The paper presents results on study of mechanical impact methods on germinated grain and the least energy-intensive method is defined. It is determined that the most promising for grinding are units of combined type. Based on the research conducted, the design of combined dryer with integrated rotary chopper (disperser dryer) has been substantiated and practically implemented. Experimental test installation was designed and manufactured to study the process of thermomechanical processing of high-moisture food raw materials. It allows to implement and study drying and grinding combined processes. Mathematical model building task for grinding process of germinated grain in disperser dryer based on Lagrange method is considered. Mathematical model of grinding process of germinated grain in unit with twisted flow based on Rehbinder theory is proposed. Mathematical model of elastic-plastic deformation of germinated grain under uniaxial static immersion is obtained. Correlation of granulometric composition of finished product with performance of disperser dryer, temperature of drying agent, shredder rotor rotation speed, initial moisture content in germinated grain have been studied. Froude number is defined. Conclusions and practical recommendations will contribute to solving problems of improving quality, safety and competitiveness, as well as increasing export potential of domestic food and agricultural products.

Numerical analysis of the dynamic behavior of a rotor-bearing-brush seal system with bristle interference

To minimize leakage and maintain the efficiency of turbomachinery, brush seal can be installed with zero clearance or interference as the flexibility. This leads to contact between the rotor and bristle pack, and may cause self-excited vibration, even instability. In this study, to establishment a mathematical model of the rotor system, a seal force model with bristle interference is proposed and the nonlinear oil-film force is applied in view of short bearing assumption. The influences of main factors containing rotor rotational speed, installing interval, disc mass, and disk eccentricity on the nonlinear characteristics of the rotor-bearing-brush seal system are conducted by adopting bifurcation diagram, spectrum cascade, axis orbit, and Poincare map. The results indicate that the vibration amplitude of the system with bristle interference is a bit larger than that without interference. The system stability is enhanced with smaller disk mass at a higher rotational speed. The proposed model could provide valuable reference for the design of a rotor-bearing-seal system.

FEATURES OF MODELING THE FLOW AROUND THE HELICOPTER MAIN ROTOR TAKING INTO ACCOUNT ARBITRARY BLADES MOTION

The article considers the problem of the flow around the helicopter main rotor taking into account blades flapping in the plane of rotation and in the plane of thrust as well as the elastic blades deformation. The rotor rotation is modeled by the method of converting Navier-Stokes equations from a fixed coordinate system associated with the incoming flow into a rotating system associated with the rotor hub. For axial flow problems, this makes it possible to formulate the problem as stationary at a constant rotational speed of rotor. For a mode of skewed flow around the rotor in the terms of incident flow in this system it is necessary to solve the non-stationary problem. To solve the problem, the method of deformable grids is used, in which the equations are copied taking into account the grid nodes motion determined in accordance with the spatial blades motion, and SST turbulence model is used for closure. The results of the test calculations of the main rotor aerodynamic characteristics with and without blade flapping are presented in this paper. The coefficients of the main rotor thrust cT and the blades hinge moments mh are compared. The calculations were carried out in the CFD software ANSYS CFX (TsAGI License No. 501024). The flow around a four-bladed main rotor of a radius of 2.5 meters is modeled in the regime of skewed flow. The speed of the incoming flow came to 85 m/s under normal atmospheric conditions. The rotor was at an angle of attack of −10˚. To calculate the rotor motion without taking into account the flapping movements, we used the nonstationary system of Navier-Stokes equations with the closure with SST turbulence model. The calculation was being carried out until the change in the maximum value of the rotor thrust during one revolution became less than 1%. For modeling flapping blade movements, the control laws and equations describing the angle of blade flapping as a function from its azimuth angle obtained from the experiment were used. The procedure for reconstructing the grid according to a given law was conducted using standard grid deformation methods presented in the ANSYS CFX software. When solving the nonstationary Navier-Stokes equations, a dual time step was used. The obtained results show that accounting of the effect of flapping movements and cyclic control of the blades has an impact on the character of changing the main rotor thrust coefficient during one revolution and significantly changes the shape of the graph of the hinge moment coefficient of each blade.

Parametric studies on dynamic stiffness of ball bearings supporting a flexible rotor

Most of the researchers in the field of dynamics of the rolling element bearing have considered bearing stiffness as time invariant and/or not related to dynamics of the bearing. In the present paper, the bearing stiffness has been taken as function of dynamic response at every time step of numerical simulation and a detailed parametric study is performed to investigate the effect of flexibility of the rotor shaft, rotational speed, and internal radial clearance on the instantaneous and average value of dynamic stiffness of the ball bearing. The mathematical formulation is based on the Timoshenko beam finite element theory. Gravity and bearing forces are considered as external forces acting on a free-free flexible shaft. A stable Newmark-β numerical integration scheme coupled with Newton–Raphson method is used for numerical integration and for convergence to an accurate value of bearing stiffness. The results showing the variation of different components of bearing stiffness as a function of time-invariant parameters has improved the understanding of the dynamic behavior of the bearing during motion. The variation pattern of bearing stiffness coefficients is observed to be sensitive to direction of rotation. The amplitude of periodic change of these coefficients increases with the increase of the stiffness ratio of shaft and the decrease of radial clearance.

Determination of the rational rotation speed of the intensive separation zone rotors of a rotary potato digger

Research and experimental results of a potato digger with a rotary separating web are published in this article. The main design characteristics of the rotors are justified by analysis of existing constructions and their working processes. Special attention is paid to definition of rotational speed of the rotors of the rotary separation web. Theoretical researches have determined that potato layer moves steadily while rotational speed of rotary working bodies equals 230 rpm. Results of experimental researches demonstrate that the rotary separation web removes 89,7% impurities while rotational speed of rotary working bodies equals 242 rpm.

The Control of Squirrel-Cage Induction Electromotor with Constant Magnetization Current

In this paper, we study the control algorithm of electromagnetic torque and rotation speed of squirrel-cage induction electromotor with constant magnetization current. We can ensure the constant magnetization current by acting on stator voltage vector. We distinguish two methods of construction of the given magnetization current. The first method is based on variation of stator voltage amplitude from the information just of rotor rotation speed. The second method is based on the stator voltage frequency and amplitude from the stator current information. The second method permits to influence the characteristic equation roots of the control system and to have magnetization current dynamic properties.

Control of Squirrel-Cage Induction Electromotor with Constant Magnetization Current

In this paper, we study the control algorithm of electromagnetic torque and rotation speed of squirrel-cage induction electromotor with constant magnetization current. We can ensure the constant magnetization current by acting on stator voltage vector. We distinguish two methods of construction of the given magnetization current. The first method is based on variation of stator voltage amplitude from the information just of rotor rotation speed. The second method is based on the stator voltage frequency and amplitude from the stator current information. The second method permits to influence the characteristic equation roots of the control system and to have magnetization current dynamic properties.

The Characteristic of Control Algorithms for an Induction Electromotor by the Parameters Change in Stator Winding Voltage

In this paper we study various control algorithms of electromagnetic torque and rotor rotation speed by parameters change in stator voltage for an induction electromotor.

Characteristic of Control Algorithms for an Induction Electromotor by the Parameters Change in Stator Winding Voltage

In this paper we study various control algorithms of electromagnetic torque and rotor rotation speed by parameters change in stator voltage for an induction electromotor.

Vector Control for an AC Drive with a Multilevel Frequency Converter Based on an Н-Bridge

Using multilevel topologies for a stand-alone inverter, which is a part of induction or synchronous ac drives, makes it possible to achieve their operation under some fault conditions related to, for example, the failure of any element in a power circuit or short-term blackout in operation of distribution line of centralized power supply system. In the last case, due to switching the speed loop into the mode of voltage control of capacitor filters, it turns out during short-term interval to maintain at the set level the magnetic condition and mechanical coordinates of electrical machine without direct disconnection of converter by corresponding signal feeding from a security unit. The work considers the design formulas for synthesis of special algorithms of vector control by an ac actuating motor under the absence of power supply based on the set distribution of the roots of characteristic polynomial on the complex plane. As well as the reduction of logarithmic amplitude–phase–frequency characteristic of the loop in open condition to the normalized form is presented in the work. Within the framework of these formulas, the regeneration of electric energy in the stand-alone inverter with series-connected H-bridges is carried out to stabilizing the voltage of capacitor bank in each power module owing to when workability recovery of three-phase network, the ac drive returns to normal operation without significant degradation of quality of processes by rotor rotational speed.

Evaluation of effects of operating parameters on combustible material recovery in coking coal flotation process using artificial neural networks

In this research work, the effects of flotation parameters on coking coal flotation combustible material recovery (CMR) were studied by the artificial neural networks (ANNs) method. The input parameters of the network were the pulp solid weight content, pH, collector dosage, frother dosage, conditioning time, flotation retention time, feed ash content, and rotor rotation speed. In order to select the most efficient model for this work, the outputs of different models were compared with each other. A five-layer ANN was found to be optimum with the architecture of 8, 15, 10, and 5 neurons in the input layer, and the first hidden, second hidden, and third hidden layers, respectively, as well one neurons in the output layer. In this work, the training, testing, validating, and data square correlation coefficients (R2) were achieved to be 0.995, 0.999, 0.999, and 0.998, respectively. The sensitivity analysis showed that the rotor speed and the solid weight content had the highest and lowest effects on CMR, respectively. It was verified that the predicted ANN values coincided very well with the experimental results.