Changes In Rotational Speed Research Articles

Об эффекте Зоммерфельда и скрытых колебаниях в асинхронном электроприводе горных машин

Рассмотрена возможность возникновения эффекта Зоммерфельда и скрытых колебаний в электромеханических системах самоходных горных машин. Отмечено, что по результату воздействия на механическое передаточное устройство (редуктор) режим пуска асинхронного электродвигателя (АД) прямым включением в сеть эквивалентен работе двигателя в опыте Зоммерфельда с эксцентрично расположенным грузиком при воздействии его на фундамент двигателя. При этом изменения положения корпуса статора АД могут повлечь за собой периодические изменения абсолютной скорости вращения электромагнитного поля статора, что приведет к возникновению во всей электромеханической системе электропривода колебаний, классифицируемых как скрытые (hidden oscillations). В качестве примера рассмотрен режим пуска проходческого комбайна КСП-32. Пример показал, что значения момента инерции корпуса комбайна могут изменяться в зависимости от загрузки углем питателя и скребкового конвейера, это означает необходимость выполнения вариантов численного моделирования для различных моментов инерции. Приведены результаты расчетов. Сделан вывод, что в электромеханических системах самоходных горных машин практически всегда при пусках можно наблюдать проявление эффекта Зоммерфельда и возникновение низкочастотных скрытых колебаний. Теоретическое предсказание этих явлений затруднено и может быть обнаружено путем численного моделирования вариантов режимов работы цифрового двойника горной машины.

The results of the production tests of the method for diagnosing the eccentricity of the rotor of an asynchronous electric motor

Ensuring the reliability of electrical equipment in agriculture remains an urgent problem, since rugged operating conditions and aggressive environment hinder its rational use. The high accident incidence rate of asynchronous motors in most cases is invariably caused by the failure of the inter-turn insulation and interphase short circuit or short circuits to the housing. The probability of an emergency situation increases with an increase in the radial clearance in the bearings and, consequently, the occurrence of static eccentricity of the rotor. The developed method for diagnosing the static eccentricity of the rotor of an asynchronous motor is based on the analysis of the rotor speed; the amplitude of the rotor speed change was used as a diagnostic parameter. The paper presents the change in the rotation frequency depending on the difference in the amplitudes, resulted from the study conducted for different values of static eccentricity. The test results have shown that with an increase in the eccentricity of the rotor, the amplitude of the speed fluctuations increases.

Numerical Simulations of Particle Motions at Continuous Rotational Speed Changes in Horizontal Rotating Drums

The motion of binary particles in three horizontal rotating drums with continuous rotational speed changes was studied based on the Discrete Element Method (DEM). Different simulation conditions were compared between two circular drums and an elliptical drum using the same number of physical properties for binary particles and drums, rotating at a speed series from 0.01 to 21.9 rad/s. By varying the rotational speed, four flow regimes were produced in the simulation. Flow regimes, velocity vectors, normal forces, and the number of contacts between 1 mm particles and 3 mm particles were comparatively analyzed, especially the particle velocity at transient changing rotational speeds. The results showed that four flow regimes were found at the same rotational speed for three different rotating drums, and normal forces were weakest for the cataracting regime; moreover, the three layers of particles were damaged when the rotational speed was suddenly decreased and the velocity direction of the particle motion was changed at the top of the particles’ bed. The maximum number of contacts was found with the rolling regime, based on the simulation results. The number of contacts of the major axis circular drum was smaller than for the minor axis at the same rotational speed, and the number of contacts of the elliptical drum was the largest among the three rotating drums.

Deflection suppression of magnetically suspended momentum wheel with varying-frequency synchronous vibration

The synchronous disturbance acting on the magnetically suspended momentum wheel (MSMW) would affect its suspension stability and control accuracy, so a varied-gain compound model is proposed to attenuate the synchronous disturbances of the MSMW with varying rotating frequencies. The disturbance frequency is varying with the rotating frequency of the MSMW, the gain and frequency of the disturbance observer are regulated to maintain the asymptotic stability, and the feedback gain of the state feedback is scheduled to avoid the complex repeated acquisition of control parameters. Finally, the numerical simulations and experiments are performed to validate the effectiveness of the proposed varied-gain control model. The results indicate that the proposed control model could effectively attenuate the synchronous disturbances and maintain the asymptotic stability of the MSMW when the rotating speed changes.

A fault diagnosis method for rotating machinery with variable speed based on multi-feature fusion and improved ShuffleNet V2

Using deep learning to classify the time-frequency images of bearing vibration signals has become a mainstream method in the field of fault diagnosis. Most studies, however, assume a constant rotational speed, and the accuracy and reliability of the diagnosis model diminishes once the rotational speed changes. Moreover, due to the large model size and high computational complexity, the convolutional neural networks are not suitable for industrial applications. This paper proposes a novel fault diagnosis method for rotating machinery with variable speed based on multi-feature fusion and improved ShuffleNet V2. First, complementary ensemble empirical mode decomposition is used to denoise the time-domain signal. Then the denoised time domain signal is converted into an angular domain signal using the resampling technique, while the envelope spectrums of the angular domain signals are obtained by the Hilbert transform, and the three signals are fused into an red-green-blue image form to enhance the sample features. Finally, to perform fast and accurate classification of the features, the squeeze and excitation blocks are placed after the branch splicing operation of ShuffleNet V2 to enhance the recognition accuracy, and the rectified linear unit activation function is replaced by the HardSwish activation function to avoid necrosis. The experimental results show that the fault recognition accuracy of the proposed method for rolling bearings under variable speed is 96.4%, and the size of the fault diagnosis model is 7.82 MB, indicating that the method can effectively improve the accuracy and ensures that the model size does not increase significantly.

An Investigation of Non-Linear Surge Characteristic in a High-Speed Centrifugal Compressor

Abstract In centrifugal compressors, it is common to observe a rapid reduction in surge margin toward high rotational speed, which shows a non-linear surge characteristic against the change of rotational speed. This paper presents a comprehensive experimental and numerical study to understand the flow mechanisms leading to the non-linear surge behavior in a high-speed centrifugal compressor. It shows that for the studied compressor, there are two critical flow coefficients (ϕ = 0.255 and 0.136) where the stability of the compressor stage is significantly weakened. At a higher speed, the impeller rotating stall happens at the first critical point where the diffuser instability is also enhanced. This is caused by the increase of the flow non-uniformity at the impeller exit as well as increased diffuser inflow angle due to the impeller compressibility effect. Therefore, both the impeller and diffuser’s instability are matched and trigger the surge at a high flow coefficient. In contrast, at a lower speed, the diffuser instability is not enhanced by the impeller rotating stall, this mismatch of the two component’s instability allows the compressor to pass through the first critical point and extend the surge limit to the second critical point where the diffuser reaches the stability limit and causes the rotating stall spontaneously. By these different behaviors at each speed, the non-linearity of the surge characteristic is established.

Effect of Periodic Changes in Rotation Speed on Torsional Stress and Screw-in Force by Alternative Rotation Technique

IntroductionThis study evaluated the effect of periodic changes in rotation speed on torsional stress and screw-in force using the dedicated alternative rotation technique (ART) motion of the EQ-M (Metabiomed, Cheongju, Korea) endodontic motor. MethodsTwo ART modes of the EQ-M motor in 2 alternative techniques (ART30 and ART50) and continuous rotation were compared using ProTaper Next X2 (Dentsply Sirona, Charlotte, NC) files and simulated resin blocks (n = 12 per group). ART30 and ART50 were operated by continuous rotation of 350 rpm for 360° and then rotated at 30% increased speed from the base speed for 180° and at 50% increased speed for 180°, respectively. Before the test, the simulated resin blocks were pre-enlarged using ProTaper Gold S1 and S2 (Dentsply Sirona) and fixed on a metal stage connected to the force- and torque-measuring unit. During shaping the simulated canal in an automatic up-and-down manner, the parameters of maximum torque, sum of torque, maximum screw-in force, and maximum apical force were measured. The data were statistically analyzed using 1-way analysis of variance and the Tukey post hoc comparison test at the 95% significance level. ResultsThe ART30 and ART50 groups showed a lower maximum torque, sum of torques, screw-in force, and apical drive force than the continuous rotation group. There was no significant difference between the ART30 and ART50 groups (P > .05). When the screw-in force increased suddenly, the torque correspondently increased. ConclusionsUnder the limitations of this study, the ART mode could reduce the torsional stress and apical forces of the screw-in during instrumentation in comparison with continuous rotation.

Designing a voltage control system of the magnetoelectric generator with magnetic flux shunting for electric power systems

The object of research in this work is a three-phase magnetoelectric generator with magnetic flux shunting based on industrial induction electric motors. The presence of a magnetic shunt makes it possible to control the voltage of the generator by changing the excitation current in the non-contact electrical winding of the magnetic shunt, which is powered by direct current. Thus, the problem of stabilization of the output voltage of the generator with permanent magnets is solved when the speed of rotation and load change. This paper reports the construction of a three-dimensional field mathematical model of the generator, which allows for electromagnetic calculations of the generator with specified parameters, taking into consideration the influence of final effects, magnetic scattering fields, as well as their radial-axial nature. The results of the calculation of the electromagnetic field are the initial parameters for building a simulation model in the MATLAB-Simulink environment. A simulation model of a magnetoelectric generator with magnetic flux shunting under conditions of changing rotational speed and load has been constructed in the MATLAB-Simulink environment. On the basis of the built models, the performance characteristics of a magnetoelectric generator with magnetic flux shunting were established, which show the limits of control of the output voltage. Adjusting characteristics were determined at zero and rated shunt current for different types of load. The adjusting characteristics of the generator are presented at the rated voltage of the generator for different types of load and with an increase to 150 % of the rated value. The study's results show the high efficiency of the voltage control system of a magnetoelectric generator with a magnetic shunt at different speeds of rotation and load

Research on Parameter Design Method and Motion Characteristics of a Ball Cage Flexible Joint

The flexible joint is an important part in ultra-short-radius drilling tools, and its structural parameters and motion characteristics are key factors affecting the success of drilling. In this work, a new type of ball cage flexible joint, which is applied in 5″ and 5.5″ cased wells, was proposed based on the working principle of the ball cage universal joint. A structural parameter design method for the ball cage flexible joint was established according to the geometric coordination relation and material strength theory. Using this new method, the length, diameter, and window size of the ball cage flexible joint were analyzed. The multi-body motion process was further analyzed using a multi-body dynamics method, and then the motion characteristics, such as impact contact force, isokinetic characteristics, transfer efficiency, deflection torque and so on, were studied. Based on the above analyses, the structural parameters of the designed joint were optimized by means of the orthogonal test method. Results demonstrate that the experimental ball cage flexible joint has excellent isokinetic transmission characteristic, which can effectively suppress vibration and shock caused by changes in rotational speed. The transmission efficiency of the structure was 89.8%, while the power loss rate was 0.102%. According to the orthogonal test analysis, the optimal structure of the flexible joint has a ball seat diameter of 80 mm, a ball head diameter of 62 mm, and a ball key diameter of 16 mm. It is important to note that the ball key diameter was the most influential factor on the flexible joint internal contact force. The ball key contact force varied periodically, and there was a significant phase difference between the contact forces of different balls. On the other hand, with an increase in the flexible joint working angle, the deflection torque increased gradually, and the vibration amplitude of the torque increased. This work can provide reference for the parameter optimization design of the new flexible joint.

Rotor Winding Short-Circuit-Fault Protection Method for VSPSGM Combining the Stator and Rotor Currents

Rotor winding short circuit faults are common faults for variable-speed pumped-storage generator-motors (VSPSGM). At present, the exciting rotor fault protection of VSPSGM is simple and has low sensitivity. It can only act when the instantaneous value of the rotor phase current reaches three times the rated current. Therefore, it is difficult to cover some rotor winding short-circuit faults with weak fault characteristics. It is urgent to study a novel rotor winding short-circuit-fault protection method for VSPSGM. In this paper, a protection method that combines the stator and rotor currents with different frequencies is proposed. The characteristics of the stator and rotor currents before and after the fault is analyzed by using Clark transformation. On this basis, a specific protection criterion is constructed based on the discrete integral operation, which is easy to implement and not affected by the change of rotor speed. Then, the calculation method of the protection setting is proposed, considering the effect of unbalanced voltage and sensor measurement error. Simulation results show that the proposed method can reliably realize the protection of rotor winding faults. It has faster protection action speed than other methods in the same field. The protection coverage rate is over 90%.

Computational Fluid Dynamics Study of a Pharmaceutical Full-Scale Hydrogenation Reactor

The pharmaceutical industry has been quite successful in developing new hydrogenation processes, and the chemistry of hydrogenation is currently well understood. However, it is a complex process to scale and optimize due to its high exothermicity, use of expensive catalysts and solvents, and its mass transfer requirements. Therefore, the aim of this work is to develop a CFD model to be able to describe the mass transfer, hydrodynamics, and mixing with respect to changes in rotational speed for a full-scale pharmaceutical hydrogenation reactor. In the first stage, a simple CFD model is used to predict the development of the surface vortex, and it is validated against literature data. In the second stage, the CFD model is tested on a full-scale configuration equipped with a Rushton turbine and a bottom kicker to study the formation of the surface vortex. Simulation results show the ability to predict the development of the surface vortex. These results are used to estimate the liquid height and mixing time as a function of several rotational speeds, allowing us to propose novel process correlations for this particular configuration. Although modelling the complete hydrogenation process would be challenging, this work is seen as a first step towards developing models that demonstrate the use of CFD at such large reactor scales.

Multi-probe linear fitting and time of arrival linear correction method to analyze blade vibration based on blade tip timing without once-per-revolution

Blade vibration monitoring can ensure the safe operation of aero-engine rotor blades. Among the methods of blade vibration monitoring, Blade Tip Timing (BTT) method has attracted more and more attention because of its advantages of non-contact measurement. However, it is difficult to install the Once-Per-Revolution (OPR) probe in the confined space of aero-engine, and the failure and instability of the OPR signal will reduce the reliability of the blade vibration analysis results, which directly affects the accuracy of the blade vibration parameters identification. The Multi-Probe linear fitting and Time of Arrival (ToA) Linear Correction method based on the BTT (MP-LC-BTT) without OPR is proposed to reduce the errors of single probe linear fitting method for blade vibration displacement analysis. The proposed method can also correct the calculation error of blade vibration displacement due to the nonlinear change of rotation speed, which can improve the analysis accuracy of the blade vibration displacement. A new blade vibration model conforming to the actual vibration characteristics is established, and the effectiveness of the proposed method is verified by numerical simulation. Finally, the reliability and accuracy of the MP-LC-BTT method have been verified by the experiments which include two high-speed blade test-benches and an industrial axial fan. This method can be used in the actual aero-engine monitoring instead of the BTT method with OPR.

Dynamics and Control of an Energy-Efficient, Power-Regenerative, Hydrostatic Wind Turbine Dynamometer

Dynamometers are used to evaluate the real-world performances of drivetrains in various loading conditions. Due to its superior power density, high bandwidth, and design flexibility, a hydrostatic power-regenerative dynamometer is an ideal candidate for hydrostatic wind turbine transmission testing. A dynamometer can emulate the wind turbine rotor dynamics and allow the investigation of the performance of a unique hydrostatic drivetrain without actually building the physical system. The proposed dynamometer is an energy-efficient system with counter-intuitive control challenges. This paper presents the dynamics, control synthesis, and experimental validation of a power-regenerative hydrostatic dynamometer. A fourth-order non-linear model with three inputs was formulated for the dynamometer. The strength of input–output couplings was identified, and two different decoupling controllers were designed and implemented. During wind turbine testing, the synchronous generator turns at a constant speed and the system model is linear. A steady-state decoupling controller was developed for independent control of the drive and transmission. The implemented decoupling controller demonstrated a negligible change in rotor speed for a 40 bar step increase in pressure, but a 20 bar pressure spike for a 4 rpm step change in rotor speed. However, during starting and stopping, the synchronous generator speed is not constant, and the system model is nonlinear. Therefore, a steady-state decoupling controller will not work. Thus, a decentralized controller with feed-forward control and gain scheduling was designed and implemented. A reference command was designed to avoid cavitation, pressure spikes, and power flow reversal during start-up. The experimental results show precise tracking in steady-state and transient operations. The decentralized controller demonstrated a negligible change in rotor speed for a 40 bar step increase in pressure but a 100 bar pressure spike for a 4 rpm step increase in rotor speed. The pressure spike was reduced by 80 bar with the implementation of feed-forward gain. The proposed electro-hydro-mechanical system requires less power and has the potential to reduce energy expenditure by 50%.

Numerical simulation of unsteady flow characteristics in a centrifugal pump during runaway process caused by power failure

Abstract Centrifugal pump is widely used in agricultural irrigation, petrochemical, mining, metallurgy and other industries. A special centrifugal pump with elbow pipe is researched in this paper. The flow rate and rotating speed change rapidly, especially in elbow pipe, causing serious pressure fluctuation and complex vorticity in the centrifugal pump. A user-defined function to solve the angular momentum equation was calculated the pump rotational speed. Unsteady numerical simulation with SST turbulence model is carried out and Short time Fourier transform (STFT) and vorticity strength are used to analyse the pressure fluctuation and vortexes respectively. The results indicate that the rotational speed first decreases to zero and then reversely increases to runaway speed. Large area vorticity appeared at the elbow pipe when the high amplitude frequency of pressure fluctuation increased. The change law of main frequency of pressure fluctuation at the elbow pipe is consistent with the rotational speed change ruler, which is equal to blade passing frequency (BPF). The main source of pressure fluctuation was rotor stator interaction. This study’s results provide a meaningful reference about pump runaway process caused by power failure, leading to the prevention of dangerous situations, for safe operations of the pumping unit.

Influence and comparison of P/Q-control based VSC-HVDC system on the grid power oscillation damping

To analyze the dynamic process of VSC-HVDC system actively participating in suppressing the grid power oscillation, under the electromechanical time control scale, this paper establishes the linear mathematical model of the VSC-HVDC connected to the single machine infinity system, and the dynamic interaction relationship between the controlled active and reactive power injected into the power grid by VSC-HVDC, moreover, the synchronization, inertia and damping level are investigated by the electrical torque method in this paper. The study shown that when the rotor speed is selected as the grid state quantity feedback signal, adjusting the PID controller gain of rotor speed control loop can effectively adjust the VSC device’s active and reactive output power to improve the system damping level, synchronous characteristics and inertial effects, which can thus restrain the rotor speed deviation and speed change rate under oscillating conditions and improve the system frequency stability. In addition, this paper proposes an index for the proportion of inverter station regulation capacity, which proves that the VSC-HVDC operating in active power control strategy has better suppression effect on power oscillation than reactive power control, reducing the design capacity and cost of inverter stations. Finally, the simulation proves the dynamic process analysis correctness of VSC-HVDC suppressing the grid power oscillation in this paper.

Analysis of Grooves Used for Bearing Lubrication Efficiency Enhancement under Multiple Parameter Coupling

Adding axial groove structures to the surface of bearing inner ring is an effective way to enhance the bearing lubrication efficiency. In this paper, the angular contact ball bearing H7006C was taken as the research object, and through visual simulations and quantitative experiments, systematic analyses and discussions were carried out to find out the relationship between groove-enhancing performance and working conditions. Firstly, simulation models of standard bearing and groove-added bearing were established. By combining the Volume of Fluid (VOF) model, the enhancing mechanism of grooves was found. Secondly, the trend of groove-enhancing performance with the change of rotation speed was studied through simulations and quantitative experiments. On this basis, through multiple parameter coupling, the effects of oil supply amount and nozzle diameter on the groove performance were discussed. The results show that the bottom oil layer is the key for grooves to achieve the lubrication efficiency enhancement, and its distribution can reflect the groove-enhancing performance. The groove width that best adapts to the change of working conditions increases with the increase of oil supply amount and nozzle diameter. To maintain the stability of bottom oil layer, the nozzle diameter should be larger than the groove width. This research is of great significance to the application of grooves in the lubrication efficiency enhancement of high-speed bearing.

Design and Control of Multi-Plate MR Clutch Featuring Friction and Magnetic Field Control Modes.

A magnetorheological (MR) multi-plate clutch was proposed with both mechanical friction mode and magnetic field control modes. The magnetic field control mode was based on an MR fluid coupler that changed its viscous properties according to the density of an applied magnetic field. This mode was used in the early stage of clutch operation to reduce the impact of friction between the disc and plate, and eliminate to the extent possible the difference in their relative speeds when contacting each other in later stages. Once the rotational speed difference between the disc and plate was reduced, the clutch was operated in mechanical friction mode by compressing the friction surfaces together. A torque modeling equation was then derived for each mode based on the Bingham model of the MR fluid, and the transmission torque of the proposed multi-plate clutch was derived using these equations as well as magnetic field analysis results obtained using ANSYS Maxwell. A multi-plate MR clutch was then fabricated, and its torque transmission characteristics were evaluated in the magnetic field control and mechanical friction modes. The results confirmed that the model-based torque calculations were consistent with the observed transmission torque. Finally, control algorithms for mechanical friction only and mixed mechanical friction/magnetic field control torque tracking of the proposed MR multi-plate clutch were designed, and their performances were evaluated when applying unit step command, half-sine-wave command, and rotational speed changes. The results indicated that the torque tracking control was performed smoothly, demonstrating the advantages of the proposed clutch.

The Design and Magnetic Field Analysis of a Double Rotor Permanent Magnet Braking Device

During long-term continuous braking, high-intensity braking, or frequent braking, the temperature of the brake disc or brake drum will increase significantly, resulting in a decrease in the friction coefficient, the aggravation of the wear degree, and the dangerous heat recession of partial or even total loss of braking efficiency. This paper focuses on an innovative double rotor permanent magnet braking device, which is located on the inner side of the wheel hub, to improve the heat decay resistance of the friction braking device. The structure and principle of the double rotor permanent magnet braking device were given, and its main structural parameters were designed, calculated, and optimized. The geometric model and finite element model of the double rotor permanent magnet braking device were established. The static and transient magnetic field analysis and the braking torque characteristic analysis of the double rotor permanent magnet braking device were carried out by using Maxwell electromagnetic analysis software. The results show that the magnetic flux density in the working area of the double rotor permanent magnet braking device increases with the increase in rotation speed, the braking torque changes with the change of rotation speed, and the maximum braking torque occurs in the low-speed area, which is consistent with the theoretical calculation results. This provides a theoretical basis for the follow-up prototype test of the double rotor permanent magnet braking device.

The aerodynamics of a blade pitch, rotor speed, and surge step for a wind turbine regarding dynamic inflow

AbstractFloater motions introduce unsteadiness in the aerodynamics of floating offshore wind turbines. The aerodynamics of a wind turbine after three perturbations are studied: a blade pitch step, a rotor speed step for which dynamic inflow is expected, and a surge velocity step. The free vortex wake method and an analytical helical vortex model based on the Joukowsky rotor model are used to study the dynamic behavior of the induced velocity at the blades. As expected, the dynamic inflow effect is clear for the blade pitch and rotor speed changes, but for a surge velocity step, the models show that very little dynamic inflow effect takes place because the velocity induced by the vortex helix is not significantly modified: the tip vortex helix circulation change is partially compensated by the geometry change of the helix. For the rate of change, the velocities induced on the rotor by the vortex helix for the pitch and rotor speed changes show a rapid adjustment at the blade tip, with a slower change throughout the rest of the blade and at the center of the rotor. The convection velocity of the tip vortices is shown to be the main variable of the temporal evolution of the dynamic inflow effect.

Transient Aeroelastic Response of a Rotor During Rotor Speed Transition in Forward Flight

Compound helicopters often have to reduce their rotor tip speeds to achieve higher forward speeds. The rotors, therefore, have to undergo a transient process of rotor speed changes. To investigate the transient loads and the related transformation from the rotating frame to the nonrotating frame, a rotor model is used to predict the transient aeroelastic responses. The rotor model is validated by using test data of a teetering model rotor during engagement and disengagement operations. The investigations indicate that a small transient lagwise root bending moment can result in a large transient contribution to rotor torque. This transient component is triggered by the force related with the sudden change of the angular acceleration of the rotor speed. Increasing the blade damping in the lagwise direction can significantly decrease the transient components of the lagwise root bending moment and the corresponding rotor torque. Making the angular acceleration continuous will not trigger the transient components, suggesting that this is a better way for the reduction of the transient rotor loads during speed changes.