Variable Rotational Speed Research Articles

Time-Varying Degradation Model for Remaining Useful Life Prediction of Rolling Bearings under Variable Rotational Speed

It is difficult to accurately extract the health index of non-stationary signals of rolling bearings under variable rotational speed, which also leads to greater prediction error for bearing degradation models with fixed parameters. For this reason, an angular domain unscented particle filter model with time-varying degradation parameters is proposed to deal with the remaining useful life (RUL) prediction of rolling bearings. Order analysis is first performed to transform the variable-speed signal from time domain to angular domain for extracting the health index in the angular domain representation. To track the bearing degradation state, a real-time finite element model is established to guide the parameters updating the procedure of the performance degradation model. Finally, the bearing degradation state is estimated by the unscented particle filter (UPF), and then the remaining useful life of the bearing is predicted. In this way, the time-varying degradation model is developed by considering both non-stationary feature extraction and dynamic state tracking for rolling bearings. The proposed method is verified by both benchmarks: bearing experimental data, and a bearing accelerated life experiment. Compared with state-of-the-art prognostic methods, the present model can predict the bearing remaining useful life (RUL) more accurately under variable rotational speed.

Phase Demodulation of Rotor Torsional Vibration Measurement under Time-Varying Speed

When torsional vibration is measured with the zebra-tape method, the modulation signals can be contaminated by electrical noise, environmental noise, step noise, sensor nonlinearities, and so on. Although the amplitudes of these types of noise are very weak relative to the amplitude of the ideal pulse test signal, they may introduce large-scale random broad-spectrum noise to the signal phases. Such noise is difficult to remove using frequency domain, time-frequency-domain, or threshold sampling methods and seriously affects the accuracy of torsional vibration measurements. This paper presents a phase demodulation algorithm based on downsampling and local resampling (DSLR) to improve the accuracy of torsional vibration measurements. To verify the proposed DSLR algorithm, torsional vibration simulations and experiments are conducted under a time-varying rotation speed. The results show that the angular displacement signal obtained from the torsional vibration test using zebra tapes is the superposition of the dynamic and static angular displacements, with the latter generated because of the varying rotation speed with respect to time. The DSLR algorithm effectively reduces the phase noise and demodulates the pulse signal phases. The work in this paper provides a method for obtaining reference torsional vibration measurements of rotors based on the zebra-tape method under time-varying speeds.

Design and test of adaptive torsional vibration suppression method for helicopter power system with variable rotor speed

In order to solve the problem of torsional vibration instability of the control system for turboshaft engine caused by low-order torsional vibration modal drift under variable rotor speed effectively, an adaptive torsional vibration suppression method based on the least mean square algorithm is proposed and designed. First, based on Lagrange equation and state space method, the structural dynamic model of torque transmission chain system is established, which takes into account fixed and variable gear ratio. It is beneficial to express the dynamic characteristics of torsional vibration in real time, so that the variation laws of low-order torsional vibration modal under variable rotor speed and gear ratio are revealed. Then, an adaptive torsional vibration filter based on least mean square algorithm is proposed and designed combined with the active control objective of helicopter power system. Finally, the effectiveness of adaptive torsional vibration suppression method is validated based on numerical simulation and hardware-in-loop simulation separately. The results show that compared with the conventional constant-coefficient notch filter, the adaptive torsional vibration filter can decrease the peaks of all low-order torsional vibration frequency by more than 50%. It proves better robustness, more remarkable effectiveness and superior adaptive ability of the adaptive torsional vibration suppression method.

Normalized Adaptive Hybrid Control Algorithms for Helicopter Vibration with Variable Rotor Speed

Variable rotor speed technology implemented in a helicopter can improve the flight performance, reduce the required power, and increase the flight speed. However, variable rotor speed changes the frequencies of rotor vibratory loads and may produce helicopter fuselage resonance under the excitation of the rotor vibratory loads. Active vibration control (AVC) has been effectively used in vibration reduction of helicopter fuselages. However, the frequency domain control algorithms that are currently used have poor adaptability in controlling vibration with variable frequencies (i.e., during time varying rotor speeds). In order to effectively improve control convergence, adaptability, and effectiveness, the normalized adaptive hybrid control algorithms containing both the normalized adaptive harmonic control algorithm and the normalized frequency tracking algorithm have been presented in this paper. Simulations of AVC with variable frequencies on a dynamically similar frame structure of a helicopter fuselage driven by piezoelectric stack actuators installed on the gearbox support struts show that the normalized adaptive hybrid control algorithms can accurately track the changes in rotor load frequencies and can be effectively used in the AVC of a helicopter with variable rotor speed.

Optimal adjustment of mine fan geometry and operation

Mine fans consume significant electrical power, so it is important to ensure high efficiency of their operation. The aim of this study is to develop a method to determine the most economically efficient method to adjust axial fan geometry and operation at the maximum average efficiency in all operating modes. The method includes a developed mathematical model of the single-stage axial fan duty and a genetic algorithm for optimizing the fan parameters. The initial data for the mathematical model were the geometry of the fan blades of the average radius and the parameters of the fan operating mode. The result of the calculation was the fan efficiency in a preset operating mode. Two adjustment scenarios are modeled: fans with variable pitch blades and fans with variable rotation speed. The fan efficiency was determined by calculating the total pressure loss at the unit stage at the middle radius with regard to the loss at the blade tips. Since the mathematical model contains a large number of independent parameters, and there exists the possibility of local extrema, the optimization is performed using the genetic algorithm. The mathematical model of the fan with variable pitch blades was tested using experimental data. The error of the mathematical model in continuous modes at high efficiency (>75%) never exceeds 1.5%. As a case-study, the optimal fan parameters are determined for two preset operating modes and for two adjustment scenarios of fans with variable pitch blades and with variable rotation speed. On the basis of the obtained geometric parameters at the average radius of blades, using the constant circulation law, the fan designs were developed and then investigated by numerical simulation in CFX program. It is shown that if the air flow rate in operating modes differs significantly and the pressure is not, it is advisable to use fans with variable pitch blades.

Enhancement efficiency of Michell-Banki turbine using NACA 6512 modified blade profile via CFD

The small hydroelectric power plants (SHPP) are implemented in non-interconnected zones (NIZ) of developing countries. In which, the provision of electrical energy from the national interconnected system is not economically feasible. Therefore, in the literature, hydroelectric generation technologies have been implemented taking advantage of the energy available in the rivers. One of these technologies is the Michell-Banki type cross-flow turbines (MBT), which, despite having lower efficiencies than turbines such as Pelton and Francis, maintain their efficiency although fluctuations in site conditions. For this reason, different studies have been made to increase the efficiency of the MBT by making geometric modifications to both the nozzle and the rotor.
 The purpose of this study is to determine numerically the effect of the geometry of the blades that form the runner on the efficiency of Michell-Banki Turbine (MBT). For this, two (2) geometries were studied corresponding to a circular sector of a standard tubular profile and an airfoil NACA 6512 modified in curvature profile and chord length, according to the profile of the standard tubular blade. For this study, transient simulations for multiphase water-air flow were implemented using a k-ε turbulence model in the Ansys 2020R1® CFX software. The two (2) turbine models were configured to the same hydraulic conditions of head and volumetric flow corresponding to 0.5 m and 16.27 L/s, respectively. Variations in rotational speed were configured between 100 and 200 RPM with 20 RPM steps. It was found that using the modified 6512 hydrodynamic profile, at 140 RPM increased efficiency by 6 %, compared to the conventional tubular type blade geometry

A fault characteristics extraction method for rolling bearing with variable rotational speed using adaptive time-varying comb filtering and order tracking

A fault characteristics extraction method for rolling bearing with variable rotational speed using adaptive time-varying comb filtering and order tracking

Alternative Solutions for Small Hydropower Plants

Obtaining energy from renewable resources is a worldwide trend in the age of increasing energy demand. Hydropower has some potential in this field, especially for low-power locations. However, construction of such facilities requires high expenses, which is why some attempts at lowering the costs have been made, i.e., by proposing alternative solutions to the classic ones. This paper proposes a selection of options for small hydropower plants (SHP) that lower the investment costs while keeping up profitable operations. The proposed solutions concern simplifying the turbine’s and generator’s integration by installing them in dedicated prefabricated concrete modules. A rare but simple and cheap semi-Kaplan type of turbine with a non-classical spiral inflow is proposed. The turbine operates a permanent magnet (PM)-excited generator, converting the energy at a variable rotational speed. Thanks to this approach, it is possible to simplify the regulation system and eliminate expensive mechanical transmission. However, on the power grid side, a power electronic converter (PEC) must be coupled with the generator. The advantage of this solution compared to the classical ones is that the reliability of power electronics is much higher than that of mechanical systems. This paper presents modeling research on semi-Kaplan turbines’ series development, and a dedicated PM generator is presented as an example of a complete hydro unit with 50 kW power.

Real-time prediction framework for frequency-modulated multirotor noise

A comprehensive multirotor noise assessment framework is developed to predict the noise of rotational-speed-controlled rotor configurations in real-time. The key objectives are to synthesize the frequency-modulated multirotor noise and analyze the frequency modulation (FM) characteristics. The framework includes modules associated with the flight control, aerodynamics, time reconstruction, noise prediction, and time-frequency analysis (TFA). In addition to the hybrid blade element momentum model, the aerodynamics module contains a linear inflow model, a Beddoes wake model, and an unsteady aerodynamic correction model. The convective form and source-time dominant algorithms are used in the acoustic analogy for tonal noise prediction. The FM characteristics are identified using the synchrosqueezing-based high-resolution TFA for strongly non-stationary signals. The framework is verified through validation and verification studies for diverse rotor configurations and flight conditions. During the cruise flight of the multirotor, the tonal noise exhibits simultaneous frequency and amplitude modulations. In wind gust conditions, these modulations result from rotational speed variations, acoustic wave interference, and Doppler shifting. By clarifying the non-stationary noise signal in diverse flight environments, the proposed framework can facilitate noise assessment in the perception-influenced design stage of multirotor configurations.

Experimental and Numerical Investigation on the Transient Cavitating Flows in a Mixed Flow Pump With Different Number of Blades at Startup

Abstract The objective of this paper is to experimentally and numerically investigate the transient cavitation flow during the startup process of mixed flow pump with emphasis on studying the influence of blade numbers. The transient cavitation simulation was studied based on the improved SST k–ω turbulence model and the Zwart cavitation model. Firstly, in order to obtain the relationship between transient flow rate and the variation of rotational speed at startup, a theoretical analysis based on the fast transients of centrifugal pump was first applied to mixed flow pump and was verified by the current experiment study. Subsequently, the influence of blade number on the cavitation flow in the startup was studied. It is found that the transient cavitation could be classified into four stages regardless of the number of blades: no cavitation stage, the cavitation growth stage, the cavitation reduction stage and the cavitation stabilization stage. However, the blade number does have an impact on the spatial-temporal evolution of cavitation. More specifically, when the blade number increases, the initial cavitation appeared lately, the coverage area of the triangular cavitation cloud and sheet cavitation both decreased, and the increase in blade number has a better inhibitory effect on the sheet cavitation at the cavitation growth stage, and can make sheet cavitation disappear more quickly at the cavitation reduction stage.

Composite adaptive backstepping controller for variable speed rotating scan optical spacecraft

AbstractIn this article, a rotating speed varying scanning strategy for multibody rotating scan optical spacecraft connected with active magnetic bearing (AMB) is introduced. This strategy can increase the imaging efficiency of the high‐resolution observation mission by speeding up the rotation in the nonimaging phase. Then, to address the lack of time delay margin problem brought by variable rotational speed, a composite adaptive backstepping controller (CABC) which composed of two controllers is derived via the Lyapunov theory to guarantee the stability of the closed‐loop system. In the system, two control methods switch for different phases. When the optical payload is working, the rotational speed of optical payload is decreased to achieve the high pointing precision. The high precision adaptive backstepping controller (HPABC) is used in this phase. When the optical payload stops working, the rotational speed is high and the high rotating speed adaptive backstepping controller (HRSABC) is designed to guarantee the stability of the system. Then, to give the time delay margin of two controllers and prove that the time delay margin of HRSABC is higher than the HPABC, the reference value, which represents the system stabilization and time delay margin and angular velocity margin, is derived using the discretization and linearization method. Finally, a series of numerical simulations have been performed and the simulation results indicated the new control method can effectively address the control problem brought by rotating speed varying.

Nonlinear Robust Control on Yaw Motion of a Variable-Speed Unmanned Aerial Helicopter under Multi-Source Disturbances

This paper studies the multi-source disturbances attenuation problem on the yaw motion of unmanned aerial helicopter with a variable-speed rotor. The yaw motion subsystem dominated by an electrically-driven tail rotor is firstly introduced, and its trajectory accuracy requires particularly close attention. To this end, we establish a fourth-order yaw error dynamic equation; subsequently, a nonlinear robust control scheme based on optimal H∞ principle is developed, consisting of laws of virtual functions, parameter estimation and a compensation signal. The novelty of this scheme lies in unifying the techniques to deal with the uncertain parameters, noise perturbations, actuator output fault and external airflow turbulence into a simple framework. Stability analysis guarantees that the yaw closed-loop system has the predefined performance of disturbance suppression in the sense of a finite L2-gain. Comparison results with the extended state observer based backstepping controller verify the effectiveness and superior performance of proposed scheme in an aircraft prototype.

Active Power Control of Wind Turbine Generators Based on the Maximum Disturbance Range of Nonpitch Regulation

Wind turbine generators (WTG) are expected to provide active power control (APC) to track active power instructions from the power grid or wind farm operators. Because the regulation of turbines’ mechanical dynamics strongly depends on pitch angle regulation, mitigating frequent pitch adjustments is a key issue, and accordingly, several rotor speed variation-first APC methods have been proposed to decrease pitch servo fatigue. However, due to the lack of a quantitative description on the utilization of rotor speed variation (RSV), the ability of reducing pitch action through RSV can hardly be analyzed and compared among the existing APC methods. Hence, the disturbance range of nonpitch regulation (DRNP) and the maximum DRNP are defined in this paper. The former represents the effect of pitch action mitigation through RSV with a specific APC strategy and provides a unified foundation for quantitatively evaluating and selecting APC methods from the perspective of pitch servo serviceability. The latter, which depends on the turbine specifications and is independent of the control method, represents the maximum effect that can be achieved for a WTG. On this basis, an improved APC method is proposed to further reduce pitch servo fatigue. Finally, the DRNP indicators and the effectiveness and feasibility of the proposed method are verified by the wind turbine simulator-based experiments.

Torque-Performance Improvement for Direct Torque-Controlled PMSM Drives Based on Duty-Ratio Regulation

This article proposes a new duty-ratio regulation-based strategy to improve the torque performance for the direct torque control (DTC) of three-phase permanent magnet synchronous motors (PMSMs). The conventional DTC schemes utilize two hysteresis regulators that are hard to be tuned to satisfy proper torque performance for wide speed ranges because of the contrary change in the positive and the negative torque deviations of the converter's voltage vectors with the rotational speed variations. In contrast, the proposed method uses a duty-ratio regulator that considers the operating speed impact on the torque deviation of the active voltage vectors and avoids triggering those of them that produce high torque deviations, therefore reducing the torque ripple of the DTC system. Moreover, it proposes a virtual reference generator to mitigate the steady-state torque error. The proposed method provides enhanced torque control performance, meanwhile maintaining the main advantages of the conventional DTC techniques, including simple structure, fast transient response, and good robustness. The feasibility and effectiveness of the proposed strategy are verified through a detailed comparative assessment with the conventional DTC scheme and two existing duty regulation-based methods using experimental results obtained from a 0.75-kW PMSM drive system.

ТЕСТОВЫЙ КОНТРОЛЬ ДАТЧИКОВ МАССОВОГО РАСХОДА ВОЗДУХА СОВРЕМЕННЫХ ДВИГАТЕЛЕЙ ВНУТРЕННЕГО СГОРАНИЯ

The authors have considered typical designs of sensors of mass air flow rate used in motor vehicles and established that the most perfect are film-type sensors. Analysis of modern means and methods for diagnostics of mass air flow rate sensors showed that there are no methods for their nondestructive inspection. The study presented in the paper is based on the use of a developed measuring device for creation of test modes. As controlled parameters the authors have selected a mass air flow rate, voltage from sensor test terminal, a position of the butterfly throttle, hourly consumption of fuel at variation of the ICE crankshaft rotation speed at the position of the butterfly throttle from 0 to 100 %. It is established that the most sensitive parameters are the mass air flow rate and the voltage of the sensor control contact.

NGAKES THE OPERATION OF THE LINK OF THE POWER TAKE-OFF SHAFT OF THE TRACTOR HTZ-150K-09

One of the effective directions on the problem of assessing the technical reliability of tractors supplied to agriculture is the study of the initial performance characteristics and wear of individual elements and components of the tractor. (Research purpose) The research purpose is considering the operation of the intermediate support as part of the cardan drive of the power take-off shaft of the tractor HTZ-150K-09; determining the loads on its bearings and the operation mode of the support and its resource. (Materials and methods) When transmitting torque in the power take-off mechanism, axial and radial forces arise, causing reactions in the intermediate support bearings. The equilibrium equations of the system of forces in space were used to determine their values. (Results and discussion) The dynamics of the driveshaft is such that when the tractor moves over an uneven field or when it turns, the rotation speed of the driven shaft does not coincide with the speed of the drive. This is due to the constant change in the angle between the shafts. The variable rotation speed of the driven shaft causes angular accelerations and inertial loads of elements in the cardan transmission itself and in other parts of the drive and the working bodies of agricultural machines. The loads on the bearings of the intermediate support from the side of the cardan transmission will have a dynamic character, since they reach the maximum and minimum twice in one revolution of the support shaft. (Conclusions) To increase the resource of the power take-off cardan drive link, it is necessary to carry out maintenance in a timely manner, while using additional damping elements.

Study on the mechanism of wheelset rotational speed variation during curves

Study on the mechanism of wheelset rotational speed variation during curves

Study on Solid Particle Erosion of Pump Materials by Fly Ash Slurry using Taguchi’s Orthogonal Array

Various grades of stainless steel are used to fabricate the pump impeller, casings, and seals used in heavy-duty erosion and corrosion conditions. In the present study, stainless steel (SS316L, SS304, SDSS2507) and grey cast iron used in the fabrication of heavy-duty pump impellers were taken for the analysis of solid particle erosion. Experiments were conducted on the lab-scale slurry pot tester. Fly ash slurry was prepared of different concentrations (wt%). Taguchi’s orthogonal array is used to design the experiments of erosion wear for the variation of rotational speed, solid concentration, time, and particle size. Results showed that SS316L showed superior microhardness and wear behavior against the fly ash slurry followed by SS304, SDSS2507 and Grey cast iron.

A NOVEL DESIGN OF PERISTALTIC CARBON NANO PUMP AND AN ANALYSIS OF HELIUM FLOW

A novel nano-scale pump that can transport atoms or small molecules with a peristaltic motion is designed. It is proven by molecular-dynamics simulations that the introduced nano-pump design works properly. The designed nano-pump consists of one main carbon nanotube named the flow tube and two rotors where multi-walled carbon nanotubes are attached. The pumping of helium atoms by the designed peristaltic carbon nano-pump is investigated by molecular-dynamics simulations. For varying rotor speeds and blade counts, time-averaged velocity, temperature, and pressure results of pumped helium atoms are calculated, and relationships between them are modeled as polynomial surfaces. The results showed that rotor frequency increases the velocity of helium linearly and the temperature and pressure of helium non-linearly. Furthermore, the blade count of the proposed mechanism does not substantially affect the velocity as per the previous studies in the literature.

Study on two-rotor interaction of counter-rotating horizontal axis tidal turbine

A counter-rotating tidal turbine can balance the axial torque and accelerate the wake recovery, leading to a more conducive array layout. This paper aims to investigate the coaxial-rotor interaction, considering variable rotor distance and rotation speed. A numerical model based on large eddy simulation (LES) is established to study the hydrodynamic performance of this turbine, and it is validated by a flume experiment. The research results show that the upstream rotor performance is severely degraded when the two rotors are configured with narrow distance; while this distance is too wide, the downstream rotor bears a large fluctuating load induced by the fully developed wake. In terms of rotation speed, the efficiency of the upstream rotor decreases with the acceleration of the downstream rotor, but the maximum reduction is less than 10%. Moreover, a severe disturbance region will be generated behind the upstream rotor caused by blade root vortex shedding, and the downstream rotor should be positioned far away from this region. Overall, the current two-rotor system can achieve the best energy efficiency at the rotor distance of 0.4D. Compared with a single rotor, this system improves power efficiency by nearly 10%.