Rotation Frequency Research Articles

Continuum approach of nonlinear dynamic analysis of a rotating wind turbine blade considering hub motion

This paper reports the nonlinear dynamics of a large wind turbine blade considering the hub motion. The investigation is based on a continuum mathematical model, which is derived using the extended Hamilton principle. The proposed model is validated via comparison with both published results and numerical simulations obtained from open source software. The steady state amplitude curves as well as the dominating frequencies of the modal forces are compared and analyzed with discussions on the effects of the hub motion amplitude, yaw angle and rotational frequency of the blade. Comparison of dominant frequencies of modal forces shows that the skewed inflow can strengthen the periodic excitation whose frequency equals to the rotating frequency of the blade. The steady state amplitude curves show that vibration of the edge-wise mode is more significant than that of the flap-wise mode when under the hub motion excitation. Moreover, internal resonance between the first three modes is also observed. The skewed inflow has a significant effect on the first mode in terms of vibration amplitude and the most unfavorable direction of hub motion. Finally, recommendation on how to avoid the resonance and internal resonance of the blades under skewed inflow are given.

Millimeter-Wave and High-Resolution Infrared Spectroscopy of 3-Furonitrile.

The rotational spectrum of 3-furonitrile has been collected from 85 to 500 GHz, spanning the most intense rotational transitions observable at room temperature. The large dipole moment imparted by the nitrile substituent confers substantial intensity to the rotational spectrum, enabling the observation of over 5600 new rotational transitions. Combined with previously published transitions, the available data set was least-squares fit to partial-octic, distorted-rotor A- and S-reduced Hamiltonian models with low statistical uncertainty (σfit < 0.031 MHz) for the ground vibrational state. Similar to its isomer 2-furonitrile, the two lowest-energy vibrationally excited states of 3-furonitrile (ν17, ν24), which correspond to the in-plane and out-of-plane nitrile bending vibrations, form an a- and b-axis Coriolis-coupled dyad. Rotationally resolved infrared transitions (30-600 cm-1) and over 4200 pure rotational transitions for both ν17 and ν24 were fit to a partial-octic, Coriolis-coupled, two-state Hamiltonian with low statistical uncertainty (σfit rot < 0.045 MHz, σfit IR < 6.1 MHz). The least-squares fitting of these vibrationally excited states provides their accurate and precise vibrational frequencies (ν17 = 168.193 164 8 (67) cm-1 and ν24 = 169.635 831 5 (77) cm-1) and seven Coriolis-coupling terms (Ga, GaJ, GaK, Fbc, FbcK, Gb, and Fac). The two fundamental states exhibit a notably small energy gap (1.442 667 (10) cm-1) and an inversion of the relative energies of ν17 and ν24 compared to those of the isomer 2-furonitrile. The rotational frequencies and spectroscopic constants of 3-furonitrile that we present herein provide a sufficient basis for conducting radioastronomical searches for this molecule across the majority of the frequency range available to current radiotelescopes.

СПОСОБИ МЕХАНІЧНОЇ СТАБІЛІЗАЦІЇ ЧАСТОТИ ОБЕРТАННЯ ЕЛЕКТРИЧНОГО ГЕНЕРАТОРА СИЛОВОЇ УСТАНОВКИ

When studying the electrical on-board system of the vehicle as a whole, it is necessary to consider the dynamic characteristics of all its components. One of the links of the system is considered - a mechanical variator for stabilizing the frequency of rotation of the generator rotor. When the generator is driven by an aircraft engine, there are factors that prevent its stable operation. The rotation frequency of the drive motor is constantly changing, so there is a problem related to the creation of a high-quality system of mechanical stabilization of the rotation frequency. Possible methods of stabilizing the frequency of rotation of the electric generator rotor by using stepless variators are considered. When analyzing the possible types of stepless variable speed variators, mechanical variators were chosen, which have a number of advantages over other types, such as their compactness, low cost, high efficiency, etc. In particular, it is proposed to use differential gear mechanisms of various schemes as stabilizers: a differential variator made using schemes IA and AI, as well as a differential mechanism AI with a free carrier. As devices that provide self-regulation of the output rotation frequency, it is proposed to use speed regulators, the principle of operation of which is based on the use of centrifugal force, which changes when the rotation frequency changes at the input to the variator. A concrete example for a differential mechanism (AI) shows how to perform kinematic and force calculations to ensure constancy of the output speed when the input speed changes within ± 6%.

Numerical Study of Low-Specific-Speed Centrifugal Pump Based on Principal Component Analysis

The characteristics of pressure pulsations in centrifugal pumps have attracted considerable attention. In this study, principal component analysis is used to discuss the pressure pulsations in a centrifugal pump with a low specific speed, and the primary causes for these pressure pulsations are analyzed in conjunction with experimental results. The results indicate that principal component analysis effectively separates the primary modes that influence the flow field characteristics. An excessive wrap angle results in the formation of a backflow vortex on the working face of the blade. Obvious stratification of the zero-order modal pressure indicates that the geometric structure of the impeller is rational and that the transient flow field is stable. The second- and third-order modes are conjugates, and their dominant frequency coincides with the dominant rotating frequency of the impeller, indicating that the pulsations of a single channel are the primary component of the pressure pulsations. The primary frequency (148.54 Hz) of the pressure pulsations at monitoring points distributed across the volute is three times the rotational frequency (49.51 Hz) of the impeller. The different positions and sub-frequencies of the monitoring points mean that the principal component analysis can effectively identify the impeller-induced sub-frequency difference.

Виявлення впливу шорсткості та радіального зазору на характеристику осьового багатоступеневого компресора

The operation of gas turbine engines inevitably increases the blade roughness and tip clearance in multistage axial compressors. The result is an increase in its thermogasodynamic parameters. The reason for the increase in the roughness of the blades and the tip clearance can be various factors: clogging of the flow part of the compressor (adhesion and deposition of dust on the surface of the blades), erosion due to the arrival of hard sand grains in the flow part, etc. The subject of this study is thermogasodynamic processes in the flow part of a multistage axial compressor, based on the presence of flow part removal. The goal is to develop a methodology for forecasting and researching the influence of the blade surface roughness and increased tip clearance on the overall characteristics of a multistage axial compressor. A twelve-stage axial compressor was used as the research object. The guiding vanes of the first four stages and the inlet guiding vanes depend on the rotation frequency. As a result, it was not possible to investigate the influence of the surface roughness of the blades and the increased tip clearance on the overall characteristics of the multistage axial compressor. The calculation of the characteristics of an axial multistage compressor with simulation of different levels of roughness and increased tip clearance in comparison with its initial values and obtained several indicators of changes in thermogasodynamic parameters and characteristics of the compressor with changes in roughness (ks = 3 μm, ks = 20 μm, ks = 40 μm) was performed. and tip clearance (Δr=1%, Δr=2%, Δr=5%). The scientific and practical novelty of the obtained results arises from the following: the method of calculating the thermogasdynamic parameters and characteristics of an axial multistage compressor has been improved, which makes it possible to evaluate the effect of the roughness of the surfaces of the blades and the increased tip clearance; new data were obtained regarding the change in the compressor characteristics at different levels of roughness and the size of the tip clearance.

Just Keep Spinning? The Impact of Auditory and Somatosensory Cues on Rotary Chair Testing.

The purpose of this study was to determine whether providing realistic auditory or somatosensory cues to spatial location would affect measures of vestibulo-ocular reflex gain in a rotary chair testing (RCT) context. This was a fully within-subject design. Thirty young adults age 18-30 years (16 men, 14 women by self-identification) completed sinusoidal harmonic acceleration testing in a rotary chair under five different conditions, each at three rotational frequencies (0.01, 0.08, and 0.32 Hz). We recorded gain as the ratio of the amplitude of eye movement to chair movement using standard clinical procedures. The five conditions consisted of two without spatial information (silence, tasking via headphones) and three with either auditory (refrigerator sound, tasking via speaker) or somatosensory (fan) information. Two of the conditions also included mental tasking (tasking via headphones, tasking via speaker) and differed only in terms of the spatial localizability of the verbal instructions. We used linear mixed-effects modeling to compare pairs of conditions, specifically examining the effects of the availability of spatial cues in the environment. This study was preregistered on Open Science Framework (https://osf.io/2gqcf/). Results showed significant effects of frequency in all conditions (p < .05), but the only pairs of conditions that were significantly different were those including tasking in one condition but not the other (e.g., tasking via headphones vs. silence). Post hoc equivalence testing showed that the lack of significance in the other comparisons could be confirmed as not meaningfully different. These findings suggest that the presence of externally localizable sensory information, whether auditory or somatosensory, does not affect measures of gain in RCT to any relevant degree. However, these findings also contribute to the increasing body of evidence suggesting that mental engagement ("tasking") does increase gain whether or not it is provided via localizable instructions.

Theoretical studies of the movement of mineral fertilizer granules in the mixing chamber of a centrifugal mixing plant

Relevance. The use of mineral fertilizers helps to improve soil fertility, stimulates the growth and development of plants, which is achieved due to the availability of necessary nutrients. In turn, it is important to observe the correct application of fertilizers, which allows you to control the level of nutrients in the soil, preventing both their excess and deficiency. Currently, the main application of fertilizers falls on complex mineral fertilizers, while one of their disadvantages is that they may contain nutrients that will not be in demand by the plant, which can lead to a violation of the ecological balance. One of the solutions to this problem is the use of flour mixtures. When using mixtures, the determining factor is the uniformity of mixing, which is largely determined by the equipment used. In this regard, the urgent task is to develop a mixing equipment that meets the necessary indicators.Methods. During the research, the processes occurring in the mixing chamber of the developed mixing plant were studied using methods of mathematical analysis, graphical and mathematical modeling.Results. As a result of the research, it was found that during the operation of the mixing plant, the mixing quality is determined by the rotation frequency of the conical rotor. At the same time, the granules of mineral fertilizers after leaving the conical rotor, pouring into the collecting funnel, continue their movement along a spiral trajectory. During the movement of the granules along the surface of the rotating cone, as well as when moving through the funnel, their trajectories will intersect with each other, which will lead to their active mixing.

Analysis of Pressure Fluctuation of a Pump-Turbine with Splitter Blades on Small Opening in Turbine Mode

Unstable flow in a pump-turbine can cause pressure pulsation, and the resulting vibration deteriorates the stability and operating safety of the unit. This study conducted three-dimensional numerical calculations of the overall flow passage of a pump-turbine with splitter blades under the small guide vane opening, and the unsteady flow characteristics of the turbine were investigated. The results showed that the pressure fluctuation was more severe at lower head operating conditions with lower efficiency, especially in the vaneless area (the runner blade passages). Under the lower head condition, the proportion of 12 times the rotational frequency (12 f/fn) increased in the vaneless area, and the amplitude of 1 f/fn as well as 2 f/fn became larger in the runner blade channel, with more space occupied by vortices and reflux areas. A spiral vortex rope formed in the draft tube, increasing the proportion of 0.4 f/fn and 0.7 f/fn pressure pulses.

Tunable acoustic vortex generation by a compact rotating disk

Acoustic vortices (AVs) carry orbital angular momentum (OAM), showing great promise in advancing communication, biomedicine, and metrology. An ideal OAM generation method that realizes the tunability of AV topological charge and working frequency in a compact way is strongly desired. Here, we utilize aerodynamic dipole sources from a rotating disk to generate AV. This method generates AVs with different topological charges through the interference of these dipole sources at the angular rotation frequency and its multiples. These AVs exhibit high purity, and their three-dimensional characteristics are explored. Furthermore, our experiment demonstrates that the generated AVs significantly enhance the sound field amplitude at their working frequency, which is the product of the topological charge and angular frequency. The results also verify that this amplitude enhancement effect is positively correlated with the AV’s stability and achieves the contactless detection of disk rotation information. The demonstrated method provides expanded versatility for OAM-based applications.

Analysis of wake and power fluctuation of a tidal current turbine under variable wave periods

In the Marine environment, waves and turbulence usually coexist, affecting the operation performance of the tidal current energy turbine. This paper conducts experiments on a scaled tidal stream turbine to study the wave period effect on the wake and power characteristics. Under a wave-current environment, the wake is found to display Gaussian distribution. Within the 4 times diameter downstream range (4D), the turbulence is significant, and both the wake velocity loss and fluctuation increase first and then decrease with wave period. After 6D, the flow field gradually recovers to the inflow level. The wave period affects the transversal turbulence, more in the near than far wake region, as the significant turbulence intensities at the hub and blade tips gradually merge and become consistent after 6D. The wave period affects little the power coefficient CP owing to the sinusoidal inflow velocity nature. However, the amplitude of the phase average power increases first and then decreases with the wave period. By contrast, the phase average power fluctuations are sensitive to cycle changes only within the low TSR interval; they decrease sharply with TSR. In addition, the energy distribution of power fluctuation in the wave flow coupling environment is mainly concentrated at the sum and difference, and as well multiples, of the rotational and wave frequency. The wave and its multiples energy distribution increases and then decreases with the wave period.

Helicopter vibration control employing superelastic pitch link with shape memory alloy

One of the main applications of shape memory alloy (SMA) concerns vibration control, especially superelastic SMA (SMA-SE), which presents a significant stress hysteresis and can work as a damper while adding minimal weight to the structure. In helicopters, vibration is a phenomenon inherent to their operation, and although cannot be eliminated, must be minimized to acceptable levels of safety and comfort. In this context, this paper aims to present the design, testing, and dynamic behavior of a new device entitled smart pitch link, a device with superelastic material for passive vibration control. The paper depicts the design process, assembly, and device testing using a whirl tower that simulates a helicopter rotor in hover. The approach adopts a comparative analysis of the dynamic response on the prototype in reference condition, with a stiff pitch link, with the modified prototype, and with the superelastic pitch link installation. In addition, beyond hover tests, cyclic commands and an asymmetrical lateral gust were employed to observe the output response of the device under transient loadings. Contrary to the literature data about the low time response of SMA, the device presents satisfactory time response and attenuation in frequencies close to main rotor frequencies, with signal attenuations between 2 to 4 dB without any external energy consumption, which, in a comparative analysis, may exceed more than 50% of vibrational amplitude attenuation.

Dynamics analysis of rotating soft core sandwich beams using the absolute nodal coordinates formulation with zigzag theory

With the widespread use of rotating sandwich structures in engineering applications, it is significant to understand their vibration characteristics and dynamic behavior. Since the absolute nodal coordinates formulation (ANCF) is one of the most effective methods for solving rotational dynamics, it is feasible to use the ANCF with zigzag theory (ANCF-ZZ) to analyze the dynamics of these structures. Therefore, this study builds upon existing research to further refine the theory of ANCF-ZZ and proposes diverse models for determining the element complexity required in modeling rotating sandwich structures. In order to better solve the dynamics of rotating sandwich beams, the ANCF-ZZ is described in a floating coordinate system by coordinate transformation. Subsequently, the dimensionless frequency and dynamic responses of rotating sandwich beams are analyzed, and the influence of core-to-face elastic modulus ratio and thickness ratio on them are investigated. The results show that the segmental description of the cross-section based on the zigzag theory is more influential than the warping description by higher-order interpolating polynomials. Consequently, reducing the order of original high-order ANCF-ZZ beam elements can improve computational efficiency without affecting accuracy. In addition, the ANCF-ZZ captures the dynamic stiffening effect and frequency veering phenomena, which are essential characteristics in rotational frequency analysis. Compared with commercial finite element software, the ANCF-ZZ not only can accurately analyze the dynamic stiffening effect of rotating sandwich beams but also can obtain the deformation response at non-constant rotational speeds and higher rotational speeds using a few elements, which is valuable for engineering applications.

Polarization and coriolis forces impact on the Kelvin- Helmholtz instability of viscous dusty plasma

The Kelvin-Helmholtz instability in a dusty plasma with sheared velocity variations is analyzed, considering the effects of viscosity, rotation, and polarization parameters in dust. A theoretical framework is proposed to describe the behavior of three distinct fluid components: electron and ion fluids governed by the Boltzmann equation, as well as magnetized dust fluids influenced by nearby particles' polarization force. The dispersion relation for the KH instability is derived using normal mode analysis on linearized perturbed equation. It is found that rotation, viscosity, and polarization force based on the dusty acoustic mode optimize the basic dispersion relation of Kelvin-Helmholtz instability accurately. The critical shear is important for exciting the Kelvin-Helmholtz instability and is influenced by factors such as rotation, polarization, and dusty cyclotron frequency. The growth rate of the Kelvin-Helmholtz instability appears to be suppressed due to the presence of rotation, viscosity, and polarization force.

Rotating target detection model under arbitrary incidence of the vortex beam based on optical RDE

The optical rotational Doppler effect (RDE) related to orbital angular momentum has attracted extensive attention in rotating targets detection. In this paper, we present a novel rotating target detection model based on optical RDE, where the vortex beam can be incident on the rotating target with an arbitrary case. Based on the proposed detection model, we investigated the mechanism of rotational Doppler shift and deduced the generalized formula of the Doppler frequency shift under arbitrary incidence of the vortex beam by phase modulation method. Subsequently, the model is studied under different incident cases, and the variation of Doppler frequency shift with different incident parameters is analyzed combining with the deduced formulas. Meanwhile, we also give the detection methods to for motion parameter estimations of the rotating target. Theoretical and simulated results verify the effectiveness of the proposed model, and more detailed motion parameters can be obtained based on RDE. This theoretical model enables us to better understand the generation of the rotational Doppler frequency and may be useful for the application of remote sensing of a rotating target.

Coherent structures decomposition of internal flow in the double-suction centrifugal pump impeller

Abstract In order to understand the unsteady flow phenomenon of the centrifugal pump, the dynamic mode decomposition method (DMD) is introduced to extract the three-dimensional coherent structure of the rotating flow field in the impeller passage under three different working conditions of the double-suction centrifugal pump. The time series collection of flow field is constructed by CFD numerical simulation, and the approximate matrix characteristic parameters and different modal data are solved. The analysis results show that the position, form and spatial-temporal evolution of the coherent structure can be accurately captured by DMD method corresponding to a single frequency in the double suction pump. For the temporal evolution, the coherent structure corresponding to low frequency is the most stable and dominate the unsteady flow. For the spatial evolution, the coherent structure corresponding to even-fold rotational frequency mostly occurs near the pressure side of the blade at the outlet of the impeller, and the coherent structure corresponding to odd-fold rotational frequency is mostly located in the flow field inside the impeller or near the blade surface.

Dynamic modeling and vibration characteristics analysis of cylinder with local defects in axial piston pump

The piston/cylinder pair suffers from excessive wear during the operation of axial piston pumps, and the local defects usually occur in the brass bush in the cylinder bore. Generally, the wear of cylinder is the main source of failure that affects the reliability of axial piston pumps. Thus, it is necessary to conduct an in-depth study on the vibration generated by the cylinder with local defects. Considering the effect of defect dimension, a novel time-varying displacement excitation model of the axial piston pump cylinder defect is proposed and establishes a 13 degrees of freedom lumped parameter dynamic model for cylinder fault. Then, investigating the effects of length and depth of the defect on the spectral amplitude and exploring the fault characteristic frequency of cylinder. Lastly, the model was validated on a test rig. The results demonstrate that the constructed model can predict the vibration caused by a locally defective cylinder with a frequency domain error of 0.69% and the fault characteristic frequency of cylinder is the same as its rotational frequency. Moreover, the defect length will influence the amplitude and duration of the cylinder-defect pulse waveform. The fault excitation amplitudes increase with the increase of defect depths.

Изменение параметров Стокса при прохождении излучения в замагниченной атмосфере

The pass of polarized radiation in magnetized atmosphere is described by the system of connected radiative transfer equations for the Stokes parameters. At multiple scattering of radiation it is necessary to know how the change of the Stokes parameters between the cases of scattering occurs. The paper presents the explicit formulas describing the transformation of the Stokes parameters for the number of situations. These formulas describe directly the transformation of the Stokes parameters in optically thin circumstellar envelopes. The formulas for mutiply scattered radiation in the system of transfer equations take into account this transformation of the Stokes parameters. The basic parameter in all cases is x = ωB/ω = 0.933 × 10−8λ(μ)B(G), where ωB is cyclotron frequency of the electron rotation and ω is the frequency of monochromatic radiation.

A wind farm planning method considering frequency security constraint based on wind farm participation in primary frequency regulation

Abstract Renewable energy sources such as wind power, connected to the grid on a large scale, reduce the rotational inertia and frequency regulation of the power system. Many studies have included frequency security constraints (FSC) in power system scheduling to ensure system frequency stability, but few studies have included FSC in grid planning. Therefore, this paper establishes a planning model for wind farms that considers the FSC based on the wind turbines’ participation in the primary frequency regulation (PFR) by obtaining the maximum deviation value constraint of the system frequency through the system frequency response (SFR) model. Tests were conducted on the IEE30-node system, and the results show that the proposed model enhances the system frequency response capability and ensures system security.

Adaptive low voltage crossing strategy for symmetrical faults of networked inverters

Abstract Due to the inability of grid-following control methods to compensate for the comprehensive reduction in system inertia, strength, and short-circuit capacity caused by the decreased proportion of synchronous machines, the grid exhibits insufficient resilience to disturbances, leading to severe stability risks in terms of rotor angle, frequency, and voltage. Grid-forming inverters have emerged to address this issue. During symmetrical faults, the low-voltage ride-through of grid-forming inverters often involves freezing the reactive power loop, resulting in a direct output of higher voltage and reactive current. However, an increase in reactive power command leads to a sharp rise in the internal potential magnitude of grid-forming inverters. Upon clearance of the grid fault, the excessively high internal potential may cause a rapid, short-term increase in terminal voltage, potentially resulting in overvoltage, which is detrimental to the operation of grid-connected equipment. In response to this issue, this paper proposes an adaptive low-voltage ride-through control strategy for grid-forming inverters under symmetrical faults controlled by a virtual synchronous machine control method. Initially, a virtual synchronous machine control model is established. Limiting current is achieved through the construction of a fixed virtual impedance loop. The issues associated with fixed virtual impedance current limiting are analyzed, leading to the proposal of an adaptive virtual impedance control strategy. Finally, the feasibility of the proposed method is verified through simulation experiments.

Adaptive reactive power control strategy for grid-forming inverter under symmetrical fault

Abstract Due to the inability of the grid-type control method to compensate for the comprehensive reduction in system inertia, strength, and short-circuit capacity caused by the proportional decrease of synchronous machines, the power grid exhibits insufficient resistance to disturbances, leading to severe stability risks in terms of rotor angle, frequency, and voltage. In response to these challenges, grid-forming inverters have emerged. Under symmetrical faults, the low-voltage ride-through of grid-forming inverters is often accompanied by a frozen reactive power environment, resulting in a direct output of increased voltage and reactive current. However, an elevated reactive power command can cause a sharp increase in the potential amplitude within grid-forming inverters. After the grid fault is cleared, the excessively high internal potential can cause a short-term and rapid increase in terminal voltage, potentially leading to overvoltage, which is detrimental to the operation of grid-connected devices. To address this issue, this paper first employs a grid-forming inverter controlled by a virtual synchronous machine control method. Using the grid positive-sequence voltage as a reference value, it identifies whether a voltage drop fault has occurred. Based on this, an adaptive reactive power control strategy is proposed, which can promptly achieve the same effect as the frozen reactive power environment during faults, while also promptly restoring the reactive power environment after fault clearance, thereby avoiding overvoltage issues. The feasibility of the proposed method is verified through the establishment of a simulation system.