Rotor Model Research Articles

Single-particle and dipole excitations in Co62

An extensive study of the level structure of $^{62}\mathrm{Co}$ has been performed following a complex multinucleon transfer reaction, $^{26}\mathrm{Mg}(^{48}\mathrm{Ca}, 2\ensuremath{\alpha}3np\ensuremath{\gamma})^{62}\mathrm{Co}$, at beam energies of 275, 290, and 320 MeV. The combination of the Gammasphere array, the fragment mass analyzer, and a focal-plane ionization chamber was used to identify and delineate excited levels in $^{62}\mathrm{Co}$. A considerable extension to the $^{62}\mathrm{Co}$ level scheme is proposed with firm spin-parity values assigned on the basis of angular distribution and correlation analyses. Various level sequences built upon states of single-particle character have been observed, and an interpretation of these structures in the framework of the spherical shell model is presented. At moderate spins, two dipole bands have been observed and, based on their phenomenological study, a possible magnetic rotation character is suggested. However, theoretical calculations performed using the particle rotor model support magnetic rotation for only one of these dipole bands.

Interpretation of enhanced electric dipole transitions in Br73 by the reflection-asymmetric triaxial particle rotor model

The recently observed positive and negative parity bands in $^{73}\mathrm{Br}$ are investigated by the reflection-asymmetric triaxial particle rotor model. The experimental energy spectra as well as the electric transition probabilities $B(E1), B(E2)$, and the ratio $B(E1)/B(E2)$ are well reproduced by the theoretical calculations. It is found that the enhanced interband $E1$ transitions between the opposite-parity bands, a crucial evidence for octupole correlations, are mainly contributed by the intrinsic single-particle electric dipole matrix elements.

A global rotor noise control method based on near-field acoustic holography and sound field reproduction

Aiming at the severe aerodynamic noise generated by the rotor of rotorcrafts, a global active noise control method is proposed based on near-field acoustic holography (NAH) and sound field reproduction (SFR). The microphone array here is not only used to evaluate errors as in existing methods, but also to predict the rotor noise by extracting acoustic modal information. The loudspeaker array reproduces a secondary sound field with the same acoustic modal components but in opposite phase to achieve global noise reduction. Specifically, by arranging microphones on the fuselage, the rotor noise prediction problem is transformed into an external domain problem of the NAH. Then, by extending the SFR to the external domain, the loudspeaker array is used to reproduce a target sound field which just achieves sound-sound cancellation with the rotor noise globally. Further, the application of the acoustic modal analysis shows that the acoustic modal distribution of the rotor noise is determined by the number of blades, which greatly reduces the scale of loudspeaker/microphone array and is conducive to on-line noise control. The acoustic modal decomposition of the rotor noise shows that the amplitude of the main acoustic mode decays the slowest with distance compared with other acoustic modes, and it is the main component of the far-field noise. The comprehensive evaluation of the model rotor noise reduction performance at different scales shows that the global noise reduction effect for controlling all acoustic modes exceeds 40 dB, while for controlling the main acoustic mode reaches 18 dB, and the required power is reduced by 84%. Finally, the global active noise control experiments for the model rotor are conducted. The results show that the global noise reduction can reach 17 dB through controlling the main acoustic mode. The GANC method shows great advantage of global noise reduction and high engineering application potential.

Proposing a sequential iterative method based on a per-unit model for rotor shape optimization in permanent magnet assisted synchronous reluctance motors

PurposeDuring the design process of synchronous reluctance motors (SynRMs), one crucial step, after its main dimensioning, is optimizing the rotor geometry for maximum average torque and minimum torque ripple. However, because of the complexity of rotor flux-barrier layers geometry, the number of rotor geometrical parameters is high and this step could be quite complex and time-consuming. To obtain a good performance, one needs a robust algorithm to optimize the rotor geometry. The purpose of this paper is to present a sequential iterative method for rotor shape optimization in SynRMs based on the per-unit rotor model to maximize the average torque and minimize the torque ripple.Design/methodology/approachIn the presented method, at first, rotor geometrical parameters are classified into several groups based on their geometrical similarities, and then optimization is done on these individual groups iteratively. The method starts with an arbitrary feasible rotor geometry and proceeds to optimize it. Because the method’s performance depends on initial rotor geometry, different cases are studied to investigate the convergence and robustness of the method. The MATLAB software is used to implement the optimization algorithm, and the ANSYS Maxwell software is used for the finite element analysis.FindingsThe performance of the proposed method is studied on a three-phase 0.75 kW-1,500 rpm permanent magnet assisted SynRM. The results show that the method improves the average torque while reducing the torque ripple. Even if the method starts with an inappropriate initial rotor geometry, it is robust enough and converges within an acceptable number of iterations.Originality/valueThe value of this paper is in introducing a per-unit rotor model. When the authors optimize the rotor geometry for a specific motor rating, it can be scaled up or down for other ratings with little effort. In this work, the number of rotor poles is four and the number of rotor flux-barrier layers per pole is three. Other combinations could be analyzed in future studies.

Generalized Yang-Mills theory under rotor mechanism

This paper follows the previous work on generalized abelian gauge field theory of higher-order derivatives under rotor model and extends the study to the most generalized non-abelian case. We find that the rotor mechanism from the abelian case applies nicely to the non-abelian case under the Lorentz gauge condition. Under the rotor mechanism, the gauge field transforms as Tμa→□nTμa. When the order of field derivative is n=0, this restores back to the original Yang-Mills action. Our work gives an extensive generalization of the Yang-Mills theory with higher-order field derivatives. We also compute the equation of motion and Noether's current of the generalized non-abelian gauge field theory. Finally, we study the dynamic instability issue of the theory by the Ostrogradsky construction and the analysis of the 00-component of the energy-momentum tensor.

Experimental and theoretical investigations of unbalance flexible rotor in active magnetic bearings considering backup bearings contacts

This paper describes the experimental verification of an unbalance flexible rotor model in active magnetic bearings. The dynamic modeling takes into account the gyroscopic moments of the disk, geometric coupling of the magnetic actuators, and contact forces of the backup bearings. The Rung–Kutta method is used to integrate the equations of motion. The nonlinear dynamic response is analyzed using bifurcation plots, disc center trajectories, Fast Fourier Transforms, Poincaré maps, and maximum Lyapunov exponent. The analysis is carried out for different values of rotating speed and unbalance eccentricity. In the unbalance test, a concentrated mass of 5 gr is attached in three radial position of the disk. The numerical simulations and experiments prove that a variety of nonlinear dynamical phenomena such as period -3, -4, -8, periodic, quasi-periodic, and chaotic motions occur in the system. The results indicate that the response of the rotor returns back to a regular motion by increasing the rotational speed. Also, by increasing the unbalance eccentricity, the first irregular motion initiates at much higher rotational speeds. Therefore, sufficient attention should be paid to these factors in design of a flexible rotor system equipped with both active magnetic bearings and backup bearings in order to ensure system reliability.

Rigid Triaxial Rotor Model Description of γγ-Band in Some Even Nuclei

Rigid Triaxial Rotor Model Description of γγ-Band in Some Even Nuclei

Study on performance of low-speed high-torque permanent magnet synchronous motor with dynamic eccentricity rotor

In actual production, errors in manufacturing and assembly may lead to misalignment of the stator and rotor and uneven air gap magnetic density, which affects the running performance of the motor. The influence of rotor dynamic eccentricity on air-gap flux density, cogging torque and loss is studied by combining analytical method and finite element analysis. The eccentric rotor model of low-speed high-torque permanent magnet synchronous motor (LHPMSM) is established on Maxwell 2D. The results show that with the increase of the rotor eccentricities, the back EMF and stator iron loss changeless, the cogging torque decreases slightly. The output torque increases slightly, but the harmonic distortion rate of air gap magnetic density and stator copper loss increase significantly.

High-fidelity numerical investigations of rotor-propeller aerodynamic interactions

This paper presents high-fidelity numerical investigations of rotor/propeller aerodynamic interactions related to thrust-augmented compound rotorcraft. High-fidelity CFD simulations of a generalised rotor/propeller integration, as studied both numerically and experimentally by ONERA, were performed using the HMB3 solver within the GARTEUR AG25. Simulations of the baseline isolated propulsors were first carried out and validated against experimental measurements. Simulations of the rotor/propeller integration were then performed and compared with ONERA numerical results. Evaluations of the spatial/temporal resolutions were first carried out at low-speed forward. The actuator disk modelling of the main rotor was shown to be an effective and efficient simulation method compared to blade-resolved results. Simulations of the installed propeller were also performed in hover, and the aerodynamic interference was found to be considerably exacerbated. A ducted propeller configuration was also proposed to study how ducting the propeller would change the aerodynamic interference. The duct offloaded the propeller and produced extra thrust, and the blades suffered less from the main rotor downwash. However, the duct generated a strong downwards force and a nose-down pitching moment because of its flow blockage. The loading variations induced by the aerodynamic interactions were found to be strong at low advance ratios but ducting provided significant alleviation.

Influence of moments of inertia on transverse wobbling mode in odd-mass nuclei

The reported transverse wobbling band in odd-mass $^{105}$Pd has been reinvestigated by the triaxial particle rotor model. Employing different parameter sets of moment of inertia (MOI), several calculated results could be in good agreement with the experimental data, which show distinct modes of rotational excitation, respectively. These modes are sensitive to the ratio between the MOI at intermediate and short axis. With the increase of this ratio, a wobble about the short axis of the total angular momentum is gradually changed to a wobble about the intermediate axis. In addition, it is exhibited that precession and tunneling are two aspects of the quantum wobbling motion. The tunneling aspect dominates in the yrare states of $^{105}$Pd. The present results in $^{105}$Pd show the complexity of the transverse wobbling mode.

Active crack control approach applied to a horizontal rotating machine

The present contribution proposes an active vibration control technique devoted to shafts with cracks aiming to minimize their propagation. The existence of a crack in rotating shafts can be characterized by 2X and 3X super-harmonic amplitudes in the vibration responses of the rotor, which can increase as the crack propagates along the shaft’s cross-section. A proportional-integral-derivative control technique is applied to suppress the 2X and 3X vibration amplitudes of a cracked shaft, which is performed by using a bandpass filter applied to the vibration responses of the rotor. Numerical and experimental results are obtained through both a representative finite element model of a horizontal rotor and its corresponding test-rig. In this case, electromagnetic actuators are used to apply the control effort to the rotor. The Mayes model is applied for simulating the breathing behavior of the transverse crack. The linear fracture mechanics theory is considered to correlate the crack depth with the corresponding additional rotor flexibility. Both numerical and experimental results demonstrate the possibility of reducing the effects of a transverse crack through active control on the dynamic behavior of a rotating machine. Moreover, it is shown that the proposed control law is capable of controlling the crack effects with the rotor operating in different rotation speeds.

Linear and Nonlinear Performance Analysis of Hydrodynamic Journal Bearings with Different Geometries

In rotor dynamics, a traditional way of representing the dynamics of hydrodynamic bearings is using stiffness/damping coefficients. It is thus necessary to carry out a linearization of hydrodynamic forces around the shaft’s equilibrium position. However, hydrodynamic bearings have highly nonlinear nature, depending on operating conditions. Therefore, this paper discusses the applicability of these linear/nonlinear approaches using a computational model of the rotating system, where the finite element method is used for rotor modelling and the finite volume method for bearing calculation. The main goal is to investigate the boundaries for linear approximation of the hydrodynamic forces present in lobed hydrodynamic bearings, with the system operating under high loading conditions. Several numerical simulations were performed varying preload parameter and rotating speed. A comparison of the system’s responses, in time domain (shaft orbits) and frequency domain (full spectrum), is made for linear and nonlinear models. Results showed that trilobed bearings are more susceptible to nonlinearities, even in situations of smaller vibration amplitudes, while elliptical bearings are sensitive only under larger vibration amplitudes. These analyses are of great importance for mapping the influence of nonlinearities in different types of lobed hydrodynamic bearings with fixed geometry, varying the preload parameter to verify the influence on the system’s dynamic response. This study is important and serves as the basis for cases of monitoring and fault diagnosis (in the field of structural health monitoring) since it is crucial to distinguish what would be a fault signature or a standard nonlinear effect created by the use of hydrodynamic bearings.

Dynamic modeling and experimental verification on the rotor-armature structure of a steam turbine-generator unit

The rotor-armature structure of an exciter rotor used in a steam turbine-generator unit is investigated in this work. The objective is to create a base verified linear dynamic model of the exciter rotor for fault diagnosis or nonlinear interactions analysis. Natural frequencies for the rotor-armature structure are obtained from modal testing in free-free conditions. An analytical model for the structure is then constructed using Timoshenko beam theory, in which the linear effect of contact interface between rotor and armature is included. The unknown parameters of the rotor-armature model are identified by comparing analytical and experimental results. The verified dynamic model serves as the base for fault diagnosis and nonlinear response analysis due to the rotor and armature interactions.

Hover Performance Analyses of Coaxial Co-Rotating Rotors for eVTOL Aircraft

Hover performance analyses of coaxial co-rotating rotors (or stacked rotors), which can be used as lifting rotors for electric VTOL (eVTOL) aircraft, are conducted here. In this study, the rotorcraft comprehensive analysis code, CAMRAD II, is used with the general free-wake model. The generic coaxial co-rotating rotor without the blade taper and built-in twist is considered as the baseline rotor model, and the rotor is trimmed to match a prescribed rotor thrust value. The hover performance, including the rotor power and Figure of Merit (FM), is investigated for various index angles, axial spacings, blade taper ratios, and built-in twist angles. A maximum FM value is obtained near an index angle of 0° and 10° when the axial spacing is below and above 5.27%R, respectively. When the index angle is 0° and axial spacing is 1.44% R, the maximum increments in the FM are 3.03% and 6.06%, respectively, for a rotor with a blade taper ratio of 0.8 and a built-in twist angle of −12°. Therefore, this simulation study demonstrates that the hover performance of coaxial co-rotating rotors can be changed by adjusting the index angle or the axial spacing.

Nonlinear Dynamic Characteristics of Multidisk Rod Fastening Rotor with Axial Unbalance Mass Distribution

During long-term operation, the blades of rod fastening rotor are very prone to fault and may cause uneven axial mass distribution. The dynamic characteristics of a multidisk rod fastening rotor with axial unbalance mass distribution are studied. A four-disk rod fastening rotor model was established by the lumped mass method. The mass unbalance on different disks was used to simulate blade faults in different parts, and nonlinear factors such as oil film force and disk contact effect were considered. The fourth-order Runge-Kutta method was used to solve the model, and the spectrum and axis trajectory curves were obtained. The influence of fault location and rotating speed on rotor dynamic characteristics was analysed when there were blade faults on two disks. The results show that a large, unbalanced mass will bring strong nonlinear characteristics. The rod fastening rotor may be in different motion states at different rotating speeds. When the fault position of two disks changes, the changes of bearing spectrum, axis trajectory, and phase difference have regularity. The results can provide a theoretical basis for condition monitoring and fault diagnosis of rod fastening rotor.

Dynamic Modeling of Tie-bolt Rotors via Fractal Contact Theory and Virtual Material Method

Tie-bolt rotors, comprised of multiple stages of discs fastened by tie bolts, are commonly used in heavy-duty gas turbines. The contact interfaces between adjacent discs have considerable influence on the dynamic characteristics of tie-bolt rotors. Although many studies on the modeling of tie-bolt rotors have been reported, it is still a challenge to develop a relatively simple, efficient, and accurate model for such a kind of complex rotors. In this article, a new virtual material modeling method is proposed to analyze the dynamic characteristics of tie-bolt rotors. The elastic modulus and Poisson ratio of the virtual material are determined from the interface contact stiffness, which is derived based on the three-dimensional fractal contact theory. To verify the modeling approach proposed here, modal tests are conducted on a tie-bolt rotor specimen, of which the measured natural frequencies are compared with the simulation results. Finally, by using the verified modeling approach, the dynamic behaviors of tie-bolt rotors are investigated comprehensively, where the effects of fractal dimension parameters and preload level on rotor dynamics are evaluated.

First observation of the coexistence of multiple chiral doublet bands and pseudospin doublet bands in the A ≈ 80 mass region

Two nearly degenerate positive-parity bands with the πg9/22⊗νg9/2−1 configuration and three nearly degenerate negative-parity bands with the πg9/2(p3/2,f5/2)⊗νg9/2−1 configuration have been identified in 81Kr. They are interpreted as chiral doublet bands and pseudospin-chiral triplet bands, which is supported by the constrained covariant density functional theory and the multiparticle plus rotor model calculations. The present work reports two new chiral configurations πg9/22⊗νg9/2−1 and πg9/2(p3/2,f5/2)⊗νg9/2−1, and the first example of pseudospin-chiral triplet bands involving the π(p3/2,f5/2) pseudospin doublet.

Dynamic characteristics analysis of a vertical Jeffcott rotor-brush seal system

ABSTRACT Turbomachinery is used widely in the energy and power industries. The configuration of the rotor system is one of the major concerns in rotating machinery. This paper describes the development of a mathematical dynamic model of the vertical Jeffcott rotor–brush seal system considering bristle interference. The effects of the main structural and operating parameters, such as the rotational speed, rotor mass, installation distance of the brush seal, and system damping, on the nonlinear dynamic behavior of the vertical system are analyzed. The bifurcation points, stability, and vibration responses of the system are investigated using axis orbits, time histories, Poincaré maps, spectrum diagrams, bifurcation diagrams, and largest Lyapunov exponents. The results indicate that the amplitude of a vertical rotor system is smaller than that of a horizontal rotor system. The amplitude decreases as the installation distance and damping level increase. Reducing the rotor mass would enhances the stability of a rotor system.

Quantization of Generalized Abelian Gauge Field Theory under Rotor Model

This paper is a follow-up work of the previous study of the generalized abelian gauge field theory under rotor model of order $n$ of higher order derivatives. We will study the quantization of this theory using path integral approach and find out the Feynman propagator (2-point correlation function) of this generalized theory. We also investigate the generalized Proca action under rotor model and derive the Feynman propagator for the massive case.

Dynamic Characteristics Analysis of a Coupled Multi-crack Rotor System

Abstract This paper establishes a coupled model for multi-crack rotor using Timoshenko beam element with six degrees of freedom, and derives the stiffness matrix in the equations of motion accounting for the coupling between multiple cracks (the interaction between cracks). Then the effects of crack orientation angles (the relative angle between cracks, γ) on dynamic characteristics of the coupled multi- crack rotor near 1/3 and 1/2 subcritical speeds are analysed. The coupling between cracks induces more complex nonlinear dynamic characteristics such as large magnitudes of the super-harmonic components, which can be used as the indicators of early crack and for multi-crack identification. This work has a promotive significance for the application of the model-based method in the field of multi-crack detection of actual rotors.