Behavior Of Rotor Research Articles

Behavior of the collective rotor in nuclear chiral motion

The behavior of the collective rotor in the chiral motion of triaxially deformed nuclei is investigated using the particle rotor model by transforming the wave functions from the $K$-representation to the $R$-representation. After examining the energy spectra of the doublet bands and their energy differences as functions of the triaxial deformation, the angular momentum components of the rotor, proton, neutron, and the total system are investigated. Moreover, the probability distributions of the rotor angular momentum ($R$-plots) and their projections onto the three principal axes ($K_R$-plots) are analyzed. The evolution of the chiral mode from a chiral vibration at the low spins to a chiral rotation at high spins is illustrated at triaxial deformations $\gamma=20^\circ$ and $30^\circ$.

Dynamic behaviors of a high-speed turbocharger rotor on elliptical floating-ring bearings

Floating-ring bearings are commonly used in automotive turbocharger applications due to their low cost and their suitability under extreme rotation speeds. This type of bearings, however, can become a source of noise due to oil whirl-induced sub-synchronous vibrations. The scope of this paper is to examine whether the concept of a floating-ring bearing with an elliptical clearance might be a solution to suppress sub-synchronous vibrations. A very time-efficient approximate solution for the Reynolds equation to the geometry of elliptical bearings is presented. The nonlinear dynamic behaviors of a turbocharger rotor supported by two concepts of elliptical floating-ring bearings are systematically investigated using run-up simulations. For the first concept of elliptical floating-ring bearings i.e. the outer bearing of the floating-ring bearing changed in the form of elliptical pattern (see Figure 1(b) in the article), some studies have pointed out that its steady-state and dynamic performances are superior to plain cylindrical floating-ring bearings but, the nonlinear run-up simulation results shown that this type of elliptical floating-ring bearings is not conducive to reduce the self-excited vibration levels. However, for the second type of elliptical floating-ring bearings i.e. both the inner and outer films of the floating-ring bearing changed in the form of elliptical pattern (see Figure 1(c) in the article), it is shown that the sub-synchronous vibrations have been considerably suppressed. Hence, the second noncircular floating-ring bearing design is an attractive measure to suppress self-excited vibrations.[Figure: see text]

Study of the Effect of an Open Transverse Crack on the Vibratory Behavior of Rotors Using the h-p Version of the Finite Element Method

In this paper, we use the hybrid h-p version of the finite element method to study the effect of an open transverse crack on the vibratory behavior of rotors, the one-dimensional finite element Euler-Bernoulli beam is used for modeling the rotor, the shape functions used are the Hermite cubic functions coupled to the special Legendre polynomials of Rodrigues. The global matrices of the equation of motion of the cracked rotor are derived by the application of the Lagrange equation taking into account the local variation in the shaft’s stiffness due to the presence of the crack, and the stiffness of the cracked element of the shaft are determined using the time-varying stiffness method. Numerical results generated by a program developed in MATLAB show the rapidity of the convergence of the h-p version of FEM compared to the classical version, after the validation of our results with theoretical and experimental results and other obtained with the simulator ANSYS Workbench, a parametric study was provided to show the influence of the depth and position of the crack on the vibratory behavior of a symmetrical and asymmetrical rotor.

Rotor Dynamic Analysis of Driving Shaft of Dry Screw Vacuum Pump

Rotor dynamics is the study of vibration behavior in axially symmetric rotating structures. Devices such as engines, motors, disk drives and turbines all develop characteristic inertia effects that can be analyzed to improve the design and decrease the possibility of failure. At higher rotational speeds, such as in a gas pumps, the inertia effects of the rotating parts must be consistently represented in order to accurately predict the rotor behavior. An important part of the inertia effects is the gyroscopic moment introduced by the precession motion of the vibrating rotor as it spins. As spin velocity increases, the gyroscopic moment acting on the rotor becomes critically significant. Not accounting for these effects at the design level can lead to bearing and/or support structure damage. The main objective of this project is to study the Rotor Dynamic behavior of the drive rotor shaft of the Dry screw vacuum pump. The design of the pump is considered from the one of the reputed pump manufacturing industry. The operational speed of the pump is 4500 rpm, whereas the maximum capable speed of the pump is 10,000 rpm. Rotating machinery produces vibrations depending on the unbalanced mass and gyroscopic effects. Thus an investigation is to be made on the rotor dynamic properties of the shaft to find the natural frequencies and critical speed. For this rotor dynamic analysis was carried out in ANSYS APDL and Workbench16 to find the natural frequencies and critical speeds in the range of 0 to 10000 rpm. Thus an effort is made to shift the mass moment of inertia of the shaft by varying the design of the shaft and to shift the critical frequency to the higher speeds of the shaft there by increasing the efficiency. The modal analysis is performed to find the natural frequencies and it is extended to harmonic analysis to plot the stresses and deflections at the critical speeds. The design of the rotor shaft is made in NX-CAD.

Modal Identification of Output-Only Systems of Composite Discs Using Zernike Modes and MAC.

The analysis of the structural dynamic behaviour of composite rotor–discs by a valid description of the eigenfrequencies and mode shapes can provide significant information for action-taking before a failure occurs. Specifically, vibration-based diagnostic methods, which are able to take into consideration the interdependencies and sequential changes of the modal properties could benefit from such an analysis. Here, on the example of composite rotors, a correlation method for experimentally determined mode shapes is developed. For this purpose the Zernike polynomials are used to enhance the identification of mode shapes. Furthermore, the modal assurance criterion (MAC) in combination with the frequency response criterion and a data processing approach are applied in order to characterize changing modal properties of composite rotors. In addition, the developed algorithms can be further extended in order to simplify the experimental evaluation of the complex dynamic behaviour of composite structures.

Identification of dynamic stiffness and damping in active magnetic bearings using transfer functions of electrical control system

The dynamic rotor behavior is significantly affected by the stiffness and damping characteristics of the bearings. Therefore, it is important to identify these bearing parameters. For active magnetic bearings (AMBs), these bearing parameters not only could be identified from rotor dynamic response, but also from electrical control system transfer function. Some identification works from rotor dynamic response have been reported, but identification from electrical control system transfer function is relatively few. In this paper, we deduced the equivalent stiffness and damping expressions with electrical control system transfer function for rotor AMBs and identified these values from electrical control system model. To evaluate the identified results, previous reported results from rotor dynamic response is employed for comparison. We found that for the stiffness, a complete and precise electrical control model will obtain relatively consistent values; however, for the damping, the accurate electrical control model is still not enough and the eddy current loss should be included.

Design and Testing of a Co-Rotating Vibration Excitation System

A vibration excitation system (VES) in a form of an active coupling is proposed, designed and manufactured. The system is equipped with a set of piezoelectric stack actuators uniformly distributed around the rotor axis and positioned parallel to each other. The actuator arrangement allows an axial displacement of the coupling halves as well as their rotation about any transverse axis. Through the application of the VES an aimed vibration excitation is realised in a co-rotating coordinate system, which enables a non-invasive and precise modal analysis of rotating components. As an example, the VES is applied for the characterisation of the structural dynamic behaviour of a generic steel rotor at different rotational speeds. The first results are promising for both stationary and rotating conditions.

A new computational method for predicting the thermal bow of a rotor

In a heavy-duty gas turbine, when hot rotor is left cooled in standstill condition, thermal bow occurs due to natural convection, which may result in high vibrations in a subsequent restart. Usually, a turning gear is immediately started after shutdown of gas turbine to slowly roll and uniformly cool the rotor in order to prevent thermal bow, which is called turning gear operation. The minimum turning time and the acceptable temperature of wheel space are two important indexes of turning gear operation, and their determination highly depends on accurate prediction of thermal bow. This paper proposes an analytical method to predict the thermal bow behavior of rotors with complex structures and investigates the effect of turning time on thermal bow. First, the general form of analytical solution of rotor thermal bow is derived and validated through both finite element analysis and experiments. Then the analytical solution is applied in a heavy-duty gas turbine to predict the most severe thermal bow behavior of the rotor with no turning gear in operation before standstill. Finally, the effect of turning time on thermal bow is investigated, and the indexes to achieve acceptable thermal bow are discussed. Results show that the shape of thermal bow of the gas turbine rotor is close to the first-order mode shape; the peak of the most severe thermal bow reaches 0.7 mm after 3.8 h of cooling and the decrease of thermal bow is much slower than the increase. Besides, the maximum thermal bow of the rotor due to insufficient turning gear operation presents an exponential decay with turning time and lies in linear relationship with the temperature of the same location. These two relationships help determine the minimum turning time and acceptable temperature of wheel space to attain an acceptable bow and thus have practical significance to develop and optimize turning gear operations.

Linear Analysis of Vibration Reduction Using an Active Helicopter Rotor

In the field of active rotor control, the use of individual blade control (IBC) systems for vibration reduction is a major topic of research. However, as most studies are focused on a specific helicopter rotor, the influence of topological rotor parameters, such as the number of rotor blades, is seldom investigated. The present investigation analyzes vibration reduction using an IBC system in a very general manner with particular focus on the influence of the number of rotor blades. To this end, a model for the quasi-steady transfer behavior of an IBC rotor with an arbitrary number of rotor blades is derived as a function of the blade transfer behavior using only a minimal set of assumptions. Using this model, a minimal set of blade-root load components relevant for the rotor hub loads is determined. Based on this set of components, a coordinate frame of effective blade-root loads is introduced. Subsequently, the vibration reduction potential for the -bladed rotor is assessed, showing no direct relation between the number of rotor blades and the vibration reduction potential. Finally, the assumptions for the model, as well as the results of the investigation of the vibration reduction potential, are validated using open-loop flight data.

Influence of Gradual Damage on the Structural Dynamic Behaviour of Composite Rotors: Simulation Assessment

Fibre-reinforced composite structures under complex loads exhibit gradual damage behaviour with degradation of effective mechanical properties and change of their structural dynamic behaviour. In case of composite rotors, this can lead to catastrophic failure if an eigenfrequency is met by the rotational speed. The description and simulation analysis of the gradual damage behaviour of composite rotors therefore provides the fundamentals for a first understanding of complex and partially-unpredicted structural phenomena. Therefore, a simulation tool is developed using a finite element model, which calculates the damage-dependent structural dynamic behaviour of selected composite rotors considering both damage initiation and in-plane damage evolution due to a combination of out-of-plane and in-plane loads. Damage initiation is determined using failure criteria, whereas the gradual damage evolution using a validated continuum damage mechanics model. Numerical results are compared with experimental results for rotor-typical stress states to assess the model quality, which could be later used for damage identification approaches.

Influence of friction‐induced heating on the dynamic behaviour of rotors supported by journal bearings

AbstractDifferent oil‐film‐induced instabilities have to be accounted for when designing rotor systems supported by hydrodynamic bearings. Because the system's behaviour is strongly dependent on the thermal state, this contribution presents an approach for calculating the thermo‐hydrodynamic behaviour of a bearing‐rotor‐system. It incorporates a solution of the three‐dimensional energy equation for the fluid film and accounts for heat conduction through the surrounding parts of the bearing. The simulation model is validated with the help of experimental data and improvements are pointed out compared to an isothermal approach.

Influence of Gradual Damage on the Structural Dynamic Behaviour of Composite Rotors: Experimental Investigations.

Fibre-reinforced composite structures subjected to complex loads exhibit gradual damage behaviour with the degradation of the effective mechanical properties and changes in their structural dynamic behaviour. Damage manifests itself as a spatial increase in inter-fibre failure and delamination growth, resulting in local changes in stiffness. These changes affect not only the residual strength but, more importantly, the structural dynamic behaviour. In the case of composite rotors, this can lead to catastrophic failure if an eigenfrequency coincides with the rotational speed. The description and analysis of the gradual damage behaviour of composite rotors, therefore, provide the fundamentals for a better understanding of unpredicted structural phenomena. The gradual damage behaviour of the example composite rotors and the resulting damage-dependent dynamic behaviour were experimentally investigated under propagating damage caused by a combination of out-of-plane and in-plane loads. A novel observation is the finding that a monotonic increase in damage results in a non-monotonic frequency shift of a significant number of eigenfrequencies.

Behavior of the collective rotor in wobbling motion

The behavior of the collective rotor in wobbling motion is investigated within the particle-rotor model for the nucleus $^{135}$Pr by transforming the wave functions from the $K$-representation to the $R$-representation. After reproducing the experimental energy spectra and wobbling frequencies, the evolution of the wobbling mode in $^{135}$Pr, from transverse at low spins to longitudinal at high spins, is illustrated by the distributions of the total angular momentum in the intrinsic reference frame (azimuthal plot). Finally, the coupling schemes of the angular momenta of the rotor and the high-$j$ particle for transverse and longitudinal wobbling are obtained from the analysis of the probability distributions of the rotor angular momentum ($R$-plots) and their projections onto the three principal axes ($K_R$-plots).

Effect of macromolecular crowding on the conformational behaviour of a porphyrin rotor

Macromolecular crowding modulates the conformational preference of a small molecular rotor, which is used as a molecular viscometer. The shift towards the planar conformation of the porphyrin rotor was observed in the presence of increasing concentrations and sizes of polyethylene glycols. This observation highlights the differences between the behaviour of this molecular viscometer in the crowding and non-crowding types of media.

Touchdown bearing models for rotor-AMB systems

This paper investigates numerically and experimentally the rotor drop dynamics when unexpected Active Magnetic Bearings (AMBs) shut down occurs. In such an event, the rotor behaviour drops on two touchdown bearings (TDBs) composed of a ball bearing and a ribbon damper providing stiffness and damping to the overall system. The aim of this paper is to establish and to validate the rotor-drop system model. A first experimental set up is used to identify the dynamic characteristics of the corrugated ribbon damper and to test the Kelvin-Voigt model and the generalized Dahl model. Then, three TDB models are proposed including either the first or the second ribbon damper models. The second experimental set-up is devoted to the rotor drop response of an industrial scale rotor-AMB system equipped with two TDBs. Rotor drop simulations in the time domain are carried out by using the Finite Element method and the three TDB models. Predicted and measured rotor drop responses are compared regarding the displacements as well as transmitted loads and permits evaluating the model efficiency.

Interconnecting Very Weak AC Systems by Multiterminal VSC-HVDC Links With a Unified Virtual Synchronous Control

In this paper, a unified virtual synchronous control (UViSynC) is proposed for multiterminal voltage-source converter (VSC)-high-voltage dc (HVDC) (MTDC) systems, which can: 1) realize grid synchronization of the VSC stations by mimicking the rotor behavior of synchronous generators with the dynamics of dc grid and dc capacitor considered and 2) ensure the stable operation of the MTDC system that interconnects very weak ac grids. Unlike conventional master–slave control strategies that assign one master VSC to control the dc voltage, the UViSynC is capable of involving all VSC stations in dc voltage regulation. In this manner, each VSC station plays an equal role to control the dc voltage, which is a better way for dc voltage regulation compared with conventional master–slave control strategies. Grid synchronization mechanism for VSC station with UViSynC is particularly analyzed. Small-signal model of the MTDC system is developed to perform stability analysis and investigate the dynamic performance when interconnecting very weak ac systems. Simulation analyses based on MATLAB/Simulink and hardware-in-the-loop platform are conducted to verify the effectiveness of the UViSynC using a four-terminal VSC-HVDC test system.

Fluorescent Molecular Rotors for Viscosity Sensors

AbstractInvited for the cover of this issue is the collaborative work of the groups of O‐Pil Kwon (Ajou University), Chang‐Lyoul Lee (Advanced Photonics Research Institute, APRI/Gwangju Institute of Science and Technology, GIST), and Sehoon Kim (Korea Institute of Science and Technology, KIST). The cover image illustrates the viscosity‐sensitive fluorescent behavior of fluorescent molecular rotors (FMRs) in various viscous media. The intensity of the FMRs increases with decreasing speed of the rotor; this is portrayed as the waterwheel in the cover image. When the waterwheel slowly rotates in winter (high viscosity media), FMR—portrayed as the house in the image—shows strong fluorescent‐light illumination (left‐hand side of the image). In contrast, the right‐hand side of image depicts decreasing fluorescence intensity with increasing rotation of the waterwheel (low viscosity media). Read the full text of the article at 10.1002/chem.201801389.

Analysis of the micro-cracking behaviour of carbon fibre reinforced flywheel rotors considering residual stresses

The main challenge in today’s power grid management is the inclusion of renewable energy sources with inconstant energy production such as wind and solar plants and modern high technology fabrication or electric transportation with their uneven power consumption. For that purpose energy storage systems, such as high efficiency flywheels, with extraordinary cycle stability and charging-discharging rates are needed. Here carbon fibre reinforced composites play an important role as rotor material. In this study the cracking behaviour of helical layers of a cylindrical flywheel rotor is analysed under consideration of fabrication induced residual stresses and their viscoelastic reduction over long term storage. Based on static and fatigue experiments with crack counting inspections a finite fracture model is identified and calibrated for modelling the damage behaviour of flywheel rotors under cyclic loading.

Stability and nonlinear dynamic analysis of gas-lubricated system with elastomer suspension

This paper presents the dynamic behavior of a rigid rotor supported by a pair of self-acting gas-lubricated bearings which is used in a turbo-expander, the key equipment in a large-scale cryogenic system. In order to restrict the vibration of the rotor relative to bearings, elastomers are mounted between bearings and shell. A finite difference method has been employed to solve the Reynolds equation in time-dependent states. The center orbits of the rotor are got by solving the motion equations. The system state trajectory, Poincare maps, logarithmic spectra maps and bifurcation diagrams are used to analyze the dynamic behavior of the system. The effect of the elastomer suspension to absorb the vibration is verified by comparison with the system with rigid suspension. A set of mass values, damping exponent values and stiffness of elastomer are calculated and compared in this paper. The results show that the rotor center loses its regular behavior gradually with the increase in the rotor mass. The square damping exponent model of the elastomer shows more stability than linear damping suspension model, and the quadratic damping exponent model has a similar motion behavior compared with a linear model. A suitable stiffness of the elastomer is important to the stability of the system. The elastomer with a low stiffness may cause the large amplitude of the vibration, and the system may lose its regular behavior when the stiffness is large enough.

Continuum damage mechanics-based analysis of creep–fatigue interaction behavior in a turbine rotor

The aim of this study is to analyze the creep–fatigue interaction behavior of a steam turbine rotor under idealized cyclic thermomechanical loading conditions. A Chaboche model-based material constitutive model is applied to simulate the multiaxial stress–strain behavior in the rotor. Influence of accumulated damage during the whole iterations on the creep–fatigue interaction behavior is described by continuum damage mechanics. Analysis of the temperature and stress variations during the startup phase reveals that the startup phase can be divided into a condensation phase, a high steam flux phase, and an elevated temperature phase and that thermal stress reaches its maximum value in the condensation phase. In addition, creep–fatigue interaction in the rotor leads to a gradual decrease in the maximum stress; furthermore, comparison of the von Mises stress displays that the impact of damage accumulation results in the shift of the location with the maximum stress. Investigation of creep–fatigue damage discloses that the total damage is concentrated on the steam inlet notch zone and the blade groove of the first and third stages.