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Showing papers on "Critical speed published in 2014"


Journal ArticleDOI
TL;DR: In this paper, the rotor radial position control of a two-pole 30 kW 3000 r/m cage induction machine with an additional four-pole stator winding to produce the radial force on the rotor is analyzed.
Abstract: This paper presents a control method for the rotor radial position control of a two-pole 30 kW 3000 r/m cage induction machine that has an additional four-pole stator winding to produce the radial force on the rotor. The controller is used to stabilize the machine, to remove vibration caused by mass-unbalance and rotation, and to produce static force to counter gravity. Both measurement results and finite element computations are shown. In the measurements, the rotor is on a long flexible shaft supported by external bearings. The proposed control strategy allows the machine to run at all operation points (speed, torque) up to the rated values, including at the first critical speed caused by the first natural bending frequency of the rotor shaft. The power consumption of the radial position control and the total effect on efficiency is analyzed. Both rotor eccentricity and the produced four-pole field affect the losses of the machine. The additional power consumption and the total efficiency are presented as a function of the radial force produced.

45 citations


Journal ArticleDOI
TL;DR: In this article, the effects of the dispersion parameters and the external bounded noise excitation on the vibrational characteristics of the system, such as the critical speed and the vibration amplitude, are investigated.

44 citations


Journal ArticleDOI
TL;DR: In this paper, an experimental set-up for a flexible rotor supported by a hybrid foil-magnetic bearing is built, and unbalance responses of the flexible rotor supporting by two different bearings: air-foil and hybrid bearings are compared.

29 citations


Journal ArticleDOI
TL;DR: In this paper, a variable geometry journal bearing (VGJB) is applied for the mounting of a large scale rotor bearing system operating at the range of medium speed, and the simulation of the rotor-bearing system incorporates a recent method for simulation of a multi-segment continuous rotor in combination with nonlinear bearing forces.

27 citations


Journal ArticleDOI
TL;DR: In this article, a simply supported carbon/epoxy composite tube mounted on viscoelastic supports is studied, using an approximation of the Rayleigh-Timoshenko equation, and the damping process is assumed to be hysteretic.

26 citations


Journal ArticleDOI
TL;DR: In this paper, an algebraic approach was used to identify unbalance and eccentricity parameters in a rotor bearing system and synthesize an active control scheme to attenuate the lateral vibration amplitudes in the rotor-bearing system.

25 citations


Journal ArticleDOI
TL;DR: In this article, an integral squeeze film damper (ISFD) solution is proposed to resolve the subsynchronous vibration and allow full load and full speed operation of a utility steam turbine.
Abstract: A 46 MW 5,500 rpm multistage single casing utility steam turbine experienced strong subsynchronous rotordynamic vibration of the first rotor mode; preventing full load operation of the unit. The root cause of the vibration stemmed from steam whirl forces generated at secondary sealing locations in combination with flexible rotor-bearing system. Several attempts were made to eliminate the subsynchronous vibration by modifying bearing geometry and clearances, which came short of enabling full load operation.The following paper presents experimental tests and analytical results focused on stabilizing a 46 MW 6,230kg utility steam turbine experiencing subsynchronous rotordynamic instability. The paper advances an integral squeeze film damper (ISFD) solution, which was implemented to resolve the subsynchronous vibration and allow full load and full speed operation of the machine. The present work addresses the bearing-damper analysis, rotordynamic analysis, and experimental validation through waterfall plots, and synchronous vibration data of the steam turbine rotor. Analytical and experimental results show that using ISFD improved the stability margin by a factor of 12 eliminating the subsynchronous instability and significantly reducing critical speed amplification factors. Additionally, by using ISFD the analysis showed significant reduction in interstage clearance closures during critical speed transitions in comparison to the hard mounted tilting pad bearing configuration.Copyright © 2014 by ASME

25 citations


Journal ArticleDOI
TL;DR: In this paper, a model-based mechatronic approach for the design of ball-screw driven servomechanisms is proposed, aimed at selecting the optimal combination of electric motor and ball screw which minimizes the motor torque, while ensuring the achievement of the prescribed dynamic performances of the closed loop system.

23 citations


Journal ArticleDOI
Adolfo Delgado1
TL;DR: In this paper, the compliant hybrid gas bearing was evaluated in a controlled-motion test rig and the results indicated that the bearing system equivalent direct damping was negatively impacted by increased inlet pressure and excitation frequency, while the crosscoupled force coefficients showed values an order of magnitude lower than the direct coefficients.
Abstract: Compliant hybrid gas bearings combine key enabling features from both fixed geometry externally pressurized gas bearings and compliant foil bearings. The compliant hybrid bearing relies on both hydrostatic and hydrodynamic film pressures to generate load capacity and stiffness to the rotor system, while providing damping through integrally mounted metal mesh bearing support dampers. This paper presents experimentally identified force coefficients for a 110 mm compliantly damped gas bearing using a controlled-motion test rig. Test parameters include hydrostatic inlet pressure, excitation frequency, and rotor speed. The experiments were structured to evaluate the feasibility of implementing these bearings in large size turbomachinery. Dynamic test results indicate weak dependency of equivalent direct stiffness coefficients to most test parameters except for frequency and speed, where higher speeds and excitation frequency decreased equivalent bearing stiffness values. The bearing system equivalent direct damping was negatively impacted by increased inlet pressure and excitation frequency, while the cross-coupled force coefficients showed values an order of magnitude lower than the direct coefficients. The experiments also include orbital excitations to simulate unbalance response representative of a target machine while synchronously traversing a critical speed. The results indicate that the gas bearing can accommodate vibration levels larger than the set bore clearance while maintaining satisfactory damping levels.Copyright © 2014 by ASME

22 citations


Journal ArticleDOI
TL;DR: In this article, the authors present an approach to global sensitivity analysis aiming at the reduction of its computational cost without compromising the results, based on sampling methods, cubature rules, high-dimensional model representation and total sensitivity indices.
Abstract: We present an approach to global sensitivity analysis aiming at the reduction of its computational cost without compromising the results. The method is based on sampling methods, cubature rules, high-dimensional model representation and total sensitivity indices. It is applied to a half car with a two-axle Cooperrider bogie, in order to study the sensitivity of the critical speed with respect to the suspension parameters. The importance of a certain suspension component is expressed by the variance in critical speed that is ascribable to it. This proves to be useful in the identification of parameters for which the accuracy of their values is critically important. The approach has a general applicability in many engineering fields and does not require the knowledge of the particular solver of the dynamical system. This analysis can be used as part of the virtual homologation procedure and to help engineers during the design phase of complex systems.

21 citations


Patent
01 Oct 2014
TL;DR: In this paper, a continuous multi-type curved segment mixed interpolation cubic polynomial feeding speed proactive planning method is proposed for numerical control machining, where the authors use an accurate solving method to solve parameters in the process of feeding speed planning, the dynamics performance of a machine tool is brought into full play, smooth compensation of speed planning residual errors is solved, and a smooth feeding speed curve of dynamic parameters and interpolation error restraints can be obtained.
Abstract: A continuous multi-type curved segment mixed interpolation cubic polynomial feeding speed proactive planning method comprises the first step of continuous multi-type curved segment generation, the second step of inter-segment connecting point critical speed solving, the third step of single-segment curve feeding speed planning, the fourth step of single-segment speed planning residual error compensation and the fifth step of feeding speed curve generation. According to the continuous multi-type curved segment mixed interpolation cubic polynomial feeding speed proactive planning method, a cubic polynomial speed curve is adopted to be applied to straight line, circular arc and parameter spline mixed interpolation feeding speed proactive planning, an accurate solving method is adopted to solve parameters in the process of feeding speed planning, the dynamics performance of a machine tool is brought into full play, smooth compensation of speed planning residual errors is solved, and a smooth feeding speed curve of dynamic parameters and interpolation error restraints can be obtained. The continuous multi-type curved segment mixed interpolation cubic polynomial feeding speed proactive planning method has the good application prospect in the field of numerical control machining.

Journal ArticleDOI
TL;DR: In this paper, an active elastic support/dry friction damper using piezoelectric ceramic actuator was designed and its effectiveness of reducing rotor vibration when rotor traverses its critical speed and blade-out event happened was experimentally verified.
Abstract: The basic operation principle of elastic support/dry friction damper in rotor system was introduced and the unbalance response of the rotor with elastic support/dry friction damper was analyzed theoretically. Based on the previous structure using an electromagnet as actuator, an active elastic support/dry friction damper using piezoelectric ceramic actuator was designed and its effectiveness of reducing rotor vibration when rotor traverses its critical speed and blade-out event happened was experimentally verified. The experimental results show that the active elastic support/dry friction damper with piezoelectric ceramic actuator can significantly reduce vibration in rotor system; the vibration amplitude of the rotor in critical speed region decreased more than 2 times, and the active damper can protect the rotor when a blade-out event happened, so the rotor can traverse the critical speed and shut down smoothly. In addition, the structure is much simpler than the previous, the weight was reduced by half and the power consumption was only 5 W.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the influence of damping, eccentric mass and time varying mesh stiffness of gear pair on the modal vibration of a herringbone gear pair under high-speed condition.
Abstract: The coupled lateral and torsional motions are significant for the herringbone gear in high-speed applications. The present work attempts to investigate the influences of damping, eccentric mass and time varying mesh stiffness of gear pair on the modal vibration of a herringbone gear pair. Under high-speed condition, the gyroscopic performance as a result of coupled lateral and torsional motions cannot be ignored. To achieve a targeted analysis, the equivalent mesh stiffness of the herringbone gear pair is calculated in preprocessing based on the finite element method by considering the thin rim and web. Subsequently, an analytical model for coupled lateral and torsional motions of the herringbone gear is proposed. Then, the natural frequencies, synchronous whirling speed, critical speed, as well as the transient behaviors with time invariant and time varying stiffness, are calculated numerically. The results in Campbell diagram show that the damping affects the critical speed slightly while the eccentric mass will reduce the critical speed significantly. Transient dynamics analysis shows that no matter which stiffness models are used, the high frequency components are predominant, which may be the results of frequency veering phenomena at high order natural frequency. The present work indicates the necessity of paying attention to the critical speed relative to mesh frequency in high speed gear applications.

Journal ArticleDOI
Lili Gu1, Fulei Chu1
TL;DR: In this article, an analytical analysis of a continuous rotor shaft subjected to universal temperature gradients is presented, where an analytical model is derived to investigate the generic thermal vibrations of rotor structures.

15 Feb 2014
TL;DR: In this paper, the authors developed a three-dimensional time-domain approach that describes how the moving dynamic loads of a high-speed train are distributed through the track and ground components.
Abstract: As high-speed trains operate in more and more countries and their maximum speed increases, the vibration induced by the train has become an important issue. The dynamic coupling between the vehicle, track and ground has to be assessed for its effects on safety, stability and maintenance costs. A particular issue, especially for soft soils, is the critical speed at which the train reaches the wave speed in the ground leading to large deflections of the track and ground. The aim of this paper is to develop a three-dimensional time-domain approach that describes how the moving dynamic loads of a high-speed train are distributed through the track components. This model should allow the critical speed to be determined and the vibration of the whole system to be analysed. To represent the complex vehicle/track/ground system a finite element approach is used based on the ABAQUS software. Rather than using a user-defined subroutine to apply the moving loads, the multi-body vehicle model and track/ground system are coupled as deformable bodies using a contact model that allows for large scale motion of the vehicle relative to the track

Journal ArticleDOI
TL;DR: In this article, a tuned vibration absorber design is proposed to improve the safety of flexible structures which are prone to excessive oscillation magnitudes under dynamic loads, where the granular material is the energy dissipating agent.

Journal ArticleDOI
29 Aug 2014-Sensors
TL;DR: Dynamic analysis, and experiments on the motor-generator, and an analytical approach considering the mechanical dynamic problems are introduced, essential to deal with dynamic stability at ultra-high speeds.
Abstract: The objective of the present study was to deal with the rotordynamics of the rotor of an ultra-high speed PM type synchronous motor-generator for a 500 W rated micro gas turbine generator. This paper introduces dynamic analysis, and experiments on the motor-generator. The focus is placed on an analytical approach considering the mechanical dynamic problems. It is essential to deal with dynamic stability at ultra-high speeds. Unbalance response analysis is performed by calculating the unbalance with and without balancing using a balancing machine. Critical speed analysis is performed to determine the operating speed with sufficient separation margin. The unbalance response analysis is compared with the experimental results considering the balancing grade (ISO 1940-1) and predicted vibration displacement with and without balancing. Based on these results, a high-speed motor-generator was successfully developed.

Journal ArticleDOI
TL;DR: In this paper, a transient CFD procedure to compute the nonlinear dynamic characteristic of the coupled rotor-seal system was presented, where the displacement diffusion model was implemented to govern the mesh deformation, and the URANS (Unsteady Reynolds averaged Navier-Stokes) equations were solved to obtain the transient fluid force on the rotor surface for the free vibrations.
Abstract: A transient CFD procedure to compute the nonlinear dynamic characteristic of the coupled rotor-seal system was presented in this study. In each time step, the displacement diffusion model was implemented to govern the mesh deformation, and the URANS (Unsteady Reynolds averaged Navier-Stokes) equations were solved to obtain the transient fluid force on the rotor surface for the free vibrations. With the obtained fluid force from the CFD solver, the nonlinear equations of motion for a simplified rotor-seal system were numerically solved on the basis of external user defined routines. During each transient time step, the computed fluid force from the CFD solver and the rotor motion from the user defined routines were transferred to each other timely. The rotor center trajectories, frequency spectrum and projection of Poincare section were calculated to investigate the nonlinear dynamic performance of the single disk rotor-seal system. The effects of the rotational speed and pressure ratio on the vibration characteristic of the rotor-seal system were analyzed by the bifurcation theorem. The results show that the coupled rotor-seal system experiences a period-one motion, resonance, periodic-doubling motion, quasi-periodic motion, and finally possible chaotic motion as the rotor speed increases. The pressure ratio has pronounced effect on the frequency response of the first-order critical speed; however, it has little influence on the motion state as well as the frequency response of the rotating speed. Although a constant-clearance annular smooth stator seal was selected as the research object in the current paper, the presented transient CFD method is still available for other complex annular seals, such as labyrinth seal, honeycomb seal, pocket damper seal, etc.

Journal ArticleDOI
TL;DR: In this article, a new kind of active magnetic stabilisation is proposed to overcome those limits, which provides an asymptotic dynamic stability of both the forward and backward whirling motions, even in the high supercritical regime.

Journal ArticleDOI
TL;DR: In this article, a fuzzy logic control algorithm is developed and experimentally applied to a rotor test rig, which is suitable to deal with problems of uncertainties and non-linearity, and the experimental results show the ability of the developed fuzzy logic controller to eliminate the oil whip instability when applied to an industrial rotor through an integrated bearing prototype which was designed and manufactured.
Abstract: Oil whip is a self-excited sub-synchronous vibration which limits the range of operating speed of Journal Bearings (JB). JB have wide range of applications due to their high loading capacity, simple geometry, and lubrication. When the speed of rotation increases, the oil whip instability is excited with a frequency corresponding to the rotor critical speed which causes excessive undesirable vibration.A solution for this instability is implemented through this paper. The control action is implemented through a new integrated bearing device. The bearing consists of JB and Electromagnetic Actuator (EMA). The oil whip control action is applied through the EMA.A fuzzy logic control algorithm is developed and experimentally applied to a rotor test rig. The fuzzy logic controller is suitable to deal with problems of uncertainties and non-linearity.The experimental results show the ability of the developed fuzzy logic controller to eliminate the oil whip instability when applied to a test rig which simulates industrial rotor through an integrated bearing prototype which was designed and manufactured.© 2014 ASME

Journal ArticleDOI
Jimei Wu, Wenjiao Lei, Qiumin Wu, Yan Wang, Li'e Ma1 
TL;DR: In this article, the authors investigated the transverse vibration characteristics and stability of a moving membrane with several intermediate elastic supports considering the translating speed of the moving membrane and derived motion equations of the vibration system according to the membrane vibration theory and the D'Alembert principle.
Abstract: The transverse vibration characteristics and stability of a moving membrane with several intermediate elastic supports are investigated considering the translating speed. The motion equations of the vibration system are derived according to the membrane vibration theory and the D'Alembert principle. The constraint of the middle printing roller to the membrane is used as the intermediate support which is replaced by the constraint force. And the vibration characteristic equation is established by using Laplace transformation method and the numerical calculation method. Finally, the relationships between the natural frequency of the moving membrane and the translating speed, tension, supporting position and rigidity modulus are analyzed respectively, and the critical speed when the membrane is in a stable state is obtained. The conclusions provide a theoretical basis and effective approaches for improving the work stability of the printing press.

Journal ArticleDOI
TL;DR: In this paper, the effect of the floating bearing stiffness coefficient on the critical rotational speeds and the shaft dynamic response due to the unbalanced mass were both analyzed using rotor dynamics theory and a finite element analysis.
Abstract: During turbocharger rotor speed-up tests, the sensor installed in the compressor greatly affects the rotor dynamics. The effect of the floating bearing stiffness coefficient on the critical rotational speeds and the shaft dynamic response due to the unbalanced mass were both analyzed using rotor dynamics theory and a finite element analysis. The results illustrate that the initial sensor design reduced the 3rd order critical speed to lower than the maximum normal operating speed which leads to the rubbing and failure of the rotor during the speed-up test. The sensor structure was then optimized to reduce the negative influence of the sensor on the rotor dynamic characteristics to ensure stability during rotor speed-up tests.

Journal ArticleDOI
TL;DR: Aiming at improving low-speed performance of variable speed hydraulic systems, the leaking parallel valve control is applied to the system during low speed period as discussed by the authors, which increases system damping ratios by increasing leakage controlled by the valve.
Abstract: Aiming at improving low-speed performance of variable speed hydraulic systems, the leaking parallel valve control is applied to the system during low-speed period. This method increases system damping ratios by increasing leakage controlled by the valve. In addition, the increase of damping ratios just compensates the reduction of damping ratios due to the friction negative slop, which helps to improve low-speed stability and achieve lower critical speed. In the whole process of closed loop control, the system in leaking parallel valve control has good speed performance with more stable and suitable damping ratios and basically avoids pressure impact at start and stop stages and still keeps comparatively high efficiency because the pump provides total flow and the valve only leaks out few flows.

Journal ArticleDOI
TL;DR: In this paper, the authors present a case study in which a high speed gas lift centrifugal compressor experienced significant vibration problems associated with start-up and operation of a two-stage 8-impeller unit.

Journal Article
TL;DR: In this paper, the design of mixing system used in stirred tank reactor (STR) biodiesel production by analytical method and numerical one (finite element method) has been made.
Abstract: Article history: The on going demand for the improved impeller designs usually comes from the users of industrial mixing equipment. Most of the industrial biodiesel reactors using blade agitator for mixing which creates a main flow in the reaction tank (reactor) with circulation on axial and tangential direction. In current study, design of mixing system used in stirred tank reactor (STR) biodiesel production by analytical method and numerical one (finite element method) has been made. Designs have been done based on a pitched blade turbine down flow with two inclined blades (45°) by assumption of maximum working conditions (using caster oil as base fluid). The mixing power and mechanical design of an agitator such as stress analysis by analytical method and numerical one (finite element method) has been carried out. The operating limitations of mixing shaft deflection and critical speed during the biodiesel production process by using both methods, has been calculated. The FEM results have displayed close values with the results obtained from the analytical method. The critical rotational speed of the mixing shaft obtained from the analytical and modal analysis show similar results 5778.26 and 7000 rpm respectively and found to be significantly higher than the impeller maximum required mixing speed.

Proceedings ArticleDOI
20 Nov 2014
Abstract: This paper will present various case studies of how the rotor or system natural frequencies can be strongly influenced by its external and internal factors and how small variations in these factors can influence the motor vibration at the manufacturer and in the field. Motors constructed to API 541 standards are required to have a rotordynamic lateral natural frequency that is removed from the operating speed by at least 15%. The location of this natural frequency can depend on many factors such as bearing clearance, bearing type, residual unbalance, oil temperature, oil viscosity, and bearing housing stiffness. Depending on the design, some motors are more sensitive to these parameters than others, and small changes in these factors may cause large variances in the motor natural frequency. As a result, small variations in test setup, manufacturing tolerances, or field installations within critical components can cause noticeable differences between the calculated and measured natural frequencies. Variation in motor vibration may also be seen between the motor operating on the manufacturer's test stand and the motor operating in the field. In the field some apparently minor changes on ambient conditions or set up can significantly change the motor vibration. Additionally this paper will propose a worst case calculation method for motor natural frequencies that will provide greater confidence to the end user that the motor will operate successfully in the field before the motor is installed.

Journal ArticleDOI
TL;DR: Based on the shallow-water wave potential flow theory and the assumption of a slender ship, a mathematical model has been established for the pressure field caused by ship moving at supercritical speed in shallow water, with nonlinear and dispersive effects taken into account as discussed by the authors.

Journal ArticleDOI
TL;DR: A novel sensor system for measuring the angular speed of a shaft rotating at a very low speed range, nearly zero speed, gives very smooth and stable traces of the AS, demonstrating its higher accuracy and reliability in obtaining the AS of the low speed operations with speed-up and down transients.
Abstract: This paper presents the theory and implementation of a novel sensor system for measuring the angular speed (AS) of a shaft rotating at a very low speed range, nearly zero speed. The sensor system consists mainly of an eccentric sleeve rotating with the shaft on which the angular speed to be measured, and an eddy current displacement sensor to obtain the profile of the sleeve for AS calculation. When the shaft rotates at constant speed the profile will be a pure sinusoidal trace. However, the profile will be a phase modulated signal when the shaft speed is varied. By applying a demodulating procedure, the AS can be obtained in a straightforward manner. The sensor system was validated experimentally based on a gearbox test rig and the result shows that the AS obtained are consistent with that obtained by a conventional encoder. However, the new sensor gives very smooth and stable traces of the AS, demonstrating its higher accuracy and reliability in obtaining the AS of the low speed operations with speed-up and down transients. In addition, the experiment also shows that it is easy and cost-effective to be realised in different applications such as condition monitoring and process control.

Patent
28 May 2014
TL;DR: In this paper, a structural dynamic design method for a high-pressure rotor of an aircraft engine is presented, where the relationship between high pressure rotor model design parameters and rotor vibration characteristics is determined.
Abstract: Disclosed is a structural dynamic design method for a high-pressure rotor of an aircraft engine. The relationship between high-pressure rotor model design parameters and rotor vibration characteristics is determined, so that the design method and criterions are provided for dynamic design of the high-pressure rotor, and the method is of great guiding significance to the design of the high-pressure rotor of the aircraft engine. The method includes: establishing a dynamic model and a dynamic equation of the high-pressure rotor to obtain a nondimensionalization characteristic equation; introducing an equivalent critical speed, and determining a two-order critical speed range of a high-pressure rotor system according to the equivalent critical speed; changing a conventional equilibrium amount configuration method by configuring residual disequilibrium amount phases; configuring a ratio of rotor pole rotation inertia to mass center rotation inertia in design according to a specific design objective; establishing configuration criterions for a rotor bearing stiffness ratio. A conventional design process is changed, structural dynamic active design of the high-pressure rotor is realized, the design process is optimized beneficially, design cycle is shortened, and the method has important construction value.

01 Aug 2014
TL;DR: In this article, a method is presented to obtain the steady state dynamic response from the finite element based equations of a rotor-bearing system with initial deflection, and the method is applied to analyze the dynamic response of the two-shaft rotor bearing system with rigid coupling offset in a heavy duty gas turbine generator.
Abstract: In this paper a analysis method is presented to obtain the steady state dynamic response from the finite element based equations of a rotor-bearing system with initial deflection. The method has been applied to analyze the dynamic response of the two-shaft rotor-bearing system with rigid coupling offset in a heavy duty gas turbine-generator. Bumps in the dynamic response of each rotor system have been observed at each critical speed due to the effect of initial deflection for rigid coupling offset. And, the dynamic responses have been shown to reduce for operating condition changes from cold to hot.