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In the active magnetic bearing (AMB)-rotor system, a displacement sensor is one of the indispensable components. It detects the displacement of the rotor in real time and feeds back to the control system to realize the stable suspension of the rotor. However, due to electromagnetic interference, unstable power supply, poor grounding, and uneven rotor surface, the signal runout of the displacement sensor can often occur, resulting in rotor vibration. Given the above problems, this paper establishes the control model of the AMB-rotor system, lists three typical sensor runout signals, then analyzes the influence of different types of sensor runout on the system, and discusses the control methods under different sensor runout conditions. The research results have a specific guiding significance for vibration control of the maglev rotor under sensor runout influence. [ABSTRACT FROM AUTHOR]

Aiming at the problem that the traditional analysis methods such as Zoom-FFT (ZFFT) heavily depend on the data length in the frequency separation accuracy when separating the unbalanced signals of the inner and outer rotors of the dual-rotor system with micro-speed difference, an improved method based on ZFFT + FT was proposed to refine the signal spectrum and accurately identify the unbalanced response of the inner and outer rotors. On the basis of sampling and filtering the micro-speed difference signal by ZFFT, DFT was used to refine the frequency segment, so as to extract the corresponding amplitude of the operating frequency components of the inner and outer rotors. The basic principles of Chirp-Z transform (CZT), ZFFT, and ZFFT + FT algorithms were introduced, and the corresponding programs of each algorithm were written based on LabVIEW software for simulation, then the signal generator was used to carry out the micro-speed difference signal extraction test and finally the dynamic balance test was carried out on the dual-rotor test bench. Data simulation and field test show that compared with the CZT and ZFFT methods, the method has better frequency resolution ability and can separate the micro-speed difference signal with higher accuracy, and has high feasibility and practicability in the dynamic balance of the micro-speed difference dual-rotor system. [ABSTRACT FROM AUTHOR]

In this paper, the synchronous motion characteristics of a two-rigid-body vibration system with three vibrating motors installed on two different vibrating rigid bodies are investigated. First, differential equations of the system are deduced according to the Lagrange equation, and their steady-state solutions are obtained. Next, the synchronization theories of the system are obtained via the average method, and the stability conditions are deduced via the Lyapunov's stability theory. The structural parameters of the system are brought into the theoretical derivation results. Finally, the theory and simulation are mutually verified by the electromechanical coupling simulation model. The results show that the system can implement stable synchronous motion when the system parameters satisfy the synchronization and stability conditions. In the resonance region (i.e., k y 2 = 100000 N / m , k y 1 ∈ [ 100000,2000000 ] N / m or k y 2 = 500000 N / m , k y 1 ∈ [ 100000,2000000 ] N / m ), the support spring stiffnesses k y 1 and k y 2 significantly affect the synchronous motion characteristics of the system. The phase differences 2 α 1 and 2 α 2 bifurcate in the regions R2, R5, and R6. However, the bifurcation phenomena have almost no effect on the steady-state responses. The parameters in the regions R3, R4, R7, and R8 are of great values in engineering applications. [ABSTRACT FROM AUTHOR]

When performing bearing fault measurements, the unbalanced magnetic pull's (UMP) influence is inadvertently incorporated. The UMP's influence distorts the measurements used for bearing fault size estimation, leading to inaccurate fault interpretations. In this paper, we combined a magnetic equivalent circuit motor model with a dynamic bearing model to isolate the UMP's effect, which is unprecedented in the state of the art. The coupled model is used to analyse the dynamic interaction between a mechanical fault and the UMP without neglecting the influence of the rotor slot harmonics nor the magnetic potential losses in the stator and rotor. We compare simulations performed with the UMP and without the UMP in the presence of (i) an outer race bearing fault and (ii) an outer race bearing fault combined with an intrinsic rotor misalignment (IRM). The study finds that the UMP amplifies the rotor eccentricity by a non-negligible amount without accounting for an IRM. Moreover, with the inclusion of an IRM, the rotor vibrations are distorted to the point where bearing fault estimation algorithms could become inoperable. The presence of rotor slot harmonics in the UMP has been identified as a key contributor to the distortion. The findings presented in this article can be used to improve bearing fault size estimation algorithms by isolating the disturbances caused by the UMP. [ABSTRACT FROM AUTHOR]

Aiming at the position coupling, gyroscopic effect, and synchronized vibration caused by the unbalance mass in the magnetic bearing rotor, a linear active disturbance rejection notch decoupling control method is proposed. Firstly, a model with coupling and unbalanced vibration of the system was established. The terms of position coupling, gyroscopic effect, and unbalanced vibration in the system are estimated by Extended State Observer and the estimator is treated as the system disturbance to be compensated, then the radially existing coupled and unbalanced vibration systems are decoupled into four independent second-order series-integrated subsystems. The nonlinear state error feedback control law is designed to implement the decoupling control of each subsystem. For the problem of unbalanced vibration of the rotor after decoupling, the suppression method of the dynamic unbalanced force of the same frequency notch filter is designed, and then the closed-loop feedback structure of the new method is deduced, and its frequency characteristics are analyzed. Then the rules and principles of controller parameter selection are summarized using Bode diagram. The simulation results show that the designed linear active disturbance rejection notch decoupling controller not only achieves the decoupling control of the respective degrees of the magnetic bearing rotor but also suppresses the unbalanced vibration of the rotor. At the same time, it solves the influence of the gyroscopic effect on the control under the high-speed running of the magnetic bearing rotor. [ABSTRACT FROM AUTHOR]

The presented work examines the stability of general rotors subject to harmonic follower force. The examined rotor consists of asymmetric Timoshenko shaft carrying asymmetric rigid disk and supported by anisotropic flexible bearings. The assumed modes method is combined with Lagrange's equation to derive the governing equations of motion with the help of symbolic computation. The employed approach resulted in equations of motion with multi-frequency periodic coefficients, and Floquet's method was used to determine stability boundaries of the considered rotors. After validation of the proposed mathematical model, it was employed to examine the combined effect of rotor asymmetry, support anisotropy, and rotor speed on its stability in the presence of harmonic follower force. The presented results show that the considered general rotor exhibits both subharmonic and combination instabilities, which were completely identified and investigated. Additional higher order subharmonic and combination instabilities are observed for general rotors only. [ABSTRACT FROM AUTHOR]

It is an attractive research topic to propose some novel damping methods for rotors, and the dry friction damping is probably an effective and stable method. In this paper, a control strategy is proposed based on the relationship between the rotor modal characteristics and rotor responses. Firstly, a rotor model with a new kind of dry friction damper is established and corresponding complex nonlinear modes are derived. Then, based on that, the rotor modal characteristics are analyzed, with the nonlinear damping ratio used to evaluate the damping performance. Considering the effective working region for traditional dry friction dampers is usually narrow, a control strategy suiting for a broader range of load conditions is proposed. The results show that the vibration amplitude of the rotor at critical speed can be effectively controlled by the proposed strategy, implying its prospects in engineering practice. [ABSTRACT FROM AUTHOR]

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 2 X and 3 X 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 2 X and 3 X 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. [ABSTRACT FROM AUTHOR]

The behavior of a Jeffcott rotor with lateral-torsional coupling is investigated in the presence of internal and external damping and eccentricity. The governing equations are derived based on the Lagrange method. Also, the Laplace method and linearization is used to solve the governing equations for free vibrations analysis. For a rotor with unbalance, the instability occurs when the real part of eigenvalues has positive values, and at the same time, it is the intersection point between the lines of natural frequencies. The instability speed increases with increasing the external damping, yet dependent on the internal damping and unbalance. Also, it is demonstrated that the rotor critical speed is affected by the order of fractional derivatives. [ABSTRACT FROM AUTHOR]

Using active magnetic bearings for vibration control of flexible rotors subject to large base motion is both interesting and challenging. Rotors on ships, airplanes, and space-crafts fall in this category. These applications pose challenge for the active magnetic bearing designer, as the large motion of base renders the rotor-shaft-AMB system, time varying in nature, and also causes parametric excitation to the rotor system. Apart from stability concerns in such systems, it is difficult to design and choose optimal values of controller parameters because the system is subject to different base motions at different times during operation. In order to address this issue, this work applies fuzzy logic and proposes a simple yet effective selftuning control (STC) to control vibrations of flexible rotors supported by active magnetic bearings, which is subject to excitations due to base motion, in addition to unbalance excitation, usually present in rotors. To this end, first, the controller parameters are optimized considering the levitation performance of active magnetic bearings based on the transient response. Next, the fuzzy logic-based self-tuning algorithm is presented. Detailed comparison of performance between optimal and self-tuning control for different base motion conditions show that the proposed self-tuning controller outperforms the optimal control. [ABSTRACT FROM AUTHOR]

In this study, the dynamics and stability of a flexible rotor containing liquid in a constant thermal environment are investigated. According to thermoelastic theory, the thermal axial force exerted on the rotor is calculated by using the analytical method. A spinning Rayleigh beam is used as a simplified model of the rotor. Applying the Hamilton principle, the governing equation of motion for the flexible liquid-filled rotor system is derived. Using the obtained model, the stability prediction model and the critical spinning speed for the rotor system are formulated. To demonstrate the validity of the developed model, the present analysis is compared with the results reported in the previous study, and good agreement is observed from the comparison results. Finally, numerical results based on the obtained model are performed for a better understanding of the parameters including filling parameters, mode number, rotatory inertia and thermal effect on the stability, and critical spinning speed of the rotor system. [ABSTRACT FROM AUTHOR]

To investigate vibration characteristics and delay crack propagations of an asymmetric cracked rotor, the 3D finite element model of the rotor system with a nonlinear contact method is established. Resonance characteristics of the asymmetrical rotor without a crack and within different locations of a crack are investigated systematically. Numerical results show that a crack affects vibration frequencies and the unstable region of the rotor. Meanwhile, an improved proportional integral differential control method with the electromagnetic actuator is used to accomplish the delay crack propagation and the vibration suppression. Based on the mapping model of opening and closing states of a crack, the effects of rotational speeds, an unbalance, and asymmetries of the rotor are discussed in detail. Experimental results show that vibrations and the breathing behavior of cracks in the rotor with the electromagnetic actuator can be suppressed, and the effectiveness of the proposed mapping model of opening and closing states of a crack is verified. [ABSTRACT FROM AUTHOR]

In this article, the coupling effects of the unbalanced magnetic pull and ball bearing on nonlinear vibration of the three-phase asynchronous motor are investigated with the experimental and numerical methods. A test rig of a motor whose rotor supported by ball bearings is used and a 2 degrees of freedom magnetic solid coupling dynamic model of the motor rotor system is presented. The nonlinear dynamic response and spectrum are obtained from experiments and numerical analysis. The numerical results are in good agreement with test data, thus validating the presented model. It is found that the unbalanced magnetic pull and ball bearing forces possess the significantly interactional and nonlinear influences on the rotor dynamic characteristics. Small magnetic pull could impact the nonlinear bearing-rotor system, resulting in remarkable changes in the dynamic characteristics of the system. The effects of rotational speed and the rotor mass eccentricity on dynamic behaviors of the motor are discussed, and the results show that the magnetic pull gradually increases the amplitude of the ball bearing-rotor system, and its effect decreases with the increment of the rotational speed and mass eccentricity. [ABSTRACT FROM AUTHOR]

Various structural health monitoring methods were recently applied to fault diagnosis of rotating machinery, in which vibration response–based techniques demonstrated to be well adapted for different scenarios. However, only severe cracks are detected when most of such techniques are applied. Thus, innovative methods are proposed to identify the existence of incipient cracks in rotating shafts. In a previous contribution, the combination resonance approach for crack identification purposes was presented. This method is based on the application of additional forces at combination frequencies along with a heuristic optimization method to identify crack signatures in the vibration responses of the rotor. In the present work, the best conditions to apply the combination resonance approach are investigated in terms of the amplitude and frequency of the so-called diagnostic force. The vibration responses and phase angles of a cracked rotor were determined by using the harmonic balance technique. The FLEX approach is used to model the crack. Numerical simulations were performed using the finite element model of a horizontal rotor. [ABSTRACT FROM AUTHOR]

The influence of unbalance on the meshing characteristic of the geared rotor system in an integrally geared compressor is investigated. Firstly, a scaled structure of the geared rotor system in an integrally geared compressor is taken as the research object, and its dynamic model is derived by a finite element method where nonlinear mesh excitation is considered. Then, based on the dynamic model, the meshing forces under unbalance effect are calculated, as well as the variation of meshing forces and the vibrations of the system under different loads and transmission errors. The results show that the side band frequencies of the rotor vibration signals have some correlation with the collision of the gear teeth. The more intensely the teeth collide, the more complex are the sideband frequencies. The frequency components are related to the center frequencies and the unbalance excitation frequencies, and the meshing state can be diagnosed according to the side band frequencies. In addition, the nonlinear gear meshing force has strong correlation with the acceleration of the box in frequency domain, but less influence on the displacement of rotor, which are verified by the test results. The results show it is a feasible approach to use the spectrum signature of acceleration on the box as essential evidence to judge the geared rotor system's running state with unbalance excitation, which will be helpful in the vibration control and condition monitoring of the equipment. [ABSTRACT FROM AUTHOR]

Vibration control, especially in cracked rotors, is an important factor that can prevent the occurrence of disastrous failures. In this paper, vibrational control of a cracked rotor with an electromagnetic actuator has been studied with a continuous model of flexural vibration of cracked rotors. The governing equation of motion for the rotor under the external excitation of the electromagnetic actuator, gravity, and unbalanced forces is presented. A control law for the optimal control method to minimize the vibration of the rotor or stress at the crack section was obtained. To this aim, two cost functions have been introduced, based on the overall vibration of the rotor and the maximum stress at the crack section. The results of these two strategies are compared with each other and their performances are discussed. [ABSTRACT FROM AUTHOR]

In this paper, the attention is confined to the suppression of multi-frequency rotor vibration. A method to control rotor’s multi-frequency periodic vibration in rotor-bearings system is proposed which uses active magnetic exciter (AME) to produce active control force to suppress rotor’s vibration and to reach a self-optimizing control of the rotor vibration. The control strategies include an arithmetic to optimize the amplitudes and phases of the control current using on-line self-optimizing algorithms in AME and applied multiple frequency-matched control force that AME generates to reduce the measured amplitudes of rotor. The model of rotor-bearings system with AME is established firstly. An active vibration control scheme for controlling transverse vibration of the rotor due to multi-frequency excitation is designed. The whole circle search algorithm and fast optimizing search algorithm about the amplitude and phase of control current are proposed. Finally, the experiments for controlling multi-frequency vibration of the rotor are carried out on the rotor-bearings test rig. The experimental results indicate that the proposed method can effectively suppress the rotor vibration for multi-frequency components through self-optimizing control of electromagnetic force. [ABSTRACT FROM AUTHOR]

Identification of the static mass imbalance is critical to the control of magnetically suspended rotors. A static mass imbalance identification method without using the closed-loop transfer function is proposed in this paper. Then the null displacement control of the magnetically suspended rotor is realized by using the identified static mass imbalance. Because null vibration is the control target for the rotor of a magnetically suspended control moment gyro (MSCMG) with active-passive magnetic bearings, a null vibration control method depending on the displacement stiffness is introduced. However, the displacement stiffness of the passive magnetic bearing is hard to obtain accurately. Therefore, the least mean square method is utilized to adjust the uncertain displacement stiffness adaptively according to the centroid acceleration. Simulation results show that adaptive null vibration control based on the static mass imbalance identification can remove the synchronous magnetic bearing force effectively, thus enabling the rotor of the MSCMG with active-passive magnetic bearings to rotate about its initial axis. [ABSTRACT FROM AUTHOR]

Torsional rotor vibrations are undesirable phenomena which are very difficult to control in rotating systems. A common method for reducing vibrations involves the use of dynamic absorbers. However, if their physical parameters are constant, the frequency range of efficiency of dynamic absorbers is tight, making them unsuitable for systems with variable speeds. The use of smart materials, due to their variable and controllable mechanical properties, may be a powerful tool for increasing the frequency range. Electrorheological (ER) fluids are attractive materials that undergo very fast reversible changes in their rheological properties upon the application of an electric field. In this study, an electrorheological dynamic torsional absorber, called the Smart ER Dynamic Absorber, has been designed in order to reduce torsional rotor vibrations. Under shear mode, the ER absorber can exhibit various torsional damping and stiffness characteristics when an electric field is applied. A nonlinear empirical model of the dynamic behavior of ER materials has been developed. An On-Off control strategy has been applied and absorber efficiency measured. The results show that the ER dynamic absorber exhibits very good performances. [ABSTRACT FROM PUBLISHER]

The aim of this work is to propose a methodology for the experimental determination of the matrix relating unbalance forces to measured displacements for a rotating machine. The goal is to obtain an alternative solution to special situations found in the industrial context, especially for highly flexible rotors that may lead to a nonlinear behavior of the system. The trial-weights-based techniques, such as the influence coefficients method or the modal method, cannot be applied in such configurations. The proposed balancing method is based on the use of an identified model for the system. A pseudo-random optimization technique using genetic algorithms was applied for the identification process. The basic idea is to obtain the flexible rotor unbalance response, which is then mimicked by using a finite element method model in which the unbalance masses and their corresponding angular positions are the design variables from the optimization viewpoint. This way, an inverse problem is solved and the corrective masses are obtained. The model characteristics of the system are adjusted experimentally. Experimental investigations were carried out and the results show the efficiency of the method developed; the limitations and improvements are finally discussed. [ABSTRACT FROM PUBLISHER]

The paper sets up a set of coupled nonlinear differential equations with time variable coefficients to research the vibration of rotating machinery under rotor to stator rub condition. The seal stiffness, which is used to calculate rotor-stator contact force and rotor surface temperature distribution, is calculated using the finite element method firstly. Then, the transient heat conduction equations and rotor dynamic equations are combined together considering the thermal bending as unbalance fore acting on the rotor. The feedback from rub to vibration, asymmetric heat and shaft bending is analyzed by transient integration. The paper gives a detailed temperature distribution, thermal bending and vibration characteristics under different rotating speeds and rub conditions. It is found that rub-induced vibration tends to grow with time when the rotor is running below its critical speed. Rub section temperature difference grows quickly. Partial rub finally turns to full annular rub. Rub-induced vibration will be spiral and oscillation versus time if the rotor runs above the critical speed in the case of light rub. At severe rub, the vibration will be aggravated despite the rotor running above or under the critical speed. Two rub-induced vibration examples showing the coupled heat and force impact symptoms occurring in real turbines are given. Abnormal vibration phenomenon is analyzed and explained using the model. [ABSTRACT FROM PUBLISHER]

This paper employs a hybrid numerical method combining the differential transformation method and the finite difference method to study the bifurcation behavior of a high speed spindle air bearing (HSSAB) system. The analytical results reveal a complex dynamic behavior comprising periodic, sub-harmonic, and quasi-periodic responses of the rotor center. Furthermore, the results reveal the changes which take place in the dynamic behavior of the bearing system as the rotor mass and bearing number are increased. The current analytical results are found to be in good agreement with those of other numerical methods. Therefore, the proposed method provides an effective means of gaining insights into the nonlinear dynamics of HSSAB systems. [ABSTRACT FROM PUBLISHER]

In this paper a magnetic bearing system is designed for the suppression of rotor vibration. Magnetic bearing is able to support the shaft without mechanical contacts, and it is also able to control the rotational vibration. Magnetic bearing is composed of position sensors, a digital controller, actuating amplifiers, and electromagnets. In order to control the vibration of a magnetic bearing system effectively, Time Delay Control (TDC) is utilized. It proposes the design skill of an optimal controller when the system has the uncertainty, i.e. it has a difficulty in extracting the exact mathematical expressions, as well as it has external disturbances. The observer with the position information is utilized as a feedback signal for regulating the rotor whirling motion. Simulation is performed first to check the validation of the proposed controller in suppressing the rotor whirling. Experiments are followed to guarantee its usefulness in the rotor rig with a magnetic actuator. The vibrating suppression is confirmed with TDC and its effect is compared with proportional and derivative controller's one. [ABSTRACT FROM AUTHOR]

Effect of the seal force on nonlinear dynamics and stability of the rotor-bearing-seal system are investigated both theoretically and experimentally. An experimental rotor-bearing-seal device is designed and corresponding tests are carried out. The experimental rotor system is simplified as the Jeffcott rotor. The nonlinear oil-film forces from the journal bearing are got under the short bearing theory. The nonlinear seal forces from the labyrinth seal are got under the Muszynska's seal force model. Through numerical calculation, the rotor rotating speed, the input-output air pressure difference and the seal clearance are used as control parameters to investigate the effect of the seal force with the help of bifurcation diagrams, waterfall plots, Poincaré maps, spectrum plots and rotor orbits. Various nonlinear phenomena and stability of the system are found and discussed. Theoretical results from numerical analysis are in good agreement with results from experiments. Conclusions are drawn and prove that this study will contribute to the further understanding of the effect of seal forces on nonlinear dynamics and stability of the rotor-bearing-seal system. [ABSTRACT FROM AUTHOR]

The present work aims at vibration control of a structure/rotor using a one-sided magnetic actuator. For such an actuator, the actuator force is a nonlinear function of current through the coil of the actuator and the gap between the actuator and the structure/rotor. Though the actuator introduces sufficient nonlinearity to the system, it has the advantage that, for applying force in a direction, this actuator needs to be placed in only one side of the structure/rotor. For vibration control of the structure/rotor, a simple digital proportional derivative (PD) control technique is suggested here. It is considered that the displacement signal from the sensor is sampled at specific instants of time and a series of discrete values of displacement is made available to the digital controller. The controller processes the above values of displacement to compute the values of control current that produces the values of appropriate control force at the corresponding instants. The input current to the actuator is kept constant between two consecutive sampling instants. The response of the controlled system (the structure/rotor along with the digital controller) is computed using standard time-marching algorithms (with time steps much smaller than the sampling interval). The effect of the sampling interval in the response pattern is observed for a single-degree-of-freedom (SDOF) system, a finite element model of a beam and a four degree-of-freedom model of a rotor. [ABSTRACT FROM AUTHOR]

We study the flow-coupled vibrations of an unbalanced rotor and a floating sealing ring. The rotor is high speed; its operating regimes are above second critical velocity. The ring is subjected to Coulomb friction force, which prevents its motion about the casing. At rotor rotation, the intensive vibrations of rotor and floating ring take place and the hydrodynamic forces in clearance between them are dominated. Non-impact and impact regimes are revealed and the latter are very dangerous for safety. In the stationary case, the analytical solutions for impact regimes are obtained; these show that synchronous oscillations of rotor and floating ring may occur. The non-stationary oscillations during startup and shutdown are also considered. Domains for the trouble-free non-impact regimes by various rotor velocities are determined. Rotor trajectories with impacts are submitted. [ABSTRACT FROM AUTHOR]

In this paper we consider a flexible Jeffcott rotor mounted at the ends by identical squeeze film dampers (SFDs). The rotative speed is supposed to increase at a constant angular acceleration. There can be one-peak and two-peak solutions for different values of SFD parameters during passage through the critical speed. Calculation shows that the rotor cannot pass through the critical speed due to the occurrence of diverging backward whirl in passage of the first or second peak, if the level of acceleration is lower than the critical ones. A flexible internal support, which can be activated or deactivated at a certain position along the rotor to change the stiffness of the system to suppress large vibration, is then applied to avoid the occurrence of backward whirl. The method is found to be effective if applied in a suitable way. [ABSTRACT FROM AUTHOR]

The hydrodynamic journal bearings-rotor system is a common machine element that is strongly nonlinear due to oil film forces. In this study, bifurcation of the response of an unbalanced bearings-rotor system with nonlinear suspension is investigated based on the assumption of an incompressible lubricant together with the short bearing approximation. Theoretical bifurcation analysis of bearing center motion is carried out by means of numerical investigation, the procedure here being numerical integration. The six major parameters characterizing the theoretical model of the system are considered with nondimensional speed. Jump phenomena, subharmonic and quasi-periodic vibrations of the bearing center trajectory, are found in this system. It is concluded that the bearing center trajectory had undesirable nonsynchronous vibrations. Understanding the bifurcation behavior of these parameters provides theoretical and practical ideas for controlling bearings-rotor systems and optimizing their operation. [ABSTRACT FROM AUTHOR]

Focuses on a study which described an optimal control law design for lateral vibration suppression and stabilization of a rotor system with anisotropic fluid-film bearings and fluid leakage. Explanations on lateral vibrations in turbomachines; Details on the model created to investigate the vibration control of a rotor-bearing system; Information on the optimal control problem; Simulation results.

Abstract: This paper presents the experimental development of a simple and effective vibration control scheme by employing smart-structure technology. Due to high accuracy and high slew rate requirements for lightweight structures, vibration control becomes a challenging task. In this paper, it is proposed to actively control rotor blade tip vibration with collocated piezoceramic sensors and actuators. To include the flexible characteristics of rotor blades in the analysis, a flexible cantilever beam is used to simulate the dynamic behavior of the blade subjected to external disturbances, generated by a magnetic shaker. The shaker was installed near the tip of the simulated rotor blade to maximize the external excitations. PZT-4 piezoceramic sensor and actuator were used and considered as elements of the smart structure. Based on the derived dynamic model, a proportional gain feedback controller was implemented to compensate for the vibratory deflections of the underlying structure. The results of the work show that the proposed control methodology along with the smart structure can suppress 85% of the measured structural vibration, which is considered satisfactory. [ABSTRACT FROM AUTHOR]

Presents a theoretical model for the nonlinear description of vibrations occurring in the rotor-bearings-supports system. Approach to the determination of viscous-elastic properties of the oil film; Journal bearings; Examples of experimental verification of the model at a special large-size test rig; Analysis of nonlinear vibrations of a real large turbo-set.