Showing papers on "Critical speed published in 2010"

Machinery Vibration and Rotordynamics

Abstract: PREFACE. 1 Fundamentals of Machine Vibration and Classical Solutions. The Main Sources of Vibration in Machinery. The Single Degree of Freedom (SDOF) Model. Using Simple Models for Analysis and Diagnostics. Six Techniques for Solving Vibration Problems with Forced Excitation. Some Examples with Forced Excitation. Illustrative Example 1. Illustrative Example 2. Illustrative Example 3. Illustrative Example 4. Some Observations about Modeling. Unstable Vibration. References. Exercises. 2 Torsional Vibration. Torsional Vibration Indicators. Objectives of Torsional Vibration Analysis. Simplified Models. Computer Models. Kinetic Energy Expression. Potential Energy. Torsional Vibration Measurement. French s Comparison Experiments. Strain Gages. Carrier Signal Transducers. Frequency-modulated Systems. Amplitude-modulated Systems. Frequency Analysis and the Sideband System. French s Test Procedure and Results. A Special Tape for Optical Transducers. Time-interval Measurement Systems. Results from Toram s Method. Results from the Barrios/Darlow Method. References. Exercises. 3 Introduction to Rotordynamics Analysis. Objectives of Rotordynamics Analysis. The Spring Mass Model. Synchronous and Nonsynchronous Whirl. Analysis of the Jeffcott Rotor. Polar Coordinates. Cartesian Coordinates. Physical Significance of the Solutions. Three Ways to Reduce Synchronous Whirl Amplitudes. Some Damping Definitions. The "Gravity Critical". Critical Speed Definitions. Effect of Flexible (Soft) Supports. Rotordynamic Effects of the Force Coefficients A Summary. The Direct Coefficients. The Cross-coupled Coefficients. Rotordynamic Instability. Effect of Cross-Coupled Stiffness on Unbalance Response. Added Complexities. Gyroscopic Effects. Effect of Support Asymmetry on Synchronous Whirl. False Instabilities. References. Exercises. 4 Computer Simulations of Rotordynamics. Different Types of Models. Bearing and Seal Matrices. Torsional and Axial Models. Different Types of Analyses. Eigenanalysis. Linear Forced Response (LFR). Transient Response. Shaft Modeling Recommendations. How Many Elements. 45-Degree Rule. Interference Fits. Laminations. Trunnions. Impeller Inertias via CAD Software. Stations for Added Weights. Rap Test Verification of Models. Stations for Bearings and Seals. Flexible Couplings. Example Simulations. Damped Natural Frequency Map (NDF). Modal Damping Map. Root Locus Map. Undamped Critical Speed Map. Mode Shapes. Bode/Polar Response Plot. Orbit Response Plot. Bearing Load Response Plot. Operating Deflected Shape (ODS). Housing Vibration (ips and g s). References. 5 Bearings and Their Effect on Rotordynamics. Fluid Film Bearings. Fixed-geometry Sleeve Bearings. Variable-geometry Tilting Pad Bearings. Fluid Film Bearing Dynamic Coefficients and Methods of Obtaining Them. Load Between Pivots Versus Load on Pivot. Influence of Preload on the Dynamic Coefficients in Tilt Pad Bearings. Influence of the Bearing Length or Pad Length. Influence of the Pivot Offset. Influence of the Number of Pads. Ball and Rolling Element Bearings. Case Study: Bearing Support Design for a Rocket Engine Turbopump. Ball Bearing Stiffness Measurements. Wire Mesh Damper Experiments and Computer Simulations. Squeeze Film Dampers. Squeeze Film Damper without a Centering Spring. O-ring Supported Dampers. Squirrel Cage Supported Dampers. Integral Squeeze Film Dampers. Squeeze Film Damper Rotordynamic Force Coefficients. Applications of Squeeze Film Dampers. Optimization for Improving Stability in a Centrifugal Process Compressor. Using Dampers to Improve the Synchronous Response. Using the Damper to Shift a Critical Speed or a Resonance. Insights into the Rotor Bearing Dynamic Interaction with Soft/Stiff Bearing Supports. Influence on Natural Frequencies with Soft/Stiff Bearing Supports. Effects of Mass Distribution on the Critical Speeds with Soft/Stiff Bearing Supports. Influence of Overhung Mass on Natural Frequencies with Soft/Stiff Supports. Influence of Gyroscopic Moments on Natural Frequencies with Soft/Stiff Bearing Supports. References. Exercises. Appendix: Shaft With No Added Weight. 6 Fluid Seals and Their Effect on Rotordynamics. Function and Classification of Seals. Plain Smooth Seals. Floating Ring Seals. Conventional Gas Labyrinth Seals. Pocket Damper Seals. Honeycomb Seals. Hole-pattern Seals. Brush Seals. Understanding and Modeling Damper Seal Force Coefficients. Alford s Hypothesis of Labyrinth Seal Damping. Cross-coupled Stiffness Measurements. Invention of the Pocket Damper Seal. Pocket Damper Seal Theory. Rotordynamic Testing of Pocket Damper Seals. Impedance Measurements of Pocket Damper Seal Force Coefficients (Stiffness and Damping) and Leakage at Low Pressures. The Fully Partitioned PDS Design. Effects of Negative Stiffness. Frequency Dependence of Damper Seals. Laboratory Measurements of Stiffness and Damping from Pocket Damper Seals at High Pressures. The Conventional Design. The Fully Partitioned Design. Field Experience with Pocket Damper Seals. Two Back-to-Back Compressor Applications. Case 1. Case 2. A Fully Partitioned Application. Designing for Desired Force Coefficient Characteristics. The Conventional PDS Design. The Fully Partitioned Pocket Damper Seal. Leakage Considerations. Some Comparisons of Different Types of Annular Gas Seals. References. 7 History of Machinery Rotordynamics. The Foundation Years, 1869 1941. Shaft Dynamics. Bearings. Refining and Expanding the Rotordynamic Model, 1942 1963. Multistage Compressors and Turbines, Rocket Engine Turbopumps, and Damper Seals, 1964 Present. Stability Problems with Multistage Centrifugal Compressors. Kaybob, 1971 72. Ekofisk, 1974 75. Subsequent Developments. New Frontiers of Speed and Power Density with Rocket Engine Turbopumps. The Space Shuttle Main Engine (SSME). High-pressure Fuel Turbopump (HPFTP). Rotordynamic Instability Problem. Noncontacting Damper Seals. Shaft Differential Heating (The Morton Effect). References. INDEX.

Dynamic Design of a High-Speed Motorized Spindle-Bearing System

Abstract: This technical brief presents a dynamic model based on the traditional transfer matrix method (TMM) and Jones-Harris nonlinear rolling bearing model to study the effects of the extended structure parameters on the vibration behavior of a high-speed motorized spindle-bearing system. The first critical speed and the dynamic stiffness of the high-speed motorized spindle-bearing system are systematically studied. A design sensitivity analysis of the structure parameters is then conducted to identify the main factor to affect the first critical speed of the spindle-bearing system. The results show that the processing condition, the shaft shoulder, the dimension of motor, and the bearing arrangement are sensitive to the spindle dynamic behavior. The TMM model of the spindle-bearing system is verified by measuring the high-speed motorized spindle overall dynamic stiffness.

Lateral Hunting Stability of Railway Vehicles Running on Elastic Track Structures

Abstract: Considering the viscoelastic property of railway track structure, it is suggested in this paper to include the influence of track dynamics in calculation of lateral stability of railway vehicles running on tracks. A direct numerical method based on the stability of time histories of vehicle components is proposed to ascertain the nonlinear critical hunting speed of railway vehicles. The time histories of the vehicle system are calculated by use of the three-dimensional vehicle-track coupled models, which are capable of taking into account the influence of dynamic properties of track structures on vehicle dynamics. The effect of track system properties such as the rail fastener stiffness and the rail profile on the lateral hunting stability of the vehicle is investigated. Differences of the critical hunting speeds of vehicles on rigid track model and on elastic track model are found out. Generally, the rigid track model overestimates the critical hunting speed by 5―10% for different types of vehicles, which implies that the classical vehicle dynamics predicts higher lateral stability of a vehicle than the vehicle-track coupled dynamics does. This conclusion is of significance to the safety design of railway vehicles and should be taken notice in the design stage. The reason that causes the differences is discussed. A full-scale field experiment was carried out to investigate the hunting behavior of a freight car with three-piece bogies on a straight track. Very obvious hunting motion was observed in the experiment when the unloaded vehicle ran at the speed of 75 km/h, which verified the theoretical calculation results.

Analysis on the nonlinear response of cracked rotor in hover flight

Abstract: The motion equations for a Jeffcott rotor in hover flight are derived. A periodically sampled peak-to-peak value diagram is used for characterizing and distinguishing different types of nonlinear responses in hovering state. The nonlinear responses become more apparent when the rotor is running above the critical speed in flat flight. There are three ways for rotor responses going to chaos, namely through quasi-periodic, intermittence, or period-3 bifurcation to chaos. The hover flight might suppress some nonlinear responses. However, the position of axis center might obviously deflect, leading to either nonlinear response or peak-to-peak value jump near the fraction frequency of swing critical speed.

Thermohydrodynamic Model Predictions and Performance Measurements of Bump-Type Foil Bearing for Oil-Free Turboshaft Engines in Rotorcraft Propulsion Systems

Abstract: An engineered thermal management is fundamental to the application of gas foil bearings (GFBs) as turboshaft supports in rotorcraft propulsion systems. The paper presents a model for the thermal energy transport in a rotor-GFB system operating at high temperature with typical inner and/or outer cooling flows. Predicted film temperatures agree with published test data, demonstrating the effectiveness of an outer cooling stream to remove heat and to control the operating temperature. The inner flow stream is not as efficient. The analysis shows paths of thermal energy by conduction and convection to assist in the design and troubleshooting of rotor-GFB systems operating hot. Bearing temperatures and shaft motions measurements are obtained in a test rotor electrically heated to 132°C. In speed-up tests to 26 krpm, the rotor motion amplitude drops suddenly just above the critical speed, thus, evidencing the typical hardening of compliant bearings. At the hottest test condition, since air is more viscous, the rotor peak motion amplitude decreases, not showing a jump. The coastdown tests show the critical speed increases slightly as the temperature increases.

Anti-jerk control apparatus and method for Hybrid Electric Vehicle

Abstract: The present invention relates to an anti-jerk control apparatus and method for an Hybrid Electric Vehicle (HEV). The anti-jerk control apparatus includes a model speed calculation unit for calculating a model speed of the motor in a state in which a vibration of a drive shaft is not considered. A vibration occurrence determination unit detects a speed vibration component while calculating a reference speed difference and an average speed difference from differences between the model speed and an actual speed of the motor, thus determining whether a vibration occurs on the drive shaft. A torque correction value calculation unit calculates a motor torque correction value for anti-jerk required to damp the vibration of the drive shaft, and controls torque of the motor if the vibration occurrence determination unit determines that the vibration occurs on the drive shaft.

Design and Implementation of a Critical Speed-Based DVFS Mechanism for the Android Operating System

Abstract: DVFS is an efficient energy saving technique for processors during program execution time. A critical speed-based DVFS mechanism that we have implemented on the Android operating system is introduced. Our studies indicate that due to memory accesses, decreasing the frequency may not always reduce the energy consumption. A critical speed is thus defined as the CPU frequency with which the energy consumption can be minimized. In our mechanism, a prediction equation based on the correlation of the memory access rate and the critical speed was constructed and used to choose a suitable frequency and voltage dynamically at run time. Our initial experiment results show that for real applications running on Android, the energy consumption can be effectively reduced.

Elimination of Unstable Ranges of Rotors Utilizing Discontinuous Spring Characteristics: An Asymmetrical Shaft System, an Asymmetrical Rotor System, and a Rotor System With Liquid

Abstract: Unstable vibration occurs in the vicinities of the major critical speeds of asymmetrical shaft and rotor systems. It occurs also in a wide rotational speed range higher than the major critical speed of a shaft with a hollow disk partially filled with liquid. The occurrence of the unstable vibrations is a serious problem because the amplitude increases exponentially, and finally, the system is destroyed. The active vibration control can suppress unstable vibrations but the method is generally complicated and costly. No simple effective method to suppress unstable vibrations has been developed yet. In the previous paper, the authors proposed a simple method by utilizing discontinuous spring characteristics, which can suppress steady-state resonances. This paper shows that this method is also effective to suppress unstable vibrations. By using this method, the unstable vibrations can be changed into almost periodic motions, and the amplitudes are suppressed to the desired small level even in an unstable range. The validity of the proposed method is also verified by experiments.

Thermal Management and Rotordynamic Performance of a Hot Rotor-Gas Foil Bearings System: Part 2—Predictions Versus Test Data

Abstract: Implementation of gas foil bearings (GFB) in micro gas turbines relies on physics based computational models anchored to test data. This two-part paper presents test data and analytical results for a test rotor and GFB system operating hot. A companion paper (Part 1) describes a test rotor-GFB system operating hot to 157°C rotor OD temperature, presents measurements of rotor dynamic response and temperatures in the bearings and rotor, and including a cooling gas stream condition to manage the system temperatures. The second part briefs on a thermoelastohydrodynamic (TEHD) model for GFBs performance and presents predictions of the thermal energy transport and forced response, static and dynamic, in the tested gas foil bearing system. The model considers the heat flow from the rotor into the bearing cartridges and also the thermal expansion of the shaft and bearing cartridge and shaft centrifugal growth due to rotation. Predictions show that bearings’ ID temperatures increase linearly with rotor speed and shaft temperature. Large cooling flow rates, in excess of 100 L/min, reduce significantly the temperatures in the bearings and rotor. Predictions, agreeing well with recorded temperatures given in Part 1, also reproduce the radial gradient of temperature between the hot shaft and the bearings ID, largest (37°C/mm) for the strongest cooling stream (150 L/min). The shaft thermal growth, more significant as the temperature grows, reduces the bearings operating clearances and also the minimum film thickness, in particular at the highest rotor speed (30 krpm). A rotor finite element (FE) structural model and GFBs force coefficients from the TEHD model are used to predict the test system critical speeds and damping ratios for operation at increasing shaft temperatures. In general, predictions of the rotor imbalance show good agreement with shaft motion measurements acquired during rotor speed coastdown tests. As the shaft temperature increases, the rotor peak motion amplitudes decrease and the system rigid-mode critical speed increases. The computational tool, benchmarked by the measurements, furthers the application of GFBs in high temperature oil-free rotating machinery.Copyright © 2010 by ASME

Dynamic analysis of an axially translating plate with time-variant length

Abstract: The linear dynamic analysis of a translating cantilever plate model characterized by time-variant length and axial velocity is investigated. A length-dependent governing partial differential equation (PDE) of motion is formulated by the extended Hamilton’s principle based on Kirchhoff–Love plate theory. The tension in the system arising from the longitudinal accelerations and in-plane stresses are incorporated. Further, the extended Galerkin method along with the Newmark direct time integration scheme is employed to simulate the response of the system. Stability and vibration characteristics are studied according to the quadratic eigenvalue problem from the governing PDE, which demonstrates that the coupling effects between the axial translation motion and the flexural deformation stabilizes the system during the extension and destabilizes it in the retraction. The computation results show that the translating velocity and the aspect ratio affect the natural frequencies and stability for the out-of-plane vibration of the moving plate. A domain for the traveling velocity associated with the stable system is given, and the critical failure velocity is also predicted based on numerical simulations.

Active Vibration Control of Flexible Rotors on Maneuvering Vehicles

Abstract: This paper presents a simulation to actively control transverse vibration of a flexible rotor shaft system mounted on a moving vehicle (e.g., a ship or an aircraft). Discretizing the rotor continuum with beam finite elements, equations of motion are written with respect to a noninertial frame attached to the frame of the moving vehicle. Such equations are linear but contain time-varying parametric terms due to the motion of the carrier vehicle. Through numerical simulation, it is shown that the transverse response in the bending vibration of the rotor shaft relative to the supporting structure is significantly influenced by the inertia force, as well as the parametric excitations due to vehicle motion. A control strategy is proposed using an electromagnetic actuator placed at a suitable location along the span of the rotor, and it is found extremely useful in reducing the vibration of the rotor and improving its stability. Examples are given in support by studying both the uncontrolled and the controlled motion of a rotor shaft system carried by an aircraft undergoing two different kinds of maneuvers.

Transverse nonlinear vibrations of a circular spinning disk with a varying rotating speed

Abstract: We analyze the transverse nonlinear vibrations of a rotating flexible disk subjected to a rotating point force with a periodically varying rotating speed. Based on Hamilton’s principle, the nonlinear governing equations of motion (coupled equations among the radial, tangential and transverse displacements) are derived for the rotating flexible disk. When the in-plane inertia is ignored and a stress function is introduced, the three nonlinearly coupled partial differential equations are reduced to two nonlinearly coupled partial differential equations. According to Galerkin’s approach, a four-degree-of-freedom nonlinear system governing the weakly split resonant modes is derived. The resonant case considered here is 1:1:2:2 internal resonance and a critical speed resonance. The primary parametric resonance for the first-order sin and cos modes and the fundamental parametric resonance for the second-order sin and cos modes are also considered. The method of multiple scales is used to obtain a set of eight-dimensional nonlinear averaged equations. Based on the averaged equations, using numerical simulations, the influence of different parameters on the nonlinear vibrations of the spinning disk is detected. It is concluded that there exist complicated nonlinear behaviors including the periodic, period-n and multi-pulse type chaotic motions for the spinning disk with a varying rotating speed. It is also found that among all parameters, the damping and excitation have great influence on the nonlinear responses of the spinning disk with a varying rotating speed.

Development of a simulation model of a high-speed vehicle for a derailment mechanism:

Abstract: During the operation of a high speed railway vehicle, safety is a basic requirement. However, due to the potentially large lateral displacements of the wheelsets, the precise mechanism of derailment is different from conventional vehicles and is not fully understood. To obtain correct simulation results for this behavior it is necessary to select methods for rapid, exact computation of the creep forces, the normal force, and the 3-D geometry at each contact point. In this paper, a dynamic model is presented and 2 types of derailment have been thoroughly investigated. High lateral force is used as a criterion for determining the critical point at which flange climb occurs and the critical speed for impact derailment is derived using the oblique-impact theory. Finally, an assessment method is proposed that distinguishes between the 2 types of derailment. The simulation model can also be used to identify the factors that lead to greatest risk of derailment.

Flutter of a viscoelastic plate in a supersonic gas flow

Abstract: The flutter of a viscoelastic plate in a supersonic gas flow is studied. A technique and algorithm for numerical solution of nonlinear integro-differential equations with weakly singular kernels are elaborated. The critical flutter speed of viscoelastic plates is determined

System and method for vibration analysis and phase analysis of vibration waveforms using dynamic statistical averaging of tachometer data to accurately calculate rotational speed

Abstract: Vibration analysis is performed on a machine having a variable frequency drive by using a tachometer to monitor rotational speed of the drive shaft and a logic device to calculate speed parameters associated with the drive shaft using the tachometer data. The speed parameters include a maximum speed, a minimum speed, and an average speed of the drive shaft. By correlating the vibration spectra of the motor drive with the speed parameters, machine faults can be identified based upon the energy distribution in the spectra. Further, vibration waveforms from two or more locations on the machine can be sequentially acquired through synchronous triggering by using a pulse edge of a stable tachometer signal. The waveforms can be compared to determine a phase difference to help in identifying any machine faults that may be present.

Dynamics of a rotating shaft—disc under a periodic axial force

Abstract: Under a periodic axial force, a rotating Timoshenko shaft with a rigid unsymmetrical disc was modelled as a parametrically excited system using the finite-element method. Using a harmonic balance method, dynamic stability of the system was checked, steady-state response, undamped resonance condition, and disc centre orbit were solved analytically and discussed numerically. Furthermore, the time history response was calculated to verify the efficiency of the solutions. The discussion shows that the fluctuating part of the axial force results in system dynamic instability, and the parameter regions of dynamic instability are enlarged with increasing amplitude of the fluctuation; the disc centre orbit of the system steady-state response is limited to an annular region, and the orbit width is increased by the axial force fluctuating amplitude; besides the neighbourhood of the system critical speed, the shaftdisc system can undergo some additional resonances due to the fluctuating axial force.

Active vibration control of a rotor-bearing system based on dynamic stiffness

Abstract: This paper presents an active vibration control scheme to reduce unbalance-induced synchronous vibration in rotor-bearing systems supported on two ball bearings, one of which can be automatically moved to control the effective rotor length and, as an immediate consequence, the rotor stiffness. This dynamic stiffness control scheme, based on frequency analysis, speed control and acceleration scheduling, is used to avoid resonant vibration of a rotor system when it passes (run-up or coast down) through its first critical speed. Algebraic identification is used for on-line unbalance estimation at the same time that the rotor is taken to the desired operating speed. Some numerical simulations and experiments are included to show the unbalance compensation properties and robustness of the proposed active vibration control scheme when the rotor is started and operated over the first critical speed.

Automatic Balancing of Bladed-Disk/Shaft System via Passive Autobalancer Devices

Abstract: Autobalancers for rotor/bearing systems are passive devices consisting of eccentrically mounted balance masses that freely revolve around the rotor's axis of rotation. At certain supercritical speeds, the balancer mass positions naturally adjust to cancel the rotor imbalance. This automatic-balancing phenomena occurs as a result of nonlinear dynamic interaction between the balancer masses and the rotor's lateral vibration. Previous studies have found that autobalancers can effectively compensate for mass imbalance in planar rigid rotors such as hard-disk drives and flywheels, however, their use in bladed-disk and turbomachinery applications has not been previously considered. This study explores the dynamics and stability of a flexible bladed-disk/rotor-bearing system equipped with a dual-ball automatic-balancing device. It is found that the autobalancer effectively compensates for both mass and aerodynamic imbalances produced by a bladed-loss condition over a wide revolutions/minute range at speeds above the first lateral natural frequency. It is also shown that for stable automatic balancing to occur, the ratio of automatic balancer damping to the blade aerodynamic drag coefficient must be above some critical value. The analysis demonstrates that the automatic balancer is able to simultaneously reduce both bearing loads and blade deflections for a simulated blade-loss event.

Nonlinear vibration analysis of an eccentric rotor with unbalance magnetic pull

Abstract: The unbalance magnetic pull of an eccentric water turbine generator set rotor has important influence on its vibration. The magnetic stiffness matrix is introduced to express the energy of the air gap magnetic field. Two vibration models are constructed through the Lagrange Equation. The difference of the two models is the boundary supporting conditions: one is rigid support and the other is elastic support through bearing. The influence of the magnetic stiffness and the elastic support on the critical speed of the rotor is studied using the Liapunov nonlinear vibration theory. The vibration amplitude of the rotor is calculated taking the magnetic stiffness and level eccentricity force into account. The sensitivity of the magnetic, mechanical and bearing parameters to the critical speed is analyzed. Some conclusions may be benefit to the study the dynamic characters of the generator set shaft system which concludes all the magnetic, mechanical and hydraulic parameters.

Rotordynamic Analysis of a Large Industrial Turbocompressor Including Finite Element Substructure Modeling

Abstract: A rotordynamic analysis of a large turbocompressor that models both the casing and supports along with the rotor-bearing system was performed. A 3D finite element model of the casing captures the intricate details of the casing and support structure. Two approaches are presented, including development of transfer functions of the casing and foundation, as well as a fully coupled rotor-casing-foundation model. The effect of bearing support compliance is captured, as well as the influence of casing modes on the rotor response. The first approach generates frequency response functions (FRFs) from the finite element case model at the bearing support locations. A high-order polynomial in numerator-denominator transfer function format is generated from a curve fit of the FRF. These transfer functions are then incorporated into the rotordynamics model. The second approach is a fully coupled rotor and casing model that is solved together. An unbalance response calculation is performed in both cases to predict the resulting rotor critical speeds and response of the casing modes. The effect of the compressor case and supports caused the second critical speed to drop to a value close to the operating speed and not compliant with the requirements of the American Petroleum Institute (API) specification 617 7th edition. A combination of rotor, journal bearing, casing, and support modifications resulted in a satisfactory and API compliant solution. The results of the fully coupled model validated the transfer function approach.

Q-value Evaluation and Rotational Test of Flexible Rotor Supported by AMBs

Abstract: Reducing the weight of industrial rotational machinery equipped with Active Magnetic Bearings (AMBs) has been shown to achieve efficient hydraulic performance at high speed rotation. It also improves space efficiency and gives cost reductions. One of our solutions for increasing rotational speed is to experimentally demonstrate the passing of the 3rd bending critical speed. In this paper, a flexible rotor supported by AMBs is introduced. The controller design for mode separation control is studied and the stability margin is evaluated according to ISO 14839-3. After checking the stability, we successfully perform the rotation test to pass a total of 5 critical speeds, i.e., 2 rigid modes and 3 bending modes, by using a modal balancing technique. This paper proves that stability and balancing are key technologies for achieving high-speed rotation.

Motor vehicle e.g. electric vehicle, has controller that moves vehicle autonomously and drive-technically below critical speed, in retaining mode, where distance sensor and input unit are provided for switching vehicle to retaining mode

Abstract: The vehicle (1) has an electric machine (3) for driving the vehicle, and a controller (6) for electric machine. A distance sensor and an input unit (9) e.g. touch screen, switch the vehicle to a retaining mode, where the retaining mode is activated only below a critical speed. The speed of the vehicle is determined during switching ON of retaining mode and the retaining mode is automatically activated during reduction of critical speed. The controller moves the vehicle autonomously and drive-technically below the critical speed, in the retaining mode. An independent claim is also included for a method for operating a motor vehicle.

Vibration Suppression of the Rotating Shaft using the Axial Control of the Repulsive Magnetic Bearing

Abstract: A repulsive magnetic bearing supports a rotating shaft without contact by utilizing a magnetic repulsive force between the magnets. However, because of the nonlinear characteristic of the magnetic repulsive force, the vibration during passage through the critical speed may increase. This paper investigates a vibration suppression method of the rotating shaft supported by the repulsive magnetic bearing. A vibration suppression method by controlling the axial displacement of the repulsive magnetic bearing is proposed. Its axial displacement control generates the changes of both the linear and the nonlinear coefficients of stiffness. The influence of the parameters of the axial displacement control are investigated, and these results are validated experimentally.