Showing papers on "Damper 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.

Optimization of multiple tuned mass dampers to suppress machine tool chatter

Abstract: Chatter is more detrimental to machining due to its instability than forced vibrations. This paper presents design and optimal tuning of multiple tuned mass dampers (TMDs) to increase chatter resistance of machine tool structures. Chatter free critical depth of cut of a machine is inversely proportional to the negative real part of frequency response function (FRF) at the tool–workpiece interface. Instead of targeting reduction of magnitude, the negative real part of FRF of the machine is reduced by designing single and multiple TMD systems. The TMDs are designed to have equal masses, and their damping and stiffness values are optimized to improve chatter resistance using minimax numerical optimization algorithm. It is shown that multiple TMDs need more accurate tuning of stiffness and natural frequency of each TMD, but are more robust to uncertainties in damping and input dynamic parameters in comparison with single TMD applications. The proposed tuned damper design and optimization strategy is experimentally illustrated to increase chatter free depth of cuts.

Comparative research on semi-active control strategies for magneto-rheological suspension

Abstract: This paper presents the comparison results of a study to identify an appropriate semi-active control algorithm for a MR suspension system from a variety of semi-active control algorithms for use with MR dampers. Five representative control algorithms are considered including the skyhook controller, the hybrid controller, the LQG controller, the sliding mode controller and the fuzzy logic controller. To compare the control performances of the five control algorithms, a quarter car model with a MR damper is adopted as the baseline model for our analysis. After deriving the governing motion equations of the proposed dynamic model, five controllers are developed. Then each control policy is applied to the baseline model equipped with a MR damper. The performances of each control algorithm under various road conditions are compared along with the equivalent passive model in both time and frequency domains through the numerical simulation. Subsequently, a road test is performed to validate the actual control performance. The results show that the performance of a MR suspension system is highly dependent on the choice of algorithm employed, and the sliding mode control strategy exhibits an excellent integrated performance.

Tracking Error-Based Servohydraulic Actuator Adaptive Compensation for Real-Time Hybrid Simulation

Abstract: Real-time hybrid simulation combines experimental testing and numerical simulation by dividing a structural system into experimental and analytical substructures. Servohydraulic actuators are typically used in a real-time hybrid simulation to apply command displacements to the experimental substructure(s). Servohydraulic actuators may develop a time delay due to inherent actuator dynamics that results in a desynchronization between the measured restoring force(s) and the integration algorithm in a real-time hybrid simulation. Inaccuracy or even instability will occur in a hybrid simulation if actuator delay is not compensated properly. This paper presents an adaptive compensation method for actuator delay. An adaptive control law is developed using an error tracking indicator to adapt a compensation parameter used in the proposed compensation method. Laboratory tests involving large-scale real-time hybrid simulations of a single degree of freedom moment resisting frame with an elastomeric damper are conducted to experimentally demonstrate the effectiveness of the proposed adaptive compensation method. The actuator tracking capability is shown to be greatly improved and exceptional experimental results are still achieved when a good estimate of actuator delay is not available.

Analysis of Tall Buildings with Damped Outriggers

Abstract: A novel damped outrigger system has been recently proposed for tall buildings, and is quite promising. To gain insight into the conceptual design of such systems, a simple beam-damper system model for a building with such dampers installed is developed and studied. A partial differential equation governing the motion is derived assuming a Bernoulli-Euler beam. A closed-form analytical solution is developed for vibration of the beam by analyzing the regions above and below the damper separately using separation of variables. By applying appropriate boundary conditions at the ends, a transcendental characteristic equation is obtained that governs the system's complex natural frequencies. An explicit form for the complex mode shape is determined for dynamic analysis. A numerical iteration scheme is adopted to solve the characteristic equation for the complex eigenvalues (i.e., the system modal frequencies and damping ratios). This solution was used to determine design curves for optimal damper position and size. For engineering convenience, empirical equations were provided by fitting numerical results. These equations include one for determining the optimal location of the damper for each mode, and two for determining the optimal damping coefficient of the damper, and for calculating the maximum modal damping ratio of the system while the beam vibrates in its first mode. Furthermore, relatively accurate approximations of the pseudoundamped natural frequency and damping ratio of the first mode were obtained using a Taylor expansion of the characteristic equation. All of the results obtained are nondimensionalized for convenience of analysis and application.

An LPV control approach for semi-active suspension control with actuator constraints

Abstract: This paper presents a new solution for the semi-active suspension control problem. First, a quarter vehicle model equipped with a semi-active damper is reformulated in the LPV framework using the nonlinear static semi-active damper model. This formulation allows to turn the control problem with dissipativity constraint into that with input saturation. Then the damper force saturation is taken into account in an original LPV fashion. This leads to the definition of a new LPV model with two parameters which is handled in a polytopic way. The H ∞ control design for polytopic systems is then applied. The interest of the provided methodology is emphasized by simulations on a nonlinear vehicle model.

Additional Losses in the Damper Winding of Large Hydrogenerators at Open-Circuit and Load Conditions

Abstract: Large salient-pole synchronous machines are typically equipped with a damper winding. At steady-state conditions, parasitic voltages are induced in the damper bars which lead to a current flow with associated power losses. This paper describes an analytical algorithm for the calculation of currents and corresponding losses in the damper winding. The presented method is based on an equivalent network of the damper winding containing all the bars of a repetitive section of the machine. The inductances are calculated with an air-gap permeance model. Contrary to similar existing approaches, the induced damper-bar voltages are computed using a numerical integration. This allows more precise results when it comes to higher harmonics. In order to validate the analytical computation, the results are compared with the results of 2-D transient finite-element studies and with a conventional analytical method based on the d-and q -axis equivalent circuits of the machine.

Vibration power generator for a linear MR damper

Abstract: The paper describes the structure and the results of numerical calculations and experimental tests of a newly developed vibration power generator for a linear magnetorheological (MR) damper. The generator consists of permanent magnets and coil with foil winding. The device produces electrical energy according to Faraday's law of electromagnetic induction. This energy is applied to vary the damping characteristics of the MR damper attached to the generator by the input current produced by the device. The objective of the numerical calculations was to determine the magnetic field distribution in the generator as well as the electric potential and current density in the generator's coil during the idle run and under the load applied to the MR damper control coil. The results of the calculations were used during the design and manufacturing stages of the device. The objective of the experimental tests carried out on a dynamic testing machine was to evaluate the generator's efficiency and to compare the experimental and predicted data. The experimental results demonstrate that the engineered device enables a change in the kinetic energy of the reciprocal motion of the MR damper which leads to variations in the damping characteristics. That is why the generator may be used to build up MR damper based vibration control systems which require no external power.

Efficient Operation of Air-Side Economizer Using Extremum Seeking Control

Abstract: As the heating, ventilating, and air conditioning (HVAC) systems accounts for a major sector of energy consumption for commercial buildings, there has been a greater demand for improving the efficiency of such systems. The air-side economizers have been developed as a class of energy-saving HVAC devices that may increase the energy efficiency by taking advantage of outdoor air during cool or cold weather. However, many economizers do not operate in the expected manner and waste even more energy than before installation, mostly due to the unreliable sensors and actuators in practice. Better control strategy is needed for optimal and robust operation. In this paper, an extremum-seeking control (ESC) based self-optimizing strategy is proposed to minimize the energy consumption, with the feedback of chilled water supply command rather than the temperature and humidity measurements. The mechanical cooling load is minimized by seeking the optimal outdoor air damper opening in real time. Such scheme does not need temperature and humidity sensors, and depends much less on the knowledge of the economizer model. Simulation was performed on a MODELICA based transient model of a single-duct air-handling unit developed with DYMOLA and AIRCONDITIONING LIBRARY . The simulation results demonstrated the potential of using ESC to achieve the minimal mechanical cooling load in a self-optimizing manner. In addition, an antiwindup ESC scheme is proposed to handle the ESC windup issue due to actuator (damper) saturation. The simulation results validated the effectiveness of the proposed antiwindup ESC.

A variable physical damping actuator (VPDA) for compliant robotic joints

Abstract: This paper introduces the development of a semi-active friction based variable physical damping actuator (VPDA) unit. The realization of this unit aims to facilitate the control of compliant robotic joints by providing physical variable damping on demand assisting on the regulation of the oscillations induced by the introduction of compliance. The mechatronics details and the dynamic model of the damper are introduced. The proposed variable damper mechanism is evaluated on a simple 1-DOF compliant joint linked to the ground through a torsion spring. This flexible connection emulates a compliant joint, generating oscillations when the link is perturbed. Preliminary results are presented to show that the unit and the proposed control scheme are capable of replicating simulated relative damping values with good fidelity.

Analysis of passive and semi active controlled suspension systems for ride comfort in an omnibus passing over a speed bump

Abstract: This paper describes the modeling, and testing of skyhook and other semi active suspension control strategies. The control performance of a three-degree-of-freedom quarter car semi active suspension systems is investigated using Matlab/Simulink, model. The objective of this paper is to present a comprehensive analysis of novel hybrid semi- active control algorithms and to compare the semi-active and passive systems in terms of human body vibrational displacements and accelerations. A theoretical model of the human seated model is developed in order to simulate the vertical motion of the Passenger in an omnibus when the vehicle passing over a speed bump. The mathematical model of these systems is presented. Ride comfort of off-road vehicles can be estimated by replacing the normal passive dampers in the vehicle suspension system with controllable, two-state, semi-active dampers.

Seismic response of dynamically similar adjacent structures connected with viscous dampers

Abstract: Structural control by implementing energy dissipation devices or control systems into structures is more effective in reducing excessive structural vibrations because of natural disturbances. This article describes the application of viscous damper for response control of seismically excited dynamically similar adjacent coupled structures. The investigation is carried out to study the structural responses of two dynamically similar structures connected with viscous dampers subjected to four different types of earthquake ground motions. A formulation of the equations of motion for the two adjacent multi-degrees-of-freedom (MDOF) structures connected with viscous dampers is presented. The numerical study is carried out in two parts, namely (a) two adjacent MDOF structures connected with viscous dampers having same damper damping coefficient and (b) two adjacent MDOF structures connected with viscous dampers having different damper damping coefficients. The damper effectiveness is investigated in terms of th...

Torque transmission device for use in drive train of motor vehicle, has torsional vibration damper with two damper elements, where centrifugal force pendulum is provided with carrier part

Abstract: The torque transmission device (1) has a torsional vibration damper (5) with two damper elements (3,4), where a centrifugal force pendulum (10) is provided with a carrier part (13) connected with one of the damper elements in rotationally locked manner. The pendulum mass (14) is enclosed radially outwards.

Limit states and failure mechanisms of viscous dampers and the implications for large earthquakes

Abstract: Fluid viscous dampers are used to control story drifts and member forces in structures during earthquake events. These elements provide satisfactory performance at the design-level or maximum considered earthquake. However, buildings using fluid viscous dampers have not been subjected to very large earthquakes with intensities greater than the design and maximum considered events. Furthermore, an extensive database of viscous damper performance during large seismic events does not exist. To address these issues, a comprehensive analytical and experimental investigation was conducted to determine the performance of damped structures subjected to large earthquakes. A critical component of this research was the development and verification of a detailed viscous damper mathematical model that incorporates limit states. The development of this model and the laboratory and simulation results conclude good correlation with the new model and the damper limit states and provide superior results compared with the typical damper model when considering near collapse evaluation of structures.

Force transmission device in particular for power transmission between a drive engine and an output

Abstract: A force transmission device, in particular or power transmission between a drive engine and an output, comprising a damper assembly with at least two dampers, which can be connected in series, and a rotational speed adaptive absorber, wherein the rotational speed adaptive tuned mass damper is disposed between the dampers at least in one force flow direction through the force transmission device.