bluuebunny/crossref_metadata_2025_split huggingface dataset:
High Cycle Fatigue Cracks at Radial Fan Impellers Caused by Aeroelastic Self-Excited Impeller Vibrations: Part 2 — Mechanism and Mathematical Model
Authors: Ni Alexander 
Published: February 2021

Abstract
The radial impeller of the main fan of hydrogen cooled generator has been noted to sustain fatigue failure. Experimental data pointed out to the impeller selfexcitation as the cause of the failure. According to the mechanism and the mathematical model suggested in the paper the impeller selfexcitation is due to the feedback between the natural impeller vibrations and the acoustic field in the side room adjacent to the impeller. The impeller vibrations induce the pressure oscillations in the side room that in turn influence the impeller. Under special conditions of the fan dynamic behaviour and the acoustic properties of the fan side room this feedback leads to the selfexcitation. The suggested mechanism and the model fit all the experimental data. Their validity has been also later confirmed by the maintaince experience of other similar machines.
A Genetic Algorithm Based Balancing Framework for Flexible Rotors
Authors: Qiu Hai , Qu Liangsheng , Sun Ruixiang 
Published: February 2021

Abstract
Most of the methods in flexible rotor balancing currently used rely on the repeated running up and down processes of the balanced machine. The ordinary balancing methods without test runs are regularly based on too many hypotheses and depended on prior knowledge of bearings. The latter restricts their wide application in practice. This paper establishes a balancing process frame with both unbalance and bearing parameters as inputs and the vibration responses on bearings as outputs. The authors determine the rotor unbalance as an inverse engineering problem using genetic algorithms (GA). This method can simultaneously evaluate the bearing parameters and their working situations in the service environments of large rotating machinery.
Identification of Rotating Asymmetry in Rotating Machines by Using Reverse dFRF
Authors: Lee Chong-Won , Kwon Kye-Si 
Published: February 2021

Abstract
A quick and easy but comprehensive identification method for asymmetry in an asymmetric rotor is proposed based on complex modal testing method. In this work, it is shown that the reverse directional frequency response function (reverse dFRF), which indicates the degree of asymmetry, can be identified with a simple method requiring only one vibration sensor and one exciter. To clarify physical realization associated with estimation of the reverse dFRF, its relation to the conventional frequency response functions, which are defined by the real input (exciter) and output (vibration sensor), are extensively discussed.
A New Approach to Prediction of the Self-Excited Torsional Vibration of Rolling Mill Drives in Rolling Slippage
Authors: Wang Zhang-Hai , Zhang W. J. , Wang De-Jun 
Published: February 2021

Abstract
This paper addresses the self-excited vibration in rolling processes, particularly in the case of rolling mill drive system. A mathematical model is developed which accounts the non-linearity of the system due to the rolling slippage for friction present between the work piece and the roller. To predicate the self-excited vibration, the condition under which the self-excited vibration occurs is derived which is related to the rolling normal force and the rolling speed. As the self-excited vibration causes instantaneous breakage of a system, the study reported here will thus be very useful and of significance.
The Integration of Structural and Fluid Film Dynamic Elements in Foil Bearings: Part II — A New Approach to the Problem
Authors: Swanson Erik E. , Heshmat Hooshang 
Published: February 2021

Abstract
In Part I of this investigation a survey was made to see how the two-tiered construction of foil bearings, consisting as they do of two generically disparate elements, one hydrodynamic in nature and the other following the laws of elasticity, have been modeled in order to obtain integrated values of bearing stiffness and damping. Here a series of experiments is reported showing that serious discrepancies exist between results obtained from conventional dynamic models and test results. A new approach to the problem is here taken in modeling the two-tiered dynamic system of foil bearings. For this purpose a series of analytical solutions were obtained for different spring and dashpot arrangements. A basic approach was taken in considering the foil bearing as consisting of a two-degrees-of-freedom system. Differences in amplitude of vibration and phase angles were plotted for the different models. Similar data were obtained separately for the hydrodynamic and structural regimes. The solutions showed substantial differences in the amplitudes and phase angles between the two domains. It is concluded that treatment of foil bearing dynamics should be based on a two-degrees-of-freedom model. Suggestions are made for an analytical and experimental program to put the technology of foil bearings on a sounder basis than has been the case heretofore.
Vibrational Characteristics of Composite Shafts
Authors: Sekhar A. S. , Kumar N. Ravi 
Published: February 2021

Abstract
The present study aims in performing eigenvalue analysis and unbalance response for a rotor system having a composite shaft, modelled based on first order shear deformation theory using finite element method with shell elements. Different materials such as boron epoxy, carbon epoxy and graphite epoxy have been tried for various stacking sequences. From the study it is clear that the stacking sequence and material have great influence on the vibrational characteristics of composite shafts.
Compressibility Effects on the Static and Dynamic Characteristics in Stepped Thrust Gas Film Bearings
Authors: Hashimoto Hiromu , Ochiai Masayukl 
Published: February 2021

Abstract
Hydrodynamic gas film bearings are used for supporting high-speed, lightly loaded rotating machinery. Stepped type gas film bearings are often used for such machinery because of their simple structure, high stability and load carrying capacity. This paper describes the measurements of compressibility effects on the static and dynamic characteristics of stepped thrust gas film bearings. In the experiments, the minimum film thickness, friction torque on the bearing surface and stiffness and damping coefficients of gas films are measured for a range of rotational speed from 10,000 rpm to 20,000 rpm under a constant stator mass and a fixed step height. The measured data are compared with the theoretical results and the gas film compressibility effects on the static and dynamic characteristics of the bearings are discussed. The experimental results agree well with the predicted results based on the compressible lubrication theory.
Design and Testing of a Permanent Magnet Biased Active Magnetic Bearing
Authors: Overstreet Ross W. , Flowers George T. , Szasz Gyorgy 
Published: February 2021

Abstract
Magnetic bearings provide rotor support without direct contact. There is a great deal of current interest in using magnetic bearings for active vibration control. Conventional designs use electrical current to provide the bias flux, which is an integral feature of most magnetic bearing control strategies. Permanent magnet biased systems are a relatively recent innovation in the field of magnetic bearings. The bias flux is supplied by permanent magnets (rather than electrically) allowing for significant decreases in resistance related energy losses. The use of permanent magnet biasing in homopolar designs results in a complex flux flow path, unlike conventional radial designs which are much simpler in this regard. In the current work, a design is developed for a homopolar permanent magnet biased magnetic bearing system. Specific features of the design and results from experimental testing are presented and discussed. Of particular interest is the issue of reduction of flux leakage and more efficient use of the permanent magnets.
Damped Vibration Absorbers Applied to Lateral Modes of Rotating Machinery
Authors: Greenhill Lyn M. , Raven Linda F. 
Published: February 2021

Abstract
Damped vibration absorbers can significantly reduce the amplitude of resonant motion. Normally, these devices are used on machinery that is non-rotating (stationary). However, as this paper demonstrates both analytically and experimentally, a damped absorber can be successfully applied on rotating equipment, particularly on vertical machines, to attenuate lateral resonances. To illustrate this application, a detailed analysis of the damped absorber is presented, focusing on mass ratio, tuning frequency, amount of damping, and speed effects. It is shown that an optimum design can be obtained for use on a rotating machine that parametrically differs from a non-rotating application. Test data is also given illustrating the effectiveness of the concept and design methodology on an actual machine. Recommendations are provided to guide the application of this technology on other rotating machines.
Clearance and Dry Friction Study in a Nonlinear Torsional Vibration of a Rotating Machinery
Authors: Mizutani Kazuki , Md. Zahid Hossain 
Published: February 2021

Abstract
Clearance problem in coupling is often experienced in a rotary torsional vibration system. We tried to analyze the qualitative and quantitative characteristics of torsional vibration by modeling the bilinear spring stiffness with changing friction torque. Symmetric and asymmetric spring stiffness with friction models are developed to investigate the behavioral characteristics of the system for simulations and experiments. The frequency response curves and time response curves with external sinusoidal excitation are observed by several non-dimensional numerical simulations. The thoroughly experiments are done to understand the actual phenomena of torsional vibration, verification of models and adjustability of simulations. The frictional property considered as dry friction in coupling is found very significant parameter to reduce the vibration within a tolerable range in both of the simulations and experiments. The difference between the results getting from simulations and experiments are also demonstrated in this paper elaborately.
Surface Damping Treatment With an Active-Passive Hybrid Constraining Layer
Authors: Liu Yanning , Wang K. W. 
Published: February 2021

Abstract
A new surface-damping concept with an active-passive hybrid constraining layer (HCL) is proposed to improve the damping performance of traditional active constrained layer (ACL) systems. Instead of using a piezoelectric constraining layer, passive and active materials are used together to constrain the viscoelastic material layer. A generic model of the HCL treatment is presented. Non-dimensional equations of motion and boundary and connecting conditions are derived. The closed-form solutions to the equations are developed and analyzed. It is shown that by properly selecting a passive constraining material and assigning appropriate lengths for the active and passive constraining parts, HCL can outperform a system with pure active PZT coversheet, both in terms of its fail-safe ability and closed-loop damping performance.
Adaptive Vibration Isolation for Axially Moving Beams
Authors: Li Yugang , Rahn Christopher D. 
Published: February 2021

Abstract
Manufacture and use of metal bands, sheets, and cables often requires high-speed axial transport of the material. Disturbance forces can cause vibration to propagate through the process due to the bending stiffness coupling between adjacent roller-supported spans. This paper introduces an active pivoting roller that adaptively decouples adjacent spans, thereby isolating a controlled span from bounded disturbances in an adjacent span. The system includes a partial differential equation for the two spans and an ordinary differential equation for the actuator. Exact model knowledge and adaptive isolation controllers, based on Lyapunov theory, regulate the controlled span from bounded disturbances in the adjacent, uncontrolled span. Assuming distributed damping in the uncontrolled span, the exact model knowledge and adaptive controllers exponentially and asymptotically drive the controlled span displacement to zero, respectively, while ensuring bounded uncontrolled span displacement and control force.
Structural Vibration Control by Tuned Distributed Vibration Damper
Authors: Liu Xiaoping , Yang Bingen 
Published: February 2021

Abstract
In this paper a new structural vibration control technique, namely tuned distributed vibration damper (DVD) is studied. Through the analysis of damping amplification factor and the comparison of the frequency response under DVD, conventional damper, absorber, etc., the advantages of DVD in the vibration control are shown. This paper still presents the variable damping DVD, and sets forward the algorithm for selecting the damping coefficients of the variable damper. Numerical results indicate that the tuned DVD can significantly reduce the vibration responses of the structure system.
Characterization of Transient Effects in Rotordynamic Vibrations Using Harmonic Wavelets
Authors: Chancey Valeta Carol , Flowers George T. 
Published: February 2021

Abstract
Traditional vibration analysis methods for rotating machinery consider steady state or near steady state behavior. Perhaps a key to identifying the source of some complex behaviors may be the transients associated with such phenomena. In an effort to develop a means of identifying transients, the application of harmonic wavelets is explored. Simple vibratory models were studied using harmonic wavelet analysis. Several general observations were made with characteristics found in the harmonic wavelet coefficients associated with particular behavior. Specifically, a relationship with transient growth and the absolute value of the harmonic wavelet coefficients was identified. Example experimental data was collected and analyzed from a bench top test rig with a journal bearing exhibiting oil whirl to illustrate the proposed methods.
Wavelet Analysis of Strong Response Records of Building With Bilinear Restoring Force
Authors: Segawa Ryutaro , Yamamoto Shizuo , Sone Akira , Masuda Arata 
Published: February 2021

Abstract
It is very important to estimate the residual life of structures by analysing a strong response quantitatively, because it is necessary to judge whether they can be used or not in the future, after they are damaged by earthquakes. During a strong earthquake, the jerk response of a structure with bilinear restoring force has discontinuity, just when the restoring force changes rapidly from the elastic region to the plastic region. Authors have tried to detect the discontinuity in the jerk by using wavelet analysis and reported a successful paper (Sone, et al., 1994). The final goal of study is to estimate the low cycle fatigue of structure by analysing the observed records in a structure. For this object, the relationship between ductility factor; that is the ratio of peak relative displacement and yield relative displacement, and the number of discontinuity detection is needed. In this paper, the method is proposed to estimate the ductility factor of structure by the wavelet analysis of absolute acceleration response. Wavelet has the ability to detect discontinuity in acceleration response record; furthermore, it is found in this study that the wavelet coefficient is proportional to the velocity at the yield point. Besides, the ductility factor is estimated from the velocity at yield point by using the energy balance between kinetic energy at the yield point and strain energy from the yield point to the maximum relative displacement. Thus, using these relationships, the ductility factor is estimated from wavelet coefficient obtained by wavelet analysis of acceleration response. The applicability of this method is verified through some simulations.
Symbolic Bifurcation Boundaries and Time-Dependent Resonance Sets of Time-Periodic Nonlinear Systems
Authors: Butcher Eric A. , Sinha S. C. 
Published: February 2021

Abstract
A recent computational technique is utilized for symbolic computation of local stability boundaries and bifurcation surfaces for nonlinear multidimensional time-periodic dynamical systems as an explicit function of the system parameters. This is made possible by the recent development of a symbolic computational algorithm for approximating the parameter-dependent fundamental solution matrix of linear time-periodic systems. By evaluating this matrix at the end of the principal period, the parameter-dependent Floquet Transition Matrix (FTM), or the linear part of the Poincaré map, is obtained. The subsequent use of well-known criteria for the local stability and bifurcation conditions of equilibria and periodic solutions enables one to obtain the equations for the bifurcation surfaces in the parameter space as polynomials of the system parameters. Because this method is not based on expansion in terms of a small parameter, it can successfully be applied to periodic systems whose internal excitation is strong. In addition, the time-dependent normal forms and resonance sets for one and two degree-of-freedom time-periodic nonlinear systems are analyzed. For this purpose, the Liapunov-Floquet (L-F) transformation is employed which transforms the periodic variational equations into an equivalent form in which the linear system matrix is constant. Both quadratic and cubic nonlinearities are investigated, and all possible cases for the single degree-of-freedom case are studied. The above algorithm for computing stability boundaries may also be employed to compute the time-dependent resonance sets of zero measure in the parameter space. Two illustrative example problems, viz., a parametrically excited simple pendulum and a double inverted pendulum subjected to a periodic follower force, are included.
Time Varying Control of a Bladed Disk Assembly Using Shaft Based Actuation
Authors: Szász György , Flowers George T. 
Published: February 2021

Abstract
A study of bladed-disk vibration control using magnetic bearings is presented. A key issue is a method for achieving practical controllability for such a system. For a tuned or symmetrically mistuned bladed disk assembly, several vibration modes are coupled only to the axial dynamics. Magnetic thrust bearings generally lack sufficient bandwidth to control even moderately high frequency vibration. A simplified model is developed and used to identify controllable vibration modes. A control strategy based upon deliberately mistuning in a non-symmetric manner is developed. The method presented does not require a thrust bearing for complete controllability of a bladed disk assembly via hub based actuators. However, since the linearized model for such a system has time periodic coefficients, an advanced time period controller is required. Controlling time periodic systems is a significant engineering challenge. One innovative approach that seems to be especially promising involves application of the Lyapunov Floquet (LF) transformation to eliminate time periodic terms from the system state matrices. Traditional control design techniques are then applied and the resulting gains transformed back to the original domain. Some simulation results are presented and discussed to illustrate the method.
Modal Observability of a Cantilevered Beam Using an Array of Point Sensors
Authors: Solook M. , Oyadiji S. O. 
Published: February 2021

Abstract
This paper presents a class of modal sensors built with an array of point sensors. A modal sensor that is able to respond to only a particular vibrating mode of a structure has been designed and tested in this study. The theory of the design is based on orthogonality principle of the modal vectors with respect to the mass matrix. Seven the small piezoelectric sensors (PZT) are bonded on the surface of a cantilevered beam at arbitrary locations. The signals of the sensors are weighted and added together in such a way as to cancel the effect of all the vibrating modes but the mode of interest. The weighting coefficients play the main roll of minimising the response of unwanted modes and maximising the response of the mode of interest. The response of the modal sensors have been fed back separately into a PZT actuator to damp and control just that particular mode. Modal observability of modes 2 and 3 of a cantilevered beam have been investigated and tested experimentally. The experimental results indicate that a specific vibrating mode can be extracted and controlled without any spill over effects on the other modes.
Transient Resonance Oscillations of a Mechanical System With Regard to Non-Linear Damping Effects
Authors: Irretier Horst , Balashov Dmitri 
Published: February 2021

Abstract
Transient, forced vibrations of a mechanical system are considered. Dissipative effects such as material damping, aerodynamic damping and damping at interfaces are taken into account. For the modeling of these effects the set of isolated weakly non-linear single degree of freedom oscillators with damping dependent non-linearities is used. The superposition of their responses approximates the resulting response of the system. The justification of this assumption is discussed. The Krylov-Bogoljubov asymptotic method is applied for the investigation of the transient resonance response. Numerical calculations are provided to demonstrate the validity of the Krylov-Bogoljubov first approximation.
Impact of Flexible Bent Beam Using Component Mode Techniques
Authors: Diaconescu Cristian I. , Marghitu Dan B. 
Published: February 2021

Abstract
The Component Mode Synthesis technique is applied to the impact of a flexible curved bar. The mode functions are selected such that the method can be made computationally as simple as possible, without compromising accuracy. From this point of view, a simple power series is selected. Both transversal and axial elastic deflection are considered. To describe the impact between the elastic beam and the rigid surface the classical Hertzian contact theory and elastio-plastic indentation theory are used.
Impact Induced Internal Fatigue Cracks
Authors: Stépán Gábor , Szabó Zsolt 
Published: February 2021

Abstract
When cracks appear on the surface of a machine element, they can often be treated and the service operation of the machine can be prolonged. When cracks appear inside the material of the corresponding machine element, the internal fatigue crack grows during operation, and when it reaches the surface, the catastrophic failure is already unavoidable. One way to handle this problem is the precise prediction of the repeated tensile stresses in the material, and the results of this method are to be used already at the design stage. The paper deals with the explanation and numerical calculation of tensile stresses related to travelling waves induced by impacts in tups during forging.
Various Substructured Models of a 900 MW Pressurized Water Reactor Under Seismic Excitation
Authors: Rousseau G. 
Published: February 2021

Abstract
This paper describes the investigation made on a 3D Finite Element Model of a 900 MW Pressurized Water Reactor to simulate its response under seismic excitation. This model is used to compute the eigenmodes of this structure at first, then to simulate the transient response of the structure due to a seismic motion. The computation method used is a component mode synthesis method (substrucruring method), which was modified to take into account a method to evaluate the added mass induced by the primary coolant. Three different models of the core were considered. Finally, a non linear transient computation was led with the three different core models and the obtained acceleration spectra on upper and lower core plates are compared with each other and with those of a simplified beam model used for engineering design.