bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transient Response Technique Applied to Active Magnetic Bearing Machinery During Rotor Drop
Authors: Ishii Toshiyasu , Kirk R. Gordon 
Published: April 2021

Abstract
The active magnetic bearing (AMB) is a relatively new technology which has many advantages compared with conventional bearing design. In an AMB system, the rolling-element back-up bearings are indispensable to protect the magnetic bearing rotor and stator, and other stationary seals along the rotor shaft. In this paper, a theoretical formulation is proposed and solved numerically to examine the transient response of the flexible rotor, from the time just previous to the AMB shuts down and including the rotor drop onto the back-up bearing. The backward whirl of the rotor, which may lead to the destructive damage of the machiner, has been analytically predicted at very light support damping and very high support damping. Also, the vibration due to the non-linearity of the contact point geometry has been included in the analysis. The influence of the support damping on the displacement of the disk and also the contact force between the journal and the inner-race of the back-up bearing have been computed for various rotor system parameters.
The Effect of Sensor Location on the Forced Response Characteristics of Rotors With Active Magnetic Bearings
Authors: Rawal D. , Keesee J. , Kirk R. Gordon 
Published: April 2021

Abstract
This paper presents a modification of existing transfer matrix methods for rotor analysis, to predict the response of rotor systems with active magnetic bearings. The position of the magnetic bearing sensors is taken into account and the effect of changing sensor position on the vibrational characteristics of rotor systems is studied. The results for a simple two-mass rotor system are presented as plots of critical frequency vs. sensor position and amplitude at critical frequency vs. sensor position. A typical eight stage centrifugal compressor rotor is analyzed using the modified transfer matrix code and the results are presented as plots of amplitude vs frequency for different cases of sensor location.
Parameter Identification of Non-Linear Impact Damper
Authors: He Kang-Yu , Yuan Xiao-Xu 
Published: April 2021

Abstract
In this paper, we presented a mew mechanical model of an impact damper based on the theoretical analyses and experiments. We also presented a method of identifying the parameters of the non∼linear method of an impact system by means of microcomputer calculations. The method of identification presented in this paper has been proved byour experiments. These works supply the theoretical foundations of designing and calculating for impact damper.
An Efficient Method for Calculating Damped Critical Speeds of Rotor-Bearing Systems
Authors: Wang D. Z. , Taylor D. L. 
Published: April 2021

Abstract
This paper describes an analytical approach for calculating the damped critical speeds of multi-degree-of-freedom rotor-bearing systems. It is shown that to calculate the critical speeds is equivalent to finding the roots of a proposed matrix algebraic equation. The technique employes a Newton-Raphson scheme and the derivatives of eigenvalues. The system left eigenvectors are used to simplify the calculations. Based on this approach, a general-purpose computer program was developed with a finite element model of rotor-bearing systems. The program automatically generates system equations and finds the critical speeds. The program is applied to analyze a turbomachine supported by two cylindrical oil-film Journal bearings. The results are compared with reported data and the agreements are very good.
Concepts and Application of the Large Mass Method in Vibration Analysis of SSME Engine Structures
Authors: Shen Lawrence K. 
Published: April 2021

Abstract
The large mass method is used to obtain the total dynamic response of structures using excitations prescribed at base points. This paper presents the concepts and application of the method derived and used in the analysis of Space Shuttle Main Engine (SSME) structures. The theory and limitations that make the method work are discussed first. The effect on the system responses, including the addition of nonelastic (rigid body and large mass) modes due to the presence of the large masses, is then covered. The resonance concept leads to the establishment of criteria to define the analytic limit of the excitation frequency. The significance of the pseudostatic component and the relationship with the nonelastic modes are investigated in a simple system. The study shows that the frequency ratios, system properties, and the similarity between excitations are key factors to make the pseudostatic term more prominent. Examples with sinusoidal excitation are used to demonstrate the concepts. The method is finally applied in the SSME structures with excitations compiled from engine test data. Results are compared to further demonstrate the concepts and define the future needs for improved test data.
Vibration Confinement Phenomena in Disordered, Mono-Coupled, Multi-Span Beams
Authors: Bouzit Djamel , Pierre Christophe 
Published: April 2021

Abstract
The effects of small, periodicity-destroying irregularities on the dynamics of multi-span beams are examined. It is shown that minute deviations of the span lengths from an ideal value alter qualitatively the dynamic response by localizing vibrations and waves to small geometric regions. These confinement phenomena are studied over a wide frequency range for beams resting on simple supports and with variable interspan coupling. Approximations of the localization factor (the average rate of spatial exponential decay of the vibration amplitude) are derived by statistical perturbation methods and validated by Monte Carlo simulations. If the interspan coupling is strong, localization effects are weak and of no practical significance for most engineering structures. On the other hand, localization is severe for small interspan coupling. Confinement is also generally stronger near the edges of frequency passbands and increases nearly linearly with frequency from passband to passband. This means that strong localization occurs at high frequencies, even for large static coupling between spans. De-localization is also observed at very high frequencies.
In-Plane Vibration of Simply Supported-Simply Supported Circular Ring Segments
Authors: Azimi S. 
Published: April 2021

Abstract
The general in-plane vibration problem of circular ring segments having linear and torsional elastic constraints at the ends has been studied. One of the interesting cases of concern for which there exists an exact solution is the case where the linear and torsional spring stiffnesses in the circumferential direction become zero (Ku = 0, Kt = 0) and the linear spring stiffness in the radial direction becomes infinity (Kw = ∞). This case is the so-called simply supported-simply supported case. The general form of the equations of motion of circular rings with the proper boundary conditions at the ends have been employed to investigate the vibration of the ring segment. Results for natural frequencies and mode shapes for different angles of the segment have been presented.
The Fourier Ultrasonic Resonant Transformers
Authors: Jwo Chin-Hung 
Published: April 2021

Abstract
To achieve a high magnification of amplitude by using an ultrasonic resonant transformer, one may choose from several different tapering rods. The basic transformers include conical, hyperbolic (catenoidal), exponential, multi-step cylindrical, and Fourier, etc. The Fourier transformers are better in the characteristics of higher bending stiffness and lower maximum strain over other single section transformers. The higher order Fourier transformers presented in this paper give more flexibility in optimization for desired mechanical characteristics.
Axisymmetric Free Vibration of Thick Orthotropic Hemispherical Shells Under Various Edge Conditions
Authors: Chao C. C. , Tung T. P. , Chern Y. C. 
Published: April 2021

Abstract
Axisymmetric free vibration of moderately thick polar orthotropic hemispherical shells are studied under the various boundary conditions of sliding, guided pin, clamped and hinged edges. Based on the improved linear elastic shell theory with the transverse shear strain and rotatory inertia taken into account, the dynamic equilibrium equations are formulated and transformed into the displacement form in terms of mid-surface meridian and radial displacements and parallel circle cross-section rotation. These partial differential equations are solved by the Galerkin method using proper Legendre polynomials as admissible displacement functions with the aid of the orthogonality and a number of special integral relations.
Numerical results of the present theory compare well with existing data, which is available only in the isotropic theories. Good convergence is obtained for natural frequencies and mode shapes. Study of the effects of thickness and modulus ratio reveals higher frequencies for the thicker and/or stiffer shells with E\ oriented parallel to the meridians. Ranking of the natural frequencies descends in the order of guided pins, sliding, clamped and hinged edges in general. Also seen are the effects of transverse shear strain from the mode shapes with clamped and sliding edges on the slant. For the guided pin and sliding edges, frequencies increase fast as thickness increases so that new fundamental modes are generated in filling up the “frequency gap”. These are the new discoveries in the field of anisotropic shells, as a result of polar orthotropy of shell material and construction.
On the Problem of Multiple-Excitation Multiple-Response Stochastic Structural Dynamics Identification
Authors: Lee Jae-Eung , Fassois Spilios D. 
Published: April 2021

Abstract
In this paper an effective approach for the identification of stochastic structural systems from multiple-excitation multiple-response forced vibration data, is introduced. The proposed approach represents a novel extension of the method of Lee and Fassois (1990b), that enables it to: (a) Operate on either vibration displacement, velocity, or acceleration data records, and, (b) perform accurate analysis of the estimated structural model by using a currently introduced exact and physically meaningful Dispersion Analysis methodology. These new features, combined with its other important properties, make the proposed approach not only capable of overcoming the limitations of current techniques, but, also, a comprehensive procedure for multiple-excitation multiple-response stochastic structural dynamics identification.
The excellent performance characteristics of the proposed approach are finally verified via numerical simulations with structural systems characterized by well-separated and closely-spaced modes, as well as data corrupted at various noise-to-signal ratios. Comparisons with the Eigensystem Realization Algorithm (ERA), through which the limitations of deterministic methods are illustrated, are also presented.
A Transfer Matrix Method for Nonlinear Vibration Analysis of Rotor-Bearing Systems
Authors: Lu Songyuan 
Published: April 2021

Abstract
In this paper, a transfer matrix method is presented for calculating nonlinear vibration of rotor-bearing systems. The method is based on the Riccati transfer matrix method and two direct integration schemes: Houbolt and Wilson-0. Since this method uses matrices with small size and new, more simple recurrence formulae, the calculation results, which do not contain the significant computation roundoff error accumulation, have been obtained and very short time is needed. Nonlinear vibration calculation becomes essential to actual rotor-bearing systems of engineering importance. This method is concise, explicit and short, and it can be executed on personal computers of present configurations.
Frequency Error Estimation in Nonlinear Systems Using Beats
Authors: Jettappa Richard Rodrigues , Sharma Seshadri 
Published: April 2021

Abstract
Real systems are inherently non-linear. True linear behaviour is rare. On the other hand, most of our models are linear. It is relatively easy to solve for a linear system compared to the corresponding non-linear system. This dichotomy between theory and practice is all pervasive. It is highly desirable that an analyst should be able to check the closeness of the predicted behavior with the actual behaviour of the system. In this paper we outline the method of beats towards this end. Even though the phenomenon of beats is well known to scientific community, its use in error analysis is unknown. This is the essence of the present paper.
Localized and Non-Localized Normal Modes in a Strongly Nonlinear Discrete System
Authors: Vakakis Alexander F. 
Published: April 2021

Abstract
The free oscillations of a strongly nonlinear, discrete oscillator are examined by computing its “nonsimilar nonlinear normal modes.” These are motions represented by curves in the configuration space of the system, and they are not encountered in classical, linear vibration theory or in existing nonlinear perturbation techniques. For an oscillator with weak coupling stiffness and “mistiming,” both localized and nonlocalized modes are detected, occurring in small neighborhoods of “degenerate” and “global” similar modes of the “tuned” system. When strong coupling is considered, only nonlocalized modes are found to exist. An interesting result of this work is the detection of mode localization in the “tuned” periodic system, a result with no counterpart in existing theories on linear mode localization.
Amplitude Dynamics of an Autoparametric Two Degree-of-Freedom System
Authors: Bajaj Anil K. , Johnson Joseph M. , Chang Seo Il 
Published: April 2021

Abstract
Forced, weakly nonlinear oscillations of a two degree-of-freedom autoparametric system are studied for resonant excitations. The method of averaging is used to obtain first order approximations to the response of the system. In the subharmonic case of internal and external resonance, where the external excitation is in the neighborhood of the higher natural frequency, a complete bifurcation analysis of the averaged equations is undertaken. The “locked pendulum” mode of response bifurcates to coupled-mode motion for some excitation frequencies and forcing amplitudes. The coupled-mode response can undergo Hopf bifurcation to limit cycle motions, though it requires mistuning from the exact internal resonance condition. The Hopf bifurcation sets are constructed and dynamic steady solutions of the amplitude or averaged equations are investigated using software packages AUTO and KAOS. It is shown that both super- and sub-critical Hopf bifurcations arise and the limit cycles quickly undergo period-doubling bifurcations to chaos. These imply chaotic amplitude modulated motions for the system.
Investigation of Parametric Vibration Stability in Slider-Crank Mechanisms With Elastic Coupler
Authors: Farhang K. , Midha A. 
Published: April 2021

Abstract
An analytical model for investigating parametric vibration stability of slider-crank mechanisms with flexible coupler is presented. The continuous model is formulated to account for initial curvature as well as internal material damping in the coupler. The governing partial differential equations are reduced to a system of ordinary differential equations in terms of the time-dependent modal coefficients. Floquet theory is employed to determine the effects of geometric stiffening as well as relative component mass on parametric stability of mechanism response. Results indicate the existence of instability regions due to combination resonances of various modes. In addition, the stability characteristics of the mechanism is found to improve when slider forces are directed away from the crank-ground pin (i.e. the connecting rod is in tension), and when a relatively smaller slider mass is used.
Cutting Process Stability of a Boring Bar With Active Dynamic Absorber
Authors: Tewani Sanjiv G. , Rouch Keith E. , Walcott Bruce L. 
Published: April 2021

Abstract
Active vibration control has been considered in the past as a viable means of controlling machine tool chatter in the boring bar. Theoretically, it has been shown that the amplitude of vibrations of the machine tool can be substantially reduced using such an active control system.
This paper looks into the cutting process stability of a boring bar equipped with an active vibration control device. An equivalent lumped mass model of the boring bar is considered. A cutting process model that considers the dynamic variation of shear and friction angle responsible for the self-excited vibration during machine tool chatter is considered. The model also considers the regeneration effect during the cutting process. Stability charts have been obtained in the form of maximum allowable width of cut as a function of cutting speed. A comparison of the stability boundaries of the boring bar with no control, with passive dynamic absorber and with active dynamic absorber is made. A substantial increase in the region of stable operation of the boring bar with active dynamic absorber is observed.
Instability and Collapse Behavior of a Seismic Structure
Authors: Cheng Franklin Y. , Ger Jeng-Fuh 
Published: April 2021

Abstract
The collapse behavior of a 22-story steel building during the September 19, 1985 Mexico earthquake is investigated by studying hysteretic behavior, ductility factors of individual structural components, and overall instability of the building. The hysteresis models for truss-type girders, bracing members, and box columns to be used in the inelastic analysis of this building are developed. A series of inelastic analyses have been performed for the building by using the multicomponent seismic input of actual Mexico City earthquake records. It was found that the structural response exceeds the original design ductility of this building because most girders in the building have suffered large ductilities. Due to the load redistribut-ion effects from the ductile-failed girders, local bucklings developed at many columns on floors 2, 3, and 4. Therefore, most columns on floors 2 through 4 lost their load carrying capacities and rigidities which then caused the building to tilt and rotate. As a result, more columns on floors 5 through 7 developed local buckling and more bracing members buckled. It is believed that ductile failures of girders combined with the local bucklings of columns in the lower part of the building resulted in significant story drift, building tilt, P-A effect, and the failure mechanism.
A Finite Element Modeling of Higher Order Shear Deformation Theory on a Plate Vibration Problem
Authors: Chang Chiang-Nan , Chen Thien-Rhei 
Published: April 2021

Abstract
Higher order Shear Defamation Plate Theories (HSDPT) are improved theories over Mindlin plate theory because their assumptions are closer to reality. However, they are seldom used in solving ordinary engineering works. This is due to the fact that mathematical formulations and computations are so lengthy that time and efforts required are close to solving a exact 3-D model.
For problems involving sharp stress variation, higher order theories are anticipated to give better results. The combination of HSDPT and Finite Element Modelings are especially attractive because a finite element modeling is much simpler.
The current research develops a finite element model on the higher order shear deformation theory. A plate vibration problem was solved. The plates contain square interior cutout. Stress distributions are much complicated than whole plates. Results of HSDPT are compared with FSDPT (First order Shear Deformation Plate Theories) and CPT (Classical Plate Theory).
Better accuracies are obtained by using the HSDPT.
Force Reconstruction Using the Inverse of the Mode-Shape Matrix
Authors: Carne Thomas G. , Bateman Vesta I. , Dohrmann Clark R. 
Published: April 2021

Abstract
A new technique for force reconstruction is developed. To estimate the externally applied force, this technique sums the weight-scaled acceleration signals, and is referred to as the Sum of Weighted Accelerations Technique (SWAT). To obtain the scalar weights the inverse of the mode shape matrix is used. Application of this technique is illustrated with both numerical calculations using a mass-spring model and experimental data from a structure impacting a rigid barrier.
The Prediction of the Substructure and System Modes by the Extended Complex Mode Indication Function
Authors: Lin Albert C. Y. , Tsuei Y. G. 
Published: April 2021

Abstract
The Modal Force Technique (MFT) which directly works with the substructure frequency response functions at connecting joints to predict the dynamical behavior of the synthesized system has been recently developed. The key point of the MFT is to formulate the Modal Force equation by eliminating the physical coordinates and retaining the forces in accordance with the boundary conditions of geometric compatibility and forces equilibrium at connecting joints. The Modal Force matrix in the Modal Force equation contains the information of the substructure modes and the synthesized system modes. To predict the natural frequency and damping of the substructure and the synthesized system modes, an Extended Complex Mode Indication Function for MFT is investigated.
A New Method for the Pile Quality Detection: Estimation of the Shape of a Pile
Authors: Mu Rangke , Zhao Chun-sheng 
Published: April 2021

Abstract
In this paper, a new method for the pile quality detection is developed, which is the Estimation of the Shape of a pile (also called the ESP method). It has considered many defects and their high time reflections in a pile by using echo technique. At this we have carried out the computer simulation and the field tests by transient impact excitation on the head of the pile. It is proved that the ESP method is feasible for the pile quality detection, and the size, type, and site of a defect in a pile can be accurately determined by using it.
The Extraction of the Fault Signature of Gearboxes Using Optimum Complex Envelope Spectrum
Authors: Wan Xiaomao , Zhao Chun-sheng 
Published: April 2021

Abstract
In this paper, a new technique using optimum complex envelope spectrum is proposed in order to diagnose the gearbox fault, and its fundamental principle is described. The result of simulated tests illustrates that method proposed is excellently sensitive to the gearbox fault and is more effective than both the power spectrum analysis and the cepstrum analysis.
An Approach to Simultaneous Optimum Design of Structure and Control Systems by Sensitivity Analysis
Authors: Kajiwara I. , Nagamatsu A. 
Published: April 2021

Abstract
An approach is proposed for simultaneous optimum design of a structure and feedback control system by sensitivity analysis for the following two purposes. One is to decrease both the response and the control force of the system under a white noise disturbance force. The other is to modify the gain, the pole and the zero-point to the desirable values. The weighting constant of the feedback control system, and mass, stiffness, shape, dimension, etc. of the structure are adopted simultaneously as the design variables. The proposed method is verified by a model simulation.
The Broad-Band Active Vibration Control Systems With Controllable Damping for Non-Conservative Self-Excited Structures
Authors: Kravchenko S. V. 
Published: April 2021

Abstract
The features of active vibration control applied to self-excited non-conservative mechanical systems (such as structures subject to flatter, rotor machines, tubes conveying fluid) are discussed. It has been found that the optimal control strategy is the broad-band compensation of the dynamic force reactions combined with narrow-band damping of the mechanical structure resonant vibration. Some problems of feedback synthesis are solved analytically for these systems. The importance of symmetry and asymmetry for the active vibration control systems is discussed. In the case of self-excited systems, it is possible to use the small asymmetry of the control system for the stabilization of the dynamic process.