bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stabilization of Inverted Coupled Pendula Using Parametric Excitation
Authors: Osada Reiko , Sato Chikara 
Published: February 2021

Abstract
Parametric stabilization of a single inverted pendulum has been extensively studied using the Mathieu equation and its corresponding stability diagram. The inverted single pendulum may be stabilized using parametric excitation at a specified frequency and amplitude given by a narrow stable region in the Mathieu diagram.
Coupled pendula with parametric excitation or corresponding resonant systems have been studied from mathematical view point (Cesari, 1959; Gambill, 1955; Richards, 1983), from electrical view point (Sato, 1962a; Sato, 1962b; Sato, 1971; Sato, 1975) and from mechanical view point (Sato, 1995). Coupled pendula with parametric excitation have been studied within a limited region by some researchers, including the authors. A study of inverted coupled pendula with parametric excitation has not been performed as far as the authors know. Usually it is assumed that inverted coupled pendula are unstable in the absence of any other stabilizing mechanism such as feedback. One question is whether the inverted coupled pendula could be stabilized only by parametric excitation? The present paper gives an affirmative answer to this question in a limited and finite region. The stability is also examined using the differential equations and other methods.
Parameter Excitation Effects in Gear Dynamics
Authors: Nataraj C. , Whitman Alan M. 
Published: February 2021

Abstract
A pair of spur gears with involute teeth is considered. Nondimensional expressions are derived for the dynamic tooth loading. The resulting parametrically excited equations are analyzed by the procedures of asymptotic analysis. The results show that instability regions can occur leading to large vibrations and failure. These instability regimes are presented as a function of speed and other parameters. Minimum damping values to prevent the instabilities are derived as a function of the gear ratio and number of pinion teeth. In addition, given some inherent damping, response amplitudes of the transmission error are presented as a function of nondimensional parameters.
Robustness of Time-Varying Systems
Authors: Colonius Fritz , Kliemann Wolfgang 
Published: February 2021

Abstract
The dynamics of many mechanical systems can be described, or approximated by smooth vector fields in d-dimensional space Rd. External and internal excitations as well as modeling uncertainties are incorporated in the vector fields as families of (time-varying) functions, possibly with their own dynamics. The problem then is to study the response behavior of the system under the given uncertainty structure. In this paper we analyze the stability of uncertain systems at an equilibrium point, using the concept of stability radii. Roughly, a stability radius is the smallest excitation range such that a (time-varying) perturbation within this range can render the system unstable. Since we consider time-varying perturbations, the precise stability radius of the system is determined by the maximal Lyapunov exponent of the linearization at the equilibrium point. Several examples illustrate the theory and compare the precise stability radius to the one obtained via Lyapunov function techniques.
Natural Frequencies of Stator in Induction Motors
Authors: Suzuki Isao , Noda Shinichi , Itomi Kazunobu , Ishibashi Fuminori 
Published: February 2021

Abstract
Totally enclosed induction motors in which the stator core is pressed in the frame are in general used in industrial machines and manufactured with similar construction around the world. These motors produce a strong electromagnetic noise, which is caused by resonance between the natural frequencies of the stator core and the harmonics of electromagnetic forces. Therefore, it is very important to estimate its natural frequencies at the stage of design. As the first stage of research to estimate the natural frequencies of the stator core pressed into the motor frame, the dual rings were chosen as the object of studies. They are similar to the motor in construction and are easy to use to solve the problems. The purpose of this study is to investigate the effects of the tight fit to the natural frequencies and to find an analytical method by FEM. The authors have found that the introduction of spring elements with radial and circumferential spring constants at the contact surfaces provides accurate calculated results of the natural frequency by FEM. This paper describes about the spring constants obtained from experiments and analysis. As a result, when the spring constants in the radial direction are infinite and those in the circumferential direction are variable, it is clear that the spring constants for natural frequency analysis by FEM were expressed as a function of contact pressure on the contact surfaces. In the second stage, the measurement and calculation of natural frequency in the actual stator core with a frame was performed, and these results showed good agreement. These spring constants will be useful in FEM analysis of stator cores pressed into cylindrical induction motor frames.
A Study on Electro-Magnetic Auto-Balancing System and its Balancing Method
Authors: Wang Xixuan , Zeng Sheng 
Published: February 2021

Abstract
A new type of on-line automatic balancing system — the electromagnetic balancing system is concerned in this composition. The balancing head in this system consists of two stators and two slide plates. Each slide plate, on which there is a correction mass, can be driven to move relative to the shaft in single direction by the electromagnetic force. The positions of both masses are able to be detected conveniently by corresponding sensors. The balancing method is a conventional one. The moving procedure of the correction mass to meet the slide’s single -direction rotating character is described. Experiment results of its application to flexible rotor are also included.
Influence of Bearing Alignment on Vibration of Multi-Span Rotor
Authors: Hirano Toshio , Yamashita Tatsuo 
Published: February 2021

Abstract
This paper describes the influence of bearing alignment (vertical position) on vibration of multi-rotor-bearing system. The rotor-bearing system used in this study consists of three rotors and six bearings. It is designed to have the equivalent dynamic characteristics to the turbo-generator-systems for utility power generation plant. And it is equipped with alignment setting devices which can set the bearing alignment in vertical direction precisely without disassembling the test rig.
It was confirmed that bearing alignment affects the rotor vibration. Some critical speeds and their peak amplitudes change. When the bearing alignment changes, the load of the bearing changes and it affects oil film characteristics. The calculated results considering this agree with the test results. The effect of the bearing alignment on the rotor vibration becomes large when the bearing load is about zero.
Gyroscopic Effects of a Vibrationally Isolated Rotating Disk and Shaft
Authors: Margolis Donald L. 
Published: February 2021

Abstract
An aircraft engine is an example of a rotating machine whose rotating imbalance will be transmitted as vibrational energy into the structure to which it is attached. There is considerable interest in understanding this energy transmission in order to design mounting systems, both passive and active, which can control this transmission the best possible way in order to reduce structurally borne noise in the cabin. It is a well established fact in acoustics[1] that in order to reduce perceived sound at the listener, the noise transmission path must be severed by 1) eliminating the source of the disturbance (usually difficult if not impossible), 2) preventing propagation of energy into the structure and ultimately to structural surfaces, 3) preventing radiation of sound energy from vibrating surfaces, and 4) preventing radiated sound from reaching the listener. In this paper we address only the prevention of energy transmission from the source into the supporting structure through use of some type of mounting system.
Flexural Vibration of a Viscoelastic Sandwich Beam in its Plane of Lamination
Authors: Nayfeh Samir A. , Slocum Alexander H. 
Published: February 2021

Abstract
When a laminated sandwich beam consisting of alternating elastic and viscoelastic layers bends in the plane normal to its plane of lamination, the relatively compliant viscoelastic layers are sheared between the adjoining elastic layers and energy is dissipated. This mechanism, known as constrained-layer or shear damping, is a proven method for damping flexural vibration, but only in the plane normal to the plane of lamination. For vibration parallel to the plane of lamination, the elastic layers need not deflect together, and the viscoelastic layers are sheared when adjoining elastic layers undergo different deflections. This mechanism of damping is discussed herein.
In this paper, we study the vibration of a symmetrically laminated five-layer sandwich beam in its plane of lamination. Taking the viscoelastic material to have frequency-independent hysteretic damping, we derive a boundary-value problem governing steady harmonic motion of the sandwich beam and then obtain its discretized counterpart. For the particular case of a beam with simply supported elastic layers, we obtain the resonant frequencies and loss factors of the composite beam, and study their dependence on geometric and material properties.
Transient Response of Distributed Parameter Systems
Authors: Zhou Jianping , Feng Zhigang 
Published: February 2021

Abstract
A semi-analytic method is presented for the analysis of transient response of distributed parameter systems which are consist of one dimensional subsystems. The system is first divided into one dimensional sub-systems. Within each subsystem, replacing differentials on time t by finite difference, the governing partial differential equations are reduced to difference-differential equations. The solution of derived ordinary differential equations is obtained in an exact and closed form by distributed transfer function method and represented in nodal displacement parameters. Assemling global equilibrium equations at each nodes according to displacement continuity and force equilibrium requirements gives simutaneous linear algebraic equations. Numerical results are illustrated and compared with that of finite element method.
Floating Slab Railway Track for Isolation of Vibration: Models of Infinite Length
Authors: Forrest James A. 
Published: February 2021

Abstract
Vibration transmitted from underground railways into nearby buildings is an increasingly significant problem affecting high-value residential and commercial developments. Various forms of vibration isolation are used in underground railways, one of which is the ‘floating slab track’. Rails are fixed directly to a massive concrete slab which in turn rests on a resilient mounting (usually rubber bearings or steel springs) so isolating the track from the tunnel invert. The effectiveness of vibration attenuation does not compare well with the simple mass-spring models typically used in the design of floating slab track.
This paper develops a model for floating slab track by conceptualising the track as two infinite beams (representing the rail and the concrete slab) separated by elastic layers representing the resilient elements used in floating slab track construction. A dynamic model for a finite-length unit of track is obtained from this physical model by the dynamic-stiffness-matrix method. A repeating unit method is utilised to create track models of infinite length from the finite track unit, an approach which much reduces the computation required. A concept of total force transmitted to the ground for a given set of inputs on the rail is developed, and the effect of various track parameters on the transmitted force is examined.
Self-Excited Harmonic and Solitary Waves in a Spinning Disk (With Video Presentation)
Authors: Boulahbal Djamil , Crandall Stephen H. 
Published: February 2021

Abstract
Solitary waves have been reported in many applications in physics and engineering. While these waves are of relatively simple shape, the mechanisms that control them are highly nonlinear and often not completely understood. In this study a flexible disk spinning against a stationary base plate and interacting with the surrounding air-field exhibits both harmonic as well as solitary waves and this, depending on the spin rate of the disk. Preliminary experimental results indicate that-in contrast with harmonic waves, the speed with which the solitary waves propagate does not depend upon the spin rate of the disk. This appears to be a lock-in phenomenon that is characteristic of well known nonlinear fluid-structure interaction problems. Furthermore, and despite the presence of dispersion in the fluid/disk medium, all solitary waves propagate with the same speed. While a full model capable of predicting these solitons has yet to be developed, a discussion is presented on both the linear model that is currently accepted in the literature, as well as on the nonlinear mechanisms that may control such interesting waves.
Stability and Bifurcations in a Model of Phase Transitions With Order Parameter
Authors: Sikora Janusz , Cusumano Joseph P. , Jester William A. 
Published: February 2021

Abstract
A one-dimensional model of phase transitions with convex strain energy is investigated within the limits of nonlinear bar theory. The model is a special case of a coupled field theory that has been developed by Fried and Gurtin to study the nucleation and propagation of phase boundaries. The system of governing equations studied here consists of a wave equation coupled to a nonlinear reaction-diffusion equation. Using phase plane methods, the equilibria of the system have been constructed in order to obtain the macroscopic response of the bar and the bifurcation diagram. It is demonstrated that a large number of coexisting spatially periodic, inhomogeneous solutions can occur, with the number of these solutions being inversely proportional to the diffusion coefficient in the reaction-diffusion subsystem. A stability analysis of the equilibria is presented.
Commercialization of Active Isolation for Jet Aircraft
Authors: Southward Steve C. , Ivers Douglas E. , Nicholson Geoff C. 
Published: February 2021

Abstract
Active Noise and Vibration Control (ANVC) technology is a proven solution for noise and vibration problems in aircraft. The challenges in commercializing this solution range from the development issues of choosing the best actuation, sensor, and control technology to obtaining sufficient flight test time and satisfying FAA requirements. This paper examines significant case histories in the progression of the Lord active vibration control program from conception to market. Throughout the development program, several important discoveries were made regarding the performance, reliability, and economics of Active Isolation Systems (AIS) in jet aircraft. First, practical speaker-based solutions cannot achieve global acoustic noise cancellation for engine tones above about 200 Hz. A comparatively small array of structural actuators placed in the dominant transmission path, such as in or near the engine mounts, are capable of global cancellation in the cabin up to at least 500 Hz. Second, the performance is generally better when cabin microphones are used as error sensor inputs because the AIS control system can compensate for flanking paths better than if accelerometers are used as error sensors. Third, when the actuators are placed in the dominant transmission path and close to the vibration source, the control system will simultaneously achieve global acoustic noise reduction in the cabin and vibration reduction in the aircraft structure without affecting the engine casing vibration levels.
Identification of Fault Signals in Rotating Machinery Using Higher Order Time Frequency Analysis
Authors: Lee Sang-Kwon , White Paul R. 
Published: February 2021

Abstract
Impulsive acoustic and vibration signals within rotating machinery are often induced by irregular impacting. Thus the detection of these impulses can be useful for fault diagnosis. Recently there is an increasing trend towards the use of higher order statistics for fault detection within mechanical systems based on the observation that impulsive signals tend to increase the kurtosis values. We show that the fourth order Wigner Moment Spectrum, called the Wigner Trispectrum, has superior detection performance to second order Wigner distribution for typical impulsive signals found in a condition monitoring application. These methods are also applied to data sets measured within a car engine and industrial gearbox.
A Singular-Value Decomposition Method for Updating the Analytical Model
Authors: Xianmin Zhang 
Published: February 2021

Abstract
Based on the theory of singular-value decomposition and the matrix approximation technique, an analytical model updating method using the identified model parameters is developed. Firstly, The identified modal matrix is decomposed by means of singular-value decomposition technique. The general updating equations for the analytical model are obtained according to the decomposition results, the eigenequation of the system, and the modal orthogonality relations. Secondly, the best matrix approximation solution for the updating equations is definited. The existence and uniqueness of the best approximation relative to the analytical model are studied. The concrete form of the best modification and two algorithms are presented. Examples demonstrate that the analytical model modification method developed in this paper possesses high modificatory accuracy comparing with some other methods. The method possesses the ability to modify the large error models.
Direct Estimation of Nonlinear Joint Parameters
Authors: Zhang X.-N. , Fritzen C.-P. , Jennewein D. 
Published: February 2021

Abstract
A method is proposed to identify nonlinear joint characteristics of a structure by means of measured data. The relation between the joint force function and the response of the system is established by use a position index matrix. The parameters of the joint force function are estimated by means of a least squares strategy. The parameter estimation can be done in time domain and also in frequency domain. Especially, when there is no excitation on the joint degrees of freedom only a part of the responses of the system are needed to identify the nonlinear joint parameters. The validity of the method is demonstrated by computer simulations.
Mathematical Model of a Buckled Spring for Vehicle Active Suspension
Authors: Yao Shiping , Morgan Colin , Leighton Nigel J. 
Published: February 2021

Abstract
The basic characteristic of a conventional spring is that of a constant rate, that is a linear force-displacement relationship. If, however, a flat, thin leaf spring is end-loaded past its buckling point it will deform into a curve and the resulting force-displacement relationship can be made virtually flat; that is a very low effective rate is seen, once the buckling force is exceeded.
A novel form of automotive active suspension system proposed by Leighton & Pullen (1994) relies upon the “buckled spring” element acting through a variable geometry wishbone assembly to provide wheel to body forces that are controllable by a low power actuator but are virtually independent of wheel to body displacement.
The dynamic behavior of the spring element is also significant, since resonance effects may affect the vibration isolating properties of the suspension system and may result in unstable modes of motion. This paper presents a rigorous derivation of the static and dynamic characteristic of the spring element and of the effect of design compromises that are essential for practical application.
Comparison of the experimental and simulation results shows that the simulation can be used to predict the static and dynamic performance of the spring.
Investigation of Stick-Slip Phenomenon Using a Two-Disk Friction System Vibration Model
Authors: Larsson Henric , Farhang Kambiz 
Published: February 2021

Abstract
A lumped parameter model is presented for studying the dynamic interaction between two disks in relative rotational motion and in frictional contact. The contact elastic and dissipative characteristics are represented by equivalent stiffnesses and damping coefficients in the axial as well as torsional directions. The formulation accounts for the coupling between the axial and angular motions by viewing the contact normal force to be the result of axial behavior of the system.
The model is used to investigate stick-slip behavior of a two-disk friction system. In this effort the friction coefficient is represented as an exponentially decaying function of relative angular velocity, varying from its static value at zero relative velocity to its kinetic value at very high velocities. This investigation result in establishment of critical curve defining two parameter regions: one in which stick-slip occurs and that in which stick-slip does not occur. Moreover, the onset and termination of stick-slip, when it occurs, is related to the highest component frequency in the system. It is found that stick-slip starts at a period nearly equal to that of the highest component frequency and terminates at a period almost three times that of the highest component frequency.
An Algorithm for Systematic Generation of Subscales With Application to a Two-Disk Friction System
Authors: Zargar Yasir S. , Farhang Kambiz 
Published: February 2021

Abstract
In this paper we propound an algorithm for development of scale models of complex physical systems. The algorithm systematically treats the three sub-tasks of scaling, which includes creation of dimensionless parameters, application of scaling law and similitude requirements, and determination of scale factors. Optimum set of dimensionless parameters are obtained in which the pertinent variables with only integer powers appear. This is achieved by seeking integer solutions to appropriate set of linear algebraic equations in the powers, using a simple iterative technique.
Application of the scaling law and similitude requirements along with a logarithmic transformation leads to a set of linear algebraic equations in the scale factors. In many applications, over-constrained systems are resulted for which true scaling can not be achieved. Two techniques are introduced in the proposed algorithm which circumvent the difficulty in treating over-constrained systems. The first method is based on a relaxation technique, whereas the second method introduces the concept of auxiliary variables to obtain the least squares solutions to the new set of linear equations. The effectiveness of the algorithm is demonstrated through its application in finding scale models of a two disk friction system.
Dynamic Response of Compliant Mechanisms Using the Pseudo-Rigid-Body Model
Authors: Lyon Scott M. , Evans Mark S. , Erickson Paul A. , Howell Larry L. 
Published: February 2021

Abstract
The pseudo-rigid-body modeling technique is used to simplify the nonlinear analysis of compliant mechanisms. This paper presents the first work that investigates the possibility of using the pseudo-rigid-body model to predict the dynamic response of compliant mechanisms. Four different configurations of the parallel-guiding mechanism are modeled and tested, as well as two configurations of compliant straight-line mechanisms. The model predictions of the first natural frequencies were compared with experimental results for all six mechanism configurations. The model predictions are within 9% of the experimental results for all cases.