bluuebunny/crossref_metadata_2025_split huggingface dataset:
Scattering and Transmission of Mixed-Mode Waves in Delaminated Thick Composite Beams
Authors: Mahapatra D. Roy , Gopalakrishnan S. , Sankar T. S. 
Published: November 2020

Abstract
A spectral finite element model is developed to study scattering and transmission of axial-flexural-torsional coupled waves in multi-sitedelaminated thick composite beams. The analysis may find its suitability and superiority to capture the high frequency dynamics of laminated composite structure in vibrating environment and for health monitoring in combination with non-destructive test data. Spectral finite element considering first order shear deformation is used to model the delaminated segments along the span of the beam, as well as the delaminated ply-groups in thickness direction. This spectral element is derived from exact solution to the 3D governing wave equations in Fourier domain. As aresult, the thin sublaminates and beam segments do not lock. Spatial discretization is carried out in a similar way as in conventional finite element method. The major differences from conventional finite element method are (1) the transformation of all the fields from temporal to frequency domain is carried out using Fast Fourier Transform (FFT) algorithm, (2) the global system is solved at each frequency step (3) fine meshing at the delamination tip to capture the crack-tip singularity (as in conventional finite element discretization) is not required (4) the overall system size becomes many order smaller than that in conventional finite element methods. The study essentially includes unsymmetry induced due to ply orientations and due to multiple delamination across beam thickness. A case study is presented to show the effect of wave transmission and scattering by a single through delamination in unidirectional composite beam.
An Experimental Study of the Nonlinear Dynamics of a Portal Frame Foundation for a Non Ideal Motor
Authors: Brasil Reyolando M. , Garzeri Flávio J. , Balthazar José M. 
Published: November 2020

Abstract
An experimental approach to the study of forced nonlinear vibrations of portal frames excited by nonideal motors is presented. The interaction of the structure with the excitation source may lead to the occurrence of interesting phenomena during the forward and reverse passage through the several resonance states of the systems. As an application, a rotating unbalanced motor with limited power is considered mounted on the horizontal beam of a simple portal frame. As a starting point the problem is reduced to a three-degree-of-freedom model, and its equations of motion, derived elsewhere via a Lagrangian approach, are presented. Next, experimental work on a prototype is described. The results show the expected phenomena associated with the passage through resonance with limited power. Further, for a two-to-one relationship between the frequencies associated with the first symmetric mode and the sway mode, modal saturation and energy transference due to internal coupling and external resonance are observed at certain levels of excitation.
Experimental Non-Linear Model Updating Applied in Cylindrical Journal Bearings
Authors: Cavalca Katia Lucchesi , Idehara Sérgio Junichi , Dedini Franco Giuseppe , Pederiva Robson 
Published: November 2020

Abstract
The present paper proposes the use of non linear model updating applying unrestricted optimization method, in order to obtain a methodology, which allows the calibration of mathematical models in rotating systems. An experimental set up for this purpose consists of a symmetric rotor, on a rigid foundation supported by two hidrodynamic cylindrical bearings and with a central disk of considerable mass, working as na unbalancing excitation force. Once the numeric and experimental values are obtained, error vectors are defined, which are the minimization parameters, through the variation of the numeric model parameters. The method presented satisfactory results, as it was able to calibrate the mathematical model, and then to obtain reliable responses for the physical system studied. The research also presents a contribution for the rotating machine desing area as it presents a relatively simple methodology on the updating and revalidation of computacional models for machines and structures.
Experimental Investigation of Dry Friction Damping and Cubic Stiffness Non-Linearity
Authors: Stanbridge Anthony B. , Ewins David J. , Sanliturk Kenan Y. , Ferreira Janito V. 
Published: November 2020

Abstract
Experimental vibration techniques used in the characterisation of the two most common types of non-linear structure are described here. The first is used to determine friction contact hysteresis loops to provide data which can be incorporated into large, otherwise linear, structural models, to predict non-linear vibration responses. The second is a method of measuring frequency response functions (FRFs) of structures with non-linear, amplitude-dependent stiffness and damping, including the ‘unstable’, overhanging part of the FRF curve, by using a controlled-amplitude, stepped-frequency sinusoidal input. These apparently rather different test techniques are in fact connected by the fact that, in order to be effective, they both require an additional mass to be installed, on the input side of the force transducer.
Nonlinear Resonance and Parametric Instability of a Power Transmission Belt: Numerical Analysis With Experiments
Authors: Vestroni Fabrizio , Pellicano Francesco , Catellani Giulia , Fregolent Annalisa 
Published: November 2020

Abstract
In this paper a numerical approach is developed to forecast the dynamic behavior of a power transmission belt running on eccentric pulleys. Basic partial differential equations are developed, considering the elastic effect of the lower branch of the belt. Nonlinear resonances and dynamic instabilities are analyzed in detail using a high dimensional discrete model, obtained through the Galerkin procedure. The numerical analysis is performed by means of direct simulations and a continuation software. Numerical results are compared with available experimental data. It is shown that the numerical method is able to predict correctly the amplitudes of oscillation in several operating conditions: direct and parametric resonances. Frequency response curves are obtained when the belt is harmonically excited close to the first and second linear natural frequency. The damping ratio and the linear frequencies are identified at zero axial speed.
Eigenstructure Calculation for Mixed Vibratory Systems Composed of a Continuous Beam and Concentrated Actuators
Authors: Panza Michael J. 
Published: November 2020

Abstract
A calculation of the eigenstructure for mixed vibratory systems composed of a continuous beam and concentrated actuators is presented. The combined distributed and lumped element systems include actuators for active vibration control. The focus of this paper is on open loop models where with zero voltage input to the actuators. The continuous beam is isolated and discretized via modal analysis and combined with the actuator dynamics to form an asymmetric system. The resulting system is cast into a generalized nondimensional form suitable for studying system behavior for a broad range of system parameters. The solution is expressed as a series using the isolated beam mode eigenfunctions as a basis. The coefficients in the series are obtained from the complex eigensolution of the asymmetric system. Two examples are used to show a comparison of the complex mixed system and real isolated beam natural frequencies and mode shapes. The effect of beam and actuator parameter values are investigated via a key dimensionless parameter.
Bifurcations and Chaos in the Response of a Rigid Rotor Supported by Eccentric Squeeze-Film Dampers
Authors: Inayat-Hussain Jawaid Iqbal , Kanki Hiroshi , Mureithi Njuki W. 
Published: November 2020

Abstract
In the unbalance response analysis of rotors supported by squeeze-film dampers with centering springs, the fluid-film forces are usually computed based on the assumption that the rotor exhibits a circular centered whirl orbit motion. The validity of this assumption is, however, limited to the ideal case of squeeze-film dampers with centering springs that are perfectly adjusted to offset the gravitational force. In most practical applications, eccentric operation of these dampers is almost unavoidable since precise setting of the centering springs in a real environment is usually not possible. In this paper the bifurcations in the response of a rigid rotor in eccentric squeeze-film dampers are investigated. The values of the bearing parameter (B), gravity parameter (W) and spring parameter (S) are respectively fixed at 0.015, 0.05 and 0.3, while the unbalance parameter (U) is varied from 0.05 to 0.8. The results indicated that the rotor might lose its stability due to period-doubling and saddle node bifurcations. Chaotic response of the rotor was also observed for 0.365 &lt; U &lt; 0.367 and 0.381 &lt; U &lt; 0.392. The transitions to chaos in these two regimes were respectively via the period-doubling and type 3 intermittency routes. The levels of rotor unbalance where non-synchronous and chaotic motions were observed in this study are only an order of magnitude higher than the specified levels for rigid rotors. Such levels of unbalance may easily occur in practice due to in-service erosion or in the event of a partial or an entire blade loss.
Dynamics and Stability of a Nonlinear Brake Model
Authors: Wauer Jörg , Heilig Jürgen 
Published: November 2020

Abstract
The dynamics of a nonlinear car disc brake model is investigated and compared with a simplified linear model. The rotating brake disc is approximated by a rotating ring. The brake pad is modeled as a point mass which is in contact with the rotating ring and visco-elastically suspended in axial and circumferential direction. The stability analysis for the nonlinear model is performed by a numerical evaluation of the top Lyapunov-exponent. Several parameter studies for the nonlinear model are discussed. It is shown that dynamic instabilities of the nonlinear model are estimated at subcritical rotating speeds lower than 10% of the critical speed. Further, the sensitivity of the nonlinear model to the initial conditions and the stiffness ratios is demonstrated.
Mechanics of Regenerative Vibration in Drilling: Analytical and Experimental Study of the Formation of Lobed Holes
Authors: Bayly Philip V. , Lamar Michael T. , Calvert Sean G. 
Published: November 2020

Abstract
Large-amplitude vibrations in drilling often occur near multiples of the rotation frequency, even when these frequencies are much lower than the system’s first natural frequency. These vibrations are responsible for out-of-round, “lobed” holes. A simplified model of the mechanics of this phenomenon is presented in this paper. The model includes cutting and “rubbing” forces on the drill, but inertia and damping of the tool are neglected at low speeds. This quasi-static model remains dynamic because of the regenerative nature of cutting; the force on each cutting element depends on both the tool’s current position and its position at the time of the previous tooth passage. Characteristic solutions, including unstable retrograde “whirling” modes, are found in terms of eigenvalues and eigenvectors of a discrete state-transition matrix. These unstable modes correspond closely to behavior observed in drilling tests.
Coupled Slow and Fast Dynamics of Flow Excited Elastic Cable Systems
Authors: Kim WanJun , Perkins N. C. 
Published: November 2020

Abstract
Analytical studies of vortex-induced vibration (VTV) of cables during lock-in have considered small amplitude and relatively fast dynamic responses about an equilibrium configuration. However, this equilibrium may change as a result of the significantly increased mean drag created during lock-in. In response to increased drag, the cable may slowly drift downstream causing appreciable changes in cable geometry and tension. The resonance conditions for lock-in may be preserved during this slow drift or they may be disrupted. A nonlinear cable/fluid model is discussed mat captures both fast (small amplitude) motions due to VIV and slow (large amplitude) motions due to drift. These two different time scales of motion are clearly observed in numerical simulations. The significant interplay of the slow drifting motion and the fast VTV is highlighted.
Nonlinear Modeling and Identification of the Dynamic Behavior of Polyurethane Foam
Authors: Singh R. , Davies P. , Bajaj A. K. 
Published: November 2020

Abstract
The analysis of the steady-state response of a polyurethane foam and mass system to harmonic excitation is given. The foam’s uni-directional dynamic behavior motion is modeled by using nonlinear stiffness, linear viscoelastic and velocity proportional damping components. The relaxation kernel for the viscoelastic model is assumed to be a sum of exponentials. Harmonic balance is used to develop one- and two-term solution approximations that are utilized for system identification. The identification process is based on least-squares minimization of a sub-optimal cost function that uses response data at various excitation frequencies and amplitudes. The effect of number, spacing and amplitudes of the harmonic input on the results of the model parameter estimation is discussed. Model-order choice and the feasibility of describing the system behavior at several input amplitudes with a single set of parameters are also addressed.
The Asymptotic Stability of Weakly Perturbed Two Dimensional Hamiltonian Systems
Authors: Arnold Ludwig , Imkeller Peter , Namachchivaya N. Sri 
Published: November 2020

Abstract
The purpose of this work is to obtain an approximation for the top Lyapunov exponent, the exponential growth rate, of the response of a single-well Kramers Oscillator driven by either a multiplicative or an additive white noise process. To this end, we consider the equations of motion as dissipative and noisy perturbations of a two-dimensional Hamiltonian system. A perturbation approach is used to obtain explicit expressions for the exponent in the presence of small intensity noise and small dissipation. We show analytically that the top Lyapunov exponent is positive, and for small values of noise intensity ε and dissipation ε the exponent grows proportional to ε1/3.
Stabilisation of Period-1 Orbits of the Hénon Map: Parametric Variation and Additive Noise
Authors: Davies Huw G. 
Published: November 2020

Abstract
Slow sinusoidal modulation of a control parameter can maintain a low period orbit of a nonlinear dynamic system into parameter regions where the low period orbit is unstable, and a higher period orbit would normally occur. We examine this case for a period-doubling bifurcation of the Hénon map. Whether or not effective stabilisation of the period-1 orbit takes place depends on both the frequency of the variation and on the noise. Increasing the frequency tends to stabilise the orbit; increasing the noise level is destabilising. We use matched asymptotic expansions to describe the response, and find explicit expressions for the response which can estimate whether and where an apparent period doubling occurs.
P-Bifurcation Aspects of a Modified Duffing Oscillator Near Equilibrium
Authors: Fofana M. S. , Szwarc Dariusz 
Published: November 2020

Abstract
A unified framework for the study of stability of solutions to delay differential equations perturbed deterministically and stochastically has been presented. We review the concepts of Hopf bifurcation, centre manifold, integral averaging method and pth–moment Lyapunov exponent, and then demonstrate their role in the stability study of a modified Duffing oscillator with time delay. Sufficient conditions ensuring Đ- and Þ–bifurcations and the changes in character of the probability density function are established for fixed and positive time delay.
Dynamics of Semi-Actively Controlled Vehicles Involving Wheel Hop
Authors: Verros G. , Natsiavas S. 
Published: November 2020

Abstract
The present study investigates dynamic response of vehicle models, subjected to road excitation. In these models, a semi-active control strategy is applied on the suspension dampers, which is based on a switch of their damping coefficient between different values, so that the resulting system approximates the performance of a vehicle involving sky-hook damping. An alternative control strategy is also applied, which is passive and is based on selecting a different damping ratio when the wheel velocity relative to the car body is positive or negative. Both of these control strategies lead to oscillator models with parameter discontinuities. Similar terms are also introduced into the equations of motion by considering wheel hop phenomena, where a vehicle wheel leaves the ground temporarily. First, simple quarter-car models are examined but the analysis is also applied to more complicated models. For these models, their dimensions are reduced substantially by applying a component mode synthesis approach. Subsequently, this allows the efficient application of appropriate methodologies for predicting response spectra of the nonlinear models to periodic road excitation. Finally, results obtained by direct integration of the equations of motion are also presented for transient road excitation. In all cases, the results are compared to those obtained for vehicles with suspensions including passive shock absorbers. Moreover, special consideration is given to cases where wheel hop is possible to occur.
A Simple Adaptive Feedback Controller for Tower Cranes
Authors: Omar Hanafy M. , Nayfeh Ali H. 
Published: November 2020

Abstract
The objective of crane control is to build an algorithm to move a load from point to point in the shortest time without inducing large swings. We assume that this objective cannot be accomplished in less than a single oscillation cycle of the load. Therefore, the controller is built to move the load such that it completes only one oscillation cycle at the end of the motion. Consequently, the settling time of the system should be equal to the period of oscillation of the load. This criterion enables the calculation of the controller feedback gains for varying load weight and cable length. The controller is built first for overhead cranes and then modified for tower cranes. Two controllers are used, one for the rotational motion of the tower and the other for the translational motion of the trolley. Numerical simulations show that the controller is effective in reducing the load oscillations and transferring the load in a reasonable time compared with that of optimal control.
The Attitude Stability for Longitudinal Motion of Underwater Vehicle
Authors: Wang Deshi , Xiao Renbin , Yang Ming 
Published: November 2020

Abstract
Although the equations describing the longitudinal motions of underwater vehicles are typically nonlinear, the linearized equations are still employed to design the depth controller by the traditional analysis methods in engineering for the sake of simplicity. The reduction of the nonlinearity loses the dynamics near the singular points, which may be responsible for the sudden climb or dive. The nonlinear systems limited in the longitudinal plane of the underwater vehicles are analyzed on center manifold through the bifurcation theory. It focuses on the case that single zero root in Jacobi matrix occurs at equilibrium points corresponding to nominal trajectory with varied angles of the elevator or the direction change of the flows. The center manifolds are calculated and one-dimensional bifurcation equations on the center manifolds are obtained and analyzed. Based on the transcritical bifurcation diagram, we have found the mechanism of the attitude stability loss as well as the abnormal trajectory of autonomous underwater vehicles. It gives good explainations to the practical climbing jump and diving fall and delivers the theoretical tools to design the controller and to design dynamics. Numerical simulation verifies the results.
Stochastic Nonlinear Dynamics of a Beam System With Impact
Authors: van de Wouw N. , de Kraker A. , Nijmeijer H. 
Published: November 2020

Abstract
In this paper, a strongly nonlinear beam-impact system under both broad-banded and small-banded, Gaussian noise excitations is investigated. The response of this system is investigated both numerically, through a multi-degree-of-freedom (MDOF) model, and experimentally focusing on frequency-domain characteristics such as stochastic equivalents of harmonic and subharmonic solutions. Improved understanding of these stochastic response characteristics is obtained by comparing them to nonlinear periodic response features of the system. It will be shown that in modeling such a continuous linear system with a local nonlinearity, the linear part can be effectively reduced to a description based on several modes. Combining this reduced linear part with the local nonlinearity in a reduced nonlinear model is shown to result in an analysis model, which can be used to accurately predict the stochastic response characteristics of the original, continuous, nonlinear system. It is shown that the inclusion of more modes in the model will result in a response, which differs significantly from that of a SDOF (single-degree-of-freedom) model, giving a better correspondence with experimental results, also in the frequency range of the first mode.
Stick-Slip Dynamics of a Two-Degree-of-Freedom System
Authors: Awrejcewicz Jan , Olejnik Pawel 
Published: November 2020

Abstract
Two-degree-of-freedom autonomous system with friction is analyzed numerically. The friction coefficient has been smoothened using are tan function. The standard, but slightly modified chaos identification tools have been applied for the analyzed discontinuous system. Some interesting examples of stick-slip regular and chaotic dynamics have been illustrated and discussed.
Application of Mechanized Mathematics in Rotor Dynamics
Authors: Wang Liguo , Huang Wenhu , Hu Chao 
Published: November 2020

Abstract
The mechanized mathematics-Wu elimination method is a vigorous method in solving nonlinear algebraic equations in China, but it is still not so popular in the West. In this paper the mechanized mathematics-Wu elimination method is introduced in brief and is used to solve the problem of dynamic behavior of a rotor-bearing system with nonlinear supports. The whirl equations of a short bearing-rotor system with two disks considering gyro-moment are studied. The idea of the characteristic set of Wu method is combined with Maple’s symbolic calculation. The whirl parameter of a rotor mounted on two supports are analyzed. The analytical results showing the relations of the bearing parameters and instability speed are presented.
Mechanical Fault Diagnosis for Abnormal Vibration Excited by Steam in High Pressure Turbine of Turbo-Generator Set
Authors: He Xiaoyin , He Zhengjia 
Published: November 2020

Abstract
Violent vibration occurred at high-pressure turbine of a turbo-generator. When steam input or load capacity was changed, the vibrations were also varied. Wavelet packets, FFT spectrum and cepstrum were adopted synthetically to obtain diagnosis information. According to signal analyses and factual evidences, it was clear that there existed violent vibration (be nonlinear) excited by steam in high-pressure turbine. We investigated the maintenance conditions, and found that the four main pipes of steam input had different lengths after their thermal expansion, which lead to skew at the body of high-pressure turbine. The intervals between rotor and stator were non-uniform. So, besides a moment of couple was generated onto the rotor, a force was also generated. This force excited the rotor of the high-pressure turbine to vibrate with its natural frequency. After repairing the four main pipes, its vibration became normal as the turbo-generator was running. It is important to combine signal processing with practical investigation. Only in this way can we obtain correct diagnosis results and achieve successful maintenance.