bluuebunny/crossref_metadata_2025_split huggingface dataset:
Beam Networks Analysis by a Power Flow Method
Authors: Ichchou Mohammed Najib , Le Bot Alain , Jezequel Louis 
Published: March 2021

Abstract
The dynamical behaviour of systems in medium and high frequency range has become a subject of increasing interest over the last few years. Recently, an original strategy called Energy Flow Method has been developed to describe the structural/acoustical response in mid frequencies. In this paper, a review of the one dimensional Energy Flow Method is first proposed. An original propagative method based on the reflection and transmission matrix is proposed to study coupled beams with longitudinal and transversal motion. The method is applied to the junction of two beams with an arbitrary angle. The results show the efficiency of such a formulation for the mid frequency analysis of beam networks.
Characteristics of the Nonlinear Hysteresis Loop for Rotor-Bearing Instability
Authors: Guo Jenq-Shan , Adams M. L. 
Published: March 2021

Abstract
The nonlinear hysteresis loop of a journal-bearing supported rotordynamic system is characterized by the Hopf-bifurcation and Saddle-Node speeds. The nonlinearity of this system occurs in the journal-bearing fluid-film forces, and requires the imbedding of a solution for the Reynolds lubrication equation within a numerical integration scheme of the coupled motion equations in order to perform proper simulations. These show that under light bearing static load, the Saddle-Node and Hopf bifurcation coalesce to a single speed at essentially two times the self-excited vibration frequency (i.e., the lowest natural frequency). At higher bearing loads, the classical instability threshold speed (i.e., Hopf bifurcation) occurs at progressively higher rotor speeds. However, the disappearance speed (Saddle Node of the periodic orbit) of the nonlinear limit cycle occurs at progressively lower rotor speeds, asymptotically approaching approximately 1.725 times the lowest natural frequency. By adding a rotor unbalance force to the model, exploratory simulations have been made to determine the extent to which chaos signal processing in the normal speed-up or coast-down vibration of actual machines could be used to locate this lower speed bound of the instability hysteresis loop.
Modal Testing of Rotating Discs Using a Scanning LDV
Authors: Stanbridge Anthony B. , Ewins David J. 
Published: March 2021

Abstract
Modal testing of rotating structures is complicated by difficulty of access and by the fact that, if the source of excitation is fixed in space, responses occur at frequencies other than that of the excitation. This paper demonstrates the use of, and derives output equations for, a Laser Doppler Vibrometer (LDV) for response measurement.
Examples are given of measurements using the LDV beam aimed (i) at a point fixed in space, (ii) at a fixed point on the disc, and (iii) rotating at a non-synchronous speed. The third technique is perhaps the most useful, enabling the circumferential spatial disc response, expressed in terms of travelling waves or orthogonal standing modes, to be directly derived at any speed, frequency or state of disc mistuning.
The same technique, applied to a non-rotating disc, provides a simple qualitative measurement of the mode shape associated with each natural frequency. An example based on a centrifugal impeller is included.
Direct Parameter Estimation of Weak Nonlinear Systems Using Vibration Test Data
Authors: Weiland Matthias , Link Michael 
Published: March 2021

Abstract
A method has been developed for the identification of structural systems which exhibit influences of weak nonlinear stiffness and damping terms. It is based on a linear method for direct identification of incomplete system matrices from vibration test data. The basic identification equations are extended by additional stiffness and damping terms. Their contribution to the overall response is governed by higher powers of the individual response amplitudes. Hence, the method is a linearisation approach to the full nonlinear solution and basically derived from the well known ‘Harmonic Balance’ method which is applied to multi-degree of freedom systems.
The paper presents the basic theory of the method and illustrates its application to several test examples. First simulated test cases with nonlinear stiffness and damping terms are discussed. Then, as a practical application, the results of an automobile motor/gearbox assembly are given.
Variation of Fluid Flow Forces in Seals With Rotor Bending
Authors: Kwanka K. 
Published: March 2021

Abstract
Fluid-induced forces in labyrinth seals can cause unstable self-excited vibrations of the turbomachine rotor. Generally, a linear approach employing dynamic coefficients is used to describe these forces. A new procedure for the identification of the coefficients which uses two excitation sources placed on a flexible rotor is presented. The change in the stability limit and vibrational frequency caused by the investigated labyrinth gas seal contains the dynamic coefficients.
It is important that problems which may also occur in the real turbomachine are considered by the identification procedure. The conservative dynamic coefficients, such as the direct stiffness, influence the bending of the mode shapes and thus affect indirectly the stability limit. The magnitude of the exciting forces depends on the axial positioning of the excitation source and also on the mode shape bending. These two dependencies are investigated by experiment and considered in the identification procedure.
Excitation of Arbitrary Displacement/Velocity Conditions in Rotationally Periodic Structures
Authors: Schmiechen P. , Ewins D. J. , Bucher I. 
Published: March 2021

Abstract
For an investigation into the structural interaction between rotating and non-rotating rotationally periodic turbine components, it was required to be able to generate experimentally prescribed response conditions. In more descriptive terms, conditions were sought to excite wave-patterns such as travelling and standing waves, and to suppress certain modes. In the paper these conditions are derived from modal properties. Simulated data are presented to demonstrate some of the phenomena and to highlight the practical difficulties.
For rotationally periodic structures, most natural frequencies are of multiplicity two, and are sometimes called ‘double modes’. Their associated mode shapes can rotate in the plane of symmetry. The responses due to the two modes can be combined and expressed in a wave form, which can be split into travelling and standing wave components.
Theoretically, it is possible to excite a pure travelling wave in a perfectly rotationally periodic structure, but there are limits to this in practice as real structures will always exhibit some degree of imperfection. These structures are said to be mistuned, and the imperfection splits the double modes into pairs of close modes.
Simulations show the predicted vibration phenomena. In particular, the case of discrete excitations relevant to modal testing is investigated. The simulations show clearly that in this case components of other modes will generally be present.
In an experiment, the results for driving the excitations will not give the theoretically expected response due to non-linearities of the shaker-structure interaction. However, the effects can be reduced by employing a computerised search algorithm.
Three Dimensional Vibration of a Ballooning String
Authors: Hall Kevin J. , Zhu Fang , Rahn Christopher D. 
Published: March 2021

Abstract
In many textile manufacturing processes, yarn is rotated at high speed forming a balloon. In this paper, Hamilton’s principle is used to derive the nonlinear partial differential equations of a ballooning string. Jacobian elliptical sine functions satisfy the nonlinear steady state equations. The steady state eyelet tension is related to the string length for a constant balloon height. For high tension and low string length cases, single loop balloons occur. As the string length increases, tension decreases and multiple loop solutions are obtained. The nonlinear partial differential equations are linearized about the steady state solutions, resulting in three coupled equations with spatially varying coefficients. The equations involve a positive definite mass matrix operator, skew symmetric gyroscopic matrix operator, and symmetric stiffness matrix operator. It is shown using a Galerkin approach that only single loop balloons are stable for practical yarn elasticity. The natural frequencies of the single loop balloon increase with decreasing balloon size and increasing yam stiffness. The effect of yarn elasticity on the first three vibration modes of a single loop balloon is analyzed. The steady state and stability analyses are experimentally verified.
Modeling, Actuation, and Control of an Active Fluid Vibration Isolator
Authors: Panza Michael J. , McGuire Dennis P. , Jones Peter J. 
Published: March 2021

Abstract
An integrated mathematical model for the dynamics, actuation, and control of an active fluid/elastomeric tuned vibration isolator in a two mass system is presented. The derivation is based on the application of physical principles for mechanics, fluid continuity, and electromagnetic circuits. Improvement of the passive isolator performance is obtained with a feedback scheme consisting of a frequency shaped notch compensator in series with integral control of output acceleration and combined with proportional control of the fluid pressure in the isolator. The control is applied via an electromagnetic actuator for excitation of the fluid in the track connecting the two pressure chambers of the isolator. Closed loop system equations are transformed to a nondimensional state space representation and a key dimensionless parameter for isolator-actuator interaction is defined. A numerical example is presented to show the effect of actuator parameter selection on system damping, the performance improvement of the active over the passive isolator, the robustness of the control scheme to parameter variation, and the electrical power requirements for the actuator.
A Variational Formulation, a Work-Energy Relation and Damping Mechanisms of Active Constrained Layer Treatments
Authors: Shen I. Y. 
Published: March 2021

Abstract
The purposes of this paper are to formulate active constrained layer (ACL) damping treatments through a variational approach, to study the work-energy relation of ACL, and to identify the damping mechanisms of ACL treatments. Application of extended Hamilton’s principle to ACL results in the equations of motion of ACL and the charge equation of electrostatics for the piezoelectric constraining layer. The work-energy equation together with the charge equation shows that the power dissipated through the active damping is the product of the electric field and the axial velocity of the piezoelectric constraining layer at the boundaries. This unique feature suggests that a self-sensing and actuating piezoelectric constraining layer may be an appropriate design in dissipating vibration energy without causing instability. To identify the damping mechanisms, a sensitivity analysis shows that the effectiveness of ACL damping primarily depends on the active and passive damping forces transmitted to the vibrating structure through the viscoelastic layer. The active damping force transmitted depends on the controller transfer function as well as a system parameter, termed active damping sensitivity factor, which is determined entirely by the dimensions and material properties of the passive constrained layer. Finally, numerical results on ACL beams are obtained to illustrate the theoretical predictions above.
Energy Flow Control of Interconnected Structures: II — Structural Subsystems
Authors: Kishimoto Yasuo , Bernstein Dennis S. , Hall Steven R. 
Published: March 2021

Abstract
The dissipative energy flow control technique for interconnected modal subsystems developed in a companion paper [1] is now applied to structural subsystems. In this paper two energy flow models for interconnected structures are derived, namely, the modal subsystem model, which views each mode as a subsystem, and the structural subsystem model, which views each substructure as a subsystem. These energy flow models provide alternative foundations for an energy flow control technique. Active feedback controllers based on both of these energy flow models are shown to reduce the vibration of a specified substructure.
Active Mode Localization in Distributed Parameter Systems With Consideration of Limited Actuator Placement
Authors: Shelley Franz J. , Clark William W. 
Published: March 2021

Abstract
The purpose of this work is to investigate the application of active mode localization to discretized models of distributed parameter systems where the number of control sensors and actuators is a limiting factor. A modified eigenvector scaling technique using singular value decomposition is developed which scales the lower-mode eigenvectors, producing localization over the range of these lower natural frequencies. An example using a simply supported beam model is provided, with mode localization achieved in at least the lower 3 modes utilizing as few as two control sensor/actuator pairs.
Finite Element Vibration Analysis of Composite Plates With Embedded Shape Memory Alloy Fibers at Elevated Temperatures
Authors: Zhong Z. W. , Mei Chuh 
Published: March 2021

Abstract
The present paper investigates the vibration behavior of the thermally buckled shape memory alloy (SMA) fiber-reinforced composite plates. The stress-strain relations are developed for a thin composite lamina with embedded SMA fibers. The finite element equation of motion including shape memory effect is presented. This equation can be mathematically separated into a static equation and a dynamic equation. The thermal postbuckling deflection and vibration of the thermally buckled position for SMA fiber-reinforced composite plates are determined. Due to the effects of nonlinear material properties of SMA, the vibration characteristics of thermally buckled composite plate with embedded SMA fibers are distinctly different from the one without SMA. Thermal postbuckling, natural frequencies and vibration modes for SMA reinforced composite rectangular plates are presented. Triangular plates with simply supported and clamped boundary conditions are also studied.
Controlling the Vibration Levels of Vibrating Vanes Using Viscoelastic Materials
Authors: Oyadiji S. O. , Tomlinson G. R. 
Published: March 2021

Abstract
The vibration characteristics of a carbon composite outlet guide vane (CCOGV), whose ends were embedded in a viscoelastic medium, were analysed by means of the finite element method. The elastic CCOGV and the viscoelastic material were modelled using twenty-noded solid brick elements. Both isotropic and orthotropic material models were used to characterise the elastic behaviour of the CCOGV. The Young’s modulus and loss factor data of the viscoelastic material were derived from the master curves of complex Young’s modulus of the material. These master curves were obtained via the application of the direct stiffness and master curve methodologies to a prismatic sample of the viscoelastic material. It is shown that the degree of correlation of the finite element predictions compared to the measured characteristics of the potted CCOGV depends on the accuracy of the elastic material properties of the CCOGV and of the complex modulus of the viscoelastic material.
Interpretation of Active Dampers As Variable-Parameter Passive Devices
Authors: Anderson Eric H. 
Published: March 2021

Abstract
This paper develops analogies between discrete devices that achieve damping by active and passive means. It describes the simplest models useful for inclusion in larger system design. Lumped-parameter models for representing passive dampers are given, and the similarity to local active feedback is shown. A model for active damper components containing piezoelectrics or similar materials is developed for force feedback compensation. This system is similar to the passive damper model when its parameters are allowed to vary. An active damper with direct feedback of the integral of measured force is represented by a model containing a single spring and a gain-dependent dashpot. Further aspects of the active damper are illustrated using a one-mode model of a vibrating structure. The effects of a feedforward modification to the system, and the analogy to changes in passive parameters, are illustrated by tracking the locus of the closed loop system poles with feedback gain.
Dynamic Analysis of the Axially Moving String Based on Wave Propagation
Authors: Ying S. , Tan C. A. 
Published: March 2021

Abstract
This paper presents an exact solution for the transverse response of an axially moving string under general boundary conditions. The response solution is derived in the frequency domain and interpreted in terms of wave propagation functions. The response in the time domain involves only several convolution integrals which can easily be obtained for many physical boundary conditions. The transient response of the translating string with a spring or a dashpot at a boundary is presented.
Existence of Periodic Solution for Equation of Motion of Simple Beams With Harmonically Variable Length
Authors: Esmailzadeh Ebrahim , Nakhaie-Jazar Gholamreza , Mehri Bahman 
Published: March 2021

Abstract
The transverse vibrating motion of a simple beam with one end fixed while driven harmonically along its axial direction from the other end is investigated. For a special case of zero value for the rigidity of the beam, the system reduces to that of a vibrating string with the corresponding equation of its motion. The sufficient condition for the periodic solution of the beam is then derived by means of the Green’s function and Schauder’s fixed point theorem.
The criteria for the stability of the system is well defined and the condition for which the performance of the beam behaves as a nonlinear function is stated.
Exact Perturbation for the Vibration of Almost Annular or Circular Plates
Authors: Parker R. G. , Mote C. D. 
Published: March 2021

Abstract
Using perturbation analysis, the eigensolutions for plate vibration problems on nearly annular or circular domains are determined. The irregular domain eigensolutions are calculated as perturbations of the corresponding annular or circular domain eigensolutions. These perturbations are determined exactly. The simplicity of these exact solutions allows the perturbation to be carried through third order for distinct unperturbed eigenvalues and through second order for degenerate unperturbed eigenvalues. Furthermore, this simplicity allows the resulting orthonormalized eigenfunctions to be readily incorporated into response, system identification, and control analyses. The clamped, nearly circular plate is studied in detail, and the exact eigensolution perturbations are derived for an arbitrary boundary shape deviation. Rules governing the splitting of degenerate unperturbed eigenvalues at both first and second orders of perturbation are presented. These rules, which apply for arbitrary shape deviation, generalize those obtained in previous works where specific, discrete asymmetries and first order splitting are examined. The eigensolution perturbations and splitting rules reduce to simple, algebraic formulae in the Fourier coefficients of the boundary shape asymmetry. Elliptical plate eigensolutions are calculated and compared to finite element analysis and, for the fundamental eigenvalue, to the exact solution given by Shibaoka (1956).
Distributed Transfer Function Analysis of Ring-Stiffened Cylindrical Shells
Authors: Zhou J. , Yang B. 
Published: March 2021

Abstract
A new analytical and numerical method is presented for modeling and analysis of cylindrical shells stiffened by circumferential rings. This method treats the shell and ring stiffeners as individual structural components, and considers the ring eccentricity with respect to the shell middle surface. Through use of the distributed transfer functions of the structural components, various static and dynamic problems of stiffened shells are systematically formulated. With this transfer function formulation, the static and dynamic response, natural frequencies and mode shapes, and buckling loads of general stiffened cylindrical shells under arbitrary external excitations and boundary conditions can be determined in exact and closed-form. The proposed method is illustrated on a Donnell-Mushtari shell, and compared with finite element method and two other modeling techniques.
On Line Estimation of Stiffness in Nonlinear Beam Models With Piezoceramic Actuators
Authors: Demetriou M. A. , Fitzpatrick B. G. 
Published: March 2021

Abstract
The ability to identify changes in material properties in flexible structures is of great importance in the design of compensators. In this paper we consider an online (adaptive) scheme for estimating stiffness changes of a beam undergoing persistent excitation from piezo-ceramic patches. The nonlinearity involved is a piecewise linear stiffness function meant to provide a simple model of damage. The estimation scheme identifies the time at which the system becomes nonlinear and it provides an estimate of the stiffness function.
Identification of Thermal and Hysteretic Response of SMA Embedded Flexible Rods
Authors: Kurdila Andrew J. , Webb Glenn 
Published: March 2021

Abstract
In this paper, the equations of motion governing the transient response of an elastomer rod with embedded shape memory alloy actuators are derived. The elastomeric flexural dynamics and elastomeric thermal dynamics are represented by a pair of parameter-dependent, coupled, partial differential equations. The response of the structural system exhibits strong hysteresis effects due to the nonlinear nature of the constitutive law of the SMA actuator. As opposed to previous work by the authors in which an explicit equation for the nonlinear constitutive law is utilized, the work herein utilizes an integral operator in a phenomenological representation of the hysteresis. Specifically, a static hysteresis operator is employed to represent the current-to-stress transformation in the SMA. The hysteresis operator consequently appears as a control influence operator in the system of governing partial differential equations. This paper presents a two-stage identification process to characterize the multivalued response associated with hysteresis. Preliminary experimental results validate the effectiveness of the method for the class of problems considered.
Updating of Dynamic Finite Element Models Based on Experimental Receptances and the Reduced Analytical Dynamic Stiffness Matrix
Authors: Lammens Stefan , Brughmans Marc , Leuridan Jan , Heylen Ward , Sas Paul 
Published: March 2021

Abstract
This paper presents a model updating method based on experimental receptances. The presented method minimises the so called ‘indirect receptance difference’. First, the reduced analytical dynamic stiffness matrix is expressed as an approximate, linearised function of the updating parameters. In a numerically stable, iterative procedure, this reduced analytical dynamic stiffness matrix is changed in such a way that the analytical receptances match the experimental receptances at the updating frequencies.
The updating frequencies are a set of selected frequency points in the frequency range of interest. Some considerations about an optimal selection of the updating frequencies are given.
Finally, a mixed static-dynamic reduction scheme is discussed. Dynamic reduction of the analytical dynamic stiffness matrix at each updating frequency is physically exact, but it involves a great computational effort. The presented mixed static-dynamic reduction scheme is a simple strategy to reduce the computational cost with a minor loss of accuracy.