bluuebunny/crossref_metadata_2025_split huggingface dataset:
Damping Machine Tools With Imbedded Viscoelastic Materials Constrained by Shear Tubes
Authors: Marsh Eric R. , Hale Layton C. 
Published: March 2021

Abstract
This paper considers a passive damping method that can be applied to beam-like structures such as machine tool bases and columns. The method uses viscoelastic materials to dissipate energy in the manner of classic constrained-layer damping; however, the layers are embedded within the structure as opposed to being applied externally. This provides a robust means of incorporating damping without encountering several of the common disadvantages associated with external damping treatments. An analytical solution to the amount of damping that can be achieved using embedded layers is available, but is known to be inaccurate when the viscoelastic stiffness approaches that of the structural components. Therefore, a new prediction of the maximum damping level that can be expected in a structure is developed and presented here. This prediction gives good results in a wide variety of applications, and offers insight into the relationship between key design parameters. Finite element and experimental verification of the maximum damping predictor are also presented.
An Electromechanical Vibration Absorber
Authors: Nagem Raymond J. , Madanshetty Sameer , Medhi Gunajit 
Published: March 2021

Abstract
A conventional vibration absorber consists of a secondary mechanical oscillator whose properties are chosen to improve the dynamic response of a primary vibratory system. The improvement in the primary system is obtained at the expense of large amplitude mechanical oscillations of the secondary system. We propose an electromechanical absorber in which the secondary system consists of a resonant electric circuit capable of withstanding large amplitude electrical oscillations. The theoretical basis for the design of the electromechanical absorber is presented, and initial experiments to test the technique are described.
Frequency Domain Approach to Solve the Time-Optimal Control of a Distributed Parameter System
Authors: Alli Hasan , Singh Tarunraj 
Published: March 2021

Abstract
In this paper, the time-optimal control of the wave equation is derived in closed form. A frequency domain approach is used to obtain the time-optimal solution which is bang-off-bang. The system studied in this paper is a uniform flexible rod with a control input at each end, whose dynamics in axial vibration is represented by the wave equation. In order to verify the optimality of the control profile derived for the distributed parameter system, the system is discretized in space and a series of time-optimal control problems are solved for the finite dimensional model, with increasing number of flexible modes. In the limit, the controllers show the convergence of the first and final switch of the bang-bang controller of the finite dimensional system to the first and final switch of the bang-off-bang controller of the distributed parameter system, in addition to the convergence of the maneuver time. The number of switches in between the first and final switch is a function of the order of the finite dimensional system. The maneuver time of the distributed parameter system is compared to that of an equivalent rigid system and the coincidence of the time-optimal controller for the flexible and rigidized systems is illustrated for certain maneuvers.
Remarks on the Modelling of Active Structures With Colocated Piezoelectric Actuators and Sensors
Authors: Loix N. , Preumont A. 
Published: March 2021

Abstract
This paper aims to attract the attention of the designers of active structures on the importance of evaluating properly the feedthrough component of the open-loop transfer functions. It is shown that overlooking the feedthrough component can change significantly the location of the zeros of the open-loop system and, as a result, alter drastically the performance of the closed-loop system.
The feedthrough term may result from the quasi-static contribution of the high frequency modes or from local effects that are neglected by over-simplified modelling techniques (e.g. plate or beam instead of shell). The problem is illustrated with a cantilever beam provided with strain actuators.
The Modeling and Active Control of Flexible Plate Structure for Reducing Noise Radiation
Authors: Seto Kazuto , Miyata Takaharu , Ren Mingzhang , Doi Fumio 
Published: March 2021

Abstract
This paper shows a new method of active vibration control of a flexible plate structure with aim to reduce the radiated noise. It involves modeling the real structure into a reduced order lumped parameter model on the basis of modal analysis, and then adopting LQ control theory to control the vibration of selected multi-modes of the plate. In this paper the modeling procedure and the control strategy design is presented, in which suboptimal control theory and digital filtering technique have been used. Simulation and preliminary experimental results are given to demonstrate the effectiveness of the proposed method.
Optimal Design of a Truss Structure for a Segmented Reflector
Authors: Hahn Mark A. , Mirmirani Maj D. , Boussalis Helen R. 
Published: March 2021

Abstract
Design requirements for a support truss used in a segmented reflector telescope test-bed are identified. From these requirements a baseline model of the support truss is developed. Multicriteria optimization and Pareto optimality concepts are employed to obtain an optimal truss structure among variations of the baseline model that yields a correct balance between strength and flexibility. Modal analysis shows that the structure exhibits the characteristics of a large space-borne structure.
Development of Six Degrees of Freedom Vibration Isolation System for Microgravity Environment
Authors: Suzuki Toshiyuki , Tanida Koji , Tanji Akira , Okubo Koichi 
Published: March 2021

Abstract
An active vibration isolation system, under development for use in microgravity environment, provides electromagnetic suspension by means of voice coils arranged in pairs to control the translational and rotational movements of the payload, three pairs of which cover the three axes to ensure control of payload movement in all six degrees of freedom.
A series of tests performed on this system in microgravity environment created by parabolic flight proved that external disturbances in frequencies above 0.1 Hz were effectively reduced by applying the system. Also, good agreement was obtained between the measured performance and results of numerical simulation.
Active Constrained Layer Damping of Seismic Excitations
Authors: Baz A. , Poh S. 
Published: March 2021

Abstract
This paper aims at demonstrating the feasibility of Active Constrained Layer Dampers (ACLD) as an effective means for damping out seismic-induced vibrations of structures. The ACLD concept is motivated by the destructive effects that seismic excitations have on most of the uncontrolled structures.
The effectiveness of the ACLD in enhancing the damping characteristics of conventional visco-elastic dampers is demonstrated experimentally for structures subjected to base excitations. Classical identification methods are used to identify a mathematical model that describes the interaction between the vibrating structures, the ACLD system and the seismic excitation. The model is integrated with a robust Continuous Sliding Mode (CSM) controller to reject the effect of the seismic excitations acting on vibrating structures with uncertain dynamic parameters. In this manner, the ACLD and the CSM algorithm present a simple but yet powerful alternative to classical control methods for rejecting seismic excitations and accommodating wide range of parameter uncertainty.
The emphasis, in this paper, is placed on multi-story two-dimensional scaled structures which are provided with diagonal braces of the ACLD. However, the techniques developed can be readily extended to three-dimensional and larger structures.
Prediction of Rotating Machinery Vibration Using Balance Simulation With Measurement Uncertainty
Authors: Andrews Rob P. 
Published: March 2021

Abstract
Vibration predictions for rotating machinery with high-speed flexible rotors must account for the methods and limitations of the balance test process which determine the residual rotor unbalance. Vibration predictions based on finite element analysis (FEA) methods are highly dependent upon the assumed rotor unbalance amplitude and phase. The actual residual unbalance distribution depends upon the measured influence coefficients and the least-mean-square (LMS) algorithm used to calculate balance correction weights. Repeatability of the vibration measurements is a key factor in successful balancing. The vibration predictions described in this paper use estimates of final residual unbalance obtained by simulating the balance test process. The simulation uses FEA based influence coefficients, a test based measurement uncertainty (repeatability) model, and LMS balance weight calculations including the specified vibration target levels. The simulations can be used to predict the limit of balance performance of the machinery and to evaluate design options for impact on residual unbalance levels.
Efficient Numerical Solution of Inverse Heat Conduction Problems
Authors: Reinhardt Hans-Jürgen , Hao Dinh Nho 
Published: March 2021

Abstract
In this contribution we propose new numerical methods for solving inverse heat conduction problems. The methods are constructed by considering the desired heat flux at the boundary as piecewise constant (in time) and then deriving an explicit expression for the solution of the equation for a stationary point of the minimizing functional. In a very special case the well-known Beck method is obtained.
For the time being, numerical tests could not be included in this contribution but will be presented in a forthcoming paper.
Identification of Forces in Vibrating Plates by Pointwise and Line Observations: Uniqueness and Stability
Authors: Yamamoto Masahiro 
Published: March 2021

Abstract
We consider determination of spatially varying external forces in a rectangle vibrating plate from displacement observed along a line parallel to a side of the plate over a finite time interval. For a suitable choice of the line and a sufficient large time interval, we prove the uniqueness of external forces and estimate them by appropriate norm of displacement. Moreover we discuss determination of external forces from displacement observed at a single point over a time interval.
A Bounded Variation Approach to Inverse Interferometry
Authors: Fitzpatrick B. G. , Keeling S. L. , Rock S. G. 
Published: March 2021

Abstract
A least squares reconstruction technique is examined for determining flow-field densities from optical data. Nonintrusive optical methods have long been used for flow visualization; however, the goal of this work is to devise mathematical techniques with which optical data can be used for quantitative flow measurement. The ill-posedness of density computation from interferogram measurements is recognized as a serious limitation in direct inversion methods. Here, least squares techniques employing compactness constraints are developed to avoid the difficulties encountered in traditional approaches.
Computer Simulation for Active Control of Vibration in Beam Structures
Authors: Tanaka Masa. , Matsumoto T. , Huang L. 
Published: March 2021

Abstract
This paper is concerned with an inverse problem of the active control of non-steady dynamic vibration in elastic beams. A simulation technique based on the boundary element method and the extended Kalman filter or a new filter theory is successfully applied to the inverse problem. The Laplace-transform integral equation method is used for the solution of dynamic bending vibration in elastic beams. Through a Taylor series expansion, the linear system of equations is derived for modification of the unknown parameters, and it is solved iteratively so that an appropriate norm is minimized. The usefulness of the proposed method of inverse analysis is demonstrated through numerical computation of a few examples.
Updating of Finite Element Models Based on a Double Condensation Procedure Using Frequency Response Functions Data
Authors: Berriet Rémi , Fillod René , Bouhaddi Noureddine 
Published: March 2021

Abstract
In order to take into account information from test data, not only at the resonances, but also in the other parts of the measured frequency spectrum, it is of interest to use directly measured Frequency Response Functions (FRF) instead of modal data. We also avoid by this way an experimental modal analysis. In return we have to introduce damping terms into the analytical model, we have to weight the FRF data in a systematic manner and to compute simultaneously a large amount of data. The presented procedure analyses overall these three aspects: definition of modal damping parameters, definition of weighted FRF data and condensation of the problem. This last notion is particularly pointed out. The condensation is performed in two steps : a static condensation of the model on the degrees of freedom corresponding to the location of the sensors, and a simultaneous condensation of experimental and analytical FRF data by a common transformation matrix. The first applications are performed on a simulated test case with large stiffness, mass and modal damping perturbations introduced in the initial model as well as strong noise pollution of measured responses and applied forces.
A Weighted Rearranged Spectral Equation Method for Structural Model Updating
Authors: Arruda José Roberto F. , Verçosa Carlson Antonio M. 
Published: March 2021

Abstract
A new structural model updating method based on the dynamic force balance is presented. The method consists of rearranging the spectral equation so that measured modes and natural frequencies can be used to compute directly updated stiffness coefficients. The proposed method preserves both the structural connectivity and reciprocity, which translate into sparsity and symmetry of the stiffness matrix, respectively. Large changes in small-valued stiffness coefficients are avoided using parameter weighting in the rearranged spectral equation solution. It is shown that the proposed method produces results which are similar to the results obtained using Alvar Kabe’s method, with the advantages of simpler formulation and smaller computational cost. A simple example of an 8 degrees-of-freedom mass-spring system, originally used by Kabe to present his method, is used here to evaluate the proposed method.
Fault Detection and Isolation Procedures Contribute to Damage Diagnosis of Rotating Machinery
Authors: Seibold Susanne 
Published: March 2021

Abstract
Fault Detection and Isolation (FDI) procedures are being increasingly used for monitoring and diagnosis in the control area. In contrast to signal-based approaches, which merely rely on an analysis of the measurements, model-based FDI-procedures utilize additionally a model of the system under investigation. By linking model and measurement algorithmically, specific parameters can be calculated which indicate type, location and extent of the fault.
In this paper, a concise introduction to model-based FDI-procedures is given. A specific algorithm is explained more thoroughly: the Extended Kalman Filter (EKF), which allows for simultaneous estimation of states and parameters of linear and nonlinear systems. A modal formulation of the EKF (MOKF) is presented, which is based on a modal reduction of the system equations. Furthermore, it is explained how EKF and the Instrumental Variables method can be combined.
The model-based procedures will be applied to a simulated rotor, and to a rotor test rig modelled by finite elements in order to diagnose a crack in the shaft.
Dynamics of a Flexible Rotating Beam Under Percussive and Constrained Motion
Authors: Hatman Victor G. , Haque Imtiaz , Bagchi Amit 
Published: March 2021

Abstract
This paper presents a dynamical and computational model for the analysis of the interaction of a flexible Euler-Bernoulli beam attached to a uniformly rotating hub, and a flat rigid surface, parallel to the axis of the hub. The dynamic model is derived using Lagrange’s equations in conjunction with an eigenfunctions-generalized-coordinates based representation of the displacement fields. It is shown that one must account for the longitudinal displacements if dynamical stiffening is to be observed. A quadratic approximation for these displacements is used and a computationally effective way of by-passing the calculation of the volume integrals at every integration step, by matrix-vector multiplications is implemented. The energy dissipating constraint, which requires the tip of the filament to move on the surface is imposed with a Lagrange multiplier and a generalized friction force. A procedure of evaluating the generalized friction force in terms of the generalized coordinates and velocities is presented. A complete numerical algorithm for the entire intermittent interaction process is developed. The presence of dynamical stiffening is tested and the calculated values of the fundamental frequency are found in excellent agreement with data from literature. Simulation results for the time history of the normal contact force indicate that the contact zone is discontinuous, and that the force is strongly dependent on the hub angular speed and on the distance from the center to the flat surface.
Vibration Measurement Using Additive Speckle Interferometry
Authors: Wang Liusheng , Fomitchov Pavel , Krishnaswamy Sridhar 
Published: March 2021

Abstract
A method for obtaining structural vibration amplitudes quantitatively is proposed based on the stroboscopic speckle interferometer. The technique requires five frames of additive speckle patterns: the first one (S0) taken with the laser illumination pulsed at instants when the vibration achieves its two zero amplitude positions within one sinusoidal vibration cycle of the specimen; and the remaining four (S1 through S4) taken with the illumination pulses arranged at times when the vibration is at its maximum and minimum amplitudes. During the acquisition of speckle patterns S1 through S4, the phase of the reference beam is appropriately shifted between the two pulses within each vibration cycle. The last four speckle patterns are then subtracted from the first one to yield four correlation fringe patterns with relative phase shifts of 0, π/2, π and 3π/2 respectively. These fringe patterns are then utilized to derive a phase map using a four-step phase calculation algorithm and finally the vibration amplitude and the sign of the vibrational nodes can be readily obtained from the phase map quantitatively. Results have been obtained using a speckle shearographic setup for the vibration measurement of a flat bottom-holed aluminum specimen vibrating at different frequencies.
Application of Laser Vibrometry to Vibration Measurement on Rotating Components
Authors: Rothberg Steven J. , Halliwell Neil A. 
Published: March 2021

Abstract
This paper describes the application of Laser Doppler Vibrometry to vibration measurements on rotating targets. The noise generating mechanism of the laser speckle phenomenon is first explained before confirmation of the insensitivity of measurements to target shape. The principal focus of the paper is on the fundamental limitation associated with the use of Laser Vibrometers for radial vibration measurements directly on rotating components. In such measurements significant cross-sensitivities to speed fluctuations, including torsional vibrations, and in-plane vibrations are evident, preventing synchronous vibration analysis. Mathematical and electronic means to resolve the correct orthogonal vibration components are presented and shown to be successful in enabling the use of Laser Vibrometry for non-synchronous vibration measurements.
Formal Basis of a Language Universal
Authors: Stanojević Miloš , Steedman Mark 
Published: March 2021

AbstractSteedman (2020) proposes as a formal universal of natural language grammar that grammatical permutations of the kind that have given rise to transformational rules are limited to a class known to mathematicians and computer scientists as the “separable” permutations. This class of permutations is exactly the class that can be expressed in combinatory categorial grammars (CCGs). The excluded non-separable permutations do in fact seem to be absent in a number of studies of crosslinguistic variation in word order in nominal and verbal constructions.The number of permutations that are separable grows in the number n of lexical elements in the construction as the Large Schröder Number Sn−1. Because that number grows much more slowly than the n! number of all permutations, this generalization is also of considerable practical interest for computational applications such as parsing and machine translation.The present article examines the mathematical and computational origins of this restriction, and the reason it is exactly captured in CCG without the imposition of any further constraints.
Interpretability Analysis for Named Entity Recognition to Understand System Predictions and How They Can Improve
Authors: Agarwal Oshin , Yang Yinfei , Wallace Byron C. , Nenkova Ani 
Published: March 2021

Abstract
Named entity recognition systems achieve remarkable performance on domains such as English news. It is natural to ask: What are these models actually learning to achieve this? Are they merely memorizing the names themselves? Or are they capable of interpreting the text and inferring the correct entity type from the linguistic context? We examine these questions by contrasting the performance of several variants of architectures for named entity recognition, with some provided only representations of the context as features. We experiment with GloVe-based BiLSTM-CRF as well as BERT. We find that context does influence predictions, but the main factor driving high performance is learning the named tokens themselves. Furthermore, we find that BERT is not always better at recognizing predictive contexts compared to a BiLSTM-CRF model. We enlist human annotators to evaluate the feasibility of inferring entity types from context alone and find that humans are also mostly unable to infer entity types for the majority of examples on which the context-only system made errors. However, there is room for improvement: A system should be able to recognize any named entity in a predictive context correctly and our experiments indicate that current systems may be improved by such capability. Our human study also revealed that systems and humans do not always learn the same contextual clues, and context-only systems are sometimes correct even when humans fail to recognize the entity type from the context. Finally, we find that one issue contributing to model errors is the use of “entangled” representations that encode both contextual and local token information into a single vector, which can obscure clues. Our results suggest that designing models that explicitly operate over representations of local inputs and context, respectively, may in some cases improve performance. In light of these and related findings, we highlight directions for future work.