bluuebunny/crossref_metadata_2025 huggingface dataset:
Automated Design Tool for Examining Microelectronic Packaging Design Alternatives
Authors: Chin Siew-Wei , Rajan Subramaniam D. , Nagaraj Ben K. , Mahalingam Mali
Published: March 2021

Microelectronic packaging design issues have been given greater attention mainly because the performance, reliability and cost of semiconductor chips are increasingly dictated by the choice and design of the package. The task of integrating the requirements imposed by different disciplines such as mechanical and thermal issues in an automated design tool, is discussed in this paper. Finite element analysis and nonlinear programming techniques are used in an iterative fashion to progress from an initial design concept to a design that satisfies all design requirements or one that is superior to other design alternatives. Two packaging design examples serve to illustrate the functionalities of the automated design optimization tool.
Computational Simulation of Hot Composite Structures
Authors: Chamis C. C. , Murthy P. L. N. , Singhal S. N.
Published: March 2021

Computational procedures are described to simulate the thermal and mechanical behavior of high temperature metal matrix composites (HT-MMC) in the following three broad areas: (1) behavior of HT-MMC from micromechanics to laminate via Metal Matrix Composite Analyzer (METCAN), (2) tailoring of HT-MMC behavior for optimum specific performance via Metal Matrix Laminate Tailoring (MMLT), and (3) HT-MMC structural response for hot structural components via High Temperature Composite Analyzer (HITCAN). The complex composite material behavior, static/fatigue life, and failure sequence of SiC/Ti ring was simulated. The observed experimental degradation in strengths of the SiC/Ti composite with increasing temperature was accurately predicted. The static/fatigue life of the SiC/Ti ring starting with the fabrication process cool-down and subjected to simulated internal pressure was predicted in terms of cyclic-stress-to-static strength-ratio versus cycles to failure.
On Interaction of Eigenvalue Branches in Non-Conservative Multi-Parameter Problems
Authors: Seyranian Alexander P. , Pedersen Pauli
Published: March 2021

In this paper two interesting mechanical (physical) phenomena are considered. The first one is the phenomenon of transference of instability between branches. The second phenomenon is the destabilization effect due to infinitely small damping. The considerations and the explanations are given from the point of view of behaviour of eigenvalue branches in the vicinity of a double eigenvalue. These questions are close connected with sensitivity analysis of non conservative systems subjected to instability phenomena, and thus the present work is a continuation of our earlier published joint research. Also the extended information available by Hurwitz determinants is focused on.
Nonlinear Response of a Clamped Plate to Nonstationary Excitation: Experiments and Theory
Authors: McCabe Sarah A. , Chang Seo I. , Davies Patricia , Bajaj Anil K.
Published: March 2021

The paper contains a description of a series of experiments conducted on a thin rectangular plate. The initial objective of the experiments was to observe behavior predicted by theoretical studies and observed in simulations of the plate response. The theoretical work centered on predicting the behavior of plates having modes with coincident natural frequencies and driven with a constant sinusoidal excitation. Of particular interest was the modal coupling, due to nonlinearities, which give rise to the possibility of a coupled mode response when only a single mode is excited. Experimental constraints, and the sensitivity of the plate in configurations where more than one mode of response is possible, meant that the best experimental excitation of the plate would be a sine wave with a very slowly varying frequency. A PC based signal generator was developed to drive an array of loudspeakers so that particular modes of the plate could be strongly excited, and the frequency of excitation could be varied. To gain an understanding of the behavior of the plate when the excitation is nonstationary, the theoretical analysis of the plate behavior was extended to incorporate sinusoidal excitation where the frequency varied with time. The results of the analysis is a prediction of the response amplitude for slow and relatively fast swept sine wave excitations. In the paper, the qualitative features of the experimental response amplitudes are compared to those predicted by theory.
Effect of Coupler Material Damping on Steady-State Response Calculation of Elastic Mechanisms
Authors: Chivate Pramod N. , Farhang Kambiz
Published: March 2021

This paper presents an investigation of the steady-state response of flexible mechanisms. Two methods are utilized to obtain the steady-state response for the flexible coupler of a slider-crank mechanism with varying degrees of material damping. The first method, based on a sixth-order Runge-Kutta formulation, is shown to be effective only for high values of material damping. The second method, which utilizes the discretization of the fundamental time period of response, is found to be effective and efficient for obtaining the steady-state response at all damping values. Algorithm results for high as well as low operating speeds are shown to be in good agreement with the Runge-Kutta method of integration. For the case of very low damping, system response is found to be aperiodic. Using the Poincare’ mapping technique, the aperiodicity is investigated and is found to be mainly due to the Runge-Kutta integration technique.
Effect of Meshing Parameters on the Dynamic Loads of a Mechanism With Spur Gears
Authors: Belnikolovsky Boris G. , Cheshankov Bozhidar I. , Abuid Bader A.
Published: March 2021

In the model used inertias of motor, machine and the gear wheels, stiffness of shafts and bearing and damping are considered. In the meshing zone, the variable stiffness of teeth, pitch error, tooth deflection, tooth modification and impact between teeth are included. Differential equations of motion are written and solved analytically and numerically. Based on the good agreement between the analytical and the numerical results, a dynamic analysis for the effect of many parameters of meshing, such as pitch error, tooth modification, module, contact ratio, tooth width and the gear ratio on the dynamic loads is made.
Use of a Pendulum for Passive Structural Vibrations Control: An Experimental Study
Authors: Ertas A. , Cuvalci O.
Published: March 2021

The dynamic response of a beam-tip mass-pendulum system subjected to sinusoidal excitations is considered. The conditions under which resonant and nonresonant oscillations occur are investigated and discussed. The main objective of this study was to conduct a series of experiments to investigate the autoparametric interaction between the first two modes of the system. The use of a pendulum as a passive control device was experimentally evaluated.
Dynamic Behavior of a Drillstring: Presentation and Validation of the Experimental Set-Up
Authors: Berlioz Alain , Hagopian Johan Der , Dufour Régis , Draoui Elyés
Published: March 2021

As part of a large study on oil drilling vibrations involving, theory, laboratory tests and development of computer code, the present paper focuses on the effects of the tangential solicitations on the lateral behavior of a rod, representative of drillstring. The lateral behavior of the drillstring is governed by time-varying parameter equations. The torsion-lateral and longitudinal-lateral couplings are both experimentally and numerically studied and particular attention is paid to lateral instabilities. The effect of the curvature of the rod, mud, stabilisers and rotation are taken into account.
Nonstationary Vibration of a Rotating Shaft With Nonlinear Spring Characteristics During Acceleration Through a Major Critical Speed: A Discussion by the Asymptotic Method and the FFT Method
Authors: Ishida Yukio , Yasuda Kimihiko , Murakami Shin
Published: March 2021

Nonstationary vibrations at the major critical speed of a rotating shaft with nonlinear spring characteristics are discussced. Firstly, the first order approximate solutions of steady-state and nonstationary oscillations are obtained by the asymptotic method. The relations between these approximate solutions and the nonlinear components in the polar coordinate expression are investigated. It is clarified that, similar to the case of the stationary oscillations, only the isotropic nonlinear component has influence on nonstationary oscillations in the first order approximation. Secondly, the complex-FFT method where non-stationary time histories obtained by numerical integrations of the equations of motion are treated as complex numbers in the complex plane which coincides with the whirling plane are proposed. By this method, the amplitude variation curves of each vibration component are obtained. From the comparison of the amplitude variation curves of the first approximation of the asymptotic method, the solution of the complex-FFT method, and direct numerical integration, it is clarified that, although all these solutions coincide well in the case of stationary solutions, the first approximation of the asymptotic method has comparatively large quantitative error in the case of nonstationary solutions. In addition, the influences of the anisotropic nonlinear components which do not appear in the first approximation of the asymptotic method are investigated.
Response of a Parametrically-Excited System to a Nonstationary Excitation
Authors: Neal H. L. , Nayfeh A. H.
Published: March 2021

The response of a single-degree-of-freedom system to a nonstationary excitation is investigated by using the method of multiple scales as well as analog- and digital-computer simulations. The unexcited system has one focus and two saddle points. The system can be used to model rolling of ships in head or follower seas. The method of multiple scales is used to derive equations governing the modulation of the amplitude and phase of the response. The modulation equations are used to find the stationary solutions and their stability. The response to nonstationary excitations is found by integrating the original governing equation as well as the modulation equations. There is good agreement between the results of both approaches. For some frequency and amplitude sweeps, the nonstationary response found from integrating the original governing equation exhibits behaviors that are analogous to symmetry-breaking bifurcations, period-doubling bifurcations, chaos, and unboundedness present in the stationary case. The maximum response amplitude and the excitation amplitude or frequency at which the response becomes unbounded are found as functions of the sweep rate. The results of the digital-computer simulations are verified with an analog computer.
Perturbation Solution of an Oscillator With Periodic van der Pol Damping
Authors: Storti Duane W. , Nevrinceanu Cornelius , Reinhall Per G.
Published: March 2021

We present a perturbation solution for a linear oscillator with a variable damping coefficient involving the limit cycle of the van der Pol equation (van der Pol 1926). This equation arises as the variational equation governing the stability of in-phase vibration in a pair of identical van der Pol oscillators with linear coupling. The van der Pol oscillator has served as the classic example of a limit cycle oscillator, and coupled limit cycle oscillators appear in mathematical models of self-excited systems ranging from tube rows in cross flow heat exchangers to arrays of stomates in plant leaves.

As in many systems modeled by coupled oscillators, criteria for phase-locking or synchronization are of fundamental importance in understanding the dynamics. In this paper we study a simple but interesting problem consisting of a pair of identical van der Pol oscillators with linear diffusive coupling which corresponds, in the mechanical analogy, to a spring connecting the masses of the two oscillators. Intuition and earlier first-order analyses suggest that the spring will pull the two masses together causing stable in-phase locking. However, previous results of a relaxation limit study (Storti and Rand 1986) indicate that the in-phase mode is not always stable and suggest the existence of an additional stability boundary.

To resolve the apparent discrepancy, we obtain a new periodic solution of the variational equation as a power series in ε, the small parameter in the sinusoidal van de Pol oscillator. This approach follows Andersen and Geer’s (1982) solution for the limit cycle of an isolated van der Pol oscillator. The coupling strength corresponding to the periodic solution of the variational equation defines an additional stability transition curve which has only been observed previously in the relaxation limit. We show that this transition curve, which provides a consistent connection between the sinusoidal and relaxation limits, is O(ε2) and could not have been delected in O(ε) analyses. We determine the analytical expression for this stability transition curve to O(ε31) and show very favorable agreement with numerical results we obtained using an Adams-Gear method.
Nonlinear Interaction of a Parametrically-Excited Coupled Column-Pendulum Oscillator
Authors: Mustafa G. , Ertas A.
Published: March 2021

A new vibration absorbing device is introduced for large flexible structures. The bifurcation diagrams obtained for the averaged system, indicate that the system loses stability via two distinct routes. One leading to a saddle-node bifurcation, normally associated with the jump phenomena. The second instability is due to the Hopf bifurcation, that results in amplitude modulated motion of the oscillator. A parameter range has been identified where these bifurcations coalesce. This phenomenon is a strong indicator of existence of homoclinic orbits. In addition to the regular solution branches, that bifurcate from the zero solution, the system also possesses isolated solutions (the so-called “isolas”) that form isolated loops bounded away from zero. As the forcing amplitude is varied, the isolas appear, disappear or coalesce with the regular solution branches. The response curves indicate that the column amplitude shows saturation. The pendulum acts as a vibration absorber over a range of frequency where the column response is saturated. However, there is also a frequency range over which a reverse flow of energy occurs, where the pendulum shows reduced amplitude at the cost of large amplitudes of the column.
Free and Forced Response of an Axially Moving String Transporting a Damped Linear Oscillator
Authors: Zhu W. D. , Mote C. D.
Published: March 2021

The transverse response of a cable transport system, which is modelled as an ideal, constant tension string travelling at constant speed between two supports with a damped linear oscillator attached to it, is predicted for arbitrary initial conditions, external forces and boundary excitations. The exact formulation of the coupled system reduces to a single integral equation of Volterra type governing the interaction force between the string and the payload oscillator. The time history of the interaction force is discontinuous for non-vanishing damping of the oscillator. These discontinuities occur at the instants when transverse waves propagating along the string interact with the oscillator. The discontinuities are treated using the theory of distributions. Numerical algorithms for computing the integrals involving generalized functions and for solution of the delay-integral-differential equation are developed. Response analysis shows a discontinuous velocity history of the payload attachment point. Special conditions leading to absence of the discontinuities above are given.
Kinematics and Dynamics of a Parallel Manipulator With Woven Joints
Authors: Pang Hyunsok
Published: March 2021

Presented is an analysis of the kinematics and the inverse dynamics of a proposed three DOF parallel manipulator resembling the Stewart platform in a general form. In the kinematic analysis, the inverse kinematics, velocity and acceleration analyses are performed, respectively, using vector analysis and general homogeneous transformations. An algorithm to solve the inverse dynamics of the proposed parallel manipulator is then presented using a Lagrangin technique. In this case, it is found that one should introduce and subsequently eliminate Lagrange multipliers in order to arrive at the governing equations. Numerical examples are finally carried out to examine the validity of the approach and the accuracy of the numerical technique employed. The trajectory of motion of the manipulator is also performed using a cubic spline.
Distributed Observing and Active Control of a Cantilever Plate
Authors: Tseng C. I. , Tzou H. S.
Published: March 2021

Structural identification and vibration control of flexible systems have drawn much attention in recent years. This article presents an analytical study on a distributed piezoelectric sensor and a distributed actuator coupled with a flexible plate. The integrated piezoelectric sensor/actuator can monitor the oscillation as well as actively control the structural vibration by the direct/converse piezoelectric effects, respectively. Based on Love assumptions, theories on distributed sensing and active vibration control of a plate using piezoelectric materials are derived. By employing the finite element technique, the integrated structure is further discretized. Applications to the dynamic measurement is demonstrated and the dynamic performance of a cantilever plate is also evaluated.
Distributed Transfer Function Synthesis of Complex Flexible Systems
Authors: Yang Bingen
Published: March 2021

This paper presents a new analytical and numerical method for modeling and synthesis of complex flexible systems (CFS) that are multiple continua combined with lumped parameter systems. In the analysis, the CFS is first divided into a number of subsystems; the distributed transfer functions of each subsystem are determined in exact and closed form by a state space technique. The CFS is then assembled by imposing displacement compatibility and force balance at the nodes where the subsystems are interconnected. With the distributed transfer functions and the transfer functions of the constraints and lumped parameter systems, exact, closed-form formulation is obtained for various dynamics and vibration problems. The method does not require a knowledge of system eigensolutions, and is valid for non-self-adjoint systems with inhomogeneous boundary conditions. In addition, the proposed method is convenient in computer coding, and suitable for computerized symbolic manipulation.
On the Identification of Localized Losses of Stiffness in Structures
Authors: Pabst Ulrich , Hagedorn Peter
Published: March 2021

In damage detection it is common to use measured modal data and a mathematical model in connection with system identification. The part of the system undergoing the largest stiffness decrease is defined to contain damage. This approach is very sensitive to measurement errors. The measurement errors are much larger for mode shape functions than for the eigen-frequencies. The errors in the mode shapes are often of the same order of magnitude as the variations due to damage leading to poor results in damage detection. Thus, the use of the mode shape functions themselves instead of their small damage induced variations would dearly be preferable. In this paper we examine the relation between the changes in the eigenfrequencies, the local stiffness losses and the mode shape functions of the undamaged system. This relation is then utilized in a damage detection procedure.
Vibration Localization in Band/Wheel Systems: Theory and Experiment
Authors: Al-jawi A. A. N. , Ulsoy A. G. , Pierre Christophe
Published: March 2021

An investigation of the localization phenomenon in band/wheel systems is presented. The effects of tension disorder, interspan coupling, and translation speed on the confinement of the natural modes of free vibration are investigated both theoretically and experimentally. Two models of the band/wheel system dynamics are discussed; a simple model proposed by the authors [1] and a more complete model originally proposed by Wang and Mote [9]. The results obtained using the simple interspan coupling model reveal phenomena (i.e., eigenvalue crossings and veerings and associated mode localization) that are qualitatively similar to those featured by the more complex model of interspan coupling, thereby confirming the usefulness of the simple coupling model. The analytical predictions of the two models are validated by an experiment. A very good agreement between the experimental results and the theoretical ones for the simple model is observed. While both the experimental observations and the theoretical predictions show that a beating phenomenon takes place for ordered stationary and axially moving beams, beating is destroyed (indicating the occurrence of localization) when any small tension disorder is introduced especially for small interspan coupling (i.e., when localization is strongest).
Input Sensitive Dynamic Resistor of a Rotating System
Authors: Lee B. K.
Published: March 2021

This paper presents the dynamic response and analysis of a dynamic resistor in a rotating system which is sensitive to the vibration of the rotating system. The sensitivity of the dynamic resistor is adjusted in order to stabilize the rotating system when acted upon by various excitation input functions. The equations of motion of the dynamic resistor and the rotating system, derived by the use of the energy method, result in coupled nonlinear differential equations, and the response of the dynamic resistor is highly correlated to the vibration of the rotating system.

In this paper, the derivation of equations of motion of the dynamic resistor and the rotating system and their dynamic responses are analyzed in order to determine the optimal design parameters that provide stability for the rotating system when it is excited by external input forcing functions. The dynamic response is obtained both by experimental data and computer simulation. The experimental data indicate that the sensitivity of the dynamic resistor is related to the vibrating response of the rotating system and the rotational system parameters including the natural frequency.

The dynamic response obtained by computer simulation is compared with the experimental data. The computer simulation results are to be used to determine the optimal values of the parameters of the dynamic resistor with respect to the rotating system.

The uniqueness of this system is that the dynamic resistor is completely isolated from other inputs except the rotational vibration of the rotating system. The conclusions include recommendations and areas for future research.
Non-Linear Vibrations and Asymmetry in Coupled Tandem Hot Rolling Mills
Authors: Jafari A. A. , Tieu A. K. , Basu A.
Published: March 2021

This paper discusses the computer simulation of the interactions between the torsional vibration mode and linear vibration mode of a vertical edging mill and a horizontal roughing mill which are coupled by a hot steel slab. The influence of the mass, rigidity and damping of the slab in both elastic and plastic regions have been considered. This non-linear simulation also takes into account backlash on the drive shaft and asymmetrical rolling condition in horizontal mill.
Vibration of a Rotating Stepped Beam by the Distributed Transfer Function Method
Authors: Kuang W. , Tan C. A.
Published: March 2021

In this paper, the distributed transfer function formulation is used to investigate the dynamic characteristics of a rotating stepped beam. The Rayleigh beam model with general boundary conditions is considered. Exact closed-form solutions are obtained for the free and forced responses. Results for the natural frequencies and mode shapes of the stepped beam are presented. For the purpose of illustration, three sets of boundary conditions are considered: simply-simply supported, clamped-clamped, and clamped-simply supported. Effects of system parameters such as the length ratio and diameter ratio of the beam on the free and forced responses are examined and discussed. It is shown that for different combinations of boundary conditions, the pair of natural frequencies for the forward and backward precession modes are associated with different mode shapes except for the simply-simply supported beam. Moreover, the difference between the forward and backward mode shapes increases with the rotation speed of the beam.
High Speed Rotating Shafts Design Algorithm
Authors: Wong Po Kee
Published: March 2021

This paper reveals an invention for the first time to the public about the fundamental concepts for the design of high speed rotating shafts based on the wave spectrum analysis of the vibrational modes of elastic circular rods and shells that was completed in 1967, even though the Pochhammer-Chree-Love solution of the transversal (n = 1) vibration of a solid elastic rod was originated by Pochhammer in 1876.
Development of an On-Line PC-Based Diagnostic Expert System
Authors: Pawtowski E. C. , Kirk R. G. , Cochran J. S.
Published: March 2021

A PC-based hardware and software system has been designed to continuously monitor large numbers of rotating machinery, evaluate each machine’s condition through a series of user-definable standards, and alert operators to potential problems. This system employs multiple program modules written in three different programming languages that multitask under the Windows operating system. These modules interact without the use of dynamic data links. It has developed as an offshoot of the WOT on-line expert system project. Preliminary versions have been tested under operating plant conditions.
Internal Rotor Friction Induced Instability in High-Speed Rotating Machinery
Authors: Walton James F. , Martin Michael R.
Published: March 2021

Results of a program to investigate internal rotor friction destabilizing effects are presented. Internal-friction-producing joints were shown to excite the rotor system first natural frequency, when operating either below or above the first critical speed. The analytical models used to predict the subsynchronous instability were also confirmed. The axial spline joint demonstrated the most severe subsynchronous instability. The interference fit joint also caused subsynchronous vibrations at the first natural frequency but these were bounded and generally smaller than the synchronous vibrations. Comparison of data from the two test joints showed that supersynchronous vibration amplitudes at the first natural frequency were generally larger for the interference fit joint than for the axial spline joint. The effects of changes in imbalance levels and side loads were not distinguishable during testing because amplitude-limiting bumpers were required to restrict orbits.
Active Vibration Control of the Axially Moving String by Wave Cancellation
Authors: Chung C. H. , Tan C. A.
Published: March 2021

Active vibration control of an axially moving string by wave cancellation is presented. The control problem is formulated in the frequency domain. An exact, closed-form expression for the transfer function of the closed-loop system, consisting of the flexible structure, a feedback control law and the dynamics of the sensing and actuation devices, is derived. It is shown that all vibration modes can be stabilized and that the controlled system has no resonance. Moreover, the designed controller is applicable to the control of the string transverse vibration under various kinds of loading and constraint conditions. Results for the response of the controlled string under different excitations are presented and discussed along with the wave propagation and cancellation characteristics.
Modeling and Control of a Nonlinear Beam
Authors: Banks H. T. , King Belinda B.
Published: March 2021

In this paper we develop a mathematical model for a nonlinear analog of the Euler-Bernoulli beam which possesses linear damping and nonlinear stiffness properties. This nonlinear model is used as a basis for approximation and linearization. Feedback design for the linear problem is applied to compute gains which are then used in the nonlinear system.
Segmented Two-Dimensional Modal-Filtering Sensors
Authors: Sumali Hartono , Cudney Harley
Published: March 2021

This paper discusses the development of a method to create modal coordinate sensors on two-dimensional structures. The sensor, which is made of a piezoelectric layer, is divided into an array of segments. The total output of the sensor is the weighted sum of the outputs of the segments. The purpose of this segmentation is to bypass the requirement for a continuous spatial variation of polarization, which is necessary in creating an ideal two-dimensional modal sensor but infeasible in practice and unworkable for most boundary conditions.

Analytical simulation on a simply-supported plate shows that the performance of a modal sensor created by configuring a segmented sensor approaches that of an ideal modal sensor. Modal filtering effects increase with the decrease in the segment size.
A Slewing Motor-Beam System With Coulomb Friction Including Experimental Results
Authors: Crassidis Agamemnon L. , Mayne Roger W.
Published: March 2021

This paper considers the effect of Coulomb friction on the behavior of a slewing motor-beam system. A model of the system is described which includes a finite element representation for the beam, dynamic interaction between the motor and the beam, and a representation for Coulomb friction. The model is used in the study of closed-loop transient response of the slewing system. Simulation results are compared against laboratory behavior. The model reasonably predicts slewing behavior. It simulates steady state error in the control of slewing angle and can represent the case of shaft lock-up which leaves the beam oscillating freely. The system gear ratio is adjusted to produce different levels of motor-beam dynamic interaction. Control performance is similar to that expected from studies of the linear slewing system. For a gear ratio that yields little motor-beam interaction, beam vibration is difficult to suppress. A gear ratio that heavily loads the motor and has too much interaction shows considerable actuation effort for a given level of transient response speed.
Modeling and Analysis of the Control System of a Satellite Tracking Antenna
Authors: Daffron William C. , Vu Hung V.
Published: March 2021

In this paper a model is developed for the 60-foot satellite tracking antenna at Vandenberg Tracking Station (VTS). The model includes the control system, the motors, and the antenna structure. The antenna performance is simulated, using MATRIXX/SystemBuild, for two kinds of inputs: step functions and satellite passes. The predicted antenna performance is then compared to real antenna data, that was recorded at VTS, in order to demonstrate the accuracy of the model. Finally, the model is used to predict the antenna performance on a satellite pass for which no real data is available. The model shows that the antenna is capable of performing this pass with tracking errors less than the specified 2 milliradians (0.114°).
Acoustic Impact Technique for Characterization of Defects in Laminated Composites
Authors: Haque A. , Raju Pollapragada K.
Published: March 2021

The Acoustic Impact Technique (AIT) of nondestructive testing (NDT) has been investigated in detecting gross defects such as delamination in laminated composites. The use of Acoustic Impact Technique has shown encouraging results by previous investigators in identifying defects like delamination and disbonds in honeycomb structures. Very limited work has been reported in the literature about the utility of AIT as a NDT tool for testing in laminated structures. The present work investigates the sensitiveness of the AIT method in detecting delamination in laminated composites in terms of size, shape, position and degree of concentration. The significant advantage of AIT is that this technique is attractive for field applications. The method involves striking the structure with an instrumented impacter in the region of interest and recording the time history of the impulse. The response of the signals received from both good and defective zones of a specimen were analyzed in the time domain. The experimental configuration used by previous investigators was very restrictive. In this study a different approach to AIT is developed. The effectiveness of AIT was evaluated by making a comparative study with ultrasonic C-scan in detecting similar types of defects.

The results indicate the sensitiveness of AIT in detecting delamination in laminated composites in terms of size, depth and degree of concentration.
Transverse Vibrations of a Roller Chain Drive With a Tensioner
Authors: Choi Woosuk , Johnson Glen E.
Published: March 2021

A dynamic model for analysis of the performance of roller chain drive with a tensioner is presented. The model is based on the axially moving material model first given by Mote, but includes extensions that allow consideration of the effects of polygonal action, impact, and the periodic span length changes. Three equations of motion are obtained — one for the tensioner and one for each of the chain spans. The motion of the tensioner interacts with the motions of the chain spans through the chain tension, the contact angles, and the transverse displacement changes of the contact points. The effects of the periodic length change, tensioner stiffness, tensioner damping, tensioner position and external periodic load are investigated. Some of the results are compared to those obtained for a comparable chain drive without a tensioner. Solutions are obtained by a finite difference method.
Dynamics of Curved Beams Undergoing Large Overall Motions Using the Mode Decomposition Concept
Authors: D’Costa Joseph F. , Stolarski Henryk K. , Erdman Arthur G.
Published: March 2021

A fully nonlinear formulation for the dynamics of initially curved and twisted beams, undergoing arbitrary spatial motions, is presented. The formulation admits finite bending, shearing and extension of the beam. The Mode decomposition method is employed to modify the strains in the finite element discretization process leading to the elimination of shear and membrane locking phenomena that arise in curved elements. The model incorporates all inertia effects and is capable of accurately capturing the phenomena of dynamic stiffening due to the coupling of the axial and membrane forces to the flexural deformation. All motion is referred to the inertial frame. The nonlinear formulation is suitable for modeling flexible multibody systems. Examples are presented to illustrate the validity of the proposed formulation.
Interval Analysis of Vibrating Systems
Authors: Dimarogonas Andrew D.
Published: March 2021

Interval calculus is a tool to evaluate a mathematical expression for ranges of values of its parameters. The basic mathematical operations are defined in the interval algebra.

Vibrating systems having system parameters, initial conditions or forcing functions defined as intervals rather than single-valued quantities have been modeled with interval calculus.

The eigenvalue problem for determining natural frequencies and vibrating modes of a system in the case of system matrix elements given as a range of values cannot be solved by exhaustion due to the prohibitively large number of solutions of the point-number eigenvalue problem. Eigenvalue solution with interval evaluation of the commonly used numerical techniques is not feasible because if they are applied directly, the solution intervals diverge. An optimization technique was used to obtain the minimum-radius intervals of the solution. To assure monotonicity and absolute inclusion, necessary for convergence to the exact interval, a converging interval halving sequence was developed. For numerical tests of the method a Monte Carlo solution was developed. Results showed that interval analysis can predict the range of the eigenvalues with sufficient accuracy.

The response of a linear system to general excitation for interval matrices of the system parameters cannot be found with interval evaluation of the commonly used numerical techniques because if they are applied directly, the solution intervals diverge. Interval modal analysis and the interval solution of the eigenvalue problem were developed.

An application is presented for the dynamic response of a rotor with interval bearing properties.
Inelastic Analysis of Reinforced Concrete Shear Wall Structures Under Seismic Excitation
Authors: Wang Ming L.
Published: March 2021

During strong ground motions, members of reinforced concrete structures undergo cyclic deformations and experience permanent damage. Members may lose their initial stiffness as well as strength. Recently, Los Alamos National Laboratory has performed experiments on scale models of shear wall structures subjected to recorded earthquake signals. In general, the results indicated that the measured structural stiffness decreased with increased levels of excitation in the linear response region. Furthermore, a significant reduction in strength as well as in stiffness was also observed in the inelastic range. Since the in-structure floor response spectra, which are used to design and qualify safety equipment, have been based on calculated structural stiffness and frequencies, it is possible that certain safety equipment could experience greater seismic loads than specified for qualification due to stiffness reduction. In this research, a hysteresis model based on the concept of accumulated damage has been developed to account for this stiffness degradation both in the linear and inelastic ranges. Single and three degrees of freedom seismic Category I structures were analyzed and compared with equivalent linear stiffness degradation models in terms of maximum displacement responses, permanent displacement, and floor response spectra. The results indicate significant differences in responses between the hysteresis model and equivalent linear stiffness degradation models. The hysteresis model is recommended in the analysis of reinforced concrete shear-wall structures to obtain the in-structure floor response spectra for equipment qualification. Results of both cumulative and one shot tests are compared.
Structural Dynamic Theory in Health Monitoring
Authors: Ju Frederick D.
Published: March 2021

The paper studies the global methods in monitoring structural health. The principle of global methods is based on the structural dynamic theorems. There are four theories available; namely, (1) the random decrement theory, (2) the modal frequency theory, (3) the transmissibility theory, and (4) the modal shape theory. This paper addresses specifically the modal frequency theory and the transmissibility theory, and their application to the location of fracture damages and the intensity of the damages. The reliability and health assessment depends on the accurate modeling of the damaged structure. With the damage assessment, the paper proposes a method to estimate the upper bound of reliability of the structure, during the hysteretic cycling of the loading.
Interval Analysis of Neural Net Adaptive Expert Systems for Diagnosis of Machinery Incipient Failure
Authors: Dimarogonas Andrew D.
Published: March 2021

Interval calculus is a tool to evaluate a mathematical expression for ranges of values of its parameters. The basic mathematical operations are defined in the interval algebra.

Neural networks is an approach leading to engineering expert systems that are capable of learning, self adapting to particular engineering applications and handling fuzzy and interval input information.

In traditional machine learning, symbolic representations, such as first order predicate calculus, are used to represent knowledge. The resulting algorithms are specific to the selected representation and presume an ad-hoc knowledge of the system represented. In the neural network representation, knowledge is distributed to a large number of weighted synapses that facilitates learning by experience, realized through modification of the synapses weights according to a chosen learning rule.

Traditional classification systems use binary logic. This assumes a clear distinction between two and only two possible states of an event. However, key elements in the human thinking are not numbers but labels of fuzzy sets, that is, classes of objects in which the transition from non-membership to membership is gradual rather than abrupt and ranges of key parameters involved.

A heteroassociative neural network is used to map the existing knowledge and acquire new knowledge in learning sessions. The inputs can be binary, fuzzy and interval variables. To process the diagnosis in a back-propagation mode, interval calculus is utilized in algebraic and matrix operations and the diagnosis results in interval output parameters, the identification scores.

Interval calculus was programmed in a software package to allow for interval computations. The package includes arithmetic, function and matrix operations. Available experience for failure diagnosis in turbomachinery was utilized to initially teach the system. Additional diagnoses from the author’s experience were taught to the system and additional features and diagnoses defined.

Convergence of the procedure depends on the monotonicity of the functions used. For usual networks and threshold functions, convergence is warranted.
Comparative Signature Analysis Using Needle Bearings
Authors: Campbell Craig M. , Tavakoll Massoud S.
Published: March 2021

Many signature analysis techniques have been developed for detecting bearing damage. In this paper, a number of these techniques are evaluated and their abilities to detect the existence and progression of damage are quantitatively compared. Needle bearings are used for this evaluation because they are noisier than ball bearings, and there has been little published regarding their vibration behavior. The signature analysis techniques are evaluated using three increasing levels of outer race damage. The Evaluation criteria are based on the ability of a technique to repeatedly detect a damaged bearing and to correctly indicate the progression of damage level.
Correlation of the SPICE Beam Expander Structural Model With Component and System Level Modal Test Results
Authors: Mimovich Mark E.
Published: March 2021

A full scale experimental beam expander structure is modeled and correlated with modal test results on a component and system level. Correlation of the FE models is completed using the LINK module of the Leuven Measurement Systems (LMS) software which is also used to acquire and reduce the modal test data. The correlation tools used to measure the agreement between test and analytic mode shapes are the Modal Assurance Criterion (MAC), Coordinate Modal Assurance Criterion (CoMAC), and mass cross-orthogonality. In addition to the tools used to measure agreement between test and analysis modal parameters, sensitivity and optimization algorithms are used to identity structural parameters which influence a particular mode and what the minimum change(s) must be in the parameter(s) to bring about the desired agreement. As part of a system level pre-test analysis, the theoretical mode shapes along with a normalized line-of-sight error associated with each mode are used to select the best measurement and excitation locations.
Mixed Planar and Spatial Modeling for Multibody Dynamics
Authors: Freeman Jeffrey S. , Velinsky Steven A.
Published: March 2021

In the process of formulating and analyzing multibody dynamics problems, situations often arise where the desire to mix planar and spatial models naturally occurs. In the analysis of vehicle powertrains, for example, there are relatively few spatial bodies, such as the engine and transmission casing, but many planar elements, such as the gearing inside the transmission. The current study differs from prior work using Euler-Lagrange techniques by developing the ability to mix three-dimensional component body and two-dimensional planar kinematic elements within a single system model. While this study was performed specifically for the modelling of vehicle powertrains, the assumptions, analysis and transformations that enable planar elements to be mixed with spatial bodies are of broad applicability in the field of multibody dynamics.
On the Dynamics of a Rotary Compressor: Part 1 — Mathematical Modeling
Authors: Padhy Sisir K.
Published: March 2021

The rotary compressor has been used in room air conditioners as well as in refrigerators for many years. Although a number of published papers has been reported on rotary compressor, in the area of dynamics only a few are found. In addition only one paper describes experimental validation with some agreement with theoretical results. Again the effect of various operating pressures and temperatures, rotational speed of shaft etc. is not fully covered in any published literature. The present paper analyzes the rotary compressor dynamics in detail. The mathematical model, the solution procedure using Runge-Kutta method, and the bearing dynamics are described. The second part of this papers describes the experimental validation and sensitivity study using different variables that affect the compressor dynamics.
Kinematics of the Generalized Slider-Crank Mechanism
Authors: Fischer Ian S. , Rahman Sahidur
Published: March 2021

Dual-number techniques are used to analyze the kinematics and dynamics of the slider crank mechanism generalized to consider the effects of the cylinder axis being offset and non-perpendicular to the crankshaft axis, conditions which result in reciprocating machinery such as engines and compressors from manufacturing tolerances. The kinematics of the mechanism are evaluated with a Newton-Raphson method using dual-number coordinate-transformation matrices which in this work is extended to include mechanisms with spherical joints. Results for various cases are shown and are ready to be used in a study of the dynamics of the generalized slider-crank.
A Compromise Decision Support Problem for Axiomatic and Robust Design
Authors: Bras Bert , Mistree Farrokh
Published: March 2021

Compromise Decision Support Problems (DSPs) are used to model engineering decisions involving multiple trade-offs. In this paper, we focus on how to use such decisions models to perform Axiomatic and Robust Design. A compromise DSP formulation is presented and solved for the concurrent achievement of the functional requirements, Suh’s independence axiom and information content axiom. A model for the selection of principal design parameters from a set of design parameters is included in this compromise DSP formulation. Taguchi’s signal to noise ratio is used as a metric for the reduction of the information content and increasing the robustness of the design. As an example, the design of a compromise DSP for designing an electrical network is used.
Development of a Unified Exact Gradient Approach to Optimal Synthesis of Mechanisms
Authors: Mariappan Jawaharlal , Krishnamurty Sundar
Published: March 2021

This paper presents the development of a unified approach to optimal synthesis of mechanisms using exact gradients. The uniqueness of this approach lies in its ability to find optimal solutions to different type of mechanism problems in a systematic and efficient manner. In this approach, the exact gradients necessary for optimization are developed using a generalized methodical solution procedure based on matrix methods. This enables direct utilization of efficient gradient-based optimization methods in the mechanism synthesis process, thus eliminating the need for time-consuming direct search methods, or, the use of finite difference approximate methods to estimate gradients during optimization. The development of exact gradients and its integration with mechanism synthesis process, thus, offers the most effective approach for finding optimal solutions in generic mechanisms.