bluuebunny/crossref_metadata_2025 huggingface dataset:
Tolerances and Available Relative Motions in Bolted Connections
Authors: Delvecchio Joseph N. , Soom Andres
Published: April 2021

The implications of geometric and dimensional tolerances on the mechanical behavior of assemblies are often indirect or unclear. Although current tolerancing practice will generally assure that components will assemble, one may also be concerned with other aspects of the functionality of an assembly. In this paper we examine one aspect of functionality, namely the effect of statistical tolerances of location on the amount of available motion or play that can occur in bolted assemblies. A mobility formulation is proposed which allows the possible part motions to be determined in terms of one of two indices, i) the average Available Translation or Rotational Motion and ii) the Relative Mobility Area. A Monte Carlo simulation is used to perform the mobility calculations. The hole locations and tolerances are normalized, allowing the available motion of assemblies with different numbers of holes and configurations to be compared. It is shown that the geometric arrangement of holes does not significantly affect mobility. Increases in average hole to hole distance reduces available rotational motions but not translations. A decrease in available motion is shown to occur as the number of hole features increases. This decrease in quantified by means of the above indices.
Algorithms for Nesting of Ship/Offshore Structural Plates
Authors: Cheok B. T. , Nee A. Y. C.
Published: April 2021

This paper discusses the development of a set of algorithms for the automatic nesting of ship/offshore structural plates. The algorithms are developed to take advantage of the peculiarity of most ship/offshore structural plates with the aims of optimising material usage and minimising computer search time. The parts to be nested are first processed by a shape processing routine which employs a simple feature extraction approach to classify the plates according to predefined rules specially adopted for ship/offshore structural shapes. The most appropriate search path for each class of plates is used to obtain the best enclosing rectangle for similar shapes. The search paths are based on heuristics developed to simulate the manual method used by the human operator. Finally, all the plates are laid out on the stock sheet using a “rectangle packing” approach. A computer package, Patnest-Ship was developed to demonstrate the efficiency of the algorithms and very encouraging results are achieved. The input and output files to and from Patnest-Ship are described in DXF format so that it can be integrated with existing CAD/CAM systems. Pre- and post-processors for this package have been implemented on AutoCAD to permit the user to define the plates and interactively improve on the solutions provided by Patnest-Ship, if necessary.
Development of Kinematic/Kinetic Performance Tools in Synthesis of Multi-D.O.F. Mechanisms
Authors: Lee Ming-Yih , Erdman Arthur G. , Gutman Yevsey
Published: April 2021

Kinematic and kinetic performance are important issues in designing multi-degree of freedom mechanisms such as robotic manipulators. In the engineering design stage, it is especially important that the designer can grasp the characteristics of the mechanism. The aim of this study is to develop a means of representing the kinematic and kinetic performance of the mechanism in such a way that the performance characteristics are quantified analytically and visible graphically to the designer in their entirety in the conceptual design stage. Various performance indices derived from the Jacobian matrix and its quadratic form. These performance indices are the local kinematic cross-coupling index, the local directional mobility index, and the local efficiency index. Graphical images of these performance characteristics using eigen-ellipsoid and workspace trajectory contours are introduced. Critical performance points in mechanism workspace are identified and elaborated for design considerations. Based on the graphical representation of these performance characteristics, design rules for achieving different performance objectives can easily be implemented. This method is applicable to computer-aided design of a mechanism and predetermination of its kinematic and kinetic performance.
Human Aspects of Design Work
Authors: Norell Margareta , Hovmark Svante
Published: April 2021

Conclusions and experiences from three examinations within a Swedish interdisciplinary research project (MANDECO) are discussed in this paper. The purpose of the research work is to find ways to satisfy both demands on the effectiveness of the designer in the product development process and personal demands from the designers on the working situation. Interviews, questionnaires and experimental studies in industrial companies and in the technical university are used to find variables related to an estimated product development process. CAD-work, implementation of the Design for Manufacture concept and Simultaneous Engineering in co-operation between design and manufacturing are important issues in the paper. Some conclusions from the use of computer tools in design work from studies in the project are: The systems should be developed to support calculations, analysis, routine work and knowledge transference in the design process and preferably to be used less than an average of about 30 hours/week to restrict physical complaints. Co-operation between design and manufacturing is supported if the same tools can be used in the two departments, if the knowledge in the system is uncontroversial and if the process is organized to support person-to-person discussions.
Kinematics of the Ball Screw Mechanism
Authors: Lin M. C. , Ravani B. , Velinsky S. A.
Published: April 2021

This paper studies the kinematics of the Ball Screw Mechanism (BSM) with the aim of developing a foundation for understanding the motion of the balls and their contact patterns with the contacting elements. It is shown that there is always slip between the balls and the nut or screw, and therefore, the no slip condition assumed in the BSM literature is not attainable. The effect of contact deformation on the motion of the balls is also studied and is used to develop the pattern of the constant sliding lines of contacts between the ball and the screw or the nut. The results have applications in efficiency analysis, design, wear analysis and finite element modeling of the BSM.
A Technique for the Design of an Interference Free Complex Planar Mechanism
Authors: Ling Zhi-Kui , Chase Thomas R.
Published: April 2021

A complex planar mechanism is usually represented by its simplified schematic representation, called the kinematic skeleton, in both synthesis and analysis. Unfortunately, interferences between links may not be evident from the kinematic skeleton. This paper presents a computer aided top-down technique to design the geometry of an interference free mechanism. The method is intended to replace intuitive and trial and error link geometry design techniques.

The geometric design of the links of a mechanism is initiated after the kinematic skeleton diagram is created using existing synthesis and analysis techniques. The solution to the interference problem is initialized by placing links into different layers. To ensure a link, called a reference link, does not interfere with other links within its layer, the work space of those links with respect to the reference link is generated. The resulting domain, called a “swept area”, establishes an illegal region whose complement identifies the feasible region to place the geometry of the reference link. The new method is demonstrated with an example.
A Strategy for Characterizing the Stability of Parts Fixtured Under Three-Point Frictional Constraint
Authors: Linder K. J. , Cipra R. J.
Published: April 2021

Flexible assembly systems require flexible fixtures which can constrain parts in a stable fashion and will adapt quickly and easily to a change in the type of part. A fixtured part is either unstable or stable depending on whether or not it moves when the clamping force is applied. This paper gives a systematic method which uses graphical techniques to characterize the stability of parts fixtured under a particular type of three-point frictional constraint. The three inputs into this method are the location of the center of gravity of the part and the geometrical and frictional properties of the fixturing system. No information about the applied clamping force is necessary for the method to characterize stability. The method first determines if it is possible that static equilibrium will not occur when the clamping force is applied. If this possibility exists, then corresponding kinematically possible motions are determined and are tested for consistency with dynamics to determine if any of them are a possible unstable mode. Finally, the method classifies a part into one of three classifications: stable, unstable, or indeterminate. If it is determined that there are no possible unstable modes then the part is stable. But if it is determined that static equilibrium cannot occur then it is unstable. If it is discovered that static equilibrium is possible yet possible unstable motions also exist then the stability of the part is indeterminate. In spite of these stability indeterminacies, the method can determine all possible unstable motions of both unstable and indeterminate parts. This characterization of the stability of parts can provide useful feedback as to how a fixture configuration can be modified in order to either provide or improve a stable clamping arrangement.
The Effects of Harmonic Drive Gears on Robot Dynamics
Authors: Lin Tsung-Chieh , Yae K. Harold
Published: April 2021

Mathematical models of the harmonic drive have been developed, and their effects on manipulator dynamics have been examined. The harmonic drive is modelled as a flexible gear with a high gear reduction ratio. The recursive Newton-Euler dynamic formulation is applied to deriving the system equations of motion that include the effects of the geared actuation. The equations include not only the nonlinear dynamic coupling between rotors and links but the gyroscopic effect due to the spinning rotors. Different modelling assumptions creates four models and their time responses are compared. As an example, a seven degree of freedom robot was chosen to make comparisons in time responses.
Automatic Planning of Smooth Trajectories for Pick-and-Place Operations
Authors: Gosselin Clément M. , Hadj-Messaoud Ammar
Published: April 2021

This paper proposes some new polynomial solutions to the trajectory planning problem encountered in pick-and-place operations. When a robotic manipulator is used for such operations, it is possible to plan the required trajectory in joint space, provided that the inverse kinematic problem has been solved for the initial and final configurations — and possibly for a lift-off and a set-down configuration — and that the workspace is free of obstacles. Polynomial solutions to this problem can be found in the literature. However, they usually provide continuity up to the second derivative only, leading to a discontinuous jerk. The solutions derived in this paper preserve the continuity of the third derivative of the joint coordinates, thereby ensuring smooth trajectories with smooth variations of the actuator currents. Moreover, whenever possible, unique polynomial expressions valid between the initial and final configurations are used in order to simplify the logic. Polynomial formulations without lift-off and set-down configurations are first presented. Then, these intermediate configurations are introduced, leading to a new set of solutions. A global algorithm is then discussed in order to clearly indicate the relationship between the different solutions. Finally, an example illustrating the application to a pick-and-place operation is solved.
H
∞ Control of Smart Structure Helicopter Rotor Blade
Authors: Kashani R. , Melkote S. , Sorgenfrei A.
Published: April 2021

Active vibration control of helicopter rotor blade is studied. For the purpose of illustration, we have considered only flap wise vibration of a hingeless rotor blade, and modelled it, using finite element method, by 20 beam elements. The first 12 bending modes of the system are considered in the model. A H∞ controller is designed for the plant formulated as above.

The result of the numerical simulation of the closed-loop system shows that the control introduces an appreciable amount of damping in the frequency region of interest. The consideration of the modelling uncertainty in the synthesis of the controller resulted in a design which is robust stable in presence of formulated model uncertainty.
Analytical and Experimental Investigation on Vibration Control of Piezoelectric Structures
Authors: Tzeng M. J. , Wu W. Z.
Published: April 2021

Active vibration control of smart structural materials (beam and plate) has been achieved by using distributed piezoelectric actuators. Numerical simulation and experimental testing have been conducted to investigate vibration suppression of the advanced structures. Results from simulation and testing are in satisfactory agreement.
A Darwinian Approach to the Actuator Number and Placement Problem With Nonnegligible Actuator Mass
Authors: Zimmerman David C.
Published: April 2021

The problem of optimal actuator number and placement for the vibration control of large flexible space structures is addressed in this work. The inherent mass of the actuators is integrated in the number and placement algorithm. The algorithm utilizes concepts from genetic programming, which is loosely based on Darwin’s “survival of the fittest” theories. The paper develops the genetic algorithm in the context of the actuator number and placement problem. Examples are presented which demonstrate the genetic algorithm and the effect of actuator mass on the placement and number problem.
Simulation and Experiment Study on System Identifications of Elastically Jointed Structures
Authors: Rong Y. , Tzou H. S.
Published: April 2021

The dynamic characteristics of elastic joints strongly affect the dynamic performance of a jointed structure. In order to study the performance of elastically jointed structure, a theoretical model of elastic joints has been developed based on the concept of dynamic contacts, in which the joint friction and clearance effects are included. A stochastic simulation technique is used to evaluate the system characteristics of jointed structures. In this paper, a time-domain system identification method is presented, which is applied to estimate the dynamic contact parameters of elastic joints and the eigenvalues of jointed structures. The identification system may use the data generated by using the theoretical model, or from experimental tests. The joint contact stiffness and contact damping are identified to be directional dependence of contact angles. The system natural frequencies and damping ratios are varied upon joint clearance variations. The simulation and experiment results are presented in this paper, and show comparisons.
Vibration Control and Shape Adjustment of Truss Structures Using Piezoelectric Actuator
Authors: Sekine Koji , Shibayama Yozu , Iwasawa Naotoshi , Inada Hiroshi , Yoshida Shiro , Arikabe Takeo , Natori Michihiro
Published: April 2021

In the field of structural dynamics of large space structure (LSS), control/structure interaction technologies have been attracting much attention of researchers, and various types of control theory have beer, proposed. Meanwhile, it is important to develop actuators for the use of structural control. Piezoelectric device has some advantages characteristics such as compact size, high frequency response, low energy consumption over the other devices. With this background a uniquely designed piezoelectric actuator both for active dumping and shape adjustment has been preliminarily developed for experimental use. This paper describes the experimental results of the actuator for active dumping of planar truss and for statical or dynamical shape adjustment. And numerical simulations of planar truss with minimum numbers of pairs of collocated actuators and sensors show that a state observer can estimate truncated modes precisely and that the excited vibration can be dumped out rapidly.
On the Dynamics of Perturbed Symmetric Systems
Authors: Happawana G. S. , Nwokah O. D. I. , Bajaj A. K.
Published: April 2021

In this work, we consider the dynamics of linear mechanical systems possessing geometrical symmetry subject to differential or small parameter variations. The machinery of group theory including the irreducible group representations, and the consideration of representations to which the translational, rotational and vibrational modes belong, allow us to predict apriori, the number and the order of degenerate eigenvalues in the symmetric system. By considering the resultant Hamiltonians of the perturbed symmetric system, we show further the effects of the perturbations on the eigenvalues and their degeneracies. Since the vibration modes of systems with degenerate eigenvalues are known to display sensitive dependence on parameters, we may use these techniques to identify in principle the possibility of maximum vibration amplitudes and where they are likely to occur. Applications of these ideas include the mistimed turbine rotor bladed disk assemblies.
Design of an Almost Critically-Damped Single Robot Arm
Authors: Abdelhamid Mohamed K. , Ko Kuan-Yuh
Published: April 2021

Modern, fast, and light robot arms are more susceptible to vibration problems than the old, slow, and massive robot arms. Passive vibration control using damping and dynamic absorbers may be used to decrease the settling time of the robot arm after it has been driven to its desired position. Implementation of an optimally damped vibration absorber has been recently investigated and results showed success in shortening the settling time of a single robot arm. This paper realizes that a critically damped structure is the fastest structure to settle in its static equilibrium position. This paper, thus, uses recent results on damping ratios of multi-degree-of-freedom systems to provide a design scheme that uses both a damped vibration absorber and distributed damping (such as a damping layer) with the robot arm to realize an almost critically damped design. Simulation results show that the new design method results a single arm link design that is faster to settle than the previously published designs.
Design of Magnetic Bearings for Rotor Systems With Harmonic Excitations
Authors: Dhar D. , Barrett L. E.
Published: April 2021

This paper presents a method for calculating the control forces and the bearing stiffness and damping coefficients to control the response of multi-mass flexible rotor systems mounted on magnetic bearings and subjected to unbalance or harmonic excitation forces. The capability for inclusion of hydrodynamic bearings is retained to model seal effects or to permit the design of magnetic bearings for hybrid systems. Control forces at the magnetic bearing locations are evaluated based on the desired shaft response specified by the modal coordinates. These forces are determined such that the error between the desired response and the achieved response is minimized in a least-square sense. Equivalent bearing coefficients are calculated from the control forces and the achieved response, which when superimposed on the nominal bearing coefficients yield the resultant magnetic bearing coefficients required for control. An example case is presented where control of rotor response has been attempted at the first and the second unbalance critical speeds. The results demonstrate appreciable improvement in response using magnetic bearings.
Transient Response Technique Applied to Active Magnetic Bearing Machinery During Rotor Drop
Authors: Ishii Toshiyasu , Kirk R. Gordon
Published: April 2021

The active magnetic bearing (AMB) is a relatively new technology which has many advantages compared with conventional bearing design. In an AMB system, the rolling-element back-up bearings are indispensable to protect the magnetic bearing rotor and stator, and other stationary seals along the rotor shaft. In this paper, a theoretical formulation is proposed and solved numerically to examine the transient response of the flexible rotor, from the time just previous to the AMB shuts down and including the rotor drop onto the back-up bearing. The backward whirl of the rotor, which may lead to the destructive damage of the machiner, has been analytically predicted at very light support damping and very high support damping. Also, the vibration due to the non-linearity of the contact point geometry has been included in the analysis. The influence of the support damping on the displacement of the disk and also the contact force between the journal and the inner-race of the back-up bearing have been computed for various rotor system parameters.
The Effect of Sensor Location on the Forced Response Characteristics of Rotors With Active Magnetic Bearings
Authors: Rawal D. , Keesee J. , Kirk R. Gordon
Published: April 2021

This paper presents a modification of existing transfer matrix methods for rotor analysis, to predict the response of rotor systems with active magnetic bearings. The position of the magnetic bearing sensors is taken into account and the effect of changing sensor position on the vibrational characteristics of rotor systems is studied. The results for a simple two-mass rotor system are presented as plots of critical frequency vs. sensor position and amplitude at critical frequency vs. sensor position. A typical eight stage centrifugal compressor rotor is analyzed using the modified transfer matrix code and the results are presented as plots of amplitude vs frequency for different cases of sensor location.
Parameter Identification of Non-Linear Impact Damper
Authors: He Kang-Yu , Yuan Xiao-Xu
Published: April 2021

In this paper, we presented a mew mechanical model of an impact damper based on the theoretical analyses and experiments. We also presented a method of identifying the parameters of the non∼linear method of an impact system by means of microcomputer calculations. The method of identification presented in this paper has been proved byour experiments. These works supply the theoretical foundations of designing and calculating for impact damper.
An Efficient Method for Calculating Damped Critical Speeds of Rotor-Bearing Systems
Authors: Wang D. Z. , Taylor D. L.
Published: April 2021

This paper describes an analytical approach for calculating the damped critical speeds of multi-degree-of-freedom rotor-bearing systems. It is shown that to calculate the critical speeds is equivalent to finding the roots of a proposed matrix algebraic equation. The technique employes a Newton-Raphson scheme and the derivatives of eigenvalues. The system left eigenvectors are used to simplify the calculations. Based on this approach, a general-purpose computer program was developed with a finite element model of rotor-bearing systems. The program automatically generates system equations and finds the critical speeds. The program is applied to analyze a turbomachine supported by two cylindrical oil-film Journal bearings. The results are compared with reported data and the agreements are very good.
Concepts and Application of the Large Mass Method in Vibration Analysis of SSME Engine Structures
Authors: Shen Lawrence K.
Published: April 2021

The large mass method is used to obtain the total dynamic response of structures using excitations prescribed at base points. This paper presents the concepts and application of the method derived and used in the analysis of Space Shuttle Main Engine (SSME) structures. The theory and limitations that make the method work are discussed first. The effect on the system responses, including the addition of nonelastic (rigid body and large mass) modes due to the presence of the large masses, is then covered. The resonance concept leads to the establishment of criteria to define the analytic limit of the excitation frequency. The significance of the pseudostatic component and the relationship with the nonelastic modes are investigated in a simple system. The study shows that the frequency ratios, system properties, and the similarity between excitations are key factors to make the pseudostatic term more prominent. Examples with sinusoidal excitation are used to demonstrate the concepts. The method is finally applied in the SSME structures with excitations compiled from engine test data. Results are compared to further demonstrate the concepts and define the future needs for improved test data.
Vibration Confinement Phenomena in Disordered, Mono-Coupled, Multi-Span Beams
Authors: Bouzit Djamel , Pierre Christophe
Published: April 2021

The effects of small, periodicity-destroying irregularities on the dynamics of multi-span beams are examined. It is shown that minute deviations of the span lengths from an ideal value alter qualitatively the dynamic response by localizing vibrations and waves to small geometric regions. These confinement phenomena are studied over a wide frequency range for beams resting on simple supports and with variable interspan coupling. Approximations of the localization factor (the average rate of spatial exponential decay of the vibration amplitude) are derived by statistical perturbation methods and validated by Monte Carlo simulations. If the interspan coupling is strong, localization effects are weak and of no practical significance for most engineering structures. On the other hand, localization is severe for small interspan coupling. Confinement is also generally stronger near the edges of frequency passbands and increases nearly linearly with frequency from passband to passband. This means that strong localization occurs at high frequencies, even for large static coupling between spans. De-localization is also observed at very high frequencies.
In-Plane Vibration of Simply Supported-Simply Supported Circular Ring Segments
Authors: Azimi S.
Published: April 2021

The general in-plane vibration problem of circular ring segments having linear and torsional elastic constraints at the ends has been studied. One of the interesting cases of concern for which there exists an exact solution is the case where the linear and torsional spring stiffnesses in the circumferential direction become zero (Ku = 0, Kt = 0) and the linear spring stiffness in the radial direction becomes infinity (Kw = ∞). This case is the so-called simply supported-simply supported case. The general form of the equations of motion of circular rings with the proper boundary conditions at the ends have been employed to investigate the vibration of the ring segment. Results for natural frequencies and mode shapes for different angles of the segment have been presented.
The Fourier Ultrasonic Resonant Transformers
Authors: Jwo Chin-Hung
Published: April 2021

To achieve a high magnification of amplitude by using an ultrasonic resonant transformer, one may choose from several different tapering rods. The basic transformers include conical, hyperbolic (catenoidal), exponential, multi-step cylindrical, and Fourier, etc. The Fourier transformers are better in the characteristics of higher bending stiffness and lower maximum strain over other single section transformers. The higher order Fourier transformers presented in this paper give more flexibility in optimization for desired mechanical characteristics.
Axisymmetric Free Vibration of Thick Orthotropic Hemispherical Shells Under Various Edge Conditions
Authors: Chao C. C. , Tung T. P. , Chern Y. C.
Published: April 2021

Axisymmetric free vibration of moderately thick polar orthotropic hemispherical shells are studied under the various boundary conditions of sliding, guided pin, clamped and hinged edges. Based on the improved linear elastic shell theory with the transverse shear strain and rotatory inertia taken into account, the dynamic equilibrium equations are formulated and transformed into the displacement form in terms of mid-surface meridian and radial displacements and parallel circle cross-section rotation. These partial differential equations are solved by the Galerkin method using proper Legendre polynomials as admissible displacement functions with the aid of the orthogonality and a number of special integral relations.

Numerical results of the present theory compare well with existing data, which is available only in the isotropic theories. Good convergence is obtained for natural frequencies and mode shapes. Study of the effects of thickness and modulus ratio reveals higher frequencies for the thicker and/or stiffer shells with E\ oriented parallel to the meridians. Ranking of the natural frequencies descends in the order of guided pins, sliding, clamped and hinged edges in general. Also seen are the effects of transverse shear strain from the mode shapes with clamped and sliding edges on the slant. For the guided pin and sliding edges, frequencies increase fast as thickness increases so that new fundamental modes are generated in filling up the “frequency gap”. These are the new discoveries in the field of anisotropic shells, as a result of polar orthotropy of shell material and construction.
On the Problem of Multiple-Excitation Multiple-Response Stochastic Structural Dynamics Identification
Authors: Lee Jae-Eung , Fassois Spilios D.
Published: April 2021

In this paper an effective approach for the identification of stochastic structural systems from multiple-excitation multiple-response forced vibration data, is introduced. The proposed approach represents a novel extension of the method of Lee and Fassois (1990b), that enables it to: (a) Operate on either vibration displacement, velocity, or acceleration data records, and, (b) perform accurate analysis of the estimated structural model by using a currently introduced exact and physically meaningful Dispersion Analysis methodology. These new features, combined with its other important properties, make the proposed approach not only capable of overcoming the limitations of current techniques, but, also, a comprehensive procedure for multiple-excitation multiple-response stochastic structural dynamics identification.

The excellent performance characteristics of the proposed approach are finally verified via numerical simulations with structural systems characterized by well-separated and closely-spaced modes, as well as data corrupted at various noise-to-signal ratios. Comparisons with the Eigensystem Realization Algorithm (ERA), through which the limitations of deterministic methods are illustrated, are also presented.
A Transfer Matrix Method for Nonlinear Vibration Analysis of Rotor-Bearing Systems
Authors: Lu Songyuan
Published: April 2021

In this paper, a transfer matrix method is presented for calculating nonlinear vibration of rotor-bearing systems. The method is based on the Riccati transfer matrix method and two direct integration schemes: Houbolt and Wilson-0. Since this method uses matrices with small size and new, more simple recurrence formulae, the calculation results, which do not contain the significant computation roundoff error accumulation, have been obtained and very short time is needed. Nonlinear vibration calculation becomes essential to actual rotor-bearing systems of engineering importance. This method is concise, explicit and short, and it can be executed on personal computers of present configurations.
Frequency Error Estimation in Nonlinear Systems Using Beats
Authors: Jettappa Richard Rodrigues , Sharma Seshadri
Published: April 2021

Real systems are inherently non-linear. True linear behaviour is rare. On the other hand, most of our models are linear. It is relatively easy to solve for a linear system compared to the corresponding non-linear system. This dichotomy between theory and practice is all pervasive. It is highly desirable that an analyst should be able to check the closeness of the predicted behavior with the actual behaviour of the system. In this paper we outline the method of beats towards this end. Even though the phenomenon of beats is well known to scientific community, its use in error analysis is unknown. This is the essence of the present paper.
Localized and Non-Localized Normal Modes in a Strongly Nonlinear Discrete System
Authors: Vakakis Alexander F.
Published: April 2021

The free oscillations of a strongly nonlinear, discrete oscillator are examined by computing its “nonsimilar nonlinear normal modes.” These are motions represented by curves in the configuration space of the system, and they are not encountered in classical, linear vibration theory or in existing nonlinear perturbation techniques. For an oscillator with weak coupling stiffness and “mistiming,” both localized and nonlocalized modes are detected, occurring in small neighborhoods of “degenerate” and “global” similar modes of the “tuned” system. When strong coupling is considered, only nonlocalized modes are found to exist. An interesting result of this work is the detection of mode localization in the “tuned” periodic system, a result with no counterpart in existing theories on linear mode localization.
Amplitude Dynamics of an Autoparametric Two Degree-of-Freedom System
Authors: Bajaj Anil K. , Johnson Joseph M. , Chang Seo Il
Published: April 2021

Forced, weakly nonlinear oscillations of a two degree-of-freedom autoparametric system are studied for resonant excitations. The method of averaging is used to obtain first order approximations to the response of the system. In the subharmonic case of internal and external resonance, where the external excitation is in the neighborhood of the higher natural frequency, a complete bifurcation analysis of the averaged equations is undertaken. The “locked pendulum” mode of response bifurcates to coupled-mode motion for some excitation frequencies and forcing amplitudes. The coupled-mode response can undergo Hopf bifurcation to limit cycle motions, though it requires mistuning from the exact internal resonance condition. The Hopf bifurcation sets are constructed and dynamic steady solutions of the amplitude or averaged equations are investigated using software packages AUTO and KAOS. It is shown that both super- and sub-critical Hopf bifurcations arise and the limit cycles quickly undergo period-doubling bifurcations to chaos. These imply chaotic amplitude modulated motions for the system.
Investigation of Parametric Vibration Stability in Slider-Crank Mechanisms With Elastic Coupler
Authors: Farhang K. , Midha A.
Published: April 2021

An analytical model for investigating parametric vibration stability of slider-crank mechanisms with flexible coupler is presented. The continuous model is formulated to account for initial curvature as well as internal material damping in the coupler. The governing partial differential equations are reduced to a system of ordinary differential equations in terms of the time-dependent modal coefficients. Floquet theory is employed to determine the effects of geometric stiffening as well as relative component mass on parametric stability of mechanism response. Results indicate the existence of instability regions due to combination resonances of various modes. In addition, the stability characteristics of the mechanism is found to improve when slider forces are directed away from the crank-ground pin (i.e. the connecting rod is in tension), and when a relatively smaller slider mass is used.
Cutting Process Stability of a Boring Bar With Active Dynamic Absorber
Authors: Tewani Sanjiv G. , Rouch Keith E. , Walcott Bruce L.
Published: April 2021

Active vibration control has been considered in the past as a viable means of controlling machine tool chatter in the boring bar. Theoretically, it has been shown that the amplitude of vibrations of the machine tool can be substantially reduced using such an active control system.

This paper looks into the cutting process stability of a boring bar equipped with an active vibration control device. An equivalent lumped mass model of the boring bar is considered. A cutting process model that considers the dynamic variation of shear and friction angle responsible for the self-excited vibration during machine tool chatter is considered. The model also considers the regeneration effect during the cutting process. Stability charts have been obtained in the form of maximum allowable width of cut as a function of cutting speed. A comparison of the stability boundaries of the boring bar with no control, with passive dynamic absorber and with active dynamic absorber is made. A substantial increase in the region of stable operation of the boring bar with active dynamic absorber is observed.
Instability and Collapse Behavior of a Seismic Structure
Authors: Cheng Franklin Y. , Ger Jeng-Fuh
Published: April 2021

The collapse behavior of a 22-story steel building during the September 19, 1985 Mexico earthquake is investigated by studying hysteretic behavior, ductility factors of individual structural components, and overall instability of the building. The hysteresis models for truss-type girders, bracing members, and box columns to be used in the inelastic analysis of this building are developed. A series of inelastic analyses have been performed for the building by using the multicomponent seismic input of actual Mexico City earthquake records. It was found that the structural response exceeds the original design ductility of this building because most girders in the building have suffered large ductilities. Due to the load redistribut-ion effects from the ductile-failed girders, local bucklings developed at many columns on floors 2, 3, and 4. Therefore, most columns on floors 2 through 4 lost their load carrying capacities and rigidities which then caused the building to tilt and rotate. As a result, more columns on floors 5 through 7 developed local buckling and more bracing members buckled. It is believed that ductile failures of girders combined with the local bucklings of columns in the lower part of the building resulted in significant story drift, building tilt, P-A effect, and the failure mechanism.
A Finite Element Modeling of Higher Order Shear Deformation Theory on a Plate Vibration Problem
Authors: Chang Chiang-Nan , Chen Thien-Rhei
Published: April 2021

Higher order Shear Defamation Plate Theories (HSDPT) are improved theories over Mindlin plate theory because their assumptions are closer to reality. However, they are seldom used in solving ordinary engineering works. This is due to the fact that mathematical formulations and computations are so lengthy that time and efforts required are close to solving a exact 3-D model.

For problems involving sharp stress variation, higher order theories are anticipated to give better results. The combination of HSDPT and Finite Element Modelings are especially attractive because a finite element modeling is much simpler.

The current research develops a finite element model on the higher order shear deformation theory. A plate vibration problem was solved. The plates contain square interior cutout. Stress distributions are much complicated than whole plates. Results of HSDPT are compared with FSDPT (First order Shear Deformation Plate Theories) and CPT (Classical Plate Theory).

Better accuracies are obtained by using the HSDPT.
Force Reconstruction Using the Inverse of the Mode-Shape Matrix
Authors: Carne Thomas G. , Bateman Vesta I. , Dohrmann Clark R.
Published: April 2021

A new technique for force reconstruction is developed. To estimate the externally applied force, this technique sums the weight-scaled acceleration signals, and is referred to as the Sum of Weighted Accelerations Technique (SWAT). To obtain the scalar weights the inverse of the mode shape matrix is used. Application of this technique is illustrated with both numerical calculations using a mass-spring model and experimental data from a structure impacting a rigid barrier.
The Prediction of the Substructure and System Modes by the Extended Complex Mode Indication Function
Authors: Lin Albert C. Y. , Tsuei Y. G.
Published: April 2021

The Modal Force Technique (MFT) which directly works with the substructure frequency response functions at connecting joints to predict the dynamical behavior of the synthesized system has been recently developed. The key point of the MFT is to formulate the Modal Force equation by eliminating the physical coordinates and retaining the forces in accordance with the boundary conditions of geometric compatibility and forces equilibrium at connecting joints. The Modal Force matrix in the Modal Force equation contains the information of the substructure modes and the synthesized system modes. To predict the natural frequency and damping of the substructure and the synthesized system modes, an Extended Complex Mode Indication Function for MFT is investigated.
A New Method for the Pile Quality Detection: Estimation of the Shape of a Pile
Authors: Mu Rangke , Zhao Chun-sheng
Published: April 2021

In this paper, a new method for the pile quality detection is developed, which is the Estimation of the Shape of a pile (also called the ESP method). It has considered many defects and their high time reflections in a pile by using echo technique. At this we have carried out the computer simulation and the field tests by transient impact excitation on the head of the pile. It is proved that the ESP method is feasible for the pile quality detection, and the size, type, and site of a defect in a pile can be accurately determined by using it.
The Extraction of the Fault Signature of Gearboxes Using Optimum Complex Envelope Spectrum
Authors: Wan Xiaomao , Zhao Chun-sheng
Published: April 2021

In this paper, a new technique using optimum complex envelope spectrum is proposed in order to diagnose the gearbox fault, and its fundamental principle is described. The result of simulated tests illustrates that method proposed is excellently sensitive to the gearbox fault and is more effective than both the power spectrum analysis and the cepstrum analysis.
An Approach to Simultaneous Optimum Design of Structure and Control Systems by Sensitivity Analysis
Authors: Kajiwara I. , Nagamatsu A.
Published: April 2021

An approach is proposed for simultaneous optimum design of a structure and feedback control system by sensitivity analysis for the following two purposes. One is to decrease both the response and the control force of the system under a white noise disturbance force. The other is to modify the gain, the pole and the zero-point to the desirable values. The weighting constant of the feedback control system, and mass, stiffness, shape, dimension, etc. of the structure are adopted simultaneously as the design variables. The proposed method is verified by a model simulation.
The Broad-Band Active Vibration Control Systems With Controllable Damping for Non-Conservative Self-Excited Structures
Authors: Kravchenko S. V.
Published: April 2021

The features of active vibration control applied to self-excited non-conservative mechanical systems (such as structures subject to flatter, rotor machines, tubes conveying fluid) are discussed. It has been found that the optimal control strategy is the broad-band compensation of the dynamic force reactions combined with narrow-band damping of the mechanical structure resonant vibration. Some problems of feedback synthesis are solved analytically for these systems. The importance of symmetry and asymmetry for the active vibration control systems is discussed. In the case of self-excited systems, it is possible to use the small asymmetry of the control system for the stabilization of the dynamic process.
Hybrid Active Vibration Control of Rotorbearing Systems Using Piezoelectric Actuators
Authors: Palazzolo A. B. , Jagannathan Shankar , Kascak A. F. , Montague G. T. , Kiraly L. J.
Published: April 2021

The vibrations of a flexible rotor are controlled using piezoelectric actuators. The controller includes active analog components and a hybrid interface with a digital computer. The computer utilizes a grid search algorithm to select feedback gains that minimize a vibration norm at a specific operating speed. These gains are then downloaded as active stiffnesses and dampings with a linear fit throughout the operating speed range to obtain a very effective vibration control.
The Problems of Active Vibration Isolation in Nonlinear and Parametric Structures
Authors: Frolov K. V.
Published: April 2021

The theory of active vibration control based on the principle of broad-band compensation coupled with controllable vibration damping is presented. The applications of this principle to parametric and nonlinear mechanical structures are discussed. For the first time the possibility of the active vibration control with the aid of stochastic self-excited vibration spectrum transformation nonlinear phenomena is investigated. The theoretical and experimental results are compared for various complex mechanical objects.
An Improved Extended Transfer Matrix Method for a Damped System
Authors: Huang Yuan Mao
Published: April 2021

Installation of a damper is a good method to reduce the torsional vibration effect and to prolong the life of a system. However, consideration of the damping effect results in a complicated system.

This study derives a mathematical model for the analysis of a single branch damped system. The extended transfer matrix method is used with Newton-Raphson iterative technique. The procedures automatically eliminate the complicated operations of the matrix inversion and reduce the multiplication of the matrix products. The natural frequencies, both real and imaginary parts of the state vectors and mode shapes of the system can be determined.
A Technological Data Base in Aircraft Production Environment
Authors: Lega Riccardo
Published: April 2021

In a factory, where many cells work togheter, we obviously have a significant proliferation of data and information concerning the production flow.

We have, of course, to control this event in order to avoid dramatic consequences, as incoherence, disalignment and data inconsistency.

On the other hand, we have to notice thatt data production is generated by many different applications, and by many people having different skills and responsibilities, and using different applications and technologies.

Trying to solve this problem, we decided to define an unique and solid data base structure at factory level, called Technological Data Base (TDB), in which all users (man or application) generating information, useful to production activities, must store data under their own responsibility.

Data stored in this Data Base are defined as “Consolidated”, to indicate data that are released by an application process and are used as an input or a trigger for another application process.

These consolidated data can be:

- Structured data, i.e. data that can be organized in fields or attributes, mainly coming from Planning Applications.

- Unstructured data, i.e. data that are stored in the Data Base as a bits sequence, mainly coming from CAD/CAM applications managed as a black-box by the DBMS, while specific applications (at cell level) provide to understand them.

This Technological Data Base is an object-oriented Data Base, where functions are implemented in order to store, manage, and distribute all multi-media information requested to drive and control the different plant work-centers.

A pilot application of this TDB is already working in Alenia-Pomigliano factory — in a conventional workshop environment, and it will be extended to the other factories in an automated environment.