bluuebunny/crossref_metadata_2025 huggingface dataset:
Transfer of Energy From High- to Low-Frequency Modes in the Bending-Torsion Oscillation of Cantilever Beams
Authors: Arafat Haider N. , Nayfeh Ali H.
Published: February 2021

We investigate the nonlinear bending-torsion response of a cantilever beam to a transverse harmonic excitation, where the forcing frequency is near the natural frequency of the first torsional mode. We analyze the case where the first in-plane bending mode is activated by a nonresonant mechanism. We use the method of time-averaged Lagrangian and virtual work to determine the equations governing the modulations of the phases and amplitudes of the interacting modes. These equations are then used to investigate the nonlinear behavior of limit-cycle oscillations of the beam as the excitation amplitude is slowly varied. As an example, we consider the response of an aluminum beam for which the natural frequency of the first in-plane bending mode is fv1 ≈ 5.7 Hz and the natural frequency of the first torsional mode is fϕ1 ≈ 138.9 Hz.
A Nonlinear Theory for Traveling and Rotating, Sagged, Elastic Tethers
Authors: Luo Albert C. J. , Gupta Arun K.
Published: February 2021

A nonlinear theory for traveling and rotating, sagged, elastic tethers are developed. Under certain conditions this nonlinear theory reduces to established models for traveling or rotating or stationary tethers.
Navigating Expensive and Complex Design Spaces Using Genetic Algorithms
Authors: Zimmerman David C.
Published: February 2021

The overall objective of this study is to formulate and study a generic procedure for navigating expensive and complex design spaces. The term generic is meant to imply that the procedure would be equally valid in exploring design problems in a multitude of fields. The term expensive design space implies that the computational cost, or burden, associated with a single function is considered “large”. What is desired is a methodology which can identify “promising regions” of the design space using as few function evaluations as possible.

To approach this problem, a neural network approach is developed to serve as an inexpensive and generic function approximation procedure. The genetic algorithm was selected as the optimization technique based on its ability to search multi-modal, discontinuous, mixed parameter, and noisy design spaces.
Dynamics of a Vibro-Impacting Hinged Beam: Rigid and Flexible Models
Authors: Fegelman Karen J. L. , Grosh Karl
Published: February 2021

This study investigates the behavior of a vibro-impacting system with a rigid body mode. The model problem has been formulated as both a one-DOF and a multi-DOF piecewise linear system. The behavior of the models for a base excitation frequency range of 50–200 Hz (4.9–19.5% of the fundamental natural frequency of the in-contact case) is shown for constant base motion acceleration and displacement. It is seen that the models do not predict the same motion for the constant acceleration case, but agree quite closely for the constant displacement case. The system is capable of chaotic motion and several examples of Poincaré sections are shown which suggest the presence of a strange attractor. Future work including analytical methods of analysis for both the one- and multi-DOF systems is discussed.
Hand-Held Percussion Machine As an Optimal Converter
Authors: Babitsky V. I.
Published: February 2021

The problem of interaction of hand-held percussion machine with operator and load is presented and optimized as a problem of dynamical conversion of the operator effort into sequence of impulses produced with the help of machine drive. Some recommendations on the estimation of the main characteristics of the machine design are presented.
The Analysis of Deflection and Free Vibration of Laminated Composite Plates Embedded With Shape Memory Alloy Fibers by Finite Element Method
Authors: Zhong W. F. , Zou J. , Tang S. B.
Published: February 2021

In this paper a finite element mode of classical symmetrically laminated composite plates embedded with shape memory alloy fibers is developed. The young’s modulus and recovery stress of SMA are calculated by using Brinson’s one-dimensional constitutive relation. The analysis of deflection and free vibration show that the SMA can reduce the deflection and increase the vibration frequencies significantly, and it is a economical and efficient design to place SMA fibers in the outer-most plies for utilizing their tuning function.
Observations on Simulation of Joint Friction
Authors: Segalman Daniel J.
Published: February 2021

Results of Ungar and of Goodman on dissipation rates in bolted joints are discussed. It is shown that an infinite network of discrete sliders and springs such as specified by Iwan in his study of “parallel-series” systems dissipates energy in a manner similar to that shown by Goodman for frictionally joined continua. The nonlinear nature of frictionally joined continua is further examined by computing the force-acceleration behavior of a single degree of freedom system with one slider, demonstrating interesting multiply closed curves.
AutoSEA2: A New Design Evaluation Tool for Noise and Vibration Engineering
Authors: Bremner Paul G. , Burton Thomas E. , Cunningham Andrew
Published: February 2021

This paper describes the development of the AutoSEA2 statistical energy analysis (SEA) code. The development includes a family of quasi-conformal 3D subsystems; an automatic subsystem connection scheme and implementation of full wave transmission theory for more robust and accurate modeling of junctions. The application of these innovations to the modeling of automobile interior noise demonstrates the potential for this evolution of SEA to define a new “design evaluation” process which is an attractive alternative to finite element methods at the design stage.
A Compliant Double Pin Track Link Model for Multibody Tracked Vehicles
Authors: Choi J. H. , Bae D. S. , Ryu H. S.
Published: February 2021

It is the objective of this investigation to develop compliant double pin track link models and investigate the use of these models in the dynamic analysis of high mobility tracked vehicles. There are two major difficulties encountered in developing the compliant track models discussed in this paper. The first is due to the fact that the integration step size must be kept small in order to maintain the numerical stability of the solution. This solution includes high oscillatory signals resulting from the impulsive contact forces and the use of stiff compliant elements to represent the joints between the track links. The characteristics of the compliant, elements used in this investigation to describe the track joints are measured experimentally. The second difficulty encountered in this investigation is due to the large number of the system equations of motion of the three dimensional multibody tracked vehicle model. The dimensionality problem is solved by decoupling the equations of motion of the chassis subsystem and the track subsystems. Recursive methods are used to obtain a minimum set of equations for the chassis subsystem. Several simulation scenarios including an accelerated motion, high speed motion, braking, and turning motion of the high mobility vehicle are tested in order to demonstrate the effectiveness and validity of the methods proposed in this investigation.
Command Preprocessor for Radiotelescopes and Microwave Antennas
Authors: Gawronski Wodek
Published: February 2021

The LQG controllers, designed for the NASA Deep Space Network antennas have small tracking errors and are resistant to wind disturbances. However, during antenna slewing, they induce limit cycling caused by the violation of the antenna rate and acceleration limits. This problem can be avoided by introduction of a command that does not exceed the limits. The command preprocessor presented in this paper generates a command that is equal to the original command if the latter does not exceed the limits, and varies with the maximal (or minimal) allowable rate and acceleration if the limits are met or exceeded. It is comparatively simple since it requires only knowledge of the command at the current and the previous time instants, while other known preprocessors require knowledge of the terminal state and the acquisition time. Thus, the presented preprocessor is more suitable for implementation. In this article analysis of the preprocessor is presented. Also the performances of the preprocessor itself, and of the antenna with the preprocessor is illustrated with typical antenna commands.
Equations of Motion of Spool Valves With Eccentric Clearance
Authors: Duan Shanzhong , Anderson Kurt S.
Published: February 2021

Equations of motion of spool valves have been established under very ideal conditions. In this paper, some important factors are brought into considerations. One of them is the eccentric clearance existing between the valve spool and the sleeve due to fabrication errors. Another is the viscosity of a Newtonian fluid assumed to flow through the valve, which generally results in shear forces acting on the valve spool. Under these conditions, equations of motion of the spool valves are derived. Concepts of Poiseuille flow and Couette flow are used to obtain axial forces acting on the valve spool. The resulting equations of motion of spool valves have the simple form of a second order linear homogeneous ordinary differential equation under the imposed idealizations. The influence of these factors on the motion characteristics of spool valves are in turn discussed.
Frequency Domain Structural Optimization of a Flexible Manipulator Incorporating a PD Controller in the Design Stage
Authors: Chang Yong Hoon , Seireg Ali
Published: February 2021

This study investigates the potential advantages of integrated design strategies for flexible manipulators that utilize a controller in the process of optimizing the structural design.

Clamped free and clamped mass beam models are considered in the investigation for the structural optimization with respect to natural frequencies and mass. A PD controller is utilized in the design process with several objective functions that incorporate weighted combinations of the mass of the structure, modal mass, modal stiffness, and the natural frequency of the rigid mode and the dominant natural frequency of the flexible mode. The results show that the objective function, which minimizes the mass and the product of the modal mass and modal stiffness of the rigid mode and maximize the natural frequency of the flexible mode with appropriate weighting factors, gave the best dynamic performance.

Although a two link tubular planar manipulator with a PD controller and assumed beam models for the links is considered in the optimization based on modal parameters, the reported approach can be extended to time domain optimization of multi-link spacial robots with complex structures designed to perform particular tasks.
Analysis of Hyper-Redundant Manipulators
Authors: Asl Farshid Maghami , Ashrafiuon Hashem , Nataraj C.
Published: February 2021

A new approach to solve the inverse kinematic problem for hyper-redundant planar manipulators following any desired path is presented. The method is singularity free and provides a robust solution even in the event of mechanical failure of some of the robot actuators. The approach is based on defining virtual layers and dividing them into virtual/real three-link or four-link sub-robots. It starts by solving the inverse kinematic problem for the sub-robot located in the lowest virtual layer, which is then used to solve the inverse kinematic equations for the sub-robots located in the upper virtual layers. An algorithm is developed which provides a singularity-free solution up to full extension through a configuration index. The configuration index can be interpreted as the average of the determinants of the Jacobians of the sub-robots. The equations for the velocities and accelerations of the manipulator are solved by extending the same approach where it is realized that the value of configuration index is critical in maintaining joint velocity continuity. The inverse dynamic problem of the robot is also solved to obtain the torques required for the robot actuators to accomplish its task. Computer simulations of several hyper-redundant manipulators using the proposed method are presented as numerical examples.
A Virtual Body and Joint for Constrained Flexible Multibody Dynamics
Authors: Bae D. S. , Han J. M. , Choi J. H.
Published: February 2021

A convenient implementation method for constrained flexible multibody dynamics is presented by introducing virtual rigid body and joint. The general purpose program for rigid and flexible multibody dynamics consists of three major parts of a set of inertia modules, a set of force modules, and a set of joint modules. Whenever a new force or joint module is added to the general purpose program, the modules for the rigid body dynamics are not reusable for the flexible body dynamics. Consequently, the corresponding modules for the flexible body dynamics must be formulated and programmed again. Since the flexible body dynamics handles more degrees of freedom than the rigid body dynamics does, implementation of the module is generally complicated and prone to coding mistakes. In order to overcome these difficulties, a virtual rigid body is introduced at every joint and force reference frames. New kinematic admissibility conditions are imposed on two body reference frames of the virtual and original bodies by introducing a virtual flexible body joint. There are some computational overheads due to the additional bodies and joints. However, since computation time is mainly depended on the frequency of flexible body dynamics, the computational overhead of the presented method could not be a critical problem, while implementation convenience is dramatically improved.
Dynamical Simulation of Flexible Multibody System by Using a Rigid Body Model
Authors: Pascal M. , Gagarina T.
Published: February 2021

The aim of this work is to show the possibility of using any dynamical codes devoted to rigid multibody systems in which the motion equations are obtained from d’Alembert Principle, for the simulation of flexible multibody systems in which the flexible components are discretized by a Rayleigh-Ritz procedure. The obtained results are a generalization of the work done in Botz and Hagedorn (1990) for planar elastic mechanisms. An application of the method is done using, as in Botz and Hagedorn (1990), the symbolic dynamical code AUTOLEV (Schaechter, Levinson and Kane 1988).
Identification of Free-Free Modes From Constrained Vibration Data for Flexible Multibody Models
Authors: Yi Tong Y. , Nikravesh Parviz E.
Published: February 2021

This paper presents a method for identifying the free-free modes of a structure by utilizing the vibration data of the same structure with boundary conditions. In modal formulations for flexible body dynamics, modal data are primary known quantities that are obtained either experimentally or analytically. The vibration measurements may be obtained for a flexible body that is constrained differently than its boundary conditions in a multibody system. For a flexible body model in a multibody system, depending upon the formulation used, we may need a set of free-free modal data or a set of constrained modal data. If a finite element model of the flexible body is available, its vibration data can be obtained analytically under any desired boundary conditions. However, if a finite element model is not available, the vibration data may be determined experimentally. Since experimentally measured vibration data are obtained for a flexible body supported by some form of boundary conditions, we may need to determine its free-free vibration data. The aim of this study is to extract, based on experimentally obtained vibration data, the necessary free-free frequencies and the associated modes for flexible bodies to be used in multibody formulations. The available vibration data may be obtained for a structure supported either by springs or by fixed boundary conditions. Furthermore, the available modes may be either a complete set; i.e., as many modes as the number of degrees of freedom of the associated FE model is available, or it can be an incomplete set.
Seismic Responses of Large Flexible Structure Including Contact Problem
Authors: Kuribara Hiroshi , Kobayashi Nobuyuki
Published: February 2021

A modeling method for the seismic response of large movable flexible structures including the contact problem between wheels attached at the bottom ends of the structure and a rail, such as a container crane and an unloader, is developed. The contact configuration and the contact force between the wheel attached at the structure and the ground, that significantly affect to the seismic response of the structure, are classified and calculated according to geometric relationships between contact judging markers defined on the wheel and the rail. From the numerical simulation using proposed method, it is clarified that the presented modeling method simulates quite well the nonlinear seismic response of the container crane including the uplifting and derailment behavior of the wheel that is obtained by results of the large scale model shaking tests.
A Numerical Algorithm for Solving Stiff ODEs and DAEs in Multibody Mechanics
Authors: Pasic Hajrudin
Published: February 2021

Presented is an algorithm suitable for numerical solutions of multibody mechanics problems. When s-stage fully implicit Runge-Kutta (RK) method is used to solve these problems described by a system of n ordinary differential equations (ODE), solution of the resulting algebraic system requires 2s3 n3 / 3 operations. In this paper we present an efficient algorithm, whose formulation differs from the traditional RK method. The procedure for uncoupling the algebraic system into a block-diagonal matrix with s blocks of size n is derived for any s. In terms of number of multiplications, the algorithm is about s2 / 2 times faster than the original, nondiagonalized system, as well as s2 times in terms of number of additions/multiplications. With s = 3 the method has the same precision and stability property as the well-known RADAU5 algorithm. However, our method is applicable with any s and not only to the explicit ODEs My′ = f(x, y), where M = constant matrix, but also to the general implicit ODEs of the form f (x, y, y′) = 0. In the solution procedure y is assumed to have a form of the algebraic polynomial whose coefficients are found by using the collocation technique. A proper choice of locations of collocation points guarantees good precision/stability properties. If constructed such as to be L-stable, the method may be used for solving differential-algebraic equations (DAEs). The application is illustrated by a constrained planar manipulator problem.
A Dynamic Performance Evaluation Model for Target Capture by Robot Mechanisms, With the Consideration of Structural Flexibility
Authors: Kövecses J. , Cleghorn W. L. , Fenton R. G.
Published: February 2021

In this paper a dynamic system consisting of a robot manipulator and a target is analyzed. The target is considered in a general way as a dynamic subsystem having finite mass and moments of inertia (e.g. a rigid body or a second robot). The situation investigated is when the robot establishes interaction with the target in such a way that it intercepts and captures a reference element of the target. The greatest attention is paid to the analysis of the phase of transition from from ‘free’ to constrained motion at the time of interception and capture (impulsive motion). Based on the use of impulsive constraints and the Jourdanian formulation of analytical dynamics, a novel approach is proposed for the modeling of target capture by a robot manipulator. The proposed approach is suitable to handle both finite and impulsive motions in a common analytical framework. Based on the dynamic model developed and using a geometric representation of the system’s dynamics, a detailed analysis and a performance evaluation framework are presented for the phase of transition. Both rigid and structurally flexible models of robots are considered. For the performance evaluation analyses, two main concepts are proposed and corresponding performance measures are derived. These tools may be used in the analysis, design and control of time varying robotic systems. The dynamic system of a three link robot arm capturing a rigid body is used to illustrate the material presented.
A Multibody Loop Constraints Approach for Modelling Cam/Follower Devices: Application in Mobile Robotics
Authors: Fisette Paul , Lipiński Krzysztof , Samin Jean-Claude
Published: February 2021

This paper proposes a formulation for modelling mechanisms with cam/follower type of contact using a multibody approach in relative coordinates. The proposed approach is inspired from the wheel/rail contact model developed in (Fisette, Samin, 1994) but in the present case, possible intermittent contact between the cam and the follower is considered, for generality purposes.

Loop kinematic constraints are introduced to satisfy tangent and punctual contact as long as the bodies lean against each other. The effective presence (or not) of the contact is governed by the sign of the normal constraint force which can be computed thanks to the Lagrange multipliers technique.

The above-mentioned option to kinematically constraint the bodies in their “contact phase” unavoidably leads to shift from one model to another when a contact disappears (or conversely reappears). Indeed, this increases (or decreases) the number of degrees of freedom of the current system. The control of the variable partitioning is thus absolutely necessary and is all the more complex that practical applications can contain several pairs of bodies in intermittent contact.

As regards the applications, a comparison with another multi-body formalism and an experimental validation are discussed at first. Then, the modelling and simulation of universal wheels of an omnimobile mobile robot, developed in our Division, are proposed. The latter model represents a quite original application of the proposed multibody formulation. Computations are now in progress to analyse the complete behaviour of the robot, including control performances.
A Study on the Dynamic Analysis of Flexible and Rigid Link System
Authors: Sugano Naoki , Honke Koichi , Imanishi Etsujiro , Hashimoto Kazuo
Published: February 2021

In this paper, the dynamic analysis of link structures including both flexible and rigid bodies is developed. The model for flexible bodies is based on FEM theory, and geometric nonlinearity effect is taken into account. Moreover, in the flexible rigid link structure, dependent variables are eliminated using topological information. The equation of the total system obtained in this study is in the form of ODE and can be solved efficiently.
Incremental Finite Element Formulations and Flexible Multibody Dynamics
Authors: Berzeri Marcello , Campanelli Marcello , Shabana A. A.
Published: February 2021

In this investigation, the performance of two different large displacement finite element formulations in the analysis of flexible multibody systems is investigated. These are the incremental corotational procedure proposed by Rankin and Brogan [8] and the non-incremental absolute nodal coordinate formulation recently proposed [9]. It is demonstrated in this investigation that the limitation resulting from the use of the nodal rotations in the incremental corotational procedure can lead to simulation problems even when very simple flexible multibody applications are considered.
A Large Displacement Formulation Using Euler’s Angles
Authors: Biakeu G. , Thouverez F. , Laine J. P. , Jezequel L.
Published: February 2021

The goal of this paper is to present a flexible multi-body formulation involving large displacements. This method is based on a separate discretisation of the kinetic and the internal energies. To introduce flexibility, we discretize the structure in elements (of two nodes): on each element of the beam discretisation, the local frame is defined using Euler’s angles. A finite element formulation is then applied to describe the evolution of these angles along the beam neutral fibre. For the kinetic energy, each element is cut into two rigid bars whose characteristics are given by a first order Taylor factorisation on the general kinetic energy expression. These bars are linked by a nonlinear relation. We obtain the equations of motion by applying the Lagrange’s equations to the system. These equations are solved using the Newmark method in dynamic and a Newton-Raphson technique while looking for a static solution. The method is then applied to very classic problems such as the curved beam problem proposed by authors such as Simo [6, 9], Lee [4] or the rotational rod presented by Avello [1] and Simo [7, 8] etc...
Multirate Integration for Multibody Dynamic Analysis With Decomposed Subsystems
Authors: Kim Sung-Soo , Freeman Jeffrey S.
Published: February 2021

This paper details a constant stepsize, multirate integration scheme which has been proposed for multibody dynamic analysis. An Adams-Bashforth Moulton integration algorithm has been implemented, using the Nordsieck form to store internal integrator information, for multirate integration. A multibody system has been decomposed into several subsystems, treating inertia coupling effects of subsystem equations of motion as the inertia forces. To each subsystem, different rate Nordsieck form of Adams integrator has been applied to solve subsystem equations of motion. Higher order derivative information from the integrator provides approximation of inertia force computation in the decomposed subsystem equations of motion. To show the effectiveness of the scheme, simulations of a vehicle multibody system that consists of high frequency suspension motion and low frequency chassis motion have been carried out with different tire excitation forces. Efficiency of the proposed scheme has been also investigated.
A Nonlinear Magnetic Circuit Analysis of a Permanent Magnet Biased Homopolar Bearing
Authors: Kenny Andrew , Palazzolo Alan
Published: February 2021

A magnetic circuit model for a homopolar magnetic bearing is presented. This model connects the fore and aft circumferential flux paths with axial flux paths through the rotor and back iron. The bias flux is provided by a circumferential permanent magnet in the back iron. Results for an analysis using the nonlinear Hyperco50 B-H curve are presented. These results are compared to the results of a three dimensional magnetostatic finite element analysis. The two analytical methods are in good agreement and show that the control flux in this type of bearing follows both circumferential and axial paths.
Application of Transfer Matrices to Non-Linear Rotor Bearing Systems
Authors: Liew A. , Feng N. S. , Hahn E. J.
Published: February 2021

To obtain the steady state unbalance response of rotor bearing systems, it is common to linearise the hydrodynamic bearing forces about their static equilibrium position. Such linearisation is increasingly approximate with increasing unbalance as it ignores the possibility of typical non-linear phenomena such as sub- and super-harmonic response and multi-stable response. Even in the case of mono-stable synchronous response, the amplitudes are differently attenuated as a result of non-linear effects. This paper shows how the transfer matrix approach, traditionally applied to linear systems, can be extended to evaluate the steady state response of non-linear systems, using harmonic balance to accommodate the various response harmonics. The technique is illustrated using a hydrodynamic journal bearing and a squeeze film damper as the non linear elements.
On Further Improvements in Predicting Rotor Vibration
Authors: Subbiah R.
Published: February 2021

Vibration is one of the primary concerns in rotating machinery. Vibration reduction will help extend turbo-machinery life and is viewed as one of the major winning points for turbine-generator (T-G) manufacturers. To better predict the level of machine vibration requires a great deal of analysis. The success of different analyses mainly rely on reliable models that are accurate and consistently verifiable by testing. Towards this objective, many researchers and businesses spent enormous amount of time and money in the development of accurate and reliable models that closely simulate reality. However, research in rotor dynamic modeling is an on-going effort. In this paper, another new modeling approach that uses strain energy is reported. This modeling technique was successfully applied for rotor torsional and lateral analyses with greater accuracy. Further, a faster and more stable solution method which uses Riccati algorithm is discussed.
On the Natural Frequency Calculation of Rotating Cantilever Uniform Beams With Coriolis Effects: A Dynamic Finite Element (DFE)
Authors: Hashemi S. M. , Richard M. J.
Published: February 2021

A Dynamic Finite Element (DFE) for vibrational analysis of rotating assemblages composed of beams is presented in which the complexity of the acceleration, due to the presence of gyroscopic, or Coriolis forces, is taken into consideration. The dynamic trigonometric shape functions of uncoupled bending and axial vibrations of an axially loaded uniform beam element are derived in an exact sense. Then, exploiting the Principle of Virtual Work together with the nodal approximations of variables, based on these dynamic shape functions, leads to a single frequency dependent stiffness matrix which is Hermitian and represents both mass and stiffness properties. A Wittrick-Williams algorithm, based on a Sturm sequence root counting technique, is then used as the solution method. The application of the theory is demonstrated by two illustrative examples of vertical and radial beams where the influence of Coriolis forces on natural frequencies of the clamped-free rotating beams is demonstrated by numerical results.
Measured Torsional Vibration Characteristics of a 100 Megawatt Wind Tunnel Drive Line
Authors: Corliss James M. , Sprysl H.
Published: February 2021

A new 100 MW (135,000 Hp) adjustable speed drive system has recently been installed in the NASA Langley National Transonic Facility. The 100 MW system is the largest of its kind in the world and consists of a salient pole synchronous motor powered by a 12-pulse Load Commutated Inverter variable frequency drive. During system commissioning the drive line torsional vibrations were measured with strain gages and a telemetry-based data acquisition system. The torque measurements included drive start-up and steady-state operation at speeds where the drive motor’s pulsating torques match the drive line’s torsional natural frequency. Rapid drive acceleration rates with short dwell times were effective in reducing torsional vibrations during drive starts. Measured peak torsional vibrations during steady-state operation were comparable to predicted values and large enough to produce noticeable lateral vibrations in the drive line shafting. Cyclic shaft stresses for all operating conditions were well within the fatigue limits of the drive line components. A comparison of the torque measurements to an analytical forced response model concluded that a 0.5% critical damping ratio was appropriately applied in the drive line’s torsional analysis.
Vibration Characteristics of a Rotor-Flexible Disk System: In Case of HDD Spindle-Motor System
Authors: Han D. C. , Choi S. H. , Park K. B. , Jung S. C.
Published: February 2021

In this paper we investigate the vibration characteristics of a rotor system with flexible disks. The coupled vibration mode between rotating shaft and the flexible disk are analyzed for lateral and axial vibrations respectively. Gyro and sheer effects are considered for the modeling of lateral vibrations. An assumed mode method was used for the disk modeling considering gyro effects. For a numerical example hard disk drive is considered. The natural frequencies of the motor-spindle system with flexible disk of hard disk drive was calculated and compared to the experimental data.
A Flexible Rotor on Flexible Bearing Supports: Part I — Stability
Authors: Vázquez José A. , Barrett Lloyd E. , Flack Ronald D.
Published: February 2021

An experimental study of the effects of bearing support flexibility on rotor stability is presented. A flexible roto supported by fluid film bearings on flexible supports was used with fifteen support configurations. The horizontal suppor stiffness was varied systematically while the vertical stiffness was kept constant. The support charactristics were determined experimentally by measuring the frequency response functions of the support structure at the bearing locations. These frequency response functions were used to calculate polynomial transfer functions that represented the support structure. Stability predictions were compared with measured stability thresholds. The predicted stability thresholds agree with the experimental data within a confidence bound for the logarithmic decrement of ±0.01. Predictions for the rotor on rigid supports are included for comparison.
A Flexible Rotor on Flexible Bearing Supports: Part II — Unbalance Response
Authors: Vázquez José A. , Barrett Lloyd E. , Flack Ronald D.
Published: February 2021

An experimental study of the effects of bearing support flexibility on rotor unbalance response is presented. A flexible rotor supported by fluid film bearings on flexible supports was used with fifteen support configurations. The horizontal support stiffness was varied systematically while the vertical stiffness was kept constant. The support characteristics were determined experimentally by measuring the frequency response functions of the support structure at the bearing locations. These frequency response functions were used to calculate polynomial transfer functions that represented the support structure. The second critical speed of the rotor varied from 3690 rpm to 5200 rpm, depending on the support configuration. The predicted first critical speeds agree with the experimental data within −1.7%. The predicted second critical speeds agree with the experimental data within 3.4%. Predictions for the rotor on rigid supports are included for comparison.
Maximum Response of a Slow-Variant Mechanical System During Transition Through a Resonance
Authors: Balashov Dmitri , Irretier Horst
Published: February 2021

A new approach to the estimation of the maximum transient response of a mechanical system with slow-variant natural frequencies and linear viscous damping is worked out. Based on the modal decomposition, the vibration response of a system is modeled using a set of simple vibrators with slow-variant natural frequencies. The passage through a resonance which is induced by a sweep of the excitation frequency during run-up or run-down is studied. Exact asymptotic formulas for the maximum transient response and the corresponding excitation frequency are derived analytically, starting from the first Krylov-Bogoliubov approximation. The obtained formulas are tested numerically and compared to known approximations.
Laser Vibrometry: The Complete 6 Degree-of-Freedom Model of Target Velocity Sensitivity
Authors: Bell John R. , Rothberg Steven J.
Published: February 2021

This paper presents the first analysis of the velocity sensed by a single laser vibrometer beam incident in an arbitrary direction on a target that is of substantial interest in engineering — a rotating shaft requiring three translational and three rotational co-ordinates to describe its vibratory motion fully. Six separate vibration sets, each a combination of motion parameters, appear in the full expression for vibration velocity sensitivity and it is not possible to resolve individual motion components within each set by arrangement, or even manipulation, of beams. While unambiguous measurement of torsional vibration is possible, measurement of radial, pitch and yaw vibrations is only possible by post-processing. Application of the new theory includes straightforward extension to include measurements made with multiple beams, underlining the model’s versatility in enabling the vibration engineer to determine the vibration component sensitivity of any measurement with any beam orientation.
Vibration Analysis of an Induction Motor Under Electromagnetic Force
Authors: Iwatsubo Takuzo , Kawamura Shozo , Hayashi Yoshiyuki , Shiohata Koki
Published: February 2021

Three-phase induction motor causes an unstable vibration because of electromagnetic force. In this paper, a criterion for unstable vibration was introduced. To confirm this criterion, numerical integration was carried out and the results showed a good agreement with the unstable region obtained by the criterion. This criterion gives us the complete story about the stability for the case when the parameters e.g., phase current, air gap length etc. are changed. It was cleared that the natural frequency changes owing to the variation of phase current, and that the unstable vibration occurs when the frequency of power supply and the natural frequency (changed by current) are nearly the same. And it was also showed that the parameters can be classified into the categories whether they have influences on the stability or not.
A Model-Based Method for Balancing of Flexible Rotors Mounted on Oil-Film Bearings Without Trial Weight
Authors: Fritzen C.-P. , Gans P. , Wiese D. , Breitwieser M.
Published: February 2021

The following paper deals with a model-based method for unbalance identification. In contrast to conventional methods there is no need for the properties of the oil-film bearings to be known. First, the rotor is modeled as a conservative system in rigid bearings and the corresponding real mode shapes are calculated. The real motion of the rotor is represented by means of these mode shapes and the superimposed rigid-body motion of the rotor. The rigid-body motion is completely determined by the measured deflections in the oil-film bearings. Modal unbalances of the rotor are identified. Initial positive test results are presented in this paper.
Nonlinear Response of Rotors Supported on Squeeze Film Dampers
Authors: Ramesh Krishnaswamy , Kirk R. Gordon
Published: February 2021

The ability of a squeeze film damper (SFD) to attenuate the amplitude of vibration and to decrease the dynamic forces transmitted to the support system, makes it an attractive means of supporting turbomachinery. The main reasons for using a squeeze film damper on a rotor are to improve the dynamic stability and also to reduce the forces transmitted to the foundation. Generally the squeeze film damper ring is centered by a retainer spring. For linearized stability evaluation this is an acceptable assumption. While evaluating the forced response of a rotor having a squeeze film damper, the damper ring is usually assumed to be centralized in the clearance space through the entire running speed range. During the actual running condition the damper does not remain in the centered position and the damper ring tends to find its own eccentric position. This paper discusses the effect of this non-linear behavior of the damper and on the response. A overhung compressor is used as an example to illustrate the influence of the non-linear damper as compared to the centered damper assumption.
Comparison of Active and Hybrid Vibration Confinement With Conventional Active Vibration Control
Authors: Corr Lawrence R. , Clark William W.
Published: February 2021

This paper presents a numerical study in which active and hybrid vibration confinement is compared with a conventional active vibration control method. Vibration confinement is a vibration control technique that is based on reshaping structural modes to produce “quiet areas” in a structure as opposed to adding damping as in conventional active or passive methods. In this paper, active and hybrid confinement is achieved in a flexible beam with two pairs of piezoelectric actuators and sensors and with two vibration absorbers. For comparison purposes, active damping is achieved also with two pairs of piezoelectric actuators and sensors using direct velocity feedback. The results show that both approaches are effective in controlling vibrations in the targeted area of the beam, with direct velocity feedback being slightly more cost effective in terms of required power. When combined with passive confinement, however, each method is improved with a significant reduction in required power.
Active Control Machine Tool Chatter Piezo Ceramic Actuators in Tool Holder Shank
Authors: Håkansson L. , Claesson I. , Pettersson L. , Lagö T.
Published: February 2021

In the turning operation chatter or vibration is a frequent problem, which affects the result of the machining, and, in particular, the surface finish. Tool life is also influenced by vibration. Severe acoustic noise in the working environment frequently occurs as a result of dynamic motion between the cutting tool and the workpiece. These problems can be reduced by active control of machine-tool vibration. Adaptive feedback control based on the filtered-x LMS-algorithm, enables a reduction of the vibration by up to 40 dB at 1.5 kHz and by approximately 40 dB at 3 kHz. The active control performed a broadband attenuation of the sound pressure level by up to 35 dB. A significant improvement of the work-piece surface was also observed. In the active control of tool vibration a tool holder construction based on integrated high magnetostrictive actuators was used. However, both the physical features and properties of a active tool holder construction based on high magnetostrictive actuators and the fact that this type of actuators generally have a non-linear behaviour highly reduce its applicability to the general lathe and turning operation. Therefor, a new generation embedded active tool holder shanks based on piezo ceramic actuators have been developed. Based on spectrum estimates, both coherence spectrum and frequency response function estimates has been calculated for both the old tool holder construction and the new generation active tool holder shank. From the results it follows that the phase delay is smaller and the linearity of the new generation active tool holder shank are superior compared to the old technology. It is also obvious that physical features and properties of new generation embedded active tool holder shanks based on piezo ceramic actuators fits the general lathe application.
The Motion of a Flyline: Part B — Solutions
Authors: Hoffmann Jon A. , Reth Peov
Published: February 2021

The motion of a level flyline during the forward cast has been investigated for the case of line release from the rod. After the work input phase, the cast was considered to be composed of loop formation, line unrolling, loop dissipation and final descent phases. Solutions to the governing equations are presented. Input energy comparisons were made as a function of the parameters which control flyline motion. Line velocities during each phase, lengths of line released, and minimum initial line velocities required to complete loop dissipation have been predicted.
Energetics and Stability of Translating Media With an Arbitrarily Varying Length
Authors: Zhu W. D. , Ni J.
Published: February 2021

The dynamics of a class of translating media with an arbitrarily varying length is investigated. The tension in the media arising from their longitudinal accelerations is incorporated. The dynamic stability of the continuous media relative to the inertial and moving coodinate systems is studied from the energy standpoint. The exact expressions for the rates of change of energies of the media are derived and interpreted from both the control volume and system viewpoints. The monotonic behavior of the energy of vibration of the translating media during extrusion and retraction is affected by their jerks rather than accelerations. Examples including a robotic arm through a prismatic joint and an elevator hoist cable in a high rise building validate the analysis. In particular, the results explain an inherent “unstable shortening cable behavior” in elevator industry.
Modeling and Experimental Characterization of the Dynamic Behavior of Piezoelectric Recurve Actuation Architectures
Authors: Ervin James D. , Brei Diann E.
Published: February 2021

There are numerous applications that require fast actuators to deliver specific force and displacement output while fitting into confined spaces. A new family of piezoelectric actuators called Recurves exhibit high work per volume and have the extra benefit of having both the force-deflection performance and packaging tailorable to fit the requirements of a given application. The focus of this paper is the dynamic performance of this novel actuation scheme. Two dynamic models, a detailed transfer matrix model and a simpler rod approximation model, are presented to predict the steady state frequency response of a general Recurve actuator driving a mass and spring load. Results from a 23 design of experiments are given that validate these models and demonstrate the impact of the architectural design parameters on the dynamic behavior of the general Recurve actuator.
Tool Breakage Detection Using Statistical Moments
Authors: Ismail Fathy , Elbik Ali
Published: February 2021

On-line monitoring and detection of tool breakage is essential for highly automated machining centers. This paper presents a tool breakage method that utilizes statistical moments of the Beta distribution. The method has been applied successfully by the first author for the detection of tooth cracks in gears. It is extended here to the detection of chipped or broken teeth (inserts) in milling cutters. The method is assessed using cutting tests of steel workpieces employing Taguchi’s approach for statistical design of experiments. Results of these experiments show the Kurtosis of the Beta distribution to be a reliable tool breakage indicator that is insensitive to operating conditions and for typical amounts of tool radial runouts.
Gearbox Fault Detection Using Neural Networks Technology
Authors: Sun Qiao , Li Xiaolei , Xu Baoyun
Published: February 2021

This paper describes the application of neural networks to gearbox fault diagnosis. In order to increase learning speed of BP network, a modified learning algorithm was presented. Considering of the difficulty of choosing neural networks’ architecture, genetic algorithm was employed. The discussion of the effect of hidden layer nodes shows that with the increase of the number of nodes, the learning speed increase also yet result in poor generalization ability. The test of fault tolerance ability tells that neural networks have ‘bench type’ tolerance ability. This ensures that when signals were contaminated by noise or feature extraction methods were not effective, the result can still be acceptable.

To test the performance of the application of neural networks on gearbox fault diagnosis, experiments of single fault and multi-faults were both implemented and diagnosed by neural networks. The results were satisfied.
Impact Force Between Rolling Ball and Surface Fault in Damaged Ball Bearings
Authors: Rubini R. , Meneghetti U.
Published: February 2021

A great deal of research work has been dedicated in the last few decades to the development of refined and effective procedures for rolling bearing monitoring and diagnostics through vibration analysis. The basic observation is that sudden impact and consequent casing vibration take place every time a rolling ball overpasses a surface defect. As far as the authors know, little work has been focused on characterizing the impact force itself, i. e. determining its actual pattern and value. In this paper, the problem of identifying impact force between rolling balls and races is tackled experimentally. The force is recovered by inverse filtering of the casing acceleration. Results indicate the potential effectiveness of the method.