bluuebunny/crossref_metadata_2025 huggingface dataset:
To Injection Mold, to Stamp, or to Assemble? Part II — A Time-to-Market Perspective
Authors: Hu Weiyi , Poli Corrado
Published: February 2021

This paper presents a time-to-market comparison of injection molding and stamping based on a comparison of overall production time periods. The general guidelines obtained and conclusions drawn in order to determine if a component should be injection molded or stamped, and/or if several components in an assembly should be combined into a single part or not, are discussed. The time evaluation and comparison are primarily in terms of the functional equivalence of feature, component, and assembly.
Performance Comparison Between Vibration Control by Confinement and Conventional Control Techniques
Authors: Allaei Daryoush
Published: February 2021

This paper presents some of the key results obtained in an investigation comparing the performance of the Vibration Control by Confinement technique with conventional vibration control methods using isolators, absorbers, and layer damping in their passive and/or active form. All four vibration suppression methods are applied to a system comprised of an elastic component resting on an elastic beam-type supporting structure. The finite element method is employed to model the system and generate the numerical results presented in this article. The system is subjected to a single harmonic disturbance applied directly to the beam. Kinematics variables are determined at the component and its interface with the supporting structure. Based on the results obtained via the FEM model, it is shown that the Vibration Control by Confinement technique outperforms, by a significant performance level, the conventional suppression methods studied in this project. Furthermore, it is concluded that the Vibration Control by Confinement technique is an effective and viable approach that not only has better performance, but has fewer limitations than current techniques. Furthermore, additional ramifications of the Vibration Control by Confinement approach as they apply to active vibration control systems are discussed.
Impedance Characteristics of Structural-Acoustic Control for Interior Noise Suppression
Authors: Jayachandran V. , Sun J. Q.
Published: February 2021

There has been a growing interest in interior noise control problems for aircraft and automobiles in recent years. While active noise cancellation (ANC) and active structural acoustic control (ASAC) are two main stream technologies, much attention has also been paid to sound absorption by active or semi-active means. Sound absorption occurs when the impedance of an absorbing medium such as an active foam or trim panel matches the impedance of the acoustic medium. To develop such an active or semi-active system for sound absorption, one needs to be able to describe the acoustic impedance accurately at the structural-acoustic interface. This paper presents a particular solution approach for solving the inhomogeneous Helmholtz equation, which allows us to obtain an accurate representation of the impedance field near the boundary. Qualitative and quantitative analysis of the impedance of the acoustic medium before and after active noise control are presented along with numerical results. The study in this paper provides a better understanding of the physics of the problem and may be useful in designing absorption systems for interior noise suppression.
Quantitative Identification of Vehicle Rattle Sources Using CAE and Experimental Tools
Authors: Her Jen Yaun , Hsieh Shang-Rou , Moore James A.
Published: February 2021

Vehicle rattle noise, generated when parts impact each other due to road, wind or powertrain induced vibration excitation, has become one of the major customer concerns in recent years. Traditional find and fix methods for rattle problems rely on a subjective assessment in identifying and locating the rattle before corrective action is taken. This paper presents a simple technique to quantitatively determine the location and strength of rattle using a microphone and an accelerometer. A CAE tools had also been introduced to identify potential rattle hot spots early in the design process before prototype vehicle have been built. The correlation between the experimental technique and CAE prediction for identifying rattle sources in a prototype vehicle is also presented.
Self-Compensating Control for Suppression of Rotational Speed Variation Excited by Reduction Gear Mechanism
Authors: Itoh Masahiko , Kasei Shinji , Fukada Shigeo
Published: February 2021

In servo-controlled mechanical systems, such as industrial machines and robots, several kinds of gear reducers are proposed and employed selectively. It is known that these gear reducers generate speed and torque variations due to their element error, alignment error, etc., which result in excitations of undesirable vibrations in driven machines. This paper presents a control technique for suppressing such vibration source in the gear reducers themselves, especially relating to excitations in a lower-frequency range. This technique is based on a self-compensating control applied to the gear reducer. This control loop has band-pass filters whose center frequencies track changes in the motor speed and gain adjusters. A gear reducer referred as harmonic drive type being taken up, theoretical approaches are performed on the stability and other performances of the control systems. Simulations and experiments show satisfactory control results in constant speed, acceleration and deceleration states of the motor.
Sliding Mode Control With Pre-Filter for Spillover and Chattering Suppression
Authors: Ito Takayuki , Nonami Kenzo
Published: February 2021

We discuss the sliding mode control to suppress a spillover phenomena caused by truncation of the higher flexible modes for a flexible system. We propose a new method to suppress a higher frequency region including a truncated flexible modes and chattering by filtering control inputs through low-pass filter. And also, we can easily design a control system and apply for an actual system. We have verified from simulations and experiments for flexible structure that the proposed method has good performance and is very useful for spillover suppression.
Fuzzy Changing Stiffness Control of the Unstable Vibration of a Centrifuge Rotor
Authors: Yuan Y. , Liu S. Y. , Wen B. C.
Published: February 2021

Fuzzy control theory is used to control the unstable vibration of a centrifuge rotor by means of changing support stiffness. The solid–liquid coupling equations of a centrifuge rotor are presented. A fuzzy changing stiffness controller with changeable control rules is designed. Parameters of the controller are optimized by an optimization method. This control method is realized on a horizontal centrifuge rotor. Experimental results show that fuzzy changing stiffness control (FCSC) can stabilize the unstable vibration of a centrifuge rotor effectively.
Development of an Active Mass Damper for Stabilizing the Load Suspended on a Floating Crane
Authors: Iwasaki Itaru , Tanida Koji , Kaji Sokichi , Mutaguchi Masao
Published: February 2021

To minimize the necessity to suspend shackling work floating crane on account of vessel rolling, an active mass damper system was developed to attenuate oscillation of the sling frame under which the shackles are suspended. The motion of actual floating crane under sea wave was measured to determine the mechanism of sling frame oscillation, and to verify from theoretical analysis the effectiveness of installing an active mass damper on the sling frame. For further ascertaining damper performance, a 1/40 size model of the crane barge mounted with the damper was tested in tank, which indicated reduction to 1/3 – 1/2 of sling frame oscillation, with good agreement between the theoretically estimated and measured results. Test at sea on actual floating crane equipped with active mass damper system confirmed that actuation of the system would reduce to roughly 1/2 the oscillation of sling frame.
Control Performance of Hadamard-Weighted H2 Controller for Multiple-Input Structure System
Authors: Watanabe Toru
Published: February 2021

In this study, a design method of a controller taking account of integrity is presented using Hadamard weighted H2 control theory. Numerical calculations are carried out by using a structure model with an active dynamic vibration absorber (ADVA) and an active vibration isolator (AISO). It is shown that the controller designed by using the proposed method realizes higher integrity than the ordinary weighted H2 controller, though it requires more amount of control inputs to achieve same vibration reduction effect in average.
Order Reduction of Controller Based on LMIs Improving Error Bounds
Authors: Saragih Roberd , Kazuo Yoshida
Published: February 2021

In this paper, we propose an order reduction method of controller based on combination of the alternating projection method and the balanced truncation. In this method both the errors of controller and the closed-loop system caused by the reduced-order controller can be improved simultaneously. By using a generalized Bounded Real Lemma, a feasible reduced-order controller can be derived. The sufficient condition for the existence of a reduced-order controller leads to a non-convex feasibility problem. To solve the problem, we can use an improved computational scheme based on the alternating projection method. But it is needed so much time to solve the problem if compared by the other methods. To validate the proposed method, some numerical calculations and simulations are carried out.
Development and Testing of Variable Gain Control Algorithms for Seismic Response Control of a Full-Scale Structure
Authors: Iemura Hirokazu , Igarashi Akira , Inoue Yutaka , Sakamoto Mitsuo
Published: February 2021

In order to use Active Mass Dampers (AMD) for the seismic response control of structures, excessive auxiliary mass displacements must be avoided even under a high level of excitation, which becomes a critical factor in the event of strong earthquakes. The control algorithm for the full-scale multi-story steel frame test structure at Disaster Prevention Research Institute, Kyoto University, takes advantage of a nonlinear control scheme based on a variable gain method to overcome this difficulty. The nonlinear control used in the test achieves effective use of AMD with a limited displacement range of the auxiliary mass for structures under various levels of seismic input. The structural control test is conducted to verify the efficiency of the variable gain control scheme when used with the full-scale test structure. The test result using a seismic record shows the effectiveness of the control method, especially when subjected to a strong earthquake excitation.
Implementation of Non-Reflecting Boundaries in a Space-Time Finite Element Method for Structural Acoustics
Authors: Thompson Lonny L.
Published: February 2021

This paper examines the development and implementation of second-order accurate non-reflecting boundary conditions in a time-discontinuous Galerkin finite element method for structural acoustics in unbounded domains. The formulation is based on a multi-field space-time variational equation for both the acoustic fluid and elastic solid together with their interaction. This approach to the modeling of the temporal variables allows for the consistent use of high-order accurate adaptive solution strategies for unstructured finite elements in both time and space. An important feature of the method is the incorporation of temporal jump operators which allow for discretizations that are discontinuous in time. Two alternative approaches are examined for implementing non-reflecting boundaries within a time-discontinuous Galerkin finite element method; direct implementation of the exterior acoustic impedance through a weighted variational equation in time and space, and indirectly through a decomposition into two equations involving an auxiliary variable defined on the non-reflecting boundary. The idea for the indirect approach was originally developed in (Kallivokas, 1991) in the context of a standard semi-discrete formulation. Extensions to general convex boundaries are also discussed — numerical results are presented for acoustic scattering from an elongated structure using a first-order accurate boundary condition applied to an elliptical absorbing boundary.
Nonlinear Wave Propagation in Elastic Submerged Cables
Authors: Behbahani-Nejad M. , Perkins N. C.
Published: February 2021

This paper analyzes the coupled nonlinear tangential-normal waves that propagate along underwater cable suspensions. Taken with the recently developed linear theory governing the in-plane structural waves (3) and an analysis of nonlinear out-of-plane waves for submerged cables (2), this investigation contributes further understanding toward a nonlinear three-dimensional theory for wave propagation along fluid loaded cables. The nonlinearities present in the in-plane model render the cable/fluid model intractable by exact analytical methods. A numerical solution is pursued in this study using finite difference algorithms. To this end, an infinite cable domain is divided to two sub domains, namely an interior (finite computational) domain and exterior (infinite far field) domain. Closed-form solutions for the approximate linear theory are employed for the far field in constructing nonreflecting boundary conditions for the computational domain. Numerical results highlight the governing role of nonlinear hydrodynamic drag for underwater cable suspentions.
Analysis of Dynamic Force Between Teeth Walls in Scroll Compressors by Elastic Contact Modelling
Authors: Suzuki Takayuki , Sato Kazuhiro
Published: February 2021

The new dynamic behavior model for excited force in scroll compressors has been developed. We were not satisfied with the results of our previous analysis model as the contact area between the teeth walls of the scrolls was limited to one point. In our new analysis model, we consider the contact at several points and the linear elastic model at contact points. Force excited at contact points between the teeth walls of the two scroll elements contributes to the level of noise radiated from the scroll compressors. By using our model, the excited force at contact points between each element in the scroll compressors can be calculated and therefore aid us in our efforts at noise and vibration reduction. This paper describes the equation of the dynamic behavior model derived from the motion of elements : an orbiting scroll, an oldham ring, a slider block, and a crank shaft. Also the theoretical and experimental results are discussed.
Experimental and Numerical Studies of Friction-Induced Oscillations of a Pin-on-Disk Apparatus
Authors: Tworzydlo W. W. , Hamzeh O. N. , Zaton W. , Judek T. , Loftus H.
Published: February 2021

The paper presents coordinated experimental and numerical studies of friction-induced vibrations of a pin-on-disk apparatus. The primary objective is to verify and expand the understanding of friction-induced vibrations, and to confirm validity of the analytical predictive technology. A special experimental apparatus was built, which possesses desirable qualities of mechanical simplicity and controllable dynamic characteristics. For this apparatus, an analytical model was devised, taking into consideration both the dynamics of the mechanical system and strongly nonlinear constitutive properties of the contact interface. These properties were determined through asperity-based homogenization approach. By variation of selected details of the apparatus, both stable and unstable configurations of the system were devised and tested. The experimental observations correlate very well with analytical predictions of dynamic instability and of limit cycle oscillations.
Periodic Optimal Control of Dampers
Authors: Kasturi Prakash S. , Dupont Pierre E.
Published: February 2021

Optimal control of dampers has been proposed to mitigate vibration effects in mechanical systems. In many cases, systems are subject to periodic forcing and the goal is to maximize the energy dissipated by the damper. In contrast to prior work utilizing instantaneous or infinite-time-horizon optimization, this paper employs periodic optimal control to maximize the energy dissipated per cycle. For single degree of freedom systems in which the maximum allowable control effort is of the same order as the forcing magnitude, a state-dependent singular control law is shown to deliver maximum energy dissipation. Alternate control laws are proposed for situations when rattlespace requirements dictate damper displacements other than that of the singular solution.
Light-Induced Non-Contact Actuation and Control With Photostrictive Actuators
Authors: Tzou H. S. , Liu B. J.
Published: February 2021

Non-contact light activated distributed opto-electromechanical actuators represent a new class of precision distributed actuator which are based on the photodeformation process and controlled by high energy lights, e.g., lasers and ultra-violet lights. Fundamental opto-thermo-electromechancial constitutive relations are discussed and formulations of optically induced control forces and moments introduced. Mathematical modeling and analysis of distributed opto-electromechanical shell actuators are presented. A generic distributed photo-actuation theory is proposed and the closed-loop opto-thermo-electromechancial equations of circular cylindrical shells are derived. The systems equations reveal the couplings among elasticity, photodeformation, pyroelectricity, and thermoelasticity. Active distributed control of flexible cylindrical shells using segmented distributed opto-electromechanical shell actuators are investigated and the control effectiveness is evaluated. Membrane and bending control effects are evaluated. Time history analyses of independent modal control reveal that the Lyapunov control is more effective than the proportional feedback control.
Vibration Control of a Multi-Layer Piezoelectric Cylindrical Shell
Authors: Qiu Jinhao , Tani Junji
Published: February 2021

Equations of motion for multi-layer piezoelectric cylindrical shells and the equations of the integrated piezoelectric sensors are derived. The state equation is obtained by solving the equations of motion with modal expansion method. The feedback control, feedforward control, and their combination are applied in the control of forced vibration of the piezoelectric cylindrical shell with integrated sensor and actuators. The simulation and experimental results show that good control effectiveness can be obtained by using the integrated piezoelectric sensor and actuators in conjunction with the combination of feedback and feedforward control methods.
Actuator Placement in Smart Structures by Discrete-Continuous Optimization
Authors: Gabbert U. , Schulz I. , Weber C.-T.
Published: February 2021

Multi-functional smart materials, which can be used as conventional load bearing structural elements as well as actuators and sensors — e.g. as part of a multi-layered composite — in conjunction with suitable control systems are the basis of the development of adaptive structural systems for shape control, vibration damping etc. The effectiveness of an adaptive structural system depends decisively on the placement of the actuators and sensors. In the present paper a general mathematical method for the determination of an optimal actuator placement is given, which takes advantage of additional mechanical information about the structural behavior, i.e. the sensitivity of the system with respect to the design variables. Following concepts of geometry and topology optimization in the present paper an optimization strategy is presented for the simultaneous determination of the discrete positions of the actuators as well as the continuous parameters of the control law. For the verification of the optimization strategy a complete variant test of the ten-bar-truss problem is analyzed. The results of the optimization strategy match the results of the variant test.
On Experiments of Adaptive Control for Structure Vibration
Authors: Ma Kougen , Peng Fujun , Gu Zhongquan , Chen Xi
Published: February 2021

The paper summarized the experimental studies of adaptive structure vibration control in Nanjing University of Aeronautics and Astronautics (NUAA). Two kinds of experimental setups are constructed, i.e. an adaptive feedback control setup and an adaptive feedforward control setup. The former is used for free vibration control, and the control law is realized by the Intel 80X87 floating point processor. A Single Input and Single Output (SISO) control strategy is presented and extended to Multi-Input and Multi-Output (MIMO) systems. Its adaptabilities to the locations of sensors and actuators are also evaluated. The latter is suitable for forced vibration control, e.g. periodic vibration control and random vibration control. Its theoretical base is adaptive filtering theory. Its data acquisition and control law calculation are finished by the master/slave computers. The master computer — an IBM PC or a compatible PC — is responsible for data acquisition, and the slave computer — the TMS320C30 Digital Signal Processor (DSP) — calculates the control law. The results for both periodic vibration control and random vibration control are shown.
Optimal Tracking Servo-System by Means of Sliding Mode Control
Authors: Uchida Hiroaki , Nonami Kenzo
Published: February 2021

This paper dealt with design scheme of sliding mode optimal tracking control in which the hyperplane is designed to follow the desired trajectory without time-delay. At first, we designed the servo system by applying conventional optimal tracking control, H1 and H∞ optimal tracking control. Secondly, we show the design method of sliding mode optimal tracking control. Thirdly, we carried out the simulation to verify the validity of the design method. In the simulation, three patterns were examined by using H2 norm. The trajectory following and the robust performance in the difference of the design methods were clarified by the simulations. Finally, we applied these control methods to a quadruped locomotion robot.
Sliding Mode Control of Motion and Vibration Without Sensors
Authors: Ohnuki Osamu , Nonami Kenzo
Published: February 2021

In this paper, a method to realize the motion and vibration control without sensors is proposed. Sensorless control is generally realized by estimating the state of the system from the measured current in the actuator by means of an observer. It is possible to estimate all state variables because of dynamic interaction in the controlled object. Then we realize nonlinear robust control system based on the observer. In this paper, first we formulate sensorless control system. As controlled objects we deal with a multi-degree-of-freedom structure as a vibration control problem and a single link robot arm as a motion control problem, respectively, and we carry out numerical simulations. Moreover, we also verify the possibility of realization of sensorless control by experiments.
Control System Design of Frequency-Feedback Magnetic Bearings
Authors: Mizuno Takeshi , Araki Kenji , Namiki Hirotaka
Published: February 2021

The structures and features of control system are discussed for active magnetic bearings (AMBs) with frequency type of displacement sensors. The control systems are classified according to the signal conversions performed there. One of them uses a counter circuit for converting the frequency to a digital format, and the converted signal for digital signal processing. It is also pointed out that self-sensing operation can be realized by using hysteresis amplifiers because their switching rates are sensitive to load impedance. A digital self-sensing AMB, which uses a counter circuit for interface and hysteresis amplifiers for energizing the electromagnets, is manufactured for experimental study. The experimental results show that accurate suspension can be achieved with the proposed digital control system.
Real-Time Recursive Least Squares Identification and Control of Lathe Chatter: Implementation and Performance Issues
Authors: Zhang Shilong , Ousterhout Karl B.
Published: February 2021

In most machining processes, the large amounts of energy that are required to accomplish the machining can lead to the development of self sustained vibrations (chatter). If chatter does develop, it severely limits the production capabilities of the machine tool — typically resulting in longer production cycles and increased tool wear rates. In this paper, a method of controlling lathe chatter is proposed, simulated, and experimentally verified. To eliminate the chatter, a feed-forward digital controller and electro-hydraulic cutting tool actuator is employed. To account for the time varying nature of the tool/workpiece dynamics, a recursive least squares parameter estimation technique is used to estimate the dynamics of the machining process in real-time. These parameter estimates are then used by the digital controller to control the cutting force at the cutting tool/workpiece interface.
Using Phase Space Reconstruction to Track Parameter Drift in a Nonlinear System
Authors: Cusumano J. P. , Chelidze D. , Hecht N. K.
Published: February 2021

A model-based experimental method for tracking parameter drift in nonlinear dynamical systems is described. Local linear tracking models are constructed using data sampled over a fast time scale. These models are used to analyze data from systems with parameters which evolve over a slow time scale according to a “hidden” rate law. The method is applied to a numerical study of a nonlinear electrical circuit with a variable resistance as the drifting parameter. The mean-square tracking model prediction error is shown to follow successfully both ramped and sinusoidal parameter variations, suggesting that, at least in the cases studied, the method provides an invertible mapping between the parameter space and the observable space. Thus it should be possible to extract rate information about hidden drift, a requirement for true prediction.
Damping Towerlike Structures by Dry Friction
Authors: Pfeiffer Friedrich , Stiegelmeyr Andreas
Published: February 2021

Towerlike structures may be excited by wind and by Karman-vortices. Damping can be achieved by a package of plates being moved by pendulum fixed at the upper end of the tower. This paper gives a method to design and to optimize such dampers.
The Double Seesaw Oscillator in a Windfield: Theory and Experiments
Authors: van der Burgh A. H. P. , Haaker T. I. , van Oudheusden B. W.
Published: February 2021

In this paper the dynamics of an oscillator with two degrees-of-freedom of a double seesaw type in a windtunnel is studied. Model equations for this aeroelastic oscillator are derived and an analysis of these equations is given for the non-resonant case. A typical result is a (local codimension two) bifurcation which describes the transfer from the unstable equilibrium state to one of the two normal modes of the oscillator. Some experimental results are presented from which on may conclude that more accurate model equations should be developed.
Van der Pol Mode Stability via Hill’s Equation
Authors: Storti Duane W. , Reinhall Per G. , Sliger David M.
Published: February 2021

The critical variational equation governing the stability of symmetric phase-locked modes for a pair of identical van der Pol oscillators with linear coupling is presented and shown to be equivalent to a Hill’s equation whose periodic coefficient involves the van der Pol limit cycle. We identify the countable set of resonances corresponding to the instability of the in-phase mode and present power series expansions for the Hill determinants which bound these resonances. An additional stability surface is associated with the transformation to Hill’s standard form and corresponds to the time-dependent damping coefficient having zero mean. We present a Padé approximant for this zero mean damping surface which is uniformly effective throughout the parameter range. Power series are also presented for the intersection of the resonance boundaries with the zero mean damping surface and the periodic solutions which occur on the intersection curves. Padé approximants computed from the power series for the intersection curves provide an improved estimate for the growth of the resonances as ε increases.
Nonlinear Regenerative Machine Tool Vibrations
Authors: Stépán Gábor , Kalmar-Nagy Tamas
Published: February 2021

The existence and the nature of the Hopf bifurcation is presented in the delay-differential equation model of the so-called regenerative machine tool vibration. The relevant nonlinearity is considered at the cutting force dependence on the chip thickness. The delayed terms show a special algebraic structure in the nonlinear part of the equation of motion. This results in a surprisingly simple and useful analytical formula in the end of the lengthy calculation based on center manifold reduction in the corresponding infinite dimensional phase space. The result gives a simple way to estimate the domain of attraction of the stable stationary cutting as well as an estimation of that technological parameter domain, where the cutting is globally stable.
Rotor Instability Due to Coupled Effect of Lateral and Torsional Modes and Improper Bearing Design
Authors: Zhang Yatao , Nyqvist Jari
Published: February 2021

This paper deals with a special subsynchronous vibration problem, namely rotor instability caused by partly coupled effect of torsional and bending modes and partly improper bearing design. A theoretical model is presented to investigate such complicated vibration problem. The analysis shows that a single bending or torsional vibration analysis is not enough to predict the stability of a geared rotor system, which includes a turbine, a gear, a generator, several bearings, a squeeze film damper and stators. Either a bearing design, which gives stability in single lateral vibration analysis, cannot guarantee the stability if a torsional vibration mode is involved. This indicates that the bearing design plays much more significant role in a geared rotor system. The theoretical model has been successfully applied to a steam turbine set, which experienced such kind of subsynchronous vibration, by modifying the original bearing design.
The Estimation of Rotor Unbalance
Authors: Lees A. W. , Friswell M. I.
Published: February 2021

A method is presented to determine the state of unbalance of a rotating machine. The only requirement of the procedure is a good numerical model for the rotor and an approximate model for the bearing behaviour. No assumptions are made concerning the operational mode shape of the rotor and the influence of the supporting structure is included in a consistent manner. For simplicity the analysis is presented in a single plane orthogonal to the rotor axis, but no difficulty is foreseen in extending the method to two planes. Examples are given for a two bearing system with both constant and varying bearing coefficients.
Spontaneous Sidebanding at Subharmonic Peaks of Rotordynamic Nonlinear Response
Authors: Ehrich Fredric , Berthillier Marc
Published: February 2021

One of the authors has shown in previous papers (Enrich, 1995; Ehrich, 1996) that, when high speed rotors are operated in the transcritical range with the rotor located eccentrically in its rotor/stator clearance with the rotor in intermittent contact with the stator, a nonlinear response, at speeds both slightly above and slightly below the critical speed, is induced. The response at a particular speed will include significant components at an asynchronous frequency which is approximately equal to the natural frequency of the system. In particular, when the speed (normalized by the natural frequency) S is approximately (J+1)/J, the dominant frequency (normalized by the natural frequency) F is precisely J/(J+1) times S or approximately 1 (where values of the whole number J < 1 give the subcritical set of speeds and values J > 1 give the supercritical set of speeds). The phenomenon has been termed spontaneous sidebanding.

Observations of similar asynchronous responses noted in a Campbell diagram of the rotordynamic response of an actual high speed rotor clustered around a subharmonic response peak at a rotational speed twice the natural frequency suggest that the phenomenon is also possible at any subharmonic pseudo-critical response peak. In this more general case, we would expect that at rotational speeds in the vicinity of the M th subharmonic pseudo-critical normalized speed where S is approximately (MJ+1)/J and the dominant normalized frequency F is precisely J/(MJ+1) times S or approximately 1 [where values of the whole number J < 1 give the sub(pseudo)critical set of speeds and values J > 1 give the super(pseudo)critical set of speeds].

A simple numerical model of the nonlinear system verifies that these asynchronous responses are indeed possible. Operation of the model at a rotational speed approximately double the natural frequency yields data which closely reproduce the asynchronous response seen in the actual machine.
Static and Dynamic Analysis of Multileaf Foil Journal Bearings Considering Misalignment Effects
Authors: Reddy D. Sudheer Kumar , Swarnamani S. , Prabhu B. S.
Published: February 2021

In the present work the analysis of gas lubricated multileaf journal bearing has been presented. The two dimensional compressible Reynolds equation was solved to establish the pressure field in the clearance space of the bearing. Elastic deformation equation is coupled with the Reynolds equation to get the foil deflections and change in film thickness. The effect of bearing misalignment on foil bearing performance characteristics has been presented. The problem has been formulated using incremental finite element method. The effect of bearing misalignment on static performance characteristics like load carrying capacity, frictional torque, minimum film thickness and on dynamic characteristics in terms of stiffness and damping coefficients have been presented.
Vibrations: Noises Produced by Rotors and Eddy Current Probes
Authors: Nguyen The Tam , Bigret Roland
Published: February 2021

• The rotating equipment monitoring, protection and diagnostic system is based mainly on the knowledge of bearing structure vibrations and shaft relative vibrations. The vibration measurements are performed respectively by seismic transducers and proximity probe transducers.

• Measured signals are affected by uncertainties, the most significant sources of which could be mechanical and electrical runout.

• These uncertainties are mentioned by well known standards which recommend or dictate general rules but do not give any advice or procedure in view of reaching the main objective, that is to optimize the efficiency of the monitoring, protection and diagnostic system to improve machine reliability.

• This paper gives two examples showing the effect of inaccuracies, due to noise, on the interpretation of the machine vibrations.

• One validation procedure identifying true noise will be given, using the rotor slow roll principle.

• Noise suppression will be presented requiring sampling and resampling of time domain signals taken on a non synchronous mode. A newly designed software will be used.

• Mechanical runout could induce inacurracies on rotors low speed balancing.

• Noises could create harmful forces on the rotor in a magnetic bearing system.

• Modern manufacturing techniques can minimize mechanical runout in order to avoid noise suppression which could generate additional incaccuracies.
Whirl Speeds and Unbalance Response of Rotor-Bearing Systems Using Finite Dynamic Elements
Authors: Yang Bo-Suk , Hwang Hyung-Sub , Oh Sae-Kyoo
Published: February 2021

The conventional finite element model for rotor-bearing system are formed using shape functions which are based on static displacements, and can lead some errors in analysis of general rotor dynamics problems. A procedure is presented for dynamic modeling of rotor-bearing system which consist of finite dynamic shaft elements, rigid disk, and bearing element. A finite dynamic element model including the effects of rotary inertia, gyroscopic moments, axial force, and axial torque is developed using the frequency dependent shape function. The natural whirl speeds, stability, and unbalance response of rotor system are calculated on several cases and compared with the conventional finite elements.
Design of Liquid Seals for Centrifugal Compressors
Authors: Kirk R. Gordon , Baheti S. K.
Published: February 2021

The use of liquid ring type oil seals in centrifugal compressors was essential for high pressure applications dating back to the early 1960’s. The analysis of high pressure oil seals was first documented in the literature in the mid 1970’s following a series of compressor instability problems that made it clear that a better understanding of how seals influence the overall rotor stability was necessary. To produce compressor designs at higher speeds requires that an adequate method of predicting the oil seal influence on rotor dynamic stability be available for the designer. With the enhanced capability of personal computers and improved finite element models of the oil film thermal and hydrodynamic solutions, it is now possible to more accurately predict the dynamic characteristics of the oil seals. This paper presents a series of predicted results from a currently available advanced state of the art computer analysis for high pressure oil seals. The evaluation of several high pressure compressor seal designs illustrate the current capability for analytical predictions for various seal bore geometries. Conclusions and recommendations for the design of liquid ring seals are presented, which can give the compressor designer guidance for application to future high performance compressor liquid seal designs.
Fly Rod Performance and Line Selection
Authors: Hoffmann Jon A. , Hooper Matthew R.
Published: February 2021

The stiffness, first mode natural frequency and deflection profile can be used to describe the performance of a fly rod. A finite element model has been developed which predicts the performance parameters of fly rod blanks as a function of the geometry and material properties of the blanks. The results of the model compare favorably with experimental results. The model was used to evaluate the effects of changes of design parameters on rod performance. The natural frequency of a rod or a rod blank is a function of the stiffness to mass ratio and the mass distribution of the rod. An empirical equation that predicts the natural frequency of a rod or a rod blank as a function of the mass of the tip section, location of the center of gravity of the tip section and rod stiffness is presented. The line weight rating for fly rods was found to be a function of the stiffness and frequency of the rods. For the first time, an empirical method for the selection of a line weight that matches the performance characteristics of a rod is presented.
A New Microslip Model for Bending Response and Hysteresis Loss of a Multiwire Strand
Authors: Jayakumar C. V. , Sathikh S. , Jebaraj C.
Published: February 2021

A new hypothesis for wire-core slip is devised to predict bending stiffness for an initially tensioned helical wire strand. In this model, the Coulomb friction stick-gross slip hypothesis and the Coulomb friction Hertzian contact microslip hypothesis are combined to form a system of two springs in series. This results in a low bending stiffness as found normally in experiments as well as in practice. The hysteresis loss and the bending stiffness predicted are compared with those available in literature. The agreement is encouraging.
Flexural Vibrations of Thick Cylindrical Panels
Authors: Hamidzadeh H. R.
Published: February 2021

Harmonic vibrations of thick viscoelastic cylindrical panels are investigated. The medium is considered to be a homogeneous, isotropic, linear viscoelastic, thick cylindrical panel of infinite extent. In the development of an analytical solution, the two dimensional elastodynamic theory is employed and the material damping is considered by introducing complex elastic moduli. The panels end conditions do not allow the displacement along the tangential direction; however, the radial displacements are not constrained. The displacements on the surface of the panel are formulated in terms of boundary stresses and their harmonic responses due to the radial and tangential boundary stresses are determined. Displacements and stresses in both the radial and tangential direction for each of the normal modes in the medium are computed. This is achieved by utilizing an algorithm for the Bessel functions of complex argument and fractional order. The algorithm is numerically stable for a wide range of exciting frequencies, circumferential mode numbers, and loss factors.
Nonlinear Vibrations in an Elastic Structure Subjected to Vertical Excitation and Coupled With Liquid Sloshing in a Rectangular Tank
Authors: Ikeda Takashi
Published: February 2021

The nonlinear coupled vibrations of an elastic structure and liquid sloshing in a rectangular tank, partially filled with liquid, are investigated. The structure containing the tank is vertically subjected to a sinusoidal excitation. In the theoretical analysis, the resonance curves for the responses of the structure and liquid surface are presented by the harmonic balance method, when the natural frequency of the structure is equal to twice the natural frequency of one of the sloshing modes. From the theoretical analysis, the following predictions have been obtained: (a) Due to the nonlinearity of the fluid force, harmonic oscillations appear in the structure, while subharmonic oscillations occur on the liquid surface, (b) the shapes of the resonance curves markedly change depending on the liquid depth, and (c) when the detuning condition is slightly deviated, almost periodic oscillations and chaotic oscillations appear at certain intervals of the excitation frequency. These were qualitatively in good agreement with the experimental results.
Three-to-One Internal Resonances in Parametrically Excited Hinged-Clamped Beams
Authors: Chin Char-Ming , Nayfeh Ali H.
Published: February 2021

The nonlinear planar response of a hinged-clamped beam to a parametric excitation of either its first mode or its second mode is investigated. The analysis accounts for mid-plane stretching, a static axial load, a restraining spring at one end, and modal damping. For a range of axial loads, the second natural frequency is approximately three times the first natural frequency and hence the first and second modes may interact via a three-to-one internal resonance. The method of multiple scales is used to attack directly the governing nonlinear integral-partial-differential equation and associated boundary conditions and derive two sets of four first-order nonlinear ordinary-differential equations describing the modulation of the amplitudes and phases of the first two modes in the case of principal parametric resonance of either the first or the second mode. Periodic motions and periodically and chaotically modulated motions of the beam are determined by investigating the equilibrium and dynamic solutions of the modulation equations. For the case of parametric resonance of the first mode, trivial and two-mode solutions are possible, whereas for the case of parametric resonance of the second mode, trivial, single-, and two-mode solutions are possible. The two-mode equilibrium solutions of the modulation equations may undergo either a supercritical or a subcritical Hopf bifurcation, depending on the magnitude of the axial load. In the region of dynamic solutions, some phenomena are documented, including period-doubling bifurcations and blue-sky catastrophes.
On the Effects of Imperfections and Mistuning on the Performance of Subharmonic Vibration Absorbers
Authors: Chao Chang-Po , Shaw Steven W.
Published: February 2021

A pair of centrifugal pendulum vibration absorbers (CPVA’s) riding on half-order epicycloidal paths have recently been found to be very effective at reducing torsional vibration levels in a rotating system that is subjected to a harmonic external torque. Previous analyses of this system have assumed perfectly manufactured and exactly tuned paths for the absorber masses. The primary goal of this study is to explore the effects that manufacturing and other imperfections and intentional mistunings have on the performance of this absorber system. To this aim, the equations of motion are first derived for a simplified model. The basic system has two and a half degrees of freedom with a one-to-one internal resonance and two-to-one resonant external excitation. Utilizing the method of averaging, the steady-state solutions are obtained and used to evaluate the absorber performance via two performance indices: the rotor acceleration and the applicable range of the disturbing torque. Finally, some guidelines are provided for designers in terms of how one should choose and/or control intensional mistuning and imperfections of the absorber paths.
Phase Space Transport in a Class of Multi-Degree of-Freedom Systems
Authors: Chen Shyh-Leh , Shaw Steven W.
Published: February 2021

In this paper we describe some recent advances in the basic theory and applications of phase space transport in nonlinear dynamic systems. These methods offer both qualitative and quantitative information about the behavior of solutions near homoclinic and heteroclinic motions in nonlinear dynamical systems. Applications of these ideas are found in fluid mixing and the escape of solutions from potential energy wells under the action of disturbances, for example, in models of ship capsize. In this work the theory is extended to a certain class of higher-order systems in which several time scales are involved. In addition, a new analytical estimate is derived and used for the rate of transport in the case of two-dimensional Poincare maps. Extensive simulation results from a specific ship dynamics model are used to demonstrate and verify these results.
Two Groups of Chaotic Vibrations in a Single-Degree-of-Freedom Maglev System
Authors: Xu Zhixiang , Tamura Hideyuki
Published: February 2021

In this paper, a single-degree-of-freedom magnetic levitation dynamic system, whose spring is composed of a magnetic repulsive force, is numerically analyzed. The numerical results indicate that a body levitated by magnetic force shows many kinds of vibrations upon adjusting the system parameters (viz., damping, excitation amplitude and excitation frequency) when the system is excited by the harmonically moving base. For a suitable combination of parameters, an aperiodic vibration occurs after a sequence of period-doubling bifurcations. Typical aperiodic vibrations that occurred after period-doubling bifurcations from several initial states are identified as chaotic vibration and classified into two groups by examining their power spectra, Poincare maps, fractal dimension analyses, etc.
Experimental Identification Technique of Nonlinear Beams in Time Domain
Authors: Yasuda Kimihio , Kamiya Keisuke
Published: February 2021

In previous papers the authors proposed a new experimental identification technique applicable to elastic structures. The proposed technique is based on the principle of harmonic balance, and can be classified as the frequency domain technique. The technique requires the excitation force to be periodic. This is in some cases a restriction. So another technique free from this restriction is of use. In this paper, as a first step for developing such techniques, a technique applicable to beams is proposed. The proposed technique can be classified as the time domain one. Two variations of the technique are proposed, depending on what methods are used for estimating the parameters of the governing equations. The first method is based on the usual least square method. The second is based on solving a minimization problem with constraints. The latter usually yields better results. But in this method, an iteration procedure is used, which requires initial values for the parameters. To determine the initial values, the first method can be used. So both methods are useful. Finally the applicability of the proposed technique is confirmed by numerical simulation and experiments.