bluuebunny/crossref_metadata_2025 huggingface dataset:
Balancing With Phase Only (Single-Plane and Multiplane)
Authors: Foiles W. C. , Bently D. E.
Published: December 2011

A balancing technique is developed which requires nothing more sophisticated in vibration instrumentation than a pencil or a crayon. This method of balancing is a calibration weight technique which uses only the phase information at 1X (rotative speed); no amplitude information is required. The basic technique is developed for both single-plane and multiplane balancing. The technique is applicable to both in situ and shop balancing. This paper presents both novel and historical balancing theory and practice. It is novel, to the knowledge of the authors, on balancing with phase only. The historical portions on the abundantly published balancing with amplitude only and “trial weight” calibration weight balancing are included for comparison.
Rotor Stability of High Pressure Multistage Centrifugal Compressors
Authors: Wyssmann H. R.
Published: December 2011

A major factor influencing rotor stability of multistage high pressure centrifugal turbocompressors are the forces caused by the fluid-rotor interaction in the interstage and balance piston gas seals. An example of a fully 3-D labyrinth flow solution shows that using time averaged Navier-Stokes solutions are still excessive in computer time and hence cannot be used for practical applications. The paper gives a theory based on a two-volume bulk flow model for the prediction of the rotor-dynamic coefficients used for rotor stability calculation by complex eigenvalue analysis. Comparisons of predicted coefficients with measurements carried out on a high pressure compressor and on labyrinth seal test stands are given. The theoretically predicted phenomenon that labyrinth damping is retained even at zero inlet swirl of the leakage flow is confirmed. An example of a stability analysis of a high pressure natural gas compressor is given, where the stability margin increases with fluid pressure, i.e., density, provided seal swirl is controlled.
Structural Excitation by a Turbulent Boundary Layer: An Overview
Authors: Leehey P.
Published: December 2011

Thirty years of theoretical and experimental research have yet to resolve a number of questions regarding the vibratory response of, and acoustic radiation from, a structure excited by a turbulent boundary layer (TBL). The most important questions are: (a) Can the TBL be characterized as a Thevenin source—particularly when vibratory power flow into the structure is maximized at hydrodynamic coincidence? Alternatively, at what level does structural vibration fundamentally change the character of the TBL? (b) Is the low wave number portion of the wall pressure spectrum of dominant importance in structural excitation away from hydrodynamic coincidence? Or do structural discontinuities cause the convective ridge of wall pressure to be of greater practical interest? (c) Can one quantify the radiation from a turbulent boundary layer about a rigid finite body? Is it dipole or quadrupole? What is the role of fluctuating wall shear stress? Current research on dense fluid loading and on modeling the behavior of the TBL is yielding new, and sometimes surprising, answers to some of these questions. Free resonant structural vibration in the dense fluid limit and the use of a bounded, non-causal, Green function representing the TBL are two of the surprises discussed.
The Noise-Producing Characteristics of Highly Loaded, Valveless, Pulse Combustors
Authors: Kentfield J. A. C.
Published: December 2011

An inherent problem of pulsating combustors is noise generation and the difficulty of predicting noise levels. Analytical data are presented which illustrate the transient velocity profiles prevailing at the open ends of the inlets and tailpipes of valveless pulse combustors. A comparison is made of measured sound pressure level spectra at these locations with corresponding predicted transient velocity profiles. It is shown that there is a correlation of the main characteristics of the noise spectra and velocity profiles. Consideration is also given to the problems of muffling valveless pulse combustors and the potential, from the noise suppression viewpoint, of twin-coupled units and relatively high frequency pulse combustors featuring multiple inlet passages. An indication is also given of how it may be possible to operate clusters, or arrays, of pulse combustors firing sequentially.
Active Vibration Control of a Distributed System With Moving Support
Authors: Bennighof J. K. , Meirovitch L.
Published: December 2011

This paper is concerned with the problem of controlling the vibration of a distributed system with a support undergoing significant persistent motion. Because of practical considerations, the control is carried out by discrete actuators and sensors. The system is discretized by a new Rayleigh-Ritz approach in which the generalized coordinates represent actual displacements at a given number of points of the system. The control is separated into two parts, one designed to mitigate the effect of the moving support on the absolute motion of the system and the other designed to minimize the remaining absolute motion. A numerical example illustrating the approach is presented.
Theoretical Study of Fluid Forces on a Centrifugal Impeller Rotating and Whirling in a Volute
Authors: Tsujimoto Y. , Acosta A. J. , Brennen C. E.
Published: December 2011

Fluid forces on a rotating and whirling centrifugal impeller in a volute are analyzed with the assumption of a two-dimensional rotational, inviscid flow. For simplicity, the flow is assumed to be perfectly guided by the impeller vanes. The theory predicts the tangential and the radial force on the whirling impeller as functions of impeller geometry, volute spacing, and whirl ratio. A good qualitative agreement with experiment is found.
Theory Versus Experiment for the Rotordynamic Coefficients of Labyrinth Gas Seals: Part I—A Two Control Volume Model
Authors: Scharrer Joseph K.
Published: December 2011

The basic equations are derived for a two-control-volume model for compressible flow in a labyrinth seal. The recirculation velocity in the cavity is incorporated into the model for the first time. The flow is assumed to be completely turbulent and isoenergetic. The wall friction factors are determined using the Blasius formula. Jet flow theory is used for the calculation of the recirculation velocity in the cavity. Linearized zeroth and first-order perturbation equations are developed for small motion about a centered position by an expansion in the eccentricity ratio. The zeroth-order pressure distribution is found by satisfying the leakage equation while the circumferential velocity distribution is determined by satisfying the momentum equations. The first-order equations are solved by a separation of variable solution. Integration of the resultant pressure distribution along and around the seal defines the reaction force developed by the seal and the corresponding dynamic coefficients.
Experimental Study on the Static and Dynamic Characteristics of Screw Grooved Seals
Authors: Kanki H. , Kawakami T.
Published: December 2011

Screw grooved annular seals are used in many heavy duty pumps such as boiler feed pumps. These annular seals have a significant effect on rotordynamic characteristics of the pumps. Studies on the dynamic characteristics of plain and circumferentially grooved annular seals have been published by many researchers. However, published works on screw grooved seals are few, and pump designers have not fully recognized the basic characteristics of screw grooved seals. Extensive experimental studies have been conducted for determining the basic characteristics of screw grooved seals. The leakage characteristics, load capacity, and dynamic characteristics for rotordynamic analysis were determined by using a specially designed test facility and test method. The test results were compared to the results of plain seals [3] and the basic differences were extracted for effective application of screw grooved seals.
Advanced Techniques for Measuring Structural Mobilities
Authors: Fabunmi J. A. , Tasker F. A.
Published: December 2011

A unified formulation of the equations for estimating structural frequency response functions is presented. The more popular approaches are shown to be special cases of a general equation which involves a weighting function, the proper selection of which can yield substantial improvements in the accuracy and efficiency of the measurement process. The theoretical basis for selecting the weighting function is also presented, along with experimental results which confirm the expected improvement in accuracy of the advanced formulations over existing methods.
Stability of Cracked Rotors in the Coupled Vibration Mode
Authors: Papadopoulos C. A. , Dimarogonas A. D.
Published: December 2011

A transverse surface crack is known to add to a shaft a local flexibility due to the stress-strain singularity in the vicinity of the crack tip. This flexibility can be represented, in the general case by way of a 6 × 6 compliance matrix describing the local flexibility in a short shaft element which includes the crack. This matrix has off-diagonal terms which cause coupling along the directions which are indicated by the off-diagonal terms. In addition, when the shaft rotates the crack opens and closes. Then the differential equations of motion have periodically varying stiffness coefficients and the solution can be expressed as a sum of harmonic functions of time. A method for the determination of the intervals of instability of the first and of second kind is developed. The results have been presented in stability charts in the frequency vs. depth of the crack domain. The coupling effect due to the crack leads to very interesting results such as new frequencies and vibration modes.
A Unified Theory of Recursive, Frequency Domain Filters With Application to System Identification in Structural Dynamics
Authors: Mottershead J. E.
Published: December 2011

In this paper a unified theory is presented for system identification in structural dynamics using recursive frequency-domain filters. Output error, equation error, and instrumental variable (I. V.) filters are developed as special cases. Parameter estimates are extracted from noisy simulated data from a multi-degree-of-freedom system. The equation error filter is strongly convergent but is prone to asymptotic bias error in the presence of measurement noise. An I. V. filter is developed in order to overcome the bias problem while maintaining the desirable convergence properties of the equation error approach.
Stress Analysis for Design of Electromagnetic Launchers
Authors: Fahrenthold E. P. , Peterson D. R. , Price J. H. , Wu A. Y.
Published: December 2011

The recent development of very high current pulsed power supplies provides an opportunity for order of magnitude improvements in electromagnetic launcher performance. Consideration of design objectives and constraints suggests that a ceramic-steel construction offers significant advantages over conventional composite-steel railguns. Structural analysis of such a system focuses upon material specific stress concentrations produced by dynamic and asymmetric electromagnetic loads.
Localization Phenomena in Mistuned Assemblies with Cyclic Symmetry Part I: Free Vibrations
Authors: Wei S.-T. , Pierre C.
Published: December 2011

An investigation of the effects of small structural irregularities on the dynamics of nearly periodic structures with cyclic symmetry is presented. The system studied may be regarded as a simple model of a continuously shrouded blade assembly accounting for one structural mode per blade. A key aspect of the approach is the use of perturbation methods that lead to a physical insight into the effects of mistuning. The study shows that the sensitivity to mistuning depends primarily upon the ratio of mistuning strength to coupling strength. For a small mistuning to coupling ratio, the mistuned system behaves like a perturbation of the corresponding tuned system, in which case mistuning has a relatively small effect on both the free and forced responses. On the other hand, for a large mistuning to coupling ratio (i.e., weak coupling), the mistuned system behaves like a perturbation of the corresponding decoupled mistuned system, in which case small mistuning dramatically changes the dynamics of the system. This paper, Part I, investigates the effects of small mistuning on the free response of the system. Specifically, it is shown that strong mode localization and eigenvalue loci veering phenomena occur in the weakly coupled system when mistuning is introduced. The effects of mistuning on the forced response are studied in the companion paper, Part II (Wei and Pierre, 1987).
Localization Phenomena in Mistuned Assemblies with Cyclic Symmetry Part II: Forced Vibrations
Authors: Wei S.-T. , Pierre C.
Published: December 2011

The effects of disorder on the forced response of nearly periodic structures with cyclic symmetry are investigated. The force model adopted here is relevant to blade assemblies. Perturbation methods for the forced response are developed to gain a physical insight into the effects of mistuning. The study shows that the internal coupling between component systems is the key parameter governing the sensitivity to mistuning and that localized forced vibrations do occur in the disordered assembly for weak internal coupling. However, although both localized free and forced vibrations occur for finite or large values of the mistuning to coupling ratio, the deflection patterns for these two types of localized vibrations are different. Also, for the forced response, the degree of localization does not necessarily increase as this ratio increases—a fundamental difference from localized free modes. An important conclusion is that the common periodicity assumption for cyclic structures may lead to qualitative errors for the forced response of weakly coupled systems when small mistuning is present.
On the Vibration of a Point-Supported Linear Distributed System
Authors: Bergman L. A. , McFarland D. Michael
Published: December 2011

The vibration of a constrained dynamical system, consisting of an Euler-Bernoulli beam with homogeneous boundary conditions, supported in its interior by arbitrarily located pin supports and translational and torsional linear springs, is studied. A generalized differential equation is obtained by the method of separation of variables and is solved in terms of the Green’s function and its derivatives of the unconstrained beam. System natural frequencies and modes are obtained, and the orthogonality relation for the natural modes is derived. A general solution for the forced response is given. Finally, two pertinent problems from the literature are examined, and results obtained are compared with those of a small, dedicated finite element formulation to assess the relative accuracy and efficiency of each.
A Method for the Improvement of Impact Printer Performance
Authors: Tung P. C. , Shaw S. W.
Published: December 2011

The stored energy type of impact printer is a commonly used computer output device. It can be operated at quite high frequencies due to the fact that it has a large initial activation force. However, limitations on printer speed exist; these are thought to be due primarily to uncertainties in the position and velocity of the armature during settle-out between excitation pulses. This results in variations in flight times and in print forces. In this paper we consider an open-loop control strategy which modifies the driving pulse in such a manner that it aids the restoring force of the print hammer and armature during the settle-out phase of the motion. Simulation studies of our simplified piecewise linear model (Tung and Shaw, 1988) and Hendriks’ (1983) model indicate that the operating speed of impact printers can be significantly increased using this method. Printer performance criteria are also established in the paper. These are based on the requirement that acceptable print quality be achieved for arbitrary combinations of driving pulses which have some minimum time lapse between pulses. We use these criteria to demonstrate the limitations on printer speed and to indicate how the control method is able to increase printer speed. Such criteria are quite general and may be used for more complicated models and controllers.
A Theoretical and Experimental Study of Vibrations of Thick Circular Cylindrical Shells and Rings
Authors: Singal R. K. , Williams K.
Published: December 2011

The free vibrations of thick circular cylindrical shells and rings are discussed in this paper. The well-known energy method, which is based on the three-dimensional theory of elasticity, is used in the derivation of the frequency equation of the shell. The frequency equation yields resonant frequencies for all the circumferential modes of vibration, including the breathing and beam-type modes. Experimental investigations were carried out on several models in order to assess the validity of the analysis. This paper first describes briefly the method of analysis. In the end, the calculated frequencies are compared with the experimental values. A very close agreement between the theoretical and experimental values of the resonant frequencies for all the models was obtained and this validates the method of analysis.
Instability and Sound Emission From a Flow Over a Curved Surface
Authors: Maestrello L. , Parikh P. , Bayliss A.
Published: December 2011

The growth and decay of a wavepacket convecting in a boundary layer over a concave-convex surface is studied numerically using direct computations of the Navier-Stokes equations. The resulting sound radiation is computed using the linearized Euler equations with the pressure from the Navier-Stokes solution as a time-dependent boundary condition. It is shown that on the concave portion the amplitude of the wavepacket increases and its bandwidth broadens while on the convex portion some of the components in the packet are stabilized. The pressure field decays exponentially away from the surface and then algebraically exhibiting a decay characteristic of acoustic waves in two dimensions. The far field acoustic pressure exhibits a peak at a frequency corresponding to the inflow instability frequency.
Synthesis of Initial Form for Structural Shape Optimization
Authors: Shah J. J.
Published: December 2011

Techniques that use qualitative reasoning for structural configuration synthesis and form design are critically examined. Both algorithmic and heuristic methods are considered. Because of the limitations of these methods a hybrid approach is presented. A shape algebra is developed for structural synthesis which leads to a systematic method for generating structural arrangements. This algebra raises the possibility of transforming structural synthesis into a science instead of the art that it currently is. The method is well-suited to automation exploiting a computer’s capability to manipulate symbols. The method searches for good candidate structures that can be used as the initial form for numerical programs for shape and size optimization.
Faster Calculations of Sound Radiation from Vibrating Cylinders Using Variational Formulations
Authors: Wu Xiao-Feng
Published: December 2011

Prediction of the sound radiation from a vibrating body often requires a computation of the acoustic pressure on the body’s surface, given the normal surface vibration. This paper explores what computational advantages a variational formulation may have over other formulations, such as those which solve the Helmholtz integral equation directly. The variational formulation is developed here for bodies of revolution in axisymmetric vibration and specialized to finite cylinders. The general implementation technique of the variational formulation is the Rayleigh-Ritz method which yields a set of simultaneous linear equations for the unknown coefficients in the expansion of the surface pressure in terms of a finite set of basis functions. A case is made to the effect that computations based on the variational formulation can often yield results of desirable accuracy with substantially less computational time. A prerequisite for such an achievement is that one makes a good selection of the basis functions. Such a selection may be aided by physical insight and common sense.
Instability Due to Fluid Leakage of a Rotor System With Anisotropic Support
Authors: Wang J. H. , Tsai M. T.
Published: December 2011

The instability caused by the fluid leakage leads to a limited performance of turbomachines. This instability may be improved by using flexible bearing supports with anisotropic stiffness. With a simplified model this effect is investigated including the influence of many parameters. The results show that the optimum range of anisotropy is strongly dependent on the parameters of rotor-bearing systems. In this paper an explanation from an energy point of view is presented to clarify the different stability behaviors with anisotropic bearing supports. Beside the simplified model, the stability of the complex rotor-bearing system with anisotropic bearing supports is investigated by the finite element model. An example of a typical 900 MW turbogenerator system is presented.
Analysis of a High-Speed Flexible Four-Bar Linkage: Part I—Formulation and Solution
Authors: Liou F. W. , Erdman A. G.
Published: December 2011

Derived from the principle of virtual displacement, a general finite element analysis computer code (FEMAP) of the flexible four-bar linkage is developed on the Apollo computer. In this part, virtual displacement method is presented as a basic theory for the general formulation of the equations of motion. Based on these results, a general finite element computer code of planar four-bar linkage is developed. All the links of the mechanism are considered to be flexible. The nonlinear terms such as coupling between the rigid body and elastic deformation terms and the effect of the axial forces are included. The Newmark direct integration method is used as solution scheme.
On the Hybrid Vibration Isolation Method
Authors: Tanaka N. , Kikushima Y.
Published: December 2011

For the purpose of isolating the vibration transmission from machines to soil and vice versa, this paper presents a new active vibration isolation method, that is, a hybrid vibration isolation method capable of isolating the vibration in the whole frequency range. The hybrid isolation method contains the following three characteristics: (1) a low-pass filter of a conventional elastic support method; (2) a high-pass filter of an active vibration isolation method; (3) suppression of a resonant peak due to an elastic support by a servo damper method; First, this paper presents the principle of the hybrid vibration isolation method and shows a fundamental structure of the system. Then by making the active isolator work as a damper, the suppression of a resonant peak due to an elastic support is achieved. Next, taking into consideration both the control effect and the stability of the system, the design procedure of the hybrid vibration isolation system is shown. Moreover, a control chart to estimate the control effect for suppressing the force transmissibility is presented. Finally, an experiment is carried out, demonstrating that the hybrid isolation method is capable of suppressing the exciting force in almost all the frequency range.
Automatic Generation of Component Modes for Rotordynamic Substructures
Authors: Crandall S. H. , Yeh N. A.
Published: December 2011

Dynamic analysis models are customarily employed in turbomachinery design to predict critical whirling speeds and estimate dynamic response due to loads imposed by unbalance, misalignment, maneuvers, etc., Traditionally these models have been assembled from beam elements and been analyzed by transfer matrix methods. Recently there has been an upsurge of interest in the development of improved dynamic models making use of finite element analysis and/or component mode synthesis. We are currently developing a procedure for modelling and analyzing multi-rotor systems [1] which employs component mode synthesis applied to rotor and stator substructures. A novel feature of our procedure is a program for the automatic generation of the component modes for substructures modelled as Timoshenko beam elements connected to other substructures by bearings, couplings, and localized structural joints. The component modes for such substructures consist of constraint modes and internal modes. The former are static deflection shapes resulting from removing the constraints one at a time and imposing unit deflections at the constraint locations. The latter have traditionally been taken to be a subset of the natural modes of free vibration of the substructure with all constraints imposed. It has however been pointed out [2] that any independent set of geometrically admissible modes may be used. We take advantage of this and employ static deflections under systematically selected loading patterns as internal modes. All component modes are thus obtained as static deflections of a simplified beam model which has the same span and same constraints as the actual substructure but which has piecewise uniform dynamic properties. With the loading patterns we employ, all modes are represented by fourth order polynomials with piecewise constant coefficients. We have developed an algorithm for the automatic calculation of these coefficients based on exact integration of the Timoshenko beam equation using singularity functions. The procedure is illustrated by applying it to a simplified system with a single rotor structure and a single stator structure. The accuracy of the procedure is examined by comparing its results with an exact analytical solution and with a component mode synthesis using true eigenfunctions as internal modes.
The Development of Natural Modes of Free Vibration for Linear Discrete Systems from the Synchronous Motion Assumption
Authors: Felszeghy S. F.
Published: December 2011

By using the method of separation of variables, or more precisely, the method of searching for synchronous motions, conditions are derived under which a linear discrete viscously damped system exhibits free motions of the form of a product of an amplitude vector and a scalar function of time. These motions are the natural modes of the system. In particular, those conditions are investigated under which some but not all of the modal vectors, or mode shapes, of the damped system coincide with the undamped “classical” normal modes.
Improved Rotor Response of the Uprated High Pressure Oxygen Turbopump for the Space Shuttle Main Engine
Authors: Beatty R. F. , Hine M. J.
Published: December 2011

During development testing of the High Pressure Oxygen Turbopump (HPOTP) of the Space Shuttle Main Engine (SSME) to produce 109 percent of the rated thrust level, subsynchronous rotor whirl was encountered. This whirl was attributed to bearing wear reducing the radial bearing stiffness that caused the rotor second bending mode critical speed to enter the operating speed range. To eliminate this whirl, the pump end bearing loads were reduced to increase bearing life and damping added between the rotor and housing. This was achieved by converting impeller annular seals into “damping” seals that react part of the applied load and also damp the rotor response. Furthermore, the second rotor critical speed was increased by the added stiffness of the seal conversion and stiffening the rotor shaft. The bearing load reduction was verified by strain gaging the pump end bearing support into a load cell. These strain gages also were used to directly measure bearing ball wear during engine tests.
Periodic Solutions in Rotor Dynamic Systems With Nonlinear Supports: A General Approach
Authors: Nataraj C. , Nelson H. D.
Published: December 2011

A new quantitative method of estimating steady state periodic behavior in nonlinear systems, based on the trigonometric collocation method, is outlined. A procedure is developed to analyze large rotor dynamic systems with nonlinear supports by the use of the above method in conjunction with Component Mode Synthesis. The algorithm discussed is seen to reduce the original problem to solving nonlinear algebraic equations in terms of only the coordinates associated with the nonlinear supports and is a big improvement over commonly used integration methods. The feasibility and advantages of the procedure so developed are illustrated with the help of an example of a typical rotor dynamic system with an uncentered squeeze film damper. Future work on the investigation of the stability of the periodic response so obtained is outlined.
Far Field Acoustic Radiation From an Expansion Chamber
Authors: Eversman W. , Park J. M.
Published: December 2011

A method is presented for the assessment of the effect of several system parameters on the radiated and transmitted acoustic fields of an expansion chamber with a flexible side wall. The approach is based on a previously developed model of a three dimensional cavity in an otherwise one dimensional acoustic transmission line. The acoustic field within the cavity is represented in terms of the cavity acoustic normal modes. The flexible side wall is represented in terms of its natural modes of free vibration. Computations are made and results presented to assess the effect on the acoustic output of parameters such as side wall thickness, side wall stiffness, inlet pipe length, and inlet and outlet pipe placement. It is concluded that radiation from the side wall can occur at significant levels at certain plate resonances and at cavity internal resonances. Reduction of radiation is achieved by thickening of the side wall and by adding appropriate stiffeners. Success in reduction of radiated noise requires an understanding of the entire coupled system.
The Dynamic Response of Rotors to Rubs During Startup
Authors: Smalley A. J.
Published: December 2011

This paper presents an initial study of rub-induced thermal bow vibration during acceleration or deceleration of a steam turbine rotor. Previous studies of the subject have been limited to constant speed operation, although the problem is often encountered during attempts to bring a rotor up to speed; observations show that acceleration rate is a factor which controls the magnitude of vibrations. Using a relatively simple numerical analysis, the influence of speed transients on rub-induced synchronous vibration is explored. The analysis reveals some significant trends and can help quantify dynamic response to speed changes under the various conditions which cause stator to rotor rubs. The analysis accounts for transient heat conduction within the rotor in the radial and circumferential directions. The result is an instantaneous temperature distribution from which bow of the rotor between the bearings is predicted. The vibration response to mass eccentricity is determined from the amplification factor and proximity of rotor speed to the critical speed. It is assumed that the bow shape and mode shape of the critical speed are similar. The results demonstrate the influence of rub severity, proximity to critical speed, unbalance level, acceleration rate and acceleration direction. In general, the results show that the effects of rubs are aggravated by slow acceleration up or down through a critical or by extended operation just below a critical.
Nonlinear Transient Response of a High Speed Driven Valve System and Stresses in Valve Springs for Internal Combustion Engines
Authors: Nagaya K.
Published: December 2011

This paper presents a method for solving the dynamic response problems of a driven valve system and the stress problem of valve springs for internal combustion engines. In this system there is hysteresis behavior in the spring constants during the rotation of the cam shaft. To treat this nonlinearity, the rigidity of each section is assumed to be one of a partly linear spring. For the valve trains, the cam profile is complex in general. To treat a general cam profile, this paper applies a combination method of the Fourier expansion, the Laplace transform and the analytical connection methods, and gives a response of valve trains. This paper also presents a theoretical result for the stresses in the valve spring due to the motion of the valve train based on the three dimensional curved beam theory.
Effect of Design Variables, Temperature Gradients, and Speed on Life and Reliability of a Rotating Disk
Authors: Zaretsky E. V. , Smith T. E. , August R.
Published: December 2011

A generalized methodology to predict the fatigue life and reliability of rotating disk such as used for aircraft engine turbines and compressors is advanced. The approach incorporates the computed life of elemental stress volumes to predict system life and reliability. Disk speed and thermal gradients as well as design variables such as disk diameter and thickness and bolt hole size, number, and location are considered.
The Effect of Surface Roughness on Fitting Strength of Shrink Fit Between Ceramic and Metal Elements
Authors: Kato K. , Kayaba T. , Nitta I. , Shimoda S.
Published: December 2011

Shrink fit is a basic and simple technique for joining metal elements. But it is not suitable for ceramic and metal elements, especially at elevated temperatures. For the accurate estimation of fitting strength between ceramic and metal elements, an understanding of the deformation of surface micro-asperities during contact is introduced in this paper. The elastic deformation of a shaft and a cylinder and the elastic-plastic deformation of the asperities were taken into consideration for the theoretical fitting strength. Theoretical estimations of fitting strength between a ceramic shaft and a metal cylinder showed good agreement wtih experimental values in various fitting interferences and at temperatures of 20°C–180°C.
Vibration Control for the Rotor-Bearing System and Calculation of the Optimum Control Forces
Authors: Yu Lie , Xie You-Bai , Zhu Jun , Qiu Damou
Published: December 2011

The objective function applied to express the optimum response of the rotor-bearing system is presented based on the complex mode analysis. Two kinds of problems about the calculation of control forces are solved: in the nonconstraint condition the optimization of control forces is treated as the evaluation of a set of linear equations; and the Powell and complex methods are used to calculate the constrained control forces. Numerical examples are also given.
How to Start Transient Response Calculations for Rotating Structures Without Causing Centrifugal Force Shocks
Authors: Niering E.
Published: December 2011

In computer programs for transient response calculations often only homogeneous and not more complicated, inhomogeneous initial conditions can be considered. The initial conditions assumed here are the stresses or displacements generated by the centrifugal force field in rotating structures. Nevertheless, calculations can be started with homogeneous initial conditions. The system has then to be transferred to operating conditions in a precalculation by a suitable rotational speed characteristic. Only then can the actual simulation begin. The rotational speed characteristic must have the additional capability of establishing the inhomogeneous initial conditions in minimum time. Precise imitation of the long technical run-up procedure is undesirable because of high computer cost and numerical inaccuracy. Modal equations are taken as the basis for formulation of an optimization problem whose solution determines the optimum speed characteristic. For the technically important case where a single prevailing natural vibration has to be controlled, it is possible to state the solution explicitly. With several natural vibrations, the control must be determined numerically. The procedure is used in calculating the effects of bird strike on rotating turbine blades.
The Dynamic Response to Impact Loading of a Fluid-Supported Rectangular Plate
Authors: Sondak E. , Perl M. , Pnueli D.
Published: December 2011

This work considers the elastodynamic response of a rectangular plate supported by a fluid on one side, and subjected to impact loading on the other side. The presence of the fluid in our problem has the effect, first, of lowering the natural frequency of the plate due to the increased inertia, and secondly, of damping its vibrations owing to the energy carried off in the form of sound waves. The deflection of the plate is approximated by a double infinite series in the spatial coordinates. Each term of the series consists of a product of two modes of deflection of beams, having the same boundary conditions as the plate, multiplied by a time dependent function. The problem is solved for various combinations of fluids, impact loadings, geometrical configurations, and boundary conditions. Excellent agreement is obtained between the present results for eigen frequencies and the static deflections in vacuo and published results. Furthermore, good agreement is obtained for the added-mass and the damping magnitude. As for the dynamic case, since no complete solutions are available, the present results are at least shown to be self-consistent.
The Elastodynamic Response of a Class of Intelligent Machinery, Part I: Theory
Authors: Soong K. , Sunappan D. , Thompson B. S.
Published: December 2011

A methodology is proposed, herein, for reducing the elastodynamic response of high-speed machine systems by introducing a retrofitment scheme which permits these systems to be subjected to an additional dynamical perturbational input which is computer-controlled. This paper is the first of two companion papers which describe a comprehensive analytical and experimental investigation on a breadboard model of the concept, in which the objective is to reduce the vibrational response at the midspan of a flexible rocker link of a four-bar mechanism. A variational formulation is employed to develop the equations of motion governing the response of the flexible member which is subjected to combined parametric and forcing functions. In Part II of these companion papers, the governing equations are solved numerically and the viability of the approach is validated by comparing the analytical predictions with response data from a complementary experimental program.
Rotating Disk Shape: Is the Equation Nonlinear?
Authors: Jettappa R. R.
Published: December 2011

The determination of the shape of a rotating disk under centrifugal loading is considered. It is shown that the governing differential equation for the shape of a rotating thin disk is reducible to a linear equation of second order with variable coefficients. However, the form of this equation is such that it can be treated as an equation of first order thereby facilitating the integration by quadratures. All this is possible without any additional mathematical assumptions so that the results are exact within the limitations of the thin disk theory.
Asymptotic Modal Analysis of Structure Borne Noise in Cross Beams
Authors: Chi R. M.
Published: December 2011

The dynamic response (structure borne noise) of two cross beams intersecting perpendicularly to each other is studied for a point load applied vertically at an arbitrary location on one beam. The modal analysis technique is used to analyze the bending and torsional responses of the system of coupled beams. The modal equations of motion are derived from Lagrange’s equations with the coupling constraint at the beam intersection point included via Lagrange multipliers. For the limiting case of a large number of participating modes, an asymptotic modal analysis is performed resulting in simple estimates of the upper and lower bounds of the beam responses. These bound estimates are compared with the corresponding SEA results.
Active Reduction of Noise by Additional Noise Source and Its Limit
Authors: Kido Ken’iti , Kanai Hiroshi , Abe Masato
Published: December 2011

This paper describes further investigations of an active noise control system in which an additional sound source is set close to the primary (noise) source. Successful application of this method to duct noise control has already been reported (Kido, 1987). The synthesized sound radiated by the additional source is identical to that of the primary source, except in polarity. The additional and primary sources form a dipole sound source with reduced effective radiation power. In theory, the distance between these two sound sources should be much less than the shortest wavelength in the required frequency range to realize an ideal dipole source. Then, the total sound pressure would be expected to attenuate in proportion to the square of the distance from the center of the sources, and little sound power would be radiated. However, in practice, the distance cannot be set small enough, so there is only a relatively small area around the dipole where the sound pressure attenuates in proportion to the square of the distance. Further afield, it attenuates in direct proportion to distance. Noise reduction is therefore limited. This paper describes the effects and the limits of performance of such a system as a function of wavelength and the dimensions of sound sources.
Torsional Vibrations of a Nonprismatic Hollow Shaft
Authors: Rezeka S. F.
Published: December 2011

Propagation of torsional waves in elastic homogeneous non-prismatic hollow shafts is investigated. Three different types of end conditions are considered: both ends fixed, both ends free, and one free—one fixed end. Design charts are presented to determine the natural frequency of a nonprismatic hollow shaft upon specifying its geometric profile, end dimensions, and end conditions.
Dynamic Mechanical Properties of Spirally Wound Paper Tubes
Authors: Bank L. C. , Gerhardt T. D. , Gordis J. H.
Published: December 2011

The use of experimental modal analysis to obtain the dynamic mechanical properties of spirally wound paper tubes is investigated. Based on experimentally measured natural frequencies in the free-free mode of transverse vibration, tube flexural stiffness properties are predicted using three beam theories: Euler-Bernoulli beam theory, Timoshenko beam theory for isotropic materials, and Timoshenko beam theory for anisotropic materials.
Limitation of Simplified Hypotheses for the Prediction of Torsional Oscillations for Thin-Walled Beams
Authors: Potiron A. , Gay D. , Czekajski C. , Laroze S.
Published: December 2011

The study of uniform torsion of thin walled beams is done fairly easily in the thin wall beam case, the effects of thickness being neglected. Then, the classical Saint-Venant warping function simplifies to the double sectorial area. The dynamical case needs the use of a more refined theory involving nonuniform warping, and characterized by supplementary dynamic torsion constants. The computed values obtained from BIEM for those constants are compared with those deduced from thin walled beam theory, and from the measurements of experimental natural frequencies. It is shown that the relative thickness acts significantly on the results in both static and dynamic torsion cases.
A Simple Numerical Method for Determining the Sensitivity of Bending Deflections of Stepped Shafts to Dimensional Changes
Authors: Umasankar G. , Mischke C. R.
Published: December 2011

A simple method of computing the effect of a dimensional change at a particular element of a stepped shaft on two bearings, on bending deflections, and on slopes of the neutral axis at any of the nodes of interest is presented. The changes in deflection and slope of the neutral axis are derived as incremental quantities and as functions of the dimension change and the prior deflections and slopes of the neutral axis of the shaft. For shaft synthesis, the implications are that one can begin with a uniform diameter bar subjected to the loading and make a complete deflection analysis with superposed closed-form relations. Then the geometry can be modified element by element and the deflectional changes easily updated. This is computationally efficient. Further, deflections and deflection changes computed using the proposed method are identical to those obtained using a finite beam element model of the shaft.
The Active Control of Forced Vibration Produced by Arbitrary Disturbances
Authors: Burdess J. S. , Metcalfe A. V.
Published: December 2011

This paper considers the vibration control of a single degree of freedom mass-spring-damper system when subjected to an arbitrary, unmeasurable disturbance. The idea of a disturbance observer is introduced and it is shown how an estimate of the excitation can be derived and used to generate a control, which reduces the vibration. This control is shown to be robust with respect to the parameters describing the behavior of the system. Experimental results are presented which show the efficacy of the method when the system is excited by periodic, random, and impact forces. Comments are made on the application of the method.
Vibration of a Bimodulus Thick Plate
Authors: Doong Ji-Liang , Chen Lien-Wen
Published: December 2011

Natural vibrations of a simply supported rectangular bimodulus thick plate subjected to a combination of pure bending stress and extensional stress in the plane of the plate is investigated. The governing equations obtained using the average stress method are sovled in exact form. The natural frequencies are compared with the previous results of the authors for ordinary thick plates, and with the neutral surface locations and natural frequencies of bimodular plates without initial stress. New results are presented for natural frequencies of bimodular plates with initial stress. The effects of various parameters on the natural frequencies are studied.
A Theoretical Model for Axial Heat Conduction Effects During Single-Phase Flow in Microchannels
Authors: Lin Ting-Yu , Kandlikar Satish G.
Published: December 2011

A model is developed to analyze the effect of axial conduction on heat transfer during single-phase flow in microchannels. The axial heat conduction in the wall introduces heat flow toward the inlet section resulting in an increase in the local fluid temperature and a corresponding increase in the wall temperature. Neglecting this effect while reducing the experimental data results in a lower value of the experimental Nusselt number. The model derived in this work takes into account this effect and offers a parameter to estimate the effect introduced by the axial heat conduction effect in the wall.
Computer Modeling of Wave-Energy Air Turbines With the SUPG/PSPG Formulation and Discontinuity-Capturing Technique
Authors: Corsini A. , Rispoli F. , Tezduyar T. E.
Published: December 2011

We present a computational fluid mechanics technique for modeling of wave-energy air turbines, specifically the Wells turbine. In this type of energy conversion, the wave motion is converted to an oscillating airflow in a duct with the turbine. This is a self-rectifying turbine in the sense that it maintains the same direction of rotation as the airflow changes direction. The blades of the turbine are symmetrical, and here we consider straight and swept blades, both with constant chord. The turbulent flow physics involved in the complex, unsteady flow is governed by nonequilibrium behavior, and we use a stabilized formulation to address the related challenges in the context of RANS modeling. The formulation is based on the streamline-upwind/Petrov-Galerkin and pressure-stabilizing/Petrov-Galerkin methods, supplemented with the DRDJ stabilization. Judicious determination of the stabilization parameters involved is also a part of our computational technique and is described for each component of the stabilized formulation. We compare the numerical performance of the formulation with and without the DRDJ stabilization and present the computational results obtained for the two blade configurations with realistic airflow data.