bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the Effect of Heated Jet Flow on the Far Field Radiation From a Noise Source
Authors: Gerhold C. H.
Published: December 2011

One factor which influences the radiation of jet noise is the interaction with the heated moving flow of a parallel twin jet. Because of the temperature and flow discontinuity between the jet and the surrounding air, the parallel jet acts as a partial barrier between the noise source and the receiver. An analytical model of jet shielding has been developed consisting of the sound field emitted from a stationary, discrete frequency point source, which impinges on a cylinder of locally parallel flow. The model is analyzed to identify the zones in which the various shielding mechanisms dominate. The effects of such parameters as jet temperature and flow speed are investigated. The analytical model is compared to experimental results for the shielding of a point noise source adjacent to a subsonic, isothermal air jet. The model estimates the trends of sound amplification and reduction by the jet in downstream azimuthal planes, showing lobe formations similar to those found experimentally. The model underestimates the shielding in the shadow zone at far downstream locations where sound diffraction is the dominant mechanism. Resolution of this discrepancy by way of modification of the shielding jet model is discussed.
Study of Elastic–Plastic Fracture Problem Using Finite Element Technique
Authors: Loo F. T. C.
Published: December 2011

Numerical methods for the analysis of the elastic-plastic fracture problem using a special finite element technique are presented. A brief description of some concepts in elastic-plastic fracture mechanics and of the finite element method is followed by the formulation procedure of the stiffness matrix using eight-noded quadrilateral isoparametric elements. After a terse discussion of the initial stress method, the procedure of computation is extended in the analysis by using an incremental load process. The size and the shape of the plastic zone of a center crack specimen is investigated. Results are presented in graphical form.
An Analysis for Crack Instability in Elastically Confined Yielding Regime
Authors: Zahoor A.
Published: December 2011

An analysis for crack instability is presented which utilizes a J-integral-based tearing modulus approach. In particular, a plane stress center-cracked panel which experiences elastically confined yielding is analyzed for a displacement controlled loading. The analysis assumes a compliant loading system, a special case of which leads to a load control mode of loading. The effects of the crack tip plasticity are taken into account by using the strip-yield model of Dugdale-Barenblatt. A method of predicting the amount of crack growth at the onset of instability is presented. Numerical results suggest that under conditions of small-scale yielding, crack instability can be achieved in materials having very low tearing modulus values.
Design Analysis of a Single-Column Pressframe
Authors: Singh U. P.
Published: December 2011

It is observed in practice that the classic (conventional) method as well as the finite element method, when using beam elements, to evaluate the strength and stiffness of a pressframe, gives results differing substantially from actual values. This discrepancy between experimental and theoretical results can be considerably narrowed if the stress-deformed state of the corner zone is separately considered in the computation of the overall strength and stiffness of the pressframe. By means of the application of the theory of thin-wall curved beam with large curvature it is economically possible to analyze the stress-deformed behavior of the pressform in general and the corner zone element in particular with fair reliability. In the present paper this method is applied to a mechanical C-frame press.
Stress Analysis Applications to Service Failures of Traveling-Wave Tubes
Authors: Yeh H.-Y.
Published: December 2011

By utilizing the mathematical analogy between the electrostatic fields and the elastic stress field, the electrostatic stresses in high voltage electronic device such as Traveling Wave Tubes (TWT) can be obtained from finite element technique. A new point of view about the vacuum electrical breakdown from the theory of elastic stress concentration has been proposed. The elastic stress concentration factors may be used as a good reference figure for TWT design works.
Thermal Buckling of a Bimetallic Strip
Authors: Orthwein W. C.
Published: December 2011

A theoretical foundation is provided for the difficulties encountered in manufacturing a snap acting bimetallic strip thermostatic which will snap within ±10 degrees of a prescribed temperature. It is obtained by modifying Timoshenko’s pioneering analysis to allow for a realistic support frame whose coefficient of thermal expansion differs from the composite coefficient for the bimetallic strip. Results are compared with those of Timoshenko and with predicted behavior when the support frame is rigid and thermally inert.
Optimal Jump Nonhomogeneity of Prismatic Bars in Torsion
Authors: Faulkner M. G. , Mioduchowski A. , Hong D. P.
Published: December 2011

The problem of optimal nonhomogeneity of a bar subjected to Saint-Venant torsion is formulated as a variational problem so that the necessary conditions for optimality may be derived. In this formulation, the shear modulus function G(x,y) which varies in a jumplike manner is to be optimized with the specified composition of two different elastic materials. It is shown in this paper that a prismatic, nonhomogeneous bar can, in fact, be optimized, and the maximum torsional rigidity is achieved by performing the proposed iterative procedure based on the derived necessary conditions. As a numerical example, the optimal solutions for prismatic bars with cross-sectional shapes of a square and an equilateral triangle are obtained by the computer program which uses the Finite Element Method formulated on the basis of the hybrid stress approach.
Synthesis of Dynamic Vibration Absorbers
Authors: Wang B. P. , Kitis L. , Pilkey W. D. , Palazzolo A.
Published: December 2011

A method for designing dynamic vibration absorbers which create antiresonances at specified points on a sinusoidally forced vibratory system is described. Spring-mass absorber systems are treated in detail. Among all possible solutions, a unique minimum mass solution is shown to exist if the relative displacement of the absorber mass is constrained. The sensitivity of the design to variations in frequency, spring constant, and absorber mass is discussed. The procedure is illustrated by numerical results for a simply supported uniform beam.
The Bifilar Pendulum: Numerical Solution to the Exact Equation of Motion
Authors: Karlin B. E. , Maday C. J.
Published: December 2011

The bifilar pendulum is often used for indirect measurements of mass moments of inertia of bodies that possess complex geometries. The exact equation of motion of the bifilar pendulum is highly nonlinear, and has not been solved in terms of elementary functions. Extensive use has been made, however, of the linearized approximation to the exact equation, and it has been assumed that the simple harmonic oscillator adequately describes the motion of the bifilar pendulum. It is shown here that such is generally not the case. Numerical solutions to the exact nonlinear differential equations of motion are obtained for a range of values of initial angular displacement, filament length, and radius of gyration. The filament length and the radius of gyration are normalized with respect to the half-spacing between the filaments. It is shown that the approximate solution gives good results only for small ranges of the system parameters.
Modeling and Analysis of Flow-Induced Vibrations in Circular Saws
Authors: Leu M. C. , Jirapongphan M.
Published: December 2011

Two types of flow-induced vibrations in idling circular saws, random vibration and resonant vibration, were modeled and analyzed. The excitation source, which is the flow pressure fluctuations, was modeled as discrete forces acting at the saw teeth. The response was assumed to be uncoupled from the excitation in the random vibration analysis but coupled with the excitation in the resonant vibration analysis. The random vibration was solved in terms of statistical rms amplitudes and the resonant vibration as a time function. The analytical results captured many characteristics of vibration phenomena observed in idling saw experiments.
Forced Vibration of a Damped Combined Linear System
Authors: Bergman L. A. , Nicholson J. W.
Published: December 2011

A new and general method for determining the exact undamped natural frequencies and natural modes of vibration, the orthogonality relation for the natural modes, and the response to arbitrary excitation for both damped and undamped combined linear systems is given. The method, based upon Green’s functions of the vibrating distributed subsystems, is demonstrated for a multiplicity of linear oscillators connected to a simple beam.
Aero/Hydrodynamic Stability of Elastically Supported Plates in Narrow Channels With Upstream Barriers Preventing Flow Redistribution
Authors: Mark W. D.
Published: December 2011

The dynamic stability of an elastically supported finite rigid plate centered in a straight narrow channel with incompressible flow on both sides of the plate and an upstream barrier preventing flow redistribution is analyzed. An integral equation for the pressure in a narrow channel having arbitrary small time-dependent boundary displacements is formulated and solved for the pressure distribution in terms of the boundary motion. The resulting expression for the time-dependent pressure distribution is combined with the plate differential equations of motion to yield the homogeneous equations of motion of the plate–fluid autonomous system. The Lie´nard–Chipart stability criterion is applied to the coefficients of the plate–fluid system equations to yield necessary and sufficient conditions for the dynamic stability of the plate–fluid system. The resulting stability requirements are expressed as algebraic inequalities involving dimensionless plate–fluid system parameters.
A Study of Active Vibration Isolation
Authors: Tanaka N. , Kikushima Y.
Published: December 2011

For the purpose of suppressing ground vibration produced by vibrating machines, such as forging hammers, press machines, etc., this paper presents an active vibration isolation method. Unlike conventional isolators, the active isolator proposed in this paper permits rigid support of the machines. First, the principle of the active isolation method is shown, and the system equations are derived. Secondly, the characteristics and the design parameters of the active isolation system are presented. Thirdly, from the point of view of the feedforward control method, the dynamic compensators are designed so as to sufficiently suppress the exciting force. Finally, an experiment is carried out to demonstrate that the active isolator is applicable for suppressing the ground vibration.
Forced Wave Motion of Liquid Partially Filling a High-Speed Rotor
Authors: Inoue J. , Jinnouchi Y. , Araki Y.
Published: December 2011

Wave motion of a liquid in a partially filled hollow cylindrical rotor, which rotates at a high speed and is forced to vibrate, is theoretically and experimentally investigated. Main emphasis is placed on the analysis of a large wave motion in the liquid which may cause self-excited vibrations of the rotor. Assuming a thin liquid layer, simplified equations of motion are derived by integration of the governing equations for a two-dimensional flow. Nonlinearity and viscosity are taken into account in the analysis. A large wave motion with a broken wavecrest is analyzed by applying a theory of hydraulic jump. Illustrating typical examples of the theoretical results together with the experimental ones, the dynamic behavior of the liquid motion and the basic relations between the liquid force and the rotor vibration are discussed.
A Constraint Function Technique for Improved Structural Dynamics
Authors: Starkey J. M. , Bernard J. E.
Published: December 2011

A constraint function approach is presented for finding design changes that remove natural frequencies from undesirable frequency bands for lightly damped structures. The technique requires the minimization of a function which becomes smaller when (1) natural frequencies clear out of undesirable bands, and (2) design changes become small. Useful forms of these functions are defined, and the number of possible minima is explored. Graphical intepretations of the constraint functions are given, and an example is included which shows the effects of the parameters which weight these two functions.
Approximate Structural Response Characterization Using Parametric and Envelope Models for Multimodal Systems
Authors: Davies P. , Hammond J. K.
Published: December 2011

In the study of the response of systems to an excitation there are circumstances when it is desirable to obtain some overall or average characterization of the system and its response rather than a detailed description. In this paper two methods are used to describe the overall features of the system: one appropriate for the frequency domain and one for the time domain. For modally dense systems the main features of the frequency response function are described in terms of low-order parametric models. While these models may be adequate for the frequency domain representation, they may not produce a good approximation to the response of the system in the time domain. The second approach relates the envelope of the input signal to the envelope of the response signal, in order to describe the overall time domain response characteristics.
Experimental Stiffness of Tapered Bore Seals
Authors: Fleming D. P.
Published: December 2011

The stiffness of taperd-bore ring seals was measured with air as the sealed fluid. Static stiffness agreed fairly well with results of a previous analysis. Cross-coupled stiffness due to shaft rotation was much less than predicted. Part of the disparity may be due to simplifying assumptions in the analysis; however, these do not appear to account for the entire difference observed.
The Tightening of Bolts to Yield and Their Performance Under Load
Authors: Chapman Ian , Newnham John , Wallace Paul
Published: December 2011

The mechanism of tightening bolted joints and the stress distribution in the bolt are analyzed. Measurements were made of static and dynamic strength of joints. It is shown that all bolts behave elastically when external loads are applied to the joint even when the fastener was tightened to its torque-tension yield point. It is shown that joints generally fail when the external loads are sufficient to overcome the bolt preload. Fatigue reesults show that joint fatigue strength increases with preload, and that high fatigue bolts gave an improvement over standard fasteners at all preloads.
The Influence of Several Combined High/Low Cycle Loading Parameters on the Crack Growth of a Turbine Disk Alloy
Authors: Petrovich A. , Ziegler W.
Published: December 2011

The interactive effects of high- and low-cycle loading on crack growth were evaluated for a high-temperature engine disk alloy (Inconel 718) over a wide range of low-cycle hold times, low-cycle stress intensity factor range (ΔK), high-cycle ΔK, and high-cycle frequency up to 1825 Hz. A series of fatigue crack growth experiments were carried out with a constant low-cycle ΔK and an increasing high-cycle ΔK. The high-frequency ΔK and crack length were measured with sufficient precision to capture details of the transition from the low-cycle dominated regime to the high-cycle dominated regime. In these experiments, the low- and high-cycle dominated growth regimes remained distinct over the entire range of low cycle ΔK, low cycle hold time and frequency investigated. An interactive effect apparent in the low-cycle dominated regime, was a retardation of the low-cycle growth rate when high-cycle loading was applied. The degree of retardation varied with low-cycle ΔK and frequency.
Roll Torque and Pressing in Plane-Strain Ring Rolling
Authors: Ryoo J. S. , Yang D. Y. , Johnson W.
Published: December 2011

A simple method of analysis using force polygon diagrams is proposed for determining roll torque and pressing load, in particular plane-strain ring rolling processes. Pressing velocity together with driven roll rotation is incorporated in constructing the hodograph for the upper-bound analysis in order to find an optimized tangential velocity pattern. Results from two types of tangential velocity discontinuity patterns and related force polygon diagrams are compared at optimized values. The ratio of resultant friction force and pressing load, or an equivalent coefficient of friction is determined from the force polygon diagrams. Experiments were carried out with AISI 1045 steel blanks in a hot condition. Theoretical torques and pressing loads are in good agreement with the experimental values. It is shown that the present method can be efficiently used for predicting pressing load and roll torque in ring rolling; the method has a flexibility and simplicity which recommends it for engineering analytical purposes and for explaining related physical phenomena.
A Theoretically Based Valve Noise Prediction Method for Compressible Fluids
Authors: Reethof G. , Ward W. C.
Published: December 2011

Noise generated by control valves in power generation, chemical and petrochemical plants must be predictable so that proper design measures can be taken to conform to OSHA’s noise regulation. Currently available noise prediction methods are empirically based and not sufficiently accurate. The method proposed is based on jet noise theory for both subcritical and choked conditions, duct acoustics theory in terms of higher order mode generation and propagation, and the theory of acoustics-structure interaction in the development of the transmission loss values for the pipe. One third octave values are calculated over the audio spectrum by incorporating spectral aspects of noise generation, propagation, transmission, and radiation. The predicted values of noise for several size cage globe valves over wide pressure ranges compare well with measured results by two prominent valve manufacturers. The method, at present, is restricted to conventional valve styles, as opposed to the special low noise valve types with their very complicated orificial elements.
Critical Spin Rate of Rotating Beams by Liapunov’s Direct Method
Authors: Kammer D. C. , Schlack A. L.
Published: December 2011

The in-plane and out-of-plane buckling of a beam subjected to axial loads due to steady rotation are investigated for various boundary conditions. The critical spin rate which will cause the beam to buckle is derived as a function of system parameters using Liapunov’s direct method. A significant advantage is offered by this method in that the equations of motion do not have to be solved in order to determine stability. Results are compared with those found in the literature.
Geometry-Based Stiffness Parameters for Predicting Approach of Limit Points in Finite-Element Studies
Authors: Shah Jami J. , Busby Henry R. , Kinzel Gary L.
Published: December 2011

Several parameters for evaluating the decrease in structural stiffness in nonlinear finite element problems are defined here. Two types of parameters were considered: those that measure the overall softening and those that measure only a selected type of response, such as ovalization or bending. These parameters were used for detecting the approach of limit points in cylinder buckling problems under combined bending and external pressure. This is necessary for determining when the Newton-Raphson scheme should be replaced by displacement control to prevent numerical instability. The two types of parameters used in conjunction provide not only a reliable means for sensing the approach of limit points but also a determination of buckling modes.
Case Studies in Corrosion-Assisted Cracking
Authors: Jur Tim A.
Published: December 2011

Corrosion-assisted cracking is treated as a time-dependent failure mechanism and is contrasted with other time-dependent phenomena, most notably fatigue. Two cases of failure are reviewed as examples of corrosion-assisted cracking. One case involves a surgical instrument which failed during an operation; the other involves a woman’s shoe. Both cases are documented with electron photomicrographs of the fractured surfaces. Basic features of corrosion-assisted cracking are reviewed and reference literature is cited.
An Euler Code Calculation of Blade-Vortex Interaction Noise
Authors: Hardin J. C. , Lamkin S. L.
Published: December 2011

An Euler code has been developed for calculation of noise radiation due to the interaction of a distributed vortex with a Joukowski airfoil. The time-dependent incompressible flow field is first determined and then integrated to yield the resulting sound production through use of the elegant low-frequency Green’s function approach. This code has several interesting numerical features involved in the vortex motion and in continuous satisfaction of the Kutta condition. In addition, it removes the limitations on Reynolds number and is much more efficient than an earlier Navier-Stokes code. Results indicate that the noise production is due to the deceleration and subsequent acceleration of the vortex as it approaches and passes the airfoil. Predicted acoustic levels and frequencies agree with measured data although a precise comparison would require the strength, size, and position of the incoming vortex to be known.
Automated Noninvasive Motion Measurement of Auditory Organs in Fish Using Ultrasound
Authors: Cox M. , Rogers P. H.
Published: December 2011

A scanning underwater, ultrasonic system has been developed to measure the in vivo vibrational amplitude response of fish hearing organs to low-frequency sound. The fish is insonified with a 20-MHz source while stimulated in a single-frequency sound field. Spectral analysis of the echoes due to the acoustic impedance mismatches at the auditory organs provides the desired amplitude information. A computer-controlled scanning system allows nearly simultaneous measurements of the response of the various organs. The system is capable of measuring displacements of 12Å with a spatial resolution of 0.28 mm.
Elastodynamic Radiation From Line Sources Buried in Layered Media Having Periodically Varying Interfaces
Authors: Lakhtakia A. , Varadan V. K. , Varadan V. V.
Published: December 2011

We describe here a method for determining the elastodynamic (P and SV waves) radiation characteristics of finite-size sources buried in a horizontally layered medium, having periodically corrugated interfaces. The presented technique utilizes the planewave spectral decomposition of the relevant fields within the framework of the extended boundary condition method (EBCM). Since the EBCM is a matrix approach, it is very attractive computationally, and is certainly more tractable than a method based on the direct solution of the integral equations involved in the scattering problem. Several problems in such diverse areas as noise control, seismology, meteorology, and oceanography can be solved using the derived methodology.
Optimal Placement of Critical Speeds in Rotor-Bearing Systems
Authors: Rajan M. , Rajan S. D. , Nelson H. D. , Chen W. J.
Published: December 2011

The design of a rotor-bearing system is an iterative process in which the parameters that influence the design are modified until the desired design objectives are achieved. Primary among the design objectives is the minimization of the response amplitude within the operating range of the rotor system. An automated design procedure for the optimal placement of the critical speeds of a rotor is presented. The desired design objective is cast as a nonlinear programming problem that minimizes an objective function subject to constraints. The optimization program interacts with an analysis program to search for the feasible optimal design.
Random Vibrations Due to Small-Scale Turbulence With the Coherence Integral Method
Authors: Brenneman B.
Published: December 2011

Conventional methods exist for obtaining the random vibration response of a finite-element model to “large-scale” turbulence, such as gust loading on an aircraft. However, this loading is random in time only. This paper presents a finite-element method for obtaining the response to “small-scale” turbulence that is random in space as well as time. Boundary-layer turbulence is an example of this type of loading. The method has been used successfully to find the random response of nonuniform, multispan tubes to inhomogeneous turbulent crossflow.
Numerical Simulation of Acoustic Agglomeration and Experimental Verification
Authors: Tiwary Rajiv , Reethof Gerhard
Published: December 2011

Acoustic agglomeration is proposed as an intermediate treatment in the flue gas cleanup train of the effluents from coal burning power plants. Acoustic agglomeration causes the micron and submicron sized particles to collide, adhere and form large particles which can be more efficiently removed from the flue gases with particle removal devices. This paper describes the results of acoustic agglomeration tests of coal fly-ash aerosols in a 200-mm dia device at acoustic levels from 140 to 160 dB, frequencies in the 2–3 kHz range and mass loadings in the 1 to 30 g/m3 range with initial log-normal particle size distributions having geometric mean diameters of about 5 micrometers. The primary thrust of the paper is to present a numerical simulation model of the acoustic agglomeration process. The model is based on the recently proven assumption of complete fillup of the agglomeration volume and neglects the effects of gravitational settling, Brownian motion, and acoustically generated turbulence. Good agreement is found between the model predictions and the experimental data.
Vibration Control in Industrial Plant: A Methodological Approach
Authors: Miconi D.
Published: December 2011

The present paper is a report on the construction of nomograms to ascertain the domain of elastic-inertial-damping characteristics required in vibrating machine-foundation systems, in order to ensure that ergonomic and other technical constraints are complied with. Nomograms, which are the graphic representation of mathematical models in nondimensional form, prove to be an effective instrument for orientation in the design stage.
A Mapped Finite Difference Study of Noise Propagation in Nonuniform Ducts With Mean Flow
Authors: Raad Peter E. , White James W.
Published: December 2011

The primary objective of this work is to study noise propagation in acoustically lined variable area ducts with mean fluid flow. The method of study is numerical in nature and involves a body-fitted grid mapping procedure in conjunction with a factored-implicit finite difference technique. The mean fluid flow model used is two-dimensional, inviscid, irrotational, incompressible, and nonheat conducting. Fully-coupled solutions of the linearized gas dynamic equations are obtained for both positive and negative Mach numbers as well as for hard and soft wall conditions. The factored-implicit finite difference technqiue used did give rise to short wavelength perturbations, but these were dampened by the introduction of higher order artificial dissipation terms into the scheme. Results compared favorably with available numerical and experimental data.
The High-Frequency Radiation of Sound from Bodies of Arbitrary Shape
Authors: Seybert A. F. , Rengarajan T. K.
Published: December 2011

In this paper the problem of calculating the sound field in a three-dimensional fluid of infinite extent due to a body of arbitrary shape which is vibrating harmonically is considered. Interest is focused on the case in which the parameter a/λ is large, where a is some characteristic dimension of the radiator. The approach here is to replace the familiar Helmholtz integral formula with an algebraic relationship which is approximately valid on the surface S of the body and to use this relationship to determine the acoustic potential at each point on S, given the normal gradient of the acoustic potential at that point. The acoustic potential exterior to the body is then calculated by numerical evaluation of the Helmholtz formula. By replacing the Helmholtz integral formula on the surface with the algebraic relationship, two troublesome problems associated with integral equation methods are avoided: the need to evaluate singular integrands and the problem of nonuniqueness of the solution at certain frequencies. The approach is evaluated by considering the high-frequency radiation from a finite cylinder up to a value of ka = 15. Comparison data are provided by solving the Helmholtz integral equation using an overdeter-mination method to circumvent nonuniqueness.
Experimental Acoustic Field Characterization of Enclosures by Impedance Estimates and Modal Analysis
Authors: Trethewey M. W. , Cafeo J. A.
Published: December 2011

An experimental method to characterize the acoustic field inside an enclosure in terms of the active and reactive components is presented. The method uses a finite difference approximation of the sound pressure from two closely spaced microphones to estimate the specific acoustic impedance and particle acceleration throughout a cavity. The impedance is then used to decompose the sound pressure at a point into components caused by the progressive and standing waves. The reactive or standing wave components within the cavity are further characterized in a normal modes fashion by extracting the modal parameters from the acoustic particle acceleration frequency response functions. The underlying theory of the technique is discussed. An experimental evaluation consisting of an analysis of the cavity characteristics of a tube with several end terminations is presented. For a reflective termination the experimental natural frequencies differed by less than 7 Hz between the analytical solution and a finite element model. For a semiabsorptive termination the experimental method shows the degradation of the high frequency reactive field due to the increased absorption and also the minimal effect on the low order acoustic mode characteristics.
The Finite Element Modelled Design of Lathe Spindles: The Static and Dynamic Analyses
Authors: Reddy Velagala R. , Sharan Anand M.
Published: December 2011

The paper presents a method for designing lathe spindles based on the static and dynamic analyses. Two types of criteria are used for the design. They are the minimum of the maximum workpiece deflection, and the minimum time required for the damped free oscillations to reach 66.666 percent of the initial displacement. The design parameters used in the study are the bearing spacing, the bearing stiffness, the workpiece diameter, and the location of an external damper. A dynamic matrix reduction technique has been used to economize on the computation time and computer memory storage.
Effects of Impact on the Behavior of a Flexible Multiple Disk Clutch and Brake
Authors: Nagaya Kosuke
Published: December 2011

This paper discusses the dynamic behavior of a flexible multiple disk clutch subjected to dynamic loads. The expressions for obtaining the dynamic response and the transmission torque of the clutch have been derived from the equation of motion of a circular plate by applying the Laplace transform procedure. The results for the clutch subjected to a static load have also been obtained. The comparison between both static and dynamic results has been made to clarify the effect of the impact of the load on the behavior of the clutch.
Development of Nonlinear Building Block Approach
Authors: Watanabe K. , Sato H.
Published: December 2011

A nonlinear building block approach (NLBBA) is proposed to evaluate frequency response characteristics of nonlinear structure systems including springs with nonlinear stiffness and clearances at slide or bearing as occur in actual systems. The advantage of the building block approach (BBA) was that dynamic performance of the total linear system can be evaluated by analyzing and synthesizing the performance of subsystems. In this paper the method was extensively developed to investigate systems with nonlinearities. The describing function was adopted to represent nonlinearity in the system equations. The compliance could be obtained by solving nonlinear simultaneous algebraic equations for multi-degrees-of-freedom system with multinonlinearities. The method was applied to a beam supported by nonlinear springs and a spindle of a machine tool. The evaluated compliance could quantitatively show effects of the nonlinearity such as transfer of the natural frequency, variance of the compliance at the natural frequency, and jump phenomena for sweep of the excitation frequency. The results of the application agreed well with those obtained by step-by-step integration in the time domain (time historical analysis) which is generally used, and also agreed well with the empirical phenomenon of the stability to the self-excited chatter. The computation time could be significantly shortened by the proposed method.
Optimal Design of Active Vibration Isolation System
Authors: Tanaka N. , Kikushima Y.
Published: December 2011

In order to eliminate ground vibration produced by machines such as forge hammers, press machines, etc., this paper presents a systematic and optimal design procedure of an active vibration isolation system which permits rigid support of machines. First, the principle of the active vibration method is presented. Secondly, from the viewpoint of feedback control, the active vibration isolation system with a series-type dynamic compensator is constructed. Thirdly, with the air of a parameter optimization technique, the necessary conditions for optimality of the system are derived. Fourthly, for the purpose of solving the conditions, an iterative algorithm based upon a quasi-Newton method is proposed. Finally, by using the design procedure, the active vibration isolation system is designed, and the effectiveness to isolate the vibration is discussed.
Interpretation of Experimental and Theoretical Data for Prediction of Mode Shapes of Vibrating Turbocharger Blades
Authors: Chapman G. M. , Wang X.
Published: December 2011

The blading in large turbochargers is subjected to vibration excitation originating from pulsations in the exhaust gas stream coupled with the blade pass frequencies. The amplitude of vibrations induced are a source of concern to design engineers as they can seriously affect the operation of the turbocharger. This paper discusses theoretical and experimental investigations aimed at identifying the natural frequencies and the associated mode shapes for a single turbocharger blade. Modal Analysis, Electronic Speckle Pattern Interferometry (ESPI), and Finite Element Analysis are all used in an attempt to categorize the modal patterns.
A Multiple Degree of Freedom Cavity Element for Acoustic Transmission Lines
Authors: Eversman W. , Ricci G.
Published: December 2011

Mathematical modelling of acoustic transmission lines containing elements which can be represented by their acoustic modes is considered. Of particular interest are tapered elements and acoustic cavities which operate at frequencies above which a simple volume expansion representation or a plane wave representation is adequate. An element matrix formulation is given which is suitable for inclusion in the Acoustic Wave Finite Element assembly procedure, or with suitable modifications, to the more traditional transfer matrix approach. Numerical examples are provided demonstrating the accuracy of the procedure.
A Noise Source Identification Technique Using an Inverse Helmholtz Integral Equation Method
Authors: Gardner B. K. , Bernhard R. J.
Published: December 2011

A technique is developed which utilizes numerical models and field pressure information to characterize acoustic fields and identify acoustic sources. The numerical models are based on boundary element numerical procedures. Either pressure, velocity, or passive boundary conditions, in the form of impedance boundary conditions, may be imposed on the numerical model. Alternatively, if no boundary information is known, a boundary condition can be left unspecified. Field pressure data may be specified to overdetermine the numerical problem. The problem is solved numerically for the complete sound field from which the acoustic sources may be determined. The model can then be used to identify acoustic intensity paths in the field. The solution can be modified and the model used to evaluate design alternatives. In this investigation the method is tested analytical and verified. In addition, the sensitivity of the method to random and bias error in the input data is demonstrated.
High Order Subharmonic Response of High Speed Rotors in Bearing Clearance
Authors: Ehrich F. F.
Published: December 2011

Subharmonic vibration refers to the response of a dynamic system to excitation at a whole-number multiple (n) of its natural frequency by vibrating asynchronously at its natural frequency, that is, at (1/n) of the excitation. The phenomenon is generally associated with asymmetry in the stiffness vs. deflection characteristic of the system. It may be characterized as the “bouncing” of the rotor on the surface of the stiff support, energized by every nth unbalance impulse prior to contact. Second, third and fourth order subharmonic vibration responses have previously been observed in high speed rotating machinery with such an asymmetry in the bearing supports. An incident is reported where 8th and 9th order subharmonic vibration responses have been observed in a high speed rotor. A simple but exact computer model of the phenomenon has been evolved based on the numerical integration of a finite difference formulation. Response curves and wave forms of rotor deflection at individual speeds are computed. It is shown that the response is a series of pseudo-critical peaks at whole-number multiples of the rotational speed. Very high orders of subharmonic vibration are found to be possible for systems with low damping and extreme nonlinearity.
On the Accuracy of Parametric and Classical Spectra
Authors: Braun S. , Sneor A.
Published: December 2011

This work investigates the accuracy of spectral estimates computed via parametric techniques. Comparisons with results obtained via classical Fourier methods are also presented. The PSD’s (power spectral densities) investigated are of the type encountered in low damped structures excited by random inputs. Qualitative results are shown for simulated as well as experimental data. The results substantiate the claims for the smoothness of parametric spectra, but not the improved resolution capabilities.
Controlled Excitation of a Cold Turbulent Swirling Free Jet
Authors: Taghavi R. , Rice E. J. , Farokhi S.
Published: December 2011

Experimental results from acoustic excitation of a cold free turbulent jet with and without swirl are presented. A flow with a swirl number of 0.35 (i.e., moderate swirl) is excited internally by plane acoustic waves at a constant sound pressure level and at various frequencies. It is observed that the cold swirling jet is excitable by plane waves, and that the instability waves grow about 50 percent less in peak r.m.s. amplitude, and saturate further upstream compared to corresponding waves in a jet without swirl having the same axial mass flux. The preferred Strouhal number based on the mass-averaged axial velocity and nozzle exit diameter for both swirling and nonswirling flows is 0.4. So far no change in the mean velocity components of the swirling jet is observed as a result of excitation.
Instability and Unbalance Response of Dissymmetric Rotor-Bearing Systems
Authors: Guilhen P. M. , Berthier P. , Ferraris G. , Lalanne M.
Published: December 2011

The study deals with the instability and unbalance response of dissymmetric rotors, when periodic differential equations are impossible to avoid. The method which yields motion instability is based on an extension of the well-known Floquet theory. A transfer matrix over one period of the motion is obtained, and the stability of the system can be tested with the eigenvalues of the matrix. To find the instability and the unbalance response, the Newmark formulation is used. Here, the dissymmetry comes either from the rotor or from the bearings in such a way that it is possible to solve a regular differential system without periodic coefficients, either in the stationary coordinate system or in the rotating one. Three examples are given, including an industrial application. The results show that the method proposed is satisfactory.
Hybrid Finite Element—Boundary Element Simulation of Rotating Machinery Supported on Flexible Foundation and Soil
Authors: Earles L. L. , Palazzolo A. B. , Lee C-K , Gerhold C. H.
Published: December 2011

Relative and absolute shaft vibration data have revealed that the commonly made assumption of rigidly supported bearings may be grossly inaccurate, especially for fans, generator sets, and natural gas transmission compressors. This paper provides a systematic method for modeling flexibly mounted rotating machinery utilizing 8 node isoparametric brick-type finite elements for the foundation and 4 node isoparametric “patch” type boundary elements for the soil. The rotor is modeled utilizing Euler-Bernoulli beam elements and includes disk gyroscopics and cross coupled bearing coefficients. The large number of degrees of freedom included in the model are reduced utilizing a nested superelement scheme and Guyan reduction.
Numerical and Analytical Study of Fluid Dynamic Forces in Seals and Bearings
Authors: Tam L. T. , Przekwas A. J. , Muszynska A. , Hendricks R. C. , Braun M. J. , Mullen R. L.
Published: December 2011

A numerical model based on a transformed, conservative form of the three-dimensional Navier-Stokes equations and an analytical model based on “lumped” fluid parameters are presented and compared with studies of modeled rotor/bearing/seal systems. The rotor destabilizing factors are related to the rotative character of the flow field. It is shown that these destabilizing factors can be reduced through a descrease in the fluid average circumferential velocity. However, the rotative character of the flow field is a complex three-dimensional system with bifurcated secondary flow patterns that significantly alter the fluid circumferential velocity. By transforming the Navier-Stokes equations to those for a rotating observer and using the numerical code PHOENICS-84 with a nonorthogonal body fitted grid, several numerical experiments were carried out to demonstrate the character of this complex flow field. In general, fluid injection and/or preswirl of the flow field opposing the shaft rotation significantly intensified these secondary recirculation zones and thus reduced the average circumferential velocity, while injection or preswirl in the direction of rotation significantly weakened these zones. A decrease in average circumferential velocity was related to an increase in the strength of the recirculation zones and thereby promoted stability. The influence of the axial flow was analyzed. The lumped model of fluid dynamic force based on the average circumferential velocity ratio (as opposed to the bearing/seal coefficient model) well described the obtained results for relatively large but limited ranges of parameters. This lumped model is extremely useful in rotor/bearing/seal system dynamic analysis and should be widely recommended. Fluid dynamic forces and leakage rates were calculated and compared with seal data where the working fluid was bromotrifluoromethane (CBrF3). The radial and tangential force predictions were in reasonable agreement with selected experimental data. Nonsynchronous perturbation provided meaningful information for system lumped parameter identification from numerical experiment data.
Self-Excitation in Guided Circular Saws
Authors: Lehmann B. F. , Hutton S. G.
Published: December 2011

The paper presents the results of an experimental and analytical study into the vibrational characteristics of guided rotating saw blades that are not perfectly flat. Experimental results are presented that show the nature of the vibrations induced by the interaction between the guides and the blade. An analytical model is developed that includes the effect of the interaction between the guide and the blade, and this model may be used as a design tool in avoiding the self-excited resonances that exist in the coupled blade/guide system.
Torsional Oscillations in Moving Bands
Authors: Ariaratnam S. T. , Asokanthan S. F.
Published: December 2011

The torsional vibration of moving bands subject to harmonic tension fluctuation is investigated. A thin rectangular strip translating longitudinally with a constant speed and simply supported at its end is considered. The linearized equation of motion, when suitably discretized, represents a linear gyroscopic system with periodically varying stiffness. The stability of the trivial solution of this system of equations, for tension fluctuations of small amplitude, is examined using the method of averaging. Analytic conditions for stability of torsional motion are obtained explicitly and shown graphically in the frequency vs excitation parameter space.
A Comparison of the Natural Frequency Changes Produced by Cracks and Slots
Authors: Cawley P. , Ray R.
Published: December 2011

The changes in the natural frequencies of a beam produced by cracks have been compared with those caused by slots of the same depth and different widths. It has been shown both theoretically and experimentally that the natural frequency changes produced by a defect of a given depth increase as the width of the defect is increased. This means that if tests with machined slots are to be used to investigate whether a crack of a particular depth can be detected in a nondestructive test based on natural frequency measurements, it is essential to correct the results of the tests with the slots to allow for the finite width of the slots. The results presented here can be used for this purpose.
Viscoelastic Analysis of Adhesive Bonded Lap Joints Between Tubes Under Torsion
Authors: Medri Gianluca
Published: December 2011

In this paper a structural analysis of cemented lap joints between tubes under torsion is presented. The behavior of the joints has been evaluated using a linear viscoelastic model of the adhesive layer and for both steady state and general loading conditions. Analytical relations for the shear stress in the adhesive layer for the torsional compliance of the joints are proposed.
An Approximate Method for Predicting Peak Transient Responses
Authors: Starkey J. M. , Bubel G. M.
Published: December 2011

A method is presented to predict the peak deflections and peak transmitted forces of a viscously-damped multi-degree-of-freedom linear vibratory system that experiences time-varying excitations which sweep through system resonances. The method relies on curve fits of the modal response envelopes. The modal responses are assumed to be in phase and are transformed back to physical coordinates giving conservative predictions.
Experimental Diagnosis of Fracture Damage in Structures by the Modal Frequency Method
Authors: Ju F. D. , Mimovich M. E.
Published: December 2011

The present paper used the modal frequency method to diagnose the fracture damage experimentally in simple structures, based on the analytical theory of the spring-loaded “fracture-hinge.” It is illustrated that the damage geometry uniquely defines the spring constant of the “fracture hinge,” which is therefore independent of the loading strength, the frequency of vibration, and the damage location. The experiment also measures the change in modal frequencies to locate the damage on the beam. With an accurate analytical model for the experimental samples, the locations of the damages can be predicted to within an accuracy of one percent of the length. The damage intensity is around four percent in accuracy.