bluuebunny/crossref_metadata_2025 huggingface dataset:
Maximum Resonant Response of Mistuned Bladed Disks
Authors: MacBain J. C. , Whaley P. W.
Published: December 2011

The turbomachinery bladed disks used in today’s advanced turbine engines must meet strict standards with regard to aeroelastic stability and forced resonant response. One structural characteristic of bladed disks that can significantly impact both of these areas is that of bladed disk mistuning. Mistuning occurs when some circumferential asymmetry exists in the bladed disk. This asymmetry can be due to such things as mass or stiffness eccentricity or slight variations in the individual blade properties and occurs in all bladed disks to a greater or lesser extent. One important structural phenomenon resulting from mistuning is the splitting of the bladed disk’s diametral modes of vibration into “twin” or “dual” modes. The presence of dual mode characteristics in a bladed disk can significantly affect either or both of its aeroelastic stability and resonant response characteristics. The present paper, expanding upon the earlier works of Tobias and Arnold [1] and of Ewins [2] addresses the prediction of the maximum resonant response of a mistuned bladed disk having closely spaced dual modes as a function of mode mistuning and modal damping. A closed form expression is derived for the maximum forced resonant response. A discussion of mistune and damping characteristics of typical turbomachinery bladed disks is also presented.
Effects of Surface Irregularity on Turbulent Boundary Layer Wall Pressure Fluctuations
Authors: Farabee T. M. , Casarella M. J.
Published: December 2011

Measurements were made of the mean velocity profiles and wall pressure field upstream and downstream of the flow over both a backward-facing and forward-facing step. For each configuration the velocity profiles show that the effects of the separation-reattachment process persist more than 24 step heights downstream of the step. Extremely high values of the RMS wall pressure are measured near reattachment. These values are 5 and 10 times larger than on a smooth flat plate for the backward-facing step and the forward-facing step, respectively. The spectral density of the wall pressure fluctuations in the recirculation region is dominated by low frequency components. Downstream of reattachment there is a reduction in the low frequency content of the wall pressures and an increase in the high frequency components. At the farthest measured position downstream, the spectral density is still higher than that found on a smooth flat plate. These results show that the complex turbulent flow generated by a surface irregularity can significantly increase the localized wall pressure field and these increases persist far downstream of the irregularity. Consequently, a surface irregularity can be a major source of turbulence-induced vibrations and flow noise, as well as a cause of the inception of cavitation in marine applications.
Modification Caused by Compliant Layers and Blankets in the Pressure Field Induced on a Boundary
Authors: Maidanik G.
Published: December 2011

A primitive analytical tool to assess the modification in the response caused by introducing various combinations of flexible layers on panels is proposed and developed. The tool is primitive in the sense that quantities which characterize the dynamic system are expressed in terms of lumped parameters. It is thus subjected to many restrictions and limitations with which the user needs to become familiar if he is to employ the tool properly. The formalism is expressed in terms of a matrix that relates the response vector to an external drive vector that induces the response. An element of the matrix identifies the surface on which an external test drive is acting and the surface on which the resulting response is assessed. The general formalism is specialized to the case of a panel that is clad with a composite consisting of a compliant layer and a blanket. The resulting elements of the matrix are used to ascertain the modification factor that is associated with this kind of cladding. The modification factor assesses the change in the response, e.g., pressure field due to the treatment of the panel by the flexible layers. It transpires that in the case of an ideal blanket the modification factor of the composite flexible layer is equal to the product of the two modification factors. Each factor relates separately to the application of one of the two individual flexible layers. A few computational examples of interest are cited and briefly discussed.
Fatigue Design of Machine Elements Under Cumulative Damage Effect, Using Bagci’s Fatigue Failure Surface Line
Authors: Bagci C.
Published: December 2011

A thorough review of the state-of-the-art of determining fatigue life of machine and structural members considering cumulative damage effect under varying stress amplitudes is given. Among the many proposed theories, Miner’s linear damage rule is seen to be as reliable as any other rule alleged to be an improvement for predicting fatigue life under cumulative damage effects. Its simplicity and amenability for easy modification have in fact been the basis for some other theories and used in design codes. In its original form, Miner’s rule, however does not account for fatigue strength reducing factors. Observing fatigue data on the effects of fatigue strength reducing factors, the article offers a modified form of the Miner’s rule to consider the effects of fatigue strength reducing factors, such as the notch, reliability, surface finish, size, and environmental factors. The mean stress effect and material properties are incorporated utilizing Bagci’s mean stress line and the S-N diagram. The safe fatigue life of a component subjected to stresses of varying magnitudes becomes Ns=df/∑i=1s(αi/10zi) where zi=A{B−log(pig/Rf)+log[1−(pi/mi)r]} in the ith block of stress range, Rf being the resultant of fatigue strength reducing factors; A, B, g are parameters defined by material properties, pi is the ratio of the basic alternating stress times the factor of safety (the failure value) to the yield strength of the material, and mi is the slope of the load line in the ith block of loading. Design charts for zi for steel and aluminum alloys for cases with and without basic mean stress for r=4 are given. Numerical examples are included. Therefore, the article offers the most general form of the Miner’s rule for designers’ use for fatigue design considering cumulative damage effect.
Elastic Deformation of End-Supported Pressure Rollers
Authors: Singh B. , Paul B.
Published: December 2011

A method is developed for calculating the line load and the deflection curves for a pair of contacting rollers supported at the ends. The formulation includes the possibility of varying flexural rigidity and the distributed weight of the rollers, nonlinear force-displacement relationship in the nip, and crowning of the roller surfaces. The resulting equations are solved by the method of “quasi-linearization.” The analysis was used to study the effects on line load of the thickness of the compliant layer covering one of the rollers. The method is applicable to problems involving partial or multiply-connected contact regions.
Influence of Wheel-Rail Profiles on the Hunting Vibrations of Rail Vehicle Trucks
Authors: D’Souza A. F. , Tsung W-J.
Published: December 2011

The effect of several wheel and rail profiles on the hunting behavior of three-piece North American freight truck is investigated by the method of describing functions. After replacing the nonlinear terms by their equivalent describing functions, the differential equations of motion are converted to a set of coupled nonlinear algebraic equations which are then solved by the Newton-Raphson method. It is shown that the wearing of the rail profile has a significant adverse effect on the dynamic behavior. It greatly lowers the critical speed for the onset of hunting and raises the frequency, thereby causing high acceleration levels. It is also shown that the modified Heumann wheel profile exhibits a superior dynamic performance for freight trucks than the standard new wheel profile used in North America. The effects of wheel wear and loads on hunting are also investigated.
Analysis of Clothes Motion in an Orbital Washer
Authors: Stokes V. K.
Published: December 2011

In a new orbital washer, the motion of clothes is exactly opposite to what might be expected in such a machine. A simple analytical model has been developed to explain this apparently anomalous motion. The mechanism of motion and the resulting predictions have been verified through high-speed cinematography and tests on an experimental orbital washer.
Creep-Rupture Reliability Analysis
Authors: Peralta-Duran A. , Wirsching P. H.
Published: December 2011

A probablistic approach to the correlation and extrapolation of creep–rupture data is presented. Time–temperature parameters (TTP) are used to correlate the data, and an analytical expression for the master curve is developed. The expression provides a simple model for the statistical distribution of strength and fits neatly into a probabilistic design format. The analysis focuses on the Larson–Miller and on the Manson–Haferd parameters, but it can be applied to any of the TTP’s. A method is developed for evaluating material dependent constants for TTP’s. It is shown that “optimized” constants can provide a significant improvement in the correlation of the data, thereby reducing modeling error. Attempts were made to quantify the performance of the proposed method in predicting long-term behavior. Bias and uncertainty in predicting long-term behavior from short-term tests were derived for several sets of data. Examples are presented which illustrate the theory and demonstrate the application of state-of-the-art reliability methods to the design of components under creep.
On the Use of Rotor-Bearing Instability Thresholds to Accurately Measure Bearing Rotordynamic Properties
Authors: Adams M. L. , Rashidi M.
Published: December 2011

A re-examination of rotor-bearing instability has led to a fresh approach that can potentially improve measurement accuracy of journal bearing rotordynamic coefficients. The approach uses a two-degree-of-freedom system and has three major parts. First, bearing stiffness coefficients are measured using static loading. Second, measured orbital motion at an adjustable threshold speed is used to extract the bearing damping coefficients by inverting the associated Eigen problem. Third, multiple displacement-measurement coordinate systems are used to allow an averaging approach which uses to advantage the tensor transformation property of bearing rotordynamic coefficients. The fundamental advantages of the overall approach stem from the physical requirement for an exact internal energy balance between positive and negative damping influences at an instability threshold, and that it does not require the measurement of dynamic forces.
Active Control of Vibrations in the Case of Asymmetrical High-Speed Rotors by Using Magnetic Bearings
Authors: Anton E. , Ulbrich H.
Published: December 2011

Rotor-bearing systems with long, fast running rotors and rotational symmetry disturbed in stiffness, damping and moments of inertia are investigated. Since a magnetic bearing is used as an actuator in a control circuit, vibrations of the system can be influenced in a desired way, A feedback control is designed with emphasis to the endangered modes of oscillation of the rotor system caused by parametrical excitation. A small number of sensors and a controller with constant gain factors are used in order to obtain a low-cost system. For illustration an elastically supported gas centrifuge with 12 degrees of freedom and asymmetrical stiffness and damping properties is considered.
Response of Rotors Subjected to Random Support Excitations
Authors: Subbiah R. , Bhat R. B. , Sankar T. S.
Published: December 2011

Response of rotor systems subjected to random support excitations is studied. Support excitations may occur for rotating machines installed either on the ground due to earthquake motion, or on board moving systems such as ships. These excitations in general are random in nature and hence the response of the machine can be obtained following a statistical analysis. In this paper, the amplitude power spectral densities (PSD) due to random support excitations are obtained for rotor systems, using modal analysis methods. The excitations are assumed to be stationary and Gaussian with a white noise type of PSD. Excitations through different supports are assumed to be statistically independent so that their cross correlations are zero. Results for rotors with various parametric combinations are presented.
An Analytical Model for the Vibration of Laminated Beams Including the Effects of Both Shear and Thickness Deformation in the Adhesive Layer
Authors: Miles R. N. , Reinhall P. G.
Published: December 2011

The equations of motion governing the vibration of a beam consisting of two metal layers bonded together with a soft viscoelastic damping adhesive are derived and solved. The adhesive is assumed to undergo both shear and thickness deformations during the vibration of the beam. In previous investigations the thickness deformation has been assumed to have negligible effect on the total damping. However, if the adhesive is very soft, and if at least one of the metal layers is stiff in bending, the thickness deformation in the adhesive can become the dominant damping mechanism. The analysis presented here comprises an extension of the well-known sixth order theory of DiTaranto, Mead, and Markus to include thickness deformation. The equations of motion are derived using Hamilton’s Principle and solutions are obtained by the Ritz method. It is shown that the use of a lightweight constraining layer which is stiff in bending will result in a design which is considerably more damped than a conventional configuration in which the adhesive is undergoing predominant shear deformation.
Identification of Mass, Damping, and Stiffness Matrices of Mechanical Systems
Authors: Fritzen Claus-Peter
Published: December 2011

A procedure is presented to calculate the mass, damping, and stiffness matrices of mechanical systems from measured input/output data. It works on the basis of the Instrumental Variable Method which is well suited for the estimation of models from data with superimposed measurement noise. Noise is present in many practical cases. The theory of the method is described with regard to vibrating systems. The first application is the estimation of the matrices of a simulated system where the noise level is varied. The results show the expected properties: less sensitivity to noise compared to the Least Squares Method. Furthermore, the procedure is applied to a real system.
Forced Response Analysis of an Aerodynamically Detuned Supersonic Turbomachine Rotor
Authors: Hoyniak D. , Fleeter S.
Published: December 2011

High-performance aircraft engine fan and compressor blades are vulnerable to aerodynamically forced vibrations generated by inlet flow distortions due to wakes from upstream blade and vane rows, atmospheric gusts, and maldistributions in inlet ducts. In this paper, an analysis is developed to predict the flow-induced forced response behavior of an aerodynamically detuned rotor operating in a supersonic flow with a subsonic axial component. The aerodynamic detuning is achieved by alternating the circumferential spacing of adjacent rotor blades. The total unsteady aerodynamic loading acting on the blading, due to the convection of the transverse gust past the airfoil cascade and the resulting motion of the cascade, is developed in terms of influence coefficients. This analysis is then utilized to investigate the effect of aerodynamic detuning on the forced response characteristics of a 12-bladed rotor, with Verdon’s Cascade B flow geometry as a uniformly spaced baseline configuration. The results of this study indicate that for forward traveling wave gust excitations, aerodynamic detuning is generally very beneficial, resulting in significantly decreased maximum amplitude blade responses for many interblade phase angles.
The Dynamics of a Rotor System with a Cracked Shaft
Authors: Nelson H. D. , Nataraj C.
Published: December 2011

A theoretical analysis of the dynamics of a rotor-bearing system with a transversely cracked rotor is presented. The rotating assembly is modeled using finite rotating shaft elements and the presence of a crack is taken into account by a rotating stiffness variation. This stiffness variation is a function of the rotor’s bending curvature at the crack location and is represented by a Fourier series expansion. The resulting parametrically excited system is nonlinear and is analyzed using a perturbation method coupled with an iteration procedure. The system equations are written in terms of complex variables and an associated computer code has been developed for simulation studies. Results obtained by this analysis procedure are compared with previous analytical and experimental work presented by Grabowski.
Fatigue Analysis of Stripper Bolt Under Combined Loading for Improvement of Stamping Die Design
Authors: Lee Sang Hoon
Published: December 2011

A common problem of fatigue failure of stamping dies was experienced during the stamping operation with socket-head screws. In order to establish a design standard for the stripper bolt, a methodology for determination of the loads and the fatigue strength of the stripper bolt was developed. Stresses due to an impulsive load and a rectangular pulse were calculated based on a simplified spring mass system and the appropriate corrections were made to elaborate the solution. This approximate solution was validated by a finite element analysis. The stripper bolt should have an infinite fatigue life to survive a half million stamping operations. The fatigue problem involves a stress concentration with combined mean and alternating stresses. The Gerber parabola and the residual stress method were employed to treat the combined loading and the stress concentration. In order to enhance the fatigue life of the stripper bolt, a cushion is introduced at the surface where an impact load is applied. The cushion is found very effective in improving the fatigue life of the stripper bolt. An interactive computer program was developed as a tool for designing stamping dies.
Cyclic Fatigue Behavior of Resinoid-Bonded Abrasives
Authors: Ritter J. E. , Fahey J. P. , Service T. H.
Published: December 2011

The cyclic fatigue behavior of a resinoid-bonded abrasive was determined in ambient air (22°C and 50 percent relative humidity). The number of cycles to failure was dependent on the cyclic stress by a power functional relation, consistent with fracture mechanics concepts of fatigue crack growth. Additionally, it was found that the cyclic fatigue behavior did not depend on the cyclic stress waveform or the test sample geometry and loading (four-point bend bars and radically loaded nonreinforced and reinforced wheels). Based upon fracture mechanics concepts, a reliability analysis was developed for reinforced, resinoid-bonded abrasives in service, taking into account the variability in strength and the fatigue behavior exhibited by these materials.
A Theoretical Prediction of the Acoustic Pressure Generated by Turbulence-Flame Front Interactions
Authors: Huff R. G.
Published: December 2011

The equations of momentum and continuity are combined and linearized yielding the one-dimensional nonhomogeneous acoustic wave equation. Three terms in the nonhomogeneous equation act as acoustic sources and are taken to be forcing functions acting on the homogeneous wave equation. The three source terms are: fluctuating entropy, turbulence gradients, and turbulence-flame interactions. Each source term is discussed. The turbulence-flame interaction source is used as the basis for computing the source acoustic pressure from the Fourier transformed wave equation. Pressure fluctuations created in turbopump gas generators and turbines may act as a forcing function for turbine and propellant tube vibrations in earth-to-orbit space propulsion systems and could reduce their life expectancy. A preliminary assessment of the acoustic pressure fluctuations in such system is presented.
On the Fragility of Acoustically Agglomerated Submicron Fly Ash Particles
Authors: George W. , Reethof G.
Published: December 2011

The concept and potential use of acoustic agglomeration as an aerosol conditioning device in a clean-up team is discussed. The experimental setup used for carrying out the room temperature agglomeration tests is briefly described. Photographic evidence is presented showing the survival of bonds holding the acoustically agglomerated particles together, after the particles were size separated in an (Anderson Mark II) inertial impactor. A theoretical analysis is developed which shows that the shearing stresses exerted on particles in the impactor are higher than would be experienced if they were being separated in a typical industrial cyclone. Thus, it is concluded that the acoustically agglomerated particles are “robust” enough to avoid breakup in a cyclone (a common industrial particle removal device).
Prediction of Stochastic Endurance Strength
Authors: Mischke C. R.
Published: December 2011

Engineers use fatigue strength modification factors as suggested by Marin in various forms, all of them deterministic. There are advantages to the designer in using these factors in a stochastic form to realize a reliabiltiy goal in critical design for strength. The paper quantifies some of these factors and presents specific examples of their use.
Critical Speeds of Turbomachinery: Computer Predictions vs. Experimental Measurements—Part II: Effect of Tilt-Pad Bearings and Foundation Dynamics
Authors: Vance J. M. , Murphy B. T. , Tripp H. A.
Published: December 2011

This is the second of two papers describing results of a research project directed at verifying computer programs used to calculate critical speeds of turbomachinery. This part describes measurements made to determine the characteristics of tilt-pad bearings and foundation dynamics. Critical speeds of a 166 kg laboratory rotor on tilt-pad bearings are then compared with predictions from a state-of-the-art damped eigenvalue computer program. Measured natural frequencies of a steam turbine are also compared with computer predictions. Accuracy of critical speed prediction is shown to depend on accuracy of 1) the “free-free” rotor models, 2) the bearing stiffness and damping coefficients, and 3) the dynamic properties of the foundation, which can be represented by an impedance that must be determined by experimental measurements.
Dynamic Response of a Radial Beam With Nonconstant Angular Velocity
Authors: Kammer D. C. , Schlack A. L.
Published: December 2011

The effects of a nonconstant angular velocity upon the vibration of a rotating Euler beam are investigated. It is assumed that the angular velocity can be written as the sum of a steady-state value and a small periodic perturbation. The time-dependence of the angular velocity results in the appearance of terms in the equations of motion which cause the system to be nonautonomous. These terms result in the existence of regions of parametric instability within which the amplitude grows exponentially. A perturbation technique called the KBM method is used to derive approximate solutions and expressions for the boundaries between stable and unstable motion. A simple perturbation function is assumed to illustrate the use of the derived general equations.
Test, Evaluation and Failure Analysis of Automotive Scissors Jacks
Authors: Chiang G. D. C.
Published: December 2011

Automotive scissors jacks have rapidly grown in popularity in past years because of their light weight, low cost and ease of use and storage. However, they may be a potential safety hazard if the scissors jack is not adequately designed, properly assembled or correctly used. This paper summarizes results from a test and evaluation program performed by the National Highway Traffic Safety Administration involving 120 automotive scissors jacks selected from 24 models and made by 14 different manufacturers. In conjunction with the test results, a mathematical model was introduced to describe the load supporting characteristics of a variety of scissors jacks. The analytical results agree fairly well with the test results. A failure mode and effects analysis was performed to analyze four observed major failure modes of the scissors jacks; i.e., collapsing, toppling over, unable to raise or lower the vehicle and penetration of the vehicle frame.
The Influence of Geometric Parameters on F. C. Centrifugal Fan Noise
Authors: Morinushi Ken
Published: December 2011

In this report, through experiments the influence of five major geometric parameters on noise and aerodynamic performance of forward curved (F.C.) centrifugal fans was studied. The parameters considered are: (1) width-inner diameter ratio of impeller, (2) axial clearance between the fan inlet nozzle and the impeller shroud plate, (3) blade-setting angle, (4) blade pitch-chord ratio, and (5) spiral extension index of the scroll. Noise characteristics were evaluated by means of the specific noise level (A-weighted) at every operating point except the surging region. The optimal values for the parameters to realize low noise are discussed. Design diagrams for low noise F.C. centrifugal fans are shown.
Corner Wear and Its Monitoring in Cylindrical Plunge Grinding
Authors: Radhakrishnan V. , Achyutha B. T.
Published: December 2011

Grinding wheel corner wear plays a very significant role in certain cylindrical plunge grinding operations in which the corner radius is critical. The corner wear affects the tolerance specified on the plunged corner radius on the component. Monitoring of corner wear is essential to know when exactly the tolerance zone has been crossed. This paper deals with the nature and geometry of corner wear and its monitoring using the fluctuations in the airflow velocity around the grinding wheel.
Radiation and Scattering of Acoustic Waves from Bodies of Arbitrary Shape in a Three-Dimensional Half Space
Authors: Seybert A. F. , Soenarko B.
Published: December 2011

This paper is concerned with the application of the Boundary Integral Equation (BIE) method to acoustic radiation and scattering in a three-dimensional half space. Problems in this class include the radiation of sound from vibrating machines near reflecting surfaces and the scattering of sound from objects in air or water that are in close proximity to rigid or free surfaces. Written in the usual way, the Helmholtz integral formula involves integrations over all surfaces that border the acoustic domain. For half-space problems these integrations include the infinite plane that forms the half-space boundary. For half-space radiation and scattering problems, it is shown that the integrals on the infinite plane may be removed by using a modified Green’s function in the Helmholtz integral. Thus, all element discretization and numerical approximation are confined to the body or obstacle. This feature simplifies the engineering effort required to set up a problem and improves the accuracy of the results. Gone also is the question of where to terminate the discretization of the infinite plane. Examples of radiation and scattering near a rigid boundary are used as illustration of the method.
Coupled Longitudinal and Bending Vibrations of a Cracked Shaft
Authors: Papadopoulos C. A. , Dimarogonas A. D.
Published: December 2011

This paper describes the coupling of bending and longitudinal vibration of a stationary cracked shaft with an open crack. The crack is modeled by way of a 2×2 local flexibility matrix with coupling terms. The elements of this matrix are obtained analytically. One of the elements compares well with experimental data of other investigators. The free vibration of the shaft, and the influence of the crack on the vibrational behavior of the shaft is studied. The relation of the eigenvalues of the system and the crack depth as functions of the slenderness ratio are presented. The forced vibration of the shaft is also studied and the coupling of the vibration modes is verified analytically and experimentally. The applicability of the method as a crack identification tool is demonstrated.
Diagnosing Vibration Problems in Vertically Mounted Pumps
Authors: Walter T. J. , Marchione M. M. , Shugars H. G.
Published: December 2011

This paper summarizes several recent efforts to develop and implement techniques to monitor and diagnose problems in submerged shaft vertical pumps. Projects based on iterative analytical and experimental efforts were implemented on several different types of vertical pumps typically found in power plants. This paper describes both the modeling and monitoring portions of these projects, including the “lessons learned” in studying six vertically mounted pumps in operational power plants.
Evaluation of Aerodynamic Instability Mechanisms for Centrifugal Compressors—Part I: Current Theory
Authors: Kirk R. G.
Published: December 2011

Current theories of calculating levels of aerodynamic excitation are reviewed and methods of applying these results to actual compressor designs are discussed in detail. Comparison of compressor stability for approximate modal aerodynamic excitation influence to published equations for static labyrinth seal cross-coupled stiffness is made to illustrate the influence of system damping on compressor stability. The results of analysis for six operating machines are presented to give further justification for the selection of the aerodynamic excitation model.
Asymptotic Modal Analysis and Statistical Energy Analysis of an Acoustic Cavity
Authors: Kubota Y. , Dionne H. D. , Dowell E. H.
Published: December 2011

One of the outstanding theoretical questions in interior noise is the connection between modal analysis and statistical energy analysis. Recently substantial progress has been made in understanding this connection for structural vibrations including both fundamental theoretical work and experimental verification. It has been shown that many of the results of Statistical Energy Analysis can be derived as an asymptotic limit of classical modal analysis and thus this approach is called Asymptotic Modal Analysis. The basic asymptotic theory for structural wall-acoustic cavity interaction is described in this paper. Several numerical examples are presented for acoustic cavity response with a prescribed wall motion to illustrate the key results of the theory.
A General Beam Element for Use in Damage Assessment of Complex Structures
Authors: Haisty B. S. , Springer W. T.
Published: December 2011

A general beam element is derived which contains a symmetric discontinuity in the form of a double-sided open crack. The method used to determine the stiffness terms necessary to model the damage present in this element is presented, and it is used to determine several of these stiffness expressions.
Active Electromagnetic Suspension of an Elastic Rotor: Modelling, Control, and Experimental Results
Authors: Salm J. R.
Published: December 2011

Electromagnetic bearings can support a flexible rotor without any contact and simultaneously influence its dynamics. Such an active suspension and vibration control requires closed-loop control of the rotor motions. In practical applications, the design of the controller is based on a simplified reduced-order model of the mechanical system. As a result, one must deal with the reduced-order control problem. A nonexpansive direct output control scheme for mechanical systems with collocated actuators and sensors (“DCD-control”) is presented. This scheme inherently guarantees stability for the real actively controlled system despite reduced-order control effects like spillover. This concept has been experimentally verified through the active suspension of an elastic rotor by means of two digitally controlled, contactless, electromagnetic bearings. Numerical results of the control design procedure and the full-order system behavior are confirmed by measurements in the experimental setup.
On the Dynamic Response of a Helical Geared System Subjected to a Static Transmission Error in the Form of Deterministic and Filtered White Noise Inputs
Authors: Neriya S. V. , Bhat R. B. , Sankar T. S.
Published: December 2011

The vibration of a helical geared shaft system is studied, considering the coupling between the torsional, flexural, rotational (about the diametral axis), and axial motions of the gear carrying shafts. The effects of the nonlinear backlash function and time varying tooth stiffness are also considered. The excitation to the geared shaft system is in the form of a static transmission error which has deterministic and filtered white noise components. The equations of motion are formulated in state space form and solved using matrix exponential approach. Piecewise linearization is used in the simulation and results for the mean and variance of the dynamic response are presented.
On the Transient Analysis of Rotor-Bearing Systems
Authors: Subbiah R. , Rieger N. F.
Published: December 2011

The transient dynamic response of a flexible rotor in nonlinear supports has been investigated using time marching methods. Several marching techniques such as Newmark β, Wilson θ, and Houbolt have been utilized in this study of rotor-bearing dynamic systems, to examine the stability of the system, and the suitability of each technique for predicting the onset of instability. The given rotor system has been modeled both in space and time using the transfer matrix method and the Houbolt method. The transient orbital response data so obtained have been compared with those obtained by a finite element model. Differences in the order of 6 percent were found. A nonlinear representation of a finite bearing has been included in the transient matrix model and the stability characteristics of different rotor systems of varied complexity have been studied. The nonlinear results have been compared with earlier results obtained using linear bearing representations.
A Vibration Diagnosis Approach to Structural Fault
Authors: Gu Song-Nian , Zhang Jian-Lin , Jiang Jie-Sheng , He Cheng-An
Published: December 2011

In this paper the sensitivity of structural vibration parameters to fault is analyzed. The frequency response function, which is sensitive to structural fault and able to reflect structural dynamical properties, is chosen as a parameter for fault diagnosis. The least square identification method, Kalman filtering method, and the adaptive filtering method are adopted to diagnose structural fault. The results of simulation tests show the diagnosis approaches presented in the paper are feasible and accurate. The model testing results indicate that the structural fault can be detected even when the model stiffness is reduced to a rate of 5 percent.
Mount Stiffnesses and Inertia Properties from Modal Test Data
Authors: Conti P. , Bretl J.
Published: December 2011

A new method for determining an analytical model of a rigid body on mounts is presented. The method uses experimental data from a modal test as input. The output is rigid body mass properties and the stiffnesses of the mounts. The theory behind the method is discussed in detail and a case history is documented.
Unbalance Response of Flexible Rotors Coupled With Torsion
Authors: Diken H. , Tadjbakhsh I. G.
Published: December 2011

The effect of coupling with torsion on the unbalance response of flexible rotors, supported by isotropic flexible and damped bearings is investigated. Flexural vibrations of the shaft-disk system are coupled with torsional oscillations through mass eccentricity. The governing equations of motion of the continuous system are solved numerically with a modified Myklestad-Prohl method without the necessity of considering an equivalent lumped system. The cases of constant or harmonic torque applied to the disk are considered. Gyroscopic, rotary inertia, shear deformation, external and internal damping effects are taken into account.
On the Dynamic Analysis of a Rigid Rotor-Gear Pair-Hydrodynamic Bearing System
Authors: Kishor B. , Gupta S. K.
Published: December 2011

This paper is an attempt to provide a dynamic analysis of a rigid rotor-gear pair-hydrodynamic bearing system with journal motions in the oil film space of the bearings. A mathematical model has been developed considering the kinematics of the gear pair as affected by journal motions and using a concept of an instantaneous line of action. Effects of bearing parameters on dynamic tooth loads have been studied. The load-speed environment of hydrodynamic bearings supporting the geared rotors is shown to be affected by journal motions in bearings. Results indicate that, for the given gear pair and the given static load-speed conditions, dynamic increments in gear tooth loads and bearing loads vary with bearing parameters (viz. clearances and oil viscosities).
Dynamic Sensitivity of Structures to Cracks
Authors: Chondros T. G. , Dimarogonas A. D.
Published: December 2011

Cracks that develop on machine members and structures influence their dynamic behavior. The Rayleigh principle is used for an estimation of the change in the natural frequencies and modes of vibation of the structure if the crack geometry is known, assuming that the eigenvalue problem for the uncracked structure has been solved in advance. The method reduces the computational effort needed for the full eigensolution of cracked structures and gives acceptable accuracy. It can be extended to higher modes and to decompose degenerate modes found in symmetric structures. To demonstrate the change in the dynamic behavior of linear structures with the crack depth, a cylindrical shaft and a plane frame consisting of prismatic bars were analyzed for dynamic sensitivity to surface cracks.
Practical Implementation Issues for Active Control of Large Flexible Structures
Authors: Zimmerman D. C. , Cudney H. H.
Published: December 2011

Most active control strategies, whether designed in the discrete or continuous domain, will most likely be implemented using a digital control system. Therefore, it is important to study the effects of digital implementation on the desired control law. In this work, the effect of quantization due to the finite wordlength of microprocessors, analog-to-digital, and digital-to-analog converters, on the desired control law is investigated. Additionally, the practical effect of actuator dynamics on the stability and performance of the control law is addressed. Finally, an active control experiment is reported on which takes into account and demonstrates some of these practical considerations.
The Influence of Geometric and Material Design Variables on the Free Vibration of Thin-Walled Composite Material Beams
Authors: Bank L. C. , Kao C. H.
Published: December 2011

The natural frequencies and mode shapes of thin-walled beams constructed of walls, or panels, of advanced composite materials depend upon both the geometry of the cross-section and the mechanical properties of the materials used in the panels. A shear deformation beam theory having the form of a Timoshenko beam theory is used to investigate the influence of these design variables. It is found that the maximum stiffness of a particular beam configuration is obtained when the contributions from the bending and shearing modes of deformation are optimized. Results show the influence of shear deformation even in the fundamental mode of vibration. Simply-supported, cantilever and free-free beams of various cross-sectional shapes and materials are analyzed.
A Method for Reasoning by Analogy in Failure Analysis
Authors: Morrill J. P. , Wright D.
Published: December 2011

An artificial intelligence computer program is being developed for automating the analysis of metallurgical failures. The purpose of this expert system is for recognizing modes of failure like stress corrosion and hydrogen embrittlement. We have previously described a method for recognizing mode of failure based on a form of diagnosis or statistical categorization. In this paper, an alternative method is developed for recognizing mode of failure as a means of confirming or disconfirming the conclusions derived by categorizing. This method is a form of reasoning by analogy that recognizes when the current case is similar to some previously encountered case and uses this information to draw conclusions. The expert system is “programmed” by providing a set of correctly solved examples rather than IF-THEN rules. Accuracy of analogical reasoning is found to increase with number of stored examples, and in recognizing modes of failure an error rate as low as 20.7 percent is observed to occur.
Modal Control of Acoustic Plants
Authors: Dohner J. L. , Shoureshi R.
Published: December 2011

This paper produces a three-dimensional closed loop active noise control system using modal control. A state space representation of the acoustic plant was produced and then expanded to include actuator and measurement dynamics. Using this state space model and linear quadratic gaussian control theory, a single input, single output feedback filter was produced by a well-damped system. Experimental results are given. For bandlimited noise excitation, the controller produced satisfactory results.
Calculating the Acoustical Properties of Plane Uniform Constructions
Authors: Byrne K. P.
Published: December 2011

A procedure for calculating the measures of the acoustical performance of a wide range of plane acoustical constructions which are used in buildings and in industry is described. These measures include the sound absorption coefficients, the sound reduction indices, and the sound insertion losses in 1/3 octave bands for a diffuse field incident upon the construction. The calculation procedure exploits the fact that a wide range of architectural and industrial acoustical constructions is formed from relatively few layer types. Common layer types are an impervious sheet, a layer of porous material, and an air-space. These layer types can be used to form absorbers, partitions, and laggings. Formulas which relate the wave impedances and the acoustic pressures on the opposite sides of the various layer types are developed and the method of combining these impedance and pressure formulas so that the appropriate measures of performance of multilayer constructions can be calculated is described. Comparisons between the calculated and the measured performance measures for a number of different constructions are used to demonstrate the value of the procedure.
Dynamic Response of Rotors Using Modal Reduction Techniques
Authors: Subbiah R. , Bhat R. B. , Sankar T. S.
Published: December 2011

A modal reduction technique is discussed and proposed for solving rotor-dynamic problems. The component mode method is used to model a rotor shaft, and the resulting system matrices are reduced in size by considering only the contribution of the more important lower modes. The final system response including the bearing and disk is obtained using complex modal analysis. Since the higher modes do not contribute significantly to the system response, this method is found to be computationally economical. Unbalance response analyses of a simple Jeffcott rotor obtained by experiments are compared with those obtained by the modal reduction technique and show strong agreement.
Dynamic Analysis of Centrifugal Pump Rotors With Fluid-Mechanical Interactions
Authors: Diewald W. , Nordmann R.
Published: December 2011

Calculating bending vibrations of centrifugal pump rotors, stability and unbalance response are of major interest. In order to predict the dynamic behavior accurately, one has to take into account the coupling mechanisms between the vibrating shaft and the surrounding fluid. This paper presents a finite-element procedure which includes the fluid forces arising from journal bearings, seals, balance pistons and impeller interactions to the dynamic calculations of turbopumps. The theoretical background is briefly explained and a simple Jeffcott rotor is used to show several effects of these fluid forces. Finally, a real multistage boiler feed pump is calculated and discussed.
Proposed Solution Methodology for the Dynamically Coupled Nonlinear Geared Rotor Mechanics Equations
Authors: Mitchell L. D. , David J. W.
Published: December 2011

The equations which describe the three-dimensional motion of an unbalanced rigid disk in a shaft system are nonlinear and contain dynamic-coupling terms. Traditionally, investigators have used an order analysis to justify ignoring the nonlinear terms in the equations of motion, producing a set of linear equations. This paper will show that, when gears are included in such a rotor system, the nonlinear dynamic-coupling terms are potentially as large as the linear terms. Because of this, one must attempt to solve the nonlinear rotor mechanics equations. A solution methodology is investigated to obtain approximate steady-state solutions to these equations. As an example of the use of the technique, a simpler set of equations is solved and the results compared to numerical simulations. These equations represent the forced, steady-state response of a spring-supported pendulum. These equations were chosen because they contain the type of nonlinear terms found in the dynamically-coupled nonlinear rotor equations. The numerical simulations indicate this method is reasonably accurate even when the nonlinearities are large.
Identifying Inefficiencies in Unsteady Pin Fin Heat Transfer Using Orthogonal Decomposition
Authors: Schwänen Markus , Duggleby Andrew
Published: December 2011

Internal cooling of the trailing edge region in a gas turbine blade is typically achieved with an array of pin fins. In order to better understand the effectiveness of this configuration, high performance computations are performed on cylindrical pin fins with a spanwise distance to fin diameter ratio of 2 and height over fin diameter ratio of one. For validation purposes, the flow Reynolds number based on hydraulic channel diameter and bulk velocity (Re = 12,800) was set to match experiments available in the open literature. Simulations included a URANS and LES on a single row of pin fins where the URANS domain was 1 pin wide versus the LES with 3 pins. The resulting time-dependent flow field was analyzed using a variation of bi-orthogonal decomposition (BOD), where the correlation matrices were built using the internal energy in addition to the three velocity components. This enables a detailed comparison of URANS and LES to assess the URANS modeling assumptions as well as a flow decomposition with respect to the flow structure’s influence on surface heat transfer. This analysis shows low order modes which do not contribute to turbulent heat flux, but instead increase the heat exchanger’s global inefficiency. In the URANS study, the forth mode showed the first nonzero temperature basis function, which means that a considerable amount of energy is contained in flow structures that do not contribute to increasing endwall heat transfer. In the LES, the first non zero temperature basis function was the seventh mode. Both orthogonal basis function sets were evaluated with respect to each mode’s contribution to turbulent heat exchange with the surface. This analysis showed that there exists one distinct, high energy mode that contributes to wall heat flux, whereas all others do not. Modifying this mode could potentially be used to improve the heat exchanger’s efficiency with respect to pressure loss.