bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis and Results of an SCS-6/Ti-15-3 MMC Reinforced Ring Structure Under Internal Radial Loading
Authors: Gravett Phillip W. , deLaneuville Robert E.
Published: March 2021

This paper presents a stress analysis method and test results of a ring structure reinforced with SCS-6/Ti-15-3 MMC under an applied internal radial load. To assess the structural integrity of an MMC reinforced component, the state of stress within the component must be determined. Two major factors complicating the state of stress in the given MMC reinforced rings are the stress concentrations caused by the load fixture and the thermal residual stresses induced during processing. To model the stress concentrations, the ring and its load fixture were modeled as a 3-d solid finite element model. To calculate the processing residual stresses, a 2-d axisymetric finite element thermal stress analysis was completed. Plasticity was modeled with the 2-d axisymetric finite element model accounting for the nonlinear response of the MMC core and monolithic sheath. Testing of the rings at room and high temperature showed good correlation to load-deflection calculations while ultimate strength was far less than predicted. Subsequent post failure analysis revealed preexisting damage within the MMC which was not detected by pretest NDE inspections. This damage did not significantly affect the measured stiffness of the ring, but diminished the ultimate strength by reducing the capability of the MMC in a localized area.
Long Duration, High Temperature Creep/Relaxation Data for Near Eutectic Pb-Sn Solder
Authors: Mason Jerry , Caroselli Rom , Russell Stan
Published: March 2021

A model for solder behavior based on nonlinear dynamics has been developed by the authors (1990–1992). Supporting this study, data have been collected for near eutectic Pb-Sn solder joints using a ring and plug geometry which has been subjected to isothermal (80°C, 120°C) creep/relaxation loading ranging over a period of time up to 260 hours. Four types of relaxation data were observed: (1) smooth, low rate of unloading, (2) smooth, high rate of unloading, (3) onset of unstable racheting, and (4) onset of unstable, irregular unloading. Types (1) and (2) appear to be related to grain boundary and matrix creep, respectively. These are two creep mechanisms which have been reported in the literature. As far as we are aware, types (3) and (4) have not been previously reported by other investigators in terms related to solder instability. Therefore, our purpose is to document, in some detail, conditions under which unstable behavior has been observed. A detailed discussion is made of variables which control and measure instability including loading, fixture load cell stiffness and material type, and checks of instrumentation accuracy. This paper reports details of the experimental study regarding test specimens, test fixture, instrumentation and calibration, and environmental control. This paper provides a summary of data collection.
Microstructurally Based Thermomechanical Fatigue Lifetime Model of Solder Joints for Electronic Applications
Authors: Frear D. R. , Rashid M. M. , Burchett S. N.
Published: March 2021

We present a new methodology for predicting the fatigue life of solder joints for electronics applications. This approach involves the integration of experimental and computational techniques. The first stage involves correlating the manufacturing and processing parameters with the starting microstructure of the solder joint. The second stage involves a series of experiments that characterize the evolution of the microstructure during thermal cycling. The third stage consists of a computer modeling and simulation effort that utilizes the starting microstructure and experimental data to produce a reliability prediction of the solder joint. This approach is an improvement over current methodologies because it incorporates the micro-structure and properties of the solder directly into the model and allows these properties to evolve as the microstructure changes during fatigue.
MMC Ring Fatigue and Fracture Life Prediction: An Engineering Model
Authors: Halford Gary R.
Published: March 2021

The framework of an engineering creep-fatigue durability model has been adapted for use in estimating the radial static burst pressure and cyclic low-cycle fatigue macro-crack initiation resistance of continuous fiber reinforced (CFR) metal matrix composite (MMC) rings for application at 800 °F. Rings of circumfrentially wrapped SCS6/Ti-15-3 were manufactured by Textron Specialty Metals and burst tested by Pratt & Whitney as a part of a cooperative program with the NASA Lewis Research Center. Fatigue tests have as yet to be performed. The engineering model is based on a 3-D elasto-plastic micromechanics analysis of the tensile-loaded composite architecture. Use is made of the rule of mixtures, strain compatibility, equilibrium, and the stress-strain relationships of the constituents. Knowledge is required of the mechanical and fatigue properties of the matrix and fibers and how the presence of each affects the sharing of imposed stresses and strains. The model addresses specific issues such as residual fabrication stresses, inelastic deformation within the ductile matrix, multiaxial constraint imposed on the matrix, cyclic relaxation of both residual and applied mean stresses in the matrix, fatigue micro-crack initiation and propagation in the matrix, and tensile fracture of both the ductile matrix and the brittle fibers. In the current application of the model, the specific issues were empirically calibrated through use of tensile and tension-tension fatigue coupons that had been subjected to essentially identical loading as the rings.
Effect of Parameter Optimization of Contact Force Models on the Impact Dynamic Responses
Authors: Lankarani H. M. , Wu F.
Published: March 2021

Reducing the severity of an impact to a structure or a multibody system is a significant aspect of engineering design. This requires the knowledge of variations of the resulting contact forces and also how these contact forces can be reduced. This paper presents an optimization methodology for the selection of proper parameters in the contact/impact force models so as to minimize the maximum value of the contact force. A two-particle model of an impact between two solids is considered, and then generalized to the impact analysis between two bodies of a multibody system. The concept of effective mass is presented in order to compensate for the effect of joint forces or impulses. The system is reduced to a single degree-of-freedom mass-spring-damper vibro-impact system. A single differential equation of motion in the direction of relative indentation of local contact surfaces is derived. Different contact force models of hysteresis form including linear and nonlinear models are described. An optimization problem is then formulated and solved by using the method of modified feasible direction for constrained minimization. A numerical integrator is used at every design iteration to obtain the system dynamic response for a given set of design variables. The objective function is to minimize the peak acceleration of the system equivalent mass resulting from the contact force. Comparison of the system with optimal parameters and non-optimal one shows that the peak contact force is greatly reduced for the optimal one. Since these parameters reflect the material properties (stiffness and damping) of the impacting bodies or surfaces, suitable materials may then be selected based upon the information provided by this optimization procedure. It is observed that the materials, which have good crashworthiness properties should posses capability of dissipating impact energy both in the forms of permanent indentation and internal damping friction. Based upon the analysis of the impact responses, mechanism of energy dissipation, and the typical force-indentation diagram for the high energy absorption materials obtained from experiments, a new contact force model is proposed which could precisely describe the impact response of high energy-absorption materials.
Recent Developments on Nonstationary Parametric Responses of Rectangular Plates
Authors: Ostlguy Germain L. , Lavigne Patrice
Published: March 2021

The non-stationary parametric response of a rectangular plate during a logarithmic sweep of the excitation frequency through a system resonance is studied using five different techniques of solution. Considering only the case of principal parametric resonance, the continuous system is spatially discretized by means of a single-term modal approximation for the lateral displacement. The general form of the resulting nonlinear temporal equation of motion for the damped parametric vibrations in any spatial mode is analyzed using the multiple time scales method and the method of asymptotic series expansion developed by Mitropolsky, in the first and second approximation. The non-stationary response of the plate during transition through parametric resonances is also evaluated by direct integration of the temporal equation of motion and the results obtained by the different techniques are compared. The non-stationary response displays several phenomena depending on the conditions of in-plane loading, the amount of damping, the initial conditions, and the rate as well as the direction of the sweep. The validity of these results is ascertained experimentally.
Numerical Simulation of Multibody Systems With Time Dependant Structure
Authors: Joli Pierre , Pascal Madeleine , Gibert René
Published: March 2021

Current dynamic simulation programs are able to calculate the continuous motions of articulated systems or more general systems of rigid bodies in the absence of contact between members of the system or between the system and its environment. Some are able to simulate the effects of isolated contacts and impacts but none are able to simulate the motion with unrestricted multiple concurrent contacts.

However, in special robotic programs such as robots performing assembly tasks or walking, it would be very interesting to simulate appropriate commands before implementing them on the robots.

This paper develops intrinsic problems of collision to produce an efficient computational algorithm. This algorithm handles the detection of collision in three dimensions, the reduction of the integration step in order to avoid interpenetration between the bodies before impact, the jump velocity caused by a new collision and indicator magnitudes which determine the addition or deletion of constraints.
An Experimental Study of Bifurcation and Chaos in a Dynamically-Buckled Magneto-Elastic System
Authors: Cusumano J. P. , Sharkady M. T.
Published: March 2021

Results are presented from an experimental study of the dynamics of a lightly-damped, flexible beam which is buckled and unbuckled magnetically. The system is parametrically excited by driving an electromagnet with a low-frequency sine wave. For voltage amplitudes in excess of the static bifurcation value, the beam will slowly switch between the one and two-well configurations. Experimental static and dynamic bifurcation results are presented. Poincaré sections of a chaotic steady-state are obtained for various values of the driving phase, and the correlation dimension of the chaotic attractor is estimated. Singular system analysis is used to demonstrate the effect of delay time on the noise level in delay-reconstructions, and to provide an independent check on the dimension estimate by directly estimating the number of independent coordinates from time series data.
Identification of Parameters for a Vehicle Submitted to a Crash
Authors: Boneill C. , Mizzi J. P.
Published: March 2021

The mathematical modelling of a vehicle when it is driving into a fixed or deformable barrier or into another vehicle must allow to reproduce the deceleration field inside it and its structural and kinematic behaviour. Although a detailed view can be obtained using finite element modelling, the more global multibody approach has the advantage of requiring considerably lower computing costs, and therefore of studying quickly the behaviour for many input data.

The main difficulty in executing the above procedure is to determine the laws governing the behaviour of the deformable links. These can first be estimated either by finite element calculations, or by static or dynamic tests. This approach can be improved using an identification methodology, provided that the kinematics in a crash trial is well known.

A non parametric identification method has been considered. But the results have not been satisfactory enough.

Conversely, if an initial estimate of the set of parameters is available, a parametric identification can be preferred. Several have been tested. Once their respective stability and strength had been determined on one-dimensional test models with one and two degrees of freedom. Predictivity and reliability trials in the presence of noisy data have been envisaged. The results have permitted to highlight which is the best adapted to solve the problem.

We have applied the chosen approach in the case of the impact of guided vehicles (the TGV Atlantic high-speed “bullet” train) and road vehicles.
Flexural-Torsional Response of a Cracked Rotating Shaft With a Disk During Passage Through a Critical Speed
Authors: Suherman Surjani , Plaut Raymond H.
Published: March 2021

The nonstationary behavior of a cracked rotating shaft with a disk is analyzed. The shaft is accelerated or decelerated through a critical speed, and both flexural and torsional responses are examined. A breathing crack is considered, which is either completely open or completely closed at any given time. Forces due to eccentricity, gravity, and internal and external damping are included. Galerkin’s method is utilized, and the resulting bilinear equations are integrated numerically. The effects of acceleration and deceleration rate, internal and external damping, crack location and depth, and location, mass, and eccentricity of the disk are investigated. Application of the results to detection of cracks is discussed.
Prediction of the Dynamic Behavior of Systems Modelled With Periodic Coefficients: Application to Asymmetric Rotors
Authors: Sayettat-Beley Aline , Couderc Phillippe , Ferraris Guy , Lalanne Michel
Published: March 2021

This work is concerned with rotors having unequal area moments of inertia which necessarily lead to equations with periodic coefficients when the bearings are asymmetric. Following a study of the main phenomena and responses to classical forces on simple models, stability and unbalance response of a large finite element model are considered using a pseudo-modal technique and Floquet theory. Results obtained are satisfactory and show that the method is effective in accurately predicting the dynamic behavior of asymmetric rotors modelled with a significant number of degrees of freedom.
Liapunov-Floquet Transformation: Computation and Applications to Periodic Systems
Authors: Pandiyan R. , Bibb J. S. , Sinha S. C.
Published: March 2021

In this paper, a new analysis technique in the study of dynamical systems with periodically varying parameters is presented. The method is based on the fact that all linear periodic systems can be replaced by similar linear time-invariant systems through a suitable periodic transformation known as the Liapunov-Floquet (L-F) transformation. A general technique for the computation of the L-F transformation matrices is suggested. In this procedure, the state vector and the periodic matrix of the linear system equations are expanded in terms of the shifted Chebyshev polynomials over the principal period. Such an expansion reduces the original differential problem to a set of linear algebraic equations from which the state transition matrix (STM) can be constructed over the period in closed form. Application of Floquet theory and eigen analysis to the resulting STM yields the L-F transformation matrix in a form suitable for algebraic manipulations. The utility of the L-F transformation in obtaining solutions of both linear and nonlinear dynamical systems with periodic coefficients is demonstrated. It is shown that the application of L-F transformation to free and harmonically forced linear periodic system directly provides the conditions for internal and combination resonances and external resonances, respectively. The application of L-F transformation to quasilinear periodic systems provides a dynamically similar quasilinear systems whose linear parts are time-invariant and the solutions of such systems can be obtained through an application of the time-dependent normal form theory. These solutions can be transformed back to the original coordinates using the inverse L-F transformation. Two dynamical systems, namely, a commutative system and a Mathieu type equation are considered to demonstrate the effectiveness of the method. It is shown that the present technique is virtually free from the small parameter restriction unlike averaging and perturbation procedures and can be used even for those systems for which the generating solutions do not exist in the classical sense. The results obtained from the proposed technique are compared with those obtained using the perturbation method and numerical solutions computed via a Runge-Kutta type algorithm. The technique is found to be very powerful in the analysis of linear and nonlinear periodic dynamical systems.
A Stability Criterion for the Mathieu-Hill Equation
Authors: Bhattacharyya Ranjan
Published: March 2021

A criterion for the stability of the solutions of the Mathieu-Hill equation containing even periodic potential is developed. The criterion is based on a result derived by Hill relating the infinite determinant, the Floquet exponent, and the constant term of the even Fourier series expansion of the potential function. It is shown that the criterion is easy to apply in practical problems to obtain stability maps in a suitable parametric plane. In the special case of the Mathieu equation, the criterion is applied to generate the stability maps that compare fairly well with those obtained by other well-known, but more tedious methods. A qualitative relation between the stable and unstable regions of the stability map and the infinite determinant is also provided. In another example, the problem of undamped, finite uniaxial vibrations coupled with a superimposed small twisting oscillation of a rigid disk attached to a hyperelastic neo-Hookean shaft is briefly discussed to bring out the usefulness of the criterion when applied to problems of engineering interest. It is found that the stability of small twisting motion is governed by the Mathieu-Hill equation containing an even periodic potential. Use of the criterion is made to generate the stability maps in a relevant parametric plane. This stability chart can be directly used in designing such a shaft-disc assembly to avoid undue high amplitude torsional vibration.
Transient Vibrations of Nonlinear Systems: Global Dynamics and Chaotic Transients
Authors: Soliman Mohamed S.
Published: March 2021

In this paper a new approach in the global transient analysis of nonlinear systems is presented; it has the advantages of being conceptually simpler and at the same time more relevant than one based soley on a stability analysis of the steady-state motions. We address the problem of analysing the global transient stability of nonlinear systems in terms of basins of attraction. We show that at a forcing level that is considerably smaller than that at which the steady state attractor loses its stability, there may exist a rapid erosion and stratification of the basin, signifying a global loss of engineering integrity of the system. This conclusion is reinforced by the fact that basin boundaries can become fractal, resulting in chaotic transients, adding a new degree of uncertainty in the response.

The techniques developed are then applied to a ship roll model with cubic and quintic nonlinearities as well as linear plus cubic damping characteristics.
Nonlinear, Damped Vibrations of Sandwich Plates With Time-Dependent Temperature
Authors: Lukasiewicz S. , Xia Z. Q.
Published: March 2021

The paper studies the effect of the rapid change of temperature on the vibrations of simply supported sandwich plates. It has been taken into consideration that the properties of the facings and of the core of the sandwich plate materials change with the change of the temperature. The effects of the viscoelastic damping and geometrical nonlinearities on the behaviour of the plate have also been included. It was found that the rapid change of temperature affects the amplitude and frequency of the vibrations.
Passive Control in Mobile Robots via Suspension Design
Authors: Wiens Gloria J. , Tsai Hungder
Published: March 2021

In this paper, the role of dynamic coupling effects in mobile robotic systems is investigated. For this study, the equations of motion for a rigid-body model of a single-linked mobile robot are derived using Lagrangian dynamics. As possible passive control elements, various spring-damper combinations for the vehicle’s suspension system are applied to the model. Analysis and design of the passive controller is executed with implementation of a computer simulation based algorithm and performance measures. The algorithm is based on the differences between the coupled and decoupled models of the mobile robotic system. The decoupled model is one in which the mobile robot is modeled as two isolated subsystems, arm and vehicle. Subsequent to the computer simulation, the appropriate passive control elements and system parameters and trajectory selections for the elimination of the instability and inaccuracies due to dynamic coupling are recommended. Via this approach in reducing the dynamic coupling effects, it is predicted that the system’s existing active controller will be able to more effectively control the system at much higher speeds and for a larger number of applications than before. That is, the arm will not have to be held stationary while the vehicle is moving or vice versa.
Computer Simulation of Dynamical Behavior of Self-Propelled Gurney
Authors: Szydlowski Wieslaw M. , Sastry Srinivas
Published: March 2021

The conventional gurneys used in hospitals to move patients from room to room have one main disadvantage: they are difficult to control. A typical gurney has a form of an oblong table moving on four castor wheels. The vehicle is difficult to maneuver, especially on corridor turns, and usually requires two operators — each at one end.

Dr. J. Bleicher from the St. Joseph’s Hospital in Omaha, Nebraska suggested a new type of a self-propelled gurney which would be a cross-breed of a motorized wheelchair and a gurney.

A new type of a gurney would have two additional wheels in the center of the gurney, each connected to a separate DC motor. The torques developed by the motors would be controlled by one operator using a joystick. Applying opposite torques to the controlled wheels would rotate a stationary gurney in place, or would curve the path of a moving gurney.

The position of two additional wheels can be changed, so that the gurney can move sideways, translate in chosen direction or move along a curvelinear path.

The work presented in the paper contains an analysis of the dynamics of such a gurney. A mathematical model of the vehicle was developed to check how much effort is needed on the part of the operator in straight path motion and during negotiating a corner.

The most difficult part of the modelling was a proper description of forces and torques exerted by the ground on the wheels.

The differential equations of motion of the gurney have been numerically integrated, and the dynamical response of the vehicle studied. The results of the computer simulation show a transient oscillatory response of the castor wheels (shimmying) which can be controlled by a proper choice of design parameters of the vehicle.
Generation of Motion Equations for a Tree-Like System of Granular Bodies
Authors: Vinogradov Oleg
Published: March 2021

An arbitrary system of 3D-bodies made out of rigid spheres and arranged topologically in a tree is considered. For such a system explicit expressions for the equations of motion are derived based on the Lagrangian approach. The equations are given in terms of the path matrix characterizing the topological tree. The analytical method of generation of equations of motion makes the computer simulation of the nonsteady motion of the discrete system of bodies more efficient in term of both computer time and accuracy. It is achieved by avoiding operations with large sparse matrices (if the equations were generated numerically) and by cancelling out some terms in Lagrange’s equations analytically.
Intelligent Constrained Layer: An Innovative Approach
Authors: Shen I. Y.
Published: March 2021

This paper is to propose an innovative damping design termed intelligent constrained layer (ICL). This technique integrates active and passive dampings through constrained layer treatments to enhance system reliability and to provide adjustable damping. The proposed ICL damping design consists of a viscoelastic shear layer sandwiched between a piezoelectric constraining cover sheet and the structure to be dampened. According to measured vibration response of the structure, a feedback controller regulates axial deformation of the piezoelectric layer to perform active vibration control. In the meantime, the viscoelastic shear layer provides additional passive damping. The active damping component of this design will produce adjustable and significant damping. The passive damping component of this design will increase gain and phase margins, eliminate spillover, reduce power consumption, improve robustness and reliability of the system, and reduce vibration response at high frequency ranges where active damping is difficult to implement. To model the dynamics of ICL, an eighth-order differential equation governing bending vibration of an elastic beam with the ICL treatment is first derived. Then an ICL treatment using an idealized, distributed sensor and a proportional-plus-derivative feedback controller is illustrated on a semi-infinite elastic beam subjected to standing wave excitations. Numerical results show that ICL will produce significant damping. The allowable deflection slope of the beam in order not to saturate the piezoelectric layer is also calculated.
Localization of Helical Flexural Waves on an Irregular Cylindrical Shell
Authors: Photiadis Douglas M.
Published: March 2021

Small amounts of irregularity are known to produce vibration localization in one-dimensional chains, but the effects on two and three dimensional systems are typically much weaker. We have considered a system with both one and two dimensional aspects, an axisymmetric, irregularly ribbed fluid-loaded cylindrical shell. A new formulation of this problem is given and each mode of the system is shown to be approximately equivilent to a nearest neighbor coupled chain with six degrees of freedom — corresponding to three left going and three right going traveling waves. Using these results all the azimuthal modes have been shown to be localized simultaneously and thus vibrational energy on an irregular cylindrical shell is Anderson localized. The slow flexural waves have been shown to localize separately from the fast waves provided the helical angle of the flexural wave is greater than about Ω1/25°, and for smaller helical angles, exponential localization is expected for distances less than a critical wave mixing length. Our results indicate that strong localization effects occur for the helical flexural waves yielding very short localization lengths of order a single rib spacing.
Formulation of Multiple Belt System and its Dynamic Analysis
Authors: Iwatsubo Takuzo , Arii Shiro , Hasegawa Kei , Shiohata Koki
Published: March 2021

This paper presents a method for analyzing the dynamic characteristics of driving systems consisting of multiple belts and pulleys. First, the algorithm which derives the linear equations of motion of arbitrary multi-coupled belt systems is shown. Secondly, by using the algorithm, the computer program which formulates the equations of motion and calculates the transient responses of the belt system is presented. The fundamental idea of the algorithm is as follows: Complicated belt systems consisting of multiple belts and pulleys are regarded as combinations of simple belt systems consisting of a single belt and some pulleys. Therefore, the equations of motion of the belt systems can be derived by the superposition of the equations of motion of the simple belt systems. By means of this method, the responses of arbitrary multi-coupled belt systems can be calculated. Finally, to verify the usefulness of this method, the simulation results are compared with the experimental results.
Rotor Whirl Forces Induced by the Tip Clearance Effect in Axial Flow Compressors
Authors: Ehrich Fredric
Published: March 2021

It is now widely recognized that destabilizing forces, tending to generate forward rotor whirl, are generated in axial flow turbines as a result of the non-uniform torque induced by the non-uniform tip-clearance in a deflected rotor — the so called Thomas/Alford force (Thomas, 1958 and Alford, 1965). It is also recognized that there will be a similar effect in axial flow compressors, but qualitative considerations cannot definitively establish the magnitude or even the direction of the induced whirling forces — that is, if they will tend to forward or backward whirl.

Applying a “parallel compressor” model to simulate the operation of a compressor rotor deflected radially in its clearance, it is possible to derive a quantitative estimate of the proportionality factor β which relates the Thomas/Alford force in axial flow compressors (i.e., the tangential force generated by a radial deflection of the rotor) to the torque level in the compressor. The analysis makes use of experimental data from the GE Aircraft Engines Low Speed Research Compressor facility comparing the performance of three different axial flow compressors, each with four stages (typical of a mid-block of an aircraft gas turbine compressor) at two different clearances (expressed as a percent of blade length) — CL/L = 1.4% and CL/L = 2.8%.

It is found that the value of β is in the range of +0.27 to −0.71 in the vicinity of the stages’ nominal operating line and +0.08 to −1.25 in the vicinity of the stages’ operation at peak efficiency. The value of β reaches a level of between −1.16 and −3.36 as the compressor is operated near its stalled condition. The final result bears a very strong resemblance to the correlation obtained by improvising a normalization of the experimental data of Vance and Laudadio (1984) and a generic relationship to the analytic results of Colding-Jorgensen (1990).
Improved Rotordynamic Unbalance Response Calculations Using the Polynomial Method
Authors: Murphy Brian T.
Published: March 2021

For rotordynamic calculations the conventional transfer matrix (CTM) method is known for its ease of application and speed of execution. This is true for eigenvalue analyses as well as forced response calculations. In 1983, Murphy and Vance significantly improved the conventional transfer matrix method for eigenvalues by developing Polynomial Transfer Matrix (PTM) method. For eigenvalue calculations this resulted in one to two orders of magnitude increase in calculation speed, and eigenvalues could be found without missing any modes. This paper extends the polynomial method to forced response calculations. The polynomial method “compiles” a polynomial representation of a rotor bearing system. Responses at many frequency increments can then be computed with amazing rapidity. Similar to the case of eigenvalue calculations, an automatic dynamic condensation feature helps the PTM attain nearly a tenfold increase in speed over the CTM method. This paper details the polynomial method applied to forced response calculations. Two example calculations are presented to compare the PTM to the CTM method and finite element method. All computations were carried out on an IBM-PC compatible computer.
A Theoretical and Experimental Investigation of a Gas Operated Bearing Damper for Turbomachinery: Part I — Theoretical Model and Predictions
Authors: Sundararajan Padmanabhan , Vance John M.
Published: March 2021

This is the first (Part I) of two papers describing recent results of a research program directed at developing a vibration damper suitable for high temperature turbomachinery applications. It is expected that such dampers will replace squeeze-film dampers that use oil as the working fluid and have limitations at higher temperatures. A novel gas operated bearing damper has been analytically and experimentally evaluated for its damping characteristics. Theory that is based on the isentropic assumptions predicts the damper performance characteristics reasonably well. A maximum damping level of 13.2 lb-s/in at a frequency of 100 hz was measured with a single actuator of the gas damper and, since many such actuators can be placed circumferentially around the squirrel cage, considerable damping levels can be realized. The study also shows that significantly higher damping levels can be achieved by modifying the current design.

Part I describes the theoretical model that has been developed based on isentropic assumptions. This model is an improved version of the previous theory [1,2] and includes the supply groove effects, dynamic area changes of the inlet feeding holes and the effects of flow choking on damper behavior. The governing equations are derived and theoretical predictions using these equations have been made for the three hardwares that were experimentally investigated (see Part II).
Asymmetrical Rolling and Self Excited Vibrations in a Hot Roughing Mill
Authors: Jafari A. A. , Tieu A. K. , Basu A.
Published: March 2021

This paper discusses the simulation of self excited torsional vibration of rolling mill drives and vertical vibration of a Horizontal Mill taking into account asymmetrical rolling. The influence of the mass, rigidity and damping of the hot steel slab have been considered in the simulation of asymmetrical self excited vibrations.
Isotropic Control of Rotor Bearing System
Authors: Kim Cheol-Soon , Lee Chong-Won
Published: March 2021

A new rotor control scheme, the isotropic control of anisotropic rotor bearing system in complex state space, is proposed, which utilizes the concepts on the eigenstructure of the isotropic rotor system. Then the control scheme is applied to an active magnetic bearing system and the control performance is investigated in relation to control energy, transient response, and unbalance response. In particular, it is shown that the proposed method is efficient for control of unbalance response.
An Integrated Approach Toward the Dynamic Analysis of High-Speed Spindles: Part II — Dynamics Under Moving End Load
Authors: Chen C. H. , Wang K. W.
Published: March 2021

This paper presents an integrated study of a rotor/bearing structure, with specific interests toward high speed spindle systems under rotating end loads. Considering the coupling between the rotating shaft and the nonlinear bearings, an iterative method is developed to derive the system equilibrium configuration for given operating conditions. With moving end loads, structural instability caused by high rotational speed is analyzed. The critical speeds and unstable speed regions are discussed. Machining chatter instability lobes are also derived using the spindle model. It is shown that significant errors will occur in predicting spindle characteristics and stability if the speed and load effects on the shaft/bearing dynamics are neglected.
Transfer Function Analysis of Non-Uniformly Distributed Parameter Systems
Authors: Yang Bingen , Fang Houfei
Published: March 2021

This paper studies a transfer function formulation for general one-dimensional, non-uniformly distributed systems subject to arbitrary boundary conditions and external disturbances. The purpose is to provide an useful alternative for modeling and analysis of distributed parameter systems. In the development, the system equations of the non-uniform system are cast into a state space form in the Laplace transform domain. The system response and distributed transfer functions are derived in term of the fundamental matrix of the state space equation. Two approximate methods for evaluating the fundamental matrix are proposed. With the transfer function formulation, various dynamics and control problems for the non-uniformly distributed system can be conveniently addressed. The transfer function analysis is also applied to constrained/combined non-uniformly distributed systems.
Design Optimization of Aircraft Engine-Mount Systems
Authors: Ashrafiuon Hashem
Published: March 2021

Design optimization of aircraft engine-mount systems for vibration isolation is presented. The engine is modeled as a rigid body connected to a flexible base representing the nacelle. The base is modeled with mass and stiffness matrices and structural damping using finite element modeling. The mounts are modeled as three-dimensional springs with hysteresis damping. The objective is to select the stiffness coefficients and orientation angles of the individual mounts to minimize the transmitted forces from the engine to the base. Meanwhile, the mounts have to be stiff enough not allowing engine deflection to exceed its limits under static and low frequency loadings. It is shown that with an optimal system the transmitted forces may be reduced significantly particularly when mount orientation angles are also treated as design variables. The optimization problems are solved using a Constraint Variable Metric approach. The closed form derivatives of the engine vibrational amplitudes with respect to design variables are derived in order to achieve a more effective optimization search technique.
Development of a Recursive Frequency Based Filter With Application to Chatter Control
Authors: Ousterhout Karl B.
Published: March 2021

In most machining processes, large amounts of energy are needed to accomplish the machining operation. When this energy is transmitted through a structure that has minimal damping characteristics, such as a lathe or a milling machine, self sustained oscillations (chatter) can develop. When chatter develops, it can be viewed as a basic performance limitation of the machine tool. In order to suppress the chatter, a real-time controller using digital signal processing techniques has been implemented. This paper discusses a novel way of computing the transfer function of the machine tool-work piece combination and illustrates how a real-time active chatter controller could be designed and integrated into existing machine tools to overcome this performance limitation. Currently, experimental verification of the analytical work is being pursued.
Semiactive Control of Structural Vibrations
Authors: Patten W. N. , Wu H. C. , Yan W. , Sack R. L. , Kuo C. C. , Shen K.
Published: March 2021

Structural control can be used to mitigate dynamic structural response and prevent structures from reaching their limit states. Typical active vibration systems utilize large electric motors, and expensive hydraulic pumping equipment to provide force inputs to a structure during a dynamic event. The work here explores the effectiveness of low power, inexpensive semi-active control hardware to provide vibration attenuation, for structures. While there are a number of electro-mechanical devices that might provide semi-active control forces, the investigation here analyzed the use of an automatically adjustable hydraulic actuator (i.e., a shock absorber). The variation in damping characteristics is accomplished by using variable orificing. While semi-active hydraulic actuators are a relatively cheap means of providing smart damping for a structure, the development of effective closed loop control strategies for these devices is not a completely resolved issue. The paper develops a dynamic model of a semi-active actuator. Two inner loop controllers are then suggested, for the operation of the actuator. The control of a simple structure is then simulated. The paper closes with a comparison of the performances between a semi-active (clipped optimal) control and active control of a three story structure that is subject to an earthquake.
Balancing of High Speed Flexible Overhung Rotor: A Case Study
Authors: Kamala V.
Published: March 2021

This paper presents a case study of balancing a high speed overhung flexible rotor system. The system had several speeds, below the operating speed, where the amplitude of vibration was high. Mode shapes were obtained by measuring amplitude of 1X component and its phase at various locations & balancing was carried out by adding weights in a single plane.
Development of a Houde Damper Using Magnetic Damping
Authors: Kobayashi H. , Aida S.
Published: March 2021

This paper presents experimental results that demonstrate the vibration suppression effectiveness of a Houde damper, a type of dynamic absorber that contains an auxiliary mass and a damping element. The damper that was developed uses an eddy current brake consisting of a pair of permanent magnets and a copper plate which acts as a conductor. A vibration test using a straight piping model was used to show that the Houde damper is effective not only in reducing small amplitude vibrations, but large amplitude vibrations as well. Analytical calculations were used to establish that the precise tuning required for effective vibration suppression using a conventional dynamic absorber (that is, a passively tuned mass damper) is not necessary for the Houde damper.
Reduction of Precision Spindle Vibration by Radial Shear-Layer Damping
Authors: Huang E. E. , Lieu D. K.
Published: March 2021

A damping technique is proposed as a simple method for reducing non-repeatable radial runout (NRR) in magnetic disk file assemblies. Using finite element methods, the behavior of a typical system is investigated using eigenvalue and steady state response analyses to assess the benefits and shortcomings of the proposed technique. Simple impact response experiments are then performed to verify the analytical results. It is seen both in the numerical analysis and experimentation that the overall magnitudes of the radial response can be reduced using the proposed technique, and topics for continued investigation of the subject are discussed.
Free Vibration of Rectangular Membranes With Linearly Varying Tension and Light Flexural Rigidity
Authors: Gorman D. J.
Published: March 2021

The proposal to utilize tensioned rectangular membranes as antennae in interspace communication has resulted in the focus of considerable attention on the free vibration of membranes with complicated in-plane loadings. In this paper the problem of analizing the vibration of a rectangular membrane with linear variation in tension in one direction is examined. This tension variation occurs due to gravitational forces when the membranes are tested experimentally in vibration laboratories. The Rayleigh-Ritz energy method is employed to obtain analytical results. Convergence is found to be rapid. Mode shapes are compared with those of known classical solutions when no tension variation is permitted. Generation of the eigenvalue matrix is demonstrated to be a very simple task.
Measurement of Static and Dynamic Properties of a Tilting Pad Bearing and Comparison With Theory
Authors: Bonner Thomas , Vohr John H.
Published: March 2021

Measurements were made of the static and dynamic properties of a seven inch diameter, four-pad, tilting pad bearing with both centrally pivoted and 60% offset pads. Data was recorded at 1500, 1800 and 3000 RPM and covered a range of Sommerfeld numbers from .055 to .625. Dynamic properties were measured by applying unbalance weights of various magnitudes to the rotor and measuring the synchronous response amplitudes and phase angles. Good agreement was obtained between measured properties and those predicted using linearized stiffness and damping coefficients obtained from isoviscous lubrication theory.
Symmetric Model Correction of Mechanical Systems
Authors: Lam Marca , Inman Daniel J. , Kress Andreas
Published: March 2021

This work examines the model updating problem for simple nonconservative proportionally damped systems. Model correction, also called model updating, refers to the practice of adjusting an analytical model until the model agrees with measured modal data. The specific case examined here assumes that natural frequencies and modal damping ratios are available from vibration tests and that the measured data disagrees in part with the modal data predicted by an analytical model. Most model correction schemes tend to produce updated damping and stiffness matrices which are asymmetric. The simple method presented here focuses on retaining the desired symmetry in the updated model.
Fractal Dimensions in Elastic-Plastic Beam Dynamics
Authors: Symonds P. S. , Lee Jae-Yeong
Published: March 2021

The final midpoint displacement of a two-degree-of-freedom beam model subjected to a short pulse of transverse loading may be either in the direction of the initial impulse or in the opposite (“negative”) direction, when moderately small plastic deformations occur. In the range where chaotic vibrations occur, the result depends with great sensitivity on the impulse magnitude. Considering a pulse of duration 0.5 × 10−3 sec, 100 calculations have been made for pulse forces P starting at 2500 N and increasing by increments of 2.0, 10−2, 10−4, and 10−6 N. It is found that the proportion and distribution of negative final displacements remain, on average, the same, independent of the size of the force increment. A fractal dimension representing a self-similarity property is calculated for the four choices of the force increment, and is found to be approximately 0.78 in each case. A correlation fractal dimension is also computed for undamped responses.
A Case Study on Concurrent Design
Authors: Guo Wei , Cha Jianzhong , Xue Qiang , Si Liming
Published: March 2021

Based on the methodology and theory proposed in (Cha and Guo, 1993) for automated concurrent design process, this paper presents a concrete engineering case practice to illustrate how to establish a descriptive model and a cognitive model for concurrent design process, as well as how to develop a computable model for the computer system to implement the automated concurrent design process. Also, a special emphasis is given to the aspects of management, control and coordination on concurrent design process, which is considered as key techniques for automated concurrent design system.
Issues in Product Life Cycle Engineering Analysis
Authors: Lee David E. , Melkanoff Michel A.
Published: March 2021

Traditional engineering analysis of product designs has focused primarily on a product’s operational performance without considering costs of manufacturing and other stages downstream from design. In contrast, life cycle analysis of a product during its initial development can play a crucial role in determining the product’s overall life cycle cost and useful life span. This paper examines product life cycle engineering analysis - measurement of product operational performance in a life cycle context. Life cycle engineering analysis is thus considered both as an extension of traditional engineering analysis methods and as a subset of a total product life cycle analysis. The issues critical to life cycle engineering analysis are defined and include product life cycle data modeling and analysis, analysis tools and their performance regimes, performance tradeoff measurement and problems of life cycle engineering analysis in an organizational context. Recommendations are provided for future research directions into life cycle engineering analysis in the context of integration architectures for concurrent engineering.