bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling and Analysis of Friction Rim Dampers for Blisks
Authors: Laxalde Denis , Sinou Jean-Jacques , Thouverez Fabrice , Lombard Jean-Pierre
Published: June 2008

A damping strategy for blisks of turbomachinery involving a friction rim is investigated. These rims, located in grooves underside the wheel of the blisks, are held in by centrifugal loads and the energy is dissipated when relative motions between the rim and the disk occur. A method of dynamical analysis of a cyclic blisk nonlinearly coupled with a split rim is presented: the steady-state response being calculated using an multi-harmonic balance method. Numerical simulations on a lumped-parameter model are presented for several damper characteristics and several excitation configurations. From these results, the performance of this damping strategy is discussed and some design guidelines are given. Finally the influence of mistuning on the damping performances is analysed.
Disturbance Attenuation Using Non-Singleton Fuzzy Logic
Authors: Simon Andra´s , Flowers George T.
Published: June 2008

Magnetic bearings are an exciting and innovative technology that has seen considerable advances in recent years. Such systems require active control, and most often, linear techniques are used very successfully. However, there are applications where such methods have limited effectiveness and other control strategies must be considered. Fuzzy logic control performs very well in nonlinear control situations where the plant parameters are either partially or mostly unidentified. Its effectiveness for nonlinear systems also offers advantages to magnetic bearing systems. Little research has been done on non-singleton fuzzy logic systems and their application to noise rejection on magnetic bearings or rotating machinery. Non-singleton fuzzy set inputs allow one to account for input measurement uncertainty. The fuzzy logic controller’s task in this work is two-fold; provide control for stable levitation of the shaft and perform noise filtering to reduce the effects of the disturbance. The current work consist of model development, controller design, simulation and experimental validation. The basic simulation model consist of a horizontal shaft supported by a radial magnetic bearing. The magnetic bearing is modeled as a nonlinear element. The controller designs are implemented and tested using a bench-top rotor rig equipped with a radial magnetic bearing. Some representative results are presented and discussed.
An Energy Analysis of Amplitude Death of a Pair of Oscillators With Delayed Coupling
Authors: Wang Zaihua , Hu Haiyan
Published: June 2008

This paper presents an energy analysis of the amplitude death, a phenomenon that the individual oscillators cease to oscillate when coupled and go to an equilibrium motion instead, of a pair of coupled oscillators with time delay that are slightly perturbed from two undamped oscillators and with delayed coupling. The energy analysis reveals that amplitude death, as well as the stability of the phase-locked periodic solutions, can be justified by the sign of the averaged total powers along a special function with harmonic entries, rather than along arbitrary solution of the coupled oscillators as in the application of the method of Lyapunov’s function for stability analysis. An illustrative example is given to show the effectiveness of the present method.
Simulation Methods for Formable Crust Skins of Digital Clay Human-Computer Interface Devices
Authors: Rosen David , Nguyen Austina
Published: June 2008

Digital clay represents a new type of 3-D human-computer interface device that enables tactile and haptic interactions. The digital clay surface is computer controlled and can be commanded to acquire a wide variety of desired shapes, or be deformed by the user in a manner similar to that of real clay. In this paper, we present one digital clay architecture that utilizes a “formable crust” surface and a set of actuators that can deform the crust according to user manipulations or under computer control. The crust behavior is based on an array of spherical joints. Rather than manufacturing a crust with spherical joints, we propose a crust design with arrays of unit cells that have links and compliant revolute joints that is based on spherical geometry. A series of formable crust models is presented that capture the behavior of the crust when the user is actively forming shapes. Algorithms are presented for computing resultant crust shapes. Simulation results are presented and analyzed. All algorithms have computational complexity that scales with the cube of the number of unit cells in the crust. It is shown that real-time response of a formable crust digital clay device is possible, if simplified models are utilized.
Experimental Investigation of Targeted Energy Transfers in Strongly and Nonlinearly Coupled Oscillators
Authors: McFarland D. M. , Kerschen G. , Kowtko J. J. , Lee Y. S. , Bergman L. A. , Vakakis A. F.
Published: June 2008

The focus of this study is on experimental investigation of the transient dynamics of an impulsively loaded linear oscillator coupled to a light-weight nonlinear energy sink. It is shown that this seemingly simple system exhibits complicated dynamics, including nonlinear beating phenomena and resonance captures. It is also demonstrated that, by facilitating targeted energy transfers to the nonlinear energy sink, a significant portion of the total input energy can be absorbed and dissipated in this oscillator.
Performance Evaluation of Semi-Active Control With Magnetorheological Damper
Authors: Yang Shaopu , Pan Cunzhi , Guo Shuqi
Published: June 2008

In this paper, a test model of a vibration isolation system with magnetorheological (MR) damper is introduced, and a simplified model using the time delay to describe the dynamic process of mechanical response and electromagnetic response for the MR damper is presented. Based on simulation, the performance evaluation with different control strategies, especially, the effects of time delay are investigated. The results show that the performance of the controlled system is highly dependent on the choice of the control strategies, and the effectiveness of semi-active on-off control is significantly determined by the time delay from the command current signal to the magnetic field of the MR damper.
Stabilization and Energy Optimization of a Dynamic Walking Gait Simulation
Authors: Peasgood Michael , McPhee John , Kubica Eric
Published: June 2008

The physiological energy requirements of prosthetic gait in above-knee amputees have been observed to be significantly greater than that for normal healthy gait. Existing models of energy flow during walking, however, have not been very successful in explaining the reasons for this additional energy cost. In this paper, a new method is developed that estimates the physiological cost of walking using a multi-body dynamic model and a muscle stress based estimate of metabolic energy cost. A distinctive feature of the method is a balance controller component that dynamically maintains the stability of the model during the walking simulation. This allows for a forward dynamic analysis of many consecutive steps, and includes the metabolic cost of maintaining balance in the model. An optimization algorithm is then applied to the joint kinematic patterns to find the optimal walking motion for the model. This approach allows the simulation to find the most energy efficient gait for the model, mimicking the natural human tendency to walk with the most efficient stride length and speed. When applied to simulations of both able-bodied and amputee models, the results indicate a higher physiological cost for the amputee model, suggesting that this method more accurately represents the relative metabolic costs of able-bodied and amputee walking gait.
Dynamic Modelling and Experimental Testing of a Piano Action Mechanism
Authors: Hirschkorn Martin C. , McPhee John , Birkett Stephen
Published: June 2008

A new model for a grand piano action is proposed in this paper. The multibody dynamic model treats each of the five main action components (key, whippen, jack, repetition lever, and hammer) as a rigid body, and incorporates a contact model to determine the normal and friction forces at 13 locations between each of the contacting bodies. All parameters in the model are directly measured from experiments on individual action components, allowing the model to be used as a prototyping tool for actions that have not yet been designed or built. The behaviour of the model was compared to the behaviour of an experimental grand piano action and found to be very accurate for high force blows, and reasonably accurate for low force blows.
Frequency Response of Vibration Isolators With Saturating Spring Elements
Authors: Mahinfalah M. , Nakhaie Jazar G. , Rastgaar Aagaah M. , Mahmoudian N.
Published: June 2008

An investigation using averaging method is carried out to obtain the frequency response of a class of vibration isolators with saturation spring. The saturation characteristics are modeled using a hyperbolic-tangent function. The hyperbolic-tangent saturation function is compared with other popular saturation functions, using piecewise nonlinear approximation. A parameteric study indicates that piecewise linear approximation of saturating functions provide results that are close enough to the results of hyperbolic tangent approximation. A sensitivity analysis of frequency response of the system is also investigated based on the piecewise linear approximation.
Time Response Dynamics of Linear Model of Microcantilever-MEMS
Authors: Mahmoudian N. , Rastgaar Aagaah M. , Nakhaie Jazar G. , Mahinfalah M.
Published: June 2008

This paper presents analytic derivation of dynamic behavior of a liniearized micro-electro-mechanical resonator. The parametric oscillation results from a displacement-dependent electrostatic force generated by oscillation of a microbeam. The utilized device is a MEMS with a time-varying capacitor. The stability and steady state dynamic behavior of the MEMS has been analyzed without polarization voltage. The main characteristic of the no-polarization model is effects of parameters in stability of the system. A set of stability charts is provided for prediction of the boundary between the stable and unstable domains for the principal resonance. Applying perturbation method, analytical equations are derived to describe both the steady state and time response of the system.
Cross-Section Deformation in the Absolute Nodal Coordinate Formulation
Authors: Sugiyama Hiroyuki , Gerstmayr Johannes , Shabana Ahmed A.
Published: June 2008

In this investigation, the deformation modes defined in the finite element absolute nodal coordinate formulation using several strain definitions are discussed. In order to accurately define strain components that can have easy physical interpretation, a material coordinate system is introduced to define the material element rotation and deformation. The results obtained in this study clearly show cross-section deformation modes eliminated when the number of the finite element nodal coordinates is systematically and consistently reduced. Using the procedure discussed in this paper, one can obtain a reduced order dynamic model, eliminate position vector gradients that introduce high frequencies to the solution of some problems, achieve the continuity of the remaining gradients at the nodal points, and obtain a formulation that automatically satisfies the principle of work and energy.
Calculation of Excimer Laser Induced Temperature Profiles in PET, PBT, and PS Polymer Films
Authors: Sancaktar Erol , Kim Jongdae
Published: June 2008

Temperature profiles in PET (Polyethylene Terephtalate), PBT (Polybutylene Terephtalate), and PS (Polystyrene) films created due to excimer laser irradiation were estimated analytically from the model of semi-infinite heat flux and numerically from the model based on 1-D heat equation. For the analytical estimation of temperature profile, we initially assumed that all of the irradiated excimer laser energy was confined in surface, and the energy was considered as a constant heat flux during the laser irradiation period. Calculation results showed that this assumption is somewhat inadequate for polymer materials especially for the polymers with low UV absorption coefficients, because we could not exclude the absorption of excimer laser energy in bulk. In order to reduce the error from this assumption, temperature profiles were estimated from numerical solution, which included a heat generating function representing absorption of excimer laser beam in polymer. Temperature measurement results showed a good agreement with this calculation, but only when ablation was not significant (i.e., for PS).
Analyzing Accidents of Jamming Body Parts in Doors
Authors: Hatamura Yotaro , Sekita Masumi
Published: June 2008

On March 26, 2004, a six-year-old boy ran into an automatic revolving door when it was about to close. The door caught the boy’s head and killed him. The accident immediately caught the attention of mass media, police, government, and the people. Amidst all the opinions and talks about how dangerous these automatic revolving doors are and how safety measures should be installed, we organized a group of volunteers to analyze the dynamics of the accident to measure the forces, door velocity, acceleration, and if available, the driving current and voltage of the motors. The group not only studied the same door that caused the fatal accident but it also ran the same series of tests on a smaller size power-assisted revolving door, an automatic sliding door, an elevator door, a building shutter, a commuter train door, a bullet train door, an automatic sliding door on an automobile, and its power window. With the safety mechanisms disabled, we measured an impact force of 548kgf on a dummy head of a 3-year old when it was jammed between the revolving door edge and the door frame. The human scull of a child crushes at only 100kgf and our results show that in addition to this large automatic revolving door, the smaller size power-assisted revolving door, the shutter, and manually closing automobile doors generate forces that exceed this limit. These doors inherit the danger of causing fatal accidents.
Lyapunov’s Exponents for Non-Smooth Dynamical Systems: Behavior Identification Across Stability Boundaries With Bifurcations
Authors: Ageno Alessio , Sinopoli Anna
Published: June 2008

In this paper some recently developed techniques to evaluate both analytically and numerically stability features of a non-smooth dynamical system, are used to investigate in detail the stability boundaries of regions corresponding to given stable periodic responses. The problem analyzed is that of a rocking block simply supported on a harmonically moving rigid ground; in this case, if the block is assumed to be a rigid body, the strong discontinuities characterizing the dynamic evolution are due to the impacts occurring each time the block crosses the initial equilibrium configuration. Therefore some special tools, specific for non-smooth functions, must be introduced to perform the stability analysis. In the present study, the theory due to Mu¨ller [19] is used to handle the evaluation of Lyapunov’s exponents upon discontinuities, by introducing the treatment, both analytical and numerical, of “saltation matrices”. Such a general theoretical method on one hand has been adapted to the numerical algorithms needed for the solution of the complete, non-linearized, problem and on the other hand, it allowed the development of the closed-form analytical reference solutions, obtained by linearizing assumptions less restrictive than those used by Hogan [8, 9]. The approximated stability boundaries obtained by the linearized closed-form solutions have been the starting point to guide the choice of the system parameters values to locate the responses in regions where bifurcations can arise. Inside these ranges several examples can be presented to illustrate the trends exhibited by the numerically evaluated Lyapunov’s exponents when the values of the forcing amplitude increase over the stability boundary of the symmetric responses while the value of the forcing frequency is fixed. Among these, investigations on sequences of responses composing period doubling cascades toward chaos, can provide a good and interesting test to appreciate the indications offered by the numerically derived Lyapunov’s exponents.
Nonlinear Identification of a Capacitive Dual-Backplate MEMS Microphone
Authors: Liu Jian , Martin David T. , Kadirvel Karthik , Nishida Toshikazu , Sheplak Mark , Mann Brian P.
Published: June 2008

This paper presents the nonlinear system identification of model parameters for a capacitive dual-backplate MEMS microphone. System parameters of the microphone are developed by lumped element modeling (LEM) and a governing nonlinear equation is thereafter obtained with coupled mechanical and electrostatic nonlinearities. The approximate solution for a general damped second order system with both quadratic and cubic nonlinearities and a non-zero external step loading is explored by the multiple time scales method. Then nonlinear finite element analysis (FEA) is performed to verify the accuracy of the lumped stiffnesses of the diaphragm. The microphone is characterized and nonlinear least-squares technique is implemented to identify system parameters from experimental data. Finally uncertainty analysis is performed. The experimentally identified natural frequency and nonlinear stiffness parameter fall into their theoretical ranges for a 95% confidence level respectively.
The Fractional Hyperbolic Functions: With Application to Fractional Differential Equations
Authors: Lorenzo Carl F. , Hartley Tom T.
Published: June 2008

This paper develops the fractional hyperbolic functions based on fractional generalization of the exponential function, the R-function. The fractional hyperbolic functions contain the traditional hyperbolic functions as proper subsets. Laplace transforms and various identities are derived for the new functions and are used to generate solution sets for various classes of fractional differential equations. Also developed are relationships between the R-function and the fractional hyperbolic functions.
Challenges and Opportunities for Solid Wastes (Invited)
Authors: Gupta Ashwani K.
Published: June 2008

Incineration of plastic and other waste has provided energy recovery opportunities, together with associated challenges on the environmentally benign energy recovery. Most of the wastes have significant energy potential, the utilization of which can save millions of dollars on the national scale. However difficulties exist for their utilization in propulsion and power systems in an environmentally acceptable manner. It is anticipated that the amount of waste generated will continue to grow in the new millennium, along with associated changes in its composition. Incineration (thermal destruction) of wastes to the molecular level allows one to more cleanly convert into usable energy. The challenges provide opportunities for combustion engineers, whose research has expanded significantly in recent years, particularly in areas related to fossil fuels and wastes being used as fuels. The field of combustion is further diversified by the complex nature of most reaction processes. Fuel chemistry, fluid mechanics, convective and radiative heat transfer, gas-phase elementary reactions, turbulence, and particle kinetics and dynamics are relevant processes that often have a direct, and sometimes controlling influence, on the behavior of a particular combustion system. Sensors, diagnostics and miniaturization of the system continue to be of major importance for successful implementation of this new technology.
A Contact Modeling Method Based on Volumetric Properties
Authors: Gonthier Yves , McPhee John , Lange Christian , Piedbœuf Jean-Claude
Published: June 2008

A novel contact model is presented which includes normal contact force and damping, rolling resistance torque and tangential friction force. This model is appropriate for the simulation of robotic tasks involving contact between objects of any shapes, occurring at relatively low velocities. It features a contact stiffness proportional to the contact area and leads automatically to the correct selection of the point of action of the force. The contact force magnitude is shown to be proportional to the interpenetration volume. A numerical simulation of a sphere impacting on the inside surface of a cylinder is presented.
Optimum Placement of Piezoelectric Ceramic Modules for Vibration Suppression of Highly Constrained Structures
Authors: Belloli Alberto , Thomaschewski Oliver , Ermanni Paolo
Published: June 2008

The vibration suppression efficiency of so-called shunted piezoelectric systems is decisively influenced by the number, shape, dimension, and position of the implemented piezoelectric ceramic elements. This paper presents a procedure based on evolutionary algorithms for optimum placement of piezoelectric ceramic modules on real-world, highly constrained lightweight structures. The optimization loop includes the CAD software CATIA V5, the FE package ANSYS and DynOPS, a proprietary software tool able to connect the Evolving Object library with any simulation software that can be started in batch-mode. A user-defined piezoelectric shell element is integrated into ANSYS 8.1. Modal generalized electromechanical coupling coefficients are used as optimization objective and constraints. Position, dimension and shape of commercial, customized and free-form patches are determined for optimum multi-mode vibration suppression of a pinned, quadratic plate. An aircraft fuselage panel with a window cutout is investigated as test object for complex, curved geometries.
Fault Diagnosis and Prognosis for Fuel Supply System in Gas Turbine Engines
Authors: Kim Kyusung , Uluyol Onder , Ball Charles
Published: June 2008

A fault diagnosis and prognosis method is developed for the fuel supply system in gas turbine engines. The engine startup profiles of the core speed (N2) and the exhaust gas temperature (EGT) collected with high speed sampling rate are extracted and processed into a more compact data set. The fuzzy clustering method is applied to the smaller number of parameters and the fault is detected by differentiating the clusters matching the failures. In this work, the actual flight data collected in the field is used to develop and validate the system, and the results are shown for the test on nine engines that experienced fuel supply system failure. The developed fault diagnosis system detects the failure successfully for all nine cases. For the earliest detection cases, the alarms start to trigger 26 days before the system completely fails and 7 days in advance for the last detection.
Multiple Solutions in an Amplitude Limited Jeffcott Rotor Including Rubbing and Stick-Slip Effect
Authors: Aidanpa¨a¨ Jan-Olov
Published: June 2008

The non-linear behaviour of rub-impact rotors have been studied in several papers. In such systems rich dynamics have been found together with the coexistence of solutions within some specific parameter ranges. In this paper an attempt is made to find all stable solutions for an amplitude limited Jeffcott rotor including rubbing and stick-slip effect. The recently suggested “multi bifurcation diagram method” is used to find and extract stable sets of bifurcation diagrams. A system is chosen where the linear stationary amplitude only exceeds the clearance in a narrow region near the natural frequency. Therefore large regions in frequency are expected to have only the linear stationary response. The results show that it is only for very low frequencies that one single solution exists. Even though periodic motions are dominant, there exist large ranges in frequency with quasi-periodic or chaotic motions. For the studied cases, three coexisting stable solutions are most common. In one case as many as four stable solutions was found to coexist. For rotors with large clearances (no impacts necessary) it is still possible to find several coexisting motions. For all cases the stick motion is the most severe one with large amplitudes and high backward whirl frequencies. In real situations the consequence of this stick motion is machine failure. These high amplitude motions were found to be stable over large frequency ranges. From the stability analysis it was found that this rolling motion can be avoided by low spin speed, low contact stiffness, low coefficient of friction, small ratio of disc radius/clearance or high damping ratio. In a design situation the parameters are seldom known with high accuracy. Therefore, it is of interest to know all solutions for parameter intervals. The multi-bifurcation diagram can be used in such situations to design a robust machine or at least be prepared for unwanted dynamics.
Active Vibration Damping Using an Inertial, Self-Sensing, Electrodynamic Actuator
Authors: Paulitsch Christoph , Gardonio Paolo , Elliott Stephen J.
Published: June 2008

Self-sensing active vibration damping is advantageous if sensors cannot be placed collocated to actuators or these sensors add too much weight or cost. When self-sensing, electrodynamic actuators are used, damping is directly added to the structure where they are attached without the need of electronic integrators or differentiators that could destabilize the system. Inertial actuators have also the advantage that they do not need to react relative to a fixed ground. In this paper self-sensing control with a shunted resistor, current feedback, induced voltage feedback with and without inductance compensation are investigated in simulations and experiments. Experiments with a lightweight, inertial actuator on a clamped plate show that vibration amplitude is decreased between 6dB and 13dB and control bandwidth is doubled when the appropriate control scheme is used.
Using Product Dissection to Integrate Product Family Design Research Into the Classroom and Improve Students’ Understanding of Platform Commonality
Authors: Simpson Timothy W. , Thevenot Henri J.
Published: June 2008

In this paper we describe a product dissection activity that has been developed for a graduate course on product family design to improve students’ understanding of platform commonality. Last spring, the product dissection activity served a second purpose, namely, it provided an opportunity to engage students in product family design research in the classroom by having them participate in a study to evaluate the variability in the Product Line Commonality Index (PCI), a commonality index from the literature. The product dissection activity consisted of five teams dissecting and analyzing three different families of products, each containing four products. Based on their results, we identified three main sources of the variability that occur during the dissection of the products and calculation of the PCI: different levels of dissection, parts omitted from the analysis, and different values for the factors used to compute the PCI. Recommendations for reducing the variability are given based on our findings. Finally, an assessment of the students’ learning reveals that the activity significantly improved their understanding of platform commonality.
Order-Tuned Vibration Absorbers for Cyclic Rotating Flexible Structures
Authors: Olson Brian J. , Shaw Steve W. , Pierre Christophe
Published: June 2008

This paper investigates the use of order-tuned absorbers to attenuate vibrations of flexible blades in a bladed disk assembly subjected to engine order excitation. The blades are modeled by a cyclic chain of N oscillators, and a single vibration absorber is fitted to each blade. These absorbers exploit the centrifugal field arising from rotation so that they are tuned to a given order of rotation, rather than to a fixed frequency. A standard change of coordinates based on the cyclic symmetry of the system essentially decouples the governing equations of motion, yielding a closed form solution for the steady-state response of the overall system. These results show that optimal reduction of blade vibrations is achieved by tuning the absorbers to the excitation order n, but that the resulting system is highly sensitive to small perturbations. Intentional detuning (meaning that the absorbers are slightly over- or under-tuned relative to n) can be implemented to improve the robustness of the design. It is shown that by slightly undertuning the absorbers there are no system resonances near the excitation order of interest and that the resulting system is robust to mistuning (i.e., small random uncertainties in the system parameters) of the absorbers and/or blades. These results offer a basic understanding of the dynamics of a bladed disk assembly fitted with order-tuned vibration absorbers, and serve as a first step to the investigation of more realistic models, where, for example, imperfections and nonlinear effects are considered, and multi-DOF and general-path absorbers are employed.
Machine Fault Detection Using Genetic Programming
Authors: Samanta B.
Published: June 2008

Applications of genetic programming (GP) include many areas. However applications of GP in the area of machine condition monitoring and diagnostics is very recent and yet to be fully exploited. In this paper, a study is presented to show the performance of machine fault detection using GP. The time domain vibration signals of a rotating machine with normal and defective gears are processed for feature extraction. The extracted features from original and preprocessed signals are used as inputs to GP for two class (normal or fault) recognition. The number of features and the features are automatically selected in GP maximizing the classification success. The results of fault detection are compared with genetic algorithm (GA) based artificial neural network (ANN)- termed here as GA-ANN. The number of hidden nodes in the ANN and the selection of input features are optimized using GAs. Two different normalization schemes for the features have been used. For each trial, the GP and GA-ANN are trained with a subset of the experimental data for known machine conditions. The trained GP and GA-ANN are tested using the remaining set of data. The procedure is illustrated using the experimental vibration data of a gearbox. The results compare the effectiveness of both types of classifiers with GP and GA based selection of features.
Torsional Vibration Suppression by a Centrifugal Pendulum Vibration Absorber
Authors: Ishida Yukio , Inoue Tsuyoshi , Kagawa Taishi , Ueda Motohiko
Published: June 2008

Driving torque of rotating machinery, such as automobile engines, changes periodically. As a result, torsional vibrations occur and cause serious noise and vibration problems. In this study, the dynamic characteristics of centrifugal pendulum vibration absorbers restraining torsional vibration is investigated both theoretically and experimentally. In the theoretical analysis, the nonlinear characteristics are taken into consideration under the assumption of large amplitude vibration of pendulum. It is clarified that the centrifugal pendulum, although it has remarkable effects on suppressing harmonic vibration, induces large amplitude harmonic vibrations, the second and third superharmonic resonances, and unstable vibrations of harmonic type. We propose various methods to suppress these secondarily induced vibration and show that it is possible to suppress torsional vibrations to substancially zero amplitude in all through the rotational speed range.
Railway Bridges Identification Techniques
Authors: Garibaldi Luigi , Bregant Luigi , Valente Claudio , Brancaleoni Fabio , Catania Giuseppe
Published: June 2008

Output-only methodologies are nowadays well established to extract modal parameters in many areas of engineering, such as civil, mechanical and aeronautical. In the past, civil engineering tests have been mainly developed for road bridges, with the vehicle passage over the bridge deck representing the main source of excitation with some contribution given by the ambient noise. In the road bridge cases, the excitation is considered to be a function of the road surface roughness, the vehicles speed, the weight and suspension vehicles characteristics, and also the random access of the vehicles over the bridge, whilst for the railway case, not all these issues are correctly addressed, and other characteristics rise-up, possibly advantageous for a correct identification process; to demonstrate this statement, we can bear in mind how the random access of the vehicles becomes meaningless for railway bridges, the single train being a quasi deterministic source; furthermore, the influence of the train weight should be considered if compared to usual road vehicles. Since output-only techniques are conceived for random excitation noise, their use in these conditions is considerably stressed and special care, or alternative techniques, has to be considered to avoid errors. In this sense, the bridge reference model becomes more important and some special techniques have to be developed.
Toward the Improvement of Education in Mechanics
Authors: Tajima Hiroshi
Published: June 2008

Two catch phrases of my half year lectures of Mechanics, which are given at two Universities, are as follows: “Three dimensions from the beginning”, and “Various methods to derive the equations of motion”. We often do not have enough time to teach kinematics and dynamics from two-dimensional matters first and then proceed to three dimensions. In many cases three-dimensional subjects are considered to be something advanced, or something which two-dimensional methods can be applied to. As a result we often lose chances to teach three-dimensional matters. I think there are few universities that give clear and firm teaching of three dimensional kinematics and dynamics. Many teachers often escape from three-dimensional discussions saying two dimensions are fundamental. I feel that there are very few teachings and discussions in Japan on the methods for deriving the equations of motion. There are many teachers who tell the importance of the equations of motion, but there are few who can discuss various methods to derive them. Discussion and Recognition of various methods not only broaden the application ability but also give clearer understanding in mechanics itself that will connect to the creation of new methodology. My lecture is a direct answer to these points, and my five year experience gives me more confidence in the importance of them. My recent effort is to get more chances to teach it not only within the universities, but also outside of them, getting more sympathetic people. At present I feel that my lecture will surely give some certain effects to the engineering education in mechanics in Japan.
A Study of Model Representations for Shape Conceptualization
Authors: Rusa´k Zolta´n , Horva´th Imre
Published: June 2008

Shape conceptualization is considered as an iterative search process with the goal to gather, generate, represent, transform, manipulate, and communicate information and knowledge related to various kinds of shape concepts. The search for shape concepts is not focused on finding a specific solution, but on exploring, analyzing and comparing various alternatives. This search is vague because shape concepts and mental models are abstract, uncertain, and incomplete. They gradually become concrete, definite, and complete as the design process advances. Therefore, the main challenges for model representation of shape design concepts are (a) facilitation of capturing, transforming and manipulating uncertain, incomplete, and abstract mental images by computer, and (b) handling coexistence of shape alternatives. Due to these features, the development of computer aided conceptual design systems for shape conceptualization applications is not without problems. Intensive research is carried on to solve the problems and to propose solutions. Due to the wide horizon of research and the lack of papers surveying the progress and the open issues, there is no comprehensive picture on the state of the art. Starting out from the methods and tools developed for shape modeling, this study investigates the means for shape conceptualization. First, a reasoning scheme is introduced to make the investigation systematic. From the point of view of information captured in a representation on a shape, simplified, nominal, and expanded shape modeling methods have been found and investigated. The paper concludes about an optimum modeling approach, which melt the advantages of the present techniques and extends it with new features.
Stability-Optimized Clearance Configuration of Fluid-Film Journal Bearings
Authors: Matsuda Koichi , Kanemitsu Yoichi , Kijimoto Shinya
Published: June 2008

A clearance configuration of fluid-film journal bearings is optimized in a sense of enhancing the stability of a full circular bearing at high rotational speeds. A performance index is chosen as the sum of the squared whirl-frequency ratios over a wide range of eccentricity ratios, and a Fourier series is used to represent an arbitrary configuration of fluid-film bearings. An optimization problem is then formulated to find the Fourier coefficients to minimize the index. The whirl-frequency ratio is inversely proportional to the stability threshold speeds of a Jeffcott rotor. The short bearing approximation is used to simplify a mathematical model that describes a pressure distribution developed in a fluid-film bearing. The designed bearing cannot destabilize the Jeffcott rotor at any high rotating speed subject to the short-bearing assumption and significantly reduces the size of the unstable region for a finite-length bearing with a small length-to-diameter ratio.
Variable Damping and Stiffness Vibration Control With Two Magnetorheological Fluid Dampers in Series
Authors: Liu Yanqing , Matsuhisa Hiroshi , Utsuno Hideo , Park Jeong Gyu
Published: June 2008

Vibration isolation methods that vary damping and stiffness have demonstrated excellent authority over system vibration, thus, potentially making them attractive for many applications. However, conventional devices for controlling variable stiffness are typically complicated and difficult to implement in most applications. To address this issue, a new method is proposed that requires two magnetorheological (MR) fluid dampers placed in series. With this configuration, variable damping and stiffness vibration control is simultaneously achieved by varying a small current to the MR dampers. This paper presents a theoretical and experimental analysis of a two degree-of-freedom system that is controlled by the MR dampers. Five different control schemes involving the variable damping and stiffness are explored. The time and frequency responses of the two degree-of-freedom system to a random input show that combined variable damping and stiffness control provides the best vibration isolation over a frequency range spanning the system’s two structural vibration modes. The experimental results agree well with the theoretical analysis.
Optimum Design of Rotor-Bearing Systems Considering the Nonlinear Effects of Bearing Fluid Forces
Authors: Chen Zhaobo , Jiao Yinghou , Xia Songbo , Huang Wenhu
Published: June 2008

Genetic algorithms (GAs) are adaptive procedures that find solution to problems by an evolutionary process that mimics natural selection. In this paper, methods based on GAs have been developed and presented for design optimization of journal bearings in nonlinear rotor system. The GA uses a 30-bit chromosome to represent the bearing radial clearance, aspect ratio and lubricant viscosity, with 10-bit for each design variable. The instability onset speed of the system is taken as the fitness function in GA, in which the nonlinear effects of the bearing fluid forces are considered. The instability onset speed is defined in two different cases, that is, periodic and quasi-periodic or chaotic motions. To verify the effectiveness of the suggested method, a rigid rotor-bearing system is taken as an example to be optimized. The different crossover probabilities, mutation probabilities and population sizes are employed to analyze their influences on GA so that a set of appropriate parameters are chosen to be used in the final calculation. The results are compared with those obtained by numerical simulation. It is shown that the proposed algorithm is effective in the optimum design of rotor-bearing system.
The Influence of Surface Treatment and Microstructural Parameters on the Rail/Wheel Tribological Behaviours
Authors: Rahman Fazli , Kharlamov Y. A. , Chattha J. A.
Published: June 2008

The long time world railways practice has shown that the rail-wheel mechanical system is one of the most unique and complex systems. During transportation a variety of rail and wheel damages can take place due to service conditions, used material and technology of their production. Damage mechanisms such as wear, surface cracks, spalls, shells and elastic deformation as a result to rolling contact stresses can significantly reduce the service life of railway wheel sets and track and causing a negative impact on the rolling noise as well as on the ridding comfort. This paper presents that a proper understanding of the heating and cooling mechanisms of the wheel surface for the required hardening purpose is necessary and a mathematical model is developed to present hardening process (local heat treatment). As the material of wheel and rail is carbon steel and the heat treatment (hardening) is the most effective and efficient methods for decreasing wear on wheel sets because wheel sets are more prone to wear due to their excessive use as compare to rail or track.. The only local heat treatment is justifiable technically and economically which is applied to the most loaded working surface of wheel sets without dealing with the central part or bulk of the material. The quality of heat treatment of working surfaces of wheels is associated with the use of concentrated energy sources, such as electron and laser beam and plasma jets. This paper presents some experimental results besides the theoretical reasoning and discussions which show that the wear on the wheel sets ridges after plasma hardening is much lower (2.5 to 3 times) than the other standard heat treatments and hence due to the proper contact of railwheel the vehicle system dynamics improves as a result.
Surprisingly Complicated Dynamics of a Single-Degree-of-Freedom Linear Oscillator Coupled to a Nonlinear Attachment
Authors: Lee Young S. , Kerschen Gae¨tan , Vakakis Alexander F. , Panagopoulos Panagiotis , Bergman Lawrence A. , McFarland D. Michael
Published: June 2008

We study the dynamics of a two-degree-of-freedom nonlinear system consisting of a linear oscillator with an essentially nonlinear attachment. For the undamped system, we perform a numerical study based on non-smooth temporal transformations to determine its periodic solutions in a frequency-energy plot. It turns out that there is a sequence of periodic solutions bifurcating from the main backbone curve of the plot. We then study analytically the periodic orbits of the undamped system using the complexification / averaging technique in order to determine the frequency contents of the various branches of solutions, and to understand the types of oscillation performed by the system at the different regimes of the motion. The transient responses of the weakly damped system are then examined, and numerical wavelet transforms are used to study the time evolutions of their harmonic components. We show that the structure of periodic orbits of the undamped system greatly influences the damped dynamics, as it causes complicated transitions between modes in the damped transient motion. In addition, there is the possibility of strong passive energy transfer from the linear oscillator to the nonlinear attachment if certain periodic orbits of the undamped dynamics are excited by the initial conditions.
Suppression of Limit Cycle Oscillations in a Van der Pol Oscillator by Means of a Passive Nonlinear Energy Sink
Authors: Lee Young S. , Vakakis Alexander F. , Bergman Lawrence A. , McFarland D. Michael
Published: June 2008

We present a study of passive but efficient vibration control, wherein a so-called nonlinear energy sink (NES) completely eliminates the limit cycle oscillations (LCOs) of a van der Pol oscillator. We first perform a parameter study in order to get overall understanding of responses with respect to parameters. Then, we establish a slow flow dynamics model to perform analytical study of the suppression mechanism which corresponds to classical nonlinear energy pumping, i.e., passive, broadband, and targeted energy transfer through 1:1 resonance capture. Utilizing the method of numerical continuation of equilibrium, we also study the bifurcation of the steady state solutions. It turns out that the system may have either subcritical or supercritical LCOs, and that for some parameter domain the LCOs are completely eliminated. This suggests applicability of the NES to vibration control in self-excited systems.
Web-Based Multimedia Lecture Delivery System With Text-to-Speech and Virtual Instructors
Authors: Wasfy Ayman M. , Wasfy Tamer M. , El-Mounayri Hazim , Aw Daniel
Published: June 2008

A web-based multimedia lecture delivery system is presented. The system provides natural-language instruction with synchronized: naturally sounding text-to-speech, written highlighted text, and animated 2D and 3D graphics. A near-photorealistic animated human avatar can present the lecture with synchronized gestures and lip-synching. The course is presented using a hierarchical structured outline. The learner can ask the virtual instructor questions using natural-language speech or typed text. The instructor first tries to answer the question from the course content. If no information is found then a web search is performed. The key elements of the lecture delivery system are: (1) a modular unstructured knowledge-base in which knowledge is stored as HTML or XML “knowledge objects” with embedded multimedia content; (2) a hierarchical rule-based expert system that provides natural-language understanding; (3) a search engine that can provide answers to the learner’s questions from the knowledge-base; (4) natural-language voice-recognition and synthesis; (5) animated human-like virtual instructor; (6) an integrated web-based framework that includes windows for course presentation, outline, speech, photo-realistic animated agent avatar, and other utilities that can be moved and sized according the user’s preference. The application of the lecture delivery system to a sample introductory lecture on CNC milling is presented in order to demonstrate the features of the system.
Analysis on Harmonic Responses of Vehicle Suspension Systems With Magnetorheological Dampers
Authors: Guo Shuqi , Yang Shaopu , Pan Cunzhi
Published: June 2008

The paper is devoted to analyze harmonic responses of vehicle suspension systems with Magneto-rheological (MR) Dampers. With two reasonable assumptions and some appropriate formulations, in light of the results of single-degree-of-freedom isolation systems with MR dampers, the solutions of harmonic responses of quarter car suspension systems with MR dampers are presented. And the solutions of sprung and unsprung transmittances for the system are also given. Numerical simulations verified the resulting solutions of theoretical analysis.
Detection of a Rotor Crack Based on the Nonlinear Vibration Diagnosis Using Periodic Excitation
Authors: Ishida Yukio , Inoue Tsuyoshi
Published: June 2008

Detection of a rotor crack based on the nonlinear vibration diagnosis using periodic excitation force is investigated. Due to the open-close mechanism of the crack, the equations of motion of a cracked rotor have linear and nonlinear parametric terms. When a periodic excitation force is applied to the cracked rotor, various kinds of resonances due to the unique vibration characteristics of a crack. Furthermore, types of resonances, resonance points and dominant frequency component of these resonances are clarified theoretically and experimentally. These results enable us to detect a crack on-line without stopping the system.