bluuebunny/crossref_metadata_2025 huggingface dataset:
Pull-In Dynamics of an Elastic Beam Actuated by Distributed Electrostatic Force
Authors: Krylov Slava , Maimon Ronen
Published: June 2008

A detailed study of the transient nonlinear dynamics of an electrically actuated micron scale beam is presented. A model developed using the Galerkin procedure with normal modes as a basis accounts for the distributed nonlinear electrostatic forces, nonlinear distributed squeezed film damping forces, and rotational inertia of a mass carried by the beam. Special attention is paid to the dynamics of the beam near instability points. Results generated by the model and confirmed experimentally show that nonlinear damping leads to shrinkage of the spatial region where stable motion is realizable. The voltage that causes dynamic instability, in turn, approaches the static pull-in value.
Nonlinear Oscillations of Microelectromechanical Resonators
Authors: Li He , Balachandran B.
Published: June 2008

Oscillations of clamped-clamped micro-electromechanical resonators are studied in this effort. Piezoelectric actuation is used to excite these structures on the input side and piezoelectric sensing is carried out on the output side. Experimental observations of nonlinear phenomena are presented and nonlinear analysis in progress is presented to explain the experimental observations.
Hysteresis Effect in Adhesive Elastic Contact
Authors: Wei Zheng , Zhao Ya-Pu
Published: June 2008

Adhesive forces in microscale or nanoscale contact play a significant role in microelectromechanical systems (MEMS); scanning probe microscope (SPM) and some other related fields. In this paper, the relationship between the pull-off force and the transition parameter as well as the variation of the pull-off radius with the transition parameter is given. When hysteresis effect is considered, hysteresis models are presented to describe the contact radius as a function of external load in loading and unloading processes. Among these models, we verified the hysteresis model from JKR, which is in a good agreement with experiment. The parameter α of dissipated elastic energy can be measured through experiment.
A Generalized Model of Electrically Actuated, Microbeam-Based MEMS Devices
Authors: Abdel-Rahman Eihab M. , Emam Samir A. , Nayfeh Ali H.
Published: June 2008

We present a model of electrically actuated microbeam-based MEMS devices incorporating the nonlinearities associated with moderately large displacements and electric forces. The model can handle any capacitor configuration disposing of the complete electrode-overlapping (parallel-plate theory) restriction. The boundary-value problem describing the static deflection of the microbeam under the electrostatic loading is solved numerically. The eigenvalue problem describing the vibration of the microbeam around its statically deflected position is solved numerically for the natural frequencies and mode shapes. Results generated by our model for the parallel-plate case are in agreement with published results. Our results show that the underlying assumptions of the closed-form formula of the parallelplate case underestimates the electrostatic force and leads to an overestimation of the pull-in voltage. The model provides an analytical tool to predict the static and dynamic response of any electrically actuated MEMS device based on clamped-clamped microbeams.
Dynamic Response Optimization of Asymmetrically Configured Piezoelectric Fans
Authors: Basak Sudipta , Raman Arvind
Published: June 2008

Piezoelectric fans typically consist of one piezoelectric patch bonded on one side of a thin, flexible elastic beam. The fan is excited at resonance and used to drive unsteady flows to cool microelectronics components. Field equations of the coupled structure governing the coupled longitudinal and bending motions of the fan are derived using linear constitutive equations, slender beam approximations, and Hamilton’s principle. Analytical solutions are found to the coupled eigenvalue problem. Eigenvalues and eigenfunctions for closed and open circuited configurations are predicted analytically and are found to be in excellent agreement with three-dimensional finite element results. Electromechanical Coupling Factors (EMCF) are computed using the analytical and finite element models and optimal fan geometries are identified for maximal EMCF. The analytical solution provides a convenient tool for the optimal design of such fans.
Passive Nonlinear Energy Pumping in Coupled Oscillators: Steady State Results
Authors: Jiang Xiaoai , McFarland D. Michael , Bergman Lawrence A. , Vakakis Alexander F.
Published: June 2008

We study theoretically and numerically the effect that a nonlinear energy sink (NES) has on the steady state dynamics of a weakly coupled system. The NES possesses essentially nonlinear (nonlinearizable) stiffness nonlinearity of the third degree. We find that, in contrast to the classical linear vibration absorber, the NES is capable of absorbing steady state vibration energy from the linear oscillator over a relatively broad frequency range. This results in localization of the steady state vibration in the NES, away from the directly forced subsystem. For a forward frequency sweep the localized branch of steady state motions is suddenly eliminated by a jump to a linearized low-amplitude motion, whereas, for a backward frequency sweep a reverse jump occurs. The difference in the frequencies of the two jumps introduces a nonlinear hysteresis loop. This work extends to the steady state case of earlier transient passive energy pumping results. The notion of passively transferring vibration energy to an a priori determined NES, weakly attached to a main structure, is novel. The use of essentially nonlinear energy sinks for passively absorbing energy from a linear main structure can form the basis of relatively simple and modular vibration and shock isolation designs of mechanical systems.
Particle Damping for Passive Vibration Suppression: Numerical Modeling With Experimental Verification
Authors: Xu Zhiwei , Wang Michael Yu , Chen Tianning
Published: June 2008

As a simple and passive means, particle damping provides vibration suppression with granular particles embedded within their containing holes in a vibrating structure. Unlike in traditional damping materials, mechanisms of energy dissipation of particle damping are primarily related to friction and impact phenomena which are highly nonlinear. In the research work reported in the paper we investigate an elastic beam structure with drilled longitudinal holes filled with damping particles. Our focus is on the form of damping due to shear friction induced by strain gradient along the length of the structure. We present physical models to take into account of the shear frictional forces between particle layers and impacts of the particles with the containing holes. A numerical procedure is presented to predict the damping effect. Experimental tests of the beam for various different damping treatments are also conducted. Model predictions are validated by experimental results.
Damping and Vibration Control via Nanoscale Technologies for Defense Oriented Applications
Authors: Anderson Gary L. , Garg Devendra P.
Published: June 2008

This paper discusses the potential of nanoscale technologies with particular attention devoted to applications in the defense area. Innovative techniques for structural damping and vibration control are of much interest to the Structures and Dynamics Program at the United States Army Research Office (ARO). Since nanotechnology is a new and different way of thinking about the creation of devices and systems, it holds much promise for such applications. Nanotechnology can be gainfully employed to create and utilize materials, devices, and systems through the control of matter on the nanometer-length scale, i.e., to engineer matter at the level of atoms and molecules, leading to the generation of larger structures having fundamentally new molecular organizations exhibiting novel physical, chemical, and biological properties and phenomena. In addition to describing an overview of nanotechnology and its relevance to the defense needs, the paper describes a few of the currently ongoing projects under the ARO sponsorship.
Damping Characteristics of Carbon Nanotube Based Composites
Authors: Zhou X. , Shin E. , Wang K. W. , Bakis C. E.
Published: June 2008

Because of their ultra small, nanometer scale size and low density, the surface area to mass ratio (specific area) of carbon nanotubes (CNTs) is extremely large. Therefore, in a nanotube-based polymeric composite structure, it is anticipated that high damping can be achieved by taking advantage of the interfacial friction between the nanotubes and the polymer resins. In addition, the CNT’s large aspect ratio and high elastic modulus features allow for the design of such composites with large differences in strain between the constituents, which could further enhance the interfacial energy dissipation ability. Despite their wonderful engineering potential, the damping properties of CNT-based composites have not been examined in any detail. The purpose of this paper is to investigate the structural damping characteristics of polymeric composites distributed with single-walled carbon nanotubes (SWNTs). In this study, the system is modeled using a four-phase composite, composed of a resin, voids, and bonded and debonded nanotubes. A micromechanical model is proposed to describe interfacial debonding evolution. To characterize the overall behavior, the Weibull’s statistical function is employed to describe the varying probability of nanotube debonding under uniaxial loading. Fictitious, perfectly bonded inclusions are used to replace debonded nanotubes such that the elastic mechanical properties can be obtained through Eshelby’s approach. To address damping effects, the concept of interfacial “stick-slip” frictional motion between the nanotubes and the resin is proposed. A critical shear (bonding) stress is used to separate the material system into an energy-conservative range due to strong interfacial bonding, and a nanotube sliding range resulting in energy dissipation. The developed method is further extended to analyze composites with randomly oriented nanotubes. The analytical results show that the critical shear stress, nanotube weight ratio and structure deformation are the factors affecting the damping characteristic. Experimental efforts are also performed to verify the trends predicted by the analysis. Through comparing with neat resin specimens, the study shows that one can indeed enhance damping by adding CNT fillers into polymeric resins. It is also observed that SWNT-based composites can achieve higher damping than composites with other types (different size, surface area, density and stiffness) of fillers. These results confirm the advantage of using CNTs for damping enhancement.
Dynamic Analysis of an Active Flexible Isolation System
Authors: Song Kongjie , Sun Lingling , Sun Yuguo , Zhang Bing
Published: June 2008

This paper is dedicated to the structure dynamic modification in an active isolation system supported by a flexible foundation, in order to improve the effectiveness of the active control strategy. The coupled vibration between machine-sprung and flexible foundation substructure is examined, using the subsystem mobility method. The vibration transmission in this coupled system is presented in terms of power flow. The interaction between structure controlled and the adaptive feed-forward controller is investigated theoretically. The numerical results show that: the location of the active mounts and the first mode frequency of the flexible foundation have evident influence on the effect of active control, especially at low-frequency band.
A New Method Seeking Optimal Parameters and Locations for Bearings of Rotating Machinery Systems
Authors: Fang Zhichu , Wang Miao
Published: June 2008

A new method to optimize oil-film bearing parameters and choose the best bearing locations was presented here for rotor-bearing systems. Through applying the independent modal space control technique, optimized modal control forces and bearing forces guaranteeing system stability were deduced. The objective function minimizing the square difference between real bearing forces and optimized bearing forces was employed to optimize the bearing parameters. And then the other objective function was established to seek the best bearing locations among several possible choices. An interesting numerical example proved that the proposed approach is correct and efficient.
Mass Measurement System Using an Undamped Dynamic Vibration Absorber for Weightless Conditions
Authors: Mizuno Takeshi , Sato Shinsuke
Published: June 2008

A new vibration-type mass measurement system with an undamped dynamic vibration absorber was developed. In the developed system, a measurement object is attached to the inertial mass of the vibration generator instead of the absorber mass. It has an advantage that the tuning condition of the absorber is not influenced by the mass of measurement objects. The measurement accuracy of the developed system was estimated experimentally when it was fixed on a massive base and on a flexible structure. The results demonstrated that measurement accuracy was almost same in both the cases. It was also shown that the vibration of the table in transient states was reduced by increasing the excitation signal gradually from zero to an amplitude for measurement.
Isolation and Vibration Transmission Reduction of Systems Mounted on a Flexible Structure
Authors: Liu Yanning , Xu Yanchu , Flynn Bill
Published: June 2008

Issues addressed in this paper are related to the isolation and vibration transmission of vibration-sensitive systems mounted on a flexible support. The normal operation of certain electronic, optical and mechanical systems requires a vibration-free environment. To obtain such an environment, these systems are usually isolated from their supports with soft springs. When an array of such systems is needed, due to space constraints or other reasons, they are typically mounted on a common support, which in practice is flexible. Although such a design generally is effective in isolating vibration from ground support, vibration from one system, due to excitations other than from its support, can easily transmit to nearby systems. The level of the transmitted vibration (also known as vibration interaction) can be very significant, especially when all the systems are designed identically for simplicity and with less damping for effective ground vibration isolation. Isolator frequency separation (decoupling), viscous and viscoelastic damping are studied for the reduction of vibration transmission among the systems and their effects on system isolation are discussed. It is found that although the isolator frequency separation and viscous damping could be used for vibration transmission reduction among the isolated systems on the flexible support, the addition of viscoelastic damping reduces the vibration transmission without sacrificing their isolation performance. The difference between viscous and viscoelastic damping on ground vibration isolation is explained theoretically in the final part of the paper using a one degree of freedom model.
Study on Power Flow and H∞ Robust Control in Raft Hybrid Vibration Isolation System
Authors: Mao Weimin , Cao Yueyun , Zhu Shijian
Published: June 2008

The raft hybrid vibration isolation system is studied. The control law of the system is designed with H∞ robust control theory. The power flow in the raft hybrid vibration isolation system is investigated. In order to verify the raft hybrid vibration isolation system numerical simulation is carried out. The simulation results show that the control algorithm is effective and robust, and that the isolation effectiveness of the hybrid vibration isolation system is much better than that of the passive isolation system in the whole frequency domain.
Analysis of Solitary Waves in Arteries
Authors: Jazar G. Nakhaie , Mahinfalah M. , Aagaah M. Rastgaar , Fahimi F.
Published: June 2008

Solitary waves are coincided with separaterices, which surrounds an equilibrium point with characteristics like a center, a sink, or a source. The existence of closed or spiral orbits in phase plane predicts the existence of such an equilibrium point. If there exists another saddle point near that equilibrium point, separatrix orbit appears. In order to prove the existence of solution for any kind of boundary value problem, we need to apply a fixed-point theorem. We have used the Schauder’s fixed-point theorem to show that there exists at least one nontrivial solution for equation of wave motion in arteries, which has a spiral characteristic. The equation of wave motion in arteries has a nonlinear character. Thus, the amplitude of the wave depends on the wave velocity. There is no general analytical or straightforward method for prediction of the amplitude of the solitary wave. Therefore, it must be found by numerical or nonstraightforward methods. We introduce and analyse three methods: saddle point trajectory, escape moving time, and escape moving energy. We apply these methods and show that the results of them are in agreement, and the amplitude of a solitary wave is predictable.
Global Attractors of High-Speed Milling: Analyses, Numerics and Experiments
Authors: Stepan Gabor , Szalai Robert , Mann Brian P. , Bayly Philip V. , Insperger Tamas , Gradisek Janez , Govekar Edvard
Published: June 2008

High-speed milling is often modeled as a kind of highly interrupted machining, when the ratio of time spent cutting to not cutting can be considered as a small parameter. In these cases, the classical regenerative vibration model, playing an essential role in machine tool vibrations, breaks down to a simplified discrete mathematical model. The linear analysis of this discrete model leads to the recognition of the doubling of the so-called instability lobes in the stability charts of the machining parameters. This kind of lobe-doubling is related to the appearance of period doubling vibrations originated in a flip bifurcation. This is a new phenomenon occurring primarily in low-immersion high-speed milling along with the Neimark-Sacker bifurcations related to the classical self-excited vibrations or Hopf bifurcations. The present work investigates the nonlinear vibrations in case of period doubling and compares this to the well-known subcritical nature of the Hopf bifurcations in turning processes. The identification of the global attractor in case of unstable cutting leads to contradiction between experiments and theory. This contradiction draws the attention to the limitations of the small parameter approach related to the highly interrupted cutting condition.
An Efficient Technique to Determine Susceptibility of Aircraft Brake to Judder at the Design Stage
Authors: Rook Todd
Published: June 2008

A new technique is developed to predict the level of brake torque fluctuations that are a major source of vibration complaints in business jets. The computational efficiency of the proposed technique permits it to be used as a design tool where it can provide the most benefit.
An Improved Noise Path Synthesis Technique for Systems With Nonlinear Joints
Authors: Rook Todd
Published: June 2008

An efficient synthesis approach is developed which permits the calculation of the steady-state frequency response (FRF) of an assembly that is comprised of linear components and nonlinear joints. Receptance or accelerance matrices are used to characterize the linear components, which permits condensation of the system to just the joint degrees-of-freedom which is an immediate computational savings. Integrated into the technique is a frequency continuation scheme which permits studies across a wide range of frequencies — a key improvement to the continuation technique is the use of spline fits for the component FRF curves which provides significant cost savings over using modal expansion series at each iteration and also permits experimental data to be used if available. Finally, the calculated nonlinear joint forces are then used to study the power flow, structural and airborne, in the assembly, as well as to provide insight into the dynamic behavior within the components.
Method of Complex Amplitudes: Harmonically Excited Oscillator With Strong Cubic Nonlinearity
Authors: Gendelman O. V. , Manevitch L. I.
Published: June 2008

Application of method of complex amplitudes for investigation of dynamics of nonlinear oscillatory systems is considered. The method is analyzed in details for harmonically forced Duffing oscillator without damping for the case of exact 1:1 resonance. It is demonstrated that the method of complex amplitudes may be formalized as a generalization of standard multiple–scales procedure. Two alternatives for elimination of secular terms in high-order approximations are proposed and compared for various values of small parameter. It is demonstrated that regardless the exact procedure chosen the necessary condition to avoid secularities is the appropriate choice of functions determining the correction of the slow time scale in any approximation. Criterion for use of the method of complex amplitudes is formulated. All analytic results are compared with data of numerical simulation and considerable agreement is observed.
Nonlinear Dynamics of One-Way Clutches in Belt-Pulley Systems
Authors: Zhu Farong , Parker Robert G.
Published: June 2008

One-way clutches are frequently used in the serpentine belt accessory drives of automobiles and heavy vehicles. The clutch plays a role similar to a vibration absorber in order to reduce belt/pulley vibration and noise and increase belt life. This paper analyzes a two-pulley system where the driven pulley has a one-way clutch between the pulley and accessory shaft that engages only for positive relative displacement between these components. The belt is modeled with linear springs that transmit torque from the driving pulley to the accessory pulley. The one-way clutch is modeled as a piecewise linear spring with discontinuous stiffness that separates the driven pulley into two degrees of freedom (DOF). The harmonic balance method (HBM) combined with arc-length continuation is employed to illustrate the nonlinear dynamic behavior of the one-way clutch. HBM with arc-length continuation yields the stable and unstable periodic solutions for given parameters. These solutions are examined across a range of excitation frequencies. The results are confirmed by numerical integration and the widely used bifurcation software AUTO. At the first primary resonance, most of the responses are aperiodic, including quasiperiodic and chaotic solutions. At the second primary resonance, the peak bends to the left with classical softening nonlinearity because clutch disengagement decouples the pulley and the accessory over portions of the response period. The dependence on system parameters such as clutch stiffness, excitation amplitude, and inertia ratio between the pulley and accessory is studied to characterize the nonlinear dynamics across a range of conditions.
Reconstructing the Phase Space With Fractional Derivatives
Authors: Feeny B. F. , Lin G. , Das T.
Published: June 2008

Fractional derivatives are applied in the reconstruction of the phase space of dynamical systems with a single observable. The fractional derivatives of time series data are obtained in the frequency domain. The method is applied to a Duffing oscillator, the Lorenz system, and data from a two-well experiment. The ability of the method to unfold the data is assessed by the method of global false nearest neighbors. The reconstructed data is used to compute recurrences and correlation dimensions. The reconstruction is compared to the method of delays in order to assess the choice of reconstruction parameters, and also the quality of results.
Nonlinear Dynamics of a Pipe Conveying Pulsatile Flow: Effect of an Asymmetric Spring Supported End
Authors: Yamashita Kiyotaka , Yoshizawa Masatsugu , Agata Jun , Motoki Arata
Published: June 2008

Flow-induced vibration of a fluid conveying pipe with a spring supported end is examined theoretically and experimentally under the condition that the fluid velocity has a small pulsatile component. The parametric resonance of the lateral pipe vibration is occurred due to the pulsating flow. In this paper, the four first-order ordinary differential equations, which govern the amplitudes and phases of the nonplanar pipe vibration, are derived from the nonlinear nonself-adjoint integro partial differential equations by the method of the Liapnov-Schmidt reduction. The effect of the asymmetric spring support on the nonlinear stability of the lateral pipe vibration is discussed with the obtained equations of amplitudes and phases. Furthermore, the experiments were conducted with the silicon rubber pipe conveying water. The lateral deflections of the pipe were measured by the image processing system, which was based on the images from two CCD cameras. The typical features of the parametric resonance were confirmed qualitatively.
Nonlinear Vibration of Sheet Metal Plates Under Interacting Parametric and External Excitation During Manufacturing
Authors: Kim Chung Hwan , Lee Chong-Won , Perkins N. C.
Published: June 2008

This study in motivated by the vibrations that plague coating processes used in the manufacturing of coated sheet metal. These vibrations arise from time-dependent tension fluctuations within the sheet metal plate as well as from the eccentricity of the rollers used to transport the plate. The time-dependent tension is observed to be rather broad-band and creates multi-frequency parametric excitation. By contrast, the roller eccentricity is largely single-frequency (synchronized with the roller speed) and creates single-frequency external excitation. The plate and excitation sources are studied herein using a single-degree-of-freedom model with a cubic nonlinearity, subject to combined parametric and external excitation. In our study, we investigate the resonances that arise from the synergistic effects of multi-frequency parametric excitation and single-frequency external excitation. For the simpler case of single-frequency parametric excitation, we observe both sum and difference combination resonances in addition to principal parametric resonance. For the case of multi-frequency parametric excitation, we observe a frequency shift for the parametric resonance that derives from the cubic nonlinearity and external excitation. Moreover, the phase relationships of the external and each parametric excitation source have a significant effect on the resulting response amplitude. We use these analyses to explain the resonance mechanisms observed in experiments conducted on an example sheet metal coating process.
Modal Interactions in a Thermally Loaded Annular Plate
Authors: Arafat Haider N. , Nayfeh Ali H.
Published: June 2008

We investigate the nonlinear forced vibrations of a thermally loaded annular plate with clamped-clamped immovable boundary conditions in the presence of a three-to-one internal resonance between the first and second axisymmetric modes. We consider the in-plane thermal load to be axisymmetric and excite the plate externally by a harmonic force near primary resonance of the second mode. We then use the nonlinear von Ka´rma´n plate equations to model the behavior of the system and apply the method of multiple scales to investigate its responses. We found that the response can be periodic oscillations consisting of both modes, with a large component from the first mode. Moreover, the periodic solutions may undergo Hopf bifurcations which lead to aperiodic oscillations of the plate.
An Experimental Study of Parametrically Excited Cantilever Beam and System Identification of Nonlinear Modes
Authors: Doughty Timothy A. , Davies Patricia , Bajaj Anil
Published: June 2008

The nonlinear response of a parametrically excited cantilevered beam is experimentally investigated and nonlinear system identification techniques are used to generate nonlinear modal models to explain the observed behavior. Three techniques are applied to data from simulation of a nonlinear single-mode model as well as from experiments, for a beam which is excited with stationary harmonic input at nearly twice the frequency of the beam’s second mode. The first technique is based on the continuous-time differential equation model of the system, the second uses relationships generated by the method of harmonic balance, and the third is based on fitting steady-state response data to steady-state amplitude and phase predictions resulting from a multiple time scales analysis. Each approach is successful when applied to identify models from simulation data. For the experimental data obtained from a beam under nominally identical conditions, difficulties with using higher harmonic information lead to the incorporation of nonlinear damping terms and an investigation of two-mode behavior. Simulated two-mode behavior demonstrates how the beam’s third mode, with natural frequency nearly three times the frequency of the second mode, is excited in the physical structure, thus explaining the mismatch between the previous model and experiment at the third harmonic in the beam’s response.
Optoelectronic Vibration Measurement System
Authors: Simonov Vladimir L.
Published: June 2008

During mechanical testing in many cases it is necessary to measure real oscillations of the objects themselves, or their parts. In such cases a method can be used, which uses optical image of the object. When the object oscillates and there is optical visibility of the object’s surface, nearly always one can form an optical image of contrast part of the object. If the object oscillates mainly in the plane which is perpendicular to the axis of optical visibility, then it is possible to measure displacements of this image. For these measurements a special optoelectronic system was designed. This paper describes the results of investigations and creation of a model of such optoelectronic system. This particular model was designed especially for vibration measurements of some hardly-accessible parts of aviation devices: turbine coolers, overheated parts of aviation engines from some distance (several meters). During investigations it was revealed, that system’s applications are much wider than the ones used at the beginning. So in this paper also presented are results of measurements of the system for aviation engine blades; for rotors’ balancing; for vibration testing of aviation turbine coolers; for vibration measurements of elements of printed circuit boards in electronic devices; for various parts of constructions; for acoustic loudspeakers; for active objects (which emit light themselves); in automobile industry; for distant measurements (hundreds of meters); and for some medical applications. The main problem during system design was to eliminate errors of measurements. These errors took place because various objects have different size and shape, and they emit or reflect different amount of light. Without compensation the total error would be about hundreds of percent. So all errors were analyzed, classified, mathematically modeled and created were special loops for errors compensation. As a result total error of measurement was less that 15% for all conditions of use. The system has build-in block for self-testing. During design it was provided that the system can be applied for indoor and outdoor conditions. Special climatic testing have confirmed that.
Implementation of the Wideband Autoparametric Vibration Absorber on a Flexible Structure
Authors: Vyas Ashwin , Bajaj Anil K. , Raman Arvind
Published: June 2008

The dynamics of a resonantly excited thin cantilever with an active controller are investigated experimentally. The controller mimics a passive wideband absorber discussed in [1]. PZT patches are bonded to both sides of the beam to actuate it, while an electromagnetic shaker drives the beam near resonance. An active controller consisting of an array of uncoupled controllers is developed, such that the governing equations for the controller are quadratically coupled to the resonating system. The control signal, in terms of the motion of the controllers, is quadratically nonlinear. The controller is implemented using a modelling software and a controller hardware board. Two sets of experiments are performed: one with a constant excitation frequency and the other with a linearly varying excitation frequency at a slow rate (non-stationary excitation). The experimental results verify the analysis presented for the passive wideband autoparametric vibration absorber. They also demonstrate the effectiveness of the absorber in reducing the response amplitude of structures, and its robustness to frequency mistuning.
Modal Characterization of Turbomachinery Bladed Disks by Optical Measurements
Authors: Lombard J.-P. , Seinturier E. , Raynaud J.-L.
Published: June 2008

The dynamic design of bladed disks consists in making sure that structural modes are not excited by the harmonics caused by engine speed (coincidences predicted after a Campbell diagram analysis). In practice, it is impossible to avoid every single coincidence over the whole operating range. An engine test is carried out at the end of the design cycle, in order to determine vibration levels. By means of this test and the validated FE model, the designer verifies frequency margins, and from this, is able to determine whether or not the bladed disk is likely to be at risk from vibration fatigue, otherwise known as High Cycle Fatigue (HCF). This analysis needs several FE calculations whose models have been updated in relation to component tests to measure stress distribution (use of strain gauges). One of the drawbacks of this type of measurement lies in the intrusive character of instrumentation used, which upsets the dynamic behavior of the blades in particular for high level modes. This document puts forward the application of non-intrusive, optical measurements, and highlights the accuracy that can be obtained by measuring mode shapes. Furthermore, this paper highlights the importance of defining levels of accuracy for measurements obtained, for example, in characterizing frequency scatterings for each blade individually, scatterings which are translated by an amplification of the structure aeroelastic response.
Experimental and Numerical Study of a New Percussive Drilling Model With a Drift
Authors: Franca Luiz Fernando P. , Weber Hans Ingo
Published: June 2008

New drilling techniques have been studied to increase the penetration in hard rock. These techniques use harmonic load and, in some cases, also impacts to generate a greater penetration rate. Analyzing only a percussive penetration phenomenon, the new model presented in this paper allows the forward motion (with a drift) in stick-slip condition without impact. Numerical and experimental investigations are presented and are qualitatively compared. Expanding the numerical analysis it is shown that the behavior may vary from periodic to chaotic motion.
Identification Method for Both Linear and Piecewise Linear Dynamical Systems
Authors: Coutel S. , Lamarque C. H. , Pernot S.
Published: June 2008

Piecewise linear systems identification method is outlined in this article. Wavelets Analysis principles are widely used in this paper. Firstly, wavelets provide a very efficient mean to construct filters that are able to cut known degree polynomial terms in experimental signal. Secondly, wavelets are introduced to detect and to localize singularities in experimental signals that are characteristic of phase changes in a piecewise linear system. Eventually, we present a method to solve inverse problem that enables extracting instantaneous parameters from experimental data of physical studied system.
Dynamic Behavior of a Revolute Clearance Joint in Multibody Mechanical Systems
Authors: Flores P. , Lankarani H. M. , Ambro´sio J. , Claro J. C. P.
Published: June 2008

This work describes the influence of the clearance size and the coefficient of friction on the dynamic response of a revolute clearance joint in multibody mechanical systems. When there is a clearance in a revolute joint, impacts between the journal and the bearing can occur, and consequently, local deformations take place. The impact is internal and the response of the system is performed using a continuous contact force model. The friction effect due to the contact between joint elements is also modeled. The clearance size and friction effects are analyzed separately. Through the use of Poincare´ maps both periodic and chaotic responses of the system are observed. The results predict the existence of the periodic or regular motion at certain clearance sizes and friction coefficients and chaotic or nonlinear in other cases. A detailed discussion of the results relative to a planar slider-crank mechanism with a revolute clearance joint is presented.
Control of Exciton Fluxes in an Excitonic Integrated Circuit
Authors: High Alex A. , Novitskaya Ekaterina E. , Butov Leonid V. , Hanson Micah , Gossard Arthur C.
Published: June 2008

Efficient signal communication uses photons. Signal processing, however, uses an optically inactive medium, electrons. Therefore, an interconnection between electronic signal processing and optical communication is required at the integrated circuit level. We demonstrated control of exciton fluxes in an excitonic integrated circuit. The circuit consists of three exciton optoelectronic transistors and performs operations with exciton fluxes, such as directional switching and merging. Photons transform into excitons at the circuit input, and the excitons transform into photons at the circuit output. The exciton flux from the input to the output is controlled by a pattern of the electrode voltages. The direct coupling of photons, used in communication, to excitons, used as the device-operation medium, may lead to the development of efficient exciton-based optoelectronic devices.
A cytological study of the development of Erysiphe graminis in its host barley, as influenced by the two fungicides ethirimol and propiconazole
Authors: Heller Annerose , Grossmann Friedrich , Frenzel Burkhard , Hippe Sigrun
Published: June 2008

Light and electron microscopy of barley epidermal cells treated with ethirimol or propiconazole and then inoculated with Erysiphe graminis f. sp. hordei showed the complex reaction of this host–parasite system to fungicides. The completely different biochemical modes of action of the two fungicides were reflected in the ultrastructural changes observed. Specific fungicidal effects could be distinguished from degenerative processes associated with senescence of untreated plants. For ethirimol, the first changes to be observed in the nucleus were blebbing of the outer nuclear membrane, invaginations into the nucleoplasm, and loss of the dark-staining material of nuclear pores. Later on, large areas of the cytoplasm were devoid of ribosomes. Moreover, electron-dense material was found in the perinuclear space and in cisternae of the endoplasmic reticulum. Round bodies, containing electron-dense material of unknown origin, appeared in the cytoplasm. Propiconazole, on the other hand, caused severe malformations of haustoria, host cell wall appositions, and wall thickening. The sheaths surrounding the haustoria were significantly enlarged, and vesicular and multivesicular bodies appeared in the extrahaustorial matrix. In later stages, degenerated haustoria were partially encapsulated by the host cell. Large, rectangular, electron-opaque structures, termed Fibrosinkörper, were observed in secondary hyphae. Both fungicides tested caused swelling of secondary hyphae. Key words: Erysiphe graminis f.sp. hordei, ethirimol, propiconazole, host–parasite system, cytology, electron microscopy.
Standing crop and net production of sedge meadows of an ungrazed polar desert oasis
Authors: Henry G. H. R. , Svoboda J. , Freedman B.
Published: June 2008

Standing crop and net production were measured in sedge meadow communities of a coastal lowland at Alexandra Fiord, Ellesmere Island (79°N), a high arctic oasis. The meadows are dominated by Carex aquatilis stans, Carex membranacea, and Eriophorum angustifolium triste. Dwarf shrubs (Dryas integrifolia and Salix arctica) are also important constituents. Total standing crop ranged from 1400 to 3200 g/m2 and was largely (50–80%) composed of attached dead matter. The accumulation of litter and dead roots and rhizomes is attributed to low rates of decomposition, and to a lack of grazing by large herbivores such as muskox. Net production (100–200 g/m2) was similar to more southerly tundra meadows, emphasizing the oasis-like nature of this high arctic location. Furthermore, net production did not vary significantly among sites or years. The consistent net production was due to similar edaphic and climatic conditions, the concentration of biomass belowground, and the apparently fixed growth period of arctic sedges. Key words: sedge meadows, high arctic, net production, standing crop, Carex.
Net alignment of cellulose in the periclinal walls of the shoot apex surface cells in Kalanchoe blossfeldiana. II. Flower development
Authors: Nelson Amy J.
Published: June 2008

Dome geometry and the pattern of net cellulose alignment in the periclinal walls of the surface cells of Kalanchoe blossfeldiana were examined during sequential stages of flower development. Floral apices of photoperiodically induced plants were dissected, stained, and observed under a dissecting microscope. The outermost cell layer(s) of the surface was surgically removed from the floral apex and viewed under a polarizing microscope. Correlations were found between the geometry of the dome, the pattern of cellulose in the surface cells, and the pattern of initiation of floral organs at the apex. Tangentially aligned cellulose was always observed around the periphery of the floral dome, whereas no net alignment of cellulose typically occurred in the centermost region. Circumferential reinforcement of cellulose was consistently observed at sites of incipient organ initiation, and the pattern of cellulose alignment on emerging primordia correlated with the type of organ development. No strict dependence was evident between the number and positioning of one whorl of floral ogans and that of the previous whorl. Key words: shoot, cellulose, flower, floral, organogenesis.
Companion plants affect colonization of Myrica cerifera by vesicular–arbuscular mycorrhizal fungi
Authors: Poole Barbara C. , Sylvia David M.
Published: June 2008

The vesicular–arbuscular mycorrhizal (VAM) status of Myrica cerifera L. (wax myrtle) was investigated under greenhouse and field conditions. Myrica cerifera and Paspalum notatum Flügge (bahiagrass) were grown in inter- and intra-specific plant combinations with and without VAM fungi. Roots of field-collected M. cerifera were also examined for colonization by VAM fungi. Myrica cerifera became colonized by VAM fungi only in the presence of a VAM colonized grass plant; however, arbuscules were consistently lacking. VAM fungi had no effect on root or shoot growth of M. cerifera. When grown in the presence of P. notatum, shoot growth of M. cerifera was reduced, regardless of inoculation treatment. Colonization of field-collected M. cerifera roots ranged from 0 to 75%; however, nearly all samples lacked arbuscules. Unexpectedly, samples from wet sites had the highest colonization levels. Failure of M. cerifera to become colonized when grown without a VAM companion plant and the absence of arbuscules when M. cerifera became colonized in the presence of a VAM companion plant suggest that the VAM association of M. cerifera is nonfunctional. Key words: arbuscule, Glomus, interspecific, intraspecific, nonhost.
The bearing capacity of rigid piles and pile groups under inclined loads in layered sand
Authors: Meyerhof G. G. , Mathur S. K. , Valsangkar A. J.
Published: June 2008

The ultimate bearing capacity of rigid vertical and batter piles and pile groups in layered sand has been determined under various inclinations of the load varying from the vertical to horizontal directions. The results of load tests on single model piles of different inclinations and on free-standing groups are compared with theoretical estimates. The influence of load inclination on the bearing capacity can be represented by simple interaction relationships between the axial and normal components of the ultimate load. The effect of eccentricity of the load on the ultimate bearing capacity of pile groups is discussed on the basis of previous theory and model test results.
Stage loading of a highway embankment on tidal flats
Authors: Burwash W. J. , Matich M. A. J.
Published: June 2008

The approach embankment to the eastern extremity of a bridge across the East River near Trenton, Nova Scotia involved construction of a 6.4 m high embankment on tidal flats. Very soft to soft slightly organic marine silts were found to underlie the tidal flats to a depth of 6–9 m where bedrock was encountered. Construction of an embankment of this height on the tidal flats would require very flat sideslopes to ensure stability. Alternatively, all or part of the silt could be removed or the embankment could be built slowly using the stage loading technique and allow the silt to consolidate and gain strength during construction of the embankment. Stage loading had a considerable economic advantage over the other alternatives and since sufficient time was available, this method was adopted.The case history of this project is presented including results of the settlement performance of the embankment and porewater pressure response in the silt. These results are compared with predicted values and conclusions are drawn regarding the stage loading technique for this particular type of application.
Performance of temporary tie-backs under winter conditions
Authors: Morgenstern N. R. , Sego D. C.
Published: June 2008

The construction of an underpass in the City of Edmonton required the temporary relocation of the CNR main-line prior to the construction of a permanent bridge. The line was placed close to the underpass excavation which was supported by a tie-back sheet pile wall. Because of the stringent requirements associated with the presence of the railway line, the supports were designed on a conservative basis and observations of tie-back loads were taken over a period of 7 months.This note presents the observations of tie-back loads from January to July, 1977. Following installation in accordance with the design requirements, substantial fluctuations in tie-back load were observed for about 3 months. Then the loads fell off gradually to about 50% of the originally applied values. The variation of the load with time bears a strong correlation with average air temperature and is accounted for by the alternate freezing and thawing of the ground adjacent to the sheet pile wall. The ultimate decline in load is attributed to relaxation of the soil behind the wall during spring thaw. The case history draws attention to special requirements associated with interpretation of earth pressure measurements during winter con struction.
Settlement limitations for cylindrical steel storage tanks
Authors: Rosenberg Peter , Journeaux Noël L.
Published: June 2008

Tank inspections in the petroleum industry often include an evaluation of settlement effects. Tank failures and floating-roof problems have often been attributed to distortion of tanks due to settlement. In geotechnical practice evaluation of excessive settlement is done by referring to empirically derived limits that vary considerably.In this study the authors took settlement data from the literature and their own studies, and compared the results with limits commonly used in tank evaluations. On this basis tentative limit criteria are suggested that can be used in estimating the probability of the occurrence of tank problems.