bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical Approximations of Power Flow for a Vehicle Structure With Uncertainties
Authors: Lee Soo-Yeol , Castanier Matthew P. , Pierre Christophe
Published: June 2008

In this paper, an efficient approach is presented for probabilistic power flow analysis of complex structures with parameter uncertainties. A component-based technique is used to generate reduced order models of low- to mid-frequency vibration and power flow. The reduced order model (ROM) is built from component mode synthesis of finite element models, followed by a secondary modal analysis to reduce the number of degrees of freedom associated with the component interfaces. This formulation allows for efficient and accurate prediction of vibration transmission in complex structural systems. Then, this methodology is extended to the study of statistical approximations of the power flow for a structure with parameter uncertainties. Two techniques are employed for probabilistic power flow analysis: (1) a locally linear interpolation (LLI) method for low-dimensional random variable domains, and (2) an advanced mean value (AMV) method for multi-dimensional random variable domains. In addition, an extended version of the AMV method is presented for uncertainties characterized by a uniform distribution. These statistical approximations of power flow are first demonstrated for a simple example system, an L-shaped plate. They are then examined in more detail for an important engineering application, a ground vehicle model.
Stability Considerations for a Vertical Mount Energy Storage Flywheel
Authors: Underwood Jess , Kirk R. Gordon
Published: June 2008

The optimum design of a flywheel mechanical battery system would have a minimum friction resistance from the bearings and the aerodynamic drag forces acting on the rotor system. To investigate the complexities involved in the design of a flywheel mechanical battery system, a test rig has been constructed at the Virginia Tech Rotor Dynamics Laboratory. This test rig consists of a fifty-pound steel flywheel that is mounted on a vertical shaft system and driven by a brushless permanent magnet motor. Initially, it was thought that the rotor could be supported with a single bearing, positioned at the upper mount point of the rotor. This pendulum-type configuration was found to have a major instability at low frequency. This paper will discuss these initial results and the further analysis and testing of a two bearing vertical shaft design. In addition, analyses of both systems have been performed using DyRoBeS, a finite element based rotor dynamics analysis code. The conclusions and recommendations presented here will be of interest to designers of future vertical rotors for such flywheel systems.
Scaling Laws for Ultra-Short Hydrostatic Gas Journal Bearings
Authors: Spakovszky Z. S. , Liu L. X.
Published: June 2008

The journal bearings of the MIT micro-devices are located at the outer periphery of the rotor and are designed to operate at rotational speeds of order 2 million rpm in order to enable high-power densities with turbomachinery tip speeds near 500 m/s. These journal bearings are very short compared to their relatively large bearing diameters such that the bearing L/D is typically less than 0.1, that is at least one order of magnitude smaller than in conventional gas bearings. Thus, the ultra-short micro gas journal bearings essentially act as short annular seals and operate at Reynolds numbers of order 300, two orders of magnitude lower than conventional annular seals. The concepts that hold for turbulent flow, large scale annular seals do not apply to micro bearings and the laminar flow regime sets new challenges in the design, implementation and operation of ultra-short, high-speed gas bearings. In order to reach the goal of operating the MIT micro devices at full design speed, the micro-bearing design must be improved and engineering solutions need to be found to overcome the challenges of high-speed bearing operation. This paper is the first to derive the scaling laws for the dynamics of ultrashort hydrostatic gas journal bearings. The theory is established from first principles and enables a physics based characterization of the dynamic behavior of ultra-short hydrostatic gas bearings. The derived scaling laws for natural frequency and damping ratio show good agreement with experimental data. A simple criterion for whirl instability is found that only depends on bearing geometry. The scaling laws together with this criterion are used to delineate engineering solutions critical for stable high-speed bearing operation. Design charts are developed which provide the link between fabrication tolerances, bearing performance, and the tolerable level of rotor unbalance for a minimum required whirl ratio.
The Experimental Study on the Shock Stiffness of Rubber Isolator
Authors: Tan Bo , Huang Yingyun , Chen Gang
Published: June 2008

The shock stiffness of rubber vibration isolators of different sizes but the same type is experimentally studied by light gas cannon and their relationships are presented. The performance of the shock resistance of rubber isolators is also analyzed.
Multivalued Stochastic Differential Equations and Its Applications in Dynamics
Authors: Bernardin F. , Lamarque C. H. , Schatzman M.
Published: June 2008

Using a maximal monotone graph we can deal with many nonlinear dynamical problems involving e.g. dry friction or impacts. When submitted to an external stochastic term, a class of differential inclusions is obtained. Existence and uniqueness results are recalled. An adapted numerical scheme is presented. Numerical results are presented for different examples of models.
Numerical and Experimental Investigations of Simple Non-Linear System Modelling a Girling Duo-Servo Brake Mechanism
Authors: Awrejcewicz Jan , Olejnik Pawel
Published: June 2008

Our analysis is focused on modeling of friction phenomena exhibited by a brake like duo-servo system. The occurred in girling duo-servo brake an frictional mechanism can be modeled approximately by two degrees-of-freedom mechanical system, where a normal force varies during displacement of a block. The Coulomb friction is used after numerical analysis, and a normal force pressing the sliding body to a belt depending on an angle bar motion of the analyzed system is applied. In addition, the numerical analysis is supported by investigation of the real laboratory object modeling the feedback reinforcement of friction forces acting on the block.
Order-Component Separation and Ranking of Dynamic Signals Using Angular-Information Kalman-Filtering Order Tracking
Authors: Pan Min-Chun , Lin Yu-Fong
Published: June 2008

This paper presents advanced order tracking techniques using the Kalman tracking filter with angular information to extract both close and cross order components from measured dynamic signals. Separated order components can be ranked for the purpose of trouble shooting and design modification. In the study, close-order components resulting from shaft unbalancing and gear meshing of a transmission element test bench can be extracted precisely. In addition, for the pass-by noise measurement of CVT-driving electrical scooters, spectral components can be ranked appropriately for a further noise reduction task.
Operating Investigation of Transmission Systems Using Advanced Time-Frequency Representations
Authors: Pan Min-Chun , Huang Jeng-Yi
Published: June 2008

This study aims at developing and implementing advanced time -frequency representation algorithms, i.e., Choi-William distribution, and cone-shape distribution, based on the spectrogram and the smoothed Wigner- Ville distribution to both improve time and frequency resolutions as compared with the spectrogram, and soothe interferences resulting from the Wigner-Ville distribution. Synthetic signals were designed to assess the effectiveness of these algorithms, and compare computing features of these schemes as well. A transmission-component test rig was built up to investigate dynamic characteristics of the gearbox, belt set and electro-magnetic brake during operation. Conducted experimentation highlights the justification of applying these advanced schemes in condition monitoring tasks of mechanical systems.
Updating Nonlinear Dynamical Models Using Response Measurements Only
Authors: Yuen Ka-Veng , Beck James L.
Published: June 2008

A spectral density approach for the identification of linear systems is extended to nonlinear dynamical systems using only incomplete noisy response measurements. A stochastic model is used for the uncertain input and a Bayesian probabilistic approach is used to update the uncertainties in the model parameters. The proposed spectral-based approach utilizes important statistical properties of the Fast Fourier Transform and their robustness with respect to the probability distribution of the response signal in order to calculate the updated probability density function for the parameters of a nonlinear model conditional on the measured response. This probabilistic approach is well suited for the identification of nonlinear systems and does not require huge amounts of dynamic data. The formulation is presented directly for multiple-degree-of freedom systems. Examples using simulated data for a Duffing oscillator and a four-DOF inelastic structure are presented to illustrate the proposed approach.
Bifurcation Analysis of Nonlinear Vibration Isolation System With Hard Stiffness by Cell Mapping
Authors: Yu Xiang , Zhu Shijian , Lou Jingjun
Published: June 2008

Period-doubling bifurcation is one of the major routes to chaos, but the methods widely used have some shortages in analyzing the bifurcation of the nonlinear vibration isolation system with hard stiffness. The location and property of bifurcation solution can be obtained conveniently by using numerical methods. Therefore, numerical research is important. In this paper, global bifurcation diagram is achieved by using Poincare´ mapping method. Subsequently, cell mapping as a useful numerical method is applied to analyze the static and dynamic bifurcation of nonlinear vibration isolation system with hard stiffness.
Variable Damping Design in Position Control of Flexible Single Arm
Authors: Panza Michael J.
Published: June 2008

The design of variable damping in the position control of a flexible single link arm is considered. Variable damping is obtained from velocity feedback with variable gain or from actuator variation. The variable damping is related to the position of the arm. The design process begins with the development of a nondimensional mathematical model of a flexible beam with one flexural mode, an actuator, and feedback control. Optimal control/arm parameters are determined for a constant damping system. Dynamic design sensitivity analysis is used to construct a variable damping scheme. Optimal scheme parameters are determined. A variable damping scheme that applies little damping for most of the motion and a great deal of damping as the arm nears its final position emerges. Vibration suppression is controlled in an optimal fashion throughout the motion. The resulting system provides a minimum response time with negligible overshoot for the tip of the arm. Numerical simulations demonstrate the method.
Comparison of Two Distributed Fuzzy Logic Controllers for Two-Link Rigid-Flexible Manipulator
Authors: Shi Linda Z. , Trabia Mohamed B.
Published: June 2008

Fuzzy logic control presents a computationally efficient and robust alternative to conventional controllers. While experts can easily design fuzzy logic controllers (FLC’s) for many applications, some systems such as multi-link flexible manipulators, which have many variables and complex behavior, offer challenges to fuzzy logic control. An earlier work, [1], presented two distributed FLC’s for a single-link flexible manipulator. This paper extends that work to the area of two-link rigid-flexible manipulator that moves in a vertical plane where the gravity field is active. The first distributed structure, which is based on observing the performance of the manipulator, uses three PD-like FLC’s. The first two FLC’s control joint angles and joint angular velocities while the third controls the tip vibration. The second distributed structure is based on evaluating the importance degrees of the system output variables of the system by randomly varying its inputs. Variables with the same rank of the importance degree are grouped together and variables with less importance degrees may be deleted to simplify the design of the controller. The fuzzy rules of FLC’s in the two structures are selected to mimic the performance of comparable linear controllers. The parameters in both structures are tuned using nonlinear programming to obtain better performance. The two distributed structures are simulated and compared.
Digital Optimal Vibration Control of a Flexible Structure Containing Piezoelectric Elements
Authors: de Abreu Gustavo L. C. M. , Ribeiro Jose´ F. , Steffen Valder
Published: June 2008

In this paper, a digital regulator is designed and experimentally implemented for a flexible beam type structure containing piezoelectric sensors and actuators by using optimal control design techniques. The controller consists of a linear quadratic regulator with a state estimator, namely a Kalman observer. The structure is a cantilever beam containing a set of sensor/actuator PVDF/PZT ceramic piezoelectric patches bonded to the beam at optimal location points. Experimental results illustrate the optimal control design of a cantilever beam structure.
Mechanically Biased Nano-Resonators for Signal Transduction
Authors: Blick Robert H. , Hoerner Andreas , Beil Florian W. , Wegscheider Werner
Published: June 2008

We realize nanomechanical resonators for studying their mechanical properties in the nonlinear regime. This is of prime importance considering signal mixing which is a direct result of nonlinear mechanical response. Combining signal mixing with the advantages of mechanical systems is very promising, especially when considering the high speed of operation currently becoming available. The resonators are implemented as hybrid wires machined in semiconductor substrates such as GaAs and Si, possessing mechanical modes up to 400 MHz. Magnetomotive excitation and capacitive on-chip detection are used to determine the mechanical response. We apply a specially designed mechanical resonator, shaped as a T-resonator or divining rod, for mechanically biasing the nanoresonator. This approach allows us to extend the parameter range accessible into the regime of nonlinear dynamics [Erb98,Krs01,Shb02a].
Recovery of Preload in Bolted Joint Using Shape Memory Alloy Elements
Authors: Ghorashi Mehrdaad , Inman Daniel J.
Published: June 2008

One of the main problems with a bolted joint is losing its preload. In this situation, it cannot provide the required clamping force needed to keep the joint members together or prevent fluid leakages. Although every effort is usually made at the design stage to prevent such failure, because of the numerous factors present in the problem, these efforts are not always successful. After loosening occurs, the joint should be retightened to regain its preload. However, there are circumstances where the joint is very important but it is not easily accessible and retightening cannot be done manually. The shape memory effect (SME) property can be used in such circumstances to produce the necessary preload. The shape memory alloy (SMA) element should be activated if monitoring the bolt preload through the application of strain gauges shows that the preload has fallen below a pre-determined threshold level. This paper presents a mathematical model for the SMA element and the whole joint behavior. The relation between SMA activation (corresponding to the amount of phase change in the SMA) and the resulting preload is estimated. To this end, it is assumed that the SMA element behaves in such a way that either its cross-sectional area or its volume remain constant. The analysis of this model shows the feasibility of the application of SMA for producing the required preload. Hence, if used properly, the required preload is achieved and a self-healing joint is obtained.
Dynamic Finite Element Analysis of a Piezoelectric Bimorph Beam Deflector With Consideration of Hysteresis Effect
Authors: Chao Paul C. P. , Chiu C. W. , Huang J. S. , Tseng H. C.
Published: June 2008

This study is devoted to propose a method of finite element technique to account for the hysteresis effect of a piezoelectric bimorph beam deflector. To this end, the constitutive equations of a general piezoelectric material are first modified to include the hysteresis effect by adding a polarization term in one of constitutive equations. Based on these modified constitutive equations and employment of Preisach model for hysteresis, the governing equations of the bimorph beam are derived through the utilization of Hamilton’s principle and calculus of variation. In addition, according to the common physical rules, boundary, transition and continuous conditions are next formulated to complement the governing equations. Simulations are finally conducted to show the effectiveness of the proposed modeling technique and decipher the dynamic behavior of the piezoelectric beam with consideration of hysteresis effect.
Mechanical Behavior of an Electrostatically Actuated Microplate
Authors: Zhao Xiaopeng , Abdel-Rahman Eihab M. , Nayfeh Ali H.
Published: June 2008

We present a nonlinear model of electrically actuated microplates. The model accounts for the nonlinearity in the electric forcing as well as mid-plane stretching of the plate. We use a Galerkin approximation to reduce the partial-differential equations of motion to a finite-dimension system of nonlinearly coupled second-order ordinary-differential equations. We find the deflection of the microplate under DC voltage and study the pull-in phenomenon. The natural frequencies and mode shapes are then obtained around the deflected position of the microplate by solving the linear eigenvalue problem. The effect of various design parameters on both the static response and the dynamic characteristics are studied.
Active Vibration Control of Meso- and Microstructures via Piezoelectric Films
Authors: Hsu Yi-Chu , Wu Chia-Che , Cao G. Z. , Shen I. Y.
Published: June 2008

The purpose of this paper is to demonstrate the feasibility of active vibration control for meso- and microstrucutres through use of PZT (Lead-Zirconium-Titanium Oxide) thick films. This paper consists of two parts. The first part is to develop a sol-gel process to fabricate crack-free PZT thick films with thickness of 2 microns and area of 4 mm × 4 mm. The PZT thick film has a Pt/Ti bottom electrode and a gold top electrode. Moreover, the PZT thick film is fabricated on a silicon cantilever, whose dimensions are 20 mm × 15 mm × 0.4 mm. The second part is an experimental demonstration of active vibration control using the PZT thick film. In the experiment, a tiny bulk PZT patch is first glued to the silicon cantilever. A function generator drives the bulk PZT simulating a source of disturbance exciting the silicon cantilever. In the meantime, a laser Doppler vibrometer (LDV) measures velocity of the cantilever tip. With a phase shifter as the controller, the LDV measurement is fed back to the PZT thick-film actuator to actively control the cantilever vibration. To evaluate the effectiveness of the active vibration control, a spectrum analyzer measures the frequency response functions (FRF) from the bulk PZT voltage to the LDV response. Experimental results show that the simple active vibration control scheme can reduce resonance amplitude of the first bending mode by 66%.
Multi-Harmonic Adaptive Vibration Control of AMB-Driveline Systems With Non-Constant Velocity Flexible Couplings
Authors: DeSmidt Hans A. , Wang K. W. , Smith Edward C.
Published: June 2008

Active Magnetic Bearings (AMB) have been proposed by many researchers and engineers as an alternative to replace traditional contact bearings in rotors and driveshafts. Such active, non-contact bearings do not have frictional wear and can be used to suppress vibration in sub- and supercritical rotor dynamic applications. One important issue that has not yet been addressed in previous AMB driveline control studies is the effect of non-constant velocity (NCV) flexible couplings, such as U-Joint or disk-type couplings. The NCV effects introduce periodic parametric and forcing actions that are functions of shaft speed, driveline misalignment and load-torque. Previous research has found that NCV couplings can greatly impact stability and cause significant harmonic excitation at integer multiples of the shaft speed. Thus, to ensure closed-loop stability and acceptable performance of any AMB-driveline with NCV couplings, these effects must be accounted for in the control law design. In this paper, a hybrid control law consisting of an analog PD feedback controller augmented with a slowly updating, multiple harmonic adaptive vibration control (MHAVC) is developed for a U-joint-driveline system supported by AMBs. The function of the PD controller is to ensure closed-loop stability and convergence of the MHAVC, while the MHAVC suppresses the steady-state vibration. Closed-loop stability, convergence, and performance are investigated over a range of shaft speeds for various misalignment and load-torque levels. It is found that there is an optimal range of P and D feedback gains that ensures both convergence of the MHAVC and maximizes the robust stability of the closed-loop system, with respect to NCV effects. Furthermore, it is demonstrated that the MHAVC can effectively suppress the multi-harmonic vibration induced by shaft imbalance and NCV coupling effects without knowledge of the disturbance input distribution.
Optimal Feedback Controls of Linear Systems With Time Delay
Authors: Sheng Jie , Elbeyli Ozer , Sun J. Q.
Published: June 2008

This paper presents an application of semi-discretization method to stability analysis and optimal design of PID feedback controls of time invariant and periodic linear systems with time delay. The method develops a mapping of the system response in a finite dimensional state space, and produces the stability boundaries and performance contours in the parametric space of control gains. Optimal feedback gains that minimize the largest absolute value of the eigenvalues of the mapping have been studied for different cases where the performance contours are either closed or open.
Active Feedback Control Systems of Floor Impulse Noise
Authors: Akishita Sadao , Ameyama Kei , Mitani Atsushi
Published: June 2008

This paper describes the active control systems for reducing floor impulse noise. The control system is comprised of actively controlled modular thin plates, which wholly cover the surface of concrete slab structure in the ceiling, and in each of which the mechanical vibration is controlled independently with bimorph type piezoelectric actuators. An active control system of modular plate is presented, where five actuators and five sensors are applied to control low frequency modes of bending vibration in the plate. The control system is now under development, main investigation items of whch are designing of vibration characteristics of modular thin plate, the active control system appropriate to the characteristics and cost reduction of the actuators and sensors.
The Multi-Degree-of-Freedom Tuned-Mass Damper for Suppression of Single-Mode Vibration Under Random and Harmonic Excitation
Authors: Zuo Lei , Nayfeh Samir A.
Published: June 2008

Whenever a tuned-mass damper is attached to a primary system, there is potential for utilization of motion of the absorber body in more than one degree of freedom relative to the primary system. In this paper, we propose that more than one mode of vibration of an absorber body relative to a primary system be tuned to a single natural frequency of the primary system. We cast the problem of optimizing the multi-degree-of-freedom connection between the absorber body and primary structure as a decentralized control problem, and develop optimization algorithms based on the H2 and H-infinity norms to minimize the response to random and harmonic excitations, respectively. We find that a two-DOF absorber can attain better performance than the optimal SDOF absorber, even for the case where the rotary inertia of the absorber tends to be zero. With properly chosen connection locations, the two-DOF absorber can achieve better vibration suppression than two separate absorbers of optimized mass distribution. We also find that a two-DOF absorber with negative dampers in some of the connections to the primary system can obtain much better performance than absorbers with only positive dampers.
Experimental Dynamic Analysis of Magneto-Rheological Tuned Vibration Absorbers
Authors: Koo Jeong-Hoi , Ahmadian Mehdi , Setareh Mehdi , Murray Thomas M.
Published: June 2008

The primary purpose of this study is to experimentally evaluate the dynamics of a Magneto-Rheological Tuned Vibration Absorber (MR TVA) with several semi-active control schemes. A test rig was built to represent a two-degree of freedom primary structure model coupled with an MR TVA, and four semi-active control policies were considered. The four control policies include: velocity-based, on-off groundhook control (on-off VBG); velocity-based, continuous groundhook control (continuous VBG); displacement-based, on-off groundhook control (on-off DBG); and displacement-based, continuous groundhook control (continuous DBG). Using the test apparatus, a series of tests were conducted to investigate the dynamics of the MR TVA with each control policy. The performances of each of the cases were then analyzed along with the equivalent passive TVA. The performance index was the transmissibility between the input and the output displacement of the structure. The experimental results indicated that the MR TVA with all of the semi-active control policies, outperformed the passive TVA in reducing structural vibrations. Furthermore, the displacement-based groundhook control policies perform better in reducing the resonant vibrations of the primary structure than the velocity-based groundhook control schemes.
Applications of the Sherman-Morrison Matrix Inversion Formula in Linear and Non-Linear Vibrations, Controls and Acoustics
Authors: Ozer Mehmet Bulent , Royston Thomas J.
Published: June 2008

Applications of the Sherman-Morrison matrix inversion formula are reviewed and demonstrated for several problems in sound and vibration control. The inversion formula enables one to easily separate the effect of a perturbation or subcomponent on the dynamic behavior of the overall system. Applications of this technique that are demonstrated here include: identifying optimal PZT electrical shunt parameter values to minimize sound radiation from a PZT-plate structure, identifying the optimal location and parameter values of a tuned dynamic vibration absorber attached to a multi-degree of freedom, damped system, and identifying and quantifying an isolated non-linearity in an otherwise linear system. Extensions to active control system design are also discussed.
Theoretical and Experimental Investigation of Fuzzy Logic Based Active Vibration Control of Beams
Authors: Sharma Manu , Singh S. P. , Sachdeva B. L.
Published: June 2008

This paper presents fuzzy logic based velocity feedback control for active vibration control of beams. The controller is first developed for a single degree of freedom spring mass system. Rule base consisting of three simple rules based on velocity is used. It is found theoretically as well as experimentally, that for the same settling time maximum applied force required by fuzzy logic controller is much less than that required by direct negative velocity feedback control. The fuzzy controller so developed is then applied for active vibration control of beams. The controller is implemented experimentally on a test beam and the results are found satisfactory. The test system consists of a cantilevered beam with piezoelectric sensor and actuator patches mounted in collocated fashion. The fuzzy logic controller is based on modal velocity of the beam. Modal velocity of the beam acts as an input to the fuzzy controller and actuation force is output from the inference engine. The issues related to design of fuzzy logic controller based on velocity are discussed.
Realization of a Suspension With Negative Stiffness for High-Performance Vibration Isolation Systems
Authors: Mizuno Takeshi , Toumiya Takefumi
Published: June 2008

A control method of realizing negative stiffness of a specified amplitude is presented for an active suspension device with a linear actuator. It is shown that the derived formula is more general than the formula for zero-power control. The validity of the control method is checked experimentally with an apparatus equipped with a voice coil motor (VCM). A suspension device that has negative stiffness of a specified amplitude is actually realized by the proposed control method. The amplitude of negative stiffness is maintained even when the VCM is flexibly supported.
Galerkin Projections for Delay Differential Equations
Authors: Wahi Pankaj , Chatterjee Anindya
Published: June 2008

We present a Galerkin projection technique by which finite-dimensional ODE approximations for DDE’s can be obtained in a straightforward fashion. The technique requires neither the system to be near a bifurcation point, nor the delayed terms to have any specific restrictive form, nor even the delay, nonlinearities and/or forcing to be small. We show through several numerical examples that the systems of ODE’s obtained using this procedure can accurately capture the dynamics of the DDE’s under study, and that the accuracy of solutions increases with increasing numbers of shape functions used in the Galerkin projection. Examples studied here include a linear constant coefficient DDE as well as forced nonlinear DDE’s with one or more delays and possibly nonlinear delayed terms. Parameter studies, with associated bifurcation diagrams, show that the qualitative dynamics of the DDE’s can be captured satisfactorily with a modest number of shape functions in the Galerkin projection.
Influence of Honing Dynamics on Surface Formation
Authors: Gouskov Alexander M. , Voronov Sergey A. , Butcher Eric A. , Sinha Subhash C.
Published: June 2008

The dynamics of the rotating tool commonly employed in deep hole honing is considered. The mathematical model of the process including the dynamic model of the tool and the interaction of the workpiece surface and honing sticks is analyzed. The honing tool is modeled as a continuous slender beam with a honing mandrel attached at the intermediate cross section. A single row of stones on the tool rotates and has reciprocational motion in the axial direction. The honing stones are expanded to the machined surface by a special rigid mechanism that provides cutting of workpiece cylindrical surface and which vibrates in the transverse and axial directions. The removal of chip and the tool vibrations cause the variation of expansion pressure and depend on the surface state formed by previous honing stone. The equations of new surface formation are separated as a specific set of the dynamic model. These equations inherently consider the regenerative effect of oscillations during cutting. The expansion pressure, tool stiffness, and technology conditions are considered as varying parameters since their influence on the process are different. The process productivity and precision can be improved by choosing rational conditions evaluated by simulation. The corresponding models and results of numerical simulation are presented. All the results are given in dimensionless form and therefore they are applicable to a wide range of real manufacturing process conditions. The model of new surface formation presented allows the simulation of the machined surface variation in time and to predict workpiece accuracy and possible correction of surface errors.
Transient Response of a Viscoelastic Axially Moving String With Power Constitutive Model
Authors: Zhao Weijia , Chen Li-Qun
Published: June 2008

In this paper, the transverse vibration of an initially stressed viscoelastic moving string is considered. The string material is assumed to obey the fractional differentiation constitutive law. The governing equation is obtained by Newtonian second law of motion and reduced to a set of nonlinear differential integral equations by using Galerkin’s method. The differential integral equation system that contains fractional derivatives is then truncated to a finite dimensional one and solved numerically by using Runge-Kutta method and some other numerical manipulations. Finally, the numerical results are analyzed. The effects of elastic and viscoelastic parameters on the moving string and the variations of the nonlinear vibration with the changing of transport velocity and some other terms are investigated by numerical experiments.
Steady-State Dynamics of Smooth and Non-Smooth Systems With Strong Nonlinearities
Authors: Jiang Xiaoai , Vakakis Alexander F.
Published: June 2008

The nonlinear energy sinks (NESs) with strong essential stiffness nonlinearities have been shown to result in vibration isolation in the studied system. In comparison, we also studied the steady-state dynamic response of a system with its smooth high-order odd nonlinearity replaced with the best fitted nonsmooth “clearance nonlinearity”. The analysis was based on the complexification technique and the separation of the dynamic terms into the “slow-varying” and the “fast-varying” components. We found that the steady-state behavior of a system with the non-smooth NES resembles that of the system with the smooth high-order nonlinearity, preserving the nonlinear energy-pumping feature. This finding paves the way for constructing practical NESs and applying them to practical vibration-isolation problems.
Motion Confinement in a Linear Chain of Coupled Oscillators With a Strongly Nonlinear End Attachment
Authors: Manevitch Leonid , Gendelman Oleg , Musienko Andrey I. , Vakakis Alexander F. , Bergman Lawrence
Published: June 2008

We study the dynamics of a semi-infinite linear chain of particles that is weakly coupled to a strongly nonlinear oscillator at its free end. We analyze families of localized standing waves situated inside the lower or upper attenuation zones of the linear chain, corresponding to energy predominantly confined in the nonlinear oscillator. These families of standing waves are generated due to resonant interactions between the chain and the nonlinear attachment. A scenario for the realization of energy pumping phenomena in the system under consideration is discussed, and is confirmed by direct numerical simulations of the chain-attachment dynamic interaction.
Measurement of Large Harmonic Vibration Amplitudes
Authors: Mozuras Almantas , Podzharov Evgueni
Published: June 2008

The greater the linearity of a transducer, the more suitable it is for vibration measurement. However, purely linear transducers are not available. It is very common to only use a transducer in a narrow range, where its converting characteristic is close to linear. Unfortunately, only a low signal level can be thus obtained. Therefore, the use of linear features in the measurement process causes non-linear distortions as well as a low signal-to-noise ratio. In this paper, a method for measurement of harmonic vibration amplitudes is presented that allows one to eliminate the above drawbacks. This method allows the extension of the range available for vibration measurement. It could be used, for example, in measurement of standing waves, calibration of devices, etc. This method also gives the ability to obtain maps of the vibration amplitudes with increased surface resolution.
Displacement Measurement, Nonlinearity, Noise, and Thermal Stability
Authors: Mozuras Almantas , Podzharov Evgueni
Published: June 2008

Nonlinear distortions, noise, and thermal instability are the most important error sources of non-contact displacement and distance measurement. In this work, the ways of elimination of these errors are considered. Two methods are proposed and analyzed. The first method helps to exclude nonlinear distortions and noise. According to this method, the nonlinear converter is driven to harmonic oscillations orthogonally to the object surface with constant amplitude. Fourier coefficients are calculated for the different node positions of the vibrating converter. Calibration curve of the converter is reconstructed from collections of derivatives, which are obtained solving system of linear equations. The second method uses ratio of the two Fourier coefficients as the informative parameter and helps to exclude thermal instability. In this paper, there is shown that when the method is more noise resistant it is less thermally stable, and vice versa.
Nonlinear Response of a Buckled Beam to a Three-to-One Internal Resonance
Authors: Emam Samir A. , Nayfeh Ali H.
Published: June 2008

We investigate the nonlinear response of a clamped-clamped buckled beam to a three-to-one internal resonance between the first and third modes when one of them is externally excited. To examine whether the first and third modes are nonlinearly coupled, we use the method of multiple scales to directly attack the partial-differential equation and associated boundary conditions and obtain the equations governing the modulation of their amplitudes and phases. We find that the two modes are nonlinearly coupled. To investigate the large-amplitude dynamics, we use a multi-mode Galerkin discretization to obtain a reduced-order model of the problem. We use a shooting method to compute periodic orbits of the discretized equations and Floquet theory to investigate the stability and bifurcations of these periodic orbits. We note an energy transfer from the first mode, which is externally excited by a primary resonance, to the third mode. We obtain preliminary experimental results of the energy exchange between the first and third modes as a result of a three-to-one internal resonance. More experimental results are being generated.
Hydropneumatic Suspension Design
Authors: Baldi Mauri´cio , Meirelles Pable Siqueira
Published: June 2008

This study proposes a robust and cheap hydropneumatic suspension system for agricultural trailers used to spread crop protection. This kind of vehicle has a high dynamic load factor that increases the axles loads when it is in use and require a height control to assure the same spraying efficiency keeping constant the distance between the spray nozzles and the crop. As the tractor has its own hydraulic system, the hydropneumatic suspension conception take in account that height control will be done by the hydraulic fluid, being the mass of gas kept constant. A mathematical model of the hydropneumatic spring stiffness behavior was developed, as well as a methodology to define the suspension parameters. Experimental validation of the mathematical model was carried out through the use of a real agricultural trailer, equipped with a hydropneumatic suspension projected using the procedure presented, and tested in a hydropuls® road simulator.
Assured Stability of Drillstrings Equipped With Polycrystalline Diamond Compact (PDC) Bits
Authors: Elsayed M. A.
Published: June 2008

Drillstrings equipped with PDC bits are commonly used to drill for oil, gas and geothermal energy. Drillstring instability — defined as the tendency of self-excited vibrations (chatter) to grow with time — causes failure of PDC bits as well as pipe joints. This problem becomes particularly severe in deep wells and hard rock. Much work has been performed in predicting stability. Bit and drillstring geometry as well as rock type affect stability. In this paper, we propose a scheme to assure stability for a given drillstring regardless of bit geometry, utilizing the desired drilling parameters. The effect of bit geometry and rock type in the classic stability analysis are replaced by the drilling parameters, namely: weight-ob-bit (WOB), rate of penetration (ROP) and speed (RPM). Experimental data obtained at Sandia National Labs, Albuquerque, N.M. is used to verify the assured stability equation. This approach is much simpler that classic stability analysis.
Experimental Validation of a Non-Linear Model Under Non-Ideal Excitation
Authors: Brasil R. M. L. R. F. , Garzeri F. J. , Balthazar J. M.
Published: June 2008

We present measurements of the non-linear oscillations of a portal frame foundation for a non ideal motor. We consider a three-time redundant structure with two columns, clamped in their bases and a horizontal beam. An electrical unbalanced motor is mounted at mid span of the beam. Two non linear phenomena are studied: a) mode saturation and energy transfer between modes; b) interaction between high amplitude motions of the structure and the rotation regime of a real limited power motor. The dynamic characteristics of the structure were chosen to have one-to-two internal resonance between the antisymmetrical mode (sway motions) and the first symmetrical mode natural frequencies. As the excitation frequency reaches near resonance conditions with the 2nd natural frequency, the amplitude of this mode grows up to a certain level and then it saturates. The surplus energy pumped into the system is transferred to the sway mode, which experiences a sudden increase in its amplitude. Energy is transformed from low amplitude high frequency motion into high amplitude low frequency motion. Such a transformation is potentially dangerous. We consider the fact that real motors, such as the one used in this study, have limited power output. In this case, this energy source is said to be non ideal, in contrast to the ideal source whose amplitude and frequency are independent of the motion of the structure. Our experimental research detected the Sommerfeld Effect: as the motor accelerates to reach near resonant conditions, a considerable part of its output energy is consumed to generate large amplitude motions of the structure and not to increase its own angular speed. For certain parameters of the system, the motor can get stuck at resonance not having enough power to reach higher rotation regimes. If some more power is available, jump phenomena may occur from near resonance to considerably higher motor speed regimes, no stable motions being possible between these two.
Active Bearing of Rotors Utilizing Robust Controlled Piezo Actuators
Authors: Alizadeh A. , Ehmann C. , Scho¨nhoff U. , Nordmann R.
Published: June 2008

This paper focuses on the active vibration control of flexible rotors by piezo actuators located at the bearings. At first general relations are derived, that allow to specify the required power and dimensions of the actuators from the balance quality factor of the rotor and the stiffness of the system. Second, two control concepts, integral force feedback and robust control, are compared. The design procedure of the robust µ-synthesis controller including uncertainty modelling and selection of weighting functions is described. Experimental results obtained from a simple test rig are shown. Finally, the design is illustrated by an realistic example.
Modulation of Gene Expression via Disruption of NF-κB Signaling by a Bacterial Small Molecule
Authors: Kravchenko Vladimir V. , Kaufmann Gunnar F. , Mathison John C. , Scott David A. , Katz Alexander Z. , Grauer David C. , Lehmann Mandy , Meijler Michael M. , Janda Kim D. , Ulevitch Richard J.
Published: June 2008

The control of innate immune responses through activation of the nuclear transcription factor NF-κB is essential for the elimination of invading microbial pathogens. We showed that the bacterial
N
-(3-oxo-dodecanoyl) homoserine lactone (C12) selectively impairs the regulation of NF-κB functions in activated mammalian cells. The consequence is specific repression of stimulus-mediated induction of NF-κB–responsive genes encoding inflammatory cytokines and other immune regulators. These findings uncover a strategy by which C12-producing opportunistic pathogens, such as
Pseudomonas aeruginosa
, attenuate the innate immune system to establish and maintain local persistent infection in humans, for example, in cystic fibrosis patients.
Censoring of Autoreactive B Cell Development by the Pre-B Cell Receptor
Authors: Keenan Rebecca A. , De Riva Alessandra , Corleis Björn , Hepburn Lucy , Licence Steve , Winkler Thomas H. , Mårtensson Inga-Lill
Published: June 2008

Antibody diversity occurs randomly as B cells recombine their immunoglobulin (Ig) heavy- and light-chain genes during development. This process inevitably generates reactivity against self structures, and several mechanisms prevent the development of autoreactive B cells. We report here a role for the pre-B cell receptor, composed of Ig heavy and surrogate light chains, in the negative selection of cells expressing Ig heavy chains with the potential to generate autoantibodies. Surrogate light-chain–deficient (
SLC
–/–
) mice harbored elevated levels of antinuclear antibodies (ANAs) in their serum and showed evidence of escape of pre-B cells expressing prototypic autoantibody heavy chains from negative selection, leading to mature autoantibody secreting CD21
–
CD23
–
B cells in the periphery. Thus, the pre-B cell receptor appears to censor the development of certain autoantibody-secreting cells and may represent an important factor in multifactorial autoimmune diseases.
Impact of Mucosal Inflammation on Cervical Human Immunodeficiency Virus (HIV-1)-Specific CD8 T-Cell Responses in the Female Genital Tract during Chronic HIV Infection
Authors: Gumbi Pamela P. , Nkwanyana Nonhlanhla N. , Bere Alfred , Burgers Wendy A. , Gray Clive M. , Williamson Anna-Lise , Hoffman Margaret , Coetzee David , Denny Lynette , Passmore Jo-Ann S.
Published: June 2008

The female genital tract is the major route of heterosexual human immunodeficiency virus (HIV) acquisition and transmission. Here, we investigated whether HIV-specific CD8 T-cell-mediated immune responses could be detected in the genital mucosa of chronically HIV-infected women and whether these were associated with either local mucosal HIV shedding or local immune factors. We found that CD8+T-cell gamma interferon responses to Gag were detectable at the cervix of HIV-infected women but that the magnitude of genital responses did not correlate with those similarly detected in blood. This indicates that ex vivo HIV responses in one compartment may not be predictive of those in the other. We found that increased genital tumor necrosis factor alpha (TNF-α) and interleukin-10 (IL-10) levels correlated significantly with levels of Gag-specific CD8+T cells at the cervix. Women who were detectably shedding virus in the genital tract had significantly increased cervical levels of TNF-α, IL-1β, IL-6, and IL-8 compared to women who were not detectably shedding virus. We were, however, unable to detect any association between the magnitude of cervical HIV-specific responses and mucosal HIV shedding. Our results support the hypothesis that proinflammatory cytokines in the female genital tract may promote HIV replication and shedding. In addition, we further show that inflammatory cytokines are associated with increased levels of HIV-specific CD8 effector cells at the genital mucosa but that these were not able to control genital HIV shedding.