Search

Based on 160 km/h prototype tests, the rigid-flexible coupling model of the full-side open boxcar is built. The car body and the connecting device between car body and car door are improved by the iterative optimization study of simulation and tests combined. Dynamics, vibration fatigue and modal analysis are made on the full-side open boxcar system based on the optimization. First-order vertical bending mode of the boxcar is increased by 31%, meeting the requirement of the relative standards. Fatigue analysis is done based on static strength meeting service requirements, and the calculations meet the requirement of line operation. [ABSTRACT FROM AUTHOR]

Stick-slip of the drill string, as one of the critical factors affecting drilling efficiency, has always been a hot topic for experts and scholars in related fields. Serious stick-slip vibration affects the well construction efficiency, drilling cost and even lead to a downhole accident. Therefore, based on the current research, this paper takes a new type of composite vibration tool as the research object, studies the working mechanism of the tool and analyzes the effect of stick-slip reduction. After establishing the multi-degree-of-freedom torsional dynamics model, we obtained the results of torsional vibration dynamics by cases analysis based on working conditions and related mechanical parameters. In addition, the results of the examples, compared with the field experimental data, verify that the vibration shock generated by the new composite tool can effectively reduce the torque fluctuation range of the system, avoid the occurrence of stick-slip phenomenon, improve the ROP (rate of penetration), and make drilling process more stable. This paper can provide reference for the optimization and development of stick-slip technology in drilling engineering, and the theoretical methods can also be developed to study the dynamics of drill string. [ABSTRACT FROM AUTHOR]

The Blade Tip-Timing is a well-known non-contact measurement technique currently employed for the identification of the dynamic behaviours of rotating bladed disks. Although the measurement system has become a typical industry equipment for bladed disks vibration surveys, the type of sensors, the positioning of the sensors around the bladed disk and the used algorithm for data post-processing are still not standard techniques, and their reliability has to be proved for different operation conditions by the comparison with other well-established measurement techniques used as reference like strain gauges. This paper aims at evaluating the accuracy of a latest generation Tip-Timing system on two dummy blisks characterized by different geometrical, structural and dynamical properties. Both disks are tested into a spin-rig where a fixed number of permanent magnets excite synchronous vibrations with respect to the rotor speed. A new positioning for the Blade Tip-Timing optical sensors is tested in the case of a shrouded bladed disk. Due to the presence of shrouds, the sensors cannot be positioned at the outer radius of the disk pointing radially toward the rotation axis as in the most common applications, since the displacements at the tips are very small and cannot be detected. For this reason a particular placement of optical laser sensors is studied in order to point at the leading and trailing edges' locations where the blades experience the largest vibration amplitudes with the aim of not interfering with the flow path. Besides the typical Blade Tip-Timing application aimed at identifying the dynamical properties of each blade, an original method is here proposed to identify the operative deflection shape of a bladed disk through the experimental determination of the nodal diameters. The method is applicable when a small mistuning pattern perturbs the ideal cyclic symmetry of the bladed disk. [ABSTRACT FROM AUTHOR]

The control of electrostatically actuated microsystems with open-loop strategies has the potential to reduce the switching time with immediate benefits on device performances and, on the other hand, to reduce the impact velocity between electrodes with benefits on the device lifetime and reliability. By applying to micro-electro-mechanical systems (MEMS) the controlled methods already validated on machines, it was demonstrated that the accuracy of the control is scalable with the dimensions. Residual vibrations of microstructures in the nanometer range are almost completely suppressed: they are reduced to 6% of the uncontrolled vibration amplitude. The reasons for implementing this kind of control are related to reliability enhancement, by reducing the impact velocity, and for the improvement of device dynamic peiformances. The robustness of the control method against errors in dynamic parameters evaluation was also demonstrated. [ABSTRACT FROM AUTHOR]

Transmission noise of the magnesium alloy cylinder head cover was researched in this paper. Firstly, the numerical calculation mode of a cylinder head cover was compared with the experimental one. Results showed that the numerical calculation model had a relatively high accuracy, and it could be used in subsequent analysis. Secondly, sound pressure inside the cylinder head cover was extracted through the four-load method and taken as the sound source. Then, it was applied in a simulation model in order to simulate transmission noise of the actual situations. Afterwards, transmission noise of the magnesium alloy cylinder head cover was compared with the aluminum alloy one. It was shown that relatively low transmission noise was generated from the magnesium alloy cylinder head cover. Meanwhile, its mass was only 0.65 times of that of the aluminum alloy one. Therefore, the requirement for low noise and light weight was achieved by the magnesium alloy cylinder head cover. Then, dynamic stresses of cylinder head covers for two materials were compared. Results showed that dynamic stress of the magnesium alloy cylinder head cover was slightly smaller than that of the aluminum alloy one. The magnesium alloy cylinder head cover satisfied the requirement for strength and had a relatively prominent comprehensive performances. Finally, sound absorption coefficient of a porous material was calculated by using the numerical simulation technology. It was also laid inside the magnesium alloy cylinder head cover to constitute a composite cylinder head cover. Transmission noise of such composite cylinder head cover was much smaller than that of the original structure. This researches provided a method for low noise and light weight design of the cylinder head cover. [ABSTRACT FROM AUTHOR]

Kalman filtering technique is applied on vibration signals to detect eccentricity fault and bearing fault in induction motor. The vibration signals are acquired during load performance tests of healthy and faulty cases of induction motor. The state space equations needed for Kalman filter structure are constructed based on autoregressive model of the signals. The harmonics of fault related frequencies are identified from the spectrum of innovation signal, which is provided from the Kalman filter response, for vibration signal and also it is seen that Kalman filter reduce the noise level. [ABSTRACT FROM AUTHOR]

The rubber floating-slab track is one of the best methods to isolate vibration induced by the interaction of the train and the rails. In order to improve its vibration reduction ability, three kinds of supporting forms, i.e. full-surface supporting, linear supporting and point-like supporting, were discussed by laboratory tests. Through time history analysis and frequency spectrum analysis, we found that the linear supporting form and the point-like supporting form have the smaller first resonant frequency than the full-surface supporting form, which is induced by the weakened supporting stiffness. Because of this reason, the maximum values of vibration acceleration of the floating slab for the linear supporting form and the point-like supporting form increase in the time domain and the frequency domain. However, the point-like supporting form has the smallest transfer ratio of vibration acceleration from the floating slab to the tunnel wall compared with the linear supporting form and the full-surface supporting form. [ABSTRACT FROM AUTHOR]

The main goal of the active suspension system used in a vehicle is reducing the vehicle vibration. In this study, an adaptive control approach is applied to a nonlinear quarter car model with an active suspension system. An electromagnetic actuator is used in the active suspension system. The attractive aspect of the applied control method is not required to both vehicle parameters and actuator parameters. Using Lyapunov based stability analysis; it is shown that all the signals in the closed loop system are bounded. Hence, the applied controller ensures the vibration reduction of the nonlinear quarter car model. The simulation results show that the applied adaptive controller provide a good ride comfort despite the parametric uncertainties while keeping suspension travel and tire deflection in acceptable limits. [ABSTRACT FROM AUTHOR]

Finite element modeling and active vibration control of a high-speed spinning flexible coupled electromechanical beam is investigated using a first-order approximation coupling (FOAC) model. Due to centrifugal forces caused by eccentricity in a spinning flexible beam, there exists coupling between axial and transverse vibration modes. The partial differential equations of motion of the beam governing this coupling are derived using Hamilton's principle based on an FOAC model, and a finite element method for discretization is given. It is observed that the zero-order approximate coupling (ZOAC) model is valid for dynamic description of the flexible beam spinning at low speeds, but no longer valid at high speeds. However, the validity of FOAC model is confirmed at different speeds. Piezoelectric elements for active vibration control of the spinning flexible beam are analyzed and a velocity feedback controller is proposed. Simulation results demonstrate good performance of the proposed velocity feedback controller. [ABSTRACT FROM AUTHOR]

This research aims at identifying the position and depth of the open transverse crack of the beam using the model based method. The stiffness matrix of the cracked beam element and the basic principle of the model based method are introduced. It is discussed to estimate the generalized displacement of all nodes of the beam by the measured displacements of a few degrees of freedom. The relative change rate of the equivalent external load between the intact and cracked elements is compared with that of mode shape, nature frequency and displacement amplitude between the intact and cracked beam. The position and depth of the crack are identified by the model based method in two cases. In first case, the measured displacement is assumed not to include noise. The identification results based on the actual displacement and rotation of all nodes are compared with the results using the estimated generalized displacement. In second case, the measured displacement includes noise and the generalized displacement of all nodes is estimated by the displacement of two measurement points. The simulation results shown there is no error to identify the position, the relative depth identification error of the crack with 1 μm depth is 2.34 % without noise, and the relative depth identification error of the crack with 200 μm depth could be down to about 5 % with the energy signal to noise ratio being about 7.00 before denoising. [ABSTRACT FROM AUTHOR]

A system-level nonlinear dynamic model for a two-stage planetary gear transmission system of a hoist is established with the consideration of time-varying meshing stiffness, backlash, damping, and bearing stiffness. Vibrational test results are also presented in accordance with simulation results computed from the dynamic model, and engagement-impacting dynamic simulations are achieved by adapting a dynamic explicit algorithm based on this model. Accordingly, variation in the contact state in relation to the engaging position is obtained together with vibration characteristics of the transmission system. This study provides a theoretical basis for the reduction of vibration and noise for the transmission system. [ABSTRACT FROM AUTHOR]

A gear-bearing coupling dynamic model that includes bearing stiffness, mesh stiffness and mesh errors for a herringbone planetary gear set (HPGS) is proposed. The proposed model is used to predict the random stress process of the gears and bearings along with Monte Carlo simulation, when the effects of tooth surface wear on meshing errors are considered. A calculation model for the random strength process is derived by applying the linear fatigue damage criterion and regarding the Poisson random process as a counting process of the random stress. Assuming that the stress and strength are random processes, a time-dependent reliability model for HPGS with failure dependency is proposed to predict the time-dependent reliability of HPGS based on the failure mode groups that are obtained by the correlation coefficient. The results show that, the meshing errors caused by the tooth surface wear, make the dynamic loads and failure dependency of the parts of HPGS gradually increase over service time. At the same time the fatigue damage, which is caused by the load action, makes the strength of parts of HPGS gradually decrease over service time. Therefore the reliability of HPGS quickly decreases over service time. If the shafts of the planets and sun gear are free in their axial direction, the failure dependency of the parts will significantly decrease, and the reliability of a herringbone planetary gear set will significantly be improved. [ABSTRACT FROM AUTHOR]

A combined method of thermal and vibratory stress relief (TVSR) to extend effects of vibratory stress relief (VSR) is presented. TVSR was implemented by imposing vibratory load on a workpiece at an assisted temperature. Residual stresses before and after treatment were measured using the modified layer removal method (MLRM) to evaluate the stress variations. A finite element (FE) model was developed to investigate and compare TVSR and VSR treatment on workpieces cut from a 7075 aluminum alloy plate. Thermal influence on TVSR equipment and vibratory treatment of the workpiece was analyzed using this model. Experiments were conducted to validate simulation results. Significant residual stress relief was observed in TVSR, however, effects of VSR were limited. [ABSTRACT FROM AUTHOR]

A lumped-parameter coupled nonlinear dynamic model for one large multi-stage wind turbine gearbox transmission system is established comprehensively including wind varying load, mesh stiffness, dynamic transmission error, gravity, and bearing nonlinear characteristics to obtain the gearbox dynamic response. The vibration differential equations of the drive-train are deduced through the Lagrange's equation. On the basis of that, the dynamics of wind turbine gearbox is investigated by a Runge-Kutta numerical method that includes simultaneous internal and external excitations. The results show that the dynamic response of the partial component is mainly superposed by high-frequency component caused by the internal excitation and low-frequency component caused by the external excitation. In medium-speed stage and high-speed stage, the vibration amplitude has obvious fluctuation, and the multiple frequency and random frequency components become increasingly obvious with increasing rotational speed and eccentricity at gear and bearing positions. Axial vibrations of the system also have some fluctuation. The bearing has self-variable stiffness frequency, which should be avoided in engineering design stage. The study results provide a theoretical foundation for dynamical characteristics evaluation and dynamic optimization of a large wind turbine gearbox transmission system. [ABSTRACT FROM AUTHOR]

In recent years, the processing technology of advanced machinery has toward precision, high-performance, and high-speed. Therefore micro-fabrication becomes more important such as the getting smaller aperture in the printed circuit board (PCB), it tends to be more severe due to vibration. The vibration has adverse effects to machining accuracy and surface roughness which will increase tool abrasion and further accelerate the destruction from material fatigue. There are many ways to produce perforations, such as laser micro-machining and micro-drilling. The industry still adopts micro drill piercing process due to the cost and technical considerations. In order to enhance the cutlery life and the quality of the drilling process, the cutting characteristic of bur is important. Hence, the vibration during drilling must be suppressed. This study is to investigate the dynamic analysis of a micro drill under ultrasonic vibration (50 kHz) excited with a piezoelectric-driven actuator experimentally and numerically by using finite element analysis. The results show that the vibration and the cutting forces are effectively reduced and thereby the cutting performance is improved when introduces ultrasonic vibrations during micro-drilling process. [ABSTRACT FROM AUTHOR]

Copyright of Technical Transactions / Czasopismo Techniczne is the property of Sciendo and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Purpose – The natural frequency of a diaphragm with residual stress in contact with a liquid is investigated theoretically in this paper. The paper aims to discuss these issues. Design/methodology/approach – An analytical calculation using the nondimensional added virtual mass incremental (NAVMI) factors is performed to find the dependency of the natural frequency on the residual stress when the diaphragm vibrating in contact with a liquid. Findings – The analysis gives the residual stress contribution to the added virtual mass. Originality/value – The magnitude of the added virtual mass depends on the residual stress. However, the magnitude of the natural frequency is found to be insignificant to the residual stress. [ABSTRACT FROM AUTHOR]

It has been shown recently that the shimmy motion of towed wheels can be predicted in a wide range of parameters by means of the so-called memory effect of tyres. This delay effect is related to the existence of a travelling-wave-like motion of the tyre points in contact with the ground relative to the wheel. This study shows that the dynamics within the small-scale contact patch can have an essential effect on the global dynamics of a four-wheeled automobile on a large scale. The stability charts identify narrow parameter regions of increased fuel consumption and tyre noise with the help of the delay models that are effective tools in dynamical problems through multiple scales. [ABSTRACT FROM AUTHOR]

In this paper, blades with tips is modeled as a three-mass with springs system. The contact collision between masses is oblique impacting. Thus, the dynamical equation of the system and collision terms is established, and the dynamical behavior of system is studied by using numerical simulation method. The effects of parameters such as gap of masses, contact angle, etc. on damping are discussed. The results show that the gap of masses and contact angle have great effects upon the damping. There exists an optimum gap and a negative contact angle range. It should be considered in the engineering design. In dynamics, as the rotational speed increases, the topological structure of system varied between chaos and periodic motion. [ABSTRACT FROM AUTHOR]

Magneto-rheological damper model suitable for helicopter air resonance and momentum theory model of hover condition involving momentum theory were built in this paper. The equations of the two models with the dynamic equations of helicopter rotor/body coupling were solved by Simulink time domain simulation method to obtain the helicopter dynamic stability influenced by Magneto-rheological damper and compared the blade flapping and lagging impacted by Magneto-rheological dampers under different voltages. It could be conclude that under a certain voltage, Magneto-rheological damper was not influenced by duel-frequent excitation, and was good at restraining the helicopter air resonance. [ABSTRACT FROM AUTHOR]

Floating ring bearings (FRBs) are widely used in high speed rotating machines. In this paper, the carrying capacity of outer oil film, which can represent the total capacity of FRBs, in floating-ring bearing was analyzed only because the bearing capacity of inner oil film is larger than that of the outer one. Based on the rotordynamic DyRoBes software and finite difference method, the pressure of outer oil film in relatively heavy load micro gas turbogenerator was computed and the results were analysed and compared. Because of the structural characteristics of FRBs, the relationship of stiffness and damping of inner and outer films is equivalent to the series of spring and damper, thus the total stiffness and damping of FRB could be calculated under different rotation speeds. The important parameters, such as eccentricity ratio, static balance position, which give the influences on the oil film characteristics and rotor dynamic behavior were also studied. At last, the stability of oil film was determined using Routh-Hurwitz criterion. [ABSTRACT FROM AUTHOR]

Automotive turbochargers are known to operate into the self-excited unstable region. In the past these instabilities have been accepted as unavoidable, but recent developments in analysis and instrumentation may make it possible to reduce or eliminate them. A test stand has been developed at Virginia Tech to measure the vibrations of a 3.9 liter diesel engine stock turbocharger with both stock floating ring journal bearings and also custom design fixed geometry bearings. Vibration spectrum content clearly identifies the shaft instabilities and provides the basis for additional evaluation of future improved bearing design modifications. The current results, for custom fixed journal bearings, have clearly revealed a distinct jump with associated shift in the spectrum frequency content. This paper will document the recent tests of custom design fluid film bearings that have experienced this nonlinear jump condition. [ABSTRACT FROM PUBLISHER]

Modal models are developed for vibro-acoustic response computation of fluid-structure interaction problems on the basis of modal frequencies and modal damping ratios. The uncoupled equations are built using in vacuo mode shapes and fluid-loaded undamped real mode shapes and are solved for the coupled response of the fluid-loaded structures. Conventional modal analysis techniques are used to obtain the response of the coupled fluid-structure systems from a reduced-order modal model. The accuracy and efficiency of the technique is demonstrated with examples of computing the vibro-acoustic response of a baffled thin plate and a baffled thick stiffened plate. The comparisons in terms of mean-square normal velocity and sound power between the present models and the conventional coupling method show a good agreement. The present modal models for computing the vibro-acoustic response of the fluid-loaded structures have the advantages of constructing a model from modal parameters that could be obtained from either numerical computation or experimental measurement; a small dimension of using only a very small number of modes; and of being applicable to conventional modal analysis techniques. These features may make the present technique a powerful tool for dynamics and the control of fluid-loaded structures. [ABSTRACT FROM PUBLISHER]

In this work we suggest hierarchical sliding mode observers for complex systems which include distributed parameter systems and combinations of distributed parameter and lumped parameter systems, modeling, for example, an actuator dynamics. The main idea is based on the observer suggested previously for general nonlinear lumped parameter systems that is using the equivalent values of the discontinuous function to obtain additional information about the system state. Such observers can be written directly into system’s original variables without requiring the state transformation. In this paper, using a modal representation of the distributed system and the hierarchy of sliding modes, we develop a structure of such an observer for a wide class of systems described by partial differential equations or combinations of ordinary and partial differential equations. An example is presented which illustrates the proposed method. [ABSTRACT FROM PUBLISHER]

In the last decade, many advances and changes have been seen in engineering theory and applications. The modern trend is to combine modeling, theoretical analysis and computer simulation. The conventional techniques of mathematical modeling of real life complicated structural systems for vibration analysis are tedious and time consuming. The finite element (FE) method is becoming popular because of its simplicity and feasibility of using for real life applications. In the present study, extraction of the system model from its FE model by using commercially available softwares such as ANSYS© and MATLAB© is demonstrated. A two-degree-of-freedom spring-mass-damper system is considered here. Its state space mathematical model in principal coordinate system is obtained in MATLAB© from the modal analysis results of its FE model done in ANSYS©. For checking the validity of model, transfer function and state space model in physical coordinates of the same system are derived mathematically by assuming proportional damping. Frequency responses of all the system models are compared and found to be in good agreement. To demonstrate the application of this study, system model of a cantilever beam is also extracted in MATLAB© from the result of modal analysis of its FE model in ANSYS© and its frequency response is plotted. Response of cantilever beam to unit impulse input is also obtained in both ANSYS© and MATLAB© and compared for validating the model. This study will definitely help in simplifying the vibration analysis of real life systems. [ABSTRACT FROM PUBLISHER]

The dynamic responses of an elastic rectangular plate to some types of moving loads’ distribution are obtained and compared. The partial differential equation describing the force vibration of each system comprising of the elastic rectangular plate and moving load is expressed in terms of each of the three moving loads’ distribution respectively. The three moving loads’ distribution considered are concentrated, uniformly and linearly distributed moving masses. An assumed Series solution in the form of the separation of variables is employed to transform each equation of motion into an ordinary coupled differential equation whose solution is obtained in form of a Duhamel integral. Numerical results are presented for simply supported boundary conditions in graphical and tabular forms. It is found that velocity, moving load’s distribution and mass ratio (Msr) significantly affect the vibration of the elastic rectangular plate. [ABSTRACT FROM PUBLISHER]

A nonlinear six degree-of-freedom dynamic model is presented for a marine surface vessel. The formulation closely follows the current literature on ship modeling. It considers the effects of inertial forces, wave excitations, retardation forces, nonlinear restoring forces, wind and current loads along with linear viscous damping terms. The capability of the model is shown through its prediction of the ship response during a turning-circle maneuver. The ship model is used herein as a test bed to assess the performance of the proposed controller. The present study assumes that the ship is fully actuated and all state variables of the system are available through measurements. A nonlinear robust controller, based on the sliding mode methodology, has been designed based on a reduced-order version of the ship model. The latter accounts only for the surge, sway and yaw motions of the ship. The initial simulation results, generated based on the reduced-order model of the marine vessel, demonstrate robust performance and good tracking characteristics of the controller in the presence of structured uncertainties and external disturbances. Furthermore, they illustrate the adverse effects of the physical limitations of the propulsion system on the controlled response of the ship. Next, the same controller is implemented on the six degree-of-freedom model of the ship. The simulation results reveal tracking characteristics of the controller that are similar to those observed in the initial results, in spite of significantly larger modeling uncertainties. [ABSTRACT FROM PUBLISHER]

All rotating systems are subjected to residual unbalance forces that are proportional to speed squared. Systems that operate close to the critical speed and have low damping can generate destructive vibrations. Dynamic vibration absorbers are simple devices attached to a mechanical structure (the primary system) to reduce vibrations and noise levels and are extensively used in non-rotating systems. This study addresses the design of viscoelastic vibration absorbers for rotating systems. The primary system is modeled using modal parameters obtained in the frequency domain of the state-space representation. Using a methodology that has a more general application, the compound system (the primary system and absorbers) is represented in a modal subspace of the primary system state space. In this modal subspace, the optimal design of the dynamic viscoelastic absorbers is performed using an optimization algorithm. The objective function to be minimized is defined as the Euclidean norm of the vector composed of the maximal absolute values of the principal coordinates. The absorbers are attached to a floating bearing located away from a nodal point. Numerical and experimental results are presented and discussed. [ABSTRACT FROM PUBLISHER]

We consider hostile conflicts between two multi-agent swarms, called pursuers and evaders. A Newtonian dynamics-based double integrator model is taken into account, as well as a control strategy using the relative positions and velocities of opposing swarm members. This control is introduced to achieve stability and the capture of the evaders by the pursuers. The present document considers only swarms with equal membership strengths and equal mass for simplicity. This effort begins with a set of suggested interaction force profiles, which are functions of local vectors. To formulate a robust control law, a Lyapunov-based stability analysis is used. The group pursuit is conceived in two phases: the approach phase, during which the two swarms act like two individual agents, and the assigned pursuit phase, where each pursuer has an assigned evader. We show that the uncontrolled dynamics, which are marginally stable, are stabilized by the new controller. [ABSTRACT FROM PUBLISHER]

Experimental techniques and identification of dynamic properties of flexible polyurethane foam used in automotive seats are described here. In the experimental fixture a rigid block is mounted on a 3 inch cube of foam material, which serves as the only flexible component. The dynamic system is modeled as a single degree-of -freedom system. The experimental fixture is excited by a small impulse at the top of the block and by a shaker on the basement. For the first situation the foam is simplified as a linear viscoelastic material. By exciting with the shaker the nonlinear and viscoelastic properties of foam materials are considered. For these two different cases not only the model response and the impact of model parameters are analyzed but also the corresponding system parameters are identified during the experimental data. [ABSTRACT FROM PUBLISHER]

Vehicle-induced bridge vibrations has become an important issue for the dynamic response of bridges especially after the achievement of long spans by cable-stayed bridges during the last two decades. In this study, the effects of vehicle speed, which is one of the important parameters of vehicle-bridge interaction, and variations in the speed are investigated to determine the bridge responses. Tatara bridge which is the second largest cable-stayed bridge in the world, is considered by 3-D finite element model. Two sets of traffic load combinations are applied for three different vehicle speed values and analyses are conducted to evaluate the speed induced dynamic responses of the bridge. The largest responses in the bridge are generally observed for low speeds. On the other hand, larger responses begin to occur in the mid-span after the vehicles leave the mid-span of the bridge for higher speeds. [ABSTRACT FROM AUTHOR]

In this study, by performing a dynamic modeling of a four-stroke single cylinder engine, its dynamic behavior in acceleration period under loaded and unloaded conditions, vibrations of engine block and angular velocity fluctuations of the crankshaft were investigated. The dynamic model consisted of motion equations of piston, connecting rod, crankshaft and engine block. The motions of the engine block and the other moving elements were described on a plane perpendicular to the crank shaft axis. The block of the engine has two degree of freedom; one is translational motion on the direction of the cylinder axis and the other is angular vibration around the crank axis. Numerical solution was performed on time domain by means of using initial conditions. The working gas pressure exerting on the piston was obtained experimentally from a four-stroke single cylinder diesel engine. The vibration characteristics of the engine components and forces occuring on the mounts were graphically presented. [ABSTRACT FROM AUTHOR]

This study presents a time-varying model to investigate dynamic responses of spur gear pairs. In particular, time-varying damping was directly used to account for the lubrication film of tooth pairs. At first, the governing equations of vibration for gear pairs were expressed in equivalent discrete models of mass, damping, and spring elements. The damping factor which incorporated the lubrication effect was derived using elastohydrodynamic-lubrication and squeezed-film theories. The time-varying property due to the moving meshing position was considered by immediately updating the meshing stiffness, damping factor, meshing force, and frictional force between the tooth pairs at each calculation step. After that, dynamic factors and fillet strains of the gear pairs under various operating conditions were obtained by performing iterative numerical integrations. The lubricant damping factor and its effects on gear dynamics was also discussed. Finally, the effects of the lubricant viscosity and applied torque on the gear dynamics were thoroughly investigated. [ABSTRACT FROM PUBLISHER]

In this paper we describe a type of new vibration isolator that is based on solid and liquid mixture (SALiM). The SALiM consists of incompressible liquid and many compressible elastic solid elements. When under shocks or vibrations, the incompressible liquid can instantly pass the pressure on to all solid elements in the container of the isolator, which causes all the solid elements to compress and deform simultaneously. As a result it could greatly absorb and dissipate the energy of vibrations and shocks. If designed properly, the isolator could have an excellent performance on both vibration isolation and shock absorbing. This paper uses hollow rubber spheres as solid elements, and investigates the dynamic properties of an isolator, assuming that the solid elements undergo finite deformation. The nonlinear force— displacement relation of the isolator is investigated. The nonlinear equation of motion of a single degree of freedom system supported by the isolator is established. The frequency response functions are evaluated theoretically and measured on a test rig, which shows positive agreement on the nonlinear dynamic behaviors. It is concluded that the isolator responses are asymmetrical and the stiffness of the isolator has softening spring characteristics. [ABSTRACT FROM PUBLISHER]

This study provides a methodology for reduced order controller design for nonlinear dynamic systems with time-periodic coefficients. The proposed methodology is quite general in a sense that it can be easily modified for nonlinear systems with constant coefficients. The equations of motion are represented by quasi-linear differential equations in state space, containing a time-periodic linear part and nonlinear monomials of states with periodic coefficients. The Lyapunov—Floquet (L-F) transformation is used to transform the time-varying linear part of the system into a time-invariant form. Eigenvalue decomposition of the time-invariant linear part can then be used to identify the dominant/nondominant dynamics of the system. The nondominant states of the system are expressed as a nonlinear, time-periodic, manifold relationship in terms of the dominant states. As a result, the original large system can be expressed as a lower order system represented only by the dominant states. A reducibility condition is derived to provide conditions under which a nonlinear order reduction is possible. Then a proper coordinate transformation and state feedback can be found under which the reduced order system is transformed into a linear, time-periodic, closed-loop system. This permits the design of a time-varying feedback controller in linear space to guarantee the stability of the system. The case of systems with constant coefficients is treated as a subset of its periodic counterpart. In this case one does not have to use the L-F transformation; moreover, the manifold and all other transformations are purely spatial. The proposed methodology is illustrated by designing a two dimensional reduced order controller for a 4-degrees of freedom, inverted pendulum subjected to a periodic force for which the equations of motion are time-periodic. An example involving a 2-dof spring-mass-damper system is also presented which yields the equations of motion with constant coefficients. [ABSTRACT FROM PUBLISHER]

This study examines the effects of variable dynamic dissipative and elastic soil characteristics on the dynamic response of a soil-structure system. Three equivalent linear modeling techniques (linear hysteretic and Kelvin-Voight constitutive models and weighted modal time history analysis) are used to incorporate the soil and structure’s unique dissipative characteristics. The soil’s critical viscous damping ratio and shear modulus are iteratively determined based upon experimentally observed, upper and lower bound strain-dependent stiffness degradation and damping curves. It is found that the three techniques produce consistent results: as the shear modulus increases, so does the primary natural frequency of the response; as the damping ratio of the soil increases, the magnitude of the response decreases. It is also found that variations in response due to using different values for a soil’s dynamic characteristics are dependent upon the equivalent linear modeling technique used. The impact of soil damping variability is seen to be as influential upon the dynamic response of a structure as shear modulus variability, because dissipative variations have a direct impact on the magnitudes of the displacement responses. The effects of variable soil damping should therefore be considered in addition to stiffness parameters as part of the dynamic characteristics of a system when determining a system’s dynamic performance. [ABSTRACT FROM PUBLISHER]

Preview control is investigated for active suspension systems. Two preview concepts are used: (1) look-ahead preview, where the information relating to roadway disturbances about to be encountered by the moving vehicle is assumed to be sensed, and (2) wheelbase preview, where knowledge of the front wheel states is used to improve performance at the rear of the vehicle. A method based on optimal control theory is presented to find the control laws for a half-car equipped with both fully active and slow-active systems under preview. The random road profile is assumed to be the output of a filtered white-noise process. Human perception of vibration is considered in the design of the active suspension systems. The design of the preview controller is reduced to the classical linear quadratic regulator of the original system and the previewed road inputs. Integral constraints are included in the performance index to achieve better body attitude control. The effect of preview control on vehicle performance characteristics in terms of ride comfort, suspension deflections and road-holding ability is investigated. The results show that the use of wheelbase preview along with look-ahead preview improves all aspects of the suspension performance. [ABSTRACT FROM PUBLISHER]

This paper performed a systematic in-depth investigation into the effectiveness of both soft and stiff wave barriers in reducing building responses to deep dynamic compaction (DDC) impacts. The effectiveness of wave barriers was evaluated in terms of two parameters, i.e., the reduction in the vibration acceleration for the floors of the building and the reduction of the settlement of the building. This investigation was achieved by a series of comprehensive parametric studies via a two-dimensional finite element method combined with a dynamic approach for simulating DDC impacts. The dynamic approach is based on the time history of tamper penetration depth. Its accuracy and reliability was validated using the field measurements and experimental data from the literature. During the parametric studies, five wave barriers were examined, which included two soft barriers (an open trench and an in-filled slurry-bentonite trench) and three stiff barriers (an in-filled concrete trench, a wood panel barrier, and a steel sheet pile wall). The geometrical (barrier locations) and dimensional effects (barrier depths and widths) on mitigation of building responses were examined for each barrier, and the efficiencies of these wave barriers were compared. [ABSTRACT FROM PUBLISHER]

This paper addresses the influence of the partial slip phenomenon on the damping capacity of jointed riveted structures with unequal thickness. The dynamic response of built-up structures is influenced by the characteristics of the joints and the damping capacity of such joints has been analyzed by mathematical modeling and experiments. Damping at structural joints is associated with frictional losses caused by micro-slip and kinematics coefficient of friction at the interfaces. Such energy dissipation at various joints has a significant effect in limiting the magnitude of vibration. The free vibration of a beam jointed with rivets of unequal thickness with ratio of 2.0 undergoing a small dynamic deflection in the transverse direction has been studied using the energy approach to evaluate its damping capacity. The results of the theoretical analysis have been compared with the experimental results to verify the authenticity of the work. It has been found that the normal pressure and the micro-slip at the interfaces are the major parameters influencing the damping capacity of jointed riveted structures. The suggested method can be effectively utilized by the designers to fabricate the engineering built-up structures depending on the requirements of the damping capacity. [ABSTRACT FROM PUBLISHER]

In this paper, a methodology for the design and evaluation of a slow-active vehicle suspension system is developed. The suspension consists of a limited bandwidth actuator in series with a passive spring; the combination being in parallel with a passive damper. An optimal multivariable controller is designed for a full car model. The controller takes the form of a linear quadratic regulator with supplementary states for added integral action. The car model is formulated as a linear lumped parameter model, comprised of five discrete rigid bodies. The three-dimensional vibratory motions of the vehicle are described in terms of seven degrees-of-freedom: bouncing, pitching and rolling motions of the sprung mass, and the bouncing motion of each unsprung mass. An integrated investigation of vehicle dynamics, roadway excitations and performance measures is developed in order to investigate the dynamic analysis and design of vehicle suspension systems and the consequences of vehicle ride quality. The ride isolation performance and road-holding qualities of the slow-active system are compared to those of a full bandwidth active suspension and a typical passive suspension system. The simulation results lead to the conclusion that the optimal control theory provides a useful mathematical tool for the design of active suspension systems. The optimally-controlled suspension designs prove to be effective in controlling vehicle vibrations, and achieve better performance than the conventional passive suspension. The slow-active systems offer significant improvements in controlling body resonances. In fact, the slow-active system tracks its full bandwidth active counterpart. The low power consumption capabilities of this type of system compared to full bandwidth active systems render it to be an attractive candidate for providing good ride qualities, with its real time implementation being promising. [ABSTRACT FROM PUBLISHER]

We changed the vibratory (dynamic) response of a micro mirror experimentally using a feedback circuit. For this purpose, we first measured the vibrational velocity of the mirror using a Laser Doppler Vibrometer and then multiplied it with a gain and fed the signal back to the mirror to change its effective damping. We also investigate the influence of velocity and position feedback on the dynamic response of the same mirror through numerical simulations. For this purpose, first, a transfer function of the mirror was obtained based on the experimental frequency sweep data of the first two vibration modes. Then, the dynamic response of the mirror was investigated for different feedback gains via simulations. The results of our study show that the vibration amplitude or settling time of the mirror can be adjusted by altering the velocity feedback gain and the coupled vibration modes of the mirror can be separated from each other by adjusting the position feedback gain. [ABSTRACT FROM PUBLISHER]

An engine is one of the major sources of automobile vibration and noise, it is of significance to obtain the excitation force features from engine for vibration control. The Modulate-FFT discrete spectrum correction method is applied to the force identification. The accurate frequency, amplitude and phase are obtained base on Modulate-FFT discrete spectrum correction method from the extracted vibration signals of cylinder surface. With the mass and inertia parameters of the engine, the dynamic properties of the mounts, the excitation force can be identified. The nonlinear problem caused by the imprecise phase of the measurement points is avoided, and the identified method is greatly simplified. The reasons for error are analyzed and the refined measurement means were offered. Simulation results confirm the validity of the methods which leads to better application in practice. [ABSTRACT FROM AUTHOR]

The torsional vibration of the transmission system is one of the most important resources of vehicle NVH (noise, vibration and harshness) problem. As a complex system, the transmission system involves non-linear gear meshing, as well as the elastic deformation of the driveline and half shaft. To solve the problem, this paper firstly analyses the non-linear gear meshing based on dynamics of gear system and the Hertz elastic theory. Then a simulation model has been built with non-linear gears meshing of a transmission, two elastic drivelines, a differential, two half shafts and two tires. The dynamic characteristics have been investigated with the model. At the end the torsional vibration of the transmission system under speeding-up condition and comparisons with a real vehicle results are studied. [ABSTRACT FROM AUTHOR]

In this paper we investigate the control of flow problems where the control objective is to reduce the oscillation amplitude while keeping the frequency of oscillation between predefined limits at all times. The governing equations are simplified to obtain the oscillatory mode dynamics, after which the conditions that the control parameters must satisfy in order to achieve the desired objective are derived in detail. The results obtained are illustrated on a physical application example, namely cavity flow control, where it is seen that the controller is successful in achieving the control goal. [ABSTRACT FROM PUBLISHER]

To control vibration of elastic structure, a new type dynamic vibration absorber is introduced to study its effect on mitigating vibration energy of structure theoretically and experimentally. While the elastic plate is certified as object to be controlled, the vibration model of plate fitted with multi composite beam at multi point is established by theory of power flow. After research on effect of single composite beam in energy absorbing, a method to obtain parameters of composite beam is formed and the advantage of composite beam in dissipating energy is proved. At the same moment, multi composite beam combined to decrease the vibration energy of plate is studied, the simulation results and experimental data shows that composite beams whose model frequencies are different with each other fitted at one point on plate can expand the bandwidth of absorber. While multi composite beam fitted at different point which is close to each other, the absorption of its combination is approximately equal to the union of absorption of each absorber in combination. It is concluded that the composite beams, which have advantages of wide bandwidth, great absorption and excellent extensibility, is fit to control vibration of plate with great effect, and its validity and feasibility is testified. [ABSTRACT FROM AUTHOR]

The modal data-based system identification (SI) algorithms normally consider the free vibration equation of motion of the dynamic system without damping for the identification of damage of existing structures. The present study intends to assess the damage of existing structures, including the effect of damping. The primary objective is to develop the equation error approach-based SI algorithm to identify both the stiffness properties and the damping parameters. The viscous damping model, which is computationally affordable and widely applicable to non-conservative systems, is considered for this objective. The formulation is hinged on the use of free vibration response in which the error norm of the eigen equation with damping is minimized. The SI algorithm is demonstrated through numerically-simulated modal data, which are obtained by the finite element analysis. The Monte Carlo simulation-based error sensitivity study confirms the consistency and robustness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

As to multi-signals, the figure of time-frequency distribution becomes difficult to understand due to cross-terms in the Wigner-Ville distribution (WVD). At present time, cross-terms suppression of time-frequency analysis is one of the top interests in signal processing, and more and more research had been put on this topic, but the present research on cross-terms suppression exist conflicting problem that these methods couldn't suppress the cross-terms while holding high time-frequency resolution. A novel method of cross-terms suppression in the WVD based on Empirical Mode Decomposition (EMD) was proposed to solve the above problem. Firstly, multi-component signals were decomposed into intrinsic mode functions (IMFs) which were single component signal by EMD ; Secondly, the relation coefficient values of IMFS and original signal were calculated to judge and delete the EMD false components ; Thirdly, these Wigner-Ville distributions of true component of IMFs were computed; Finally, WVDs of each single component signal were added linearly to reconstruct the WVD of original signal. Test on synthetic data shows the effectiveness of the proposed method, which can suppress the cross-terms while holding high time-frequency resolution. The proposed method was applied in I. C. Engine vibration signals time-frequency analysis, and the EMD-Wigner-Ville time-frequency distributions of two examples reflect I. C. engine vibration signal feature information effectively. Its merit of proposed method shows EMD-Wigner-Ville is an effective time-frequency distribution to analyze I. C. Engine vibration signals by comparing with Hilbert-Huang transform and Wigner-Ville distribution. [ABSTRACT FROM AUTHOR]

A parameter identification method is presented in this paper based on state space and wavelet transform method. For an arbitrarily linear time-varying system, the second-order vibration equations can firstly be rewritten and reduced to first-order difference equations by using state-space method. Subsequently, free response signals are decomposed using the Daubechies wavelet scaling functions , and then the state-space equations of the time-varying dynamic system are transformed into simple linear equations based on the orthogonality of the scaling functions. The varying equivalent state-space system matrices of structures at each moment are then identified directly by solving the linear equations. The system modal parameters are extracted though eigenvalue decomposition of the state-space system matrices and the stiffness and damping matrices are determined by comparing the identified equivalent system matrices with the physical system matrices. Finally, a four-storey shear-beam building model with three kinds of time-varying cases is investigated. Numerical results show that the proposed method is accurate and effective to identify the time-varying physical parameters. [ABSTRACT FROM AUTHOR]

Based on Biot' s wave propagation equation, the quadratic shape function TLM (thin-layer method) is adopted to derive the solution of Lamb's problem for saturated ground. The displacement expression in the frequency-wave number domain for saturated soil is obtained by dividing Biot's axisymmetric dynamic equation in vertical coordinates, and by the Fourier series decomposition in tangential coordinates and Hankel transform in axial coordinates. Then the inversion of Hankel transform and Fourier synthesis are used to get the displacement expression in the frequency domain. By a moving train-track-ground interaction model, a parametric study is given to evaluate the ground vibration induced by a moving train on the saturated ground. The effect of the soil parameters (such as dynamic permeability coefficient, porosity and dynamic fluid viscosity coefficient) on the attenuation of ground vibration are investigated and discussed in detail. The amplitude attenuation of ground vibration is compared between elastic ground and saturated one. The results show that the vertical displacement responses for poroelastic medium are quite different from those for elastic medium at the different train speeds. It is also found that the dynamic permeability coefficient of soil, porosity and the fluid viscosity coefficient have great influence on ground vibration. [ABSTRACT FROM AUTHOR]

Magnetorheological tuned liquid column damper (MR-TLCD) is a new kind of device for vibration control. It has a good performance and can be realized in project easily. A theoretical model of MR-TLCD for suppressing horizontal vibration is developed. The structure with single degree of freedom—MR-TLCD interactive equations are formulated. To start from the dynamic equations of system, the reasonable damping of MR-TLCD is determined according to the off-and-towards-equilibrium control strategy. In numerical calculation, wind load which is simulated by superposition of harmonic acts on the system. The control in time is carried out by adjusting the voltage of MR-TLCD. The simulation results show that the proposed is feasible and effective. Besides, MR-TLCD is an optimal semi-active control device. [ABSTRACT FROM AUTHOR]