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We propose an algorithm for the evaluation of frequencies and forms of natural vibrations of a thin-walled circular cylindrical shell reinforced by a transverse annular elastic rib of small width with regard for the presence of discontinuities of the first kind in the force factors acting on the line of contact of the rib with the shell. To construct approximate solutions of the analyzed spectral problem, we use the variational method in combination with the partition of the domain of definition of the required functions into regular subdomains in each of which the displacements, forces, and moments have the properties of continuity and differentiability. The Ritz method proposed for the solution of the analyzed problem guarantees convergence in the uniform metric for displacements and the force factors of elastic shell., Introduction Thin-walled shells reinforced by stiffening ribs are extensively used in various fields of contemporary engineering and building. As one of the most important applied problems in this case, we [...]

Free vibrations are analyzed for isotropic plates in the form of isosceles triangles. We deduce the formula for the evaluation of the frequencies of free vibrations for plates of regular triangular shape with free edges and compute the coefficients of vibration mode and boundary conditions. The frequencies and modes of free vibrations of the isotropic thin isosceles triangular plates with free edges and different apex angles are computed by the finite-element method. Keywords: triangular plates, free vibrations, coefficients of the vibration mode and boundary conditions, frequencies of vibrations, finite-element method., Introduction Lamellar elements, in particular, of the triangular form are frequently used in the design of thin-walled engineering structures, modern buildings, auto-, aircraft-, and rocket-space structures. In the process of [...]

To investigate the characteristics of vibration-induced shear resistance reduction (ViSRR) in granular soils, laboratory tests were performed using a modified triaxial apparatus. Monotonic loading and vibration with controlled frequency and acceleration amplitude were superimposed to soil specimens under drained conditions. Tests were conducted for dry and saturated specimens at relative densities of [D.sub.r] = 35% and 70%. The tests revealed that superimposed vibration causes a reduction of shear resistance in addition to an additional volume change of the specimen. After the termination of vibration, the shear resistance was found to be recovered as the monotonic shearing continued. It was confirmed that the shear resistance reduction was not caused by vibration-induced variation of excess pore pressure in the specimen. For high-frequency vibration with frequency varying between 60 and 120 Hz, the relative shear resistance loss tended to increase linearly with the peak acceleration. Based on the test results, the concept of 'vibro-critical state' is proposed to describe the ViSRR of granular soil subjected to monotonic shear and vibration simultaneously. Key words: shear resistance reduction, granular soil, vibration, vibro-critical state, experimental investigation, 1. Introduction Owing to its discrete feature, a granular material may behave as a solid, liquid, or even gas depending on its density and loading conditions (Jaeger et al. 1996). [...]

To study the effect of the high-frequency vibration time on the mechanical properties of the injection molding workpieces, apply an improved ultrasonic vibrator which contains the original ultrasonic vibrator and the mold insert to change the crystal structure during the melt cooling stage. The crystallinity, crystal perfection, and yield stress characteristics of the workpieces under three injection temperatures were compared with those without ultrasonic vibration. Results manifested that the change of the yield stress and cross-section crystallinity of the sample obeys the Gaussian distribution at a specific ultrasonic vibration time. The maximum yield strength and the maximum change of the workpiece were 39.06 MPa (220[degrees]C, 8 s) and 12.70% (240[degrees]C, 10 s), respectively. With the ultrasonic vibration time increased, the crystallinity of the specimen surface decreased; the transition layer and crystal perfection increased first and then decreased. Therefore, considering the relationship between the ultrasonic vibration time and the yield stress, the vibration effect played a critical role at the initial stage of the ultrasonic vibration; the vibration induced the thermodynamics effect required a certain vibration time. This study contributed to changing the mechanism of crystal structure and yield stress under different ultrasonic vibration time. KEYWORDS cooling, crystallization, injection molding, molecular stacking, surface-core structure, ultrasonic vibration time, 1 | INTRODUCTION The demand for injection molding workpieces in various industrial fields is increasing day by day, and the requirements in performance are also getting higher. Therefore, obtaining high-quality [...]

Polylactic acid (PLA) is an environmentally friendly, biodegradable, and low-cost thermoplastic material suitable for 3D printing. Complex shapes can be easily produced and hence PLA has been used for many applications. This study presents the damping characteristics of two robotic gripper fingers. The first gripper is composed of a PLA surface layer and a magnetorheological (MR) fluid core and the second gripper is composed of a PLA surface layer bonded to a surface of unimorph piezoelectric Macro Fiber Composite (MFC). The magnetic field is applied by using permanent magnets while the magnetic field strength is varied by changing the distance between the permanent magnets. The electric field is applied by using a micro-amplifier and regulated using data acquisition systems. The natural frequency and damping ratio of the PLA gripper finger are determined by free vibration analysis using LabVIEW software. The damping ratio and vibration amplitude suppression for the PLA grippers was increased as the magnetic field strength changed from 0G to 600G (MR) and as the electric field changed from 0V to 360V (MFC). KEYWORDS cantilever structure, free vibration analysis, material testing, mechanical properties, MFC, MR fluid, PLA, resonance study: Polymers, robotic gripper finger, vibration damping, 1 | INTRODUCTION Vibration damping plays a major role in the broad area of components in aerospace, Civil Engineering, transport, robotics, marine, and so on. There are many vibration-damping approaches. [...]

An increase in the operation speed of high-speed trains often leads to an increase in the loading frequency on subgrade soil. Hence, the long-term dynamic behavior of the subgrade and the service performance of high-speed tracks are affected. To determine the stress-strain characteristics of granular soil under high-frequency loading, a triaxial test setup was modified to investigate the effects of loading acceleration and duration, water content, vibration frequency, cell pressure, and initial soil density. The experimental results indicate that there are reductions in axial stress and volumetric strain during high-frequency loading. The reduction in axial stress is as high as 40%, and that of volumetric strain, which is permanent, could approach 0.1%. The stress reduction, strain compression, and excess pore pressure are found to vary linearly with vibration acceleration when a/g > 0.02, where a is vertical vibration acceleration and g is gravitational acceleration. The reduction in strength and strains are found to depend on the loading acceleration and effective cell pressure, but independent of the loading duration, water content, frequency, and initial density. A threshold acceleration a = 0.02g is observed, below which the changes in the shear strength and volumetric strain induced by vibration are negligible. At high vibration acceleration, the strain amplitude could increase, eventually leading to a collapse of the specimen. Key words: granular soil, critical state, fluidization, deviatoric stress, volumetric strain. L'augmentation de la vitesse d'exploitation des trains a grande vitesse entraine souvent une augmentation de la frequence de chargement du sol de la plate-forme. Le comportement dynamique a long terme de la plate-forme et les performances de service des voies a grande vitesse sont donc affectes. Afin de determiner les caracteristiques de contraintedeformation du sol granulaire sous un chargement a haute frequence, un montage d'essai triaxial a ete modifie pour etudier les effets de l'acceleration et de la duree du chargement, de la teneur en eau, de la frequence de vibration, de la pression des cellules et de la densite initiale du sol. Les resultats experimentaux indiquent qu'il y a des reductions de la contrainte axiale et de la deformation volumetrique pendant le chargement a haute frequence. La reduction de la contrainte axiale peut atteindre 40% et celle de la deformation volumetrique, qui est permanente, peut approcher 0,1%. La reduction des contraintes, la compression des deformations et l'exces de pression interstitielle varient lineairement avec l'acceleration des vibrations lorsque a/g > 0,02 ou a est l'acceleration de vibration verticale et g est l'acceleration gravitationnelle. La reduction de la resistance et des deformations depend de l'acceleration de la charge et de la pression effective des cellules, mais est independante de la duree de la charge, de la teneur en eau, de la frequence et de la densite initiale. Un seuil d'acceleration a = 0.02g est observe, en dessous duquel les changements de la resistance au cisaillement et de la deformation volumetrique induits par la vibration sont negligeables. En cas d'acceleration elevee, l'amplitude de la deformation peut augmenter et conduire a l'effondrement du specimen. [Traduit par la Redaction] Mots-cles: sol granulaire, etat critique, fluidization, contrainte deviatorique, deformation volumetrique., 1. Introduction Vibrations induced by high-speed trains frequently lead to long-term settlement of the track owing to the permanent compression of the subgrade. When the speed of a high-speed train [...]

Investigations of the soil-foundation interaction behaviour of wind turbine foundations and transfer of energy from the wind to the ground have not been reported in Canada. Indeed, very few vibration monitoring studies have been conducted globally around wind farms. It has been found that turbines predominantly produce vibrations related to structural resonances and blade-passing frequencies. Energy is found to be modified with distance and is dominated by surface waves. This paper describes a study of the effect of wind-structure interaction on the behaviour of a turbine foundation and the generation of ground-based vibrations around a working commercial wind turbine in Ontario. The field monitoring system and meteorological instrumentation are described in this paper and the responses of the structure and surrounding ground due to the fluctuating wind-field are discussed. The spectral analysis shows that the higher frequency vibrations attenuate more rapidly than the lower frequency vibrations. The tilted elliptical particle motions are found to be non-Gaussian because of the non-Gaussian wind conditions. The response attenuation with distance indicates that both geometric and material attenuation may dominate the vibration attenuation in the near field and only geometric attenuation occurs in the far field. Key words: wind turbine, foundation vibration, ground vibration, wind, soil- foundation interaction. Des enquetes sur le comportement des fondations d'eoliennes en matiere d'interaction sol-fondation et de transfert d'energie du vent au sol n'ont pas ete signalees au Canada. En effet, tres peu d'etudes de surveillance des vibrations ont ete menees a l'echelle mondiale autour des parcs eoliens. Il a ete constate que les turbines produisent principalement des vibrations liees aux resonances structurelles et aux frequences de passage des pales. On constate que l'energie se modifie avec la distance et qu'elle est dominee par les ondes de surface. Cet article decrit une etude de l'effet de l'interaction entre le vent et la structure sur le comportement des fondations d'une turbine et la production de vibrations au sol autour d'une turbine eolienne commerciale en fonctionnement en Ontario. Le systeme de surveillance sur le terrain et l'instrumentation meteorologique sont decrits dans ce document et les reactions de la structure et du sol environnant dues a la fluctuation du champ de vent sont examinees. L'analyse spectrale montre que les vibrations de haute frequence s'attenuent plus rapidement que les vibrations de basse frequence. Les mouvements elliptiques inclines des particules s'averent etre non gaussiens en raison des conditions de vent non gaussiennes. L'attenuation de la reponse avec la distance indique que l'attenuation geometrique et materielle peut dominer l'attenuation des vibrations dans le champ proche et que seule l'attenuation geometrique se produit dans le champ lointain. [Traduit par la Redaction] Mots-cles: turbine eolienne, vibration des fondations, vibration du sol, vent, interaction sol-fondation., Introduction Wind is a major source of renewable energy and has been the largest source of new electricity in Canada for the last 11 years. Wind turbines are subjected to [...]

Visible-light absorption and transport of the resultant electronic excitations to a reaction centre through Förster resonance energy transfer.sup.1-3 (FRET) are critical to the operation of biological light-harvesting systems.sup.4, and are used in various artificial systems made of synthetic dyes.sup.5, polymers.sup.6 or nanodots.sup.7,8. The fundamental equations describing FRET are similar to those describing vibration-to-vibration (V-V) energy transfer.sup.9, and suggest that transport and localization of vibrational energy should, in principle, also be possible. Although it is known that vibrational excitation can promote reactions.sup.10-16, transporting and concentrating vibrational energy has not yet been reported. We have recently demonstrated orientational isomerization enabled by vibrational energy pooling in a CO adsorbate layer on a NaCl(100) surface.sup.17. Here we build on that work to show that the isomerization reaction proceeds more efficiently with a thick .sup.12C.sup.16O overlayer that absorbs more mid-infrared photons and transports the resultant vibrational excitations by V-V energy transfer to a .sup.13C.sup.18O-NaCl interface. The vibrational energy density achieved at the interface is 30 times higher than that obtained with direct excitation of the interfacial CO. We anticipate that with careful system design, these concepts could be used to drive other chemical transformations, providing new approaches to condensed phase chemistry. Infrared absorption by a thick CO crystal produces many vibrational quanta that can be transported and concentrated at a salt interface to drive orientational isomerization of CO molecules with enhanced efficiency., Author(s): Jascha A. Lau [sup.1] [sup.2] , Li Chen [sup.2] [sup.5] , Arnab Choudhury [sup.1] [sup.2] , Dirk Schwarzer [sup.2] , Varun B. Verma [sup.3] , Alec M. Wodtke [sup.1] [...]

We study a three-dimensional problem of the theory of elasticity for a rectangular parallelepiped in the case of steady-state forced vibrations. By the method of superposition, we reduce the problem to an infinite system of linear algebraic equations for the coefficients of double Fourier series. For this infinite system, we prove that the conditions of quasiregularity are satisfied and that the bounded solution exists. We also construct the asymptotics that describes the behavior of unknowns in the infinite system. The method is illustrated by several numerical examples., To the blessed memory of my dear colleague and teacher Vyacheslav Vladimirovich Meleshko UDC 539.3 The three-dimensional problem for a rectangular parallelepiped is one of the oldest problems of the [...]

The governing equations of transverse motion and heat conduction of a homogenous, isotropic, thermally conducting, Kelvin-Voigt-type medium, based on Kirchhoff-Love plate theory, are established for out-of-plane vibrations of a generalized viscothermoelastic circular thin plate. The analytical expressions for thermoelastic damping of vibration and frequency shift are obtained for generalized and coupled viscothermoelastic plates. It is noticed that the damping of vibrations significantly depends on mechanical relaxation times and thermal relaxation time in addition to thermomechanical coupling in a circular plate under resonance conditions. The surface conditions also impose significant effects on the vibrations of such resonators. The numerical results may also be illustrated in the case of a circular plate and an axisymmetric circular plate for clamped and simply supported boundary conditions for fixed aspect ratio, fixed radius, and fixed thickness, respectively. Key words: viscothermoelasticity, circular plate, clamped, simply supported, damping. Nous construisons les equations directrices pour le mouvement transverse et la conduction de chaleur dans un milieu de Kelvin-Voigt thermiquement conducteur, isotrope et homogene, sur la base de la theorie des plaques de Kirchhoff-Love pour des vibrations hors du plan de plaques minces circulaires rondes. Nous obtenons les expressions analytiques pour l'amortissement thermoelastique de la vibration et le deplacement en frequence pour des plaques viscothermoelastiques couplees et generalisees. Nous notons que l'amortissement de la vibration depend de fa^on significative des temps de relaxation mecanique, du temps de relaxation thermique en plus du couplage thermomecanique dans la plaque circulaire en condition de resonance. Les conditions de surface ont egalement des effets significatifs sur la vibration de tels resonateurs. Les resultats numeriques peuvent etre presentes pour des plaques circulaires et axisymetriques avec des conditions limites encastrees ou simplement supportees, pour un rapport de forme donne, un rayon donne et une epaisseur donnee respectivement. [Traduit par la Redaction] Mots-cles: viscothermoelasticite, plaque circulaire, encastre, simplement supporte, amortissement. PACS Nos.: 46.25Hf, 46.60.Da, 46.35.+Z., 1. Introduction The dominant damping mechanism in structures is usually considered to be thermoelastic damping. There is a long history of studying thermoelastic damping beginning from Zener [1] and other [...]

The aim of this paper is to study the free vibration problem of a thermoelastic hollow cylinder in the context of the Lord and Shulman theory with one relaxation time. The eigenvalue approach is used to get the analytical solutions. The dispersion relations for the existence of various types of possible modes of vibrations are obtained. The validation of the roots for the dispersion relation is presented. The numerical results of frequency shift, natural frequency, and thermoelastic damping of vibrations have been presented graphically. PACS No.: 62.20.Dc. Nous etudions ici les vibrations libres d'un cylindre creux fait d'un materiau thermoelastique, en utilisant la theorie de Lord et Shulman avec un seul temps de relaxation. Nous utilisons une approche aux valeurs propres afin de trouver des solutions analytiques et obtenons les relations de dispersion pour les differents modes possibles de vibration. Nous validons les racines de ces relations de dispersion. Nous presentons graphiquement le deplacement en frequence, la frequence naturelle et l'amortissement thermoelastique des vibrations. [Traduit par la Redaction], 1. Introduction The linear theory of elasticity is of paramount importance in the stress analysis of steel, which is the most common engineering structural material. To a lesser extent, linear [...]

On the basis of relations of a version of the refined theory of dynamic deformation of composite plates, we propose a mathematical model of the process of free vibration of layered plates-strips with components compliant to transverse shear and compression. A characteristic equation is deduced for the case of hinging of elongated edges of the lower component. An analytic expression is obtained for the spectrum of natural frequencies of a two-layer plate-strip. We also analyze the influence of discreteness of the investigated structure in thickness and the compliance of plates to transverse compression on these frequencies. UDC 539.3, Introduction Layered composite plates with controlled characteristics of strength and specific consumption of materials belong to extensively used load-bearing elements of structures and equipment used for various purposes. The action [...]

UDC 539.3: 629.7.01 To describe the dynamic process of deformation of a plate, we construct the corresponding equation of motion for small strains and displacements with regard for the internal and external aerodynamic damping. This equation is based on the Kirchhoff-Love kinematic hypotheses, the generalized Kelvin-Voigt constitutive model, and the solutions of hydrodynamic wave equations for the acoustic media surrounding the plate obtained in the one-dimensional approximation within the framework of the well-known hypothesis of plane reflection and emission of acoustic waves. By using the constructed equation, we find the exact analytic solutions of the problem of damped vibrations of a rectangular plate, preliminarily bent and hingedly supported over its contour and of the emission of sound waves by the plate after its liberation from constraints. We also solve the problem of emission of sound waves caused by the shock of the plate by a transverse load., Introduction The level of admissible vibration of any structure intended for any purpose is determined by its influence on the strength characteristics of the structure and its elements, on the [...]

In an atomic force microscope (AFM), the cantilever vibrates by excitation at a frequency near the fundamental frequency, and the changes in vibration parameters, which result from the nonlinear forces of interaction between sample and cantilever tip, can be used as a tool to reveal the properties of the sample. To properly describe the images acquired by the AFM and to approximate the properties of the investigated sample, it is essential to use analytical and numerical models that can accurately simulate the dynamics of the cantilever and sample. For short beams, the Timoshenko model seems to be very accurate. Considering the fact that short beams (cantilevers) have many applications including the imaging of biological samples in liquid environments, the use of this theory seems to be necessary. In this paper, by employing the Timoshenko beam model, the effect of rotational inertia and shear deformation has been taken into consideration. The interaction forces between sample and cantilever in liquid, ambient air, and vacuum environments are quite different in terms of magnitude and formulation, and they play a significant role in the system's dynamic response. These forces include hydrodynamic forces, electrostatic double layer force, etc. Using an accurate model for the interaction forces will improve the simulation results significantly. In this paper, the frequency response of the atomic force microscope has been investigated by applying the Timoshenko beam model and considering the forces of interaction between sample and tip in the air and liquid environments. The results indicate that the resonant frequency changes and cantilever vibration amplitude diminishes in a liquid environment compared to the air environment. The simulation results have good agreement with the experimental ones. The frequency responses for the attractive and repulsive regions in the two environments are compared and it is demonstrated that the dynamic response is highly dependent on the hydrodynamic and interaction forces in the liquid medium. PACS No.: 68.37.Ps. Dans un microscope a force atomique (AFM), le cantilever est excite par des vibrations a une frequence proche de la frequence fondamentale. Les changements dans les parametres de vibration sont causes par des forces non lineaires d'interaction entre la pointe du cantilever et l'echantillon et peuvent etre utilises pour sonder les proprietes de l'echantillon. Afin de decrire correctement les images obtenues de l'AFM et d'approximer les proprietes de l'echantillon etudie, il devient essentiel d'utiliser des modeles analytiques et numeriques qui simulent de fa^on precise la dynamique du cantilever et de l'echantillon. Pour des bras courts, le modele de Timoshenko semble le plus approprie. Considerant que les cantilevers courts ont beaucoup d'applications AFM, incluant l'imagerie d'echantillons biologiques dans des environnements liquides, l'utilisation de ce modele apparait necessaire. Nous utilisons donc ici le modele de Timoshenko, avec ses effets d'inertie de rotation et de deformation de cisaillement. Les forces d'interaction entre le cantilever et l'echantillon varient considerablement, en grandeur et en formulation, selon que nous travaillons en milieu liquide, dans l'air ou dans le vide et elles jouent un role important dans la reponse dynamique. Ces forces incluent des forces hydrodynamiques, des forces a double couche, etc. L'utilisation d'un modele precis pour les forces d'interaction va ameliorer significativement les resultats de la simulation. Nous etudions ici la reponse en frequence d'un AFM en utilisant le modele du cantilever de Timoshenko et considerons les forces d'interaction dans un liquide et dans l'air. Les resultats indiquent que la frequence de resonance change et que l'amplitude du mouvement est plus faible dans le liquide que dans l'air. Les simulations sont en bon accord avec l'experience. Nous comparons les reponses en frequence dans les deux milieux et montrons que la reponse dynamique depend beaucoup de l'hydrodynamique et des forces d'interaction dans le liquid. [Traduit par la Redaction], 1. Introduction Nowadays, atomic force microscopy (AFM) is widely used, at micrometre to nanometre scales, for imaging the surfaces of materials and measuring different material properties, such as viscoelasticity. The [...]

Using the spectral element method (SEM), a 2-D numerical model of multi-storey frame structures has been developed. The model has been used to predict traffic-induced vibrations of two, six, and twelve-story concrete buildings measured along the route of a future metro line in Belgrade, the capital of Serbia. Vibration simulations of the six-storey frame match satisfactorily the measured dynamic response. However, there is a difference between numerical simulation and the actual measurements for the two-storey and twelve-story buildings. The results indicate a great potential of the proposed SEM to simulate ground-induced vibrations of frame buildings. However, more complex structural models should be developed to better replicate actual situations. Key words: traffic-induced vibrations, spectral elements, frequency domain, SEM modeling. Un modele numerique a deux dimensions de constructions de plusieurs etages a ete developpe en utilisant la methode d'analyse spectrale. Le modele a ete utilise pour predire les vibrations, engendrees par la circulation de voitures autour d'immeubles en beton de deux, six et douze etages, mesurees le long du trajet d'une future ligne de metro a Belgrade, la capitale de la Serbie. Les simulations de vibration des ossatures a six etages correspondent de maniere satisfaisante a la reaction dynamique mesuree. Toutefois, il existe une difference entre la simulation numerique et les vraies mesures pour les immeubles a deux et a 12 etages. Les resultats indiquent le tres bon potentiel de la methode d'analyse proposee pour simuler les vibrations induites par le sol sur les immeubles. Toutefois, des modeles structuraux plus complexes devraient etre developpes pour mieux simuler la realite. [Traduit par la Redaction] Mots-cles: vibrations engendrees par la circulation, elements spectraux, domaine des frequences, modelisation de la methode d'analyse spectrale., 1. Introduction Rapid urbanization of modern cities has led to the construction of buildings near roads, highways, and railways. In the last few decades the use of new high-strength structural [...]

We consider an axisymmetric problem of free longitudinal vibrations of hollow piezoelectric cylinders for some types of boundary conditions on the end faces. The piezoceramic material is polarized in the radial direction. The side faces of a cylinder are covered with short-circuited thin electrodes. The method of solution of the problem is based on the combination of the spline collocation method along the longitudinal coordinate and the step-by-step search method along the radial coordinate. We present results of a numerical analysis of a cylinder of PZT 4 ceramic in a wide range of changes in the geomet-ric parameters of the cylinder., UDC 539.3 The solution of dynamic problems for thick-walled elements as spatial problems of the theory of elasticity is connected with substantial difficulties caused by the complexity of the system [...]

We consider a problem of nonlinear parametric vibrations of a cylindrical shell. The vibrations are de-scribed by the Donnell-Mushtari-Vlasov equations. Motions are expanded in the modes of natural vibrations of the shell. A dynamic system with six degrees of freedom is obtained by the Bubnov-Galerkin method. The system is investigated by the method of multiple scales. The solution of the problem is represented with the use of amplitude-frequency characteristics., UDC 539.3 1. Introduction Shell structures form a wide class of mechanical objects used in mechanical engineering, rocketry, astronautics, and the building industry. This is why it is no wonder [...]

This essay reflects on two models of indelibility or persistence that emerge from the nineteenth-century geological and archaeological imagination, advanced and illustrated by figures who attended to a peculiar intuition that voices and faces are forms that, in their different ways, persist and are susceptible to interpretative historical recovery. The essay proposes that these models, represented in Florence McLandburgh's short story 'The Automaton-Ear' (1873) and in Francis Galton's technique of composite photography, stage two sides of a significant debate in the nineteenth century concerning the extent to which the social and physical world was increasingly apprehended in ways defined by such notions as the general, the pattern, the statistical and the average, and the compound and the layered., In 1844, the geologist, rambler, and writer Hugh Miller stood on the Hebridean coastline and contemplated the rocks: There are no sermons that seem stranger or more impressive to one [...]

The sound wave in a cylindrical steel bar, generated by a light tap on one of its ends, is recorded by a microphone located near the other end. A sound analysis software is used to obtain the resonance spectrum of the bar. Longitudinal and flexural vibration frequencies are obtained from the peaks of the spectrum. The speed of sound, Young's modulus, and Poisson's ratio of steel are obtained. [c] 2010 American Association of Physics Teachers. [DOI: 10.1119/1.3493403]

Linearized continuum models of a suspended span with unloaded backstays and of a symmetric three-span suspension bridge are used to study the effects of the flexibility of the hangers on the vertical vibrations of suspension bridges. The models include elastic parabolic cables, flexible distributed hangers with variable length, and a stiffening girder represented by an elastic beam. It is shown that the free vibrations of a suspended span with unloaded backstays are controlled by five dimensionless parameters, while six dimensionless parameters control the response of a symmetric three-span suspension bridge. The results indicate that the flexibility of the hangers has a significant effect on the natural frequencies of the higher modes only when the relative stiffness of the girder is very high. The effects of hanger flexibility on the response of a suspension bridge to localized impulsive loads are also found to be small. These findings confirm the traditional, albeit previously untested, assumption of inextensible hangers. Finally, the threshold amplitudes of free vibrations that would result in the incipient slackening of the hangers are determined. DOI: 10.1061/(ASCE)EM.1943-7889.0000185 CE Database subject headings: Dynamic loads; Bridges, suspension; Continuum mechanics; Vibration. Author keywords: Dynamic loads; Suspension bridges; Continuum models; Linear response; Vibrations.

We have solved the problem of determination of the stressed state in an isotropic elastic body near ring-shaped defects (a crack or a thin rigid inclusion) as a result of the action of a harmonic torsional wave. The method of solution is based on the use of discontinuous solutions of the equation of torsional vibrations and lies in the reduction of the initial boundary-value problems to integral equations for the un-known jumps of angular displacement or tangential stress., UDC 539.3 The strength analysis of structures with regard for the presence of cracks or thin inclusions in them requires using criteria that establish the limit equilibrium of bodies containing [...]

A dynamic model is reported herein for the study of vibrations of deep groove ball bearings having single and multiple defects on surfaces of inner and outer races. Masses of shaft, housing, races, and balls are considered in the modeling. The coupled solution of governing equations of motions is obtained using Runge-Kutta method. The model provides the vibrations of shaft, balls, and housing in time and frequency domains. Computed results from the model are validated with experimental results, which are generated using healthy and defective deep groove ball bearings. Characteristic defect frequencies and its harmonics are broadly investigated using both theoretical and experimental results. Comparison of vibration spectra for the cases having single and two defects on races reveals relatively higher velocity amplitudes with two defects. Good correlations between theoretical and experimental results are observed. Authors believe that this dynamic model can be used with confidence for the study and prediction of vibrations of healthy and defective deep groove ball bearings. [DOI: 10.1115/1.4002333] Keywords: vibration, multiple defects, time domain, frequency domain, deep groove ball bearing