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The lateral vibration serviceability of slender footbridges has been the subject of many studies over the last few decades. However, in spite of the large amount of research, a common criterion has not been set yet. Although the human−structure interaction phenomenon is widely accepted as the main cause of the sudden onset of high amplitudes of vibration, the current design recommendations do not include an expression for the auto-induced component of the pedestrian action and, as a consequence, it is not possible to evaluate the footbridge comfort once the lock-in effect has developed. Hence, the purpose of this paper is to propose a general formulation, which allows the analysis of the different load scenarios that the footbridge will experience during its overall life cycle. An important advantage over most current design guidelines is that the procedure permits the evaluation of the comfort level of the footbridge, even with crowd densities above the “critical number”, and thus takes informed decisions about the possible use of external devices to control the vibration response, depending on the probability of occurrence of the problem. The performance of the proposed method is successfully evaluated through numerical response simulations of two real footbridges, showing a good agreement with the experimental data.

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Fatigue crack in a rotary shaft is a common failure observed in rotor systems. Since vibration of the shaft causes alternating fatigue loads, the crack propagates slowly. Meanwhile, the propagating crack may cause nonlinear or unstable vibration of the rotor system. In fact, growth of the crack and vibration of the shaft are coupled with each other. Hence, it is necessary to study the fatigue degradation behavior of the cracked rotor accounting for this coupling effect. In this paper, a coupling model of rotor vibration and crack growth is established through dynamic theory and fracture mechanics, and a sequential iterative procedure is proposed to solve the coupling model. Then, the competing degradation failure mode of the cracked rotor is analyzed with regard to the rapid crack growth failure and the unstable vibration failure. And degradation measures are proposed based on the competing degradation failure criterion. At last, degradation behaviors with the coupling effect of nonlinear vibration behavior and multiple parameters including rotation speed, unbalance eccentricity and orientation angle, and damping are investigated by numerical simulation. The results indicate that nonlinear vibration behavior and multiple parameters have considerable influence on the degradation behaviors, which present complex regularity. The findings are of significance to guide the safety design of the rotor system for long time operation and help to the further research on prognostics and lifetime prediction.

A switching stiffness control and a modified variable stiffness control were applied to reduce vibration in the lateral directions in active magnetic suspension system with electromagnets operated in the differential mode. The magnetic suspension system using the attractive force between magnetized bodies is inherently unstable in the normal direction so that feedback control is necessary to achieve stable suspension. In contrast, it is usually stable in the lateral directions because of the edge effects in the magnetic circuits. However, damping in the lateral directions is poor so that vibration is easily induced. In this work, a switching stiffness control was applied to attenuate such vibration. The effectiveness of the switching stiffness control was confirmed experimentally. In addition, a modified control method that varies stiffness continuously was proposed to overcome problems occurring in switching. The efficacy of the modified control method was also confirmed experimentally.

This article considers lateral vibration of an automobile in a so-called quasi-planar model where both the loss of contact and road deformation are taken into account. The automobile with dependent suspension is modeled as a vibration system which has two masses and four degrees of freedom. The deformed road is modeled as an elastic beam which has uniform rectangular cross-section, is simply supported at the two ends and lies on the Kelvin's visco-elastic ground. The loss of contact and the change in dimensions of contact areas are considered. The differential equations of motion of the vehicle-road coupled system which contains a partial differential equation are transformed into a set of all ordinary differential equations by applying the Bubnov-Galerkin's method. A procedure for numerically solving the transformed differential equations of motion is proposed. Some illustrating results coming from numerical consideration are also presented in the paper. [ABSTRACT FROM AUTHOR]

With advances in internet of things technology and fossil fuel depletion, energy harvesting has emerged rapidly as a means of supplying small electronics with electricity. As a method of enhancing the electrical output of the triboelectric nanogenerator, specialized for harvesting mechanical energy, structural modification to amplify the input force is receiving attention due to the limited input energy level. In this research, a lever structure was employed for delivering the amplified input force to a triboelectric nanogenerator. With structural optimization of a 2.5 cm : 5 cm distance ratio of the first and second parts using two lever structures, the highest electrical outputs were achieved: a V OC of 51.03 V, current density of 3.34 mA m -2 at 12 MΩ in the second part. As applications of this triboelectric generator, a vertical vibration sensor and a wearable reloading trigger in a gun shooting game were demonstrated. The possibility for a wearable finger bending sensor with low-level input was checked using a minimized device. Enhanced low-detection limit with amplified input force from the structural advantage of this lever-based triboelectric nanogenerator device can expand its applicability to the mechanical trigger for wearable electronics.-2 at 12 MΩ in the second part. As applications of this triboelectric generator, a vertical vibration sensor and a wearable reloading trigger in a gun shooting game were demonstrated. The possibility for a wearable finger bending sensor with low-level input was checked using a minimized device. Enhanced low-detection limit with amplified input force from the structural advantage of this lever-based triboelectric nanogenerator device can expand its applicability to the mechanical trigger for wearable electronics.

The lateral vibration of monatomic chains considering atomic longitudinal displacements is studied by using the string vibration theory. The modes of lateral vibration of monatomic chains are assumed as the modes of string vibration. Based on the string assumption, the equation of string vibration for monatomic chains is established. Coordinates of the vibration atoms can be calculated by utilizing boundary conditions and symmetry conditions of monatomic chains. The natural angular frequencies of transverse vibration of monatomic chains are calculated by the string vibration method. The tension of the quantum limitation is given and the value of limitation can be used to distinguish nanoelectromechanical systems from quantum-electromechanical Systems. Natural angular frequencies and resonant frequencies of the monatomic chain string are associated with the axial tension acting on the string and the length of monatomic chains, and they can be altered by changing the length of the string and the axial tension acting on the string. The nonlinear vibration of single atomic chain can be analyzed using the improved Lindstedt–Poincaré multiscale method. The study found that the stiffness of the carbon monatomic chain can be altered by changing the length of the string and the tension acting on the string. [ABSTRACT FROM AUTHOR]

The reversal and lateral vibration of the drill string are very complex motion and can affect the normal operation of the drill string. The movement of the drill string in the stepped well is different from the movement of the drill string in the regular well. The vibration of the drill string in the stepped well varies with the size of the wellbore and can be visually reflected by the phase speed. To find out the relationship between reversal and lateral vibration, the natural frequency of lateral vibration of the drill string was solved by using the method of energy conservation. The analysis shows that the phase speed of flexural wave in the stepped well is faster in small size wellbore than in large size wellbore. The reversal and lateral resonance is easy to happen in small size wellbore, and the reversal will excite lateral vibration. When the sum of reversal and rotational angular frequencies approaches the natural angular frequency of lateral vibration, the lateral resonance will occur. [ABSTRACT FROM AUTHOR]

We studied coarse particle behavior in a laterally vibrated vessel under microgravity. Vibration conditions were a frequency of 75-150 Hz and a displacement amplitude of 86-310 μm. The two dimensional displacement distribution of particles moving in three dimensions was measured by particle image sampling within the depth of field. Observations revealed a saddle-shaped distribution in which concentration was higher at the center in the lateral direction and the ends in the longitudinal direction. This tendency became distinct with increasing total particle concentration. The round corners of the vessel made the distribution more uniform due to enhanced circulation. We also found that particle concentration increased with velocity amplitude.† This report was originally printed in J. Soc. Powder Technology, Japan. 34(11), 834-839 (1997) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.

In this study, the chaotic behavior of a viscoelastic plate under integrated non-Gaussian additive and multiplicative bounded noise is investigated with an analytical approach. First, the governing equation of motion of the system was derived by introducing a set of dimensionless parameters. After that, the modified version of Melinkov's function in terms of statistical indices was obtained, and then, for a spectrum of bounded noises, the boarder curves of chaotic areas were obtained. The model of sine/cosine Wiener was chosen for the bounded noise which enables the researcher to produce a range of wide and narrowband noises. For the case that the excitation is only additive, or only multiplicative, and that both excitations exist simultaneously, the effect of variations in structural properties and noise characteristics on the chaos area were investigated. It was shown that at frequencies close to the natural frequency of the corresponding linear system, narrowband excitations affected the chaotic behavior more than the wideband ones and vice versa. To validate the results, a numerical simulation was also made. [ABSTRACT FROM AUTHOR]