1,721,136 research outputs found
Dynamic instability of circular cylindrical shells subject to base excitation
No full textThis paper is focused on the experimental and theoretical analysis of circular cylindrical shells subject to base excitation. The shell axis is vertical, it is clamped at the base and connected to a rigid body on the top; the base provides a vertical seismic-like excitation. The goal is to investigate the shell response when a resonant harmonic forcing is applied: the first axisymmetric mode is excited around the resonance at relatively low frequency and low amplitude of excitation. A violent resonant phenomenon is experimentally observed as well as an interesting saturation phenomenon close to the previously mentioned resonance. A theoretical model is developed to reproduce the experimental evidence and provide an explanation of the complex dynamics observed experimentally; the model takes into account geometric shell nonlinearities, electro-dynamic shaker equations and the shell shaker interaction. © Civil-Comp Press, 2012
Nonlinear dynamics of axially moving systems
No full textThe object of the present paper is a deep analysis of some recent numerical and experimental results regarding the complex dynamics of axially moving systems. Such important mechanical systems exhibit interesting dynamic behaviors: homoclinic orbits; sub-harmonic responses; amplitude modulations and chaos. These dynamics have been obtained numerically and in some case have been experimentally observed. Using recent techniques of the Nonlinear Time Series analysis, the response of axially moving systems is studied for a large variety of test cases. The correlation dimension of the time series, which is deeply related to the minimal dimension of a system able to reproduce the dynamics, is estimated. Lyapunov exponents are evaluated in order to quantify the response regularity. The present work give a contribution in understanding complex dynamics observed both in conservative and dissipative systems. The dynamical phenomena are analyzed within the unified framework fo the Nonlinear Time Series Analysis. In the case of experimental data the new nonlinear filtering techniques, based on the embedding techniques, have been applied to reduce high noise when classical techniques give bad results. Copyright © 2004 by ASME
Dynamic instabilities of circular cylindrical shells subjected to seismic excitations
No full textThe present paper is focused on the dynamic analysis of circular cylindrical shells under seismic excitation: the excitation direction is the cylinder axis, the shell is clamped at the base and connected to a rigid body on the top, the base provides the seismic excitation which is supposed sinusoidal. The goal is to investigate the shell response when a resonant forcing is applied: the first axisymmetric mode is excited around the resonance at relatively low frequency and low amplitude excitation. A violent resonant phenomenon is experimentally observed as well as an interesting saturation phenomenon close to the previously mentioned resonance. A theoretical model is developed to reproduce the experimental evidence and provide an explanation of the complex dynamics observed experimentally
Correction to: Asymmetric vibrations and chaos in spherical caps under uniform time-varying pressure fields (Nonlinear Dynamics, (2022), 107, 1, (313-329), 10.1007/s11071-021-07033-7)
No full textThe original article was published with erroneous author information. The correct authorship is as it stands in this correction. The original article has been corrected
Vibrations of circular cylindrical shells with complex boundary conditions
No full textIn the present paper vibrations of circular cylindrical shells having different boundary conditions are analyzed. Sanders-Koiter theory is considered for shell modeling: both linear and nonlinear vibrations are analyzed. An energy approach based on Lagrange equations is considered; a mixed expansion of displacement fields, based on harmonic functions and Tchebyshev polynomials, is applied. Several boundary conditions are analyzed: simply supported, clamped-clamped, connection with rigid bodies. Comparisons with experiments and finite element analyses show that the technique is capable to model several and complex boundary conditions. Applications to geometrically nonlinear shells show that the technique is effective also in the case of nonlinear vibration: comparisons with the literature confirm the accuracy of the approach. Copyright © 2006 by ASME
Imperfection Sensitivity of Compressed Circular Cylindrical Shells Under Periodic Axial Loads
No full textIn the present paper the dynamic stability of circular cylindrical shells is investigated; the combined effect of compressive static and periodic axial loads is considered. The Sanders-Koiter theory is applied to model the nonlinear dynamics of the system in the case of finite amplitude of vibration; Lagrange equations are used to reduce the nonlinear partial differential equations to a set of ordinary differential equations. The dynamic stability is investigated using direct numerical simulation and a dichotomic algorithm to find the instability boundaries as the excitation frequency is varied; the effect of geometric imperfections is investigated in detail. The accuracy of the approach is checked by means of comparisons with the literature.</jats:p
Post-critical response of an axially moving beam
No full textIn this paper the dynamic response of a simply supported traveling beam, subjected to a pointwise transversal load, is investigated. The motion is described by means of a high dimensional system of ordinary differential equations with linear gyroscopic part and cubic nonlinearities obtained through the Galerkin method. The system is studied in the super-critical speed range with emphasis on the stability and the global dynamics that exhibits special features after the first bifurcation. A sample case of a physical beam is developed and numerical results are presented concerning bifurcation analysis and stability, and direct simulations of global postcritical dynamics. In the supercritical speed range a regular motion around bifurcated equilibrium position becomes chaotic for particular values of frequency and force. The bifurcation diagram for varying force intensity is shown, it can be noticed that a chaotic motion occurs in a wide range of the forcing parameter, co-existiig with a 3T periodic solution in a limited window
Thermal effects on dynamics of circular cylindrical shell
No full textIn this paper, an experimental study on the dynamic of cylindrical shells made of Polyethylene terephthalate (PET) is presented; a thermic gradient has been applied on a specimen of the present work to obtain a functionally gradient material (FGM) equivalent properties: the PET shell had been exposed at a thermal temperature gradient in the range of its glass transition temperature of 79°C. A complex setup has been specifically designed and built to characterise, with dynamic tests, the structural properties of the specimen on temperature change from -10°C up to about 90°C and under thermic gradient with different forcing load. Predicting the mechanical properties of shells, panels and plates is one of the main concern of structural engineers; since shell elements present complicated stability behaviours, rich linear vibration spectra (high modal density), high sensitivity to perturbations and strong interactions with surrounding elements. The linear and dynamic behaviour have been investigated. The shell behaviour is also investigated by means of a finite element model, in order to enhance the comprehension of experimental results
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