The Experts below are selected from a list of 12678 Experts worldwide ranked by ideXlab platform
F.m. Detinko - One of the best experts on this subject based on the ideXlab platform.
-
Lumped Damping and stability of Beck column with a tip mass
International Journal of Solids and Structures, 2003Co-Authors: F.m. DetinkoAbstract:Abstract Lumped External Damping, acting on the concentrated mass at the tip of Beck’s column, is taken into account. This additional External Damping removes the prolonged inconsistency between theory and experiment for a column with a tip mass, subjected to follower force. In Sugiyama et al. [J. Aerospace Eng. 8 (1995) 9] and Wood et al. [Proc. Roy. Soc. Lond. Ser. A. 313 (1969) 239] the experimental critical loads for a beam with a tip mass agree well with theoretical values for an undamped system. On the other hand, the critical loads, calculated in Sugiyama et al. with account for the internal and distributed External Damping, were 50% lower than the experimental values. Since the actual experimental system is subject to Damping, the experiment and theory come into conflict. This conflict is resolved in this paper by observing that the experimental system was subjected not only to the distributed External Damping (due to distributed mass), but also to the lumped Damping, acting on the tip mass. When the lumped External Damping included in the analysis, analytical critical forces are in good agreement with experimental ones.
-
Some phenomena for lateral flutter of beams under follower load
International Journal of Solids and Structures, 2001Co-Authors: F.m. DetinkoAbstract:Abstract Simple model of a slender beam loaded by a transverse follower force and undergoing a lateral flutter is used to demonstrate the following phenomena: 1. If an analysis does not include any Damping, an extraction of only two lowest eigenvalues can lead to a wrong conclusion that the critical load is infinite. This is so because, when the ratio of two principal rigidities of a beam is not small, the eigenvalue with a positive real part emerges first not at the very beginning of the spectrum. 2. For the Kelvin-type material, and with no External Damping, the critical load becomes infinitely small when the Damping in the normal stress vanishes while the shear stress Damping is finite. 3. When the External Damping is increased, the critical load approaches the value calculated with no internal Damping. The nonlinear equilibrium is presented in the closed form and the eigenvalues of the torsional–flexural dynamic perturbed equations are found by the finite element approach and subdomain collocation method.
Francesco Marotti De Sciarra - One of the best experts on this subject based on the ideXlab platform.
-
Random vibrations of stress-driven nonlocal beams with External Damping
Meccanica, 2020Co-Authors: Francesco P. Pinnola, Marzia S. Vaccaro, Raffaele Barretta, Francesco Marotti De SciarraAbstract:Stochastic flexural vibrations of small-scale Bernoulli–Euler beams with External Damping are investigated by stress-driven nonlocal mechanics. Damping effects are simulated considering viscous interactions between beam and surrounding environment. Loadings are modeled by accounting for their random nature. Such a dynamic problem is characterized by a stochastic partial differential equation in space and time governing time-evolution of the relevant displacement field. Differential eigenanalyses are performed to evaluate modal time coordinates and mode shapes, providing a complete stochastic description of response solutions. Closed-form expressions of power spectral density, correlation function, stationary and non-stationary variances of displacement fields are analytically detected. Size-dependent dynamic behaviour is assessed in terms of stiffness, variance and power spectral density of displacements. The outcomes can be useful for design and optimization of structural components of modern small-scale devices, such as micro- and nano-electro-mechanical-systems.
Oleg N. Kirillov - One of the best experts on this subject based on the ideXlab platform.
-
FLUTTER AND DISSIPATION INSTABILITIES IN STRUCTURES SUBJECT TO FRICTION FOLLOWER FORCES
2016Co-Authors: Davide Bigoni, D. Misseroni, Oleg N. Kirillov, Giovanni Noselli, Mirko TommasiniAbstract:Flutter and divergence instabilities are theoretically and experimentally analyzed in elastic structures with internal and External Damping. Despite of the fact that only the former (and not the latter) was believed to be a destabilizing effect, it is theoretically demonstrated that the External Damping plays a role similar to internal Damping, so that both yield a pronounced destabilization paradox (in the Ziegler sense). This finding and other features of the Beck and Pflueger columns are substantiated by an experimental campaign in which the follower forces are obtained via dry friction with a newly designed experimental apparatus.
-
The destabilizing effect of External Damping: Singular flutter boundary for the Pflüger column with vanishing External dissipation
Journal of The Mechanics and Physics of Solids, 2016Co-Authors: Mirko Tommasini, Oleg N. Kirillov, D. Misseroni, Davide BigoniAbstract:Elastic structures loaded by non-conservative positional forces are prone to instabilities induced by dissipation: it is well-known that internal viscous Damping destabilizes the marginally stable Ziegler's pendulum and Pfluger column (of which the Beck's column is a special case), two structures loaded by a tangential follower force. The result is the so-called ‘destabilization paradox’, where the critical force for flutter instability decreases by an order of magnitude when the coefficient of internal Damping becomes infinitesimally small. Until now External Damping, such as that related to air drag, is believed to provide only a stabilizing effect, as one would intuitively expect. Contrary to this belief, it will be shown that the effect of External Damping is qualitatively the same as the effect of internal Damping, yielding a pronounced destabilization paradox. Previous results relative to destabilization by External Damping of the Ziegler's and Pfluger's elastic structures are corrected in a definitive way leading to a new understanding of the destabilizating role played by viscous terms.
-
The effect of small internal and External Damping on the stability of distributed non-conservative systems
Journal of Applied Mathematics and Mechanics, 2006Co-Authors: Oleg N. Kirillov, Alexander P. SeyranianAbstract:The effect of small internal and External Damping on the stability of distributed non-conservative systems is investigated. A theory is constructed for the qualitative and quantitative description of the “destabilization paradox” in these systems, one manifestation of which is an abrupt drop in the critical load and frequency when small dissipative forces are taken ino account. The theory is base on an analysis of the bifurcations of multiple eigenvalues of non-self-adjoint differential operators that depend on parameters. Explicit formulae are obtained for the collapse of multiple eigenvalues with Keldysh chains of arbitrary length, for linear differential operators that depend analytically on a complex spectral parameter and are smooth functions of a vector of real parameters. It is shown that the “destabilization paradox” is related to the perturbation by small Damping of a double eigenvalue of a circulatory system with a Keldysh chain of length 2, which is responsible for the formation of a singularity on the boundary of the stability domain. Formulae describing the behaviour of the eigenvalues of a non-conservative system when the load and disspitation parameters are varied are described. Explicit expressions are obtained for the jumps in the critical loads and frequency of the loss of stability. Approximations are obtained in analytical form of the asymptotic stability domain in the parameter space of the system. The stabilization effect, in which a distributed circularity system is stabilized by small dissipative forces and which consists of an increase in the critical load, is explained, and stabilization conditions are derived. As a mechanical example, the stability of a visco-elastic rod with small internal and External Damping is investigated; unlike earlier publications, it is shown that the boundary of the stability domain has a “Whitney umbrella” singularity. The dependence of the critical load on the internal and External friction parameters is obtained in analytical form, yielding an explicit expression for the jump in critical load. On the basis of the analytical relations, the domains of stabilization and destabilization in the parameter space of the system are constructed. It is shown that the analytical formulae are in good agreement with the numerical results of earlier research.
-
Dissipation induced instabilities in continuous non‐conservative systems
Pamm, 2005Co-Authors: Oleg N. Kirillov, Alexander P. SeyranianAbstract:In this contribution we analyze the stabilizing and destabilizing effect of small Damping for rather general class of continuous non-conservative systems, described by the non-self-adjoint boundary eigenvalue problems. Explicit asymptotic expressions obtained for the stability domain allow us to predict when a given combination of the Damping parameters leads to increase or to decrease in the critical non-conservative load. The results obtained explain why different types of internal and External Damping so surprisingly influence on the stability of non-conservative systems. As a mechanical example the stability of a viscoelastic rod with small internal and External Damping, loaded by tangential follower force, is studied in detail. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
-
EFFECT OF SMALL INTERNAL AND External Damping ON THE STABILITY OF CONTINUOUS NON-CONSERVATIVE SYSTEMS
2005Co-Authors: Oleg N. Kirillov, Alexander P. SeyranianAbstract:An effect of small internal and External Damping on the stability of continuous non-conservative systems is investigated. A theory is developed, qualitatively and quantitatively describing the destabilization paradox in non-conservative systems, i.e. the jump in the critical load and frequency of the system when small dissipative forces are taken into account. The theory is based on the bifurcation analysis of multiple eigenvalues of non-self-adjoint boundary eigenvalue problems depending on parameters. It is shown that the destabilization paradox is related to the perturbation of the double eigenvalue of a circulatory system by small Damping. The formulae are derived, which describe the behavior of eigenvalues of a non-conservative system due to change of the load and Damping parameters. Explicit expressions for the jumps in the critical load and frequency are found. Stabilization conditions for small Damping are established. As a mechanical example the stability of a viscoelastic rod with small internal and External Damping, loaded by tangential follower force, is studied in detail.
Francesco P. Pinnola - One of the best experts on this subject based on the ideXlab platform.
-
random vibrations of stress driven nonlocal beams with External Damping
arXiv: Applied Physics, 2020Co-Authors: Francesco P. Pinnola, Marzia S. Vaccaro, Raffaele Barretta, Francesco Marotti De SciarraAbstract:Stochastic flexural vibrations of small-scale Bernoulli-Euler beams with External Damping are investigated by stress-driven nonlocal mechanics. Damping effects are simulated considering viscous interactions between beam and surrounding environment. Loadings are modeled by accounting for their random nature. Such a dynamic problem is characterized by a stochastic partial differential equation in space and time governing time-evolution of the relevant displacement field. Differential eigenanalyses are performed to evaluate modal time coordinates and mode shapes, providing a complete stochastic description of response solutions. Closed-form expressions of power spectral density, correlation function, stationary and non-stationary variances of displacement fields are analytically detected. Size-dependent dynamic behaviour is assessed in terms of stiffness, variance and power spectral density of displacements. The outcomes can be useful for design and optimization of structural components of modern small-scale devices, such as Micro- and Nano-Electro-Mechanical-Systems (MEMS and NEMS).
-
Random vibrations of stress-driven nonlocal beams with External Damping
Meccanica, 2020Co-Authors: Francesco P. Pinnola, Marzia S. Vaccaro, Raffaele Barretta, Francesco Marotti De SciarraAbstract:Stochastic flexural vibrations of small-scale Bernoulli–Euler beams with External Damping are investigated by stress-driven nonlocal mechanics. Damping effects are simulated considering viscous interactions between beam and surrounding environment. Loadings are modeled by accounting for their random nature. Such a dynamic problem is characterized by a stochastic partial differential equation in space and time governing time-evolution of the relevant displacement field. Differential eigenanalyses are performed to evaluate modal time coordinates and mode shapes, providing a complete stochastic description of response solutions. Closed-form expressions of power spectral density, correlation function, stationary and non-stationary variances of displacement fields are analytically detected. Size-dependent dynamic behaviour is assessed in terms of stiffness, variance and power spectral density of displacements. The outcomes can be useful for design and optimization of structural components of modern small-scale devices, such as micro- and nano-electro-mechanical-systems.
Raffaele Barretta - One of the best experts on this subject based on the ideXlab platform.
-
random vibrations of stress driven nonlocal beams with External Damping
arXiv: Applied Physics, 2020Co-Authors: Francesco P. Pinnola, Marzia S. Vaccaro, Raffaele Barretta, Francesco Marotti De SciarraAbstract:Stochastic flexural vibrations of small-scale Bernoulli-Euler beams with External Damping are investigated by stress-driven nonlocal mechanics. Damping effects are simulated considering viscous interactions between beam and surrounding environment. Loadings are modeled by accounting for their random nature. Such a dynamic problem is characterized by a stochastic partial differential equation in space and time governing time-evolution of the relevant displacement field. Differential eigenanalyses are performed to evaluate modal time coordinates and mode shapes, providing a complete stochastic description of response solutions. Closed-form expressions of power spectral density, correlation function, stationary and non-stationary variances of displacement fields are analytically detected. Size-dependent dynamic behaviour is assessed in terms of stiffness, variance and power spectral density of displacements. The outcomes can be useful for design and optimization of structural components of modern small-scale devices, such as Micro- and Nano-Electro-Mechanical-Systems (MEMS and NEMS).
-
Random vibrations of stress-driven nonlocal beams with External Damping
Meccanica, 2020Co-Authors: Francesco P. Pinnola, Marzia S. Vaccaro, Raffaele Barretta, Francesco Marotti De SciarraAbstract:Stochastic flexural vibrations of small-scale Bernoulli–Euler beams with External Damping are investigated by stress-driven nonlocal mechanics. Damping effects are simulated considering viscous interactions between beam and surrounding environment. Loadings are modeled by accounting for their random nature. Such a dynamic problem is characterized by a stochastic partial differential equation in space and time governing time-evolution of the relevant displacement field. Differential eigenanalyses are performed to evaluate modal time coordinates and mode shapes, providing a complete stochastic description of response solutions. Closed-form expressions of power spectral density, correlation function, stationary and non-stationary variances of displacement fields are analytically detected. Size-dependent dynamic behaviour is assessed in terms of stiffness, variance and power spectral density of displacements. The outcomes can be useful for design and optimization of structural components of modern small-scale devices, such as micro- and nano-electro-mechanical-systems.
