The Experts below are selected from a list of 15633 Experts worldwide ranked by ideXlab platform
Vissarion Papadopoulos - One of the best experts on this subject based on the ideXlab platform.
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the effect of non uniformity of axial loading on the buckling behaviour of shells with random Imperfections
International Journal of Solids and Structures, 2007Co-Authors: Vissarion Papadopoulos, Pavlos IglesisAbstract:Abstract In the present paper, the effect of random non-uniform axial loading on the buckling behaviour of isotropic thin-walled Imperfect cylindrical shells is investigated. Random initial (out-of-plane) geometric Imperfections, thickness and material property variability, together with a non-uniform stochastic axial loading are incorporated into a cost-effective non-linear stochastic finite element analysis using the non-linear TRIC shell element. For this purpose, the concept of an initial ‘Imperfect’ Structure is introduced involving not only deviations of the shell Structure from its perfect geometry but also a spatial variability of the modulus of elasticity as well as of the thickness of the shell. The initial Imperfections as well as the axial loading are modeled as stochastic fields with statistical properties that are either based on an available data bank of measured initial Imperfections or assumed, in cases where no experimental data is available. Based on these simulation features, a simple and realistic approach is proposed for the estimation of the variability (scatter) of the limit loads by means of a brute-force Monte Carlo Simulation procedure. In addition, ‘worst case’ buckling scenarios are identified by means of a sensitivity analysis with respect to assumed parameters used for the description of stochastic fields that are not supported by corresponding experimental measurements. In addition it is shown that in the context of such sensitivity analysis, modeling of the non-uniformity of the axial loading is, from a computational point of view, fully equivalent to modeling the geometric boundary Imperfections. The numerical tests performed demonstrate the significant role that the random varying axial loading plays on the buckling behaviour of Imperfection sensitive Structures like the axially compressed thin-walled cylinder considered in this study.
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the effect of material and thickness variability on the buckling load of shells with random initial Imperfections
Computer Methods in Applied Mechanics and Engineering, 2005Co-Authors: Vissarion Papadopoulos, Manolis PapadrakakisAbstract:Abstract The effect of material and thickness Imperfections on the buckling load of isotropic shells is investigated in this paper. For this purpose, the concept of an initial ‘Imperfect’ Structure is introduced involving not only geometric deviations of the shell Structure from its perfect geometry but also a spatial variability of the modulus of elasticity as well as the thickness of the shell. The initial geometric Imperfections are described as a two-dimensional uni-variate (2D-1V) stochastic field with statistical properties that are either based on an available data bank of measured initial Imperfections or assumed, in cases where no experimental data is available. In order to describe the non-homogeneous characteristics of the initial Imperfections, the spectral representation method is used in conjunction with an autoregressive moving average model with evolutionary power spectra based on a statistical analysis of the experimentally measured Imperfections. In cases where no experimental results is available, the initial Imperfections are assumed to be homogeneous and their impact on the buckling load is investigated on the basis of ‘worst’-case scenarios with respect to the correlation length parameters of the stochastic fields. The elastic modulus and the shell thickness are described as 2D-1V non-correlated homogeneous stochastic fields, while the stochastic stiffness matrix of the shell elements is formulated using the local average method. The Monte Carlo Simulation method is used to calculate the variability of the buckling load, while for the determination of the limit load of the shell, a stochastic formulation of the elastoplastic and geometrically non-linear TRIC facet triangular shell element is implemented.
Manolis Papadrakakis - One of the best experts on this subject based on the ideXlab platform.
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the effect of material and thickness variability on the buckling load of shells with random initial Imperfections
Computer Methods in Applied Mechanics and Engineering, 2005Co-Authors: Vissarion Papadopoulos, Manolis PapadrakakisAbstract:Abstract The effect of material and thickness Imperfections on the buckling load of isotropic shells is investigated in this paper. For this purpose, the concept of an initial ‘Imperfect’ Structure is introduced involving not only geometric deviations of the shell Structure from its perfect geometry but also a spatial variability of the modulus of elasticity as well as the thickness of the shell. The initial geometric Imperfections are described as a two-dimensional uni-variate (2D-1V) stochastic field with statistical properties that are either based on an available data bank of measured initial Imperfections or assumed, in cases where no experimental data is available. In order to describe the non-homogeneous characteristics of the initial Imperfections, the spectral representation method is used in conjunction with an autoregressive moving average model with evolutionary power spectra based on a statistical analysis of the experimentally measured Imperfections. In cases where no experimental results is available, the initial Imperfections are assumed to be homogeneous and their impact on the buckling load is investigated on the basis of ‘worst’-case scenarios with respect to the correlation length parameters of the stochastic fields. The elastic modulus and the shell thickness are described as 2D-1V non-correlated homogeneous stochastic fields, while the stochastic stiffness matrix of the shell elements is formulated using the local average method. The Monte Carlo Simulation method is used to calculate the variability of the buckling load, while for the determination of the limit load of the shell, a stochastic formulation of the elastoplastic and geometrically non-linear TRIC facet triangular shell element is implemented.
G Caruso - One of the best experts on this subject based on the ideXlab platform.
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analysis of the vibration localization phenomenon in rotationally periodic Structures using a homogenized model
The 14th International Symposium on: Smart Structures and Materials & Nondestructive Evaluation and Health Monitoring, 2007Co-Authors: P Bisegna, G CarusoAbstract:Rotationally periodic Structures, like turbine, bladed disks, stators and rotors of electric machinery or satellite antennae, play a very important role in many fields of the technology. It is well known that when even small structural Imperfections are present, destroying the perfect periodicity of the Structure, each couple of degenerate modal frequencies splits into two different values (mistuning) and the corresponding modal shapes exhibit peaks of vibration amplitude (localization phenomenon). In this paper, a continuous model describing the in-plane vibrations of an Imperfect bladed rotor is derived via the homogenization theory and is applied to the analysis of the localization phenomenon. Imperfections are modeled as perturbations of the geometrical dimensions and material characteristics of some blades, and a perturbation approach is adopted in order to find out the split eigenfrequencies and eigenmodes of the Imperfect Structure. Numerical simulations show that the proposed model is suitable and effective for the identification and analysis of the localization phenomenon, requiring much lower computational effort than classical finite element models.
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a homogenized model for the analysis of the vibration localization phenomenon in rotationally periodic Structures
XVIII Congresso AIMETA, 2007Co-Authors: P Bisegna, G CarusoAbstract:Rotationally periodic Structures, like turbines, bladed disks, stators and rotors of electric machineries or satellite antennae, play an important role in many fields of the technology. It is well known that when even small structural Imperfections are present, destroying the perfect periodicity of the Structure, each couple of degenerate modal frequencies splits into two different values (mistuning) and the corresponding modal shapes exhibit peaks of vibration amplitude (localization phenomenon). In this paper a continuous model describing the in-plane vibrations of an Imperfect bladed rotor is derived via the homogenization theory, and is applied to the analysis of the localization phenomenon. Imperfections are modeled as perturbations of mass and bending stiffness of some blades, and a perturbation approach is adopted in order to find out the split eigenfrequencies and eigenmodes of the Imperfect Structure. Numerical simulations show that the proposed model is suitable and effective for the identification and analysis of the localization phenomenon, requiring much lower computational effort than classical finite element models.
Pavlos Iglesis - One of the best experts on this subject based on the ideXlab platform.
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the effect of non uniformity of axial loading on the buckling behaviour of shells with random Imperfections
International Journal of Solids and Structures, 2007Co-Authors: Vissarion Papadopoulos, Pavlos IglesisAbstract:Abstract In the present paper, the effect of random non-uniform axial loading on the buckling behaviour of isotropic thin-walled Imperfect cylindrical shells is investigated. Random initial (out-of-plane) geometric Imperfections, thickness and material property variability, together with a non-uniform stochastic axial loading are incorporated into a cost-effective non-linear stochastic finite element analysis using the non-linear TRIC shell element. For this purpose, the concept of an initial ‘Imperfect’ Structure is introduced involving not only deviations of the shell Structure from its perfect geometry but also a spatial variability of the modulus of elasticity as well as of the thickness of the shell. The initial Imperfections as well as the axial loading are modeled as stochastic fields with statistical properties that are either based on an available data bank of measured initial Imperfections or assumed, in cases where no experimental data is available. Based on these simulation features, a simple and realistic approach is proposed for the estimation of the variability (scatter) of the limit loads by means of a brute-force Monte Carlo Simulation procedure. In addition, ‘worst case’ buckling scenarios are identified by means of a sensitivity analysis with respect to assumed parameters used for the description of stochastic fields that are not supported by corresponding experimental measurements. In addition it is shown that in the context of such sensitivity analysis, modeling of the non-uniformity of the axial loading is, from a computational point of view, fully equivalent to modeling the geometric boundary Imperfections. The numerical tests performed demonstrate the significant role that the random varying axial loading plays on the buckling behaviour of Imperfection sensitive Structures like the axially compressed thin-walled cylinder considered in this study.
Vasiliy V Kochegarov - One of the best experts on this subject based on the ideXlab platform.
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molecule conformations in a sample with Imperfect Structure
Saratov Fall Meeting '99: Optical Technologies in Biophysics and Medicine, 2000Co-Authors: Sergey I Tatarinov, Mariya A Shnurkina, Vasiliy V KochegarovAbstract:Activity of molecules in biological system depends on their conformation. NMR spectroscopy study of molecule conformations requires replacement of atoms by their isotopes. X-ray diffraction study is limited by an opportunity of reception of crystal samples with perfect Structure. Biological systems, for example the cell membranes, are liquid crystal systems hence have Imperfect crystal Structure. Molecule conformations of substances with such Structure can be investigated by use of more long-wave radiation. In this case the Imperfection of Structure will be less essential. In this paper we show the efficiency of joint application of experimental molecular vibrational IR spectroscopy and computer simulation of spectra, with correction of force constants and electrooptical data for phase state change, in study of conformations of liquid crystal molecules.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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study of molecule conformations in sample with Imperfect Structure
Optical technologies in biophysics and medicine. Meeting, 2000Co-Authors: Sergey I Tatarinov, Mariya A Shnurkina, Vasiliy V KochegarovAbstract:Activity of molecules in biological systems depends on their conformation. NMR spectroscopy study of molecule conformations requires replacement of atoms by their isotopes. X-ray diffraction study is limited by an opportunity of reception of crystal samples with perfect Structure. Biological systems, for example the cell membranes, are liquid crystal systems [1] hence have Imperfect crystal Structure. Molecule conformations of substances with such Structure can be investigated by use of more long-wave radiation. In this case the Imperfection of Structure will be less essential. In this paper we show the efficiency of joint application of experimental molecular vibrational infrared spectroscopy and computer simulation of spectra, with correction of force constants and electrooptical data for phase state change, in study of conformations of liquid crystal molecules.