The Experts below are selected from a list of 4221 Experts worldwide ranked by ideXlab platform
A N Timokha - One of the best experts on this subject based on the ideXlab platform.
-
transient and steady state amplitudes of resonant three dimensional sloshing in a square base tank with a finite fluid depth
Physics of Fluids, 2006Co-Authors: Odd M Faltinsen, Olav F Rognebakke, A N TimokhaAbstract:An adaptive asymptotic nonlinear modal system is used for systematic quantification of three-dimensional steady-state resonant sloshing in a square base tank with a finite fill depth. The depth/breadth ratios are ⩾0.4. The tank is laterally excited with Frequency close to the Lowest Natural Frequency. The main emphasis is on the “swirling” wave regime and its special features, e.g., stability, feedback of higher modes, and regular and irregular switch of the apparent direction of rotation. Theoretical results are validated for both steady-state solutions and “beating” that does not die out in experimental investigations. Frequency domains with no stable steady-state waves and occurrence of “chaotic” waves are discussed.
-
asymptotic modal approximation of nonlinear resonant sloshing in a rectangular tank with small fluid depth
Journal of Fluid Mechanics, 2002Co-Authors: Odd M Faltinsen, A N TimokhaAbstract:The modal system describing nonlinear sloshing with inviscid flows in a rectangular rigid tank is revised to match both shallow fluid and secondary (internal) resonance asymptotics. The main goal is to examine nonlinear resonant waves for intermediate depth/breadth ratio 0.1 [lsim ] h / l [lsim ] 0.24 forced by surge/pitch excitation with Frequency in the vicinity of the Lowest Natural Frequency. The revised modal equations take full account of nonlinearities up to fourth-order polynomial terms in generalized coordinates and h / l and may be treated as a modal Boussinesq-type theory. The system is truncated with a high number of modes and shows good agreement with experimental data by Rognebakke (1998) for transient motions, where previous finite depth modal theories failed. However, difficulties may occur when experiments show significant energy dissipation associated with run-up at the walls and wave breaking. After reviewing published results on damping rates for lower and higher modes, the linear damping terms due to the linear laminar boundary layer near the tank's surface and viscosity in the fluid bulk are incorporated. This improves the simulation of transient motions. The steady-state response agrees well with experiments by Chester & Bones (1968) for shallow water, and Abramson et al. (1974), Olsen & Johnsen (1975) for intermediate fluid depths. When h / l [lsim ] 0.05, convergence problems associated with increasing the dimension of the modal system are reported.
Odd M Faltinsen - One of the best experts on this subject based on the ideXlab platform.
-
transient and steady state amplitudes of resonant three dimensional sloshing in a square base tank with a finite fluid depth
Physics of Fluids, 2006Co-Authors: Odd M Faltinsen, Olav F Rognebakke, A N TimokhaAbstract:An adaptive asymptotic nonlinear modal system is used for systematic quantification of three-dimensional steady-state resonant sloshing in a square base tank with a finite fill depth. The depth/breadth ratios are ⩾0.4. The tank is laterally excited with Frequency close to the Lowest Natural Frequency. The main emphasis is on the “swirling” wave regime and its special features, e.g., stability, feedback of higher modes, and regular and irregular switch of the apparent direction of rotation. Theoretical results are validated for both steady-state solutions and “beating” that does not die out in experimental investigations. Frequency domains with no stable steady-state waves and occurrence of “chaotic” waves are discussed.
-
asymptotic modal approximation of nonlinear resonant sloshing in a rectangular tank with small fluid depth
Journal of Fluid Mechanics, 2002Co-Authors: Odd M Faltinsen, A N TimokhaAbstract:The modal system describing nonlinear sloshing with inviscid flows in a rectangular rigid tank is revised to match both shallow fluid and secondary (internal) resonance asymptotics. The main goal is to examine nonlinear resonant waves for intermediate depth/breadth ratio 0.1 [lsim ] h / l [lsim ] 0.24 forced by surge/pitch excitation with Frequency in the vicinity of the Lowest Natural Frequency. The revised modal equations take full account of nonlinearities up to fourth-order polynomial terms in generalized coordinates and h / l and may be treated as a modal Boussinesq-type theory. The system is truncated with a high number of modes and shows good agreement with experimental data by Rognebakke (1998) for transient motions, where previous finite depth modal theories failed. However, difficulties may occur when experiments show significant energy dissipation associated with run-up at the walls and wave breaking. After reviewing published results on damping rates for lower and higher modes, the linear damping terms due to the linear laminar boundary layer near the tank's surface and viscosity in the fluid bulk are incorporated. This improves the simulation of transient motions. The steady-state response agrees well with experiments by Chester & Bones (1968) for shallow water, and Abramson et al. (1974), Olsen & Johnsen (1975) for intermediate fluid depths. When h / l [lsim ] 0.05, convergence problems associated with increasing the dimension of the modal system are reported.
Marco Amabili - One of the best experts on this subject based on the ideXlab platform.
-
Non-linear vibrations of shallow circular cylindrical panels with complex geometry. Meshless discretization with the R-functions method
International Journal of Non-Linear Mechanics, 2012Co-Authors: Galina Pilgun, Marco AmabiliAbstract:Geometrically non-linear forced vibrations of a shallow circular cylindrical panel with a complex shape, clamped at the edges and subjected to a radial harmonic excitation in the spectral neighborhood of the fundamental mode, are investigated. Both Donnell and the Sanders–Koiter non-linear shell theories retaining in-plane inertia are used to calculate the elastic strain energy. The discrete model of the non-linear vibrations is build using the meshfree technique based on classic approximate functions and the R-function theory, which allows for constructing the sequences of admissible functions that satisfy given boundary conditions in domains with complex geometries; Chebyshev orthogonal polynomials are used to expand shell displacements. A two-step approach is implemented in order to solve the problem: first a linear analysis is conducted to identify Natural frequencies and corresponding Natural modes to be used in the second step as a basis for expanding the non-linear displacements. Lagrange approach is applied to obtain a system of ordinary differential equations on both steps. Different multimodal expansions, having from 15 up to 35 generalized coordinates associated with Natural modes, are used to study the convergence of the solution. The pseudo-arclength continuation method and bifurcation analysis are applied to study non-linear equations of motion. Numerical responses are obtained in the spectral neighborhood of the Lowest Natural Frequency; results are compared to those available in the literature. Internal resonances are also detected and discussed.
-
polynomial versus trigonometric expansions for nonlinear vibrations of circular cylindrical shells with different boundary conditions
Journal of Sound and Vibration, 2010Co-Authors: Ye Kurylov, Marco AmabiliAbstract:Abstract Large-amplitude (geometrically nonlinear) forced vibrations of circular cylindrical shells with different boundary conditions are investigated. The Sanders–Koiter nonlinear shell theory, which includes in-plane inertia, is used to calculate the elastic strain energy. The shell displacements (longitudinal, circumferential and radial) are expanded by means of a double mixed series: harmonic functions for the circumferential variable and three different formulations for the longitudinal variable; these three different formulations are: (a) Chebyshev orthogonal polynomials, (b) power polynomials, and (c) trigonometric functions. The same formulation is applied to study different boundary conditions; results are presented for simply supported and clamped shells. The analysis is performed in two steps: first a liner analysis is performed to identify Natural modes, which are then used in the nonlinear analysis as generalized coordinates. The Lagrangian approach is applied to obtain a system of nonlinear ordinary differential equations. Different expansions involving from 14 to 34 generalized coordinates, associated with Natural modes of both simply supported and clamped–clamped shells, are used to study the convergence of the solution. The nonlinear equations of motion are studied by using arclength continuation method and bifurcation analysis. Numerical responses obtained in the spectral neighborhood of the Lowest Natural Frequency are compared with results available in literature.
-
a comparison of shell theories for large amplitude vibrations of circular cylindrical shells lagrangian approach
Journal of Sound and Vibration, 2003Co-Authors: Marco AmabiliAbstract:Abstract Large-amplitude (geometrically non-linear) vibrations of circular cylindrical shells subjected to radial harmonic excitation in the spectral neighbourhood of the Lowest resonances are investigated. The Lagrange equations of motion are obtained by an energy approach, retaining damping through Rayleigh's dissipation function. Four different non-linear thin shell theories, namely Donnell's, Sanders–Koiter, Flugge–Lur’e-Byrne and Novozhilov's theories, which neglect rotary inertia and shear deformation, are used to calculate the elastic strain energy. The formulation is also valid for orthotropic and symmetric cross-ply laminated composite shells. The large-amplitude response of perfect and imperfect, simply supported circular cylindrical shells to harmonic excitation in the spectral neighbourhood of the Lowest Natural Frequency is computed for all these shell theories. Numerical responses obtained by using these four non-linear shell theories are also compared to results obtained by using the Donnell's non-linear shallow-shell equation of motion. A validation of calculations by comparison with experimental results is also performed. Both empty and fluid-filled shells are investigated by using a potential fluid model. The effects of radial pressure and axial load are also studied. Boundary conditions for simply supported shells are exactly satisfied. Different expansions involving from 14 to 48 generalized co-ordinates, associated with Natural modes of simply supported shells, are used. The non-linear equations of motion are studied by using a code based on an arclength continuation method allowing bifurcation analysis.
Hiroyuki Matsunaga - One of the best experts on this subject based on the ideXlab platform.
-
vibration and stability of cross ply laminated composite plates according to a global higher order plate theory
Composite Structures, 2000Co-Authors: Hiroyuki MatsunagaAbstract:Natural frequencies and buckling stresses of cross-ply laminated composite plates are analyzed by taking into account the effects of shear deformation, thickness change and rotatory inertia. By using the method of power series expansion of displacement components, a set of fundamental dynamic equations of a two-dimensional higher-order theory for thick rectangular laminates subjected to in-plane stresses is derived through Hamilton's principle. Several sets of truncated approximate theories are applied to solve the eigenvalue problems of a simply supported thick laminated plate. In order to assure the accuracy of the present theory, convergence properties of the Lowest Natural Frequency and buckling stress are examined in detail. Numerical results are compared with those of the published existing theories and FEM solutions. The modal displacement and stress distributions in the thickness direction are obtained and plotted in figures. It is noticed that the present global higher-order approximate theories can predict the Natural frequencies, buckling stresses and stresses of thick multilayered composite laminates as accurately as three-dimensional solutions.
Haim Abramovich - One of the best experts on this subject based on the ideXlab platform.
-
dynamic buckling of a laminated composite stringer stiffened cylindrical panel
Composites Part B-engineering, 2012Co-Authors: H Less, Haim AbramovichAbstract:Abstract The present study deals with the “dynamic buckling” of a laminated composite stringer–stiffened curved panel. The “dynamic buckling”, in the present study, is concerned with the unbounded lateral response of the panel, which is subjected to an axial impact load. In reinforced panels with widely spaced adequately stiff stringers, the structure may pass through two major states before its total collapse: buckling of the panel skin between stiffeners and buckling of the stiffeners themselves. This study focuses on the Lowest buckling load of the stringer–stiffened panel, which is, buckling of the panel skin between stiffeners. The analysis of the laminated composite stringer–stiffened cylindrical panel was performed by using the commercial ANSYS finite element software. The model simulates the structure and its associated boundary conditions. The boundary conditions simulate the stringer–stiffened cylindrical panel as a part of a fuselage. The static buckling analysis was performed using the eigenvalue buckling approach to determine the static critical load. Modal analysis was used to calculate the first Natural Frequency and corresponding mode shape of the structure. Nonlinear transient dynamic analysis was used to determine the dynamic critical load. In the transient dynamic analysis the Newmark method with the Newton–Raphson scheme were used. In the present study, the equation of motion approach was applied. By this approach, the equations of motion were numerically solved for various load parameter values (loading amplitude and loading duration) to obtain the system response. Special attention was given to the neighborhood of loading durations corresponding to the period of the Lowest bending Frequency of the skin. For each load duration, the dynamic buckling load was calculated using a load versus lateral displacement curve generated by the ANSYS code. The results were plotted on a dynamic load amplification factor (DLF) graph. The DLF is defined, as the ratio of the dynamic buckling to the static buckling of the panel. For loading periods in the neighborhood of the Lowest Natural Frequency of the panel, the DLF was less than unity. It means that, for those particular loading periods, the dynamic buckling load is lower than the static one.
