1,721,092 research outputs found
Homogenization and free-vibration analysis of elastic metamaterial plates by Carrera Unified Formulation finite elements
Full text linkThis work focuses on the assessment of a novel so-called “homogenization method” allowing to transform a heterogeneous material with inclusions or holes into an equivalent homogeneous material with equal mechanical behavior. The aim is to avoid meshing holes of the real material in finite-element codes, thus improving computation time for further analysis of the material. Typical periodic structure of passive acoustic metamaterial plates is considered here, with inclusions/holes that should improve the acoustic performances in the low-frequency range. The three-dimensional homogenization method, based on Carrera unified formulation (CUF) [E. Carrera, M. Cinefra, M. Petrolo, and E. Zappino. Finite Element Analysis of Structures through Unified Formulation. John Wiley & Sons, 2014] and Mechanics of Structure Genome, is assessed for a perforated plate made of a linear elastic material with periodic arrangement of holes. Different configurations of the metamaterial plate are considered, changing the number of the holes. The results obtained from the free-vibration analysis of the homogenized plates, performed by higher-order two-dimensional models contained in CUF, are compared with ABAQUS results and both numerical and experimental results provided in literature
Adaptive mesh using non-conventional 1D and 2D finite elements based on CUF
No full textWhen dealing with complex structures with a several number of degrees of freedom (DOFs), it is useful trying to reduce the mesh for computational cost reasons, seeking not affecting the accuracy in results. The Finite Element Method can become very costly in calculations and time because of the use of very fine 3D meshes. A possible solution can be the application of the Adaptive Mesh (AM), which allows to concentrate the very fine mesh only in regions where critical conditions are present, in terms of geometrical or loads constrains. By exploiting the Node-Dependent Kinematic approach of the Carrera Unified Formulation and using Lagrange expanding functions, this work presents the application of non-conventional 1D and 2D elements for mesh refinement, offering a new and convenient technique to apply in the framework of AM. The static analysis of some typical study cases is performed and the results are provided in terms of displacements and stresses. The presented elements allow us to combine them in order to obtain a mesh refinement employing much less degrees of freedom with respect to the use of classical 3D finite elements
Free-vibration analysis of laminated shells via refined MITC9 elements
Full text linkThis article presents the free-vibration analysis of composite shell structures with double-curvature geometry by means of a shell finite element with variable through-the-thickness kinematic. The refined models used are grouped in the Unified Formulation by Carrera (CUF) and they permit the distribution of displacements and stresses along the thickness of the multilayered shell to be accurately described. The shell element has nine nodes and the mixed interpolation of tensorial components (MITC) method is used to contrast the membrane and shear locking phenomenon. The governing equations are derived from the principle of virtual displacements (PVD). Laminated cylindrical and spherical shells with simply-supported edges are analyzed. Various laminations, orthotropic ratios and thickness ratios are considered. The results, obtained with different theories contained in the CUF, are compared with both the elasticity solutions given in the literature and the analytical solutions obtained using the CUF and the Navier's method. The shell element based on the CUF is very efficient, and refined models provide better results than classical ones in the free-vibration analysis of multilayered composite shells. Finally, spherical shells with different boundary conditions are analyzed using various theories in order to provide finite element method benchmark solutions
Some results on thermal stress of layered plates and shells by using unified formulation
No full textThis work presents some results on two-dimensional modelling of thermal stress problems in multilayered structures. The governing equations are written by referring to the Unified Formulation (UF) introduced by the first author. These equations are obtained in a compact form, that doesn't depend on the order of expansion of variables in the thickness direction or the variable description (layer-wise models and equivalent single layers models). Classical and refined theories based on the Principle of Virtual Displacements (PVD) and advanced mixed theories based on the Reissner Mixed Variational Theorem (RMVT) are both considered. As a result, a large variety of theories are derived and compared. The temperature profile along the thickness of the plate/shell is calculated by solving the Fourier's heat conduction equation. Alternatively, thermo-mechanical coupling problems can be considered, in which the thermal variation is influenced by mechanical loading. Exact closed-form solutions are provided for plates and shells, but also the applications of the Ritz method and the Finite Element Method (FEM) are presented. Copyright © Taylor & Francis Group, LLC
DYNAMIC ANALYSIS OF VARIABLE THICKNESS SHELLS IN AEROSPACE APPLICATIONS VIA CUF ADAPTIVE FINITE ELEMENTS
No full textNew technologies and tools lead to design structures with increasingly more complex and disruptive geometries. In the field of thin structures, such as plates and shells, it is necessary to have numerical analysis tools that take into account these innovations and the use of advanced materials, such as composites, metamaterials or sandwich plates, or in general muti-layer materials. Within the Carrera’s Unified Formulation (CUF) framework, this article proposes a formulation based on adaptive finite elements that can study complex geometries, as variable thickness plates or with edges not orthogonal to the midsurface, while retaining the advantages of CUF theories for the study of multi-layer structures, both in terms of accuracy and reduced computational cost. The adaptability of these new elements concerns both the geometry and the possibility of using different structural models within the same element. Two case studies are presented in the following paper in order to demonstrate the new formulation: a plate with a topology optimized thickness and a semi-cylinder with a sinusoidal thickness
Refined Finite Element Solutions for Anisotropic Laminated Plates
Full text linkThis paper presents some solutions for mechanical responses of angle-ply laminated plates under transverse distributed loads, which are obtained by using refined finite element models adopting variable kinematics based on Carrera's Unified Formulation (CUF). Plates with several types of stacking sequence under different boundary conditions are considered. Layer-wise (LW) models based on Chebyshev polynomials (first kind) and Equivalent Single Layer (ESL) models based on Trigonometric series are used in the analysis. To compare the performances of different displacement-based kinematic models, a set of simply supported boundary conditions and mixed clamped-free boundaries are adopted in the numerical study. A nine-node MITC (Mixed Interpolated of Tensorial Components) plate element is employed to contrast the shear locking phenomenon of thin plates. CUF-based variable kinematic models are used in the numerical study and the number of expansion terms in the thickness direction is increased until the requisite numerical accuracy is achieved. By comparing the numerical results obtained with CUF-based refined models and ABAQUS 3D models as well as reference solutions from literature, the effectiveness of the adopted models is verified. The newly studied numerical cases can be taken as benchmarks for future research
Advanced layer-wise shells theories based on trigonometric functions expansion
No full textAdvanced layer-wise shells theories based on trigonometric functions expansions are considered to evaluate the static behavior of multi-layered, orthotropic shells. The aim of the present work is to extend the basis functions used for layer-wise formulation to a trigonometric basis functions properly defined. Carrera Unified Formulation for the modeling of composite shell structures is adopted. Via this approach, higher order, zig-zag, layer-wise and mixed theories can be easily formulated. The governing differential equations of the problem are presented in a compact general form. These equations are solved via a Navier-type, closed form solution. As assessment, results are compared with available exact solutions present in literature. ©2012 AIAA
Coupled thermo-mechanical finite element models with node-dependent kinematics for multi-layered shell structures
Full text linkNode-dependent Kinematic (NDK) shell finite element (FE) formulations are presented for the steady-state thermo-mechanical analysis of laminated structures. The displacements and temperature change are treated as primary variables in the FE models and are directly solved through the coupled thermo-mechanical models. The enforcement of distributed temperature boundary conditions on the top or the bottom surface of hierarchical shell elements is conducted through the Linear Least Squares. The effectiveness of the proposed FE approaches is verified by comparing the results against those from the literature. The application of adaptive refinement approach based on the hierarchical elements and NDK to build FE models with optimal efficiency is demonstrated through numerical examples
Transmission loss investigation of acoustic metamaterials via Adaptive Finite Elements
No full textThis work develops the integration of the Rayleigh’s integral method for calculating transmission loss into a new class of 2D finite elements, the adaptive finite elements. These
elements, recently developed within Carrera’s Unified Formulation framework, allow 2D
structures to be studied independently of expansion along the thickness, allowing for increased
computational efficiency over traditional solid elements. In this paper, they are used to calculate
the transmission loss on a panel of sandwich material. The aim is to demonstrate their efficiency
within a future core geometry optimisation process. These elements make studying different
thickness geometries accurate and fast, always based on the same 2D mesh. The article briefly
presents the formulation of the adaptive finite elements and Rayleigh’s integral method. Then,
the implementation is validated, and a series of geometries chosen as examples are studied by
calculating their transmission loss
Vibroacoustic analysis of an innovative windowless cabin with metamaterial trim panels in regional turboprops
No full textThe purpose of this work is to study the possible noise reduction, in terms of sound pressure level, in the passenger cabin of a regional turboprop aircraft under multiple tonal and broadband noise components characterizing the noise generated by the engines during cruise flight conditions. In particular, we want to show the acoustic performances of innovative passive noise and vibration technologies, such as acoustic metamaterials applied to the trim panel of the cabin, in the low-frequency range, from 100 to 300 Hz. Moreover, the removal of windows from the passenger cabin is evaluated, in acoustic terms. Analyses are performed using a numerical tool, Actran, a finite element based software, and a numerical model of a regional aircraft fuselage. According to the results, metamaterials seem to have significant acoustic performances that lead to a reduction in noise and therefore an increase in passenger comfort
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