394 research outputs found
A variable kinematic doubly-curved MITC9 shell element for the analysis of laminated composites
No full textThe present article considers the linear static 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 displacement (PVD) and the finite element method (FEM) is employed to solve them. Cross-ply spherical shells with simply-supported edges and subjected to bi-sinusoidal pressure are analyzed. Various laminations, thickness ratios, and curvature 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. From the analysis, one can conclude that the shell element based on the CUF is very efficient and its use is mandatory with respect to the classical models in the study of composite structures. Finally, shells with different lamination, boundary conditions, and loads are also analyzed using high-order layer-wise theories in order to provide FEM benchmark solution
A MULTILAYERED PLATE ELEMENTS ACCOUNTING NODE-DEPENDENT KINEMATICS FOR STATIC ANALYSIS OF PIEZOELECTRIC STRUCTURES
No full textThermal Stress Analysis of laminated structures by a variable kinematic MITC9 shell element
No full textA linear static thermal stress analysis of composite shell structures is carried out by means of a shell nite element with variable through-the-thickness kinematic. The re- ned models used are both Equivalent Single Layer (ESL) and Layer Wise (LW) and they are grouped in the Unied Formulation by Carrera (CUF). These models permit the distribution of displacements, stresses and temperature along the thickness of the multi- layered shell to be accurately described. The Principle of Virtual Displacement (PVD) is employed to derive the governing equations. The Mixed Interpolation of Tensorial Components (MITC) method is used to contrast the membrane and shear locking phe- nomenon for a nine-node shell element. Cross-ply plate, cylindrical and spherical shells with simply-supported edges and subjected to bi-sinusoidal thermal load are analyzed and various thickness ratios are considered. The results, obtained with dierent theories con- tained in the CUF, are compared with both the elasticity solutions given in the literature and the analytical solutions obtained using higher-order models and the Navier's method. From the analysis, one can conclude that the shell element based on the CUF is very ef- cient, and its use leads to reach higher accuracy than classical models in the study of layered structure
Heat conduction and thermal stress analysis of laminated composites by a variable kinematic MITC9 shell element
No full textThe present paper considers the linear static
thermal stress analysis of composite structures by means
of a shell finite element with variable through-thethickness
kinematic. The temperature profile along the
thickness direction is calculated by solving the Fourier
heat conduction equation. The refined models considered
are both Equivalent Single Layer (ESL) and Layer
Wise (LW) and are grouped in the Unified Formulation
by Carrera (CUF). These permit the distribution of displacements,
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 Displacement
(PVD). Cross-ply plate, cylindrical and spherical
shells with simply-supported edges and subjected to
bi-sinusoidal thermal load are analyzed.Various thickness
ratios and curvature 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. Finally, plates and shells
with different lamination and boundary conditions are analyzed
using high-order theories in order to provide FEM
benchmark solutions
A layer-wise MITC9 finite element for the free-vibration analysis of plates with piezo-patches
No full textThe present article considers the free-vibration analysis of plate structures with piezoelectric patches by means of a plate finite element with variable through-the-thickness layer-wise kinematic. The refined models used are derived from Carrera’s Unified Formulation (CUF) and they permit the vibration modes along the thickness to be accurately described. The finite-element method is employed and the plate element implemented has nine nodes, and the mixed interpolation of tensorial component (MITC) method is used to contrast the membrane and shear locking phenomenon. The related governing equations are derived from the principle of virtual displacement, extended to the analysis of electromechanical problems. An isotropic plate with piezoelectric patches is analyzed, with clamped-free boundary conditions and subjected to open- and short-circuit configurations. The results, obtained with different theories, are compared with the higher-order type solutions given in the literature. The conclusion is reached that the plate element based on the CUF is more suitable and efficient compared to the classical models in the study of multilayered structures embedding piezo-patches
Classical, higher-order, zig-zag and variable kinematic shell elements for the analysis of composite multilayered structures
No full textIn the present work, a shell finite element with a variable kinematic field based on a new zig-zag power function
is proposed for the analysis of laminated shell structures. The kinematic field is written by using an arbitrary
number of continuous piecewise polynomial functions. The polynomial expansion order of a generic subdomain
is a combination of zig-zag power functions depending on the shell thickness coordinate. As in the classical layerwise approach, the shell thickness can be divided into a variable number of mathematical subdomains. The
expansion order of each subdomain is an input parameter of the analysis. This feature enables the solution to be
locally refined over generic regions of the shell thickness by enriching the kinematic field. The advanced finite
shell elements with variable kinematics are formulated in the framework of the Carrera Unified Formulation.
The finite element arrays are formulated in terms of fundamental nuclei, which are invariants of the theory
approximation order and the modelling technique (Equivalent-Single-Layer, Layer-Wise). In this work, the attention is focused on linear static stress analyses of composite laminated shell structures. The governing equations are obtained by applying the Principle of Virtual Displacements, and they are solved using the Finite
Element method. Furthermore, the Mixed Interpolated Tensorial Components (MITC) method is employed to
contrast the shear locking phenomenon. Several numerical investigations are carried out to validate and demonstrate the accuracy and efficiency of the present shell element
Molecular cloning of the Haemophilus influenzae gmhA (lpcA) gene encoding a phosphoheptose isomerase required for lipooligosaccharide biosynthesis
No full textWe have determined that gene HI#1181 of Haemophilus influenzae is a homolog of Escherichia coli gmhA (previously designated lpcA) (J. S. Brooke and M. A. Valvano, J. Biol. Chem. 271:3608-3614, 1996), which encodes a phosphoheptose isomerase catalyzing the first step of the biosynthesis of ADP-L-glycero-D-manno heptose. Mutations in this gene are associated with a heptoseless core lipopolysaccharide which determines an increased outer membrane permeability to hydrophobic compounds. The cloned H. influenzae gmhA restored the synthesis of a complete core in the gmhA-deleted E. coli strain chi711. Amino acid sequence comparisons of the GmhA proteins of E. coli and H. influenzae with other proteins in the databases revealed the existence of a novel family of phosphosugar a1do-keto isomerases
Variable kinematic shell elements for the analysis of electro-mechanical problems
No full textThe present article considers the linear static analysis of both composite plate and shell structures embedding piezoelectric layers 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 to accurately describe the distribution of displacements and stresses along the thickness of the multilayered shell. The shell element has nine nodes and the mixed interpolation of tensorial components (MITC) method is employed to contrast the membrane and shear locking phenomenon. The governing equations are derived from the principle of virtual displacement (PVD) and the finite element method (FEM) is employed to solve them. Cross-ply multilayered plates and cylindrical shells embedding piezoelectric layers are analyzed with simply-supported boundary conditions and subjected to sensor and actuator configurations. Various thickness ratios are considered. The results, obtained with different theories contained in the CUF, are compared with both the elasticity solutions given in literature and the analytical solutions obtained using the CUF and the Naviers method. From the analysis, one can conclude that the shell element based on the CUF is very efficient and its use is mandatory with respect to the classical models in the study of multilayered structures embedding piezo-layers. © 201
Electro-mechanical analysis of composite and sandwich multilayered structures by shell elements with node-dependent kinematics
No full textIn this work, a new class of finite elements for the analysis of composite and sandwich shells embedding piezoelectric skins and patches is proposed. The main idea of models coupling is developed by presenting the concept of nodal dependent kinematics where the same finite element can present at each node a different approximation of the main unknowns by setting a node-wise through-the-thickness approximation base. In a global/local approach scenario, the computational costs can be reduced drastically by assuming refined theories only in those zones/nodes of the structural domain where the resulting strain and stress states, and their electro-mechanical coupling present a complex distribution. Several numerical investigations are carried out to validate the accuracy and efficiency of the present shell element. An accurate representation of mechanical stresses and electric displacements in localized zones is possible with reduction of the computational costs if an accurate distribution of the higher-order kinematic capabilities is performed. On the contrary, the accuracy of the solution in terms of mechanical displacements and electric potential values depends on the global approximation over the whole structure. The efficacy of the present node-dependent variable kinematic models, thus, depends on the characteristics of the problem under consideration as well as on the required analysis type
Aminoarabinose is essential for lipopolysaccharide export and intrinsic antimicrobial peptide resistance in Burkholderia cenocepacia
No full textOne common mechanism of resistance against antimicrobial peptides in Gram-negative bacteria is the addition of 4-amino-4-deoxy-l-arabinose (l-Ara4N) to the lipopolysaccharide (LPS) molecule. Burkholderia cenocepacia exhibits extraordinary intrinsic resistance to antimicrobial peptides and other antibiotics. We have previously discovered that unlike other bacteria, B. cenocepacia requires l-Ara4N for viability. Here, we describe the isolation of B. cenocepacia suppressor mutants that remain viable despite the deletion of genes required for l-Ara4N synthesis and transfer to the LPS. The absence of l-Ara4N is the only structural difference in the LPS of the mutants compared with that of the parental strain. The mutants also become highly sensitive to polymyxin B and melittin, two different classes of antimicrobial peptides. The suppressor phenotype resulted from a single amino acid replacement (aspartic acid to histidine) at position 31 of LptG, a protein component of the multi-protein pathway responsible for the export of the LPS molecule from the inner to the outer membrane. We propose that l-Ara4N modification of LPS provides a molecular signature required for LPS export and proper assembly at the outer membrane of B. cenocepacia, and is the most critical determinant for the intrinsic resistance of this bacterium to antimicrobial peptides
- …
