1,721,181 research outputs found
A discontinuous Galerkin formulation for nonlinear analysis of multilayered shells refined theories
Full text linkA novel pure penalty discontinuous Galerkin method is proposed for the geometrically nonlinear analysis of
multilayered composite plates and shells, modelled via high-order refined theories. The approach allows to
build different two-dimensional equivalent single layer structural models, which are obtained by expressing
the covariant components of the displacement field through-the-thickness via Taylor’s polynomial expansion
of different order. The problem governing equations are deduced starting from the geometrically nonlinear
principle of virtual displacements in a total Lagrangian formulation. They are addressed with a pure penalty
discontinuous Galerkin method using Legendre polynomials trial functions. The resulting nonlinear algebraic
system is solved by a Newton–Raphson arc-length linearization scheme. Numerical tests involving plates and
shells are proposed to validate the method, by comparison with literature benchmark problems and finite
element solutions, and to assess its features. The obtained results demonstrate the accuracy of the method as
well as the effectiveness of high-order elements
Finite deformation analysis of laminated shell via the discontinuous Galerkin method
No full textIn this work, we propose a novel formulation for the large displacements and post-buckling response
analysis of laminated composite shell structures. In order to accurately recover the solution in the case
of multilayered shells, the covariant components of the displacement field are approximated through
the thickness using high-order structural theories. The non-linear two-dimensional total Lagrangian
formulation is obtained starting from the Principle of Virtual Displacements for the three-dimensional
elasticity assuming a linear constitutive relationship between the second Piola–Kirchhoff stress tensor
and the Green-Lagrange strain tensor. The discontinuous Galerkin method is used in combination
with a Newton-Raphson linearization scheme to solve the non-linear problem. High-order elements
are employed to obtain high accuracy with limited computational effort. Several numerical tests are
performed on shell structures with different shapes and lamination sequences. To show the accuracy of
the proposed approach, the results are compared with benchmarks taken from the literature or obtained
using the Finite Element Method available on commercial software
Nandrolone decreases mu opioid receptor expression in SH-SY5Y human neuroblastoma cells
No full textNandrolone and other anabolic androgenic steroids alter the expression and function of neurotransmitter systems and contribute to drug dependence. Nandrolone treatment (10-10 M) caused a time-dependent and concentration-dependent downregulation of mu opioid receptor (MOPr) transcripts in SH-SY5Y human neuroblastoma cells. This effect was prevented by the androgen receptor antagonist hydroxyflutamide. Receptor binding assays confirmed a decrease in MOPr of approximately 40% in nandrolone-treated cells. Treatment with actinomycin D (10 (-5)M), a transcription inhibitor, revealed that nandrolone might regulate MOPr mRNA stability. In SH-SY5Y cells transfected with a human MOPr luciferase promoter/reporter construct, nandrolone did not alter the rate of gene transcription. These results suggest that nandrolone may regulate MOPr expression through posttranscriptional mechanisms requiring the androgen receptor
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Buckling and post-buckling of variable stiffness plates with cutouts by a single-domain Ritz method
Full text linkStructural components with variable stiffness can provide better performances with respect to classical ones and
offer an enlarged design space for their optimization. They are attractive candidates for advanced lightweight
structural applications whose functionalities often impose the presence of cutouts that requires accurate
and effective analysis for their design. In the present work, a single-domain Ritz formulation is proposed,
implemented and validated for the analysis of buckling and post-buckling behaviour of variable stiffness plates
with cutouts. The plate model is based on the first-order shear deformation theory with nonlinear von Karman
strain–displacement relationships. The plate generalized displacements are approximated with trial functions
built as products of one-dimensional Legendre orthogonal polynomials. The non linear governing equations
system is then deduced from the stationarity of the energy functional; the involved matrices are numerically
computed by a special integration algorithm based on the implicit description of the cutout via suitable level-set
functions. The formulation has been implemented in a computer code which has been used to validate the
method through comparison with literature solutions for variable angle tow laminates with circular cutouts.
Several investigations on buckling and post-buckling behaviour of variable angle tow composite plates with
cutouts having different shapes and dimensions are then presented to illustrate the approach capabilities,
provide benchmark results and point out features and design opportunities of the variable stiffness concept
for the buckling and post-buckling design of advanced lightweight structures
High-fidelity analysis of multilayered shells with cut-outs via the discontinuous Galerkin method
Full text linkA novel numerical method for the analysis of multilayered shells with cut-outs is presented. In the proposed approach, the shell geometry is represented via either analytical functions or NURBS parametrizations, while generally-shaped cut-outs are defined implicitly within the shell modelling domain via a level set function. The multilayered shell problem is addressed via the Equivalent-Single-Layer approach whereby high-order polynomial functions are employed to approximate the covariant components of the displacement field throughout the shell thickness. The shell governing equations are then derived from the Principle of Virtual Displacements of three-dimensional elasticity and solved via an Interior Penalty discontinuous Galerkin method over a discretization of the shell modelling domain that is obtained by intersecting a background structured grid with the level set function defining the cut-outs. To maintain high-order accuracy even in proximity of the embedded cut-outs, high-order accurate quadrature rules for implicitly-defined regions are employed to compute the integrals of the method while a cell-merging technique avoids the presence of overly small cut cells. The combined use of these features represents the novelty of the proposed method and provides a high-fidelity approach to the analysis of multilayered shells with cut-outs. Numerical tests are performed to model the static response of a cylindrical shell and a NURBS-based shell with a cut-out. The obtained results are compared with those obtained using the Finite Element method and show the accuracy and the computational efficiency of method
TRANSIENT AND FREE-VIBRATION ANALYSIS OF LAMINATED SHELLS THROUGH THE DISCONTINUOUS GALERKIN METHOD
No full textThis paper presents a novel formulation for linear transient and free-vibration analysis of laminated shell structures
based on Interior Penalty discontinuous Galerkin (DG) methods and variable-order through-the-thickness
kinematics, whose combined use allows solving the shell problem with high-order accuracy throughout both
the shell thickness and the shell modelling domain. The shell geometry is described via a generic system of
curvilinear coordinates using either an analytical or a NURBS-based parametrization of the shell mid surface;
the formulation also allows for the presence of cut-outs, which are implicitly represented by means of a level set
function. After deriving the governing equations of the shell problem from the weak form of three-dimensional
elasto-dynamics, the spatial discretization is performed via the DG approach, whereas the temporal timestepping
by the Newmark scheme. Damping of the dynamic system is considered using the classical Rayleigh
model. Various numerical tests and the corresponding comparison with reference solutions are provided to
assess the accuracy of the proposed formulation
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