1,720,967 research outputs found
Hygro-Thermo-Mechanical Equivalent Layer-Wise Theory of Laminated Shell Structures
No full textThis study presents a generalized two-dimensional model for evaluating the stationary hygro-thermo-mechanical response of laminated shell structures made of advanced materials. It introduces a generalized kinematic model, enabling the assessment of arbitrary values of temperature variation and mass concentration variation for the unvaried configuration at the top and bottom surfaces. This is achieved through the Equivalent Layer-Wise description of the unknown field variable using higher-order polynomials and zigzag functions. In addition, an elastic foundation is modeled utilizing the Winkler-Pasternak theory. The fundamental equations, derived from the total free energy of the system, are solved analytically using Navier’s method. Then, the Fourier-based generalized differential quadrature numerical method is adopted to efficiently recover the through-the-thickness distribution of secondary variables in agreement with the hygro-thermal loading conditions. The formulation is applied in some examples of investigation where the response of panels of different curvature and lamination schemes is evaluated under external hygro-thermal fluxes and prescribed values of temperature and moisture concentration. In addition, this study investigates the effect of the hygro-thermal coupling due to Dufour and Soret effect. The present formulation is verified to be a valuable tool for reducing computational effort and determining the effect on the mechanical response of laminated structures in a thermal and hygrometric environment
Effect of Porosity on the Modal Response of Doubly-Curved Laminated Shell Structures Made of Functionally Graded Materials Employing Higher Order Theories
No full textThe manuscript investigates the modal response of laminated anisotropic doubly-curved shell structures of variable thickness made of Functionally Graded Materials (FGM), according to an efficient equivalent single layer strategy where the displacement field is described employing a condensed unified formulation, accounting for a higher order through-the-thickness expansion. A generalized power law distribution is adopted for the assessment of the FGM layers, whereas the presence of voids is considered starting from different homogenization assumptions. Unlike previous works which presented a variation of the homogenized material properties within the shell solid, in this paper the problem of material porosity is addressed, therefore a general distribution of the volume fraction of the constituent materials is considered, along with the presence of voids. To this end, both linear and trigonometric through-the-thickness distributions are here assumed. The fundamental governing equations are derived starting from a proper set of curvilinear principal coordinates, while a generalized set of blending functions accounts for arbitrarily shaped structures. Non-conventional boundary conditions are, here, modelled with a distribution of linear springs along the shell edges. The numerical implementation of the problem is performed with the generalized differential quadrature method. A systematic set of validating examples is presented, whose results are compared to predictions based on refined models, as well as some experimental evidence. After a validation step, an extensive parametric analysis points out the sensitivity of the porosity parameters on the modal response of structures with different curvatures and external constraints, with valid findings for engineering design purposes
Static Analysis of Doubly-Curved Shell Structures of Smart Materials and Arbitrary Shape Subjected to General Loads Employing Higher Order Theories and Generalized Differential Quadrature Method
No full textThe article proposes an Equivalent Single Layer (ESL) formulation for the linear static analysis of arbitrarily-shaped shell structures subjected to general surface loads and boundary conditions. A parametrization of the physical domain is provided by employing a set of curvilinear principal coordinates. The generalized blending methodology accounts for a distortion of the structure so that disparate geometries can be considered. Each layer of the stacking sequence has an arbitrary orientation and is modelled as a generally anisotropic continuum. In addition, re-entrant auxetic three-dimensional honeycomb cells with soft-core behaviour are considered in the model. The unknown variables are described employing a generalized displacement field and pre-determined through-the-thickness functions assessed in a unified formulation. Then, a weak assessment of the structural problem accounts for shape functions defined with an isogeometric approach starting from the computational grid. A generalized methodology has been proposed to define two-dimensional distributions of static surface loads. In the same way, boundary conditions with three-dimensional features are implemented along the shell edges employing linear springs. The fundamental relations are obtained from the stationary configuration of the total potential energy, and they are numerically tackled by employing the Generalized Differential Quadrature (GDQ) method, accounting for nonuniform computational grids. In the post-processing stage, an equilibrium-based recovery procedure allows the determination of the three-dimensional dispersion of the kinematic and static quantities. Some case studies have been presented, and a successful benchmark of different structural responses has been performed with respect to various refined theories
General boundary conditions implementation for the static analysis of anisotropic doubly-curved shells resting on a winkler foundation
No full textIn the present work an Equivalent Single Layer (ESL) formulation is proposed for the static analysis of doubly-curved anisotropic structures of arbitrary geometry and variable stiffness resting on a Winkler elastic foundation. In-plane and out-of-plane general distributions of linear elastic springs are provided for the implementation of general external constraints along the edges of the structure. The structure is geometrically described accounting for the principal curvatures of the shell object of analysis. A generalized set of blending functions based on Non-Uniform Rational Basis Spline (NURBS) curves is adopted so that arbitrary shaped structures can be modelled with the same approach. The fundamental governing equations are obtained in terms of displacement field unknowns, which has been effectively described accounting for a unified formulation based on the minimum potential energy principle. General anisotropic lamination schemes are considered, setting a general orientation of each lamina, as well as all possible material symmetries. The numerical implementation is performed by means of the Generalized Differential Quadrature (GDQ) method, thus allowing a strong formulation of the structural problem. A series of validation examples is performed on shells with zero, single and double curvatures in which the static structural response provided with the proposed formulation has been compared to that obtained from a refined three-dimensional finite element model, showing a great accordance between these different approaches. The research shows that the employment of higher order theories, together with the GDQ method, allows to obtain very accurate results with a reduced computational cost, compared to finite element simulations
Static Analysis of Anisotropic Doubly-Curved Shell Subjected to Concentrated Loads Employing Higher Order Layer-Wise Theories
Full text linkIn the present manuscript, a Layer-Wise (LW) generalized model is proposed for the linear static analysis of doublycurved shells constrained with general boundary conditions under the influence of concentrated and surface loads. The unknown field variable is modelled employing polynomials of various orders, each of them defined within each layer of the structure. As a particular case of the LW model, an Equivalent Single Layer (ESL) formulation is derived too. Different approaches are outlined for the assessment of external forces, as well as for non-conventional constraints. The doubly-curved shell is composed by superimposed generally anisotropic laminae, each of them characterized by an arbitrary orientation. The fundamental governing equations are derived starting from an orthogonal set of principal coordinates. Furthermore, generalized blending functions account for the distortion of the physical domain. The implementation of the fundamental governing equations is performed by means of the Generalized Differential Quadrature (GDQ) method, whereas the numerical integrations are computed employing the Generalized Integral Quadrature (GIQ) method. In the post-processing phase, an effective procedure is adopted for the reconstruction of stress and strain through-the-thickness distributions based on the exact fulfillment of three-dimensional equilibrium equations. A series of systematic investigations are performed in which the static response of structures with various curvatures and lamination schemes, calculated by the present methodology, have been successfully compared to those ones obtained from refined finite element three-dimensional simulations. Even though the present LW approach accounts for a two-dimensional assessment of the structural problem, it is capable of well predicting the three-dimensional response of structures with different characteristics, taking into account a reduced computational cost and pretending to be a valid alternative to widespread numerical implementations
Dynamic Analysis of Doubly-Curved Shells Made of Advanced Materials with Higher Order Theories and Generalized Differential Quadrature
No full textIn the present work, a refined theory with three-dimensional capabilities is proposed for the structural analysis of shell structures made of smart materials for advanced engineering applications. Principal curvilinear coordinates are used for the geometry definition of the structure. The kinematic description of the configuration variables is performed according to the Equivalent Single Layer (ESL) approach with higher order theories. A constitutive relation for elastic anisotropic laminates is considered. The fundamental equations, written in the strong form, are derived from the Hamilton principle together with the boundary conditions, and they are numerically solved by means of the Generalized Differential Quadrature (GDQ) method. The accuracy and the computational efficiency of the present theory is shown by means of different applicative examples. The numerical predictions of the present ESL model are compared to refined solutions coming from three-dimensional Finite-Element-based simulations. Furthermore, some parametric investigations are performed on a doubly-curved panel made of Variable Angle Tow (VAT) anisotropic materials in order to show the sensitivity of the VAT distribution on the dynamic response of the shell under consideration. The present formulation is very accurate if compared to refined models, despite its reduced computational demand, and it can be useful for design purposes of doubly-curved elements made of advanced materials
Hygro-Thermo-Electro-Mechanical Coupled Modeling of Laminated Curved Panels
No full textThe manuscript presents a generalized two-dimensional model for evaluating the stationary hygro-thermo-mechanical response of laminated shell structures made of heterogeneous piezoelectric composite materials with thermal and hygrometric properties. In particular, the static bending response of these structures is studied, along with their coupled hygro-thermo-electrical behavior. A generalized kinematic model is introduced, enabling the assessment of arbitrary temperature and mass concentration variations with respect to the unvaried configuration at the top and bottom surfaces. This is achieved through an Equivalent Layer-Wise description of the unknown field variables using higher order polynomials and zigzag functions. Furthermore, an elastic foundation is modelled according to the Winkler-Pasternak theory. The fundamental equations, derived from the total free energy of the system, are solved analytically using Navier’s method. Then, the Fourier-based generalized differential quadrature numerical method is adopted to efficiently recover the through-the-thickness distribution of secondary variables, in agreement with the hygro-thermal loading conditions. The formulation is applied in some examples of investigation where the response of panels with different curvatures and lamination schemes is evaluated under external hygro-thermal fluxes and prescribed values of temperature and moisture concentration. In addition, we investigate the effect of the hygro-thermal coupling due to Dufour and Soret effect. The present formulation is verified to be a valuable tool for assessing the mechanical response of laminated structures in a thermal and hygrometric environment with reduced computational effort
On the Importance of the Recovery Procedure in the Semi-Analytical Solution for the Static Analysis of Curved Laminated Panels: Comparison with 3D Finite Elements
Full text linkThe manuscript presents an efficient semi-analytical solution with three-dimensional capabilities for the evaluation of the static response of laminated curved structures subjected to general external loads. A two-dimensional model is presented based on the Equivalent Single Layer (ESL) approach, where the displacement field components are described with a generalized formulation based on a higher-order expansion along the thickness direction. The fundamental equations are derived from the Hamiltonian principle, and the solution is found by means of Navier’s approach. Then, an efficient recovery procedure, derived from the three-dimensional elasticity equations and based on the Generalized Differential Quadrature (GDQ) method, is adopted for the derivation of the three-dimensional solution. Some examples of investigation are presented, where the numerical predictions of refined three-dimensional Finite-Element-based models are matched with a high level of accuracy. The model is validated for both straight and curved panels, taking into account different lamination schemes and load shapes. Furthermore, it is shown that the numerical solution to the elasticity problem in the recovery procedure is determining and accurately predicting the three-dimensional static response of the doubly-curved shell solid
Valutazione statistica della prestazione energetica degli edifici nella provincia di Lecce
Full text linkNel presente articolo si effettua un'analisi della prestazione energetica del parco edilizio della Provincia di Lecce. Lo scopo principale è quello di fornire uno strumento in grado di fornire un quadro complessivo sintetico e significativo del comportamento degli edifici al fine di descrivere la situazione as-is, ma soprattutto valutare l'efficienza ed efficacia di interventi di retrofit sulla popolazione
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