1,721,063 research outputs found
Variable kinematic 1D, 2D and 3D Models for the Analysis of Aerospace Structures
No full textThe aerospace structure design is one of the most challenging field in the mechanical engineering. The advanced structural configurations, introduced to satisfy the weight and strength requirements, require advanced analysis techniques able to predict complex physical phenomena.
Finite Element Method, FEM, is one of the most used approach to perform analyses of complex structures. The use of FEM method allows the classical structural models to be used to investigate complex structures where a close form solution is not available. The FEM formulation can be easily implemented in automatic calculation routines therefore this approach can take advantage of the improvements of computers. In the last fifty years many commercial codes, base on FEM, has been developed and commercialized, as examples it is possible to refer to Nastran R by MSC or Abaqus R by Dassault Systémes.
All the commercial codes are based on classical structural models. The beam model are based on Euler-Bernoulli or Timoshenko theories while two-dimensional models deal with Kirchhoff or Mindlin theories. The limitations introduced by the kinematic assumptions of such theories make the FEM elements based oh these models inef-
fective in the analysis of advanced structures. The physical phenomena introduced by composite and smart materials, multi-field application and unconventional loads configurations can not be investigated using the classical FEM models, where the
only solution improvement can be reached by refining the mesh and increasing the number of degrees of freedom.
This scenario makes the development of advanced structural models very attractive in the structural engineering. With the development of new materials and structural solutions, a number of new structural models have been introduced in order to perform an accurate design of advanced structures. Classical structural model have been im-
proved introducing more refined kinematics formulation. One- and two- dimensional models are widely used in aerospace structure design, the limitations introduced by the classical models have been overcame by introducing refined kinematic formulations able to deal with the complexities of the problems.
On the other hand, while in the classical models each point is characterized by 3 translations and 3 rotations, the use of advanced models with complex kinematic introduces a number of complication in the analysis of complex geometries, in fact is much more difficult to combine models with different kinematics.
The aim of this thesis is to develop new approaches that allow different kinematic models to be used in the same structural analysis. The advanced models used in the present thesis have been derived using the Carrera Unified Formulations, CUF. The CUF allows any structural model do be derived by means of a general formulation
independent from the kinematics assumed by the theory. One-, two- and three- dimensional models are derived using the same approach. These models are therefore combined together using different techniques in order to perform structural analysis of complex structures.
The results show the capabilities of the present approach to deal with the analysis of typical complex aerospace structure. The performances of variable kinematics models have been investigated and many assessment have been proposed. This walled structure, reinforced structure and composite and sandwich material have been con-
sidered. The advanced models introduced in this thesis have been used to perform static, dynamic and aeroelastic analysis in order to highlight the capabilities of the approach in different field. The results show that the present models are able to provide accurate results with a strong reduction in the computational cost with respect
classical approaches
Electro-thermo-mechanical analysis of an amplified piezoelectric actuator using refined one-dimensional models
Full text linkDOCUMENTO FINALE ATTIVITA' PANNELLO VTI (LIVELLO-3): VTI real panel Guidelines and Results Summary Report. RESEARCH CONTRACT: THALES ALENIA SPACE ITALIA S.p.A N. 861/2010 (VS. N.571051570090):
No full textDOCUMENTO FINALE ATTIVITA' PANNELLO VTI (LIVELLO-1): Literature overview of panel flutter phenomena for the simply-supported (SS) cylindrical panels and analysis of the critical conditions of VTI-panels in case of SS-BCs.RESEARCH CONTRACT: THALES ALENIA SPACE ITALIA S.p.A N. 861/2010 (VS. N.571051570090): ”VERSATILE THERMAL INSULATION (VTI) FLUTTER ANALYSIS” RESP. PROF. E. CARRERA
No full textAeroelastic analysis of pinched panels in a variable supersonic flow changing with altitude
No full text
Carrera Unified Formulation for Free-Vibration Analysis of Aircraft Structures
Full text linkAdvanced structural models, based on variable one-, two-, and three-dimensional kinematics, are proposed in this paper and applied to the analysis of the free vibration of reinforced aircraft shell structures. The used models go beyond classical structural theories, that is, Euler–Bernoulli (for one-dimensional beams) and Kirchhoff (for two-dimensional plates) type assumptions. The order of the expansion of the displacement fields over the cross section (one-dimensional case) and along the plate thickness (two-dimensional case) is, in fact, a free parameter of the problem. In this paper, Lagrange polynomials are used to build such expansions, and as a consequence, only displacements are used as the problem unknowns (no rotations or derivatives of displacements, which are typical of one-dimensional/two-dimensional classical theories, are introduced). The finite-element method is used to provide numerical solutions. The related arrays and the governing dynamical equations are written in terms of a few fundamental nuclei according to the Carrera unified formulation. Classical three-dimensional finite-element solid models are also considered. One-, two-, and three-dimensional finite elements are easily connected to each other to make the most appropriate computational model of the reinforced shell structures. The capability to use the same fundamental nucleus to derive finite-element matrices of one-, two-, and three-dimensional elements of the present model is unique because it is usually not available in other finite-element formulations, that is, no ad hoc techniques are required in the present case to couple finite elements with different kinematics. Three main benchmarks have been analyzed: a plate stiffened by means of bidirectional I-stiffeners, a simplified model of a complete aircraft, and a fuselage–wing connection. Comparison with commercial finite-element software (MSC Nastran) is provided for most of the quoted numerical investigations. The modal assurance criterion has been used to compare the free-vibration modes of the different models. The present mathematical models appear closer to reality and cheaper, from the computational point of view, than those of other existing formulations. Carrera unified-formulation-based finite elements do not require the definition of virtual lines (beam axes) or virtual surfaces (plate reference surfaces), and only physical lines/surfaces are therefore used
Thermo-Piezo-Elastic Analysis of Complex Structures Using a Node Dependent Kinematic One-Dimensional Model
Full text linkAerospace structures can be subject to complex stress fields that are originated by different external loads. The classical structural analysis considers the mechanical loads and aims to evaluate the stress fields due to these external forces. When complex structures are subject to a strong temperature variation they may present a large deformation that may produce complex stress fields. The evaluation of these deformations is mandatory in order to avoid the failure of the structure, that is, a thermo-mechanical analysis should be performed. Moreover, the use of advanced materials, such as piezo-electric materials, allows the displacement filed to be evaluated, if they are used as sensors, or, the deformations to be reduced, if they are used as actuators. Multi-field analyses are mandatory in these cases and accurate thermo-piezo-elastic models must be used to predict the response of the structure. Complex stress fields cannot be investigated using classical structural models, beams and plates, because their kinematic assumptions, e.g. rigid cross-section for the beam of constant thickness for the plates. The use of three-dimensional models may achieve accurate results but it may require a huge computational cost. The present work extends the use of a refined node-dependent kinematic one-dimensional model to the thermo-piezo-mechanical analysis. Node-dependent kinematic one-dimensional models allow refined kinematic models to be used only in the area of the structure where complex phenomena are expected, that is, these models are able to reduce the computational cost preserving the accuracy of the results only where is required. The fully coupled thermo-piezo-elastic model has been derived in the framework of the Carrera unified Formulation that allows the structural matrices to be written in a general and compact form. Static and dynamic analysis have been performed in order to assess the present model. The results have been compared with those from literature and with those from refined models with a constant kinematic. The outcome of this research show that node-dependent kinematic one-dimensional models may preserve the accuracy of a three-dimensional solution with a lower computational cost if compared with the refined models with a constant kinematic
DOCUMENTO FINALE ATTIVITA' PANNELLO VTI (LIVELLO-2): Development of a FE model suitable for Piston Theory (Supersonic Flow) analysis of VTI-panels with real BCs, 4/6 points pinched case. Calculation of critical Mach number. RESEARCH CONTRACT: THALES ALENIA SPACE ITALIA S.p.A N. 861/2010 (VS. N.571051570090): ”VERSATILE THERMAL INSULATION (VTI) FLUTTER ANALYSIS” RESP. PROF. E. CARRERA
No full textLaminated Beam Analysis by Polynomial, rigonometric, Exponential and Zig-Zag Theories
No full textA number of refined beam theories are discussed in this paper. These theories were obtained by expanding the unknown displacement variables over the beam section axes by adopting Taylor's polynomials, trigonometric series, exponential, hyperbolic and zig-zag functions. The Finite Element method is used to derive governing equations in weak form. By using the Unified Formulation introduced by the first author, these equations are written in terms of a small number of fundamental nuclei, whose forms do not depend on the expansions used. The results from the different models considered are compared in terms of displacements, stress and degrees of freedom (DOFs). Mechanical tests for thick laminated beams are presented in order to evaluate the capability of the finite elements. They show that the use of various different functions can improve the performance of the higher-order theories by yielding satisfactory results with a low computational cost
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