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A variable kinematic Ritz formulation for vibration study of quadrilateral plates with arbitrary thickness
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Analysis of multiple-core sandwich cylindrical shells using a sublaminate formulation
Full text linkAn advanced modelling approach is presented for the linear analysis of multilayered cylindrical shells. It relies on the combined use of a sublaminate shell formulation along with the Ritz method. The approach is particularly suitable for the analysis of sandwich shells, and can be naturally applied for studying non-conventional configurations characterized by the presence of multiple cores. The formulation relies upon a displacement-based approach and makes it possible the analysis of thin and thick configurations, without restrictions regarding the shallowness of the shell. The quality of the predictions is assessed by comparison against 3D solutions, and the advantages offered by current modeling approach are highlighted in terms of required theory-related degrees of freedom. The flexibility of the formulation is exploited to illustrate the analysis of a triple-core sandwich panel, giving evidence of the advantages offered by the proposed approach for modeling shells characterized by an arbitrary degree of complexity. Novel results are presented for future benchmarking purposes
Thermal Buckling Behaviour of Thin and Thick Variable-Stiffness Panels
Full text linkThe possibility of designing composite panels with non-uniform stiffness properties offers a chance for achieving highly-efficient configurations. This is particularly true for buckling-prone structures, whose response can be shaped through a proper distribution of the membrane and bending stiffnesses. The thermal buckling behaviour of composite panels is among the aspects that could largely benefit from the adoption of a variable-stiffness design, but, in spite of that, it has rarely been addressed. The paper illustrates a semi-analytical approach for evaluating the thermal buckling response of variable-stiffness plates (VSP) by considering different boundary conditions. The formulation relies upon the method of Ritz and a variable-kinematic approach, leading to a computationally efficient implementation, which is particularly useful for exploring the larger design spaces, typical of variable-stiffness configurations. Due to the possibility of choosing the underlying kinematic approach as an input of the analysis, the formulation is not restricted to thin plates, but is suitable for analyzing the response of thick plates as well. Novel results are derived, which can be useful for benchmarking purposes and for gathering insight into the mechanical behaviour of variable-stiffness plates. Furthermore, the importance of transverse shear flexibility is illustrated with respect to the boundary conditions as well as the degree of steering of the fibers
Transferring an Earth-based adaptive optics technology to space telescopes
No full textThe present work is aimed at studying the application of a contactless voice-coil actuation technology, currently developed for some new-generation earth telescopes, to an hypothetical secondary mirror of a space telescope subjected to nanometric precision requirements. The technology involves a large number of electromagnetic actuators which are not in contact with the optical mirror. Each actuator is made by a fixed coil wound on a cold finger and a moving magnet, glued to the rear surface of the thin adaptive mirror. A stiff backplate provides the position reference. The gap between the mirror and the backplate is measured through co-located capacitive sensors. Since future space telescopes will operate at cryogenics temperatures, where the material damping is extremely small, the design of high-performance and stable active shape controllers without detrimental spillover effects is challenging. Due to the impossibility to exploit aerodynamic damping arising from the squeezed air film between the mirror and the backplate, as done on earth-based mirrors, there is the need of finding an alternative to damp out vibrations. For this purpose, the current-driven technology implemented in earth-based applications is replaced by a voltage-driven solution, which provides damping augmentation by means of eddy currents. This is crucial in achieving a sufficiently stable dynamic response. The related limitation in the control bandwidth is fully compatible with the promptness requirements of the control system for the application under study
Sublaminate variable kinematics shell models for functionally graded sandwich panels: Bending and free vibration response
Full text linkAn advanced kinematic formulation is applied to multilayered cylindrical sandwich panels with continuously graded layers. Free vibration and bending problems are considered. The mean mechanical properties of the composite material are estimated by means of the extended rule of mixture or the Eshelby-Mori-Tanaka method. The displacement field is postulated by means of variable-kinematics sublaminate models, therefore the applicability is not restricted to monolithic panels, on the contrary, the approach is well suited for sandwich panels with marked thickness-wise heterogeneity. Due to the efficiency of the formulation, the effect of various design parameters, either geometrical or mechanical, can be easily explored. The validation is performed against benchmarks of increasing complexities, namely a single-layer square plate, a shell reinforced by randomly oriented nanotubes, sandwich panels with three distinct configurations. The importance of allowing kinematic descriptions of tunable accuracy within a unique framework is well demonstrated by the proposed assessments
Analysis of Functionally Graded Carbon Nanotubes Reinforced Composite Panels Using Sublaminate Variable-Kinematics Models
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A framework based on physics-informed neural networks and extreme learning for the analysis of composite structures
Full text linkThis paper presents a novel approach for solving direct problems in linear elasticity involving plate and shell structures. The method relies upon a combination of Physics-Informed Neural Networks and Extreme Learning Machine. A subdomain decomposition method is proposed as a viable mean for studying structures composed by multiple plate/shell elements, as well as improving the solution in domains composed by one single element. Sensitivity studies are presented to gather insight into the effects of different network configurations and sets of hyperparameters. Within the framework presented here, direct problems can be solved with or without available sampled data. In addition, the approach can be extended to the solution of inverse problems. The results are compared with exact elasticity solutions and finite element calculations, illustrating the potential of the approach as an effective mean for addressing a wide class of problems in structural mechanics
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