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Totaro G.,Italian Aerospace Research Center
Composite Structures | Year: 2013

The analytical modelling of the local buckling failure mode for composite anisogrid lattice cylindrical shells with the typical system of hexagonal cells is here discussed. The aim is to complement the set of constraint equations that are associated with the preliminary design phase of such structures under axial compressive loads, and to prospectively improve the final solutions. The basic constraint equations for anisogrids without the skin are focused on the global buckling of the shell, the local buckling of helical ribs, and the material failure of these ribs. However, the local buckling of helical ribs is normally based on a simplified and qualitative approach. Conversely, the developed modelling, which is based on the Ritz method, accounts for the helical angle of the periodic cell, the stiffness of intersecting hoop and helical ribs, and the positive effect of the prebuckling tensile force in hoop ribs. This model has been verified with the aid of finite-element analysis, demonstrating a noteworthy accuracy. Thanks to the comparison with the parallel study on anisogrid shells with triangular cells, the effect of hoop rib positioning on the local buckling strength (i.e., hexagonal or triangular system of cells) is finally assessed. © 2012 Elsevier Ltd. Source


Pezzella G.,Italian Aerospace Research Center
Aerospace Science and Technology | Year: 2012

In the frame of the Future Launchers Preparatory Program, being developed by the European Space Agency, several Reusable Launch Vehicle concepts are under investigation. In this paper the current design activities at phase-A level, carried out by Centro Italiano Ricerche Aerospaziali, are described. The goal has been to define the preliminary hypersonic aerodynamic and aerothermodynamic databases of each vehicle for concept competition. To this end, different design approaches have been addressed as engineering methods and computational fluid dynamics. The re-entry scenario with the corresponding loading environment for each launcher concept is reported and analyzed. The final results, applicable for the prosecution of the launcher design activities, are that, at the condition of descent trajectory peak heating, the vehicle features a stagnation point heat flux ranging form about 500 to 40 kW/m2 whereas the aerodynamic lift-to-drag ratio at 40 deg angle of attach is about 1.0. © 2011 Elsevier Masson SAS © 2011 Elsevier Masson SAS. All rights reserved. Source


Totaro G.,Italian Aerospace Research Center
Composite Structures | Year: 2012

The paper deals with a refined analytical model for the local buckling failure modes of composite anisogrid lattice cylindrical shells made of a regular system of triangular cells. Such structures are preliminarily designed with the aid of closed-form solutions specifying the minimum mass and the corresponding optimal design variables under a set of formulated constraint equations. These equations address the main failure mechanisms that can be typically experienced by the structure due to axial compressive loads, namely, the global buckling of the shell, the local buckling of helical ribs, and the material failure of helical ribs. However, the local buckling of helical ribs is normally based on a simplified and qualitative approach. Thus, the scope of the present work is to improve the prediction of this failure mode by means of a rather accurate modelling which accounts for the interaction of intersecting hoop and helical ribs, the influence of the number of hoop sections of the shell, and the effect of the prebuckling tensile force in hoop ribs. The proposed model - that has been verified with the aid of finite-element analysis - lastly suggests the possibility to improve the preliminary design solution with respect to the fully analytical approach. © 2011 Elsevier Ltd. Source


Pezzella G.,Italian Aerospace Research Center
Acta Astronautica | Year: 2011

This paper deals with the aerodynamic and aerothermodynamic trade-off analysis aiming to design a small hypersonic flying test bed with a relatively simple vehicle architecture. Such vehicle will have to be launched with a sounding rocket and shall re-enter the Earth atmosphere allowing to perform several experiments on critical re-entry technologies such as boundary-layer transition and shockshock interaction phenomena. The flight shall be conducted at hypersonic Mach number, in the range 68 at moderate angles of attack. In the paper some design analyses are shown as, for example, the longitudinal and lateral-directional stability analysis. A preliminary optimization of the configuration has been also done to improve the aerodynamic performance and stability of the vehicle. Several design results, based both on engineering approach and computational fluid dynamics, are reported and discussed in the paper. The aerodynamic model of vehicle is also provided. © 2011 Elsevier Ltd. All rights reserved. Source


Pezzella G.,Italian Aerospace Research Center
Aerospace Science and Technology | Year: 2013

This paper deals with design activities performed by CIRA in the frame of its flying test bed vehicle development, named FTB-X. The re-entry scenario with the corresponding loading environment for the proposed vehicle, devoted to research activities in re-entry technologies, is reported and analyzed. The hypersonic environment characteristics of FTB-X are investigated on a trajectory-based design approach by means of several engineering and CFD analyses. Being a phase A design, the air is modeled only as a perfect gas and the analyses were based on laminar flow conditions, while only a preliminary analysis of real gas and turbulence effects has been performed in time. The results show that the aerodynamics derived from engineering design approach is sufficiently accurate for preliminary analysis purpose; moreover, surface heat loads were computed on the vehicle configuration for thermal shield design scopes. © 2012 Elsevier Masson SAS. All rights reserved. Source

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