Primary Response Assessment Method for Concept Design of Monotonous Thin-Walled Structures

A concept design methodology for monotonous, tapered thin-walled structures (wing/fuselage/ship/bridge) is presented including modules for: model generation; loads; primary (longitudinal) and secondary (transverse) strength calculations; structural feasibility (buckling/fatigue/ultimate strength criteria); design optimization modules based on ES/GA/FFE; graphics. A method for primary strength calculation is presented in detail. It provides the dominant response field for design feasibility assessment. Bending and torsion of the structure are modelled with the accuracy required for concept design. A ‘2.5D-FEM’ model is developed by coupling a 1D-FEM model along the ‘monotonity’ axis and a 2D-FEM model(s) transverse to it. The shear flow and stiffness characteristics of the cross-section for bending and pure/restrained torsion are given, based upon the warping field of the cross-section. Examples: aircraft wing and ship hull.

Cosmological Perturbations in Flux Compactifications

Kaluza-Klein compactifications with four-dimensional inflationary geometry combine the attractive idea of higher dimensional models with the attempt to incorporate four-dimensional early-time or late-time cosmology. We analyze the mass spectrum of cosmological perturbations around such compactifications, including the scalar, vector, and tensor sector. Whereas scalar perturbations were discussed before, the spectrum of vector and tensor perturbations is a new result of this article. Moreover, the complete analysis shows, that possible instabilities of such compactifications are restricted to the scalar sector. The mass squares of the vector and tensor perturbations are all non-negative. We discuss form fields with a non-trivial background flux in the extra space as matter degrees of freedom. They provide a source of scalar and vector perturbations in the effective four-dimensional theory. We analyze the perturbations in Freund-Rubin compactifications. Although it can only be considered as a toy model, we expect the results to qualitatively generalize to similar configurations. We find that there are two possible channels of instabilities in the scalar sector of perturbations, whose stabilization has to be addressed in any cosmological model that incorporates extra dimensions und form fields. One of the instabilities is associated with the perturbations of the form field.Comment: 16 pages, v2 figure and references added, accepted version for JCA

Proceeding of IMPROVE EU Project (FP6 n°031382) Workshop

Coord. Ph Rigo; Editor V. Zanic; Publ. Univ. of Zagre