Attitude stability eriteria are developed for "dual spin" spacecraft, which consist of two primary bodies capable of unlimited relative rotation about a common axis. Such vehieles, typified in existing hardware by the Orbiting Solar Observatory (OSO) satellites, have applicability to missions for which the simplicity, reliability, and longevity of spin stabilization combine with a requirement for unidirectional pointing of a component, such as an antenna or a solar panel. The utility of dual spin systems is substantially increased by the results of attitude stability analysis, which reveals the possibility of obtaining passive stable spin-axis attitude by spinning a vehicle about its axis of greatest or least inertia, providing only that an effective energy dissipation device is attaced to a counter-rotating platform which has greatly reduced "spin." This result is coutrary to common interpretation of the familiar "major axis spin" requirement for stability, according to which energy dissipation in a vchicle rotating about its axis of least inertia must produce instability. Stability eriteria are developed first by Routhian analysis of a system with energy dissipation capability in only one of the two primary bodies, and subsequently in more general (but less rigorous) terms for a fully dissipative vehiele. Numerical integration and model studies provide corroboration.

Attitude Stability Criteria for Dual Spin Spacecraft

This paper deals with a theoretical analysis of the dynamic response of shear deformable symmetrically laminated rectangular composite flat panels exposed to sonic boom and explosive blast loadings. The pertinent governing equations incorporating transverse shear deformation, transverse normal stress, as well as the higher-order effects are solved by using the integral-transform technique. The obtained results are compared with their counterparts obtained within the framework of the first-order transverse shear deformation and the classical plate theories and some conclusions concerning their range of applicability are outlined. The paper also contains a detailed analysis of the influence played by the various parameters characterizing the considered pressure pulses as well as the material and geometry of the plate.

Response of laminated composite flat panels to sonic boom and explosive blast loadings

The non-linear dynamic equations of the first-order shear deformation theory and the third-order shear deformation plate theory of Reddy are reformulated into equations describing the interior and edge-zone problems of rectangular plates. Viscous damping terms are also included. It is shown that, for certain boundary conditions, the number of governing equations can be reduced to three, as in the classical plate theory. Two problems related to static large-deflection and dynamic small-deflection of rectangular plates are considered. Numerical results are presented to demonstrate the effects of non-linearity, shear deformation, rotatory inertia, damping and sonic boom type loadings.

A study of non-linear dynamic equations of higher-order shear deformation plate theories

The accuracy and convergence properties of two new Timoshenko beam finite elements are compared to those now widely used. Both of the new elements are consistently derived from a variational principle written in terms of the transverse beam deflection and normal rotation. The deflection is expanded as a cubic and the rotation as a quadratic in the axial co-ordinate of the beam, giving rise to a seven degrees of freedom element. The first element, called TIM7, includes all the degrees of freedom while the second, called TIM4, reduces this number to four through a constraint introduced by Egle. Both elements display monotonic covergence for beam natural frequencies as a function of the number of degrees of freedom and both will give the analyst some measure of confidence in response calculations for beams excited at high frequencies.

Convergence of consistently derived Timoshenko beam finite elements

The problem of the dynamic response of sandwich flat panels exposed to blast loadings is addressed. The sandwich model includes a number of non-classical effects such as the anisotropy and heterogeneity of face sheets, transverse orthotropy of the core layer, the geometrical non-linearities considered in the von Karman sense, as well as the initial geometric imperfections. As concerns the blast pulses considered in this analysis, these are due to either an underwater/in-air explosion, or are due to a pressure wave traveling across the panel span. Implications of the explosive charge, stand-off distance, directionality property of face sheets material, damping ratio, geometric non-linearity, initial geometric imperfection, and of the characteristics of the blast, on dynamic response and dynamic magnification factor are put into evidence via a parametric study, and pertinent conclusions are outlined.

Linear and non-linear dynamic response of sandwich panels to blast loading

Sonic Boom Effects on Structures - A Simplified Approach

Division of engineering: sonic boom effects on structures—a simplified approach*

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Dynamic response of structural elements exposed to sonic booms.

Euler-Bernoulli and Timoshenko beam impact models compared for case of finite beam resting on spring supports

Jacques E. Benveniste

Papers

Sonic Boom Effects on Structures - A Simplified Approach

Division of engineering: sonic boom effects on structures—a simplified approach*

Dynamic response of structural elements exposed to sonic booms.

Comparison of beam impact models