Vibration of Thin-Walled Tubes in Thermal Environment

Vibrations induced by fast varying thermal gradients were first investigated by Boley in the Fifties with respect to the case of beams operating in extra-atmospheric microgravity environment. Indeed, spacecrafts and orbiting satellites crossing from the Earth’s shadow into sunlight experience rapid changes in the thermal loading due to the solar radiation. Such loading is responsible of time dependent bending moments and transverse shear forces on appendages and booms. Those are typically lightweight structures having high flexibility with low frequency and damping characteristic. The thermally-induced bending moment produces a sudden deflection of such flexible structures, accompanied by a change of sunlight incidence angle. These two set up the onset of vibrations with fluctuating moment that could not be correctly analyzed if the inertia effect and the coupling between temperature and strain fields are not taken into account. A correct comprehension of the phenomenon is of interest since thermally-induced vibrations may interfere with system operations of booms, often carrying a payload for measurement. In the worst cases thermal flutter, a self-excited vibration of increasing amplitudes, may lead to the failure of the structural member. In problems in which thermal effect induces deflections and vibrations of a slender body, thermal conductivity, material stiffness and mass density play an important role. If correctly selected these properties could improve the material robustness against deflection and oscillation. Hence, the question is if indeed does exist a certain combination of those material properties which can help to lower deflections and damp oscillations. In the proposed contribution a cantilever beam with a circular hollow cross-section is considered and the possibility to protect the beam from thermal effects by optimizing the structure of the cross-sectional wall is investigated. Some preliminary results seem encouraging and may pave the way for passive control of deflection and thermal flutter effects.