Vibrational phenomena in near-critical fluids and granular matter
Résumé
Often, experiments are performed under microgravity because of their sensitivity to gravitational effects, which means they are also sensitive in space to inertial effects and g-jitter. Any movement by an astronaut or experiment is efficiently transmitted by the spacecraft structure; this vibration may perturb other experiments. Knowledge, prediction and minimisation of vibration is a necessity for controlling space experiments. The natural mechanical noise of a spacecraft, which is probably non-homogeneous and non-isotropic, can largely be avoided by positioning and orienting experiments carefully. Any apparatus moves as a whole with random rotation and translation in the frame of the space laboratory. If the part sensitive to gravity is composed of different fluids, for example, it will behave as heterogeneous fluids submitted to translation and rotation vibrations.The accurate control of such an experiment requires knowledge of the five different components of vibration (3 translational, 2 rotational) because it can be viewed as a rigid device within a moving laboratory. The effects of rotational vibration and translational vibration are treated here separately. Rotational vibration acts even on homogeneous fluids, where it generates periodic flow. It is an unavoidable phenomenon that can be studied on Earth. By contrast, translational vibration affects only heterogeneous fluids. On the ground, these heterogeneities are stratified and oriented by gravity, which is not true in microgravity.