Sloshing in microgravity

摘要

The international space station provides a lowgravity environment for experiments that require very lowacceleration. The steady component of acceleration due to thegravity gradient is in the microgravity range. It is possible toachieve microgravity levels for the variable component by usingisolation racks. For experiments cooled by liquid cryogenssloshing may increase the variable acceleration at the experimentbeyond acceptable levels. Sloshing of cryogens in microgravity canbe predicted using a surface wave model. The model shouldinclude: a calculation of the shape of the unperturbed liquid –gasinterface; a listing of the normal modes and resonant frequenciesfor the container; a prediction of he amplitude of the modes inresponse to the motion of the container; and a test to detect thebreakdown of linear theory. A model is presented that containsthese components. The shape of the interface is calculated and it isfound that for most anticipated applications the interface is nearlycylindrical or spherical. Since gravity is not aligned with thesymmetry of the container, the depth of the liquid is variable.Examples are presented to show how to estimate the extent ofvariable depth and curve interface on the normal modes andresonant frequencies. Equations are derived for the dynamicinteraction of the isolation rack, the dewar and the sloshing motion.Damping is introduced by suing boundary layer theory. Randomvibration theory is applied to the incoherent component of thedriving spectrum while standard resonance formalism is used forthe coherent component. The model cannot be used if the waveamplitude becomes so large that linear theory does not apply. Aprocedure is developed to check for nonlinear difficulties. 2000Elsevier Science Ltd. All rights reserved.