Descripción: The dynamics of open balloons in an atmosphere may be studied with a body-fluid coupled model. A numerical approach is required to solve the corresponding equation set. Solutions under different conditions are obtained here for the vertical and one horizontal direction. Relevant dynamical features during ascent, flotation, and descent depend on balloon thermodynamics, wind, air small-scale turbulence, and perturbations to the background atmosphere. After analysis of the results it is found that approximate analytical solutions may be found in certain cases. The effect of nonlinear drag on balloon oscillation period and damping near flotation is evaluated. © 2003 American Institute of Physics.

Descripción: The subfilter-scale (SFS) physics of regularization models are investigated to understand the regularizations' performance as SFS models. Suppression of spectrally local SFS interactions and conservation of small-scale circulation in the Lagrangian-averaged Navier-Stokes α-model (LANS-α) is found to lead to the formation of rigid bodies. These contaminate the superfilter-scale energy spectrum with a scaling that approaches k +1 as the SFS spectra is resolved. The Clark-α and Leray-α models, truncations of LANS-α, do not conserve small-scale circulation and do not develop rigid bodies. LANS-α, however, is closest to Navier-Stokes in intermittency properties. All three models are found to be stable at high Reynolds number. Differences between L 2 and H 1 norm models are clarified. For magnetohydrodynamics (MHD), the presence of the Lorentz force as a source (or sink) for circulation and as a facilitator of both spectrally nonlocal large to small scale interactions as well as local SFS interactions prevents the formation of rigid bodies in Lagrangian-averaged MHD (LAMHD-α). LAMHD-α performs well as a predictor of superfilter-scale energy spectra and of intermittent current sheets at high Reynolds numbers. It may prove generally applicable as a MHD-LES. © 2010 Springer Science+Business Media, LLC.