Stability of Couette flow past a gel film

We study instability of a Newtonian Couette flow past a gel-like film in the limit of vanishing Reynolds number. Three models are explored including one hyperelastic（neo-Hookean） solid, and two viscoelastic（Kelvin–Voigt and Zener） solids. Instead of using the conventional Lagrangian description in the solid phase for solving the displacement field, we construct equivalent ‘‘differential＇＇ models in an Eulerian reference frame, and solve for the velocity, pressure, and stress in both fluid and solid phases simultaneously. We find the interfacial instability is driven by the first-normal stress difference in the basestate solution in both hyperelastic and viscoelastic models. For the neo-Hookean solid, when subjected to a shear flow, the interface exhibits a short-wave（finite-wavelength） instability when the film is thin（thick）. In the Kelvin–Voigt and Zener solids where viscous effects are incorporated, instability growth is enhanced at small wavenumber but suppressed at large wavenumber, leading to a dominant finitewavelength instability. In addition, adding surface tension effectively stabilizes the interface to sustain fluid shear.

Mechanics and physics under supergravity conditions

"Supergravity"refers to the conditions where the effective gravity is greater than that of Earth.Supergravity conditions are generally relevant to stellar evolution,geophysical movement,astrophysical flows,and more.They also frequently occur in various engineering scenarios involving acceleration,such as the launch of space shuttles,operation of rotor engines,impacts and explosions,chemical separation processes,and overloaded testing experiments.It is already demonstrated in physiological experiments that living organisms of animals or plants could be damaged,either temporarily or permanently,when subjected to supergravity.To create supergravity conditions for scientific research on the Earth,centrifugal equipment or rapidly rotating devices are omnipresent in various fields,such as aerospace engineering,geophysical science,chemical and biomedical engineering,nuclear engineering,rotating flows,and physical modeling tests.

Cavitation dynamics in a vitrimer

Vitrimer is a polymer network with dynamic covalent bonds,which can be dynamically broken and reformed.Thanks to the dynamic covalent bonds,vitrimer behaves like an elastomer at high deformation rate or low temperature but a viscous fluid at low deformation rate or high temperature.In this article,we study the cavitation dynamics in a vitrimer,which is known to be an important damaging mechanism in it.In the formulation,a nonlinear three-dimensional rate-dependent constitutive model for the vitrimer is adopted,in which both of the strain stiffening and the kinetics of dynamic exchanging reactions are considered.The theory predicts strong dependence of the cavitation dynamics on the loading rate.The computational results may help to reveal some critical insights into the rate-dependent fracture in vitrimer.