Abstract

We prove global existence of weak solutions to regularized versions of balance equations representing the dynamics over a torus of complex fluids, with microstructure described by a vector field taking values in the unit ball. Regularization is offered by the presence of second-neighbor microstructural interactions and our choice of filtering the balance of macroscopic momentum by inverse Helmholtz operator with unit length scale.

Highlights

  • We prove global existence of weak solutions to regularized versions of balance equations representing the dynamics over a torus of complex fluids, with microstructure described by a vector field taking values in the unit ball

  • For sufficiently differentiable maps u : T2 × [0, T ] → R2 and ν : T2 × [0, T ] → S 2, with T2 a torus and S 2 the unit sphere, we have shown in reference [12] that the system ut + (u · ∇)u − ∆u + ∇π = −∇ · (∇ν ∇ν) − ∇ν ∆νt, ∇ · u = 0, ∆νt + ∆((u · ∇)ν) − ∆2ν = νt + (u · ∇)ν + |∇ν|2ν − ∆ν, reasonably describes the dynamics over T2 of oriented fluids, a representation in which we account for second-neighbor director interactions in a minimalistic way, the one giving us sufficient amount of regularity to allow existence of a certain class of weak solutions

  • In the balance of microstructural actions governing the evolution of ν, an hyper-stress behaving like ∇2ν accounts for second-neighbor interactions; it enters the equation through its double divergence, which generates the term ∆2ν

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Summary

Introduction

For sufficiently differentiable maps u : T2 × [0, T ] → R2 and ν : T2 × [0, T ] → S 2, with T2 a torus and S 2 the unit sphere, we have shown in reference [12] that the system ut + (u · ∇)u − ∆u + ∇π = −∇ · (∇ν ∇ν) − ∇ν ∆νt, ∇ · u = 0, ∆νt + ∆((u · ∇)ν) − ∆2ν = νt + (u · ∇)ν + |∇ν|2ν − ∆ν, reasonably describes the dynamics over T2 of oriented (i.e., polarized or spin) fluids, a representation in which we account for second-neighbor director interactions in a minimalistic way, the one giving us sufficient amount of regularity to allow existence of a certain class of weak solutions. We have explicitly underlined in reference [12] the terms neglected in the previous balance equations with respect to a complete representation of second-neighbor director interactions, and their contribution to the Ericksen stress. All these aspects will be matter of a forthcoming work

Notation and preliminaries
Existence and regularity result
Approximate Galerkin solutions
B: Let νn
Global existence
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