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- ItemExistence of weak solutions to a dynamic model for smectic-A liquid crystals under undulations(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2019) Emmrich, Etienne; Lasarzik, RobertA nonlinear model due to Soddemann et al. [37] and Stewart [38] describing incompressible smectic-A liquid crystals under flow is studied. In comparison to previously considered models, this particular model takes into account possible undulations of the layers away from equilibrium, which has been observed in experiments. The emerging decoupling of the director and the layer normal is incorporated by an additional evolution equation for the director. Global existence of weak solutions to this model is proved via a Galerkin approximation with eigenfunctions of the associated linear differential operators in the three-dimensional case.
- ItemMeasure-valued solutions to the Ericksen-Leslie model equipped with the Oseen-Frank energy(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2018) Lasarzik, RobertIn this article, we prove the existence of measure-valued solutions to the EricksenLeslie system equipped with the OseenFrank energy. We introduce the concept of generalized gradient Young measures. Via a Galerkin approximation, we show the existence of weak solutions to a regularized system and attain measure-valued solutions for vanishing regularization. Additionally, it is shown that the measure-valued solution fulfills an energy inequality.
- ItemWeak entropy solutions to a model in induction hardening, existence and weak-strong uniqueness(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2019) Hömberg, Dietmar; Lasarzik, RobertIn this paper, we investigate a model describing induction hardening of steel. The related system consists of an energy balance, an ODE for the different phases of steel, and Maxwell's equations in a potential formulation. The existence of weak entropy solutions is shown by a suitable regularization and discretization technique. Moreover, we prove the weak-strong uniqueness of these solutions, i.e., that a weak entropy solutions coincides with a classical solution emanating form the same initial data as long as the classical one exists. The weak entropy solution concept has advantages in comparison to the previously introduced weak solutions, e.g., it allows to include free energy functions with low regularity properties corresponding to phase transitions.
- ItemAnalysis of a thermodynamically consistent Navier--Stokes--Cahn--Hilliard model(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2020) Lasarzik, RobertIn this paper, existence of generalized solutions to a thermodynamically consistent Navier--Stokes--Cahn--Hilliard model introduced in [19] is proven in any space dimension. The generalized solvability concepts are measure-valued and dissipative solutions. The measure-valued formulation incorporates an entropy inequality and an energy inequality instead of an energy balance in a nowadays standard way, the Gradient flow of the internal variable is fulfilled in a weak and the momentum balance in a measure-valued sense. In the dissipative formulation, the distributional relations of the momentum balance and the energy as well as entropy inequality are replaced by a relative energy inequality. Additionally, we prove the weak-strong uniqueness of the proposed solution concepts and that all generalized solutions with additional regularity are indeed strong solutions.