Browsing by Subject "Topology optimization"

Now showing 1 - 2 of 2

Open Access
Active lubrication interfaces with tunable micro-textures
(2023-07) Pekol, Sena
This thesis investigates a homogenization-based space-time optimization framework in the context of hydrodynamic lubrication in order to design micro-textures which can be actively controlled through external stimuli. The response at the interface is established via the Reynolds equation to describe the physics of the lubrication for a small film thickness. Subsequently, the interface is subjected to multiscale analysis and effective macroscopic parameters are derived via homogenization method. In order to calculate the macroscopic parameters, Finite Element (FE) formulation is employed and the implementation of the parameters in the in-house FE code is demonstrated. For the suboptimality problem due to typically employed fixed unit cell in FE analysis, a geometry optimization scheme is developed. Thereafter, a sensitivity based topology optimization framework is introduced with the aim of identifying the spatial distribution and temporal variation of the micro-texture, and the shape of the unit cell which together help achieve the targeted lubrication response. The performance of the employed framework is assessed through objectives which ultimately determine the macroscopic flux at the interface as well as the frictional traction that is associated with the macroscopic dissipation at the interface. Finally, three-dimensional realizations are constructed for active micro-textures by adopting a readily deployable experimental architecture.
Open Access
Multiscale analysis and texture design for interfaces hydrodynamically lubricated by variable viscosity and density liquids
(2024-08) Koç, Sarp Ilgaz
Optimization is fundamental in lubrication, as it is utilized to minimize the energy and durability loss due to friction. To be able to analyze such systems, efficient and accurate mathematical and numerical techniques are required during the modeling and the computation process. Although direct analyses of smooth surfaces for both Newtonian and non-Newtonian flows are well documented in literature, analysis for rough surface textures can be challenging both in terms of modeling and solution. As severity of roughness increases, the accuracy of the available models decreases while the necessary computational cost increases substantially. In this work, a model is developed for piezoviscous, compressible and shear-thinning lubricants using the novel modified viscosity approach alongside homogenization as a mathematical technique for the solution of the Reynolds equation to alleviate the inherent computational difficulties to model roughness. Our results demonstrate good agreement between rough DNS and Reynolds and homogenized results. Furthermore, the developed numerical framework has been used in conjunction with topology optimization algorithm to acquire different surface textures dependent on the fluid rheology. The obtained textures are shown to (i) minimize energy dissipation, or (ii) increase the traction to amplify the grip between the surfaces depending on the respective lubrication application.