WEB Adjoint optimization of surface textures in mixed lubrication regimeThursday (24.09.2020) 12:05 - 12:20 F: Functional Materials, Surfaces, and Devices 2 Part of:
The adjoint method represents a promising and versatile technique for the optimization of tribological systems. In particular, complex designs of engineered surfaces, such as textured ones, can thoroughly benefit from this method, as it allows to deal with a large number of degrees of freedom at low computational costs. Since most of the beneficial effects of surface texturing are seen in the mixed lubrication regime, this work aims to extend the applicability of the adjoint optimization from the hydrodynamic regime to the mixed one.
The mixed lubrication problem is modeled through the coupling of the Reynolds equation with mass-conserving cavitation, the elastic half space model and the dry friction model proposed by Boden and Tabor.
The corner stone of the adjoint method is represented by the computation of the sensitivity function, which relates the increment of the aim function (e.g. the load carrying capacity) with respect to the variation in the design parameters (e.g. the gap height distribution). Such computation is based on the Lagragian formulation of the above-mentioned governing equations coupled with the aim function. Once the sensitivity function is known, it can be used to iteratively update the initial geometry until no more changes are required to achieve the desired performance. The optimization may run also under user-defined constraints in order to exclude trivial solutions or to account for possible manufacturing restrictions.
The optimization approach is applied to the macro geometry of a pin-on-disc tribometer, in order to ease an eventual comparison with experimental data. The optimization is focused at first on the improvement of the load carrying capacity hence only by applying the adjoint method on the Reynolds equation. Subsequently the complete EHL system will be considered in the optimization. Thanks to the mixed lubrication model the impact of the optimized texture is studied directly on the Stribeck curve where the texture is able to reduce friction especially in the mixed lubrication regime.
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