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In this paper first results of controller design and implementation applied to the UNIWEX wind turbine system are presented. Identification experiments have been designed such that all relevant dynamics are excited. Experiments on a real life wind turbine have been caried out. Using prediction error methods experimental models with Box-Jenkins structure have been calculated. Experimental models have been compared to theoretical models of the test turbine. Based on normalized coprime factorization of one experimental model a controller has been designed such that it robustly stabilizes all models. The implemented controller has been evaluated by means of measurements on the UNIWEX wind turbine and has proven to satisfy our design objective.

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Purpose This paper aims to explore the fluid flow in the stereolithography process during the recoating step. The understanding of the flow dynamics can be used as an input for an active control of the resin surface height map. The recoating over a rectangular cavity has been considered to investigate the influence of the cavity depth on the resin surface height map. Design/methodology/approach Two-dimensional numerical simulations have been used to obtain the flow characteristics as function of the cavity depth. An experimental setup, which mimics the recoating process in the stereolithography process, was used to verify the results of simulations and to test the suitability of the 2D model. The surface height profile along the centreline was measured by a confocal chromatic distance sensor and compared to the 2D numerical results. Findings By means of computational fluid dynamics (CFD) simulation, the flow in the cavity and the free-surface behaviour of the resin was explained for different cavity depths and confirmed by experiments. Research limitations/implications The study is focused only on the cavity depth variation to show feasibility and suitability of the presented CFD model and the proposed analytical expression to estimate the layer thickness. Practical implications The proposed approach can serve as a tool for designing the closed-loop control for the recoating system in the next generation of stereolithography equipment. Originality/value In the present work, the fluid flow behaviour, a source of significant imperfection in the recoating process, has been investigated during the recoating step over a rectangular cavity.

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