Percorrer por autor "Giacomitti, Nickolas"
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- Experimental investigation of cellular steel beams at ambient and elevated temperaturesPublication . Silva, Luana Vidoti da; Giacomitti, Nickolas; Ferreira, Débora; Lopes, Nuno; Mesquita, Luís M.R.Cellular steel beams, commonly used in modern construction, exhibit complex failure mechanisms that have not been thoroughly explored, especially under fire conditions. This research investigates the structural behaviour of cellular beams under both ambient and elevated temperatures, with a focus on load-bearing capacity and failure modes. Experimental tests were conducted on a solid beam and six cellular beams with varying hole spacings and diameters at different temperatures. All beams were tested under three-point bending, subjecting the openings and the web posts to different combinations of bending moments and shear forces. Experimental maximum loads and failure modes are compared with the design method of EN1993-1-13 and EN1993-1-2. At ambient temperature, failure modes varied with beam design: specimens with smaller opening spacings failed by web-post buckling, while larger openings resulted in a Vierendeel mechanism. While the Eurocode predictions for load capacity were conservative under ambient conditions, the design model did not accurately predict the correct failure mode. Elevated temperatures significantly reduced the load capacity and, in some cases, changed the collapse mechanism. These results highlight that current design rules are unreliable in predicting the failure mode and may not ensure safety at higher temperatures, stressing the need for specific design rules for cellular beams in fire conditions.
- Optimization of Machining Parameters for the Fixed Pocket CyclePublication . Stein, Felipe Yukio Miyasaki; Giacomitti, Nickolas; Valério, Gustavo; Paulo, Jorge; Ribeiro, J.E.; Rocha, JoãoIn a competitive industrial setting, optimizing machining processes is important for enhancing surface quality and productivity. This study focuses on optimizing pocket milling parameters for 5083 H111 aluminum alloy using three toolpath strategies: Zig-Zag, Parallel Spiral, and One-Way. To achieve these goals, the Taguchi method, Grey Relational Analysis (GRA), ANOVA, and visual amplification were employed to evaluate the influence of cutting speed (Vc), feed per tooth (fz), and axial depth of cut (ap) on surface roughness and production rate. For the Zig-Zag and Parallel Spiral tool paths, cutting speed was the most important factor affecting surface roughness. For the One-Way strategy, axial penetration was the most important factor. The Parallel Spiral toolpath, under the Vc of 150 m/min, the fz of 0.025 mm/tooth, and the ap of 1.0 mm (A3-B3-C1) configuration, achieved the best balance between surface finish and production rate. Visual analysis also showed significative differences in how rough the wall was along perpendicular and parallel tool paths, which made it clear that finishing passes are needed in some cases. This research shows that using both statistical methods and visual amplification together makes process optimization more organized and effective, which leads to better machining performance.
- Phase change materials for thermal storage in solar dehydratorsPublication . Giacomitti, Nickolas; Ribeiro, Luís Frölén; Silva, Cláudio Tavares daThis thesis examines the feasibility of Phase Change Material (PCM)-based Thermal Energy Storage (TES) systems designed for use in solar thermal collectors for air heating and food dehydration applications. Through a combination of analytical methods and numerical simulations, the study evaluates the thermal behavior of selected PCM under diverse environmental conditions, focusing on their liquefaction and solidification properties. The simulations were conducted in Ansys Fluent for both summer and winter conditions, using its integrated solar calculator to simulate solar radiation and energy output. Although the solar calculator required correction to match expected solar irradiance, the results aligned with anticipated outcomes. The findings highlight the efficacy of different PCM in regulating temperature and storing thermal energy during off-sun hours in solar collector applications. Key results demonstrate that while Sodium Sulfate Decahydrate (SSD) performs well for winter applications, requiring 90 kg of material at a cost of €5,42 per m² of solar collector and yielding a 4,84°C temperature difference between the collector inlet and outlet in peak winter, Iron (III) Sulfate Heptahydrate (ISH) shows stability and efficiency in summer conditions. The ISH requires 112 kg of material, costs €17,38, and achieves a 13,1°C temperature difference between inlet and outlet for peak summer. Both materials exhibit the lowest cost per m² for capturing direct solar irradiance, with SSD demonstrating a phase-change temperature suitable for winter conditions and ISH performing optimally in summer conditions.