http://hdl.handle.net/10174/29521 2026-04-11T17:11:12Z 2026-04-11T17:11:12Z Capello, Riccardo Garção, José Catalanotti, Giuseppe Pitarresi, Giuseppe http://hdl.handle.net/10174/41406 2026-02-23T11:43:50Z 2025-09-30T23:00:00Z

Title: On the Identification of Dissipative Phenomena in Fatigue-Loaded 2024 Aluminum by Means of Second Harmonic of Temperature Analysis Authors: Capello, Riccardo; Garção, José; Catalanotti, Giuseppe; Pitarresi, Giuseppe Abstract: This study explores the use of temperature harmonics to detect intrinsic dissipation during cyclic loading in aluminum alloys. Under sinusoidal loading, the temperature of a solid is modulated by thermomechanical heat sources. The primary source is the thermoelastic effect, which modulates the temperature at the load frequency and twice the load frequency (second harmonic). Thermoelastic stress analysis (TSA) signal processing is employed to extract the temperature harmonics and analyze their evolution when the stress amplitude increases. The detected second harmonic comprises three main contributions: a thermoelastic component, predicted by the second-order thermoelastic effect theory, a spurious contribution due to load components at twice the nominal frequency, and a dissipative second harmonic. The main aim of this work is to separate the thermoelastic and spurious contributions from the measured second harmonic to isolate and capture dissipation. AL 2024 alloy samples, which exhibits strong second-order thermoelastic response, are employed in the investigation. Aluminum has already been reported as a material where thermomechanical dissipation is difficult to quantify, or even qualitatively observe, with other more traditional thermographic methods. The results show interesting features of the second-harmonic decoupled components, providing insight into intrinsic dissipation of aluminum alloys under fatigue-loading conditions.

2025-09-30T23:00:00Z Garção, José Barbosa, Joaquim http://hdl.handle.net/10174/41404 2026-02-23T11:43:20Z 2023-03-29T23:00:00Z

Title: An extended piecewise functions formalism for computing the internal forces and deflections of beams Authors: Garção, José; Barbosa, Joaquim Abstract: Beams are slender bodies vastly used to build many kinds of structures. In sit- uations where a beam can be accurately modeled using a set of governing equations given by linear differential equations, the solution for a loading case that is the combination of sev- eral loading cases, is given by the superposition of the solutions for each particular loading case. In structural mechanics this result is called the superposition principle. The most usual loading cases appearing in practice impose discontinuities in the derivatives of the internal forces and the deflection (displacements) of a beam. Therefore, when solving the governing equations, the domain must be partitioned in regions where all the derivatives are defined, then a solution is found in each region, and finally the boundary conditions and a set of compatibility conditions at the points of discontinuity are applied. Conse- quently the solutions are piecewise functions and the solution process becomes lengthy. Several techniques have been proposed to abbreviate this procedure, all supported in the validity of the superposition of solutions. One very straightforward technique involving a compact and intuitive notation, sometimes designated Macaulay’s method, is the use of the so called ”singularity functions” [1], ”step functions” [2] or Macaulay brackets, a sort of generalization of the Heaviside function, an idea introduced by Macaulay in 1919 [3], and further refined by other authors, as explained in [4]. This technique considers loadings involving only point forces, point couples or distributed forces of polynomial type which are active from some starting point until de end of the beam. When a distributed force is nonzero in only an interior segment of the beam, it must be modeled as two dis- tributed loads that are nonzero until the end of the beam, but which cancel each other in the portion of the beam where the original loading is zero. Besides possible mistakes with finding the fictitious cancellation load, this extra load doubles the computations when evaluating the solution. We consider that this technique can be extended to any loading case and avoid the need for fictitious loads, using therefore less computations, by adding another piecewise term to the formalism, at the expense of an arguably less expressive notation. Basically the superposition of solutions given by piecewise functions, with each function representing the complete solution for a single load, is generated and applied in a very systematic way. This communication is devoted to present this extension, as well as the corresponding au- tomation of the solution procedure using symbolic computation. Several illustrative exam- ples of application, which can appear in a context of teaching as well as in real structural design, are considered. With the availability of free computer algebraic systems, a few lines of code can provide solutions for any beam and frame problem that are accurately modeled by linear differential equations. Therefore symbolic computational tools should be introduced in the curricula and used when teaching these subjects.

2023-03-29T23:00:00Z Ajuda, Ana Silva, Goncalo Semiao, Viriato http://hdl.handle.net/10174/39249 2025-09-04T20:31:33Z 2025-09-02T23:00:00Z

Title: Performance Analysis of Multi Capillary Knudsen Heat Pumps Authors: Ajuda, Ana; Silva, Goncalo; Semiao, Viriato Abstract: The present work investigates the theoretical performance of the Knudsen heat pump (KHP), a novel heat pump concept in which the conventional mechanical compressor is replaced by a Knudsen compressor. This modification has the potential to reduce both maintenance requirements and energy consumption. The flow behavior within the Knudsen compressor, the core element of the KHP, is described using a simplified gas model derived from the formulation originally proposed by Muntz et al. The model predictions are initially validated against well-established data reported in the literature, and subsequently employed to analyze the performance of the KHP, with the final objective of enhancing its operational efficiency. To ensure the practical relevance of the performance assessment, the analysis is conducted using realistic geometrical and operational parameters derived from previously reported experimental studies of Knudsen compressors featuring rectangular or circular cross-sectional geometries. The results of this study suggest that, while the original KHP configuration exhibits limited performance, parametric analysis suggests the possibility to enhance its performance by more than 100% under optimal conditions, with additional factors identified that may enable further gains.

2025-09-02T23:00:00Z Mané, Júnior Malico, Isabel Domingues, Nuno Ait El Cadi, Radia Horta, Pedro http://hdl.handle.net/10174/39010 2025-07-14T08:37:52Z 2025-01-01T00:00:00Z

Title: Preliminary simulation results of a molten salt thermal storage thank for concentrated solar power Authors: Mané, Júnior; Malico, Isabel; Domingues, Nuno; Ait El Cadi, Radia; Horta, Pedro Abstract: Molten salt thermal storage systems play a critical role in concentrated solar power (CSP) plants, ensuring energy storage and dispatchability. Among these, thermocline tanks offer the potential for cost reduction, compared to the standard thermal storage system implemented in CSP plants: a two-tank solution (for hot and cold fluid, individually). This paper presents initial results from a Computational Fluid Dynamics (CFD) simulation of the 2.86 MWhth thermocline-tank installed at the EMSP – Évora Molten Salt Platform. The tank incorporates a filler material to enhance thermal stratification. The CFD model integrates the transport equations for mass, momentum and energy, along with closure models to account for the pressure drop imposed by the presence of the filler material and the heat transfer between the molten salts and the filler material. Validation of the model is conducted using experimental data from the literature. The simulation investigates the thermal performance of the tank during the discharging phase, where the axial temperature at the centerline of the tank was monitored periodically. The results were obtained for a simplified geometry of the tank as more improvements can still be made in future work to ensure the accuracy of the model.

2025-01-01T00:00:00Z