ISEL - Matemática - Comunicações
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- Wind power forecasting with machine learning: single and combined methodsPublication . Rosa, J.; Pestana, Rui; Leandro, Carlos; Brás-Geraldes, Carlos; Esteves, João; Carvalho, D.In Portugal, wind power represents one of the largest renewable sources of energy in the national energy mix. The investment in wind power started several decades ago and is still on the roadmap of political and industrial players. One example is that by 2030 it is estimated that wind power is going to represent up to 35% of renewable energy production in Portugal. With the growth of the installed wind capacity, the development of methods to forecast the amount of energy generated becomes increasingly necessary. Historically, Numerical Weather Prediction (NWP) models were used. However, forecasting accuracy depends on many variables such as on-site conditions, surrounding terrain relief, local meteorology, etc. Thus, it becomes a challenge to obtain improved results using such methods. This article aims to report the development of a machine learning pipeline with the objective of improving the forecasting capability of the NWP’s to obtain an error lower than 10%.
- Fractal reconstruction of fiber-reinforced epoxy microstructurePublication . Radovic, Ivona; Stajčić, A.; Mitić, V. V.; Serpa, Cristina; Paunović, V.; Randelović, B.In the past century, the use of polymers and composites with a polymer matrix has expanded to such a level that today it is impossible to imagine life without these materials. Epoxy resin and epoxy-based composites are widely used as construction materials, due to their excellent adhesion, thermal and chemical stability. Fractal nature analysis can provide insight in morphological changes at fiber-matrix interface level, which could give direction for the processing of composites. This mathematical technique can be performed on field emission scanning electron microscopy (FESEM) images, by identifying fiber phase and pores shapes and boundaries, as well as fiber-matrix bonding at the interface. In this study, fiberglass mat was used for the reinforcement of epoxy. FESEM image of enlarged fiber after the composite fracture was used for the reconstruction of data. With the use of affine fractal regression model, software Fractal Real Finder was employed for the reconstruction of fiber shape and the determination of Hausdorff dimension.
- Q-topological complexityPublication . Fernández-Suárez, Lucía; Vandembroucq, LucileBy analogy with the invariant Q-category defined by Scheerer, Stanley and Tanre, we introduce the notions of Q-sectional category and Q-topological complexity. We establish several properties of these invariants. We also obtain a formula for the behaviour of the sectional category with respect to a fibration which generalizes the classical formulas for Lusternik-Schnirelmann category and topological complexity.
- Environmental and economic optimisation of buildings for different climatesPublication . Kiss, B.; Silvestre, J. D.; Madeira, Jose Firmino Aguilar; Santos, R. A.; Szalay, ZsIntroduction: Life Cycle Assessment (LCA) is a scientific method for evaluating the environmental impact of products. Standards provide a general framework for conducting an LCA study and calculation rules specifically for buildings. A challenge is to design energy efficient buildings that have a low environmental impact, reasonable costs, and provide high thermal comfort, as these are usually conflicting aspects. Efficient mathematical optimisation algorithms can be applied to such engineering problems. Methodology: In this paper, a multiobjective optimisation technique, the Direct MultiSearch method, is described and its applicability is tested on a multi-story residential building’s case study for two locations, Portugal and Hungary. The objectives are to minimise the life cycle environmental impacts and costs. Results and conclusions: The results indicate that optimum solutions are found at a higher cost but lower Global Warming Potential for Portugal than for Hungary. Optimum solutions have walls with a thermal transmittance of about 0.23 and 0.15 W/m2K for Portugal and Hungary, respectively. Multi-objective optimisation algorithms can be successfully applied to find solutions with low environmental impact and eco-efficient thermal envelope.
- Modelling spreading process of a wildfire in heterogeneous orography, fuel distribution and environmental conditions - a complex networks approachPublication . Perestrelo, Sara; Grácio, Maria; Ribeiro, Nuno; Lopes, LuísForest fires are phenomena that represent a great danger for the population and have severe environmental consequences. The greatest efforts in regard to direct confrontation require a large investment in terms of both financial and human resources, partly due to the unpredictability of fire behaviour and the fuel distribution that feeds its growth and spread. To deal with this unpredictability in a more efficient manner, our work focuses around the establishment of an optimal fire-break structure whose purpose is to block the spread along the landscape, at a minimal cost. It’s a preventative approach, which acts as a complement to direct confrontation and contributes to the reduction of material, economic and human losses. For the establishment of this optimal fire-break structure it is necessary to model fire spreading process and, for that, we use the multilayer network model, within the area of complex networks. We aim the construction of a network of networks that allows us to simulate the fire spreading process both at a local scale and at a more global scale.
- Modeling the strategic behavior of the iberian electricity market producers using time series analysisPublication . Faria, Ricardo; Sousa, Jorge A. M.; Martins, Ana Alexandra; Lagarto, JoãoThe Iberian Electricity Market (MIBEL) emerges in the context of the integration and cooperation between the Portuguese and Spanish electricity markets, in response to the European Union incentive for regional electricity markets creation. The present study, focus on the modeling and forecasting of the hourly competitive strategies of the electricity producers in the MIBEL. For this analysis, the studied variable was the MIBEL's conjectural variation, which estimates the level of competitiveness of the electricity producers on the day-ahead electricity market. The methodology adopted for forecasting was time series analysis, using ARIMA and exponential smoothing models. The results obtained show that the estimated models that best suit the hourly MIBEL conjectural variation forecast were mainly of the ARIMA seasonal type with daily seasonality, followed by ARIMA non-seasonal type models. It was also observed, that the selected models were mainly estimated with a time series of 5 working days.
- Electricity spot prices structural changes in the Iberian electricity marketPublication . Bolas, João; Sousa, Jorge A. M.; Martins, Ana Alexandra; Lagarto, JoãoIn recent years, the power sector has undergone a restructuring process in many economies in the world. This movement towards liberalization led to the establishment of electricity markets that promote the competitiveness of the production and trading segments of the power sector. In these markets, the agents have to deal with frequent electricity price changes leading to different strategies in their daily bidding behavior. There are a set of variables that can have an impact in the electricity price definition, such as: fuel prices, CO 2 emissions prices, electricity production and demand. This paper proposes to analyze structural changes in the Iberian electricity market price between two periods of time: 2007/2008 and 2010/2011. For this purpose, three quantitative analysis methods were used: correlation, causality and Principal Components. Results suggest that the electricity price had a structural change between the analyzed periods, in particular the increasing importance of special regime production.
- Optimal renewable generation mix of hydro, wind and photovoltaic for integration into the Portuguese power systemPublication . Sousa, Jorge A. M.; Martins, Ana AlexandraIn spite of the advantages of renewable energy sources (RES), their variability and uncertainty raises important issues in power systems operation, such as the need to balance demand with a highly variable and uncertain power generation. In this context, is of utmost importance the choice of the optimal renewable generation mix to be integrated in the power system in order to accomplish the established renewable energy targets with the lowest technical impacts. With this aim, this paper presents a methodology that supports decision making on the renewable energy policy by deriving the optimal renewable generation mix from different available technologies - hydro, wind and photovoltaic - that integrates a given amount of electricity from renewable sources, taking into account the variability of the renewable generation mix and the target share of renewable generation. This methodology is applied to a case study of one month using renewable generation data of the Portuguese power system.
- Allee's dynamics and bifurcation structures in von Bertalanffy's population size functionsPublication . Rocha, J. Leonel; Taha, Abdel-Kaddous; Fournier-Prunaret, D.The interest and the relevance of the study of the population dynamics and the extinction phenomenon are our main motivation to investigate the induction of Allee Effect in von Bertalanffy's population size functions. The adjustment or correction factor of rational type introduced allows us to analyze simultaneously strong and weak Allee's functions and functions with no Allee effect, whose classification is dependent on the stability of the fixed point x = 0. This classification is founded on the concepts of strong and weak Allee's effects to the population growth rates associated. The transition from strong Allee effect to no Allee effect, passing through the weak Allee effect, is verified with the evolution of the rarefaction critical density or Allee's limit. The existence of cusp points on a fold bifurcation curve is related to this phenomenon of transition on Allee's dynamics. Moreover, the "foliated" structure of the parameter plane considered is also explained, with respect to the evolution of the Allee limit. The bifurcation analysis is based on the configurations of fold and flip bifurcation curves. The chaotic semistability and the nonadmissibility bifurcation curves are proposed to this family of 1D maps, which allow us to define and characterize the corresponding Allee effect region.
- Detection and adsorption of Triclosan on sensors based on PAH/PVS thin-filmsPublication . Pereira-da-Silva, J.; Zagalo, P. M..; Magro, Cátia; Pinto, Iola; Ribeiro, P. A.; Raposo, MariaGiven the vital role of water in life it is paramount to thrive and succeed in areas that look to clean and prevent further contamination in water bodies. Triclosan (TCS) is present in most of our day-to-day products and if left unchecked it can lead to long-term significant problems due to its many inauspicious effects in both human and animal health. Thus arose the need to develop sensors to detect and possibly remove TCS for aqueous solutions. This work was rooted on this premise and sensors based on LbL polyectrolyte thin-films were developed, such as poly(allylamine hydrochloride) (PAH) and poly(vinylsulfonic acid, sodium salt) (PVS), namely (PAH/PVS)(10) and (PAH/PVS)/PAH(10). The goal of this work was to analyze the amount of TCS adsorbed onto reused (PAH/PVS)(10) and (PAH/PVS)/PAH(10) LbL thin-films when immersed in TCS aqueous solutions with decreasing pH. It was demonstrated that sensors with an outer layer of PAH led to a significantly better TCS molecules adsorption (removal). Additionally, sensors composed of (PAH/PVS)(10) presented higher sensibility in discriminating TCS solutions with concentrations between 10(-5) M and 10(-8) M, using impedance spectroscopy.