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Publicações

Publicações por LIAAD

2022

Statistical study of curing conditions in alkali activation of Portuguese mine tailings

Autores
Correia, E; Miranda, T; Cerveira, A; Castro, F; Fernandez Jimenez, A; Cristelo, N; Coelho, J;

Publicação
ENVIRONMENTAL GEOTECHNICS

Abstract
The use of industrial by-products to produce new types of cement-substitute binders is gaining significant momentum, particularly through the alkaline activation technique. However, the exact curing conditions that should be considered with each binder variation have not been fully understood yet. The aim of the present work is thus the statistical analysis of the effects of curing conditions (humidity and temperature) on the mechanical response (uniaxial compression strength and elastic modulus) of different aggregate/binder weight ratios. Five blends of solid mine tailings (as an aggregate) and fly ash (as a precursor), both collected from the Portuguese industry, were activated with sodium hydroxide solution and cured under nine different temperature and humidity combinations. The data analysis was performed using multivariate analysis of variance and analysis of variance, followed by Tukey's post hoc test, whenever appropriate. Results show that the curing humidity factor showed a lower impact than the curing temperature. Although the increase in temperature and decrease in humidity produced higher compression strengths, the best results were obtained with a specific combination of both (60 degrees C and 50% relative humidity). In general, the increase in tailings' content produced a reduction in compression strength, but only for values above 20% (by weight of the sum of solids).

2022

Wind Energy Assessment for Small Wind Turbines in Different Roof Shapes Based on CFD Simulations

Autores
Oliveira, C; Cerveira, A; Baptista, J;

Publicação
SUSTAINABLE SMART CITIES AND TERRITORIES

Abstract
With a still high rate of use of energy from non-renewable sources, it is crucial that new energy generation solutions are adopted to reach greenhouse gas reduction targets. The integration of renewable energy sources in buildings is an interesting solution that allows reducing the need for energy from the power grid, contributing to a significant increase in the energy efficiency of buildings. The main aim of this paper is to evaluate the impact that the aerodynamics of the buildings in particular the roof shape has considering the integration of wind energy systems. The results of Computational Fluid Dynamics (CFD) simulations are presented in order to identify the effect of the two roof shapes on energy production by wind turbines (WT). For this purpose, the factor matrices (FM) that gives information about the wind profile around the building taking into account the building's roof profile were calculated. Comparing the results for the wind flow obtained by the FM and the CFD simulations for the flat and gabled roofs, similarities are observed for them, allowing to conclude that the CFD analysis results in a methodology with great accuracy for the aerodynamic study of buildings roof shape.

2022

Natural Regeneration of Maritime Pine: A Review of the Influencing Factors and Proposals for Management

Autores
Ribeiro, S; Cerveira, A; Soares, P; Fonseca, T;

Publicação
FORESTS

Abstract
The main objective of the present work was to review the current knowledge about the factors that influence the different phases of the natural regeneration of maritime pine (Pinus pinaster Aiton) and propose scientifically based management schedules. The review focused on the natural regeneration of maritime pine within its most representative areas (Portugal, Spain, and France). First, a brief characterisation of the main phases of the natural regeneration of maritime pine is described. Next, information on the factors affecting the natural regeneration of the species is provided, highlighting its positive and negative effects. Finally, management proposals are presented to promote the natural regeneration of maritime pine species. Numerous factors influencing the natural regeneration of maritime pine were identified. Fires and climatic factors can intervene in all three regeneration phases (seeding, germination, and seedling survival and development). The natural regeneration failure of maritime pine species can be aggravated in drier scenarios. Forest management plays an important role as it can promote the natural regeneration of the species.

2022

Optimization of Forest Management in Large Areas Arising from Grouping of Several Management Bodies: An Application in Northern Portugal

Autores
Cabral, M; Fonseca, TF; Cerveira, A;

Publicação
FORESTS

Abstract
The success of forest management towards achieving desired outcomes depends on various factors and can be improved through forest planning based on optimization approaches. Regardless of the owner type (state, private or common land) and/or governance model, the number of owners or management bodies considered in most studies is low, typically involving one owner/management body or a very small group. This study extends the approach of formulating a Forest Management Plan (FMP) to a large forest area, consisting of areas with different management bodies. The FMP model returns the harvest schedule that maximizes the volume of wood harvested during the planning horizon, while ensuring (1) sustainability and environmental constraints at the overall scale and (2) independent revenues for each management body. The FMP is tested in a real forested area, consisting of 22 common lands, governed by local communities for a planning period of 30 years. The results show that our approach is appropriate for several management bodies. When evaluating the impact of grouping areas (and their owner bodies) on the total volume removed, a comparison of the FMP model with an alternative model that allows for independent management (FMP-IND) showed significant differences, in terms of total volume removed at the end of the horizon. Global management leads to a reduction of about 8.6% in the total removed volume; however, it will ensure a heritage of well-diversified stands, in terms of age classes. The results highlight the importance of managing multi-stakeholder forest areas as a whole, instead of being managed independently, if the aim is to assure more sustainable management of forest resources in the mid and long term.

2022

Optimal location of Power Quality Monitors in distribution grids based on MRA methodology

Autores
Ferreira, V; Cerveira, A; Baptista, J;

Publicação
Renewable Energy and Power Quality Journal

Abstract
Distribution grids currently face news paradigms where Power Quality (PQ) has become one of the most important aspects for distribution system operators (DSO) and consumers. To ensure a PQ within the limits defined by international standards, there is a permanent need to monitor all parameters associated with the distributed voltage by the grid. This task is carried out using the installation of Power Quality Monitors (PQM) at strategic points of the grid. The main aim of this paper is to define a methodology to optimize the best location for the PQM installation. To achieve this target the Monitor Reach Area (MRA) matrix is calculated and an Integer Linear Programming (ILP) optimization model was used to find the best solution. Two case studies were carried out, in which residual voltage values were observed when three-phase short circuits are applied to all nodes. The results obtained show the good effectiveness of the developed method, presenting solutions that allow the total monitoring of the studied networks, using the smallest possible number of PQMs. In this way, it is possible for the DSO to keep the network monitored in real-time with huge efficiency gains. © 2022, European Association for the Development of Renewable Energy, Environment and Power Quality (EA4EPQ). All rights reserved.

2022

Optimization of Offshore Wind Farms Configuration Minimizing the Wake Effect

Autores
Jesus, B; Cerveira, A; Baptista, J;

Publicação
Renewable Energy and Power Quality Journal

Abstract
Currently, there has been a great development of the wind energy market, which is accompanied by an increase in the number of wind farms at sea, the offshore wind farms. Therefore, it is crucial to ensure that efficiency in energy production is maximum and that the levelized cost of energy (LCOE) is minimal. In this paper, a mixed-integer linear programming model (MILP) is proposed to find the best wind farm layout taking into account the wake effect in order to maximize energy production. The design of an offshore wind farm located at the North Sea is considered as a case study, contemplating three situations regarding the number of wind turbines to be installed and to determine the best positioning of them in order to maximize energy production, taking into account the wake effect and the lowest LCOE. © 2022, European Association for the Development of Renewable Energy, Environment and Power Quality (EA4EPQ). All rights reserved.

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