ISEP - LEMA - Laboratório de Engenharia Matemática
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O LEMA (Laboratório de Engenharia Matemática), constituído por 12 investigadores Doutorados e 4 Mestres em doutoramento, é um grupo de investigação associado ao Centro de Matemática da Universidade do Porto (CMUP), com o objectivo de promover e organizar actividades de investigação em áreas de Matemática Aplicada, das Ciências da Engenharia e da Engenharia Matemática.
Sendo um grupo multidisciplinar, o LEMA desenvolve actividades em domínios da Análise Numérica, dos Sistemas Dinâmicos e da Modelação e Análise de Dados, predominantemente, aplicadas à resolução de problemas nas áreas de especialização de Engenharia do ISEP.
Entre os objectivos do LEMA estão a organização de acções de formação, de seminários, de reuniões científicas e de estágios dirigidos a alunos.
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- Spectral solution for the air stripping pollutants removal dynamic model with non linear steady state conditionsPublication . Meira Castro, Ana C.; Matos, José; Gavina, A.This work deals with the numerical simulation of air stripping process for the pre-treatment of groundwater used in human consumption. The model established in steady state presents an exponential solution that is used, together with the Tau Method, to get a spectral approach of the solution of the system of partial differential equations associated to the model in transient state.
- Fuzzy modelling of prescribed burning effects on soil physical propertiesPublication . Carvalho, João P.; Meira Castro, Ana C.This paper presents the preliminary work of an approach where Fuzzy Boolean Nets (FBN) are being used to extract qualitative knowledge regarding the effect of prescribed fire burning on soil chemical physical properties. FBN were chosen due to the scarcity on available quantitative data.
- Study on the changes of soil chemical characteristics as result of prescribed firePublication . Ribeiro, S.; Delerue-Matos, Cristina; Meira Castro, Ana C.; Albergaria, José TomásEvery year, particularly during the summer period, the Portuguese forests are devastated by forest fire that destroys their ecosystems. So in order to prevent these forest fires, public and private authorities frequently use methods for the reduction of combustible mass as the prescribed fire and the mechanical vegetation pruning. All of these methods of prevention of forest fires alter the vegetation layer and/or soil [1-2]. This work aimed the study of the variation of some chemical characteristics of soil that suffered prescribed fire. The studied an area was located in the Serra of Cabreira (Figure 1) with 54.6 ha. Twenty sampling points were randomly selected and samples were collected with a shovel before, just after the prescribed fire, and 125 and 196 days after that event. The parameters that were studied were: pH, soil moisture, organic matter and iron, magnesium and potassium total concentration. All the analysis followed International Standard Methodologies. This work allowed to conclude that: a) after the prescribed fire; i) the pH remained practically equal to the the initial value; ii) occurred a slight increase of the average of the organic matter contents and iron total contents; b) at the end of the sampling period compared to the initial values; i) the pH didn´t change significantly; ii) the average of the contents of organic matter decreased; and iii) the average of the total contents of Fe, Mg and K increased.
- Space-time monitoring of prescribed burnt soils performance – an effective tool for forest managementPublication . Meira Castro, Ana C.; Góis, Joaquim; Meixedo, João PauloAmong the most important measures to prevent wild forest fires is the use of prescribed and controlled burning actions in order to reduce the availability of fuel mass. However, the impact of these activities on soil physical and chemical properties varies according to the type of both soil and vegetation and is not fully understood. Therefore, soil monitoring campaigns are often used to measure these impacts. In this paper we have successfully used three statistical data treatments - the Kolmogorov-Smirnov test followed by the ANOVA and the Kruskall-Wallis tests – to investigate the variability among the soil pH, soil moisture, soil organic matter and soil iron variables for different monitoring times and sampling procedures.
- Optimization process of polyester polymer mortars modified with recycled GFRP waste aggregates – application of factorial experiment design-Publication . Ribeiro, M. C. S.; Fiúza, António; Dinis, M. L.; Meira Castro, Ana C.; Silva, F.J.G.; Costa, C.; Ferreira, F.Glass fibre-reinforced plastics (GFRP), nowadays commonly used in the construction, transportation and automobile sectors, have been considered inherently difficult to recycle due to both: cross-linked nature of thermoset resins, which cannot be remolded, and complex composition of the composite itself, which includes glass fibres, matrix and different types of inorganic fillers. Presently, most of the GFRP waste is landfilled leading to negative environmental impacts and supplementary added costs. With an increasing awareness of environmental matters and the subsequent desire to save resources, recycling would convert an expensive waste disposal into a profitable reusable material. There are several methods to recycle GFR thermostable materials: (a) incineration, with partial energy recovery due to the heat generated during organic part combustion; (b) thermal and/or chemical recycling, such as solvolysis, pyrolisis and similar thermal decomposition processes, with glass fibre recovering; and (c) mechanical recycling or size reduction, in which the material is subjected to a milling process in order to obtain a specific grain size that makes the material suitable as reinforcement in new formulations. This last method has important advantages over the previous ones: there is no atmospheric pollution by gas emission, a much simpler equipment is required as compared with ovens necessary for thermal recycling processes, and does not require the use of chemical solvents with subsequent environmental impacts. In this study the effect of incorporation of recycled GFRP waste materials, obtained by means of milling processes, on mechanical behavior of polyester polymer mortars was assessed. For this purpose, different contents of recycled GFRP waste materials, with distinct size gradings, were incorporated into polyester polymer mortars as sand aggregates and filler replacements. The effect of GFRP waste treatment with silane coupling agent was also assessed. Design of experiments and data treatment were accomplish by means of factorial design and analysis of variance ANOVA. The use of factorial experiment design, instead of the one factor at-a-time method is efficient at allowing the evaluation of the effects and possible interactions of the different material factors involved. Experimental results were promising toward the recyclability of GFRP waste materials as polymer mortar aggregates, without significant loss of mechanical properties with regard to non-modified polymer mortars.
- Numerical solution of a PDE system with non-linear steady state conditions that translates the air stripping pollutants removalPublication . Meira Castro, Ana C.; Matos, José; Gavina, A.This work deals with the numerical simulation of air stripping process for the pre-treatment of groundwater used in human consumption. The model established in steady state presents an exponential solution that is used, together with the Tau Method, to get a spectral approach of the solution of the system of partial differential equations associated to the model in transient state.
- The word problem for omega-terms over DAPublication . Moura, AnaIn this paper, we solve the word problem for ω-terms over DA. We extend to DA the ideas used by Almeida and Zeitoun to solve the analogous problem for the pseudovariety R applying also a representation by automata of implicit operations on DA, which was recently obtained by the author. Considering certain types of factors of an implicit operation on DA, we can prove that a pseudoword on DA is an ω-term if and only if the associated minimal DA- automaton is finite. Finally, we complete the result by effectively computing in polynomial time the minimal DA-automaton associated to an ω-term.
- Prescribed burning impact on forest soil properties – a fuzzy boolean nets approachPublication . Meira Castro, Ana C.; Carvalho, João P.; Ribeiro, S.The Portuguese northern forests are often and severely affected by wildfires during the Summer season. These occurrences significantly affect and negatively impact all ecosystems, namely soil, fauna and flora. In order to reduce the occurrences of natural wildfires, some measures to control the availability of fuel mass are regularly implemented. Those preventive actions concern mainly prescribed burnings and vegetation pruning. This work reports on the impact of a prescribed burning on several forest soil properties, namely pH, soil moisture, organic matter content and iron content, by monitoring the soil self-recovery capabilities during a one year span. The experiments were carried out in soil cover over a natural site of Andaluzitic schist, in Gramelas, Caminha, Portugal, which was kept intact from prescribed burnings during a period of four years. Soil samples were collected from five plots at three different layers (0–3, 3–6 and 6–18) 1 day before prescribed fire and at regular intervals after the prescribed fire. This paper presents an approach where Fuzzy Boolean Nets (FBN) and Fuzzy reasoning are used to extract qualitative knowledge regarding the effect of prescribed fire burning on soil properties. FBN were chosen due to the scarcity on available quantitative data. The results showed that soil properties were affected by prescribed burning practice and were unable to recover their initial values after one year.
- Idempotent-generated semigroups and pseudovarietiesPublication . Almeida, Jorge; Moura, AnaThe operator which constructs the pseudovariety generated by the idempotent-generated semigroups of a given pseudovariety is investigated. Several relevant examples of pseudovarieties generated by their idempotent- generated elements are given as well as some properties of this operator. Particular attention is paid to the pseudovarieties in {J, R, L, DA} concerning this operator and their generator ranks and idempotent-generator ranks.
- Representations of the free profinite object over DAPublication . Moura, AnaIn this paper, we extend to DA some techniques developed by Almeida and Weil, and Almeida and Zeitoun for the pseudovariety R to obtain representations of the implicit operations on DA: by labeled trees of finite height, by quasi-ternary labeled trees, and by labeled linear orderings. We prove that two implicit operations are equal over DA if and only if they have the same representation, for any of the three representations. We end the paper by relating these representations.