ESTiG - Artigos em Revistas Indexados à WoS/Scopus
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- Three-dimensional modelling of in-isolation tensile response of geogrids using hyperbolic constitutive modelsPublication . Paiva, Lucas; Pinho-Lopes, Margarida; Valente, Robertt; Paula, António MiguelNumerical modelling of geogrids is a challenging task, with extruded geogrids often presenting complex geometries and nonlinear tensile response even at low strain rates. In this study, threedimensional (3D) models were developed in ABAQUS to investigate the in-isolation tensile response of extruded geogrids, accounting for a detailed geometric discretization. Hyperbolic constitutive models were used to represent the nonlinear tensile response, including fracture simulation. A benchmarking exercise was initially performed using the literature data to assess the main numerical modelling parameters for a precise and time efficient simulation. Then, a case study composed of three extruded geogrids were used to validate the model. Particular emphasis was given on the data treatment of the case study, namely with the development of a data-driven model to obtain the most representative load strain curve from experimental specimens. The modelling approach proposed in this study was capable of capturing the inisolation tensile response of extruded geogrids with good accuracy, and accounting for softening and fracture responses.
- Tensile behavior of weathered thermally bonded polypropylene geotextiles: analysis using constitutive modelsPublication . Carneiro, Jose Ricardo; Paula, António Miguel; Pinho-Lopes, MargaridaWeathering agents can significantly affect the mechanical response of geotextiles, particularly when long exposure periods are involved. Usually, in design, changes in the mechanical behavior of geotextiles are represented by reduction factors for their tensile strength. However, their full tensile force versus elongation response can be affected. The main aim of this work was to contribute to defining simple procedures to estimate tensile force versus elongation curves for weathered samples of geotextiles. The tensile response of two thermally bonded polypropylene geotextiles, before and after natural and artificial weathering, was assessed experimentally and analyzed using different constitutive models: polynomial (Orders 4 and 6) and hyperbolic. The influence of weathering on the mechanical response of the geotextiles was analyzed, polynomial and hyperbolic models for representing the tensile force versus elongation response were adopted and their parameters derived, and simple relations were implemented to estimate model parameters for weathered samples. Results revealed the occurrence of changes in the tensile behavior of the geotextiles, both under natural and artificial weathering conditions. Both groups of models fitted the experimental data properly. The Order 4 and 6 polynomial models are shown to have limited application, as the model parameters had no link to the tensile properties of the geotextiles. By contrast, the parameters of the hyperbolic model were linked to the tensile properties, particularly if affected by correction factors. The hyperbolic model parameters of the weathered samples were estimated using the model parameters of the reference samples and the reduction factors to allow for weathering (initial stiffness and tensile strength). These estimates proved to be adequate for representing the tensile response of weathered samples, particularly for low ranges of elongation. Finally, a simple procedure to represent the tensile response of weathered geotextiles was proposed. This procedure has shown promise in generating realistic tensile versus elongation curves.
- A constitutive model for describing the tensile response of woven polyethylene terephthalate geogrids after damagePublication . Lombardi, Giovani; Pinho-Lopes, Margarida; Paula, António Miguel; Pereira, AntónioA constitutive model was used to describe the tensile response of two woven Polyethylene Terephthalate (PET) geogrids, before and after mechanical damage. The model parameters of undamaged and damaged specimens were estimated via numerical regressions of test results. For each sample, the experimental and fitted tensile strengths were statistically compared using hypothesis tests. For each geogrid, tensile load-strain curves of damaged samples were drawn by applying scaling factors to the plot of the undamaged sample. The curve fittings resulted in high R-2 values for undamaged and damaged specimens of the geogrids. For most samples, there was no significant mean difference between the experimental and fitted tensile strength. The model allowed us to describe the load-strain curve of a geogrid from its tensile properties: & epsilon;(max), T-max and J(i). Regardless of the type of damage (in laboratory or in situ), the model was able to describe the load-strain curves of damaged samples using data from undamaged samples and scaling factors.
- 3D Numerical modeling of geosynthetics for soil reinforcement: a bibliometric analysis and literature reviewPublication . Paiva, Lucas; Pinho-Lopes, Margarida; Paula, António Miguel; Valente, RoberttSoil reinforcement using geosynthetics is an efficient and cost-effective solution for a variety of geotechnical structures. Along with the increasing use of geosynthetics, there is a need to expand and enhance the design methodologies for these elements, which are still frequently based on conservative limit equilibrium approaches. In this paper, a bibliometric analysis was conducted on geosynthetic-reinforced soil structures (GRS), identifying the state of the art, research trends, and other indicators. The data were obtained from the Scopus platform and processed by VOSViewer v1.6 software. The initial search comprised 552 papers and the screening process selected 516 relevant papers from 1992 to October 2023. The study analyzed the occurrence of publications by year, keyword trends, authors, citations/co-citations, and bibliographic coupling. Then, a focus was given to 3D modeling research on geosynthetics, highlighting the dominant modeling techniques, material properties, and design challenges in GRS. The bibliometric analysis provided a crucial guideline in the identification of relevant papers and research trends, and a series of conclusions were presented regarding the 3D modeling techniques, choice of material properties, and boundary conditions.
- A simple 3D orthotropic model for the tensile response of geogrids: in-isolation and soil-geogrid interaction applicationsPublication . Paiva, Lucas; Pinho-Lopes, Margarida; Valente, Robertt; Paula, António MiguelThe short-term tensile response is one of the key aspects in designing geogrid-reinforced soil structures. In this paper a simple data-driven 3D orthotropic model for the short-term tensile response is proposed. The Hill48 yield model is chosen to represent the orthotropic behaviour of the geogrid, and a procedure to obtain the necessary parameters, from simple tensile test data, is presented. The model is then implemented in ABAQUS, and validated against a realistic problem where the geogrid is embedded in soil. The influence of the orthotropy (against isotropy) on both the reinforcement and the overall soil-geogrid structure is evaluated. The results show that the orthotropic model can accurately predict the tensile response of the geogrid in different directions, with the orthotropy having a significant influence on the reinforcement and the overall structural response, especially in highly orthotropic materials. The study further examined stress redistribution capabilities in geogrids with notches, revealing enhanced stabilization performance using the orthotropic model. Parametric tests indicated that traditional isotropic assumptions might underpredict or overpredict reinforcement performance, emphasizing the advantages for accurate orthotropic characterization. The proposed 3D framework provides a robust, straightforward method for evaluating and optimizing geogrid designs, enabling better prediction of reinforced soil behaviour in geotechnical applications.
- Assessing the impact of working capital on free cash flow: evidence from portuguese accommodation companiesPublication . Fernandes, António B. ; Cardim, Sofia; Ferreira, Jessica; Pinto, LígiaThis study analyses the impact of working capital (WC) on free cash flow (FCF) for Portuguese firms operating in Division 55 (Accommodation), a sector that is a central pillar of the national tourism industry and characterised by high capital intensity and pronounced seasonality. The empirical analysis is based on an unbalanced panel dataset of 5,744 firms, corresponding to 27,689 firm-year observations for the period 2011–2023, obtained from the SABI database. A panel data model is estimated using generalised estimating equations (GEE) with firm- and year-fixed effects to examine how changes in WC and its components influence firms’ capacity to generate FCF. Twelve research hypotheses are formulated and empirically tested within a cash-flow-based valuation framework. The results show that variations in WC have a negative and statistically significant effect on FCF, indicating that increased investment in short-term operational assets constrains liquidity generation in the accommodation sector. Several components of WC are identified as significant determinants of FCF, while others do not exhibit statistically significant effects, underscoring the heterogeneous influence of short-term assets and liabilities on cash flow dynamics. The model adjustment criteria (QIC and QICC), assessed within the scope of the GEE, indicate that the estimated specification is well suited and robust, supporting the reliability of the results obtained. Although the analysis is limited to the accommodation sector, which may restrict the generalisability of the findings, the study makes an important contribution by adopting an FCF-based perspective on WC management. By focusing on liquidity generation rather than traditional profitability measures, this research enhances understanding of financial management dynamics in tourism-related firms and provides insights into firms’ strategic flexibility and capacity to invest in market-facing activities.
- Building resilient tourism systems: the strategic role of financial sustainability in portuguese tourism firmsPublication . Fernandes, António B. ; Ferreira, Jessica; Seidi, Fadiba; Cardim, SofiaThis study examines the economic and financial sustainability of Portuguese tourism firms operating within Division 55 (Accommodation) and Division 56 (Food and Beverage Service Activities), using Return on Assets (ROA) as the central indicator of economic and financial sustainability to assess variations over time, across firm sizes and among regions. Drawing on a dataset of 8,735 firms and 113,559 observations from 2011 to 2023, the analysis relies on ROA due to its analytical robustness and suitability for longitudinal and cross-sectional comparison. Given the absence of normality and homogeneity of variances, robust statistical techniques were applied, namely Welch’s ANOVA and the Games-Howell post hoc test with bootstrapping, to ensure reliable inference. The findings reveal significant differences in financial sustainability over the study period, between firms of different sizes and across regions. Small firms record higher average ROA than micro, medium or large firms, while the Algarve emerges as the highest-performing region and the Autonomous Region of the Azores presents the weakest results. The study is limited by its exclusive reliance on quantitative financial indicators, without incorporating qualitative dimensions that might enrich understanding of sustainability drivers, and by the constraints posed by data non-normality. The results emphasise the need for policy measures tailored to regional characteristics and highlight the pivotal role of small firms in resilience in the tourism sector. The study adds value by providing a rigorous, longitudinal and regionally differentiated analysis of financial sustainability within the Portuguese tourism industry.
- Collaborative fault tolerance for cyber–physical systems: the diagnosis stagePublication . Piardi, Luís; Costa, Pedro; Schneider, André; Leitão, PauloThe reliability and robustness of cyber-physical systems (CPS) are critical aspects of the current industrial landscape. The high level of autonomous and distributed components associated with a large number of devices makes CPS prone to faults. Despite their importance and benefits, traditional fault tolerance methodologies, namely local and/or centralized, often overlook the potential benefits of collaboration between cyber-physical components. This paper introduces a collaborative fault diagnosis methodology for CPS, integrating self-fault diagnosis capabilities in agents and leveraging collaborative behavior to enhance fault diagnosis. The contribution of this paper relay in propose a methodology for fault diagnosis for CPS, based on multi-agent system (MAS) technology as a backbone of infra-structure, highlighting the components, agent behavior, functionalities, and interaction protocols, to explore the benefits of communication and collaboration between agents. The proposed methodology enhance the accuracy of fault diagnosis when compared with local approach. A case study was conducted in a laboratory-scale warehouse, focusing on diagnosing drift, bias, and precision faults in temperature and humidity sensors. Experimental results reveal that the collaborative methodology significantly outperforms the local approach in fault diagnosis, as evidenced by performance improvements in diagnosis classification. The statistical significance of these results was validated using the Wilcoxon signed-ranks test for paired samples.
- From a techno-economic towards a socio-technical approach—a review of the influences and policies on home energy renovations’ decisionsPublication . Abreu, Maria Isabel; Pereira, Andreia; Gervásio, HelenaOver the past decades, the debate on how to encourage energy efficiency in existing homes has been guided by a technic-economic model that has a strong focus on technologies and cost savings, in which human behavior has been devalued to a narrow behavioral economics overview. While this specific area of behavioral science enabled to capture of the dimension of energy renovations as a problem of homeowners’ individual choice, the collective and social aspects of energy efficiency are still largely overlooked on the energy policy agenda. With its emphasis on how social structures interpenetrate individual actions, social sciences offer additional insights that go beyond the identification of barrier-drivers underlying investment choices and also help to identify positive opportunities for renovation within the conditions of domestic and social life. Until recently, comprehensive behavioral aspects and the social dimension of home energy renovation have been ignored in policy initiatives, and the integration of complementary disciplines is only in its early stages. Based on a broad literature review, this paper aims to provide an up-to-date interdisciplinary perspective of the theoretical evolutionary background, which has been the support to gradually redefine and address the problems associated with energy improvements in homes.
- An agent-based approach for implementing asset administration shell type 3Publication . Sakurada, Lucas; De la Prieta, Fernando; Leitão, PauloIndustry 4.0 (I4.0) is driving the digitization of traditional manufacturing systems toward intelligent and adaptable factories, where industrial assets are interconnected and capable of collaborating inside and cross-company to enhance production processes. A key enabler of this transition is the Asset Administration Shell (AAS), a standardized digital representation of an asset that encapsulates all asset-relevant information throughout its lifecycle. The AAS ensures that all assets, regardless of their type or function, can be seamlessly integrated into the I4.0, facilitating interoperability and efficient data exchange across the entire production network. However, traditional AAS solutions, namely AAS Types 1 and 2, cannot address all the requirements of modern industry environments. To overcome these limitations, the AAS Type 3 (proactive) extends beyond the conventional functionalities of traditional AAS by incorporating more sophisticated features, enabling I4.0 components to operate with greater autonomy, intelligence, and collaborative capabilities. While traditional AAS implementations (Types 1 and 2) have been widely studied and adopted, research on AAS Type 3 is still in its early stages, lacking formal specifications and standardized guidelines for its design and implementation. In this context, this article presents an agent-based AAS approach for implementing AAS Type 3, offering readers a clearer, more accessible description of its features and practical applicability while encouraging further research and development in this emerging topic. For this purpose, several experiments were performed to gain a better understanding of its application in industrial scenarios. Additionally, the article discusses the experiences, insights, limitations and future perspectives derived from the design and experimental implementation of the agent-based AAS approach.