Centre for Mechanical and Aerospace Science and Technologies

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Publications

Plasma Actuators Based on Alumina Ceramics for Active Flow Control Applications

Publication . Rodrigues, Frederico; Shvydyuk, Kateryna; Nunes-Pereira, João; Pascoa, Jose; Silva, Abilio

Plasma actuators have demonstrated great potential for active flow control applications, including boundary layer control, flow separation delay, turbulence control, and aircraft noise reduction. In particular, the material used as a dielectric barrier is crucial for the proper operation of the device. Currently, the variety of dielectrics reported in the literature is still quite restricted to polymers including Kapton, Teflon, poly(methyl methacrylate) (PMMA), Cirlex, polyisobutylene (PIB) rubber, or polystyrene. Nevertheless, several studies have highlighted the fragilities of polymeric dielectric layers when actuators operate at significantly high-voltage and -frequency levels or for long periods. In the current study, we propose the use of alumina-based ceramic composites as alternative materials for plasma actuator dielectric layers. The alumina composite samples were fabricated and characterized in terms of microstructure, electrical parameters, and plasma-induced flow velocity and compared with a conventional Kapton-based actuator. It was concluded that alumina-based dielectrics are suitable materials for plasma actuator applications, being able to generate plasma-induced flow velocities of approximately 4.5 m/s. In addition, it was verified that alumina-based ceramic actuators can provide similar fluid mechanical efficiencies to Kapton actuators. Furthermore, the ceramic dielectrics present additional characteristics, such as high-temperature resistance, which are not encompassed by conventional Kapton actuators, which makes them suitable for high-temperature applications such as turbine blade film cooling enhancement and plasma-assisted combustion. The high porosity of the ceramic results in lower plasma-induced flow velocity and lower fluid mechanical efficiency, but by minimizing the porosity, the fluid mechanical efficiency is increased.

2024Journal article

Open access

Manufacturing and characterisation of a piezoresistive strain sensor based on the rGO@PDMS composite for skin and prosthetic support systems

Publication . Gonçalves Ferreira, Rodrigo; Pereira Silva, A; Nunes-Pereira, João

Due to an ever-increasing amount of population focusing more on their personal health, thanks to rising living standards, there is a pressing need to improve personal healthcare devices. These devices presently require laborious, time-consuming, and convoluted procedures that heavily rely on cumbersome equipment, causing discomfort and pain for the patients during invasive methods such as sample-gathering, blood sampling, and other traditional bench-top techniques [1]. The solution lies in the development of new flexible sensors with temperature, humidity, strain, pressure, and sweat detection and monitoring capabilities, mimicking some of the sensory capabilities of the skin [2]. Along these lines, carbon-based composite materials, which include graphene and other allotropes, have also garnered significant interest due to their electromechanical stability, extraordinary electrical conductivity, high specific surface area, variety, and relatively low cost [3].Thus, in this work, a piezoresistive strain sensor based on a polydimethylsiloxane (PDMS) composite nano reinforced with reduced graphene oxide (rGO) was manufactured, characterised, and tested for possible applications which include joint movement and breathing pattern monitoring, exhibiting the physical and electromechanical characteristics required for the effective detection of physiological signals. The samples were prepared via solution casting, followed by characterisation of the piezoresistive effect of the material, mechanical (3-point bending and tensile), morphological (SEM), structural (FTIR), and thermal (TGA) properties, along with performance testing in live-human’s body parts. Regarding results, it was observed the influence of the used PDMS elastomer-crosslinker ratio, cure temperature and time, dispersant and rGO content in the final performance of the sensor, with the possibility to tune certain characteristics to be better adjusted to specific applications. For this kind of application, the indicated elastomer-crosslinker is 15:1 cured at 120 °C for 20 minutes, with isopropyl alcohol as the dispersant and a rGO content between 3-5 wt.%. The obtained average gauge factors ranged from 7.49-14.85 for 3 wt.%, 9.84-30.8 for 4 wt.%, and 0.56-9.16 for 5 wt.% rGO, establishing these samples as effective piezoresistive sensors for bioengineering applications. It was also concluded that the manufactured composites exhibited good linearity and piezoresistive performance in the 1.54-2.87% strain range, some stability in the 100 cycle 3-point bending tests, the tensile strength varied from 1.05 MPa to 3.084 MPa, the degradation temperature ranged from 380 °C to 410 °C, as well as composites reversibly losing their electrical component before the structure integrity was lost, when tensile tested. Lastly, two proofs of concept were developed, where real-time acquisition and monitoring of data related to joint movements and breathing patterns was successfully performed in volunteers.

2024Conference object

Open access

Estudo da Atomização de Jatos Eletrohidrodinâmicos: modelação, desempenho e aplicações

Publication . Cândido, Sílvio Miguel Rodrigues; Marques, José Carlos Páscoa

Nesta tese apresenta-se primeiramente uma descrição preliminar da literatura existente sobre a formação de jatos por efeitos eletrohidrodinâmicos, usualmente referenciados como “cones de Taylor”. Este fenómeno é de carácter multifísico e tem vindo a ser estudado a fim de podermos controlar eficazmente a forma e dimensão das gotas. Contudo é necessário conhecer melhor a interação entre o campo elétrico e a dinâmica do escoamento, sendo este o propósito geral deste trabalho. A presente tese concentra-se na atomização de jatos eletrohidrodinâmicos (EHD) através de uma abordagem numérica tridimensional para investigar as instabilidades associadas a estes mesmos jatos. No âmbito desta investigação foi realizada uma validação meticulosa da implementação de equações que acoplam as equações de Navier-Stokes, responsáveis pela dinâmica dos fluidos, e as equações de Maxwell para a eletrostática. Estas validações foram realizadas em cenários específicos, tais como a deformação de gotas individuais suspensas em meio dielétrico e a formação de jatos 2D em modo axissimétrico. Em particular, a quebra destes jatos em gotas foi analisada e comparada com leis teóricas de escala e dados experimentais. Os resultados mostraram desvios inferiores a 2%. Estudos pioneiros da simulação do cone de Taylor tridimensional mostrou erros médios na morfologia da mesma ordem de grandeza. No decorrer destas investigações foram explorados métodos avançados de análise e otimização. Entre eles destaca-se a utilização da Decomposição Modal e especificamente técnicas como POD (Proper Orthogonal Decomposition) e DMD (Dynamic Mode Decomposition). Estas técnicas oferecem uma visão aprofundada das características dominantes dos jatos e das instabilidades associadas. Adicionalmente, abordagens de aprendizagem de máquina, nomeadamente Redes Neuronais Artificiais, foram exploradas com o intuito de criar “gémeos digitais” (digital twins) para otimização dos processos envolvidos na atomização de jatos EHD. Por fim, a tese propõe um novo modelo híbrido combinando o Volume of Fluid (VOF) com a técnica de Lagrangian Particle Tracking (LPT). Este modelo é sugerido como uma alternativa eficaz e rápida para cálculo numérico no contexto de eletrosprays, potenciando assim aplicações práticas na indústria e na investigação da compreensão da física destes escoamentos. Contribuindo significativamente para o campo da atomização de jatos EHD, oferecendo novas perspetivas e ferramentas para melhor compreensão e aplicação deste fenómeno.

2024-05-06Doctoral thesis

Open access

Sociodemographic Data and Work-Related Musculoskeletal Symptoms in the Metal Polishing Industry: A Case Study in Central Portugal

Publication . Alves, Joel; Lima, Tânia M.; Gaspar, Pedro Dinis

The prevalence of work-related musculoskeletal disorders is a red flag in industries and is considered an occupational health issue that affects the operator’s well-being, safety, and health. This study contributes to understanding the impact of Industry 5.0 on the workforce and emphasizes the importance of promoting a safe and healthy working environment. Thus, it focuses on the assessment of anthropometric characteristics and work-related musculoskeletal symptoms in a real industrial environment, specifically in the metal polishing sector of a metallurgical industry in Portugal. The research collected data on physical attributes, health status, and musculoskeletal symptoms using the Portuguese version of the Nordic Musculoskeletal Questionnaire, and incorporated sociodemographic data, including age, gender, and professional status, to provide a comprehensive understanding of the active workforce. The results were analyzed by gender and age clusters and revealed a prevalence of musculoskeletal symptoms, particularly in the spinal column and upper limbs, with a significant impact on the ability to perform work tasks. The need for preventive measures and ergonomic interventions to minimize the high predominance of musculoskeletal symptoms in Portuguese industries is also highlighted to improve the working conditions and enhance the well-being and health of operators.

2024-08-19Journal article

Open access

Assessing Psychosocial Work Conditions: Preliminary Validation of the Portuguese Short Version of the Copenhagen Psychosocial Questionnaire III

Publication . Pinto, Ana; Carvalho, Carla; Mónico, Lisete S.; Moio, Isabel; Alves, Joel; Lima, Tânia M.

The working environment is a crucial aspect to considerfor guaranteeing a sustainable life. However, workers are exposed to various health risks daily, namely, psychological risks. These risks can be due to imbalances on the part of the workers themselves or to organisational and interfunctional risk factors arising from interactions within companies and the challenges of professional responsibilities. Over the past 20 years, the Copenhagen Psychosocial Questionnaire (COPSOQ) has become one of the most prominent tools for assessing psychological and social factors at work. This study aimed to present, discuss, and evaluate aspects of the cultural adaptation and preliminary psychometric validation of the short version of COPSOQ III for a Portuguese sample. For this purpose, we used data from 361 participants employed in the industrial (30.7%) and services (69.3%) sectors across various regions of Portugal. A third-order confirmatory factor analysis (CFA) was performed using AMOS, revealing an acceptable fit. The results also demonstrate the robustness of the measurement model, confirming its reliability and validity. In light of some limitations of this preliminary study, directions for future research are proposed. Thus, a tool for assessing psychosocial risks is disseminated, making it possible to achieve more sustainable working environments where the operator’s health and well-being are prioritised.

2024-08-29Journal article

Open access