1,723,670 research outputs found
Relação entre a Fadiga e a Atividade Física na DPOC
Full text linkIntrodução e Objetivos: A Doença Pulmonar Obstrutiva Crónica (DPOC) manifesta-se através da dispneia, tosse e expetoração. Porém, o 2º sintoma mais prevalente – a fadiga - é muitas vezes negligenciado e pode estar associado a uma menor capacidade para a prática de Atividade Física (AF). Assim, explorou-se a relação entre a fadiga e a AF na DPOC, e a influência de outros fatores na fadiga (objetivo secundário).
Material e Métodos: Foi realizado um estudo transversal em pessoas com DPOC. Foram recolhidos dados de espirometria e dos instrumentos: Modified Medical Research Council (mMRC) para avaliar a dispneia; n.º de exacerbações no último ano; classificação GOLD e ABCD; Checklist of Individual Strength (CIS20) e a sua Dimensão Subjetiva de Fadiga (DSF); acelerómetro Actigraph GT3X para avaliar a AF (i.e., AF leve, AF Moderada-a-Vigorosa (AFMV), AF total e n.º de passos). Realizaram-se correlações de Spearman (ρ) e de Phi (ϕ) e regressões lineares.
Resultados: A amostra incluiu 83 participantes (68±8 anos; 83% homens; 47±18 FEV1% previsto), em que 72% relatou presença de fadiga (DSF≥27) e apresentou uma média de 73±25 no score total do CIS20-P. Foi observada uma correlação negativa entre a fadiga e a AF (AFMV e CIS20-P: ρ=-0,29; AFMV e DSF: ρ=-0,28; passos/dia e CIS20-P: ρ=-0,30; passos/dia e DSF: ρ=-0,25) (p<0,05). Verificaram-se correlações positivas entre a fadiga e as exacerbações (CIS20-P: ρ=0,30; DSF: ρ=0,27), classificação ABCD (CIS20-P: ρ=0,43; DSF: ρ=0,38) e a dispneia (CIS20-P ρ=0,50; DSF: ρ=0,47) (p<0,05). A correlação entre ‘ter fadiga’ e a participação num programa de reabilitação respiratória, hábitos tabágicos e nível de dispneia (mMRC<2 vs. mMRC≥2) foi fraca (ϕ= 0,12, ϕ= 0,16, ϕ= 0,30, respetivamente). A dispneia revelou-se o maior preditor do CIS20-P e da DSF (ambos β=0,48, p<0,005).
Conclusões: As pessoas com DPOC menos ativas apresentam maiores níveis de fadiga, embora a relação seja fraca. A dispneia parece ter a maior influência sobre a fadiga. São necessários mais estudos para explorar a relação entre a fadiga, a AF e outros fatores nesta população.N/
Structured mesh generation and numerical analysis of a scroll expander in an open-source environment
No full textThe spread of the organic rankine cycle applications has driven researchers and companies to focus on the improvement of their performance. In small to medium-sized plants, cyanthe expander is the component that has typically attracted the most attention. One of the most used types of machine in this scenario is the scroll. Among the other methods, numerical analyses have been increasingly exploited for the investigation of the machine's behaviour. Nonetheless, there are major challenges for the successful application of computational fluid dynamics cyan(CFD) to scrolls. Specifically, the dynamic mesh treatment required to capture the movement of working chambers and the nature of the expanding fluids require special care. In this work, a mesh generator for scroll machines is presented. Given few inputs, the software described provides the mesh and the nodal positions required for the evolution of the motion in a predefined mesh motion approach. The mesh generator is developed ad hoc for the coupling with the open-source CFD suite OpenFOAM. A full analysis is then carried out on a reverse-engineered commercial machine, including the refrigerant properties calculations via CoolProp. It is demonstrated that the proposed methodology allows for a fast simulation and achieves a good agreement with respect to former analyses
CoolFOAM: The CoolProp wrapper for OpenFOAM
No full textNowadays, the evaluation of the transport and thermodynamic properties in computational fluid dynamics (CFD) analysis is based on common real gas equations (such as Redlich-Kwong and Peng-Robinson equations of state) and polynomial models. Such quantities are not always accurate: very large pressure ranges, working conditions close to the critical point or phase change could introduce an error during the computation of the thermophysical properties of interest. Moreover, the computational effort of numerical simulations is strongly affected by the evaluation of such properties. In light of these considerations, and to extend the modeling capabilities of CFD software suites, a fluid thermophysical property library can be included in the computation of the quantities required for the solution of the flow field. The focus of this work is the coupling of an open source CFD tool (OpenFOAM) with the open source CoolProp library. The proposed wrapper is intended to provide a connection between the most popular open-source thermophysical library and one of the most used open-source CFD software. CoolFOAM extends the thermophysical modeling possibilities of OpenFOAM. The formal implementation of this library follows the coding standards of the CFD suite
Pressure pulsation and cavitation phenomena in a micro-ORC system
No full textMicro-ORC systems are usually equipped with positive displacement machines such as expanders and pumps. The pumping system has to guarantee the mass flow rate and allows a pressure rise from the condensation to the evaporation pressure values. In addition, the pumping system supplies the organic fluid, characterized by pressure and temperature very close to the saturation. In this work, a CFD approach is developed to analyze from a novel point of view the behavior of the pumping system of a regenerative lab-scale micro-ORC system. In fact, starting from the liquid receiver, the entire flow path, up to the inlet section of the evaporator, has been numerically simulated (including the Coriolis flow meter installed between the receiver and the gear pump). A fluid dynamic analysis has been carried out by means of a transient simulation with a mesh morphing strategy in order to analyze the transient phenomena and the effects of pump operation. The analysis has shown how the accuracy of the mass flow rate measurement could be affected by the pump operation being installed in the same circuit branch. In addition, the results have shown how the cavitation phenomenon affects the pump and the ORC system operation compared to control system actions
A LOW-NOISE AIRFOIL FOR LOW REYNOLDS APPLICATIONS: A MULTI-FIDELITY OPTIMIZATION
No full textAutomotive fans, small wind turbines, and manned and unmanned aerial vehicles (MAVs/UAVs) are just a few of the examples in which noise generated by the flow interaction with the aerodynamic surfaces is a major concern. The current work shows the potential of a new airfoil shape to minimize noise generation, maintaining high lift-to-drag ratio in the low-Re regime (Re ≤2e5). The investigation is carried out by means of a multi-fidelity approach: a low-fidelity semi-empirical model is exploited for evaluating the sound pressure level (SPL). The fast evaluation of the low-cost function enables the computation of a large range of possible profiles, and accuracy is added to the low-fidelity response surface with high-fidelity CFD data. The constraint of maintaining a pre-defined range of the lift coefficient and lift-to-drag ratio ensures the possibility of using this profile in usual design procedures
Multi-component numerical investigation of a micro organic rankine cycle
No full textOrganic Rankine Cycles are frequently adopted for waste heat recovery applications from industrial processes. Micro-ORCs are characterized by low-grade heat sources (temperatures below 150 °C) with non-stationary operating conditions and small output power. ORC designers need to understand the system dynamics to perform the most efficient choice of components and working fluid. Furthermore, the analysis of off-design conditions can contribute tuning control strategies capable to deal with this variability. The authors propose a three-dimensional approach based on Computational Fluid Dynamics (CFD) for the study of the dynamics of ORCs. The simulation of a scroll expander coupled with plate heat exchangers has allowed the investigation of the dynamic behaviour of the two components. This demonstration shows the potentiality of this approach, investigating component mutual interaction, off-design conditions and the system's transient behaviour. The analysis is performed with an open-source CFD tool showing the importance of fully integrated 3D analyses
Flow computation inside a scroll compressor based on open-source code
No full textComputational fluid dynamics (CFD) is an essential tool for improving the performance of positive displacement machines, which are commonly adopted in vapour compression applications. The numerical analysis of such machines is characterized by several modelling challenges. Firstly, the relative motion of the wraps and the presence of particularly small gap sizes need to be considered during the implementation of a reliable meshing strategy.
In addition to that, the operating conditions are close to the saturated-vapour line, requiring a real gas equation of state for the determination of fluid thermophysical properties.
In this work, a commercial scroll compressor has been simulated at three different operating conditions. The geometrical modelling, meshing strategy and compression process have been obtained thanks to a set of libraries built in OpenFOAM-v2006. The results have been compared with experimental data of the pressure evolution in the compression chambers. Furthermore, a complete fluid flow analysis is presented to assess the capabilities of the developed tool when applied to a compressor operating with R410
FADIGA E ESTRESSE ACADÊMICO NO ESTUDANTE DE MEDICINA
Full text linkA saúde, segundo a Organização Mundial da Saúde (OMS), é definida como um completo bem-estar físico, mental e social. Assim, a rotina exaustiva dos estudantes de Medicina resulta em privação de sono, má alimentação e sedentarismo, aumentando o desgaste psicológico e físico, o que tem como consequência o comprometimento da qualidade de vida e o aumento da fadiga e do estresse. Este estudo teve por objetivo analisar os fatores associados e a correlação entre fadiga e estresse acadêmico em estudantes de medicina. Trata-se de um estudo transversal analítico com abordagem quantitativa. A pesquisa foi realizada através de questionários aplicados on-line aos estudantes de medicina do Brasil. Tais questionários foram: sociodemográfico, Escala de Fadiga de Chalder e Escala de Estresse Acadêmico. O estudo considerou 306 estudantes de medicina, sendo predominante o sexo feminino (65,7%) e a média de idade 22 anos. Observou-se o escore de fadiga com significância estatística nos estudantes que não praticavam nenhuma atividade física (p=0,001), dormiam menos de 7 horas por noite (p=0,001), não estavam satisfeitos com o próprio rendimento acadêmico (p=0,001), que tinham pensado em abandonar o curso (p=0,001) e aqueles que referiram ter alguma doença psiquiátrica diagnosticada (p=0,001). Já em relação ao estresse acadêmico, identificou-se o escore de estresse com significância estatística nos estudantes que não praticavam atividade física (p=0,013), que dormiam menos de 7 horas por noite (p=0,013), não estavam satisfeitos com o rendimento acadêmico (p=0,001), já tinham pensado em abandonar o curso (p=0,001), referiram ter alguma doença psiquiátrica diagnosticada (p=0,006) e dedicavam menos de 2 horas ao lazer diariamente (p=0,019). Dessa forma, o estudo comprovou que a fadiga e o estresse acadêmico estão correlacionados e que ambos sofrem influência de aspectos sociodemográficos dos estudantes de medicina. Tal constatação é relevante, visto que a fadiga e o estresse causam impactos negativos na vida desses estudantes
PADRÃO DE SONO, FADIGA E PERFIL ANTROPOMÉTRICO DE ESTUDANTES UNIVERSITÁRIOS
Full text linkResumo. As atividades acadêmicas na graduação universitária podem acarretar mudanças na saúde destes indivíduos. Assim, objetivou-se avaliar a prevalência da má qualidade do sono, nível de fadiga, atividade física e perfil antropométrico de estudantes universitários. Estudo transversal, realizado com 401 estudantes universitários de ambos os gêneros da Universidade Federal de Goiás, Regional Catalão, entre 08 a 10 de maio de 2019. Avaliou-se dados sociodemográficos, padrão de sono, perfil antropométrico, nível de fadiga e atividade física. Verificou-se maior prevalência de estudantes do gênero feminino, brancos, com excesso de peso, alto nível de fadiga e má qualidade do sono. A compreensão da relação existente entre indicadores antropométrico, qualidade do sono e atividade física dos universitários pode ajudar em campanhas e na oferta de atividades efetivas e variadas, a fim de melhorar as condições de saúde dessa população. Palavras-chave: Fadiga. Excesso de peso. Estudantes.
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