SMT-Based Bounded Model Checking of Fixed-Point Digital Controllers

Digital controllers have several advantages with respect to their flexibility and design's simplicity. However, they are subject to problems that are not faced by analog controllers. In particular, these problems are related to the finite word-length implementation that might lead to overflows, limit cycles, and time constraints in fixed-point processors. This paper proposes a new method to detect design's errors in digital controllers using a state-of-the art bounded model checker based on satisfiability modulo theories. The experiments with digital controllers for a ball and beam plant demonstrate that the proposed method can be very effective in finding errors in digital controllers than other existing approaches based on traditional simulations tools

Direct Normal Irradiance and circumsolar radiation: modelling, measurement and impact on Concentrating Solar Power

In this work, the modelling and measurement of direct and circumsolar normal irradiance (DNI and CSNI, respectively) is studied, as well as their impact on the energy generation of concentrating solar power systems (CSP). To model DNI, two approaches are used: (i) developing a fast and simple model to estimate diffuse horizontal irradiance, and consequently, DNI; and (ii) assess the performance of three distinct state-of-the-art models with different degrees of complexity. Regarding the first approach, it was found that the developed model that considers the climate zone was able to outperform the models available in the literature. Regarding the second approach, it was found that the radiative transfer model libRadtran and the parametrization model SMARTS are the models that provide the best DNI predictions. In this way, libRadtran is used to generate a database of DNI and CSNI values. Then, a new CSNI model is developed to estimate CSNI for a half-opening angle of 2.5◦ that only requires solar radiation data as input. It was found that the proposed CSNI model outperforms the models available in the literature in almost all of the locations analysed. However, the half-opening angles of common CSP systems are lower than 2.5◦. Therefore, an upgrade of the CSNI model is developed that enables the determination of CSNI for a specific half-opening angle. The improved model is then able to predict the CSNI that reaches the CSP receiver and estimate the variation in the system’s intercept factor caused by CSNI variation. It was found that discarding CSNI could lead to up to a 7% difference between the measured DNI and the DNI that is captured by the CSP system. Furthermore, it was also found that higher rim angles are needed if the impact of CSNI variation is to be mitigated in parabolic trough concentrators; Resumo: Irradiância Direta Normal e radiação circunsolar: modelação, medição e impacto em Sistemas de Concentração Solar Neste trabalho, são estudadas a modelação e a medição da irradiância direta normal e circunsolar direta normal (DNI e CSNI, respetivamente), assim como o seu impacto na geração de energia em sistemas de concentração solar (CSP). São usadas duas abordagens para modelar a DNI: (i) desenvolvimento de um modelo simples e rápido para estimar a irradiância difusa horizontal e consequentemente a DNI; (ii) avaliar a performance de três modelos de última geração com diferentes graus de complexidade. Relativamente à primeira abordagem, verificou-se que o modelo desenvolvido e que considera a zona climática é capaz de superar os modelos disponíveis na literatura. Relativamente à segunda abordagem, verificou-se que os modelos de transferência radiativa libRadtran e de parametrização SMARTS são os que apresentam as melhores estimativas de DNI. Desta forma, o libRadtran é usado para gerar uma base de dados de valores de DNI e CSNI. De seguida, é desenvolvido um novo modelo para estimar a CSNI para um meio-ângulo de abertura de 2.5◦ que apenas necessita de dados de radiação solar. Verificou-se que o modelo desenvolvido supera os modelos disponíveis na literatura em quase todos os locais analisados. No entanto, o meio-ângulo de abertura de sistemas CSP comuns é inferior a 2.5◦. Por isso, foi desenvolvida uma atualização ao modelo que permite a determinação da CSNI para um meio-ângulo de abertura específico. O modelo atualizado é capaz de prever a CSNI que chega ao recetor do sistema CSP e estimar a variação do fator de interceção do sistema causada pela variação da CSNI. Verificou-se que descartar a CSNI pode levar a uma diferença de até 7% entre a DNI medida e a DNI que é intercetada pelo sistema CSP. Verificou-se ainda que para mitigar o impacto da variação da CSNI em concentradores cilindro-parabólicos é necessário ter rim angles maiores

Modifying a pyrheliometer to measure direct normal and circumsolar irradiance

Direct normal irradiance (DNI) is key to concentrating solar power (CSP) systems energy generation. However, pyrheliometric measurements of DNI also include a circumsolar normal irradiance (CSNI) component because the aperture angle of the instrument is larger than the sun disk. CSNI is due to the scattering of the sun rays by molecules, aerosols and some cloud types such as cirrus clouds [1]. As a result, energy is transferred from the direct solar beam to the circumsolar region, i.e., the region in the vicinity of the sun disk [2]. Typically, CSP systems have a lower aperture angle than that of pyrheliometers, which means that these systems are not able to absorb the same amount of CSNI as the amount that is present in the DNI measurements, leading to an inaccurate forecast of energy generation of CSP systems if DNI measurements are directly used in its sizing and operation. In this way, measuring CSNI for different aperture angles is important to better size, operate and optimize the energy generation of CSP systems. In this work, a conventional pyrheliometer field-of-view is modified through the variation of its collimator length and diameter in order to gather information on the circumsolar irradiance [3]. The modified pyrheliometer is composed by a revolver with four possible combinations of tube lengths and diameters and a stepper motor, which automatically enable varying the field-of-view of the pyrheliometer

Prediction of circumsolar irradiance and its impact on CSP systems under clear skies

In this work, a model to estimate circumsolar normal irradiance (CSNI) for several half-opening angles under clear skies was developed. This approach used a look-up table to determine the model parameters and estimate CSNI for half-opening angles between 0.5° and 5°. To develop and validate the proposed model, data from five locations worldwide were used. It was found that the proposed model performs better at the locations under study than the models available in the literature, with relative mean bias error ranging from −13.94% to 0.70%. The impact of CSNI for these different half-opening angles on concentrating solar power (CSP) systems was also studied. It was found that neglecting CSNI could lead to up to a 7% difference between the direct normal irradiance (DNI) measured by a field pyrheliometer and the DNI that is captured by CSP systems. Additionally, a case study for parabolic trough concentrators was performed as a way to estimate the impact of higher circumsolar ratios (CSR) on the decrease of the intercept factor for these systems. It was also concluded that if parabolic trough designers aim to reduce the impact of CSNI variation on the intercept factor, then parabolic troughs with higher rim angles are preferred

Contribution to the diffuse radiation modelling in Évora, Portugal

Solar radiation data is crucial for the design of energy systems based on the solar resource. Since diffuse radiation measurements are not always available in the archive data series, either due to the inexistence of measuring equipment, shading device misplacement or missing data, models to generate these data are needed. In this work, one year of hourly and daily horizontal solar global and diffuse irradiation measurements in Évora are used to establish a new relation between the diffuse radiation and the clearness index. The proposed model includes a fitting parameter, which was adjusted through a simple optimization procedure to minimize the Least Square Error as compared to measurements. A comparison against several other fitting models presented in the literature was also carried out using the Root Mean Square Error as statistical indicator, and it was found that the present model is more accurate than the previous fitting models for the diffuse radiation data in Évora

Comparison and assessment of circumsolar ratio models for Évora, Portugal

The sun rays are scattered due to molecules, aerosols and some cloud types, such as cirrus clouds, and a region near to the vicinity of the sun disk, known as circumsolar region, with relatively high diffuse sky radiance is formed [1]. Consequently, this diffuse radiation is called circumsolar normal irradiance (CSNI). Modelling the CSNI is important because pyrheliometers (the instruments that are used to measure direct normal irradiance – DNI), have an aperture angle wider than the circumsolar region, and thus DNI measurements obtained with these instruments cannot resolve the distribution of solar radiance in that region [2]. Moreover, since concentrated solar power (CSP) systems only capture solar radiation from this region but with a narrower aperture angle than that of the pyrheliometers, this leads to an overestimation of the energy reaching the receiver of the CSP systems [1]. This can result in misleading power output estimations, which can harm the bankability of CSP projects. Information on CSNI is also crucial when designing, sizing and operating CSP powerplants

Prediction of diffuse horizontal irradiance using a new climate zone model

Knowledge on the diffuse horizontal irradiance (DHI), and direct normal irradiance (DNI) is crucial for the estimation of the irradiance on tilted surfaces, which in turn is critical for photovoltaic (PV) applications and for designing and simulating concentrated solar power (CSP) plants. Since global horizontal irradiance (GHI) is the most commonly measured solar radiation variable, it is advantageous for establishing a suitable method that uses it to compute DHI and DNI. In this way, a new model for predicting the diffuse fraction (K_d) based on the climate zone is proposed, using only the clearness index (K_t) as the predictor and 1-min resolution GHI data. A review of the literature on models that use hourly and sub-hourly K_t values to compute K_d was also carried out, and an extensive performance assessment of both the proposed model and the models from the literature was conducted using ten statistical indicators and a global performance index (GPI). A set of model parameters was determined for each climate zone considered in this study (arid, high albedo, temperate and tropical) using 48 worldwide radiometric stations. It was found that the best overall performing model was the model proposed in this work

Determinação do Ano Médio de Radiação Solar e do Ano Meteorológico Típico para a região do Funchal na ilha da Madeira

This paper presents the determination of a mean solar radiation year and of a typical meteorological year for the region of Funchal in the Madeira Island, Portugal. The data set includes hourly mean and extreme values for air temperature, relative humidity and wind speed and hourly mean values for solar global and diffuse radiation for the period 2004-2014, with maximum data coverage of 99.7%. The determination of the mean solar radiation year consisted, in a first step, in the average of all values for each pair hour/day and, in a second step, in the application of a five days centred moving average of hourly values. The determination of the typical meteorological year was based on Finkelstein-Schafer statistics, which allows to obtain a complete year of real measurements through the selection and combination of typical months, preserving the long term averages while still allowing the analysis of short term events. The typical meteorological year validation was carried out through the comparison of the monthly averages for the typical year with the long term monthly averages. The values obtained were very close, so that the typical meteorological year can accurately represent the long term data series. The typical meteorological year can be used in the simulation of renewable energy systems, namely solar energy systems, and for predicting the energy performance of buildings

RELATÓRIO DE ESTÁGIO - Desenvolvimento de Competências Especializadas em Enfermagem na Área da Pessoa em Situação Crítica

O desenvolvimento da especialidade em Enfermagem Médica Cirúrgica na Área da Pessoa em Situação Critica compreende a aquisição de competências comuns e específicas inerentes à mesma. Os estágios realizados visam contribuir para a formação do enfermeiro especialista, fomentando a prática baseada na evidência na prestação de cuidados de enfermagem, quer pelo próprio quer pelos pares. Neste sentido foi desenvolvido uma investigação-ação no contexto de local de trabalho, na temática da pronação em doentes despertos com dificuldade respiratória. Os objetivos deste trabalho visam evidenciar as competências comuns e específicas adquiridas em Enfermagem Médico-Cirúrgica na Área da Pessoa em Situação Crítica e capacitar os enfermeiros, de um serviço de um hospital da região centro, para a tomada de decisão de pronar doentes com dificuldade respiratória. O trabalho desenvolvido tem cariz quantitativo, correlacional e prospetivo. A partir de uma revisão integrativa da literatura elaborou-se um questionário para avaliação do conhecimento dos enfermeiros sobre a técnica de pronar e um fluxograma sobre tomada de decisão. Após aplicação do fluxograma, como intervenção da técnica de pronar, constituíram-se dois grupos focais, um com enfermeiros especialistas e outro com enfermeiros generalistas. Na fase anterior à aplicação do fluxograma não se observaram a adoção de técnica de pronação. Após formação de pares observaram-se 14 casos com critérios de pronação, dos quais seis foram alvo deste posicionamento. A tomada de decisão foi efetuada por enfermeiros que frequentaram a formação (valor p <0,05), detentores de especialidade (valor p < 0,05). Conclusão: A formação de pares contribuiu para a tomada de decisão no ato de pronar doentes com dificuldade respiratória, sobretudo em enfermeiros especialistas. Abordagens complementares à formação poderão contribuir para uma maior capacitação dos enfermeiros, tais como a construção e divulgação de protocolo de tomada de decisão por meios eletrónicos e presencialmente junto dos profissionais

Tratamento de dados associados com a radiação solar fornecidos pelo Instituto Português do Mar e da Atmosfera, Madeira

Este relatório técnico tem como objetivo descrever o modo como os registos das amostras de dados, i.e., medições das grandezas meteorológicas fornecidas pelo Instituto Português do Mar e da Atmosfera (IPMA), ilha da Madeira, foram tratadas. Foram utilizados registos de oito estações meteorológicas distribuídas pela ilha. No relatório técnico estão descritos os processos de filtragem das medições de radiação solar global e radiação solar difusa, de temperatura máxima e mínima do ar, a correção da radiação solar difusa, o preenchimento de lacunas nas medições e a dimensão da amostra de dados utilizada em cada estação. Este relatório também descreve os métodos utilizados para preencher as lacunas nas séries de dados originais, bem como os métodos utilizados na construção do ano médio e do ano meteorológico típico. O ano meteorológico típico será posteriormente usado na simulação da produção de energia solar através de sistemas fotovoltaicos instalados na ilha da Madeira