Browsing by Author "Ribeiro, Luís Frölén"
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- Accuracy/speed analysis of pipe friction factor correlationsPublication . Muzzo, Luiz Eduardo; Pinho, Diana; Lima, Luiz Eduardo Melo; Ribeiro, Luís FrölénThe Colebrook [1] equation is considered the standard for the calculation of friction factor for turbulent flow in commercial pipes, but it is implicit, and therefore it must be computed by iterative methods. Although such iterative computation quickly converges, the computational time in large pipe system simulations can be reduced using an accurate explicit correlation. A review of the up to date literature identified 30 different explicit correlations. In order to determine which correlation is the best alternative to Colebrook’s, both accuracy and computational burden were compared. The accuracy of each explicit correlation was compared against Colebrook’s correlation using the mean and maximum relative errors and the coefficient of determination. Also, the computational time of each equation was measured using the tic and toc functions in GNU Octave software. It was found that the iterative computation of the Colebrook equation demands about 2.6 times the computational time of the slowest explicit correlation. The correlations with the best balance between accuracy and computational burden are, in decreasing order of accuracy and increasing order of speed, correlations by Serghides [13] (Eqs. (17), (18), (19), and (20)), by Shacham [8] (Eqs. (10) and (11)), by Brkić and Praks [33] (Eqs. (53), (54), (55), and (56)), and by Fang et al. [19] (Eq. (28)).
- Aerial sonic anemometry - preleminary resultsPublication . Marques, Filipe; Ribeiro, Luís Frölén; Meles, V.ASA (Aerial Sonic Anemometry) project intends to use sonic anemometers in airborne platforms, complementing meteorological masts measurements over mountainous terrain. The additional information will be inputted into CFD models to assess complex mean and turbulent flow fields over mountainous terrain for wind energy purposes. The kind of platform and its distortion over the sonic measuring volume was considered: sonic anemometer structure over the platform and its behavior, and sonic transducers location relatively to platform. These limitations conditioned the choice of model planes to units with central or rear plan propulsion. Due to the lack of commercial offer, this type of configuration combined with payload capacity, led our choice to the Hobbyking FPV 168 with a wingspan of 1660 mm, fuselage of 1190 mm and a payload capacity of 2.3 kg. To prevent the distortion on the measurement volume, the minimal distance from the sonic head to the plane model was set to be equal to the distance from the front to the wing’s leading edge. The concept of flying a model plane with a sonic anemometer installed on it was validated, and it was possible to fly the model hauling a proxy of a Young 81000 sonic anemometer with perfect flying control. Flying tests were made in order to establish the best configuration of the center of mass of whole setup: airframe, batteries and sonic proxy structure. An electrical engine was used for commodity. The plane equipped with a 10”x7” 3 bladed pusher propeller, and at maximum engine rotation and local atmospheric conditions the batteries yielded a maximum of 37 Ah for the whole electric system. The flight autonomy is estimated to be between 8 to 10 minutes depending on local winds (1 battery of 4 elements of 4.2 V and 3700mAh). Future steps of this project are the use of the present setup to explore GPS, autopilot and data acquisition features. The increase of flight autonomy with the sonic platform will require larger aircrafts that are undergoing a process of selection.
- Aerial sonic anemometry for wind resource assessmentPublication . Ribeiro, Luís Frölén; Marques, FilipeThis project intends to recur to sonic anemometers in a airborne platforms to get wind information over the flying area between met masts or waypoints. Multiple platforms measuring simultaneously to complement ground based measurements. The concept is being tested and preliminary results show that key issues are related to the positioning system – differential GPS and autopilot.
- Affective relationships from youth and adults’ perspectives.Publication . Veiga-Branco, Augusta; Ribeiro, Maria Isabel; Antão, Celeste; Rodrigues, Cristiana; Anastácio, Zélia; Ribeiro, Luís Frölén; Prada, Ana Raquel RussoThis study aims to compare youth and adults’perspectives about affective relationships, essential for maturity construction and subjective well-being. Quantitative and descriptive study, developed through a questionnaire applied to 233 individuals (82,5% female/ 17,5% male, 51,7% single), aged between 16–76 years, from north and central of Portugal, divided in two classes: 31% young (16–25 years) and 68,7% adults (≥25 years). In their affective life, 208 individuals, representing 89,3% (32,2% young; 67,8% adults), contrary to 10,7% (24% young; 76% adults), consider «to have stable relationships». A total of 167–71,7% individuals (35,9% young; 64,1% adults), contrary to 66-28,3% (19,7% young; 80,3% adults),recognize «relationships because falls in love». Nonetheless, 22–9,4% (54,5% young; 45,5% adults) assume «short and successive relationships». Also 17-7,3% ( 41,2% young; 58,8% adults) recognize «dating, not relationships», and 102-43,8% agree that «relationships start from physical attraction» (27,5% young; 72,5% adults). Some individuals (69-29,6%) agree that «the most important in relationships is sexual component» (21,7% young; 78,3% adults) and 51-21,9% that «love is not the most important in affective relationships» (15,7% young-84,3% adults). The findings suggest that adults are, for better or worse, an expressive model to youth. Emotional education is essential to develop youth responsibility and awareness.
- Automation of optimization synthesis for modular technological equipmentPublication . Zaleta, Olha M.; Povstyanoy, Oleksandr; Ribeiro, Luís Frölén; Redko, Rostyslav G.; Bozhko, Tetiana Ye; Chetverzhuk, Taras I.Technological equipment design based on functionally modular methods is widely used in various technical fields. The designed object can be a technological machine, a production line, or a manufacturing complex. Special attention is paid to the optimization of its structure. The sequence of performing all stages of the optimization synthesis problem is presented in the article. To find a solution to this task, the developer should apply the complete or directed search of acceptable structure options and determine the best one using some optimization criteria to evaluate their quality. It can be simple enough if the designed technical system structure consists of no more than several elements. For example, if the number of alternative elements options is several dozen, it takes much time to accomplish the search correctly. Thus, the greater the number of components considered, the more difficult it is to do all the necessary calculations manually. In this case, machine resources should be involved. This scientific work aims to identify procedures of optimization synthesis that can be automated. Also, appropriate software has to be developed. Our computer program is based on the algorithm of a complete search of all options of the technical system structure. It can process an extensive array of input data and produce all possible and logically permissible results in the form the designer can analyze using the Pareto method to choose the best one. This software can be used for any technical system with a modular structure.
- Automation of optimization synthesis for modular technological equipmentPublication . Zaleta, Olha; Povstyanoy, O.Yu.; Ribeiro, Luís Frölén; Redko, R.G.; Bozhko, T.Ye.; Chetverzhuk, T.I.Technological equipment design based on functionally modular methods is widely used in various technical fields. The designed object can be a technological machine, a production line, or a manufacturing complex. Special attention is paid to the optimization of its structure. The sequence of performing all stages of the optimization synthesis problem is presented in the article. To find a solution to this task, the developer should apply the complete or directed search of acceptable structure options and determine the best one using some optimization criteria to evaluate their quality. It can be simple enough if the designed technical system structure consists of no more than several elements. For example, if the number of alternative elements options is several dozen, it takes much time to accomplish the search correctly. Thus, the greater the number of components considered, the more difficult it is to do all the necessary calculations manually. In this case, machine resources should be involved. This scientific work aims to identify procedures of optimization synthesis that can be automated. Also, appropriate software has to be developed. Our computer program is based on the algorithm of a complete search of all options of the technical system structure. It can process an extensive array of input data and produce all possible and logically permissible results in the form the designer can analyze using the Pareto method to choose the best one. This software can be used for any technical system with a modular structure.
- Business plan windScanner.pt research infrastructure - national research infrastructure (PINFRA/22207/2016)Publication . Grosso, José; Campos, José; Ribeiro, Luís Frölén; Simões, TeresaWind energy is becoming one of the leading sources of power in Europe. The installed capacity increases each year, with the offshore wind gradually evolving with even more significant potential than onshore [1]. This growing tendency has also been promoting a more extensive research effort in this area, pushed by the climatic crisis that has also driven political support from multiple nations across Europe. Wind energy has employed over 250 thousand EU citizens and contributed to around 10% of European electrical consumption. Although high milestones have been achieved, there is still much room to grow in the wind energy sector, particularly cost reduction.The WindScanner.pt project aims to create a European distributed research infrastructure based on high precision sensors able to analyze fluid dynamics in tridimensional volumes, offering the ability to understand atmospheric conditions and turbulence better. This asset will not only allow better assessment of the wind conditions. Still, it will also enable the evaluation of projects in other areas where fluid dynamics are relevant, such as civil engineering and the building industry, by scanning the surroundings of large structures such as bridges and viaducts and measuring structure oscillations [3].
- A case for including solar dehydrators in food processingPublication . Silva, Paulo Bruno Rossi da; Farrero, Bernardo; Ribeiro, Luís FrölénThe access of small-scale food producers and big agro-industry players to equipment is abyssal. The latter have access to well-developed and appropriate technology. In this article, one proposes a novel design for food dehydration equipment to serve small-scale producers, reducing their technological gap regarding dehydration. Equipment that dries more than 1000 kg daily is costly and consumes much energy. Lower capacity machines, up to 100 kg per day, are often one-off handcrafted projects built with reused materials without dimensioning supporting the design. They are usually not easily transportable and underperform: the drying chamber tends to overheat; the solar collector's area is usually 50% inferior to the required product quantity. One proposes a mobile dehydrator with a solar collector area 7 times larger than average, promoting moisture removal by naturally convected airflow at lower temperatures, reaching up to 4,5 m/s and 44,3 °C inside the entrance of the drying chamber. Under these flow conditions, the food's organoleptic properties are preserved compared to the often high-temperature drying handspun machines continually adopted by small-scale producers. The internal layout of the drying chamber was also changed to promote the increase of turbulence and reduce the existence of recirculation areas, thus facilitating the transfer of moisture from the food to the airflow. The expected result from implementing this novel design is avoiding food losses due to natural degradation by increasing the product's shelf life before transport and transformation. Solar equipment has zero operational costs, and all these advantages are expected to encourage small-scale dehydration technology.
- Convergent-diffuser for small horizontal wind turbinesPublication . Ribeiro, Luís Frölén; Paulo, Jorge Alexandre Rente; Garcia, ValdemarA small horizontal axis wind turbine (HAWT) equipped with an annular Convergent-Diffuser (C-D) is under development. Small to medium wind turbines equipped solely with a diffuser are becoming quite common: the annular structure around the rotor decreases the pressure downstream the rotor, augmenting the air velocity and power output. It also may replace the wind vane. Previous studies for such designs, for instance Ohya, Y. 2010, report a maximum increase in power output up to 150%. We present the preliminary results of an alternative design for a convergent-divergent annular structure that involves the rotor. This structure was optimized in CFD-simulations and 2 models where built for wind tunnel measurements. The maximum power output obtained was 187% higher than the case for a rotor without the C-D structure. Field tests are undergoing at this moment for a C-D adapted in model Rutland 913 Windcharger of 90 W.
- Decommissioned wind turbine blades: a pedagogical project on the uses of the raw materialPublication . Ribeiro, Luís Frölén; Ribeiro, J.E.; Costa, Carlos Casimiro da; Savosh, LarysaThe incorporation of new technical challenges created by the increase of the wind power industry in the world and how they were integrated into a MSc Course of Mechanical Engineering is addressed in this article.