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Modelos dinâmicos aplicados a sistemas de manufatura utilizando grafos de ligação: proposta de modificações
(Universidade Federal de São Carlos, 2020-08-24) Maluf, Arthur Sarro; Sagawa, Juliana Keiko; https://lattes.cnpq.br/6549481623896786; https://lattes.cnpq.br/8495817893158097
Companies compete in a fierce market, where the main focus is consumer satisfaction, forcing them to respond dynamically to market changes and instabilities. Due to these factors, more accurate, adaptable, robust and exploitable models are needed to represent these production systems. In this way, the present study analyzes dynamic models applied to manufacturing using the bond graph method. The aim is to present a detailed comparative analysis, discussing the variables used in the models, the mathematical equation and the context of their application. From the analysis of existing models, a model was taken as a basis. The chosen model uses a source of effort, represented by a minimum function, which introduces non-linearity and makes the design of controllers difficult. The effort variable has no physical meaning and becomes null due to the infinite capacities of the stocks, also making the transfer of power between the elements null, which is the main feature of the approach. The new equations for the model limit the capacities of the stocks, allowing the transfer of power between the elements and the use of the minimum function is not necessary. The systematic and extensive search carried out in the literature showed that models based on bond graphs with application in manufacturing are scarce. Thus, this work aims to contribute to the development of future works in this line of research. The manufacturing and operations management area benefits from this type of approach, which allows the use of control theory tools for dynamic analysis and for proposing prescriptive management guidelines from the simulation of closed-loop systems. In relation to other approaches used in the modeling of production systems, the bond graph approach stands out for its modularity, which allows the integration of different systems, subsystems and components. This, in turn, allows the representation of different configurations of production systems (e.g. flow shop, job shop).
Estudo sobre o desempenho de válvulas não-mecânicas como alimentadores de biomassa residual de borra de café em reatores de leito pneumático circulante: experimentação e modelagem via CFD-TFM
(Universidade Federal de São Carlos, 2020-08-24) Sousa, Lucas Massaro; Ferreira, Maria do Carmo; https://lattes.cnpq.br/7070885875161111; https://lattes.cnpq.br/6375928540784651
The continuous and stable feeding of particulate solids to reactors is essential for energy cogeneration in industrial processes, for example, by using biomass residues. Nevertheless, flow instabilities and blockage of mechanical feeder’s moving parts are commonly reported with these materials, which jeopardizes the process’ performance, automation, and safety. This study is aimed at evaluating the performance of non-mechanical devices (an L-valve and a spouted bed) to promote the feeding of spent coffee grounds to circulating fluidized bed (CFB) units. The physical and flow properties were determined for dry spent coffee grounds with mean sizes between 225 and 550 μm, as well as for samples with moisture content up to 60%. Some of the properties determined were the true, apparent, and bulk densities, minimum fluidization velocity, Hausner ratio, static and dynamic repose angle, and effective internal friction angle. Then, feeding experiments using both feeders were carried out at pilot-scale CFB reactors (riser diameter and height of 21 mm and 2 m), available at the Drying Center/UFSCar. The fluid dynamics of the systems with spent coffee grounds was assessed by pressure and solids flowrate (Ws) measurements under different operating conditions, such as different air flowrates in the riser and feeder, as well as with different distances between the riser and air inlets with the spouted bed. The solids flowrate with the L-valve lies between 0.6 and 10.0 g/s, while it ranges from 1.2 to 11.0 g/s with the spouted bed feeder. The pressure measured at the feeders and Ws were accurately related by linear equations. The feeders’ performance was related to the samples’ properties, then flow instabilities and lower values of Ws were observed for samples with poorer flowability. Overall, the spouted bed exhibited improved performance and flexibility than the L-valve in handling dry and wet spent coffee grounds to the CFB unit. The experimental data was used to validate simulations based on computational fluid dynamics with the Two-Fluid model (TFM) approach. The difference between experimental and simulated solids flowrate was less than 20% for different operating conditions with the feeders. From the validated TFM simulations, details on the gas-solid flow dynamics in the feeders and riser were verified by means of volume fraction contours, and velocity vectors for gas and solid phases. Finally, new operating conditions and different feeder and riser geometries were numerically investigated for the spouted bed feeder, and the maximum solid flowrate could be increased from 11 to 30 g/s. The simulations proved to be reliable and cost-effective tools to optimize spent coffee grounds handling or to implement the feeders in larger-scale commercial applications.
Mudanças identificáveis no nível de Hemerobia resultantes da dinâmica do uso da terra na Bacia Hidrográfica do Rio Grande Comitán (Chiapas, México). uma análise do período 1999-2019
(Universidade Federal de São Carlos, 2020-08-24) Aguilar López, Flor Magali; Santos, José Eduardo dos; https://lattes.cnpq.br/8533387365058570; https://lattes.cnpq.br/1545330182318071
The intensification of agricultural and non-agricultural anthropic uses in a watershed generates a high dependence on the consumption of local natural resources, in contrast to the increase in the condition of hemeroby and the reduction of the capacity for self-regulation, due to the decline in naturalness. This research evaluated the changes in the hemeroby levels resulting from the land use and cover dynamic, using the Index Distance to Nature (D2N) as a tool for the environmental monitoring and planning of the Rio Grande Comitán watershed (Chiapas, Mexico), over the 20-year period (1999 - 2019). The classification and quantification of the land use and cover of the watershed were obtained based on the images Land-Sat-5 (1999 and 2009) and Land-Sat 8 (2019), through the Semi-automatic Classification module in ArcGis software 10.5. The total area of the land uses natural class (native vegetation, wetlands and riparian forest) reduced, in contrast to the increase in anthropic agricultural use (agriculture and bare soil), as the most representative land use class, over the 20-year period (1999 to 2019). Five (5) hemeroby levels were identified for the Rio Grande Comitán watershed, with some adaptations to contemplate the biotic and cultural local characteristics, whose quantitative variations in the areas evidenced the anthropogenic pattern trajectory, over the period 20 years. This scenario resulted from the increase of the areas of the Cultural hemeroby level (agriculture and bare soil), Artificial (urban area and road network) and Artificial with natural elements (rural settlements, mining and airport), in contrast to the reduction of the areas of the Near to Natural hemeroby level (natural areas and aquatic environments) and Altered hemeroby level (pastures), over the period of 20 years. The analysis of the land use transition matrix, between the years 1999 - 2009/2009 - 2019, and 1999 - 2019, showed that, over the period of 20 years, about 40% of the total watershed area remained with the same spatial composition of land uses. In the remaining total area (60%), the main transition values were represented by the reduction of the areas of the hemeroby level Near to Natural and Altered, and a consequent increase in the areas of Cultural and Artificial / Artificial with natural elements hemeroby levels. The results of the Index Distance to Nature(D2N), over the 20-year period, confirmed the dynamics of the anthropization process of the Rio Grande Comitán watershed, in which the Near to Natural landscape was reduced and replaced by an anthropogenic landscape, related to the expansion of agriculture and urbanization. The D2N values, over the 20-year period, for the watershed area and for the municipal territories of Comitán de Domíngez, La Independencia and La Trinitária proved to be easy to understand and interpret, in addition to enabling comparative conditions in the international and national context, since the index calculation is related to land use values with different themes and at different spatial scales. The D2N demonstrated the potential to support the decision-making process regarding the environmental planning and monitoring of the watershed, adding the issue of developing a sustainable land use policy. The quantitative spatio-temporal analysis of the dynamics of D2N values, grouped into three and five categories, showed the main changes in the trajectory of anthropic activities that occurred in the Rio Grande Comitán watershed, in the period of 20 years. Particularly, for the 0.35 - 1 range, corresponding to human activities associated with agriculture and urbanization. Quite peculiar to the fraction of urbanization related to the performance of rural settlements (Ejidos), in the form of spaces legally instituted for the effective insertion of campesino and indigenous communities, as part of the history of the issue of land tenure. The reported scenario indicates a trend towards the watershed sustainability, over time, due to the gradual and continuous reduction of naturalness, over the 20-year period. The dynamics of the watershed anthropogenic pattern proves to be extremely dependent on agricultural development policies, as well as on the historical and social context of land tenure in the Rio Grande Comitán watershed region.