Engenharias
http://hdl.handle.net/10183/19217
2021-04-12T19:07:01ZA modeling assessment of large-scale hydrologic alteration in south american Pantanal due to upstream dam operation
http://hdl.handle.net/10183/216864
A modeling assessment of large-scale hydrologic alteration in south american Pantanal due to upstream dam operation
Jardim, Pedro Frediani; Melo, Maria Marcella Medeiros; Ribeiro, Larissa de Castro; Collischonn, Walter; Paz, Adriano Rolim da
Natural river flow provides the conditions required to sustain freshwater ecosystems, and the greater the departure from the natural regime, the greater the loss of those ecosystems. In South America, new hydropower dams are continuously being constructed and planned in regions within and around the Amazon basin and in the Upper Paraguay river basin, a region notable for the Pantanal, a huge wetland ecosystem that is largely dependent on the flow regime of the Paraguay river and its tributaries. In this context, it is meaningful to examine the hydrological changes caused by the major Manso dam, that is operating since 2001 at the headwaters of one of the major tributaries of the Paraguay river. This was done for the same case study by other authors in previous studies using only gauging stations data. However, those previous assessments were limited due to the confounding effects of climate variability and the necessity of relatively long term observed time series. Here, we applied a modeling approach to evaluate the changes in hydrological regime caused by Manso dam operation. Our modeling approach was based on the combination of the MGB large-scale hydrologic model with the SIRIPLAN large-scale wetland model. The models were applied, using river reaches from 2 to 10 km, in two scenarios during the period from 2003 to 2015. In the first scenario we used naturalized streamflow at the dam site as input to the hydrological model. In the second scenario we used observed reservoir outflow time series as input to the hydrological model. Our results show that Manso dam has a regulation effect that decreases high flows, increases low flows and reduces lateral connectivity. The decrease in high flows is more pronounced in the region upstream of the Pantanal floodplain, but not limited to, while increase in low flows extends into Pantanal. Timing of maximum and minimum flows is less affected, except for the river reach immediately downstream of the dam. Our results improve the assessment of spatial patterns of hydrologic alteration, giving more confidence in the assessment of magnitude and spatial extension of the effects of Manso dam in the Pantanal region.
2020-01-01T00:00:00ZAnalytical solution of deep tunnels in a strain-hardening elasto-plastic rock mass
http://hdl.handle.net/10183/216768
Analytical solution of deep tunnels in a strain-hardening elasto-plastic rock mass
Maghous, Denise Bernaud; Quevedo, Felipe Pinto da Motta
Excavation of tunnels produces a redistribuition of stresses and induces deformations in the rock mass around the tunnel’s cross section. In the case of elasto-plastic behavior of rock mass, plastic zones may appear. It is important to quantify the influence of this zone on the overall response of the tunnel. In this paper, we deduce a fully analytical solution in terms of displacements and stresses around a circular deep tunnel. The aim here is not to replace a 3D numerical calculation. This kind of analytical calculation are only useful to have a good understanding of the tunnel behavior in the preliminary phases of the project. For example, to perform parametric studies useful to choosing good parameters to introduce in a 3D numerical calculation. A homogeneous and isotropic rock mass is considered. For elasto-plastic behavior, the Tresca’s constitutive model with associate flow rule and Mohr-Coulomb’s constitutive model with non-associate flow rule are considered. For both, the idealized stress-strain curve presents a linear istropic hardening law. A geostatichydrostatic state of initial stresses and infinitesimal strains is assumed. The analytical solutions are compared with the FEM solutions demonstrating excellent agreement.
2020-01-01T00:00:00ZInverse design methodology to optimize sensible thermal energy storage systems working as rectifiers
http://hdl.handle.net/10183/216712
Inverse design methodology to optimize sensible thermal energy storage systems working as rectifiers
Andriotty, Tiago Haubert; Schneider, Paulo Smith; Rodrigues, Letícia Jenisch
The main goal of this paper is to present a methodology to achieve the optimal design of a sensible thermal energy storage system (T3S) working as a thermal rectifier. The system was composed by the heat storage material (HSM), distributed in a set of flat parallel plates, and the working fluid, both modeled by a simplified lumped element model (LEM). The ratio of operational outlet temperature range to source temperature oscillation is defined as the designed rectifying duty. Optimization procedure combines a one‐factor‐at‐a‐time (OFAT) and line search strategies in order to find optimal T3S design that satisfies the designed rectifying duty with the minimum HSM mass. The inverse design philosophy is applied to the optimal results to generalize the T3S dynamic behavior as functions fitting curves of the number of transfer unit (NTU) and the time constant τ. These fitting curves can be used to identify T3S geometric parameters, HSM thermal properties, fluid inlet conditions, among others, which guarantee the outlet fluid temperature to be found within the operational range with the minimum HSM mass. A three step‐by‐step sequence design methodology is presented and detailed, based on design charts from the NTU and τ correlations. The proposed design methodology is able to find the optimal plate length L, plate thickness es, and plate distance e f that satisfies the designed rectifying duty for three test cases. These optimal T3S designs are simulated in a computer fluid dynamics (CFD) code, with deviations below 1.5% between the designed rectifying duty and the one simulated. With the proposed approach, several design solutions or configurations can be found for T3S operating as a thermal rectifier based on NTU and τ fitting curves submitted to a sinusoidal cyclic temperature input and with constant and uniform HSM and fluid properties.
2019-01-01T00:00:00ZHybrid system simulation to supply heated air to a solar food dryer
http://hdl.handle.net/10183/216710
Hybrid system simulation to supply heated air to a solar food dryer
Rodrigues, Letícia Jenisch; Basso, Diego Morello
The intermittence of solar radiation, due to continuous rainy or cloudy days, is a limitation of simple and small solar dryers. These conditions often make them impossible to use. By including storage systems (thermal accumulation) and/or auxiliary energy sources, drying processes or dehydration can be conducted continuously, even during periods of low insolation. Therefore, the present work simulates and evaluates the thermal and energetic behavior of a hybrid system for heating the air that is directed to the dehydration chamber of a solar food dryer. The software selected for the simulation was TRNSYS. The simulated hybrid system consists of a flat plate solar collector and an arrangement of electrical resistors that guarantee the entry of air, at a constant temperature, into the dehydration chamber. The target temperature selected is 70 °C, and the absence of food products in the chamber is assumed. An arrangement with four electric resistors totaling 1900 W, with three different powers of 1000 W, 500 W, and 200 W proved adequate to guarantee the entrance of air at a constant temperature when considering the climatic conditions of a city in the South of Brazil.
2020-01-01T00:00:00Z