Abstract: This paper presents the validation of active and passive, made by a dissipation beach, numerical absorbing methods implemented in RANS-VOF FLUENT® code for modelling long time series of wave propagation interacting with coastal structures. Verification of both numerical techniques was performed in 2D – wave flume, and 3D – wave tank, this one using a multiple active absorption wave makers. The active absorption wave maker allows maintaining the incident wave generation and the mean water level along the time. Good results were obtained for 2D and 3D applications for active absorption wave maker at the generation boundary and both numerical beach and active absorption at the end of the flume/tank.
Abstract: With the increasing demand for energy and fuels in Brazil, the storage of liquid fuels in multiple tanks is becoming much more usual, posing challenges from the point of view of fire safety. To study this type of phenomenon and to evaluate its possible causes, detecting failures such as ones in design and erection of storage systems or in detection and protection equipment, numerical simulations are performed based on real data. This work presents numerical simulations of a small-scale tank for gasoline storage, based on an experimental study reported in literature. The present research shows results related to temperature in the region adjacent to the tank on fire, fuel mass burning rate, heat release rate and average flame height. Comparisons are made between numerical and experimental results, as well as with available literature results for similar conditions. In addition to gasoline type C (which has anhydrous ethanol in its composition), also gasoline type A (anhydrous ethanol free) is considered. The results obtained for simulations with gasoline type A presented better agreement with literature data than those for gasoline type C, the differences being due to the variable composition of the type C fuel. For example, the reported fuel mass burning rate for gasoline in literature is 0.045 kg/(m2∙s), while the present simulations provided values of 0.038 kg/(m2∙s) for type C and 0.047 kg/(m2∙s) for type A.
Abstract: This work presents a numerical study of the phase change process of PCM (Phase Change Materials) stored in spherical cavities. The numerical model is two-dimensional and it is composed by the equations of conservation of mass, momentum, energy and volumetric fraction, which are modeled using the enthalpy-porosity technique. The computational mesh is tetrahedral, with refinements on regions that have large thermic and fluid dynamic gradients. The numeric model was validated with result from literature. It was studied the melting process of PCM RT35, RT 55 and RT 82 in spherical cavity with constant wall temperature. Four diameters of spheres D were used (40, 60, 80 and 100 mm) and three temperature differences ΔT (10, 20 and 30 oC) between the wall temperature and the melting temperature of the PCM. Liquid fraction results from the 36 cases studied are presented. It was observed that the time required to reach a certain liquid fraction increases with the diameter and reduces with the increment of ΔT, being possible to predict the fusion time by knowing the characteristic length of the sphere. The largest percentage reduction of the fusion time was obtained with ΔT = 10 oC – 20 oC for all the D considered. The shortest fusion time was obtained with the largest ΔT combined with the smallest D. It is possible to see the dependence of the liquid fraction results in relation with the PCM properties and the its independence in relation its melting temperature, since all the PCM studied presented equal fusion time for the same ΔT and D.
Abstract: This article applies the constructal design method to analyze how to improve the thermal performance of earth-air heat exchangers (EAHE) composed by four ducts. The paper evaluates two types of arrangements for which the centers of the ducts take the shape of rectangles and diamonds. Under volumetric constraints, the vertical Sv and horizontal Sh spacings between the ducts are left free to vary. The objective is to maximize the magnitude of the EAHE instantaneous thermal potential P which is an average of the differences between the temperatures at the ducts outlets and inlets at any instant of time. The temperature fields are computed through numerical simulations, adopting a verified and validated three-dimensional model. Among the results, this work shows how the design can raise by 11% the annual thermal efficiency of the EAHE.
Abstract: The motion of the free-surface inside a surface-piercing vertical cylindrical tube can be seen as a simplified approximation of an oscillating-water-column ocean-wave energy-converter (OWC-OWEC). In the present work the IHFOAM code, which solves the Reynolds-averaged Navier-Stokes (RANS) equations by a finite-volume method using the volume-of-fluid (VoF) technique, was used to simulate the action of a regular wave on the free-surface inside a vertical cylinder open to the atmosphere. In this paper the results obtained by IHFOAM are compared with other numerical results and with experimental data, showing a good correspondence between these results. In this way the IHFOAM code was verified (by comparison with other numerical results) and validated (by comparison with experimental data).
Abstract: In this work, the Analytical Discrete Ordinates Method (ADO method) is used to provide a closed form solution for a class of one-dimensional neutron transport problems in Cartesian geometry, considering heterogeneous media with linearly anisotropic scattering effects. In this context, the mathematical model will describe a steady-state phenomenon, with neutron sources located inside and on the boundaries of the domain of interest. In the process, the integro-differential transport equation is transformed into an ODE system by the SN angular discretization, which homogeneous solution is obtained with a quadratic eigenvalues problem with reduced order. A particular solution in terms of constants is used. To validate the code, the method and provide benchmark results, test problems will be treated and results will be discussed.
Abstract: The methods of asymptotic homogenization, domain decomposition and finite elements are combined for the computation of the effective thermal conductivity of periodic biphasic fibrous composites with interfacial thermal resistance. The asymptotic homogenization method is used to obtain the so-called local problems on the periodic cell whose solution allows the calculation of the effective conductivity tensor. The numerical solution of the local problems requires a special treatment because of the temperature discontinuity on the interfaces due to the thermal barrier. In the present work these problems are decomposed into two, one for each phase, linked via a coupling condition. The finite element method, implemented in the software FreeFEM++, is employed to solve the resulting problems on each phase. FreeFEM++, which is based on the variational formulation of the problems, potentially allows to consider arbitrary shapes for both the fiber and the periodic cell cross sections. Numerical results for a square periodic cell with fibers of circular cross-section are presented and compared with results from other reported approaches.
Abstract: Numerical models have been widely used to simulate and predict the behavior and transport of oil spills in marine environments. Their behavior is governed by physical, chemical and biological processes which are related to the hydrocarbon properties, hydrodynamic and weather conditions, and other environmental variables. The transport and interactions of oil particles were evaluated in simulations reproducing two oil spills recorded in the northern part of the Southern Brazilian Shelf (SBS). The numerical simulations were performed using the ECOS (Easy Coupling Oil System) model coupled to the three-dimensional hydrodynamic module TELEMAC3D. The hydrodynamic model provides the variables needed by oil spill model to calculate and infer the properties and behavior of the oil slick. The results indicate that the local wind forcing is the most important factor in determining the oil fate, followed by the intensities and directions of coastal currents. Regarding the events, in 2012 the oil reached the coast after 10 hours of the leak while in 2014 it was transported towards the ocean. The simulation strategy used in this article did not prove to be appropriate for estimates of the oil risk in the region, due to the distinct susceptibility responses between the events simulated.
Abstract: This paper describes the analysis of the propagation of regular and irregular waves in a flume by using Fluent® model, which is based on the Navier-Stokes (NS) equations and employs the finite volume method and the Volume of Fluid (VoF) technique to deal with two-phase flows (air and water). At the end of the flume, a numerical beach is used to suppress wave reflections. The methodology consists of adding a damping sink term to the momentum equation. In this study, this term is calibrated for three cases of regular incident waves (H = 1 m, T = 5, 7.5, and 12 s) by varying the linear and quadratic damping coefficients of the formulation. In general, while lower values of damping coefficients cause residuals on the free surface elevation due to wave interactions with the outlet boundary, reflection occurs on the numerical beach when higher values are used. A range of optimal damping coefficients are found considering one of them null. In one of these cases, temporal series of free surface elevation are compared with theoretical ones and very good agreement is reached. Afterwards, an irregular wave propagation, characterized by a JONSWAP spectrum, is investigated. Several gauges along the flume are evaluated and good agreement between the spectrum obtained numerically and the ones imposed at beginning of the flume is verified. This study shows the capacity of NS models, such as Fluent®, to simulate adequately regular and irregular wave propagations in a flume with numerical beach to avoid reflections.