Defect and Diffusion Forum Vol. 427

Abstract: The modeling of energy transport via radiative transfer is important to many practical high temperature engineering applications. Furthermore, the computation of solutions to the radiative transfer equation (RTE) plays a fundamental part in it. The quasi-random discrete ordinates method was developed as an alternative to mitigate the ray effect found in the classical discrete ordinates method solutions. The former method was originally developed for transport problems with isotropic scattering and it is here extended and tested to problems with linear anisotropic scattering. Its main idea is to approximate the integral term of the RTE by a quasi-Monte Carlo integration. The discrete system of differential equations arising from it can be solved by a variety of classical discretization methods, here computed with a SUPG finite element scheme. The novel developments are tested for selected manufactured solutions. The achieved good results indicate the potential of the novel method to be applied to the solution of radiative transfer problems with anisotropic scattering.

Abstract: The data center industry consumes between 196 and 400 terawatt-hours annually, between 1% and 2% of the world's energy consumption. A high percentage of data center energy consumption is associated with air conditioning and cooling systems. The optimization of the data center cooling process can occur at multiple scales, being one of the most relevant to the generation and heat transfer processes within servers. In this approach, we must study the temperature fields of each server’s components and understand airflow behavior within the server chassis. The present work, in its first stage, performs a thermal and cooling analysis for a two-unit rack server (2U-Rack) using computational fluid dynamics (CFD) techniques via Ansys Fluent code. A geometric server model was developed, considering heat generation in the main electrical components and heat and air mass transfer with the data center. The model was validated by comparing simulation results with the server's sensor values and the results of thermography testing. Following CFD simulation, airflow velocity fields, temperature contours, and sensitivity scenarios were obtained, with the goal of proposing an optimization model that would allow us to improve server heat transfer processes in the following steps.

Abstract: The following work aims to present the numerical solution for a two-dimensional and transient model for heat transfer on storage bins during the period of one year, in which it was supposed that the structure is exposed to ambient temperature, which depends on time. From this hypothesis, it was executed curve fitting of a relation between those quantities, using meteorological data from the city of Pelotas/RS in the year 2021, and the influence that the outside temperature of a bin has over the process of heat transfer that occurs inside the structure was analyzed. Upon executing simulations of heat transfer inside fictitious bins located in this southern Brazilian city, results show that the boundary condition causes considerable variations in grain temperature, which are more intense in points near the bin's surface. Furthermore, it was concluded that containers of least storage show larger variations in inner temperature during the analyzed period when compared to the behavior of bins containing larger sizes.

Abstract: Rice is one of the most consumed cereals in the world, and the cultivation of this crop has significant relevance in the southern region of Brazil. When subjected to inadequate conditions of temperature and humidity, rice becomes susceptible to attacks from pests and fungi and, therefore, care in the storage process is of paramount importance, since this is largely responsible for the quality of the harvest. Such care allows the food to arrive without harm to the consumer. In this sense, the mathematical modeling, among numerous possibilities, allows for evaluating the internal temperature of a silo and, through this, taking preventive measures so that the grains maintain their quality. The objective of this work is to model the heat transfer process in a silo prototype containing rice in husk through the explicit finite difference method for a one-dimensional and transient model considering two approaches centered on the spatial derivative: error of order 2 and 4. In addition, the thermal diffusivity of the grain with average value was analyzed. The results obtained by the solutions were analyzed through graphs and statistical indexes comparing with the experimental data of the literature, and the computer simulation was performed through the Google Colab platform. The chosen methodology proved effective for the work, and the predicted temperatures for the approximations of order 2 and 4 denote similarities both graphically and in the precision of the statistical indexes.

Abstract: Since the emergence of van der Waals equation of state, several equations have been proposed to represent the behavior of pure compounds and mixtures, such as GEOS, which is a new generalized cubic equation of state form that employs a temperature function dependent on two or three adjustable parameters. Recently, multiobjective optimization has started to be applied in equations of state for parameters estimation, due to the conflicting nature of the objective functions. This methodology is attractive because it can be used to compare different models or variants of the same problem, through the trade-off analysis of the so-called Pareto front. In this context, the multiobjective PSO algorithm, based on the Pareto dominance principle, is used in this work for estimating the parameters of the generalized cubic equation of state, by fitting its results to synthetic experimental data of vapor pressure and saturated liquid volume. The performance of the new estimated parameters of the three temperature functions is investigated through the calculation of thermodynamic properties of interest in industry and academia. In addition, comparisons against real experimental data available in the literature are performed.

Abstract: Since the emergence of the van der Waals model, a lot of equations of state have been proposed to represent the pressure-volume-temperature (PVT) behavior of pure compounds, as is the case with GEOS3C, which is a form of generalized cubic equation of state that uses a temperature function dependent on three adjustable parameters. As the predictive capacity of an equation of state is directly related to the use of adequate and efficient methods for estimating the model's parameters, it is advised to use the multiobjective optimization in this class of problems, due to the conflicting nature of the objective functions. In this context, a MOPSO algorithm, based on the Pareto dominance principle, is used to estimate the parameters of the GEOS3C, through the minimization of the deviations in the prediction of different thermodynamic properties: saturation pressure, saturated liquid volume, enthalpy of vaporization and isobaric heat capacity, in order to assess whether it is possible to obtain a model parameterization that is adequate to represent the different properties simultaneously. Comparisons with experimental data available in the literature are performed showing that multiobjective optimization offers new perspectives for improvements in the parameters estimation of equations of state compared to traditional methods.

Abstract: Covid-19 is a highly contagious aero-transmissible virus. Even after two years of its emergence, new strains appear that require strengthening security measures such as social distancing, the use of masks, etc. It is crucial to prevent contamination, and care for the sanity of the air in closed environments, occupied by two or more people. Aerosols expelled by contaminated individuals dissolve in environments and can contaminate individuals regardless of their location. In this project, an air purifier for individual use was proposed to mitigate the risk of contamination by Covid-19 in closed environments. The equipment has been developed and prototyped, but has yet to be presented in the scope of this article. In this phase of the project, a study was conducted through numerical simulation to understand the effect of using this purifier on air circulation and its scope in the environment. Nine scenarios were developed: five two-dimensional and four three-dimensional, subject to different conditions: (i) closed environment, (ii) air infiltration through doors and windows, (iii) air-conditioner use, and purifier use. In individual use of the purifier, even if it is approximately 50 cm from the person in the room, the curtain of “clean air” coming from the purifier has become ineffective due to the existence of another, more intense outlet. The scenario with the airflow from the air-conditioner showed that the higher intensity of the airflow compared to the prototype purifier's airflow, meant that the prototype's airflow could not protect the user from the theoretically contaminated air mixed in the room. When the simulation of the use of the purifier was not done together with the air-conditioner runoff, the purifier proved effective in providing clean air and "protecting" the user with a wind curtain. However, even when the purified air cannot directly protect the user, the effects of the purifier can be beneficial by reducing the contamination of the air in the room as a whole (with a flow rate of 0.016 m3/s or 57.6 m3/h), and potentially reducing the chances of virus infection.

Abstract: The present numerical study proposes the application of the constructal theory for the build of empty channels inserted in a porous domain, representing the liquid resin infusion process. Two different strategies are employed: 1) I-shaped pre-defined configuration for the empty channel, 2) constructive technique (evolutionary) where the empty channel is built from an elemental configuration and using the performance indicator to define the new position of each empty channel element. It is investigated the influence of geometry over the impregnation time and the amount of wasted mass of resin during the process. The same fluid dynamic conditions and the maximum occupation area of the empty channel were defined for the different strategies. The finite volume method (FVM) and volume of fluid (VOF) were used for the solution of mass, momentum, and transport of resin equations, which model the flow of resin/air mixture. Darcy’s law is applied to represent the porous medium resistance. Results showed that the constructive technique was highly promising in the proposition of configurations that reduced the time of impregnation of resin in the porous medium. Moreover, it was observed that, for the present fluid dynamic conditions, giving more freedom for the formation of empty channels shape also led to a reduction of filling time of resin impregnation in the porous mold.

Abstract: The present work proposes the development of numerical tools for solving fluid-structure interaction (FSI) problems where the structure is coupled with cables. For the numerical treatment of fluids in incompressible flow, the Navier-Stokes and continuity equations are discretized using a semi-implicit version of the characteristic-based split (CBS) method in the context of the finite element method (FEM), where linear tetrahedral elements are used. In the presence of moving structures, the flow equations are described through an arbitrary Lagrangian-Eulerian (ALE) formulation and a numerical scheme of mesh movement is adopted. The structure is treated through a three-dimensional rigid body approach and the cable through an elastic model with geometric nonlinearity and spatial discretization by the nodal position finite element method (NPFEM). The system of equations of motion can be temporally discretized using the implicit Newmark and generalized-α methods and a partitioned coupling scheme is used taking into account fluid-structure and cable-structure couplings. The algorithms proposed here are verified using numerical applications.

Abstract: SAFEPORT safety system aims to daily reports to the Sines harbor administration, potential emergency situations regarding ships’ operation in port areas caused by extreme weather-oceanographic conditions, that may occur in the next three days. It consists of a set of numerical models and a qualitative risk assessment and forecasting. It uses forecasts provided offshore of the area under the study of sea agitation, wind and tide. The characterization of the response of the free and moored ships at a berth is performed using numerical models which deal with formulations in the frequency and time domain. The system issue alerts, through danger levels associated with risk levels of exceedance of recommended values for movements and forces imposed on ship mooring systems. SAFEPORT can be adapted to any port. So far, it has been developed and adapted to three terminals of the port of Sines, where three different ships were simulated. This paper presents the developments made to date of the safety system, in terms of its implementation and validation. The numerical models run every day, in real-time mode, in a computer cluster. The results are disseminated on a web page and a mobile application in a variety of formats.