Jeferson Avila Souza

Notional all-electric ship thermal simulation and visualization

The impact of unpredicted or unplanned thermal disturbances on any future all-electric ship may well lead to unexpected and untimely failure of mechanical-electrical systems (e.g., power electronics, high power sensors, and pulsed weapons) to the detriment of the ships combat mission. The high power, rapid transients, and harsh environment expected to be imposed on both the electrical and thermal systems may well be unique to this class of ship. In order to develop the thermal analysis, a comprehensive visualization tool to display the temperature and heat dissipation distributions in the entire ship has been developed. This tool includes a simplified physical model, which combines principles of classical thermodynamics and heat transfer, resulting in a system of three-dimensional differential equations which are discretized in space using a three-dimensional cell centered finite volume scheme. Therefore, the combination of the proposed simplified physical model with the adopted finite volume scheme for the numerical discretization of the differential equations is called a volume element model (VEM). In this work, a 3D simulation is performed in order to determine the temperature distribution inside the ship for six different operating conditions. Visit visualization tool is used to plot the results.

Notional all-electric ship systems integration thermal simulation and visualization

This work presents a simplified mathematical model for fast visualization and thermal simulation of complex and integrated energy systems that is capable of providing quick responses during system design. The tool allows for the determination of the resulting whole system temperature and relative humidity distribution. For that, the simplified physical model combines principles of classical thermodynamics and heat transfer, resulting in a system of three-dimensional (3D) differential equations that are discretized in space using a 3D cell-centered finite volume scheme. As an example of a complex and integrated system analysis, 3D simulations are performed in order to determine the temperature and relative humidity distributions inside an all-electric ship for a baseline medium voltage direct current power system architecture, under different operating conditions. A relatively coarse mesh was used (9410 volume elements) to obtain converged results for a large computational domain (185m×24m×34m) containing diverse equipment. The largest computational time required for obtaining results was 560 s, that is, less than 10 min. Therefore, after experimental validation for a particular system, it is reasonable to state that the model could be used as an efficient tool for complex and integrated systems thermal design, control and optimization.

Influence of calcium carbonate on RTM and RTM light processing and properties of molded composites

In the RTM light composite manufacturing process, inorganic fillers are commonly added to the resin to reduce cost and alter the final composite properties, especially rigidity, even though they also adversely affect processability. The aim of this study is to evaluate resin characteristics, reinforcement permeability, and mechanical properties of the composite and analyze the detrimental effects when a variable amount of calcium carbonate (CaCO3) is added to the resin. The addition of calcium carbonate increased the viscosity and gel time of the resin and considerably decreased the permeability of the reinforcement and therefore the expected process productivity. Besides, Barcol hardness, short-beam strength, and elastic modulus increased for higher CaCO3 content, whereas Izod impact, flexural, and tensile strengths decreased. Besides, the coarser CaCO3 filler particles managed to penetrate only partially into the fiber-rich layer of the combination mat used, which comprised of a PP flow media core and glass fibers at the surface.

Temperature and Pressure Drop Model for Gaseous Helium Cooled Superconducting DC Cables

The need to transfer large amounts of power in applications where cabling weight and space are a major issue has increased the interest in superconducting cables. Gaseous helium and neon are being considered as possible coolants due to their suitability for the expected operating temperature ranges. Gaseous helium is preferred due to its higher thermal conductivity and relatively lower cost than neon. This paper enhances a previously presented mathematical model of a superconducting cable contained in a flexible cryostat by including flow pressure drops. In this way, the model is capable of properly sizing and minimizing fan power, and allows the prediction of system response to localized heating events (e.g., quenching). A volume element model approach was used to develop a physics model, based on fundamental correlations, and principles of classical thermodynamics, mass and heat transfer, which resulted in a system of ordinary differential equations with time as the independent variable. The spatial dependence of the model is accounted for through the three-dimensional distribution of the volume elements in the computational domain. The model numerically obtains the temperature distribution under different environmental conditions. Pressure drop calculations are based on realistic correlations that account for the wavy nature of the coolant channels. Converged solutions were obtained within the imposed numerical accuracy even with coarse meshes.

Three-dimensional numerical modeling of RTM and LRTM processes

Resin Transfer Molding (RTM) is a manufacturing process in which a liquid resin is injected into a closed mold pre-loaded with a porous fibrous preform, producing complex composite parts with good surface finishing. Resin flow is a critical step in the process. In this work, the numerical study of the resin flow in RTM applications was performed employing a general Computational Fluid Dynamics software which does not have a specific RTM module, making it necessary to use the Volume of Fluid method for the filling problem solution. Examples were presented and compared with analytical, experimental and numerical results showing the validity and effectiveness of the present study, with maximum difference among these solutions of around 8%. Besides, based on the computational model for the RTM process, a new computational methodology was developed to simulate Light Resin Transfer Molding (LRTM). In this process, resin is injected into the mold through an empty injection channel (without porous medium) which runs all around the perimeter of the mold. The ability of FLUENT® package to simulate geometries which combine porous media regions with open (empty) regions was used. Two specific cases were simulated, showing the differences in time and behavior between RTM and LRTM processes.

Thermal Modeling of Helium Cooled High-Temperature Superconducting DC Transmission Cable

The recent increase in distributed power generation is highlighting the demand to investigate and implement better and more efficient power distribution grids. High-temperature superconducting (HTS) DC transmission cables have the potential to address the need for more efficient transmission and their usage is expected to increase in the future. Thermal modeling of HTS DC cables is a critical tool to have in order to better understand and characterize the operation of such transmission lines. This paper introduces a general computational model for a HTS DC cable. A physical model, based on fundamental correlations and principles of classical thermodynamics, mass and heat transfer, was developed and the resulting differential equations were discretized in space. Therefore, the combination of the physical model with the finite volume scheme for the discretization of the differential equations is referenced as Volume Element Model, (VEM). The model accounts for heat transfer by conduction, convection and radiation obtaining numerically the temperature distribution of superconductive cables operating under different environmental, operational and design conditions. As a result, the model is expected to be a useful tool for simulation, design, and optimization of HTS DC transmission cables.

Three-dimensional launch simulation and active cooling analysis of a single-shot electromagnetic railgun

An electromagnetic railgun is one of the applications of electromagnetic launchers, which are devices used to accelerate projectiles to velocities exceeding those attained with conventional propelling systems. A magnetic field is generated when current flows through two conductive rails connected by a moving armature. The current that passes through the rails exerts an electromagnetic force on the armature and causes it to accelerate to high speeds. In this work, a three-dimensional transient model for the thermal and electromagnetic solutions of the launch process is presented. The model accounts for the determination of the current and temperature profiles inside the rails, the projectile movement, and the cooling process after the first launch. Focus is given to the thermal management where five different arrangements, one without cooling and four that include cooling channels, are studied. A 10 to 50 K reduction in the peak temperature was obtained with the inclusion of cooling channels when compared to the no-cooling-channel case. It was also shown that the position and size of these channels can be optimized in order to reduce this peak temperature.

Constructal Design of High-Conductivity Inserts

Bejan presented the Constructal Theory by solving an optimization problem for the cooling of a heat generating volume [1]. The proposed problem was “how to collect and channel to one point the heat generated volumetrically in a low conductivity volume of given size.” The proposed approach defined an elemental construct for which the geometry was optimized. The elemental construct had rectangular shape and consisted of two regions: one region with a low-conductivity material and heat generation and a second region with high-conductivity material that was used to conduct the generated heat to the exterior through one end (Fig. 6.1a). The fraction of high-conductivity material was fixed. More complex forms (assemblies) were obtained by combining the optimized elemental form as shown in Fig. 6.1b–d.

Two-dimensional control volume modeling of the resin infiltration of a porous medium with a heterogeneous permeability tensor

Resin Transfer Molding (RTM) is a polymer composite processing technique widely used in the aeronautics and automotive sectors. This paper describes the numerical simulation of the RTM process where Darcys law was used for the mathematical formulation of the problem. A control volume finite element method was used for the determination of pressure gradients inside the mold, and a geometric reconstruction algorithm is used for the resin flow-front determination. Permeability of the medium was considered either a constant or a two dimensional tensor. The application was validated by direct comparison with literature data and good qualitative and quantitative agreement was obtained. The finite volume method was built to be used with a two-dimensional unstructured grid, hence allowing the analysis of complex geometries. The results showed that the proposed methodology is fully capable of predicting resin flow advancement in a multi-layer (with distinct physical properties) reinforced media.

Resin transfer molding process: a numerical and experimental investigation

Resin Transfer Molding (RTM) is one of the composite manufacturing technique that consists in injecting a resin pre-catalysed thermosetting in a closed mold containing a dry fiber preform, where the resin is impregnated. In this sense, the aim of this research is to study theoretically and experimentally the RTM process. Experimental and simulations of the rectilinear infiltration of polyester resin (filled and non filled with CaCO 3 ) in mold with glass fiber preform were performed in cavity with dimensions 320 · 150 · 3.6 mm. Numerical results of the filling time and fluid front position over time were assessed by comparison with experimental data and good accuracy was obtained. It was verified that, the CaCO 3 content affect resin velocity during filling, the permeability of the reinforcement and resin viscosity, thus the filling time is affected strongly.