Papers by Keyword: Numerical

Abstract: This work presents a non-steady state and three-dimensional mathematical modeling to predict moisture transport (based on the Langmuir-Type Model) inside the vegetable fiber-reinforced composite materials. The numerical solutions of the governing equations have been obtain using the finite-volume method. The model was apply for vegetable fiber-reinforced polymer composites. Emphasis to the geometrical dimension effect of the composite in the water absorption process was given. Results of the average moisture content, free and entrapped water molecules concentration kinetics and free and entrapped water molecules concentration distributions inside the material along the process are shown and analyzed. In the distributions of the analyzed properties, it was observed that the geometric dimensions of the composite has influence in the water absorption process.

Abstract: Cashew is a fruit with high nutritional value and great economic importance in the Northeast region of Brazil, however, due to high moisture content, it is highly perishable. Freezing is one the most efficient methods for conservationof biological products, especially, fruits and vegetables. Then, the optimizationof the freezing process by numerical simulation is crucial. In this sense, the objective of this work was to investigate the influence of the moisture content on the cooling and freezing processes of cashew appleby using thecomputational fluid dynamics technique. Results of the cooling and freezing kinetics of the cashew apple and temperature distribution inside the fruitduring these processes are presented and analyzed. It was verified that the variation inthe initial moisture content had small effect in the total time of the process, however the samples with higher moisture content presented higher heat transfer rate during the cooling period and lesser during the freezing period.

Abstract: Freezing is one the most efficient methods for conservation, especially, fruits and vegetables. Cashew is a fruit with high nutritional value and great economic importance in the Northeast region of Brazil, however, due to high moisture content, it is highly perishable. The numerical study of the freezing process is of great importance for the optimization of the process. In this sense, the objective of this work was to study the cooling and freezing processes of cashew apple using computational fluid dynamics technique. Experiments of cooling and freezing of the fruit, with the aid of a refrigerator,data acquisition system and thermocouples, and simulation using Ansys CFX^® software for obtain the cooling and freezing kinetics of the product were realized. Results of the cooling and freezing kinetics of the cashew apple and temperature distribution inside the cashew apple are presented, compared and analyzed. The model was able to predict temperaturetransient behavior with good accuracy, except in the post-freezing period.

Abstract: Food drying is one of the most used methods of preservation. To accurately describe moisture migration within biological products (grains, fruits, vegetables, etc.) during drying and explain the effects of this process on the quality of the material, have been proposed several mathematical models, but few incorporate the phenomena of simultaneous heat and mass transport applied to complex geometry. In this sense, this paper aims to present a mathematical model, based on the thermodynamics of irreversible processes to describe the heat and mass transfer (liquid and vapor) during the drying of bodies with oblate spheroidal geometry. This model was applied to describe drying of lentil, considering the variables transport coefficients and equilibrium conditions at the surface of the solid. Results of the average moisture content, average temperature, liquid flux, vapor flux, and moisture content and temperature distributions inside a lentil kernel during drying process, at different temperatures (40 and 60 oC) were presented and analyzed.

Abstract: The use of externally-bonded composite materials for strengthening and rehabilitation of existing structures is among the most popular reinforcement techniques. Technologies, such as Fabric Reinforced Cementitious Matrix (FRCM) have been recently developed to address some of the issues of Fiber Reinforced Polymers (FRP), such as sensitivity to elevated temperatures and UV, impermeability, restricted application in presence of moisture or uneven substrate. For a detailed strengthening design with FRCM composites, the mechanical properties of the materials are required. Analytical models in literature discuss the interaction between the FRCM matrix and fabric using a fracture mechanics approach. These analytical laws were simplified using a trilinear curve in which a constant branch correlated to the friction is added. In the United States, “Acceptance Criteria AC434” includes the test methods to evaluate the mechanical properties of the FRCM through a direct tensile test which uses clevis grips. The material characterization per AC434 is in harmony with ACI 549.4R design guidelines. This study deals with the analysis of FRCM materials using 2D Augmented-Finite Element Method (A-FEM) approach. Constitutive material behaviors were used to implement on A-FE model, which can predict the failure modes of the composite material. The damage of the mortar was described by a trilinear curve, and the number and position of the cracks were fixed preliminarily. The fabric was modelled as a continuum layer attached to the mortar with no-thickness cohesive elements. The cohesive law between fabric and mortar was taken from the literature. The tensile test on the FRCM coupon with one layer of fabric was numerically modeled and compared to the experimental stress-strain curves. Results show that the numerical curves matched the experimental ones and capture the three branches of the FRCM constitutive law as well as the failure mode. This modelling tool will allow researchers to predict the constitutive law of an FRCM mater

Abstract: Reinforced concrete flat slabs are frequently used structural members in building construction. One of the most dangerous form of structural failure of these system is punching of the slab by support. The best way how to verify the reliability of standard model for the assessment of punching capacity is comparison of the resistance obtained from the experiments, with the resistances calculated according to the standard. To determine the reliability of the standards a large database of test results is required, but from economical point of view, it is not possible to prepare so many tests in order to fulfill this requirement. The problem can be solved by non-linear analysis which is a tool that allows to substitute actual tests with theoretical ones. The paper deals with non-linear analysis of punching of flat slabs, where the numerical model of flat slab specimens using results taken from the experimental program carried out at the laboratory of Slovak University of Technology. The task was to find the suitable non-linear material model for concrete and reinforcement, choose the proper boundary conditions, the correct load application and choose the appropriate way of modeling. The correct adjustment of the numerical model allows to carry out parametric study of flat slabs.

Abstract: Composite structures is a combination of structural steel shapes and reinforced concrete and these two materials are combined in such a way to benefit each material characteristic. This paper investigates the behaviour and strength of axially loaded concrete encased steel composite columns. A nonlinear 3-D finite element (FE) model has been developed to analyse the inelastic behaviour of steel, concrete, and longitudinal reinforcement as well as the effect of concrete confinement on fully encased composite (FEC) columns. The model has been verified against the experiments conducted in the laboratory under concentric gravity loads. It has been found that the FE model is capable of predicting the nonlinear behaviour of the FEC columns up to failure with good accuracy. The capacities of each constituent of FEC columnssuch as steel-I section, concrete and rebars were also determined from the numerical study. Concrete is observed to provide around 57% of the total axial capacity of the column whereas the steel I-sections contributes to the rest of the capacity as well as to the ductility of the overall system. The nonlinear FE model developed in this study is also used to explore the effects of concrete strength on the behaviour of FEC columns under concentric loads. The axial capacity of FEC columns has been found to increase significantly by increasing the strength of concrete.

Abstract: Thermal conductivity of composites is anisotropic in nature and data about thermal conductivity of resin facilitates to reduce stresses related to shrinkage of composites during cure and mismatch in thermal expansion coefficients. Before conducting experiments to determine thermal conductivity of various composites, knowledge about effect of different parameters influencing thermal conductivity is essential. The increasing use of composites, for various applications, emphasizes its importance/significance in the thermal property analysis of an engineering system. Published literature is rich with investigations of mechanical properties of composites, but fewer publications are focused on thermal properties. Several publications addressing different theoretical approaches for predicting thermal conductivity of composite materials have been noted. Various theoretical approaches are used to yield the thermal conductivity of a composite material so that the heat flow in anisotropic composite material in any direction can be estimated. In this paper few models will be considered and a theoretical study on thermal conductivity uncertainties will be conducted and discussed. The results identified the need and importance of carrying out further investigations on thermal behavior of composites materials.

Abstract: The objective of this study was to investigate numerically heat and mass transport during drying of grains with particular reference to bean and rough rice. The proposed mathematical models based on the Fick’s and Fourier’s Laws consider constant physical properties and convective boundary condition at the surface of the solid. The solutions of the governing equations were performed using ANSYS CFX^® software. The grains were regarded as an ellipsoid of revolution. Results of the drying and heating kinetics and moisture content and temperature distributions in the grains along the drying process are presented and analyzed.

Abstract: A numerical study is conducted to investigate the turbulent periodic flow and heat transfer characteristics in a channel fitted with sinusoidal wavy-baffles placed on upper and lower walls. The finite volume method is introduced and implemented with the SIMPLE algorithm. The flow structure, friction factor and heat transfer characteristics for different wavy-baffle configurations are evaluated. According to numerical result, the maximum thermal performance is found to be 1.22–1.66 times to smooth channel corresponding to the baffle a/H=0.75 and b/H=0.10. Consequently, the application of wavy-baffles can be utilized effectively to enhance the thermal performance of solar air heater.