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Dam-breaking Flow Simulations by Particle-based Scheme Using Logarithmic Weighting Function
Get PDFThe application of a CPU/GPU-based particle method to dam-breaking incompressible viscous fluid flow problems is presented. The particle approach is based on the MPS (Moving Particle Semi-implicit) scheme using logarithmic weighting function to stabilize the spurious oscillatory solutions for solving the Poisson equation with respect to the pressure fields by using GPU-based SCG (Scaled Conjugate Gradient) method. The physics-based computer graphics for the results of three-dimensional simulation consist of the POV-Ray (Persistence of Vision Raytracer) rendering using marching cubes algorithm as polygonization. Numerical results demonstrate the workability and the validity of the present approach through the dam-breaking flow problem
Detailed CVFEM Algorithm for Three Dimensional Advection-diffusion Problems
Get PDFThe Control Volume Finite Element Method (CVFEM) combines the geometric flexibility of the Finite Element Method (FEM) with the physical intuition of the Control Volume Method (CVM). These two features of the CVFEM make it a very powerful tool for solving heat and fluid flow problems within complex domain geometries. In solving problems in the two-dimensional domains the development of the CVFEM has been well documented. For the three-dimensional problems, while there is extensive reporting on the details of the numerical approximation, there is relatively sparse information on important issues related to data structure and interpolation. Here, in the context of a general 3D advection-diffusion problem, a step-by-step derivation of the CVFEM is provided. Significant emphasis is placed on clearly defining an appropriate geometric data structure and detailing the key elements required to arrive at the final discrete equation. The performance and operation of the resulting 3D CVFEM scheme is highlighted by comparing its predictions against existing analytical solutions
DRBEM Solution of Incompressible MHD Flow with Magnetic Potential
Get PDFThe dual reciprocity boundary element method (DRBEM) formulation is presented for solving incompressible magnetohydrodynamic (MHD) flow equations. The combination of Navier-Stokes equations of fluid dynamics and Maxwell’s equations of electromagnetics through Ohm’s law is considered in terms of stream function, vorticity and magnetic potential in 2D. The velocity field and the induced magnetic field can be determined through the relations with stream function and magnetic potential, respectively. The numerical results are visualized for several values of Reynolds (Re), Hartmann (Ha) and magnetic Reynolds number (Rem) in a lid-driven cavity, and in a channel with a square cylinder. The well-known characteristics of the fluid flow and MHD flow are exhibited. These are the shift of the core region of the flow and the development of the main vortex in the vorticity through the center of the cavity as Re increases. An increase in Ha causes Hartmann layers for the flow at the bottom and top walls. Higher values of Rem result in circulation of the magnetic potential at the center of the cavity. An increase in Re causes symmetric vortices behind the cylinder to elongate through the channel, and an increase in Hartmann number suppresses this elongation
Solution of the Inverse Radiative Transfer Problem of Simultaneous Identification of the Optical Thickness and Space-Dependent Albedo Using Bayesian Inference
Get PDFInverse radiative transfer problems in heterogeneous participating media applications include determining gas properties in combustion chambers, estimating environmental and atmospheric conditions, and remote sensing, among others. In recent papers the spatially variable single scattering albedo has been estimated by expanding this unknown function as a series of known functions, and then estimating the expansion coefficients with parameter estimation techniques. In the present work we assume that there is no prior information on the functional form of the unknown spatially variable albedo and, making use of the Bayesian approach, we propose the development of a posterior probability density, which is explored using the Markov Chain Monte Carlo method (MCMC) implemented with the Metropolis-Hastings algorithm. Moreover, since the scattering and the absorption coefficients, which are in fact the primary properties that produce the single scattering albedo, are considered unknown, then the optical thickness must also be considered unknown. Thus, in this work, the optical thickness is simultaneously estimated with the spatially variable single scattering albedo. Simulated experimental data have been used for the inverse problem solution considering different functional forms for the spatially variable albedo, and different optical thicknesses of the medium. The results are critically investigated, and the good performance observed demonstrates the feasibility of this approach
Simulations of Three-dimensional Thermal Residual Stress and Warpage in Injection Molding
Get PDFThe three-dimensional (3D) mathematical models for thermal residual stress and warpage are proposed in injection molding, in which the temperature model is rebuilt by considering the phase-change effect to improve the computational accuracy. The 3D thermal residual stress model is transformed into the incremental displacement model so that the boundary conditions can be imposed easily. A modified finite element neural network (FENN) method is used for solving 3D warpage model based on the advantages of finite element method and neural network. The influence of phase-change on temperature is discussed. The numerical simulations of thermal residual stress and warpage are realized, and the influences of processing parameters on thermal residual stress and warpage are studied. The numerical results are in accordance with the results in related literature and the theoretic analysis
Heat transfer studies in a vertical channel filled with aporous medium
No full textThis paper reports the results of an experimental study on the enhancement in the heat transfer from a heated aluminium plate placed in a vertical channeland filled with an aluminium metal foam. Hydrodynamic and heat transfer experiments have been conducted for different foam thicknesses. The results of the hy-drodynamic experiments show no significant variation in the pressure drop with anincrease in the foam thickness. However, an increase in the foam thickness contributes an average heat transfer enhancement of 2 to 4 times over an empty channelfor the same Reynolds number. Correlations for Nusselt number are also developedfor porous and empty channels. From these correlations, the heat transfer coefficient on the heater wall is found to be proportional to the foam thickness for a given Reynolds number. However, for an empty channel, the heat transfer coefficient isfound to be independent of the channel width for a given Reynolds number
Soret driven thermosolutal convection in an inclined porous layer: search of optimum conditions of separation and validity of the boundary layer theory
Get PDFIn this paper we present an analytical and numerical study of Soret convection in an inclined rectangular porous layer saturated with a binary fluid and subject to uniform heat fluxes. In the problem formulation, the Darcy model is considered and the results are presented for wide ranges of RT (50 ≤ RT ≤ 1000), θ(0°≤θ≤180°) and φ(-1 ≤ φ ≤ 1) for Le = 10, where RT, θ, φ, and Le are the thermal Darcy-Rayleigh number, the cavity inclination, the separation parameter, and the Lewis number, respectively. An analytical solution, derived on the basis of the parallel flow approximation, is validated numerically by solving the full governing equations with a finite difference method. It is found that the heat transfer is more sensitive to the variation of the cavity inclination than to the separation parameter while the mass transfer sensitivity is essentially related to positive values of φ in a short range of θ. The thresholds of RT and φ from which the boundary layer approximations can be considered valid (with a maximum deviation of 5% for the numerical results) are determined; they are found to be dependent on θ. For positive values of the separation parameter, the boundary layer regime is reached at relatively lower values of RT
Computational Studies on the Transient Electrohydrodynamics of a Liquid Drop
Get PDFThis study aims to gain a detailed understanding of the transient behavior of solitary liquid drops in electric fields at finite Reynolds number. A front tracking/finite difference method, in conjunction with Taylor-Melcher leaky dielectric model, is used to solve the governing electrohydrodynamic equations. The evolution of the flow field and drop deformation is studied for a few representative fluid systems, corresponding to the different regions of the deformation-circulation map. It is shown that for the range of the physical parameters used here, the deformationtime history is governed by one time scale while the fluid flow (characterized by kinetic energy) is governed by two or more time scales. The effect of the material property ratios and the wall on the electrohydrodynamics of the drop is also investigated
Aerothermal Analysis of a Sample-Return Reentry Capsule
Get PDFThe article deals with the aerothermal analysis of a sample-return hypersonic capsule reentering on Earth from an interplanetary exploration mission. The main objective of the work is to estimate the heat flux distribution on the capsule surface and to perform one-dimensional thermal analyses for its ablative heat shield. After a short review of sample-return missions, the numerical models implemented are described and the computational results, obtained along a feasible reentry trajectory, are presented and discussed. Particular attention has been paid to compare the convective stagnation point heat fluxes obtained by means of Computational Fluid Dynamic (CFD) analyses with the ones computed with engineering correlations. A further comparison between CFD and with Direct Simulation Monte Carlo (DSMC), in order to investigate the air rarefaction effects, is reported. The article shows an overall satisfactory agreement between engineering correlation and numerical results and also presents a preliminary dimensioning of the capsule ablative heat shield at the stagnation point
A Theoretical Analysis on Elastic and Elastoplastic Stress Solutions for Functionally Graded Materials Using Averaging Technique of Composites
Get PDFFunctionally Graded Materials (FGMs) are being used in an everexpanding set of applications. For better applications, an analytical methodology using averaging technique of composites is developed to describe the thermo-elastic and thermo-elastoplastic behaviors of a three-layered FGM system subjected to thermal loading Solutions using averaging technique of composites for the stress distributions in a generic FGM system subjected to arbitrary temperature loading conditions are presented. The power-law strain hardening behaviour is assumed for the FGM metallic phase and the stress of the metallic phase are calculated to judge the plastic in this work The stress distributions within the FGM systems are compared with accurate numerical solutions obtained from finite element analyses and good agreement is found