A New Characteristic Nonconforming Mixed Finite Element Scheme for Convection-Dominated Diffusion Problem

A characteristic nonconforming mixed finite element method (MFEM) is proposed for the convection-dominated diffusion problem based on a new mixed variational formulation. The optimal order error estimates for both the original variable u and the auxiliary variable σ with respect to the space are obtained by employing some typical characters of the interpolation operator instead of the mixed (or expanded mixed) elliptic projection which is an indispensable tool in the traditional MFEM analysis. At last, we give some numerical results to confirm the theoretical analysis

Simulations of incompressible viscous thermal flows by Lattice Boltzmann method

Ph.DDOCTOR OF PHILOSOPH

Modeling of combustion and propulsion processes of a new concept gun using a gaseous propellant

The combustion light gas gun (CLGG) uses a low molecular weight gas as the propellant to burn, expand and propel the projectile out of the barrel with higher muzzle velocities.In order to better understand the interior ballistic process of CLGG, an multidimensional combustion and flow model for CLGG is established. It contains unsteady Reynolds-averaged Navier-Stokes (RANS) equations, the RNG k

Constitutive Relationships and Models in Continuum Theories of Multiphase Flows

In April, 1989, a workshop on constitutive relationships and models in continuum theories of multiphase flows was held at NASA's Marshall Space Flight Center. Topics of constitutive relationships for the partial or per phase stresses, including the concept of solid phase pressure are discussed. Models used for the exchange of mass, momentum, and energy between the phases in a multiphase flow are also discussed. The program, abstracts, and texts of the presentations from the workshop are included

Modeling and Simulation of Metallurgical Processes in Ironmaking and Steelmaking

In recent years, improving the sustainability of the steel industry and reducing its CO2 emissions has become a global focus. To achieve this goal, further process optimization in terms of energy and resource efficiency and the development of new processes and process routes are necessary. Modeling and simulation have established themselves as invaluable sources of information for otherwise unknown process parameters and as an alternative to plant trials that involves lower costs, risks, and time. Models also open up new possibilities for model-based control of metallurgical processes. This Special Issue focuses on recent advances in the modeling and simulation of unit processes in iron and steelmaking. It includes reviews on the fundamentals of modeling and simulation of metallurgical processes, as well as contributions from the areas of iron reduction/ironmaking, steelmaking via the primary and secondary route, and continuous casting

Detailed Numerical Simulation of Multi-Dimensional Plasma Assisted Combustion

Interaction between flames and plasmas are the guiding thread of this work. Nanosecond Repetitively Pulsed (NRP) discharges are non-thermal plasmas which have shown interesting features for combustion control. They can interact with flames not only through heat, but also chemically by producing active species. In this work, fully-coupled plasma assited combustion simulations are targeted. To achieve this goal, plasma discharge capabilities are built in the low temperature plasma code, AVIP. The corresponding numerical methods, as well as validation cases regarding each set of equations, are first presented. To simulate plasma discharges, the coupled drift-diffusion equations and the Poisson equation are considered. AVIP is coupled to the AVBP code which solves the reactive Navier-Stokes equations to describe combustion phenomena. In a second part, we start by constructing and validating a fully-detailed chemistry for methane-air mixtures in zero-dimensional reactors before reducing it for multi dimensional simulations. The multi-dimensional streamer simulation capabilities of the code are then assessed using simple chemistries. All the validated parts of the code come together in a fully detailed simulation of ignition using NRP discharges. We finish by discussing phenomenological models built upon the knowledge that we gained from fully-detailed simulations. In a last part, finally, attempt to solve the Poisson and generalized Poisson equations using neural networks, which have a potential for speedup compared to classical linear solvers, is carried out

Solid sponges as support for heterogeneous catalysts in gas-phase reactions

Solid sponges combine large specific surface areas and low pressure losses with excellent heat transport properties. Thus, they are promising catalyst supports for endo- and exothermic processes. Nevertheless, design tradeoffs regarding the porosity and window diameter of solid sponges with respect to high catalyst densities, low pressure losses, and high effective thermal conductivities remain unsolved. Therefore, a 2-d pseudo-homogeneous multi-scale reactor model for solid sponges is developed in this work. The model is validated against polytropic lab-scale experiments for the methanation of carbon dioxide in a fixed-bed reactor. In order to quantify and analyze the design tradeoffs, the model is used to solve the outlined multi-objective optimization problem. Moreover, tailored graded solid sponges with an optimal porosity distribution in the radial direction are introduced to successfully resolve the existing design tradeoffs