Kamyar Haghighi

Rill erosion and morphological evolution: A simulation model

A mathematical model is advanced to simulate dynamically and spatially varied shallow water flow and soil detachment, transport, and deposition in rills. The model mimics the dynamic process of rill evolution, including variable rates of sediment redistribution along the bed and changes in local bed morphology. The sediment source term in the model uses a point scale, probabilistic relationship based on turbulent flow mechanics and a recently developed sediment transport relationship for rills based on stream power. The interdependent feedback loops between channel bed morphology, local flow hydraulics, and local scour and deposition, within the framework of the full hydrodynamic equations with inertial terms, constitute a mathematical model with the capacity to represent spatial variability and temporal evolution of the rill. Finite elements were applied to numerically solve the hydrodynamic and sediment continuity equations. A series of laboratory flume experiments were performed to evaluate the model. Initial bed slopes were 3, 5, and 7% with step increases of water inflow rates of 7.6, 11.4, and 15.2 L min−1. The soil material used in the flume was a kaolinitic, sandy-clay loam. The rill model equations were solved for increasingly complex cases of spatial and temporal variabilities. The model followed measured patterns of morphological changes as the rill evolved, which suggests that the feedback loops in the model between erosion, bed morphological changes, and hydraulics were adequate to capture the essence of rill evolution.

Finite element analysis of drying with application to cereal grains

A finite element procedure for two sets of non-linear coupled drying models for three-dimensional axisymmetric and two-dimensional problems are presented. The models consider temperature and moisture dependent material properties. The two different solution procedures used are the implicit two-level and the explicit three-level time stepping schemes. Application is made to drying of single soybean, barley and corn kernels. The simulation results from the heat and mass transfer models agree well with the available experimental results. Model one accounts for diffusion of moisture through vapour and liquid phases. Model two assumes that moisture diffuses to the outer boundaries of the kernel in the liquid form and that evaporation takes place only at the surface of the grain. In all simulations, temperature predictions using model one approached the equilibrium temperature faster than model two. The overall grain kernel temperature and moisture predictions from model two were better than model one. The choice of a model depends upon the type of application and availability of material properties.

Grain kernel drying simulation using the finite element method.

A finite element formulation and solution of a set of coupled conductive heat and diffusive moisture transfer equations to improve grain drying simulation of axisymmetric bodies is presented. The model considers the temperature and moisture dependence of the diffusion coefficient, thermal conductivity, and specific heat. It assumes that moisture diffuses to the outer boundaries of the kernel in liquid form and that evaporation takes place only at the surface of grain. Application was made to drying of a barley kernel and predicted results agreed well with the experimental data. The simulated temperature and moisture profiles and gradients are directly usable for stress cracking analyses of grain. The results of the finite element analysis can be used for grain quality evaluation and drying simulation studies.

NONLINEAR FINITE ELEMENT ANALYSIS OF COUPLED HEAT AND MASS TRANSFER PROBLEMS WITH AN APPLICATION TO TIMBER DRYING

A finite element formulation and solution of a set of nonlinear coupled heat and mass transfer equations for porous capillary media is presented. The model considers temperature and moisture dependent material properties and can accomodate diffusion of moisture as either a liquid or a vapor. Application was made to drying of timber and predicted results agreed well with the experimental data.

Conjugate heat and mass transfer in convective drying of porous media

A methodology for the analysis of conjugate problems in the convective drying of porous media is presented. In this study, the interface between porous medium and external convective flow is treated as an internal boundary within a two-phase system rather than a geometric limit. The problems of solid drying and convection boundary layer are connected by expressing the continuity of the state variables and their respective fluxes through the interface. The performance of the proposed methodology is evaluated by applying it to wood-drying problems. The analysis of the drying of porous media as a conjugate problem allows the assessment of the effect of the heat and mass transfer within the solid on the transfer in the adjacent fluid, providing good insight on the complexity of the transfer mechanisms.

A multi-scale stochastic drug release model for polymer-coated targeted drug delivery systems.

A multi-scale mathematical model for drug release of oral targeted drug delivery systems was developed and applied to a commercially available delayed release tablet (Asacol) that delivers 5-aminosalicyclic acid (5-ASA) to the colon. Underlying physical and biochemical principles governing the involved processes (diffusion and dissolution) were employed to develop the mathematical description. Finite element formulation was used to numerically solve the model equations. Molecular dynamics (MD) simulations were used to predict macro-scale transport properties of the drug and the biologic fluid. The effect of pH variability in the gastrointestinal tract environment on the dissolution of the polymeric enteric coating was investigated using the Monte Carlo method. The direct coupling method employed (MD) predicted a sufficiently accurate diffusion coefficient (5.7x10(-6) cm2 s-1) of the drug molecules in reasonable (3 h) computation times. The model was validated using experimental data from in vitro dissolution experiments and provided accurate prediction of the drug release from the delivery system (root mean square error of 5%). The amount of drug entering the systemic circulation, computed from the predicted drug release in varying pH environments in the small bowel, was 15-24%. This range was in good agreement with clinical in vivo data (13-36%) obtained from literature. This research shows that in silico experiments using mechanistic models and stochastic approaches can be used for drug design and optimization and as a decision making tool for physicians.

ADAPTIVE FINITE ELEMENT ANALYSIS OF TRANSIENT THERMAL PROBLEMS

Abstract A new adaptive finite element procedure for the solution of transient heat conduction problems is described. The proposed technique is capable of accounting for the effect of the boundary conditions on the discretization error, which is usually significant in boundary-value problems and is neglected by other researchers. A new adaptive strategy for transient problems considering the error behavior is also presented. The technique can be applied to both linear and nonlinear problems. Several heat conduction problems are used to evaluate the performance of the method. Results obtained show significant improvements when compared with the conventional finite element approach.

CONJUGATE ANALYSIS OF NATURAL CONVECTIVE DRYING OF BIOLOGICAL MATERIALS

ABSTRACT This paper presents a numerical analysis of heat and mass transport during natural convective drying of an extruded com meal plate. The conjugate problem of drying and natural convection boundary layer Is modeled. The finite volume technique was used to discretize and solve the highly nonlinear system of coupled differential equations governing the transport inside the plate. The boundary layer solution was obtained by means of a finite difference software package that utilizes Runge-Kuttas 5th order method to solve the inherent transport equations. A methodology for evaluating the heat and mass transfer coefficients during the numerical simulation was developed and successfully implemented. The results showed that there is no analogy between heat and mass transfer coefficients for this type of problem.

VALIDATION OF A FINITE–ELEMENT STORED GRAIN ECOSYSTEM MODEL

An axisymmetric finite–element model was validated with respect to predicting the heat, mass, and momentum transfer that occurred in upright corrugated–steel storage bins due to conduction, diffusion, and natural convection using realistic boundary conditions. Hourly weather data that included hourly total solar radiation, wind speed, ambient temperature, and relative humidity were used to model the corn temperature and moisture content during storage with no aeration, and with ambient and chilled aeration. Periods of aeration were simulated assuming a uniform airflow rate through the grain mass. Sixteen bins with a capacity of 11.7 t each and instrumented with temperature cables were available to validate the model using two years of measured corn temperatures and moisture contents during summer storage. The average standard error between the experimental and predicted temperatures was 2.4³C (1.1³C to 5.7³C range), and the standard error between experimental and predicted moisture contents was 0.7 percentage points. The average standard error was 1.5³C in three non–aerated bins with sealed plenums when corn temperature was predicted as a function of the natural convection equation. The predicted natural convection effect was not applicable unless the plenum was assumed sealed.

CONJUGATE HEAT AND MASS TRANSFER IN CONVECTIVE DRYING OF MULTIPARTICLE SYSTEMS PART II: SOYBEAN DRYING

Abstract This is the second of two papers concerning conjugate transport in convective drying of multiparticle systems. In the first paper (part 1), a solution methodology for conjugate transport problems was porposed and successfully tested for assemblages of spheres. This paper deals with the application of the proposed methodology to a soybean drying problem. The analysis in this study allowed certain phenomena, that are usually not present in single-kernel and deep-bed drying analyses, to be captured by the drying rate curves. The results presented here reinforce the need to take into account particle interactions when studying the drying mechanisms of multiparticle systems.