Eulerian–Lagrangian localized adjoint methods for reactive transport with biodegradation

The microbial degradation of organic contaminants in the subsurface holds significant potential as a mechanism for in-situ remediation strategies. The mathematical models that describe contaminant transport with biodegradation involve a set of advective–diffusive–reactive transport equations. These equations are coupled through the nonlinear reaction terms, which may involve reactions with all of the species and are themselves coupled to growth equations for the subsurface bacterial populations. In this article, we develop Eulerian–Lagrangian localized adjoint methods (ELLAM) to solve these transport equations. ELLAM are formulated to systematically adapt to the changing features of governing partial differential equations. The relative importance of retardation, advection, diffusion, and reaction is directly incorporated into the numerical method by judicious choice of the test functions that appear in the weak form of the governing equation. Different ELLAM schemes for linear variable–coefficient advective–diffusive–reactive transport equations are developed based on different operator splittings. Specific linearization techniques are discussed and are combined with the ELLAM schemes to solve the nonlinear, multispecies transport equations. © 1995 John Wiley & Sons, Inc.     

Decomposition method for solving multi-species reactive transport problems coupled with first-order kinetics applicable to a chain with identical reaction rates

A new method for decomposing of multiple solute transport equations, coupled by first-order reactions, is developed. The approach is based on the semigroup theory and reduces the multi-species problem to single-species equations with various initial and boundary conditions. Analytical formulas are derived for all reactants. This new method overcomes some of the limitations that were implicit in previously published algorithms. More exactly, the derivation of closed formulas for a reaction chain with identical reaction rates is possible. The proposed approach is flexible for solving one-, two- or three-dimensional advection-dispersion systems. The methodology is demonstrated on the reductive biodegradation of chlorinated solvents, such as tetrachloroethene (PCE) and trichloroethene (TCE).     

A perturbation solution for bacterial growth and bioremediation in a porous medium with bio-clogging

We investigate a flow problem of relevance in bioremediation and develop a mathematical model for transport of contamination by groundwater and the spreading, confinement, and remediation of chemical waste. The model is based on the fluid mass and momentum balance equations and simultaneous transport and consumption of the pollutant (hydrocarbon) and nutrient (oxygen). Particular emphasis is placed on the study of processes involving the full coupling of reaction, transport and mechanical effects. Dimensional analysis and asymptotic reduction are used to simplify the governing equations, which are then solved numerically.     

Monotone method for equations describing transport phenomena in a Banach space

In this paper monotone methods have been developed for equations arising in transport processes in a Banach space. This method proves the existence of extremal solutions for such equations. The advantage of the method for such type of equations is that the successive iterates are solutions of the corresponding initial value problems.     

Pointwise Estimates and Regularity in Geometric Optics and Other Generated Jacobian Equations

The study of reflector surfaces in geometric optics necessitates the analysis of certain nonlinear equations of Monge‐Ampère type known as generated Jacobian equations. This class of equations, whose general existence theory has been recently developed by Trudinger, goes beyond the framework of optimal transport. We obtain pointwise estimates for weak solutions of such equations under minimal structural and regularity assumptions, covering situations analogous to those of costs satisfying the A3‐weak condition introduced by Ma, Trudinger, and Wang in optimal transport. These estimates are used to develop a C^1,α regularity theory for weak solutions of Aleksandrov type. The results are new even for all known near‐field reflector/refractor models, including the point source and parallel beam reflectors, and are applicable to problems in other areas of geometry, such as the generalized Minkowski problem.© 2017 Wiley Periodicals, Inc.     

Mobile and immobile gaseous transport: Embedded analytical solutions to finite volume methods

The motivation is driven by deposition processes based on chemical vapor problems. The underlying model problem is based on coupled transport–reaction equations with mobile and immobile areas. We deal with systems of ordinary and partial differential equations. Such equation systems are delicate to solve and we introduce a novel solver method, that takes into account ways to solve analytically parts of the transport and reaction equations. The main idea is to embed the analytical and semianalytical solutions, which can then be explicitly given to standard numerical schemes of higher order. The numerical scheme is based on flux‐based characteristic methods, which is a finite volume method. Such a method is an attractive alternative to the standard numerical schemes, which fully discretize the full equations. We instead reduce the computational time while embedding fast computable analytical parts. Here, we can accelerate the solver process, with a priori explicitly given solutions. We will focus on the derivation of the analytical solutions for general and special solutions of the characteristic methods that are embedded into a finite volume method. In the numerical examples, we illustrate the higher‐order method for different benchmark problems. Finally, the method is verified with realistic results. © 2011 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2012     

Approximate solutions to large nonsymmetric differential Riccati problems with applications to transport theory

In this paper, we consider large‐scale nonsymmetric differential matrix Riccati equations with low‐rank right‐hand sides. These matrix equations appear in many applications such as control theory, transport theory, applied probability, and others. We show how to apply Krylov‐type methods such as the extended block Arnoldi algorithm to get low‐rank approximate solutions. The initial problem is projected onto small subspaces to get low dimensional nonsymmetric differential equations that are solved using the exponential approximation or via other integration schemes such as backward differentiation formula (BDF) or Rosenbrock method. We also show how these techniques can be easily used to solve some problems from the well‐known transport equation. Some numerical examples are given to illustrate the application of the proposed methods to large‐scale problems.     

Surface Reaction Near a Stagnation Point

To measure rate constants while performing biomolecular interaction analysis (BIA), scientists often use resonant mirror devices such as the IAsys^TM. A full mathematical model of the IAsys^TM consists of a convection–diffusion equation in a closed well with a reacting surface at the bottom. The flow in the well is complex, but near the sensor, the qualitative nature of the reaction can be analyzed by reducing to stagnation point flow. The concentration of the reacting species in several cases is analyzed using singular perturbation techniques. Linear and nonlinear integral equations result from the analysis; explicit and series solutions are constructed for physically realizable cases. These solutions, which include the effects of transport on the reaction, provide improved estimates for the rate constants from raw IAsys^TM binding data.     

Multiphase transport based on compact distributions

Many multiphase transport problems are characterized by a random mixing of the phases (e.g., transport in porous media). In general, because of this randomness, instrumentation windows are designed such that only averages of field properties over the various phases are measured. In this article we identify an instrument window with a compact distribution. If the field property being filtered lies in the space of tempered distributions, then constraints may be derived on the structure of the filter. Distributional equations are derived which represent transport of a filtered property. The equations are general enough to allow for the use of different instruments to measure different properties. An equation representing the relationship between phase properties and filtered properties is derived when the filter is given by a measure with compact support.     

Asymptotic analysis and reaction-diffusion approximation forBGK kinetic models of chemical processes in multispecies gas mixtures

A BGK-type model is derived to describe the interaction between transport and chemical reactions in multispecies gas mixtures, at the kinetic level. The underlying kinetic process is modelled by a Fokker-Planck-type equation, in the Kramers-Smoluchowski limit. When the reaction terms in the kinetic equation are properly scaled, an expansion in powers of a small parameter related to the mean collison time yields a reaction-diffusion equation for the densities of the chemical species involved. For different scalings of the reaction terms, the related macroscopic equations describe the prevailing of transport processes on chemical reactions, orvice versa. The spatially homogeneous case with its own peculiarities is addressed, and the Selkov model is considered as an example.     

A multiscale finite element method for the solution of transport equations

A multiscale Galerkin finite element scheme based on the residual free bubble function method is proposed to generate stable and accurate solutions for the transport equations namely diffusion-reaction (DR), convection-diffusion (CD) and convection-diffusion-reaction (CDR) equations. These equations show multiscale behavior in reaction or convection dominated situations. The idea is based on the approximation of the definite integral of the interpolation function within the element, instead of the function approximation. The numerical experiments are performed using the bilinear Lagrangian elements. To validate the approach, the numerical results obtained for a benchmark problem are compared with the analytical solution in a wide range of Peclet and Damköhler numbers. The results show that the developed method is capable of generating stable and accurate solutions.     

Numerical exploration of a system of reaction–diffusion equations with internal and transient layers

A reaction pathway for a classical two-species reaction is considered with one reaction that is several orders of magnitudes faster than the other. To sustain the fast reaction, the transport and reaction effects must balance in such a way as to give an internal layer in space. For the steady-state problem, existing singular perturbation analysis rigorously proves the correct scaling of the internal layer. This work reports the results of exploratory numerical simulations that are designed to provide guidance for the analysis to be performed for the transient problem. The full model is comprised of a system of time-dependent reaction–diffusion equations coupled through the non-linear reaction terms with mixed Dirichlet and Neumann boundary conditions. In addition to internal layers in space, the time-dependent problem possesses an initial transient layer in time. To resolve both types of layers as accurately as possible, we design a finite element method with analytic evaluation of all integrals. This avoids all errors associated with the evaluation of the non-linearities and allows us to provide an analytic Jacobian matrix to the implicit time stepping method. The numerical results show that the method resolves the localized sharp gradients accurately and can predict the scaling of the internal layers for the time-dependent problem.     

Vorticity transport in a viscoelastic fluid in the presence of suspended particles through porous media

We consider the transport of vorticity in an Oldroydian viscoelastic fluid in the presence of suspended magnetic particles through porous media. We obtain the equations governing such a transport of vorticity from the equations of magnetic fluid flow. It follows from these equations that the transport of solid vorticity is coupled to the transport of fluid vorticity in a porous medium. Further, we find that because of a thermokinetic process, fluid vorticity can exist in the absence of solid vorticity in a porous medium, but when fluid vorticity is zero, then solid vorticity is necessarily zero. We also study a two-dimensional case.     

Iterative solution of the drift-diffusion equations

The drift-diffusion model can be described by a nonlinear Poisson equation for the electrostatic potential coupled with a system of convection-reaction-diffusion equations for the transport of charge. We use a Gummel-like process [10] to decouple this system. Each of the obtained equations is discretised with the finite element method. We use a local scaling method to avoid breakdown in the numerical algorithm introduced by the use of Slotboom variables. Solution of the discrete nonlinear Poisson equation is accomplished with quasi-Newton methods. The nonsymmetric discrete transport equations are solved using an incomplete LU factorization preconditioner in conjunction with some robust linear solvers, such as (CGS), (BI-CGSTAB) and (GMRES). We investigate the behaviour of these iterative methods to define the effective strategy for this class of problems. This revised version was published online in June 2006 with corrections to the Cover Date.     

Generalized solution of some parabolic equations with a random drift

Some stochastic partial differential equations arising from a turbulent transport model are studied using Hida's theory of Brownian functionals. For the spatially homogeneous case, the solutions are constructed as a regular or generalized Brownian functional, depending on a small parameter. The regularity property of such solutions is also determined. However, for the spatially nonhomogeneous equations, only generalized solutions in a series form involving iterated singular Wiener integrals are found.This work was supported in part by NSF Grant DMS-87-02236.     

On Nonlinear Galerkin Approximation

1.IntroductionInordertosolvetheproblemoflongtimeilltegrationofevolutionpartialdifferentialequations,nPnlinearGalerkinmethodsareintroducedinrecentyears.SuchmethodsstemfromthetheoryofinertialmanifoldsandaPprokimateinertialmanifolds.Werecallaninertialmanifoldisafinitedimensionalsmoothmanifoldwhichcontainstheglobalattractora-ndattractseveryorbitatanexponelltial.ate[1'2].However,therearestillmanydissipativepartialdifferelltialequationsforwhichtheexistenceofinertialmanifoldsisnotknown;thereareeven…     

Spatio‐temporal Pattern Formation in Chemical Reactions

In our paper numerical simulations of chemical pattern in ionic reaction‐diffusion‐migration system assuming a “self‐consistent” electric field are presented. Chemical waves as well as stationary concentration pattern arise due to an interplay of an autocatalytic chemical reaction with transport processes. Concentration gradient inside the chemical pattern lead to electric diffusion‐potential which in turn affect the patterns. Thus, the model equations take the general form of the Fokker‐Planck equation.