RnDif.het: 2D Steady-state radon diffusion in a heterogeneous porous...

In RadTran: Radon and Soil Gas Transport in 2D Porous Medium

Description

Calls function RnDif.het for 2D steady diffusion of radon. Gives the radon concentrations and fluxes in a heterogeneous porous medium.

Usage

RnDif.het(lx, ly, nx, ny, rho, x.poro, x.hum,
y.poro, y.hum, bdc_top, rn_lam, rn_ema, rn_dif,
rn_sol, solution, ...)

Arguments

lx	x axis length of the soil column [L].
ly	y axis length (depth) of the soil column [L]. Only positive values are accepted.
nx	Number of grid cells in the x direction.
ny	Number of grid cells in the y direction.
rho	Soil grain material density [M/L2]. A constant value over the entire column.
x.poro	Soil porosity in the x direction [-]. A constant value input.
x.hum	Soil moisture [-] in the x direction. A constant value input.
y.poro	Soil porosity in the y direction [-]. A function input that describes the porosity profile in the y-axis.
y.hum	Soil moisture in the y direction [-]. A function input that describes the moisture profile in the y-axis.
bdc_top	Fixed value in the upstream boundary in y-direction (top of the soil column) for a constant value of radon concentration [(1/T)*(1/L3)].
rn_lam	Radon decay constant [1/T].
rn_ema	Radon emanation ratio [atoms (1/L3)*(1/T)].
rn_dif	Radon diffusivity in free air [L2/T].
rn_sol	Radon solubility in water [-].
solution	Type of solution to be computed. Only "steady" is avaiable at the moment.
...	...

Details

To optimize the code: The number of grid cells (nx,ny) will depend on the user's own computer capability. Higher numbers will give a closer approximation to the exact solution. The quantity for ny should be larger than nx, this allows a greater discretization in the y-axis.

Boundary conditions: Fixed value for radon concentration in the upstream boundary in y-direction (a negative y axis is considered), while the downstream boundary remains open. All the otther boundaries are closed off for transport.

Fluxes output: The output of the fluxes indicates the flow direction in correspondence with y-axis. In the case where a negative y-axis is considered, a negative flux value represents upward flow (from bottom to top). If the y-axis considered is positive, then a negative flux value represents downward flow (from top to bottom). The radon fluxes are computed at the interface of each grid cell.

Value

A list containing:

x.axis	X axis vector (1:nx) for radon concentrations and fluxes [L].
y.axis.conc	Y axis vector (1:ny) for the radon concentrations output [L].
y.axis.flux	Y axis vector (1:ny+1) for the radon fluxes output [L].
conc	Radon concentrations in the center of each grid cell, a [1:nx,1:ny] matrix [(1/T)*(1/L3)].
flux	Radon fluxes in the interface of each grid cell in the y-direction, a [1:nx,1:ny+1] matrix [1/T2].

Note

At the moment there is no provision to deal with cross-diffusion between x and y-axis.

The concentrations of radon are only computed at the center of each grid cell, this implies that the exact value in a cell interface (or in a boundary domain) will not be shown. Thus, the closest value is taken as an approximation at this locations.

Author(s)

Francisco Lopes <[e-mail]>

References

Andersen CE. Radon Transport Modelling: Users guide to RnMod3d. Riso National Laboratory, Roskilde, Denmark, 2000.

Andersen CE, Albarracin D, Csige I, van der Graaf ER, Jiranek M, Rehs B, Svoboda Z, Toro L. ERRICCA radon model intercomparison exercise. Riso-R-1120 (EN), Riso National Laboratory, DK-4000 Roskilde, Denmark (available as a internet publication at www.risoe.dk), 1999.

Soetaert K., Meysman F., 2012. R-package ReacTran: Reactive Transport Modelling in R.

Soetaert K., Meysman F., 2011. Reactive transport in aquatic ecosystems: Rapid model prototyping in the open source software R.

Soetaert K., Meysman F., 2009. Solving partial differential equations, using R package ReacTran.

See Also

p.lin p.exp p.sig

Examples

#################################################
#####---- Direct input for the function ----#####
#################################################

###--defining porosity and moisture functions for y-axis profiles--###
###---------------------------examples-----------------------------###

require(RadTran)

#porosity linear decrease until 3m depth
y.poro  =  function(X,Y)
           return(p.lin(Y,x.L=1.0,y.0=0.5,y.inf=0.3,x.att=0))

	
#moisture non-linear decrease until 3m depth, function input is m(z)=-0.4z+2.0
lin.inc  =  function(x,y.0=0,y.inf=0.5,x.L=0,x.att=2) 
            return(1 - p.lin(x,y.0,y.inf,x.L,x.att))
             
y.hum=function(X,Y)
			return(lin.inc(Y,y.0=0.8,y.inf=0))


Dif=RnDif.het(lx=1,ly=3,nx=50,ny=100,rho=2.65e3,x.poro=0.3,
x.hum=0.4,y.poro=y.poro,y.hum=y.hum,bdc_top=1000,rn_lam=2.09838e-6,
rn_ema=10,rn_dif=1.1e-5,rn_sol=0.3565,solution="steady")
			

RadTran documentation built on May 1, 2019, 9:02 p.m.