Code Manual for CONTAIN 2.0 - Federation of American Scientists

The user-specified trapping rate is normally a constant; however, time-varying rates can be specified
through the use of user tables. To speci~ a constant trapping rate in a cell the value desired is given ~
in the DCH-CELL block as explained in Section 14.3.1.11. User trapping values specified in the
global DHEAT block are used as default constant trapping rates for all cells. To specify a timevarying
trapping rate, the VAR-PARM keyword is used in the DCH-CELL input block. The name
of the VAR-Y variable in the VAR-PARM block must be TRAPRATE to specifi the trapping rate
as the dependent variable in the table.
6.3.4 GIW Trapping Model
In this model, the trapping rate is taken to be controlled by the gravitational fall rate of a sphere in
the cell atmosphere:
(6-88)
where the terminal fall veloclty for debris parhcles
. .
m field n and cell 1 IS vx~,i,~. In the interest of
notational convenience, this velocity is simply referred to as vti~hereafter, but the reader should
remember that Vgt for each field and in each cell is unique. The characteristic gravitational fall
height for debris particles in cell i is L@t,i. Again, the i subscript will be dropped for notational
convenience, but the reader should remember that Lqt for each cell can be unique.
The terminal fall velocity, vg~,is computed using the following drag correlation for spheres:
V.=[-cl+q=pk.-l
(6-89)
where g is the acceleration of gravity, p~ is the gas viscosity, p~is the gas density, d is the particle
diameter, and p~is the debris material density.
Note that Vx,is dependent upon both cell i and field n, through the gas density, gas viscosity, debris
density, and particle diameter. The above correlation assumes that the particles are spheres, the
atmosphere is stagnant, and that the particles do not physically interact with each other as they fall.
The characteristic gravitational fall height, L@,by default, is calculated to be the cube root of the
initial cell gas volume. A DCH-specific Lti~value can also be specified independent of the cell
volume. This is done using the LENGFT keyword in the DCH-CELL input block.
Rev O 638 6/30/97