Partial Differential Equations - Modelling and ... - ResearchGate
Partial Differential Equations - Modelling and ... - ResearchGate
Partial Differential Equations - Modelling and ... - ResearchGate
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248 J.-M. Brun <strong>and</strong> B. Mohammadi<br />
2.2 Long Range Transport <strong>and</strong> Non-Symmetric Geometry<br />
The modelling above gives a local distribution for the advected quantities.<br />
We are now interested by the quantities c<strong>and</strong>idate for a transport over large<br />
distances. We suppose that those are given by<br />
∫<br />
c + (x, y) = c l dz or c + (x, y) =u + l c l ,<br />
where H ∼ 2 − 3m <strong>and</strong> u + l<br />
transported is given by<br />
z>H<br />
= max(0, (u · z)/‖u‖). The total quantity being<br />
∫<br />
C = c + (x, y)dσ,<br />
R 2<br />
which should be conserved by the reduced-order transport model we would<br />
like to build <strong>and</strong> for which c + is the input condition.<br />
One aims now to again reduce the search space for the solution. The primary<br />
factors influencing the dispersion of a neutral plume are advection by<br />
the wind <strong>and</strong> turbulent mixing. The simplest model of this process is to assume<br />
that the plume advects downwind <strong>and</strong> spreads out in the horizontal<br />
<strong>and</strong> vertical directions. Hence, the distribution of a passive scalar c, emitted<br />
from a given point <strong>and</strong> transported by a uniform plane flow filed U along<br />
x-coordinate, is given by<br />
where<br />
c(x, y, z) =c c (x)f( √ y 2 + z 2 ,δ(x)), (3)<br />
c c (x) ∼ exp(−a(U)x) <strong>and</strong> f( √ y 2 + z 2 ,δ(x)) ∼ exp(−b(U, δ(x)) √ y 2 + z 2 ).<br />
c c is the behavior along the central axis of the distribution <strong>and</strong> δ(x) characterizes<br />
the thickness of the distribution at a given x-coordinate. An analogy<br />
exists with plane or axisymmetric mixing layers <strong>and</strong> neutral plumes where δ is<br />
parabolic for a laminar jet <strong>and</strong> linear in turbulent cases [Cou89, Sim97]. a(·)<br />
is a positive monotonic decreasing function <strong>and</strong> b(·, ·) is positive, monotonic<br />
increasing in U <strong>and</strong> decreasing in δ. In a uniform atmospheric flow field, this<br />
solution can be used for the transport of c + above.<br />
We would like to generalize this solution in a non-symmetric metric defined<br />
by migration times based on the flow field <strong>and</strong> hence treat the case of variable<br />
flow fields.<br />
Nonsymmetric Geometry<br />
In a symmetric geometry the distance function between two points A <strong>and</strong> B<br />
verifies<br />
d(A, B) =0⇒ A = B, d(A, B) =d(B,A), d(A, B) ≤ d(A, C)+d(C, B).