Alistair,
I don't really remember, but I think the if(no_slip_bottom) part was simply
historical. I developed my adjustment of the original code keeping the
no_slip_bottom flag. This did prove useful for me to debug the implicit
diffusion problem, since I could let no_slip_bottom be false, and return to
your original code. At this point, I don't think there's much reason to keep
it.
The drag term in the equations of motion is (conventionally)
du/dt ... = ... + (1/rho)ddz(u'w')
Quadratic:
-(u'w')@bottom = tau_b = Cd rho |u| u
Cd, the quadratic drag coeff, is non-dimensional.
Units:
tau_b ~ N/m^2 = kg /ms^2
rho |u|u ~ kg/m^3 m/s m/s ~ kg/m s^2
Linear:
-(u'w')@bottom = tau_b = r rho u
r, the linear drag coeff, is in units m/s.
r rho u ~ m/s kg/m^3 m/s ~ kg/m s^2
For shallow water flow, the divergence of the stresses should lead to
du/dt ... = ... - ru/H -Cd|u|u/H
which shows an equivalent check for r (m/s) and Cd (nd).
Haven't yet tried the flux-corrected transport. Good seeing you Friday.
-Chris
On 15-Feb-2001 Alistair Adcroft wrote:
> Hi Chris (E),
>
> Did you take a look at c35 yet?
>
> I'm in the process of re-organizing the calc_mom_rhs.F to allow vector
> invariant form and noticed these lines near the top:
> IF (no_slip_bottom) THEN
> bottomDragTerms=.TRUE.
> ELSE
> bottomDragTerms=.FALSE.
> ENDIF
>
> which imply we can only use the linear of quadratic drag if
> we also use the no-slip boundary condition for viscosity too.
> I know I wrote the above but can't quite figure the reasoning!
> Probably just a quick decision to get it done before you left
> that day. Except for very large viscosities it probably doesn't
> matter but it seems like an unnecessary inflexibility.
> Any reason not to fix this?
>
> Also, the quantity
> & 2.*KappaRU(i,j,kp1)*rkFac*rdrckp1
> & + bottomDragLinear
> & + bottomDragQuadratic*sqrt(KE(i,j)+KE(i-1,j))
> & )*(1.-maskDown)*uVel(i,j,k,bi,bj)
> is meant to be the divergence of a stress (the rho's get cancelled).
> Do we have the conventional units for bottomDragLinear
> and bottomDragQuaratic? I think CNH asked me this earlier but I
> didn't know.
>
> A.
--
---------------------------------------------------------------------
Christopher Edwards christopher.edwards at uconn.edu
Department of Marine Sciences phone: (860) 405-9173
University of Connecticut fax: (860) 405-9153
1084 Shennecossett Road
Groton, CT 06340
---------------------------------------------------------------------