friction.F90 4.69 KB
 dumoda01 committed Jan 19, 2011 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 !$Id: friction.F90,v 1.10 2006-11-20 17:28:58 kbk Exp$ #include"cppdefs.h" !----------------------------------------------------------------------- !BOP ! ! !ROUTINE: The vertical friction \label{sec:friction} ! ! !INTERFACE: subroutine friction(kappa,avmolu,tx,ty) ! ! !DESCRIPTION: ! This subroutine updates the bottom roughness ! ! \label{Defz0b} ! z_0^b = 0.1 \frac{\nu}{u_*^b} + 0.03 h_0^b + z_a \point ! ! The first term on the right hand side of \eq{Defz0b} represents ! the limit for hydraulically smooth surfaces, the second term the limit ! for completely rough surfaces. Note that the third term, $z_a$, ! is the contribution of suspended sediments to the ! roughness length, see \cite{SmithMcLean77}. It is updated during calls ! to the sediment-routines. ! ! The law-of-the-wall relations are used to compute the friction velocity ! ! \label{uStar} ! u_*^b = r \sqrt{U_1^2 + V_1^2} ! \comma ! ! where $U_1$ and $V_1$ are the components of the mean velocity ! at the center of the lowest cell. ! We used the abbreviation ! ! \label{rParam} ! r=\frac{\kappa}{\ln \left( \frac{0.5h_1+z_0^b}{z^b_0} \right)} ! \comma ! ! where $\kappa$ is the von K{\'a}rm{\'a}n constant and ! the index 1' indicates values at the center of the first ! grid box at the bottom (version 1). Another expression for $r$ can be ! derived using the mean value of the velocity in the lowest ! grid box, and not its value in the middle of the box (version 2). Also ! this method is supported in {\tt friction()} and can be activated by ! uncommenting one line in the code. ! ! If no breaking surface waves are considered, the law of the wall ! also holds at the surface. The surface roughness length may ! be calculated according to the \cite{Charnock55} formula, ! ! \label{Charnock} ! z_0^s=\alpha \frac{(u_*^s)^2}{g} ! \point ! ! The model constant $\alpha$ is read in as {\tt charnock\_val} from ! the {\tt meanflow} namelist. ! ! !USES: use meanflow, only: h,z0b,h0b,MaxItz0b,z0s,za use meanflow, only: u,v,gravity use meanflow, only: u_taub,u_taus,drag use meanflow, only: charnock,charnock_val,z0s_min ! IMPLICIT NONE ! ! !INPUT PARAMETERS: REALTYPE, intent(in) :: kappa,avmolu,tx,ty ! ! !REVISION HISTORY: ! Original author(s): Hans Burchard & Karsten Bolding ! ! $Log: friction.F90,v$ ! Revision 1.10 2006-11-20 17:28:58 kbk ! [Cc]harnok -> [Cc]harnock - A. Jenkins ! ! Revision 1.9 2006-11-20 17:26:15 kbk ! [Cc]harnok -> [Cc]harnock - A. Jenkins ! ! Revision 1.8 2005/08/11 12:31:54 lars ! corrected error in documentation. Thanks to Patrizio Mariani ! ! Revision 1.7 2005/06/27 13:44:07 kbk ! modified + removed traling blanks ! ! Revision 1.6 2004/08/18 12:33:30 lars ! updated documentation ! ! Revision 1.5 2004/01/13 08:39:49 lars ! included roughness due to suspended sediments ! ! Revision 1.4 2003/03/28 09:20:35 kbk ! added new copyright to files ! ! Revision 1.3 2003/03/28 08:56:56 kbk ! removed tabs ! ! Revision 1.2 2003/03/10 08:50:06 gotm ! Improved documentation and cleaned up code ! ! Revision 1.1.1.1 2001/02/12 15:55:57 gotm ! initial import into CVS ! !EOP ! ! !LOCAL VARIABLES: integer :: i REALTYPE :: rr ! !----------------------------------------------------------------------- !BOC drag = _ZERO_ ! use the Charnock formula to compute the surface roughness if (charnock) then z0s=charnock_val*u_taus**2/gravity if (z0s.lt.z0s_min) z0s=z0s_min else z0s=z0s_min end if ! iterate bottom roughness length MaxItz0b times do i=1,MaxItz0b if (avmolu.le.0) then z0b=0.03*h0b + za else z0b=0.1*avmolu/max(avmolu,u_taub)+0.03*h0b + za end if ! compute the factor r (version 1, with log-law) rr=kappa/(log((z0b+h(1)/2)/z0b)) ! compute the factor r (version 2, with meanvalue log-law) ! frac=(z0b+h(1))/z0b ! rr=kappa/((z0b+h(1))/h(1)*log(frac)-1.) ! compute the friction velocity at the bottom u_taub = rr*sqrt( u(1)*u(1) + v(1)*v(1) ) end do ! add bottom friction as source term for the momentum equation drag(1) = drag(1) + rr*rr ! be careful: tx and ty are the surface shear-stresses ! already divided by rho! u_taus=(tx**2+ty**2)**(1./4.) return end subroutine friction !EOC !----------------------------------------------------------------------- ! Copyright by the GOTM-team under the GNU Public License - www.gnu.org !-----------------------------------------------------------------------`