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- 2018-03-09T16:57:00+01:00 (6 years ago)
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branches/2017/dev_merge_2017/DOC/tex_sub/chap_time_domain.tex
r9389 r9392 91 91 \end{equation} 92 92 where the subscript $F$ denotes filtered values and $\gamma$ is the Asselin 93 coefficient. $\gamma$ is initialized as \np{rn \_atfp} (namelist parameter).94 Its default value is \np{rn \_atfp}=$10^{-3}$ (see \S~\ref{STP_mLF}),93 coefficient. $\gamma$ is initialized as \np{rn_atfp} (namelist parameter). 94 Its default value is \np{rn_atfp}=$10^{-3}$ (see \S~\ref{STP_mLF}), 95 95 causing only a weak dissipation of high frequency motions (\citep{Farge1987}). 96 96 The addition of a time filter degrades the accuracy of the … … 141 141 constraint on the time step. Two solutions are available in \NEMO to overcome 142 142 the stability constraint: $(a)$ a forward time differencing scheme using a 143 time splitting technique (\np{ln \_zdfexp} = true) or $(b)$ a backward (or implicit)144 time differencing scheme (\np{ln \_zdfexp} = false). In $(a)$, the master143 time splitting technique (\np{ln_zdfexp} = true) or $(b)$ a backward (or implicit) 144 time differencing scheme (\np{ln_zdfexp} = false). In $(a)$, the master 145 145 time step $\Delta $t is cut into $N$ fractional time steps so that the 146 146 stability criterion is reduced by a factor of $N$. The computation is performed as … … 156 156 \end{equation} 157 157 with DF a vertical diffusion term. The number of fractional time steps, $N$, is given 158 by setting \np{nn \_zdfexp}, (namelist parameter). The scheme $(b)$ is unconditionally158 by setting \np{nn_zdfexp}, (namelist parameter). The scheme $(b)$ is unconditionally 159 159 stable but diffusive. It can be written as follows: 160 160 \begin{equation} \label{Eq_STP_imp} … … 309 309 gradient (see \S\ref{DYN_hpg_imp}), an extra three-dimensional field has to be 310 310 added to the restart file to ensure an exact restartability. This is done optionally 311 via the \np{nn \_dynhpg\_rst} namelist parameter, so that the size of the311 via the \np{nn_dynhpg_rst} namelist parameter, so that the size of the 312 312 restart file can be reduced when restartability is not a key issue (operational 313 313 oceanography or in ensemble simulations for seasonal forecasting).
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