Publish in OALib Journal
APC: Only $99
Most numerical transient flow models that consider dynamic friction
employ a finite differences approach or the method of characteristics. These
models assume a single fluid (water only) with constant density and pressure
wave velocity. But when transient flow modeling attempts to integrate the
presence of air, which produces a variable density and pressure-wave velocity, the
resolution scheme becomes increasingly complex. Techniques such as finite volumes
are often used to improve the quality of results because of their conservative
form. This paper focuses on a resolution technique for unsteady friction using
the Godunov approach in a finite volume method employing single-equivalent twophase
flow equations. The unsteady friction component is determined by taking into
account local and convective instantaneous accelerations and the sign of both
convective acceleration and velocity values. The approach is used to reproduce
a set of transient flow experiments reported in the literature, and good
agreement between simulated and experimental results is found.
Maximum and minimum
temperatures time series of Congo-Brazzaville are analyzed for trend and discontinuities over the period 1932 to 2010. Temperatures series show an irregular increase. A total of 8 synoptic stations show positive
trends in their annual mean maximum temperature series, and 7 of them are
significant, with higher trends for urban stations. Annual mean minimum
temperature showed 6 stations having positive trends. This increase is in relation with observations at regional scale.
However, the differences are observed between large towns (Brazzaville and
Pointe-Noire), and small or rural towns (Dolisie, Sibiti, Impfondo, Djambala).
Trends in diurnal temperature range (DTR) are large positive trends in maximum
temperature that are mainly observed in cities. The curve of DTR shows a
decreasing trend which indicates the increasing of minimum temperatures. The
effects of urbanization on temperature trends are investigated. Most stations
regarded as urban stations are still useful for trend analysis; being situated
on the suburban of the studied cities, they are therefore, not substantially
influenced by the urban heat island.