Page 165 - Biosystems Engineering

144 Cha pte r F o u r

a pioneering simulation language that was largely incompatible
with PCs (Evett and Lascano 1993), was used by Horton et al. (1984a,
1984b) to model soil temperature. Later, the ENergy and WATer
BALance (ENWATBAL) was included in the BASIC language to emu-
late CSMP functions and was used by Lascano (1989) to predict sur-
face temperatures. Van Donk et al. (2004) modified the ENWATBAL
model that simulated soil water and temperature profiles, evapora-
tion from soil, and transpiration from crops including the effects of
a mulch layer. Measured soil temperatures lagged behind those
simulated, indicating that conduction was an important process of
heat transfer through the mulch.
Kroes et al. (2000) used a different code, SWAP 2.0, which inte-
grated the equations governing heat and mass transfer in soil through
numerical methods and allowed for one-dimensional analysis of
water movement, solute transport, and heat flows in flooded soils.
Specific tools that are useful in modeling soil processes have been
developed during the last few years. One example is the FEM soft-
ware code developed by Thomas and Cleall (2000) to model thermal–
hydraulic–mechanical (THM) behavior in unsaturated soils. Renaud
et al. (2001) built a one-dimensional FEM model to predict seasonal
temperature distribution in rice crops. The model was implemented
in MATLAB and included the analytical computation of surface tem-
perature by harmonic analysis.
Another computer two-dimensional FEM simulation model is
2DSOIL. This model simulates water flow, chemical flow, and water
uptake by the plant roots, processes of physical balance, heat transfer,
and gas diffusion in the soil under atmosphere environmental condi-
tions. Timlin et al. (2002) evaluated the model to determine the error in
hourly temperature data based on the maximum and minimum daily
temperatures and obtained better results for hourly temperatures.
Moroizumi and Horino (2002) presented a one-dimensional
model for coupled heat and water flows solved by FEM with error
estimation by the Galerkin method. After the model was validated,
the authors observed good agreement between measured and simu-
lated temperature values, with worse results for matric pressure val-
ues. The authors attributed these results to the inaccuracy of the
physical properties of the soil or inappropriate boundary conditions
but not to the numerical method used. Qin et al. (2002) developed a
model that coupled soil temperature changes simultaneously with
soil moisture movement and tackled the problem by using FEM. They
used the Crank–Nicolson implicit method to expand the differential
equations and the Newton–Raphson method to solve the equations.
The validation of the model in the South Israeli desert obtained good
results. The accurate results obtained for thermal conductivity and
hydraulic conductivity were particularly relevant due to their influ-
ence on the overall results.