Add heat-sfcc implicit T form example

examples/heat_sfcc_samoylov_implicitT.jl

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+# This example demonstrates how to simulate two-phase heat conduction without water flow
+# and using the temperature-based formulation of the heat equation.
+using CryoGrid
+using OrdinaryDiffEq
+
+import Plots
+
+# Here we define the boundary conditions and stratigraphy.
+forcings = loadforcings(CryoGrid.Forcings.Samoylov_ERA_MkL3_CCSM4_long_term);
+upperbc = TemperatureBC(Input(:Tair), NFactor(0.65,0.9))
+ssinit = ThermalSteadyStateInit(T0=-15.0u"°C");
+
+# Create and plot the SFCC for sandy soil that we will use.
+sfcc = PainterKarra(swrc=VanGenuchten("sand"))
+Plots.plot(-0.5u"°C":0.001u"K":0.0u"°C", sfcc)
+
+# Define soil stratigraphy.
+soilprofile = SoilProfile(
+    0.0u"m" => SimpleSoil(; por=0.80, org=0.75, freezecurve=sfcc),
+    0.1u"m" => SimpleSoil(; por=0.80, org=0.25, freezecurve=sfcc),
+    0.4u"m" => SimpleSoil(; por=0.55, org=0.25, freezecurve=sfcc),
+    3.0u"m" => SimpleSoil(; por=0.50, org=0.0, freezecurve=sfcc),
+    10.0u"m" => SimpleSoil(; por=0.30, org=0.0, freezecurve=sfcc),
+)
+
+# Set up model using the temperature formulation of the heat equation.
+# This is also sometimes referred to as the "apparent heat capacity method".
+heat = HeatBalance(:T)
+soil_layers = map(para -> Ground(para; heat), soilprofile);
+modelgrid = CryoGrid.DefaultGrid_2cm
+strat = Stratigraphy(
+    0.0u"m" => Top(upperbc),
+    soil_layers,
+    modelgrid[end] => Bottom(GeothermalHeatFlux(0.053u"W/m^2"))
+);
+tile = Tile(strat, modelgrid, forcings, ssinit);
+
+tspan = (DateTime(2000,10,1), DateTime(2002,10,1))
+u0, du0 = initialcondition!(tile, tspan);
+prob = CryoGridProblem(tile, u0, tspan, saveat=24*3600, savevars=(:T,:θw,:∂H∂T), step_limiter=nothing)
+integrator = init(prob, ImplicitEuler(autodiff=false))
+# test one step
+@time step!(integrator)
+last_t = integrator.t
+for i in integrator
+    if integrator.t - last_t > 24*3600
+        println("t=$(convert_t(integrator.t)), dt=$(integrator.dt)")
+        last_t = integrator.t
+    end
+end
+out = CryoGridOutput(integrator.sol)
+
+# Plot the results!
+zs = [1,5,10,15,20,25,30,40,50,100]u"cm"
+cg = Plots.cgrad(:copper,rev=true);
+Plots.plot(out.T[Z(Near(zs))], color=cg[LinRange(0.0,1.0,length(zs))]', ylabel="Temperature", title="", leg=false, dpi=150)