Zero-conductivity case (#128)

* Update heat_conduction.jl

* Update .gitignore

* Update runtests.jl

* Create TPM_zero-conductivity.jl

* Update TPM_zero-conductivity.jl

* Update TPM_zero-conductivity.jl

* Update TPM_zero-conductivity.jl

* Update heat_conduction.jl

.gitignore

@@ -11,6 +11,7 @@
 
 /test/TPM_Ryugu/output
 /test/TPM_non-uniform_thermoparams/output
+/test/TPM_zero-conductivity/output
 /test/TPM_Didymos/output
 
 # Keep these shape models

src/heat_conduction.jl

@@ -8,6 +8,8 @@
     update_temperature!(stpm::SingleTPM, Δt)
 
 Calculate the temperature for the next time step based on 1D heat conduction equation.
+If the thermal inertia (conductivity) is zero, omit to solve the heat conduction equation.
+The surface termperature is determined only by radiative equilibrium.
 
 # Arguments
 - `stpm` : Thermophysical model for a single asteroid
@@ -62,23 +64,39 @@ function forward_euler!(stpm::SingleTPM, Δt)
     n_depth = size(T, 1)
     n_face = size(T, 2)
 
-    for i_face in 1:n_face
-        P  = stpm.thermo_params.P
-        Δz = stpm.thermo_params.Δz
-        l  = (stpm.thermo_params.l isa Real ? stpm.thermo_params.l : stpm.thermo_params.l[i_face])
+    ## Zero-conductivity (thermal inertia) case
+    if iszero(stpm.thermo_params.Γ)
+        for i_face in 1:n_face
+            A_B  = (stpm.thermo_params.A_B  isa Real ? stpm.thermo_params.A_B  : stpm.thermo_params.A_B[i_face] )
+            A_TH = (stpm.thermo_params.A_TH isa Real ? stpm.thermo_params.A_TH : stpm.thermo_params.A_TH[i_face])
+            ε    = (stpm.thermo_params.ε    isa Real ? stpm.thermo_params.ε    : stpm.thermo_params.ε[i_face]   )
+            εσ = ε * σ_SB
 
-        λ = (Δt/P) / (Δz/l)^2 / 4π
-        λ ≥ 0.5 && error("The forward Euler method is unstable because λ = $λ. This should be less than 0.5.")
+            F_sun, F_scat, F_rad = stpm.flux[i_face, :]
+            F_total = flux_total(A_B, A_TH, F_sun, F_scat, F_rad)
 
-        for i_depth in 2:(n_depth-1)
-            stpm.SOLVER.T[i_depth] = (1-2λ)*T[i_depth, i_face] + λ*(T[i_depth+1, i_face] + T[i_depth-1, i_face])  # Predict temperature at next time step
+            stpm.temperature[begin, i_face] = (F_total / εσ)^(1/4)
         end
+    ## Non-zero-conductivity (thermal inertia) case
+    else
+        for i_face in 1:n_face
+            P  = stpm.thermo_params.P
+            Δz = stpm.thermo_params.Δz
+            l  = (stpm.thermo_params.l isa Real ? stpm.thermo_params.l : stpm.thermo_params.l[i_face])
+
+            λ = (Δt/P) / (Δz/l)^2 / 4π
+            λ ≥ 0.5 && error("The forward Euler method is unstable because λ = $λ. This should be less than 0.5.")
 
-        ## Apply boundary conditions
-        update_upper_temperature!(stpm, i_face)
-        update_lower_temperature!(stpm)
+            for i_depth in 2:(n_depth-1)
+                stpm.SOLVER.T[i_depth] = (1-2λ)*T[i_depth, i_face] + λ*(T[i_depth+1, i_face] + T[i_depth-1, i_face])  # Predict temperature at next time step
+            end
 
-        T[:, i_face] .= stpm.SOLVER.T  # Copy temperature at next time step
+            ## Apply boundary conditions
+            update_upper_temperature!(stpm, i_face)
+            update_lower_temperature!(stpm)
+
+            T[:, i_face] .= stpm.SOLVER.T  # Copy temperature at next time step
+        end
     end
 end
 

test/TPM_zero-conductivity/TPM_zero-conductivity.jl

@@ -0,0 +1,75 @@
+# See https://github.com/Astroshaper/Astroshaper-examples/tree/main/TPM_Ryugu for more information.
+@testset "TPM_zero-conductivity" begin
+    DIR_OUTPUT = joinpath(@__DIR__, "output")
+    rm(DIR_OUTPUT; recursive=true, force=true)
+    mkpath(DIR_OUTPUT)
+
+    msg = """\n
+    ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
+    |              Test: TPM_zero-conductivity               |
+    ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+    """
+    println(msg)
+
+    ##= Ephemerides =##
+    P = SPICE.convrt(8, "hours", "seconds")  # Rotation period of the asteroid [s]
+    ncycles = 2                              # Number of cycles to perform TPM
+    nsteps_in_cycle = 72                     # Number of time steps in one rotation period
+
+    et_begin = 0.0                     # Start time of TPM
+    et_end   = et_begin + P * ncycles  # End time of TPM
+    et_range = range(et_begin, et_end; length=nsteps_in_cycle*ncycles+1)
+
+    """
+    - `time` : Ephemeris times
+    - `sun`  : Sun's position in the asteroid-fixed frame
+    """
+    ephem = (
+        time = collect(et_range),
+        sun  = [inv(RotZ(2π * et / P)) * [SPICE.convrt(1, "au", "m"), 0, 0] for et in et_range],
+    )
+
+    ##= Load obj file =##
+    path_obj = joinpath("shape", "ryugu_test.obj")
+    shape = AsteroidThermoPhysicalModels.load_shape_obj(path_obj; scale=1000, find_visible_facets=true)
+
+    ##= Thermal properties: zero-conductivity case =##
+    thermo_params = AsteroidThermoPhysicalModels.thermoparams(
+        P       = P,
+        l       = 0.0,
+        Γ       = 0.0,
+        A_B     = 0.1,
+        A_TH    = 0.0,
+        ε       = 1.0,
+        z_max   = 0.6,
+        n_depth = 11,
+    )
+
+    println(thermo_params)
+
+    ##= Setting of TPM =##
+    stpm = AsteroidThermoPhysicalModels.SingleTPM(shape, thermo_params;
+        SELF_SHADOWING = true,
+        SELF_HEATING   = false,
+        SOLVER         = AsteroidThermoPhysicalModels.ForwardEulerSolver(thermo_params),
+        BC_UPPER       = AsteroidThermoPhysicalModels.RadiationBoundaryCondition(),
+        BC_LOWER       = AsteroidThermoPhysicalModels.InsulationBoundaryCondition(),
+    )
+    AsteroidThermoPhysicalModels.init_temperature!(stpm, 0)
+
+    ##= Run TPM =##
+    times_to_save = ephem.time[end-nsteps_in_cycle:end]  # Save temperature during the final rotation
+    face_ID = [1, 2]  # Face indices to save subsurface temperature
+
+    result = AsteroidThermoPhysicalModels.run_TPM!(stpm, ephem, times_to_save, face_ID)
+
+    ##= Save TPM result =##
+    @testset "Save TPM result" begin
+        AsteroidThermoPhysicalModels.export_TPM_results(DIR_OUTPUT, result)
+
+        @test isfile(joinpath(DIR_OUTPUT, "physical_quantities.csv"))
+        @test isfile(joinpath(DIR_OUTPUT, "subsurface_temperature.csv"))
+        @test isfile(joinpath(DIR_OUTPUT, "surface_temperature.csv"))
+        @test isfile(joinpath(DIR_OUTPUT, "thermal_force.csv"))
+    end
+end

test/runtests.jl

@@ -15,5 +15,6 @@ Aqua.test_all(AsteroidThermoPhysicalModels, ambiguities=false)
 include("find_visiblefacets.jl")
 include("TPM_Ryugu/TPM_Ryugu.jl")
 include("TPM_non-uniform_thermoparams/TPM_non-uniform_thermoparams.jl")
+include("TPM_zero-conductivity/TPM_zero-conductivity.jl")
 include("TPM_Didymos/TPM_Didymos.jl")
 include("heat_conduction_1D.jl")