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Introduction Water flow in soil Freezing soil Numerical method
FREEZING-THAWING PROCESSES STUDYWITH NUMERICAL MODEL
Niccolò Tubini
Università degli Studi di Trento
6th October 2016
Introduction Water flow in soil Freezing soil Numerical method
Contents
1 Introduction
2 Water flow in soilDarcy’s equationDarcy-Buckingham’s equationRichards’ equation
3 Freezing soilMass conservation lawEnergy conservation lawGround energy budget
4 Numerical method
Introduction Water flow in soil Freezing soil Numerical method
What is the purpose?
The aim of my Master’s thesis is to develop a solver ofRichards’s equation 3D plus freezing soil with the NestedNewton method.
Introduction Water flow in soil Freezing soil Numerical method
Why studing the influence of coupled heat and water flow insoils?
studies have shown that proper frozen soil schemes helpimprove land surface and climate model simulation(e.g. Viterbo et al., 1999 and Smirnova et al., 2000);
to simulate more realistic soil temperature(Luo et al., 2003);phase change in the ground;
Introduction Water flow in soil Freezing soil Numerical method
Why studing the influence of coupled heat and water flow insoils?
studies have shown that proper frozen soil schemes helpimprove land surface and climate model simulation(e.g. Viterbo et al., 1999 and Smirnova et al., 2000);
to simulate more realistic soil temperature(Luo et al., 2003);
phase change in the ground;
Introduction Water flow in soil Freezing soil Numerical method
Why studing the influence of coupled heat and water flow insoils?
studies have shown that proper frozen soil schemes helpimprove land surface and climate model simulation(e.g. Viterbo et al., 1999 and Smirnova et al., 2000);to simulate more realistic soil temperature(Luo et al., 2003);
phase change in the ground;
Introduction Water flow in soil Freezing soil Numerical method
Darcy’s equationR.
Rigo
n
Darcy’s experiment:
Jv = QA ∝
∆hL
Mathematically Darcy’s law:
Jv = −Ks∂h∂z
Introduction Water flow in soil Freezing soil Numerical method
Darcy’s equationR.
Rigo
n
Darcy’s experiment:
Jv = QA ∝
∆hL
Mathematically Darcy’s law:
Jv = −Ks∂h∂z
Introduction Water flow in soil Freezing soil Numerical method
Darcy’s equation
Go to in detail...
Physical quantities Unit ofmeasurement
h = z + pρwg Hydraulic head [L]
z Elevation head [L]
ψ = pρwg Pressure head [L]
Introduction Water flow in soil Freezing soil Numerical method
Darcy’s equation
Go to in detail...
Physical quantities Unit ofmeasurement
h = z + pρwg Hydraulic head [L]
z Elevation head [L]
ψ = pρwg Pressure head [L]
Introduction Water flow in soil Freezing soil Numerical method
Darcy’s equation
Go to in detail...
Physical quantities Unit ofmeasurement
h = z + pρwg Hydraulic head [L]
z Elevation head [L]
ψ = pρwg Pressure head [L]
Introduction Water flow in soil Freezing soil Numerical method
Darcy-Buckingham’s equationPh
ukan,198
5
Watercontent:
θw = Vw
Vc
Introduction Water flow in soil Freezing soil Numerical method
Darcy-Buckingham’s equation
Vadose zoneInfiltration often involves unsaturated flow through porousmedia.As a result:
capillary pressure arise;
cross-sectional area of the water conducting region isreduced.
Introduction Water flow in soil Freezing soil Numerical method
Darcy-Buckingham’s equation
Capillary pressurePressure is determined by the tesion andcurvature of air-water interface as given:
pw − pA = −γwa2r
{ pA = 0pw = −γwa
2r = −gρwz
Introduction Water flow in soil Freezing soil Numerical method
Darcy-Buckingham’s equation
Capillary pressurePressure is determined by the tesion andcurvature of air-water interface as given:
pw − pA = −γwa2r
{ pA = 0pw = −γwa
2r = −gρwz
Introduction Water flow in soil Freezing soil Numerical method
Darcy-Buckingham’s equation
Soil Water Retention Curve: θw = θw (ψ)https://
www.re
searchgate.net/
Introduction Water flow in soil Freezing soil Numerical method
Darcy-Buckingham’s equation
Soil Water Retention Curve: θw = θw (ψ)
Hypotesissolid matrix is rigid;
hydraulic hysteresis is ignored.
Introduction Water flow in soil Freezing soil Numerical method
Darcy-Buckingham’s equation
Parametric form of the SWRC
Equation Authors
θ = θr + (θs − θr )(ψm/ψe)λ Brooks and Corey
θ = θr + (θs − θr ) [1 + (αψm)n]−m Van Genuchten
Introduction Water flow in soil Freezing soil Numerical method
Darcy-Buckingham’s equation
Reduction of cross-sectional areaDarcy’s law is independent of the size of particles or the stateof packing:
Ks → K (θw )
Introduction Water flow in soil Freezing soil Numerical method
Darcy-Buckingham’s equation
Parametric form of the capillary conductivity
Mualem, 1976
K (Se) = KsSνe[
f (Se)f (1)
]2
f (Se) =∫ Se
0
1ψ(x)dx
Se = θ(ψ)− θr
θs − θr
Introduction Water flow in soil Freezing soil Numerical method
Darcy-Buckingham’s equation
Parametric form of the capillary conductivity
Choosing Van Genuchten’s parametric SWRC
K (Se) = KsSνe[1−
(1− S1/m
e
)m]2m = 1− 1/n
or
K (ψ) =Ks{1− (αψ)mn [1 + (αψ)n]−m}2
[1 + (αψ)n]mν m = 1− 1/n
Introduction Water flow in soil Freezing soil Numerical method
Darcy-Buckingham’s equation
Darcy-Buckingham’s lawIn vadose zone, specif discharge can be written as:
~Jv = K (θ(ψ))~∇(h)
Introduction Water flow in soil Freezing soil Numerical method
Richards’ equation
Equation of continuity for capillary flow
HypotesisIt is assumed that no phase transition takes place;density of water is constant.
∂θ
∂t = ~∇ · ~Jv (ψ)
Introduction Water flow in soil Freezing soil Numerical method
Richards’ equation
To sum up
C(ψ)∂ψ∂t = ∇ ·
(K (θ) ~∇(z + ψ)
)C(ψ) = ∂θ
∂ψ
Se = [1 + (−αψ)m]−n
Se = θ − θr
θs − θr
K (Se) = Ks√
Se[(1− (1− Se)1/m
)m]2
Introduction Water flow in soil Freezing soil Numerical method
Phuk
an,1
985
Ice content:
θi = Vi
Vc
Introduction Water flow in soil Freezing soil Numerical method
What is needed to study freezing soil?water can be both in liquid and solid phase;
freezing/thawing processes involve energy fluxes;
soil temperature.
Introduction Water flow in soil Freezing soil Numerical method
What is needed to study freezing soil?water can be both in liquid and solid phase;
freezing/thawing processes involve energy fluxes;
soil temperature.
Introduction Water flow in soil Freezing soil Numerical method
What is needed to study freezing soil?water can be both in liquid and solid phase;
freezing/thawing processes involve energy fluxes;
soil temperature.
Introduction Water flow in soil Freezing soil Numerical method
Hypotesisrigid soil scheme ⇒ ρw = ρi ;
"Freezing = drying" (Miller, 1965; Spaans and Baker,1996).
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
We need of new closure equationsθw = θw (ψ, ?)
θi = ?
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
Pressure and temperature under freezing conditionDall’A
mico,
2010
Air-water interfacepw0 = pa − 2γaw/r0
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
Pressure and temperature under freezing conditionDall’A
mico,
2010
Air-ice interfacepi = pa − 2γai/r0
Ice-water interfacepw1 = pi − 2γiw/r1
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
Pressure and temperature under freezing conditionDall’A
mico,
2010
Air-water interfacepw1 = pa − 2γaw/r1
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
Clapeyron’s equation
ρwLfdTT = dpw
Integrating ∫ T∗
TmLf
dTT =
∫ pw0
0dp′w
∫ T∗
TmLf
dTT = Lf ln
(T ∗Tm
)≈ Lf
T ∗ − Tm
Tm
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
Clapeyron’s equation
ρwLfdTT = dpw
Integrating ∫ T∗
TmLf
dTT =
∫ pw0
0dp′w
∫ T∗
TmLf
dTT = Lf ln
(T ∗Tm
)≈ Lf
T ∗ − Tm
Tm
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
Integrating ∫ T∗
TmLf
dTT =
∫ pw0
0dp′w
Melting temperature at unsatured conditions
T ∗ = Tm + gTm
Lfψw0
If the soil is unsaturated, the surface tension at water-airinterface
decreases the water melting temperature to a value T ∗ < Tm.
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
Integrating ∫ T∗
TmLf
dTT =
∫ pw0
0dp′w
Melting temperature at unsatured conditions
T ∗ = Tm + gTm
Lfψw0
If the soil is unsaturated, the surface tension at water-airinterface
decreases the water melting temperature to a value T ∗ < Tm.
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
Integrating ∫ T
TmLf
dTT =
∫ pw
pw0dp′w
Melting temperature at unsatured conditions
ψ(T ) = ψw0gTm
Lf(T − T ∗)
Water pressure depends on the intensity of freezing conditionprovided by T .
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
Integrating ∫ T
TmLf
dTT =
∫ pw
pw0dp′w
Melting temperature at unsatured conditions
ψ(T ) = ψw0gTm
Lf(T − T ∗)
Water pressure depends on the intensity of freezing conditionprovided by T .
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
Therefore ψ(T ) = ψw0 + Lf
gT ∗ (T − T ∗) T < T ∗
ψ(T ) = ψw0 T ≥ T ∗
K = K (θw )10−ωq T < T ∗K = K (θw ) T ≥ T ∗
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
Therefore ψ(T ) = ψw0 + Lf
gT ∗ (T − T ∗) T < T ∗
ψ(T ) = ψw0 T ≥ T ∗
K = K (θw )10−ωq T < T ∗K = K (θw ) T ≥ T ∗
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
Total water content, liquid water content and ice contentAccording to the Van Genuchten model:
Θv = θr + (θs − θr ) · {1 + [−αψw0]n}−m
θw = θr + (θs − θr ) · {1 + [−αψ(T )]n}−m
θi = Θv (ψw0)− θw [ψ(T )]
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
Total water content, liquid water content and ice contentAccording to the Van Genuchten model:
Θv = θr + (θs − θr ) · {1 + [−αψw0]n}−m
θw = θr + (θs − θr ) · {1 + [−αψ(T )]n}−m
θi = Θv (ψw0)− θw [ψ(T )]
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
Total water content, liquid water content and ice contentAccording to the Van Genuchten model:
Θv = θr + (θs − θr ) · {1 + [−αψw0]n}−m
θw = θr + (θs − θr ) · {1 + [−αψ(T )]n}−m
θi = Θv (ψw0)− θw [ψ(T )]
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
SWC and SFCDall’A
mico,
2010
Introduction Water flow in soil Freezing soil Numerical method
Mass conservation law
Richards’equation in freezing soil∂Θm(ψw0,T )
∂t + ~∇ · ~Jv (ψw0,T ) + Sw = 0
~Jv = −K ~∇(z + ψ)
Θm = θw + ρi
ρwθi
Introduction Water flow in soil Freezing soil Numerical method
Energy conservation law
UThe energy content of the soil is represented by the internalenergy U [Jm−3].
U = Usp + Ui + Uw
Introduction Water flow in soil Freezing soil Numerical method
Energy conservation law
Energy conservation law∂U∂t + ~∇ · (~G + ~J) + Sen = 0
Introduction Water flow in soil Freezing soil Numerical method
Energy conservation law
Go in details
Sen
It represents a sink term due to energy losses. [Wm−3]
Introduction Water flow in soil Freezing soil Numerical method
Energy conservation law
Go in details
~GIt is the conduction flux through the volume boundaries.[Wm−2]
~G = −λT ~∇T
Introduction Water flow in soil Freezing soil Numerical method
Energy conservation law
Go in details
~JIt is the heat advected by flowing water. [Wm−2]
~J = ρw · [Lf + cw (T − Tref ] · ~Jv
Introduction Water flow in soil Freezing soil Numerical method
Ground energy budget
Ground energy budget
Cp∂T∂t +
∑k∈{w ,i}
ρkhk = R − λeET − H
Introduction Water flow in soil Freezing soil Numerical method
Richards’ equation 1D∂θ(ψ)∂t = ∂
∂x
[K (ψ)∂ψ
∂x + K (ψ)]
Introduction Water flow in soil Freezing soil Numerical method
Finite volume scheme: FTCS
θn+1i = θn
i + ∆t∆x
[K n
i+1/2ψn+1
i+1 − ψn+1i
∆x + K ni+1/2
]−
∆t∆x
[K n
i−1/2ψn+1
i − ψn+1i−1
∆x − K ni−1/2
]
System in matrix form~θ + T~ψ = ~rhs
Introduction Water flow in soil Freezing soil Numerical method
Finite volume scheme: FTCS
θn+1i = θn
i + ∆t∆x
[K n
i+1/2ψn+1
i+1 − ψn+1i
∆x + K ni+1/2
]−
∆t∆x
[K n
i−1/2ψn+1
i − ψn+1i−1
∆x − K ni−1/2
]
System in matrix form~θ + T~ψ = ~rhs
Introduction Water flow in soil Freezing soil Numerical method
Newton-Raphson methodThe system is non linear so it must be solved by iteration.
The moisture content is in general a nonlinear function of thepressure head: it’s derivative isn’t nondecreasing nonincreasingfunction.
Introduction Water flow in soil Freezing soil Numerical method
Jordan decompositionIf the derivative of the functions is nondecreasing, thenNewton’s method converge.
The idea is to find two nondecreasing function whose differenceapproximate θ.
θ(ψ) = θ1(ψ)− θ2(ψ)
Introduction Water flow in soil Freezing soil Numerical method
Jordan decompositionIf the derivative of the functions is nondecreasing, thenNewton’s method converge.
The idea is to find two nondecreasing function whose differenceapproximate θ.
θ(ψ) = θ1(ψ)− θ2(ψ)
Introduction Water flow in soil Freezing soil Numerical method
Nested Newton method
Splitting ~θ~θ1(~ψn+1)− ~θ2(~ψn+1) + T~ψn+1 − ~rhs
n= 0
~θ1 linearization−~θ2(T n) +
[M + ~θ1(T n)′
]· ~T n+1,k +[
~θ1(T n)− ~θ1(T n)′ ~T n − ~bn+1]
= 0
~θ2 linearization[M + ~θ1(T n)′ − ~θ2(T n)′
]· ~T n+1,k,l +[
~θ1(T n)− ~θ2(T n)−(~θ1(T n)′ − ~θ2(T n)′
)~T n − ~bn+1
]= 0
Introduction Water flow in soil Freezing soil Numerical method
Nested Newton method
Splitting ~θ~θ1(~ψn+1)− ~θ2(~ψn+1) + T~ψn+1 − ~rhs
n= 0
~θ1 linearization−~θ2(T n) +
[M + ~θ1(T n)′
]· ~T n+1,k +[
~θ1(T n)− ~θ1(T n)′ ~T n − ~bn+1]
= 0
~θ2 linearization[M + ~θ1(T n)′ − ~θ2(T n)′
]· ~T n+1,k,l +[
~θ1(T n)− ~θ2(T n)−(~θ1(T n)′ − ~θ2(T n)′
)~T n − ~bn+1
]= 0
Introduction Water flow in soil Freezing soil Numerical method
Nested Newton method
Splitting ~θ~θ1(~ψn+1)− ~θ2(~ψn+1) + T~ψn+1 − ~rhs
n= 0
~θ1 linearization−~θ2(T n) +
[M + ~θ1(T n)′
]· ~T n+1,k +[
~θ1(T n)− ~θ1(T n)′ ~T n − ~bn+1]
= 0
~θ2 linearization[M + ~θ1(T n)′ − ~θ2(T n)′
]· ~T n+1,k,l +[
~θ1(T n)− ~θ2(T n)−(~θ1(T n)′ − ~θ2(T n)′
)~T n − ~bn+1
]= 0