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Sequential Methods for Coupled Geomechanics and Multiphase Flow

Sequential Methods for Coupled Geomechanics and Multiphase Flow

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52 CHAPTER 3. STABILITY OF THE DRAINED AND UNDRAINED SPLITS<br />

the drained split can be expressed as<br />

⎡<br />

⎣ dun<br />

dp n<br />

⎤<br />

⎦ Au dr<br />

−→<br />

⎡<br />

⎣ dun+1<br />

dp n<br />

⎤<br />

⎦ Ap<br />

dr<br />

−→<br />

⎡<br />

⎣ dun+1<br />

⎤<br />

dp n+1<br />

⎦, where<br />

⎧<br />

⎪⎨<br />

⎪⎩<br />

A u dr<br />

: Div dσ = 0, δ(dp) = 0,<br />

A p<br />

dr : ˙<br />

dm + Div dw = 0,<br />

dε ˙ = 0, dεp<br />

˙ = 0, dξ ˙ = 0,<br />

(3.86)<br />

which has homogeneous boundary conditions with no source terms. Since ˙ε, εp, ˙ <strong>and</strong> ˙ ξ<br />

are prescribed, they are not affected by the perturbation of the initial condition, yielding<br />

dε ˙ = 0, dεp<br />

˙ = 0, <strong>and</strong> ˙ dξ = 0. When we solve the mechanical problem Au dr<br />

split, we have,<br />

dΨ d<br />

dt =<br />

=<br />

=<br />

<br />

<br />

<br />

Ω<br />

Ω<br />

<br />

dσ : ˙<br />

dε + dp<br />

ρf,0<br />

<br />

dm ˙ dΩ −<br />

<br />

dσ ′ : dεp<br />

˙ + κ · ˙<br />

<br />

dξ dΩ<br />

Ω <br />

D<br />

<br />

d p<br />

<br />

dσ : dε ˙<br />

dp<br />

+ b<br />

ρf,0<br />

˙<br />

<br />

dεv dΩ − D d p (from δ(dp) = 0)<br />

dp<br />

by the drained<br />

b<br />

Ω ρf,0<br />

˙ dεvdΩ − D d p ≤ 0 (from Div dσ = 0) . (3.87)<br />

Equation 3.87 proves that the drained split is not contractive when we solve the mechanical<br />

problem. This non-contractivity of the drained split has been pointed out by Armero <strong>and</strong><br />

Simo (1992) <strong>and</strong> Armero (1999).<br />

Then, when we solve the flow problem A p<br />

dr by the drained split, we have<br />

dΨ d<br />

dt =<br />

<br />

Ω<br />

<br />

<br />

dσ : dε ˙<br />

dp<br />

<br />

+ dm ˙ dΩ − dσ<br />

ρf,0<br />

Ω<br />

′ : dεp<br />

˙ + dκ · ˙<br />

<br />

dξ dΩ<br />

<br />

=<br />

<br />

−dp Div(dv)dΩ<br />

<br />

.. .<br />

dε ˙ = 0, dεp<br />

˙ = 0, dξ ˙ = 0<br />

Ω<br />

= − dv · µk −1 dvdΩ ≤ 0. (3.88)<br />

Ω<br />

Dp

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