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Sequential Methods for Coupled Geomechanics and Multiphase Flow

Sequential Methods for Coupled Geomechanics and Multiphase Flow

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6.4. STABILITY ANALYSIS VIA THE ENERGY METHOD 185<br />

6.4.3 Contractivity of the undrained split<br />

Similar to Equation 6.78 of the fully coupled method, Equation 6.4 gives<br />

⎡<br />

⎣ dun<br />

⎤<br />

⎡<br />

dpn ⎦<br />

J<br />

Au,m<br />

ud<br />

−→ ⎣ dun+1<br />

dp∗ ⎦<br />

J<br />

Ap,m<br />

ud<br />

−→ ⎣ dun+1<br />

dp n+1<br />

J<br />

⎤<br />

⎡<br />

⎤<br />

⎦, where<br />

⎧<br />

A<br />

⎪⎨<br />

u,m<br />

ud : Div dσ = 0, δdmJ = 0,<br />

A p,m<br />

ud : ˙<br />

dmJ + Div dwJ = 0,<br />

⎪⎩ dε ˙ = 0, dεp<br />

˙ = 0, dξ ˙ = 0,<br />

(6.82)<br />

where maximum plastic dissipation is assumed <strong>for</strong> elastoplasticity. We have homogeneous<br />

boundary conditions. When solving the mechanical problem A u,m<br />

ud<br />

obtain<br />

d dχm 2<br />

Nm<br />

dt<br />

=<br />

<br />

<br />

Ω<br />

<br />

dσ : ˙<br />

dε +<br />

<br />

dp<br />

ρ J<br />

<br />

dmJ<br />

˙<br />

<br />

dΩ −<br />

of Equation 6.82, we<br />

<br />

dσ ′ <br />

: dεp<br />

˙ + dκ · dξ ˙ dΩ<br />

Ω <br />

D<br />

<br />

d p<br />

= dσ : ˙ d<br />

dεdΩ − Dp Ω<br />

= −D d p ≤ 0 (from Equation 6.821), (6.83)<br />

which shows the contractivity property relative to the norm · Nm .<br />

Then when solving the flow problem A p,m<br />

ud<br />

d dχm 2<br />

Nm<br />

dt<br />

=<br />

=<br />

<br />

<br />

= −<br />

Ω<br />

<br />

dσ : ˙<br />

dε +<br />

<br />

dp<br />

ρ J<br />

−dpJ Div(dvJ)dΩ<br />

Ω<br />

of Equation 6.82,<br />

<br />

dmJ<br />

˙<br />

<br />

dΩ −<br />

<br />

dσ ′ <br />

: dεp<br />

˙ + dκ · dξ ˙ dΩ<br />

Ω <br />

D<br />

<br />

d p<br />

<br />

.. .<br />

dε ˙ = 0, dεp<br />

˙ = 0, dξ ˙ = 0<br />

dvJ · k<br />

Ω<br />

−1<br />

p,JKdvKdΩ ≤ 0, (6.84)<br />

which shows the contractivity property relative to the norm · Nm . There<strong>for</strong>e, the undrained<br />

split holds the contractivity property relative to the norms · Nm <strong>and</strong> · Tm <strong>for</strong> coupled

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