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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 187<br />

d dχm 2<br />

Nm<br />

dt<br />

=<br />

<br />

Ω<br />

<br />

dσ : ˙<br />

dε +<br />

<br />

dp<br />

ρ J<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 />

= − dvJ · k<br />

Ω<br />

−1<br />

p,JK µdvK<br />

<br />

dΩ − D d p ≤ 0. (6.88)<br />

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

ss , we show the contractivity of the fixed-stress<br />

split as<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 />

<br />

dσ ′ <br />

: dεp<br />

˙ + dκ · dξ ˙ dΩ<br />

Ω <br />

D<br />

<br />

d p<br />

= dσ<br />

Ω<br />

′ : dεdΩ ˙ d<br />

− Dp = −D d p ≤ 0, (6.89)<br />

<br />

dσ<br />

Ω<br />

′ : dεdΩ ˙ = 0 from Equation 6.852<br />

There<strong>for</strong>e, the fixed-stress split holds the contractivity property relative to the norms<br />

· Nm <strong>and</strong> · Tm .<br />

6.4.5 B-stability of the sequential methods<br />

Since the undrained <strong>and</strong> fixed-stress splits are contractive, we study the two sequential<br />

schemes <strong>for</strong> discrete stability, B-stability relative to the norms · Nm or · Tm , which is<br />

expressed as<br />

<br />

dχm n+1 ≤ dχm Nm n , Nm<br />

<br />

dζm n+1 ≤ dζm Tm n . (6.90)<br />

Tm<br />

We use the generalized midpoint rule <strong>for</strong> time discretization. Thus, the return mapping<br />

<br />

.

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