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Sequential Methods for Coupled Geomechanics and Multiphase Flow

Sequential Methods for Coupled Geomechanics and Multiphase Flow

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4.2. SPECTRAL ANALYSIS 93<br />

where<br />

⎛<br />

⎜<br />

A1ξ = ⎜<br />

⎝<br />

vk<br />

1<br />

ρb Div(Cdr : ε − bp1)<br />

0<br />

⎞<br />

⎛<br />

⎟<br />

⎠ , s1<br />

⎜<br />

= ⎜<br />

⎝<br />

0<br />

1<br />

ρb Div bp01 + g<br />

0<br />

⎞<br />

⎟<br />

⎟,<br />

(4.42)<br />

⎠<br />

⎛<br />

⎜<br />

A2ξ = ⎜<br />

⎝<br />

0<br />

0<br />

M Div kp<br />

µ Gradp − bM Grads ⎞<br />

vk : 1<br />

⎛<br />

⎟<br />

⎟,<br />

⎠<br />

(4.43)<br />

⎜<br />

s2 = ⎜<br />

⎝<br />

0<br />

0<br />

−M Div kp<br />

µ ρfg<br />

⎞<br />

+ f<br />

⎟<br />

⎟.<br />

⎠<br />

(4.44)<br />

Equation 4.40 implies that the product <strong>for</strong>mula of the operator splitting converges to the<br />

original operator as the time step size goes to zero. Thus, the drained split of the coupled<br />

flow <strong>and</strong> dynamics is convergent, whereas the drained split of the coupled flow <strong>and</strong> statics<br />

is not convergent, especially close to the stability limit.<br />

Remark 4.5. Similar to coupled flow <strong>and</strong> statics in Remark 4.4, max|γe| ≤ 1 <strong>for</strong> all<br />

θ in Equation 4.38 provides a necessary condition <strong>for</strong> stability in the coupled flow <strong>and</strong><br />

dynamics. Consider the undrained limit corresponding to kp = 0 in order to compare with<br />

the stability estimate of thermoelasticity in Armero <strong>and</strong> Simo (1992). Then, the stability<br />

condition becomes (see Appendix B.2)<br />

<br />

2as<br />

2 ∆t<br />

(τ − 1) ≤ 1, (4.45)<br />

h<br />

where a 2 s = Kdr<br />

ρb , <strong>and</strong> as is the speed of sound (Hughes, 1987). Equation 4.45 has a similar<br />

<strong>for</strong>m to that of Armero <strong>and</strong> Simo (1992). The slight difference between the two is due<br />

to the different space <strong>and</strong> time discretization. In contrast to coupled flow <strong>and</strong> statics, we

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