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VERSION:2.0
PRODID:icalendar-ruby
CALSCALE:GREGORIAN
X-WR-CALNAME:PhD Dissertation Defense: Sohail Waziri
X-WR-TIMEZONE:Pacific Time (US & Canada)
BEGIN:VEVENT
DTSTAMP:20261008T094454Z
UID:tag:localist.com\,2008:EventInstance_53729135619695
DTSTART:20260824T200000Z
DTEND:20260824T210000Z
DESCRIPTION:Trust-region based fully implicit nonlinear solver for condensa
 tion-dominated geothermal systems \n\nAbstract: Thermal multiphase flow si
 mulation is central to the sustainable management of subsurface energy sys
 tems. The fully coupled\, fully implicit method (FIM) is the standard meth
 od for such problems\, but it suffers from stability and convergence issue
 s in geothermal systems undergoing steam condensation. FIM is unconditiona
 lly stable only when the underlying PDE is stable\, yet the coupled mass a
 nd energy conservation equations for flow with condensation are inherently
  unstable\, owing to the negative apparent compressibility of the steam–
 water mixture. FIM thus resolves the unstable mode only below a critical t
 ime-step size\, and its convergence is further restricted by the highly no
 nlinear residual space arising from the orders-of-magnitude contrast betwe
 en water and steam properties. We recast the governing equations in dimens
 ionless form\, derive the apparent compressibility—showing it takes oppo
 site signs in the two-phase and liquid regions—and obtain the stability 
 and convergence limits of FIM. We then introduce a multi-pass precondition
 ed fully implicit method (mppFIM)\, which combines nonlinear preconditioni
 ng of the condensation problem with physics-guided trust-region correction
 s to the post-Newton updates\, applied adaptively—most tightly at the fr
 ont—until convergence. Unlike FIM\, mppFIM converges for arbitrarily lar
 ge time steps on challenging problems\, yielding substantial computational
  savings. Negative apparent compressibility also degrades linear solver pe
 rformance. Using the true-IMPES constrained pressure residual (CPR) operat
 or to extract the pressure system\, we assess its suitability for M-matrix
 -based solvers such as AMG. The operator's departure from the M-matrix sig
 n structure is confined to liquid/two-phase interfaces and stems directly 
 from the contrasting compressibility signs of the two regions. The effects
  of rock energy accumulation and thermal conduction are also examined.
GEO:37.426823;-122.174006
LOCATION:Green Earth Sciences Building\, 365
SUMMARY:PhD Dissertation Defense: Sohail Waziri
URL;VALUE=URI:https://events.stanford.edu/event/phd-dissertation-defense-so
 hail-waziri
CATEGORIES:PhD Defense
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