Numerical Simulation of the Hydrological and Geochemical Environment in the Martian Subsurface, 20-9313

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Principal Investigators
Scott L. Painter
Cynthia Dinwiddie

Inclusive Dates: 04/01/02 - 04/06/03

Background - Methods for simulating non-isothermal, multiphase flow and geochemical transport in unsaturated geological media have matured in recent years, and are now used in a range of advanced terrestrial applications. Similar general-purpose computational tools have a range of potential applications in Mars research. They may be used, for example, to support data analysis, test hypotheses regarding the evolution and current state of subsurface hydrological systems, and evaluate potential perturbations from future drilling. This project has developed a computer code, MarsFlo, which simulates the hydrological environment of the Martian subsurface.

Approach - The prototype version of MarsFlo is based on a power balance equation coupled with mass conservation equations for CO2 and for water in the vapor, liquid and ice phases. The general modeling strategy is to use equilibrium constraints to reduce the system to three non-linear coupled conservation equations, which are then solved using an integral-finite-difference method and fully implicit time stepping similar to the SwRI-developed MULTIFLO™ code. The required constitutive relationships were developed from the theory of freezing terrestrial soils and modified for Martian conditions. Gaps in the existing theory for geochemical processes in frozen soils were identified for further research.

Accomplishments - A detailed modeling approach based on existing theory of freezing soils and published curve fits to thermophysical properties of water and ice was finalized. A flexible and modular code design was completed. Generic data structures were implemented, and key numerical routines from the MULTIFLO™ code were adapted to an object-oriented format to facilitate re-use in MarsFlo. Demonstration simulations using the prototype code successfully modeled both a laboratory freezing experiment and freezing of a Martian aquifer. Future development of the MarsFlo code will focus on improving numerical performance, on models for atmosphere/subsurface interactions, and on coupling with geochemistry codes.

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