Tesis doctoral de Juan José Hidalgo González
Groundwater models have become an irreplaceable tool in hydrology. Density-dependent flow and transport simulation is specially challenging for numerical models because of its non linear coupled nature. Density dependence affects many groundwater problems, e.G., Saltwater intrusion in coastal aquifers, heat storage or contaminant remediation. This thesis deals with four open issues in density-dependent flow and transport in groundwater problems. first, boundary and internal salt sources are usually neglected in the fluid mass balance. Here, they are formally introduced. Their effect is quantified on two examples. These show that neglecting salt sources causes head to decrease, which contradicts basic physical principles. As a result, an inversion in the flow direction is observed. Discrepancies in concentrations are mild, except when the prescribed salt mass fraction is close to one. However, it can be concluded that pure salt sources, when present, need to be included in the flow equation whenever detailed descriptions of flow or accurate mass balances are sought. second, injection of dioxc in saline aquifers is often studied under a number of simplifications. Dispersion is neglected and the dioxc-brine interface is treated as a prescribed concentration boundary by analogy with a thermal convection problem. In this thesis, the effect of accounting for the dioxc mass flux across the prescribed concentration boundary and hydrodynamic dispersion on the onset of convection during dioxc injection is studied. It was found that accounting for the dioxc mass flux does not change qualitatively the time for the onset of the convective regime but accounting for dispersion causes a significant reduction on the time it takes for convection to become the dominant transport mechanism. This implies that dioxc dissolution can be accelerated by activating dispersion as a transport mechanism, which can be achieved by adopting a fluctuating injection regime. spatial variability of hydraulic conductivity is known to cause dispersion. However, the use of a dispersion term in addition to thermal conductivity is not widely accepted. The third objective addressed in this thesis is to investigate the dispersion of a heat plume generated by a groundwater heat exchanger under steady state conditions. To that end, a three-dimensional model of a groundwater heat exchanger is studied under a stochastic approach. Density effects are not included in the model because they are considered of smaller order compared to those of heterogeneity in the hydraulic conductivity. Results show that heterogeneity in aquifer conductivity increases transverse dispersion near the heat source. Then, it decreases with the distance from the heat source. Despite the influence in the plume dispersion, no relevant effects in the performance of the thermal device were found. finally, a new algorithm for the calibration of density-dependent flow and transport models is presented. The algorithm takes advantage of the newton method and the analytical computation of the sensitivity matrix. A synthetic saltwater intrusion model is calibrated to test the efficiency of the algorithm. its performance is compared with the usual combination of picard method and parameter perturbation for the computation of sensitivities. computational performance tests showed a reduction in the cpu time needed for calibration. Moreover, it was found that the cost per additional calibrated parameter was significantly lower using the new algorithm. This allows modellers to increase the number of parameters to calibrate, i.E., The complexity of the model, without substantially increasing the cost of the calibration process.
Datos académicos de la tesis doctoral «Simulation and calibration of density-dependent flow problems in porous media«
- Título de la tesis: Simulation and calibration of density-dependent flow problems in porous media
- Autor: Juan José Hidalgo González
- Universidad: Politécnica de catalunya
- Fecha de lectura de la tesis: 08/01/2009
Dirección y tribunal
- Director de la tesis
- Jesús Carrera Ramírez
- Tribunal
- Presidente del tribunal: philippe Ackerer
- rubén Juan es (vocal)
- xavier Sánchez vila (vocal)
- orlando Silva rojas (vocal)