Statistical analysis of liquid seepage in partially saturated heterogeneous fracture systems

Field evidence suggests that water flow in unsaturated fracture systems may occur along fast preferential flow paths. However, conventional macroscale continuum approaches generally predict the downward migration of water as a spatially uniform wetting front subjected to strong inhibition into the partially saturated rock matrix. One possible cause of this discrepancy may be the spatially random geometry of the fracture surfaces, and hence, the irregular fracture aperture. Therefore, a numerical model was developed in this study to investigate the effects of geometric features of natural rock fractures on liquid seepage and solute transport in 2-D planar fractures under isothermal, partially saturated conditions. The fractures were conceptualized as 2-D heterogeneous porous media that are characterized by their spatially correlated permeability fields. A statistical simulator, which uses a simulated annealing (SA) algorithm, was employed to generate synthetic permeability fields. Hypothesized geometric features that are expected to be relevant for seepage behavior, such as spatially correlated asperity contacts, were considered in the SA algorithm. Most importantly, a new perturbation mechanism for SA was developed in order to consider specifically the spatial correlation near conditioning asperity contacts. Numerical simulations of fluid flow and solute transport were then performed in these synthetic fractures by the flow simulator TOUGH2, assuming that the effects of matrix permeability, gas phase pressure, capillary/permeability hysteresis, and molecular diffusion can be neglected. Results of flow simulation showed that liquid seepage in partially saturated fractures is characterized by localized preferential flow, along with bypassing, funneling, and localized ponding. Seepage pattern is dominated by the fraction of asperity contracts, and their shape, size, and spatial correlation. However, the correlation structure of permeability field is less important than the spatial correlation of asperity contacts. A faster breakthrough was observed in fractures subjected to higher normal stress, accompanied with a nonlinearly decreasing trend of the effective permeability. Interestingly, seepage dispersion is generally higher in fractures with intermediate fraction of asperity contacts; but it is lower for small or large fractions of asperity contacts. However, it may become higher if the ponding becomes significant. Transport simulations indicate that tracers bypass dead-end pores and travel along flow paths that have less flow resistance. Accordingly, tracer breakthrough curves generally show more spreading than breakthrough curves for water. Further analyses suggest that the log-normal time model generally fails to fit the breakthrough curves for water, but it is a good approximation for breakthrough curves for the tracer

Statistical analysis of liquid seepage in partially saturated heterogeneous fracture systems

Field evidence suggests that water flow in unsaturated fracture systems may occur along fast preferential flow paths. However, conventional macroscale continuum approaches generally predict the downward migration of water as a spatially uniform wetting front subjected to strong inhibition into the partially saturated rock matrix. One possible cause of this discrepancy may be the spatially random geometry of the fracture surfaces, and hence, the irregular fracture aperture. Therefore, a numerical model was developed in this study to investigate the effects of geometric features of natural rock fractures on liquid seepage and solute transport in 2-D planar fractures under isothermal, partially saturated conditions. The fractures were conceptualized as 2-D heterogeneous porous media that are characterized by their spatially correlated permeability fields. A statistical simulator, which uses a simulated annealing (SA) algorithm, was employed to generate synthetic permeability fields. Hypothesized geometric features that are expected to be relevant for seepage behavior, such as spatially correlated asperity contacts, were considered in the SA algorithm. Most importantly, a new perturbation mechanism for SA was developed in order to consider specifically the spatial correlation near conditioning asperity contacts. Numerical simulations of fluid flow and solute transport were then performed in these synthetic fractures by the flow simulator TOUGH2, assuming that the effects of matrix permeability, gas phase pressure, capillary/permeability hysteresis, and molecular diffusion can be neglected. Results of flow simulation showed that liquid seepage in partially saturated fractures is characterized by localized preferential flow, along with bypassing, funneling, and localized ponding. Seepage pattern is dominated by the fraction of asperity contracts, and their shape, size, and spatial correlation. However, the correlation structure of permeability field is less important than the spatial correlation of asperity contacts. A faster breakthrough was observed in fractures subjected to higher normal stress, accompanied with a nonlinearly decreasing trend of the effective permeability. Interestingly, seepage dispersion is generally higher in fractures with intermediate fraction of asperity contacts; but it is lower for small or large fractions of asperity contacts. However, it may become higher if the ponding becomes significant. Transport simulations indicate that tracers bypass dead-end pores and travel along flow paths that have less flow resistance. Accordingly, tracer breakthrough curves generally show more spreading than breakthrough curves for water. Further analyses suggest that the log-normal time model generally fails to fit the breakthrough curves for water, but it is a good approximation for breakthrough curves for the tracer

Identification of the origin of salinization in groundwater using multivariate statistical analysis and geochemical modeling: a case study of Kaohsiung, Southwest Taiwan

The study of brine aquifers in southern Taiwan is highly complicated by hybrid geochemical reactions, which obscure important geochemical information. Using multivariate analysis on major and minor ion compositions normalized by Cl(-) content, chemical constituents were combined into two principal components representing brine mixing and mineral precipitation. Comparing to multivariate analysis on the original data, this procedure reveals more geochemical information. It demonstrates that the brine groundwater of the region is primarily composed of highly evaporated seawater. The evaporation ratio is > 70%; a point at which calcite, dolomite and gypsum precipitate. Oxygen and hydrogen isotopic compositions confirm this inference; and further, geochemical modeling quantitatively determined the evaporation ratio to be about 85%. Natural boron contamination is a consequence of brine groundwater. Two evolutionary trends in the plotting of the Cl/B ratio versus Cl(-) can be identified: (1) Cl/B ratio decreases with boron being released from clay minerals when brine aquifers are flushed with freshwater; and (2) Cl/B ratio increases when seawater of a high Cl/B ratio infiltrates coastal aquifers

Methodology for Ideation of Interaction Design

This paper explores new methodology, tools, and techniques for ideation of interaction design. On one hand, our work takes a mixed approach to developing design methodology by integrating usability tests and ethnographic studies in the ideation process. On the other hand, parallel design with user participation is attempted to reduce interactive design life cycle. An interaction design example is drawn from i-Awn project, an activity-coordination and reminding system in smart homes. This example demonstrates our mixed approach and shows how a new methodology is developed for validating the quality of user experience in a critical process of designing. The objective is to get the right interaction and the interaction right, provoking new ways of thinking about usability evaluation in the ideation process. The social, cultural and emotional uses of interactive systems in smart homes are discussed

Use of geochemical modeling to evaluate the hydraulic connection of aquifers: a case study from Chianan Plain, Taiwan

Aquifers are generally composed of highly permeable layers that can conduct a considerable amount of groundwater. Traditionally, aquifer units are correlated through the concept of lithostratigraphy. For low-permeable aquifers, it is difficult to define the spatial distribution of hydrogeological units, and this study attempts to use geochemical modeling to identify the groundwater flow paths in an area of Taiwan. Multiple geochemical analyses, including groundwater chemistry; stable isotopic compositions of hydrogen, oxygen and carbon; and radiocarbon contents were performed. Using these parameters as the constraints of geochemical models, the hydraulic connection was examined between pairs of possibly interlinked wells along four selected cross sections, and the conceptual groundwater model was accordingly established. The resultant model suggests that the hydraulic connection between aquifers should be correlated with the concept of chronological stratigraphy, especially for low-permeable, unconsolidated aquifers. Using Darcy's law, the hydraulic conductivities of the fine-sand aquifers were estimated to be between 3.14x10(-5) and 1.80x(-4) m/s, which are roughly one order of magnitude higher than those derived by in situ pumping tests. The substantial extraction of groundwater over a long period in the studied area could accelerate groundwater flow, leading to an overestimation of the aquifer permeability

Fuzzy Decision Analysis for Alternative Selection Using a Fuzzy Annual Worth Criterion

[[abstract]]Very often, in industry, discounted cash flow techniques are applied for analyzing and selecting investment alternatives under consideration. These techniques are usually based on the data under certainty or risk. In reality, however, the decision makers are often facing the situation of vague cash flows and discount rates, or even uncertain durations, when evaluating and selecting potential investments. Fuzzy set theory has the capability of capturing vague data and allows mathematical operations. This article proposes a fuzzy equivalent uniform annual worth (fuzzy EUAW) method to assist practitioners in evaluating investment alternatives utilizing the theory of fuzzy sets. Triangular fuzzy numbers (TFNs) are used throughout the analysis to represent the uncertain cash flows and discount rates. Further, fuzzy capital recovery factors and fuzzy sinking fund factor are derived. Using these two factors, the fuzzy equivalent annual worth of each investment alternative can be found. By ranking these fuzzy numbers with the integral value, the optimal investment alternative is selected. A numerical example is provided to illustrate the results of the alternative selection