10 research outputs found
Recommended from our members
Sensitivity of hydrological performance assessment analysis to variations in material properties, conceptual models, and ventilation models
The Yucca Mountain Site Characterization Project is studying Yucca Mountain in southwestern Nevada as a potential site for a high-level nuclear waste repository. Site characterization includes surface- based and underground testing. Analyses have been performed to support the design of an Exploratory Studies Facility (ESF) and the design of the tests performed as part of the characterization process, in order to ascertain that they have minimal impact on the natural ability of the site to isolate waste. The information in this report pertains to sensitivity studies evaluating previous hydrological performance assessment analyses to variation in the material properties, conceptual models, and ventilation models, and the implications of this sensitivity on previous recommendations supporting ESF design. This document contains information that has been used in preparing recommendations for Appendix I of the Exploratory Studies Facility Design Requirements document
Recommended from our members
Numerical methods for fluid flow in unsaturated heterogeneous tuff
A numerical approach for modeling unsaturated flow is developed for heterogeneous simulations of fractured tuff generated using a geostatistical method. Cross correlations of hydrologic properties and upscaling of moisture retention curves is discussed. The approach is demonstrated for a study of infiltration at Yucca Mountain
Recommended from our members
Modeling heterogeneous unsaturated porous media flow at Yucca Mountain
Geologic systems are inherently heterogeneous and this heterogeneity can have a significant impact on unsaturated flow through porous media. Most previous efforts to model groundwater flow through Yucca Mountain have used stratigraphic units with homogeneous properties. However, modeling heterogeneous porous and fractured tuff in a more realistic manner requires numerical methods for generating heterogeneous simulations of the media, scaling of material properties from core scale to computational scale, and flow modeling that allows channeling. The Yucca Mountain test case of the INTRAVAL project is used to test the numerical approaches. Geostatistics is used to generate more realistic representations of the stratigraphic units and heterogeneity within units is generated using sampling from property distributions. Scaling problems are reduced using an adaptive grid that minimizes heterogeneity within each flow element. A flow code based on the dual mixed-finite-element method that allows for heterogeneity and channeling is employed. In the Yucca Mountain test case, the simulated volumetric water contents matched the measured values at drill hole USW UZ-16 except in the nonwelded portion of Prow Pass
Recommended from our members
Recent developments in stochastic modeling and upscaling of hydrologic properties in tuff
A set of detailed geostatistical simulations of porosity has been produced for a layered stratigraphic sequence of welded and nonwelded volcanic tuffs at Yucca Mountain, Nevada. The simulations are produced using a composite. model of spatial continuity and they are highly conditioned to abundant drill hole (core) information. A set of derivative simulations of saturated hydraulic conductivity has been produced, in the absence of conditioning data, using a cross-variable relationship developed from similar data elsewhere. The detailed simulations reproduce both the major stratigraphic units and finer scale layering indicated by the drill hole data. These simulations have been scaled up several order of magnitude to represent block-scale effective hydrologic properties suitable for use in numerical modeling of groundwater flow and transport. The upscaling process involves the reformulation of a previously reported method that iteratively adapts an initial arbitrary grid to ``homogenize`` the detailed hydraulic properties contained within the adjusted cell limits and to minimize the size of cell in highly heterogeneous regions. Although the computation of the block-effective property involves simple numerical averaging, the blocks over which these averages are computed are relatively homogeneous, which reduces the numerical difficulties involved in averaging non-additive properties, such as permeability. The entire process of simulation and upscaling is rapid and computationally efficient compared with alterative techniques. It is thus suitable for the Monte Carlo evaluation of the uncertainty in site characterization as it affects the results of groundwater flow and transport calculations
Recommended from our members
Development of stochastic indicator models of lithology, Yucca Mountain, Nevada
Indicator geostatistical techniques have been used to produce a number of fully three-dimensional stochastic simulations of large-scale lithologic categories at the Yucca Mountain site. Each realization reproduces the available drill hole data used to condition the simulation. Information is propagated away from each point of observation in accordance with a mathematical model of spatial continuity inferred through soft data taken from published geologic cross sections. Variations among the simulated models collectively represent uncertainty in the lithology at unsampled locations. These stochastic models succeed in capturing many major features of welded-nonwelded lithologic framework of Yucca Mountain. However, contacts between welded and nonwelded rock types for individual simulations appear more complex than suggested by field observation, and a number of probable numerical artifacts exist in these models. Many of the apparent discrepancies between the simulated models and the general geology of Yucca Mountain represent characterization uncertainty, and can be traced to the sparse site data used to condition the simulations. Several vertical stratigraphic columns have been extracted from the three-dimensional stochastic models for use in simplified total-system performance assessment exercises. Simple, manual adjustments are required to eliminate the more obvious simulation artifacts and to impose a secondary set of deterministic geologic features on the overall stratigraphic framework provided by the indictor models
A Paradigmatic and Methodological Examination of Information Systems Research from 1991 to 2001
The field of information systems (IS) has evolved for more than three decades. Although many schools of thought have emerged and even become well established, few historical analyses of research paradigms and methodologies have been undertaken. One of the rare exceptions is Orlikowski & Baroudi (1991). Yet, the IS research community has evolved substantially since 1991 in many aspects. A variety of journal outlets have emerged and become well established. More attention has been paid to paradigmatic and methodological issues. Political and professional contexts have also changed noticeably. Therefore, it should be an opportune time for the field to ask: âWhat changes are manifested in journal publications?ââIs the field making progress regarding pluralism in IS research?â âHow will the fieldâs publications practices change in the future?â The purpose of this paper is to investigate these questions and, in turn, reflect on the paradigmatic and methodological progress made since 1991. We examined 1893 articles published in eight major IS publication outlets between 1991 and 2001. Our findings suggest that the long-term endeavours of interpretivist researchers might need to continue because the paradigmatic progress appears somewhat inconsequential; positivist research still dominates 81% of published empirical research. In particular, US journals, as opposed to European journals, tend to be more positivist, quantitative, cross-sectional and survey oriented. With respect to research design, survey research is still the most widely used method (41%), although case studies have gained substantial recognition (36%). Further, the increase of qualitative research (30%), empirical studies (61%) and longitudinal cases (33%) at the expense of laboratory experiments (18%) might suggest that IS researchers have become more interested in obtaining scientific knowledge in real world settings. In summary, we
suggest that the field has been dominated by the positivist paradigm, despite calls to the contrary. Indeed, if the field was to truly embrace pluralism, it would have to find ways to fundamentally change the publication practices of the journal system, including the current tenure and promotion system, which pose considerable obstacles for the acceptance of alternative paradigms