Sharing scientific experiments and workflows in environmental applications

Environmental applications have been stimulating the cooperation among scientists from different disciplines. There are many examples where this cooperation takes place through exchanging scientific resources, such as data, programs and mathematical models. The LeSelect architecture supports environmental applications, where scientists may share their data and programs. We believe that besides programs and data, models, as well as experiments and workflows are scientific resources that need to be shared in environmental applications. Therefore, in this paper we propose an extension to LeSelect architecture that allows sharing of models, experiments and workflows

Covalidation of Dissimilarly Structured Models

A methodology is presented which allows comparison between models constructed under different modeling paradigms. Consider the following situation: Two models are constructed to study different aspects of the same system. One model simulates a fleet of aircraft moving a given combination of cargo and passengers from an onload point to an offload point. A second model is a linear programming model that optimizes the aircraft and route selection required for the same scenario. We develop a methodology to structure the comparison between large-scale models such as these. Models that compare favorably using this methodology are deemed covalid. Models that perform similarly under the same input conditions are covalid in a narrow sense. Models that are covalid (in this narrow sense) hold the potential to be used in an iterative fashion to improve the input (and thus, the output) of one another We prove that, under certain regularity conditions, this method of output/input crossflow converges, and if the convergence is to a valid representation of the real-world system, the models are covalid in a wide sense. Further, if one of the models has been independently validated, then we may effect a validation by association of the other model through this process

Exploration and assessment of the environmental design space for commercial aircraft and future technologies

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004.Includes bibliographical references (p. 83-86).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Design and regulatory initiatives for aircraft noise and emissions should appreciate the integrated nature of the aircraft system. The computational ability exists to consider environmental and traditional performance objectives of aircraft concurrently. This context of multi-disciplinary system design is named the Environmental Design Space (EDS) and is studied in this thesis with an integrated aircraft-engine conceptual design framework. With this tool, the objectives of this thesis were to assess the fidelity and level of uncertainty of the design framework, to characterize the tradeoffs between aircraft noise, emissions and aircraft performance and to evaluate the system-level impacts of a future noise reduction technology. Assessment of the EDS framework was accomplished with a probabilistic model assessment methodology. The assessment involved the selection of stochastic inputs and generation of output distributions through Monte Carlo simulations. A sensitivity analysis of the key drivers of uncertainty and the user-defined input distributions is also provided. This methodology was applied to one of the framework modules, the NASA Engine Performance Program (NEPP), and found that the modeling error was subsumed within the modeling uncertainty. A sensitivity study indicated that the component efficiencies had the largest impact on the output distribution. When the level of NEPFP uncertainty was propagated to the system level, the resulting coefficient of variance for fuel burn was 4.1%. The tradeoffs between the competing EDS objectives were characterized through Pareto fronts generated by multi-objective genetic algorithms.(cont.) The quantification of these trades for a given aircraft, 8 dB in cumulative EPNL vs. 8kg of LTO-NO[sub]x for example, give designers and regulators supporting information for their decisions. A future noise reduction technology, fan trailing edge blowing, was also evaluated at the system level. A probabilistic analysis of the technology design in the EDS framework revealed poor tolerance of engine cycle variability. A robust design procedure was employed, and showed that while the technology offered a flyover noise reduction of 11.9 dB, it incurred a fuel burn and LTO-NO[sub]x penalty of 2.8% and 11.0%, respectively.by Garrett E. Barter.S.M

A quantitative approach to assessing the effectiveness of catchment management for the improvement of drinking water quality

Access to safe water is essential to maintain life. An understanding of all the potential contamination risks and an ability to manage those risks is imperative in the supply of water for human consumption. Having multiple scientifically validated barriers to contamination is the most widely accepted management technique for drinking water protection. Catchment management is a barrier that aims to control contamination at the source thereby reducing the reliance of removal of contamination by treatment. Buffer strips are one such measure. They are known to be effective at minimising waterway pollution by reducing the momentum and magnitude of surface and sub-surface runoff thereby aiding infiltration into the soil column and promoting entrapment of pollutants. This process has been well researched in terms of constituents such as sediments and nutrients. In a drinking water catchment, however, the ability of these buffer strips to trap or remove human infectious pathogens is of most interest as they are the greatest risk to consumers. The aim of this research is to determine a way of predicting the decrease in risk to public health due to the implementation of buffer strips in an agricultural catchment and to validate their effectiveness. A drinking water catchment with an extensive amount of water quality data and an active catchment management program was chosen as the study catchment. Detailed statistical analysis was performed to evaluate the spatial and temporal changes in water quality and to determine trends. Additionally the processes most affecting water quality were established. To enable prediction of any changes a model that specifically simulated pathogen fate and transport through a catchment was necessary. A simple lumped conceptual model, EG, was chosen. EG was not, however, specifically developed to determine the effectiveness of buffer strips and therefore modifications to the pathogen transport processes were required. Calibration, validation and uncertainty analyses were undertaken. This research shows that it is possible to quantify the benefits of buffer strip implementation to final drinking water quality. Validation of the barrier’s effectiveness will allow the comparison of investing in catchment management to treatment costs and an assessment of the risk reduction benefits of both