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Modeling Tools (modeling + tool)
Selected AbstractsFEFLOW: A Finite-Element Ground Water Flow and Transport Modeling ToolGROUND WATER, Issue 5 2007Mike G. Trefry First page of article [source] Model Based Evaluation of Bridge Decks Using Ground Penetrating RadarCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 1 2008Kimberly Belli Interpretation of the radar signal is typically performed through preliminary filtering techniques and interpretation is based on viewing numerous signals in the form of a scan. Although anomalies can be evident in the scanned image, quantification and interpretation of the main issue remain ambiguous. This article presents the ambiguity and common methods of interpretation based on response amplitude and travel time. An integrated medium is developed and used as a forward modeling tool to generate a realistic radar reflection of a reinforced concrete bridge deck with defects. A healthy deck reflection is obtained from a separate model and is combined with an inverse solution to quantifiably estimate unknown subsurface properties such as layer thickness and dielectric constants of subsurface materials evident in the realistic radar trace as well as. The forward modeling tool and associated model based assessment provides an objective computational alternative to the interpretation of scanned images. [source] Fuel Cell Vehicle Simulation , Part 1: Benchmarking Available Fuel Cell Vehicle Simulation ToolsFUEL CELLS, Issue 3 2003K.H. Hauer Abstract Fuel cell vehicle simulation is one method for systematic and fast investigation of the different vehicle options (fuel choice, hybridization, reformer technologies). However, a sufficient modeling program, capable of modeling the different design options, is not available today. Modern simulation programs should be capable of serving as tools for analysis as well as development. Shortfalls of the existing programs, initially developed for internal combustion engine hybrid vehicles, are: (i)Insufficient modeling of transient characteristics; (ii) Insufficient modeling of the fuel cells system; (iii) Insufficient modeling of advanced hybrid systems; (iv) Employment of a non-causal (backwards looking) structure; (v) Significant shortcomings in the area of controls. In the area of analysis, a modeling tool for fuel cell vehicles needs to address the transient dynamic interaction between the electric drive train and the fuel cell system. Especially for vehicles with slow responding on-board fuel processor, this interaction is very different from the interaction between a battery (as power source) and an electric drive train in an electric vehicle design. Non-transient modeling leads to inaccurate predictions of vehicle performance and fuel consumption. When applied in the area of development, the existing programs do not support the employment of newer techniques, such as rapid prototyping. This is because the program structure merges control algorithms and component models, or different control algorithms (from different components) are lumped together in one single control block and not assigned to individual components as they are in real vehicles. In both cases, the transfer of control algorithms from the model into existing hardware is not possible. This paper is the first part of a three part series and benchmarks the "state of the art" of existing programs. The second paper introduces a new simulation program, which tries to overcome existing barriers. Specifically it explicitly recognizes the dynamic interaction between fuel cell system, drive train and optional additional energy storage. [source] Karst Spring Responses Examined by Process-Based ModelingGROUND WATER, Issue 6 2006Steffen Birk Ground water in karst terrains is highly vulnerable to contamination due to the rapid transport of contaminants through the highly conductive conduit system. For contamination risk assessment purposes, information about hydraulic and geometric characteristics of the conduits and their hydraulic interaction with the fissured porous rock is an important prerequisite. The relationship between aquifer characteristics and short-term responses to recharge events of both spring discharge and physicochemical parameters of the discharged water was examined using a process-based flow and transport model. In the respective software, a pipe-network model, representing fast conduit flow, is coupled to MODFLOW, which simulates flow in the fissured porous rock. This hybrid flow model was extended to include modules simulating heat and reactive solute transport in conduits. The application of this modeling tool demonstrates that variations of physicochemical parameters, such as solute concentration and water temperature, depend to a large extent on the intensity and duration of recharge events and provide information about the structure and geometry of the conduit system as well as about the interaction between conduits and fissured porous rock. Moreover, the responses of solute concentration and temperature of spring discharge appear to reflect different processes, thus complementing each other in the aquifer characterization. [source] Shortest paths in fuzzy weighted graphsINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 11 2004Chris Cornelis The task of finding shortest paths in weighted graphs is one of the archetypical problems encountered in the domain of combinatorial optimization and has been studied intensively over the past five decades. More recently, fuzzy weighted graphs, along with generalizations of algorithms for finding optimal paths within them, have emerged as an adequate modeling tool for prohibitively complex and/or inherently imprecise systems. We review and formalize these algorithms, paying special attention to the ranking methods used for path comparison. We show which criteria must be met for algorithm correctness and present an efficient method, based on defuzzification of fuzzy weights, for finding optimal paths. © 2004 Wiley Periodicals, Inc. Int J Int Syst 19: 1051,1068, 2004. [source] Modeling the partial nitrification in sequencing batch reactor for biomass adapted to high ammonia concentrationsBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2006V. Pambrun Abstract Partial nitrification has proven to be an economic way for treatment of industrial N-rich effluent, reducing oxygen and external COD requirements during nitrification/denitrification process. One of the key issues of this system is the intermediate nitrite accumulation stability. This work presents a control strategy and a modeling tool for maintaining nitrite build-up. Partial nitrification process has been carried out in a sequencing batch reactor at 30°C, maintaining strong changing ammonia concentration in the reactor (sequencing feed). Stable nitrite accumulation has been obtained with the help of an on-line oxygen uptake rate (OUR)-based control system, with removal rate of 2 kg NH -N,·,m,3/day and 90%,95% of conversion of ammonium into nitrite. A mathematical model, identified through the occurring biological reactions, is proposed to optimize the process (preventing nitrate production). Most of the kinetic parameters have been estimated from specific respirometric tests on biomass and validated on pilot-scale experiments of one-cycle duration. Comparison of dynamic data at different pH confirms that NH3 and NO should be considered as the true substrate of nitritation and nitratation, respectively. The proposed model represents major features: the inhibition of ammonia-oxidizing bacteria by its substrate (NH3) and product (HNO2), the inhibition of nitrite-oxidizing bacteria by free ammonia (NH3), the INFluence of pH. It appears that the model correctly describes the short-term dynamics of nitrogenous compounds in SBR, when both ammonia oxidizers and nitrite oxidizers are present and active in the reactor. The model proposed represents a useful tool for process design and optimization. © 2006 Wiley Periodicals, Inc. [source] Simulating the Dynamics of Spouted-Bed Nuclear Fuel Coaters,CHEMICAL VAPOR DEPOSITION, Issue 9 2007S. Pannala Abstract We describe simulation studies of the dynamics of spouted beds used for CVD coating of nuclear fuel particles. Our principal modeling tool is the Multiphase Flow with Interphase eXchanges (MFIX) code that was originally developed by the National Energy Technology Laboratory (NETL) for fossil energy process applications. In addition to standard MFIX features that allow coupling of transient hydrodynamics, heat and mass transfer, and chemical kinetics, we employ special post-processing tools to track particle mixing and circulation as functions of operating conditions and bed design. We describe in detail one major feature of the dynamics, which is the occurrence of very regular spontaneous pulsations of gas and particle flow in the spout. These pulsations appear to be critically linked to the entrainment and circulation of solids, and they produce readily accessible dynamic pressure variations that can be used for direct comparisons of model predictions with experiments. Spouted-bed dynamics are important from a CVD perspective because they directly determine the magnitude and variability of the concentration and species gradients in the zone where reactant gases first come into contact with hot particles. As this unsteady spouted-bed environment differs from other types of CVD reactors, the design and scale-up of such reactors is likely to involve unique modeling issues. Our primary goal here is to lay the groundwork for how computational simulation can be used to address these modeling issues in the specific context of nuclear fuel particle coating. [source] Case,Based Reasoning for Assessing Intelligent Transportation Systems BenefitsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 3 2003Adel Sadek Existing transportation planning modeling tools have critical limitations with respect to assessing the benefits of intelligent transportation systems (ITS) deployment. In this article, we present a novel framework for developing modeling tools for quantifying ITS deployments benefits. This approach is based on using case,based reasoning (CBR), an artificial intelligence paradigm, to capture and organize the insights gained from running a dynamic traffic assignment (DTA) model. To demonstrate the feasibility of the approach, the study develops a prototype system for evaluating the benefits of diverting traffic away from incident locations using variable message signs. A real,world network from the Hartford area in Connecticut is used in developing the system. The performance of the prototype is evaluated by comparing its predictions to those obtained using a detailed DTA model. The prototype system is shown to yield solutions comparable to those obtained from the DTA model, thus demonstrating the feasibility of the approach. [source] Environmental and economic analysis of the fully integrated biorefineryGCB BIOENERGY, Issue 5 2009ELIZABETH D. SENDICH Abstract Cellulosic biofuel systems have the potential to significantly reduce the environmental impact of the world's transportation energy requirements. However, realizing this potential will require systems level thinking and scale integration. Until now, we have lacked modeling tools for studying the behavior of integrated cellulosic biofuel systems. In this paper, we describe a new research tool, the Biorefinery and Farm Integration Tool (BFIT) in which the production of fuel ethanol from cellulosic biomass is integrated with crop and animal (agricultural) production models. Uniting these three subsystems in a single combined model has allowed, for the first time, basic environmental and economic analysis of biomass production, possible secondary products, fertilizer production, and bioenergy production across various regions of the United States. Using BFIT, we simulate cellulosic ethanol production embedded in realistic agricultural landscapes in nine locations under a collection of farm management scenarios. This combined modeling approach permits analysis of economic profitability and highlights key areas for environmental improvement. These results show the advantages of introducing integrated biorefinery systems within agricultural landscapes. This is particularly true in the Midwest, which our results suggest is a good setting for the cellulosic ethanol industry. Specifically, results show that inclusion of cellulosic biofuel systems into existing agriculture enhances farm economics and reduces total landscape emissions. Model results also indicate a limited ethanol price effect from increased biomass transportation distance. Sensitivity analysis using BFIT revealed those variables having the strongest effects on the overall system performance, namely: biorefinery size, switchgrass yield, and biomass farm gate price. [source] Beyond Mule Kicks: The Poisson Distribution in Geographical AnalysisGEOGRAPHICAL ANALYSIS, Issue 2 2006Daniel A. Griffith The Poisson model, discovered nearly two centuries ago, is the basis for analyses of rare events. Its first applications included descriptions of deaths from mule kicks. More than half a century ago the Poisson model began being used in geographical analysis. Its initial descriptions of geographic distributions of points, disease maps, and spatial flows were accompanied by an assumption of independence. Today this unrealistic assumption is replaced by one allowing for the presence of spatial autocorrelation in georeferenced counts. Contemporary statistical theory has led to the creation of powerful Poisson-based modeling tools for geographically distributed count data. [source] A Screening Model for Injection-Extraction Treatment Well Recirculation System DesignGROUND WATER MONITORING & REMEDIATION, Issue 4 2008Monica Y. Wu Implementation of injection-extraction treatment well pairs for in situ, in-well, or on-site remediation may be facilitated by development and application of modeling tools to aid in hydraulic design and remediation technology selection. In this study, complex potential theory was employed to derive a simple one-step design equation and related type curves that permit the calculation of the extraction well capture zone and the hydraulic recirculation between an injection and extraction well pair oriented perpendicular to regional flow. This equation may be used to aid in the design of traditional fully screened injection-extraction wells as well as innovative tandem recirculating wells when an adequate geologic barrier to vertical ground water flow exists. Simplified models describing in situ bioremediation, in-well vapor stripping, and in-well metal reactor treatment efficiency were adapted from the literature and coupled with the hydraulic design equation presented here. Equations and type curves that combine the remediation treatment efficiency with the hydraulic design equation are presented to simulate overall system treatment efficiency under various conditions. The combined model is applied to predict performance of in situ bioremediation and in-well palladium reactor designs that were previously described in the literature. This model is expected to aid practitioners in treatment system screening and evaluation. [source] Crystal structure prediction for eniluracilJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2001Mark Sacchetti Abstract State-of-the-art molecular modeling tools were used to predict the crystal structure of eniluracil, a compound for which it has not been possible to grow a single crystal. Two methods were used, one that incorporates molecular structure and powder X-ray diffraction data and another that employs molecular structure and lattice energy calculations into the search algorithm. Two structures were identified, one with P21/c and the other with P21 symmetry, both of which are consistent with the infrared and Raman spectra. A detailed analysis of the simulated and experimental powder X-ray diffraction patterns indicates that the P21/c structure is the best representation of the crystal structure. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1049,1055, 2001 [source] Models, Assumptions, and Stakeholders: Planning for Water Supply Variability in the Colorado River Basin,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2008Dustin Garrick Abstract:, Declining reservoir storage has raised the specter of the first water shortage on the Lower Colorado River since the completion of Glen Canyon and Hoover Dams. This focusing event spurred modeling efforts to frame alternatives for managing the reservoir system during prolonged droughts. This paper addresses the management challenges that arise when using modeling tools to manage water scarcity under variable hydroclimatology, shifting use patterns, and institutional complexity. Assumptions specified in modeling simulations are an integral feature of public processes. The policymaking and management implications of assumptions are examined by analyzing four interacting sources of physical and institutional uncertainty: inflow (runoff), depletion (water use), operating rules, and initial reservoir conditions. A review of planning documents and model reports generated during two recent processes to plan for surplus and shortage in the Colorado River demonstrates that modeling tools become useful to stakeholders by clarifying the impacts of modeling assumptions at several temporal and spatial scales. A high reservoir storage-to-runoff ratio elevates the importance of assumptions regarding initial reservoir conditions over the three-year outlook used to assess the likelihood of reaching surplus and shortage triggers. An ensemble of initial condition predictions can provide more robust initial conditions estimates. This paper concludes that water managers require model outputs that encompass a full range of future potential outcomes, including best and worst cases. Further research into methods of representing and communicating about hydrologic and institutional uncertainty in model outputs will help water managers and other stakeholders to assess tradeoffs when planning for water supply variability. [source] Multiscale simulation of polycrystal mechanics of textured ,-Ti alloys using ab initio and crystal-based finite element methodsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2008D. Ma Abstract Crystal-based finite element methods (FEM) are versatile continuum approaches for predicting mechanical properties and deformation-induced crystallographic textures. They can be applied to both, elastic,plastic and elastic problems. The methodology is based on (i) a detailed understanding of the underlying crystal deformation mechanisms and (ii) a number of constitutive material parameters that are often difficult to measure. First principle calculations, that take into account the discrete nature of matter at the atomic scale, are an alternative way to study mechanical properties of single crystals without using empirical parameters. In this study we demonstrate how to combine these two well-established modeling tools, viz., ab initio modeling and crystal mechanical FEM, for an improved approach to design of polycrystalline materials. The combination is based on (i) the determination of basic thermodynamic and elastic parameter trends in metallurgical alloy design using density-functional (DFT) calculations (P. Hohenberg and W. Kohn, Phys. Rev. 136, B864 (1964), W. Kohn and L. J. Sham, Phys. Rev. 140, A1133 (1965) [1, 2], respectively) and (ii) the up-scale transfer of these results into crystal-based finite element simulations which take into account the anisotropic nature of the elastic,plastic deformation of metals. The method is applied to three body-centered cubic (bcc, ,) Ti,Nb alloys for bio-medical applications. The study addresses two technological processes, namely, the prediction of texture evolution during cold rolling (elastic-plastic problem) and elastic bending of textured polycrystals (elastic problem). (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Gene-Trait Similarity Regression for Multimarker-Based Association AnalysisBIOMETRICS, Issue 3 2009Jung-Ying Tzeng Summary We propose a similarity-based regression method to detect associations between traits and multimarker genotypes. The model regresses similarity in traits for pairs of "unrelated" individuals on their haplotype similarities, and detects the significance by a score test for which the limiting distribution is derived. The proposed method allows for covariates, uses phase-independent similarity measures to bypass the needs to impute phase information, and is applicable to traits of general types (e.g., quantitative and qualitative traits). We also show that the gene-trait similarity regression is closely connected with random effects haplotype analysis, although commonly they are considered as separate modeling tools. This connection unites the classic haplotype sharing methods with the variance-component approaches, which enables direct derivation of analytical properties of the sharing statistics even when the similarity regression model becomes analytically challenging. [source] Pyrolysis Kinetics of Wood and Wood ComponentsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2005T. Willner Abstract The kinetics of pyrolysis decomposition reactions of wood and its components are described employing mathematical modeling tools for first and nth order reactions, autocatalytic reactions, and parallel first order and autocatalytic reactions. Secondary reactions may accelerate the reaction rate and a new autocatalytic reaction model was developed to describe this specific behavior. [source] | ||||||||||||||||