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Sample records for reactivity transients simulation

  1. Reactivity Initiated Accident Simulation to Inform Transient Testing of Candidate Advanced Cladding

    SciTech Connect

    Brown, Nicholas R; Wysocki, Aaron J; Terrani, Kurt A

    2016-01-01

    Abstract. Advanced cladding materials with potentially enhanced accident tolerance will yield different light water reactor performance and safety characteristics than the present zirconium-based cladding alloys. These differences are due to different cladding material properties and responses to the transient, and to some extent, reactor physics, thermal, and hydraulic characteristics. Some of the differences in reactors physics characteristics will be driven by the fundamental properties (e.g., absorption in iron for an iron-based cladding) and others will be driven by design modifications necessitated by the candidate cladding materials (e.g., a larger fuel pellet to compensate for parasitic absorption). Potential changes in thermal hydraulic limits after transition from the current zirconium-based cladding to the advanced materials will also affect the transient response of the integral fuel. This paper leverages three-dimensional reactor core simulation capabilities to inform on appropriate experimental test conditions for candidate advanced cladding materials in a control rod ejection event. These test conditions are using three-dimensional nodal kinetics simulations of a reactivity initiated accident (RIA) in a representative state-of-the-art pressurized water reactor with both nuclear-grade iron-chromium-aluminum (FeCrAl) and silicon carbide based (SiC-SiC) cladding materials. The effort yields boundary conditions for experimental mechanical tests, specifically peak cladding strain during the power pulse following the rod ejection. The impact of candidate cladding materials on the reactor kinetics behavior of RIA progression versus reference zirconium cladding is predominantly due to differences in: (1) fuel mass/volume/specific power density, (2) spectral effects due to parasitic neutron absorption, (3) control rod worth due to hardened (or softened) spectrum, and (4) initial conditions due to power peaking and neutron transport cross sections in the

  2. Regulatory Analysis of Reactivity Transients

    SciTech Connect

    Beyer, Carl E.; Clifford, Paul M.; Geelhood, Kenneth J.; Voglewede, John C.

    2009-08-01

    This paper will describe modifications made to the FRAPCON-3 and FRAPTRAN fuel performance codes and models that impact reactivity initiated accident (RIA) analyses. The modified models include an upper bound empirical and best estimate release models for fast transients, and a revised fuel failure model that accounts for ductile and brittle failure. Because experimental data exists for discrete test conditions, the codes and models are used to interpolate and to some extent, to extrapolate these test conditions. An upper bound empirical model for release is used to establish new recommended release fractions for long-lived and short lived (radioactive) isotopes for RIA events in Regulatory Guide 1.183. A best estimate release model is used in FRAPTRAN 1.4 based on grain boundary gas concentrations from FRAPCON-3.4 to predict release for RIA events. Code and model predictions will be compared to failure and release data from RIA tests to demonstrate accuracy.

  3. Reactivity Transients in Nuclear Research Reactors

    SciTech Connect

    2015-01-01

    Version 01 AIREMOD-RR is a point kinetics code which can simulate fast transients in nuclear research reactor cores. It can also be used for theoretical reactor dynamics studies. It is used for research reactor kinetic analysis and provides a point neutron kinetic capability. The thermal hydraulic behavior is governed by a one-dimensional heat balance equation. The calculations are restricted to a single equivalent unit cell which consists of fuel, clad and coolant.

  4. Nonlinear transient simulation of transformers

    SciTech Connect

    Pierrat, L.; Tran-Quoc, T. |; Montmeat, A.

    1995-12-31

    In this paper, a nonlinear model of transformer which takes into account both the saturation and the hysteresis is proposed. In order to simulate transient phenomena in transformers, a system of equations is presented. The digital simulation of the energization and de-energization of a three-phase distribution transformer is studied. Ferroresonant phenomena in iron core transformers supplied through capacitive links are presented. Finally, the influence of MOV arresters on overvoltage reduction is investigated.

  5. Transient simulation of absorption machines

    NASA Astrophysics Data System (ADS)

    Anand, D. K.; Allen, R. W.; Kumar, B.

    A model for a water-cooled Lithium-Bromide/water absorption chiller is presented. Its transient response both during the start-up phase and during the shut-off period is predicted. The simulation model incorporates such influencing factors as the thermodynamic properties of the working fluid, the absorbent, the heat-transfer configuration of different components of the chiller and related physical data. The time constants of different components are controlled by a set of key parameters that have been identified. The results show a variable but at times significant amount of time delay before the chiller capacity gets close to its steady-state value. The model is intended to provide an insight into the mechanism of build-up to steady-state performance. By recognizing the significant factors contributing to transient degradation, steps can be taken to reduce such degradation.

  6. Transient simulation of absorption machines

    NASA Astrophysics Data System (ADS)

    Anand, D. K.; Allen, R. W.; Kumar, B.

    1982-08-01

    This paper presents a model for a water-cooled Lithium-Bromide/water absorption chiller and predicts its transient response both during the start-up phase and during the shutoff period. The simulation model incorporates such influencing factors as the thermodynamic properties of the working fluid, the absorbent, the heat-transfer configuration of different components of the chiller and related physical data. The time constants of different components are controlled by a set of key parameters that have been identified in this study. The results show a variable but at times significant amount of time delay before the chiller capacity gets close to its steady-state value. The model is intended to provide an insight into the mechanism of build-up to steady-state performance. By recognizing the significant factors contributing to transient degradation, steps can be taken to reduce such degradation. The evaluation of the residual capacity in the shut-off period will yield more realistic estimates of chiller COP for a chiller satisfying dynamic space cooling load.

  7. General Reactive Atomistic Simulation Program

    SciTech Connect

    Thompson, Aidan P.

    2004-09-22

    GRASP (General Reactive Atomistic Simulation Program) is primarily intended as a molecular dynamics package for complex force fields, The code is designed to provide good performance for large systems, either in parallel or serial execution mode, The primary purpose of the code is to realistically represent the structural and dynamic properties of large number of atoms on timescales ranging from picoseconds up to a microsecond. Typically the atoms form a representative sample of some material, such as an interface between polycrystalline silicon and amorphous silica. GRASP differs from other parallel molecular dynamics codes primarily due to it’s ability to handle relatively complicated interaction potentials and it’s ability to use more than one interaction potential in a single simulation. Most of the computational effort goes into the calculation of interatomic forces, which depend in a complicated way on the positions of all the atoms. The forces are used to integrate the equations of motion forward in time using the so-called velocity Verlet integration scheme. Alternatively, the forces can be used to find a minimum energy configuration, in which case a modified steepest descent algorithm is used.

  8. General Reactive Atomistic Simulation Program

    2004-09-22

    GRASP (General Reactive Atomistic Simulation Program) is primarily intended as a molecular dynamics package for complex force fields, The code is designed to provide good performance for large systems, either in parallel or serial execution mode, The primary purpose of the code is to realistically represent the structural and dynamic properties of large number of atoms on timescales ranging from picoseconds up to a microsecond. Typically the atoms form a representative sample of some material,more » such as an interface between polycrystalline silicon and amorphous silica. GRASP differs from other parallel molecular dynamics codes primarily due to it’s ability to handle relatively complicated interaction potentials and it’s ability to use more than one interaction potential in a single simulation. Most of the computational effort goes into the calculation of interatomic forces, which depend in a complicated way on the positions of all the atoms. The forces are used to integrate the equations of motion forward in time using the so-called velocity Verlet integration scheme. Alternatively, the forces can be used to find a minimum energy configuration, in which case a modified steepest descent algorithm is used.« less

  9. Transient simulation of ram accelerator flowfields

    NASA Astrophysics Data System (ADS)

    Drabczuk, Randall P.; Rolader, G.; Dash, S.; Sinha, N.; York, B.

    1993-01-01

    This paper describes the development of an advanced computational fluid dynamic (CFD) simulation capability in support of the USAF Armament Directorate ram accelerator research initiative. The state-of-the-art CRAFT computer code has been specialized for high fidelity, transient ram accelerator simulations via inclusion of generalized dynamic gridding, solution adaptive grid clustering, and high pressure thermo-chemistry. Selected ram accelerator simulations are presented that serve to exhibit the CRAFT code capabilities and identify some of the principle research/design Issues.

  10. Transient simulation of ram accelerator flowfields

    NASA Astrophysics Data System (ADS)

    Sinha, N.; York, B. J.; Dash, S. M.; Drabczuk, R.; Rolader, G. E.

    1992-10-01

    This paper describes the development of an advanced computational fluid dynamic (CFD) simulation capability in support of the U.S. Air Force Armament Directorate's ram accelerator research initiative. The state-of-the-art CRAFT computer code has been specialized for high fidelity, transient ram accelerator simulations via inclusion of generalized dynamic gridding, solution adaptive grid clustering, high pressure thermochemistry, etc. Selected ram accelerator simulations are presented which serve to exhibit the CRAFT code's capabilities and identify some of the principal research/design issues.

  11. Transient simulation of molten salt central receiver

    NASA Astrophysics Data System (ADS)

    Doupis, Dimitri; Wang, Chuan; Carcorze-Soto, Jorge; Chen, Yen-Ming; Maggi, Andrea; Losito, Matteo; Clark, Michael

    2016-05-01

    Alstom is developing concentrated solar power (CSP) utilizing 60/40wt% NaNO3-KNO3 molten salt as the working fluid in a tower receiver for the global renewable energy market. In the CSP power generation cycle, receivers undergo a daily cyclic operation due to the transient nature of solar energy. Development of robust and efficient start-up and shut-down procedures is critical to avoiding component failures due to mechanical fatigue resulting from thermal transients, thus maintaining the performance and availability of the CSP plant. The Molten Salt Central Receiver (MSCR) is subject to thermal transients during normal daily operation, a cycle that includes warmup, filling, operation, draining, and shutdown. This paper describes a study to leverage dynamic simulation and finite element analysis (FEA) in development of start-up, shutdown, and transient operation concepts for the MSCR. The results of the FEA also verify the robustness of the MSCR design to the thermal transients anticipated during the operation of the plant.

  12. Reactive Simulations for Biochemical Processes

    NASA Astrophysics Data System (ADS)

    Boero, M.

    After a brief review of the hybrid QM/MM molecular dynamics scheme and its coupling to the metadynamics method, I will show how such a combination of computational tools can be used to study chemical reactions of general biological interest. Specifically, by using such a reactive hybrid paradigm, where the QM driver is a Car-Parrinello Lagrangian dynamics, we have inspected the ATP hydrolysis reaction in the anti-freezing protein known as heat shock cognate protein (Hsc70) and the unconventional propagation of protons across peptide groups in the H-path of the bovine cytochrome c oxidase. While the former represents a fundamental reaction operated by all living beings in a wealth of processes and functions, the second one is involved in cell respiration. For both systems accurate X-ray data are available, yet the actual reaction mechanism escapes experimental probes. The simulations presented here provide the complementary information missing in experiments, offer a direct insight into the reaction mechanisms at a molecular level, and allow to understand which pathways nature can follow to realize these processes fundamental to living organisms.

  13. COYOTE: A computer program for 2-D reactive flow simulations

    SciTech Connect

    Cloutman, L.D.

    1990-04-01

    We describe the numerical algorithm used in the COYOTE two- dimensional, transient, Eulerian hydrodynamics program for reactive flows. The program has a variety of options that provide capabilities for a wide range of applications, and it is designed to be robust and relatively easy to use while maintaining adequate accuracy and efficiency to solve realistic problems. It is based on the ICE method, and it includes a general species and chemical reaction network for simulating reactive flows. It also includes swirl, turbulence transport models, and a nonuniform mesh capability. We describe several applications of the program. 33 refs., 4 figs.

  14. Zero-gravity transient thermal mixing simulation

    NASA Technical Reports Server (NTRS)

    Lands, J. F., Jr.; Ried, R. C., Jr.

    1971-01-01

    The experimental program described is an outgrowth of independent investigations into alternate redesign concepts for the Apollo SM cryogenic oxygen storage system. The experiments were continued, after the redesign was established, to provide physical insight into transient thermal mixing in zero-gravity and to aid in the characterization of the system performance in flight. Zero-gravity heat transfer and fluid mixing were simulated experimentally through an analogy between unsteady heat conduction and species diffusion. To further support numerical analyses of the cryogenic oxygen storage system, the experimental investigation was extended to include a cubical tank geometry, representative of existing numerical models. In general, the transient flow patterns in the cubical tank are far more complex than those of the spherical tank and the extent of fluid mixing is significantly greater but less repeatable.

  15. Transient aero-thermal simulations for TMT

    NASA Astrophysics Data System (ADS)

    Vogiatzis, Konstantinos

    2014-08-01

    Aero-thermal simulations are an integral part of the design process for the Thirty Meter Telescope (TMT). These simulations utilize Computational Solid-Fluid Dynamics (CSFD) to estimate wind jitter and blur, dome and mirror seeing, telescope pointing error due to thermal drift, and to predict thermal effects on performance of components such as the primary mirror segments. Design guidance obtained from these simulations is provided to the Telescope, Enclosure, Facilities and Adaptive Optics groups. Computational advances allow for model enhancements and inclusion of phenomena not previously resolved, such as transient effects on wind loading and thermal seeing due to vent operation while observing or long exposure effects, with potentially different flow patterns corresponding to the beginning and end of observation. Accurate knowledge of the Observatory aero-thermal environment will result in developing reliable look-up tables for effective open loop correction of key active optics system elements, and cost efficient operation of the Observatory.

  16. Reactive multiphase flow simulation workshop summary

    SciTech Connect

    VanderHeyden, W.B.

    1995-09-01

    A workshop on computer simulation of reactive multiphase flow was held on May 18 and 19, 1995 in the Computational Testbed for Industry at Los Alamos National Laboratory (LANL), Los Alamos, New Mexico. Approximately 35 to 40 people attended the workshop. This included 21 participants from 12 companies representing the petroleum, chemical, environmental and consumer products industries, two representatives from the DOE Office of Industrial Technologies and several from Los Alamos. The dialog at the meeting suggested that reactive multiphase flow simulation represents an excellent candidate for government/industry/academia collaborative research. A white paper on a potential consortium for reactive multiphase flow with input from workshop participants will be issued separately.

  17. Simulated transient behavior of HT9 cladding

    SciTech Connect

    Cannon, N.S.; Huang, F.H.; Hamilton, M.L.

    1988-09-01

    Simulated transient tests were performed on sections of HT9 fast- reactor fuel pin cladding irradiated to a fast fluence of nearly 16 /times/ 10/sup 22/ n/cm/sup 2/ at temperatures ranging from 370 to 620/degree/C. After removing fuel, these specimens were internally pressurized and heated at one of several constant rates (0.56, 5.6, or 110/degree/C/s) until specimen failure occurred. A slight reduction of strength was observed in irradiated cladding, particularly at 110/degree/C/s, when compared with transient results from unirradiated HT9 control specimens; however, this strength reduction did not correlate with either fluence or irradiation temperature. A small reduction of ductility was also observed for irradiated cladding failing at temperatures above 800/degree/C at the lower heating rates (0.56 or 5.6/degree/C/s); irradiated cladding was generally more ductile at 110/degree/C/s than unirradiated HT9 cladding. The HT9 cladding results were compared with similar transient data obtained previously from 20% Cold-Worked Type 316 Stainless Steel (316 SS) cladding. In the unirradiated state, this austenitic cladding is stronger and less ductile than HT9 cladding. However, the 316 SS cladding undergoes a significant loss of strength and ductility during irradiation when in contact with oxide fuel, by a mechanism labeled the fuel adjacency effect (FAE). The FAE is believed to be liquid metal embrittlement from fission products. The HT9 fuel pin cladding remained as strong or stronger than the 316 SS cladding when irradiated in contact with fuel, showing no evidence of the FAE up to the high fluences reported here. The ductility of the irradiated HT9 fuel pin cladding remained significantly greater than that of irradiated 316 SS cladding. 14 refs., 11 figs., 1 tab.

  18. Simulation of centrifugal compressor transient performance for process plant applications

    SciTech Connect

    MacDougal, I.; Elder, R.L.

    1983-01-01

    The development of a theoretical model capable of simulating centrifugal compressor transient performance (including compressor surge) is detailed. Simulation results from a Fortran computer program are compared with measured compressor transient data. Good simulation of compressor transients between stable operating points, and compressor presurge flow oscillations has been obtained. General application criteria are presented for the geometric distribution of model elements within a compressor system. Model applications and future work are outlined.

  19. Simulation Prediction of Transient Dropwise Condensation

    NASA Astrophysics Data System (ADS)

    Macner, Ashley; Daniel, Susan; Steen, Paul

    2014-11-01

    In order to design effective surfaces for large-scale dropwise condensation, an understanding of how surface functionalization affects drop growth and coalescence is needed. The long term technological goal is a set of design conditions to help NASA achieve maximum heat transfer rates of waste heat generated from electronics and habitable environments under microgravity conditions. Prediction of condenser surface heat transfer performance requires accurate simulation and modeling of the evolution of populations of drops in time. At shorter times, drops are primarily isolated and grow mainly by condensation onto the liquid-gas interface. At longer times, drops grow mainly by coalescence with neighbors. Simulation of dropwise condensation on a neutrally wetting surface and comparison with our previous experimental results is reported. A steady-state single drop conduction model is empirically fitted to determine a temperature profile that captures the drop size evolution. The simulation accurately predicts the continuous time evolution of number-density of drops, drop-size distributions, total condensate volume, fractional coverage, and median drop-size for both transient and steady states, all with no free parameters. This work was supported by a NASA Office of the Chief Technologist's Space Technology Research Fellowship.

  20. Buckybomb: Reactive Molecular Dynamics Simulation.

    PubMed

    Chaban, Vitaly V; Fileti, Eudes Eterno; Prezhdo, Oleg V

    2015-03-01

    Energetic materials, such as explosives, propellants, and pyrotechnics, are widely used in civilian and military applications. Nanoscale explosives represent a special group because of the high density of energetic covalent bonds. The reactive molecular dynamics (ReaxFF) study of nitrofullerene decomposition reported here provides a detailed chemical mechanism of explosion of a nanoscale carbon material. Upon initial heating, C60(NO2)12 disintegrates, increasing temperature and pressure by thousands of Kelvins and bars within tens of picoseconds. The explosion starts with NO2 group isomerization into C-O-N-O, followed by emission of NO molecules and formation of CO groups on the buckyball surface. NO oxidizes into NO2, and C60 falls apart, liberating CO2. At the highest temperatures, CO2 gives rise to diatomic carbon. The study shows that the initiation temperature and released energy depend strongly on the chemical composition and density of the material. PMID:26262672

  1. Buckybomb: Reactive Molecular Dynamics Simulation.

    PubMed

    Chaban, Vitaly V; Fileti, Eudes Eterno; Prezhdo, Oleg V

    2015-03-01

    Energetic materials, such as explosives, propellants, and pyrotechnics, are widely used in civilian and military applications. Nanoscale explosives represent a special group because of the high density of energetic covalent bonds. The reactive molecular dynamics (ReaxFF) study of nitrofullerene decomposition reported here provides a detailed chemical mechanism of explosion of a nanoscale carbon material. Upon initial heating, C60(NO2)12 disintegrates, increasing temperature and pressure by thousands of Kelvins and bars within tens of picoseconds. The explosion starts with NO2 group isomerization into C-O-N-O, followed by emission of NO molecules and formation of CO groups on the buckyball surface. NO oxidizes into NO2, and C60 falls apart, liberating CO2. At the highest temperatures, CO2 gives rise to diatomic carbon. The study shows that the initiation temperature and released energy depend strongly on the chemical composition and density of the material.

  2. Assessment of reactivity transient experiments with high burnup fuel

    SciTech Connect

    Ozer, O.; Yang, R.L.; Rashid, Y.R.; Montgomery, R.O.

    1996-03-01

    A few recent experiments aimed at determining the response of high-burnup LWR fuel during a reactivity initiated accident (RIA) have raised concerns that existing failure criteria may be inappropriate for such fuel. In particular, three experiments (SPERT CDC-859, NSRR HBO-1 and CABRI REP Na-1) appear to have resulted in fuel failures at only a fraction of the anticipated enthalpy levels. In evaluating the results of such RIA simulation experiments, however, it is necessary that the following two key considerations be taken into account: (1) Are the experiments representative of conditions that LWR fuel would experience during an in-reactor RIA event? (2) Is the fuel that is being utilized in the tests representative of the present (or anticipated) population of LWR fuel? Conducting experiments under conditions that can not occur in-reactor can trigger response modes that could not take place during in-reactor operation. Similarly, using unrepresentative fuel samples for the tests will produce failure information that is of limited relevance to commercial LWR fuel. This is particularly important for high-burnup fuel since the manner under which the test samples are base-irradiated prior to the test will impact the mechanical properties of the cladding and will therefore affect the RIA response. A good example of this effect can be seen in the results of the SPERT CDC-859 test and in the NSRR JM-4 and JM-5 tests. The conditions under which the fuel used for these tests was fabricated and/or base-irradiated prior to the RIA pulse resulted in the formation of multiple cladding defects in the form of hydride blisters. When this fuel was subjected to the RIA power pulse, it failed by developing multiple cracks that were closely correlated with the locations of the pre-existing hydride blisters. In the case of the JM tests, many of the cracks formed within the blisters themselves and did not propagate beyond the heavily hydrided regions.

  3. Automated Fluid Feature Extraction from Transient Simulations

    NASA Technical Reports Server (NTRS)

    Haimes, Robert

    1998-01-01

    In the past, feature extraction and identification were interesting concepts, but not required to understand the underlying physics of a steady flow field. This is because the results of the more traditional tools like iso-surfaces, cuts and streamlines were more interactive and easily abstracted so they could be represented to the investigator. These tools worked and properly conveyed the collected information at the expense of much interaction. For unsteady flow-fields, the investigator does not have the luxury of spending time scanning only one 'snap-shot' of the simulation. Automated assistance is required in pointing out areas of potential interest contained within the flow. This must not require a heavy compute burden (the visualization should not significantly slow down the solution procedure for co-processing environments like pV3). And methods must be developed to abstract the feature and display it in a manner that physically makes sense. The following is a list of the important physical phenomena found in transient (and steady-state) fluid flow: Shocks; Vortex ores; Regions of Recirculation; Boundary Layers; Wakes.

  4. Automated Fluid Feature Extraction from Transient Simulations

    NASA Technical Reports Server (NTRS)

    Haimes, Robert; Lovely, David

    1999-01-01

    In the past, feature extraction and identification were interesting concepts, but not required to understand the underlying physics of a steady flow field. This is because the results of the more traditional tools like iso-surfaces, cuts and streamlines were more interactive and easily abstracted so they could be represented to the investigator. These tools worked and properly conveyed the collected information at the expense of much interaction. For unsteady flow-fields, the investigator does not have the luxury of spending time scanning only one "snap-shot" of the simulation. Automated assistance is required in pointing out areas of potential interest contained within the flow. This must not require a heavy compute burden (the visualization should not significantly slow down the solution procedure for co-processing environments like pV3). And methods must be developed to abstract the feature and display it in a manner that physically makes sense. The following is a list of the important physical phenomena found in transient (and steady-state) fluid flow: (1) Shocks, (2) Vortex cores, (3) Regions of recirculation, (4) Boundary layers, (5) Wakes. Three papers and an initial specification for the (The Fluid eXtraction tool kit) FX Programmer's guide were included. The papers, submitted to the AIAA Computational Fluid Dynamics Conference, are entitled : (1) Using Residence Time for the Extraction of Recirculation Regions, (2) Shock Detection from Computational Fluid Dynamics results and (3) On the Velocity Gradient Tensor and Fluid Feature Extraction.

  5. Exploring the transient sky: from surveys to simulations

    NASA Astrophysics Data System (ADS)

    Carbone, Dario

    2016-01-01

    The transient sky is very important to study the dynamics of the Universe on human timescales. Transient sources are seen in every band of the electromagnetic spectrum, from low radio frequencies to gamma-ray energies, and produced by nearby flare stars to cosmological gamma-ray bursts.We have performed a transient survey of four different fields with the LOw Frequency Array (LOFAR) at 150 MHz. LOFAR is a new generation radio interferometer which is observing at very low radio frequencies, a so far relatively unexplored frequency domain for transient searches. No credible transients were detected in our survey, but we were able to set stringent upper limits on the transient surface density using three new statistical methods. We also calculated the transient surface density as a function of the timescale of the transients, and established that the upper limits we can set vary up to two orders of magnitude for different timescales.We have explored the complex relation between flux density, timescale and transient surface density, and developed a simulation method to calculate the transient rate as a function of both the flux and the duration of transients for different shapes of their lightcurves and for a given observing strategy. This method is independent of the nature of transient sources, and the instrument or the frequency of the observations. Therefore, this provides a tool for transient surveys carried out by current and future observatories across the electromagnetic spectrum.

  6. Three-dimensional transient analysis capability in SIMULATE-3

    SciTech Connect

    Borkowski, J.; Rhodes, J. III; Esser, P.; Smith, K.

    1994-12-31

    Transient analysis capability has been added to the advanced nodal methodology of SIMULATE-3. The transient modules couple a transient version of the steady-state nodal method QPANDA with a one-dimensional, bundle-by-bundle thermal-hydraulic feedback module. The accuracy of the code has been assessed by using several benchmark problems, including the LMW benchmark and the Nuclear Energy Agency Committee on Reactor Physics (NEACRP) pressurized water reactor (PWR) rod ejection benchmarks.

  7. Reactive programming of simulations in physics

    NASA Astrophysics Data System (ADS)

    Boussinot, Frédéric; Monasse, Bernard; Susini, Jean-Ferdy

    2015-04-01

    We consider the Reactive Programming (RP) approach to simulate physical systems. The choice of RP is motivated by the fact that RP genuinely offers logical parallelism, instantaneously broadcast events, and dynamic creation/destruction of parallel components and events. To illustrate our approach, we consider the implementation of a system of Molecular Dynamics, in the context of Java with the Java3D library for 3D visualization.

  8. Code System For Calculating Reactivity Transients In a LWR.

    1999-03-16

    Version 00 RETRANS is appropriate to calculate power excursions in light water reactors initiated by reactivity insertions due to withdrawal of control elements. The neutron physical model is based on the time-dependent two-group neutron diffusion equations. The equation of state of the coolant is approximated by a table built into the code. RETRANS solves the heat conduction equation and calculates the heat transfer coefficient for representative fuel rods at each time-step.

  9. Large liquid rocket engine transient performance simulation system

    NASA Technical Reports Server (NTRS)

    Mason, J. R.; Southwick, R. D.

    1991-01-01

    A simulation system, ROCETS, was designed and developed to allow cost-effective computer predictions of liquid rocket engine transient performance. The system allows a user to generate a simulation of any rocket engine configuration using component modules stored in a library through high-level input commands. The system library currently contains 24 component modules, 57 sub-modules and maps, and 33 system routines and utilities. FORTRAN models from other sources can be operated in the system upon inclusion of interface information on comment cards. Operation of the simulation is simplified for the user by run, execution, and output processors. The simulation system makes available steady-state trim balance, transient operation, and linear partial generation. The system utilizes a modern equation solver for efficient operation of the simulations. Transient integration methods include integral and differential forms for the trapezoidal, first order Gear, and second order Gear corrector equations. A detailed technology test bed engine (TTBE) model was generated to be used as the acceptance test of the simulation system. The general level of model detail was that reflected in the Space Shuttle Main Engine DTM. The model successfully obtained steady-state balance in main stage operation and simulated throttle transients, including engine starts and shutdown. A NASA FORTRAN control model was obtained, ROCETS interface installed in comment cards, and operated with the TTBE model in closed-loop transient mode.

  10. Transient analysis and startup simulation of a thermionic space nuclear reactor system

    SciTech Connect

    El-Genk, M.S.; Xue, Huimin; Paramonov, D. . Dept. of Chemical and Nuclear Engineering)

    1994-01-01

    The thermionic transient analysis model is used to simulate the startup of the TOPAZ-2 space nuclear power system in orbit. The simulated startup procedures are assumed for the purpose of demonstrating the capabilities of the model and may not represent an accurate account of the actual startup procedures of the TOPAZ-2 system. The temperature reactivity feedback effects of the moderator, UO[sub 2] fuel, electrodes, coolant, and other components in the core are calculated, and their effects on the thermal and criticality conditions of the reactor are investigated. Also, estimates of the time constants of the temperature reactivity feedback for the UO[sub 2] fuel and the ZrH moderator during startup, as well as of the total temperature reactivity feedback as a function of the reactor steady-state thermal power, are obtained.

  11. Transient simulation of superconducting synchronous machines

    NASA Astrophysics Data System (ADS)

    Koronides, A. G.

    1980-11-01

    A computer model is developed to study the electromechanical interactions between superconducting generators and power systems during various fault conditions. A large set of equivalent circuits is used to represent the eddy currents on the finite length electromagnetic cylindrical shields which surround the superconducting field winding. The armature and field windings are represented by coupled circuits as in conventional generator models. The rotor turbine shaft dynamics are introduced in the model by a set of lumped masses representing the various stages of the turbine and the rotor, connected by springs representing the shaft. The electrical and mechanical equations of the machine are related by the air gap torque equation in a large system of simultaneous, nonlinear differential equations. The developed computer algorithms used to study the transient behavior of a 300 MCA superconducting generator and the results are reported.

  12. Reactive transport benchmarks for subsurface environmental simulation

    SciTech Connect

    Steefel, Carl I.; Yabusaki, Steven B.; Mayer, K. U.

    2015-06-01

    Over the last 20 years, we have seen firsthand the evolution of multicomponent reactive transport modeling and the expanding range and increasing complexity of subsurface applications it is being used to address. There is a growing reliance on reactive transport modeling (RTM) to address some of the most compelling issues facing our planet: climate change, nuclear waste management, contaminant remediation, and pollution prevention. While these issues are motivating the development of new and improved capabilities for subsurface environmental modeling using RTM (e.g., biogeochemistry from cell-scale physiology to continental-scale terrestrial ecosystems, nonisothermal multiphase conditions, coupled geomechanics), there remain longstanding challenges in characterizing the natural variability of hydrological, biological, and geochemical properties in subsurface environments and limited success in transferring models between sites and across scales. An equally important trend over the last 20 years is the evolution of modeling from a service sought out after data has been collected to a multifaceted research approach that provides (1) an organizing principle for characterization and monitoring activities; (2) a systematic framework for identifying knowledge gaps, developing and integrating new knowledge; and (3) a mechanistic understanding that represents the collective wisdom of the participating scientists and engineers. There are now large multidisciplinary projects where the research approach is model-driven, and the principal product is a holistic predictive simulation capability that can be used as a test bed for alternative conceptualizations of processes, properties, and conditions. Much of the future growth and expanded role for RTM will depend on its continued ability to exploit technological advancements in the earth and environmental sciences. Advances in measurement technology, particularly in molecular biology (genomics), isotope fractionation, and high

  13. An example of neutronic penalizations in reactivity transient analysis using 3D coupled chain HEMERA

    SciTech Connect

    Dubois, F.; Normand, B.; Sargeni, A.

    2012-07-01

    HEMERA (Highly Evolutionary Methods for Extensive Reactor Analyses), is a fully coupled 3D computational chain developed jointly by IRSN and CEA. It is composed of CRONOS2 (core neutronics, cross sections library from APOLLO2), FLICA4 (core thermal-hydraulics) and the system code CATHARE. Multi-level and multi-dimensional models are developed to account for neutronics, core thermal-hydraulics, fuel thermal analysis and system thermal-hydraulics, dedicated to best-estimate, conservative simulations and sensitivity analysis. In IRSN, the HEMERA chain is widely used to study several types of reactivity accidents and for sensitivity studies. Just as an example of the HEMERA possibilities, we present here two types of neutronic penalizations and their impact on a power transient due to a REA (Rod Ejection Accident): in the first one, we studied a bum-up distribution modification and in the second one, a delayed-neutron fraction modification. Both modifications are applied to the whole core or localized in a few assemblies. Results show that it is possible to use global or local changes but 1) in case of bum-up modification, the total core power can increase when assembly peak power decrease so, care has to be taken if the goal is to maximize a local power peak and 2) for delayed-neutron fraction, a local modification can have the same effect as the one on the whole core, provided that it is large enough. (authors)

  14. Simulation of SEU transients in CMOS ICs

    SciTech Connect

    Kaul, N.; Bhuva, B.L.; Kerns, S.E. )

    1991-12-01

    This paper reports that available analytical models of the number of single-event-induced errors (SEU) in combinational logic systems are not easily applicable to real integrated circuits (ICs). An efficient computer simulation algorithm set, SITA, predicts the vulnerability of data stored in and processed by complex combinational logic circuits to SEU. SITA is described in detail to allow researchers to incorporate it into their error analysis packages. Required simulation algorithms are based on approximate closed-form equations modeling individual device behavior in CMOS logic units. Device-level simulation is used to estimate the probability that ion-device interactions produce erroneous signals capable of propagating to a latch (or n output node), and logic-level simulation to predict the spread of such erroneous, latched information through the IC. Simulation results are compared to those from SPICE for several circuit and logic configurations. SITA results are comparable to this established circuit-level code, and SITA can analyze circuits with state-of-the-art device densities (which SPICE cannot). At all IC complexity levels, SITAS offers several factors of 10 savings in simulation time over SPICE.

  15. Design of transient light signal simulator based on FPGA

    NASA Astrophysics Data System (ADS)

    Kang, Jing; Chen, Rong-li; Wang, Hong

    2014-11-01

    A design scheme of transient light signal simulator based on Field Programmable gate Array (FPGA) was proposed in this paper. Based on the characteristics of transient light signals and measured feature points of optical intensity signals, a fitted curve was created in MATLAB. And then the wave data was stored in a programmed memory chip AT29C1024 by using SUPERPRO programmer. The control logic was realized inside one EP3C16 FPGA chip. Data readout, data stream cache and a constant current buck regulator for powering high-brightness LEDs were all controlled by FPGA. A 12-Bit multiplying CMOS digital-to-analog converter (DAC) DAC7545 and an amplifier OPA277 were used to convert digital signals to voltage signals. A voltage-controlled current source constituted by a NPN transistor and an operational amplifier controlled LED array diming to achieve simulation of transient light signal. LM3405A, 1A Constant Current Buck Regulator for Powering LEDs, was used to simulate strong background signal in space. Experimental results showed that the scheme as a transient light signal simulator can satisfy the requests of the design stably.

  16. Automated Fluid Feature Extraction from Transient Simulations

    NASA Technical Reports Server (NTRS)

    Haimes, Robert

    2000-01-01

    In the past, feature extraction and identification were interesting concepts, but not required in understanding the physics of a steady flow field. This is because the results of the more traditional tools like iso-surfaces, cuts and streamlines, were more interactive and easily abstracted so they could be represented to the investigator. These tools worked and properly conveyed the collected information at the expense of a great deal of interaction. For unsteady flow-fields, the investigator does not have the luxury of spending time scanning only one 'snap-shot' of the simulation. Automated assistance is required in pointing out areas of potential interest contained within the flow. This must not require a heavy compute burden (the visualization should not significantly slow down the solution procedure for co-processing environments like pV3). And methods must be developed to abstract the feature and display it in a manner that physically makes sense.

  17. Experimental Validation of a Closed Brayton Cycle System Transient Simulation

    NASA Technical Reports Server (NTRS)

    Johnson, Paul K.; Hervol, David S.

    2006-01-01

    The Brayton Power Conversion Unit (BPCU) located at NASA Glenn Research Center (GRC) in Cleveland, Ohio was used to validate the results of a computational code known as Closed Cycle System Simulation (CCSS). Conversion system thermal transient behavior was the focus of this validation. The BPCU was operated at various steady state points and then subjected to transient changes involving shaft rotational speed and thermal energy input. These conditions were then duplicated in CCSS. Validation of the CCSS BPCU model provides confidence in developing future Brayton power system performance predictions, and helps to guide high power Brayton technology development.

  18. Experimental Validation of a Closed Brayton Cycle System Transient Simulation

    NASA Astrophysics Data System (ADS)

    Johnson, Paul K.; Hervol, David S.

    2006-01-01

    The Brayton Power Conversion Unit (BPCU) located at NASA Glenn Research Center (GRC) in Cleveland, OH was used to validate the results of a computational code known as Closed Cycle System Simulation (CCSS). Conversion system thermal transient behavior was the focus of this validation. The BPCU was operated at various steady state points and then subjected to transient changes involving shaft rotational speed and thermal energy input. These conditions were then duplicated in CCSS. Validation of the CCSS BPCU model provides confidence in developing future Brayton power system performance predictions, and helps to guide high power Brayton technology development.

  19. Accelerating transient simulation of linear reduced order models.

    SciTech Connect

    Thornquist, Heidi K.; Mei, Ting; Keiter, Eric Richard; Bond, Brad

    2011-10-01

    Model order reduction (MOR) techniques have been used to facilitate the analysis of dynamical systems for many years. Although existing model reduction techniques are capable of providing huge speedups in the frequency domain analysis (i.e. AC response) of linear systems, such speedups are often not obtained when performing transient analysis on the systems, particularly when coupled with other circuit components. Reduced system size, which is the ostensible goal of MOR methods, is often insufficient to improve transient simulation speed on realistic circuit problems. It can be shown that making the correct reduced order model (ROM) implementation choices is crucial to the practical application of MOR methods. In this report we investigate methods for accelerating the simulation of circuits containing ROM blocks using the circuit simulator Xyce.

  20. Unsteady Cavitation Simulation in Transient Process of Turbine Flow Meter

    NASA Astrophysics Data System (ADS)

    Chen, Gang; Liu, Shuhong; Cao, Guangjun

    In a turbine flow meter, cavitation will take place when local pressure falls below the vapor pressure of liquid products and it usually speeds up the rotor at the given high flow rate. In order to study its effects on meter factor, numerical simulation on transient unsteady turbulent flow is carried out based on the mixture homogeneous two phase cavitation model which is deduced from the theory of evaporation and condensation on a plane. The momentum source terms from the variation rotating speed of transient processes and the cavitation mass transport source terms are introduced into the transient unsteady governing equations. The results show that the meter factor grows with the increase of the cavitation number and meter factor will be affected by cavitation.

  1. Testing of an Integrated Reactor Core Simulator and Power Conversion System with Simulated Reactivity Feedback

    NASA Technical Reports Server (NTRS)

    Bragg-Sitton, Shannon M.; Hervol, David S.; Godfroy, Thomas J.

    2010-01-01

    A Direct Drive Gas-Cooled (DDG) reactor core simulator has been coupled to a Brayton Power Conversion Unit (BPCU) for integrated system testing at NASA Glenn Research Center (GRC) in Cleveland, Ohio. This is a closed-cycle system that incorporates an electrically heated reactor core module, turboalternator, recuperator, and gas cooler. Nuclear fuel elements in the gas-cooled reactor design are replaced with electric resistance heaters to simulate the heat from nuclear fuel in the corresponding fast spectrum nuclear reactor. The thermodynamic transient behavior of the integrated system was the focus of this test series. In order to better mimic the integrated response of the nuclear-fueled system, a simulated reactivity feedback control loop was implemented. Core power was controlled by a point kinetics model in which the reactivity feedback was based on core temperature measurements; the neutron generation time and the temperature feedback coefficient are provided as model inputs. These dynamic system response tests demonstrate the overall capability of a non-nuclear test facility in assessing system integration issues and characterizing integrated system response times and response characteristics.

  2. Testing of an Integrated Reactor Core Simulator and Power Conversion System with Simulated Reactivity Feedback

    NASA Technical Reports Server (NTRS)

    Bragg-Sitton, Shannon M.; Hervol, David S.; Godfroy, Thomas J.

    2009-01-01

    A Direct Drive Gas-Cooled (DDG) reactor core simulator has been coupled to a Brayton Power Conversion Unit (BPCU) for integrated system testing at NASA Glenn Research Center (GRC) in Cleveland, OH. This is a closed-cycle system that incorporates an electrically heated reactor core module, turbo alternator, recuperator, and gas cooler. Nuclear fuel elements in the gas-cooled reactor design are replaced with electric resistance heaters to simulate the heat from nuclear fuel in the corresponding fast spectrum nuclear reactor. The thermodynamic transient behavior of the integrated system was the focus of this test series. In order to better mimic the integrated response of the nuclear-fueled system, a simulated reactivity feedback control loop was implemented. Core power was controlled by a point kinetics model in which the reactivity feedback was based on core temperature measurements; the neutron generation time and the temperature feedback coefficient are provided as model inputs. These dynamic system response tests demonstrate the overall capability of a non-nuclear test facility in assessing system integration issues and characterizing integrated system response times and response characteristics.

  3. Zscan4 transiently reactivates early embryonic genes during the generation of induced pluripotent stem cells.

    PubMed

    Hirata, Tetsuya; Amano, Tomokazu; Nakatake, Yuhki; Amano, Misa; Piao, Yulan; Hoang, Hien G; Ko, Minoru S H

    2012-01-01

    The generation of induced pluripotent stem cells (iPSCs) by the forced expression of defined transcription factors in somatic cells holds great promise for the future of regenerative medicine. However, the initial reprogramming mechanism is still poorly understood. Here we show that Zscan4, expressed transiently in2-cell embryos and embryonic stem cells (ESCs), efficiently produces iPSCs from mouse embryo fibroblasts when coexpressed with Klf4, Oct4, and Sox2. Interestingly, the forced expression of Zscan4 is required onlyfor the first few days of iPSC formation. Microarray analysis revealed transient and early induction of preimplantation-specific genes in a Zscan4-dependent manner. Our work indicates that Zscan4 is a previously unidentified potent natural factor that facilitates the reprogramming process and reactivates early embryonic genes.

  4. Runaway transient simulation of a model Kaplan turbine

    NASA Astrophysics Data System (ADS)

    Liu, S.; Zhou, D.; Liu, D.; Wu, Y.; Nishi, M.

    2010-08-01

    The runaway transient is a typical transient process of a hydro power unit, where the rotational speed of a turbine runner rapidly increases up to the runaway speed under a working head as the guide vanes cannot be closed due to some reason at the load rejection. In the present paper, the characteristics of the runaway transient of a model Kaplan turbine having ns = 479(m-kW) is simulated by using a time-dependent CFD technique where equation of rotational motion of runner, continuity equation and unsteady RANS equations with RNG k-epsilon turbulence model are solved iteratively. In the calculation, unstructured mesh is used to the whole flow passage, which consists of several sub-domains: entrance, casing, stay vanes + guide vanes, guide section, runner and draft tube. And variable speed sliding mesh technique is used to exchange interface flow information between moving part and stationary part, and three-dimensional unstructured dynamic mesh technique is also adopted to ensure mesh quality. Two cases were treated in the simulation of runaway transient characteristics after load rejection: one is the rated operating condition as the initial condition, and the other is the condition at the maximum head. Regarding the runaway speed, the experimental speed is 1.45 times the initial speed and the calculation is 1.47 times the initial for the former case. In the latter case, the experiment and the calculation are 1.67 times and 1.69 times respectively. From these results, it is recognized that satisfactorily prediction will be possible by using the present numerical method. Further, numerical results show that the swirl in the draft-tube flow becomes stronger in the latter part of the transient process so that a vortex rope will occur in the draft tube and its precession will cause the pressure fluctuations which sometimes affect the stability of hydro power system considerably.

  5. Reactive power generation in high speed induction machines by continuously occurring space-transients

    NASA Astrophysics Data System (ADS)

    Laithwaite, E. R.; Kuznetsov, S. B.

    1980-09-01

    A new technique of continuously generating reactive power from the stator of a brushless induction machine is conceived and tested on a 10-kw linear machine and on 35 and 150 rotary cage motors. An auxiliary magnetic wave traveling at rotor speed is artificially created by the space-transient attributable to the asymmetrical stator winding. At least two distinct windings of different pole-pitch must be incorporated. This rotor wave drifts in and out of phase repeatedly with the stator MMF wave proper and the resulting modulation of the airgap flux is used to generate reactive VA apart from that required for magnetization or leakage flux. The VAR generation effect increases with machine size, and leading power factor operation of the entire machine is viable for large industrial motors and power system induction generators.

  6. Uncertainty in simulated groundwater-quality trends in transient flow

    USGS Publications Warehouse

    Starn, J. Jeffrey; Bagtzoglou, Amvrossios; Robbins, Gary A.

    2013-01-01

    In numerical modeling of groundwater flow, the result of a given solution method is affected by the way in which transient flow conditions and geologic heterogeneity are simulated. An algorithm is demonstrated that simulates breakthrough curves at a pumping well by convolution-based particle tracking in a transient flow field for several synthetic basin-scale aquifers. In comparison to grid-based (Eulerian) methods, the particle (Lagrangian) method is better able to capture multimodal breakthrough caused by changes in pumping at the well, although the particle method may be apparently nonlinear because of the discrete nature of particle arrival times. Trial-and-error choice of number of particles and release times can perhaps overcome the apparent nonlinearity. Heterogeneous aquifer properties tend to smooth the effects of transient pumping, making it difficult to separate their effects in parameter estimation. Porosity, a new parameter added for advective transport, can be accurately estimated using both grid-based and particle-based methods, but predictions can be highly uncertain, even in the simple, nonreactive case.

  7. Transient Climate Simulation of the last deglaciation in CCSM3

    SciTech Connect

    He, Feng; Erickson III, David J; Jacob, Robert L.

    2009-12-01

    We conducted the first synchronously coupled atmosphere-ocean general circulation model simulation of global climate evolution of the last deglaciation (21,000-10,000 years ago) using the NCAR CCSM3. With realistic climate forcings associated with greenhouse gasses, orbital forcing and continental ice sheet, as well as a reasonable melting water forcing, our model reproduces some major deglacial climate features, such as the H1 event, the BA warming and the YD event. A preliminary model-data comparison shows a global climate evolution largely consistent with the reconstruction. The magnitude of our model climate responses are largely consistent with the reconstruction, suggesting a good agreement between observed and modeled climate sensitivity. In contrast to previous simulations of intermediate climate models, our model AMOC has little hysteresis. As a result, the model simulates the abrupt onset of the BA warming and the abrupt termination of the YD cooling as transient responses of the Atlantic meridional overturning circulation (AMOC) to abrupt terminations of freshwater discharges. Further implications to transient model-data comparison will also be discussed.

  8. Simulation of the transient electromechanical behaviour of dielectric elastomer transducers

    NASA Astrophysics Data System (ADS)

    Mößinger, Holger; Förster-Zügel, Florentine; Schlaak, Helmut F.

    2016-04-01

    To design systems utilizing dielectric elastomer transducers (DET) models are necessary to describe the behaviour of the DET and assess the system performance in advance. For basic set-ups simple analytical models or lumped parameter models are available and provide reasonable results. For more complex set-ups these models only allow a rough estimation of the system performance, not accurate enough to achieve an optimal system design. Therefore system designers typically resort to numerical simulation tools. Commercially available tools and models specialize on either electrical or mechanical domain thus simplifying or even neglecting effects in the other domain respectively. In this work we present a simulation tool taking into account the transient electrical and mechanical behaviour of DET under different mechanical load conditions and electrical driving frequencies. Our model can describe transient electrical and mechanical behaviour, such as electrical resistance, mechanical hyperelastic and viscosity of the electrodes and dielectric material. Model parameters are derived from measurements of the dielectric and the electrode resistance as well as e.g. the materials Young's modulus. The results from the simulation are compared to simple lumped parameter based models.

  9. Reactive Oxygen Species (ROS) generation by lunar simulants

    NASA Astrophysics Data System (ADS)

    Kaur, Jasmeet; Rickman, Douglas; Schoonen, Martin A.

    2016-05-01

    The current interest in human exploration of the Moon and past experiences of Apollo astronauts has rekindled interest into the possible harmful effects of lunar dust on human health. In comparison to the Apollo-era explorations, human explorers may be weeks on the Moon, which will raise the risk of inhalation exposure. The mineralogical composition of lunar dust is well documented, but its effects on human health are not fully understood. With the aim of understanding the reactivity of dusts that may be encountered on geologically different lunar terrains, we have studied Reactive Oxygen Species (ROS) generation by a suite of lunar simulants of different mineralogical-chemical composition dispersed in water and Simulated Lung Fluid (SLF). To further explore the reactivity of simulants under lunar environmental conditions, we compared the reactivity of simulants both in air and inert atmosphere. As the impact of micrometeorites with consequent shock-induced stresses is a major environmental factor on the Moon, we also studied the effect of mechanical stress on samples. Mechanical stress was induced by hand crushing the samples both in air and inert atmosphere. The reactivity of samples after crushing was analyzed for a period of up to nine days. Hydrogen peroxide (H2O2) in water and SLF was analyzed by an in situ electrochemical probe and hydroxyl radical (•OH) by Electron Spin Resonance (ESR) spectroscopy and Adenine probe. Out of all simulants, CSM-CL-S was found to be the most reactive simulant followed by OB-1 and then JSC-1A simulant. The overall reactivity of samples in the inert atmosphere was higher than in air. Fresh crushed samples showed a higher level of reactivity than uncrushed samples. Simulant samples treated to create agglutination, including the formation of zero-valent iron, showed less reactivity than untreated simulants. ROS generation in SLF is initially slower than in deionized water (DI), but the ROS formation is sustained for as long as 7

  10. Simulation of transient infrared spectra of a photoswitchable peptide.

    PubMed

    Kobus, Maja; Lieder, Martin; Nguyen, Phuong H; Stock, Gerhard

    2011-12-14

    In transient infrared (IR) experiments, a molecular system may be photoexcited in a nonstationary conformational state, whose time evolution is monitored via IR spectroscopy with high temporal and structural resolution. As a theoretical formulation of these experiments, this work derives explicit expressions for transient one- and two-dimensional IR spectra and discusses various levels of approximation and sampling strategies. Adopting a photoswitchable octapeptide in water as a representative example, nonequilibrium molecular dynamics simulations are performed and the photoinduced conformational dynamics and associated IR spectra are discussed in detail. Interestingly, it is found that the time scales of dynamics and spectra may differ from residue to residue by up to an order of magnitude. Considering merely the cumulative spectrum of all residues, the contributions of the individual residues largely compensate each other, which may explain the surprisingly small frequency shifts and short photoproduct rise times found in experiment. Even when a localized amide I mode is probed (e.g., via isotope labeling), the vibrational frequency shift is shown to depend in a complicated way on the conformation of the entire peptide as well as on the interaction with the solvent. In this context, various issues concerning the interpretation of transient IR spectra and conformational dynamics in terms of a few exponential time scales are discussed. PMID:22168727

  11. Thermodynamic and kinetic simulation of transient liquid-phase bonding

    NASA Astrophysics Data System (ADS)

    Lindner, Brad

    The use of numeric computational methods for the simulation of materials systems is becoming more prevalent and an understanding of these tools may soon be a necessity for Materials Engineers and Scientists. The applicability of numerical simulation methods to transient liquid-phase (TLP) bonding is evaluated using a type 316L/MBF-51 material system. The comparisons involve the calculation of bulk diffusivities, tracking of interface positions during dissolution, widening, and isothermal solidification stages, as well as comparison of elemental composition profiles. The simulations were performed with Thermo-Calc and DICTRA software packages and the experiments with differential scanning calorimetry (DSC), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and optical microscopic methods. Analytical methods are also discussed to enhance understanding. The results of the investigation show that while general agreement between simulations and experiments can be obtained, assumptions made with the simulation programs may cause difficulty in interpretation of the results unless the user has sufficient, mathematical, thermodynamic, kinetic, and simulation background.

  12. Numerical simulation of transient hypervelocity flow in an expansion tube

    NASA Technical Reports Server (NTRS)

    Jacobs, P. A.

    1992-01-01

    Several numerical simulations of the transient flow of helium in an expansion tube are presented. The aim of the exercise is to provide further information on the operational problems of the NASA Langley expansion tube. The calculations were performed with an axisymmetric Navier-Stokes code based on a finite-volume formulation and upwinding techniques. Although laminar flow and ideal bursting of the diaphragms was assumed, the simulations showed some of the important features seen in the experiments. In particular, the discontinuity in the tube diameter at the primary diaphragm station introduced a transverse perturbation to the expanding driver gas, and this perturbation was seen to propagate into the test gas under some flow conditions. The disturbances seen in the test flow can be characterized as either 'small-amplitude' noise possibly introduced during shock compression or 'large-amplitude' noise associated with the passage of the reflected head of the unsteady expansion.

  13. Numerical simulation of transient hypervelocity flow in an expansion tube

    NASA Technical Reports Server (NTRS)

    Jacobs, P. A.

    1992-01-01

    Several numerical simulations of the transient flow of helium in an expansion tube are presented in an effort to identify some of the basic mechanisms which cause the noisy test flows seen in experiments. The calculations were performed with an axisymmetric Navier-Stokes code based on a finite volume formulation and upwinding techniques. Although laminar flow and ideal bursting of the diaphragms was assumed, the simulations showed some of the important features seen in experiments. In particular, the discontinuity in tube diameter of the primary diaphragm station introduced a transverse perturbation to the expanding driver gas and this perturbation was seen to propagate into the test gas under some flow conditions. The disturbances seen in the test flow can be characterized as either small amplitude, low frequency noise possibly introduced during shock compression or large amplitude, high frequency noise associated with the passage of the reflected head of the unsteady expansion.

  14. Network Flow Simulation of Fluid Transients in Rocket Propulsion Systems

    NASA Technical Reports Server (NTRS)

    Bandyopadhyay, Alak; Hamill, Brian; Ramachandran, Narayanan; Majumdar, Alok

    2011-01-01

    Fluid transients, also known as water hammer, can have a significant impact on the design and operation of both spacecraft and launch vehicle propulsion systems. These transients often occur at system activation and shutdown. The pressure rise due to sudden opening and closing of valves of propulsion feed lines can cause serious damage during activation and shutdown of propulsion systems. During activation (valve opening) and shutdown (valve closing), pressure surges must be predicted accurately to ensure structural integrity of the propulsion system fluid network. In the current work, a network flow simulation software (Generalized Fluid System Simulation Program) based on Finite Volume Method has been used to predict the pressure surges in the feed line due to both valve closing and valve opening using two separate geometrical configurations. The valve opening pressure surge results are compared with experimental data available in the literature and the numerical results compared very well within reasonable accuracy (< 5%) for a wide range of inlet-to-initial pressure ratios. A Fast Fourier Transform is preformed on the pressure oscillations to predict the various modal frequencies of the pressure wave. The shutdown problem, i.e. valve closing problem, the simulation results are compared with the results of Method of Characteristics. Most rocket engines experience a longitudinal acceleration, known as "pogo" during the later stage of engine burn. In the shutdown example problem, an accumulator has been used in the feed system to demonstrate the "pogo" mitigation effects in the feed system of propellant. The simulation results using GFSSP compared very well with the results of Method of Characteristics.

  15. Coke Reactivity in Simulated Blast Furnace Shaft Conditions

    NASA Astrophysics Data System (ADS)

    Haapakangas, Juho; Suopajärvi, Hannu; Iljana, Mikko; Kemppainen, Antti; Mattila, Olli; Heikkinen, Eetu-Pekka; Samuelsson, Caisa; Fabritius, Timo

    2016-08-01

    Despite the fact that H2 and H2O are always present in the gas atmosphere of a blast furnace shaft, their role in the solution-loss reactions of coke has not been thoroughly examined. This study focuses on how H2 and H2O affect the reaction behavior and whether a strong correlation can be found between reactivity in the conditions of the CRI test (Coke Reactivity Index) and various simulated blast furnace shaft gas atmospheres. Partial replacement of CO/CO2 with H2/H2O was found to significantly increase the reactivity of all seven coke grades at 1373 K (1100 °C). H2 and H2O, however, did not have a significant effect on the threshold temperature of gasification. The reactivity increasing effect was found to be temperature dependent and clearly at its highest at 1373 K (1100 °C). Mathematical models were used to calculate activation energies for the gasification, which were notably lower for H2O gasification compared to CO2 indicating the higher reactivity of H2O. The reactivity results in gas atmospheres with CO2 as the sole gasifying component did not directly correlate with reactivity results in gases also including H2O, which suggests that the widely used CRI test is not entirely accurate for estimating coke reactivity in the blast furnace.

  16. Optimal subinterval selection approach for power system transient stability simulation

    SciTech Connect

    Kim, Soobae; Overbye, Thomas J.

    2015-10-21

    Power system transient stability analysis requires an appropriate integration time step to avoid numerical instability as well as to reduce computational demands. For fast system dynamics, which vary more rapidly than what the time step covers, a fraction of the time step, called a subinterval, is used. However, the optimal value of this subinterval is not easily determined because the analysis of the system dynamics might be required. This selection is usually made from engineering experiences, and perhaps trial and error. This paper proposes an optimal subinterval selection approach for power system transient stability analysis, which is based on modal analysis using a single machine infinite bus (SMIB) system. Fast system dynamics are identified with the modal analysis and the SMIB system is used focusing on fast local modes. An appropriate subinterval time step from the proposed approach can reduce computational burden and achieve accurate simulation responses as well. As a result, the performance of the proposed method is demonstrated with the GSO 37-bus system.

  17. Optimal subinterval selection approach for power system transient stability simulation

    DOE PAGES

    Kim, Soobae; Overbye, Thomas J.

    2015-10-21

    Power system transient stability analysis requires an appropriate integration time step to avoid numerical instability as well as to reduce computational demands. For fast system dynamics, which vary more rapidly than what the time step covers, a fraction of the time step, called a subinterval, is used. However, the optimal value of this subinterval is not easily determined because the analysis of the system dynamics might be required. This selection is usually made from engineering experiences, and perhaps trial and error. This paper proposes an optimal subinterval selection approach for power system transient stability analysis, which is based on modalmore » analysis using a single machine infinite bus (SMIB) system. Fast system dynamics are identified with the modal analysis and the SMIB system is used focusing on fast local modes. An appropriate subinterval time step from the proposed approach can reduce computational burden and achieve accurate simulation responses as well. As a result, the performance of the proposed method is demonstrated with the GSO 37-bus system.« less

  18. Modelling of HVDC converters for real-time transient simulators

    NASA Astrophysics Data System (ADS)

    Acevedo, Salvador

    This thesis presents developments in the computer modelling of High Voltage Direct Current (HVDC) converters and other FACTS devices for EMTP-type simulators. The high number and frequency of switching operations in power electronic converters cause numerical difficulties that require additional computational effort. The additional computational burden requires the development of techniques that can accelerate the simulation speeds of conventional electromagnetic transient modelling and may allow real-time simulations. The main results are two models that effectively reduce the computational time required to obtain the solution of an electrical network containing HVDC converters. Both approaches have in common the principle of subdividing an electrical circuit containing a 6n-valve converter into at least n subsystems. For each 6-valve subsystem, the 64 matrix combinations are precalculated and prestored in computer memory. The interaction between subsystems to obtain the network solution is particular to each approach. With this criterion, the number of precalculated combinations for a 24-valve HVDC substation is reduced from more than 16 million to only 256. Both models present a considerable reduction in the computational time required to simulate circuits containing HVDC converters. The most efficient model has been successfully implemented in the real time power systems simulator under development by the power research group at the University of British Columbia. The exact calculation of the network solution at switching events is another important aspect required to accurately simulate power electronic converters in power systems. The thesis proposes the zero crossing detection algorithm, which eliminates the erroneous delays present in traditional EMTP simulators. The proposed algorithm resynchronizes the solution to the original simulation time increment. To solve the problem originated by the forced commutation of Gate Turn Off Thyristors, an exploratory

  19. Reactivity of simulated lunar material with fluorine

    NASA Technical Reports Server (NTRS)

    Odonnell, P. M.

    1972-01-01

    Simulated lunar surface material was caused to react with fluorine to determine the feasibility of producing oxygen by this method. The maximum total fluorine pressure used was 53.3 kilonewtons per square meter (400 torr) at temperatures up to 523 K (250 C). Postreaction analysis of both the gas and solid phases indicated that the reaction is feasible but that the efficiency is only about 4 percent of that predicted by theory.

  20. The Multiscale Material Point Method for Simulating Transient Responses

    NASA Astrophysics Data System (ADS)

    Chen, Zhen; Su, Yu-Chen; Zhang, Hetao; Jiang, Shan; Sewell, Thomas

    2015-06-01

    To effectively simulate multiscale transient responses such as impact and penetration without invoking master/slave treatment, the multiscale material point method (Multi-MPM) is being developed in which molecular dynamics at nanoscale and dissipative particle dynamics at mesoscale might be concurrently handled within the framework of the original MPM at microscale (continuum level). The proposed numerical scheme for concurrently linking different scales is described in this paper with simple examples for demonstration. It is shown from the preliminary study that the mapping and re-mapping procedure used in the original MPM could coarse-grain the information at fine scale and that the proposed interfacial scheme could provide a smooth link between different scales. Since the original MPM is an extension from computational fluid dynamics to solid dynamics, the proposed Multi-MPM might also become robust for dealing with multiphase interactions involving failure evolution. This work is supported in part by DTRA and NSFC.

  1. Transient Simulation of the Integrated Powerhead Demonstrator (IPD) Rocket Engine

    NASA Technical Reports Server (NTRS)

    Guidos, Mike; Seymour, Dave

    2003-01-01

    The IPD rocket engine is the product of a joint Air Force/NASA program to demonstrate the concept of a full-flow staged combustion power cycle. In this type of rocket engine cycle, both the entire fuel flow and the entire oxidizer flow are combusted in one of two pre-bumers and used to drive two turbopumps, thus utilizing the flow work of the total propellant flow. The basis of the IPD engine program relies on integrating newly developed and pre-existing hardware to demonstrate the component and material technologies to make this concept feasible, while simultaneously saving development time and costs. To provide insight to the project team and contractors during engine development and test phases, the engine system was modeled at MSFC using the Rocket Engine Transient Simulation (ROCETS) software to analyze system performance and determine component integration issues. The ROCETS software is used extensively a MSFC to perform steady-state power-balances and transient simulations of thermodynamic power and general fluid systems. The software is favored for its capability to solve large systems of non-linear equations, its librarie of fluid properties and flow devices, its flexibility to modify existing code to improve the physics-derived approximations of real fluid thermodynamic behavior, and the ability to add unique system constraints. The purpose of this paper is to present the methodology used to model the IPD engine system, detail the pitfalls encountered with the software, and explain the approximations made to more accurately represent engine component and fluid behavior. Engine system performance output from the model will be presented and explained in comparison with real fluid and component behavior.

  2. Transient productivity index for numerical well test simulations

    SciTech Connect

    Blanc, G.; Ding, D.Y.; Ene, A.

    1997-08-01

    The most difficult aspect of numerical simulation of well tests is the treatment of the Bottom Hole Flowing (BHF) Pressure. In full field simulations, this pressure is derived from the Well-block Pressure (WBP) using a numerical productivity index which accounts for the grid size and permeability, and for the well completion. This productivity index is calculated assuming a pseudo-steady state flow regime in the vicinity of the well and is therefore constant during the well production period. Such a pseudo-steady state assumption is no longer valid for the early time of a well test simulation as long as the pressure perturbation has not reached several grid-blocks around the well. This paper offers two different solutions to this problem: (1) The first one is based on the derivation of a Numerical Transient Productivity Index (NTPI) to be applied to Cartesian grids; (2) The second one is based on the use of a Corrected Transmissibility and Accumulation Term (CTAT) in the flow equation. The representation of the pressure behavior given by both solutions is far more accurate than the conventional one as shown by several validation examples which are presented in the following pages.

  3. Production of Nitrogen Oxides by Laboratory Simulated Transient Luminous Events

    NASA Astrophysics Data System (ADS)

    Peterson, H.; Bailey, M.; Hallett, J.; Beasley, W.

    2007-12-01

    Restoration of the polar stratospheric ozone layer has occurred at rates below those originally expected following reductions in chlorofluorocarbon (CFC) usage. Additional reactions affecting ozone depletion now must also be considered. This research examines nitrogen oxides (NOx) produced in the middle atmosphere by transient luminous events (TLEs), with NOx production in this layer contributing to the loss of stratospheric ozone. In particular, NOx produced by sprites in the mesosphere would be transported to the polar stratosphere via the global meridional circulation and downward diffusion. A pressure-controlled vacuum chamber was used to simulate middle atmosphere pressures, while a power supply and in-chamber electrodes were used to simulate TLEs in the pressure controlled environment. Chemiluminescence NOx analyzers were used to sample NOx produced by the chamber discharges- originally a Monitor Labs Model 8440E, later a Thermo Environment Model 42. Total NOx production for each discharge as well as NOx per ampere of current and NOx per Joule of discharge energy were plotted. Absolute NOx production was greatest for discharge environments with upper tropospheric pressures (100-380 torr), while NOx/J was greatest for discharge environments with stratospheric pressures (around 10 torr). The different production efficiencies in NOx/J as a function of pressure pointed to three different production regimes, each with its own reaction mechanisms: one for tropospheric pressures, one for stratospheric pressures, and one for upper stratospheric to mesospheric pressures (no greater than 1 torr).

  4. Simulations of reactive transport and precipitation with smoothed particle hydrodynamics

    NASA Astrophysics Data System (ADS)

    Tartakovsky, Alexandre M.; Meakin, Paul; Scheibe, Timothy D.; Eichler West, Rogene M.

    2007-03-01

    A numerical model based on smoothed particle hydrodynamics (SPH) was developed for reactive transport and mineral precipitation in fractured and porous materials. Because of its Lagrangian particle nature, SPH has several advantages for modeling Navier-Stokes flow and reactive transport including: (1) in a Lagrangian framework there is no non-linear term in the momentum conservation equation, so that accurate solutions can be obtained for momentum dominated flows and; (2) complicated physical and chemical processes such as surface growth due to precipitation/dissolution and chemical reactions are easy to implement. In addition, SPH simulations explicitly conserve mass and linear momentum. The SPH solution of the diffusion equation with fixed and moving reactive solid-fluid boundaries was compared with analytical solutions, Lattice Boltzmann [Q. Kang, D. Zhang, P. Lichtner, I. Tsimpanogiannis, Lattice Boltzmann model for crystal growth from supersaturated solution, Geophysical Research Letters, 31 (2004) L21604] simulations and diffusion limited aggregation (DLA) [P. Meakin, Fractals, scaling and far from equilibrium. Cambridge University Press, Cambridge, UK, 1998] model simulations. To illustrate the capabilities of the model, coupled three-dimensional flow, reactive transport and precipitation in a fracture aperture with a complex geometry were simulated.

  5. Experimental Validation of a Closed Brayton Cycle System Transient Simulation

    NASA Technical Reports Server (NTRS)

    Johnson, Paul K.; Hervol, David S.

    2006-01-01

    The Brayton Power Conversion Unit (BPCU) is a closed cycle system with an inert gas working fluid. It is located in Vacuum Facility 6 at NASA Glenn Research Center. Was used in previous solar dynamic technology efforts (SDGTD). Modified to its present configuration by replacing the solar receiver with an electrical resistance heater. The first closed-Brayton-cycle to be coupled with an ion propulsion system. Used to examine mechanical dynamic characteristics and responses. The focus of this work was the validation of a computer model of the BPCU. Model was built using the Closed Cycle System Simulation (CCSS) design and analysis tool. Test conditions were then duplicated in CCSS. Various steady-state points. Transients involving changes in shaft rotational speed and heat input. Testing to date has shown that the BPCU is able to generate meaningful, repeatable data that can be used for computer model validation. Results generated by CCSS demonstrated that the model sufficiently reproduced the thermal transients exhibited by the BPCU system. CCSS was also used to match BPCU steady-state operating points. Cycle temperatures were within 4.1% of the data (most were within 1%). Cycle pressures were all within 3.2%. Error in alternator power (as much as 13.5%) was attributed to uncertainties in the compressor and turbine maps and alternator and bearing loss models. The acquired understanding of the BPCU behavior gives useful insight for improvements to be made to the CCSS model as well as ideas for future testing and possible system modifications.

  6. Rapid and transient stimulation of intracellular reactive oxygen species by melatonin in normal and tumor leukocytes

    SciTech Connect

    Radogna, Flavia; Paternoster, Laura; De Nicola, Milena; Cerella, Claudia; Ammendola, Sergio; Bedini, Annalida; Tarzia, Giorgio; Aquilano, Katia; Ciriolo, Maria; Ghibelli, Lina

    2009-08-15

    Melatonin is a modified tryptophan with potent biological activity, exerted by stimulation of specific plasma membrane (MT1/MT2) receptors, by lower affinity intracellular enzymatic targets (quinone reductase, calmodulin), or through its strong anti-oxidant ability. Scattered studies also report a perplexing pro-oxidant activity, showing that melatonin is able to stimulate production of intracellular reactive oxygen species (ROS). Here we show that on U937 human monocytes melatonin promotes intracellular ROS in a fast (< 1 min) and transient (up to 5-6 h) way. Melatonin equally elicits its pro-radical effect on a set of normal or tumor leukocytes; intriguingly, ROS production does not lead to oxidative stress, as shown by absence of protein carbonylation, maintenance of free thiols, preservation of viability and regular proliferation rate. ROS production is independent from MT1/MT2 receptor interaction, since a) requires micromolar (as opposed to nanomolar) doses of melatonin; b) is not contrasted by the specific MT1/MT2 antagonist luzindole; c) is not mimicked by a set of MT1/MT2 high affinity melatonin analogues. Instead, chlorpromazine, the calmodulin inhibitor shown to prevent melatonin-calmodulin interaction, also prevents melatonin pro-radical effect, suggesting that the low affinity binding to calmodulin (in the micromolar range) may promote ROS production.

  7. Transient Analysis Generator /TAG/ simulates behavior of large class of electrical networks

    NASA Technical Reports Server (NTRS)

    Thomas, W. J.

    1967-01-01

    Transient Analysis Generator program simulates both transient and dc steady-state behavior of a large class of electrical networks. It generates a special analysis program for each circuit described in an easily understood and manipulated programming language. A generator or preprocessor and a simulation system make up the TAG system.

  8. Transient Modeling of Reactive Solute Transport in a Submarine Groundwater Discharge Zone

    NASA Astrophysics Data System (ADS)

    Colman, J. A.; Bratton, J. F.; Crusius, J.; Kroeger, K. D.; Baldwin, S.; Lee, K.

    2009-12-01

    Submarine groundwater discharge (SGD) is the dominant means of freshwater delivery to many coastal embayments on the glaciated coast of Cape Cod (Mass.). This discharge is the focus of considerable research, in part because the common disposal of sewage via septic systems has led to elevated concentrations of nutrients in groundwater. Subsurface mixing and chemical reactivity prior to discharge can affect the amounts of nutrients entering the embayments. Water-quality problems including eutrophication and harmful algal blooms appear to be controlled by the timing and intensity of SGD at our field site, Salt Pond, a weakly stratified estuary 8.2 ha in area with a maximum depth of 9 m and tidal amplitude of 2 m. The site is located at the northern (inland) end of Nauset Marsh on outer Cape Cod. We estimated mixing and reaction rates in the discharge area by fitting a 2-D reactive-solute-transport model (PHAST) to chemical observations in the intertidal subsurface using hydrologic forcing from aquifer recharge and tides. Chemical measurements in the subsurface, taken at 5 intervals spanning the seasons from a multilevel-sampler (MLS) array, 20 m long by 6 m deep, indicate a change in the position of the groundwater salt front on both tidal and seasonal time scales, with a maximum horizontal movement of approximately 4 m. Observed movement of the salt front corresponded with simulated movement modeled by changing seasonal recharge to the aquifer. Kinetics of oxygen consumption in the subsurface were modeled using end-member concentrations of oxygen in upgradient fresh groundwater and in water-column saltwater, assumed biological oxygen demand in saltwater, and model-determined residence time in the subsurface. High measured concentrations of nitrate (up to 7 mg/L as N) in intertidal groundwater were unaffected by denitrification prior to discharge based on both chemical analysis of denitrification indicators in MLS samples, and model results. This work demonstrates

  9. Large liquid rocket engine transient performance simulation system

    NASA Technical Reports Server (NTRS)

    Mason, J. R.; Southwick, R. D.

    1989-01-01

    Phase 1 of the Rocket Engine Transient Simulation (ROCETS) program consists of seven technical tasks: architecture; system requirements; component and submodel requirements; submodel implementation; component implementation; submodel testing and verification; and subsystem testing and verification. These tasks were completed. Phase 2 of ROCETS consists of two technical tasks: Technology Test Bed Engine (TTBE) model data generation; and system testing verification. During this period specific coding of the system processors was begun and the engineering representations of Phase 1 were expanded to produce a simple model of the TTBE. As the code was completed, some minor modifications to the system architecture centering on the global variable common, GLOBVAR, were necessary to increase processor efficiency. The engineering modules completed during Phase 2 are listed: INJTOO - main injector; MCHBOO - main chamber; NOZLOO - nozzle thrust calculations; PBRNOO - preburner; PIPE02 - compressible flow without inertia; PUMPOO - polytropic pump; ROTROO - rotor torque balance/speed derivative; and TURBOO - turbine. Detailed documentation of these modules is in the Appendix. In addition to the engineering modules, several submodules were also completed. These submodules include combustion properties, component performance characteristics (maps), and specific utilities. Specific coding was begun on the system configuration processor. All functions necessary for multiple module operation were completed but the SOLVER implementation is still under development. This system, the Verification Checkout Facility (VCF) allows interactive comparison of module results to store data as well as provides an intermediate checkout of the processor code. After validation using the VCF, the engineering modules and submodules were used to build a simple TTBE.

  10. Transient state kinetics tutorial using the kinetics simulation program, KINSIM.

    PubMed Central

    Wachsstock, D H; Pollard, T D

    1994-01-01

    This article provides an introduction to a computer tutorial on transient state kinetics. The tutorial uses our Macintosh version of the computer program, KINSIM, that calculates the time course of reactions. KINSIM is also available for other popular computers. This program allows even those investigators not mathematically inclined to evaluate the rate constants for the transitions between the intermediates in any reaction mechanism. These rate constants are one of the insights that are essential for understanding how biochemical processes work at the molecular level. The approach is applicable not only to enzyme reactions but also to any other type of process of interest to biophysicists, cell biologists, and molecular biologists in which concentrations change with time. In principle, the same methods could be used to characterize time-dependent, large-scale processes in ecology and evolution. Completion of the tutorial takes students 6-10 h. This investment is rewarded by a deep understanding of the principles of chemical kinetics and familiarity with the tools of kinetics simulation as an approach to solve everyday problems in the laboratory. PMID:7811941

  11. Assessment of Controlling Processes for Field-Scale Uranium Reactive Transport under Highly Transient Flow Conditions

    SciTech Connect

    Ma, Rui; Zheng, Chunmiao; Liu, Chongxuan; Greskowiak, Janek; Prommer, Henning; Zachara, John M.

    2014-02-06

    This paper presents the results of a comprehensive model-based analysis of a uranium tracer test conducted at the U.S Department of Energy Hanford 300 Area (300A) IFRC site. A three-dimensional multi-component reactive transport model was employed to assess the key factors and processes that control the field-scale uranium reactive transport. Taking into consideration of relevant physical and chemical processes, the selected conceptual/numerical model replicates the spatial and temporal variations of the observed U(VI) concentrations reasonably well in spite of the highly complex field conditions. A sensitivity analysis was performed to interrogate the relative importance of various processes and factors for reactive transport of U(VI) at the field-scale. The results indicate that multi-rate U(VI) sorption/desorption, U(VI) surface complexation reactions, and initial U(VI) concentrations were the most important processes and factors controlling U(VI) migration. On the other hand, cation exchange reactions, the choice of the surface complexation model, and dual-domain mass transfer processes, which were previously identified to be important in laboratory experiments, played less important roles under the field-scale experimental condition at the 300A site. However, the model simulations also revealed that the groundwater chemistry was relatively stable during the uranium tracer experiment and therefore presumably not dynamic enough to appropriately assess the effects of ion exchange reaction and the choice of surface complexation models on U(VI) sorption and desorption. Furthermore, it also showed that the field experimental duration (16 days) was not sufficiently long to precisely assess the role of a majority of the sorption sites that were accessed by slow kinetic processes within the dual domain model. The sensitivity analysis revealed the crucial role of the intraborehole flow that occurred within the long-screened monitoring wells and thus significantly

  12. Rotating cylindrical magnetron sputtering: Simulation of the reactive process

    SciTech Connect

    Depla, D.; Mahieu, S.; Van Aeken, K.; Leroy, W. P.; Haemers, J.; De Gryse, R.; Li, X. Y.; Bogaerts, A.

    2010-06-15

    A rotating cylindrical magnetron consists of a cylindrical tube, functioning as the cathode, which rotates around a stationary magnet assembly. In stationary mode, the cylindrical magnetron behaves similar to a planar magnetron with respect to the influence of reactive gas addition to the plasma. However, the transition from metallic mode to poisoned mode and vice versa depends on the rotation speed. An existing model has been modified to simulate the influence of target rotation on the well known hysteresis behavior during reactive magnetron sputtering. The model shows that the existing poisoning mechanisms, i.e., chemisorption, direct reactive ion implantation and knock on implantation, are insufficient to describe the poisoning behavior of the rotating target. A better description of the process is only possible by including the deposition of sputtered material on the target.

  13. Quadrature Moments Method for the Simulation of Turbulent Reactive Flows

    NASA Technical Reports Server (NTRS)

    Raman, Venkatramanan; Pitsch, Heinz; Fox, Rodney O.

    2003-01-01

    A sub-filter model for reactive flows, namely the DQMOM model, was formulated for Large Eddy Simulation (LES) using the filtered mass density function. Transport equations required to determine the location and size of the delta-peaks were then formulated for a 2-peak decomposition of the FDF. The DQMOM scheme was implemented in an existing structured-grid LES solver. Simulations of scalar shear layer using an experimental configuration showed that the first and second moments of both reactive and inert scalars are in good agreement with a conventional Lagrangian scheme that evolves the same FDF. Comparisons with LES simulations performed using laminar chemistry assumption for the reactive scalar show that the new method provides vast improvements at minimal computational cost. Currently, the DQMOM model is being implemented for use with the progress variable/mixture fraction model of Pierce. Comparisons with experimental results and LES simulations using a single-environment for the progress-variable are planned. Future studies will aim at understanding the effect of increase in environments on predictions.

  14. Transient climate-carbon simulations of planetary geoengineering.

    PubMed

    Matthews, H Damon; Caldeira, Ken

    2007-06-12

    Geoengineering (the intentional modification of Earth's climate) has been proposed as a means of reducing CO2-induced climate warming while greenhouse gas emissions continue. Most proposals involve managing incoming solar radiation such that future greenhouse gas forcing is counteracted by reduced solar forcing. In this study, we assess the transient climate response to geoengineering under a business-as-usual CO2 emissions scenario by using an intermediate-complexity global climate model that includes an interactive carbon cycle. We find that the climate system responds quickly to artificially reduced insolation; hence, there may be little cost to delaying the deployment of geoengineering strategies until such a time as "dangerous" climate change is imminent. Spatial temperature patterns in the geoengineered simulation are comparable with preindustrial temperatures, although this is not true for precipitation. Carbon sinks in the model increase in response to geoengineering. Because geoengineering acts to mask climate warming, there is a direct CO2-driven increase in carbon uptake without an offsetting temperature-driven suppression of carbon sinks. However, this strengthening of carbon sinks, combined with the potential for rapid climate adjustment to changes in solar forcing, leads to serious consequences should geoengineering fail or be stopped abruptly. Such a scenario could lead to very rapid climate change, with warming rates up to 20 times greater than present-day rates. This warming rebound would be larger and more sustained should climate sensitivity prove to be higher than expected. Thus, employing geoengineering schemes with continued carbon emissions could lead to severe risks for the global climate system.

  15. Transient simulation of EPROM writing characteristics, with a novel hot electron injection model

    NASA Astrophysics Data System (ADS)

    Huang, Chimoon; Wang, Tahui

    1995-02-01

    A two-dimensional transient simulation of EPROM writing characteristics is presented. A Monte Carlo-based hot electron injection model which accounts for Fowler-Nordheim tunneling and thermionic emission has been included in the simulation. The simulated EPROM writing transient characteristics is compared favorably with experimental results for channel lengths down to 0.5 μm. The importance of the two injection mechanisms, thermionic emission and quantum tunneling; is evaluated.

  16. Programmable AC power supply for simulating power transient expected in fusion reactor

    SciTech Connect

    Halimi, B.; Suh, K. Y.

    2012-07-01

    This paper focus on control engineering of the programmable AC power source which has capability to simulate power transient expected in fusion reactor. To generate the programmable power source, AC-AC power electronics converter is adopted to control the power of a set of heaters to represent the transient phenomena of heat exchangers or heat sources of a fusion reactor. The International Thermonuclear Experimental Reactor (ITER) plasma operation scenario is used as the basic reference for producing this transient power source. (authors)

  17. A transient decrease in reactive oxygen species in roots leads to root hair deformation in the legume-rhizobia symbiosis.

    PubMed

    Lohar, Dasharath Prasad; Haridas, Sajeet; Gantt, J Stephen; VandenBosch, Kathryn A

    2007-01-01

    * A possible role for reactive oxygen species (ROS) in root hair deformation in response to Nod factor (NF) was investigated using Medicago truncatula nodulation mutants, and an inhibitor and precursors of ROS. * In wild-type roots, ROS efflux transiently decreased approximately 1 h after NF treatment. Transcript accumulation of two NADPH oxidase homologs, respiratory burst oxidase homolog 2 (MtRBOH2) and MtRBOH3, also transiently decreased at 1 h. However, in the nonnodulating mutant Nod factor perception (nfp), transcript accumulation did not change. * Exogenous application of ROS prevented root hair swelling and branching induced by NF. When accumulation of ROS was prevented by diphenylene iodonium (DPI), NF did not induce root hair branching. Root treatment with DPI alone reduced ROS efflux and induced root hair tip swelling. Transient treatment of roots with DPI mimicked NF treatment and resulted in root hair branching in the absence of NF. A transient DPI treatment did not induce root hair branching in the nonlegumes Arabidopsis thaliana and tomato (Lycopersicon esculentum). * The results suggest a role for the transient reduction of ROS accumulation in governing NF-induced root hair deformation in legumes.

  18. Voltage equilibration for reactive atomistic simulations of electrochemical processes

    SciTech Connect

    Onofrio, Nicolas; Strachan, Alejandro

    2015-08-07

    We introduce electrochemical dynamics with implicit degrees of freedom (EChemDID), a model to describe electrochemical driving force in reactive molecular dynamics simulations. The method describes the equilibration of external electrochemical potentials (voltage) within metallic structures and their effect on the self-consistent partial atomic charges used in reactive molecular dynamics. An additional variable assigned to each atom denotes the local potential in its vicinity and we use fictitious, but computationally convenient, dynamics to describe its equilibration within connected metallic structures on-the-fly during the molecular dynamics simulation. This local electrostatic potential is used to dynamically modify the atomic electronegativities used to compute partial atomic changes via charge equilibration. Validation tests show that the method provides an accurate description of the electric fields generated by the applied voltage and the driving force for electrochemical reactions. We demonstrate EChemDID via simulations of the operation of electrochemical metallization cells. The simulations predict the switching of the device between a high-resistance to a low-resistance state as a conductive metallic bridge is formed and resistive currents that can be compared with experimental measurements. In addition to applications in nanoelectronics, EChemDID could be useful to model electrochemical energy conversion devices.

  19. Attempting to link hydro-morphology, transient storage and metabolism in streams: Insights from reactive tracer experiments

    NASA Astrophysics Data System (ADS)

    Kurz, Marie J.; Schmidt, Christian; Blaen, Phillip; Knapp, Julia L. A.; Drummond, Jennifer D.; Martí, Eugenia; Zarnetske, Jay P.; Ward, Adam S.; Krause, Stefan

    2016-04-01

    In-stream transient storage zones, including the hyporheic zone and vegetation beds, can be hotspots of biogeochemical processing in streams, enhancing ecosystem functions such as metabolism and nutrient uptake. The spatio-temporal dynamics and reactivity of these storage zones are influenced by multiple factors, including channel geomorphology, substrate composition and hydrology, and by anthropogenic modifications to flow regimes and nutrient loads. Tracer injections are a commonly employed method to evaluate solute transport and transient storage in streams; however, reactive tracers are needed to differentiate between metabolically active and inactive transient storage zones. The reactive stream tracer resazurin (Raz), a weakly fluorescent dye which irreversibly transforms to resorufin (Rru) under mildly reducing conditions, provides a proxy for aerobic respiration and an estimate of the metabolic activity associated with transient storage zones. Across a range of lotic ecosystems, we try to assess the influence of stream channel hydro-morphology, morphologic heterogeneity, and substrate type on reach (103 m) and sub-reach (102 m) scale transient storage, respiration, and nutrient uptake. To do so, we coupled injections of Raz and conservative tracers (uranine and/or salt) at each study site. The study sites included: vegetated mesocosms controlled for water depth; vegetated and un-vegetated sediment-filled mesocosms fed by waste-water effluent; a contrasting sand- vs. gravel-bedded lowland stream (Q = 0.08 m3/s); and a series of upland streams with varying size (Q = 0.1 - 1.5 m3/s) and prevalence of morphologic features. Continuous time-series of tracer concentrations were recorded using in-situ fluorometers and EC loggers. At the stream sites, time-series were recorded at multiple downstream locations in order to resolve sub-reach dynamics. Analyses yielded highly variable transport metrics and Raz-Rru transformation between study sites and between sub

  20. Transient simulation of LOX/LH2 rocket engine, LE-7

    NASA Astrophysics Data System (ADS)

    Kanmuri, Akio; Wakamatsu, Yoshio; Kanda, Takeshi; Torii, Yoshihiro; Nagao, Ryuuji; Kitakura, Kazuhisa; Okada, Masashi; Imoto, Takayuki; Saito, Takashi; Hasegawa, Keiichi

    A start transient simulation calculation program was developed for the LE-7 LOX/LH2 rocket engine based on the quasi-steady model. Comparisons between simulation and test results are reported which show that simulation improvements and engine parameter adjustments are required. A brief description of the engine system is given.

  1. Numerical simulations of unsteady reactive flows in a combustion chamber

    SciTech Connect

    Kailasanath, K.; Gardner, J.H.; Oran, E.S.; Boris, J.P. )

    1991-07-01

    This paper reports on a potentially important source of large-pressure oscillations in combustors that is an instability induced by the interactions between large-scale vortex structures, acoustic waves, and chemical energy release. To study these interactions, we have performed time-dependent, compressible numerical simulations of the flow field in an idealized ramjet consisting of an axisymmetric inlet and combustor and a choked nozzle. Both reactive and nonreactive flows have been simulated. The nonreactive flow calculations show complex interactions among the natural instability frequency of the shear layer at the inlet-combustor junction and the acoustics of both the inlet and the combustor. Vortex shedding occurs at the natural instability frequency of the shear layer but vortex mergings are affected by the acoustic frequencies of the system. The entire flow oscillates at a low frequency that corresponds to that of a quarter-wave mode in the inlet. For the particular reactive flow case studies, energy release alters the flow field substantially.

  2. ESCRIPT-RT: Reactive transport simulation in PYTHON using ESCRIPT

    NASA Astrophysics Data System (ADS)

    Poulet, T.; Gross, L.; Georgiev, D.; Cleverley, J.

    2012-08-01

    We present ESCRIPT-RT, a new reactive transport simulation code for fully saturated porous media which is based on a finite element method (FEM) combined with three other components: (i) a Gibbs minimisation solver for equilibrium modelling of fluid-rock interactions, (ii) an equation of state for pure water to calculate fluid properties and (iii) a thermodynamically consistent material database to determine rocks' material properties. Using decoupling of most of the standard governing equations, this code solves sequentially for temperature, pressure, mass transport and chemical equilibrium. In contrast, pressure and Darcy flow velocities are solved as a coupled system. The reactive transport itself is performed using the masses of chemical elements instead of chemical species. In such way it requires less computing memory and time than the majority of other packages. The code is based on ESCRIPT, a parallelised platform which supports efficient stepwise simulation of realistic geodynamic scenarios at multiple scales. It is particularly suitable to analyse hydrothermal systems involving geometrically complex geological structures with strong permeability contrasts and subject to complex fluid-rock chemical interactions. The modular architecture of the code and its high level Python interface also provide flexibility for modellers who can easily modify or add new feedbacks between the different physical processes. In addition, the implemented abstract user interface allows geologists to run the code without knowledge of the underlying numerical implementation. As an example we show the simulation of hydrothermal gold precipitation in a granite-greenstone geological sequence, which illustrates the important coupling between thermal response and mass transfer to the localisation of gold.

  3. Transient CFD simulation of a Francis turbine startup

    NASA Astrophysics Data System (ADS)

    Nicolle, J.; Morissette, J. F.; Giroux, A. M.

    2012-11-01

    To assess the life expectancy of hydraulic turbines, it is essential to obtain the loading on the blades, especially during transient operations known to be the most damaging. This paper presents a simplified CFD setup to model the startup phase of a Francis turbine while it goes from rest to speed no-load condition. The fluid domain included one distributor sector coupled with one runner passage. The guide vane motion and change in the angular velocity were included in a commercial code with user functions. Comparisons between numerical results and measurements acquired on a full-size turbine showed that most of the flow physics occurring during startup were captured.

  4. Numerical simulation on influence of bonding temperature in transient liquid phase bonding

    NASA Astrophysics Data System (ADS)

    Hynes, N. Rajesh Jesudoss; Raja, M. Karthick

    2016-05-01

    In this article, numerical simulation of transient liquid phase bonding of ceramic/metal joint has been carried out by using Finite Element Analysis (FEA) software. To increase the wettability, aluminium sheet was used as an interlayer. Hence, numerical simulation of TLP bonding process is done by varying the bonding temperature. Transient thermal analysis had been carried out for each cases and temperature distribution was predicted by the developed numerical model. From the simulation studies, it is found that the decrease in bonding temperature enhances favourable temperature distribution and eventually improves the joint efficiency of graphite/copper joints.

  5. Manipulations to reduce simulator-related transient adverse health effects during simulated driving.

    PubMed

    Jäger, M; Gruber, N; Müri, R; Mosimann, U P; Nef, T

    2014-07-01

    User comfort during simulated driving is of key importance, since reduced comfort can confound the experiment and increase dropout rates. A common comfort-affecting factor is simulator-related transient adverse health effect (SHE). In this study, we propose and evaluate methods to adapt a virtual driving scene to reduce SHEs. In contrast to the manufacturer-provided high-sensory conflict scene (high-SCS), we developed a low-sensory conflict scene (low-SCS). Twenty young, healthy participants drove in both the high-SCS and the low-SCS scene for 10 min on two different days (same time of day, randomized order). Before and after driving, participants rated SHEs by completing the Simulator Sickness Questionnaire (SSQ). During driving, several physiological parameters were recorded. After driving in the high-SCS, the SSQ score increased in average by 129.4 (122.9 %, p = 0.002) compared to an increase of 5.0 (3.4 %, p = 0.878) after driving in the low-SCS. In the low-SCS, skin conductance decreased by 13.8 % (p < 0.01) and saccade amplitudes increased by 16.1 % (p < 0.01). Results show that the investigated methods reduce SHEs in a younger population, and the low-SCS is well accepted by the users. We expect that these measures will improve user comfort. PMID:24888755

  6. Modular high-temperature gas-cooled reactor short-term thermal response to flow and reactivity transients

    SciTech Connect

    Cleveland, J.C. )

    1993-02-01

    The research reported here has been conducted at the Oak Ridge National Laboratory for the Nuclear Regulatory Commission's Division of Regulatory Applications of the Office of Nuclear Regulatory Research. The short-term thermal response of the Modular High-Temperature Gas-Cooled Reactor (MHTGR) is analyzed for a range of flow and reactivity transients. These transients include loss of forced circulation without scram, spurious withdrawal of a control rod group, moisture ingress, control rod and control rod group ejections, and a rapid core cooling event. For each event analyzed, an event description, a discussion of the analysis approach and assumptions, and results are presented. When possible, results of these analyses are compared with those presented by the designers in the MHTGR Preliminary Safety Information Document and in the MHTGR Probabilistic Risk Assessment. The importance of inherent safety features is illustrated, and conclusions are presented regarding the safety performance of the MHTGR. Recommendations are made for a more in-depth examination of MHTGR response for some of the analyzed transients. The coupled heat transfer-neutron kinetics model is described in detail in Appendix A.

  7. Characterization and Simulation of Transient Vibrations Using Band Limited Temporal Moments

    DOE PAGES

    Smallwood, David O.

    1994-01-01

    A method is described to characterize shocks (transient time histories) in terms of the Fourier energy spectrum and the temporal moments of the shock passed through a contiguous set of band pass filters. The product model is then used to generate of a random process as simulations that in the mean will have the same energy and moments as the characterization of the transient event.

  8. Numerical Simulation of Transient Liquid Phase Bonding under Temperature Gradient

    NASA Astrophysics Data System (ADS)

    Ghobadi Bigvand, Arian

    Transient Liquid Phase bonding under Temperature Gradient (TG-TLP bonding) is a relatively new process of TLP diffusion bonding family for joining difficult-to-weld aerospace materials. Earlier studies have suggested that in contrast to the conventional TLP bonding process, liquid state diffusion drives joint solidification in TG-TLP bonding process. In the present work, a mass conservative numerical model that considers asymmetry in joint solidification is developed using finite element method to properly study the TG-TLP bonding process. The numerical results, which are experimentally verified, show that unlike what has been previously reported, solid state diffusion plays a major role in controlling the solidification behavior during TG-TLP bonding process. The newly developed model provides a vital tool for further elucidation of the TG-TLP bonding process.

  9. Guanosine radical reactivity explored by pulse radiolysis coupled with transient electrochemistry.

    PubMed

    Latus, A; Alam, M S; Mostafavi, M; Marignier, J-L; Maisonhaute, E

    2015-06-01

    We follow the reactivity of a guanosine radical created by a radiolytic electron pulse both by spectroscopic and electrochemical methods. This original approach allows us to demonstrate that there is a competition between oxidation and reduction of these intermediates, an important result to further analyse the degradation or repair pathways of DNA bases.

  10. Simulation of thermal-transient-induced-pipe-flow stratification using COMMIX-2

    SciTech Connect

    Shah, V.L.; Domanus, H.M.; Miao, C.C.; Schmitt, R.C.; Sha, W.T.

    1982-01-01

    At low-flow (high Richardson number) in a piping system with thermal transient, thermal-buoyancy-induced secondary flows exist. Three-dimensional computer codes are, therefore, necessary to model correctly the non-axisymmetric, thermally stratified flow through a piping system. This paper presents the results of the numerical simulation of thermal-hydraulic behavior in a pipe during a thermal transient. The particular transient considered was the experimental test No. PIPE2, and carried out at the Mixing Components Test Facility (MCTF). The numerical simulation was performed using COMMIX-2. COMMIX-2 is a computer code for steady/unsteady, three-dimensional, two-phase thermal-hydraulic analysis of reactor components under normal and off-normal operating conditions. The results of simulation are compared with the experimental measurements and they are in reasonable agreement with experimental data.

  11. On the behavior of approaches to simulate reactive transport.

    PubMed

    Saaltink, M W; Carrera, J; Ayora, C

    2001-04-01

    Two families of approaches exist to simulate reactive transport in groundwater: The Direct Substitution Approach (DSA), based on Newton-Raphson and the Picard or Sequential Iteration Approach (SIA). We applied basic versions of both methods to several test cases and compared both computational demands and quality of the solution for varying grid size. Results showed that the behavior of the two approaches is sensitive to both grid size and chemistry. As a general rule, the DSA is more robust than the SIA, in the sense that its convergence is less sensitive to time step size (any approach will converge given a sufficiently small time step). Moreover, the DSA leads to a better simulation of sharp fronts, which can only be reproduced with fine grids after many iterations when the SIA is used. As a consequence, the DSA runs faster than SIA in chemically difficult cases (i.e., highly non-linear and/or very retarded), because the SIA may require very small time steps to converge. On the other hand, the size of the system of equations is much larger for the DSA than for the SIA, so that its CPU time and memory requirements tend to be less favorable with increasing grid size. As a result, the SIA may become faster than the DSA for very large, chemically simple problems. The use of an iterative linear solver for the DSA makes its CPU time less sensitive to grid size. PMID:11285932

  12. Transient deformation properties of Zircaloy for LOCA simulation. Final report

    SciTech Connect

    Hann, C. R.; Mohr, C. L.; Busness, K. M.; Olson, N. J.; Reich, F. R.; Stewart, K. B.

    1980-05-01

    This experimental data report is Volume 4 of a series of 5 volumes describing the oxidation and deformation rate behavior of Zircaloy cladding under simulated LOCA conditions. It contains listings of strain versus stress, time, and temperature evaluated from the numerical constitutive relationships and the original data used to develop them. This volume also contains listings of the ramp load, pressure, and temperature test data from both current and previous phases of the series, as well as material describing applications of the data.

  13. Peach Bottom Turbine Trip Simulations with RETRAN Using INER/TPC BWR Transient Analysis Method

    SciTech Connect

    Kao Lainsu; Chiang, Show-Chyuan

    2005-03-15

    The work described in this paper is benchmark calculations of pressurization transient turbine trip tests performed at the Peach Bottom boiling water reactor (BWR). It is part of an overall effort in providing qualification basis for the INER/TPC BWR transient analysis method developed for the Kuosheng and Chinshan plants. The method primarily utilizes an advanced system thermal hydraulics code, RETRAN02/MOD5, for transient safety analyses. Since pressurization transients would result in a strong coupling effect between core neutronic and system thermal hydraulics responses, the INER/TPC method employs the one-dimensional kinetic model in RETRAN with a cross-section data library generated by the Studsvik-CMS code package for the transient calculations. The Peach Bottom Turbine Trip (PBTT) tests, including TT1, TT2, and TT3, have been successfully performed in the plant and assigned as standards commonly for licensing method qualifications for years. It is an essential requirement for licensing purposes to verify integral capabilities and accuracies of the codes and models of the INER/TPC method in simulating such pressurization transients. Specific Peach Bottom plant models, including both neutronics and thermal hydraulics, are developed using modeling approaches and experiences generally adopted in the INER/TPC method. Important model assumptions in RETRAN for the PBTT test simulations are described in this paper. Simulation calculations are performed with best-estimated initial and boundary conditions obtained from plant test measurements. The calculation results presented in this paper demonstrate that the INER/TPC method is capable of calculating accurately the core and system transient behaviors of the tests. Excellent agreement, both in trends and magnitudes between the RETRAN calculation results and the PBTT measurements, shows reliable qualifications of the codes/users/models involved in the method. The RETRAN calculated peak neutron fluxes of the PBTT

  14. Transient simulation of hydropower station with consideration of three-dimensional unsteady flow in turbine

    NASA Astrophysics Data System (ADS)

    Huang, W. D.; Fan, H. G.; Chen, N. X.

    2012-11-01

    To study the interaction between the transient flow in pipe and the unsteady turbulent flow in turbine, a coupled model of the transient flow in the pipe and three-dimensional unsteady flow in the turbine is developed based on the method of characteristics and the fluid governing equation in the accelerated rotational relative coordinate. The load-rejection process under the closing of guide vanes of the hydraulic power plant is simulated by the coupled method, the traditional transient simulation method and traditional three-dimensional unsteady flow calculation method respectively and the results are compared. The pressure, unit flux and rotation speed calculated by three methods show a similar change trend. However, because the elastic water hammer in the pipe and the pressure fluctuation in the turbine have been considered in the coupled method, the increase of pressure at spiral inlet is higher and the pressure fluctuation in turbine is stronger.

  15. Observation of transient electric fields in particle-in-cell simulation of capacitively coupled discharges

    SciTech Connect

    Sharma, S. Mishra, S. K.; Kaw, Predhiman K.

    2014-07-15

    The analytical prediction of the presence of transient electric field regions between the bulk plasma and sheath edge in radio frequency capacitively coupled plasma (RF-CCP) discharges has been reported by Kaganovich [Phys. Rev. Lett. 89, 265006 (2002)]. In this paper, we have used the semi-infinite particle-in-cell (PIC) simulation technique to verify the theoretical prediction for the existence of transient electric field in the linear regime; it is shown that the PIC simulation results are in good agreement with the results predicted by analytical model in this regime. It is also demonstrated that the linear theory overestimates the transient electric field as one moves from linear to weakly nonlinear regime. The effect of applied RF current density and electron temperature on evolution of transition field and phase mixing regime has been explored.

  16. Computer simulation of magnetization-controlled shunt reactors for calculating electromagnetic transients in power systems

    SciTech Connect

    Karpov, A. S.

    2013-01-15

    A computer procedure for simulating magnetization-controlled dc shunt reactors is described, which enables the electromagnetic transients in electric power systems to be calculated. It is shown that, by taking technically simple measures in the control system, one can obtain high-speed reactors sufficient for many purposes, and dispense with the use of high-power devices for compensating higher harmonic components.

  17. Numerical simulation of transient moisture transfer into an electronic enclosure

    NASA Astrophysics Data System (ADS)

    Nasirabadi, P. Shojaee; Jabbari, M.; Hattel, J. H.

    2016-06-01

    Electronic systems are sometimes exposed to harsh environmental conditions of temperature and humidity. Moisture transfer into electronic enclosures and condensation can cause several problems such as corrosion and alteration in thermal stresses. It is therefore essential to study the local climate inside the enclosures to be able to protect the electronic systems. In this work, moisture transfer into a typical electronic enclosure is numerically studied using CFD. In order to reduce the CPU-time and make a way for subsequent factorial design analysis, a simplifying modification is applied in which the real 3D geometry is approximated by a 2D axial symmetry one. The results for 2D and 3D models were compared in order to calibrate the 2D representation. Furthermore, simulation results were compared with experimental data and good agreement was found.

  18. Transient Simulation of Accumulating Particle Deposition in Pipe Flow

    NASA Astrophysics Data System (ADS)

    Hewett, James; Sellier, Mathieu

    2015-11-01

    Colloidal particles that deposit in pipe systems can lead to fouling which is an expensive problem in both the geothermal and oil & gas industries. We investigate the gradual accumulation of deposited colloids in pipe flow using numerical simulations. An Euler-Lagrangian approach is employed for modelling the fluid and particle phases. Particle transport to the pipe wall is modelled with Brownian motion and turbulent diffusion. A two-way coupling exists between the fouled material and the pipe flow; the local mass flux of depositing particles is affected by the surrounding fluid in the near-wall region. This coupling is modelled by changing the cells from fluid to solid as the deposited particles exceed each local cell volume. A similar method has been used to model fouling in engine exhaust systems (Paz et al., Heat Transfer Eng., 34(8-9):674-682, 2013). We compare our deposition velocities and deposition profiles with an experiment on silica scaling in turbulent pipe flow (Kokhanenko et al., 19th AFMC, 2014).

  19. Lunar Dust Chemical, Electrical, and Mechanical Reactivity: Simulation and Characterization

    NASA Technical Reports Server (NTRS)

    VanderWal, Randy L.

    2008-01-01

    Lunar dust is recognized to be a highly reactive material in its native state. Many, if not all Constellation systems will be affected by its adhesion, abrasion, and reactivity. A critical requirement to develop successful strategies for dealing with lunar dust and designing tolerant systems will be to produce similar material for ground-based testing.

  20. One- and two-dimensional STEALTH simulations of fuel-pin transient response. Final report. [BWR; PWR

    SciTech Connect

    Wahi, K.K.

    1980-08-01

    This report presents an assessment of the adaptability of EPRI's one- and two-dimensional STEALTH computer codes to perform transient fuel rod analysis. The ability of the STEALTH code to simulate transient mechanical or thermomechanical loss-of-coolant accident is described. Analytic models of one- and two-dimensional formulations and features included in the two-dimensional simulation are discussed.

  1. Mars atmospheric dynamics as simulated by the NASA AMES General Circulation Model. II - Transient baroclinic eddies

    NASA Astrophysics Data System (ADS)

    Barnes, J. R.; Pollack, J. B.; Haberle, R. M.; Leovy, C. B.; Zurek, R. W.; Lee, H.; Schaeffer, J.

    1993-02-01

    A large set of experiments performed with the NASA Ames Mars General Circulation Model is analyzed to determine the properties, structure, and dynamics of the simulated transient baroclinic eddies. There is strong transient baroclinic eddy activity in the extratropics of the Northern Hemisphere during the northern autumn, winter, and spring seasons. The eddy activity remains strong for very large dust loadings, though it shifts northward. The eastward propagating eddies are characterized by zonal wavenumbers of 1-4 and periods of about 2-10 days. The properties of the GCM baroclinic eddies in the northern extratropics are compared in detail with analogous properties inferred from Viking Lander meteorology observations.

  2. Numerical simulation of transient inviscid gas flows in a shock tube

    NASA Technical Reports Server (NTRS)

    Yang, J. Y.; Lombard, C. K.; Nagaraj, N.; Bershader, D.

    1985-01-01

    Time-dependent upwind high resolution schemes for solving the Euler equations were developed and applied to simulate 1-D and 2-D transient inviscid gas flows in a shock tube. Using obstacles of different geometries, a series of calculations were carried out to investigate the transient complex shock-wave diffraction phenomena. Shock-wave and objects interactions with shock Mach-number Ms ranging from 2 to 20 were considered. Comparison with analytical and available experimental results indicate good agreement. Display of detailed flow structures including multiple Mach shocks, slip surfaces, and vortex are also given.

  3. Response of standard and high-capacity HEPA filters to simulated tornado and explosive transients

    SciTech Connect

    Gregory, W.S.; Smith, P.R.

    1982-03-01

    An investigation was performed to determine the response of standard and high-capacity high-efficiency particulate air filters to simulated tornado and explosive transients. Most of the tests were directed toward evaluating the structural response of high-capacity filters to explosive transients. Selected tests were performed to evaluate the effects of particulate loading on filtration efficiencies. Also, several of the high-capacity filters were subjected to simulated toronado transients. The results indicate that the upper structural limits of high-capacity filters for explosive loading is 6.89-kPa (1-psi) peak pressure and 100-kPa-ms (14.51-psi-ms) impulse. These limits are below the approximately 13.78-kPa (2-psi) peak pressure loadings found for standard HEPA filters. Tests of high-capacity filters preloaded with aerosol indicated that the structural limits were further degraded by approximately 40%. The filtration efficiencies were degraded to approximately 70% when the filters were subjected to aerosol entrained within the shock pulse. The effect of simulated tornado transients on high-capacity filters resulted in an upper structural limit of 11.02 kPa (1.6 psi) for peak pressure.

  4. Comparison of the Accuracy and Speed of Transient Mobile A/C System Simulation Models: Preprint

    SciTech Connect

    Kiss, T.; Lustbader, J.

    2014-03-01

    The operation of air conditioning (A/C) systems is a significant contributor to the total amount of fuel used by light- and heavy-duty vehicles. Therefore, continued improvement of the efficiency of these mobile A/C systems is important. Numerical simulation has been used to reduce the system development time and to improve the electronic controls, but numerical models that include highly detailed physics run slower than desired for carrying out vehicle-focused drive cycle-based system optimization. Therefore, faster models are needed even if some accuracy is sacrificed. In this study, a validated model with highly detailed physics, the 'Fully-Detailed' model, and two models with different levels of simplification, the 'Quasi-Transient' and the 'Mapped- Component' models, are compared. The Quasi-Transient model applies some simplifications compared to the Fully-Detailed model to allow faster model execution speeds. The Mapped-Component model is similar to the Quasi-Transient model except instead of detailed flow and heat transfer calculations in the heat exchangers, it uses lookup tables created with the Quasi-Transient model. All three models are set up to represent the same physical A/C system and the same electronic controls. Speed and results of the three model versions are compared for steady state and transient operation. Steady state simulated data are also compared to measured data. The results show that the Quasi-Transient and Mapped-Component models ran much faster than the Fully-Detailed model, on the order of 10- and 100-fold, respectively. They also adequately approach the results of the Fully-Detailed model for steady-state operation, and for drive cycle-based efficiency predictions

  5. Simulation of solute transport in a mountain pool-and-riffle stream: a transient storage model.

    USGS Publications Warehouse

    Bencala, K.E.; Walters, R.A.

    1983-01-01

    A transient storage model, which couples dead zones with the one-dimensional convection-dispersion equation, simulates the general characteristics of the solute transport behavior and a set of simulation parameters were determined that yield an adequate fit to the data. However, considerable uncertainty remains in determining physically realistic values of these parameters. The values of the simulation parameters used are compared to values used by other authors for other streams. The comparison supports, at least qualitatively, the determined parameter values. -from Authors

  6. Transient simulation of global changes of the hydrological cycle during the last deglaciation (Invited)

    NASA Astrophysics Data System (ADS)

    He, F.; Shakun, J. D.; Clark, P. U.

    2013-12-01

    The future changes of the hydrological cycle caused by the anthropogenic carbon emission have great impact on regional water management, national food security and global health. The IPCC AR4 report concluded that it is very likely that the frequency of heavy rainfall will increase over most of the land area, while area affected by drought will likely increase as well. However, the level of the scientific understanding of the hydrological changes is hindered by the short instrumental records and the inherent delay of the response of climate system to greenhouse gas forcing. The last deglaciation witnessed the last natural global warming and represents the unique opportunity to overcome the above challenges when carbon dioxide concentrations rose from 185 ppm to 260 ppm over the approximately 10,000 years. Clark et al. [2012, PNAS] has compiled the changes of the global hydrological cycle during the last deglaciation with 39 high-resolution precipitation proxies over the land area. Here we compare the transient simulation of the last deglaciation in fully coupled Community Climate System Model version 3 (CCSM3) with the reconstructed hydrological changes to check whether the current climate models used to predict the future is capable of reproducing the evolution of global hydrological cycle in the past. Over Greenland, the transient simulation reproduces the abrupt increase of precipitation during the Bølling and the reduction of precipitation during the Younger Dryas (YD). The transient simulation also reproduces the global impacts of these abrupt climate events. In the Arabian Sea, the transient simulation produces the decrease of precipitation during the Oldest Dryas (OD) and YD, and the increase of precipitation during the Bølling. In South America, the transient simulation reproduces the meridional shifts of the ITCZ, with increase of precipitation over Brazil and Bolivia during the OD and YD and decrease of precipitation during the Bølling. The transient

  7. Low Dissipative High Order Numerical Simulations of Supersonic Reactive Flows

    NASA Technical Reports Server (NTRS)

    Sjoegreen, B.; Yee, H. C.; Mansour, Nagi (Technical Monitor)

    2001-01-01

    The objective of this paper is to evaluate the performance of a newly developed low dissipative sixth-order spatial and fourth-order temporal scheme for viscous reactive flows interacting with shock waves that contain fine scale flow structures. The accuracy and efficiency of the scheme, and to what degree the scheme can capture the correct physical wave speeds of stiff reactive flows will be included.

  8. Large Eddy Simulation of Transient Flow, Solidification, and Particle Transport Processes in Continuous-Casting Mold

    NASA Astrophysics Data System (ADS)

    Liu, Zhongqiu; Li, Linmin; Li, Baokuan; Jiang, Maofa

    2014-07-01

    The current study developed a coupled computational model to simulate the transient fluid flow, solidification, and particle transport processes in a slab continuous-casting mold. Transient flow of molten steel in the mold is calculated using the large eddy simulation. An enthalpy-porosity approach is used for the analysis of solidification processes. The transport of bubble and non-metallic inclusion inside the liquid pool is calculated using the Lagrangian approach based on the transient flow field. A criterion of particle entrapment in the solidified shell is developed using the user-defined functions of FLUENT software (ANSYS, Inc., Canonsburg, PA). The predicted results of this model are compared with the measurements of the ultrasonic testing of the rolled steel plates and the water model experiments. The transient asymmetrical flow pattern inside the liquid pool exhibits quite satisfactory agreement with the corresponding measurements. The predicted complex instantaneous velocity field is composed of various small recirculation zones and multiple vortices. The transport of particles inside the liquid pool and the entrapment of particles in the solidified shell are not symmetric. The Magnus force can reduce the entrapment ratio of particles in the solidified shell, especially for smaller particles, but the effect is not obvious. The Marangoni force can play an important role in controlling the motion of particles, which increases the entrapment ratio of particles in the solidified shell obviously.

  9. Fluid-solid coupled simulation of the ignition transient of solid rocket motor

    NASA Astrophysics Data System (ADS)

    Li, Qiang; Liu, Peijin; He, Guoqiang

    2015-05-01

    The first period of the solid rocket motor operation is the ignition transient, which involves complex processes and, according to chronological sequence, can be divided into several stages, namely, igniter jet injection, propellant heating and ignition, flame spreading, chamber pressurization and solid propellant deformation. The ignition transient should be comprehensively analyzed because it significantly influences the overall performance of the solid rocket motor. A numerical approach is presented in this paper for simulating the fluid-solid interaction problems in the ignition transient of the solid rocket motor. In the proposed procedure, the time-dependent numerical solutions of the governing equations of internal compressible fluid flow are loosely coupled with those of the geometrical nonlinearity problems to determine the propellant mechanical response and deformation. The well-known Zeldovich-Novozhilov model was employed to model propellant ignition and combustion. The fluid-solid coupling interface data interpolation scheme and coupling instance for different computational agents were also reported. Finally, numerical validation was performed, and the proposed approach was applied to the ignition transient of one laboratory-scale solid rocket motor. For the application, the internal ballistics were obtained from the ground hot firing test, and comparisons were made. Results show that the integrated framework allows us to perform coupled simulations of the propellant ignition, strong unsteady internal fluid flow, and propellant mechanical response in SRMs with satisfactory stability and efficiency and presents a reliable and accurate solution to complex multi-physics problems.

  10. Transient aerodynamic forces on a fighter model during simulated approach and landing with thrust reversers

    NASA Technical Reports Server (NTRS)

    Humphreys, A. P.; Paulson, J. W., Jr.; Kemmerly, G. T.

    1988-01-01

    Previous wind tunnel tests of fighter configurations have shown that thrust reverser jets can induce large, unsteady aerodynamic forces and moments during operation in ground proximity. This is a concern for STOL configurations using partial reversing to spoil the thrust while keeping the engine output near military (MIL) power during landing approach. A novel test technique to simulate approach and landing was developed under a cooperative Northrop/NASA/USAF program. The NASA LaRC Vortex Research Facility was used for the experiments in which a 7-percent F-18 model was moved horizontally at speeds of up to 100 feet per second over a ramp simulating an aircraft to ground rate of closure similar to a no-flare STOL approach and landing. This paper presents an analysis of data showing the effect of reverser jet orientation and jet dynamic pressure ratio on the transient forces for different angles of attack, and flap and horizontal tail deflection. It was found, for reverser jets acting parallel to the plane of symmetry, that the jets interacted strongly with the ground, starting approximately half a span above the ground board. Unsteady rolling moment transients, large enough to cause the probable upset of an aircraft, and strong normal force and pitching moment transients were measured. For jets directed 40 degrees outboard, the transients were similar to the jet-off case, implying only minor interaction.

  11. Transient Influx of nickel in root mitochondria modulates organic acid and reactive oxygen species production in nickel hyperaccumulator Alyssum murale.

    PubMed

    Agrawal, Bhavana; Czymmek, Kirk J; Sparks, Donald L; Bais, Harsh P

    2013-03-01

    Mitochondria are important targets of metal toxicity and are also vital for maintaining metal homeostasis. Here, we examined the potential role of mitochondria in homeostasis of nickel in the roots of nickel hyperaccumulator plant Alyssum murale. We evaluated the biochemical basis of nickel tolerance by comparing the role of mitochondria in closely related nickel hyperaccumulator A. murale and non-accumulator Alyssum montanum. Evidence is presented for the rapid and transient influx of nickel in root mitochondria of nickel hyperaccumulator A. murale. In an early response to nickel treatment, substantial nickel influx was observed in mitochondria prior to sequestration in vacuoles in the roots of hyperaccumulator A. murale compared with non-accumulator A. montanum. In addition, the mitochondrial Krebs cycle was modulated to increase synthesis of malic acid and citric acid involvement in nickel hyperaccumulation. Furthermore, malic acid, which is reported to form a complex with nickel in hyperaccumulators, was also found to reduce the reactive oxygen species generation induced by nickel. We propose that the interaction of nickel with mitochondria is imperative in the early steps of nickel uptake in nickel hyperaccumulator plants. Initial uptake of nickel in roots results in biochemical responses in the root mitochondria indicating its vital role in homeostasis of nickel ions in hyperaccumulation.

  12. Transient Influx of Nickel in Root Mitochondria Modulates Organic Acid and Reactive Oxygen Species Production in Nickel Hyperaccumulator Alyssum murale*

    PubMed Central

    Agrawal, Bhavana; Czymmek, Kirk J.; Sparks, Donald L.; Bais, Harsh P.

    2013-01-01

    Mitochondria are important targets of metal toxicity and are also vital for maintaining metal homeostasis. Here, we examined the potential role of mitochondria in homeostasis of nickel in the roots of nickel hyperaccumulator plant Alyssum murale. We evaluated the biochemical basis of nickel tolerance by comparing the role of mitochondria in closely related nickel hyperaccumulator A. murale and non-accumulator Alyssum montanum. Evidence is presented for the rapid and transient influx of nickel in root mitochondria of nickel hyperaccumulator A. murale. In an early response to nickel treatment, substantial nickel influx was observed in mitochondria prior to sequestration in vacuoles in the roots of hyperaccumulator A. murale compared with non-accumulator A. montanum. In addition, the mitochondrial Krebs cycle was modulated to increase synthesis of malic acid and citric acid involvement in nickel hyperaccumulation. Furthermore, malic acid, which is reported to form a complex with nickel in hyperaccumulators, was also found to reduce the reactive oxygen species generation induced by nickel. We propose that the interaction of nickel with mitochondria is imperative in the early steps of nickel uptake in nickel hyperaccumulator plants. Initial uptake of nickel in roots results in biochemical responses in the root mitochondria indicating its vital role in homeostasis of nickel ions in hyperaccumulation. PMID:23322782

  13. Transient Simulation of Last Deglaciation with a New Mechanism for B lling-Aller d Warming

    SciTech Connect

    Erickson, David J

    2009-01-01

    We conducted the first synchronously coupled atmosphere-ocean general circulation model simulation from the Last Glacial Maximum to the Boelling-Alleroed (BA) warming. Our model reproduces several major features of the deglacial climate evolution, suggesting a good agreement in climate sensitivity between the model and observations. In particular, our model simulates the abrupt BA warming as a transient response of the Atlantic meridional overturning circulation (AMOC) to a sudden termination of freshwater discharge to the North Atlantic before the BA. In contrast to previous mechanisms that invoke AMOC multiple equilibrium and Southern Hemisphere climate forcing, we propose that the BA transition is caused by the superposition of climatic responses to the transient CO{sub 2} forcing, the AMOC recovery from Heinrich Event 1, and an AMOC overshoot.

  14. Transient simulation of last deglaciation with a new mechanism for Bolling-Allerod warming.

    PubMed

    Liu, Z; Otto-Bliesner, B L; He, F; Brady, E C; Tomas, R; Clark, P U; Carlson, A E; Lynch-Stieglitz, J; Curry, W; Brook, E; Erickson, D; Jacob, R; Kutzbach, J; Cheng, J

    2009-07-17

    We conducted the first synchronously coupled atmosphere-ocean general circulation model simulation from the Last Glacial Maximum to the Bølling-Allerød (BA) warming. Our model reproduces several major features of the deglacial climate evolution, suggesting a good agreement in climate sensitivity between the model and observations. In particular, our model simulates the abrupt BA warming as a transient response of the Atlantic meridional overturning circulation (AMOC) to a sudden termination of freshwater discharge to the North Atlantic before the BA. In contrast to previous mechanisms that invoke AMOC multiple equilibrium and Southern Hemisphere climate forcing, we propose that the BA transition is caused by the superposition of climatic responses to the transient CO(2) forcing, the AMOC recovery from Heinrich Event 1, and an AMOC overshoot. PMID:19608916

  15. Numerical simulation of transient emission from deep level traps in polysilicon thin film transistors

    NASA Astrophysics Data System (ADS)

    Armstrong, G. A.; Ayres, J. R.; Brotherton, S. D.

    1997-06-01

    Numerical simulation was used to model transient carrier emission from deep level traps in polycrystalline silicon (poly-Si) thin film transistors and to validate the analytical approximations used to interpret DLTS measurements. Transient emission from a single trap was compared with that from a continuous density of states. Numerical simulation was used to quantify the degree of error in the analytical analysis and show that it yields substantially correct values for a typical double exponential poly-Si trap state density as a function of energy, to within ± 10%. The major source of discrepancy was associated with the omission of the effects of displacement current from the analytical analysis. The DLTS spectra associated with a constant density of states was shown to give a decreasing signal with decreasing temperature, while that of an exponential density of states was found to be essentially flat.

  16. Waterhammer Transient Simulation and Model Anchoring for the Robotic Lunar Lander Propulsion System

    NASA Technical Reports Server (NTRS)

    Stein, William B.; Trinh, Huu P.; Reynolds, Michael E.; Sharp, David J.

    2011-01-01

    Waterhammer transients have the potential to adversely impact propulsion system design if not properly addressed. Waterhammer can potentially lead to system plumbing, and component damage. Multi-thruster propulsion systems also develop constructive/destructive wave interference which becomes difficult to predict without detailed models. Therefore, it is important to sufficiently characterize propulsion system waterhammer in order to develop a robust design with minimal impact to other systems. A risk reduction activity was performed at Marshall Space Flight Center to develop a tool for estimating waterhammer through the use of anchored simulation for the Robotic Lunar Lander (RLL) propulsion system design. Testing was performed to simulate waterhammer surges due to rapid valve closure and consisted of twenty-two series of waterhammer tests, resulting in more than 300 valve actuations. These tests were performed using different valve actuation schemes and three system pressures. Data from the valve characterization tests were used to anchor the models that employed MSCSoftware.EASY5 v.2010 to model transient fluid phenomena by using transient forms of mass and energy conservation. The anchoring process was performed by comparing initial model results to experimental data and then iterating the model input to match the simulation results with the experimental data. The models provide good correlation with experimental results, supporting the use of EASY5 as a tool to model fluid transients and provide a baseline for future RLL system modeling. This paper addresses tasks performed during the waterhammer risk reduction activity for the RLL propulsion system. The problem of waterhammer simulation anchoring as applied to the RLL system is discussed with results from the corresponding experimental valve tests. Important factors for waterhammer mitigation are discussed along with potential design impacts to the RLL propulsion system.

  17. An Introduction to Transient Engine Applications Using the Numerical Propulsion System Simulation (NPSS) and MATLAB

    NASA Technical Reports Server (NTRS)

    Chin, Jeffrey C.; Csank, Jeffrey T.; Haller, William J.; Seidel, Jonathan A.

    2016-01-01

    This document outlines methodologies designed to improve the interface between the Numerical Propulsion System Simulation framework and various control and dynamic analyses developed in the Matlab and Simulink environment. Although NPSS is most commonly used for steady-state modeling, this paper is intended to supplement the relatively sparse documentation on it's transient analysis functionality. Matlab has become an extremely popular engineering environment, and better methodologies are necessary to develop tools that leverage the benefits of these disparate frameworks. Transient analysis is not a new feature of the Numerical Propulsion System Simulation (NPSS), but transient considerations are becoming more pertinent as multidisciplinary trade-offs begin to play a larger role in advanced engine designs. This paper serves to supplement the relatively sparse documentation on transient modeling and cover the budding convergence between NPSS and Matlab based modeling toolsets. The following sections explore various design patterns to rapidly develop transient models. Each approach starts with a base model built with NPSS, and assumes the reader already has a basic understanding of how to construct a steady-state model. The second half of the paper focuses on further enhancements required to subsequently interface NPSS with Matlab codes. The first method being the simplest and most straightforward but performance constrained, and the last being the most abstract. These methods aren't mutually exclusive and the specific implementation details could vary greatly based on the designer's discretion. Basic recommendations are provided to organize model logic in a format most easily amenable to integration with existing Matlab control toolsets.

  18. Analog-digital simulation of transient-induced logic errors and upset susceptibility of an advanced control system

    NASA Technical Reports Server (NTRS)

    Carreno, Victor A.; Choi, G.; Iyer, R. K.

    1990-01-01

    A simulation study is described which predicts the susceptibility of an advanced control system to electrical transients resulting in logic errors, latched errors, error propagation, and digital upset. The system is based on a custom-designed microprocessor and it incorporates fault-tolerant techniques. The system under test and the method to perform the transient injection experiment are described. Results for 2100 transient injections are analyzed and classified according to charge level, type of error, and location of injection.

  19. Simulation of transient behavior in a pulse-line-driven gyrotron oscillator

    NASA Astrophysics Data System (ADS)

    Lin, A. T.; Lin, Chih-Chien; Yang, Z. H.; Chu, K. R.; Fliflet, A. W.

    1988-04-01

    Results are reported for a set of slow-time-scale single-mode and fast-time-scale single-mode and multimode simulations of the transient-mode excitation phenomena in a short-pulse high-peak-power Ka-band gyrotron oscillator experiment. Both the slow- and fast-time-scale single-mode simulations are generally in good agreement with each other and, within experimental uncertainties, with the experimental observations of the time dependence and magnetic-field dependence of 35-GHz emission in the TE62 mode. However, the multimode simulations suggest the presence of mode suppression, mode beating, and other nonlinear multimode phenomena that could not easily be observed in the experiment, and generally agree less well with the experimental measurements than the single-mode simulations. The multimode simulations also suggest that steady-state behavior may not be obtainable with the highly time-dependent voltage waveform employed in the experiment, and indicate the importance of carrying out future high-voltage gyrotron experiments with less highly transient voltage waveforms.

  20. A parallel algorithm for transient solid dynamics simulations with contact detection

    SciTech Connect

    Attaway, S.; Hendrickson, B.; Plimpton, S.; Gardner, D.; Vaughan, C.; Heinstein, M.; Peery, J.

    1996-06-01

    Solid dynamics simulations with Lagrangian finite elements are used to model a wide variety of problems, such as the calculation of impact damage to shipping containers for nuclear waste and the analysis of vehicular crashes. Using parallel computers for these simulations has been hindered by the difficulty of searching efficiently for material surface contacts in parallel. A new parallel algorithm for calculation of arbitrary material contacts in finite element simulations has been developed and implemented in the PRONTO3D transient solid dynamics code. This paper will explore some of the issues involved in developing efficient, portable, parallel finite element models for nonlinear transient solid dynamics simulations. The contact-detection problem poses interesting challenges for efficient implementation of a solid dynamics simulation on a parallel computer. The finite element mesh is typically partitioned so that each processor owns a localized region of the finite element mesh. This mesh partitioning is optimal for the finite element portion of the calculation since each processor must communicate only with the few connected neighboring processors that share boundaries with the decomposed mesh. However, contacts can occur between surfaces that may be owned by any two arbitrary processors. Hence, a global search across all processors is required at every time step to search for these contacts. Load-imbalance can become a problem since the finite element decomposition divides the volumetric mesh evenly across processors but typically leaves the surface elements unevenly distributed. In practice, these complications have been limiting factors in the performance and scalability of transient solid dynamics on massively parallel computers. In this paper the authors present a new parallel algorithm for contact detection that overcomes many of these limitations.

  1. Transient dynamics simulations: Parallel algorithms for contact detection and smoothed particle hydrodynamics

    SciTech Connect

    Hendrickson, B.; Plimpton, S.; Attaway, S.; Swegle, J.

    1996-09-01

    Transient dynamics simulations are commonly used to model phenomena such as car crashes, underwater explosions, and the response of shipping containers to high-speed impacts. Physical objects in such a simulation are typically represented by Lagrangian meshes because the meshes can move and deform with the objects as they undergo stress. Fluids (gasoline, water) or fluid-like materials (earth) in the simulation can be modeled using the techniques of smoothed particle hydrodynamics. Implementing a hybrid mesh/particle model on a massively parallel computer poses several difficult challenges. One challenge is to simultaneously parallelize and load-balance both the mesh and particle portions of the computation. A second challenge is to efficiently detect the contacts that occur within the deforming mesh and between mesh elements and particles as the simulation proceeds. These contacts impart forces to the mesh elements and particles which must be computed at each timestep to accurately capture the physics of interest. In this paper we describe new parallel algorithms for smoothed particle hydrodynamics and contact detection which turn out to have several key features in common. Additionally, we describe how to join the new algorithms with traditional parallel finite element techniques to create an integrated particle/mesh transient dynamics simulation. Our approach to this problem differs from previous work in that we use three different parallel decompositions, a static one for the finite element analysis and dynamic ones for particles and for contact detection. We have implemented our ideas in a parallel version of the transient dynamics code PRONTO-3D and present results for the code running on a large Intel Paragon.

  2. Heterogeneous reactive transport under unsaturated transient conditions characterized by 3D electrical resistivity tomography and advanced lysimeter methods

    NASA Astrophysics Data System (ADS)

    Wehrer, Markus; Slater, Lee

    2015-04-01

    Our ability to predict flow and transport processes in the unsaturated critical zone is considerably limited by two characteristics: heterogeneity of flow and transience of boundary conditions. The causes of heterogeneous flow and transport are fairly well understood, yet the characterization and quantification of such processes in natural profiles remains challenging. This is due to current methods of observation, such as staining and isotope tracers, being unable to observe multiple events on the same profile and offering limited spatial information. In our study we demonstrate an approach to characterize preferential flow and transport processes applying a combination of geoelectrical methods and advanced lysimeter techniques. On an agricultural soil profile, which was transferred undisturbed into a lysimeter container, we systematically applied a variety of input flow boundary conditions, resembling natural precipitation events. We measured breakthroughs of a conservative tracer and of nitrate, originating from the application of a slow release fertilizer and serving as a reactive tracer. Flow and transport in the soil column were observed using electrical resistivity tomography (ERT), tensiometers, water content probes and a multicompartment suction plate (MSP). These techniques allowed a direct validation of water content dynamics and tracer breakthrough under transient boundary conditions characterized noninvasively by ERT. We were able to image the advancing infiltration front and the advancing front of tracer and nitrate using time lapse ERT. Water content changes associated with the advancing infiltration front dominated over pore fluid conductivity changes during short term precipitation events. Conversely, long-term displacement of the solute fronts was monitored during periods of constant water content in between infiltration events. We observed preferential flow phenomena through ERT and through the MSP, which agreed in general terms. The preferential

  3. Reactive Oxygen Species Generation by Lunar Simulants in Simulated Lung Fluid

    NASA Astrophysics Data System (ADS)

    Schoonen, M. A.; Kaur, J.; Rickman, D.

    2015-12-01

    The current interest in human exploration of the Moon and other airless planetary bodies has rekindled research into the harmful effects of Lunar dust on human health. Our team has evaluated the spontaneous formation of Reactive Oxygen Species (ROS; hydroxyl radicals, superoxide, and hydrogen peroxide) of a suite of lunar simulants when dispersed in deionized water. Of these species, hydroxyl radical reacts almost immediately with any biomolecule leading to oxidative damage. Sustained production of OH radical as a result of mineral exposure can initiate or enhance disease. The results in deionized water indicate that mechanical stress and the absence of molecular oxygen and water, important environmental characteristics of the lunar environment, can lead to enhanced production of ROS in general. On the basis of the results with deionized water, a few of the simulants were selected for additional studies to evaluate the formation of hydrogen peroxide, a precursor of hydroxyl radical in Simulated Lung Fluid. These simulants dispersed in deionized water typically produce a maximum in H2O2 within 10 to 40 minutes. However, experiments in SLF show a slow steady increase in H2O2 concentration that has been documented to continue for as long as 7 hours. Control experiments with one simulant demonstrate that the rise in H2O2 depends on the availability of dissolved O2. We speculate that this continuous rise in oxygenated SLF might be a result of metal ion-mediated oxidation of organic components, such as glycine in SLF. Ion-mediated oxidation essentially allows dissolved molecular oxygen to react with dissolved organic compounds by forming a metal-organic complex. Results of separate experiments with dissolved Fe, Ni, and Cu and speciation calculations support this notion.

  4. Apoplastic reactive oxygen species transiently decrease auxin signaling and cause stress-induced morphogenic response in Arabidopsis.

    PubMed

    Blomster, Tiina; Salojärvi, Jarkko; Sipari, Nina; Brosché, Mikael; Ahlfors, Reetta; Keinänen, Markku; Overmyer, Kirk; Kangasjärvi, Jaakko

    2011-12-01

    Reactive oxygen species (ROS) are ubiquitous signaling molecules in plant stress and development. To gain further insight into the plant transcriptional response to apoplastic ROS, the phytotoxic atmospheric pollutant ozone was used as a model ROS inducer in Arabidopsis (Arabidopsis thaliana) and gene expression was analyzed with microarrays. In contrast to the increase in signaling via the stress hormones salicylic acid, abscisic acid, jasmonic acid (JA), and ethylene, ROS treatment caused auxin signaling to be transiently suppressed, which was confirmed with a DR5-uidA auxin reporter construct. Transcriptomic data revealed that various aspects of auxin homeostasis and signaling were modified by apoplastic ROS. Furthermore, a detailed analysis of auxin signaling showed that transcripts of several auxin receptors and Auxin/Indole-3-Acetic Acid (Aux/IAA) transcriptional repressors were reduced in response to apoplastic ROS. The ROS-derived changes in the expression of auxin signaling genes partially overlapped with abiotic stress, pathogen responses, and salicylic acid signaling. Several mechanisms known to suppress auxin signaling during biotic stress were excluded, indicating that ROS regulated auxin responses via a novel mechanism. Using mutants defective in various auxin (axr1, nit1, aux1, tir1 afb2, iaa28-1, iaa28-2) and JA (axr1, coi1-16) responses, ROS-induced cell death was found to be regulated by JA but not by auxin. Chronic ROS treatment resulted in altered leaf morphology, a stress response known as "stress-induced morphogenic response." Altered leaf shape of tir1 afb2 suggests that auxin was a negative regulator of stress-induced morphogenic response in the rosette.

  5. Simulation of ITER ELM transient heat events on tungsten grades using long pulse laser beams

    NASA Astrophysics Data System (ADS)

    Suslova, Anastassiya

    Tungsten has been chosen as the main candidate for plasma facing components (PFCs) in the magnetic confinement nuclear fusion reactors such as International Thermonuclear Experimental Reactor (ITER) and beyond due to its superior properties under extreme operating conditions expected in fusion rectors. One of the serious issues for the plasma facing components is the heat load during transient events such as edge localized modes (ELMs) and disruption in the reactor. High temperature gradient and high thermal stresses developed during transients could lead to material recrystallization and grain growth, formation of a melt layer, material erosion, and crack formation, which can limit the power handling capacity of PFCs, decrease lifetime, and contribute to plasma contamination that affect subsequent operations. Mechanical and surface properties of different tungsten grades and their behavior under ITER-like conditions are the main focus of current research efforts in the fusion research community. The current work was focused primarily on detailed investigation of the effect of ELM-like transient heat events on pristine samples of two different grades of deformed tungsten with ultrafine and nanocrystlline grains. Significant efforts were made to understand the mechanisms behind recrystallization, grain growth, crack formation, surface nano-structuring, melting, and other phenomena observed under repeated transient heat loads, simulated by the use of long pulse laser beams. It was observed that cold rolled tungsten overall demonstrated better power handling capabilities and higher thermal stress fatigue resistance. It had higher recrystallization and melting threshold parameters, slower grain growth at similar irradiation conditions, lower degree of surface roughening, and less material losses. The difference in behavior of the two grades of tungsten under similar heat load conditions was attributed to the initial tensile properties of the samples, initial impurities

  6. Response of centrifugal blowers to simulated tornado transients, July-September 1981

    SciTech Connect

    Idar, E S; Gregory, W S; Martin, R A; Littleton, P E

    1982-03-01

    During this quarter, quasi-steady and dynamic testing of the 24-in. centrifugal blower was completed using the blowdown facility located at New Mexico State University. The data were obtained using a new digital data-acquisition system. Software was developed at the Los Alamos National Laboratory to reduce the dynamic test data and create computer-generated movies showing the dynamic performance of the blower under simulated tornado transient pressure conditions relative to its quasi-steady-state performance. Currently, quadrant-four (outrunning flow) data have been reduced for the most severe and a less severe tornado pressure transient. The results indicate that both the quasi-steady and dynamic blower performance are very similar. Some hysteresis in the dynamic performance occurs because of rotational inertia effects in the blower rotor and drive system. Currently quadrant-two (backflow) data are being transferred to the LTSS computer system at Los Alamos and will be reduced shortly.

  7. Computer simulation and experimental study of transient processes in a single-phase voltage transformer

    NASA Astrophysics Data System (ADS)

    Kruzhaev, A. V.; Elagin, I. A.; Pavleino, M. A.; Dmitriev, V. A.; Chaly, A. M.

    2015-02-01

    We perform simulation and experimental investigation of transient processes emerging in a single-phase transformer when it is connected to the network. The transformer model constructed taking into account the saturation of the steel of the core differs from standard models in detailed accounting for the magnetic flux leakage, which is required, for example, for a correct description of inrush current. Universality of the model for the type of transformers under study is ensured by the allowance for eddy current losses and calculation of the magnetic hysteresis in the steel core. The latter makes it possible to estimate the effect of residual magnetization of the core on the form of a transient process, which is studied in detail. The methods for computing model parameters are described and its experimental verification is carried out.

  8. Transient earth system model simulations as age-scale generators for paleo proxy data?

    NASA Astrophysics Data System (ADS)

    Timmermann, A.; Stockhecke, M.; Friedrich, T.; Menviel, L.

    2015-12-01

    Generating age models for paleo proxy data can be extremely difficult. Oftentimes assumptions are made which are based on hypothetical relationships between climate and orbital forcings. Whether these relationships (expressed in terms of correlation models) are physically justified and whether they are stationary is testable using transient climate model simulations. Several standard methods to generate age models for paleo-proxy data are scrutinized here, such as orbital tuning and synchronization to benthic stacks. To overcome some of the fundamental weaknesses of these methods we propose to use transient paleo climate model simulations to derive dynamically and physically consistent age models for paleo-proxy data. We illustrate this suggestion using 1) millennial-scale climate variations during MIS 2) orbital-scale climate variability during the past ~800 ka Ad 1) A physically forced MIS3 global hindcast model simulation with an earth system model, designed to match the reconstructed North Atlantic SST variability, can be used to determine the relative timing of different climate and biogeochemical variables at various locations with respect to an initial absolute reference timescale (GICC05 in our case). Corresponding leads and lags are a result of the physical equations of the climate system - not of oversimplisitic statistical assumptions (such as wiggle matching). The key assumption for this approach is that global patterns of Dansgaard-Oeschger variability are caused by centennial to millennial-scale AMOC variability. Ad 2) A transient earth system model simulation of the past ~800 ka is forced with observed greenhouse gas variations (on EDC3), orbital and estimated ice-sheet forcing. Simulated rainfall variations over the Eastern Mediterranean are compared with hydroclimate reconstructions from Lake Van. The simulated rainfall agrees well with the hydroclimate reconstruction (on the MoSto27 timescale) for the first 200 ka. Following this we demonstrate

  9. Reactivity-controlled compression ignition drive cycle emissions and fuel economy estimations using vehicle system simulations

    DOE PAGES

    Curran, Scott J.; Gao, Zhiming; Wagner, Robert M.

    2014-12-22

    In-cylinder blending of gasoline and diesel to achieve reactivity-controlled compression ignition has been shown to reduce NOX and soot emissions while maintaining or improving brake thermal efficiency as compared with conventional diesel combustion. The reactivity-controlled compression ignition concept has an advantage over many advanced combustion strategies in that the fuel reactivity can be tailored to the engine speed and load, allowing stable low-temperature combustion to be extended over more of the light-duty drive cycle load range. In this paper, a multi-mode reactivity-controlled compression ignition strategy is employed where the engine switches from reactivity-controlled compression ignition to conventional diesel combustion whenmore » speed and load demand are outside of the experimentally determined reactivity-controlled compression ignition range. The potential for reactivity-controlled compression ignition to reduce drive cycle fuel economy and emissions is not clearly understood and is explored here by simulating the fuel economy and emissions for a multi-mode reactivity-controlled compression ignition–enabled vehicle operating over a variety of US drive cycles using experimental engine maps for multi-mode reactivity-controlled compression ignition, conventional diesel combustion, and a 2009 port-fuel injected gasoline engine. Drive cycle simulations are completed assuming a conventional mid-size passenger vehicle with an automatic transmission. Multi-mode reactivity-controlled compression ignition fuel economy simulation results are compared with the same vehicle powered by a representative 2009 port-fuel injected gasoline engine over multiple drive cycles. Finally, engine-out drive cycle emissions are compared with conventional diesel combustion, and observations regarding relative gasoline and diesel tank sizes needed for the various drive cycles are also summarized.« less

  10. Reactivity-controlled compression ignition drive cycle emissions and fuel economy estimations using vehicle system simulations

    SciTech Connect

    Curran, Scott J.; Gao, Zhiming; Wagner, Robert M.

    2014-12-22

    In-cylinder blending of gasoline and diesel to achieve reactivity-controlled compression ignition has been shown to reduce NOX and soot emissions while maintaining or improving brake thermal efficiency as compared with conventional diesel combustion. The reactivity-controlled compression ignition concept has an advantage over many advanced combustion strategies in that the fuel reactivity can be tailored to the engine speed and load, allowing stable low-temperature combustion to be extended over more of the light-duty drive cycle load range. In this paper, a multi-mode reactivity-controlled compression ignition strategy is employed where the engine switches from reactivity-controlled compression ignition to conventional diesel combustion when speed and load demand are outside of the experimentally determined reactivity-controlled compression ignition range. The potential for reactivity-controlled compression ignition to reduce drive cycle fuel economy and emissions is not clearly understood and is explored here by simulating the fuel economy and emissions for a multi-mode reactivity-controlled compression ignition–enabled vehicle operating over a variety of US drive cycles using experimental engine maps for multi-mode reactivity-controlled compression ignition, conventional diesel combustion, and a 2009 port-fuel injected gasoline engine. Drive cycle simulations are completed assuming a conventional mid-size passenger vehicle with an automatic transmission. Multi-mode reactivity-controlled compression ignition fuel economy simulation results are compared with the same vehicle powered by a representative 2009 port-fuel injected gasoline engine over multiple drive cycles. Finally, engine-out drive cycle emissions are compared with conventional diesel combustion, and observations regarding relative gasoline and diesel tank sizes needed for the various drive cycles are also summarized.

  11. Reactively and Anticipatory Behaving Agents for Artificial Life Simulations

    NASA Astrophysics Data System (ADS)

    Kohout, Karel; Nahodil, Pavel

    2010-11-01

    Reactive behavior is still considered and the exact opposite for the anticipatory one. Despite the advances on the field of anticipation there are little thoughts on relation with the reactive behavior, the similarities and where the boundary is. In this article we will present our viewpoint and we will try to show that reactive and anticipatory behavior can be combined. This is the basic ground of our unified theory for anticipatory behavior architecture. We still miss such compact theory, which would integrate multiple aspects of anticipation. My multi-level anticipatory behavior approach is based on the current understanding of anticipation from both the artificial intelligence and biology point of view. As part of the explanation we will also elaborate on the topic of weak and strong artificial life. Anticipation is not matter of a single mechanism in a living organism. It was noted already that it happens on many different levels even in the very simple creatures. What we consider to be important for our work and what is our original though is that it happens even without voluntary control. We believe that this is novelty though for the anticipation theory. Naturally research of anticipation was in the beginning of this decade focused on the anticipatory principles bringing advances on the field itself. This allowed us to build on those, look at them from higher perspective, and use not one but multiple levels of anticipation in a creature design. This presents second original though and that is composition of the agent architecture that has anticipation built in almost every function. In this article we will focus only on first two levels within the 8-factor anticipation framework. We will introduce them as defined categories of anticipation and describe them from theory and implementation algorithm point of view. We will also present an experiment conducted, however this experiment serves more as explanatory example. These first two levels may seem trivial

  12. Polyethylene glygol conjugated superoxide dismutase (PEG-SOD) improves recovery of hypercapnia cerebral blood flow (CBF) reactivity following transient global ischemia in piglets

    SciTech Connect

    Traystman, R.J.; Kirsch, J.R.; Helfaer, M.A.; Haun, S.E. )

    1991-03-15

    This study tested the hypothesis that alteration in hypercapnic cerebral blood flow (CBF) reactivity is due to oxygen-derived free radical mediated vascular damage and therefore could be inhibited by treatment with PEG-SOD. Pentobarbital anesthetized piglets were mechanically ventilated and hemodynamically monitored. CBF was measured at PaCO{sub 2} of approximately 25, 40 and 55 mmHg. Reactivity was tested in all piglets prior to and 2 hours following reperfusion from global ischemia. Control piglets received PEG prior to ischemia and at reperfusion. Experimental piglets received either PEG-SOD prior to ischemia and PEG at reperfusion or PEG prior to ischemia and PEG-SOD at reperfusion. During reperfusion cerebral perfusion pressure was maintained constant between groups by intravenous infusion of epinephrine. Pre-ischemic hypercapnic reactivity was not different between groups. At 2 hr reperfusion hypercapnic CBF reactivity in control piglets was diminished to forebrain and brainstem but hypercapnic reactivity was not different than preischemic values in either group receiving PEG-SOD. The authors conclude that administration of PEG-SOD, either prior to or following transient global ischemia, improves recovery of post-ischemic hypercapnic reactivity in piglets. This implicates oxygen-derived free radicals as important mediators of reperfusion injury in brain.

  13. A Dynamic Transient Model to Simulate the Time Dependent Pultrusion Process of Glass/Polyester Composites

    NASA Astrophysics Data System (ADS)

    Shokrieh, Mahmood M.; Mahmoud Aghdami, Ashkan

    2011-12-01

    The objective of this paper is to introduce a novel dynamic transient model to simulate the time dependent pultrusion process of glass/polyester composites. The model is able to simulate the resin curing process systematically. The resin curing process is divided in two liquid and gel-solid phases. Physical properties of the resin including resin specific heat, viscosity and thermal conductivity change by altering the resin temperature and the degree of cure. It is shown that in liquid and gel-solid phases, some of the resin physical properties have significant role in heat transfer phenomenon and affect simulation results. The physical and mechanical properties of fibers do not change during the curing process of composites; therefore, an equivalent material is introduced instead of the resin-fiber compound. The model simulates the heat generation during the resin curing process. The degree of cure of the resin, used for the resin viscosity calculation, is an important parameter indicating the final stage of simulation of resin curing process. The components of the model are integrated in a finite element method. As case studies, the process of pultrusion of circular, rectangular and I cross-sections are simulated by the model. The results show that the model is able to simulate the pultrusion process very well.

  14. Surrogate model approach for improving the performance of reactive transport simulations

    NASA Astrophysics Data System (ADS)

    Jatnieks, Janis; De Lucia, Marco; Sips, Mike; Dransch, Doris

    2016-04-01

    Reactive transport models can serve a large number of important geoscientific applications involving underground resources in industry and scientific research. It is common for simulation of reactive transport to consist of at least two coupled simulation models. First is a hydrodynamics simulator that is responsible for simulating the flow of groundwaters and transport of solutes. Hydrodynamics simulators are well established technology and can be very efficient. When hydrodynamics simulations are performed without coupled geochemistry, their spatial geometries can span millions of elements even when running on desktop workstations. Second is a geochemical simulation model that is coupled to the hydrodynamics simulator. Geochemical simulation models are much more computationally costly. This is a problem that makes reactive transport simulations spanning millions of spatial elements very difficult to achieve. To address this problem we propose to replace the coupled geochemical simulation model with a surrogate model. A surrogate is a statistical model created to include only the necessary subset of simulator complexity for a particular scenario. To demonstrate the viability of such an approach we tested it on a popular reactive transport benchmark problem that involves 1D Calcite transport. This is a published benchmark problem (Kolditz, 2012) for simulation models and for this reason we use it to test the surrogate model approach. To do this we tried a number of statistical models available through the caret and DiceEval packages for R, to be used as surrogate models. These were trained on randomly sampled subset of the input-output data from the geochemical simulation model used in the original reactive transport simulation. For validation we use the surrogate model to predict the simulator output using the part of sampled input data that was not used for training the statistical model. For this scenario we find that the multivariate adaptive regression splines

  15. Calendar effect on phase study in paleoclimate transient simulation with orbital forcing

    NASA Astrophysics Data System (ADS)

    Chen, Guang-Shan; Kutzbach, J. E.; Gallimore, R.; Liu, Zhengyu

    2011-11-01

    Several studies have shown that the use of different calendars in paleoclimate simulations can cause artificial phase shifts on insolation forcing and climatic responses. However, these important calendar corrections are still often neglected. In this paper, the phase shifts at the precession band is quantitatively assessed by converting the model data of the transient GCM climate simulation of Kutzbach et al. (Clim Dyn 30:567-579, 2008) from the "fixed-day" calendar to the "fixed-angular" calendar with a new and efficient approach. We find that insolation has a big phase shift in September-October-November (SON) when the vernal equinox (VE) is fixed to March 21. At high latitude, the phase bias is up to 60° (about 3650 years). The insolation phase bias in SON in Southern Hemisphere (SH) is especially important because it can influence the timing of the SH summer monsoon response due to the large heat capacity of ocean. The calendar correction has minor effect (±2°) on the phase relationships between forcing and precipitation responses of the six global summer monsoons studied in Kutzbach et al. (2008). After correcting the calendar effect, especial on SH ocean temperature, the new phase wheel results are more similar for both hemispheres. The results suggest that the calendar effect should be corrected before discussing the dynamics between orbital forcing and climatic responses in phase studies of transient simulations.

  16. Numerical Simulation of Roughness-Induced Transient Growth in a Laminar Boundary Layer

    NASA Technical Reports Server (NTRS)

    Fischer, Paul; Choudhari, Meelan

    2004-01-01

    Numerical simulations are used to examine the roughness-induced transient growth in a laminar boundary-layer flow. Based on the spectral element method, these simulations model the stationary disturbance field associated with a nonsmooth roughness geometry, such as the spanwise periodic array of circular disks used by White and co-workers during a series of wind tunnel experiments at Case Western Reserve University. Besides capturing the major trends from the recent measurements by White and Ergin, the simulations provide additional information concerning the relative accuracy of the experimental findings derived from two separate wall-finding procedures. The paper also explores the dependence of transient growth on geometric characteristics of the roughness distribution, including the height and planform shape of the roughness element and the ratio of roughness due to spacing between an adjacent pair of elements. Results are used for a preliminary assessment of the differences between recently reported theoretical results of Tumin and Reshotko and the measurements by White and Ergin.

  17. Measurement of transient strain and surface temperature on simulated turbine blades using noncontacting techniques

    NASA Technical Reports Server (NTRS)

    Calfo, F. D.; Pollack, F. G.

    1978-01-01

    Noncontacting techniques were used to measure strain and temperature in thermally cycled simulated turbine blades. An electro-optical extensometer was used to measure the displacement between parallel targets mounted on the leading edge of the blades throughout a complete heating and cooling cycle. An infrared photographic pyrometry method was used to measure blade steady state surface temperature. The blade was cyclically heated and cooled by moving it into and out of a Mach 1 hot-gas stream. Transient leading edge strain and steady state surface temperature distributions are presented for blades of three different configurations.

  18. Kinetic modelling and simulation of laccase catalyzed degradation of reactive textile dyes.

    PubMed

    Cristóvão, Raquel O; Tavares, Ana P M; Ribeiro, Adriano S; Loureiro, José M; Boaventura, Rui A R; Macedo, Eugénia A

    2008-07-01

    A kinetic model based on Michaelis-Menten equation was developed to simulate the dye decolourisation of Reactive Black 5 (RB5), Reactive Blue 114 (RB114), Reactive Yellow 15 (RY15), Reactive Red 239 (RR239) and Reactive Red 180 (RR180) dyes by commercial laccase. The unusual kinetic behavior of some of these reactions suggests that the kinetic model must consider the activation of the laccase-mediator system. Several reactions at different concentrations of each dye were performed in batch reactors and time courses were obtained. A LSODE code to solve the differential equation obtained from the batch reactor was combined with an optimization Fortran program to obtain the theoretical time courses. The time courses obtained from the developed program were compared with the experimentally obtained ones to estimate the kinetic constants that minimized the difference between them. The close correlation between the predicted and the experimental results seems to support the reliability of the established models.

  19. Transient dual-porosity simulations of unsaturated flow in fractured rocks

    SciTech Connect

    Zimmerman, R.W.; Hadgu, T.; Bodvarsson, G.S.

    1995-01-01

    This report describes the development and use of a semi-analytical dual-porosity simulator for unsaturated flow in fractured rock masses. Fluid flow between the fracture network and the matrix blocks is described by a nonlinear equation that relates the imbibition rate to the local difference in liquid-phase pressure between the fractures and the matrix blocks. This equation is a generalization of the Warren-Root equation, but is accurate in both early and late time regimes. The fracture/matrix interflow equation has been incorporated into a computational module that acts as a source/sink term for fracture elements; this module is compatible with the unsaturated flow simulator TOUGH. Flow processes are then simulated using only fracture elements in the computational grid. This semi-analytical dual-porosity module has been tested with TOUGH on various problems involving transient flow in fractured/porous media, and compared with simulations performed using explicit discretization of the matrix blocks. The new semi-analytical dual-porosity model accurately simulates flow processes in unsaturated fractured rocks, and typically requires an order of magnitude less computational time than do simulations using fully-discretized matrix blocks.

  20. Transient analysis of a pulsed detonation combustor using the numerical propulsion system simulation

    NASA Astrophysics Data System (ADS)

    Hasler, Anthony Scott

    The performance of a hybrid mixed flow turbofan (with detonation tubes installed in the bypass duct) is investigated in this study and compared with a baseline model of a mixed flow turbofan with a standard combustion chamber as a duct burner. Previous studies have shown that pulsed detonation combustors have the potential to be more efficient than standard combustors, but they also present new challenges that must be overcome before they can be utilized. The Numerical Propulsion System Simulation (NPSS) will be used to perform the analysis with a pulsed detonation combustor model based on a numerical simulation done by Endo, Fujiwara, et. al. Three different cases will be run using both models representing a take-off situation, a subsonic cruise and a supersonic cruise situation. Since this study investigates a transient analysis, the pulse detonation combustor is run in a rig setup first and then its pressure and temperature are averaged for the cycle to obtain quasi-steady results.

  1. Interactive simulations of gas-turbine modular HTGR transients and heatup accidents

    SciTech Connect

    Ball, S.J.; Nypaver, D.J.

    1994-06-01

    An interactive workstation-based simulator has been developed for performing analyses of modular high-temperature gas-cooled reactor (MHTGR) core transients and accidents. It was originally developed at Oak Ridge National Laboratory for the US Nuclear Regulatory Commission to assess the licensability of the US Department of Energy (DOE) steam cycle design 350-MW(t) MHTGR. Subsequently, the code was modified under DOE sponsorship to simulate the 450-MW(t) Gas Turbine (GT) design and to aid in development and design studies. Features of the code (MORECA-GT) include detailed modeling of 3-D core thermal-hydraulics, interactive workstation capabilities that allow user/analyst or ``operator`` involvement in accident scenarios, and options for studying anticipated transients without scram (ATWS) events. In addition to the detailed models for the core, MORECA includes models for the vessel, Shutdown Cooling System (SCS), and Reactor Cavity Cooling System (RCCS), and core point kinetics to accommodate ATWS events. The balance of plant (BOP) is currently not modeled. The interactive workstation features include options for on-line parameter plots and 3-D graphic temperature profiling. The studies to date show that the proposed MHTGR designs are very robust and can generally withstand the consequences of even the extremely low probability postulated accidents with little or no damage to the reactor`s fuel or metallic components.

  2. A fixed-grid method for transient simulations of dopant segregation in VGF-RMF growth

    NASA Astrophysics Data System (ADS)

    Nikrityuk, Petr A.; Pätzold, Olf; Stelter, Michael

    2012-01-01

    In this work a fixed-grid, virtual-front tracking model originally developed for modeling dendritic growth has been adopted for transient simulations of dopant segregation in vertical gradient freeze (VGF) melt growth of Ga-doped germanium under the influence of a rotating magnetic field (RMF). The interfacial Stefan conditions for temperature and solute are formulated in volumetric terms in energy and solute conservation equations, which allow the interface to be tracked implicitly with no need to calculate the growth velocity. The model and the code are validated against an analytical solution for the transient solidification of a binary alloy at constant velocity. The numerical results show the strong relationship between the melt flow pattern and the dopant concentration in the crystal grown. The better melt mixing during growth under the influence of RMF is found to have a significant impact on the axial and radial macrosegregation of dopants. Simulation results are in good qualitative agreement with previous experimental observations of the dopant segregation in VGF-RMF growth, which now are seen ass a direct consequence of the mixing state of the melt.

  3. Simulating Subsurface Reactive Flows on Ultrascale Computers with PFLOTRAN

    NASA Astrophysics Data System (ADS)

    Mills, R. T.; Hammond, G. E.; Lichtner, P. C.; Lu, C.; Smith, B. F.; Philip, B.

    2009-12-01

    To provide true predictive utility, subsurface simulations often must accurately resolve--in three dimensions--complicated, multi-phase flow fields in highly heterogeneous geology with numerous chemical species and complex chemistry. This task is especially daunting because of the wide range of spatial scales involved--from the pore scale to the field scale--ranging over six orders of magnitude, and the wide range of time scales ranging from seconds or less to millions of years. This represents a true "Grand Challenge" computational problem, requiring not only the largest-scale ("ultrascale") supercomputers, but accompanying advances in algorithms for the efficient numerical solution of systems of PDEs using these machines, and in mathematical modeling techniques that can adequately capture the truly multi-scale nature of these problems. We describe some of the specific challenges involved and present the software and algorithmic approaches that are being using in the computer code PFLOTRAN to provide scalable performance for such simulations on tens of thousands of processors. We focus particularly on scalable techniques for solving the large (up to billions of total degrees of freedom), sparse algebraic systems that arise. We also describe ongoing work to address disparate time and spatial scales by both the development of adaptive mesh refinement methods and the use of multiple continuum formulations. Finally, we present some examples from recent simulations conducted on Jaguar, the 150152 processor core Cray XT5 system at Oak Ridge National Laboratory that is currently one of the most powerful supercomputers in the world.

  4. Calculating frequency at loads in simulations of electro-mechanical transients

    SciTech Connect

    Nutaro, James J; Protopopescu, Vladimir A

    2012-01-01

    This paper introduces a new method for calculating frequency at an electrical load in simulations of electro-mechanical transients. The method is designed for simulation studies that require accurate models of sensors such as phasor measurement units and F-Net devices, which measure frequency at locations away from generating plants. These sensors are poised to become critical components in the control systems of electrical power grids, and therefore simulation tools that incorporate accurate models of these devices are essential. The method proposed here corrects two drawbacks of using numerically computed phase angle derivatives to approximate frequency. First, it eliminates spurious spikes in frequencies calculated at loads. Second, it eliminates instabilities induced by the simulator in studies of frequency responsive loads. The proposed method is derived from a simplified model of the generators and loads in an electrical system, but in the final analysis does not depend critically on these simplifications and is therefore applicable to more sophisticated models. The method is demonstrated with the simplified model applied to the IEEE 14 and 300 bus systems.

  5. Molecular simulation of shocked materials using the reactive Monte Carlo method

    NASA Astrophysics Data System (ADS)

    Brennan, John K.; Rice, Betsy M.

    2002-08-01

    We demonstrate the applicability of the reactive Monte Carlo (RxMC) simulation method [J. K. Johnson, A. Z. Panagiotopoulos, and K. E. Gubbins, Mol. Phys. 81, 717 (1994); W. R. Smith and B. Tříska, J. Chem. Phys. 100, 3019 (1994)] for calculating the shock Hugoniot properties of a material. The method does not require interaction potentials that simulate bond breaking or bond formation; it requires only the intermolecular potentials and the ideal-gas partition functions for the reactive species that are present. By performing Monte Carlo sampling of forward and reverse reaction steps, the RxMC method provides information on the chemical equilibria states of the shocked material, including the density of the reactive mixture and the mole fractions of the reactive species. We illustrate the methodology for two simple systems (shocked liquid NO and shocked liquid N2), where we find excellent agreement with experimental measurements. The results show that the RxMC methodology provides an important simulation tool capable of testing models used in current detonation theory predictions. Further applications and extensions of the reactive Monte Carlo method are discussed.

  6. Simulation of transients in natural gas pipelines using hybrid TVD schemes

    NASA Astrophysics Data System (ADS)

    Zhou, Junyang; Adewumi, Michael A.

    2000-02-01

    The mathematical model describing transients in natural gas pipelines constitutes a non-homogeneous system of non-linear hyperbolic conservation laws. The time splitting approach is adopted to solve this non-homogeneous hyperbolic model. At each time step, the non-homogeneous hyperbolic model is split into a homogeneous hyperbolic model and an ODE operator. An explicit 5-point, second-order-accurate total variation diminishing (TVD) scheme is formulated to solve the homogeneous system of non-linear hyperbolic conservation laws. Special attention is given to the treatment of boundary conditions at the inlet and the outlet of the pipeline. Hybrid methods involving the Godunov scheme (TVD/Godunov scheme) or the Roe scheme (TVD/Roe scheme) or the Lax-Wendroff scheme (TVD/LW scheme) are used to achieve appropriate boundary handling strategy. A severe condition involving instantaneous closure of a downstream valve is used to test the efficacy of the new schemes. The results produced by the TVD/Roe and TVD/Godunov schemes are excellent and comparable with each other, while the TVD/LW scheme performs reasonably well. The TVD/Roe scheme is applied to simulate the transport of a fast transient in a short pipe and the propagation of a slow transient in a long transmission pipeline. For the first example, the scheme produces excellent results, which capture and maintain the integrity of the wave fronts even after a long time. For the second example, comparisons of computational results are made using different discretizing parameters. Copyright

  7. A Reactive Transport Simulator for Biogeochemical Processes in Subsurface System

    2003-04-01

    BIOGEOCHEM is a Fortran code that mumerically simulates the coupled processes of solute transport, microbial population dynamics, microbial metabolism, and geochemical reactions. The potential applications of the code include, but not limited to, (a) sensitivity and uncertainty analyses for assessing the impact of microbial activity on subsurface geochemical systems; (b) extraction of biogeochemical parameter values from field observations or laboratory measurements, (c) helping to design and optimize laboratory biogeochemical experiments, and (d) data integration. Methodmore » of Solution: A finite difference method and a Newton-Raphson technique are used to solve a set of coupled nonlinear partial differential equations and algebraic equations. Practical Application: Environmental analysis, bioremediation performance assessments of radioactive or non-radioactive wase disposal, and academic research.« less

  8. Simulations of transient shock motion within a biological contoured-shock-tube system

    NASA Astrophysics Data System (ADS)

    Liu, Y.

    2008-02-01

    This study is motivated by the author’s interest in developing needle-free powdered vaccine/drug delivery systems. One system configuration is called the Contoured Shock Tube (CST). Of great importance is the behaviour of a transonic gas flow with a strongly nonlinear starting process, which accelerates powdered vaccines in micro-form to a sufficient momentum to penetrate the outer layer of human skin or mucosal tissue. In this paper, an established Modified Implicit Flux Vector Splitting (MIFVS) solver for the Navier-Stokes equations is extended to numerically study these transient transonic gas flows. A low Reynolds number k-ɛ turbulence model, with the compressibility effect considered, is integrated into the MIFVS solver to predict the turbulent structures and interactions with inherent shock systems. The MIFVS is first calibrated for NASA validation case, NPARC, and the resulting flow characteristic are compared with experimental date and simulations published. The MIFVS calculation with the modified k-ɛ model shows the best agreement. Subsequently, the MIFVS is applied to model the transient gas flow within a biolistic CST prototype. Comparison with experimental pressure traces shows the MIFVS captures gas flow mechanics with more accuracy than calculations with a commercial code (Fluent). This illustrates that the MIFVS is well-suited to model the strongly nonlinear fluid dynamics associated with the CST biolistic particle delivery system.

  9. Transient 1D transport equation simulated by a mixed Green element formulation

    NASA Astrophysics Data System (ADS)

    Taigbenu, Akpofure Efemena; Onyejekwe, Okey Oseloka

    1997-08-01

    New discrete element equations or coefficients are derived for the transient 1D diffusion-advection or transport equation based on the Green element replication of the differential equation using linear elements. The Green element method (GEM), which solves the singular boundary integral theory (a Fredholm integral equation of the second kind) on a typical element, gives rise to a banded global coefficient matrix which is amenable to efficient matrix solvers. It is herein derived for the transient 1D transport equation with uniform and non-uniform ambient flow conditions and in which first-order decay of the containment is allowed to take place. Because the GEM implements the singular boundary integral theory within each element at a time, the integrations are carried out in exact fashion, thereby making the application of the boundary integral theory more utilitarian. This system of discrete equations, presented herein for the first time, using linear interpolating functions in the spatial dimensions shows promising stable characteristics for advection-dominant transport. Three numerical examples are used to demonstrate the capabilities of the method. The second-order-correct Crank-Nicolson scheme and the modified fully implicit scheme with a difference weighting value of two give superior solutions in all simulated examples.

  10. Simulating transient dynamics of the time-dependent time fractional Fokker-Planck systems

    NASA Astrophysics Data System (ADS)

    Kang, Yan-Mei

    2016-09-01

    For a physically realistic type of time-dependent time fractional Fokker-Planck (FP) equation, derived as the continuous limit of the continuous time random walk with time-modulated Boltzmann jumping weight, a semi-analytic iteration scheme based on the truncated (generalized) Fourier series is presented to simulate the resultant transient dynamics when the external time modulation is a piece-wise constant signal. At first, the iteration scheme is demonstrated with a simple time-dependent time fractional FP equation on finite interval with two absorbing boundaries, and then it is generalized to the more general time-dependent Smoluchowski-type time fractional Fokker-Planck equation. The numerical examples verify the efficiency and accuracy of the iteration method, and some novel dynamical phenomena including polarized motion orientations and periodic response death are discussed.

  11. Numerical simulation of the transient shape of the red blood cell in microcapillary flow

    NASA Astrophysics Data System (ADS)

    Shi, Xing; Wang, Shuanglian; Zhang, Shuai

    2013-01-01

    The transient shape of a red blood cell (RBC) in a microcapillary flow is simulated under different initial conditions, including various axis orientations and centroid locations, using the LBM-DLM/FD method, which is derived from the lattice Boltzmann method and the distributed Lagrange multiplier/fictitious domain method. Although the terminal velocity is not sensitive to the initial configuration, the evolution of the velocity and the shape are determined by the initial conditions. The parachute and the slipper shape are the most probable shapes for a deformed RBC in the flow. An RBC with an initial axis orientation of 90 degrees exhibits a more complicated deformation. RBCs have a tendency to move to the centerline of a tube if an offset between the RBC centroid and the centerline exists. Our numerical results are validated by experiments, and some details beyond the experiment are provided.

  12. CFD transient simulation of an isolator shock train in a scramjet engine

    NASA Astrophysics Data System (ADS)

    Hoeger, Troy Christopher

    For hypersonic flight, the scramjet engine uses an isolator to contain the pre-combustion shock train formed by the pressure difference between the inlet and the combustion chamber. If this shock train were to reach the inlet, it would cause an engine unstart, disrupting the flow through the engine and leading to a loss of thrust and potential loss of the vehicle. Prior to this work, a Computational Fluid Dynamics (CFD) simulation of the isolator was needed for simulating and characterizing the isolator flow and for finding the relationship between back pressure and changes in the location of the leading edge of the shock train. In this work, the VULCAN code was employed with back pressure as an input to obtain the time history of the shock train leading location. Results were obtained for both transient and steady-state conditions. The simulation showed a relationship between back-to-inlet pressure ratios and final locations of the shock train. For the 2-D runs, locations were within one isolator duct height of experimental results while for 3-D runs, the results were within two isolator duct heights.

  13. Flow path oscillations in transient ground-water simulations of large peatland systems

    NASA Astrophysics Data System (ADS)

    Reeve, Andrew S.; Evensen, Robin; Glaser, Paul H.; Siegel, Donald I.; Rosenberry, Donald

    2006-01-01

    Transient numerical simulations of the Glacial Lake Agassiz Peatland near the Red Lakes in Northern Minnesota were constructed to evaluate observed reversals in vertical ground-water flow. Seasonal weather changes were introduced to a ground-water flow model by varying evapotranspiration and recharge over time. Vertical hydraulic reversals, driven by changes in recharge and evapotranspiration were produced in the simulated peat layer. These simulations indicate that the high specific storage associated with the peat is an important control on hydraulic reversals. Seasonally driven vertical flow is on the order of centimeters in the deep peat, suggesting that seasonal vertical advective fluxes are not significant and that ground-water flow into the deep peat likely occurs on decadal or longer time scales. Particles tracked within the ground-water flow model oscillate over time, suggesting that seasonal flow reversals will enhance vertical mixing in the peat column. The amplitude of flow path oscillations increased with increasing peat storativity, with amplitudes of about 5 cm occurring when peat specific storativity was set to about 0.05 m -1.

  14. Flow path oscillations in transient ground-water simulations of large peatland systems

    USGS Publications Warehouse

    Reeve, A.S.; Evensen, R.; Glaser, P.H.; Siegel, D.I.; Rosenberry, D.

    2006-01-01

    Transient numerical simulations of the Glacial Lake Agassiz Peatland near the Red Lakes in Northern Minnesota were constructed to evaluate observed reversals in vertical ground-water flow. Seasonal weather changes were introduced to a ground-water flow model by varying evapotranspiration and recharge over time. Vertical hydraulic reversals, driven by changes in recharge and evapotranspiration were produced in the simulated peat layer. These simulations indicate that the high specific storage associated with the peat is an important control on hydraulic reversals. Seasonally driven vertical flow is on the order of centimeters in the deep peat, suggesting that seasonal vertical advective fluxes are not significant and that ground-water flow into the deep peat likely occurs on decadal or longer time scales. Particles tracked within the ground-water flow model oscillate over time, suggesting that seasonal flow reversals will enhance vertical mixing in the peat column. The amplitude of flow path oscillations increased with increasing peat storativity, with amplitudes of about 5 cm occurring when peat specific storativity was set to about 0.05 m-1. ?? 2005 Elsevier B.V. All rights reserved.

  15. Global Carbon Cycle Inside GISS ModelE GCM: Results of Equilibrium and Transient Simulations.

    NASA Astrophysics Data System (ADS)

    Aleinov, I.; Kiang, N. Y.; Romanou, A.; Puma, M. J.; Kharecha, P.; Moorcroft, P. R.; Kim, Y.

    2008-12-01

    We present simulation results for a fully coupled carbon cycle inside the ModelE General Circulation Model (GCM) developed at the NASA Goddard Institute for Space Studies (GISS). The current implementation utilizes the GISS dynamical atmospheric core coupled to the HYCOM ocean model. The atmospheric core uses a Quadratic Upstream Scheme (QUS) for advection of gas tracers, while HYCOM has its own built-in algorithm for advection of ocean tracers. The land surface part of the model consists of the GISS ground hydrology model coupled to the Ent dynamic global terrestrial ecosystem model. The ocean biogeochemistry model based on Watson Gregg's model was implemented inside the HYCOM ocean model. Together with ocean tracer transport, it describes all aspects of the carbon cycle inside the ocean and provides CO2 fluxes for exchange with the atmosphere. CO2 fluxes from land vegetation are provided by the Ent model, which employs well-known photosynthesis relationships of Farquhar, von Caemmerer, and Berry and stomatal conductance of Ball and Berry. Soil CO2 fluxes are also computed by the Ent model according to the CASA soil biogeochemistry model. We present results of fully coupled GCM simulations as well as off-line tests for different components. For GCM simulations, we present results of both equilibrium and transient runs and discuss implications of biases in GCM-predicted climate for accurate modeling of the carbon cycle.

  16. Simulations of transient membrane behavior in cells subjected to a high-intensity ultrashort electric pulse

    NASA Astrophysics Data System (ADS)

    Hu, Q.; Viswanadham, S.; Joshi, R. P.; Schoenbach, K. H.; Beebe, S. J.; Blackmore, P. F.

    2005-03-01

    A molecular dynamics (MD) scheme is combined with a distributed circuit model for a self-consistent analysis of the transient membrane response for cells subjected to an ultrashort (nanosecond) high-intensity ( ˜0.01-V/nm spatially averaged field) voltage pulse. The dynamical, stochastic, many-body aspects are treated at the molecular level by resorting to a course-grained representation of the membrane lipid molecules. Coupling the Smoluchowski equation to the distributed electrical model for current flow provides the time-dependent transmembrane fields for the MD simulations. A good match between the simulation results and available experimental data is obtained. Predictions include pore formation times of about 5-6 ns. It is also shown that the pore formation process would tend to begin from the anodic side of an electrically stressed membrane. Furthermore, the present simulations demonstrate that ions could facilitate pore formation. This could be of practical importance and have direct relevance to the recent observations of calcium release from the endoplasmic reticulum in cells subjected to such ultrashort, high-intensity pulses.

  17. Simulations of transient membrane behavior in cells subjected to a high-intensity ultrashort electric pulse.

    PubMed

    Hu, Q; Viswanadham, S; Joshi, R P; Schoenbach, K H; Beebe, S J; Blackmore, P F

    2005-03-01

    A molecular dynamics (MD) scheme is combined with a distributed circuit model for a self-consistent analysis of the transient membrane response for cells subjected to an ultrashort (nanosecond) high-intensity (approximately 0.01-V/nm spatially averaged field) voltage pulse. The dynamical, stochastic, many-body aspects are treated at the molecular level by resorting to a course-grained representation of the membrane lipid molecules. Coupling the Smoluchowski equation to the distributed electrical model for current flow provides the time-dependent transmembrane fields for the MD simulations. A good match between the simulation results and available experimental data is obtained. Predictions include pore formation times of about 5-6 ns. It is also shown that the pore formation process would tend to begin from the anodic side of an electrically stressed membrane. Furthermore, the present simulations demonstrate that ions could facilitate pore formation. This could be of practical importance and have direct relevance to the recent observations of calcium release from the endoplasmic reticulum in cells subjected to such ultrashort, high-intensity pulses.

  18. Reactive Flow Modeling of Liquid Explosives via ALE3D/Cheetah Simulations

    SciTech Connect

    Kuo, I W; Bastea, S; Fried, L E

    2010-03-10

    We carried out reactive flow simulations of liquid explosives such as nitromethane using the hydrodynamic code ALE3D coupled with equations of state and reaction kinetics modeled by the thermochemical code Cheetah. The simulation set-up was chosen to mimic cylinder experiments. For pure unconfined nitromethane we find that the failure diameter and detonation velocity dependence on charge diameter are in agreement with available experimental results. Such simulations are likely to be useful for determining detonability and failure behavior for a wide range of experimental conditions and explosive compounds.

  19. Simulations of the transient climate response to climate engineering in the form of cirrus cloud seeding

    NASA Astrophysics Data System (ADS)

    Storelvmo, Trude; Boos, William R.

    2015-04-01

    We present a global modeling study of a so far understudied climate engineering mechanism (CEM), namely the seeding of cirrus clouds to reduce their lifetimes in the upper troposphere, and hence their greenhouse effect. Different from most CEMs, the intention of cirrus seeding is not to reduce the amount of solar radiation reaching Earth's surface. This particular CEM rather targets the greenhouse effect, by reducing the trapping of infrared radiation by high clouds. This avoids some of the caveats that have been identified for solar radiation management, for example the delayed recovery of stratospheric ozone or drastic changes to Earth's hydrological cycle. Here, we contrast transient simulations of the 21st century, using a modified version of the Community Earth System Model (CESM). We simulate three future scenarios: (i) A simulation with the conventional high emission scenario RCP8.5, (ii) A simulation in which climate engineering in the form of high-latitude cirrus seeding is introduced in the middle of the century without any accompanying emission reductions, and (iii) The same as (ii), but with emissions that are reduced by 50% over the period 2050 to 2100. We consider the last scenario to be one in which climate engineering is used to buy time for mitigation efforts to become effective, while scenario (iii) is one in which high emissions are allowed to continue due to the naïve belief that climate engineering can be used to prevent global warming in perpetuity. Our analysis focuses on the contrasts between the regional and global climates of year 2100 produced by the three scenarios.

  20. TRACE Model for Simulation of Anticipated Transients Without Scram in a BWR

    SciTech Connect

    Cheng L. Y.; Baek J.; Cuadra,A.; Aronson, A.; Diamond, D.; Yarsky, P.

    2013-11-10

    A TRACE model has been developed for using theTRACE/PARCS computational package [1, 2] to simulate anticipated transients without scram (ATWS) events in a boiling water reactor (BWR). The model represents a BWR/5 housed in a Mark II containment. The reactor and the balance of plant systems are modeled in sufficient detail to enable the evaluation of plant responses and theeffectiveness of automatic and operator actions tomitigate this beyond design basis accident.The TRACE model implements features thatfacilitate the simulation of ATWS events initiated by turbine trip and closure of the main steam isolation valves (MSIV). It also incorporates control logic to initiate actions to mitigate the ATWS events, such as water levelcontrol, emergency depressurization, and injection of boron via the standby liquid control system (SLCS). Two different approaches have been used to model boron mixing in the lower plenum of the reactor vessel: modulate coolant flow in the lower plenum by a flow valve, and use control logic to modular.

  1. Numerical Simulation of Transient and Steady State Nonlinear Beam-Cavity Dynamics in High Power Klystrons.

    NASA Astrophysics Data System (ADS)

    Zambre, Yadunath Bhagvantrao

    1988-03-01

    A 2-1over2 dimensional analysis of klystrons, assuming cylindrical space symmetry but retaining all velocity effects, is presented. The model handles all relativistic, electromagnetic, and non-linear effects. The klystron geometry is viewed as a conducting cylinder (the tube) to which are attached a number of resonant cavities at various locations. Within this tube, particle in cell plasma simulation techniques are used to model the electron beam dynamics and electromagnetic fields. The effects of the cavities are then "patched in" by the use of eigenmode expansions over the cavity geometries. These expansions reduce the effects of the cavity fields into relatively simple time varying boundary conditions on the tube. The plasma simulation in the tube is carried out using a number of "macroparticles," each representing many electrons and each obeying the equations of motion for an electron. A time centered cycloid fitting algorithm is used to move the particles. A time centered spectral method using Fourier series in z and Chebyschev polynomials in r is used to advance the fields. A non-uniform grid permits the use of FFT's to carry out the Chebyschev expansions. A method for finding time periodic solutions is also presented. This method will compute a qualitatively correct transient solution and yield a quantitatively correct steady state solution.

  2. Pseudo-transient Continuation Based Variable Relaxation Solve in Nonlinear Magnetohydrodynamic Simulations

    SciTech Connect

    Jin Chen

    2009-12-07

    Efficient and robust Variable Relaxation Solver, based on pseudo-transient continuation, is developed to solve nonlinear anisotropic thermal conduction arising from fusion plasma simulations. By adding first and/or second order artificial time derivatives to the system, this type of method advances the resulting time-dependent nonlinear PDEs to steady state, which is the solution to be sought. In this process, only the stiffness matrix itself is involved so that the numerical complexity and errors can be greatly reduced. In fact, this work is an extension of integrating efficient linear elliptic solvers for fusion simulation on Cray XIE. Two schemes are derived in this work, first and second order Variable Relaxations. Four factors are observed to be critical for efficiency and preservation of solution's symmetric structure arising from periodic boundary condition: refining meshes in different coordinate directions, initializing nonlinear process, varying time steps in both temporal and spatial directions, and accurately generating nonlinear stiffness matrix. First finer mesh scale should be taken in strong transport direction; Next the system is carefully initialized by the solution with linear conductivity; Third, time step and relaxation factor are vertex-based varied and optimized at each time step; Finally, the nonlinear stiffness matrix is updated by just scaling corresponding linear one with the vector generated from nonlinear thermal conductivity.

  3. Parametric Study of ReaxFF Simulation Parameters for Molecular Dynamics Modeling of Reactive Carbon Gases.

    PubMed

    Jensen, Benjamin D; Bandyopadhyay, Ananyo; Wise, Kristopher E; Odegard, Gregory M

    2012-09-11

    The development of innovative carbon-based materials can be greatly facilitated by molecular modeling techniques. Although the Reax Force Field (ReaxFF) can be used to simulate the chemical behavior of carbon-based systems, the simulation settings required for accurate predictions have not been fully explored. Using the ReaxFF, molecular dynamics (MD) simulations are used to simulate the chemical behavior of pure carbon and hydrocarbon reactive gases that are involved in the formation of carbon structures such as graphite, buckyballs, amorphous carbon, and carbon nanotubes. It is determined that the maximum simulation time step that can be used in MD simulations with the ReaxFF is dependent on the simulated temperature and selected parameter set, as are the predicted reaction rates. It is also determined that different carbon-based reactive gases react at different rates, and that the predicted equilibrium structures are generally the same for the different ReaxFF parameter sets, except in the case of the predicted formation of large graphitic structures with the Chenoweth parameter set under specific conditions.

  4. Parametric study of ReaxFF simulation parameters for molecular dynamics modeling of reactive carbon gases

    NASA Astrophysics Data System (ADS)

    Jensen, Benjamin D.

    The development of innovative carbon-based materials can be greatly facilitated by molecular modeling techniques. Although the Reax Force Field (ReaxFF) can be used to simulate the chemical behavior of carbon-based systems, the simulation settings required for accurate predictions have not been fully explored. Using the ReaxFF, molecular dynamics (MD) simulations are used to simulate the chemical behavior of pure carbon and hydrocarbon reactive gases that are involved in the formation of carbon structures such as graphite, buckyballs, amorphous carbon, and carbon nanotubes. It is determined that the maximum simulation time step that can be used in MD simulations with the ReaxFF is dependent on the simulated temperature and selected parameter set, as are the predicted reaction rates. It is also determined that different carbon-based reactive gases react at different rates, and that the predicted equilibrium structures are generally the same for the different ReaxFF parameter sets, except in the case of the predicted formation of large graphitic structures with the Chenoweth parameter set under specific conditions.

  5. Parametric Study of ReaxFF Simulation Parameters for Molecular Dynamics Modeling of Reactive Carbon Gases.

    PubMed

    Jensen, Benjamin D; Bandyopadhyay, Ananyo; Wise, Kristopher E; Odegard, Gregory M

    2012-09-11

    The development of innovative carbon-based materials can be greatly facilitated by molecular modeling techniques. Although the Reax Force Field (ReaxFF) can be used to simulate the chemical behavior of carbon-based systems, the simulation settings required for accurate predictions have not been fully explored. Using the ReaxFF, molecular dynamics (MD) simulations are used to simulate the chemical behavior of pure carbon and hydrocarbon reactive gases that are involved in the formation of carbon structures such as graphite, buckyballs, amorphous carbon, and carbon nanotubes. It is determined that the maximum simulation time step that can be used in MD simulations with the ReaxFF is dependent on the simulated temperature and selected parameter set, as are the predicted reaction rates. It is also determined that different carbon-based reactive gases react at different rates, and that the predicted equilibrium structures are generally the same for the different ReaxFF parameter sets, except in the case of the predicted formation of large graphitic structures with the Chenoweth parameter set under specific conditions. PMID:26605713

  6. Coupled Transient Finite Element Simulation of Quench in Jefferson Lab's 11 GeV Super High Momentum Spectrometer Superconducting Magnets

    SciTech Connect

    E. Sun, P. Brindza, S. Lassiter, M. Fowler, E. Xu

    2010-06-01

    This paper presents coupled transient thermal and electromagnetic finite element analysis of quench in the Q2, Q3, and dipole superconducting magnets using Vector Fields Quench code. Detailed temperature distribution within coils and aluminum force collars were computed at each time step. Both normal (quench with dump resistor) and worst-case (quench without dump resistor) scenarios were simulated to investigate the maximum temperatures. Two simulation methods were utilized, and their algorithms, implementation, advantages, and disadvantages are discussed. The first method simulated the coil using nonlinear transient thermal analysis directly linked with the transient circuit analysis. It was faster because only the coil was meshed and no eddy current was modeled. The second method simulated the whole magnet including the coil, the force collar, and the iron yoke. It coupled thermal analysis with transient electromagnetic field analysis which modeled electromagnetic fields including eddy currents within the force collar. Since eddy currents and temperature in the force collars were calculated in various configurations, segmentation of the force collars was optimized under the condition of fast discharge.

  7. RAFT: A simulator for ReActive Flow and Transport of groundwater contaminants

    SciTech Connect

    Chilakapati, A

    1995-07-01

    This report documents the use of the simulator RAFT for the ReActive flow and Transport of groundwater contaminants. RAFT can be used as a predictive tool in the design and analysis of laboratory and field experiments or it can be used for the estimation of model/process parameters from experiments. RAFT simulates the reactive transport of groundwater contaminants in one, two-, or three-dimensions and it can model user specified source/link configurations and arbitrary injection strategies. A suite of solvers for transport, reactions and regression are employed so that a combination of numerical methods best suited for a problem can be chosen. User specified coupled equilibrium and kinetic reaction systems can be incorporated into RAFT. RAFT is integrated with a symbolic computational language MAPLE, to automate code generation for arbitrary reaction systems. RAFT is expected to be used as a simulator for engineering design for field experiments in groundwater remediation including bioremediation, reactive barriers and redox manipulation. As an integrated tool with both the predictive ability and the ability to analyze experimental data, RAFT can help in the development of remediation technologies, from laboratory to field.

  8. Uncertainty of simulated groundwater levels arising from stochastic transient climate change scenarios

    NASA Astrophysics Data System (ADS)

    Goderniaux, Pascal; Brouyère, Serge; Blenkinsop, Stephen; Burton, Aidan; Fowler, Hayley; Dassargues, Alain

    2010-05-01

    The evaluation of climate change impact on groundwater reserves represents a difficult task because both hydrological and climatic processes are complex and difficult to model. In this study, we present an innovative methodology that combines the use of integrated surface - subsurface hydrological models with advanced stochastic transient climate change scenarios. This methodology is applied to the Geer basin (480 km²) in Belgium, which is intensively exploited to supply the city of Liège (Belgium) with drinking water. The physically-based, spatially-distributed, surface-subsurface flow model has been developed with the finite element model HydroGeoSphere . The simultaneous solution of surface and subsurface flow equations in HydroGeoSphere, as well as the internal calculation of the actual evapotranspiration as a function of the soil moisture at each node of the evaporative zone, enables a better representation of interconnected processes in all domains of the catchment (fully saturated zone, partially saturated zone, surface). Additionally, the use of both surface and subsurface observed data to calibrate the model better constrains the calibration of the different water balance terms. Crucially, in the context of climate change impacts on groundwater resources, the evaluation of groundwater recharge is improved. . This surface-subsurface flow model is combined with advanced climate change scenarios for the Geer basin. Climate change simulations were obtained from six regional climate model (RCM) scenarios assuming the SRES A2 greenhouse gases emission (medium-high) scenario. These RCM scenarios were statistically downscaled using a transient stochastic weather generator technique, combining 'RainSim' and the 'CRU weather generator' for temperature and evapotranspiration time series. This downscaling technique exhibits three advantages compared with the 'delta change' method usually used in groundwater impact studies. (1) Corrections to climate model output are

  9. Simulation studies of plasma waves in the electron foreshock - The transition from reactive to kinetic instability

    NASA Technical Reports Server (NTRS)

    Dum, C. T.

    1990-01-01

    Particle simulation experiments were used to analyze the electron beam-plasma instability. It is shown that there is a transition from the reactive state of the electron beam-plasma instability to the kinetic instability of Langmuir waves. Quantitative tests, which include an evaluation of the dispersion relation for the evolving non-Maxwellian beam distribution, show that a quasi-linear theory describes the onset of this transition and applies again fully to the kinetic stage. This stage is practically identical to the late stage seen in simulations of plasma waves in the electron foreshock described by Dum (1990).

  10. Simulation studies of plasma waves in the electron foreshock - The transition from reactive to kinetic instability

    NASA Astrophysics Data System (ADS)

    Dum, C. T.

    1990-06-01

    Particle simulation experiments were used to analyze the electron beam-plasma instability. It is shown that there is a transition from the reactive state of the electron beam-plasma instability to the kinetic instability of Langmuir waves. Quantitative tests, which include an evaluation of the dispersion relation for the evolving non-Maxwellian beam distribution, show that a quasi-linear theory describes the onset of this transition and applies again fully to the kinetic stage. This stage is practically identical to the late stage seen in simulations of plasma waves in the electron foreshock described by Dum (1990).

  11. Transient simulation of groundwater levels within a sandbar of the Colorado River, Marble Canyon, Arizona, 2004

    USGS Publications Warehouse

    Sabol, Thomas A.; Springer, Abraham E.

    2013-01-01

    Seepage erosion and mass failure of emergent sandy deposits along the Colorado River in Grand Canyon National Park, Arizona, are a function of the elevation of groundwater in the sandbar, fluctuations in river stage, the exfiltration of water from the bar face, and the slope of the bar face. In this study, a generalized three-dimensional numerical model was developed to predict the time-varying groundwater level, within the bar face region of a freshly deposited eddy sandbar, as a function of river stage. Model verification from two transient simulations demonstrates the ability of the model to predict groundwater levels within the onshore portion of the sandbar face across a range of conditions. Use of this generalized model is applicable across a range of typical eddy sandbar deposits in diverse settings. The ability to predict the groundwater level at the onshore end of the sandbar face is essential for both physical and numerical modeling efforts focusing on the erosion and mass failure of eddy sandbars downstream of Glen Canyon Dam along the Colorado River.

  12. Using the extended finite element method for simulation of transient well leakage in multilayer aquifers

    NASA Astrophysics Data System (ADS)

    Craig, James R.; Gracie, Robert

    2011-09-01

    The extended finite element (XFEM) is applied to the problem of transient leakage from abandoned or free-flowing artesian wells in perforated aquifer-aquitard systems. To more accurately capture the singularities in potentiometric head at the wells, the standard linear finite element basis is locally augmented with asymptotic analytical solutions which enable more accurate calculations of leakage rates between aquifers. Highly accurate flux estimates are obtained without the need for higher mesh resolution near wells. Simulations are carried out to test both the accuracy and convergence properties of the XFEM implementation, and the XFEM results are compared to those of a high-resolution standard finite element model. It is seen that for the type of singularity-driven problem posed here, the standard FEM is unable to resolve leakage rates without very fine discretization, but that the XFEM performs robustly with fewer degrees of freedom. The impact of aquifer geometric heterogeneity on leakage rates is assessed and seen to be an important factor in determining total leakage. It is demonstrated that the XFEM may be a valuable tool in many water resources applications where small-scale effects can impact global system behavior.

  13. An 8-node tetrahedral finite element suitable for explicit transient dynamic simulations

    SciTech Connect

    Key, S.W.; Heinstein, M.W.; Stone, C.M.

    1997-12-31

    Considerable effort has been expended in perfecting the algorithmic properties of 8-node hexahedral finite elements. Today the element is well understood and performs exceptionally well when used in modeling three-dimensional explicit transient dynamic events. However, the automatic generation of all-hexahedral meshes remains an elusive achievement. The alternative of automatic generation for all-tetrahedral finite element is a notoriously poor performer, and the 10-node quadratic tetrahedral finite element while a better performer numerically is computationally expensive. To use the all-tetrahedral mesh generation extant today, the authors have explored the creation of a quality 8-node tetrahedral finite element (a four-node tetrahedral finite element enriched with four midface nodal points). The derivation of the element`s gradient operator, studies in obtaining a suitable mass lumping and the element`s performance in applications are presented. In particular, they examine the 80node tetrahedral finite element`s behavior in longitudinal plane wave propagation, in transverse cylindrical wave propagation, and in simulating Taylor bar impacts. The element only samples constant strain states and, therefore, has 12 hourglass modes. In this regard, it bears similarities to the 8-node, mean-quadrature hexahedral finite element. Given automatic all-tetrahedral meshing, the 8-node, constant-strain tetrahedral finite element is a suitable replacement for the 8-node hexahedral finite element and handbuilt meshes.

  14. Simulation of reactive transport of uranium(VI) in groundwater with variable chemical conditions

    USGS Publications Warehouse

    Curtis, G.P.; Davis, J.A.; Naftz, D.L.

    2006-01-01

    The reactive transport of U(VI) in a shallow alluvial aquifer beneath a former U(VI) mill located near Naturita, CO, was simulated using a surface complexation model (SCM) to describe U(VI) adsorption. The groundwater had variable U(VI) concentrations (0.01-20 ??M), variable alkalinity (2.5-18 meq/L), and a nearly constant pH equal to 7.1. U(VI) KD values decreased with increasing U(VI) and alkalinity, and these parameters were more important than sediment variability in controlling KD values. Reactive transport simulations were fit to the observed U(VI) and alkalinity by varying the concentration of U(VI) and alkalinity in recharge at the source area. Simulated KD values varied temporally and spatially because of the differential transport of U(VI) and alkalinity and the nonlinearity of U(VI) adsorption. The model also simulated the observed U(VI) tailing, which would not be expected from a constant KD model. The simulated U(VI) concentrations were sensitive to the recharge flux because of the increased flux of U(VI) to the aquifer. The geochemical behavior of U(VI) was most sensitive to the alkalinity and was relatively insensitive to pH.

  15. An RL10A-3-3A rocket engine model using the rocket engine transient simulator (ROCETS) software

    NASA Technical Reports Server (NTRS)

    Binder, Michael

    1993-01-01

    Steady-state and transient computer models of the RL10A-3-3A rocket engine have been created using the Rocket Engine Transient Simulation (ROCETS) code. These models were created for several purposes. The RL10 engine is a critical component of past, present, and future space missions; the model will give NASA an in-house capability to simulate the performance of the engine under various operating conditions and mission profiles. The RL10 simulation activity is also an opportunity to further validate the ROCETS program. The ROCETS code is an important tool for modeling rocket engine systems at NASA Lewis. ROCETS provides a modular and general framework for simulating the steady-state and transient behavior of any desired propulsion system. Although the ROCETS code is being used in a number of different analysis and design projects within NASA, it has not been extensively validated for any system using actual test data. The RL10A-3-3A has a ten year history of test and flight applications; it should provide sufficient data to validate the ROCETS program capability. The ROCETS models of the RL10 system were created using design information provided by Pratt & Whitney, the engine manufacturer. These models are in the process of being validated using test-stand and flight data. This paper includes a brief description of the models and comparison of preliminary simulation output against flight and test-stand data.

  16. Investigation of the groundwater system at Masaya Caldera, Nicaragua, using transient electromagnetics and numerical simulation

    USGS Publications Warehouse

    MacNeil, R.E.; Sanford, W.E.; Connor, C.B.; Sandberg, S.K.; Diez, M.

    2007-01-01

    The distribution of groundwater beneath Masaya Volcano, in Nicaragua, and its surrounding caldera was characterized using the transient electromagnetic method (TEM). Multiple soundings were conducted at 30 sites. Models of the TEM data consistently indicate a resistive layer that is underlain by one or more conductive layers. These two layers represent the unsaturated and saturated zones, respectively, with the boundary between them indicating the water-table elevation. A map of the TEM data shows that the water table in the caldera is a subdued replica of the topography, with higher elevations beneath the edifice in the south-central caldera and lower elevations in the eastern caldera, coinciding with the elevation of Laguna de Masaya. These TEM data, combined with regional hydrologic data, indicate that the caldera in hydrologically isolated from the surrounding region, with as much as 60??m of difference in elevation of the groundwater table across caldera-bounding faults. The water-table information and estimates of fluxes of water through the system were used to constrain a numerical simulation of groundwater flow. The simulation results indicate that basalt flows in the outer parts of the caldera have a relatively high transmissivity, whereas the central edifice has a substantially lower transmissivity. A layer of relatively high transmissivity must be present at depth within the edifice in order to deliver the observed flux of water and steam to the active vent. This hydrologic information about the caldera provides a baseline for assessing the response of this isolated groundwater system to future changes in magmatic activity. ?? 2007.

  17. An extended-Lagrangian scheme for charge equilibration in reactive molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Nomura, Ken-ichi; Small, Patrick E.; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

    2015-07-01

    Reactive molecular dynamics (RMD) simulations describe chemical reactions at orders-of-magnitude faster computing speed compared with quantum molecular dynamics (QMD) simulations. A major computational bottleneck of RMD is charge-equilibration (QEq) calculation to describe charge transfer between atoms. Here, we eliminate the speed-limiting iterative minimization of the Coulombic energy in QEq calculation by adapting an extended-Lagrangian scheme that was recently proposed in the context of QMD simulations, Souvatzis and Niklasson (2014). The resulting XRMD simulation code drastically improves energy conservation compared with our previous RMD code, Nomura et al. (2008), while substantially reducing the time-to-solution. The XRMD code has been implemented on parallel computers based on spatial decomposition, achieving a weak-scaling parallel efficiency of 0.977 on 786,432 IBM Blue Gene/Q cores for a 67.6 billion-atom system.

  18. Development of a New and Fast Linear Solver for Multi-component Reactive Transport Simulation

    NASA Astrophysics Data System (ADS)

    Qiao, C.; Li, L.; Bao, C.; Hu, X.; Johns, R.; Xu, J.

    2013-12-01

    Reactive transport models (RTM) have been extensively used to understand the coupling between solute transport and (bio) geochemical reactions in complex earth systems. RTM typically involves a large number of primary and secondary species with a complex reaction network in large domains. The computational expenses increase significantly with the number of grid blocks and the number of chemical species. Within both the operator splitting approach (OS) and the global implicit approach (GI) that are commonly used, the steps that involve Newton-Raphson method are typically one of the most time-consuming parts (up to 80% to 90% of CPU times). Under such circumstances, accelerating reactive transport simulation is very essential. In this research, we present a physics-based linear system solution strategy for general reactive transport models with many species. We observed up to five times speed up for the linear solver portion of the simulations in our test cases. Our new linear solver takes advantage of the sparsity of the Jacobian matrix arising from the reaction network. The Jacobian matrix for the speciation problem is typically considered as a dense matrix and solved with a direct method such as Gaussian elimination. For the reactive transport problem, the graph of the local Jacobian matrix has a one-to-one correspondence to the reaction network graph. The Jacobian matrix is commonly sparse and has the same sparsity structure for the same reaction network. We developed a strategy that performs a minimum degree of reordering and symbolic factorization to determine the non-zero pattern at the beginning of the OS and GI simulation. During the speciation calculation in OS, we calculate the L and U factors and solve the triangular matrices according to the non-zero pattern. For GI, our strategy can be applied to inverse the diagonal blocks in the block-Jacobi preconditioner and smoothers of the multigrid preconditioners in iterative solvers. Our strategy is naturally

  19. Analytical resolution of the reactive diffusion equation for transient electronics including materials whose porosity value changes in terms of their thickness

    NASA Astrophysics Data System (ADS)

    Vargas Toro, Agustín.

    2014-05-01

    Transient electronic devices are a new technology development whose main characteristic is that its components can disappear in a programmed and controlled way, which means such devices have a pre-engineered service life. Nowadays, transient electronics have a large application field, involving from the reduction of e-waste in the planet until the development of medical instruments and implants that can be discarded when the patients do not need it anymore, avoiding the trouble of having an extra procedure for them. These devices must be made from biocompatible materials avoiding long-term adverse effects in the environment and patients. It is fundamental to develop an analytical model that allows describing the behavior of these materials considering cases which its porosity may be constant or not, in presence of water or any other biofluid. In order to accomplish this analysis was solve the reactive diffusion equation based on Bromwich's integral and the Residue theorem for two material cases, those whose porosity is constant, and those whose porosity increases linearly in terms of its thickness, where was found a general expression. This allows to the analysis of the relation of the electric resistance (per unit length) and the rate of dissolution of the material.

  20. Atomistic Simulations of Chemical Reactivity of TATB Under Thermal and Shock Conditions

    SciTech Connect

    Manaa, M R; Reed, E J; Fried, L E

    2009-09-23

    The study of chemical transformations that occur at the reactive shock front of energetic materials provides important information for the development of predictive models at the grain-and continuum scales. A major shortcoming of current high explosives models is the lack of chemical kinetics data of the reacting explosive in the high pressure and temperature regimes. In the absence of experimental data, long-time scale atomistic molecular dynamics simulations with reactive chemistry become a viable recourse to provide an insight into the decomposition mechanism of explosives, and to obtain effective reaction rate laws. These rates can then be incorporated into thermo-chemical-hydro codes (such as Cheetah linked to ALE3D) for accurate description of the grain and macro scales dynamics of reacting explosives. In this talk, I will present quantum simulations of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) crystals under thermal decomposition (high density and temperature) and shock compression conditions. This is the first time that condensed phase quantum methods have been used to study the chemistry of insensitive high explosives. We used the quantum-based, self-consistent charge density functional tight binding method (SCC{_}DFTB) to calculate the interatomic forces for reliable predictions of chemical reactions, and to examine electronic properties at detonation conditions for a relatively long time-scale on the order of several hundreds of picoseconds. For thermal decomposition of TATB, we conducted constant volume-temperature simulations, ranging from 0.35 to 2 nanoseconds, at {rho} = 2.87 g/cm{sup 3} at T = 3500, 3000, 2500, and 1500 K, and {rho} = 2.9 g/cm{sup 3} and 2.72 g/cm{sup 3}, at T = 3000 K. We also simulated crystal TATB's reactivity under steady overdriven shock compression using the multi-scale shock technique. We conducted shock simulations with specified shock speeds of 8, 9, and 10 km/s for up to 0.43 ns duration, enabling us to track the

  1. Evaluating Transient Global and Regional Model Simulations: Bridging the Model/Observations Information Gap

    NASA Astrophysics Data System (ADS)

    Rutledge, G. K.; Karl, T. R.; Easterling, D. R.; Buja, L.; Stouffer, R.; Alpert, J.

    2001-05-01

    A major transition in our ability to evaluate transient Global Climate Model (GCM) simulations is occurring. Real-time and retrospective numerical weather prediction analysis, model runs, climate simulations and assessments are proliferating from a handful of national centers to dozens of groups across the world. It is clear that it is no longer sufficient for any one national center to develop its data services alone. The comparison of transient GCM results with the observational climate record is difficult for several reasons. One limitation is that the global distributions of a number of basic climate quantities, such as precipitation, are not well known. Similarly, observational limitations exist with model re-analysis data. Both the NCEP/NCAR, and the ECMWF, re-analysis eliminate the problems of changing analysis systems but observational data also contain time-dependant biases. These changes in input data are blended with the natural variability making estimates of true variability uncertain. The need for data homogeneity is critical to study questions related to the ability to evaluate simulation of past climate. One approach to correct for time-dependant biases and data sparse regions is the development and use of high quality 'reference' data sets. The primary U.S. National responsibility for the archive and service of weather and climate data rests with the National Climatic Data Center (NCDC). However, as supercomputers increase the temporal and spatial resolution of both Numerical Weather Prediction (NWP) and GCM models, the volume and varied formats of data presented for archive at NCDC, using current communications technologies and data management techniques is limiting the scientific access of these data. To address this ever expanding need for climate and NWP information, NCDC along with the National Center's for Environmental Prediction (NCEP) have initiated the NOAA Operational Model Archive and Distribution System (NOMADS). NOMADS is a

  2. Reactive transport of metal contaminants in alluvium - Model comparison and column simulation

    USGS Publications Warehouse

    Brown, J.G.; Bassett, R.L.; Glynn, P.D.

    2000-01-01

    A comparative assessment of two reactive-transport models, PHREEQC and HYDROGEOCHEM (HGC), was done to determine the suitability of each for simulating the movement of acidic contamination in alluvium. For simulations that accounted for aqueous complexation, precipitation and dissolution, the breakthrough and rinseout curves generated by each model were similar. The differences in simulated equilibrium concentrations between models were minor and were related to (1) different units in model output, (2) different activity coefficients, and (3) ionic-strength calculations. When adsorption processes were added to the models, the rinseout pH simulated by PHREEQC using the diffuse double-layer adsorption model rose to a pH of 6 after pore volume 15, about 1 pore volume later than the pH simulated by HGC using the constant-capacitance model. In PHREEQC simulation of a laboratory column experiment, the inability of the model to match measured outflow concentrations of selected constituents was related to the evident lack of local geochemical equilibrium in the column. The difference in timing and size of measured and simulated breakthrough of selected constituents indicated that the redox and adsorption reactions in the column occurred slowly when compared with the modeled reactions. MINTEQA2 and PHREEQC simulations of the column experiment indicated that the number of surface sites that took part in adsorption reactions was less than that estimated from the measured concentration of Fe hydroxide in the alluvium.

  3. Numerical simulation of reactive processes in an experiment with partially saturated bentonite

    NASA Astrophysics Data System (ADS)

    Xie, Mingliang; Bauer, Sebastian; Kolditz, Olaf; Nowak, Thomas; Shao, Hua

    2006-02-01

    Bentonites are preferred materials for use as engineered barriers for high-level nuclear waste repositories. Simulation of geochemical processes in bentonite is therefore important for long-term safety assessment of those repositories. In this work, the porewater chemistry of a bentonite sample subject to simultaneous heating and hydration, as studied by Cuevas et al. [Cuevas, J., Villar, M., Fernández, A., Gómez, P., Martín, P., 1997. Porewaters extracted from compacted bentonite subjected to simultaneous heating and hydration. Applied Geochemistry 12, 473-481.], was assessed with a non-isothermal reactive transport model by coupling the geochemical software PHREEQC2 with the object-oriented FEM simulator GeoSys/RockFlow. Reactive transport modelling includes heat transport, two-phase flow, multicomponent transport and geochemical reactions in the liquid phase, i.e. ion exchange, mineral dissolution/precipitation and equilibrium reactions. Simulations show that the easily soluble minerals in bentonite determine the porewater chemistry. Temperature affects both two-phase flow and geochemical reactions. Porosity change due to dissolution/precipitation is low during the experiment. However, changes of the effective porosity caused by bentonite swelling can be very large. The simulated results agree well with the experimental data.

  4. THC-MP: High performance numerical simulation of reactive transport and multiphase flow in porous media

    NASA Astrophysics Data System (ADS)

    Wei, Xiaohui; Li, Weishan; Tian, Hailong; Li, Hongliang; Xu, Haixiao; Xu, Tianfu

    2015-07-01

    The numerical simulation of multiphase flow and reactive transport in the porous media on complex subsurface problem is a computationally intensive application. To meet the increasingly computational requirements, this paper presents a parallel computing method and architecture. Derived from TOUGHREACT that is a well-established code for simulating subsurface multi-phase flow and reactive transport problems, we developed a high performance computing THC-MP based on massive parallel computer, which extends greatly on the computational capability for the original code. The domain decomposition method was applied to the coupled numerical computing procedure in the THC-MP. We designed the distributed data structure, implemented the data initialization and exchange between the computing nodes and the core solving module using the hybrid parallel iterative and direct solver. Numerical accuracy of the THC-MP was verified through a CO2 injection-induced reactive transport problem by comparing the results obtained from the parallel computing and sequential computing (original code). Execution efficiency and code scalability were examined through field scale carbon sequestration applications on the multicore cluster. The results demonstrate successfully the enhanced performance using the THC-MP on parallel computing facilities.

  5. Comparing approaches for simulating the reactive transport of U(VI) in ground water

    USGS Publications Warehouse

    Curtis, G.P.; Kohler, M.; Davis, J.A.

    2009-01-01

    The reactive transport of U(VI) in a well-characterized shallow alluvial aquifer at a former U(VI) mill located near Naturita, CO, was predicted for comparative purposes using a surface complexation model (SCM) and a constant K d approach to simulate U(VI) adsorption. The ground water at the site had U(VI) concentrations that ranged from 0.01 to 20 ??M, alkalinities that ranged from 2.5 to 18 meq/L, and a nearly constant pH of 7.1. The SCM used to simulate U(VI) adsorption was previously determined independently using laboratory batch adsorption experiments. Simulations obtained using the SCM approach were compared with simulations that used a constant K d approach to simulate adsorption using previously determined site-specific K d values. In both cases, the ground water flow and transport models used a conceptual model that was previously calibrated to a chloride plume present at the site. Simulations with the SCM approach demonstrated that the retardation factor varied temporally and spatially because of the differential transport of alkalinity and dissolved U(VI) and the nonlinearity of the U(VI) adsorption. The SCM model also simulated a prolonged slow decline in U(VI) concentration, which was not simulated using a constant K d model. Simulations using the SCM approach and the constant K d approach were similar after 20 years of transport but diverged significantly after 60 years. The simulations demonstrate the need for site-specific geochemical information on U(VI) adsorption to produce credible simulations of future transport. ?? 2009 Springer-Verlag.

  6. Cerebral blood flow and CO/sub 2/ reactivity in transient ischemic attacks: comparison between TIAs due to the ICA occlusion and ICA mild stenosis

    SciTech Connect

    Tsuda, Y.; Kimura, K.; Yoneda, S.; Etani, H.; Asai, T.; Nakamura, M.; Abe, H.

    1983-01-01

    Hemispheric mean cerebral blood flow (CBF), together with its CO2 reactivity in response to hyperventilation, was investigated in 18 patients with transient ischemic attacks (TIAs) by intraarterial 133Xe injection method in a subacute-chronic stage of the clinical course. In 8 patients, the lesion responsible for symptoms was regarded as unilateral internal carotid artery (ICA) occlusion, and in 10 patients, it was regarded as unilateral ICA mild stenosis (less than 50% stenosis in diameter). Resting flow values were significantly decreased in the affected hemisphere of TIA due to the ICA occlusion as compared with the unaffected hemisphere of the same patient, regarded as the relative control. It was not decreased in the affected hemisphere of TIA due to the ICA mild stenosis as compared with the control. With respect to the responsiveness of CBF to changes in PaCO2, it was preserved in both TIAs, due to the ICA occlusion and ICA mild stenosis. Vasoparalysis was not observed in either types of TIAs in the subacute-chronic stage. However, in the relationship of blood pressure and CO2 reactivity, expressed as delta CBF(%)/delta PaCO2, pressure-dependent CO2 reactivity as a group was observed with significance in 8 cases of TIA due to the ICA occlusion, while no such relationship was noted in 10 cases of TIA due to the ICA mild stenosis. Moreover, clinical features were different between TIAs due to the ICA occlusion and ICA mild stenosis, i.e., more typical, repeatable TIA (6.3 +/- 3.7 times) with shorter duration (less than 30 minutes) was observed in TIAs due to the ICA mild stenosis, while more prolonged, less repeatable TIA (2.4 +/- 1.4 times) was observed in TIAs due to fixed obstruction of the ICA. From these observations, two different possible mechanisms as to the pathogenesis of TIA might be expected.

  7. A hybrid model for coupling kinetic corrections of fusion reactivity to hydrodynamic implosion simulations

    NASA Astrophysics Data System (ADS)

    Tang, Xian-Zhu; McDevitt, C. J.; Guo, Zehua; Berk, H. L.

    2014-03-01

    Inertial confinement fusion requires an imploded target in which a central hot spot is surrounded by a cold and dense pusher. The hot spot/pusher interface can take complicated shape in three dimensions due to hydrodynamic mix. It is also a transition region where the Knudsen and inverse Knudsen layer effect can significantly modify the fusion reactivity in comparison with the commonly used value evaluated with background Maxwellians. Here, we describe a hybrid model that couples the kinetic correction of fusion reactivity to global hydrodynamic implosion simulations. The key ingredient is a non-perturbative treatment of the tail ions in the interface region where the Gamow ion Knudsen number approaches or surpasses order unity. The accuracy of the coupling scheme is controlled by the precise criteria for matching the non-perturbative kinetic model to perturbative solutions in both configuration space and velocity space.

  8. An Improvement of Stillinger-Weber Interatomic Potential Model for Reactive Ion Etching Simulations

    NASA Astrophysics Data System (ADS)

    Ohta, Hiroaki; Nagaoka, Tatsuya; Eriguchi, Koji; Ono, Kouichi

    2009-02-01

    An approach to improve the interatomic potential model by Stillinger and Weber (SW), which has been frequently utilized for molecular dynamics simulations of energetic-particle-induced surface reactions, was proposed. It was found that this well-known model for Si/halogen systems had a flaw in its three-body potential form if it was applied to reactive ion etching simulations. The repulsive interaction is overestimated owing to the simple summation form ∑i, j,khjik when a halogen atom is surrounded by more than three atoms. This situation always occurs when a high-energy halogen penetrates a Si lattice and, in this case, the penetration energy into the lattice is overestimated. The test simulations using our model showed that the surface structures predicted were markedly different from those using the original model. This improved model has a profound effect on the prediction of surface structures.

  9. High-Performance Reactive Fluid Flow Simulations Using Adaptive Mesh Refinement on Thousands of Processors

    NASA Astrophysics Data System (ADS)

    Calder, A. C.; Curtis, B. C.; Dursi, L. J.; Fryxell, B.; Henry, G.; MacNeice, P.; Olson, K.; Ricker, P.; Rosner, R.; Timmes, F. X.; Tufo, H. M.; Truran, J. W.; Zingale, M.

    We present simulations and performance results of nuclear burning fronts in supernovae on the largest domain and at the finest spatial resolution studied to date. These simulations were performed on the Intel ASCI-Red machine at Sandia National Laboratories using FLASH, a code developed at the Center for Astrophysical Thermonuclear Flashes at the University of Chicago. FLASH is a modular, adaptive mesh, parallel simulation code capable of handling compressible, reactive fluid flows in astrophysical environments. FLASH is written primarily in Fortran 90, uses the Message-Passing Interface library for inter-processor communication and portability, and employs the PARAMESH package to manage a block-structured adaptive mesh that places blocks only where the resolution is required and tracks rapidly changing flow features, such as detonation fronts, with ease. We describe the key algorithms and their implementation as well as the optimizations required to achieve sustained performance of 238 GLOPS on 6420 processors of ASCI-Red in 64-bit arithmetic.

  10. Decoration of gold nanoparticles with cysteine in solution: reactive molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Monti, Susanna; Carravetta, Vincenzo; Ågren, Hans

    2016-06-01

    The dynamics of gold nanoparticle functionalization by means of adsorption of cysteine molecules in water solution is simulated through classical reactive molecular dynamics simulations based on an accurately parametrized force field. The adsorption modes of the molecules are characterized in detail disclosing the nature of the cysteine-gold interactions and the stability of the final material. The simulation results agree satisfactorily with recent experimental and theoretical data and confirm previous findings for a similar system. The covalent attachments of the molecules to the gold support are all slow physisorptions followed by fast chemisorptions. However, a great variety of binding arrangements can be observed. Interactions with the adsorbate caused surface modulations in terms of adatoms and dislocations which contributed to strengthen the cysteine adsorption.The dynamics of gold nanoparticle functionalization by means of adsorption of cysteine molecules in water solution is simulated through classical reactive molecular dynamics simulations based on an accurately parametrized force field. The adsorption modes of the molecules are characterized in detail disclosing the nature of the cysteine-gold interactions and the stability of the final material. The simulation results agree satisfactorily with recent experimental and theoretical data and confirm previous findings for a similar system. The covalent attachments of the molecules to the gold support are all slow physisorptions followed by fast chemisorptions. However, a great variety of binding arrangements can be observed. Interactions with the adsorbate caused surface modulations in terms of adatoms and dislocations which contributed to strengthen the cysteine adsorption. Electronic supplementary information (ESI) available: Different views of the AuNP surface coverage. Distance map describing the position of each molecule in relation to the others on the AuNP (alpha carbon distances). See DOI: 10.1039/C

  11. Compressible, diffusive, reactive flow simulations of the double Mach reflection phenomenon

    NASA Astrophysics Data System (ADS)

    Ziegler, J. L.; Deiterding, R.; Shepherd, J. E.; Pullin, D. I.

    2010-11-01

    We describe direct numerical simulations of the multi-component, compressible, reactive Navier-Stokes equations in two spatial dimensions. The simulations utilize a hybrid, WENO/centered-difference numerical method, with low numerical dissipation, high-order shock-capturing, and structured adaptive mesh refinement (SAMR). These features enable resolution of diffusive processes within reaction zones. A series of one- and two-dimensional test problems are used to verify the implementation, specifically the high-order accuracy of the diffusion terms, including a viscous shock wave, the decaying Lamb-Oseen vortex, laminar flame and unstable ZND detonation. High-resolution simulations are discussed of the reactive double Mach reflection phenomenon. The diffusive scales (shear/mixing/boundary layers and flame thicknesses) and weak shocks are resolved while the strong shocks emanating from the triple points are captured. Additionally, a minimally reduced chemistry and transport model for hydrocarbon detonation is used to accurately capture the induction time, chemical relaxation, and the diffusive mixing within vortical structures evolving from the triple-point shear layer.

  12. ReaxFF reactive force field for molecular dynamics simulations of hydrocarbon oxidation.

    PubMed

    Chenoweth, Kimberly; van Duin, Adri C T; Goddard, William A

    2008-02-01

    To investigate the initial chemical events associated with high-temperature gas-phase oxidation of hydrocarbons, we have expanded the ReaxFF reactive force field training set to include additional transition states and chemical reactivity of systems relevant to these reactions and optimized the force field parameters against a quantum mechanics (QM)-based training set. To validate the ReaxFF potential obtained after parameter optimization, we performed a range of NVT-MD simulations on various hydrocarbon/O2 systems. From simulations on methane/O2, o-xylene/O2, propene/O2, and benzene/O2 mixtures, we found that ReaxFF obtains the correct reactivity trend (propene > o-xylene > methane > benzene), following the trend in the C-H bond strength in these hydrocarbons. We also tracked in detail the reactions during a complete oxidation of isolated methane, propene, and o-xylene to a CO/CO2/H2O mixture and found that the pathways predicted by ReaxFF are in agreement with chemical intuition and our QM results. We observed that the predominant initiation reaction for oxidation of methane, propene, and o-xylene under fuel lean conditions involved hydrogen abstraction of the methyl hydrogen by molecular oxygen forming hydroperoxyl and hydrocarbon radical species. While under fuel rich conditions with a mixture of these hydrocarbons, we observed different chemistry compared with the oxidation of isolated hydrocarbons including a change in the type of initiation reactions, which involved both decomposition of the hydrocarbon or attack by other radicals in the system. Since ReaxFF is capable of simulating complicated reaction pathways without any preconditioning, we believe that atomistic modeling with ReaxFF provides a useful method for determining the initial events of oxidation of hydrocarbons under extreme conditions and can enhance existing combustion models. PMID:18197648

  13. Reactive oxygen species and antioxidant enzymes activity of Anabaena sp. PCC 7120 (Cyanobacterium) under simulated microgravity

    NASA Astrophysics Data System (ADS)

    Li, Gen-bao; Liu, Yong-ding; Wang, Gao-hong; Song, Li-rong

    2004-12-01

    It was found that reactive oxygen species in Anabaena cells increased under simulated microgravity provided by clinostat. Activities of intracellular antioxidant enzymes, such as superoxide dismutase, catalase were higher than those in the controlled samples during the 7 days' experiment. However, the contents of gluathione, an intracellular antioxidant, decreased in comparison with the controlled samples. The results suggested that microgravity provided by clinostat might break the oxidative/antioxidative balance. It indicated a protective mechanism in algal cells, that the total antioxidant system activity increased, which might play an important role for algal cells to adapt the environmental stress of microgravity.

  14. Numerical simulation of fracture permeability evolution due to reactive transport and pressure solution processes

    NASA Astrophysics Data System (ADS)

    Watanabe, N.; Sun, Y.; Taron, J.; Shao, H.; Kolditz, O.

    2013-12-01

    Modeling fracture permeability evolution is of great interest in various geotechnical applications including underground waste repositories, carbon capture and storage, and engineered geothermal systems where fractures dominate transport behaviors. In this study, a numerical model is presented to simulate fracture permeability evolution due to reactive transport and pressure solution processes in single fractures. The model was developed within the international benchmarking project for radioactive waste disposals, DECOVALEX 2015 (Task C1). The model combines bulk behavior in pore spaces with intergranular process at asperity contacts. Hydraulic flow and reactive transport including mineral dissolution and precipitation in fracture pore space are simulated using the Galerkin finite element method. A pressure solution model developed by Taron and Elsworth (2010 JGR) is applied to simulating stress-enhanced dissolution, solute exchange with pore space, and volume removal at grain contacts. Fracture aperture and contact area ratio are updated as a result of the pore-space reaction and intergranular dissolution. In order to increase robustness and time step size, relevant processes are monolithically coupled with the simulations. The model is implemented in a scientific open-source project OpenGeoSys (www.opengeosys.org) for numerical simulation of thermo-hydro-mechanical/chemical processes in porous and fractured media. Numerical results are compared to previous experiment performed by Yasuhara et al. (2006) on flow through fractures in the Arkansas novaculite sample. The novaculite is approximated as pure quartz aggregates. Only with fitted quartz dissolution rate constants and solubility is the current model capable of reproducing observed hydraulic aperture reduction and aqueous silicate concentrations. Future work will examine reaction parameters and further validate the model against experimental results.

  15. Stochastic downscaling of numerically simulated spatial rain and cloud fields using a transient multifractal approach

    NASA Astrophysics Data System (ADS)

    Nogueira, M.; Barros, A. P.; Miranda, P. M.

    2012-04-01

    Atmospheric fields can be extremely variable over wide ranges of spatial scales, with a scale ratio of 109-1010 between largest (planetary) and smallest (viscous dissipation) scale. Furthermore atmospheric fields with strong variability over wide ranges in scale most likely should not be artificially split apart into large and small scales, as in reality there is no scale separation between resolved and unresolved motions. Usually the effects of the unresolved scales are modeled by a deterministic bulk formula representing an ensemble of incoherent subgrid processes on the resolved flow. This is a pragmatic approach to the problem and not the complete solution to it. These models are expected to underrepresent the small-scale spatial variability of both dynamical and scalar fields due to implicit and explicit numerical diffusion as well as physically based subgrid scale turbulent mixing, resulting in smoother and less intermittent fields as compared to observations. Thus, a fundamental change in the way we formulate our models is required. Stochastic approaches equipped with a possible realization of subgrid processes and potentially coupled to the resolved scales over the range of significant scale interactions range provide one alternative to address the problem. Stochastic multifractal models based on the cascade phenomenology of the atmosphere and its governing equations in particular are the focus of this research. Previous results have shown that rain and cloud fields resulting from both idealized and realistic numerical simulations display multifractal behavior in the resolved scales. This result is observed even in the absence of scaling in the initial conditions or terrain forcing, suggesting that multiscaling is a general property of the nonlinear solutions of the Navier-Stokes equations governing atmospheric dynamics. Our results also show that the corresponding multiscaling parameters for rain and cloud fields exhibit complex nonlinear behavior

  16. Enhancing chemical identification efficiency by SAW sensor transients through a data enrichment and information fusion strategy—a simulation study

    NASA Astrophysics Data System (ADS)

    Singh, Prashant; Yadava, R. D. S.

    2013-05-01

    The paper proposes a new approach for improving the odor recognition efficiency of a surface acoustic wave (SAW) transient sensor system based on a single polymer coating. The vapor identity information is hidden in transient response shapes through dependences on specific vapor solvation and diffusion parameters in the polymer coating. The variations in the vapor exposure and purge durations and the sensor operating frequency have been used to create diversity in transient shapes via termination of the vapor-polymer equilibration process up to different stages. The transient signals were analyzed by the discrete wavelet transform using Daubechies-4 mother wavelet basis. The wavelet approximation coefficients were then processed by principal component analysis for creating feature space. The set of principal components define the vapor identity information. In an attempt to enhance vapor class separability we analyze two types of information fusion methods. In one, the sensor operation frequency is fixed and the sensing and purge durations are varied, and in the second, the sensing and purge durations are fixed and the sensor operating frequency is varied. The fusion is achieved by concatenation of discrete wavelet coefficients corresponding to various transients prior to the principal component analysis. The simulation experiments with polyisobutylene SAW sensor coating for operation frequencies over [55-160] MHz and sensing durations over [5-60] s were analyzed. The target vapors are seven volatile organics: chloroform, chlorobenzene, o-dichlorobenzene, n-heptane, toluene, n-hexane and n-octane whose concentrations were varied over [10-100] ppm. The simulation data were generated using a SAW sensor transient response model that incorporates the viscoelastic effects due to polymer coating and an additive noise source in the output. The analysis reveals that: (i) in single transient analysis the class separability increases with sensing duration for a given

  17. Investigating short-pulse shock initiation thresholds in HMX-based explosives with reactive mesoscale simulations

    NASA Astrophysics Data System (ADS)

    Springer, H.; May, C.; Tarver, C.; Reaugh, J.

    2013-06-01

    Short-pulse loading experiments have demonstrated the probabilistic nature of shock initiation thresholds in a variety of explosives. The intensely loaded region of explosive adjacent to the flyer impact zone, and its potential hot spots, influences the overall sample shock sensitivity. As the size of this region decreases below the representative volume element size, the likelihood of sampling differing hot spot densities in it increases from sample to sample. We hypothesize that this variation in active hot spots contributes to the probabilistic nature of short-pulse shock initiation. We investigate the role of microstructure and explosive reactive properties on shock initiation response with mesoscale simulations of miniature flyer plate experiments. LX-10 (95%wt HMX, 5%wt Viton A) is the model explosive. To investigate the influence of microstructure, we vary void size and spatial position. While void volume fraction and HMX grain size distributions are fixed, assigning random spatial positions to these parameters leads to hot spot density variations over many microstructural realizations. HMX reactivity is also investigated. The influences of microstructure and reactivity parameters are discussed. This study enables the development of predictive shock sensitivity models with basic structure-property information. This work performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344. This work was funded in part by the Joint DoD-DOE Munitions Program.

  18. Decolourisation of simulated reactive dyebath effluents by electrochemical oxidation assisted by UV light.

    PubMed

    López-Grimau, V; Gutiérrez, M C

    2006-01-01

    This study is focused on the optimisation of the electrochemical decolourisation of textile effluents containing reactive dyes with the aim of making feasible-technically and economically-this method at industrial scale. Coloured waters were treated in continuous at low current density, to reduce the electrical consumption. Ti/PtO(x) electrodes were used to oxidize simulated dyebaths prepared with an azo/dichlorotriazine reactive dye (C.I. Reactive Orange 4). The decolourisation yield was dependent on the dyeing electrolyte (NaCl or Na(2)SO(4)). Dyeing effluents which contained from 0.5 to 20 gl(-1) of NaCl reached a high decolourisation yield, depending on the current density, immediately after the electrochemical process. These results were improved when the effluents were stored for several hours under solar light. After the electrochemical treatment the effluents were stored in a tank and exposed under different lighting conditions: UV light, solar light and darkness. The evolution of the decolourisation versus the time of storage was reported and kinetic constants were calculated. The time of storage was significantly reduced by the application of UV light. A dye mineralization study was also carried out on a concentrated dyebath. A TOC removal of 81% was obtained when high current density was applied for a prolonged treatment with recirculation. This treatment required a high electrical consumption.

  19. Large Eddy Simulation of Transient Flow and Inclusions Transport in Continuous Casting Mold under Different Electromagnetic Brakes

    NASA Astrophysics Data System (ADS)

    Liu, Zhongqiu; Li, Linmin; Li, Baokuan

    2016-08-01

    A mathematical model has been developed to analyze transient fluid flow and inclusions transport in a slab continuous casting mold, considering the effects of electromagnetic brake (EMBr) arrangement and magnetic field strength. Transient flow of molten steel in the mold is calculated by using the large eddy simulation. The electromagnetic force is incorporated into the Navier-Stokes equation. The transport of inclusion inside the mold is calculated using the Lagrangian approach based on the transient flow field. The predicted results of this model are compared with the measurements of the ultrasonic testing of the rolled steel plates and the water model experiments. The transient asymmetrical flow pattern and inclusion transport inside the mold exhibits satisfactory agreement with the corresponding measurements. With electromagnetic brake effect, the velocities around the braking region are significantly suppressed, and the recirculating flow in the lower part drops and tends to develop a plug-like flow. The EMBr arrangement has an insignificant effect on the overall removal fraction of inclusions, especially for larger inclusions. The inclusion removal rate for the flow-control mold (FCM arrangement) reduces instead compared with no EMBr, especially for smaller inclusions.

  20. eReaxFF: A Pseudoclassical Treatment of Explicit Electrons within Reactive Force Field Simulations.

    PubMed

    Islam, Md Mahbubul; Kolesov, Grigory; Verstraelen, Toon; Kaxiras, Efthimios; van Duin, Adri C T

    2016-08-01

    We present a computational tool, eReaxFF, for simulating explicit electrons within the framework of the standard ReaxFF reactive force field method. We treat electrons explicitly in a pseudoclassical manner that enables simulation several orders of magnitude faster than quantum chemistry (QC) methods, while retaining the ReaxFF transferability. We delineate here the fundamental concepts of the eReaxFF method and the integration of the Atom-condensed Kohn-Sham DFT approximated to second order (ACKS2) charge calculation scheme into the eReaxFF. We trained our force field to capture electron affinities (EA) of various species. As a proof-of-principle, we performed a set of molecular dynamics (MD) simulations with an explicit electron model for representative hydrocarbon radicals. We establish a good qualitative agreement of EAs of various species with experimental data, and MD simulations with eReaxFF agree well with the corresponding Ehrenfest dynamics simulations. The standard ReaxFF parameters available in the literature are transferrable to the eReaxFF method. The computationally economic eReaxFF method will be a useful tool for studying large-scale chemical and physical systems with explicit electrons as an alternative to computationally demanding QC methods. PMID:27399177

  1. eReaxFF: A Pseudoclassical Treatment of Explicit Electrons within Reactive Force Field Simulations.

    PubMed

    Islam, Md Mahbubul; Kolesov, Grigory; Verstraelen, Toon; Kaxiras, Efthimios; van Duin, Adri C T

    2016-08-01

    We present a computational tool, eReaxFF, for simulating explicit electrons within the framework of the standard ReaxFF reactive force field method. We treat electrons explicitly in a pseudoclassical manner that enables simulation several orders of magnitude faster than quantum chemistry (QC) methods, while retaining the ReaxFF transferability. We delineate here the fundamental concepts of the eReaxFF method and the integration of the Atom-condensed Kohn-Sham DFT approximated to second order (ACKS2) charge calculation scheme into the eReaxFF. We trained our force field to capture electron affinities (EA) of various species. As a proof-of-principle, we performed a set of molecular dynamics (MD) simulations with an explicit electron model for representative hydrocarbon radicals. We establish a good qualitative agreement of EAs of various species with experimental data, and MD simulations with eReaxFF agree well with the corresponding Ehrenfest dynamics simulations. The standard ReaxFF parameters available in the literature are transferrable to the eReaxFF method. The computationally economic eReaxFF method will be a useful tool for studying large-scale chemical and physical systems with explicit electrons as an alternative to computationally demanding QC methods.

  2. Integrated atomistic chemical imaging and reactive force field molecular dynamic simulations on silicon oxidation

    SciTech Connect

    Dumpala, Santoshrupa; Broderick, Scott R.; Rajan, Krishna; Khalilov, Umedjon; Neyts, Erik C.; Duin, Adri C. T. van; Provine, J; Howe, Roger T.

    2015-01-05

    In this paper, we quantitatively investigate with atom probe tomography, the effect of temperature on the interfacial transition layer suboxide species due to the thermal oxidation of silicon. The chemistry at the interface was measured with atomic scale resolution, and the changes in chemistry and intermixing at the interface were identified on a nanometer scale. We find an increase of suboxide (SiOx) concentration relative to SiO{sub 2} and increased oxygen ingress with elevated temperatures. Our experimental findings are in agreement with reactive force field molecular dynamics simulations. This work demonstrates the direct comparison between atom probe derived chemical profiles and atomistic-scale simulations for transitional interfacial layer of suboxides as a function of temperature.

  3. A Modular Computer Code for Simulating Reactive Multi-Species Transport in 3-Dimensional Groundwater Systems

    SciTech Connect

    TP Clement

    1999-06-24

    RT3DV1 (Reactive Transport in 3-Dimensions) is computer code that solves the coupled partial differential equations that describe reactive-flow and transport of multiple mobile and/or immobile species in three-dimensional saturated groundwater systems. RT3D is a generalized multi-species version of the US Environmental Protection Agency (EPA) transport code, MT3D (Zheng, 1990). The current version of RT3D uses the advection and dispersion solvers from the DOD-1.5 (1997) version of MT3D. As with MT3D, RT3D also requires the groundwater flow code MODFLOW for computing spatial and temporal variations in groundwater head distribution. The RT3D code was originally developed to support the contaminant transport modeling efforts at natural attenuation demonstration sites. As a research tool, RT3D has also been used to model several laboratory and pilot-scale active bioremediation experiments. The performance of RT3D has been validated by comparing the code results against various numerical and analytical solutions. The code is currently being used to model field-scale natural attenuation at multiple sites. The RT3D code is unique in that it includes an implicit reaction solver that makes the code sufficiently flexible for simulating various types of chemical and microbial reaction kinetics. RT3D V1.0 supports seven pre-programmed reaction modules that can be used to simulate different types of reactive contaminants including benzene-toluene-xylene mixtures (BTEX), and chlorinated solvents such as tetrachloroethene (PCE) and trichloroethene (TCE). In addition, RT3D has a user-defined reaction option that can be used to simulate any other types of user-specified reactive transport systems. This report describes the mathematical details of the RT3D computer code and its input/output data structure. It is assumed that the user is familiar with the basics of groundwater flow and contaminant transport mechanics. In addition, RT3D users are expected to have some experience in

  4. Transient elastohydrodynamic lubrication analysis of metal-on-metal hip implant under simulated walking conditions.

    PubMed

    Liu, F; Jin, Z M; Hirt, F; Rieker, C; Roberts, P; Grigoris, P

    2006-01-01

    The transient elastohydrodynamic lubrication (EHL) analysis was performed in this study for a typical metal-on-metal bearing employing a polyethylene backing underneath a metallic cup inlay under dynamic operating conditions of load and speed representative of normal walking. A ball-in-socket configuration was adopted to represent the articulation between the femoral head and the acetabular cup. The governing Reynolds and elasticity equations were solved simultaneously by using both finite difference and finite element methods. The predicted transient film thickness from the present study was compared with the estimation based on the quasi-static analysis. It was found that the polyethylene backing employed in the typical metal-on-metal hip bearing, combined with dynamic squeeze-film action, significantly improved the transient lubricant film thickness under cyclic walking and consequently a fluid film lubrication regime was possible for smooth bearing surfaces with an average roughness less than 0.005 microm.

  5. Enhancing the ABAQUS Thermomechanics Code to Simulate Steady and Transient Fuel Rod Behavior

    SciTech Connect

    R. L. Williamson; D. A. Knoll

    2009-09-01

    A powerful multidimensional fuels performance capability, applicable to both steady and transient fuel behavior, is developed based on enhancements to the commercially available ABAQUS general-purpose thermomechanics code. Enhanced capabilities are described, including: UO2 temperature and burnup dependent thermal properties, solid and gaseous fission product swelling, fuel densification, fission gas release, cladding thermal and irradiation creep, cladding irradiation growth , gap heat transfer, and gap/plenum gas behavior during irradiation. The various modeling capabilities are demonstrated using a 2D axisymmetric analysis of the upper section of a simplified multi-pellet fuel rod, during both steady and transient operation. Computational results demonstrate the importance of a multidimensional fully-coupled thermomechanics treatment. Interestingly, many of the inherent deficiencies in existing fuel performance codes (e.g., 1D thermomechanics, loose thermo-mechanical coupling, separate steady and transient analysis, cumbersome pre- and post-processing) are, in fact, ABAQUS strengths.

  6. Simulated gastrointestinal digestion reduces the allergic reactivity of shrimp extract proteins and tropomyosin.

    PubMed

    Gámez, Cristina; Zafra, Ma Paz; Sanz, Verónica; Mazzeo, Carla; Ibáñez, Ma Dolores; Sastre, Joaquín; del Pozo, Victoria

    2015-04-15

    Shrimp are highly allergenic foods. Current management are limited to the avoidance of foods. Therefore, there is an unmet need for a safe and effective therapy using modified allergens. This study focuses on assessing the potential for modification of the allergenicity of shrimp proteins following heat treatment or simulated gastric digestion. Shrimp proteins do not reduce their IgE reactivity after heat treatment but it is reduced by simulated gastric digestion in a time- and dose-dependent manner. Tropomyosin in shrimp extract is worse digested than purified tropomyosin. After 60 min of 10 U/μg pepsin digestion, a strong inhibition was produced in the in vivo skin reactivity of shrimp extracts and in activation of basophils from allergic patients. Immunisation experiments performed in rabbits demonstrated that digested boiled shrimp extract is able to induce IgG antibodies that block the IgE binding to the untreated boiled shrimp extract in shrimp-allergic patients. Building on our observations, digestion treatment could be an effective method for reducing shrimp allergenicity while maintaining the immunogenicity.

  7. Increased expression of Slit2 and its receptors Robo1 and Robo4 in reactive astrocytes of the rat hippocampus after transient forebrain ischemia.

    PubMed

    Park, Joo-Hee; Pak, Ha-Jin; Riew, Tae-Ryong; Shin, Yoo-Jin; Lee, Mun-Yong

    2016-03-01

    Slit2 is a secreted glycoprotein that was originally identified as a chemorepulsive factor in the developing brain; however, it was recently reported that Slit2 is associated with adult neuronal function including a variety of pathophysiological processes. To elucidate whether Slit2 is implicated in the pathophysiology of ischemic injury, we investigated the temporal changes and cellular localization of Slit2 and its predominant receptors, Robo1 and Robo4, for 28 days after transient forebrain ischemia. Slit2 and its receptors had similar overall expression patterns in the control and ischemic hippocampi. The ligand and receptors were constitutively expressed in hippocampal neurons in control animals; however, in animals with ischemic injury, their upregulation was detected in reactive astrocytes, but not in neurons or activated microglia, in the CA1 region. Astroglial induction of Slit2 and its receptors occurred by day 3 after reperfusion, and appeared to increase progressively until the final time point on day 28. Their temporal expression patterns overlapped with the time period in which reactive astrocytes undergo dynamic structural changes and appear hypertrophic in the ischemic hippocampus. The immunohistochemical data were consistent with the results of the immunoblot analyses, indicating that the expression of Slit2 and Robo increased progressively over the relatively long period of 28 days examined here. Collectively, these results suggest that Slit2/Robo signaling may be involved in regulating the astroglial reaction via autocrine or paracrine mechanisms in post-ischemic processes. Moreover, this may contribute to the dynamic morphological changes that occur in astrocytes in response to ischemic injury.

  8. Tracking reactive pollutants in large groundwater systems by particle-based simulations

    NASA Astrophysics Data System (ADS)

    Kalbacher, T.; Sun, Y.; He, W.; Jang, E.; Delfs, J.; Shao, H.; Park, C.; Kolditz, O.

    2013-12-01

    Worldwide, great amounts of human and financial resources are being invested to protect and secure clean water resources. Especially in arid and semi-arid regions civilization depends on the availability of freshwater from the underlying aquifer systems where water quality and quantity are often dramatically deteriorating. Main reasons for the mitigation of water quality are extensive fertilizer use in agriculture and waste water from cities and various industries. It may be assumed that climate and demographic changes will add further stress to this situation in the future. One way to assess water quality is to model the coupled groundwater and chemical system, e.g.to assess the impact of possible contaminant precipitation, absorption and migration in subsurface media. Currently, simulating such scenarios at large scales is a challenging task due to the extreme computational load, numerical stability issues, scale-dependencies and spatially and temporally infrequently distributed or missing data, which can lead e.g. to in appropriate model simplifications and additionally uncertainties in the results. The simulation of advective-dispersive mass transport is usually solved by standard finite differences, finite element or finite volume methods. Particle tracking is an alternative method and commonly used e.g. to delineate contaminant travel times, with the advantage of being numerically more stable and computational less expensive. Since particle tracking is used to evaluate groundwater residence times, it seems natural and straightforward to include reactive processes to track geochemical changes as well. The main focus of the study is the evaluation of reactive transport processes at large scales. Therefore, a number of new methods have been developed and implemented into the OpenGeoSys project, which is a scientific, FEM-based, open source code for numerical simulation of thermo-hydro-mechanical-chemical processes in porous and fractured media (www

  9. Reactive wetting properties of TiO2 nanoparticles predicted by ab initio molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Brandt, Erik G.; Agosta, Lorenzo; Lyubartsev, Alexander P.

    2016-07-01

    Small-sized wet TiO2 nanoparticles have been investigated by ab initio molecular dynamics simulations. Chemical and physical adsorption of water on the TiO2-water interface was studied as a function of water content, ranging from dry nanoparticles to wet nanoparticles with monolayer coverage of water. The surface reactivity was shown to be a concave function of water content and driven by surface defects. The local coordination number at the defect was identified as the key factor to decide whether water adsorption proceeds through dissociation or physisorption on the surface. A consistent picture of TiO2 nanoparticle wetting at the microscopic level emerges, which corroborates existing experimental data and gives further insight into the molecular mechanisms behind nanoparticle wetting. These calculations will facilitate the engineering of metal oxide nanoparticles with a controlled catalytic water activity.Small-sized wet TiO2 nanoparticles have been investigated by ab initio molecular dynamics simulations. Chemical and physical adsorption of water on the TiO2-water interface was studied as a function of water content, ranging from dry nanoparticles to wet nanoparticles with monolayer coverage of water. The surface reactivity was shown to be a concave function of water content and driven by surface defects. The local coordination number at the defect was identified as the key factor to decide whether water adsorption proceeds through dissociation or physisorption on the surface. A consistent picture of TiO2 nanoparticle wetting at the microscopic level emerges, which corroborates existing experimental data and gives further insight into the molecular mechanisms behind nanoparticle wetting. These calculations will facilitate the engineering of metal oxide nanoparticles with a controlled catalytic water activity. Electronic supplementary information (ESI) available: Simulation data on equilibration of energies and structures (root-mean-square-deviations and

  10. Phast4Windows: a 3D graphical user interface for the reactive-transport simulator PHAST.

    PubMed

    Charlton, Scott R; Parkhurst, David L

    2013-01-01

    Phast4Windows is a Windows® program for developing and running groundwater-flow and reactive-transport models with the PHAST simulator. This graphical user interface allows definition of grid-independent spatial distributions of model properties-the porous media properties, the initial head and chemistry conditions, boundary conditions, and locations of wells, rivers, drains, and accounting zones-and other parameters necessary for a simulation. Spatial data can be defined without reference to a grid by drawing, by point-by-point definitions, or by importing files, including ArcInfo® shape and raster files. All definitions can be inspected, edited, deleted, moved, copied, and switched from hidden to visible through the data tree of the interface. Model features are visualized in the main panel of the interface, so that it is possible to zoom, pan, and rotate features in three dimensions (3D). PHAST simulates single phase, constant density, saturated groundwater flow under confined or unconfined conditions. Reactions among multiple solutes include mineral equilibria, cation exchange, surface complexation, solid solutions, and general kinetic reactions. The interface can be used to develop and run simple or complex models, and is ideal for use in the classroom, for analysis of laboratory column experiments, and for development of field-scale simulations of geochemical processes and contaminant transport.

  11. Micron-scale Reactive Atomistic Simulation of Void Collapse and Hotspot Growth in PETN

    NASA Astrophysics Data System (ADS)

    Thompson, Aidan; Shan, Tzu-Ray

    2014-03-01

    Material defects and heterogeneities such as dislocations, grain boundaries, and micro-porosity play key roles in the shock-induced initiation of detonation in energetic materials. Non-equilibrium molecular dynamics simulations (NEMD) with the ReaxFF force field (ReaxFF) in LAMMPS were performed to explore the effect of nanoscale voids on hotspot growth and initiation in pentaerythritol tetranitrate (PETN) crystals under weak shock conditions. Previously, we have performed reactive NEMD simulations of weak shocks in a (20 nm) 3 PETN crystal containing a spherical void. We observed hotspot formation and an exothermic reaction zone. To observe growth of the hotspot, we have now greatly extended the time and lengthscale of the simulation. We created a cylindrical pore in a 0 . 3 × 0 . 2 × 0 . 001 μm3 crystal. Once the shockwave reached the free surface we continued the simulation using the shock-front absorbing boundary condition. Results show steadily increasing axial and lateral spatial extent of the hotspot and a complex coupling of exothermic chemistry to hotspot growth. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy NNSA under contract DE-AC04-94AL85000.

  12. Particle swarm optimization-based continuous cellular automaton for the simulation of deep reactive ion etching

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Gosálvez, Miguel A.; Pal, Prem; Sato, Kazuo; Xing, Yan

    2015-05-01

    We combine the particle swarm optimization (PSO) method and the continuous cellular automaton (CCA) in order to simulate deep reactive ion etching (DRIE), also known as the Bosch process. By considering a generic growth/etch process, the proposed PSO-CCA method provides a general, integrated procedure to optimize the parameter values of any given theoretical model conceived to describe the corresponding experiments, which are simulated by the CCA method. To stress the flexibility of the PSO-CCA method, two different theoretical models of the DRIE process are used, namely, the ballistic transport and reaction (BTR) model, and the reactant concentration (RC) model. DRIE experiments are designed and conducted to compare the simulation results with the experiments on different machines and process conditions. Previously reported experimental data are also considered to further test the flexibility of the proposed method. The agreement between the simulations and experiments strongly indicates that the PSO-CCA method can be used to adjust the theoretical parameters by using a limited amount of experimental data. The proposed method has the potential to be applied on the modeling and optimization of other growth/etch processes.

  13. PuReMD-GPU: A reactive molecular dynamics simulation package for GPUs

    SciTech Connect

    Kylasa, S.B.; Aktulga, H.M.; Grama, A.Y.

    2014-09-01

    We present an efficient and highly accurate GP-GPU implementation of our community code, PuReMD, for reactive molecular dynamics simulations using the ReaxFF force field. PuReMD and its incorporation into LAMMPS (Reax/C) is used by a large number of research groups worldwide for simulating diverse systems ranging from biomembranes to explosives (RDX) at atomistic level of detail. The sub-femtosecond time-steps associated with ReaxFF strongly motivate significant improvements to per-timestep simulation time through effective use of GPUs. This paper presents, in detail, the design and implementation of PuReMD-GPU, which enables ReaxFF simulations on GPUs, as well as various performance optimization techniques we developed to obtain high performance on state-of-the-art hardware. Comprehensive experiments on model systems (bulk water and amorphous silica) are presented to quantify the performance improvements achieved by PuReMD-GPU and to verify its accuracy. In particular, our experiments show up to 16× improvement in runtime compared to our highly optimized CPU-only single-core ReaxFF implementation. PuReMD-GPU is a unique production code, and is currently available on request from the authors.

  14. Parallel contact detection algorithm for transient solid dynamics simulations using PRONTO3D

    SciTech Connect

    Attaway, S.W.; Hendrickson, B.A.; Plimpton, S.J.

    1996-09-01

    An efficient, scalable, parallel algorithm for treating material surface contacts in solid mechanics finite element programs has been implemented in a modular way for MIMD parallel computers. The serial contact detection algorithm that was developed previously for the transient dynamics finite element code PRONTO3D has been extended for use in parallel computation by devising a dynamic (adaptive) processor load balancing scheme.

  15. Microsecond Molecular Simulations Reveal a Transient Proton Pathway in the Calcium Pump.

    PubMed

    Espinoza-Fonseca, L Michel; Ramírez-Salinas, G Lizbeth

    2015-06-10

    The calcium pump sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) counter-transports Ca(2+) and H(+) at the expense of ATP hydrolysis. SERCA uses separate proton and metal ion pathways during active transport to neutralize the highly charged transport site, thus preserving SERCA's structural stability during active Ca(2+) transport. Although separate metal ion and proton pathways have been identified during slow (millisecond) structural transitions of SERCA, the existence of simultaneous metal and proton pathways during fast (microsecond) structural transitions remains unknown. We have analyzed microsecond-long trajectories of E1·H(+)771, a protonated intermediate of the pump populated during SERCA regulation. We found a transiently established hydrophobic pore in the luminal side of the transmembrane helices 6, 8, and 9. This narrow (0.5-0.6 nm) pore connects the transport sites to the sarcoplasmic reticulum lumen through a chain of water molecules. Protein pKa calculations of the transport site residues and structural analysis of the water molecules showed that this pore is suitable for proton transport. This transient proton pathway ensures neutralization of the transport sites during the rapid structural transitions associated with regulation of the pump. We conclude that this transient proton pathway plays a central role in optimizing active Ca(2+) transport by SERCA. Our discovery provides insight into ion-exchange mechanisms through transient hydrophobic pores in P-type ATPases.

  16. Increases in reactive oxygen species enhance vascular endothelial cell migration through a mechanism dependent on the transient receptor potential melastatin 4 ion channel.

    PubMed

    Sarmiento, Daniela; Montorfano, Ignacio; Cerda, Oscar; Cáceres, Mónica; Becerra, Alvaro; Cabello-Verrugio, Claudio; Elorza, Alvaro A; Riedel, Claudia; Tapia, Pablo; Velásquez, Luis A; Varela, Diego; Simon, Felipe

    2015-03-01

    A hallmark of severe inflammation is reactive oxygen species (ROS) overproduction induced by increased inflammatory mediators secretion. During systemic inflammation, inflammation mediators circulating in the bloodstream interact with endothelial cells (ECs) raising intracellular oxidative stress at the endothelial monolayer. Oxidative stress mediates several pathological functions, including an exacerbated EC migration. Because cell migration critically depends on calcium channel-mediated Ca(2+) influx, the molecular identification of the calcium channel involved in oxidative stress-modulated EC migration has been the subject of intense investigation. The transient receptor potential melastatin 4 (TRPM4) protein is a ROS-modulated non-selective cationic channel that performs several cell functions, including regulating intracellular Ca(2+) overload and Ca(2+) oscillation. This channel is expressed in multiple tissues, including ECs, and contributes to the migration of certain immune cells. However, whether the TRPM4 ion channel participates in oxidative stress-mediated EC migration is not known. Herein, we investigate whether oxidative stress initiates or enhances EC migration and study the role played by the ROS-modulated TRPM4 ion channel in oxidative stress-mediated EC migration. We demonstrate that oxidative stress enhances, but does not initiate, EC migration in a dose-dependent manner. Notably, we demonstrate that the TRPM4 ion channel is critical in promoting H2O2-enhanced EC migration. These results show that TRPM4 is a novel pharmacological target for the possible treatment of severe inflammation and other oxidative stress-mediated inflammatory diseases.

  17. Epac2-deficiency leads to more severe retinal swelling, glial reactivity and oxidative stress in transient middle cerebral artery occlusion induced ischemic retinopathy.

    PubMed

    Liu, Jin; Yeung, Patrick Ka Kit; Cheng, Lu; Lo, Amy Cheuk Yin; Chung, Stephen Sum Man; Chung, Sookja Kim

    2015-06-01

    Ischemia occurs in diabetic retinopathy with neuronal loss, edema, glial cell reactivity and oxidative stress. Epacs, consisting of Epac1 and Epac2, are cAMP mediators playing important roles in maintenance of endothelial barrier and neuronal functions. To investigate the roles of Epacs in the pathogenesis of ischemic retinopathy, transient middle cerebral artery occlusion (tMCAO) was performed on Epac1-deficient (Epac1 (-/-)) mice, Epac2-deficient (Epac2 (-/-)) mice, and their wild type counterparts (Epac1 (+/+) and Epac2 (+/+)). Two-hour occlusion and 22-hour reperfusion were conducted to induce ischemia/reperfusion injury to the retina. After tMCAO, the contralateral retinae displayed similar morphology between different genotypes. Neuronal loss, retinal edema and increase in immunoreactivity for aquaporin 4 (AQP4), glial fibrillary acidic protein (GFAP), peroxiredoxin 6 (Prx6) were observed in ipsilateral retinae. Epac2 (-/-) ipsilateral retinae showed more neuronal loss in retinal ganglion cell layer, increased retinal thickness and stronger immunostaining of AQP4, GFAP, and Prx6 than those of Epac2 (+/+). However, Epac1 (-/-) ipsilateral retinae displayed similar pathology as those in Epac1 (+/+) mice. Our observations suggest that Epac2-deficiency led to more severe ischemic retinopathy after retinal ischemia/reperfusion injury.

  18. Increases in reactive oxygen species enhance vascular endothelial cell migration through a mechanism dependent on the transient receptor potential melastatin 4 ion channel.

    PubMed

    Sarmiento, Daniela; Montorfano, Ignacio; Cerda, Oscar; Cáceres, Mónica; Becerra, Alvaro; Cabello-Verrugio, Claudio; Elorza, Alvaro A; Riedel, Claudia; Tapia, Pablo; Velásquez, Luis A; Varela, Diego; Simon, Felipe

    2015-03-01

    A hallmark of severe inflammation is reactive oxygen species (ROS) overproduction induced by increased inflammatory mediators secretion. During systemic inflammation, inflammation mediators circulating in the bloodstream interact with endothelial cells (ECs) raising intracellular oxidative stress at the endothelial monolayer. Oxidative stress mediates several pathological functions, including an exacerbated EC migration. Because cell migration critically depends on calcium channel-mediated Ca(2+) influx, the molecular identification of the calcium channel involved in oxidative stress-modulated EC migration has been the subject of intense investigation. The transient receptor potential melastatin 4 (TRPM4) protein is a ROS-modulated non-selective cationic channel that performs several cell functions, including regulating intracellular Ca(2+) overload and Ca(2+) oscillation. This channel is expressed in multiple tissues, including ECs, and contributes to the migration of certain immune cells. However, whether the TRPM4 ion channel participates in oxidative stress-mediated EC migration is not known. Herein, we investigate whether oxidative stress initiates or enhances EC migration and study the role played by the ROS-modulated TRPM4 ion channel in oxidative stress-mediated EC migration. We demonstrate that oxidative stress enhances, but does not initiate, EC migration in a dose-dependent manner. Notably, we demonstrate that the TRPM4 ion channel is critical in promoting H2O2-enhanced EC migration. These results show that TRPM4 is a novel pharmacological target for the possible treatment of severe inflammation and other oxidative stress-mediated inflammatory diseases. PMID:24518820

  19. Large-Scale Reactive Atomistic Simulation of Shock-induced Initiation Processes in Energetic Materials

    NASA Astrophysics Data System (ADS)

    Thompson, Aidan

    2013-06-01

    Initiation in energetic materials is fundamentally dependent on the interaction between a host of complex chemical and mechanical processes, occurring on scales ranging from intramolecular vibrations through molecular crystal plasticity up to hydrodynamic phenomena at the mesoscale. A variety of methods (e.g. quantum electronic structure methods (QM), non-reactive classical molecular dynamics (MD), mesoscopic continuum mechanics) exist to study processes occurring on each of these scales in isolation, but cannot describe how these processes interact with each other. In contrast, the ReaxFF reactive force field, implemented in the LAMMPS parallel MD code, allows us to routinely perform multimillion-atom reactive MD simulations of shock-induced initiation in a variety of energetic materials. This is done either by explicitly driving a shock-wave through the structure (NEMD) or by imposing thermodynamic constraints on the collective dynamics of the simulation cell e.g. using the Multiscale Shock Technique (MSST). These MD simulations allow us to directly observe how energy is transferred from the shockwave into other processes, including intramolecular vibrational modes, plastic deformation of the crystal, and hydrodynamic jetting at interfaces. These processes in turn cause thermal excitation of chemical bonds leading to initial chemical reactions, and ultimately to exothermic formation of product species. Results will be presented on the application of this approach to several important energetic materials, including pentaerythritol tetranitrate (PETN) and ammonium nitrate/fuel oil (ANFO). In both cases, we validate the ReaxFF parameterizations against QM and experimental data. For PETN, we observe initiation occurring via different chemical pathways, depending on the shock direction. For PETN containing spherical voids, we observe enhanced sensitivity due to jetting, void collapse, and hotspot formation, with sensitivity increasing with void size. For ANFO, we

  20. Simulating variably-saturated reactive transport of selenium and nitrogen in agricultural groundwater systems

    NASA Astrophysics Data System (ADS)

    Bailey, Ryan T.; Gates, Timothy K.; Halvorson, Ardell D.

    2013-06-01

    Selenium (Se) contamination in environmental systems has become a major issue in many regions world-wide during the previous decades, with both elevated and deficient Se concentrations in groundwater, surface water, soils and associated cultivated crops reported. To provide a tool that can assess baseline conditions and explore remediation strategies, this paper presents a numerical model capable of simulating the reactive transport of Se species in large-scale variably-saturated groundwater systems influenced by agricultural practices. Developed by incorporating a Se reaction module into the multi-species, variably-saturated reactive transport model UZF-RT3D, model features include near-surface Se cycling due to agricultural practices, oxidation-reduction reactions, and the inclusion of a nitrogen (N) cycle and reaction module due to the dependence of Se transformation and speciation on the presence of nitrate (NO3). Although the primary motivation is applying the model to large-scale systems, this paper presents applications to agricultural soil profile systems to corroborate the near-surface module processes that are vital in estimating mass loadings to the saturated zone in large-scale fate and transport studies. The first application jointly tests the Se and N modules for corn test plots receiving varying loadings of fertilizer, whereas the second application tests the N module for fertilized and unfertilized test plots. Results indicate that the model is successful in reproducing observed measurements of Se and NO3 concentrations, particularly in lower soil layers and hence in regards to leaching. For the first application, the Ensemble Kalman Filter (EnKF) is used to condition model parameters, demonstrating the usefulness of the EnKF in real-world reactive transport systems.

  1. A Dual Regime Reactive Transport Model for Simulation of High Level Waste Tank Closure Scenarios - 13375

    SciTech Connect

    Sarkar, Sohini; Kosson, David S.; Brown, Kevin; Garrabrants, Andrew C.; Meeussen, Hans; Van der Sloot, Hans

    2013-07-01

    A numerical simulation framework is presented in this paper for estimating evolution of pH and release of major species from grout within high-level waste tanks after closure. This model was developed as part of the Cementitious Barriers Partnership. The reactive transport model consists of two parts - (1) transport of species, and (2) chemical reactions. The closure grout can be assumed to have varying extents of cracking and composition for performance assessment purposes. The partially or completely degraded grouted tank is idealized as a dual regime system comprising of a mobile region having solid materials with cracks and macro-pores, and an immobile/stagnant region having solid matrix with micropores. The transport profiles of the species are calculated by incorporating advection of species through the mobile region, diffusion of species through the immobile/stagnant region, and exchange of species between the mobile and immobile regions. A geochemical speciation code in conjunction with the pH dependent test data for a grout material is used to obtain a mineral set that best describes the trends in the test data of the major species. The dual regime reactive transport model predictions are compared with the release data from an up-flow column percolation test. The coupled model is then used to assess effects of crack state of the structure, rate and composition of the infiltrating water on the pH evolution at the grout-waste interface. The coupled reactive transport model developed in this work can be used as part of the performance assessment process for evaluating potential risks from leaching of a cracked tank containing elements of human health and environmental concern. (authors)

  2. Simulating variably-saturated reactive transport of selenium and nitrogen in agricultural groundwater systems.

    PubMed

    Bailey, Ryan T; Gates, Timothy K; Halvorson, Ardell D

    2013-06-01

    Selenium (Se) contamination in environmental systems has become a major issue in many regions world-wide during the previous decades, with both elevated and deficient Se concentrations in groundwater, surface water, soils and associated cultivated crops reported. To provide a tool that can assess baseline conditions and explore remediation strategies, this paper presents a numerical model capable of simulating the reactive transport of Se species in large-scale variably-saturated groundwater systems influenced by agricultural practices. Developed by incorporating a Se reaction module into the multi-species, variably-saturated reactive transport model UZF-RT3D, model features include near-surface Se cycling due to agricultural practices, oxidation-reduction reactions, and the inclusion of a nitrogen (N) cycle and reaction module due to the dependence of Se transformation and speciation on the presence of nitrate (NO₃). Although the primary motivation is applying the model to large-scale systems, this paper presents applications to agricultural soil profile systems to corroborate the near-surface module processes that are vital in estimating mass loadings to the saturated zone in large-scale fate and transport studies. The first application jointly tests the Se and N modules for corn test plots receiving varying loadings of fertilizer, whereas the second application tests the N module for fertilized and unfertilized test plots. Results indicate that the model is successful in reproducing observed measurements of Se and NO₃ concentrations, particularly in lower soil layers and hence in regards to leaching. For the first application, the Ensemble Kalman Filter (EnKF) is used to condition model parameters, demonstrating the usefulness of the EnKF in real-world reactive transport systems.

  3. Artificial neural networks based subgrid chemistry model for turbulent reactive flow simulations

    NASA Astrophysics Data System (ADS)

    Sen, Baris A.

    Computational analysis of turbulent reactive flow applications requires resolution of the wide range of scales both in time and space from a flow modeling perspective. From a thermo-chemistry point of view, information regarding the radical chemical species is needed in order to capture flame-turbulence interactions accurately. A detailed investigation of all of these processes is time consuming. Thus, there is a need for speeding-up the computations by using the state-of-the art modeling capabilities. This study seeks to answer this problem and focuses in particular on the chemical kinetics calculations. The new approach proposed here is based on incorporating the artificial neural network (ANN) based modeling of the chemical kinetics into the large eddy simulation (LES) of reactive flows. Two separate and new ANN based modeling approaches relevant to the LES are proposed within the thesis work. Here, the first approach depends on employing ANN to predict the species instantaneous reaction rates as a function of the thermochemical state vector ( ẇi = ANN(Yk, T)). The second one is based on using ANN specifically to predict the spatially filtered chemical source terms in the LES modeling as a function of the filtered thermo-chemical state vector and flow quantities ( ẇ¯ i = ANN(Ỹk, T˜, ReDelta, 6Ỹi 6x )). First part of the thesis work dealt with testing different thermo-chemical tabulation techniques that can be used in connection with the ANN approach for the LES. Basically, three distinct methods (and tools) are developed here: thermo-chemical tables based on (i) laminar flames, (ii) laminar flame-vortex interactions (FVI) and (iii) laminar flame-turbulence interactions (FTI). Results based on premixed flame-vortex-turbulence interaction simulations showed that the tables generated based on the second and third approaches are capable of representing the actual thermo-chemical state-space accessed by the LES. Once the tabulation procedure and the ANN

  4. Fluoride-containing bioactive glasses: surface reactivity in simulated body fluids solutions.

    PubMed

    Lusvardi, G; Malavasi, G; Menabue, L; Aina, V; Morterra, C

    2009-11-01

    The issue of the contribution of the addition of F to glass bioactivity is not well resolved. This work reports on the surface reactivity in different solutions (DMEM and Tris) for some potentially bioactive glasses based on the composition of 45S5 glass, in which CaF(2) is substituted alternately for (part of) CaO and Na(2)O. The reactivity of F-containing glasses has been compared with that of the reference 45S5 system. The aim of this study is to explain in detail the mechanism of formation of an apatitic crystalline phase at the interface between the inorganic material and simulated biological media. A multi-technique investigation approach proposes a set of reactions involving Ca-carbonate formation, which are somewhat different from that formerly proposed by Hench for 45S5 bioactive glass, and which occur when a F-containing glass surface is in contact with a SBF. The usefulness of IR spectroscopy in recognizing the starting step of apatite (and/or FA) formation with respect to XRD technique is well established here. PMID:19523544

  5. Comparison of OH reactivity instruments in the atmosphere simulation chamber SAPHIR

    NASA Astrophysics Data System (ADS)

    Fuchs, Hendrik

    2016-04-01

    OH reactivity measurement has become an important measurement to constrain the total OH loss frequency in field experiments. Different techniques have been developed by various groups. They can be based on flow-tube or pump and probe techniques, which include direct OH detection by fluorescence, or on a comparative method, in which the OH loss of a reference species competes with the OH loss of trace gases in the sampled air. In order to ensure that these techniques deliver equivalent results, a comparison exercise was performed under controlled conditions. Nine OH reactivity instruments measured together in the atmosphere simulation chamber SAPHIR (volume 270 m3) during ten daylong experiments in October 2015 at ambient temperature (5 to 10° C) and pressure (990-1010 hPa). The chemical complexity of air mixtures in these experiments varied from CO in pure synthetic air to emissions from real plants and VOC/NOx mixtures representative of urban atmospheres. Potential differences between measurements were systematically investigated by changing the amount of reactants (including isoprene, monoterpenes and sesquiterpenes), water vapour, and nitrogen oxides. Some of the experiments also included the oxidation of reactants with ozone or hydroxyl radicals, in order to elaborate, if the presence of oxidation products leads to systematic differences between measurements of different instruments. Here we present first results of this comparison exercise.

  6. Reactive molecular dynamics simulations of the initial stage of brown coal oxidation at high temperatures

    NASA Astrophysics Data System (ADS)

    Yan, Guochao; Zhang, Zhiqiang; Yan, Kefeng

    2013-01-01

    To investigate the detailed mechanisms for brown coal oxidation at high temperatures, a ReaxFF reactive forcefield was used to perform a series of molecular dynamics simulations from 1000 K to 2500 K. Analyses indicated that the chemical system tend to be more reactive with increasing temperature. It was found that the oxidation process of brown coal primarily initiates from hydrogen abstraction reactions by O2 and related oxygenated radicals from phenolic hydroxyl groups, methyl groups, especially carboxyl groups in lower temperature to form peroxygen species, or by either thermal decomposition of brown coal backbone in higher temperature. These peroxygen species usually could chemically adsorb on the C-centered radicals of brown coal backbone. The weak O-O bond in peroxygen makes them easier to break into oxygenated radical, which could also chemically adsorb on the C-centred radical to form hydroxyl group and other oxygenated compounds. In the oxidation process of brown coal, the decomposition and oxidation of aliphatic chain is easier than aromatic ring. The chemisorption of peroxygen radical induces the breakage of aromatic ring and accelerates the depth oxidation of brown coal. An increasing number of products are observed with increasing temperature.

  7. Simulation of Nitrate Biogeochemistry and Reactive Transport in a California Groundwater Basin

    SciTech Connect

    Tompson, A B; Kane, S R; Beller, H R; Hudson, G B; McNab, W W; Moran, J E; Carle, S F; Esser, B K

    2004-01-16

    Nitrate is the number one drinking water contaminant in the United States. It is pervasive in surface and groundwater systems, and its principal anthropogenic sources have increased dramatically in the last 50 years. In California alone, one third of the public drinking-water wells has been lost since 1988 and nitrate contamination is the most common reason for abandonment. Effective nitrate management in groundwater is complicated by uncertainties related to multiple point and non-point sources, hydrogeologic complexity, geochemical reactivity, and quantification of dentrification processes. In this paper, we review an integrated experimental and simulation-based framework being developed to study the fate of nitrate in a 25 km-long groundwater subbasin south of San Jose, California, a historically agricultural area now undergoing rapid urbanization with increasing demands for groundwater. The modeling approach is driven by a need to integrate new and archival data that support the hypothesis that nitrate fate and transport at the basin scale is intricately related to hydrostratigraphic complexity, variability of flow paths and groundwater residence times, microbial activity, and multiple geochemical reaction mechanisms. This study synthesizes these disparate and multi-scale data into a three-dimensional and highly resolved reactive transport modeling framework.

  8. Reactive molecular dynamic simulations of hydrocarbon dissociations on Ni(111) surfaces

    NASA Astrophysics Data System (ADS)

    Liu, Bin; Lusk, Mark T.; Ely, James F.

    2012-03-01

    Empirical potential parameters for H, C and Ni elements have been developed for the ReaxFF force field in order to study the decomposition of small hydrocarbon molecules on nickel using molecular dynamics simulations. These parameters were optimized using the geometrical and energetic information obtained from density functional (DFT) calculations on a subset of hydrogen and methane reactions with nickel (111) surfaces. The resulting force field was then used to obtain a molecular perspective of the dynamics of the methane dissociative adsorption on Ni(111) as well as two other small alkane molecules, ethane and n-butane. NVT simulations of dissociative adsorption of methane over a range of temperatures enabled the estimation of the sticking coefficient for the adsorption as well as the activation energy of the first C-H bond breaking. The rate constants of each elementary step (both forward and reverse) of CHx dissociation on Ni(111) were obtained by monitoring the surface species and a microkinetic model was constructed as a result. Qualitative analyses of the simulations of ethane and n-butane decompositions on Ni(111) demonstrate that such reactive MD technique can also be used to obtain useful information on complex reaction networks.

  9. Virus-Specific CD8(+) T Cells Cross-Reactive to Donor-Alloantigen Are Transiently Present in the Circulation of Kidney Transplant Recipients Infected With CMV and/or EBV.

    PubMed

    Heutinck, K M; Yong, S L; Tonneijck, L; van den Heuvel, H; van der Weerd, N C; van der Pant, K A M I; Bemelman, F J; Claas, F H J; Ten Berge, I J M

    2016-05-01

    T cells play a dual role in transplantation: They mediate transplant rejection and are crucial for virus control. Memory T cells generated in response to pathogens can cross-react to alloantigen, a phenomenon called heterologous immunity. Virus-specific CD8(+) T cells cross-reacting to donor-alloantigen might affect alloimmune responses and hamper tolerance induction following transplantation. Here, we longitudinally studied these cross-reactive cells in peripheral blood of 25 kidney transplant recipients with a cytomegalovirus and/or Epstein-Barr virus infection. Cross-reactive T cells were identified by flow cytometry as virus-specific T cells that proliferate in response to donor cells in a mixed-lymphocyte reaction. In 13 of 25 patients, we found cross-reactivity to donor cells for at least 1 viral epitope before (n = 7) and/or after transplantation (n = 8). Cross-reactive T cells were transiently present in the circulation, and their precursor frequency did not increase following transplantation or viral infection. Cross-reactive T cells expressed interferon-γ and CD107a in response to both alloantigen and viral peptide and resembled virus-specific T cells in phenotype and function. Their presence was not associated with impaired renal function, proteinuria, or rejection. In conclusion, virus-specific T cells that cross-react to donor-alloantigen are transiently detectable in the circulation of kidney transplant recipients. PMID:26603974

  10. Reduced yield stress for zirconium exposed to iodine: Reactive force field simulation

    SciTech Connect

    Rossi, Matthew L.; Taylor, Christopher D.; van Duin, Adri C. T.

    2014-11-04

    Iodine-induced stress-corrosion cracking (ISCC), a known failure mode for nuclear fuel cladding, occurs when iodine generated during the irradiation of a nuclear fuel pellet escapes the pellet through diffusion or thermal cracking and chemically interacts with the inner surface of the clad material, inducing a subsequent effect on the cladding’s resistance to mechanical stress. To complement experimental investigations of ISCC, a reactive force field (ReaxFF) compatible with the Zr-I chemical and materials systems has been developed and applied to simulate the impact of iodine exposure on the mechanical strength of the material. The study shows that the material’s resistance to stress (as captured by the yield stress of a high-energy grain boundary) is related to the surface coverage of iodine, with the implication that ISCC is the result of adsorption-enhanced decohesion.

  11. Reduced yield stress for zirconium exposed to iodine: Reactive force field simulation

    DOE PAGES

    Rossi, Matthew L.; Taylor, Christopher D.; van Duin, Adri C. T.

    2014-11-04

    Iodine-induced stress-corrosion cracking (ISCC), a known failure mode for nuclear fuel cladding, occurs when iodine generated during the irradiation of a nuclear fuel pellet escapes the pellet through diffusion or thermal cracking and chemically interacts with the inner surface of the clad material, inducing a subsequent effect on the cladding’s resistance to mechanical stress. To complement experimental investigations of ISCC, a reactive force field (ReaxFF) compatible with the Zr-I chemical and materials systems has been developed and applied to simulate the impact of iodine exposure on the mechanical strength of the material. The study shows that the material’s resistance tomore » stress (as captured by the yield stress of a high-energy grain boundary) is related to the surface coverage of iodine, with the implication that ISCC is the result of adsorption-enhanced decohesion.« less

  12. Treatment of simulated Reactive Yellow 22 (azo) dye effluents using Spirogyra species.

    PubMed

    Mohan, S Venkata; Rao, N Chandrasekhar; Srinivas, S; Prasad, K Krishna; Karthikeyan, J

    2002-01-01

    The potential of commonly available green algae belonging to Spirogyra species was investigated as viable biomaterials for biological treatment of simulated synthetic azo dye (Reactive Yellow 22) effluents. The results obtained from the batch experiments revealed the ability of the algal species in removing the dye colour and was dependent both on the dye concentration and algal biomass. Maximum dye colour removal was observed on the third day for all the system conditions. Monitoring of ORP values helped to understand the overlying biochemical mechanism of algal-dye system. Based upon the results, the dye-algal treatment mechanism was attributed to biosorption (sorption of dye molecules over the surface of algal cells), bioconversion (diffusion of dye molecules into the algal cells and subsequent conversion) and biocoagulation (coagulation of dye molecules present in the aqueous phase onto the biopolymers released as metabolic intermediates during metabolic conversion of dye and subsequent settlement).

  13. Transformer modeling for low- and mid-frequency electromagnetic transients simulation

    NASA Astrophysics Data System (ADS)

    Lambert, Mathieu

    In this work, new models are developed for single-phase and three-phase shell-type transformers for the simulation of low-frequency transients, with the use of the coupled leakage model. This approach has the advantage that it avoids the use of fictitious windings to connect the leakage model to a topological core model, while giving the same response in short-circuit as the indefinite admittance matrix (BCTRAN) model. To further increase the model sophistication, it is proposed to divide windings into coils in the new models. However, short-circuit measurements between coils are never available. Therefore, a novel analytical method is elaborated for this purpose, which allows the calculation in 2-D of short-circuit inductances between coils of rectangular cross-section. The results of this new method are in agreement with the results obtained from the finite element method in 2-D. Furthermore, the assumption that the leakage field is approximately 2-D in shell-type transformers is validated with a 3-D simulation. The outcome of this method is used to calculate the self and mutual inductances between the coils of the coupled leakage model and the results are showing good correspondence with terminal short-circuit measurements. Typically, leakage inductances in transformers are calculated from short-circuit measurements and the magnetizing branch is calculated from no-load measurements, assuming that leakages are unimportant for the unloaded transformer and that magnetizing current is negligible during a short-circuit. While the core is assumed to have an infinite permeability to calculate short-circuit inductances, and it is a reasonable assumption since the core's magnetomotive force is negligible during a short-circuit, the same reasoning does not necessarily hold true for leakage fluxes in no-load conditions. This is because the core starts to saturate when the transformer is unloaded. To take this into account, a new analytical method is developed in this

  14. Cr(VI)-contaminated groundwater remediation with simulated permeable reactive barrier (PRB) filled with natural pyrite as reactive material: Environmental factors and effectiveness.

    PubMed

    Liu, Yuanyuan; Mou, Haiyan; Chen, Liqun; Mirza, Zakaria A; Liu, Li

    2015-11-15

    Permeable reactive barriers (PRBs) are efficient technologies for in situ remediation of contaminated groundwater, the effectiveness of which greatly depends on the reactive media filled. Natural pyrite is an iron sulfide material with a very low content of iron and sulfur, and a mining waste which is a potential material for Cr(VI) immobilization. In this study, we conducted a series of batch tests to research the effects of typical environmental factors on Cr(VI) removal and also simulated PRB filled with natural pyrite to investigate its effectiveness, in order to find a both environmentally and economically fine method for groundwater remediation. Batch tests showed that pH had the significant impact on Cr(VI) removal with an apparently higher efficiency under acidic conditions, and dissolved oxygen (DO) would inhibit Cr(VI) reduction; a relatively high initial Cr(VI) concentration would decrease the rate of Cr(VI) sorption; ionic strength and natural organic matter resulted in no significant effects on Cr(VI) removal. Column tests demonstrated that the simulated PRB with natural pyrite as the reactive media was considerably effective for removing Cr(VI) from groundwater, with a sorption capability of 0.6222 mg Cr per gram of natural pyrite at an initial Cr(VI) concentration of 10mg/L at pH 5.5 in an anoxic environment. PMID:26026959

  15. Cr(VI)-contaminated groundwater remediation with simulated permeable reactive barrier (PRB) filled with natural pyrite as reactive material: Environmental factors and effectiveness.

    PubMed

    Liu, Yuanyuan; Mou, Haiyan; Chen, Liqun; Mirza, Zakaria A; Liu, Li

    2015-11-15

    Permeable reactive barriers (PRBs) are efficient technologies for in situ remediation of contaminated groundwater, the effectiveness of which greatly depends on the reactive media filled. Natural pyrite is an iron sulfide material with a very low content of iron and sulfur, and a mining waste which is a potential material for Cr(VI) immobilization. In this study, we conducted a series of batch tests to research the effects of typical environmental factors on Cr(VI) removal and also simulated PRB filled with natural pyrite to investigate its effectiveness, in order to find a both environmentally and economically fine method for groundwater remediation. Batch tests showed that pH had the significant impact on Cr(VI) removal with an apparently higher efficiency under acidic conditions, and dissolved oxygen (DO) would inhibit Cr(VI) reduction; a relatively high initial Cr(VI) concentration would decrease the rate of Cr(VI) sorption; ionic strength and natural organic matter resulted in no significant effects on Cr(VI) removal. Column tests demonstrated that the simulated PRB with natural pyrite as the reactive media was considerably effective for removing Cr(VI) from groundwater, with a sorption capability of 0.6222 mg Cr per gram of natural pyrite at an initial Cr(VI) concentration of 10mg/L at pH 5.5 in an anoxic environment.

  16. Molecular dynamics simulation of hydrated Nafion with a reactive force field for water.

    PubMed

    Hofmann, Detlef W M; Kuleshova, Liudmila; D'Aguanno, Bruno

    2008-03-01

    We apply a newly parameterized central force field to highlight the problem of proton transport in fuel cell membranes and show that central force fields are potential candidates to describe chemical reactions on a classical level. After a short sketch of the parameterization of the force field, we validate the obtained force field for several properties of water. The experimental and simulated radial distribution functions are reproduced very accurately as a consequence of the applied parameterization procedure. Further properties, geometry, coordination, diffusion coefficient and density, are simulated adequately for our purposes. Afterwards we use the new force field for the molecular dynamics simulation of a swollen polyelectrolyte membrane similar to the widespread Nafion 117. We investigate the equilibrated structures, proton transfer, lifetimes of hydronium ions, the diffusion coefficients, and the conductivity in dependence of water content. In a short movie we demonstrate the ability of the obtained force field to describe the bond breaking/formation, and conclude that this force field can be considered as a kind of a reactive force field. The investigations of the lifetimes of hydronium ions give us the information about the kinetics of the proton transfer in a membrane with low water content. We found the evidence for the second order reaction. Finally, we demonstrate that the model is simple enough to handle the large systems sufficient to calculate the conductivity from molecular dynamics simulations. The detailed analysis of the conductivity reveals the importance of the collective moving of hydronium ions in membrane, which might give an interesting encouragement for further development of membranes.

  17. First-principles particle simulation and Boltzmann equation analysis of negative differential conductivity and transient negative mobility effects in xenon

    NASA Astrophysics Data System (ADS)

    Donko, Zoltan; Dyatko, Nikolay

    2016-06-01

    The Negative Differential Conductivity and Transient Negative Mobility effects in xenon gas are analyzed by a first-principles particle simulation technique and via an approximate solution of the Boltzmann transport equation (BE). The particle simulation method is devoid of the approximations that are traditionally adopted in the BE solutions in which: (i) the distribution function is searched for in a two-term form; (ii) the Coulomb part of the collision integral for the anisotropic part of the distribution function is neglected; (iii) Coulomb collisions are treated as binary events; and (iv) the range of the electron-electron interaction is limited to a cutoff distance. The results obtained from the two methods are, for both effects, in good qualitative agreement, small differences are attributed to the approximations listed above.

  18. The high current transient generator, theory and operation for simulating lightning induced voltages into aerospace electrical circuits

    NASA Technical Reports Server (NTRS)

    Schulte, E. H.

    1975-01-01

    Because of the difficulty, hazard, and cost of simulating full-scale lightning currents on flight vehicles, a nondestructive test technique using reduced-scale lightning currents was used to determine if threat level voltages will be induced into aircraft electrical circuits in the event the aircraft is actually struck by lightning. The reasoning and theory of selecting a particular simulated lightning waveshape and magnitude is given, showing that extrapolation of induced waveforms over several orders of magnitude should be avoided. The operation of high-current transient generators and hardware are described along with typical applications. The means by which voltages were generated, induced, and measured, as well as possible sources of error, are discussed.

  19. Numerical simulation of the transient photoconductivity in a-Si:H as a function of excitation density

    SciTech Connect

    Feist, H.; Kunst, M.

    1997-07-01

    The dependence of the transient photoconductivity induced by pulsed excitation (TPC) on the excitation density is discussed with the help of numerical simulations. It is shown that recombination between excess mobile electrons and all excess holes (mainly localized) can explain the excitation density dependence of the TPC amplitude of standard a-Si:H at room temperature using a rate parameter k{sub BB} of 10{sup {minus}8} cm{sup 3}/s. This model leads to a decay faster than experimentally observed in the time range from 40 ns to 1 {micro}s. A variation of the recombination model is presented that gives short time range. Moreover comparison of the simulations with experimental data yields limits for the parameters of the conduction band tail. In particular, the time necessary to establish a dynamic equilibrium of excess electrons between delocalized states in the conduction band and localized states in the tail appears to be very informative.

  20. High-temperature deformation field measurement by combining transient aerodynamic heating simulation system and reliability-guided digital image correlation

    NASA Astrophysics Data System (ADS)

    Pan, Bing; Wu, Dafang; Xia, Yong

    2010-09-01

    To determine the full-field high-temperature thermal deformation of the structural materials used in high-speed aerospace flight vehicles, a novel non-contact high-temperature deformation measurement system is established by combining transient aerodynamic heating simulation device with the reliability-guided digital image correlation (RG-DIC). The test planar sample with size varying from several mm 2 to several hundreds mm 2 can be heated from room temperature to 1100 °C rapidly and accurately using the infrared radiator of the transient aerodynamic heating simulation system. The digital images of the test sample surface at various temperatures are recorded using an ordinary optical imaging system. To cope with the possible local decorrelated regions caused by black-body radiation within the deformed images at the temperatures over 450 °C, the RG-DIC technique is used to extract full-field in-plane thermal deformation from the recorded images. In validation test, the thermal deformation fields and the values of coefficient of thermal expansion (CTEs) of a chromiumnickel austenite stainless steel sample from room temperature to 550 °C is measured and compared with the well-established handbook value, confirming the effectiveness and accuracy of the proposed technique. The experimental results reveal that the present system using an ordinary optical imaging system, is able to accurately measure full-field thermal deformation of metals and alloys at temperatures not exceeding 600 °C.

  1. Studying Extreme Ultraviolet Wave Transients with a Digital Laboratory: Direct Comparison of Extreme Ultraviolet Wave Observations to Global Magnetohydrodynamic Simulations

    NASA Astrophysics Data System (ADS)

    Downs, Cooper; Roussev, Ilia I.; van der Holst, Bart; Lugaz, Noé; Sokolov, Igor V.; Gombosi, Tamas I.

    2011-02-01

    In this work, we describe our effort to explore the signatures of large-scale extreme ultraviolet (EUV) transients in the solar corona (EUV waves) using a three-dimensional thermodynamic magnetohydrodynamic model. We conduct multiple simulations of the 2008 March 25 EUV wave (~18:40 UT), observed both on and off of the solar disk by the STEREO-A and B spacecraft. By independently varying fundamental parameters thought to govern the physical mechanisms behind EUV waves in each model, such as the ambient magneto-sonic speed, eruption free energy, and eruption handedness, we are able to assess their respective contributions to the transient signature. A key feature of this work is the ability to synthesize the multi-filter response of the STEREO Extreme UltraViolet Imagers directly from model data, which gives a means for direct interpretation of EUV observations with full knowledge of the three-dimensional magnetic and thermodynamic structures in the simulations. We discuss the implications of our results with respect to some commonly held interpretations of EUV waves (e.g., fast-mode magnetosonic wave, plasma compression, reconnection front, etc.) and present a unified scenario which includes both a wave-like component moving at the fast magnetosonic speed and a coherent driven compression front related to the eruptive event itself.

  2. Experimental and numerical simulations of ELM-like transient damage behaviors to different grade tungsten and tungsten alloys

    NASA Astrophysics Data System (ADS)

    Liu, Xiang; Lian, Youyun; Chen, Lei; Chen, Zhenkui; Chen, Jiming; Duan, Xuru; Fan, Jinlian; Song, Jiupeng

    2015-08-01

    Transient heat loads, such as plasma disruptions and ELMs, could induce plastic deformations, cracking, melting, even fatigue cracks and creep of tungsten (W) surface. A high purity W, CVD-W coating, TiC dispersion strengthened and K doped tungsten alloys were tested in a 60 kW electron-beam facility by simulating the transient load events under different base temperatures. It was found that CVD-W, W-TiC and W-K alloys have higher crack thresholds than high purity W, meanwhile CVD-W is more sensitive to the crack disappearing at elevated base temperatures. On the other hand, repetitive pulse loading like ELMs can induce serious network cracks even the power density was quite lower than the crack threshold determined by a single shot. The ABAQUS code was used to simulate the crack behaviors of ITER grade pure W by a single shot and a FE-SAFE code was adopted to estimate the fatigue life under ELMs-like loads. A good agreement with experiment results was found.

  3. Simulations of the global carbon cycle and anthropogenic CO{sub 2} transient. Annual report

    SciTech Connect

    Sarmiento, J.L.

    1994-07-01

    This research focuses on improving the understanding of the anthropogenic carbon dioxide transient using observations and models of the past and present. In addition, an attempt is made to develop an ability to predict the future of the carbon cycle in response to continued anthropogenic perturbations and climate change. Three aspects of the anthropogenic carbon budget were investigated: (1) the globally integrated budget at the present time; (2) the time history of the carbon budget; and (3) the spatial distribution of carbon fluxes. One of the major activities of this study was the participation in the model comparison study of Enting, et al. [1994] carried out in preparation for the IPCC 1994 report.

  4. Atomistic-scale simulations of energetic materials with ReaxFF reactive force fields

    NASA Astrophysics Data System (ADS)

    Goddard, W. A., III; Strachan, A.

    2005-07-01

    Understanding the response of energetic materials to thermal or shock loading at the atomistic level demands a highly accurate description of the reaction dynamics of million atom systems to capture the complex chemical and mechanical behavior involved: nonequilibrium energy/mass transfer, molecule excitation and decomposition under high strain/heat rates, formation of defects, plastic flow, and phase transitions. To enable such simulations, we developed the ReaxFF reactive force fields based on quantum mechanics (QM) calculations of reactants, products, high-energy intermediates and transition states, but using functional forms suitable for large-scale molecular dynamics simulations of chemical reactions under extreme conditions. We will present an overview of recent progress in ReaxFF developments, including the extension of ReaxFF to new nitramine- based (nitromethane, HMX, PETN, TATB) and peroxide-based (TATP) explosives. To demonstrate the versatility and transferability of ReaxFF, we will present applications to solid composite propellants such as Al/Al2O3-metal nanoparticles embedded into solid explosive matrices (RDX, PETN).

  5. A scalable parallel algorithm for large-scale reactive force-field molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Nomura, Ken-ichi; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

    2008-01-01

    A scalable parallel algorithm has been designed to perform multimillion-atom molecular dynamics (MD) simulations, in which first principles-based reactive force fields (ReaxFF) describe chemical reactions. Environment-dependent bond orders associated with atomic pairs and their derivatives are reused extensively with the aid of linked-list cells to minimize the computation associated with atomic n-tuple interactions ( n⩽4 explicitly and ⩽6 due to chain-rule differentiation). These n-tuple computations are made modular, so that they can be reconfigured effectively with a multiple time-step integrator to further reduce the computation time. Atomic charges are updated dynamically with an electronegativity equalization method, by iteratively minimizing the electrostatic energy with the charge-neutrality constraint. The ReaxFF-MD simulation algorithm has been implemented on parallel computers based on a spatial decomposition scheme combined with distributed n-tuple data structures. The measured parallel efficiency of the parallel ReaxFF-MD algorithm is 0.998 on 131,072 IBM BlueGene/L processors for a 1.01 billion-atom RDX system.

  6. Interaction Between Hyperalkaline Fluids and Rocks Hosting Repositories for Radioactive Waste: Reactive Transport Simulations

    SciTech Connect

    Soler, Josep M.; Maeder, Urs K.

    2005-09-15

    Reactive transport calculations simulating the interaction between hyperalkaline solutions derived from the degradation of cement and potential host rocks for repositories for low- and intermediate-level radioactive waste have been performed. Two different cases are shown: (a) The example of the planned repository at Wellenberg and (b) the modeling of the GTS-HPF experiment at the Grimsel Test Site. The GIMRT code has been used for the simulations. Mineral reactions are described by kinetic rate laws. The reaction rates for the primary minerals are based on experimentally determined rates published in the literature and geometric considerations combined with measurements regarding mineral surface areas. Relatively fast rates for the secondary minerals have been used, so the results resemble the local equilibrium solution for these minerals. In both cases, the alteration of the rock and the precipitation of secondary phases cause a reduction in the permeability of the system, which would actually be beneficial for the performance of a repository. Mineral surface area controls, to a large extent, the amount of mineral alteration and the change in permeability.

  7. The effects of parametric uncertainties in simulations of a reactive plume using a Lagrangian stochastic model

    NASA Astrophysics Data System (ADS)

    Ziehn, Tilo; Dixon, Nick S.; Tomlin, Alison S.

    2009-12-01

    A combined Lagrangian stochastic model with micro-mixing and chemical sub-models is used to investigate a reactive plume of nitrogen oxides (NO x) released into a turbulent grid flow doped with ozone (O 3). Sensitivities to the model input parameters are explored for different source NO x scenarios. The wind tunnel experiments of Brown and Bilger (1996) provide the simulation conditions for the first case study where photolysis reactions are not included and the main uncertainties occur in parameters defining the turbulence scales, source size and reaction rate of NO with O 3. Using nominal values of the parameters from previous studies, the model gives a good representation of the radial profile of the conserved mean scalar Γ although slightly over predicts peak mean NO 2 concentrations Γ compared to the experiments. The high dimensional model representation (HDMR) method is used to investigate the effects of uncertainties in model inputs on the simulation of chemical species concentrations. For this scenario, the Lagrangian velocity structure function coefficient has the largest impact on simulated Γ profiles. Photolysis reactions are then included in a chemical scheme consisting of eight reactions between species NO, O, O 3 and NO 2. Independent and interactive effects of 22 input parameters are studied for two source NO x scenarios using HDMR, including turbulence parameters, temperature dependant rate parameters, photolysis rates, temperature, fraction of NO in total NO x at the source and background ozone concentration [O 3]. For this reactive case, the variance in the predicted mean plume centre Γ is caused by parameters describing both physical (mixing time-scale coefficient) and chemical processes (activation energy for the reaction O 3+NO). The variance in predicted plume centre Γ and root mean square NO 2 concentration γNO', is strongly influenced by the fraction of NO in the source NO x, and to a lesser extent the mixing time-scale coefficient

  8. Defining Condensed Phase Reactive Force Fields from ab Initio Molecular Dynamics Simulations: The Case of the Hydrated Excess Proton.

    PubMed

    Knight, Chris; Maupin, C Mark; Izvekov, Sergei; Voth, Gregory A

    2010-10-12

    In this report, a general methodology is presented for the parametrization of a reactive force field using data from a condensed phase ab initio molecular dynamics (AIMD) simulation. This algorithm allows for the creation of an empirical reactive force field that accurately reproduces the underlying ab initio reactive surface while providing the ability to achieve long-time statistical sampling for large systems not possible with AIMD alone. In this work, a model for the hydrated excess proton is constructed where the hydronium cation and proton hopping portions of the model are statistically force-matched to the results of Car-Parrinello Molecular Dynamics (CPMD) simulations. The flexible nature of the algorithm also allows for the use of the more accurate classical simple point-charge flexible water (SPC/Fw) model to describe the water-water interactions while utilizing the ab initio data to create an overall multistate molecular dynamics (MS-MD) reactive model of the hydrated excess proton in water. The resulting empirical model for the system qualitatively reproduces thermodynamic and dynamic properties calculated from the ab initio simulation while being in good agreement with experimental results and previously developed multistate empirical valence bond (MS-EVB) models. The present methodology, therefore, bridges the AIMD technique with the MS-MD modeling of reactive events, while incorporating key strengths of both. PMID:26616784

  9. Numerical simulation of transient thermoreflectance of thin films in the picosecond regime

    SciTech Connect

    Kowalski, G.J.

    1996-12-31

    Transient thermoreflectance techniques, especially the picosecond transient thermoreflectance method (PTTR), provide a means of determining the thermo-physical properties of a thin film and of measuring thin film properties and temperature during manufacturing. In these techniques a pump and probe method is used to heat the sample and to measure the reflectance from it. It has been shown using a plane wave analysis and a one-dimensional thermal analysis based on uniform spatial irradiation that internal reflections caused by the spatial temperature field significantly affect the accuracy of the method in some materials. The internal reflection mechanism alters the temperature field as compared to that predicted without it. Criteria to define the range of importance of the internal reflection mechanism have been developed based on these assumptions. These results are extended using numerical analysis to investigate the effects of an incident Gaussian beam instead of uniform irradiation. The code includes mechanisms to describe the temperature and intensity dependent absorption coefficients and index of refraction. It is found that the two-dimensional effects decrease the one dimensional normalized reflectance change by 24%. A technique for the incorporating the code into the analysis of the PTTR is described.

  10. Thermal safety simulations of transient temperature rise during acoustic radiation force-based ultrasound elastography.

    PubMed

    Liu, Yunbo; Herman, Bruce A; Soneson, Joshua E; Harris, Gerald R

    2014-05-01

    Ultrasound transient elastography is a new diagnostic imaging technique that uses acoustic radiation force to produce motion in solid tissue via a high-intensity, long-duration "push" beam. In our previous work, we developed analytical models for calculating transient temperature rise, both in soft tissue and at a bone/soft tissue interface, during a single acoustic radiation force impulse (ARFI) imaging frame. The present study expands on these temperature rise calculations, providing applicable range assessment and error analysis for a single ARFI frame. Furthermore, a "virtual source" approach is described for temperature and thermal dose calculation under multiple ARFI frames. By use of this method, the effect of inter-frame cooling duration on temperature prediction is analyzed, and a thermal buildup phenomenon is revealed. Thermal safety assessment indicates that the thermal dose values, especially at the absorptive bone/soft tissue interface, could approach recommended dose thresholds if the cooling interval of multiple-frame ARFI elastography is too short.

  11. Simulation of time-dependent pool shape during laser spot welding: Transient effects

    NASA Astrophysics Data System (ADS)

    Ehlen, Georg; Ludwig, Andreas; Sahm, Peter R.

    2003-12-01

    The shape and depth of the area molten during a welding process is of immense technical importance. This study investigates how the melt pool shape during laser welding is influenced by Marangoni convection and tries to establish general qualitative rules of melt pool dynamics. A parameter study shows how different welding powers lead to extremely different pool shapes. Special attention is paid to transient effects that occur during the melting process as well as after switching off the laser source. It is shown that the final pool shape can depend strongly on the welding duration. The authors use an axisymmetric two-dimensional (2-D) control-volume-method (CVM) code based on the volume-averaged two-phase model of alloy solidification by Ni and Beckermann[1] and the SIMPLER algorithm by Patankar.[2] They calculate the transient distribution of temperatures, phase fractions, flow velocities, pressures, and concentrations of alloying elements in the melt and two solid phases (peritectic solidification) for a stationary laser welding process. Marangoni flow is described using a semiempirical model for the temperature-dependent surface tension gradient. The software was parallelized using the shared memory standard OpenMP.

  12. A computer simulation of the transient response of a 4 cylinder Stirling engine with burner and air preheater in a vehicle

    NASA Astrophysics Data System (ADS)

    Martini, W. R.

    1981-03-01

    A series of computer programs are presented with full documentation which simulate the transient behavior of a modern 4 cylinder Siemens arrangement Stirling engine with burner and air preheater. Cold start, cranking, idling, acceleration through 3 gear changes and steady speed operation are simulated. Sample results and complete operating instructions are given. A full source code listing of all programs are included.

  13. A computer simulation of the transient response of a 4 cylinder Stirling engine with burner and air preheater in a vehicle

    NASA Technical Reports Server (NTRS)

    Martini, W. R.

    1981-01-01

    A series of computer programs are presented with full documentation which simulate the transient behavior of a modern 4 cylinder Siemens arrangement Stirling engine with burner and air preheater. Cold start, cranking, idling, acceleration through 3 gear changes and steady speed operation are simulated. Sample results and complete operating instructions are given. A full source code listing of all programs are included.

  14. Effect of tidal fluctuations on transient dispersion of simulated contaminant concentrations in coastal aquifers

    USGS Publications Warehouse

    La Licata, Ivana; Langevin, Christian D.; Dausman, Alyssa M.; Alberti, Luca

    2013-01-01

    Variable-density groundwater models require extensive computational resources, particularly for simulations representing short-term hydrologic variability such as tidal fluctuations. Saltwater-intrusion models usually neglect tidal fluctuations and this may introduce errors in simulated concentrations. The effects of tides on simulated concentrations in a coastal aquifer were assessed. Three analyses are reported: in the first, simulations with and without tides were compared for three different dispersivity values. Tides do not significantly affect the transfer of a hypothetical contaminant into the ocean; however, the concentration difference between tidal and non-tidal simulations could be as much as 15%. In the second analysis, the dispersivity value for the model without tides was increased in a zone near the ocean boundary. By slightly increasing dispersivity in this zone, the maximum concentration difference between the simulations with and without tides was reduced to as low as 7%. In the last analysis, an apparent dispersivity value was calculated for each model cell using the simulated velocity variations from the model with tides. Use of apparent dispersivity values in models with a constant ocean boundary seems to provide a reasonable approach for approximating tidal effects in simulations where explicit representation of tidal fluctuations is not feasible.

  15. Effect of tidal fluctuations on transient dispersion of simulated contaminant concentrations in coastal aquifers

    USGS Publications Warehouse

    La Licata, Ivana; Langevin, Christian D.; Dausman, Alyssa M.; Alberti, Luca

    2011-01-01

    Variable-density groundwater models require extensive computational resources, particularly for simulations representing short-term hydrologic variability such as tidal fluctuations. Saltwater-intrusion models usually neglect tidal fluctuations and this may introduce errors in simulated concentrations. The effects of tides on simulated concentrations in a coastal aquifer were assessed. Three analyses are reported: in the first, simulations with and without tides were compared for three different dispersivity values. Tides do not significantly affect the transfer of a hypothetical contaminant into the ocean; however, the concentration difference between tidal and non-tidal simulations could be as much as 15%. In the second analysis, the dispersivity value for the model without tides was increased in a zone near the ocean boundary. By slightly increasing dispersivity in this zone, the maximum concentration difference between the simulations with and without tides was reduced to as low as 7%. In the last analysis, an apparent dispersivity value was calculated for each model cell using the simulated velocity variations from the model with tides. Use of apparent dispersivity values in models with a constant ocean boundary seems to provide a reasonable approach for approximating tidal effects in simulations where explicit representation of tidal fluctuations is not feasible.

  16. Development of a ReaxFF reactive force field for ettringite and study of its mechanical failure modes from reactive dynamics simulations.

    PubMed

    Liu, Lianchi; Jaramillo-Botero, Andres; Goddard, William A; Sun, Huai

    2012-04-19

    Ettringite is a hexacalcium aluminate trisulfate hydrate mineral that forms during Portland cement hydration. Its presence plays an important role in controlling the setting rate of the highly reactive aluminate phases in cement paste and has also been associated with severe cracking in cured hardened cement. To understand how it forms and how its properties influence those of hardened cement and concrete, we have developed a first-principles-based ReaxFF reactive force field for Ca/Al/H/O/S. Here, we report on the development of this ReaxFF force field and on its validation and application using reactive molecular dynamics (RMD) simulations to characterize and understand the elastic, plastic, and failure response of ettringite at the atomic scale. The ReaxFF force field was validated by comparing the lattice parameters, pairwise distribution functions, and elastic constants of an ettringite crystal model obtained from RMD simulations with those from experiments. The predicted results are in close agreement with published experimental data. To characterize the atomistic failure modes of ettringite, we performed stress-strain simulations to find that Ca-O bonds are responsible for failure of the calcium sulfate and tricalcium aluminate (C3A) column in ettringite during uniaxial compression and tension and that hydrogen bond re-formation during compression induces an increase in plastic strain beyond the material's stress-strain proportionality limit. These results provide essential insight into understanding the mechanistic role of this mineral in cement and concrete degradation, and the ReaxFF potential developed in this work serves as a fundamental tool to further study the kinetics of hydration in cement and concrete. PMID:22413941

  17. Occurrence of transient puffs in a rotary-kiln incinerator simulator

    SciTech Connect

    Linak, W.P.; Kilgroe, J.D.; McSorley, J.A.; Wendt, J.O.L.; Dunn, J.E.

    1987-01-01

    This article discusses a statistically designed parametric investigation to determine which waste and kiln variables (charge mass, charge surface area, charge composition, and kiln temperature) significantly affect both instantaneous intensity and total magnitude of the puffs leaving a kiln used to incinerate simple prototype plastic wastes, ranging from polyethylene to polyvinychloride. Results show the relative ease with which failure conditions are achieved, even at high excess air values and high kiln temperatures. Transient puffs leaving the kiln contain a number of hazardous compounds. Increasing kiln temperature does not necessarily decrease the puff intensity and may in fact cause an increase. However, the total mass emitted always decreases with increasing temperature. In addition, the mass, surface area, and composition of the charge are all important.

  18. Simulation of an X-ray laser in the transient gain-saturation regime

    SciTech Connect

    Starikov, F A; Volkov, V A; Gasparyan, P D; Roslov, V I

    2009-09-30

    By using the TRANS code, we performed three-dimensional calculations of amplified spontaneous emission (ASE) in X-ray lasers on the 3p-3s transition in Ne-like Ge ({lambda} = 19.6 nm) and Ti ({lambda} = 2.6 nm) operating in the transient regime upon irradiation of a flat target by a high-power picosecond laser pulse focused into a line with one or two nanosecond prepulses. The hydrodynamics and population kinetics of the active medium of X-ray lasers were calculated by using the SS-9M code. The pulse duration, the gain, the spatial structure of the laser beam and the type of influence of a 'travelling' pump wave on the ASE brightness obtained in calculations are in agreement with the experimental data. The use of the 'travelling pump wave' leads not only to the increase in the ASE brightness but also considerably reduces its angular divergence. (active media)

  19. WHTSubmersible: a simulator for estimating transient circulation temperature in offshore wells with the semi-submersible platform

    NASA Astrophysics Data System (ADS)

    Song, Xun-cheng; Liu, Yong-wang; Guan, Zhi-chuan

    2015-10-01

    Offshore wellbore temperature field is significant to drilling fluids program, equipment selection, evaluations on potential risks caused by casing thermal stress, etc. This paper mainly describes the theoretical basis, module structure and field verification of the simulator WHTSubmersible. This computer program is a useful tool for estimating transient temperature distribution of circulating drilling fluid on semi-submersible platform. WHTSubmersible is based on a mathematical model which is developed to consider radial and axial two-dimensional heat exchange of the inner drill pipe, the annulus, the drill pipe wall, the sea water and the formation in the process of drilling fluid circulation. The solution of the discrete equations is based on finite volume method with an implicit scheme. This scheme serves to demonstrate the numerical solution procedure. Besides, the simulator also considers the heating generated by drilling fluid circulation friction, drill bit penetrating rocks, friction between the drill column and the borehole wall, and the temperature effect on thermal physical properties and rheology of the drilling fluid. These measures ensure more accurate results. The simulator has been programmed as a dynamic link library using Visual C++, the routine interface is simple, which can be connected with other computer programs conveniently. The simulator is validated with an actual well temperature filed developed on a semi-submersible platform in South China, and the error is less than 5 %.

  20. The influence of large-scale structures on entrainment in a decelerating transient turbulent jet revealed by large eddy simulation

    NASA Astrophysics Data System (ADS)

    Hu, Bing; Musculus, Mark P. B.; Oefelein, Joseph C.

    2012-04-01

    To provide a better understanding of the fluid mechanical mechanisms governing entrainment in decelerating jets, we performed a large eddy simulation (LES) of a transient air jet. The ensemble-averaged LES calculations agree well with the available measurements of centerline velocity, and they reveal a region of increased entrainment that grows as it propagates downstream during deceleration. Within the temporal and spatial domains of the simulation, entrainment during deceleration temporarily increases by roughly a factor of two over that of the quasi-steady jet, and thereafter decays to a level lower than the quasi-steady jet. The LES results also provide large-structure flow details that lend insight into the effects of deceleration on entrainment. The simulations show greater growth and separation of large vortical structures during deceleration. Ambient fluid is engulfed into the gaps between the large-scale structures, causing large-scale indentations in the scalar jet boundary. The changes in the growth and separation of large structures during deceleration are attributed to changes in the production and convection of vorticity. Both the absolute and normalized scalar dissipation rates decrease during deceleration, implying that changes in small-scale mixing during deceleration do not play an important role in the increased entrainment. Hence, the simulations predict that entrainment in combustion devices may be controlled by manipulating the fuel-jet boundary conditions, which affect structures at large scales much more than at small scales.

  1. ELM simulation experiments using transient heat and particle load produced by a magnetized coaxial plasma gun

    NASA Astrophysics Data System (ADS)

    Shoda, K.; Sakuma, I.; Iwamoto, D.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.

    2011-10-01

    It is considered that thermal transient events such as type I edge-localized modes (ELMs) and disruptions will limit the lifetime of plasma-facing components (PFCs) in ITER. It is predicted that the heat load onto the PFCs during type I ELMs in ITER is 0.2-2MJ/m2 with pulse length of ~0.1-1ms. We have investigated interaction between transient heat and particle load and the PFCs by using a magnetized coaxial plasma gun (MCPG) at University of Hyogo. In the experiment, a pulsed plasma with duration of ~0.5ms, incident ion energy of ~30eV, and surface absorbed energy density of ~0.3-0.7MJ/m2 was produced by the MCPG. However, no melting occurred on a tungsten surface exposed to a single plasma pulse of ~0.7MJ/m2, while cracks clearly appeared at the edge part of the W surface. Thus, we have recently started to improve the performance of the MCPG in order to investigate melt layer dynamics of a tungsten surface such as vapor cloud formation. In the modified MCPG, the capacitor bank energy for the plasma discharge is increased from 24.5 kJ to 144 kJ. In the preliminary experiments, the plasmoid with duration of ~0.6 ms, incident ion energy of ~ 40 eV, and the surface absorbed energy density of ~2 MJ/m2 was successfully produced at the gun voltage of 6 kV.

  2. Simulation of advective flow under steady-state and transient recharge conditions, Camp Edwards, Massachusetts Military Reservation, Cape Cod, Massachusetts

    USGS Publications Warehouse

    Walter, Donald A.; Masterson, John P.

    2003-01-01

    The U.S. Geological Survey has developed several ground-water models in support of an investigation of ground-water contamination being conducted by the Army National Guard Bureau at Camp Edwards, Massachusetts Military Reservation on western Cape Cod, Massachusetts. Regional and subregional steady-state models and regional transient models were used to (1) improve understanding of the hydrologic system, (2) simulate advective transport of contaminants, (3) delineate recharge areas to municipal wells, and (4) evaluate how model discretization and time-varying recharge affect simulation results. A water-table mound dominates ground-water-flow patterns. Near the top of the mound, which is within Camp Edwards, hydraulic gradients are nearly vertically downward and horizontal gradients are small. In downgradient areas that are further from the top of the water-table mound, the ratio of horizontal to vertical gradients is larger and horizontal flow predominates. The steady-state regional model adequately simulates advective transport in some areas of the aquifer; however, simulation of ground-water flow in areas with local hydrologic boundaries, such as ponds, requires more finely discretized subregional models. Subregional models also are needed to delineate recharge areas to municipal wells that are inadequately represented in the regional model or are near other pumped wells. Long-term changes in recharge rates affect hydraulic heads in the aquifer and shift the position of the top of the water-table mound. Hydraulic-gradient directions do not change over time in downgradient areas, whereas they do change substantially with temporal changes in recharge near the top of the water-table mound. The assumption of steady-state hydraulic conditions is valid in downgradient area, where advective transport paths change little over time. In areas closer to the top of the water-table mound, advective transport paths change as a function of time, transient and steady-state paths

  3. 2D fluid simulations of discharges at atmospheric pressure in reactive gas mixtures

    NASA Astrophysics Data System (ADS)

    Bourdon, Anne

    2015-09-01

    Since a few years, low-temperature atmospheric pressure discharges have received a considerable interest as they efficiently produce many reactive chemical species at a low energy cost. This potential is of great interest for a wide range of applications as plasma assisted combustion or biomedical applications. Then, in current simulations of atmospheric pressure discharges, there is the need to take into account detailed kinetic schemes. It is interesting to note that in some conditions, the kinetics of the discharge may play a role on the discharge dynamics itself. To illustrate this, we consider the case of the propagation of He-N2 discharges in long capillary tubes, studied for the development of medical devices for endoscopic applications. Simulation results put forward that the discharge dynamics and structure depend on the amount of N2 in the He-N2 mixture. In particular, as the amount of N2 admixture increases, the discharge propagation velocity in the tube increases, reaches a maximum for about 0 . 1 % of N2 and then decreases, in agreement with experiments. For applications as plasma assisted combustion with nanosecond repetitively pulsed discharges, there is the need to handle the very different timescales of the nanosecond discharge with the much longer (micro to millisecond) timescales of combustion processes. This is challenging from a computational point of view. It is also important to better understand the coupling of the plasma induced chemistry and the gas heating. To illustrate this, we present the simulation of the flame ignition in lean mixtures by a nanosecond pulsed discharge between two point electrodes. In particular, among the different discharge regimes of nanosecond repetitively pulsed discharges, a ``spark'' regime has been put forward in the experiments, with an ultra-fast local heating of the gas. For other discharge regimes, the gas heating is much weaker. We have simulated the nanosecond spark regime and have observed shock waves

  4. Progress towards the development of transient ram accelerator simulation as part of the U.S. Air Force Armament Directorate Research Program

    NASA Astrophysics Data System (ADS)

    Sinha, N.; York, B. J.; Dash, S. M.; Drabczuk, R.; Rolader, G. E.

    1992-07-01

    This paper describes the development of an advanced CFD simulation capability in support of the U.S. Air Force Armament Directorate's ram accelerator research initiative. The state-of-the-art CRAFT computer code has been specialized for high fidelity, transient ram accelerator simulations via inclusion of generalized dynamic gridding, solution adaptive grid clustering, high pressure thermochemistry, etc. Selected ram accelerator simulations are presented which serve to exhibit the CRAFT code's capabilities and identify some of the principal research/design issues.

  5. Hierarchical Testing with Automated Document Generation for Amanzi, ASCEM's Subsurface Flow and Reactive Transport Simulator

    NASA Astrophysics Data System (ADS)

    Moulton, J. D.; Steefel, C. I.; Yabusaki, S.; Castleton, K.; Scheibe, T. D.; Keating, E. H.; Freedman, V. L.

    2013-12-01

    The Advanced Simulation Capabililty for Environmental Management (ASCEM) program is developing an approach and open-source tool suite for standardized risk and performance assessments at legacy nuclear waste sites. These assessments use a graded and iterative approach, beginning with simplified highly abstracted models, and adding geometric and geologic complexity as understanding is gained. To build confidence in this assessment capability, extensive testing of the underlying tools is needed. Since the tools themselves, such as the subsurface flow and reactive-transport simulator, Amanzi, are under active development, testing must be both hierarchical and highly automated. In this presentation we show how we have met these requirements, by leveraging the python-based open-source documentation system called Sphinx with several other open-source tools. Sphinx builds on the reStructured text tool docutils, with important extensions that include high-quality formatting of equations, and integrated plotting through matplotlib. This allows the documentation, as well as the input files for tests, benchmark and tutorial problems, to be maintained with the source code under a version control system. In addition, it enables developers to build documentation in several different formats (e.g., html and pdf) from a single source. We will highlight these features, and discuss important benefits of this approach for Amanzi. In addition, we'll show that some of ASCEM's other tools, such as the sampling provided by the Uncertainty Quantification toolset, are naturally leveraged to enable more comprehensive testing. Finally, we will highlight the integration of this hiearchical testing and documentation framework with our build system and tools (CMake, CTest, and CDash).

  6. Reactive simulations of the activation barrier to dissolution of amorphous silica in water.

    PubMed

    Kagan, Michael; Lockwood, Glenn K; Garofalini, Stephen H

    2014-05-28

    Molecular dynamics simulations employing reactive potentials were used to determine the activation barriers to the dissolution of the amorphous SiO2 surface in the presence of a 2 nm overlayer of water. The potential of mean force calculations of the reactions of water molecules with 15 different starting Q4 sites (Qi is the Si site with i bridging oxygen neighbors) to eventually form the dissolved Q0 site were used to obtain the barriers. Activation barriers for each step in the dissolution process, from the Q4 to Q3 to Q2 to Q1 to Q0 were obtained. Relaxation runs between each reaction step enabled redistribution of the water above the surface in response to the new Qi site configuration. The rate-limiting step observed in the simulations was in both the Q32 reaction (a Q3 site changing to a Q2 site) and the Q21 reaction, each with an average barrier of ∼14.1 kcal mol(-1). However, the barrier for the overall reaction from the Q4 site to a Q0 site, averaged over the maximum barrier for each of the 15 samples, was 15.1 kcal mol(-1). This result is within the lower end of the experimental data, which varies from 14-24 kcal mol(-1), while ab initio calculations using small cluster models obtain values that vary from 18-39 kcal mol(-1). Constraints between the oxygen bridges from the Si site and the connecting silica structure, the presence of pre-reaction strained siloxane bonds, and the location of the reacting Si site within slight concave surface contours all affected the overall activation barriers.

  7. A reactive transport model to simulate uranium immobilization through pH manipulation

    SciTech Connect

    Zhang, Fan; Luo, Wensui; Watson, David B; Peterson, Mark J; Gu, Baohua; Spalding, Brian Patrick; Jardine, Philip M

    2008-07-01

    Saprolite cores collected from around the former S-3 Ponds waste disposal site on the Oak Ridge Reservation in east Tennessee, USA, exhibit low pH and high concentrations of Al, Ca, Mg, Mn, various trace metals such as Ni and Co, and radionuclides such as U and Tc. Because uranium is one of the major contaminants of concern at the site, its behavior was of particular interest. The mobility of uranium depends highly on pH. Groundwater titration experiments showed that when pH was increased from 3.87 to 5.45 with addition of dissolved sodium hydroxide, concentration of aqueous uranium decreased from 50 ppm to less than 5 ppm. However, base additions to the sediments to increase pH are strongly buffered by various precipitation and sorption reactions. This study was undertaken to investigate the geochemical processes that control contaminant mobility and to develop a practical model to predict uranium immobilization under conditions where pH is manipulated for remediation of geochemically complex sites. The method of Spalding and Spalding was utilized to model soil buffer capacity by treating aquifer solids as a polyprotic acid. Aluminum precipitation and dissolution kinetics was included in HydroGeoChem v5.0 in addition to an equilibrium reaction model that considers aqueous complexation, precipitation, sorption and soil buffering with pH-dependent ion exchange capacity. The HydroGeoChem model was successfully utilized to simulate batch titration experiments and comparison of reactive transport model results with pH manipulation column experiments were in close agreement. The model was also calibrated to simulate acidic groundwater percolating through carbonate gravel at the site.

  8. Reactive molecular dynamics simulations of shock through a single crystal of pentaerythritol tetranitrate.

    PubMed

    Budzien, Joanne; Thompson, Aidan P; Zybin, Sergey V

    2009-10-01

    Large-scale molecular dynamics simulations and the reactive force field ReaxFF were used to study shock-induced initiation in crystalline pentaerythritol tetranitrate (PETN). In the calculations, a PETN single crystal was impacted against a wall, driving a shockwave back through the crystal in the [100] direction. Two impact speeds (4 and 3 km/s) were used to compare strong and moderate shock behavior. The primary difference between the two shock strengths is the time required to exhibit the same qualitative behaviors with the lower impact speed lagging behind the faster impact speed. For both systems, the shock velocity exhibits an initial deceleration due to onset of endothermic reactions followed by acceleration due to the onset of exothermic reactions. At long times, the shock velocity reaches a steady value. After the initial deceleration period, peaks are observed in the profiles of the density and axial stress with the strongly shocked system having sharp peaks while the weakly shocked system developed broad peaks due to the slower shock velocity acceleration. The dominant initiation reactions in both systems lead to the formation of NO(2) with lesser quantities of NO(3) and formaldehyde also produced.

  9. Simulation of reactive transport of injected CO2 on the Colorado Plateau, Utah, USA

    USGS Publications Warehouse

    White, S.P.; Allis, R.G.; Moore, J.; Chidsey, T.; Morgan, C.; Gwynn, W.; Adams, M.

    2005-01-01

    This paper investigates injection of CO2 into non-dome-shaped geological structures that do not provide the traps traditionally deemed necessary for the development of artificial CO2 reservoirs. We have developed a conceptual and two numerical models of the geology and groundwater along a cross-section lying approximately NW-SE and in the vicinity of the Hunter power station on the Colorado Plateau, Central Utah and identified a number of potential sequestration sites on this cross-section. Preliminary modeling identified the White Rim Sandstone as appearing to offer the properties required of a successful sequestration site. Detailed modeling of injection of CO2 into the White Rim Sandstone using the reactive chemical simulator ChemTOUGH found that 1000 years after the 30 year injection period began approximately 21% of the injected CO2 was permanently sequestered as a mineral, 52% was beneath the ground surface as a gas or dissolved in the groundwater and 17% had leaked to the surface and leakage to the surface was continuing. ?? 2005 Elsevier B.V. All rights reserved.

  10. CHARMM force field parameters for simulation of reactive intermediates in native and thio-substituted ribozymes.

    PubMed

    Mayaan, Evelyn; Moser, Adam; MacKerell, Alexander D; York, Darrin M

    2007-01-30

    Force field parameters specifically optimized for residues important in the study of RNA catalysis are derived from density-functional calculations, in a fashion consistent with the CHARMM27 all-atom empirical force field. Parameters are presented for residues that model reactive RNA intermediates and transition state analogs, thio-substituted phosphates and phosphoranes, and bound Mg(2+) and di-metal bridge complexes. Target data was generated via density-functional calculations at the B3LYP/6-311++G(3df,2p)// B3LYP/6-31++G(d,p) level. Partial atomic charges were initially derived from CHelpG electrostatic potential fitting and subsequently adjusted to be consistent with the CHARMM27 charges. Lennard-Jones parameters were determined to reproduce interaction energies with water molecules. Bond, angle, and torsion parameters were derived from the density-functional calculations and renormalized to maintain compatibility with the existing CHARMM27 parameters for standard residues. The extension of the CHARMM27 force field parameters for the nonstandard biological residues presented here will have considerable use in simulations of ribozymes, including the study of freeze-trapped catalytic intermediates, metal ion binding and occupation, and thio effects.

  11. Simulating transient subsurface thermal fields in support of geomorphic process research

    NASA Astrophysics Data System (ADS)

    Gruber, S.; Endrizzi, S.; Gubler, S.

    2012-12-01

    The analysis or up-scaling of thermal control on weathering, erosion or transport phenomena usually requires the ability to simulate subsurface thermal fields as a function of time, depth, topographic position or material type. Using air temperature or temperatures measured at only one location usually does not suffice in this context. Three examples will motivate this presentation: (a) frost cracking investigated by outdoor monitoring of acoustic emissions, temperature and moisture in rock, (b) rock fall triggering investigated by numerical experiments, and (c) kinematics of permafrost slopes and rock glaciers investigated by distributed continuous GPS and simulated subsurface conditions. Based on the data needs of these examples, a simulation strategy and system that has evolved from permafrost modeling over the last decade is introduced. The basic structure of the models used is shown and current success and challenges in simulations discussed. The sparse data available for validation as well as the strong extrapolations involved necessitate an increasing attention to model uncertainty and its effect on the products or conclusions based on simulated data.

  12. Evaluation of a transient, simultaneous, arbitrary Lagrange-Euler based multi-physics method for simulating the mitral heart valve.

    PubMed

    Espino, Daniel M; Shepherd, Duncan E T; Hukins, David W L

    2014-01-01

    A transient multi-physics model of the mitral heart valve has been developed, which allows simultaneous calculation of fluid flow and structural deformation. A recently developed contact method has been applied to enable simulation of systole (the stage when blood pressure is elevated within the heart to pump blood to the body). The geometry was simplified to represent the mitral valve within the heart walls in two dimensions. Only the mitral valve undergoes deformation. A moving arbitrary Lagrange-Euler mesh is used to allow true fluid-structure interaction (FSI). The FSI model requires blood flow to induce valve closure by inducing strains in the region of 10-20%. Model predictions were found to be consistent with existing literature and will undergo further development.

  13. Three-dimensional transient numerical simulation for intake process in the engine intake port-valve-cylinder system.

    PubMed

    Luo, Ma-Ji; Chen, Guo-Hua; Ma, Yuan-Hao

    2003-01-01

    This paper presents a KIVA-3 code based numerical model for three-dimensional transient intake flow in the intake port-valve-cylinder system of internal combustion engine using body-fitted technique, which can be used in numerical study on internal combustion engine with vertical and inclined valves, and has higher calculation precision. A numerical simulation (on the intake process of a two-valve engine with a semi-sphere combustion chamber and a radial intake port) is provided for analysis of the velocity field and pressure field of different plane at different crank angles. The results revealed the formation of the tumble motion, the evolution of flow field parameters and the variation of tumble ratios as important information for the design of engine intake system.

  14. Development of single fluid volume element method for simulation of transient fluid flow in self-siphons

    NASA Astrophysics Data System (ADS)

    Viridi, S.; Novitrian, Nurhayati, Hidayat, W.; Latief, F. D. E.; Zen, F. P.

    2014-09-01

    A simple model for transient flow in a narrow pipe is presented in this work. The model is simply derived from Newton's second law of motion. As an example it is used to predict flow occurrence in two forms of self-siphon, which are inverted-U and M-like forms. Simulation for system consists only a vertical pipe is also presented since it is actually part of the both siphon systems. For the simple systems the model can have good predictions but for the complex system it can only have 89.6 % good prediction. Its simplicity can be used to illustrate how the interface between fluid and air, single fluid volume element (SFVE) moves along the siphon. The method itself is named as SFVE method.

  15. Dynamic vapor generator that simulates transient odor emissions of victims entrapped in the voids of collapsed buildings.

    PubMed

    Statheropoulos, M; Pallis, G C; Mikedi, K; Giannoukos, S; Agapiou, A; Pappa, A; Cole, A; Vautz, W; Thomas, C L Paul

    2014-04-15

    The design, development, and validation of a dynamic vapor generator are presented. The generator simulates human scent (odor) emissions from trapped victims in the voids of collapsed buildings. The validation of the device was carried out using a reference detector: a quadrupole mass spectrometer equipped with a pulsed sampling (PS-MS) system. A series of experiments were conducted for evaluating the simulator's performance, defining types and weights of different factors, and proposing further optimization of the device. The developed device enabled the production of stable and transient odor profiles in a controllable and reproducible way (relative standard deviation, RSD < 11%) at ppbv to low ppmv concentrations and allowed emission durations up to 30 min. Moreover, the factors affecting its optimum performance (i.e., evaporation chamber temperature, air flow rate through the mixing chamber, air flow rate through the evaporation chamber, and type of compound) were evaluated through an analysis of variance (ANOVA) tool revealing the next steps toward optimizing the generator. The developed simulator, potentially, can also serve the need for calibrating and evaluating the performance of analytical devices (e.g., gas chromatographers, ion mobility spectrometers, mass spectrometers, sensors, e-noses) in the field. Furthermore, it can contribute in better training of urban search and rescue (USaR) canines.

  16. Transient Simulation of Climate Evolution over the Last 21,000 years (TraCE-21,000): First Results

    NASA Astrophysics Data System (ADS)

    Otto-Bliesner, B. L.; Liu, Z.; He, F.; Brady, E.; Clark, P.; Carlson, A.; Tomas, R.; Erickson, D.; Jacob, R.

    2008-12-01

    This is a report of the first transient simulation of global climate change from the Last Glacial Maximum to 14 kyr BP employing the synchronously coupled NCAR CCSM3. Forced by realistic orbital influences, greenhouse gas concentrations, continental ice sheets, as well as a reasonable characterization of melting water forcing, CCSM3 is able to simulate many major features of the deglaciation climate evolution and abrupt climate changes. Most notably, the Heinrich 1 event, the Bolling-Allerod (BA) warming, and the associated changes of the Atlantic thermohaline circulation are replicated in our simulation. The numerical results suggest that the abrupt climate change towards the BA is induced by the rebounding of the thermohaline circulation and the associated high latitude climate feedbacks in response to the demise of the North Atlantic meltwater forcing. This is in contrast to other theories involving hysteresis of the thermohaline circulation. Our analysis also suggests that the abrupt change in the North Atlantic region has a significant impact on low latitude climate and monsoon systems through atmospheric and oceanic teleconnections.

  17. Kinetic Monte Carlo simulations for transient thermal fields: Computational methodology and application to the submicrosecond laser processes in implanted silicon.

    PubMed

    Fisicaro, G; Pelaz, L; Lopez, P; La Magna, A

    2012-09-01

    Pulsed laser irradiation of damaged solids promotes ultrafast nonequilibrium kinetics, on the submicrosecond scale, leading to microscopic modifications of the material state. Reliable theoretical predictions of this evolution can be achieved only by simulating particle interactions in the presence of large and transient gradients of the thermal field. We propose a kinetic Monte Carlo (KMC) method for the simulation of damaged systems in the extremely far-from-equilibrium conditions caused by the laser irradiation. The reference systems are nonideal crystals containing point defect excesses, an order of magnitude larger than the equilibrium density, due to a preirradiation ion implantation process. The thermal and, eventual, melting problem is solved within the phase-field methodology, and the numerical solutions for the space- and time-dependent thermal field were then dynamically coupled to the KMC code. The formalism, implementation, and related tests of our computational code are discussed in detail. As an application example we analyze the evolution of the defect system caused by P ion implantation in Si under nanosecond pulsed irradiation. The simulation results suggest a significant annihilation of the implantation damage which can be well controlled by the laser fluence.

  18. Transient simulations of nitrogen load for a coastal aquifer and embayment, Cape Cod, MA

    USGS Publications Warehouse

    Colman, J.A.; Masterson, J.P.

    2008-01-01

    A time-varying, multispecies, modular, three-dimensional transport model (MT3DMS) was developed to simulate groundwater transport of nitrogen from increasing sources on land to the shore of Nauset Marsh, a coastal embayment of the Cape Cod National Seashore. Simulated time-dependent nitrogen loads at the coast can be used to correlate with current observed coastal eutrophic effects, to predict current and ultimate effects of development, and to predict loads resulting from source remediation. A time-varying nitrogen load, corrected for subsurface loss, was applied to the land subsurface in the transport model based on five land-use coverages documenting increasing development from 1951 to 1999. Simulated nitrogen loads to Nauset Marsh increased from 230 kg/yr before 1930 to 4390 kg/yr in 2001 to 7130 kg/yr in 2100, assuming future nitrogen sources constant at the 1999 land-use rate. The simulated nitrogen load per area of embayment was 5 times greater for Salt Pond, a eutrophic landward extension of Nauset Marsh, than for other Nauset Marsh areas. Sensitivity analysis indicated that load results were little affected by changes in vertical discretization and annual recharge but much affected by the nitrogen loss rate assumed for a kettle lake downgradient from a landfill.

  19. Transient simulations of nitrogen load for a coastal aquifer and embayment, Cape Cod, MA.

    PubMed

    Colman, John A; Masterson, John P

    2008-01-01

    A time-varying, multispecies, modular, three-dimensional transport model (MT3DMS) was developed to simulate groundwater transport of nitrogen from increasing sources on land to the shore of Nauset Marsh, a coastal embayment of the Cape Cod National Seashore. Simulated time-dependent nitrogen loads at the coast can be used to correlate with current observed coastal eutrophic effects, to predict current and ultimate effects of development, and to predict loads resulting from source remediation. A time-varying nitrogen load, corrected for subsurface loss, was applied to the land subsurface in the transport model based on five land-use coverages documenting increasing development from 1951 to 1999. Simulated nitrogen loads to Nauset Marsh increased from 230 kg/yr before 1930 to 4390 kg/yr in 2001 to 7130 kg/yr in 2100, assuming future nitrogen sources constant at the 1999 land-use rate. The simulated nitrogen load per area of embayment was 5 times greater for Salt Pond, a eutrophic landward extension of Nauset Marsh, than for other Nauset Marsh areas. Sensitivity analysis indicated that load results were little affected by changes in vertical discretization and annual recharge but much affected by the nitrogen loss rate assumed for a kettle lake downgradient from a landfill.

  20. Tool for the Integrated Dynamic Numerical Propulsion System Simulation (NPSS)/Turbine Engine Closed-Loop Transient Analysis (TTECTrA) User's Guide

    NASA Technical Reports Server (NTRS)

    Chin, Jeffrey C.; Csank, Jeffrey T.

    2016-01-01

    The Tool for Turbine Engine Closed-Loop Transient Analysis (TTECTrA ver2) is a control design tool thatenables preliminary estimation of transient performance for models without requiring a full nonlinear controller to bedesigned. The program is compatible with subsonic engine models implemented in the MATLAB/Simulink (TheMathworks, Inc.) environment and Numerical Propulsion System Simulation (NPSS) framework. At a specified flightcondition, TTECTrA will design a closed-loop controller meeting user-defined requirements in a semi or fully automatedfashion. Multiple specifications may be provided, in which case TTECTrA will design one controller for each, producing acollection of controllers in a single run. Each resulting controller contains a setpoint map, a schedule of setpointcontroller gains, and limiters; all contributing to transient characteristics. The goal of the program is to providesteady-state engine designers with more immediate feedback on the transient engine performance earlier in the design cycle.

  1. LATDYN - PROGRAM FOR SIMULATION OF LARGE ANGLE TRANSIENT DYNAMICS OF FLEXIBLE AND RIGID STRUCTURES

    NASA Technical Reports Server (NTRS)

    Housner, J. M.

    1994-01-01

    LATDYN is a computer code for modeling the Large Angle Transient DYNamics of flexible articulating structures and mechanisms involving joints about which members rotate through large angles. LATDYN extends and brings together some of the aspects of Finite Element Structural Analysis, Multi-Body Dynamics, and Control System Analysis; three disciplines that have been historically separate. It combines significant portions of their distinct capabilities into one single analysis tool. The finite element formulation for flexible bodies in LATDYN extends the conventional finite element formulation by using a convected coordinate system for constructing the equation of motion. LATDYN's formulation allows for large displacements and rotations of finite elements subject to the restriction that deformations within each are small. Also, the finite element approach implemented in LATDYN provides a convergent path for checking solutions simply by increasing mesh density. For rigid bodies and joints LATDYN borrows extensively from methodology used in multi-body dynamics where rigid bodies may be defined and connected together through joints (hinges, ball, universal, sliders, etc.). Joints may be modeled either by constraints or by adding joint degrees of freedom. To eliminate error brought about by the separation of structural analysis and control analysis, LATDYN provides symbolic capabilities for modeling control systems which are integrated with the structural dynamic analysis itself. Its command language contains syntactical structures which perform symbolic operations which are also interfaced directly with the finite element structural model, bypassing the modal approximation. Thus, when the dynamic equations representing the structural model are integrated, the equations representing the control system are integrated along with them as a coupled system. This procedure also has the side benefit of enabling a dramatic simplification of the user interface for modeling

  2. Simulating Water-Quality Trends in Public-Supply Wells in Transient Flow Systems

    PubMed Central

    Jeffrey Starn, J; Green, Christopher T; Hinkle, Stephen R; Bagtzoglou, Amvrossios C; Stolp, Bernard J

    2014-01-01

    Models need not be complex to be useful. An existing groundwater-flow model of Salt Lake Valley, Utah, was adapted for use with convolution-based advective particle tracking to explain broad spatial trends in dissolved solids. This model supports the hypothesis that water produced from wells is increasingly younger with higher proportions of surface sources as pumping changes in the basin over time. At individual wells, however, predicting specific water-quality changes remains challenging. The influence of pumping-induced transient groundwater flow on changes in mean age and source areas is significant. Mean age and source areas were mapped across the model domain to extend the results from observation wells to the entire aquifer to see where changes in concentrations of dissolved solids are expected to occur. The timing of these changes depends on accurate estimates of groundwater velocity. Calibration to tritium concentrations was used to estimate effective porosity and improve correlation between source area changes, age changes, and measured dissolved solids trends. Uncertainty in the model is due in part to spatial and temporal variations in tracer inputs, estimated tracer transport parameters, and in pumping stresses at sampling points. For tracers such as tritium, the presence of two-limbed input curves can be problematic because a single concentration can be associated with multiple disparate travel times. These shortcomings can be ameliorated by adding hydrologic and geologic detail to the model and by adding additional calibration data. However, the Salt Lake Valley model is useful even without such small-scale detail. PMID:25039912

  3. Simulating water-quality trends in public-supply wells in transient flow systems

    USGS Publications Warehouse

    Starn, J. Jeffrey; Green, Christopher T.; Hinkle, Stephen R.; Bagtzoglou, Amvrossios C.; Stolp, Bernard J.

    2014-01-01

    Models need not be complex to be useful. An existing groundwater-flow model of Salt Lake Valley, Utah, was adapted for use with convolution-based advective particle tracking to explain broad spatial trends in dissolved solids. This model supports the hypothesis that water produced from wells is increasingly younger with higher proportions of surface sources as pumping changes in the basin over time. At individual wells, however, predicting specific water-quality changes remains challenging. The influence of pumping-induced transient groundwater flow on changes in mean age and source areas is significant. Mean age and source areas were mapped across the model domain to extend the results from observation wells to the entire aquifer to see where changes in concentrations of dissolved solids are expected to occur. The timing of these changes depends on accurate estimates of groundwater velocity. Calibration to tritium concentrations was used to estimate effective porosity and improve correlation between source area changes, age changes, and measured dissolved solids trends. Uncertainty in the model is due in part to spatial and temporal variations in tracer inputs, estimated tracer transport parameters, and in pumping stresses at sampling points. For tracers such as tritium, the presence of two-limbed input curves can be problematic because a single concentration can be associated with multiple disparate travel times. These shortcomings can be ameliorated by adding hydrologic and geologic detail to the model and by adding additional calibration data. However, the Salt Lake Valley model is useful even without such small-scale detail.

  4. Simulating water-quality trends in public-supply wells in transient flow systems.

    PubMed

    Jeffrey Starn, J; Green, Christopher T; Hinkle, Stephen R; Bagtzoglou, Amvrossios C; Stolp, Bernard J

    2014-09-01

    Models need not be complex to be useful. An existing groundwater-flow model of Salt Lake Valley, Utah, was adapted for use with convolution-based advective particle tracking to explain broad spatial trends in dissolved solids. This model supports the hypothesis that water produced from wells is increasingly younger with higher proportions of surface sources as pumping changes in the basin over time. At individual wells, however, predicting specific water-quality changes remains challenging. The influence of pumping-induced transient groundwater flow on changes in mean age and source areas is significant. Mean age and source areas were mapped across the model domain to extend the results from observation wells to the entire aquifer to see where changes in concentrations of dissolved solids are expected to occur. The timing of these changes depends on accurate estimates of groundwater velocity. Calibration to tritium concentrations was used to estimate effective porosity and improve correlation between source area changes, age changes, and measured dissolved solids trends. Uncertainty in the model is due in part to spatial and temporal variations in tracer inputs, estimated tracer transport parameters, and in pumping stresses at sampling points. For tracers such as tritium, the presence of two-limbed input curves can be problematic because a single concentration can be associated with multiple disparate travel times. These shortcomings can be ameliorated by adding hydrologic and geologic detail to the model and by adding additional calibration data. However, the Salt Lake Valley model is useful even without such small-scale detail.

  5. Large-scale tropical transients in aquaplanet simulations with zonally symmetric sea surface temperature distributions (Invited)

    NASA Astrophysics Data System (ADS)

    Kuang, Z.

    2010-12-01

    Spectral analyses of sub-seasonal variations of tropical convection revealed features such as convectively coupled equatorial waves (CCEW) and the Madden-Julian Oscillations (MJO) over a red noise background. In this work, the super-parameterized Community Atmosphere Model (SPCAM) is used in aquaplanet experiments forced with zonally symmetric sea surface temperature distributions to investigate the roles of various processes in shaping the tropical spectra. Control experiments with the SPCAM model were able to produce the red noise background spectrum, CCEWs, and in some Intertropical Convergence Zone (ITCZ) configurations, “MJO-like” disturbances. To unravel the roles of various processes, experiments with simplified dynamics/settings are performed. In experiments where the large-scale dynamics in the model is largely linearized and with no feedbacks from radiative heating or surface sensible/latent heat and momentum fluxes, the spectra of large-scale tropical convectively coupled transients are dominated by the CCEWs, in ways generally consistent with results from the simple model of Andersen and Kuang (2008), and there are no red noise background spectra. Additional experiments show that the red noise aspect of the spectrum is mostly due to eddy stirring of the moisture field across its meridional gradient at the edge of the ITCZ, in particular the deep dry intrusions from the subtropics to the tropics. We will also discuss the effects of surface friction and idealized moist static energy sources, and use a simple model to understand these behaviors. It is hoped that through these and additional idealized studies, the various mechanisms that shape the tropical spectra can be elucidated. Ref:Andersen, J. A., Z. Kuang, A toy model of the instability in the equatorially trapped convectively coupled waves on the equatorial beta plane, Journal of Atmospheric Sciences, 65, 3736-3757, (2008)

  6. Simulations of compressible, diffusive, reactive flows with detailed chemistry using a high-order hybrid WENO-CD scheme

    NASA Astrophysics Data System (ADS)

    Ziegler, Jack L.

    A hybrid weighted essentially non-oscillatory (WENO)/centered-difference (CD) numerical method, with low numerical dissipation, high-order shock-capturing, and structured adaptive mesh refinement (SAMR), has been developed for the direct numerical simulation (DNS) of the multicomponent, compressive, reactive Navier-Stokes equations. The method enables accurate resolution of diffusive processes within reaction zones. This numerical method is verified with a series of one- and two-dimensional test problems, including a convergence test of a two-dimensional unsteady reactive double Mach reflection problem. Validation of the method is conducted with experimental comparisons of three applications all of which model multi-dimensional, unsteady reactive flow: an irregular propane detonation, shock and detonation bifurcations, and spark ignition deflagrations.

  7. Numerical simulation to study the transient self focusing of laser beam in plasma

    SciTech Connect

    Sharma, R. P.; Hussain, Saba Gaur, Nidhi

    2015-02-15

    In this paper, we present the numerical simulation for the coupled system of equations governing the dynamics of laser and Ion Acoustic Wave (IAW) in a collisionless plasma, when the coupling between the waves is through ponderomotive non-linearity. The nonlinear evolution of the laser beam is studied when the pump laser is perturbed by a periodic perturbation. By changing the perturbation wave number, we have studied its effect on the nonlinear evolution pattern of laser beam. In order to have a physical insight into the nonlinear dynamics of laser beam evolution in time and space, we have studied the laser and IAW spectra containing spatial harmonics. The magnitude of these harmonics changes with time and leads to time dependent localization of laser beam in spatial domain. The nonlinear dynamics of this localization is investigated in detail by using simulation and a semi-analytical model.

  8. A hybrid Boltzmann electrons and PIC ions model for simulating transient state of partially ionized plasma

    SciTech Connect

    Kwok, Dixon T.K.

    2008-05-10

    A robust and stable numerical algorithm is developed for the hybrid method of particle-in-cell ions and Boltzmann distribution of electrons. A different approach to estimate the electron density reference and its proper potential reference is developed to overcome the problems of instability and divergence of previous approaches. The electron density reference is precisely calculated, the tolerance criterion is well-defined, and convergence is guaranteed by applying bi-section golden rule. To increase the rate of convergence, an external loop is incorporated with the bi-section golden rule to vary the brackets. The validity of the method is proved by comparing the simulated result with well-known analytical formula. The simulated sheath potential at a floating wall fit well to the analytic result. The collisionless ion kinetic energy acquired from the voltage difference between the pre-sheath and ion sheath does not violate the Bohm sheath criterion. For work that focuses on the plasma process at the ion sheath and not on the generation of plasma, this method saves simulation time by avoiding time consuming particle or kinetic model of electrons. The new approach reproduces the ion density profile at the ion sheaths region of a plasma with bi-Maxwellian electrons coupling with radio-frequency (RF) signal by introducing two Boltzmann relations to describe the cold and hot thermal electrons for the first time.

  9. Ability of Preissmann slot scheme to simulate smooth pressurisation transient in sewers.

    PubMed

    Ferreri, Giovanni Battista; Freni, Gabriele; Tomaselli, Pietro

    2010-01-01

    Urban drainage networks are generally designed to operate in a free-surface flow condition. However, as a consequence of heavy rainfall events or network malfunctions, the filling of sewers (pressurisation) and network overflow may occur. Several modelling software products are commonly used to simulate floods in drainage networks, and their results are usually thought to be reliable and robust. However, no specific studies have been carried out on the behaviour of these modelling products during the pressurisation transition. Mathematical models often use the Preissmann slot concept to handle pressurisation. In this paper, on the basis of laboratory pipe tests, the reliability of such a scheme is studied by means of a popular and open-source software product: SWMM (Storm Water Management Model). Many numerical tests were carried out with SWMM, varying the spatial and time steps and the Preissmann slot width, in order to examine the performance of the modelling software over intervals of these parameters even wider than what is usual in practical applications. The comparison between simulated and experimental surges allows one to draw interesting conclusions regarding the effectiveness of software products analogous to SWMM in simulating pressurisation, as well as the choice of the parameters themselves.

  10. Numerical simulation and experimental study of transient liquid phase bonding of single crystal superalloys

    NASA Astrophysics Data System (ADS)

    Ghoneim, Adam

    The primary goals of the research in this dissertation are to perform a systematic study to identify and understand the fundamental cause of prolonged processing time during transient liquid phase bonding of difficult-to-bond single crystal Ni-base materials, and use the acquired knowledge to develop an effective way to reduce the isothermal solidification time without sacrificing the single crystalline nature of the base materials. To achieve these objectives, a multi-scale numerical modeling approach, that involves the use of a 2-D fully implicit moving-mesh Finite Element method and a Cellular Automata method, was developed to theoretically investigate the cause of long isothermal solidification times and determine a viable way to minimize the problem. Subsequently, the predictions of the theoretical models are experimentally validated. Contrary to previous suggestions, numerical calculations and experimental verifications have shown that enhanced intergranular diffusivity has a negligible effect on solidification time in cast superalloys and that another important factor must be responsible. In addition, it was found that the concept of competition between solute diffusivity and solubility as predicted by standard analytical TLP bonding models and reported in the literature as a possible cause of long solidification times is not suitable to explain salient experimental observations. In contrast, however, this study shows that the problem of long solidification times, which anomalously increase with temperature is fundamentally caused by departure from diffusion controlled parabolic migration of the liquid-solid interface with holding time during bonding due to a significant reduction in the solute concentration gradient in the base material. Theoretical analyses showed it is possible to minimize the solidification time and prevent formation of stray-grains in joints between single crystal substrates by using a composite powder mixture of brazing alloy and base

  11. REACTIVE TRANSPORT MODELING USING A PARALLEL FULLY-COUPLED SIMULATOR BASED ON PRECONDITIONED JACOBIAN-FREE NEWTON-KRYLOV

    SciTech Connect

    Luanjing Guo; Chuan Lu; Hai Huang; Derek R. Gaston

    2012-06-01

    Systems of multicomponent reactive transport in porous media that are large, highly nonlinear, and tightly coupled due to complex nonlinear reactions and strong solution-media interactions are often described by a system of coupled nonlinear partial differential algebraic equations (PDAEs). A preconditioned Jacobian-Free Newton-Krylov (JFNK) solution approach is applied to solve the PDAEs in a fully coupled, fully implicit manner. The advantage of the JFNK method is that it avoids explicitly computing and storing the Jacobian matrix during Newton nonlinear iterations for computational efficiency considerations. This solution approach is also enhanced by physics-based blocking preconditioning and multigrid algorithm for efficient inversion of preconditioners. Based on the solution approach, we have developed a reactive transport simulator named RAT. Numerical results are presented to demonstrate the efficiency and massive scalability of the simulator for reactive transport problems involving strong solution-mineral interactions and fast kinetics. It has been applied to study the highly nonlinearly coupled reactive transport system of a promising in situ environmental remediation that involves urea hydrolysis and calcium carbonate precipitation.

  12. Accelerating moderately stiff chemical kinetics in reactive-flow simulations using GPUs

    NASA Astrophysics Data System (ADS)

    Niemeyer, Kyle E.; Sung, Chih-Jen

    2014-01-01

    The chemical kinetics ODEs arising from operator-split reactive-flow simulations were solved on GPUs using explicit integration algorithms. Nonstiff chemical kinetics of a hydrogen oxidation mechanism (9 species and 38 irreversible reactions) were computed using the explicit fifth-order Runge-Kutta-Cash-Karp method, and the GPU-accelerated version performed faster than single- and six-core CPU versions by factors of 126 and 25, respectively, for 524,288 ODEs. Moderately stiff kinetics, represented with mechanisms for hydrogen/carbon-monoxide (13 species and 54 irreversible reactions) and methane (53 species and 634 irreversible reactions) oxidation, were computed using the stabilized explicit second-order Runge-Kutta-Chebyshev (RKC) algorithm. The GPU-based RKC implementation demonstrated an increase in performance of nearly 59 and 10 times, for problem sizes consisting of 262,144 ODEs and larger, than the single- and six-core CPU-based RKC algorithms using the hydrogen/carbon-monoxide mechanism. With the methane mechanism, RKC-GPU performed more than 65 and 11 times faster, for problem sizes consisting of 131,072 ODEs and larger, than the single- and six-core RKC-CPU versions, and up to 57 times faster than the six-core CPU-based implicit VODE algorithm on 65,536 ODEs. In the presence of more severe stiffness, such as ethylene oxidation (111 species and 1566 irreversible reactions), RKC-GPU performed more than 17 times faster than RKC-CPU on six cores for 32,768 ODEs and larger, and at best 4.5 times faster than VODE on six CPU cores for 65,536 ODEs. With a larger time step size, RKC-GPU performed at best 2.5 times slower than six-core VODE for 8192 ODEs and larger. Therefore, the need for developing new strategies for integrating stiff chemistry on GPUs was discussed.

  13. Numerical simulation of coastal flooding after potential reactivation of an active normal fault in northern Taiwan

    NASA Astrophysics Data System (ADS)

    Chan, Yu-Chang; Kuo, Chih-Yu; Chang, Kuo-Jen; Chen, Rou-Fei; Hsieh, Yu-Chung

    2016-04-01

    Rapid coastal flooding from seawards may be resulted from storm surge, tsunamis, and sudden land subsidence due to fault activities. Many observations and numerical modeling of flooding have been made for cases resulted from storm surge and tsunami events; however, coastal flooding caused by a potential normal faulting event nearby coastal areas is rarely reported. In addition to the earthquake hazards from fault rupturing and ground shaking, the accompanied hazards of earthquake-induced flooding is also important to be investigated. The Jinshan area in northern Taiwan was reported to have been flooded by a tsunami event in the year of 1867 possibly resulted from the reactivation of the Shanchiao normal fault offshore. Historical records have shown that the Shanchiao Fault that extends from Shulin along the western edge of the Taipei Basin to the town of Jinshan may have also ruptured in the year of 1694. The rupturing event has created a depression on the western side of the Taipei Basin that was later filled by sea water called the Taipei Lake. The geological conditions in northern Taiwan provide an opportunity for numerically simulating the dynamic processes of sea water flooding nearby the coastal area immediately after an earthquake-induced normal faulting event. In this study, we focused on the potential active normal faulting that may occur and result in an expected catastrophic flooding in lowland area of Jinshan in northern Taiwan. We applied the continuum shallow water equation to evaluate the unknown inundation processes including location, extent, velocity and water depths after the flooding initiated and the final state of the flooding event. The modeling results were well compared with borehole observations of the extent of previous flooding events possibly due to tsunami events. In addition, the modeling results may provide a future basis for safety evaluation of the two nuclear power plants nearby the region.

  14. An alternative to fully coupled reactive transport simulations for long-term prediction of chemical reactions in complex geological systems

    NASA Astrophysics Data System (ADS)

    De Lucia, Marco; Kempka, Thomas; Kühn, Michael

    2014-05-01

    Fully-coupled reactive transport simulations involving multiphase hydrodynamics and chemical reactions in heterogeneous settings are extremely challenging from a computational point of view. This often leads to oversimplification of the investigated system: coarse spatial discretization, to keep the number of elements in the order of few thousands; simplified chemistry, disregarding many potentially important reactions. A novel approach for coupling non-reactive hydrodynamic simulations with the outcome of single batch geochemical simulations was therefore introduced to assess the potential long-term mineral trapping at the Ketzin pilot site for underground CO2 storage in Germany [1],[2]. The advantage of the coupling is the ability to use multi-million grid non-reactive hydrodynamics simulations on one side and few batch 0D geochemical simulations on the other, so that the complexity of both systems does not need to be reduced. This contribution shows the approach which was taken to validate this simplified coupling scheme. The procedure involved batch simulations of the reference geochemical model, then performing both non-reactive and fully coupled 1D and 3D reactive transport simulations and finally applying the simplified coupling scheme based on the non-reactive and geochemical batch model. The TOUGHREACT/ECO2N [3] simulator was adopted for the validation. The degree of refinement of the spatial grid and the complexity and velocity of the mineral reactions, along with a cut-off value for the minimum concentration of dissolved CO2 allowed to originate precipitates in the simplified approach were found out to be the governing parameters for the convergence of the two schemes. Systematic discrepancies between the approaches are not reducible, simply because there is no feedback between chemistry and hydrodynamics, and can reach 20 % - 30 % in unfavourable cases. However, even such discrepancy is completely acceptable, in our opinion, given the amount of

  15. Early and transient stages of Cu oxidation: Atomistic insights from theoretical simulations and in situ experiments

    NASA Astrophysics Data System (ADS)

    Zhu, Qing; Zou, Lianfeng; Zhou, Guangwen; Saidi, Wissam A.; Yang, Judith C.

    2016-10-01

    Understanding of metal oxidation is critical to corrosion control, catalysis synthesis, and advanced materials engineering. Although, metal oxidation process is rather complicated, different processes, many of them coupled, are involved from the onset of reaction. Since first introduced, there has been great success in applying heteroepitaxial theory to the oxide growth on a metal surface as demonstrated in the Cu oxidation experiments. In this paper, we review the recent progress in experimental findings on Cu oxidation as well as the advances in the theoretical simulations of the Cu oxidation process. We focus on the effects of defects such as step edges, present on realistic metal surfaces, on the oxide growth dynamics. We show that the surface steps can change the mass transport of both Cu and O atoms during oxide growth, and ultimately lead to the formation of different oxide morphology. We also review the oxidation of Cu alloys and explore the effect of a secondary element to the oxide growth on a Cu surface. From the review of the work on Cu oxidation, we demonstrate the correlation of theoretical simulations at multiple scales with various experimental techniques.

  16. Results of transient simulations of a digital model of the Arikaree Aquifer near Wheatland, southeastern Wyoming

    USGS Publications Warehouse

    Hoxie, Dwight T.

    1979-01-01

    Revised ground-water pumpage data have been imposed on a ground-water flow model previously developed for the Arikaree aquifer in a 400 square-mile area in central Platte County, Wyo. Maximum permitted annual ground-water withdrawals of 750 acre-feet for industrial use were combined with three irrigation-pumping scenarios to predict the long-term effects on ground-water levels and streamflows. Total annual ground-water withdrawals of 8,806 acre-feet, 8,033 acre-feet, and 5,045 acre-feet were predicted to produce average water-level declines of 5 feet or more over areas of 99, 96, and 68 square miles, respectively, at the end of a 40-year simulation period. The first two pumping scenarios were predicted to produce average drawdowns of more than 50 feet over areas of 1.5 and 0.8 square miles, respectively, while the third scenario resulted in average drawdowns of less than 50 feet throughout the study area. In addition, these three pumping scenarios were predicted to cause streamflow reductions of 2.6, 2.0, and 1.4 cubic feet per second, respectively, in the Laramie River and 4.9, 4.7, and 3.7 cubic feet per second, respectively, in the North Laramie River at the end of the 40-year simulation period. (Kosco-USGS)

  17. Role of dayside transients in a substorm process: Results from the global kinetic simulation Vlasiator

    NASA Astrophysics Data System (ADS)

    Palmroth, M.; Hoilijoki, S.; Pfau-Kempf, Y.; Hietala, H.; Nishimura, Y.; Angelopoulos, V.; Pulkkinen, T. I.; Ganse, U.; Hannuksela, O.; von Alfthan, S.; Battarbee, M. C.; Vainio, R. O.

    2015-12-01

    We investigate the dayside-nightside coupling of the magnetospheric dynamics in a global kinetic simulation displaying the entire magnetosphere. We use the newly developed Vlasiator (http://vlasiator.fmi.fi), which is the world's first global hybrid-Vlasov simulation modelling the ions as distribution functions, while electrons are treated as a charge-neutralising fluid. Here, we run Vlasiator in the 5-dimensional (5D) setup, where the ordinary space is presented in the 2D noon-midnight meridional plane, embedding in each grid cell the 3D velocity space. This approach combines the improved physical solution with fine resolution, allowing to investigate kinetic processes as a consequence of the global magnetospheric evolution. The simulation is during steady southward interplanetary magnetic field. We observe dayside reconnection and the resulting 2D representations of flux transfer events (FTE). FTE's move tailwards and distort the magnetopause, while the largest of them even modify the plasma sheet location. In the nightside, the plasma sheet shows bead-like density enhancements moving slowly earthward. The tailward side of the dipolar field stretches. Strong reconnection initiates first in the near-Earth region, forming a tailward-moving magnetic island that cannibalises other islands forming further down the tail, increasing the island's volume and complexity. After this, several reconnection lines are formed again in the near-Earth region, resulting in several magnetic islands. At first, none of the earthward moving islands reach the closed field region because just tailward of the dipolar region exists a relatively stable X-line, which is strong enough to push most of the magnetic islands tailward. However, finally one of the tailward X-lines is strong enough to overcome the X-line nearest to Earth, forming a strong surge into the dipolar field region as there is nothing anymore to hold back the propagation of the structure. We investigate this substorm

  18. Simulation procedure for modeling transient water table and artesian stress and response

    USGS Publications Warehouse

    Reed, J.E.; Bedinger, M.S.; Terry, J.E.

    1976-01-01

    The series of computer programs described in this report were designed specifically to model the ground-water regime in sufficient detail to determine the effects of the imposition of various types of stress upon the system, and to display the results in a convenient manner during calibration and when presenting projected data. SUPERMOCK simulates the ground-water system and DATE and HYDROG aid in the display of computed data. During calibration, DATE is especially useful because it has the optional feature of comparing computed data with observed data. Although the programs can be run independently, experience dictates that for best results the three should be run as steps in the same job. English units of inches, feet, and days are used in each of the programs. The units for any parameters not given in the text are clearly specified in the instructions for input to the individual programs. (Woodard-USGS)

  19. Transient simulation of nozzle geometry change during ablation in high-voltage circuit breakers

    NASA Astrophysics Data System (ADS)

    Arabi, Sina; Trépanier, Jean-Yves; Camarero, Ricardo

    2015-02-01

    In high voltage circuit breakers, radiated heat from the electric arc is strongly absorbed by surrounding poly-tetra-fluro-ethylene (PTFE) parts and causes them to reach their vaporization temperature and ablate. Ablation deforms the PTFE parts, widens the throat and hence, changes the nozzle geometry. This paper presents a physical model coupling plasma flow simulation with erosion and movement of the PTFE walls to study this phenomena. The model is first applied and validated on a segmented tube case and on a model SF6 circuit breaker for which the experimental data is available. Then, the model is used to investigate the effect of the surface ablation on the nozzle geometry in a long-operation time.

  20. Numerical simulation of the transient temperature field from an annular focused ultrasonic transducer.

    PubMed

    Zhang, Qiang; Li, Faqi; Feng, Ruo; Xu, Jianyi; Bai, Jin; Wang, Zhibiao; Wang, Yaojun

    2003-04-01

    Knowledge of the extent of the "heated necrosis element" from a single exposure in target tissue created by an ultrasonic beam is critical for the application of focal ultrasound (US) surgery (FUS). This study uses the O'Nell and Pennes formulas to simulate the heated necrosis element from an annular focused transducer and to examine its dependence on exposure dosage, as well as some design parameters of the transducer. Several conclusions may be drawn from our numerical results: 1. With increasing exposure, the heated necrosis element increases, but its contour becomes plumper and the influence of sound intensity I is found to be greater than that of the exposure time t. 2. To get a similar heated necrosis element, the exposure approximately satisfies a relation: It(0. 4 3)=constant. 3. Increasing the US frequency or the outer-radius of the annular transducer leads to a decrease in the heated necrosis volume. PMID:12749928

  1. In situ measurement and simulation of nano-magnetite mobility in porous media subject to transient salinity

    NASA Astrophysics Data System (ADS)

    Becker, Matthew D.; Wang, Yonggang; L. Paulsen, Jeffrey; Song, Yi-Qiao; Abriola, Linda M.; Pennell, Kurt D.

    2014-12-01

    Nanotechnologies have been proposed for a variety of environmental applications, including subsurface characterization, enhanced oil recovery, and in situ contaminant remediation. For such applications, quantitative predictive models will be of great utility for system design and implementation. Electrolyte chemistry, which can vary substantially within subsurface pore waters, has been shown to strongly influence nanoparticle aggregation and deposition in porous media. Thus, it is essential that mathematical models be capable of tracking changes in electrolyte chemistry and predicting its influence on nanoparticle mobility. In this work, a modified version of a multi-dimensional multispecies transport simulator (SEAWAT) was employed to model nanoparticle transport under transient electrolyte conditions. The modeling effort was supported by experimental measurements of paramagnetic magnetite (Fe3O4) nanoparticle, coated with polyacrylamide-methylpropane sulfonic acid - lauryl acrylate (nMag-PAMPS), mobility in columns packed with 40-50 mesh Ottawa sand. Column effluent analyses and magnetic resonance imaging (MRI) were used to quantify nanoparticle breakthrough and in situ aqueous phase concentrations, respectively. Experimental observations revealed that introduction of de-ionized water into the brine saturated column (80 g L-1 NaCl + 20 g L-1 CaCl2) promoted release and remobilization of deposited nanoparticles along a diagonal front, coincident with the variable density flow field. This behavior was accurately captured by the simulation results, which indicated that a two-site deposition-release model provided the best fit to experimental observations, suggesting that heterogeneous nanoparticle-surface interactions governed nanoparticle attachment. These findings illustrate the importance of accounting for both physical and chemical processes associated with changes in electrolyte chemistry when predicting nanoparticle transport behavior in subsurface formations

  2. Development of EEM based silicon–water and silica–water wall potentials for non-reactive molecular dynamics simulations

    SciTech Connect

    Kim, Junghan; Iype, Eldhose; Frijns, Arjan J.H.; Nedea, Silvia V.; Steenhoven, Anton A. van

    2014-07-01

    Molecular dynamics simulations of heat transfer in gases are computationally expensive when the wall molecules are explicitly modeled. To save computational time, an implicit boundary function is often used. Steele's potential has been used in studies of fluid–solid interface for a long time. In this work, the conceptual idea of Steele's potential was extended in order to simulate water–silicon and water–silica interfaces. A new wall potential model is developed by using the electronegativity-equalization method (EEM), a ReaxFF empirical force field and a non-reactive molecular dynamics package PumMa. Contact angle simulations were performed in order to validate the wall potential model. Contact angle simulations with the resulting tabulated wall potentials gave a silicon–water contact angle of 129°, a quartz–water contact angle of 0°, and a cristobalite–water contact angle of 40°, which are in reasonable agreement with experimental values.

  3. 3D transient electromagnetic simulation using a modified correspondence principle for wave and diffusion fields

    NASA Astrophysics Data System (ADS)

    Hu, Y.; Ji, Y.; Egbert, G. D.

    2015-12-01

    simulation problems for non-point sources.

  4. Simulation of bombe radiocarbon transient in the Mediterranean Sea using a high-resolution regional model.

    NASA Astrophysics Data System (ADS)

    Ayache, Mohamed; Dutay, Jean-claude; Mouchet, Anne; Tisnérat-Laborde, Nadine; Houma-Bachari, Fouzia; Louanchi, Ferial; jean-baptiste, Philippe

    2016-04-01

    The radiocarbon isotope of carbon "14C", which a half-life of 5730 years, is continually formed naturally in the atmosphere by the neutron bombardment of 14N atoms. However, in the 1950s and early1960s, the atmospheric testing of thermonuclear weapons added a large amount of 14C into the atmosphere. The gradual infusion and spread of this "bomb" 14C through the oceans has provided a unique opportunity to gain insight into the specific rates characterizing the carbon cycle and ocean ventilations on such timescales. This numerical study provides, for the first time in the Mediterranean Sea, a simulation of the anthropogenic 14C invasion covers a 70-years period spanning the entire 14C generated by the bomb test, by using a high resolution regional model NEMO-MED12 (1/12° of horizontal resolution). This distribution and evolution of Δ14C of model is compared with recent high resolution 14C measurements obtained from surface water corals (Tisnérat-Laborde et al, 2013). In addition to providing constraints on the air-sea transfer of 14C, our work provides information on the thermohaline circulation and the ventilation of the deep waters to constrain the degree to which the NEMO-MED12 can reproduce correctly the main hydrographic features of the Mediterranean Sea circulation and its variations estimated from corals 14C time series measurements. This study is part of the work carried out to assess the robustness of the NEMO-MED12 model, which will be used to study the evolution of the climate and its effect on the biogeochemical cycles in the Mediterranean Sea, and to improve our ability to predict the future evolution of the Mediterranean Sea under the increasing anthropogenic pressure.

  5. In situ measurement and simulation of nano-magnetite mobility in porous media subject to transient salinity

    NASA Astrophysics Data System (ADS)

    Becker, Matthew D.; Wang, Yonggang; L. Paulsen, Jeffrey; Song, Yi-Qiao; Abriola, Linda M.; Pennell, Kurt D.

    2014-12-01

    Nanotechnologies have been proposed for a variety of environmental applications, including subsurface characterization, enhanced oil recovery, and in situ contaminant remediation. For such applications, quantitative predictive models will be of great utility for system design and implementation. Electrolyte chemistry, which can vary substantially within subsurface pore waters, has been shown to strongly influence nanoparticle aggregation and deposition in porous media. Thus, it is essential that mathematical models be capable of tracking changes in electrolyte chemistry and predicting its influence on nanoparticle mobility. In this work, a modified version of a multi-dimensional multispecies transport simulator (SEAWAT) was employed to model nanoparticle transport under transient electrolyte conditions. The modeling effort was supported by experimental measurements of paramagnetic magnetite (Fe3O4) nanoparticle, coated with polyacrylamide-methylpropane sulfonic acid - lauryl acrylate (nMag-PAMPS), mobility in columns packed with 40-50 mesh Ottawa sand. Column effluent analyses and magnetic resonance imaging (MRI) were used to quantify nanoparticle breakthrough and in situ aqueous phase concentrations, respectively. Experimental observations revealed that introduction of de-ionized water into the brine saturated column (80 g L-1 NaCl + 20 g L-1 CaCl2) promoted release and remobilization of deposited nanoparticles along a diagonal front, coincident with the variable density flow field. This behavior was accurately captured by the simulation results, which indicated that a two-site deposition-release model provided the best fit to experimental observations, suggesting that heterogeneous nanoparticle-surface interactions governed nanoparticle attachment. These findings illustrate the importance of accounting for both physical and chemical processes associated with changes in electrolyte chemistry when predicting nanoparticle transport behavior in subsurface formations

  6. Regional Warming from Aerosol Removal over the United States: Results from a Transient 2010-2050 Climate Simulation

    NASA Technical Reports Server (NTRS)

    Mickley, L. J.; Leibensperger, E. M.; Jacob, D. J.; Rind, D.

    2012-01-01

    We use a general circulation model (NASA Goddard Institute for Space Studies GCM 3) to investigate the regional climate response to removal of aerosols over the United States. We perform a pair of transient 2010e2050 climate simulations following a scenario of increasing greenhouse gas concentrations, with and without aerosols over the United States and with present-day aerosols elsewhere. We find that removing U.S. aerosol significantly enhances the warming from greenhouse gases in a spatial pattern that strongly correlates with that of the aerosol. Warming is nearly negligible outside the United States, but annual mean surface temperatures increase by 0.4e0.6 K in the eastern United States. Temperatures during summer heat waves in the Northeast rise by as much as 1e2 K due to aerosol removal, driven in part by positive feedbacks involving soil moisture and low cloud cover. Reducing U.S. aerosol sources to achieve air quality objectives could thus have significant unintended regional warming consequences.

  7. Molecular dynamics simulation study on the transient response of solvation structure during the translational diffusion of solute.

    PubMed

    Yamaguchi, T; Matsuoka, T; Koda, S

    2005-01-01

    The transient response function of the density profile of the solvent around a solute during the translational diffusion of the solute is formulated based on the generalized Langevin formalism. The resultant theory is applied to both neat Lennard-Jones fluids and cations in liquid water, and the response functions are obtained from the analysis of the molecular dynamics simulations. In the case of the self-diffusion of Lennard-Jones fluids, the responses of the solvation structures are in harmony with conventional pictures based on the mode-coupling theory, that is, the binary collision in the low-density fluids, the backflow effect from medium to high density fluids, and the backscatter effect in the liquids near the triple point. In the case of cations in water, the qualitative behavior is strongly dependent on the size of cations. The pictures similar to simple dense liquids are obtained for the large ion and the neutral molecule, while the solvent waters within the first solvation shell of small ions show an oscillatory response in the short-time region. In particular, the oscillation is remarkably underdumped for lithium ion. The origin of the oscillation is discussed in relation to the theoretical treatment of the translational diffusion of ions in water. PMID:15638679

  8. Molecular dynamics simulation study on the transient response of solvation structure during the translational diffusion of solute

    NASA Astrophysics Data System (ADS)

    Yamaguchi, T.; Matsuoka, T.; Koda, S.

    2005-01-01

    The transient response function of the density profile of the solvent around a solute during the translational diffusion of the solute is formulated based on the generalized Langevin formalism. The resultant theory is applied to both neat Lennard-Jones fluids and cations in liquid water, and the response functions are obtained from the analysis of the molecular dynamics simulations. In the case of the self-diffusion of Lennard-Jones fluids, the responses of the solvation structures are in harmony with conventional pictures based on the mode-coupling theory, that is, the binary collision in the low-density fluids, the backflow effect from medium to high density fluids, and the backscatter effect in the liquids near the triple point. In the case of cations in water, the qualitative behavior is strongly dependent on the size of cations. The pictures similar to simple dense liquids are obtained for the large ion and the neutral molecule, while the solvent waters within the first solvation shell of small ions show an oscillatory response in the short-time region. In particular, the oscillation is remarkably underdumped for lithium ion. The origin of the oscillation is discussed in relation to the theoretical treatment of the translational diffusion of ions in water.

  9. Parallelization of TWOPORFLOW, a Cartesian Grid based Two-phase Porous Media Code for Transient Thermo-hydraulic Simulations

    NASA Astrophysics Data System (ADS)

    Trost, Nico; Jiménez, Javier; Imke, Uwe; Sanchez, Victor

    2014-06-01

    TWOPORFLOW is a thermo-hydraulic code based on a porous media approach to simulate single- and two-phase flow including boiling. It is under development at the Institute for Neutron Physics and Reactor Technology (INR) at KIT. The code features a 3D transient solution of the mass, momentum and energy conservation equations for two inter-penetrating fluids with a semi-implicit continuous Eulerian type solver. The application domain of TWOPORFLOW includes the flow in standard porous media and in structured porous media such as micro-channels and cores of nuclear power plants. In the latter case, the fluid domain is coupled to a fuel rod model, describing the heat flow inside the solid structure. In this work, detailed profiling tools have been utilized to determine the optimization potential of TWOPORFLOW. As a result, bottle-necks were identified and reduced in the most feasible way, leading for instance to an optimization of the water-steam property computation. Furthermore, an OpenMP implementation addressing the routines in charge of inter-phase momentum-, energy- and mass-coupling delivered good performance together with a high scalability on shared memory architectures. In contrast to that, the approach for distributed memory systems was to solve sub-problems resulting by the decomposition of the initial Cartesian geometry. Thread communication for the sub-problem boundary updates was accomplished by the Message Passing Interface (MPI) standard.

  10. Transients from initial conditions based on Lagrangian perturbation theory in N-body simulations II: the effect of the transverse mode

    SciTech Connect

    Tatekawa, Takayuki

    2014-04-01

    We study the initial conditions for cosmological N-body simulations for precision cosmology. In general, Zel'dovich approximation has been applied for the initial conditions of N-body simulations for a long time. These initial conditions provide incorrect higher-order growth. These error caused by setting up the initial conditions by perturbation theory is called transients. We investigated the impact of transient on non-Gaussianity of density field by performing cosmological N-body simulations with initial conditions based on first-, second-, and third-order Lagrangian perturbation theory in previous paper. In this paper, we evaluates the effect of the transverse mode in the third-order Lagrangian perturbation theory for several statistical quantities such as power spectrum and non-Gaussianty. Then we clarified that the effect of the transverse mode in the third-order Lagrangian perturbation theory is quite small.

  11. Transient Measurements Under Simulated Mantle Conditions - Simultaneous DTF-Ultrasonic Interferometry, X-Radiography, XRD

    NASA Astrophysics Data System (ADS)

    Mueller, H. J.; Schilling, F. R.; Lathe, C.; Wunder, B.

    2004-12-01

    The interpretation of seismic data from the Earth's deep interior requires measurements of the physical properties of Earth materials under experimental simulated mantle conditions. Elastic wave velocity measurement by ultrasonic interferometry is an important tool for the determination of the elastic properties in multi-anvil devices. Whereas the classical sweep method is very time-consuming, the ultrasonic data transfer function technique (DTF), simultaneously generating all the frequencies used in the experiment, first described by Li et al. (2002), requires just few seconds to save the response of the system. The success of the technique substantially depends on the excitation function and the resolution used for saving the DTF (Mueller et al., 2004a). Background discussion as well as high pressure AƒA_A,A¿A,A 1/2 high temperature results demonstrate how to optimize the technique. All Ultrasonic interferometry allows highly precise travel time measurement at a sample enclosed in a high-pressure multi-anvil device. But under high pressure conditions the influence of sample deformation on the frequencies for destructive and constructive interference used for the evaluation of the elastic properties might be stronger than that from the shift of the elastic moduli. Consequently ultrasonic interferometry requires the exact sample length measurement under in situ conditions. X-ray imaging using brillant synchrotron radiation, called X-radiography, produces grey-scale images of the sample under in situ conditions by converting the X-ray image to an optical one by a CE-YAG-crystal. Saving the optical image by a CCD-camera after redirection by a mirrow, also requires few seconds. To derive the sample length, the different brightness of sample, buffer rod and reflector at the electronic image is evaluated (Mueller et al., 2004b). Contrary to XRD measurements, imaging the sample by X-rays requires a beam diameter larger than the sample length. Therefore the fixed

  12. Shock Simulations of Single-Site Coarse-Grain RDX using the Dissipative Particle Dynamics Method with Reactivity

    NASA Astrophysics Data System (ADS)

    Sellers, Michael; Lisal, Martin; Schweigert, Igor; Larentzos, James; Brennan, John

    2015-06-01

    In discrete particle simulations, when an atomistic model is coarse-grained, a trade-off is made: a boost in computational speed for a reduction in accuracy. Dissipative Particle Dynamics (DPD) methods help to recover accuracy in viscous and thermal properties, while giving back a small amount of computational speed. One of the most notable extensions of DPD has been the introduction of chemical reactivity, called DPD-RX. Today, pairing the current evolution of DPD-RX with a coarse-grained potential and its chemical decomposition reactions allows for the simulation of the shock behavior of energetic materials at a timescale faster than an atomistic counterpart. In 2007, Maillet et al. introduced implicit chemical reactivity in DPD through the concept of particle reactors and simulated the decomposition of liquid nitromethane. We have recently extended the DPD-RX method and have applied it to solid hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) under shock conditions using a recently developed single-site coarse-grain model and a reduced RDX decomposition mechanism. A description of the methods used to simulate RDX and its tranition to hot product gases within DPD-RX will be presented. Additionally, examples of the effect of microstructure on shock behavior will be shown. Approved for public release. Distribution is unlimited.

  13. In situ measurement and simulation of nano-magnetite mobility in porous media subject to transient salinity.

    PubMed

    Becker, Matthew D; Wang, Yonggang; L Paulsen, Jeffrey; Song, Yi-Qiao; Abriola, Linda M; Pennell, Kurt D

    2015-01-21

    Nanotechnologies have been proposed for a variety of environmental applications, including subsurface characterization, enhanced oil recovery, and in situ contaminant remediation. For such applications, quantitative predictive models will be of great utility for system design and implementation. Electrolyte chemistry, which can vary substantially within subsurface pore waters, has been shown to strongly influence nanoparticle aggregation and deposition in porous media. Thus, it is essential that mathematical models be capable of tracking changes in electrolyte chemistry and predicting its influence on nanoparticle mobility. In this work, a modified version of a multi-dimensional multispecies transport simulator (SEAWAT) was employed to model nanoparticle transport under transient electrolyte conditions. The modeling effort was supported by experimental measurements of paramagnetic magnetite (Fe3O4) nanoparticle, coated with polyacrylamide-methylpropane sulfonic acid - lauryl acrylate (nMag-PAMPS), mobility in columns packed with 40-50 mesh Ottawa sand. Column effluent analyses and magnetic resonance imaging (MRI) were used to quantify nanoparticle breakthrough and in situ aqueous phase concentrations, respectively. Experimental observations revealed that introduction of de-ionized water into the brine saturated column (80 g L(-1) NaCl + 20 g L(-1) CaCl2) promoted release and remobilization of deposited nanoparticles along a diagonal front, coincident with the variable density flow field. This behavior was accurately captured by the simulation results, which indicated that a two-site deposition-release model provided the best fit to experimental observations, suggesting that heterogeneous nanoparticle-surface interactions governed nanoparticle attachment. These findings illustrate the importance of accounting for both physical and chemical processes associated with changes in electrolyte chemistry when predicting nanoparticle transport behavior in subsurface

  14. A 3D simulation of the early winter distribution of reactive chlorine in the north polar vortex

    NASA Technical Reports Server (NTRS)

    Douglass, A.; Rood, R.; Waters, J.; Froidevaux, L.; Read, W.; Elson, L.; Geller, M.; Chi, Y.; Cerniglia, M.; Steenrod, S.

    1993-01-01

    Early in December 1991, high values of ClO are seen by the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite at latitudes south of areas of temperatures cold enough to form polar stratospheric clouds (PSCs). A 3D simulation shows that the heterogeneous conversion of chlorine reservoirs to reactive chlorine on the surfaces of PSCs (processing) takes place at high latitudes. Often the processed air must be transported to lower latitudes, where the reactive chlorine is photochemically converted to ClO, to be observed by MLS. In this simulation, one incidence of cold temperatures is associated with an anticyclone, and a second with a cyclone. The transport of processed air associated with the anticyclone is marked by shearing; a decrease in the maximum of the processed air is accompanied by growth of the area influenced by the processing. In contrast, the air processed in the cyclonic event spreads more slowly. This shows that transport and shearing is a crucial element to the evolution of reactive chlorine associated with a processing event. In particular, transport and shearing, as well as photochemical processes, can cause variations in observed ClO.

  15. Permeability Evolution During Reactive Flow Experiments on Cores Under CO2 Sequestration Conditions and Development of Fully Coupled Reactive Flow Simulations at the Reservoir Scale

    NASA Astrophysics Data System (ADS)

    Saar, M. O.; Kong, X. Z.; Luhmann, A. J.; Tutolo, B. M.; Seyfried, W. E., Jr.

    2015-12-01

    Physical, chemical, thermal, and mechanical processes can modify permeability and affect CO2 injectivity and reactive fluid flow during geologic CO2 sequestration. Here we report permeability evolutions observed in core-flood experiments using CO2-charged fluids under various formation conditions. Temperature-series experiments on consolidated dolomite cores show a permeability increase due to dissolution, followed by a two-step permeability decrease due to CO2 exsolution and secondary dolomite precipitation, as temperature is increased from 21 to 50°C and then to 100°C, respectively. CO2 mass balance calculations suggest that, under dynamic steady-state conditions, CO2 saturation and its relative permeability can only reach up to ~0.5 and ~0.0065, respectively. Permeability reductions of ~1/3 and mass losses of ~2% are observed both in a 52-day recycling and in two 3-day single-pass experiments with K-feldspar-rich sandstone (150°C, 200 bar). Water chemistry, SEM, and XRCT data suggest feldspar dissolution and precipitation of either boehmite (recycling) or kaolinite (single-pass) during the experiments. These observations indicate that permeability can decrease with increasing porosity due to mineral precipitation in critical pore throats. Single-pass experiments on nine dolomite cores (150°C and 150 bar with NaCl) reveal permeability enhancements and dissolution patterns at different flow rates. Permeability-porosity data indicate an increase in permeability enhancement rate per increase in porosity with reaction progress as dissolution channels lengthen along the core. These experimental observations provide the requisite data for informing up-scaled, fully-coupled reactive transport simulations of CO2 sequestration in interbedded siliclastic-carbonate sedimentary reservoirs, which we present.

  16. Subsurface Transport Over Reactive Multiphases (STORM): A general, coupled, nonisothermal multiphase flow, reactive transport, and porous medium alteration simulator, Version 2 user's guide

    SciTech Connect

    DH Bacon; MD White; BP McGrail

    2000-03-07

    The Hanford Site, in southeastern Washington State, has been used extensively to produce nuclear materials for the US strategic defense arsenal by the Department of Energy (DOE) and its predecessors, the US Atomic Energy Commission and the US Energy Research and Development Administration. A large inventory of radioactive and mixed waste has accumulated in 177 buried single- and double shell tanks. Liquid waste recovered from the tanks will be pretreated to separate the low-activity fraction from the high-level and transuranic wastes. Vitrification is the leading option for immobilization of these wastes, expected to produce approximately 550,000 metric tons of Low Activity Waste (LAW) glass. This total tonnage, based on nominal Na{sub 2}O oxide loading of 20% by weight, is destined for disposal in a near-surface facility. Before disposal of the immobilized waste can proceed, the DOE must approve a performance assessment, a document that described the impacts, if any, of the disposal facility on public health and environmental resources. Studies have shown that release rates of radionuclides from the glass waste form by reaction with water determine the impacts of the disposal action more than any other independent parameter. This report describes the latest accomplishments in the development of a computational tool, Subsurface Transport Over Reactive Multiphases (STORM), Version 2, a general, coupled non-isothermal multiphase flow and reactive transport simulator. The underlying mathematics in STORM describe the rate of change of the solute concentrations of pore water in a variably saturated, non-isothermal porous medium, and the alteration of waste forms, packaging materials, backfill, and host rocks.

  17. A Reactive Transport Model for the Distribution and Age of Carbon in Soils and Sediments Through Direct Simulation of the Stable and Radiogenic Isotopologues

    NASA Astrophysics Data System (ADS)

    Druhan, J. L.; Lawrence, C. R.

    2015-12-01

    We present a reactive transport (RT) approach to link hydrologic transport, geochemical transformations and microbial activity influencing the magnitude and residence time of different carbon pools under variably saturated conditions. This model explicitly simulates the simultaneous transport, transformation, fractionation and decay of the three isotopes of carbon (12C, 13C and 14C) through a mechanistic framework. This is demonstrated with a modification of the CrunchTope multi-component RT software to extend the isotope-specific versions of both microbially-mediated and transition state theory (TST) rate laws to accommodate a three-isotope system. In addition both aqueous and solid phase decay of 14C are tracked, yielding in an implicit means of accounting for the 13C/12C correction in normalized radiocarbon ages. The capacity of this approach to quantify the storage and flux of carbon through subsurface compartments is demonstrated using two examples distinguished by timescale. The first considers a simplified flow path in which an influent containing labile organic carbon is distributed by biogenic reduction and mineralization into a suite of reaction products. The residence time of these pools and their characteristic stable isotope ratios are tracked through a variety of transient processes occurring at short timescales (e.g. months). These include a change in fluid flow rate, a limitation of ammonium supporting anabolic growth and an influx of oxygenated fluid. The second example considers the distribution of carbon over the timescale of soil development (e.g., millennia), using a dataset of stable isotope ratios and radiocarbon ages of organic and inorganic carbon present in both dissolved and solid phases from a soil chronosequence near Santa Cruz, CA. The results of these model simulations suggest the promise of this tool for improving our understanding of coupling between hydrologic transport and biogeochemical reactions in soils.

  18. Assessment of groundwater chemical evolution for a spent nuclear fuel repository under prolonged temperate conditions: an application of efficient coupled groundwater flow and reactive transport simulation

    NASA Astrophysics Data System (ADS)

    Gylling, B.; Hartley, L. J.; Joyce, S. J.; Woollard, H.; Marsic, N.; Sidborn, M.; Puigdomenech, I.; Selroos, J. O.

    2014-12-01

    SKB has submitted a license application for a spent nuclear fuel repository at Forsmark sited in crystalline rocks of the Fennoscandian shield. In support of this application various quantitative assessments were made to demonstrate the long-term safety of the proposed repository. One such assessment involved simulation of groundwater chemical evolution to quantify impacts on safety functions for the disposal system related to the geochemical conditions, particularly salinity, pH and redox conditions. In the reference case the current temperate period lasts until 12,000 AD. A case of prolonged meteoric infiltration to 60,000 AD is also considered resulting from e.g. global warming. This is to fulfil a regulatory request to assess whether extended dilute water infiltration might lead to a rise in redox potential and also to an increase in erosion of the bentonite barrier due to formation of colloids. In order to perform long transient simulations of groundwater flow and solute transport with water-solute-rock interactions, new tools have been developed to closely couple geochemical, groundwater flow and transport calculations, and perform these efficiently using parallel computing techniques. In assessing this case, sensitivities are tested to the geochemical reaction schemes appropriate to the site. The results of this work predict that the chemical environment at repository depth stabilises at around 20,000 AD and shows little change beyond that. The salinity of the groundwater is governed by the low permeability (c. 10-19 m2) of the bedrock and by rock matrix diffusion, resulting in relatively shallow and slow circulation of groundwater. The chemical reactions influence concentrations of reactive species, the calculated pH and redox potential. In particular, the redox reactions thought to be relevant for the Forsmark site maintain reducing conditions at repository depth, even with infiltration at the ground surface of meteoric water with relatively high redox

  19. Basin scale reactive-transport simulations of CO2 leakage and resulting metal transport in a shallow drinking water aquifer

    NASA Astrophysics Data System (ADS)

    Navarre-Sitchler, A.; Maxwell, R. M.; Hammond, G. E.; Lichtner, P. C.

    2011-12-01

    Leakage of CO2 from underground storage formations into overlying aquifers will decrease groundwater pH resulting in a geochemical response of the aquifer. If metal containing aquifer minerals dissolve as a part of this response, there is a risk of exceeding regulatory limits set by the EPA. Risk assessment methods require a realistic prediction of the maximum metal concentration at wells or other points of exposure. Currently, these predictions are based on numerical reactive transport simulations of CO2 leaks. While previous studies have simulated galena dissolution as a source of lead to explore the potential for contamination of drinking water aquifers, it may be more realistic to simulate lead release from more common minerals that are known to contain trace amounts of metals, e.g. calcite. Model domains for these previous studies are often sub-km in scale or have very coarse grid resolution, due to computation limitations. In this study we simulate CO2 leakage into a drinking water aquifer using the massively parallel subsurface flow and reactive transport code PFLOTRAN. The regional model domain is 4km x 1km x 0.1 km. Even with fairly coarse grid spacing (~ 9 m x 9 m x 0.9 m), the simulations have > 49 million degrees of freedom, requiring the use of High-Performance Computing (HPC). Our simulations are run on Jaguar at Oak Ridge National Laboratory. Lead concentrations in extraction wells 3 km down gradient from a CO2 leak increase above background concentrations due to kinetic mineral dissolution along the flow path. Increases in aqueous concentrations are less when lead is allowed to sorb onto mineral surfaces. Surprisingly, lead concentration increases are greater in simulations where lead is present as a trace constituent in calcite (5% by volume) relative to simulations with galena (0.001% by volume) as the lead source. It appears that galena becomes oversaturated and begins to precipitate, a result observed in previous modeling studies, and its low

  20. A quantitative method for evaluating numerical simulation accuracy of time-transient Lamb wave propagation with its applications to selecting appropriate element size and time step.

    PubMed

    Wan, Xiang; Xu, Guanghua; Zhang, Qing; Tse, Peter W; Tan, Haihui

    2016-01-01

    Lamb wave technique has been widely used in non-destructive evaluation (NDE) and structural health monitoring (SHM). However, due to the multi-mode characteristics and dispersive nature, Lamb wave propagation behavior is much more complex than that of bulk waves. Numerous numerical simulations on Lamb wave propagation have been conducted to study its physical principles. However, few quantitative studies on evaluating the accuracy of these numerical simulations were reported. In this paper, a method based on cross correlation analysis for quantitatively evaluating the simulation accuracy of time-transient Lamb waves propagation is proposed. Two kinds of error, affecting the position and shape accuracies are firstly identified. Consequently, two quantitative indices, i.e., the GVE (group velocity error) and MACCC (maximum absolute value of cross correlation coefficient) derived from cross correlation analysis between a simulated signal and a reference waveform, are proposed to assess the position and shape errors of the simulated signal. In this way, the simulation accuracy on the position and shape is quantitatively evaluated. In order to apply this proposed method to select appropriate element size and time step, a specialized 2D-FEM program combined with the proposed method is developed. Then, the proper element size considering different element types and time step considering different time integration schemes are selected. These results proved that the proposed method is feasible and effective, and can be used as an efficient tool for quantitatively evaluating and verifying the simulation accuracy of time-transient Lamb wave propagation. PMID:26315506

  1. Nature, correlates, and consequences of stress-related biological reactivity and regulation in Army nurses during combat casualty simulation.

    PubMed

    McGraw, Leigh K; Out, Dorothée; Hammermeister, Jon J; Ohlson, Carl J; Pickering, Michael A; Granger, Douglas A

    2013-01-01

    This study examined the nature, concomitants, and consequences of stress-related biological reactivity and regulation among Army nurses. Saliva was collected, heart rate (HR) and blood pressure (BP) recorded from 38 Army nurses (74% female; mean age 28.5 years [SD=6.5]) before, during, and after participation in the Combat Casualty Stress Scenario (CCSS). Saliva was assayed for cortisol and alpha-amylase (sAA). The CCSS simulates emergency combat rescue, employing two simulated combat casualties, aversive body odors, recorded battlefield sounds, and smoke in a low light environment. Participants locate and conduct preliminary assessments of the simulated patients, triage based on injury severity, initiate treatment, and coordinate medical evacuation by radio. Results revealed large magnitude increases in cortisol, sAA, HR, systolic BP and diastolic BP in response to the CCSS, followed by recovery to baseline levels 30min after the task for all physiological parameters except cortisol. Age, gender, perceived difficulty of the CCSS, and previous nursing experience were associated with individual differences in the magnitude of the physiological responses. Lower levels of performance related to triage and treatment were associated with higher levels of reactivity and slower recovery for some of the physiological measures. The findings raise important questions regarding the utility of integrating measures of the psychobiology of the stress response into training programs designed to prepare first responders to handle highly complex and chaotic rescue situations. PMID:22710003

  2. Reactive molecular simulations of protonation of water clusters and depletion of acidity in H-ZSM-5 zeolite.

    PubMed

    Joshi, Kaushik L; Psofogiannakis, George; van Duin, Adri C T; Raman, Sumathy

    2014-09-14

    Using reactive molecular dynamics (RMD), we present an atomistic insight into the interaction between water molecules and acidic centers of H-ZSM-5 zeolite. The reactive force field method, ReaxFF, was used to evaluate the adsorption and diffusion of water as well as to study the protonation of water molecules inside zeolite channels. The existing Si/Al/O/H parameters were refitted against DFT calculations to improve the ReaxFF description of interaction between water molecules and the acidic sites of zeolites. The diffusion coefficient of water in the zeolite obtained from refitted parameters is in excellent agreement with experimental results. The molecular dynamics (MD) simulations indicate that protonation of water molecules and acidity of the zeolite catalyst depend on water loadings and temperature and the observed trends compare favorably with existing experimental and theoretical studies. At higher water loadings, protonation of water molecules is more frequent leading to formation and growth of protonated water clusters inside zeolite channels. From the analysis of various reaction channels that were observed during the simulations, we found that such water clusters have relatively short life due to frequent interchange of protons and water molecules among the water clusters. Such proton hopping events play a key role in moving the protons between different acidic centers of zeolite. These simulations show the capability of ReaxFF in providing atomistic details of complex chemical interactions between the water phase and solid acid zeolites.

  3. Photogeneration of reactive transient species upon irradiation of natural water samples: Formation quantum yields in different spectral intervals, and implications for the photochemistry of surface waters.

    PubMed

    Marchisio, Andrea; Minella, Marco; Maurino, Valter; Minero, Claudio; Vione, Davide

    2015-04-15

    Chromophoric dissolved organic matter (CDOM) in surface waters is a photochemical source of several transient species such as CDOM triplet states ((3)CDOM*), singlet oxygen ((1)O2) and the hydroxyl radical (OH). By irradiation of lake water samples, it is shown here that the quantum yields for the formation of these transients by CDOM vary depending on the irradiation wavelength range, in the order UVB > UVA > blue. A possible explanation is that radiation at longer wavelengths is preferentially absorbed by the larger CDOM fractions, which show lesser photoactivity compared to smaller CDOM moieties. The quantum yield variations in different spectral ranges were definitely more marked for (3)CDOM* and OH compared to (1)O2. The decrease of the quantum yields with increasing wavelength has important implications for the photochemistry of surface waters, because long-wavelength radiation penetrates deeper in water columns compared to short-wavelength radiation. The average steady-state concentrations of the transients ((3)CDOM*, (1)O2 and OH) were modelled in water columns of different depths, based on the experimentally determined wavelength trends of the formation quantum yields. Important differences were found between such modelling results and those obtained in a wavelength-independent quantum yield scenario.

  4. Comparison of approaches for simulating reactive solute transport involving organic degradation reactions by multiple terminal electron acceptors

    USGS Publications Warehouse

    Curtis, G.P.

    2003-01-01

    Reactive solute transport models are useful tools for analyzing complex geochemical behavior resulting from biodegradation of organic compounds by multiple terminal electron acceptors (TEAPs). The usual approach of simulating the reactions of multiple TEAPs by an irreversible Monod rate law was compared with simulations that assumed a partial local equilibrium or kinetically controlled reactions subject to the requirement that the Gibbs free energy of reaction (?? G) was either less than zero or less than a threshold value. Simulations were performed using a single organic substrate and O2, FeOOH, SO4-2 and CO2 as the terminal electron acceptors. It was assumed that the organic substrate was slowly and completely fermented to CO2 and H2 and the H2 was oxidized by the TEAPs. Simulations using the Monod approach showed that this irreversible rate law forced the reduction of both FeOOH and CO2 to proceed even when ?? G was positive. This resulted in an over prediction in amount of FeOOH reduced to Fe(II) in parts of the domain and it resulted in large errors in pH. Simulations using mass action kinetics agreed with equilibrium simulations for the case of large rate constants. The extent of reductive dissolution of FeOOH was strongly dependent on the thermodynamic stability of the FeOOH phase. Transport simulations performed assuming that the reactions of the TEAPs stopped when ?? G exceeded a threshold value showed that only simulated H2 concentrations were affected if the threshold value was the same for each TEAP. Simulated H2 concentrations were controlled by the fastest reaction of the TEAP, but it was common for reactions to occur concomitantly rather than sequentially. ?? 2003. Published by Elsevier Science Ltd.

  5. Simulating adsorption of U(VI) under transient groundwater flow and hydrochemistry: Physical versus chemical nonequilibrium model

    USGS Publications Warehouse

    Greskowiak, J.; Hay, M.B.; Prommer, H.; Liu, C.; Post, V.E.A.; Ma, R.; Davis, J.A.; Zheng, C.; Zachara, J.M.

    2011-01-01

    Coupled intragrain diffusional mass transfer and nonlinear surface complexation processes play an important role in the transport behavior of U(VI) in contaminated aquifers. Two alternative model approaches for simulating these coupled processes were analyzed and compared: (1) the physical nonequilibrium approach that explicitly accounts for aqueous speciation and instantaneous surface complexation reactions in the intragrain regions and approximates the diffusive mass exchange between the immobile intragrain pore water and the advective pore water as multirate first-order mass transfer and (2) the chemical nonequilibrium approach that approximates the diffusion-limited intragrain surface complexation reactions by a set of multiple first-order surface complexation reaction kinetics, thereby eliminating the explicit treatment of aqueous speciation in the intragrain pore water. A model comparison has been carried out for column and field scale scenarios, representing the highly transient hydrological and geochemical conditions in the U(VI)-contaminated aquifer at the Hanford 300A site, Washington, USA. It was found that the response of U(VI) mass transfer behavior to hydrogeochemically induced changes in U(VI) adsorption strength was more pronounced in the physical than in the chemical nonequilibrium model. The magnitude of the differences in model behavior depended particularly on the degree of disequilibrium between the advective and immobile phase U(VI) concentrations. While a clear difference in U(VI) transport behavior between the two models was noticeable for the column-scale scenarios, only minor differences were found for the Hanford 300A field scale scenarios, where the model-generated disequilibrium conditions were less pronounced as a result of frequent groundwater flow reversals. Copyright 2011 by the American Geophysical Union.

  6. The importance of conceptual models in the reactive transport simulation of oxygen ingress in sparsely fractured crystalline rock.

    PubMed

    Macquarrie, K T B; Mayer, K U; Jin, B; Spiessl, S M

    2010-03-01

    Redox evolution in sparsely fractured crystalline rocks is a key, and largely unresolved, issue when assessing the geochemical suitability of deep geological repositories for nuclear waste. Redox zonation created by the influx of oxygenated waters has previously been simulated using reactive transport models that have incorporated a variety of processes, resulting in predictions for the depth of oxygen penetration that may vary greatly. An assessment and direct comparison of the various underlying conceptual models are therefore needed. In this work a reactive transport model that considers multiple processes in an integrated manner is used to investigate the ingress of oxygen for both single fracture and fracture zone scenarios. It is shown that the depth of dissolved oxygen migration is greatly influenced by the a priori assumptions that are made in the conceptual models. For example, the ability of oxygen to access and react with minerals in the rock matrix may be of paramount importance for single fracture conceptual models. For fracture zone systems, the abundance and reactivity of minerals within the fractures and thin matrix slabs between the fractures appear to provide key controls on O(2) attenuation. The findings point to the need for improved understanding of the coupling between the key transport-reaction feedbacks to determine which conceptual models are most suitable and to provide guidance for which parameters should be targeted in field and laboratory investigations.

  7. Calcite surface structure and reactivity: molecular dynamics simulations and macroscopic surface modelling of the calcite-water interface.

    PubMed

    Wolthers, M; Di Tommaso, D; Du, Z; de Leeuw, N H

    2012-11-21

    Calcite-water interactions are important not only in carbon sequestration and the global carbon cycle, but also in contaminant behaviour in calcite-bearing host rock and in many industrial applications. Here we quantify the effect of variations in surface structure on calcite surface reactivity. Firstly, we employ classical Molecular Dynamics simulations of calcite surfaces containing an etch pit and a growth terrace, to show that the local environment in water around structurally different surface sites is distinct. In addition to observing the expected formation of more calcium-water interactions and hydrogen-bonds at lower-coordinated sites, we also observed subtle differences in hydrogen bonding around acute versus obtuse edges and corners. We subsequently used this information to refine the protonation constants for the calcite surface sites, according to the Charge Distribution MUltiSite Ion Complexation (CD-MUSIC) approach. The subtle differences in hydrogen bonding translate into markedly different charging behaviour versus pH, in particular for acute versus obtuse corner sites. The results show quantitatively that calcite surface reactivity is directly related to surface topography. The information obtained in this study is not only crucial for the improvement of existing macroscopic surface models of the reactivity of calcite towards contaminants, but also improves our atomic-level understanding of mineral-water interactions.

  8. Security assessment of power systems including energy storage and with the integration of wind energy. Volume I. Digital transient simulation effort consulting Agreement No. 1. Final report

    SciTech Connect

    Anderson, P. M.

    1982-06-30

    The purpose of the effort reported has been to adapt the MOD-2 simulation models for implementation on a digital transient stability program. This has involved: selection of an appropriate host program, examination of the host program interface, analysis of the analog models for digital implementation, FORTRAN coding of the model equations, installation and debugging on the host program, and final model verification. Synchronous machine equations are analyzed, with particular emphasis on numerical solution. (LEW)

  9. Reactivity of aldehydes at the air-water interface. Insights from molecular dynamics simulations and ab initio calculations.

    PubMed

    Martins-Costa, Marilia T C; García-Prieto, Francisco F; Ruiz-López, Manuel F

    2015-02-14

    Understanding the influence of solute-solvent interactions on chemical reactivity has been a subject of intense research in the last few decades. Theoretical studies have focused on bulk solvation phenomena and a variety of models and methods have been developed that are now widely used by both theoreticians and experimentalists. Much less attention has been paid, however, to processes that occur at liquid interfaces despite the important role such interfaces play in chemistry and biology. In this study, we have carried out sequential molecular dynamics simulations and quantum mechanical calculations to analyse the influence of the air-water interface on the reactivity of formaldehyde, acetaldehyde and benzaldehyde, three simple aldehydes of atmospheric interest. The calculated free-energy profiles exhibit a minimum at the interface, where the average reactivity indices may display large solvation effects. The study emphasizes the role of solvation dynamics, which are responsible for large fluctuations of some molecular properties. We also show that the photolysis rate constant of benzaldehyde in the range 290-308 nm increases by one order of magnitude at the surface of a water droplet, from 2.7 × 10(-5) s(-1) in the gas phase to 2.8 × 10(-4) s(-1) at the air-water interface, and we discuss the potential impact of this result on the chemistry of the troposphere. Experimental data in this domain are still scarce and computer simulations like those presented in this work may provide some insights that can be useful to design new experiments.

  10. A comparison of results obtained with two subsurface non-isothermal multiphase reactive transport simulators, FADES-CORE and TOUGHREACT

    SciTech Connect

    Juncosa Rivera, Ricardo; Xu, Tianfu; Pruess, Karsten

    2001-01-01

    FADES-CORE and TOUGHREACT are codes used to model the non-isothermal multiphase flow with multicomponent reactive transport in porous media. Different flow and reactive transport problems were used to compare the FADES-CORE and TOUGHREACT codes. These problems take into account the different cases of multiphase flow with and without heat transport, conservative transport, and reactive transport. Consistent results were obtained from both codes, which use different numerical methods to solve the differential equations resulting from the various physicochemical processes. Here we present the results obtained from both codes for various cases. Some results are slightly different with minor discrepancies, which have been remedied, so that both codes would be able to reproduce the same processes using the same parameters. One of the discrepancies found is related to the different calculation for thermal conductivity in heat transport, which affects the calculation of the temperatures, as well as the pH of the reaction of calcite dissolution problem modeled. Therefore it is possible to affirm that the pH is highly sensitive to temperature. Generally speaking, the comparison was concluded to be highly satisfactory, leading to the complete verification of the FADES-CORE code. However, we must keep in mind that, as there are no analytical solutions available with which to verify the codes, the TOUGHREACT code has been thoroughly corroborated, given that the only possible way to prove that the code simulation is correct, is by comparing the results obtained with both codes for the identical problems, or to validate the simulation results with actual measured data.

  11. TOUGHREACT Version 2.0: A simulator for subsurface reactive transport under non-isothermal multiphase flow conditions

    NASA Astrophysics Data System (ADS)

    Xu, Tianfu; Spycher, Nicolas; Sonnenthal, Eric; Zhang, Guoxiang; Zheng, Liange; Pruess, Karsten

    2011-06-01

    TOUGHREACT is a numerical simulation program for chemically reactive non-isothermal flows of multiphase fluids in porous and fractured media, and was developed by introducing reactive chemistry into the multiphase fluid and heat flow simulator TOUGH2 V2. The first version of TOUGHREACT was released to the public through the U.S. Department of Energy's Energy Science and Technology Software Center (ESTSC) in August 2004. It is among the most frequently requested of ESTSC's codes. The code has been widely used for studies in CO 2 geological sequestration, nuclear waste isolation, geothermal energy development, environmental remediation, and increasingly for petroleum applications. Over the past several years, many new capabilities have been developed, which were incorporated into Version 2 of TOUGHREACT. Major additions and improvements in Version 2 are discussed here, and two application examples are presented: (1) long-term fate of injected CO 2 in a storage reservoir and (2) biogeochemical cycling of metals in mining-impacted lake sediments.

  12. TOUGHREACT Version 2.0: A simulator for subsurface reactive transport under non-isothermal multiphase flow conditions

    SciTech Connect

    Xu, T.; Spycher, N.; Sonnenthal, E.; Zhang, G.; Zheng, L.; Pruess, K.

    2010-08-01

    TOUGHREACT is a numerical simulation program for chemically reactive non-isothermal flows of multiphase fluids in porous and fractured media, and was developed by introducing reactive chemistry into the multiphase fluid and heat flow simulator TOUGH2 V2. The first version of TOUGHREACT was released to the public through the U.S. Department of Energy's Energy Science and Technology Software Center (ESTSC) in August 2004. It is among the most frequently requested of ESTSC's codes. The code has been widely used for studies in CO{sub 2} geological sequestration, nuclear waste isolation, geothermal energy development, environmental remediation, and increasingly for petroleum applications. Over the past several years, many new capabilities have been developed, which were incorporated into Version 2 of TOUGHREACT. Major additions and improvements in Version 2 are discussed here, and two application examples are presented: (1) long-term fate of injected CO{sub 2} in a storage reservoir and (2) biogeochemical cycling of metals in mining-impacted lake sediments.

  13. TOURGHREACT: A Simulation Program for Non-isothermal MultiphaseReactive Geochemical Transport in Variably Saturated GeologicMedia

    SciTech Connect

    Xu, Tianfu; Sonnenthal, Eric; Spycher, Nicolas; Pruess, Karsten

    2004-12-07

    TOUGHREACT is a numerical simulation program for chemically reactive non-isothermal flows of multiphase fluids in porous and fractured media. The program was written in Fortran 77 and developed by introducing reactive geochemistry into the multiphase fluid and heat flow simulator TOUGH2. A variety of subsurface thermo-physical-chemical processes are considered under a wide range of conditions of pressure, temperature, water saturation, ionic strength, and pH and Eh. Interactions between mineral assemblages and fluids can occur under local equilibrium or kinetic rates. The gas phase can be chemically active. Precipitation and dissolution reactions can change formation porosity and permeability. The program can be applied to many geologic systems and environmental problems, including geothermal systems, diagenetic and weathering processes, subsurface waste disposal, acid mine drainage remediation, contaminant transport, and groundwater quality. Here we present two examples to illustrate applicability of the program: (1) injectivity effects of mineral scaling in a fractured geothermal reservoir and (2) CO2 disposal in a deep saline aquifer.

  14. Atomistic Origin of Brittle Failure of Boron Carbide from Large-Scale Reactive Dynamics Simulations: Suggestions toward Improved Ductility.

    PubMed

    An, Qi; Goddard, William A

    2015-09-01

    Ceramics are strong, but their low fracture toughness prevents extended engineering applications. In particular, boron carbide (B(4)C), the third hardest material in nature, has not been incorporated into many commercial applications because it exhibits anomalous failure when subjected to hypervelocity impact. To determine the atomistic origin of this brittle failure, we performed large-scale (∼200,000  atoms/cell) reactive-molecular-dynamics simulations of shear deformations of B(4)C, using the quantum-mechanics-derived reactive force field simulation. We examined the (0001)/⟨101̅0⟩ slip system related to deformation twinning and the (011̅1̅)/⟨1̅101⟩ slip system related to amorphous band formation. We find that brittle failure in B(4)C arises from formation of higher density amorphous bands due to fracture of the icosahedra, a unique feature of these boron based materials. This leads to negative pressure and cavitation resulting in crack opening. Thus, to design ductile materials based on B(4)C we propose alloying aimed at promoting shear relaxation through intericosahedral slip that avoids icosahedral fracture.

  15. Atomistic Origin of Brittle Failure of Boron Carbide from Large-Scale Reactive Dynamics Simulations: Suggestions toward Improved Ductility

    NASA Astrophysics Data System (ADS)

    An, Qi; Goddard, William A.

    2015-09-01

    Ceramics are strong, but their low fracture toughness prevents extended engineering applications. In particular, boron carbide (B4C ), the third hardest material in nature, has not been incorporated into many commercial applications because it exhibits anomalous failure when subjected to hypervelocity impact. To determine the atomistic origin of this brittle failure, we performed large-scale (˜200 000 atoms /cell ) reactive-molecular-dynamics simulations of shear deformations of B4C , using the quantum-mechanics-derived reactive force field simulation. We examined the (0001 )/⟨10 1 ¯ 0 ⟩ slip system related to deformation twinning and the (01 1 ¯ 1 ¯ )/⟨1 ¯ 101 ⟩ slip system related to amorphous band formation. We find that brittle failure in B4C arises from formation of higher density amorphous bands due to fracture of the icosahedra, a unique feature of these boron based materials. This leads to negative pressure and cavitation resulting in crack opening. Thus, to design ductile materials based on B4C we propose alloying aimed at promoting shear relaxation through intericosahedral slip that avoids icosahedral fracture.

  16. Modeling the transport of chemical warfare agents and simulants in polymeric substrates for reactive decontamination

    NASA Astrophysics Data System (ADS)

    Pearl, Thomas; Mantooth, Brent; Varady, Mark; Willis, Matthew

    2014-03-01

    Chemical warfare agent simulants are often used for environmental testing in place of highly toxic agents. This work sets the foundation for modeling decontamination of absorbing polymeric materials with the focus on determining relationships between agents and simulants. The correlations of agents to simulants must consider the three way interactions in the chemical-material-decontaminant system where transport and reaction occur in polymer materials. To this end, diffusion modeling of the subsurface transport of simulants and live chemical warfare agents was conducted for various polymer systems (e.g., paint coatings) with and without reaction pathways with applied decontamination. The models utilized 1D and 2D finite difference diffusion and reaction models to simulate absorption and reaction in the polymers, and subsequent flux of the chemicals out of the polymers. Experimental data including vapor flux measurements and dynamic contact angle measurements were used to determine model input parameters. Through modeling, an understanding of the relationship of simulant to live chemical warfare agent was established, focusing on vapor emission of agents and simulants from materials.

  17. Simulation of the infrared signature of transient luminous events in the middle atmosphere for a limb line of sight

    NASA Astrophysics Data System (ADS)

    Romand, Frédéric; Croizé, Laurence; Payan, Sébastien; Huret, Nathalie

    2016-04-01

    Transient Luminous Events (TLE) are electrical and optical events which occurs above thunderstorms. Visual signatures are reported since the beginning of the 20th century but the first picture is accidentally recorded from a television camera in 1989. Their occurrence is closely linked with the lightning activity below thunderstorms. TLEs are observed from the base of the stratosphere to the thermosphere (15 - 110 km). They are a very brief phenomenon which lasts from 1 to 300 milliseconds. At a worldwide scale, four TLEs occur each minute. The energy deposition, about some tenth of megajoules, is able to ionize, dissociate and excite the molecules of the atmosphere. Atmospheric discharges in the troposphere are important sources of NO and NO2. TLEs might have the same effects at higher altitudes, in the stratosphere. NOx then can affect the concentration of O3 and OH. Consequently, TLEs could be locally important contributors to the chemical budget of the middle atmosphere. The perturbation of the atmospheric chemistry induced by TLEs has the consequence to locally modify the radiations in the infrared during the minutes following the event. The interest of studying the infrared signature of a TLE is twofold. For the atmospheric sciences it allows to link the perturbed composition to the resulting infrared spectrum. Then, some Defense systems like detection and guiding devices are equipped with airborne infrared sensors so that the TLE infrared signature might disturb them. We want to obtain a quantitative and kinetic evaluation of the infrared signature of the atmosphere locally perturbed by a TLE. In order to do so we must model three phenomena. 1) The plasma/chemistry coupling, which describes how the different energetic levels of atmospheric molecules are populated by the energetic deposition of the TLE. This step lasts the time of the lightning itself. 2) The chemical kinetics which describes how these populations will evolve in the following minutes. 3) The

  18. Data and results of a laboratory investigation of microprocessor upset caused by simulated lightning-induced analog transients

    NASA Technical Reports Server (NTRS)

    Belcastro, C. M.

    1984-01-01

    A methodology was developed a assess the upset susceptibility/reliability of a computer system onboard an aircraft flying through a lightning environment. Upset error modes in a general purpose microprocessor were studied. The upset tests involved the random input of analog transients which model lightning induced signals onto interface lines of an 8080 based microcomputer from which upset error data was recorded. The program code on the microprocessor during tests is designed to exercise all of the machine cycles and memory addressing techniques implemented in the 8080 central processing unit. A statistical analysis is presented in which possible correlations are established between the probability of upset occurrence and transient signal inputs during specific processing states and operations. A stochastic upset susceptibility model for the 8080 microprocessor is presented. The susceptibility of this microprocessor to upset, once analog transients have entered the system, is determined analytically by calculating the state probabilities of the stochastic model.

  19. Transient simulation of a miniature Joule-Thomson (J-T) cryocooler with and without the distributed J-T effect

    NASA Astrophysics Data System (ADS)

    Damle, R. M.; Atrey, M. D.

    2015-01-01

    The aim of this work is to develop a transient program for the simulation of a miniature Joule-Thomson (J-T) cryocooler to predict its cool-down characteristics. A one dimensional transient model is formulated for the fluid streams and the solid elements of the recuperative heat exchanger. Variation of physical properties due to pressure and temperature is considered. In addition to the J-T expansion at the end of the finned tube, the distributed J-T effect along its length is also considered. It is observed that the distributed J-T effect leads to additional cooling of the gas in the finned tube and that it cannot be neglected when the pressure drop along the length of the finned tube is large. The mathematical model, method of resolution and the global transient algorithm, within a modular object-oriented framework, are detailed in this paper. As a part of verification and validation of the developed model, cases available in the literature are simulated and the results are compared with the corresponding numerical and experimental data.

  20. Reactive-transport simulation of phosphorus in the sewage plume at the Massachusetts Military Reservation, Cape Cod, Massachusetts

    USGS Publications Warehouse

    Parkhurst, David L.; Stollenwerk, Kenneth G.; Colman, John A.

    2003-01-01

    The subsurface transport of phosphorus introduced by the disposal of treated sewage effluent to ground-infiltration disposal beds at the Massachusetts Military Reservation on western Cape Cod was simulated with a three-dimensional reactive-transport model. The simulations were used to estimate the load of phosphorus transported to Ashumet Pond during operation of the sewage-treatment plant?from 1936 to 1995?and for 60 years following cessation of sewage disposal. The model accounted for spatial and temporal changes in water discharge from the sewage-treatment plant, ground-water flow, transport of associated chemical constituents, and a set of chemical reactions, including phosphorus sorption on aquifer materials, dissolution and precipitation of iron- and manganese-oxyhydroxide and iron phosphate minerals, organic carbon sorption and decomposition, cation sorption, and irreversible denitrification. The flow and transport in the aquifer were simulated by using parameters consistent with those used in previous flow models of this area of Cape Cod, except that numerical dispersion was much larger than the physical dispersion estimated in previous studies. Sorption parameters were fit to data derived from phosphorus sorption and desorption laboratory column experiments. Rates of organic carbon decomposition were adjusted to match the location of iron concentrations in an anoxic iron zone within the sewage plume. The sensitivity of the simulated load of phosphorus transported to Ashumet Pond was calculated for a variety of processes and input parameters. Model limitations included large uncertainties associated with the loading of the sewage beds, the flow system, and the chemistry and sorption characteristics in the aquifer. The results of current model simulations indicate a small load of phosphorus transported to Ashumet Pond during 1965?85, but this small load was particularly sensitive to model parameters that specify flow conditions and the chemical process by

  1. Operator-splitting errors in coupled reactive transport codes for transient variably saturated flow and contaminant transport in layered soil profiles.

    PubMed

    Jacques, D; Simůnek, J; Mallants, D; van Genuchten, M Th

    2006-12-15

    One possible way of integrating subsurface flow and transport processes with (bio)geochemical reactions is to couple by means of an operator-splitting approach two completely separate codes, one for variably-saturated flow and solute transport and one for equilibrium and kinetic biogeochemical reactions. This paper evaluates the accuracy of the operator-splitting approach for multicomponent systems for typical soil environmental problems involving transient atmospheric boundary conditions (precipitation, evapotranspiration) and layered soil profiles. The recently developed HP1 code was used to solve the coupled transport and chemical equations. For steady-state flow conditions, the accuracy was found to be mainly a function of the adopted spatial discretization and to a lesser extent of the temporal discretization. For transient flow situations, the accuracy depended in a complex manner on grid discretization, time stepping and the main flow conditions (infiltration versus evaporation). Whereas a finer grid size reduced the numerical errors during steady-state flow or the main infiltration periods, the errors sometimes slightly increased (generally less than 50%) when a finer grid size was used during periods with a high evapotranspiration demand (leading to high pressure head gradients near the soil surface). This indicates that operator-splitting errors are most significant during periods with high evaporative boundary conditions. The operator-splitting errors could be decreased by constraining the time step using the performance index (the product of the grid Peclet and Courant numbers) during infiltration, or the maximum time step during evapotranspiration. Several test problems were used to provide guidance for optimal spatial and temporal discretization. PMID:16919364

  2. Intra-/inter-laboratory validation study on reactive oxygen species assay for chemical photosafety evaluation using two different solar simulators.

    PubMed

    Onoue, Satomi; Hosoi, Kazuhiro; Toda, Tsuguto; Takagi, Hironori; Osaki, Naoto; Matsumoto, Yasuhiro; Kawakami, Satoru; Wakuri, Shinobu; Iwase, Yumiko; Yamamoto, Toshinobu; Nakamura, Kazuichi; Ohno, Yasuo; Kojima, Hajime

    2014-06-01

    A previous multi-center validation study demonstrated high transferability and reliability of reactive oxygen species (ROS) assay for photosafety evaluation. The present validation study was undertaken to verify further the applicability of different solar simulators and assay performance. In 7 participating laboratories, 2 standards and 42 coded chemicals, including 23 phototoxins and 19 non-phototoxic drugs/chemicals, were assessed by the ROS assay using two different solar simulators (Atlas Suntest CPS series, 3 labs; and Seric SXL-2500V2, 4 labs). Irradiation conditions could be optimized using quinine and sulisobenzone as positive and negative standards to offer consistent assay outcomes. In both solar simulators, the intra- and inter-day precisions (coefficient of variation; CV) for quinine were found to be below 10%. The inter-laboratory CV for quinine averaged 15.4% (Atlas Suntest CPS) and 13.2% (Seric SXL-2500V2) for singlet oxygen and 17.0% (Atlas Suntest CPS) and 7.1% (Seric SXL-2500V2) for superoxide, suggesting high inter-laboratory reproducibility even though different solar simulators were employed for the ROS assay. In the ROS assay on 42 coded chemicals, some chemicals (ca. 19-29%) were unevaluable because of limited solubility and spectral interference. Although several false positives appeared with positive predictivity of ca. 76-92% (Atlas Suntest CPS) and ca. 75-84% (Seric SXL-2500V2), there were no false negative predictions in both solar simulators. A multi-center validation study on the ROS assay demonstrated satisfactory transferability, accuracy, precision, and predictivity, as well as the availability of other solar simulators. PMID:24384453

  3. Digital system upset. The effects of simulated lightning-induced transients on a general-purpose microprocessor

    NASA Technical Reports Server (NTRS)

    Belcastro, C. M.

    1983-01-01

    Flight critical computer based control systems designed for advanced aircraft must exhibit ultrareliable performance in lightning charged environments. Digital system upset can occur as a result of lightning induced electrical transients, and a methodology was developed to test specific digital systems for upset susceptibility. Initial upset data indicates that there are several distinct upset modes and that the occurrence of upset is related to the relative synchronization of the transient input with the processing sate of the digital system. A large upset test data base will aid in the formulation and verification of analytical upset reliability modeling techniques which are being developed.

  4. Slip reactivation model for the 2011 Mw9 Tohoku earthquake: Dynamic rupture, sea floor displacements and tsunami simulations.

    NASA Astrophysics Data System (ADS)

    Galvez, P.; Dalguer, L. A.; Rahnema, K.; Bader, M.

    2014-12-01

    The 2011 Mw9 Tohoku earthquake has been recorded with a vast GPS and seismic network given unprecedented chance to seismologists to unveil complex rupture processes in a mega-thrust event. In fact more than one thousand near field strong-motion stations across Japan (K-Net and Kik-Net) revealed complex ground motion patterns attributed to the source effects, allowing to capture detailed information of the rupture process. The seismic stations surrounding the Miyagi regions (MYGH013) show two clear distinct waveforms separated by 40 seconds. This observation is consistent with the kinematic source model obtained from the inversion of strong motion data performed by Lee's et al (2011). In this model two rupture fronts separated by 40 seconds emanate close to the hypocenter and propagate towards the trench. This feature is clearly observed by stacking the slip-rate snapshots on fault points aligned in the EW direction passing through the hypocenter (Gabriel et al, 2012), suggesting slip reactivation during the main event. A repeating slip on large earthquakes may occur due to frictional melting and thermal fluid pressurization effects. Kanamori & Heaton (2002) argued that during faulting of large earthquakes the temperature rises high enough creating melting and further reduction of friction coefficient. We created a 3D dynamic rupture model to reproduce this slip reactivation pattern using SPECFEM3D (Galvez et al, 2014) based on a slip-weakening friction with sudden two sequential stress drops . Our model starts like a M7-8 earthquake breaking dimly the trench, then after 40 seconds a second rupture emerges close to the trench producing additional slip capable to fully break the trench and transforming the earthquake into a megathrust event. The resulting sea floor displacements are in agreement with 1Hz GPS displacements (GEONET). The seismograms agree roughly with seismic records along the coast of Japan.The simulated sea floor displacement reaches 8-10 meters of

  5. Caffeine Ingestion Increases Estimated Glycolytic Metabolism during Taekwondo Combat Simulation but Does Not Improve Performance or Parasympathetic Reactivation

    PubMed Central

    2015-01-01

    Objectives The aim of this study was to evaluate the effect of caffeine ingestion on performance and estimated energy system contribution during simulated taekwondo combat and on post-exercise parasympathetic reactivation. Methods Ten taekwondo athletes completed two experimental sessions separated by at least 48 hours. Athletes consumed a capsule containing either caffeine (5 mg∙kg-1) or placebo (cellulose) one hour before the combat simulation (3 rounds of 2 min separated by 1 min passive recovery), in a double-blind, randomized, repeated-measures crossover design. All simulated combat was filmed to quantify the time spent fighting in each round. Lactate concentration and rating of perceived exertion were measured before and after each round, while heart rate (HR) and the estimated contribution of the oxidative (WAER), ATP-PCr (WPCR), and glycolytic (W[La-]) systems were calculated during the combat simulation. Furthermore, parasympathetic reactivation after the combat simulation was evaluated through 1) taking absolute difference between the final HR observed at the end of third round and the HR recorded 60-s after (HRR60s), 2) taking the time constant of HR decay obtained by fitting the 6-min post-exercise HRR into a first-order exponential decay curve (HRRτ), or by 3) analyzing the first 30-s via logarithmic regression analysis (T30). Results Caffeine ingestion increased estimated glycolytic energy contribution in relation to placebo (12.5 ± 1.7 kJ and 8.9 ± 1.2 kJ, P = 0.04). However, caffeine did not improve performance as measured by attack number (CAF: 26. 7 ± 1.9; PLA: 27.3 ± 2.1, P = 0.48) or attack time (CAF: 33.8 ± 1.9 s; PLA: 36.6 ± 4.5 s, P = 0.58). Similarly, RPE (CAF: 11.7 ± 0.4 a.u.; PLA: 11.5 ± 0.3 a.u., P = 0.62), HR (CAF: 170 ± 3.5 bpm; PLA: 174.2 bpm, P = 0.12), oxidative (CAF: 109.3 ± 4.5 kJ; PLA: 107.9 kJ, P = 0.61) and ATP-PCr energy contributions (CAF: 45.3 ± 3.4 kJ; PLA: 46.8 ± 3.6 kJ, P = 0.72) during the combat simulation

  6. Preliminary reactive geochemical transport simulation study on CO2 geological sequestration at the Changhua Coastal Industrial Park Site, Taiwan

    NASA Astrophysics Data System (ADS)

    Sung, R.; Li, M.

    2013-12-01

    assumed throughout the simulation domain. Comparisons among simulated results with different mesh systems of nested meshes and non-nested meshes and considerations of multiphase reactive transport and physical transport were demonstrated in this study. Preliminary results of injection CO2 for 50 years are: (1) about 7 wt.% of injected CO2 was trapped as carbonate minerals mainly as ankerite; (2) porosities were decreased by 0.014 % and increased by 0.102 % at the injection point and beneath the cap rock, respectively, and were subsequently decreased with time due to minerals precipitation mostly as illite and ankerite; (3) differences of simulated aquifer responses between reactive transport and physical transport were insignificant; and (4) projected CO2 plumes with the nested meshes was smaller than those by the non-nested meshes after cease of CO2 injection. Keywords: CO2-Saline-Mineral Interaction, Reactive Geochemical Transport, TOUGHREACT, Mineral Trapping Assessment, Changhua Costal Industrial Park Site, Taiwan Reference: Marini, L., 2006, Geological Sequestration of Carbon Dioxide, Volume 11: Thermodynamics, Kinetics, and Reaction Path Modeling, Elsevier Science, pp.470. Xu, T., J. A. Apps and K. Pruess, 2004, Numerical simulation of CO2 disposal by mineral trapping in deep aquifers, Applied Geochemistry, Vol. 19:917-936.

  7. Simulating reactive nitrogen, carbon monoxide, and ozone in California during ARCTAS-CARB 2008 with high wildfire activity

    NASA Astrophysics Data System (ADS)

    Cai, Chenxia; Kulkarni, Sarika; Zhao, Zhan; Kaduwela, Ajith P.; Avise, Jeremy C.; DaMassa, John A.; Singh, Hanwant B.; Weinheimer, Andrew J.; Cohen, Ronald C.; Diskin, Glenn S.; Wennberg, Paul; Dibb, Jack E.; Huey, Greg; Wisthaler, Armin; Jimenez, Jose L.; Cubison, Michael J.

    2016-03-01

    Predictions of O3, CO, total NOy and individual NOy species (NO, NO2, HNO3, PAN, alkyl nitrates and aerosol nitrate) from a fine resolution regional air quality modeling system for the South Coast Air Basin (SoCAB) and San Joaquin Valley Air Basin (SJVAB) of California are presented and evaluated for the 2008 ARCTAS-CARB campaign. The measurements of the chemical compounds from the fire plumes during the field campaign allow for the evaluation of the model's ability to simulate fire-influenced air masses as well. In general, the model successfully simulated the broad spatial distribution of chemical compounds in both air basins as well as the variation within the basins. Using inventories that reflect 2008 emissions levels, the model performed well in simulating NOx (NO + NO2) in SoCAB. Therefore, the under prediction of O3 over these areas is more likely caused by uncertainties with the VOC emissions, chemistry, or discrepancies in the meteorology. The model did not capture the relatively high levels of O3, and some reactive nitrogen species that were measured off shore of the SoCAB, indicating potential missing sources or the transport from on shore to off shore was not successfully captured. In SJVAB, the model had good performance in simulating different chemical compounds in the Fresno and Arvin areas. However, enhanced concentrations of O3, NOx, HNO3 and PAN near dairy farms were significantly underestimated in the model. Negative biases also exist for O3 and HNO3 near oil fields, suggesting larger uncertainties associated with these emission sources. While the model simulated the total NOy mixing ratios reasonably well, the prediction for partitioning between individual compounds showed larger uncertainties in the model simulation. Although the fire emissions inventory was updated to include the latest emissions estimates and speciation profiles, our model shows limited improvement in simulating the enhancement of O3, CO, and PAN under fire impact as

  8. Reactive atomistic simulations of shock-induced initiation processes in mixtures of ammonium nitrate and fuel oil

    NASA Astrophysics Data System (ADS)

    Thompson, Aidan P.; Shan, Tzu-Ray

    2014-05-01

    Ammonium nitrate mixed with fuel oil (ANFO) is a commonly used blasting agent. In this paper we investigated the shock properties of pure ammonium nitrate (AN) and two different mixtures of ammonium nitrate and n-dodecane by characterizing their Hugoniot states. We simulated shock compression of pure AN and ANFO mixtures using the Multi-scale Shock Technique, and observed differences in chemical reaction. We also performed a large-scale explicit sub-threshold shock of AN crystal with a 10 nm void filled with 4.4 wt% of n-dodecane. We observed the formation of hotspots and enhanced reactivity at the interface region between AN and n-dodecane molecules.

  9. Investigating short-pulse shock initiation in HMX-based explosives with reactive meso-scale simulations

    NASA Astrophysics Data System (ADS)

    Springer, H. K.; Tarver, C. M.; Reaugh, J. E.; May, C. M.

    2014-05-01

    We performed reactive meso-scale simulations of short-pulse experiments to study the influence of flyer velocity and pore structure on shock initiation of LX-10 (95wt% HMX, 5wt% Viton A). Our calculations show that the reaction evolution fit a power law relationship in time and increases with increasing porosity, decreasing pore size, and increasing flyer velocity. While heterogeneous shock initiation modes, dependent on hot spot mechanisms, are predicted at lower flyer velocities, mixed heterogeneous-homogeneous shock initiation modes, less dependent on hot spots, are predicted at higher velocities. These studies are important because they enable the development of predictive shock initiation models that incorporate complex microstructure and can be used to optimize performance-safety characteristics of explosives.

  10. PoreFlow: A complex pore-network model for simulation of reactive transport in variably saturated porous media

    NASA Astrophysics Data System (ADS)

    Raoof, A.; Nick, H. M.; Hassanizadeh, S. M.; Spiers, C. J.

    2013-12-01

    This study introduces PoreFlow, a pore-network modeling tool capable of simulating fluid flow and multi-component reactive and adsorptive transport under saturated and variably saturated conditions. PoreFlow includes a variety of modules, such as: pore network generator, drainage simulator, calculation of pressure and velocity distributions, and modeling of reactive solute transport accounting for advection and diffusion. The pore space is represented using a multi-directional pore-network capable of capturing the random structure of a given porous media with user-defined directional connectivities for anisotropic pore structures. The chemical reactions can occur within the liquid phase, as well as between the liquid and solid phases which may result in an evolution of porosity and permeability. Under variably saturated conditions the area of interfaces changes with degree of the fluid saturation. PoreFlow uses complex formulations for more accurate modeling of transport problems in presence of the nonwetting phase. This is done by refining the discretization within drained pores. An implicit numerical scheme is used to solve the governing equations, and an efficient substitution method is applied to considerably minimize computational times. Several examples are provided, under saturated and variably saturated conditions, to demonstrate the model applicability in hydrogeology problems and petroleum fields. We show that PoreFlow is a powerful tool for upscaling of flow and transport in porous media, utilizing different pore scale information such as various interfaces, phase distributions and local fluxes and concentrations to determine macro scale properties such as average saturation, relative permeability, solute dispersivity, adsorption coefficients, effective diffusion and tortuosity. Such information can be used as constitutive relations within continuum scale governing equations to model physical and chemical processes more accurately at the larger scales.

  11. A 2.5D Reactive Transport Model for Fracture Alteration Simulation.

    PubMed

    Deng, Hang; Molins, Sergi; Steefel, Carl; DePaolo, Donald; Voltolini, Marco; Yang, Li; Ajo-Franklin, Jonathan

    2016-07-19

    Understanding fracture alteration resulting from geochemical reactions is critical in predicting fluid migration in the subsurface and is relevant to multiple environmental challenges. Here, we present a novel 2.5D continuum reactive transport model that captures and predicts the spatial pattern of fracture aperture change and the development of an altered layer in the near-fracture region. The model considers permeability heterogeneity in the fracture plane and updates fracture apertures and flow fields based on local reactions. It tracks the reaction front of each mineral phase and calculates the thickness of the altered layer. Given this treatment, the model is able to account for the diffusion limitation on reaction rates associated with the altered layer. The model results are in good agreement with an experimental study in which a CO2-acidified brine was injected into a fracture in the Duperow Dolomite, causing dissolution of calcite and dolomite that result in the formation of a preferential flow channel and an altered layer. With an effective diffusion coefficient consistent with the experimentally observed porosity of the altered layer, the model captures the progressive decrease in the dissolution rate of the fast-reacting mineral in the altered layer. PMID:27357572

  12. Molecular dynamics simulation of reactive ion etching of Si by energetic Cl ions

    SciTech Connect

    Hanson, D.E.; Voter, A.F.; Kress, J.D.

    1997-10-01

    We report results from molecular dynamics simulations of the etching of a Si surface by energetic Cl atoms (15eV{le}E{le}200eV). We find that the energy dependence of the Si yield (number of Si atoms desorbed per incident Cl ion) is in reasonable agreement with recent experiments and with previous simulations performed up to 50 eV. We also investigate the variation of the Si yield with the impact angle of incidence, the stoichiometry of the desorbed material, and the effect of a thermal background Cl flux to the surface in the presence of an ion flux at 50 eV. Surface roughening due to etching was observed and the calculated rms roughness is in reasonable agreement with experiments. {copyright} {ital 1997 American Institute of Physics.}

  13. A Many-Task Parallel Approach for Multiscale Simulations of Subsurface Flow and Reactive Transport

    SciTech Connect

    Scheibe, Timothy D.; Yang, Xiaofan; Schuchardt, Karen L.; Agarwal, Khushbu; Chase, Jared M.; Palmer, Bruce J.; Tartakovsky, Alexandre M.

    2014-12-16

    Continuum-scale models have long been used to study subsurface flow, transport, and reactions but lack the ability to resolve processes that are governed by pore-scale mixing. Recently, pore-scale models, which explicitly resolve individual pores and soil grains, have been developed to more accurately model pore-scale phenomena, particularly reaction processes that are controlled by local mixing. However, pore-scale models are prohibitively expensive for modeling application-scale domains. This motivates the use of a hybrid multiscale approach in which continuum- and pore-scale codes are coupled either hierarchically or concurrently within an overall simulation domain (time and space). This approach is naturally suited to an adaptive, loosely-coupled many-task methodology with three potential levels of concurrency. Each individual code (pore- and continuum-scale) can be implemented in parallel; multiple semi-independent instances of the pore-scale code are required at each time step providing a second level of concurrency; and Monte Carlo simulations of the overall system to represent uncertainty in material property distributions provide a third level of concurrency. We have developed a hybrid multiscale model of a mixing-controlled reaction in a porous medium wherein the reaction occurs only over a limited portion of the domain. Loose, minimally-invasive coupling of pre-existing parallel continuum- and pore-scale codes has been accomplished by an adaptive script-based workflow implemented in the Swift workflow system. We describe here the methods used to create the model system, adaptively control multiple coupled instances of pore- and continuum-scale simulations, and maximize the scalability of the overall system. We present results of numerical experiments conducted on NERSC supercomputing systems; our results demonstrate that loose many-task coupling provides a scalable solution for multiscale subsurface simulations with minimal overhead.

  14. CCC7-119 Reactive Molecular Dynamics Simulations of Hot Spot Growth in Shocked Energetic Materials

    SciTech Connect

    Thompson, Aidan P.

    2015-03-01

    The purpose of this work is to understand how defects control initiation in energetic materials used in stockpile components; Sequoia gives us the core-count to run very large-scale simulations of up to 10 million atoms and; Using an OpenMP threaded implementation of the ReaxFF package in LAMMPS, we have been able to get good parallel efficiency running on 16k nodes of Sequoia, with 1 hardware thread per core.

  15. Thermal reactivity of mixtures of VDDT lubricant and simulated Hanford Tank 241-SY-101 waste

    SciTech Connect

    Scheele, R.D.; Panisko, F.E.; Sell, R.L.

    1996-09-01

    To predict whether the Polywater G lubricant residue remaining in the velocity, density, and temperature tree (VDTT) and the waste in Tank 241-SY-101 (101SY) will be chemically compatible with wastes in 101SY when two VDTTs are removed from 101SY, the Pacific Northwest National Laboratory measured the thermal reaction sensitivity of the lubricant residue. This residue is a simulated 101SY waste containing the organic surrogate trisodium hydroxyethyl-ethylenediaminetriacetate (Na{sub 3}HEDTA) and two simulated potential waste and lubricant residue mixtures containing 10 and 90 percent lubricant residue. These studies using accelerating rate calorimetry found that the residue did not react at a rate exceeding 0.1 J/min/g mixture up to 190 degrees C with simulated 101SY waste containing Na{sub 3}HEDTA as the organic surrogate. Also, the dried lubricant residue did not decompose exothermically at a rate exceeding 0.1 J/min/g. Using guidelines used by the chemical industry, these results indicate that the lubricant residue should not react as a significant rate with the waste in 101SY when added to the waste at 60 degrees C or when the mixture cools to the waste`s temperature of 48 degrees C.

  16. TOUGHREACT User's Guide: A Simulation Program for Non-isothermal Multiphase Reactive geochemical Transport in Variable Saturated Geologic Media

    SciTech Connect

    Xu, Tianfu; Sonnenthal, Eric; Spycher, Nicolas; Pruess, Karsten

    2004-05-24

    Coupled modeling of subsurface multiphase fluid and heat flow, solute transport and chemical reactions can be used for the assessment of mineral alteration in hydrothermal systems, waste disposal sites, acid mine drainage remediation, contaminant transport, and groundwater quality. A comprehensive non-isothermal multi-component reactive fluid flow and geochemical transport simulator, TOUGHREACT, has been developed. A wide range of subsurface thermo-physical-chemical processes is considered under various thermohydrological and geochemical conditions of pressure, temperature, water saturation, and ionic strength. The program can be applied to one-, two- or three-dimensional porous and fractured media with physical and chemical heterogeneity. The model can accommodate any number of chemical species present in liquid, gas and solid phases. A variety of equilibrium chemical reactions are considered, such as aqueous complexation, gas dissolution/exsolution, and cation exchange. Mineral dissolution/precipitation can proceed either subject to local equilibrium or kinetic conditions. Changes in porosity and permeability due to mineral dissolution and precipitation can be considered. Linear adsorption and decay can be included. For the purpose of future extensions, surface complexation by double layer model is coded in the program. Xu and Pruess (1998) developed a first version of a non-isothermal reactive geochemical transport model, TOUGHREACT, by introducing reactive geochemistry into the framework of the existing multi-phase fluid and heat flow code TOUGH2 (Pruess, 1991). Xu, Pruess, and their colleagues have applied the program to a variety of problems such as: (1) supergene copper enrichment (Xu et al, 2001), (2) caprock mineral alteration in a hydrothermal system (Xu and Pruess, 2001a), and (3) mineral trapping for CO{sub 2} disposal in deep saline aquifers (Xu et al, 2003b and 2004a). For modeling the coupled thermal, hydrological, and chemical processes during

  17. Simulating Titan's upper atmosphere reactivity with a N2-CH4 plasma discharge

    NASA Astrophysics Data System (ADS)

    Carrasco, N.; Gautier, T.; Mahjoub, A.; Pernot, P.; Cernogora, G.

    2012-12-01

    Titan is the largest satellite of Saturn. It has a dense atmosphere of 1.5 bar at the surface mainly composed of nitrogen and methane. One of the most important results delivered by the ongoing Cassini space mission was to affirm that Titan's aerosols synthesis begins in the upper atmosphere. However, the Cassini mission has also highlighted the incompleteness of our knowledge on Titan's ionopheric chemistry, showing numerous unexplained species and a fortiori unknown processes coupling nitrogen and hydrocarbon chemistry, and involving neutrals, and positive and negative ions. The complex mechanisms leading to the production of the organic aerosols surrounding Titan remain thus mostly unknown. One way to study this reactivity is to reproduce in the laboratory the whole chain of reactions occurring in Titan's atmosphere. Several experimental setups have been developed in order to reproduce Titan's atmospheric chemistry in the laboratory. Among them the RF-CCP device PAMPRE provided significant clues on the understanding of the polymeric chemical structure of tholins, analogs of the atmospheric aerosols. The influence of the methane initial concentration on the aerosol production efficiency was studied, highlighting a surprising decrease of the aerosol production yield with the methane concentration. In order to find some clues on the volatile products controlling the aerosol production, we performed an extensive study on the gas phase composition correlated with the aerosol production. Moreover, in Titan's atmosphere, the CH4 concentration may have varied through time during the evolution of this atmosphere. So we studied the sensitivity of the optical constants of tholins towards different CH4 concentration.

  18. Using aquatic vegetation to remediate nitrate, ammonium, and soluble reactive phosphorus in simulated runoff.

    PubMed

    Moore, M T; Locke, M A; Kröger, R

    2016-10-01

    Within the agriculturally-intensive Mississippi River Basin of the United States, significant conservation efforts have focused on management practices that reduce nutrient runoff into receiving aquatic ecosystems. Only a small fraction of those efforts have focused on phytoremediation techniques. Each of six different aquatic macrophytes were planted, in monoculture, in three replicate mesocosms (1.2 m × 0.15 m × 0.65 m). Three additional unvegetated mesocosms served as controls for a total number of 21 mesocosms. Over two years, mesocosms were amended once each summer with sodium nitrate, ammonium sulfate, and potassium phosphate dibasic to represent nitrogen and phosphorus in agricultural runoff. System retention was calculated using a simple aqueous mass balance approach. Ammonium retention in both years differed greatly, as Panicum hemitomon and Echinodorus cordifolius retentions were significantly greater than controls in the first year, while only Myriophyllum aquaticum and Typha latifolia were significantly greater than controls in the second year. Greater soluble reactive phosphorus retention was observed in T. latifolia compared to controls in both years. Several other significant differences were observed in either the first or second year, but not both years. In the first year's exposure, P. hemitomon was significantly more efficient than the control, Saururus cernuus, and T. latifolia for overall percent nitrate decrease. Results of this novel study highlight inherent variability within and among species for nutrient specific uptake and the temporal variations of species for nutrient retention. By examining this natural variability, scientists may design phytoremediation systems with greater impact on improving agricultural runoff water quality. PMID:27372264

  19. Reactor System Transient Code.

    1999-07-14

    RELAP3B describes the behavior of water-cooled nuclear reactors during postulated accidents or power transients, such as large reactivity excursions, coolant losses or pump failures. The program calculates flows, mass and energy inventories, pressures, temperatures, and steam qualities along with variables associated with reactor power, reactor heat transfer, or control systems. Its versatility allows one to describe simple hydraulic systems as well as complex reactor systems.

  20. Data and results of a laboratory investigation of microprocessor upset caused by simulated lightning-induced analog transients

    NASA Technical Reports Server (NTRS)

    Belcastro, C. M.

    1984-01-01

    Advanced composite aircraft designs include fault-tolerant computer-based digital control systems with thigh reliability requirements for adverse as well as optimum operating environments. Since aircraft penetrate intense electromagnetic fields during thunderstorms, onboard computer systems maya be subjected to field-induced transient voltages and currents resulting in functional error modes which are collectively referred to as digital system upset. A methodology was developed for assessing the upset susceptibility of a computer system onboard an aircraft flying through a lightning environment. Upset error modes in a general-purpose microprocessor were studied via tests which involved the random input of analog transients which model lightning-induced signals onto interface lines of an 8080-based microcomputer from which upset error data were recorded. The application of Markov modeling to upset susceptibility estimation is discussed and a stochastic model development.

  1. Reactivity and Selectivity of Heterogenized Homogeneous Catalysts: Insights from Molecular Simulations

    NASA Astrophysics Data System (ADS)

    Malek, Kourosh; van Santen, Rutger A.

    Immobilized metal complexes on nanoporous materials have recently been proposed as a novel class of heterogeneous enantioselective catalyst for epoxidation of unfunctionalized olefins as well as hydrogenation, alkylation, and nitroaldol reactions. The porous hosted materials affect catalytic performance due to a cooperative interaction among the nanoporous solid, immobilizing linker, and metal complex asymmetry. The effects of mesoporous materials and immobilizing agents on chiral catalysis are not well understood, however, the catalysts confined in nanopores show comparable or even higher conversions and enantioselectivity compared to their homogeneous counterparts. This chapter highlights major scientific problems for fundamental understanding and design of heterogenized homogeneous catalysts. It describes in detail the pivotal role of a sound framework in physical theory and molecular modeling in systematic efforts towards better materials and catalytic performance optimization. The common threads of the various topics addressed is the wide range of scales that has to be considered in establishing relations between structure, physicochemical properties, and catalytic performance. Physical theory and modeling employ a variety of methods, encompassing ab-initio calculations, molecular simulations, and the continuum model of transport and reaction in nanoporous materials. We particularly describe how molecular simulations can be used to investigate the origin of enantioselectivity of an anchored metal complex in nanoporous materials. These studies provide new insights into the steric effects that relate to choices of substrate and linker and to the interplay with mesopore confinement. We also bring detailed example of employing molecular simulations to unravel the catalytic properties of metallomacrocyclics for the electrochemical reduction of molecular oxygen in aqueous media. We rationalize the importance of immobilization and show how it relates to the steric

  2. Simulation on the Comparison of Steady-State Responses Synthesized by Transient Templates Based on Superposition Hypothesis

    PubMed Central

    Tan, Xiao-dan; Yu, Xue-fei; Lin, Lin; Wang, Tao

    2015-01-01

    The generation of auditory-evoked steady-state responses (SSRs) is associated with the linear superposition of transient auditory-evoked potentials (AEPs) that cannot be directly observed. A straightforward way to justify the superposition hypothesis is the use of synthesized SSRs by a transient AEP under a predefined condition based on the forward process of this hypothesis. However, little is known about the inverse relation between the transient AEP and its synthetic SSR, which makes the interpretation of the latter less convincible because it may not necessarily underlie the true solution. In this study, we chose two pairs of AEPs from the conventional and deconvolution paradigms, which represent the homo-AEPs from a homogenous group and the hetero-AEPs from two heterogeneous groups. Both pairs of AEPs were used as templates to synthesize SSRs at rates of 20–120 Hz. The peak-peak amplitudes and the differences between the paired waves were measured. Although amplitude enhancement occurred at ~40 Hz, comparisons between the available waves demonstrated that the relative differences of the synthetic SSRs could be dramatically larger at other rates. Moreover, two virtually identical SSRs may come from clearly different AEPs. These results suggested inconsistent relationships between the AEPs and their corresponding SSRs over the tested rates. PMID:26600868

  3. Modeling of Calcite Precipitation Driven by Bacteria-facilitated Urea Hydrolysis in A Flow Column Using A Fully Coupled, Fully Implicit Parallel Reactive Transport Simulator

    NASA Astrophysics Data System (ADS)

    Guo, L.; Huang, H.; Gaston, D.; Redden, G. D.

    2009-12-01

    One approach for immobilizing subsurface metal contaminants involves stimulating the in situ production of mineral phases that sequester or isolate contaminants. One example is using calcium carbonate to immobilize strontium. The success of such approaches depends on understanding how various processes of flow, transport, reaction and resulting porosity-permeability change couple in subsurface systems. Reactive transport models are often used for such purpose. Current subsurface reactive transport simulators typically involve a de-coupled solution approach, such as operator-splitting, that solves the transport equations for components and batch chemistry sequentially, which has limited applicability for many biogeochemical processes with fast kinetics and strong medium property-reaction interactions. A massively parallel, fully coupled, fully implicit reactive transport simulator has been developed based on a parallel multi-physics object oriented software environment computing framework (MOOSE) developed at the Idaho National Laboratory. Within this simulator, the system of transport and reaction equations is solved simultaneously in a fully coupled manner using the Jacobian Free Newton-Krylov (JFNK) method with preconditioning. The simulator was applied to model reactive transport in a one-dimensional column where conditions that favor calcium carbonate precipitation are generated by urea hydrolysis that is catalyzed by urease enzyme. Simulation results are compared to both laboratory column experiments and those obtained using the reactive transport simulator STOMP in terms of: the spatial and temporal distributions of precipitates and reaction rates and other major species in the reaction system; the changes in porosity and permeability; and the computing efficiency based on wall clock simulation time.

  4. Micron-scale Reactive Atomistic Simulation of Void Collapse and Hotspot Growth in PETN

    NASA Astrophysics Data System (ADS)

    Thompson, Aidan; Shan, Tzu-Ray; Wixom, Ryan

    2015-06-01

    Material defects and other heterogeneities such as dislocations, micro-porosity, and grain boundaries play key roles in the shock-induced initiation of detonation in energetic materials. We performed non-equilibrium molecular dynamics simulations to explore the effect of nanoscale voids on hotspot growth and initiation in micron-scale pentaerythritol tetranitrate (PETN) crystals under weak shock loading (Up = 1.25 km/s; Us = 4.5 km/s). We used the ReaxFF potential implemented in LAMMPS. We built a pseudo-2D PETN crystal with dimensions 0.3 μm × 0.22 μm × 1.3 nm containing a 20 nm cylindrical void. Once the initial shockwave traversed the entire sample, the shock-front absorbing boundary condition was applied, allowing the simulation to continue beyond 1 nanosecond. Results show an exponentially increasing hotspot growth rate. The hotspot morphology is initially symmetric about the void axis, but strong asymmetry develops at later times, due to strong coupling between exothermic chemistry, temperature, and divergent secondary shockwaves emanating from the collapsing void. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DOE National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  5. Transient climate simulations of the deglaciation 21-9 thousand years before present; PMIP4 Core experiment design and boundary conditions

    NASA Astrophysics Data System (ADS)

    Ivanovic, Ruza; Gregoire, Lauren; Kageyama, Masa; Roche, Didier; Valdes, Paul; Burke, Andrea; Drummond, Rosemarie; Peltier, W. Richard; Tarasov, Lev

    2016-04-01

    The last deglaciation, which marked the transition between the last glacial and present interglacial periods, was punctuated by a series of rapid (centennial and decadal) climate changes. Numerical climate models are useful for investigating mechanisms that underpin the events, especially now that some of the complex models can be run for multiple millennia. We have set up a Paleoclimate Modelling Intercomparison Project (PMIP) working group to coordinate efforts to run transient simulations of the last deglaciation, and to facilitate the dissemination of expertise between modellers and those engaged with reconstructing the climate of the last 21 thousand years. Here, we present the design of a coordinated Core simulation over the period 21-9 thousand years before present (ka) with time varying orbital forcing, greenhouse gases, ice sheets, and other geographical changes. A choice of two ice sheet reconstructions is given. Additional focussed simulations will also be coordinated on an ad-hoc basis by the working group, for example to investigate the effect of ice sheet and iceberg meltwater, and the uncertainty in other forcings. Some of these focussed simulations will concentrate on shorter durations around specific events to allow the more computationally expensive models to take part. Ivanovic, R. F., Gregoire, L. J., Kageyama, M., Roche, D. M., Valdes, P. J., Burke, A., Drummond, R., Peltier, W. R., and Tarasov, L.: Transient climate simulations of the deglaciation 21-9 thousand years before present; PMIP4 Core experiment design and boundary conditions, Geosci. Model Dev. Discuss., 8, 9045-9102, doi:10.5194/gmdd-8-9045-2015, 2015.

  6. Reactive solute transport in acidic streams

    USGS Publications Warehouse

    Broshears, R.E.

    1996-01-01

    Spatial and temporal profiles of Ph and concentrations of toxic metals in streams affected by acid mine drainage are the result of the interplay of physical and biogeochemical processes. This paper describes a reactive solute transport model that provides a physically and thermodynamically quantitative interpretation of these profiles. The model combines a transport module that includes advection-dispersion and transient storage with a geochemical speciation module based on MINTEQA2. Input to the model includes stream hydrologic properties derived from tracer-dilution experiments, headwater and lateral inflow concentrations analyzed in field samples, and a thermodynamic database. Simulations reproduced the general features of steady-state patterns of observed pH and concentrations of aluminum and sulfate in St. Kevin Gulch, an acid mine drainage stream near Leadville, Colorado. These patterns were altered temporarily by injection of sodium carbonate into the stream. A transient simulation reproduced the observed effects of the base injection.

  7. Reactive ion etching of Si by Cl and Cl{sub 2} ions: Molecular dynamics simulations with comparisons to experiment

    SciTech Connect

    Hanson, D.E.; Kress, J.D.; Voter, A.F.

    1999-07-01

    We present results of molecular dynamics simulations of reactive ion etching (RIE) of a reconstructed Si(100)(2{times}1) surface. The existing Stillinger{endash}Weber interatomic potential for Si/Cl of Feil {ital et al.} has been modified by correcting the Si{endash}Si bond strength for a SiCl{sub n} moiety bound to a Si surface and the Si{endash}Cl bond strength in SiCl{sub m} molecules. This potential has been used to study RIE of Si by Cl and Cl{sub 2} ions. The calculated properties such as the Si yield, product stoichiometry, stoichiometry of the chlorosilyl surface, and Cl content of the chlorosilyl layer are in reasonable agreement with experiment. The dissociative chemisorption probability of Cl{sub 2} on Si(100)(2{times}1) as a function of energy has been simulated and the results are in reasonable agreement with experiment. {copyright} {ital 1999 American Vacuum Society.}

  8. Estimating pathway-specific contributions to biodegradation in aquifers based on dual isotope analysis: theoretical analysis and reactive transport simulations.

    PubMed

    Centler, Florian; Heße, Falk; Thullner, Martin

    2013-09-01

    At field sites with varying redox conditions, different redox-specific microbial degradation pathways contribute to total contaminant degradation. The identification of pathway-specific contributions to total contaminant removal is of high practical relevance, yet difficult to achieve with current methods. Current stable-isotope-fractionation-based techniques focus on the identification of dominant biodegradation pathways under constant environmental conditions. We present an approach based on dual stable isotope data to estimate the individual contributions of two redox-specific pathways. We apply this approach to carbon and hydrogen isotope data obtained from reactive transport simulations of an organic contaminant plume in a two-dimensional aquifer cross section to test the applicability of the method. To take aspects typically encountered at field sites into account, additional simulations addressed the effects of transverse mixing, diffusion-induced stable-isotope fractionation, heterogeneities in the flow field, and mixing in sampling wells on isotope-based estimates for aerobic and anaerobic pathway contributions to total contaminant biodegradation. Results confirm the general applicability of the presented estimation method which is most accurate along the plume core and less accurate towards the fringe where flow paths receive contaminant mass and associated isotope signatures from the core by transverse dispersion. The presented method complements the stable-isotope-fractionation-based analysis toolbox. At field sites with varying redox conditions, it provides a means to identify the relative importance of individual, redox-specific degradation pathways.

  9. Hybrid approach combining dissipative particle dynamics and finite-difference diffusion model: simulation of reactive polymer coupling and interfacial polymerization.

    PubMed

    Berezkin, Anatoly V; Kudryavtsev, Yaroslav V

    2013-10-21

    A novel hybrid approach combining dissipative particle dynamics (DPD) and finite difference (FD) solution of partial differential equations is proposed to simulate complex reaction-diffusion phenomena in heterogeneous systems. DPD is used for the detailed molecular modeling of mass transfer, chemical reactions, and phase separation near the liquid∕liquid interface, while FD approach is applied to describe the large-scale diffusion of reactants outside the reaction zone. A smooth, self-consistent procedure of matching the solute concentration is performed in the buffer region between the DPD and FD domains. The new model is tested on a simple model system admitting an analytical solution for the diffusion controlled regime and then applied to simulate practically important heterogeneous processes of (i) reactive coupling between immiscible end-functionalized polymers and (ii) interfacial polymerization of two monomers dissolved in immiscible solvents. The results obtained due to extending the space and time scales accessible to modeling provide new insights into the kinetics and mechanism of those processes and demonstrate high robustness and accuracy of the novel technique.

  10. Numerical simulation of the reactive flow in advanced (HSR) combustors using KIVA-2

    NASA Technical Reports Server (NTRS)

    Winowich, Nicholas S.

    1991-01-01

    Recent work has been done with the goal of establishing ultralow emission aircraft gas turbine combustors. A significant portion of the effort is the development of three dimensional computational combustor models. The KIVA-II computer code which is based on the Implicit Continuous Eulerian Difference mesh Arbitrary Lagrangian Eulerian (ICED-ALE) numerical scheme is one of the codes selected by NASA to achieve these goals. This report involves a simulation of jet injection through slanted slots within the Rich burn/Quick quench/Lean burn (RQL) baseline experimental rig. The RQL combustor distinguishes three regions of combustion. This work specifically focuses on modeling the quick quench mixer region in which secondary injection air is introduced radially through 12 equally spaced slots around the mixer circumference. Steady state solutions are achieved with modifications to the KIVA-II program. Work currently underway will evaluate thermal mixing as a function of injection air velocity and angle of inclination of the slots.

  11. Direct Numerical Simulation of Pore Scale Flow and Reactive Transport of CO2 in Porous Media.

    NASA Astrophysics Data System (ADS)

    Alizadeh Nomeli, M.

    2014-12-01

    Recently, the need to decrease CO2 concentration in the atmosphere has been recognized because of the role of CO2 as a greenhouse gas that contributes to global warming. Carbon Capture and Sequestration (CCS) is one of the most promising long term solutions for the reduction of CO2 in the atmosphere. To this end, injection of CO2 into deep geological formations has been proposed and investigated theoretically and experimentally in the last years. The fracture permeability, an important parameter controlling CO2 migration throughout sequestration, affects the amount of mineralization trapping of CO2 which enhances the long-term CO2 storage. A long-term geochemical modeling of subsurface CO2 storage is carried out in a single fracture to investigate its impact on CO2 transport and storage capacity. We model the fracture by considering flow of CO2 between finite plates. CO2 is initially dissolved in the brine and then precipitates during the geochemical reactions between H2O-CO2 and minerals. We study the physics and the critical time of blockage for a fracture to interpret the results. We employ direct numerical simulation tools and algorithms to simulate incompressible flow along with necessary transport equations that capture the kinetics of relevant chemical reactions. The numerical model is based on a finite difference method using a sequential non-iterative approach. It is found that mineral precipitation has an important effect on reservoir porosity and permeability. The fracture ceases to be a fluid channel because of the precipitation of minerals.

  12. Effects of oxidation on tensile deformation of iron nanowires: Insights from reactive molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Aral, Gurcan; Wang, Yun-Jiang; Ogata, Shigenobu; van Duin, Adri C. T.

    2016-10-01

    The influence of oxidation on the mechanical properties of nanostructured metals is rarely explored and remains poorly understood. To address this knowledge gap, in this work, we systematically investigate the mechanical properties and changes in the metallic iron (Fe) nanowires (NWs) under various atmospheric conditions of ambient dry O2 and in a vacuum. More specifically, we focus on the effect of oxide shell layer thickness over Fe NW surfaces at room temperature. We use molecular dynamics (MD) simulations with the variable charge ReaxFF force field potential model that dynamically handles charge variation among atoms as well as breaking and forming of the chemical bonds associated with the oxidation reaction. The ReaxFF potential model allows us to study large length scale mechanical atomistic deformation processes under the tensile strain deformation process, coupled with quantum mechanically accurate descriptions of chemical reactions. To study the influence of an oxide layer, three oxide shell layer thicknesses of ˜4.81 Å, ˜5.33 Å, and ˜6.57 Å are formed on the pure Fe NW free surfaces. It is observed that the increase in the oxide layer thickness on the Fe NW surface reduces both the yield stress and the critical strain. We further note that the tensile mechanical deformation behaviors of Fe NWs are dependent on the presence of surface oxidation, which lowers the onset of plastic deformation. Our MD simulations show that twinning is of significant importance in the mechanical behavior of the pure and oxide-coated Fe NWs; however, twin nucleation occurs at a lower strain level when Fe NWs are coated with thicker oxide layers. The increase in the oxide shell layer thickness also reduces the external stress required to initiate plastic deformation.

  13. Reactive solute transport in streams. 2. Simulation of a pH modification experiment

    USGS Publications Warehouse

    Runkel, R.L.; McKnight, Diane M.; Bencala, K.E.; Chapra, S.C.

    1996-01-01

    We present an application of an equilibrium-based solute transport model to a pH-modification experiment conducted on the Snake River, an acidic, metal-rich stream located in the Rocky Mountains of Colorado. During the experiment, instream pH decreased from 4.2 to 3.2, causing a marked increase in dissolved iron concentrations. Model application requires specification of several parameters that are estimated using tracer techniques, mass balance calculations, and geochemical data. Two basic questions are addressed through model application: (1) What are the processes responsible for the observed increase in dissolved iron concentrations? (2) Can the identified processes be represented within the equilibrium-based transport model? Simulation results indicate that the increase in iron was due to the dissolution of hydrous iron oxides and the photoreduction of ferric iron. Dissolution from the streambed is represented by considering a trace compartment consisting of freshly precipitated hydrous iron oxide and an abundant compartment consisting of aged precipitates that are less soluble. Spatial variability in the solubility of hydrous iron oxide is attributed to heterogeneity in the streambed sediments, temperature effects, and/or variability in the effects of photoreduction. Solubility products estimated via simulation fall within a narrow range (pK(sp) from 40.2 to 40.8) relative to the 6 order of magnitude variation reported for laboratory experiments (pK(sp) from 37.3 to 43.3). Results also support the use of an equilibrium-based transport model as the predominate features of the iron and p H profiles are reproduced. The model provides a valuable tool for quantifying the nature and extent of pH- dependent processes within the context of hydrologic transport.

  14. A coupling alternative to reactive transport simulations for long-term prediction of chemical reactions in heterogeneous CO2 storage systems

    NASA Astrophysics Data System (ADS)

    De Lucia, M.; Kempka, T.; Kühn, M.

    2015-02-01

    Fully coupled, multi-phase reactive transport simulations of CO2 storage systems can be approximated by a simplified one-way coupling of hydrodynamics and reactive chemistry. The main characteristics of such systems, and hypotheses underlying the proposed alternative coupling, are (i) that the presence of CO2 is the only driving force for chemical reactions and (ii) that its migration in the reservoir is only marginally affected by immobilisation due to chemical reactions. In the simplified coupling, the exposure time to CO2 of each element of the hydrodynamic grid is estimated by non-reactive simulations and the reaction path of one single batch geochemical model is applied to each grid element during its exposure time. In heterogeneous settings, analytical scaling relationships provide the dependency of velocity and amount of reactions to porosity and gas saturation. The analysis of TOUGHREACT fully coupled reactive transport simulations of CO2 injection in saline aquifer, inspired to the Ketzin pilot site (Germany), both in homogeneous and heterogeneous settings, confirms that the reaction paths predicted by fully coupled simulations in every element of the grid show a high degree of self-similarity. A threshold value for the minimum concentration of dissolved CO2 considered chemically active is shown to mitigate the effects of the discrepancy between dissolved CO2 migration in non-reactive and fully coupled simulations. In real life, the optimal threshold value is unknown and has to be estimated, e.g. by means of 1-D or 2-D simulations, resulting in an uncertainty ultimately due to the process de-coupling. However, such uncertainty is more than acceptable given that the alternative coupling enables using grids of the order of millions of elements, profiting from much better description of heterogeneous reservoirs at a fraction of the calculation time of fully coupled models.

  15. A coupling alternative to reactive transport simulations for long-term prediction of chemical reactions in heterogeneous CO2 storage systems

    NASA Astrophysics Data System (ADS)

    De Lucia, M.; Kempka, T.; Kühn, M.

    2014-09-01

    Fully-coupled, multi-phase reactive transport simulations of CO2 storage systems can be approximated by a simplified one-way coupling of hydrodynamics and reactive chemistry. The main characteristics of such systems, and hypotheses underlying the proposed alternative coupling, are (i) that the presence of CO2 is the only driving force for chemical reactions and (ii) that its migration in the reservoir is only marginally affected by immobilization due to chemical reactions. In the simplified coupling, the exposure time to CO2 of each element of the hydrodynamic grid is estimated by non-reactive simulations and the reaction path of one single batch geochemical model is applied to each grid element during its exposure time. In heterogeneous settings, analytical scaling relationships provide the dependency of velocity and amount of reactions to porosity and gas saturation. The analysis of TOUGHREACT fully coupled reactive transport simulations of CO2 injection in saline aquifer, inspired to the Ketzin pilot site (Germany), both in homogeneous and heterogeneous settings, confirms that the reaction paths predicted by fully coupled simulations in every element of the grid show a high degree of self-similarity. A threshold value for the minimum concentration of dissolved CO2 considered chemically active is showed to mitigate the effects of the discrepancy between dissolved CO2 migration in non-reactive and fully coupled simulations. In real life, the optimal threshold value is unknown and has to be estimated, e.g., by means of 1-D or 2-D simulations, resulting in an uncertainty ultimately due to the process de-coupling. However, such uncertainty is more than acceptable given that the alternative coupling enables using grids in the order of million elements, profiting from much better description of heterogeneous reservoirs at a fraction of the calculation time of fully coupled models.

  16. Simulating Effects of Non-Isothermal Flow on Reactive Transport of Radionuclides Originating from an Underground Nuclear Test

    SciTech Connect

    Carle, S F; Zavarin, M; Shumaker, D E; Tompson, A B; Maxwell, R M; Pawloski, G A

    2006-03-06

    Temperature can significantly affect radionuclide transport behavior. In simulation of radionuclide transport originating from an underground nuclear test, temperature effects from residual test heat include non-isothermal groundwater flow behavior (e.g. convection cells), increased dissolution rates of melt glass containing refractory radionuclides, changes in water chemistry, and, in turn, changes in radionuclide sorption behavior. The low-yield (0.75 kiloton) Cambric underground nuclear test situated in alluvium below the water table offers unique perspectives on radionuclide transport in groundwater. The Cambric test was followed by extensive post-test characterization of the radionuclide source term and a 16-year pumping-induced radionuclide migration experiment that captured more mobile radionuclides in groundwater. Discharge of pumped groundwater caused inadvertent recirculation of radionuclides through a 220-m thick vadose zone to the water table and below, including partial re-capture in the pumping well. Non-isothermal flow simulations indicate test-related heat persists at Cambric for about 10 years and induces limited thermal convection of groundwater. The test heat has relatively little impact on mobilizing radionuclides compared to subsequent pumping effects. However, our reactive transport models indicate test-related heat can raise melt glass dissolution rates up to 10{sup 4} faster than at ambient temperatures depending on pH and species activities. Non-isothermal flow simulations indicate that these elevated glass dissolution rates largely decrease within 1 year. Thermally-induced increases in fluid velocity may also significantly increase rates of melt glass dissolution by changing the fluid chemistry in contact with the dissolving glass.

  17. Modeling and simulation of pore-scale multiphase fluid flow and reactive transport in fractured and porous media

    NASA Astrophysics Data System (ADS)

    Meakin, Paul; Tartakovsky, Alexandre M.

    2009-07-01

    In the subsurface, fluids play a critical role by transporting dissolved minerals, colloids, and contaminants (sometimes over long distances); by mediating dissolution and precipitation processes; and by enabling chemical transformations in solution and at mineral surfaces. Although the complex geometries of fracture apertures, fracture networks, and pore spaces may make it difficult to accurately predict fluid flow in saturated (single-phase) subsurface systems, well-developed methods are available. The simulation of multiphase fluid flow in the subsurface is much more challenging because of the large density and/or viscosity ratios found in important applications (water/air in the vadose zone; water/oil, water/gas, gas/oil, and water/oil/gas in hydrocarbon reservoirs; water/air/nonaqueous phase liquids (nonaqueous phase liquids/dense nonaqueous phase liquids) in contaminated vadose zone systems; and gas/molten rock in volcanic systems, for example). In addition, the complex behavior of fluid-fluid-solid contact lines and their impact on dynamic contact angles must also be taken into account and coupled with the fluid flow. Here we review the methods that are currently being used to simulate pore-scale multiphase fluid flow and reactive transport in fractured and porous media. After the introduction, the review begins with an overview of the fundamental physics of multiphase fluids flow followed by a more detailed discussion of the complex dynamic behavior of contact lines and contact angles, an important barrier to accurate pore-scale modeling and simulation. The main part of the review focuses on five different approaches: pore network models, lattice gas and lattice Boltzmann methods, Monte Carlo methods, particle methods (molecular dynamics, dissipative particle dynamics, and smoothed particle hydrodynamics), and traditional grid-based computational fluid dynamics coupled with interface tracking and a contact angle model. Finally, the review closes with a

  18. Improving the spatial resolution in CZT detectors using charge sharing effect and transient signal analysis: Simulation study

    NASA Astrophysics Data System (ADS)

    Zheng, Xiaoqing; Cheng, Zeng; Deen, M. Jamal; Peng, Hao

    2016-02-01

    Cadmium Zinc Telluride (CZT) semiconductor detectors are capable of providing superior energy resolution and three-dimensional position information of gamma ray interactions in a large variety of fields, including nuclear physics, gamma-ray imaging and nuclear medicine. Some dedicated Positron Emission Tomography (PET) systems, for example, for breast cancer detection, require higher contrast recovery and more accurate event location compared with a whole-body PET system. The spatial resolution is currently limited by electrode pitch in CZT detectors. A straightforward approach to increase the spatial resolution is by decreasing the detector electrode pitch, but this leads to higher fabrication cost and a larger number of readout channels. In addition, inter-electrode charge spreading can negate any improvement in spatial resolution. In this work, we studied the feasibility of achieving sub-pitch spatial resolution in CZT detectors using two methods: charge sharing effect and transient signal analysis. We noted that their valid ranges of usage were complementary. The dependences of their corresponding valid ranges on electrode design, depth-of-interaction (DOI), voltage bias and signal triggering threshold were investigated. The implementation of these two methods in both pixelated and cross-strip configuration of CZT detectors were discussed. Our results show that the valid range of charge sharing effect increases as a function of DOI, but decreases with increasing gap width and bias voltage. For a CZT detector of 5 mm thickness, 100 μm gap and biased at 400 V, the valid range of charge sharing effect was found to be about 112.3 μm around the gap center. This result complements the valid range of the transient signal analysis within one electrode pitch. For a signal-to-noise ratio (SNR) of ~17 and preliminary measurements, the sub-pitch spatial resolution is expected to be ~30 μm and ~250 μm for the charge sharing and transient signal analysis methods

  19. Decoupling instead of grid coarsening: how to achieve reservoir scale reactive transport simulations in highly heterogeneous settings. Example from CO2 storage

    NASA Astrophysics Data System (ADS)

    De Lucia, M.; Kempka, T.; Kuehn, M.

    2014-12-01

    The characteristics of a typical CO2 storage system allow simplification strategies for reactive transport simulations based on process decoupling. In such systems the feedback of the slow chemical reactions to hydrodynamics is low until the system reaches a substantial hydrodynamic equilibrium. Furthermore, the presence of CO2 is the main driving force for chemical reactions, which are for most reactants kinetically controlled. Hence, the same reaction path is substantially replicated in all elements of the grid exposed to the injected CO2, either in gaseous or in dissolved form. The analysis offully coupled 3D simulations of the Ketzin pilot site for CO2 storage performed with the TOUGHREACT simulator confirms these hypotheses to a large extent, both in homogeneous and in heterogeneous settings. This allows the definition of a simplified one-way coupling combining independent non-reactive hydrodynamic and batch geochemical models. The exposure time to CO2 of each grid element is estimated by the conservative simulations, then the outcome of one single geochemical model per lithofacies is applied to each grid element. A threshold value for the minimum concentration of dissolved CO2 required to start chemical reactions permits to mitigate the discrepancy due to the lack of a mass balance between the independently run simulations. The comparison with fully coupled simulations validates the novel approach. The simplified coupling can tackle a wide class of problems, not only CO2 storage; it allows calculating reactive chemistry on grids comprising millions of elements, overcoming a major limitation of reactive transport models, which are often bounded to 2D radial domains. This is particularly advantageous in highly heterogeneous settings with complex hydrodynamics. The new coupling is demonstrated at full scale for the Ketzin site with simulations up to 15000 years, a result which cannot yet be achieved by fully coupled simulations.

  20. Simulation of emission spectra from nonuniform reactive laser-induced plasmas.

    PubMed

    Hermann, Jörg; Lorusso, Antonella; Perrone, Alessio; Strafella, Francesco; Dutouquet, Christophe; Torralba, Béatrice

    2015-11-01

    We demonstrate that chemical reactions leading to the formation of AlO radicals in plasmas produced by ablation of aluminum or Ti-sapphire with ultraviolet nanosecond laser pulses can be predicted by the model of local thermodynamic equilibrium. Therefore, emission spectra recorded with an echelle spectrometer and a gated detector were compared to the spectral radiance computed for uniform and nonuniform equilibrium plasmas. The calculations are based on analytical solutions of the radiation transfer equation. The simulations show that the plasmas produced in argon background gas are almost uniform, whereas temperature and density gradients are evidenced in air. Furthermore, chemical reactions exclusively occur in the cold plume periphery for ablation in air. The formation of AlO is negligible in argon as the plasma temperature is too large in the time interval of interest up to several microseconds. Finally, the validity of local thermodynamic equilibrium is shown to depend on time, space, and on the elemental composition. The presented conclusions are of interest for material analysis via laser-induced breakdown spectroscopy and for laser materials processing.

  1. 1-D Transient Thermal Modeling of an Ablative Material (MCC-1) Exposed to a Simulated Convective Titan 4 Launch Environment

    NASA Technical Reports Server (NTRS)

    Reinarts, Thomas R.; Crain, William K.; Stuckey, C. Irvin; Palko, Richard L.

    1998-01-01

    The purpose of the work is to demonstrate that the flat test panel substrate temperatures are consistent with analysis predictions for MCC-1 applied to a aluminum substrate. The testing was performed in an aerothermal facility on samples of three different thicknesses of MCC-1 on an aluminum substrate. The results of the test were compared with a Transient Thermal model. The key assumptions of the Transient Thermal model were: (1) a one-dimensional heat transfer; (2) a constant ablation recession rate (determined from pre and post-test measurements); (3) ablation temperature of 540 degrees F; (4) Char left behind the ablation front; and (5) temperature jump correction for incident heat transfer coefficient. Two methods were used to model the heating of bare MCC-1: (1) Directly input surface temperature as a function of time; and (2) Aerothermal heating using calibration plate data and subtracting the radiation losses to tunnel walls. The results are presented as graphs. This article is presented in Viewgraph format.

  2. A method for simulating transient ground-water recharge in deep water-table settings in central Florida by using a simple water-balance/transfer-function model

    USGS Publications Warehouse

    O'Reilly, Andrew M.

    2004-01-01

    A relatively simple method is needed that provides estimates of transient ground-water recharge in deep water-table settings that can be incorporated into other hydrologic models. Deep water-table settings are areas where the water table is below the reach of plant roots and virtually all water that is not lost to surface runoff, evaporation at land surface, or evapotranspiration in the root zone eventually becomes ground-water recharge. Areas in central Florida with a deep water table generally are high recharge areas; consequently, simulation of recharge in these areas is of particular interest to water-resource managers. Yet the complexities of meteorological variations and unsaturated flow processes make it difficult to estimate short-term recharge rates, thereby confounding calibration and predictive use of transient hydrologic models. A simple water-balance/transfer-function (WBTF) model was developed for simulating transient ground-water recharge in deep water-table settings. The WBTF model represents a one-dimensional column from the top of the vegetative canopy to the water table and consists of two components: (1) a water-balance module that simulates the water storage capacity of the vegetative canopy and root zone; and (2) a transfer-function module that simulates the traveltime of water as it percolates from the bottom of the root zone to the water table. Data requirements include two time series for the period of interest?precipitation (or precipitation minus surface runoff, if surface runoff is not negligible) and evapotranspiration?and values for five parameters that represent water storage capacity or soil-drainage characteristics. A limiting assumption of the WBTF model is that the percolation of water below the root zone is a linear process. That is, percolating water is assumed to have the same traveltime characteristics, experiencing the same delay and attenuation, as it moves through the unsaturated zone. This assumption is more accurate if

  3. Reactive geochemical transport simulation to study mineral trapping for CO2 disposal in deep saline arenaceous aquifers

    SciTech Connect

    Xu, Tianfu; Apps, John A.; Pruess, Karsten

    2002-04-01

    A reactive fluid flow and geochemical transport numerical model for evaluating long-term CO{sub 2} disposal in deep aquifers has been developed. Using this model, we performed a number of sensitivity simulations under CO{sub 2} injection conditions for a commonly encountered Gulf Coast sediment to analyze the impact of CO{sub 2} immobilization through carbonate precipitation. Geochemical models are needed because alteration of the predominant host rock aluminosilicate minerals is very slow and is not amenable to laboratory experiment under ambient deep-aquifer conditions. Under conditions considered in our simulations, CO{sub 2} trapping by secondary carbonate minerals such as calcite (CaCO{sub 3}), dolomite (CaMg(CO{sub 3}){sub 2}), siderite (FeCO{sub 3}), and dawsonite (NaAlCO{sub 3}(OH){sub 2}) could occur in the presence of high pressure CO{sub 2}. Variations in precipitation of secondary carbonate minerals strongly depend on rock mineral composition and their kinetic reaction rates. Using the data presented in this paper, CO{sub 2} mineral-trapping capability after 10,000 years is comparable to CO{sub 2} dissolution in pore waters (2-5 kg CO{sub 2} per cubic meter of formation). Under favorable conditions such as increase of the Mg-bearing mineral clinochlore (Mg{sub 5}Al{sub 2}Si{sub 3}O{sub 10}(OH){sub 8}) abundance, the capacity can be larger (10 kg CO{sub 2} per cubic meter of formation) due to increase of dolomite precipitation. Carbon dioxide-induced rock mineral alteration and the addition of CO{sub 2} mass as secondary carbonates to the solid matrix results in decreases in porosity. A maximum 3% porosity decrease is obtained in our simulations. A small decrease in porosity may result in a significant decrease in permeability. The numerical simulations described here provide useful insight into sequestration mechanisms, and their controlling conditions and parameters.

  4. Stress effects on the initial lithiation of crystalline silicon nanowires: Reactive molecular dynamics simulations using ReaxFF

    SciTech Connect

    Ostadhossein, Alireza; Cubuk, Ekin D.; Tritsaris, Georgios A.; Kaxiras, Efthimios; Zhang, Sulin; Adri C. T. van Duin

    2014-12-18

    Silicon (Si) has been recognized as a promising anode material for the next-generation high-capacity lithium (Li)-ion batteries because of its high theoretical energy density. Recent in situ transmission electron microscopy (TEM) revealed that the electrochemical lithiation of crystalline Si nanowires (c-SiNWs) proceeds by the migration of the interface between the lithiated Si (LixSi) shell and the pristine unlithiated core, accompanied by solid-state amorphization. The underlying atomic mechanisms of Li insertion into c-Si remain poorly understood. In this research, we perform molecular dynamics (MD) simulations using the reactive force field (ReaxFF) to characterize the lithiation process of c-SiNWs. Our calculations show that ReaxFF can accurately reproduce the energy barriers of Li migration from DFT calculations in both crystalline (c-Si) and amorphous Si (a-Si). The ReaxFF-based MD simulations reveal that Li insertion into interlayer spacing between two adjacent (111) planes results in the peeling-off of the (111) facets and subsequent amorphization, in agreement with experimental observations. We find that breaking of the Si–Si bonds between (111)-bilayers requires a rather high local Li concentration, which explains the atomically sharp amorphous–crystalline interface (ACI). Our stress analysis shows that lithiation induces compressive stress at the ACI layer, causing retardation or even the stagnation of the reaction front, also in good agreement with TEM observations. Lithiation at high temperatures (e.g. 1200 K) shows that Li insertion into c-SiNW results in an amorphous to crystalline phase transformation at Li : Si composition of ~4.2:1. In conclusion, our modeling results provide a comprehensive picture of the effects of reaction and diffusion-induced stress on the interfacial dynamics and mechanical degradation of SiNW anodes under chemo-mechanical lithiation.

  5. Stress effects on the initial lithiation of crystalline silicon nanowires: Reactive molecular dynamics simulations using ReaxFF

    DOE PAGES

    Ostadhossein, Alireza; Cubuk, Ekin D.; Tritsaris, Georgios A.; Kaxiras, Efthimios; Zhang, Sulin; Adri C. T. van Duin

    2014-12-18

    Silicon (Si) has been recognized as a promising anode material for the next-generation high-capacity lithium (Li)-ion batteries because of its high theoretical energy density. Recent in situ transmission electron microscopy (TEM) revealed that the electrochemical lithiation of crystalline Si nanowires (c-SiNWs) proceeds by the migration of the interface between the lithiated Si (LixSi) shell and the pristine unlithiated core, accompanied by solid-state amorphization. The underlying atomic mechanisms of Li insertion into c-Si remain poorly understood. In this research, we perform molecular dynamics (MD) simulations using the reactive force field (ReaxFF) to characterize the lithiation process of c-SiNWs. Our calculations showmore » that ReaxFF can accurately reproduce the energy barriers of Li migration from DFT calculations in both crystalline (c-Si) and amorphous Si (a-Si). The ReaxFF-based MD simulations reveal that Li insertion into interlayer spacing between two adjacent (111) planes results in the peeling-off of the (111) facets and subsequent amorphization, in agreement with experimental observations. We find that breaking of the Si–Si bonds between (111)-bilayers requires a rather high local Li concentration, which explains the atomically sharp amorphous–crystalline interface (ACI). Our stress analysis shows that lithiation induces compressive stress at the ACI layer, causing retardation or even the stagnation of the reaction front, also in good agreement with TEM observations. Lithiation at high temperatures (e.g. 1200 K) shows that Li insertion into c-SiNW results in an amorphous to crystalline phase transformation at Li : Si composition of ~4.2:1. In conclusion, our modeling results provide a comprehensive picture of the effects of reaction and diffusion-induced stress on the interfacial dynamics and mechanical degradation of SiNW anodes under chemo-mechanical lithiation.« less

  6. Description of the Mountain Cloud Chemistry Program version of the PLUVIUS MOD 5. 0 reactive storm simulation model

    SciTech Connect

    Luecken, D.J.; Whiteman, C.D.; Chapman, E.G.; Andrews, G.L.; Bader, D.C.

    1987-07-01

    Damage to forest ecosystems on mountains in the eastern United States has prompted a study conducted for the US Environmental Protection Agency's Mountain Cloud Chemistry Program (MCCP). This study has led to the development of a numerical model called MCCP PLUVIUS, which has been used to investigate the chemical transformations and cloud droplet deposition in shallow, nonprecipitating orographic clouds. The MCCP PLUVIUS model was developed as a specialized version of the existing PLUVIUS MOD 5.0 reactive storm model. It is capable of simulating aerosol scavenging, nonreactive gas scavenging, aqueous phase SO/sub 2/ reactions, and cloud water deposition. A description of the new model is provided along with information on model inputs and outputs, as well as suggestions for its further development. The MCCP PLUVIUS incorporates a new method to determine the depth of the layer of air which flows over a mountaintop to produce an orographic cloud event. It provides a new method for calculating hydrogen ion concentrations, and provides updated expressions and values for solubility, dissociation and reaction rate constants.

  7. THORAX pretest prediction of a sodium-boiling transient in a 19-pin simulated LMFBR driver bundle

    SciTech Connect

    Rose, S.D.

    1982-01-01

    Experiments will be conducted in the Thermal-Hydraulic Out-of-Reactor Safety-Shutdown Heat Removal System (THORS-SHRS) Assembly 1 loop at Oak Ridge National Laboratory (ORNL) to model the behavior of a reactor during degraded decay heat removal conditions. The test section is to consist of two parallel 19-pin electrically-heated driver bundles, typical of U.S. Large Developmental Plant (LDP) Liquid Metal Fast Breeder Reactor (LMFBR) design. Analysis of these experiments will include using THORAX, a two-dimensional boiling model which assumes an equilibrium mixture two-phase flow (with slip). A THORAX prediction is presented for a single-bundle forced convection boiling-to-dryout transient at 15.8 kW/pin.

  8. Transient nonlinear optically-thick radiative-convective double-diffusive boundary layers in a Darcian porous medium adjacent to an impulsively started surface: Network simulation solutions

    NASA Astrophysics Data System (ADS)

    Anwar Bég, O.; Zueco, J.; Takhar, H. S.; Bég, T. A.; Sajid, A.

    2009-11-01

    A boundary-layer model is described for the two-dimensional nonlinear transient thermal convection heat and mass transfer in an optically-thick fluid in a Darcian porous medium adjacent to an impulsively started vertical surface, in the presence of significant thermal radiation and buoyancy forces in an (X∗,Y∗,t∗) coordinate system. An algebraic approximation is employed to simplify the integro-differential equation of radiative transfer for unidirectional flux normal to the plate into the boundary-layer regime, by incorporating this flux term in the energy conservation equation. The conservation equations are non-dimensionalized into an (X,Y,T) coordinate system and solved using the Network Simulation Method (NSM), a robust numerical technique which demonstrates high efficiency and accuracy. The transient variation of non-dimensional streamwise velocity component (u) and temperature (T) and concentration (C) functions is computed for various selected values of Stark number (radiation-conduction interaction parameter) and Darcy number. Transient velocity (u) and steady-state local skin friction (τX) are also studied for various thermal Grashof number (Gr), species Grashof number (Gm), Schmidt number (Sc) and Stark number (N) values. These computations for the infinite permeability case (Da → ∞) are compared with previous finite difference solutions [Prasad et al. Int J Therm Sci 2007;46(12):1251-8] and shown to be in excellent agreement. An increase in Darcy number is seen to accelerate the flow and boost velocity. A decrease in Stark number (corresponding to an increase in thermal radiation heat transfer contribution) is shown to increase the velocity values. Temperature function is observed to fall in value with a rise in Da and increase with decrease in N (corresponding to an increase in thermal radiation heat transfer contribution). Applications of the study include rocket combustion chambers, astrophysical flows, spacecraft thermal fluid dynamics in

  9. Experimental and simulation studies of pore scale flow and reactive transport associated with supercritical CO2 injection into brine-filled reservoir rocks (Invited)

    NASA Astrophysics Data System (ADS)

    DePaolo, D. J.; Steefel, C. I.; Bourg, I. C.

    2013-12-01

    This talk will review recent research relating to pore scale reactive transport effects done in the context of the Department of Energy-sponsored Energy Frontier Research Center led by Lawrence Berkeley National Laboratory with several other laboratory and University partners. This Center, called the Center for Nanoscale Controls on Geologic CO2 (NCGC) has focused effort on the behavior of supercritical CO2 being injected into and/or residing as capillary trapped-bubbles in sandstone and shale, with particular emphasis on the description of nanoscale to pore scale processes that could provide the basis for advanced simulations. In general, simulation of reservoir-scale behavior of CO2 sequestration assumes a number of mostly qualitative relationships that are defensible as nominal first-order descriptions of single-fluid systems, but neglect the many complications that are associated with a two-phase or three-phase reactive system. The contrasts in properties, and the mixing behavior of scCO2 and brine provide unusual conditions for water-rock interaction, and the NCGC has investigated the underlying issues by a combination of approaches including theoretical and experimental studies of mineral nucleation and growth, experimental studies of brine films, mineral wetting properties, dissolution-precipitation rates and infiltration patterns, molecular dynamic simulations and neutron scattering experiments of fluid properties for fluid confined in nanopores, and various approaches to numerical simulation of reactive transport processes. The work to date has placed new constraints on the thickness of brine films, and also on the wetting properties of CO2 versus brine, a property that varies between minerals and with salinity, and may also change with time as a result of the reactivity of CO2-saturated brine. Mineral dissolution is dependent on reactive surface area, which can be shown to vary by a large factor for various minerals, especially when correlated with

  10. TREAT Transient Analysis Benchmarking for the HEU Core

    SciTech Connect

    Kontogeorgakos, D. C.; Connaway, H. M.; Wright, A. E.

    2014-05-01

    This work was performed to support the feasibility study on the potential conversion of the Transient Reactor Test Facility (TREAT) at Idaho National Laboratory from the use of high enriched uranium (HEU) fuel to the use of low enriched uranium (LEU) fuel. The analyses were performed by the GTRI Reactor Conversion staff at the Argonne National Laboratory (ANL). The objective of this study was to benchmark the transient calculations against temperature-limited transients performed in the final operating HEU TREAT core configuration. The MCNP code was used to evaluate steady-state neutronics behavior, and the point kinetics code TREKIN was used to determine core power and energy during transients. The first part of the benchmarking process was to calculate with MCNP all the neutronic parameters required by TREKIN to simulate the transients: the transient rod-bank worth, the prompt neutron generation lifetime, the temperature reactivity feedback as a function of total core energy, and the core-average temperature and peak temperature as a functions of total core energy. The results of these calculations were compared against measurements or against reported values as documented in the available TREAT reports. The heating of the fuel was simulated as an adiabatic process. The reported values were extracted from ANL reports, intra-laboratory memos and experiment logsheets and in some cases it was not clear if the values were based on measurements, on calculations or a combination of both. Therefore, it was decided to use the term “reported” values when referring to such data. The methods and results from the HEU core transient analyses will be used for the potential LEU core configurations to predict the converted (LEU) core’s performance.

  11. Calibration of a transient transport model to tritium data in streams and simulation of groundwater ages in the western Lake Taupo catchment, New Zealand

    NASA Astrophysics Data System (ADS)

    Gusyev, M. A.; Toews, M.; Morgenstern, U.; Stewart, M.; White, P.; Daughney, C.; Hadfield, J.

    2013-03-01

    Here we present a general approach of calibrating transient transport models to tritium concentrations in river waters developed for the MT3DMS/MODFLOW model of the western Lake Taupo catchment, New Zealand. Tritium has a known pulse-shaped input to groundwater systems due to the bomb tritium in the early 1960s and, with its radioactive half-life of 12.32 yr, allows for the determination of the groundwater age. In the transport model, the tritium input (measured in rainfall) passes through the groundwater system, and the simulated tritium concentrations are matched to the measured tritium concentrations in the river and stream outlets for the Waihaha, Whanganui, Whareroa, Kuratau and Omori catchments from 2000-2007. For the Kuratau River, tritium was also measured between 1960 and 1970, which allowed us to fine-tune the transport model for the simulated bomb-peak tritium concentrations. In order to incorporate small surface water features in detail, an 80 m uniform grid cell size was selected in the steady-state MODFLOW model for the model area of 1072 km2. The groundwater flow model was first calibrated to groundwater levels and stream baseflow observations. Then, the transient tritium transport MT3DMS model was matched to the measured tritium concentrations in streams and rivers, which are the natural discharge of the groundwater system. The tritium concentrations in the rivers and streams correspond to the residence time of the water in the groundwater system (groundwater age) and mixing of water with different age. The transport model output showed a good agreement with the measured tritium values. Finally, the tritium-calibrated MT3DMS model is applied to simulate groundwater ages, which are used to obtain groundwater age distributions with mean residence times (MRTs) in streams and rivers for the five catchments. The effect of regional and local hydrogeology on the simulated groundwater ages is investigated by demonstrating groundwater ages at five model

  12. TRICHLOROETHYLENE REMOVAL FROM GROUNDWATER IN FLOW-THROUGH COLUMNS SIMULATING A PERMEABLE REACTIVE BARRIER CONSTRUCTED WITH PLANT MULCH

    EPA Science Inventory

    Ground water contaminated with TCE is commonly treated with a passive reactive barrier (PRB) constructed with zero-valence iron. The cost of iron as the reactive matrix has driven a search for less costly alternatives, and composted plant mulch has been used as an alternative re...

  13. Eulerian-Lagrangian numerical scheme for simulating advection, dispersion, and transient storage in streams and a comparison of numerical methods

    USGS Publications Warehouse

    Cox, T.J.; Runkel, R.L.

    2008-01-01

    Past applications of one-dimensional advection, dispersion, and transient storage zone models have almost exclusively relied on a central differencing, Eulerian numerical approximation to the nonconservative form of the fundamental equation. However, there are scenarios where this approach generates unacceptable error. A new numerical scheme for this type of modeling is presented here that is based on tracking Lagrangian control volumes across a fixed (Eulerian) grid. Numerical tests are used to provide a direct comparison of the new scheme versus nonconservative Eulerian numerical methods, in terms of both accuracy and mass conservation. Key characteristics of systems for which the Lagrangian scheme performs better than the Eulerian scheme include: nonuniform flow fields, steep gradient plume fronts, and pulse and steady point source loadings in advection-dominated systems. A new analytical derivation is presented that provides insight into the loss of mass conservation in the nonconservative Eulerian scheme. This derivation shows that loss of mass conservation in the vicinity of spatial flow changes is directly proportional to the lateral inflow rate and the change in stream concentration due to the inflow. While the nonconservative Eulerian scheme has clearly worked well for past published applications, it is important for users to be aware of the scheme's limitations. ?? 2008 ASCE.

  14. Transient effects in beam-plasma interactions in a space simulation chamber stimulated by a fast pulse electron gun

    NASA Technical Reports Server (NTRS)

    Raitt, W. J.; Banks, P. M.; Denig, W. F.; Anderson, H. R.

    1982-01-01

    Interest in the interaction of electron beams with plasma generated by ionization caused by the primary electron beam was stimulated by the need to develop special vacuum tubes to operate in the kMHz frequency region. The experiments of Getty and Smullin (1963) indicated that the interaction of an energetic electron beam with its self-produced plasma resulted in the emission of wave energy over a wide range of frequencies associated with cyclotron and longitudinal plasma instabilities. This enhanced the thermal plasma density in the vicinity of the beam, and the term Beam-Plasma Discharge (BPD) was employed to described this phenomenon. The present investigation is concerned with some of the transient phenomena associated with wave emission during the beam switch-on and switch-off periods. Results are presented on the changes in electron energy spectra on a time scale of tens of milliseconds following beam switch-on. The results are discussed in terms of the beam plasma discharge phenomenon.

  15. Transient two-phase CFD simulation of overload pressure pulsation in a prototype sized Francis turbine considering the waterway dynamics

    NASA Astrophysics Data System (ADS)

    Mössinger, P.; Conrad, P.; Jung, A.

    2014-03-01

    At high load operation points, Francis turbines generally produce large cavitation volumes of central vortex character in the draft tube. In order to gain a deeper understanding of the flow behaviour at high load conditions a combined 1D-3D transient two-phase numerical investigation at prototype size was carried out and these results were compared with measured site data. A one-dimensional model to capture hydroacoustic effects along a pipeline will be presented. The corresponding PDEs were solved using an implicit finite difference scheme on a staggered grid. In contrast to previous studies this model is coupled to the commercial software ANSYS CFX through an interface which exchanges pressure and discharge data within every time step until convergence. Results of the one-dimensional approach as well as the coupled solution were validated with commercial one-dimensional software (SIMSEN) and a full threedimensional calculation for hydroacoustic test cases. Unlike former investigations the described 1D-3D approach is used to compare site data with a numerical analysis at prototype size focused on the amplitude and frequency of the pressure pulsation at overload condition. The combined model is able to capture the occurring phase change in the draft tube as well as the propagating pressure oscillation through the hydraulic system without solving for the whole penstock in a 3D manner, thus saving time and computational resources.

  16. Transient and steady state CO oxidation kinetics on nanolithographically prepared supported Pd model catalysts: Experiments and simulations

    SciTech Connect

    Laurin, M.; Johanek, V.; Grant, A.W.; Kasemo, B.; Libuda, J.; Freund, H.-J.

    2005-08-01

    Applying molecular-beam methods to a nanolithographically prepared planar Pd/SiO{sub 2} model catalyst, we have performed a detailed study of the kinetics of CO oxidation. The model catalyst was prepared by electron-beam lithography, allowing individual control of particle size and position. The sample was structurally characterized by atomic force microscopy and scanning electron microscopy before and after reaction. In the kinetic experiments, the O-rich and CO-rich regimes were investigated systematically with respect to their transient and steady-state behaviors, both under bistable and monostable reaction conditions. Separate molecular beams were used in order to supply the reactants, allowing individual control over the reactant fluxes. The desorbing CO{sub 2} was detected by both angle-resolved and angle-integrated mass spectrometries. The experimental results were analyzed using different types of microkinetic models, including a detailed reaction-diffusion model, which takes into account the structural parameters of the catalyst as well as scattering of the reactants from the support. The model quantitatively reproduces the results as a function of the reactant fluxes and the surface temperature. Various kinetic effects observed are discussed in detail on the basis of the model. Specifically, it is shown that under conditions of limited oxygen mobility, the switching behavior between the kinetic regimes is largely driven by the surface mobility of CO.

  17. Transient climate simulations of the deglaciation 21-9 thousand years before present (version 1) - PMIP4 Core experiment design and boundary conditions

    NASA Astrophysics Data System (ADS)

    Ivanovic, Ruza F.; Gregoire, Lauren J.; Kageyama, Masa; Roche, Didier M.; Valdes, Paul J.; Burke, Andrea; Drummond, Rosemarie; Peltier, W. Richard; Tarasov, Lev

    2016-07-01

    The last deglaciation, which marked the transition between the last glacial and present interglacial periods, was punctuated by a series of rapid (centennial and decadal) climate changes. Numerical climate models are useful for investigating mechanisms that underpin the climate change events, especially now that some of the complex models can be run for multiple millennia. We have set up a Paleoclimate Modelling Intercomparison Project (PMIP) working group to coordinate efforts to run transient simulations of the last deglaciation, and to facilitate the dissemination of expertise between modellers and those engaged with reconstructing the climate of the last 21 000 years. Here, we present the design of a coordinated Core experiment over the period 21-9 thousand years before present (ka) with time-varying orbital forcing, greenhouse gases, ice sheets and other geographical changes. A choice of two ice sheet reconstructions is given, and we make recommendations for prescribing ice meltwater (or not) in the Core experiment. Additional focussed simulations will also be coordinated on an ad hoc basis by the working group, for example to investigate more thoroughly the effect of ice meltwater on climate system evolution, and to examine the uncertainty in other forcings. Some of these focussed simulations will target shorter durations around specific events in order to understand them in more detail and allow for the more computationally expensive models to take part.

  18. Transient Simulation of the Evolution and Abrupt Change of Northern Africa Atmosphere-Ocean-Terrestrial Ecosystem in the Holocene: What causes the abrupt change?

    NASA Astrophysics Data System (ADS)

    Liu, Z.; Wang, Y.; Gallimore, R.; Gasse, F.; Johnson, T.; Demenocal, P.; Adkins, J.; Notaro, M.; Prentice, C.; Kutzbach, J.; Jacob, R.; Behling, P.; Ong, E.; Wang, L.

    2006-12-01

    We present the first synchronously coupled transient simulation of the evolution of northern Africa climate- ecosystem for the last 6500 years in a global general circulation ocean-atmosphere-terrestrial ecosystem model. The model successfully simulated the major abrupt vegetation collapse in the southern Sahara at about 5ka, consistent with the proxy records. Local precipitation, however, shows a much more gradual decline with time. The vegetation change in northern Africa is clearly driven by local precipitation decline and strong precipitation variability. In contrast, the change of precipitation is dominated by internal climate variability and a gradual monsoonal climate response to orbital forcing. In addition, some minor vegetation changes are also simulated in different regions across northern Africa. The model simulated a reduced seasonal cycle of SST and a gradual annual mean surface cooling in the subtropical North Atlantic towards the latest Holocene. The SST response is caused largely by the insolation forcing, while the annual mean cooling is also reinforced by the increased coastal upwelling near the east boundary. The increased upwelling results from a southward retreat of the North Africa monsoon system, and, in turn, an increased northeasterly trade wind. The simulated changes of SST and upwelling are also largely consistent with recent marine proxy records, albeit with a weaker magnitude in the model. A further analysis of the mechanism of the abrupt vegetation collapse suggests that the abrupt vegetation collapse is caused by a strong decadal climate variability in a stable climate-ecosystem, rather than a positive vegetation-climate feedback on a multi-equilibrium system. We propose that strong climate variability can induce a dramatic vegetation collapse with a gradual reduction in precipitation during the mid-Holocene. Our study highlights climate variability as a critical forcing for the vegetation collapse in both models and the real world.

  19. Chemical dynamics simulations of energy transfer, surface-induced dissociation, soft-landing, and reactive-landing in collisions of protonated peptide ions with organic surfaces.

    PubMed

    Pratihar, Subha; Barnes, George L; Hase, William L

    2016-07-01

    There are two components to the review presented here regarding simulations of collisions of protonated peptide ions peptide-H(+) with organic surfaces. One is a detailed description of the classical trajectory chemical dynamics simulation methodology. Different simulation approaches are used, and identified as MM, QM + MM, and QM/MM dependent on the potential energy surface used to represent the peptide-H(+) + surface collision. The second are representative examples of the information that may be obtained from the simulations regarding energy transfer and peptide-H(+) surface-induced dissociation, soft-landing, and reactive-landing for the peptide-H(+) + surface collisions. Good agreement with experiment is obtained for each of these four collision properties. The simulations provide atomistic interpretations of the peptide-H(+) + surface collision dynamics. PMID:26563571

  20. Transient nucleation in condensed systems

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.; Greer, A. L.; Thompson, C. V.

    1983-01-01

    Using classical nucleation theory we consider transient nucleation occurring in a one-component, condensed system under isothermal conditions. We obtain an exact closed-form expression for the time dependent cluster populations. In addition, a more versatile approach is developed: a numerical simulation technique which models directly the reactions by which clusters are produced. This simulation demonstrates the evolution of cluster populations and nucleation rate in the transient regime. Results from the simulation are verified by comparison with exact analytical solutions for the steady state. Experimental methods for measuring transient nucleation are assessed, and it is demonstrated that the observed behavior depends on the method used. The effect of preexisting cluster distributions is studied. Previous analytical and numerical treatments of transient nucleation are compared to the solutions obtained from the simulation. The simple expressions of Kashchiev are shown to give good descriptions of the nucleation behavior.

  1. AT123D: analytical transient one-, two-, and three-dimensional simulation of waste transport in the aquifer system

    SciTech Connect

    Yeh, G.T.

    1981-03-01

    A generalized analytical transient, one-, two-, and/or three-dimensional (AT123D) computer code is developed for estimating the transport of wastes in a groundwater aquifer system. It contains 450 options: 288 for the three-dimensional case, 72 for the two-dimensional case in the x-y plane, 73 for the two-dimensional case in the x-z plane, and 18 for the one-dimensional case in the longitudinal direction. These are the combinations of three types of wastes, eight sets of source configurations, three kinds of source releases, and four variations of the aquifer dimensions. Three types of the wastes are radioactive waste, chemicals, and heat. The eight types of source configurations are a point source, a line source parallel to the x-axis, a line source parallel to the y-axis, a line source parallel to the z-axis, an area source perpendicular to the x-axis, an area source perpendicular to the y-axis, an area source perpendicular to the z-axis, and a volume source. Three kinds of source releases are instantaneous, continuous, and finite duration releases. Four variations of the aquifer dimensions are finite depth and finite width, finite depth and infinite width, infinite depth and finite width, and infinite depth and infinite width. The mechanisms of transport included in the analysis are advection, hydrodynamic dispersion, adsorption, decay/degeneration, and waste losses to the atmosphere. Boundary conditions included Dirichlet, Neumann, mixed type, and/or radiation boundaries. Fifty sample cases are provided to illustrate the application of AT1230 to various situations.

  2. Numerical simulation of transient temperature profiles for canned apple puree in semi-rigid aluminum based packaging during pasteurization.

    PubMed

    Shafiekhani, Soraya; Zamindar, Nafiseh; Hojatoleslami, Mohammad; Toghraie, Davood

    2016-06-01

    Pasteurization of canned apple puree was simulated for a 3-D geometry in a semi-rigid aluminum based container which was heated from all sides at 378 K. The computational fluid dynamics code Ansys Fluent 14.0 was used and the governing equations for energy, momentum, and continuity were computed using a finite volume method. The food model was assumed to have temperature-dependent properties. To validate the simulation, the apple puree was pasteurized in a water cascading retort. The effect of the mesh structures was studied for the temperature profiles during thermal processing. The experimental temperature in the slowest heating zone in the container was compared with the temperature predicted by the model and the difference was not significant. The study also investigated the impact of head space (water-vapor) on heat transfer. PMID:27478233

  3. Numerical simulation of transient temperature profiles for canned apple puree in semi-rigid aluminum based packaging during pasteurization.

    PubMed

    Shafiekhani, Soraya; Zamindar, Nafiseh; Hojatoleslami, Mohammad; Toghraie, Davood

    2016-06-01

    Pasteurization of canned apple puree was simulated for a 3-D geometry in a semi-rigid aluminum based container which was heated from all sides at 378 K. The computational fluid dynamics code Ansys Fluent 14.0 was used and the governing equations for energy, momentum, and continuity were computed using a finite volume method. The food model was assumed to have temperature-dependent properties. To validate the simulation, the apple puree was pasteurized in a water cascading retort. The effect of the mesh structures was studied for the temperature profiles during thermal processing. The experimental temperature in the slowest heating zone in the container was compared with the temperature predicted by the model and the difference was not significant. The study also investigated the impact of head space (water-vapor) on heat transfer.

  4. SUSPNDRS: a numerical simulation tool for the nonlinear transient analysis of cable support bridge structures, part 1: theoretical development

    SciTech Connect

    McCallen, D.; Astaneh-Asl, A.

    1997-06-01

    The work reprint on herein was aimed at developing methodologies and tools for efficient and accurate numerical simulation of the seismic response of suspension and cable-stayed structures. A special purpose finite element program has been constructed and the underlying theory and demonstration example problems are presented. A companion report [Ref 1] discusses the application of this technology for a major suspension bridge structure.

  5. Transient dynamics and food-web complexity in the Lotka-Volterra cascade model.

    PubMed

    Chen, X; Cohen, J E

    2001-04-22

    How does the long-term behaviour near equilibrium of model food webs correlate with their short-term transient dynamics? Here, simulations of the Lotka -Volterra cascade model of food webs provide the first evidence to answer this question. Transient behaviour is measured by resilience, reactivity, the maximum amplification of a perturbation and the time at which the maximum amplification occurs. Model food webs with a higher probability of local asymptotic stability may be less resilient and may have a larger transient growth of perturbations. Given a fixed connectance, the sizes and durations of transient responses to perturbations increase with the number of species. Given a fixed number of species, as connectance increases, the sizes and durations of transient responses to perturbations may increase or decrease depending on the type of link that is varied. Reactivity is more sensitive to changes in the number of donor-controlled links than to changes in the number of recipient-controlled links, while resilience is more sensitive to changes in the number of recipient-controlled links than to changes in the number of donor-controlled links. Transient behaviour is likely to be one of the important factors affecting the persistence of ecological communities.

  6. Use of RSM modeling for optimizing decolorization of simulated textile wastewater by Pseudomonas aeruginosa strain ZM130 capable of simultaneous removal of reactive dyes and hexavalent chromium.

    PubMed

    Maqbool, Zahid; Hussain, Sabir; Ahmad, Tanvir; Nadeem, Habibullah; Imran, Muhammad; Khalid, Azeem; Abid, Muhammad; Martin-Laurent, Fabrice

    2016-06-01

    Remediation of colored wastewater loaded with dyes and metal ions is a matter of interest nowadays. In this study, 220 bacteria isolated from textile wastewater were tested for their potential to decolorize each of the four reactive dyes (reactive red-120, reactive black-5, reactive yellow-2, and reactive orange-16) in the presence of a mixture of four different heavy metals (Cr, Zn, Pb, Cd) commonly found in textile effluents. Among the tested bacteria, the isolate ZM130 was found to be the most efficient in decolorizing reactive dyes in the presence of the mixture of heavy metals and was identified as Pseudomonas aeruginosa strain ZM130 by 16S rRNA gene analysis. The strain ZM130 was highly effective in simultaneously removing hexavalent chromium (25 mg L(-1)) and the azo dyes (100 mg L(-1)) from the simulated wastewater even in the presence of other three heavy metals (Zn, Pb, Cd). Simultaneous removal of chromium and azo dyes ranged as 76.6-98.7 % and 51.9-91.1 %, respectively, after 180 h incubation. On the basis of quadratic polynomial equation and response surfaces given by the response surface methodology (RSM), optimal salt content, pH, carbon co-substrate content, and level of multi-metal mixtures for decolorization of reactive red-120 in a simulated textile wastewater by the strain ZM130 were predicted to be 19.8, 7.8, and 6.33 g L(-1) and a multi-metal mixture (Cr 13.10 mg L(-1), Pb 26.21 mg L(-1), Cd 13.10 mg L(-1), Zn 26.21 mg L(-1)), respectively. Moreover, the strain ZM130 also exhibited laccase and nicotinamide adenine dinucleotide (reduced)-dichlorophenolindophenol reductase (NADH-DCIP reductase) activity during the decolorization of reactive red-120. However, the laccase activity was found to be maximum in the presence of 300 mg L(-1) of the dye as compared to other concentrations. Hence, the isolation of this strain might serve as a potential bio-resource required for developing the strategies aiming at bioremediation of the

  7. Use of RSM modeling for optimizing decolorization of simulated textile wastewater by Pseudomonas aeruginosa strain ZM130 capable of simultaneous removal of reactive dyes and hexavalent chromium.

    PubMed

    Maqbool, Zahid; Hussain, Sabir; Ahmad, Tanvir; Nadeem, Habibullah; Imran, Muhammad; Khalid, Azeem; Abid, Muhammad; Martin-Laurent, Fabrice

    2016-06-01

    Remediation of colored wastewater loaded with dyes and metal ions is a matter of interest nowadays. In this study, 220 bacteria isolated from textile wastewater were tested for their potential to decolorize each of the four reactive dyes (reactive red-120, reactive black-5, reactive yellow-2, and reactive orange-16) in the presence of a mixture of four different heavy metals (Cr, Zn, Pb, Cd) commonly found in textile effluents. Among the tested bacteria, the isolate ZM130 was found to be the most efficient in decolorizing reactive dyes in the presence of the mixture of heavy metals and was identified as Pseudomonas aeruginosa strain ZM130 by 16S rRNA gene analysis. The strain ZM130 was highly effective in simultaneously removing hexavalent chromium (25 mg L(-1)) and the azo dyes (100 mg L(-1)) from the simulated wastewater even in the presence of other three heavy metals (Zn, Pb, Cd). Simultaneous removal of chromium and azo dyes ranged as 76.6-98.7 % and 51.9-91.1 %, respectively, after 180 h incubation. On the basis of quadratic polynomial equation and response surfaces given by the response surface methodology (RSM), optimal salt content, pH, carbon co-substrate content, and level of multi-metal mixtures for decolorization of reactive red-120 in a simulated textile wastewater by the strain ZM130 were predicted to be 19.8, 7.8, and 6.33 g L(-1) and a multi-metal mixture (Cr 13.10 mg L(-1), Pb 26.21 mg L(-1), Cd 13.10 mg L(-1), Zn 26.21 mg L(-1)), respectively. Moreover, the strain ZM130 also exhibited laccase and nicotinamide adenine dinucleotide (reduced)-dichlorophenolindophenol reductase (NADH-DCIP reductase) activity during the decolorization of reactive red-120. However, the laccase activity was found to be maximum in the presence of 300 mg L(-1) of the dye as compared to other concentrations. Hence, the isolation of this strain might serve as a potential bio-resource required for developing the strategies aiming at bioremediation of the

  8. The dynamical simulation of transient three-dimensional cryogenic liquid sloshing oscillations under low-gravity and microgravity

    NASA Astrophysics Data System (ADS)

    Chi, Yong Mann

    A numerical simulation model has been developed for the dynamical behavior of spacecraft propellant, both during the draining and the closing of the tank outlet at the onset of suction dip affected by the asymmetric combined gravity gradient and gravity jitter accelerations. In particular the effect of the surface tension of the fluids in the partially filled dewar (applicable to the Gravity Probe-B spacecraft dewar tank and fuel tanks for a liquid rocket) with rotation has been simulated and investigated. Two different cases of accelerations, one with gravity jitter dominated and the other equally weighted between gravity gradient and gravity jitter accelerations, are studied. In the development of this numerical simulation model, the NASA-VOF3D has been used as a supplement to the numerical program of this dissertation. The NASA-VOF3D code has been used for performing the three-dimensional incompressible flows with free surface. This is also used for controlling liquid sloshing inside the tank when the spacecraft is orbiting. To keep track of the location of the liquid, the fractional volume of fluid (VOF) technique was used. The VOF is based on the indicator function of the region occupied by the liquid with an Eulerian approach to solve the free surface phenomena between liquid and gas phases. For the calculation of surface tension force, the VOF model is also used. The newly developed simulation model is used to investigate the characteristics of liquid hydrogen draining in terms of the residual amount of trapped liquid at the onset of the suction dip and residual liquid volume at the time the dip of the liquid-vapor interface formed. This investigation simulates the characteristics of liquid oscillations due to liquid container outlet shut-off at the onset of suction dip. These phenomena checked how these mechanisms affected the excitation of slosh waves during the course of liquid draining and after shut-off tank outlet. In the present study, the dynamical

  9. Transient β-hairpin formation in α-synuclein monomer revealed by coarse-grained molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Yu, Hang; Han, Wei; Ma, Wen; Schulten, Klaus

    2015-12-01

    Parkinson's disease, originating from the intrinsically disordered peptide α-synuclein, is a common neurodegenerative disorder that affects more than 5% of the population above age 85. It remains unclear how α-synuclein monomers undergo conformational changes leading to aggregation and formation of fibrils characteristic for the disease. In the present study, we perform molecular dynamics simulations (over 180 μs in aggregated time) using a hybrid-resolution model, Proteins with Atomic details in Coarse-grained Environment (PACE), to characterize in atomic detail structural ensembles of wild type and mutant monomeric α-synuclein in aqueous solution. The simulations reproduce structural properties of α-synuclein characterized in experiments, such as secondary structure content, long-range contacts, chemical shifts, and 3J(HNHCα)-coupling constants. Most notably, the simulations reveal that a short fragment encompassing region 38-53, adjacent to the non-amyloid-β component region, exhibits a high probability of forming a β-hairpin; this fragment, when isolated from the remainder of α-synuclein, fluctuates frequently into its β-hairpin conformation. Two disease-prone mutations, namely, A30P and A53T, significantly accelerate the formation of a β-hairpin in the stated fragment. We conclude that the formation of a β-hairpin in region 38-53 is a key event during α-synuclein aggregation. We predict further that the G47V mutation impedes the formation of a turn in the β-hairpin and slows down β-hairpin formation, thereby retarding α-synuclein aggregation.

  10. Transient β-hairpin formation in α-synuclein monomer revealed by coarse-grained molecular dynamics simulation

    SciTech Connect

    Yu, Hang; Ma, Wen; Han, Wei; Schulten, Klaus

    2015-12-28

    Parkinson’s disease, originating from the intrinsically disordered peptide α-synuclein, is a common neurodegenerative disorder that affects more than 5% of the population above age 85. It remains unclear how α-synuclein monomers undergo conformational changes leading to aggregation and formation of fibrils characteristic for the disease. In the present study, we perform molecular dynamics simulations (over 180 μs in aggregated time) using a hybrid-resolution model, Proteins with Atomic details in Coarse-grained Environment (PACE), to characterize in atomic detail structural ensembles of wild type and mutant monomeric α-synuclein in aqueous solution. The simulations reproduce structural properties of α-synuclein characterized in experiments, such as secondary structure content, long-range contacts, chemical shifts, and {sup 3}J(H{sub N}H{sub C{sub α}})-coupling constants. Most notably, the simulations reveal that a short fragment encompassing region 38-53, adjacent to the non-amyloid-β component region, exhibits a high probability of forming a β-hairpin; this fragment, when isolated from the remainder of α-synuclein, fluctuates frequently into its β-hairpin conformation. Two disease-prone mutations, namely, A30P and A53T, significantly accelerate the formation of a β-hairpin in the stated fragment. We conclude that the formation of a β-hairpin in region 38-53 is a key event during α-synuclein aggregation. We predict further that the G47V mutation impedes the formation of a turn in the β-hairpin and slows down β-hairpin formation, thereby retarding α-synuclein aggregation.

  11. An Interface-Enriched eXtended Finite Element-Level Set Simulation of Solutal Melting of Additive Powder Particles during Transient Liquid Phase Bonding

    NASA Astrophysics Data System (ADS)

    Ghoneim, A.; Hunedy, J.; Ojo, O. A.

    2013-02-01

    A new numerical simulation model is developed by using an interface-enriched eXtended Finite Element-Level Set (XFE-LS) method to study the solute-induced melting of additive powder particles (APPs) during transient liquid phase (TLP) bonding. The robust model captures rapidly occurring concurrent interfacial events at multiple propagating liquid-solid interfaces to simulate the melting behavior. In contrast to the critical assumption in analytical models, numerical calculations show that solute-transport into the APPs during the equilibration of the liquid composition is a significant factor that affects the APPs melting behavior. Also, the study shows that the solute-transport dependence of extent of APPs melting is influenced by the kinetics of solid-state solute diffusion within the particles. The understanding generated by the numerical analysis has resulted in the use of interlayer powder mixture that contains base-alloy APPs to produce single crystal TLP joint that has matching crystallographic orientations with single crystal substrate material, at a substantially reduced processing time, which has been previously considered unfeasible.

  12. Numerical simulation of transient detonation structures in H2-O2 mixtures in smooth pipe bends

    SciTech Connect

    Deiterding, Ralf

    2007-01-01

    While the detailed structure of detonations in low-pressure hydrogen-oxygen mixtures with high argon dilution has been fairly well analyzed by means of numerical simulation for two-dimensional rectangular channels, open questions remain for three space dimensions and non-rectangular geometries. In the present paper, we simulate the transient structural evolution as Chapman-Jouguet detonation waves in a perfectly stirred 2 H2+O2+7 Ar mixture at initial pressure 10kPa and room temperature propagate through smooth two-dimensional pipeline bends. The pipes have the constant width 8cm and encompass initially five regular detonation cells. For an unchanged inner radius of 15cm, we consider the bending angles 15, 30, 45, and 60 degree. The computations employ detailed chemical kinetics with 9 thermally perfect species and have been carried out with a massively parallel high-resolution finite volume code with temporal and spatial dynamic mesh adaptation. While we observe only changes in the detonation cell size for 15 degree, a partial decoupling of shock and reaction front occurs in the expansion region for larger bend angles. For 45 and 60 degree, a violent transverse detonation wave reignites the failure region. It is found that the reignition wave itself exhibits an instationary triple point around which the maximal pressure and temperature levels of the entire configuration do occur.

  13. Assessment of RELAP5/MOD3.1 with the LSTF SB-SG-06 experiment simulating a steam generator tube rupture transient

    SciTech Connect

    Seul, K.W.; Bang, Y.S.; Lee, S.; Kim, H.J.

    1996-09-01

    The objective of the present work is to identify the predictability of RELAP5/MOD3.1 regarding thermal-hydraulic behavior during a steam generator tube rupture (SGTR). To evaluate the computed results, LSTF SB-SG-06 test data simulating the SGTR that occurred at the Mihama Unit 2 in 1991 are used. Also, some sensitivity studies of the code change in RELAP5, the break simulation model, and the break valve discharge coefficient are performed. The calculation results indicate that the RELAP5/MOD3.1 code predicted well the sequence of events and the major phenomena during the transient, such as the asymmetric loop behavior, reactor coolant system (RCS) cooldown and heat transfer by natural circulation, the primary and secondary system depressurization by the pressurizer auxiliary spray and the steam dump using the intact loop steam generator (SG) relief valve, and so on. However, there are some differences from the experimental data in the number of the relief valve cycling in the affected SG, and the flow regime of the hot leg with the pressurizer, and the break flow rates. Finally, the calculation also indicates that the coolant in the core could remain in a subcooled state as a result of the heat transfer caused by the natural circulation flow even if the reactor coolant pumps (RCPs) turned off and that the affected SG could be properly isolated to minimize the radiological release after the SGTR.

  14. The LOFAR Transients Pipeline

    NASA Astrophysics Data System (ADS)

    Swinbank, John D.; Staley, Tim D.; Molenaar, Gijs J.; Rol, Evert; Rowlinson, Antonia; Scheers, Bart; Spreeuw, Hanno; Bell, Martin E.; Broderick, Jess W.; Carbone, Dario; Garsden, Hugh; van der Horst, Alexander J.; Law, Casey J.; Wise, Michael; Breton, Rene P.; Cendes, Yvette; Corbel, Stéphane; Eislöffel, Jochen; Falcke, Heino; Fender, Rob; Grießmeier, Jean-Mathias; Hessels, Jason W. T.; Stappers, Benjamin W.; Stewart, Adam J.; Wijers, Ralph A. M. J.; Wijnands, Rudy; Zarka, Philippe

    2015-06-01

    Current and future astronomical survey facilities provide a remarkably rich opportunity for transient astronomy, combining unprecedented fields of view with high sensitivity and the ability to access previously unexplored wavelength regimes. This is particularly true of LOFAR, a recently-commissioned, low-frequency radio interferometer, based in the Netherlands and with stations across Europe. The identification of and response to transients is one of LOFAR's key science goals. However, the large data volumes which LOFAR produces, combined with the scientific requirement for rapid response, make automation essential. To support this, we have developed the LOFAR Transients Pipeline, or TraP. The TraP ingests multi-frequency image data from LOFAR or other instruments and searches it for transients and variables, providing automatic alerts of significant detections and populating a lightcurve database for further analysis by astronomers. Here, we discuss the scientific goals of the TraP and how it has been designed to meet them. We describe its implementation, including both the algorithms adopted to maximize performance as well as the development methodology used to ensure it is robust and reliable, particularly in the presence of artefacts typical of radio astronomy imaging. Finally, we report on a series of tests of the pipeline carried out using simulated LOFAR observations with a known population of transients.

  15. Comparison of oxidation resistance of UHMWPE and POM in H2O2 solution from ReaxFF reactive molecular dynamics simulations.

    PubMed

    Chen, Wu; Duan, Hai-tao; Hua, Meng; Gu, Ka-li; Shang, Hong-fei; Li, Jian

    2014-08-28

    The oxidation mechanism of ultra-high-molecular-weight polyethylene (UHMWPE) and polyoxymethylene (POM) in hydrogen peroxide solution was investigated by molecular dynamics (MD) simulations via reactive force field (ReaxFF) method. MD results from ReaxFF suggested that UHMWPE provided better antioxidation activity at high temperature (>373 K) than its POM counterpart in the same concentration of hydrogen peroxide solution. Furthermore, POM was relatively more susceptible to erosion and swelling because of the infiltration of H2O2 solution. Calculations of the diffusion coefficient at different temperatures permit further understanding of the chemical phenomena involved in the level of oxidation in the course of MD simulations. Results of the simulations are generally consistent with the previous experimental available in literature. The simulations also provide new insights into understanding the mechanism resulting oxidation products among the interested polymers.

  16. Modeling and simulation of the transient response of temperature and relative humidity sensors with and without protective housing.

    PubMed

    Rocha, Keller Sullivan Oliveira; Martins, José Helvecio; Martins, Marcio Arêdes; Tinôco, Ilda de Fátima Ferreira; Saraz, Jairo Alexander Osorio; Lacerda Filho, Adílio Flauzino; Fernandes, Luiz Henrique Martins

    2014-01-01

    Based on the necessity for enclosure protection of temperature and relative humidity sensors installed in a hostile environment, a wind tunnel was used to quantify the time that the sensors take to reach equilibrium in the environmental conditions to which they are exposed. Two treatments were used: (1) sensors with polyvinyl chloride (PVC) enclosure protection, and (2) sensors with no enclosure protection. The primary objective of this study was to develop and validate a 3-D computational fluid dynamics (CFD) model for analyzing the temperature and relative humidity distribution in a wind tunnel using sensors with PVC enclosure protection and sensors with no enclosure protection. A CFD simulation model was developed to describe the temperature distribution and the physics of mass transfer related to the airflow relative humidity. The first results demonstrate the applicability of the simulation. For verification, a sensor device was successfully assembled and tested in an environment that was optimized to ensure fast change conditions. The quantification setup presented in this paper is thus considered to be adequate for testing different materials and morphologies for enclosure protection. The results show that the boundary layer flow regime has a significant impact on the heat flux distribution. The results indicate that the CFD technique is a powerful tool which provides a detailed description of the flow and temperature fields as well as the time that the relative humidity takes to reach equilibrium with the environment in which the sensors are inserted.

  17. Simulation experiment of interaction of plasma facing materials and transient heat loads in ITER divertor by use of magnetized coaxial plasma gun

    NASA Astrophysics Data System (ADS)

    Nakatsuka, M.; Ando, K.; Higashi, T.; Kikuchi, Y.; Fukumoto, N.; Nagata, M.

    2009-11-01

    Interaction of plasma facing materials and transient head loads such as type I ELMs is one of the critical issues in ITER divertor. The heat load to the ITER divertor during type I ELMs is estimated to be 0.5-3 MJ/m^2 with a pulse length of 0.1-0.5 ms. We have developed a magnetized coaxial plasma gun (MCPG) for the simulation experiment of transient heat load during type I ELMs in ITER divertor. The MCPG has inner and outer electrodes made of stainless steel 304. In addition, the inner electrode is covered with molybdenum so as to suppress the release of impurities from the electrode during the discharge. The diameters of inner and outer electrodes are 0.06 m and 0.14 m, respectively. The power supply for the MCPG is a capacitor bank (7 kV, 1 mF, 25 kJ). The plasma velocity estimated by the time of flight measurement of the magnetic fields was about 50 km/s, corresponding to the ion energy of 15 eV (H) or 30 eV (D). The absorbed energy density of the plasma stream was measured a calorimeter made of graphite. It was found that the absorbed energy density was 0.9 MJ/m^2 with a pulse width of 0.5 ms at the distance of 100 mm from the inner electrode. In the conference, experimental results of plasma exposure on the plasma facing materials in ITER divertor will be shown.

  18. Micro-topography and reactivity of implant surfaces: an in vitro study in simulated body fluid (SBF).

    PubMed

    Gandolfi, M G; Taddei, P; Siboni, F; Perrotti, V; Iezzi, G; Piattelli, A; Prati, C

    2015-02-01

    The creation of micro-textured dental implant surfaces possessing a stimulating activity represents a challenge in implant dentistry; particularly, the formation of a thin, biologically active, calcium-phosphate layer on their surface could help to strengthen the bond to the surrounding bone. The aim of the present study was to characterize in terms of macrostructure, micro-topography and reactivity in simulated body fluid (SBF), the surface of titanium (Ti) implants blasted with TiO2 particles, acid etched with hydrofluoric acid, and activated with Ca and Mg-containing nanoparticles. Sandblasted and acid-etched implants were analyzed by ESEM-EDX (environmental scanning electron microscope with energy dispersive X-ray system) to study the micromorphology of the surface and to perform elemental X-ray microanalysis (microchemical analyses) and element mapping. ESEM-EDX analyses were performed at time 0 and after a 28-day soaking period in SBF Hank's balanced salt solution (HBSS) following ISO 23317 (implants for surgery—in vitro evaluation for apatite-forming ability of implant materials). Microchemical analyses (weight % and atomic %) and element mapping were carried out to evaluate the relative element content, element distribution, and calcium/phosphorus (Ca/P) atomic ratio. Raman spectroscopy was used to assess the possible presence of impurities due to manufacturing and to investigate the phases formed upon HBSS soaking. Micro-morphological analyses showed a micro-textured, highly rough surface with microgrooves. Microchemical analyses showed compositional differences among the apical, middle, and distal thirds. The micro-Raman analyses of the as-received implant showed the presence of amorphous Ti oxide and traces of anatase, calcite, and a carbonaceous material derived from the decomposition of an organic component of lipidic nature (presumably used as lubricant). A uniform layer of Ca-poor calcium phosphates (CaPs) (Ca/P ratio <1.47) was observed after

  19. Cement kiln dust (CKD)-filter sand permeable reactive barrier for the removal of Cu(II) and Zn(II) from simulated acidic groundwater.

    PubMed

    Sulaymon, Abbas H; Faisal, Ayad A H; Khaliefa, Qusey M

    2015-10-30

    The hydraulic conductivity and breakthrough curves of copper and zinc contaminants were measured in a set of continuous column experiments for 99 days using cement kiln dust (CKD)-filter sand as the permeable reactive barrier. The results of these experiments proved that the weight ratios of the cement kiln dust-filter sand (10:90 and 20:80) are adequate in preventing the loss of reactivity and hydraulic conductivity and, in turn, avoiding reduction in the groundwater flow. These results reveal a decrease in the hydraulic conductivity, which can be attributed to an accumulation of most of the quantity of the contaminant masses in the first sections of the column bed. Breakthrough curves for the description of the temporal contaminant transport within the barrier were found to be more representative by the Belter-Cussler-Hu and Yan models based on the coefficient of determination and Nash-Sutcliffe efficiency. The longevity of the barrier was simulated for the field scale, based on the laboratory column tests and the values verified that cement kiln dust can be effectively used in the future, as the reactive material in permeable reactive barrier technology. These results signify that the longevity of the barrier is directly proportional to its thickness and inversely to the percentage of the CKD used.

  20. Cement kiln dust (CKD)-filter sand permeable reactive barrier for the removal of Cu(II) and Zn(II) from simulated acidic groundwater.

    PubMed

    Sulaymon, Abbas H; Faisal, Ayad A H; Khaliefa, Qusey M

    2015-10-30

    The hydraulic conductivity and breakthrough curves of copper and zinc contaminants were measured in a set of continuous column experiments for 99 days using cement kiln dust (CKD)-filter sand as the permeable reactive barrier. The results of these experiments proved that the weight ratios of the cement kiln dust-filter sand (10:90 and 20:80) are adequate in preventing the loss of reactivity and hydraulic conductivity and, in turn, avoiding reduction in the groundwater flow. These results reveal a decrease in the hydraulic conductivity, which can be attributed to an accumulation of most of the quantity of the contaminant masses in the first sections of the column bed. Breakthrough curves for the description of the temporal contaminant transport within the barrier were found to be more representative by the Belter-Cussler-Hu and Yan models based on the coefficient of determination and Nash-Sutcliffe efficiency. The longevity of the barrier was simulated for the field scale, based on the laboratory column tests and the values verified that cement kiln dust can be effectively used in the future, as the reactive material in permeable reactive barrier technology. These results signify that the longevity of the barrier is directly proportional to its thickness and inversely to the percentage of the CKD used. PMID:25956647

  1. On the absolute thermodynamics of water from computer simulations: A comparison of first-principles molecular dynamics, reactive and empirical force fields

    NASA Astrophysics Data System (ADS)

    Pascal, Tod A.; Schärf, Daniel; Jung, Yousung; Kühne, Thomas D.

    2012-12-01

    We present the absolute enthalpy, entropy, heat capacity, and free energy of liquid water at ambient conditions calculated by the two-phase thermodynamic method applied to ab initio, reactive and classical molecular dynamics simulations. We find that the absolute entropy and heat capacity of liquid water from ab initio molecular dynamics (AIMD) is underestimated, but falls within the range of the flexible empirical as well as the reactive force fields. The origin of the low absolute entropy of liquid water from AIMD simulations is due to an underestimation of the translational entropy by 20% and the rotational entropy by 40% compared to the TIP3P classical water model, consistent with previous studies that reports low diffusivity and increased ordering of liquid water from AIMD simulations. Classical MD simulations with rigid water models tend to be in better agreement with experiment (in particular TIP3P yielding the best agreement), although the TIP4P-ice water model, the only empirical force field that reproduces the experimental melting temperature, has the lowest entropy, perhaps expectedly. This reiterates the limitations of existing empirical water models in simultaneously capturing the thermodynamics of solid and liquid phases. We find that the quantum corrections to heat capacity of water can be as large as 60%. Although certain water models are computed to yield good absolute free energies of water compared to experiments, they are often due to the fortuitous enthalpy-entropy cancellation, but not necessarily due to the correct descriptions of enthalpy and entropy separately.

  2. User's Guide of TOUGH2-EGS. A Coupled Geomechanical and Reactive Geochemical Simulator for Fluid and Heat Flow in Enhanced Geothermal Systems Version 1.0

    SciTech Connect

    Fakcharoenphol, Perapon; Xiong, Yi; Hu, Litang; Winterfeld, Philip H.; Xu, Tianfu; Wu, Yu-Shu

    2013-05-01

    TOUGH2-EGS is a numerical simulation program coupling geomechanics and chemical reactions for fluid and heat flows in porous media and fractured reservoirs of enhanced geothermal systems. The simulator includes the fully-coupled geomechanical (THM) module, the fully-coupled geochemical (THC) module, and the sequentially coupled reactive geochemistry (THMC) module. The fully-coupled flow-geomechanics model is developed from the linear elastic theory for the thermo-poro-elastic system and is formulated with the mean normal stress as well as pore pressure and temperature. The chemical reaction is sequentially coupled after solution of flow equations, which provides the flow velocity and phase saturation for the solute transport calculation at each time step. In addition, reservoir rock properties, such as porosity and permeability, are subjected to change due to rock deformation and chemical reactions. The relationships between rock properties and geomechanical and chemical effects from poro-elasticity theories and empirical correlations are incorporated into the simulator. This report provides the user with detailed information on both mathematical models and instructions for using TOUGH2-EGS for THM, THC or THMC simulations. The mathematical models include the fluid and heat flow equations, geomechanical equation, reactive geochemistry equations, and discretization methods. Although TOUGH2-EGS has the capability for simulating fluid and heat flows coupled with both geomechanical and chemical effects, it is up to the users to select the specific coupling process, such as THM, THC, or THMC in a simulation. There are several example problems illustrating the applications of this program. These example problems are described in details and their input data are presented. The results demonstrate that this program can be used for field-scale geothermal reservoir simulation with fluid and heat flow, geomechanical effect, and chemical reaction in porous and fractured media.

  3. Stochastic simulation of fission product activity in primary coolant due to fuel rod failures in typical PWRs under power transients

    NASA Astrophysics Data System (ADS)

    Javed Iqbal, M.; Mirza, Nasir M.; Mirza, Sikander M.

    2008-01-01

    During normal operation of PWRs, routine fuel rods failures result in release of radioactive fission products (RFPs) in the primary coolant of PWRs. In this work, a stochastic model has been developed for simulation of failure time sequences and release rates for the estimation of fission product activity in primary coolant of a typical PWR under power perturbations. In the first part, a stochastic approach is developed, based on generation of fuel failure event sequences by sampling the time dependent intensity functions. Then a three-stage model based deterministic methodology of the FPCART code has been extended to include failure sequences and random release rates in a computer code FPCART-ST, which uses state-of-the-art LEOPARD and ODMUG codes as its subroutines. The value of the 131I activity in primary coolant predicted by FPCART-ST code has been found in good agreement with the corresponding values measured at ANGRA-1 nuclear power plant. The predictions of FPCART-ST code with constant release option have also been found to have good agreement with corresponding experimental values for time dependent 135I, 135Xe and 89Kr concentrations in primary coolant measured during EDITHMOX-1 experiments.

  4. Global approach for transient shear wave inversion based on the adjoint method: a comprehensive 2D simulation study.

    PubMed

    Arnal, B; Pinton, G; Garapon, P; Pernot, M; Fink, M; Tanter, M

    2013-10-01

    Shear wave imaging (SWI) maps soft tissue elasticity by measuring shear wave propagation with ultrafast ultrasound acquisitions (10 000 frames s(-1)). This spatiotemporal data can be used as an input for an inverse problem that determines a shear modulus map. Common inversion methods are local: the shear modulus at each point is calculated based on the values of its neighbour (e.g. time-of-flight, wave equation inversion). However, these approaches are sensitive to the information loss such as noise or the lack of the backscattered signal. In this paper, we evaluate the benefits of a global approach for elasticity inversion using a least-squares formulation, which is derived from full waveform inversion in geophysics known as the adjoint method. We simulate an acoustic waveform in a medium with a soft and a hard lesion. For this initial application, full elastic propagation and viscosity are ignored. We demonstrate that the reconstruction of the shear modulus map is robust with a non-uniform background or in the presence of noise with regularization. Compared to regular local inversions, the global approach leads to an increase of contrast (∼+3 dB) and a decrease of the quantification error (∼+2%). We demonstrate that the inversion is reliable in the case when there is no signal measured within the inclusions like hypoechoic lesions which could have an impact on medical diagnosis.

  5. Transient climate simulation from the Maunder Minimum to present day using prescribed changes in GHG, total/spectral solar irradiance and ozone

    NASA Astrophysics Data System (ADS)

    Spangehl, Thomas; Cubasch, Ulrich; Schimanke, Semjon

    A fully coupled AO-GCM including representation of the middle atmosphere is used for tran-sient simulation of climate from 1630 to 2000 AD. For better representation of changes in the UV/visible part of the solar spectrum an improved short-wave radiation scheme is implemented. The model is driven by changes in GHG concentrations, solar activity and volcanic eruptions. Solar variability is introduced via changes in total/spectral solar irradiance (TSI/SSI) and pre-scribed changes in stratospheric ozone. The secular trend in TSI is in the range of 0.1 percent increase from Maunder Minimum to present-day. Volcanic eruptions are represented via abrupt reduction in TSI. With the applied forcings the model does not simulate a clear reduction of the annual Northern Hemisphere (NH) mean near surface temperature during Maunder Minimum. By contrast the Dalton Minimum is characterized by distinct cooling and there is a significant raise of NH mean near surface temperature until the end of the 20th century. Focusing on the North Atlantic/European region the winter mean near surface temperature change pat-tern from Late Maunder Minimum (1675-1715) to present-day (1960-1990) reveals maximum warming over north-eastern Europe and cooling over the western North Atlantic with maxi-mum cooling west of Greenland. These changes can partly be explained by a shift of the NAO towards a more positive phase. The simulated changes in tropospheric circulation are discussed with special emphasize on the role of the solar forcing. Besides the stratospheric solar forcing which may affect NAO variability via downward propagation of the solar signal from the strato-sphere to the troposphere the magnitude of the secular trend in TSI might play a role. For the period from Maunder Minimum to present-day the simulation shows less near surface temper-ature increase especially over arctic regions when compared to simulations performed with the same model including the standard radiation scheme but

  6. Do we really need a large number of particles to simulate bimolecular reactive transport with random walk methods? A kernel density estimation approach

    NASA Astrophysics Data System (ADS)

    Rahbaralam, Maryam; Fernàndez-Garcia, Daniel; Sanchez-Vila, Xavier

    2015-12-01

    Random walk particle tracking methods are a computationally efficient family of methods to solve reactive transport problems. While the number of particles in most realistic applications is in the order of 106-109, the number of reactive molecules even in diluted systems might be in the order of fractions of the Avogadro number. Thus, each particle actually represents a group of potentially reactive molecules. The use of a low number of particles may result not only in loss of accuracy, but also may lead to an improper reproduction of the mixing process, limited by diffusion. Recent works have used this effect as a proxy to model incomplete mixing in porous media. In this work, we propose using a Kernel Density Estimation (KDE) of the concentrations that allows getting the expected results for a well-mixed solution with a limited number of particles. The idea consists of treating each particle as a sample drawn from the pool of molecules that it represents; this way, the actual location of a tracked particle is seen as a sample drawn from the density function of the location of molecules represented by that given particle, rigorously represented by a kernel density function. The probability of reaction can be obtained by combining the kernels associated to two potentially reactive particles. We demonstrate that the observed deviation in the reaction vs time curves in numerical experiments reported in the literature could be attributed to the statistical method used to reconstruct concentrations (fixed particle support) from discrete particle distributions, and not to the occurrence of true incomplete mixing. We further explore the evolution of the kernel size with time, linking it to the diffusion process. Our results show that KDEs are powerful tools to improve computational efficiency and robustness in reactive transport simulations, and indicates that incomplete mixing in diluted systems should be modeled based on alternative mechanistic models and not on a

  7. The background rate of false positives: Combining simulations of gravitational wave events with an unsupervised algorithm for transient identification in crowded image-subtracted data

    NASA Astrophysics Data System (ADS)

    Ackley, Kendall; Eikenberry, Stephen; Klimenko, Sergey; LIGO Collaboration

    2016-03-01

    We are now entering the era of multimessenger gravitational wave (GW) astronomy with the completion of the first observing run of Advanced LIGO. Multiwavelength electromagnetic (EM) emission is expected to accompany gravitational radiation from compact object binary mergers, such as those between neutron stars and stellar-mass black holes, where Advanced LIGO is most sensitive to their detection. Attempting to perform EM follow-up over the 10-100s deg2 error regions will be faced with many challenges, including the identification and removal of O (105) false positive transients that appear as a commotion of background events and as image artifacts in crowded image-subtracted fields. We present an update to our automated unsupervised algorithm including how our pipeline uses the existing coherent WaveBurst pipeline in an attempt to develop optimized EM follow-up schema. Our end-to-end pipeline combines simulated GW events with actual observational data from a number of ground-based optical observatories, including PTF, ROTSE, and DECam. Our performance is reported both in terms of the number of coincident false positives as well as the efficiency of recovery.

  8. A Transient Numerical Simulation of Perched Ground-Water Flow at the Test Reactor Area, Idaho National Engineering and Environmental Laboratory, Idaho, 1952-94

    SciTech Connect

    B. R. Orr

    1999-11-01

    Studies of flow through the unsaturated zone and perched ground-water zones above the Snake River Plain aquifer are part of the overall assessment of ground-water flow and determination of the fate and transport of contaminants in the subsurface at the Idaho National Engineering and Environmental Laboratory (INEEL). These studies include definition of the hydrologic controls on the formation of perched ground-water zones and description of the transport and fate of wastewater constituents as they moved through the unsaturated zone. The definition of hydrologic controls requires stratigraphic correlation of basalt flows and sedimentary interbeds within the saturated zone, analysis of hydraulic properties of unsaturated-zone rocks, numerical modeling of the formation of perched ground-water zones, and batch and column experiments to determine rock-water geochemical processes. This report describes the development of a transient numerical simulation that was used to evaluate a conceptual model of flow through perched ground-water zones beneath wastewater infiltration ponds at the Test Reactor Area (TRA).

  9. Assessment of RELAP5/MOD3 with the LOFT L9-1/L3-3 experiment simulating an anticipated transient with multiple failures

    SciTech Connect

    Bang, Y.S.; Seul, K.W.; Kim, H.J.

    1994-02-01

    The RELAP5/MOD3 5m5 code is assessed using the L9-1/L3-3 test carried out in the LOFT facility, a 1/60-scaled experimental reactor, simulating a loss of feedwater accident with multiple failures and the sequentially-induced small break loss-of-coolant accident. The code predictability is evaluated for the four separated sub-periods with respect to the system response; initial heatup phase, spray and power operated relief valve (PORV) cycling phase, blowdown phase and recovery phase. Based on the comparisons of the results from the calculation with the experiment data, it is shown that the overall thermal-hydraulic behavior important to the scenario such as a heat removal between the primary side and the secondary side and a system depressurization can be well-predicted and that the code could be applied to the full-scale nuclear power plant for an anticipated transient with multiple failures within a reasonable accuracy. The minor discrepancies between the prediction and the experiment are identified in reactor scram time, post-scram behavior in the initial heatup phase, excessive heatup rate in the cycling phase, insufficient energy convected out the PORV under the hot leg stratified condition in the saturated blowdown phase and void distribution in secondary side in the recovery phase. This may come from the code uncertainties in predicting the spray mass flow rate, the associated condensation in pressurizer and junction fluid density under stratified condition.

  10. Plant data comparisons for Comanche Peak 50% load rejection transient

    SciTech Connect

    Boatwright, W.J.; Choe, W.G.; Hiltbrand, D.W.; Devore, C.V.

    1994-12-31

    The RETRAN-02 codes is used for the transient and accident analysis. Benchmarks have been performed in order to qualify the Comanche Pear Steam electric station (CPSES) RETRAN-02 model, particularly the protection and control systems , reactivity feedback, noding, and primary-to-secondary heat transfer modeling. The 50% load rejection test was performed as part of the initial start-up test sequence for CPSES-1. The results of this analysis demonstrate that the RETRAN-02 model of CPSES-1 allows for quite good predictions of (1) the primary-to-secondary heat transfer rate; (2) the core power response, including the reactivity feedback effects due to changes in moderator and fuel temperatures and control rod position; and (3) the rod control model, which correctly simulates actual plant response in which the control rods are inserted and withdrawn in response to temperature and power error signals.

  11. Natural removal of added N-nutrients, reactive phosphorus, crude oil, and heavy metals from the water phase in a simulated water/sediment system

    SciTech Connect

    Lam-Leung, S.Y.; Cheung, M.T.; He, Y.Q.

    1996-08-01

    Water/sediment simulation systems were constructed by using an aquarium (0.45 x 0.29 x 0.35 m{sup 3}), filled with suitable amounts of water and sediment collected from three selected locations: Lan Hau Shan (LHS), Tai Hu (TH), and Loong Yu Tao (LYT) of the Zhujiang (Pearl River) Estuary of China in November 1992 at low-tide period. The salinities of the water samples collected form LHS, TH, LYT were found to be 0.2, 4.6, 16.2 g L{sup -1}, respectively. Known amounts of ammonium, nitrate, nitrite, reactive phosphorous, crude oil, arsenate(III), cadmium (II), copper(II), and zinc(II) were added as pollutants into each of the water/sediment simulation systems. The rates of the natural removal of each added pollutant in all water/sediment simulation systems were studied by monitoring their concentrations at various intrevals in the investigation period. Except for Cr(III) and reactive phosphorous in the water/sediment systems of the LHS, TH, and LYT sites, and nitrate in the TH and LYT sites, the concentrations of the added pollutants in the water phase of the studied systems under a flow-condition simulation were reduced to 8% or less of the corresponding added amount on or before the 12th day by natural processes. The rate of self-purification and the estimated assimulative capacity of each added pollutant in all water/sediment simulation systems is discussed. 30 refs., 11 figs., 4 tabs.

  12. Selective removal and recovery of Black B reactive dye from simulated textile wastewater using the supported liquid membrane process.

    PubMed

    Harruddin, Norlisa; Othman, Norasikin; Ee Sin, Andeline Lim; Raja Sulaiman, Raja Norimie

    2015-01-01

    Effluent containing colour/dyes, especially reactive dyes, becomes a great concern of wastewater treatment because it is toxic to human life and aquatic life. In this study, reactive dye of Black B was separated using the supported liquid membrane process. Commercial polypropylene membrane was used as a support of the kerosene-tridodecylamine liquid membrane. Several parameters were tested and the result showed that almost 100% of 70 ppm Black B was removed and 99% of 70 ppm Black B was recovered at pH 2 of the feed phase containing 0.00001 M Na2SiO3, flow rate of 150 ml/min and 0.2 M NaOH. The membrane support also remained stable for up to 36 hours under an optimum condition.

  13. Future Transient Testing of Advanced Fuels

    SciTech Connect

    Jon Carmack

    2009-09-01

    The transient in-reactor fuels testing workshop was held on May 4–5, 2009 at Idaho National Laboratory. The purpose of this meeting was to provide a forum where technical experts in transient testing of nuclear fuels could meet directly with technical instrumentation experts and nuclear fuel modeling and simulation experts to discuss needed advancements in transient testing to support a basic understanding of nuclear fuel behavior under off-normal conditions. The workshop was attended by representatives from Commissariat à l'Énergie Atomique CEA, Japanese Atomic Energy Agency (JAEA), Department of Energy (DOE), AREVA, General Electric – Global Nuclear Fuels (GE-GNF), Westinghouse, Electric Power Research Institute (EPRI), universities, and several DOE national laboratories. Transient testing of fuels and materials generates information required for advanced fuels in future nuclear power plants. Future nuclear power plants will rely heavily on advanced computer modeling and simulation that describes fuel behavior under off-normal conditions. TREAT is an ideal facility for this testing because of its flexibility, proven operation and material condition. The opportunity exists to develop advanced instrumentation and data collection that can support modeling and simulation needs much better than was possible in the past. In order to take advantage of these opportunities, test programs must be carefully designed to yield basic information to support modeling before conducting integral performance tests. An early start of TREAT and operation at low power would provide significant dividends in training, development of instrumentation, and checkout of reactor systems. Early start of TREAT (2015) is needed to support the requirements of potential users of TREAT and include the testing of full length fuel irradiated in the FFTF reactor. The capabilities provided by TREAT are needed for the development of nuclear power and the following benefits will be realized by the

  14. Simulation of Transient Ground-Water Flow in the Valley-Fill Aquifers of the Upper Rockaway River Basin, Morris County, New Jersey

    USGS Publications Warehouse

    Gordon, Alison D.

    2002-01-01

    More than 90 percent of the public water supply in the upper Rockaway River Valley in Morris County, New Jersey, is obtained from ground-water withdrawals from the valley-fill aquifers. During 1997, an average of 9.6 million gallons per day of ground water was withdrawn from these aquifers. The aquifer system consists of an unconfined aquifer (upper aquifer) and a locally confined aquifer (lower aquifer), which are composed of sands and gravels. These aquifers are separated by a discontinuous confining unit that consists mostly of silt and clay. Increases in ground-water withdrawals can induce movement of water from streams to wells, increase flow from the upper aquifer to the lower aquifer, and reduce base flow in the Rockaway River downstream. A ground-water-flow model was used to simulate and quantify the effects of current withdrawals on the valley-fill aquifer system under transient monthly conditions. Recharge over the model area varies both spatially and temporally. Part of model calibration consisted of adjusting percentages of monthly precipitation that recharges the valley-fill aquifer system. More recharge occurs during winter and spring than during summer and fall. This seasonal variation affects ground-water discharge to the Rockaway River. Ground-water withdrawals from the valleyfill aquifers also affect ground-water discharge to the Rockaway River. Three scenarios were simulated to observe the effects of ground-water withdrawals on ground-water discharge to the Rockaway River and to determine the extent to which variations in rates of withdrawals correspond to variations in rates of streamflow depletion. Streamflow depletion was estimated by comparing model-computed ground-water discharge for the three scenarios with the modelcomputed ground-water discharge under transient conditions. In scenario 1, all pumpage was removed from the model. In scenarios 2 and 3, 1 million gallons per day of ground-water withdrawals in excess of the current pumpage was

  15. Excess electron reactivity in amino acid aqueous solution revealed by ab initio molecular dynamics simulation: anion-centered localization and anion-relayed electron transfer dissociation.

    PubMed

    Wu, Xiuxiu; Gao, Liang; Liu, Jinxiang; Yang, Hongfang; Wang, Shoushan; Bu, Yuxiang

    2015-10-28

    Studies on the structure, states, and reactivity of excess electrons (EEs) in biological media are of great significance. Although there is information about EE interaction with desolvated biological molecules, solution effects are hardly explored. In this work, we present an ab initio molecular dynamics simulation study on the interaction and reactivity of an EE with glycine in solution. Our simulations reveal two striking results. Firstly, a pre-solvated EE partially localizes on the negatively charged -COO(-) group of the zwitterionic glycine and the remaining part delocalizes over solvent water molecules, forming an anion-centered quasi-localized structure, due to relative alignment of the lowest unoccupied molecular orbital energy levels of potential sites for EE residence in the aqueous solution. Secondly, after a period of anion-centered localization of an EE, the zwitterionic glycine is induced to spontaneously fragment through the cleavage of the N-Cα bond, losing ammonia (deamination), and leaving a ˙CH2-COO(-) anion radical, in good agreement with experimental observations. Introduction of the same groups (-COO(-) or -NH3(+)) in the side chain (taking lysine and aspartic acid as examples) can affect EE localization, with the fragmentation of the backbone part of these amino acids dependent on the properties of the side chain groups. These findings provide insights into EE interaction mechanisms with the backbone parts of amino acids and low energy EE induced fragmentation of amino acids and even peptides and proteins.

  16. Calculation of MCPR for BWR transients using the BNL plant analyzer

    SciTech Connect

    Horak, W.C.; Diamond, D.J.

    1987-01-01

    A class of transients of interest includes those from full power that involve some changes from the plant's technical specifications. These changes are allowed if it can be demonstrated that the effect on key parameters, such as the minimum critical power ratio (MCPR), is acceptable. Another class of transients is of interest for similar reasons, those that are initiated from the maximum extended operating domain (MEOD) or with partial feedwater heating. In the MEOD, the reactor conditions may be different from previous experience to increase the speed of the power ascension or obtain more power out of the core at end-of-cycle when the reactivity of the fuel is low. The critical power ratio (CPR) is used to determine the thermal limits of boiling water reactors (BWRs). In this study, CPRs for a series of transients run on the Brookhaven Plant Analyzer (BPA) have been calculated. The transients include nominal base case simulations; simulations with variations in relief valve setpoints and the number of failed feedwater heaters; simulations at the 100% power, 75% flow point on the extended load line of the MEOD; and a simulation with partial feedwater heating. The plant represented with the BPA is a BWR/4 rated at 3293 MW with a 6.38-m vessel.

  17. Analysis of the Role of Climate Forcings and Feedbacks for the Mid-Pliocene Climate Using a set of Transient Simulations from an Earth System Model

    NASA Astrophysics Data System (ADS)

    Ganopolski, A.; Calov, R.; Robinson, A.; Willeit, M.

    2011-12-01

    The mid-Pliocene warm period (3.3-3.0 million years before present) is believed to be a useful paleo-analog for the future greenhouse world. Paleoclimate reconstructions in conjunction with modeling results suggest that during the mid-Pliocene, the atmospheric CO2 concentration was 350-400 ppm, global temperature 2-3oC higher and sea level up to 20 m higher than today. However, using mid-Pleistocene climate reconstructions to assess Earth-system sensitivity to CO2 forcing is complicated by the fact that the 300 kyr-long mid-Pliocene time interval is characterized by strong orbital forcing and high-resolution paleoclimate records (such as benthic δ18O) show pronounced climate variability on astronomical periods. Since it is likely that some mid-Pliocene temperature and vegetation reconstructions can be warm- or seasonally-biased, they may reflect not only the elevated CO2 level, but also the direct effect of the orbital forcing. To quantify the role of different forcing and climate feedbacks for the climate of mid-Pliocene, we performed a set of transient simulations through the whole mid-Pliocene and beyond using the Earth system model of intermediate complexity CLIMBER-2. The model includes interactive ice sheets and terrestrial vegetation and has been already used to study different aspects of Quaternary climate variability. We performed a set of experiments with several plausible CO2 scenarios and realistic orbital forcing as well as with a constant (present day) orbital configuration. The results reveal the important contribution of the orbital forcing to the temperature variations in middle and high latitudes comparable or even larger (for the warm season) than that induced by changes in the CO2 concentration. If mid-Pliocene SST reconstructions are indeed biased towards the warmest intervals, accounting for the orbital forcing helps to explain the stronger polar temperature amplification implied by paleoclimate reconstructions than is simulated by the

  18. LMR Transient Calculation Code System (version 5).

    1993-09-01

    Version: 00 The Liquid Metal Reactor (LMR) may undergo an unscrammed Transient Over-Power (TOP) or a Loss of Heat Sink (LOHS) type of accident involving power, temperature, and reactivity changes. The LTC (LMR Transient Calculation) Program calculates the time dependent reactor temperatures, reactivities, and power of the LMR after the initiation of the accident. A printout of the results including the input table of data is offered after the program run. No graphics are usedmore » in the program and the LTC.EXE (Quick Basic compiled) can make use of a math co-processor if available (GW Basic doesn't).« less

  19. Evaluations of NOx and highly reactive VOC emission inventories in Texas and their implications for ozone plume simulations during the Texas Air Quality Study 2006

    NASA Astrophysics Data System (ADS)

    Kim, S.-W.; McKeen, S. A.; Frost, G. J.; Lee, S.-H.; Trainer, M.; Richter, A.; Angevine, W. M.; Atlas, E.; Bianco, L.; Boersma, F. K.; Brioude, J.; Burrows, J. P.; de Gouw, J.; Fried, A.; Gleason, J.; Hilboll, A.; Mellqvist, J.; Peischl, J.; Richter, D.; Rivera, C.; Ryerson, T.; Te Lintel Hekkert, S.; Walega, J.; Warneke, C.; Weibring, P.; Williams, E.

    2011-07-01

    Satellite and aircraft observations made during the 2006 Texas Air Quality Study (TexAQS) detected strong urban, industrial and power plant plumes in Texas. We simulated these plumes using the Weather Research and Forecasting - Chemistry (WRF-Chem) model with input from the US EPA's 2005 National Emission Inventory (NEI-2005), in order to evaluate emissions of nitrogen oxides (NOx = NO + NO2) and volatile organic compounds (VOCs) in the cities of Houston and Dallas-Fort Worth. We compared the model results with satellite retrievals of tropospheric nitrogen dioxide (NO2) columns and airborne in-situ observations of several trace gases including NOx and a number of VOCs. The model and satellite NO2 columns agree well for regions with large power plants and for urban areas that are dominated by mobile sources, such as Dallas. However, in Houston, where significant mobile, industrial, and in-port marine vessel sources contribute to NOx emissions, the model NO2 columns are approximately 50 %-70 % higher than the satellite columns. Similar conclusions are drawn from comparisons of the model results with the TexAQS 2006 aircraft observations in Dallas and Houston. For Dallas plumes, the model-simulated NO2 showed good agreement with the aircraft observations. In contrast, the model-simulated NO2 is ~60 % higher than the aircraft observations in the Houston plumes. Further analysis indicates that the NEI-2005 NOx emissions over the Houston Ship Channel area are overestimated while the urban Houston NOx emissions are reasonably represented. The comparisons of model and aircraft observations confirm that highly reactive VOC emissions originating from industrial sources in Houston are underestimated in NEI-2005. The update of VOC emissions based on Solar Occultation Flux measurements during the field campaign leads to improved model simulations of ethylene, propylene, and formaldehyde. Reducing NOx emissions in the Houston Ship Channel and increasing highly reactive VOC

  20. Evaluations of NOx and highly reactive VOC emission inventories in Texas and their implications for ozone plume simulations during the Texas Air Quality Study 2006

    NASA Astrophysics Data System (ADS)

    Kim, S.-W.; McKeen, S. A.; Frost, G. J.; Lee, S.-H.; Trainer, M.; Richter, A.; Angevine, W. M.; Atlas, E.; Bianco, L.; Boersma, K. F.; Brioude, J.; Burrows, J. P.; de Gouw, J.; Fried, A.; Gleason, J.; Hilboll, A.; Mellqvist, J.; Peischl, J.; Richter, D.; Rivera, C.; Ryerson, T.; Te Lintel Hekkert, S.; Walega, J.; Warneke, C.; Weibring, P.; Williams, E.

    2011-11-01

    Satellite and aircraft observations made during the 2006 Texas Air Quality Study (TexAQS) detected strong urban, industrial and power plant plumes in Texas. We simulated these plumes using the Weather Research and Forecasting-Chemistry (WRF-Chem) model with input from the US EPA's 2005 National Emission Inventory (NEI-2005), in order to evaluate emissions of nitrogen oxides (NOx = NO + NO2) and volatile organic compounds (VOCs) in the cities of Houston and Dallas-Fort Worth. We compared the model results with satellite retrievals of tropospheric nitrogen dioxide (NO2) columns and airborne in-situ observations of several trace gases including NOx and a number of VOCs. The model and satellite NO2 columns agree well for regions with large power plants and for urban areas that are dominated by mobile sources, such as Dallas. However, in Houston, where significant mobile, industrial, and in-port marine vessel sources contribute to NOx emissions, the model NO2 columns are approximately 50%-70% higher than the satellite columns. Similar conclusions are drawn from comparisons of the model results with the TexAQS 2006 aircraft observations in Dallas and Houston. For Dallas plumes, the model-simulated NO2 showed good agreement with the aircraft observations. In contrast, the model-simulated NO2 is ~60% higher than the aircraft observations in the Houston plumes. Further analysis indicates that the NEI-2005 NOx emissions over the Houston Ship Channel area are overestimated while the urban Houston NOx emissions are reasonably represented. The comparisons of model and aircraft observations confirm that highly reactive VOC emissions originating from industrial sources in Houston are underestimated in NEI-2005. The update of VOC emissions based on Solar Occultation Flux measurements during the field campaign leads to improved model simulations of ethylene, propylene, and formaldehyde. Reducing NOx emissions in the Houston Ship Channel and increasing highly reactive VOC emissions

  1. Simulation of variable-density flow and transport of reactive and nonreactive solutes during a tracer test at Cape Cod, Massachusetts

    USGS Publications Warehouse

    Zhang, H.; Schwartz, F.W.; Wood, W.W.; Garabedian, S.P.; LeBlanc, D.R.

    1998-01-01

    A multispecies numerical code was developed to simulate flow and mass transport with kinetic adsorption in variable-density flow systems. The two-dimensional code simulated the transport of bromide (Br-), a nonreactive tracer, and lithium (Li+), a reactive tracer, in a large-scale tracer test performed in a sand-and-gravel aquifer at Cape Cod, Massachusetts. A two-fraction kinetic adsorption model was implemented to simulate the interaction of Li+ with the aquifer solids. Initial estimates for some of the transport parameters were obtained from a nonlinear least squares curve-fitting procedure, where the breakthrough curves from column experiments were matched with one-dimensional theoretical models. The numerical code successfully simulated the basic characteristics of the two plumes in the tracer test. At early times the centers of mass of Br- and Li+ sank because the two plumes were closely coupled to the density-driven velocity field. At later times the rate of downward movement in the Br- plume due to gravity slowed significantly because of dilution by dispersion. The downward movement of the Li+ plume was negligible because the two plumes moved in locally different velocity regimes, where Li+ transport was retarded relative to Br-. The maximum extent of downward transport of the Li+ plume was less than that of the Br- plume. This study also found that at early times the downward movement of a plume created by a three-dimensional source could he much more extensive than the case with a two-dimensional source having the same cross-sectional area. The observed shape of the Br- plume at Cape Cod was simulated by adding two layers with different hydraulic conductivities at shallow depth across the region. The large dispersion and asymmetrical shape of the Li+ plume were simulated by including kinetic adsorption-desorption reactions.

  2. Transient enthalpy probe development

    NASA Astrophysics Data System (ADS)

    Bennett, Brian K.

    A reliable diagnostic probe has been developed to measure the local enthalpy in high-pressure, arc heated test streams that simulate atmospheric reentry conditions. The probe employs the double sonic-throat technique and is designed for the sweep (transient) mode to survive the severe heating environment. Tests in the high-pressure arc heater facilities show that, under certain conditions, the enthalpy probe measurements are in good agreement with enthalpy profiles inferred from heat flux measurements using the theory of Fay and Riddell (1958).

  3. Reactive arthritis

    PubMed Central

    Hind, C. R. K.

    1982-01-01

    Reactive arthritis is a rare complication of certain infections. The similar features and HLA associations with the seronegative arthropathies have raised the possibility that the latter may be forms of reactive arthritis. This review describes the clinical and epidemiological features, and the recent advances in our understanding of the underlying pathogenesis of reactive arthritis. PMID:7100033

  4. Fault-related dolomitization in the Orpesa Ranges (Iberian Chain, E Spain): reactive transport simulations and field data constraints

    NASA Astrophysics Data System (ADS)

    Gomez-Rivas, E.; Martin-Martin, J. D.; Corbella, M.; Teixell, A.

    2009-04-01

    The relationships between hydrothermal fluid circulation and fracturing that lead to mineral dissolution and/or precipitation in carbonate rocks have direct impacts on the evolution and final distribution of hydrocarbon reservoir permeability. Understanding the coupling between these processes is important for predicting permeability and improving hydrocarbon recovery. We present a case study of dolomitization processes in Cretaceous limestone from the Orpesa Ranges (Iberian Chain, E Spain). Extending over part of the Maestrat Cretaceous Basin, the Orpesa area is deformed by extensional faults. These faults accommodated thick sequences of shallow marine limestone, mainly during Aptian times. The syn-rift carbonates are partially dolomitized due to the circulation and mixing of hydrothermal fluids along normal faults and bedding. Both Aptian and later Neogene extensional faults must have served as conduits for the circulation of fluids. MVT deposits of Paleocene age are well documented in the Maestrat basin and may also be related to dolomitization. Samples of host rocks and vein fillings have been collected along strike and analyzed in different fault sections to characterize fluid and rock composition, track flow pathways and map the relationships of fluid flow with respect to the main normal faults in the area. Using field and geochemical data from the Orpesa Ranges carbonates, we have developed reactive-transport models to study the influence of different parameters in the dolomitization of carbonates related to the circulation and mixing of hydrothermal fluids at the outcrop scale. We present results from models that were run with constant and non-constant permeability. The main parameters analyzed include: initial porosity and permeability of layers and fractures, composition of fluids, groundwater and brines flux, composition of layers, reactive surface of minerals, differences in vertical and horizontal permeability, and presence or absence of stratigraphic

  5. Mineralization of reactive azo dyes present in simulated textile waste water using down flow microaerophilic fixed film bioreactor.

    PubMed

    Balapure, Kshama; Bhatt, Nikhil; Madamwar, Datta

    2015-01-01

    The present research emphasizes on degradation of azo dyes from simulated textile wastewater using down flow microaerophilic fixed film reactor. Degradation of simulated textile wastewater (COD 7200mg/L and dye concentration 300mg/L) was studied in a microaerophilic fixed film reactor using pumice stone as a support material under varying hydraulic retention time (HRT) and organic loading rate (OLR). The intense metabolic activity of the inoculated bacterial consortium in the reactor led to 97.5% COD reduction and 99.5% decolorization of simulated wastewater operated under OLR of 7.2kgCODm(3)/d and 24h of HRT. FTIR, (1)H NMR and GC-MS studies revealed the formation of lower molecular weight aliphatic compounds under 24h of HRT, leading to complete mineralization of simulated wastewater. The detection of oxido-reductive enzyme activities suggested the enzymatic reduction of azo bonds prior to mineralization. Toxicity studies indicated that microbial treatment favors detoxification of simulated wastewater.

  6. Mineralization of reactive azo dyes present in simulated textile waste water using down flow microaerophilic fixed film bioreactor.

    PubMed

    Balapure, Kshama; Bhatt, Nikhil; Madamwar, Datta

    2015-01-01

    The present research emphasizes on degradation of azo dyes from simulated textile wastewater using down flow microaerophilic fixed film reactor. Degradation of simulated textile wastewater (COD 7200mg/L and dye concentration 300mg/L) was studied in a microaerophilic fixed film reactor using pumice stone as a support material under varying hydraulic retention time (HRT) and organic loading rate (OLR). The intense metabolic activity of the inoculated bacterial consortium in the reactor led to 97.5% COD reduction and 99.5% decolorization of simulated wastewater operated under OLR of 7.2kgCODm(3)/d and 24h of HRT. FTIR, (1)H NMR and GC-MS studies revealed the formation of lower molecular weight aliphatic compounds under 24h of HRT, leading to complete mineralization of simulated wastewater. The detection of oxido-reductive enzyme activities suggested the enzymatic reduction of azo bonds prior to mineralization. Toxicity studies indicated that microbial treatment favors detoxification of simulated wastewater. PMID:25459797

  7. Low-energy oxygen bombardment of silicon by MD simulations making use of a reactive force field

    NASA Astrophysics Data System (ADS)

    Philipp, P.; Briquet, L.; Wirtz, T.; Kieffer, J.

    2011-07-01

    In the field of Secondary Ion Mass Spectrometry (SIMS), ion-matter interactions have been largely investigated by numerical simulations. For MD simulations related to inorganic samples, mostly classical force fields assuming stable bonding structure have been used. In materials science, level-three force fields capable of simulating the breaking and formation of chemical bonds have recently been conceived. One such force field has been developed by John Kieffer [1,2]. This potential includes directional covalent bonds, Coulomb and dipolar interaction terms, dispersion terms, etc. Important features of this force field for simulating systems that undergo significant structural reorganization are (i) the ability to account for the redistribution of electron density upon ionization, formation, or breaking of bonds, through a charge transfer term, and (ii) the fact that the angular constraints dynamically adjust when a change in the coordination number of an atom occurs. In this paper, the modification of the force field to allow for an exact description of the sputtering process, the influence of this modification on previous results obtained for phase transitions in glasses as well as properties of particles sputtered at 250-1000 eV from a mono-crystalline silicon sample will be presented. The simulation results agree qualitatively with predictions from experiments or models. Most atoms are sputtered from the first monolayer: for an impact energy of 250 eV up to 86% of the atoms are sputtered from the first monolayer and for 750 eV, this percentage drops to 61%, with 89% of the atoms being sputtered from the first two monolayers. For sputtering yields, 250 and 500 eV results agree with experimental data, but for 750 eV sub-channelling in the pristine sample becomes more important than in experiments where samples turn amorphous under ion bombardment.

  8. Reactive geothermal transport simulations to study the formation mechanism of an impermeable barrier between acidic and neutral fluid zones in the Onikobe Geothermal Field, Japan

    NASA Astrophysics Data System (ADS)

    Todaka, Norifumi; Akasaka, Chitoshi; Xu, Tianfu; Pruess, Karsten

    2004-05-01

    Two types of fluids are encountered in the Onikobe geothermal reservoir (Japan): one is neutral and the other is acidic. It is hypothesized that acidic fluid might be upwelling along a fault zone from magma and that an impermeable barrier might be present between the acidic and neutral fluid zones. To test such a conceptual model and to study the geochemical behavior due to mixing of the two fluids, reactive geothermal transport simulations under both natural and production conditions were carried out using the code TOUGHREACT. Results indicate Mn-rich smectite precipitates near the mixing front. Precipitation of sphalerite and galena occurs in a similar region as the Mn-rich smectite. Precipitation of these minerals depends on pH and temperature. In addition, quartz, pyrite, and calcite precipitate in the shallow zone resulting in further development of caprock. The changes in porosity and permeability due to precipitation of Mn-rich smectite are small compared with that of quartz, calcite, and pyrite. However, the smectite precipitation is likely to fill open fractures and to form an impermeable barrier between acidic and neutral fluid regions. The simulated mineral assemblage is generally consistent with observations in the Onikobe field. The numerical simulations described here provide useful insight into geochemical behavior and formation of impermeable barriers from fluid mixing. The method presented in this paper may be useful in fundamental analysis of hydrothermal systems and in the exploration of geothermal reservoirs, including chemical evolution, mineral alteration, mineral scaling, and changes in porosity and permeability.

  9. Response curves for phosphorus plume lengths from reactive-solute-transport simulations of onland disposal of wastewater in noncarbonate sand and gravel aquifers

    USGS Publications Warehouse

    Colman, John A.

    2005-01-01

    Surface-water resources in Massachusetts often are affected by eutrophication, excessive plant growth, which has resulted in impaired use for a majority of the freshwater ponds and lakes and a substantial number of river-miles in the State. Because supply of phosphorus usually is limiting to plant growth in freshwater systems, control of phosphorus input to surface waters is critical to solving the impairment problem. Wastewater is a substantial source of phosphorus for surface water, and removal of phosphorus before disposal may be necessary. Wastewater disposed onland by infiltration loses phosphorus from the dissolved phase during transport through the subsurface and may be an effective disposal method; quantification of the phosphorus loss can be simulated to determine disposal feasibility. In 2003, the U.S. Geological Survey, in cooperation with the Massachusetts Department of Environmental Protection, initiated a project to simulate distance of phosphorus transport in the subsurface for plausible conditions of onland wastewater disposal and subsurface properties. A coupled one-dimensional unsaturated-zone and three-dimensional saturated-zone reactive-solute-transport model (PHAST) was used to simulate lengths of phosphorus plumes. Knowledge of phosphorus plume length could facilitate estimates of setback distances for wastewater-infiltration sites from surface water that would be sufficient to protect the surface water from eutrophication caused by phosphorus transport through the subsurface and ultimate discharge to surface water. The reactive-solute-transport model PHAST was used to simulate ground-water flow, solute transport, equilibrium chemistry for dissolved and sorbed species, and kinetic regulation of organic carbon decomposition and phosphate mineral formation. The phosphorus plume length was defined for the simulations as the maximum extent of the contour for the 0.015 milligram-per-liter concentration of dissolved phosphorus downgradient from the

  10. Transient changes in the pattern of food intake following a simulated time-zone transition to the east across eight time zones.

    PubMed

    Waterhouse, Jim; Kao, Shaoyuan; Edwards, Benjamin; Weinert, Dietmar; Atkinson, Greg; Reilly, Thomas

    2005-01-01

    most when appetite before the meal, enjoyment during it, and satiety afterward were considered. However, evidence suggested that the degree to which larger hot meals were preferred to cold meals was significantly less marked after the time-zone transition. On control days, sleep was unbroken; whereas, after the time-zone transition, all subjects woke on at least one of the 3 nights studied. During the first post-shift night, about half of the subjects ate a meal, the reason given being that they were "hungry." On those occasions when subjects woke but did not eat a meal, the reason cited was because they "could not be bothered" as frequently as because they were "not hungry.". A simulated time-zone transition is associated with significant changes to the incidence of indigestion, pattern of food intake, and subjective responses to food. However, these changes are generally transient and are only weakly linked to the sensation of jet lag.

  11. Assessment of the turbine trip transient in Cofrentes NPP with TRAC-BF1

    SciTech Connect

    Castrillo, F.; Gomez, A.; Gallego, I.

    1993-06-01

    This report presents the results of the assessment of TRAC-BF1 (G1-J1) code with the model of C. N. Cofrentes for simulation of the transient originated by the manual trip of the main turbine. C. N. Cofrentes is a General Electric designed BWR/6 plant, with a nominal core thermal power of 2894 Mwt, in commercial operation since 1985, owned and operated by Hidroelectrica Espa{tilde n}ola, S. A. The plant incorporates all the characteristics of BWR/6 reactors, with two turbine driven FW pumps. As a result of this assessment a model of C. N. Cofrentes has been developed for TRAC-BF1 that fairly reproduces operational transient behavior of the plant. A special purpose code was generated to obtain reactivity coefficients, as required by TRAC-BF1, from the 3D simulator.

  12. Assessment of the turbine trip transient in Cofrentes NPP with TRAC-BF1

    SciTech Connect

    Castrillo, F. ); Gomez, A.; Gallego, I. )

    1993-06-01

    This report presents the results of the assessment of TRAC-BF1 (G1-J1) code with the model of C. N. Cofrentes for simulation of the transient originated by the manual trip of the main turbine. C. N. Cofrentes is a General Electric designed BWR/6 plant, with a nominal core thermal power of 2894 Mwt, in commercial operation since 1985, owned and operated by Hidroelectrica Espa[tilde n]ola, S. A. The plant incorporates all the characteristics of BWR/6 reactors, with two turbine driven FW pumps. As a result of this assessment a model of C. N. Cofrentes has been developed for TRAC-BF1 that fairly reproduces operational transient behavior of the plant. A special purpose code was generated to obtain reactivity coefficients, as required by TRAC-BF1, from the 3D simulator.

  13. Process Simulation of Complex Biological Pathways in Physical Reactive Space and Reformulated for Massively Parallel Computing Platforms.

    PubMed

    Ganesan, Narayan; Li, Jie; Sharma, Vishakha; Jiang, Hanyu; Compagnoni, Adriana

    2016-01-01

    Biological systems encompass complexity that far surpasses many artificial systems. Modeling and simulation of large and complex biochemical pathways is a computationally intensive challenge. Traditional tools, such as ordinary differential equations, partial differential equations, stochastic master equations, and Gillespie type methods, are all limited either by their modeling fidelity or computational efficiency or both. In this work, we present a scalable computational framework based on modeling biochemical reactions in explicit 3D space, that is suitable for studying the behavior of large and complex biological pathways. The framework is designed to exploit parallelism and scalability offered by commodity massively parallel processors such as the graphics processing units (GPUs) and other parallel computing platforms. The reaction modeling in 3D space is aimed at enhancing the realism of the model compared to traditional modeling tools and framework. We introduce the Parallel Select algorithm that is key to breaking the sequential bottleneck limiting the performance of most other tools designed to study biochemical interactions. The algorithm is designed to be computationally tractable, handle hundreds of interacting chemical species and millions of independent agents by considering all-particle interactions within the system. We also present an implementation of the framework on the popular graphics processing units and apply it to the simulation study of JAK-STAT Signal Transduction Pathway. The computational framework will offer a deeper insight into various biological processes within the cell and help us observe key events as they unfold in space and time. This will advance the current state-of-the-art in simulation study of large scale biological systems and also enable the realistic simulation study of macro-biological cultures, where inter-cellular interactions are prevalent.

  14. Application of Simulated Reactivity Feedback in Nonnuclear Testing of a Direct-Drive Gas-Cooled Reactor

    NASA Technical Reports Server (NTRS)

    Bragg-Sitton, S. M.; Webster, K. L.

    2007-01-01

    Nonnuclear testing can be a valuable tool in the development of an in-space nuclear power or propulsion system. In a nonnuclear test facility, electric heaters are used to simulate heat from nuclear fuel. Standard testing allows one to fully assess thermal, heat transfer, and stress related attributes of a given system but fails to demonstrate the dynamic response that would be present in an integrated, fueled reactor system. The integration of thermal hydraulic hardware tests with simulated neutronic response provides a bridge between electrically heated testing and full nuclear testing. By implementing a neutronic response model to simulate the dynamic response that would be expected in a fueled reactor system, one can better understand system integration issues, characterize integrated system response times and response and response characteristics, and assess potential design improvements with a relatively small fiscal investment. Initial system dynamic response testing was demonstrated on the integrated SAFE 100a heat pipe cooled, electrically heated reactor and heat exchanger hardware. This Technical Memorandum discusses the status of the planned dynamic test methodology for implementation in the direct-drive gas-cooled reactor testing and assesses the additional instrumentation needed to implement high-fidelity dynamic testing.

  15. The 'reactive

    NASA Astrophysics Data System (ADS)

    Battista Piccardo, Giovanni; Guarnieri, Luisa

    2010-05-01

    proportions (in range 2-10% vol. modal content) in the same peridotite body. Notwithstanding this strong Cpx modal variation, the Cpx C1-normalized REE patterns are closely similar, at the scale of the same massif. Cpx does not show progressive trace element depletion/fractionation concordantly with progressive decrease of the Cpx content, as expected during progressive partial melting. Cpx shows both: 1) sinusoidal patterns enriched in the L-MREE and depleted in the HREE, and 2) strongly LREE fractionated patterns, almost flat in the MREE-HREE region. Type-1 Cpx sinusoidal REE patterns are consistent with trace element equilibration with melts which record transient geochemical gradients formed during melt-peridotite interaction under long time-integrated melt-rock ratios. Type-2 Cpx fractionated REE patterns are closely similar to those of Cpx that attained trace element equilibration with fractional melts with MORB affinity. The fractionated and sinusoidal Cpx REE patterns indicate that the depleted peridotites underwent melt-peridotite interaction under open system melt migration, both at high melt/rock ratios and long time-integrated melt-rock ratios. The compositional characteristics of the percolating melts in equilibrium with Cpx, assuming that mantle Cpx and percolating liquids attained trace element equilibration during melt-peridotite interaction, are quite similar to those of liquids produced by 4-7% fractional melting of a Sp-facies DM asthenospheric mantle source. In summary, the micro-structural features and the compositional characteristics indicate that their petrogenetic process is represented by melt/peridotite interaction via reactive diffuse porous flow percolation. They are closely similar to the Huinan harzburgite xenoliths (Xu et al., 2003) that show a secondary recrystallized texture and compositions that deviate from the partial melting trend of residual peridotites. They are considered "reactive" harzburgites likely resulted from basaltic melt

  16. TOUGHREACT—A simulation program for non-isothermal multiphase reactive geochemical transport in variably saturated geologic media: Applications to geothermal injectivity and CO 2 geological sequestration

    NASA Astrophysics Data System (ADS)

    Xu, Tianfu; Sonnenthal, Eric; Spycher, Nicolas; Pruess, Karsten

    2006-03-01

    TOUGHREACT is a numerical simulation program for chemically reactive non-isothermal flows of multiphase fluids in porous and fractured media. The program was written in Fortran 77 and developed by introducing reactive geochemistry into the multiphase fluid and heat flow simulator TOUGH2. A variety of subsurface thermo-physical-chemical processes are considered under a wide range of conditions of pressure, temperature, water saturation, ionic strength, and pH and Eh. Interactions between mineral assemblages and fluids can occur under local equilibrium or kinetic rates. The gas phase can be chemically active. Precipitation and dissolution reactions can change formation porosity and permeability. The program can be applied to many geologic systems and environmental problems, including geothermal systems, diagenetic, and weathering processes, subsurface waste disposal, acid mine drainage remediation, contaminant transport, and groundwater quality. Here we present two examples to illustrate applicability of the program. The first example deals with injectivity effects of mineral scaling in a fractured geothermal reservoir. A major concern in the development of hot dry rock and hot fractured rock reservoirs is achieving and maintaining adequate injectivity, while avoiding the development of preferential short-circuiting flow paths. Rock-fluid interactions and associated mineral dissolution and precipitation effects could have a major impact on the long-term performance of these reservoirs. We used recent European studies as a starting point to explore chemically induced effects of fluid circulation in the geothermal systems. We examine ways in which the chemical composition of reinjected waters can be modified to improve reservoir performance by maintaining or even enhancing injectivity. The second TOUGHREACT application example is related to CO 2 geologic sequestration in a saline aquifer. We performed numerical simulations for a commonly encountered Gulf Coast sediment

  17. CO2 leakage impacts on shallow groundwater. Field-scale reactive-transport simulations informed by observations at a natural analog site

    SciTech Connect

    Keating, Elizabeth H.; Hakala, J. Alexandra; Viswanathan, Hari; Carey, J. William; Pawar, Rajesh; Guthrie, George D.; Fessenden-Rahn, Julianna

    2013-03-01

    It is challenging to predict the degree to which shallow groundwater might be affected by leaks from a CO2 sequestration reservoir, particularly over long time scales and large spatial scales. In this study observations at a CO2 enriched shallow aquifer natural analog were used to develop a predictive model which is then used to simulate leakage scenarios. This natural analog provides the opportunity to make direct field observations of groundwater chemistry in the presence of elevated CO2, to collect aquifer samples and expose them to CO2 under controlled conditions in the laboratory, and to test the ability of multiphase reactive transport models to reproduce measured geochemical trends at the field-scale. The field observations suggest that brackish water entrained with the upwelling CO2 are a more significant source of trace metals than in situ mobilization of metals due to exposure to CO2. The study focuses on a single trace metal of concern at this site: U. Experimental results indicate that cation exchange/adsorption and dissolution/precipitation of calcite containing trace amounts of U are important reactions controlling U in groundwater at this site, and that the amount of U associated with calcite is fairly well constrained. Simulations incorporating these results into a 3-D multi-phase reactive transport model are able to reproduce the measured ranges and trends between pH, pCO2, Ca, total C, U and Cl-at the field site. Although the true fluxes at the natural analog site are unknown, the cumulative CO2 flux inferred from these simulations are approximately equivalent to 37.8E-3 MT, approximately corresponding to a .001% leak rate for injection at a large (750 MW) power plant. The leakage scenario simulations suggest that if the leak only persists for a short time the volume of aquifer contaminated by CO2-induced mobilization of U will be

  18. H2S Reactivity on Oxygen-Deficient Heterotrimetallic Cores: Cluster Fluxionality Simulates Dynamic Aspects of Surface Chemical Reactions.

    PubMed

    Adhikari, Debashis; Raghavachari, Krishnan

    2016-01-28

    Understanding the mechanistic aspects of heterogeneous reactions on supported metal catalysts is challenging due to several disparate factors, among which the dynamic nature of the surface is a major contributor. In this study, the dynamic aspect of a surface has been probed by choosing small metal clusters as illustrative models. Two anionic hetero-trimetallic clusters, namely, W2TcO6(-) and W2OsO6(-), were reacted with H2S gas to exhibit splitting of the gas molecule and complete oxygen-sulfur exchange in the metal core. During this atom-exchange process, the core exhibits remarkable fluxionality to augment a thiol proton migration from one metal center to another, as well as a rapid interchange of the terminal and bridging oxygens. The fluxional nature of the core is further evidenced by two oppositely oriented oxo groups working in concert to accomplish the proton transfer, upon introduction of sulfur inside the core. These fluxional processes in the small hetero-trimetallic cores closely resemble the dynamic nature of the surface in a heterogeneous reaction. Throughout the fluxional processes investigated in this study, two-state reactivity and multiple instances of spin crossover are observed in our computational studies. Interestingly, the neutral hetero-trimetallic cores can also undergo complete oxygen-sulfur exchange reaction with H2S. The investigated metal clusters are promising materials, since they not only can liberate dihydrogen from water (reported in J. Phys. Chem. A, 2014, 118, 11047) but also can completely strip the sulfur from environmentally hazardous H2S gas.

  19. FRINK - A Code to Evaluate Space Reactor Transients

    SciTech Connect

    Poston, David I.; Marcille, Thomas F.; Dixon, David D.; Amiri, Benjamin W.

    2007-01-30

    One of the biggest needs for space reactor design and development is detailed system modeling. Most proposed space fission systems are very different from previously operated fission power systems, and extensive testing and modeling will be required to demonstrate integrated system performance. There are also some aspects of space reactors that make them unique from most terrestrial application, and require different modeling approaches. The Fission Reactor Integrated Nuclear Kinetics (FRINK) code was developed to evaluate simplified space reactor transients (note: the term ''space reactor'' inherently includes planetary and lunar surface reactors). FRINK is an integrated point kinetic/thermal-hydraulic transient analysis FORTRAN code - ''integrated'' refers to the simultaneous solution of the thermal and neutronic equations. In its current state FRINK is a very simple system model, perhaps better referred to as a reactor model. The ''system'' only extends to the primary loop power removal boundary condition; however this allows the simulation of simplified transients (e.g. loss of primary heat sink, loss of flow, large reactivity insertion, etc.), which are most important in bounding early system conceptual design. FRINK could then be added to a complete system model later in the design and development process as system design matures.

  20. Simulating near-road reactive dispersion of gaseous air pollutants using a three-dimensional Eulerian model.

    PubMed

    Kota, Sri Harsha; Ying, Qi; Zhang, Yunlong

    2013-06-01

    In this study, the TAMNROM-3D model, a 3D Eulerian near-road air quality model with vehicle induced turbulence parameterization and a MOVES based emission preprocessor, is tested using near-road gaseous pollutants data collected near a rural freeway with 34% heavy duty vehicle traffic. Exhaust emissions of gasses from the vehicles are estimated using a lumped vehicle classification scheme based on the number of vehicle axles and the default county-level MOVES vehicle fleet database. The predicted dilution of CO and NOx in the downwind direction agrees well with observation, although the total NOx emission has to be scaled to 85% of its original emission rate estimated by the MOVES model. Using the atmospheric turbulent diffusion coefficient parameterization of Degrazia et al. (2000) with variable horizontal turbulent diffusion coefficient (Kxx) leads to slightly better predictions than a traditional non-height-dependent Kxx parameterization. The NO2 concentrations can be better predicted when emission of total NOx is split into NO and NO2 using the NO2 to NOx ratio of 29% measured near the road. Simulations using the SAPRC99 photochemical mechanism do not show significant changes in the predicted NO and NO2 concentrations near the road compared to simulations using a simple three-reaction mechanism that involves only NOx and O3. A regional air quality simulation in Houston, Texas during a high O3 episode in August 2000 shows that using the NO2 to NOx ratio of 29% instead of the traditional 5% leads to as much as 6ppb increase in 8-h O3 predictions.

  1. Inverse Reactive Transport Simulator (Inverts): An Inverse Model for Contaminant Transport with Nonlinear Adsorption and Source Terms

    SciTech Connect

    McGrail, B. Peter

    2001-10-31

    A numerically based simulator was developed to assist in the interpretation of complex laboratory experiments examining transport processes of chemical and biological contaminants subject to nonlinear adsorption and/or source terms. The inversion is performed with any of three nonlinear regression methods, Marquardt-Levenberg, conjugate gradient, or quasi-Newton. The governing equations for the problem are solved by the method of finite-differences including any combination of three boundary conditions: (1) Dirichlet, (2) Neumann, and (3) Cauchy. The dispersive terms in the transport equations were solved using the second-order accurate in time and space Crank-Nicolson scheme, while the advective terms were handled using a third-order in time and space, total variation diminishing (TVD) scheme that damps spurious oscillations around sharp concentration fronts. The numerical algorithms were implemented in the computer code INVERTS, which runs on any standard personal computer. Apart from a comprehensive set of test problems, INVERTS was also used to model the elution of a nonradioactive tracer, {sup 185}Re, in a pressurized unsaturated flow (PUF) experiment with a simulated waste glass for low-activity waste immobilization. Interpretation of the elution profile was best described with a nonlinear kinetic model for adsorption.

  2. Collision induced dissociation of doubly-charged ions: Coulomb explosion vs. neutral loss in [Ca(urea)]{sup 2+} gas phase unimolecular reactivity via chemical dynamics simulations

    SciTech Connect

    Spezia, Riccardo; Salpin, Jean-Yves; Cimas, Alvaro; Gaigeot, Marie-Pierre; Song, Kihyung; Hase, William L.

    2012-07-01

    In this paper we report different theoretical approaches to study the gas-phase unimolecular dissociation of the doubly-charged cation [Ca(urea)]{sup 2+}, in order to rationalize recent experimental findings. Quantum mechanical plus molecular mechanical (QM/MM) direct chemical dynamics simulations were used to investigate collision induced dissociation (CID) and rotational-vibrational energy transfer for Ar{sup +} [Ca(urea)]{sup 2+} collisions. For the picosecond time-domain of the simulations, both neutral loss and Coulomb explosion reactions were found and the differences in their mechanisms elucidated. The loss of neutral urea subsequent to collision with Ar occurs via a shattering mechanism, while the formation of two singly-charged cations follows statistical (or almost statistical) dynamics. Vibrational-rotational energy transfer efficiencies obtained for trajectories that do not dissociate during the trajectory integration were used in conjunction with RRKM rate constants to approximate dissociation pathways assuming complete intramolecular vibrational energy redistribution (IVR) and statistical dynamics. This statistical limit predicts, as expected, that at long time the most stable species on the potential energy surface (PES) dominate. These results, coupled with experimental CID from which both neutral loss and Coulomb explosion products were obtained, show that the gas phase dissociation of this ion occurs by multiple mechanisms leading to different products and that reactivity on the complicated PES is dynamically complex. (authors)

  3. OS3D/GIMRT software for modeling multicomponent-multidimensional reactive transport

    SciTech Connect

    CI Steefel; SB Yabusaki

    2000-05-17

    OS3D/GIMRT is a numerical software package for simulating multicomponent reactive transport in porous media. The package consists of two principal components: (1) the code OS3D (Operator Splitting 3-Dimensional Reactive Transport) which simulates reactive transport by either splitting the reaction and transport steps in time, i.e., the classic time or operator splitting approach, or by iterating sequentially between reactions and transport, and (2) the code GIMRT (Global Implicit Multicomponent Reactive Transport) which treats up to two dimensional reactive transport with a one step or global implicit approach. Although the two codes do not yet have totally identical capabilities, they can be run from the same input file, allowing comparisons to be made between the two approaches in many cases. The advantages and disadvantages of the two approaches are discussed more fully below, but in general OS3D is designed for simulation of transient concentration fronts, particularly under high Peclet number transport conditions, because of its use of a total variation diminishing or TVD transport algorithm. GIMRT is suited for simulating water-rock alteration over long periods of time where the aqueous concentration field is at or close to a quasi-stationary state and the numerical transport errors are less important. Where water-rock interaction occurs over geological periods of time, GIMRT may be preferable to OS3D because of its ability to take larger time steps.

  4. Modeling and Simulation of Pore Scale Multiphase Fluid Flow and Reactive Transport in Fractured and Porous Media

    SciTech Connect

    Paul Meakin; Alexandre Tartakovsky

    2009-07-01

    In the subsurface fluids play a critical role by transporting dissolved minerals, colloids and contaminants (sometimes over long distances), by mediating dissolution and precipitation processes and enabling chemical transformations in solution and at mineral surfaces. Although the complex geometries of fracture apertures, fracture networks and pore spaces may make it difficult to accurately predict fluid flow in saturated (single-phase) subsurface systems, well developed methods are available. The simulation of multiphase fluid flow in the subsurface is much more challenging because of the large density and/or viscosity ratios found in important applications (water/air in the vadose zone, water/oil, water/gas, gas/oil and water/oil/gas in oil reservoirs, water/air/non-aqueous phase liquids (NAPL) in contaminated vadose zone systems and gas/molten rock in volcanic systems, for example). In addition, the complex behavior of fluid-fluid-solid contact lines, and its impact on dynamic contact angles, must also be taken into account, and coupled with the fluid flow. Pore network models and simple statistical physics based models such as the invasion percolation and diffusion-limited aggregation models have been used quite extensively. However, these models for multiphase fluid flow are based on simplified models for pore space geometries and simplified physics. Other methods such a lattice Boltzmann and lattice gas models, molecular dynamics, Monte Carlo methods, and particle methods such as dissipative particle dynamics and smoothed particle hydrodynamics are based more firmly on first principles, and they do not require simplified pore and/or fracture geometries. However, they are less (in some cases very much less) computationally efficient that pore network and statistical physics models. Recently a combination of continuum computation fluid dynamics, fluid-fluid interface tracking or capturing and simple models for the dependence of contact angles on fluid velocity

  5. Modeling and simulation of pore-scale multiphase fluid flow and reactive transport in fractured and porous media

    SciTech Connect

    Meakin, Paul; Tartakovsky, Alexandre M.

    2009-07-14

    In the subsurface fluids play a critical role by transporting dissolved minerals, colloids and contaminants (sometimes over long distances), by mediating dissolution and precipitation processes and enabling chemical transformations in solution and at mineral surfaces. Although the complex geometries of fracture apertures, fracture networks and pore spaces may make it difficult to accurately predict fluid flow in saturated (single-phase) subsurface systems, well developed methods are available. The simulation of multiphase fluid flow in the subsurface is much more challenging because of the large density and/or viscosity ratios found in important applications (water/air in the vadose zone, water/oil, water/gas, gas/oil and water/oil/gas in oil reservoirs, water/air/non-aqueous phase liquids (NAPL) in contaminated vadose zone systems and gas/molten rock in volcanic systems, for example). In addition, the complex behavior of fluid-fluid-solid contact lines, and its impact on dynamic contact angles, must also be taken into account, and coupled with the fluid flow. Pore network models and simple statistical physics based models such as the invasion percolation and diffusion-limited aggregation models have been used quite extensively. However, these models for multiphase fluid flow are based on simplified models for pore space geometries and simplified physics. Other methods such a lattice Boltzmann and lattice gas models, molecular dynamics, Monte Carlo methods, and particle methods such as dissipative particle dynamics and smoothed particle hydrodynamics are based more firmly on first principles, and they do not require simplified pore and/or fracture geometries. However, they are less (in some cases very much less) computationally efficient that pore network and statistical physics models. Recently a combination of continuum computation fluid dynamics, fluid-fluid interface tracking or capturing and simple models for the dependence of contact angles on fluid velocity

  6. ENHANCED SEVERE TRANSIENT ANALYSIS FOR PREVENTION TECHNICAL PROGRAM PLAN

    SciTech Connect

    Gougar, Hans

    2014-09-01

    This document outlines the development of a high fidelity, best estimate nuclear power plant severe transient simulation capability that will complement or enhance the integral system codes historically used for licensing and analysis of severe accidents. As with other tools in the Risk Informed Safety Margin Characterization (RISMC) Toolkit, the ultimate user of Enhanced Severe Transient Analysis and Prevention (ESTAP) capability is the plant decision-maker; the deliverable to that customer is a modern, simulation-based safety analysis capability, applicable to a much broader class of safety issues than is traditional Light Water Reactor (LWR) licensing analysis. Currently, the RISMC pathway’s major emphasis is placed on developing RELAP-7, a next-generation safety analysis code, and on showing how to use RELAP-7 to analyze margin from a modern point of view: that is, by characterizing margin in terms of the probabilistic spectra of the “loads” applied to systems, structures, and components (SSCs), and the “capacity” of those SSCs to resist those loads without failing. The first objective of the ESTAP task, and the focus of one task of this effort, is to augment RELAP-7 analyses with user-selected multi-dimensional, multi-phase models of specific plant components to simulate complex phenomena that may lead to, or exacerbate, severe transients and core damage. Such phenomena include: coolant crossflow between PWR assemblies during a severe reactivity transient, stratified single or two-phase coolant flow in primary coolant piping, inhomogeneous mixing of emergency coolant water or boric acid with hot primary coolant, and water hammer. These are well-documented phenomena associated with plant transients but that are generally not captured in system codes. They are, however, generally limited to specific components, structures, and operating conditions. The second ESTAP task is to similarly augment a severe (post-core damage) accident integral analyses code

  7. GRIZZLY Model of Multi-Reactive Species Diffusion, Moisture/Heat Transfer and Alkali-Silica Reaction for Simulating Concrete Aging and Degradation

    SciTech Connect

    Huang, Hai; Spencer, Benjamin W.; Cai, Guowei

    2015-09-01

    Concrete is widely used in the construction of nuclear facilities because of its structural strength and its ability to shield radiation. The use of concrete in nuclear power plants for containment and shielding of radiation and radioactive materials has made its performance crucial for the safe operation of the facility. As such, when life extension is considered for nuclear power plants, it is critical to have accurate and reliable predictive tools to address concerns related to various aging processes of concrete structures and the capacity of structures subjected to age-related degradation. The goal of this report is to document the progress of the development and implementation of a fully coupled thermo-hydro-mechanical-chemical model in GRIZZLY code with the ultimate goal to reliably simulate and predict long-term performance and response of aged NPP concrete structures subjected to a number of aging mechanisms including external chemical attacks and volume-changing chemical reactions within concrete structures induced by alkali-silica reactions and long-term exposure to irradiation. Based on a number of survey reports of concrete aging mechanisms relevant to nuclear power plants and recommendations from researchers in concrete community, we’ve implemented three modules during FY15 in GRIZZLY code, (1) multi-species reactive diffusion model within cement materials; (2) coupled moisture and heat transfer model in concrete; and (3) anisotropic, stress-dependent, alkali-silica reaction induced swelling model. The multi-species reactive diffusion model was implemented with the objective to model aging of concrete structures subjected to aggressive external chemical attacks (e.g., chloride attack, sulfate attack, etc.). It considers multiple processes relevant to external chemical attacks such as diffusion of ions in aqueous phase within pore spaces, equilibrium chemical speciation reactions and kinetic mineral dissolution/precipitation. The moisture

  8. Monte Carlo simulations of the critical properties of a Ziff-Gulari-Barshad model of catalytic CO oxidation with long-range reactivity

    NASA Astrophysics Data System (ADS)

    Chan, C. H.; Rikvold, P. A.

    2015-01-01

    The Ziff-Gulari-Barshad (ZGB) model, a simplified description of the oxidation of carbon monoxide (CO) on a catalyst surface, is widely used to study properties of nonequilibrium phase transitions. In particular, it exhibits a nonequilibrium, discontinuous transition between a reactive and a CO poisoned phase. If one allows a nonzero rate of CO desorption (k ), the line of phase transitions terminates at a critical point (kc). In this work, instead of restricting the CO and atomic oxygen (O) to react to form carbon dioxide (CO2) only when they are adsorbed in close proximity, we consider a modified model that includes an adjustable probability for adsorbed CO and O atoms located far apart on the lattice to react. We employ large-scale Monte Carlo simulations for system sizes up to 240 ×240 lattice sites, using the crossing of fourth-order cumulants to study the critical properties of this system. We find that the nonequilibrium critical point changes from the two-dimensional Ising universality class to the mean-field universality class upon introducing even a weak long-range reactivity mechanism. This conclusion is supported by measurements of cumulant fixed-point values, cluster percolation probabilities, correlation-length finite-size scaling properties, and the critical exponent ratio β /ν . The observed behavior is consistent with that of the equilibrium Ising ferromagnet with additional weak long-range interactions [T. Nakada, P. A. Rikvold, T. Mori, M. Nishino, and S. Miyashita, Phys. Rev. B 84, 054433 (2011), 10.1103/PhysRevB.84.054433]. The large system sizes and the use of fourth-order cumulants also enable determination with improved accuracy of the critical point of the original ZGB model with CO desorption.

  9. ATWS Transients for the 2400 MWt Gas-Cooled Fast Reactor

    SciTech Connect

    Cheng,L.Y.; Ludewig, H.

    2007-08-05

    Reactivity transients have been analyzed with an updated RELAPS-3D (ver. 2.4.2) system model of the pin core design for the 2400MWt gas-cooled fast reactor (GCFR). Additional reactivity parameters were incorporated in the RELAP5 point-kinetics model to account for reactivity feedbacks due to axial and radial expansion of the core, fuel temperature changes (Doppler effect), and pressure changes (helium density changes). Three reactivity transients without scram were analyzed and the incidents were initiated respectively by reactivity ramp, loss of load, and depressurization. During the course of the analysis the turbine bypass model for the power conversion unit (PCU) was revised to enable a better utilization of forced flow cooling after the PCU is tripped. The analysis of the reactivity transients demonstrates the significant impact of the PCU on system pressure and core flow. Results from the modified turbine bypass model suggest a success path for the GCFR to mitigate reactivity transients without scram.

  10. Particle Tracking-Based Strategies For Simulating Transport in a Transient Groundwater Flow Field at Yucca Flat, Nevada Test Site, USA

    NASA Astrophysics Data System (ADS)

    Keating, E. H.; Srinivasan, G.; Kang, Q.; Li, C.; Dash, Z.; Kwicklis, E. M.

    2009-12-01

    Developing probabilistic-based calculations of contaminant concentrations over the next 1000 years at Yucca Flat, Nevada Test site, require tremendous computational effort in this highly complex hydrogeologic surface environment. The sources of contamination, underground nuclear tests conducted between 1951 and 1992, not only released radionuclides to the subsurface but also created abrupt, significant changes in rock properties and caused large transients in the measured hydraulic gradients. To efficiently model contaminant migration from these sources we use a particle-based approach within a transient flow field. Here, we present results using two methods; first, an explicit representation of time-varying sources using large numbers of particles introduced at source-specific rates over time, each representing a unique mass of solute. This method provides good results, but is computationally expensive since sensitivity to uncertainty in source term and transport parameters can only be explored with discrete process-model runs. The second method employs a convolution method (PLUMECALC) which can efficiently consider a large number of variations in the source terms and in certain transport parameters with a single process-model run. Implementation of this second approach required extension of the existing methodology to conditions of transient flow. We find very good comparison between the two methods on small test problems and excellent computational advantages when applying the convolution method in the NTS application

  11. Transient Eddies in the UCLA GCM

    NASA Technical Reports Server (NTRS)

    White, G. H.

    1985-01-01

    The simulation of transient eddies in the nine level UCLA general circulation model (GCM) was examined and compared to observations, with emphasis on the Northern Hemisphere winter. Qualitatively, the UCLA GCM reproduces many features of the observed circulation and the relationship between the time mean flow and transient eddies; however, the magnitudes of transient eddies in the UCLA GCM, particularly at frequencies lower than those associated with baroclinic instability, appear to be much less than those observed. The pattern of low level transient eddy heat fluxes were similar to observations and acted to dissipate the low level seasonal mean temperature field. The simulated transient eddy kinetic energy at 300 mb is given for eddies of all time scales shorter than a season.

  12. Carbonated hydroxyapatite starting from calcite and different orthophosphates under moderate hydrothermal conditions: Synthesis and surface reactivity in simulated body fluid

    SciTech Connect

    Pham Minh, Doan Nzihou, Ange; Sharrock, Patrick

    2014-12-15

    Highlights: • Carbonated apatite (CAP) could be easily obtained from CaCO{sub 3} and orthophosphates. • Highest CaCO{sub 3} dissolution and apatitic carbonate content were obtained with H{sub 3}PO{sub 4}. • A-B-type CAP was formed. • The synthesized CAP was thermally stable up to 1000 °C. • This CAP showed high biomineralization activity before and after thermal treatment. - Abstract: The one-step synthesis of carbonated hydroxyapatite (CAP) using calcite and different orthophosphates was investigated in a closed batch reactor. Only orthophosphoric acid could lead to the complete decomposition of calcite particles, when the reaction temperature was set at 80 °C. On the other hand, the reaction time and the dilution of the initial calcite suspension had no significant influence on the formation of the solid products. CAP was formed as the main crystalline calcium phosphate with the carbonate content in the range of 4.2–4.6 wt.%. The thermal decarbonation of the synthesized CAP started at 750 °C but it was only significant at 1000 °C under air atmosphere. This thermal decarbonation was total at 1200 °C or above. All CAP samples and products following thermal treatments were found bioactive in the test using simulated body fluid (SBF) solution.

  13. Mechanisms of strong pressure wave generations during knocking combustion: compressible reactive flow simulations with detailed chemical kinetics

    NASA Astrophysics Data System (ADS)

    Terashima, Hiroshi; Koshi, Mitsuo

    2014-11-01

    Knocking is a very severe pressure oscillation caused by interactions between flame propagation and end-gas autoignition in spark-assisted engines. In this study, knocking combustion modeled in one-dimensional space is simulated using a highly efficient compressible flow solver with detailed chemical kinetics for clarifying the process of knocking occurrence. Especially, mechanisms of strong pressure wave generation are addressed. A robust and fast explicit integration method is used to efficiently handle stiff chemistry, and species bundling for effectively estimating the diffusion coefficients. The detailed mechanisms such as n-butane of 113 species and n-heptane of 373 species are directly applied. Results demonstrate that the negative temperature coefficient (NTC) region of n-heptane significantly influence the knocking timing and intensity. In the NTC region, stronger pressure wave is generated due to rapid heat release of a very small portion in the end-gas, which is attributed to low temperature oxidation and inhomogeneous temperature distributions in the end-gas. The knocking intensity is thus amplified in the NTC region, taking a maximum value. In the case of n-butane with no NTC region, relatively weak knocking intensity is observed in all conditions with no clear peak.

  14. Building Decision Trees for Characteristic Ellipsoid Method to Monitor Power System Transient Behaviors

    SciTech Connect

    Ma, Jian; Diao, Ruisheng; Makarov, Yuri V.; Etingov, Pavel V.; Zhou, Ning; Dagle, Jeffery E.

    2010-12-01

    The characteristic ellipsoid is a new method to monitor the dynamics of power systems. Decision trees (DTs) play an important role in applying the characteristic ellipsoid method to system operation and analysis. This paper presents the idea and initial results of building DTs for detecting transient dynamic events using the characteristic ellipsoid method. The objective is to determine fault types, fault locations and clearance time in the system using decision trees based on ellipsoids of system transient responses. The New England 10-machine 39-bus system is used for running dynamic simulations to generate a sufficiently large number of transient events in different system configurations. Comprehensive transient simulations considering three fault types, two fault clearance times and different fault locations were conducted in the study. Bus voltage magnitudes and monitored reactive and active power flows are recorded as the phasor measurements to calculate characteristic ellipsoids whose volume, eccentricity, center and projection of the longest axis are used as indices to build decision trees. The DT performances are tested and compared by considering different sets of PMU locations. The proposed method demonstrates that the characteristic ellipsoid method is a very efficient and promising tool to monitor power system dynamic behaviors.

  15. CO2 leakage impacts on shallow groundwater. Field-scale reactive-transport simulations informed by observations at a natural analog site

    DOE PAGES

    Keating, Elizabeth H.; Hakala, J. Alexandra; Viswanathan, Hari; Carey, J. William; Pawar, Rajesh; Guthrie, George D.; Fessenden-Rahn, Julianna

    2013-03-01

    It is challenging to predict the degree to which shallow groundwater might be affected by leaks from a CO2 sequestration reservoir, particularly over long time scales and large spatial scales. In this study observations at a CO2 enriched shallow aquifer natural analog were used to develop a predictive model which is then used to simulate leakage scenarios. This natural analog provides the opportunity to make direct field observations of groundwater chemistry in the presence of elevated CO2, to collect aquifer samples and expose them to CO2 under controlled conditions in the laboratory, and to test the ability of multiphase reactivemore » transport models to reproduce measured geochemical trends at the field-scale. The field observations suggest that brackish water entrained with the upwelling CO2 are a more significant source of trace metals than in situ mobilization of metals due to exposure to CO2. The study focuses on a single trace metal of concern at this site: U. Experimental results indicate that cation exchange/adsorption and dissolution/precipitation of calcite containing trace amounts of U are important reactions controlling U in groundwater at this site, and that the amount of U associated with calcite is fairly well constrained. Simulations incorporating these results into a 3-D multi-phase reactive transport model are able to reproduce the measured ranges and trends between pH, pCO2, Ca, total C, U and Cl-at the field site. Although the true fluxes at the natural analog site are unknown, the cumulative CO2 flux inferred from these simulations are approximately equivalent to 37.8E-3 MT, approximately corresponding to a .001% leak rate for injection at a large (750 MW) power plant. The leakage scenario simulations suggest that if the leak only persists for a short time the volume of aquifer contaminated by CO2-induced mobilization of U will be relatively small, yet persistent over 100 a.« less

  16. Mechanical and electrical properties of functionalized graphene nanoribbon: A study of reactive molecular dynamic simulation and density functional tight-binding theory

    NASA Astrophysics Data System (ADS)

    Zaminpayma, Esmaeil; Nayebi, Payman

    2015-02-01

    Graphene has novel electronic structure, such as unusual transport properties, high carrier mobility and excellent mechanical properties like high Young's modulus. These properties can be modified by many methods, such as functionalized with adding chemical groups, cutting graphene as a nanoribbon and Appling a stress along graphene. In this work, we studied the mechanical and electrical properties of functionalized graphene nanoribbon with -NH2, -CH3, -OH, -C5H6 groups. In mechanical section, we calculated Young's modulus of functionalized graphene nanoribbon as a function of temperature by method of reactive molecular dynamic simulation. Our results show that Young's modulus decrease by increasing temperature. Also we studied the effect of functionalized groups on Young's modulus. We show that Young's modulus decreases by adding these groups. It is in the order of Y (nanoribbon)>Y (NH2)>Y (C6H5)>Y (OH)>Y (CH3). In electrical section, we calculated current-voltage curve for functionalized nanoribbon with density functional tight-binding method at two different 0% and 5% strain. We found for both strains, the functionalized groups decrease the electrical resistance of nanoribbon and increase its current. The relationship of the current is in the order of I(CH3) >I(C5H6) >I(NH2) >I(OH) >I (nanoribbon).

  17. Transient tachypnea - newborn

    MedlinePlus

    TTN; Wet lungs - newborns; Retained fetal lung fluid; Transient RDS; Prolonged transition; Neonatal - transient tachypnea ... As the baby grows in the womb, the lungs make a special fluid. This fluid fills the ...

  18. Transient drainage summary report

    SciTech Connect

    1996-09-01

    This report summarizes the history of transient drainage issues on the Uranium Mill Tailings Remedial Action (UMTRA) Project. It defines and describes the UMTRA Project disposal cell transient drainage process and chronicles UMTRA Project treatment of the transient drainage phenomenon. Section 4.0 includes a conceptual cross section of each UMTRA Project disposal site and summarizes design and construction information, the ground water protection strategy, and the potential for transient drainage.

  19. Multiscale reactive molecular dynamics

    PubMed Central

    Knight, Chris; Lindberg, Gerrick E.; Voth, Gregory A.

    2012-01-01

    Many processes important to chemistry, materials science, and biology cannot be described without considering electronic and nuclear-level dynamics and their coupling to slower, cooperative motions of the system. These inherently multiscale problems require computationally efficient and accurate methods to converge statistical properties. In this paper, a method is presented that uses data directly from condensed phase ab initio simulations to develop reactive molecular dynamics models that do not require predefined empirical functions. Instead, the interactions used in the reactive model are expressed as linear combinations of interpolating functions that are optimized by using a linear least-squares algorithm. One notable benefit of the procedure outlined here is the capability to minimize the number of parameters requiring nonlinear optimization. The method presented can be generally applied to multiscale problems and is demonstrated by generating reactive models for the hydrated excess proton and hydroxide ion based directly on condensed phase ab initio molecular dynamics simulations. The resulting models faithfully reproduce the water-ion structural properties and diffusion constants from the ab initio simulations. Additionally, the free energy profiles for proton transfer, which is sensitive to the structural diffusion of both ions in water, are reproduced. The high fidelity of these models to ab initio simulations will permit accurate modeling of general chemical reactions in condensed phase systems with computational efficiency orders of magnitudes greater than currently possible with ab initio simulation methods, thus facilitating a proper statistical sampling of the coupling to slow, large-scale motions of the system. PMID:23249062

  20. TOUGHREACT User's Guide: A Simulation Program for Non-isothermal Multiphase Reactive Geochemical Transport in Variably Saturated Geologic Media, V1.2.1

    SciTech Connect

    Xu, Tianfu; Sonnenthal, Eric; Spycher, Nicolas; Pruess, Karsten

    2008-09-29

    Coupled modeling of subsurface multiphase fluid and heat flow, solute transport, and chemical reactions can be applied to many geologic systems and environmental problems, including geothermal systems, diagenetic and weathering processes, subsurface waste disposal, acid mine drainage remediation, contaminant transport, and groundwater quality. TOUGHREACT has been developed as a comprehensive non-isothermal multi-component reactive fluid flow and geochemical transport simulator to investigate these and other problems. A number of subsurface thermo-physical-chemical processes are considered under various thermohydrological and geochemical conditions of pressure, temperature, water saturation, and ionic strength. TOUGHREACT can be applied to one-, two- or three-dimensional porous and fractured media with physical and chemical heterogeneity. The code can accommodate any number of chemical species present in liquid, gas and solid phases. A variety of equilibrium chemical reactions are considered, such as aqueous complexation, gas dissolution/exsolution, and cation exchange. Mineral dissolution/precipitation can take place subject to either local equilibrium or kinetic controls, with coupling to changes in porosity and permeability and capillary pressure in unsaturated systems. Chemical components can also be treated by linear adsorption and radioactive decay. The first version of the non-isothermal reactive geochemical transport code TOUGHREACT was developed (Xu and Pruess, 1998) by introducing reactive geochemistry into the framework of the existing multi-phase fluid and heat flow code TOUGH2 (Pruess, 1991). TOUGHREACT was further enhanced with the addition of (1) treatment of mineral-water-gas reactive-transport under boiling conditions, (2) an improved HKF activity model for aqueous species, (3) gas species diffusion coefficients calculated as a function of pressure, temperature, and molecular properties, (4) mineral reactive surface area formulations for fractured

  1. Transient Ischemic Attack

    MedlinePlus

    Transient Ischemic Attack TIA , or transient ischemic attack, is a "mini stroke" that occurs when a blood clot blocks an artery for a short time. The only ... TIA is that with TIA the blockage is transient (temporary). TIA symptoms occur rapidly and last a ...

  2. TRACE/PARCS modelling of rips trip transients for Lungmen ABWR

    SciTech Connect

    Chang, C. Y.; Lin, H. T.; Wang, J. R.; Shih, C.

    2012-07-01

    The objectives of this study are to examine the performances of the steady-state results calculated by the Lungmen TRACE/PARCS model compared to SIMULATE-3 code, as well as to use the analytical results of the final safety analysis report (FSAR) to benchmark the Lungmen TRACE/PARCS model. In this study, three power generation methods in TRACE were utilized to analyze the three reactor internal pumps (RIPs) trip transient for the purpose of validating the TRACE/PARCS model. In general, the comparisons show that the