Numerical simulation of hydrogen plasma in MPCVD reactor
NASA Astrophysics Data System (ADS)
Huang, Di
A numerical study was conducted to build a model able to estimate the plasma properties under different working conditions for pure hydrogen plasma in a MPCVD reactor. A plasma model based on standing wave assumption and a linear estimation of ne and coupled the EM simulation, heat transfer simulation and UDF calculations of plasma properties was built in COMSOL Muitiphysics and tested with six different working conditions. The reliability of COMSOL EM solver was tested through comparing the simulation results with a benchmark EM solver, ANSYS HFSS. The validities of two assumptions made about the electrical field, standing wave assumption and sinusoidal oscillation field assumption, were tested by a PDE solver in COMSOL for utilizing the drift-diffusion model of ne.
Numerical simulation of vortex pyrolysis reactors for condensable tar production from biomass
Miller, R.S.; Bellan, J.
1998-08-01
A numerical study is performed in order to evaluate the performance and optimal operating conditions of vortex pyrolysis reactors used for condensable tar production from biomass. A detailed mathematical model of porous biomass particle pyrolysis is coupled with a compressible Reynolds stress transport model for the turbulent reactor swirling flow. An initial evaluation of particle dimensionality effects is made through comparisons of single- (1D) and multi-dimensional particle simulations and reveals that the 1D particle model results in conservative estimates for total pyrolysis conversion times and tar collection. The observed deviations are due predominantly to geometry effects while directional effects from thermal conductivity and permeability variations are relatively small. Rapid ablative particle heating rates are attributed to a mechanical fragmentation of the biomass particles that is modeled using a critical porosity for matrix breakup. Optimal thermal conditions for tar production are observed for 900 K. Effects of biomass identity, particle size distribution, and reactor geometry and scale are discussed.
Large-Scale Simulations of Realistic Fluidized Bed Reactors using Novel Numerical Methods
NASA Astrophysics Data System (ADS)
Capecelatro, Jesse; Desjardins, Olivier; Pepiot, Perrine; National Renewable Energy Lab Collaboration
2011-11-01
Turbulent particle-laden flows in the form of fluidized bed reactors display good mixing properties, low pressure drops, and a fairly uniform temperature distribution. Understanding and predicting the flow dynamics within the reactor is necessary for improving the efficiency, and providing technologies for large-scale industrialization. A numerical strategy based on an Eulerian representation of the gas phase and Lagrangian tracking of the particles is developed in the framework of NGA, a high- order fully conservative parallel code tailored for turbulent flows. The particles are accounted for using a point-particle assumption. Once the gas-phase quantities are mapped to the particle location a conservative, implicit diffusion operation smoothes the field. Normal and tangential collisions are handled via soft-sphere model, modified to allow the bed to reach close packing at rest. The pressure drop across the bed is compared with theory to accurately predict the minimum fluidization velocity. 3D simulations of the National Renewable Energy Lab's 4-inch reactor are then conducted. Tens of millions of particles are tracked. The reactor's geometry is modeled using an immersed boundary scheme. Statistics for volume fraction, velocities, bed expansion, and bubble characteristics are analyzed and compared with experimental data.
Gas Core Reactor Numerical Simulation Using a Coupled MHD-MCNP Model
NASA Technical Reports Server (NTRS)
Kazeminezhad, F.; Anghaie, S.
2008-01-01
Analysis is provided in this report of using two head-on magnetohydrodynamic (MHD) shocks to achieve supercritical nuclear fission in an axially elongated cylinder filled with UF4 gas as an energy source for deep space missions. The motivation for each aspect of the design is explained and supported by theory and numerical simulations. A subsequent report will provide detail on relevant experimental work to validate the concept. Here the focus is on the theory of and simulations for the proposed gas core reactor conceptual design from the onset of shock generations to the supercritical state achieved when the shocks collide. The MHD model is coupled to a standard nuclear code (MCNP) to observe the neutron flux and fission power attributed to the supercritical state brought about by the shock collisions. Throughout the modeling, realistic parameters are used for the initial ambient gaseous state and currents to ensure a resulting supercritical state upon shock collisions.
Models and numerical methods for the simulation of loss-of-coolant accidents in nuclear reactors
NASA Astrophysics Data System (ADS)
Seguin, Nicolas
2014-05-01
In view of the simulation of the water flows in pressurized water reactors (PWR), many models are available in the literature and their complexity deeply depends on the required accuracy, see for instance [1]. The loss-of-coolant accident (LOCA) may appear when a pipe is broken through. The coolant is composed by light water in its liquid form at very high temperature and pressure (around 300 °C and 155 bar), it then flashes and becomes instantaneously vapor in case of LOCA. A front of liquid/vapor phase transition appears in the pipes and may propagate towards the critical parts of the PWR. It is crucial to propose accurate models for the whole phenomenon, but also sufficiently robust to obtain relevant numerical results. Due to the application we have in mind, a complete description of the two-phase flow (with all the bubbles, droplets, interfaces…) is out of reach and irrelevant. We investigate averaged models, based on the use of void fractions for each phase, which represent the probability of presence of a phase at a given position and at a given time. The most accurate averaged model, based on the so-called Baer-Nunziato model, describes separately each phase by its own density, velocity and pressure. The two phases are coupled by non-conservative terms due to gradients of the void fractions and by source terms for mechanical relaxation, drag force and mass transfer. With appropriate closure laws, it has been proved [2] that this model complies with all the expected physical requirements: positivity of densities and temperatures, maximum principle for the void fraction, conservation of the mixture quantities, decrease of the global entropy… On the basis of this model, it is possible to derive simpler models, which can be used where the flow is still, see [3]. From the numerical point of view, we develop new Finite Volume schemes in [4], which also satisfy the requirements mentioned above. Since they are based on a partial linearization of the physical
Servant, G; Caltagirone, J P; Gérard, A; Laborde, J L; Hita, A
2000-10-01
The use of high frequency ultrasound in chemical systems is of major interest to optimize chemical procedures. Characterization of an open air 477 kHz ultrasound reactor shows that, because of the collapse of transient cavitation bubbles and pulsation of stable cavitation bubbles, chemical reactions are enhanced. Numerical modelling is undertaken to determine the spatio-temporal evolution of cavitation bubbles. The calculus of the emergence of cavitation bubbles due to the acoustic driving (by taking into account interactions between the sound field and bubbles' distribution) gives a cartography of bubbles' emergence within the reactor. Computation of their motion induced by the pressure gradients occurring in the reactor show that they migrate to the pressure nodes. Computed bubbles levitation sites gives a cartography of the chemical activity of ultrasound. Modelling of stable cavitation bubbles' motion induced by the motion of the liquid gives some insight on degassing phenomena. PMID:11062879
NASA Astrophysics Data System (ADS)
Ohshima, Hiroyuki; Uwaba, Tomoyuki; Hashimoto, Akihiko; Imai, Yasutomo; Ito, Masahiro
2015-12-01
A numerical simulation system, which consists of a deformation analysis program and three kinds of thermal-hydraulics analysis programs, is being developed in Japan Atomic Energy Agency in order to offer methodologies to clarify thermal-hydraulic phenomena in fuel assemblies of sodium-cooled fast reactors under various operating conditions. This paper gives the outline of the system and its applications to fuel assembly analyses as a validation study.
Ohshima, Hiroyuki; Uwaba, Tomoyuki; Hashimoto, Akihiko; Imai, Yasutomo; Ito, Masahiro
2015-12-31
A numerical simulation system, which consists of a deformation analysis program and three kinds of thermal-hydraulics analysis programs, is being developed in Japan Atomic Energy Agency in order to offer methodologies to clarify thermal-hydraulic phenomena in fuel assemblies of sodium-cooled fast reactors under various operating conditions. This paper gives the outline of the system and its applications to fuel assembly analyses as a validation study.
Hakan Ozaltun & Herman Shen
2011-11-01
This article presents assessment of the mechanical behavior of U-10wt% Mo (U10Mo) alloy based monolithic fuel plates subject to irradiation. Monolithic, plate-type fuel is a new fuel form being developed for research and test reactors to achieve higher uranium densities within the reactor core to allow the use of low-enriched uranium fuel in high-performance reactors. Identification of the stress/strain characteristics is important for understanding the in-reactor performance of these plate-type fuels. For this work, three distinct cases were considered: (1) fabrication induced residual stresses (2) thermal cycling of fabricated plates; and finally (3) transient mechanical behavior under actual operating conditions. Because the temperatures approach the melting temperature of the cladding during the fabrication and thermal cycling, high temperature material properties were incorporated to improve the accuracy. Once residual stress fields due to fabrication process were identified, solution was used as initial state for the subsequent simulations. For thermal cycling simulation, elasto-plastic material model with thermal creep was constructed and residual stresses caused by the fabrication process were included. For in-service simulation, coupled fluid-thermal-structural interaction was considered. First, temperature field on the plates was calculated and this field was used to compute the thermal stresses. For time dependent mechanical behavior, thermal creep of cladding, volumetric swelling and fission induced creep of the fuel foil were considered. The analysis showed that the stresses evolve very rapidly in the reactor. While swelling of the foil increases the stress of the foil, irradiation induced creep causes stress relaxation.
Dubey, Hitesh; Das, Sarit Kumar; Panda, Tapobrata
2006-11-01
A modified mixing plane approach for steady state simulation of flow field in fully baffled biological reactor is presented and discussed. Without requiring any experimental input, this approach of dividing the vessel into suitable number of connected and disconnected zones; solving steady state equation separately in each zone and then transferring information between them, provides a computationally less intensive alternative for simulating the flow in the whole vessel. Impeller used is the standard Rushton Turbine positioned at mid-height of the reactor and simulations are carried out using standard k-epsilon turbulence model implemented in CFD code FLUENT. Meshing is done using tetrahedral elements such that mesh size gradually increases from the center to the periphery. Most of the previous simulation works present only a few aspects of the flow field with scant importance to the energy balance in the tank and near tip turbulence. In this work, complete model prediction for velocity field and turbulence parameters (near tip and in the bulk region) are validated by comparison with experimental data. As compared to previous simulation works, the results predicted by this "Differential circumferential averaging mixing plane approach" show a better qualitative and quantitative agreement with the published experimental data. A distribution of energy dissipation in various zones of vessel is presented. Also a qualitative picture of flow field and stagnant zones inside the reactor is presented and discussed. Comparison of flow characteristics for different number of baffles shows that for the present dimension of the vessel, five baffles gives maximum enhanced mixing. PMID:16767780
Numerical simulation of turbulent flow in the throttle of the MBIR reactor's low-pressure chamber
NASA Astrophysics Data System (ADS)
Yarunichev, V. A.; Orlova, E. E.; Lemekhov, Yu. V.; Shpanskii, V. A.
2015-08-01
This work in devoted to numerical calculation of turbulent flow in a labyrinth-type throttle. A system of such throttles is installed at the inlet to the MBIR reactor's low-pressure chamber and serves for setting up the required pressure difference and coolant flow rate. MBIR is a multipurpose fourthgeneration fast-neutron research reactor intended for investigating new kinds of nuclear fuel, structural materials, and coolants. The aim of this work is to develop a verified procedure for carrying out 3D calculation of the throttle using CFD modeling techniques. The investigations on determining the throttle hydraulic friction coefficient were carried out in the range of Reynolds numbers Re = 52000-136000. The reactor coolant (liquid sodium) was modeled by tap water. The calculations were carried out using high-Reynolds-number turbulence models with the near-wall functions k-ɛ and RNG k-ɛ, where k is the turbulent pulsation kinetic energy and ɛ is the turbulence kinetic energy dissipation rate. The obtained results have shown that the calculated value of hydraulic friction coefficient differs from its experimental value by no more than 10%. The developed procedure can be applied in determining the hydraulic friction coefficient of a modified labyrinth throttle design. The use of such calculation will make it possible to predict an experiment with the preset accuracy.
Dogan, Hakan; Popov, Viktor
2016-05-01
We investigate the acoustic wave propagation in bubbly liquid inside a pilot sonochemical reactor which aims to produce antibacterial medical textile fabrics by coating the textile with ZnO or CuO nanoparticles. Computational models on acoustic propagation are developed in order to aid the design procedures. The acoustic pressure wave propagation in the sonoreactor is simulated by solving the Helmholtz equation using a meshless numerical method. The paper implements both the state-of-the-art linear model and a nonlinear wave propagation model recently introduced by Louisnard (2012), and presents a novel iterative solution procedure for the nonlinear propagation model which can be implemented using any numerical method and/or programming tool. Comparative results regarding both the linear and the nonlinear wave propagation are shown. Effects of bubble size distribution and bubble volume fraction on the acoustic wave propagation are discussed in detail. The simulations demonstrate that the nonlinear model successfully captures the realistic spatial distribution of the cavitation zones and the associated acoustic pressure amplitudes. PMID:26611813
Zhuchenko, S. V.
2014-11-12
This report presents a PC-based program for solution gas dynamics and heat exchange mathematical tasks in fuel assemblies of the fast-neutron nuclear reactors. A fuel assembly consisting of bulk heat-generating elements, which are integrated together by the system of supply and pressure manifolds, is examined. Spherical heat-generating microelements, which contain nuclear fuel, are pulled into the heat-generating elements. Gaseous coolant proceed from supply manifolds to heat-generating elements, where it withdraws the nuclear reaction heat and assembles in pressure manifolds.
Numerical Aerodynamic Simulation
NASA Technical Reports Server (NTRS)
1989-01-01
An overview of historical and current numerical aerodynamic simulation (NAS) is given. The capabilities and goals of the Numerical Aerodynamic Simulation Facility are outlined. Emphasis is given to numerical flow visualization and its applications to structural analysis of aircraft and spacecraft bodies. The uses of NAS in computational chemistry, engine design, and galactic evolution are mentioned.
Tudela, Ignacio; Sáez, Verónica; Esclapez, María Deseada; Díez-García, María Isabel; Bonete, Pedro; González-García, José
2014-05-01
Numerical methods for the calculation of the acoustic field inside sonoreactors have rapidly emerged in the last 15 years. This paper summarizes some of the most important works on this topic presented in the past, along with the diverse numerical works that have been published since then, reviewing the state of the art from a qualitative point of view. In this sense, we illustrate and discuss some of the models recently developed by the scientific community to deal with some of the complex events that take place in a sonochemical reactor such as the vibration of the reactor walls and the nonlinear phenomena inherent to the presence of ultrasonic cavitation. In addition, we point out some of the upcoming challenges that must be addressed in order to develop a reliable tool for the proper designing of efficient sonoreactors and the scale-up of sonochemical processes. PMID:24355287
Rocket engine numerical simulation
NASA Technical Reports Server (NTRS)
Davidian, Ken
1993-01-01
The topics are presented in view graph form and include the following: a definition of the rocket engine numerical simulator (RENS); objectives; justification; approach; potential applications; potential users; RENS work flowchart; RENS prototype; and conclusions.
Rosa, M.P.; Podowski, M.Z.
1995-09-01
This paper is concerned with the analysis of dynamics and stability of boiling channels and systems. The specific objectives are two-fold. One of them is to present the results of a study aimed at analyzing the effects of various modeling concepts and numerical approaches on the transient response and stability of parallel boiling channels. The other objective is to investigate the effect of closed-loop feedback on stability of a boiling water reactor (BWR). Various modeling and computational issues for parallel boiling channels are discussed, such as: the impact of the numerical discretization scheme for the node containing the moving boiling boundary on the convergence and accuracy of computations, and the effects of subcooled boiling and other two-phase flow phenomena on the predictions of marginal stability conditions. Furthermore, the effects are analyzed of local loss coefficients around the recirculation loop of a boiling water reactor on stability of the reactor system. An apparent paradox is explained concerning the impact of changing single-phase losses on loop stability. The calculations have been performed using the DYNOBOSS computer code. The results of DYNOBOSS validation against other computer codes and experimental data are shown.
Skibinski, Jakub; Wejrzanowski, Tomasz; Caban, Piotr; Kurzydlowski, Krzysztof J.
2014-10-06
In the present study numerical simulations of epitaxial growth of gallium nitride in Metal Organic Vapor Phase Epitaxy reactor AIX-200/4RF-S is addressed. Epitaxial growth means crystal growth that progresses while inheriting the laminar structure and the orientation of substrate crystals. One of the technological problems is to obtain homogeneous growth rate over the main deposit area. Since there are many agents influencing reaction on crystal area such as temperature, pressure, gas flow or reactor geometry, it is difficult to design optimal process. According to the fact that it's impossible to determine experimentally the exact distribution of heat and mass transfer inside the reactor during crystal growth, modeling is the only solution to understand the process precisely. Numerical simulations allow to understand the epitaxial process by calculation of heat and mass transfer distribution during growth of gallium nitride. Including chemical reactions in numerical model allows to calculate the growth rate of the substrate and estimate the optimal process conditions for obtaining the most homogeneous product.
NASA Astrophysics Data System (ADS)
Skibinski, Jakub; Caban, Piotr; Wejrzanowski, Tomasz; Kurzydlowski, Krzysztof J.
2014-10-01
In the present study numerical simulations of epitaxial growth of gallium nitride in Metal Organic Vapor Phase Epitaxy reactor AIX-200/4RF-S is addressed. Epitaxial growth means crystal growth that progresses while inheriting the laminar structure and the orientation of substrate crystals. One of the technological problems is to obtain homogeneous growth rate over the main deposit area. Since there are many agents influencing reaction on crystal area such as temperature, pressure, gas flow or reactor geometry, it is difficult to design optimal process. According to the fact that it's impossible to determine experimentally the exact distribution of heat and mass transfer inside the reactor during crystal growth, modeling is the only solution to understand the process precisely. Numerical simulations allow to understand the epitaxial process by calculation of heat and mass transfer distribution during growth of gallium nitride. Including chemical reactions in numerical model allows to calculate the growth rate of the substrate and estimate the optimal process conditions for obtaining the most homogeneous product.
Numerical simulations in combustion
NASA Technical Reports Server (NTRS)
Chung, T. J.
1989-01-01
This paper reviews numerical simulations in reacting flows in general and combustion phenomena in particular. It is shown that use of implicit schemes and/or adaptive mesh strategies can improve convergence, stability, and accuracy of the solution. Difficulties increase as turbulence and multidimensions are considered, particularly when finite-rate chemistry governs the given combustion problem. Particular attention is given to the areas of solid-propellant combustion dynamics, turbulent diffusion flames, and spray droplet vaporization.
Numerical Propulsion System Simulation
NASA Technical Reports Server (NTRS)
Naiman, Cynthia
2006-01-01
The NASA Glenn Research Center, in partnership with the aerospace industry, other government agencies, and academia, is leading the effort to develop an advanced multidisciplinary analysis environment for aerospace propulsion systems called the Numerical Propulsion System Simulation (NPSS). NPSS is a framework for performing analysis of complex systems. The initial development of NPSS focused on the analysis and design of airbreathing aircraft engines, but the resulting NPSS framework may be applied to any system, for example: aerospace, rockets, hypersonics, power and propulsion, fuel cells, ground based power, and even human system modeling. NPSS provides increased flexibility for the user, which reduces the total development time and cost. It is currently being extended to support the NASA Aeronautics Research Mission Directorate Fundamental Aeronautics Program and the Advanced Virtual Engine Test Cell (AVETeC). NPSS focuses on the integration of multiple disciplines such as aerodynamics, structure, and heat transfer with numerical zooming on component codes. Zooming is the coupling of analyses at various levels of detail. NPSS development includes capabilities to facilitate collaborative engineering. The NPSS will provide improved tools to develop custom components and to use capability for zooming to higher fidelity codes, coupling to multidiscipline codes, transmitting secure data, and distributing simulations across different platforms. These powerful capabilities extend NPSS from a zero-dimensional simulation tool to a multi-fidelity, multidiscipline system-level simulation tool for the full development life cycle.
Numerical Aerodynamic Simulation (NAS)
NASA Technical Reports Server (NTRS)
Peterson, V. L.; Ballhaus, W. F., Jr.; Bailey, F. R.
1983-01-01
The history of the Numerical Aerodynamic Simulation Program, which is designed to provide a leading-edge capability to computational aerodynamicists, is traced back to its origin in 1975. Factors motivating its development and examples of solutions to successively refined forms of the governing equations are presented. The NAS Processing System Network and each of its eight subsystems are described in terms of function and initial performance goals. A proposed usage allocation policy is discussed and some initial problems being readied for solution on the NAS system are identified.
Confidence in Numerical Simulations
Hemez, Francois M.
2015-02-23
This PowerPoint presentation offers a high-level discussion of uncertainty, confidence and credibility in scientific Modeling and Simulation (M&S). It begins by briefly evoking M&S trends in computational physics and engineering. The first thrust of the discussion is to emphasize that the role of M&S in decision-making is either to support reasoning by similarity or to “forecast,” that is, make predictions about the future or extrapolate to settings or environments that cannot be tested experimentally. The second thrust is to explain that M&S-aided decision-making is an exercise in uncertainty management. The three broad classes of uncertainty in computational physics and engineering are variability and randomness, numerical uncertainty and model-form uncertainty. The last part of the discussion addresses how scientists “think.” This thought process parallels the scientific method where by a hypothesis is formulated, often accompanied by simplifying assumptions, then, physical experiments and numerical simulations are performed to confirm or reject the hypothesis. “Confidence” derives, not just from the levels of training and experience of analysts, but also from the rigor with which these assessments are performed, documented and peer-reviewed.
Adams, J.P.; Dobbe, C.A.; Bayless, P.D.
1986-01-01
Calculations have been made of the response of pressurized water reactors (PWRs) during a small-break, loss-of-coolant accident with the reactor coolant pumps (RCPs) operating. This study was conducted, as part of a comprehensive project, to assess the relationship between measurable RCP parameters, such as motor power or current, and fluid density, both local (at the RCP inlet) and global (average reactor coolant system). Additionally, the efficacy of using these RCP parameters, together with fluid temperature, to identify an off-nominal transient as either a LOCA, a heatup transient, or a cooldown transient and to follow recovery from the transient was assessed. The RELAP4 and RELAP5 computer codes were used with three independent sets of RCP, two-phase degradation multipliers. These multipliers were based on data obtained in two-phase flow conditions for the Semiscale, LOFT, and Creare/Combustion Engineering (CE)/Electric Power Research Institute (EPRI) pumps, respectively. Two reference PWRs were used in this study: Zion, a four-loop, 1100-MWe, Westinghouse plant operated by Commonwealth Edison Co. in Zion, Illinois and Bellefonte, a two-by-four loop, 1213 MWe, Babcock and Wilcox designed plant being built by the Tennessee Valley Authority in Scottsboro, Alabama. The results from this study showed that RCP operation resulted in an approximately homogeneous reactor coolant system and that this result was independent of reference plant, computer code, or two-phase RCP head degradation multiplier used in the calculation.
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).
Numerical simulation of dusty plasmas
Winske, D.
1995-09-01
The numerical simulation of physical processes in dusty plasmas is reviewed, with emphasis on recent results and unresolved issues. Three areas of research are discussed: grain charging, weak dust-plasma interactions, and strong dust-plasma interactions. For each area, we review the basic concepts that are tested by simulations, present some appropriate examples, and examine numerical issues associated with extending present work.
Reactor Simulator Testing Overview
NASA Technical Reports Server (NTRS)
Schoenfeld, Michael P.
2013-01-01
Test Objectives Summary: a) Verify operation of the core simulator, the instrumentation & control system, and the ground support gas and vacuum test equipment. b) Examine cooling & heat regeneration performance of the cold trap purification. c) Test the ALIP pump at voltages beyond 120V to see if the targeted mass flow rate of 1.75 kg/s can be obtained in the RxSim. Testing Highlights: a) Gas and vacuum ground support test equipment performed effectively for operations (NaK fill, loop pressurization, and NaK drain). b) Instrumentation & Control system effectively controlled loop temperature and flow rates or pump voltage to targeted settings and ramped within prescribed constraints. It effectively interacted with reactor simulator control model and defaulted back to temperature control mode if the transient fluctuations didn't dampen. c) Cold trap design was able to obtain the targeted cold temperature of 480 K. An outlet temperature of 636 K was obtained which was lower than the predicted 750 K but 156 K higher than the minimum temperature indicating the design provided some heat regeneration. d) ALIP produce a maximum flow rate of 1.53 kg/s at 800 K when operated at 150 V and 53 Hz.
NASA Technical Reports Server (NTRS)
Schoenfeld, Michael P.; Webster, Kenny L.; Pearson, Boise J.
2013-01-01
As part of the Nuclear Systems Office Fission Surface Power Technology Demonstration Unit (TDU) project, a reactor simulator test loop (RxSim) was design & built to perform integrated testing of the TDU components. In particular, the objectives of RxSim testing was to verify the operation of the core simulator, the instrumentation and control system, and the ground support gas and vacuum test equipment. In addition, it was decided to include a thermal test of a cold trap purification design and a pump performance test at pump voltages up to 150 V since the targeted mass flow rate of 1.75 kg/s was not obtained in the RxSim at the originally constrained voltage of 120 V. This paper summarizes RxSim testing. The gas and vacuum ground support test equipment performed effectively in NaK fill, loop pressurization, and NaK drain operations. The instrumentation and control system effectively controlled loop temperature and flow rates or pump voltage to targeted settings. The cold trap design was able to obtain the targeted cold temperature of 480 K. An outlet temperature of 636 K was obtained which was lower than the predicted 750 K but 156 K higher than the cold temperature indicating the design provided some heat regeneration. The annular linear induction pump (ALIP) tested was able to produce a maximum flow rate of 1.53 kg/s at 800 K when operated at 150 V and 53 Hz.
Numerical Simulation of Nix's Rotation
This is a numerical simulation of the orientation of Nix as seen from the center of the Pluto system. It has been sped up so that one orbit of Nix around Pluto takes 2 seconds instead of 25 days. L...
NASA Technical Reports Server (NTRS)
Schoenfeld, Michael P.; Webster, Kenny L.; Pearson, Boise Jon
2013-01-01
As part of the Nuclear Systems Office Fission Surface Power Technology Demonstration Unit (TDU) project, a reactor simulator test loop (RxSim) was design & built to perform integrated testing of the TDU components. In particular, the objectives of RxSim testing was to verify the operation of the core simulator, the instrumentation and control system, and the ground support gas and vacuum test equipment. In addition, it was decided to include a thermal test of a cold trap purification design and a pump performance test at pump voltages up to 150 V since the targeted mass flow rate of 1.75 kg/s was not obtained in the RxSim at the originally constrained voltage of 120 V. This paper summarizes RxSim testing. The gas and vacuum ground support test equipment performed effectively in NaK fill, loop pressurization, and NaK drain operations. The instrumentation and control system effectively controlled loop temperature and flow rates or pump voltage to targeted settings. The cold trap design was able to obtain the targeted cold temperature of 480 K. An outlet temperature of 636 K was obtained which was lower than the predicted 750 K but 156 K higher than the cold temperature indicating the design provided some heat regeneration. The annular linear induction pump (ALIP) tested was able to produce a maximum flow rate of 1.53 kg/s at 800 K when operated at 150 V and 53 Hz. Keywords: fission, space power, nuclear, liquid metal, NaK.
Requirements definition by numerical simulation
NASA Astrophysics Data System (ADS)
Hickman, James J.; Kostas, Chris; Tsang, Kang T.
1994-10-01
We are investigating the issues involved in requirements definition for narcotics interdiction: how much of a particular signature is possible, how does this amount change for different conditions, and what is the temporal relationship in various scenarios. Our approach has been to simulate numerically the conditions that arise during vapor or particulate transport. The advantages of this approach are that (1) a broad range of scenarios can be rapidly and inexpensively analyzed by simulation, and (2) simulations can display quantities that are difficult or impossible to measure. The drawback of this approach is that simulations cannot include all of the phenomena present in a real measurement, and therefore the fidelity of the simulation results is always an issue. To address this limitation, we will ultimately combine the results of numerical simulations with measurements of physical parameters for inclusion in the simulation. In this paper, we discuss these issues and how they apply to the current problems in narcotics interdictions, especially cargo containers. We also show the results of 1D and 3D numerical simulations, and compare these results with analytical solutions. The results indicate that this approach is viable. We also present data from 3D simulations of vapor transport in a loaded cargo container and some of the issues present in this ongoing work.
Numerical simulations of hot spots
NASA Astrophysics Data System (ADS)
Norman, Michael L.
Numerical simulations of hot spots and their associated jets are examined with emphasis on their dynamical variability. Attention is given to two-dimensional simulations, which incorporate dynamically passive and important magnetic fields in the ideal MHD limit. Distributions of total and polarized radio brightness have been derived for comparison with observations. The move toward three-dimensional simulations is documented, and hydrodynamical models for multiple hot spots are discussed. It is suggested that useful insights can be obtained from two-dimensional slab jet simulation, which relax the axisymmetric constraints while allowing high numerical resolution. In particular the dentist-drill model of Scheuer (1982) for working-surface variability is substantiated, and it is shown to result from self-excited jet instabilities near the working surface.
Energy Science and Technology Software Center (ESTSC)
1996-07-30
PLUG is a computer program that solves the coupled steady state continuity, momentum, energy, and species balance equations for a plug flow reactor. Both homogeneous (gas-phase) and heterogenous (surface) reactions can be accommodated. The reactor may be either isothermal or adiabatic or may have a specified axial temperature or heat flux profile; alternatively, an ambient temperature and an overall heat-transfer coefficient can be specified. The crosssectional area and surface area may vary with axial position,more » and viscous drag is included. Ideal gas behavior and surface site conservation are assumed.« less
Larson, Richard S.
1996-07-30
PLUG is a computer program that solves the coupled steady state continuity, momentum, energy, and species balance equations for a plug flow reactor. Both homogeneous (gas-phase) and heterogenous (surface) reactions can be accommodated. The reactor may be either isothermal or adiabatic or may have a specified axial temperature or heat flux profile; alternatively, an ambient temperature and an overall heat-transfer coefficient can be specified. The crosssectional area and surface area may vary with axial position, and viscous drag is included. Ideal gas behavior and surface site conservation are assumed.
Numerical simulation of electrochemical desalination
NASA Astrophysics Data System (ADS)
Hlushkou, D.; Knust, K. N.; Crooks, R. M.; Tallarek, U.
2016-05-01
We present an effective numerical approach to simulate electrochemically mediated desalination of seawater. This new membraneless, energy efficient desalination method relies on the oxidation of chloride ions, which generates an ion depletion zone and local electric field gradient near the junction of a microchannel branch to redirect sea salt into the brine stream, consequently producing desalted water. The proposed numerical model is based on resolution of the 3D coupled Navier–Stokes, Nernst–Planck, and Poisson equations at non-uniform spatial grids. The model is implemented as a parallel code and can be employed to simulate mass–charge transport coupled with surface or volume reactions in 3D systems showing an arbitrarily complex geometrical configuration.
Numerical simulation of electrochemical desalination.
Hlushkou, D; Knust, K N; Crooks, R M; Tallarek, U
2016-05-18
We present an effective numerical approach to simulate electrochemically mediated desalination of seawater. This new membraneless, energy efficient desalination method relies on the oxidation of chloride ions, which generates an ion depletion zone and local electric field gradient near the junction of a microchannel branch to redirect sea salt into the brine stream, consequently producing desalted water. The proposed numerical model is based on resolution of the 3D coupled Navier-Stokes, Nernst-Planck, and Poisson equations at non-uniform spatial grids. The model is implemented as a parallel code and can be employed to simulate mass-charge transport coupled with surface or volume reactions in 3D systems showing an arbitrarily complex geometrical configuration. PMID:27089841
Numerical Propulsion System Simulation Architecture
NASA Technical Reports Server (NTRS)
Naiman, Cynthia G.
2004-01-01
The Numerical Propulsion System Simulation (NPSS) is a framework for performing analysis of complex systems. Because the NPSS was developed using the object-oriented paradigm, the resulting architecture is an extensible and flexible framework that is currently being used by a diverse set of participants in government, academia, and the aerospace industry. NPSS is being used by over 15 different institutions to support rockets, hypersonics, power and propulsion, fuel cells, ground based power, and aerospace. Full system-level simulations as well as subsystems may be modeled using NPSS. The NPSS architecture enables the coupling of analyses at various levels of detail, which is called numerical zooming. The middleware used to enable zooming and distributed simulations is the Common Object Request Broker Architecture (CORBA). The NPSS Developer's Kit offers tools for the developer to generate CORBA-based components and wrap codes. The Developer's Kit enables distributed multi-fidelity and multi-discipline simulations, preserves proprietary and legacy codes, and facilitates addition of customized codes. The platforms supported are PC, Linux, HP, Sun, and SGI.
Numerical simulations of Lake Vostok
NASA Astrophysics Data System (ADS)
Curchitser, E.; Tremblay, B.
2003-04-01
Numerical simulations of Lake Vostok We present a systematic approach towards a realistic hydrodynamic model of lake Vostok. The lake is characterized by the unusual combination of size (permitting significant geostrophic motion) and an overlying ice sheet several kilometers thick. A priori estimates of the circulation in the deep lake predict a mostly geostrophic circulation driven by horizontal temperature gradients produced by the pressure-dependent freezing point at the base of the (non-uniform) ice sheet. Further preliminary (remote) research has revealed the steep topography and the elliptical geometry of the lake. A three dimensional, primitive equation, free surface, model is used as a starting point for the Lake configuration. We show how the surface pressure gradient forces are modified to permit a simulation that includes the hydrostatic effects of the overlying ice sheet. A thermodynamic ice model is coupled with the circulation component to simulate the ice accretion/melting at the base of the ice sheet. A stretching of the terrain following vertical coordinate is used to resolve the boundary layer in the ice/water interface. Furthermore, the terrain-following coordinate evolves in time, and is used to track the evolution of the ice sheet due to ice accretion/melting. Both idealized and realistic ice sheet bottom topographies (from remote radar data) are used to drive the simulations. Steady state and time evolving simulations (i.e., constant and evolving ice sheet geometry) will be descirbed, as well as a comparison to an idealized box model (Tremblay, Clarke, and Hohman). The coastline and lake bathymetry used in the simulation are derived from radar data and are accurately represented in our model.
Reactor Simulator Testing Overview
NASA Technical Reports Server (NTRS)
Schoenfeld, Michael P.
2013-01-01
OBJECTIVE: Integrated testing of the TDU components TESTING SUMMARY: a) Verify the operation of the core simulator, the instrumentation and control system, and the ground support gas and vacuum test equipment. b) Thermal test heat regeneration design aspect of a cold trap purification filter. c) Pump performance test at pump voltages up to 150 V (targeted mass flow rate of 1.75 kg/s was not obtained in the RxSim at the originally constrained voltage of 120 V). TESTING HIGHLIGHTS: a) Gas and vacuum ground support test equipment performed effectively for NaK fill, loop pressurization, and NaK drain operations. b) Instrumentation and control system effectively controlled loop temperature and flow rates or pump voltage to targeted settings. c) Cold trap design was able to obtain the targeted cold temperature of 480 K. An outlet temperature of 636 K was obtained which was lower than the predicted 750 K but 156 K higher than the cold temperature indicating the design provided some heat regeneration. d) ALIP produce a maximum flow rate of 1.53 kg/s at 800 K when operated at 150 V and 53 Hz.
Simulating reionization in numerical cosmology
NASA Astrophysics Data System (ADS)
Sokasian, Aaron
2003-11-01
The incorporation of radiative transfer effects into cosmological hydrodynamical simulations is essential for understanding how the intergalactic medium (IGM) makes the transition from a neutral medium to one that is almost fully ionized. I present an approximate numerical method designed to study in a statistical sense how a cosmological density field is ionized by various sets of sources. The method requires relatively few time steps and can be employed with simulations of high resolution. First, I explore the reionization history of Helium II by z < 6 quasars. Comparisons between HeII opacities measured observationally and inferred from our analysis reveal that the uncertainties in the empirical luminosity function provide enough leeway to provide a satisfactory match. A property common to all the calculations is that the epoch of Helium II reionization must have occurred between 3≲
Status report on high fidelity reactor simulation.
Palmiotti, G.; Smith, M.; Rabiti, C.; Lewis, E.; Yang, W.; Leclere,M.; Siegel, A.; Fischer, P.; Kaushik, D.; Ragusa, J.; Lottes, J.; Smith, B.
2006-12-11
This report presents the effort under way at Argonne National Laboratory toward a comprehensive, integrated computational tool intended mainly for the high-fidelity simulation of sodium-cooled fast reactors. The main activities carried out involved neutronics, thermal hydraulics, coupling strategies, software architecture, and high-performance computing. A new neutronics code, UNIC, is being developed. The first phase involves the application of a spherical harmonics method to a general, unstructured three-dimensional mesh. The method also has been interfaced with a method of characteristics. The spherical harmonics equations were implemented in a stand-alone code that was then used to solve several benchmark problems. For thermal hydraulics, a computational fluid dynamics code called Nek5000, developed in the Mathematics and Computer Science Division for coupled hydrodynamics and heat transfer, has been applied to a single-pin, periodic cell in the wire-wrap geometry typical of advanced burner reactors. Numerical strategies for multiphysics coupling have been considered and higher-accuracy efficient methods proposed to finely simulate coupled neutronic/thermal-hydraulic reactor transients. Initial steps have been taken in order to couple UNIC and Nek5000, and simplified problems have been defined and solved for testing. Furthermore, we have begun developing a lightweight computational framework, based in part on carefully selected open source tools, to nonobtrusively and efficiently integrate the individual physics modules into a unified simulation tool.
Numerical study of the effects of surface roughness on water disinfection UV reactor.
Sultan, Tipu; Ahmad, Sarfraz; Cho, Jinsoo
2016-04-01
UV reactors are an emerging choice as a big barrier against the pathogens present in drinking water. However, the precise role of reactor's wall roughness for cross flow ultraviolet (CF-UV) and axial flow ultraviolet (AF-UV) water disinfection reactors are unknown. In this paper, the influences of reactor's wall roughness were investigated with a view to identify their role on the performance factors namely dose distribution and reduction equivalent dose (RED). Herein, the relative effects of reactor's wall roughness on the performance of CF-UV and AF-UV reactors were also highlighted. This numerical study is a first step towards the comprehensive analysis of the effects of reactor's wall roughness for UV reactor. A numerical analysis was performed using ANSYS Fluent 15 academic version. The reactor's wall roughness has a significant effect on the RED. We found that the increase in RED is Reynolds number dependent (at lower value of turbulent Reynolds number the effects are remarkable). The effects of reactor's roughness were more pronounced for AF-UV reactor. The simulation results suggest that the study of reactor's wall roughness provides valuable insight to fully understand the effects of reactor's wall roughness and its impact on the flow behavior and other features of CF-UV and AF-UV water disinfection reactors. PMID:26802269
Linking scales through numerical simulations
NASA Astrophysics Data System (ADS)
Lunati, I.
2012-12-01
Field-scale models of flow through porous media rely on a continuum description, which disregard pore-scale details and focus on macroscopic effects. As it is always the case, this choice is quite effective in reducing the number of model parameters, but this comes at expenses of an inherent loss of information and generality. Models based on Darcy's law, for instance, require spatial and temporal scale separation (locality and equilibrium). Although these conditions are generally met for single-phase flow, multiphase flow is far more complex: the interaction between nonlinearity of the interface behavior and the pore structure (disorder) creates a variety of flow regimes for which scale separation does not hold. In recent years, the increased computational power has led to a revival of pore-scale modeling in order to overcome this issue and describe the flow at the scale in which it physically occurs. If appropriate techniques are chosen, it is possible to use numerical simulations to complement experimental observations and advance our understanding of multiphase flow. By means of examples, we discuss the role played by these models in contributing to solve open problems and in devising alternatives to the standard description of flow through porous media.
Numerical Simulations of Thermobaric Explosions
Kuhl, A L; Bell, J B; Beckner, V E; Khasainov, B
2007-05-04
A Model of the energy evolution in thermobaric explosions is presented. It is based on the two-phase formulation: conservation laws for the gas and particle phases along with inter-phase interaction terms. It incorporates a Combustion Model based on the mass conservation laws for fuel, air and products; source/sink terms are treated in the fast-chemistry limit appropriate for such gas dynamic fields. The Model takes into account both the afterburning of the detonation products of the booster with air, and the combustion of the fuel (Al or TNT detonation products) with air. Numerical simulations were performed for 1.5-g thermobaric explosions in five different chambers (volumes ranging from 6.6 to 40 liters and length-to-diameter ratios from 1 to 12.5). Computed pressure waveforms were very similar to measured waveforms in all cases - thereby proving that the Model correctly predicts the energy evolution in such explosions. The computed global fuel consumption {mu}(t) behaved as an exponential life function. Its derivative {dot {mu}}(t) represents the global rate of fuel consumption. It depends on the rate of turbulent mixing which controls the rate of energy release in thermobaric explosions.
Numerical Simulations of Granular Processes
NASA Astrophysics Data System (ADS)
Richardson, Derek C.; Michel, Patrick; Schwartz, Stephen R.; Ballouz, Ronald-Louis; Yu, Yang; Matsumura, Soko
2014-11-01
Spacecraft images and indirect observations including thermal inertia measurements indicate most small bodies have surface regolith. Evidence of granular flow is also apparent in the images. This material motion occurs in very low gravity, therefore in a completely different gravitational environment than on the Earth. Understanding and modeling these motions can aid in the interpretation of imaged surface features that may exhibit signatures of constituent material properties. Also, upcoming sample-return missions to small bodies, and possible future manned missions, will involve interaction with the surface regolith, so it is important to develop tools to predict the surface response. We have added new capabilities to the parallelized N-body gravity tree code pkdgrav [1,2] that permit the simulation of granular dynamics, including multi-contact physics and friction forces, using the soft-sphere discrete-element method [3]. The numerical approach has been validated through comparison with laboratory experiments (e.g., [3,4]). Ongoing and recently completed projects include: impacts into granular materials using different projectile shapes [5]; possible tidal resurfacing of asteroid Apophis during its 2029 encounter [6]; the Brazil-nut effect in low gravity [7]; and avalanche modeling.Acknowledgements: DCR acknowledges NASA (grants NNX08AM39G, NNX10AQ01G, NNX12AG29G) and NSF (AST1009579). PM acknowledges the French agency CNES. SRS works on the NEOShield Project funded under the European Commission’s FP7 program agreement No. 282703. SM acknowledges support from the Center for Theory and Computation at U Maryland and the Dundee Fellowship at U Dundee. Most simulations were performed using the YORP cluster in the Dept. of Astronomy at U Maryland and on the Deepthought High-Performance Computing Cluster at U Maryland.References: [1] Richardson, D.C. et al. 2000, Icarus 143, 45; [2] Stadel, J. 2001, Ph.D. Thesis, U Washington; [3] Schwartz, S.R. et al. 2012, Gran
Numerical simulations of multifluid flows
NASA Astrophysics Data System (ADS)
Unverdi, Salih Ozen
1990-01-01
A method for full numerical simulations of unsteady, incompressible Navier-Stokes equations for multi-fluid systems is developed. Moving interfaces between dissimilar fluids are explicitly tracked and fluid properties are constructed on a stationary grid using the position of the interfaces. While the interfaces are explicitly tracked, they are not kept completely sharp but are given a finite thickness of the order of the mesh size to provide stability and smoothness. This thickness remains constant for all time but decreases with finer resolution of the stationary grid. A unique feature of the method is that the tracked interfaces carry the jump in properties across the interface and that, at each time step, the property fields are reconstructed by solving a Poisson equation. The advantage of this approach is that interfaces can interact in a natural way, since the gradients add or cancel as the grid distribution is constructed from the information carried by the tracked front. The emphasis is on the shape regimes of bubbles and bubble-bubble interactions in a stationary fluid. The circular, elliptical and skirted shape regimes and wake structures of two-dimensional bubbles are studied. Three-dimensional evolution of the interaction of two bubbles in a stationary fluid is investigated. Interaction of bubbles in a periodic array is also studied and it is found that a pair of bubbles in a free rise can interact in the absence of a toroidal wake below the upper bubble and that the interaction time is smaller as the viscosity of the outer fluid decreases. It is shown that the kinetic energy of the flow field decreases during this interaction. Sensitivity of the bubble interaction process to fluid properties is shown by different trajectories followed by bubbles in fluids of different viscosity. The Rayleigh-Taylor instability is also studied.
Simulated nuclear reactor fuel assembly
Berta, V.T.
1993-04-06
An apparatus for electrically simulating a nuclear reactor fuel assembly. It includes a heater assembly having a top end and a bottom end and a plurality of concentric heater tubes having electrical circuitry connected to a power source, and radially spaced from each other. An outer target tube and an inner target tube is concentric with the heater tubes and with each other, and the outer target tube surrounds and is radially spaced from the heater tubes. The inner target tube is surrounded by and radially spaced from the heater tubes and outer target tube. The top of the assembly is generally open to allow for the electrical power connection to the heater tubes, and the bottom of the assembly includes means for completing the electrical circuitry in the heater tubes to provide electrical resistance heating to simulate the power profile in a nuclear reactor. The embedded conductor elements in each heater tube is split into two halves for a substantial portion of its length and provided with electrical isolation such that each half of the conductor is joined at one end and is not joined at the other end.
Simulated nuclear reactor fuel assembly
Berta, Victor T.
1993-01-01
An apparatus for electrically simulating a nuclear reactor fuel assembly. It includes a heater assembly having a top end and a bottom end and a plurality of concentric heater tubes having electrical circuitry connected to a power source, and radially spaced from each other. An outer target tube and an inner target tube is concentric with the heater tubes and with each other, and the outer target tube surrounds and is radially spaced from the heater tubes. The inner target tube is surrounded by and radially spaced from the heater tubes and outer target tube. The top of the assembly is generally open to allow for the electrical power connection to the heater tubes, and the bottom of the assembly includes means for completing the electrical circuitry in the heater tubes to provide electrical resistance heating to simulate the power profile in a nuclear reactor. The embedded conductor elements in each heater tube is split into two halves for a substantial portion of its length and provided with electrical isolation such that each half of the conductor is joined at one end and is not joined at the other end.
Relativistic positioning systems: Numerical simulations
NASA Astrophysics Data System (ADS)
Puchades Colmenero, Neus
The position of users located on the Earth's surface or near it may be found with the classic positioning systems (CPS). Certain information broadcast by satellites of global navigation systems, as GPS and GALILEO, may be used for positioning. The CPS are based on the Newtonian formalism, although relativistic post-Newtonian corrections are done when they are necessary. This thesis contributes to the development of a different positioning approach, which is fully relativistic from the beginning. In the relativistic positioning systems (RPS), the space-time position of any user (ship, spacecraft, and so on) can be calculated with the help of four satellites, which broadcast their proper times by means of codified electromagnetic signals. In this thesis, we have simulated satellite 4-tuples of the GPS and GALILEO constellations. If a user receives the signals from four satellites simultaneously, the emission proper times read -after decoding- are the user "emission coordinates". In order to find the user "positioning coordinates", in an appropriate almost inertial reference system, there are two possibilities: (a) the explicit relation between positioning and emission coordinates (broadcast by the satellites) is analytically found or (b) numerical codes are designed to calculate the positioning coordinates from the emission ones. Method (a) is only viable in simple ideal cases, whereas (b) allows us to consider realistic situations. In this thesis, we have designed numerical codes with the essential aim of studying two appropriate RPS, which may be generalized. Sometimes, there are two real users placed in different positions, which receive the same proper times from the same satellites; then, we say that there is bifurcation, and additional data are needed to choose the real user position. In this thesis, bifurcation is studied in detail. We have analyzed in depth two RPS models; in both, it is considered that the satellites move in the Schwarzschild's space
Hybrid Reactor Simulation of Boiling Water Reactor Power Oscillations
Huang Zhengyu; Edwards, Robert M.
2003-08-15
Hybrid reactor simulation (HRS) of boiling water reactor (BWR) instabilities, including in-phase and out-of-phase (OOP) oscillations, has been implemented on The Pennsylvania State University TRIGA reactor. The TRIGA reactor's power response is used to simulate reactor neutron dynamics for in-phase oscillation or the fundamental mode of the reactor modal kinetics for OOP oscillations. The reactor power signal drives a real-time boiling channel simulation, and the calculated reactivity feedback is in turn fed into the TRIGA reactor via an experimental changeable reactivity device. The thermal-hydraulic dynamics, together with first harmonic mode power dynamics, is digitally simulated in the real-time environment. The real-time digital simulation of boiling channel thermal hydraulics is performed by solving constitutive equations for different regions in the channel and is realized by a high-performance personal computer. The nonlinearity of the thermal-hydraulic model ensures the capability to simulate the oscillation phenomena, limit cycle and OOP oscillation, in BWR nuclear power plants. By adjusting reactivity feedback gains for both modes, various oscillation combinations can be realized in the experiment. The dynamics of axially lumped power distribution over the core is displayed in three-dimensional graphs. The HRS reactor power response mimics the BWR core-wide power stability phenomena. In the OOP oscillation HRS, the combination of reactor response and the simulated first harmonic power using shaping functions mimics BWR regional power oscillations. With this HRS testbed, a monitoring and/or control system designed for BWR power oscillations can be experimentally tested and verified.
Rocket Engine Numerical Simulator (RENS)
NASA Technical Reports Server (NTRS)
Davidian, Kenneth O.
1997-01-01
Work is being done at three universities to help today's NASA engineers use the knowledge and experience of their Apolloera predecessors in designing liquid rocket engines. Ground-breaking work is being done in important subject areas to create a prototype of the most important functions for the Rocket Engine Numerical Simulator (RENS). The goal of RENS is to develop an interactive, realtime application that engineers can utilize for comprehensive preliminary propulsion system design functions. RENS will employ computer science and artificial intelligence research in knowledge acquisition, computer code parallelization and objectification, expert system architecture design, and object-oriented programming. In 1995, a 3year grant from the NASA Lewis Research Center was awarded to Dr. Douglas Moreman and Dr. John Dyer of Southern University at Baton Rouge, Louisiana, to begin acquiring knowledge in liquid rocket propulsion systems. Resources of the University of West Florida in Pensacola were enlisted to begin the process of enlisting knowledge from senior NASA engineers who are recognized experts in liquid rocket engine propulsion systems. Dr. John Coffey of the University of West Florida is utilizing his expertise in interviewing and concept mapping techniques to encode, classify, and integrate information obtained through personal interviews. The expertise extracted from the NASA engineers has been put into concept maps with supporting textual, audio, graphic, and video material. A fundamental concept map was delivered by the end of the first year of work and the development of maps containing increasing amounts of information is continuing. Find out more information about this work at the Southern University/University of West Florida. In 1996, the Southern University/University of West Florida team conducted a 4day group interview with a panel of five experts to discuss failures of the RL10 rocket engine in conjunction with the Centaur launch vehicle. The
Numerical wind speed simulation model
Ramsdell, J.V.; Athey, G.F.; Ballinger, M.Y.
1981-09-01
A relatively simple stochastic model for simulating wind speed time series that can be used as an alternative to time series from representative locations is described in this report. The model incorporates systematic seasonal variation of the mean wind, its standard deviation, and the correlation speeds. It also incorporates systematic diurnal variation of the mean speed and standard deviation. To demonstrate the model capabilities, simulations were made using model parameters derived from data collected at the Hanford Meteorology Station, and results of analysis of simulated and actual data were compared.
NUMERICAL SIMULATION OF LARYNGEAL FLOW
In this study, we have investigated laryngeal air flows by numerically solving the corresponding Navier-Stokes equations expressed in a two-dimensional cylindrical coordinate system. The glottal aperture, defined by the geometry of the vocal folds was allowed to change with the v...
A numerical method for cardiac mechanoelectric simulations.
Pathmanathan, Pras; Whiteley, Jonathan P
2009-05-01
Much effort has been devoted to developing numerical techniques for solving the equations that describe cardiac electrophysiology, namely the monodomain equations and bidomain equations. Only a limited selection of publications, however, address the development of numerical techniques for mechanoelectric simulations where cardiac electrophysiology is coupled with deformation of cardiac tissue. One problem commonly encountered in mechanoelectric simulations is instability of the coupled numerical scheme. In this study, we develop a stable numerical scheme for mechanoelectric simulations. A number of convergence tests are carried out using this stable technique for simulations where deformations are of the magnitude typically observed in a beating heart. These convergence tests demonstrate that accurate computation of tissue deformation requires a nodal spacing of around 1 mm in the mesh used to calculate tissue deformation. This is a much finer computational grid than has previously been acknowledged, and has implications for the computational efficiency of the resulting numerical scheme. PMID:19263223
Reactor Simulator Integration and Testing
NASA Technical Reports Server (NTRS)
Schoenfield, M. P.; Webster, K. L.; Pearson, J. B.
2013-01-01
As part of the Nuclear Systems Office Fission Surface Power Technology Demonstration Unit (TDU) project, a reactor simulator (RxSim) test loop was designed and built to perform integrated testing of the TDU components. In particular, the objectives of RxSim testing were to verify the operation of the core simulator, the instrumentation and control system, and the ground support gas and vacuum test equipment. In addition, it was decided to include a thermal test of a cold trap purification design and a pump performance test at pump voltages up to 150 V because the targeted mass flow rate of 1.75 kg/s was not obtained in the RxSim at the originally constrained voltage of 120 V. This Technical Memorandum summarizes RxSim testing. The gas and vacuum ground support test equipment performed effectively in NaK fill, loop pressurization, and NaK drain operations. The instrumentation and control system effectively controlled loop temperature and flow rates or pump voltage to targeted settings. The cold trap design was able to obtain the targeted cold temperature of 480 K. An outlet temperature of 636 K was obtained, which was lower than the predicted 750 K but 156 K higher than the cold temperature, indicating the design provided some heat regeneration. The annular linear induction pump tested was able to produce a maximum flow rate of 1.53 kg/s at 800 K when operated at 150 V and 53 Hz.
Numerical simulation of conservation laws
NASA Technical Reports Server (NTRS)
Chang, Sin-Chung; To, Wai-Ming
1992-01-01
A new numerical framework for solving conservation laws is being developed. This new approach differs substantially from the well established methods, i.e., finite difference, finite volume, finite element and spectral methods, in both concept and methodology. The key features of the current scheme include: (1) direct discretization of the integral forms of conservation laws, (2) treating space and time on the same footing, (3) flux conservation in space and time, and (4) unified treatment of the convection and diffusion fluxes. The model equation considered in the initial study is the standard one dimensional unsteady constant-coefficient convection-diffusion equation. In a stability study, it is shown that the principal and spurious amplification factors of the current scheme, respectively, are structurally similar to those of the leapfrog/DuFort-Frankel scheme. As a result, the current scheme has no numerical diffusion in the special case of pure convection and is unconditionally stable in the special case of pure diffusion. Assuming smooth initial data, it will be shown theoretically and numerically that, by using an easily determined optimal time step, the accuracy of the current scheme may reach a level which is several orders of magnitude higher than that of the MacCormack scheme, with virtually identical operation count.
Coincidental match of numerical simulation and physics
NASA Astrophysics Data System (ADS)
Pierre, B.; Gudmundsson, J. S.
2010-08-01
Consequences of rapid pressure transients in pipelines range from increased fatigue to leakages and to complete ruptures of pipeline. Therefore, accurate predictions of rapid pressure transients in pipelines using numerical simulations are critical. State of the art modelling of pressure transient in general, and water hammer in particular include unsteady friction in addition to the steady frictional pressure drop, and numerical simulations rely on the method of characteristics. Comparison of rapid pressure transient calculations by the method of characteristics and a selected high resolution finite volume method highlights issues related to modelling of pressure waves and illustrates that matches between numerical simulations and physics are purely coincidental.
NUMERICAL SIMULATIONS OF CHROMOSPHERIC MICROFLARES
Jiang, R. L.; Fang, C.; Chen, P. F.
2010-02-20
With gravity, ionization, and radiation being considered, we perform 2.5 dimensional (2.5D) compressible resistive magnetohydrodynamic (MHD) simulations of chromospheric magnetic reconnection using the CIP-MOCCT scheme. The temperature distribution of the quiet-Sun atmospheric model VALC and the helium abundance (10%) are adopted. Our 2.5D MHD simulation reproduces qualitatively the temperature enhancement observed in chromospheric microflares. The temperature enhancement DELTAT is demonstrated to be sensitive to the background magnetic field, whereas the total evolution time DELTAt is sensitive to the magnitude of the anomalous resistivity. Moreover, we found a scaling law, which is described as DELTAT/DELTAt {approx} n{sub H} {sup -1.5} B {sup 2.1}eta{sub 0} {sup 0.88}. Our results also indicate that the velocity of the upward jet is much greater than that of the downward jet, and the X-point may move up or down.
Numerical simulation of jet noise
NASA Astrophysics Data System (ADS)
Paliath, Umesh
In the present work, computational aeroacoustics and parallel computers are used to conduct a study of flow-induced noise from different jet nozzle geometries. The nozzle is included as part of the computational domain. This is important to predict jet noise from nozzles associated with military aircraft engines. The Detached Eddy Simulation (DES) approach is used to simulate both the jet nozzle internal and external flows as well as the jet plume. This methodology allows the turbulence model to transition from an unsteady Reynolds Averaged Navier-Stokes (URANS) method for attached boundary layers to a Large Eddy Simulation (LES) in separated regions. Thus, it is ideally suited to jet flow simulations where the nozzle is included. Both cylindrical polar and Cartesian coordinate systems are used. A spectral method is used to avoid the centerline singularity when using the cylindrical coordinate system. The one equation Spalart-Allmaras turbulence model, in DES mode, is used to describe the evolution of the turbulent eddy viscosity. An explicit 4th order Runge-Kutta time marching scheme is used. For spatial discritization the Dispersion Relation Preserving scheme(DRP) is used. The farfield sound is evaluated using the Ffowcs Williams-Hawkings permeable surface wave extrapolation method. This permits the noise to be predicted at large distances from the jet based on fluctuations in the jets near field. The present work includes a study of the effect of different nozzle geometries such as axisymmetric/non-axisymmetric and planar/non-planar exits on the far field noise predictions. Also the effect of operating conditions such as a heated/unheated jet, the effect of forward flight, a jet flow at an angle of attack, and the effect of a supersonic exit Mach number, are included in the study.
Numerical tools for atomistic simulations.
Fang, H.; Gullett, Philip Michael; Slepoy, Alexander; Horstemeyer, Mark F.; Baskes, Michael I.; Wagner, Gregory John; Li, Mo
2004-01-01
The final report for a Laboratory Directed Research and Development project entitled 'Parallel Atomistic Computing for Failure Analysis of Micromachines' is presented. In this project, atomistic algorithms for parallel computers were developed to assist in quantification of microstructure-property relations related to weapon micro-components. With these and other serial computing tools, we are performing atomistic simulations of various sizes, geometries, materials, and boundary conditions. These tools provide the capability to handle the different size-scale effects required to predict failure. Nonlocal continuum models have been proposed to address this problem; however, they are phenomenological in nature and are difficult to validate for micro-scale components. Our goal is to separately quantify damage nucleation, growth, and coalescence mechanisms to provide a basis for macro-scale continuum models that will be used for micromachine design. Because micro-component experiments are difficult, a systematic computational study that employs Monte Carlo methods, molecular statics, and molecular dynamics (EAM and MEAM) simulations to compute continuum quantities will provide mechanism-property relations associated with the following parameters: specimen size, number of grains, crystal orientation, strain rates, temperature, defect nearest neighbor distance, void/crack size, chemical state, and stress state. This study will quantify sizescale effects from nanometers to microns in terms of damage progression and thus potentially allow for optimized micro-machine designs that are more reliable and have higher fidelity in terms of strength. In order to accomplish this task, several atomistic methods needed to be developed and evaluated to cover the range of defects, strain rates, temperatures, and sizes that a material may see in micro-machines. Therefore we are providing a complete set of tools for large scale atomistic simulations that include pre-processing of
Numerical simulation of transitional flow
NASA Technical Reports Server (NTRS)
Biringen, Sedat
1986-01-01
The applicability of active control of transition by periodic suction-blowing is investigated via direct simulations of the Navier-Stokes equations. The time-evolution of finite-amplitude disturbances in plane channel flow is compared in detail with and without control. The analysis indicates that, for relatively small three-dimensional amplitudes, a two-dimensional control effectively reduces disturbance growth rates even for linearly unstable Reynolds numbers. After the flow goes through secondary instability, three-dimensional control seems necessary to stabilize the flow. An investigation of the temperature field suggests that passive temperature contamination is operative to reflect the flow dynamics during transition.
Numerical Simulations of Thermographic Responses in Composites
NASA Technical Reports Server (NTRS)
Winfree, William P.; Cramer, K. Elliot; Zalameda, Joseph N.; Howell, Patricia A.
2015-01-01
Numerical simulations of thermographic responses in composite materials have been a useful for evaluating and optimizing thermographic analysis techniques. Numerical solutions are particularly beneficial for thermographic techniques, since the fabrication of specimens with realistic flaws is difficult. Simulations are presented with different ply layups that incorporated the anisotropic thermal properties that exist in each ply. The results are compared to analytical series solutions and thermal measurements on composites with flat bottom holes and delaminations.
Numerical simulations of the reditron
NASA Astrophysics Data System (ADS)
Kwan, Thomas J. T.; Davis, Harold A.
1988-04-01
The reflected-electrons discrimination microwave generator (reditron) is a high-power, narrow-band, and single-mode microwave generation that makes exclusive use of the oscillatory character of the virtual-cathode of a relativistic electron beam. The complex, nonlinear character of the virtual-cathode device necessitates particle-in-cell plasma simulation techniques. Investigations indicate two sources of the radiation: (1) the trapped electrons reflexing between the real and virtual cathodes, and (2) the oscillation of the virtual cathode. In the conventional design, the two mechanisms coexist and interfere with each other destructively, causing degradation of the efficiency of microwave generation. The authors have investigated a configuration with a slotted, thick anode and an external magnetic field, which effectively eliminates the reflexing electrons. Two-dimensional particle-in-cell simulations showed that such a configuration exploits the oscillation of the virtual cathode exclusively, and it generates single-mode, narrowbandwidth, and high-power microwave radiation with a potential efficiency over 10 percent. It was found that further optimization could be achieved by the use of a density (current) modulated electron beam at appropriate frequencies.
Numerical simulations of disordered superconductors
Bedell, K.S.; Gubernatis, J.E.; Scalettar, R.T.; Zimanyi, G.T.
1997-12-01
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The authors carried out Monte Carlo studies of the critical behavior of superfluid {sup 4}He in aerogel. They found the superfluid density exponent increases in the presence of fractal disorder with a value roughly consistent with experimental results. They also addressed the localization of flux lines caused by splayed columnar pins. Using a Sine-Gordon-type of renormalization group study they obtained an analytic form for the critical temperature. They also determined the critical temperature from I-V characteristics obtained from a molecular dynamics simulation. The combined studies enabled one to construct the phase diagram as a function of interaction strength, temperature, and disorder. They also employed the recently developed mapping between boson world-lines and the flux motion to use quantum Monte Carlo simulations to analyze localization in the presence of disorder. From measurements of the transverse flux line wandering, they determined the critical ratio of columnar to point disorder strength needed to localize the bosons.
Numerical simulations of protostellar jets
NASA Astrophysics Data System (ADS)
Suttner, Gerhard; Smith, Michael D.; Yorke, Harold W.; Zinnecker, Hans
Molecular jets announce the successful birth of a protostar. We develop here a model for the jets and their environments, adapting a multi-dimensional hydrocode to follow the molecular-atomic transitions of hydrogen. We examine powerful outflows into dense gas. The cocoon which forms around a jet is a very low density cavity of atomic gas. These atoms originate from strong shocks which dissociate the molecules. The rest of the molecules are either within the jet or swept up into very thin layers. Pulsed jets produce wider cavities and molecular layers which can grow onto resolvable jet knots. Three-dimensional simulations produce shocked molecular knots, distorted and multiple bow shocks and arclike structures. Spectroscopic and excitation properties of the hydrogen molecules are calculated. In the infrared, strong emission is seen from shocks within the jet (when pulsed) as well as from discrete regions along the cavity walls. Excitation, as measured by line ratios, is not generally constant. Broad double-peaked, shifted emission lines are predicted. The jet model for protostellar outflows is confronted with the constraints imposed by CO spectroscopic observations. From the three dimensional simulations we calculate line profiles and construct position-velocity diagrams for the (low-J) CO transitions. We find (1) the profiles imply power law variation of integrated brightness with velocity over a wide range of velocities, (2) the velocity field resembles a `Hubble Law' and (3) a hollow-shell structure at low velocities becomes an elongated lobe at high velocities. Deviations from the simple power law dependence of integrated brightness versus velocity occur at high velocities in our simulations. The curve first dips to a shallow minimum and then rises rapidly and peaks sharply. Reanalysis of the NGC 2264G and Cepheus E data confirm these predictions. We identify these two features with a jet-ambient shear layer and the jet itself. A deeper analysis reveals that
Numerical simulations of pendant droplets
NASA Astrophysics Data System (ADS)
Pena, Carlos; Kahouadji, Lyes; Matar, Omar; Chergui, Jalel; Juric, Damir; Shin, Seungwon
2015-11-01
We simulate the evolution of a three-dimensional pendant droplet through pinch-off using a new parallel two-phase flow solver called BLUE. The parallelization of the code is based on the technique of algebraic domain decomposition where the velocity field is solved by a parallel GMRes method for the viscous terms and the pressure by a parallel multigrid/GMRes method. Communication is handled by MPI message passing procedures. The method for the treatment of the fluid interfaces uses a hybrid Front Tracking/Level Set technique which defines the interface both by a discontinuous density field as well as by a local triangular Lagrangian mesh. This structure allows the interface to undergo large deformations including the rupture and coalescence of fluid interfaces. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1.
Numerical simulation of plasma treatment of charge used in vitrification of radioactive wastes
Krasovskaya, L.I.; Svidunovich, N.A.; Vasil`kov, V.E.
1995-12-01
The process of plasma treatment of charge used in vitrification of radioactive wastes is simulated numerically. Optimum conditions providing heating of particles in the charge to vitrification temperatures are determined for a 200-k W reactor.
Numerical Simulation of Nanostructure Growth
NASA Technical Reports Server (NTRS)
Hwang, Helen H.; Bose, Deepak; Govindan, T. R.; Meyyappan, M.
2004-01-01
Nanoscale structures, such as nanowires and carbon nanotubes (CNTs), are often grown in gaseous or plasma environments. Successful growth of these structures is defined by achieving a specified crystallinity or chirality, size or diameter, alignment, etc., which in turn depend on gas mixture ratios. pressure, flow rate, substrate temperature, and other operating conditions. To date, there has not been a rigorous growth model that addresses the specific concerns of crystalline nanowire growth, while demonstrating the correct trends of the processing conditions on growth rates. Most crystal growth models are based on the Burton, Cabrera, and Frank (BCF) method, where adatoms are incorporated into a growing crystal at surface steps or spirals. When the supersaturation of the vapor is high, islands nucleate to form steps, and these steps subsequently spread (grow). The overall bulk growth rate is determined by solving for the evolving motion of the steps. Our approach is to use a phase field model to simulate the growth of finite sized nanowire crystals, linking the free energy equation with the diffusion equation of the adatoms. The phase field method solves for an order parameter that defines the evolving steps in a concentration field. This eliminates the need for explicit front tracking/location, or complicated shadowing routines, both of which can be computationally expensive, particularly in higher dimensions. We will present results demonstrating the effect of process conditions, such as substrate temperature, vapor supersaturation, etc. on the evolving morphologies and overall growth rates of the nanostructures.
NUMERICAL SIMULATIONS OF SPICULE ACCELERATION
Guerreiro, N.; Carlsson, M.; Hansteen, V. E-mail: mats.carlsson@astro.uio.no
2013-04-01
Observations in the H{alpha} line of hydrogen and the H and K lines of singly ionized calcium on the solar limb reveal the existence of structures with jet-like behavior, usually designated as spicules. The driving mechanism for such structures remains poorly understood. Sterling et al. shed some light on the problem mimicking reconnection events in the chromosphere with a one-dimensional code by injecting energy with different spatial and temporal distributions and tracing the thermodynamic evolution of the upper chromospheric plasma. They found three different classes of jets resulting from these injections. We follow their approach but improve the physical description by including non-LTE cooling in strong spectral lines and non-equilibrium hydrogen ionization. Increased cooling and conversion of injected energy into hydrogen ionization energy instead of thermal energy both lead to weaker jets and smaller final extent of the spicules compared with Sterling et al. In our simulations we find different behavior depending on the timescale for hydrogen ionization/recombination. Radiation-driven ionization fronts also form.
Computer simulation of FCC riser reactors.
Chang, S. L.; Golchert, B.; Lottes, S. A.; Petrick, M.; Zhou, C. Q.
1999-04-20
A three-dimensional computational fluid dynamics (CFD) code, ICRKFLO, was developed to simulate the multiphase reacting flow system in a fluid catalytic cracking (FCC) riser reactor. The code solve flow properties based on fundamental conservation laws of mass, momentum, and energy for gas, liquid, and solid phases. Useful phenomenological models were developed to represent the controlling FCC processes, including droplet dispersion and evaporation, particle-solid interactions, and interfacial heat transfer between gas, droplets, and particles. Techniques were also developed to facilitate numerical calculations. These techniques include a hybrid flow-kinetic treatment to include detailed kinetic calculations, a time-integral approach to overcome numerical stiffness problems of chemical reactions, and a sectional coupling and blocked-cell technique for handling complex geometry. The copyrighted ICRKFLO software has been validated with experimental data from pilot- and commercial-scale FCC units. The code can be used to evaluate the impacts of design and operating conditions on the production of gasoline and other oil products.
Boundary acquisition for setup of numerical simulation
Diegert, C.
1997-12-31
The author presents a work flow diagram that includes a path that begins with taking experimental measurements, and ends with obtaining insight from results produced by numerical simulation. Two examples illustrate this path: (1) Three-dimensional imaging measurement at micron scale, using X-ray tomography, provides information on the boundaries of irregularly-shaped alumina oxide particles held in an epoxy matrix. A subsequent numerical simulation predicts the electrical field concentrations that would occur in the observed particle configurations. (2) Three-dimensional imaging measurement at meter scale, again using X-ray tomography, provides information on the boundaries fossilized bone fragments in a Parasaurolophus crest recently discovered in New Mexico. A subsequent numerical simulation predicts acoustic response of the elaborate internal structure of nasal passageways defined by the fossil record. The author must both add value, and must change the format of the three-dimensional imaging measurements before the define the geometric boundary initial conditions for the automatic mesh generation, and subsequent numerical simulation. The author applies a variety of filters and statistical classification algorithms to estimate the extents of the structures relevant to the subsequent numerical simulation, and capture these extents as faceted geometries. The author will describe the particular combination of manual and automatic methods used in the above two examples.
Numerical simulations of cryogenic cavitating flows
NASA Astrophysics Data System (ADS)
Kim, Hyunji; Kim, Hyeongjun; Min, Daeho; Kim, Chongam
2015-12-01
The present study deals with a numerical method for cryogenic cavitating flows. Recently, we have developed an accurate and efficient baseline numerical scheme for all-speed water-gas two-phase flows. By extending such progress, we modify the numerical dissipations to be properly scaled so that it does not show any deficiencies in low Mach number regions. For dealing with cryogenic two-phase flows, previous EOS-dependent shock discontinuity sensing term is replaced with a newly designed EOS-free one. To validate the proposed numerical method, cryogenic cavitating flows around hydrofoil are computed and the pressure and temperature depression effect in cryogenic cavitation are demonstrated. Compared with Hord's experimental data, computed results are turned out to be satisfactory. Afterwards, numerical simulations of flow around KARI turbopump inducer in liquid rocket are carried out under various flow conditions with water and cryogenic fluids, and the difference in inducer flow physics depending on the working fluids are examined.
NASA Technical Reports Server (NTRS)
Gokoglu, S. A.; Kuczmarski, M.; Veitch, L.; Tsui, P.; Chait, A.
1990-01-01
The computational fluid dynamics (CFD) code FLUENT is adopted to simulate a cylindrical upflow reactor designed for chemical vapor deposition (CVD) on monofilaments. Equilibrium temperature profiles along the fiber and quartz reactor wall are experimentally measured and used as boundary conditions in numerical simulations. Two-dimensional axisymmetric flow and temperature fields are calculated for hydrogen and argon; the effect of free convection is assessed. The gas and surface chemistry is included for predicting silicon deposition from silane. The model predictions are compared with experimentally measured silicon CVD rates. Inferences are made for optimum conditions to obtain uniformity.
Reliability of Complex Nonlinear Numerical Simulations
NASA Technical Reports Server (NTRS)
Yee, H. C.
2004-01-01
This work describes some of the procedure to ensure a higher level of confidence in the predictability and reliability (PAR) of numerical simulation of multiscale complex nonlinear problems. The focus is on relating PAR of numerical simulations with complex nonlinear phenomena of numerics. To isolate sources of numerical uncertainties, the possible discrepancy between the chosen partial differential equation (PDE) model and the real physics and/or experimental data is set aside. The discussion is restricted to how well numerical schemes can mimic the solution behavior of the underlying PDE model for finite time steps and grid spacings. The situation is complicated by the fact that the available theory for the understanding of nonlinear behavior of numerics is not at a stage to fully analyze the nonlinear Euler and Navier-Stokes equations. The discussion is based on the knowledge gained for nonlinear model problems with known analytical solutions to identify and explain the possible sources and remedies of numerical uncertainties in practical computations. Examples relevant to turbulent flow computations are included.
Numerically simulating the sandwich plate system structures
NASA Astrophysics Data System (ADS)
Feng, Guo-Qing; Li, Gang; Liu, Zhi-Hui; Niu, Huai-Lei; Li, Chen-Feng
2010-09-01
Sandwich plate systems (SPS) are advanced materials that have begun to receive extensive attention in naval architecture and ocean engineering. At present, according to the rules of classification societies, a mixture of shell and solid elements are required to simulate an SPS. Based on the principle of stiffness decomposition, a new numerical simulation method for shell elements was proposed. In accordance with the principle of stiffness decomposition, the total stiffness can be decomposed into the bending stiffness and shear stiffness. Displacement and stress response related to bending stiffness was calculated with the laminated shell element. Displacement and stress response due to shear was calculated by use of a computational code write by FORTRAN language. Then the total displacement and stress response for the SPS was obtained by adding together these two parts of total displacement and stress. Finally, a rectangular SPS plate and a double-bottom structure were used for a simulation. The results show that the deflection simulated by the elements proposed in the paper is larger than the same simulated by solid elements and the analytical solution according to Hoff theory and approximate to the same simulated by the mixture of shell-solid elements, and the stress simulated by the elements proposed in the paper is approximate to the other simulating methods. So compared with calculations based on a mixture of shell and solid elements, the numerical simulation method given in the paper is more efficient and easier to do.
Numerical propulsion system simulation - An interdisciplinary approach
NASA Technical Reports Server (NTRS)
Nichols, Lester D.; Chamis, Christos C.
1991-01-01
The tremendous progress being made in computational engineering and the rapid growth in computing power that is resulting from parallel processing now make it feasible to consider the use of computer simulations to gain insights into the complex interactions in aerospace propulsion systems and to evaluate new concepts early in the design process before a commitment to hardware is made. Described here is a NASA initiative to develop a Numerical Propulsion System Simulation (NPSS) capability.
Numerical propulsion system simulation: An interdisciplinary approach
NASA Technical Reports Server (NTRS)
Nichols, Lester D.; Chamis, Christos C.
1991-01-01
The tremendous progress being made in computational engineering and the rapid growth in computing power that is resulting from parallel processing now make it feasible to consider the use of computer simulations to gain insights into the complex interactions in aerospace propulsion systems and to evaluate new concepts early in the design process before a commitment to hardware is made. Described here is a NASA initiative to develop a Numerical Propulsion System Simulation (NPSS) capability.
A numerical simulation of galaxy subcluster mergers
NASA Technical Reports Server (NTRS)
Roettiger, Kurt; Burns, Jack O.; Loken, Chris
1993-01-01
We present preliminary results of a 3-D numerical simulation of two merging subclusters of galaxies. By self-consistently modelling the intracluster gas and dark matter dynamics, we hope to gain insight as to how the dynamics of both relate to such observables as the cluster x-ray emission, radio source morphology, and velocity dispersions.
IRIS Spectrum Line Plot - Numeric Simulation
This video is similar to the IRIS Spectrum Line Plot video at http://www.youtube.com/watch?v=E4V_vF3qMSI, but now as derived from a numerical simulation of the Sun by the University of Oslo. Credit...
Simple Numerical Simulation of Strain Measurement
NASA Technical Reports Server (NTRS)
Tai, H.
2002-01-01
By adopting the basic principle of the reflection (and transmission) of a plane polarized electromagnetic wave incident normal to a stack of films of alternating refractive index, a simple numerical code was written to simulate the maximum reflectivity (transmittivity) of a fiber optic Bragg grating corresponding to various non-uniform strain conditions including photo-elastic effect in certain cases.
Numerical simulation of plasma opening switches
Mason, R.J.; Jones, M.E.; Bergman, C.D.
1989-01-01
Plasma Opening Switches have been examined numerically with the aid of the ANTHEM plasma simulation model. A generic bi-cylindrical switch is studied. The switching of generator pulses ranging from 50 ns to 1 ..mu..sec is reviewed, for a variety of plasma fill lengths and densities, and for a range of resistive loads. 7 refs., 9 figs.
Simulation of a marine nuclear reactor
Kusunoki, Tsuyoshi; Kyouya, Masahiko; Kobayashi, Hideo; Ochiai, Masaaki
1995-02-01
A Nuclear-powered ship Engineering Simulation SYstem (NESSY) has been developed by the Japan Atomic Energy Research Institute as an advanced design tool for research and development of future marine reactors. A marine reactor must respond to changing loads and to the ship`s motions because of the ship`s maneuvering and its presence in a marine environment. The NESSY has combined programs for the reactor plant behavior calculations and the ship`s motion calculations. Thus, it can simulate reactor power fluctuations caused by changing loads and the ship`s motions. It can also simulate the behavior of water in the pressurizer and steam generators. This water sloshes in response to the ship`s motions. The performance of NESSY has been verified by comparing the simulation calculations with the measured data obtained by experiments performed using the nuclear ship Mutsu. The effects of changing loads and the ship`s motions on the reactor behavior can be accurately simulated by NESSY.
Numerical simulation of supersonic boundary layer transition
NASA Technical Reports Server (NTRS)
Guo, Y.; Adams, N. A.; Sandham, N. D.; Kleiser, L.
1994-01-01
The present contribution reviews some of the recent progress obtained at our group in the direct numerical simulation (DNS) of compressible boundary layer transition. Elements of the different simulation approaches and numerical techniques employed are surveyed. Temporal and spatial simulations, as well as comparisons with results obtained from Parabolized Stability Equations, are discussed. DNS results are given for flat plate boundary layers in the Mach number range 1.6 to 4.5. A temporal DNS at Mach 4.5 has been continued through breakdown all the way to the turbulent stage. In addition results obtained with a recently developed extended temporal DNS approach are presented, which takes into account some nonparallel effects of a growing boundary layer. Results from this approach are quite close to those of spatial DNS, while preserving the efficiency of the temporal DNS.
Numerical Simulation of a Convective Turbulence Encounter
NASA Technical Reports Server (NTRS)
Proctor, Fred H.; Hamilton, David W.; Bowles, Roland L.
2002-01-01
A numerical simulation of a convective turbulence event is investigated and compared with observational data. The numerical results show severe turbulence of similar scale and intensity to that encountered during the test flight. This turbulence is associated with buoyant plumes that penetrate the upper-level thunderstorm outflow. The simulated radar reflectivity compares well with that obtained from the aircraft's onboard radar. Resolved scales of motion as small as 50 m are needed in order to accurately diagnose aircraft normal load accelerations. Given this requirement, realistic turbulence fields may be created by merging subgrid-scales of turbulence to a convective-cloud simulation. A hazard algorithm for use with model data sets is demonstrated. The algorithm diagnoses the RMS normal loads from second moments of the vertical velocity field and is independent of aircraft motion.
Numerical simulation of centrifugal casting of pipes
NASA Astrophysics Data System (ADS)
Kaschnitz, E.
2012-07-01
A numerical simulation model for the horizontal centrifugal pipe casting process was developed with the commercial simulation package Flow3D. It considers - additionally to mass, energy and momentum conservation equations and free surface tracking - the fast radial and slower horizontal movement of the mold. The iron inflow is not steady state but time dependent. Of special importance is the friction between the liquid and the mold in connection with the viscosity and turbulence of the iron. Experiments with the mold at controlled revolution speeds were carried out using a high-speed camera. From these experiments friction coefficients for the description of the interaction between mold and melt were obtained. With the simulation model, the influence of typical process parameters (e.g. melts inflow, mold movement, melt temperature, cooling media) on the wall thickness of the pipes can be studied. The comparison to results of pipes from production shows a good agreement between simulation and reality.
Numerical Simulation of a Tornado Generating Supercell
NASA Technical Reports Server (NTRS)
Proctor, Fred H.; Ahmad, Nashat N.; LimonDuparcmeur, Fanny M.
2012-01-01
The development of tornadoes from a tornado generating supercell is investigated with a large eddy simulation weather model. Numerical simulations are initialized with a sounding representing the environment of a tornado producing supercell that affected North Carolina and Virginia during the Spring of 2011. The structure of the simulated storm was very similar to that of a classic supercell, and compared favorably to the storm that affected the vicinity of Raleigh, North Carolina. The presence of mid-level moisture was found to be important in determining whether a supercell would generate tornadoes. The simulations generated multiple tornadoes, including cyclonic-anticyclonic pairs. The structure and the evolution of these tornadoes are examined during their lifecycle.
Issues in Numerical Simulation of Fire Suppression
Tieszen, S.R.; Lopez, A.R.
1999-04-12
This paper outlines general physical and computational issues associated with performing numerical simulation of fire suppression. Fire suppression encompasses a broad range of chemistry and physics over a large range of time and length scales. The authors discuss the dominant physical/chemical processes important to fire suppression that must be captured by a fire suppression model to be of engineering usefulness. First-principles solutions are not possible due to computational limitations, even with the new generation of tera-flop computers. A basic strategy combining computational fluid dynamics (CFD) simulation techniques with sub-grid model approximations for processes that have length scales unresolvable by gridding is presented.
Numerical simulations of catastrophic disruption: Recent results
NASA Technical Reports Server (NTRS)
Benz, W.; Asphaug, E.; Ryan, E. V.
1994-01-01
Numerical simulations have been used to study high velocity two-body impacts. In this paper, a two-dimensional Largrangian finite difference hydro-code and a three-dimensional smooth particle hydro-code (SPH) are described and initial results reported. These codes can be, and have been, used to make specific predictions about particular objects in our solar system. But more significantly, they allow us to explore a broad range of collisional events. Certain parameters (size, time) can be studied only over a very restricted range within the laboratory; other parameters (initial spin, low gravity, exotic structure or composition) are difficult to study at all experimentally. The outcomes of numerical simulations lead to a more general and accurate understanding of impacts in their many forms.
The Consortium for Advanced Simulation of Light Water Reactors
Ronaldo Szilard; Hongbin Zhang; Doug Kothe; Paul Turinsky
2011-10-01
The Consortium for Advanced Simulation of Light Water Reactors (CASL) is a DOE Energy Innovation Hub for modeling and simulation of nuclear reactors. It brings together an exceptionally capable team from national labs, industry and academia that will apply existing modeling and simulation capabilities and develop advanced capabilities to create a usable environment for predictive simulation of light water reactors (LWRs). This environment, designated as the Virtual Environment for Reactor Applications (VERA), will incorporate science-based models, state-of-the-art numerical methods, modern computational science and engineering practices, and uncertainty quantification (UQ) and validation against data from operating pressurized water reactors (PWRs). It will couple state-of-the-art fuel performance, neutronics, thermal-hydraulics (T-H), and structural models with existing tools for systems and safety analysis and will be designed for implementation on both today's leadership-class computers and the advanced architecture platforms now under development by the DOE. CASL focuses on a set of challenge problems such as CRUD induced power shift and localized corrosion, grid-to-rod fretting fuel failures, pellet clad interaction, fuel assembly distortion, etc. that encompass the key phenomena limiting the performance of PWRs. It is expected that much of the capability developed will be applicable to other types of reactors. CASL's mission is to develop and apply modeling and simulation capabilities to address three critical areas of performance for nuclear power plants: (1) reduce capital and operating costs per unit energy by enabling power uprates and plant lifetime extension, (2) reduce nuclear waste volume generated by enabling higher fuel burnup, and (3) enhance nuclear safety by enabling high-fidelity predictive capability for component performance.
Numerical simulations of hyperfine transitions of antihydrogen
NASA Astrophysics Data System (ADS)
Kolbinger, B.; Capon, A.; Diermaier, M.; Lehner, S.; Malbrunot, C.; Massiczek, O.; Sauerzopf, C.; Simon, M. C.; Widmann, E.
2015-08-01
One of the ASACUSA (Atomic Spectroscopy And Collisions Using Slow Antiprotons) collaboration's goals is the measurement of the ground state hyperfine transition frequency in antihydrogen, the antimatter counterpart of one of the best known systems in physics. This high precision experiment yields a sensitive test of the fundamental symmetry of CPT. Numerical simulations of hyperfine transitions of antihydrogen atoms have been performed providing information on the required antihydrogen events and the achievable precision.
Numerical simulation of magma energy extraction
Hickox, C.E.
1991-01-01
The Magma Energy Program is a speculative endeavor regarding practical utility of electrical power production from the thermal energy which reside in magma. The systematic investigation has identified an number of research areas which have application to the utilization of magma energy and to the field of geothermal energy. Eight topics were identified which involve thermal processes and which are areas for the application of the techniques of numerical simulation. These areas are: (1) two-phase flow of the working fluid in the wellbore, (2) thermodynamic cycles for the production of electrical power, (3) optimization of the entire system, (4) solidification and fracturing of the magma caused by the energy extraction process, (5) heat transfer and fluid flow within an open, direct-contact, heat-exchanger, (6) thermal convection in the overlying geothermal region, (7) thermal convection within the magma body, and (8) induced natural convection near the thermal energy extraction device. Modeling issues have been identified which will require systematic investigation in order to develop the most appropriate strategies for numerical simulation. It appears that numerical simulations will be of ever increasing importance to the study of geothermal processes as the size and complexity of the systems of interest increase. It is anticipated that, in the future, greater emphasis will be placed on the numerical simulation of large-scale, three-dimensional, transient, mixed convection in viscous flows and porous media. Increased computational capabilities, e.g.; massively parallel computers, will allow for the detailed study of specific processes in fractured media, non-Darcy effects in porous media, and non-Newtonian effects. 23 refs., 13 figs., 1 tab.
Numerical Simulations of Ion Cloud Dynamics
NASA Astrophysics Data System (ADS)
Sillitoe, Nicolas; Hilico, Laurent
We explain how to perform accurate numerical simulations of ion cloud dynamics by discussing the relevant orders of magnitude of the characteristic times and frequencies involved in the problem and the computer requirement with respect to the ion cloud size. We then discuss integration algorithms and Coulomb force parallelization. We finally explain how to take into account collisions, cooling laser interaction and chemical reactions in a Monte Carlo approach and discuss how to use random number generators to that end.
Numerical Simulations of Boundary-Driven Dynamos
NASA Astrophysics Data System (ADS)
White, K.; Brummell, N.; Glatzmaier, G. A.
2012-12-01
An important topic of physics research is how magnetic fields are generated and maintained in the many astrophysical bodies where they are ubiquitously observed. Of particular interest, are reversals of magnetic fields of planets and stars, especially those of the Earth and the Sun. In an attempt to provide intuition on this problem, numerous physical dynamo experiments have been performed in different configurations. Recently, a tremendous breakthrough was made in the Von Karman sodium (VKS) experiments in France when the most realistic laboratory fluid dynamo to date was produced by driving an unconstrained flow in a cylinder of liquid sodium (Monchaux et al, 2007, PRL). One of the curiosities of the VKS experiment however is the effect of the composition of the impellers that drive the flow. Steel blades failed to produce a dynamo, but soft iron impellers, which have much higher magnetic permeability, succeeded. The role of the magnetic properties of the boundaries in boundary-driven dynamos is therefore clearly of interest. Kinematic and laminar numerical dynamo simulations (Giesecke et al, 2010, PRL & Gissinger et al, 2008 EPL) have shed some light but turbulent, nonlinear simulations are necessary. Roberts, Glatzmaier & Clune 2010 created a simplified model of the VKS setup by using three-dimensional numerical simulations in a spherical geometry with differential zonal motions of the boundary replacing the driving impellers of the VKS experiment. We have extended these numerical simulations further towards a more complete understanding of such boundary-forced dynamos. In particular, we have examined the effect of the magnetic boundary conditions - changes in the wall thickness, the magnetic permeability, and the electrical conductivity - on the mechanisms responsible for dynamo generation. Enhanced permeability, conductivity and wall thickness all help dynamo action to different degrees. We are further extending our investigations to asymmetric forcing to
Direct numerical simulation of a recorder.
Giordano, N
2013-02-01
The aeroacoustics of a recorder are studied using a direct numerical simulation based on the Navier-Stokes equations in two dimensions. Spatial maps for the air pressure and velocity give a detailed picture of vortex shedding near the labium. Changes in the spectrum as a result of variations in the blowing speed are also investigated. The results are in good semi-quantitative agreement with general results for these phenomena from experiments. PMID:23363126
Numerical simulation of droplet impact on interfaces
NASA Astrophysics Data System (ADS)
Kahouadji, Lyes; Che, Zhizhao; Matar, Omar; Shin, Seungwon; Chergui, Jalel; Juric, Damir
2015-11-01
Simulations of three-dimensional droplet impact on interfaces are carried out using BLUE, a massively-parallel code based on a hybrid Front-Tracking/Level-Set algorithm for Lagrangian tracking of arbitrarily deformable phase interfaces. High resolution numerical results show fine details and features of droplet ejection, crown formation and rim instability observed under similar experimental conditions. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1.
Numerical simulation of swept-wing flows
NASA Technical Reports Server (NTRS)
Reed, Helen L.
1991-01-01
The transition process characteristics of flows over swept wings were computationally modelled. The crossflow instability and crossflow/T-S wave interaction are analyzed through the numerical solution of the full three dimensional Navier-Stokes equations including unsteadiness, curvature, and sweep. The leading-edge region of a swept wing is considered in a three-dimensional spatial simulation with random disturbances as the initial conditions.
Numerical simulation and nasal air-conditioning
Keck, Tilman; Lindemann, Jörg
2011-01-01
Heating and humidification of the respiratory air are the main functions of the nasal airways in addition to cleansing and olfaction. Optimal nasal air conditioning is mandatory for an ideal pulmonary gas exchange in order to avoid desiccation and adhesion of the alveolar capillary bed. The complex three-dimensional anatomical structure of the nose makes it impossible to perform detailed in vivo studies on intranasal heating and humidification within the entire nasal airways applying various technical set-ups. The main problem of in vivo temperature and humidity measurements is a poor spatial and time resolution. Therefore, in vivo measurements are feasible only to a restricted extent, solely providing single temperature values as the complete nose is not entirely accessible. Therefore, data on the overall performance of the nose are only based on one single measurement within each nasal segment. In vivo measurements within the entire nose are not feasible. These serious technical issues concerning in vivo measurements led to a large number of numerical simulation projects in the last few years providing novel information about the complex functions of the nasal airways. In general, numerical simulations merely calculate predictions in a computational model, e.g. a realistic nose model, depending on the setting of the boundary conditions. Therefore, numerical simulations achieve only approximations of a possible real situation. The aim of this review is the synopsis of the technical expertise on the field of in vivo nasal air conditioning, the novel information of numerical simulations and the current state of knowledge on the influence of nasal and sinus surgery on nasal air conditioning. PMID:22073112
Coupled simulation of the reactor core using CUPID/MASTER
Lee, J. R.; Cho, H. K.; Yoon, H. Y.; Jeong, J. J.
2012-07-01
The CUPID is a component-scale thermal hydraulics code which is aimed for the analysis of transient two-phase flows in nuclear reactor components such as the reactor vessel, steam generator, containment. This code adopts a three-dimensional, transient, two-phase and three-field model, and includes physical models and correlations of the interfacial mass, momentum, and energy transfer for the closure. In the present paper, a multi-physics simulation was performed by coupling CUPID with a three dimensional neutron kinetics code, MASTER. MASTER is merged into CUPID as a dynamic link library (DLL). The APR1400 reactor core during a control rod drop/ejection accident was simulated as an example by adopting a porous media approach to employ a fuel assembly. The following sections present the numerical modeling for the reactor core, coupling of the kinetics code, and the simulation results. And also, a preliminary study for multi-scale simulation between CUPID and system-scaled thermal hydraulics code, MARS will be introduced as well. (authors)
Numerical analysis of hydrodynamics in a rotor-stator reactor for biodiesel synthesis
NASA Astrophysics Data System (ADS)
Wen, Zhuqing; Petera, Jerzy
2016-06-01
A rotor-stator spinning disk reactor for intensified biodiesel synthesis is described and numerically simulated. The reactor consists of two flat disks, located coaxially and parallel to each other with a gap ranging from 0.1 mm to 0.2 mm between the disks. The upper disk is located on a rotating shaft while the lower disk is stationary. The feed liquids, triglycerides (TG) and methanol are introduced coaxially along the center line of rotating disk and stationary disk, respectively. Fluid hydrodynamics in the reactor for synthesis of biodiesel from TG and methanol in the presence of a sodium hydroxide catalyst are simulated, using convection-diffusion-reaction species transport model by the CFD software ANSYS©Fluent v. 13.0. The effects of upper disk's spinning speed, gap size and flow rates at inlets are evaluated.
2001 Numerical Propulsion System Simulation Review
NASA Technical Reports Server (NTRS)
Lytle, John; Follen, Gregory; Naiman, Cynthia; Veres, Joseph; Owen, Karl; Lopez, Isaac
2002-01-01
The technologies necessary to enable detailed numerical simulations of complete propulsion systems are being developed at the NASA Glenn Research Center in cooperation with industry, academia and other government agencies. Large scale, detailed simulations will be of great value to the nation because they eliminate some of the costly testing required to develop and certify advanced propulsion systems. In addition, time and cost savings will be achieved by enabling design details to be evaluated early in the development process before a commitment is made to a specific design. This concept is called the Numerical Propulsion System Simulation (NPSS). NPSS consists of three main elements: (1) engineering models that enable multidisciplinary analysis of large subsystems and systems at various levels of detail, (2) a simulation environment that maximizes designer productivity, and (3) a cost-effective, high-performance computing platform. A fundamental requirement of the concept is that the simulations must be capable of overnight execution on easily accessible computing platforms. This will greatly facilitate the use of large-scale simulations in a design environment. This paper describes the current status of the NPSS with specific emphasis on the progress made over the past year on air breathing propulsion applications. Major accomplishments include the first formal release of the NPSS object-oriented architecture (NPSS Version 1) and the demonstration of a one order of magnitude reduction in computing cost-to-performance ratio using a cluster of personal computers. The paper also describes the future NPSS milestones, which include the simulation of space transportation propulsion systems in response to increased emphasis on safe, low cost access to space within NASA's Aerospace Technology Enterprise. In addition, the paper contains a summary of the feedback received from industry partners on the fiscal year 2000 effort and the actions taken over the past year to
2000 Numerical Propulsion System Simulation Review
NASA Technical Reports Server (NTRS)
Lytle, John; Follen, Greg; Naiman, Cynthia; Veres, Joseph; Owen, Karl; Lopez, Isaac
2001-01-01
The technologies necessary to enable detailed numerical simulations of complete propulsion systems are being developed at the NASA Glenn Research Center in cooperation with industry, academia, and other government agencies. Large scale, detailed simulations will be of great value to the nation because they eliminate some of the costly testing required to develop and certify advanced propulsion systems. In addition, time and cost savings will be achieved by enabling design details to be evaluated early in the development process before a commitment is made to a specific design. This concept is called the Numerical Propulsion System Simulation (NPSS). NPSS consists of three main elements: (1) engineering models that enable multidisciplinary analysis of large subsystems and systems at various levels of detail, (2) a simulation environment that maximizes designer productivity, and (3) a cost-effective. high-performance computing platform. A fundamental requirement of the concept is that the simulations must be capable of overnight execution on easily accessible computing platforms. This will greatly facilitate the use of large-scale simulations in a design environment. This paper describes the current status of the NPSS with specific emphasis on the progress made over the past year on air breathing propulsion applications. Major accomplishments include the first formal release of the NPSS object-oriented architecture (NPSS Version 1) and the demonstration of a one order of magnitude reduction in computing cost-to-performance ratio using a cluster of personal computers. The paper also describes the future NPSS milestones, which include the simulation of space transportation propulsion systems in response to increased emphasis on safe, low cost access to space within NASA'S Aerospace Technology Enterprise. In addition, the paper contains a summary of the feedback received from industry partners on the fiscal year 1999 effort and the actions taken over the past year to
Numerical simulations and modeling of turbulent combustion
NASA Astrophysics Data System (ADS)
Cuenot, B.
Turbulent combustion is the basic physical phenomenon responsible for efficient energy release by any internal combustion engine. However it is accompanied by other undesirable phenomena such as noise, pollutant species emission or damaging instabilities that may even lead to the system desctruction. It is then crucial to control this phenomenon, to understand all its mecanisms and to master it in industrial systems. For long time turbulent combustion has been explored only through theory and experiment. But the rapid increase of computers power during the last years has allowed an important development of numerical simulation, that has become today an essential tool for research and technical design. Direct numerical simulation has then allowed to rapidly progress in the knowledge of turbulent flame structures, leading to new modelisations for steady averaged simulations. Recently large eddy simulation has made a new step forward by refining the description of complex and unsteady flames. The main problem that arises when performing numerical simulation of turbulent combustion is linked to the description of the flame front. Being very thin, it can not however be reduced to a simple interface as it is the location of intense chemical transformation and of strong variations of thermodynamical quantities. Capturing the internal structure of a zone with a thickness of the order of 0.1 mm in a computation with a mesh step 10 times larger being impossible, it is necessary to model the turbulent flame. Models depend on the chemical structure of the flame, on the ambiant turbulence, on the combustion regime (flamelets, distributed combustion, etc.) and on the reactants injection mode (premixed or not). One finds then a large class of models, from the most simple algebraic model with a one-step chemical kinetics, to the most complex model involving probablity density functions, cross-correlations and multiple-step or fully complex chemical kinetics.
Numerical simulation of freeway traffic flow
Liu, G.; Lyrintzis, A.S.; Michalopoulos, P.G.
1997-11-01
A new high-order continuum model is presented in this paper. This high-order model exhibits smooth solutions rather than discontinuities, is able to describe the amplification of small disturbances on heavy traffic, and allows fluctuations of speed around the equilibrium values. Furthermore, unlike some earlier high-order models, it does not result in negative speeds at the tail of congested regions and disturbance propagation speeds greater than the flow speed. The model takes into account the relaxation time as a function of density and, in the equilibrium limit, it is consistent with the simple continuum model. A Riemann-problem-based numerical method is proposed for the solution of the new high-order model. Modeling of interrupted flow behavior such as merging, diverging, and weaving is also investigated. Based on the new high order model, the proposed numerical method and the modeling of interrupted flow, a versatile code is developed for the numerical simulation of freeway traffic flow that includes several freeway geometries. The authors compare the high-order model with the simple continuum model and the proposed numerical method with the Lax method based on 30-s and 5-min field data. The model is tested in interrupted flow situations (e.g., pipeline, merging, diverging, and weaving areas). A comparison of numerical results with limited field data shows that the high-order model performs better than the simple continuum model and describes better than a previously proposed method.
Direct Numerical Simulation of the Leidenfrost Effect
NASA Astrophysics Data System (ADS)
Tanguy, Sebastien; Rueda Villegas, Lucia; Fluid Mechanics Institute of Toulouse Team
2015-11-01
The development of numerical methods for the direct numerical simulation of two-phase flows with phase changes, is the main topic of this study. We propose a novel numerical method which allows dealing with both evaporation and boiling at the interface between a liquid and a gas. For instance it can occur for a Leidenfrost droplet; a water drop levitating above a hot plate which temperature is much higher than the boiling temperature. In this case, boiling occurs in the film of saturated vapor which is entrapped between the bottom of the drop and the plate, whereas the top of the water droplet evaporates in contact of ambient air. Thus, boiling and evaporation can occur simultaneously on different regions of the same liquid interface or occur successively at different times of the history of an evaporating droplet. Usual numerical methods are not able to perform computations in these transient regimes, therefore, we propose in this paper a novel numerical method to achieve this challenging task. Finally, we present several accurate validations against experimental results on Leidenfrost Droplets to strengthen the relevance of this new method.
Numerical Simulation of a Seaway with Breaking
NASA Astrophysics Data System (ADS)
Dommermuth, Douglas; O'Shea, Thomas; Brucker, Kyle; Wyatt, Donald
2012-11-01
The focus of this presentation is to describe the recent efforts to simulate a fully non-linear seaway with breaking by using a high-order spectral (HOS) solution of the free-surface boundary value problem to drive a three-dimensional Volume of Fluid (VOF) solution. Historically, the two main types of simulations to simulate free-surface flows are the boundary integral equations method (BIEM) and high-order spectral (HOS) methods. BIEM calculations fail at the point at which the surface impacts upon itself, if not sooner, and HOS methods can only simulate a single valued free-surface. Both also employ a single-phase approximation in which the effects of the air on the water are neglected. Due to these limitations they are unable to simulate breaking waves and air entrainment. The Volume of Fluid (VOF) method on the other hand is suitable for modeling breaking waves and air entrainment. However it is computationally intractable to generate a realistic non-linear sea-state. Here, we use the HOS solution to quickly drive, or nudge, the VOF solution into a non-linear state. The computational strategies, mathematical formulation, and numerical implementation will be discussed. The results of the VOF simulation of a seaway with breaking will also be presented, and compared to the single phase, single valued HOS results.
Numerical recipes for mold filling simulation
Kothe, D.; Juric, D.; Lam, K.; Lally, B.
1998-07-01
Has the ability to simulate the filling of a mold progressed to a point where an appropriate numerical recipe achieves the desired results? If results are defined to be topological robustness, computational efficiency, quantitative accuracy, and predictability, all within a computational domain that faithfully represents complex three-dimensional foundry molds, then the answer unfortunately remains no. Significant interfacial flow algorithm developments have occurred over the last decade, however, that could bring this answer closer to maybe. These developments have been both evolutionary and revolutionary, will continue to transpire for the near future. Might they become useful numerical recipes for mold filling simulations? Quite possibly. Recent progress in algorithms for interface kinematics and dynamics, linear solution methods, computer science issues such as parallelization and object-oriented programming, high resolution Navier-Stokes (NS) solution methods, and unstructured mesh techniques, must all be pursued as possible paths toward higher fidelity mold filling simulations. A detailed exposition of these algorithmic developments is beyond the scope of this paper, hence the authors choose to focus here exclusively on algorithms for interface kinematics. These interface tracking algorithms are designed to model the movement of interfaces relative to a reference frame such as a fixed mesh. Current interface tracking algorithm choices are numerous, so is any one best suited for mold filling simulation? Although a clear winner is not (yet) apparent, pros and cons are given in the following brief, critical review. Highlighted are those outstanding interface tracking algorithm issues the authors feel can hamper the reliable modeling of today`s foundry mold filling processes.
Computer simulation of two-phase flow in nuclear reactors
Wulff, W.
1992-09-01
Two-phase flow models dominate the economic resource requirements for development and use of computer codes for analyzing thermohydraulic transients in nuclear power plants. Six principles are presented on mathematical modeling and selection of numerical methods, along with suggestions on programming and machine selection, all aimed at reducing the cost of analysis. Computer simulation is contrasted with traditional computer calculation. The advantages of run-time interactive access operation in a simulation environment are demonstrated. It is explained that the drift-flux model is better suited for two-phase flow analysis in nuclear reactors than the two-fluid model, because of the latter`s closure problem. The advantage of analytical over numerical integration is demonstrated. Modeling and programming techniques are presented which minimize the number of needed arithmetical and logical operations and thereby increase the simulation speed, while decreasing the cost.
Direct numerical simulation of the Leidenfrost Effect
NASA Astrophysics Data System (ADS)
Rueda Villegas, Lucia; Tanguy, Sébastien
2012-11-01
We present direct numerical simulations of the impact of a single droplet on a heated flat surface in the Leidenfrost regime. To that end, we solve the Navier-Stokes equations, the energy equation, and the species mass fraction equation. The Level Set method is used to track the liquid-gas interface motion and the Ghost Fluid Method is implemented to treat the jump conditions. To get rid of the temporal stability condition due to viscosity, an implicit temporal discretization is used. Some specific numerical methods have been developed to deal with droplet vaporization interface jump conditions. Since the vapor layer is very thin compared to the droplet size, a non-uniform structured grid strongly refined near the wall is used to capture the droplet bounce. We present numerical simulations that enable us to study accurately the bouncing dynamics by analyzing the momentum balance during the droplet bounce. Moreover, we determine from such computation the ratio of the droplet heat transfer flux by comparing the energy used for the phase change (latent heat) to the energy used for droplet heating (specific heat). We then compare the shape of the droplet during the impact with some experimental results.
Dynamic stiffness removal for direct numerical simulations
Lu, Tianfeng; Law, Chung K.; Yoo, Chun Sang; Chen, Jacqueline H.
2009-08-15
A systematic approach was developed to derive non-stiff reduced mechanisms for direct numerical simulations (DNS) with explicit integration solvers. The stiffness reduction was achieved through on-the-fly elimination of short time-scales induced by two features of fast chemical reactivity, namely quasi-steady-state (QSS) species and partial-equilibrium (PE) reactions. The sparse algebraic equations resulting from QSS and PE approximations were utilized such that the efficiency of the dynamic stiffness reduction is high compared with general methods of time-scale reduction based on Jacobian decomposition. Using the dimension reduction strategies developed in our previous work, a reduced mechanism with 52 species was first derived from a detailed mechanism with 561 species. The reduced mechanism was validated for ignition and extinction applications over the parameter range of equivalence ratio between 0.5 and 1.5, pressure between 10 and 50 atm, and initial temperature between 700 and 1600 K for ignition, and worst-case errors of approximately 30% were observed. The reduced mechanism with dynamic stiffness removal was then applied in homogeneous and 1-D ignition applications, as well as a 2-D direct numerical simulation of ignition with temperature inhomogeneities at constant volume with integration time-steps of 5-10 ns. The integration was numerically stable and good accuracy was achieved. (author)
Numerical Simulations of Radar Acoustic Scattering
NASA Astrophysics Data System (ADS)
Boluriaan, Said; Morris, Philip J.
1998-11-01
Wake vortices are produced by the lifting surfaces of all aircraft. The vortex created by a large aircraft can have a catastrophic effect on a small plane following closely behind. A vortex detection system would not only increase airport productivity by allowing adaptive spacing, but would also increase the safety of all aircraft operating around the airport by alerting controllers to hazardous conditions that might exist near the runways. In the present research, one and two-dimensional models have been considered for the study of wake vortex detection using a Radar Acoustic Sounding System (RASS). The permittivity perturbation caused by the vortex is modeled as a traveling wave with a Gaussian envelope and a variable propagation speed. The model equations are solved numerically. The one-dimensional model is also solved analytically. The main problem with a time domain simulation is the number of samples required to resolve the Doppler shift. Even for a 1D model with a typical scatterer size, the CPU time required to run the code is far beyond the currently available computer resources. One way to make the time domain simulation feasible is to recast the governing differential equation in order to remove the carrier frequency and solve only for the frequency shift in the scattered wave. The numerical stability characteristics of the resulting equation with complex coefficients are discussed. In order to validate the numerical scheme, the code is run for a fictitious speed of light.
Numerical Simulation of Fluid Mud Gravity Currents
NASA Astrophysics Data System (ADS)
Yilmaz, N. A.; Testik, F. Y.
2011-12-01
Fluid mud bottom gravity currents are simulated numerically using a commercial computational fluid dynamics software, ANSYS-Fluent. In this study, Eulerian-Eulerian multi-fluid method is selected since this method treats all phases in a multiphase system as interpenetrated continua. There are three different phases in the computational model constructed for this study: water, fluid mud, and air. Water and fluid mud are defined as two miscible fluids and the mass and momentum transfers between these two phases are taken into account. Fluid mud, which is a dense suspension of clay particles and water, is defined as a single-phase non-Newtonian fluid via user-defined-functions. These functions define the physical characteristics (density, viscosity, etc.) of the fluid mud and these characteristics vary with changing suspension concentration due to mass transfer between the fluid mud and the water phase. Results of this two-dimensional numerical model are verified with data obtained from experiments conducted in a laboratory flume with a lock-release set-up. Numerical simulations are currently being conducted to elucidate turbulent entrainment of ambient water into fluid mud gravity currents. This study is motivated by coastal dredge disposal operations.
Direct numerical simulation of hot jets
NASA Technical Reports Server (NTRS)
Jacob, Marc C.
1993-01-01
The ultimate motivation of this work is to investigate the stability of two dimensional heated jets and its implications for aerodynamic sound generation from data obtained with direct numerical simulations (DNS). As pointed out in our last report, these flows undergo two types of instabilities, convective or absolute, depending on their temperature. We also described the limits of earlier experimental and theoretical studies and explained why a numerical investigation could give us new insight into the physics of these instabilities. The aeroacoustical interest of these flows was also underlined. In order to reach this goal, we first need to succeed in the DNS of heated jets. Our past efforts have been focused on this issue which encountered several difficulties. Our numerical difficulties are directly related to the physical problem we want to investigate since these absolutely or almost absolutely unstable flows are by definition very sensitive to the smallest disturbances and are very likely to reach nonlinear saturation through a numerical feedback mechanism. As a result, it is very difficult to compute a steady laminar solution using a spatial DNS. A steady state was reached only for strongly co-flowed jets, but these flows are almost equivalent to two independent mixing layers. Thus they are far from absolute instability and have much lower growth rates.
Numerical simulation of real-world flows
NASA Astrophysics Data System (ADS)
Hayase, Toshiyuki
2015-10-01
Obtaining real flow information is important in various fields, but is a difficult issue because measurement data are usually limited in time and space, and computational results usually do not represent the exact state of real flows. Problems inherent in the realization of numerical simulation of real-world flows include the difficulty in representing exact initial and boundary conditions and the difficulty in representing unstable flow characteristics. This article reviews studies dealing with these problems. First, an overview of basic flow measurement methodologies and measurement data interpolation/approximation techniques is presented. Then, studies on methods of integrating numerical simulation and measurement, namely, four-dimensional variational data assimilation (4D-Var), Kalman filters (KFs), state observers, etc are discussed. The first problem is properly solved by these integration methodologies. The second problem can be partially solved with 4D-Var in which only initial and boundary conditions are control parameters. If an appropriate control parameter capable of modifying the dynamical structure of the model is included in the formulation of 4D-Var, unstable modes are properly suppressed and the second problem is solved. The state observer and KFs also solve the second problem by modifying mathematical models to stabilize the unstable modes of the original dynamical system by applying feedback signals. These integration methodologies are now applied in simulation of real-world flows in a wide variety of research fields. Examples are presented for basic fluid dynamics and applications in meteorology, aerospace, medicine, etc.
Numerical reproducibility for implicit Monte Carlo simulations
Cleveland, M.; Brunner, T.; Gentile, N.
2013-07-01
We describe and compare different approaches for achieving numerical reproducibility in photon Monte Carlo simulations. Reproducibility is desirable for code verification, testing, and debugging. Parallelism creates a unique problem for achieving reproducibility in Monte Carlo simulations because it changes the order in which values are summed. This is a numerical problem because double precision arithmetic is not associative. In [1], a way of eliminating this roundoff error using integer tallies was described. This approach successfully achieves reproducibility at the cost of lost accuracy by rounding double precision numbers to fewer significant digits. This integer approach, and other extended reproducibility techniques, are described and compared in this work. Increased precision alone is not enough to ensure reproducibility of photon Monte Carlo simulations. A non-arbitrary precision approaches required a varying degree of rounding to achieve reproducibility. For the problems investigated in this work double precision global accuracy was achievable by using 100 bits of precision or greater on all unordered sums which where subsequently rounded to double precision at the end of every time-step. (authors)
Direct Numerical Simulation of Cosmological Reionization
NASA Astrophysics Data System (ADS)
So, Geoffrey C.
We examine the epoch of hydrogen reionization using a new numerical method that allows us to self-consistently couple all the relevant physical processes (gas dynamics, dark matter dynamics, self-gravity, star formation/feedback, radiative transfer, ionization, recombination, heating and cooling) and evolve the system of coupled equations on the same high resolution mesh. We refer to this approach as direct numerical simulation, in contrast to existing approaches which decouple and coarse-grain the radiative transfer and ionization balance calculations relative to the underlying dynamical calculation. Our method is scalable with respect to the number of radiation sources, size of the mesh, and the number of computer processors employed, and is described in Chapter 2 of this thesis. This scalability permits us to simulate cosmological reionization in large cosmological volumes (~100 Mpc) while directly modeling the sources and sinks of ionizing radiation, including radiative feedback effects such as photoevaporation of gas from halos, Jeans smoothing of the IGM, and enhanced recombination due to small scale clumping. With our fiducial simulation, we find that roughly 2 ionizing photons per baryon is needed to highly ionize the intergalactic medium. The complicated events during reionization that lead to this number can be generally described as inside-out, but in reality the narrative depends on the level of ionization of the gas one defines as ionized. We have updated the formula observers often use for estimating the ionized volume filling fraction formula with a delta b and trec,eff to get from O(10%) to O(1%) consistency with our simulation results. This improvement comes from not using the traditional clumping factor, but instead, considering the history and local effects which were neglected in formulating the original expression. And finally, we have a new upper limit for the escape fraction of ~0.6 from our simulation, which takes into account the photons in
Numerical simulation of platelet margination in microcirculation
NASA Astrophysics Data System (ADS)
Zhao, Hong; Shaqfeh, Eric
2009-11-01
The adhesion of platelets to vascular walls is the first step in clotting. This process critically depends on the preferential concentration of platelets near walls. The presence of red blood cells, which are the predominant blood constituents, is known to affect the steady state platelet concentration and the dynamic platelet margination, but the underlying mechanism is not well understood to-day. We use a direct numerical simulation to study the platelet margination process, with particular emphasis on the Stokesian hydrodynamic interactions among red cells, platelets, and vessel walls. Well-known mechanical models are used for the shearing and bending stiffness of red cell membranes, and the stiffer platelets are modeled as rigid discoids. A boundary integral formulation is used to solve the flow field, where the numerical solution procedure is accelerated by a parallel O(N N) smooth particle-mesh Ewald method. The effects of red cell hematocrit and deformability will be discussed.
Numerical simulation of boundary-layer transition
NASA Technical Reports Server (NTRS)
Spalart, P. R.
1984-01-01
The transition to turbulence in boundary layers was investigated by direct numerical solution of the nonlinear, three-dimensional, incompressible Navier-Stokes equations in the half-infinite domain over a flat plate. Periodicity was imposed in the streamwise and spanwise directions. A body force was applied to approximate the effect of a nonparallel mean flow. The numerical method was spectra, based on Fourier series and Jacobi polynomials, and used divergence-free basis functions. Extremely rapid convergence was obtained when solving the linear Orr-Sommerfeld equation. The early nonlinear and three-dimensional stages of transition, in a boundary layer disturbed by a vibrating ribbon, were successfully simulated. Excellent qualitative agreement was observed with either experiments or weakly nonlinear theories. In particular, the breakdown pattern was staggered or nonstaggered depending on the disturbance amplitude.
Numerical simulation for fan broadband noise prediction
NASA Astrophysics Data System (ADS)
Hase, Takaaki; Yamasaki, Nobuhiko; Ooishi, Tsutomu
2011-03-01
In order to elucidate the broadband noise of fan, the numerical simulation of fan operating at two different rotational speeds is carried out using the three-dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) equations. The computed results are compared to experiment to estimate its accuracy and are found to show good agreement with experiment. A method is proposed to evaluate the turbulent kinetic energy in the framework of the Spalart-Allmaras one equation turbulence model. From the calculation results, the turbulent kinetic energy is visualized as the turbulence of the flow which leads to generate the broadband noise, and its noise sources are identified.
Numerical simulation of swept-wing flows
NASA Technical Reports Server (NTRS)
Reed, Helen L.
1991-01-01
Efforts of the last six months to computationally model the transition process characteristics of flow over swept wings are described. Specifically, the crossflow instability and crossflow/Tollmien-Schlichting wave interactions are analyzed through the numerical solution of the full 3D Navier-Stokes equations including unsteadiness, curvature, and sweep. This approach is chosen because of the complexity of the problem and because it appears that linear stability theory is insufficient to explain the discrepancies between different experiments and between theory and experiment. The leading edge region of a swept wing is considered in a 3D spatial simulation with random disturbances as the initial conditions.
Direct numerical simulation of turbulent mixing.
Statsenko, V P; Yanilkin, Yu V; Zhmaylo, V A
2013-11-28
The results of three-dimensional numerical simulations of turbulent flows obtained by various authors are reviewed. The paper considers the turbulent mixing (TM) process caused by the development of the main types of instabilities: those due to gravitation (with either a fixed or an alternating-sign acceleration), shift and shock waves. The problem of a buoyant jet is described as an example of the mixed-type problem. Comparison is made with experimental data on the TM zone width, profiles of density, velocity and turbulent energy and degree of homogeneity. PMID:24146009
Numerical simulation of coupler cavities for linacs
Ng, C.K.; Derutyer, H.; Ko, K.
1993-04-01
We present numerical procedures involved in the evaluation of the performance of coupler cavities for linacs. The MAFIA code is used to simulate an X-Band accelerator section in the time domain. The input/output coupler cavities for the structure arc of the symmetrical double-input design. We calculate the transmission properties of the coupler and compare the results with measurements. We compare the performance of the symmetrical double-input design with that of the conventional single-input type by evaluating the field amplitude and phase asymmetries. We also evaluate the peak field gradient in the computer.
NASA Astrophysics Data System (ADS)
Holladay, J. D.; Wang, Y.
2015-05-01
Microscale (<5 W) reformers for hydrogen production have been investigated for over a decade. These devices are intended to provide hydrogen for small fuel cells. Due to the reformer's small size, numerical simulations are critical to understand heat and mass transfer phenomena occurring in the systems and help guide the further improvements. This paper reviews the development of the numerical codes and details the reaction equations used. The majority of the devices utilized methanol as the fuel due to methanol's low reforming temperature and high conversion, although, there are several methane fueled systems. The increased computational power and more complex codes have led to improved accuracy of numerical simulations. Initial models focused on the reformer, while more recently, the simulations began including other unit operations such as vaporizers, inlet manifolds, and combustors. These codes are critical for developing the next generation systems. The systems reviewed included plate reactors, microchannel reactors, and annulus reactors for both wash-coated and packed bed systems.
Numerical simulation of flow through biofluid devices
NASA Technical Reports Server (NTRS)
Rogers, Stuart E.; Kwak, Dochan; Kiris, Cetin; Chang, I-Dee
1990-01-01
The results of a numerical simulation of flow through an artificial heart and through an artificial tilting-disk heart valve are presented. The simulation involves solving the incompressible Navier-Stokes equations; the solution process is described. The details and difficulties of modeling these particular geometries are discussed. The artificial heart geometry uses a single moving grid, and the valve computation uses an overlaid-grid approach with one moving grid and one stationary grid. The equations must be solved iteratively for each discrete time step of the computations, requiring a significant amount of computing time. It is particularly difficult to analyze and present the fluid physics represented by these calculations because of the time-varying nature of the flow, and because the flows are internal. Three-dimensional graphics and scientific visualization techniques have become instrumental in solving these problems.
Numerical simulation of large fabric filter
NASA Astrophysics Data System (ADS)
Sedláček, Jan; Kovařík, Petr
2012-04-01
Fabric filters are used in the wide range of industrial technologies for cleaning of incoming or exhaust gases. To achieve maximal efficiency of the discrete phase separation and long lifetime of the filter hoses, it is necessary to ensure uniform load on filter surface and to avoid impacts of heavy particles with high velocities to the filter hoses. The paper deals with numerical simulation of two phase flow field in a large fabric filter. The filter is composed of six chambers with approx. 1600 filter hoses in total. The model was simplified to one half of the filter, the filter hoses walls were substituted by porous zones. The model settings were based on experimental data, especially on the filter pressure drop. Unsteady simulations with different turbulence models were done. Flow field together with particles trajectories were analyzed. The results were compared with experimental observations.
Method for numerical simulations of metastable states
Heller, U.M.; Seiberg, N.
1983-06-15
We present a numerical simulation of metastable states near a first-order phase transition in the example of a U(1) lattice gauge theory with a generalized action. In order to make measurements in these states possible their decay has to be prevented. We achieve this by using a microcanonical simulation for a finite system. We then obtain the coupling constant (inverse temperature) as a function of the action density. It turns out to be nonmonotonic and hence not uniquely invertible. From it we derive the effective potential for the action density. This effective potential is not always convex, a property that seems to be in contradiction with the standard lore about its convexity. This apparent ''paradox'' is resolved in a discussion about different definitions of the effective potential.
The numerical simulation of accelerator components
Herrmannsfeldt, W.B.; Hanerfeld, H.
1987-05-01
The techniques of the numerical simulation of plasmas can be readily applied to problems in accelerator physics. Because the problems usually involve a single component ''plasma,'' and times that are at most, a few plasma oscillation periods, it is frequently possible to make very good simulations with relatively modest computation resources. We will discuss the methods and illustrate them with several examples. One of the more powerful techniques of understanding the motion of charged particles is to view computer-generated motion pictures. We will show several little movie strips to illustrate the discussions. The examples will be drawn from the application areas of Heavy Ion Fusion, electron-positron linear colliders and injectors for free-electron lasers. 13 refs., 10 figs., 2 tabs.
Numerical Simulations of Double White Dwarf Mergers
NASA Astrophysics Data System (ADS)
Motl, Patrick M.; Clayton, G.; Tohline, J. E.; Even, W.; Fryer, C.; Diehl, S.; Geballe, T.; Herwig, F.
2010-03-01
We will present evolutions of white dwarf binaries from two independent codes (one SPH and one Eulerian). We attempt to match the initial data for semi-detached synchronously rotating binaries between these two fluid representations. Our set of simulations includes various initial mass ratios and we assume one of two different equations of state (polytropic or ideal gas) to span the parameter space between the two possible extreme cases of rapid, catastrophic merger through to long-lived, steady mass transfer. In this presentation, we will primarily highlight the level of agreement between the two codes and how the results vary with increasing numerical resolution. We will also discuss future work incorporating nuclear reactions into our simulations and the possible connections of double white dwarf mergers to astrophysical sources.
Numerical Simulations of the Wake of Kauai
NASA Astrophysics Data System (ADS)
Lane, Todd P.; Sharman, Robert D.; Frehlich, Rod G.; Brown, John M.
2006-09-01
This study uses a series of numerical simulations to examine the structure of the wake of the Hawaiian island of Kauai. The primary focus is on the conditions on 26 June 2003, which was the day of the demise of the Helios aircraft within Kauai’s wake. The simulations show that, in an east-northeasterly trade wind flow, Kauai produces a well-defined wake that can extend 40 km downstream of the island. The wake is bounded to the north and south by regions of strong vertical and horizontal shear—that is, shear lines. These shear lines mark the edge of the wake in the horizontal plane and are aligned approximately parallel to the upstream flow direction at each respective height. The highest-resolution simulations show that these shear lines can become unstable and break down through Kelvin Helmholtz instability. The breakdown generates turbulent eddies that are advected both downstream and into the recirculating wake flow. Turbulence statistics are estimated from the simulation using a technique that analyzes model-derived structure functions. A number of sensitivity studies are also completed to determine the influence of the upstream conditions on the structure of the wake. These simulations show that directional shear controls the tilt of the wake in the north south plane with height. These simulations also show that at lower incident wind speeds the wake has a qualitatively similar structure but is less turbulent. At higher wind speeds, the flow regime changes, strong gravity waves are generated, and the wake is poorly defined. These results are consistent with previous idealized studies of stratified flow over isolated obstacles.
Visualization techniques in plasma numerical simulations
NASA Astrophysics Data System (ADS)
Kulhánek, P.; Smetana, M.
2004-03-01
Numerical simulations of plasma processes usually yield a huge amount of raw numerical data. Information about electric and magnetic fields and particle positions and velocities can be typically obtained. There are two major ways of elaborating these data. First of them is called plasma diagnostics. We can calculate average values, variances, correlations of variables, etc. These results may be directly comparable with experiments and serve as the typical quantitative output of plasma simulations. The second possibility is the plasma visualization. The results are qualitative only, but serve as vivid display of phenomena in the plasma followed-up. An experience with visualizing electric and magnetic fields via Line Integral Convolution method is described in the first part of the paper. The LIC method serves for visualization of vector fields in two dimensional section of the three dimensional plasma. The field values can be known only in grid points of three-dimensional grid. The second part of the paper is devoted to the visualization techniques of the charged particle motion. The colour tint can be used for particle’s temperature representation. The motion can be visualized by a trace fading away with the distance from the particle. In this manner the impressive animations of the particle motion can be achieved.
Direct Numerical Simulations of Transient Dispersion
NASA Astrophysics Data System (ADS)
Porter, M.; Valdes-Parada, F.; Wood, B.
2008-12-01
Transient dispersion is important in many engineering applications, including transport in porous media. A common theoretical approach involves upscaling the micro-scale mass balance equations for convection- diffusion to macro-scale equations that contain effective medium quantities. However, there are a number of assumptions implicit in the various upscaling methods. For example, results obtained from volume averaging are often dependent on a given set of length and time scale constraints. Additionally, a number of the classical models for dispersion do not fully capture the early-time dispersive behavior of the solute for a general set of initial conditions. In this work, we present direct numerical simulations of micro-scale transient mass balance equations for convection-diffusion in both capillary tubes and porous media. Special attention is paid to analysis of the influence of a new time- decaying coefficient that filters the effects of the initial conditions. The direct numerical simulations were compared to results obtained from solving the closure problem associated with volume averaging. These comparisons provide a quantitative measure of the significance of (1) the assumptions implicit in the volume averaging method and (2) the importance of the early-time dispersive behavior of the solute due to various initial conditions.
Numerical simulations of rotating axisymmetric sunspots
NASA Astrophysics Data System (ADS)
Botha, G. J. J.; Busse, F. H.; Hurlburt, N. E.; Rucklidge, A. M.
2008-07-01
A numerical model of axisymmetric convection in the presence of a vertical magnetic flux bundle and rotation about the axis is presented. The model contains a compressible plasma described by the non-linear MHD equations, with density and temperature gradients simulating the upper layer of the Sun's convection zone. The solutions exhibit a central magnetic flux tube in a cylindrical numerical domain, with convection cells forming collar flows around the tube. When the numerical domain is rotated with a constant angular velocity, the plasma forms a Rankine vortex, with the plasma rotating as a rigid body where the magnetic field is strong, as in the flux tube, while experiencing sheared azimuthal flow in the surrounding convection cells, forming a free vortex. As a result, the azimuthal velocity component has its maximum value close to the outer edge of the flux tube. The azimuthal flow inside the magnetic flux tube and the vortex flow is prograde relative to the rotating cylindrical reference frame. A retrograde flow appears at the outer wall. The most significant convection cell outside the flux tube is the location for the maximum value of the azimuthal magnetic field component. The azimuthal flow and magnetic structure are not generated spontaneously, but decay exponentially in the absence of any imposed rotation of the cylindrical domain.
Direct numerical simulation of turbulent reacting flows
Chen, J.H.
1993-12-01
The development of turbulent combustion models that reflect some of the most important characteristics of turbulent reacting flows requires knowledge about the behavior of key quantities in well defined combustion regimes. In turbulent flames, the coupling between the turbulence and the chemistry is so strong in certain regimes that is is very difficult to isolate the role played by one individual phenomenon. Direct numerical simulation (DNS) is an extremely useful tool to study in detail the turbulence-chemistry interactions in certain well defined regimes. Globally, non-premixed flames are controlled by two limiting cases: the fast chemistry limit, where the turbulent fluctuations. In between these two limits, finite-rate chemical effects are important and the turbulence interacts strongly with the chemical processes. This regime is important because industrial burners operate in regimes in which, locally the flame undergoes extinction, or is at least in some nonequilibrium condition. Furthermore, these nonequilibrium conditions strongly influence the production of pollutants. To quantify the finite-rate chemistry effect, direct numerical simulations are performed to study the interaction between an initially laminar non-premixed flame and a three-dimensional field of homogeneous isotropic decaying turbulence. Emphasis is placed on the dynamics of extinction and on transient effects on the fine scale mixing process. Differential molecular diffusion among species is also examined with this approach, both for nonreacting and reacting situations. To address the problem of large-scale mixing and to examine the effects of mean shear, efforts are underway to perform large eddy simulations of round three-dimensional jets.
A research reactor simulator for operators training and teaching
De Carvalho, R. P.; Maiorino, J. R.
2006-07-01
This work describes a training simulator of Research Reactors (RR). The simulator is an interactive tool for teaching and operator training of the bases of the RR operation, reactor physics and thermal hydraulics. The Brazilian IEA-R1 RR was taken as the reference (default configuration). The implementation of the simulator consists of the modeling of the process and system (neutronics, thermal hydraulics), its numerical solution, and the implementation of the man-machine interface through visual interactive screens. The point kinetics model was used for the nuclear process and the heat and mass conservation models were used for the thermal hydraulic feed back in the average core channel. The heat exchanger and cooling tower were also modeled. The main systems were: the reactivity control system, including the automatic control, and the primary and secondary coolant systems. The Visual C++ was used to codes and graphics lay-outs. The simulator is to be used in a PC with Windows XP system. The simulator allows simulation in real time of start up, power maneuver, and shut down. (authors)
Numerical Simulations of High Enthalpy Pulse Facilities
NASA Technical Reports Server (NTRS)
Wilson, Gregory J.; Edwards, Thomas A. (Technical Monitor)
1995-01-01
Axisymmetric flows within shock tubes and expansion tubes are simulated including the effects of finite rate chemistry and both laminar and turbulent boundary layers. The simulations demonstrate the usefulness of computational fluid dynamics for characterizing the flows in high enthalpy pulse facilities. The modeling and numerical requirements necessary to simulate these flows accurately are also discussed. Although there is a large body of analysis which explains and quantifies the boundary layer growth between the shock and the interface in a shock tube, there is a need for more detailed solutions. Phenomena such as thermochemical nonequilibrium. or turbulent transition behind the shock are excluded in the assumptions of Mirels' analysis. Additionally there is inadequate capability to predict the influence of the boundary layer on the expanded gas behind the interface. Quantifying the gas in this region is particularly important in expansion tubes because it is the location of the test gas. Unsteady simulations of the viscous flow in shock tubes are computationally expensive because they must follow features such as a shock wave over the length of the facility and simultaneously resolve the small length scales within the boundary layer. As a result, efficient numerical algorithms are required. The numerical approach of the present work is to solve the axisymmetric gas dynamic equations using an finite-volume formulation where the inviscid fluxes are computed with a upwind TVD scheme. Multiple species equations are included in the formulation so that finite-rate chemistry can be modeled. The simulations cluster grid points at the shock and interface and translate this clustered grid with these features to minimize numerical errors. The solutions are advanced at a CFL number of less than one based on the inviscid gas dynamics. To avoid limitations on the time step due to the viscous terms, these terms are treated implicitly. This requires a block tri
The Numerical Propulsion System Simulation: An Overview
NASA Technical Reports Server (NTRS)
Lytle, John K.
2000-01-01
Advances in computational technology and in physics-based modeling are making large-scale, detailed simulations of complex systems possible within the design environment. For example, the integration of computing, communications, and aerodynamics has reduced the time required to analyze major propulsion system components from days and weeks to minutes and hours. This breakthrough has enabled the detailed simulation of major propulsion system components to become a routine part of designing systems, providing the designer with critical information about the components early in the design process. This paper describes the development of the numerical propulsion system simulation (NPSS), a modular and extensible framework for the integration of multicomponent and multidisciplinary analysis tools using geographically distributed resources such as computing platforms, data bases, and people. The analysis is currently focused on large-scale modeling of complete aircraft engines. This will provide the product developer with a "virtual wind tunnel" that will reduce the number of hardware builds and tests required during the development of advanced aerospace propulsion systems.
Numerical simulation of premixed turbulent methane combustion
Bell, John B.; Day, Marcus S.; Grcar, Joseph F.
2001-12-14
In this paper we study the behavior of a premixed turbulent methane flame in three dimensions using numerical simulation. The simulations are performed using an adaptive time-dependent low Mach number combustion algorithm based on a second-order projection formulation that conserves both species mass and total enthalpy. The species and enthalpy equations are treated using an operator-split approach that incorporates stiff integration techniques for modeling detailed chemical kinetics. The methodology also incorporates a mixture model for differential diffusion. For the simulations presented here, methane chemistry and transport are modeled using the DRM-19 (19-species, 84-reaction) mechanism derived from the GRIMech-1.2 mechanism along with its associated thermodynamics and transport databases. We consider a lean flame with equivalence ratio 0.8 for two different levels of turbulent intensity. For each case we examine the basic structure of the flame including turbulent flame speed and flame surface area. The results indicate that flame wrinkling is the dominant factor leading to the increased turbulent flame speed. Joint probability distributions are computed to establish a correlation between heat release and curvature. We also investigate the effect of turbulent flame interaction on the flame chemistry. We identify specific flame intermediates that are sensitive to turbulence and explore various correlations between these species and local flame curvature. We identify different mechanisms by which turbulence modulates the chemistry of the flame.
3D Numerical simulations of oblique subduction
NASA Astrophysics Data System (ADS)
Malatesta, C.; Gerya, T.; Scambelluri, M.; Crispini, L.; Federico, L.; Capponi, G.
2012-04-01
In the past 2D numerical studies (e.g. Gerya et al., 2002; Gorczyk et al., 2007; Malatesta et al., 2012) provided evidence that during intraoceanic subduction a serpentinite channel forms above the downgoing plate. This channel forms as a result of hydration of the mantle wedge by uprising slab-fluids. Rocks buried at high depths are finally exhumed within this buoyant low-viscosity medium. Convergence rate in these 2D models was described by a trench-normal component of velocity. Several present and past subduction zones worldwide are however driven by oblique convergence between the plates, where trench-normal motion of the subducting slab is coupled with trench-parallel displacement of the plates. Can the exhumation mechanism and the exhumation rates of high-pressure rocks be affected by the shear component of subduction? And how uprise of these rocks can vary along the plate margin? We tried to address these questions performing 3D numerical models that simulate an intraoceanic oblique subduction. The models are based on thermo-mechanical equations that are solved with finite differences method and marker-in-cell techniques combined with multigrid approach (Gerya, 2010). In most of the models a narrow oceanic basin (500 km-wide) surrounded by continental margins is depicted. The basin is floored by either layered or heterogeneous oceanic lithosphere with gabbro as discrete bodies in serpentinized peridotite and a basaltic layer on the top. A weak zone in the mantle is prescribed to control the location of subduction initiation and therefore the plate margins geometry. Finally, addition of a third dimension in the simulations allowed us to test the role of different plate margin geometries on oblique subduction dynamics. In particular in each model we modified the dip angle of the weak zone and its "lateral" geometry (e.g. continuous, segmented). We consider "continuous" weak zones either parallel or increasingly moving away from the continental margins
Numerical Simulation of DC Coronal Heating
NASA Astrophysics Data System (ADS)
Dahlburg, Russell B.; Einaudi, G.; Taylor, Brian D.; Ugarte-Urra, Ignacio; Warren, Harry; Rappazzo, A. F.; Velli, Marco
2016-05-01
Recent research on observational signatures of turbulent heating of a coronal loop will be discussed. The evolution of the loop is is studied by means of numerical simulations of the fully compressible three-dimensional magnetohydrodynamic equations using the HYPERION code. HYPERION calculates the full energy cycle involving footpoint convection, magnetic reconnection, nonlinear thermal conduction and optically thin radiation. The footpoints of the loop magnetic field are convected by random photospheric motions. As a consequence the magnetic field in the loop is energized and develops turbulent nonlinear dynamics characterized by the continuous formation and dissipation of field-aligned current sheets: energy is deposited at small scales where heating occurs. Dissipation is non-uniformly distributed so that only a fraction of thecoronal mass and volume gets heated at any time. Temperature and density are highly structured at scales which, in the solar corona, remain observationally unresolved: the plasma of the simulated loop is multi thermal, where highly dynamical hotter and cooler plasma strands are scattered throughout the loop at sub-observational scales. Typical simulated coronal loops are 50000 km length and have axial magnetic field intensities ranging from 0.01 to 0.04 Tesla. To connect these simulations to observations the computed number densities and temperatures are used to synthesize the intensities expected in emission lines typically observed with the Extreme ultraviolet Imaging Spectrometer (EIS) on Hinode. These intensities are then employed to compute differential emission measure distributions, which are found to be very similar to those derived from observations of solar active regions.
History of the numerical aerodynamic simulation program
NASA Technical Reports Server (NTRS)
Peterson, Victor L.; Ballhaus, William F., Jr.
1987-01-01
The Numerical Aerodynamic Simulation (NAS) program has reached a milestone with the completion of the initial operating configuration of the NAS Processing System Network. This achievement is the first major milestone in the continuing effort to provide a state-of-the-art supercomputer facility for the national aerospace community and to serve as a pathfinder for the development and use of future supercomputer systems. The underlying factors that motivated the initiation of the program are first identified and then discussed. These include the emergence and evolution of computational aerodynamics as a powerful new capability in aerodynamics research and development, the computer power required for advances in the discipline, the complementary nature of computation and wind tunnel testing, and the need for the government to play a pathfinding role in the development and use of large-scale scientific computing systems. Finally, the history of the NAS program is traced from its inception in 1975 to the present time.
Numerical Simulation of Coherent Error Correction
NASA Astrophysics Data System (ADS)
Crow, Daniel; Joynt, Robert; Saffman, Mark
A major goal in quantum computation is the implementation of error correction to produce a logical qubit with an error rate lower than that of the underlying physical qubits. Recent experimental progress demonstrates physical qubits can achieve error rates sufficiently low for error correction, particularly for codes with relatively high thresholds such as the surface code and color code. Motivated by experimental capabilities of neutral atom systems, we use numerical simulation to investigate whether coherent error correction can be effectively used with the 7-qubit color code. The results indicate that coherent error correction does not work at the 10-qubit level in neutral atom array quantum computers. By adding more qubits there is a possibility of making the encoding circuits fault-tolerant which could improve performance.
Polarimetric bio-aerosol detection: numerical simulation
NASA Astrophysics Data System (ADS)
Snow, J. William; Bicknell, W. Ed; Burke, Hsiao-hua K.
2005-11-01
This paper examines the use of bi-static lidar to remotely detect the release of aerosolized biological agent. The detection scheme exploits bio-aerosol induced changes in the Stokes parameters of scattered radiation in comparison to scattered radiation from ambient background aerosols alone. A polarization distance metric is introduced to discriminate between changes caused by the two types of aerosols. Scattering code computations are the information source. Three application scenarios are considered: outdoor arena, indoor auditorium, and building heating-ventilation-air-conditioning (HVAC) system. Numerical simulations are employed to determine sensitivity of detection to laser wavelength and to particle physical properties. Results of the study are described and details are given for the specific example of a 1.50 μm lidar system operating outdoors over a 1000-m range.
Numerical aerodynamic simulation facility feasibility study
NASA Technical Reports Server (NTRS)
1979-01-01
There were three major issues examined in the feasibility study. First, the ability of the proposed system architecture to support the anticipated workload was evaluated. Second, the throughput of the computational engine (the flow model processor) was studied using real application programs. Third, the availability reliability, and maintainability of the system were modeled. The evaluations were based on the baseline systems. The results show that the implementation of the Numerical Aerodynamic Simulation Facility, in the form considered, would indeed be a feasible project with an acceptable level of risk. The technology required (both hardware and software) either already exists or, in the case of a few parts, is expected to be announced this year. Facets of the work described include the hardware configuration, software, user language, and fault tolerance.
Numerical Simulations of Acoustically Driven, Burning Droplets
NASA Technical Reports Server (NTRS)
Kim, H.-C.; Karagozian, A. R.; Smith, O. I.; Urban, Dave (Technical Monitor)
1999-01-01
This computational study focuses on understanding and quantifying the effects of external acoustical perturbations on droplet combustion. A one-dimensional, axisymmetric representation of the essential diffusion and reaction processes occurring in the vicinity of the droplet stagnation point is used here in order to isolate the effects of the imposed acoustic disturbance. The simulation is performed using a third order accurate, essentially non-oscillatory (ENO) numerical scheme with a full methanol-air reaction mechanism. Consistent with recent microgravity and normal gravity combustion experiments, focus is placed on conditions where the droplet is situated at a velocity antinode in order for the droplet to experience the greatest effects of fluid mechanical straining of flame structures. The effects of imposed sound pressure level and frequency are explored here, and conditions leading to maximum burning rates are identified.
Computing abstraction hierarchies by numerical simulation
Bundy, A.; Giunchiglia, F.; Sebastiani, R.; Walsh, T.
1996-12-31
We present a novel method for building ABSTRIPS-style abstraction hierarchies in planning. The aim of this method is to minimize the amount of backtracking between abstraction levels. Previous approaches have determined the criticality of operator preconditions by reasoning about plans directly. Here, we adopt a simpler and faster approach where we use numerical simulation of the planning process. We demonstrate the theoretical advantages of our approach by identifying some simple properties lacking in previous approaches but possessed by our method. We demonstrate the empirical advantages of our approach by a set of four benchmark experiments using the ABTWEAK system. We compare the quality of the abstraction hierarchies generated with those built by the ALPINE and HIGHPOINT algorithms.
Numerical simulation of three dimensional transonic flows
NASA Technical Reports Server (NTRS)
Sahu, Jubaraj; Steger, Joseph L.
1987-01-01
The three-dimensional flow over a projectile has been computed using an implicit, approximately factored, partially flux-split algorithm. A simple composite grid scheme has been developed in which a single grid is partitioned into a series of smaller grids for applications which require an external large memory device such as the SSD of the CRAY X-MP/48, or multitasking. The accuracy and stability of the composite grid scheme has been tested by numerically simulating the flow over an ellipsoid at angle of attack and comparing the solution with a single grid solution. The flowfield over a projectile at M = 0.96 and 4 deg angle-of-attack has been computed using a fine grid, and compared with experiment.
Numerical relativistic hydrodynamic simulations of neutron stars
NASA Astrophysics Data System (ADS)
Haywood, Joe R.
Developments in numerical relativistic hydrodynamics over the past thirty years, along with the advent of high speed computers, have made problems needing general relativity and relativistic hydrodynamics tractable. One such problem is the relativistic evolution of neutron stars, either in a head on collision or in binary orbit. Also of current interest is the detection of gravitational radiation from binary neutron stars, black-hole neutron star binaries, binary black holes, etc. Such systems expected to emit gravitational radiation with amplitude large enough to be detected on Earth by such groups as LIGO and VIRGO. Unfortunately, the expected signal strength is below the current noise level. However, signal processing techniques have been developed which should eventually find a signal, if a good theoretical template can be found. In the cases above it is not possible to obtain an analytic solution to the Einstein equations and a numerical approximation is therefore most necessary. In this thesis the Einstein equations are written using the formalism of Arnowitt, Desser and Misner and a conformally flat metric is assumed. Numerical simulations of colliding neutron stars, having either a realistic or Gamma = 2 polytropic equation of state (EOS), are presented which confirm the rise in central density seen by [51, 89] for the softer EOS. For the binary calculation, the results of Wilson et al. [89] are confirmed, which show that the neutron stars can collapse to black holes before colliding when the EOS is realistic and we also confirm results of Miller [56] and others that there is essentially no compression, the central density does not increase, when the stiffer equation of state is used. Finally, a template for the gravitational radiation emitted from the binary is calculated and we show that the frequency of the emitted gravitational waves changes more slowly for the [89] EOS, which may result in a stronger signal in the 50-100 Hz band of LIGO.
The Beam Break-Up Numerical Simulator
Travish, G.A.
1989-11-01
Beam Break-Up (BBU) is a severe constraint in accelerator design, limiting beam current and quality. The control of BBU has become the focus of much research in the design of the next generation collider, recirculating and linear induction accelerators and advanced accelerators. Determining the effect on BBU of modifications to cavities, the focusing elements or the beam is frequently beyond the ability of current analytic models. A computer code was written to address this problem. The Beam Break-Up Numerical Simulator (BBUNS) was designed to numerically solve for beam break-up (BBU) due to an arbitrary transverse wakefield. BBUNS was developed to be as user friendly as possible on the Cray computer series. The user is able to control all aspects of input and output by using a single command file. In addition, the wakefield is specified by the user and read in as a table. The program can model energy variations along and within the beam, focusing magnetic field profiles can be specified, and the graphical output can be tailored. In this note we discuss BBUNS, its structure and application. Included are detailed instructions, examples and a sample session of BBUNS. This program is available for distribution. 50 refs., 18 figs., 5 tabs.
Numerical simulation of detonation failure in nitromethane
Kipp, M.E.; Nunziato, J.W.
1981-01-01
Detonation failure in the homogeneous liquid explosive nitromethane has been observed experimentally in a wide variety of confining geometries. However, numerical simulation of these failure situations with a wave propagation code has been essentially non-existent due to the large differences between the critical diameter and the length of the reaction zone - characteristic dimensions which differ by about two orders of magnitude. This inability to spatially resolve both the reaction zone and geometries of significant size has led us to propose a new numerical technique, based on the stability criterion for rate-type material models, in which only temporal resolution of the reaction zone is required. Using an improved model for nitromethane, we have carried out a series of two-dimensional calculations which illustrate the utility of the present approach in predicting a wide range of experimental observations. Of particular computational significance is the removal of the difficulty requiring spatial resolution of the reaction zone, so that problems of practical size can be analyzed with existing computer capabilities.
Direct Numerical Simulation of Automobile Cavity Tones
NASA Technical Reports Server (NTRS)
Kurbatskii, Konstantin; Tam, Christopher K. W.
2000-01-01
The Navier Stokes equation is solved computationally by the Dispersion-Relation-Preserving (DRP) scheme for the flow and acoustic fields associated with a laminar boundary layer flow over an automobile door cavity. In this work, the flow Reynolds number is restricted to R(sub delta*) < 3400; the range of Reynolds number for which laminar flow may be maintained. This investigation focuses on two aspects of the problem, namely, the effect of boundary layer thickness on the cavity tone frequency and intensity and the effect of the size of the computation domain on the accuracy of the numerical simulation. It is found that the tone frequency decreases with an increase in boundary layer thickness. When the boundary layer is thicker than a certain critical value, depending on the flow speed, no tone is emitted by the cavity. Computationally, solutions of aeroacoustics problems are known to be sensitive to the size of the computation domain. Numerical experiments indicate that the use of a small domain could result in normal mode type acoustic oscillations in the entire computation domain leading to an increase in tone frequency and intensity. When the computation domain is expanded so that the boundaries are at least one wavelength away from the noise source, the computed tone frequency and intensity are found to be computation domain size independent.
Assisted Sonication vs Conventional Transesterification Numerical Simulation and Sensitivity Study
NASA Astrophysics Data System (ADS)
Janajreh, Isam; Noorul Hussain, Mohammed; El Samad, Tala
2015-10-01
Transeterification is known as slow reaction that can take over several hours to complete as the two immiscible liquid reactants combine to form biodiesel and the less favorable glycerol. The quest of finding the perfect catalyst, optimal operational conditions, and reactor configuration to accelerate the reaction in mere few minutes that ensures high quality biodiesel, in economically viable way is coming along with sonication. This drastic reduction is a key enabler for the development of a continuous processing that otherwise is fairly costly and low throughput using conventional method. The reaction kinetics of sonication assisted as inferred by several authors is several time faster and this work implements these rates in a high fidelity numerical simulation model. This flow model is based on Navier-Stokes equations coupled with energy equation for non-isothermal flow and the transport equations of the multiple reactive species. The model is initially validated against experimental data from previous work of the authors using an annular reactor configuration. Following the validation, comparison of the reaction rate is shown to gain more insight to the distribution of the reaction and its attained rates. The two models (conventional and sonication) then compared on the basis of their sensitivity to the methane to oil molar ratio as the most pronounced process parameter. Both the exit reactor yield and the distribution of the species are evaluated with favorable yield under sonication process. These results pave the way to build a more robust process intensified reactor having an integrated selective heterogeneous catalyst to steer the reaction. This can avoid the downstream cleaning processes, cutting reaction time, and render economic benefit to the process.
Autoignition of hydrogen and air using direct numerical simulation
NASA Astrophysics Data System (ADS)
Doom, Jeffrey; Mahesh, Krishnan
2008-11-01
Direct numerical simulation (DNS) is used to study to auto--ignition in laminar vortex rings and turbulent diffusion flames. A novel, all--Mach number algorithm developed by Doom et al (J. Comput. Phys. 2007) is used. The chemical mechanism is a nine species, nineteen reaction mechanism for H2 and Air from Mueller at el (Int. J. Chem. Kinet. 1999). The vortex ring simulations inject diluted H2 at ambient temperature into hot air, and study the effects of stroke ratio, air to fuel ratio and Lewis number. At smaller stroke ratios, ignition occurs in the wake of the vortex ring and propagates into the vortex core. At larger stroke ratios, ignition occurs along the edges of the trailing column before propagating towards the vortex core. The turbulent diffusion flame simulations are three--dimensional and consider the interaction of initially isotropic turbulence with an unstrained diffusion flame. The simulations examine the nature of distinct ignition kernels, the relative roles of chemical reactions, and the relation between the observed behavior and laminar flames and the perfectly stirred reactor problem. These results will be discussed.
Numerical simulation of `DMSP` dosimeter response
Jordan, T.M. ||
1993-12-31
Four Defense Meteorological Satellite Program (DMSP) dosimeters were modeled for numerical simulation of radiation response. The modeling included the hemispherical aluminum dome, the solid state detector, and the tungsten base plate. Orbits were generated for 840 km and 98 degrees inclination and used with 1965 and 1985 magnetic field models and the AP8 and AE8 data sets to obtain solar minimum and solar maximum integral fluences for protons and electrons. Adjoint Monte Carlo methods were then used to simulate the transport of these environments in the geometric models of the dosimeters. Volume average dose calculations were used to calculate the response of the LOLET (less than 1 MeV deposited per particle) channels to electrons and secondary bremsstrahlung. Monte Carlo methods were used, in conjunction with a pulse height analysis, to obtain the proton response of the LOLET and HILET (1 to 10 MeV deposited per particle) channels. The HILET and LOLET responses obtained from these calculations are in good agreement with DMSP measurements for 1984-85.
Numerical simulation of turbulence over tensegrity fabric
NASA Astrophysics Data System (ADS)
Luo, Haoxiang; Bewley, Thomas
2003-11-01
In this research we aim to reduce turbulent skin friction by designing and optimizing tensegrity fabrics. Such fabrics form a new class of compliant surfaces consisting of a weave of both members under tension and members under compression. Boundary conditions on the flow are handled with a time-dependent coordinate transformation. We first note that, when designing the numerical algorithm for approximating the Navier-Stokes equation in the flow domain (with moving boundaries), special care (intrinsic differentiation of a contravariant vector) is needed to handle the temporal differentiation of the momentum term when using a contravariant formulation. A Cartesian-based formulation may also be used, and has proven to be more tractable in the 3D setting. The spectral DNS flow code is coupled with a tensegrity simulation code to compute the flow/structure interaction; recent simulation results will be presented. A complex-step derivative (CSD) technique may then be used to optimize the response characteristics of the tensegrity structure in order to minimize the drag at the flow/structure interface; this strategy will also be discussed.
Numerical simulations of capillary barrier field tests
Morris, C.E.; Stormont, J.C.
1997-12-31
Numerical simulations of two capillary barrier systems tested in the field were conducted to determine if an unsaturated flow model could accurately represent the observed results. The field data was collected from two 7-m long, 1.2-m thick capillary barriers built on a 10% grade that were being tested to investigate their ability to laterally divert water downslope. One system had a homogeneous fine layer, while the fine soil of the second barrier was layered to increase its ability to laterally divert infiltrating moisture. The barriers were subjected first to constant infiltration while minimizing evaporative losses and then were exposed to ambient conditions. The continuous infiltration period of the field tests for the two barrier systems was modelled to determine the ability of an existing code to accurately represent capillary barrier behavior embodied in these two designs. Differences between the field test and the model data were found, but in general the simulations appeared to adequately reproduce the response of the test systems. Accounting for moisture retention hysteresis in the layered system will potentially lead to more accurate modelling results and is likely to be important when developing reasonable predictions of capillary barrier behavior.
Numerical simulation of tulip flame dynamics
Cloutman, L.D.
1991-11-30
A finite difference reactive flow hydrodynamics program based on the full Navier-Stokes equations was used to simulate the combustion process in a homogeneous-charge, constant-volume combustion bomb in which an oddly shaped flame, known as a ``tulip flame`` in the literature, occurred. The ``tulip flame`` was readily reproduced in the numerical simulations, producing good agreement with the experimental flame shapes and positions at various times. The calculations provide sufficient detail about the dynamics of the experiment to provide some insight into the physical mechanisms responsible for the peculiar flame shape. Several factors seem to contribute to the tulip formation. The most important process is the baroclinic production of vorticity by the flame front, and this rate of production appears to be dramatically increased by the nonaxial flow generated when the initial semicircular flame front burns out along the sides of the chamber. The vorticity produces a pair of vortices behind the flame that advects the flame into the tulip shape. Boundary layer effects contribute to the details of the flame shape next to the walls of the chamber, but are otherwise not important. 24 refs.
Numerical simulation of tulip flame dynamics
Cloutman, L.D.
1991-11-30
A finite difference reactive flow hydrodynamics program based on the full Navier-Stokes equations was used to simulate the combustion process in a homogeneous-charge, constant-volume combustion bomb in which an oddly shaped flame, known as a tulip flame'' in the literature, occurred. The tulip flame'' was readily reproduced in the numerical simulations, producing good agreement with the experimental flame shapes and positions at various times. The calculations provide sufficient detail about the dynamics of the experiment to provide some insight into the physical mechanisms responsible for the peculiar flame shape. Several factors seem to contribute to the tulip formation. The most important process is the baroclinic production of vorticity by the flame front, and this rate of production appears to be dramatically increased by the nonaxial flow generated when the initial semicircular flame front burns out along the sides of the chamber. The vorticity produces a pair of vortices behind the flame that advects the flame into the tulip shape. Boundary layer effects contribute to the details of the flame shape next to the walls of the chamber, but are otherwise not important. 24 refs.
Numerical simulations of phase change in microgravity
Juric, D.; Tryggvason, G.
1996-12-31
Direct numerical simulations of liquid-solid and liquid-vapor phase change are conducted under microgravity conditions. The time-dependent governing equations are solved using a two-dimensional finite-difference/front-tracking method. Large interface deformations, topology change, latent heat, surface tension and unequal material properties between the phases are included in the simulations. Results are presented for two specific problems: directional solidification of a dilute binary alloy and the rapid evaporation of a superheated liquid (vapor explosion). For the directional solidification problem, solution of the fully coupled solute and energy equations reveals the evolution of morphologically complex structures such as tip splitting, coarsening and droplet detachment from deep intercellular grooves. A variety of important solute segregation patterns such as necking, coring and banding are also observed. The boiling problem couples the phase change with fluid flow. This requires the solution of the Navier-Stokes and energy equations with interphase mass transfer. The energetic growth of instabilities on planar and circular interfaces during the unstable explosive evaporation of a superheated liquid in microgravity is demonstrated.
Numerical simulation of LIGO input optics
NASA Astrophysics Data System (ADS)
None, Shivanand; Jamal, Nafis; Yoshida, Sanichiro
2005-11-01
Numerical analysis has been carried out to understand the performance of the Input Optics used in the first generation of LIGO (Laser Interferometer Gravitational-wave Observatory) detector. The input optics is a subsystem consisting of a mode cleaner and mode-matching telescope, where all the optics are suspended and installed in vacuum. Using the end-to-end package (LIGO programming language), computer codes have been made to simulate the input optics. Giving realistic seismic noise to the suspension point of the optics and using the length sensing/alignment sensing control for the mode cleaner, the performance of the input optics has been simulated under various scenarios such as with an order of magnitude higher seismic noise than the normal level, and with/without the alignment sensing control feedback from the arm cavity to the mode-matching telescope. The results are assessed in terms of the beam pointing fluctuation of the laser beam going into the arm cavities, and its influence on the optical coupling to the arm cavities and the noise level at the gravitational wave port signal.
NASA Astrophysics Data System (ADS)
Aroudam, El. H.
In this paper, we present a modelling of the performance of a reactor of a solar cooling machine based carbon-ammonia activated bed. Hence, for a solar radiation, measured in the Energetic Laboratory of the Faculty of Sciences in Tetouan (northern Morocco), the proposed model computes the temperature distribution, the pressure and the ammonia concentration within the activated carbon bed. The Dubinin-Radushkevich formula is used to compute the ammonia concentration distribution and the daily cycled mass necessary to produce a cooling effect for an ideal machine. The reactor is heated at a maximum temperature during the day and cool at the night. A numerical simulation is carried out employing the recorded solar radiation data measured locally and the daily ambient temperature for the typical clear days. Initially the reactor is at ambient temperature, evaporating pressure; Pev=Pst(Tev=0 ∘C) and maintained at uniform concentration. It is heated successively until the threshold temperature corresponding to the condensing pressure; Pcond=Pst(Tam) (saturation pressure at ambient temperature; in the condenser) and until a maximum temperature at a constant pressure; Pcond. The cooling of the reactor is characterised by a fall of temperature to the minimal values at night corresponding to the end of a daily cycle. We use the mass balance equations as well as energy equation to describe heat and mass transfer inside the medium of three phases. A numerical solution of the obtained non linear equations system based on the implicit finite difference method allows to know all parameters characteristic of the thermodynamic cycle and consider principally the daily evolution of temperature, ammonia concentration for divers positions inside the reactor. The tube diameter of the reactor shows the dependence of the optimum value on meteorological parameters for 1 m2 of collector surface.
Numerical Simulations of Falling Sphere Viscometry Experiments.
NASA Astrophysics Data System (ADS)
O Dwyer, L.; Kellogg, L. H.; Lesher, C. E.
2007-12-01
The falling sphere technique based on Stokes' law is widely used to determine the viscosities of geologically relevant melts at high pressures. Stokes' law is valid when a rigid sphere falls slowly and steadily through a stationary and infinite Newtonian medium of uniform properties. High-pressure falling sphere experiments however, usually involve dropping a dense, refractory sphere through a liquid contained by a cylindrical capsule of finite size. The sphere velocity is influenced by the walls (Faxen correction) and ends of the capsule, and possible convective motion of the fluid. Efforts are made to minimize thermal gradients in laboratory experiments, but small temperature differences within the capsule can lead to convection complicating interpretation. We utilize GALE (Moresi et al., 2003;), a finite element particle-in-cell code, to examine these factors in numerical models of conditions similar to those of high-pressure experiments. Our modeling considers a three- dimensional box or cylinder containing a cluster of particles that represent the dense sphere in laboratory experiments surrounded by low viscosity particles representing the melt. GALE includes buoyancy forces, heat flow, and viscosity variations so our model can be used to assess the effects of the capsule's walls and ends, and the consequences of thermal gradients on the sphere's velocity and trajectory. Comparisons between our numerical simulations and real-time falling sphere experiments involving lower viscosity molten komatiite are made to assess the validity of Stokes' law with the standard Faxen correction included, and formulations considering end effects. The modeling also permits an evaluation of the uncertainties in recovering accurate liquid viscosities from Stokes' law when a dense sphere falls through a convecting low viscosity melt. It also allows us to assess acceleration to a terminal velocity that can provide constraints on melt viscosity in experiments in which the terminal
Numerical simulation of "an American haboob"
NASA Astrophysics Data System (ADS)
Vukovic, A.; Vujadinovic, M.; Pejanovic, G.; Andric, J.; Kumjian, M. R.; Djurdjevic, V.; Dacic, M.; Prasad, A. K.; El-Askary, H. M.; Paris, B. C.; Petkovic, S.; Nickovic, S.; Sprigg, W. A.
2014-04-01
A dust storm of fearful proportions hit Phoenix in the early evening hours of 5 July 2011. This storm, an American haboob, was predicted hours in advance because numerical, land-atmosphere modeling, computing power and remote sensing of dust events have improved greatly over the past decade. High-resolution numerical models are required for accurate simulation of the small scales of the haboob process, with high velocity surface winds produced by strong convection and severe downbursts. Dust productive areas in this region consist mainly of agricultural fields, with soil surfaces disturbed by plowing and tracks of land in the high Sonoran Desert laid barren by ongoing draught. Model simulation of the 5 July 2011 dust storm uses the coupled atmospheric-dust model NMME-DREAM (Non-hydrostatic Mesoscale Model on E grid, Janjic et al., 2001; Dust REgional Atmospheric Model, Nickovic et al., 2001; Pérez et al., 2006) with 4 km horizontal resolution. A mask of the potentially dust productive regions is obtained from the land cover and the normalized difference vegetation index (NDVI) data from the Moderate Resolution Imaging Spectroradiometer (MODIS). The scope of this paper is validation of the dust model performance, and not use of the model as a tool to investigate mechanisms related to the storm. Results demonstrate the potential technical capacity and availability of the relevant data to build an operational system for dust storm forecasting as a part of a warning system. Model results are compared with radar and other satellite-based images and surface meteorological and PM10 observations. The atmospheric model successfully hindcasted the position of the front in space and time, with about 1 h late arrival in Phoenix. The dust model predicted the rapid uptake of dust and high values of dust concentration in the ensuing storm. South of Phoenix, over the closest source regions (~25 km), the model PM10 surface dust concentration reached ~2500 μg m-3, but
Numerical simulation of "An American Haboob"
NASA Astrophysics Data System (ADS)
Vukovic, A.; Vujadinovic, M.; Pejanovic, G.; Andric, J.; Kumjian, M. R.; Djurdjevic, V.; Dacic, M.; Prasad, A. K.; El-Askary, H. M.; Paris, B. C.; Petkovic, S.; Nickovic, S.; Sprigg, W. A.
2013-10-01
A dust storm of fearful proportions hit Phoenix in the early evening hours of 5 July 2011. This storm, an American haboob, was predicted hours in advance because numerical, land-atmosphere modeling, computing power and remote sensing of dust events have improved greatly over the past decade. High resolution numerical models are required for accurate simulation of the small-scales of the haboob process, with high velocity surface winds produced by strong convection and severe downbursts. Dust productive areas in this region consist mainly of agricultural fields, with soil surfaces disturbed by plowing and tracks of land in the high Sonoran desert laid barren by ongoing draught. Model simulation of the 5 July 2011 dust storm uses the coupled atmospheric-dust model NMME-DREAM with 3.5 km horizontal resolution. A mask of the potentially dust productive regions is obtained from the land cover and the Normalized Difference Vegetation Index (NDVI) data from the Moderate Resolution Imaging Spectroradiometer (MODIS). Model results are compared with radar and other satellite-based images and surface meteorological and PM10 observations. The atmospheric model successfully hindcasted the position of the front in space and time, with about 1 h late arrival in Phoenix. The dust model predicted the rapid uptake of dust and high values of dust concentration in the ensuing storm. South of Phoenix, over the closest source regions (~ 25 km), the model PM10 surface dust concentration reached ~ 2500 μg m-3, but underestimated the values measured by the PM10stations within the city. Model results are also validated by the MODIS aerosol optical depth (AOD), employing deep blue (DB) algorithms for aerosol loadings. Model validation included Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), equipped with the lidar instrument, to disclose the vertical structure of dust aerosols as well as aerosol subtypes. Promising results encourage further research and
Numerical simulation of magma chamber dynamics.
NASA Astrophysics Data System (ADS)
Longo, Antonella; Papale, Paolo; Montagna, Chiara Paola; Vassalli, Melissa; Giudice, Salvatore; Cassioli, Andrea
2010-05-01
Magma chambers are characterized by periodic arrivals of deep magma batches that give origin to complex patterns of magma convection and mixing, and modify the distribution of physical quantities inside the chamber. We simulate the transient, 2D, multi-component homogeneous dynamics in geometrically complex dyke+chamber systems, by means of GALES, a finite element parallel C++ code solving mass, momentum and energy equations for multi-component homogeneous gas-liquid (± crystals) mixtures in compressible-to-incompressible flow conditions. Code validation analysis includes several cases from the classical engineering literature, corresponding to a variety of subsonic to supersonic gas-liquid flow regimes (see http://www.pi.ingv.it/~longo/gales/gales.html). The model allows specification of the composition of the different magmas in the domain, in terms of ten major oxides plus the two volatile species H2O and CO2. Gas-liquid thermodynamics are modeled by using the compositional dependent, non-ideal model in Papale et al. (Chem.. Geol., 2006). Magma properties are defined in terms of local pressure, temperature, and composition including volatiles. Several applications are performed within domains characterized by the presence of one or more magma chambers and one or more dykes, with different geometries and characteristic size from hundreds of m to several km. In most simulations an initial compositional interface is placed at the top of a feeding dyke, or at larger depth, with the deeper magma having a lower density as a consequence of larger volatile content. The numerical results show complex patterns of magma refilling in the chamber, with alternating phases of magma ingression and magma sinking from the chamber into the feeding dyke. Intense mixing takes place in feeding dykes, so that the new magma entering the chamber is always a mixture of the deep and the initially resident magma. Buoyant plume rise occurs through the formation of complex convective
Numerical Simulations of Saturn's Polar Cyclones
NASA Astrophysics Data System (ADS)
Brueshaber, Shawn R.; Sayanagi, Kunio M.
2014-11-01
Shawn R. Brueshaber, Department of Mechanical Engineering, Western Michigan UniversityKunio M. Sayanagi, Atmospheric and Planetary Sciences, Hampton UniversityCassini mission to Saturn has revealed evidences of a warm core cyclone centered on each of the poles of the planet. The morphology of the clouds in these cyclones resembles that of a terrestrial hurricane. The formation and maintenance mechanisms of these large polar cyclones are yet to be explained. Scott (2011, Astrophys. Geophys. Fluid Dyn) proposed that cyclonic vortices beta-drifting poleward can result in a polar cyclone, and demonstrated that beta-drifting cyclonic vortices can indeed cause accumulation of cyclonic vorticity at the pole using a 1-layer quasi-geostrophic model.The objectives of our project is to test Scott's hypothesis using a 1.5-layer shallow-water model and many-layer primitive equations model. We use the Explicit Planetary Isentropic Coordinate (EPIC) model (Dowling et al. 1998, 2004, Icarus) to perform direct numerical simulations of Saturn's polar atmosphere. To date, our project has focused on modifying the model to construct a polar rectangular model grid in order to avoid the problem of polar singularity associated with the conventional latitude-longitude grids employed in many general circulation models. We present our preliminary simulations, which show beta-drifting cyclones cause a poleward flux of cyclonic vorticity, which is consistent with Scott's results.Our study is partially supported by NASA Outer Planets Research Grant NNX12AR38G and NSF Astronomy and Astrophysics Grant 1212216 to KMS.
Numeric Simulation of Plant Signaling Networks1
Genoud, Thierry; Trevino Santa Cruz, Marcela B.; Métraux, Jean-Pierre
2001-01-01
Plants have evolved an intricate signaling apparatus that integrates relevant information and allows an optimal response to environmental conditions. For instance, the coordination of defense responses against pathogens involves sophisticated molecular detection and communication systems. Multiple protection strategies may be deployed differentially by the plant according to the nature of the invading organism. These responses are also influenced by the environment, metabolism, and developmental stage of the plant. Though the cellular signaling processes traditionally have been described as linear sequences of events, it is now evident that they may be represented more accurately as network-like structures. The emerging paradigm can be represented readily with the use of Boolean language. This digital (numeric) formalism allows an accurate qualitative description of the signal transduction processes, and a dynamic representation through computer simulation. Moreover, it provides the required power to process the increasing amount of information emerging from the fields of genomics and proteomics, and from the use of new technologies such as microarray analysis. In this review, we have used the Boolean language to represent and analyze part of the signaling network of disease resistance in Arabidopsis. PMID:11500542
Numerical simulations of Modified Newtonian Dynamics
NASA Astrophysics Data System (ADS)
Candlish, G. N.; Smith, R.; Fellhauer, M.
2016-05-01
The ΛCDM standard cosmological model is strongly supported by multiple lines of evidence, particularly from observations at large scales such as the CMB and large scale structure. There are some indications, however, of problems at smaller scales. An alternative to the CDM approach is to modify the gravitational force, as exemplified by the MOdified Newtonian Dynamics (MOND) idea. While evidence suggests MOND cannot account for dynamics at all scales without dark matter, it has been successful at galactic scales. Due to the complexity of the theory, however, most tests of MOND have extended no further than using a simple scaling relation to determine rotation curves or velocity dispersions. Therefore, to test the concept more thoroughly we require numerical simulations. We discuss the development and testing of a new N-body solver, using two distinct formulations of MOND, that is incorporated into the RAMSES code. The theory of MOND as a modification of Newtonian gravity is briefly summarised. We then show how it is implemented in the code, providing an example of an idealised test case and future applications.
Numeric simulation of plant signaling networks.
Genoud, T; Trevino Santa Cruz, M B; Métraux, J P
2001-08-01
Plants have evolved an intricate signaling apparatus that integrates relevant information and allows an optimal response to environmental conditions. For instance, the coordination of defense responses against pathogens involves sophisticated molecular detection and communication systems. Multiple protection strategies may be deployed differentially by the plant according to the nature of the invading organism. These responses are also influenced by the environment, metabolism, and developmental stage of the plant. Though the cellular signaling processes traditionally have been described as linear sequences of events, it is now evident that they may be represented more accurately as network-like structures. The emerging paradigm can be represented readily with the use of Boolean language. This digital (numeric) formalism allows an accurate qualitative description of the signal transduction processes, and a dynamic representation through computer simulation. Moreover, it provides the required power to process the increasing amount of information emerging from the fields of genomics and proteomics, and from the use of new technologies such as microarray analysis. In this review, we have used the Boolean language to represent and analyze part of the signaling network of disease resistance in Arabidopsis. PMID:11500542
Numerical simulation of noninvasive blood pressure measurement.
Hayashi, Satoru; Hayase, Toshiyuki; Shirai, Atsushi; Maruyama, Masaru
2006-10-01
In this paper, a simulation model based on the partially pressurized collapsible tube model for reproducing noninvasive blood pressure measurement is presented. The model consists of a collapsible tube, which models the pressurized part of the artery, rigid pipes connected to the collapsible tube, which model proximal and distal region far from the pressurized part, and the Windkessel model, which represents the capacitance and the resistance of the distal part of the circulation. The blood flow is simplified to a one-dimensional system. Collapse and expansion of the tube is represented by the change in the cross-sectional area of the tube considering the force balance acting on the tube membrane in the direction normal to the tube axis. They are solved using the Runge-Kutta method. This simple model can easily reproduce the oscillation of inner fluid and corresponding tube collapse typical for the Korotkoff sounds generated by the cuff pressure. The numerical result is compared with the experiment and shows good agreement. PMID:16995754
Direct Numerical Simulation of Cell Printing
NASA Astrophysics Data System (ADS)
Qiao, Rui; He, Ping
2010-11-01
Structural cell printing, i.e., printing three dimensional (3D) structures of cells held in a tissue matrix, is gaining significant attention in the biomedical community. The key idea is to use desktop printer or similar devices to print cells into 3D patterns with a resolution comparable to the size of mammalian cells, similar to that in living organs. Achieving such a resolution in vitro can lead to breakthroughs in areas such as organ transplantation and understanding of cell-cell interactions in truly 3D spaces. Although the feasibility of cell printing has been demonstrated in the recent years, the printing resolution and cell viability remain to be improved. In this work, we investigate one of the unit operations in cell printing, namely, the impact of a cell-laden droplet into a pool of highly viscous liquids using direct numerical simulations. The dynamics of droplet impact (e.g., crater formation and droplet spreading and penetration) and the evolution of cell shape and internal stress are quantified in details.
Direct numerical simulation of active fiber composite
NASA Astrophysics Data System (ADS)
Kim, Seung J.; Hwang, Joon S.; Paik, Seung H.
2003-08-01
Active Fiber Composites (AFC) possess desirable characteristics for smart structure applications. One major advantage of AFC is the ability to create anisotropic laminate layers useful in applications requiring off-axis or twisting motions. AFC is naturally composed of two different constituents: piezoelectric fiber and matrix. Therefore, homogenization method, which is utilized in the analysis of laminated composite material, has been used to characterize the material properties. Using this approach, the global behaviors of the structures are predicted in an averaged sense. However, this approach has intrinsic limitations in describing the local behaviors in the level of the constituents. Actually, the failure analysis of AFC requires the knowledge of the local behaviors. Therefore, microscopic approach is necessary to predict the behaviors of AFC. In this work, a microscopic approach for the analysis of AFC was performed. Piezoelectric fiber and matrix were modeled separately and finite element method using three-dimensional solid elements was utilized. Because fine mesh is essential, high performance computing technology was applied to the solution of the immense degree-of-freedom problem. This approach is called Direct Numerical Simulation (DNS) of structure. Through the DNS of AFC, local stress distribution around the interface of fiber and matrix was analyzed.
Direct numerical simulations of aeolian sand ripples
Durán, Orencio; Claudin, Philippe; Andreotti, Bruno
2014-01-01
Aeolian sand beds exhibit regular patterns of ripples resulting from the interaction between topography and sediment transport. Their characteristics have been so far related to reptation transport caused by the impacts on the ground of grains entrained by the wind into saltation. By means of direct numerical simulations of grains interacting with a wind flow, we show that the instability turns out to be driven by resonant grain trajectories, whose length is close to a ripple wavelength and whose splash leads to a mass displacement toward the ripple crests. The pattern selection results from a compromise between this destabilizing mechanism and a diffusive downslope transport which stabilizes small wavelengths. The initial wavelength is set by the ratio of the sediment flux and the erosion/deposition rate, a ratio which increases linearly with the wind velocity. We show that this scaling law, in agreement with experiments, originates from an interfacial layer separating the saltation zone from the static sand bed, where momentum transfers are dominated by midair collisions. Finally, we provide quantitative support for the use of the propagation of these ripples as a proxy for remote measurements of sediment transport. PMID:25331873
Direct numerical simulations of aeolian sand ripples.
Durán, Orencio; Claudin, Philippe; Andreotti, Bruno
2014-11-01
Aeolian sand beds exhibit regular patterns of ripples resulting from the interaction between topography and sediment transport. Their characteristics have been so far related to reptation transport caused by the impacts on the ground of grains entrained by the wind into saltation. By means of direct numerical simulations of grains interacting with a wind flow, we show that the instability turns out to be driven by resonant grain trajectories, whose length is close to a ripple wavelength and whose splash leads to a mass displacement toward the ripple crests. The pattern selection results from a compromise between this destabilizing mechanism and a diffusive downslope transport which stabilizes small wavelengths. The initial wavelength is set by the ratio of the sediment flux and the erosion/deposition rate, a ratio which increases linearly with the wind velocity. We show that this scaling law, in agreement with experiments, originates from an interfacial layer separating the saltation zone from the static sand bed, where momentum transfers are dominated by midair collisions. Finally, we provide quantitative support for the use of the propagation of these ripples as a proxy for remote measurements of sediment transport. PMID:25331873
Numerical simulations of drainage flows on Mars
NASA Astrophysics Data System (ADS)
Parish, Thomas R.; Howard, Alan D.
Data collected by Viking Landers have shown that the meteorology of the near surface Martian environment is analogous to desertlike terrestrial conditions. Geological evidence such as dunes and frost streaks indicate that the surface wind is a potentially important factor in scouring of the martian landscape. In particular, the north polar basin shows erosional features that suggest katabatic wind convergence into broad valleys near the margin of the polar cap. The pattern of katabatic wind drainage off the north polar cap is similar to that observed on Earth over Antarctica or Greenland. The sensitivity is explored of Martian drainage flows to variations in terrain slope and diurnal heating using a numerical modeling approach. The model used is a 2-D sigma coordinate primitive equation system that has been used for simulations of Antarctic drainage flows. Prognostic equations include the flux forms of the horizontal scalar momentum equations, temperature, and continuity. Parameterization of both longwave (terrestrial) and shortwave (solar) radiation is included. Turbulent transfer of heat and momentum in the Martian atmosphere remains uncertain since relevant measurements are essentially nonexistent.
Numerical simulations of drainage flows on Mars
NASA Technical Reports Server (NTRS)
Parish, Thomas R.; Howard, Alan D.
1992-01-01
Data collected by Viking Landers have shown that the meteorology of the near surface Martian environment is analogous to desertlike terrestrial conditions. Geological evidence such as dunes and frost streaks indicate that the surface wind is a potentially important factor in scouring of the martian landscape. In particular, the north polar basin shows erosional features that suggest katabatic wind convergence into broad valleys near the margin of the polar cap. The pattern of katabatic wind drainage off the north polar cap is similar to that observed on Earth over Antarctica or Greenland. The sensitivity is explored of Martian drainage flows to variations in terrain slope and diurnal heating using a numerical modeling approach. The model used is a 2-D sigma coordinate primitive equation system that has been used for simulations of Antarctic drainage flows. Prognostic equations include the flux forms of the horizontal scalar momentum equations, temperature, and continuity. Parameterization of both longwave (terrestrial) and shortwave (solar) radiation is included. Turbulent transfer of heat and momentum in the Martian atmosphere remains uncertain since relevant measurements are essentially nonexistent.
Cloud interactions and merging - Numerical simulations
NASA Technical Reports Server (NTRS)
Tao, W.-K.; Simpson, J.
1984-01-01
A total of 48 numerical experiments have been performed to study cloud interactions adn merging by means of a two-dimensional multi-cell model. Two soundings of deep convection during GATE and two different magnitudes of large-scale lifting have been used as the initial conditions and as the main forcing on the model. Over two hundred groups of cloud systems with a life history of over sixty minutes have been generated under the influence of different combinations of the stratification and large-scale lifting. The results demonstrate the increase in convective activity and in amount of precipitation with increased intensity of large-scale lifting. The results also show increased occurrence of cloud merger with increased intensity of large-scale lifting. The most unfavorable environmental conditions for cloud merging are (1) less unstable stratification of the atmosphere and (2) weaker large-scale lifting. A total of fourteen cloud systems qualify as mergers. Two selected cases will be described dynamically and thermodynamically in this paper. Although these cloud mergers have been simulated under the influence of different synoptic-scale conditions, the major physical mechanism related to the cloud merging process is the same as that proposed by Simpson. Cumulus downdrafts and associated cold outflows play a dominant role in the merging process in all cases studied.
Numerical simulation of ball-racket impact
NASA Astrophysics Data System (ADS)
Yu, Yingpang
The collision of a ball with a tennis racket is usually modeled in terms of rigid body dynamics or an elastic system involving only a few springs. In this paper, we study the impact between a tennis ball and racket, by modeling the tennis ball in two different yaws. One method models the tennis ball as a Hertz elastic body and the other one models the ball by a more accurate finite element analysis. In the first model, we assume that the elastic properties of the ball obeys Hertz's law. In the finite element model, we consider the tennis ball as a shell witch is a elastic system constructed out of many isotropic small linear flat, elements, witch have both elastic and damping properties. The damping in each way is approximated as viscous term. In both methods, we study the static condition of deformation against a rigid surface before applying these models to dynamical processes. We compare these two methods and eventually determine how the racket parameters effect the performance of the racket, using numerical simulations. Comparison with experiment are show to confirm the general conclusion of the model.
Advanced in turbulence physics and modeling by direct numerical simulations
NASA Technical Reports Server (NTRS)
Reynolds, W. C.
1987-01-01
The advent of direct numerical simulations of turbulence has opened avenues for research on turbulence physics and turbulence modeling. Direct numerical simulation provides values for anything that the scientist or modeler would like to know about the flow. An overview of some recent advances in the physical understanding of turbulence and in turbulence modeling obtained through such simulations is presented.
Direct numerical simulation of turbulent aerosol coagulation
NASA Astrophysics Data System (ADS)
Reade, Walter Caswell
There are numerous systems-including both industrial applications and natural occurring phenomena-in which the collision/coagulation rates of aerosols are of significant interest. Two examples are the production of fine powders (such as titanium dioxide) and the formation of rain drops in the atmosphere. During the last decade, it has become apparent that dense aerosol particles behave much differently in a turbulent fluid than has been previously assumed. Particles with a response time on the order of the small-scale fluid time scale tend to collect in regions of low vorticity. The result is a particle concentration field that can be highly non-uniform. Sundaram and Collins (1997) recently demonstrated the effect that turbulence can have on the particle collision rate of a monodisperse system. The collision rates of finite-inertia particles can be as much as two orders of magnitude greater than particles that precisely follow the fluid streamlines. Sundaram and Collins derived a general collision expression that explicitly accounted for the two phenomena that affect the collision rate-changes in the particle concentration field and changes in the particle relative velocities. The result of Sundaram and Collins has generated further interest in the turbulent-aerosol problem. This thesis shows that, in addition to changing the rate that an aerosol size distribution might form, turbulence has the potential of dramatically changing the shape of the distribution. This result is demonstrated using direct numerical simulation of a turbulent-aerosol system over a wide range of particle parameters, and a moderate range of turbulence levels. Results show that particles with a small (but finite) initial inertia have the greatest potential of forming broad size distributions. The shape of the resulting size distribution is also affected by the initial size of the particles. Observations are explained using the statistics identified by Sundaram and Collins (1997). A major
Neutronic/Thermalhydraulic Coupling Technigues for Sodium Cooled Fast Reactor Simulations
Jean Ragusa; Andrew Siegel; Jean-Michel Ruggieri
2010-09-28
The objective of this project was to test new coupling algorithms and enable efficient and scalable multi-physics simulations of advanced nuclear reactors, with considerations regarding the implementation of such algorithms in massively parallel environments. Numerical tests were carried out to verify the proposed approach and the examples included some reactor transients. The project was directly related to the Sodium Fast Reactor program element of the Generation IV Nuclear Energy Systems Initiative and the Advanced Fuel cycle Initiative, and, supported the requirement of high-fidelity simulation as a mean of achieving the goals of the presidential Global Nuclear Energy Partnership (GNEP) vision.
Holladay, Jamelyn D.; Wang, Yong
2015-05-01
Microscale (<5W) reformers for hydrogen production have been investigated for over a decade. These devices are intended to provide hydrogen for small fuel cells. Due to the reformer’s small size, numerical simulations are critical to understand heat and mass transfer phenomena occurring in the systems. This paper reviews the development of the numerical codes and details the reaction equations used. The majority of the devices utilized methanol as the fuel due to methanol’s low reforming temperature and high conversion, although, there are several methane fueled systems. As computational power has decreased in cost and increased in availability, the codes increased in complexity and accuracy. Initial models focused on the reformer, while more recently, the simulations began including other unit operations such as vaporizers, inlet manifolds, and combustors. These codes are critical for developing the next generation systems. The systems reviewed included, plate reactors, microchannel reactors, annulus reactors, wash-coated, packed bed systems.
Computational Fluid Dynamics Simulation of Fluidized Bed Polymerization Reactors
Rong Fan
2006-08-09
, monovariate population balance, bivariate population balance, aggregation and breakage equation and DQMOM-Multi-Fluid model are described. In the last section of Chapter 3, numerical methods involved in the multi-fluid model and time-splitting method are presented. Chapter 4 is based on a paper about application of DQMOM to polydisperse gas-solid fluidized beds. Results for a constant aggregation and breakage kernel and a kernel developed from kinetic theory are shown. The effect of the aggregation success factor and the fragment distribution function are investigated. Chapter 5 shows the work on validation of mixing and segregation phenomena in gas-solid fluidized beds with a binary mixture or a continuous size distribution. The simulation results are compared with available experiment data and discrete-particle simulation. Chapter 6 presents the project with Univation Technologies on CFD simulation of a Polyethylene pilot-scale FB reactor, The fluid dynamics, mass/heat transfer and particle size distribution are investigated through CFD simulation and validated with available experimental data. The conclusions of this study and future work are discussed in Chapter 7.
Multi-physics nuclear reactor simulator for advanced nuclear engineering education
Yamamoto, A.
2012-07-01
Multi-physics nuclear reactor simulator, which aims to utilize for advanced nuclear engineering education, is being introduced to Nagoya Univ.. The simulator consists of the 'macroscopic' physics simulator and the 'microscopic' physics simulator. The former performs real time simulation of a whole nuclear power plant. The latter is responsible to more detail numerical simulations based on the sophisticated and precise numerical models, while taking into account the plant conditions obtained in the macroscopic physics simulator. Steady-state and kinetics core analyses, fuel mechanical analysis, fluid dynamics analysis, and sub-channel analysis can be carried out in the microscopic physics simulator. Simulation calculations are carried out through dedicated graphical user interface and the simulation results, i.e., spatial and temporal behaviors of major plant parameters are graphically shown. The simulator will provide a bridge between the 'theories' studied with textbooks and the 'physical behaviors' of actual nuclear power plants. (authors)
Numerical Simulation of Complex Turbomachinery Flows
NASA Technical Reports Server (NTRS)
Chernobrovkin, A. A.; Lakshiminarayana, B.
1999-01-01
An unsteady, multiblock, Reynolds Averaged Navier Stokes solver based on Runge-Kutta scheme and Pseudo-time step for turbo-machinery applications was developed. The code was validated and assessed against analytical and experimental data. It was used to study a variety of physical mechanisms of unsteady, three-dimensional, turbulent, transitional, and cooling flows in compressors and turbines. Flow over a cylinder has been used to study effects of numerical aspects on accuracy of prediction of wake decay and transition, and to modify K-epsilon models. The following simulations have been performed: (a) Unsteady flow in a compressor cascade: Three low Reynolds number turbulence models have been assessed and data compared with Euler/boundary layer predictions. Major flow features associated with wake induced transition were predicted and studied; (b) Nozzle wake-rotor interaction in a turbine: Results compared to LDV data in design and off-design conditions, and cause and effect of unsteady flow in turbine rotors were analyzed; (c) Flow in the low-pressure turbine: Assessed capability of the code to predict transitional, attached and separated flows at a wide range of low Reynolds numbers and inlet freestream turbulence intensity. Several turbulence and transition models have been employed and comparisons made to experiments; (d) leading edge film cooling at compound angle: Comparisons were made with experiments, and the flow physics of the associated vortical structures were studied; and (e) Tip leakage flow in a turbine. The physics of the secondary flow in a rotor was studied and sources of loss identified.
Numerical simulation of 3D breaking waves
NASA Astrophysics Data System (ADS)
Fraunie, Philippe; Golay, Frederic
2015-04-01
Numerical methods dealing with two phase flows basically can be classified in two ways : the "interface tracking" methods when the two phases are resolved separately including boundary conditions fixed at the interface and the "interface capturing" methods when a single flow is considered with variable density. Physical and numerical properties of the two approaches are discussed, based on some numerical experiments performed concerning 3D breaking waves. Acknowledgements : This research was supported by the Modtercom program of Region PACA.
Numerical simulation of small perturbation transonic flows
NASA Technical Reports Server (NTRS)
Seebass, A. R.; Yu, N. J.
1976-01-01
The results of a systematic study of small perturbation transonic flows are presented. Both the flow over thin airfoils and the flow over wedges were investigated. Various numerical schemes were employed in the study. The prime goal of the research was to determine the efficiency of various numerical procedures by accurately evaluating the wave drag, both by computing the pressure integral around the body and by integrating the momentum loss across the shock. Numerical errors involved in the computations that affect the accuracy of drag evaluations were analyzed. The factors that effect numerical stability and the rate of convergence of the iterative schemes were also systematically studied.
NUMERICAL NOISE PM SIMULATION IN CMAQ
We have found that numerical noise in the latest release of CMAQ using the yamo advection scheme when compiled on Linux cluster with pgf90 (5.0 or 6.0). We recommend to use -C option to eliminate the numerical noise.
Numerical simulation of seasonal groundwater pumping
NASA Astrophysics Data System (ADS)
Filimonova, Elena; Baldenkov, Mikhail
2015-04-01
Increasing scarcity and contamination of water recourses require innovative water management strategies such as combined water system. The combined water system is a complex technology comprising two separate wells, major catchment-zone well and compensation pumping well, located inside a single stream basin. The major well is supplied by the well's catchment zone or surface flow, thus depleting the stream flow. The pumping rate of a major well is determined by the difference between the current stream flow and the minimum permissible stream flow. The deficiency of the stream flow in dry seasons can be compensated for by the short-term pumping of groundwater. The compensation pumping rate is determined by the difference between water demand and the permissible water withdrawal of the major well. The source for the compensation well is the aquifer storage. The estimation of streamflow depletion caused by compensation pumping is major question to evaluate the efficiency of the combined water system. Short-term groundwater pumping can use aquifer storage instead of catchment-zone water until the drawdown reaches the edge of the stream. Traditionally pumping simulation calculates in two-step procedure. Natural conditions, an aquifer system is in an approximate dynamic equilibrium, describe by steady-state model. A steady-state solution provides an initial heads, a set of flows through boundaries, and used as initial state for transient solutions, when pumping is imposed on an aquifer system. The transient solutions provide the total change in flows through the boundaries. A difference between the transient and steady-state solutions estimates the capture and the streamflow depletion. Numerical modeling of cyclical compensation pumping has special features: the periodic solution, the seasonal changes through the boundaries and the importance even small drawdown of stream level. When seasonality is a modeling feature, traditional approach leads to mistaken values of
Coupling Schemes for Multiphysics Reactor Simulation
Vijay Mahadeven; Jean Ragusa
2007-11-01
This report documents the progress of the student Vijay S. Mahadevan from the Nuclear Engineering Department of Texas A&M University over the summer of 2007 during his visit to the INL. The purpose of his visit was to investigate the physics-based preconditioned Jacobian-free Newton-Krylov method applied to physics relevant to nuclear reactor simulation. To this end he studied two test problems that represented reaction-diffusion and advection-reaction. These two test problems will provide the basis for future work in which neutron diffusion, nonlinear heat conduction, and a twophase flow model will be tightly coupled to provide an accurate model of a BWR core.
MONTE CARLO SIMULATIONS OF PERIODIC PULSED REACTOR WITH MOVING GEOMETRY PARTS
Cao, Yan; Gohar, Yousry
2015-11-01
In a periodic pulsed reactor, the reactor state varies periodically from slightly subcritical to slightly prompt supercritical for producing periodic power pulses. Such periodic state change is accomplished by a periodic movement of specific reactor parts, such as control rods or reflector sections. The analysis of such reactor is difficult to perform with the current reactor physics computer programs. Based on past experience, the utilization of the point kinetics approximations gives considerable errors in predicting the magnitude and the shape of the power pulse if the reactor has significantly different neutron life times in different zones. To accurately simulate the dynamics of this type of reactor, a Monte Carlo procedure using the transfer function TRCL/TR of the MCNP/MCNPX computer programs is utilized to model the movable reactor parts. In this paper, two algorithms simulating the geometry part movements during a neutron history tracking have been developed. Several test cases have been developed to evaluate these procedures. The numerical test cases have shown that the developed algorithms can be utilized to simulate the reactor dynamics with movable geometry parts.
Numerical simulation of the 1988 midwestern drought
Chern, Jiun-Dar; Sun, Wen-Yih
1997-11-01
In this study, the Purdue Regional Model (PRM) is utilized to simulate the monthly evolution of the weather patterns during the summer of 1988. The primary goal of this study is to develop and validate the PRM. The PRM, a regional climate model, is a hydrostatic primitive-equation model that uses the Arakawa C staggered grid in the horizontal and a terrain-following vertical coordinate. The model was used to simulate the 1988 drought for one month with lateral boundary conditions. The simulation reproduced the driest events in the Midwest; however, the simulated precipitation along the Gulf coast and Florida was underestimated. This suggests that the 60 km model resolution used in the simulation was not high enough to simulate the convective precipitation associated with the sea breeze circulations. 10 refs., 5 figs.
Numerical Simulation Of Cutting Of Gear Teeth
NASA Technical Reports Server (NTRS)
Oswald, Fred B.; Huston, Ronald L.; Mavriplis, Dimitrios
1994-01-01
Shapes of gear teeth produced by gear cutters of specified shape simulated computationally, according to approach based on principles of differential geometry. Results of computer simulation displayed as computer graphics and/or used in analyses of design, manufacturing, and performance of gears. Applicable to both standard and non-standard gear-tooth forms. Accelerates and facilitates analysis of alternative designs of gears and cutters. Simulation extended to study generation of surfaces other than gears. Applied to cams, bearings, and surfaces of arbitrary rolling elements as well as to gears. Possible to develop analogous procedures for simulating manufacture of skin surfaces like automobile fenders, airfoils, and ship hulls.
Numerical Simulation of Two Phase Flows
NASA Technical Reports Server (NTRS)
Liou, Meng-Sing
2001-01-01
Two phase flows can be found in broad situations in nature, biology, and industry devices and can involve diverse and complex mechanisms. While the physical models may be specific for certain situations, the mathematical formulation and numerical treatment for solving the governing equations can be general. Hence, we will require information concerning each individual phase as needed in a single phase. but also the interactions between them. These interaction terms, however, pose additional numerical challenges because they are beyond the basis that we use to construct modern numerical schemes, namely the hyperbolicity of equations. Moreover, due to disparate differences in time scales, fluid compressibility and nonlinearity become acute, further complicating the numerical procedures. In this paper, we will show the ideas and procedure how the AUSM-family schemes are extended for solving two phase flows problems. Specifically, both phases are assumed in thermodynamic equilibrium, namely, the time scales involved in phase interactions are extremely short in comparison with those in fluid speeds and pressure fluctuations. Details of the numerical formulation and issues involved are discussed and the effectiveness of the method are demonstrated for several industrial examples.
NASA Astrophysics Data System (ADS)
Yoshida, Hiroyuki; Takase, Kazuyuki
Thermal-hydraulic design of the current boiling water reactor (BWR) is performed with the subchannel analysis codes which incorporated the correlations based on empirical results including actual-size tests. Then, for the Innovative Water Reactor for Flexible Fuel Cycle (FLWR) core, an actual size test of an embodiment of its design is required to confirm or modify such correlations. In this situation, development of a method that enables the thermal-hydraulic design of nuclear reactors without these actual size tests is desired, because these tests take a long time and entail great cost. For this reason, we developed an advanced thermal-hydraulic design method for FLWRs using innovative two-phase flow simulation technology. In this study, a detailed Two-Phase Flow simulation code using advanced Interface Tracking method: TPFIT is developed to calculate the detailed information of the two-phase flow. In this paper, firstly, we tried to verify the TPFIT code by comparing it with the existing 2-channel air-water mixing experimental results. Secondary, the TPFIT code was applied to simulation of steam-water two-phase flow in a model of two subchannels of a current BWRs and FLWRs rod bundle. The fluid mixing was observed at a gap between the subchannels. The existing two-phase flow correlation for fluid mixing is evaluated using detailed numerical simulation data. This data indicates that pressure difference between fluid channels is responsible for the fluid mixing, and thus the effects of the time average pressure difference and fluctuations must be incorporated in the two-phase flow correlation for fluid mixing. When inlet quality ratio of subchannels is relatively large, it is understood that evaluation precision of the existing two-phase flow correlations for fluid mixing are relatively low.
Numerical simulation of turbulent combustion: Scientific challenges
NASA Astrophysics Data System (ADS)
Ren, ZhuYin; Lu, Zhen; Hou, LingYun; Lu, LiuYan
2014-08-01
Predictive simulation of engine combustion is key to understanding the underlying complicated physicochemical processes, improving engine performance, and reducing pollutant emissions. Critical issues as turbulence modeling, turbulence-chemistry interaction, and accommodation of detailed chemical kinetics in complex flows remain challenging and essential for high-fidelity combustion simulation. This paper reviews the current status of the state-of-the-art large eddy simulation (LES)/prob-ability density function (PDF)/detailed chemistry approach that can address the three challenging modelling issues. PDF as a subgrid model for LES is formulated and the hybrid mesh-particle method for LES/PDF simulations is described. Then the development need in micro-mixing models for the PDF simulations of turbulent premixed combustion is identified. Finally the different acceleration methods for detailed chemistry are reviewed and a combined strategy is proposed for further development.
Polarization transmission at RHIC, numerical simulations
Meot F.; Bai, M.; Liu, C.; Minty, M.; Ranjbar, V.
2012-05-20
Typical tracking simulations regarding the transmission of the polarization in the proton-proton collider RHIC are discussed. They participate in general studies aimed at understanding and improving polarization performances during polarized proton-proton runs.
Numerical simulation of non-Newtonian free shear flows
NASA Technical Reports Server (NTRS)
Homsy, G. M.; Azaiez, J.
1993-01-01
Free shear flows, like those of mixing layers, are encountered in aerodynamics, in the atmosphere, and in the ocean as well as in many industrial applications such as flow reactors or combustion chambers. It is, therefore, crucial to understand the mechanisms governing the process of transition to turbulence in order to predict and control the evolution of the flow. Delaying transition to turbulence as far downstream as possible allows a gain in energy expenditure while accelerating the transition can be of interest in processes where high mixing is desired. Various methods, including the use of polymer additives, can be effective in controlling fluid flows. The drag reduction obtained by the addition of small amounts of high polymers has been an active area of research for the last three decades. It is now widely believed that polymer additives can affect the stability of a large variety of flows and that dilute solutions of these polymers have been shown to produce drag reductions of over 80 percent in internal flows and over 60 percent in external flows under a wide range of conditions. The major thrust of this work is to study the effects of polymer additives on the stability of the incompressible mixing layer through large scale numerical simulations. In particular, we focus on the two dimensional flow and examine how the presence of viscoelasticity may affect the typical structures of the flow, namely roll-up and pairing of vortices.
Numerical study of error propagation in Monte Carlo depletion simulations
Wyant, T.; Petrovic, B.
2012-07-01
Improving computer technology and the desire to more accurately model the heterogeneity of the nuclear reactor environment have made the use of Monte Carlo depletion codes more attractive in recent years, and feasible (if not practical) even for 3-D depletion simulation. However, in this case statistical uncertainty is combined with error propagating through the calculation from previous steps. In an effort to understand this error propagation, a numerical study was undertaken to model and track individual fuel pins in four 17 x 17 PWR fuel assemblies. By changing the code's initial random number seed, the data produced by a series of 19 replica runs was used to investigate the true and apparent variance in k{sub eff}, pin powers, and number densities of several isotopes. While this study does not intend to develop a predictive model for error propagation, it is hoped that its results can help to identify some common regularities in the behavior of uncertainty in several key parameters. (authors)
Numerical error in groundwater flow and solute transport simulation
NASA Astrophysics Data System (ADS)
Woods, Juliette A.; Teubner, Michael D.; Simmons, Craig T.; Narayan, Kumar A.
2003-06-01
Models of groundwater flow and solute transport may be affected by numerical error, leading to quantitative and qualitative changes in behavior. In this paper we compare and combine three methods of assessing the extent of numerical error: grid refinement, mathematical analysis, and benchmark test problems. In particular, we assess the popular solute transport code SUTRA [Voss, 1984] as being a typical finite element code. Our numerical analysis suggests that SUTRA incorporates a numerical dispersion error and that its mass-lumped numerical scheme increases the numerical error. This is confirmed using a Gaussian test problem. A modified SUTRA code, in which the numerical dispersion is calculated and subtracted, produces better results. The much more challenging Elder problem [Elder, 1967; Voss and Souza, 1987] is then considered. Calculation of its numerical dispersion coefficients and numerical stability show that the Elder problem is prone to error. We confirm that Elder problem results are extremely sensitive to the simulation method used.
Numerical simulation of turbulent forced convection in liquid metals
NASA Astrophysics Data System (ADS)
Vodret, S.; Vitale Di Maio, D.; Caruso, G.
2014-11-01
In the frame of the future generation of nuclear reactors, liquid metals are foreseen to be used as a primary coolant. Liquid metals are characterized by a very low Prandtl number due to their very high heat diffusivity. As such, they do not meet the so-called Reynolds analogy which assumes a complete similarity between the momentum and the thermal boundary layers via the use of the turbulent Prandtl number. Particularly, in the case of industrial fluid-dynamic calculations where a resolved computation near walls could be extremely time consuming and could need very large computational resources, the use of the classical wall function approach could lead to an inaccurate description of the temperature profile close to the wall. The first aim of the present study is to investigate the ability of a well- established commercial code (ANSYS FLUENT v.14) to deal with this issue, validating a suitable expression for the turbulent Prandtl number. Moreover, a thermal wall-function developed at Universite Catholique de Louvain has been implemented in FLUENT and validated, overcoming the limits of the solver to define it directly. Both the resolved and unresolved approaches have been carried out for a channel flow case and assessed against available direct numerical and large eddy simulations. A comparison between the numerically evaluated Nusselt number and the main correlations available in the literature has been also carried out. Finally, an application of the proposed methodology to a typical sub-channel case has been performed, comparing the results with literature correlations for tube banks.
Numerical Simulation Of Buckling In Waffle Plants
NASA Technical Reports Server (NTRS)
Yin, Dah N.; Tran, Vu M.
1990-01-01
Accurate results obtained when fillet radii considered. Two reports describe numerical and experimental study of application of PASCO and WAFFLE computer programs to analysis of buckling in integrally machined, biaxially stiffened panel. PASCO (Panal Analysis and Sizing Code) is finite-element stress-and-strain code written for analysis and sizing of uniaxially stiffened panels. WAFFLE program provides comprehensive stress analysis of waffle panel, used to determine bending moments at interfaces.
Numerical simulation of in situ bioremediation
Travis, B.J.
1998-12-31
Models that couple subsurface flow and transport with microbial processes are an important tool for assessing the effectiveness of bioremediation in field applications. A numerical algorithm is described that differs from previous in situ bioremediation models in that it includes: both vadose and groundwater zones, unsteady air and water flow, limited nutrients and airborne nutrients, toxicity, cometabolic kinetics, kinetic sorption, subgridscale averaging, pore clogging and protozoan grazing.
Numerical simulation of hemorrhage in human injury
NASA Astrophysics Data System (ADS)
Chong, Kwitae; Jiang, Chenfanfu; Santhanam, Anand; Benharash, Peyman; Teran, Joseph; Eldredge, Jeff
2015-11-01
Smoothed Particle Hydrodynamics (SPH) is adapted to simulate hemorrhage in the injured human body. As a Lagrangian fluid simulation, SPH uses fluid particles as computational elements and thus mass conservation is trivially satisfied. In order to ensure anatomical fidelity, a three-dimensional reconstruction of a portion of the human body -here, demonstrated on the lower leg- is sampled as skin, bone and internal tissue particles from the CT scan image of an actual patient. The injured geometry is then generated by simulation of ballistic projectiles passing through the anatomical model with the Material Point Method (MPM) and injured vessel segments are identified. From each such injured segment, SPH is used to simulate bleeding, with inflow boundary condition obtained from a coupled 1-d vascular tree model. Blood particles interact with impermeable bone and skin particles through the Navier-Stokes equations and with permeable internal tissue particles through the Brinkman equations. The SPH results are rendered in post-processing for improved visual fidelity. The overall simulation strategy is demonstrated on several injury scenarios in the lower leg.
Numerical simulation of magmatic hydrothermal systems
Ingebritsen, S.E.; Geiger, S.; Hurwitz, S.; Driesner, T.
2010-01-01
The dynamic behavior of magmatic hydrothermal systems entails coupled and nonlinear multiphase flow, heat and solute transport, and deformation in highly heterogeneous media. Thus, quantitative analysis of these systems depends mainly on numerical solution of coupled partial differential equations and complementary equations of state (EOS). The past 2 decades have seen steady growth of computational power and the development of numerical models that have eliminated or minimized the need for various simplifying assumptions. Considerable heuristic insight has been gained from process-oriented numerical modeling. Recent modeling efforts employing relatively complete EOS and accurate transport calculations have revealed dynamic behavior that was damped by linearized, less accurate models, including fluid property control of hydrothermal plume temperatures and three-dimensional geometries. Other recent modeling results have further elucidated the controlling role of permeability structure and revealed the potential for significant hydrothermally driven deformation. Key areas for future reSearch include incorporation of accurate EOS for the complete H2O-NaCl-CO2 system, more realistic treatment of material heterogeneity in space and time, realistic description of large-scale relative permeability behavior, and intercode benchmarking comparisons. Copyright 2010 by the American Geophysical Union.
Numerical simulations in the development of propellant management devices
NASA Astrophysics Data System (ADS)
Gaulke, Diana; Winkelmann, Yvonne; Dreyer, Michael
Propellant management devices (PMDs) are used for positioning the propellant at the propel-lant port. It is important to provide propellant without gas bubbles. Gas bubbles can inflict cavitation and may lead to system failures in the worst case. Therefore, the reliable operation of such devices must be guaranteed. Testing these complex systems is a very intricate process. Furthermore, in most cases only tests with downscaled geometries are possible. Numerical sim-ulations are used here as an aid to optimize the tests and to predict certain results. Based on these simulations, parameters can be determined in advance and parts of the equipment can be adjusted in order to minimize the number of experiments. In return, the simulations are validated regarding the test results. Furthermore, if the accuracy of the numerical prediction is verified, then numerical simulations can be used for validating the scaling of the experiments. This presentation demonstrates some selected numerical simulations for the development of PMDs at ZARM.
A numerical simulation of auroral ionospheric electrodynamics
NASA Technical Reports Server (NTRS)
Mallinckrodt, A. J.
1985-01-01
A computer simulation of auroral ionospheric electrodynamics in the altitude range 80 to 250 km has been developed. The routine will either simulate typical electron precipitation profiles or accept observed data. Using a model background ionosphere, ion production rates are calculated from which equilibrium electron densities and the Hall and Pedersen conductivities may be determined. With the specification of suitable boundary conditions, the entire three-dimensional current system and electric field may be calculated within the simulation region. The results of the application of the routine to a typical inverted-V precipitation profile are demonstrated. The routine is used to explore the observed anticorrelation between electric field magnitude and peak energy in the precipitating electron spectrum of an auroral arc.
Numerical simulations of plasma double layers
NASA Technical Reports Server (NTRS)
Goertz, C. K.; Borovsky, J. E.
1983-01-01
The results of analytical studies of quasi-static electric fields along geomagnetic field lines are discussed. The calculations were targeted at the structure, generation mechanisms and stability parameters. The field consists of two oppositely charged layers, either weakly or strongly charged, with an electric field between. Existence conditions are defined for the double layer field and balancing requirements are explored. Details of the simulation techniques, i.e., particle in cell and Vlasov simulations, for studying the double layer are outlined, noting that both periodic and quasi-periodic simulations are used. Solutions to Poisson's equation for fixed and floating point boundary conditions are generated. Finally, attention is also given to oblique and two-dimensional magnetic double layers.
Numerical Simulation of Two-Phase Critical Flow with the Phase Change in the Nozzle Tube
NASA Astrophysics Data System (ADS)
Ishigaki, Masahiro; Watanabe, Tadashi; Nakamura, Hideo
Two-phase critical flow in the nozzle tube is analyzed numerically by the best estimate code TRACE and the CFD code FLUENT, and the performance of the mass flow rate estimation by the numerical codes is discussed. For the best estimate analysis by the TRACE code, the critical flow option is turned on. The mixture model is used with the cavitation model and the evaporation-condensation model for the numerical simulation by the FLUENT code. Two test cases of the two-phase critical flow are analyzed. One case is the critical flashing flow in a convergent-divergent nozzle (Super Moby Dick experiment), and the other case is the break nozzle flow for a steam generator tube rupture experiment of pressurized water reactors at Large Scale Test Facility of Japan Atomic Energy Agency. The calculation results of the mass flow rates by the numerical simulations show good agreements with the experimental results.
Numerical simulation of interacting vortex tubes
Pumir, A.; Kerr, R.M.
1987-04-20
The structure of the cores of interacting vortex tubes in three-dimensional incompressible hydrodynamics has been simulated by a pseudospectral method. A fast reconnection is observed for Reynolds numbers of order 1 000. At higher Reynolds numbers, the core tends to flatten, suggesting the formation of vortex ribbons.
Sultan, Tipu
2016-07-01
This article describes the assessment of a numerical procedure used to determine the UV lamp configuration and surface roughness effects on an open channel water disinfection UV reactor. The performance of the open channel water disinfection UV reactor was numerically analyzed on the basis of the performance indictor reduction equivalent dose (RED). The RED values were calculated as a function of the Reynolds number to monitor the performance. The flow through the open channel UV reactor was modelled using a k-ε model with scalable wall function, a discrete ordinate (DO) model for fluence rate calculation, a volume of fluid (VOF) model to locate the unknown free surface, a discrete phase model (DPM) to track the pathogen transport, and a modified law of the wall to incorporate the reactor wall roughness effects. The performance analysis was carried out using commercial CFD software (ANSYS Fluent 15.0). Four case studies were analyzed based on open channel UV reactor type (horizontal and vertical) and lamp configuration (parallel and staggered). The results show that lamp configuration can play an important role in the performance of an open channel water disinfection UV reactor. The effects of the reactor wall roughness were Reynolds number dependent. The proposed methodology is useful for performance optimization of an open channel water disinfection UV reactor. PMID:27108375
Brush seal numerical simulation: Concepts and advances
NASA Astrophysics Data System (ADS)
Braun, M. J.; Kudriavtsev, V. V.
1994-07-01
The development of the brush seal is considered to be most promising among the advanced type seals that are presently in use in the high speed turbomachinery. The brush is usually mounted on the stationary portions of the engine and has direct contact with the rotating element, in the process of limiting the 'unwanted' leakage flows between stages, or various engine cavities. This type of sealing technology is providing high (in comparison with conventional seals) pressure drops due mainly to the high packing density (around 100 bristles/sq mm), and brush compliance with the rotor motions. In the design of modern aerospace turbomachinery leakage flows between the stages must be minimal, thus contributing to the higher efficiency of the engine. Use of the brush seal instead of the labyrinth seal reduces the leakage flow by one order of magnitude. Brush seals also have been found to enhance dynamic performance, cost less, and are lighter than labyrinth seals. Even though industrial brush seals have been successfully developed through extensive experimentation, there is no comprehensive numerical methodology for the design or prediction of their performance. The existing analytical/numerical approaches are based on bulk flow models and do not allow the investigation of the effects of brush morphology (bristle arrangement), or brushes arrangement (number of brushes, spacing between them), on the pressure drops and flow leakage. An increase in the brush seal efficiency is clearly a complex problem that is closely related to the brush geometry and arrangement, and can be solved most likely only by means of a numerically distributed model.
Brush seal numerical simulation: Concepts and advances
NASA Technical Reports Server (NTRS)
Braun, M. J.; Kudriavtsev, V. V.
1994-01-01
The development of the brush seal is considered to be most promising among the advanced type seals that are presently in use in the high speed turbomachinery. The brush is usually mounted on the stationary portions of the engine and has direct contact with the rotating element, in the process of limiting the 'unwanted' leakage flows between stages, or various engine cavities. This type of sealing technology is providing high (in comparison with conventional seals) pressure drops due mainly to the high packing density (around 100 bristles/sq mm), and brush compliance with the rotor motions. In the design of modern aerospace turbomachinery leakage flows between the stages must be minimal, thus contributing to the higher efficiency of the engine. Use of the brush seal instead of the labyrinth seal reduces the leakage flow by one order of magnitude. Brush seals also have been found to enhance dynamic performance, cost less, and are lighter than labyrinth seals. Even though industrial brush seals have been successfully developed through extensive experimentation, there is no comprehensive numerical methodology for the design or prediction of their performance. The existing analytical/numerical approaches are based on bulk flow models and do not allow the investigation of the effects of brush morphology (bristle arrangement), or brushes arrangement (number of brushes, spacing between them), on the pressure drops and flow leakage. An increase in the brush seal efficiency is clearly a complex problem that is closely related to the brush geometry and arrangement, and can be solved most likely only by means of a numerically distributed model.
Numerical simulations at CEBAF using PARMELA
NASA Astrophysics Data System (ADS)
Liu, H.
1993-12-01
PARMELA has been used at CEBAF for numerical modeling of the nuclear physics injector chopping system, a possible FEL laser gun injector, and the rf steering and focusing effects of the standard CEBAF SRF cavities. These applications call for the code to input field data consistently from SUPERFISH, POISSON, and MAFIA, to properly treat a focusing solenoidal lens having an actual field profile either individually or together with its adjacent rf cavity, to deal with the space charge forces, to model the longitudinal phase space matching required for bunching electrons using a phase-compressor chicane, etc. In this paper, we describe in detail these issues of general interest.
Numerical simulation of oil pool boundary evolution
NASA Astrophysics Data System (ADS)
Khudobina, Yulia; Bubenchikov, Aleksey; Bubenchikov, Mikhail; Matvienko, Oleg; Libin, Eduard
2016-01-01
The study of spatial distribution of hydrocarbon resources and forecasting their geographical location is of great importance for the most complete recovery of hydrocarbons from deposits. The present study gives new mathematical results in the theory of stratified fluid flow in a porous medium. This paper analyzes the evolution of oil pool boundary basing on vortex numerical model for movement of the boundary separating fluids of different densities. It presents the investigation of how the location of light fluid regarding the heavier fluid influences on the changes in the boundary between two media in case of various shifting of the well.
NASA Astrophysics Data System (ADS)
Recktenwald, Geoff; Deinert, Mark
2010-03-01
Determining the time dependent concentration of isotopes within a nuclear reactor core is central to the analysis of nuclear fuel cycles. We present a fast, flexible tool for determining the time dependent neutron spectrum within fast reactors. The code (VBUDS: visualization, burnup, depletion and spectra) uses a two region, multigroup collision probability model to simulate the energy dependent neutron flux and tracks the buildup and burnout of 24 actinides, as well as fission products. While originally developed for LWR simulations, the model is shown to produce fast reactor spectra that show high degree of fidelity to available fast reactor benchmarks.
Study on Applicability of Numerical Simulation to Evaluation of Gas Entrainment From Free Surface
Kei Ito; Takaaki Sakai; Hiroyuki Ohshima
2006-07-01
An onset condition of gas entrainment (GE) due to free surface vortex has been studied to establish a design of fast breeder reactor with higher coolant velocity than conventional designs, because the GE might cause the reactor operation instability and therefore should be avoided. The onset condition of the GE has been investigated experimentally and theoretically, however, dependency of the vortex type GE on local geometry configuration of each experimental system and local velocity distribution has prevented researchers from formulating the universal onset condition of the vortex type GE. A real scale test is considered as an accurate method to evaluate the occurrence of the vortex type GE, but the real scale test is generally expensive and not useful in the design study of large and complicated FBR systems, because frequent displacement of inner equipments accompanied by the design change is difficult in the real scale test. Numerical simulation seems to be promising method as an alternative to the real scale test. In this research, to evaluate the applicability of the numerical simulation to the design work, numerical simulations were conducted on the basic experimental system of the vortex type GE. This basic experiment consisted of rectangular flow channel and two important equipments for vortex type GE in the channel, i.e. vortex generation and suction equipments. Generated vortex grew rapidly interacting with the suction flow and the grown vortex formed a free surface dent (gas core). When the tip of the gas core or the bubbles detached from the tip of the gas core reached the suction mouth, the gas was entrained to the suction tube. The results of numerical simulation under the experimental conditions were compared to the experiment in terms of velocity distributions and free surface shape. As a result, the numerical simulation showed qualitatively good agreement with experimental data. The numerical simulation results were similar to the experimental
Numerical simulation of the 1993 midwestern flood
NASA Astrophysics Data System (ADS)
Bosilovich, Michael Gerard
During the summer of 1993, persistent and heavy precipitation caused a long-lived catastrophic flood in the midwestern United States. In this paper, Midwest hydrology, atmospheric circulation of the 1993 summer, and feedback between the surface and precipitating systems were investigated using the Purdue Regional Model (PRM). Observational analyses of the monthly mean circulation have identified several differences between June and July 1993 that should be considered when studying the interaction of the surface and precipitation systems. The PRM is utilized to simulate the weather during each thirty day period. The PRM is verified against European Centre for Medium Range Weather Forecasts (ECMWF) monthly mean observational analyses. Key features, such as the upper level jet stream and trough, moisture transport and heavy precipitation are reproduced by the PRM. Furthermore, the model is able to simulate the different daily precipitation patterns observed during each month. Some model biases are identified and discussed. The verisimilitude between the model and observed circulations allows for sensitivity experiments to investigate the interaction between the surface and precipitation systems. In general, the results indicated that the June (transient cyclone period) simulations were not as sensitive to the surface anomalies as the July (stationary convective period) simulations. While a large-scale dry soil anomaly slightly decreased the moist convective instability of the planetary boundary layer (PBL), a large scale surface pressure perturbation occurred and weakened the low level jet and moisture transport from the Gulf of Mexico. Both wet and dry soil moisture anomalies, imposed across the southern Great Plains, caused a reduction in the low level jet and Midwestern precipitation. Differential heating at the surface in the control simulations associated with the gradient of soil moisture in the southern Great Plains enhanced the mean southerly wind in the PBL
Numerical Simulation of Taylor Cone-Jet
NASA Astrophysics Data System (ADS)
Toledo, Ronne
The Taylor cone-jet is a particular type of electrohydrodynamic phenomenon where electrostatic stresses and surface tension effects shape the interface of the jet in a peculiar conical shape. A thin jet is issued from the cone apex that further breaks up into a fine aerosol. Due to its monodispersive properties, this fine aerosol has found a number of applications, ranging from mass spectrometry, colloidal space propulsion, combustion, nano-fabrication, coating/painting, and many others. In this study, a general non-dimensional analysis is performed to derive the governing equations and boundary conditions. In accordance with the observations of Gamero-Castano (2010), noting that droplet electric potential is insensitive to the flow rate conditions, a particular set of characteristic parameters is proposed, based on the terminal jet diameter. In order to solve the non-dimensional set of governing equations and boundary conditions, a numerical method combining the Boundary Element Method and the Finite Volume Method is developed. Results of electric current have shown good agreement with numerical and experimental data available in the literature. The main feature of the algorithm developed is related to the decoupling of the electrostatic from the hydrodynamic problem, allowing us to accurately prescribe the far field electric potential boundary conditions away from the hydrodynamic computational domain used to solve the hydrodynamics of the transition region near the cone apex.
High order hybrid numerical simulations of two dimensional detonation waves
NASA Technical Reports Server (NTRS)
Cai, Wei
1993-01-01
In order to study multi-dimensional unstable detonation waves, a high order numerical scheme suitable for calculating the detailed transverse wave structures of multidimensional detonation waves was developed. The numerical algorithm uses a multi-domain approach so different numerical techniques can be applied for different components of detonation waves. The detonation waves are assumed to undergo an irreversible, unimolecular reaction A yields B. Several cases of unstable two dimensional detonation waves are simulated and detailed transverse wave interactions are documented. The numerical results show the importance of resolving the detonation front without excessive numerical viscosity in order to obtain the correct cellular patterns.
Jung, Y. S.; Joo, H. G.; Yoon, J. I.
2013-07-01
The nTRACER direct whole core transport code employing the planar MOC solution based 3-D calculation method, the subgroup method for resonance treatment, the Krylov matrix exponential method for depletion, and a subchannel thermal/hydraulic calculation solver was developed for practical high-fidelity simulation of power reactors. Its accuracy and performance is verified by comparing with the measurement data obtained for three pressurized water reactor cores. It is demonstrated that accurate and detailed multi-physic simulation of power reactors is practically realizable without any prior calculations or adjustments. (authors)
Numerical simulations of bent, disrupted radio jets
NASA Technical Reports Server (NTRS)
Loken, Chris; Burns, Jack O.
1993-01-01
We present preliminary results from three-dimensional hydrodynamical simulations designed to investigate the physics of jet bending and disruption. The specific scenario considered here involves a mildly supersonic jet crossing a contact discontinuity at the interface between the interstellar medium (ISM) and the intercluster medium (ICM) and then encountering a cross-wind in the ICM. The resultant morphologies show many of the features observed in radio sources including jet flaring, bending, and extended tails.
Numerical Simulation of Ion Thruster Optics
NASA Technical Reports Server (NTRS)
Rawlin, Vincent K. (Technical Monitor); Farnell, Cody C.; Williams, John D.; Wilbur, Paul J.
2003-01-01
A three-dimensional simulation code (ffx) designed to analyze ion thruster optics is described. It is an extension of an earlier code and includes special features like the ability to model a wide range of grid geometries, cusp details, and mis-aligned aperture pairs to name a few. However, the principle reason for advancing the code was in the study of ion optics erosion. Ground based testing of ion thruster optics, essential to the understanding of the processes of grid erosion, can be time consuming and costly. Simulation codes that can accurately predict grid lifetimes and the physical mechanisms of grid erosion can be of great utility in the development of future ion thruster optics designed for more ambitious applications. Results of simulations are presented that describe wear profiles for several standard and nonstandard aperture geometries, such as those grid sets with square- or slotted-hole layout patterns. The goal of this paper will be to introduce the methods employed in the ffx code and to briefly demonstrate their use.
Numerical Simulations of Plasma Jets for PLX
NASA Astrophysics Data System (ADS)
Wu, L.; Messer, S.; Case, A.; Phillips, M.; Witherspoon, F. D.; Welch, D.; Thoma, C.; Bogatu, I. N.; Galkin, S.; Thompson, J. R.; Kim, J. S.; Macfarlane, J.; Golovkin, I.
2011-10-01
Two and three-dimensional simulations are performed using the hybrid particle-in-cell code LSP to study liner formation for the Plasma Liner Experiment (PLX). These include studies of plasma transport within small parallel-plate MiniRailguns, issues related to detachment of the jet from the nozzle, and the subsequent propagation of single jets in Cartesian coordinates. Merging of plasma jets is studied mainly in cylindrical coordinates at present. Varied number of railguns (or jets) are used in this study with initial velocity of 50-100 km/s, initial argon number density of 1016 cm-3 to 1017 cm-3, and initial temperature of ~3 eV. The effects on liner formation from jet initial profiles (density, velocity and temperature distribution) are studied to explore behavior. Simulation results are presented and compared with experimental data from merging jet experiments currently being conducted at HyperV using 1cm bore MiniRailguns. The LSP code is used to perform the simulations using improved fluid algorithms and equation-of-state models from Voss and atomic data from Prism.
Numerical Simulations of Europa Hydrothermal Plumes
NASA Astrophysics Data System (ADS)
Goodman, J. C.; Lenferink, E.
2009-12-01
The liquid water interiors of Europa and other icy moons of the outer solar system are likely to be driven by geothermal heating from the sea floor, leading to the development of buoyant hydrothermal plumes. These plumes potentially control icy surface geomorphology, and are of interest to astrobiologists. We have performed a series of simulations of these plumes using the MITGCM. We assume in this experiment that Europa's ocean is deep (of order 100 km) and unstratified, and that plume buoyancy is controlled by temperature, not composition. A series of experiments was performed to explore a limited region of parameter space, with ocean depth H ranging from 50 to 100 km deep, source heat flux Q between 1 and 10 GW, and values of the Coriolis parameter f between 30% and 90% of the Europa average value. As predicted by earlier work, the plumes in our simulations form narrow cylindrical chimneys (a few km across) under the influence of the Coriolis effect. These plumes broaden over time until they become baroclinically unstable, breaking up into cone-shaped eddies when they become 20-35 km in diameter; the shed eddies are of a similar size. Large-scale currents in the region of the plume range between 1.5 and 5 cm/s; temperature anomalies in the plume far from the seafloor are tiny, varying between 30 and 160 microkelvin. Variations in plume size, shape, speed, and temperature are in excellent agreement with previous laboratory tank experiments, and in rough agreement with theoretical predictions. Plume dynamics and geometry are controlled by a "natural Rossby number" which depends strongly on depth H and Coriolis parameter f, but only weakly on source heat flux Q. However, some specific theoretical predictions are not borne out by these simulations. The time elapsed between startup of the source and the beginning of eddy-shedding is much less variable than predicted; also, the plume temperature varies with ocean depth H when our theory says it should not. Both of
Numerical simulation of electrophoresis separation processes
NASA Technical Reports Server (NTRS)
Ganjoo, D. K.; Tezduyar, T. E.
1986-01-01
A new Petrov-Galerkin finite element formulation has been proposed for transient convection-diffusion problems. Most Petrov-Galerkin formulations take into account the spatial discretization, and the weighting functions so developed give satisfactory solutions for steady state problems. Though these schemes can be used for transient problems, there is scope for improvement. The schemes proposed here, which consider temporal as well as spatial discretization, provide improved solutions. Electrophoresis, which involves the motion of charged entities under the influence of an applied electric field, is governed by equations similiar to those encountered in fluid flow problems, i.e., transient convection-diffusion equations. Test problems are solved in electrophoresis and fluid flow. The results obtained are satisfactory. It is also expected that these schemes, suitably adapted, will improve the numerical solutions of the compressible Euler and the Navier-Stokes equations.
Scramjet Propulsive Flowpath Design and Numerical Simulation
NASA Astrophysics Data System (ADS)
Li, Jian-ping; Song, Wen-yan; Liu, Xin
2014-06-01
The integrated propulsive flowpath of scramjet configuration was preliminarily designed and analyzed in this paper. The flow-fields characteristics and performance of the designed two-dimensional integrated propulsive flowpath were numerically calculated under various equivalent fuel-air ratio conditions, using computational fluid dynamics methods. The calculation results were then compared with the experimental data on some typical conditions, and the flow-field and performance of the integrated scramjet flowpath with different equivalent fuel-air ratios were analyzed and discussed in detail. The investigation results from these efforts showed that: (1) the inlet function was beyond disturbances by combustion induced shock wave and pressure fluctuations under the equivalent fuel-air ratio condition of 1.0, which well satisfied the design requirements; (2) with the increasing equivalent fuel-air ratio, the combustion intensity in the combustor was significantly enhanced, resulting in an increasing net-thrust of the propulsive flowpath.
Dynamics of a compound vesicle: numerical simulations
NASA Astrophysics Data System (ADS)
Veerapaneni, Shravan; Young, Yuan-Nan; Vlahovska, Petia; Blawzdziewicz, Jerzy
2010-11-01
Vesicles (self-enclosing lipid membranes) in simple linear flows are known to exhibit rich dynamics such as tank-treading, tumbling, trembling (swinging), and vacillating breathing. Recently, vesicles have been used as a multi-functional platform for drug-delivery. In this work, the dynamics of simplified models for such compound vesicles is investigated numerically using a state-of-the-art boundary-integral code that has been validated with high accuracy and efficiency. Results show that for a vesicle enclosing a rigid particle in a simple shear flow, transition from tank-treading to tumbling is possible even in the absence of viscosity mismatch in the interior and exterior fluids. We will discuss the shape transformations, multiple particle interactions and the flow properties. Comparison with results from analytical modeling gives insights to the underlying physics for such novel dynamics.
Numerical simulation of an axial blood pump.
Chua, Leok Poh; Su, Boyang; Lim, Tau Meng; Zhou, Tongming
2007-07-01
The axial blood pump with a magnetically suspended impeller is superior to other artificial blood pumps because of its small size. In this article, the distributions of velocity, path line, pressure, and shear stress in the straightener, the rotor, and the diffuser of the axial blood pump, as well as the gap zone were obtained using the commercial software, Fluent (version 6.2). The main focus was on the flow field of the blood pump. The numerical results showed that the axial blood pump could produce 5.14 L/min of blood at 100 mm Hg through the outlet when rotating at 11,000 rpm. However, there was a leakage flow of 1.06 L/min in the gap between the rotor cylinder and the pump housing, and thus the overall flow rate the impeller could generate was 6.2 L/min. The numerical results showed that 75% of the scalar shear stresses (SSs) were less than 250 Pa, and 10% were higher than 500 Pa within the whole pump. The high SS region appeared around the blade tip where a large variation of velocity direction and magnitude was found, which might be due to the steep angle variation at the blade tip. Because the exposure time of the blood cell at the high SS region within the pump was relatively short, it might not cause serious damage to the blood cells, but the improvement of blade profile should be considered in the future design of the axial pump. PMID:17584481
Numerical simulation of waste tyres gasification.
Janajreh, Isam; Raza, Syed Shabbar
2015-05-01
Gasification is a thermochemical pathway used to convert carbonaceous feedstock into syngas (CO and H2) in a deprived oxygen environment. The process can accommodate conventional feedstock such as coal, discarded waste including plastics, rubber, and mixed waste owing to the high reactor temperature (1000 °C-1600 °C). Pyrolysis is another conversion pathway, yet it is more selective to the feedstock owing to the low process temperature (350 °C-550 °C). Discarded tyres can be subjected to pyrolysis, however, the yield involves the formation of intermediate radicals additional to unconverted char. Gasification, however, owing to the higher temperature and shorter residence time, is more opted to follow quasi-equilibrium and being predictive. In this work, tyre crumbs are subjected to two levels of gasification modelling, i.e. equilibrium zero dimension and reactive multi-dimensional flow. The objective is to investigate the effect of the amount of oxidising agent on the conversion of tyre granules and syngas composition in a small 20 kW cylindrical gasifier. Initially the chemical compositions of several tyre samples are measured following the ASTM procedures for proximate and ultimate analysis as well as the heating value. The measured data are used to carry out equilibrium-based and reactive flow gasification. The result shows that both models are reasonably predictive averaging 50% gasification efficiency, the devolatilisation is less sensitive than the char conversion to the equivalence ratio as devolatilisation is always complete. In view of the high attained efficiency, it is suggested that the investigated tyre gasification system is economically viable. PMID:25755167
Direct Numerical Simulations of Turbulent Autoigniting Hydrogen Jets
NASA Astrophysics Data System (ADS)
Asaithambi, Rajapandiyan
Autoignition is an important phenomenon and a tool in the design of combustion engines. To study autoignition in a canonical form a direct numerical simulation of a turbulent autoigniting hydrogen jet in vitiated coflow conditions at a jet Reynolds number of 10,000 is performed. A detailed chemical mechanism for hydrogen-air combustion and non-unity Lewis numbers for species transport is used. Realistic inlet conditions are prescribed by obtaining the velocity eld from a fully developed turbulent pipe flow simulation. To perform this simulation a scalable modular density based method for direct numerical simulation (DNS) and large eddy simulation (LES) of compressible reacting flows is developed. The algorithm performs explicit time advancement of transport variables on structured grids. An iterative semi-implicit time advancement is developed for the chemical source terms to alleviate the chemical stiffness of detailed mechanisms. The algorithm is also extended from a Cartesian grid to a cylindrical coordinate system which introduces a singularity at the pole r = 0 where terms with a factor 1/r can be ill-defined. There are several approaches to eliminate this pole singularity and finite volume methods can bypass this issue by not storing or computing data at the pole. All methods however face a very restrictive time step when using a explicit time advancement scheme in the azimuthal direction (theta) where the cell sizes are of the order DelrDeltheta. We use a conservative finite volume based approach to remove the severe time step restriction imposed by the CFL condition by merging cells in the azimuthal direction. In addition, fluxes in the radial direction are computed with an implicit scheme to allow cells to be clustered along the jet's shear layer. This method is validated and used to perform the large scale turbulent reacting simulation. The resulting flame structure is found to be similar to a turbulent diusion flame but stabilized by autoignition at the
Numerical simulation of optically trapped particles
NASA Astrophysics Data System (ADS)
Volpe, Giorgio; Volpe, Giovanni
2014-07-01
Some randomness is present in most phenomena, ranging from biomolecules and nanodevices to financial markets and human organizations. However, it is not easy to gain an intuitive understanding of such stochastic phenomena, because their modeling requires advanced mathematical tools, such as sigma algebras, the Itô formula and martingales. Here, we discuss a simple finite difference algorithm that can be used to gain understanding of such complex physical phenomena. In particular, we simulate the motion of an optically trapped particle that is typically used as a model system in statistical physics and has a wide range of applications in physics and biophysics, for example, to measure nanoscopic forces and torques.
Numerical simulations of two-dimensional QED
Carson, S.R.; Kenway, R.D.
1986-02-01
We describe the computer simulation of two-dimensional QED on a 64 x 64 Euclidean space-time lattice using the Susskind lattice fermion action. Theorder parameter for chiral symmetry breaking and the low-lying meson masses are calculated for both the model with two continuum flavours, which arises naturally in this formulation, and the model with one continuum falvour obtained by including a nonsymmetric mass term and setting one fermion mass equal to the cut-off. Results are compared with those obtined using the quenched approximation, and with analytic predictions.
Floret Test, Numerical Simulations of the Dent, Comparison with Experiments
Lefrancois, A.; Cutting, J.; Gagliardi, F.; Tarver, C.; Tran, T.
2006-02-14
The Floret test has been developed as a screening test to study the performance of a small amount of HE. Numerical simulations have been performed recently using CTH. The objective of this study is to perform numerical simulations in order to better understand the shock waves interactions, involved in the dent formation. Different 3D wedge configurations have been tested using the Ignition and Growth reactive flow model for the HE receptor with Ls-Dyna.
Numerical Simulation of Physical and Chemical Processes in Fluidized Bed
NASA Astrophysics Data System (ADS)
Baturin, D. A.; Gil, A. V.
2015-10-01
The paper presents a numerical simulation of the furnace with a circulating fluidized bed. Numerical study carried out for the bottom of the combustion chamber with the varying heights of volume filling. The results contours of particulate matter concentration and of velocities, as well as a graphical representation of changes in the concentration of particles on the bed height are shown. Simulation performed in Eulerian - Eulerian representation on a 2D model.
NUMERICAL METHODS FOR THE SIMULATION OF HIGH INTENSITY HADRON SYNCHROTRONS.
LUCCIO, A.; D'IMPERIO, N.; MALITSKY, N.
2005-09-12
Numerical algorithms for PIC simulation of beam dynamics in a high intensity synchrotron on a parallel computer are presented. We introduce numerical solvers of the Laplace-Poisson equation in the presence of walls, and algorithms to compute tunes and twiss functions in the presence of space charge forces. The working code for the simulation here presented is SIMBAD, that can be run as stand alone or as part of the UAL (Unified Accelerator Libraries) package.
Numerical simulation of turbulent flows around airfoil and wing
NASA Technical Reports Server (NTRS)
Marx, Yves P.
1990-01-01
During the last years the simulation of compressible viscous flows has received much attention. While the numerical methods were improved drastically, a satisfactory modeling of the Reynolds stresses is still missing. In this paper, after a short description of the numerical procedure used for solving the Reynolds equations, experiments with a promising simple turbulence model are discussed.
Numerical simulations of moon-ringlet interaction
NASA Astrophysics Data System (ADS)
Hanninen, J.
1993-05-01
Nonaxisymmetric ring features excited by perturbations of shepherd satellites are studied in terms of direct particle simulations using Aarseth's N-body integrator combined with the calculation of particle-particle impacts. Interaction parameters typical to Saturn's F-ring are investigated. The generation of clumps by external satellites is verified, but the interparticle collisions tend to smooth sharp features. Using F-ring parameters the clumps are observed to cover the total azimuthal length, but it is not clear whether these azimuthally overlapping clumps would be detectable in the actual F-ring. Gravitational scattering by ring particles increases the velocity dispersion, smearing regular azimuthal features at least in the rings of low optical depths. Considerable accretion is observed to occur, particles sticking pairwise to each other, even if the tendency of the particles to accrete is artificially reduced in the simulations. A new explanation for the braided appearance of the F-ring is proposed, based on the interaction between the shepherding satellites and the ring containing embedded moonlets. In our model the braiding is a dynamic phenomenon: the braids are destroyed and recreated in a cyclical manner.
Numerical and laboratory simulations of auroral acceleration
Gunell, H.; De Keyser, J.; Mann, I.
2013-10-15
The existence of parallel electric fields is an essential ingredient of auroral physics, leading to the acceleration of particles that give rise to the auroral displays. An auroral flux tube is modelled using electrostatic Vlasov simulations, and the results are compared to simulations of a proposed laboratory device that is meant for studies of the plasma physical processes that occur on auroral field lines. The hot magnetospheric plasma is represented by a gas discharge plasma source in the laboratory device, and the cold plasma mimicking the ionospheric plasma is generated by a Q-machine source. In both systems, double layers form with plasma density gradients concentrated on their high potential sides. The systems differ regarding the properties of ion acoustic waves that are heavily damped in the magnetosphere, where the ion population is hot, but weakly damped in the laboratory, where the discharge ions are cold. Ion waves are excited by the ion beam that is created by acceleration in the double layer in both systems. The efficiency of this beam-plasma interaction depends on the acceleration voltage. For voltages where the interaction is less efficient, the laboratory experiment is more space-like.
Numerical simulation of electromagnetic turbulence in tokamaks
Waltz, R.E.
1985-02-01
Nonlinear two- and three-fluid equations are written for the time evolution of the perturbed electrostatic potential, densities, vector potential, and parallel ion motion of collisional and trapped electron plasmas in tokamak geometry. The nonlinear terms arise from the E x B/sub 0/ convection (d/dt = partial/partialt+v/sub E/ x del/sub perpendicular/) and magnetic flutter (del-tilde/sub parallel/ = del/sub parallel/+(B/sub perpendicular//B/sub 0/) x del/sub perpendicular/). Simplified two-dimensional (k/sub perpendicular/) mode coupling simulations with a fixed average parallel wavenumber (k/sub parallel/ = 1/Rq) and curvature drift (..omega../sub g/ = (L/sub n//R)..omega../sub asterisk/ ) characteristic of outward ballooning are performed. Homogeneous stationary turbulent states of the dissipative drift and interchange modes from 0< or =..beta..<..beta../sub crit/ for both the collisional and trapped electron plasmas are obtained. Transport coefficients associated with E x B and magnetic motions are calculated. The problem of simulating plasmas with high viscous Reynolds number is treated with an absorbing mantle at the largest wavenumbers.
Numerical Simulations of the Mechanics of Vitrectomy
NASA Astrophysics Data System (ADS)
Young, Ethan; Eldredge, Jeff; Hubschman, Jean-Pierre
2015-11-01
Vitreous is the clear, gel-like substance that fills the cavity between the lens and retina in the eye. Treating certain eye abnormalities requires removing this substance using a minimally-invasive device called a vitreous cutter. Understanding the behavior of this viscoelastic biofluid during surgeries is essential to improving the effectiveness of the procedure. In this study, three-dimensional computational models of vitreous cutters are investigated using an immersed boundary method paired with a viscoelastic constitutive model. The solver uses a fractional-step method to satisfy continuity and traction boundary conditions to simulate the applied suction. The current work extends previous efforts to accurately model the rheological parameters measured by Sharif-Kashani et al. using the Giesekus constitutive equation [Retina, 2013]. The simulations were used to quantify both the average and time-varying flow rate through the device. Values for flow rate are compared with experimental results from Hubschman et al. [Retina, 2009]. Flow features associated with the cutting dynamics are of particular interest, as is the geometry of the cutter itself. These operational and design changes are a target for improving cutter efficacy while minimizing potential tissue damage.
Numerical Simulations of the Mechanics of Vitrectomy
NASA Astrophysics Data System (ADS)
Young, Ethan; Eldredge, Jeff D.; Hubschman, Jean-Pierre
2014-11-01
Filling the cavity between the lens and retina in the eye is a clear, gel-like substance known as vitreous humor. The treatment of certain eye abnormalities necessitates the removal of this substance, in a surgical procedure called a vitrectomy, using a device called a vitreous cutter. Understanding the behavior of this viscoelastic biofluid during operations is essential to improving the effectiveness of the procedure. In this work, a three-dimensional computational model of a vitreous cutter is investigated using an immersed boundary method and a viscoelastic constitutive model. The solver uses a fractional-step method to satisfy continuity and traction boundary conditions to simulate the applied suction. The Giesekus constitutive equation is used to model the vitreous, as it captures both elastic and shear-thinning effects. Rheological parameters were obtained from the work of Sharif-Kashani et al. [Retina, 2013]. These simulations were used to quantify both the average and time-varying flow rate through the device during different stages in the cutting cycle. Characteristics of the flow field illustrate how surgical variables like cutting speed, duty cycle, and aspiration pressure affect overall flow rate and suggest targets for improving cutter efficacy.
Numerical simulation of the SOFIA flowfield
NASA Technical Reports Server (NTRS)
Klotz, Stephen P.
1994-01-01
This report provides a concise summary of the contribution of computational fluid dynamics (CFD) to the SOFIA (Stratospheric Observatory for Infrared Astronomy) project at NASA Ames and presents results obtained from closed- and open-cavity SOFIA simulations. The aircraft platform is a Boeing 747SP and these are the first SOFIA simulations run with the aircraft empennage included in the geometry database. In the open-cavity run the telescope is mounted behind the wings. Results suggest that the cavity markedly influences the mean pressure distribution on empennage surfaces and that 110-140 decibel (db) sound pressure levels are typical in the cavity and on the horizontal and vertical stabilizers. A strong source of sound was found to exist on the rim of the open telescope cavity. The presence of this source suggests that additional design work needs to be performed in order to minimize the sound emanating from that location. A fluid dynamic analysis of the engine plumes is also contained in this report. The analysis was part of an effort to quantify the degradation of telescope performance resulting from the proximity of the port engine exhaust plumes to the open telescope bay.
Numerical simulation of the SOFIA flow field
NASA Technical Reports Server (NTRS)
Klotz, Stephen P.
1995-01-01
This report provides a concise summary of the contribution of computational fluid dynamics (CFD) to the SOFIA (Stratospheric Observatory for Infrared Astronomy) project at NASA Ames and presents results obtained from closed- and open-cavity SOFIA simulations. The aircraft platform is a Boeing 747SP and these are the first SOFIA simulations run with the aircraft empennage included in the geometry database. In the open-cavity runs the telescope is mounted behind the wings. Results suggest that the cavity markedly influences the mean pressure distribution on empennage surfaces and that 110-140 decibel (db) sound pressure levels are typical in the cavity and on the horizontal and vertical stabilizers. A strong source of sound was found to exist on the rim of the open telescope cavity. The presence of this source suggests that additional design work needs to be performed in order to minimize the sound emanating from that location. A fluid dynamic analysis of the engine plumes is also contained in this report. The analysis was part of an effort to quantify the degradation of telescope performance resulting from the proximity of the port engine exhaust plumes to the open telescope bay.
Numerical Simulations of a Flux Rope Ejection
NASA Astrophysics Data System (ADS)
Pagano, P.; Mackay, D. H.; Poedts, S.
2015-03-01
Coronal mass ejections (CMEs) are the most violent phenomena observed on the Sun. One of the most successful models to explain CMEs is the flux rope ejection model, where a magnetic flux rope is expelled from the solar corona after a long phase along which the flux rope stays in equilibrium while magnetic energy is being accumulated. However, still many questions are outstanding on the detailed mechanism of the ejection and observations continuously provide new data to interpret and put in the context. Currently, extreme ultraviolet (EUV) images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) are providing new insights into the early phase of CME evolution. In particular, observations show the ejection of magnetic flux ropes from the solar corona and how they evolve into CMEs. However, these observations are difficult to interpret in terms of basic physical mechanisms and quantities, thus, we need to compare equivalent quantities to test and improve our models. In our work, we intend to bridge the gap between models and observations with our model of flux rope ejection where we consistently describe the full life span of a flux rope from its formation to ejection. This is done by coupling the global non-linear force-free model (GNLFFF) built to describe the slow low- β formation phase, with a full MHD simulation run with the software MPI-AMRVAC, suitable to describe the fast MHD evolution of the flux rope ejection that happens in a heterogeneous β regime. We also explore the parameter space to identify the conditions upon which the ejection is favoured (gravity stratification and magnetic field intensity) and we produce synthesised AIA observations (171 Å and 211 Å). To carry this out, we run 3D MHD simulation in spherical coordinates where we include the role of thermal conduction and radiative losses, both of which are important for determining the temperature distribution of the solar corona during a CME. Our model of
Numerical Simulation of Supersonic Gap Flow
Jing, Xu; Haiming, Huang; Guo, Huang; Song, Mo
2015-01-01
Various gaps in the surface of the supersonic aircraft have a significant effect on airflows. In order to predict the effects of attack angle, Mach number and width-to-depth ratio of gap on the local aerodynamic heating environment of supersonic flow, two-dimensional compressible Navier-Stokes equations are solved by the finite volume method, where convective flux of space term adopts the Roe format, and discretization of time term is achieved by 5-step Runge-Kutta algorithm. The numerical results reveal that the heat flux ratio is U-shaped distribution on the gap wall and maximum at the windward corner of the gap. The heat flux ratio decreases as the gap depth and Mach number increase, however, it increases as the attack angle increases. In addition, it is important to find that chamfer in the windward corner can effectively reduce gap effect coefficient. The study will be helpful for the design of the thermal protection system in reentry vehicles. PMID:25635395
Numerical simulation of supersonic gap flow.
Jing, Xu; Haiming, Huang; Guo, Huang; Song, Mo
2015-01-01
Various gaps in the surface of the supersonic aircraft have a significant effect on airflows. In order to predict the effects of attack angle, Mach number and width-to-depth ratio of gap on the local aerodynamic heating environment of supersonic flow, two-dimensional compressible Navier-Stokes equations are solved by the finite volume method, where convective flux of space term adopts the Roe format, and discretization of time term is achieved by 5-step Runge-Kutta algorithm. The numerical results reveal that the heat flux ratio is U-shaped distribution on the gap wall and maximum at the windward corner of the gap. The heat flux ratio decreases as the gap depth and Mach number increase, however, it increases as the attack angle increases. In addition, it is important to find that chamfer in the windward corner can effectively reduce gap effect coefficient. The study will be helpful for the design of the thermal protection system in reentry vehicles. PMID:25635395
Numerical simulation of synthesis gas incineration
NASA Astrophysics Data System (ADS)
Kazakov, A. V.; Khaustov, S. A.; Tabakaev, R. B.; Belousova, Y. A.
2016-04-01
The authors have analysed the expediency of the suggested low-grade fuels application method. Thermal processing of solid raw materials in the gaseous fuel, called synthesis gas, is investigated. The technical challenges concerning the applicability of the existing gas equipment developed and extensively tested exclusively for natural gas were considered. For this purpose computer simulation of three-dimensional syngas-incinerating flame dynamics was performed by means of the ANSYS Multiphysics engineering software. The subjects of studying were: a three-dimensional aerodynamic flame structure, heat-release and temperature fields, a set of combustion properties: a flare range and the concentration distribution of burnout reagents. The obtained results were presented in the form of a time-averaged pathlines with color indexing. The obtained results can be used for qualitative and quantitative evaluation of complex multicomponent gas incineration singularities.
Numerical simulation of the world ocean circulation
NASA Technical Reports Server (NTRS)
Takano, K.; Mintz, Y.; Han, Y. J.
1973-01-01
A multi-level model, based on the primitive equations, is developed for simulating the temperature and velocity fields produced in the world ocean by differential heating and surface wind stress. The model ocean has constant depth, free slip at the lower boundary, and neglects momentum advection; so that there is no energy exchange between the barotropic and baroclinic components of the motion, although the former influences the latter through temperature advection. The ocean model was designed to be coupled to the UCLA atmospheric general circulation model, for the study of the dynamics of climate and climate changes. But here, the model is tested by prescribing the observed seasonally varying surface wind stress and the incident solar radiation, the surface air temperature and humidity, cloudiness and the surface wind speed, which, together with the predicted ocean surface temperature, determine the surface flux of radiant energy, sensible heat and latent heat.
Numerical aerodynamic simulation facility. Preliminary study extension
NASA Technical Reports Server (NTRS)
1978-01-01
The production of an optimized design of key elements of the candidate facility was the primary objective of this report. This was accomplished by effort in the following tasks: (1) to further develop, optimize and describe the function description of the custom hardware; (2) to delineate trade off areas between performance, reliability, availability, serviceability, and programmability; (3) to develop metrics and models for validation of the candidate systems performance; (4) to conduct a functional simulation of the system design; (5) to perform a reliability analysis of the system design; and (6) to develop the software specifications to include a user level high level programming language, a correspondence between the programming language and instruction set and outline the operation system requirements.
Numerical simulation of a porous honeycomb burner
Hackert, C.L.; Elizey, J.L.; Ezekoye, O.A.
1997-07-01
A two-dimensional simulation of a honeycomb burner using single step global chemistry is used to investigate the importance of thermal properties and boundary conditions to inert porous burners. Comparisons to available experimental results are made where possible, and a parametric study of the effects of burner properties on the flame is performed. The burner solid emissivity is found to be relatively unimportant to the achievable burning rate and radiant output fraction, so long as it is above a certain minimum value (about 0.3). In contrast, increases in solid conductivity always lead to marked increases in burning rate. The flame is shown to exhibit significant curvature on both a pore scale and burner scale.
Numerical simulation of tides in Ontario Lacus
NASA Astrophysics Data System (ADS)
Vincent, David; Karatekin, Ozgür
2015-04-01
Hydrocarbons liquid filled lakes has been recently detected on Titan's surface. Most of these lakes are located in the northern latitudes but there is a substantial lake in the southern latitudes: Ontario Lacus. This lake gets our attention because of possible shoreline changes suggested by Cassini flybys over Ontario Lacus between September 2005 (T7) et January 2010 (T65). The shoreline changes could be due to evaporation-precipitation processes but could also be a consequence of tides. Previous studies showed that the maximal tidal amplitudes of Ontario Lacus would be about 0.2m (for an uniform bathymetry of 20m). In this study we simulate tidal amplitude and currents with SLIM (Second-generation Louvain-la-Neuve Ice-ocean Model, http://sites.uclouvain.be/slim/ ) which resolves 2D shallow water equation on an unstructured mesh. Unstructured mesh prevents problems like mesh discontinuities at poles and allows higher accuracy at some place like coast or straits without drastically increasing computing costs. The tide generating force modeled in this work is the gradient of tidal potential due to titan's obliquity and titan's orbital eccentricity around Saturn (other contribution such as sun tide generating force are unheeded). The uncertain input parameters such as the wind direction and amplitude, bottom friction and thermo-physical properties of hydrocarbons liquids are varied within their expected ranges. SAR data analysis can result in different bathymetry according to the method. We proceed simulations for different bathymetries: tidal amplitudes doesn't change but this is not the case for tidal currents. Using a recent bathymetry deduced from most recent RADAR/SAR observations and a finer mesh, the peak-to peak tidal amplitudes are calculated to be up to 0.6 m. which is more than a factor two larger than the previous results. The maximal offshore tidal currents magnitude is about 0.06 m/s.