Frequency-Response Identification of XV-15 Tilt-Rotor Aircraft Dynamics.

DTIC Science & Technology

1987-05-01

and the rotor interference with the other 2 aircraft elements are modeled in detail. Also modeled are numerous sub- system dynamics such as the engine ...scope and quality, as a dissertation for the degree of Doctor of Philosophy. (Electrical Engineering ) Approved for the University Com ittee on Graduate...Spectral Relationships .................................. 143 B.2 Numerical Study......................................... 149 B.3 Conclusions of

Numerical study of fractional nonlinear Schrödinger equations.

PubMed

Klein, Christian; Sparber, Christof; Markowich, Peter

2014-12-08

Using a Fourier spectral method, we provide a detailed numerical investigation of dispersive Schrödinger-type equations involving a fractional Laplacian in an one-dimensional case. By an appropriate choice of the dispersive exponent, both mass and energy sub- and supercritical regimes can be identified. This allows us to study the possibility of finite time blow-up versus global existence, the nature of the blow-up, the stability and instability of nonlinear ground states and the long-time dynamics of solutions. The latter is also studied in a semiclassical setting. Moreover, we numerically construct ground state solutions of the fractional nonlinear Schrödinger equation.

Numerical study of fractional nonlinear Schrödinger equations

PubMed Central

Klein, Christian; Sparber, Christof; Markowich, Peter

2014-01-01

Using a Fourier spectral method, we provide a detailed numerical investigation of dispersive Schrödinger-type equations involving a fractional Laplacian in an one-dimensional case. By an appropriate choice of the dispersive exponent, both mass and energy sub- and supercritical regimes can be identified. This allows us to study the possibility of finite time blow-up versus global existence, the nature of the blow-up, the stability and instability of nonlinear ground states and the long-time dynamics of solutions. The latter is also studied in a semiclassical setting. Moreover, we numerically construct ground state solutions of the fractional nonlinear Schrödinger equation. PMID:25484604

Cellular structure of lean hydrogen flames in microgravity

NASA Technical Reports Server (NTRS)

Patnaik, G.; Kailasanath, K.

1990-01-01

Detailed, time-dependent, two-dimensional numerical simulations of premixed laminar flames have been used to study the initiation and subsequent development of cellular structures in lean hydrogen-air flames. The model includes detailed hydrogen-oxygen combustion with 24 elementary reactions of eight reactive species and a nitrogen diluent, molecular diffusion of all species, thermal conduction, viscosity, and convection. This model has been used to study the nonlinear evolution of cellular flame structure and shows that cell splitting, as observed in experiments, can be predicted numerically for sufficiently reactive mixtures. The structures that evolved also resembled the cellular structures observed in experiments. The present study shows that the 'cell-split limit' postulated from experimental observations is an intrinsic property of the mixture and that external factors such as heat losses are not necessary to cause this limit.

Flow in curved ducts of varying cross-section

NASA Astrophysics Data System (ADS)

Sotiropoulos, F.; Patel, V. C.

1992-07-01

Two numerical methods for solving the incompressible Navier-Stokes equations are compared with each other by applying them to calculate laminar and turbulent flows through curved ducts of regular cross-section. Detailed comparisons, between the computed solutions and experimental data, are carried out in order to validate the two methods and to identify their relative merits and disadvantages. Based on the conclusions of this comparative study a numerical method is developed for simulating viscous flows through curved ducts of varying cross-sections. The proposed method is capable of simulating the near-wall turbulence using fine computational meshes across the sublayer in conjunction with a two-layer k-epsilon model. Numerical solutions are obtained for: (1) a straight transition duct geometry, and (2) a hydroturbine draft-tube configuration at model scale Reynolds number for various inlet swirl intensities. The report also provides a detailed literature survey that summarizes all the experimental and computational work in the area of duct flows.

Numerically solving the relativistic Grad-Shafranov equation in Kerr spacetimes: numerical techniques

NASA Astrophysics Data System (ADS)

Mahlmann, J. F.; Cerdá-Durán, P.; Aloy, M. A.

2018-07-01

The study of the electrodynamics of static, axisymmetric, and force-free Kerr magnetospheres relies vastly on solutions of the so-called relativistic Grad-Shafranov equation (GSE). Different numerical approaches to the solution of the GSE have been introduced in the literature, but none of them has been fully assessed from the numerical point of view in terms of efficiency and quality of the solutions found. We present a generalization of these algorithms and give a detailed background on the algorithmic implementation. We assess the numerical stability of the implemented algorithms and quantify the convergence of the presented methodology for the most established set-ups (split-monopole, paraboloidal, BH disc, uniform).

Numerically solving the relativistic Grad-Shafranov equation in Kerr spacetimes: Numerical techniques

NASA Astrophysics Data System (ADS)

Mahlmann, J. F.; Cerdá-Durán, P.; Aloy, M. A.

2018-04-01

The study of the electrodynamics of static, axisymmetric and force-free Kerr magnetospheres relies vastly on solutions of the so called relativistic Grad-Shafranov equation (GSE). Different numerical approaches to the solution of the GSE have been introduced in the literature, but none of them has been fully assessed from the numerical point of view in terms of efficiency and quality of the solutions found. We present a generalization of these algorithms and give detailed background on the algorithmic implementation. We assess the numerical stability of the implemented algorithms and quantify the convergence of the presented methodology for the most established setups (split-monopole, paraboloidal, BH-disk, uniform).

Numerical Simulations of Single Flow Element in a Nuclear Thermal Thrust Chamber

NASA Technical Reports Server (NTRS)

Cheng, Gary; Ito, Yasushi; Ross, Doug; Chen, Yen-Sen; Wang, Ten-See

2007-01-01

The objective of this effort is to develop an efficient and accurate computational methodology to predict both detailed and global thermo-fluid environments of a single now element in a hypothetical solid-core nuclear thermal thrust chamber assembly, Several numerical and multi-physics thermo-fluid models, such as chemical reactions, turbulence, conjugate heat transfer, porosity, and power generation, were incorporated into an unstructured-grid, pressure-based computational fluid dynamics solver. The numerical simulations of a single now element provide a detailed thermo-fluid environment for thermal stress estimation and insight for possible occurrence of mid-section corrosion. In addition, detailed conjugate heat transfer simulations were employed to develop the porosity models for efficient pressure drop and thermal load calculations.

Comparative Study Of Four Models Of Turbulence

NASA Technical Reports Server (NTRS)

Menter, Florian R.

1996-01-01

Report presents comparative study of four popular eddy-viscosity models of turbulence. Computations reported for three different adverse pressure-gradient flowfields. Detailed comparison of numerical results and experimental data given. Following models tested: Baldwin-Lomax, Johnson-King, Baldwin-Barth, and Wilcox.

Air Force Health Study (Project RANCH HAND II). An Epidemiologic Investigation of Health Effects in Air Force Personnel Following Exposure to Herbicides. Baseline Morbidity Study Results

DTIC Science & Technology

1984-02-24

of body fat appeared to be reasonably normal in its distribu- tion. No signif icant differences were detected between the variances (P- 0.34) or the...a minor or undetermined nature , that require detailed fol.low-up. In full context, the baseline study results should be viewed as reassuring to the...The study has disclosed numerous medical findings, mostly of a minor or undetermined nature , that require " detailed follow-up. in full context, the

Micromagnetic study of auto-oscillation modes in spin-Hall nano-oscillators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ulrichs, H., E-mail: henning.ulrichs@uni-muenster.de; Demidov, V. E.; Demokritov, S. O.

2014-01-27

We present a numerical study of magnetization dynamics in a recently introduced spin torque nano-oscillator, whose operational principle relies on the spin-Hall effect—spin-Hall nano-oscillators. Our numerical results show good agreement with the experimentally observed behaviors and provide detailed information about the features of the primary auto-oscillation mode observed in the experiments. They also clarify the physical nature of the secondary auto-oscillation mode, which was experimentally observed under certain conditions only.

Runge-Kutta methods combined with compact difference schemes for the unsteady Euler equations

NASA Technical Reports Server (NTRS)

Yu, Sheng-Tao

1992-01-01

Recent development using compact difference schemes to solve the Navier-Stokes equations show spectral-like accuracy. A study was made of the numerical characteristics of various combinations of the Runge-Kutta (RK) methods and compact difference schemes to calculate the unsteady Euler equations. The accuracy of finite difference schemes is assessed based on the evaluations of dissipative error. The objectives are reducing the numerical damping and, at the same time, preserving numerical stability. While this approach has tremendous success solving steady flows, numerical characteristics of unsteady calculations remain largely unclear. For unsteady flows, in addition to the dissipative errors, phase velocity and harmonic content of the numerical results are of concern. As a result of the discretization procedure, the simulated unsteady flow motions actually propagate in a dispersive numerical medium. Consequently, the dispersion characteristics of the numerical schemes which relate the phase velocity and wave number may greatly impact the numerical accuracy. The aim is to assess the numerical accuracy of the simulated results. To this end, the Fourier analysis is to provide the dispersive correlations of various numerical schemes. First, a detailed investigation of the existing RK methods is carried out. A generalized form of an N-step RK method is derived. With this generalized form, the criteria are derived for the three and four-step RK methods to be third and fourth-order time accurate for the non-linear equations, e.g., flow equations. These criteria are then applied to commonly used RK methods such as Jameson's 3-step and 4-step schemes and Wray's algorithm to identify the accuracy of the methods. For the spatial discretization, compact difference schemes are presented. The schemes are formulated in the operator-type to render themselves suitable for the Fourier analyses. The performance of the numerical methods is shown by numerical examples. These examples are detailed. described. The third case is a two-dimensional simulation of a Lamb vortex in an uniform flow. This calculation provides a realistic assessment of various finite difference schemes in terms of the conservation of the vortex strength and the harmonic content after travelling a substantial distance. The numerical implementation of Giles' non-refelctive equations coupled with the characteristic equations as the boundary condition is discussed in detail. Finally, the single vortex calculation is extended to simulate vortex pairing. For the distance between two vortices less than a threshold value, numerical results show crisp resolution of the vortex merging.

Analytical theory of two-dimensional ring dark soliton in nonlocal nonlinear media

NASA Astrophysics Data System (ADS)

Chen, Wei; Wang, Qi; Shi, Jielong; Shen, Ming

2017-11-01

Completely stable two-dimensional ring dark soliton in nonlocal media with an arbitrary degree of nonlocality are investigated. The exact solution of the ring dark solitons is obtained with the variational method and a cylindrical nonlocal response function. The analytical results are confirmed by directly numerical simulations. We also analytically and numerically study the expansion dynamics of the gray ring dark solitons in detail.

A numerically efficient finite element hydroelastic analysis. Volume 2: Implementation in NASTRAN, part 1

NASA Technical Reports Server (NTRS)

Coppolino, R. N.

1974-01-01

Details are presented of the implementation of the new formulation into NASTRAN including descriptions of the DMAP statements required for conversion of the program and details pertaining to problem definition and bulk data considerations. Details of the current 1/8-scale space shuttle external tank mathematical model, numerical results and analysis/test comparisons are also presented. The appendices include a description and listing of a FORTRAN program used to develop harmonic transformation bulk data (multipoint constraint statements) and sample bulk data information for a number of hydroelastic problems.

Numerical optimization of conical flow waveriders including detailed viscous effects

NASA Technical Reports Server (NTRS)

Bowcutt, Kevin G.; Anderson, John D., Jr.; Capriotti, Diego

1987-01-01

A family of optimized hypersonic waveriders is generated and studied wherein detailed viscous effects are included within the optimization process itself. This is in contrast to previous optimized waverider work, wherein purely inviscid flow is used to obtain the waverider shapes. For the present waveriders, the undersurface is a streamsurface of an inviscid conical flowfield, the upper surface is a streamsurface of the inviscid flow over a tapered cylinder (calculated by the axisymmetric method of characteristics), and the viscous effects are treated by integral solutions of the boundary layer equations. Transition from laminar to turbulent flow is included within the viscous calculations. The optimization is carried out using a nonlinear simplex method. The resulting family of viscous hypersonic waveriders yields predicted high values of lift/drag, high enough to break the L/D barrier based on experience with other hypersonic configurations. Moreover, the numerical optimization process for the viscous waveriders results in distinctly different shapes compared to previous work with inviscid-designed waveriders. Also, the fine details of the viscous solution, such as how the shear stress is distributed over the surface, and the location of transition, are crucial to the details of the resulting waverider geometry. Finally, the moment coefficient variations and heat transfer distributions associated with the viscous optimized waveriders are studied.

Analytical and Numerical solutions of a nonlinear alcoholism model via variable-order fractional differential equations

NASA Astrophysics Data System (ADS)

Gómez-Aguilar, J. F.

2018-03-01

In this paper, we analyze an alcoholism model which involves the impact of Twitter via Liouville-Caputo and Atangana-Baleanu-Caputo fractional derivatives with constant- and variable-order. Two fractional mathematical models are considered, with and without delay. Special solutions using an iterative scheme via Laplace and Sumudu transform were obtained. We studied the uniqueness and existence of the solutions employing the fixed point postulate. The generalized model with variable-order was solved numerically via the Adams method and the Adams-Bashforth-Moulton scheme. Stability and convergence of the numerical solutions were presented in details. Numerical examples of the approximate solutions are provided to show that the numerical methods are computationally efficient. Therefore, by including both the fractional derivatives and finite time delays in the alcoholism model studied, we believe that we have established a more complete and more realistic indicator of alcoholism model and affect the spread of the drinking.

Generating Neuron Geometries for Detailed Three-Dimensional Simulations Using AnaMorph.

PubMed

Mörschel, Konstantin; Breit, Markus; Queisser, Gillian

2017-07-01

Generating realistic and complex computational domains for numerical simulations is often a challenging task. In neuroscientific research, more and more one-dimensional morphology data is becoming publicly available through databases. This data, however, only contains point and diameter information not suitable for detailed three-dimensional simulations. In this paper, we present a novel framework, AnaMorph, that automatically generates water-tight surface meshes from one-dimensional point-diameter files. These surface triangulations can be used to simulate the electrical and biochemical behavior of the underlying cell. In addition to morphology generation, AnaMorph also performs quality control of the semi-automatically reconstructed cells coming from anatomical reconstructions. This toolset allows an extension from the classical dimension-reduced modeling and simulation of cellular processes to a full three-dimensional and morphology-including method, leading to novel structure-function interplay studies in the medical field. The developed numerical methods can further be employed in other areas where complex geometries are an essential component of numerical simulations.

Modeling and Analysis of Realistic Fire Scenarios in Spacecraft

NASA Technical Reports Server (NTRS)

Brooker, J. E.; Dietrich, D. L.; Gokoglu, S. A.; Urban, D. L.; Ruff, G. A.

2015-01-01

An accidental fire inside a spacecraft is an unlikely, but very real emergency situation that can easily have dire consequences. While much has been learned over the past 25+ years of dedicated research on flame behavior in microgravity, a quantitative understanding of the initiation, spread, detection and extinguishment of a realistic fire aboard a spacecraft is lacking. Virtually all combustion experiments in microgravity have been small-scale, by necessity (hardware limitations in ground-based facilities and safety concerns in space-based facilities). Large-scale, realistic fire experiments are unlikely for the foreseeable future (unlike in terrestrial situations). Therefore, NASA will have to rely on scale modeling, extrapolation of small-scale experiments and detailed numerical modeling to provide the data necessary for vehicle and safety system design. This paper presents the results of parallel efforts to better model the initiation, spread, detection and extinguishment of fires aboard spacecraft. The first is a detailed numerical model using the freely available Fire Dynamics Simulator (FDS). FDS is a CFD code that numerically solves a large eddy simulation form of the Navier-Stokes equations. FDS provides a detailed treatment of the smoke and energy transport from a fire. The simulations provide a wealth of information, but are computationally intensive and not suitable for parametric studies where the detailed treatment of the mass and energy transport are unnecessary. The second path extends a model previously documented at ICES meetings that attempted to predict maximum survivable fires aboard space-craft. This one-dimensional model implies the heat and mass transfer as well as toxic species production from a fire. These simplifications result in a code that is faster and more suitable for parametric studies (having already been used to help in the hatch design of the Multi-Purpose Crew Vehicle, MPCV).

Recommendations for Achieving Accurate Numerical Simulation of Tip Clearance Flows in Transonic Compressor Rotors

NASA Technical Reports Server (NTRS)

VanZante, Dale E.; Strazisar, Anthony J.; Wood, Jerry R,; Hathaway, Michael D.; Okiishi, Theodore H.

2000-01-01

The tip clearance flows of transonic compressor rotors are important because they have a significant impact on rotor and stage performance. While numerical simulations of these flows are quite sophisticated. they are seldom verified through rigorous comparisons of numerical and measured data because these kinds of measurements are rare in the detail necessary to be useful in high-speed machines. In this paper we compare measured tip clearance flow details (e.g. trajectory and radial extent) with corresponding data obtained from a numerical simulation. Recommendations for achieving accurate numerical simulation of tip clearance flows are presented based on this comparison. Laser Doppler Velocimeter (LDV) measurements acquired in a transonic compressor rotor, NASA Rotor 35, are used. The tip clearance flow field of this transonic rotor was simulated using a Navier-Stokes turbomachinery solver that incorporates an advanced k-epsilon turbulence model derived for flows that are not in local equilibrium. Comparison between measured and simulated results indicates that simulation accuracy is primarily dependent upon the ability of the numerical code to resolve important details of a wall-bounded shear layer formed by the relative motion between the over-tip leakage flow and the shroud wall. A simple method is presented for determining the strength of this shear layer.

Simulation Study of Structure and Properties of Plasma Liners for the PLX- α Project

NASA Astrophysics Data System (ADS)

Samulyak, Roman; Shih, Wen; Hsu, Scott; PLX-Alpha Team

2017-10-01

Detailed numerical studies of the propagation and merger of high-Mach-number plasma jets and the formation and implosion of plasma liners have been performed using the FronTier code in support of the Plasma Liner Experiment-ALPHA (PLX- α) project. Physics models include radiation, physical diffusion, plasma-EOS models, and an anisotropic diffusion model that mimics deviations from fully collisional hydrodynamics in outer layers of plasma jets. Detailed structure and non-uniformity of plasma liners of due to primary and secondary shock waves have been studies as well as averaged quantities of ram pressure and Mach number. Synthetic data from simulations have been compared with available experimental data from a multi-chord interferometer and survey and high-resolution spectrometers. Numerical studies of the sensitivity of liner properties to experimental errors in the initial masses of jets and the synchronization of plasma gun valves have also been performed. Supported by the ARPA-E ALPHA program.

Detailed and reduced chemical-kinetic descriptions for hydrocarbon combustion

NASA Astrophysics Data System (ADS)

Petrova, Maria V.

Numerical and theoretical studies of autoignition processes of fuels such as propane are in need of realistic simplified chemical-kinetic descriptions that retain the essential features of the detailed descriptions. These descriptions should be computationally feasible and cost-effective. Such descriptions are useful for investigating ignition processes that occur, for example, in homogeneous-charge compression-ignition engines, for studying the structures and dynamics of detonations and in fields such as multi-dimensional Computational Fluid Dynamics (CFD). Reduced chemistry has previously been developed successfully for a number of other hydrocarbon fuels, however, propane has not been considered in this manner. This work focuses on the fuels of propane, as well propene, allene and propyne, for several reasons. The ignition properties of propane resemble those of other higher hydrocarbons but are different from those of the lower hydrocarbons (e.g. ethylene and acetylene). Propane, therefore, may be the smallest hydrocarbon that is representative of higher hydrocarbons in ignition and detonation processes. Since the overall activation energy and ignition times for propane are similar to those of other higher hydrocarbons, including liquid fuels that are suitable for many applications, propane has been used as a model fuel for several numerical and experimental studies. The reason for studying elementary chemistry of propene and C3H4 (allene or propyne) is that during the combustion process, propane breaks down to propene and C3H4 before proceeding to products. Similarly, propene combustion includes C3H4 chemistry. In studying propane combustion, it is therefore necessary to understand the underlying combustion chemistry of propene as well as C3H 4. The first part of this thesis focuses on obtaining and testing a detailed chemical-kinetic description for autoignition of propane, propene and C 3H4, by comparing predictions obtained with this detailed mechanism against numerous experimental data available from shock-tube studies and flame-speed measurements. To keep the detailed mechanism small, attention is restricted to pressures below about 100 atm, temperatures above about 1000 K and equivalence ratios less than about 3. Based on this detailed chemistry description, short (or skeletal) mechanisms are then obtained for each of the three fuels by eliminating reactions that are unimportant for the autoignition process under conditions presented above. This was achieved by utilizing tools such as sensitivity and reaction pathway analyses. Two distinct methodologies were then used in order to obtain a reduced mechanism for autoignition from the short mechanisms. A Systematic Reduction approach is first taken that involves introducing steady-state approximations to as many species as analytically possible. To avoid resorting to numerical methods, the analysis for obtaining ignition times for heptane, presented by Peters and co-workers is followed in order to obtain a rough estimate for an expression of propane ignition time. The results from this expression are then compared to the ignition times obtained computationally with the detailed mechanism. The second method is an Empirical Approach in which chemistry is not derived formally, but rather postulated empirically on the basis of experimental, computational and theoretical observations. As a result, generalized reduced mechanisms are proposed for autoignition of propane, propene and C3H 4. Expressions for ignition times obtained via this empirical approach are compared to the computational results obtained from the detailed mechanism.

A numerical study of shock wave reflections on low density foam

NASA Astrophysics Data System (ADS)

Baer, M. R.

1992-06-01

A continuum mixture theory is used to describe shock wave reflections on low density open-cell polyurethane foam. Numerical simulations are compared to the shock tube experiments of Skews (1991) and detailed wave fields are shown of a shock wave interacting with a layer of foam adjacent to a rigid wall boundary. These comparisons demonstrate that a continuum mixture theory describes well the shock interactions with low density foam.

Numerical Modeling of Ultra Wideband Combined Antennas

NASA Astrophysics Data System (ADS)

Zorkal'tseva, M. Yu.; Koshelev, V. I.; Petkun, A. A.

2017-12-01

With the help of a program we developed, based on the finite difference method in the time domain, we have investigated the characteristics of ultra wideband combined antennas in detail. The antennas were developed to radiate bipolar pulses with durations in the range 0.5-3 ns. Data obtained by numerical modeling are compared with the data of experimental studies on antennas and have been used in the synthesis of electromagnetic pulses with maximum field strength.

Numerical Study of Periodic Traveling Wave Solutions for the Predator-Prey Model with Landscape Features

NASA Astrophysics Data System (ADS)

Yun, Ana; Shin, Jaemin; Li, Yibao; Lee, Seunggyu; Kim, Junseok

We numerically investigate periodic traveling wave solutions for a diffusive predator-prey system with landscape features. The landscape features are modeled through the homogeneous Dirichlet boundary condition which is imposed at the edge of the obstacle domain. To effectively treat the Dirichlet boundary condition, we employ a robust and accurate numerical technique by using a boundary control function. We also propose a robust algorithm for calculating the numerical periodicity of the traveling wave solution. In numerical experiments, we show that periodic traveling waves which move out and away from the obstacle are effectively generated. We explain the formation of the traveling waves by comparing the wavelengths. The spatial asynchrony has been shown in quantitative detail for various obstacles. Furthermore, we apply our numerical technique to the complicated real landscape features.

Information sharing and sorting in a community

NASA Astrophysics Data System (ADS)

Bhattacherjee, Biplab; Manna, S. S.; Mukherjee, Animesh

2013-06-01

We present the results of a detailed numerical study of a model for the sharing and sorting of information in a community consisting of a large number of agents. The information gathering takes place in a sequence of mutual bipartite interactions where randomly selected pairs of agents communicate with each other to enhance their knowledge and sort out the common information. Although our model is less restricted compared to the well-established naming game, the numerical results strongly indicate that the whole set of exponents characterizing this model are different from those of the naming game and they assume nontrivial values. Finally, it appears that in analogy to the emergence of clusters in the phenomenon of percolation, one can define clusters of agents here having the same information. We have studied in detail the growth of the largest cluster in this article and performed its finite-size scaling analysis.

Numerical modeling of the early interaction of a planar shock with a dense particle field

NASA Astrophysics Data System (ADS)

Regele, Jonathan; Blanquart, Guillaume

2011-11-01

Dense compressible multiphase flows are of interest for multiphase turbomachinary and energetic material detonations. Still, there is little understanding of the detailed interaction mechanisms between shock waves and dense (particle volume fraction αd > 0 . 001) particle fields. A recent experimental study [Wagner et al, AIAA Aero. Sci., Orlando, 2011-188] has focused on the impingement of a planar shock wave on a dense particle curtain. In the present work, numerical solutions of the Euler equations in one and two dimensions are performed for a planar shock wave impinging on a fixed particle curtain and are compared to the experimental data for early times. Comparison of the one- and two-dimensional results demonstrate that the one-dimensional description captures the large scale flow behavior, but is inadequate to capture all the details observed in the experiments. The two-dimensional solutions are shown to reproduce the experimentally observed flow structures and provide insight into how these details originate.

A new numerical formulation of gas leakage and spread into a residential space in terms of hazard analysis.

PubMed

Nagaosa, Ryuichi S

2014-04-30

This study proposes a new numerical formulation of the spread of a flammable gas leakage. A new numerical approach has been applied to establish fundamental data for a hazard assessment of flammable gas spread in an enclosed residential space. The approach employs an extended version of a two-compartment concept, and determines the leakage concentration of gas using a mass-balance based formulation. The study also introduces a computational fluid dynamics (CFD) technique for calculating three-dimensional details of the gas spread by resolving all the essential scales of fluid motions without a turbulent model. The present numerical technique promises numerical solutions with fewer uncertainties produced by the model equations while maintaining high accuracy. The study examines the effect of gas density on the concentration profiles of flammable gas spread. It also discusses the effect of gas leakage rate on gas concentration profiles. Copyright © 2014 The Authors. Published by Elsevier B.V. All rights reserved.

A numerical study of the effects of a large sandbar upon sea breeze development

NASA Technical Reports Server (NTRS)

Kessler, R. C.; Pielke, R. A.; Mcqueen, J.; Eppel, D.

1985-01-01

Two-dimensional numerical simulations of sea breeze development over a large sandbar on the North Sea coast of Germany are reported. The numerical model used in these experiments contains a detailed treatment of soil moisture, which allows evaluation of the effects of differential surface characteristics on the airflow pattern. Results of the simulations indicate that the contrast between the moist sandbar and adjacent dry land, the tidal inundation of the sandbar, and the westward penetration of the Baltic sea breeze play important roles in the development of mesoscale airflow patterns in the sandbar region.

Direct numerical simulations of a reacting turbulent mixing layer by a pseudospectral-spectral element method

NASA Technical Reports Server (NTRS)

Mcmurtry, Patrick A.; Givi, Peyman

1992-01-01

An account is given of the implementation of the spectral-element technique for simulating a chemically reacting, spatially developing turbulent mixing layer. Attention is given to experimental and numerical studies that have investigated the development, evolution, and mixing characteristics of shear flows. A mathematical formulation is presented of the physical configuration of the spatially developing reacting mixing layer, in conjunction with a detailed representation of the spectral-element method's application to the numerical simulation of mixing layers. Results from 2D and 3D calculations of chemically reacting mixing layers are given.

Numerical evaluation of heating in the human head due to magnetic resonance imaging (MRI)

NASA Astrophysics Data System (ADS)

Nguyen, Uyen; Brown, Steve; Chang, Isaac; Krycia, Joe; Mirotznik, Mark S.

2003-06-01

In this paper we present a numerical model for evaluating tissue heating during magnetic resonance imaging (MRI). Our method, which included a detailed anatomical model of a human head, calculated both the electromagnetic power deposition and the associated temperature elevations during a MRI head examination. Numerical studies were conducted using a realistic birdcage coil excited at frequencies ranging from 63 MHz to 500 MHz. The model was validated both experimentally and analytically. The experimental validation was performed at the MR test facility located at the FDA's Center for Devices and Radiological Health (CDRH).

Study of effects of injector geometry on fuel-air mixing and combustion

NASA Technical Reports Server (NTRS)

Bangert, L. H.; Roach, R. L.

1977-01-01

An implicit finite-difference method has been developed for computing the flow in the near field of a fuel injector as part of a broader study of the effects of fuel injector geometry on fuel-air mixing and combustion. Detailed numerical results have been obtained for cases of laminar and turbulent flow without base injection, corresponding to the supersonic base flow problem. These numerical results indicated that the method is stable and convergent, and that significant savings in computer time can be achieved, compared with explicit methods.

G-Jitter Effects in Protein Crystal Growth - A Numerical Study

NASA Technical Reports Server (NTRS)

Ramachandran, N.; Baugher, C. R.

1995-01-01

The impact of spacecraft acceleration environment on Protein Crystal Growth (PCG) is studied. A brief overview of the Space Shuttle acceleration environment is provided followed by a simple scaling procedure used to obtain estimates of the flow and concentration field characteristics in PCG. A detailed two-dimensional numerical model is then used to simulate the PCG system response to different disturbance scenarios; viz. residual g effects, impulse type disturbances and oscillatory inputs. The results show that PCG is susceptible to g-jitter and is a good candidate for vibration isolation.

A numerical study of mixing in supersonic combustors with hypermixing injectors

NASA Technical Reports Server (NTRS)

Lee, J.

1993-01-01

A numerical study was conducted to evaluate the performance of wall mounted fuel-injectors designed for potential Supersonic Combustion Ramjet (SCRAM-jet) engine applications. The focus of this investigation was to numerically simulate existing combustor designs for the purpose of validating the numerical technique and the physical models developed. Three different injector designs of varying complexity were studied to fully understand the computational implications involved in accurate predictions. A dual transverse injection system and two streamwise injector designs were studied. The streamwise injectors were designed with swept ramps to enhance fuel-air mixing and combustion characteristics at supersonic speeds without the large flow blockage and drag contribution of the transverse injection system. For this study, the Mass-Average Navier-Stokes equations and the chemical species continuity equations were solved. The computations were performed using a finite-volume implicit numerical technique and multiple block structured grid system. The interfaces of the multiple block structured grid systems were numerically resolved using the flux-conservative technique. Detailed comparisons between the computations and existing experimental data are presented. These comparisons show that numerical predictions are in agreement with the experimental data. These comparisons also show that a number of turbulence model improvements are needed for accurate combustor flowfield predictions.

A numerical study of mixing in supersonic combustors with hypermixing injectors

NASA Technical Reports Server (NTRS)

Lee, J.

1992-01-01

A numerical study was conducted to evaluate the performance of wall mounted fuel-injectors designed for potential Supersonic Combustion Ramjet (SCRAM-jet) engine applications. The focus of this investigation was to numerically simulate existing combustor designs for the purpose of validating the numerical technique and the physical models developed. Three different injector designs of varying complexity were studied to fully understand the computational implications involved in accurate predictions. A dual transverse injection system and two streamwise injector designs were studied. The streamwise injectors were designed with swept ramps to enhance fuel-air mixing and combustion characteristics at supersonic speeds without the large flow blockage and drag contribution of the transverse injection system. For this study, the Mass-Averaged Navier-Stokes equations and the chemical species continuity equations were solved. The computations were performed using a finite-volume implicit numerical technique and multiple block structured grid system. The interfaces of the multiple block structured grid systems were numerically resolved using the flux-conservative technique. Detailed comparisons between the computations and existing experimental data are presented. These comparisons show that numerical predictions are in agreement with the experimental data. These comparisons also show that a number of turbulence model improvements are needed for accurate combustor flowfield predictions.

Personality and Subjective Well-Being: What Hides behind Global Analyses?

ERIC Educational Resources Information Center

Albuquerque, Isabel; de Lima, Margarida Pedroso; Matos, Marcela; Figueiredo, Claudia

2012-01-01

The relation between personality and subjective well-being (SWB) remains involved in a considerable ambiguity and the numerous studies conducted have neglected an approach at a more detailed level of analysis. This study explores the idea that neuroticism, extraversion and conscientiousness facets predict differentially each SWB component. A…

Alternatives for jet engine control

NASA Technical Reports Server (NTRS)

Sain, M. K.

1984-01-01

The technical progress of researches Alternatives for Jet Engine Control is reported. A numerical study employing feedback tensors for optimal control of nonlinear systems was completed. It is believed that these studies are the first of their kind. State regulation, with a decrease in control power is demonstrated. A detailed treatment follows.

Errors in logic and statistics plague a meta-analysis

USDA-ARS?s Scientific Manuscript database

The non-target effects of transgenic insecticidal crops has been a topic of debate for over a decade and many laboratory and field studies have addressed the issue in numerous countries. In 2009 Lovei et al. (Transgenic Insecticidal Crops and Natural Enemies: A Detailed Review of Laboratory Studies)...

Dynamics of Numerics & Spurious Behaviors in CFD Computations. Revised

NASA Technical Reports Server (NTRS)

Yee, Helen C.; Sweby, Peter K.

1997-01-01

The global nonlinear behavior of finite discretizations for constant time steps and fixed or adaptive grid spacings is studied using tools from dynamical systems theory. Detailed analysis of commonly used temporal and spatial discretizations for simple model problems is presented. The role of dynamics in the understanding of long time behavior of numerical integration and the nonlinear stability, convergence, and reliability of using time-marching approaches for obtaining steady-state numerical solutions in computational fluid dynamics (CFD) is explored. The study is complemented with examples of spurious behavior observed in steady and unsteady CFD computations. The CFD examples were chosen to illustrate non-apparent spurious behavior that was difficult to detect without extensive grid and temporal refinement studies and some knowledge from dynamical systems theory. Studies revealed the various possible dangers of misinterpreting numerical simulation of realistic complex flows that are constrained by available computing power. In large scale computations where the physics of the problem under study is not well understood and numerical simulations are the only viable means of solution, extreme care must be taken in both computation and interpretation of the numerical data. The goal of this paper is to explore the important role that dynamical systems theory can play in the understanding of the global nonlinear behavior of numerical algorithms and to aid the identification of the sources of numerical uncertainties in CFD.

A Numerical and Experimental Study of Damage Growth in a Composite Laminate

NASA Technical Reports Server (NTRS)

McElroy, Mark; Ratcliffe, James; Czabaj, Michael; Wang, John; Yuan, Fuh-Gwo

2014-01-01

The present study has three goals: (1) perform an experiment where a simple laminate damage process can be characterized in high detail; (2) evaluate the performance of existing commercially available laminate damage simulation tools by modeling the experiment; (3) observe and understand the underlying physics of damage in a composite honeycomb sandwich structure subjected to low-velocity impact. A quasi-static indentation experiment has been devised to provide detailed information about a simple mixed-mode damage growth process. The test specimens consist of an aluminum honeycomb core with a cross-ply laminate facesheet supported on a stiff uniform surface. When the sample is subjected to an indentation load, the honeycomb core provides support to the facesheet resulting in a gradual and stable damage growth process in the skin. This enables real time observation as a matrix crack forms, propagates through a ply, and then causes a delamination. Finite element analyses were conducted in ABAQUS/Explicit(TradeMark) 6.13 that used continuum and cohesive modeling techniques to simulate facesheet damage and a geometric and material nonlinear model to simulate core crushing. The high fidelity of the experimental data allows a detailed investigation and discussion of the accuracy of each numerical modeling approach.

Detailed study on the statistical properties of optimized phase distribution in focusing light through turbid media

NASA Astrophysics Data System (ADS)

Zhang, Xicheng; Fang, Longjie; Zuo, Haoyi; Du, Jinglei; Gao, Fuhua; Pang, Lin

2018-07-01

It is studied in detail that whether the optimized phase distributions obtained from different approaches have relations in focusing light through turbid media. A view is proposed that there exists a strong correlation among the optimized phase distributions from different approaches. The numeric simulations and experiments indicate that the larger the number of segments is, the greater the correlation coefficient of optimized phase distributions from different approaches will be. This study might give an important insight into the essence of focusing light through turbid media by phase modulation.

N -jettiness subtractions for g g →H at subleading power

NASA Astrophysics Data System (ADS)

Moult, Ian; Rothen, Lorena; Stewart, Iain W.; Tackmann, Frank J.; Zhu, Hua Xing

2018-01-01

N -jettiness subtractions provide a general approach for performing fully-differential next-to-next-to-leading order (NNLO) calculations. Since they are based on the physical resolution variable N -jettiness, TN , subleading power corrections in τ =TN/Q , with Q a hard interaction scale, can also be systematically computed. We study the structure of power corrections for 0-jettiness, T0, for the g g →H process. Using the soft-collinear effective theory we analytically compute the leading power corrections αsτ ln τ and αs2τ ln3τ (finding partial agreement with a previous result in the literature), and perform a detailed numerical study of the power corrections in the g g , g q , and q q ¯ channels. This includes a numerical extraction of the αsτ and αs2τ ln2τ corrections, and a study of the dependence on the T0 definition. Including such power suppressed logarithms significantly reduces the size of missing power corrections, and hence improves the numerical efficiency of the subtraction method. Having a more detailed understanding of the power corrections for both q q ¯ and g g initiated processes also provides insight into their universality, and hence their behavior in more complicated processes where they have not yet been analytically calculated.

Numerical implementation of the S-matrix algorithm for modeling of relief diffraction gratings

NASA Astrophysics Data System (ADS)

Yaremchuk, Iryna; Tamulevičius, Tomas; Fitio, Volodymyr; Gražulevičiūte, Ieva; Bobitski, Yaroslav; Tamulevičius, Sigitas

2013-11-01

A new numerical implementation is developed to calculate the diffraction efficiency of relief diffraction gratings. In the new formulation, vectors containing the expansion coefficients of electric and magnetic fields on boundaries of the grating layer are expressed by additional constants. An S-matrix algorithm has been systematically described in detail and adapted to a simple matrix form. This implementation is suitable for the study of optical characteristics of periodic structures by using modern object-oriented programming languages and different standard mathematical software. The modeling program has been developed on the basis of this numerical implementation and tested by comparison with other commercially available programs and experimental data. Numerical examples are given to show the usefulness of the new implementation.

Risk assessment based on a combination of historical analysis, a detailed field study and numerical modeling on the alluvial fan Gadeinerbach as a basis for a risk management concept

NASA Astrophysics Data System (ADS)

Moser, M.

2009-04-01

The catchment Gadeinerbach in the District of Lungau/Salzburg/Austria is prone to debris flows. Large debris flow events dates back from the years 1934 and 1953. In the upper catchment large mass movements represent debris sources. A field study shows the debris potential and the catchment looks like a "sleeping torrential giant". To carry out mitigation measures a detailed risk management concept, based on a risk assessment in combination of historical analysis, field study and numerical modeling on the alluvial fan was conducted. Human activities have partly altered the surface of the alluvial fan Gadeinerbach but nevertheless some important hazard indicators could be found. With the hazard indicators and photo analysis from the large debris flow event 1934 the catchment character could be pointed out. With the help of these historical data sets (hazard indicators, sediment and debris amount...) it is possible to calibrate the provided numerical models and to win useful knowledge over the pro and cons and their application. The results were used to simulate the design event and furthermore to derive mitigation measures. Therefore the most effective protection against debris with a reduction of the high energy level to a lower level under particular energy change in combination with a debris/bedload deposition place has been carried out. Expert opinion, the study of historical data and a field work is in addition to numerical simulation techniques very necessary for the work in the field of natural hazard management.

Parallel 3-D numerical simulation of dielectric barrier discharge plasma actuators

NASA Astrophysics Data System (ADS)

Houba, Tomas

Dielectric barrier discharge plasma actuators have shown promise in a range of applications including flow control, sterilization and ozone generation. Developing numerical models of plasma actuators is of great importance, because a high-fidelity parallel numerical model allows new design configurations to be tested rapidly. Additionally, it provides a better understanding of the plasma actuator physics which is useful for further innovation. The physics of plasma actuators is studied numerically. A loosely coupled approach is utilized for the coupling of the plasma to the neutral fluid. The state of the art in numerical plasma modeling is advanced by the development of a parallel, three-dimensional, first-principles model with detailed air chemistry. The model incorporates 7 charged species and 18 reactions, along with a solution of the electron energy equation. To the author's knowledge, a parallel three-dimensional model of a gas discharge with a detailed air chemistry model and the solution of electron energy is unique. Three representative geometries are studied using the gas discharge model. The discharge of gas between two parallel electrodes is used to validate the air chemistry model developed for the gas discharge code. The gas discharge model is then applied to the discharge produced by placing a dc powered wire and grounded plate electrodes in a channel. Finally, a three-dimensional simulation of gas discharge produced by electrodes placed inside a riblet is carried out. The body force calculated with the gas discharge model is loosely coupled with a fluid model to predict the induced flow inside the riblet.

Utilization of satellite data and regional scale numerical models in short range weather forecasting

NASA Technical Reports Server (NTRS)

Kreitzberg, C. W.

1985-01-01

Overwhelming evidence was developed in a number of studies of satellite data impact on numerical weather prediction that it is unrealistic to expect satellite temperature soundings to improve detailed regional numerical weather prediction. It is likely that satellite data over the United States would substantially impact mesoscale dynamical predictions if the effort were made to develop a composite moisture analysis system. The horizontal variability of moisture, most clearly depicited in images from satellite water vapor channels, would not be determined from conventional rawinsondes even if that network were increased by a doubling of both the number of sites and the time frequency.

Full-Scale Direct Numerical Simulation of Two- and Three-Dimensional Instabilities and Rivulet Formulation in Heated Falling Films

NASA Technical Reports Server (NTRS)

Krishnamoorthy, S.; Ramaswamy, B.; Joo, S. W.

1995-01-01

A thin film draining on an inclined plate has been studied numerically using finite element method. Three-dimensional governing equations of continuity, momentum and energy with a moving boundary are integrated in an arbitrary Lagrangian Eulerian frame of reference. Kinematic equation is solved to precisely update interface location. Rivulet formation based on instability mechanism has been simulated using full-scale computation. Comparisons with long-wave theory are made to validate the numerical scheme. Detailed analysis of two- and three-dimensional nonlinear wave formation and spontaneous rupture forming rivulets under the influence of combined thermocapillary and surface-wave instabilities is performed.

Numerical Simulation for the Unsteady MHD Flow and Heat Transfer of Couple Stress Fluid over a Rotating Disk

PubMed Central

2014-01-01

The present work is devoted to study the numerical simulation for unsteady MHD flow and heat transfer of a couple stress fluid over a rotating disk. A similarity transformation is employed to reduce the time dependent system of nonlinear partial differential equations (PDEs) to ordinary differential equations (ODEs). The Runge-Kutta method and shooting technique are employed for finding the numerical solution of the governing system. The influences of governing parameters viz. unsteadiness parameter, couple stress and various physical parameters on velocity, temperature and pressure profiles are analyzed graphically and discussed in detail. PMID:24835274

Numerical Study on Electroosmotic Flow in Trapezoidal Microchannels

NASA Astrophysics Data System (ADS)

Zuo, C. C.; Ji, F.; Wang, L. F.

The analysis of electroosmotic flow mechanism in trapezoidal microchannels is performed in this work. The coupled Poisson-Boltzmann equation, Laplace equation, and modified Navier-Stokes equation are solved by finite volume method to describe distribution of electroosmotic flow. The detailed numerical results show that the salt concentration and applied electrical potential have great effects on the fundamental characteristics of elelctroosmotic flow. The most important finding is that the corner and wall effects in trapezoidal microchannels are stronger than those in rectangular microchannels.

Modelling crystal growth: Convection in an asymmetrically heated ampoule

NASA Technical Reports Server (NTRS)

Alexander, J. Iwan D.; Rosenberger, Franz; Pulicani, J. P.; Krukowski, S.; Ouazzani, Jalil

1990-01-01

The objective was to develop and implement a numerical method capable of solving the nonlinear partial differential equations governing heat, mass, and momentum transfer in a 3-D cylindrical geometry in order to examine the character of convection in an asymmetrically heated cylindrical ampoule. The details of the numerical method, including verification tests involving comparison with results obtained from other methods, are presented. The results of the study of 3-D convection in an asymmetrically heated cylinder are described.

Numerical Simulation of the Motion of Aerosol Particles in Open Cell Foam Materials

NASA Astrophysics Data System (ADS)

Solovev, S. A.; Soloveva, O. V.; Popkova, O. S.

2018-03-01

The motion of aerosol particles in open cell foam material is studied. The porous medium is investigated for a three-dimensional case with detailed simulation of cellular structures within an ordered geometry. Numerical calculations of the motion of particles and their deposition due to inertial and gravitational mechanisms are performed. Deposition efficiency curves for a broad range of particle sizes are constructed. The effect deposition mechanisms have on the efficiency of the porous material as a filter is analyzed.

Experimental and Numerical Study of the Buckling of Composite Profiles with Open Cross Section under Axial Compression

NASA Astrophysics Data System (ADS)

Rozylo, Patryk; Teter, Andrzej; Debski, Hubert; Wysmulski, Pawel; Falkowicz, Katarzyna

2017-10-01

The object of the research are short, thin-walled columns with an open top-hat cross section made of multilayer laminate. The walls of the investigated profiles are made of plate elements. The entire columns are subjected to uniform compression. A detailed analysis allowed us to determine critical forces and post-critical equilibrium paths. It is assumed that the columns are articulately supported on the edges forming their ends. The numerical investigation is performed by the finite element method. The study involves solving the problem of eigenvalue and the non-linear problem of stability of the structure. The numerical analysis is performed by the commercial simulation software ABAQUS®. The numerical results are then validated experimentally. In the discussed cases, it is assumed that the material operates within a linearly-elastic range, and the non-linearity of the FEM model is due to large displacements.

Faster and more accurate transport procedures for HZETRN

NASA Astrophysics Data System (ADS)

Slaba, T. C.; Blattnig, S. R.; Badavi, F. F.

2010-12-01

The deterministic transport code HZETRN was developed for research scientists and design engineers studying the effects of space radiation on astronauts and instrumentation protected by various shielding materials and structures. In this work, several aspects of code verification are examined. First, a detailed derivation of the light particle ( A ⩽ 4) and heavy ion ( A > 4) numerical marching algorithms used in HZETRN is given. References are given for components of the derivation that already exist in the literature, and discussions are given for details that may have been absent in the past. The present paper provides a complete description of the numerical methods currently used in the code and is identified as a key component of the verification process. Next, a new numerical method for light particle transport is presented, and improvements to the heavy ion transport algorithm are discussed. A summary of round-off error is also given, and the impact of this error on previously predicted exposure quantities is shown. Finally, a coupled convergence study is conducted by refining the discretization parameters (step-size and energy grid-size). From this study, it is shown that past efforts in quantifying the numerical error in HZETRN were hindered by single precision calculations and computational resources. It is determined that almost all of the discretization error in HZETRN is caused by the use of discretization parameters that violate a numerical convergence criterion related to charged target fragments below 50 AMeV. Total discretization errors are given for the old and new algorithms to 100 g/cm 2 in aluminum and water, and the improved accuracy of the new numerical methods is demonstrated. Run time comparisons between the old and new algorithms are given for one, two, and three layer slabs of 100 g/cm 2 of aluminum, polyethylene, and water. The new algorithms are found to be almost 100 times faster for solar particle event simulations and almost 10 times faster for galactic cosmic ray simulations.

Faster and more accurate transport procedures for HZETRN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Slaba, T.C., E-mail: Tony.C.Slaba@nasa.go; Blattnig, S.R., E-mail: Steve.R.Blattnig@nasa.go; Badavi, F.F., E-mail: Francis.F.Badavi@nasa.go

The deterministic transport code HZETRN was developed for research scientists and design engineers studying the effects of space radiation on astronauts and instrumentation protected by various shielding materials and structures. In this work, several aspects of code verification are examined. First, a detailed derivation of the light particle (A {<=} 4) and heavy ion (A > 4) numerical marching algorithms used in HZETRN is given. References are given for components of the derivation that already exist in the literature, and discussions are given for details that may have been absent in the past. The present paper provides a complete descriptionmore » of the numerical methods currently used in the code and is identified as a key component of the verification process. Next, a new numerical method for light particle transport is presented, and improvements to the heavy ion transport algorithm are discussed. A summary of round-off error is also given, and the impact of this error on previously predicted exposure quantities is shown. Finally, a coupled convergence study is conducted by refining the discretization parameters (step-size and energy grid-size). From this study, it is shown that past efforts in quantifying the numerical error in HZETRN were hindered by single precision calculations and computational resources. It is determined that almost all of the discretization error in HZETRN is caused by the use of discretization parameters that violate a numerical convergence criterion related to charged target fragments below 50 AMeV. Total discretization errors are given for the old and new algorithms to 100 g/cm{sup 2} in aluminum and water, and the improved accuracy of the new numerical methods is demonstrated. Run time comparisons between the old and new algorithms are given for one, two, and three layer slabs of 100 g/cm{sup 2} of aluminum, polyethylene, and water. The new algorithms are found to be almost 100 times faster for solar particle event simulations and almost 10 times faster for galactic cosmic ray simulations.« less

Multiscale Numerical Methods for Non-Equilibrium Plasma

DTIC Science & Technology

2015-08-01

current paper reports on the implementation of a numerical solver on the Graphic Processing Units (GPUs) to model reactive gas mixtures with detailed...Governing equations The flow ismodeled as amixture of gas specieswhile neglecting viscous effects. The chemical reactions taken place between the gas ...components are to be modeled in great detail. The set of the Euler equations for a reactive gas mixture can be written as: ∂Q ∂t + ∇ · F̄ = Ω̇ (1) where Q

'Buildings in Use' Study. Technical Factors.

ERIC Educational Resources Information Center

Wisconsin Univ., Milwaukee. School of Architecture and Urban Planning.

The second report of the 'Buildings in Use' study documents the results of over 100 field tests conducted at four elementary schools, as well as discussion of these results and relevant technical specifications and details. The procedural framework used in the Field Tests Manual is followed and test results are rated numerically wherever possible.…

Engaging College Science Students and Changing Academic Achievement with Technology: A Quasi-Experimental Preliminary Investigation

ERIC Educational Resources Information Center

Carle, Adam C.; Jaffee, David; Miller, Deborah

2009-01-01

Can modern, computer-based technology engage college students and improve their academic achievement in college? Although numerous examples detail technology's classroom uses, few studies empirically examine whether technologically oriented pedagogical changes factually lead to positive outcomes among college students. In this pilot study, we used…

Studying Turbulence Using Numerical Simulation Databases, 2. Proceedings of the 1988 Summer Program

NASA Technical Reports Server (NTRS)

1988-01-01

The focus of the program was on the use of direct numerical simulations of turbulent flow for study of turbulence physics and modeling. A special interest was placed on turbulent mixing layers. The required data for these investigations were generated from four newly developed codes for simulation of time and spatially developing incompressible and compressible mixing layers. Also of interest were the structure of wall bounded turbulent and transitional flows, evaluation of diagnostic techniques for detection of organized motions, energy transfer in isotropic turbulence, optical propagation through turbulent media, and detailed analysis of the interaction of vortical structures.

A numerical and experimental study of confined swirling jets

NASA Technical Reports Server (NTRS)

Nikjooy, M.; Mongia, H. C.; Samuelsen, G. S.; Mcdonell, V. G.

1989-01-01

A numerical and experimental study of a confined strong swirling flow is presented. Detailed velocity measurements are made using a two-component laser Doppler velocimeter (LDV) technique. Computations are performed using a differential second-moment (DSM) closure. The effect of inlet dissipation rate on calculated mean and turbulence fields is investigated. Various model constants are employed in the pressure-strain model to demonstrate their influences on the predicted results. Finally, comparison of the DSM calculations with the algebraic second-monent (ASM) closure results shows that the DSM is better suited for complex swirling flow analysis.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cipolla, C.L.; Mayerhofer, M.

The paper details the acquisition of detailed core and pressure data and the subsequent reservoir modeling in the Ozona Gas Field, Crockett County, Texas. The Canyon formation is the focus of the study and consists of complex turbidite sands characterized by numerous lenticular gas bearing members. The sands cannot be characterized using indirect measurements (logs) and no reliable porosity-permeability relationship could be developed. The reservoir simulation results illustrate the problems associated with interpreting typical pressure and production data in tight gas sands and details procedures to identify incremental reserves. Reservoir layering was represented by five model layers and layer permeabilitiesmore » were estimated based on statistical distributions from core measurements.« less

Resolution requirements for numerical simulations of transition

NASA Technical Reports Server (NTRS)

Zang, Thomas A.; Krist, Steven E.; Hussaini, M. Yousuff

1989-01-01

The resolution requirements for direct numerical simulations of transition to turbulence are investigated. A reliable resolution criterion is determined from the results of several detailed simulations of channel and boundary-layer transition.

Numerical simulations of turbulent jet ignition and combustion

NASA Astrophysics Data System (ADS)

Validi, Abdoulahad; Irannejad, Abolfazl; Jaberi, Farhad

2013-11-01

The ignition and combustion of a homogeneous lean hydrogen-air mixture by a turbulent jet flow of hot combustion products injected into a colder gas mixture are studied by a high fidelity numerical model. Turbulent jet ignition can be considered as an efficient method for starting and controlling the reaction in homogeneously charged combustion systems used in advanced internal combustion and gas turbine engines. In this work, we study in details the physics of turbulent jet ignition in a fundamental flow configuration. The flow and combustion are modeled with the hybrid large eddy simulation/filtered mass density function (LES/FMDF) approach, in which the filtered form the compressible Navier-Stokes equations are solved with a high-order finite difference scheme for the turbulent velocity and the FMDF transport equations are solved with a Lagrangian stochastic method to obtain the scalar (temperature and species mass fractions) field. The hydrogen oxidation is described by a detailed reaction mechanism with 37 elementary reactions and 9 species.

Simulation of a shock tube with a small exit nozzle

NASA Astrophysics Data System (ADS)

Luan, Yigang; Olzmann, Matthias; Magagnato, Franco

2018-02-01

Shock tubes are frequently used to rapidly heat up reaction mixtures to study chemical reaction mechanisms and kinetics in the field of combustion chemistry [1]. In the present work, the flow field inside a shock tube with a small nozzle in the end plate has been investigated to support the analysis of reacting chemical mixtures with an attached mass spectrometer and to clarify whether the usual assumptions for the flow field and the related thermodynamics are fulfilled. In the present work, the details of the flow physics inside the tube and the flow out of the nozzle in the end plate have been investigated. Due to the large differences in the typical length scales and the large pressure ratios of this special device, a very strong numerical stiffness prevails during the simulation process. Second-order ROE numerical schemes have been employed to simulate the flow field inside the shock tube. The simulations were performed with the commercial code ANSYS Fluent [2]. Axial-symmetric boundary conditions are employed to reduce the consumption of CPU time. A density-based transient scheme has been used and validated in terms of accuracy and efficiency. The simulation results for pressure and density are compared with analytical solutions. Numerical results show that a density-based numerical scheme performs better when dealing with shock-tube problems [5]. The flow field near the nozzle is studied in detail, and the effects of the nozzle to pressure and temperature variations inside the tube are investigated. The results show that this special shock-tube setup can be used to study high-temperature gas-phase chemical reactions with reasonable accuracy.

Non-robust numerical simulations of analogue extension experiments

NASA Astrophysics Data System (ADS)

Naliboff, John; Buiter, Susanne

2016-04-01

Numerical and analogue models of lithospheric deformation provide significant insight into the tectonic processes that lead to specific structural and geophysical observations. As these two types of models contain distinct assumptions and tradeoffs, investigations drawing conclusions from both can reveal robust links between first-order processes and observations. Recent studies have focused on detailed comparisons between numerical and analogue experiments in both compressional and extensional tectonics, sometimes involving multiple lithospheric deformation codes and analogue setups. While such comparisons often show good agreement on first-order deformation styles, results frequently diverge on second-order structures, such as shear zone dip angles or spacing, and in certain cases even on first-order structures. Here, we present finite-element experiments that are designed to directly reproduce analogue "sandbox" extension experiments at the cm-scale. We use material properties and boundary conditions that are directly taken from analogue experiments and use a Drucker-Prager failure model to simulate shear zone formation in sand. We find that our numerical experiments are highly sensitive to numerous numerical parameters. For example, changes to the numerical resolution, velocity convergence parameters and elemental viscosity averaging commonly produce significant changes in first- and second-order structures accommodating deformation. The sensitivity of the numerical simulations to small parameter changes likely reflects a number of factors, including, but not limited to, high angles of internal friction assigned to sand, complex, unknown interactions between the brittle sand (used as an upper crust equivalent) and viscous silicone (lower crust), highly non-linear strain weakening processes and poor constraints on the cohesion of sand. Our numerical-analogue comparison is hampered by (a) an incomplete knowledge of the fine details of sand failure and sand properties, and (b) likely limitations to the use of a continuum Drucker-Prager model for representing shear zone formation in sand. In some cases our numerical experiments provide reasonable fits to first-order structures observed in the analogue experiments, but the numerical sensitivity to small parameter variations leads us to conclude that the numerical experiments are not robust.

Experimental and numerical study of premixed hydrogen/air flame propagating in a combustion chamber.

PubMed

Xiao, Huahua; Sun, Jinhua; Chen, Peng

2014-03-15

An experimental and numerical study of dynamics of premixed hydrogen/air flame in a closed explosion vessel is described. High-speed shlieren cinematography and pressure recording are used to elucidate the dynamics of the combustion process in the experiment. A dynamically thickened flame model associated with a detailed reaction mechanism is employed in the numerical simulation to examine the flame-flow interaction and effect of wall friction on the flame dynamics. The shlieren photographs show that the flame develops into a distorted tulip shape after a well-pronounced classical tulip front has been formed. The experimental results reveal that the distorted tulip flame disappears with the primary tulip cusp and the distortions merging into each other, and then a classical tulip is repeated. The combustion dynamics is reasonably reproduced in the numerical simulations, including the variations in flame shape and position, pressure build-up and periodically oscillating behavior. It is found that both the tulip and distorted tulip flames can be created in the simulation with free-slip boundary condition at the walls of the vessel and behave in a manner quite close to that in the experiments. This means that the wall friction could be unimportant for the tulip and distorted tulip formation although the boundary layer formed along the sidewalls has an influence to a certain extent on the flame behavior near the sidewalls. The distorted tulip flame is also observed to be produced in the absence of vortex flow in the numerical simulations. The TF model with a detailed chemical scheme is reliable for investigating the dynamics of distorted tulip flame propagation and its underlying mechanism. Copyright © 2014 Elsevier B.V. All rights reserved.

Transition and mixing in axisymmetric jets and vortex rings

NASA Technical Reports Server (NTRS)

Allen, G. A., Jr.; Cantwell, B. J.

1986-01-01

A class of impulsively started, axisymmetric, laminar jets produced by a time dependent joint source of momentum are considered. These jets are different flows, each initially at rest in an unbounded fluid. The study is conducted at three levels of detail. First, a generalized set of analytic creeping flow solutions are derived with a method of flow classification. Second, from this set, three specific creeping flow solutions are studied in detail: the vortex ring, the round jet, and the ramp jet. This study involves derivation of vorticity, stream function, entrainment diagrams, and evolution of time lines through computer animation. From entrainment diagrams, critical points are derived and analyzed. The flow geometry is dictated by the properties and location of critical points which undergo bifurcation and topological transformation (a form of transition) with changing Reynolds number. Transition Reynolds numbers were calculated. A state space trajectory was derived describing the topological behavior of these critical points. This state space derivation yielded three states of motion which are universal for all axisymmetric jets. Third, the axisymmetric round jet is solved numerically using the unsteady laminar Navier Stokes equations. These equations were shown to be self similar for the round jet. Numerical calculations were performed up to a Reynolds number of 30 for a 60x60 point mesh. Animations generated from numerical solution showed each of the three states of motion for the round jet, including the Re = 30 case.

Spirals in a reaction-diffusion system: Dependence of wave dynamics on excitability.

PubMed

Mahanta, Dhriti; Das, Nirmali Prabha; Dutta, Sumana

2018-02-01

A detailed study of the effects of excitability of the Belousov-Zhabotinsky (BZ) reaction on spiral wave properties has been carried out. Using the Oregonator model, we explore the various regimes of wave activity, from sustained oscillations to wave damping, as the system undergoes a Hopf bifurcation, that is achieved by varying the excitability parameter, ε. We also discover a short range of parameter values where random oscillations are observed. With an increase in the value of ε, the frequency of the wave decreases exponentially, as the dimension of the spiral core expands. These numerical results are confirmed by carrying out experiments in thin layers of the BZ system, where the excitability is changed by varying the concentrations of the reactant species. Effect of reactant concentrations on wave properties like time period and wavelength are also explored in detail. Drifting and meandering spirals are found in the parameter space under investigation, with the excitability affecting the tip trajectory in a way predicted by the numerical studies. This study acts as a quantitative evidence of the relationship between the excitability parameter, ε, and the substrate concentrations.

Spirals in a reaction-diffusion system: Dependence of wave dynamics on excitability

NASA Astrophysics Data System (ADS)

Mahanta, Dhriti; Das, Nirmali Prabha; Dutta, Sumana

2018-02-01

A detailed study of the effects of excitability of the Belousov-Zhabotinsky (BZ) reaction on spiral wave properties has been carried out. Using the Oregonator model, we explore the various regimes of wave activity, from sustained oscillations to wave damping, as the system undergoes a Hopf bifurcation, that is achieved by varying the excitability parameter, ɛ . We also discover a short range of parameter values where random oscillations are observed. With an increase in the value of ɛ , the frequency of the wave decreases exponentially, as the dimension of the spiral core expands. These numerical results are confirmed by carrying out experiments in thin layers of the BZ system, where the excitability is changed by varying the concentrations of the reactant species. Effect of reactant concentrations on wave properties like time period and wavelength are also explored in detail. Drifting and meandering spirals are found in the parameter space under investigation, with the excitability affecting the tip trajectory in a way predicted by the numerical studies. This study acts as a quantitative evidence of the relationship between the excitability parameter, ɛ , and the substrate concentrations.

Numerical studies of laminar and turbulent drag reduction, part 2

NASA Technical Reports Server (NTRS)

Balasubramanian, R.; Orszag, S. A.

1983-01-01

The flow over wave shaped surfaces is studied using a Navier Stokes solver. Detailed comparisons with theoretical results are presented, including the stability of a laminar flow over wavy surfaces. Drag characteristics of nonplanar surfaces are predicted using the Navier-Stokes solver. The secondary instabilities of wall bounded and free shear flows are also discussed.

Cholera studies*†

PubMed Central

Pollitzer, R.; Burrows, W.

1955-01-01

Relevant information regarding the numerous problems encountered in cholera immunity is dealt with in great detail in this study. Toxin production, bacterial virulence, serological reactions, and the antigenic structure of V. cholerae are discussed. Natural, passive, and active cholera immunity receives special attention, the authors describing the various means of vaccination as well as the evaluation of the immunity induced. PMID:13240451

Development of an Efficient CFD Model for Nuclear Thermal Thrust Chamber Assembly Design

NASA Technical Reports Server (NTRS)

Cheng, Gary; Ito, Yasushi; Ross, Doug; Chen, Yen-Sen; Wang, Ten-See

2007-01-01

The objective of this effort is to develop an efficient and accurate computational methodology to predict both detailed thermo-fluid environments and global characteristics of the internal ballistics for a hypothetical solid-core nuclear thermal thrust chamber assembly (NTTCA). Several numerical and multi-physics thermo-fluid models, such as real fluid, chemically reacting, turbulence, conjugate heat transfer, porosity, and power generation, were incorporated into an unstructured-grid, pressure-based computational fluid dynamics solver as the underlying computational methodology. The numerical simulations of detailed thermo-fluid environment of a single flow element provide a mechanism to estimate the thermal stress and possible occurrence of the mid-section corrosion of the solid core. In addition, the numerical results of the detailed simulation were employed to fine tune the porosity model mimic the pressure drop and thermal load of the coolant flow through a single flow element. The use of the tuned porosity model enables an efficient simulation of the entire NTTCA system, and evaluating its performance during the design cycle.

Searching for a Common Ground--A Literature Review of Empirical Research on Scientific Inquiry Activities

ERIC Educational Resources Information Center

Rönnebeck, Silke; Bernholt, Sascha; Ropohl, Mathias

2016-01-01

Despite the importance of scientific inquiry in science education, researchers and educators disagree considerably regarding what features define this instructional approach. While a large body of literature addresses theoretical considerations, numerous empirical studies investigate scientific inquiry on quite different levels of detail and also…

Pressure Modeling of Char-Forming and Laminated Materials.

DTIC Science & Technology

1983-06-01

flame spread rates for various types of materials. For instance, the PMMA fuel used for the laminated wall fires in the present study has a pyroly - sis...thermal conduction and pyroly - sis with one-step Arrhenius kinetics. This numerical procedure is documented in detail in Appendix A, which is taken from

Numerical study of the Kadomtsev-Petviashvili equation and dispersive shock waves

NASA Astrophysics Data System (ADS)

Grava, T.; Klein, C.; Pitton, G.

2018-02-01

A detailed numerical study of the long time behaviour of dispersive shock waves in solutions to the Kadomtsev-Petviashvili (KP) I equation is presented. It is shown that modulated lump solutions emerge from the dispersive shock waves. For the description of dispersive shock waves, Whitham modulation equations for KP are obtained. It is shown that the modulation equations near the soliton line are hyperbolic for the KPII equation while they are elliptic for the KPI equation leading to a focusing effect and the formation of lumps. Such a behaviour is similar to the appearance of breathers for the focusing nonlinear Schrödinger equation in the semiclassical limit.

A fully coupled method for massively parallel simulation of hydraulically driven fractures in 3-dimensions: FULLY COUPLED PARALLEL SIMULATION OF HYDRAULIC FRACTURES IN 3-D

DOE PAGES

Settgast, Randolph R.; Fu, Pengcheng; Walsh, Stuart D. C.; ...

2016-09-18

This study describes a fully coupled finite element/finite volume approach for simulating field-scale hydraulically driven fractures in three dimensions, using massively parallel computing platforms. The proposed method is capable of capturing realistic representations of local heterogeneities, layering and natural fracture networks in a reservoir. A detailed description of the numerical implementation is provided, along with numerical studies comparing the model with both analytical solutions and experimental results. The results demonstrate the effectiveness of the proposed method for modeling large-scale problems involving hydraulically driven fractures in three dimensions.

A fully coupled method for massively parallel simulation of hydraulically driven fractures in 3-dimensions: FULLY COUPLED PARALLEL SIMULATION OF HYDRAULIC FRACTURES IN 3-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Settgast, Randolph R.; Fu, Pengcheng; Walsh, Stuart D. C.

This study describes a fully coupled finite element/finite volume approach for simulating field-scale hydraulically driven fractures in three dimensions, using massively parallel computing platforms. The proposed method is capable of capturing realistic representations of local heterogeneities, layering and natural fracture networks in a reservoir. A detailed description of the numerical implementation is provided, along with numerical studies comparing the model with both analytical solutions and experimental results. The results demonstrate the effectiveness of the proposed method for modeling large-scale problems involving hydraulically driven fractures in three dimensions.

Methods in the study of discrete upper hybrid waves

NASA Astrophysics Data System (ADS)

Yoon, P. H.; Ye, S.; Labelle, J.; Weatherwax, A. T.; Menietti, J. D.

2007-11-01

Naturally occurring plasma waves characterized by fine frequency structure or discrete spectrum, detected by satellite, rocket-borne instruments, or ground-based receivers, can be interpreted as eigenmodes excited and trapped in field-aligned density structures. This paper overviews various theoretical methods to study such phenomena for a one-dimensional (1-D) density structure. Among the various methods are parabolic approximation, eikonal matching, eigenfunction matching, and full numerical solution based upon shooting method. Various approaches are compared against the full numerical solution. Among the analytic methods it is found that the eigenfunction matching technique best approximates the actual numerical solution. The analysis is further extended to 2-D geometry. A detailed comparative analysis between the eigenfunction matching and fully numerical methods is carried out for the 2-D case. Although in general the two methods compare favorably, significant differences are also found such that for application to actual observations it is prudent to employ the fully numerical method. Application of the methods developed in the present paper to actual geophysical problems will be given in a companion paper.

An Experimental and Numerical Study of a Supersonic Burner for CFD Model Development

NASA Technical Reports Server (NTRS)

Magnotti, G.; Cutler, A. D.

2008-01-01

A laboratory scale supersonic burner has been developed for validation of computational fluid dynamics models. Detailed numerical simulations were performed for the flow inside the combustor, and coupled with finite element thermal analysis to obtain more accurate outflow conditions. A database of nozzle exit profiles for a wide range of conditions of interest was generated to be used as boundary conditions for simulation of the external jet, or for validation of non-intrusive measurement techniques. A set of experiments was performed to validate the numerical results. In particular, temperature measurements obtained by using an infrared camera show that the computed heat transfer was larger than the measured value. Relaminarization in the convergent part of the nozzle was found to be responsible for this discrepancy, and further numerical simulations sustained this conclusion.

Detailed Studies on the Structure and Dynamics of Reacting Dusty Flows at Normal and Microgravity

NASA Technical Reports Server (NTRS)

Andac, M. Gurhan; Cracchiola, Brad; Egolfopoulos, Fokion N.; Campbell, Charles S.

1999-01-01

Dusty reacting flows are of particular interest for a wide range of applications. Inert particles can alter the flammability and extinction limits of a combustible mixture. Reacting particles can release substantial amount of heat and can be used either for power generation or propulsion. Accumulation of combustible particles in air can result in explosions which, for example, can occur in grain elevators, during lumber milling and in mine galleries. Furthermore, inert particles are used as flow velocity markers in reacting flows, and their velocity is measured by non-intrusive laser diagnostic techniques. Despite their importance, dusty reacting flows have been less studied and understood compared to gas phase as well as sprays. The addition of solid particles in a flowing gas stream can lead to strong couplings between the two phases, which can be of dynamic, thermal, and chemical nature. The dynamic coupling between the two phases is caused by the inertia that causes the phases to move with different velocities. Furthermore, gravitational, thermophoretic, photophoretic, electrophoretic, diffusiophoretic, centrifugal, and magnetic forces can be exerted on the particles. In general, magnetic, electrophoretic, centrifugal, photophoretic, and diffusiophoretic can be neglected. On the other hand, thermophoretic forces, caused by steep temperature gradients, can be important. The gravitational forces are almost always present and can affect the dynamic response of large particles. Understanding and quantifying the chemical coupling between two phases is a challenging task. However, all reacting particles begin this process as inert particles, and they must be heated before they participate in the combustion process. Thus, one must first understand the interactions of inert particles in a combustion environment. The in-detail understanding of the dynamics and structure of dusty flows can be only advanced by considering simple flow geometries such as the opposed-jet, stagnation-type. In such configurations the imposed strain rate is well characterized, and the in-depth understanding of the details of the physico-chemical processes can be systematically obtained. A number of computational and experimental studies on spray and particle flows have been conducted in stagnation-type configurations. Numerically, the need for a hybrid Eulerian-Lagrangian approach has been identified by Continillo and Sirignano, and the use of such approach has allowed for the prediction of the phenomenon of droplet flow reversal. Gomez and Rosner have conducted a detailed study on the particle response in the opposed-jet configuration, and the particle thermophoretic diffusivities were determined experimentally. Sung, Law and co-workers have conducted numerical studies on the effect of strain rate and temperature gradients on the dynamics of inert particles, as a way of understanding potential errors in experimental LDV data that may arise from thermophoretic forces. This investigation is a combined experimental and numerical study on the details of reacting dusty flows. The specific tasks are: (1) Experimental determination of laminar flame speeds, and extinction strain rates of dusty flows at normal- and micro-gravity as functions of the particle type, particle initial diameter, particle initial number density, and gas phase chemical composition; (2) Detailed numerical simulation of the experiments. Results are compared with experiments and the adequacy of theoretical models is assessed; and (3) Provision of enhanced insight into the thermo-chemical coupling between the two phases.

Improved numerical solutions for chaotic-cancer-model

NASA Astrophysics Data System (ADS)

Yasir, Muhammad; Ahmad, Salman; Ahmed, Faizan; Aqeel, Muhammad; Akbar, Muhammad Zubair

2017-01-01

In biological sciences, dynamical system of cancer model is well known due to its sensitivity and chaoticity. Present work provides detailed computational study of cancer model by counterbalancing its sensitive dependency on initial conditions and parameter values. Cancer chaotic model is discretized into a system of nonlinear equations that are solved using the well-known Successive-Over-Relaxation (SOR) method with a proven convergence. This technique enables to solve large systems and provides more accurate approximation which is illustrated through tables, time history maps and phase portraits with detailed analysis.

Evaluating nuclear physics inputs in core-collapse supernova models

NASA Astrophysics Data System (ADS)

Lentz, E.; Hix, W. R.; Baird, M. L.; Messer, O. E. B.; Mezzacappa, A.

Core-collapse supernova models depend on the details of the nuclear and weak interaction physics inputs just as they depend on the details of the macroscopic physics (transport, hydrodynamics, etc.), numerical methods, and progenitors. We present preliminary results from our ongoing comparison studies of nuclear and weak interaction physics inputs to core collapse supernova models using the spherically-symmetric, general relativistic, neutrino radiation hydrodynamics code Agile-Boltztran. We focus on comparisons of the effects of the nuclear EoS and the effects of improving the opacities, particularly neutrino--nucleon interactions.

Information Based Numerical Practice.

DTIC Science & Technology

1987-02-01

characterization by comparative computational studies of various benchmark problems. See e.g. [MacNeal, Harder (1985)], [Robinson, Blackham (1981)] any...FOR NONADAPTIVE METHODS 2.1. THE QUADRATURE FORMULA The simplest example studied in detail in the literature is the problem of the optimal quadrature...formulae and the functional analytic prerequisites for the study of optimal formulae, we refer to the large monography (808 p) of [Sobolev (1974)]. Let us

Operation of the Institute for Computer Applications in Science and Engineering

NASA Technical Reports Server (NTRS)

1975-01-01

The ICASE research program is described in detail; it consists of four major categories: (1) efficient use of vector and parallel computers, with particular emphasis on the CDC STAR-100; (2) numerical analysis, with particular emphasis on the development and analysis of basic numerical algorithms; (3) analysis and planning of large-scale software systems; and (4) computational research in engineering and the natural sciences, with particular emphasis on fluid dynamics. The work in each of these areas is described in detail; other activities are discussed, a prognosis of future activities are included.

Population projections for AIDS using an actuarial model.

PubMed

Wilkie, A D

1989-09-05

This paper gives details of a model for forecasting AIDS, developed for actuarial purposes, but used also for population projections. The model is only appropriate for homosexual transmission, but it is age-specific, and it allows variation in the transition intensities by age, duration in certain states and calendar year. The differential equations controlling transitions between states are defined, the method of numerical solution is outlined, and the parameters used in five different Bases of projection are given in detail. Numerical results for the population of England and Wales are shown.

Detailed characteristics of drop-laden mixing layers: LES predictions compared to DNS

NASA Technical Reports Server (NTRS)

Okong'o, N.; Leboissetier, A.; Bellan, J.

2004-01-01

Results have been compared from Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) of a temporal mixing layer laden with evaporating drops, to assess the ability of LES to reproduce detailed characteristics of DNS.

Surface properties of ocean fronts

NASA Technical Reports Server (NTRS)

Wolff, P. M.; Hubert, W. E.

1976-01-01

Background information on oceanic fronts is presented and the results of several models which were developed to study the dynamics of oceanic fronts and their effects on various surface properties are described. The details of the four numerical models used in these studies are given in separate appendices which contain all of the physical equations, program documentation and running instructions for the models.

Numerical simulations of water flow and tracer transport in soils at the USDA-ARS Beltsville OPE3 field site

USDA-ARS?s Scientific Manuscript database

The objective of this study was to develop a realistic model to simulate the complex processes of flow and tracer transport in USDA-ARS OPE3 field site and to compare simulation results with the detailed monitoring observations. The site has been studied for over 10 years with the extensive availabl...

Transport of Perfluorocarbon Tracers in the Cranfield Geological Carbon Sequestration Project

NASA Astrophysics Data System (ADS)

Moortgat, J.; Soltanian, M. R.; Amooie, M. A.; Cole, D. R.; Graham, D. E.; Pfiffner, S. M.; Phelps, T.

2017-12-01

A field-scale carbon dioxide (CO2) injection pilot project was conducted by the Southeast Regional Sequestration Partnership (SECARB) at Cranfield, Mississippi. Two associated campaigns in 2009 and 2010 were carried out to co-inject perfluorocarbon tracers (PFTs) and sulfur hexafluoride (SF6) with CO2. Tracers in gas samples from two observation wells were analyzed to construct breakthrough curves. We present the compiled field data as well as detailed numerical modeling of the flow and transport of CO2, brine, and introduced tracers. A high-resolution static model of the formation geology in the Detailed Area Study (DAS) was used in order to capture the impact of connected flow pathways created by fluvial channels on breakthrough curves and breakthrough times of PFTs and SF6 tracers. We use the cubic-plus-association (CPA) equation of state, which takes into account the polar nature of water molecules, to describe the phase behavior of CO2-brine-tracer mixtures. We show how the combination of multiple tracer injection pulses with detailed numerical simulations provide a powerful tool in constraining both formation properties and how complex flow pathways develop over time.

Experimental And Numerical Investigation Of Aerothermal Characteristics Of The IXV Hypersonic Vehicle

NASA Astrophysics Data System (ADS)

Paris, S.; Charbonnier, D.; Tran, D.

2011-05-01

The main results of the aerothermodynamic hypersonic characterization of Intermediate eXperimental Vehicle (IXV), by means of both CFD simulations and wind tunnel measurements, have been reported and analyzed. In the framework of ESA FLPP Program, the VKI (Von Karman Institute) was in charge of an experimental test campaign for the consolidation of the aerothermal database in cold hypersonic regime. The tests campaign has been carried out at VKI Free Piston Longshot wind tunnel at mach 14. The numerical simulations have been performed for VKI wind tunnel conditions by CFSE with the in-house NSMB flow solver (Navier-Stokes Multi-Blocks 3D), the goal being to support the procedure of extrapolation-to-flight of the measurements and the general aerothermal characterization. Laminar, transitional and fully turbulent flows have been computed, with air considered as an ideal gas, for the wind tunnel tests numerical rebuilding. A detailed comparison of all measured and predicted hypersonic relevant phenomena and parameters (surface pressure and heat flux) is reported in the paper, together with a detailed description of configuration, freestream conditions, model attitude effects and flap deflection effect. The detailed analyze of the experimental and numerical data gives information on the nature of the flow on the body and on the flaps for the most critical configuration

Numerical studies of unsteady two dimensional subsonic flows using the ICE method. Ph.D. Thesis - Toledo Univ.

NASA Technical Reports Server (NTRS)

Wieber, P. R.

1973-01-01

A numerical program was developed to compute transient compressible and incompressible laminar flows in two dimensions with multicomponent mixing and chemical reaction. The algorithm used the Los Alamos Scientific Laboratory ICE (Implicit Continuous-Fluid Eulerian) method as its base. The program can compute both high and low speed compressible flows. The numerical program incorporating the stabilization techniques was quite successful in treating both old and new problems. Detailed calculations of coaxial flow very close to the entry plane were possible. The program treated complex flows such as the formation and downstream growth of a recirculation cell. An implicit solution of the species equation predicted mixing and reaction rates which compared favorably with the literature.

Data and numerical analysis of astronomic tides, wind-waves, and hurricane storm surge along the northern Gulf of Mexico

NASA Astrophysics Data System (ADS)

Bilskie, M. V.; Hagen, S. C.; Medeiros, S. C.; Cox, A. T.; Salisbury, M.; Coggin, D.

2016-05-01

The northern Gulf of Mexico (NGOM) is a unique geophysical setting for complex tropical storm-induced hydrodynamic processes that occur across a variety of spatial and temporal scales. Each hurricane includes its own distinctive characteristics and can cause unique and devastating storm surge when it strikes within the intricate geometric setting of the NGOM. While a number of studies have explored hurricane storm surge in the NGOM, few have attempted to describe storm surge and coastal inundation using observed data in conjunction with a single large-domain high-resolution numerical model. To better understand the oceanic and nearshore response to these tropical cyclones, we provide a detailed assessment, based on field measurements and numerical simulation, of the evolution of wind waves, water levels, and currents for Hurricanes Ivan (2004), Dennis (2005), Katrina (2005), and Isaac (2012), with focus on Mississippi, Alabama, and the Florida Panhandle coasts. The developed NGOM3 computational model describes the hydraulic connectivity among the various inlet and bay systems, Gulf Intracoastal Waterway, coastal rivers and adjacent marsh, and built infrastructure along the coastal floodplain. The outcome is a better understanding of the storm surge generating mechanisms and interactions among hurricane characteristics and the NGOM's geophysical configuration. The numerical analysis and observed data explain the ˜2 m/s hurricane-induced geostrophic currents across the continental shelf, a 6 m/s outflow current during Ivan, the hurricane-induced coastal Kelvin wave along the shelf, and for the first time a wealth of measured data and a detailed numerical simulation was performed and was presented for Isaac.

Computational reacting gas dynamics

NASA Technical Reports Server (NTRS)

Lam, S. H.

1993-01-01

In the study of high speed flows at high altitudes, such as that encountered by re-entry spacecrafts, the interaction of chemical reactions and other non-equilibrium processes in the flow field with the gas dynamics is crucial. Generally speaking, problems of this level of complexity must resort to numerical methods for solutions, using sophisticated computational fluid dynamics (CFD) codes. The difficulties introduced by reacting gas dynamics can be classified into three distinct headings: (1) the usually inadequate knowledge of the reaction rate coefficients in the non-equilibrium reaction system; (2) the vastly larger number of unknowns involved in the computation and the expected stiffness of the equations; and (3) the interpretation of the detailed reacting CFD numerical results. The research performed accepts the premise that reacting flows of practical interest in the future will in general be too complex or 'untractable' for traditional analytical developments. The power of modern computers must be exploited. However, instead of focusing solely on the construction of numerical solutions of full-model equations, attention is also directed to the 'derivation' of the simplified model from the given full-model. In other words, the present research aims to utilize computations to do tasks which have traditionally been done by skilled theoreticians: to reduce an originally complex full-model system into an approximate but otherwise equivalent simplified model system. The tacit assumption is that once the appropriate simplified model is derived, the interpretation of the detailed numerical reacting CFD numerical results will become much easier. The approach of the research is called computational singular perturbation (CSP).

Sensitivity of a numerical wave model on wind re-analysis datasets

NASA Astrophysics Data System (ADS)

Lavidas, George; Venugopal, Vengatesan; Friedrich, Daniel

2017-03-01

Wind is the dominant process for wave generation. Detailed evaluation of metocean conditions strengthens our understanding of issues concerning potential offshore applications. However, the scarcity of buoys and high cost of monitoring systems pose a barrier to properly defining offshore conditions. Through use of numerical wave models, metocean conditions can be hindcasted and forecasted providing reliable characterisations. This study reports the sensitivity of wind inputs on a numerical wave model for the Scottish region. Two re-analysis wind datasets with different spatio-temporal characteristics are used, the ERA-Interim Re-Analysis and the CFSR-NCEP Re-Analysis dataset. Different wind products alter results, affecting the accuracy obtained. The scope of this study is to assess different available wind databases and provide information concerning the most appropriate wind dataset for the specific region, based on temporal, spatial and geographic terms for wave modelling and offshore applications. Both wind input datasets delivered results from the numerical wave model with good correlation. Wave results by the 1-h dataset have higher peaks and lower biases, in expense of a high scatter index. On the other hand, the 6-h dataset has lower scatter but higher biases. The study shows how wind dataset affects the numerical wave modelling performance, and that depending on location and study needs, different wind inputs should be considered.

Carlavirus detection 2008 to 2011 in Germany using electron microscopy

USDA-ARS?s Scientific Manuscript database

Latency of animal and human viruses has been well studied in viruses such as Herpes viruses and Retroviruses. Although the term “latent” has long been used in the naming of numerous plant viruses, a detailed functional analysis of this phenomenon is missing in plants. Carlaviruses belong to the fami...

GO2OGS 1.0: a versatile workflow to integrate complex geological information with fault data into numerical simulation models

NASA Astrophysics Data System (ADS)

Fischer, T.; Naumov, D.; Sattler, S.; Kolditz, O.; Walther, M.

2015-11-01

We offer a versatile workflow to convert geological models built with the ParadigmTM GOCAD© (Geological Object Computer Aided Design) software into the open-source VTU (Visualization Toolkit unstructured grid) format for usage in numerical simulation models. Tackling relevant scientific questions or engineering tasks often involves multidisciplinary approaches. Conversion workflows are needed as a way of communication between the diverse tools of the various disciplines. Our approach offers an open-source, platform-independent, robust, and comprehensible method that is potentially useful for a multitude of environmental studies. With two application examples in the Thuringian Syncline, we show how a heterogeneous geological GOCAD model including multiple layers and faults can be used for numerical groundwater flow modeling, in our case employing the OpenGeoSys open-source numerical toolbox for groundwater flow simulations. The presented workflow offers the chance to incorporate increasingly detailed data, utilizing the growing availability of computational power to simulate numerical models.

Physical mechanisms of longitudinal vortexes formation, appearance of zones with high heat fluxes and early transition in hypersonic flow over delta wing with blunted leading edges

NASA Astrophysics Data System (ADS)

Alexandrov, S. V.; Vaganov, A. V.; Shalaev, V. I.

2016-10-01

Processes of vortex structures formation and they interactions with the boundary layer in the hypersonic flow over delta wing with blunted leading edges are analyzed on the base of experimental investigations and numerical solutions of Navier-Stokes equations. Physical mechanisms of longitudinal vortexes formation, appearance of abnormal zones with high heat fluxes and early laminar turbulent transition are studied. These phenomena were observed in many high-speed wind tunnel experiments; however they were understood only using the detailed analysis of numerical modeling results with the high resolution. Presented results allowed explaining experimental phenomena. ANSYS CFX code (the DAFE MIPT license) on the grid with 50 million nodes was used for the numerical modeling. The numerical method was verified by comparison calculated heat flux distributions on the wing surface with experimental data.

New conformal mapping for adaptive resolving of the complex singularities of Stokes wave

PubMed Central

Dyachenko, Sergey A.; A. Silantyev, Denis

2017-01-01

A new highly efficient method is developed for computation of travelling periodic waves (Stokes waves) on the free surface of deep water. A convergence of numerical approximation is determined by the complex singularities above the free surface for the analytical continuation of the travelling wave into the complex plane. An auxiliary conformal mapping is introduced which moves singularities away from the free surface thus dramatically speeding up numerical convergence by adapting the numerical grid for resolving singularities while being consistent with the fluid dynamics. The efficiency of that conformal mapping is demonstrated for the Stokes wave approaching the limiting Stokes wave (the wave of the greatest height) which significantly expands the family of numerically accessible solutions. It allows us to provide a detailed study of the oscillatory approach of these solutions to the limiting wave. Generalizations of the conformal mapping to resolve multiple singularities are also introduced. PMID:28690418

New conformal mapping for adaptive resolving of the complex singularities of Stokes wave.

PubMed

Lushnikov, Pavel M; Dyachenko, Sergey A; A Silantyev, Denis

2017-06-01

A new highly efficient method is developed for computation of travelling periodic waves (Stokes waves) on the free surface of deep water. A convergence of numerical approximation is determined by the complex singularities above the free surface for the analytical continuation of the travelling wave into the complex plane. An auxiliary conformal mapping is introduced which moves singularities away from the free surface thus dramatically speeding up numerical convergence by adapting the numerical grid for resolving singularities while being consistent with the fluid dynamics. The efficiency of that conformal mapping is demonstrated for the Stokes wave approaching the limiting Stokes wave (the wave of the greatest height) which significantly expands the family of numerically accessible solutions. It allows us to provide a detailed study of the oscillatory approach of these solutions to the limiting wave. Generalizations of the conformal mapping to resolve multiple singularities are also introduced.

A human body model for efficient numerical characterization of UWB signal propagation in wireless body area networks.

PubMed

Lim, Hooi Been; Baumann, Dirk; Li, Er-Ping

2011-03-01

Wireless body area network (WBAN) is a new enabling system with promising applications in areas such as remote health monitoring and interpersonal communication. Reliable and optimum design of a WBAN system relies on a good understanding and in-depth studies of the wave propagation around a human body. However, the human body is a very complex structure and is computationally demanding to model. This paper aims to investigate the effects of the numerical model's structure complexity and feature details on the simulation results. Depending on the application, a simplified numerical model that meets desired simulation accuracy can be employed for efficient simulations. Measurements of ultra wideband (UWB) signal propagation along a human arm are performed and compared to the simulation results obtained with numerical arm models of different complexity levels. The influence of the arm shape and size, as well as tissue composition and complexity is investigated.

The method of projected characteristics for the evolution of magnetic arches

NASA Technical Reports Server (NTRS)

Nakagawa, Y.; Hu, Y. Q.; Wu, S. T.

1987-01-01

A numerical method of solving fully nonlinear MHD equation is described. In particular, the formulation based on the newly developed method of projected characteristics (Nakagawa, 1981) suitable to study the evolution of magnetic arches due to motions of their foot-points is presented. The final formulation is given in the form of difference equations; therefore, the analysis of numerical stability is also presented. Further, the most important derivation of physically self-consistent, time-dependent boundary conditions (i.e. the evolving boundary equations) is given in detail, and some results obtained with such boundary equations are reported.

Improved numerical methods for turbulent viscous flows aerothermal modeling program, phase 2

NASA Technical Reports Server (NTRS)

Karki, K. C.; Patankar, S. V.; Runchal, A. K.; Mongia, H. C.

1988-01-01

The details of a study to develop accurate and efficient numerical schemes to predict complex flows are described. In this program, several discretization schemes were evaluated using simple test cases. This assessment led to the selection of three schemes for an in-depth evaluation based on two-dimensional flows. The scheme with the superior overall performance was incorporated in a computer program for three-dimensional flows. To improve the computational efficiency, the selected discretization scheme was combined with a direct solution approach in which the fluid flow equations are solved simultaneously rather than sequentially.

An improved cylindrical FDTD method and its application to field-tissue interaction study in MRI.

PubMed

Chi, Jieru; Liu, Feng; Xia, Ling; Shao, Tingting; Mason, David G; Crozier, Stuart

2010-01-01

This paper presents a three dimensional finite-difference time-domain (FDTD) scheme in cylindrical coordinates with an improved algorithm for accommodating the numerical singularity associated with the polar axis. The regularization of this singularity problem is entirely based on Ampere's law. The proposed algorithm has been detailed and verified against a problem with a known solution obtained from a commercial electromagnetic simulation package. The numerical scheme is also illustrated by modeling high-frequency RF field-human body interactions in MRI. The results demonstrate the accuracy and capability of the proposed algorithm.

Numerical study of the characteristics of a dielectric barrier discharge plasma actuator

NASA Astrophysics Data System (ADS)

Shi, C. A.; Adamiak, K.; Castle, G. S. P.

2018-03-01

A dielectric barrier discharge actuator to control airflow along a flat dielectric plate has been numerically investigated in this paper. In order to avoid large computing times, streamers, Trichel pulses and the ionic reactions involving photons and electrons are neglected. The numerical model assumes two types of generic ions, one positive and one negative, whose drift in the electric field produces the electrohydrodynamic flow. This study provides detailed insights into the physical mechanisms of DBD that include the electric field, space charge transport, surface charge accumulation and air flow motion. The results show the V-I characteristics, velocity profiles and drag force estimates. In addition, the effects of the voltage level, frequency and inlet air velocity on the actuator performance are presented and interpreted. The simulation results show a good agreement with theoretical expectations and experimental data available in literature.

Effect of corrosion on the buckling capacity of tubular members

NASA Astrophysics Data System (ADS)

Øyasæter, F. H.; Aeran, A.; Siriwardane, S. C.; Mikkelsen, O.

2017-12-01

Offshore installations are subjected to harsh marine environment and often have damages from corrosion. Several experimental and numerical studies were performed in the past to estimate buckling capacity of corroded tubular members. However, these studies were either based on limited experimental tests or numerical analyses of few cases resulting in semi-empirical relations. Also, there are no guidelines and recommendations in the currently available design standards. To fulfil this research gap, a new formula is proposed to estimate the residual strength of tubular members considering corrosion and initial geometrical imperfections. The proposed formula is verified with results from finite element analyses performed on several members and for varying corrosion patch parameters. The members are selected to represent the most relevant Eurocode buckling curve for tubular members. It is concluded that corrosion reduces the buckling capacity significantly and the proposed formula can be easily applied by practicing engineers without performing detailed numerical analyses.

Numerical Study on Sensitivity of Pollutant Dispersion on Turbulent Schmidt Number in a Street Canyon

NASA Astrophysics Data System (ADS)

WANG, J.; Kim, J.

2014-12-01

In this study, sensitivity of pollutant dispersion on turbulent Schmidt number (Sct) was investigated in a street canyon using a computational fluid dynamics (CFD) model. For this, numerical simulations with systematically varied Sct were performed and the CFD model results were validated against a wind‒tunnel measurement data. The results showed that root mean square error (RMSE) was quite dependent on Sct and dispersion patterns of non‒reactive scalar pollutant with different Sct were quite different among the simulation results. The RMSE was lowest in the case of Sct = 0.35 and the apparent dispersion pattern was most similar to the wind‒tunnel data in the case of Sct = 0.35. Also, numerical simulations using spatially weighted Sct were additionally performed in order for the best reproduction of the wind‒tunnel data. Detailed method and procedure to find the best reproduction will be presented.

Numerical simulation of heat transfer and fluid flow in laser drilling of metals

NASA Astrophysics Data System (ADS)

Zhang, Tingzhong; Ni, Chenyin; Zhou, Jie; Zhang, Hongchao; Shen, Zhonghua; Ni, Xiaowu; Lu, Jian

2015-05-01

Laser processing as laser drilling, laser welding and laser cutting, etc. is rather important in modern manufacture, and the interaction of laser and matter is a complex phenomenon which should be detailed studied in order to increase the manufacture efficiency and quality. In this paper, a two-dimensional transient numerical model was developed to study the temperature field and molten pool size during pulsed laser keyhole drilling. The volume-of-fluid method was employed to track free surfaces, and melting and evaporation enthalpy, recoil pressure, surface tension, and energy loss due to evaporating materials were considered in this model. Besides, the enthalpy-porosity technique was also applied to account for the latent heat during melting and solidification. Temperature fields and melt pool size were numerically simulated via finite element method. Moreover, the effectiveness of the developed computational procedure had been confirmed by experiments.

Amplification of intrinsic fluctuations by the Lorenz equations

NASA Astrophysics Data System (ADS)

Fox, Ronald F.; Elston, T. C.

1993-07-01

Macroscopic systems (e.g., hydrodynamics, chemical reactions, electrical circuits, etc.) manifest intrinsic fluctuations of molecular and thermal origin. When the macroscopic dynamics is deterministically chaotic, the intrinsic fluctuations may become amplified by several orders of magnitude. Numerical studies of this phenomenon are presented in detail for the Lorenz model. Amplification to macroscopic scales is exhibited, and quantitative methods (binning and a difference-norm) are presented for measuring macroscopically subliminal amplification effects. In order to test the quality of the numerical results, noise induced chaos is studied around a deterministically nonchaotic state, where the scaling law relating the Lyapunov exponent to noise strength obtained for maps is confirmed for the Lorenz model, a system of ordinary differential equations.

Flame-Generated Vorticity Production in Premixed Flame-Vortex Interactions

NASA Technical Reports Server (NTRS)

Patnaik, G.; Kailasanath, K.

2003-01-01

In this study, we use detailed time-dependent, multi-dimensional numerical simulations to investigate the relative importance of the processes leading to FGV in flame-vortex interactions in normal gravity and microgravity and to determine if the production of vorticity in flames in gravity is the same as that in zero gravity except for the contribution of the gravity term. The numerical simulations will be performed using the computational model developed at NRL, FLAME3D. FLAME3D is a parallel, multi-dimensional (either two- or three-dimensional) flame model based on FLIC2D, which has been used extensively to study the structure and stability of premixed hydrogen and methane flames.

Numerical and experimental investigation of DNAPL removal mechanisms in a layered porous medium by means of soil vapor extraction.

PubMed

Yoon, Hongkyu; Oostrom, Mart; Wietsma, Thomas W; Werth, Charles J; Valocchi, Albert J

2009-10-13

The purpose of this work is to identify the mechanisms that govern the removal of carbon tetrachloride (CT) during soil vapor extraction (SVE) by comparing numerical and analytical model simulations with a detailed data set from a well-defined intermediate-scale flow cell experiment. The flow cell was packed with a fine-grained sand layer embedded in a coarse-grained sand matrix. A total of 499 mL CT was injected at the top of the flow cell and allowed to redistribute in the variably saturated system. A dual-energy gamma radiation system was used to determine the initial NAPL saturation profile in the fine-grained sand layer. Gas concentrations at the outlet of the flow cell and 15 sampling ports inside the flow cell were measured during subsequent CT removal using SVE. Results show that CT mass was removed quickly in coarse-grained sand, followed by a slow removal from the fine-grained sand layer. Consequently, effluent gas concentrations decreased quickly at first, and then started to decrease gradually, resulting in long-term tailing. The long-term tailing was mainly due to diffusion from the fine-grained sand layer to the coarse-grained sand zone. An analytical solution for a one-dimensional advection and a first-order mass transfer model matched the tailing well with two fitting parameters. Given detailed knowledge of the permeability field and initial CT distribution, we were also able to predict the effluent concentration tailing and gas concentration profiles at sampling ports using a numerical simulator assuming equilibrium CT evaporation. The numerical model predictions were accurate within the uncertainty of independently measured or literature derived parameters. This study demonstrates that proper numerical modeling of CT removal through SVE can be achieved using equilibrium evaporation of NAPL if detailed fine-scale knowledge of the CT distribution and physical heterogeneity is incorporated into the model. However, CT removal could also be fit by a first-order mass transfer analytical model, potentially leading to an erroneous conclusion that the long-term tailing in the experiment was kinetically controlled due to rate-limited NAPL evaporation.

Benchmarking a Visual-Basic based multi-component one-dimensional reactive transport modeling tool

NASA Astrophysics Data System (ADS)

Torlapati, Jagadish; Prabhakar Clement, T.

2013-01-01

We present the details of a comprehensive numerical modeling tool, RT1D, which can be used for simulating biochemical and geochemical reactive transport problems. The code can be run within the standard Microsoft EXCEL Visual Basic platform, and it does not require any additional software tools. The code can be easily adapted by others for simulating different types of laboratory-scale reactive transport experiments. We illustrate the capabilities of the tool by solving five benchmark problems with varying levels of reaction complexity. These literature-derived benchmarks are used to highlight the versatility of the code for solving a variety of practical reactive transport problems. The benchmarks are described in detail to provide a comprehensive database, which can be used by model developers to test other numerical codes. The VBA code presented in the study is a practical tool that can be used by laboratory researchers for analyzing both batch and column datasets within an EXCEL platform.

Proposal of a micromagnetic standard problem for ferromagnetic resonance simulations

NASA Astrophysics Data System (ADS)

Baker, Alexander; Beg, Marijan; Ashton, Gregory; Albert, Maximilian; Chernyshenko, Dmitri; Wang, Weiwei; Zhang, Shilei; Bisotti, Marc-Antonio; Franchin, Matteo; Hu, Chun Lian; Stamps, Robert; Hesjedal, Thorsten; Fangohr, Hans

2017-01-01

Nowadays, micromagnetic simulations are a common tool for studying a wide range of different magnetic phenomena, including the ferromagnetic resonance. A technique for evaluating reliability and validity of different micromagnetic simulation tools is the simulation of proposed standard problems. We propose a new standard problem by providing a detailed specification and analysis of a sufficiently simple problem. By analyzing the magnetization dynamics in a thin permalloy square sample, triggered by a well defined excitation, we obtain the ferromagnetic resonance spectrum and identify the resonance modes via Fourier transform. Simulations are performed using both finite difference and finite element numerical methods, with OOMMF and Nmag simulators, respectively. We report the effects of initial conditions and simulation parameters on the character of the observed resonance modes for this standard problem. We provide detailed instructions and code to assist in using the results for evaluation of new simulator tools, and to help with numerical calculation of ferromagnetic resonance spectra and modes in general.

Quantitative Studies on the Propagation and Extinction of Near-Limit Premixed Flames Under Normal and Microgravity

NASA Technical Reports Server (NTRS)

Dong, Y.; Spedding, G. R.; Egolfopoulos, F. N.; Miller, F. J.

2003-01-01

The main objective of this research is to introduce accurate fluid mechanics measurements diagnostics in the 2.2-s drop tower for the determination of the detailed flow-field at the states of extinction. These results are important as they can then be compared with confidence with detailed numerical simulations so that important insight is provided into near-limit phenomena that are controlled by not well-understood kinetics and thermal radiation processes. Past qualitative studies did enhance our general understanding on the subject. However, quantitative studies are essential for the validation of existing models that subsequently be used to describe near-limit phenomena that can initiate catastrophic events in micro- and/or reduced gravity environments.

Nano-sized Adsorbate Structure Formation in Anisotropic Multilayer System

NASA Astrophysics Data System (ADS)

Kharchenko, Vasyl O.; Kharchenko, Dmitrii O.; Yanovsky, Vladimir V.

2017-05-01

In this article, we study dynamics of adsorbate island formation in a model plasma-condensate system numerically. We derive the generalized reaction-diffusion model for adsorptive multilayer system by taking into account anisotropy in transfer of adatoms between neighbor layers induced by electric field. It will be found that with an increase in the electric field strength, a structural transformation from nano-holes inside adsorbate matrix toward separated nano-sized adsorbate islands on a substrate is realized. Dynamics of adsorbate island sizes and corresponding distributions are analyzed in detail. This study provides an insight into details of self-organization of adatoms into nano-sized adsorbate islands in anisotropic multilayer plasma-condensate systems.

Simple Numerical Modelling for Gasdynamic Design of Wave Rotors

NASA Astrophysics Data System (ADS)

Okamoto, Koji; Nagashima, Toshio

The precise estimation of pressure waves generated in the passages is a crucial factor in wave rotor design. However, it is difficult to estimate the pressure wave analytically, e.g. by the method of characteristics, because the mechanism of pressure-wave generation and propagation in the passages is extremely complicated as compared to that in a shock tube. In this study, a simple numerical modelling scheme was developed to facilitate the design procedure. This scheme considers the three dominant factors in the loss mechanism —gradual passage opening, wall friction and leakage— for simulating the pressure waves precisely. The numerical scheme itself is based on the one-dimensional Euler equations with appropriate source terms to reduce the calculation time. The modelling of these factors was verified by comparing the results with those of a two-dimensional numerical simulation, which were previously validated by the experimental data in our previous study. Regarding wave rotor miniaturization, the leakage flow effect, which involves the interaction between adjacent cells, was investigated extensively. A port configuration principle was also examined and analyzed in detail to verify the applicability of the present numerical modelling scheme to the wave rotor design.

Modeling of Passive Acoustic Liners from High Fidelity Numerical Simulations

NASA Astrophysics Data System (ADS)

Ferrari, Marcello do Areal Souto

Noise reduction in aviation has been an important focus of study in the last few decades. One common solution is setting up acoustic liners in the internal walls of the engines. However, measurements in the laboratory with liners are expensive and time consuming. The present work proposes a nonlinear physics-based time domain model to predict the acoustic behavior of a given liner in a defined flow condition. The parameters of the model are defined by analysis of accurate numerical solutions of the flow obtained from a high-fidelity numerical code. The length of the cavity is taken into account by using an analytical procedure to account for internal reflections in the interior of the cavity. Vortices and jets originated from internal flow separations are confirmed to be important mechanisms of sound absorption, which defines the overall efficiency of the liner. Numerical simulations at different frequency, geometry and sound pressure level are studied in detail to define the model parameters. Comparisons with high-fidelity numerical simulations show that the proposed model is accurate, robust, and can be used to define a boundary condition simulating a liner in a high-fidelity code.

A combined experimental and numerical study on upper airway dosimetry of inhaled nanoparticles from an electrical discharge machine shop.

PubMed

Tian, Lin; Shang, Yidan; Chen, Rui; Bai, Ru; Chen, Chunying; Inthavong, Kiao; Tu, Jiyuan

2017-07-12

Exposure to nanoparticles in the workplace is a health concern to occupational workers with increased risk of developing respiratory, cardiovascular, and neurological disorders. Based on animal inhalation study and human lung tumor risk extrapolation, current authoritative recommendations on exposure limits are either on total mass or number concentrations. Effects of particle size distribution and the implication to regional airway dosages are not elaborated. Real time production of particle concentration and size distribution in the range from 5.52 to 98.2 nm were recorded in a wire-cut electrical discharge machine shop (WEDM) during a typical working day. Under the realistic exposure condition, human inhalation simulations were performed in a physiologically realistic nasal and upper airway replica. The combined experimental and numerical study is the first to establish a realistic exposure condition, and under which, detailed dose metric studies can be performed. In addition to mass concentration guided exposure limit, inhalation risks to nano-pollutant were reexamined accounting for the actual particle size distribution and deposition statistics. Detailed dosimetries of the inhaled nano-pollutants in human nasal and upper airways with respect to particle number, mass and surface area were discussed, and empirical equations were developed. An astonishing enhancement of human airway dosages were detected by current combined experimental and numerical study in the WEDM machine shop. Up to 33 folds in mass, 27 folds in surface area and 8 folds in number dosages were detected during working hours in comparison to the background dosimetry measured at midnight. The real time particle concentration measurement showed substantial emission of nano-pollutants by WEDM machining activity, and the combined experimental and numerical study provided extraordinary details on human inhalation dosimetry. It was found out that human inhalation dosimetry was extremely sensitive to real time particle concentration and size distribution. Averaged particle concentration over 24-h period will inevitably misrepresent the sensible information critical for realistic inhalation risk assessment. Particle size distribution carries very important information in determining human airway dosimetry. A pure number or mass concentration recommendation on the exposure limit at workplace is insufficient. A particle size distribution, together with the deposition equations, is critical to recognize the actual exposure risks. In addition, human airway dosimetry in number, mass and surface area varies significantly. A complete inhalation risk assessment requires the knowledge of toxicity mechanisms in response to each individual metric. Further improvements in these areas are needed.

A new multi-symplectic scheme for the generalized Kadomtsev-Petviashvili equation

NASA Astrophysics Data System (ADS)

Li, Haochen; Sun, Jianqiang

2012-09-01

We propose a new scheme for the generalized Kadomtsev-Petviashvili (KP) equation. The multi-symplectic conservation property of the new scheme is proved. Back error analysis shows that the new multi-symplectic scheme has second order accuracy in space and time. Numerical application on studying the KPI equation and the KPII equation are presented in detail.

Retention Models for STEM Majors and Alignment to Community Colleges: A Review of the Literature

ERIC Educational Resources Information Center

Snyder, Jennifer; Cudney, Elizabeth A.

2017-01-01

During the last decade, there have been numerous reports detailing the importance of increasing science, technology, engineering, and math (STEM) majors in the United States. Simultaneously, an increasing number of studies are being developed to predict a student's success and completion of a STEM degree, recognizing that retention is a…

Bimolecular dynamics by computer analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eilbeck, J.C.; Lomdahl, P.S.; Scott, A.C.

1984-01-01

As numerical tools (computers and display equipment) become more powerful and the atomic structures of important biological molecules become known, the importance of detailed computation of nonequilibrium biomolecular dynamics increases. In this manuscript we report results from a well developed study of the hydrogen bonded polypeptide crystal acetanilide, a model protein. Directions for future research are suggested. 9 references, 6 figures.

Numerical study of a stochastic particle algorithm solving a multidimensional population balance model for high shear granulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Braumann, Andreas; Kraft, Markus, E-mail: mk306@cam.ac.u; Wagner, Wolfgang

2010-10-01

This paper is concerned with computational aspects of a multidimensional population balance model of a wet granulation process. Wet granulation is a manufacturing method to form composite particles, granules, from small particles and binders. A detailed numerical study of a stochastic particle algorithm for the solution of a five-dimensional population balance model for wet granulation is presented. Each particle consists of two types of solids (containing pores) and of external and internal liquid (located in the pores). Several transformations of particles are considered, including coalescence, compaction and breakage. A convergence study is performed with respect to the parameter that determinesmore » the number of numerical particles. Averaged properties of the system are computed. In addition, the ensemble is subdivided into practically relevant size classes and analysed with respect to the amount of mass and the particle porosity in each class. These results illustrate the importance of the multidimensional approach. Finally, the kinetic equation corresponding to the stochastic model is discussed.« less

Experimental and Numerical Investigation of Local Scour Around Submarine Piggyback Pipeline Under Steady Current

NASA Astrophysics Data System (ADS)

Zhao, Enjin; Shi, Bing; Qu, Ke; Dong, Wenbin; Zhang, Jing

2018-04-01

As a new type of submarine pipeline, the piggyback pipeline has been gradually adopted in engineering practice to enhance the performance and safety of submarine pipelines. However, limited simulation work and few experimental studies have been published on the scour around the piggyback pipeline under steady current. This study numerically and experimentally investigates the local scour of the piggyback pipe under steady current. The influence of prominent factors such as pipe diameter, inflow Reynolds number, and gap between the main and small pipes, on the maximum scour depth have been examined and discussed in detail. Furthermore, one formula to predict the maximum scour depth under the piggyback pipeline has been derived based on the theoretical analysis of scour equilibrium. The feasibility of the proposed formula has been effectively calibrated by both experimental data and numerical results. The findings drawn from this study are instructive in the future design and application of the piggyback pipeline.

A numerical and experimental study on the nonlinear evolution of long-crested irregular waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goullet, Arnaud; Choi, Wooyoung; Division of Ocean Systems Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701

2011-01-15

The spatial evolution of nonlinear long-crested irregular waves characterized by the JONSWAP spectrum is studied numerically using a nonlinear wave model based on a pseudospectral (PS) method and the modified nonlinear Schroedinger (MNLS) equation. In addition, new laboratory experiments with two different spectral bandwidths are carried out and a number of wave probe measurements are made to validate these two wave models. Strongly nonlinear wave groups are observed experimentally and their propagation and interaction are studied in detail. For the comparison with experimental measurements, the two models need to be initialized with care and the initialization procedures are described. Themore » MNLS equation is found to approximate reasonably well for the wave fields with a relatively smaller Benjamin-Feir index, but the phase error increases as the propagation distance increases. The PS model with different orders of nonlinear approximation is solved numerically, and it is shown that the fifth-order model agrees well with our measurements prior to wave breaking for both spectral bandwidths.« less

Transfer of numeric ASCII data files between Apple and IBM personal computers.

PubMed

Allan, R W; Bermejo, R; Houben, D

1986-01-01

Listings for programs designed to transfer numeric ASCII data files between Apple and IBM personal computers are provided with accompanying descriptions of how the software operates. Details of the hardware used are also given. The programs may be easily adapted for transferring data between other microcomputers.

Numerical Calabi-Yau metrics

NASA Astrophysics Data System (ADS)

Douglas, Michael R.; Karp, Robert L.; Lukic, Sergio; Reinbacher, René

2008-03-01

We develop numerical methods for approximating Ricci flat metrics on Calabi-Yau hypersurfaces in projective spaces. Our approach is based on finding balanced metrics and builds on recent theoretical work by Donaldson. We illustrate our methods in detail for a one parameter family of quintics. We also suggest several ways to extend our results.

Finite element solutions of free convective Casson fluid flow past a vertically inclined plate submitted in magnetic field in presence of heat and mass transfer

NASA Astrophysics Data System (ADS)

Raju, R. Srinivasa; Reddy, B. Mahesh; Reddy, G. Jithender

2017-09-01

The aim of this research work is to study the influence of thermal radiation on steady magnetohydrodynamic-free convective Casson fluid flow of an optically thick fluid over an inclined vertical plate with heat and mass transfer. Combined phenomenon of heat and mass transfer is considered. Numerical solutions in general form are obtained by using the finite element method. The sum of thermal and mechanical parts is expressed as velocity of fluid. Corresponding limiting solutions are also reduced from the general solutions. It is found that the obtained numerical solutions satisfy all imposed initial and boundary conditions and reduce to some known solutions from the literature as special cases. Numerical results for the controlling flow parameters are drawn graphically and discussed in detail. In some special cases, the obtained numerical results are compared and found to be in good agreement with the previously published results which are available in literature. Applications of this study includes laminar magneto-aerodynamics, materials processing and magnetohydrodynamic propulsion thermo-fluid dynamics, etc.

Faster and More Accurate Transport Procedures for HZETRN

NASA Technical Reports Server (NTRS)

Slaba, Tony C.; Blattnig, Steve R.; Badavi, Francis F.

2010-01-01

Several aspects of code verification are examined for HZETRN. First, a detailed derivation of the numerical marching algorithms is given. Next, a new numerical method for light particle transport is presented, and improvements to the heavy ion transport algorithm are discussed. A summary of various coding errors is also given, and the impact of these errors on exposure quantities is shown. Finally, a coupled convergence study is conducted. From this study, it is shown that past efforts in quantifying the numerical error in HZETRN were hindered by single precision calculations and computational resources. It is also determined that almost all of the discretization error in HZETRN is caused by charged target fragments below 50 AMeV. Total discretization errors are given for the old and new algorithms, and the improved accuracy of the new numerical methods is demonstrated. Run time comparisons are given for three applications in which HZETRN is commonly used. The new algorithms are found to be almost 100 times faster for solar particle event simulations and almost 10 times faster for galactic cosmic ray simulations.

The Problem of Modeling the Elastomechanics in Engineering

DTIC Science & Technology

1990-02-01

element method by the code PROBE (McNeil Schwendler- Noetic ) and STRIPE (Aeronautical Institute of Sweden). These codes have various error checks so that...Mindlin solutions converge to the Kirchhoff solution as d--O, see eg. [12), [19]. For a detailed study of the asymptotic behavior of Reissner...of study and research for foreign students in numerical mathematics who are supported by foreign govern- ments or exchange agencies (Fulbright, etc

Numerical studies of film formation in context of steel coating

NASA Astrophysics Data System (ADS)

Aniszewski, Wojciech; Zaleski, Stephane; Popinet, Stephane

2017-11-01

In this work, we present a detailed example of numerical study of film formation in the context of metal coating. Liquid metal is drawn from a reservoir onto a retracting solid sheet, forming a coating film characterized by phenomena such as longitudinal thickness variation (in 3D) or waves akin to that predicted by Kapitza and Kapitza (visible in two dimensions as well). While the industry standard configuration for Zinc coating is marked by coexistence of medium Capillary number (Ca = 0.03) and film Reynolds number above 1000, we present also parametric studies in order to establish more clearly to what degree does the numerical method influence film regimes obtained in the target configuration. The simulations have been performed using Basilisk, a grid-adapting, strongly optimized code derived from Gerris . Mesh adaptation allows for arbitrary precision in relevant regions such as the contact line or the meniscus, while a coarse grid is applied elsewhere. This adaptation strategy, as the results indicate, is the only realistic approach for numerical method to cover the wide range of necessary scales from the predicted film thickness (hundreds of microns) to the domain size (meters).

Studies of aerothermal loads generated in regions of shock/shock interaction in hypersonic flow

NASA Technical Reports Server (NTRS)

Holden, Michael S.; Moselle, John R.; Lee, Jinho

1991-01-01

Experimental studies were conducted to examine the aerothermal characteristics of shock/shock/boundary layer interaction regions generated by single and multiple incident shocks. The presented experimental studies were conducted over a Mach number range from 6 to 19 for a range of Reynolds numbers to obtain both laminar and turbulent interaction regions. Detailed heat transfer and pressure measurements were made for a range of interaction types and incident shock strengths over a transverse cylinder, with emphasis on the 3 and 4 type interaction regions. The measurements were compared with the simple Edney, Keyes, and Hains models for a range of interaction configurations and freestream conditions. The complex flowfields and aerothermal loads generated by multiple-shock impingement, while not generating as large peak loads, provide important test cases for code prediction. The detailed heat transfer and pressure measurements proved a good basis for evaluating the accuracy of simple prediction methods and detailed numerical solutions for laminar and transitional regions or shock/shock interactions.

Finite element analysis and simulation of rheological properties of bulk molding compound (BMC)

NASA Astrophysics Data System (ADS)

Ergin, M. Fatih; Aydin, Ismail

2013-12-01

Bulk molding compound (BMC) is one of the important composite materials with various engineering applications. BMC is a thermoset plastic resin blend of various inert fillers, fiber reinforcements, catalysts, stabilizers and pigments that form a viscous, molding compound. Depending on the end-use application, bulk molding compounds are formulated to achieve close dimensional control, flame and scratch resistance, electrical insulation, corrosion and stain resistance, superior mechanical properties, low shrink and color stability. Its excellent flow characteristics, dielectric properties, and flame resistance make this thermoset material well-suited to a wide variety of applications requiring precision in detail and dimensions as well as high performance. When a BMC is used for these purposes, the rheological behavior and properties of the BMC is the main concern. In this paper, finite element analysis of rheological properties of bulk molding composite material was studied. For this purpose, standard samples of composite material were obtained by means of uniaxial hot pressing. 3 point flexural tests were then carried out by using a universal testing machine. Finite element analyses were then performed with defined material properties within a specific constitutive material behavior. Experimental and numerical results were then compared. Good correlation between the numerical simulation and the experimental results was obtained. It was expected with this study that effects of various process parameters and boundary conditions on the rheological behavior of bulk molding compounds could be determined by means of numerical analysis without detailed experimental work.

Morphology of Block Copolymer Electrolytes: A Numerical Self-Consistent Field Theory Study

NASA Astrophysics Data System (ADS)

Hou, Kevin; Qin, Jian

Engineering the morphology of ion-containing block copolymers is imperative for the optimization of their charge-transport and mechanical properties. Existing experiments have demonstrated that the addition of ions has a dramatic effect on the morphology and thermodynamic behavior of these structured electrolytes. We have developed an efficient, symmetry-adapted algorithm to calculate the ionic interactions in the SCFT for ion-containing polymers. We present the results of a numerical SCFT study examining how dielectric heterogeneity, ion concentration, and ion solvation affect morphology, domain spacing, ion distribution, and polymer density profiles. Particular attention is given to the detailed morphological analysis of the bicontinuous gyroidal phase, as well as the relevance of the aforementioned results to ionic conductivity.

Evaluation of electrical power alternatives for the Pacific Northwest

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

This study evaluates the concept of implementation of large-scale energy conservation to reduce end-use demand for electrical energy as an alternative to the need for continued construction of new power plants to meet projected energy requirements for the Pacific Northwest. In particular, the numerical accuracy, economic feasibility, and institutional impact of a conservation-oriented scenario developed by the Natural Resources Defense Council, Inc., is assessed, relative to the energy forecast prepared by the Pacific Northwest Utilities Conference Commission. The results of this study are presented in four detailed sections following an introductory and summary section: Reconstruction and Numerical Evaluation of Alternativemore » Scenario; Economic Analysis; Institutional Impact; and Impact of New National Energy Policy.« less

Trapped mountain wave excitations over the Kathmandu valley, Nepal

NASA Astrophysics Data System (ADS)

Regmi, Ram P.; Maharjan, Sangeeta

2015-11-01

Mid-wintertime spatial and temporal distributions of mountain wave excitation over the Kathmandu valley has been numerically simulated using Weather Research and Forecasting (WRF) modeling system. The study shows that low-level trapped mountain waves may remain very active during the night and early morning in the sky over the southern rim of the surrounding mountains, particularly, over the lee of Mt. Fulchoki. Calculations suggest that mountain wave activities are at minimum level during afternoon. The low-level trapped mountain waves in the sky over southern gateway of Tribhuvan International Airport (TIA) may pose risk for landings and takeoffs of light aircrafts. Detailed numerical and observational studies would be very important to reduce risk of air accidents and discomfort in and around the Kathmandu valley.

Numerical study of propagation of forest fires in the presence of fire breaks using an averaged setting

NASA Astrophysics Data System (ADS)

Marzaeva, S. I.; Galtseva, O. V.

2018-05-01

The forest fires spread in the pine forests have been numerically simulated using a three-dimensional mathematical model. The model was integrated with respect to the vertical coordinate because horizontal sizes of forest are much greater than the heights of trees. In this paper, the assignment and theoretical investigations of the problems of crown forest fires spread pass the firebreaks were carried out. In this context, a study ( mathematical modeling) of the conditions of forest fire spreading that would make it possible to obtain a detailed picture of the change in the temperature and component concentration fields with time, and determine as well as the limiting condition of fire propagation in forest with these fire breaks.

Experimental study and numerical simulation of the salinity effect on water-freezing point and ice-melting rate

NASA Astrophysics Data System (ADS)

Qin, N.; Wu, Y.; Wang, H. W.; Wang, Y. Y.

2017-12-01

In this paper, based on the background of snowmelt de-icing tools, we studied the effect of salt on freezing point and melting rate of ice through laboratory test and FLUENT numerical simulation analysis. It was confirmed that the freezing point is inversely proportional to the salt solid content, and with the salt solid content increasing, the freezing process of salt water gradually accepts the curing rule of non-crystal solids. At the same temperature, an increase in the salt solid content, the ice melting rate increase by the empirical formula linking the melting time with temperature and salt content. The theoretical aspects of solid/fluid transformation are discussed in detail.

Numerical study of shock-induced combustion in methane-air mixtures

NASA Technical Reports Server (NTRS)

Yungster, Shaye; Rabinowitz, Martin J.

1993-01-01

The shock-induced combustion of methane-air mixtures in hypersonic flows is investigated using a new reaction mechanism consisting of 19 reacting species and 52 elementary reactions. This reduced model is derived from a full kinetic mechanism via the Detailed Reduction technique. Zero-dimensional computations of several shock-tube experiments are presented first. The reaction mechanism is then combined with a fully implicit Navier-Stokes computational fluid dynamics (CFD) code to conduct numerical simulations of two-dimensional and axisymmetric shock-induced combustion experiments of stoichiometric methane-air mixtures at a Mach number of M = 6.61. Applications to the ram accelerator concept are also presented.

A numerical study of transition control by periodic suction-blowing

NASA Technical Reports Server (NTRS)

Biringen, Sedat

1987-01-01

The applicability of active control of transition by periodic suction-blowing is investigated via direct numerical 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.

Detailed heat/mass transfer distributions in a rotating two pass coolant channel with engine-near cross section and smooth walls.

PubMed

Rathjen, L; Hennecke, D K; Bock, S; Kleinstück, R

2001-05-01

This paper shows results obtained by experimental and numerical investigations concerning flow structure and heat/mass transfer in a rotating two-pass coolant channel with engine-near geometry. The smooth two passes are connected by a 180 degrees U-bend in which a 90 degrees turning vane is mounted. The influence of rotation number, Reynolds number and geometry is investigated. The results show a detailed picture of the flow field and distributions of Sherwood number ratios determined experimentally by the use of the naphthalene sublimation technique as well as Nusselt number ratios obtained from the numerical work. Especially the heat/mass transfer distributions in the bend and in the region after the bend show strong gradients, where several separation zones exist and the flow is forced to follow the turbine airfoil shape. Comparisons of numerical and experimental results show only partly good agreement.

MS overline -on-shell quark mass relation up to four loops in QCD and a general SU (N ) gauge group

NASA Astrophysics Data System (ADS)

Marquard, Peter; Smirnov, Alexander V.; Smirnov, Vladimir A.; Steinhauser, Matthias; Wellmann, David

2016-10-01

We compute the relation between heavy quark masses defined in the modified minimal subtraction and the on-shell schemes. Detailed results are presented for all coefficients of the SU (Nc) color factors. The reduction of the four-loop on-shell integrals is performed for a general QCD gauge parameter. Altogether there are about 380 master integrals. Some of them are computed analytically, others with high numerical precision using Mellin-Barnes representations, and the rest numerically with the help of FIESTA. We discuss in detail the precise numerical evaluation of the four-loop master integrals. Updated relations between various short-distance masses and the MS ¯ quark mass to next-to-next-to-next-to-leading order accuracy are provided for the charm, bottom and top quarks. We discuss the dependence on the renormalization and factorization scale.

Numerical analysis for the fractional diffusion and fractional Buckmaster equation by the two-step Laplace Adam-Bashforth method

NASA Astrophysics Data System (ADS)

Jain, Sonal

2018-01-01

In this paper, we aim to use the alternative numerical scheme given by Gnitchogna and Atangana for solving partial differential equations with integer and non-integer differential operators. We applied this method to fractional diffusion model and fractional Buckmaster models with non-local fading memory. The method yields a powerful numerical algorithm for fractional order derivative to implement. Also we present in detail the stability analysis of the numerical method for solving the diffusion equation. This proof shows that this method is very stable and also converges very quickly to exact solution and finally some numerical simulation is presented.

Realistic numerical modelling of human head tissue exposure to electromagnetic waves from cellular phones

NASA Astrophysics Data System (ADS)

Scarella, Gilles; Clatz, Olivier; Lanteri, Stéphane; Beaume, Grégory; Oudot, Steve; Pons, Jean-Philippe; Piperno, Sergo; Joly, Patrick; Wiart, Joe

2006-06-01

The ever-rising diffusion of cellular phones has brought about an increased concern for the possible consequences of electromagnetic radiation on human health. Possible thermal effects have been investigated, via experimentation or simulation, by several research projects in the last decade. Concerning numerical modeling, the power absorption in a user's head is generally computed using discretized models built from clinical MRI data. The vast majority of such numerical studies have been conducted using Finite Differences Time Domain methods, although strong limitations of their accuracy are due to heterogeneity, poor definition of the detailed structures of head tissues (staircasing effects), etc. In order to propose numerical modeling using Finite Element or Discontinuous Galerkin Time Domain methods, reliable automated tools for the unstructured discretization of human heads are also needed. Results presented in this article aim at filling the gap between human head MRI images and the accurate numerical modeling of wave propagation in biological tissues and its thermal effects. To cite this article: G. Scarella et al., C. R. Physique 7 (2006).

Experimental and Detailed Numerical Studies of Fundamental Flame Properties of Gaseous and Liquid Fuels

DTIC Science & Technology

2006-12-01

Form Approved REPORT DOCUMENTATION PAGE OMB No. 0704-0188 Putk repoDng bunrds for the oosbon of •fornraon .5 estniated to aerage I hour per respose ...plied to activate the H2 /air/catalyst system and initiate the heat pro- duction, after which the system is completely self -sustaining. The use of a

Carolina bays of the Savannah River Plant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schalles, J.F.; Sharitz, R.R.; Gibbons, J.W.

1989-01-01

Much of the research to date on the Carolina bays of the Savannah River Plant and elsewhere has focused on certain species or on environmental features. Different levels of detail exist for different groups of organisms and reflect the diverse interests of previous investigators. This report summarizes aspects of research to date and presents data from numerous studies. 70 refs., 14 figs., 12 tabs.

Numerical Ordering Ability Mediates the Relation between Number-Sense and Arithmetic Competence

ERIC Educational Resources Information Center

Lyons, Ian M.; Beilock, Sian L.

2011-01-01

What predicts human mathematical competence? While detailed models of number representation in the brain have been developed, it remains to be seen exactly how basic number representations link to higher math abilities. We propose that representation of ordinal associations between numerical symbols is one important factor that underpins this…

78 FR 54377 - Airworthiness Directives; Airbus Airplanes

Federal Register 2010, 2011, 2012, 2013, 2014

2013-09-04

... family THSA P/N 47145-XXX (where XXX stands for any numerical value) ballscrews might be affected by this... requires repetitive detailed inspections of the ballscrew lower splines of THSAs having P/N 47145-XXX to... ballscrew shaft and tie-rod splines on any THSA having P/N 47145-XXX (where XXX stands for any numerical...

Desirable floating-point arithmetic and elementary functions for numerical computation

NASA Technical Reports Server (NTRS)

Hull, T. E.

1978-01-01

The topics considered are: (1) the base of the number system, (2) precision control, (3) number representation, (4) arithmetic operations, (5) other basic operations, (6) elementary functions, and (7) exception handling. The possibility of doing without fixed-point arithmetic is also mentioned. The specifications are intended to be entirely at the level of a programming language such as FORTRAN. The emphasis is on convenience and simplicity from the user's point of view. Conforming to such specifications would have obvious beneficial implications for the portability of numerical software, and for proving programs correct, as well as attempting to provide facilities which are most suitable for the user. The specifications are not complete in every detail, but it is intended that they be complete in spirit - some further details, especially syntatic details, would have to be provided, but the proposals are otherwise relatively complete.

Three-Dimensional Numerical Simulation on Triaxial Failure Mechanical Behavior of Rock-Like Specimen Containing Two Unparallel Fissures

NASA Astrophysics Data System (ADS)

Huang, Yan-Hua; Yang, Sheng-Qi; Zhao, Jian

2016-12-01

A three-dimensional particle flow code (PFC3D) was used for a systematic numerical simulation of the strength failure and cracking behavior of rock-like material specimens containing two unparallel fissures under conventional triaxial compression. The micro-parameters of the parallel bond model were first calibrated using the laboratory results of intact specimens and then validated from the experimental results of pre-fissured specimens under triaxial compression. Numerically simulated stress-strain curves, strength and deformation parameters and macro-failure modes of pre-fissured specimens were all in good agreement with the experimental results. The relationship between stress and the micro-crack numbers was summarized. Crack initiation, propagation and coalescence process of pre-fissured specimens were analyzed in detail. Finally, horizontal and vertical cross sections of numerical specimens were derived from PFC3D. A detailed analysis to reveal the internal damage behavior of rock under triaxial compression was carried out. The experimental and simulated results are expected to improve the understanding of the strength failure and cracking behavior of fractured rock under triaxial compression.

Interaction between an elastic structure and free-surface flows: experimental versus numerical comparisons using the PFEM

NASA Astrophysics Data System (ADS)

Idelsohn, S. R.; Marti, J.; Souto-Iglesias, A.; Oñate, E.

2008-12-01

The paper aims to introduce new fluid structure interaction (FSI) tests to compare experimental results with numerical ones. The examples have been chosen for a particular case for which experimental results are not much reported. This is the case of FSI including free surface flows. The possibilities of the Particle Finite Element Method (PFEM) [1] for the simulation of free surface flows is also tested. The simulations are run using the same scale as the experiment in order to minimize errors due to scale effects. Different scenarios are simulated by changing the boundary conditions for reproducing flows with the desired characteristics. Details of the input data for all the examples studied are given. The aim is to identifying benchmark problems for FSI including free surface flows for future comparisons between different numerical approaches.

A numerical projection technique for large-scale eigenvalue problems

NASA Astrophysics Data System (ADS)

Gamillscheg, Ralf; Haase, Gundolf; von der Linden, Wolfgang

2011-10-01

We present a new numerical technique to solve large-scale eigenvalue problems. It is based on the projection technique, used in strongly correlated quantum many-body systems, where first an effective approximate model of smaller complexity is constructed by projecting out high energy degrees of freedom and in turn solving the resulting model by some standard eigenvalue solver. Here we introduce a generalization of this idea, where both steps are performed numerically and which in contrast to the standard projection technique converges in principle to the exact eigenvalues. This approach is not just applicable to eigenvalue problems encountered in many-body systems but also in other areas of research that result in large-scale eigenvalue problems for matrices which have, roughly speaking, mostly a pronounced dominant diagonal part. We will present detailed studies of the approach guided by two many-body models.

Swift and GLAST Cooperative Efforts

NASA Technical Reports Server (NTRS)

Thompson, D. J.

2007-01-01

Because gamma-ray astrophysics depends in many ways on multiwavelength studies, the Gamma-ray Large Area Space Telescope (GLAST) instrument teams are eagerly anticipating coordinated observations with the Swift observatory. Swift and GLAST combined cover most of twelve orders of magnitude in the electromagnetic spectrum, offering numerous opportunities for cooperation. Three of the high-priority interests are: (1) gamma-ray burst studies; (2) broad-spectrum studies of blazars in both quiescent and flaring states; and (3) identification and detailed study of unidentified gamma-ray sources.

The onset of convection in a binary fluid mixture with temperature dependent viscosity and Coriolis force with Soret presence

NASA Astrophysics Data System (ADS)

Abidin, Nurul Hafizah Zainal; Mokhtar, Nor Fadzillah Mohd; Majid, Zanariah Abdul; Ghani, Siti Salwa Abd

2017-11-01

Temperature dependent viscosity and Coriolis force were applied to the steady Benard-Marangoni convection where the lower boundary of a horizontal layer of the binary mixture is heated from below and cooled from above. The purpose of this paper is to study in detail the onset of convection with these effects. Few cases of boundary conditions are studied which are rigid-rigid, rigid-free and free-free representing the lower-upper boundaries. A detailed numerical calculation of the marginal stability curves was performed by using the Galerkin method and it is showed that temperature dependent viscosity and Soret number destabilize the binary fluid layer system and Taylor number act oppositely.

Study of a pursuit-evasion guidance law for high performance aircraft

NASA Technical Reports Server (NTRS)

Williams, Peggy S.; Menon, P. K. A.; Antoniewicz, Robert F.; Duke, Eugene L.

1989-01-01

The study of a one-on-one aircraft pursuit-evasion guidance scheme for high-performance aircraft is discussed. The research objective is to implement a guidance law derived earlier using differential game theory in conjunction with the theory of feedback linearization. Unlike earlier research in this area, the present formulation explicitly recognizes the two-sided nature of the pursuit-evasion scenario. The present research implements the guidance law in a realistic model of a modern high-performance fighter aircraft. Also discussed are the details of the guidance law, implementation in a highly detailed simulation of a high-performance fighter, and numerical results for two engagement geometries. Modifications of the guidance law for onboard implementation is also discussed.

Spreading dynamics of an e-commerce preferential information model on scale-free networks

NASA Astrophysics Data System (ADS)

Wan, Chen; Li, Tao; Guan, Zhi-Hong; Wang, Yuanmei; Liu, Xiongding

2017-02-01

In order to study the influence of the preferential degree and the heterogeneity of underlying networks on the spread of preferential e-commerce information, we propose a novel susceptible-infected-beneficial model based on scale-free networks. The spreading dynamics of the preferential information are analyzed in detail using the mean-field theory. We determine the basic reproductive number and equilibria. The theoretical analysis indicates that the basic reproductive number depends mainly on the preferential degree and the topology of the underlying networks. We prove the global stability of the information-elimination equilibrium. The permanence of preferential information and the global attractivity of the information-prevailing equilibrium are also studied in detail. Some numerical simulations are presented to verify the theoretical results.

Impact of Demographic Siting Criteria and Environmental Suitability on Land Availability for Nuclear Reactor Siting

NASA Technical Reports Server (NTRS)

Hansen, K. L.

1982-01-01

The effect of population and certain environmental characteristics on the availability of land for siting nuclear power plants was assessed. The study area, consisting of the 48 contiguous states, was divided into 5 kilometer (km) square grid cells yielding a total of 600,000 cells. Through the use of a modern geographic information system, it was possible to provide a detailed analysis of a quite large area. Numerous maps and statistical tables were produced, the detail of which were limited only by available data. Evaluation issues included population density, restricted lands, seismic hardening, site preparation, water availability, and cost factors.

The Development and Comparison of Molecular Dynamics Simulation and Monte Carlo Simulation

NASA Astrophysics Data System (ADS)

Chen, Jundong

2018-03-01

Molecular dynamics is an integrated technology that combines physics, mathematics and chemistry. Molecular dynamics method is a computer simulation experimental method, which is a powerful tool for studying condensed matter system. This technique not only can get the trajectory of the atom, but can also observe the microscopic details of the atomic motion. By studying the numerical integration algorithm in molecular dynamics simulation, we can not only analyze the microstructure, the motion of particles and the image of macroscopic relationship between them and the material, but can also study the relationship between the interaction and the macroscopic properties more conveniently. The Monte Carlo Simulation, similar to the molecular dynamics, is a tool for studying the micro-molecular and particle nature. In this paper, the theoretical background of computer numerical simulation is introduced, and the specific methods of numerical integration are summarized, including Verlet method, Leap-frog method and Velocity Verlet method. At the same time, the method and principle of Monte Carlo Simulation are introduced. Finally, similarities and differences of Monte Carlo Simulation and the molecular dynamics simulation are discussed.

Using Growth and Arrest of Richtmyer-Meshkov Instabilities and Lagrangian Simulations to Study High-Rate Material Strength

NASA Astrophysics Data System (ADS)

Prime, Michael; Vaughan, Diane; Preston, Dean; Oro, David; Buttler, William

2013-06-01

Rayleigh-Taylor instabilities have been widely used to study the deviatoric (flow) strength of solids at high strain rates. More recently, experiments applying a supported shock through mating surfaces (Atwood number = 1) with geometrical perturbations have been proposed for studying strength at strain rates up to 107/sec using Richtmyer-Meshkov (RM) instabilities. Buttler et al. [J. Fluid Mech., 2012] recently reported experimental results for RM instability growth but with an unsupported shock applied by high explosives and the geometrical perturbations on the opposite free surface (Atwood number = -1). This novel configuration allowed detailed experimental observation of the instability growth and arrest. We present results and detailed interpretation from numerical simulations of the Buttler experiments on copper. Highly-resolved, two-dimensional simulations were performed using a Lagrangian hydrocode and the Preston-Tonks-Wallace (PTW) strength model. The model predictions show good agreement with the data in spite of the PTW model being calibrated on lower strain rate data. The numerical simulations are used to 1) examine various assumptions previously made in an analytical model, 2) to estimate the sensitivity of such experiments to material strength and 3) to explore the possibility of extracting meaningful strength information in the face of complicated spatial and temporal variations of stress, pressure, and temperature during the experiments.

Numerical Propulsion System Simulation (NPSS) 1999 Industry Review

NASA Technical Reports Server (NTRS)

Lytle, John; Follen, Greg; Naiman, Cynthia; Evans, Austin

2000-01-01

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. In addition, the paper contains a summary of the feedback received from industry partners in the development effort and the actions taken over the past year to respond to that feedback. The NPSS development was supported in FY99 by the High Performance Computing and Communications Program.

An Investigation of the Tensile Strength of a Composite-To-Metal Adhesive Joint

NASA Astrophysics Data System (ADS)

Tsouvalis, Nicholas G.; Karatzas, Vassilios A.

2011-04-01

The present study examines the feasibility of a simple concept composite-to-metal butt joint through the performance of both numerical and experimental studies. The composite part is made of glass/epoxy unidirectional layers made with the vacuum bag method. The geometry of the joint is typical for marine applications and corresponds to a low stiffness ratio. Two major parameters are investigated, namely the overlap length and the surface preparation of the steel adherent. Manufacturing of specimens and the procedure of the tensile tests are described in detail, giving hints for obtaining a better quality joint. Axial elongation and strains at various places of the joint were monitored and also numerically calculated. The tests revealed that the joint is quite effective, irrespectively of the steel surface preparation method. The failure loads are comparable and in some cases superior to other corresponding values found in the literature. The numerical models proved to adequately predict the structural response of the joint up to the loading where debonding starts.

Thermal transport in phosphorene and phosphorene-based materials: A review on numerical studies

NASA Astrophysics Data System (ADS)

Hong, Yang; Zhang, Jingchao; Zeng, Xiao Cheng

2018-03-01

The recently discovered two-dimensional (2D) layered material phosphorene has attracted considerable interest as a promising p-type semiconducting material. In this article, we review the recent advances in numerical studies of the thermal properties of monolayer phosphorene and phosphorene-based heterostructures. We first briefly review the commonly used first-principles and molecular dynamics (MD) approaches to evaluate the thermal conductivity and interfacial thermal resistance of 2D phosphorene. Principles of different steady-state and transient MD techniques have been elaborated on in detail. Next, we discuss the anisotropic thermal transport of phosphorene in zigzag and armchair chiral directions. Subsequently, the in-plane and cross-plane thermal transport in phosphorene-based heterostructures such as phosphorene/silicon and phosphorene/graphene is summarized. Finally, the numerical research in the field of thermal transport in 2D phosphorene is highlighted along with our perspective of potentials and opportunities of 2D phosphorenes in electronic applications such as photodetectors, field-effect transistors, lithium ion batteries, sodium ion batteries, and thermoelectric devices.

Comparative numerical study on the optimal vulcanization of rubber compounds through traditional curing and microwaves

NASA Astrophysics Data System (ADS)

Milani, Gabriele; Milani, Federico

2012-12-01

The main problem in the industrial production process of thick EPM/EPDM elements is constituted by the different temperatures which undergo internal (cooler) and external regions. Indeed, while internal layers remain essentially under-vulcanized, external coating is always over-vulcanized, resulting in an overall average tensile strength insufficient to permit the utilization of the items in several applications where it is required a certain level of performance. Possible ways to improve rubber output mechanical properties include a careful calibration of exposition time and curing temperature in traditional heating or a vulcanization through innovative techniques, such as microwaves. In the present paper, a comprehensive numerical model able to give predictions on the optimized final mechanical properties of vulcanized 2D and 3D thick rubber items is presented and applied to a meaningful example of engineering interest. A detailed comparative numerical study is finally presented in order to establish pros and cons of traditional vulcanization vs microwaves curing.

Uncertain viscoelastic models with fractional order: A new spectral tau method to study the numerical simulations of the solution

NASA Astrophysics Data System (ADS)

Ahmadian, A.; Ismail, F.; Salahshour, S.; Baleanu, D.; Ghaemi, F.

2017-12-01

The analysis of the behaviors of physical phenomena is important to discover significant features of the character and the structure of mathematical models. Frequently the unknown parameters involve in the models are assumed to be unvarying over time. In reality, some of them are uncertain and implicitly depend on several factors. In this study, to consider such uncertainty in variables of the models, they are characterized based on the fuzzy notion. We propose here a new model based on fractional calculus to deal with the Kelvin-Voigt (KV) equation and non-Newtonian fluid behavior model with fuzzy parameters. A new and accurate numerical algorithm using a spectral tau technique based on the generalized fractional Legendre polynomials (GFLPs) is developed to solve those problems under uncertainty. Numerical simulations are carried out and the analysis of the results highlights the significant features of the new technique in comparison with the previous findings. A detailed error analysis is also carried out and discussed.

Modelling the impact, spreading and freezing of a water droplet on horizontal and inclined superhydrophobic cooled surfaces

NASA Astrophysics Data System (ADS)

Yao, Yina; Li, Cong; Zhang, Hui; Yang, Rui

2017-10-01

It is quite important to clearly understand the dynamic and freezing process of water droplets impacting a cold substrate for the prevention of ice accretion. In this study, a three-dimensional model including an extended phase change method was developed on OpenFOAM platform to simulate the impact, spreading and freezing of a water droplet on a cooled solid substrate. Both normal and oblique impact conditions were studied numerically. The evolution of the droplet shape and dynamic characteristics such as area ratio and spread factor were compared between numerical and experimental results. Good agreements were obtained. The effects of Weber number and Ohnersorge number on the oblique impact and freezing process were investigated. A regime map which depicts the different responses of droplets as a function of normal Weber number and Ohnesorge number was obtained. Moreover, the impact, spreading and freezing behaviour of water droplets were analyzed in detail from the numerical results.

Simulation study of the thermal and the thermoelastic effects induced by pulsed laser absorption in human skin

NASA Astrophysics Data System (ADS)

Kim, Jae-Young; Jang, Kyungmin; Yang, Seung-Jin; Baek, Jun-Hyeok; Park, Jong-Rak; Yeom, Dong-Il; Kim, Ji-Sun; Kim, Hyung-Sik; Jun, Jae-Hoon; Chung, Soon-Cheol

2016-04-01

We studied the thermal and the mechanical effects induced by pulsed laser absorption in human skin by numerically solving the heat-transfer and the thermoelastic wave equations. The simulation of the heat-transfer equation yielded the spatiotemporal distribution of the temperature increase in the skin, which was then used in the driving term of the thermoelastic wave equation. We compared our simulation results for the temperature increase and the skin displacements with the measured and numerical results, respectively. For the comparison, we used a recent report by Jun et al. [Sci. Rep. 5, 11016 (2015)], who measured in vivo skin temperature and performed numerical simulation of the thermoelastic wave equation using a simple assumption about the temporal evolution of the temperature distribution, and found their results to be in good agreement with our results. In addition, we obtained solutions for the stresses in the human skin and analyzed their dynamic behaviors in detail.

Experimental and Numerical Study on the Tensile Behaviour of UACS/Al Fibre Metal Laminate

NASA Astrophysics Data System (ADS)

Xue, Jia; Wang, Wen-Xue; Zhang, Jia-Zhen; Wu, Su-Jun; Li, Hang

2015-10-01

A new fibre metal laminate fabricated with aluminium sheets and unidirectionally arrayed chopped strand (UACS) plies is proposed. The UACS ply is made by cutting parallel slits into a unidirectional carbon fibre prepreg. The UACS/Al laminate may be viewed as aluminium laminate reinforced by highly aligned, discontinuous carbon fibres. The tensile behaviour of UACS/Al laminate, including thermal residual stress and failure progression, is investigated through experiments and numerical simulation. Finite element analysis was used to simulate the onset and propagation of intra-laminar fractures occurring within slits of the UACS plies and delamination along the interfaces. The finite element models feature intra-laminar cohesive elements inserted into the slits and inter-laminar cohesive elements inserted at the interfaces. Good agreement are obtained between experimental results and finite element analysis, and certain limitations of the finite element models are observed and discussed. The combined experimental and numerical studies provide a detailed understanding of the tensile behaviour of UACS/Al laminates.

Development of a Aerothermoelastic-Acoustics Simulation Capability of Flight Vehicles

NASA Technical Reports Server (NTRS)

Gupta, K. K.; Choi, S. B.; Ibrahim, A.

2010-01-01

A novel numerical, finite element based analysis methodology is presented in this paper suitable for accurate and efficient simulation of practical, complex flight vehicles. An associated computer code, developed in this connection, is also described in some detail. Thermal effects of high speed flow obtained from a heat conduction analysis are incorporated in the modal analysis which in turn affects the unsteady flow arising out of interaction of elastic structures with the air. Numerical examples pertaining to representative problems are given in much detail testifying to the efficacy of the advocated techniques. This is a unique implementation of temperature effects in a finite element CFD based multidisciplinary simulation analysis capability involving large scale computations.

Numerical experiments in homogeneous turbulence

NASA Technical Reports Server (NTRS)

Rogallo, R. S.

1981-01-01

The direct simulation methods developed by Orszag and Patternson (1972) for isotropic turbulence were extended to homogeneous turbulence in an incompressible fluid subjected to uniform deformation or rotation. The results of simulations for irrotational strain (plane and axisymmetric), shear, rotation, and relaxation toward isotropy following axisymmetric strain are compared with linear theory and experimental data. Emphasis is placed on the shear flow because of its importance and because of the availability of accurate and detailed experimental data. The computed results are used to assess the accuracy of two popular models used in the closure of the Reynolds-stress equations. Data from a variety of the computed fields and the details of the numerical methods used in the simulation are also presented.

Return Trajectory of the SpaceShipTwo Spacecraft--Numerical Solution

ERIC Educational Resources Information Center

Slegr, J.; Kraus, I.

2012-01-01

SpaceShipTwo is a private spaceplane project which is intended for space tourism. Very few details about its construction and flight characteristics are available for the public, but with proper numerical methods some interesting results can be obtained using secondary school mathematics. An exercise about SpaceShipTwo can be used as a…

Cosmological perturbations in the DGP braneworld: Numeric solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cardoso, Antonio; Koyama, Kazuya; Silva, Fabio P.

2008-04-15

We solve for the behavior of cosmological perturbations in the Dvali-Gabadadze-Porrati (DGP) braneworld model using a new numerical method. Unlike some other approaches in the literature, our method uses no approximations other than linear theory and is valid on large scales. We examine the behavior of late-universe density perturbations for both the self-accelerating and normal branches of DGP cosmology. Our numerical results can form the basis of a detailed comparison between the DGP model and cosmological observations.

Equilibrium vortex lattices of a binary rotating atomic Bose–Einstein condensate with unequal atomic masses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Biao; Wang, Lin-Xue; Chen, Guang-Ping

We perform a detailed numerical study of the equilibrium ground-state structures of a binary rotating Bose–Einstein condensate with unequal atomic masses. Our results show that the ground-state distribution and its related vortex configurations are complex events that differ markedly depending strongly on the strength of rotation frequency, as well as on the ratio of atomic masses. We also discuss the structures and radii of the clouds, the number and the size of the core region of the vortices, as a function of the rotation frequency, and of the ratio of atomic masses, and the analytical results agree well with ourmore » numerical simulations. This work may open an alternate way in the quantum control of the binary rotating quantum gases with unequal atomic masses. - Highlights: • A binary quantum gases with unequal atomic masses is considered. • Effects of the ratio of atomic masses and rotation frequency are discussed in full parameter space. • The detailed information about both the cloud and vortices are also discussed.« less

Comparisons of Calculations with PARTRAC and NOREC: Transport of Electrons in Liquid Water

PubMed Central

Dingfelder, M.; Ritchie, R. H.; Turner, J. E.; Friedland, W.; Paretzke, H. G.; Hamm, R. N.

2013-01-01

Monte Carlo computer models that simulate the detailed, event-by-event transport of electrons in liquid water are valuable for the interpretation and understanding of findings in radiation chemistry and radiation biology. Because of the paucity of experimental data, such efforts must rely on theoretical principles and considerable judgment in their development. Experimental verification of numerical input is possible to only a limited extent. Indirect support for model validity can be gained from a comparison of details between two independently developed computer codes as well as the observable results calculated with them. In this study, we compare the transport properties of electrons in liquid water using two such models, PARTRAC and NOREC. Both use interaction cross sections based on plane-wave Born approximations and a numerical parameterization of the complex dielectric response function for the liquid. The models are described and compared, and their similarities and differences are highlighted. Recent developments in the field are discussed and taken into account. The calculated stopping powers, W values, and slab penetration characteristics are in good agreement with one another and with other independent sources. PMID:18439039

Studies of Low Luminosity Active Galactic Nuclei with Monte Carlo and Magnetohydrodynamic Simulations

NASA Astrophysics Data System (ADS)

Hilburn, Guy Louis

Results from several studies are presented which detail explorations of the physical and spectral properties of low luminosity active galactic nuclei. An initial Sagittarius A* general relativistic magnetohydrodynamic simulation and Monte Carlo radiation transport model suggests accretion rate changes as the dominant flaring method. A similar study on M87 introduces new methods to the Monte Carlo model for increased consistency in highly energetic sources. Again, accretion rate variation seems most appropriate to explain spectral transients. To more closely resolve the methods of particle energization in active galactic nuclei accretion disks, a series of localized shearing box simulations explores the effect of numerical resolution on the development of current sheets. A particular focus on numerically describing converged current sheet formation will provide new methods for consideration of turbulence in accretion disks.

Spatiotemporal behaviour of isodiffracting hollow Gaussian pulsed beams

NASA Astrophysics Data System (ADS)

Xu, Yanbing; Lü, Baida

2007-05-01

A model of isodiffracting hollow Gaussian pulsed beams (HGPBs) is presented. Based on the Fourier transform method, an analytical formula for the HGPBs propagating in free space is derived, which enables us to study the spatiotemporal behaviour of the ultrashort pulsed beams. Some interesting phenomena of ultrashort pulsed beams, such as the symmetrical temporal profiles, the dark rings, etc, are discussed in detail and illustrated numerically.

Numerical Simulation Of Flow Through An Artificial Heart

NASA Technical Reports Server (NTRS)

Rogers, Stuart; Kutler, Paul; Kwak, Dochan; Kiris, Centin

1991-01-01

Research in both artificial hearts and fluid dynamics benefits from computational studies. Algorithm that implements Navier-Stokes equations of flow extended to simulate flow of viscous, incompressible blood through articifial heart. Ability to compute details of such flow important for two reasons: internal flows with moving boundaries of academic interest in their own right, and many of deficiencies of artificial hearts attributable to dynamics of flow.

Numerical analysis of tailored sheets to improve the quality of components made by SPIF

NASA Astrophysics Data System (ADS)

Gagliardi, Francesco; Ambrogio, Giuseppina; Cozza, Anna; Pulice, Diego; Filice, Luigino

2018-05-01

In this paper, the authors pointed out a study on the profitable combination of forming techniques. More in detail, the attention has been put on the combination of the single point incremental forming (SPIF) and, generally, speaking, of an additional process that can lead to a material thickening on the initial blank considering the local thinning which the sheets undergo at. Focalizing the attention of the research on the excessive thinning of parts made by SPIF, a hybrid approach can be thought as a viable solution to reduce the not homogeneous thickness distribution of the sheet. In fact, the basic idea is to work on a blank previously modified by a deformation step performed, for instance, by forming, additive or subtractive processes. To evaluate the effectiveness of this hybrid solution, a FE numerical model has been defined to analyze the thickness variation on tailored sheets incrementally formed optimizing the material distribution according to the shape to be manufactured. Simulations based on the explicit formulation have been set up for the model implementation. The mechanical properties of the sheet material have been taken in literature and a frustum of cone as benchmark profile has been considered for the performed analysis. The outcomes of numerical model have been evaluated in terms of both maximum thinning and final thickness distribution. The feasibility of the proposed approach will be deeply detailed in the paper.

Quality Assessment of the Cobel-Isba Numerical Forecast System of Fog and Low Clouds

NASA Astrophysics Data System (ADS)

Bergot, Thierry

2007-06-01

Short-term forecasting of fog is a difficult issue which can have a large societal impact. Fog appears in the surface boundary layer and is driven by the interactions between land surface and the lower layers of the atmosphere. These interactions are still not well parameterized in current operational NWP models, and a new methodology based on local observations, an adaptive assimilation scheme and a local numerical model is tested. The proposed numerical forecast method of foggy conditions has been run during three years at Paris-CdG international airport. This test over a long-time period allows an in-depth evaluation of the forecast quality. This study demonstrates that detailed 1-D models, including detailed physical parameterizations and high vertical resolution, can reasonably represent the major features of the life cycle of fog (onset, development and dissipation) up to +6 h. The error on the forecast onset and burn-off time is typically 1 h. The major weakness of the methodology is related to the evolution of low clouds (stratus lowering). Even if the occurrence of fog is well forecasted, the value of the horizontal visibility is only crudely forecasted. Improvements in the microphysical parameterization and in the translation algorithm converting NWP prognostic variables into a corresponding horizontal visibility seems necessary to accurately forecast the value of the visibility.

Numerical study of impact erosion of multiple solid particle

NASA Astrophysics Data System (ADS)

Zheng, Chao; Liu, Yonghong; Chen, Cheng; Qin, Jie; Ji, Renjie; Cai, Baoping

2017-11-01

Material erosion caused by continuous particle impingement during hydraulic fracturing results in significant economic loss and increased production risks. The erosion process is complex and has not been clearly explained through physical experiments. To address this problem, a multiple particle model in a 3D configuration was proposed to investigate the dynamic erosion process. This approach can significantly reduce experiment costs. The numerical model considered material damping and elastic-plastic material behavior of target material. The effects of impact parameters on erosion characteristics, such as plastic deformation, contact time, and energy loss rate, were investigated. Based on comprehensive studies, the dynamic erosion mechanism and geometry evolution of eroded crater was obtained. These findings can provide a detailed erosion process of target material and insights into the material erosion caused by multiple particle impingement.

Study and evaluation of impulse mass spectrometers for ion analysis in the D and E regions of the ionosphere

NASA Technical Reports Server (NTRS)

Kendall, B. R.

1979-01-01

Theoretical and numerical analyses were made of planar, cylindrical and spherical electrode time-of-flight mass spectrometers in order to optimize their operating conditions. A numerical analysis of potential barrier gating in time-of-flight spectrometers was also made. The results were used in the design of several small mass spectrometers. These were constructed and tested in a laboratory space simulator. Detailed experimental studies of a miniature cylindrical electrode time of flight mass spectrometer and of a miniature hemispherical electrode time of flight mass spectrometer were made. The extremely high sensitivity of these instruments and their ability to operate at D region pressures with an open source make them ideal instruments for D region ion composition measurements.

Numerical modelling of the flow in the resin infusion process on the REV scale: A feasibility study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jabbari, M.; Spangenberg, J.; Hattel, J. H.

2016-06-08

The resin infusion process (RIP) has developed as a low cost method for manufacturing large fibre reinforced plastic parts. However, the process still presents some challenges to industry with regards to reliability and repeatability, resulting in expensive and inefficient trial and error development. In this paper, we show the implementation of 2D numerical models for the RIP using the open source simulator DuMu{sup X}. The idea of this study is to present a model which accounts for the interfacial forces coming from the capillary pressure on the so-called representative elementary volume (REV) scale. The model is described in detail andmore » three different test cases — a constant and a tensorial permeability as well as a preform/Balsa domain — are investigated. The results show that the developed model is very applicable for the RIP for manufacturing of composite parts. The idea behind this study is to test the developed model for later use in a real application, in which the preform medium has numerous layers with different material properties.« less

Numerical viscosity and resolution of high-order weighted essentially nonoscillatory schemes for compressible flows with high Reynolds numbers.

PubMed

Zhang, Yong-Tao; Shi, Jing; Shu, Chi-Wang; Zhou, Ye

2003-10-01

A quantitative study is carried out in this paper to investigate the size of numerical viscosities and the resolution power of high-order weighted essentially nonoscillatory (WENO) schemes for solving one- and two-dimensional Navier-Stokes equations for compressible gas dynamics with high Reynolds numbers. A one-dimensional shock tube problem, a one-dimensional example with parameters motivated by supernova and laser experiments, and a two-dimensional Rayleigh-Taylor instability problem are used as numerical test problems. For the two-dimensional Rayleigh-Taylor instability problem, or similar problems with small-scale structures, the details of the small structures are determined by the physical viscosity (therefore, the Reynolds number) in the Navier-Stokes equations. Thus, to obtain faithful resolution to these small-scale structures, the numerical viscosity inherent in the scheme must be small enough so that the physical viscosity dominates. A careful mesh refinement study is performed to capture the threshold mesh for full resolution, for specific Reynolds numbers, when WENO schemes of different orders of accuracy are used. It is demonstrated that high-order WENO schemes are more CPU time efficient to reach the same resolution, both for the one-dimensional and two-dimensional test problems.

Separating stages of arithmetic verification: An ERP study with a novel paradigm.

PubMed

Avancini, Chiara; Soltész, Fruzsina; Szűcs, Dénes

2015-08-01

In studies of arithmetic verification, participants typically encounter two operands and they carry out an operation on these (e.g. adding them). Operands are followed by a proposed answer and participants decide whether this answer is correct or incorrect. However, interpretation of results is difficult because multiple parallel, temporally overlapping numerical and non-numerical processes of the human brain may contribute to task execution. In order to overcome this problem here we used a novel paradigm specifically designed to tease apart the overlapping cognitive processes active during arithmetic verification. Specifically, we aimed to separate effects related to detection of arithmetic correctness, detection of the violation of strategic expectations, detection of physical stimulus properties mismatch and numerical magnitude comparison (numerical distance effects). Arithmetic correctness, physical stimulus properties and magnitude information were not task-relevant properties of the stimuli. We distinguished between a series of temporally highly overlapping cognitive processes which in turn elicited overlapping ERP effects with distinct scalp topographies. We suggest that arithmetic verification relies on two major temporal phases which include parallel running processes. Our paradigm offers a new method for investigating specific arithmetic verification processes in detail. Copyright © 2015 Elsevier Ltd. All rights reserved.

Rigor or mortis: best practices for preclinical research in neuroscience.

PubMed

Steward, Oswald; Balice-Gordon, Rita

2014-11-05

Numerous recent reports document a lack of reproducibility of preclinical studies, raising concerns about potential lack of rigor. Examples of lack of rigor have been extensively documented and proposals for practices to improve rigor are appearing. Here, we discuss some of the details and implications of previously proposed best practices and consider some new ones, focusing on preclinical studies relevant to human neurological and psychiatric disorders. Copyright © 2014 Elsevier Inc. All rights reserved.

Analysis of the regulation of viral transcription.

PubMed

Gloss, Bernd; Kalantari, Mina; Bernard, Hans-Ulrich

2005-01-01

Despite the small genomes and number of genes of papillomaviruses, regulation of their transcription is very complex and governed by numerous transcription factors, cis-responsive elements, and epigenetic phenomena. This chapter describes the strategies of how one can approach a systematic analysis of these factors, elements, and mechanisms. From the numerous different techniques useful for studying transcription, we describe in detail three selected protocols of approaches that have been relevant in shaping our knowledge of human papillomavirus transcription. These are DNAse I protection ("footprinting") for location of transcription-factor binding sites, electrophoretic mobility shifts ("gelshifts") for analysis of bound transcription factors, and bisulfite sequencing for analysis of DNA methylation as a prerequisite for epigenetic transcriptional regulation.

Large eddy simulations and direct numerical simulations of high speed turbulent reacting flows

NASA Technical Reports Server (NTRS)

Givi, Peyman; Madnia, Cyrus K.; Steinberger, Craig J.

1990-01-01

This research is involved with the implementation of advanced computational schemes based on large eddy simulations (LES) and direct numerical simulations (DNS) to study the phenomenon of mixing and its coupling with chemical reactions in compressible turbulent flows. In the efforts related to LES, a research program to extend the present capabilities of this method was initiated for the treatment of chemically reacting flows. In the DNS efforts, the focus is on detailed investigations of the effects of compressibility, heat release, and non-equilibrium kinetics modelings in high speed reacting flows. Emphasis was on the simulations of simple flows, namely homogeneous compressible flows, and temporally developing high speed mixing layers.

Partial Variance of Increments Method in Solar Wind Observations and Plasma Simulations

NASA Astrophysics Data System (ADS)

Greco, A.; Matthaeus, W. H.; Perri, S.; Osman, K. T.; Servidio, S.; Wan, M.; Dmitruk, P.

2018-02-01

The method called "PVI" (Partial Variance of Increments) has been increasingly used in analysis of spacecraft and numerical simulation data since its inception in 2008. The purpose of the method is to study the kinematics and formation of coherent structures in space plasmas, a topic that has gained considerable attention, leading the development of identification methods, observations, and associated theoretical research based on numerical simulations. This review paper will summarize key features of the method and provide a synopsis of the main results obtained by various groups using the method. This will enable new users or those considering methods of this type to find details and background collected in one place.

Comprehensive Numerical Simulation of Filling and Solidification of Steel Ingots

PubMed Central

Pola, Annalisa; Gelfi, Marcello; La Vecchia, Giovina Marina

2016-01-01

In this paper, a complete three-dimensional numerical model of mold filling and solidification of steel ingots is presented. The risk of powder entrapment and defects formation during filling is analyzed in detail, demonstrating the importance of using a comprehensive geometry, with trumpet and runner, compared to conventional simplified models. By using a case study, it was shown that the simplified model significantly underestimates the defects sources, reducing the utility of simulations in supporting mold and process design. An experimental test was also performed on an instrumented mold and the measurements were compared to the calculation results. The good agreement between calculation and trial allowed validating the simulation. PMID:28773890

Electronic transport in disordered chains with saturable nonlinearity

NASA Astrophysics Data System (ADS)

dos Santos, J. L. L.; Nguyen, Ba Phi; de Moura, F. A. B. F.

2015-10-01

In this work we study numerically the dynamics of an initially localized wave packet in one-dimensional disordered chains with saturable nonlinearity. By using the generalized discrete nonlinear Schrödinger equation, we calculate two different physical quantities as a function of time, which are the participation number and the mean square displacement from the excitation site. From detailed numerical analysis, we find that the saturable nonlinearity can promote a sub-diffusive spreading of the wave packet even in the presence of diagonal disorder for a long time. In addition, we also investigate the effect of the saturated nonlinearity for initial times of the electronic evolution thus showing the possibility of mobile breather-like modes.

Spherical gyroscopic moment stabilizer for attitude control of microsatellites

NASA Astrophysics Data System (ADS)

Keshtkar, Sajjad; Moreno, Jaime A.; Kojima, Hirohisa; Uchiyama, Kenji; Nohmi, Masahiro; Takaya, Keisuke

2018-02-01

This paper presents a new and improved concept of recently proposed two-degrees of freedom spherical stabilizer for triaxial orientation of microsatellites. The analytical analysis of the advantages of the proposed mechanism over the existing inertial attitude control devices are introduced. The extended equations of motion of the stabilizing satellite including the spherical gyroscope, for control law design and numerical simulations, are studied in detail. A new control algorithm based on continuous high-order sliding mode algorithms, for managing the torque produced by the stabilizer and therefore the attitude control of the satellite in the presence of perturbations/uncertainties, is presented. Some numerical simulations are carried out to prove the performance of the proposed mechanism and control laws.

Dynamics of Aerosol Particles in Stationary, Isotropic Turbulence

NASA Technical Reports Server (NTRS)

Collins, Lance R.; Meng, Hui

2004-01-01

A detailed study of the dynamics of sub-Kolmogorov-size aerosol particles in stationary isotropic turbulence has been performed. The study combined direct numerical simulations (DNS; directed by Prof. Collins) and high-resolution experimental measurements (directed by Prof. Meng) under conditions of nearly perfect geometric and parametric overlap. The goal was to measure the accumulation of particles in low-vorticity regions of the flow that arises from the effect commonly referred to as preferential concentration. The grant technically was initiated on June 13, 2000; however, funding was not available until July 11, 2000. The grant was originally awarded to Penn State University (numerical simulations) and SUNY-Buffalo (experiments); however, Prof. Collins effort was moved to Cornell University on January 2002 when he joined that university. He completed the study there. A list of the specific tasks that were completed under this study is presented.

Direct numerical simulations of magmatic differentiation at the microscopic scale

NASA Astrophysics Data System (ADS)

Sethian, J.; Suckale, J.; Elkins-Tanton, L. T.

2010-12-01

A key question in the context of magmatic differentiation and fractional crystallization is the ability of crystals to decouple from the ambient fluid and sink or rise. Field data indicates a complex spectrum of behavior ranging from rapid sedimentation to continued entrainment. Theoretical and laboratory studies paint a similarly rich picture. The goal of this study is to provide a detailed numerical assessment of the competing effects of sedimentation and entrainment at the scale of individual crystals. The decision to simulate magmatic differentiation at the grain scale comes at the price of not being able to simultaneously solve for the convective velocity field at the macroscopic scale, but has the crucial advantage of enabling us to fully resolve the dynamics of the systems from first principles without requiring any simplifying assumptions. The numerical approach used in this study is a customized computational methodology developed specifically for simulations of solid-fluid coupling in geophysical systems. The algorithm relies on a two-step projection scheme: In the first step, we solve the multiple-phase Navier-Stokes or Stokes equation in both domains. In the second step, we project the velocity field in the solid domain onto a rigid-body motion by enforcing that the deformation tensor in the respective domain is zero. This procedure is also used to enforce the no-slip boundary-condition on the solid-fluid interface. We have extensively validated and benchmarked the method. Our preliminary results indicate that, not unexpectedly, the competing effects of sedimentation and entrainment depend sensitively on the size distribution of the crystals, the aspect ratio of individual crystals and the vigor of the ambient flow field. We provide a detailed scaling analysis and quantify our results in terms of the relevant non-dimensional numbers.

Numerical determination of lateral loss coefficients for subchannel analysis in nuclear fuel bundles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sin Kim; Goon-Cherl Park

1995-09-01

An accurate prediction of cross-flow based on detailed knowledge of the velocity field in subchannels of a nuclear fuel assembly is of importance in nuclear fuel performance analysis. In this study, the low-Reynolds number {kappa}-{epsilon} turbulence model has been adopted in two adjacent subchannels with cross-flow. The secondary flow is estimated accurately by the anisotropic algebraic Reynolds stress model. This model was numerically calculated by the finite element method and has been verified successfully through comparison with existing experimental data. Finally, with the numerical analysis of the velocity field in such subchannel domain, an analytical correlation of the lateral lossmore » coefficient is obtained to predict the cross-flow rate in subchannel analysis codes. The correlation is expressed as a function of the ratio of the lateral flow velocity to the donor subchannel axial velocity, recipient channel Reynolds number and pitch-to-diameter.« less

Modeling the Compression of Merged Compact Toroids by Multiple Plasma Jets

NASA Technical Reports Server (NTRS)

Thio, Y. C. Francis; Knapp, Charles E.; Kirkpatrick, Ron; Rodgers, Stephen L. (Technical Monitor)

2000-01-01

A fusion propulsion scheme has been proposed that makes use of the merging of a spherical distribution of plasma jets to dynamically form a gaseous liner. The gaseous liner is used to implode a magnetized target to produce the fusion reaction in a standoff manner. In this paper, the merging of the plasma jets to form the gaseous liner is investigated numerically. The Los Alamos SPHINX code, based on the smoothed particle hydrodynamics method is used to model the interaction of the jets. 2-D and 3-D simulations have been performed to study the characteristics of the resulting flow when these jets collide. The results show that the jets merge to form a plasma liner that converge radially which may be used to compress the central plasma to fusion conditions. Details of the computational model and the SPH numerical methods will be presented together with the numerical results.

Dynamics of epidemic spreading model with drug-resistant variation on scale-free networks

NASA Astrophysics Data System (ADS)

Wan, Chen; Li, Tao; Zhang, Wu; Dong, Jing

2018-03-01

Considering the influence of the virus' drug-resistant variation, a novel SIVRS (susceptible-infected-variant-recovered-susceptible) epidemic spreading model with variation characteristic on scale-free networks is proposed in this paper. By using the mean-field theory, the spreading dynamics of the model is analyzed in detail. Then, the basic reproductive number R0 and equilibriums are derived. Studies show that the existence of disease-free equilibrium is determined by the basic reproductive number R0. The relationships between the basic reproductive number R0, the variation characteristic and the topology of the underlying networks are studied in detail. Furthermore, our studies prove the global stability of the disease-free equilibrium, the permanence of epidemic and the global attractivity of endemic equilibrium. Numerical simulations are performed to confirm the analytical results.

Endodontic and Clinical Considerations in the Management of Variable Anatomy in Mandibular Premolars: A Literature Review

PubMed Central

Hammo, Mohammad

2014-01-01

Mandibular premolars are known to have numerous anatomic variations of their roots and root canals, which are a challenge to treat endodontically. The paper reviews literature to detail the various clinically relevant anatomic considerations with detailed techniques and methods to successfully manage these anomalies. An emphasis and detailed description of every step of treatment including preoperative diagnosis, intraoperative identification and management, and surgical endodontic considerations for the successful management of these complex cases have been included. PMID:24895584

1983 lightning, turbulence, wind shear, and Doppler radar studies at the National Severe Storms Laboratory

NASA Technical Reports Server (NTRS)

Lee, J. T.

1984-01-01

As part of continuing research on aviation related weather hazards, numerous experiments were incorporated into the 1983 Spring Observation Program. This year's program was an abbreviated one because of commitments made to the development of the Next Generation Radar (NEXRAD) project. The National Oceanic and Atmospheric Administration's (NOAA) P-3 Orion and the National Aeronautics and Space Administration's (NASA) RB-57B and U-2 were the main aircraft involved in the studies of lightning, wind shear, turbulence, and storm structure. A total of 14 flights were made by these aircraft during the period of May 16 through June 5, 1983. Aircraft instrumentation experiments are described, and resultant data sets available for research are detailed. Aircraft instrumentation and Doppler radar characteristics are detailed.

Explosively produced fracture of oil shale

NASA Astrophysics Data System (ADS)

Morris, W. A.

1982-05-01

Rock fragmentation research in oil shale to develop the blasting technologies and designs required to prepare a rubble bed for a modified in situ retort is reported. Experimental work is outlined, proposed studies in explosive characterization are detailed and progress in numerical calculation techniques to predict fracture of the shale is described. A detailed geologic characterization of two Anvil Points experiment sites is related to previous work at Colony Mine. The second section focuses on computer modeling and theory. The latest generation of the stress wave code SHALE, its three dimensional potential, and the slide line package for it are described. A general stress rate equation that takes energy dependence into account is discussed.

Modeling of MOEMS electromagnetic scanning grating mirror for NIR micro-spectrometer

NASA Astrophysics Data System (ADS)

Zhou, Ying; Wen, Quan; Wen, Zhiyu; Yang, Tingyan

2016-02-01

In this paper, the mathematical model is developed for researching the detailed electromagnetic mechanism of MOEMS scanning mirror. We present the relationship between spectral range and optical scanning angle. Furthermore, the variation tendencies of resonant frequency and maximal torsional angle are studied in detail under different aspect ratios of MOEMS scanning mirror and varied dimensions of torsional bar. The numerical results and Finite Element Analysis simulations both indicate that the thickness of torsional bar is the most important factor. The maximal torsional angle appears when the aspect ratio equals to 1. This mathematical model is an effective way for designing the MOEMS electromagnetic scanning grating mirror in actual fabrication.

Molecular dynamics simulations of large macromolecular complexes.

PubMed

Perilla, Juan R; Goh, Boon Chong; Cassidy, C Keith; Liu, Bo; Bernardi, Rafael C; Rudack, Till; Yu, Hang; Wu, Zhe; Schulten, Klaus

2015-04-01

Connecting dynamics to structural data from diverse experimental sources, molecular dynamics simulations permit the exploration of biological phenomena in unparalleled detail. Advances in simulations are moving the atomic resolution descriptions of biological systems into the million-to-billion atom regime, in which numerous cell functions reside. In this opinion, we review the progress, driven by large-scale molecular dynamics simulations, in the study of viruses, ribosomes, bioenergetic systems, and other diverse applications. These examples highlight the utility of molecular dynamics simulations in the critical task of relating atomic detail to the function of supramolecular complexes, a task that cannot be achieved by smaller-scale simulations or existing experimental approaches alone. Copyright © 2015 Elsevier Ltd. All rights reserved.

Observation of extremely strong shock waves in solids launched by petawatt laser heating

DOE PAGES

Lancaster, K. L.; Robinson, A. P. L.; Pasley, J.; ...

2017-08-25

Understanding hydrodynamic phenomena driven by fast electron heating is important for a range of applications including fast electron collimation schemes for fast ignition and the production and study of hot, dense matter. In this work, detailed numerical simulations modelling the heating, hydrodynamic evolution, and extreme ultra-violet (XUV) emission in combination with experimental XUV images indicate shock waves of exceptional strength (200 Mbar) launched due to rapid heating of materials via a petawatt laser. In conclusion, we discuss in detail the production of synthetic XUV images and how they assist us in interpreting experimental XUV images captured at 256 eV usingmore » a multi-layer spherical mirror.« less

Computer numerical control grinding of spiral bevel gears

NASA Technical Reports Server (NTRS)

Scott, H. Wayne

1991-01-01

The development of Computer Numerical Control (CNC) spiral bevel gear grinding has paved the way for major improvement in the production of precision spiral bevel gears. The object of the program was to decrease the setup, maintenance of setup, and pattern development time by 50 percent of the time required on conventional spiral bevel gear grinders. Details of the process are explained.

A Comparative Study Of Dust Devils

NASA Astrophysics Data System (ADS)

Lange, C. F.; Prieto, L. E.

2005-12-01

Spatial variations in the column of water vapour in the Martian near-surface are due to the combined effects of several process within water underground reservoirs and the atmosphere. Among these process, dust devils could be an important local factor in the water concentration levels. In fact, the apparently high occurrence of dust devils could potentially affect the mass transfer rate of water vapour from the Martian regolith. A detailed study of these atmospheric vortices may help to better understand the complex relation between the cycle of water and this Martian atmospheric event. Subsequently, field data are required to provide a close estimation of the dynamics presented in Martian surface. The upcoming Phoenix mission is being designed to investigate these natural events on Mars. However, field studies of dust devils are difficult because of their sporadic, unpredictable occurrence and distance. In contrast, laboratory simulations present a better physical insight into this complex swirling flow by consideration of a much simplified, and more controllable and reproducible model flow. The use of numerical simulations in addition to laboratory experiments can provide complementary information on flow properties in regions where measurements are difficult due to flow profiles. Computational models also allow for significant flexibility in the model layout and they are, therefore, ideally suited for a comparison of different types of model flows. A 3-D numerical study is presented for two different types of dust devil laboratory simulators (Ward, 1952 and Greeley et al., 2001). An initial numerical study was conducted to validate the simulation results with previous laboratory measurements (Lund and Snow, 1993). Secondly, a numerical comparison was carried out between the two tornado-like vortex representations based on kinematic similarities to provide a clear method to relate dust devils in several nature environments, laboratory simulations, and computational models. This was accomplished by examining features of the dust devils in the form of three main flow parameters: the ratio of the inflow layer height h to the updraft radius r_0 (aspect ratio), the radial Reynolds number characterizing the updraft zone, and the ratio of the tangential velocity to the mean radial velocity (swirl ratio) at the radius of the updraft zone, r_0. The detailed analysis of the numerical flow solutions led to a simple definition of h and r_0, valid for the types of model flows analyzed. This study is a necessary part of a larger effort to examine and compare both numerical and laboratory simulations of atmospheric vortices in terrestrial and Martian conditions. References [1] R. Greeley et al., XXXII Lunar and Planetary Science, 2001. [2] D. E. Lund and J. T. Snow, The Tornado: Its Structure, Dynamics, Prediction, and Hazards, 1993, p. 297--306. [3] N. B. Ward, J. Atmos. Sci., 1972, 1194--1204.

Emission processes and dynamics of hot gases in astrophysics

NASA Technical Reports Server (NTRS)

Chevalier, Roger A.; Sarazin, Craig L.

1991-01-01

A detailed model was developed for Kepler's supernova remnant (SNR). Observations of the SNR revealed a strong interaction with the surrounding circumstellar medium, which was studied through both analytical and numerical calculations. Effects were studied of electron thermal conduction on the structure of radiative interstellar shock waves. An explanation is sought for the observed line emission from metal rich ejecta in SNR, incorporating atomic data. Light echoes around SN 1987A was also studied. Analysis of infrared and scattered circumstellar light echoes was accomplished with early observations to set limits on the mass of circumstellar dust. Work was completed on the emission from heavy element gas ejected in the supernova explosion of massive stars. It was assumed that a radioactive energy source was present and calculated the detailed heating and ionization of the gas. The evolution was studied of SNR in the very high pressure environment of a starburst galaxy.

Use of paired simple and complex models to reduce predictive bias and quantify uncertainty

NASA Astrophysics Data System (ADS)

Doherty, John; Christensen, Steen

2011-12-01

Modern environmental management and decision-making is based on the use of increasingly complex numerical models. Such models have the advantage of allowing representation of complex processes and heterogeneous system property distributions inasmuch as these are understood at any particular study site. The latter are often represented stochastically, this reflecting knowledge of the character of system heterogeneity at the same time as it reflects a lack of knowledge of its spatial details. Unfortunately, however, complex models are often difficult to calibrate because of their long run times and sometimes questionable numerical stability. Analysis of predictive uncertainty is also a difficult undertaking when using models such as these. Such analysis must reflect a lack of knowledge of spatial hydraulic property details. At the same time, it must be subject to constraints on the spatial variability of these details born of the necessity for model outputs to replicate observations of historical system behavior. In contrast, the rapid run times and general numerical reliability of simple models often promulgates good calibration and ready implementation of sophisticated methods of calibration-constrained uncertainty analysis. Unfortunately, however, many system and process details on which uncertainty may depend are, by design, omitted from simple models. This can lead to underestimation of the uncertainty associated with many predictions of management interest. The present paper proposes a methodology that attempts to overcome the problems associated with complex models on the one hand and simple models on the other hand, while allowing access to the benefits each of them offers. It provides a theoretical analysis of the simplification process from a subspace point of view, this yielding insights into the costs of model simplification, and into how some of these costs may be reduced. It then describes a methodology for paired model usage through which predictive bias of a simplified model can be detected and corrected, and postcalibration predictive uncertainty can be quantified. The methodology is demonstrated using a synthetic example based on groundwater modeling environments commonly encountered in northern Europe and North America.

The study of the effects of sea-spray drops on the marine atmospheric boundary layer by direct numerical simulation

NASA Astrophysics Data System (ADS)

Druzhinin, O.; Troitskaya, Yu; Zilitinkevich, S.

2018-01-01

The detailed knowledge of turbulent exchange processes occurring in the atmospheric marine boundary layer are of primary importance for their correct parameterization in large-scale prognostic models. These processes are complicated, especially at sufficiently strong wind forcing conditions, by the presence of sea-spray drops which are torn off the crests of sufficiently steep surface waves by the wind gusts. Natural observations indicate that mass fraction of sea-spray drops increases with wind speed and their impact on the dynamics of the air in the vicinity of the sea surface can become quite significant. Field experiments, however, are limited by insufficient accuracy of the acquired data and are in general costly and difficult. Laboratory modeling presents another route to investigate the spray-mediated exchange processes in much more detail as compared to the natural experiments. However, laboratory measurements, contact as well as Particle Image Velocimetry (PIV) methods, also suffer from inability to resolve the dynamics of the near-surface air-flow, especially in the surface wave troughs. In this report, we present a first attempt to use Direct Numerical Simulation (DNS) as tool for investigation of the drops-mediated momentum, heat and moisture transfer in a turbulent, droplet-laden air flow over a wavy water surface. DNS is capable of resolving the details of the transfer processes and do not involve any closure assumptions typical of Large-Eddy and Reynolds Averaged Navier-Stokes (LES and RANS) simulations. Thus DNS provides a basis for improving parameterizations in LES and RANS closure models and further development of large-scale prognostic models. In particular, we discuss numerical results showing the details of the modification of the air flow velocity, temperature and relative humidity fields by multidisperse, evaporating drops. We use Eulerian-Lagrangian approach where the equations for the air-flow fields are solved in a Eulerian frame whereas the drops dymanics equations are solved in a Largangain frame. The effects of air flow and drops on the water surface wave are neglected. A point-force approximation is employed to model the feed-back contributions by the drops to the air momentum, heat and moisture transfer.

The numerical modelling of falling film thickness flow on horizontal tubes

NASA Astrophysics Data System (ADS)

Hassan, I. A.; Sadikin, A.; Isa, N. Mat

2017-04-01

This paper presents a computational modelling of water falling film flowing over horizontal tubes. The objective of this study is to use numerical predictions for comparing the film thickness along circumferential direction of tube on 2-D CFD models. The results are then validated with a theoretical result in previous literatures. A comprehensive design of 2-D models have been developed according to the real application and actual configuration of the falling film evaporator as well as previous experimental parameters. A computational modelling of the water falling film is presented with the aid of Ansys Fluent software. The Volume of Fluid (VOF) technique is adapted in this analysis since its capabilities of determining the film thickness on tubes surface is highly reliable. The numerical analysis is carried out under influence of ambient pressures at temperature of 27 °C. Three types of CFD numerical models were analyzed in this simulation with inter tube spacing of 30 mm, 20 mm and 10 mm respectively. The use of a numerical simulation tool on water falling film has resulted in a detailed investigation of film thickness. Based on the numerical simulated results, it is found that the average values of water film thickness for each model are 0.53 mm, 0.58 mm, and 0.63 mm.

An approach to achieve progress in spacecraft shielding

NASA Astrophysics Data System (ADS)

Thoma, K.; Schäfer, F.; Hiermaier, S.; Schneider, E.

2004-01-01

Progress in shield design against space debris can be achieved only when a combined approach based on several tools is used. This approach depends on the combined application of advanced numerical methods, specific material models and experimental determination of input parameters for these models. Examples of experimental methods for material characterization are given, covering the range from quasi static to very high strain rates for materials like Nextel and carbon fiber-reinforced materials. Mesh free numerical methods have extraordinary capabilities in the simulation of extreme material behaviour including complete failure with phase changes, combined with shock wave phenomena and the interaction with structural components. In this paper the benefits from combining numerical methods, material modelling and detailed experimental studies for shield design are demonstrated. The following examples are given: (1) Development of a material model for Nextel and Kevlar-Epoxy to enable numerical simulation of hypervelocity impacts on complex heavy protection shields for the International Space Station. (2) The influence of projectile shape on protection performance of Whipple Shields and how experimental problems in accelerating such shapes can be overcome by systematic numerical simulation. (3) The benefits of using metallic foams in "sandwich bumper shields" for spacecraft and how to approach systematic characterization of such materials.

Morphological studies of the vestibular nerve

NASA Technical Reports Server (NTRS)

Bergstroem, B.

1973-01-01

The anatomy of the intratemporal part of the vestibular nerve in man, and the possible age related degenerative changes in the nerve were studied. The form and structure of the vestibular ganglion was studied with the light microscope. A numerical analysis of the vestibular nerve, and caliber spectra of the myelinated fibers in the vestibular nerve branches were studied in individuals of varying ages. It was found that the peripheral endings of the vestibular nerve form a complicated pattern inside the vestibular sensory epithelia. A detailed description of the sensory cells and their surface organelles is included.

An experimental and numerical investigation of shock-wave induced turbulent boundary-layer separation at hypersonic speeds

NASA Technical Reports Server (NTRS)

Marvin, J. G.; Horstman, C. C.; Rubesin, M. W.; Coakley, T. J.; Kussoy, M. I.

1975-01-01

An experiment designed to test and guide computations of the interaction of an impinging shock wave with a turbulent boundary layer is described. Detailed mean flow-field and surface data are presented for two shock strengths which resulted in attached and separated flows, respectively. Numerical computations, employing the complete time-averaged Navier-Stokes equations along with algebraic eddy-viscosity and turbulent Prandtl number models to describe shear stress and heat flux, are used to illustrate the dependence of the computations on the particulars of the turbulence models. Models appropriate for zero-pressure-gradient flows predicted the overall features of the flow fields, but were deficient in predicting many of the details of the interaction regions. Improvements to the turbulence model parameters were sought through a combination of detailed data analysis and computer simulations which tested the sensitivity of the solutions to model parameter changes. Computer simulations using these improvements are presented and discussed.

Fold-related-fracturing at the Livingstone River anticline (AB; Canada) by coupling field surveying and numerical modelling

NASA Astrophysics Data System (ADS)

Humair, Florian; Epard, Jean-Luc; Bauville, Arthur; Jaboyedoff, Michel; Pana, Dinu; Kaus, Boris; Schmalholz, Stefan

2016-04-01

The interpretation of fold-related joints and faults is of primary importance in terms of fluids prospection (e.g. water, oil, gas, C02) since anticlines are potential structural trap while fracturing can strongly influence the storage capacity as well as the migration pathways. Located at the front of the Foothills of the Rocky Mountains in Alberta (Canada), the Livingstone Range (LRA) is analogous to hydrocarbon reservoir that occur elsewhere in the Foothills (Cooley et al., 2011). The Livingstone Range fold system is related to the development of the Livingstone thrust that cuts around 1000m up-section from a regional decollement in the Palliser Formation (Devonian) to another in the Fernie Formation (Jurassic). Our study focuses on the detailed structural investigation of the Livingstone River anticline (northern part of the LRA). It aims at characterizing the anticline geometry as well as the fracturing pattern (orientation, mode, infilling, spacing, trace length, density, and cross-cutting relationships) in order to propose a kinematic interpretation of the fold-related fracturing genesis. The study area is investigated at different scales by combining field surveys with remote sensing (HR-Digital Elevation Model, Ground-based LiDAR, Gigapixel photography) and thin-sections analyses. In a second step we performed finite difference 3D numerical simulations in order to compute the evolution of local principal stress orientation during folding. We compared the fracture (or plastic bands) distribution in the field with 1) a dynamic numerical model of detachment folding; and 2) an instantaneous numerical model based on the final fold geometry. Cooley, M.A., Price, R.A., Dixon, J.M., Kyser, T.K. 2011. Along-strike variations and internal details of chevron-style flexural slip thrust-propagation folds within the southern Livingstone Range anticlinorium, a paleo-hydrocarbon reservoir in southern Alberta Foothills, Canada. AAPG bulletin, 95 (11), 1821-1849.

Voyages to Saturn

NASA Technical Reports Server (NTRS)

Morrison, D.

1982-01-01

The Voyager mission to Saturn is explained in detail. A history of Saturn observations from ancient times to the present is given. The Voyager spacecraft and their instruments are described. An overview of planetary astronomy is presented. The text is supplemented by numerous black and white and color photographs. The Saturn satellites are discussed in detail, and preliminary pictorial maps of the satellites are given.

Numerical Experiments Investigating the Source of Explosion S-Waves

DTIC Science & Technology

2007-09-01

simulations in this study are based on the well-recorded 1993 Nonproliferation experiment (NPE) ( chemical kiloton). A regional 3-dimensional model...1-kiloton chemical explosion at the NTS. NPE details and research reports can be found in Denny and Stull (1994). Figure 3 shows the extensive...T., D. Helmberger, and G. Engen (1985). Evidence for tectonic release from underground nuclear explosions in long period S waves, Bull. Seismol. Soc

Quality Attribute-Guided Evaluation of NoSQL Databases: An Experience Report

DTIC Science & Technology

2014-10-18

detailed technical evaluations of NoSQL databases specifically, and big data systems in general, that have become apparent during our study... big data , software systems [Agarwal 2011]. Internet-born organizations such as Google and Amazon are at the cutting edge of this revolution...Chang 2008], along with those of numerous other big data innovators, have made a variety of open source and commercial data management technologies

Numerical study of a VM type multi-bypass pulse tube cryocooler operating at 4K

NASA Astrophysics Data System (ADS)

Pan, Changzhao; Zhang, Tong; Wang, Jue; Chen, Liubiao; Cui, Chen; Wang, Junjie; Zhou, Yuan

2017-12-01

VM cryocooler is one kind of Stirling type cryocooler working at low frequency. At present, we have obtained the liquid helium temperature by using a two-stage VM/pulse tube hybrid cryocooler. As a new kind of 4K cryocooler, there are many aspects need to be studied and optimized in detail. In order to reducing the vibration and improving the stability of this cryocooler, a pulse tube cryocooler was designed to get rid of the displacer in the first stage. This paper presents a detail numerical investigation on this pulse tube cryocooler by using the SAGE software. The low temperature phase shifters were adopted in this cryocooler, which were low temperature gas reservoir, low temperature double-inlet and multi-bypass. After optimizing, the structure parameters and the best diameters of orifice, multi-bypass and double-inlet were obtained. With the pressure ratio of about 1.6 and operating frequency 2Hz, this cryocooler could supply above 40mW cooling power at 4.2K, and the total input power needs no more than 60W at 77K. Based on the highest efficiency of 77K high capacity cryocooler, the overall efficiency of this VM type pulse tube cryocooler is above 0.5% relative Carnot efficient.

Noise and Dissipation on Coadjoint Orbits

NASA Astrophysics Data System (ADS)

Arnaudon, Alexis; De Castro, Alex L.; Holm, Darryl D.

2018-02-01

We derive and study stochastic dissipative dynamics on coadjoint orbits by incorporating noise and dissipation into mechanical systems arising from the theory of reduction by symmetry, including a semidirect product extension. Random attractors are found for this general class of systems when the Lie algebra is semi-simple, provided the top Lyapunov exponent is positive. We study in details two canonical examples, the free rigid body and the heavy top, whose stochastic integrable reductions are found and numerical simulations of their random attractors are shown.

Frontal Polymerization in Microgravity Summary of Research

NASA Technical Reports Server (NTRS)

Pojman, John A.

2002-01-01

The project began with frontal polymerization (FP). We studied many aspects of FP on the ground and performed two successful weeks of flying on the KC-135. The project evolved into the current flight investigation, Transient Interfacial Phenomena in Miscible Polymer Systems (TIPMPS), as we recognized that an essential question could best be studied using a non-frontal approach. We present detailed results from our ground-based work on FP, KC-135 results and the background, justification and numerical work for the TIPMPS project.

Numerical models of salt marsh evolution: ecological, geomorphic, and climatic factors

USGS Publications Warehouse

Fagherazzi, Sergio; Kirwan, Matthew L.; Mudd, Simon M.; Guntenspergen, Glenn R.; Temmerman, Stijn; D'Alpaos, Andrea; van de Koppel, Johan; Rybczyk, John; Reyes, Enrique; Craft, Chris; Clough, Jonathan

2012-01-01

Salt marshes are delicate landforms at the boundary between the sea and land. These ecosystems support a diverse biota that modifies the erosive characteristics of the substrate and mediates sediment transport processes. Here we present a broad overview of recent numerical models that quantify the formation and evolution of salt marshes under different physical and ecological drivers. In particular, we focus on the coupling between geomorphological and ecological processes and on how these feedbacks are included in predictive models of landform evolution. We describe in detail models that simulate fluxes of water, organic matter, and sediments in salt marshes. The interplay between biological and morphological processes often produces a distinct scarp between salt marshes and tidal flats. Numerical models can capture the dynamics of this boundary and the progradation or regression of the marsh in time. Tidal channels are also key features of the marsh landscape, flooding and draining the marsh platform and providing a source of sediments and nutrients to the marsh ecosystem. In recent years, several numerical models have been developed to describe the morphogenesis and long-term dynamics of salt marsh channels. Finally, salt marshes are highly sensitive to the effects of long-term climatic change. We therefore discuss in detail how numerical models have been used to determine salt marsh survival under different scenarios of sea level rise.

Numerical models of salt marsh evolution: Ecological, geomorphic, and climatic factors

USGS Publications Warehouse

Fagherazzi, S.; Kirwan, M.L.; Mudd, S.M.; Guntenspergen, G.R.; Temmerman, S.; D'Alpaos, A.; Van De Koppel, J.; Rybczyk, J.M.; Reyes, E.; Craft, C.; Clough, J.

2012-01-01

Salt marshes are delicate landforms at the boundary between the sea and land. These ecosystems support a diverse biota that modifies the erosive characteristics of the substrate and mediates sediment transport processes. Here we present a broad overview of recent numerical models that quantify the formation and evolution of salt marshes under different physical and ecological drivers. In particular, we focus on the coupling between geomorphological and ecological processes and on how these feedbacks are included in predictive models of landform evolution. We describe in detail models that simulate fluxes of water, organic matter, and sediments in salt marshes. The interplay between biological and morphological processes often produces a distinct scarp between salt marshes and tidal flats. Numerical models can capture the dynamics of this boundary and the progradation or regression of the marsh in time. Tidal channels are also key features of the marsh landscape, flooding and draining the marsh platform and providing a source of sediments and nutrients to the marsh ecosystem. In recent years, several numerical models have been developed to describe the morphogenesis and long-term dynamics of salt marsh channels. Finally, salt marshes are highly sensitive to the effects of long-term climatic change. We therefore discuss in detail how numerical models have been used to determine salt marsh survival under different scenarios of sea level rise. Copyright 2012 by the American Geophysical Union.

Simulation of wind turbine wakes using the actuator line technique

PubMed Central

Sørensen, Jens N.; Mikkelsen, Robert F.; Henningson, Dan S.; Ivanell, Stefan; Sarmast, Sasan; Andersen, Søren J.

2015-01-01

The actuator line technique was introduced as a numerical tool to be employed in combination with large eddy simulations to enable the study of wakes and wake interaction in wind farms. The technique is today largely used for studying basic features of wakes as well as for making performance predictions of wind farms. In this paper, we give a short introduction to the wake problem and the actuator line methodology and present a study in which the technique is employed to determine the near-wake properties of wind turbines. The presented results include a comparison of experimental results of the wake characteristics of the flow around a three-bladed model wind turbine, the development of a simple analytical formula for determining the near-wake length behind a wind turbine and a detailed investigation of wake structures based on proper orthogonal decomposition analysis of numerically generated snapshots of the wake. PMID:25583862

Computational aeroacoustics and numerical simulation of supersonic jets

NASA Technical Reports Server (NTRS)

Morris, Philip J.; Long, Lyle N.

1996-01-01

The research project has been a computational study of computational aeroacoustics algorithms and numerical simulations of the flow and noise of supersonic jets. During this study a new method for the implementation of solid wall boundary conditions for complex geometries in three dimensions has been developed. In addition, a detailed study of the simulation of the flow in and noise from supersonic circular and rectangular jets has been conducted. Extensive comparisons have been made with experimental measurements. A summary of the results of the research program are attached as the main body of this report in the form of two publications. Also, the report lists the names of the students who were supported by this grant, their degrees, and the titles of their dissertations. In addition, a list of presentations and publications made by the Principal Investigators and the research students is also included.

Numerical modeling of aquifer thermal energy storage

NASA Astrophysics Data System (ADS)

Tsang, C. F.; Doughty, C.; Kincaid, C. T.

1982-12-01

During 1981 and 1982, Auburn University has been performing a three cycle ATES field experiment in Mobile County, Alabama. Details of the experiment are described elsewhere in this volume. Concurrent with the first two cycles (59 C and 82 C), Lawrence Berkeley Laboratory (LBL) did numerical simulations based on field operating conditions to predict the outcome of each cycle before its conclusion. Prior to the third cycle, a series of numerical simulations were made to aid in the design of an experiment that would yield the highest recovery factor possible.

Sensitivity Tests Between Vs30 and Detailed Shear Wave Profiles Using 1D and 3D Site Response Analysis, Las Vegas Valley

NASA Astrophysics Data System (ADS)

West, Loyd Travis

Site characterization is an essential aspect of hazard analysis and the time-averaged shear-wave velocity to 30 m depth "Vs30" for site-class has become a critical parameter in site-specific and probabilistic hazard analysis. Yet, the general applicability of Vs30 can be ambiguous and much debate and research surround its application. In 2007, in part to mitigate the uncertainty associated with the use of Vs30 in Las Vegas Valley, the Clark County Building Department (CCBD) in collaboration with the Nevada System of Higher Education (NSHE) embarked on an endeavor to map Vs30 using a geophysical methods approach for a site-class microzonation map of over 500 square miles (1500 km2) in southern Nevada. The resulting dataset, described by Pancha et al. (2017), contains over 10,700 1D shear-wave-velocity-depth profiles (SWVP) that constitute a rich database of 3D shear-wave velocity structure that is both laterally and vertical heterogenous. This study capitalizes on the uniquely detailed and spatially dense CCBD database to carry out sensitivity tests on the detailed shear-wave-velocity-profiles and the Vs30 utilizing 1D and 3D site-response approaches. Sensitivity tests are derived from the 1D oscillator response of a single-degree-of-freedom-oscillator and from 3D finite-difference deterministic simulations up to 15 Hz frequency using similar model parameters. Results demonstrate that the detailed SWVP are amplifying ground motions by roughly 50% over the simple Vs30 models, above 4.6 Hz frequency. Numerical simulations also depict significant lateral resonance, focusing, and scattering from seismic energy attributed to the 3D small-scale heterogeneities of the shear-wave-velocity profiles that result in a 70% increase in peak ground velocity. Additionally, PGV ratio maps clearly establish that the increased amplification from the detailed SWVPs is consistent throughout the model space. As a corollary, this study demonstrates the use of finite-differencing numerical based methods to simulate ground motions at high frequencies, up to 15 Hz.

Numerical simulation of the casting process of titanium tooth crowns and bridges.

PubMed

Wu, M; Augthun, M; Wagner, I; Sahm, P R; Spiekermann, H

2001-06-01

The objectives of this paper were to simulate the casting process of titanium tooth crowns and bridges; to predict and control porosity defect. A casting simulation software, MAGMASOFT, was used. The geometry of the crowns with fine details of the occlusal surface were digitized by means of laser measuring technique, then converted and read in the simulation software. Both mold filling and solidification were simulated, the shrinkage porosity was predicted by a "feeding criterion", and the gas pore sensitivity was studied based on the mold filling and solidification simulations. Two types of dental prostheses (a single-crown casting and a three-unit-bridge) with various sprue designs were numerically "poured", and only one optimal design for each prosthesis was recommended for real casting trial. With the numerically optimized design, real titanium dental prostheses (five replicas for each) were made on a centrifugal casting machine. All the castings endured radiographic examination, and no porosity was detected in the cast prostheses. It indicates that the numerical simulation is an efficient tool for dental casting design and porosity control. Copyright 2001 Kluwer Academic Publishers

Analytic and numeric Green's functions for a two-dimensional electron gas in an orthogonal magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cresti, Alessandro; Grosso, Giuseppe; Parravicini, Giuseppe Pastori

2006-05-15

We have derived closed analytic expressions for the Green's function of an electron in a two-dimensional electron gas threaded by a uniform perpendicular magnetic field, also in the presence of a uniform electric field and of a parabolic spatial confinement. A workable and powerful numerical procedure for the calculation of the Green's functions for a large infinitely extended quantum wire is considered exploiting a lattice model for the wire, the tight-binding representation for the corresponding matrix Green's function, and the Peierls phase factor in the Hamiltonian hopping matrix element to account for the magnetic field. The numerical evaluation of themore » Green's function has been performed by means of the decimation-renormalization method, and quite satisfactorily compared with the analytic results worked out in this paper. As an example of the versatility of the numerical and analytic tools here presented, the peculiar semilocal character of the magnetic Green's function is studied in detail because of its basic importance in determining magneto-transport properties in mesoscopic systems.« less

A review of numerical techniques approaching microstructures of crystalline rocks

NASA Astrophysics Data System (ADS)

Zhang, Yahui; Wong, Louis Ngai Yuen

2018-06-01

The macro-mechanical behavior of crystalline rocks including strength, deformability and failure pattern are dominantly influenced by their grain-scale structures. Numerical technique is commonly used to assist understanding the complicated mechanisms from a microscopic perspective. Each numerical method has its respective strengths and limitations. This review paper elucidates how numerical techniques take geometrical aspects of the grain into consideration. Four categories of numerical methods are examined: particle-based methods, block-based methods, grain-based methods, and node-based methods. Focusing on the grain-scale characters, specific relevant issues including increasing complexity of micro-structure, deformation and breakage of model elements, fracturing and fragmentation process are described in more detail. Therefore, the intrinsic capabilities and limitations of different numerical approaches in terms of accounting for the micro-mechanics of crystalline rocks and their phenomenal mechanical behavior are explicitly presented.

Spatial Modeling of Geometallurgical Properties: Techniques and a Case Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deutsch, Jared L., E-mail: jdeutsch@ualberta.ca; Palmer, Kevin; Deutsch, Clayton V.

High-resolution spatial numerical models of metallurgical properties constrained by geological controls and more extensively by measured grade and geomechanical properties constitute an important part of geometallurgy. Geostatistical and other numerical techniques are adapted and developed to construct these high-resolution models accounting for all available data. Important issues that must be addressed include unequal sampling of the metallurgical properties versus grade assays, measurements at different scale, and complex nonlinear averaging of many metallurgical parameters. This paper establishes techniques to address each of these issues with the required implementation details and also demonstrates geometallurgical mineral deposit characterization for a copper–molybdenum deposit inmore » South America. High-resolution models of grades and comminution indices are constructed, checked, and are rigorously validated. The workflow demonstrated in this case study is applicable to many other deposit types.« less

Propagation properties of hollow sinh-Gaussian beams through fractional Fourier transform optical systems

NASA Astrophysics Data System (ADS)

Tang, Bin; Jiang, ShengBao; Jiang, Chun; Zhu, Haibin

2014-07-01

A hollow sinh-Gaussian beam (HsG) is an appropriate model to describe the dark-hollow beam. Based on Collins integral formula and the fact that a hard-edged-aperture function can be expanded into a finite sum of complex Gaussian functions, the propagation properties of a HsG beam passing through fractional Fourier transform (FRFT) optical systems with and without apertures have been studied in detail by some typical numerical examples. The results obtained using the approximate analytical formula are in good agreement with those obtained using numerical integral calculation. Further, the studies indicate that the normalized intensity distribution of the HsG beam in FRFT plane is closely related with not only the fractional order but also the beam order and the truncation parameter. The FRFT optical systems provide a convenient way for laser beam shaping.

Method of and Apparatus for Histological Human Tissue Characterization Using Ultrasound

NASA Technical Reports Server (NTRS)

Yost, William T. (Inventor); Cantrell, John H. (Inventor); TalEr, George A. (Inventor)

1999-01-01

A method and apparatus for determining important histological characteristics of tissue, including a determination of the tissue's health. Electrical pulses are converted into meaningful numerical representations through the use of Fourier Transforms. These numerical representations are then used to determine important histological characteristics of tissue. This novel invention does not require rectification and thus provides for detailed information from the ultrasonic scan.

Method of and Apparatus for Histological Human Tissue Characterization Using Ultrasound

NASA Technical Reports Server (NTRS)

Yost, William T. (Inventor); Cantrell, John H. (Inventor); Taler, George A. (Inventor)

1998-01-01

A method and apparatus for determining important histological characteristics of tissue, including a determination of the tissue's health is discussed. Electrical pulses are converted into meaningful numerical representations through the use of Fourier Transforms. These numerical representations are then used to determine important histological characteristics of tissue. This novel invention does not require rectification and thus provides for detailed information from the ultrasonic scan.

Improving the Navy’s Passive Underwater Acoustic Monitoring of Marine Mammal Populations

DTIC Science & Technology

2014-09-30

species using passive acoustic monitoring, with application to obtaining density estimates of transiting humpback whale populations in the Southern...of the density estimates, 3) to apply the numerical modeling methods for humpback whale vocalizations to understand distortions caused by...obtained. The specific approach being followed to accomplish objectives 1-4 above is listed below. 1) Detailed numerical modeling of humpback whale

The challenges of numerically simulating analogue brittle thrust wedges

NASA Astrophysics Data System (ADS)

Buiter, Susanne; Ellis, Susan

2017-04-01

Fold-and-thrust belts and accretionary wedges form when sedimentary and crustal rocks are compressed into thrusts and folds in the foreland of an orogen or at a subduction trench. For over a century, analogue models have been used to investigate the deformation characteristics of such brittle wedges. These models predict wedge shapes that agree with analytical critical taper theory and internal deformation structures that well resemble natural observations. In a series of comparison experiments for thrust wedges, called the GeoMod2004 (1,2) and GeoMod2008 (3,4) experiments, it was shown that different numerical solution methods successfully reproduce sandbox thrust wedges. However, the GeoMod2008 benchmark also pointed to the difficulties of representing frictional boundary conditions and sharp velocity discontinuities with continuum numerical methods, in addition to the well-known challenges of numerical plasticity. Here we show how details in the numerical implementation of boundary conditions can substantially impact numerical wedge deformation. We consider experiment 1 of the GeoMod2008 brittle thrust wedge benchmarks. This experiment examines a triangular thrust wedge in the stable field of critical taper theory that should remain stable, that is, without internal deformation, when sliding over a basal frictional surface. The thrust wedge is translated by lateral displacement of a rigid mobile wall. The corner between the mobile wall and the subsurface is a velocity discontinuity. Using our finite-element code SULEC, we show how different approaches to implementing boundary friction (boundary layer or contact elements) and the velocity discontinuity (various smoothing schemes) can cause the wedge to indeed translate in a stable manner or to undergo internal deformation (which is a fail). We recommend that numerical studies of sandbox setups not only report the details of their implementation of boundary conditions, but also document the modelling attempts that failed. References 1. Buiter and the GeoMod2004 Team, 2006. The numerical sandbox: comparison of model results for a shortening and an extension experiment. Geol. Soc. Lond. Spec. Publ. 253, 29-64 2. Schreurs and the GeoMod2004 Team, 2006. Analogue benchmarks of shortening and extension experiments. Geol. Soc. Lond. Spec. Publ. 253, 1-27 3. Buiter, Schreurs and the GeoMod2008 Team, 2016. Benchmarking numerical models of brittle thrust wedges, J. Struct. Geol. 92, 140-177 4. Schreurs, Buiter and the GeoMod2008 Team, 2016. Benchmarking analogue models of brittle thrust wedges, J. Struct. Geol. 92, 116-13

Unsteady numerical simulations of the stability and dynamics of flames

NASA Technical Reports Server (NTRS)

Kailasanath, K.; Patnaik, G.; Oran, E. S.

1995-01-01

In this report we describe the research performed at the Naval Research Laboratory in support of the NASA Microgravity Science and Applications Program over the past three years (from Feb. 1992) with emphasis on the work performed since the last microgravity combustion workshop. The primary objective of our research is to develop an understanding of the differences in the structure, stability, dynamics and extinction of flames in earth gravity and in microgravity environments. Numerical simulations, in which the various physical and chemical processes can be independently controlled, can significantly advance our understanding of these differences. Therefore, our approach is to use detailed time-dependent, multi-dimensional, multispecies numerical models to perform carefully designed computational experiments. The basic issues we have addressed, a general description of the numerical approach, and a summary of the results are described in this report. More detailed discussions are available in the papers published which are referenced herein. Some of the basic issues we have addressed recently are (1) the relative importance of wall losses and gravity on the extinguishment of downward-propagating flames; (2) the role of hydrodynamic instabilities in the formation of cellular flames; (3) effects of gravity on burner-stabilized flames, and (4) effects of radiative losses and chemical-kinetics on flames near flammability limits. We have also expanded our efforts to include hydrocarbon flames in addition to hydrogen flames and to perform simulations in support of other on-going efforts in the microgravity combustion sciences program. Modeling hydrocarbon flames typically involves a larger number of species and a much larger number of reactions when compared to hydrogen. In addition, more complex radiation models may also be needed. In order to efficiently compute such complex flames recent developments in parallel computing have been utilized to develop a state-of-the-art parallel flame code. This is discussed below in some detail after a brief discussion of the numerical models.

Problems in Catalytic Oxidation of Hydrocarbons and Detailed Simulation of Combustion Processes

NASA Astrophysics Data System (ADS)

Xin, Yuxuan

This dissertation research consists of two parts, with Part I on the kinetics of catalytic oxidation of hydrocarbons and Part II on aspects on the detailed simulation of combustion processes. In Part I, the catalytic oxidation of C1--C3 hydrocarbons, namely methane, ethane, propane and ethylene, was investigated for lean hydrocarbon-air mixtures over an unsupported Pd-based catalyst, from 600 to 800 K and under atmospheric pressure. In Chapter 2, the experimental facility of wire microcalorimetry and simulation configuration were described in details. In Chapter 3 and 4, the oxidation rate of C1--C 3 hydrocarbons is demonstrated to be determined by the dissociative adsorption of hydrocarbons. A detailed surface kinetics model is proposed with deriving the rate coefficient of hydrocarbon dissociative adsorption from the wire microcalorimetry data. In Part II, four fundamental studies were conducted through detailed combustion simulations. In Chapter 5, self-accelerating hydrogen-air flames are studied via two-dimensional detailed numerical simulation (DNS). The increase in the global flame velocity is shown to be caused by the increase of flame surface area, and the fractal structure of the flame front is demonstrated by the box-counting method. In Chapter 6, skeletal reaction models for butane combustion are derived by using directed relation graph (DRG) and DRG-aided sensitivity analysis (DRGASA), and uncertainty minimization by polynomial chaos expansion (MUM-PCE) mothodes. The dependence of model uncertainty is subjected to the completeness of the model. In Chapter 7, a systematic strategy is proposed to reduce the cost of the multicomponent diffusion model by accurately accounting for the species whose diffusivity is important to the global responses of the combustion systems, and approximating those of less importance by the mixture-averaged model. The reduced model is validated in an n-heptane mechanism with 88 species. In Chapter 8, the influence of Soret diffusion on the n-heptane/air flames is investigated numerically. In the unstretched flames, Soret diffusion primarily affects the chemical kinetics embedded in the flame structure and the net effect is small; while in the stretched flames, its impact is mainly through those of n-heptane and the secondary fuel, H2, in modifying the flame temperature, with substantial effects.

Modelling Detailed-Chemistry Effects on Turbulent Diffusion Flames using a Parallel Solution-Adaptive Scheme

NASA Astrophysics Data System (ADS)

Jha, Pradeep Kumar

Capturing the effects of detailed-chemistry on turbulent combustion processes is a central challenge faced by the numerical combustion community. However, the inherent complexity and non-linear nature of both turbulence and chemistry require that combustion models rely heavily on engineering approximations to remain computationally tractable. This thesis proposes a computationally efficient algorithm for modelling detailed-chemistry effects in turbulent diffusion flames and numerically predicting the associated flame properties. The cornerstone of this combustion modelling tool is the use of parallel Adaptive Mesh Refinement (AMR) scheme with the recently proposed Flame Prolongation of Intrinsic low-dimensional manifold (FPI) tabulated-chemistry approach for modelling complex chemistry. The effect of turbulence on the mean chemistry is incorporated using a Presumed Conditional Moment (PCM) approach based on a beta-probability density function (PDF). The two-equation k-w turbulence model is used for modelling the effects of the unresolved turbulence on the mean flow field. The finite-rate of methane-air combustion is represented here by using the GRI-Mech 3.0 scheme. This detailed mechanism is used to build the FPI tables. A state of the art numerical scheme based on a parallel block-based solution-adaptive algorithm has been developed to solve the Favre-averaged Navier-Stokes (FANS) and other governing partial-differential equations using a second-order accurate, fully-coupled finite-volume formulation on body-fitted, multi-block, quadrilateral/hexahedral mesh for two-dimensional and three-dimensional flow geometries, respectively. A standard fourth-order Runge-Kutta time-marching scheme is used for time-accurate temporal discretizations. Numerical predictions of three different diffusion flames configurations are considered in the present work: a laminar counter-flow flame; a laminar co-flow diffusion flame; and a Sydney bluff-body turbulent reacting flow. Comparisons are made between the predicted results of the present FPI scheme and Steady Laminar Flamelet Model (SLFM) approach for diffusion flames. The effects of grid resolution on the predicted overall flame solutions are also assessed. Other non-reacting flows have also been considered to further validate other aspects of the numerical scheme. The present schemes predict results which are in good agreement with published experimental results and reduces the computational cost involved in modelling turbulent diffusion flames significantly, both in terms of storage and processing time.

The NASA Ames 16-Inch Shock Tunnel Nozzle Simulations and Experimental Comparison

NASA Technical Reports Server (NTRS)

TokarcikPolsky, S.; Papadopoulos, P.; Venkatapathy, E.; Delwert, G. S.; Edwards, Thomas A. (Technical Monitor)

1995-01-01

The 16-Inch Shock Tunnel at NASA Ames Research Center is a unique test facility used for hypersonic propulsion testing. To provide information necessary to understand the hypersonic testing of the combustor model, computational simulations of the facility nozzle were performed and results are compared with available experimental data, namely static pressure along the nozzle walls and pitot pressure at the exit of the nozzle section. Both quasi-one-dimensional and axisymmetric approaches were used to study the numerous modeling issues involved. The facility nozzle flow was examined for three hypersonic test conditions, and the computational results are presented in detail. The effects of variations in reservoir conditions, boundary layer growth, and parameters of numerical modeling are explored.

Simulating Damage Due to a Lightning Strike Event: Effects of Temperature Dependent Properties on Interlaminar Damage

NASA Technical Reports Server (NTRS)

Ghezeljeh, Paria Naghipour; Pineda, Evan Jorge

2014-01-01

A multidirectional, carbon fiber-epoxy, composite panel is subjected to a simulated lightning strike, within a finite element method framework, and the effect of material properties on the failure (delamination) response is investigated through a detailed numerical study. The numerical model of the composite panel consists of individual homogenized plies with user-defined, cohesive interface elements between them. Lightning strikes are simulated as an assumed combination of excessive heat and high pressure loadings. It is observed that the initiation and propagation of lightning-induced delamination is a significant function of the temperature dependency of interfacial fracture toughness. This dependency must be defined properly in order to achieve reliable predictions of the present lightning-induced delamination in the composite panel.

Numerical demonstration of neuromorphic computing with photonic crystal cavities.

PubMed

Laporte, Floris; Katumba, Andrew; Dambre, Joni; Bienstman, Peter

2018-04-02

We propose a new design for a passive photonic reservoir computer on a silicon photonics chip which can be used in the context of optical communication applications, and study it through detailed numerical simulations. The design consists of a photonic crystal cavity with a quarter-stadium shape, which is known to foster interesting mixing dynamics. These mixing properties turn out to be very useful for memory-dependent optical signal processing tasks, such as header recognition. The proposed, ultra-compact photonic crystal cavity exhibits a memory of up to 6 bits, while simultaneously accepting bitrates in a wide region of operation. Moreover, because of the inherent low losses in a high-Q photonic crystal cavity, the proposed design is very power efficient.

On a phase field approach for martensitic transformations in a crystal plastic material at a loaded surface

NASA Astrophysics Data System (ADS)

Schmitt, Regina; Kuhn, Charlotte; Müller, Ralf

2017-07-01

A continuum phase field model for martensitic transformations is introduced, including crystal plasticity with different slip systems for the different phases. In a 2D setting, the transformation-induced eigenstrain is taken into account for two martensitic orientation variants. With aid of the model, the phase transition and its dependence on the volume change, crystal plastic material behavior, and the inheritance of plastic deformations from austenite to martensite are studied in detail. The numerical setup is motivated by the process of cryogenic turning. The resulting microstructure qualitatively coincides with an experimentally obtained martensite structure. For the numerical calculations, finite elements together with global and local implicit time integration scheme are employed.

Large eddy simulations and direct numerical simulations of high speed turbulent reacting flows

NASA Technical Reports Server (NTRS)

Givi, Peyman; Madnia, C. K.; Steinberger, C. J.; Tsai, A.

1991-01-01

This research is involved with the implementations of advanced computational schemes based on large eddy simulations (LES) and direct numerical simulations (DNS) to study the phenomenon of mixing and its coupling with chemical reactions in compressible turbulent flows. In the efforts related to LES, a research program was initiated to extend the present capabilities of this method for the treatment of chemically reacting flows, whereas in the DNS efforts, focus was on detailed investigations of the effects of compressibility, heat release, and nonequilibrium kinetics modeling in high speed reacting flows. The efforts to date were primarily focussed on simulations of simple flows, namely, homogeneous compressible flows and temporally developing hign speed mixing layers. A summary of the accomplishments is provided.

A numerical model simulation of the regional air pollution meteorology of the greater Chesapeake Bay area - Summer day case study

NASA Technical Reports Server (NTRS)

Segal, M.; Pielke, R. A.; Mcnider, R. T.; Mcdougal, D. S.

1982-01-01

The mesoscale numerical model of the University of Virginia (UVMM), has been applied to the greater Chesapeake Bay area in order to provide a detailed description of the air pollution meteorology during a typical summer day. This model provides state of the art simulations for land-sea thermally induced circulations. The model-predicted results agree favorably with available observed data. The effects of synoptic flow and sea breeze coupling on air pollution meteorological characteristics in this region, are demonstrated by a spatial and temporal presentation of various model predicted fields. A transport analysis based on predicted wind velocities indicated possible recirculation of pollutants back onto the Atlantic coast due to the sea breeze circulation.

Propagation of coherently combined truncated laser beam arrays with beam distortions in non-Kolmogorov turbulence.

PubMed

Tao, Rumao; Si, Lei; Ma, Yanxing; Zhou, Pu; Liu, Zejin

2012-08-10

The propagation properties of coherently combined truncated laser beam arrays with beam distortions through non-Kolmogorov turbulence are studied in detail both analytically and numerically. The analytical expressions for the average intensity and the beam width of coherently combined truncated laser beam arrays with beam distortions propagating through turbulence are derived based on the combination of statistical optics methods and the extended Huygens-Fresnel principle. The effect of beam distortions, such as amplitude modulation and phase fluctuation, is studied by numerical examples. The numerical results reveal that phase fluctuations have significant influence on the spreading of coherently combined truncated laser beam arrays in non-Kolmogorov turbulence, and the effects of the phase fluctuations can be negligible as long as the phase fluctuations are controlled under a certain level, i.e., a>0.05 for the situation considered in the paper. Furthermore, large phase fluctuations can convert the beam distribution rapidly to a Gaussian form, vary the spreading, weaken the optimum truncation effects, and suppress the dependence of spreading on the parameters of the non-Kolmogorov turbulence.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Chao; Xu, Jun; Cao, Lei

The electrodes of lithium-ion batteries (LIB) are known to be brittle and to fail earlier than the separators during an external crush event. Thus, the understanding of mechanical failure mechanism for LIB electrodes (anode and cathode) is critical for the safety design of LIB cells. In this paper, we present experimental and numerical studies on the constitutive behavior and progression of failure in LIB electrodes. Mechanical tests were designed and conducted to evaluate the constitutive properties of porous electrodes. Constitutive models were developed to describe the stress-strain response of electrodes under uniaxial tensile and compressive loads. The failure criterion andmore » a damage model were introduced to model their unique tensile and compressive failure behavior. The failure mechanism of LIB electrodes was studied using the blunt rod test on dry electrodes, and numerical models were built to simulate progressive failure. The different failure processes were examined and analyzed in detail numerically, and correlated with experimentally observed failure phenomena. Finally, the test results and models improve our understanding of failure behavior in LIB electrodes, and provide constructive insights on future development of physics-based safety design tools for battery structures under mechanical abuse.« less

Detailed Multidimensional Simulations of the Structure and Dynamics of Flames

NASA Technical Reports Server (NTRS)

Patnaik, G.; Kailasanath, K.

1999-01-01

Numerical simulations in which the various physical and chemical processes can be independently controlled can significantly advance our understanding of the structure, stability, dynamics and extinction of flames. Therefore, our approach has been to use detailed time-dependent, multidimensional, multispecies numerical models to perform carefully designed computational experiments of flames on Earth and in microgravity environments. Some of these computational experiments are complementary to physical experiments performed under the Microgravity Program while others provide a fundamental understanding that cannot be obtained from physical experiments alone. In this report, we provide a brief summary of our recent research highlighting the contributions since the previous microgravity combustion workshop. There are a number of mechanisms that can cause flame instabilities and result in the formation of dynamic multidimensional structures. In the past, we have used numerical simulations to show that it is the thermo-diffusive instability rather than an instability due to preferential diffusion that is the dominant mechanism for the formation of cellular flames in lean hydrogen-air mixtures. Other studies have explored the role of gravity on flame dynamics and extinguishment, multi-step kinetics and radiative losses on flame instabilities in rich hydrogen-air flames, and heat losses on burner-stabilized flames in microgravity. The recent emphasis of our work has been on exploring flame-vortex interactions and further investigating the structure and dynamics of lean hydrogen-air flames in microgravity. These topics are briefly discussed after a brief discussion of our computational approach for solving these problems.

On the suitability of steady RANS CFD for forced mixing ventilation at transitional slot Reynolds numbers.

PubMed

van Hooff, T; Blocken, B; van Heijst, G J F

2013-06-01

Accurate prediction of ventilation flow is of primary importance for designing a healthy, comfortable, and energy-efficient indoor environment. Since the 1970s, the use of computational fluid dynamics (CFD) has increased tremendously, and nowadays, it is one of the primary methods to assess ventilation flow in buildings. The most commonly used numerical approach consists of solving the steady Reynolds-averaged Navier-Stokes (RANS) equations with a turbulence model to provide closure. This article presents a detailed validation study of steady RANS for isothermal forced mixing ventilation of a cubical enclosure driven by a transitional wall jet. The validation is performed using particle image velocimetry (PIV) measurements for slot Reynolds numbers of 1000 and 2500. Results obtained with the renormalization group (RNG) k-ε model, a low-Reynolds k-ε model, the shear stress transport (SST) k-ω model, and a Reynolds stress model (RSM) are compared with detailed experimental data. In general, the RNG k-ε model shows the weakest performance, whereas the low-Re k-ε model shows the best agreement with the measurements. In addition, the influence of the turbulence model on the predicted air exchange efficiency in the cubical enclosure is analyzed, indicating differences up to 44% for this particular case. This article presents a detailed numerical study of isothermal forced mixing ventilation driven by a low-velocity (transitional) wall jet using steady computational fluid dynamics (CFD) simulations. It is shown that the numerically obtained room airflow patterns are highly dependent on the chosen turbulence model and large differences with experimentally obtained velocity fields can be present. The renormalization group (RNG) k-ε model, which is commonly used for room airflow modeling, shows the largest deviations from the measured velocities, indicating the care that must be taken when selecting a turbulence model for room airflow prediction. As a result of the different predictions of the flow pattern in the room, large differences are present between the predicted air exchange efficiency obtained with the four tested turbulence models, which can be as high as 44%. © 2012 John Wiley & Sons A/S. Published by Blackwell Publishing Ltd.

A numerical simulation method and analysis of a complete thermoacoustic-Stirling engine.

PubMed

Ling, Hong; Luo, Ercang; Dai, Wei

2006-12-22

Thermoacoustic prime movers can generate pressure oscillation without any moving parts on self-excited thermoacoustic effect. The details of the numerical simulation methodology for thermoacoustic engines are presented in the paper. First, a four-port network method is used to build the transcendental equation of complex frequency as a criterion to judge if temperature distribution of the whole thermoacoustic system is correct for the case with given heating power. Then, the numerical simulation of a thermoacoustic-Stirling heat engine is carried out. It is proved that the numerical simulation code can run robustly and output what one is interested in. Finally, the calculated results are compared with the experiments of the thermoacoustic-Stirling heat engine (TASHE). It shows that the numerical simulation can agrees with the experimental results with acceptable accuracy.

Dynamic stability analysis for capillary channel flow: One-dimensional and three-dimensional computations and the equivalent steady state technique

NASA Astrophysics Data System (ADS)

Grah, Aleksander; Dreyer, Michael E.

2010-01-01

Spacecraft technology provides a series of applications for capillary channel flow. It can serve as a reliable means for positioning and transport of liquids under low gravity conditions. Basically, capillary channels provide liquid paths with one or more free surfaces. A problem may be flow instabilities leading to a collapse of the liquid surfaces. A result is undesired gas ingestion and a two phase flow which can in consequence cause several technical problems. The presented capillary channel consists of parallel plates with two free liquid surfaces. The flow rate is established by a pump at the channel outlet, creating a lower pressure within the channel. Owing to the pressure difference between the liquid phase and the ambient gas phase the free surfaces bend inwards and remain stable as long as they are able to resist the steady and unsteady pressure effects. For the numerical prediction of the flow stability two very different models are used. The one-dimensional unsteady model is mainly based on the Bernoulli equation, the continuity equation, and the Gauss-Laplace equation. For three-dimensional evaluations an open source computational fluid dynamics (CFD) tool is applied. For verifications the numerical results are compared with quasisteady and unsteady data of a sounding rocket experiment. Contrary to previous experiments this one results in a significantly longer observation sequence. Furthermore, the critical point of the steady flow instability could be approached by a quasisteady technique. As in previous experiments the comparison to the numerical model evaluation shows a very good agreement for the movement of the liquid surfaces and for the predicted flow instability. The theoretical prediction of the flow instability is related to the speed index, based on characteristic velocities of the capillary channel flow. Stable flow regimes are defined by stability criteria for steady and unsteady flow. The one-dimensional computation of the speed index is based on the technique of the equivalent steady system, which is published for the first time in the present paper. This approach assumes that for every unsteady state an equivalent steady state with a special boundary condition can be formulated. The equivalent steady state technique enables a reformulation of the equation system and an efficient and reliable speed index computation. Furthermore, the existence of the numerical singularity at the critical point of the steady flow instability, postulated in previous publication, is demonstrated in detail. The numerical singularity is related to the stability criterion for steady flow and represents the numerical consequence of the liquid surface collapse. The evaluation and generation of the pressure diagram is demonstrated in detail with a series of numerical dynamic flow studies. The stability diagram, based on one-dimensional computation, gives a detailed overview of the stable and instable flow regimes. This prediction is in good agreement with the experimentally observed critical flow conditions and results of three-dimensional CFD computations.

Knudsen Cell Studies of Ti-Al Thermodynamics

NASA Technical Reports Server (NTRS)

Jacobson, Nathan S.; Copland, Evan H.; Mehrotra, Gopal M.; Auping, Judith; Gray, Hugh R. (Technical Monitor)

2002-01-01

In this paper we describe the Knudsen cell technique for measurement of thermodynamic activities in alloys. Numerous experimental details must be adhered to in order to obtain useful experimental data. These include introduction of an in-situ standard, precise temperature measurement, elimination of thermal gradients, and precise cell positioning. Our first design is discussed and some sample data on Ti-Al alloys is presented. The second modification and associated improvements are also discussed.

Mesoscale Modeling, Forecasting and Remote Sensing Research.

DTIC Science & Technology

remote sensing , cyclonic scale diagnostic studies and mesoscale numerical modeling and forecasting are summarized. Mechanisms involved in the release of potential instability are discussed and simulated quantitatively, giving particular attention to the convective formulation. The basic mesoscale model is documented including the equations, boundary condition, finite differences and initialization through an idealized frontal zone. Results of tests including a three dimensional test with real data, tests of convective/mesoscale interaction and tests with a detailed

Antenna modeling considerations for accurate SAR calculations in human phantoms in close proximity to GSM cellular base station antennas.

PubMed

van Wyk, Marnus J; Bingle, Marianne; Meyer, Frans J C

2005-09-01

International bodies such as International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the Institute for Electrical and Electronic Engineering (IEEE) make provision for human exposure assessment based on SAR calculations (or measurements) and basic restrictions. In the case of base station exposure this is mostly applicable to occupational exposure scenarios in the very near field of these antennas where the conservative reference level criteria could be unnecessarily restrictive. This study presents a variety of critical aspects that need to be considered when calculating SAR in a human body close to a mobile phone base station antenna. A hybrid FEM/MoM technique is proposed as a suitable numerical method to obtain accurate results. The verification of the FEM/MoM implementation has been presented in a previous publication; the focus of this study is an investigation into the detail that must be included in a numerical model of the antenna, to accurately represent the real-world scenario. This is accomplished by comparing numerical results to measurements for a generic GSM base station antenna and appropriate, representative canonical and human phantoms. The results show that it is critical to take the disturbance effect of the human phantom (a large conductive body) on the base station antenna into account when the antenna-phantom spacing is less than 300 mm. For these small spacings, the antenna structure must be modeled in detail. The conclusion is that it is feasible to calculate, using the proposed techniques and methodology, accurate occupational compliance zones around base station antennas based on a SAR profile and basic restriction guidelines. (c) 2005 Wiley-Liss, Inc.

Diagnosis of an intense atmospheric river impacting the pacific northwest: Storm summary and offshore vertical structure observed with COSMIC satellite retrievals

USGS Publications Warehouse

Neiman, P.J.; Ralph, F.M.; Wick, G.A.; Kuo, Y.-H.; Wee, T.-K.; Ma, Z.; Taylor, G.H.; Dettinger, M.D.

2008-01-01

This study uses the new satellite-based Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission to retrieve tropospheric profiles of temperature and moisture over the data-sparse eastern Pacific Ocean. The COSMIC retrievals, which employ a global positioning system radio occultation technique combined with "first-guess" information from numerical weather prediction model analyses, are evaluated through the diagnosis of an intense atmospheric river (AR; i.e., a narrow plume of strong water vapor flux) that devastated the Pacific Northwest with flooding rains in early November 2006. A detailed analysis of this AR is presented first using conventional datasets and highlights the fact that ARs are critical contributors to West Coast extreme precipitation and flooding events. Then, the COSMIC evaluation is provided. Offshore composite COSMIC soundings north of, within, and south of this AR exhibited vertical structures that are meteorologically consistent with satellite imagery and global reanalysis fields of this case and with earlier composite dropsonde results from other landfalling ARs. Also, a curtain of 12 offshore COSMIC soundings through the AR yielded cross-sectional thermodynamic and moisture structures that were similarly consistent, including details comparable to earlier aircraft-based dropsonde analyses. The results show that the new COSMIC retrievals, which are global (currently yielding ???2000 soundings per day), provide high-resolution vertical-profile information beyond that found in the numerical model first-guess fields and can help monitor key lower-tropospheric mesoscale phenomena in data-sparse regions. Hence, COSMIC will likely support a wide array of applications, from physical process studies to data assimilation, numerical weather prediction, and climate research. ?? 2008 American Meteorological Society.

Numerical comparisons of ground motion predictions with kinematic rupture modeling

NASA Astrophysics Data System (ADS)

Yuan, Y. O.; Zurek, B.; Liu, F.; deMartin, B.; Lacasse, M. D.

2017-12-01

Recent advances in large-scale wave simulators allow for the computation of seismograms at unprecedented levels of detail and for areas sufficiently large to be relevant to small regional studies. In some instances, detailed information of the mechanical properties of the subsurface has been obtained from seismic exploration surveys, well data, and core analysis. Using kinematic rupture modeling, this information can be used with a wave propagation simulator to predict the ground motion that would result from an assumed fault rupture. The purpose of this work is to explore the limits of wave propagation simulators for modeling ground motion in different settings, and in particular, to explore the numerical accuracy of different methods in the presence of features that are challenging to simulate such as topography, low-velocity surface layers, and shallow sources. In the main part of this work, we use a variety of synthetic three-dimensional models and compare the relative costs and benefits of different numerical discretization methods in computing the seismograms of realistic-size models. The finite-difference method, the discontinuous-Galerkin method, and the spectral-element method are compared for a range of synthetic models having different levels of complexity such as topography, large subsurface features, low-velocity surface layers, and the location and characteristics of fault ruptures represented as an array of seismic sources. While some previous studies have already demonstrated that unstructured-mesh methods can sometimes tackle complex problems (Moczo et al.), we investigate the trade-off between unstructured-mesh methods and regular-grid methods for a broad range of models and source configurations. Finally, for comparison, our direct simulation results are briefly contrasted with those predicted by a few phenomenological ground-motion prediction equations, and a workflow for accurately predicting ground motion is proposed.

Numerical analysis of field-scale transport of bromacil

NASA Astrophysics Data System (ADS)

Russo, David; Tauber-Yasur, Inbar; Laufer, Asher; Yaron, Bruno

Field-scale transport of bromacil (5-bromo-3- sec-butyl-6-methyluracil) was analyzed using two different model processes for local description of the transport. The first was the classical, one-region convection dispersion equation (CDE) model while the second was the two-region, mobile-immobile (MIM) model. The analyses were performed by means of detailed three-dimensional, numerical simulations of the flow and the transport [Russo, D., Zaidel, J. and Laufer, A., Numerical analysis of flow and transport in a three-dimensional partially saturated heterogeneous soil. Water Resour. Res., 1998, in press], employing local soil hydraulic properties parameters from field measurements and local adsorption/desorption coefficients and the first-order degradation rate coefficient from laboratory measurements. Results of the analyses suggest that for a given flow regime, mass exchange between the mobile and the immobile regions retards the bromacil degradation, considerably affects the distribution of the bromacil resident concentration, c, at relatively large travel times, slightly affects the spatial moments of the distribution of c, and increases the skewing of the bromacil breakthrough and the uncertainty in its prediction, compared with the case in which the soil contained only a single (mobile) region. Mean and standard deviation of the simulated concentration profiles at various elapsed times were compared with measurements from a field-scale transport experiment [Tauber-Yasur, I., Hadas, A., Russo, D. and Yaron, B., Leaching of terbuthylazine and bromacil through field soils. Water, Air Soil Poln., 1998, in press] conducted at the Bet Dagan site. Given the limitations of the present study (e.g. the lack of detailed field data on the spatial variability of the soil chemical properties) the main conclusion of the present study is that the field-scale transport of bromacil at the Bet Dagan site is better quantified with the MIM model than the CDE model.

Numerical Estimation of the Outer Bank Resistance Characteristics in AN Evolving Meandering River

NASA Astrophysics Data System (ADS)

Wang, D.; Konsoer, K. M.; Rhoads, B. L.; Garcia, M. H.; Best, J.

2017-12-01

Few studies have examined the three-dimensional flow structure and its interaction with bed morphology within elongate loops of large meandering rivers. The present study uses a numerical model to simulate the flow pattern and sediment transport, especially the flow close to the outer-bank, at two elongate meandering loops in Wabash River, USA. The numerical grid for the model is based on a combination of airborne LIDAR data on floodplains and the multibeam data within the river channel. A Finite Element Method (FEM) is used to solve the non-hydrostatic RANS equation using a K-epsilon turbulence closure scheme. High-resolution topographic data allows detailed numerical simulation of flow patterns along the outer bank and model calibration involves comparing simulated velocities to ADCP measurements at 41 cross sections near this bank. Results indicate that flow along the outer bank is strongly influenced by large resistance elements, including woody debris, large erosional scallops within the bank face, and outcropping bedrock. In general, patterns of bank migration conform with zones of high near-bank velocity and shear stress. Using the existing model, different virtual events can be simulated to explore the impacts of different resistance characteristics on patterns of flow, sediment transport, and bank erosion.

Morphodynamic Responses of a River-Floodplain System to a Chute Cutoff: Numerical Experiments to Investigate the Role of Multiple Active Factors

NASA Astrophysics Data System (ADS)

Li, Z.; Garcia, M. H.

2017-12-01

Unlike neck cutoffs, which are caused by meander migration to an over-mature stage, a chute cutoff is governed by many more factors. A chute cutoff always occurs when there is over-bank flow caused by floods. During this process, the river-floodplain system characteristics will determine the newly formed cutoff channel location and extent. Hence, a comprehensive study of the influence which different active factors have on a cutoff channel is necessary. Numerical experiments are well suited in this case because of the possibility of studying a large number of scenarios and also the practical and econocmical challenges of collecting high quality data during floods in the field. Numerical simulations were performed using the open TELEMAC-MASCARET modeling suite, which can solve the two-dimensional Shallow Water Equations, the three-dimensional, Reynolds-averaged Navier-Stokes equations (RANS). It can also be coupled with sediment transport equations. It is implemented on unstructured meshes using the Finite Element Method (FEM). The modeling results show the great detail the morphodynamic response attributed to each active factor (flow magnitude, sediment erosive properties, channel sinuosity, etc.), as well as paving the way and showing how to use the dimensionless relations obtained with the numerical experiments.

Direct Numerical Simulation of a Cavity-Stabilized Ethylene/Air Premixed Flame

NASA Astrophysics Data System (ADS)

Chen, Jacqueline; Konduri, Aditya; Kolla, Hemanth; Rauch, Andreas; Chelliah, Harsha

2016-11-01

Cavity flame holders have been shown to be important for flame stabilization in scramjet combustors. In the present study the stabilization of a lean premixed ethylene/air flame in a rectangular cavity at thermo-chemical conditions relevant to scramjet combustors is simulated using a compressible reacting multi-block direct numerical simulation solver, S3D, incorporating a 22 species ethylene-air reduced chemical model. The fuel is premixed with air to an equivalence ratio of 0.4 and enters the computational domain at Mach numbers between 0.3 and 0.6. An auxiliary inert channel flow simulation is used to provide the turbulent velocity profile at the inlet for the reacting flow simulation. The detailed interaction between intense turbulence, nonequilibrium concentrations of radical species formed in the cavity and mixing with the premixed main stream under density variations due to heat release rate and compressibility effects is quantified. The mechanism for flame stabilization is quantified in terms of relevant non-dimensional parameters, and detailed analysis of the flame and turbulence structure will be presented. We acknowledge the sponsorship of the AFOSR-NSF Joint Effort on Turbulent Combustion Model Assumptions and the DOE Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences.

The nonlinear Galerkin method: A multi-scale method applied to the simulation of homogeneous turbulent flows

NASA Technical Reports Server (NTRS)

Debussche, A.; Dubois, T.; Temam, R.

1993-01-01

Using results of Direct Numerical Simulation (DNS) in the case of two-dimensional homogeneous isotropic flows, the behavior of the small and large scales of Kolmogorov like flows at moderate Reynolds numbers are first analyzed in detail. Several estimates on the time variations of the small eddies and the nonlinear interaction terms were derived; those terms play the role of the Reynolds stress tensor in the case of LES. Since the time step of a numerical scheme is determined as a function of the energy-containing eddies of the flow, the variations of the small scales and of the nonlinear interaction terms over one iteration can become negligible by comparison with the accuracy of the computation. Based on this remark, a multilevel scheme which treats differently the small and the large eddies was proposed. Using mathematical developments, estimates of all the parameters involved in the algorithm, which then becomes a completely self-adaptive procedure were derived. Finally, realistic simulations of (Kolmorov like) flows over several eddy-turnover times were performed. The results are analyzed in detail and a parametric study of the nonlinear Galerkin method is performed.

E-detailing: information technology applied to pharmaceutical detailing.

PubMed

Montoya, Isaac D

2008-11-01

E-detailing can be best described as the use of information technology in the field of pharmaceutical detailing. It is becoming highly popular among pharmaceutical companies because it maximizes the time of the sales force, cuts down the cost of detailing and increases physician prescribing. Thus, the application of information technology is proving to be beneficial to both physicians and pharmaceutical companies. When e-detailing was introduced in 1996, it was limited to the US; however, numerous other countries soon adopted this novel approach to detailing and now it is popular in many developed nations. The objective of this paper is to demonstrate the rapid growth of e-detailing in the field of pharmaceutical marketing. A review of e-detailing literature was conducted in addition to personal conversations with physicians. E-detailing has the potential to reduce marketing costs, increase accessibility to physicians and offer many of the advantages of face-to-face detailing. E-detailing is gaining acceptance among physicians because they can access the information of a pharmaceutical product at their own time and convenience. However, the drug safety aspect of e-detailing has not been examined and e-detailing remains a supplement to traditional detailing and is not yet a replacement to it.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stubos, A.K.; Caseiras, C.P.; Buchlin, J.M.

The transient two-phase flow and phase change heat transfer processes in porous media are investigated. Based on an enthalpic approach, a one-domain formulation of the problem is developed, avoiding explicit internal boundary tracking between single- and two-phase regions. An efficient numerical scheme is applied to obtain the solution on a fixed two-dimensional grid. The transient response of a liquid-saturated, self-heated porous bed is examined in detail. A physical interpretation of a liquid-saturated, self-heated porous bed is examined in detail. A physical interpretation of the computed response to fast power transients is attempted. Comparisons with experimental data are made regarding themore » average void fraction and the limiting dryout heat flux. The numerical approach is extended, keeping the one-domain formulation, to include the surrounding wall structure in the calculation.« less

The Effects of Magnetic Nozzle Configurations on Plasma Thrusters

NASA Technical Reports Server (NTRS)

Turchi, P. J.

1997-01-01

Over the course of eight years, the Ohio State University has performed research in support of electric propulsion development efforts at the NASA Lewis Research Center, Cleveland, OH. This research has been largely devoted to plasma propulsion systems including MagnetoPlasmaDynamic (MPD) thrusters with externally-applied, solenoidal magnetic fields, hollow cathodes, and Pulsed Plasma Microthrusters (PPT's). Both experimental and theoretical work has been performed, as documented in four master's theses, two doctoral dissertations, and numerous technical papers. The present document is the final report for the grant period 5 December 1987 to 31 December 1995, and summarizes all activities. Detailed discussions of each area of activity are provided in appendices: Appendix 1 - Experimental studies of magnetic nozzle effects on plasma thrusters; Appendix 2 - Numerical modeling of applied-field MPD thrusters; Appendix 3 - Theoretical and experimental studies of hollow cathodes; and Appendix 4 -Theoretical, numerical and experimental studies of pulsed plasma thrusters. Especially notable results include the efficacy of using a solenoidal magnetic field downstream of a plasma thruster to collimate the exhaust flow, the development of a new understanding of applied-field MPD thrusters (based on experimentally-validated results from state-of-the art, numerical simulation) leading to predictions of improved performance, an experimentally-validated, first-principles model for orificed, hollow-cathode behavior, and the first time-dependent, two-dimensional calculations of ablation-fed, pulsed plasma thrusters.

On the limits of numerical astronomical solutions used in paleoclimate studies

NASA Astrophysics Data System (ADS)

Zeebe, Richard E.

2017-04-01

Numerical solutions of the equations of the Solar System estimate Earth's orbital parameters in the past and represent the backbone of cyclostratigraphy and astrochronology, now widely applied in geology and paleoclimatology. Given one numerical realization of a Solar System model (i.e., obtained using one code or integrator package), various parameters determine the properties of the solution and usually limit its validity to a certain time period. Such limitations are denoted here as "internal" and include limitations due to (i) the underlying physics/physical model and (ii) numerics. The physics include initial coordinates and velocities of Solar System bodies, treatment of the Moon and asteroids, the Sun's quadrupole moment, and the intrinsic dynamics of the Solar System itself, i.e., its chaotic nature. Numerical issues include solver algorithm, numerical accuracy (e.g., time step), and round-off errors. At present, internal limitations seem to restrict the validity of astronomical solutions to perhaps the past 50 or 60 myr. However, little is currently known about "external" limitations, that is, how do different numerical realizations compare, say, between different investigators using different codes and integrators? Hitherto only two solutions for Earth's eccentricity appear to be used in paleoclimate studies, provided by two different groups that integrated the full Solar System equations over the past >100 myr (Laskar and coworkers and Varadi et al. 2003). In this contribution, I will present results from new Solar System integrations for Earth's eccentricity obtained using the integrator package HNBody (Rauch and Hamilton 2002). I will discuss the various internal limitations listed above within the framework of the present simulations. I will also compare the results to the existing solutions, the details of which are still being sorted out as several simulations are still running at the time of writing.

Experimental and numerical studies of rotating drum grate furnace

NASA Astrophysics Data System (ADS)

Basista, Grzegorz; Szubel, Mateusz; Filipowicz, Mariusz; Tomczyk, Bartosz; Krakowiak, Joanna

Waste material from the meat industry can be taken into account as a biofuel. Studies confirm, that calorific value is higher and ash content is lower comparing to some conventional fuels. EU directives regulate details of thermal disposal of the waste material from the meat industry - especially in range of the process temperature and time of the particle presence in area of the combustion zone. The paper describes design of the rotating drum grate stove, dedicated to thermal disposal of the meat wastes as well as solid biomass (pellet, small bricket, wood chips) combustion. Device has been developed in frames of cooperation between AGH University of Science and Technology (Krakow, Poland) and producer focused on technologies of energy utilization of biomass in distributed generation. Results of measurements of selected operational parameters performed during startup of the furnace have been presented and discussed. Furthermore, numerical model of the combustion process has been developed to complement experimental results in range of the temperature and oxygen distribution in the area of the combustion chamber. ANSYS CFX solver has been applied to perform simulations including rotational domain related with specifics of operation of the device. Results of numerical modelling and experimental studies have been summarized and compared.

On the numerical modeling of sliding beams: A comparison of different approaches

NASA Astrophysics Data System (ADS)

Steinbrecher, Ivo; Humer, Alexander; Vu-Quoc, Loc

2017-11-01

The transient analysis of sliding beams represents a challenging problem of structural mechanics. Typically, the sliding motion superimposed by large flexible deformation requires numerical methods as, e.g., finite elements, to obtain approximate solutions. By means of the classical sliding spaghetti problem, the present paper provides a guideline to the numerical modeling with conventional finite element codes. For this purpose, two approaches, one using solid elements and one using beam elements, respectively, are employed in the analysis, and the characteristics of each approach are addressed. The contact formulation realizing the interaction of the beam with its support demands particular attention in the context of sliding structures. Additionally, the paper employs the sliding-beam formulation as a third approach, which avoids the numerical difficulties caused by the large sliding motion through a suitable coordinate transformation. The present paper briefly outlines the theoretical fundamentals of the respective approaches for the modeling of sliding structures and gives a detailed comparison by means of the sliding spaghetti serving as a representative example. The specific advantages and limitations of the different approaches with regard to accuracy and computational efficiency are discussed in detail. Through the comparison, the sliding-beam formulation, which proves as an effective approach for the modeling, can be validated for the general problem of a sliding structure subjected to large deformation.

Numerical modeling of runback water on ice protected aircraft surfaces

NASA Technical Reports Server (NTRS)

Al-Khalil, Kamel M.; Keith, Theo G., Jr.; Dewitt, Kenneth J.

1992-01-01

A numerical simulation for 'running wet' aircraft anti-icing systems is developed. The model includes breakup of the water film, which exists in regions of direct impingement, into individual rivulets. The wetness factor distribution resulting from the film breakup and the rivulet configuration on the surface are predicted in the numerical solution procedure. The solid wall is modeled as a multilayer structure and the anti-icing system used is of the thermal type utilizing hot air and/or electrical heating elements embedded with the layers. Details of the calculation procedure and the methods used are presented.

Numerical Algorithms Based on Biorthogonal Wavelets

NASA Technical Reports Server (NTRS)

Ponenti, Pj.; Liandrat, J.

1996-01-01

Wavelet bases are used to generate spaces of approximation for the resolution of bidimensional elliptic and parabolic problems. Under some specific hypotheses relating the properties of the wavelets to the order of the involved operators, it is shown that an approximate solution can be built. This approximation is then stable and converges towards the exact solution. It is designed such that fast algorithms involving biorthogonal multi resolution analyses can be used to resolve the corresponding numerical problems. Detailed algorithms are provided as well as the results of numerical tests on partial differential equations defined on the bidimensional torus.

Forward-facing cavity and opposing jet combined thermal protection system

NASA Astrophysics Data System (ADS)

Lu, H. B.; Liu, W. Q.

2012-12-01

This paper focuses on the design of a forward-facing cavity and opposing jet combined configuration for thermal protection system (TPS) of hypersonic vehicles. The cooling efficiency of the combined TPS was investigated numerically, and the numerical method was validated by the related experiment in the open literature. The flow field parameters, aerodynamic force, and surface heat flux distribution were obtained. The detailed numerical results show that this kind of combined TPS has an excellent impact on cooling the nose-tip, and it is suitable for the thermal protection of hypersonic vehicles which require long-range and time to cruise.

compuGUT: An in silico platform for simulating intestinal fermentation

NASA Astrophysics Data System (ADS)

Moorthy, Arun S.; Eberl, Hermann J.

The microbiota inhabiting the colon and its effect on health is a topic of significant interest. In this paper, we describe the compuGUT - a simulation tool developed to assist in exploring interactions between intestinal microbiota and their environment. The primary numerical machinery is implemented in C, and the accessory scripts for loading and visualization are prepared in bash (LINUX) and R. SUNDIALS libraries are employed for numerical integration, and googleVis API for interactive visualization. Supplementary material includes a concise description of the underlying mathematical model, and detailed characterization of numerical errors and computing times associated with implementation parameters.

Multidisciplinary optimization of an HSCT wing using a response surface methodology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Giunta, A.A.; Grossman, B.; Mason, W.H.

1994-12-31

Aerospace vehicle design is traditionally divided into three phases: conceptual, preliminary, and detailed. Each of these design phases entails a particular level of accuracy and computational expense. While there are several computer programs which perform inexpensive conceptual-level aircraft multidisciplinary design optimization (MDO), aircraft MDO remains prohibitively expensive using preliminary- and detailed-level analysis tools. This occurs due to the expense of computational analyses and because gradient-based optimization requires the analysis of hundreds or thousands of aircraft configurations to estimate design sensitivity information. A further hindrance to aircraft MDO is the problem of numerical noise which occurs frequently in engineering computations. Computermore » models produce numerical noise as a result of the incomplete convergence of iterative processes, round-off errors, and modeling errors. Such numerical noise is typically manifested as a high frequency, low amplitude variation in the results obtained from the computer models. Optimization attempted using noisy computer models may result in the erroneous calculation of design sensitivities and may slow or prevent convergence to an optimal design.« less

Characterization and compression of dissipative-soliton-resonance pulses in fiber lasers

PubMed Central

Li, Daojing; Li, Lei; Zhou, Junyu; Zhao, Luming; Tang, Dingyuan; Shen, Deyuan

2016-01-01

We report numerical and experimental studies of dissipative-soliton-resonance (DSR) in a fiber laser with a nonlinear optical loop mirror. The DSR pulse presents temporally a flat-top profile and a clamped peak power. Its spectrum has a rectangle profile with characteristic steep edges. It shows a unique behavior as pulse energy increases: The rectangle part of the spectrum is unchanged while the newly emerging spectrum sits on the center part and forms a peak. Experimental observations match well with the numerical results. Moreover, the detailed evolution of the DSR pulse compression is both numerically and experimentally demonstrated for the first time. An experimentally obtained DSR pulse of 63 ps duration is compressed down to 760 fs, with low-intensity pedestals using a grating pair. Before being compressed to its narrowest width, the pulse firstly evolves into a cat-ear profile, and the corresponding autocorrelation trace shows a crown shape, which distinguishes itself from properties of other solitons formed in fiber lasers. PMID:27025189

On the performance of the moment approximation for the numerical computation of fiber stress in turbulent channel flow

NASA Astrophysics Data System (ADS)

Gillissen, J. J. J.; Boersma, B. J.; Mortensen, P. H.; Andersson, H. I.

2007-03-01

Fiber-induced drag reduction can be studied in great detail by means of direct numerical simulation [J. S. Paschkewitz et al., J. Fluid Mech. 518, 281 (2004)]. To account for the effect of the fibers, the Navier-Stokes equations are supplemented by the fiber stress tensor, which depends on the distribution function of fiber orientation angles. We have computed this function in turbulent channel flow, by solving the Fokker-Planck equation numerically. The results are used to validate an approximate method for calculating fiber stress, in which the second moment of the orientation distribution is solved. Since the moment evolution equations contain higher-order moments, a closure relation is required to obtain as many equations as unknowns. We investigate the performance of the eigenvalue-based optimal fitted closure scheme [J. S. Cintra and C. L. Tucker, J. Rheol. 39, 1095 (1995)]. The closure-predicted stress and flow statistics in two-way coupled simulations are within 10% of the "exact" Fokker-Planck solution.

All-optical 4-bit binary to binary coded decimal converter with the help of semiconductor optical amplifier-assisted Sagnac switch

NASA Astrophysics Data System (ADS)

Bhattachryya, Arunava; Kumar Gayen, Dilip; Chattopadhyay, Tanay

2013-04-01

All-optical 4-bit binary to binary coded decimal (BCD) converter has been proposed and described, with the help of semiconductor optical amplifier (SOA)-assisted Sagnac interferometric switches in this manuscript. The paper describes all-optical conversion scheme using a set of all-optical switches. BCD is common in computer systems that display numeric values, especially in those consisting solely of digital logic with no microprocessor. In many personal computers, the basic input/output system (BIOS) keep the date and time in BCD format. The operations of the circuit are studied theoretically and analyzed through numerical simulations. The model accounts for the SOA small signal gain, line-width enhancement factor and carrier lifetime, the switching pulse energy and width, and the Sagnac loop asymmetry. By undertaking a detailed numerical simulation the influence of these key parameters on the metrics that determine the quality of switching is thoroughly investigated.

An Analytical-Numerical Model for Two-Phase Slug Flow through a Sudden Area Change in Microchannels

DOE PAGES

Momen, A. Mehdizadeh; Sherif, S. A.; Lear, W. E.

2016-01-01

In this article, two new analytical models have been developed to calculate two-phase slug flow pressure drop in microchannels through a sudden contraction. Even though many studies have been reported on two-phase flow in microchannels, considerable discrepancies still exist, mainly due to the difficulties in experimental setup and measurements. Numerical simulations were performed to support the new analytical models and to explore in more detail the physics of the flow in microchannels with a sudden contraction. Both analytical and numerical results were compared to the available experimental data and other empirical correlations. Results show that models, which were developed basedmore » on the slug and semi-slug assumptions, agree well with experiments in microchannels. Moreover, in contrast to the previous empirical correlations which were tuned for a specific geometry, the new analytical models are capable of taking geometrical parameters as well as flow conditions into account.« less

Cylindrical and spherical Akhmediev breather and freak waves in ultracold neutral plasmas

NASA Astrophysics Data System (ADS)

El-Tantawy, S. A.; El-Awady, E. I.

2018-01-01

The properties of cylindrical and spherical ion-acoustic breathers Akhmediev breather and freak waves in strongly coupled ultracold neutral plasmas (UNPs), whose constituents are inertial strongly coupled ions and weakly coupled Maxwellian electrons, are investigated numerically. Using the derivative expansion method, the basic set of fluid equations is reduced to a nonplanar (cylindrical and spherical)/modified nonlinear Schrödinger equation (mNLSE). The analytical solutions of the mNLSE were not possible until now, so their numerical solutions are obtained using the finite difference scheme with the help of the Dirichlet boundary conditions. Moreover, the criteria for the existence and propagation of breathers are discussed in detail. The geometrical effects due to the cylindrical and spherical geometries on the breather profile are studied numerically. It is found that the propagation of the ion-acoustic breathers in one-dimensional planar and nonplanar geometries is very different. Finally, our results may help to manipulate matter breathers experimentally in UNPs.

Testing numerical models for boulder transport due to high energy marine wave events: examples from the Saurashtra coast, Western India

NASA Astrophysics Data System (ADS)

Chavare, Kushal; Bhatt, Nilesh; Prizomwala, Siddharth

2017-04-01

The boulder deposits on the coasts are interpreted and evaluated as high energy marine wave events like tsunami. Several numerical models are now available to estimate wave height and/or run up of the tsunami wave. The coast of Saurashtra, facing the Arabian Sea on its west hosts such deposits in younger ( 1 and 6 ka) and older ( 35 ka) coastal records. The dimensions, characteristics and morphology of these boulders were studied with different numeric models and were applied with reference to submerged, sub-aerial and joint bounded boulder scenarios which were combined with the local control variables like roughness coefficient, slope of platforms, fractures, shoaling effect, etc. The application of these models indicated a significant role of local control variables in boulder dislodgment, transport and final emplacement on shore platform. Examples from three different sites from the coast of Saurashtra, western India are reported and discussed in detail.

Effect of Second-Order and Fully Nonlinear Wave Kinematics on a Tension-Leg-Platform Wind Turbine in Extreme Wave Conditions: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robertson, Amy N; Jonkman, Jason; Pegalajar-Jurado, Antonio

In this study, we assess the impact of different wave kinematics models on the dynamic response of a tension-leg-platform wind turbine. Aero-hydro-elastic simulations of the floating wind turbine are carried out employing linear, second-order, and fully nonlinear kinematics using the Morison equation for the hydrodynamic forcing. The wave kinematics are computed from either theoretical or measured signals of free-surface elevation. The numerical results from each model are compared to results from wave basin tests on a scaled prototype. The comparison shows that sub and superharmonic responses can be introduced by second-order and fully nonlinear wave kinematics. The response at themore » wave frequency range is better reproduced when kinematics are generated from the measured surface elevation. In the future, the numerical response may be further improved by replacing the global, constant damping coefficients in the model by a more detailed, customizable definition of the user-defined numerical damping.« less

Effect of Second-Order and Fully Nonlinear Wave Kinematics on a Tension-Leg-Platform Wind Turbine in Extreme Wave Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robertson, Amy N; Jonkman, Jason; Pegalajar-Jurado, Antonio

In this study, we assess the impact of different wave kinematics models on the dynamic response of a tension-leg-platform wind turbine. Aero-hydro-elastic simulations of the floating wind turbine are carried out employing linear, second-order, and fully nonlinear kinematics using the Morison equation for the hydrodynamic forcing. The wave kinematics are computed from either theoretical or measured signals of free-surface elevation. The numerical results from each model are compared to results from wave basin tests on a scaled prototype. The comparison shows that sub and superharmonic responses can be introduced by second-order and fully nonlinear wave kinematics. The response at themore » wave frequency range is better reproduced when kinematics are generated from the measured surface elevation. In the future, the numerical response may be further improved by replacing the global, constant damping coefficients in the model by a more detailed, customizable definition of the user-defined numerical damping.« less

Perforation of thin aluminum alloy plates by blunt projectiles: An experimental and numerical investigation

NASA Astrophysics Data System (ADS)

Wei, G.; Zhang, W.

2014-04-01

Reducing the armor weight has become a research focus in terms of armored material. Due to high strength-to-density ratio, aluminum alloy has become a potential light armored material. In this study, both lab-scale ballistic test and finite element simulation were adopted to examine the ballistic resistance of aluminum alloy targets. Blunt high strength steel projectiles with 12.7 mm diameter were launched by light gas gun against 3.3 mm thickness 7A04 aluminum alloy plates at a velocity of 90~170 m/s. The ballistic limit velocity was obtained. Plugging failure and obvious structure deformation of targets were observed. Corresponding 2D finite element simulations were conducted by ABAQUS/EXPLICIT combined with material performance testing. The validity of numerical simulations was verified by comparing with the experimental results. Detailed analysis of the failure modes and characters of the targets were carried out to reveal the target damage mechanism combined with the numerical simulation.

Numerical investigation of homogeneous cavitation nucleation in a microchannel

NASA Astrophysics Data System (ADS)

Lyu, Xiuxiu; Pan, Shucheng; Hu, Xiangyu; Adams, Nikolaus A.

2018-06-01

The physics of nucleation in water is an important issue for many areas, ranging from biomedical to engineering applications. Within the present study, we investigate numerically homogeneous nucleation in a microchannel induced by shock reflection to gain a better understanding of the mechanism of homogeneous nucleation. The liquid expands due to the reflected shock and homogeneous cavitation nuclei are generated. An Eulerian-Lagrangian approach is employed for modeling this process in a microchanel. Two-dimensional axisymmetric Euler equations are solved for obtaining the time evolution of shock, gas bubble, and the ambient fluid. The dynamics of dispersed vapor bubbles is coupled with the surrounding fluid in a Lagrangian framework, describing bubble location and bubble size variation. Our results reproduce nuclei distributions at different stages of homogeneous nucleation and are in good agreement with experimental results. We obtain numerical data for the negative pressure that water can sustain under the process of homogeneous nucleation. An energy transformation description for the homogeneous nucleation inside a microchannel flow is derived and analyzed in detail.

Numerical studies of the fluid and optical fields associated with complex cavity flows

NASA Technical Reports Server (NTRS)

Atwood, Christopher A.

1992-01-01

Numerical solutions for the flowfield about several cavity configurations have been computed using the Reynolds averaged Navier-Stokes equations. Comparisons between numerical and experimental results are made in two dimensions for free shear layers and a rectangular cavity, and in three dimensions for the transonic aero-window problem of the Stratospheric Observatory for Infrared Astronomy (SOFIA). Results show that dominant acoustic frequencies and magnitudes of the self excited resonant cavity flows compare well with the experiment. In addition, solution sensitivity to artificial dissipation and grid resolution levels are determined. Optical path distortion due to the flow field is modelled geometrically and is found to match the experiment. The fluid field was computed using a diagonalized scheme within an overset mesh framework. An existing code, OVERFLOW, was utilized with the additions of characteristic boundary condition and output routines required for reduction of the unsteady data. The newly developed code is directly applicable to a generalized three dimensional structured grid zone. Details are provided in a paper included in Appendix A.

Structural characterization and numerical simulations of flow properties of standard and reservoir carbonate rocks using micro-tomography

NASA Astrophysics Data System (ADS)

Islam, Amina; Chevalier, Sylvie; Sassi, Mohamed

2018-04-01

With advances in imaging techniques and computational power, Digital Rock Physics (DRP) is becoming an increasingly popular tool to characterize reservoir samples and determine their internal structure and flow properties. In this work, we present the details for imaging, segmentation, as well as numerical simulation of single-phase flow through a standard homogenous Silurian dolomite core plug sample as well as a heterogeneous sample from a carbonate reservoir. We develop a procedure that integrates experimental results into the segmentation step to calibrate the porosity. We also look into using two different numerical tools for the simulation; namely Avizo Fire Xlab Hydro that solves the Stokes' equations via the finite volume method and Palabos that solves the same equations using the Lattice Boltzmann Method. Representative Elementary Volume (REV) and isotropy studies are conducted on the two samples and we show how DRP can be a useful tool to characterize rock properties that are time consuming and costly to obtain experimentally.

Using growth and arrest of Richtmyer-Meshkov instabilities and Lagrangian simulations to study high-rate material strength

NASA Astrophysics Data System (ADS)

Prime, M. B.; Vaughan, D. E.; Preston, D. L.; Buttler, W. T.; Chen, S. R.; Oró, D. M.; Pack, C.

2014-05-01

Experiments applying a supported shock through mating surfaces (Atwood number = 1) with geometrical perturbations have been proposed for studying strength at strain rates up to 107/s using Richtmyer-Meshkov (RM) instabilities. Buttler et al. recently reported experimental results for RM instability growth in copper but with an unsupported shock applied by high explosives and the geometrical perturbations on the opposite free surface (Atwood number = -1). This novel configuration allowed detailed experimental observation of the instability growth and arrest. We present results and interpretation from numerical simulations of the Buttler RM instability experiments. Highly-resolved, two-dimensional simulations were performed using a Lagrangian hydrocode and the Preston-Tonks-Wallace (PTW) strength model. The model predictions show good agreement with the data. The numerical simulations are used to examine various assumptions previously made in an analytical model and to estimate the sensitivity of such experiments to material strength.

The analysis of composite laminated beams using a 2D interpolating meshless technique

NASA Astrophysics Data System (ADS)

Sadek, S. H. M.; Belinha, J.; Parente, M. P. L.; Natal Jorge, R. M.; de Sá, J. M. A. César; Ferreira, A. J. M.

2018-02-01

Laminated composite materials are widely implemented in several engineering constructions. For its relative light weight, these materials are suitable for aerospace, military, marine, and automotive structural applications. To obtain safe and economical structures, the modelling analysis accuracy is highly relevant. Since meshless methods in the recent years achieved a remarkable progress in computational mechanics, the present work uses one of the most flexible and stable interpolation meshless technique available in the literature—the Radial Point Interpolation Method (RPIM). Here, a 2D approach is considered to numerically analyse composite laminated beams. Both the meshless formulation and the equilibrium equations ruling the studied physical phenomenon are presented with detail. Several benchmark beam examples are studied and the results are compared with exact solutions available in the literature and the results obtained from a commercial finite element software. The results show the efficiency and accuracy of the proposed numeric technique.

Calculation of H2-He Flow with Nonequilibrium Ionization and Radiation: an Interim Report

NASA Technical Reports Server (NTRS)

Furudate, Michiko; Chang, Keun-Shik

2005-01-01

The nonequilibrium ionization process in hydrogen-helium mixture behind a strong shock wave is studied numerically using the detailed ionization rate model developed recently by Park which accounts for emission and absorption of Lyman lines. The study finds that, once the avalanche ionization is started, the Lyman line is self-absorbed. The intensity variation of the radiation at 5145 Angstroms found by Leibowitz in a shock tube experiment can be numerically reproduced by assuming that ionization behind the shock wave prior to the onset of avalanche ionization is 1.3%. Because 1.3% initial ionization is highly unlikely, Leibowitz s experimental data is deemed questionable. By varying the initial electron density value in the calculation, the calculated ionization equilibration time is shown to increase approximately as inverse square-root of the initial electron density value. The true ionization equilibration time is most likely much longer than the value found by Leibowitz.

Quantification of topological changes of vorticity contours in two-dimensional Navier-Stokes flow.

PubMed

Ohkitani, Koji; Al Sulti, Fayeza

2010-06-01

A characterization of reconnection of vorticity contours is made by direct numerical simulations of the two-dimensional Navier-Stokes flow at a relatively low Reynolds number. We identify all the critical points of the vorticity field and classify them by solving an eigenvalue problem of its Hessian matrix on the basis of critical-point theory. The numbers of hyperbolic (saddles) and elliptic (minima and maxima) points are confirmed to satisfy Euler's index theorem numerically. Time evolution of these indices is studied for a simple initial condition. Generally speaking, we have found that the indices are found to decrease in number with time. This result is discussed in connection with related works on streamline topology, in particular, the relationship between stagnation points and the dissipation. Associated elementary procedures in physical space, the merging of vortices, are studied in detail for a number of snapshots. A similar analysis is also done using the stream function.

A two-dimensional numerical simulation of a supersonic, chemically reacting mixing layer

NASA Technical Reports Server (NTRS)

Drummond, J. Philip

1988-01-01

Research has been undertaken to achieve an improved understanding of physical phenomena present when a supersonic flow undergoes chemical reaction. A detailed understanding of supersonic reacting flows is necessary to successfully develop advanced propulsion systems now planned for use late in this century and beyond. In order to explore such flows, a study was begun to create appropriate physical models for describing supersonic combustion, and to develop accurate and efficient numerical techniques for solving the governing equations that result from these models. From this work, two computer programs were written to study reacting flows. Both programs were constructed to consider the multicomponent diffusion and convection of important chemical species, the finite rate reaction of these species, and the resulting interaction of the fluid mechanics and the chemistry. The first program employed a finite difference scheme for integrating the governing equations, whereas the second used a hybrid Chebyshev pseudospectral technique for improved accuracy.

A numerical study of linear and nonlinear kinematic models in fish swimming with the DSD/SST method

NASA Astrophysics Data System (ADS)

Tian, Fang-Bao

2015-03-01

Flow over two fish (modeled by two flexible plates) in tandem arrangement is investigated by solving the incompressible Navier-Stokes equations numerically with the DSD/SST method to understand the differences between the geometrically linear and nonlinear models. In the simulation, the motions of the plates are reconstructed from a vertically flowing soap film tunnel experiment with linear and nonlinear kinematic models. Based on the simulations, the drag, lift, power consumption, vorticity and pressure fields are discussed in detail. It is found that the linear and nonlinear models are able to reasonably predict the forces and power consumption of a single plate in flow. Moreover, if multiple plates are considered, these two models yield totally different results, which implies that the nonlinear model should be used. The results presented in this work provide a guideline for future studies in fish swimming.

A motion artefact study and locally deforming objects in computerized tomography

NASA Astrophysics Data System (ADS)

Hahn, Bernadette N.

2017-11-01

Movements of the object during the data collection in computerized tomography can introduce motion artefacts in the reconstructed image. They can be reduced by employing information about the dynamic behaviour within the reconstruction step. However, inaccuracies concerning the movement are inevitable in practice. In this article, we give an explicit characterization of what is visible in an image obtained by a reconstruction algorithm with incorrect motion information. Then, we use this result to study in detail the situation of locally deforming objects, i.e. individual parts of the object have a different dynamic behaviour. In this context, we prove that additional artefacts arise due to the global nature of the Radon transform, even if the motion is exactly known. Based on our analysis, we propose a numerical scheme to reduce these artefacts in the reconstructed image. All our results are illustrated by numerical examples.

Numerical and experimental study on a pulsed-dc plasma jet

NASA Astrophysics Data System (ADS)

Liu, X. Y.; Pei, X. K.; Lu, X. P.; Liu, D. W.

2014-06-01

A numerical and experimental study of plasma jet propagation in a low-temperature, atmospheric-pressure, helium jet in ambient air is presented. A self-consistent, multi-species, two-dimensional axially symmetric plasma model with detailed finite-rate chemistry of helium-air mixture composition is used to provide insights into the propagation of the plasma jet. The obtained simulation results suggest that the sheath forms near the dielectric tube inner surface and shields the plasma channel from the tube surface. The strong electric field at the edge of the dielectric field enhances the ionization in the air mixing layer; therefore, the streamer head becomes ring-shaped when the streamer runs out of the tube. The avalanche-to-streamer transition is the main mechanism of streamer advancement. Penning ionization dominates the ionization reactions and increases the electrical conductivity of the plasma channel. The simulation results are supported by experimental observations under similar discharge conditions.

25 Years of Self-organized Criticality: Numerical Detection Methods

NASA Astrophysics Data System (ADS)

McAteer, R. T. James; Aschwanden, Markus J.; Dimitropoulou, Michaila; Georgoulis, Manolis K.; Pruessner, Gunnar; Morales, Laura; Ireland, Jack; Abramenko, Valentyna

2016-01-01

The detection and characterization of self-organized criticality (SOC), in both real and simulated data, has undergone many significant revisions over the past 25 years. The explosive advances in the many numerical methods available for detecting, discriminating, and ultimately testing, SOC have played a critical role in developing our understanding of how systems experience and exhibit SOC. In this article, methods of detecting SOC are reviewed; from correlations to complexity to critical quantities. A description of the basic autocorrelation method leads into a detailed analysis of application-oriented methods developed in the last 25 years. In the second half of this manuscript space-based, time-based and spatial-temporal methods are reviewed and the prevalence of power laws in nature is described, with an emphasis on event detection and characterization. The search for numerical methods to clearly and unambiguously detect SOC in data often leads us outside the comfort zone of our own disciplines—the answers to these questions are often obtained by studying the advances made in other fields of study. In addition, numerical detection methods often provide the optimum link between simulations and experiments in scientific research. We seek to explore this boundary where the rubber meets the road, to review this expanding field of research of numerical detection of SOC systems over the past 25 years, and to iterate forwards so as to provide some foresight and guidance into developing breakthroughs in this subject over the next quarter of a century.

Numerical method for predicting flow characteristics and performance of nonaxisymmetric nozzles. Part 2: Applications

NASA Technical Reports Server (NTRS)

Thomas, P. D.

1980-01-01

A computer implemented numerical method for predicting the flow in and about an isolated three dimensional jet exhaust nozzle is summarized. The approach is based on an implicit numerical method to solve the unsteady Navier-Stokes equations in a boundary conforming curvilinear coordinate system. Recent improvements to the original numerical algorithm are summarized. Equations are given for evaluating nozzle thrust and discharge coefficient in terms of computed flowfield data. The final formulation of models that are used to simulate flow turbulence effect is presented. Results are presented from numerical experiments to explore the effect of various quantities on the rate of convergence to steady state and on the final flowfield solution. Detailed flowfield predictions for several two and three dimensional nozzle configurations are presented and compared with wind tunnel experimental data.

Examination of two methods of describing the thermodynamic properties of oxygen near the critical point

NASA Technical Reports Server (NTRS)

Rees, T. H.; Suttles, J. T.

1972-01-01

A computer study was conducted to compare the numerical behavior of two approaches to describing the thermodynamic properties of oxygen near the critical point. Data on the relative differences between values of specific heats at constant pressure (sub p) density, and isotherm and isochor derivatives of the equation of state are presented for selected supercritical pressures at temperatures in the range 100 to 300 K. The results of a more detailed study of the sub p representations afforded by the two methods are also presented.

A Sneak Preview of the E-ELT Design Reference Science Plan Questionnaire Results

NASA Astrophysics Data System (ADS)

Kissler-Patig, M.; Küpcü Yoldaş, A.; Liske, J.

2009-12-01

The European Extremely Large Telescope is in its detailed design phase until the end of 2010. During this period, the telescope design is being consolidated and instrument and operation concepts are being studied. The scientific users are feeding back requirements into the project in numerous ways. One of them, the Design Reference Science Plan, was an opportunity for the entire community to provide direct feedback to the project. Here, we summarise the first results from this study. The full report will appear in the first half of 2010.

Energy balance in TM-1-MH Tokamak (ohmical heating)

NASA Astrophysics Data System (ADS)

Stoeckel, J.; Koerbel, S.; Kryska, L.; Kopecky, V.; Dadalec, V.; Datlov, J.; Jakubka, K.; Magula, P.; Zacek, F.; Pereverzev, G. V.

1981-10-01

Plasma in the TM-1-MH Tokamak was experimentally studied in the parameter range: tor. mg. field B = 1,3 T, plasma current I sub p = 14 kA, electron density N sub E 3.10 to the 19th power cubic meters. The two numerical codes are available for the comparison with experimental data. TOKATA-code solves simplified energy balance equations for electron and ion components. TOKSAS-code solves the detailed energy balance of the ion component.

Theoretical and experimental studies of hyperreflective polymer-network cholesteric liquid crystal structures with helicity inversion

NASA Astrophysics Data System (ADS)

Tasolamprou, A. C.; Mitov, M.; Zografopoulos, D. C.; Kriezis, E. E.

2009-03-01

Single-layer cholesteric liquid crystals exhibit a reflection coefficient which is at most 50% for unpolarized incident light. We give theoretical and experimental evidence of single-layer polymer-stabilized cholesteric liquid-crystalline structures that demonstrate hyper-reflective properties. Such original features are derived by the concurrent and randomly interlaced presence of both helicities. The fundamental properties of such structures are revealed by detailed numerical simulations based on a stochastic approach.

Three-dimensional poor man's Navier-Stokes equation: a discrete dynamical system exhibiting k(-5/3) inertial subrange energy scaling.

PubMed

McDonough, J M

2009-06-01

Outline of the derivation and mathematical and physical interpretations are presented for a discrete dynamical system known as the "poor man's Navier-Stokes equation." Numerical studies demonstrate that velocity fields produced by this dynamical system are similar to those seen in laboratory experiments and in detailed simulations, and they lead to scaling for the turbulence kinetic energy spectrum in accord with Kolmogorov K41 theory.

Orbital evolution studies of planet-crossing asteroids

NASA Astrophysics Data System (ADS)

Hahn, Gerhard; Lagerkvist, Claes-Ingvar

The orbits of 26 planet-crossing Aten-Apollo-Amor asteroids are predicted on the basis of numerical integrations covering 33,000 or 100,000 yrs; the values reported supplement the preliminary findings of Hahn and Lagerkvist (1987). A solar-system dynamics model accounting for the effects of all planets from Venus to Neptune is employed, along with the 15th-order integration algorithm RADAU (Everhart, 1985). The results are presented in extensive tables and graphs and discussed in detail.

The behavior limestone under explosive load

NASA Astrophysics Data System (ADS)

Orlov, M. Yu; Orlova, Yu N.; Bogomolov, G. N.

2016-11-01

Limestone behavior under explosive loading was investigated. The behavior of the limestone by the action of the three types of explosives, including granular, ammonite and emulsion explosives was studied in detail. The shape and diameter of the explosion craters were obtained. The observed fragments after the blast have been classified as large, medium and small fragments. Three full-scale experiments were carried out. The research results can be used as a qualitative test for the approbation of numerical methods.

Simulation study on combustion of biomass

NASA Astrophysics Data System (ADS)

Zhao, M. L.; Liu, X.; Cheng, J. W.; Liu, Y.; Jin, Y. A.

2017-01-01

Biomass combustion is the most common energy conversion technology, offering the advantages of low cost, low risk and high efficiency. In this paper, the transformation and transfer of biomass in the process of combustion are discussed in detail. The process of furnace combustion and gas phase formation was analyzed by numerical simulation. The experimental results not only help to optimize boiler operation and realize the efficient combustion of biomass, but also provide theoretical basis for the improvement of burner technology.

Fourier/Chebyshev methods for the incompressible Navier-Stokes equations in finite domains

NASA Technical Reports Server (NTRS)

Corral, Roque; Jimenez, Javier

1992-01-01

A fully spectral numerical scheme for the incompressible Navier-Stokes equations in domains which are infinite or semi-infinite in one dimension. The domain is not mapped, and standard Fourier or Chebyshev expansions can be used. The handling of the infinite domain does not introduce any significant overhead. The scheme assumes that the vorticity in the flow is essentially concentrated in a finite region, which is represented numerically by standard spectral collocation methods. To accomodate the slow exponential decay of the velocities at infinity, extra expansion functions are introduced, which are handled analytically. A detailed error analysis is presented, and two applications to Direct Numerical Simulation of turbulent flows are discussed in relation with the numerical performance of the scheme.

Problems with numerical techniques: Application to mid-loop operation transients

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bryce, W.M.; Lillington, J.N.

1997-07-01

There has been an increasing need to consider accidents at shutdown which have been shown in some PSAs to provide a significant contribution to overall risk. In the UK experience has been gained at three levels: (1) Assessment of codes against experiments; (2) Plant studies specifically for Sizewell B; and (3) Detailed review of modelling to support the plant studies for Sizewell B. The work has largely been carried out using various versions of RELAP5 and SCDAP/RELAP5. The paper details some of the problems that have needed to be addressed. It is believed by the authors that these kinds ofmore » problems are probably generic to most of the present generation system thermal-hydraulic codes for the conditions present in mid-loop transients. Thus as far as possible these problems and solutions are proposed in generic terms. The areas addressed include: condensables at low pressure, poor time step calculation detection, water packing, inadequate physical modelling, numerical heat transfer and mass errors. In general single code modifications have been proposed to solve the problems. These have been very much concerned with means of improving existing models rather than by formulating a completely new approach. They have been produced after a particular problem has arisen. Thus, and this has been borne out in practice, the danger is that when new transients are attempted, new problems arise which then also require patching.« less

Performance testing of a vertical Bridgman furnace using experiments and numerical modeling

NASA Astrophysics Data System (ADS)

Rosch, W. R.; Fripp, A. L.; Debnam, W. J.; Pendergrass, T. K.

1997-04-01

This paper details a portion of the work performed in preparation for the growth of lead tin telluride crystals during a Space Shuttle flight. A coordinated effort of experimental measurements and numerical modeling was completed to determine the optimum growth parameters and the performance of the furnace. This work was done using NASA's Advanced Automated Directional Solidification Furnace, but the procedures used should be equally valid for other vertical Bridgman furnaces.

3D numerical simulation of transient processes in hydraulic turbines

NASA Astrophysics Data System (ADS)

Cherny, S.; Chirkov, D.; Bannikov, D.; Lapin, V.; Skorospelov, V.; Eshkunova, I.; Avdushenko, A.

2010-08-01

An approach for numerical simulation of 3D hydraulic turbine flows in transient operating regimes is presented. The method is based on a coupled solution of incompressible RANS equations, runner rotation equation, and water hammer equations. The issue of setting appropriate boundary conditions is considered in detail. As an illustration, the simulation results for runaway process are presented. The evolution of vortex structure and its effect on computed runaway traces are analyzed.

Stability analysis of multigrid acceleration methods for the solution of partial differential equations

NASA Technical Reports Server (NTRS)

Fay, John F.

1990-01-01

A calculation is made of the stability of various relaxation schemes for the numerical solution of partial differential equations. A multigrid acceleration method is introduced, and its effects on stability are explored. A detailed stability analysis of a simple case is carried out and verified by numerical experiment. It is shown that the use of multigrids can speed convergence by several orders of magnitude without adversely affecting stability.

Stochastic porous media modeling and high-resolution schemes for numerical simulation of subsurface immiscible fluid flow transport

NASA Astrophysics Data System (ADS)

Brantson, Eric Thompson; Ju, Binshan; Wu, Dan; Gyan, Patricia Semwaah

2018-04-01

This paper proposes stochastic petroleum porous media modeling for immiscible fluid flow simulation using Dykstra-Parson coefficient (V DP) and autocorrelation lengths to generate 2D stochastic permeability values which were also used to generate porosity fields through a linear interpolation technique based on Carman-Kozeny equation. The proposed method of permeability field generation in this study was compared to turning bands method (TBM) and uniform sampling randomization method (USRM). On the other hand, many studies have also reported that, upstream mobility weighting schemes, commonly used in conventional numerical reservoir simulators do not accurately capture immiscible displacement shocks and discontinuities through stochastically generated porous media. This can be attributed to high level of numerical smearing in first-order schemes, oftentimes misinterpreted as subsurface geological features. Therefore, this work employs high-resolution schemes of SUPERBEE flux limiter, weighted essentially non-oscillatory scheme (WENO), and monotone upstream-centered schemes for conservation laws (MUSCL) to accurately capture immiscible fluid flow transport in stochastic porous media. The high-order schemes results match well with Buckley Leverett (BL) analytical solution without any non-oscillatory solutions. The governing fluid flow equations were solved numerically using simultaneous solution (SS) technique, sequential solution (SEQ) technique and iterative implicit pressure and explicit saturation (IMPES) technique which produce acceptable numerical stability and convergence rate. A comparative and numerical examples study of flow transport through the proposed method, TBM and USRM permeability fields revealed detailed subsurface instabilities with their corresponding ultimate recovery factors. Also, the impact of autocorrelation lengths on immiscible fluid flow transport were analyzed and quantified. A finite number of lines used in the TBM resulted into visual artifact banding phenomenon unlike the proposed method and USRM. In all, the proposed permeability and porosity fields generation coupled with the numerical simulator developed will aid in developing efficient mobility control schemes to improve on poor volumetric sweep efficiency in porous media.

Spectra, current flow, and wave-function morphology in a model PT -symmetric quantum dot with external interactions

NASA Astrophysics Data System (ADS)

Tellander, Felix; Berggren, Karl-Fredrik

2017-04-01

In this paper we use numerical simulations to study a two-dimensional (2D) quantum dot (cavity) with two leads for passing currents (electrons, photons, etc.) through the system. By introducing an imaginary potential in each lead the system is made symmetric under parity-time inversion (PT symmetric). This system is experimentally realizable in the form of, e.g., quantum dots in low-dimensional semiconductors, optical and electromagnetic cavities, and other classical wave analogs. The computational model introduced here for studying spectra, exceptional points (EPs), wave-function symmetries and morphology, and current flow includes thousands of interacting states. This supplements previous analytic studies of few interacting states by providing more detail and higher resolution. The Hamiltonian describing the system is non-Hermitian; thus, the eigenvalues are, in general, complex. The structure of the wave functions and probability current densities are studied in detail at and in between EPs. The statistics for EPs is evaluated, and reasons for a gradual dynamical crossover are identified.

Effect of baffle size and orientation on lateral sloshing of partially filled containers: a numerical study

NASA Astrophysics Data System (ADS)

Ali, Sajid; Kamran, Muhammad Ali; Khan, Sikandar

2017-11-01

The fluid sloshing in partially filled road tankers has significantly increased the number of road accidents for the last few decades. Significant research is needed to investigate and to come up with optimum baffles designs that can help to increase the rollover stability of the partially filled tankers. In this investigation, a detailed analysis of the anti-slosh effectiveness of different baffle configurations is presented. This investigation extends the already available studies in the literature by introducing new modified rectangular tank's shapes that correspond to maximum rollover stability as compared to the already available standard tank designs. The various baffles configurations that are analysed in this study are horizontal, vertical, vertical-horizontal and diagonal. In the current study, numerical investigations are performed for rectangular, elliptical and circular tank shapes. Lateral sloshing, caused by constant radius turn manoeuvre, was simulated numerically using the volume-of-fluid method, and effect of the different baffle configurations was analysed. The effect of tank fill levels on sloshing measured in terms of horizontal force and pressure moments is also reported for with and without baffles configurations. Vertical baffles were the most effective at reducing sloshing in modified rectangular tanks, whereas a combination of horizontal and vertical baffles gave better results for the circular and elliptical tanks geometries.

Dissipative exciton transfer in donor-bridge-acceptor systems: numerical renormalization group calculation of equilibrium properties.

PubMed

Tornow, Sabine; Tong, Ning-Hua; Bulla, Ralf

2006-07-05

We present a detailed model study of exciton transfer processes in donor-bridge-acceptor (DBA) systems. Using a model which includes the intermolecular Coulomb interaction and the coupling to a dissipative environment we calculate the phase diagram, the absorption spectrum as well as dynamic equilibrium properties with the numerical renormalization group. This method is non-perturbative and therefore allows one to cover the full parameter space, especially the case when the intermolecular Coulomb interaction is of the same order as the coupling to the environment and perturbation theory cannot be applied. For DBA systems with up to six sites we found a transition to the localized phase (self-trapping) depending on the coupling to the dissipative environment. We discuss various criteria which favour delocalized exciton transfer.

Numerical studies of identification in nonlinear distributed parameter systems

NASA Technical Reports Server (NTRS)

Banks, H. T.; Lo, C. K.; Reich, Simeon; Rosen, I. G.

1989-01-01

An abstract approximation framework and convergence theory for the identification of first and second order nonlinear distributed parameter systems developed previously by the authors and reported on in detail elsewhere are summarized and discussed. The theory is based upon results for systems whose dynamics can be described by monotone operators in Hilbert space and an abstract approximation theorem for the resulting nonlinear evolution system. The application of the theory together with numerical evidence demonstrating the feasibility of the general approach are discussed in the context of the identification of a first order quasi-linear parabolic model for one dimensional heat conduction/mass transport and the identification of a nonlinear dissipation mechanism (i.e., damping) in a second order one dimensional wave equation. Computational and implementational considerations, in particular, with regard to supercomputing, are addressed.

Bonded orthotropic strips with cracks

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.

1978-01-01

The elastostatic problem for a nonhomogeneous plane which consists of two sets of periodically arranged dissimilar orthotropic strips is considered. First, the problem of cracks fully imbedded into the homogeneous strips is considered. Then, the singular behavior of the stresses for two special crack geometries is studied in some detail. The first is the case of a broken laminate in which the crack tips touch the interfaces. The second is the case of cracks crossing the interfaces. A number of numerical examples are worked out in order to separate the primary material parameters influencing the stress intensity factors and the powers of stress singularity, and to determine the trends regarding the influence of the secondary parameters. Finally, some numerical results are given for the stress intensity factors in certain basic crack geometries and for typical material combinations.

Hysteretic Flux Response and Nondegenerate Gain of Flux-Driven Josephson Parametric Amplifiers

NASA Astrophysics Data System (ADS)

Pogorzalek, Stefan; Fedorov, Kirill G.; Zhong, Ling; Goetz, Jan; Wulschner, Friedrich; Fischer, Michael; Eder, Peter; Xie, Edwar; Inomata, Kunihiro; Yamamoto, Tsuyoshi; Nakamura, Yasunobu; Marx, Achim; Deppe, Frank; Gross, Rudolf

2017-08-01

Josephson parametric amplifiers (JPAs) have become key devices in quantum science and technology with superconducting circuits. In particular, they can be utilized as quantum-limited amplifiers or as a source of squeezed microwave fields. Here, we report on the detailed measurements of five flux-driven JPAs exhibiting a hysteretic dependence of the resonant frequency on the applied magnetic flux. We model the measured characteristics by numerical simulations based on the two-dimensional potential landscape of the dc superconducting quantum interference devices, which provide the JPA nonlinearity for a nonzero screening parameter βL>0 and demonstrate excellent agreement between the numerical results and the experimental data. Furthermore, we study the nondegenerate response of different JPAs and accurately describe the experimental results with our theory.

Modelling the 21-cm Signal from the Epoch of Reionization and Cosmic Dawn

NASA Astrophysics Data System (ADS)

Choudhury, T. Roy; Datta, Kanan; Majumdar, Suman; Ghara, Raghunath; Paranjape, Aseem; Mondal, Rajesh; Bharadwaj, Somnath; Samui, Saumyadip

2016-12-01

Studying the cosmic dawn and the epoch of reionization through the redshifted 21-cm line are among the major science goals of the SKA1. Their significance lies in the fact that they are closely related to the very first stars in the Universe. Interpreting the upcoming data would require detailed modelling of the relevant physical processes. In this article, we focus on the theoretical models of reionization that have been worked out by various groups working in India with the upcoming SKA in mind. These models include purely analytical and semi-numerical calculations as well as fully numerical radiative transfer simulations. The predictions of the 21-cm signal from these models would be useful in constraining the properties of the early galaxies using the SKA data.

Grain-scale supercharging and breakdown on airless regoliths

NASA Astrophysics Data System (ADS)

Zimmerman, M. I.; Farrell, W. M.; Hartzell, C. M.; Wang, X.; Horanyi, M.; Hurley, D. M.; Hibbitts, K.

2016-10-01

Interactions of the solar wind and emitted photoelectrons with airless bodies have been studied extensively. However, the details of how charged particles interact with the regolith at the scale of a single grain have remained largely uncharacterized. Recent efforts have focused upon determining total surface charge under photoemission and solar wind bombardment and the associated electric field and potential. In this work, theory and simulations are used to show that grain-grain charge differences can exceed classical sheath predictions by several orders of magnitude, sometimes reaching dielectric breakdown levels. Temperature-dependent electrical conductivity works against supercharging by allowing current to leak through individual grains; the balance between internal conduction and surface charging controls the maximum possible grain-to-grain electric field. Understanding the finer details of regolith grain charging, conductive equilibrium, and dielectric breakdown will improve future numerical studies of space weathering and dust levitation on airless bodies.

A Critical Look at Entropy-Based Gene-Gene Interaction Measures.

PubMed

Lee, Woojoo; Sjölander, Arvid; Pawitan, Yudi

2016-07-01

Several entropy-based measures for detecting gene-gene interaction have been proposed recently. It has been argued that the entropy-based measures are preferred because entropy can better capture the nonlinear relationships between genotypes and traits, so they can be useful to detect gene-gene interactions for complex diseases. These suggested measures look reasonable at intuitive level, but so far there has been no detailed characterization of the interactions captured by them. Here we study analytically the properties of some entropy-based measures for detecting gene-gene interactions in detail. The relationship between interactions captured by the entropy-based measures and those of logistic regression models is clarified. In general we find that the entropy-based measures can suffer from a lack of specificity in terms of target parameters, i.e., they can detect uninteresting signals as interactions. Numerical studies are carried out to confirm theoretical findings. © 2016 WILEY PERIODICALS, INC.

Grain-Scale Supercharging and Breakdown on Airless Regoliths

NASA Technical Reports Server (NTRS)

Zimmerman, M. I.; Farrell, W. M.; Hartzell, C.M.; Wang, X.; Horanyi, M.; Hurley, D. M.; Hibbitts, K.

2016-01-01

Interactions of the solar wind and emitted photoelectrons with airless bodies have been studied extensively. However, the details of how charged particles interact with the regolith at the scale of a single grain have remained largely uncharacterized. Recent efforts have focused upon determining total surface charge under photoemission and solar wind bombardment and the associated electric field and potential. In this work, theory and simulations are used to show that grain-grain charge differences can exceed classical sheath predictions by several orders of magnitude, sometimes reaching dielectric breakdown levels. Temperature-dependent electrical conductivity works against supercharging by allowing current to leak through individual grains; the balance between internal conduction and surface charging controls the maximum possible grain-to-grain electric field. Understanding the finer details of regolith grain charging, conductive equilibrium, and dielectric breakdown will improve future numerical studies of space weathering and dust levitation on airless bodies.

Gene Regulation and Signal Transduction in the ICE-CBF-COR Signaling Pathway during Cold Stress in Plants.

PubMed

Wang, Da-Zhi; Jin, Ya-Nan; Ding, Xi-Han; Wang, Wen-Jia; Zhai, Shan-Shan; Bai, Li-Ping; Guo, Zhi-Fu

2017-10-01

Low temperature is an abiotic stress that adversely affects the growth and production of plants. Resistance and adaptation of plants to cold stress is dependent upon the activation of molecular networks and pathways involved in signal transduction and the regulation of cold-stress related genes. Because it has numerous and complex genes, regulation factors, and pathways, research on the ICE-CBF-COR signaling pathway is the most studied and detailed, which is thought to be rather important for cold resistance of plants. In this review, we focus on the function of each member, interrelation among members, and the influence of manipulators and repressors in the ICE-CBF-COR pathway. In addition, regulation and signal transduction concerning plant hormones, circadian clock, and light are discussed. The studies presented provide a detailed picture of the ICE-CBF-COR pathway.

5. Historic American Buildings Survey Nathaniel R. Ewan, Photographer September ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

5. Historic American Buildings Survey Nathaniel R. Ewan, Photographer September 8, 1937 INTERIOR - DETAIL OF NUMERALS (1776) ON ENCLOSED END OF ORIGINAL HOUSE - Haines-Budd House, Lumberton, Burlington County, NJ

Numerical calculation and analysis of radial force on the single-action vane pump

NASA Astrophysics Data System (ADS)

Y He, Y.; Y Kong, F.

2013-12-01

Unbalanced radial force is a serious adversity that restricts the working pressure and reduces service life of the single-action vane pump. For revealing and predicting the distribution of radial force on the rotor, a numerical simulation about its transient flow field was performed by using dynamic mesh method with RNG κ ε-turbulent model. The details of transient flow characteristic and pressure fluctuation were obtained, and the radial force and periodic variation can be calculated based on the details. The results show: the radial force has a close relationship with the pressure pulsation; the radial force can be reduced drastically by optimizing the angle of port plate and installing the V-shaped cavity; if the odd number vanes are chosen, it will help reduce the radial force of rotor and optimize the pressure fluctuation effectively.

Mesoscale research activities with the LAMPS model

NASA Technical Reports Server (NTRS)

Kalb, M. W.

1985-01-01

Researchers achieved full implementation of the LAMPS mesoscale model on the Atmospheric Sciences Division computer and derived balanced and real wind initial states for three case studies: March 6, April 24, April 26, 1982. Numerical simulations were performed for three separate studies: (1) a satellite moisture data impact study using Vertical Atmospheric Sounder (VAS) precipitable water as a constraint on model initial state moisture analyses; (2) an evaluation of mesoscale model precipitation simulation accuracy with and without convective parameterization; and (3) the sensitivity of model precipitation to mesoscale detail of moisture and vertical motion in an initial state.

Convergence acceleration of the Proteus computer code with multigrid methods

NASA Technical Reports Server (NTRS)

Demuren, A. O.; Ibraheem, S. O.

1992-01-01

Presented here is the first part of a study to implement convergence acceleration techniques based on the multigrid concept in the Proteus computer code. A review is given of previous studies on the implementation of multigrid methods in computer codes for compressible flow analysis. Also presented is a detailed stability analysis of upwind and central-difference based numerical schemes for solving the Euler and Navier-Stokes equations. Results are given of a convergence study of the Proteus code on computational grids of different sizes. The results presented here form the foundation for the implementation of multigrid methods in the Proteus code.

On Dynamics of Spinning Structures

NASA Technical Reports Server (NTRS)

Gupta, K. K.; Ibrahim, A.

2012-01-01

This paper provides details of developments pertaining to vibration analysis of gyroscopic systems, that involves a finite element structural discretization followed by the solution of the resulting matrix eigenvalue problem by a progressive, accelerated simultaneous iteration technique. Thus Coriolis, centrifugal and geometrical stiffness matrices are derived for shell and line elements, followed by the eigensolution details as well as solution of representative problems that demonstrates the efficacy of the currently developed numerical procedures and tools.

Optimal design of similariton fiber lasers without gain-bandwidth limitation.

PubMed

Li, Xingliang; Zhang, Shumin; Yang, Zhenjun

2017-07-24

We have numerically investigated broadband high-energy similariton fiber lasers, demonstrated that the self-similar evolution of pulses can locate in a segment of photonic crystal fiber without gain-bandwidth limitation. The effects of various parameters, including the cavity length, the spectral filter bandwidth, the pump power, the length of the photonic crystal fiber and the output coupling ratio have also been studied in detail. Using the optimal parameters, a single pulse with spectral width of 186.6 nm, pulse energy of 23.8 nJ, dechirped pulse duration of 22.5 fs and dechirped pulse peak power of 1.26 MW was obtained. We believe that this detailed analysis of the behaviour of pulses in the similariton regime may have major implications in the development of broadband high-energy fiber lasers.

Intermittent Reconnection and Plasmoids in UV Bursts in the Low Solar Atmosphere

NASA Astrophysics Data System (ADS)

Rouppe van der Voort, L.; De Pontieu, B.; Scharmer, G. B.; de la Cruz Rodríguez, J.; Martínez-Sykora, J.; Nóbrega-Siverio, D.; Guo, L. J.; Jafarzadeh, S.; Pereira, T. M. D.; Hansteen, V. H.; Carlsson, M.; Vissers, G.

2017-12-01

Magnetic reconnection is thought to drive a wide variety of dynamic phenomena in the solar atmosphere. Yet, the detailed physical mechanisms driving reconnection are difficult to discern in the remote sensing observations that are used to study the solar atmosphere. In this Letter, we exploit the high-resolution instruments Interface Region Imaging Spectrograph and the new CHROMIS Fabry-Pérot instrument at the Swedish 1-m Solar Telescope (SST) to identify the intermittency of magnetic reconnection and its association with the formation of plasmoids in so-called UV bursts in the low solar atmosphere. The Si IV 1403 Å UV burst spectra from the transition region show evidence of highly broadened line profiles with often non-Gaussian and triangular shapes, in addition to signatures of bidirectional flows. Such profiles had previously been linked, in idealized numerical simulations, to magnetic reconnection driven by the plasmoid instability. Simultaneous CHROMIS images in the chromospheric Ca II K 3934 Å line now provide compelling evidence for the presence of plasmoids by revealing highly dynamic and rapidly moving brightenings that are smaller than 0.″2 and that evolve on timescales of the order of seconds. Our interpretation of the observations is supported by detailed comparisons with synthetic observables from advanced numerical simulations of magnetic reconnection and associated plasmoids in the chromosphere. Our results highlight how subarcsecond imaging spectroscopy sensitive to a wide range of temperatures combined with advanced numerical simulations that are realistic enough to compare with observations can directly reveal the small-scale physical processes that drive the wide range of phenomena in the solar atmosphere.

Numerical Simulation of Dispersion from Urban Greenhouse Gas Sources

NASA Astrophysics Data System (ADS)

Nottrott, Anders; Tan, Sze; He, Yonggang; Winkler, Renato

2017-04-01

Cities are characterized by complex topography, inhomogeneous turbulence, and variable pollutant source distributions. These features create a scale separation between local sources and urban scale emissions estimates known as the Grey-Zone. Modern computational fluid dynamics (CFD) techniques provide a quasi-deterministic, physically based toolset to bridge the scale separation gap between source level dynamics, local measurements, and urban scale emissions inventories. CFD has the capability to represent complex building topography and capture detailed 3D turbulence fields in the urban boundary layer. This presentation discusses the application of OpenFOAM to urban CFD simulations of natural gas leaks in cities. OpenFOAM is an open source software for advanced numerical simulation of engineering and environmental fluid flows. When combined with free or low cost computer aided drawing and GIS, OpenFOAM generates a detailed, 3D representation of urban wind fields. OpenFOAM was applied to model scalar emissions from various components of the natural gas distribution system, to study the impact of urban meteorology on mobile greenhouse gas measurements. The numerical experiments demonstrate that CH4 concentration profiles are highly sensitive to the relative location of emission sources and buildings. Sources separated by distances of 5-10 meters showed significant differences in vertical dispersion of plumes, due to building wake effects. The OpenFOAM flow fields were combined with an inverse, stochastic dispersion model to quantify and visualize the sensitivity of point sensors to upwind sources in various built environments. The Boussinesq approximation was applied to investigate the effects of canopy layer temperature gradients and convection on sensor footprints.

The influence of aerosol particle number and hygroscopicity on the evolution of convective cloud systems and their precipitation

NASA Astrophysics Data System (ADS)

Planche, C.; Flossmann, A. I.; Wobrock, W.

2009-04-01

A 3D cloud model with detailed microphysics for ice, water and aerosol particles (AP) is used to study the role of AP on the evolution of summertime convective mixed phase clouds and the subsequent precipitation. The model couples the dynamics of the NCAR Clark-Hall cloud scale model (Clark et al., 1996) with the detailed scavenging model (DESCAM) of Flossmann and Pruppacher (1988) and the ice phase module of Leroy et al. (2007). The microphysics follows the evolution of AP, drop, and ice crystal spectra each with 39 bins. Aerosol mass in drops and ice crystals is also predicted by two distribution functions to close the aerosol budget. The simulated cases are compared with radar observations over the northern Vosges mountains and the Rhine valley which were performed on 12 and 13 August 2007 during the COPS field campaign. Using a 3D grid resolution of 250m, our model, called DESCAM-3D, is able to simulate very well the dynamical, cloud and precipitation features observed for the two different cloud systems. The high horizontal grid resolution provides new elements for the understanding of the formation of orographic convection. In addition the fine numerical scale compares well with the high resolved radar observation given by the LaMP X-band radar and Poldirad. The prediction of the liquid and ice hydrometeor spectra allows a detailed calculation of the cloud radar reflectivity. Sensitivity studies realized by the use of different mass-diameter relationships for ice crystals demonstrate the role of the crystal habits on the simulated reflectivities. In order to better understand the role of AP on cloud evolution and precipitation formation several sensitivity studies were performed by modifying not only aerosol number concentration but also their physico-chemical properties. The numerical results show a strong influence of the aerosol number concentration on the precipitation intensity but no effect of the aerosol particle solubility on the rain formation can be found.

Simulation of wind turbine wakes using the actuator line technique.

PubMed

Sørensen, Jens N; Mikkelsen, Robert F; Henningson, Dan S; Ivanell, Stefan; Sarmast, Sasan; Andersen, Søren J

2015-02-28

The actuator line technique was introduced as a numerical tool to be employed in combination with large eddy simulations to enable the study of wakes and wake interaction in wind farms. The technique is today largely used for studying basic features of wakes as well as for making performance predictions of wind farms. In this paper, we give a short introduction to the wake problem and the actuator line methodology and present a study in which the technique is employed to determine the near-wake properties of wind turbines. The presented results include a comparison of experimental results of the wake characteristics of the flow around a three-bladed model wind turbine, the development of a simple analytical formula for determining the near-wake length behind a wind turbine and a detailed investigation of wake structures based on proper orthogonal decomposition analysis of numerically generated snapshots of the wake. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

A Compliant Casing for Transonic Axial Compressors

NASA Technical Reports Server (NTRS)

Bloch, Gregory S.; Hah, Chunill

2003-01-01

A viewgraph presentation on the concept of compliant casing for transonic axial compressors is shown. The topics include: 1) Concept for compliant casing; 2) Rig and facility details; 3) Experimental results; and 4) Numerical results.

Coupling artificial intelligence and numerical computation for engineering design (Invited paper)

NASA Astrophysics Data System (ADS)

Tong, S. S.

1986-01-01

The possibility of combining artificial intelligence (AI) systems and numerical computation methods for engineering designs is considered. Attention is given to three possible areas of application involving fan design, controlled vortex design of turbine stage blade angles, and preliminary design of turbine cascade profiles. Among the AI techniques discussed are: knowledge-based systems; intelligent search; and pattern recognition systems. The potential cost and performance advantages of an AI-based design-generation system are discussed in detail.

Constitutive behavior and progressive mechanical failure of electrodes in lithium-ion batteries

NASA Astrophysics Data System (ADS)

Zhang, Chao; Xu, Jun; Cao, Lei; Wu, Zenan; Santhanagopalan, Shriram

2017-07-01

The electrodes of lithium-ion batteries (LIB) are known to be brittle and to fail earlier than the separators during an external crush event. Thus, the understanding of mechanical failure mechanism for LIB electrodes (anode and cathode) is critical for the safety design of LIB cells. In this paper, we present experimental and numerical studies on the constitutive behavior and progression of failure in LIB electrodes. Mechanical tests were designed and conducted to evaluate the constitutive properties of porous electrodes. Constitutive models were developed to describe the stress-strain response of electrodes under uniaxial tensile and compressive loads. The failure criterion and a damage model were introduced to model their unique tensile and compressive failure behavior. The failure mechanism of LIB electrodes was studied using the blunt rod test on dry electrodes, and numerical models were built to simulate progressive failure. The different failure processes were examined and analyzed in detail numerically, and correlated with experimentally observed failure phenomena. The test results and models improve our understanding of failure behavior in LIB electrodes, and provide constructive insights on future development of physics-based safety design tools for battery structures under mechanical abuse.

Constitutive behavior and progressive mechanical failure of electrodes in lithium-ion batteries

DOE PAGES

Zhang, Chao; Xu, Jun; Cao, Lei; ...

2017-05-05

The electrodes of lithium-ion batteries (LIB) are known to be brittle and to fail earlier than the separators during an external crush event. Thus, the understanding of mechanical failure mechanism for LIB electrodes (anode and cathode) is critical for the safety design of LIB cells. In this paper, we present experimental and numerical studies on the constitutive behavior and progression of failure in LIB electrodes. Mechanical tests were designed and conducted to evaluate the constitutive properties of porous electrodes. Constitutive models were developed to describe the stress-strain response of electrodes under uniaxial tensile and compressive loads. The failure criterion andmore » a damage model were introduced to model their unique tensile and compressive failure behavior. The failure mechanism of LIB electrodes was studied using the blunt rod test on dry electrodes, and numerical models were built to simulate progressive failure. The different failure processes were examined and analyzed in detail numerically, and correlated with experimentally observed failure phenomena. Finally, the test results and models improve our understanding of failure behavior in LIB electrodes, and provide constructive insights on future development of physics-based safety design tools for battery structures under mechanical abuse.« less

Preliminary Experimental Results for Charge Drag in a Simulated Low Earth Orbit Environment

NASA Astrophysics Data System (ADS)

Azema-Rovira, Monica

Interest in the Low Earth Orbit (LEO) environment is growing in the science community as well as in the private sector. The number of spacecraft launched in these altitudes (150 - 700 km) keeps growing, and this region is accumulating space debris. In this scenario, the precise location of all LEO objects is a key factor to avoid catastrophic collisions and to safely perform station-keeping maneuvers. The detailed study of the atmospheric models in LEO can enhance the disturbances forces calculation of an orbiting object. Recent numerical studies indicate that one of the biggest non-conservative forces on a spacecraft is underestimated, the charge drag phenomenon. Validating these numerical models experimentally, will help to improve the numerical models for future spacecraft mission design. For this reason, the motivation of this thesis is to characterize a plasma source to later be used for charged drag measurements. The characterization has been done at the University of Colorado Colorado Springs in the Chamber for Atmospheric and Orbital Space Simulation. In the characterization process, a nano-Newton Thrust Stand has been characterized as a plasma diagnosis tool and compared with Langmuir Probe data.

The influence of surface roughness of deserts on the July circulation - A numerical study

NASA Technical Reports Server (NTRS)

Sud, Y. C.; Smith, W. E.

1985-01-01

The effect of the low surface roughness characteristics of deserts on atmospheric circulation in July is examined using numerical simulations with the GCM of the Goddard Laboratory for Atmospheric Science (GLAS). Identical sets of simulations were carried out with the model starting from the initial state of the atmosphere on June 15, for the years 1979 and 1980. The first simulation included a surface roughness factor of 45 cm, and the second set had a surface roughness factor of 0.02 cm for desert regions, and 45 cm for all other land. A comparative analysis of the numerical data was carried out in order to study the variations for the desert regions. It is shown that rainfall in the Sahara desert was reduced significantly in the data set with the nonuniform surface roughness factor in comparison with the other data set. The inter-tropical convergence zone (ITCZ) moved southward to about 15 degrees, which was close to its observed location at about 10 degrees N. In other deserts, the North American Great Plains, Rajputana in India, and the Central Asian desert, no similar changes were observed. Detailed contour maps of the weather conditions in the different desert regions are provided.

Indepth diagnosis of a secondary clarifier by the application of radiotracer technique and numerical modeling.

PubMed

Kim, H S; Shin, M S; Jang, D S; Jung, S H

2006-01-01

To make an indepth diagnosis of a full-scale rectangular secondary clarifier, an experimental and numerical study has been performed in a wastewater treatment facility. Calculation results by the numerical model with the adoption of the SIMPLE algorithm of Patankar are validated with radiotracer experiments. Emphasis is given to the prediction of residence time distribution (RTD) curves. The predicted RTD profiles are in good agreement with the experimental RTD curves at the upstream and center sections except for the withdrawal zone of the complex effluent weir structure. The simulation results predict successfully the well-known flow characteristics of each stage such as the waterfall phenomenon at the front of the clarifier, the bottom density current and the surface return flow in the settling zone, and the upward flow in the exit zone. The detailed effects of density current are thoroughly investigated in terms of high SS loading and temperature difference between influent and ambient fluid. The program developed in this study shows the high potential to assist in the design and determination of optimal operating conditions to improve effluent quality in a full-scale secondary clarifier.

Numerical Simulation and Analyses of the Loss of Feedwater Transient at the Unit 4 of Kola NPP

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stevanovic, Vladimir D.; Stosic, Zoran V.; Kiera, Michael

2002-07-01

A three-dimensional numerical simulation of the loss-of-feed water transient at the horizontal steam generator of the Kola nuclear power plant is performed. Presented numerical results show transient change of integral steam generator parameters, such as steam generation rate, water mass inventory, outlet reactor coolant temperature, as well as detailed distribution of shell side thermal-hydraulic parameters: swell and collapsed levels, void fraction distributions, mass flux vectors, etc. Numerical results are compared with measurements at the Kola NPP. The agreement is satisfactory, while differences are close to or below the measurement uncertainties. Obtained numerical results are the first ones that give completemore » insight into the three-dimensional and transient horizontal steam generator thermal-hydraulics. Also, the presented results serve as benchmark tests for the assessment and further improvement of one-dimensional models of horizontal steam generator built with safety codes. (authors)« less

Simulating the universe(s) II: phenomenology of cosmic bubble collisions in full general relativity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wainwright, Carroll L.; Aguirre, Anthony; Johnson, Matthew C.

2014-10-01

Observing the relics of collisions between bubble universes would provide direct evidence for the existence of an eternally inflating Multiverse; the non-observation of such events can also provide important constraints on inflationary physics. Realizing these prospects requires quantitative predictions for observables from the properties of the possible scalar field Lagrangians underlying eternal inflation. Building on previous work, we establish this connection in detail. We perform a fully relativistic numerical study of the phenomenology of bubble collisions in models with a single scalar field, computing the comoving curvature perturbation produced in a wide variety of models. We also construct a setmore » of analytic predictions, allowing us to identify the phenomenologically relevant properties of the scalar field Lagrangian. The agreement between the analytic predictions and numerics in the relevant regions is excellent, and allows us to generalize our results beyond the models we adopt for the numerical studies. Specifically, the signature is completely determined by the spatial profile of the colliding bubble just before the collision, and the de Sitter invariant distance between the bubble centers. The analytic and numerical results support a power-law fit with an index 1< κ ∼< 2. For collisions between identical bubbles, we establish a lower-bound on the observed amplitude of collisions that is set by the present energy density in curvature.« less

Meshless collocation methods for the numerical solution of elliptic boundary valued problems the rotational shallow water equations on the sphere

NASA Astrophysics Data System (ADS)

Blakely, Christopher D.

This dissertation thesis has three main goals: (1) To explore the anatomy of meshless collocation approximation methods that have recently gained attention in the numerical analysis community; (2) Numerically demonstrate why the meshless collocation method should clearly become an attractive alternative to standard finite-element methods due to the simplicity of its implementation and its high-order convergence properties; (3) Propose a meshless collocation method for large scale computational geophysical fluid dynamics models. We provide numerical verification and validation of the meshless collocation scheme applied to the rotational shallow-water equations on the sphere and demonstrate computationally that the proposed model can compete with existing high performance methods for approximating the shallow-water equations such as the SEAM (spectral-element atmospheric model) developed at NCAR. A detailed analysis of the parallel implementation of the model, along with the introduction of parallel algorithmic routines for the high-performance simulation of the model will be given. We analyze the programming and computational aspects of the model using Fortran 90 and the message passing interface (mpi) library along with software and hardware specifications and performance tests. Details from many aspects of the implementation in regards to performance, optimization, and stabilization will be given. In order to verify the mathematical correctness of the algorithms presented and to validate the performance of the meshless collocation shallow-water model, we conclude the thesis with numerical experiments on some standardized test cases for the shallow-water equations on the sphere using the proposed method.

Two modelling approaches to water-quality simulation in a flooded iron-ore mine (Saizerais, Lorraine, France): a semi-distributed chemical reactor model and a physically based distributed reactive transport pipe network model.

PubMed

Hamm, V; Collon-Drouaillet, P; Fabriol, R

2008-02-19

The flooding of abandoned mines in the Lorraine Iron Basin (LIB) over the past 25 years has degraded the quality of the groundwater tapped for drinking water. High concentrations of dissolved sulphate have made the water unsuitable for human consumption. This problematic issue has led to the development of numerical tools to support water-resource management in mining contexts. Here we examine two modelling approaches using different numerical tools that we tested on the Saizerais flooded iron-ore mine (Lorraine, France). A first approach considers the Saizerais Mine as a network of two chemical reactors (NCR). The second approach is based on a physically distributed pipe network model (PNM) built with EPANET 2 software. This approach considers the mine as a network of pipes defined by their geometric and chemical parameters. Each reactor in the NCR model includes a detailed chemical model built to simulate quality evolution in the flooded mine water. However, in order to obtain a robust PNM, we simplified the detailed chemical model into a specific sulphate dissolution-precipitation model that is included as sulphate source/sink in both a NCR model and a pipe network model. Both the NCR model and the PNM, based on different numerical techniques, give good post-calibration agreement between the simulated and measured sulphate concentrations in the drinking-water well and overflow drift. The NCR model incorporating the detailed chemical model is useful when a detailed chemical behaviour at the overflow is needed. The PNM incorporating the simplified sulphate dissolution-precipitation model provides better information of the physics controlling the effect of flow and low flow zones, and the time of solid sulphate removal whereas the NCR model will underestimate clean-up time due to the complete mixing assumption. In conclusion, the detailed NCR model will give a first assessment of chemical processes at overflow, and in a second time, the PNM model will provide more detailed information on flow and chemical behaviour (dissolved sulphate concentrations, remaining mass of solid sulphate) in the network. Nevertheless, both modelling methods require hydrological and chemical parameters (recharge flow rate, outflows, volume of mine voids, mass of solids, kinetic constants of the dissolution-precipitation reactions), which are commonly not available for a mine and therefore call for calibration data.

Evidence for a scaling solution in cosmic-string evolution

NASA Technical Reports Server (NTRS)

Bennett, David P.; Bouchet, Francois R.

1988-01-01

Numerical simulations are used to study the most fundamental issue of cosmic-string evolution: the existence of a scaling solution. Strong evidence is found that a scaling solution does indeed exist. This justifies the main assumption on which the cosmic-string theories of galaxy formation is based. The main conclusion coincides with that of Albrecht and Turok (1985) but the results are not consistent with theirs. In fact, the results indicate that the details of string evolution are very different from the standard dogma.

Large-Eddy Simulations of Dust Devils and Convective Vortices

NASA Astrophysics Data System (ADS)

Spiga, Aymeric; Barth, Erika; Gu, Zhaolin; Hoffmann, Fabian; Ito, Junshi; Jemmett-Smith, Bradley; Klose, Martina; Nishizawa, Seiya; Raasch, Siegfried; Rafkin, Scot; Takemi, Tetsuya; Tyler, Daniel; Wei, Wei

2016-11-01

In this review, we address the use of numerical computations called Large-Eddy Simulations (LES) to study dust devils, and the more general class of atmospheric phenomena they belong to (convective vortices). We describe the main elements of the LES methodology. We review the properties, statistics, and variability of dust devils and convective vortices resolved by LES in both terrestrial and Martian environments. The current challenges faced by modelers using LES for dust devils are also discussed in detail.

A dimensionless parameter approach to the thermal behavior of an aquifer thermal energy storage system

NASA Astrophysics Data System (ADS)

Doughty, C.; Hellstrom, G.; Tsang, C. F.; Claesson, J.

1982-09-01

The purpose of aquifer thermal energy storage (ATES) site-characterization studies is to develop a general procedure whereby the energy recovery factor for a given site may be predicted readily for a wide range of operating conditions without doing detailed numerical simulations. The thermal behavior of a ATES system with steady radial fluid flow around a single injection/production well is discussed. Buoyancy flow is neglected, and the aquifer is confined above and below by impermeable confining layers.

Scaling properties of multitension domain wall networks

NASA Astrophysics Data System (ADS)

Oliveira, M. F.; Martins, C. J. A. P.

2015-02-01

We study the asymptotic scaling properties of domain wall networks with three different tensions in various cosmological epochs. We discuss the conditions under which a scale-invariant evolution of the network (which is well established for simpler walls) still applies and also consider the limiting case where defects are locally planar and the curvature is concentrated in the junctions. We present detailed quantitative predictions for scaling densities in various contexts, which should be testable by means of future high-resolution numerical simulations.

Analytical and numerical techniques for predicting the interfacial stresses of wavy carbon nanotube/polymer composites

NASA Astrophysics Data System (ADS)

Yazdchi, K.; Salehi, M.; Shokrieh, M. M.

2009-03-01

By introducing a new simplified 3D representative volume element for wavy carbon nanotubes, an analytical model is developed to study the stress transfer in single-walled carbon nanotube-reinforced polymer composites. Based on the pull-out modeling technique, the effects of waviness, aspect ratio, and Poisson ratio on the axial and interfacial shear stresses are analyzed in detail. The results of the present analytical model are in a good agreement with corresponding results for straight nanotubes.

Dynamical Approach Study of Spurious Steady-State Numerical Solutions of Nonlinear Differential Equations. Part 2; Global Asymptotic Behavior of Time Discretizations

NASA Technical Reports Server (NTRS)

Yee, H. C.; Sweby, P. K.

1995-01-01

The global asymptotic nonlinear behavior of 11 explicit and implicit time discretizations for four 2 x 2 systems of first-order autonomous nonlinear ordinary differential equations (ODEs) is analyzed. The objectives are to gain a basic understanding of the difference in the dynamics of numerics between the scalars and systems of nonlinear autonomous ODEs and to set a baseline global asymptotic solution behavior of these schemes for practical computations in computational fluid dynamics. We show how 'numerical' basins of attraction can complement the bifurcation diagrams in gaining more detailed global asymptotic behavior of time discretizations for nonlinear differential equations (DEs). We show how in the presence of spurious asymptotes the basins of the true stable steady states can be segmented by the basins of the spurious stable and unstable asymptotes. One major consequence of this phenomenon which is not commonly known is that this spurious behavior can result in a dramatic distortion and, in most cases, a dramatic shrinkage and segmentation of the basin of attraction of the true solution for finite time steps. Such distortion, shrinkage and segmentation of the numerical basins of attraction will occur regardless of the stability of the spurious asymptotes, and will occur for unconditionally stable implicit linear multistep methods. In other words, for the same (common) steady-state solution the associated basin of attraction of the DE might be very different from the discretized counterparts and the numerical basin of attraction can be very different from numerical method to numerical method. The results can be used as an explanation for possible causes of error, and slow convergence and nonconvergence of steady-state numerical solutions when using the time-dependent approach for nonlinear hyperbolic or parabolic PDEs.

Dynamical Approach Study of Spurious Steady-State Numerical Solutions of Nonlinear Differential Equations. 2; Global Asymptotic Behavior of Time Discretizations; 2. Global Asymptotic Behavior of time Discretizations

NASA Technical Reports Server (NTRS)

Yee, H. C.; Sweby, P. K.

1995-01-01

The global asymptotic nonlinear behavior of 1 1 explicit and implicit time discretizations for four 2 x 2 systems of first-order autonomous nonlinear ordinary differential equations (ODES) is analyzed. The objectives are to gain a basic understanding of the difference in the dynamics of numerics between the scalars and systems of nonlinear autonomous ODEs and to set a baseline global asymptotic solution behavior of these schemes for practical computations in computational fluid dynamics. We show how 'numerical' basins of attraction can complement the bifurcation diagrams in gaining more detailed global asymptotic behavior of time discretizations for nonlinear differential equations (DEs). We show how in the presence of spurious asymptotes the basins of the true stable steady states can be segmented by the basins of the spurious stable and unstable asymptotes. One major consequence of this phenomenon which is not commonly known is that this spurious behavior can result in a dramatic distortion and, in most cases, a dramatic shrinkage and segmentation of the basin of attraction of the true solution for finite time steps. Such distortion, shrinkage and segmentation of the numerical basins of attraction will occur regardless of the stability of the spurious asymptotes, and will occur for unconditionally stable implicit linear multistep methods. In other words, for the same (common) steady-state solution the associated basin of attraction of the DE might be very different from the discretized counterparts and the numerical basin of attraction can be very different from numerical method to numerical method. The results can be used as an explanation for possible causes of error, and slow convergence and nonconvergence of steady-state numerical solutions when using the time-dependent approach for nonlinear hyperbolic or parabolic PDES.

Buckling analysis of SMA bonded sandwich structure – using FEM

NASA Astrophysics Data System (ADS)

Katariya, Pankaj V.; Das, Arijit; Panda, Subrata K.

2018-03-01

Thermal buckling strength of smart sandwich composite structure (bonded with shape memory alloy; SMA) examined numerically via a higher-order finite element model in association with marching technique. The excess geometrical distortion of the structure under the elevated environment modeled through Green’s strain function whereas the material nonlinearity counted with the help of marching method. The system responses are computed numerically by solving the generalized eigenvalue equations via a customized MATLAB code. The comprehensive behaviour of the current finite element solutions (minimum buckling load parameter) is established by solving the adequate number of numerical examples including the given input parameter. The current numerical model is extended further to check the influence of various structural parameter of the sandwich panel on the buckling temperature including the SMA effect and reported in details.

High-Order Methods for Incompressible Fluid Flow

NASA Astrophysics Data System (ADS)

Deville, M. O.; Fischer, P. F.; Mund, E. H.

2002-08-01

High-order numerical methods provide an efficient approach to simulating many physical problems. This book considers the range of mathematical, engineering, and computer science topics that form the foundation of high-order numerical methods for the simulation of incompressible fluid flows in complex domains. Introductory chapters present high-order spatial and temporal discretizations for one-dimensional problems. These are extended to multiple space dimensions with a detailed discussion of tensor-product forms, multi-domain methods, and preconditioners for iterative solution techniques. Numerous discretizations of the steady and unsteady Stokes and Navier-Stokes equations are presented, with particular sttention given to enforcement of imcompressibility. Advanced discretizations. implementation issues, and parallel and vector performance are considered in the closing sections. Numerous examples are provided throughout to illustrate the capabilities of high-order methods in actual applications.

Sound propagation in and radiation from acoustically lined flow ducts: A comparison of experiment and theory

NASA Technical Reports Server (NTRS)

Plumblee, H. E., Jr.; Dean, P. D.; Wynne, G. A.; Burrin, R. H.

1973-01-01

The results of an experimental and theoretical study of many of the fundamental details of sound propagation in hard wall and soft wall annular flow ducts are reported. The theory of sound propagation along such ducts and the theory for determining the complex radiation impedance of higher order modes of an annulus are outlined, and methods for generating acoustic duct modes are developed. The results of a detailed measurement program on propagation in rigid wall annular ducts with and without airflow through the duct are presented. Techniques are described for measuring cut-on frequencies, modal phase speed, and radial and annular mode shapes. The effects of flow velocity on cut-on frequencies and phase speed are measured. Comparisons are made with theoretical predictions for all of the effects studies. The two microphone method of impedance is used to measure the effects of flow on acoustic liners. A numerical study of sound propagation in annular ducts with one or both walls acoustically lined is presented.

Peer tutoring programs in health professions schools.

PubMed

Santee, Jennifer; Garavalia, Linda

2006-06-15

Peer tutoring programs may be one method of maintaining quality of pharmacy education in the face of growing student enrollment and a small faculty body. A critical review of the literature was performed to ascertain whether peer tutoring programs improve or maintain the academic performance of health care professional students. Various electronic databases and abstracts from past American Association of Colleges of Pharmacy's annual meetings were searched to identify pertinent research. Only those articles with quantitative data, an experimental design, and comparative statistical analysis were included for review. Most studies found that peer tutoring had a positive impact on academic performance. These results may not be readily generalizable as there were numerous methodological flaws and limited descriptions of the programs and participants. Studies with better designs and more detail are needed to answer definitively whether peer tutoring is of benefit. Details of what resources were required should be included in the study to allow the reader to determine the feasibility of the intervention.

Peer Tutoring Programs in Health Professions Schools

PubMed Central

Garavalia, Linda

2006-01-01

Objective Peer tutoring programs may be one method of maintaining quality of pharmacy education in the face of growing student enrollment and a small faculty body. A critical review of the literature was performed to ascertain whether peer tutoring programs improve or maintain the academic performance of health care professional students. Methods Various electronic databases and abstracts from past American Association of Colleges of Pharmacy's annual meetings were searched to identify pertinent research. Only those articles with quantitative data, an experimental design, and comparative statistical analysis were included for review. Results Most studies found that peer tutoring had a positive impact on academic performance. These results may not be readily generalizable as there were numerous methodological flaws and limited descriptions of the programs and participants. Implications Studies with better designs and more detail are needed to answer definitively whether peer tutoring is of benefit. Details of what resources were required should be included in the study to allow the reader to determine the feasibility of the intervention. PMID:17136190

A detailed observation of the ejection and retraction of defense tissue acontia in sea anemone (Exaiptasia pallida).

PubMed

Lam, Julie; Cheng, Ya-Wen; Chen, Wan-Nan U; Li, Hsing-Hui; Chen, Chii-Shiarng; Peng, Shao-En

2017-01-01

Acontia, located in the gastrovascular cavity of anemone, are thread-like tissue containing numerous stinging cells which serve as a unique defense tissue against predators of the immobile acontiarian sea anemone. Although its morphology and biological functions, such as defense and digestion, have been studied, the defense behavior and the specific events of acontia ejection and retraction are unclear. The aim of this study is to observe and record the detailed process of acontia control in anemones. Observations reveal that the anemone, Exaiptasia pallida , possibly controls a network of body muscles and manipulates water pressure in the gastrovascular cavity to eject and retract acontia. Instead of resynthesizing acontia after each ejection, the retraction and reuse of acontia enables the anemone to respond quickly at any given time, thus increasing its overall survivability. Since the Exaiptasia anemone is an emerging model for coral biology, this study provides a foundation to further investigate the biophysics, neuroscience, and defense biology of this marine model organism.

A detailed observation of the ejection and retraction of defense tissue acontia in sea anemone (Exaiptasia pallida)

PubMed Central

Lam, Julie; Cheng, Ya-Wen; Chen, Wan-Nan U.; Li, Hsing-Hui; Chen, Chii-Shiarng

2017-01-01

Acontia, located in the gastrovascular cavity of anemone, are thread-like tissue containing numerous stinging cells which serve as a unique defense tissue against predators of the immobile acontiarian sea anemone. Although its morphology and biological functions, such as defense and digestion, have been studied, the defense behavior and the specific events of acontia ejection and retraction are unclear. The aim of this study is to observe and record the detailed process of acontia control in anemones. Observations reveal that the anemone, Exaiptasia pallida, possibly controls a network of body muscles and manipulates water pressure in the gastrovascular cavity to eject and retract acontia. Instead of resynthesizing acontia after each ejection, the retraction and reuse of acontia enables the anemone to respond quickly at any given time, thus increasing its overall survivability. Since the Exaiptasia anemone is an emerging model for coral biology, this study provides a foundation to further investigate the biophysics, neuroscience, and defense biology of this marine model organism. PMID:28243530

Detailed Studies on Flame Extinction by Inert Particles in Normal- and Micro-gravity

NASA Technical Reports Server (NTRS)

Andac, M. G.; Egolfopoulos, F. N.; Campbell, C. S.

2001-01-01

The combustion of dusty flows has been studied to lesser extent than pure gas phase flows and sprays. Particles can have a strong effect by modifying the dynamic response and detailed structure of flames through the dynamic, thermal, and chemical couplings between the two phases. A rigorous understanding of the dynamics and structure of two-phase flows can be attained in stagnation flow configurations, which have been used by others to study spray combustion as well as reacting dusty flows. In earlier studies on reacting dusty flows, the thermal coupling between the two phases as well as the effect of gravity on the flame response were not considered. However, in Ref. 6, the thermal coupling between chemically inert particles and the gas was addressed in premixed flames. The effects of gravity was also studied showing that it can substantially affect the profiles of the particle velocity, number density, mass flux, and temperature. The results showed a strong dynamic and thermal dependence of reacting dusty flows to particle number density. However, the work was only numerical and limited to twin-flames, stagnation, premixed flames. In Ref. 7 the effects of chemically inert particle clouds on the extinction of strained premixed and non-premixed flames were studied both experimentally and numerically at 1-g. It was shown and explained that large particles can cause more effective flame cooling compared to smaller particles. The effects of flame configuration and particle injection orientation were also addressed. The complexity of the coupling between the various parameters in such flows was demonstrated and it was shown that it was impossible to obtain a simple and still meaningful scaling that captured all the pertinent physics.

Numerical Study of Rotating Turbulence with External Forcing

NASA Technical Reports Server (NTRS)

Yeung, P. K.; Zhou, Ye

1998-01-01

Direct numerical simulation at 256(exp 3) resolution have been carried out to study the response of isotropic turbulence to the concurrent effects of solid-body rotation and numerical forcing at the large scales. Because energy transfer to the smaller scales is weakened by rotation, energy input from forcing gradually builds up at the large scales, causing the overall kinetic energy to increase. At intermediate wavenumbers the energy spectrum undergoes a transition from a limited k(exp -5/3) inertial range to k(exp -2) scaling recently predicted in the literature. Although the Reynolds stress tensor remains approximately isotropic and three-components, evidence for anisotropy and quasi- two-dimensionality in length scales and spectra in different velocity components and directions is strong. The small scales are found to deviate from local isotropy, primarily as a result of anisotropic transfer to the high wavenumbers. To understand the spectral dynamics of this flow we study the detailed behavior of nonlinear triadic interactions in wavenumber space. Spectral transfer in the velocity component parallel to the axis of rotation is qualitatively similar to that in non-rotating turbulence; however the perpendicular component is characterized by a greatly suppressed energy cascade at high wavenumber and a local reverse transfer at the largest scales. The broader implications of this work are briefly addressed.

Numerical modelling for quantitative environmental risk assessment for the disposal of drill cuttings and mud

NASA Astrophysics Data System (ADS)

Wahab, Mohd Amirul Faiz Abdul; Shaufi Sokiman, Mohamad; Parsberg Jakobsen, Kim

2017-10-01

To investigate the fate of drilling waste and their impacts towards surrounding environment, numerical models were generated using an environmental software; MIKE by DHI. These numerical models were used to study the transportation of suspended drill waste plumes in the water column and its deposition on seabed in South China Sea (SCS). A random disposal site with the model area of 50 km × 25 km was selected near the Madalene Shoal in SCS and the ambient currents as well as other meteorological conditions were simulated in details at the proposed location. This paper was focusing on sensitivity study of different drill waste particle characteristics on impacts towards marine receiving environment. The drilling scenarios were obtained and adapted from the oil producer well at offshore Sabah (Case 1) and data from actual exploration drilling case at Pumbaa location (PL 469) in the Norwegian Sea (Case 2). The two cases were compared to study the effect of different drilling particle characteristics and their behavior in marine receiving environment after discharged. Using the Hydrodynamic and Sediment Transport models simulated in MIKE by DHI, the variation of currents and the behavior of the drilling waste particles can be analyzed and evaluated in terms of multiple degree zones of impacts.

Migration by soaring or flapping: numerical atmospheric simulations reveal that turbulence kinetic energy dictates bee-eater flight mode

PubMed Central

Sapir, Nir; Horvitz, Nir; Wikelski, Martin; Avissar, Roni; Mahrer, Yitzhak; Nathan, Ran

2011-01-01

Aerial migrants commonly face atmospheric dynamics that may affect their movement and behaviour. Specifically, bird flight mode has been suggested to depend on convective updraught availability and tailwind assistance. However, this has not been tested thus far since both bird tracks and meteorological conditions are difficult to measure in detail throughout extended migratory flyways. Here, we applied, to our knowledge, the first comprehensive numerical atmospheric simulations by mean of the Regional Atmospheric Modeling System (RAMS) to study how meteorological processes affect the flight behaviour of migrating birds. We followed European bee-eaters (Merops apiaster) over southern Israel using radio telemetry and contrasted bird flight mode (flapping, soaring–gliding or mixed flight) against explanatory meteorological variables estimated by RAMS simulations at a spatial grid resolution of 250 × 250 m2. We found that temperature and especially turbulence kinetic energy (TKE) determine bee-eater flight mode, whereas, unexpectedly, no effect of tailwind assistance was found. TKE during soaring–gliding was significantly higher and distinct from TKE during flapping. We propose that applying detailed atmospheric simulations over extended migratory flyways can elucidate the highly dynamic behaviour of air-borne organisms, help predict the abundance and distribution of migrating birds, and aid in mitigating hazardous implications of bird migration. PMID:21471116

PARAMETER MONITORING FOR REAL-TIME ELECTROSTATIC PRECIPITATOR TROUBLESHOOTING

EPA Science Inventory

The paper discusses detailed numerical calculations of particle charge and extinction coefficient performed using current models. The results suggest that information about rapping reentrainment, back corona, and, possibly, sulfuric acid condensation can be gained from simultaneo...

VCSEL Applications and Simulation

NASA Technical Reports Server (NTRS)

Cheung, Samson; Goorjian, Peter; Ning, Cun-Zheng; Li, Jian-Zhong

2000-01-01

This viewgraph presentation gives an overview of Vertical Cavity Surface Emitting Laser (VCSEL) simulation and its applications. Details are given on the optical interconnection in information technology of VCSEL, the formulation of the simulation, its numeric algorithm, and the computational results.

The Numerical Propulsion System Simulation: A Multidisciplinary Design System for Aerospace Vehicles

NASA Technical Reports Server (NTRS)

Lytle, John K.

1999-01-01

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 ma or 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 design process and to provide 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 multidisciplinary system of analysis tools that is focussed on extending the simulation capability from components to the full system. 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.

Nozzle Numerical Analysis Of The Scimitar Engine

NASA Astrophysics Data System (ADS)

Battista, F.; Marini, M.; Cutrone, L.

2011-05-01

This work describes part of the activities on the LAPCAT-II A2 vehicle, in which starting from the available conceptual vehicle design and the related pre- cooled turbo-ramjet engine called SCIMITAR, well- thought assumptions made for performance figures of different components during the iteration process within LAPCAT-I will be assessed in more detail. In this paper it is presented a numerical analysis aimed at the design optimization of the nozzle contour of the LAPCAT A2 SCIMITAR engine designed by Reaction Engines Ltd. (REL) (see Figure 1). In particular, nozzle shape optimization process is presented for cruise conditions. All the computations have been carried out by using the CIRA C3NS code in non equilibrium conditions. The effect of considering detailed or reduced chemical kinetic schemes has been analyzed with a particular focus on the production of pollutants. An analysis of engine performance parameters, such as thrust and combustion efficiency has been carried out.

Preconditioning for Numerical Simulation of Low Mach Number Three-Dimensional Viscous Turbomachinery Flows

NASA Technical Reports Server (NTRS)

Tweedt, Daniel L.; Chima, Rodrick V.; Turkel, Eli

1997-01-01

A preconditioning scheme has been implemented into a three-dimensional viscous computational fluid dynamics code for turbomachine blade rows. The preconditioning allows the code, originally developed for simulating compressible flow fields, to be applied to nearly-incompressible, low Mach number flows. A brief description is given of the compressible Navier-Stokes equations for a rotating coordinate system, along with the preconditioning method employed. Details about the conservative formulation of artificial dissipation are provided, and different artificial dissipation schemes are discussed and compared. The preconditioned code was applied to a well-documented case involving the NASA large low-speed centrifugal compressor for which detailed experimental data are available for comparison. Performance and flow field data are compared for the near-design operating point of the compressor, with generally good agreement between computation and experiment. Further, significant differences between computational results for the different numerical implementations, revealing different levels of solution accuracy, are discussed.

Numerical Modeling of River Ice Processes on the Lower Nelson River

NASA Astrophysics Data System (ADS)

Malenchak, Jarrod Joseph

Water resource infrastructure in cold regions of the world can be significantly impacted by the existence of river ice. Major engineering concerns related to river ice include ice jam flooding, the design and operation of hydropower facilities and other hydraulic structures, water supplies, as well as ecological, environmental, and morphological effects. The use of numerical simulation models has been identified as one of the most efficient means by which river ice processes can be studied and the effects of river ice be evaluated. The continued advancement of these simulation models will help to develop new theories and evaluate potential mitigation alternatives for these ice issues. In this thesis, a literature review of existing river ice numerical models, of anchor ice formation and modeling studies, and of aufeis formation and modeling studies is conducted. A high level summary of the two-dimensional CRISSP numerical model is presented as well as the developed freeze-up model with a focus specifically on the anchor ice and aufeis growth processes. This model includes development in the detailed heat transfer calculations, an improved surface ice mass exchange model which includes the rapids entrainment process, and an improved dry bed treatment model along with the expanded anchor ice and aufeis growth model. The developed sub-models are tested in an ideal channel setting as somewhat of a model confirmation. A case study of significant anchor ice and aufeis growth on the Nelson River in northern Manitoba, Canada, will be the primary field test case for the anchor ice and aufeis model. A second case study on the same river will be used to evaluate the surface ice components of the model in a field setting. The results from these cases studies will be used to highlight the capabilities and deficiencies in the numerical model and to identify areas of further research and model development.

Getting a Kick Out of Numerical Relativity

NASA Technical Reports Server (NTRS)

2006-01-01

Operating ground-based gravitational wave detectors and a planned instrument in space are bringing about the new field of gravitational wave astronomy. A prime source for any of these observatories is the merger of a system of two black holes. Brought together by copious losses of gravitational-wave energy, these systems merge in a burst of energy with a peak power exceeding any electromagnetic source. Observations of these sources will generate a wealth of astrophysical information, and may provide an unparalleled probe of strong-field gravitational physics, but a full interpretation of the observations will require detailed predictions from General Relativity. I will discuss recent advances in numerical simulations of binary black hole systems which are generating dramatic progress in understanding binary black hole mergers. Recent achievements include the first simulations of binary black hole systems through several orbits and merger, leading to detailed predictions for the final portion of the gravitational radiation waveforms from equal-mass mergers. For unequal-mass mergers, it has recently become possible to measure the impulsive kick imparted to the final black hole, by the asymmetry of the merger radiation. These first results announce an accelerating wave of progress soon to come from the energetic field of numerical relativity.

Numerical modeling of experimental observations on gas formation and multi-phase flow of carbon dioxide in subsurface formations

NASA Astrophysics Data System (ADS)

Pawar, R.; Dash, Z.; Sakaki, T.; Plampin, M. R.; Lassen, R. N.; Illangasekare, T. H.; Zyvoloski, G.

2011-12-01

One of the concerns related to geologic CO2 sequestration is potential leakage of CO2 and its subsequent migration to shallow groundwater resources leading to geochemical impacts. Developing approaches to monitor CO2 migration in shallow aquifer and mitigate leakage impacts will require improving our understanding of gas phase formation and multi-phase flow subsequent to CO2 leakage in shallow aquifers. We are utilizing an integrated approach combining laboratory experiments and numerical simulations to characterize the multi-phase flow of CO2 in shallow aquifers. The laboratory experiments involve a series of highly controlled experiments in which CO2 dissolved water is injected in homogeneous and heterogeneous soil columns and tanks. The experimental results are used to study the effects of soil properties, temperature, pressure gradients and heterogeneities on gas formation and migration. We utilize the Finite Element Heat and Mass (FEHM) simulator (Zyvoloski et al, 2010) to numerically model the experimental results. The numerical models capture the physics of CO2 exsolution, multi-phase fluid flow as well as sand heterogeneity. Experimental observations of pressure, temperature and gas saturations are used to develop and constrain conceptual models for CO2 gas-phase formation and multi-phase CO2 flow in porous media. This talk will provide details of development of conceptual models based on experimental observation, development of numerical models for laboratory experiments and modelling results.

Development of a radial ventricular assist device using numerical predictions and experimental haemolysis.

PubMed

Carswell, Dave; Hilton, Andy; Chan, Chris; McBride, Diane; Croft, Nick; Slone, Avril; Cross, Mark; Foster, Graham

2013-08-01

The objective of this study was to demonstrate the potential of Computational Fluid Dynamics (CFD) simulations in predicting the levels of haemolysis in ventricular assist devices (VADs). Three different prototypes of a radial flow VAD have been examined experimentally and computationally using CFD modelling to assess device haemolysis. Numerical computations of the flow field were computed using a CFD model developed with the use of the commercial software Ansys CFX 13 and a set of custom haemolysis analysis tools. Experimental values for the Normalised Index of Haemolysis (NIH) have been calculated as 0.020 g/100 L, 0.014 g/100 L and 0.0042 g/100 L for the three designs. Numerical analysis predicts an NIH of 0.021 g/100 L, 0.017 g/100 L and 0.0057 g/100 L, respectively. The actual differences between experimental and numerical results vary between 0.0012 and 0.003 g/100 L, with a variation of 5% for Pump 1 and slightly larger percentage differences for the other pumps. The work detailed herein demonstrates how CFD simulation and, more importantly, the numerical prediction of haemolysis may be used as an effective tool in order to help the designers of VADs manage the flow paths within pumps resulting in a less haemolytic device. Copyright © 2013 IPEM. Published by Elsevier Ltd. All rights reserved.

Numerical analysis of the performance of rock weirs: Effects of structure configuration on local hydraulics

USGS Publications Warehouse

Holmquist-Johnson, C. L.

2009-01-01

River spanning rock structures are being constructed for water delivery as well as to enable fish passage at barriers and provide or improve the aquatic habitat for endangered fish species. Current design methods are based upon anecdotal information applicable to a narrow range of channel conditions. The complex flow patterns and performance of rock weirs is not well understood. Without accurate understanding of their hydraulics, designers cannot address the failure mechanisms of these structures. Flow characteristics such as jets, near bed velocities, recirculation, eddies, and plunging flow govern scour pool development. These detailed flow patterns can be replicated using a 3D numerical model. Numerical studies inexpensively simulate a large number of cases resulting in an increased range of applicability in order to develop design tools and predictive capability for analysis and design. The analysis and results of the numerical modeling, laboratory modeling, and field data provide a process-based method for understanding how structure geometry affects flow characteristics, scour development, fish passage, water delivery, and overall structure stability. Results of the numerical modeling allow designers to utilize results of the analysis to determine the appropriate geometry for generating desirable flow parameters. The end product of this research will develop tools and guidelines for more robust structure design or retrofits based upon predictable engineering and hydraulic performance criteria. ?? 2009 ASCE.

Characterization of fracture aperture for groundwater flow and transport

NASA Astrophysics Data System (ADS)

Sawada, A.; Sato, H.; Tetsu, K.; Sakamoto, K.

2007-12-01

This paper presents experiments and numerical analyses of flow and transport carried out on natural fractures and transparent replica of fractures. The purpose of this study was to improve the understanding of the role of heterogeneous aperture patterns on channelization of groundwater flow and dispersion in solute transport. The research proceeded as follows: First, a precision plane grinder was applied perpendicular to the fracture plane to characterize the aperture distribution on a natural fracture with 1 mm of increment size. Although both time and labor were intensive, this approach provided a detailed, three dimensional picture of the pattern of fracture aperture. This information was analyzed to provide quantitative measures for the fracture aperture distribution, including JRC (Joint Roughness Coefficient) and fracture contact area ratio. These parameters were used to develop numerical models with corresponding synthetic aperture patterns. The transparent fracture replica and numerical models were then used to study how transport is affected by the aperture spatial pattern. In the transparent replica, transmitted light intensity measured by a CCD camera was used to image channeling and dispersion due to the fracture aperture spatial pattern. The CCD image data was analyzed to obtain the quantitative fracture aperture and tracer concentration data according to Lambert-Beer's law. The experimental results were analyzed using the numerical models. Comparison of the numerical models to the transparent replica provided information about the nature of channeling and dispersion due to aperture spatial patterns. These results support to develop a methodology for defining representative fracture aperture of a simplified parallel fracture model for flow and transport in heterogeneous fractures for contaminant transport analysis.

Numerical investigation of MHD flow with Soret and Dufour effect

NASA Astrophysics Data System (ADS)

Hayat, Tasawar; Nasir, Tehreem; Khan, Muhammad Ijaz; Alsaedi, Ahmed

2018-03-01

This paper describes the flow due to an exponentially curved surface subject to Soret and Dufour effects. Nonlinear velocity is considered. Exponentially curved stretchable sheet induced the flow. Fluid is electrical conducting through constant applied magnetic field. The governing flow expressions are reduced to ordinary ones and then tackled by numerical technique (Built-in-Shooting). Impacts of various flow variables on the dimensionless velocity, concentration and temperature fields are graphically presented and discussed in detail. Skin friction coefficient and Sherwood and Nusselt numbers are studied through graphs. Furthermore it is observed that Soret and Dufour variables regulate heat and mass transfer rates. It is also noteworthy that velocity decays for higher magnetic variable. Skin friction magnitude decays via curvature and magnetic variables. Also mass transfer gradient or rate of mass transport enhances for higher estimations of curvature parameter and Schmidt number.

Multi-objective optimal design of sandwich panels using a genetic algorithm

NASA Astrophysics Data System (ADS)

Xu, Xiaomei; Jiang, Yiping; Pueh Lee, Heow

2017-10-01

In this study, an optimization problem concerning sandwich panels is investigated by simultaneously considering the two objectives of minimizing the panel mass and maximizing the sound insulation performance. First of all, the acoustic model of sandwich panels is discussed, which provides a foundation to model the acoustic objective function. Then the optimization problem is formulated as a bi-objective programming model, and a solution algorithm based on the non-dominated sorting genetic algorithm II (NSGA-II) is provided to solve the proposed model. Finally, taking an example of a sandwich panel that is expected to be used as an automotive roof panel, numerical experiments are carried out to verify the effectiveness of the proposed model and solution algorithm. Numerical results demonstrate in detail how the core material, geometric constraints and mechanical constraints impact the optimal designs of sandwich panels.

Numerical investigation of turbulent channel flow

NASA Technical Reports Server (NTRS)

Moin, P.; Kim, J.

1981-01-01

Fully developed turbulent channel flow was simulated numerically at Reynolds number 13800, based on centerline velocity and channel halt width. The large-scale flow field was obtained by directly integrating the filtered, three dimensional, time dependent, Navier-Stokes equations. The small-scale field motions were simulated through an eddy viscosity model. The calculations were carried out on the ILLIAC IV computer with up to 516,096 grid points. The computed flow field was used to study the statistical properties of the flow as well as its time dependent features. The agreement of the computed mean velocity profile, turbulence statistics, and detailed flow structures with experimental data is good. The resolvable portion of the statistical correlations appearing in the Reynolds stress equations are calculated. Particular attention is given to the examination of the flow structure in the vicinity of the wall.

The Four-Quadrant Phase-Mask Coronagraph. II. Simulations

NASA Astrophysics Data System (ADS)

Riaud, P.; Boccaletti, A.; Rouan, D.; Lemarquis, F.; Labeyrie, A.

2001-09-01

In the first paper in this series, we described the principle of a coronagraph utilizing a four-quadrant phase mask and the results of numerical simulations obtained in the perfect case. In this second paper, we performed additional numerical simulations to assess in more detail the performances and limitations of this coronagraph under real conditions. The effect of geometrical parameters such as shape and size of both the phase mask and the Lyot stop is studied. We also analyze the effect of low- and high-order aberrations generated, for instance, by the atmospheric turbulence. An important issue is the wavelength dependence of the phase mask. We show that the performance decreases rapidly as the spectral bandwidth is increased, and as a consequence, we discuss the manufacturing of achromatized masks using multiple thin films. An optical concept is proposed.

Be/X-Ray Pulsar Binary Science with LOFT

NASA Technical Reports Server (NTRS)

Wilson-Hodge, Colleen A.

2011-01-01

Accretion disks are ubiquitous in astronomical sources. Accretion powered pulsars are a good test bed for accretion disk physics, because unlike for other objects, the spin of the neutron star is directly observable allowing us to see the effects of angular momentum transfer onto the pulsar. The combination of a sensitive wide-field monitor and the large area detector on LOFT will enable new detailed studies of accretion powered pulsars which I will review. RXTE observations have shown an unusually high number of Be/X-ray pulsar binaries in the SMC. Unlike binaries in the Milky Way, these systems are all at the same distance, allowing detailed population studies using the sensitive LOFT WFM, potentially providing connections to star formation episodes. For Galactic accreting pulsar systems, LOFT will allow measurement of spectral variations within individual pulses, mapping the accretion column in detail for the first time. LOFT will also provide better constraints on magnetic fields in accreting pulsars, allowing measurements of cyclotron features, observations of transitions into the centrifugal inhibition regime, and monitoring of spin-up rate vs flux correlations. Coordinated multi-wavelength observations are crucial to extracting the best science from LOFT from these and numerous other objects.

On the Collision Nature of Two Coronal Mass Ejections: A Review

NASA Astrophysics Data System (ADS)

Shen, Fang; Wang, Yuming; Shen, Chenglong; Feng, Xueshang

2017-08-01

Observational and numerical studies have shown that the kinematic characteristics of two or more coronal mass ejections (CMEs) may change significantly after a CME collision. The collision of CMEs can have a different nature, i.e. inelastic, elastic, and superelastic processes, depending on their initial kinematic characteristics. In this article, we first review the existing definitions of collision types including Newton's classical definition, the energy definition, Poisson's definition, and Stronge's definition, of which the first two were used in the studies of CME-CME collisions. Then, we review the recent research progresses on the nature of CME-CME collisions with the focus on which CME kinematic properties affect the collision nature. It is shown that observational analysis and numerical simulations can both yield an inelastic, perfectly inelastic, merging-like collision, or a high possibility of a superelastic collision. Meanwhile, previous studies based on a 3D collision picture suggested that a low approaching speed of two CMEs is favorable for a superelastic nature. Since CMEs are an expanding magnetized plasma structure, the CME collision process is quite complex, and we discuss this complexity. Moreover, the models used in both observational and numerical studies contain many limitations. All of the previous studies on collisions have not shown the separation of two colliding CMEs after a collision. Therefore the collision between CMEs cannot be considered as an ideal process in the context of a classical Newtonian definition. In addition, many factors are not considered in either observational analysis or numerical studies, e.g. CME-driven shocks and magnetic reconnections. Owing to the complexity of the CME collision process, a more detailed and in-depth observational analysis and simulation work are needed to fully understand the CME collision process.

A Spreadsheet Simulation Tool for Terrestrial and Planetary Balloon Design

NASA Technical Reports Server (NTRS)

Raquea, Steven M.

1999-01-01

During the early stages of new balloon design and development, it is necessary to conduct many trade studies. These trade studies are required to determine the design space, and aid significantly in determining overall feasibility. Numerous point designs then need to be generated as details of payloads, materials, mission, and manufacturing are determined. To accomplish these numerous designs, transient models are both unnecessary and time intensive. A steady state model that uses appropriate design inputs to generate system-level descriptive parameters can be very flexible and fast. Just such a steady state model has been developed and has been used during both the MABS 2001 Mars balloon study and the Ultra Long Duration Balloon Project. Using Microsoft Excel's built-in iteration routine, a model was built. Separate sheets were used for performance, structural design, materials, and thermal analysis as well as input and output sheets. As can be seen from figure 1, the model takes basic performance requirements, weight estimates, design parameters, and environmental conditions and generates a system level balloon design. Figure 2 shows a sample output of the model. By changing the inputs and a few of the equations in the model, balloons on earth or other planets can be modeled. There are currently several variations of the model for terrestrial and Mars balloons, as well there are versions of the model that perform crude material design based on strength and weight requirements. To perform trade studies, the Visual Basic language built into Excel was used to create an automated matrix of designs. This trade study module allows a three dimensional trade surface to be generated by using a series of values for any two design variables. Once the fixed and variable inputs are defined, the model automatically steps through the input matrix and fills a spreadsheet with the resulting point designs. The proposed paper will describe the model in detail, including current variations. The assumptions, governing equations, and capabilities will be addressed. Detailed examples of the model in practice will also be used.

Optimality conditions for the numerical solution of optimization problems with PDE constraints :

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aguilo Valentin, Miguel Alejandro; Ridzal, Denis

2014-03-01

A theoretical framework for the numerical solution of partial di erential equation (PDE) constrained optimization problems is presented in this report. This theoretical framework embodies the fundamental infrastructure required to e ciently implement and solve this class of problems. Detail derivations of the optimality conditions required to accurately solve several parameter identi cation and optimal control problems are also provided in this report. This will allow the reader to further understand how the theoretical abstraction presented in this report translates to the application.

Results from Numerical General Relativity

NASA Technical Reports Server (NTRS)

Baker, John G.

2011-01-01

For several years numerical simulations have been revealing the details of general relativity's predictions for the dynamical interactions of merging black holes. I will review what has been learned of the rich phenomenology of these mergers and the resulting gravitational wave signatures. These wave forms provide a potentially observable record of the powerful astronomical events, a central target of gravitational wave astronomy. Asymmetric radiation can produce a thrust on the system which may accelerate the single black hole resulting from the merger to high relative velocity.

Surface electrical properties experiment, Part 3

NASA Technical Reports Server (NTRS)

1974-01-01

A complete unified discussion of the electromagnetic response of a plane stratified structure is reported. A detailed and comprehensive analysis of the theoretical parts of the electromagnetic is given. The numerical problem of computing numbers of the electromagnetic field strengths is discussed. It is shown that the analysis of the conductive media is not very far removed from the theoretical analysis and the numerical difficulties are not as accute as for the low-loss problem. For Vol. 1, see N75-15570; for Vol. 2 see N75-15571.

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 respond to that feedback. NPSS was supported in fiscal year 2000 by the High Performance Computing and Communications Program.

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 respond to that feedback. NPSS was supported in fiscal year 2001 by the High Performance Computing and Communications Program.

Comparative study on the wake deflection behind yawed wind turbine models

NASA Astrophysics Data System (ADS)

Schottler, Jannik; Mühle, Franz; Bartl, Jan; Peinke, Joachim; Adaramola, Muyiwa S.; Sætran, Lars; Hölling, Michael

2017-05-01

In this wind tunnel campaign, detailed wake measurements behind two different model wind turbines in yawed conditions were performed. The wake deflections were quantified by estimating the rotor-averaged available power within the wake. By using two different model wind turbines, the influence of the rotor design and turbine geometry on the wake deflection caused by a yaw misalignment of 30° could be judged. It was found that the wake deflections three rotor diameters downstream were equal while at six rotor diameters downstream insignificant differences were observed. The results compare well with previous experimental and numerical studies.

Cogeneration Technology Alternatives Study (CTAS). Volume 2: Analytical approach

NASA Technical Reports Server (NTRS)

Gerlaugh, H. E.; Hall, E. W.; Brown, D. H.; Priestley, R. R.; Knightly, W. F.

1980-01-01

The use of various advanced energy conversion systems were compared with each other and with current technology systems for their savings in fuel energy, costs, and emissions in individual plants and on a national level. The ground rules established by NASA and assumptions made by the General Electric Company in performing this cogeneration technology alternatives study are presented. The analytical methodology employed is described in detail and is illustrated with numerical examples together with a description of the computer program used in calculating over 7000 energy conversion system-industrial process applications. For Vol. 1, see 80N24797.

Reflow dynamics of thin patterned viscous films

NASA Astrophysics Data System (ADS)

Leveder, T.; Landis, S.; Davoust, L.

2008-01-01

This letter presents a study of viscous smoothening dynamics of a nanopatterned thin film. Ultrathin film manufacturing processes appearing to be a key point of nanotechnology engineering and numerous studies have been recently led in order to exhibit driving parameters of this transient surface motion, focusing on time scale accuracy method. Based on nanomechanical analysis, this letter shows that controlled shape measurements provided much more detailed information about reflow mechanism. Control of reflow process of any complex surface shape, or measurement of material parameter as thin film viscosity, free surface energy, or even Hamaker constant are therefore possible.

Crater studies: Part A: lunar crater morphometry

USGS Publications Warehouse

Pike, Richard J.

1973-01-01

Morphometry, the quantitative study of shape, complements the visual observation and photointerpretation in analyzing the most outstanding landforms of the Moon, its craters (refs. 32-1 and 32-2). All three of these interpretative tools, which were developed throughout the long history of telescopic lunar study preceding the Apollo Program, will continue to be applicable to crater analysis until detailed field work becomes possible. Although no large (>17.5 km diameter) craters were examined in situ on any of the Apollo landings, the photographs acquired from the command modules will markedly strengthen results of less direct investigations of the craters. For morphometry, the most useful materials are the orbital metric and panoramic photographs from the final three Apollo missions. These photographs permit preparation of contour maps, topographic profiles, and other numerical data that accurately portray for the first time the surface geometry of lunar craters of all sizes. Interpretations of craters no longer need be compromised by inadequate topographic data. In the pre-Apollo era, hypotheses for the genesis of lunar craters usually were constructed without any numerical descriptive data. Such speculations will have little credibility unless supported by accurate, quantitative data, especially those generated from Apollo orbital photographs. This paper presents a general study of the surface geometry of 25 far-side craters and a more detailed study of rim-crest evenness for 15 near-side and far-side craters. Analysis of this preliminary sample of Apollo 15 and 17 data, which includes craters between 1.5 and 275 km in diameter, suggests that most genetic interpretations of craters made from pre-Apollo topographic measurements may require no drastic revision. All measurements were made from topographic profiles generated on a stereoplotter at the Photogrammetric Unit of the U.S. Geological Survey, Center of Astrogeology, Flagstaff, Arizona.

The 1996-2006 Job Outlook in Brief.

ERIC Educational Resources Information Center

Melchionno, Rick; Steinman, Michael Sean

1998-01-01

Detailed projections of number employed in 1996, percent change 1996-2006, numerical change, and prospects are provided for occupations in the following clusters: executive/administrative/managerial, professional/technical, marketing/sales, administrative support/clerical, service, mechanics/installers/repairers, construction, production,…

High Throughput Screening For Hazard and Risk of Environmental Contaminants

EPA Science Inventory

High throughput toxicity testing provides detailed mechanistic information on the concentration response of environmental contaminants in numerous potential toxicity pathways. High throughput screening (HTS) has several key advantages: (1) expense orders of magnitude less than an...

New apodizing functions for Fourier spectrometry

NASA Technical Reports Server (NTRS)

Norton, R. H.; Beer, R.

1976-01-01

A new class of apodizing functions suitable for Fourier spectrometry (and similar applications) is introduced. From this class, three specific functions are discussed in detail, and the resulting instrumental line shapes are compared to numerous others proposed for the same purpose.

An efficient numerical method for solving the Boltzmann equation in multidimensions

NASA Astrophysics Data System (ADS)

Dimarco, Giacomo; Loubère, Raphaël; Narski, Jacek; Rey, Thomas

2018-01-01

In this paper we deal with the extension of the Fast Kinetic Scheme (FKS) (Dimarco and Loubère, 2013 [26]) originally constructed for solving the BGK equation, to the more challenging case of the Boltzmann equation. The scheme combines a robust and fast method for treating the transport part based on an innovative Lagrangian technique supplemented with conservative fast spectral schemes to treat the collisional operator by means of an operator splitting approach. This approach along with several implementation features related to the parallelization of the algorithm permits to construct an efficient simulation tool which is numerically tested against exact and reference solutions on classical problems arising in rarefied gas dynamic. We present results up to the 3 D × 3 D case for unsteady flows for the Variable Hard Sphere model which may serve as benchmark for future comparisons between different numerical methods for solving the multidimensional Boltzmann equation. For this reason, we also provide for each problem studied details on the computational cost and memory consumption as well as comparisons with the BGK model or the limit model of compressible Euler equations.

GEOSIM: A numerical model for geophysical fluid flow simulation

NASA Technical Reports Server (NTRS)

Butler, Karen A.; Miller, Timothy L.; Lu, Huei-Iin

1991-01-01

A numerical model which simulates geophysical fluid flow in a wide range of problems is described in detail, and comparisons of some of the model's results are made with previous experimental and numerical studies. The model is based upon the Boussinesq Navier-Stokes equations in spherical coordinates, which can be reduced to a cylindrical system when latitudinal walls are used near the pole and the ratio of latitudinal length to the radius of the sphere is small. The equations are approximated by finite differences in the meridional plane and spectral decomposition in the azimuthal direction. The user can specify a variety of boundary and initial conditions, and there are five different spectral truncation options. The results of five validation cases are presented: (1) the transition between axisymmetric flow and baroclinic wave flow in the side heated annulus; (2) the steady baroclinic wave of the side heated annulus; (3) the wave amplitude vacillation of the side heated annulus; (4) transition to baroclinic wave flow in a bottom heated annulus; and (5) the Spacelab Geophysical Fluid Flow Cell (spherical) experiment.

Optical design of GaN nanowire arrays for photocatalytic applications

NASA Astrophysics Data System (ADS)

Winnerl, Julia; Hudeczek, Richard; Stutzmann, Martin

2018-05-01

GaN nanowire (NW) arrays are interesting candidates for photocatalytic applications due to their high surface-to-volume ratio and their waveguide character. The integration of GaN NW arrays on GaN-based light emitting diodes (LEDs), serving as a platform for electrically driven NW-based photocatalytic devices, enables an efficient coupling of the light from the planar LED to the GaN NWs. Here, we present a numerical study of the influence of the NW geometries, i.e., the NW diameter, length, and period, and the illumination wavelength on the transmission of GaN NW arrays on transparent substrates. A detailed numerical analysis reveals that the transmission characteristics for large periods are determined by the waveguide character of the single NW, whereas for dense GaN NW arrays inter-wire coupling and diffraction effects originating from the periodic arrangement of the GaN NWs dominate the transmission. The numerically simulated results are confirmed by experimental transmission measurements. We also investigate the influence of a dielectric NW shell and of the surrounding medium on the transmission characteristics of a GaN NW array.

Unsteady slip flow of Carreau nanofluid over a wedge with nonlinear radiation and new mass flux condition

NASA Astrophysics Data System (ADS)

Khan, M.; Azam, M.; Alshomrani, A. S.

This article addresses a numerical investigation for the unsteady 2D slip flow of Carreau nanofluid past a static and/or moving wedge with the nonlinear radiation. A zero nanoparticle mass flux and convective boundary conditions are implemented. Further, the most recently devised model for nanofluid is adopted that incorporates the effects of Brownian motion and thermophoresis. A set of suitable transformation is demonstrated to alter the nonlinear partial differential equations into nonlinear ordinary differential equations and then tackled numerically by employing bvp4c in Matlab package. The numerical computations for the wall heat flux (Nusselt number) and wall mass flux (Sherwood number) are also performed. Effects of several controlling parameters on the velocity, temperature and nanoparticles concentration are explored and discussed in detail. Our study reveals that the temperature and the associated thermal boundary layer thickness are enhancing function of the temperature ratio parameter for both shear thickening and shear thinning fluids. Moreover, it is noticed that the velocity in case of moving wedge is higher than static wedge.

Urban pluvial flood prediction: a case study evaluating radar rainfall nowcasts and numerical weather prediction models as model inputs.

PubMed

Thorndahl, Søren; Nielsen, Jesper Ellerbæk; Jensen, David Getreuer

2016-12-01

Flooding produced by high-intensive local rainfall and drainage system capacity exceedance can have severe impacts in cities. In order to prepare cities for these types of flood events - especially in the future climate - it is valuable to be able to simulate these events numerically, both historically and in real-time. There is a rather untested potential in real-time prediction of urban floods. In this paper, radar data observations with different spatial and temporal resolution, radar nowcasts of 0-2 h leadtime, and numerical weather models with leadtimes up to 24 h are used as inputs to an integrated flood and drainage systems model in order to investigate the relative difference between different inputs in predicting future floods. The system is tested on the small town of Lystrup in Denmark, which was flooded in 2012 and 2014. Results show it is possible to generate detailed flood maps in real-time with high resolution radar rainfall data, but rather limited forecast performance in predicting floods with leadtimes more than half an hour.

Luminescence emission from Al0.3Ga0.7N/GaN multi quantum disc core/shell nanowire: Numerical approach

NASA Astrophysics Data System (ADS)

Namvari, E.; Shojaei, S.; Asgari, A.

2017-09-01

In this work, a numerical approach to investigate the room temperature luminescence emission from core/shell nanowire is presented where GaN quantum discs (QDiscs), periodically distributed in AlxGa1-xN nanowire, is considered as core and AlxGa1-xN as shell. Thin disc shaped (Ring shaped) n-doped region has been placed at the GaN/ AlxGa1-xN (AlxGa1-xN /air) interface in AlxGa1-xN region in axial (radial) directions. To obtain energy levels and related wavefunctions, self-consistent procedure has been employed to solve Schrodinger-Poisson equations with considering the spontaneous and piezoelectric polarization. Then luminescence spectrum is studied in details to recognize the parameters influent in luminescence. The results show that the amount of doping, size of QDiscs and theirs numbers have remarkable effects on the band to band luminescence emission. Our numerical calculations gives some insights into the luminescence emission of core/shell nanowire and exhibits a useful tool to analyze findings in experiments.

Numerical Analysis of Infiltration Into a Sand Profile Bounded by a Capillary Fringe

NASA Astrophysics Data System (ADS)

Curtis, Alan A.; Watson, Keith K.

1980-04-01

The rapid response sometimes observed in a tile drain system following surface ponding of water is discussed in terms of the air compressibility effect. An earlier numerical study describing water movement into a bounded profile with a lower boundary impermeable to the passage of both air and water is reviewed with particular reference to the validity of the time-dependent boundary condition transformation used in simulating the inhibiting effects of the air pressure increase on infiltration. The extension of the transformation approach to a profile bounded by a capillary fringe is then considered in detail, and the results of numerical analyses are presented for infiltration into two columns of a fine sand initially in hydraulic equilibrium from a prior gravity drainage regime. The shorter column develops a steady state flow condition at short times which is consistent with earlier experimental findings. In contrast, the pressure of the entrapped air in the longer column gradually increases as infiltration proceeds until the analysis is terminated when air escape through the lower boundary is imminent.

3D lattice distortions and defect structures in ion-implanted nano-crystals

DOE PAGES

Hofmann, Felix; Robinson, Ian K.; Tarleton, Edmund; ...

2017-04-06

The ability of Focused Ion Beam (FIB) techniques to cut solid matter at the nano-scale revolutionized the study of material structure across the life-, earth- and material sciences. But a detailed understanding of the damage caused by the ion beam and its effect on material properties remains elusive. We examine this damage in 3D using coherent X-ray diffraction to measure the full lattice strain tensor in FIB-milled gold nano-crystals. We also found that even very low ion doses, previously thought to be negligible, cause substantial lattice distortions. At higher doses, extended self-organized defect structures appear. Combined with detailed numerical calculations,more » these observations allow fundamental insight into the nature of the damage created and the structural instabilities that lead to a surprisingly inhomogeneous morphology.« less

3D lattice distortions and defect structures in ion-implanted nano-crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hofmann, Felix; Robinson, Ian K.; Tarleton, Edmund

The ability of Focused Ion Beam (FIB) techniques to cut solid matter at the nano-scale revolutionized the study of material structure across the life-, earth- and material sciences. But a detailed understanding of the damage caused by the ion beam and its effect on material properties remains elusive. We examine this damage in 3D using coherent X-ray diffraction to measure the full lattice strain tensor in FIB-milled gold nano-crystals. We also found that even very low ion doses, previously thought to be negligible, cause substantial lattice distortions. At higher doses, extended self-organized defect structures appear. Combined with detailed numerical calculations,more » these observations allow fundamental insight into the nature of the damage created and the structural instabilities that lead to a surprisingly inhomogeneous morphology.« less

Measuring the Carotid to Femoral Pulse Wave Velocity (Cf-PWV) to Evaluate Arterial Stiffness.

PubMed

Ji, Hongwei; Xiong, Jing; Yu, Shikai; Chi, Chen; Bai, Bin; Teliewubai, Jiadela; Lu, Yuyan; Zhang, Yi; Xu, Yawei

2018-05-03

For the elderly, arterial stiffening is a good marker for aging evaluation and it is recommended that the arterial stiffness be determined noninvasively by the measurement of carotid to femoral pulse wave velocity (cf-PWV) (Class I; Level of Evidence A). In literature, numerous community-based or disease-specific studies have reported that higher cf-PWV is associated with increased cardiovascular risk. Here, we discuss strategies to evaluate arterial stiffness with cf-PWV. Following the well-defined steps detailed here, e.g., proper position operator, distance measurement, and tonometer position, we will obtain a standard cf-PWV value to evaluate arterial stiffness. In this paper, a detailed stepwise method to record a good quality PWV and pulse wave analysis (PWA) using a non-invasive tonometry-based device will be discussed.

An integrated Navier-Stokes - full potential - free wake method for rotor flows

NASA Astrophysics Data System (ADS)

Berkman, Mert Enis

1998-12-01

The strong wake shed from rotary wings interacts with almost all components of the aircraft, and alters the flow field thus causing performance and noise problems. Understanding and modeling the behavior of this wake, and its effect on the aerodynamics and acoustics of helicopters have remained as challenges. This vortex wake and its effect should be accurately accounted for in any technique that aims to predict rotor flow field and performance. In this study, an advanced and efficient computational technique for predicting three-dimensional unsteady viscous flows over isolated helicopter rotors in hover and in forward flight is developed. In this hybrid technique, the advantages of various existing methods have been combined to accurately and efficiently study rotor flows with a single numerical method. The flow field is viewed in three parts: (i) an inner zone surrounding each blade where the wake and viscous effects are numerically captured, (ii) an outer zone away from the blades where wake is modeled, and (iii) a Lagrangean wake which induces wake effects in the outer zone. This technique was coded in a flow solver and compared with experimental data for hovering and advancing rotors including a two-bladed rotor, the UH-60A rotor and a tapered tip rotor. Detailed surface pressure, integrated thrust and torque, sectional thrust, and tip vortex position predictions compared favorably against experimental data. Results indicated that the hybrid solver provided accurate flow details and performance information typically in one-half to one-eighth cost of complete Navier-Stokes methods.

Assessing the groundwater fortunes of aquifers in the White Volta Basin, Ghana: An application of numerical groundwater flow modeling and isotopic studies

NASA Astrophysics Data System (ADS)

Oteng, F. M.; Yidana, S. M.; Alo, C. A.

2012-12-01

Effective development and informed management of groundwater resources represent a critical opportunity for improved rural water supply in Ghana and enhanced livelihoods particularly in the northern part of the White Volta Basin, a region already prone to a myriad of water-related infirmities. If adequately developed, the resource will form a sufficient buffer against the effects of climate change/variability and foster food security and sustainable livelihoods among the largely peasant communities in the region. This research presents the results of a preliminary assessment of the hydrogeological conditions and recharge regimes of the aquifers in the Northern parts of the White Volta Basin, Ghana. Results of estimates of groundwater recharge through the conventional isotopic and mass balance techniques are presented. Details of the groundwater flow pattern and preliminary delineation of local and regional groundwater recharge areas are presented from initial simulations of the hydrogeological system with a robust groundwater flow simulation code, MODFLOW, in the Groundwater Modeling System, GMS, version 7.1. The stream flow and evapotranspiration components of the program were activated to incorporate surface flow processes, so that the resulting model represents the conditions of the entire hydrological system. The results of this study form a platform for detailed numerical assessment of the conditions of the aquifers in the area under transient conditions of fluctuating rainfall patterns in the face of climate change/variability.

Implementation details of the coupled QMR algorithm

NASA Technical Reports Server (NTRS)

Freund, Roland W.; Nachtigal, Noel M.

1992-01-01

The original quasi-minimal residual method (QMR) relies on the three-term look-ahead Lanczos process, to generate basis vectors for the underlying Krylov subspaces. However, empirical observations indicate that, in finite precision arithmetic, three-term vector recurrences are less robust than mathematically equivalent coupled two-term recurrences. Therefore, we recently proposed a new implementation of the QMR method based on a coupled two-term look-ahead Lanczos procedure. In this paper, we describe implementation details of this coupled QMR algorithm, and we present results of numerical experiments.

Lagrangian continuum dynamics in ALEGRA.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wong, Michael K. W.; Love, Edward

Alegra is an ALE (Arbitrary Lagrangian-Eulerian) multi-material finite element code that emphasizes large deformations and strong shock physics. The Lagrangian continuum dynamics package in Alegra uses a Galerkin finite element spatial discretization and an explicit central-difference stepping method in time. The goal of this report is to describe in detail the characteristics of this algorithm, including the conservation and stability properties. The details provided should help both researchers and analysts understand the underlying theory and numerical implementation of the Alegra continuum hydrodynamics algorithm.

Thermal radiative properties: Nonmetallic solids.

NASA Technical Reports Server (NTRS)

Touloukian, Y. S.; Dewitt, D. P.

1972-01-01

The volume consists of a text on theory, estimation, and measurement, together with its bibliography, the main body of numerical data and its references, and the material index. The text material assumes a role complementary to the main body of numerical data. The physics and basic concepts of thermal radiation are discussed in detail, focusing attention on treatment of nonmetallic materials: theory, estimation, and methods of measurement. Numerical data is presented in a comprehensive manner. The scope of coverage includes the nonmetallic elements and their compounds, intermetallics, polymers, glasses, and minerals. Analyzed data graphs provide an evaluative review of the data. All data have been obtained from their original sources, and each data set is so referenced.

Lagrangian analysis of multiscale particulate flows with the particle finite element method

NASA Astrophysics Data System (ADS)

Oñate, Eugenio; Celigueta, Miguel Angel; Latorre, Salvador; Casas, Guillermo; Rossi, Riccardo; Rojek, Jerzy

2014-05-01

We present a Lagrangian numerical technique for the analysis of flows incorporating physical particles of different sizes. The numerical approach is based on the particle finite element method (PFEM) which blends concepts from particle-based techniques and the FEM. The basis of the Lagrangian formulation for particulate flows and the procedure for modelling the motion of small and large particles that are submerged in the fluid are described in detail. The numerical technique for analysis of this type of multiscale particulate flows using a stabilized mixed velocity-pressure formulation and the PFEM is also presented. Examples of application of the PFEM to several particulate flows problems are given.

Large-Scale Simulations and Detailed Flow Field Measurements for Turbomachinery Aeroacoustics

NASA Technical Reports Server (NTRS)

VanZante, Dale

2008-01-01

The presentation is a review of recent work in highly loaded compressors, turbine aeroacoustics and cooling fan noise. The specific topics are: the importance of correct numerical modeling to capture blade row interactions in the Ultra Efficient Engine Technology Proof-of-Concept Compressor, the attenuation of a detonation pressure wave by an aircraft axial turbine stage, current work on noise sources and acoustic attenuation in turbines, and technology development work on cooling fans for spaceflight applications. The topic areas were related to each other by certain themes such as the advantage of an experimentalist s viewpoint when analyzing numerical simulations and the need to improve analysis methods for very large numerical datasets.

Isogeometric analysis: a powerful numerical tool for the elastic analysis of historical masonry arches

NASA Astrophysics Data System (ADS)

Cazzani, Antonio; Malagù, Marcello; Turco, Emilio

2016-03-01

We illustrate a numerical tool for analyzing plane arches such as those frequently used in historical masonry heritage. It is based on a refined elastic mechanical model derived from the isogeometric approach. In particular, geometry and displacements are modeled by means of non-uniform rational B-splines. After a brief introduction, outlining the basic assumptions of this approach and the corresponding modeling choices, several numerical applications to arches, which are typical of masonry structures, show the performance of this novel technique. These are discussed in detail to emphasize the advantage and potential developments of isogeometric analysis in the field of structural analysis of historical masonry buildings with complex geometries.

Numerical study of the direct pressure effect of acoustic waves in planar premixed flames

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmidt, H.; Jimenez, C.

Recently the unsteady response of 1-D premixed flames to acoustic pressure waves for the range of frequencies below and above the inverse of the flame transit time was investigated experimentally using OH chemiluminescence Wangher (2008). They compared the frequency dependence of the measured response to the prediction of an analytical model proposed by Clavin et al. (1990), derived from the standard flame model (one-step Arrhenius kinetics) and to a similar model proposed by McIntosh (1991). Discrepancies between the experimental results and the model led to the conclusion that the standard model does not provide an adequate description of the unsteadymore » response of real flames and that it is necessary to investigate more realistic chemical models. Here we follow exactly this suggestion and perform numerical studies of the response of lean methane flames using different reaction mechanisms. We find that the global flame response obtained with both detailed chemistry (GRI3.0) and a reduced multi-step model by Peters (1996) lies slightly above the predictions of the analytical model, but is close to experimental results. We additionally used an irreversible one-step Arrhenius reaction model and show the effect of the pressure dependence of the global reaction rate in the flame response. Our results suggest first that the current models have to be extended to capture the amplitude and phase results of the detailed mechanisms, and second that the correlation between the heat release and the measured OH* chemiluminescence should be studied deeper. (author)« less

Age-of-Air, Tape Recorder, and Vertical Transport Schemes

NASA Technical Reports Server (NTRS)

Lin, S.-J.; Einaudi, Franco (Technical Monitor)

2000-01-01

A numerical-analytic investigation of the impacts of vertical transport schemes on the model simulated age-of-air and the so-called 'tape recorder' will be presented using an idealized 1-D column transport model as well as a more realistic 3-D dynamical model. By comparing to the 'exact' solutions of 'age-of-air' and the 'tape recorder' obtainable in the 1-D setting, useful insight is gained on the impacts of numerical diffusion and dispersion of numerical schemes used in global models. Advantages and disadvantages of Eulerian, semi-Lagrangian, and Lagrangian transport schemes will be discussed. Vertical resolution requirement for numerical schemes as well as observing systems for capturing the fine details of the 'tape recorder' or any upward propagating wave-like structures can potentially be derived from the 1-D analytic model.

Numerical FEM modeling in dental implantology

NASA Astrophysics Data System (ADS)

Roateşi, Iulia; Roateşi, Simona

2016-06-01

This paper is devoted to a numerical approach of the stress and displacement calculation of a system made up of dental implant, ceramic crown and surrounding bone. This is the simulation of a clinical situation involving both biological - the bone tissue, and non-biological - the implant and the crown, materials. On the other hand this problem deals with quite fine technical structure details - the threads, tapers, etc with a great impact in masticatory force transmission. Modeling the contact between the implant and the bone tissue is important to a proper bone-implant interface model and implant design. The authors proposed a three-dimensional numerical model to assess the biomechanical behaviour of this complex structure in order to evaluate its stability by determining the risk zones. A comparison between this numerical analysis and clinical cases is performed and a good agreement is obtained.

Fire Suppression in Low Gravity Using a Cup Burner

NASA Technical Reports Server (NTRS)

Takahashi, Fumiaki; Linteris, Gregory T.; Katta, Viswanath R.

2004-01-01

Longer duration missions to the moon, to Mars, and on the International Space Station increase the likelihood of accidental fires. The goal of the present investigation is to: (1) understand the physical and chemical processes of fire suppression in various gravity and O2 levels simulating spacecraft, Mars, and moon missions; (2) provide rigorous testing of numerical models, which include detailed combustion suppression chemistry and radiation sub-models; and (3) provide basic research results useful for advances in space fire safety technology, including new fire-extinguishing agents and approaches. The structure and extinguishment of enclosed, laminar, methane-air co-flow diffusion flames formed on a cup burner have been studied experimentally and numerically using various fire-extinguishing agents (CO2, N2, He, Ar, CF3H, and Fe(CO)5). The experiments involve both 1g laboratory testing and low-g testing (in drop towers and the KC-135 aircraft). The computation uses a direct numerical simulation with detailed chemistry and radiative heat-loss models. An agent was introduced into a low-speed coflowing oxidizing stream until extinguishment occurred under a fixed minimal fuel velocity, and thus, the extinguishing agent concentrations were determined. The extinguishment of cup-burner flames, which resemble real fires, occurred via a blowoff process (in which the flame base drifted downstream) rather than the global extinction phenomenon typical of counterflow diffusion flames. The computation revealed that the peak reactivity spot (the reaction kernel) formed in the flame base was responsible for attachment and blowoff of the trailing diffusion flame. Furthermore, the buoyancy-induced flame flickering in 1g and thermal and transport properties of the agents affected the flame extinguishment limits.

Fire Suppression in Low Gravity Using a Cup Burner

NASA Technical Reports Server (NTRS)

Takahashi, Fumiaki; Linteris, Gregory T.; Katta, Viswanath R.

2004-01-01

Longer duration missions to the moon, to Mars, and on the International Space Station increase the likelihood of accidental fires. The goal of the present investigation is to: (1) understand the physical and chemical processes of fire suppression in various gravity and O2 levels simulating spacecraft, Mars, and moon missions; (2) provide rigorous testing of numerical models, which include detailed combustion-suppression chemistry and radiation sub-models; and (3) provide basic research results useful for advances in space fire safety technology, including new fire-extinguishing agents and approaches.The structure and extinguishment of enclosed, laminar, methane-air co-flow diffusion flames formed on a cup burner have been studied experimentally and numerically using various fire-extinguishing agents (CO2, N2, He, Ar, CF3H, and Fe(CO)5). The experiments involve both 1g laboratory testing and low-g testing (in drop towers and the KC-135 aircraft). The computation uses a direct numerical simulation with detailed chemistry and radiative heat-loss models. An agent was introduced into a low-speed coflowing oxidizing stream until extinguishment occurred under a fixed minimal fuel velocity, and thus, the extinguishing agent concentrations were determined. The extinguishment of cup-burner flames, which resemble real fires, occurred via a blowoff process (in which the flame base drifted downstream) rather than the global extinction phenomenon typical of counterflow diffusion flames. The computation revealed that the peak reactivity spot (the reaction kernel) formed in the flame base was responsible for attachment and blowoff of the trailing diffusion flame. Furthermore, the buoyancy-induced flame flickering in 1g and thermal and transport properties of the agents affected the flame extinguishment limits.

Detailed Analysis of the Interoccurrence Time Statistics in Seismic Activity

NASA Astrophysics Data System (ADS)

Tanaka, Hiroki; Aizawa, Yoji

2017-02-01

The interoccurrence time statistics of seismiciry is studied theoretically as well as numerically by taking into account the conditional probability and the correlations among many earthquakes in different magnitude levels. It is known so far that the interoccurrence time statistics is well approximated by the Weibull distribution, but the more detailed information about the interoccurrence times can be obtained from the analysis of the conditional probability. Firstly, we propose the Embedding Equation Theory (EET), where the conditional probability is described by two kinds of correlation coefficients; one is the magnitude correlation and the other is the inter-event time correlation. Furthermore, the scaling law of each correlation coefficient is clearly determined from the numerical data-analysis carrying out with the Preliminary Determination of Epicenter (PDE) Catalog and the Japan Meteorological Agency (JMA) Catalog. Secondly, the EET is examined to derive the magnitude dependence of the interoccurrence time statistics and the multi-fractal relation is successfully formulated. Theoretically we cannot prove the universality of the multi-fractal relation in seismic activity; nevertheless, the theoretical results well reproduce all numerical data in our analysis, where several common features or the invariant aspects are clearly observed. Especially in the case of stationary ensembles the multi-fractal relation seems to obey an invariant curve, furthermore in the case of non-stationary (moving time) ensembles for the aftershock regime the multi-fractal relation seems to satisfy a certain invariant curve at any moving times. It is emphasized that the multi-fractal relation plays an important role to unify the statistical laws of seismicity: actually the Gutenberg-Richter law and the Weibull distribution are unified in the multi-fractal relation, and some universality conjectures regarding the seismicity are briefly discussed.

Computations of Complex Three-Dimensional Turbulent Free Jets

NASA Technical Reports Server (NTRS)

Wilson, Robert V.; Demuren, Ayodeji O.

1997-01-01

Three-dimensional, incompressible turbulent jets with rectangular and elliptical cross-sections are simulated with a finite-difference numerical method. The full Navier- Stokes equations are solved at low Reynolds numbers, whereas at high Reynolds numbers filtered forms of the equations are solved along with a sub-grid scale model to approximate the effects of the unresolved scales. A 2-N storage, third-order Runge-Kutta scheme is used for temporary discretization and a fourth-order compact scheme is used for spatial discretization. Although such methods are widely used in the simulation of compressible flows, the lack of an evolution equation for pressure or density presents particular difficulty in incompressible flows. The pressure-velocity coupling must be established indirectly. It is achieved, in this study, through a Poisson equation which is solved by a compact scheme of the same order of accuracy. The numerical formulation is validated and the dispersion and dissipation errors are documented by the solution of a wide range of benchmark problems. Three-dimensional computations are performed for different inlet conditions which model the naturally developing and forced jets. The experimentally observed phenomenon of axis-switching is captured in the numerical simulation, and it is confirmed through flow visualization that this is based on self-induction of the vorticity field. Statistical quantities such as mean velocity, mean pressure, two-point velocity spatial correlations and Reynolds stresses are presented. Detailed budgets of the mean momentum and Reynolds stresses are presented. Detailed budgets of the mean momentum and Reynolds stress equations are presented to aid in the turbulence modeling of complex jets. Simulations of circular jets are used to quantify the effect of the non-uniform curvature of the non-circular jets.

Testing the conditional mass function of dark matter haloes against numerical N-body simulations

NASA Astrophysics Data System (ADS)

Tramonte, D.; Rubiño-Martín, J. A.; Betancort-Rijo, J.; Dalla Vecchia, C.

2017-05-01

We compare the predicted conditional mass function (CMF) of dark matter haloes from two theoretical prescriptions against numerical N-body simulations, both in overdense and underdense regions and at different Eulerian scales ranging from 5 to 30 h-1 Mpc. In particular, we consider in detail a locally implemented rescaling of the unconditional mass function (UMF) already discussed in the literature, and also a generalization of the standard rescaling method described in the extended Press-Schechter formalism. First, we test the consistency of these two rescalings by verifying the normalization of the CMF at different scales, and showing that none of the proposed cases provides a normalized CMF. In order to satisfy the normalization condition, we include a modification in the rescaling procedure. After this modification, the resulting CMF generally provides a better description of numerical results. We finally present an analytical fit to the ratio between the CMF and the UMF (also known as the matter-to-halo bias function) in underdense regions, which could be of special interest to speed up the computation of the halo abundance when studying void statistics. In this case, the CMF prescription based on the locally implemented rescaling provides a slightly better description of the numerical results when compared to the standard rescaling.

Numerical analysis of the turbulent fluid flow through valves. Geometrical aspects influence at different positions

NASA Astrophysics Data System (ADS)

Rigola, J.; Aljure, D.; Lehmkuhl, O.; Pérez-Segarra, C. D.; Oliva, A.

2015-08-01

The aim of this paper is to carry out a group of numerical experiments over the fluid flow through a valve reed, using the CFD&HT code TermoFluids, an unstructured and parallel object-oriented CFD code for accurate and reliable solving of industrial flows. Turbulent flow and its solution is a very complex problem due to there is a non-lineal interaction between viscous and inertial effects further complicated by their rotational nature, together with the three-dimensionality inherent in these types of flow and the non-steady state solutions. In this work, different meshes, geometrical conditions and LES turbulence models (WALE, VMS, QR and SIGMA) are tested and results compared. On the other hand, the fluid flow boundary conditions are obtained by means of the numerical simulation model of hermetic reciprocating compressors tool, NEST-compressor code. The numerical results presented are based on a specific geometry, where the valve gap opening percentage is 11% of hole diameter and Reynolds numbers given by the one-dimensional model is 4.22 × 105, with density meshes of approximately 8 million CVs. Geometrical aspects related with the orifice's shape and its influence on fluid flow behaviour and pressure drop are analysed in detail, furthermore, flow results for different valve openings are also studied.

Combination of experimental and numerical methods for mechanical characterization of Al-Si alloys

NASA Astrophysics Data System (ADS)

Kruglova, A.; Roland, M.; Diebels, S.; Mücklich, F.

2017-10-01

In general, mechanical properties of Al-Si alloys strongly depend on the morphology and arrangement of microconstituents, such as primary aluminium dendrites, silicon particles, etc. Therefore, a detailed characterization of morphological and mechanical properties of the alloys is necessary to better understand the relations between the underlined properties and to tailor the material’s microstructure to the specific application needs. The mechanical characterization usually implies numerical simulations and mechanical tests, which allow to investigate the influence of different microstructural aspects on different scales. In this study, the uniaxial tension and compression tests have been carried out on Al-Si alloys having different microstructures. The mechanical behavior of the alloys has been interpreted with respect to the morphology of the microconstituents and has been correlated with the results of numerical simulations. The advantages and limitations of the experimental and numerical methods have been disclosed and the importance of combining both techniques for the interpretation of the mechanical behavior of Al-Si alloys has been shown. Thereby, it has been suggested that the density of Si particles and the size of Al dendrites are more important for the strengthening of the alloys than the size-shape features of the eutectic Si induced by the modification.

A Gaussian quadrature method for total energy analysis in electronic state calculations

NASA Astrophysics Data System (ADS)

Fukushima, Kimichika

This article reports studies by Fukushima and coworkers since 1980 concerning their highly accurate numerical integral method using Gaussian quadratures to evaluate the total energy in electronic state calculations. Gauss-Legendre and Gauss-Laguerre quadratures were used for integrals in the finite and infinite regions, respectively. Our previous article showed that, for diatomic molecules such as CO and FeO, elliptic coordinates efficiently achieved high numerical integral accuracy even with a numerical basis set including transition metal atomic orbitals. This article will generalize straightforward details for multiatomic systems with direct integrals in each decomposed elliptic coordinate determined from the nuclear positions of picked-up atom pairs. Sample calculations were performed for the molecules O3 and H2O. This article will also try to present, in another coordinate, a numerical integral by partially using the Becke's decomposition published in 1988, but without the Becke's fuzzy cell generated by the polynomials of internuclear distance between the pair atoms. Instead, simple nuclear weights comprising exponential functions around nuclei are used. The one-center integral is performed with a Gaussian quadrature pack in a spherical coordinate, included in the author's original program in around 1980. As for this decomposition into one-center integrals, sample calculations are carried out for Li2.

Lax-Wendroff and TVD finite volume methods for unidimensional thermomechanical numerical simulations of impacts on elastic-plastic solids

NASA Astrophysics Data System (ADS)

Heuzé, Thomas

2017-10-01

We present in this work two finite volume methods for the simulation of unidimensional impact problems, both for bars and plane waves, on elastic-plastic solid media within the small strain framework. First, an extension of Lax-Wendroff to elastic-plastic constitutive models with linear and nonlinear hardenings is presented. Second, a high order TVD method based on flux-difference splitting [1] and Superbee flux limiter [2] is coupled with an approximate elastic-plastic Riemann solver for nonlinear hardenings, and follows that of Fogarty [3] for linear ones. Thermomechanical coupling is accounted for through dissipation heating and thermal softening, and adiabatic conditions are assumed. This paper essentially focuses on one-dimensional problems since analytical solutions exist or can easily be developed. Accordingly, these two numerical methods are compared to analytical solutions and to the explicit finite element method on test cases involving discontinuous and continuous solutions. This allows to study in more details their respective performance during the loading, unloading and reloading stages. Particular emphasis is also paid to the accuracy of the computed plastic strains, some differences being found according to the numerical method used. Lax-Wendoff two-dimensional discretization of a one-dimensional problem is also appended at the end to demonstrate the extensibility of such numerical scheme to multidimensional problems.

Wing galaxies: A formation mechanism of the clumpy irregular galaxy Markarian 297

NASA Technical Reports Server (NTRS)

Taniguchi, Yoshiaki; Noguchi, Masafumi

1990-01-01

In order to contribute to an understanding of collision-induced starburst activities, the authors present a detailed case study on the starburst galaxy Markarian 297 (= NGC 6052 = Arp 209; hereafter Mrk 297). This galaxy is classified as a clumpy irregular galaxy (CIG) according to its morphological properties (cf. Heidmann, 1987). Two major clumps and many small clumps are observed in the entire region of Mrk 297 (Hecquet, Coupinot, and Maucherat 1987). The overall morphology of Mrk 297 is highly chaotic and thus it seems difficult to determine possible orbits of galaxy-galaxy collision. However, the authors have serendipitously found a possible orbit during a course of numerical simulations for a radial-penetration collision between galaxies. The radial-penetration collision means that an intruder penetrates a target galaxy radially passing by its nucleus. This kind of collision is known to explain a formation mechanism of ripples around disk galaxies (Wallin and Struck-Marcell 1988). Here, the authors show that the radial-penetration collision between galaxies successfully explains both overall morphological and kinematical properties of Mrk 297. The authors made two kinds of numerical simulations for Mrk 297. One is N-body (1x10(exp 4) particles) simulations in which effects of self gravity of the stellar disk are taken into account. These simulations are used to study detailed morphological feature of Mrk 297. The response of gas clouds are also investigated in order to estimate star formation rates in such collisions. The other is test-particle simulations, which are utilized to obtain a rough picture of Mrk 297 and to analyze the velocity field of Mrk 297. The techniques of the numerical simulations are the same as those in Noguchi (1988) and Noguchi and Ishibashi (1986). In the present model, an intruding galaxy with the same mass of a target galaxy moves on a rectilinear orbit which passes the center of the target.

A Numerical Study on Toppling Failure of a Jointed Rock Slope by Using the Distinct Lattice Spring Model

NASA Astrophysics Data System (ADS)

Lian, Ji-Jian; Li, Qin; Deng, Xi-Fei; Zhao, Gao-Feng; Chen, Zu-Yu

2018-02-01

In this work, toppling failure of a jointed rock slope is studied by using the distinct lattice spring model (DLSM). The gravity increase method (GIM) with a sub-step loading scheme is implemented in the DLSM to mimic the loading conditions of a centrifuge test. A classical centrifuge test for a jointed rock slope, previously simulated by the finite element method and the discrete element model, is simulated by using the GIM-DLSM. Reasonable boundary conditions are obtained through detailed comparisons among existing numerical solutions with experimental records. With calibrated boundary conditions, the influences of the tensional strength of the rock block, cohesion and friction angles of the joints, as well as the spacing and inclination angles of the joints, on the flexural toppling failure of the jointed rock slope are investigated by using the GIM-DLSM, leading to some insight into evaluating the state of flexural toppling failure for a jointed slope and effectively preventing the flexural toppling failure of jointed rock slopes.

Numerical Investigation of Nanofluid Laminar Forced Convective Heat Transfer inside an Equilateral Triangular Tube

NASA Astrophysics Data System (ADS)

Etminan, Amin; Harun, Zambri; Sharifian, Ahmad

2017-01-01

In this article distilled water and CuO particles with volume fraction of 1%, 2% and 4% are studied numerically. The steady state flow regime is considered laminar with Reynolds number of 100 and nanoparticles diameters (dp) are set in the range of 20 nm and 80 nm. The hydraulic diameter and the length of equilateral triangular channel are 8 mm and 1000 mm respectively. The problem is solved using finite volume method with constant heat flux for two sides and constant temperature for one side. Convective heat transfer coefficient, Nusselt number and convective heat transfer coefficient distribution on walls are investigated in details. The fluid flow is supposed to be one phase flow. It can be observed that nanofluid leads to a remarkable enhancement on heat transfer coefficient pressure loss through the channel. The computations reveal that the size of nanoparticles has no significant influence on heat transfer properties. Besides, the study shows a good agreement between current results and experimental data in the literatures.

Numerical study of the ignition behavior of a post-discharge kernel injected into a turbulent stratified cross-flow

NASA Astrophysics Data System (ADS)

Jaravel, Thomas; Labahn, Jeffrey; Ihme, Matthias

2017-11-01

The reliable initiation of flame ignition by high-energy spark kernels is critical for the operability of aviation gas turbines. The evolution of a spark kernel ejected by an igniter into a turbulent stratified environment is investigated using detailed numerical simulations with complex chemistry. At early times post ejection, comparisons of simulation results with high-speed Schlieren data show that the initial trajectory of the kernel is well reproduced, with a significant amount of air entrainment from the surrounding flow that is induced by the kernel ejection. After transiting in a non-flammable mixture, the kernel reaches a second stream of flammable methane-air mixture, where the successful of the kernel ignition was found to depend on the local flow state and operating conditions. By performing parametric studies, the probability of kernel ignition was identified, and compared with experimental observations. The ignition behavior is characterized by analyzing the local chemical structure, and its stochastic variability is also investigated.

Thermal Property Measurement of Semiconductor Melt using Modified Laser Flash Method

NASA Technical Reports Server (NTRS)

Lin, Bochuan; Zhu, Shen; Ban, Heng; Li, Chao; Scripa, Rosalla N.; Su, Ching-Hua; Lehoczky, Sandor L.

2003-01-01

This study further developed standard laser flash method to measure multiple thermal properties of semiconductor melts. The modified method can determine thermal diffusivity, thermal conductivity, and specific heat capacity of the melt simultaneously. The transient heat transfer process in the melt and its quartz container was numerically studied in detail. A fitting procedure based on numerical simulation results and the least root-mean-square error fitting to the experimental data was used to extract the values of specific heat capacity, thermal conductivity and thermal diffusivity. This modified method is a step forward from the standard laser flash method, which is usually used to measure thermal diffusivity of solids. The result for tellurium (Te) at 873 K: specific heat capacity 300.2 Joules per kilogram K, thermal conductivity 3.50 Watts per meter K, thermal diffusivity 2.04 x 10(exp -6) square meters per second, are within the range reported in literature. The uncertainty analysis showed the quantitative effect of sample geometry, transient temperature measured, and the energy of the laser pulse.

Unsteady Analysis of Turbine Main Flow Coupled with Secondary Air Flow

NASA Technical Reports Server (NTRS)

Hah, Chunill

2006-01-01

Two numerical approaches are used to model the interaction between the turbine main gas flow and the wheelspace cavity seal flow. The 3-D, unsteady Reynolds-averaged Navier-Stokes equations are solved with a CFD code based on a structured grid to study the interaction between the turbine main gas flow and the wheelspace cavity seal flow. A CFD code based on an unstructured grid is used to solve detailed flow feature in the cavity seal which has a complex geometry. The numerical results confirm various observations from earlier experimental studies under similar flow conditions. When the flow rate through the rim cavity seal is increased, the ingestion of the main turbine flow into the rim seal area decreases drastically. However, a small amount of main gas flow is ingested to the rim seal area even with very high level of seal flow rate. This is due to the complex nature of 3-D, unsteady flow interaction near the hub of the turbine stage.

Numerical modeling and simulation studies for the M4 adaptive mirror of the E-ELT

NASA Astrophysics Data System (ADS)

Carbillet, Marcel; Riccardi, Armando; Xompero, Marco

2012-07-01

We report in this paper on the progress of numerical modeling and simulation studies of the M4 adaptive mirror, a representative of the "adaptive secondary mirrors" technology, for the European Extremely Large Telescope (E-ELT). This is based on both dedicated routines and the existing code of the Software Package CADS. The points approached are basically the specific problems encountered with this particular type of voice-coil adaptive mirrors on the E-ELT: (*) the segmentation of the adaptive mirror, implying a fitting error due also to the edges of its six petals, as well as possible co-phasing problems to be evaluated in terms of interaction with the wavefront sensor (a pyramid here); (**) the necessary presence of "master" and "slave" actuators which management, in terms of wavefront reconstruction, implies to consider different strategies. The on-going work being performed for the two above points is described in details, and some preliminary results are given.

Locating damage using integrated global-local approach with wireless sensing system and single-chip impedance measurement device.

PubMed

Lin, Tzu-Hsuan; Lu, Yung-Chi; Hung, Shih-Lin

2014-01-01

This study developed an integrated global-local approach for locating damage on building structures. A damage detection approach with a novel embedded frequency response function damage index (NEFDI) was proposed and embedded in the Imote2.NET-based wireless structural health monitoring (SHM) system to locate global damage. Local damage is then identified using an electromechanical impedance- (EMI-) based damage detection method. The electromechanical impedance was measured using a single-chip impedance measurement device which has the advantages of small size, low cost, and portability. The feasibility of the proposed damage detection scheme was studied with reference to a numerical example of a six-storey shear plane frame structure and a small-scale experimental steel frame. Numerical and experimental analysis using the integrated global-local SHM approach reveals that, after NEFDI indicates the approximate location of a damaged area, the EMI-based damage detection approach can then identify the detailed damage location in the structure of the building.

Experimental study of transport of a dimer on a vertically oscillating plate

PubMed Central

Wang, Jiao; Liu, Caishan; Ma, Daolin

2014-01-01

It has recently been shown that a dimer, composed of two identical spheres rigidly connected by a rod, under harmonic vertical vibration can exhibit a self-ordered transport behaviour. In this case, the mass centre of the dimer will perform a circular orbit in the horizontal plane, or a straight line if confined between parallel walls. In order to validate the numerical discoveries, we experimentally investigate the temporal evolution of the dimer's motion in both two- and three-dimensional situations. A stereoscopic vision method with a pair of high-speed cameras is adopted to perform omnidirectional measurements. All the cases studied in our experiments are also simulated using an existing numerical model. The combined investigations detail the dimer's dynamics and clearly show that its transport behaviours originate from a series of combinations of different contact states. This series is critical to our understanding of the transport properties in the dimer's motion and related self-ordered phenomena in granular systems. PMID:25383029

Consumers' Kansei Needs Clustering Method for Product Emotional Design Based on Numerical Design Structure Matrix and Genetic Algorithms.

PubMed

Yang, Yan-Pu; Chen, Deng-Kai; Gu, Rong; Gu, Yu-Feng; Yu, Sui-Huai

2016-01-01

Consumers' Kansei needs reflect their perception about a product and always consist of a large number of adjectives. Reducing the dimension complexity of these needs to extract primary words not only enables the target product to be explicitly positioned, but also provides a convenient design basis for designers engaging in design work. Accordingly, this study employs a numerical design structure matrix (NDSM) by parameterizing a conventional DSM and integrating genetic algorithms to find optimum Kansei clusters. A four-point scale method is applied to assign link weights of every two Kansei adjectives as values of cells when constructing an NDSM. Genetic algorithms are used to cluster the Kansei NDSM and find optimum clusters. Furthermore, the process of the proposed method is presented. The details of the proposed approach are illustrated using an example of electronic scooter for Kansei needs clustering. The case study reveals that the proposed method is promising for clustering Kansei needs adjectives in product emotional design.

Consumers' Kansei Needs Clustering Method for Product Emotional Design Based on Numerical Design Structure Matrix and Genetic Algorithms

PubMed Central

Chen, Deng-kai; Gu, Rong; Gu, Yu-feng; Yu, Sui-huai

2016-01-01

Consumers' Kansei needs reflect their perception about a product and always consist of a large number of adjectives. Reducing the dimension complexity of these needs to extract primary words not only enables the target product to be explicitly positioned, but also provides a convenient design basis for designers engaging in design work. Accordingly, this study employs a numerical design structure matrix (NDSM) by parameterizing a conventional DSM and integrating genetic algorithms to find optimum Kansei clusters. A four-point scale method is applied to assign link weights of every two Kansei adjectives as values of cells when constructing an NDSM. Genetic algorithms are used to cluster the Kansei NDSM and find optimum clusters. Furthermore, the process of the proposed method is presented. The details of the proposed approach are illustrated using an example of electronic scooter for Kansei needs clustering. The case study reveals that the proposed method is promising for clustering Kansei needs adjectives in product emotional design. PMID:27630709

Langley Stability and Transition Analysis Code (LASTRAC) Version 1.2 User Manual

NASA Technical Reports Server (NTRS)

Chang, Chau-Lyan

2004-01-01

LASTRAC is a general-purposed, physics-based transition prediction code released by NASA for Laminar Flow Control studies and transition research. The design and development of the LASTRAC code is aimed at providing an engineering tool that is easy to use and yet capable of dealing with a broad range of transition related issues. It was written from scratch based on the state-of-the-art numerical methods for stability analysis and modern software technologies. At low fidelity, it allows users to perform linear stability analysis and N-factor transition correlation for a broad range of flow regimes and configurations by using either the linear stability theory or linear parabolized stability equations method. At high fidelity, users may use nonlinear PSE to track finite-amplitude disturbances until the skin friction rise. This document describes the governing equations, numerical methods, code development, detailed description of input/output parameters, and case studies for the current release of LASTRAC.

Determination of lateral size distribution of type-II ZnTe/ZnSe stacked submonolayer quantum dots via spectral analysis of optical signature of the Aharanov-Bohm excitons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ji, Haojie; Dhomkar, Siddharth; Roy, Bidisha

2014-10-28

For submonolayer quantum dot (QD) based photonic devices, size and density of QDs are critical parameters, the probing of which requires indirect methods. We report the determination of lateral size distribution of type-II ZnTe/ZnSe stacked submonolayer QDs, based on spectral analysis of the optical signature of Aharanov-Bohm (AB) excitons, complemented by photoluminescence studies, secondary-ion mass spectroscopy, and numerical calculations. Numerical calculations are employed to determine the AB transition magnetic field as a function of the type-II QD radius. The study of four samples grown with different tellurium fluxes shows that the lateral size of QDs increases by just 50%, evenmore » though tellurium concentration increases 25-fold. Detailed spectral analysis of the emission of the AB exciton shows that the QD radii take on only certain values due to vertical correlation and the stacked nature of the QDs.« less

Numerical analysis of tangential slot blowing on a generic chined forebody

NASA Technical Reports Server (NTRS)

Agosta, Roxana M.

1994-01-01

A numerical study is performed to investigate the effects of tangential slot blowing on a generic chined forebody. The Reynolds-averaged, thin-layer, Navier-Stokes equations are solved to obtain the high-angle-of-attack viscous flow field about a generic chined forebody. Tangential slot blowing is investigated as a means of forebody flow control to generate side force and yawing moment on the forebody. The effects of jet mass flow ratios, angle of attack, and blowing slot location in the axial and circumferential directions are studied. The computed results are compared with available wind tunnel experimental data. The solutions with and without blowing are also analyzed using helicity density contours, surface flow patterns, and off-surface instantaneous streamlines. The results of this analysis provide details of the flow field about the generic chined forebody, as well as show that tangential slot blowing can be used as a means of forebody flow control to generate side force and yawing moment.

Chemical laser exhaust pipe design research

NASA Astrophysics Data System (ADS)

Sun, Yunqiang; Huang, Zhilong; Chen, Zhiqiang; Ren, Zebin; Guo, Longde

2016-10-01

In order to weaken the chemical laser exhaust gas influence of the optical transmission, a vent pipe is advised to emissions gas to the outside of the optical transmission area. Based on a variety of exhaust pipe design, a flow field characteristic of the pipe is carried out by numerical simulation and analysis in detail. The research results show that for uniform deflating exhaust pipe, although the pipeline structure is cyclical and convenient for engineering implementation, but there is a phenomenon of air reflows at the pipeline entrance slit which can be deduced from the numerical simulation results. So, this type of pipeline structure does not guarantee seal. For the design scheme of putting the pipeline contract part at the end of the exhaust pipe, or using the method of local area or tail contraction, numerical simulation results show that backflow phenomenon still exists at the pipeline entrance slit. Preliminary analysis indicates that the contraction of pipe would result in higher static pressure near the wall for the low speed flow field, so as to produce counter pressure gradient at the entrance slit. In order to eliminate backflow phenomenon at the pipe entrance slit, concerned with the pipeline type of radial size increase gradually along the flow, flow field property in the pipe is analyzed in detail by numerical simulation methods. Numerical simulation results indicate that there is not reflow phenomenon at entrance slit of the dilated duct. However the cold air inhaled in the slit which makes the temperature of the channel wall is lower than the center temperature. Therefore, this kind of pipeline structure can not only prevent the leak of the gas, but also reduce the wall temperature. In addition, compared with the straight pipe connection way, dilated pipe structure also has periodic structure, which can facilitate system integration installation.

Reduced Order Modeling Incompressible Flows

NASA Technical Reports Server (NTRS)

Helenbrook, B. T.

2010-01-01

The details: a) Need stable numerical methods; b) Round off error can be considerable; c) Not convinced modes are correct for incompressible flow. Nonetheless, can derive compact and accurate reduced-order models. Can be used to generate actuator models or full flow-field models

User's Manual for Downscaler Fusion Software

EPA Science Inventory

Recently, a series of 3 papers has been published in the statistical literature that details the use of downscaling to obtain more accurate and precise predictions of air pollution across the conterminous U.S. This downscaling approach combines CMAQ gridded numerical model output...

Phoneme Similarity and Confusability

ERIC Educational Resources Information Center

Bailey, T.M.; Hahn, U.

2005-01-01

Similarity between component speech sounds influences language processing in numerous ways. Explanation and detailed prediction of linguistic performance consequently requires an understanding of these basic similarities. The research reported in this paper contrasts two broad classes of approach to the issue of phoneme similarity-theoretically…

77 FR 70741 - Agency Information Collection Extension

Federal Register 2010, 2011, 2012, 2013, 2014

2012-11-27

... DEPARTMENT OF ENERGY U.S. Energy Information Administration Agency Information Collection Extension AGENCY: U.S. Energy Information Administration (EIA), U.S. Department of Energy. ACTION: Notice... being achieved. These data are also needed to satisfy numerous public requests for detailed information...

Data access and decision tools for coastal water resources management

EPA Science Inventory

US EPA has supported the development of numerous models and tools to support implementation of environmental regulations. However, transfer of knowledge and methods from detailed technical models to support practical problem solving by local communities and watershed or coastal ...

Numerical Study of Splash Detail Due to Grain Impact on Granular Bed

NASA Astrophysics Data System (ADS)

Tanabe, Takahiro; Niiya, Hirofumi; Awazu, Akinori; Nishimori, Hiraku

2017-04-01

Massive sediment transport phenomena, such as sand storm and drifting snow, pose a considerable threat to human life. Further, the formation of geomorphological patterns on sand-desert and snowfield surfaces as a result of sediment transport, such as dunes and ripples, is of considerable research interest. Because the major component of the grain entrainment into the air is caused by both the collision and ejection, it is necessary to focus on the collisions between wind-blown grains and surface of sand field along with the resultant ejection grains from the surfaces, which processes are, as a whole, called a splash process. However, because of complexity of jumping grains over the ground surface, detailed measurement is very hard. Therefore, to investigate the splash process, we simulate detailed process of splash caused by 1-grain impact onto a randomly packed granular bed using discrete element method. As a result, we obtained good correspondence between our numerical results and the findings of previous experiments for the movement of ejected grains. Furthermore, the distributions of the ejection angle and the vertical ejection speed for individual grains vary depending on the relative timing at which the grains are ejected after the initial impact. Obvious differences are observed between the distributions of grains ejected during the earlier and later splash periods: the form of the vertical ejection-speed distribution varies from a power-law form to a lognormal form with time, and this difference is related to the grain trajectory after ejection [1]. In addition, we focus on the bulk dynamics inside the granular bed to relate the ejected grains behavior to the force propagations from the first impact to the ejection of each grain. [1] T. Tanabe, T. Shimada, N. Ito, and, H. Nishimori, (submitted)

Forecasting of wet snow avalanche activity: Proof of concept and operational implementation

NASA Astrophysics Data System (ADS)

Gobiet, Andreas; Jöbstl, Lisa; Rieder, Hannes; Bellaire, Sascha; Mitterer, Christoph

2017-04-01

State-of-the-art tools for the operational assessment of avalanche danger include field observations, recordings from automatic weather stations, meteorological analyses and forecasts, and recently also indices derived from snowpack models. In particular, an index for identifying the onset of wet-snow avalanche cycles (LWCindex), has been demonstrated to be useful. However, its value for operational avalanche forecasting is currently limited, since detailed, physically based snowpack models are usually driven by meteorological data from automatic weather stations only and have therefore no prognostic ability. Since avalanche risk management heavily relies on timely information and early warnings, many avalanche services in Europe nowadays start issuing forecasts for the following days, instead of the traditional assessment of the current avalanche danger. In this context, the prognostic operation of detailed snowpack models has recently been objective of extensive research. In this study a new, observationally constrained setup for forecasting the onset of wet-snow avalanche cycles with the detailed snow cover model SNOWPACK is presented and evaluated. Based on data from weather stations and different numerical weather prediction models, we demonstrate that forecasts of the LWCindex as indicator for wet-snow avalanche cycles can be useful for operational warning services, but is so far not reliable enough to be used as single warning tool without considering other factors. Therefore, further development currently focuses on the improvement of the forecasts by applying ensemble techniques and suitable post processing approaches to the output of numerical weather prediction models. In parallel, the prognostic meteo-snow model chain is operationally used by two regional avalanche warning services in Austria since winter 2016/2017 for the first time. Experiences from the first operational season and first results from current model developments will be reported.

Role of sediment transport model to improve the tsunami numerical simulation

NASA Astrophysics Data System (ADS)

Sugawara, D.; Yamashita, K.; Takahashi, T.; Imamura, F.

2015-12-01

Are we overlooking an important factor for improved numerical prediction of tsunamis in shallow sea to onshore? In this presentation, several case studies on numerical modeling of tsunami-induced sediment transport are reviewed, and the role of sediment transport models for tsunami inundation simulation is discussed. Large-scale sediment transport and resulting geomorphological change occurred in the coastal areas of Tohoku, Japan, due to the 2011 Tohoku Earthquake Tsunami. Datasets obtained after the tsunami, including geomorphological and sedimentological data as well as hydrodynamic records, allows us to validate the numerical model in detail. The numerical modeling of the sediment transport by the 2011 tsunami depicted the severest erosion of sandy beach, as well as characteristic spatial patterns of erosion and deposition on the seafloor, which have taken place in Hirota Bay, Sanriku Coast. Quantitative comparisons of observation and simulation of the geomorphological changes in Sanriku Coast and Sendai Bay showed that the numerical model can predict the volumes of erosion and deposition with a right order. In addition, comparison of the simulation with aerial video footages demonstrated the numerical model is capable of tracking the overall processes of tsunami sediment transport. Although tsunami-induced sediment erosion and deposition sometimes cause significant geomorphological change, and may enhance tsunami hydrodynamic impact to the coastal zones, most tsunami simulations do not include sediment transport modeling. A coupled modeling of tsunami hydrodynamics and sediment transport draws a different picture of tsunami hazard, comparing with simple hydrodynamic modeling of tsunami inundation. Since tsunami-induced erosion, deposition and geomorphological change sometimes extend more than several kilometers across the coastline, two-dimensional horizontal model are typically used for the computation of tsunami hydrodynamics and sediment transport. Limitations of the conventional model and future challenges are discussed regarding further improvement of numerical modeling of tsunami and sediment transport. Improved numerical modeling may provide useful information for assessing sediment-related damages and planning post-disaster recovery.

Understanding bistability in yeast glycolysis using general properties of metabolic pathways.

PubMed

Planqué, Robert; Bruggeman, Frank J; Teusink, Bas; Hulshof, Josephus

2014-09-01

Glycolysis is the central pathway in energy metabolism in the majority of organisms. In a recent paper, van Heerden et al. showed experimentally and computationally that glycolysis can exist in two states, a global steady state and a so-called imbalanced state. In the imbalanced state, intermediary metabolites accumulate at low levels of ATP and inorganic phosphate. It was shown that Baker's yeast uses a peculiar regulatory mechanism--via trehalose metabolism--to ensure that most yeast cells reach the steady state and not the imbalanced state. Here we explore the apparent bistable behaviour in a core model of glycolysis that is based on a well-established detailed model, and study in great detail the bifurcation behaviour of solutions, without using any numerical information on parameter values. We uncover a rich suite of solutions, including so-called imbalanced states, bistability, and oscillatory behaviour. The techniques employed are generic, directly suitable for a wide class of biochemical pathways, and could lead to better analytical treatments of more detailed models. Copyright © 2014 Elsevier Inc. All rights reserved.

LES-based characterization of a suction and oscillatory blowing fluidic actuator

NASA Astrophysics Data System (ADS)

Kim, Jeonglae; Moin, Parviz

2015-11-01

Recently, a novel fluidic actuator using steady suction and oscillatory blowing was developed for control of turbulent flows. The suction and oscillatory blowing (SaOB) actuator combines steady suction and pulsed oscillatory blowing into a single device. The actuation is based upon a self-sustained mechanism of confined jets and does not require any moving parts. The control output is determined by a pressure source and the geometric details, and no additional input is needed. While its basic mechanisms have been investigated to some extent, detailed characteristics of internal turbulent flows are not well understood. In this study, internal flows of the SaOB actuator are simulated using large-eddy simulation (LES). Flow characteristics within the actuator are described in detail for a better understanding of the physical mechanisms and improving the actuator design. LES predicts the self-sustained oscillations of the turbulent jet. Switching frequency, maximum velocity at the actuator outlets, and wall pressure distribution are in good agreement with the experimental measurements. The computational results are used to develop simplified boundary conditions for numerical experiments of active flow control. Supported by the Boeing company.

I. The theory of aberrations of quadrupole focusing arrays. II. Ion optical design of high quality extracted synchrotron beams with application to the bevatron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meads, Jr, Philip Francis

In Part One they formulate in a general way the problem of analyzing and evaluating the aberrations of quadrupole magnet beam systems, and of characterizing the shapes and other properties of the beam envelopes in the neighborhood of foci. They consider all aberrations, including those due to misalignments and faulty construction, through third order in small parameters, for quadrupole beam systems. One result of this study is the development of analytic and numerical techniques for treating these aberrations, yielding useful expressions for the comparison of the aberrations of different beam systems. A second result of this study is a comprehensivemore » digital computer program that determines the magnitude and nature of the aberrations of such beam systems. The code, using linear programming techniques, will adjust the parameters of a beam system to obtain specified optical properties and to reduce the magnitude of aberrations that limit the performance of that system. They examine numerically, in detail, the aberrations of two typical beam systems. In Part Two, they examine the problem of extracting the proton beam from a synchrotron of 'H' type magnet construction. They describe the optical studies that resulted in the design of an external beam from the Bevatron that is optimized with respect to linear, dispersive, and aberration properties and that uses beam elements of conservative design. The design of the beam is the result of the collaboration of many people representing several disciplines. They describe the digital computer programs developed to carry out detailed orbit studies which were required because of the existence of large second order aberrations in the beam.« less

A study of the temporal stability of multiple cell vortices

NASA Technical Reports Server (NTRS)

Khorrami, Mehdi R.

1989-01-01

The effect of initial mean velocity field on the stability characteristics of longitudinal vortices is documented in detail. The temporal stability of isolated multiple cell vortices is considered. The types of vortices studied include single cell as well as two and three cell vortices. It is shown that cell multiplicity in the vortex core has drastic effects on the stability characteristics. On the basis of numerical calculations, it is concluded that the growth rates of instabilities in multiple cell vortices are substantially larger (two to threefold increases are observed) than those of a single cell vortex. It is also determined that there is a substantial increase in the effective range of axial and azimuthal wavenumbers where instabilities are present. But most importantly, there is the appearance of a variety of viscous modes of instability. In the case of vortices, these latter instabilities which highlight the importance of viscous forces have never been reported before. These effects are discussed in detail for the case of a two cell vortex.

Anatomical and spiral wave reentry in a simplified model for atrial electrophysiology.

PubMed

Richter, Yvonne; Lind, Pedro G; Seemann, Gunnar; Maass, Philipp

2017-04-21

For modeling the propagation of action potentials in the human atria, various models have been developed in the past, which take into account in detail the influence of the numerous ionic currents flowing through the cell membrane. Aiming at a simplified description, the Bueno-Orovio-Cherry-Fenton (BOCF) model for electric wave propagation in the ventricle has been adapted recently to atrial physiology. Here, we study this adapted BOCF (aBOCF) model with respect to its capability to accurately generate spatio-temporal excitation patterns found in anatomical and spiral wave reentry. To this end, we compare results of the aBOCF model with the more detailed one proposed by Courtemanche, Ramirez and Nattel (CRN model). We find that characteristic features of the reentrant excitation patterns seen in the CRN model are well captured by the aBOCF model. This opens the possibility to study origins of atrial fibrillation based on a simplified but still reliable description. Copyright © 2017 Elsevier Ltd. All rights reserved.

Role of hybridization in the superconducting properties of an extended d p Hubbard model: a detailed numerical study

NASA Astrophysics Data System (ADS)

Calegari, E. J.; Magalhães, S. G.; Gomes, A. A.

2005-04-01

The Roth's two-pole approximation has been used by the present authors to study the effects of the hybridization in the superconducting properties of a strongly correlated electron system. The model used is the extended Hubbard model which includes the d-p hybridization, the p-band and a narrow d-band. The present work is an extension of our previous work (J. Mod. Phys. B 18(2) (2004) 241). Nevertheless, some important correlation functions necessary to estimate the Roth's band shift, are included together with the temperature T and the Coulomb interaction U to describe the superconductivity. The superconducting order parameter of a cuprate system, is obtained following Beenen and Edwards formalism. Here, we investigate in detail the change of the order parameter associated to temperature, Coulomb interaction and Roth's band shift effects on superconductivity. The phase diagram with Tc versus the total occupation number nT, shows the difference respect to the previous work.

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.

A new numerical approximation of the fractal ordinary differential equation

NASA Astrophysics Data System (ADS)

Atangana, Abdon; Jain, Sonal

2018-02-01

The concept of fractal medium is present in several real-world problems, for instance, in the geological formation that constitutes the well-known subsurface water called aquifers. However, attention has not been quite devoted to modeling for instance, the flow of a fluid within these media. We deem it important to remind the reader that the concept of fractal derivative is not to represent the fractal sharps but to describe the movement of the fluid within these media. Since this class of ordinary differential equations is highly complex to solve analytically, we present a novel numerical scheme that allows to solve fractal ordinary differential equations. Error analysis of the method is also presented. Application of the method and numerical approximation are presented for fractal order differential equation. The stability and the convergence of the numerical schemes are investigated in detail. Also some exact solutions of fractal order differential equations are presented and finally some numerical simulations are presented.

Comparison of alternative image reformatting techniques in micro-computed tomography and tooth clearing for detailed canal morphology.

PubMed

Lee, Ki-Wook; Kim, Yeun; Perinpanayagam, Hiran; Lee, Jong-Ki; Yoo, Yeon-Jee; Lim, Sang-Min; Chang, Seok Woo; Ha, Byung-Hyun; Zhu, Qiang; Kum, Kee-Yeon

2014-03-01

Micro-computed tomography (MCT) shows detailed root canal morphology that is not seen with traditional tooth clearing. However, alternative image reformatting techniques in MCT involving 2-dimensional (2D) minimum intensity projection (MinIP) and 3-dimensional (3D) volume-rendering reconstruction have not been directly compared with clearing. The aim was to compare alternative image reformatting techniques in MCT with tooth clearing on the mesiobuccal (MB) root of maxillary first molars. Eighteen maxillary first molar MB roots were scanned, and 2D MinIP and 3D volume-rendered images were reconstructed. Subsequently, the same MB roots were processed by traditional tooth clearing. Images from 2D, 3D, 2D + 3D, and clearing techniques were assessed by 4 endodontists to classify canal configuration and to identify fine anatomic structures such as accessory canals, intercanal communications, and loops. All image reformatting techniques in MCT showed detailed configurations and numerous fine structures, such that none were classified as simple type I or II canals; several were classified as types III and IV according to Weine classification or types IV, V, and VI according to Vertucci; and most were nonclassifiable because of their complexity. The clearing images showed less detail, few fine structures, and numerous type I canals. Classification of canal configuration was in 100% intraobserver agreement for all 18 roots visualized by any of the image reformatting techniques in MCT but for only 4 roots (22.2%) classified according to Weine and 6 (33.3%) classified according to Vertucci, when using the clearing technique. The combination of 2D MinIP and 3D volume-rendered images showed the most detailed canal morphology and fine anatomic structures. Copyright © 2014 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Behaviour of several fatigue prone bridge details

NASA Astrophysics Data System (ADS)

Kubiš, Petr; Ryjáček, Pavel

2017-09-01

Three fatigue welded bridge joints analysed in this work are the alternative details of the bottom flange connection. This construction detail is mainly used for the erection connection for steel and composite bridges. If applied in the place, where live load is significant, the fatigue becomes the main design criterion. The detail category is thus very important factor. The aim of this paper is to analyse the possibilities of the improving the behaviour of this detail, by various methods. First solution is to modify the shape of the cope hole to the elliptic shape. Second option is to use the “Olemutz” fully welded detail. This detail is often used in bridge designing despite there is no exact information about the fatigue category, and doubts of the performance exists. “Olemutz” is a long web plate slit that is filled by the double bevel weld after the execution of the bottom flange weld. The last detail is the elliptic cope hole filled by the plate-cap welded into an empty hole. The geometry is the same, as in the first case. The conclusion of the numerical analysis and the pilot fatigue experiments is discussed with several practical recommendations for designing.

Dynamical systems analysis of phantom dark energy models

NASA Astrophysics Data System (ADS)

Roy, Nandan; Bhadra, Nivedita

2018-06-01

In this work, we study the dynamical systems analysis of phantom dark energy models considering five different potentials. From the analysis of these five potentials we have found a general parametrization of the scalar field potentials which is obeyed by many other potentials. Our investigation shows that there is only one fixed point which could be the beginning of the universe. However, future destiny has many possible options. A detailed numerical analysis of the system has been presented. The observed late time behaviour in this analysis shows very good agreement with the recent observations.

An equivalent domain integral method in the two-dimensional analysis of mixed mode crack problems

NASA Technical Reports Server (NTRS)

Raju, I. S.; Shivakumar, K. N.

1990-01-01

An equivalent domain integral (EDI) method for calculating J-integrals for two-dimensional cracked elastic bodies is presented. The details of the method and its implementation are presented for isoparametric elements. The EDI method gave accurate values of the J-integrals for two mode I and two mixed mode problems. Numerical studies showed that domains consisting of one layer of elements are sufficient to obtain accurate J-integral values. Two procedures for separating the individual modes from the domain integrals are presented.

Cavity BPM with Dipole-Mode-Selective Coupler

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zenghai; Johnson, Ronald; Smith, Stephen R.

2006-06-21

In this paper, we present a novel position sensitive signal pickup scheme for a cavity BPM. The scheme utilizes the H-plane of the waveguide to couple magnetically to the side of the cavity, which results in a selective coupling to the dipole mode and a total rejection of the monopole mode. This scheme greatly simplifies the BPM geometry and relaxes machining tolerances. We will present detailed numerical studies on such a cavity BPM, analyze its resolution limit and tolerance requirements for a nanometer resolution. Finally present the measurement results of a X-band prototype.

Direct computational approach to lattice supersymmetric quantum mechanics

NASA Astrophysics Data System (ADS)

Kadoh, Daisuke; Nakayama, Katsumasa

2018-07-01

We study the lattice supersymmetric models numerically using the transfer matrix approach. This method consists only of deterministic processes and has no statistical uncertainties. We improve it by performing a scale transformation of variables such that the Witten index is correctly reproduced from the lattice model, and the other prescriptions are shown in detail. Compared to the precious Monte-Carlo results, we can estimate the effective masses, SUSY Ward identity and the cut-off dependence of the results in high precision. Those kinds of information are useful in improving lattice formulation of supersymmetric models.

Self-awareness deficits following loss of inner speech: Dr. Jill Bolte Taylor's case study.

PubMed

Morin, Alain

2009-06-01

In her 2006 book "My Stroke of Insight" Dr. Jill Bolte Taylor relates her experience of suffering from a left hemispheric stroke caused by a congenital arteriovenous malformation which led to a loss of inner speech. Her phenomenological account strongly suggests that this impairment produced a global self-awareness deficit as well as more specific dysfunctions related to corporeal awareness, sense of individuality, retrieval of autobiographical memories, and self-conscious emotions. These are examined in details and corroborated by numerous excerpts from Taylor's book.

Slat Noise Predictions Using Higher-Order Finite-Difference Methods on Overset Grids

NASA Technical Reports Server (NTRS)

Housman, Jeffrey A.; Kiris, Cetin

2016-01-01

Computational aeroacoustic simulations using the structured overset grid approach and higher-order finite difference methods within the Launch Ascent and Vehicle Aerodynamics (LAVA) solver framework are presented for slat noise predictions. The simulations are part of a collaborative study comparing noise generation mechanisms between a conventional slat and a Krueger leading edge flap. Simulation results are compared with experimental data acquired during an aeroacoustic test in the NASA Langley Quiet Flow Facility. Details of the structured overset grid, numerical discretization, and turbulence model are provided.

Defect dynamics in active nematics

PubMed Central

Giomi, Luca; Bowick, Mark J; Mishra, Prashant; Sknepnek, Rastko; Cristina Marchetti, M

2014-01-01

Topological defects are distinctive signatures of liquid crystals. They profoundly affect the viscoelastic behaviour of the fluid by constraining the orientational structure in a way that inevitably requires global changes not achievable with any set of local deformations. In active nematic liquid crystals, topological defects not only dictate the global structure of the director, but also act as local sources of motion, behaving as self-propelled particles. In this article, we present a detailed analytical and numerical study of the mechanics of topological defects in active nematic liquid crystals. PMID:25332389

Information Management System for the California State Water Resources Control Board (SWRCB)

NASA Technical Reports Server (NTRS)

Heald, T. C.; Redmann, G. H.

1973-01-01

A study was made to establish the requirements for an integrated state-wide information management system for water quality control and water quality rights for the State of California. The data sources and end requirements were analyzed for the data collected and used by the numerous agencies, both State and Federal, as well as the nine Regional Boards under the jurisdiction of the State Board. The report details the data interfaces and outlines the system design. A program plan and statement of work for implementation of the project is included.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Voynikova, D. S., E-mail: desi-sl2000@yahoo.com; Gocheva-Ilieva, S. G., E-mail: snegocheva@yahoo.com; Ivanov, A. V., E-mail: aivanov-99@yahoo.com

Numerous time series methods are used in environmental sciences allowing the detailed investigation of air pollution processes. The goal of this study is to present the empirical analysis of various aspects of stochastic modeling and in particular the ARIMA/SARIMA methods. The subject of investigation is air pollution in the town of Kardzhali, Bulgaria with 2 problematic pollutants – sulfur dioxide (SO2) and particulate matter (PM10). Various SARIMA Transfer Function models are built taking into account meteorological factors, data transformations and the use of different horizons selected to predict future levels of concentrations of the pollutants.

Nonlinear wave vacillation in the atmosphere

NASA Technical Reports Server (NTRS)

Antar, Basil N.

1987-01-01

The problem of vacillation in a baroclinically unstable flow field is studied through the time evolution of a single nonlinearly unstable wave. To this end a computer code is being developed to solve numerically for the time evolution of the amplitude of such a wave. The final working code will be the end product resulting from the development of a heirarchy of codes with increasing complexity. The first code in this series was completed and is undergoing several diagnostic analyses to verify its validity. The development of this code is detailed.

Update on tolterodine extended-release for treatment of overactive bladder

PubMed Central

Omotosho, Tola; Chen, Chi Chiung Grace

2010-01-01

Overactive bladder is a prevalent condition which negatively impacts quality of life and puts a significant economical burden on society. First-line therapy often includes pharmacotherapy with antimuscarinic medications, and numerous research studies have demonstrated that tolterodine extended-release (ER) is an efficacious and tolerable formulation of this class of medication. This review provides an update on the clinical use of tolterodine ER, detailing the current literature on its efficacy, tolerability, adverse effects, and comparability with other commonly prescribed medications for the treatment of overactive bladder. PMID:24198627

Numerical simulation of the vortical flow around a pitching airfoil

NASA Astrophysics Data System (ADS)

Fu, Xiang; Li, Gaohua; Wang, Fuxin

2017-04-01

In order to study the dynamic behaviors of the flapping wing, the vortical flow around a pitching NACA0012 airfoil is investigated. The unsteady flow field is obtained by a very efficient zonal procedure based on the velocity-vorticity formulation and the Reynolds number based on the chord length of the airfoil is set to 1 million. The zonal procedure divides up the whole computation domain in to three zones: potential flow zone, boundary layer zone and Navier-Stokes zone. Since the vorticity is absent in the potential flow zone, the vorticity transport equation needs only to be solved in the boundary layer zone and Navier-Stokes zone. Moreover, the boundary layer equations are solved in the boundary layer zone. This arrangement drastically reduces the computation time against the traditional numerical method. After the flow field computation, the evolution of the vortices around the airfoil is analyzed in detail.

Implication of Two-Coupled Differential Van der Pol Duffing Oscillator in Weak Signal Detection

NASA Astrophysics Data System (ADS)

Peng, Hang-hang; Xu, Xue-mei; Yang, Bing-chu; Yin, Lin-zi

2016-04-01

The principle of the Van der Pol Duffing oscillator for state transition and for determining critical value is described, which has been studied to indicate that the application of the Van der Pol Duffing oscillator in weak signal detection is feasible. On the basis of this principle, an improved two-coupled differential Van der Pol Duffing oscillator is proposed which can identify signals under any frequency and ameliorate signal-to-noise ratio (SNR). The analytical methods of the proposed model and the construction of the proposed oscillator are introduced in detail. Numerical experiments on the properties of the proposed oscillator compared with those of the Van der Pol Duffing oscillator are carried out. Our numerical simulations have confirmed the analytical treatment. The results demonstrate that this novel oscillator has better detection performance than the Van der Pol Duffing oscillator.

Comparison of deterministic and stochastic methods for time-dependent Wigner simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Sihong, E-mail: sihong@math.pku.edu.cn; Sellier, Jean Michel, E-mail: jeanmichel.sellier@parallel.bas.bg

2015-11-01

Recently a Monte Carlo method based on signed particles for time-dependent simulations of the Wigner equation has been proposed. While it has been thoroughly validated against physical benchmarks, no technical study about its numerical accuracy has been performed. To this end, this paper presents the first step towards the construction of firm mathematical foundations for the signed particle Wigner Monte Carlo method. An initial investigation is performed by means of comparisons with a cell average spectral element method, which is a highly accurate deterministic method and utilized to provide reference solutions. Several different numerical tests involving the time-dependent evolution ofmore » a quantum wave-packet are performed and discussed in deep details. In particular, this allows us to depict a set of crucial criteria for the signed particle Wigner Monte Carlo method to achieve a satisfactory accuracy.« less

Microwave fields driven domain wall motions in antiferromagnetic nanowires

NASA Astrophysics Data System (ADS)

Chen, Z. Y.; Yan, Z. R.; Zhang, Y. L.; Qin, M. H.; Fan, Z.; Lu, X. B.; Gao, X. S.; Liu, J.-M.

2018-06-01

In this work, we study the microwave field driven domain wall (DW) motion in an antiferromagnetic nanowire, using the numerical calculations based on a classical Heisenberg spin model with the biaxial magnetic anisotropy. We show that a proper combination of a static magnetic field plus an oscillating field perpendicular to the nanowire axis is sufficient to drive the DW propagation along the nanowire. More importantly, the drift velocity at the resonance frequency is comparable to that induced by temperature gradients, suggesting that microwave field can be a very promising tool to control DW motions in antiferromagnetic nanostructures. The dependences of resonance frequency and drift velocity on the static and oscillating fields, the axial anisotropy, and the damping constant are discussed in details. Furthermore, the optimal orientations of the field are also numerically determined and explained. This work provides useful information for the spin dynamics in antiferromagnetic nanostructures for spintronics applications.

Math anxiety: A review of its cognitive consequences, psychophysiological correlates, and brain bases.

PubMed

Suárez-Pellicioni, Macarena; Núñez-Peña, María Isabel; Colomé, Àngels

2016-02-01

A decade has passed since the last published review of math anxiety, which was carried out by Ashcraft and Ridley (2005). Given the considerable interest aroused by this topic in recent years and the growing number of publications related to it, the present article aims to provide a full and updated review of the field, ranging from the initial studies of the impact of math anxiety on numerical cognition, to the latest research exploring its electrophysiological correlates and brain bases from a cognitive neuroscience perspective. Finally, this review describes the factors and mechanisms that have been claimed to play a role in the origins and/or maintenance of math anxiety, and it examines in detail the main explanations proposed to account for the negative effects of math anxiety on performance: competition for working memory resources, a deficit in a low-level numerical representation, and inhibition/attentional control deficit.

Effect of atmospheric scattering and surface reflection on upwelling solar radiation

NASA Technical Reports Server (NTRS)

Suttles, J. T.; Barkstrom, B. R.; Tiwari, S. N.

1981-01-01

A study is presented of the solar radiation transfer in the complete earth-atmosphere system, and numerical results are compared with satellite data obtained during the Earth Radiation Budget Experiment on Nimbus 6, in August, 1975. Emphasis is placed on the upwelling radiance distribution at the top of the atmosphere, assumed to be at 50 km. The numerical technique is based on the finite difference method, which includes azimuth and spectral variations for the entire solar wavelength range. Detailed solar properties, atmospheric physical properties, and optical properties are used. However, since the property descriptions are based on a trade-off between accuracy and computational realities, aerosol and cloud optical properties are treated with simple approximations. The radiative transfer model is in good agreement with the satellite radiance observations. The method provides a valuable tool in analyzing satellite- and ground-based radiation budget measurements and in designing instrumentation.

Next-to-leading-logarithmic power corrections for N -jettiness subtraction in color-singlet production

NASA Astrophysics Data System (ADS)

Boughezal, Radja; Isgrò, Andrea; Petriello, Frank

2018-04-01

We present a detailed derivation of the power corrections to the factorization theorem for the 0-jettiness event shape variable T . Our calculation is performed directly in QCD without using the formalism of effective field theory. We analytically calculate the next-to-leading logarithmic power corrections for small T at next-to-leading order in the strong coupling constant, extending previous computations which obtained only the leading-logarithmic power corrections. We address a discrepancy in the literature between results for the leading-logarithmic power corrections to a particular definition of 0-jettiness. We present a numerical study of the power corrections in the context of their application to the N -jettiness subtraction method for higher-order calculations, using gluon-fusion Higgs production as an example. The inclusion of the next-to-leading-logarithmic power corrections further improves the numerical efficiency of the approach beyond the improvement obtained from the leading-logarithmic power corrections.

Investigation of thermocapillary convection in a three-liquid-layer system

NASA Astrophysics Data System (ADS)

Géoris, Ph.; Hennenberg, M.; Lebon, G.; Legros, J. C.

1999-06-01

This paper presents the first experimental results on Marangoni Bénard instability in a symmetrical three-layer system. A pure thermocapillary phenomenon has been observed by performing the experiment in a microgravity environment where buoyancy forces can be neglected. This configuration enables the hydrodynamic stability of two identical liquid liquid interfaces subjected to a normal gradient of temperature to be studied. The flow is driven by one interface only and obeys the criterion based on the heat diffusivity ratio proposed by Scriven & Sternling (1959) and Smith (1966). The measured critical temperature difference for the onset of convection is compared to the value obtained from two-dimensional numerical simulations. The results of the simulations are in reasonable agreement with the velocimetry and the thermal experimental data for moderate supercriticality. Numerically and experimentally, the convective pattern exhibits a transition between different convective regimes for similar temperature gradients. Their common detailed features are discussed.

Analysis and modeling of summertime convective cloud and precipitation structure over the southeastern United States

NASA Technical Reports Server (NTRS)

Knupp, Kevin R.

1988-01-01

Described is work performed under NASA Grant NAG8-654 for the period 15 March to 15 September 1988. This work entails primarily data analysis and numerical modeling efforts related to the 1986 Satellite Precipitation and Cloud Experiment (SPACE). In the following, the SPACE acronym is used along with the acronym COHMEX, which represents the encompassing Cooperative Huntsville Meteorological Experiment. Progress made during the second half of the first year of the study included: (1) installation and testing of the RAMS numerical Modeling system on the Alabama CRAY X-MP/24; (2) a start on the analysis of the mesoscale convection system (MCS) of 13 July 1986 COHMEX case; and (3) a cursory examination of a small MCS that formed over the COHMEX region on 15 July 1986. Details of each of these individual tasks are given.

Structure of the disturbed region of the atmosphere after the nuclear explosion in Hiroshima

NASA Astrophysics Data System (ADS)

Shcherbin, M. D.; Pavlyukov, K. V.; Salo, A. A.; Pertsev, S. F.; Rikunov, A. V.

2013-09-01

An attempt is undertaken to describe the development of the disturbed region of the atmosphere caused by the nuclear explosion over Hiroshima on August 6, 1945. Numerical simulation of the phenomenon is performed using the dynamic equations for a nonconducting inviscid gas taking into account the combustion of urban buildings, phase changes of water, electrification of ice particles, and removal of soot particles. The results of the numerical calculation of the development of the disturbed region indicate heavy rainfall, the formation of a storm cloud with lightning discharges, removal of soot particles, and the formation of vertical vortices. The temporal sequence of these meteorological phenomena is consistent with the data of observations. Because of the assumptions and approximations used in solving the problem, the results are of qualitative nature. Refinement of the results can be obtained by a more detailed study of the approximate initial and boundary conditions of the problem.

A rare case of haboob in Tehran: Observational and numerical study

NASA Astrophysics Data System (ADS)

Karami, S.; Ranjbar, A.; Mohebalhojeh, A. R.; Moradi, M.

2017-03-01

A great dust storm occurred in Tehran on 2 June 2014 and caused severe damage to properties and involved loss of human life. From the visual evidence available, it can be regarded as a case of haboob. As a lower latitude phenomenon, its occurrence in Tehran was unprecedented in the last 50 years. This paper aims to present a detailed analysis of the weather conditions, the pathways by which dust particles were ingested by the haboob, as well as the impact of the urban boundary layer on the intensity and propagation of the dust storm. Using numerical simulation carried out by the WRF-Chem model and various observational techniques, the coupling of a low-level small-scale deformation field with a lower-tropospheric cold pool produced by precipitating mid-tropospheric clouds is identified as the main process involved in shaping this rare dust storm.

Detailed Comparison of DNS to PSE for Oblique Breakdown at Mach 3

NASA Technical Reports Server (NTRS)

Mayer, Christian S. J.; Fasel, Hermann F.; Choudhari, Meelan; Chang, Chau-Lyan

2010-01-01

A pair of oblique waves at low amplitudes is introduced in a supersonic flat-plate boundary layer. Their downstream development and the concomitant process of laminar to turbulent transition is then investigated numerically using Direct Numerical Simulations (DNS) and Parabolized Stability Equations (PSE). This abstract is the last part of an extensive study of the complete transition process initiated by oblique breakdown at Mach 3. In contrast to the previous simulations, the symmetry condition in the spanwise direction is removed for the simulation presented in this abstract. By removing the symmetry condition, we are able to confirm that the flow is indeed symmetric over the entire computational domain. Asymmetric modes grow in the streamwise direction but reach only small amplitude values at the outflow. Furthermore, this abstract discusses new time-averaged data from our previous simulation CASE 3 and compares PSE data obtained from NASA's LASTRAC code to DNS results.

The acoustic and instability waves of jets confined inside an acoustically lined rectangular duct

NASA Technical Reports Server (NTRS)

Hu, Fang Q.

1993-01-01

An analysis of linear wave modes associated with supersonic jets confined inside an acoustically lined rectangular duct is presented. Mathematical formulations are given for the vortex-sheet model and continuous mean flow model of the jet flow profiles. Detailed dispersion relations of these waves in a two-dimensional confined jet as well as an unconfined free jet are computed. Effects of the confining duct and the liners on the jet instability and acoustic waves are studied numerically. It is found that the effect of the liners is to attenuate waves that have supersonic phase velocities relative to the ambient flow. Numerical results also show that the growth rates of the instability waves could be reduced significantly by the use of liners. In addition, it is found that the upstream propagating neutral waves of an unconfined jet could become attenuated when the jet is confined.

Isentropic Compression up to 200 KBars for LX 04, Numerical Simulations and Comparison with Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lefrancois, A.; Hare, D.; L'Eplattenier, P.

2006-02-13

Isentropic compression experiments and numerical simulations on LX-04 (HMX / Viton 85/15) were performed respectively at Z accelerator facility from Sandia National Laboratory and at Lawrence Livermore National Laboratory in order to study the isentrope and associated Hugoniot of this HE. 2D and 3D configurations have been calculated here to test the new beta version of the electromagnetism package coupled with the dynamics in Ls-Dyna and compared with the ICE Z shot 1067 on LX 04. The electromagnetism module is being developed in the general-purpose explicit and implicit finite element program LS-DYNA{reg_sign} in order to perform coupled mechanical/thermal/electromagnetism simulations. Themore » Maxwell equations are solved using a Finite Element Method (FEM) for the solid conductors coupled with a Boundary Element Method (BEM) for the surrounding air (or vacuum). More details can be read in the references.« less

Bidirectional reaction steps in metabolic networks: I. Modeling and simulation of carbon isotope labeling experiments.

PubMed

Wiechert, W; de Graaf, A A

1997-07-05

The extension of metabolite balancing with carbon labeling experiments, as described by Marx et al. (Biotechnol. Bioeng. 49: 11-29), results in a much more detailed stationary metabolic flux analysis. As opposed to basic metabolite flux balancing alone, this method enables both flux directions of bidirectional reaction steps to be quantitated. However, the mathematical treatment of carbon labeling systems is much more complicated, because it requires the solution of numerous balance equations that are bilinear with respect to fluxes and fractional labeling. In this study, a universal modeling framework is presented for describing the metabolite and carbon atom flux in a metabolic network. Bidirectional reaction steps are extensively treated and their impact on the system's labeling state is investigated. Various kinds of modeling assumptions, as usually made for metabolic fluxes, are expressed by linear constraint equations. A numerical algorithm for the solution of the resulting linear constrained set of nonlinear equations is developed. The numerical stability problems caused by large bidirectional fluxes are solved by a specially developed transformation method. Finally, the simulation of carbon labeling experiments is facilitated by a flexible software tool for network synthesis. An illustrative simulation study on flux identifiability from available flux and labeling measurements in the cyclic pentose phosphate pathway of a recombinant strain of Zymomonas mobilis concludes this contribution.

A numerical study of nonlinear infrasound propagation in a windy atmosphere.

PubMed

Sabatini, R; Marsden, O; Bailly, C; Bogey, C

2016-07-01

Direct numerical simulations of the two-dimensional unsteady compressible Navier-Stokes equations are performed to study the acoustic field generated by an infrasonic source in a realistic atmosphere. Some of the main phenomena affecting the propagation of infrasonic waves at large distances from the source are investigated. The effects of thermal and wind-related refraction on the signals recorded at ground level are highlighted, with particular emphasis on the phase shift induced by the presence of caustics in the acoustic field. Nonlinear waveform steepening associated with harmonic generation, and period lengthening, both of which are typical of large source amplitudes, are illustrated, and the importance of thermoviscous absorption in the upper atmosphere is clearly demonstrated. The role of diffraction in the shadow zone, around caustics and at stratospheric altitudes is also pointed out. The Navier-Stokes equations are solved using high-order finite-differences and a Runge-Kutta time integration method both originally developed for aeroacoustic applications, along with an adaptive shock-capturing algorithm which allows high-intensity acoustic fields to be examined. An improvement to the shock detection procedure is also proposed in order to meet the specificities of nonlinear propagation at long range. The modeling as well as the numerical results are reported in detail and discussed.

Numerical simulations of an impinging liquid spray in a cross-flow

NASA Astrophysics Data System (ADS)

Gomatam, Sreekar; Vengadesan, S.; Chakravarthy, S. R.

2017-11-01

The characteristics of a liquid spray in a uniform cross-flow field are numerically simulated in this study. A hollow cone liquid spray is injected perpendicular to the air stream flowing through a rectangular duct under room temperature and pressure. An Eulerian-Lagrangian framework is adopted to simulate the spray in cross-flow phenomenon. The cross-flow velocity is varied from 6-12 m/s while the liquid injection pressure is varied from 0.3-0.6 MPa. The liquid droplets from the injected spray undergo breakup and/or coalescence further in the cross-flow. Moreover, the spray injected into the cross-flow impinges on the opposite wall resulting in the formation of a liquid film. This liquid film disintegrates further into discrete droplets because of the impingement of the droplets from the spray and the shear from the cross-flow. The overall distribution of the droplets in the cross-flow for varying conditions is studied in detail. The evolution of the liquid film with space and time for varying conditions is also investigated. Suitable sub-models are used to numerically model the droplet break-up, coalescence, liquid film formation and disintegration, splashing of the droplets on the film and subsequent formation of daughter droplets. Department of Applied Mechanics, Indian Inst of Tech-Madras.

Quantifying Turbulent Kinetic Energy in an Aortic Coarctation with Large Eddy Simulation and Magnetic Resonance Imaging

NASA Astrophysics Data System (ADS)

Lantz, Jonas; Ebbers, Tino; Karlsson, Matts

2012-11-01

In this study, turbulent kinetic energy (TKE) in an aortic coarctation was studied using both a numerical technique (large eddy simulation, LES) and in vivo measurements using magnetic resonance imaging (MRI). High levels of TKE are undesirable, as kinetic energy is extracted from the mean flow to feed the turbulent fluctuations. The patient underwent surgery to widen the coarctation, and the flow before and after surgery was computed and compared to MRI measurements. The resolution of the MRI was about 7 × 7 voxels in axial cross-section while 50x50 mesh cells with increased resolution near the walls was used in the LES simulation. In general, the numerical simulations and MRI measurements showed that the aortic arch had no or very low levels of TKE, while elevated values were found downstream the coarctation. It was also found that TKE levels after surgery were lowered, indicating that the diameter of the constriction was increased enough to decrease turbulence effects. In conclusion, both the numerical simulation and MRI measurements gave very similar results, thereby validating the simulations and suggesting that MRI measured TKE can be used as an initial estimation in clinical practice, while LES results can be used for detailed quantification and further research of aortic flows.

Numerical modelling of the effect of dry air traces in a helium parallel plate dielectric barrier discharge

NASA Astrophysics Data System (ADS)

Lazarou, C.; Belmonte, T.; Chiper, A. S.; Georghiou, G. E.

2016-10-01

A validated numerical model developed for the study of helium barrier discharges in the presence of dry air impurities is presented in this paper. The model was used to numerically investigate the influence of air traces on the evolution of the helium dielectric barrier discharge (DBD). The level of dry air used as impurity was in the range from 0 to 1500 ppm, which corresponds to the most commonly encountered range in atmospheric pressure discharge experiments. The results presented in this study clearly show that the plasma chemistry and consequently the discharge evolution is highly affected by the concentration level of impurities in the mixture. In particular, it was observed that air traces assist the discharge ignition at low concentration levels (~55 ppm), while on the other hand, they increase the burning voltage at higher concentration levels (~1000 ppm). Furthermore, it was found that the discharge symmetry during the voltage cycle highly depends on the concentration of air. For the interpretation of the results, a detailed analysis of the processes that occur in the discharge gap is performed and the main reaction pathways of ion production are described. Thanks to this approach, useful insight into the physics behind the evolution of the discharge is obtained.

Reprint of: A numerical modelling of gas exchange mechanisms between air and turbulent water with an aquarium chemical reaction

NASA Astrophysics Data System (ADS)

Nagaosa, Ryuichi S.

2014-08-01

This paper proposes a new numerical modelling to examine environmental chemodynamics of a gaseous material exchanged between the air and turbulent water phases across a gas-liquid interface, followed by an aquarium chemical reaction. This study uses an extended concept of a two-compartment model, and assumes two physicochemical substeps to approximate the gas exchange processes. The first substep is the gas-liquid equilibrium between the air and water phases, A(g)⇌A(aq), with Henry's law constant H. The second is a first-order irreversible chemical reaction in turbulent water, A(aq)+H2O→B(aq)+H+ with a chemical reaction rate κA. A direct numerical simulation (DNS) technique has been employed to obtain details of the gas exchange mechanisms and the chemical reaction in the water compartment, while zero velocity and uniform concentration of A is considered in the air compartment. The study uses the different Schmidt numbers between 1 and 8, and six nondimensional chemical reaction rates between 10(≈0) to 101 at a fixed Reynolds number. It focuses on the effects of the Schmidt number and the chemical reaction rate on fundamental mechanisms of the gas exchange processes across the interface.

48 CFR 204.7101 - Definitions.

Code of Federal Regulations, 2010 CFR

2010-10-01

... Definitions. Accounting classification reference number (ACRN) means any combination of a two position alpha/numeric code used as a method of relating the accounting classification citation to detailed line item... 48 Federal Acquisition Regulations System 3 2010-10-01 2010-10-01 false Definitions. 204.7101...

OOGENESIS AND OVARIAN HISTOLOGY OF THE AMERICAN ALLIGATOR ALLIGATOR MISSISSIPPIENSIS

EPA Science Inventory

Although folliculogenesis and oogenesis have been observed in numerous reptiles, these phenomena have not been described in detail in a crocodilian. Oogenesis and histological features of the adult ovary of Alligator mississippiensis are described. Using a complex process, the ov...

Analysis of Dust Devils on Mars using CFD

NASA Astrophysics Data System (ADS)

Lange, C. F.; Chen, K.; Davis, J. A.; Gheynani, B. T.

2009-05-01

Recent Mars missions have reported evidence of the existence of dust devils. A detailed study of vortex dynamics will provide a better understanding of this swirling flow of the Martian atmosphere. Further, it is believed that there is a relationship between dust devils and water transport. Recently, the Phoenix Mars mission, designed to investigate ice water and natural events on Mars, has successfully finished. The Phoenix Surface Stereo Imager (SSI) camera captured images of the passage of dust devils over or close to the lander. Additionally, dustless devils, which have similar vortex characteristics but insufficient strength to raise dust from the surface, have been detected in the lander's pressure measurements. It was found that dust devils occur mainly in the early afternoon. Because of this, numerical models of a vortex generator are used to study the physics of this complex swirling flow and the effect of dust devils on the transport of water vapour from the regolith. Characteristic parameters such as core radius and swirl ratio are being explored for scaling factors. Scaling factors will be studied and tested, comparing the small and large scales of numerically generated vortices and laboratory generated vortices. Small scale of numerical models of atmospheric vortices are studied using a commercial software package, ANSYS/CFX11.0 with finite volume method (FVM). Large eddy simulations (LES) of planetary boundary layers are based on NCAR LES code to simulate convective vertical vortices that naturally form in quiescent convective boundary layers (CBL) over homogeneous flat surfaces. This will help to find the approximate location and physical characteristics of the vortices on the surface. The numerical models of atmospheric vortices and the experimental vortex generator validations will help to define the water vapour cycle on Mars.

Merging field mapping and numerical simulation to interpret the lithofacies variations from unsteady pyroclastic density currents on uneven terrain: The case of La Fossa di Vulcano (Aeolian Islands, Italy)

NASA Astrophysics Data System (ADS)

Doronzo, Domenico M.; Dellino, Pierfrancesco; Sulpizio, Roberto; Lucchi, Federico

2017-01-01

In order to obtain results from computer simulations of explosive volcanic eruptions, one either needs a statistical approach to test a wide range of initial and boundary conditions, or needs using a well-constrained field case study via stratigraphy. Here we followed the second approach, using data obtained from field mapping of the Grotta dei Palizzi 2 pyroclastic deposits (Vulcano Island, Italy) as input for numerical modeling. This case study deals with impulsive phreatomagmatic explosions of La Fossa Cone that generated ash-rich pyroclastic density currents, interacting with the topographic high of the La Fossa Caldera rim. One of the simplifications in dealing with well-sorted ash (one particle size in the model) is to highlight the topographic effects on the same pyroclastic material in an unsteady current. We demonstrate that by merging field data with 3D numerical simulation results it is possible to see key details of the dynamical current-terrain interaction, and to interpret the lithofacies variations of the associated deposits as a function of topography-induced sedimentation (settling) rate. Results suggest that a value of the sedimentation rate lower than 5 kg/m2 s at the bed load can still be sheared by the overlying current, producing tractional structures (laminae) in the deposits. Instead, a sedimentation rate higher than that threshold can preclude the formation of tractional structures, producing thicker massive deposits. We think that the approach used in this study could be applied to other case studies (both for active and ancient volcanoes) to confirm or refine such threshold value of the sedimentation rate, which is to be considered as an upper value as for the limitations of the numerical model.

Experimental and numerical analysis of interlocking rib formation at sheet metal blanking

NASA Astrophysics Data System (ADS)

Bolka, Špela; Bratuš, Vitoslav; Starman, Bojan; Mole, Nikolaj

2018-05-01

Cores for electrical motors are typically produced by blanking of laminations and then stacking them together, with, for instance, interlocking ribs or welding. Strict geometrical tolerances, both on the lamination and on the stack, combined with complex part geometry and harder steel strip material, call for use of predictive methods to optimize the process before actual blanking to reduce the costs and speed up the process. One of the major influences on the final stack geometry is the quality of the interlocking ribs. A rib is formed in one step and joined with the rib of the preceding lamination in the next. The quality of the joint determines the firmness of the stack and also influences its. The geometrical and positional accuracy is thus crucial in rib formation process. In this study, a complex experimental and numerical analysis of interlocking rib formation has been performed. The aim of the analysis is to numerically predict the shape of the rib in order to perform a numerical simulation of the stack formation in the next step of the process. A detailed experimental research has been performed in order to characterize influential parameters on the rib formation and the geometry of the ribs itself, using classical and 3D laser microscopy. The formation of the interlocking rib is then simulated using Abaqus Explicit. The Hilll 48 constitutive material model is based on extensive and novel material characterization process, combining data from in-plane and out-of-plane material tests to perform a 3D analysis of both, rib formation and rib joining. The study shows good correlation between the experimental and numerical results.

Modelling runoff on ceramic tile roofs using the kinematic wave equations

NASA Astrophysics Data System (ADS)

Silveira, Alexandre; Abrantes, João; de Lima, João; Lira, Lincoln

2016-04-01

Rainwater harvesting is a water saving alternative strategy that presents many advantages and can provide solutions to address major water resources problems, such as fresh water scarcity, urban stream degradation and flooding. In recent years, these problems have become global challenges, due to climatic change, population growth and increasing urbanisation. Generally, roofs are the first to come into contact with rainwater; thus, they are the best candidates for rainwater harvesting. In this context, the correct evaluation of roof runoff quantity and quality is essential to effectively design rainwater harvesting systems. Despite this, many studies usually focus on the qualitative aspects in detriment of the quantitative aspects. Laboratory studies using rainfall simulators have been widely used to investigate rainfall-runoff processes. These studies enabled a detailed exploration and systematic replication of a large range of hydrologic conditions, such as rainfall spatial and temporal characteristics, providing for a fast way to obtain precise and consistent data that can be used to calibrate and validate numerical models. This study aims to evaluate the performance of a kinematic wave based numerical model in simulating runoff on sloping roofs, by comparing the numerical results with the ones obtained from laboratory rainfall simulations on a real-scale ceramic tile roof (Lusa tiles). For all studied slopes, simulated discharge hydrographs had a good adjust to observed ones. Coefficient of determination and Nash-Sutcliffe efficiency values were close to 1.0. Particularly, peak discharges, times to peak and peak durations were very well simulated.