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Sample records for chaplygin gas model

  1. Interacting Entropy-Corrected Holographic Chaplygin Gas Model

    NASA Astrophysics Data System (ADS)

    Farooq, M. Umar; Jamil, Mubasher; Rashid, Muneer A.

    2010-10-01

    Holographic dark energy (HDE), presents a dynamical view of dark energy which is consistent with the observational data and has a solid theoretical background. Its definition follows from the entropy-area relation S( A), where S and A are entropy and area respectively. In the framework of loop quantum gravity, a modified definition of HDE called “entropy-corrected holographic dark energy” (ECHDE) has been proposed recently to explain dark energy with the help of quantum corrections to the entropy-area relation. Using this new definition, we establish a correspondence between modified variable Chaplygin gas, new modified Chaplygin gas and the viscous generalized Chaplygin gas with the entropy corrected holographic dark energy and reconstruct the corresponding scalar potentials which describe the dynamics of the scalar field.

  2. Modified Chaplygin gas inspired inflationary model in braneworld scenario

    NASA Astrophysics Data System (ADS)

    Jawad, Abdul; Rani, Shamaila; Mohsaneen, Sidra

    2016-05-01

    We investigate the modified Chaplygin gas inspired inflationary regime in the brane-world framework in the presence of standard and tachyon scalar fields. We consider the intermediate inflationary scenario and construct the slow-roll parameters, e-folding numbers, spectral index, scalar and tensor power spectra, tensor to scalar ratio for both scalar field models. We develop the ns - N and r - N planes and concluded that ns˜eq96^{+0.5}_{-0.5} and r≤0.0016 for N˜eq60^{+5}_{-5} in both cases of scalar field models as well as for all values of m. These constraints are consistent with observational data such as WMAP7, WMAP9 and Planck data.

  3. Reduced modified Chaplygin gas cosmology

    NASA Astrophysics Data System (ADS)

    Lu, Jianbo; Geng, Danhua; Xu, Lixin; Wu, Yabo; Liu, Molin

    2015-02-01

    In this paper, we study cosmologies containing the reduced modified Chaplygin gas (RMCG) fluid which is reduced from the modified Chaplygin gas p = Aρ - Bρ -α for the value of α = -1 /2. In this special case, dark cosmological models can be realized for different values of model parameter A. We investigate the viabilities of these dark cosmological models by discussing the evolutions of cosmological quantities and using the currently available cosmic observations. It is shown that the special RMCG model ( A = 0 or A = 1) which unifies the dark matter and dark energy should be abandoned. For A = 1 /3, RMCG which unifies the dark energy and dark radiation is the favorite model according to the objective Akaike information criteria. In the case of A < 0, RMCG can achieve the features of the dynamical quintessence and phantom models, where the evolution of the universe is not sensitive to the variation of model parameters.

  4. Matter power spectrum for the generalized Chaplygin gas model: The Newtonian approach

    SciTech Connect

    Fabris, J. C.; Goncalves, S. V. B.; Velten, H. E. S.; Zimdahl, W.

    2008-11-15

    We model the cosmic medium as the mixture of a generalized Chaplygin gas and a pressureless matter component. Within a neo-Newtonian approach (in which, different from standard Newtonian cosmology, the pressure enters the homogeneous and isotropic background dynamics) we compute the matter power spectrum. The 2dFGRS data are used to discriminate between unified models of the dark sector (a purely baryonic matter component of roughly 5% of the total energy content and roughly 95% generalized Chaplygin gas) and different models, for which there is separate dark matter, in addition to that accounted for by the generalized Chaplygin gas. Leaving the corresponding density parameters free, we find that the unified models are strongly disfavored. On the other hand, using unified model priors, the observational data are also well described, in particular, for small and large values of the generalized Chaplygin gas parameter {alpha}. The latter result is in agreement with a recent, more qualitative but fully relativistic, perturbation analysis in [V. Gorini, A. Y. Kamenshchik, U. Moschella, O. F. Piatella, and A. A. Starobinsky, J. Cosmol. Astropart. Phys. 02 (2008) 016.].

  5. Viscous Chaplygin gas models as spherical top-hat collapsing fluids

    NASA Astrophysics Data System (ADS)

    Jawad, Abdul; Iqbal, Ayesha

    2016-05-01

    We study the spherical top-hat collapse in Einstein gravity and loop quantum cosmology (LQC) by taking the nonlinear evolution of viscous modified variable Chaplygin gas (CG) and viscous generalized cosmic chaplygin gas (GCCG). We calculate the equation of state (EoS) parameter, square speed of sound, perturbed (EoS) parameter, perturbed square speed of sound, density contrast and divergence of peculiar velocity in perturbed region and discussed their behavior. It is observed that both CG models support the spherical collapse (SC) in Einstein as well as LQC because density contrast remains positive in both cases and the perturbed EoS parameter remains positive at the present epoch as well as near future. It is remarked here that these parameters provide consistent results for both CG models in both gravities.

  6. Effects of viscous pressure on warm inflationary generalized cosmic Chaplygin gas model

    SciTech Connect

    Sharif, M.; Saleem, Rabia E-mail: rabiasaleem1988@yahoo.com

    2014-12-01

    This paper is devoted to study the effects of bulk viscous pressure on an inflationary generalized cosmic Chaplygin gas model using FRW background. The matter contents of the universe are assumed to be inflaton and imperfect fluid. We evaluate inflaton fields, potentials and entropy density for variable as well as constant dissipation and bulk viscous coefficients in weak as well as high dissipative regimes during intermediate era. In order to discuss inflationary perturbations, we evaluate entropy density, scalar (tensor) power spectra, their corresponding spectral indices, tensor-scalar ratio and running of spectral index in terms of inflaton which are constrained using recent Planck, WMAP7 and Bicep2 probes.

  7. Observational constraints on a unified dark matter and dark energy model based on generalized Chaplygin gas

    SciTech Connect

    Park, Chan-Gyung; Hwang, Jai-chan; Park, Jaehong; Noh, Hyerim

    2010-03-15

    We study a generalized version of Chaplygin gas as unified model of dark matter and dark energy. Using realistic theoretical models and the currently available observational data from the age of the universe, the expansion history based on the type Ia supernovae, the matter power spectrum, the cosmic microwave background radiation anisotropy power spectra, and the perturbation growth factor we put the unified model under observational test. As the model has only two free parameters in the flat Friedmann background [{Lambda}CDM (cold dark matter) model has only one free parameter] we show that the model is already tightly constrained by currently available observations. The only parameter space extremely close to the {Lambda}CDM model is allowed in this unified model.

  8. Observational constraints on cosmological models with Chaplygin gas and quadratic equation of state

    NASA Astrophysics Data System (ADS)

    Sharov, G. S.

    2016-06-01

    Observational manifestations of accelerated expansion of the universe, in particular, recent data for Type Ia supernovae, baryon acoustic oscillations, for the Hubble parameter H(z) and cosmic microwave background constraints are described with different cosmological models. We compare the ΛCDM, the models with generalized and modified Chaplygin gas and the model with quadratic equation of state. For these models we estimate optimal model parameters and their permissible errors with different approaches to calculation of sound horizon scale rs(zd). Among the considered models the best value of χ2 is achieved for the model with quadratic equation of state, but it has 2 additional parameters in comparison with the ΛCDM and therefore is not favored by the Akaike information criterion.

  9. Cosmological Imprints of a Generalized Chaplygin Gas Model for the Early Universe

    SciTech Connect

    Bouhmadi-Lopez, Mariam; Chen, Pisin; Liu, Yen-Wei; /Taiwan, Natl. Taiwan U.

    2012-06-06

    We propose a phenomenological model for the early universe where there is a smooth transition between an early quintessence phase and a radiation-dominated era. The matter content is modeled by an appropriately modified Chaplygin gas for the early universe. We constrain the model observationally by mapping the primordial power spectrum of the scalar perturbations to the latest data of WMAP7. We compute as well the spectrum of the primordial gravitational waves as would be measured today. We show that the high frequencies region of the spectrum depends on the free parameter of the model and most importantly this region of the spectrum can be within the reach of future gravitational waves detectors.

  10. Constructing an inflaton potential by mimicking modified Chaplygin gas

    NASA Astrophysics Data System (ADS)

    Kahya, E. O.; Pourhassan, B.; Uraz, S.

    2015-11-01

    In this paper, we consider an inflationary model that effectively behaves as a modified Chaplygin gas in the context of quintessence cosmology. We reconstruct the inflaton potential from the bottom up and using the recent observational data we fix the free parameters of the model. We show that the modified Chaplygin gas-inspired model is suitable for both the early and the late time acceleration but has shortcomings between the two periods.

  11. Interacting extended Chaplygin gas cosmology in Lyra manifold

    NASA Astrophysics Data System (ADS)

    Khurshudyan, Martiros

    2015-12-01

    Subject of our interest is an extended Chaplygin gas cosmology and new receipts providing accelerated expansion of the large scale universe. In Literature a variety of cosmological models exist studying the behavior of the universe in the presence of Chaplygin gas. From its initial form Chaplygin gas evolved and accepted different EoS-s and we will work with one of them. The main purpose of this work is to study behavior of the universe in Lyra Manifold with a varying \\varLambda-term, which does give us modified field equations. Modified field equations compared to field equations of General Relativity provide a new parametrization of dark energy sector of the large scale universe. It is also interesting to study the behavior of the universe in case of an existing coupling between quintessence DE and extended Chaplygin gas. We applied observational constraints and causality issue to separate physically relevant behavior of the phenomenological model.

  12. Scalar perturbations in the late Universe: viability of the Chaplygin gas models

    NASA Astrophysics Data System (ADS)

    Bouhmadi-López, Mariam; Brilenkov, Maxim; Brilenkov, Ruslan; Morais, João; Zhuk, Alexander

    2015-12-01

    We study the late-time evolution of the Universe where dark energy (DE) is parametrised by a modified generalised Chaplygin gas (mGCG) on top of cold dark matter (CDM) . We also take into account the radiation content of the Universe. In this context, the late stage of the evolution of the universe refers to the epoch where CDM is already clustered into inhomogeneously distributed discrete structures (galaxies, groups and clusters of galaxies). Under these conditions, the mechanical approach is an adequate tool to study the Universe deep inside the cell of uniformity. To be more accurate, we study scalar perturbations of the Friedmann-Lemaȋtre-Robertson-Walker metric due to inhomogeneities of CDM as well as fluctuations of radiation and mGCG, the later driving the late-time acceleration of the universe. Our analysis applies as well to the case where mGCG plays the role of DM and DE . We select the sets of parameters of the mGCG that are compatible with the mechanical approach. These sets define prospective mGCG models. By comparing the selected sets of models with some of the latest observational data results, we conclude that the mGCG is in tight agreement with those observations particularly for a mGCG playing the role of DE and DM.

  13. Thermodynamics of the variable modified Chaplygin gas

    NASA Astrophysics Data System (ADS)

    Panigrahi, D.; Chatterjee, S.

    2016-05-01

    A cosmological model with a new variant of Chaplygin gas obeying an equation of state(EoS), P = Aρ ‑ B/ρα where B= B0an is investigated in the context of its thermodynamical behaviour. Here B0 and n are constants and a is the scale factor. We show that the equation of state of this `Variable Modified Chaplygin gas' (VMCG) can describe the current accelerated expansion of the universe. Following standard thermodynamical criteria we mainly discuss the classical thermodynamical stability of the model and find that the new parameter, n introduced in VMCG plays a crucial role in determining the stability considerations and should always be negative. We further observe that although the earlier model of Lu explains many of the current observational findings of different probes it fails the desirable tests of thermodynamical stability. We also note that for 0n < our model points to a phantom type of expansion which, however, is found to be compatible with current SNe Ia observations and CMB anisotropy measurements. Further the third law of thermodynamics is obeyed in our case. Our model is very general in the sense that many of earlier works in this field may be obtained as a special case of our solution. An interesting point to note is that the model also apparently suggests a smooth transition from the big bang to the big rip in its whole evaluation process.

  14. Cosmological constraints on generalized Chaplygin gas model: Markov Chain Monte Carlo approach

    SciTech Connect

    Xu, Lixin; Lu, Jianbo E-mail: lvjianbo819@163.com

    2010-03-01

    We use the Markov Chain Monte Carlo method to investigate a global constraints on the generalized Chaplygin gas (GCG) model as the unification of dark matter and dark energy from the latest observational data: the Constitution dataset of type supernovae Ia (SNIa), the observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. In a non-flat universe, the constraint results for GCG model are, Ω{sub b}h{sup 2} = 0.0235{sup +0.0021}{sub −0.0018} (1σ) {sup +0.0028}{sub −0.0022} (2σ), Ω{sub k} = 0.0035{sup +0.0172}{sub −0.0182} (1σ) {sup +0.0226}{sub −0.0204} (2σ), A{sub s} = 0.753{sup +0.037}{sub −0.035} (1σ) {sup +0.045}{sub −0.044} (2σ), α = 0.043{sup +0.102}{sub −0.106} (1σ) {sup +0.134}{sub −0.117} (2σ), and H{sub 0} = 70.00{sup +3.25}{sub −2.92} (1σ) {sup +3.77}{sub −3.67} (2σ), which is more stringent than the previous results for constraint on GCG model parameters. Furthermore, according to the information criterion, it seems that the current observations much support ΛCDM model relative to the GCG model.

  15. Extended Chaplygin gas in Horava-Lifshitz gravity

    NASA Astrophysics Data System (ADS)

    Pourhassan, B.

    2016-09-01

    In this paper, we investigate cosmological models of the extended Chaplygin gas in a universe governed by Horava-Lifshitz gravity. The equation of state for an extended Chaplygin gas is a (n + 2) -variable equation determined by An, α, and B. In this work, we are interested to the case of second order (n = 2) equation of state which recovers quadratic barotropic equation of state. In that case there are four free parameters. We solve conservation equation approximately and obtain energy density in terms of scale factor with mentioned free parameters. Under some assumptions we relate free parameters to each other to have only one free independent parameter (A2) . It help us to obtain explicit expression for energy density in terms of scale factor. The allowed values of the second order extended Chaplygin gas parameter is fixed using the recent astrophysical and cosmological observational data. Thermodynamics of the model investigated based on the first and second law of thermodynamics.

  16. Quintessence and (anti-)Chaplygin gas in loop quantum cosmology

    SciTech Connect

    Lamon, Raphael; Woehr, Andreas J.

    2010-01-15

    The concordance model of cosmology contains several unknown components such as dark matter and dark energy. Many proposals have been made to describe them by choosing an appropriate potential for a scalar field. We study four models in the realm of loop quantum cosmology: the Chaplygin gas, an inflationary and radiationlike potential, quintessence and an anti-Chaplygin gas. For the latter we show that all trajectories start and end with a type II singularity and, depending on the initial value, may go through a bounce. On the other hand the evolution under the influence of the first three scalar fields behaves classically at times far away from the big bang singularity and bounces as the energy density approaches the critical density.

  17. Quintessence and (anti-)Chaplygin gas in loop quantum cosmology

    NASA Astrophysics Data System (ADS)

    Lamon, Raphael; Wöhr, Andreas J.

    2010-01-01

    The concordance model of cosmology contains several unknown components such as dark matter and dark energy. Many proposals have been made to describe them by choosing an appropriate potential for a scalar field. We study four models in the realm of loop quantum cosmology: the Chaplygin gas, an inflationary and radiationlike potential, quintessence and an anti-Chaplygin gas. For the latter we show that all trajectories start and end with a type II singularity and, depending on the initial value, may go through a bounce. On the other hand the evolution under the influence of the first three scalar fields behaves classically at times far away from the big bang singularity and bounces as the energy density approaches the critical density.

  18. Effects of extrinsic curvature as modified Chaplygin gas and Lorentz violation

    NASA Astrophysics Data System (ADS)

    Ahmadi, F.

    2016-05-01

    The modified Chaplygin gas may be considered as a popular candidate for dark energy. We apply a gravitational explanation for the modified Chaplygin gas within the context of brane-world theory without using any junction condition or Z2 symmetry. Then, we study the behavior of the deceleration parameter and age of the universe in this framework. Also, we investigate the effect of the modified Chaplygin gas on the speed of the propagation of gravitational waves and explore local Lorentz violation in this model.

  19. Generalized cosmic Chaplygin gas inspired intermediate standard scalar field inflation

    NASA Astrophysics Data System (ADS)

    Jawad, Abdul; Rani, Shamaila; Mohsaneen, Sidra

    2016-08-01

    We study the warm intermediate inflationary regime in the presence of generalized cosmic Chaplygin gas and an inflaton decay rate proportional to the temperature. For this purpose, we consider standard scalar field model during weak and strong dissipative regimes. We explore inflationary parameters like spectral index, scalar and tensor power spectra, tensor to scalar ratio and decay rate in order to compare the present model with recent observational data. The physical behavior of inflationary parameters is presented and found that all the results are agreed with recent observational data such as WMAP7, WMAP9 and Planck 2015.

  20. Observational tests of non-adiabatic Chaplygin gas

    SciTech Connect

    Carneiro, S.; Pigozzo, C. E-mail: cpigozzo@ufba.br

    2014-10-01

    In a previous paper [1] it was shown that any dark sector model can be mapped into a non-adiabatic fluid formed by two interacting components, one with zero pressure and the other with equation-of-state parameter ω = -1. It was also shown that the latter does not cluster and, hence, the former is identified as the observed clustering matter. This guarantees that the dark matter power spectrum does not suffer from oscillations or instabilities. It applies in particular to the generalised Chaplygin gas, which was shown to be equivalent to interacting models at both background and perturbation levels. In the present paper we test the non-adiabatic Chaplygin gas against the Hubble diagram of type Ia supernovae, the position of the first acoustic peak in the anisotropy spectrum of the cosmic microwave background and the linear power spectrum of large scale structures. We consider two different compilations of SNe Ia, namely the Constitution and SDSS samples, both calibrated with the MLCS2k2 fitter, and for the power spectrum we use the 2dFGRS catalogue. The model parameters to be adjusted are the present Hubble parameter, the present matter density and the Chaplygin gas parameter α. The joint analysis best fit gives α ≈ - 0.5, which corresponds to a constant-rate energy flux from dark energy to dark matter, with the dark energy density decaying linearly with the Hubble parameter. The ΛCDM model, equivalent to α = 0, stands outside the 3σ confidence interval.

  1. Inflationary cosmology with Chaplygin gas in Palatini formalism

    NASA Astrophysics Data System (ADS)

    Borowiec, Andrzej; Stachowski, Aleksander; Szydłowski, Marek; Wojnar, Aneta

    2016-01-01

    We present a simple generalisation of the ΛCDM model which on the one hand reaches very good agreement with the present day experimental data and provides an internal inflationary mechanism on the other hand. It is based on Palatini modified gravity with quadratic Starobinsky term and generalized Chaplygin gas as a matter source providing, besides a current accelerated expansion, the epoch of endogenous inflation driven by type III freeze singularity. It follows from our statistical analysis that astronomical data favors negative value of the parameter coupling quadratic term into Einstein-Hilbert Lagrangian and as a consequence the bounce instead of initial Big-Bang singularity is preferred.

  2. Chaplygin gas braneworld inflation according to WMAP7 data

    SciTech Connect

    Zarrouki, R.; Bennai, M.

    2010-12-15

    We consider a Chaplygin gas model with an exponential potential in framework of braneworld inflation. We apply the slow-roll approximation in the high-energy limit to derive various inflationary spectrum perturbation parameters. We show that the inflation observables depend only on the e-folding number N and the final value of the slow-roll parameter {epsilon}{sub end}. Whereas for small running of the scalar spectral index (dn{sub s}/dlnk), the inflation observables are in good agreement with recent WMAP7 data.

  3. Single-field inflation à la generalized Chaplygin gas

    SciTech Connect

    Campo, Sergio del

    2013-11-01

    In the simplest scenario for inflation, i.e. in the single-field inflation, it is presented an inflaton field with properties equivalent to a generalized Chaplygin gas. Their study is performed using the Hamilton-Jacobi approach to cosmology. The main results are contrasted with the measurements recently released by the Planck data, combined with the WMAP large-angle polarization. If the measurements released by Planck for the scalar spectral index together with its running are taken into account it is found a value for the α-parameter associated to the generalized Chaplygin gas given by α = 0.2578±0.0009.

  4. Spherical thin-shell wormholes and modified Chaplygin gas

    SciTech Connect

    Sharif, M.; Azam, M. E-mail: azammath@gmail.com

    2013-05-01

    The purpose of this paper is to construct spherical thin-shell wormhole solutions through cut and paste technique and investigate the stability of these solutions in the vicinity of modified Chaplygin gas. The Darmois-Israel formalism is used to formulate the stresses of the surface concentrating the exotic matter. We explore the stability of the wormhole solutions by using the standard potential method. We conclude that there exist more stable as well as unstable solutions than the previous study with generalized Chaplygin gas [19].

  5. Chaplygin dark star

    SciTech Connect

    Bertolami, O.; Paramos, J.

    2005-12-15

    We study the general properties of a spherically symmetric body described through the generalized Chaplygin equation of state. We conclude that such an object, dubbed generalized Chaplygin dark star, should exist within the context of the generalized Chaplygin gas (GCG) model of unification of dark energy and dark matter, and derive expressions for its size and expansion velocity. A criteria for the survival of the perturbations in the GCG background that give origin to the dark star are developed, and its main features are analyzed.

  6. On the Thermodynamic Stability of Variable Chaplygin Gas

    NASA Astrophysics Data System (ADS)

    Panigrahi, Dibyendu

    We have studied the properties of Variable Chaplygin gas (VCG) model in the context of its thermodynamical stability with the help of an equation of state. We have found that VCG satisfies the two basic characteristics of thermodynamic stability. Using the best fit value of n = -3.4 as previously found by Guo et al. gives that the fluid is thermodynamically stable throughout the evolution. The effective equation of state for the special case of, n = 0 goes to ΛCDM model. Again for n < 0 it favors phantom-like cosmology which is in agreement with the current SNe Ia constraints like VCG model. The deceleration parameter is also studied in the context of thermodynamics and the analysis shows that the flip (deceleration to acceleration) occurs for the value of n < 4. Finally the thermal equation of state is discussed which is found to be an explicit function of temperature only. We also observe that the third law of thermodynamics is satisfied for this model. In conformity with our expectation we also find that for an isoentropic system as volume expands the temperature falls.

  7. Chaplygin gas inspired scalar fields inflation via well-known potentials

    NASA Astrophysics Data System (ADS)

    Jawad, Abdul; Butt, Sadaf; Rani, Shamaila

    2016-08-01

    Brane inflationary universe models in the context of modified Chaplygin gas and generalized cosmic Chaplygin gas are being studied. We develop these models in view of standard scalar and tachyon fields. In both models, the implemented inflationary parameters such as scalar and tensor power spectra, scalar spectral index and tensor to scalar ratio are derived under slow roll approximations. We also use chaotic and exponential potential in high energy limits and discuss the characteristics of inflationary parameters for both potentials. These models are compatible with recent astronomical observations provided by WMAP7{+}9 and Planck data, i.e., ηs=1.027±0.051, 1.009±0.049, 0.096±0.025 and r<0.38, 0.36, 0.11.

  8. Observational constraints on modified Chaplygin gas from cosmic growth

    SciTech Connect

    Paul, B.C.; Thakur, P. E-mail: prasenjit_thakur1@yahoo.co.in

    2013-11-01

    We investigate the linear growth function for the large scale structures of the universe considering modified Chaplygin gas as dark energy. Taking into account observational growth data for a given range of redshift from the Wiggle-Z measurements and rms mass fluctuations from Ly-α measurements we numerically analyze cosmological models to constrain the parameters of the MCG. The observational data of Hubble parameter with redshift z is also considered. The Wang-Steinhardt ansatz for growth index γ and growth function f (defined as f = Ω{sub m}{sup γ}(a)) are considered for the numerical analysis. The best-fit values of the equation of state parameters obtained here is employed to study the growth function (f), growth index (γ) and equation of state (ω) with redshift z. The observational constraints on MCG parameters obtained here are compared with that of the GCG model for viable cosmology. It is noted that MCG also satisfactorily accommodates an accelerating phase followed by a matter dominated phase of the universe.

  9. Einstein static universe on the brane supported by extended Chaplygin gas

    NASA Astrophysics Data System (ADS)

    Heydarzade, Y.; Darabi, F.; Atazadeh, K.

    2016-08-01

    We study the cosmological models in which an extended Chaplygin gas universe is merged with the braneworld scenario. In particular, we examine the realization of Einstein static universe on the brane embedded in a non-constant curvature bulk space and perform a detailed perturbation analysis. We extract the stability conditions and find their impacts on the geometric equation of state parameter and the spatial curvature of the universe.

  10. Tolman-Oppenheimer-Volkoff equations in the presence of the Chaplygin gas: Stars and wormholelike solutions

    SciTech Connect

    Gorini, V.; Moschella, U.; Kamenshchik, A. Yu.; Pasquier, V.; Starobinsky, A. A.

    2008-09-15

    We study static solutions of the Tolman-Oppenheimer-Volkoff equations for spherically symmetric objects (stars) living in a space filled with the Chaplygin gas. Two cases are considered. In the normal case, all solutions (excluding the de Sitter one) realize a three-dimensional spheroidal geometry because the radial coordinate achieves a maximal value (the 'equator'). After crossing the equator, three scenarios are possible: a closed spheroid having a Schwarzschild-type singularity with infinite blueshift at the 'south pole', a regular spheroid, and a truncated spheroid having a scalar curvature singularity at a finite value of the radial coordinate. The second case arises when the modulus of the pressure exceeds the energy density (the phantom Chaplygin gas). There is no more equator and all solutions have the geometry of a truncated spheroid with the same type of singularity. We also consider static spherically symmetric configurations existing in a universe filled with only the phantom Chaplygin gas. In this case, two classes of solutions exist: truncated spheroids and solutions of the wormhole type with a throat. However, the latter are not asymptotically flat and possess curvature singularities at finite values of the radial coordinate. Thus, they may not be used as models of observable compact astrophysical objects.

  11. Born-Infeld thin-shell wormholes supported by generalized Cosmic Chaplygin gas

    NASA Astrophysics Data System (ADS)

    Azam, M.

    2016-03-01

    This paper investigates thin-shell wormholes in Born-Infeld theory supported by generalized Cosmic Chaplygin gas (GCCG). We study their stability via radial perturbations for distinct values of charge and Born-Infeld parameter. The comparison of wormhole solutions corresponding to generalized Chaplygin gas, modified Chaplygin gas with GCCG quation of state is established. It is found that similar type of wormhole solutions exists for small value of charge and Born-Infeld parameter for all type of equation of state, while some extra stable as well as unstable solution are found corresponding to large value of charge and Born-Infeld parameter. Thus, it is concluded that GCCG and large value of charge may responsible for such extra solutions.

  12. Co-Existence of Modified Chaplygin Gas and Other Dark Energies in the Framework of Fractal Universe

    NASA Astrophysics Data System (ADS)

    Maity, Sayani; Debnath, Ujjal

    2016-05-01

    In this work, we consider a non-flat universe in the framework of fractal cosmology. We have investigated the co-existence of different kinds of dark energy models such as tachyonic field, DBI-essence, hessence, k-essence, dilaton, quintessence with the modified Chaplygin gas (MCG) in fractal universe and obtained the statefinder parameters. The natures of the scalar fields and the concerned potentials have been analyzed by the correspondence scenario in the fractal universe.

  13. Interacting closed string tachyon with modified Chaplygin gas and its stability

    NASA Astrophysics Data System (ADS)

    Amani, Ali R.; Escamilla-Rivera, Celia; Faghani, H. R.

    2013-12-01

    In this paper, we have considered a closed string tachyon model with a constant dilaton field and interacted it with Chaplygin gas for evaluating cosmology parameters. The model has been studied in 26 dimensions, with 22 dimensions related to compactification on an internal nonflat space and its other 4 dimensions related to the Friedmann-Lemaître-Robertson-Walker metric. By taking the internal curvature as a negative constant, we reconstructed the closed string tachyon potential in terms of tachyon field as a quartic equation. The tachyon field and the scale factor have been achieved as a function of time evolution and geometry of curved space where the behavior of the scale factor describes an accelerated expansion of the Universe. Next, we discussed the stability of our model by introducing a sound speed factor, which must be, in our case, a positive function. By drawing sound speed against time evolution, we investigated stability conditions for a nonflat universe in its three stages: early, late, and future time. As a result we shall see that in these cases there remains an instability at early time and a stability point at late time.

  14. Extended Chaplygin gas as a unified fluid of dark components in varying gravitational constant theory

    NASA Astrophysics Data System (ADS)

    Lu, Jianbo; Xu, Lixin; Tan, Hongyan; Gao, Shanshan

    2014-03-01

    Varying gravitational constant G(t) (VG) cosmology is studied in this paper, where the modified Friedmann equation and the modified energy conservation equation are given with respect to the constant-G theory. Considering the extended Chaplygin gas (ECG) as background fluid (or thinking that ECG fluid is induced by the variation of G), the unified model of dark matter and dark energy is obtained in VG theory. The parameter spaces are investigated in the VG-ECG model by using the recent cosmic data. Constraint results show β =-G/.HG =-0.003-0.020-0.055+0.021+0.034 for the VG-GCG unified model and β=-0.027-0.032-0.066+0.032+0.059 for the VG-MCG unified model. Equivalently, they correspond to the limits on the current variation of Newton's gravitational constant at 95.4% confidence level |G/.G|today≲4.1×10-12 yr-1 and |G/.G|today≲6.6×10-12 yr-1. And for z ≤3.5, bounds on the variation of G/.G in the VG-ECG unified model are in accordance with the experiment explorations of varying G. In addition, in VG theory the used observational data point still cannot distinguish the VG-GCG and VG-MCG unified model from the most popular ΛCDM cosmology. Furthermore, to see the effects of varying G and physical properties for VG-ECG fluid, we discuss the evolutionary behaviors of cosmological quantities in VG theory, such as G/.G, G./.G and equation of state w, etc. For β <0 a quintom scenario crossing over w=-1 can be realized in the VG-GCG model.

  15. The exact Riemann solutions to the generalized Chaplygin gas equations with friction

    NASA Astrophysics Data System (ADS)

    Sun, Meina

    2016-07-01

    The exact solutions to the Riemann problem for the one-dimensional generalized Chaplygin gas equations with a Coulomb-like friction term are constructed explicitly. The delta shock wave arises in the Riemann solutions provided that the initial data satisfy some certain conditions, although the system is strictly hyperbolic and the two characteristic fields are genuinely nonlinear. The position, strength and propagation speed of delta shock wave are obtained from the generalized Rankine-Hugoniot conditions. It is shown that the Coulomb-like friction term make waves (including rarefaction, shock and delta shock) bend into parabolic shapes for the Riemann solutions.

  16. Chaplygin gas of Tachyon Nature Imposed by Noether Symmetry and constrained via H(z) data

    NASA Astrophysics Data System (ADS)

    Gardai Collodel, Lucas; Medeiros Kremer, Gilberto

    2016-04-01

    An action of general form is proposed for a Universe containing matter, radiation and dark energy. The latter is interpreted as a tachyon field non-minimally coupled to the scalar curvature. The Palatini approach is used when varying the action so the connection is given by a more generic form. Both the self-interaction potential and the non-minimally coupling function are obtained by constraining the system to present invariability under global point transformation of the fields (Noether Symmetry). The only possible solution is shown to be that of minimal coupling and constant potential (Chaplygin gas). The behavior of the dynamical properties of the system is compared to recent observational data, which infers that the tachyon field must indeed be dynamical.

  17. Chaplygin traversable wormholes

    SciTech Connect

    Lobo, Francisco S.N.

    2006-03-15

    The generalized Chaplygin gas (GCG) is a candidate for the unification of dark energy and dark matter, and is parametrized by an exotic equation of state given by p{sub ch}=-A/{rho}{sub ch}{sup {alpha}}, where A is a positive constant and 0<{alpha}{<=}1. In this paper, exact solutions of spherically symmetric traversable wormholes supported by the GCG are found, possibly arising from a density fluctuation in the GCG cosmological background. To be a solution of a wormhole, the GCG equation of state imposes the following generic restriction A<(8{pi}r{sub 0}{sup 2}){sup -(1+{alpha})}, where r{sub 0} is the wormhole throat radius, consequently violating the null energy condition. The spatial distribution of the exotic GCG is restricted to the throat neighborhood, and the physical properties and characteristics of these Chaplygin wormholes are further analyzed. Four specific solutions are explored in some detail, namely, that of a constant redshift function, a specific choice for the form function, a constant energy density, and finally, isotropic pressure Chaplygin wormhole geometries.

  18. Friedman—Robertson—Walker Models with Late-Time Acceleration

    NASA Astrophysics Data System (ADS)

    Abdussattar; Prajapati, S. R.

    2011-02-01

    In order to account for the observed cosmic acceleration, a modification of the ansatz for the variation of density in Friedman—Robertson—Walker (FRW) FRW models given by Islam is proposed. The modified ansatz leads to an equation of state which corresponds to that of a variable Chaplygin gas, which in the course of evolution reduces to that of a modified generalized Chaplygin gas (MGCG) and a Chaplygin gas (CG), exhibiting late-time acceleration.

  19. Anisotropic charged fluids with Chaplygin equation of state in (2+1) dimension

    NASA Astrophysics Data System (ADS)

    Bhar, Piyali; Rahaman, Farook; Jawad, Abdul; Islam, Sayeedul

    2015-11-01

    Present paper provides a new non-singular model for anisotropic charged fluid sphere in (2+1)-dimensional anti de-Sitter spacetime corresponding to the exterior BTZ spacetime (Banados et al., Phys. Rev. Lett. 69:1849, 1992). The model is obtained by assuming Krori and Barua (KB) ansatz (Krori and Barua, J. Phys. A, Math. Gen., 8:508, 1975). To solve the Einstein-Maxwell field equations we choose modified Chaplygin gas. Various physical quantities have been discussed and from our analysis we show that our model satisfies all required physical conditions for representing compact stars.

  20. A Cosmological Model of the Early Universe Based on ECG with Variable Λ-Term in Lyra Geometry

    NASA Astrophysics Data System (ADS)

    Saadat, H.

    2016-05-01

    In this paper, we study interacting extended Chaplygin gas as dark matter and quintessence scalar field as dark energy with an effective Λ-term in Lyra manifold. As we know Chaplygin gas behaves as dark matter at the early universe while cosmological constant at the late time. Modified field equations are given and motivation of the phenomenological models discussed in details. Four different models based on the interaction term are investigated in this work. Then, we consider other models where Extended Chaplygin gas and quintessence field play role of dark matter and dark energy respectively with two different forms of interaction between the extended Chaplygin gas and quintessence scalar field for both constant and varying Λ. Concerning to the mathematical hardness of the problems we discuss results numerically and graphically. Obtained results give us hope that proposed models can work as good models for the early universe with later stage of evolution containing accelerated expansion.

  1. A note on observational signatures in superluminal unified dark matter models

    SciTech Connect

    Urakawa, Yuko; Kobayashi, Tsutomu E-mail: tsutomu@gravity.phys.waseda.ac.jp

    2010-07-01

    We explore the possibility that the dark matter and dark energy are mimicked by a single fluid or by a single k-essence-like scalar field. The so called Chaplygin gas unified dark matter models can reproduce the observed matter power spectrum by adding a baryon component. It has been argued that the evolution of the baryon fluctuations is particularly favoured for the ''superluminal'' case where the sound speed of the Chaplygin gas exceeds the speed of light at late times, as well as for the models with the negligibly small sound speed. In this note we compute the integrated Sachs-Wolfe signal in the Chaplygin gas models, focusing on the superluminal case which has not been investigated before because of the premature understanding of causality. It is shown that the superluminal model leads to large enhancement of the integrated Sachs-Wolfe effect, which is inconsistent with the CMB measurements.

  2. Discriminating dark energy models by using the Statefinder hierarchy and the growth rate of matter perturbations

    SciTech Connect

    Li, Jun; Yang, Rongjia; Chen, Bohai E-mail: yangrj08@gmail.com

    2014-12-01

    We apply the Statefinder hierarchy and the growth rate of matter perturbations to discriminate modified Chaplygin gas (MCG), generalized Chaplygin gas (GCG), superfluid Chaplygin gas (SCG), purely kinetic k-essence (PKK), and ΛCDM model. We plot the evolutional trajectories of these models in the Statefinder plane and in the composite diagnostic plane. We find that GCG, MCG, SCG, PKK, and ΛCDM can be distinguished well from each other at the present epoch by using the composite diagnostic (ε(z), S{sup (1)}{sub 5}). Using other combinations, such as (S{sup (1)}{sub 3}, S{sup (1)}{sub 4}), (S{sup (1)}{sub 3}, S{sub 5}), (ε(z), S{sup (1)}{sub 3}), and (ε(z), S{sub 4}), some of these five dark energy models cannot be distinguished.

  3. Studies of systems with nonholonomic constraints: The Segway and the Chaplygin sleigh

    NASA Astrophysics Data System (ADS)

    Tuttle, Joseph T.

    In this thesis, two systems with nonholonomic systems are investigated: the Segway and the Chaplygin sleigh. Using Lagrangian mechanics, the constrained nonlinear equations of motion for both systems are derived. By use of the nullspace of the constraint matrices, the unconstrained equations of motion can be obtained. For the Segway, these equations are linearized about a zero equilibrium state, placed into state space form and decoupled. A feedback controller is designed about the velocity and heading angle rate reference commands. To compare to the real data from the built Segway, measurement noise was also included in the model. Experimental data is taken for the case of both zero and constant reference commands. The data is then compared to the simulated results. The model is shown to be satisfactory, but better parameter measurements of the Segway is needed for a more conclusive comparison. The unconstrained equations of motion for the Chaplygin sleigh can not be linearized. Thus Lyapunov stability theory was used for analysis. The Chaplygin sleigh with constant input was shown to spiral outward and settle into a circle. If a PD feedback controller was designed about the heading angle, then the Chaplygin sleigh would be driven to the angle, but would eventually coast to a stop. From simulations, the addition of a sinusoidal component appears to move in the desired direction without slowing down. A sinusoidal component was also added to a constant input to result in roulette like paths in the simulation. Future investigation would require a more definite analysis of the sinusoidal term in the input.

  4. World Natural Gas Model

    Energy Science and Technology Software Center (ESTSC)

    1994-12-01

    RAMSGAS, the Research and Development Analysis Modeling System World Natural Gas Model, was developed to support planning of unconventional gaseoues fuels research and development. The model is a scenario analysis tool that can simulate the penetration of unconventional gas into world markets for oil and gas. Given a set of parameter values, the model estimates the natural gas supply and demand for the world for the period from 1980 to 2030. RAMSGAS is based onmore » a supply/demand framwork and also accounts for the non-renewable nature of gas resources. The model has three fundamental components: a demand module, a wellhead production cost module, and a supply/demand interface module. The demand for gas is a product of total demand for oil and gas in each of 9 demand regions and the gas share. Demand for oil and gas is forecast from the base year of 1980 through 2030 for each demand region, based on energy growth rates and price-induced conservation. For each of 11 conventional and 19 unconventional gas supply regions, wellhead production costs are calculated. To these are added transportation and distribution costs estimates associated with moving gas from the supply region to each of the demand regions and any economic rents. Based on a weighted average of these costs and the world price of oil, fuel shares for gas and oil are computed for each demand region. The gas demand is the gas fuel share multiplied by the total demand for oil plus gas. This demand is then met from the available supply regions in inverse proportion to the cost of gas from each region. The user has almost complete control over the cost estimates for each unconventional gas source in each year and thus can compare contributions from unconventional resources under different cost/price/demand scenarios.« less

  5. Statefinder Parameters for Different Dark Energy Models with Variable G Correction in Kaluza-Klein Cosmology

    NASA Astrophysics Data System (ADS)

    Chakraborty, Shuvendu; Debnath, Ujjal; Jamil, Mubasher; Myrzakulov, Ratbay

    2012-07-01

    In this work, we have calculated the deceleration parameter, statefinder parameters and EoS parameters for different dark energy models with variable G correction in homogeneous, isotropic and non-flat universe for Kaluza-Klein Cosmology. The statefinder parameters have been obtained in terms of some observable parameters like dimensionless density parameter, EoS parameter and Hubble parameter for holographic dark energy, new agegraphic dark energy and generalized Chaplygin gas models.

  6. On the Chaplygin system on the sphere with velocity dependent potential

    NASA Astrophysics Data System (ADS)

    Tsiganov, A. V.

    2015-06-01

    We discuss how to get variables of separation, separated relations and the Lax matrix for the Chaplygin system on the sphere with velocity dependent potential starting with the Lax matrix for other integrable system separable in elliptic coordinates on the sphere.

  7. Linear and nonlinear instabilities in unified dark energy models

    SciTech Connect

    Avelino, P. P.; Beca, L. M. G.; Martins, C. J. A. P.

    2008-03-15

    We revisit the paradigm of unified dark energy discussing in detail the averaging problem in this type of scenario, highlighting the need for a full nonlinear treatment. We also address the question of if and how models with one or several dark fluids can be observationally distinguished. Simpler and physically clearer derivations of some key results, most notably on the relation between the generalized Chaplygin gas and the standard ({lambda}CDM) 'concordance' model and on a Jeans-type small-scale instability of some coupled dark energy/dark matter models are presented.

  8. Riemann problem with delta initial data for the isentropic relativistic Chaplygin Euler equations

    NASA Astrophysics Data System (ADS)

    Shao, Zhiqiang

    2016-06-01

    In this paper, we study the Riemann problem with the initial data containing the Dirac delta function for the isentropic relativistic Chaplygin Euler equations. Under suitably generalized Rankine-Hugoniot relation and entropy condition, we constructively obtain the global existence of generalized solutions including delta shock waves that explicitly exhibit four kinds of different structures. Moreover, it can be found that the solutions constructed here are stable for the perturbation of the initial data.

  9. Exact cosmological solutions of models with an interacting dark sector

    NASA Astrophysics Data System (ADS)

    Pavan, A. B.; Ferreira, Elisa G. M.; Micheletti, Sandro M. R.; de Souza, J. C. C.; Abdalla, E.

    2012-11-01

    In this work we extend the first order formalism for cosmological models that present an interaction between a fermionic and a scalar field. Cosmological exact solutions describing universes filled with interacting dark energy and dark matter have been obtained. Viable cosmological solutions with an early period of decelerated expansion followed by late acceleration have been found, notably one which presents a dark matter component dominating in the past and a dark energy component dominating in the future. In another one, the dark energy alone is the responsible for both periods, similar to a Chaplygin gas case. Exclusively accelerating solutions have also been obtained.

  10. Modeling Leaking Gas Plume Migration

    SciTech Connect

    Silin, Dmitriy; Patzek, Tad; Benson, Sally M.

    2007-08-20

    In this study, we obtain simple estimates of 1-D plume propagation velocity taking into account the density and viscosity contrast between CO{sub 2} and brine. Application of the Buckley-Leverett model to describe buoyancy-driven countercurrent flow of two immiscible phases leads to a transparent theory predicting the evolution of the plume. We obtain that the plume does not migrate upward like a gas bubble in bulk water. Rather, it stretches upward until it reaches a seal or until the fluids become immobile. A simple formula requiring no complex numerical calculations describes the velocity of plume propagation. This solution is a simplification of a more comprehensive theory of countercurrent plume migration that does not lend itself to a simple analytical solution (Silin et al., 2006). The range of applicability of the simplified solution is assessed and provided. This work is motivated by the growing interest in injecting carbon dioxide into deep geological formations as a means of avoiding its atmospheric emissions and consequent global warming. One of the potential problems associated with the geologic method of sequestration is leakage of CO{sub 2} from the underground storage reservoir into sources of drinking water. Ideally, the injected green-house gases will stay in the injection zone for a geologically long time and eventually will dissolve in the formation brine and remain trapped by mineralization. However, naturally present or inadvertently created conduits in the cap rock may result in a gas leak from primary storage. Even in supercritical state, the carbon dioxide viscosity and density are lower than those of the indigenous formation brine. Therefore, buoyancy will tend to drive the CO{sub 2} upward unless it is trapped beneath a low permeability seal. Theoretical and experimental studies of buoyancy-driven supercritical CO{sub 2} flow, including estimation of time scales associated with plume evolution, are critical for developing technology

  11. Hazardous gas model evaluation with field observations

    NASA Astrophysics Data System (ADS)

    Hanna, S. R.; Chang, J. C.; Strimaitis, D. G.

    Fifteen hazardous gas models were evaluated using data from eight field experiments. The models include seven publicly available models (AFTOX, DEGADIS, HEGADAS, HGSYSTEM, INPUFF, OB/DG and SLAB), six proprietary models (AIRTOX, CHARM, FOCUS, GASTAR, PHAST and TRACE), and two "benchmark" analytical models (the Gaussian Plume Model and the analytical approximations to the Britter and McQuaid Workbook nomograms). The field data were divided into three groups—continuous dense gas releases (Burro LNG, Coyote LNG, Desert Tortoise NH 3-gas and aerosols, Goldfish HF-gas and aerosols, and Maplin Sands LNG), continuous passive gas releases (Prairie Grass and Hanford), and instantaneous dense gas releases (Thorney Island freon). The dense gas models that produced the most consistent predictions of plume centerline concentrations across the dense gas data sets are the Britter and McQuaid, CHARM, GASTAR, HEGADAS, HGSYSTEM, PHAST, SLAB and TRACE models, with relative mean biases of about ±30% or less and magnitudes of relative scatter that are about equal to the mean. The dense gas models tended to overpredict the plume widths and underpredict the plume depths by about a factor of two. All models except GASTAR, TRACE, and the area source version of DEGADIS perform fairly well with the continuous passive gas data sets. Some sensitivity studies were also carried out. It was found that three of the more widely used publicly-available dense gas models (DEGADIS, HGSYSTEM and SLAB) predicted increases in concentration of about 70% as roughness length decreased by an order of magnitude for the Desert Tortoise and Goldfish field studies. It was also found that none of the dense gas models that were considered came close to simulating the observed factor of two increase in peak concentrations as averaging time decreased from several minutes to 1 s. Because of their assumption that a concentrated dense gas core existed that was unaffected by variations in averaging time, the dense gas

  12. Dairy gas emissions model: reference manual

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The Dairy Gas Emissions Model (DairyGEM) is a software tool for estimating ammonia, hydrogen sulfide, and greenhouse gas (GHG) emissions of dairy production systems as influenced by climate and farm management. A production system is defined to include emissions during the production of all feeds wh...

  13. Modelling magmatic gas scrubbing in hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Di Napoli, Rossella; Aiuppa, Alessandro; Valenza, Mariano; Bergsson, Baldur; Ilyinskaya, Evgenia; Pfeffer, Melissa Anne; Rakel Guðjónsdóttir, Sylvía

    2015-04-01

    In volcano-hosted hydrothermal systems, the chemistry of deeply rising magmatic gases is extensively modified by gas-water-rock interactions taking place within the hydrothermal reservoir, and/or at shallow groundwaters conditions. These reactions can scrub reactive, water-soluble species (S, halogens) from the magmatic gas phase, so that their quantitative assessment is central to understanding the chemistry of surface gas manifestations, and brings profound implications to the interpretation of volcanic-hydrothermal unrests. Here, we present the results of numerical simulations of magmatic gas scrubbing, in which the reaction path modelling approach (Helgeson, 1968) is used to reproduce hydrothermal gas-water-rock interactions at both shallow (temperature up to 109°C; low-T model runs) and deep reservoir (temperature range: 150-250 °C; high-T model runs) conditions. The model was built based upon the EQ3/6 software package (Wolery and Daveler, 1992), and consisted into a step by step addition of a high-temperature magmatic gas to an initial meteoric water, in the presence of a dissolving aquifer rock. The model outputted, at each step of gas addition, the chemical composition of a new aqueous solution formed after gas-water-rock interactions; which, upon reaching gas over-pressuring (PgasTOT > Psat(H2O) at run T), is degassed (by single-step degassing) to separate a scrubbed gas phase. As an application of the model results, the model compositions of the separated gases are finally compared with compositions of natural gas emissions from Hekla volcano (T< 100°C) and from Krisuvik geothermal system (T> 100°C), resulting into an excellent agreement. The compositions of the model solutions are also in fair agreement with compositions of natural thermal water samples. We conclude that our EQ3/6-based reaction path simulations offer a realistic representation of gas-water-rock interaction processes occurring underneath active magmatic-hydrothermal systems

  14. Computational modeling of intraocular gas dynamics.

    PubMed

    Noohi, P; Abdekhodaie, M J; Cheng, Y L

    2015-01-01

    The purpose of this study was to develop a computational model to simulate the dynamics of intraocular gas behavior in pneumatic retinopexy (PR) procedure. The presented model predicted intraocular gas volume at any time and determined the tolerance angle within which a patient can maneuver and still gas completely covers the tear(s). Computational fluid dynamics calculations were conducted to describe PR procedure. The geometrical model was constructed based on the rabbit and human eye dimensions. SF6 in the form of pure and diluted with air was considered as the injected gas. The presented results indicated that the composition of the injected gas affected the gas absorption rate and gas volume. After injection of pure SF6, the bubble expanded to 2.3 times of its initial volume during the first 23 h, but when diluted SF6 was used, no significant expansion was observed. Also, head positioning for the treatment of retinal tear influenced the rate of gas absorption. Moreover, the determined tolerance angle depended on the bubble and tear size. More bubble expansion and smaller retinal tear caused greater tolerance angle. For example, after 23 h, for the tear size of 2 mm the tolerance angle of using pure SF6 is 1.4 times more than that of using diluted SF6 with 80% air. Composition of the injected gas and conditions of the tear in PR may dramatically affect the gas absorption rate and gas volume. Quantifying these effects helps to predict the tolerance angle and improve treatment efficiency. PMID:26682529

  15. Computational modeling of intraocular gas dynamics

    NASA Astrophysics Data System (ADS)

    Noohi, P.; Abdekhodaie, M. J.; Cheng, Y. L.

    2015-12-01

    The purpose of this study was to develop a computational model to simulate the dynamics of intraocular gas behavior in pneumatic retinopexy (PR) procedure. The presented model predicted intraocular gas volume at any time and determined the tolerance angle within which a patient can maneuver and still gas completely covers the tear(s). Computational fluid dynamics calculations were conducted to describe PR procedure. The geometrical model was constructed based on the rabbit and human eye dimensions. SF6 in the form of pure and diluted with air was considered as the injected gas. The presented results indicated that the composition of the injected gas affected the gas absorption rate and gas volume. After injection of pure SF6, the bubble expanded to 2.3 times of its initial volume during the first 23 h, but when diluted SF6 was used, no significant expansion was observed. Also, head positioning for the treatment of retinal tear influenced the rate of gas absorption. Moreover, the determined tolerance angle depended on the bubble and tear size. More bubble expansion and smaller retinal tear caused greater tolerance angle. For example, after 23 h, for the tear size of 2 mm the tolerance angle of using pure SF6 is 1.4 times more than that of using diluted SF6 with 80% air. Composition of the injected gas and conditions of the tear in PR may dramatically affect the gas absorption rate and gas volume. Quantifying these effects helps to predict the tolerance angle and improve treatment efficiency.

  16. Adsorption Model for Off-Gas Separation

    SciTech Connect

    Veronica J. Rutledge

    2011-03-01

    The absence of industrial scale nuclear fuel reprocessing in the U.S. has precluded the necessary driver for developing the advanced simulation capability now prevalent in so many other countries. Thus, it is essential to model complex series of unit operations to simulate, understand, and predict inherent transient behavior and feedback loops. A capability of accurately simulating the dynamic behavior of advanced fuel cycle separation processes will provide substantial cost savings and many technical benefits. The specific fuel cycle separation process discussed in this report is the off-gas treatment system. The off-gas separation consists of a series of scrubbers and adsorption beds to capture constituents of interest. Dynamic models are being developed to simulate each unit operation involved so each unit operation can be used as a stand-alone model and in series with multiple others. Currently, an adsorption model has been developed in gPROMS software. Inputs include gas stream constituents, sorbent, and column properties, equilibrium and kinetic data, and inlet conditions. It models dispersed plug flow in a packed bed under non-isothermal and non-isobaric conditions for a multiple component gas stream. The simulation outputs component concentrations along the column length as a function of time from which the breakthrough data is obtained. It also outputs temperature along the column length as a function of time and pressure drop along the column length. Experimental data will be input into the adsorption model to develop a model specific for iodine adsorption on silver mordenite as well as model(s) specific for krypton and xenon adsorption. The model will be validated with experimental breakthrough curves. Another future off-gas modeling goal is to develop a model for the unit operation absorption. The off-gas models will be made available via the server or web for evaluation by customers.

  17. Lattice Gas Model with Nonlocal Interactions

    NASA Astrophysics Data System (ADS)

    Das, Shankar P.

    We analyze the nature of the hydrodynamic modes in a Lattice Gas Automata (LGA) model defined on a hexagonal lattice and having nonlocal interactions of attractive and repulsive type simultaneously. The model is similar in spirit to the liquid gas model of Appert and Zaleski [Phys. Rev. Lett. 64, 1 (1990)]. The phase diagram for the model is computed using the kinetic pressure. The dynamics is studied with a mean field type approach in the Boltzmann approximation ignoring effects of correlated collisions. We compute the transport coefficients and the speed of sound propagation. The presence of attractive interactions show increase in the transport coefficients at intermediate densities.

  18. International Natural Gas Model 2011, Model Documentation Report

    EIA Publications

    2013-01-01

    This report documents the objectives, analytical approach and development of the International Natural Gas Model (INGM). It also catalogues and describes critical assumptions, computational methodology, parameter estimation techniques, and model source code.

  19. World Energy Projection System Plus Model Documentation: Natural Gas Model

    EIA Publications

    2011-01-01

    This report documents the objectives, analytical approach and development of the World Energy Projection System Plus (WEPS ) Natural Gas Model. It also catalogues and describes critical assumptions, computational methodology, parameter estimation techniques, and model source code.

  20. Comet Gas and Dust Dynamics Modeling

    NASA Technical Reports Server (NTRS)

    Von Allmen, Paul A.; Lee, Seungwon

    2010-01-01

    This software models the gas and dust dynamics of comet coma (the head region of a comet) in order to support the Microwave Instrument for Rosetta Orbiter (MIRO) project. MIRO will study the evolution of the comet 67P/Churyumov-Gerasimenko's coma system. The instrument will measure surface temperature, gas-production rates and relative abundances, and velocity and excitation temperatures of each species along with their spatial temporal variability. This software will use these measurements to improve the understanding of coma dynamics. The modeling tool solves the equation of motion of a dust particle, the energy balance equation of the dust particle, the continuity equation for the dust and gas flow, and the dust and gas mixture energy equation. By solving these equations numerically, the software calculates the temperature and velocity of gas and dust as a function of time for a given initial gas and dust production rate, and a dust characteristic parameter that measures the ability of a dust particle to adjust its velocity to the local gas velocity. The software is written in a modular manner, thereby allowing the addition of more dynamics equations as needed. All of the numerical algorithms are added in-house and no third-party libraries are used.

  1. GAS eleven node thermal model (GEM)

    NASA Technical Reports Server (NTRS)

    Butler, Dan

    1988-01-01

    The Eleven Node Thermal Model (GEM) of the Get Away Special (GAS) container was originally developed based on the results of thermal tests of the GAS container. The model was then used in the thermal analysis and design of several NASA/GSFC GAS experiments, including the Flight Verification Payload, the Ultraviolet Experiment, and the Capillary Pumped Loop. The model description details the five cu ft container both with and without an insulated end cap. Mass specific heat values are also given so that transient analyses can be performed. A sample problem for each configuration is included as well so that GEM users can verify their computations. The model can be run on most personal computers with a thermal analyzer solution routine.

  2. Modeling dynamical geometry with lattice gas automata

    SciTech Connect

    Hasslacher, B.; Meyer, D.A.

    1998-06-27

    Conventional lattice gas automata consist of particles moving discretely on a fixed lattice. While such models have been quite successful for a variety of fluid flow problems, there are other systems, e.g., flow in a flexible membrane or chemical self-assembly, in which the geometry is dynamical and coupled to the particle flow. Systems of this type seem to call for lattice gas models with dynamical geometry. The authors construct such a model on one dimensional (periodic) lattices and describe some simulations illustrating its nonequilibrium dynamics.

  3. Combustion modeling in advanced gas turbine systems

    SciTech Connect

    Smoot, L.D.; Hedman, P.O.; Fletcher, T.H.; Brewster, B.S.; Kramer, S.K.

    1995-12-31

    Goal of DOE`s Advanced Turbine Systems program is to develop and commercialize ultra-high efficiency, environmentally superior, cost competitive gas turbine systems for base-load applications in utility, independent power producer, and industrial markets. Primary objective of the program here is to develop a comprehensive combustion model for advanced gas turbine combustion systems using natural gas (coal gasification or biomass fuels). The efforts included code evaluation (PCGC-3), coherent anti-Stokes Raman spectroscopy, laser Doppler anemometry, and laser-induced fluorescence.

  4. Combustion modeling in advanced gas turbine systems

    SciTech Connect

    Smoot, L.D.; Hedman, P.O.; Fletcher, T.H.

    1995-10-01

    The goal of the U.S. Department of Energy`s Advanced Turbine Systems (ATS) program is to help develop and commercialize ultra-high efficiency, environmentally superior, and cost competitive gas turbine systems for base-load applications in the utility, independent power producer, and industrial markets. Combustion modeling, including emission characteristics, has been identified as a needed, high-priority technology by key professionals in the gas turbine industry.

  5. Performance Evaluation of Dense Gas Dispersion Models.

    NASA Astrophysics Data System (ADS)

    Touma, Jawad S.; Cox, William M.; Thistle, Harold; Zapert, James G.

    1995-03-01

    This paper summarizes the results of a study to evaluate the performance of seven dense gas dispersion models using data from three field experiments. Two models (DEGADIS and SLAB) are in the public domain and the other five (AIRTOX, CHARM, FOCUS, SAFEMODE, and TRACE) are proprietary. The field data used are the Desert Tortoise pressurized ammonia releases, Burro liquefied natural gas spill tests, and the Goldfish anhydrous hydrofluoric acid spill experiments. Desert Tortoise and Goldfish releases were simulated as horizontal jet releases, and Burro as a liquid pool. Performance statistics were used to compare maximum observed concentrations and plume half-width to those predicted by each model. Model performance varied and no model exhibited consistently good performance across all three databases. However, when combined across the three databases, all models performed within a factor of 2. Problems encountered are discussed in order to help future investigators.

  6. Modeling internal ballistics of gas combustion guns.

    PubMed

    Schorge, Volker; Grossjohann, Rico; Schönekess, Holger C; Herbst, Jörg; Bockholdt, Britta; Ekkernkamp, Axel; Frank, Matthias

    2016-05-01

    Potato guns are popular homemade guns which work on the principle of gas combustion. They are usually constructed for recreational rather than criminal purposes. Yet some serious injuries and fatalities due to these guns are reported. As information on the internal ballistics of homemade gas combustion-powered guns is scarce, it is the aim of this work to provide an experimental model of the internal ballistics of these devices and to investigate their basic physical parameters. A gas combustion gun was constructed with a steel tube as the main component. Gas/air mixtures of acetylene, hydrogen, and ethylene were used as propellants for discharging a 46-mm caliber test projectile. Gas pressure in the combustion chamber was captured with a piezoelectric pressure sensor. Projectile velocity was measured with a ballistic speed measurement system. The maximum gas pressure, the maximum rate of pressure rise, the time parameters of the pressure curve, and the velocity and path of the projectile through the barrel as a function of time were determined according to the pressure-time curve. The maximum gas pressure was measured to be between 1.4 bar (ethylene) and 4.5 bar (acetylene). The highest maximum rate of pressure rise was determined for hydrogen at (dp/dt)max = 607 bar/s. The muzzle energy was calculated to be between 67 J (ethylene) and 204 J (acetylene). To conclude, this work provides basic information on the internal ballistics of homemade gas combustion guns. The risk of injury to the operator or bystanders is high, because accidental explosions of the gun due to the high-pressure rise during combustion of the gas/air mixture may occur. PMID:26239103

  7. A Model of Solid State Gas Sensors

    NASA Astrophysics Data System (ADS)

    Woestman, J. T.; Brailsford, A. D.; Shane, M.; Logothetis, E. M.

    1997-03-01

    Solid state gas sensors are widely used to measure the concentrations of gases such as CO, CH_4, C_3H_6, H_2, C_3H8 and O2 The applications of these sensors range from air-to-fuel ratio control in combustion processes including those in automotive engines and industrial furnaces to leakage detection of inflammable and toxic gases in domestic and industrial environments. As the need increases to accurately measure smaller and smaller concentrations, problems such as poor selectivity, stability and response time limit the use of these sensors. In an effort to overcome some of these limitations, a theoretical model of the transient behavior of solid state gas sensors has been developed. In this presentation, a model for the transient response of an electrochemical gas sensor to gas mixtures containing O2 and one reducing species, such as CO, is discussed. This model accounts for the transport of the reactive species to the sampling electrode, the catalyzed oxidation/reduction reaction of these species and the generation of the resulting electrical signal. The model will be shown to reproduce the results of published steady state models and to agree with experimental steady state and transient data.

  8. Scale factor self-dual cosmological models

    NASA Astrophysics Data System (ADS)

    Camara da Silva, U.; Lima, A. A.; Sotkov, G. M.

    2015-07-01

    We implement a conformal time scale factor duality for Friedmann-Robertson-Walker cosmological models, which is consistent with the weak energy condition. The requirement for self-duality determines the equations of state for a broad class of barotropic fluids. We study the example of a universe filled with two interacting fluids, presenting an accelerated and a decelerated period, with manifest UV/IR duality. The associated self-dual scalar field interaction turns out to coincide with the "radiation-like" modified Chaplygin gas models. We present an equivalent realization of them as gauged Kähler sigma models (minimally coupled to gravity) with very specific and interrelated Kähler- and super-potentials. Their applications in the description of hilltop inflation and also as quintessence models for the late universe are discussed.

  9. A varying polytropic gas universe and phase space analysis

    NASA Astrophysics Data System (ADS)

    Khurshudyan, M.

    2016-05-01

    In this paper, we will consider a phenomenological model of a dark fluid that is able to explain an accelerated expansion of our low redshift universe and the phase transition to this accelerated expanding universe. Recent developments in modern cosmology towards understanding of the accelerated expansion of the large scale universe involve various scenarios and approaches. Among these approaches, one of well-known and accepted practice is modeling of the content of our universe via dark fluid. There are various models of dark energy fluid actively studied in recent literature and polytropic gas is among them. In this work, we will consider a varying polytropic gas which is a phenomenological modification of polytropic gas. Our model of varying polytropic dark fluid has been constructed to analogue to a varying Chaplygin gas actively discussed in the literature. We will consider interacting models, where dark matter is a pressureless fluid, to have a comprehensive picture. Phase space analysis is an elegant mathematical tool to earn general understanding of large scale universe and easily see an existence of a solution to cosmological coincidence problem. Imposing some constraints on parameters of the models, we found late time attractors for each case analytically. Cosmological consequences for the obtained late time attractors are discussed.

  10. A thermodynamic model for gas adsorption isotherms

    SciTech Connect

    Riazi, M.R.; Khan, A.R.

    1999-02-15

    In this paper based on the principle of solution thermodynamics for gas-solid equilibrium, a relation is developed to express gas adsorption isotherms. An activity coefficient model based on weight fraction of sorbate in the solid phase has been derived that well describes the behavior of various gases on different types of adsorbents. The proposed model has been evaluated and compared with four other models commonly used for gas adsorption isotherms in the literature. For 12 different systems at various isotherms for the temperature range {minus}128 to 100 C and the pressure range 0.02 to 1219 kPa for 689 data points, the proposed model predicts equilibrium pressure with an average deviation of 5.3%, which is about half of the error obtained from other methods. The proposed model clearly outperforms other available methods such as the vacancy solution theory, the ideal adsorption solution model, and other various modified forms of the Langmuir isotherm. Unique features of the proposed model are its simplicity, generality, and accuracy over the entire pressure and temperature ranges.

  11. A lattice gas model for thermohydrodynamics

    SciTech Connect

    Chen, Shiyi; Chen, Hudong; Doolen, G.D.; Gutman, S.; Lee, M.

    1990-05-03

    The FHP lattice gas model is extended to include a temperature variable in order to study thermohydrodynamics. The compressible Navier-Stokes equations are derived using a Chapman-Enskog expansion. Heat conduction and convention problems are investigated, including Benard convention. It is shown that the usual FHP rescaling procedure can be avoided by controlling the temperature. 20 refs., 12 figs.

  12. Generalized models of unification of dark matter and dark energy

    NASA Astrophysics Data System (ADS)

    Čaplar, Neven; Štefančić, Hrvoje

    2013-01-01

    A model of unification of dark matter and dark energy based on the modeling of the speed of sound as a function of the parameter of the equation of state is introduced. It is found that the model in which the speed of sound depends on the power of the parameter of the equation of state, cs2=α(-w)γ, contains the generalized Chaplygin gas models as its subclass. An effective scalar field description of the model is obtained in a parametric form which in some cases can be translated into a closed form solution for the scalar field potential. A constraint on model parameters is obtained using the observational data on the Hubble parameter at different redshifts.

  13. Optimization of solver for gas flow modeling

    NASA Astrophysics Data System (ADS)

    Savichkin, D.; Dodulad, O.; Kloss, Yu

    2014-05-01

    The main purpose of the work is optimization of the solver for rarefied gas flow modeling based on the Boltzmann equation. Optimization method is based on SIMD extensions for ×86 processors. Computational code is profiled and manually optimized with SSE instructions. Heat flow, shock waves and Knudsen pump are modeled with optimized solver. Dependencies of computational time from mesh sizes and CPU capabilities are provided.

  14. A topological classification of the Chaplygin systems in the dynamics of a rigid body in a fluid

    SciTech Connect

    Nikolaenko, S S

    2014-02-28

    The paper is concerned with the topological analysis of the Chaplygin integrable case in the dynamics of a rigid body in a fluid. A full list of the topological types of Chaplygin systems in their dependence on the energy level is compiled on the basis of the Fomenko-Zieschang theory. An effective description of the topology of the Liouville foliation in terms of natural coordinate variables is also presented, which opens a direct way to calculating topological invariants. It turns out that on all nonsingular energy levels Chaplygin systems are Liouville equivalent to the well-known Euler case in the dynamics of a rigid body with fixed point. Bibliography: 23 titles.

  15. A Phenomenological Model of Industrial Gas Sensors

    NASA Astrophysics Data System (ADS)

    Woestman, J. T.; Logothetis, E. M.; Shane, M. D.; Brailsford, A. D.

    1997-08-01

    Gas sensors are widely used in industry for applications ranging from air-to-fuel ratio control in combustion processes, including those in automotive engines and industrial furnaces, to leakage detection of inflammable and toxic gases. This presentation reports on a model to describe the response of typical electrochemical solid state gas sensors in environments of air (80% N2 and 20% O_2) and one reducing species such as CO, H2 or CH_4. The goal of the model is to predict the time-dependent sensor output resulting from a time-dependent gas composition. Through a set of coupled differential equations, the model accounts for the flow of the gases into the sensor, their diffusion through a porous spinel coating, their adsorption/desorption on/off a catalytic electrode and their redox reaction on the electrode. The solution of these equations provides an oxygen adatom concentration on the electrode surface. This oxygen concentration is used in the Nernst equation to determine an instantaneous sensor emf and a first order filter is user to account for the time delay associated with the emf generation processes. The model was applied to the operation of an automotive oxygen sensor exposed to mixtures of O2 and CO in N2 and mixtures of O2 and H2 in N_2. Good agreement was found with experimental results under both steady state and dynamic operating conditions.

  16. A nonlinear model for gas chromatograph systems

    NASA Technical Reports Server (NTRS)

    Feinberg, M. P.

    1975-01-01

    Fundamental engineering design techniques and concepts were studied for the optimization of a gas chromatograph-mass spectrometer chemical analysis system suitable for use on an unmanned, Martian roving vehicle. Previously developed mathematical models of the gas chromatograph are found to be inadequate for predicting peak heights and spreading for some experimental conditions and chemical systems. A modification to the existing equilibrium adsorption model is required; the Langmuir isotherm replaces the linear isotherm. The numerical technique of Crank-Nicolson was studied for use with the linear isotherm to determine the utility of the method. Modifications are made to the method eliminate unnecessary calculations which result in an overall reduction of the computation time of about 42 percent. The Langmuir isotherm is considered which takes into account the composition-dependent effects on the thermodynamic parameter, mRo.

  17. Modeling the Molecular Gas in NGC 6240

    NASA Astrophysics Data System (ADS)

    Tunnard, R.; Greve, T. R.; Garcia-Burillo, S.; Graciá Carpio, J.; Fuente, A.; Tacconi, L.; Neri, R.; Usero, A.

    2015-12-01

    We present the first observations of H13CN (1-0), H13CO+(1-0), and SiO (2-1)in NGC 6240, obtained with the IRAM Plateau de Bure Interferometer. Combining a Markov Chain Monte Carlo code with Large Velocity Gradient (LVG) modeling, and with additional data from the literature, we simultaneously fit three gas phases and six molecular species to constrain the physical condition of the molecular gas, including mass-luminosity conversion factors. We find ˜ {10}10{M}⊙ of dense molecular gas in cold, dense clouds ({T}{{k}}˜ 10 K, {n}{{{H}}2}˜ {10}6 cm-3) with a volume filling factor \\lt 0.002, embedded in a shock heated molecular medium ({T}{{k}}˜ 2000 K, {n}{{{H}}2}˜ {10}3.6 cm-3), both surrounded by an extended diffuse phase ({T}{{k}}˜ 200 K, {n}{{{H}}2}˜ {10}2.5 cm-3). We derive a global {α }{{CO}}={1.5}1.17.1 with gas masses {{log}}10≤ft(M/[{M}⊙ ]\\right)={10.1}10.010.8, dominated by the dense gas. We also find {α }{{HCN}}={32}1389, which traces the cold, dense gas. The [12C]/[13C] ratio is only slightly elevated ({98}65230), contrary to the very high [CO]/[13CO] ratio (300-500) reported in the literature. However, we find very high [HCN]/[H13CN] and [HCO+]/[H13CO+] abundance ratios ({300}200500) which we attribute to isotope fractionation in the cold, dense clouds.

  18. Catalytic seawater flue gas desulfurization model.

    PubMed

    Vidal Barrero, F; Ollero, P; Villanueva Perales, A L; Gómez-Barea, A

    2009-12-15

    A model of a seawater flue gas desulfurization process (SFGD) where oxidation of the absorbed SO(2) is catalyzed by activated carbon is presented. The modeled SFGD process is comprised of two main units, an absorption packed scrubber, where SO(2) absorption takes place, and an oxidation basin, where the absorbed SO(2) is catalytically oxidized to sulfate, a natural component of seawater. The model takes into account the complex physical-chemical features of the process, combining mass-transfer, kinetics and equilibrium equations, and considering the electrolyte nature of the liquid phase. The model was validated with data from a SFGD pilot plant and a sensitivity analysis was performed, showing its predictive capability. The model is a useful tool for designing industrial desulfurization units with seawater. PMID:20000534

  19. PERFORMANCE AND MODELING OF A HOT POTASSIUM CARBONATE ACID GAS REMOVAL SYSTEM IN TREATING COAL GAS

    EPA Science Inventory

    The report discusses the performance and modeling of a hot potassium carbonate (K2CO3) acid gas removal system (AGRS) in treating coal gas. Aqueous solutions of K2CO3, with and without amine additive, were used as the acid gas removal solvent in the Coal Gasification/Gas Cleaning...

  20. Mathematical analysis of intermittent gas injection model in oil production

    NASA Astrophysics Data System (ADS)

    Tasmi, Silvya, D. R.; Pudjo, S.; Leksono, M.; Edy, S.

    2016-02-01

    Intermittent gas injection is a method to help oil production process. Gas is injected through choke in surface and then gas into tubing. Gas forms three areas in tubing: gas column area, film area and slug area. Gas column is used to propel slug area until surface. A mathematical model of intermittent gas injection is developed in gas column area, film area and slug area. Model is expanding based on mass and momentum conservation. Using assume film thickness constant in tubing, model has been developed by Tasmi et. al. [14]. Model consists of 10 ordinary differential equations. In this paper, assumption of pressure in gas column is uniform. Model consist of 9 ordinary differential equations. Connection of several variables can be obtained from this model. Therefore, dynamics of all variables that affect to intermittent gas lift process can be seen from four equations. To study the behavior of variables can be analyzed numerically and mathematically. In this paper, simple mathematically analysis approach is used to study behavior of the variables. Variables that affect to intermittent gas injection are pressure in upstream valve and in gas column. Pressure in upstream valve will decrease when gas mass in valve greater than gas mass in choke. Dynamic of the pressure in the gas column will decrease and increase depending on pressure in upstream valve.

  1. Reservoir model for Hillsboro gas storage field management

    USGS Publications Warehouse

    Udegbunam, Emmanuel O.; Kemppainen, Curt; Morgan, Jim

    1995-01-01

    A 3-dimensional reservoir model is used to understand the behavior of the Hillsboro Gas Storage Field and to investigate the field's performance under various future development. Twenty-two years of the gas storage reservoir history, comprising the initial gas bubble development and seasonal gas injection and production cycles, are examined with a full-field, gas water, reservoir simulation model. The results suggest that the gas-water front is already in the vicinity of the west observation well that increasing the field's total gas-in-place volume would cause gas to migrate beyond the east, north and west observation well. They also suggest that storage enlargement through gas injection into the lower layers may not prevent gas migration. Moreover, the results suggest that the addition of strategically-located new wells would boost the simulated gas deliverabilities.

  2. Dynamic and Structural Gas Turbine Engine Modeling

    NASA Technical Reports Server (NTRS)

    Turso, James A.

    2003-01-01

    Model the interactions between the structural dynamics and the performance dynamics of a gas turbine engine. Generally these two aspects are considered separate, unrelated phenomena and are studied independently. For diagnostic purposes, it is desirable to bring together as much information as possible, and that involves understanding how performance is affected by structural dynamics (if it is) and vice versa. This can involve the relationship between thrust response and the excitation of structural modes, for instance. The job will involve investigating and characterizing these dynamical relationships, generating a model that incorporates them, and suggesting and/or developing diagnostic and prognostic techniques that can be incorporated in a data fusion system. If no coupling is found, at the least a vibration model should be generated that can be used for diagnostics and prognostics related to blade loss, for instance.

  3. Modeling of gas turbine fuel nozzle spray

    SciTech Connect

    Rizk, N.K.; Chin, J.S.; Razdan, M.K.

    1997-01-01

    Satisfactory performance of the gas turbine combustor relies on the careful design of various components, particularly the fuel injector. It is, therefore, essential to establish a fundamental basis for fuel injection modeling that involves various atomization processes. A two-dimensional fuel injection model has been formulated to simulate the airflow within and downstream of the atomizer and address the formation and breakup of the liquid sheet formed at the atomizer exit. The sheet breakup under the effects of airblast, fuel pressure, or the combined atomization mode of the air-assist type is considered in the calculation. The model accounts for secondary breakup of drops and the stochastic Lagrangian treatment of spray. The calculation of spray evaporation addresses both droplet heat-up and steady-state mechanisms, and fuel vapor concentration is based on the partial pressure concept. An enhanced evaporation model has been developed that accounts for multicomponent, finite mass diffusivity and conductivity effects, and addresses near-critical evaporation. The present investigation involved predictions of flow and spray characteristics of two distinctively different fuel atomizers under both nonreacting and reacting conditions. The predictions of the continuous phase velocity components and the spray mean drop sizes agree well with the detailed measurements obtained for the two atomizers, which indicates the model accounts for key aspects of atomization. The model also provides insight into ligament formation and breakup at the atomizer exit and the initial drop sizes formed in the atomizer near field region where measurements are difficult to obtain. The calculations of the reacting spray show the fuel-rich region occupied most of the spray volume with two-peak radial gas temperature profiles. The results also provided local concentrations of unburned hydrocarbon and CO in atomizer flowfield.

  4. Integrated Belowground Greenhouse Gas Flux Modeling (Invited)

    NASA Astrophysics Data System (ADS)

    Davidson, E. A.; Savage, K. E.

    2013-12-01

    Soil greenhouse gas (GHG) emissions play a significant role as biotic feedbacks to climate change. However, these complex processes, involving C, N, and O2 substrates and inhibitors, interactions with plant processes, and environmental influences of temperature, moisture, and gas transport, remain challenging to simulate in process models. Because CO2, CH4, and N2O production and consumption processes are inter-linked through common substrates and the contrasting effects of O2 as either an essential substrate or a potential inhibitor, the simulation of fluxes of any one gas must be consistent with mechanistic simulations and observations of fluxes of the other gases. Simulating the fluxes of one gas alone is a simpler task, but simulating all three gases simultaneously would provide multiple constraints and would afford greater confidence that the most important mechanisms are aptly simulated. A case in point is the challenge of resolving the apparent paradox of observed simultaneous CO2 production by aerobic respiration, CH4 uptake (oxidation), CH4 production, and N2O uptake (reduction) in the same soil profile. Consumption of atmospheric N2O should occur only under reducing conditions, and yet we have observed uptake of atmospheric CH4 (oxidation) and N2O (reduction) simultaneously. One of the great challenges of numerical modeling is determining the appropriate level of complexity when representing the most important environmental controllers. Ignoring complexity, such as simulating microbial processes with only simple Q10 functions, often results in poor model performance, because soil moisture and substrate supply can also be important factors. On the other hand, too much complexity, while perhaps mechanistically compelling, may result in too many poorly constrained parameters. Here we explore a parsimonious modeling framework for consistently integrated mechanistic and mathematical representation of the biophysical processes of belowground GHG production and

  5. Numerical modeling of the gas lift process in gas lift wells

    NASA Astrophysics Data System (ADS)

    Temirbekov, N. M.; Turarov, A. K.; Baigereyev, D. R.

    2016-06-01

    In this paper, one-dimensional and two-dimensional axisymmetric motion of gas, liquid and a gas-liquid mixture in a gas-lift well is studied. Numerical simulation of the one-dimensional model of gas-lift process is considered where the movement in a gas-lift well is described by partial differential equations of hyperbolic type. Difference schemes for the gas-lift model of the process are developed on a nonuniform grid condensing in subdomains with big gradients of the solution. The results of the proposed algorithm are illustrated on the example of a real well.

  6. The Dairy Greenhouse Gas Emission Model: Reference Manual

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The Dairy Greenhouse Gas Model (DairyGHG) is a software tool for estimating the greenhouse gas emissions and carbon footprint of dairy production systems. A relatively simple process-based model is used to predict the primary greenhouse gas emissions, which include the net emission of carbon dioxide...

  7. Parametric modeling of exhaust gas emission from natural gas fired gas turbines

    SciTech Connect

    Bakken, L.E.; Skogly, L.

    1996-07-01

    Increased focus on air pollution from gas turbines in the Norwegian sector of the North Sea has resulted in taxes on CO{sub 2}. Statements made by the Norwegian authorities imply regulations and/or taxes on NO{sub x} emissions in the near future. The existing CO{sub 2} tax of NOK 0.82/Sm{sup 3} (US Dollars 0.12/Sm{sup 3}) and possible future tax on NO{sub x} are analyzed mainly with respect to operating and maintenance costs for the gas turbine. Depending on actual tax levels, the machine should be operated on full load/optimum thermal efficiency or part load to reduce specific exhaust emissions. Based on field measurements, exhaust emissions (CO{sub 2}, CO, NO{sub x}, N{sub 2}O, UHC, etc.) are established with respect to load and gas turbine performance, including performance degradation. Different NO{sub x} emission correlations are analyzed based on test results, and a proposed prediction model presented. The impact of machinery performance degradation on emission levels is particularly analyzed. Good agreement is achieved between measured and predicted NO{sub x} emissions from the proposed correlation. To achieve continuous exhaust emission control, the proposed NO{sub x} model is implemented to the on-line condition monitoring system on the Sleipner A platform, rather than introducing sensitive emission sensors in the exhaust gas stack. The on-line condition monitoring system forms an important tool in detecting machinery condition/degradation and air pollution, and achieving optimum energy conservation.

  8. Estatística de lentes gravitacionais e o gás de chaplygin generalizado

    NASA Astrophysics Data System (ADS)

    Oliveira, A. L. S.

    2003-08-01

    A estatística de lentes gravitacionais constitui uma poderosa ferramenta utilizada na obtenção de vínculos sobre parâmetros cosmológicos, principalmente sobre modelos com uma constante cosmológica. Embora de forma às vezes controversa, antes de 1998, a análise tradicional mostrava que modelos com o parâmetro de densidade da matéria da ordem da unidade são preferidos. Esse resultado começou a ser questionado, alguns anos atrás, com as indicações, advindas da análise de supernovas com alto valor de desvio para o vermelho, de que nosso Universo está acelerando. Atualmente há enorme interesse em saber qual é a natureza da componente responsável pela aceleração cósmica. Energia escura é a denominação usual dessa componente e sua característica principal é possuir pressão negativa. Nos modelos cosmológicos tradicionais, além da energia escura, considera-se também uma outra componente de origem desconhecida. Ela é denominada matéria escura e possui pressão nula. Mais recentemente modelos unificadores em que energia escura e matéria escura são manifestações distintas de um mesmo fluido (altas densidades matéria escura, baixas densidades energia escura) foram sugeridos. Um desses modelos é conhecido como Gás de Chaplygin Generalizado que é o modelo que investigaremos. Em nosso trabalho apresentamos vínculos sobre parâmetros desse modelo usando a estatística de lentes gravitacionais. Usamos observações de quasares na faixa do visível e consideramos extinção em nosso estudo. Análises semelhantes anteriores com esse tipo de objetos e que não consideram extinção são inconsistentes. Comparação dos vínculos obtidos através de lentes gravitacionais com outros advindos de outros testes será também apresentada.

  9. A modeling of buoyant gas plume migration

    SciTech Connect

    Silin, D.; Patzek, T.; Benson, S.M.

    2008-12-01

    This work is motivated by the growing interest in injecting carbon dioxide into deep geological formations as a means of avoiding its atmospheric emissions and consequent global warming. Ideally, the injected greenhouse gas stays in the injection zone for a geologic time, eventually dissolves in the formation brine and remains trapped by mineralization. However, one of the potential problems associated with the geologic method of sequestration is that naturally present or inadvertently created conduits in the cap rock may result in a gas leakage from primary storage. Even in a supercritical state, the carbon dioxide viscosity and density are lower than those of the formation brine. Buoyancy tends to drive the leaked CO{sub 2} plume upward. Theoretical and experimental studies of buoyancy-driven supercritical CO{sub 2} flow, including estimation of time scales associated with plume evolution and migration, are critical for developing technology, monitoring policy, and regulations for safe carbon dioxide geologic sequestration. In this study, we obtain simple estimates of vertical plume propagation velocity taking into account the density and viscosity contrast between CO{sub 2} and brine. We describe buoyancy-driven countercurrent flow of two immiscible phases by a Buckley-Leverett type model. The model predicts that a plume of supercritical carbon dioxide in a homogeneous water-saturated porous medium does not migrate upward like a bubble in bulk water. Rather, it spreads upward until it reaches a seal or until it becomes immobile. A simple formula requiring no complex numerical calculations describes the velocity of plume propagation. This solution is a simplification of a more comprehensive theory of countercurrent plume migration (Silin et al., 2007). In a layered reservoir, the simplified solution predicts a slower plume front propagation relative to a homogeneous formation with the same harmonic mean permeability. In contrast, the model yields much higher

  10. Strangeness conservation constraints in hadron gas models

    SciTech Connect

    Tiwari, V.K.; Singh, S.K.; Uddin, S.; Singh, C.P.

    1996-05-01

    We examine the implications of the constraints arising due to strangeness conservation on the strangeness production in various existing thermal hadron-gas models. The dependence of strangeness chemical potential {mu}{sub {ital S}} on the baryon chemical potential {mu}{sub {ital B}} and temperature {ital T} is investigated. The incorporation of finite-size, hard-core, repulsive interactions in the thermodynamically consistent description of hot and dense hadron gas alters the results obtained for pointlike particles. We compare results in two extreme alternative cases: (1) {ital K} and {ital K}{sup {asterisk}} mesons are treated as point particles and they can penetrate all volumes occupied by baryons and antibaryons and (2) the volume occupied by the baryons and antibaryons is not accessible to them. We find that the results indeed depend on the assumptions made. Moreover, the anomalous results obtained for the ratios {bar {Xi}}/{Xi} and {bar {Lambda}}/{Lambda} rule out the second possibility. {copyright} {ital 1996 The American Physical Society.}

  11. Evaluation of the gas production economics of the gas hydrate cyclic thermal injection model

    SciTech Connect

    Kuuskraa, V.A.; Hammersheimb, E.; Sawyer, W.

    1985-05-01

    The objective of the work performed under this directive is to assess whether gas hydrates could potentially be technically and economically recoverable. The technical potential and economics of recovering gas from a representative hydrate reservoir will be established using the cyclic thermal injection model, HYDMOD, appropriately modified for this effort, integrated with economics model for gas production on the North Slope of Alaska, and in the deep offshore Atlantic. The results from this effort are presented in this document. In Section 1, the engineering cost and financial analysis model used in performing the economic analysis of gas production from hydrates -- the Hydrates Gas Economics Model (HGEM) -- is described. Section 2 contains a users guide for HGEM. In Section 3, a preliminary economic assessment of the gas production economics of the gas hydrate cyclic thermal injection model is presented. Section 4 contains a summary critique of existing hydrate gas recovery models. Finally, Section 5 summarizes the model modification made to HYDMOD, the cyclic thermal injection model for hydrate gas recovery, in order to perform this analysis.

  12. Design and modeling of a photonic crystal fiber gas sensor.

    PubMed

    Hoo, Yeuk L; Jin, Wei; Shi, Chunzheng; Ho, Hoi L; Wang, Dong N; Ruan, Shuang C

    2003-06-20

    We report the modeling results of an all-fiber gas detector that uses photonic crystal fiber (PCF). The relative sensitivity of the PCF as a function of the fiber parameters is calculated. Gas-diffusion dynamics that affect the sensor response time is investigated theoretically and experimentally. A practical PCF sensor aiming for high sensitivity gas detection is proposed. PMID:12833952

  13. Modeling of heavy-gas effects on airfoil flows

    NASA Technical Reports Server (NTRS)

    Drela, Mark

    1992-01-01

    Thermodynamic models were constructed for a calorically imperfect gas and for a non-ideal gas. These were incorporated into a quasi one dimensional flow solver to develop an understanding of the differences in flow behavior between the new models and the perfect gas model. The models were also incorporated into a two dimensional flow solver to investigate their effects on transonic airfoil flows. Specifically, the calculations simulated airfoil testing in a proposed high Reynolds number heavy gas test facility. The results indicate that the non-idealities caused significant differences in the flow field, but that matching of an appropriate non-dimensional parameter led to flows similar to those in air.

  14. Adsorption modeling for off-gas treatment

    SciTech Connect

    Ladshaw, A.; Sharma, K.; Yiacoumi, S.; Tsouris, C.; De Paoli, D.W.

    2013-07-01

    Off-gas generated from the reprocessing of used nuclear fuel contains a mixture of several radioactive gases including {sup 129}I{sub 2}, {sup 85}Kr, HTO, and {sup 14}CO{sub 2}. Over the past few decades, various separation and recovery processes have been studied for capturing these gases. Adsorption data for gaseous mixtures of species can be difficult to determine experimentally. Therefore, procedures capable of predicting the adsorption behavior of mixtures need to be developed from the individual isotherms of each of the pure species. A particular isotherm model of interest for the pure species is the Generalized Statistical Thermodynamic Adsorption isotherm. This model contains an adjustable number of parameters and will therefore describe a wide range of adsorption isotherms for a variety of components. A code has been developed in C++ to perform the non-linear regression analysis necessary for the determination of the isotherm parameters, as well as the least number of parameters needed to describe an entire set of data. (authors)

  15. GASCAP: Wellhead Gas Productive Capacity Model documentation, June 1993

    SciTech Connect

    Not Available

    1993-07-01

    The Wellhead Gas Productive Capacity Model (GASCAP) has been developed by EIA to provide a historical analysis of the monthly productive capacity of natural gas at the wellhead and a projection of monthly capacity for 2 years into the future. The impact of drilling, oil and gas price assumptions, and demand on gas productive capacity are examined. Both gas-well gas and oil-well gas are included. Oil-well gas productive capacity is estimated separately and then combined with the gas-well gas productive capacity. This documentation report provides a general overview of the GASCAP Model, describes the underlying data base, provides technical descriptions of the component models, diagrams the system and subsystem flow, describes the equations, and provides definitions and sources of all variables used in the system. This documentation report is provided to enable users of EIA projections generated by GASCAP to understand the underlying procedures used and to replicate the models and solutions. This report should be of particular interest to those in the Congress, Federal and State agencies, industry, and the academic community, who are concerned with the future availability of natural gas.

  16. Modeling of Devonian shale gas reservoirs. Task 16. Mathematical modeling of shale gas production (2D model). Final report

    SciTech Connect

    Not Available

    1980-07-31

    The Department of Energy (DOE), Morgantown Energy Technology Center (METC) has been supporting the development of flow models for Devonian shale gas reservoirs. The broad objectives of this modeling program are to: (1) develop and validate a mathematical model which describes gas flow through Devonian shales; (2) determine the sensitive parameters that affect deliverability and recovery of gas from Devonian shales; (3) recommend laboratory and field measurements for determination of those parameters critical to the productivity and timely recovery of gas from the Devonian shales; (4) analyze pressure and rate transient data from observation and production gas wells to determine reservoir parameters and well performance; and (5) study and determine the overall performance of Devonian shale reservoirs in terms of well stimulation, well spacing, and resource recovery as a function of gross reservoir properties such as anisotropy, porosity and thickness variations, and boundary effects. During the previous annual period, a mathematical model describing gas flow through Devonian shales and the software for a radial one-dimensional numerical model for single well performance were completed and placed into operation. Although the radial flow model is a powerful tool for studying single well behavior, it is inadequate for determining the effects of well spacing, stimulation treatments, and variation in reservoir properties. Hence, it has been necessary to extend the model to two-dimensions, maintaining full capability regarding Klinkerberg effects, desorption, and shale matrix parameters. During the current annual period, the radial flow model has been successfully extended to provide the two-dimensional capability necessary for the attainment of overall program objectives, as described above.

  17. Tachyon cosmology with non-vanishing minimum potential: a unified model

    SciTech Connect

    Li, Huiquan

    2012-07-01

    We investigate the tachyon condensation process in the effective theory with non-vanishing minimum potential and its implications to cosmology. It is shown that the tachyon condensation on an unstable three-brane described by this modified tachyon field theory leads to lower-dimensional branes (defects) forming within a stable three-brane. Thus, in the cosmological background, we can get well-behaved tachyon matter after tachyon inflation, (partially) avoiding difficulties encountered in the original tachyon cosmological models. This feature also implies that the tachyon inflated and reheated universe is followed by a Chaplygin gas dark matter and dark energy universe. Hence, such an unstable three-brane behaves quite like our universe, reproducing the key features of the whole evolutionary history of the universe and providing a unified description of inflaton, dark matter and dark energy in a very simple single-scalar field model.

  18. Modeling of Fission Gas Release in UO2

    SciTech Connect

    MH Krohn

    2006-01-23

    A two-stage gas release model was examined to determine if it could provide a physically realistic and accurate model for fission gas release under Prometheus conditions. The single-stage Booth model [1], which is often used to calculate fission gas release, is considered to be oversimplified and not representative of the mechanisms that occur during fission gas release. Two-stage gas release models require saturation at the grain boundaries before gas is release, leading to a time delay in release of gases generated in the fuel. Two versions of a two-stage model developed by Forsberg and Massih [2] were implemented using Mathcad [3]. The original Forsbers and Massih model [2] and a modified version of the Forsberg and Massih model that is used in a commercially available fuel performance code (FRAPCON-3) [4] were examined. After an examination of these models, it is apparent that without further development and validation neither of these models should be used to calculate fission gas release under Prometheus-type conditions. There is too much uncertainty in the input parameters used in the models. In addition. the data used to tune the modified Forsberg and Massih model (FRAPCON-3) was collected under commercial reactor conditions, which will have higher fission rates relative to Prometheus conditions [4].

  19. Model documentation: Natural gas transmission and distribution model of the National Energy Modeling System. Volume 1

    SciTech Connect

    1995-02-17

    The Natural Gas Transmission and Distribution Model (NGTDM) is the component of the National Energy Modeling System (NEMS) that is used to represent the domestic natural gas transmission and distribution system. NEMS was developed in the Office of integrated Analysis and Forecasting of the Energy information Administration (EIA). NEMS is the third in a series of computer-based, midterm energy modeling systems used since 1974 by the EIA and its predecessor, the Federal Energy Administration, to analyze domestic energy-economy markets and develop projections. The NGTDM is the model within the NEMS that represents the transmission, distribution, and pricing of natural gas. The model also includes representations of the end-use demand for natural gas, the production of domestic natural gas, and the availability of natural gas traded on the international market based on information received from other NEMS models. The NGTDM determines the flow of natural gas in an aggregate, domestic pipeline network, connecting domestic and foreign supply regions with 12 demand regions. The methodology employed allows the analysis of impacts of regional capacity constraints in the interstate natural gas pipeline network and the identification of pipeline capacity expansion requirements. There is an explicit representation of core and noncore markets for natural gas transmission and distribution services, and the key components of pipeline tariffs are represented in a pricing algorithm. Natural gas pricing and flow patterns are derived by obtaining a market equilibrium across the three main elements of the natural gas market: the supply element, the demand element, and the transmission and distribution network that links them. The NGTDM consists of four modules: the Annual Flow Module, the Capacity F-expansion Module, the Pipeline Tariff Module, and the Distributor Tariff Module. A model abstract is provided in Appendix A.

  20. Development and evaluation of a dense gas plume model

    SciTech Connect

    Matthias, C.S.

    1994-12-31

    The dense gas plume model (continuous release) described in this paper has been developed using the same principles as for a dense gas puff model (instantaneous release). It is a box model for which the main goal is to predict the height H, width W, and maximum concentration C{sub b} for a steady dense plume. A secondary goal is to distribute the mass more realistically by empirically attaching Gaussian distributions in the horizontal and vertical directions. For ease of reference, the models and supporting programs will be referred to as DGM (Dense Gas Models).

  1. Goryachev-Chaplygin, Kovalevskaya, and Brdička-Eardley-Nappi-Witten pp-waves spacetimes with higher rank Stäckel-Killing tensors

    NASA Astrophysics Data System (ADS)

    Gibbons, G. W.; Rugina, C.

    2011-12-01

    Hidden symmetries of the Goryachev-Chaplygin and Kovalevskaya gyrostats spacetimes, as well as the Brdička-Eardley-Nappi-Witten pp-waves are studied. We find out that these spacetimes possess higher rank Stäckel-Killing tensors and that in the case of the pp-wave spacetimes, the symmetry group of the Stäckel-Killing tensors is the well-known Newton-Hooke group.

  2. The modified ASEP as a model of ideal gas

    NASA Astrophysics Data System (ADS)

    Mironov, D.; Sossinsky, A.

    2015-01-01

    A modified version of the ASEP model is interpreted as a two-dimensional model of ideal gas. Its properties are studied by simulating its behavior in different situations, using an animation program designed for that purpose.

  3. Gas-phase diffusion in porous media: Comparison of models

    SciTech Connect

    Webb, S.W.

    1998-09-01

    Two models are commonly used to analyze gas-phase diffusion in porous media in the presence of advection, the Advective-Dispersive Model (ADM) and the Dusty-gas Model (DGM). The ADM, which is used in TOUGH2, is based on a simple linear addition of advection calculated by Darcy`s law and ordinary diffusion using Fick`s law with a porosity-tortuosity-gas saturation multiplier to account for the porous medium. Another approach for gas-phase transport in porous media is the Dusty-Gas Model. This model applies the kinetic theory of gases to the gaseous components and the porous media (or dust) to combine transport due to diffusion and advection that includes porous medium effects. The two approaches are compared in this paper.

  4. Development of a gas systems analysis model (GSAM)

    SciTech Connect

    Godec, M.L.

    1995-04-01

    The objectives of developing a Gas Systems Analysis Model (GSAM) are to create a comprehensive, non-proprietary, PC based model of domestic gas industry activity. The system is capable of assessing the impacts of various changes in the natural gas system within North America. The individual and collective impacts due to changes in technology and economic conditions are explicitly modeled in GSAM. Major gas resources are all modeled, including conventional, tight, Devonian Shale, coalbed methane, and low-quality gas sources. The modeling system asseses all key components of the gas industry, including available resources, exploration, drilling, completion, production, and processing practices, both for now and in the future. The model similarly assesses the distribution, storage, and utilization of natural gas in a dynamic market-based analytical structure. GSAM is designed to provide METC managers with a tool to project the impacts of future research, development, and demonstration (RD&D) benefits in order to determine priorities in a rapidly changing, market-driven gas industry.

  5. A community firn densification and gas transport model

    NASA Astrophysics Data System (ADS)

    Stevens, C.; Lundin, J.; Harris, P.; Leahy, W.; Waddington, E. D.

    2012-12-01

    Gas bubbles trapped in ice preserve a record of Earth's climate history. Interpretation of ice-core records is complicated by the difference in age (called delta age) between the gas trapped in bubbles and the ice enclosing the gas. Determining delta age requires understanding both densification of polar firn and gas transport through the firn. Independent models of firn densification and firn gas transport have been developed in the past by individual research groups. We are developing a web-based model of firn densification and gas transport that combines the best features of those models and is freely accessible to research teams. Users input site-specific data, and the model provides depth-density-age and delta-age results. In addition to the web-based model, state-of-the-art transient firn-densification and gas-transport models are in development. These models allow physical properties to evolve, which results in more accurate delta-age approximations at times of rapid climate change in the past. These community models will be downloadable as open-source code. They will provide a baseline to make intercomparisons between datasets or other models. The models are modular, allowing users to choose preferred physical models and physical processes to include, based on available pre-coded options. Alternatively, users can adapt the code to include new or different physics. Here, we present results from the web-based model and early stages of the transient models and compare with known firn-density and gas-concentration profiles.

  6. A Mathematical Model of Coupled Gas Flow and Coal Deformation with Gas Diffusion and Klinkenberg Effects

    NASA Astrophysics Data System (ADS)

    Liu, Qingquan; Cheng, Yuanping; Zhou, Hongxing; Guo, Pinkun; An, Fenghua; Chen, Haidong

    2015-05-01

    The influence of gas diffusion behavior on gas flow and permeability evolution in coal seams is evaluated in this paper. Coalbed methane (CBM) reservoirs differ from conventional porous media and fractured gas reservoirs due to certain unique features, which lead to two distinct gas pressures: one in fractures and the other in the coal matrix. The latter pressure, also known as the sorption pressure, will be used in calculating sorption-based volume changes. The effective stress laws for single-porosity media is not suitable for CBM reservoirs, and the effective stress laws for multi-porosity media need to be applied. The realization of the above two points is based on the study of the two-phase state of gas migration (involving Fickian diffusion and Darcy flow) in a coal seam. Then, a general porosity and permeability model based on the P-M model is proposed to fit this phenomenon. Moreover, the Klinkenberg effect has been taken into account and set as a reference object. Finally, a coupled gas flow and coal deformation model is proposed and solved by using a finite element method. The numerical results indicate that the effects of gas diffusion behavior and Klinkenberg behavior can have a critical influence on the gas pressure, residual gas content, and permeability evolution during the entire methane degasification period, and the impacts of the two effects are of the same order of magnitude. Without considering the gas diffusion effect, the gas pressure and residual gas content will be underestimated, and the permeability will be overestimated.

  7. Development of a natural Gas Systems Analysis Model (GSAM)

    SciTech Connect

    Godec, M.; Haas, M.; Pepper, W.; Rose, J.

    1993-12-31

    Recent dramatic changes in natural gas markets have significant implications for the scope and direction of DOE`s upstream as well as downstream natural gas R&D. Open access transportation changes the way gas is bought and sold. The end of the gas deliverability surplus requires increased reserve development above recent levels. Increased gas demand for power generation and other new uses changes the overall demand picture in terms of volumes, locations and seasonality. DOE`s Natural Gas Strategic Plan requires that its R&D activities be evaluated for their ability to provide adequate supplies of reasonably priced gas. Potential R&D projects are to be evaluated using a full fuel cycle, benefit-cost approach to estimate likely market impact as well as technical success. To assure R&D projects are evaluated on a comparable basis, METC has undertaken the development of a comprehensive natural gas technology evaluation framework. Existing energy systems models lack the level of detail required to estimate the impact of specific upstream natural gas technologies across the known range of geological settings and likely market conditions. Gas Systems Analysis Model (GSAM) research during FY 1993 developed and implemented this comprehensive, consistent natural gas system evaluation framework. Rather than a isolated research activity, however, GSAM represents the integration of many prior and ongoing natural gas research efforts. When complete, it will incorporate the most current resource base description, reservoir modeling, technology characterization and other geologic and engineering aspects developed through recent METC and industry gas R&D programs.

  8. Common inconsistencies in modeling gas transport in porous electrodes: The dusty-gas model and the Fick law

    NASA Astrophysics Data System (ADS)

    Bertei, A.; Nicolella, C.

    2015-04-01

    The paper shows as two assumptions typically made in modeling gas transport in solid oxide fuel cell electrodes, i.e., a) uniform pressure in the dusty-gas model, and b) validity of the Bosanquet formula in the Fick model, may lead to serious inconsistencies (such as molar fractions that do not sum up to one or fluxes that do not obey reaction stoichiometry), thus nullifying the efforts of the mechanistic modeling of transport phenomena. The nature of the inconsistent use of the models is explained with clear examples, then the correct implementation of the gas transport models is discussed. The study aims to promote a coherent physically-based modeling of gas transport phenomena in porous electrodes in order to assist their rational design.

  9. Physical modeling of gas dispersion over urban area

    NASA Astrophysics Data System (ADS)

    Michálek, Petr; Zacho, David

    2016-06-01

    Experimental study of gas dispersion over urban area model was conducted in boundary layer wind tunnel in VZLU Prague. A scale model of urban area near the Centre of Liberec was made and dispersion of gas emissions from nearby heating plant was measured. The measurements included velocity field and concentration field by means of hot wire anemometer and flame ionization detector. The purpose of this work was to validate and verify a new computational dispersion model, which was developed in VZLU.

  10. A model for deepwater oil/gas blowouts.

    PubMed

    Yapa, P D; Zheng, L; Chen, F

    2001-01-01

    When gas is released in deepwater, the high pressure and low temperature can convert the gases into hydrates, which are buoyant. As these hydrates travel upwards they will encounter regions of lower pressure and can decompose into free gas. The presence or absence of hydrates has a significant impact on the behaviour of the jet/plume due to the alteration of the buoyancy. The free gas may dissolve in water. This paper describes a computer model developed to simulate the behaviour of oil and gas released from deepwater locations in the ocean. The model integrates the hydrodynamics and thermodynamics of the jet/plume with kinetics and thermodynamics of hydrate formation/decomposition. Model formulation and comparison of results with laboratory data for hydrates is presented. Scenario simulations show the behaviour of oil/gas under different deepwater conditions. PMID:11760189

  11. Modification of TOUGH2 to Include the Dusty Gas Model for Gas Diffusion

    SciTech Connect

    WEBB, STEPHEN W.

    2001-10-01

    The GEO-SEQ Project is investigating methods for geological sequestration of CO{sub 2}. This project, which is directed by LBNL and includes a number of other industrial, university, and national laboratory partners, is evaluating computer simulation methods including TOUGH2 for this problem. The TOUGH2 code, which is a widely used code for flow and transport in porous and fractured media, includes simplified methods for gas diffusion based on a direct application of Fick's law. As shown by Webb (1998) and others, the Dusty Gas Model (DGM) is better than Fick's Law for modeling gas-phase diffusion in porous media. In order to improve gas-phase diffusion modeling for the GEO-SEQ Project, the EOS7R module in the TOUGH2 code has been modified to include the Dusty Gas Model as documented in this report. In addition, the liquid diffusion model has been changed from a mass-based formulation to a mole-based model. Modifications for separate and coupled diffusion in the gas and liquid phases have also been completed. The results from the DGM are compared to the Fick's law behavior for TCE and PCE diffusion across a capillary fringe. The differences are small due to the relatively high permeability (k = 10{sup -11} m{sup 2}) of the problem and the small mole fraction of the gases. Additional comparisons for lower permeabilities and higher mole fractions may be useful.

  12. Revisions to the hydrogen gas generation computer model

    SciTech Connect

    Jerrell, J.W.

    1992-08-31

    Waste Management Technology has requested SRTC to maintain and extend a previously developed computer model, TRUGAS, which calculates hydrogen gas concentrations within the transuranic (TRU) waste drums. TRUGAS was written by Frank G. Smith using the BASIC language and is described in the report A Computer Model of gas Generation and Transport within TRU Waste Drums (DP- 1754). The computer model has been partially validated by yielding results similar to experimental data collected at SRL and LANL over a wide range of conditions. The model was created to provide the capability of predicting conditions that could potentially lead to the formation of flammable gas concentrations within drums, and to assess proposed drum venting methods. The model has served as a tool in determining how gas concentrations are affected by parameters such as filter vent sizes, waste composition, gas generation values, the number and types of enclosures, water instrusion into the drum, and curie loading. The success of the TRUGAS model has prompted an interest in the program`s maintenance and enhancement. Experimental data continues to be collected at various sites on such parameters as permeability values, packaging arrangements, filter designs, and waste contents. Information provided by this data is used to improve the accuracy of the model`s predictions. Also, several modifications to the model have been made to enlarge the scope of problems which can be analyzed. For instance, the model has been used to calculate hydrogen concentrations inside steel cabinets containing retired glove boxes (WSRC-RP-89-762). The revised TRUGAS computer model, H2GAS, is described in this report. This report summarizes all modifications made to the TRUGAS computer model and provides documentation useful for making future updates to H2GAS.

  13. RAETRAD MODEL OF RADON GAS GENERATION, TRANSPORT, AND INDOOR ENTRY

    EPA Science Inventory

    The report describes the theoretical basis, implementation, and validation of the Radon Emanation and Transport into Dwellings (RAETRAD) model, a conceptual and mathematical approach for simulating radon (222Rn) gas generation and transport from soils and building foundations to ...

  14. Gas migration modeling improves volumetric method of well control

    SciTech Connect

    Leach, C.P.; Quentin, K.M. )

    1994-12-26

    In the volumetric method, gas expansion during gas migration is allowed for by bleeding small quantities of fluid through the choke. When gas first reaches the choke, the influx is distributed near the surface in the annulus. Rapid gas migration then occurs, and mud and gas may need to be bled to maintain constant bottom hole pressure. The volumetric method is a technique for controlling gas kicks when circulation is not possible. The industry-recognized method is based on simple calculations which assume a single bubble of gas, the classic kick. This technique can now be evaluated by using more realistic, deterministic kick models. The results from such models cast double on some of the conventional procedures taught and used in the industry. This article details the analysis of influx behavior following a typical volumetric method. Numerical modeling of fluid losses as the surface pressure rises, gas migration, and dispersion are included to correspond accurately with field observations of kicks. Revised procedures are suggested to deal with these events better, such that the goals of the volumetric method are still attained.

  15. Revisions to the hydrogen gas generation computer model

    SciTech Connect

    Jerrell, J.W.

    1992-08-31

    Waste Management Technology has requested SRTC to maintain and extend a previously developed computer model, TRUGAS, which calculates hydrogen gas concentrations within the transuranic (TRU) waste drums. TRUGAS was written by Frank G. Smith using the BASIC language and is described in the report A Computer Model of gas Generation and Transport within TRU Waste Drums (DP- 1754). The computer model has been partially validated by yielding results similar to experimental data collected at SRL and LANL over a wide range of conditions. The model was created to provide the capability of predicting conditions that could potentially lead to the formation of flammable gas concentrations within drums, and to assess proposed drum venting methods. The model has served as a tool in determining how gas concentrations are affected by parameters such as filter vent sizes, waste composition, gas generation values, the number and types of enclosures, water instrusion into the drum, and curie loading. The success of the TRUGAS model has prompted an interest in the program's maintenance and enhancement. Experimental data continues to be collected at various sites on such parameters as permeability values, packaging arrangements, filter designs, and waste contents. Information provided by this data is used to improve the accuracy of the model's predictions. Also, several modifications to the model have been made to enlarge the scope of problems which can be analyzed. For instance, the model has been used to calculate hydrogen concentrations inside steel cabinets containing retired glove boxes (WSRC-RP-89-762). The revised TRUGAS computer model, H2GAS, is described in this report. This report summarizes all modifications made to the TRUGAS computer model and provides documentation useful for making future updates to H2GAS.

  16. Sensitivity analysis of the fission gas behavior model in BISON.

    SciTech Connect

    Swiler, Laura Painton; Pastore, Giovanni; Perez, Danielle; Williamson, Richard

    2013-05-01

    This report summarizes the result of a NEAMS project focused on sensitivity analysis of a new model for the fission gas behavior (release and swelling) in the BISON fuel performance code of Idaho National Laboratory. Using the new model in BISON, the sensitivity of the calculated fission gas release and swelling to the involved parameters and the associated uncertainties is investigated. The study results in a quantitative assessment of the role of intrinsic uncertainties in the analysis of fission gas behavior in nuclear fuel.

  17. USERS MANUAL: LANDFILL GAS EMISSIONS MODEL - VERSION 2.0

    EPA Science Inventory

    The document is a user's guide for a computer model, Version 2.0 of the Landfill Gas Emissions Model (LandGEM), for estimating air pollution emissions from municipal solid waste (MSW) landfills. The model can be used to estimate emission rates for methane, carbon dioxide, nonmet...

  18. A generalized kinetic model for heterogeneous gas-solid reactions.

    PubMed

    Xu, Zhijie; Sun, Xin; Khaleel, Mohammad A

    2012-08-21

    We present a generalized kinetic model for gas-solid heterogeneous reactions taking place at the interface between two phases. The model studies the reaction kinetics by taking into account the reactions at the interface, as well as the transport process within the product layer. The standard unreacted shrinking core model relies on the assumption of quasi-static diffusion that results in a steady-state concentration profile of gas reactant in the product layer. By relaxing this assumption and resolving the entire problem, general solutions can be obtained for reaction kinetics, including the reaction front velocity and the conversion (volume fraction of reacted solid). The unreacted shrinking core model is shown to be accurate and in agreement with the generalized model for slow reaction (or fast diffusion), low concentration of gas reactant, and small solid size. Otherwise, a generalized kinetic model should be used. PMID:22920132

  19. A generalized kinetic model for heterogeneous gas-solid reactions

    NASA Astrophysics Data System (ADS)

    Xu, Zhijie; Sun, Xin; Khaleel, Mohammad A.

    2012-08-01

    We present a generalized kinetic model for gas-solid heterogeneous reactions taking place at the interface between two phases. The model studies the reaction kinetics by taking into account the reactions at the interface, as well as the transport process within the product layer. The standard unreacted shrinking core model relies on the assumption of quasi-static diffusion that results in a steady-state concentration profile of gas reactant in the product layer. By relaxing this assumption and resolving the entire problem, general solutions can be obtained for reaction kinetics, including the reaction front velocity and the conversion (volume fraction of reacted solid). The unreacted shrinking core model is shown to be accurate and in agreement with the generalized model for slow reaction (or fast diffusion), low concentration of gas reactant, and small solid size. Otherwise, a generalized kinetic model should be used.

  20. Dissipative model for a two component gas system with friction

    SciTech Connect

    Lopez, G.; Murgia, M.; Sosa, M.

    1994-02-01

    For a mixture of small and large component of gases, the large component is treated as an ideal gas. A dissipative model is proposed for the small component, and the thermodynamic characteristics of the gas are derived through a statistical mechanical approach. The model requires for the small component to have a big dimension and its number of particles to be smaller than the large one. Using the associated partition function, the internal energy and the equation of state are calculated. The internal energy does not suffer any deviation from that of the two component ideal gas, but the equation of state deviates from that of the ideal gas for large values of the parameter which characterizes the dissipative model.

  1. Empirical Modeling of Plant Gas Fluxes in Controlled Environments

    NASA Technical Reports Server (NTRS)

    Cornett, Jessie David

    1994-01-01

    As humans extend their reach beyond the earth, bioregenerative life support systems must replace the resupply and physical/chemical systems now used. The Controlled Ecological Life Support System (CELSS) will utilize plants to recycle the carbon dioxide (CO2) and excrement produced by humans and return oxygen (O2), purified water and food. CELSS design requires knowledge of gas flux levels for net photosynthesis (PS(sub n)), dark respiration (R(sub d)) and evapotranspiration (ET). Full season gas flux data regarding these processes for wheat (Triticum aestivum), soybean (Glycine max) and rice (Oryza sativa) from published sources were used to develop empirical models. Univariate models relating crop age (days after planting) and gas flux were fit by simple regression. Models are either high order (5th to 8th) or more complex polynomials whose curves describe crop development characteristics. The models provide good estimates of gas flux maxima, but are of limited utility. To broaden the applicability, data were transformed to dimensionless or correlation formats and, again, fit by regression. Polynomials, similar to those in the initial effort, were selected as the most appropriate models. These models indicate that, within a cultivar, gas flux patterns appear remarkably similar prior to maximum flux, but exhibit considerable variation beyond this point. This suggests that more broadly applicable models of plant gas flux are feasible, but univariate models defining gas flux as a function of crop age are too simplistic. Multivariate models using CO2 and crop age were fit for PS(sub n), and R(sub d) by multiple regression. In each case, the selected model is a subset of a full third order model with all possible interactions. These models are improvements over the univariate models because they incorporate more than the single factor, crop age, as the primary variable governing gas flux. They are still limited, however, by their reliance on the other environmental

  2. Dynamic Absorption Model for Off-Gas Separation

    SciTech Connect

    Veronica J. Rutledge

    2011-07-01

    Modeling and simulations will aid in the future design of U.S. advanced reprocessing plants for the recovery and recycle of actinides in used nuclear fuel. The specific fuel cycle separation process discussed in this report is the off-gas treatment system. The off-gas separation consists of a series of scrubbers and adsorption beds to capture constituents of interest. Dynamic models are being developed to simulate each unit operation involved so each unit operation can be used as a stand-alone model and in series with multiple others. Currently, a rate based, dynamic absorption model is being developed in gPROMS software. Inputs include liquid and gas stream constituents, column properties, liquid and gas phase reactions, number of stages, and inlet conditions. It simulates multiple component absorption with countercurrent flow and accounts for absorption by mass transfer and chemical reaction. The assumption of each stage being a discrete well-mixed entity was made. Therefore, the model is solved stagewise. The simulation outputs component concentrations in both phases as a function of time from which the rate of absorption is determined. Temperature of both phases is output as a function of time also. The model will be used able to be used as a standalone model in addition to in series with other off-gas separation unit operations. The current model is being generated based on NOx absorption; however, a future goal is to develop a CO2 specific model. The model will have the capability to be modified for additional absorption systems. The off-gas models, both adsorption and absorption, will be made available via the server or web for evaluation by customers.

  3. Model documentation Natural Gas Transmission and Distribution Model of the National Energy Modeling System. Volume 1

    SciTech Connect

    1996-02-26

    The Natural Gas Transmission and Distribution Model (NGTDM) of the National Energy Modeling System is developed and maintained by the Energy Information Administration (EIA), Office of Integrated Analysis and Forecasting. This report documents the archived version of the NGTDM that was used to produce the natural gas forecasts presented in the Annual Energy Outlook 1996, (DOE/EIA-0383(96)). The purpose of this report is to provide a reference document for model analysts, users, and the public that defines the objectives of the model, describes its basic approach, and provides detail on the methodology employed. Previously this report represented Volume I of a two-volume set. Volume II reported on model performance, detailing convergence criteria and properties, results of sensitivity testing, comparison of model outputs with the literature and/or other model results, and major unresolved issues.

  4. A GIS-based Model for Natural Gas Data Conversion

    NASA Astrophysics Data System (ADS)

    Bitik, E.; Seker, D. Z.; Denli, H. H.

    2014-12-01

    In Turkey gas utility sector has undergone major changes in terms of increased competition between gas providers, efforts in improving services, and applying new technological solutions. This paper discusses the challenges met by gas companies to switch from long workflows of gas distribution, sales and maintenance into IT driven efficient management of complex information both spatially and non-spatially. The aim of this study is migration of all gas data and information into a GIS environment in order to manage and operate all infrastructure investments with a Utility Management System. All data conversion model for migration was designed and tested during the study. A flowchart is formed to transfer the old data layers to the new structure based on geodatabase.

  5. Gas hydrate dynamics in heterogeneous media - challenges for numerical modeling

    NASA Astrophysics Data System (ADS)

    Burwicz, Ewa; Ruepke, Lars; Wallmann, Klaus

    2013-04-01

    Gas hydrates are ice-like crystalline cage structures containing various greenhouse gases, such as methane or CO2, which are locked within their spatial structure. Gas hydrate distribution in oceanic settings is mainly controlled by three factors: 1) low temperature regimes, 2) high pressure regimes, and 3) presence of biodegradable organic matter. Due to their composition, hydrates are vulnerable to temperature, pressure, and, to a smaller degree, salinity changes. The occurrence of gas hydrates in marine sediments was discovered mainly along continental margins (slope and rise) where water depths exceed 400 m and the bottom water temperatures are small enough to sustain their presence. The amount of gas hydrates present in marine sediments on a global scale is still under debate. Several numerical models of a different complexity have been developed to estimate the potential amount of clathrates locked world-wide within marine sediments. The range of estimates starts from 500 Gt up to 57,000 Gt of methane carbon which implies a variation of several orders of magnitude. It has been already established that current climate changes are triggering some of the methane releases around the world. Prominent gas hydrate occurrence zones, such as Blake Ridge, can provide important information of the scale of potential hazards and help to predict a future impact of such events. Blake Ridge is a well investigated gas hydrate province containing a large amount of a locked methane gas. With the new numerical multiphase model we have been investigating 1) the potential risk of gas hydrate destabilization caused by several environmental factors (e.g. bottom water temperature rise, sea-level variations), 2) the effect of changing sedimentation regimes to the total amount of gas hydrate, 3) dynamics of hydrate formation in heterogeneous sediment layers, and 4) the impact of dynamic compaction on fluid and gas flow regimes. The model contains four phases (solid porous matrix, pore

  6. Estimating Predictive Variance for Statistical Gas Distribution Modelling

    SciTech Connect

    Lilienthal, Achim J.; Asadi, Sahar; Reggente, Matteo

    2009-05-23

    Recent publications in statistical gas distribution modelling have proposed algorithms that model mean and variance of a distribution. This paper argues that estimating the predictive concentration variance entails not only a gradual improvement but is rather a significant step to advance the field. This is, first, since the models much better fit the particular structure of gas distributions, which exhibit strong fluctuations with considerable spatial variations as a result of the intermittent character of gas dispersal. Second, because estimating the predictive variance allows to evaluate the model quality in terms of the data likelihood. This offers a solution to the problem of ground truth evaluation, which has always been a critical issue for gas distribution modelling. It also enables solid comparisons of different modelling approaches, and provides the means to learn meta parameters of the model, to determine when the model should be updated or re-initialised, or to suggest new measurement locations based on the current model. We also point out directions of related ongoing or potential future research work.

  7. Transient Catalytic Combustor Model With Detailed Gas and Surface Chemistry

    NASA Technical Reports Server (NTRS)

    Struk, Peter M.; Dietrich, Daniel L.; Mellish, Benjamin P.; Miller, Fletcher J.; Tien, James S.

    2005-01-01

    In this work, we numerically investigate the transient combustion of a premixed gas mixture in a narrow, perfectly-insulated, catalytic channel which can represent an interior channel of a catalytic monolith. The model assumes a quasi-steady gas-phase and a transient, thermally thin solid phase. The gas phase is one-dimensional, but it does account for heat and mass transfer in a direction perpendicular to the flow via appropriate heat and mass transfer coefficients. The model neglects axial conduction in both the gas and in the solid. The model includes both detailed gas-phase reactions and catalytic surface reactions. The reactants modeled so far include lean mixtures of dry CO and CO/H2 mixtures, with pure oxygen as the oxidizer. The results include transient computations of light-off and system response to inlet condition variations. In some cases, the model predicts two different steady-state solutions depending on whether the channel is initially hot or cold. Additionally, the model suggests that the catalytic ignition of CO/O2 mixtures is extremely sensitive to small variations of inlet equivalence ratios and parts per million levels of H2.

  8. Statistical time-dependent model for the interstellar gas

    NASA Technical Reports Server (NTRS)

    Gerola, H.; Kafatos, M.; Mccray, R.

    1974-01-01

    We present models for temperature and ionization structure of low, uniform-density (approximately 0.3 per cu cm) interstellar gas in a galactic disk which is exposed to soft X rays from supernova outbursts occurring randomly in space and time. The structure was calculated by computing the time record of temperature and ionization at a given point by Monte Carlo simulation. The calculation yields probability distribution functions for ionized fraction, temperature, and their various observable moments. These time-dependent models predict a bimodal temperature distribution of the gas that agrees with various observations. Cold regions in the low-density gas may have the appearance of clouds in 21-cm absorption. The time-dependent model, in contrast to the steady-state model, predicts large fluctuations in ionization rate and the existence of cold (approximately 30 K), ionized (ionized fraction equal to about 0.1) regions.

  9. Simulation of Wave Motion Using a Lattice Gas Model

    NASA Astrophysics Data System (ADS)

    Buick, J.; Easson, W.; Greated, C.

    1996-02-01

    The lattice gas model for simulating two-phase flow, proposed by Appert and Zaleski, has been modified by the introduction of gravitational interactions and the new model has been used to simulate standing wave patterns on the free surface of a fluid. The results compare well with linear theory.

  10. SHAWNEE FLUE GAS DESULFURIZATION COMPUTER MODEL USERS MANUAL

    EPA Science Inventory

    The manual describes a Shawnee flue gas desulfurization (FGD) computer model and gives detailed instructions for its use. The model, jointly developed by Bechtel National, Inc. and TVA (in conjunction with the EPA-sponsored Shawnee test program), is capable of projecting prelimin...

  11. Gas Path On-line Fault Diagnostics Using a Nonlinear Integrated Model for Gas Turbine Engines

    NASA Astrophysics Data System (ADS)

    Lu, Feng; Huang, Jin-quan; Ji, Chun-sheng; Zhang, Dong-dong; Jiao, Hua-bin

    2014-08-01

    Gas turbine engine gas path fault diagnosis is closely related technology that assists operators in managing the engine units. However, the performance gradual degradation is inevitable due to the usage, and it result in the model mismatch and then misdiagnosis by the popular model-based approach. In this paper, an on-line integrated architecture based on nonlinear model is developed for gas turbine engine anomaly detection and fault diagnosis over the course of the engine's life. These two engine models have different performance parameter update rate. One is the nonlinear real-time adaptive performance model with the spherical square-root unscented Kalman filter (SSR-UKF) producing performance estimates, and the other is a nonlinear baseline model for the measurement estimates. The fault detection and diagnosis logic is designed to discriminate sensor fault and component fault. This integration architecture is not only aware of long-term engine health degradation but also effective to detect gas path performance anomaly shifts while the engine continues to degrade. Compared to the existing architecture, the proposed approach has its benefit investigated in the experiment and analysis.

  12. Computer modeling of gas flow and gas loading of rock in a bench blasting environment

    SciTech Connect

    Preece, D.S.; Baer, M.R. ); Knudsen, S.D. )

    1991-01-01

    Numerical modeling can contribute greatly to an understanding of the physics involved in the blasting process. This paper will describe the latest enhancements to the blast modeling code DMC (Distinct Motion Code) (Taylor and Preece, 1989) and will demonstrate the ability of DMC to model gas flow and rock motion in a bench blasting environment. DMC has been used previously to model rock motion associated with blasting in a cratering environment (Preece and Taylor, 1990) and in confined volume blasting associated with in-situ oil shale retorting (Preece, 1990 a b). These applications of DMC treated the explosive loading as force versus time functions on specific spheres which were adjusted to obtain correct face velocities. It was recognized that a great need in explosives modeling was the coupling of an ability to simulate gas flow with the rock motion simulation capability of DMC. This was accomplished by executing a finite difference code that computes gas flow through a porous media (Baer and Gross, 1989) in conjunction with DMC. The marriage of these two capabilities has been documented by Preece and Knudsen, 1991. The capabilities that have been added recently to DMC and which will be documented in this paper include: (1) addition of a new equation of state for the explosive gases; (2) modeling of gas flow and sphere loading in a bench environment. 8 refs., 5 figs.

  13. A Continuum Model for Metabolic Gas Exchange in Pear Fruit

    PubMed Central

    Ho, Q. Tri; Verboven, Pieter; Verlinden, Bert E.; Lammertyn, Jeroen; Vandewalle, Stefan; Nicolaï, Bart M.

    2008-01-01

    Exchange of O2 and CO2 of plants with their environment is essential for metabolic processes such as photosynthesis and respiration. In some fruits such as pears, which are typically stored under a controlled atmosphere with reduced O2 and increased CO2 levels to extend their commercial storage life, anoxia may occur, eventually leading to physiological disorders. In this manuscript we have developed a mathematical model to predict the internal gas concentrations, including permeation, diffusion, and respiration and fermentation kinetics. Pear fruit has been selected as a case study. The model has been used to perform in silico experiments to evaluate the effect of, for example, fruit size or ambient gas concentration on internal O2 and CO2 levels. The model incorporates the actual shape of the fruit and was solved using fluid dynamics software. Environmental conditions such as temperature and gas composition have a large effect on the internal distribution of oxygen and carbon dioxide in fruit. Also, the fruit size has a considerable effect on local metabolic gas concentrations; hence, depending on the size, local anaerobic conditions may result, which eventually may lead to physiological disorders. The model developed in this manuscript is to our knowledge the most comprehensive model to date to simulate gas exchange in plant tissue. It can be used to evaluate the effect of environmental stresses on fruit via in silico experiments and may lead to commercial applications involving long-term storage of fruit under controlled atmospheres. PMID:18369422

  14. Modeling natural gas market volatility using GARCH with different distributions

    NASA Astrophysics Data System (ADS)

    Lv, Xiaodong; Shan, Xian

    2013-11-01

    In this paper, we model natural gas market volatility using GARCH-class models with long memory and fat-tail distributions. First, we forecast price volatilities of spot and futures prices. Our evidence shows that none of the models can consistently outperform others across different criteria of loss functions. We can obtain greater forecasting accuracy by taking the stylized fact of fat-tail distributions into account. Second, we forecast volatility of basis defined as the price differential between spot and futures. Our evidence shows that nonlinear GARCH-class models with asymmetric effects have the greatest forecasting accuracy. Finally, we investigate the source of forecasting loss of models. Our findings based on a detrending moving average indicate that GARCH models cannot capture multifractality in natural gas markets. This may be the plausible explanation for the source of model forecasting losses.

  15. Geomechanical Modeling of Gas Hydrate Bearing Sediments

    NASA Astrophysics Data System (ADS)

    Sanchez, M. J.; Gai, X., Sr.

    2015-12-01

    This contribution focuses on an advance geomechanical model for methane hydrate-bearing soils based on concepts of elasto-plasticity for strain hardening/softening soils and incorporates bonding and damage effects. The core of the proposed model includes: a hierarchical single surface critical state framework, sub-loading concepts for modeling the plastic strains generally observed inside the yield surface and a hydrate enhancement factor to account for the cementing effects provided by the presence of hydrates in sediments. The proposed framework has been validated against recently published experiments involving both, synthetic and natural hydrate soils, as well as different sediments types (i.e., different hydrate saturations, and different hydrates morphologies) and confinement conditions. The performance of the model in these different case studies was very satisfactory.

  16. Modeling of neutral gas dynamics in high-density plasmas

    NASA Astrophysics Data System (ADS)

    Canupp, Patrick Wellington

    This thesis describes a physical model of chemically reactive neutral gas flow and discusses numerical solutions of this model for the flow in an inductively coupled plasma etch reactor. To obtain these solutions, this research develops an efficient, implicit numerical method. As a result of the enhanced numerical stability of the scheme, large time steps advance the solution from initial conditions to a final steady state in fewer iterations and with less computational expense than simpler explicit methods. This method would incorporate suitably as a module in currently existing large scale plasma simulation tools. In order to demonstrate the accuracy of the numerical technique, this thesis presents results from two simulations of flows that possess theoretical solutions. The first case is the inviscid flow of a gas through a converging nozzle. A comparison of the numerical solution to isentropic flow theory shows that the numerical technique capably captures the essential flow features of this environment. The second case is the Couette flow of a gas between two parallel plates. The simulation results compare well with the exact solution for this flow. After establishing the accuracy of the numerical technique, this thesis discusses results for the flow of chemically reactive gases in a chlorine plasma etch reactor. This research examines the influence of the plasma on the neutral gas and the dynamics exhibited by the neutral gas in the reactor. This research finds that the neutral gas temperature strongly depends on the rate at which inelastic, electron-impact dissociation reactions occur and on atomic chlorine wall recombination rates. Additionally, the neutral gas Aow in the reactor includes a significant mass flux of etch product from the wafer surface. Resolution of these effects is useful for neutral gas simulation. Finally, this thesis demonstrates that continuum fluid models provide reasonable accuracy for these low pressure reactor flows due to the fact

  17. Modeling gas separation from a bent deepwater oil and gas jet/plume

    NASA Astrophysics Data System (ADS)

    Chen, Fanghui; Yapa, Poojitha D.

    2004-04-01

    Socolofsky et al. [Socolofsky, S.A., Leos-Urbel, A. and Adams, E.E., 1999. Draft final report: exploratory experiments with droplet plumes in a cross-flow. In Final Report: Experimental Study of Multi-Phase Plumes with a Lication to Deep Ocean Oil Spills. U.S. Department of the Interior Minerals Management Service Contract No. 1435-01-98-CT-30964.] and Hugi [Hugi, C., 1993. Modelluntersuchungen von Blasenstrahlen fur die Seebeluftung. PhD thesis, Inst. f. Hydromechanik u. Wasserwirtschaft, ETH, Zurich.] observed that gas could separate from the main jet/plume of an oil and gas mix under certain ambient cross-flow conditions. There are locations in deepwater where cross currents are significant (e.g., Gulf of Mexico). Out of the few models available for oil and gas behavior simulation under deepwater conditions, Johansen's [Spill Sci. Technol. Bull. 6 (2000) 103] is the only one that can take into effect the separation of gases from the main jet/plume. A strong ambient current causes a jet/plume to bend. Because gas rises faster than oil, it can separate from the bent plume. This gas separation can lower the neutral buoyancy level (NBL) of plume. Consequently, the overall trajectory of the oil droplets underwater and slicks at the water surface may vary significantly because the location of transition of the jet/plume mixing to the far-field turbulent mixing has drastically changed. In this paper, the turbulent, multi-phase (oil and gas) jet/plume in a cross-flow is modeled by using the integral Lagrangian control volume (CV) method. A comparison of the model results with the experimental data shows good agreement. A scenario for a deepwater blowout simulation shows that taking gas separation into account is very important in a bent plume.

  18. Modeling gas-liquid head performance of electrical submersible pumps

    NASA Astrophysics Data System (ADS)

    Sun, Datong

    The objectives of this study are to develop a simple and accurate theoretical model and to implement the model into a computational tool to predict Electrical Submersible Pumps (ESP) head performance under two-phase flow conditions. A new two-phase model including a set of one-dimensional mass and momentum balance equations was developed. The derived gas-liquid momentum equations along pump channels has improved Sachdeva (1992, 1994)'s model in petroleum industry and generalized Minemura (1998)'s model in nuclear industry. The resulting pressure ODE for frictionless incompressible single-phase flow is consistent with the pump Euler equation. In the two-phase momentum equations, new models for wall frictional losses for each phase, through using gas-liquid stratified assumption and existing correlations for impeller rotating effect, channel curvature effect, and channel cross section effect, have been proposed. New equations for radius of curvature along ESP channels, used in the curvature effect calculation, have been derived. A new shock loss model incorporating rotational speeds has been developed. A new correlation for drag coefficient and interfacial characteristic length effects has been obtained through fitting the model results with experimental data. An algorithm to solve the model equations has been developed and implemented. The model predicts pressure and void fraction distributions along impellers and diffusers and can also be used to predict the pump head performance curve under different fluid properties, pump intake conditions, and rotational speeds. The new two-phase model is validated with air-water experimental data. Results show the model provides a very good prediction for pump head performance under different gas flow rates, liquid flow rates, and different intake pressures. The new model is capable of predicting surging and gas lock conditions.

  19. An analysis of oil and gas supply modeling techniques and a survey of offshore supply models

    SciTech Connect

    Walls, M.A.

    1990-01-01

    This report surveys the literature on empirical oil and gas supply modeling techniques. These techniques are categorized as either geologic/engineering, econometric, or hybrid - the last being a combination of geologic and econometric techniques. The geologic/ engineering models are further disaggregated into play analysis models and discovery process models. The strengths and weaknesses of each of the models are discussed. The report concludes with a discussion of how these techniques have been applied to offshore oil and gas supply.

  20. Modeling and technical use of gas evolving electrodes. Part 2: Modeling of gas-evolving electrolyzers with free electrolyte circulation

    NASA Technical Reports Server (NTRS)

    Schleiff, M.; Thiele, W.; Matschiner, H.

    1983-01-01

    In an electrochemical reactor with gas-evolving electrodes, the transporting action of the gas bubbles can be used to move the electrolyte in a cycle flow, when the structure of the flow channels is suitable. For an electrolysis cell with such a circulation system a mathematic model was set up and evaluated. It is shown that in this manner, a rapid flow through the electrode gap can be achieved without additional energy consumption, in addition to a low gas fraction and a low cell voltage. The cell voltage and the attainable cycle spread are investigated as a function of the geometric parameters for their optimum values.

  1. Microplume model of spatial-yield spectra. [applying to electron gas degradation in molecular nitrogen gas

    NASA Technical Reports Server (NTRS)

    Green, A. E. S.; Singhal, R. P.

    1979-01-01

    An analytic representation for the spatial (radial and longitudinal) yield spectra is developed in terms of a model containing three simple 'microplumes'. The model is applied to electron energy degradation in molecular nitrogen gas for 0.1 to 5 keV incident electrons. From the nature of the cross section input to this model it is expected that the scaled spatial yield spectra for other gases will be quite similar. The model indicates that each excitation, ionization, etc. plume should have its individual spatial and energy dependence. Extensions and aeronomical and radiological applications of the model are discussed.

  2. An Equilibrium-Based Model of Gas Reaction and Detonation

    SciTech Connect

    Trowbridge, L.D.

    2000-04-01

    During gaseous diffusion plant operations, conditions leading to the formation of flammable gas mixtures may occasionally arise. Currently, these could consist of the evaporative coolant CFC-114 and fluorinating agents such as F2 and ClF3. Replacement of CFC-114 with a non-ozone-depleting substitute is planned. Consequently, in the future, the substitute coolant must also be considered as a potential fuel in flammable gas mixtures. Two questions of practical interest arise: (1) can a particular mixture sustain and propagate a flame if ignited, and (2) what is the maximum pressure that can be generated by the burning (and possibly exploding) gas mixture, should it ignite? Experimental data on these systems, particularly for the newer coolant candidates, are limited. To assist in answering these questions, a mathematical model was developed to serve as a tool for predicting the potential detonation pressures and for estimating the composition limits of flammability for these systems based on empirical correlations between gas mixture thermodynamics and flammability for known systems. The present model uses the thermodynamic equilibrium to determine the reaction endpoint of a reactive gas mixture and uses detonation theory to estimate an upper bound to the pressure that could be generated upon ignition. The model described and documented in this report is an extended version of related models developed in 1992 and 1999.

  3. Gas Centrifuge Enrichment Plant Safeguards System Modeling

    SciTech Connect

    Elayat, H A; O'Connell, W J; Boyer, B D

    2006-06-05

    The U.S. Department of Energy (DOE) is interested in developing tools and methods for potential U.S. use in designing and evaluating safeguards systems used in enrichment facilities. This research focuses on analyzing the effectiveness of the safeguards in protecting against the range of safeguards concerns for enrichment plants, including diversion of attractive material and unauthorized modes of use. We developed an Extend simulation model for a generic medium-sized centrifuge enrichment plant. We modeled the material flow in normal operation, plant operational upset modes, and selected diversion scenarios, for selected safeguards systems. Simulation modeling is used to analyze both authorized and unauthorized use of a plant and the flow of safeguards information. Simulation tracks the movement of materials and isotopes, identifies the signatures of unauthorized use, tracks the flow and compilation of safeguards data, and evaluates the effectiveness of the safeguards system in detecting misuse signatures. The simulation model developed could be of use to the International Atomic Energy Agency IAEA, enabling the IAEA to observe and draw conclusions that uranium enrichment facilities are being used only within authorized limits for peaceful uses of nuclear energy. It will evaluate improved approaches to nonproliferation concerns, facilitating deployment of enhanced and cost-effective safeguards systems for an important part of the nuclear power fuel cycle.

  4. Potential biodefense model applications for portable chlorine dioxide gas production.

    PubMed

    Stubblefield, Jeannie M; Newsome, Anthony L

    2015-01-01

    Development of decontamination methods and strategies to address potential infectious disease outbreaks and bioterrorism events are pertinent to this nation's biodefense strategies and general biosecurity. Chlorine dioxide (ClO2) gas has a history of use as a decontamination agent in response to an act of bioterrorism. However, the more widespread use of ClO2 gas to meet current and unforeseen decontamination needs has been hampered because the gas is too unstable for shipment and must be prepared at the application site. Newer technology allows for easy, onsite gas generation without the need for dedicated equipment, electricity, water, or personnel with advanced training. In a laboratory model system, 2 unique applications (personal protective equipment [PPE] and animal skin) were investigated in the context of potential development of decontamination protocols. Such protocols could serve to reduce human exposure to bacteria in a decontamination response effort. Chlorine dioxide gas was capable of reducing (2-7 logs of vegetative and spore-forming bacteria), and in some instances eliminating, culturable bacteria from difficult to clean areas on PPE facepieces. The gas was effective in eliminating naturally occurring bacteria on animal skin and also on skin inoculated with Bacillus spores. The culturable bacteria, including Bacillus spores, were eliminated in a time- and dose-dependent manner. Results of these studies suggested portable, easily used ClO2 gas generation systems have excellent potential for protocol development to contribute to biodefense strategies and decontamination responses to infectious disease outbreaks or other biothreat events. PMID:25812425

  5. Spectral constraints on models of gas in clusters of galaxies

    NASA Technical Reports Server (NTRS)

    Henriksen, M. J.; Mushotzky, R.

    1985-01-01

    The HEAO 1A2 spectra of clusters of galaxies are used to determine the temperature profile which characterizes the X-ray emitting gas. Strong evidence of nonisothermality is found for the Coma, A85, and A1795 clusters. Properties of the cluster potential which binds the gas are calculated for a range of model parameters. The typical binding mass, if the gas is adiabatic, is 2-4E14 solar masses and is quite centrally concentrated. In addition, the Fe abundance in Coma is .26 + or - .06 solar, less than the typical value (.5) found for rich clusters. The results for the gas in Coma may imply a physical description of the cluster which is quite different from what was previously believed.

  6. Algebraic operator approach to gas kinetic models

    NASA Astrophysics Data System (ADS)

    Il'ichov, L. V.

    1997-02-01

    Some general properties of the linear Boltzmann kinetic equation are used to present it in the form ∂ tϕ = - †Âϕ with the operators Âand† possessing some nontrivial algebraic properties. When applied to the Keilson-Storer kinetic model, this method gives an example of quantum ( q-deformed) Lie algebra. This approach provides also a natural generalization of the “kangaroo model”.

  7. Off-gas Adsorption Model and Simulation - OSPREY

    SciTech Connect

    Veronica J Rutledge

    2013-10-01

    The absence of industrial scale nuclear fuel reprocessing in the U.S. has precluded the necessary driver for developing the advanced simulation capability now prevalent in so many other countries. Thus, it is essential to model complex series of unit operations to simulate, understand, and predict inherent transient behavior. A capability of accurately simulating the dynamic behavior of advanced fuel cycle separation processes is expected to provide substantial cost savings and many technical benefits. To support this capability, a modeling effort focused on the off-gas treatment system of a used nuclear fuel recycling facility is in progress. The off-gas separation consists of a series of scrubbers and adsorption beds to capture constituents of interest. Dynamic models are being developed to simulate each unit operation involved so each unit operation can be used as a stand-alone model and in series with multiple others. Currently, an adsorption model has been developed within Multi-physics Object Oriented Simulation Environment (MOOSE) developed at the Idaho National Laboratory (INL). Off-gas Separation and REcoverY (OSPREY) models the adsorption of offgas constituents for dispersed plug flow in a packed bed under non-isothermal and non-isobaric conditions. Inputs to the model include gas composition, sorbent and column properties, equilibrium and kinetic data, and inlet conditions. The simulation outputs component concentrations along the column length as a function of time from which breakthrough data can be obtained. The breakthrough data can be used to determine bed capacity, which in turn can be used to size columns. In addition to concentration data, the model predicts temperature along the column length as a function of time and pressure drop along the column length. A description of the OSPREY model, results from krypton adsorption modeling and plans for modeling the behavior of iodine, xenon, and tritium will be discussed.

  8. Model documentation: Natural Gas Transmission and Distribution Model of the National Energy Modeling System; Volume 1

    SciTech Connect

    1994-02-24

    The Natural Gas Transmission and Distribution Model (NGTDM) is a component of the National Energy Modeling System (NEMS) used to represent the domestic natural gas transmission and distribution system. NEMS is the third in a series of computer-based, midterm energy modeling systems used since 1974 by the Energy Information Administration (EIA) and its predecessor, the Federal Energy Administration, to analyze domestic energy-economy markets and develop projections. This report documents the archived version of NGTDM that was used to produce the natural gas forecasts used in support of the Annual Energy Outlook 1994, DOE/EIA-0383(94). The purpose of this report is to provide a reference document for model analysts, users, and the public that defines the objectives of the model, describes its basic design, provides detail on the methodology employed, and describes the model inputs, outputs, and key assumptions. It is intended to fulfill the legal obligation of the EIA to provide adequate documentation in support of its models (Public Law 94-385, Section 57.b.2). This report represents Volume 1 of a two-volume set. (Volume 2 will report on model performance, detailing convergence criteria and properties, results of sensitivity testing, comparison of model outputs with the literature and/or other model results, and major unresolved issues.) Subsequent chapters of this report provide: (1) an overview of the NGTDM (Chapter 2); (2) a description of the interface between the National Energy Modeling System (NEMS) and the NGTDM (Chapter 3); (3) an overview of the solution methodology of the NGTDM (Chapter 4); (4) the solution methodology for the Annual Flow Module (Chapter 5); (5) the solution methodology for the Distributor Tariff Module (Chapter 6); (6) the solution methodology for the Capacity Expansion Module (Chapter 7); (7) the solution methodology for the Pipeline Tariff Module (Chapter 8); and (8) a description of model assumptions, inputs, and outputs (Chapter 9).

  9. Modelling and identification for control of gas bearings

    NASA Astrophysics Data System (ADS)

    Theisen, Lukas R. S.; Niemann, Hans H.; Santos, Ilmar F.; Galeazzi, Roberto; Blanke, Mogens

    2016-03-01

    Gas bearings are popular for their high speed capabilities, low friction and clean operation, but suffer from poor damping, which poses challenges for safe operation in presence of disturbances. Feedback control can achieve enhanced damping but requires low complexity models of the dominant dynamics over its entire operating range. Models from first principles are complex and sensitive to parameter uncertainty. This paper presents an experimental technique for "in situ" identification of a low complexity model of a rotor-bearing-actuator system and demonstrates identification over relevant ranges of rotational speed and gas injection pressure. This is obtained using parameter-varying linear models that are found to capture the dominant dynamics. The approach is shown to be easily applied and to suit subsequent control design. Based on the identified models, decentralised proportional control is designed and shown to obtain the required damping in theory and in a laboratory test rig.

  10. Wind tunnel modeling of toxic gas releases at industrial facilities

    SciTech Connect

    Petersen, R.L.

    1994-12-31

    Government agencies and the petroleum, chemical and gas industries in the US and abroad have become increasingly concerned about the issues of toxic gas dispersal. Because of this concern, research programs have been sponsored by these various groups to improve the capabilities in hazard mitigation and response. Present computer models used to predict pollutant concentrations at industrial facilities do not properly account for the effects of structures. Structures can act to trap or deflect the cloud and modify the cloud dimensions, thereby possibly increasing or reducing downwind concentrations. The main purpose of this evaluation was to develop a hybrid modeling approach, which combines wind tunnel and dispersion modeling, to obtain more accurate concentration estimates when buildings or structures affect the dispersion of hazardous chemical vapors. To meet the study objectives, wind tunnel testing was performed on a building cluster typical of two industrial settings where accidental releases of toxic gases might occur. This data set was used to test the validity of the AFTOX and SLAB models for estimating concentrations and was used to develop and test two hybrid models. Two accident scenarios were simulated, an evaporating pool of a gas slightly heavier than air (Hydrazine-N{sub 2}H{sub 4}) and a liquid jet release of Nitrogen Tetroxide (N{sub 2}O{sub 4}) where dense gas dispersion effects would be significant. Tests were conducted for a range of wind directions and wind speeds for two different building configurations (low rise and high rise structures).

  11. Multiscale Aspects of Modeling Gas-Phase Nanoparticle Synthesis

    PubMed Central

    Buesser, B.; Gröhn, A.J.

    2013-01-01

    Aerosol reactors are utilized to manufacture nanoparticles in industrially relevant quantities. The development, understanding and scale-up of aerosol reactors can be facilitated with models and computer simulations. This review aims to provide an overview of recent developments of models and simulations and discuss their interconnection in a multiscale approach. A short introduction of the various aerosol reactor types and gas-phase particle dynamics is presented as a background for the later discussion of the models and simulations. Models are presented with decreasing time and length scales in sections on continuum, mesoscale, molecular dynamics and quantum mechanics models. PMID:23729992

  12. Off-gas adsorption model and simulation - OSPREY

    SciTech Connect

    Rutledge, V.J.

    2013-07-01

    A capability of accurately simulating the dynamic behavior of advanced fuel cycle separation processes is expected to provide substantial cost savings and many technical benefits. To support this capability, a modeling effort focused on the off-gas treatment system of a used nuclear fuel recycling facility is in progress. The off-gas separation consists of a series of scrubbers and adsorption beds to capture constituents of interest. Dynamic models are being developed to simulate each unit operation involved so each unit operation can be used as a stand-alone model and in series with multiple others. Currently, an adsorption model has been developed within Multi-physics Object Oriented Simulation Environment (MOOSE) developed at the Idaho National Laboratory (INL). Off-gas Separation and Recovery (OSPREY) models the adsorption of offgas constituents for dispersed plug flow in a packed bed under non-isothermal and non-isobaric conditions. Inputs to the model include gas composition, sorbent and column properties, equilibrium and kinetic data, and inlet conditions. The simulation outputs component concentrations along the column length as a function of time from which breakthrough data can be obtained. The breakthrough data can be used to determine bed capacity, which in turn can be used to size columns. In addition to concentration data, the model predicts temperature along the column length as a function of time and pressure drop along the column length. A description of the OSPREY model, results from krypton adsorption modeling and plans for modeling the behavior of iodine, xenon, and tritium will be discussed. (author)

  13. Modeling CO2 air dispersion from gas driven lake eruptions

    NASA Astrophysics Data System (ADS)

    Chiodini, Giovanni; Costa, Antonio; Rouwet, Dmitri; Tassi, Franco

    2016-04-01

    The most tragic event of gas driven lake eruption occurred at Lake Nyos (Cameroon) on 21 August 1986, when a dense cloud of CO2 suffocated more than 1700 people and an uncounted number of animals in just one night. The event stimulated a series of researches aimed to understand gas origins, gas release mechanisms and strategies for gas hazard mitigation. Very few studies have been carried out for describing the transport of dense CO2 clouds in the atmosphere. Although from a theoretical point of view, gas dispersion can be fully studied by solving the complete equations system for mass, momentum and energy transport, in actual practice, different simplified models able to describe only specific phases or aspects have to be used. In order to simulate dispersion of a heavy gas and to assess the consequent hazard we used a model based on a shallow layer approach (TWODEE2). This technique which uses depth-averaged variables to describe the flow behavior of dense gas over complex topography represents a good compromise between the complexity of computational fluid dynamic models and the simpler integral models. Recently the model has been applied for simulating CO2 dispersion from natural gas emissions in Central Italy. The results have shown how the dispersion pattern is strongly affected by the intensity of gas release, the topography and the ambient wind speed. Here for the first time we applied TWODEE2 code to simulate the dispersion of the large CO2 clouds released by limnic eruptions. An application concerns the case of the 1986 event at lake Nyos. Some difficulties for the simulations were related to the lack of quantitative information: gas flux estimations are not well constrained, meteorological conditions are only qualitatively known, the digital model of the terrain is of poor quality. Different scenarios were taken into account in order to reproduce the qualitative observations available for such episode. The observations regard mainly the effects of gas on

  14. Natural Gas Transmission and Distribution Model of the National Energy Modeling System. Volume 1

    SciTech Connect

    1998-01-01

    The Natural Gas Transmission and Distribution Model (NGTDM) is the component of the National Energy Modeling System (NEMS) that is used to represent the domestic natural gas transmission and distribution system. The NGTDM is the model within the NEMS that represents the transmission, distribution, and pricing of natural gas. The model also includes representations of the end-use demand for natural gas, the production of domestic natural gas, and the availability of natural gas traded on the international market based on information received from other NEMS models. The NGTDM determines the flow of natural gas in an aggregate, domestic pipeline network, connecting domestic and foreign supply regions with 12 demand regions. The purpose of this report is to provide a reference document for model analysts, users, and the public that defines the objectives of the model, describes its basic design, provides detail on the methodology employed, and describes the model inputs, outputs, and key assumptions. Subsequent chapters of this report provide: an overview of NGTDM; a description of the interface between the NEMS and NGTDM; an overview of the solution methodology of the NGTDM; the solution methodology for the Annual Flow Module; the solution methodology for the Distributor Tariff Module; the solution methodology for the Capacity Expansion Module; the solution methodology for the Pipeline Tariff Module; and a description of model assumptions, inputs, and outputs.

  15. Modeling acid-gas generation from boiling chloride brines

    SciTech Connect

    Zhang, Guoxiang; Spycher, Nicolas; Sonnenthal, Eric; Steefel, Carl

    2009-11-16

    This study investigates the generation of HCl and other acid gases from boiling calcium chloride dominated waters at atmospheric pressure, primarily using numerical modeling. The main focus of this investigation relates to the long-term geologic disposal of nuclear waste at Yucca Mountain, Nevada, where pore waters around waste-emplacement tunnels are expected to undergo boiling and evaporative concentration as a result of the heat released by spent nuclear fuel. Processes that are modeled include boiling of highly concentrated solutions, gas transport, and gas condensation accompanied by the dissociation of acid gases, causing low-pH condensate. Simple calculations are first carried out to evaluate condensate pH as a function of HCl gas fugacity and condensed water fraction for a vapor equilibrated with saturated calcium chloride brine at 50-150 C and 1 bar. The distillation of a calcium-chloride-dominated brine is then simulated with a reactive transport model using a brine composition representative of partially evaporated calcium-rich pore waters at Yucca Mountain. Results show a significant increase in boiling temperature from evaporative concentration, as well as low pH in condensates, particularly for dynamic systems where partial condensation takes place, which result in enrichment of HCl in condensates. These results are in qualitative agreement with experimental data from other studies. The combination of reactive transport with multicomponent brine chemistry to study evaporation, boiling, and the potential for acid gas generation at the proposed Yucca Mountain repository is seen as an improvement relative to previously applied simpler batch evaporation models. This approach allows the evaluation of thermal, hydrological, and chemical (THC) processes in a coupled manner, and modeling of settings much more relevant to actual field conditions than the distillation experiment considered. The actual and modeled distillation experiments do not represent

  16. Modeling acid-gas generation from boiling chloride brines

    PubMed Central

    2009-01-01

    Background This study investigates the generation of HCl and other acid gases from boiling calcium chloride dominated waters at atmospheric pressure, primarily using numerical modeling. The main focus of this investigation relates to the long-term geologic disposal of nuclear waste at Yucca Mountain, Nevada, where pore waters around waste-emplacement tunnels are expected to undergo boiling and evaporative concentration as a result of the heat released by spent nuclear fuel. Processes that are modeled include boiling of highly concentrated solutions, gas transport, and gas condensation accompanied by the dissociation of acid gases, causing low-pH condensate. Results Simple calculations are first carried out to evaluate condensate pH as a function of HCl gas fugacity and condensed water fraction for a vapor equilibrated with saturated calcium chloride brine at 50-150°C and 1 bar. The distillation of a calcium-chloride-dominated brine is then simulated with a reactive transport model using a brine composition representative of partially evaporated calcium-rich pore waters at Yucca Mountain. Results show a significant increase in boiling temperature from evaporative concentration, as well as low pH in condensates, particularly for dynamic systems where partial condensation takes place, which result in enrichment of HCl in condensates. These results are in qualitative agreement with experimental data from other studies. Conclusion The combination of reactive transport with multicomponent brine chemistry to study evaporation, boiling, and the potential for acid gas generation at the proposed Yucca Mountain repository is seen as an improvement relative to previously applied simpler batch evaporation models. This approach allows the evaluation of thermal, hydrological, and chemical (THC) processes in a coupled manner, and modeling of settings much more relevant to actual field conditions than the distillation experiment considered. The actual and modeled distillation

  17. Gas Exchange Models for a Flexible Insect Tracheal System.

    PubMed

    Simelane, S M; Abelman, S; Duncan, F D

    2016-06-01

    In this paper two models for movement of respiratory gases in the insect trachea are presented. One model considers the tracheal system as a single flexible compartment while the other model considers the trachea as a single flexible compartment with gas exchange. This work represents an extension of Ben-Tal's work on compartmental gas exchange in human lungs and is applied to the insect tracheal system. The purpose of the work is to study nonlinear phenomena seen in the insect respiratory system. It is assumed that the flow inside the trachea is laminar, and that the air inside the chamber behaves as an ideal gas. Further, with the isothermal assumption, the expressions for the tracheal partial pressures of oxygen and carbon dioxide, rate of volume change, and the rates of change of oxygen concentration and carbon dioxide concentration are derived. The effects of some flow parameters such as diffusion capacities, reaction rates and air concentrations on net flow are studied. Numerical simulations of the tracheal flow characteristics are performed. The models developed provide a mathematical framework to further investigate gas exchange in insects. PMID:27209375

  18. Turbulence modeling of gas-solid suspension flows

    NASA Technical Reports Server (NTRS)

    Chen, C. P.

    1988-01-01

    The purpose here is to discuss and review advances in two-phase turbulent modeling techniques and their applications in various gas-solid suspension flow situations. In addition to the turbulence closures, heat transfer effect, particle dispersion and wall effects are partially covered.

  19. Evaluation of dense-gas simulation models. Final report

    SciTech Connect

    Zapert, J.G.; Londergan, R.J.; Thistle, H.

    1991-05-01

    The report describes the approach and presents the results of an evaluation study of seven dense gas simulation models using data from three experimental programs. The models evaluated are two in the public domain (DEGADIS and SLAB) and five that are proprietary (AIRTOX, CHARM, FOCUS, SAFEMODE, and TRACE). The data bases used in the evaluation are the Desert Tortoise Pressurized Ammonia Releases, Burro Liquefied Natural Gas Spill Tests and the Goldfish Anhydrous Hydroflouric Acid Spill Experiments. A uniform set of performance statistics are calculated and tabulated to compare maximum observed concentrations and cloud half-width to those predicted by each model. None of the models demonstrated good performance consistently for all three experimental programs.

  20. An integral representation of functions in gas-kinetic models

    NASA Astrophysics Data System (ADS)

    Perepelitsa, Misha

    2016-08-01

    Motivated by the theory of kinetic models in gas dynamics, we obtain an integral representation of lower semicontinuous functions on {{{R}}^d,} {d≥1}. We use the representation to study the problem of compactness of a family of the solutions of the discrete time BGK model for the compressible Euler equations. We determine sufficient conditions for strong compactness of moments of kinetic densities, in terms of the measures from their integral representations.

  1. Asymptotic-preserving Boltzmann model equations for binary gas mixture

    NASA Astrophysics Data System (ADS)

    Liu, Sha; Liang, Yihua

    2016-02-01

    An improved system of Boltzmann model equations is developed for binary gas mixture. This system of model equations has a complete asymptotic preserving property that can strictly recover the Navier-Stokes equations in the continuum limit with the correct constitutive relations and the correct viscosity, thermal conduction, diffusion, and thermal diffusion coefficients. In this equation system, the self- and cross-collision terms in Boltzmann equations are replaced by single relaxation terms. In monocomponent case, this system of equations can be reduced to the commonly used Shakhov equation. The conservation property and the H theorem which are important for model equations are also satisfied by this system of model equations.

  2. Asymptotic-preserving Boltzmann model equations for binary gas mixture.

    PubMed

    Liu, Sha; Liang, Yihua

    2016-02-01

    An improved system of Boltzmann model equations is developed for binary gas mixture. This system of model equations has a complete asymptotic preserving property that can strictly recover the Navier-Stokes equations in the continuum limit with the correct constitutive relations and the correct viscosity, thermal conduction, diffusion, and thermal diffusion coefficients. In this equation system, the self- and cross-collision terms in Boltzmann equations are replaced by single relaxation terms. In monocomponent case, this system of equations can be reduced to the commonly used Shakhov equation. The conservation property and the H theorem which are important for model equations are also satisfied by this system of model equations. PMID:26986408

  3. Microeconomics of the ideal gas like market models

    NASA Astrophysics Data System (ADS)

    Chakrabarti, Anindya S.; Chakrabarti, Bikas K.

    2009-10-01

    We develop a framework based on microeconomic theory from which the ideal gas like market models can be addressed. A kinetic exchange model based on that framework is proposed and its distributional features have been studied by considering its moments. Next, we derive the moments of the CC model (Eur. Phys. J. B 17 (2000) 167) as well. Some precise solutions are obtained which conform with the solutions obtained earlier. Finally, an output market is introduced with global price determination in the model with some necessary modifications.

  4. Axisymmetric model of the ionized gas in the Orion Nebula

    NASA Technical Reports Server (NTRS)

    Rubin, R. H.; Simpson, J. P.; Haas, M. R.; Erickson, E. F.

    1991-01-01

    New ionization and thermal equilibrium models for the ionized gas in the Orion Nebula with an axisymmetric two-dimensional 'blister' geometry/density distribution are presented. The HII region is represented more realistically than in previous models, while the physical detail of the microphysics and radiative transfer of the earlier spherical modeling is maintained. The predicted surface brightnesses are compared with observations for a large set of lines at different positions to determine the best-fitting physical parameters. The model explains the strong singly ionized line emission along the lines of sight near the Trapezium.

  5. A heterogeneous lattice gas model for simulating pedestrian evacuation

    NASA Astrophysics Data System (ADS)

    Guo, Xiwei; Chen, Jianqiao; Zheng, Yaochen; Wei, Junhong

    2012-02-01

    Based on the cellular automata method (CA model) and the mobile lattice gas model (MLG model), we have developed a heterogeneous lattice gas model for simulating pedestrian evacuation processes in an emergency. A local population density concept is introduced first. The update rule in the new model depends on the local population density and the exit crowded degree factor. The drift D, which is one of the key parameters influencing the evacuation process, is allowed to change according to the local population density of the pedestrians. Interactions including attraction, repulsion, and friction between every two pedestrians and those between a pedestrian and the building wall are described by a nonlinear function of the corresponding distance, and the repulsion forces increase sharply as the distances get small. A critical force of injury is introduced into the model, and its effects on the evacuation process are investigated. The model proposed has heterogeneous features as compared to the MLG model or the basic CA model. Numerical examples show that the model proposed can capture the basic features of pedestrian evacuation, such as clogging and arching phenomena.

  6. Multi-dimensional modelling of gas turbine combustion using a flame sheet model in KIVA II

    NASA Technical Reports Server (NTRS)

    Cheng, W. K.; Lai, M.-C.; Chue, T.-H.

    1991-01-01

    A flame sheet model for heat release is incorporated into a multi-dimensional fluid mechanical simulation for gas turbine application. The model assumes that the chemical reaction takes place in thin sheets compared to the length scale of mixing, which is valid for the primary combustion zone in a gas turbine combustor. In this paper, the details of the model are described and computational results are discussed.

  7. Evaluation of the gas production economics of the gas hydrate cyclic thermal injection model. [Cyclic thermal injection

    SciTech Connect

    Kuuskraa, V.A.; Hammersheimb, E.; Sawyer, W.

    1985-05-01

    The objective of the work performed under this directive is to assess whether gas hydrates could potentially be technically and economically recoverable. The technical potential and economics of recovering gas from a representative hydrate reservoir will be established using the cyclic thermal injection model, HYDMOD, appropriately modified for this effort, integrated with economics model for gas production on the North Slope of Alaska, and in the deep offshore Atlantic. The results from this effort are presented in this document. In Section 1, the engineering cost and financial analysis model used in performing the economic analysis of gas production from hydrates -- the Hydrates Gas Economics Model (HGEM) -- is described. Section 2 contains a users guide for HGEM. In Section 3, a preliminary economic assessment of the gas production economics of the gas hydrate cyclic thermal injection model is presented. Section 4 contains a summary critique of existing hydrate gas recovery models. Finally, Section 5 summarizes the model modification made to HYDMOD, the cyclic thermal injection model for hydrate gas recovery, in order to perform this analysis.

  8. Exact solutions in a model of vertical gas migration

    SciTech Connect

    Silin, Dmitriy B.; Patzek, Tad W.; Benson, Sally M.

    2006-06-27

    This work is motivated by the growing interest in injectingcarbon dioxide into deep geological formations as a means of avoidingatmospheric emissions of carbon dioxide and consequent global warming.One of the key questions regarding the feasibility of this technology isthe potential rate of leakage out of the primary storage formation. Weseek exact solutions in a model of gas flow driven by a combination ofbuoyancy, viscous and capillary forces. Different combinations of theseforces and characteristic length scales of the processes lead todifferent time scaling and different types of solutions. In the case of athin, tight seal, where the impact of gravity is negligible relative tocapillary and viscous forces, a Ryzhik-type solution implies square-rootof time scaling of plume propagation velocity. In the general case, a gasplume has two stable zones, which can be described by travelling-wavesolutions. The theoretical maximum of the velocity of plume migrationprovides a conservative estimate for the time of vertical migration.Although the top of the plume has low gas saturation, it propagates witha velocity close to the theoretical maximum. The bottom of the plumeflows significantly more slowly at a higher gas saturation. Due to localheterogeneities, the plume can break into parts. Individual plumes alsocan coalesce and from larger plumes. The analytical results are appliedto studying carbon dioxide flow caused by leaks from deep geologicalformations used for CO2 storage. The results are also applicable formodeling flow of natural gas leaking from seasonal gas storage, or formodeling of secondary hydrocarbon migration.

  9. Preliminary numerical analysis of improved gas chromatograph model

    NASA Technical Reports Server (NTRS)

    Woodrow, P. T.

    1973-01-01

    A mathematical model for the gas chromatograph was developed which incorporates the heretofore neglected transport mechanisms of intraparticle diffusion and rates of adsorption. Because a closed-form analytical solution to the model does not appear realizable, techniques for the numerical solution of the model equations are being investigated. Criteria were developed for using a finite terminal boundary condition in place of an infinite boundary condition used in analytical solution techniques. The class of weighted residual methods known as orthogonal collocation is presently being investigated and appears promising.

  10. Analytical Modeling of Shale Hydraulic Fracturing and Gas Production

    NASA Astrophysics Data System (ADS)

    Xu, W.

    2012-12-01

    Shale gas is abundant all over the world. Due to its extremely low permeability, extensive stimulation of a shale reservoir is always required for its economic production. Hydraulic fracturing has been the primary method of shale reservoir stimulation. Consequently the design and optimization of a hydraulic fracturing treatment plays a vital role insuring job success and economic production. Due to the many variables involved and the lack of a simple yet robust tool based on fundamental physics, horizontal well placement and fracturing job designs have to certain degree been a guessing game built on previous trial and error experience. This paper presents a method for hydraulic fracturing design and optimization in these environments. The growth of a complex hydraulic fracture network (HFN) during a fracturing job is equivalently represented by a wiremesh fracturing model (WFM) constructed on the basis of fracture mechanics and mass balance. The model also simulates proppant transport and placement during HFN growth. Results of WFM simulations can then be used as the input into a wiremesh production model (WPM) constructed based on WFM. WPM represents gas flow through the wiremesh HFN by an elliptic flow and the flow of gas in shale matrix by a novel analytical solution accounting for contributions from both free and adsorbed gases stored in the pore space. WPM simulation is validated by testing against numerical simulations using a commercially available reservoir production simulator. Due to the analytical nature of WFM and WPM, both hydraulic fracturing and gas production simulations run very fast on a regular personal computer and are suitable for hydraulic fracturing job design and optimization. A case study is presented to demonstrate how a non-optimized hydraulic fracturing job might have been optimized using WFM and WPM simulations.Fig. 1. Ellipsoidal representation of (a) stimulated reservoir and (b) hydraulic fracture network created by hydraulic

  11. Gas Modelling in the Disc of HD 163296

    NASA Technical Reports Server (NTRS)

    Tilling, I.; Woitke, P.; Meeus, G.; Mora, A.; Montesinos, B.; Riviere-Marichalar, P.; Eiroa, C.; Thi, W. -F.; Isella, A.; Roberge, A.; Martin-Zaidi, C.; Kamp, I.; Pinte, C.; Sandell, G.; Vacca, W. D.; Menard, F.; Mendigutia, I.; Duchene, G.; Dent, W. R. F.; Aresu, G.; Meijerink, R.; Spaans, M.

    2011-01-01

    We present detailed model fits to observations of the disc around the Herbig Ae star HD 163296. This well-studied object has an age of approx. 4Myr, with evidence of a circumstellar disc extending out to approx. 540AU. We use the radiation thermo-chemical disc code ProDiMo to model the gas and dust in the circumstellar disc of HD 163296, and attempt to determine the disc properties by fitting to observational line and continuum data. These include new Herschel/PACS observations obtained as part of the open-time key program GASPS (Gas in Protoplanetary Systems), consisting of a detection of the [Oi] 63 m line and upper limits for several other far infrared lines. We complement this with continuum data and ground-based observations of the CO-12 3-2, 2-1 and CO-13 J=1-0 line transitions, as well as the H2 S(1) transition. We explore the effects of stellar ultraviolet variability and dust settling on the line emission, and on the derived disc properties. Our fitting efforts lead to derived gas/dust ratios in the range 9-100, depending on the assumptions made. We note that the line fluxes are sensitive in general to the degree of dust settling in the disc, with an increase in line flux for settled models. This is most pronounced in lines which are formed in the warm gas in the inner disc, but the low excitation molecular lines are also affected. This has serious implications for attempts to derive the disc gas mass from line observations. We derive fractional PAH abundances between 0.007 and 0.04 relative to ISM levels. Using a stellar and UV excess input spectrum based on a detailed analysis of observations, we find that the all observations are consistent with the previously assumed disc geometry

  12. Parameters of cosmological models and recent astronomical observations

    SciTech Connect

    Sharov, G.S.; Vorontsova, E.G. E-mail: elenavor@inbox.ru

    2014-10-01

    For different gravitational models we consider limitations on their parameters coming from recent observational data for type Ia supernovae, baryon acoustic oscillations, and from 34 data points for the Hubble parameter H(z) depending on redshift. We calculate parameters of 3 models describing accelerated expansion of the universe: the ΛCDM model, the model with generalized Chaplygin gas (GCG) and the multidimensional model of I. Pahwa, D. Choudhury and T.R. Seshadri. In particular, for the ΛCDM model 1σ estimates of parameters are: H{sub 0}=70.262±0.319 km {sup -1}Mp {sup -1}, Ω{sub m}=0.276{sub -0.008}{sup +0.009}, Ω{sub Λ}=0.769±0.029, Ω{sub k}=-0.045±0.032. The GCG model under restriction 0α≥ is reduced to the ΛCDM model. Predictions of the multidimensional model essentially depend on 3 data points for H(z) with z≥2.3.

  13. Calculations of hot gas ingestion for a STOVL aircraft model

    NASA Technical Reports Server (NTRS)

    Fricker, David M.; Holdeman, James D.; Vanka, Surya P.

    1992-01-01

    Hot gas ingestion problems for Short Take-Off, Vertical Landing (STOVL) aircraft are typically approached with empirical methods and experience. In this study, the hot gas environment around a STOVL aircraft was modeled as multiple jets in crossflow with inlet suction. The flow field was calculated with a Navier-Stokes, Reynolds-averaged, turbulent, 3D computational fluid dynamics code using a multigrid technique. A simple model of a STOVL aircraft with four choked jets at 1000 K was studied at various heights, headwind speeds, and thrust splay angles in a modest parametric study. Scientific visualization of the computed flow field shows a pair of vortices in front of the inlet. This and other qualitative aspects of the flow field agree well with experimental data.

  14. Urban multitarget tracking via gas-kinetic dynamics models

    NASA Astrophysics Data System (ADS)

    Mahler, Ronald

    2013-05-01

    Multitarget tracking in urban environments presents a major theoretical and practical challenge. A recently suggested approach is that of modeling traffic dynamics using the fluid-kinetic methods of traffic-flow theory (TFT). I propose use of the newer, more general, gas-kinetic (GK) approach to TFT. In GK, traffic flow is modeled as a one- or two-dimensional constrained gas. The paper demonstrates the following. (1) The foundational concept in GK--the "phase-space density"--is the same thing as the probability hypothesis density (PHD) of multitarget tracking theory. (2) The theoretically best-that-one-can do approach to TFT-based tracking is a PHD filter. (3) Better performance can be obtained by augmenting this PHD filter as a cardinalized PHD (CPHD) filter. A simple example is presented to illustrate how PHD/CPHD filters can be integrated with conventional macroscopic, mesoscopic, and microscopic TFT.

  15. Estimating methane gas generation from Devil's swamp landfill using greenhouse gas emission models

    NASA Astrophysics Data System (ADS)

    Adeyemi, Ayodeji Thompson

    Greenhouse gas (GHG) has been a key issue in the study, design, and management of landfills. Landfill gas (LFG) is considered either as a significant source of renewable energy (if extracted and processed accordingly) or significant source of pollution and risk (if not mitigated or processed). A municipal solid waste (MSW) landfill emits a significant amount of methane, a potent GHG. Thus, quantification and mitigation of GHG emissions is an important area of study in engineering and other sciences related to landfill technology and management. The present study will focus on estimating methane generation from Devils swamp landfill (DSLF), a closed landfill in Baton Rouge, LA. The landfill operated for 53 years (1940-1993) and contains both industrial and municipal waste products. Since the Clean Air Act of 1963, landfills are now classified as New Source Performance Standard (NSPS) waste (i.e., waste that will decompose to generate LFG). Currently, the DSLF is being used as source of renewable energy through the "Waste to Energy" program. For this study, to estimate the methane potential in the DSLF, it is important to determine the characteristics and classification of the landfill's wastes. The study uses and compares different GHG modeling tools---LandGEM, a multiphase model, and a simple first-order model---to estimate methane gas emission and compare results with the actual emissions from the DSLF. The sensitivity of the methane generation rate was analyzed by the methane generation models to assess the effects of variables such as initial conditions, specific growth rate, and reaction rate constants. The study concludes that methane (L0) and initial organic concentration in waste (k) are the most important parameters when estimating methane generation using the models.

  16. Using Coupled Harmonic Oscillators to Model Some Greenhouse Gas Molecules

    SciTech Connect

    Go, Clark Kendrick C.; Maquiling, Joel T.

    2010-07-28

    Common greenhouse gas molecules SF{sub 6}, NO{sub 2}, CH{sub 4}, and CO{sub 2} are modeled as harmonic oscillators whose potential and kinetic energies are derived. Using the Euler-Lagrange equation, their equations of motion are derived and their phase portraits are plotted. The authors use these data to attempt to explain the lifespan of these gases in the atmosphere.

  17. Robustness of disaggregate oil and gas discovery forecasting models

    USGS Publications Warehouse

    Attanasi, E.D.; Schuenemeyer, J.H.

    1989-01-01

    The trend in forecasting oil and gas discoveries has been to develop and use models that allow forecasts of the size distribution of future discoveries. From such forecasts, exploration and development costs can more readily be computed. Two classes of these forecasting models are the Arps-Roberts type models and the 'creaming method' models. This paper examines the robustness of the forecasts made by these models when the historical data on which the models are based have been subject to economic upheavals or when historical discovery data are aggregated from areas having widely differing economic structures. Model performance is examined in the context of forecasting discoveries for offshore Texas State and Federal areas. The analysis shows how the model forecasts are limited by information contained in the historical discovery data. Because the Arps-Roberts type models require more regularity in discovery sequence than the creaming models, prior information had to be introduced into the Arps-Roberts models to accommodate the influence of economic changes. The creaming methods captured the overall decline in discovery size but did not easily allow introduction of exogenous information to compensate for incomplete historical data. Moreover, the predictive log normal distribution associated with the creaming model methods appears to understate the importance of the potential contribution of small fields. ?? 1989.

  18. Gas/Aerosol partitioning: a simplified method for global modeling

    NASA Astrophysics Data System (ADS)

    Metzger, S. M.

    2000-09-01

    The main focus of this thesis is the development of a simplified method to routinely calculate gas/aerosol partitioning of multicomponent aerosols and aerosol associated water within global atmospheric chemistry and climate models. Atmospheric aerosols are usually multicomponent mixtures, partly composed of acids (e.g. H2SO4, HNO3), their salts (e.g. (NH4)2SO4, NH4NO3, respectively), and water. Because these acids and salts are highly hygroscopic, water, that is associated with aerosols in humid environments, often exceeds the total dry aerosol mass. Both the total dry aerosol mass and the aerosol associated water are important for the role of atmospheric aerosols in climate change simulations. Still, multicomponent aerosols are not yet routinely calculated within global atmospheric chemistry or climate models. The reason is that these particles, especially volatile aerosol compounds, require a complex and computationally expensive thermodynamical treatment. For instance, the aerosol associated water depends on the composition of the aerosol, which is determined by the gas/liquid/solid partitioning, in turn strongly dependent on temperature, relative humidity, and the presence of pre-existing aerosol particles. Based on thermodynamical relations such a simplified method has been derived. This method is based on the assumptions generally made by the modeling of multicomponent aerosols, but uses an alternative approach for the calculation of the aerosol activity and activity coefficients. This alternative approach relates activity coefficients to the ambient relative humidity, according to the vapor pressure reduction and the generalization of Raoult s law. This relationship, or simplification, is a consequence of the assumption that the aerosol composition and the aerosol associated water are in thermodynamic equilibrium with the ambient relative humidity, which determines the solute activity and, hence, activity coefficients of a multicomponent aerosol mixture

  19. An efficient model for the analysis of fission gas release

    NASA Astrophysics Data System (ADS)

    Bernard, L. C.; Jacoud, J. L.; Vesco, P.

    2002-04-01

    This paper presents the fission gas release (FGR) model that has been developed at Framatome ANP and incorporated into its fuel rod performance code COPERNIC in order to accurately predict FGR into pressurized water reactor fuel rods under normal and off-normal operating conditions including UO 2, gadolinia and MOX fuels. The model is analytical, thus enabling fast and robust fuel rod calculations, a must within an industrial framework where safety evaluations may require the analyses of a full core and of a very large number of transients. Although the model is simple, it includes the most important FGR features: athermal, thermal, steady-state, and transient regimes, burst effect, rim formation, and MOX-type microstructure. The validation of the model covers 400 irradiated rods that include high burnups, high powers, short to long transients, and shows the quality of the prediction of the model in all types of conditions. As temperature is a key parameter that affects FGR, the COPERNIC thermal model is briefly described and its impact on fission gas released uncertainty is discussed.

  20. Photoionized Mixing Layer Models of the Diffuse Ionized Gas

    NASA Astrophysics Data System (ADS)

    Binette, Luc; Flores-Fajardo, Nahiely; Raga, Alejandro C.; Drissen, Laurent; Morisset, Christophe

    2009-04-01

    It is generally believed that O stars, confined near the galactic midplane, are somehow able to photoionize a significant fraction of what is termed the "diffuse ionized gas" (DIG) of spiral galaxies, which can extend up to 1-2 kpc above the galactic midplane. The heating of the DIG remains poorly understood, however, as simple photoionization models do not reproduce the observed line ratio correlations well or the DIG temperature. We present turbulent mixing layer (TML) models in which warm photoionized condensations are immersed in a hot supersonic wind. Turbulent dissipation and mixing generate an intermediate region where the gas is accelerated, heated, and mixed. The emission spectrum of such layers is compared with observations of Rand of the DIG in the edge-on spiral NGC 891. We generate two sequence of models that fit the line ratio correlations between [S II]/Hα, [O I]/Hα, [N II]/[S II], and [O III]/Hβ reasonably well. In one sequence of models, the hot wind velocity increases, while in the other, the ionization parameter and layer opacity increase. Despite the success of the mixing layer models, the overall efficiency in reprocessing the stellar UV is much too low, much less than 1%, which compels us to reject the TML model in its present form.

  1. Material point method modeling in oil and gas reservoirs

    DOEpatents

    Vanderheyden, William Brian; Zhang, Duan

    2016-06-28

    A computer system and method of simulating the behavior of an oil and gas reservoir including changes in the margins of frangible solids. A system of equations including state equations such as momentum, and conservation laws such as mass conservation and volume fraction continuity, are defined and discretized for at least two phases in a modeled volume, one of which corresponds to frangible material. A material point model technique for numerically solving the system of discretized equations, to derive fluid flow at each of a plurality of mesh nodes in the modeled volume, and the velocity of at each of a plurality of particles representing the frangible material in the modeled volume. A time-splitting technique improves the computational efficiency of the simulation while maintaining accuracy on the deformation scale. The method can be applied to derive accurate upscaled model equations for larger volume scale simulations.

  2. Shawnee flue gas desulfurization computer model users manual

    SciTech Connect

    Sudhoff, F.A.; Torstrick, R.L.

    1985-03-01

    In conjunction with the US Enviromental Protection Agency sponsored Shawnee test program, Bechtel National, Inc., and the Tennessee Valley Authority jointly developed a computer model capable of projecting preliminary design and economics for lime- and limestone-scrubbing flue gas desulfurization systems. The model is capable of projecting relative economics for spray tower, turbulent contact absorber, and venturi-spray tower scrubbing options. It may be used to project the effect on system design and economics of variations in required SO/sub 2/ removal, scrubber operating parameters (gas velocity, liquid-to-gas (L/G) ration, alkali stoichiometry, liquor hold time in slurry recirculation tanks), reheat temperature, and scrubber bypass. It may also be used to evaluate alternative waste disposal methods or additives (MgO or adipic acid) on costs for the selected process. Although the model is not intended to project the economics of an individual system to a high degree of accuracy, it allows prospective users to quickly project comparative design and costs for limestone and lime case variations on a common design and cost basis. The users manual provides a general descripton of the Shawnee FGD computer model and detailed instructions for its use. It describes and explains the user-supplied input data which are required such as boiler size, coal characteristics, and SO/sub 2/ removal requirments. Output includes a material balance, equipment list, and detailed capital investment and annual revenue requirements. The users manual provides information concerning the use of the overall model as well as sample runs to serve as a guide to prospective users in identifying applications. The FORTRAN-based model is maintained by TVA, from whom copies or individual runs are available. 25 refs., 3 figs., 36 tabs.

  3. Semiphenomenological model for gas-liquid phase transitions.

    PubMed

    Benilov, E S; Benilov, M S

    2016-03-01

    We examine a rarefied gas with inter-molecular attraction. It is argued that the attraction force amplifies random density fluctuations by pulling molecules from lower-density regions into high-density regions and thus may give rise to an instability. To describe this effect, we use a kinetic equation where the attraction force is taken into account in a way similar to how electromagnetic forces in plasma are treated in the Vlasov model. It is demonstrated that the instability occurs when the temperature T is lower than a certain threshold value T(s) depending on the gas density. It is further shown that, even if T is only marginally lower than T(s), the instability generates clusters with density much higher than that of the gas. These results suggest that the instability should be interpreted as a gas-liquid phase transition, with T(s) being the temperature of saturated vapor and the high-density clusters representing liquid droplets. PMID:27078333

  4. Electro-thermal modeling of a microbridge gas sensor

    SciTech Connect

    Manginell, R.P.; Smith, J.H.; Ricco, A.J.; Hughes, R.C.; Moreno, D.J.; Huber, R.J.

    1997-08-01

    Fully CMOS-compatible, surface-micromachined polysilicon microbridges have been designed, fabricated, and tested for use in catalytic, calorimetric gas sensing. To improve sensor behavior, extensive electro-thermal modeling efforts were undertaken using SPICE. The validity of the SPICE model was verified comparing its simulated behavior with experiment. Temperature distribution of an electrically heated microbridges was measured using an infrared microscope. Comparisons among the measured distribution, the SPICE simulation, and distributions obtained by analytical methods show that heating at the ends of a microbridges has important implications for device response. Additional comparisons between measured and simulated current-voltage characteristics, as well as transient response, further support the accuracy of the model. A major benefit of electro- thermal modeling with SPICE is the ability to simultaneously simulate the behavior of a device and its control/sensing electronics. Results for the combination of a unique constant-resistance control circuit and microbridges gas sensor are given. Models of in situ techniques for monitoring catalyst deposition are shown to be in agreement with experiment. Finally, simulated chemical response of the detector is compared with the data, and methods of improving response through modifications in bridge geometry are predicted.

  5. Empirical slip and viscosity model performance for microscale gas flows.

    SciTech Connect

    Gallis, Michail A.; Boyd, Iain D.; McNenly, Matthew J.

    2004-07-01

    For the simple geometries of Couette and Poiseuille flows, the velocity profile maintains a similar shape from continuum to free molecular flow. Therefore, modifications to the fluid viscosity and slip boundary conditions can improve the continuum based Navier-Stokes solution in the non-continuum non-equilibrium regime. In this investigation, the optimal modifications are found by a linear least-squares fit of the Navier-Stokes solution to the non-equilibrium solution obtained using the direct simulation Monte Carlo (DSMC) method. Models are then constructed for the Knudsen number dependence of the viscosity correction and the slip model from a database of DSMC solutions for Couette and Poiseuille flows of argon and nitrogen gas, with Knudsen numbers ranging from 0.01 to 10. Finally, the accuracy of the models is measured for non-equilibrium cases both in and outside the DSMC database. Flows outside the database include: combined Couette and Poiseuille flow, partial wall accommodation, helium gas, and non-zero convective acceleration. The models reproduce the velocity profiles in the DSMC database within an L{sub 2} error norm of 3% for Couette flows and 7% for Poiseuille flows. However, the errors in the model predictions outside the database are up to five times larger.

  6. Sorption Modeling and Verification for Off-Gas Treatment

    SciTech Connect

    Tavlarides, Lawrence L.; Lin, Ronghong; Nan, Yue; Yiacoumi, Sotira; Tsouris, Costas; Ladshaw, Austin; Sharma, Ketki; Gabitto, Jorge; DePaoli, David

    2015-04-29

    The project has made progress toward developing a comprehensive modeling capability for the capture of target species in off gas evolved during the reprocessing of nuclear fuel. The effort has integrated experimentation, model development, and computer code development for adsorption and absorption processes. For adsorption, a modeling library has been initiated to include (a) equilibrium models for uptake of off-gas components by adsorbents, (b) mass transfer models to describe mass transfer to a particle, diffusion through the pores of the particle and adsorption on the active sites of the particle, and (c) interconnection of these models to fixed bed adsorption modeling which includes advection through the bed. For single-component equilibria, a Generalized Statistical Thermodynamic Adsorption (GSTA) code was developed to represent experimental data from a broad range of isotherm types; this is equivalent to a Langmuir isotherm in the two-parameter case, and was demonstrated for Kr on INL-engineered sorbent HZ PAN, water sorption on molecular sieve A sorbent material (MS3A), and Kr and Xe capture on metal-organic framework (MOF) materials. The GSTA isotherm was extended to multicomponent systems through application of a modified spreading pressure surface activity model and generalized predictive adsorbed solution theory; the result is the capability to estimate multicomponent adsorption equilibria from single-component isotherms. This advance, which enhances the capability to simulate systems related to off-gas treatment, has been demonstrated for a range of real-gas systems in the literature and is ready for testing with data currently being collected for multicomponent systems of interest, including iodine and water on MS3A. A diffusion kinetic model for sorbent pellets involving pore and surface diffusion as well as external mass transfer has been established, and a methodology was developed for determining unknown diffusivity parameters from transient

  7. Generalized gas-solid adsorption modeling: Single-component equilibria

    SciTech Connect

    Ladshaw, Austin; Yiacoumi, Sotira; Tsouris, Costas; DePaoli, David W.

    2015-01-07

    Over the last several decades, modeling of gas–solid adsorption at equilibrium has generally been accomplished through the use of isotherms such as the Freundlich, Langmuir, Tóth, and other similar models. While these models are relatively easy to adapt for describing experimental data, their simplicity limits their generality to be used with many different sets of data. This limitation forces engineers and scientists to test each different model in order to evaluate which one can best describe their data. Additionally, the parameters of these models all have a different physical interpretation, which may have an effect on how they can be further extended into kinetic, thermodynamic, and/or mass transfer models for engineering applications. Therefore, it is paramount to adopt not only a more general isotherm model, but also a concise methodology to reliably optimize for and obtain the parameters of that model. A model of particular interest is the Generalized Statistical Thermodynamic Adsorption (GSTA) isotherm. The GSTA isotherm has enormous flexibility, which could potentially be used to describe a variety of different adsorption systems, but utilizing this model can be fairly difficult due to that flexibility. To circumvent this complication, a comprehensive methodology and computer code has been developed that can perform a full equilibrium analysis of adsorption data for any gas-solid system using the GSTA model. The code has been developed in C/C++ and utilizes a Levenberg–Marquardt’s algorithm to handle the non-linear optimization of the model parameters. Since the GSTA model has an adjustable number of parameters, the code iteratively goes through all number of plausible parameters for each data set and then returns the best solution based on a set of scrutiny criteria. Data sets at different temperatures are analyzed serially and then linear correlations with temperature are made for the parameters of the model. The end result is a full set of

  8. Generalized gas-solid adsorption modeling: Single-component equilibria

    DOE PAGESBeta

    Ladshaw, Austin; Yiacoumi, Sotira; Tsouris, Costas; DePaoli, David W.

    2015-01-07

    Over the last several decades, modeling of gas–solid adsorption at equilibrium has generally been accomplished through the use of isotherms such as the Freundlich, Langmuir, Tóth, and other similar models. While these models are relatively easy to adapt for describing experimental data, their simplicity limits their generality to be used with many different sets of data. This limitation forces engineers and scientists to test each different model in order to evaluate which one can best describe their data. Additionally, the parameters of these models all have a different physical interpretation, which may have an effect on how they can bemore » further extended into kinetic, thermodynamic, and/or mass transfer models for engineering applications. Therefore, it is paramount to adopt not only a more general isotherm model, but also a concise methodology to reliably optimize for and obtain the parameters of that model. A model of particular interest is the Generalized Statistical Thermodynamic Adsorption (GSTA) isotherm. The GSTA isotherm has enormous flexibility, which could potentially be used to describe a variety of different adsorption systems, but utilizing this model can be fairly difficult due to that flexibility. To circumvent this complication, a comprehensive methodology and computer code has been developed that can perform a full equilibrium analysis of adsorption data for any gas-solid system using the GSTA model. The code has been developed in C/C++ and utilizes a Levenberg–Marquardt’s algorithm to handle the non-linear optimization of the model parameters. Since the GSTA model has an adjustable number of parameters, the code iteratively goes through all number of plausible parameters for each data set and then returns the best solution based on a set of scrutiny criteria. Data sets at different temperatures are analyzed serially and then linear correlations with temperature are made for the parameters of the model. The end result is a full set

  9. A new model for gas/solid pipe flow

    SciTech Connect

    Wu, Bangxian; Chang, S.L.; Lottes, S.A.; Petrick, M.

    1995-12-31

    A new model of particle turbulent dispersion in vertical gas/solid pipe flow is presented in this paper. The essence of the model is to pay more attention to the active and discrete behavior of particles in the dispersion process in non-homogeneous turbulent vertical pipe flows using two-fluid approaches. In the new model, a non-gradient type of diffusion term is included in the expression of radial particle dispersion flux; the transport equation for particle turbulent kinetic energy (PTKE) is developed and solved for its distribution; the effect of intra-particle collision is considered for the generation and dissipation of PTKE; turbulence modulation due to particle presence is taken into account. Preliminary numerical results based on this new model are also presented in this paper.

  10. Natural gas production problems : solutions, methodologies, and modeling.

    SciTech Connect

    Rautman, Christopher Arthur; Herrin, James M.; Cooper, Scott Patrick; Basinski, Paul M.; Olsson, William Arthur; Arnold, Bill Walter; Broadhead, Ronald F.; Knight, Connie D.; Keefe, Russell G.; McKinney, Curt; Holm, Gus; Holland, John F.; Larson, Rich; Engler, Thomas W.; Lorenz, John Clay

    2004-10-01

    Natural gas is a clean fuel that will be the most important domestic energy resource for the first half the 21st centtuy. Ensuring a stable supply is essential for our national energy security. The research we have undertaken will maximize the extractable volume of gas while minimizing the environmental impact of surface disturbances associated with drilling and production. This report describes a methodology for comprehensive evaluation and modeling of the total gas system within a basin focusing on problematic horizontal fluid flow variability. This has been accomplished through extensive use of geophysical, core (rock sample) and outcrop data to interpret and predict directional flow and production trends. Side benefits include reduced environmental impact of drilling due to reduced number of required wells for resource extraction. These results have been accomplished through a cooperative and integrated systems approach involving industry, government, academia and a multi-organizational team within Sandia National Laboratories. Industry has provided essential in-kind support to this project in the forms of extensive core data, production data, maps, seismic data, production analyses, engineering studies, plus equipment and staff for obtaining geophysical data. This approach provides innovative ideas and technologies to bring new resources to market and to reduce the overall environmental impact of drilling. More importantly, the products of this research are not be location specific but can be extended to other areas of gas production throughout the Rocky Mountain area. Thus this project is designed to solve problems associated with natural gas production at developing sites, or at old sites under redevelopment.

  11. Analytical model for thermal boundary conductance and equilibrium thermal accommodation coefficient at solid/gas interfaces.

    PubMed

    Giri, Ashutosh; Hopkins, Patrick E

    2016-02-28

    We develop an analytical model for the thermal boundary conductance between a solid and a gas. By considering the thermal fluxes in the solid and the gas, we describe the transmission of energy across the solid/gas interface with diffuse mismatch theory. From the predicted thermal boundary conductances across solid/gas interfaces, the equilibrium thermal accommodation coefficient is determined and compared to predictions from molecular dynamics simulations on the model solid-gas systems. We show that our model is applicable for modeling the thermal accommodation of gases on solid surfaces at non-cryogenic temperatures and relatively strong solid-gas interactions (εsf ≳ kBT). PMID:26931716

  12. Self-similarity of phase-space networks of frustrated spin models and lattice gas models

    NASA Astrophysics Data System (ADS)

    Peng, Yi; Wang, Feng; Han, Yilong

    2013-03-01

    We studied the self-similar properties of the phase-spaces of two frustrated spin models and two lattice gas models. The frustrated spin models included (1) the anti-ferromagnetic Ising model on a two-dimensional triangular lattice (1a) at the ground states and (1b) above the ground states and (2) the six-vertex model. The two lattice gas models were (3) the one-dimensional lattice gas model and (4) the two-dimensional lattice gas model. The phase spaces were mapped to networks so that the fractal analysis of complex networks could be applied, i.e. the box-covering method and the cluster-growth method. These phase spaces, in turn, establish new classes of networks with unique self-similar properties. Models 1a, 2, and 3 with long-range power-law correlations in real space exhibit fractal phase spaces, while models 1b and 4 with short-range exponential correlations in real space exhibit nonfractal phase spaces. This behavior agrees with one of untested assumptions in Tsallis nonextensive statistics. Hong Kong GRC grants 601208 and 601911

  13. Modeling the hole configuration on gas turbine blade vane

    NASA Astrophysics Data System (ADS)

    Zakaria, Mohamad Shukri; Manaf, Muhammad Zaidan Abdul; Saadun, Mohd Noor Asril; Jumaidin, Ridhwan; Hafizan, Andi Hairul

    2015-05-01

    The performance of Gas Turbine can be improved by increasing the inlet temperature gradually. The high level temperature of component that contact with hot gases due to internal combustion in gas turbine will make possibility failure especially on turbine vane. Thus, this study aims to identify the best hole arrangement of cooling on turbine vane, and investigate the critical region for failure possibilities occur on turbine vane caused by the hot gases that considered into two parameter which are steady temperature profile and average temperature decreasing on blade. This study will implement C3X type vane in order to improve the process in turbine blades. An arrangement of two dimensional blade hole will be model Commercial software ANSYS Fluent. It is found that best arrangement and configuration between the hole shape can improve resistances in relation to thermal collapse and satisfied the blade cooling goal.

  14. The magnetic field of Mars - Implications from gas dynamic modeling

    NASA Technical Reports Server (NTRS)

    Russell, C. T.; Luhmann, J. G.; Spreiter, J. R.; Stahara, S. S.

    1984-01-01

    On January 21, 1972, the Mars 3 spacecraft observed a variation in the magnetic field during its periapsis passage over the dayside of Mars that was suggestive of entry into a Martian magnetosphere. Original data and trajectory of the spacecraft have been obtained (Dolginov, 1983) and an attempt is made to simulate the observed variation of the magnetic field by using a gas dynamic simulation. In the gas dynamic model a flow field is generated and this flow field is used to carry the interplanetary magnetic field through the Martian magnetosheath. The independence of the flow field and magnetic field calculation makes it possible to converge rapidly on an IMF orientation that would result in a magnetic variation similar to that observed by Mars 3. There appears to be no need to invoke an entry into a Martian magnetosphere to explain these observations.

  15. The nonequilibrium Ehrenfest gas: A chaotic model with flat obstacles?

    NASA Astrophysics Data System (ADS)

    Bianca, Carlo; Rondoni, Lamberto

    2009-03-01

    It is known that the nonequilibrium version of the Lorentz gas (a billiard with dispersing obstacles [Ya. G. Sinai, Russ. Math. Surv. 25, 137 (1970)], electric field, and Gaussian thermostat) is hyperbolic if the field is small [N. I. Chernov, Ann. Henri Poincare 2, 197 (2001)]. Differently the hyperbolicity of the nonequilibrium Ehrenfest gas constitutes an open problem since its obstacles are rhombi and the techniques so far developed rely on the dispersing nature of the obstacles [M. P. Wojtkowski, J. Math. Pures Appl. 79, 953 (2000)]. We have developed analytical and numerical investigations that support the idea that this model of transport of matter has both chaotic (positive Lyapunov exponent) and nonchaotic steady states with a quite peculiar sensitive dependence on the field and on the geometry, not observed before. The associated transport behavior is correspondingly highly irregular, with features whose understanding is of both theoretical and technological interests.

  16. Analytical and Numerical Modeling of Strongly Rotating Rarefied Gas Flows

    NASA Astrophysics Data System (ADS)

    Pradhan, Sahadev; Kumaran, Viswanathan

    2015-11-01

    Centrifugal gas separation processes effect separation by utilizing the difference in the mole fraction in a high speed rotating cylinder caused by the difference in molecular mass, and consequently the centrifugal force density. These have been widely used in isotope separation because chemical separation methods cannot be used to separate isotopes of the same chemical species. More recently, centrifugal separation has also been explored for the separation of gases such as carbon dioxide and methane. The efficiency of separation is critically dependent on the secondary flow generated due to temperature gradients at the cylinder wall or due to inserts, and it is important to formulate accurate models for this secondary flow. The widely used Onsager model for secondary flow is restricted to very long cylinders where the length is large compared to the diameter, the limit of high stratification parameter, where the gas is restricted to a thin layer near the wall of the cylinder, and it assumes that there is no mass difference in the two species while calculating the secondary flow. There are two objectives of the present analysis of the rarefied gas flow in a rotating cylinder. The first is to remove the restriction of high stratification parameter, and to generalize the solutions to low rotation speeds where the stratification parameter may be O(1), and to apply for dissimilar gases considering the difference in molecular mass of the two species. Secondly, we would like to compare the predictions with molecular simulations based on the direct simulation Monte Carlo (DSMC) method for rarefied gas flows, in order to quantify the errors resulting from the approximations at different aspect ratios, Reynolds number and stratification parameter.

  17. Gas-Grain Models for Interstellar Anion Chemistry

    NASA Technical Reports Server (NTRS)

    Cordiner, M. A.; Charnely, S. B.

    2012-01-01

    Long-chain hydrocarbon anions C(sub n) H(-) (n = 4, 6, 8) have recently been found to be abundant in a variety of interstellar clouds. In order to explain their large abundances in the denser (prestellar/protostellar) environments, new chemical models are constructed that include gas-grain interactions. Models including accretion of gas-phase species onto dust grains and cosmic-ray-induced desorption of atoms are able to reproduce the observed anion-to-neutral ratios, as well as the absolute abundances of anionic and neutral carbon chains, with a reasonable degree of accuracy. Due to their destructive effects, the depletion of oxygen atoms onto dust results in substantially greater polyyne and anion abundances in high-density gas (with n(sub H2) approx > / cubic cm). The large abundances of carbon-chain-bearing species observed in the envelopes of protostars such as L1527 can thus be explained without the need for warm carbon-chain chemistry. The C6H(-) anion-to-neutral ratio is found to be most sensitive to the atomic O and H abundances and the electron density. Therefore, as a core evolves, falling atomic abundances and rising electron densities are found to result in increasing anion-to-neutral ratios. Inclusion of cosmic-ray desorption of atoms in high-density models delays freeze-out, which results in a more temporally stable anion-to-neutral ratio, in better agreement with observations. Our models include reactions between oxygen atoms and carbon-chain anions to produce carbon-chain-oxide species C6O, C7O, HC6O, and HC7O, the abundances of which depend on the assumed branching ratios for associative electron detachment

  18. Dissolved gas transport in the presence of a trapped gas phase: Experimental evaluation of a two-dimensional kinetic model

    SciTech Connect

    Donaldson, J.H.; Istok, J.D.; O`Reilly, K.T.

    1998-01-01

    Quantitative information on dissolved gas transport in ground water aquifers is needed for a variety of site characterization and remedial design applications. The objective of this study was to gain further understanding of dissolved gas transport in the presence of trapped gas in the pore space of an otherwise water saturated porous medium, using a combination of laboratory experiments and numerical modeling. Transport experiments were conducted in a large-scale laboratory physical aquifer model containing a homogeneous sandpack. Tracer (Br{sup {minus}}) and dissolved gas (O{sub 2} or H{sub 2}) plumes were created using a two-well injection/extraction scheme and then were allowed to drift in a uniform flow field. Plume locations and shapes were monitored by measuring tracer and dissolved gas concentrations as a function of position within the sandpack and time. In all experiments, partitioning of the dissolved gases between the mobile ground water and stationary trapped gas phases resulted in substantial retardation and tailing of the dissolved O{sub 2} and H{sub 2} plumes relative to the Br{sup {minus}} plumes. Most observed plume features could be reproduced in simulations performed with a numerical model that combined the advection-dispersion equation with diffusion controlled mass transfer of dissolved gas between the mobile aqueous and stationary trapped gas phases. Fitted values of the volumetric trapped gas content and mass transfer coefficient ranged from 0.04 to 0.08 and from 10{sup {minus}6} to 10{sup {minus}5} sec{sup {minus}1}, respectively. Sensitivity analyses were used to examine how systematic variations in these parameters would be expected to affect dissolved gas transport under a range of potential field conditions. The experimental and modeling results indicate that diffusion controlled mass transfer should be considered when predicting dissolved gas transport in ground water aquifers in the presence of trapped gas.

  19. MODELING THE POLLUTION OF PRISTINE GAS IN THE EARLY UNIVERSE

    SciTech Connect

    Pan, Liubin; Scannapieco, Evan; Scalo, Jon E-mail: evan.scannapieco@asu.edu

    2013-10-01

    We conduct a comprehensive theoretical and numerical investigation of the pollution of pristine gas in turbulent flows, designed to provide useful new tools for modeling the evolution of the first generation of stars. The properties of such Population III (Pop III) stars are thought to be very different than those of later stellar generations, because cooling is dramatically different in gas with a metallicity below a critical value Z{sub c}, which lies between ∼10{sup –6} and ∼10{sup –3} Z{sub ☉}. The critical value is much smaller than the typical overall average metallicity, , and therefore the mixing efficiency of the pristine gas in the interstellar medium plays a crucial role in determining the transition from Pop III to normal star formation. The small critical value, Z{sub c}, corresponds to the far left tail of the probability distribution function (PDF) of the metal abundance. Based on closure models for the PDF formulation of turbulent mixing, we derive evolution equations for the fraction of gas, P, lying below Z{sub c}, in statistically homogeneous compressible turbulence. Our simulation data show that the evolution of the pristine fraction P can be well approximated by a generalized 'self-convolution' model, which predicts that P-dot = - (n/τ{sub con}) P (1-P{sup 1/n}), where n is a measure of the locality of the mixing or PDF convolution events and the convolution timescale τ{sub con} is determined by the rate at which turbulence stretches the pollutants. Carrying out a suite of numerical simulations with turbulent Mach numbers ranging from M = 0.9 to 6.2, we are able to provide accurate fits to n and τ{sub con} as a function of M, Z{sub c}/(Z), and the length scale, L{sub p}, at which pollutants are added to the flow. For pristine fractions above P = 0.9, mixing occurs only in the regions surrounding blobs of pollutants, such that n = 1. For smaller values of P, n is larger as the mixing process becomes more global. We show how

  20. Thermal barrier coating life modeling in aircraft gas turbine engines

    NASA Technical Reports Server (NTRS)

    Nissley, David M.

    1995-01-01

    Analytical models for predicting ceramic thermal barrier coating (TBC) spalling life in aircraft gas turbine engines are presented. Electron beam-physical vapor deposited (EB-PVD) and plasma sprayed TBC systems are discussed. An overview of the following TBC spalling mechanisms is presented: metal oxidation at the ceramic-metal interface, ceramic-metal interface stress singularities at edges and corners, ceramic-metal interface stresses caused by radius of curvature and interface roughness, material properties and mechanical behavior, temperature gradients, component design features and object impact damage. TBC spalling life analytical models are proposed based on observations of TBC spalling and plausible failure theories. TBC spalling was assumed to occur when the imposed stresses exceed the material strength (at or near the ceramic-metal interface). TBC failure knowledge gaps caused by lack of experimental evidence and analytical understanding are noted. The analytical models are considered initial engineering approaches that capture observed TBC failure trends.

  1. Two relaxation time lattice Boltzmann model for rarefied gas flows

    NASA Astrophysics Data System (ADS)

    Esfahani, Javad Abolfazli; Norouzi, Ali

    2014-01-01

    In this paper, the lattice Boltzmann equation (LBE) with two relaxation times (TRT) is implemented in order to study gaseous flow through a long micro/nano-channel. A new relation is introduced for the reflection factor in the bounce-back/specular reflection (BSR) boundary condition based on the analytical solution of the Navier-Stokes equations. The focus of the present study is on comparing TRT with the other LBE models called multiple relaxation times (MRT) and single relaxation time (SRT) in simulation of rarefied gas flows. After a stability analysis for the TRT and SRT models, the numerical results are presented and validated by the analytical solution of the Navier-Stokes equations with slip boundary condition, direct simulation of Monte Carlo (DSMC) and information preservation (IP) method. The effect of various gases on flow behavior is also investigated by using the variable hard sphere (VHS) model through the symmetrical relaxation time.

  2. Modeling coiled-tubing velocity strings for gas wells

    SciTech Connect

    Martinez, J.; Martinez, A.

    1998-02-01

    Because of its ability to prolong well life, its relatively low expense, and the relative ease with which it is installed, coiled tubing has become a preferred remedial method of tubular completion for gas wells. Of course, the difficulty in procuring wireline-test data is a drawback to verifying the accuracy of the assumptions and predictions used for coiled-tubing selection. This increases the importance of the prediction-making process, and, as a result, places great emphasis on the modeling methods that are used. This paper focuses on the processes and methods for achieving sound multiphase-flow predictions by looking at the steps necessary to arrive at coiled-tubing selection. Furthermore, this paper examines the variables that serve as indicators of the viability of each tubing size, especially liquid holdup. This means that in addition to methodology, emphasis is placed on the use of a good wellbore model. The computer model discussed is in use industry wide.

  3. Reactive Transport Modeling of Acid Gas Generation and Condensation

    SciTech Connect

    G. Zhahg; N. Spycher; E. Sonnenthal; C. Steefel

    2005-01-25

    Pulvirenti et al. (2004) recently conducted a laboratory evaporation/condensation experiment on a synthetic solution of primarily calcium chloride. This solution represents one potential type of evaporated pore water at Yucca Mountain, Nevada, a site proposed for geologic storage of high-level nuclear waste. These authors reported that boiling this solution to near dryness (a concentration factor >75,000 relative to actual pore waters) leads to the generation of acid condensate (pH 4.5) presumably due to volatilization of HCl (and minor HF and/or HNO{sub 3}). To investigate the various processes taking place, including boiling, gas transport, and condensation, their experiment was simulated by modifying an existing multicomponent and multiphase reactive transport code (TOUGHREACT). This code was extended with a Pitzer ion-interaction model to deal with high ionic strength. The model of the experiment was set-up to capture the observed increase in boiling temperature (143 C at {approx}1 bar) resulting from high concentrations of dissolved salts (up to 8 m CaCl{sub 2}). The computed HCI fugacity ({approx} 10{sup -4} bars) generated by boiling under these conditions is not sufficient to lower the pH of the condensate (cooled to 80 and 25 C) down to observed values unless the H{sub 2}O mass fraction in gas is reduced below {approx}10%. This is because the condensate becomes progressively diluted by H{sub 2}O gas condensation. However, when the system is modeled to remove water vapor, the computed pH of instantaneous condensates decreases to {approx}1.7, consistent with the experiment (Figure 1). The results also show that the HCl fugacity increases, and calcite, gypsum, sylvite, halite, MgCl{sub 2}4H{sub 2}O and CaCl{sub 2} precipitate sequentially with increasing concentration factors.

  4. Study on Turbulent Modeling in Gas Entrainment Evaluation Method

    NASA Astrophysics Data System (ADS)

    Ito, Kei; Ohshima, Hiroyuki; Nakamine, Yoshiaki; Imai, Yasutomo

    Suppression of gas entrainment (GE) phenomena caused by free surface vortices are very important to establish an economically superior design of the sodium-cooled fast reactor in Japan (JSFR). However, due to the non-linearity and/or locality of the GE phenomena, it is not easy to evaluate the occurrences of the GE phenomena accurately. In other words, the onset condition of the GE phenomena in the JSFR is not predicted easily based on scaled-model and/or partial-model experiments. Therefore, the authors are developing a CFD-based evaluation method in which the non-linearity and locality of the GE phenomena can be considered. In the evaluation method, macroscopic vortex parameters, e.g. circulation, are determined by three-dimensional CFD and then, GE-related parameters, e.g. gas core (GC) length, are calculated by using the Burgers vortex model. This procedure is efficient to evaluate the GE phenomena in the JSFR. However, it is well known that the Burgers vortex model tends to overestimate the GC length due to the lack of considerations on some physical mechanisms. Therefore, in this study, the authors develop a turbulent vortex model to evaluate the GE phenomena more accurately. Then, the improved GE evaluation method with the turbulent viscosity model is validated by analyzing the GC lengths observed in a simple experiment. The evaluation results show that the GC lengths analyzed by the improved method are shorter in comparison to the original method, and give better agreement with the experimental data.

  5. Mathematical model of gas plasma applied to chronic wounds

    NASA Astrophysics Data System (ADS)

    Wang, J. G.; Liu, X. Y.; Liu, D. W.; Lu, X. P.; Zhang, Y. T.

    2013-11-01

    Chronic wounds are a major burden for worldwide health care systems, and patients suffer pain and discomfort from this type of wound. Recently gas plasmas have been shown to safely speed chronic wounds healing. In this paper, we develop a deterministic mathematical model formulated by eight-species reaction-diffusion equations, and use it to analyze the plasma treatment process. The model follows spatial and temporal concentration within the wound of oxygen, chemoattractants, capillary sprouts, blood vessels, fibroblasts, extracellular matrix material, nitric oxide (NO), and inflammatory cell. Two effects of plasma, increasing NO concentration and reducing bacteria load, are considered in this model. The plasma treatment decreases the complete healing time from 25 days (normal wound healing) to 17 days, and the contributions of increasing NO concentration and reducing bacteria load are about 1/4 and 3/4, respectively. Increasing plasma treatment frequency from twice to three times per day accelerates healing process. Finally, the response of chronic wounds of different etiologies to treatment with gas plasmas is analyzed.

  6. Mathematical model of gas plasma applied to chronic wounds

    SciTech Connect

    Wang, J. G.; Liu, X. Y.; Liu, D. W.; Lu, X. P.; Zhang, Y. T.

    2013-11-15

    Chronic wounds are a major burden for worldwide health care systems, and patients suffer pain and discomfort from this type of wound. Recently gas plasmas have been shown to safely speed chronic wounds healing. In this paper, we develop a deterministic mathematical model formulated by eight-species reaction-diffusion equations, and use it to analyze the plasma treatment process. The model follows spatial and temporal concentration within the wound of oxygen, chemoattractants, capillary sprouts, blood vessels, fibroblasts, extracellular matrix material, nitric oxide (NO), and inflammatory cell. Two effects of plasma, increasing NO concentration and reducing bacteria load, are considered in this model. The plasma treatment decreases the complete healing time from 25 days (normal wound healing) to 17 days, and the contributions of increasing NO concentration and reducing bacteria load are about 1/4 and 3/4, respectively. Increasing plasma treatment frequency from twice to three times per day accelerates healing process. Finally, the response of chronic wounds of different etiologies to treatment with gas plasmas is analyzed.

  7. Modeling of Linear Gas Tungsten Arc Welding of Stainless Steel

    NASA Astrophysics Data System (ADS)

    Maran, P.; Sornakumar, T.; Sundararajan, T.

    2008-08-01

    A heat and fluid flow model has been developed to solve the gas tungsten arc (GTA) linear welding problem for austenitic stainless steel. The moving heat source problem associated with the electrode traverse has been simplified into an equivalent two-dimensional (2-D) transient problem. The torch residence time has been calculated from the arc diameter and torch speed. The mathematical formulation considers buoyancy, electromagnetic induction, and surface tension forces. The governing equations have been solved by the finite volume method. The temperature and velocity fields have been determined. The theoretical predictions for weld bead geometry are in good agreement with experimental measurements.

  8. CFD modeling of high temperature gas cooled reactors

    SciTech Connect

    Janse van Rensburg, J.J.; Viljoen, C.; Van Staden, M.P.

    2006-07-01

    This paper presents an overview of how CFD has been applied to model the gas flow and heat transfer within the PBMR (Pebble Bed Modular reactor) with the aim of providing valuable design and safety information. The thermo-hydraulic calculations are performed using the STAR-CD [1] Computational Fluid Dynamics (CFD) code and the neutronic calculations are performed using VSOP [2]. Results are presented for steady-state normal operation and for a transient De-pressurized Loss Of Forced Cooling event (DLOFC). (authors)

  9. Natural gas transmission and distribution model of the National Energy Modeling System

    SciTech Connect

    1997-02-01

    The Natural Gas Transmission and Distribution Model (NGTDM) is the component of the National Energy Modeling System (NEMS) that is used to represent the domestic natural gas transmission and distribution system. NEMS was developed in the Office of Integrated Analysis and Forecasting of the Energy Information Administration (EIA). NEMS is the third in a series of computer-based, midterm energy modeling systems used since 1974 by the EIA and its predecessor, the Federal Energy Administration, to analyze domestic energy-economy markets and develop projections. From 1982 through 1993, the Intermediate Future Forecasting System (IFFS) was used by the EIA for its analyses, and the Gas Analysis Modeling System (GAMS) was used within IFFS to represent natural gas markets. Prior to 1982, the Midterm Energy Forecasting System (MEFS), also referred to as the Project Independence Evaluation System (PIES), was employed. NEMS was developed to enhance and update EIA`s modeling capability by internally incorporating models of energy markets that had previously been analyzed off-line. In addition, greater structural detail in NEMS permits the analysis of a broader range of energy issues. The time horizon of NEMS is the midterm period (i.e., through 2015). In order to represent the regional differences in energy markets, the component models of NEMS function at regional levels appropriate for the markets represented, with subsequent aggregation/disaggregation to the Census Division level for reporting purposes.

  10. Modeling heating curve for gas hydrate dissociation in porous media.

    PubMed

    Dicharry, Christophe; Gayet, Pascal; Marion, Gérard; Graciaa, Alain; Nesterov, Anatoliy N

    2005-09-15

    A method for modeling the heating curve for gas hydrate dissociation in porous media at isochoric conditions (constant cell volume) is presented. This method consists of using an equation of state of the gas, the cumulative volume distribution (CVD) of the porous medium, and a van der Waals-Platteeuw-type thermodynamic model that includes a capillary term. The proposed method was tested to predict the heating curves for methane hydrate dissociation in a mesoporous silica glass for saturated conditions (liquid volume = pore volume) and for a fractional conversion of water to hydrate of 1 (100% of the available water was converted to hydrate). The shape factor (F) of the hydrate-water interface was found equal to 1, supporting a cylindrical shape for the hydrate particles during hydrate dissociation. Using F = 1, it has been possible to predict the heating curve for different ranges of pressure and temperature. The excellent agreement between the calculated and experimental heating curves supports the validity of our approach. PMID:16853195

  11. Steady state model of electrochemical gas sensors with multiple reactions

    SciTech Connect

    Brailsford, A.D.; Yussouff, M.; Logothetis, E.M.

    1996-12-31

    A general first-principles model of the steady state response of metal oxide gas sensors was developed by the authors and applied to the case of both electrochemical and resistive type oxygen sensors. It can describe many features of the experimentally observed response of commercial electrochemical zirconia sensors exposed to non-equilibrium gas mixtures consisting of O{sub 2} and one or more reducing species (CO, H{sub 2} , etc). However, the calculated sensor emf as a function of R`= 2p{sub O2}/P{sub CO} (or 2p{sub O2}/P{sub H2}) always showed a sharp transition from high to low values at some R` value and had a small value for R` >> 1. These results do not agree with the broad transitions and relatively high emf values for large R`, as observed experimentally at low temperatures. This paper discusses an extension of the model which is able to describe all aspects of the observed response.

  12. Phonon Gas Model (PGM) workflow in the VLab Science Gateway

    NASA Astrophysics Data System (ADS)

    da Silveira, P.; Zhang, D.; Wentzcovitch, R. M.

    2013-12-01

    This contribution describes a scientific workflow for first principles computations of free energy of crystalline solids using the phonon gas model (PGM). This model was recently implemented as a hybrid method combining molecular dynamics and phonon normal mode analysis to extract temperature dependent phonon frequencies and life times beyond perturbation theory. This is a demanding high throughout workflow and is currently being implemented in VLab Cyberinfrastructure [da Silveira et al., 2008], which has recently been integrated to the XSEDE. First we review the underlying PGM, its practical implementation, and calculation requirements. We then describe the workflow management and its general method for handling actions. We illustrate the PGM application with a calculation of MgSiO3-perovskite's anharmonic phonons. We conclude with an outlook of workflows to compute other material's properties that will use the PGM workflow. Research supported by NSF award EAR-1019853.

  13. Breakdown parameter for kinetic modeling of multiscale gas flows.

    PubMed

    Meng, Jianping; Dongari, Nishanth; Reese, Jason M; Zhang, Yonghao

    2014-06-01

    Multiscale methods built purely on the kinetic theory of gases provide information about the molecular velocity distribution function. It is therefore both important and feasible to establish new breakdown parameters for assessing the appropriateness of a fluid description at the continuum level by utilizing kinetic information rather than macroscopic flow quantities alone. We propose a new kinetic criterion to indirectly assess the errors introduced by a continuum-level description of the gas flow. The analysis, which includes numerical demonstrations, focuses on the validity of the Navier-Stokes-Fourier equations and corresponding kinetic models and reveals that the new criterion can consistently indicate the validity of continuum-level modeling in both low-speed and high-speed flows at different Knudsen numbers. PMID:25019910

  14. Modeling of Explosion Gas Dynamics with Account of Detonation

    NASA Astrophysics Data System (ADS)

    Morozov, D. O.

    2013-11-01

    The physical and hydrodynamic processes in the initial phase of explosion of condensed explosives in the air have been considered. The role of the processes of energy release connected with the explosive detonation has been analyzed. The equations of formal kinetics for modeling the processes of transformation of the original substance into detonation products have been described. The results obtained with the use of the equation of state of an ideal gas with a constant adiabatic index have been compared with calculations, where for the equation of state wide-range tables of properties of the air and explosion products were used. The stage of detonation of an explosive is included in the self-consistent hydrodynamic model used for describing the explosion processes from the moment of initiation of the detonation wave to the moment the air shock wave is formed, as well as in describing its propagation and attenuation.

  15. New Constraints on Gas and Gas Hydrate Estimates in the Bering Sea using an Automated Sediment Physics Modeling Approach

    NASA Astrophysics Data System (ADS)

    Wood, W. T.; Martin, K. M.; Barth, G. A.; Scholl, D. W.

    2015-12-01

    We have developed a technique to invert vertical sound speed profiles, like those obtained from reflection seismic data, for grain and pore fluid properties. We have applied this process to seismic data from the Bering Sea to better constrain gas and gas hydrate concentrations. The inversion is based on iterative forward modeling of the sediment constituents and pressure-temperature (PT) regime to match the observed sound speed profile. Inversion input can be either interval or stacking velocities, and we avoid the assumption that stacking velocities are the same as root mean square average velocities. We use a series of constituent sediment physics models whose inputs are mainly porosity, gas saturation, temperature, pressure, effective pressure and grain type (for calculation of effective elastic moduli). The value of this approach is that every model run in the forward algorithm is geologically consistent. Vast portions of model space are eliminated from searching because, e.g. gas hydrate cannot exist outside its PT stability zone. Of particular interest in the Bering Sea are large (~5 km wide) anomalies in seismic reflection profiles almost certainly associated with gas accumulation at the base of gas hydrate stability (BGHS). We applied the inversion across one of these anomalies using stacking velocities from finely discretized semblance scans of seismic common midpoint gathers. Preliminary results suggest that little or no gas or gas hydrate need be present in areas away from the anomaly, in order to match the observed velocity profile. Directly over the center of the anomaly, the significantly reduced velocity below the BGHS requires at least 1-2% gas saturation, and the mildly elevated velocity above the BGHS requires 5-15% gas hydrate saturation.

  16. Estimation of Trace Gas Fluxes by Inverse Modelling

    NASA Astrophysics Data System (ADS)

    Prinn, R. G.; Chen, Y.; Huang, J.; Golombek, A.

    2003-12-01

    A wide range of scientific questions regarding chemically and/or radiatively important trace gases necessitate determinations of their sources and sinks at local to global scales. A powerful method for such determinations involves solution of an inverse problem in which the observed concentrations are effectively Lagrangian line integrals and the unknown sources or sinks are contained in the integrands. The inverse problem consists of calculating optimal estimates of the unknowns in the Bayesian sense using an atmospheric transport model and trace gas measurements gathered over space and time. Great care is necessary to include the effects of both measurement and transport model errors in calculating the uncertainty in the optimal estimates. We review the results of recent studies which use three-dimensional Eulerian (specifically MATCH) or Lagrangian transport models and Kalman filter and other optimization methods to compute emissions of methane, nitrous oxide, and selected halocarbons. These studies use high frequency trace gas observations from global networks (AGAGE, CMDL) to calibrate a priori emission maps for particular processes and geographic regions. The methods allow estimation of time varying emissions. For the hydrogen-containing gases these emission estimates require accurate specification of the concentrations of the hydroxyl radical which constitute their major sink. Hydroxyl radical levels can be optimally estimated in a separate problem using measurements of methyl chloroform whose global emissions are already very well known. The results show that the inverse approach is a powerful complement to traditional surface flux aggregation methods. At the same time, the inverse approach has its own limitations associated especially with transport model errors and/or inadequate atmospheric measurements.

  17. BIODEGRADATION AND GAS-EXCHANGE OF GASEOUS ALKANES IN MODEL ESTUARINE ECOSYSTEMS

    EPA Science Inventory

    Gas exchange-biodegradation experiments conducted in model estuarine ecosystems indicate that the ease of degradation of gaseious normal alkanes increases with chain length. The behavior of gaseous perhalogenated alkanes can be explained by gas exchange alone with no degradation....

  18. Wound healing modeling: investigating ambient gas plasma treatment efficacy

    NASA Astrophysics Data System (ADS)

    Orazov, Marat; Sakiyama, Yukinori; Graves, David B.

    2012-11-01

    Chronic wounds are thought to be caused, in part, by the presence and persistence of aerobic microbes that deplete the local oxygen concentration and prevent or slow the rate of oxygen-dependent healing. Atmospheric-pressure gas plasmas have been shown to be strong bactericidal agents and there is evidence that plasma treatment can safely kill bacteria in wounds and speed wound healing. In this study, we adapted a six-species reaction-diffusion model of epithelial wound healing and used it to predict the efficacy of various plasma treatment protocols. We assume that the only effect of plasma application to the wound is to reduce the bacterial load and that this in turn reduces the bacterial oxygen consumption in the wound. The model follows the spatial and temporal concentration or density profiles within the wound of oxygen, chemoattractants, capillary sprouts, blood vessels, fibroblasts and extracellular matrix material. We highlight the importance of the effects of plasma application on the rate of bacterial regrowth in the wound. Even a relatively large initial reduction in the bacterial wound population may not be sufficient for improved healing if bacterial regrowth is not limited. Although it is clear that current efforts to model wound healing in general and the effects of plasma in particular are in their early stage, the present results suggest several important directions for coupling plasma models with models of tissue biochemical responses.

  19. Adapting a weather forecast model for greenhouse gas simulation

    NASA Astrophysics Data System (ADS)

    Polavarapu, S. M.; Neish, M.; Tanguay, M.; Girard, C.; de Grandpré, J.; Gravel, S.; Semeniuk, K.; Chan, D.

    2015-12-01

    The ability to simulate greenhouse gases on the global domain is useful for providing boundary conditions for regional flux inversions, as well as for providing reference data for bias correction of satellite measurements. Given the existence of operational weather and environmental prediction models and assimilation systems at Environment Canada, it makes sense to use these tools for greenhouse gas simulations. In this work, we describe the adaptations needed to reasonably simulate CO2 with a weather forecast model. The main challenges were the implementation of a mass conserving advection scheme, and the careful implementation of a mixing ratio defined with respect to dry air. The transport of tracers through convection was also added, and the vertical mixing through the boundary layer was slightly modified. With all these changes, the model conserves CO2 mass well on the annual time scale, and the high resolution (0.9 degree grid spacing) permits a good description of synoptic scale transport. The use of a coupled meteorological/tracer transport model also permits an assessment of approximations needed in offline transport model approaches, such as the neglect of water vapour mass when computing a tracer mixing ratio with respect to dry air.

  20. Greenhouse Gas Source Attribution: Measurements Modeling and Uncertainty Quantification

    SciTech Connect

    Liu, Zhen; Safta, Cosmin; Sargsyan, Khachik; Najm, Habib N.; van Bloemen Waanders, Bart Gustaaf; LaFranchi, Brian W.; Ivey, Mark D.; Schrader, Paul E.; Michelsen, Hope A.; Bambha, Ray P.

    2014-09-01

    In this project we have developed atmospheric measurement capabilities and a suite of atmospheric modeling and analysis tools that are well suited for verifying emissions of green- house gases (GHGs) on an urban-through-regional scale. We have for the first time applied the Community Multiscale Air Quality (CMAQ) model to simulate atmospheric CO2 . This will allow for the examination of regional-scale transport and distribution of CO2 along with air pollutants traditionally studied using CMAQ at relatively high spatial and temporal resolution with the goal of leveraging emissions verification efforts for both air quality and climate. We have developed a bias-enhanced Bayesian inference approach that can remedy the well-known problem of transport model errors in atmospheric CO2 inversions. We have tested the approach using data and model outputs from the TransCom3 global CO2 inversion comparison project. We have also performed two prototyping studies on inversion approaches in the generalized convection-diffusion context. One of these studies employed Polynomial Chaos Expansion to accelerate the evaluation of a regional transport model and enable efficient Markov Chain Monte Carlo sampling of the posterior for Bayesian inference. The other approach uses de- terministic inversion of a convection-diffusion-reaction system in the presence of uncertainty. These approaches should, in principle, be applicable to realistic atmospheric problems with moderate adaptation. We outline a regional greenhouse gas source inference system that integrates (1) two ap- proaches of atmospheric dispersion simulation and (2) a class of Bayesian inference and un- certainty quantification algorithms. We use two different and complementary approaches to simulate atmospheric dispersion. Specifically, we use a Eulerian chemical transport model CMAQ and a Lagrangian Particle Dispersion Model - FLEXPART-WRF. These two models share the same WRF

  1. Ammonia concentration modeling based on retained gas sampler data

    SciTech Connect

    Terrones, G.; Palmer, B.J.; Cuta, J.M.

    1997-09-01

    The vertical ammonia concentration distributions determined by the retained gas sampler (RGS) apparatus were modeled for double-shell tanks (DSTs) AW-101, AN-103, AN-104, and AN-105 and single-shell tanks (SSTs) A-101, S-106, and U-103. One the vertical transport of ammonia in the tanks were used for the modeling. Transport in the non-convective settled solids and floating solids layers is assumed to occur primarily via some type of diffusion process, while transport in the convective liquid layers is incorporated into the model via mass transfer coefficients based on empirical correlations. Mass transfer between the top of the waste and the tank headspace and the effects of ventilation of the headspace are also included in the models. The resulting models contain a large number of parameters, but many of them can be determined from known properties of the waste configuration or can be estimated within reasonable bounds from data on the waste samples themselves. The models are used to extract effective diffusion coefficients for transport in the nonconvective layers based on the measured values of ammonia from the RGS apparatus. The modeling indicates that the higher concentrations of ammonia seen in bubbles trapped inside the waste relative to the ammonia concentrations in the tank headspace can be explained by a combination of slow transport of ammonia via diffusion in the nonconvective layers and ventilation of the tank headspace by either passive or active means. Slow transport by diffusion causes a higher concentration of ammonia to build up deep within the waste until the concentration gradients between the interior and top of the waste are sufficient to allow ammonia to escape at the same rate at which it is being generated in the waste.

  2. Non-condensable gas in a Mars General Circulation Model

    NASA Astrophysics Data System (ADS)

    Guo, X.; Richardson, M. I.; Newman, C.; Sprague, A. L.; Boynton, W. V.

    2007-12-01

    We model the variation of non-condensable trace gases that results from the seasonal cycle of CO2 on Mars. A simple condensation scheme has been incorporated into MarsWRF, a 3-dimensional numerical model for the atmospheres of Mars. Non-condensable trace gas (mostly N2 and Ar) mass mixing ratios are affected by the phase change of CO2 and by transport. The distribution of Ar abundance has been observed by the Gamma Ray Spectrometer on the Mars 2001 Odyssey spacecraft. We are able to qualitatively reproduce the Ar observations, including the seasonal evolving latitudinal distribution. However, the modeled magnitudes of maximum enrichment are lower than observed. Smoothing Ar enrichment in the vertical reduces susceptibility to transport by near-surface, off-cap circulation, therefore gives further enhancement of non-condensable tracer in the winter pole. We suggest that a missing process in the model may account for the underestimation. An extra buoyancy term in the dynamics should result from the vertical gradient in mean molecular mass as Ar mass mixing ratio increases.

  3. Simulation of gas-assisted injection mold-cooling process using line source model approach for gas channel

    SciTech Connect

    Chang, Y.P.; Hu, S.Y.; Chen, S.C.

    1998-10-01

    Gas-assisted injection molding (GAIM) process, being an innovative injection molding process, can substantially reduce production expenses through reduction in material cost, reduction in clamp tonnage and reduction in cycle time. Whether it is feasible to perform an integrated simulation for process simulation based on a unified CAE model for gas-assisted injection molding (GAIM) is a great concern. In the present study, numerical algorithms based on the same CAE model used for process simulation regarding filling and packaging stages were developed to simulate the cooling phase of GAIM using a cycle-averaged three-dimensional modified boundary element technique similar to that used for conventional injection molding. However, to use the current CAE model for analysis, gas channel was modeled by two-node elements using line source approach. It was found that this new modeling not only affects the mold wall temperature calculation very slightly but also reduces the computer time by 95% as compared with a full gas channel modeling required a lot of triangular elements on gas channel surface. This investigation indicates that it is feasible to achieve an integrated process simulation for GAIM under one CAE model resulting in great computational efficiency for industrial application.

  4. Constraining Intracluster Gas Models with AMiBA13

    NASA Astrophysics Data System (ADS)

    Molnar, Sandor M.; Umetsu, Keiichi; Birkinshaw, Mark; Bryan, Greg; Haiman, Zoltán; Hearn, Nathan; Shang, Cien; Ho, Paul T. P.; Locutus Huang, Chih-Wei; Koch, Patrick M.; Liao, Yu-Wei Victor; Lin, Kai-Yang; Liu, Guo-Chin; Nishioka, Hiroaki; Wang, Fu-Cheng; Proty Wu, Jiun-Huei

    2010-11-01

    Clusters of galaxies have been extensively used to determine cosmological parameters. A major difficulty in making the best use of Sunyaev-Zel'dovich (SZ) and X-ray observations of clusters for cosmology is that using X-ray observations it is difficult to measure the temperature distribution and therefore determine the density distribution in individual clusters of galaxies out to the virial radius. Observations with the new generation of SZ instruments are a promising alternative approach. We use clusters of galaxies drawn from high-resolution adaptive mesh refinement cosmological simulations to study how well we should be able to constrain the large-scale distribution of the intracluster gas (ICG) in individual massive relaxed clusters using AMiBA in its configuration with 13 1.2 m diameter dishes (AMiBA13) along with X-ray observations. We show that non-isothermal β models provide a good description of the ICG in our simulated relaxed clusters. We use simulated X-ray observations to estimate the quality of constraints on the distribution of gas density, and simulated SZ visibilities (AMiBA13 observations) for constraints on the large-scale temperature distribution of the ICG. We find that AMiBA13 visibilities should constrain the scale radius of the temperature distribution to about 50% accuracy. We conclude that the upgraded AMiBA, AMiBA13, should be a powerful instrument to constrain the large-scale distribution of the ICG.

  5. CFD modeling of water spray interaction with dense gas plumes

    NASA Astrophysics Data System (ADS)

    Meroney, Robert N.

    2012-07-01

    Numerical calculations are performed to reproduce the transport and dispersion of the continuous release of dense gases over flat homogeneous surfaces with and without the mitigating influence of a downwind water curtain. Frequently such plumes are released as a result of a chemical manufacturing, storage or gas transportation accident resulting in a ground-level hazard due to gas flammability or toxicity. A field situation in which cold carbon dioxide was released upwind of water curtains (Moodie et al., 1981) was simulated using the open-source software FDS (Fire Dynamic Simulator) a full 3-d CFD model. Only water-spray enhancement of dispersion was considered; hence, no chemical removal or reactions were present or simulated. Wind-tunnel measurements for a 1:28.9 scale replication of the Moodie experiments are also compared with the 3-d CFD results. Concentration distributions, percent dilution and forced diffusion parameters were compared in scatter diagrams. Concentration field contours with and without active spray curtains are also presented.

  6. Models for grains and gas ejection dynamics from a silo

    NASA Astrophysics Data System (ADS)

    Zhou, Yixian; Aussillous, Pascale; Ruyer, Pierre; Iusti/Gep Team; Semia/Limar Team

    2015-11-01

    In the hypothetical conditions of a reactivity initiated accident in a nuclear power plant, some of the fuel rods could break. If fuel fragmentation occurs, hot fuel particles and pressurized gas could interact with the surrounding fluid. The violence of this interaction depends on the discharge rate toward the fluid. In the present work, we study the discharge dynamics and identify the parameters governing this flow. In this paper, we focus on the experimental study of the discharge of a silo composed of spherical glass beads, with an orifice either lateral or at the bottom, with or without air flow. The measured parameters are the mass flow rate and the pressure along the silo, whereas the controlled parameters are the size of particles, the size of orifices, and the flow rate of air. For the case without air flow we found that the flow rate of particles ejected from the bottom orifice is 3 times greater than from the lateral orifice. For the case of a lateral orifice, when the form of the orifice is rectangular with width W and height D, we identify two regimes which depend on the ratio of width to height W / D . For the case with air flow, we found that the flow rate increases with the air flow. A simple physical model is proposed to describe the grains and gas ejection.

  7. Modeling of Gas Production from Shale Reservoirs Considering Multiple Transport Mechanisms.

    PubMed

    Guo, Chaohua; Wei, Mingzhen; Liu, Hong

    2015-01-01

    Gas transport in unconventional shale strata is a multi-mechanism-coupling process that is different from the process observed in conventional reservoirs. In micro fractures which are inborn or induced by hydraulic stimulation, viscous flow dominates. And gas surface diffusion and gas desorption should be further considered in organic nano pores. Also, the Klinkenberg effect should be considered when dealing with the gas transport problem. In addition, following two factors can play significant roles under certain circumstances but have not received enough attention in previous models. During pressure depletion, gas viscosity will change with Knudsen number; and pore radius will increase when the adsorption gas desorbs from the pore wall. In this paper, a comprehensive mathematical model that incorporates all known mechanisms for simulating gas flow in shale strata is presented. The objective of this study was to provide a more accurate reservoir model for simulation based on the flow mechanisms in the pore scale and formation geometry. Complex mechanisms, including viscous flow, Knudsen diffusion, slip flow, and desorption, are optionally integrated into different continua in the model. Sensitivity analysis was conducted to evaluate the effect of different mechanisms on the gas production. The results showed that adsorption and gas viscosity change will have a great impact on gas production. Ignoring one of following scenarios, such as adsorption, gas permeability change, gas viscosity change, or pore radius change, will underestimate gas production. PMID:26657698

  8. Modeling of Gas Production from Shale Reservoirs Considering Multiple Transport Mechanisms

    PubMed Central

    Guo, Chaohua; Wei, Mingzhen; Liu, Hong

    2015-01-01

    Gas transport in unconventional shale strata is a multi-mechanism-coupling process that is different from the process observed in conventional reservoirs. In micro fractures which are inborn or induced by hydraulic stimulation, viscous flow dominates. And gas surface diffusion and gas desorption should be further considered in organic nano pores. Also, the Klinkenberg effect should be considered when dealing with the gas transport problem. In addition, following two factors can play significant roles under certain circumstances but have not received enough attention in previous models. During pressure depletion, gas viscosity will change with Knudsen number; and pore radius will increase when the adsorption gas desorbs from the pore wall. In this paper, a comprehensive mathematical model that incorporates all known mechanisms for simulating gas flow in shale strata is presented. The objective of this study was to provide a more accurate reservoir model for simulation based on the flow mechanisms in the pore scale and formation geometry. Complex mechanisms, including viscous flow, Knudsen diffusion, slip flow, and desorption, are optionally integrated into different continua in the model. Sensitivity analysis was conducted to evaluate the effect of different mechanisms on the gas production. The results showed that adsorption and gas viscosity change will have a great impact on gas production. Ignoring one of following scenarios, such as adsorption, gas permeability change, gas viscosity change, or pore radius change, will underestimate gas production. PMID:26657698

  9. Modeling of non-thermal plasma in flammable gas mixtures

    NASA Astrophysics Data System (ADS)

    Napartovich, A. P.; Kochetov, I. V.; Leonov, S. B.

    2008-07-01

    An idea of using plasma-assisted methods of fuel ignition is based on non-equilibrium generation of chemically active species that speed up the combustion process. It is believed that gain in energy consumed for combustion acceleration by plasmas is due to the non-equilibrium nature of discharge plasma, which allows radicals to be produced in an above-equilibrium amount. Evidently, the size of the effect is strongly dependent on the initial temperature, pressure, and composition of the mixture. Of particular interest is comparison between thermal ignition of a fuel-air mixture and non-thermal plasma initiation of the combustion. Mechanisms of thermal ignition in various fuel-air mixtures have been studied for years, and a number of different mechanisms are known providing an agreement with experiments at various conditions. The problem is -- how to conform thermal chemistry approach to essentially non-equilibrium plasma description. The electric discharge produces much above-equilibrium amounts of chemically active species: atoms, radicals and ions. The point is that despite excess concentrations of a number of species, total concentration of these species is far below concentrations of the initial gas mixture. Therefore, rate coefficients for reactions of these discharge produced species with other gas mixture components are well known quantities controlled by the translational temperature, which can be calculated from the energy balance equation taking into account numerous processes initiated by plasma. A numerical model was developed combining traditional approach of thermal combustion chemistry with advanced description of the plasma kinetics based on solution of electron Boltzmann equation. This approach allows us to describe self-consistently strongly non-equilibrium electric discharge in chemically unstable (ignited) gas. Equations of pseudo-one-dimensional gas dynamics were solved in parallel with a system of thermal chemistry equations, kinetic equations

  10. Gas Phase Model of Surface Reactions for N{2} Afterglows

    NASA Astrophysics Data System (ADS)

    Marković, V. Lj.; Petrović, Z. Lj.; Pejović, M. M.

    1996-07-01

    The adequacy of the homogeneous gas phase model as a representation of the surface losses of diffusing active particles in gas phase is studied. As an example the recent data obtained for the surface recombination coefficients are reanalyzed. The data were obtained by the application of the breakdown delay times which consists of the measurements of the breakdown delay times t_d as a function of the afterglow period tau. It was found that for the conditions of our experiment, the diffusion should not be neglected as the final results are significantly different when obtained by approximate gas phase representation and by exact numerical solution to the diffusion equation. While application of the gas phase effective coefficients to represent surface losses gives an error in the value of the recombination coefficient, it reproduces correctly other characteristics such as order of the process which can be obtained from simple fits to the experimental data. Dans cet article, nous étudions la validité du modèle approximatif représentant les pertes superficielles des particules actives qui diffusent de la phase gazeuse comme pertes dans la phase homogène du gaz. Les données actuelles du coefficient de recombination en surface sont utilisées par cette vérification . Les données experimentales sont obtenues en utilisant la technique qui consiste en la mesure du temps de retard du début de la décharge en fonction de la période de relaxation. Nous avons trouvé que, pour nos conditions expérimentales, la diffusion ne peut être négligée. Aussi, les résultats finals sont considérablement différents quand ils sont obtenus en utilisant le modèle approximatif par comparaison aves les résultats obtenus par la solution numérique exacte de l'équation de la diffusion. L'application des coefficients effectifs dans la phase gaseuse pour la présentation des pertes superficielles donne, pour les coefficients de la recombinaison, des valeurs qui diffèrent en

  11. Spatial concentration distribution model for short-range continuous gas leakage of small amount

    NASA Astrophysics Data System (ADS)

    Wang, Meirong; Wang, Lingxue; Li, Jiakun; Long, Yunting; Gao, Yue

    2012-06-01

    Passive infrared gas imaging systems have been utilized in the equipment leak detection and repair in chemical manufacturers and petroleum refineries. The detection performance mainly relates to the sensitivity of infrared detector, optical depth of gas, atmospheric transmission, wind speed, and so on. Based on our knowledge, the spatial concentration distribution of continuously leaking gas plays an important part in leak detection. Several computational model of gas diffusion were proposed by researchers, such as Gaussian model, BM model, Sutton model and FEM3 model. But these models focus on calculating a large scale gas concentration distribution for a great amount of gas leaks above over 100- meter height, and not applicable to assess detection limit of a gas imaging system in short range. In this paper, a wind tunnel experiment is designed. Under different leaking rate and wind speed, concentration in different spatial positions is measured by portable gas detectors. Through analyzing the experimental data, the two parameters σy(x) and σz (x) that determine the plume dispersion in Gaussian model are adjusted to produce the best curve fit to the gas concentration data. Then a concentration distribution model for small mount gas leakage in short range is established. Various gases, ethylene and methane are used to testify this model.

  12. Common features in phase-space networks of frustrated spin models and lattice-gas models

    NASA Astrophysics Data System (ADS)

    Wang, Feng; Peng, Yi; Han, Yilong

    2012-02-01

    We mapped the phase spaces of the following four models into networks: (1a) the Ising antiferromagnet on triangular lattice at the ground state and (1b) above the ground state, (2) the six-vertex model (i.e. square ice or spin ice), (3) 1D lattice gas and (4) 2D lattice gas. Their phase-space networks share some common features including the Gaussian degree distribution, the Gaussian spectral density, and the small-world properties. Models 1a, 2 and 3 with long-range correlations in real space exhibit fractal phase spaces, while models 1b and 4 with short-range correlations in real space exhibit non-fractal phase spaces. This result supports one of the untested assumptions in Tsallis's non-extensive statistics.

  13. Modeling of information flows in natural gas storage facility

    NASA Astrophysics Data System (ADS)

    Ranjbari, Leyla; Bahar, Arifah; Aziz, Zainal Abdul

    2013-09-01

    The paper considers the natural-gas storage valuation based on the information-based pricing framework of Brody-Hughston-Macrina (BHM). As opposed to many studies which the associated filtration is considered pre-specified, this work tries to construct the filtration in terms of the information provided to the market. The value of the storage is given by the sum of the discounted expectations of the cash flows under risk-neutral measure, conditional to the constructed filtration with the Brownian bridge noise term. In order to model the flow of information about the cash flows, we assume the existence of a fixed pricing kernel with liquid, homogenous and incomplete market without arbitrage.

  14. New models for success emerge for US natural gas industry

    SciTech Connect

    Addy, W.M. ); Hutchinson, R.A. )

    1994-11-14

    Very few companies in the US natural gas industry are confident in their ability to compete effectively in the brave new world of deregulation. Boston Consulting Group recently conducted an internal study to help the industry think about its future and identify models for success in this new environment. The authors examined the historical performance of 800 companies using several shareholder-value indicators, including cash-flow returns on investment, a measure of cash returns on cash invested that correlates closely to share price. Based on that review and discussions with investment managers and industry analysts, the authors were able to focus on a handful of companies that actually have thrived and created value against the difficult landscape of the past decade. Interviews with their senior executives provided important strategic and operational insights.

  15. Thermal barrier coating life modeling in aircraft gas turbine engines

    NASA Technical Reports Server (NTRS)

    Nissley, D. M.

    1995-01-01

    Analytical models useful for predicting ceramic thermal barrier coating (TBC) spalling life in aircraft gas turbine engines are presented. Electron beam-physical vapor deposited (EB-PVD) and plasma sprayed TBC systems are discussed. TBC spalling was attributed to a combination of mechanisms such as metal oxidation at the ceramic-metal interface, ceramic-metal interface stress concentrations at free surfaces due to dissimilar materials, ceramic-metal interface stresses caused by local radius of curvature and interface roughness, material properties and mechanical behavior, transient temperature gradients across the ceramic layer and component design features. TBC spalling life analytical models were developed based on observations of TBC failure modes and plausible failure theories. TBC failure was assumed to occur when the imposed stresses exceeded the material strength (at or near the ceramic-metal interface). TBC failure knowledge gaps caused by lack of experimental evidence and analytical understanding are noted. The analytical models are considered initial engineering approaches that capture observed TBC failure trends.

  16. Thermal barrier coating life modeling in aircraft gas turbine engines

    NASA Astrophysics Data System (ADS)

    Nissley, D. M.

    1997-03-01

    Analytical models for predicting ceramic thermal barrier coating (TBC) spalling life in aircraft gas tur-bine engines are presented. Electron beam/physical vapor-deposited and plasma-sprayed TBC systems are discussed. An overview of the following TBC spalling mechanisms is presented: (1) metal oxidation at the ceramic/metal interface, (2) ceramic/metal interface stresses caused by radius of curvature and inter-face roughness, (3) material properties and mechanical behavior, (4) component design features, (5) tem-perature gradients, (6) ceramic/metal interface stress singularities at edges and corners, and (7) object impact damage. Analytical models for TBC spalling life are proposed based on observations of TBC spall-ing and plausible failure theories. Spalling was assumed to occur when the imposed stresses exceed the material strength (at or near the ceramic/metal interface). Knowledge gaps caused by lack of experimen-tal evidence and analytical understanding of TBC failure are noted. The analytical models are considered initial engineering approaches that capture observed TBC spalling failure trends.

  17. System Modeling of Gas Engine Driven Heat Pump

    SciTech Connect

    Mahderekal, Isaac; Shen, Bo; Vineyard, Edward

    2012-01-01

    To improve the system performance of the GHP, modeling and experimental study has been made by using desiccant system in cooling operation (particularly in high humidity operations) and suction line waste heat recovery to augment heating capacity and efficiency. The performance of overall GHP system has been simulated by using ORNL Modulating Heat Pump Design Software, which is used to predict steady-state heating and cooling performance of variable-speed vapor compression air-to-air heat pumps for a wide range of operational variables. The modeling includes: (1) GHP cycle without any performance improvements (suction liquid heat exchange and heat recovery) as a baseline (both in cooling and heating mode), (2) the GHP cycle in cooling mode with desiccant system regenerated by waste heat from engine incorporated, (3) GHP cycle in heating mode with heat recovery (recovered heat from engine). According to the system modeling results, by using desiccant system regenerated by waste heat from engine, the SHR can be lowered to 40%. The waste heat of the gas engine can boost the space heating efficiency by 25% in rated operating conditions.

  18. Hierarchical framework for coupling a biogeochemical trace gas model to a general circulation model

    SciTech Connect

    Miller, N.L.; Foster, I.T.

    1994-04-01

    A scheme is described for the computation of terrestrial biogeochemical trace gas fluxes in the context of a general circulation model. This hierarchical system flux scheme (HSFS) incorporates five major components: (1) a general circulation model (GCM), which provides a medium-resolution (i.e., 1{degrees} by 1{degrees}) simulation of the atmospheric circulation; (2) a procedure for identifying regions of defined homogeneity of surface type within GCM grid cells; (3) a set of surface process models, to be run within each homogeneous region, which include a biophysical model, the Biosphere Atmospheric Transfer Scheme (BATS), and a biogeochemical model (BGCM); (4) an interpolation/integration system that transfers information between the GCM and surface process models with finer resolution; and (5) an interactive data array based on a geographic information system (GIS), which provides land characteristic information via the interpolator. The goals of this detailed investigation are to compute the local and global sensitivities of trace gas fluxes to GCM and BATS variables, the effects of trace gas fluxes on global climate, and the effects of global climate on specific biomes.

  19. Modeling Grade IV Gas Emboli using a Limited Failure Population Model with Random Effects

    NASA Technical Reports Server (NTRS)

    Thompson, Laura A.; Conkin, Johnny; Chhikara, Raj S.; Powell, Michael R.

    2002-01-01

    Venous gas emboli (VGE) (gas bubbles in venous blood) are associated with an increased risk of decompression sickness (DCS) in hypobaric environments. A high grade of VGE can be a precursor to serious DCS. In this paper, we model time to Grade IV VGE considering a subset of individuals assumed to be immune from experiencing VGE. Our data contain monitoring test results from subjects undergoing up to 13 denitrogenation test procedures prior to exposure to a hypobaric environment. The onset time of Grade IV VGE is recorded as contained within certain time intervals. We fit a parametric (lognormal) mixture survival model to the interval-and right-censored data to account for the possibility of a subset of "cured" individuals who are immune to the event. Our model contains random subject effects to account for correlations between repeated measurements on a single individual. Model assessments and cross-validation indicate that this limited failure population mixture model is an improvement over a model that does not account for the potential of a fraction of cured individuals. We also evaluated some alternative mixture models. Predictions from the best fitted mixture model indicate that the actual process is reasonably approximated by a limited failure population model.

  20. Development of a natural gas systems analysis model (GSAM)

    SciTech Connect

    1999-10-01

    This report provides an overview of the activities to date and schedule for future testing, validation, and authorized enhancements of Natural Gas Systems Analysis Model (GSAM). The goal of this report is to inform DOE managers of progress in model development and to provide a benchmark for ongoing and future research. Section II of the report provides a detailed discussion on the major GSAM development programs performed and completed during the period of performance, July 1, 1998 to September 30, 1999. Key improvements in the new GSAM version are summarized in Section III. Programmer's guides for GSAM main modules were produced to provide detailed descriptions of all major subroutines and main variables of the computer code. General logical flowcharts of the subroutines are also presented in the guides to provide overall picture of interactions between the subroutines. A standard structure of routine explanation is applied in every programmer's guide. The explanation is started with a brief description or main purpose of the routine, lists of input and output files read and created, and lists of invoked/child and calling/parent routines. In some of the guides, interactions between the routine itself and its parent and child routines are presented in the form of graphical flowchart. The explanation is then proceeded with step by step description of computer code in the subroutine where each step delegates a section of related code. Between steps, if a certain section of code needs further explanation, a Note is inserted with relevant explanation.

  1. Polyakov loop and the hadron resonance gas model.

    PubMed

    Megías, E; Arriola, E Ruiz; Salcedo, L L

    2012-10-12

    The Polyakov loop has been used repeatedly as an order parameter in the deconfinement phase transition in QCD. We argue that, in the confined phase, its expectation value can be represented in terms of hadronic states, similarly to the hadron resonance gas model for the pressure. Specifically, L(T)≈1/2[∑(α)g(α)e(-Δ(α)/T), where g(α) are the degeneracies and Δ(α) are the masses of hadrons with exactly one heavy quark (the mass of the heavy quark itself being subtracted). We show that this approximate sum rule gives a fair description of available lattice data with N(f)=2+1 for temperatures in the range 150 MeVmodels. For temperatures below 150 MeV different lattice results disagree. One set of data can be described if exotic hadrons are present in the QCD spectrum while other sets do not require such states. PMID:23102292

  2. Computational fluid dynamics modeling of gas dispersion in multi impeller bioreactor.

    PubMed

    Ahmed, Syed Ubaid; Ranganathan, Panneerselvam; Pandey, Ashok; Sivaraman, Savithri

    2010-06-01

    In the present study, experiments have been carried out to identify various flow regimes in a dual Rushton turbines stirred bioreactor for different gas flow rates and impeller speeds. The hydrodynamic parameters like fractional gas hold-up, power consumption and mixing time have been measured. A two fluid model along with MUSIG model to handle polydispersed gas flow has been implemented to predict the various flow regimes and hydrodynamic parameters in the dual turbines stirred bioreactor. The computational model has been mapped on commercial solver ANSYS CFX. The flow regimes predicted by numerical simulations are validated with the experimental results. The present model has successfully captured the flow regimes as observed during experiments. The measured gross flow characteristics like fractional gas hold-up, and mixing time have been compared with numerical simulations. Also the effect of gas flow rate and impeller speed on gas hold-up and power consumption have been investigated. PMID:20471599

  3. Formation of natural gas hydrates in marine sediments 1. Conceptual model of gas hydrate growth conditioned by host sediment properties

    USGS Publications Warehouse

    Clennell, M.B.; Hovland, M.; Booth, J.S.; Henry, P.; Winters, W.J.

    1999-01-01

    The stability of submarine gas hydrates is largely dictated by pressure and temperature, gas composition, and pore water salinity. However, the physical properties and surface chemistry of deep marine sediments may also affect the thermodynamic state, growth kinetics, spatial distributions, and growth forms of clathrates. Our conceptual model presumes that gas hydrate behaves in a way analogous to ice in a freezing soil. Hydrate growth is inhibited within fine-grained sediments by a combination of reduced pore water activity in the vicinity of hydrophilic mineral surfaces, and the excess internal energy of small crystals confined in pores. The excess energy can be thought of as a "capillary pressure" in the hydrate crystal, related to the pore size distribution and the state of stress in the sediment framework. The base of gas hydrate stability in a sequence of fine sediments is predicted by our model to occur at a lower temperature (nearer to the seabed) than would be calculated from bulk thermodynamic equilibrium. Capillary effects or a build up of salt in the system can expand the phase boundary between hydrate and free gas into a divariant field extending over a finite depth range dictated by total methane content and pore-size distribution. Hysteresis between the temperatures of crystallization and dissociation of the clathrate is also predicted. Growth forms commonly observed in hydrate samples recovered from marine sediments (nodules, and lenses in muds; cements in sands) can largely be explained by capillary effects, but kinetics of nucleation and growth are also important. The formation of concentrated gas hydrates in a partially closed system with respect to material transport, or where gas can flush through the system, may lead to water depletion in the host sediment. This "freeze-drying" may be detectable through physical changes to the sediment (low water content and overconsolidation) and/or chemical anomalies in the pore waters and metastable

  4. A SIMPLE PHYSICAL MODEL FOR THE GAS DISTRIBUTION IN GALAXY CLUSTERS

    SciTech Connect

    Patej, Anna; Loeb, Abraham

    2015-01-01

    The dominant baryonic component of galaxy clusters is hot gas whose distribution is commonly probed through X-ray emission arising from thermal bremsstrahlung. The density profile thus obtained has been traditionally modeled with a β-profile, a simple function with only three parameters. However, this model is known to be insufficient for characterizing the range of cluster gas distributions and attempts to rectify this shortcoming typically introduce additional parameters to increase the fitting flexibility. We use cosmological and physical considerations to obtain a family of profiles for the gas with fewer parameters than the β-model but which better accounts for observed gas profiles over wide radial intervals.

  5. Ammonia quantitative analysis model based on miniaturized Al ionization gas sensor and non-linear bistable dynamic model.

    PubMed

    Ma, Rongfei

    2015-01-01

    In this paper, ammonia quantitative analysis based on miniaturized Al ionization gas sensor and non-linear bistable dynamic model was proposed. Al plate anodic gas-ionization sensor was used to obtain the current-voltage (I-V) data. Measurement data was processed by non-linear bistable dynamics model. Results showed that the proposed method quantitatively determined ammonia concentrations. PMID:25975362

  6. Calculating soil gas fluxes from gas concentration profiles: can we use standard DS models or should we use site-specific DS models?

    NASA Astrophysics Data System (ADS)

    Paulus, Sinikka; Jochheim, Hubert; Wirth, Stephan; Maier, Martin

    2015-04-01

    The apparent gas diffusion coefficient in soil (DS) is an important parameter describing soil aeration. It also links the profiles of soil gas concentration and soil gas flux using Fick's law. Soil gas diffusivity depends mainly on the structure of the pore system and the soil moisture status. There are several standard DS-models available that can easily be used for calculating DS. Another, more laborious option is to calibrate site specific DS models on soil core samples from the respective profile. We tested 4 standard DS models and a site-specific model and compared the resulting soil gas fluxes in two forest soils. Differences between the models were substantial. Another very important effect, however, is that standard DS models are usually derived from a single soil moisture measurement (device), that can result in an substantial offset in soil moisture estimation. The mean soil moisture content at a depth can be addressed more accurately by taking several soil cores. As a consequence, using standard DS models in combination with a single soil moisture measurement is less reliable than using site-specific models based on several soil samples.

  7. Leakage detection of Marcellus Shale natural gas at an Upper Devonian gas monitoring well: a 3-d numerical modeling approach.

    PubMed

    Zhang, Liwei; Anderson, Nicole; Dilmore, Robert; Soeder, Daniel J; Bromhal, Grant

    2014-09-16

    Potential natural gas leakage into shallow, overlying formations and aquifers from Marcellus Shale gas drilling operations is a public concern. However, before natural gas could reach underground sources of drinking water (USDW), it must pass through several geologic formations. Tracer and pressure monitoring in formations overlying the Marcellus could help detect natural gas leakage at hydraulic fracturing sites before it reaches USDW. In this study, a numerical simulation code (TOUGH 2) was used to investigate the potential for detecting leaking natural gas in such an overlying geologic formation. The modeled zone was based on a gas field in Greene County, Pennsylvania, undergoing production activities. The model assumed, hypothetically, that methane (CH4), the primary component of natural gas, with some tracer, was leaking around an existing well between the Marcellus Shale and the shallower and lower-pressure Bradford Formation. The leaky well was located 170 m away from a monitoring well, in the Bradford Formation. A simulation study was performed to determine how quickly the tracer monitoring could detect a leak of a known size. Using some typical parameters for the Bradford Formation, model results showed that a detectable tracer volume fraction of 2.0 × 10(-15) would be noted at the monitoring well in 9.8 years. The most rapid detection of tracer for the leak rates simulated was 81 days, but this scenario required that the leakage release point was at the same depth as the perforation zone of the monitoring well and the zones above and below the perforation zone had low permeability, which created a preferred tracer migration pathway along the perforation zone. Sensitivity analysis indicated that the time needed to detect CH4 leakage at the monitoring well was very sensitive to changes in the thickness of the high-permeability zone, CH4 leaking rate, and production rate of the monitoring well. PMID:25144442

  8. Rarefied gas flow simulations using high-order gas-kinetic unified algorithms for Boltzmann model equations

    NASA Astrophysics Data System (ADS)

    Li, Zhi-Hui; Peng, Ao-Ping; Zhang, Han-Xin; Yang, Jaw-Yen

    2015-04-01

    This article reviews rarefied gas flow computations based on nonlinear model Boltzmann equations using deterministic high-order gas-kinetic unified algorithms (GKUA) in phase space. The nonlinear Boltzmann model equations considered include the BGK model, the Shakhov model, the Ellipsoidal Statistical model and the Morse model. Several high-order gas-kinetic unified algorithms, which combine the discrete velocity ordinate method in velocity space and the compact high-order finite-difference schemes in physical space, are developed. The parallel strategies implemented with the accompanying algorithms are of equal importance. Accurate computations of rarefied gas flow problems using various kinetic models over wide ranges of Mach numbers 1.2-20 and Knudsen numbers 0.0001-5 are reported. The effects of different high resolution schemes on the flow resolution under the same discrete velocity ordinate method are studied. A conservative discrete velocity ordinate method to ensure the kinetic compatibility condition is also implemented. The present algorithms are tested for the one-dimensional unsteady shock-tube problems with various Knudsen numbers, the steady normal shock wave structures for different Mach numbers, the two-dimensional flows past a circular cylinder and a NACA 0012 airfoil to verify the present methodology and to simulate gas transport phenomena covering various flow regimes. Illustrations of large scale parallel computations of three-dimensional hypersonic rarefied flows over the reusable sphere-cone satellite and the re-entry spacecraft using almost the largest computer systems available in China are also reported. The present computed results are compared with the theoretical prediction from gas dynamics, related DSMC results, slip N-S solutions and experimental data, and good agreement can be found. The numerical experience indicates that although the direct model Boltzmann equation solver in phase space can be computationally expensive

  9. Model operating permits for natural gas processing plants

    SciTech Connect

    Arend, C.

    1995-12-31

    Major sources as defined in Title V of the Clean Air Act Amendments of 1990 that are required to submit an operating permit application will need to: Evaluate their compliance status; Determine a strategic method of presenting the general and specific conditions of their Model Operating Permit (MOP); Maintain compliance with air quality regulations. A MOP is prepared to assist permitting agencies and affected facilities in the development of operating permits for a specific source category. This paper includes a brief discussion of example permit conditions that may be applicable to various types of Title V sources. A MOP for a generic natural gas processing plant is provided as an example. The MOP should include a general description of the production process and identify emission sources. The two primary elements that comprise a MOP are: Provisions of all existing state and/or local air permits; Identification of general and specific conditions for the Title V permit. The general provisions will include overall compliance with all Clean Air Act Titles. The specific provisions include monitoring, record keeping, and reporting. Although Title V MOPs are prepared on a case-by-case basis, this paper will provide a general guideline of the requirements for preparation of a MOP. Regulatory agencies have indicated that a MOP included in the Title V application will assist in preparation of the final permit provisions, minimize delays in securing a permit, and provide support during the public notification process.

  10. Numerical modeling of the interaction between an electric arc and a turbulent gas flow - A turbulence model

    NASA Astrophysics Data System (ADS)

    Artemov, V. I.; Sinkevich, O. A.

    1986-02-01

    A semiempirical turbulence model describing the interaction between an electric arc and a turbulent gas flow is proposed which is based on the closure of the balance equations of second-order moments. The model accounts for the effect of gas density and electrodynamic parameter fluctuations. Based on the model proposed here, an algorithm is developed for calculating turbulent plasma flows in channels with complex boundary conditions, such as injection and suction. The efficiency of the model is verified experimentally.