Mechanical disequilibria in two-phase flow models: approaches by relaxation and by a reduced model
International Nuclear Information System (INIS)
Labois, M.
2008-10-01
This thesis deals with hyperbolic models for the simulation of compressible two-phase flows, to find alternatives to the classical bi-fluid model. We first establish a hierarchy of two-phase flow models, obtained according to equilibrium hypothesis between the physical variables of each phase. The use of Chapman-Enskog expansions enables us to link the different existing models to each other. Moreover, models that take into account small physical unbalances are obtained by means of expansion to the order one. The second part of this thesis focuses on the simulation of flows featuring velocity unbalances and pressure balances, in two different ways. First, a two-velocity two-pressure model is used, where non-instantaneous velocity and pressure relaxations are applied so that a balancing of these variables is obtained. A new one-velocity one-pressure dissipative model is then proposed, where the arising of second-order terms enables us to take into account unbalances between the phase velocities. We develop a numerical method based on a fractional step approach for this model. (author)
Relaxed states with plasma flow
International Nuclear Information System (INIS)
Avinash, K.; Taylor, J.B.
1991-01-01
In the theory of relaxation, a turbulent plasma reaches a state of minimum energy subject to constant magnetic helicity. In this state the plasma velocity is zero. Attempts have been made by introducing a number of different constraints, to obtain relaxed states with plasma flow. It is shown that these alternative constraints depend on two self-helicities, one for ions, and one for electrons. However, whereas there are strong arguments for the effective invariance of the original magnetic-helicity, these arguments do not apply to the self-helicities. Consequently the existence of relaxed states with flow remains in doubt. (author)
Multi-region relaxed Hall magnetohydrodynamics with flow
Energy Technology Data Exchange (ETDEWEB)
Lingam, Manasvi, E-mail: mlingam@princeton.edu [Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544 (United States); Abdelhamid, Hamdi M., E-mail: hamdi@ppl.k.u-tokyo.ac.jp [Graduate School of Frontier Sciences, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Physics Department, Faculty of Science, Mansoura University, Mansoura 35516 (Egypt); Hudson, Stuart R., E-mail: shudson@pppl.gov [Princeton Plasma Physics Laboratory, PO Box 451, Princeton, New Jersey 08543 (United States)
2016-08-15
The recent formulations of multi-region relaxed magnetohydrodynamics (MRxMHD) have generalized the famous Woltjer-Taylor states by incorporating a collection of “ideal barriers” that prevent global relaxation and flow. In this paper, we generalize MRxMHD with flow to include Hall effects, and thereby obtain the partially relaxed counterparts of the famous double Beltrami states as a special subset. The physical and mathematical consequences arising from the introduction of the Hall term are also presented. We demonstrate that our results (in the ideal MHD limit) constitute an important subset of ideal MHD equilibria, and we compare our approach against other variational principles proposed for deriving the partially relaxed states.
Multi-region relaxed magnetohydrodynamics with flow
Energy Technology Data Exchange (ETDEWEB)
Dennis, G. R., E-mail: graham.dennis@anu.edu.au; Dewar, R. L.; Hole, M. J. [Research School of Physics and Engineering, Australian National University, ACT 0200 (Australia); Hudson, S. R. [Princeton Plasma Physics Laboratory, PO Box 451, Princeton, New Jersey 08543 (United States)
2014-04-15
We present an extension of the multi-region relaxed magnetohydrodynamics (MRxMHD) equilibrium model that includes plasma flow. This new model is a generalization of Woltjer's model of relaxed magnetohydrodynamics equilibria with flow. We prove that as the number of plasma regions becomes infinite, our extension of MRxMHD reduces to ideal MHD with flow. We also prove that some solutions to MRxMHD with flow are not time-independent in the laboratory frame, and instead have 3D structure which rotates in the toroidal direction with fixed angular velocity. This capability gives MRxMHD potential application to describing rotating 3D MHD structures such as 'snakes' and long-lived modes.
Energy Technology Data Exchange (ETDEWEB)
Labois, M
2008-10-15
This thesis deals with hyperbolic models for the simulation of compressible two-phase flows, to find alternatives to the classical bi-fluid model. We first establish a hierarchy of two-phase flow models, obtained according to equilibrium hypothesis between the physical variables of each phase. The use of Chapman-Enskog expansions enables us to link the different existing models to each other. Moreover, models that take into account small physical unbalances are obtained by means of expansion to the order one. The second part of this thesis focuses on the simulation of flows featuring velocity unbalances and pressure balances, in two different ways. First, a two-velocity two-pressure model is used, where non-instantaneous velocity and pressure relaxations are applied so that a balancing of these variables is obtained. A new one-velocity one-pressure dissipative model is then proposed, where the arising of second-order terms enables us to take into account unbalances between the phase velocities. We develop a numerical method based on a fractional step approach for this model. (author)
State resolved vibrational relaxation modeling for strongly nonequilibrium flows
Boyd, Iain D.; Josyula, Eswar
2011-05-01
Vibrational relaxation is an important physical process in hypersonic flows. Activation of the vibrational mode affects the fundamental thermodynamic properties and finite rate relaxation can reduce the degree of dissociation of a gas. Low fidelity models of vibrational activation employ a relaxation time to capture the process at a macroscopic level. High fidelity, state-resolved models have been developed for use in continuum gas dynamics simulations based on computational fluid dynamics (CFD). By comparison, such models are not as common for use with the direct simulation Monte Carlo (DSMC) method. In this study, a high fidelity, state-resolved vibrational relaxation model is developed for the DSMC technique. The model is based on the forced harmonic oscillator approach in which multi-quantum transitions may become dominant at high temperature. Results obtained for integrated rate coefficients from the DSMC model are consistent with the corresponding CFD model. Comparison of relaxation results obtained with the high-fidelity DSMC model shows significantly less excitation of upper vibrational levels in comparison to the standard, lower fidelity DSMC vibrational relaxation model. Application of the new DSMC model to a Mach 7 normal shock wave in carbon monoxide provides better agreement with experimental measurements than the standard DSMC relaxation model.
Directory of Open Access Journals (Sweden)
Makswell Seyiti Kawashima
2015-01-01
Full Text Available En este artículo nosotros exploramos una formulación de flujo multiproductos para el Problema del Agente Viajero Asimétrico (ATSP en la obtención de cotas duales de este problema. El procedimiento empleado es una variante del método relax and cut propuesto en la literatura que computa los multiplicadores lagrangianos asociados a las restricciones de eliminación de subrutas preservando la optimalidad de los multiplicadores asociados a las restricciones de asignación. Los resultados obtenidos con la experimentación computacional son alentadores y muestran que el algoritmo propuesto genera buenas cotas duales con un tiempo de ejecución bajo.
Stability and suppression of turbulence in relaxing molecular gas flows
Grigoryev, Yurii N
2017-01-01
This book presents an in-depth systematic investigation of a dissipative effect which manifests itself as the growth of hydrodynamic stability and suppression of turbulence in relaxing molecular gas flows. The work describes the theoretical foundations of a new way to control stability and laminar turbulent transitions in aerodynamic flows. It develops hydrodynamic models for describing thermal nonequilibrium gas flows which allow the consideration of suppression of inviscid acoustic waves in 2D shear flows. Then, nonlinear evolution of large-scale vortices and Kelvin-Helmholtz waves in relaxing shear flows are studied. Critical Reynolds numbers in supersonic Couette flows are calculated analytically and numerically within the framework of both linear and nonlinear classical energy hydrodynamic stability theories. The calculations clearly show that the relaxation process can appreciably delay the laminar-turbulent transition. The aim of the book is to show the new dissipative effect, which can be used for flo...
Stability investigations of relaxing molecular gas flows. Results and perspectives
Grigor'ev, Yurii N.; Ershov, Igor V.
2017-10-01
This article presents results of systematic investigations of a dissipative effect which manifests itself as the growth of hydrodynamic stability and suppression of turbulence in relaxing molecular gas flows. The effect can be a new way for control stability and laminar turbulent transition in aerodynamic flows. The consideration of suppression of inviscid acoustic waves in 2D shear flows is presented. Nonlinear evolution of large-scale vortices and Kelvin — Helmholtz waves in relaxing shear flows are studied. Critical Reynolds numbers in supersonic Couette flows are calculated analytically and numerically within the framework of both classical linear and nonlinear energy hydrodynamic stability theories. The calculations clearly show that the relaxation process can appreciably delay the laminar-turbulent transition. The aim of this article is to show the new dissipative effect, which can be used for flow control and laminarization.
Multi-region relaxed magnetohydrodynamics with anisotropy and flow
Energy Technology Data Exchange (ETDEWEB)
Dennis, G. R., E-mail: graham.dennis@anu.edu.au; Dewar, R. L.; Hole, M. J. [Research School of Physics and Engineering, Australian National University, Canberra, Australian Capital Territory 0200 (Australia); Hudson, S. R. [Princeton Plasma Physics Laboratory, PO Box 451, Princeton, New Jersey 08543 (United States)
2014-07-15
We present an extension of the multi-region relaxed magnetohydrodynamics (MRxMHD) equilibrium model that includes pressure anisotropy and general plasma flows. This anisotropic extension to our previous isotropic model is motivated by Sun and Finn's model of relaxed anisotropic magnetohydrodynamic equilibria. We prove that as the number of plasma regions becomes infinite, our anisotropic extension of MRxMHD reduces to anisotropic ideal MHD with flow. The continuously nested flux surface limit of our MRxMHD model is the first variational principle for anisotropic plasma equilibria with general flow fields.
Generalized approach to non-exponential relaxation
Indian Academy of Sciences (India)
Non-exponential relaxation is a universal feature of systems as diverse as glasses, spin ... which changes from a simple exponential to a stretched exponential and a power law by increasing the constraints in the system. ... Current Issue
DEFF Research Database (Denmark)
Ding, Tao; Li, Cheng; Yang, Yongheng
2017-01-01
The detailed topology of renewable resource bases may have the impact on the optimal power flow of the VSC-HVDC transmission network. To address this issue, this paper develops an optimal power flow with the hybrid VSC-HVDC transmission and active distribution networks to optimally schedule...... the generation output and voltage regulation of both networks, which leads to a non-convex programming model. Furthermore, the non-convex power flow equations are based on the Second Order Cone Programming (SOCP) relaxation approach. Thus, the proposed model can be relaxed to a SOCP that can be tractably solved...
Relaxed impact craters on Ganymede: Regional variation and high heat flows
Singer, Kelsi N.; Bland, Michael T.; Schenk, Paul M.; McKinnon, William B.
2018-05-01
Viscously relaxed craters provide a window into the thermal history of Ganymede, a satellite with copious geologic signs of past high heat flows. Here we present measurements of relaxed craters in four regions for which suitable imaging exists: near Anshar Sulcus, Tiamat Sulcus, northern Marius Regio, and Ganymede's south pole. We describe a technique to measure apparent depth, or depth of the crater with respect to the surrounding terrain elevation. Measured relaxation states are compared with results from finite element modeling to constrain heat flow scenarios [see companion paper: Bland et al. (2017)]. The presence of numerous, substantially relaxed craters indicates high heat flows-in excess of 30-40 mW m-2 over 2 Gyr, with many small (heat flows. Crater relaxation states are bimodal for some equatorial regions but not in the region studied near the south pole, which suggests regional variations in Ganymede's thermal history.
Relaxed impact craters on Ganymede: Regional variation and high heat flows
Singer, Kelsi N.; Bland, Michael T.; Schenk, Paul M.; McKinnon, William B.
2018-01-01
Viscously relaxed craters provide a window into the thermal history of Ganymede, a satellite with copious geologic signs of past high heat flows. Here we present measurements of relaxed craters in four regions for which suitable imaging exists: near Anshar Sulcus, Tiamat Sulcus, northern Marius Regio, and Ganymede's south pole. We describe a technique to measure apparent depth, or depth of the crater with respect to the surrounding terrain elevation. Measured relaxation states are compared with results from finite element modeling to constrain heat flow scenarios [see companion paper: Bland et al. (2017)]. The presence of numerous, substantially relaxed craters indicates high heat flows—in excess of 30–40 mW m−2 over 2 Gyr, with many small (heat flows. Crater relaxation states are bimodal for some equatorial regions but not in the region studied near the south pole, which suggests regional variations in Ganymede's thermal history.
Efficient relaxations for joint chance constrained AC optimal power flow
Energy Technology Data Exchange (ETDEWEB)
Baker, Kyri; Toomey, Bridget
2017-07-01
Evolving power systems with increasing levels of stochasticity call for a need to solve optimal power flow problems with large quantities of random variables. Weather forecasts, electricity prices, and shifting load patterns introduce higher levels of uncertainty and can yield optimization problems that are difficult to solve in an efficient manner. Solution methods for single chance constraints in optimal power flow problems have been considered in the literature, ensuring single constraints are satisfied with a prescribed probability; however, joint chance constraints, ensuring multiple constraints are simultaneously satisfied, have predominantly been solved via scenario-based approaches or by utilizing Boole's inequality as an upper bound. In this paper, joint chance constraints are used to solve an AC optimal power flow problem while preventing overvoltages in distribution grids under high penetrations of photovoltaic systems. A tighter version of Boole's inequality is derived and used to provide a new upper bound on the joint chance constraint, and simulation results are shown demonstrating the benefit of the proposed upper bound. The new framework allows for a less conservative and more computationally efficient solution to considering joint chance constraints, specifically regarding preventing overvoltages.
A computational study of inviscid hypersonic flows using energy relaxation method
International Nuclear Information System (INIS)
Nagdewe, Suryakant; Kim, H. D.; Shevare, G. R.
2008-01-01
Reasonable analysis of hypersonic flows requires a thermodynamic non-equilibrium model to properly simulate strong shock waves or high pressure and temperature states in the flow field. The energy relaxation method (ERM) has been used to model such a non-equilibrium effect which is generally expressed as a hyperbolic system of equations with a stiff relaxation source term. Relaxation time that is multiplied with source terms is responsible for nonequilibrium in the system. In the present study, a numerical analysis has been carried out with varying values of relaxation time for several hypersonic flows with AUSM (advection upstream splitting method) as a numerical scheme. Vibration modes of thermodynamic nonequilibrium effects are considered. The results obtained showed that, as the relaxation time reduces to zero, the solution marches toward equilibrium, while it shows non-equilibrium effects, as the relaxation time increases. The present computations predicted the experiment results of hypersonic flows with good accuracy. The work carried out suggests that the present energy relaxation method can be robust for analysis of hypersonic flows
Comparison of Vibrational Relaxation Modeling for Strongly Non-Equilibrium Flows
2014-01-01
important pro- cess in a wide range of high speed flows. High temperature shock layers that form in front of hypersonic vehicles can lead to significant...continuum flows for use in traditional Computational Fluid Dynamics ( CFD ) and non-continuum flows for use with rarefied flow de- scriptions, such as the...145 .98 4396 V. Summary and Conclusions The form of two vibrational relaxation models that are commonly used in DSMC and CFD simula- tions have been
Flux-split algorithms for flows with non-equilibrium chemistry and vibrational relaxation
Grossman, B.; Cinnella, P.
1990-01-01
The present consideration of numerical computation methods for gas flows with nonequilibrium chemistry thermodynamics gives attention to an equilibrium model, a general nonequilibrium model, and a simplified model based on vibrational relaxation. Flux-splitting procedures are developed for the fully-coupled inviscid equations encompassing fluid dynamics and both chemical and internal energy-relaxation processes. A fully coupled and implicit large-block structure is presented which embodies novel forms of flux-vector split and flux-difference split algorithms valid for nonequilibrium flow; illustrative high-temperature shock tube and nozzle flow examples are given.
Non-equilibrium reacting gas flows kinetic theory of transport and relaxation processes
Nagnibeda, Ekaterina; Nagnibeda, Ekaterina
2009-01-01
This volume develops the kinetic theory of transport phenomena and relaxation processes in the flows of reacting gas mixtures. The theory is applied to the modeling of non-equilibrium flows behind strong shock waves, in the boundary layer, and in nozzles.
DEFF Research Database (Denmark)
Huang, Shaojun; Wu, Qiuwei; Zhao, Haoran
2016-01-01
Renewable energies are increasingly integrated in electric distribution networks and will cause severe overvoltage issues. Smart grid technologies make it possible to use coordinated control to mitigate the overvoltage issues and the optimal power flow (OPF) method is proven to be efficient...... in the applications such as curtailment management and reactive power control. Nonconvex nature of the OPF makes it difficult to solve and convex relaxation is a promising method to solve the OPF very efficiently. This paper investigates the geometry of the power flows and the convex-relaxed power flows when high...
A modified homogeneous relaxation model for CO2 two-phase flow in vapour ejector
International Nuclear Information System (INIS)
Haida, M.; Palacz, M.; Smolka, J.; Nowak, A. J.; Hafner, A.; Banasiak, K.
2016-01-01
In this study, the homogenous relaxation model (HRM) for CO 2 flow in a two-phase ejector was modified in order to increase the accuracy of the numerical simulations The two- phase flow model was implemented on the effective computational tool called ejectorPL for fully automated and systematic computations of various ejector shapes and operating conditions. The modification of the HRM was performed by a change of the relaxation time and the constants included in the relaxation time equation based on the experimental result under the operating conditions typical for the supermarket refrigeration system. The modified HRM was compared to the HEM results, which were performed based on the comparison of motive nozzle and suction nozzle mass flow rates. (paper)
A modified homogeneous relaxation model for CO2 two-phase flow in vapour ejector
Haida, M.; Palacz, M.; Smolka, J.; Nowak, A. J.; Hafner, A.; Banasiak, K.
2016-09-01
In this study, the homogenous relaxation model (HRM) for CO2 flow in a two-phase ejector was modified in order to increase the accuracy of the numerical simulations The two- phase flow model was implemented on the effective computational tool called ejectorPL for fully automated and systematic computations of various ejector shapes and operating conditions. The modification of the HRM was performed by a change of the relaxation time and the constants included in the relaxation time equation based on the experimental result under the operating conditions typical for the supermarket refrigeration system. The modified HRM was compared to the HEM results, which were performed based on the comparison of motive nozzle and suction nozzle mass flow rates.
Qin, Feifei; Mazloomi Moqaddam, Ali; Kang, Qinjun; Derome, Dominique; Carmeliet, Jan
2018-03-01
An entropic multiple-relaxation-time lattice Boltzmann approach is coupled to a multirange Shan-Chen pseudopotential model to study the two-phase flow. Compared with previous multiple-relaxation-time multiphase models, this model is stable and accurate for the simulation of a two-phase flow in a much wider range of viscosity and surface tension at a high liquid-vapor density ratio. A stationary droplet surrounded by equilibrium vapor is first simulated to validate this model using the coexistence curve and Laplace's law. Then, two series of droplet impact behavior, on a liquid film and a flat surface, are simulated in comparison with theoretical or experimental results. Droplet impact on a liquid film is simulated for different Reynolds numbers at high Weber numbers. With the increase of the Sommerfeld parameter, onset of splashing is observed and multiple secondary droplets occur. The droplet spreading ratio agrees well with the square root of time law and is found to be independent of Reynolds number. Moreover, shapes of simulated droplets impacting hydrophilic and superhydrophobic flat surfaces show good agreement with experimental observations through the entire dynamic process. The maximum spreading ratio of a droplet impacting the superhydrophobic flat surface is studied for a large range of Weber numbers. Results show that the rescaled maximum spreading ratios are in good agreement with a universal scaling law. This series of simulations demonstrates that the proposed model accurately captures the complex fluid-fluid and fluid-solid interfacial physical processes for a wide range of Reynolds and Weber numbers at high density ratios.
Arctigenin exhibits relaxation effect on bronchus by affecting transmembrane flow of calcium.
Zhao, Zhenying; Yin, Yongqiang; Wang, Zengyong; Fang, Runping; Wu, Hong; Jiang, Min; Bai, Gang; Luo, Guo'an
2013-12-01
Arctigenin, a lignan extract from Arctium lappa (L.), exhibits anti-inflammation, antioxidation, vasodilator effects, etc. However, the effects of arctigenin on bronchus relaxation are not well investigated. This study aimed to investigate how arctigenin regulates bronchus tone and calcium ion (Ca(2+)) flow. Trachea strips of guinea pigs were prepared for testing the relaxation effect of arctigenin to acetylcholine, histamine, KCl, and CaCl2, respectively. Furthermore, L-type calcium channel currents were detected by patch-clamp, and intracellular Ca(2+) concentration was detected by confocal microscopy. The results showed that arctigenin exhibited relaxation effect on tracheae to different constrictors, and this was related to decreasing cytoplasmic Ca(2+) concentration by inhibiting Ca(2+) influx partly through L-type calcium channel as well as promoting Ca(2+) efflux. In summary, this study provides new insight into the mechanisms by which arctigenin exhibits relaxation effect on bronchus and suggests its potential use for airway disease therapy.
Simulation of Cavity Flow by the Lattice Boltzmann Method using Multiple-Relaxation-Time scheme
International Nuclear Information System (INIS)
Ryu, Seung Yeob; Kang, Ha Nok; Seo, Jae Kwang; Yun, Ju Hyeon; Zee, Sung Quun
2006-01-01
Recently, the lattice Boltzmann method(LBM) has gained much attention for its ability to simulate fluid flows, and for its potential advantages over conventional CFD method. The key advantages of LBM are, (1) suitability for parallel computations, (2) absence of the need to solve the time-consuming Poisson equation for pressure, and (3) ease with multiphase flows, complex geometries and interfacial dynamics may be treated. The LBM using relaxation technique was introduced by Higuerea and Jimenez to overcome some drawbacks of lattice gas automata(LGA) such as large statistical noise, limited range of physical parameters, non- Galilean invariance, and implementation difficulty in three-dimensional problem. The simplest LBM is the lattice Bhatnager-Gross-Krook(LBGK) equation, which based on a single-relaxation-time(SRT) approximation. Due to its extreme simplicity, the lattice BGK(LBGK) equation has become the most popular lattice Boltzmann model in spite of its well-known deficiencies, for example, in simulating high-Reynolds numbers flow. The Multiple-Relaxation-Time(MRT) LBM was originally developed by D'Humieres. Lallemand and Luo suggests that the use of a Multiple-Relaxation-Time(MRT) models are much more stable than LBGK, because the different relaxation times can be individually tuned to achieve 'optimal' stability. A lid-driven cavity flow is selected as the test problem because it has geometrically singular points in the flow, but geometrically simple. Results are compared with those using SRT, MRT model in the LBGK method and previous simulation data using Navier-Stokes equations for the same flow conditions. In summary, LBM using MRT model introduces much less spatial oscillations near geometrical singular points, which is important for the successful simulation of higher Reynolds number flows
Relaxation-type nonlocal inertial-number rheology for dry granular flows
Lee, Keng-lin; Yang, Fu-ling
2017-12-01
We propose a constitutive model to describe the nonlocality, hysteresis, and several flow features of dry granular materials. Taking the well-known inertial number I as a measure of sheared-induced local fluidization, we derive a relaxation model for I according to the evolution of microstructure during avalanche and dissipation processes. The model yields a nonmonotonic flow law for a homogeneous flow, accounting for hysteretic solid-fluid transition and intermittency in quasistatic flows. For an inhomogeneous flow, the model predicts a generalized Bagnold shear stress revealing the interplay of two microscopic nonlocal mechanisms: collisions among correlated structures and the diffusion of fluidization within the structures. In describing a uniform flow down an incline, the model reproduces the hysteretic starting and stopping heights and the Pouliquen flow rule for mean velocity. Moreover, a dimensionless parameter reflecting the nonlocal effect on the flow is discovered, which controls the transition between Bagnold and creeping flow dynamics.
Interrelation of creep and relaxation: a modeling approach for ligaments.
Lakes, R S; Vanderby, R
1999-12-01
Experimental data (Thornton et al., 1997) show that relaxation proceeds more rapidly (a greater slope on a log-log scale) than creep in ligament, a fact not explained by linear viscoelasticity. An interrelation between creep and relaxation is therefore developed for ligaments based on a single-integral nonlinear superposition model. This interrelation differs from the convolution relation obtained by Laplace transforms for linear materials. We demonstrate via continuum concepts of nonlinear viscoelasticity that such a difference in rate between creep and relaxation phenomenologically occurs when the nonlinearity is of a strain-stiffening type, i.e., the stress-strain curve is concave up as observed in ligament. We also show that it is inconsistent to assume a Fung-type constitutive law (Fung, 1972) for both creep and relaxation. Using the published data of Thornton et al. (1997), the nonlinear interrelation developed herein predicts creep behavior from relaxation data well (R > or = 0.998). Although data are limited and the causal mechanisms associated with viscoelastic tissue behavior are complex, continuum concepts demonstrated here appear capable of interrelating creep and relaxation with fidelity.
A Sufficient Condition on Convex Relaxation of AC Optimal Power Flow in Distribution Networks
DEFF Research Database (Denmark)
Huang, Shaojun; Wu, Qiuwei; Wang, Jianhui
2016-01-01
This paper proposes a sufficient condition for the convex relaxation of AC Optimal Power Flow (OPF) in radial distribution networks as a second order cone program (SOCP) to be exact. The condition requires that the allowed reverse power flow is only reactive or active, or none. Under the proposed...... solution of the SOCP can be converted to an optimal solution of the original AC OPF. The efficacy of the convex relaxation to solve the AC OPF is demonstrated by case studies of an optimal multi-period planning problem of electric vehicles (EVs) in distribution networks....... sufficient condition, the feasible sub-injection region (power injections of nodes excluding the root node) of the AC OPF is convex. The exactness of the convex relaxation under the proposed condition is proved through constructing a group of monotonic series with limits, which ensures that the optimal...
Convex Relaxations of Chance Constrained AC Optimal Power Flow
DEFF Research Database (Denmark)
Venzke, Andreas; Halilbasic, Lejla; Markovic, Uros
2017-01-01
, reactive power, and voltage. We state a tractable formulation for two types of uncertainty sets. Using a scenario-based approach and making no prior assumptions about the probability distribution of the forecast errors, we obtain a robust formulation for a rectangular uncertainty set. Alternatively...
An approach to the magnetic relaxation processes in lithium ferrites
International Nuclear Information System (INIS)
Torres, C.; Gonzalez Arias, A.; Hernandez-Gomez, P.; Francisco, C. de; Alejos, O.; Munoz, J.M.; Zazo, M.
2007-01-01
The relaxation of the initial magnetic permeability has been measured in polycrystalline Li x Fe 3- x O 4 samples, with x ranging from 0 to 0.5, by means of the magnetic disaccommodation (DA) technique. We have found that there is no abrupt transition for a given composition, but there is a progressive modification of the characteristic relaxation processes of magnetite. These results have been interpreted on the basis of the increasing amount of Li ions in the spinel lattice and hence, the resulting modifications on their proximities
Directory of Open Access Journals (Sweden)
Tintin Sukartini
2017-07-01
Full Text Available Introduction: Limited progressive air flow in Chronic Obstructive Pulmonary Disease (COPD can caused by small airway disease (bronchiolitis obstructive and loss of elasticity of the lung (emphysema. Further it can be decreasing the quality of life in COPD patients because dyspnea and uncomfortable in activity. Progressive muscle relaxation (PMR is one of the relaxation technique that can repair pulmonary ventilation by decreasing chronic constriction of the respiratory muscles. The objective of this study was to analyze the effect of progressive muscle relaxation on raised peak expiratory flow rate (PEFR. Method: A pre-experimental one group pre-post test design was used in this study. Population was all of the COPD patients at Pulmonary Specialist Polyclinic Dr Mohamad Soewandhie Surabaya. There were 8 respondents taken by using purposive sampling. PEFR was counted by using peak flow meter every six day. Data were analyzed by using Paired t-Test with significance level p≤0.05. Result: The result showed that PMR had significance level on increasing of PEFR (p=0.012. Discussion: It can be concluded that PMR has an effect on raise PEFR. Further studies are recommended to measure the effect of PMR on respiratory rate (RR, heart rate (HR subjective dyspnoe symptoms, forced expiration volume on the first minute (FEV1 and mid maximum flow rate (MMFR in COPD patients.
Dynamical renormalization group approach to relaxation in quantum field theory
International Nuclear Information System (INIS)
Boyanovsky, D.; Vega, H.J. de
2003-01-01
The real time evolution and relaxation of expectation values of quantum fields and of quantum states are computed as initial value problems by implementing the dynamical renormalization group (DRG). Linear response is invoked to set up the renormalized initial value problem to study the dynamics of the expectation value of quantum fields. The perturbative solution of the equations of motion for the field expectation values of quantum fields as well as the evolution of quantum states features secular terms, namely terms that grow in time and invalidate the perturbative expansion for late times. The DRG provides a consistent framework to resum these secular terms and yields a uniform asymptotic expansion at long times. Several relevant cases are studied in detail, including those of threshold infrared divergences which appear in gauge theories at finite temperature and lead to anomalous relaxation. In these cases the DRG is shown to provide a resummation akin to Bloch-Nordsieck but directly in real time and that goes beyond the scope of Bloch-Nordsieck and Dyson resummations. The nature of the resummation program is discussed in several examples. The DRG provides a framework that is consistent, systematic, and easy to implement to study the non-equilibrium relaxational dynamics directly in real time that does not rely on the concept of quasiparticle widths
Pradipto; Purqon, Acep
2017-07-01
Lattice Boltzmann Method (LBM) is the novel method for simulating fluid dynamics. Nowadays, the application of LBM ranges from the incompressible flow, flow in the porous medium, until microflows. The common collision model of LBM is the BGK with a constant single relaxation time τ. However, BGK suffers from numerical instabilities. These instabilities could be eliminated by implementing LBM with multiple relaxation time. Both of those scheme have implemented for incompressible 2 dimensions lid-driven cavity. The stability analysis has done by finding the maximum Reynolds number and velocity for converged simulations. The accuracy analysis is done by comparing the velocity profile with the benchmark results from Ghia, et al and calculating the net velocity flux. The tests concluded that LBM with MRT are more stable than BGK, and have a similar accuracy. The maximum Reynolds number that converges for BGK is 3200 and 7500 for MRT respectively.
Relaxation and self-organization in two-dimensional plasma and neutral fluid flow systems
International Nuclear Information System (INIS)
Das, Amita
2008-01-01
Extensive numerical studies in the framework of a simplified two-dimensional model for neutral and plasma fluid for a variety of initial configurations and for both decaying and driven cases are carried out to illustrate relaxation toward a self-organized state. The dynamical model equation constitutes a simple choice for this purpose, e.g., the vorticity equation of the Navier-Stokes dynamics for the incompressible neutral fluids and the Hasegawa-Mima equation for plasma fluid flow system. Scatter plots are employed to observe a development of functional relationship, if any, amidst the generalized vorticity and its Laplacian. It is seen that they do not satisfy a linear relationship as the well known variational approach of enstrophy minimization subject to constancy of the energy integral for the two-dimensional (2D) system suggests. The observed nonlinear functional relationship is understood by separating the contribution to the scatter plot from spatial regions with intense vorticity patches and those of the background flow region where the background vorticity is weak or absent altogether. It is shown that such a separation has close connection with the known exact analytical solutions of the system. The analytical solutions are typically obtained by assuming a finite source of vorticity for the inner core of the localized structure, which is then matched with the solution in the outer region where vorticity is chosen to be zero. The work also demonstrates that the seemingly ad hoc choice of the linear vorticity source function for the inner region is in fact consistent with the self-organization paradigm of the 2D systems
Inelastic structural design approach using their relaxation locus
International Nuclear Information System (INIS)
Kasahara, Naoto
2000-08-01
Elevated temperature structural design codes pay attention to strain concentration at structural discontinuities due to creep and plasticity, since it causes to enlarge creep-fatigue damage of materials. One of the difficulties to predict strain concentration is its dependency on loading, constitutive equations, and relaxation time. This study investigated fundamental mechanism of strain concentration and its main factors. The results revealed that strain concentration was caused from strain redistribution between elastic and inelastic region, which can be quantified by the characteristics of structural compliance. Characteristic of compliance is controlled by elastic region in structures and is insensitive to constitutive equations. It means that inelastic analysis is easily applied to get compliance characteristics. By utilizing this fact, simplified inelastic analysis method was proposed based on characteristics of compliance change for prediction of strain concentration. (author)
Convex relaxation of Optimal Power Flow in Distribution Feeders with embedded solar power
DEFF Research Database (Denmark)
Hermann, Alexander Niels August; Wu, Qiuwei; Huang, Shaojun
2016-01-01
There is an increasing interest in using Distributed Energy Resources (DER) directly coupled to end user distribution feeders. This poses an array of challenges because most of today’s distribution feeders are designed for unidirectional power flow. Therefore when installing DERs such as solar...... panels with uncontrolled inverters, the upper limit of installable capacity is quickly reached in many of today’s distribution feeders. This problem can often be mitigated by optimally controlling the voltage angles of inverters. However, the optimal power flow problem in its standard form is a large...... scale non-convex optimization problem, and thus can’t be solved precisely and also is computationally heavy and intractable for large systems. This paper examines the use of a convex relaxation using Semi-definite programming to optimally control solar power inverters in a distribution grid in order...
Relaxation with high-speed plasma flows and singularity analysis in MHD equilibrium
International Nuclear Information System (INIS)
Shiraishi, Junya; Ohsaki, Shuichi; Yoshida, Zensho
2004-01-01
Relaxation model that leads to plasma confinement with rigid-rotation is presented. This model applies to Jupiter's magnetosphere. It is shown that the invariance of canonical angular momentum of electron fluid, which is realized by axisymmetry through self-organization process, yields plasma confinement. including poloidal flows in equilibrium equation makes the problem rather complicated. Singularity due to the poloidal flow is focused on. It is shown that the singular equation for equilibrium has the same structure as the equation for linear Alfven wave. Since the singular solution for equilibrium equation is physically inadequate, the singularity may be removed by another physical effect. The Hall-effect is taken into account as a singular perturbation that removes the singularity of equilibrium equation for ideal magnetohydrodynamics. (author)
International Nuclear Information System (INIS)
Park, Jong Woon; Choi, Hyun Gyung
2014-01-01
A turbulent fluid flow over staggered tube bundles is of great interest in many engineering fields including nuclear fuel rods, heat exchangers and especially a gas cooled reactor lower plenum. Computational methods have evolved for the simulation of such flow for decades and lattice Boltzmann method (LBM) is one of the attractive methods due to its sound physical basis and ease of computerization including parallelization. In this study to find computational performance of the LBM in turbulent flows over staggered tubes, a fluid flow analysis code employing multi-relaxation time lattice Boltzmann method (MRT-LBM) is developed based on a 2-dimensional D2Q9 lattice model and classical sub-grid eddy viscosity model of Smagorinsky. As a first step, fundamental performance MRT-LBM is investigated against a standard problem of a flow past a cylinder at low Reynolds number in terms of drag forces. As a major step, benchmarking of the MRT-LBM is performed over a turbulent flow through staggered tube bundles at Reynolds number of 18,000. For a flow past a single cylinder, the accuracy is validated against existing experimental data and previous computations in terms of drag forces on the cylinder. Mainly, the MRT-LBM computation for a flow through staggered tube bundles is performed and compared with experimental data and general purpose computational fluid dynamic (CFD) analyses with standard k-ω turbulence and large eddy simulation (LES) equipped with turbulence closures of Smagrinsky-Lilly and wall-adapting local eddy-viscosity (WALE) model. The agreement between the experimental and the computational results from the present MRT-LBM is found to be reasonably acceptable and even comparable to the LES whereas the computational efficiency is superior. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Park, Jong Woon; Choi, Hyun Gyung [Dongguk Univ., Gyeongju (Korea, Republic of). Nuclear and Energy Engineering Dept.
2014-02-15
A turbulent fluid flow over staggered tube bundles is of great interest in many engineering fields including nuclear fuel rods, heat exchangers and especially a gas cooled reactor lower plenum. Computational methods have evolved for the simulation of such flow for decades and lattice Boltzmann method (LBM) is one of the attractive methods due to its sound physical basis and ease of computerization including parallelization. In this study to find computational performance of the LBM in turbulent flows over staggered tubes, a fluid flow analysis code employing multi-relaxation time lattice Boltzmann method (MRT-LBM) is developed based on a 2-dimensional D2Q9 lattice model and classical sub-grid eddy viscosity model of Smagorinsky. As a first step, fundamental performance MRT-LBM is investigated against a standard problem of a flow past a cylinder at low Reynolds number in terms of drag forces. As a major step, benchmarking of the MRT-LBM is performed over a turbulent flow through staggered tube bundles at Reynolds number of 18,000. For a flow past a single cylinder, the accuracy is validated against existing experimental data and previous computations in terms of drag forces on the cylinder. Mainly, the MRT-LBM computation for a flow through staggered tube bundles is performed and compared with experimental data and general purpose computational fluid dynamic (CFD) analyses with standard k-ω turbulence and large eddy simulation (LES) equipped with turbulence closures of Smagrinsky-Lilly and wall-adapting local eddy-viscosity (WALE) model. The agreement between the experimental and the computational results from the present MRT-LBM is found to be reasonably acceptable and even comparable to the LES whereas the computational efficiency is superior. (orig.)
International Nuclear Information System (INIS)
Petitpas, Fabien; Franquet, Erwin; Saurel, Richard; Le Metayer, Olivier
2007-01-01
The relaxation-projection method developed in Saurel et al. [R. Saurel, E. Franquet, E. Daniel, O. Le Metayer, A relaxation-projection method for compressible flows. Part I: The numerical equation of state for the Euler equations, J. Comput. Phys. (2007) 822-845] is extended to the non-conservative hyperbolic multiphase flow model of Kapila et al. [A.K. Kapila, Menikoff, J.B. Bdzil, S.F. Son, D.S. Stewart, Two-phase modeling of deflagration to detonation transition in granular materials: reduced equations, Physics of Fluids 13(10) (2001) 3002-3024]. This model has the ability to treat multi-temperatures mixtures evolving with a single pressure and velocity and is particularly interesting for the computation of interface problems with compressible materials as well as wave propagation in heterogeneous mixtures. The non-conservative character of this model poses however computational challenges in the presence of shocks. The first issue is related to the Riemann problem resolution that necessitates shock jump conditions. Thanks to the Rankine-Hugoniot relations proposed and validated in Saurel et al. [R. Saurel, O. Le Metayer, J. Massoni, S. Gavrilyuk, Shock jump conditions for multiphase mixtures with stiff mechanical relaxation, Shock Waves 16 (3) (2007) 209-232] exact and approximate 2-shocks Riemann solvers are derived. However, the Riemann solver is only a part of a numerical scheme and non-conservative variables pose extra difficulties for the projection or cell average of the solution. It is shown that conventional Godunov schemes are unable to converge to the exact solution for strong multiphase shocks. This is due to the incorrect partition of the energies or entropies in the cell averaged mixture. To circumvent this difficulty a specific Lagrangian scheme is developed. The correct partition of the energies is achieved by using an artificial heat exchange in the shock layer. With the help of an asymptotic analysis this heat exchange takes a similar form as
Petitpas, Fabien; Franquet, Erwin; Saurel, Richard; Le Metayer, Olivier
2007-08-01
The relaxation-projection method developed in Saurel et al. [R. Saurel, E. Franquet, E. Daniel, O. Le Metayer, A relaxation-projection method for compressible flows. Part I: The numerical equation of state for the Euler equations, J. Comput. Phys. (2007) 822-845] is extended to the non-conservative hyperbolic multiphase flow model of Kapila et al. [A.K. Kapila, Menikoff, J.B. Bdzil, S.F. Son, D.S. Stewart, Two-phase modeling of deflagration to detonation transition in granular materials: reduced equations, Physics of Fluids 13(10) (2001) 3002-3024]. This model has the ability to treat multi-temperatures mixtures evolving with a single pressure and velocity and is particularly interesting for the computation of interface problems with compressible materials as well as wave propagation in heterogeneous mixtures. The non-conservative character of this model poses however computational challenges in the presence of shocks. The first issue is related to the Riemann problem resolution that necessitates shock jump conditions. Thanks to the Rankine-Hugoniot relations proposed and validated in Saurel et al. [R. Saurel, O. Le Metayer, J. Massoni, S. Gavrilyuk, Shock jump conditions for multiphase mixtures with stiff mechanical relaxation, Shock Waves 16 (3) (2007) 209-232] exact and approximate 2-shocks Riemann solvers are derived. However, the Riemann solver is only a part of a numerical scheme and non-conservative variables pose extra difficulties for the projection or cell average of the solution. It is shown that conventional Godunov schemes are unable to converge to the exact solution for strong multiphase shocks. This is due to the incorrect partition of the energies or entropies in the cell averaged mixture. To circumvent this difficulty a specific Lagrangian scheme is developed. The correct partition of the energies is achieved by using an artificial heat exchange in the shock layer. With the help of an asymptotic analysis this heat exchange takes a similar form as
International Nuclear Information System (INIS)
Saleh, K.
2012-01-01
This thesis deals with the Baer-Nunziato two-phase flow model. The main objective of this work is to propose some techniques to cope with phase vanishing regimes which produce important instabilities in the model and its numerical simulations. Through analysis and simulation methods using Suliciu relaxation approximations, we prove that in these regimes, the solutions can be stabilised by introducing some extra dissipation of the total mixture entropy. In a first approach, called the Eulerian approach, the exact resolution of the relaxation Riemann problem provides an accurate entropy-satisfying numerical scheme, which turns out to be much more efficient in terms of CPU-cost than the classical and very simple Rusanov's scheme. Moreover, the scheme is proved to handle the vanishing phase regimes with great stability. The scheme, first developed in 1D, is then extended in 3D and implemented in an industrial code developed by EDF. The second approach, called the acoustic splitting approach, considers a separation of fast acoustic waves from slow material waves. The objective is to avoid the resonance due to the interaction between these two types of waves, and to allow an implicit treatment of the acoustics, while material waves are explicitly discretized. The resulting scheme is very simple and allows to deal simply with phase vanishing. The originality of this work is to use new dissipative closure laws for the interfacial velocity and pressure, in order to control the solutions of the Riemann problem associated with the acoustic step, in the phase vanishing regimes. (author)
An inversion-relaxation approach for sampling stationary points of spin model Hamiltonians
International Nuclear Information System (INIS)
Hughes, Ciaran; Mehta, Dhagash; Wales, David J.
2014-01-01
Sampling the stationary points of a complicated potential energy landscape is a challenging problem. Here, we introduce a sampling method based on relaxation from stationary points of the highest index of the Hessian matrix. We illustrate how this approach can find all the stationary points for potentials or Hamiltonians bounded from above, which includes a large class of important spin models, and we show that it is far more efficient than previous methods. For potentials unbounded from above, the relaxation part of the method is still efficient in finding minima and transition states, which are usually the primary focus of attention for atomistic systems
A unified aggregation and relaxation approach for stress-constrained topology optimization
DEFF Research Database (Denmark)
Verbart, Alexander; Langelaar, Matthijs; Keulen, Fred van
2017-01-01
design-independent set of constraints. The next step is to perform constraint aggregation over the reformulated local constraints using a lower bound aggregation function. We demonstrate that this approach concurrently aggregates the constraints and relaxes the feasible domain, thereby making singular...... optima accessible. The main advantage is that no separate constraint relaxation techniques are necessary, which reduces the parameter dependence of the problem. Furthermore, there is a clear relationship between the original feasible domain and the perturbed feasible domain via this aggregation parameter....
Producing Satisfactory Solutions to Scheduling Problems: An Iterative Constraint Relaxation Approach
Chien, S.; Gratch, J.
1994-01-01
One drawback to using constraint-propagation in planning and scheduling systems is that when a problem has an unsatisfiable set of constraints such algorithms typically only show that no solution exists. While, technically correct, in practical situations, it is desirable in these cases to produce a satisficing solution that satisfies the most important constraints (typically defined in terms of maximizing a utility function). This paper describes an iterative constraint relaxation approach in which the scheduler uses heuristics to progressively relax problem constraints until the problem becomes satisfiable. We present empirical results of applying these techniques to the problem of scheduling spacecraft communications for JPL/NASA antenna resources.
International Nuclear Information System (INIS)
Sabass, Benedikt; Schwarz, Ulrich S
2010-01-01
In migrating cells, retrograde flow of the actin cytoskeleton is related to traction at adhesion sites located at the base of the lamellipodium. The coupling between the moving cytoskeleton and the stationary adhesions is mediated by the continuous association and dissociation of molecular bonds. We introduce a simple model for the competition between the stochastic dynamics of elastic bonds at the moving interface and relaxation within the moving actin cytoskeleton represented by an internal viscous friction coefficient. Using exact stochastic simulations and an analytical mean field theory, we show that the stochastic bond dynamics lead to biphasic friction laws as observed experimentally. At low internal dissipation, stochastic bond dynamics lead to a regime of irregular stick-and-slip motion. High internal dissipation effectively suppresses cooperative effects among bonds and hence stabilizes the adhesion.
Relaxation of plasma potential and poloidal flows in the boundary of tokamak plasmas
International Nuclear Information System (INIS)
Hron, M.; Duran, I.; Stoeckel, J.; Hidalgo, C.; Gunn, J.
2003-01-01
The relaxation times of plasma parameters after a sudden change of electrode voltage have been measured in the plasma boundary during polarization experiments on the CASTOR tokamak (R = 0.4 m, a = 75 mm, B t = 1 T, I p ∼ 9 kA, q a ∼ 10). The time evolution of the floating potential after the biasing voltage switch-off can be well fitted by an exponential decay with characteristic time in the range of 10 - 20 μs. The poloidal flow shows a transient behaviour with a time scale of about 10 - 30 μs. These time scales are smaller than the expected damping time based on neoclassical parallel viscosity (which is in the range of 100 νs) and atomic physics via charge exchange (in the range of 100 - 1000 νs). But, they are larger than the correlation time of plasma turbulence (about 5 μs). These findings suggest that anomalous damping rate mechanisms for radial electric fields and poloidal flows may play a role in the boundary of tokamak plasmas. (authors)
Dynamic relaxation processes in compressible multiphase flows. Application to evaporation phenomena
Directory of Open Access Journals (Sweden)
Le Métayer O.
2013-07-01
Full Text Available Phase changes and heat exchanges are examples of physical processes appearing in many industrial applications involving multiphase compressible flows. Their knowledge is of fundamental importance to reproduce correctly the resulting effects in simulation tools. A fine description of the flow topology is thus required to obtain the interfacial area between phases. This one is responsible for the dynamics and the kinetics of heat and mass transfer when evaporation or condensation occurs. Unfortunately this exchange area cannot be obtained easily and accurately especially when complex mixtures (drops, bubbles, pockets of very different sizes appear inside the transient medium. The natural way to solve this specific trouble consists in using a thin grid to capture interfaces at all spatial scales. But this possibility needs huge computing resources and can be hardly used when considering physical systems of large dimensions. A realistic method is to consider instantaneous exchanges between phases by the way of additional source terms in a full non-equilibrium multiphase flow model [2,15,17]. In this one each phase obeys its own equation of state and has its own set of equations and variables (pressure, temperature, velocity, energy, entropy,.... When enabling the relaxation source terms the multiphase mixture instantaneously tends towards a mechanical or thermodynamic equilibrium state at each point of the flow. This strategy allows to mark the boundaries of the real flow behavior and to magnify the dominant physical effects (heat exchanges, evaporation, drag,... inside the medium. A description of the various relaxation processes is given in the paper. Les changements de phase et les transferts de chaleur sont des exemples de phénomènes physiques présents dans de nombreuses applications industrielles faisant intervenir des écoulements compressibles multiphasiques. La connaissance des mécanismes associés est primordiale afin de reproduire
The influence of temperature, viscosity and pH on the relaxation time T1 in flowing liquids
International Nuclear Information System (INIS)
Toczylowska, B.
1995-01-01
The designed and constructed at the Institute of Biocybernetics and Biomedical Engineering facility for the relaxation time (T 1 ) measurements of liquids flow has been presented. The influence of temperature, viscosity and pH has been determined for several liquids, especially physiological fluids
Courbin, L.; Benayad, A.; Panizza, P.
2006-01-01
By means of several rheophysics techniques, we report on an extensive study of the couplings between flow and microstructures in a two-phase fluid made of lamellar (Lα) and sponge (L3) phases. Depending on the nature of the imposed dynamical parameter (stress or shear rate) and on the experimental conditions (brine salinity or temperature), we observe several different structural steady states consisting of either multilamellar droplets (with or without a long range order) or elongated (L3) phase domains. Two different astonishing phenomena, shear-induced phase inversion and relaxation oscillations, are observed. We show that (i) phase inversion is related to a shear-induced topological change between monodisperse multilamellar droplets and elongated structures and (ii) droplet size relaxation oscillations result from a shear-induced change of the surface tension between both coexisting (Lα) and (L3) phases. To explain these relaxation oscillations, we present a phenomenological model and compare its numerical predictions to our experimental results.
Lattice Boltzmann approach for complex nonequilibrium flows.
Montessori, A; Prestininzi, P; La Rocca, M; Succi, S
2015-10-01
We present a lattice Boltzmann realization of Grad's extended hydrodynamic approach to nonequilibrium flows. This is achieved by using higher-order isotropic lattices coupled with a higher-order regularization procedure. The method is assessed for flow across parallel plates and three-dimensional flows in porous media, showing excellent agreement of the mass flow with analytical and numerical solutions of the Boltzmann equation across the full range of Knudsen numbers, from the hydrodynamic regime to ballistic motion.
International Nuclear Information System (INIS)
Saurel, Richard; Franquet, Erwin; Daniel, Eric; Le Metayer, Olivier
2007-01-01
A new projection method is developed for the Euler equations to determine the thermodynamic state in computational cells. It consists in the resolution of a mechanical relaxation problem between the various sub-volumes present in a computational cell. These sub-volumes correspond to the ones traveled by the various waves that produce states with different pressures, velocities, densities and temperatures. Contrarily to Godunov type schemes the relaxed state corresponds to mechanical equilibrium only and remains out of thermal equilibrium. The pressure computation with this relaxation process replaces the use of the conventional equation of state (EOS). A simplified relaxation method is also derived and provides a specific EOS (named the Numerical EOS). The use of the Numerical EOS gives a cure to spurious pressure oscillations that appear at contact discontinuities for fluids governed by real gas EOS. It is then extended to the computation of interface problems separating fluids with different EOS (liquid-gas interface for example) with the Euler equations. The resulting method is very robust, accurate, oscillation free and conservative. For the sake of simplicity and efficiency the method is developed in a Lagrange-projection context and is validated over exact solutions. In a companion paper [F. Petitpas, E. Franquet, R. Saurel, A relaxation-projection method for compressible flows. Part II: computation of interfaces and multiphase mixtures with stiff mechanical relaxation. J. Comput. Phys. (submitted for publication)], the method is extended to the numerical approximation of a non-conservative hyperbolic multiphase flow model for interface computation and shock propagation into mixtures
Healing and relaxation in flows of helium II. Part II. First, second, and fourth sound
International Nuclear Information System (INIS)
Hills, R.N.; Roberts, P.H.
1978-01-01
In Part I of this series, a theory of helium II incorporating the effects of quantum healing and relaxation was developed. In this paper, the propagation of first, second, and fourth sound is discussed. Particular attention is paid to sound propagation in the vicinity of the lambda point where the effects of relaxation and quantum healing become important
International Nuclear Information System (INIS)
Wang Weihua
2011-01-01
We study the similarity and correlations between relaxations and plastic deformation in metallic glasses (MGs) and MG-forming liquids. It is shown that the microscope plastic events, the initiation and formation of shear bands, and the mechanical yield in MGs where the atomic sites are topologically unstable induced by applied stress, can be treated as the glass to supercooled liquid state transition induced by external shear stress. On the other hand, the glass transition, the primary and secondary relaxations, plastic deformation and yield can be attributed to the free volume increase induced flow, and the flow can be modeled as the activated hopping between the inherent states in the potential energy landscape. We then propose an extended elastic model to describe the flow based on the energy landscape theory. That is, the flow activation energy density is linear proportional to the instantaneous elastic moduli, and the activation energy density ρ E is determined to be a simple expression of ρ E =(10/11)G+(1/11)K. The model indicates that both shear and bulk moduli are critical parameters accounting for both the homogeneous and inhomogeneous flows in MGs and MG-forming liquids. The elastic model is experimentally certified. We show that the elastic perspectives offers a simple scenario for the flow in MGs and MG-forming liquids and are suggestive for understanding the glass transition, plastic deformation, and nature and characteristics of MGs
Kang, Yunesik
2010-09-01
Emotional support and a stress management program should be simultaneously provided to clients as effective preventive services for healthy behavioral change. This study was conducted to review various relaxation and meditation intervention methods and their applicability for a preventive service program. The author of this paper tried to find various relaxation and meditation programs through a literature review and program searching and to introduce them. The 'Relaxation Response' and 'Mindfulness Based Stress Reduction (MBSR)' are the most the widely used meditative programs in mainstream medical systems. Abdominal breathing, Progressive Musclular Relaxation (PMR), Relaxative Imagery, Autogenic Training (AT) and Biofeedback are other well-known techniques for relaxation and stress management. I have developed and implemented some programs using these methods. Relaxation and meditation classes for cancer patients and a meditation based stress coping workshop are examples of this program. Relaxation and meditation seem to be good and effective methods for primary, secondary and tertiary preventive service programs. Program development and standardization and further study are needed for more and wider use of the mind-body approach in the preventive service area of medicine.
Relaxation approximations to second-order traffic flow models by high-resolution schemes
International Nuclear Information System (INIS)
Nikolos, I.K.; Delis, A.I.; Papageorgiou, M.
2015-01-01
A relaxation-type approximation of second-order non-equilibrium traffic models, written in conservation or balance law form, is considered. Using the relaxation approximation, the nonlinear equations are transformed to a semi-linear diagonilizable problem with linear characteristic variables and stiff source terms with the attractive feature that neither Riemann solvers nor characteristic decompositions are in need. In particular, it is only necessary to provide the flux and source term functions and an estimate of the characteristic speeds. To discretize the resulting relaxation system, high-resolution reconstructions in space are considered. Emphasis is given on a fifth-order WENO scheme and its performance. The computations reported demonstrate the simplicity and versatility of relaxation schemes as numerical solvers
Three-dimensional multi-relaxation-time lattice Boltzmann front-tracking method for two-phase flow
International Nuclear Information System (INIS)
Xie Hai-Qiong; Zeng Zhong; Zhang Liang-Qi
2016-01-01
We developed a three-dimensional multi-relaxation-time lattice Boltzmann method for incompressible and immiscible two-phase flow by coupling with a front-tracking technique. The flow field was simulated by using an Eulerian grid, an adaptive unstructured triangular Lagrangian grid was applied to track explicitly the motion of the two-fluid interface, and an indicator function was introduced to update accurately the fluid properties. The surface tension was computed directly on a triangular Lagrangian grid, and then the surface tension was distributed to the background Eulerian grid. Three benchmarks of two-phase flow, including the Laplace law for a stationary drop, the oscillation of a three-dimensional ellipsoidal drop, and the drop deformation in a shear flow, were simulated to validate the present model. (paper)
International Nuclear Information System (INIS)
Koning, M.M.G.
1990-01-01
The subject of this thesis is the structure determination of DNA molecules in solution with the use of NMR. For this purpose a new relaxation matrix approach is introduced. The emphasis is on the interpretation of nuclear Overhauser effects (NOEs) in terms of proton-proton distances and related three dimensional structures. The DNA molecules studied are obligonucleotides, unmodifief as well as modified molecules bu UV radiation. From comparison with unmodified molecules it turned out that UV irradiation scarcely influences the helical structure of the DNA string. At one place of the string a nucleotide is rotated towards the high-ANTI conformation which results in a slight unwinding of the DNA string but sufficient for blocking of the normal reading of genetic information. (H.W.). 456 refs.; 50 figs.; 30 tabs
Directory of Open Access Journals (Sweden)
Nemati Hasan
2011-01-01
Full Text Available A numerical investigation of the two-dimensional laminar flow and heat transfer a rotating circular cylinder with uniform planar shear, where the free-stream velocity varies linearly across the cylinder using Multi-Relaxation-Time Lattice Boltzmann method is conducted. The effects of variation of Reynolds number, rotational speed ratio at shear rate 0.1, blockage ratio 0.1 and Prandtl number 0.71 are studied. The Reynolds number changing from 50 to 160 for three rotational speed ratios of 0, 0.5, 1 is investigated. Results show that flow and heat transfer depends significantly on the rotational speed ratio as well as the Reynolds number. The effect of Reynolds number on the vortex-shedding frequency and period-surface Nusselt numbers is overall very strong compared with rotational speed ratio. Flow and heat conditions characteristics such as lift and drag coefficients, Strouhal number and Nusselt numbers are studied.
Directory of Open Access Journals (Sweden)
Song-Gui Chen
2016-01-01
Full Text Available This paper presents a three-dimensional (3D parallel multiple-relaxation-time lattice Boltzmann model (MRT-LBM for Bingham plastics which overcomes numerical instabilities in the simulation of non-Newtonian fluids for the Bhatnagar–Gross–Krook (BGK model. The MRT-LBM and several related mathematical models are briefly described. Papanastasiou’s modified model is incorporated for better numerical stability. The impact of the relaxation parameters of the model is studied in detail. The MRT-LBM is then validated through a benchmark problem: a 3D steady Poiseuille flow. The results from the numerical simulations are consistent with those derived analytically which indicates that the MRT-LBM effectively simulates Bingham fluids but with better stability. A parallel MRT-LBM framework is introduced, and the parallel efficiency is tested through a simple case. The MRT-LBM is shown to be appropriate for parallel implementation and to have high efficiency. Finally, a Bingham fluid flowing past a square-based prism with a fixed sphere is simulated. It is found the drag coefficient is a function of both Reynolds number (Re and Bingham number (Bn. These results reveal the flow behavior of Bingham plastics.
Multiple-Relaxation-Time Lattice Boltzmann Approach to Richtmyer-Meshkov Instability
International Nuclear Information System (INIS)
Chen Feng; Li Yingjun; Xu Aiguo; Zhang Guangcai
2011-01-01
The aims of the present paper are twofold. At first, we further study the Multiple-Relaxation-Time (MRT) Lattice Boltzmann (LB) model proposed in [Europhys. Lett. 90 (2010) 54003]. We discuss the reason why the Gram-Schmidt orthogonalization procedure is not needed in the construction of transformation matrix M; point out a reason why the Kataoka-Tsutahara model [Phys. Rev. E 69 (2004) 035701 (R)] is only valid in subsonic flows. The von Neumann stability analysis is performed. Secondly, we carry out a preliminary quantitative study on the Richtmyer-Meshkov instability using the proposed MRT LB model. When a shock wave travels from a light medium to a heavy one, the simulated growth rate is in qualitative agreement with the perturbation model by Zhang-Sohn. It is about half of the predicted value by the impulsive model and is closer to the experimental result. When the shock wave travels from a heavy medium to a light one, our simulation results are also consistent with physical analysis. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
International Nuclear Information System (INIS)
Han, Jeong Woo; Han, Seung Ho; Shin, Byung Chun; Kim, Jae Hoon
2003-01-01
The fatigue strength of welded joint is influenced by the welding residual stress which is relaxed depending on local stress distributed in vicinity of stress raisers, eg. under cut, overlap and blow hole. To evaluate its fatigue life the geometry of the stress raisers and the welding residual stress should be taken into account. The several methods based on notch strain approach have been proposed in order to consider the two factors above mentioned. These methods, however, have shown considerable differences between analytical and experimental results. It is due to the fact that the amount of the relaxed welding residual stress evaluated by the cyclic stress-strain relationship do not correspond with that occurred in reality. In this paper the residual stress relaxation model based on experimental results was used in order to reduce the discrepancy of the estimated amount of the relaxed welding residual stress. Under an assumption of the superimposition of the relaxed welding residual stress and the local stress, a modified notch strain approach was proposed and verified to the cruciform welded joint
International Nuclear Information System (INIS)
Laude, D.A. Jr.; Lee, R.W.K.; Wilkins, C.L.
1985-01-01
The utility of a recycled flow system for the efficient quantitative analysis of NMR spectra is demonstrated. Requisite conditions are first established for the quantitative flow experiment and then applied to a variety of compounds. An application of the technique to determination of the average polymer chain length for a silicone polymer by quantitative flow 29 Si NMR is also presented. 10 references, 4 figures, 3 tables
A novel approach to modelling non-exponential spin glass relaxation
Energy Technology Data Exchange (ETDEWEB)
Pickup, R.M. [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)]. E-mail: r.cywinski@leeds.ac.uk; Cywinski, R. [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom); Pappas, C. [Hahn-Meitner Institut, Glienicker Strasse 100, 14109 Berlin (Germany)
2007-07-15
A probabilistic cluster model, originally proposed by Weron to explain the universal power law of dielectric relaxation, is shown to account for the non-exponential relaxation in spin glasses above T {sub g}. Neutron spin echo spectra measured for the cluster glass compound Co{sub 55}Ga{sub 45} are well described by the Weron relaxation function, {phi}(t)={phi} {sub o}(1+k(t/{tau}) {sup {beta}}){sup -1/k}, with the interaction parameter k scaling linearly with the non-Curie-Weiss susceptibility.
Simulations of Bingham plastic flows with the multiple-relaxation-time lattice Boltzmann model
Chen, SongGui; Sun, QiCheng; Jin, Feng; Liu, JianGuo
2014-03-01
Fresh cement mortar is a type of workable paste, which can be well approximated as a Bingham plastic and whose flow behavior is of major concern in engineering. In this paper, Papanastasiou's model for Bingham fluids is solved by using the multiplerelaxation-time lattice Boltzmann model (MRT-LB). Analysis of the stress growth exponent m in Bingham fluid flow simulations shows that Papanastasiou's model provides a good approximation of realistic Bingham plastics for values of m > 108. For lower values of m, Papanastasiou's model is valid for fluids between Bingham and Newtonian fluids. The MRT-LB model is validated by two benchmark problems: 2D steady Poiseuille flows and lid-driven cavity flows. Comparing the numerical results of the velocity distributions with corresponding analytical solutions shows that the MRT-LB model is appropriate for studying Bingham fluids while also providing better numerical stability. We further apply the MRT-LB model to simulate flow through a sudden expansion channel and the flow surrounding a round particle. Besides the rich flow structures obtained in this work, the dynamics fluid force on the round particle is calculated. Results show that both the Reynolds number Re and the Bingham number Bn affect the drag coefficients C D , and a drag coefficient with Re and Bn being taken into account is proposed. The relationship of Bn and the ratio of unyielded zone thickness to particle diameter is also analyzed. Finally, the Bingham fluid flowing around a set of randomly dispersed particles is simulated to obtain the apparent viscosity and velocity fields. These results help simulation of fresh concrete flowing in porous media.
Heuristic approach to Satellite Range Scheduling with Bounds using Lagrangian Relaxation.
Energy Technology Data Exchange (ETDEWEB)
Brown, Nathanael J. K.; Arguello, Bryan; Nozick, Linda Karen; Xu, Ningxiong [Cornell
2017-03-01
This paper focuses on scheduling antennas to track satellites using a heuristic method. In order to validate the performance of the heuristic, bounds are developed using Lagrangian relaxation. The performance of the algorithm is established using several illustrative problems.
Dual resonance approach to optical signal processing beyond the carrier relaxation rate
DEFF Research Database (Denmark)
Heuck, Mikkel; Kristensen, Philip Trøst; Mørk, Jesper
2014-01-01
We propose using two optical cavities in a differential control scheme to increase the bandwidth of cavity-based semiconductor optical signal processing devices beyond the limit given by the slowest carrier relaxation rate of the medium.......We propose using two optical cavities in a differential control scheme to increase the bandwidth of cavity-based semiconductor optical signal processing devices beyond the limit given by the slowest carrier relaxation rate of the medium....
Control of muscle relaxation during anesthesia: a novel approach for clinical routine.
Stadler, Konrad S; Schumacher, Peter M; Hirter, Sibylle; Leibundgut, Daniel; Bouillon, Thomas W; Glattfelder, Adolf H; Zbinden, Alex M
2006-03-01
During general anesthesia drugs are administered to provide hypnosis, ensure analgesia, and skeletal muscle relaxation. In this paper, the main components of a newly developed controller for skeletal muscle relaxation are described. Muscle relaxation is controlled by administration of neuromuscular blocking agents. The degree of relaxation is assessed by supramaximal train-of-four stimulation of the ulnar nerve and measuring the electromyogram response of the adductor pollicis muscle. For closed-loop control purposes, a physiologically based pharmacokinetic and pharmacodynamic model of the neuromuscular blocking agent mivacurium is derived. The model is used to design an observer-based state feedback controller. Contrary to similar automatic systems described in the literature this controller makes use of two different measures obtained in the train-of-four measurement to maintain the desired level of relaxation. The controller is validated in a clinical study comparing the performance of the controller to the performance of the anesthesiologist. As presented, the controller was able to maintain a preselected degree of muscle relaxation with excellent precision while minimizing drug administration. The controller performed at least equally well as the anesthesiologist.
Fakhari, Abbas; Bolster, Diogo; Luo, Li-Shi
2017-07-01
We present a lattice Boltzmann method (LBM) with a weighted multiple-relaxation-time (WMRT) collision model and an adaptive mesh refinement (AMR) algorithm for direct numerical simulation of two-phase flows in three dimensions. The proposed WMRT model enhances the numerical stability of the LBM for immiscible fluids at high density ratios, particularly on the D3Q27 lattice. The effectiveness and efficiency of the proposed WMRT-LBM-AMR is validated through simulations of (a) buoyancy-driven motion and deformation of a gas bubble rising in a viscous liquid; (b) the bag-breakup mechanism of a falling drop; (c) crown splashing of a droplet on a wet surface; and (d) the partial coalescence mechanism of a liquid drop at a liquid-liquid interface. The numerical simulations agree well with available experimental data and theoretical approximations where applicable.
Relaxation of potential, flows, and density in the edge plasma of Castor tokamak
International Nuclear Information System (INIS)
Hron, M.; Weinzettl, V.; Dufkova, E.; Duran, I.; Stoeckel, J.; Hidalgo, C.
2004-01-01
Decay times of plasma flows and plasma profiles have been measured after a sudden biasing switch-off in experiments on the Castor tokamak. A biased electrode has been used to polarize the edge plasma. The edge plasma potential and flows have been characterized by means of Langmuir and Mach probes, the radiation was measured using an array of bolometers. Potential profiles and poloidal flows can be well fitted by an exponential decay time in the range of 10 - 30 μs when the electrode biasing is turned off in the Castor tokamak. The radiation shows a slower time scale (about 1 ms), which is linked to the evolution in the plasma density and particle confinement. (authors)
Aliat, A; Vedula, P; Josyula, E
2011-02-01
In this paper a simple model is proposed for computation of rate coefficients related to vibration-translation transitions based on the forced harmonic oscillator theory. This model, which is developed by considering a quadrature method, provides rate coefficients that are in very good agreement with those found in the literature for the high temperature regime (≳10,000 K). This model is implemented to study a one-dimensional nonequilibrium inviscid N(2) flow behind a plane shock by considering a state-to-state approach. While the effects of ionization and chemical reactions are neglected in our study, our results show that multiquantum transitions have a great influence on the relaxation of the macroscopic parameters of the gas flow behind the shock, especially on vibrational distributions of high levels. All vibrational states are influenced by multiquantum processes, but the effective number of transitions decreases inversely according to the vibrational quantum number. For the initial conditions considered in this study, excited electronic states are found to be weakly populated and can be neglected in modeling. Moreover, the computing time is considerably reduced with the model described in this paper compared to others found in the literature. ©2011 American Physical Society
Slip-flow in complex porous media as determined by a multi-relaxation-time lattice Boltzmann model
Landry, C. J.; Prodanovic, M.; Eichhubl, P.
2014-12-01
The pores and throats of shales and mudrocks are predominantly found within a range of 1-100 nm, within this size range the flow of gas at reservoir conditions will fall within the slip-flow and low transition-flow regime (0.001 clays). Molecular dynamics (MD) simulations can be used to predict slip-flow in complex geometries, but due to prohibitive computational demand are generally limited to small volumes (one to several pores). Here we present a multi-relaxation-time lattice Boltzmann model (LBM) parameterized for slip-flow (Guo et al. 2008) and adapted here to complex geometries. LBMs are inherently parallelizable, such that flow in complex geometries of significant (near REV-scale) volumes can be readily simulated at a fraction of the computational cost of MD simulations. At the macroscopic-scale the LBM is parameterized with local effective viscosities at each node to capture the variance of the mean-free-path of gas molecules in a bounded system. The corrected mean-free-path for each lattice node is determined using the mean distance of the node to the pore-wall and Stop's correction for mean-free-paths in an infinite parallel-plate geometry. At the microscopic-scale, a combined bounce-back specular-reflection boundary condition is applied to the pore-wall nodes to capture Maxwellian-slip. The LBM simulation results are first validated in simple tube and channel geometries, where good agreement is found for Knudsen numbers below 0.1, and fair agreement is found for Knudsen numbers between 0.1 and 0.5. More complex geometries are then examined including triangular-ducts and ellipsoid-ducts, both with constant and tapering/expanding cross-sections, as well as a clay pore-network imaged from a hydrocarbon producing shale by sequential focused ion-beam scanning electron microscopy. These results are analyzed to determine grid-independent resolutions, and used to explore the relationship between effective permeability and Knudsen number in complex geometries.
Approach to equilibrium in a pure superconductor. The relaxation of the Cooper pair density
Energy Technology Data Exchange (ETDEWEB)
Schid, A
1968-01-01
Electron-phonon and electron-electron collisions are the processes which determine the relaxation time r/sub R/ of the Cooper pair density. The case is considered for which the deviation of the pair density from equilibrium is small and where the equilibrium state is homogeneous. Starting from the Eliashberg equation one is able to reduce the problem to a quadrature once the equilibrium Green functions are known.
From medium heterogeneity to flow and transport: A time-domain random walk approach
Hakoun, V.; Comolli, A.; Dentz, M.
2017-12-01
The prediction of flow and transport processes in heterogeneous porous media is based on the qualitative and quantitative understanding of the interplay between 1) spatial variability of hydraulic conductivity, 2) groundwater flow and 3) solute transport. Using a stochastic modeling approach, we study this interplay through direct numerical simulations of Darcy flow and advective transport in heterogeneous media. First, we study flow in correlated hydraulic permeability fields and shed light on the relationship between the statistics of log-hydraulic conductivity, a medium attribute, and the flow statistics. Second, we determine relationships between Eulerian and Lagrangian velocity statistics, this means, between flow and transport attributes. We show how Lagrangian statistics and thus transport behaviors such as late particle arrival times are influenced by the medium heterogeneity on one hand and the initial particle velocities on the other. We find that equidistantly sampled Lagrangian velocities can be described by a Markov process that evolves on the characteristic heterogeneity length scale. We employ a stochastic relaxation model for the equidistantly sampled particle velocities, which is parametrized by the velocity correlation length. This description results in a time-domain random walk model for the particle motion, whose spatial transitions are characterized by the velocity correlation length and temporal transitions by the particle velocities. This approach relates the statistical medium and flow properties to large scale transport, and allows for conditioning on the initial particle velocities and thus to the medium properties in the injection region. The approach is tested against direct numerical simulations.
Oesterling, Sven; Schalk, Oliver; Geng, Ting; Thomas, Richard D; Hansson, Tony; de Vivie-Riedle, Regina
2017-01-18
For the series furan, furfural and β-furfural we investigated the effect of substituents and their positioning on the photoinduced relaxation dynamics in a combined theoretical and experimental approach. Using time resolved photoelectron spectroscopy with a high intensity probe pulse, we can, for the first time, follow the whole deactivation process of furan through a two photon probe signal. Using the extended 2-electron 2-orbital model [Nenov et al., J. Chem. Phys., 2011, 135, 034304] we explain the formation of one central conical intersection and predict the influence of the aldehyde group of the derivatives on its geometry. This, as well as the relaxation mechanisms from photoexcitation to the final outcome was investigated using a variety of theoretical methods. Complete active space self consistent field was used for on-the-fly calculations while complete active space perturbation theory and coupled cluster theory were used to accurately describe critical configurations. Experiment and theory show the relaxation dynamics of furfural and β-furfural to be slowed down, and together they disclose an additional deactivation pathway, which is attributed to the n O lonepair state introduced with the aldehyde group.
A New Fokker-Planck Approach for the Relaxation-driven Evolution of Galactic Nuclei
Vasiliev, Eugene
2017-10-01
We present an approach for simulating the collisional evolution of spherical isotropic stellar systems based on the one-dimensional Fokker-Planck equation. A novel aspect is that we use the phase volume as the argument of the distribution function instead of the traditionally used energy, which facilitates the solution. The publicly available code PhaseFlow implements a high-accuracy finite-element method for the Fokker-Planck equation, and can handle multiple-component systems, optionally with the central black hole and taking into account loss-cone effects and star formation. We discuss the energy balance in the general setting, and in application to the Bahcall-Wolf cusp around a central black hole, for which we derive a perturbative solution. We stress that the cusp is not a steady-state structure, but rather evolves in amplitude while retaining an approximately ρ \\propto {r}-7/4 density profile. Finally, we apply the method to the nuclear star cluster of the milky Way, and illustrate a possible evolutionary scenario in which a two-component system of lighter main-sequence stars and stellar-mass black holes develops a Bahcall-Wolf cusp in the heavier component and a weaker ρ \\propto {r}-3/2 cusp in the lighter, visible component, over the period of several Gyr. The present-day density profile is consistent with the recently detected mild cusp inside the central parsec, and is weakly sensitive to initial conditions.
DEFF Research Database (Denmark)
Ruban, Andrei; Simak, S.I.; Shallcross, S.
2003-01-01
We present a simple effective tetrahedron model for local lattice relaxation effects in random metallic alloys on simple primitive lattices. A comparison with direct ab initio calculations for supercells representing random Ni0.50Pt0.50 and Cu0.25Au0.75 alloys as well as the dilute limit of Au-ri......-rich CuAu alloys shows that the model yields a quantitatively accurate description of the relaxtion energies in these systems. Finally, we discuss the bond length distribution in random alloys....
An improved Lagrangian relaxation and dual ascent approach to facility location problems
DEFF Research Database (Denmark)
Jörnsten, Kurt; Klose, Andreas
2016-01-01
not be reduced to the same extent as in the case of ordinary semi-Lagrangian relaxation. Hence, an effective method for optimizing the Lagrangian dual function is of utmost importance for obtaining a computational advantage from the simplified Lagrangian dual function. In this paper, we suggest a new dual ascent...... method for optimizing both the semi-Lagrangian dual function as well as its simplified form for the case of a generic discrete facility location problem and apply the method to the uncapacitated facility location problem. Our computational results show that the method generally only requires a very few...
Song-Gui Chen; Chuan-Hu Zhang; Yun-Tian Feng; Qi-Cheng Sun; Feng Jin
2016-01-01
This paper presents a three-dimensional (3D) parallel multiple-relaxation-time lattice Boltzmann model (MRT-LBM) for Bingham plastics which overcomes numerical instabilities in the simulation of non-Newtonian fluids for the Bhatnagar–Gross–Krook (BGK) model. The MRT-LBM and several related mathematical models are briefly described. Papanastasiou’s modified model is incorporated for better numerical stability. The impact of the relaxation parameters of the model is studied in detail. The MRT-L...
Meng, Xuhui; Guo, Zhaoli
2015-10-01
A lattice Boltzmann model with a multiple-relaxation-time (MRT) collision operator is proposed for incompressible miscible flow with a large viscosity ratio as well as a high Péclet number in this paper. The equilibria in the present model are motivated by the lattice kinetic scheme previously developed by Inamuro et al. [Philos. Trans. R. Soc. London, Ser. A 360, 477 (2002), 10.1098/rsta.2001.0942]. The fluid viscosity and diffusion coefficient depend on both the corresponding relaxation times and additional adjustable parameters in this model. As a result, the corresponding relaxation times can be adjusted in proper ranges to enhance the performance of the model. Numerical validations of the Poiseuille flow and a diffusion-reaction problem demonstrate that the proposed model has second-order accuracy in space. Thereafter, the model is used to simulate flow through a porous medium, and the results show that the proposed model has the advantage to obtain a viscosity-independent permeability, which makes it a robust method for simulating flow in porous media. Finally, a set of simulations are conducted on the viscous miscible displacement between two parallel plates. The results reveal that the present model can be used to simulate, to a high level of accuracy, flows with large viscosity ratios and/or high Péclet numbers. Moreover, the present model is shown to provide superior stability in the limit of high kinematic viscosity. In summary, the numerical results indicate that the present lattice Boltzmann model is an ideal numerical tool for simulating flow with a large viscosity ratio and/or a high Péclet number.
A service and value based approach to estimating environmental flows
DEFF Research Database (Denmark)
Korsgaard, Louise; Jensen, R.A.; Jønch-Clausen, Torkil
2008-01-01
at filling that gap by presenting a new environmental flows assessment approach that explicitly links environmental flows to (socio)-economic values by focusing on ecosystem services. This Service Provision Index (SPI) approach is a novel contribution to the existing field of environmental flows assessment...... of sustaining ecosystems but also a matter of supporting humankind/livelihoods. One reason for the marginalisation of environmental flows is the lack of operational methods to demonstrate the inherently multi-disciplinary link between environmental flows, ecosystem services and economic value. This paper aims...
Garcia, M J; Smedira, N G; Greenberg, N L; Main, M; Firstenberg, M S; Odabashian, J; Thomas, J D
2000-01-01
To determine the effect of preload in color M-mode Doppler flow propagation velocity (v(p)). The interpretation of Doppler filling patterns is limited by confounding effects of left ventricular (LV) relaxation and preload. Color M-mode v(p) has been proposed as a new index of LV relaxation. We studied four dogs before and during inferior caval (IVC) occlusion at five different inotropic stages and 14 patients before and during partial cardiopulmonary bypass. Left ventricular (LV) end-diastolic volumes (LV-EDV), the time constant of isovolumic relaxation (tau), left atrial (LA) pre-A and LV end-diastolic pressures (LV-EDP) were measured. Peak velocity during early filling (E) and v(p) were extracted by digital analysis of color M-mode Doppler images. In both animals and humans, LV-EDV and LV-EDP decreased significantly from baseline to IVC occlusion (both p < 0.001). Peak early filling (E) velocity decreased in animals from 56 +/- 21 to 42 +/- 17 cm/s (p < 0.001) without change in v(p) (from 35 +/- 15 to 35 +/- 16, p = 0.99). Results were similar in humans (from 69 +/- 15 to 53 +/- 22 cm/s, p < 0.001, and 37 +/- 12 to 34 +/- 16, p = 0.30). In both species, there was a strong correlation between LV relaxation (tau) and v(p) (r = 0.78, p < 0.001, r = 0.86, p < 0.001). Our results indicate that color M-mode Doppler v(p) is not affected by preload alterations and confirms that LV relaxation is its main physiologic determinant in both animals during varying lusitropic conditions and in humans with heart disease.
The flow equation approach to many-particle systems
Kehrein, Stefan; Fujimori, A; Varma, C; Steiner, F
2006-01-01
This self-contained monograph addresses the flow equation approach to many-particle systems. The flow equation approach consists of a sequence of infinitesimal unitary transformations and is conceptually similar to renormalization and scaling methods. Flow equations provide a framework for analyzing Hamiltonian systems where these conventional many-body techniques fail. The text first discusses the general ideas and concepts of the flow equation method. In a second part these concepts are illustrated with various applications in condensed matter theory including strong-coupling problems and non-equilibrium systems. The monograph is accessible to readers familiar with graduate- level solid-state theory.
CFD Modeling of Wall Steam Condensation: Two-Phase Flow Approach versus Homogeneous Flow Approach
International Nuclear Information System (INIS)
Mimouni, S.; Mechitoua, N.; Foissac, A.; Hassanaly, M.; Ouraou, M.
2011-01-01
The present work is focused on the condensation heat transfer that plays a dominant role in many accident scenarios postulated to occur in the containment of nuclear reactors. The study compares a general multiphase approach implemented in NEPTUNE C FD with a homogeneous model, of widespread use for engineering studies, implemented in Code S aturne. The model implemented in NEPTUNE C FD assumes that liquid droplets form along the wall within nucleation sites. Vapor condensation on droplets makes them grow. Once the droplet diameter reaches a critical value, gravitational forces compensate surface tension force and then droplets slide over the wall and form a liquid film. This approach allows taking into account simultaneously the mechanical drift between the droplet and the gas, the heat and mass transfer on droplets in the core of the flow and the condensation/evaporation phenomena on the walls. As concern the homogeneous approach, the motion of the liquid film due to the gravitational forces is neglected, as well as the volume occupied by the liquid. Both condensation models and compressible procedures are validated and compared to experimental data provided by the TOSQAN ISP47 experiment (IRSN Saclay). Computational results compare favorably with experimental data, particularly for the Helium and steam volume fractions.
Hugueny, Bernard; Movellan, A.; Belliard, J.
2011-01-01
Aim To estimate population extinction rates within freshwater fish communities since the fragmentation of palaeo-rivers due to sea level rise at the end of the Pleistocene; to combine this information with rates estimated by other approaches (population surveys, fossil records); and to build an empirical extinction-area relationship. Location Temperate rivers from the Northern Hemisphere, with a special focus on rivers discharging into the English Channel, in north-western France. Methods (1)...
A Logical Approach to the Statement of Cash Flows
Petro, Fred; Gean, Farrell
2014-01-01
Of the three financial statements in financial reporting, the Statement of Cash Flows (SCF) is perhaps the most challenging. The most difficult aspect of the SCF is in developing an understanding of how previous transactions are finalized in this document. The purpose of this paper is to logically explain the indirect approach of cash flow whereby…
New approach for simulating groundwater flow in discrete fracture network
Fang, H.; Zhu, J.
2017-12-01
In this study, we develop a new approach to calculate groundwater flowrate and hydraulic head distribution in two-dimensional discrete fracture network (DFN) where both laminar and turbulent flows co-exist in individual fractures. The cubic law is used to calculate hydraulic head distribution and flow behaviors in fractures where flow is laminar, while the Forchheimer's law is used to quantify turbulent flow behaviors. Reynolds number is used to distinguish flow characteristics in individual fractures. The combination of linear and non-linear equations is solved iteratively to determine flowrates in all fractures and hydraulic heads at all intersections. We examine potential errors in both flowrate and hydraulic head from the approach of uniform flow assumption. Applying the cubic law in all fractures regardless of actual flow conditions overestimates the flowrate when turbulent flow may exist while applying the Forchheimer's law indiscriminately underestimate the flowrate when laminar flows exist in the network. The contrast of apertures of large and small fractures in the DFN has significant impact on the potential errors of using only the cubic law or the Forchheimer's law. Both the cubic law and Forchheimer's law simulate similar hydraulic head distributions as the main difference between these two approaches lies in predicting different flowrates. Fracture irregularity does not significantly affect the potential errors from using only the cubic law or the Forchheimer's law if network configuration remains similar. Relative density of fractures does not significantly affect the relative performance of the cubic law and Forchheimer's law.
Flow cytometry approach for studying the interaction between ...
African Journals Online (AJOL)
Flow cytometry approach for studying the interaction between Bacillus mojavensis and Alternaria alternata. Asma Milet, Noreddine Kacem Chaouche, Laid Dehimat, Asma Ait Kaki, Mounira Kara Ali, Philippe Thonart ...
Kloos, G.
1996-01-01
The interpretation of relaxation spectra of second-order cross-effects is a problem that arises in some branches of materials science when coupling between thermal, mechanical and dielectric quantities is investigated. In this article, a transfer-function approach is combined with thermodynamics to
Flow Regime Identification of Co-Current Downward Two-Phase Flow With Neural Network Approach
International Nuclear Information System (INIS)
Hiroshi Goda; Seungjin Kim; Ye Mi; Finch, Joshua P.; Mamoru Ishii; Jennifer Uhle
2002-01-01
Flow regime identification for an adiabatic vertical co-current downward air-water two-phase flow in the 25.4 mm ID and the 50.8 mm ID round tubes was performed by employing an impedance void meter coupled with the neural network classification approach. This approach minimizes the subjective judgment in determining the flow regimes. The signals obtained by an impedance void meter were applied to train the self-organizing neural network to categorize these impedance signals into a certain number of groups. The characteristic parameters set into the neural network classification included the mean, standard deviation and skewness of impedance signals in the present experiment. The classification categories adopted in the present investigation were four widely accepted flow regimes, viz. bubbly, slug, churn-turbulent, and annular flows. These four flow regimes were recognized based upon the conventional flow visualization approach by a high-speed motion analyzer. The resulting flow regime maps classified by the neural network were compared with the results obtained through the flow visualization method, and consequently the efficiency of the neural network classification for flow regime identification was demonstrated. (authors)
An Approach to Predict Debris Flow Average Velocity
Directory of Open Access Journals (Sweden)
Chen Cao
2017-03-01
Full Text Available Debris flow is one of the major threats for the sustainability of environmental and social development. The velocity directly determines the impact on the vulnerability. This study focuses on an approach using radial basis function (RBF neural network and gravitational search algorithm (GSA for predicting debris flow velocity. A total of 50 debris flow events were investigated in the Jiangjia gully. These data were used for building the GSA-based RBF approach (GSA-RBF. Eighty percent (40 groups of the measured data were selected randomly as the training database. The other 20% (10 groups of data were used as testing data. Finally, the approach was applied to predict six debris flow gullies velocities in the Wudongde Dam site area, where environmental conditions were similar to the Jiangjia gully. The modified Dongchuan empirical equation and the pulled particle analysis of debris flow (PPA approach were used for comparison and validation. The results showed that: (i the GSA-RBF predicted debris flow velocity values are very close to the measured values, which performs better than those using RBF neural network alone; (ii the GSA-RBF results and the MDEE results are similar in the Jiangjia gully debris flow velocities prediction, and GSA-RBF performs better; (iii in the study area, the GSA-RBF results are validated reliable; and (iv we could consider more variables in predicting the debris flow velocity by using GSA-RBF on the basis of measured data in other areas, which is more applicable. Because the GSA-RBF approach was more accurate, both the numerical simulation and the empirical equation can be taken into consideration for constructing debris flow mitigation works. They could be complementary and verified for each other.
A dielectric relaxation approach
Indian Academy of Sciences (India)
The complex permittivity spectra were studied using the time domain reflectometry [6,7] method. The Hewlett Packard HP 54750 sampling oscilloscope with HP 54754A TDR plug in module has been used. A fast rising step voltage pulse of about 40 ps rise time was propagated through a coaxial line system. Transmission ...
Energetic Variational Approach to Multi-Component Fluid Flows
Kirshtein, Arkadz; Liu, Chun; Brannick, James
2017-11-01
In this talk I will introduce the systematic energetic variational approach for dissipative systems applied to multi-component fluid flows. These variational approaches are motivated by the seminal works of Rayleigh and Onsager. The advantage of this approach is that we have to postulate only energy law and some kinematic relations based on fundamental physical principles. The method gives a clear, quick and consistent way to derive the PDE system. I will compare different approaches to three-component flows using diffusive interface method and discuss their advantages and disadvantages. The diffusive interface method is an approach for modeling interactions among complex substances. The main idea behind this method is to introduce phase field labeling functions in order to model the contact line by smooth change from one type of material to another. The work of Arkadz Kirshtein and Chun Liu is partially supported by NSF Grants DMS-141200 and DMS-1216938.
Variational formulation of relaxed and multi-region relaxed magnetohydrodynamics
Dewar, R. L.; Yoshida, Z.; Bhattacharjee, A.; Hudson, S. R.
2015-12-01
> Ideal magnetohydrodynamics (IMHD) is strongly constrained by an infinite number of microscopic constraints expressing mass, entropy and magnetic flux conservation in each infinitesimal fluid element, the latter preventing magnetic reconnection. By contrast, in the Taylor relaxation model for formation of macroscopically self-organized plasma equilibrium states, all these constraints are relaxed save for the global magnetic fluxes and helicity. A Lagrangian variational principle is presented that leads to a new, fully dynamical, relaxed magnetohydrodynamics (RxMHD), such that all static solutions are Taylor states but also allows state with flow. By postulating that some long-lived macroscopic current sheets can act as barriers to relaxation, separating the plasma into multiple relaxation regions, a further generalization, multi-region relaxed magnetohydrodynamics (MRxMHD) is developed.
Gupta, R. N.
1972-01-01
The relaxation of the accelerating-gas boundary layer to the test-gas boundary layer over a flat plate in an expansion tube is analyzed. Several combinations of test gas and acceleration gas are considered. The problem is treated in two conically similar limits: (1) when the time lag between the arrival of the shock and the interface at the leading edge of the plate is very large, and (2) when this lag is negligible. The time-dependent laminar-boundary-layer equations of a binary mixture of perfect gases are taken as the flow-governing equations. This coupled set of differential equations, written in terms of the Lam-Crocco variables, has been solved by a line-relaxation finite-difference techniques. The results presented include the Stanton number and the local skin-friction coefficient as functions of shock Mach number and the nondimensional distance-time variable. The results indicate that more than 95 percent of the test-gas boundary layer exists over a length, measured from the leading edge of the plate, equal to about three-tenths of the distance traversed by the interface in the free stream.
An active, collaborative approach to learning skills in flow cytometry.
Fuller, Kathryn; Linden, Matthew D; Lee-Pullen, Tracey; Fragall, Clayton; Erber, Wendy N; Röhrig, Kimberley J
2016-06-01
Advances in science education research have the potential to improve the way students learn to perform scientific interpretations and understand science concepts. We developed active, collaborative activities to teach skills in manipulating flow cytometry data using FlowJo software. Undergraduate students were given compensated clinical flow cytometry listmode output (FCS) files and asked to design a gating strategy to diagnose patients with different hematological malignancies on the basis of their immunophenotype. A separate cohort of research trainees was given uncompensated data files on which they performed their own compensation, calculated the antibody staining index, designed a sequential gating strategy, and quantified rare immune cell subsets. Student engagement, confidence, and perceptions of flow cytometry were assessed using a survey. Competency against the learning outcomes was assessed by asking students to undertake tasks that required understanding of flow cytometry dot plot data and gating sequences. The active, collaborative approach allowed students to achieve learning outcomes not previously possible with traditional teaching formats, for example, having students design their own gating strategy, without forgoing essential outcomes such as the interpretation of dot plots. In undergraduate students, favorable perceptions of flow cytometry as a field and as a potential career choice were correlated with student confidence but not the ability to perform flow cytometry data analysis. We demonstrate that this new pedagogical approach to teaching flow cytometry is beneficial for student understanding and interpretation of complex concepts. It should be considered as a useful new method for incorporating complex data analysis tasks such as flow cytometry into curricula. Copyright © 2016 The American Physiological Society.
1987-01-01
Environ Corporation's relaxation system is built around a body lounge, a kind of super easy chair that incorporates sensory devices. Computer controlled enclosure provides filtered ionized air to create a feeling of invigoration, enhanced by mood changing aromas. Occupant is also surrounded by multidimensional audio and the lighting is programmed to change colors, patterns, and intensity periodically. These and other sensory stimulators are designed to provide an environment in which the learning process is stimulated, because research has proven that while an individual is in a deep state of relaxation, the mind is more receptive to new information.
Kenkre, V. M.; Chase, M.
2017-08-01
The approach to equilibrium of a quantum mechanical system in interaction with a bath is studied from a practical as well as a conceptual point of view. Explicit memory functions are derived for given models of bath couplings. If the system is a harmonic oscillator representing a molecule in interaction with a reservoir, the generalized master equation derived becomes an extension into the coherent domain of the well-known Montroll-Shuler equation for vibrational relaxation and unimolecular dissociation. A generalization of the Bethe-Teller result regarding energy relaxation is found for short times. The theory has obvious applications to relaxation dynamics at ultra-short times as in observations on the femtosecond time scale and to the investigation of quantum coherence at those short times. While vibrational relaxation in chemical physics is a primary target of the study, another system of interest in condensed matter physics, an electron or hole in a lattice subjected to a strong DC electric field that gives rise to well-known Wannier-Stark ladders, is naturally addressed with the theory. Specific system-bath interactions are explored to obtain explicit details of the dynamics. General phenomenological descriptions of the reservoir are considered rather than specific microscopic realizations.
DEFF Research Database (Denmark)
Heuck, Mikkel; Kristensen, Philip Trøst; Mørk, Jesper
2014-01-01
We propose and analyze a differential control scheme for cavity-enhanced optical signal processing devices based on carrier nonlinearities. The scheme relies on two optical cavities to increase the bandwidth beyond the limit given by the slowest carrier relaxation rate of the medium. Practical...
Partial Averaged Navier-Stokes approach for cavitating flow
International Nuclear Information System (INIS)
Zhang, L; Zhang, Y N
2015-01-01
Partial Averaged Navier Stokes (PANS) is a numerical approach developed for studying practical engineering problems (e.g. cavitating flow inside hydroturbines) with a resonance cost and accuracy. One of the advantages of PANS is that it is suitable for any filter width, leading a bridging method from traditional Reynolds Averaged Navier-Stokes (RANS) to direct numerical simulations by choosing appropriate parameters. Comparing with RANS, the PANS model will inherit many physical nature from parent RANS but further resolve more scales of motion in great details, leading to PANS superior to RANS. As an important step for PANS approach, one need to identify appropriate physical filter-width control parameters e.g. ratios of unresolved-to-total kinetic energy and dissipation. In present paper, recent studies of cavitating flow based on PANS approach are introduced with a focus on the influences of filter-width control parameters on the simulation results
Detailed debris flow hazard assessment in Andorra: A multidisciplinary approach
Hürlimann, Marcel; Copons, Ramon; Altimir, Joan
2006-08-01
In many mountainous areas, the rapid development of urbanisation and the limited space in the valley floors have created a need to construct buildings in zones potentially exposed to debris flow hazard. In these zones, a detailed and coherent hazard assessment is necessary to provide an adequate urban planning. This article presents a multidisciplinary procedure to evaluate the debris flow hazard at a local scale. Our four-step approach was successfully applied to five torrent catchments in the Principality of Andorra, located in the Pyrenees. The first step consisted of a comprehensive geomorphologic and geologic analysis providing an inventory map of the past debris flows, a magnitude-frequency relationship, and a geomorphologic-geologic map. These data were necessary to determine the potential initiation zones and volumes of future debris flows for each catchment. A susceptibility map and different scenarios were the principal outcome of the first step, as well as essential input data for the second step, the runout analysis. A one-dimensional numerical code was applied to analyse the scenarios previously defined. First, the critical channel sections in the fan area were evaluated, then the maximum runout of the debris flows on the fan was studied, and finally simplified intensity maps for each defined scenario were established. The third step of our hazard assessment was the hazard zonation and the compilation of all the results from the two previous steps in a final hazard map. The base of this hazard map was the hazard matrix, which combined the intensity of the debris flow with its probability of occurrence and determined a certain hazard degree. The fourth step referred to the hazard mitigation and included some recommendations for hazard reduction. In Andorra, this four-step approach is actually being applied to assess the debris flow hazard. The final hazard maps, at 1 : 2000 scale, provide an obligatory tool for local land use planning. Experience
Approaching multiphase flows from the perspective of computational fluid dynamics
International Nuclear Information System (INIS)
Banas, A.O.
1992-01-01
Thermalhydraulic simulation methodologies based on subchannel and porous-medium concepts are briefly reviewed and contrasted with the general approach of Computational Fluid Dynamics (CFD). An outline of the advanced CFD methods for single-phase turbulent flows is followed by a short discussion of the unified formulation of averaged equations for turbulent and multiphase flows. Some of the recent applications of CFD at Chalk River Laboratories are discussed, and the complementary role of CFD with regard to the established thermalhydraulic methods of analysis is indicated. (author). 8 refs
Relaxation and Distraction in Experimental Desensitization.
Weir, R. O.; Marshall, W. L.
1980-01-01
Compared experimental desensitization with a procedure that replaced relaxation with a distraction task and with an approach that combined both relaxation and distraction. Desensitization generally was more effective than the other two procedures. (Author)
Kabir, Russell S.; Haramaki, Yutaka; Ki, Hyeyoung; Ohno, Hiroyuki
2018-01-01
Relaxation programs are known for their versatility, cost-effectiveness, and ability to help people obtain skills to regulate their mental states and promote and maintain health. Self-Active Relaxation Therapy (SART) is a body-oriented approach to psychological rehabilitation that grew out of the suite of movement tasks developed in the Japanese psychotherapy known as Dohsa-hou, or the body movement method. The program for SART is designed to stretch, twist, and release areas of the upper, lower, and whole body through a set of movements which are guided by the practitioner and performed “self-actively” by the client to empower them to learn to recognize points of tension in the body and act on their own to achieve a relaxed state. Numerous studies have showed that SART is associated with reduced negative mood states and enhanced body awareness. A short version of SART has been investigated as a psychological support salon activity for the elderly, mothers raising children, special needs students, and children adapting to school. The full program has also been applied in clinical settings to address or supplement treatments for psychological and developmental conditions, and longitudinally employed in community contexts to assist residents facing long-term disaster recovery circumstances in Japan. This paper reviews the research and applications of SART as a bodymind approach by critically examining evidence and research gaps for future studies, comparing it with techniques established in the literature, and positing a self-regulatory framework for SART as a tool to become aware of bodily states, regulate mood, and manage stress through the deliberate practice of relaxation. PMID:29472851
A Galerkin least squares approach to viscoelastic flow.
Energy Technology Data Exchange (ETDEWEB)
Rao, Rekha R. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Schunk, Peter Randall [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2015-10-01
A Galerkin/least-squares stabilization technique is applied to a discrete Elastic Viscous Stress Splitting formulation of for viscoelastic flow. From this, a possible viscoelastic stabilization method is proposed. This method is tested with the flow of an Oldroyd-B fluid past a rigid cylinder, where it is found to produce inaccurate drag coefficients. Furthermore, it fails for relatively low Weissenberg number indicating it is not suited for use as a general algorithm. In addition, a decoupled approach is used as a way separating the constitutive equation from the rest of the system. A Pressure Poisson equation is used when the velocity and pressure are sought to be decoupled, but this fails to produce a solution when inflow/outflow boundaries are considered. However, a coupled pressure-velocity equation with a decoupled constitutive equation is successful for the flow past a rigid cylinder and seems to be suitable as a general-use algorithm.
Synthetic Aperture Flow Imaging Using a Dual Beamformer Approach
DEFF Research Database (Denmark)
Li, Ye
Color flow mapping systems have become widely used in clinical applications. It provides an opportunity to visualize the velocity profile over a large region in the vessel, which makes it possible to diagnose, e.g., occlusion of veins, heart valve deficiencies, and other hemodynamic problems....... However, while the conventional ultrasound imaging of making color flow mapping provides useful information in many circumstances, the spatial velocity resolution and frame rate are limited. The entire velocity distribution consists of image lines from different directions, and each image line...... on the current commercial ultrasound scanner. The motivation for this project is to develop a method lowering the amount of calculations and still maintaining beamforming quality sufficient for flow estimation. Synthetic aperture using a dual beamformer approach is investigated using Field II simulations...
Numerical schemes for the hybrid modeling approach of gas-particle turbulent flows
International Nuclear Information System (INIS)
Dorogan, K.
2012-01-01
Hybrid Moments/PDF methods have shown to be well suitable for the description of poly-dispersed turbulent two-phase flows in non-equilibrium which are encountered in some industrial situations involving chemical reactions, combustion or sprays. They allow to obtain a fine enough physical description of the poly-dispersity, non-linear source terms and convection phenomena. However, their approximations are noised with the statistical error, which in several situations may be a source of a bias. An alternative hybrid Moments-Moments/PDF approach examined in this work consists in coupling the Moments and the PDF descriptions, within the description of the dispersed phase itself. This hybrid method could reduce the statistical error and remove the bias. However, such a coupling is not straightforward in practice and requires the development of accurate and stable numerical schemes. The approaches introduced in this work rely on the combined use of the up-winding and relaxation-type techniques. They allow to obtain stable unsteady approximations for a system of partial differential equations containing non-smooth external data which are provided by the PDF part of the model. A comparison of the results obtained using the present method with those of the 'classical' hybrid approach is presented in terms of the numerical errors for a case of a co-current gas-particle wall jet. (author)
The pdf approach to turbulent polydispersed two-phase flows
Minier, Jean-Pierre; Peirano, Eric
2001-10-01
The purpose of this paper is to develop a probabilistic approach to turbulent polydispersed two-phase flows. The two-phase flows considered are composed of a continuous phase, which is a turbulent fluid, and a dispersed phase, which represents an ensemble of discrete particles (solid particles, droplets or bubbles). Gathering the difficulties of turbulent flows and of particle motion, the challenge is to work out a general modelling approach that meets three requirements: to treat accurately the physically relevant phenomena, to provide enough information to address issues of complex physics (combustion, polydispersed particle flows, …) and to remain tractable for general non-homogeneous flows. The present probabilistic approach models the statistical dynamics of the system and consists in simulating the joint probability density function (pdf) of a number of fluid and discrete particle properties. A new point is that both the fluid and the particles are included in the pdf description. The derivation of the joint pdf model for the fluid and for the discrete particles is worked out in several steps. The mathematical properties of stochastic processes are first recalled. The various hierarchies of pdf descriptions are detailed and the physical principles that are used in the construction of the models are explained. The Lagrangian one-particle probabilistic description is developed first for the fluid alone, then for the discrete particles and finally for the joint fluid and particle turbulent systems. In the case of the probabilistic description for the fluid alone or for the discrete particles alone, numerical computations are presented and discussed to illustrate how the method works in practice and the kind of information that can be extracted from it. Comments on the current modelling state and propositions for future investigations which try to link the present work with other ideas in physics are made at the end of the paper.
A stochastic programming approach to manufacturing flow control
Haurie, Alain; Moresino, Francesco
2012-01-01
This paper proposes and tests an approximation of the solution of a class of piecewise deterministic control problems, typically used in the modeling of manufacturing flow processes. This approximation uses a stochastic programming approach on a suitably discretized and sampled system. The method proceeds through two stages: (i) the Hamilton-Jacobi-Bellman (HJB) dynamic programming equations for the finite horizon continuous time stochastic control problem are discretized over a set of sample...
A measure theoretic approach to traffic flow optimization on networks
Cacace, Simone; Camilli, Fabio; De Maio, Raul; Tosin, Andrea
2018-01-01
We consider a class of optimal control problems for measure-valued nonlinear transport equations describing traffic flow problems on networks. The objective isto minimise/maximise macroscopic quantities, such as traffic volume or average speed,controlling few agents, for example smart traffic lights and automated cars. The measuretheoretic approach allows to study in a same setting local and nonlocal drivers interactionsand to consider the control variables as additional measures interacting ...
A service and value based approach to estimating environmental flows
DEFF Research Database (Denmark)
Korsgaard, Louise; Jensen, R.A.; Jønch-Clausen, Torkil
2008-01-01
An important challenge of Integrated Water Resources Management (IWRM) is to balance water allocation between different users and uses. While economically and/or politically powerful users have relatively well developed methods for quantifying and justifying their water needs, this is not the case...... methodologies. The SPI approach is a pragmatic and transparent tool for incorporating ecosystems and environmental flows into the evaluation of water allocation scenarios, negotiations of trade-offs and decision-making in IWRM....
Heterogeneity of cerebral blood flow: a fractal approach
International Nuclear Information System (INIS)
Kuikka, J.T.; Hartikainen, P.
2000-01-01
Aim: We demonstrate the heterogeneity of regional cerebral blood flow using a fractal approach and single-photon emission computed tomography (SPECT). Method: Tc-99m-labelled ethylcysteine dimer was injected intravenously in 10 healthy controls and in 10 patients with dementia of frontal lobe type. The head was imaged with a gamma camera and transaxial, sagittal and coronal slices were reconstructed. Two hundred fifty-six symmetrical regions of interest (ROIs) were drawn onto each hemisphere of functioning brain matter. Fractal analysis was used to examine the spatial heterogeneity of blood flow as a function of the number of ROIs. Results: Relative dispersion (=coefficient of variation of the regional flows) was fractal-like in healthy subjects and could be characterized by a fractal dimension of 1.17±0.05 (mean±SD) for the left hemisphere and 1.15±0.04 for the right hemisphere, respectively. The fractal dimension of 1.0 reflects completely homogeneous blood flow and 1.5 indicates a random blood flow distribution. Patients with dementia of frontal lobe type had a significantly lower fractal dimension of 1.04±0.03 than in healthy controls. (orig.) [de
Statistical Approaches for Spatiotemporal Prediction of Low Flows
Fangmann, A.; Haberlandt, U.
2017-12-01
An adequate assessment of regional climate change impacts on streamflow requires the integration of various sources of information and modeling approaches. This study proposes simple statistical tools for inclusion into model ensembles, which are fast and straightforward in their application, yet able to yield accurate streamflow predictions in time and space. Target variables for all approaches are annual low flow indices derived from a data set of 51 records of average daily discharge for northwestern Germany. The models require input of climatic data in the form of meteorological drought indices, derived from observed daily climatic variables, averaged over the streamflow gauges' catchments areas. Four different modeling approaches are analyzed. Basis for all pose multiple linear regression models that estimate low flows as a function of a set of meteorological indices and/or physiographic and climatic catchment descriptors. For the first method, individual regression models are fitted at each station, predicting annual low flow values from a set of annual meteorological indices, which are subsequently regionalized using a set of catchment characteristics. The second method combines temporal and spatial prediction within a single panel data regression model, allowing estimation of annual low flow values from input of both annual meteorological indices and catchment descriptors. The third and fourth methods represent non-stationary low flow frequency analyses and require fitting of regional distribution functions. Method three is subject to a spatiotemporal prediction of an index value, method four to estimation of L-moments that adapt the regional frequency distribution to the at-site conditions. The results show that method two outperforms successive prediction in time and space. Method three also shows a high performance in the near future period, but since it relies on a stationary distribution, its application for prediction of far future changes may be
Meskhidze, N.; Royalty, T. M.; Phillips, B.; Dawson, K. W.; Petters, M. D.; Reed, R.; Weinstein, J.; Hook, D.; Wiener, R.
2017-12-01
The accurate representation of aerosols in climate models requires direct ambient measurement of the size- and composition-dependent particle production fluxes. Here we present the design, testing, and analysis of data collected through the first instrument capable of measuring hygroscopicity-based, size-resolved particle fluxes using a continuous-flow Hygroscopicity-Resolved Relaxed Eddy Accumulation (Hy-Res REA) technique. The different components of the instrument were extensively tested inside the US Environmental Protection Agency's Aerosol Test Facility for sea-salt and ammoniums sulfate particle fluxes. The new REA system design does not require particle accumulation, therefore avoids the diffusional wall losses associated with long residence times of particles inside the air collectors of the traditional REA devices. The Hy-Res REA system used in this study includes a 3-D sonic anemometer, two fast-response solenoid valves, two Condensation Particle Counters (CPCs), a Scanning Mobility Particle Sizer (SMPS), and a Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA). A linear relationship was found between the sea-salt particle fluxes measured by eddy covariance and REA techniques, with comparable theoretical (0.34) and measured (0.39) proportionality constants. The sea-salt particle detection limit of the Hy-Res REA flux system is estimated to be 6x105 m-2s-1. For the conditions of ammonium sulfate and sea-salt particles of comparable source strength and location, the continuous-flow Hy-Res REA instrument was able to achieve better than 90% accuracy of measuring the sea-salt particle fluxes. In principle, the instrument can be applied to measure fluxes of particles of variable size and distinct hygroscopic properties (i.e., mineral dust, black carbon, etc.).
Approaches to the simulation of unconfined flow and perched groundwater flow in MODFLOW
Bedekar, Vivek; Niswonger, Richard G.; Kipp, Kenneth; Panday, Sorab; Tonkin, Matthew
2012-01-01
Various approaches have been proposed to manage the nonlinearities associated with the unconfined flow equation and to simulate perched groundwater conditions using the MODFLOW family of codes. The approaches comprise a variety of numerical techniques to prevent dry cells from becoming inactive and to achieve a stable solution focused on formulations of the unconfined, partially-saturated, groundwater flow equation. Keeping dry cells active avoids a discontinuous head solution which in turn improves the effectiveness of parameter estimation software that relies on continuous derivatives. Most approaches implement an upstream weighting of intercell conductance and Newton-Raphson linearization to obtain robust convergence. In this study, several published approaches were implemented in a stepwise manner into MODFLOW for comparative analysis. First, a comparative analysis of the methods is presented using synthetic examples that create convergence issues or difficulty in handling perched conditions with the more common dry-cell simulation capabilities of MODFLOW. Next, a field-scale three-dimensional simulation is presented to examine the stability and performance of the discussed approaches in larger, practical, simulation settings.
Moment approach to neoclassical flows, currents and transport in auxiliary heated tokamaks
International Nuclear Information System (INIS)
Kim, Yil Bong.
1988-02-01
The moment approach is utilized to derive the full complement of neoclassical transport processes in auxiliary heated tokamaks. The effects of auxiliary heating [neutral beam injection (NBI) and ion cyclotron resonance heating (ICRH)] considered arise from the collisional interaction between the background plasma species and the fast-ion-tail species. From a known fast ion distribution function we evaluate the parallel (to the magnetic field) momentum and heat flow inputs to the background plasma. Then, through the momentum and heat flow balance equations, we can determine the induced parallel flows (and current) and radial transpot fluxes in ''equilibrium'' (on the time scale much longer than the collisional relaxation time, i.e., t >> 1ν/sub ii/). In addition to the fast-ion-induced current, the total neoclassical current includes the boostap current, which is driven by the pressure and temperature gradients, the Pfirsch-Schlueter current which is required for charge neutrality, and the neoclassical (including trapped particle effects) Spitzer current due to the parallel electric field. The radial transport fluxes also include off-diagonal compnents in the transport matrix which correspond to the Ware (neoclassical) pinch due to the inductive applied electric field an the fast-ion-induced radial fluxes, in addition to the usual pressure- and temperature-gradient-driven fluxes (particle diffusion and heat conduction). Once the tranport coefficient are completely determined, the radial fluxes and the heat fluxes can be substituted into the density and energy evolution equations to provide a complete description of ''equilibrium'' (δδt << ν/sub ii/) neoclassical transport processes in a plasma. 47 refs., 14 figs
Cryogenic parallel, single phase flows: an analytical approach
Eichhorn, R.
2017-02-01
Managing the cryogenic flows inside a state-of-the-art accelerator cryomodule has become a demanding endeavour: In order to build highly efficient modules, all heat transfers are usually intercepted at various temperatures. For a multi-cavity module, operated at 1.8 K, this requires intercepts at 4 K and at 80 K at different locations with sometimes strongly varying heat loads which for simplicity reasons are operated in parallel. This contribution will describe an analytical approach, based on optimization theories.
Zhu, Ming; Liu, Tingting; Wang, Shu; Zhang, Kesheng
2017-08-01
Existing two-frequency reconstructive methods can only capture primary (single) molecular relaxation processes in excitable gases. In this paper, we present a reconstructive method based on the novel decomposition of frequency-dependent acoustic relaxation spectra to capture the entire molecular multimode relaxation process. This decomposition of acoustic relaxation spectra is developed from the frequency-dependent effective specific heat, indicating that a multi-relaxation process is the sum of the interior single-relaxation processes. Based on this decomposition, we can reconstruct the entire multi-relaxation process by capturing the relaxation times and relaxation strengths of N interior single-relaxation processes, using the measurements of acoustic absorption and sound speed at 2N frequencies. Experimental data for the gas mixtures CO2-N2 and CO2-O2 validate our decomposition and reconstruction approach.
A Hybrid Genetic Algorithm Approach for Optimal Power Flow
Directory of Open Access Journals (Sweden)
Sydulu Maheswarapu
2011-08-01
Full Text Available This paper puts forward a reformed hybrid genetic algorithm (GA based approach to the optimal power flow. In the approach followed here, continuous variables are designed using real-coded GA and discrete variables are processed as binary strings. The outcomes are compared with many other methods like simple genetic algorithm (GA, adaptive genetic algorithm (AGA, differential evolution (DE, particle swarm optimization (PSO and music based harmony search (MBHS on a IEEE30 bus test bed, with a total load of 283.4 MW. Its found that the proposed algorithm is found to offer lowest fuel cost. The proposed method is found to be computationally faster, robust, superior and promising form its convergence characteristics.
Relaxation from particle production
Energy Technology Data Exchange (ETDEWEB)
Hook, Anson; Marques-Tavares, Gustavo [Stanford Institute for Theoretical Physics, Stanford University, Stanford, CA 94305 (United States)
2016-12-20
We consider using particle production as a friction force by which to implement a “Relaxion” solution to the electroweak hierarchy problem. Using this approach, we are able to avoid superplanckian field excursions and avoid any conflict with the strong CP problem. The relaxation mechanism can work before, during or after inflation allowing for inflationary dynamics to play an important role or to be completely decoupled.
A Potential Approach for Low Flow Selection in Water Resource Supply and Management
Ying Ouyang
2012-01-01
Low flow selections are essential to water resource management, water supply planning, and watershed ecosystem restoration. In this study, a new approach, namely the frequent-low (FL) approach (or frequent-low index), was developed based on the minimum frequent-low flow or level used in minimum flows and/or levels program in northeast Florida, USA. This FL approach was...
An improved approach for flow-based cloud point extraction.
Frizzarin, Rejane M; Rocha, Fábio R P
2014-04-11
Novel strategies are proposed to circumvent the main drawbacks of flow-based cloud point extraction (CPE). The surfactant-rich phase (SRP) was directly retained into the optical path of the spectrophotometric cell, thus avoiding its dilution previously to the measurement and yielding higher sensitivity. Solenoid micro-pumps were exploited to improve mixing by the pulsed flow and also to modulate the flow-rate for retention and removal of the SRP, thus avoiding the elution step, often carried out with organic solvents. The heat released and the increase of the salt concentration provided by an on-line neutralization reaction were exploited to induce the cloud point without an external heating device. These innovations were demonstrated by the spectrophotometric determination of iron, yielding a linear response from 10 to 200 μg L(-1) with a coefficient of variation of 2.3% (n=7). Detection limit and sampling rate were estimated at 5 μg L(-1) (95% confidence level) and 26 samples per hour, respectively. The enrichment factor was 8.9 and the procedure consumed only 6 μg of TAN and 390 μg of Triton X-114 per determination. At the 95% confidence level, the results obtained for freshwater samples agreed with the reference procedure and those obtained for digests of bovine muscle, rice flour, brown bread and tort lobster agreed with the certified reference values. The proposed procedure thus shows advantages in relation to previously proposed approaches for flow-based CPE, being a fast and environmental friendly alternative for on-line separation and pre-concentration. Copyright © 2014 Elsevier B.V. All rights reserved.
Experiments in paramagnetic relaxation
International Nuclear Information System (INIS)
Lijphart, E.E.
1976-01-01
This thesis presents two attempts to improve the resolving power of the relaxation measurement technique. The first attempt reconsiders the old technique of steady state saturation. When used in conjunction with the pulse technique, it offers the possibility of obtaining additional information about the system in which all-time derivatives are zero; in addition, non-linear effects may be distinguished from each other. The second attempt involved a systematic study of only one system: Cu in the Tutton salts (K and Rb). The systematic approach, the high accuracy of the measurement and the sheer amount of experimental data for varying temperature, magnetic field and concentration made it possible in this case to separate the prevailing relaxation mechanisms reliably
A Hybrid Harmony Search Algorithm Approach for Optimal Power Flow
Directory of Open Access Journals (Sweden)
Mimoun YOUNES
2012-08-01
Full Text Available Optimal Power Flow (OPF is one of the main functions of Power system operation. It determines the optimal settings of generating units, bus voltage, transformer tap and shunt elements in Power System with the objective of minimizing total production costs or losses while the system is operating within its security limits. The aim of this paper is to propose a novel methodology (BCGAs-HSA that solves OPF including both active and reactive power dispatch It is based on combining the binary-coded genetic algorithm (BCGAs and the harmony search algorithm (HSA to determine the optimal global solution. This method was tested on the modified IEEE 30 bus test system. The results obtained by this method are compared with those obtained with BCGAs or HSA separately. The results show that the BCGAs-HSA approach can converge to the optimum solution with accuracy compared to those reported recently in the literature.
Sheng, Chunhua; Hyams, Daniel G.; Sreenivas, Kidambi; Gaither, J. Adam; Marcum, David L.; Whitfield, David L.
2000-01-01
A multiblock unstructured grid approach is presented for solving three-dimensional incompressible inviscid and viscous turbulent flows about complete configurations. The artificial compressibility form of the governing equations is solved by a node-based, finite volume implicit scheme which uses a backward Euler time discretization. Point Gauss-Seidel relaxations are used to solve the linear system of equations at each time step. This work employs a multiblock strategy to the solution procedure, which greatly improves the efficiency of the algorithm by significantly reducing the memory requirements by a factor of 5 over the single-grid algorithm while maintaining a similar convergence behavior. The numerical accuracy of solutions is assessed by comparing with the experimental data for a submarine with stem appendages and a high-lift configuration.
Directory of Open Access Journals (Sweden)
Cecilia Maya Ochoa
2004-12-01
Full Text Available There exists an abysm between market prices and traditional valuation approaches such as Discounted Cash Flows (DCF, a fact that neither academics nor practitioners could continue ignoring. Recently, a complementary approach has taken a foothold into the valuation world. Building on the DCF approach yet going further in the sense of incorporating flexibility in management investment decisions, and taking advantage of the advances in option pricing theory, the real options approach (ROA has become the alternative to capital budgeting and, lately, to corporate valuation. Empirical evidence shows that ROA explains actual prices better than DCF approaches and nowadays there is no question that from a theoretical point of view, ROA is a much more appealing concept than passive NPV. However, its acceptance by practitioners has been very slow due to the complexity of real options pricing.Existe un abismo entre precios de Mercado y la valoración estimada por métodos tradicionales tales como Flujos de Caja Descontados, un hecho que ni académicos ni practicantes pueden continuar ignorando. Recientemente, una metodología complementaria ha tomado gran fuerza. Partiendo de los Flujos de Caja Descontados, pero incorporando flexibilidad en las decisiones de inversión y aprovechando los avances en la teoría de valoración de opciones, el enfoque de opciones reales (ROA se ha convertido en la alternativa para presupuestación de capital y valoración de empresas. La evidencia empírica muestra que ROA explica los precios de mercado mejor que los enfoques basados en flujos de caja descontados y, hoy en día, no hay discusión de que es más atractivo desde un punto de vista teórico; sin embargo, su utilización en la práctica ha sido muy limitada debido a las dificultades que presenta la valoración de las opciones reales.
Energy Technology Data Exchange (ETDEWEB)
Yokoi, Koki [Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, WI (United States); Raicu, Valerică, E-mail: vraicu@uwm.edu [Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, WI (United States); Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI (United States)
2017-06-28
Relaxation in fractal structures was investigated theoretically starting from a simple model of a Cantorian tree and kinetic equations linking the change in the number of particles (e.g., electrical charges) populating each branch of the tree and their transfer to other branches or to the ground state. We numerically solved the system of differential equations obtained and determined the so-called cumulative distribution function of particles, which, in dielectric or mechanical relaxation parlance, is the same as the relaxation function of the system. As a physical application, we studied the relationship between the dielectric relaxation in time-domain and the dielectric dispersion in the frequency-domain. Upon choosing appropriate rate constants, our model described accurately well-known non-exponential and non-Debye time- and frequency-domain functions, such as stretched exponentials, Havrilliak–Negami, and frequency power law. Our approach opens the door to applying kinetic models to describe a wide array of relaxation processes, which traditionally have posed great challenges to theoretical modeling based on first principles. - Highlights: • Relaxation was investigated for a system of particles flowing through a Cantorian tree. • A set of kinetic equations was formulated and used to compute the relaxation function of the system. • The dispersion function of the system was computed from the relaxation function. • An analytical method was used to recover the original relaxation function from the dispersion function. • This formalism was used to study dielectric relaxation and dispersion in fractal structures.
Discontinuous Galerkin Approaches for Stokes Flow and Flow in Porous Media
Lehmann, Ragnar; Kaus, Boris; Lukacova, Maria
2014-05-01
Firstly, we present results of a study comparing two different numerical approaches for solving the Stokes equations with strongly varying viscosity: the continuous Galerkin (i.e., FEM) and the discontinuous Galerkin (DG) method. Secondly, we show how the latter method can be extended and applied to flow in porous media governed by Darcy's law. Nonlinearities in the viscosity or other material parameters can lead to discontinuities in the velocity-pressure solution that may not be approximated well with continuous elements. The DG method allows for discontinuities across interior edges of the underlying mesh. Furthermore, depending on the chosen basis functions, it naturally enforces local mass conservation, i.e., in every mesh cell. Computationally, it provides the capability to locally adapt the polynomial degree and needs communication only between directly adjacent mesh cells making it highly flexible and easy to parallelize. The methods are compared for several geophysically relevant benchmarking setups and discussed with respect to speed, accuracy, computational efficiency.
Relaxation property of the fractional Brownian particle
International Nuclear Information System (INIS)
Wang Litan; Lung, C.W.
1988-08-01
Dynamic susceptibility of a diffusion system associated with the fractional Brownian motion (fBm) was examined for the fractal property of the Non-Debye relaxation process. The comparisons between fBm and other approaches were made. Anomalous diffusion and the Non-Debye relaxation processes were discussed with this approach. (author). 8 refs, 1 fig
Adaptive under relaxation factor of MATRA code for the efficient whole core analysis
International Nuclear Information System (INIS)
Kwon, Hyuk; Kim, S. J.; Seo, K. W.; Hwang, D. H.
2013-01-01
Such nonlinearities are handled in MATRA code using outer iteration with Picard scheme. The Picard scheme involves successive updating of the coefficient matrix based on the previously calculated values. The scheme is a simple and effective method for the nonlinear problem but the effectiveness greatly depends on the under-relaxing capability. Accuracy and speed of calculation are very sensitively dependent on the under-relaxation factor in outer-iteration updating the axial mass flow using the continuity equation. The under-relaxation factor in MATRA is generally utilized with a fixed value that is empirically determined. Adapting the under-relaxation factor to the outer iteration is expected to improve the calculation effectiveness of MATRA code rather than calculation with the fixed under-relaxation factor. The present study describes the implementation of adaptive under-relaxation within the subchannel code MATRA. Picard iterations with adaptive under-relaxation can accelerate the convergence for mass conservation in subchannel code MATRA. The most efficient approach for adaptive under relaxation appears to be very problem dependent
Flow Equation Approach to the Statistics of Nonlinear Dynamical Systems
Marston, J. B.; Hastings, M. B.
2005-03-01
The probability distribution function of non-linear dynamical systems is governed by a linear framework that resembles quantum many-body theory, in which stochastic forcing and/or averaging over initial conditions play the role of non-zero . Besides the well-known Fokker-Planck approach, there is a related Hopf functional methodootnotetextUriel Frisch, Turbulence: The Legacy of A. N. Kolmogorov (Cambridge University Press, 1995) chapter 9.5.; in both formalisms, zero modes of linear operators describe the stationary non-equilibrium statistics. To access the statistics, we investigate the method of continuous unitary transformationsootnotetextS. D. Glazek and K. G. Wilson, Phys. Rev. D 48, 5863 (1993); Phys. Rev. D 49, 4214 (1994). (also known as the flow equation approachootnotetextF. Wegner, Ann. Phys. 3, 77 (1994).), suitably generalized to the diagonalization of non-Hermitian matrices. Comparison to the more traditional cumulant expansion method is illustrated with low-dimensional attractors. The treatment of high-dimensional dynamical systems is also discussed.
Evaluation of approaches for improving diesel cold flow properties
Energy Technology Data Exchange (ETDEWEB)
Sharafutdinov, Ilshat; Stratiev, Dicho; Dinkov, Rossen [Lukoil Neftochim Bourgas AD, Bourgas (Bulgaria); Bachvarov, Assen [Edinburgh Univ. (United Kingdom); Petkov, Petko [Bourgas Univ. ' ' Assen Zlatarov' ' (Bulgaria)
2012-06-15
Four heavy diesel fractions (FBP according to ASTM D-2887 of about 420 C), one lower boilingmiddle distillate fraction (FBP according to ASTM D-2887 of 310 C) and kerosene fraction (FBP according to ASTM D-2887 of 271 C) obtained from the Lukoil Neftochim Burgas (LNB) process units during the processing of Russian Export Crude Blend (REBCO) along with four heavy diesel fractions (FBP according to ASTM D-2887 of about 370 C) obtained by fractionation of four crudes: Oil Blend, REBCO, Siberian Light Crude Oil (SLCO) and CPC (Caspian Consortium Pipeline) were investigated for their cold flow properties. It was found that undercutting diesel improves cloud point (CP) and cold filter plugging point (CFPP) by 4 C/10 C cut point. Blending of kerosene improves CP and CFPP by about 2 C/10% added kerosene. The treatment with CP depressants may improve CP by about 2 C if the proper combination diesel - depressant is selected and the improvement can reach up to 6 C for a definite diesel. The treatment with CFPP depressant is much more efficient achieving an improvement of 18 C. By assuming definite fuel prices (Platts) and by applying the LNB linear programming model using Honeywell's RPMS software it was found that catalytic dewaxing is the most efficient approach for producing diesel with improved cold flowproperties if the diesel yield from the dewaxing process is higher than 90%. (orig.)
Unsteady flow phenomena in human undulatory swimming: a numerical approach.
Pacholak, Steffen; Hochstein, Stefan; Rudert, Alexander; Brücker, Christoph
2014-06-01
The undulatory underwater sequence is one of the most important phases in competitive swimming. An understanding of the recurrent vortex dynamics around the human body and their generation could therefore be used to improve swimming techniques. In order to produce a dynamic model, we applied human joint kinematics to three-dimensional (3D) body scans of a female swimmer. The flow around this dynamic model was then calculated using computational fluid dynamics with the aid of moving 3D meshes. Evaluation of the numerical results delivered by the various motion cycles identified characteristic vortex structures for each of the cycles, which exhibited increasing intensity and drag influence. At maximum thrust, drag forces appear to be 12 times higher than those of a passive gliding swimmer. As far as we know, this is the first disclosure of vortex rings merging into vortex tubes in the wake after vortex recapturing. All unsteady structures were visualized using a modified Q-criterion also incorporated into our methods. At the very least, our approach is likely to be suited to further studies examining swimmers engaging in undulatory swimming during training or competition.
Terekhov, Maxim; Krummenacker, Jan; Denysenkov, Vasyl; Gerz, Kathrin; Prisner, Thomas; Schreiber, Laura Maria
2016-03-01
Overhauser dynamic nuclear polarization (DNP) allows the production of liquid hyperpolarized substrate inside the MRI magnet bore as well as its administration in continuous flow mode to acquire MR images with enhanced signal-to-noise ratio. We implemented inversion recovery preparation in order to improve contrast-to-noise ratio and to quantify the overall imaging performance of Overhauser DNP-enhanced MRI. The negative enhancement created by DNP in combination with inversion recovery (IR) preparation allows canceling selectively the signal originated from Boltzmann magnetization and visualizing only hyperpolarized fluid. The theoretical model describing gain of MR image intensity produced by steady-state continuous flow DNP hyperpolarized magnetization was established and proved experimentally. A precise quantification of signal originated purely from DNP hyperpolarization was achieved. A temperature effect on longitudinal relaxation had to be taken into account to fit experimental results with numerical prediction. Using properly adjusted IR preparation, the complete zeroing of thermal background magnetization was achieved, providing an essential increase of contrast-to-noise ratio of DNP-hyperpolarized water images. To quantify and optimize the steady-state conditions for MRI with continuous flow DNP, an approach similar to that incorporating transient-state thermal magnetization equilibrium in spoiled fast field echo imaging sequences can be used. © 2015 Wiley Periodicals, Inc.
A potential approach for low flow selection in water resource supply and management
Ouyang, Ying
2012-08-01
SummaryLow flow selections are essential to water resource management, water supply planning, and watershed ecosystem restoration. In this study, a new approach, namely the frequent-low (FL) approach (or frequent-low index), was developed based on the minimum frequent-low flow or level used in minimum flows and/or levels program in northeast Florida, USA. This FL approach was then compared to the conventional 7Q10 approach for low flow selections prior to its applications, using the USGS flow data from the freshwater environment (Big Sunflower River, Mississippi) as well as from the estuarine environment (St. Johns River, Florida). Unlike the FL approach that is associated with the biological and ecological impacts, the 7Q10 approach could lead to the selections of extremely low flows (e.g., near-zero flows) that may hinder its use for establishing criteria to prevent streams from significant harm to biological and ecological communities. Additionally, the 7Q10 approach could not be used when the period of data records is less than 10 years by definition while this may not the case for the FL approach. Results from both approaches showed that the low flows from the Big Sunflower River and the St. Johns River decreased as time elapsed, demonstrating that these two rivers have become drier during the last several decades with a potential of salted water intrusion to the St. Johns River. Results from the FL approach further revealed that the recurrence probability of low flow increased while the recurrence interval of low flow decreased as time elapsed in both rivers, indicating that low flows occurred more frequent in these rivers as time elapsed. This report suggests that the FL approach, developed in this study, is a useful alternative for low flow selections in addition to the 7Q10 approach.
A study of internal energy relaxation in shocks using molecular dynamics based models
International Nuclear Information System (INIS)
Li, Zheng; Parsons, Neal; Levin, Deborah A.
2015-01-01
Recent potential energy surfaces (PESs) for the N 2 + N and N 2 + N 2 systems are used in molecular dynamics (MD) to simulate rates of vibrational and rotational relaxations for conditions that occur in hypersonic flows. For both chemical systems, it is found that the rotational relaxation number increases with the translational temperature and decreases as the rotational temperature approaches the translational temperature. The vibrational relaxation number is observed to decrease with translational temperature and approaches the rotational relaxation number in the high temperature region. The rotational and vibrational relaxation numbers are generally larger in the N 2 + N 2 system. MD-quasi-classical trajectory (QCT) with the PESs is also used to calculate the V-T transition cross sections, the collision cross section, and the dissociation cross section for each collision pair. Direct simulation Monte Carlo (DSMC) results for hypersonic flow over a blunt body with the total collision cross section from MD/QCT simulations, Larsen-Borgnakke with new relaxation numbers, and the N 2 dissociation rate from MD/QCT show a profile with a decreased translational temperature and a rotational temperature close to vibrational temperature. The results demonstrate that many of the physical models employed in DSMC should be revised as fundamental potential energy surfaces suitable for high temperature conditions become available
Robust Traffic Flow Management: Coevolutionary Approach, Phase I
National Aeronautics and Space Administration — We will develop a Coevolutionary Decision Support Tool (CDST) that explicitly incorporates weather uncertainty (non-probabilistically) into strategic Traffic Flow...
Energy Technology Data Exchange (ETDEWEB)
Buecking, N
2007-11-05
In this work a new theoretical formalism is introduced in order to simulate the phononinduced relaxation of a non-equilibrium distribution to equilibrium at a semiconductor surface numerically. The non-equilibrium distribution is effected by an optical excitation. The approach in this thesis is to link two conventional, but approved methods to a new, more global description: while semiconductor surfaces can be investigated accurately by density-functional theory, the dynamical processes in semiconductor heterostructures are successfully described by density matrix theory. In this work, the parameters for density-matrix theory are determined from the results of density-functional calculations. This work is organized in two parts. In Part I, the general fundamentals of the theory are elaborated, covering the fundamentals of canonical quantizations as well as the theory of density-functional and density-matrix theory in 2{sup nd} order Born approximation. While the formalism of density functional theory for structure investigation has been established for a long time and many different codes exist, the requirements for density matrix formalism concerning the geometry and the number of implemented bands exceed the usual possibilities of the existing code in this field. A special attention is therefore attributed to the development of extensions to existing formulations of this theory, where geometrical and fundamental symmetries of the structure and the equations are used. In Part II, the newly developed formalism is applied to a silicon (001)surface in a 2 x 1 reconstruction. As first step, density-functional calculations using the LDA functional are completed, from which the Kohn-Sham-wave functions and eigenvalues are used to calculate interaction matrix elements for the electron-phonon-coupling an the optical excitation. These matrix elements are determined for the optical transitions from valence to conduction bands and for electron-phonon processes inside the
Modeling skin blood flow: a neuro-physiological approach
Kingma, B.R.M.; Saris, W.H.M.; Frijns, A.J.H.; Steenhoven, van A.A.; Marken Lichtenbelt, van W.D.
2010-01-01
In humans skin blood flow (SBF) plays a major role in body heat loss. Therefore the accuracy of models ofhuman thermoregulation depends for a great deal on their ability to predict skin blood flow. Most SBFmodelsuse body temperatures directly for calculation of skin perfusion. However, humans do not
Tripsanas, E. K.; Bryant, W. R.; Prior, D. B.
2003-04-01
A large number of Jumbo Piston cores (up to 20 m long), acquired from the continental slope and rise of the Northwest Gulf of Mexico (Bryant Canyon area and eastern Sigsbee Escarpment), have recovered various mass-transport deposits. The main cause of slope instabilities over these areas is oversteepening of the slopes due to the seaward mobilization of the underlying allochthonous salt masses. Cohesive flow deposits were the most common recoveries in the sediment cores. Four types of cohesive flow deposits have been recognized: a) fluid debris flow, b) mud flow, c) mud-matrix dominated debris flow, and d) clast-dominated debris flow deposits. The first type is characterized by its relatively small thickness (less than 1 m), a mud matrix with small (less than 0.5 cm) and soft mud-clasts, and a faint layering. The mud-clasts reveal a normal grading and become more abundant towards the base of each layer. That reveals that their deposition resulted by several successive surges/pulses, developed in the main flow, than the sudden “freezing” of the whole flow. The main difference between mud flow and mud-matrix dominated debris flow deposits is the presence of small to large mud-clasts in the later. Both deposits consist of a chaotic mud-matrix, and a basal shear laminated zone, where the strongest shearing of the flow was exhibited. Convolute laminations, fault-like surfaces, thrust faults, and microfaults are interpreted as occurring during the “freezing” of the flows and/or by adjustments of the rested deposits. Clast-dominated debris flow deposits consist of three zones: a) an upper plug-zone, characterized by large interlocked clasts, b) a mid-zone, of higher reworked, inversely graded clasts, floating in a mud-matrix, and c) a lower shear laminated zone. The structure of the last three cohesive flow deposits indicate that they represent deposition of typical Bingham flows, consisting of an upper plug-zone in which the yield stress is not exceeded and an
Dynamic flow-through approaches for metal fractionation in environmentally relevant solid samples
DEFF Research Database (Denmark)
Miró, Manuel; Hansen, Elo Harald; Chomchoei, Roongrat
2005-01-01
generations of flow-injection analysis. Special attention is also paid to a novel, robust, non-invasive approach for on-site continuous sampling of soil solutions, capitalizing on flow-through microdialysis, which presents itself as an appealing complementary approach to the conventional lysimeter experiments...
... Find a Doctor Relaxation is the absence of tension in muscle groups and a minimum or absence ... Drill Meditation Progressive Muscle Relaxation Minimizing Shortness of Breath Visualization This information has been approved by Shelby ...
Sergey Krylov
2012-01-01
The article treats a new methodological approach to the company cash flows target-oriented forecasting based on its financial position analysis. The approach is featured to be universal and presumes application of the following techniques developed by the author: financial ratio values correction techniques and correcting cash flows techniques. The financial ratio values correction technique assumes to analyze and forecast company financial position while the correcting cash flows technique i...
A Risk-Based Ecohydrological Approach to Assessing Environmental Flow Regimes
Mcgregor, Glenn B.; Marshall, Jonathan C.; Lobegeiger, Jaye S.; Holloway, Dean; Menke, Norbert; Coysh, Julie
2018-03-01
For several decades there has been recognition that water resource development alters river flow regimes and impacts ecosystem values. Determining strategies to protect or restore flow regimes to achieve ecological outcomes is a focus of water policy and legislation in many parts of the world. However, consideration of existing environmental flow assessment approaches for application in Queensland identified deficiencies precluding their adoption. Firstly, in managing flows and using ecosystem condition as an indicator of effectiveness, many approaches ignore the fact that river ecosystems are subjected to threatening processes other than flow regime alteration. Secondly, many focus on providing flows for responses without considering how often they are necessary to sustain ecological values in the long-term. Finally, few consider requirements at spatial-scales relevant to the desired outcomes, with frequent focus on individual places rather than the regions supporting sustainability. Consequently, we developed a risk-based ecohydrological approach that identifies ecosystem values linked to desired ecological outcomes, is sensitive to flow alteration and uses indicators of broader ecosystem requirements. Monitoring and research is undertaken to quantify flow-dependencies and ecological modelling is used to quantify flow-related ecological responses over an historical flow period. The relative risk from different flow management scenarios can be evaluated at relevant spatial-scales. This overcomes the deficiencies identified above and provides a robust and useful foundation upon which to build the information needed to support water planning decisions. Application of the risk assessment approach is illustrated here by two case studies.
International Nuclear Information System (INIS)
Chang, Chih-Hao; Liou, Meng-Sing
2007-01-01
In this paper, we propose a new approach to compute compressible multifluid equations. Firstly, a single-pressure compressible multifluid model based on the stratified flow model is proposed. The stratified flow model, which defines different fluids in separated regions, is shown to be amenable to the finite volume method. We can apply the conservation law to each subregion and obtain a set of balance equations. Secondly, the AUSM + scheme, which is originally designed for the compressible gas flow, is extended to solve compressible liquid flows. By introducing additional dissipation terms into the numerical flux, the new scheme, called AUSM + -up, can be applied to both liquid and gas flows. Thirdly, the contribution to the numerical flux due to interactions between different phases is taken into account and solved by the exact Riemann solver. We will show that the proposed approach yields an accurate and robust method for computing compressible multiphase flows involving discontinuities, such as shock waves and fluid interfaces. Several one-dimensional test problems are used to demonstrate the capability of our method, including the Ransom's water faucet problem and the air-water shock tube problem. Finally, several two dimensional problems will show the capability to capture enormous details and complicated wave patterns in flows having large disparities in the fluid density and velocities, such as interactions between water shock wave and air bubble, between air shock wave and water column(s), and underwater explosion
Maharjan, Rijan; Brown, Eric
2017-12-01
We investigated the transient relaxation of a discontinuous shear thickening (DST) suspension of cornstarch in water. We performed two types of relaxation experiments starting from a steady shear in a parallel-plate rheometer, followed either by stopping the top plate rotation and measuring the transient torque relaxation or by removing the torque on the plate and measuring the transient rotation of the tool. We found that at low effective weight fraction ϕeffmodel. The regime where the relaxation was inconsistent with the generalized Newtonian model was the same where we found positive normal stress during relaxation, and in some cases we found an oscillatory response, suggestive of a solidlike structure consisting of a system-spanning contact network of particles. This regime also corresponds to the same packing fraction range where we consistently found discontinuous shear thickening in rate-controlled, steady-state measurements. The relaxation time in this range scales with the inverse of the critical shear rate at the onset of shear thickening, which may correspond to a contact relaxation time for nearby particles in the structure to flow away from each other. In this range, the relaxation time was the same in both stress- and rate-controlled relaxation experiments, indicating the relaxation time is more intrinsic than an effective viscosity in this range and is needed in addition to the steady-state viscosity function to describe transient flows. The discrepancy between the measured relaxation times and the generalized Newtonian prediction was found to be as large as four orders of magnitude, and extrapolations diverge in the limit as ϕeff→ϕc as the generalized Newtonian prediction approaches 0. This quantitative discrepancy indicates the relaxation is not controlled by the dissipative terms in the constitutive relation. At the highest weight fractions, the relaxation time scales were measured to be on the order of ˜1 s. The fact that this time scale is
Mechanisms of Coupled Vibrational Relaxation and Dissociation in Carbon Dioxide.
Armenise, Iole; Kustova, Elena
2018-05-21
A complete vibrational state-specific kinetic scheme describing dissociating carbon dioxide mixtures is proposed. CO 2 symmetric, bending and asymmetric vibrations and dissociation-recombination are strongly coupled through inter-mode vibrational energy transfers. Comparative study of state-resolved rate coefficients is carried out; the effect of different transitions may vary considerably with temperature. A non-equilibrium 1-D boundary layer flow typical to hypersonic planetary entry is studied in the state-to-state approach. To assess the sensitivity of fluid-dynamic variables and heat transfer to various vibrational transitions and chemical reactions, corresponding processes are successively included to the kinetic scheme. It is shown that vibrational-translational (VT) transitions in the symmetric and asymmetric modes do not alter the flow and can be neglected whereas the VT 2 exchange in the bending mode is the main channel of vibrational relaxation. Inter-mode vibrational exchanges affect the flow implicitly, through energy redistribution enhancing VT relaxation; the dominating role belongs to near-resonant transitions between symmetric and bending modes as well as between CO molecules and CO 2 asymmetric mode. Strong coupling between VT 2 relaxation and chemical reactions is emphasized. While vibrational distributions and average vibrational energy show strong dependence on the kinetic scheme, the heat flux is more sensitive to chemical reactions.
Peeling mode relaxation ELM model
International Nuclear Information System (INIS)
Gimblett, C. G.
2006-01-01
This paper discusses an approach to modelling Edge Localised Modes (ELMs) in which toroidal peeling modes are envisaged to initiate a constrained relaxation of the tokamak outer region plasma. Relaxation produces both a flattened edge current profile (which tends to further destabilise a peeling mode), and a plasma-vacuum negative current sheet which has a counteracting stabilising influence; the balance that is struck between these two effects determines the radial extent (rE) of the ELM relaxed region. The model is sensitive to the precise position of the mode rational surfaces to the plasma surface and hence there is a 'deterministic scatter' in the results that has an accord with experimental data. The toroidal peeling stability criterion involves the edge pressure, and using this in conjunction with predictions of rE allows us to evaluate the ELM energy losses and compare with experiment. Predictions of trends with the edge safety factor and collisionality are also made
A water budget approach to instream flow maintenance
International Nuclear Information System (INIS)
Waddle, T.
1991-01-01
Storage reallocation is a current issue at many Federal water storage facilities that have hydroelectric generation. Allocation of storage to support instream flows is one of the changes being considered. In this paper, a portion of storage is dedicated to supplying instream flows. The author defines this storage account as a water budget and operate it to provide instream habitat below the reservoir. The author uses a limiting event model, the effective habitat time series, to determine when water budget releases will produce habitat benefits. The effective habitat time series acts as a surrogate for fish population and reflects the mid to long term influence of water management decisions on the life cycle of a fish species. The author develops an operation rule for the water budget that considers water rights and habitat events. The paper concludes by contrasting the habitat benefits of water budget operation with fixed minimum flow requirements
International Nuclear Information System (INIS)
Nakano, Masayoshi; Kishi, Ryohei; Nitta, Tomoshige; Yamaguchi, Kizashi
2004-01-01
We investigate the relaxation effects on the quantum dynamics in a two-state molecular system interacting with a single-mode strongly amplitude-squeezed coherent field using the second-order Monte Carlo wave-function method. The molecular population inversion (collapse-revival behavior of Rabi oscillations) is known to show the echoes after each revival, which are referred to as ringing revivals, in the case of strongly squeezed coherent fields with oscillatory photon-number distributions due to the phase-space interference effect. Two types of relaxation effects, i.e., cavity relaxation (the dissipation of an internal single mode to outer mode) and molecular coherent (phase) relaxation caused by nuclear vibrations on ringing revivals are investigated from the viewpoint of the quantum-phase dynamics using the quasiprobability (Q function) distribution of a single-mode field and the off-diagonal molecular density matrix ρ elec1,2 (t). It turns out that the molecular phase relaxation attenuates both the entire revival-collapse behavior and the increase in ρ elec1,2 (t) during the quiescent region, whereas a very slight cavity relaxation particularly suppresses the echoes in ringing revivals more significantly than the first revival but hardly changes a primary variation in envelope of ρ elec1,2 (t) in the nonrelaxation case
A new approach to flow simulation using hybrid models
Solgi, Abazar; Zarei, Heidar; Nourani, Vahid; Bahmani, Ramin
2017-11-01
The necessity of flow prediction in rivers, for proper management of water resource, and the need for determining the inflow to the dam reservoir, designing efficient flood warning systems and so forth, have always led water researchers to think about models with high-speed response and low error. In the recent years, the development of Artificial Neural Networks and Wavelet theory and using the combination of models help researchers to estimate the river flow better and better. In this study, daily and monthly scales were used for simulating the flow of Gamasiyab River, Nahavand, Iran. The first simulation was done using two types of ANN and ANFIS models. Then, using wavelet theory and decomposing input signals of the used parameters, sub-signals were obtained and were fed into the ANN and ANFIS to obtain hybrid models of WANN and WANFIS. In this study, in addition to the parameters of precipitation and flow, parameters of temperature and evaporation were used to analyze their effects on the simulation. The results showed that using wavelet transform improved the performance of the models in both monthly and daily scale. However, it had a better effect on the monthly scale and the WANFIS was the best model.
Variational approach to coarse-graining of generalized gradient flows
Duong, M.H.; Lamacz, A.; Peletier, M.A.; Sharma, U.
2017-01-01
In this paper we present a variational technique that handles coarse-graining and passing to a limit in a unified manner. The technique is based on a duality structure, which is present in many gradient flows and other variational evolutions, and which often arises from a large-deviations principle.
Simulation of fluid flow in fractured rock: a probabilistic approach
International Nuclear Information System (INIS)
Samaniego, J.A.; Priest, S.D.
1985-02-01
This report describes the results of a research project designed to investigate the influence of discontinuities on fluid flow through fractured rock masses. The aim has been to provide a rational basis for the assessment of prospective intermediate level radioactive waste repository sites. The results of this work are presented in the form of two groups of FORTRAN computer programs. The first of these is designed to process data obtained from exposed rock faces and thereby provide an unbiased estimate of discontinuity characteristics. The resulting data are input to the second group of programs which generate a two-dimensional random realisation of discontinuity geometry. When appropriate boundary conditions have been specified, the resulting network of channels is solved numerically to determine nodal potentials, flow quantities and equivalent permeabilities. A number of validation runs are presented, together with some parametric studies, to investigate the influence of excavation size and discontinuity geometry on fluid flow. A practical application is given in the form of a case study involving the prediction of fluid flow into a 2.8 m diameter tunnel in water bearing, fractured rock. Finally, the applications and limitations of the programs in site assessment for radioactive waste repositories are discussed. (author)
National policy measures. Right approach to foreign direct investment flows
Directory of Open Access Journals (Sweden)
Cătălin-Emilian HUIDUMAC-PETRESCU
2013-02-01
Full Text Available 2011 was a difficult year for all the countries, developed and emerging ones. For overcoming the negative effects of the financial crisis, many economies have established as purpose to adopt new economic policies regarding the foreign direct investment flows (FDI, even to stimulate the flows or to reduce it (protectionism measures. So, there can be identified two categories of national policies: measures for the FDI flows stimulation and measures whose aim was the weighting of FDI developing, through restriction and regulation. In the first category we could include the liberalization measures and promotional and faciletation policies. In this study we evidenced that the fundament of the second category of policies is the belief that the FDI outward lead to job exports, to a raise of unemployment and a weakness of the industrial base.Many reports on FDI flows, here we talk about those made by UNCTAD, show that the regulation and restriction policies are seen as a possible protectionism, especially in the agricultural and extractive industries, where there have been required nationalization processes and divestments. Even more, the economies which adopted this kind of policies have been less interested in investing abroad, the outward of FDI being affected and globally the total outward decreased.
Modelling of boiling bubbly flows using a polydisperse approach
International Nuclear Information System (INIS)
Zaepffel, D.
2011-01-01
The objective of this work was to improve the modelling of boiling bubbly flows.We focused on the modelling of the polydisperse aspect of a bubble population, i.e. the fact that bubbles have different sizes and different velocities. The multi-size aspect of a bubble population can originate from various mechanisms. For the bubbly flows we are interested in, bubble coalescence, bubble break-up, phase change kinematics and/or gas compressibility inside the bubbles can be mentioned. Since, bubble velocity depends on bubble size, the bubble size spectrum also leads to a bubble velocity spectrum. An averaged model especially dedicated to dispersed flows is introduced in this thesis. Closure of averaged interphase transfer terms are written in a polydisperse framework, i.e. using a distribution function of the bubble sizes and velocities. A quadratic law and a cubic law are here proposed for the modelling of the size distribution function, whose evolution in space and time is then obtained with the use of the moment method. Our averaged model has been implemented in the NEPTUNE-CFD computation code in order to simulate the DEBORA experiment. The ability of our model to deal with sub-cooled boiling flows has therefore been evaluated. (author) [fr
Efficient flow and human centred assembly by an interactive approach
Eikhout, S.M.; Helmes, R.B.M.; Rhijn, J.W. van
2004-01-01
Due to fluctuations on the market, manufacturing of many product variations, and wish for fine-tuning between production and assembly a fan and motor manufacturing company wanted to improve their assembly line. The aims were efficient flow and human centered assembly in the new product line.
Probabilistic approach to diffusion in shear flows of generalized viscoelastic second-grade fluids
International Nuclear Information System (INIS)
Wafo Soh, C
2010-01-01
We study diffusion in point-source-driven shear flows of generalized second-grade fluids. We start by obtaining exact solutions of shear flows triggered by point sources under various boundary conditions. For unrestricted flows, we demonstrate that the velocity distribution is the probability density function of a coupled or uncoupled continuous-time random walk. In the first instance, the motion is described by a compound Poisson process with an explicit probability density function corresponding to the velocity distribution. The average waiting time in this situation is finite and is identified with the structural relaxation time. In the second case, we obtain an explicit formula for the probability density function in terms of special functions. In both cases, the probability density functions of the associated stochastic processes are leptokurtic at all finite times with variances linear in time. By using the method of images, we infer velocity fields for restricted flows from those of unrestricted flows. Equipped with some exact expressions of the velocity field, we analyze advection–diffusion via the Feynman–Kac formula, which lends itself naturally to Monte Carlo simulation
An integrated approach to combating flow assurance problems
Energy Technology Data Exchange (ETDEWEB)
Abney, Laurence; Browne, Alan [Halliburton, Houston, TX (United States)
2005-07-01
Any upset to the internal pipe surface of a pipeline can significantly impact both pipeline through-put and energy requirements for maintaining design flow rates. Inefficient flow through pipelines can have a significant negative impact on operating expense (Opex) and the energy requirements necessary to maintain pipeline through-put. Effective flow maintenance helps ensure that Opex remains within budget, processing equipment life is extended and that excessive use of energy is minimized. A number of events can result in debris generation and deposition in a pipeline. Corrosion, hydrate formation, paraffin deposition, asphaltene deposition, development of 'black powder' and scale formation are the most common sources of pipeline debris. Generally, a combination of pigging and chemical treatments is used to remove debris; these two techniques are commonly used in isolation. Incorporation of specialized fluids with enhanced solid-transport capabilities, specialized dispersants, or specialized surfactants can improve the success of routine pigging operations. An array of alternative and often complementary remediation technologies can be used to effect the removal of deposits or even full restrictions from pipelines. These include the application of acids, specialized chemical products, and intrusive interventions techniques. This paper presents a review of methods of integrating existing technologies. (author)
Negative Saturation Approach for Non-Isothermal Compositional Two-Phase Flow Simulations
Salimi, H.; Wolf, K.H.; Bruining, J.
2011-01-01
This article deals with developing a solution approach, called the non-isothermal negative saturation (NegSat) solution approach. The NegSat solution approach solves efficiently any non-isothermal compositional flow problem that involves phase disappearance, phase appearance, and phase transition.
A new approach in development of data flow control and investigation system for computer networks
International Nuclear Information System (INIS)
Frolov, I.; Vaguine, A.; Silin, A.
1992-01-01
This paper describes a new approach in development of data flow control and investigation system for computer networks. This approach was developed and applied in the Moscow Radiotechnical Institute for control and investigations of Institute computer network. It allowed us to solve our network current problems successfully. Description of our approach is represented below along with the most interesting results of our work. (author)
Paramagnetic metal complexes as potential relaxation agents for NMR imaging
International Nuclear Information System (INIS)
Coroiu, Ilioara; Demco, D. E.; Darabont, Al.; Bogdan, M.
1997-01-01
The development of nuclear magnetic resonance (NMR) imaging technique as a clinical diagnostic modality has prompted the need for a new class of pharmaceuticals. These drugs must be administered to a patient in order to enhance the image contrast between the normal and diseased tissue and/or indicate the status of organ function or blood flow. Paramagnetic compounds are presently undergoing extensive evaluation as contrast agents in magnetic resonance imaging (MRI). These agents increase contrast in MRI by differentially localizing in tissue where they increase the relaxation rates of nearby water protons. The longitudinal R 1 and transverse R 2 relaxivities were measured as a function of molar concentrations for some new paramagnetic complexes like the following: dysprosium, erbium and gadolinium citrates, gadolinium methylene diphosphonate, dysprosium and gadolinium iminodiacetate, manganese para-aminobenzoate and copper nicotinate. The available theoretical approaches for quantitative understanding are presented. (authors)
Mechanical relaxation in glasses
International Nuclear Information System (INIS)
Hiki, Y.
2004-01-01
The basic properties of glasses and the characteristics of mechanical relaxation in glasses were briefly reviewed, and then our studies concerned were presented. Experimental methods adopted were viscosity, internal friction, ultrasonic attenuation, and Brillouin scattering measurements. The specimens used were several kinds of inorganic, organic, and metallic glasses. The measurements were mainly carried out from the room temperature up to the glass transition temperature, and the relaxation time was determined as a function of temperature. The 'double relaxation' composed of two Arrhenius-type relaxations was observed in many materials. In both relaxations, the 'compensation effect' showing a correlation of the pre-exponential factor and the activation energy was observed. These results were explained by considering the 'complex relaxation' due to cooperative motions of atoms or group of atoms. Values of activation energy near the glass transition determined by the various experimental methods were compared with each other
A Variable Flow Modelling Approach To Military End Strength Planning
2016-12-01
function. The MLRPS is more complex than the variable flow model as it has to cater for a force structure that is much larger than just the MT branch...essential positions in a Ship’s complement, or by the biggest current deficit in forecast end strength. The model can be adjusted to cater for any of these...is unlikely that the RAN will be able to cater for such an increase in hires, so this scenario is not likely to solve their problem. Each transition
Novel approach for dam break flow modeling using computational intelligence
Seyedashraf, Omid; Mehrabi, Mohammad; Akhtari, Ali Akbar
2018-04-01
A new methodology based on the computational intelligence (CI) system is proposed and tested for modeling the classic 1D dam-break flow problem. The reason to seek for a new solution lies in the shortcomings of the existing analytical and numerical models. This includes the difficulty of using the exact solutions and the unwanted fluctuations, which arise in the numerical results. In this research, the application of the radial-basis-function (RBF) and multi-layer-perceptron (MLP) systems is detailed for the solution of twenty-nine dam-break scenarios. The models are developed using seven variables, i.e. the length of the channel, the depths of the up-and downstream sections, time, and distance as the inputs. Moreover, the depths and velocities of each computational node in the flow domain are considered as the model outputs. The models are validated against the analytical, and Lax-Wendroff and MacCormack FDM schemes. The findings indicate that the employed CI models are able to replicate the overall shape of the shock- and rarefaction-waves. Furthermore, the MLP system outperforms RBF and the tested numerical schemes. A new monolithic equation is proposed based on the best fitting model, which can be used as an efficient alternative to the existing piecewise analytic equations.
New approach for dynamic flow management within the PEMFC stack
International Nuclear Information System (INIS)
Varlam, Mihai; Culcer, Mihai; Carcadea, Elena; Stefanescu, Ioan; Iliescu, Mariana; Enache, Adrian
2009-01-01
An adequate gas and water flow management is a key issue to reach and maintain a higher output power for a PEM fuel cell stack. One of the main aspects which could limit the performance of a PEM fuel cell stack is the weak capability for a non-uniform water distribution management within the fuel cell. The produced water could become a handicap to attain the best working performance by blocking the catalytic surfaces and by preventing the mass transport process. Usually, the excess water is removed in one cell, comparatively to others from the stack and taking into account that all the cells are supplied in parallel from a common air admission pipe, a limitation of gas flow rate within that cell is created. Consequently, this constraint will reduce further the water removal speed. This feedback process will generate finally a drastic decrease of the fuel cell stack performance. A new practical solution to this water and gas non-uniformity of distributions problem is to use a sequential purge procedure of several fuel cell groups inside the stack which could guarantee a right management of water. An experimental setup has been built based on four fuel cell stack. Every fuel cell was connected to a single removal pipe via a solenoid valve. A computer-controlled hardware and software system has been designed and built, in order to generate a given opening-closing sequence for the automatic valve system. (authors)
A Monte Carlo Comparison between the Free Cash Flow and Discounted Cash Flow Approaches
Mehari Mekonnen Akalu; Rodney Turner
2002-01-01
textabstractOne of the debates in the capital budgeting model selection is between the free cash flow and DCF methods. In this paper an attempt is made to compare SVA against NPV model based on Monte Carlo simulations. Accordingly, NPV is found less sensitive to value driver variations and has got higher forecast errors as compared to SVA model.
A Monte Carlo Comparison between the Free Cash Flow and Discounted Cash Flow Approaches
M.M. Akalu; J.R. Turner (Rodney)
2002-01-01
textabstractOne of the debates in the capital budgeting model selection is between the free cash flow and DCF methods. In this paper an attempt is made to compare SVA against NPV model based on Monte Carlo simulations. Accordingly, NPV is found less sensitive to value driver variations and has got
Stancanelli, Laura Maria; Peres, David Johnny; Cancelliere, Antonino; Foti, Enrico
2017-07-01
Rainfall-induced shallow slides can evolve into debris flows that move rapidly downstream with devastating consequences. Mapping the susceptibility to debris flow is an important aid for risk mitigation. We propose a novel practical approach to derive debris flow inundation maps useful for susceptibility assessment, that is based on the integrated use of DEM-based spatially-distributed hydrological and slope stability models with debris flow propagation models. More specifically, the TRIGRS infiltration and infinite slope stability model and the FLO-2D model for the simulation of the related debris flow propagation and deposition are combined. An empirical instability-to-debris flow triggering threshold calibrated on the basis of observed events, is applied to link the two models and to accomplish the task of determining the amount of unstable mass that develops as a debris flow. Calibration of the proposed methodology is carried out based on real data of the debris flow event occurred on 1 October 2009, in the Peloritani mountains area (Italy). Model performance, assessed by receiver-operating-characteristics (ROC) indexes, evidences fairly good reproduction of the observed event. Comparison with the performance of the traditional debris flow modeling procedure, in which sediment and water hydrographs are inputed as lumped at selected points on top of the streams, is also performed, in order to assess quantitatively the limitations of such commonly applied approach. Results show that the proposed method, besides of being more process-consistent than the traditional hydrograph-based approach, can potentially provide a more accurate simulation of debris-flow phenomena, in terms of spatial patterns of erosion and deposition as well on the quantification of mobilized volumes and depths, avoiding overestimation of debris flow triggering volume and, thus, of maximum inundation flow depths.
Relaxation characteristics of hastelloy X
International Nuclear Information System (INIS)
Suzuki, Kazuhiko
1980-02-01
Relaxation diagrams of Hastelloy X (relaxation curves, relaxation design diagrams, etc.) were generated from the creep constitutive equation of Hastelloy X, using inelastic stress analysis code TEPICC-J. These data are in good agreement with experimental relaxation data of ORNL-5479. Three typical inelastic stress analyses were performed for various relaxation behaviors of the high-temperature structures. An attempt was also made to predict these relaxation behaviors by the relaxation curves. (author)
Czech Academy of Sciences Publication Activity Database
Kotek, Jiří; Brus, Jiří
2014-01-01
Roč. 59, č. 9 (2014), s. 662-666 ISSN 0032-2725 R&D Projects: GA ČR(CZ) GA13-29009S Institutional support: RVO:61389013 Keywords : polyamide 6 * nanocomposite * T1ρ(13C) relaxation Subject RIV: JI - Composite Materials Impact factor: 0.633, year: 2014
Flow-based approach for holistic factory engineering and design
Constantinescu, C.; Westkämper, E.
2010-01-01
The engineering of future factories requires digital tools along life cycle phases from investment planning to ramp-up. Manufacturers need scientific-based integrated highly dynamic data management systems for the participative and integrated factory planning. The paper presents a new approach for the continuously integrated product design, factory and process planning, through a service-oriented architecture for the implementation of digital factory tools. A first prototype of the digital fa...
Spatial dynamics of ecosystem service flows: a comprehensive approach to quantifying actual services
Bagstad, Kenneth J.; Johnson, Gary W.; Voigt, Brian; Villa, Ferdinando
2013-01-01
Recent ecosystem services research has highlighted the importance of spatial connectivity between ecosystems and their beneficiaries. Despite this need, a systematic approach to ecosystem service flow quantification has not yet emerged. In this article, we present such an approach, which we formalize as a class of agent-based models termed “Service Path Attribution Networks” (SPANs). These models, developed as part of the Artificial Intelligence for Ecosystem Services (ARIES) project, expand on ecosystem services classification terminology introduced by other authors. Conceptual elements needed to support flow modeling include a service's rivalness, its flow routing type (e.g., through hydrologic or transportation networks, lines of sight, or other approaches), and whether the benefit is supplied by an ecosystem's provision of a beneficial flow to people or by absorption of a detrimental flow before it reaches them. We describe our implementation of the SPAN framework for five ecosystem services and discuss how to generalize the approach to additional services. SPAN model outputs include maps of ecosystem service provision, use, depletion, and flows under theoretical, possible, actual, inaccessible, and blocked conditions. We highlight how these different ecosystem service flow maps could be used to support various types of decision making for conservation and resource management planning.
TEACHING NEUROMUSCULAR RELAXATION.
NORRIS, JEANNE E.; STEINHAUS, ARTHUR H.
THIS STUDY ATTEMPTED TO FIND OUT WHETHER (1) THE METHODS FOR ATTAINING NEUROMUSCULAR RELAXATION THAT HAVE PROVED FRUITFUL IN THE ONE-TO-ONE RELATIONSHIP OF THE CLINIC CAN BE SUCCESSFULLY ADAPTED TO THE TEACHER-CLASS RELATIONSHIP OF THE CLASSROOM AND GYMNASIUM, AND (2) NEUROMUSCULAR RELAXATION CAN BE TAUGHT SUCCESSFULLY BY AN APPROPRIATELY TRAINED…
Relaxation of Anisotropic Glasses
DEFF Research Database (Denmark)
Deubener, Joachim; Martin, Birgit; Wondraczek, Lothar
2004-01-01
. When the load was removed at room temperature a permanent optical anisotropy (birefringence) was observed only perpendicular to cylinder axis and the pressure direction indicating complete elimination of thermal stresses. Relaxation of structural anisotropy was studied from reheating experiments using...... the energy release, thermo-mechanical and optical relaxation behaviour are drawn....
Relaxation techniques for stress
... raise your heart rate. This is called the stress response. Relaxation techniques can help your body relax and lower your blood pressure ... also many other types of breathing techniques you can learn. In many cases, you do not need much ... including those that cause stress. Meditation has been practiced for thousands of years, ...
Directory of Open Access Journals (Sweden)
Dzobko Iryna P.
2016-02-01
Full Text Available The formation of a methodological approach to evaluating management of the state of enterprise flow processes has been considered. Proceeding from the developed and presented in literary sources theoretical propositions on organization of management of enterprise flow processes, the hypothesis of the study is correlation of quantitative and qualitative evaluations of management effectiveness and formation of the integral index on their basis. The article presents stages of implementation of a methodological approach to evaluating the state of management of enterprise flow processes, which implies indicating the components, their characteristics and methods of research. The composition of indicators, on the basis of which it is possible to evaluate effectiveness of management of enterprise flow processes, has been determined. Grouping of such indicators based on the flow nature of enterprise processes has been performed. The grouping of indicators is justified by a pairwise determination of canonical correlations between the selected groups (the obtained high correlation coefficients confirmed the author’s systematization of indicators. It is shown that a specificity of the formation of a methodological approach to evaluating the state of management of enterprise flow processes requires expansion in the direction of aggregation of the results and determination of factors that influence effectiveness of flow processes management. The article carries out such aggregation using the factor analysis. Distribution of a set of objects into different classes according to the results of the cluster analysis has been presented. To obtain an integral estimation of effectiveness of flow processes management, the taxonomic index of a multidimensional object has been built. A peculiarity of the formed methodological approach to evaluating the state of management of enterprise flow processes is in the matrix correlation of integral indicators calculated on
Stanisavljevic, Nemanja; Brunner, Paul H
2014-08-01
The novelty of this paper is the demonstration of the effectiveness of combining material flow analysis (MFA) with substance flow analysis (SFA) for decision making in waste management. Both MFA and SFA are based on the mass balance principle. While MFA alone has been applied often for analysing material flows quantitatively and hence to determine the capacities of waste treatment processes, SFA is more demanding but instrumental in evaluating the performance of a waste management system regarding the goals "resource conservation" and "environmental protection". SFA focuses on the transformations of wastes during waste treatment: valuable as well as hazardous substances and their transformations are followed through the entire waste management system. A substance-based approach is required because the economic and environmental properties of the products of waste management - recycling goods, residues and emissions - are primarily determined by the content of specific precious or harmful substances. To support the case that MFA and SFA should be combined, a case study of waste management scenarios is presented. For three scenarios, total material flows are quantified by MFA, and the mass flows of six indicator substances (C, N, Cl, Cd, Pb, Hg) are determined by SFA. The combined results are compared to the status quo in view of fulfilling the goals of waste management. They clearly point out specific differences between the chosen scenarios, demonstrating potentials for improvement and the value of the combination of MFA/SFA for decision making in waste management. © The Author(s) 2014.
Drag reduction in a turbulent channel flow using a passivity-based approach
Heins, Peter; Jones, Bryn; Sharma, Atul
2013-11-01
A new active feedback control strategy for attenuating perturbation energy in a turbulent channel flow is presented. Using a passivity-based approach, a controller synthesis procedure has been devised which is capable of making the linear dynamics of a channel flow as close to passive as is possible given the limitations on sensing and actuation. A controller that is capable of making the linearized flow passive is guaranteed to globally stabilize the true flow. The resulting controller is capable of greatly restricting the amount of turbulent energy that the nonlinearity can feed back into the flow. DNS testing of a controller using wall-sensing of streamwise and spanwise shear stress and actuation via wall transpiration acting upon channel flows with Reτ = 100 - 250 showed significant reductions in skin-friction drag.
Microbial Eco-Physiology of the human intestinal tract: a flow cytometric approach
Amor, Ben K.
2004-01-01
This thesis describes a multifaceted approach to further enhance our view of the complex human intestinal microbial ecosystem. This approach combines me advantages of flow cyrometry (FCM), a single cell and high-throughput technology, and molecular techniques that have proven themselves to be
Transition to turbulence in pulsatile flow through heart valves--a modified stability approach.
Bluestein, D; Einav, S
1994-11-01
The presence of turbulence in the cardiovascular system is generally an indication of some type of abnormality. Most cardiologists agree that turbulence near a valve indicates either valvular stenosis or regurgitation, depending on the phase of its occurrence during the cardiac cycle. As no satisfying analytical solutions of the stability of turbulent pulsatile flow exist, accurate, unbiased flow stability criteria are needed for the identification of turbulence initiation. The traditional approach uses a stability diagram based upon the stability of a plane Stokes layer where alpha (the Womersley parameter) is defined by the fundamental heart rate. We suggest a modified approach that involves the decomposition of alpha into its frequency components, where alpha is derived from the preferred modes induced on the flow by interaction between flow pulsation and the valve. Transition to turbulence in pulsatile flow through heart values was investigated in a pulse duplicator system using three polymer aortic valve models representing a normal aortic valve, a 65 percent stenosed valve and a 90 percent severely stenosed valve, and two mitral valve models representing a normal mitral valve and a 65 percent stenosed valve. Valve characteristics were closely simulated as to mimic the conditions that alter flow stability and initiate turbulent flow conditions. Valvular velocity waveforms were measured by laser Doppler anemometry (LDA). Spectral analysis was performed on velocity signals at selected spatial and temporal points to produce the power density spectra, in which the preferred frequency modes were identified. The spectra obtained during the rapid closure stage of the valves were found to be governed by the stenosis geometry. A shift toward higher dominant frequencies was correlated with the severity of the stenosis. According to the modified approach, stability of the flow is represented by a cluster of points, each corresponding to a specific dominant mode apparent
Denis-Alpizar, Otoniel; Bemish, Raymond J; Meuwly, Markus
2017-03-21
Vibrational energy relaxation (VER) of diatomics following collisions with the surrounding medium is an important elementary process for modeling high-temperature gas flow. VER is characterized by two parameters: the vibrational relaxation time τ vib and the state relaxation rates. Here the vibrational relaxation of CO(ν=0←ν=1) in Ar is considered for validating a computational approach to determine the vibrational relaxation time parameter (pτ vib ) using an accurate, fully dimensional potential energy surface. For lower temperatures, comparison with experimental data shows very good agreement whereas at higher temperatures (up to 25 000 K), comparisons with an empirically modified model due to Park confirm its validity for CO in Ar. Additionally, the calculations provide insight into the importance of Δν>1 transitions that are ignored in typical applications of the Landau-Teller framework.
Le Chatelier's principle with multiple relaxation channels
Gilmore, R.; Levine, R. D.
1986-05-01
Le Chatelier's principle is discussed within the constrained variational approach to thermodynamics. The formulation is general enough to encompass systems not in thermal (or chemical) equilibrium. Particular attention is given to systems with multiple constraints which can be relaxed. The moderation of the initial perturbation increases as additional constraints are removed. This result is studied in particular when the (coupled) relaxation channels have widely different time scales. A series of inequalities is derived which describes the successive moderation as each successive relaxation channel opens up. These inequalities are interpreted within the metric-geometry representation of thermodynamics.
Modeling of annular two-phase flow using a unified CFD approach
Energy Technology Data Exchange (ETDEWEB)
Li, Haipeng, E-mail: haipengl@kth.se; Anglart, Henryk, E-mail: henryk@kth.se
2016-07-15
Highlights: • Annular two-phase flow has been modeled using a unified CFD approach. • Liquid film was modeled based on a two-dimensional thin film assumption. • Both Eulerian and Lagrangian methods were employed for the gas core flow modeling. - Abstract: A mechanistic model of annular flow with evaporating liquid film has been developed using computational fluid dynamics (CFD). The model is employing a separate solver with two-dimensional conservation equations to predict propagation of a thin boiling liquid film on solid walls. The liquid film model is coupled to a solver of three-dimensional conservation equations describing the gas core, which is assumed to contain a saturated mixture of vapor and liquid droplets. Both the Eulerian–Eulerian and the Eulerian–Lagrangian approach are used to describe the droplet and vapor motion in the gas core. All the major interaction phenomena between the liquid film and the gas core flow have been accounted for, including the liquid film evaporation as well as the droplet deposition and entrainment. The resultant unified framework for annular flow has been applied to the steam-water flow with conditions typical for a Boiling Water Reactor (BWR). The simulation results for the liquid film flow rate show good agreement with the experimental data, with the potential to predict the dryout occurrence based on criteria of critical film thickness or critical film flow rate.
Modeling of annular two-phase flow using a unified CFD approach
International Nuclear Information System (INIS)
Li, Haipeng; Anglart, Henryk
2016-01-01
Highlights: • Annular two-phase flow has been modeled using a unified CFD approach. • Liquid film was modeled based on a two-dimensional thin film assumption. • Both Eulerian and Lagrangian methods were employed for the gas core flow modeling. - Abstract: A mechanistic model of annular flow with evaporating liquid film has been developed using computational fluid dynamics (CFD). The model is employing a separate solver with two-dimensional conservation equations to predict propagation of a thin boiling liquid film on solid walls. The liquid film model is coupled to a solver of three-dimensional conservation equations describing the gas core, which is assumed to contain a saturated mixture of vapor and liquid droplets. Both the Eulerian–Eulerian and the Eulerian–Lagrangian approach are used to describe the droplet and vapor motion in the gas core. All the major interaction phenomena between the liquid film and the gas core flow have been accounted for, including the liquid film evaporation as well as the droplet deposition and entrainment. The resultant unified framework for annular flow has been applied to the steam-water flow with conditions typical for a Boiling Water Reactor (BWR). The simulation results for the liquid film flow rate show good agreement with the experimental data, with the potential to predict the dryout occurrence based on criteria of critical film thickness or critical film flow rate.
International Nuclear Information System (INIS)
Weisman, J.
1991-01-01
This paper reports on the phenomena governing the critical heat flux in flow boiling. Inducts which vary with the flow pattern. Separate models are needed for dryout in annular flow, wall overheating in plug or slug flow and formation of a vapor blanket in dispersed flow. The major theories and their current status are described for the annular and dispersed regions. The need for development of the theoretical approach in the plug and slug flow region is indicated
The relaxation time approximation
International Nuclear Information System (INIS)
Gairola, R.P.; Indu, B.D.
1991-01-01
A plausible approximation has been made to estimate the relaxation time from a knowledge of the transition probability of phonons from one state (r vector, q vector) to other state (r' vector, q' vector), as a result of collision. The relaxation time, thus obtained, shows a strong dependence on temperature and weak dependence on the wave vector. In view of this dependence, relaxation time has been expressed in terms of a temperature Taylor's series in the first Brillouin zone. Consequently, a simple model for estimating the thermal conductivity is suggested. the calculations become much easier than the Callaway model. (author). 14 refs
Isochronous relaxation curves for type 304 stainless steel after monotonic and cyclic strain
International Nuclear Information System (INIS)
Swindeman, R.W.
1978-01-01
Relaxation tests to 100 hr were performed on type 304 stainless steel in the temperature range 480 to 650 0 C and were used to develop isochronous relaxation curves. Behavior after monotonic and cyclic strain was compared. Relaxation differed only slightly as a consequence of the type of previous strain, provided that plastic flow preceded the relaxation period. We observed that the short-time relaxation behavior did not manifest strong heat-to-heat variation in creep strength
Directory of Open Access Journals (Sweden)
Antonio Costa
2014-07-01
Full Text Available Production processes in Cellular Manufacturing Systems (CMS often involve groups of parts sharing the same technological requirements in terms of tooling and setup. The issue of scheduling such parts through a flow-shop production layout is known as the Flow-Shop Group Scheduling (FSGS problem or, whether setup times are sequence-dependent, the Flow-Shop Sequence-Dependent Group Scheduling (FSDGS problem. This paper addresses the FSDGS issue, proposing a hybrid metaheuristic procedure integrating features from Genetic Algorithms (GAs and Biased Random Sampling (BRS search techniques with the aim of minimizing the total flow time, i.e., the sum of completion times of all jobs. A well-known benchmark of test cases, entailing problems with two, three, and six machines, is employed for both tuning the relevant parameters of the developed procedure and assessing its performances against two metaheuristic algorithms recently presented by literature. The obtained results and a properly arranged ANOVA analysis highlight the superiority of the proposed approach in tackling the scheduling problem under investigation.
Kang, Sinhang; Lee, Seung-Rae
2018-05-01
Many debris flow spreading analyses have been conducted during recent decades to prevent damage from debris flows. An empirical approach that has been used in various studies on debris flow spreading has advantages such as simple data acquisition and good applicability for large areas. In this study, a GIS-based empirical model that was developed at the University of Lausanne (Switzerland) is used to assess the debris flow susceptibility. Study sites are classified based on the types of soil texture or geological conditions, which can indirectly consider geotechnical or rheological properties, to supplement the weaknesses of Flow-R which neglects local controlling factors. The mean travel angle for each classification is calculated from a debris flow inventory map. The debris flow susceptibility is assessed based on changes in the flow-direction algorithm, an inertial function with a 5-m DEM resolution. A simplified friction-limited model was applied to the runout distance analysis by using the appropriate travel angle for the corresponding classification with a velocity limit of 28 m/s. The most appropriate algorithm combinations that derived the highest average of efficiency and sensitivity for each classification are finally determined by applying a confusion matrix with the efficiency and the sensitivity to the results of the susceptibility assessment. The proposed schemes can be useful for debris flow susceptibility assessment in both the study area and the central region of Korea, which has similar environmental factors such as geological conditions, topography and rainfall characteristics to the study area.
Two-Phase Immiscible Flows in Porous Media: The Mesocopic Maxwell–Stefan Approach
DEFF Research Database (Denmark)
Shapiro, Alexander
2015-01-01
We develop an approach to coupling between viscous flows of the two phases in porous media, based on the Maxwell–Stefan formalism. Two versions of the formalism are presented: the general form, and the form based on the interaction of the flowing phases with the interface between them. The last...... of mixing” between the flowing phases. Comparison to the available experimental data on the steady-state two-phase relative permeabilities is presented....... approach is supported by the description of the flow on the mesoscopic level, as coupled boundary problems for the Brinkmann or Stokes equations. It becomes possible, in some simplifying geometric assumptions, to derive exact expressions for the phenomenological coefficients in the Maxwell–Stefan transport...
A parametric level-set approach for topology optimization of flow domains
DEFF Research Database (Denmark)
Pingen, Georg; Waidmann, Matthias; Evgrafov, Anton
2010-01-01
of the design variables in the traditional approaches is seen as a possible cause for the slow convergence. Non-smooth material distributions are suspected to trigger premature onset of instationary flows which cannot be treated by steady-state flow models. In the present work, we study whether the convergence...... and the versatility of topology optimization methods for fluidic systems can be improved by employing a parametric level-set description. In general, level-set methods allow controlling the smoothness of boundaries, yield a non-local influence of design variables, and decouple the material description from the flow...... field discretization. The parametric level-set method used in this study utilizes a material distribution approach to represent flow boundaries, resulting in a non-trivial mapping between design variables and local material properties. Using a hydrodynamic lattice Boltzmann method, we study...
Parametric Approach to Assessing Performance of High-Lift Device Active Flow Control Architectures
Directory of Open Access Journals (Sweden)
Yu Cai
2017-02-01
Full Text Available Active Flow Control is at present an area of considerable research, with multiple potential aircraft applications. While the majority of research has focused on the performance of the actuators themselves, a system-level perspective is necessary to assess the viability of proposed solutions. This paper demonstrates such an approach, in which major system components are sized based on system flow and redundancy considerations, with the impacts linked directly to the mission performance of the aircraft. Considering the case of a large twin-aisle aircraft, four distinct active flow control architectures that facilitate the simplification of the high-lift mechanism are investigated using the demonstrated approach. The analysis indicates a very strong influence of system total mass flow requirement on architecture performance, both for a typical mission and also over the entire payload-range envelope of the aircraft.
Juvonen, Piia
2012-01-01
ABSTRACT Juvonen, Piia Suvi Päivikki 2012. Effective information flow through efficient supply chain management -Value stream mapping approach - Case Outokumpu Tornio Works. Master`s Thesis. Kemi-Tornio University of Applied Sciences. Business and Culture. Pages 63. Appendices 2. The general aim of this thesis is to explore effective information flow through efficient supply chain management by following one of the lean management principles, value stream mapping. The specific research...
Directory of Open Access Journals (Sweden)
Ирина Александровна Гавриленко
2016-02-01
Full Text Available The approach to automated management of load flow in engineering networks considering functional reliability was proposed in the article. The improvement of the concept of operational and strategic management of load flow in engineering networks was considered. The verbal statement of the problem for thesis research is defined, namely, the problem of development of information technology for exact calculation of the functional reliability of the network, or the risk of short delivery of purpose-oriented product for consumers
Are Flow Injection-based Approaches Suitable for Automated Handling of Solid Samples?
DEFF Research Database (Denmark)
Miró, Manuel; Hansen, Elo Harald; Cerdà, Victor
Flow-based approaches were originally conceived for liquid-phase analysis, implying that constituents in solid samples generally had to be transferred into the liquid state, via appropriate batch pretreatment procedures, prior to analysis. Yet, in recent years, much effort has been focused...... electrolytic or aqueous leaching, on-line dialysis/microdialysis, in-line filtration, and pervaporation-based procedures have been successfully implemented in continuous flow/flow injection systems. In this communication, the new generation of flow analysis, including sequential injection, multicommutated flow.......g., soils, sediments, sludges), and thus, ascertaining the potential mobility, bioavailability and eventual impact of anthropogenic elements on biota [2]. In this context, the principles of sequential injection-microcolumn extraction (SI-MCE) for dynamic fractionation are explained in detail along...
Passenger flow analysis of Beijing urban rail transit network using fractal approach
Li, Xiaohong; Chen, Peiwen; Chen, Feng; Wang, Zijia
2018-04-01
To quantify the spatiotemporal distribution of passenger flow and the characteristics of an urban rail transit network, we introduce four radius fractal dimensions and two branch fractal dimensions by combining a fractal approach with passenger flow assignment model. These fractal dimensions can numerically describe the complexity of passenger flow in the urban rail transit network and its change characteristics. Based on it, we establish a fractal quantification method to measure the fractal characteristics of passenger follow in the rail transit network. Finally, we validate the reasonability of our proposed method by using the actual data of Beijing subway network. It has been shown that our proposed method can effectively measure the scale-free range of the urban rail transit network, network development and the fractal characteristics of time-varying passenger flow, which further provides a reference for network planning and analysis of passenger flow.
Directional synthetic aperture flow imaging using a dual stage beamformer approach
DEFF Research Database (Denmark)
Li, Ye; Jensen, Jørgen Arendt
2011-01-01
. The new method has been studied using the Field II simulations and experimental flow rig measurements. A linear array transducer with 7 MHz center frequency is used, and 64 elements are active to transmit and receive signals. The data is processed in two stages. The first stage has a fixed focus point......A new method for directional synthetic aperture flow imaging using a dual stage beamformer approach is presented. The velocity estimation is angle independent and the amount of calculations is reduced compared to full synthetic aperture, but still maintains all the advantages at the same time....... In the second stage, focal points are considered as virtual sources and data is beamformed along the flow direction. Then the velocities are estimated by finding the spatial shift between two signals. In the experimental measurements the angle between the transmit beam and flow vessel was 70 and a laminar flow...
Kozaka, Orçun E.; Özkan, Gökhan; Özdemir, Bedii I.
2004-01-01
Turbulent structure of flow behind a model car is investigated with local velocity measurements with emphasis on large structures and their relevance to aerodynamic forces. Results show that two counter-rotating helical vortices, which are formed within the inner wake region, play a key role in determining the flux of kinetic energy. The turbulence is generated within the outermost shear layers due to the instabilities, which also seem to be the basic drive for these relatively organized structures. The measured terms of the turbulent kinetic energy production, which are only part of the full expression, indicate that vortex centres act similar to the manifolds draining the energy in the streamwise direction. As the approach velocity increases, the streamwise convection becomes the dominant means of turbulent transport and, thus, the acquisition of turbulence by relatively non-turbulent flow around the wake region is suppressed.
International Nuclear Information System (INIS)
Wang, J.S.Y.; Narasimhan, T.N.
1993-06-01
This report discusses conceptual models and mathematical equations, analyzes distributions and correlations among hydrological parameters of soils and tuff, introduces new path integration approaches, and outlines scaling procedures to model potential-driven fluid flow in heterogeneous media. To properly model the transition from fracture-dominated flow under saturated conditions to matrix-dominated flow under partially saturated conditions, characteristic curves and permeability functions for fractures and matrix need to be improved and validated. Couplings from two-phase flow, heat transfer, solute transport, and rock deformation to liquid flow are also important. For stochastic modeling of alternating units of welded and nonwelded tuff or formations bounded by fault zones, correlations and constraints on average values of saturated permeability and air entry scaling factor between different units need to be imposed to avoid unlikely combinations of parameters and predictions. Large-scale simulations require efficient and verifiable numerical algorithms. New path integration approaches based on postulates of minimum work and mass conservation to solve flow geometry and potential distribution simultaneously are introduced. This verifiable integral approach, together with fractal scaling procedures to generate statistical realizations with parameter distribution, correlation, and scaling taken into account, can be used to quantify uncertainties and generate the cumulative distribution function for groundwater travel times
Energy Technology Data Exchange (ETDEWEB)
De Pretto, Lucas R., E-mail: lucas.de.pretto@usp.br; Nogueira, Gesse E. C.; Freitas, Anderson Z. [Instituto de Pesquisas Energéticas e Nucleares, IPEN–CNEN/SP, Avenida Lineu Prestes, 2242, 05508-000 São Paulo (Brazil)
2016-04-28
Functional modalities of Optical Coherence Tomography (OCT) based on speckle analysis are emerging in the literature. We propose a simple approach to the autocorrelation of OCT signal to enable volumetric flow rate differentiation, based on decorrelation time. Our results show that this technique could distinguish flows separated by 3 μl/min, limited by the acquisition speed of the system. We further perform a B-scan of gradient flow inside a microchannel, enabling the visualization of the drag effect on the walls.
Hermite-Pade approximation approach to hydromagnetic flows in convergent-divergent channels
International Nuclear Information System (INIS)
Makinde, O.D.
2005-10-01
The problem of two-dimensional, steady, nonlinear flow of an incompressible conducting viscous fluid in convergent-divergent channels under the influence of an externally applied homogeneous magnetic field is studied using a special type of Hermite-Pade approximation approach. This semi-numerical scheme offers some advantages over solutions obtained by using traditional methods such as finite differences, spectral method, shooting method, etc. It reveals the analytical structure of the solution function and the important properties of overall flow structure including velocity field, flow reversal control and bifurcations are discussed. (author)
CFD model of diabatic annular two-phase flow using the Eulerian–Lagrangian approach
International Nuclear Information System (INIS)
Li, Haipeng; Anglart, Henryk
2015-01-01
Highlights: • A CFD model of annular two-phase flow with evaporating liquid film has been developed. • A two-dimensional liquid film model is developed assuming that the liquid film is sufficiently thin. • The liquid film model is coupled to the gas core flow, which is represented using the Eulerian–Lagrangian approach. - Abstract: A computational fluid dynamics (CFD) model of annular two-phase flow with evaporating liquid film has been developed based on the Eulerian–Lagrangian approach, with the objective to predict the dryout occurrence. Due to the fact that the liquid film is sufficiently thin in the diabatic annular flow and at the pre-dryout conditions, it is assumed that the flow in the wall normal direction can be neglected, and the spatial gradients of the dependent variables tangential to the wall are negligible compared to those in the wall normal direction. Subsequently the transport equations of mass, momentum and energy for liquid film are integrated in the wall normal direction to obtain two-dimensional equations, with all the liquid film properties depth-averaged. The liquid film model is coupled to the gas core flow, which currently is represented using the Eulerian–Lagrangian technique. The mass, momentum and energy transfers between the liquid film, gas, and entrained droplets have been taken into account. The resultant unified model for annular flow has been applied to the steam–water flow with conditions typical for a Boiling Water Reactor (BWR). The simulation results for the liquid film flow rate show favorable agreement with the experimental data, with the potential to predict the dryout occurrence based on criteria of critical film thickness or critical film flow rate
A comparison and assessment of approaches for modelling flow over in-line tube banks
International Nuclear Information System (INIS)
Iacovides, Hector; Launder, Brian; West, Alastair
2014-01-01
Highlights: • We present wall-resolved LES and URANS simulations of periodic flow in heated in-line tube banks. • Simulations of flow in a confined in-line tube-bank are compared with experimental data. • When pitch-to-diameter (P/D) ratio becomes less than 1.6, the periodic flow becomes skewed. • URANS tested here unable to mimic the periodic flow at P/D = 1.6. • In confined tube banks URANS suggest alternate, in the axial direction, flow deflection. - Abstract: The paper reports experiences from applying alternative strategies for modelling turbulent flow and local heat-transfer coefficients around in-line tube banks. The motivation is the simulation of conditions in the closely packed cross-flow heat exchangers used in advanced gas-cooled nuclear reactors (AGRs). The main objective is the flow simulation in large-scale tube banks with confining walls. The suitability and accuracy of wall-resolved large-eddy simulation (LES) and Unsteady Reynolds-Averaged Navier–Stokes (URANS) approaches are examined for generic, square, in-line tube banks, where experimental data are limited but available. Within the latter approach, both eddy-viscosity and Reynolds-stress-transport models have been tested. The assumption of flow periodicity in all three directions is investigated by varying the domain size. It is found that the path taken by the fluid through the tube-bank configuration differs according to the treatment of turbulence and whether the flow is treated as two- or three-dimensional. Finally, the important effect of confining walls has been examined by making direct comparison with the experiments of the complete test rig of Aiba et al. (1982)
Far-from-equilibrium attractors and nonlinear dynamical systems approach to the Gubser flow
Behtash, Alireza; Cruz-Camacho, C. N.; Martinez, M.
2018-02-01
The nonequilibrium attractors of systems undergoing Gubser flow within relativistic kinetic theory are studied. In doing so we employ well-established methods of nonlinear dynamical systems which rely on finding the fixed points, investigating the structure of the flow diagrams of the evolution equations, and characterizing the basin of attraction using a Lyapunov function near the stable fixed points. We obtain the attractors of anisotropic hydrodynamics, Israel-Stewart (IS) and transient fluid (DNMR) theories and show that they are indeed nonplanar and the basin of attraction is essentially three dimensional. The attractors of each hydrodynamical model are compared with the one obtained from the exact Gubser solution of the Boltzmann equation within the relaxation time approximation. We observe that the anisotropic hydrodynamics is able to match up to high numerical accuracy the attractor of the exact solution while the second-order hydrodynamical theories fail to describe it. We show that the IS and DNMR asymptotic series expansions diverge and use resurgence techniques to perform the resummation of these divergences. We also comment on a possible link between the manifold of steepest descent paths in path integrals and the basin of attraction for the attractors via Lyapunov functions that opens a new horizon toward an effective field theory description of hydrodynamics. Our findings indicate that the reorganization of the expansion series carried out by anisotropic hydrodynamics resums the Knudsen and inverse Reynolds numbers to all orders and thus, it can be understood as an effective theory for the far-from-equilibrium fluid dynamics.
Conceptual Model and Numerical Approaches for Unsaturated Zone Flow and Transport
International Nuclear Information System (INIS)
H.H. Liu
2004-01-01
The purpose of this model report is to document the conceptual and numerical models used for modeling unsaturated zone (UZ) fluid (water and air) flow and solute transport processes. This work was planned in ''Technical Work Plan for: Unsaturated Zone Flow Model and Analysis Report Integration'' (BSC 2004 [DIRS 169654], Sections 1.2.5, 2.1.1, 2.1.2 and 2.2.1). The conceptual and numerical modeling approaches described in this report are mainly used for models of UZ flow and transport in fractured, unsaturated rock under ambient conditions. Developments of these models are documented in the following model reports: (1) UZ Flow Model and Submodels; (2) Radionuclide Transport Models under Ambient Conditions. Conceptual models for flow and transport in unsaturated, fractured media are discussed in terms of their applicability to the UZ at Yucca Mountain. The rationale for selecting the conceptual models used for modeling of UZ flow and transport is documented. Numerical approaches for incorporating these conceptual models are evaluated in terms of their representation of the selected conceptual models and computational efficiency; and the rationales for selecting the numerical approaches used for modeling of UZ flow and transport are discussed. This report also documents activities to validate the active fracture model (AFM) based on experimental observations and theoretical developments. The AFM is a conceptual model that describes the fracture-matrix interaction in the UZ of Yucca Mountain. These validation activities are documented in Section 7 of this report regarding use of an independent line of evidence to provide additional confidence in the use of the AFM in the UZ models. The AFM has been used in UZ flow and transport models under both ambient and thermally disturbed conditions. Developments of these models are documented
Analyzing Unsaturated Flow Patterns in Fractured Rock Using an Integrated Modeling Approach
International Nuclear Information System (INIS)
Y.S. Wu; G. Lu; K. Zhang; L. Pan; G.S. Bodvarsson
2006-01-01
Characterizing percolation patterns in unsaturated fractured rock has posed a greater challenge to modeling investigations than comparable saturated zone studies, because of the heterogeneous nature of unsaturated media and the great number of variables impacting unsaturated flow. This paper presents an integrated modeling methodology for quantitatively characterizing percolation patterns in the unsaturated zone of Yucca Mountain, Nevada, a proposed underground repository site for storing high-level radioactive waste. The modeling approach integrates a wide variety of moisture, pneumatic, thermal, and isotopic geochemical field data into a comprehensive three-dimensional numerical model for modeling analyses. It takes into account the coupled processes of fluid and heat flow and chemical isotopic transport in Yucca Mountain's highly heterogeneous, unsaturated fractured tuffs. Modeling results are examined against different types of field-measured data and then used to evaluate different hydrogeological conceptualizations and their results of flow patterns in the unsaturated zone. In particular, this model provides a much clearer understanding of percolation patterns and flow behavior through the unsaturated zone, both crucial issues in assessing repository performance. The integrated approach for quantifying Yucca Mountain's flow system is demonstrated to provide a practical modeling tool for characterizing flow and transport processes in complex subsurface systems
A new approach to flow through a region bounded by two ellipses of the same ellipticity
Lal, K.; Chorlton, F.
1981-05-01
A new approach is presented to calculate steady flow of a laminar viscous incompressible fluid through a channel whose cross section is bounded by two ellipses with the same ellipticity. The Milne-Thomas approach avoids the stream function and is similar to the Rayleigh-Ritz approximation process of the calculus of variations in its first satisfying boundary conditions and then adjusting constants or multiplying functions to fit the differential equation.
A modeling approach to establish environmental flow threshold in ungauged semidiurnal tidal river
Akter, A.; Tanim, A. H.
2018-03-01
Due to shortage of flow monitoring data in ungauged semidiurnal river, 'environmental flow' (EF) determination based on its key component 'minimum low flow' is always difficult. For EF assessment this study selected a reach immediately after the Halda-Karnafuli confluence, a unique breeding ground for Indian Carp fishes of Bangladesh. As part of an ungauged tidal river, EF threshold establishment faces challenges in changing ecological paradigms with periodic change of tides and hydrologic alterations. This study describes a novel approach through modeling framework comprising hydrological, hydrodynamic and habitat simulation model. The EF establishment was conceptualized according to the hydrologic process of an ungauged semi-diurnal tidal regime in four steps. Initially, a hydrologic model coupled with a hydrodynamic model to simulate flow considering land use changes effect on streamflow, seepage loss of channel, friction dominated tidal decay as well as lack of long term flow characteristics. Secondly, to define hydraulic habitat feature, a statistical analysis on derived flow data was performed to identify 'habitat suitability'. Thirdly, to observe the ecological habitat behavior based on the identified hydrologic alteration, hydraulic habitat features were investigated. Finally, based on the combined habitat suitability index flow alteration and ecological response relationship was established. Then, the obtained EF provides a set of low flow indices of desired regime and thus the obtained discharge against maximum Weighted Usable Area (WUA) was defined as EF threshold for the selected reach. A suitable EF regime condition was obtained within flow range 25-30.1 m3/s i.e., around 10-12% of the mean annual runoff of 245 m3/s and these findings are within researchers' recommendation of minimum flow requirement. Additionally it was observed that tidal characteristics are dominant process in semi-diurnal regime. However, during the study period (2010-2015) the
Grosso, Juan M.; Ocampo-Martinez, Carlos; Puig, Vicenç
2017-10-01
This paper proposes a distributed model predictive control approach designed to work in a cooperative manner for controlling flow-based networks showing periodic behaviours. Under this distributed approach, local controllers cooperate in order to enhance the performance of the whole flow network avoiding the use of a coordination layer. Alternatively, controllers use both the monolithic model of the network and the given global cost function to optimise the control inputs of the local controllers but taking into account the effect of their decisions over the remainder subsystems conforming the entire network. In this sense, a global (all-to-all) communication strategy is considered. Although the Pareto optimality cannot be reached due to the existence of non-sparse coupling constraints, the asymptotic convergence to a Nash equilibrium is guaranteed. The resultant strategy is tested and its effectiveness is shown when applied to a large-scale complex flow-based network: the Barcelona drinking water supply system.
Mode decomposition methods for flows in high-contrast porous media. A global approach
Ghommem, Mehdi; Calo, Victor M.; Efendiev, Yalchin R.
2014-01-01
We apply dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD) methods to flows in highly-heterogeneous porous media to extract the dominant coherent structures and derive reduced-order models via Galerkin projection. Permeability fields with high contrast are considered to investigate the capability of these techniques to capture the main flow features and forecast the flow evolution within a certain accuracy. A DMD-based approach shows a better predictive capability due to its ability to accurately extract the information relevant to long-time dynamics, in particular, the slowly-decaying eigenmodes corresponding to largest eigenvalues. Our study enables a better understanding of the strengths and weaknesses of the applicability of these techniques for flows in high-contrast porous media. Furthermore, we discuss the robustness of DMD- and POD-based reduced-order models with respect to variations in initial conditions, permeability fields, and forcing terms. © 2013 Elsevier Inc.
Physiome approach for the analysis of vascular flow reserve in the heart and brain.
Lee, Kyung Eun; Ryu, Ah-Jin; Shin, Eun-Seok; Shim, Eun Bo
2017-06-01
This work reviews the key aspects of coronary and neurovascular flow reserves with an emphasis on physiomic modeling characteristics by the use of a variety of numerical approaches. First, we explain the definition of fractional flow reserve (FFR) in coronary artery and introduce its clinical significance. Then, computational researches for obtaining FFR are reviewed, and their clinical outcomes are compared. In the case of cerebrovascular reserve (CVR), in spite of substantial progress in the simulation of cerebral hemodynamics, only a few computational studies exist. Thus, we discuss the limitations of CVR simulation study and suggest the challenging issue to overcome these. Also, the future direction of physiomic researches for the flow reserves in coronary arteries and cerebral arteries is described. Also, we introduce a machine learning algorithm trained by the existing physiomic simulation data of flow reserve and suggest a prospective research direction related to this.
Weighted L2 and Lq approaches to fluid flow past a rotating body
Czech Academy of Sciences Publication Activity Database
Farwig, R.; Kračmar, S.; Krbec, Miroslav; Nečasová, Šárka; Penel, P.
2009-01-01
Roč. 86, - (2009), s. 59-81 ISSN 0137-6934 R&D Projects: GA AV ČR IAA100190505; GA AV ČR IAA100190804 Institutional research plan: CEZ:AV0Z10190503 Keywords : variational approach * maximal operator * Littlewood-Paley theory * Oseen flow Subject RIV: BA - General Mathematics
Study of the parabolic and elliptic approaches validities for a turbulent co-flowing jet
Directory of Open Access Journals (Sweden)
Mahmoud Houda
2012-01-01
Full Text Available An axisymmetric turbulent jet discharged in a co-flowing stream was studied with the aid of parabolic and elliptic approaches. The simulations were performed with two in-house codes. Detailed comparisons of data show good agreement with the corresponding experiments; and different behaviors of jet dilution were found in initial region at different ranges of velocities ratios. It has been found that the two approaches give practically the same results for the velocities ratios Ru ≤ 1.5. Further from this value, the elliptic approach highlights the appearance of the fall velocity zone and that’s due to the presence of a trough low pressure. This fall velocity has not been detected by the parabolic approach and that’s due to the jet entrainment by the ambient flow. The intensity of this entrainment is directly related to the difference between the primary (jet and the secondary flow (co-flow. In fact, by increasing the velocities ratios Ru, the sucked flux by the outer stream becomes more important; the fall velocity intensifies and changes into a recirculation zone for Ru ≥ 5.
Validation of a LES turbulence modeling approach on a steady engine head flow
Huijnen, V.; Somers, L.M.T.; Baert, R.S.G.; Goey, de L.P.H.; Dias, V.
2005-01-01
The application of the LES turbulence modeling approach in the Kiva-environment is validated on a complex geometry. Results for the steady flow in a realistic geometry of a production type heavy-duty diesel engine head with 120 mm cylinder bore are presented. The bulk Reynolds number is Reb = 1 fl
Two Experiments to Approach the Boltzmann Factor: Chemical Reaction and Viscous Flow
Fazio, Claudio; Battaglia, Onofrio R.; Guastella, Ivan
2012-01-01
In this paper we discuss a pedagogical approach aimed at pointing out the role played by the Boltzmann factor in describing phenomena usually perceived as regulated by different mechanisms of functioning. Experimental results regarding some aspects of a chemical reaction and of the viscous flow of some liquids are analysed and described in terms…
A flow balance approach to scenarios for water reclamation by Ania ...
African Journals Online (AJOL)
drinie
ISSN 0378-4738 = Water SA Vol. 27 No. 1 January 2001 115. Available on website http://www.wrc.org.za. Comments on: A flow balance approach to scenarios for water reclamation by Ania MW Grobicki and B Cohen. I would like to offer a brief comment on the above paper, which appeared in Water SA 25 (4), October ...
Directory of Open Access Journals (Sweden)
Carmignani Luca
2015-01-01
Full Text Available Opposed-flow flame spread over solid fuels is a fundamental area of research in fire science. Typically combustion wind tunnels are used to generate the opposing flow of oxidizer against which a laminar flame spread occurs along the fuel samples. The spreading flame is generally embedded in a laminar boundary layer, which interacts with the strong buoyancy-induced flow to affect the mechanism of flame spread. In this work, two different approaches for creating the opposed-flow are compared. In the first approach, a vertical combustion tunnel is used where a thin fuel sample, thin acrylic or ashless filter paper, is held vertically along the axis of the test-section with the airflow controlled by controlling the duty cycles of four fans. As the sample is ignited, a flame spreads downward in a steady manner along a developing boundary layer. In the second approach, the sample is held in a movable cart placed in an eight-meter tall vertical chamber filled with air. As the sample is ignited, the cart is moved downward (through a remote-controlled mechanism at a prescribed velocity. The results from the two approaches are compared to establish the boundary layer effect on flame spread over thin fuels.
Directory of Open Access Journals (Sweden)
Lucky Purwantini
2017-08-01
Full Text Available Flow is a condition when individual merges within his/her activity. When a person in flow state, he/she can develop his/her abilities and more success in learning. The purpose of the study is to understand flow experience in learning among undergraduate student. The study used case study qualitative approach. Informant of this research was an undergraduate student which had flow experience. Data was collected by an interview. According to the result, the subject did not experience flow in the learning process, as likes he was in meditation. It happened because when he learned something, he felt be pressed by tasks. It’s important for individual to relax when they are learning.
Gultom, Syamsul; Darma Sitepu, Indra; Hasibuan, Nurman
2018-03-01
Fatigue due to long and continuous computer usage can lead to problems of dominant fatigue associated with decreased performance and work motivation. Specific targets in the first phase have been achieved in this research such as: (1) Identified complaints on workers using computers, using the Bourdon Wiersma test kit. (2) Finding the right relaxation & work posture draft for a solution to reduce muscle fatigue in computer-based workers. The type of research used in this study is research and development method which aims to produce the products or refine existing products. The final product is a prototype of back-holder, monitoring filter and arranging a relaxation exercise as well as the manual book how to do this while in front of the computer to lower the fatigue level for computer users in Unimed’s Administration Center. In the first phase, observations and interviews have been conducted and identified the level of fatigue on the employees of computer users at Uniemd’s Administration Center using Bourdon Wiersma test and has obtained the following results: (1) The average velocity time of respondents in BAUK, BAAK and BAPSI after working with the value of interpretation of the speed obtained value of 8.4, WS 13 was in a good enough category, (2) The average of accuracy of respondents in BAUK, in BAAK and in BAPSI after working with interpretation value accuracy obtained Value of 5.5, WS 8 was in doubt-category. This result shows that computer users experienced a significant tiredness at the Unimed Administration Center, (3) the consistency of the average of the result in measuring tiredness level on computer users in Unimed’s Administration Center after working with values in consistency of interpretation obtained Value of 5.5 with WS 8 was put in a doubt-category, which means computer user in The Unimed Administration Center suffered an extreme fatigue. In phase II, based on the results of the first phase in this research, the researcher offers
Pressure from particle image velocimetry for convective flows: a Taylor’s hypothesis approach
International Nuclear Information System (INIS)
De Kat, R; Ganapathisubramani, B
2013-01-01
Taylor’s hypothesis is often applied in turbulent flow analysis to map temporal information into spatial information. Recent efforts in deriving pressure from particle image velocimetry (PIV) have proposed multiple approaches, each with its own weakness and strength. Application of Taylor’s hypothesis allows us to counter the weakness of an Eulerian approach that is described by de Kat and van Oudheusden (2012 Exp. Fluids 52 1089–106). Two different approaches of using Taylor’s hypothesis in determining planar pressure are investigated: one where pressure is determined from volumetric PIV data and one where pressure is determined from time-resolved stereoscopic PIV data. A performance assessment on synthetic data shows that application of Taylor’s hypothesis can improve determination of pressure from PIV data significantly compared with a time-resolved volumetric approach. The technique is then applied to time-resolved PIV data taken in a cross-flow plane of a turbulent jet (Ganapathisubramani et al 2007 Exp. Fluids 42 923–39). Results appear to indicate that pressure can indeed be obtained from PIV data in turbulent convective flows using the Taylor’s hypothesis approach, where there are no other methods to determine pressure. The role of convection velocity in determination of pressure is also discussed. (paper)
A Flow Rate Control Approach on Off-Design Analysis of an Organic Rankine Cycle System
Directory of Open Access Journals (Sweden)
Ben-Ran Fu
2016-09-01
Full Text Available This study explored effects of off-design heat source temperature (TW,in or flow rate (mW on heat transfer characteristics and performance of an organic Rankine cycle system by controlling the flow rate of working fluid R245fa (i.e., the operation flow rate of R245fa was controlled to ensure that R245fa reached saturation liquid and vapor states at the outlets of the preheater and evaporator, respectively. The results showed that the operation flow rate of R245fa increased with TW,in or mW; higher TW,in or mW yielded better heat transfer performance of the designed preheater and required higher heat capacity of the evaporator; heat transfer characteristics of preheater and evaporator differed for off-design TW,in and mW; and net power output increased with TW,in or mW. The results further indicated that the control strategy should be different for various off-design conditions. Regarding maximum net power output, the flow rate control approach is optimal when TW,in or mW exceeds the design point, but the pressure control approach is better when TW,in or mW is lower than the design point.
Relaxation strain measurements in cellular dislocation structures
International Nuclear Information System (INIS)
Tsai, C.Y.; Quesnel, D.J.
1984-01-01
The conventional picture of what happens during a stress relaxation usually involves imagining the response of a single dislocation to a steadily decreasing stress. The velocity of this dislocation decreases with decreasing stress in such a way that we can measure the stress dependence of the dislocation velocity. Analysis of the data from a different viewpoint enables us to calculate the apparent activation volume for the motion of the dislocation under the assumption of thermally activated glie. Conventional thinking about stress relaxation, however, does not consider the eventual fate of this dislocation. If the stress relaxes to a low enough level, it is clear that the dislocation must stop. This is consistent with the idea that we can determine the stress dependence of the dislocation velocity from relaxation data only for those cases where the dislocation's velocity is allowed to approach zero asymptotically, in short, for those cases where the dislocation never stops. This conflict poses a dilemma for the experimentalist. In real crystals, however, obstacles impede the dislocation's progress so that those dislocations which are stopped at a given stress will probably never resume motion under the influence of the steadily declining stress present during relaxation. Thus one could envision stress relaxation as a process of exhaustion of mobile dislocations, rather than a process of decreasing dislocation velocity. Clearly both points of view have merit and in reality both mechanisms contribute to the phenomena
Garbin, Silvia; Alessi Celegon, Elisa; Fanton, Pietro; Botter, Gianluca
2017-04-01
The temporal variability of river flow regime is a key feature structuring and controlling fluvial ecological communities and ecosystem processes. In particular, streamflow variability induced by climate/landscape heterogeneities or other anthropogenic factors significantly affects the connectivity between streams with notable implication for river fragmentation. Hydrologic connectivity is a fundamental property that guarantees species persistence and ecosystem integrity in riverine systems. In riverine landscapes, most ecological transitions are flow-dependent and the structure of flow regimes may affect ecological functions of endemic biota (i.e., fish spawning or grazing of invertebrate species). Therefore, minimum flow thresholds must be guaranteed to support specific ecosystem services, like fish migration, aquatic biodiversity and habitat suitability. In this contribution, we present a probabilistic approach aiming at a spatially-explicit, quantitative assessment of hydrologic connectivity at the network-scale as derived from river flow variability. Dynamics of daily streamflows are estimated based on catchment-scale climatic and morphological features, integrating a stochastic, physically based approach that accounts for the stochasticity of rainfall with a water balance model and a geomorphic recession flow model. The non-exceedance probability of ecologically meaningful flow thresholds is used to evaluate the fragmentation of individual stream reaches, and the ensuing network-scale connectivity metrics. A multi-dimensional Poisson Process for the stochastic generation of rainfall is used to evaluate the impact of climate signature on reach-scale and catchment-scale connectivity. The analysis shows that streamflow patterns and network-scale connectivity are influenced by the topology of the river network and the spatial variability of climatic properties (rainfall, evapotranspiration). The framework offers a robust basis for the prediction of the impact of
Directory of Open Access Journals (Sweden)
M. S. Najiha
2012-12-01
Full Text Available This paper presents a two-dimensional steady-state incompressible analysis for the minimum quantity of lubricant flow in milling operations using a computational fluid dynamics (CFD approach. The analysis of flow and heat transfer in a four-teeth milling cutter operation was undertaken. The domain of the rotating cutter along with the spray nozzle is defined. Operating cutting and boundary conditions are taken from the literature. A steady-state, pressure-based, planar analysis was performed with a viscous, realizable k-ε model. A mixture of oils and air were sprayed on the tool, which is considered to be rotating and is at a temperature near the melting temperature of the workpiece. Flow fields are obtained from the study. The vector plot of the flow field shows that the flow is not evenly distributed over the cutter surface, as well as the uneven distribution of the lubricant in the direction of the cutter rotation. It can be seen that the cutting fluid has not completely penetrated the tool edges. The turbulence created by the cutter rotation in the proximity of the tool throws oil drops out of the cutting zone. The nozzle position in relation to the feed direction is very important in order to obtain the optimum effect of the MQL flow.
DC Voltage Droop Control Implementation in the AC/DC Power Flow Algorithm: Combinational Approach
DEFF Research Database (Denmark)
Akhter, F.; Macpherson, D.E.; Harrison, G.P.
2015-01-01
of operational flexibility, as more than one VSC station controls the DC link voltage of the MTDC system. This model enables the study of the effects of DC droop control on the power flows of the combined AC/DC system for steady state studies after VSC station outages or transient conditions without needing...... to use its complete dynamic model. Further, the proposed approach can be extended to include multiple AC and DC grids for combined AC/DC power flow analysis. The algorithm is implemented by modifying the MATPOWER based MATACDC program and the results shows that the algorithm works efficiently....
Mozart versus new age music: relaxation states, stress, and ABC relaxation theory.
Smith, Jonathan C; Joyce, Carol A
2004-01-01
Smith's (2001) Attentional Behavioral Cognitive (ABC) relaxation theory proposes that all approaches to relaxation (including music) have the potential for evoking one or more of 15 factor-analytically derived relaxation states, or "R-States" (Sleepiness, Disengagement, Rested / Refreshed, Energized, Physical Relaxation, At Ease/Peace, Joy, Mental Quiet, Childlike Innocence, Thankfulness and Love, Mystery, Awe and Wonder, Prayerfulness, Timeless/Boundless/Infinite, and Aware). The present study investigated R-States and stress symptom-patterns associated with listening to Mozart versus New Age music. Students (N = 63) were divided into three relaxation groups based on previously determined preferences. Fourteen listened to a 28-minute tape recording of Mozart's Eine Kleine Nachtmusik and 14 listened to a 28-minute tape of Steven Halpern's New Age Serenity Suite. Others (n = 35) did not want music and instead chose a set of popular recreational magazines. Participants engaged in their relaxation activity at home for three consecutive days for 28 minutes a session. Before and after each session, each person completed the Smith Relaxation States Inventory (Smith, 2001), a comprehensive questionnaire tapping 15 R-States as well as the stress states of somatic stress, worry, and negative emotion. Results revealed no differences at Session 1. At Session 2, those who listened to Mozart reported higher levels of At Ease/Peace and lower levels of Negative Emotion. Pronounced differences emerged at Session 3. Mozart listeners uniquely reported substantially higher levels of Mental Quiet, Awe and Wonder, and Mystery. Mozart listeners reported higher levels, and New Age listeners slightly elevated levels, of At Ease/Peace and Rested/Refreshed. Both Mozart and New Age listeners reported higher levels of Thankfulness and Love. In summary, those who listened to Mozart's Eine Kleine Nachtmusik reported more psychological relaxation and less stress than either those who listened to
A discontinuous finite element approach to cracking in coupled poro-elastic fluid flow models
Wilson, C. R.; Spiegelman, M. W.; Evans, O.; Ulven, O. I.; Sun, W.
2016-12-01
Reaction-driven cracking is a coupled process whereby fluid-induced reactions drive large volume changes in the host rock which produce stresses leading to crack propagation and failure. This in turn generates new surface area and fluid-flow pathways for subsequent reaction in a potentially self-sustaining system. This mechanism has has been proposed for the pervasive serpentinization and carbonation of peridotite, as well as applications to mineral carbon sequestration and hydrocarbon extraction. The key computational issue in this problem is implementing algorithms that adequately model the formation of discrete fractures. Here we present models using a discontinuous finite element method for modeling fracture formation (Radovitsky et al., 2011). Cracks are introduced along facets of the mesh by the relaxation of penalty parameters once a failure criterion is met. It is fully described in the weak form of the equations, requiring no modification of the underlying mesh structure and allowing fluid properties to be easily adjusted along cracked facets. To develop and test the method, we start by implementing the algorithm for the simplified Biot equations for poro-elasticity using the finite element model assembler TerraFERMA. We consider hydro-fracking around a borehole (Grassl et al., 2015), where elevated fluid pressure in the poro-elastic solid causes it to fail radially in tension. We investigate the effects of varying the Biot coefficient and adjusting the fluid transport properties in the vicinity of the crack and compare our results to related dual-graph models (Ulven & Sun, submitted). We discuss issues arising from this method, including the formation of null spaces and appropriate preconditioning and solution strategies. Initial results suggest that this method provides a promising way to incorporate cracking into our reactive fluid flow models and future work aims to integrate the mechanical and chemical aspects of this process.
Stress relaxation in a ferrofluid with clustered nanoparticles
International Nuclear Information System (INIS)
Borin, Dmitry Yu; Odenbach, Stefan; Zubarev, Andrey Yu; Chirikov, Dmitry N
2014-01-01
The formation of structures in a ferrofluid by an applied magnetic field causes various changes in the rheological behaviour of the ferrofluid. A ferrofluid based on clustered iron nanoparticles was investigated. We experimentally and theoretically consider stress relaxation in the ferrofluid under the influence of a magnetic field, when the flow is suddenly interrupted. It is shown that the residual stress observed in the fluid after the relaxation is correlated with the measured and theoretically predicted magnetic field-induced yield stress. Furthermore, we have shown that the total macroscopic stress in the ferrofluid after the flow is interrupted is defined by the presence of both linear chains and dense, drop-like bulk aggregates. The proposed theoretical approach is consistent with the experimentally observed behaviour, despite a number of simplifications which have been made in the formulation of the model. Thus, the obtained results contribute a lot to the understanding of the complex, magnetic field-induced rheological properties of magnetic colloids near the yield stress point. (paper)
Relaxed Binaural LCMV Beamforming
Koutrouvelis, A.; Hendriks, R.C.; Heusdens, R.; Jensen, Jesper Rindom
2017-01-01
In this paper, we propose a new binaural beamforming technique, which can be seen as a relaxation of the linearly constrained minimum variance (LCMV) framework. The proposed method can achieve simultaneous noise reduction and exact binaural cue preservation of the target source, similar to the
Spear, Timothy T; Nishimura, Michael I; Simms, Patricia E
2017-08-01
Advancement in flow cytometry reagents and instrumentation has allowed for simultaneous analysis of large numbers of lineage/functional immune cell markers. Highly complex datasets generated by polychromatic flow cytometry require proper analytical software to answer investigators' questions. A problem among many investigators and flow cytometry Shared Resource Laboratories (SRLs), including our own, is a lack of access to a flow cytometry-knowledgeable bioinformatics team, making it difficult to learn and choose appropriate analysis tool(s). Here, we comparatively assess various multidimensional flow cytometry software packages for their ability to answer a specific biologic question and provide graphical representation output suitable for publication, as well as their ease of use and cost. We assessed polyfunctional potential of TCR-transduced T cells, serving as a model evaluation, using multidimensional flow cytometry to analyze 6 intracellular cytokines and degranulation on a per-cell basis. Analysis of 7 parameters resulted in 128 possible combinations of positivity/negativity, far too complex for basic flow cytometry software to analyze fully. Various software packages were used, analysis methods used in each described, and representative output displayed. Of the tools investigated, automated classification of cellular expression by nonlinear stochastic embedding (ACCENSE) and coupled analysis in Pestle/simplified presentation of incredibly complex evaluations (SPICE) provided the most user-friendly manipulations and readable output, evaluating effects of altered antigen-specific stimulation on T cell polyfunctionality. This detailed approach may serve as a model for other investigators/SRLs in selecting the most appropriate software to analyze complex flow cytometry datasets. Further development and awareness of available tools will help guide proper data analysis to answer difficult biologic questions arising from incredibly complex datasets. © Society
First-order system least squares and the energetic variational approach for two-phase flow
Adler, J. H.; Brannick, J.; Liu, C.; Manteuffel, T.; Zikatanov, L.
2011-07-01
This paper develops a first-order system least-squares (FOSLS) formulation for equations of two-phase flow. The main goal is to show that this discretization, along with numerical techniques such as nested iteration, algebraic multigrid, and adaptive local refinement, can be used to solve these types of complex fluid flow problems. In addition, from an energetic variational approach, it can be shown that an important quantity to preserve in a given simulation is the energy law. We discuss the energy law and inherent structure for two-phase flow using the Allen-Cahn interface model and indicate how it is related to other complex fluid models, such as magnetohydrodynamics. Finally, we show that, using the FOSLS framework, one can still satisfy the appropriate energy law globally while using well-known numerical techniques.
I. Magdych
2015-01-01
The article explores the methodological approaches to the analysis of cash flows in investment activity of the enterprise; the system of motion net cash flows, reflecting the impact of cash management efficiency on the amount and source of investment cash flows of the enterprise; analytical model of definition of effectiveness of cash management of the enterprise is proposed, based on the selected principals of modeling, comprehensive analysis of cash flows in investing activities and their o...
International Nuclear Information System (INIS)
Ishii, Mamoru; Sun, Xiaodong
2004-01-01
This paper presents new experimental and modeling approaches in characterizing interfacial structures in gas-liquid two-phase flow. For the experiments, two objective approaches are developed to identify flow regimes and to obtain local interfacial structure data. First, a global measurement technique using a non-intrusive ring-type impedance void-meter and a self-organizing neural network is presented to identify the one-dimensional'' flow regimes. In the application of this measurement technique, two methods are discussed, namely, one based on the probability density function of the impedance probe measurement (PDF input method) and the other based on the sorted impedance signals, which is essentially the cumulative probability distribution function of the impedance signals (instantaneous direct signal input method). In the latter method, the identification can be made close to instantaneously since the required signals can be acquired over a very short time period. In addition, a double-sensor conductivity probe can also be used to obtain ''local'' flow regimes by using the instantaneous direct signal input method with the bubble chord length information. Furthermore, a newly designed conductivity probe with multiple double-sensor heads is proposed to obtain ''two-dimensional'' flow regimes across the flow channel. Secondly, a state-of-the-art four-sensor conductivity probe technique has been developed to obtain detailed local interfacial structure information. The four-sensor conductivity probe accommodates the double-sensor probe capability and can be applied in a wide range of flow regimes spanning from bubbly to churn-turbulent flows. The signal processing scheme is developed such that it categorizes the acquired parameters into two groups based on bubble cord length information. Furthermore, for the modeling of the interfacial structure characterization, the interfacial area transport equation proposed earlier has been studied to provide a dynamic and
Groundwater flow system stability in shield settings a multi-disciplinary approach
International Nuclear Information System (INIS)
Jensen, M.R.; Goodwin, B.W.
2004-01-01
Within the Deep Geologic Repository Technology Program (DGRTP) several Geoscience activities are focused on advancing the understanding of groundwater flow system evolution and geochemical stability in a Shield setting as affected by long-term climate change. A key aspect is developing confidence in predictions of groundwater flow patterns and residence times as they relate to the safety of a Deep Geologic Repository for used nuclear fuel waste. A specific focus in this regard has been placed on constraining redox stability and groundwater flow system dynamics during the Pleistocene. Attempts are being made to achieve this through a coordinated multi-disciplinary approach intent on; i) demonstrating coincidence between independent geo-scientific data; ii) improving the traceability of geo-scientific data and its interpretation within a conceptual descriptive model(s); iii) improving upon methods to assess and demonstrate robustness in flow domain prediction(s) given inherent flow domain uncertainties (i.e. spatial chemical/physical property distributions; boundary conditions) in time and space; and iv) improving awareness amongst geo-scientists as to the utility various geo-scientific data in supporting a repository safety case. Coordinated by the DGRTP, elements of this program include the development of a climate driven Laurentide ice-sheet model to constrain the understanding of time rate of change in boundary conditions most affecting the groundwater flow domain and its evolution. Further work has involved supporting WRA Paleo-hydrogeologic studies in which constrained thermodynamic analyses coupled with field studies to characterize the paragenesis of fracture infill mineralogy are providing evidence to premise understandings of possible depth of penetration by oxygenated glacial recharge. In parallel. numerical simulations have been undertaken to illustrate aspect of groundwater flow system stability and evolution in a Shield setting. Such simulations
Culbert, Timothy
2017-04-04
It has been well-established that a variety of mind-body (MB) techniques, including yoga, mental imagery, hypnosis, biofeedback, and meditation, are effective at addressing symptoms such as pain, anxiety, nausea, and insomnia, as well as helping with a wide variety of medical, emotional, and behavioral issues in pediatric populations. In addition, MB skills can also be health promoting in the long-term, and with regular practice, could potentially contribute to longer attention spans, social skills, emotional regulation, and enhanced immune system functioning. Importantly, the benefits accrued from MB skills are largely dose dependent, meaning that individuals who practice with some consistency tend to benefit the most, both in the short- and long-term. However, clinical experience suggests that for busy patients, the regular practice of MB skills can be challenging and treatment adherence commonly becomes an issue. This commentary reviews the concept of technology assisted relaxation as an engaging and effective option to enhance treatment adherence (i.e., daily practice) for pediatric patients, for whom MB skills have been recommended to address physical and mental health challenges.
Directory of Open Access Journals (Sweden)
Satish S. Jalisatgi
2013-07-01
Full Text Available An icosahedral closo-B122− scaffold based nano-sized assembly capable of carrying a high payload of Gd3+-chelates in a sterically crowded configuration is developed by employing the azide-alkyne click reaction. The twelve copies of DO3A-t-Bu-ester ligands were covalently attached to an icosahedral closo-B122− core via suitable linkers through click reaction. This nanomolecular structure supporting a high payload of Gd3+-chelate is a new member of the closomer MRI contrast agents that we are currently developing in our laboratory. The per Gd ion relaxivity (r1 of the newly synthesized MRI contrast agent was obtained in PBS, 2% tween/PBS and bovine calf serum using a 7 Tesla micro MRI instrument and was found to be slightly higher (r1 = 4.7 in PBS at 25 °C compared to the clinically used MRI contrast agents Omniscan (r1 = 4.2 in PBS at 25 °C and ProHance (r1 = 3.1 in PBS at 25 °C.
Directory of Open Access Journals (Sweden)
Timothy Culbert
2017-04-01
Full Text Available It has been well-established that a variety of mind-body (MB techniques, including yoga, mental imagery, hypnosis, biofeedback, and meditation, are effective at addressing symptoms such as pain, anxiety, nausea, and insomnia, as well as helping with a wide variety of medical, emotional, and behavioral issues in pediatric populations. In addition, MB skills can also be health promoting in the long-term, and with regular practice, could potentially contribute to longer attention spans, social skills, emotional regulation, and enhanced immune system functioning. Importantly, the benefits accrued from MB skills are largely dose dependent, meaning that individuals who practice with some consistency tend to benefit the most, both in the short- and long-term. However, clinical experience suggests that for busy patients, the regular practice of MB skills can be challenging and treatment adherence commonly becomes an issue. This commentary reviews the concept of technology assisted relaxation as an engaging and effective option to enhance treatment adherence (i.e., daily practice for pediatric patients, for whom MB skills have been recommended to address physical and mental health challenges.
A simplified approach for the computation of steady two-phase flow in inverted siphons.
Diogo, A Freire; Oliveira, Maria C
2016-01-15
Hydraulic, sanitary, and sulfide control conditions of inverted siphons, particularly in large wastewater systems, can be substantially improved by continuous air injection in the base of the inclined rising branch. This paper presents a simplified approach that was developed for the two-phase flow of the rising branch using the energy equation for a steady pipe flow, based on the average fluid fraction, observed slippage between phases, and isothermal assumption. As in a conventional siphon design, open channel steady uniform flow is assumed in inlet and outlet chambers, corresponding to the wastewater hydraulic characteristics in the upstream and downstream sewers, and the descending branch operates in steady uniform single-phase pipe flow. The proposed approach is tested and compared with data obtained in an experimental siphon setup with two plastic barrels of different diameters operating separately as in a single-barrel siphon. Although the formulations developed are very simple, the results show a good adjustment for the set of the parameters used and conditions tested and are promising mainly for sanitary siphons with relatively moderate heights of the ascending branch. Copyright © 2015 Elsevier Ltd. All rights reserved.
Investigation of the thermal mixing in a T-junction flow with different SRS approaches
Energy Technology Data Exchange (ETDEWEB)
Gritskevich, M.S., E-mail: gritskevich@ymail.com [St. Petersburg State Polytechnical University, 195251 St. Petersburg (Russian Federation); Garbaruk, A.V. [St. Petersburg State Polytechnical University, 195251 St. Petersburg (Russian Federation); Frank, Th.; Menter, F.R. [Software Development Department, ANSYS, 83714 Otterfing (Germany)
2014-11-15
Highlights: • Global (SAS, DDES) and zonal (ELES-WMLES) models are compared for the T-junction flow. • All the models accurately predict mean, RMS, and spectral quantities. • ELES-WMLES approach yields very good results independent of the advection scheme. • SAS and the DDES models are slightly less accurate. • SAS depends on the advection scheme. - Abstract: An investigation of different turbulence Scale-Resolving Simulation (SRS) modeling approaches for the flow in a T-junction has been conducted using the Scale-Adaptive Simulation (SAS), the Delayed Detached Eddy Simulation (DDES) and the Embedded Large Eddy Simulation (ELES) methods. The results show that all models are able to accurately predict mean and RMS velocity profiles and velocity spectra, when are used in combination with a low dissipation advection scheme. However, when a slightly more dissipative scheme is used, the SAS model yields less accurate results, indicating that this flow does not produce a strong enough flow instability to allow the safe application of this model. The DDES and the ELES models show less sensitivity to the numerical setting compared to the SAS model. The main goal of the study is the accurate prediction of heat transfer on the walls in the mixing zone. In that respect, the ELES method produces the most consistent agreement with the experimental data.
A scalable approach to modeling groundwater flow on massively parallel computers
International Nuclear Information System (INIS)
Ashby, S.F.; Falgout, R.D.; Tompson, A.F.B.
1995-12-01
We describe a fully scalable approach to the simulation of groundwater flow on a hierarchy of computing platforms, ranging from workstations to massively parallel computers. Specifically, we advocate the use of scalable conceptual models in which the subsurface model is defined independently of the computational grid on which the simulation takes place. We also describe a scalable multigrid algorithm for computing the groundwater flow velocities. We axe thus able to leverage both the engineer's time spent developing the conceptual model and the computing resources used in the numerical simulation. We have successfully employed this approach at the LLNL site, where we have run simulations ranging in size from just a few thousand spatial zones (on workstations) to more than eight million spatial zones (on the CRAY T3D)-all using the same conceptual model
Application of a stereoscopic digital subtraction angiography approach to blood flow analysis
International Nuclear Information System (INIS)
Fencil, L.E.; Doi, K.; Hoffmann, K.R.
1986-01-01
The authors are developing a stereoscopic digital subtraction angiographic (DSA) approach for accurate measurement of the size, magnification factor, orientation, and blood flow of a selected vessel segment. We employ a Siemens Digitron 2 and a Stereolix x-ray tube with a 25-mm tube shift. Absolute vessel sizes in each stereoscopic image are determined using the magnification factor and an iterative deconvolution technique employing the LSF of the DSA system. From data on vessel diameter and three-dimensional orientation, the effective attenuation coefficient of the diluted contrast medium can be determined, thus allowing accurate blood flow analysis in high-frame-rate DSA images. The accuracy and precision of the approach will be studied using both static and dynamic phantoms
A new lumped-parameter approach to simulating flow processes in unsaturated dual-porosity media
Energy Technology Data Exchange (ETDEWEB)
Zimmerman, R.W.; Hadgu, T.; Bodvarsson, G.S. [Lawrence Berkeley Laboratory, CA (United States)
1995-03-01
We have developed a new lumped-parameter dual-porosity approach to simulating unsaturated flow processes in fractured rocks. Fluid flow between the fracture network and the matrix blocks is described by a nonlinear equation that relates the imbibition rate to the local difference in liquid-phase pressure between the fractures and the matrix blocks. This equation is a generalization of the Warren-Root equation, but unlike the Warren-Root equation, is accurate in both the early and late time regimes. The fracture/matrix interflow equation has been incorporated into a computational module, compatible with the TOUGH simulator, to serve as a source/sink term for fracture elements. The new approach achieves accuracy comparable to simulations in which the matrix blocks are discretized, but typically requires an order of magnitude less computational time.
Approaching a universal scaling relationship between fracture stiffness and fluid flow
Pyrak-Nolte, Laura J.; Nolte, David D.
2016-02-01
A goal of subsurface geophysical monitoring is the detection and characterization of fracture alterations that affect the hydraulic integrity of a site. Achievement of this goal requires a link between the mechanical and hydraulic properties of a fracture. Here we present a scaling relationship between fluid flow and fracture-specific stiffness that approaches universality. Fracture-specific stiffness is a mechanical property dependent on fracture geometry that can be monitored remotely using seismic techniques. A Monte Carlo numerical approach demonstrates that a scaling relationship exists between flow and stiffness for fractures with strongly correlated aperture distributions, and continues to hold for fractures deformed by applied stress and by chemical erosion as well. This new scaling relationship provides a foundation for simulating changes in fracture behaviour as a function of stress or depth in the Earth and will aid risk assessment of the hydraulic integrity of subsurface sites.
Computation of wall bounded flows with heat transfer in the framework of SRS approaches
Gritskevich, M. S.; Garbaruk, A. V.; Menter, F. R.
2014-12-01
A detailed assessment of Scale Adaptive Simulation (SAS) and Improved Delayed Detached Eddy Simulation (IDDES) is performed for prediction of heat transfer for several wall bounded flow. For that purpose a zero pressure gradient boundary layer, a backward facing step, and a thermal mixing in a T-Junction test cases are considered. The results, obtained with the use of ANSYS-FLUENT, show that both approaches are capable to predict both mean and RMS velocity and temperature with sufficient accuracy.
A computational approach to modeling cellular-scale blood flow in complex geometry
Balogh, Peter; Bagchi, Prosenjit
2017-04-01
We present a computational methodology for modeling cellular-scale blood flow in arbitrary and highly complex geometry. Our approach is based on immersed-boundary methods, which allow modeling flows in arbitrary geometry while resolving the large deformation and dynamics of every blood cell with high fidelity. The present methodology seamlessly integrates different modeling components dealing with stationary rigid boundaries of complex shape, moving rigid bodies, and highly deformable interfaces governed by nonlinear elasticity. Thus it enables us to simulate 'whole' blood suspensions flowing through physiologically realistic microvascular networks that are characterized by multiple bifurcating and merging vessels, as well as geometrically complex lab-on-chip devices. The focus of the present work is on the development of a versatile numerical technique that is able to consider deformable cells and rigid bodies flowing in three-dimensional arbitrarily complex geometries over a diverse range of scenarios. After describing the methodology, a series of validation studies are presented against analytical theory, experimental data, and previous numerical results. Then, the capability of the methodology is demonstrated by simulating flows of deformable blood cells and heterogeneous cell suspensions in both physiologically realistic microvascular networks and geometrically intricate microfluidic devices. It is shown that the methodology can predict several complex microhemodynamic phenomena observed in vascular networks and microfluidic devices. The present methodology is robust and versatile, and has the potential to scale up to very large microvascular networks at organ levels.
Jain, Ashu; Srinivasulu, Sanaga
2006-02-01
This paper presents the findings of a study aimed at decomposing a flow hydrograph into different segments based on physical concepts in a catchment, and modelling different segments using different technique viz. conceptual and artificial neural networks (ANNs). An integrated modelling framework is proposed capable of modelling infiltration, base flow, evapotranspiration, soil moisture accounting, and certain segments of the decomposed flow hydrograph using conceptual techniques and the complex, non-linear, and dynamic rainfall-runoff process using ANN technique. Specifically, five different multi-layer perceptron (MLP) and two self-organizing map (SOM) models have been developed. The rainfall and streamflow data derived from the Kentucky River catchment were employed to test the proposed methodology and develop all the models. The performance of all the models was evaluated using seven different standard statistical measures. The results obtained in this study indicate that (a) the rainfall-runoff relationship in a large catchment consists of at least three or four different mappings corresponding to different dynamics of the underlying physical processes, (b) an integrated approach that models the different segments of the decomposed flow hydrograph using different techniques is better than a single ANN in modelling the complex, dynamic, non-linear, and fragmented rainfall runoff process, (c) a simple model based on the concept of flow recession is better than an ANN to model the falling limb of a flow hydrograph, and (d) decomposing a flow hydrograph into the different segments corresponding to the different dynamics based on the physical concepts is better than using the soft decomposition employed using SOM.
Directory of Open Access Journals (Sweden)
Kaisheng Zhang
2016-12-01
Full Text Available Recently, population density has grown quickly with the increasing acceleration of urbanization. At the same time, overcrowded situations are more likely to occur in populous urban areas, increasing the risk of accidents. This paper proposes a synthetic approach to recognize and identify the large pedestrian flow. In particular, a hybrid pedestrian flow detection model was constructed by analyzing real data from major mobile phone operators in China, including information from smartphones and base stations (BS. With the hybrid model, the Log Distance Path Loss (LDPL model was used to estimate the pedestrian density from raw network data, and retrieve information with the Gaussian Progress (GP through supervised learning. Temporal-spatial prediction of the pedestrian data was carried out with Machine Learning (ML approaches. Finally, a case study of a real Central Business District (CBD scenario in Shanghai, China using records of millions of cell phone users was conducted. The results showed that the new approach significantly increases the utility and capacity of the mobile network. A more reasonable overcrowding detection and alert system can be developed to improve safety in subway lines and other hotspot landmark areas, such as the Bundle, People’s Square or Disneyland, where a large passenger flow generally exists.
Mode decomposition methods for flows in high-contrast porous media. Global-local approach
Ghommem, Mehdi; Presho, Michael; Calo, Victor M.; Efendiev, Yalchin R.
2013-01-01
In this paper, we combine concepts of the generalized multiscale finite element method (GMsFEM) and mode decomposition methods to construct a robust global-local approach for model reduction of flows in high-contrast porous media. This is achieved by implementing Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) techniques on a coarse grid computed using GMsFEM. The resulting reduced-order approach enables a significant reduction in the flow problem size while accurately capturing the behavior of fully-resolved solutions. We consider a variety of high-contrast coefficients and present the corresponding numerical results to illustrate the effectiveness of the proposed technique. This paper is a continuation of our work presented in Ghommem et al. (2013) [1] where we examine the applicability of POD and DMD to derive simplified and reliable representations of flows in high-contrast porous media on fully resolved models. In the current paper, we discuss how these global model reduction approaches can be combined with local techniques to speed-up the simulations. The speed-up is due to inexpensive, while sufficiently accurate, computations of global snapshots. © 2013 Elsevier Inc.
Mode decomposition methods for flows in high-contrast porous media. Global-local approach
Ghommem, Mehdi
2013-11-01
In this paper, we combine concepts of the generalized multiscale finite element method (GMsFEM) and mode decomposition methods to construct a robust global-local approach for model reduction of flows in high-contrast porous media. This is achieved by implementing Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) techniques on a coarse grid computed using GMsFEM. The resulting reduced-order approach enables a significant reduction in the flow problem size while accurately capturing the behavior of fully-resolved solutions. We consider a variety of high-contrast coefficients and present the corresponding numerical results to illustrate the effectiveness of the proposed technique. This paper is a continuation of our work presented in Ghommem et al. (2013) [1] where we examine the applicability of POD and DMD to derive simplified and reliable representations of flows in high-contrast porous media on fully resolved models. In the current paper, we discuss how these global model reduction approaches can be combined with local techniques to speed-up the simulations. The speed-up is due to inexpensive, while sufficiently accurate, computations of global snapshots. © 2013 Elsevier Inc.
... For Consumers Consumer Information by Audience For Women Hair Dye and Hair Relaxers Share Tweet Linkedin Pin it More sharing ... products. If you have a bad reaction to hair dyes and relaxers, you should: Stop using the ...
Directory of Open Access Journals (Sweden)
Zhi-Feng Yao
2016-01-01
Full Text Available The turbulent flow in a centrifugal pump impeller is bounded by complex surfaces, including blades, a hub and a shroud. The primary challenge of the flow simulation arises from the generation of a boundary layer between the surface of the impeller and the moving fluid. The principal objective is to evaluate the near-wall solution approaches that are typically used to deal with the flow in the boundary layer for the large-eddy simulation (LES of a centrifugal pump impeller. Three near-wall solution approaches –the wall-function approach, the wall-resolved approach and the hybrid Reynolds averaged Navier–Stoke (RANS and LES approach – are tested. The simulation results are compared with experimental results conducted through particle imaging velocimetry (PIV and laser Doppler velocimetry (LDV. It is found that the wall-function approach is more sparing of computational resources, while the other two approaches have the important advantage of providing highly accurate boundary layer flow prediction. The hybrid RANS/LES approach is suitable for predicting steady-flow features, such as time-averaged velocities and hydraulic losses. Despite the fact that the wall-resolved approach is expensive in terms of computing resources, it exhibits a strong ability to capture a small-scale vortex and predict instantaneous velocity in the near-wall region in the impeller. The wall-resolved approach is thus recommended for the transient simulation of flows in centrifugal pump impellers.
Active nematic gels as active relaxing solids
Turzi, Stefano S.
2017-11-01
I propose a continuum theory for active nematic gels, defined as fluids or suspensions of orientable rodlike objects endowed with active dynamics, that is based on symmetry arguments and compatibility with thermodynamics. The starting point is our recent theory that models (passive) nematic liquid crystals as relaxing nematic elastomers. The interplay between viscoelastic response and active dynamics of the microscopic constituents is naturally taken into account. By contrast with standard theories, activity is not introduced as an additional term of the stress tensor, but it is added as an external remodeling force that competes with the passive relaxation dynamics and drags the system out of equilibrium. In a simple one-dimensional channel geometry, we show that the interaction between nonuniform nematic order and activity results in either a spontaneous flow of particles or a self-organization into subchannels flowing in opposite directions.
Magnetic relaxation in anisotropic magnets
DEFF Research Database (Denmark)
Lindgård, Per-Anker
1971-01-01
The line shape and the kinematic and thermodynamic slowing down of the critical and paramagnetic relaxation in axially anisotropic materials are discussed. Kinematic slowing down occurs only in the longitudinal relaxation function. The thermodynamic slowing down occurs in either the transverse...... or longitudinal relaxation function depending on the sign of the axial anisotropy....
Momentum constraint relaxation
International Nuclear Information System (INIS)
Marronetti, Pedro
2006-01-01
Full relativistic simulations in three dimensions invariably develop runaway modes that grow exponentially and are accompanied by violations of the Hamiltonian and momentum constraints. Recently, we introduced a numerical method (Hamiltonian relaxation) that greatly reduces the Hamiltonian constraint violation and helps improve the quality of the numerical model. We present here a method that controls the violation of the momentum constraint. The method is based on the addition of a longitudinal component to the traceless extrinsic curvature A ij -tilde, generated by a vector potential w i , as outlined by York. The components of w i are relaxed to solve approximately the momentum constraint equations, slowly pushing the evolution towards the space of solutions of the constraint equations. We test this method with simulations of binary neutron stars in circular orbits and show that it effectively controls the growth of the aforementioned violations. We also show that a full numerical enforcement of the constraints, as opposed to the gentle correction of the momentum relaxation scheme, results in the development of instabilities that stop the runs shortly
Structural relaxation dynamics and annealing effects of sodium silicate glass.
Naji, Mohamed; Piazza, Francesco; Guimbretière, Guillaume; Canizarès, Aurélien; Vaills, Yann
2013-05-09
Here we report high-precision measurements of structural relaxation dynamics in the glass transition range at the intermediate and short length scale for a strong sodium silicate glass during long annealing times. We evidence for the first time the heterogeneous dynamics at the intermediate range order by probing the acoustic longitudinal frequency in the GHz region by Brillouin light scattering spectroscopy. Or, from in-situ Raman measurements, we show that relaxation is indeed homogeneous at the interatomic length scale. Our results show that the dynamics at the intermediate range order contains two distinct relaxation time scales, a fast and a slow component, differing by about a 10-fold factor below Tg and approaching to one another past the glass transition. The slow relaxation time agrees with the shear relaxation time, proving that Si-O bond breaking constitutes the primary control of structural relaxation at the intermediate range order.
Optimal relaxed causal sampler using sampled-date system theory
Shekhawat, Hanumant; Meinsma, Gjerrit
This paper studies the design of an optimal relaxed causal sampler using sampled data system theory. A lifted frequency domain approach is used to obtain the existence conditions and the optimal sampler. A state space formulation of the results is also provided. The resulting optimal relaxed causal
Variations in the Flow Approach to CFCLP-TC for Multiobjective Supply Chain Design
Directory of Open Access Journals (Sweden)
Minor P. Hertwin
2014-01-01
Full Text Available We review the problem for the design of supply chains called Capacitated Fixed Cost Facility Location Problem with Transportation Choices (CFCLP-TC. The problem is based on a production network of two echelons with multiple plants, a set of potential distribution centers, and customers. The problem is formulated as an optimization model with two objective functions based on time and cost. This paper proposes three changes to the original model to compare the sets of efficient solutions and the computational time required to obtain them. The main contribution of this paper is to extend the existing literature by incorporating approaches for the supply of product to customers through multiple sources, the direct flow between plants and customers, without this necessarily implying removing the distribution centers, and the product flow between distribution centers. From these approaches, we generate mathematical programming models and propose to solve through the epsilon-constraint approach for generating Pareto fronts and thus compare each of these approaches with the original model. The models are implemented in GAMS and solved with CPLEX.
Optimized Structure of the Traffic Flow Forecasting Model With a Deep Learning Approach.
Yang, Hao-Fan; Dillon, Tharam S; Chen, Yi-Ping Phoebe
2017-10-01
Forecasting accuracy is an important issue for successful intelligent traffic management, especially in the domain of traffic efficiency and congestion reduction. The dawning of the big data era brings opportunities to greatly improve prediction accuracy. In this paper, we propose a novel model, stacked autoencoder Levenberg-Marquardt model, which is a type of deep architecture of neural network approach aiming to improve forecasting accuracy. The proposed model is designed using the Taguchi method to develop an optimized structure and to learn traffic flow features through layer-by-layer feature granulation with a greedy layerwise unsupervised learning algorithm. It is applied to real-world data collected from the M6 freeway in the U.K. and is compared with three existing traffic predictors. To the best of our knowledge, this is the first time that an optimized structure of the traffic flow forecasting model with a deep learning approach is presented. The evaluation results demonstrate that the proposed model with an optimized structure has superior performance in traffic flow forecasting.
Institute of Scientific and Technical Information of China (English)
高文; 陈熙霖
1997-01-01
The blur in target images caused by camera vibration due to robot motion or hand shaking and by object(s) moving in the background scene is different to deal with in the computer vision system.In this paper,the authors study the relation model between motion and blur in the case of object motion existing in video image sequence,and work on a practical computation algorithm for both motion analysis and blut image restoration.Combining the general optical flow and stochastic process,the paper presents and approach by which the motion velocity can be calculated from blurred images.On the other hand,the blurred image can also be restored using the obtained motion information.For solving a problem with small motion limitation on the general optical flow computation,a multiresolution optical flow algoritm based on MAP estimation is proposed. For restoring the blurred image ,an iteration algorithm and the obtained motion velocity are used.The experiment shows that the proposed approach for both motion velocity computation and blurred image restoration works well.
Relaxation dynamics of multilayer triangular Husimi cacti
Galiceanu, Mircea; Jurjiu, Aurel
2016-09-01
We focus on the relaxation dynamics of multilayer polymer structures having, as underlying topology, the Husimi cactus. The relaxation dynamics of the multilayer structures is investigated in the framework of generalized Gaussian structures model using both Rouse and Zimm approaches. In the Rouse type-approach, we determine analytically the complete eigenvalues spectrum and based on it we calculate the mechanical relaxation moduli (storage and loss modulus) and the average monomer displacement. First, we monitor these physical quantities for structures with a fixed generation number and we increase the number of layers, such that the linear topology will smoothly come into play. Second, we keep constant the size of the structures, varying simultaneously two parameters: the generation number of the main layer, G, and the number of layers, c. This fact allows us to study in detail the crossover from a pure Husimi cactus behavior to a predominately linear chain behavior. The most interesting situation is found when the two limiting topologies cancel each other. For this case, we encounter in the intermediate frequency/time domain regions of constant slope for different values of the parameter set (G, c) and we show that the number of layers follows an exponential-law of G. In the Zimm-type approach, which includes the hydrodynamic interactions, the quantities that describe the mechanical relaxation dynamics do not show scaling behavior as in the Rouse model, except the limiting case, namely, a very high number of layers and low generation number.
Babu, C. Rajesh; Kumar, P.; Rajamohan, G.
2017-07-01
Computation of fluid flow and heat transfer in an economizer is simulated by a porous medium approach, with plain tubes having a horizontal in-line arrangement and cross flow arrangement in a coal-fired thermal power plant. The economizer is a thermal mechanical device that captures waste heat from the thermal exhaust flue gasses through heat transfer surfaces to preheat boiler feed water. In order to evaluate the fluid flow and heat transfer on tubes, a numerical analysis on heat transfer performance is carried out on an 110 t/h MCR (Maximum continuous rating) boiler unit. In this study, thermal performance is investigated using the computational fluid dynamics (CFD) simulation using ANSYS FLUENT. The fouling factor ε and the overall heat transfer coefficient ψ are employed to evaluate the fluid flow and heat transfer. The model demands significant computational details for geometric modeling, grid generation, and numerical calculations to evaluate the thermal performance of an economizer. The simulation results show that the overall heat transfer coefficient 37.76 W/(m2K) and economizer coil side pressure drop of 0.2 (kg/cm2) are found to be conformity within the tolerable limits when compared with existing industrial economizer data.
Del Ventisette, C.; Garfagnoli, F.; Ciampalini, A.; Battistini, A.; Gigli, G.; Moretti, S.; Casagli, N.
2012-09-01
On 1 October 2009, a prolonged and intense rainstorm triggered hundreds of landslides (predominantly debris flows) in an area of about 50 km2 in the north-eastern sector of Sicily (Italy). Debris flows swept the highest parts of many villages and passed over the SS114 state highway and the Messina-Catania railway, causing more than 30 fatalities. This region has a high relief, due to recent uplift. The peculiar geological and geomorphological framework represents one of the most common predisposing causes of rainstorm-triggered debris flows. This paper deals with the geological and hydro-geomorphological studies performed as a part of the post-disaster activities operated in collaboration with Civil Protection Authority, with the aim at examining landslides effects and mechanisms. The data were elaborated into a GIS platform, to evaluate the influence of urbanisation on the drainage pattern, and were correlated with the lithological and structural framework of the area. Our study points at the evaluation of the volume involved, the detection of triggering mechanisms and the precise reconstruction of the influence of urbanisation as fundamental tools for understanding the dynamics of catastrophic landslides. This kind of analysis, including all the desirable approaches for the correct management of debris flow should be the starting point for robust urban planning.
Magnetic relaxation in analytical, coordination and bioinorganic chemistry
International Nuclear Information System (INIS)
Mikhajlov, O.
1982-01-01
Nuclear magnetic relaxation is a special type of nuclear magnetic resonance in which the rate is measured of energy transfer between the excited nuclei and their molecular medium (spin-lattice relaxation) or the whole nuclear spin system (spin-spin relaxation). Nuclear magnetic relaxation relates to nuclei with a spin of 1/2, primarily H 1 1 , and is mainly measured in water solutions. It is suitable for (1) analytical chemistry because the relaxation time rapidly reduces in the presence of paramagnetic ions, (2) the study of complex compounds, (3) the study of biochemical reactions in the presence of different metal ions. It is also suitable for testing the composition of a flowing liquid. Its disadvantage is that it requires complex and expensive equipment. (Ha)
Stress relaxation and hillock growth in thin films
International Nuclear Information System (INIS)
Jackson, M.S.; Li, C.Y.
1978-01-01
The relaxation of thermal stress in a thin film adhering to a substrate of differing expansion coefficient is discussed. Good agreement is found between literature data on relaxation during isothermal anneals of Pb films at up to 350 0 K and model calculations based on a state variable description of plastic flow. The stress system during relaxation is explored, and the absence of diffusional creep is explained. The plasticity-dominated relaxation process suggested by this analysis is shown to be in good qualitative agreement with data on rapid relaxation over the course of a cycle between room and cryogenic temperatures. The implications of this for long-range material transport in the film are discussed. It is shown that hillock volume should increase over the course of a temperature cycle. Finally, a mechanism for hillock nucleation based on grain boundary sliding is suggested
A hybrid least squares support vector machines and GMDH approach for river flow forecasting
Samsudin, R.; Saad, P.; Shabri, A.
2010-06-01
This paper proposes a novel hybrid forecasting model, which combines the group method of data handling (GMDH) and the least squares support vector machine (LSSVM), known as GLSSVM. The GMDH is used to determine the useful input variables for LSSVM model and the LSSVM model which works as time series forecasting. In this study the application of GLSSVM for monthly river flow forecasting of Selangor and Bernam River are investigated. The results of the proposed GLSSVM approach are compared with the conventional artificial neural network (ANN) models, Autoregressive Integrated Moving Average (ARIMA) model, GMDH and LSSVM models using the long term observations of monthly river flow discharge. The standard statistical, the root mean square error (RMSE) and coefficient of correlation (R) are employed to evaluate the performance of various models developed. Experiment result indicates that the hybrid model was powerful tools to model discharge time series and can be applied successfully in complex hydrological modeling.
International Nuclear Information System (INIS)
Ababou, R.
1991-08-01
This report develops a broad review and assessment of quantitative modeling approaches and data requirements for large-scale subsurface flow in radioactive waste geologic repository. The data review includes discussions of controlled field experiments, existing contamination sites, and site-specific hydrogeologic conditions at Yucca Mountain. Local-scale constitutive models for the unsaturated hydrodynamic properties of geologic media are analyzed, with particular emphasis on the effect of structural characteristics of the medium. The report further reviews and analyzes large-scale hydrogeologic spatial variability from aquifer data, unsaturated soil data, and fracture network data gathered from the literature. Finally, various modeling strategies toward large-scale flow simulations are assessed, including direct high-resolution simulation, and coarse-scale simulation based on auxiliary hydrodynamic models such as single equivalent continuum and dual-porosity continuum. The roles of anisotropy, fracturing, and broad-band spatial variability are emphasized. 252 refs
DEFF Research Database (Denmark)
Simurda, Matej; Lassen, Benny; Duggen, Lars
2017-01-01
A numerical model for a clamp-on transit-time ultrasonic flowmeter (TTUF) under multi-phase flow conditions is presented. The method solves equations of linear elasticity for isotropic heterogeneous materials with background flow where acoustic media are modeled by setting shear modulus to zero....... Spatial derivatives are calculated by a Fourier collocation method allowing the use of the fast Fourier transform (FFT) and time derivatives are approximated by a finite difference (FD) scheme. This approach is sometimes referred to as a pseudospectral time-domain method. Perfectly matched layers (PML......) are used to avoid wave-wrapping and staggered grids are implemented to improve stability and efficiency. The method is verified against exact analytical solutions and the effect of the time-staggering and associated lowest number of points per minimum wavelengths value is discussed. The method...
Relaxation oscillations and transport barrier dynamics in tokamak edge plasmas
International Nuclear Information System (INIS)
Benkadda, Sadruddin; Beyer, Peter; Fuhr-Chaudier, Guillaume; Garbet, Xavier; Ghendrih, Philippe; Sarazin, Yanick
2004-01-01
Oscillations of turbulent transport of particles and energy in magnetically confined plasmas can be easily observed in simulations of a variety of turbulence models. These oscillations typically involve a mechanism of energy exchange between fluctuations and a poloidal shear flow. This kind of ''predator-prey'' mechanism is found to be not relevant for transport barrier relaxations. In RBM simulations of resistive ballooning turbulence with transport barrier, relaxation oscillations of the latter are observed even in the case of frozen poloidal shear flow. These relaxations are due to a transitory growth of a mode localized at the barrier center. A one-dimensional model for the evolution of such a mode in the presence of a shear flow describes a transitory growth of an initial perturbation. Oscillations in the case of a finite steady-state shear flow are possible due to the coupling of the mode to the dynamics of the pressure profile. (author)
Jones, A. A.; Holt, R. M.
2017-12-01
Image capturing in flow experiments has been used for fluid mechanics research since the early 1970s. Interactions of fluid flow between the vadose zone and permanent water table are of great interest because this zone is responsible for all recharge waters, pollutant transport and irrigation efficiency for agriculture. Griffith, et al. (2011) developed an approach where constructed reproducible "geologically realistic" sand configurations are deposited in sandfilled experimental chambers for light-transmitted flow visualization experiments. This method creates reproducible, reverse graded, layered (stratified) thin-slab sand chambers for point source experiments visualizing multiphase flow through porous media. Reverse-graded stratification of sand chambers mimic many naturally occurring sedimentary deposits. Sandfilled chambers use light as nonintrusive tools for measuring water saturation in two-dimensions (2-D). Homogeneous and heterogeneous sand configurations can be produced to visualize the complex physics of the unsaturated zone. The experimental procedure developed by Griffith, et al. (2011) was designed using now outdated and obsolete equipment. We have modernized this approach with new Parker Deadel linear actuator and programed projects/code for multiple configurations. We have also updated the Roper CCD software and image processing software with the latest in industry standards. Modernization of transmitted-light source, robotic equipment, redesigned experimental chambers, and newly developed analytical procedures have greatly reduced time and cost per experiment. We have verified the ability of the new equipment to generate reproducible heterogeneous sand-filled chambers and demonstrated the functionality of the new equipment and procedures by reproducing several gravity-driven fingering experiments conducted by Griffith (2008).
Near-wall effects in rarefied gas micro-flows: some modern hydrodynamic approaches
International Nuclear Information System (INIS)
O'Hare, Lynne; Lockerby, Duncan A.; Reese, Jason M.; Emerson, David R.
2007-01-01
Methods for simulating the critical near-wall region in hydrodynamic models of gas micro-flows are discussed. Two important non-equilibrium flow features - velocity slip at solid walls, and the Knudsen layer (which extends one or two molecular mean free paths into the gas from a surface) - are investigated using different modelling approaches. In addition to a discussion of Maxwell's slip boundary condition, a newly implemented 'wall-function' model that has been developed to improve hydrodynamic simulations of the Knudsen layer is described. Phenomenological methods are compared to physical modelling and it is shown that, while both simulation types have merit, and both can quantitatively improve results in most cases, there are drawbacks associated with each approach. Phenomenological techniques, for example, may not be sufficiently general, whilst issues with applicability and stability are known to exist in some physical models. It is concluded that, at present, neither approach is unambiguously preferable to the other, and that both physical and phenomenological modelling should be the subject of future work
The complex approach to the flow accelerated cracking in Czech nuclear power plants
Energy Technology Data Exchange (ETDEWEB)
Ruscak, M; Splichal, K; Kaplan, J [Nuclear Research Institute, Rez (Czech Republic)
1994-12-31
The paper shows the approach of NRI to the problems of flow accelerated cracking of the secondary piping in VVER nuclear power plants. The utilization of the CHECMATE family codes is described in the framework of other activities to support the prediction and evaluation of damage. The code allows the effects of parameters such as temperature, geometry, mass transport conditions, void fraction and material composition to be assessed. The influence of exact measurement of chromium content is discussed. 2 refs., 6 figs., 1 tab.
The complex approach to the flow accelerated cracking in Czech nuclear power plants
International Nuclear Information System (INIS)
Ruscak, M.; Splichal, K.; Kaplan, J.
1994-01-01
The paper shows the approach of NRI to the problems of flow accelerated cracking of the secondary piping in VVER nuclear power plants. The utilization of the CHECMATE family codes is described in the framework of other activities to support the prediction and evaluation of damage. The code allows the effects of parameters such as temperature, geometry, mass transport conditions, void fraction and material composition to be assessed. The influence of exact measurement of chromium content is discussed. 2 refs., 6 figs., 1 tab
Tangarife, Walter; Tobioka, Kohsaku; Ubaldi, Lorenzo; Volansky, Tomer
2018-02-01
The cosmological relaxation of the electroweak scale has been proposed as a mechanism to address the hierarchy problem of the Standard Model. A field, the relaxion, rolls down its potential and, in doing so, scans the squared mass parameter of the Higgs, relaxing it to a parametrically small value. In this work, we promote the relaxion to an inflaton. We couple it to Abelian gauge bosons, thereby introducing the necessary dissipation mechanism which slows down the field in the last stages. We describe a novel reheating mechanism, which relies on the gauge-boson production leading to strong electro-magnetic fields, and proceeds via the vacuum production of electron-positron pairs through the Schwinger effect. We refer to this mechanism as Schwinger reheating. We discuss the cosmological dynamics of the model and the phenomenological constraints from CMB and other experiments. We find that a cutoff close to the Planck scale may be achieved. In its minimal form, the model does not generate sufficient curvature perturbations and additional ingredients, such as a curvaton field, are needed.
State of the Art High-Throughput Approaches to Genotoxicity: Flow Micronucleus, Ames II, GreenScreen and Comet (Presented by Dr. Marilyn J. Aardema, Chief Scientific Advisor, Toxicology, Dr. Leon Stankowski, et. al. (6/28/2012)
Directory of Open Access Journals (Sweden)
Zhiyin Yang
2014-12-01
Full Text Available A complex flow field is created when a vertical/short take-off and landing aircraft is operating near ground. One major concern for this kind of aircraft in ground effect is the possibility of ingestion of hot gases from the jet engine exhausts back into the engine, known as hot gas ingestion, which can increase the intake air temperature and also reduce the oxygen content in the intake air, potentially leading to compressor stall, low combustion efficiency and causing a dramatic loss of lift. This flow field can be represented by the configuration of twin impinging jets in a cross-flow. Accurate prediction of this complicated flow field under the Reynolds averaged Navier–Stokes (RANS approach (current practise in industry is a great challenge as previous studies suggest that some important flow features cannot be captured by the Steady-RANS (SRANS approach even with a second-order Reynolds stress model (RSM. This paper presents a numerical study of this flow using the Unsteady-RANS (URANS approach with a RSM and the results clearly indicate that the URANS approach is superior than the SRANS approach but still the predictions of Reynolds stress are not accurate enough.
NARX prediction of some rare chaotic flows: Recurrent fuzzy functions approach
Energy Technology Data Exchange (ETDEWEB)
Goudarzi, Sobhan [Biomedical Engineering Department, Amirkabir University of Technology, Tehran 15875-4413 (Iran, Islamic Republic of); Jafari, Sajad, E-mail: sajadjafari@aut.ac.ir [Biomedical Engineering Department, Amirkabir University of Technology, Tehran 15875-4413 (Iran, Islamic Republic of); Moradi, Mohammad Hassan [Biomedical Engineering Department, Amirkabir University of Technology, Tehran 15875-4413 (Iran, Islamic Republic of); Sprott, J.C. [Department of Physics, University of Wisconsin–Madison, Madison, WI 53706 (United States)
2016-02-15
The nonlinear and dynamic accommodating capability of time domain models makes them a useful representation of chaotic time series for analysis, modeling and prediction. This paper is devoted to the modeling and prediction of chaotic time series with hidden attractors using a nonlinear autoregressive model with exogenous inputs (NARX) based on a novel recurrent fuzzy functions (RFFs) approach. Case studies of recently introduced chaotic systems with hidden attractors plus classical chaotic systems demonstrate that the proposed modeling methodology exhibits better prediction performance from different viewpoints (short term and long term) compared to some other existing methods. - Highlights: • A new method is proposed for prediction of chaotic time series. • This method is based on novel recurrent fuzzy functions (RFFs) approach. • Some rare chaotic flows are used as test systems. • The new method shows proper performance in short-term prediction. • It also shows proper performance in prediction of attractor's topology.
Modeling flow in fractured medium. Uncertainty analysis with stochastic continuum approach
International Nuclear Information System (INIS)
Niemi, A.
1994-01-01
For modeling groundwater flow in formation-scale fractured media, no general method exists for scaling the highly heterogeneous hydraulic conductivity data to model parameters. The deterministic approach is limited in representing the heterogeneity of a medium and the application of fracture network models has both conceptual and practical limitations as far as site-scale studies are concerned. The study investigates the applicability of stochastic continuum modeling at the scale of data support. No scaling of the field data is involved, and the original variability is preserved throughout the modeling. Contributions of various aspects to the total uncertainty in the modeling prediction can also be determined with this approach. Data from five crystalline rock sites in Finland are analyzed. (107 refs., 63 figs., 7 tabs.)
NARX prediction of some rare chaotic flows: Recurrent fuzzy functions approach
International Nuclear Information System (INIS)
Goudarzi, Sobhan; Jafari, Sajad; Moradi, Mohammad Hassan; Sprott, J.C.
2016-01-01
The nonlinear and dynamic accommodating capability of time domain models makes them a useful representation of chaotic time series for analysis, modeling and prediction. This paper is devoted to the modeling and prediction of chaotic time series with hidden attractors using a nonlinear autoregressive model with exogenous inputs (NARX) based on a novel recurrent fuzzy functions (RFFs) approach. Case studies of recently introduced chaotic systems with hidden attractors plus classical chaotic systems demonstrate that the proposed modeling methodology exhibits better prediction performance from different viewpoints (short term and long term) compared to some other existing methods. - Highlights: • A new method is proposed for prediction of chaotic time series. • This method is based on novel recurrent fuzzy functions (RFFs) approach. • Some rare chaotic flows are used as test systems. • The new method shows proper performance in short-term prediction. • It also shows proper performance in prediction of attractor's topology.
AN AERIAL-IMAGE DENSE MATCHING APPROACH BASED ON OPTICAL FLOW FIELD
Directory of Open Access Journals (Sweden)
W. Yuan
2016-06-01
Full Text Available Dense matching plays an important role in many fields, such as DEM (digital evaluation model producing, robot navigation and 3D environment reconstruction. Traditional approaches may meet the demand of accuracy. But the calculation time and out puts density is hardly be accepted. Focus on the matching efficiency and complex terrain surface matching feasibility an aerial image dense matching method based on optical flow field is proposed in this paper. First, some high accurate and uniformed control points are extracted by using the feature based matching method. Then the optical flow is calculated by using these control points, so as to determine the similar region between two images. Second, the optical flow field is interpolated by using the multi-level B-spline interpolation in the similar region and accomplished the pixel by pixel coarse matching. Final, the results related to the coarse matching refinement based on the combined constraint, which recognizes the same points between images. The experimental results have shown that our method can achieve per-pixel dense matching points, the matching accuracy achieves sub-pixel level, and fully meet the three-dimensional reconstruction and automatic generation of DSM-intensive matching’s requirements. The comparison experiments demonstrated that our approach’s matching efficiency is higher than semi-global matching (SGM and Patch-based multi-view stereo matching (PMVS which verifies the feasibility and effectiveness of the algorithm.
An integrated approach for hazard assessment and mitigation of debris flows in the Italian Dolomites
Pasuto, Alessandro; Soldati, Mauro
2004-07-01
This paper shows the results of research on a debris flow occurring on 4 September 1997 in the territory of Cortina d'Ampezzo (Dolomites, Italy) where it caused a significant threat owing to the intense urban development, typical of several Alpine valleys. The event, which affected the talus fans at the foot of Mt. Pomagagnon near the village of Fiames, blocked the state road no. 51 "Alemagna" and, after sparing some houses, barred the course of the Torrent Boite and formed an impoundment. This debris flow aroused great concern among local authorities and the Belluno Civil Engineers Board; therefore, the construction of embankments for protecting the buildings threatened by the debris flow was started immediately. This area was studied in detail during this research in order to identify the hazard situations of the whole slope. The investigations made use of an integrated approach including historical, geomorphological, geostructural, meteorological, pedological, and forest-management aspects. Furthermore, assessments of the debris volumes potentially removable in the source area were carried out. The geomorphological evolution of the area was reconstructed, pinpointing the morphological changes occurring in the past 45 years. Taking into account the increased frequency and magnitude of recent events and considering the location of roads and buildings in the accumulation area, the risk conditions were analysed in order to identify a risk zonation and to propose mitigation measures.
Continuous-Flow Production of Injectable Liposomes via a Microfluidic Approach
Zizzari, Alessandra; Bianco, Monica; Perrone, Elisabetta; Amato, Francesco; Maruccio, Giuseppe; Rendina, Filippo; Arima, Valentina
2017-01-01
Injectable liposomes are characterized by a suitable size and unique lipid mixtures, which require time-consuming and nonstraightforward production processes. The complexity of the manufacturing methods may affect liposome solubility, the phase transition temperatures of the membranes, the average particle size, and the associated particle size distribution, with a possible impact on the drug encapsulation and release. By leveraging the precise steady-state control over the mixing of miscible liquids and a highly efficient heat transfer, microfluidic technology has proved to be an effective and direct methodology to produce liposomes. This approach results particularly efficient in reducing the number of the sizing steps, when compared to standard industrial methods. Here, Microfluidic Hydrodynamic Focusing chips were produced and used to form liposomes upon tuning experimental parameters such as lipids concentration and Flow-Rate-Ratios (FRRs). Although modelling evidenced the dependence of the laminar flow on the geometric constraints and the FRR conditions, for the specific formulation investigated in this study, the lipids concentration was identified as the primary factor influencing the size of the liposomes and their polydispersity index. This was attributed to a predominance of the bending elasticity modulus over the vesiculation index in the lipid mixture used. Eventually, liposomes of injectable size were produced using microfluidic one-pot synthesis in continuous flow. PMID:29232873
Continuous-Flow Production of Injectable Liposomes via a Microfluidic Approach
Directory of Open Access Journals (Sweden)
Alessandra Zizzari
2017-12-01
Full Text Available Injectable liposomes are characterized by a suitable size and unique lipid mixtures, which require time-consuming and nonstraightforward production processes. The complexity of the manufacturing methods may affect liposome solubility, the phase transition temperatures of the membranes, the average particle size, and the associated particle size distribution, with a possible impact on the drug encapsulation and release. By leveraging the precise steady-state control over the mixing of miscible liquids and a highly efficient heat transfer, microfluidic technology has proved to be an effective and direct methodology to produce liposomes. This approach results particularly efficient in reducing the number of the sizing steps, when compared to standard industrial methods. Here, Microfluidic Hydrodynamic Focusing chips were produced and used to form liposomes upon tuning experimental parameters such as lipids concentration and Flow-Rate-Ratios (FRRs. Although modelling evidenced the dependence of the laminar flow on the geometric constraints and the FRR conditions, for the specific formulation investigated in this study, the lipids concentration was identified as the primary factor influencing the size of the liposomes and their polydispersity index. This was attributed to a predominance of the bending elasticity modulus over the vesiculation index in the lipid mixture used. Eventually, liposomes of injectable size were produced using microfluidic one-pot synthesis in continuous flow.
Communication: Relaxation-limited electronic currents in extended reservoir simulations
Gruss, Daniel; Smolyanitsky, Alex; Zwolak, Michael
2017-10-01
Open-system approaches are gaining traction in the simulation of charge transport in nanoscale and molecular electronic devices. In particular, "extended reservoir" simulations, where explicit reservoir degrees of freedom are present, allow for the computation of both real-time and steady-state properties but require relaxation of the extended reservoirs. The strength of this relaxation, γ, influences the conductance, giving rise to a "turnover" behavior analogous to Kramers turnover in chemical reaction rates. We derive explicit, general expressions for the weak and strong relaxation limits. For weak relaxation, the conductance increases linearly with γ and every electronic state of the total explicit system contributes to the electronic current according to its "reduced" weight in the two extended reservoir regions. Essentially, this represents two conductors in series—one at each interface with the implicit reservoirs that provide the relaxation. For strong relaxation, a "dual" expression-one with the same functional form-results, except now proportional to 1/γ and dependent on the system of interest's electronic states, reflecting that the strong relaxation is localizing electrons in the extended reservoirs. Higher order behavior (e.g., γ2 or 1/γ2) can occur when there is a gap in the frequency spectrum. Moreover, inhomogeneity in the frequency spacing can give rise to a pseudo-plateau regime. These findings yield a physically motivated approach to diagnosing numerical simulations and understanding the influence of relaxation, and we examine their occurrence in both simple models and a realistic, fluctuating graphene nanoribbon.
Regional Balance Model of Financial Flows through Sectoral Approaches System of National Accounts
Directory of Open Access Journals (Sweden)
Ekaterina Aleksandrovna Zaharchuk
2017-03-01
Full Text Available The main purpose of the study, the results of which are reflected in this article, is the theoretical and methodological substantiation of possibilities to build a regional balance model of financial flows consistent with the principles of the construction of the System of National Accounts (SNA. The paper summarizes the international experience of building regional accounts in the SNA as well as reflects the advantages and disadvantages of the existing techniques for constructing Social Accounting Matrix. The authors have proposed an approach to build the regional balance model of financial flows, which is based on the disaggregated tables of the formation, distribution and use of the added value of territory in the framework of institutional sectors of SNA (corporations, public administration, households. Within the problem resolution of the transition of value added from industries to sectors, the authors have offered an approach to the accounting of development, distribution and use of value added within the institutional sectors of the territories. The methods of calculation are based on the publicly available information base of statistics agencies and federal services. The authors provide the scheme of the interrelations of the indicators of the regional balance model of financial flows. It allows to coordinate mutually the movement of regional resources by the sectors of «corporation», «public administration» and «households» among themselves, and cash flows of the region — by the sectors and directions of use. As a result, they form a single account of the formation and distribution of territorial financial resources, which is a regional balance model of financial flows. This matrix shows the distribution of financial resources by income sources and sectors, where the components of the formation (compensation, taxes and gross profit, distribution (transfers and payments and use (final consumption, accumulation of value added are
Manners, R.; Wilcox, A. C.; Merritt, D. M.
2016-12-01
The ecogeomorphic response of riparian ecosystems to a change in hydrologic properties is difficult to predict because of the interactions and feedbacks among plants, water, and sediment. Most riparian models of community dynamics assume a static channel, yet geomorphic processes strongly control the establishment and survival of riparian vegetation. Using a combination of approaches that includes empirical relationships and hydrodynamic models, we model the coupled vegetation-topographic response of three cross-sections on the Yampa and Green Rivers in Dinosaur National Monument, to a shift in the flow regime. The locations represent the variable geomorphology and vegetation composition of these canyon-bound rivers. We account for the inundation and hydraulic properties of vegetation plots surveyed over three years within International River Interface Cooperative (iRIC) Fastmech, equipped with a vegetation module that accounts for flexible stems and plant reconfiguration. The presence of functional groupings of plants, or those plants that respond similarly to environmental factors such as water availability and disturbance are determined from flow response curves developed for the Yampa River. Using field measurements of vegetation morphology, distance from the channel centerline, and dominant particle size and modeled inundation properties we develop an empirical relationship between these variables and topographic change. We evaluate vegetation and channel form changes over decadal timescales, allowing for the integration of processes over time. From our analyses, we identify thresholds in the flow regime that alter the distribution of plants and reduce geomorphic complexity, predominately through side-channel and backwater infilling. Simplification of some processes (e.g., empirically-derived sedimentation) and detailed treatment of others (e.g., plant-flow interactions) allows us to model the coupled dynamics of riparian ecosystems and evaluate the impact of
Nanda, Tarun; Kumar, B. Ravi; Singh, Vishal
2017-11-01
Micromechanical modeling is used to predict material's tensile flow curve behavior based on microstructural characteristics. This research develops a simplified micromechanical modeling approach for predicting flow curve behavior of dual-phase steels. The existing literature reports on two broad approaches for determining tensile flow curve of these steels. The modeling approach developed in this work attempts to overcome specific limitations of the existing two approaches. This approach combines dislocation-based strain-hardening method with rule of mixtures. In the first step of modeling, `dislocation-based strain-hardening method' was employed to predict tensile behavior of individual phases of ferrite and martensite. In the second step, the individual flow curves were combined using `rule of mixtures,' to obtain the composite dual-phase flow behavior. To check accuracy of proposed model, four distinct dual-phase microstructures comprising of different ferrite grain size, martensite fraction, and carbon content in martensite were processed by annealing experiments. The true stress-strain curves for various microstructures were predicted with the newly developed micromechanical model. The results of micromechanical model matched closely with those of actual tensile tests. Thus, this micromechanical modeling approach can be used to predict and optimize the tensile flow behavior of dual-phase steels.
Directory of Open Access Journals (Sweden)
Ruiqing Ming
2017-01-01
Full Text Available Current common models for calculating continuous liquid-carrying critical gas velocity are established based on vertical wells and laminar flow without considering the influence of deviation angle and Reynolds number on liquid-carrying. With the increase of the directional well in transition flow or turbulent flow, the current common models cannot accurately predict the critical gas velocity of these wells. So we built a new model to predict continuous liquid-carrying critical gas velocity for directional well in transition flow or turbulent flow. It is shown from sensitivity analysis that the correction coefficient is mainly influenced by Reynolds number and deviation angle. With the increase of Reynolds number, the critical liquid-carrying gas velocity increases first and then decreases. And with the increase of deviation angle, the critical liquid-carrying gas velocity gradually decreases. It is indicated from the case calculation analysis that the calculation error of this new model is less than 10%, where accuracy is much higher than those of current common models. It is demonstrated that the continuous liquid-carrying critical gas velocity of directional well in transition flow or turbulent flow can be predicted accurately by using this new model.
Energy Technology Data Exchange (ETDEWEB)
Sari, Salih [Hacettepe University, Department of Nuclear Engineering, Beytepe, 06800 Ankara (Turkey); Erguen, Sule [Hacettepe University, Department of Nuclear Engineering, Beytepe, 06800 Ankara (Turkey); Barik, Muhammet; Kocar, Cemil; Soekmen, Cemal Niyazi [Hacettepe University, Department of Nuclear Engineering, Beytepe, 06800 Ankara (Turkey)
2009-03-15
In this study, isothermal turbulent bubbly flow is mechanistically modeled. For the modeling, Fluent version 6.3.26 is used as the computational fluid dynamics solver. First, the mechanistic models that simulate the interphase momentum transfer between the gas (bubbles) and liquid (continuous) phases are investigated, and proper models for the known flow conditions are selected. Second, an interfacial area transport equation (IATE) solution is added to Fluent's solution scheme in order to model the interphase momentum transfer mechanisms. In addition to solving IATE, bubble number density (BND) approach is also added to Fluent and this approach is also used in the simulations. Different source/sink models derived for the IATE and BND models are also investigated. The simulations of experiments based on the available data in literature are performed by using IATE and BND models in two and three-dimensions. The results show that the simulations performed by using IATE and BND models agree with each other and with the experimental data. The simulations performed in three-dimensions give better agreement with the experimental data.
International Nuclear Information System (INIS)
Sari, Salih; Erguen, Sule; Barik, Muhammet; Kocar, Cemil; Soekmen, Cemal Niyazi
2009-01-01
In this study, isothermal turbulent bubbly flow is mechanistically modeled. For the modeling, Fluent version 6.3.26 is used as the computational fluid dynamics solver. First, the mechanistic models that simulate the interphase momentum transfer between the gas (bubbles) and liquid (continuous) phases are investigated, and proper models for the known flow conditions are selected. Second, an interfacial area transport equation (IATE) solution is added to Fluent's solution scheme in order to model the interphase momentum transfer mechanisms. In addition to solving IATE, bubble number density (BND) approach is also added to Fluent and this approach is also used in the simulations. Different source/sink models derived for the IATE and BND models are also investigated. The simulations of experiments based on the available data in literature are performed by using IATE and BND models in two and three-dimensions. The results show that the simulations performed by using IATE and BND models agree with each other and with the experimental data. The simulations performed in three-dimensions give better agreement with the experimental data
A hybrid load flow and event driven simulation approach to multi-state system reliability evaluation
International Nuclear Information System (INIS)
George-Williams, Hindolo; Patelli, Edoardo
2016-01-01
Structural complexity of systems, coupled with their multi-state characteristics, renders their reliability and availability evaluation difficult. Notwithstanding the emergence of various techniques dedicated to complex multi-state system analysis, simulation remains the only approach applicable to realistic systems. However, most simulation algorithms are either system specific or limited to simple systems since they require enumerating all possible system states, defining the cut-sets associated with each state and monitoring their occurrence. In addition to being extremely tedious for large complex systems, state enumeration and cut-set definition require a detailed understanding of the system's failure mechanism. In this paper, a simple and generally applicable simulation approach, enhanced for multi-state systems of any topology is presented. Here, each component is defined as a Semi-Markov stochastic process and via discrete-event simulation, the operation of the system is mimicked. The principles of flow conservation are invoked to determine flow across the system for every performance level change of its components using the interior-point algorithm. This eliminates the need for cut-set definition and overcomes the limitations of existing techniques. The methodology can also be exploited to account for effects of transmission efficiency and loading restrictions of components on system reliability and performance. The principles and algorithms developed are applied to two numerical examples to demonstrate their applicability. - Highlights: • A discrete event simulation model based on load flow principles. • Model does not require system path or cut sets. • Applicable to binary and multi-state systems of any topology. • Supports multiple output systems with competing demand. • Model is intuitive and generally applicable.
Energy Technology Data Exchange (ETDEWEB)
Tamada, Takashi (Okayama Univ. (Japan). School of Medicine)
1992-06-01
To evaluate a proliferative activity of post-irradiated malignant cells, we studied the kinetics of HeLa cells using immunohistochemical approach and flow cytometry. HeLa cells were stained with two proliferation-associated monoclonal antibodies, Ki-67 and anti-DNA polymerase {alpha} antibody. Nucleoli of non-irradiated cells were granularly stained with Ki-67. After irradiation, only the center of nuclei was diffusely stained with Ki-67. One hundred forty-four hours after low-dose irradiation, the staining patterns became the same as the control. On the other hand, after high-dose irradiation, the center of nuclei was weakly stained. DNA polymerase {alpha} was diffusely labelled with nuclei of the control. It was located around the border of nuclei of low-dose irradiated cells like a ring. But after high-dose irradiation, it was granularly distributed in the periphery of nuclei. FITC conjugated Ki-67/PI two parameter analysis was done by a single laser flow cytometer. Twenty-four hours after irradiation, DNA-histograms showed the accumulation to G{sub 2}/M phase and the increase of DNA content of G{sub 2}/M cells, as exposure dose was increased. Two parameter analysis showed the increase of FITC uptake of G{sub 2}/M phase as dose increased. These changes of flow cytometry were remarkably observed after 24 hours' incubation. It was shown that the difference of Ki-67 antigen and DNA polymerase {alpha} appearance depended on the irradiation dose. These findings suggest that immunohistochemical staining with Ki-67 or anti-DNA polymerase {alpha} antibody and flow cytometry using Ki-67 are available to evaluate cell damages after irradiation. (author).
Large scale debris-flow hazard assessment: a geotechnical approach and GIS modelling
Directory of Open Access Journals (Sweden)
G. Delmonaco
2003-01-01
Full Text Available A deterministic distributed model has been developed for large-scale debris-flow hazard analysis in the basin of River Vezza (Tuscany Region – Italy. This area (51.6 km 2 was affected by over 250 landslides. These were classified as debris/earth flow mainly involving the metamorphic geological formations outcropping in the area, triggered by the pluviometric event of 19 June 1996. In the last decades landslide hazard and risk analysis have been favoured by the development of GIS techniques permitting the generalisation, synthesis and modelling of stability conditions on a large scale investigation (>1:10 000. In this work, the main results derived by the application of a geotechnical model coupled with a hydrological model for the assessment of debris flows hazard analysis, are reported. This analysis has been developed starting by the following steps: landslide inventory map derived by aerial photo interpretation, direct field survey, generation of a database and digital maps, elaboration of a DTM and derived themes (i.e. slope angle map, definition of a superficial soil thickness map, geotechnical soil characterisation through implementation of a backanalysis on test slopes, laboratory test analysis, inference of the influence of precipitation, for distinct return times, on ponding time and pore pressure generation, implementation of a slope stability model (infinite slope model and generalisation of the safety factor for estimated rainfall events with different return times. Such an approach has allowed the identification of potential source areas of debris flow triggering. This is used to detected precipitation events with estimated return time of 10, 50, 75 and 100 years. The model shows a dramatic decrease of safety conditions for the simulation when is related to a 75 years return time rainfall event. It corresponds to an estimated cumulated daily intensity of 280–330 mm. This value can be considered the hydrological triggering
A moving mesh method with variable relaxation time
Soheili, Ali Reza; Stockie, John M.
2006-01-01
We propose a moving mesh adaptive approach for solving time-dependent partial differential equations. The motion of spatial grid points is governed by a moving mesh PDE (MMPDE) in which a mesh relaxation time \\tau is employed as a regularization parameter. Previously reported results on MMPDEs have invariably employed a constant value of the parameter \\tau. We extend this standard approach by incorporating a variable relaxation time that is calculated adaptively alongside the solution in orde...
Modern problems of relaxation gas dynamics
International Nuclear Information System (INIS)
Losev, S.A.; Osipov, A.I.
1985-01-01
Some of the dynamical characteristics of relaxation processes are studied. Unfortunately, many dynamical characteristics of relaxation processes, necessary for the solution of important scientific and applied problems, are not known. These problems require further development of experimental methods of the study of nonequilibrium gas. It is known, that gas systems are shifted from the equilibrium by different methods: by acoustic and shock wav es, by means of gas expansion in nozzles and jets, by powerful radiations (laser, first of all), by electric discharges, in burning and combustion devices, etc. Non-equilibrium gas is produced in installations of continuum, impulse and periodic regime. Molecular beams, shock tubes (especially with nozzles), flow and jet installations, aerodynamical tubes, plasmatrons, vessels with a gas, influenced by the strong radiation, burners and combustion devices, where the study of non-euilibrium gas is helpful to solve the problems of the determination of kinetic equations and constants of physico-chemical kinetics
The shear and bulk relaxation times from the general correlation functions
Czajka, Alina; Jeon, Sangyong
2017-11-01
In this paper we present two quantum field theoretical analyses on the shear and bulk relaxation times. First, we discuss how to find Kubo formulas for the shear and the bulk relaxation times. Next, we provide results on the shear viscosity relaxation time obtained within the diagrammatic approach for the massless λϕ4 theory.
A Bayesian Hierarchical Modeling Approach to Predicting Flow in Ungauged Basins
Gronewold, A.; Alameddine, I.; Anderson, R. M.
2009-12-01
Recent innovative approaches to identifying and applying regression-based relationships between land use patterns (such as increasing impervious surface area and decreasing vegetative cover) and rainfall-runoff model parameters represent novel and promising improvements to predicting flow from ungauged basins. In particular, these approaches allow for predicting flows under uncertain and potentially variable future conditions due to rapid land cover changes, variable climate conditions, and other factors. Despite the broad range of literature on estimating rainfall-runoff model parameters, however, the absence of a robust set of modeling tools for identifying and quantifying uncertainties in (and correlation between) rainfall-runoff model parameters represents a significant gap in current hydrological modeling research. Here, we build upon a series of recent publications promoting novel Bayesian and probabilistic modeling strategies for quantifying rainfall-runoff model parameter estimation uncertainty. Our approach applies alternative measures of rainfall-runoff model parameter joint likelihood (including Nash-Sutcliffe efficiency, among others) to simulate samples from the joint parameter posterior probability density function. We then use these correlated samples as response variables in a Bayesian hierarchical model with land use coverage data as predictor variables in order to develop a robust land use-based tool for forecasting flow in ungauged basins while accounting for, and explicitly acknowledging, parameter estimation uncertainty. We apply this modeling strategy to low-relief coastal watersheds of Eastern North Carolina, an area representative of coastal resource waters throughout the world because of its sensitive embayments and because of the abundant (but currently threatened) natural resources it hosts. Consequently, this area is the subject of several ongoing studies and large-scale planning initiatives, including those conducted through the United
A Generalized Hybrid Multiscale Modeling Approach for Flow and Reactive Transport in Porous Media
Yang, X.; Meng, X.; Tang, Y. H.; Guo, Z.; Karniadakis, G. E.
2017-12-01
Using emerging understanding of biological and environmental processes at fundamental scales to advance predictions of the larger system behavior requires the development of multiscale approaches, and there is strong interest in coupling models at different scales together in a hybrid multiscale simulation framework. A limited number of hybrid multiscale simulation methods have been developed for subsurface applications, mostly using application-specific approaches for model coupling. The proposed generalized hybrid multiscale approach is designed with minimal intrusiveness to the at-scale simulators (pre-selected) and provides a set of lightweight C++ scripts to manage a complex multiscale workflow utilizing a concurrent coupling approach. The workflow includes at-scale simulators (using the lattice-Boltzmann method, LBM, at the pore and Darcy scale, respectively), scripts for boundary treatment (coupling and kriging), and a multiscale universal interface (MUI) for data exchange. The current study aims to apply the generalized hybrid multiscale modeling approach to couple pore- and Darcy-scale models for flow and mixing-controlled reaction with precipitation/dissolution in heterogeneous porous media. The model domain is packed heterogeneously that the mixing front geometry is more complex and not known a priori. To address those challenges, the generalized hybrid multiscale modeling approach is further developed to 1) adaptively define the locations of pore-scale subdomains, 2) provide a suite of physical boundary coupling schemes and 3) consider the dynamic change of the pore structures due to mineral precipitation/dissolution. The results are validated and evaluated by comparing with single-scale simulations in terms of velocities, reactive concentrations and computing cost.
Immersed Boundary-Lattice Boltzmann Method Using Two Relaxation Times
Directory of Open Access Journals (Sweden)
Kosuke Hayashi
2012-06-01
Full Text Available An immersed boundary-lattice Boltzmann method (IB-LBM using a two-relaxation time model (TRT is proposed. The collision operator in the lattice Boltzmann equation is modeled using two relaxation times. One of them is used to set the fluid viscosity and the other is for numerical stability and accuracy. A direct-forcing method is utilized for treatment of immersed boundary. A multi-direct forcing method is also implemented to precisely satisfy the boundary conditions at the immersed boundary. Circular Couette flows between a stationary cylinder and a rotating cylinder are simulated for validation of the proposed method. The method is also validated through simulations of circular and spherical falling particles. Effects of the functional forms of the direct-forcing term and the smoothed-delta function, which interpolates the fluid velocity to the immersed boundary and distributes the forcing term to fixed Eulerian grid points, are also examined. As a result, the following conclusions are obtained: (1 the proposed method does not cause non-physical velocity distribution in circular Couette flows even at high relaxation times, whereas the single-relaxation time (SRT model causes a large non-physical velocity distortion at a high relaxation time, (2 the multi-direct forcing reduces the errors in the velocity profile of a circular Couette flow at a high relaxation time, (3 the two-point delta function is better than the four-point delta function at low relaxation times, but worse at high relaxation times, (4 the functional form of the direct-forcing term does not affect predictions, and (5 circular and spherical particles falling in liquids are well predicted by using the proposed method both for two-dimensional and three-dimensional cases.
Directory of Open Access Journals (Sweden)
I. Magdych
2015-06-01
Full Text Available The article explores the methodological approaches to the analysis of cash flows in investment activity of the enterprise; the system of motion net cash flows, reflecting the impact of cash management efficiency on the amount and source of investment cash flows of the enterprise; analytical model of definition of effectiveness of cash management of the enterprise is proposed, based on the selected principals of modeling, comprehensive analysis of cash flows in investing activities and their optimization for the purpose of maximization of social and economic benefit. The research performed here allowed generalization and definition of stages of analysis for investing cash flow of the enterprise with the appropriate reasoning. It is necessary that research is going concern in this direction of effectiveness valuation of cash flow management in investing activity of the enterprise.
Numerical approach of multi-field two-phase flow models in the OVAP code
International Nuclear Information System (INIS)
Anela Kumbaro
2005-01-01
Full text of publication follows: A significant progress has been made in modeling the complexity of vapor-liquid two-phase flow. Different three-dimensional models exist in order to simulate the evolution of parameters which characterize a two-phase model. These models can be classified into various groups depending on the inter-field coupling. A hierarchy of increasing physical complexity can be defined. The simplest group corresponds to the homogeneous mixture models where no interactions are taken into account. Another group is constituted by the two-fluid models employing physically important interfacial forces between two-phases, liquid, and water. The last group is multi-field modeling where inter-field couplings can be taken into account at different degrees, such as the MUltiple Size Group modeling [2], the consideration of separate equations for the transport and generation of mass and momentum for each field under the assumption of the same energy for all the fields of the same phase, and a full multi-field two-phase model [1]. The numerical approach of the general three-dimensional two-phase flow is by complexity of the phenomena a very challenging task; the ideal numerical method should be at the same time simple in order to apply to any model, from equilibrium to multi-field model and conservative in order to respect the fundamental conservation physical laws. The approximate Riemann solvers have the good properties of conservation of mass, momentum and energy balance and have been extended successfully to two-fluid models [3]- [5]. But, the up-winding of the flux is based on the Eigen-decomposition of the two-phase flow model and the computation of the Eigen-structure of a multi-field model can be a high cost procedure. Our contribution will present a short review of the above two-phase models, and show numerical results obtained for some of them with an approximate Riemann solver and with lower-complexity alternative numerical methods that do not
Transport of nuclear waste flows - a modelling and simulation approach - 59136
International Nuclear Information System (INIS)
Adams, Jonathan F.W.; Biggs, Simon R.; Fairweather, Michael; Yao, Jun; Young, James
2012-01-01
accurate technique of large eddy simulation (LES) is compared against the current industrial standard technique of Reynolds-averaged Navier-Stokes (RANS) modelling to ascertain how each can be best utilised to understand and predict the mobilisation and transport of nuclear waste sludges. Both approaches are coupled with a Lagrangian particle tracking (LPT) technique and have been applied to examine particle dispersion and deposition behaviour across a range of Reynolds numbers in square duct flows. Single-phase predictions are found to be in good agreement with the available experimental data. LES and RANS results are in agreement over particle deposition rate, although disagree on the final locations of deposited particles. The RANS based work is further extended to consider particle deposition in circular pipes with variable bed height (B h ). Average particle distance from the nearest wall for spherical particles with sizes ranging from 5-500 μm is monitored in pipes of circular cross-section with bed heights = 0, 0.25 and 0.5 of the pipe diameter. The particle deposition rate is compared over particle sizes and for all values of B h , with the implications for sludge transport in practical situations commented upon. The presence of an increasing B h is found to increase particle deposition for smaller particles. The presence of a bed is found to have little, if any, effect on larger, gravity dominated, particles. (authors)
Dou, Haiyang; Li, Yueqiu; Choi, Jaeyeong; Huo, Shuying; Ding, Liang; Shen, Shigang; Lee, Seungho
2016-09-23
The capability of asymmetrical flow field-flow fractionation (AF4) coupled with UV/VIS, multiangle light scattering (MALS) and quasi-elastic light scattering (QELS) (AF4-UV-MALS-QELS) for separation and characterization of egg yolk plasma was evaluated. The accuracy of hydrodynamic radius (Rh) obtained from QELS and AF4 theory (using both simplified and full expression of AF4 retention equations) was discussed. The conformation of low density lipoprotein (LDL) and its aggregates in egg yolk plasma was discussed based on the ratio of radius of gyration (Rg) to Rh together with the results from bio-transmission electron microscopy (Bio-TEM). The results indicate that the full retention equation is more relevant than simplified version for the Rh determination at high cross flow rate. The Rh from online QELS is reliable only at a specific range of sample concentration. The effect of programmed cross flow rate (linear and exponential decay) on the analysis of egg yolk plasma was also investigated. It was found that the use of an exponentially decaying cross flow rate not only reduces the AF4 analysis time of the egg yolk plasma, but also provides better resolution than the use of either a constant or linearly decaying cross flow rate. A combination of an exponentially decaying cross flow AF4-UV-MALS-QELS and the utilization of full retention equation was proved to be a useful method for the separation and characterization of egg yolk plasma. Copyright © 2016 Elsevier B.V. All rights reserved.
Cermakova, Lucie; Moneta, Giovanni B.; Spada, Marcantonio M.
2010-01-01
This study investigated how attentional control and study-related dispositional flow influence students' approaches to studying when preparing for academic examinations. Based on information-processing theories, it was hypothesised that attentional control would be positively associated with deep and strategic approaches to studying, and…
A porous flow approach to model thermal non-equilibrium applicable to melt migration
Schmeling, Harro; Marquart, Gabriele; Grebe, Michael
2018-01-01
We develop an approach for heat exchange between a fluid and a solid phase of a porous medium where the temperatures of the fluid and matrix are not in thermal equilibrium. The formulation considers moving of the fluid within a resting or deforming porous matrix in an Eulerian coordinate system. The approach can be applied, for example, to partially molten systems or to brine transport in porous rocks. We start from an existing theory for heat exchange where the energy conservation equations for the fluid and the solid phases are separated and coupled by a heat exchange term. This term is extended to account for the full history of heat exchange. It depends on the microscopic geometry of the fluid phase. For the case of solid containing hot, fluid-filled channels, we derive an expression based on a time-dependent Fourier approach for periodic half-waves. On the macroscopic scale, the temporal evolution of the heat exchange leads to a convolution integral along the flow path of the solid, which simplifies considerably in case of a resting matrix. The evolution of the temperature in both phases with time is derived by inserting the heat exchange term into the energy equations. We explore the effects of thermal non-equilibrium between fluid and solid by considering simple cases with sudden temperature differences between fluid and solid as initial or boundary conditions, and by varying the fluid velocity with respect to the resting porous solid. Our results agree well with an analytical solution for non-moving fluid and solid. The temperature difference between solid and fluid depends on the Peclet number based on the Darcy velocity. For Peclet numbers larger than 1, the temperature difference after one diffusion time reaches 5 per cent of \\tilde{T} or more (\\tilde{T} is a scaling temperature, e.g. the initial temperature difference). Thus, our results imply that thermal non-equilibrium can play an important role for melt migration through partially molten systems
Relaxation and Numerical Approximation of a Two-Fluid Two-Pressure Diphasic Model
International Nuclear Information System (INIS)
Ambroso, A.; Chalons, Ch.; Galie, Th.; Chalons, Ch.; Coquel, F.; Coquel, F.
2009-01-01
This paper is concerned with the numerical approximation of the solutions of a two-fluid two-pressure model used in the modelling of two-phase flows. We present a relaxation strategy for easily dealing with both the nonlinearities associated with the pressure laws and the nonconservative terms that are inherently present in the set of convective equations and that couple the two phases. In particular, the proposed approximate Riemann solver is given by explicit formulas, preserves the natural phase space, and exactly captures the coupling waves between the two phases. Numerical evidences are given to corroborate the validity of our approach. (authors)
Self-organization in three-dimensional compressible magnetohydrodynamic flow
International Nuclear Information System (INIS)
Horiuchi, Ritoku; Sato, Tetsuya.
1987-07-01
A three-dimensional self-organization process of a compressible dissipative plasma with a velocity-magnetic field correlation is investigated in detail by means of a variational method and a magnetohydrodynamic simulation. There are two types of relaxation, i.e., fast relaxation in which the cross helicity is not conserved, and slow relaxation in which the cross helicity is approximately conserved. In the slow relaxation case the cross helicity consists of two components with opposite sign which have almost the same amplitude in the large wavenumber region. In both cases the system approaches a high correlation state, dependent on the initial condition. These results are consistent with an observational data of the solar wind. Selective dissipation of magnetic energy, normal cascade of magnetic energy spectrum and inverse cascade of magnetic helicity spectrum are observed for the sub-Alfvenic flow case as was previously observed for the zero flow case. When the flow velocity is super-Alfvenic, the relaxation process is significantly altered from the zero flow case. (author)
A modular RANS approach for modelling laminar–turbulent transition in turbomachinery flows
International Nuclear Information System (INIS)
Liang Wang; Song Fu; Carnarius, Angelo; Mockett, Charles; Thiele, Frank
2012-01-01
Highlights: ► We propose a laminar–turbulent transition model for turbomachinery applications. ► The model considers the effects of the various instability modes. ► The pressure–diffusion process is represented by an elliptic formulation. ► The mixed-mode transition scenario benefits from our modular prediction approach. - Abstract: In this study we propose a laminar–turbulent transition model, which considers the effects of the various instability modes that exist in turbomachinery flows. This model is based on a K–ω–γ three-equation eddy-viscosity concept with K representing the fluctuating kinetic energy, ω the specific dissipation rate and γ the intermittency factor. As usual, the local mechanics by which the freestream disturbances penetrate into the laminar boundary layer, namely convection and viscous diffusion, are described by the transport equations. However, as a novel feature, the non-local effects due to pressure diffusion are additionally represented by an elliptic formulation. Such an approach allows the present model to respond accurately to freestream turbulence intensity properly and to predict both long and short bubble lengths well. The success in its application to a 3-D cascade indicates that the mixed-mode transition scenario indeed benefits from such a modular prediction approach, which embodies current conceptual understanding of the transition process.
An objective and parsimonious approach for classifying natural flow regimes at a continental scale
Archfield, S. A.; Kennen, J.; Carlisle, D.; Wolock, D.
2013-12-01
Hydroecological stream classification--the process of grouping streams by similar hydrologic responses and, thereby, similar aquatic habitat--has been widely accepted and is often one of the first steps towards developing ecological flow targets. Despite its importance, the last national classification of streamgauges was completed about 20 years ago. A new classification of 1,534 streamgauges in the contiguous United States is presented using a novel and parsimonious approach to understand similarity in ecological streamflow response. This new classification approach uses seven fundamental daily streamflow statistics (FDSS) rather than winnowing down an uncorrelated subset from 200 or more ecologically relevant streamflow statistics (ERSS) commonly used in hydroecological classification studies. The results of this investigation demonstrate that the distributions of 33 tested ERSS are consistently different among the classes derived from the seven FDSS. It is further shown that classification based solely on the 33 ERSS generally does a poorer job in grouping similar streamgauges than the classification based on the seven FDSS. This new classification approach has the additional advantages of overcoming some of the subjectivity associated with the selection of the classification variables and provides a set of robust continental-scale classes of US streamgauges.
Tardiole Kuehne, Bruno; Estrella, Julio Cezar; Nunes, Luiz Henrique; Martins de Oliveira, Edvard; Hideo Nakamura, Luis; Gomes Ferreira, Carlos Henrique; Carlucci Santana, Regina Helena; Reiff-Marganiec, Stephan; Santana, Marcos José
2015-01-01
This paper proposes a system named AWSCS (Automatic Web Service Composition System) to evaluate different approaches for automatic composition of Web services, based on QoS parameters that are measured at execution time. The AWSCS is a system to implement different approaches for automatic composition of Web services and also to execute the resulting flows from these approaches. Aiming at demonstrating the results of this paper, a scenario was developed, where empirical flows were built to demonstrate the operation of AWSCS, since algorithms for automatic composition are not readily available to test. The results allow us to study the behaviour of running composite Web services, when flows with the same functionality but different problem-solving strategies were compared. Furthermore, we observed that the influence of the load applied on the running system as the type of load submitted to the system is an important factor to define which approach for the Web service composition can achieve the best performance in production.
Chen, Gui-Qiang G.; Schrecker, Matthew R. I.
2018-04-01
We are concerned with globally defined entropy solutions to the Euler equations for compressible fluid flows in transonic nozzles with general cross-sectional areas. Such nozzles include the de Laval nozzles and other more general nozzles whose cross-sectional area functions are allowed at the nozzle ends to be either zero (closed ends) or infinity (unbounded ends). To achieve this, in this paper, we develop a vanishing viscosity method to construct globally defined approximate solutions and then establish essential uniform estimates in weighted L p norms for the whole range of physical adiabatic exponents γ\\in (1, ∞) , so that the viscosity approximate solutions satisfy the general L p compensated compactness framework. The viscosity method is designed to incorporate artificial viscosity terms with the natural Dirichlet boundary conditions to ensure the uniform estimates. Then such estimates lead to both the convergence of the approximate solutions and the existence theory of globally defined finite-energy entropy solutions to the Euler equations for transonic flows that may have different end-states in the class of nozzles with general cross-sectional areas for all γ\\in (1, ∞) . The approach and techniques developed here apply to other problems with similar difficulties. In particular, we successfully apply them to construct globally defined spherically symmetric entropy solutions to the Euler equations for all γ\\in (1, ∞).
Sadeghi, Arman
2018-03-01
Modeling of fluid flow in polyelectrolyte layer (PEL)-grafted microchannels is challenging due to their two-layer nature. Hence, the pertinent studies are limited only to circular and slit geometries for which matching the solutions for inside and outside the PEL is simple. In this paper, a simple variational-based approach is presented for the modeling of fully developed electroosmotic flow in PEL-grafted microchannels by which the whole fluidic area is considered as a single porous medium of variable properties. The model is capable of being applied to microchannels of a complex cross-sectional area. As an application of the method, it is applied to a rectangular microchannel of uniform PEL properties. It is shown that modeling a rectangular channel as a slit may lead to considerable overestimation of the mean velocity especially when both the PEL and electric double layer (EDL) are thick. It is also demonstrated that the mean velocity is an increasing function of the fixed charge density and PEL thickness and a decreasing function of the EDL thickness and PEL friction coefficient. The influence of the PEL thickness on the mean velocity, however, vanishes when both the PEL thickness and friction coefficient are sufficiently high.
A neural network approach to the study of internal energy flow in molecular systems
International Nuclear Information System (INIS)
Sumpter, B.G.; Getino, C.; Noid, D.W.
1992-01-01
Neural networks are used to develop a new technique for efficient analysis of data obtained from molecular-dynamics calculations and is applied to the study of mode energy flow in molecular systems. The methodology is based on teaching an appropriate neural network the relationship between phase-space points along a classical trajectory and mode energies for stretch, bend, and torsion vibrations. Results are discussed for reactive and nonreactive classical trajectories of hydrogen peroxide (H 2 O 2 ) on a semiempirical potential-energy surface. The neural-network approach is shown to produce reasonably accurate values for the mode energies, with average errors between 1% and 12%, and is applicable to any region within the 24-dimensional phase space of H 2 O 2 . In addition, the generic knowledge learned by the neural network allows calculations to be made for other molecular systems. Results are discussed for a series of tetratomic molecules: H 2 X 2 , X=C, N, O, Si, S, or Se, and preliminary results are given for energy flow predictions in macromolecules
An Integrated Design approach to Power Systems: from Power Flows to Electricity Markets
Bose, Subhonmesh
Power system is at the brink of change. Engineering needs, economic forces and environmental factors are the main drivers of this change. The vision is to build a smart electrical grid and a smarter market mechanism around it to fulfill mandates on clean energy. Looking at engineering and economic issues in isolation is no longer an option today; it needs an integrated design approach. In this thesis, I shall revisit some of the classical questions on the engineering operation of power systems that deals with the nonconvexity of power flow equations. Then I shall explore some issues of the interaction of these power flow equations on the electricity markets to address the fundamental issue of market power in a deregulated market environment. Finally, motivated by the emergence of new storage technologies, I present an interesting result on the investment decision problem of placing storage over a power network. The goal of this study is to demonstrate that modern optimization and game theory can provide unique insights into this complex system. Some of the ideas carry over to applications beyond power systems.
Warid, Warid; Hizam, Hashim; Mariun, Norman; Abdul-Wahab, Noor Izzri
2016-01-01
This paper proposes a new formulation for the multi-objective optimal power flow (MOOPF) problem for meshed power networks considering distributed generation. An efficacious multi-objective fuzzy linear programming optimization (MFLP) algorithm is proposed to solve the aforementioned problem with and without considering the distributed generation (DG) effect. A variant combination of objectives is considered for simultaneous optimization, including power loss, voltage stability, and shunt capacitors MVAR reserve. Fuzzy membership functions for these objectives are designed with extreme targets, whereas the inequality constraints are treated as hard constraints. The multi-objective fuzzy optimal power flow (OPF) formulation was converted into a crisp OPF in a successive linear programming (SLP) framework and solved using an efficient interior point method (IPM). To test the efficacy of the proposed approach, simulations are performed on the IEEE 30-busand IEEE 118-bus test systems. The MFLP optimization is solved for several optimization cases. The obtained results are compared with those presented in the literature. A unique solution with a high satisfaction for the assigned targets is gained. Results demonstrate the effectiveness of the proposed MFLP technique in terms of solution optimality and rapid convergence. Moreover, the results indicate that using the optimal DG location with the MFLP algorithm provides the solution with the highest quality.
Granular flow in static mixers by coupled DEM/CFD approach
Directory of Open Access Journals (Sweden)
Pezo Lato
2016-01-01
Full Text Available The mixing process greatly influence the mixing efficiency, as well as the quality and the price of the intermediate and/or the final product. Static mixer is used for premixing action before the main mixing process, for significant reduction of mixing time and energy consumption. This type of premixing action is not investigated in detail in the open literature. In this article, the novel numerical approach called Discrete Element Method is used for modelling of granular flow in multiple static mixer applications (1 - 3 Komax or Ross mixing elements were utilized, while the Computational Fluid Dynamic method was chosen for fluid flow modelling, using the Eulerian multiphase model. The main aim of this article is to predict the behaviour of granules being gravitationally transported in different mixer configuration and to choose the best configuration of the mixer taking into account the total particle path, the number of mixing elements and the quality of the obtained mixture. The results of the numerical simulations in the static mixers were compared to experimental results, the mixing quality is examined by RSD (relative standard deviation criterion, and the effects on the mixer type and the number of mixing elements on mixing process were studied. The effects of the mixer type and the number of mixing elements on mixing process were studied using analysis of variance (ANOVA. Mathematical modelling is used for optimization of number of Ross and Komax segments in mixer in order to gain desirable mixing results. [Projekat Ministarstva nauke Republike Srbije, br. TR31055
A finite difference, multipoint flux numerical approach to flow in porous media: Numerical examples
Osman, Hossam Omar; Salama, Amgad; Sun, Shuyu; Bao, Kai
2012-01-01
It is clear that none of the current available numerical schemes which may be adopted to solve transport phenomena in porous media fulfill all the required robustness conditions. That is while the finite difference methods are the simplest of all, they face several difficulties in complex geometries and anisotropic media. On the other hand, while finite element methods are well suited to complex geometries and can deal with anisotropic media, they are more involved in coding and usually require more execution time. Therefore, in this work we try to combine some features of the finite element technique, namely its ability to work with anisotropic media with the finite difference approach. We reduce the multipoint flux, mixed finite element technique through some quadrature rules to an equivalent cell-centered finite difference approximation. We show examples on using this technique to single-phase flow in anisotropic porous media.
Modified rational Legendre approach to laminar viscous flow over a semi-infinite flat plate
International Nuclear Information System (INIS)
Tajvidi, T.; Razzaghi, M.; Dehghan, M.
2008-01-01
A numerical method for solving the classical Blasius' equation is proposed. The Blasius' equation is a third order nonlinear ordinary differential equation , which arises in the problem of the two-dimensional laminar viscous flow over a semi-infinite flat plane. The approach is based on a modified rational Legendre tau method. The operational matrices for the derivative and product of the modified rational Legendre functions are presented. These matrices together with the tau method are utilized to reduce the solution of Blasius' equation to the solution of a system of algebraic equations. A numerical evaluation is included to demonstrate the validity and applicability of the method and a comparison is made with existing results
An acoustic-convective splitting-based approach for the Kapila two-phase flow model
Energy Technology Data Exchange (ETDEWEB)
Eikelder, M.F.P. ten, E-mail: m.f.p.teneikelder@tudelft.nl [EDF R& D, AMA, 7 boulevard Gaspard Monge, 91120 Palaiseau (France); Eindhoven University of Technology, Department of Mathematics and Computer Science, P.O. Box 513, 5600 MB Eindhoven (Netherlands); Daude, F. [EDF R& D, AMA, 7 boulevard Gaspard Monge, 91120 Palaiseau (France); IMSIA, UMR EDF-CNRS-CEA-ENSTA 9219, Université Paris Saclay, 828 Boulevard des Maréchaux, 91762 Palaiseau (France); Koren, B.; Tijsseling, A.S. [Eindhoven University of Technology, Department of Mathematics and Computer Science, P.O. Box 513, 5600 MB Eindhoven (Netherlands)
2017-02-15
In this paper we propose a new acoustic-convective splitting-based numerical scheme for the Kapila five-equation two-phase flow model. The splitting operator decouples the acoustic waves and convective waves. The resulting two submodels are alternately numerically solved to approximate the solution of the entire model. The Lagrangian form of the acoustic submodel is numerically solved using an HLLC-type Riemann solver whereas the convective part is approximated with an upwind scheme. The result is a simple method which allows for a general equation of state. Numerical computations are performed for standard two-phase shock tube problems. A comparison is made with a non-splitting approach. The results are in good agreement with reference results and exact solutions.
Innovations in ILC detector design using a particle flow algorithm approach
International Nuclear Information System (INIS)
Magill, S.; High Energy Physics
2007-01-01
The International Linear Collider (ILC) is a future e + e - collider that will produce particles with masses up to the design center-of-mass (CM) energy of 500 GeV. The ILC complements the Large Hadron Collider (LHC) which, although colliding protons at 14 TeV in the CM, will be luminosity-limited to particle production with masses up to ∼1-2 TeV. At the ILC, interesting cross-sections are small, but there are no backgrounds from underlying events, so masses should be able to be measured by hadronic decays to dijets (∼80% BR) as well as in leptonic decay modes. The precise measurement of jets will require major detector innovations, in particular to the calorimeter, which will be optimized to reconstruct final state particle 4-vectors--called the particle flow algorithm approach to jet reconstruction
A Stochastic Flows Approach for Asset Allocation with Hidden Economic Environment
Directory of Open Access Journals (Sweden)
Tak Kuen Siu
2015-01-01
Full Text Available An optimal asset allocation problem for a quite general class of utility functions is discussed in a simple two-state Markovian regime-switching model, where the appreciation rate of a risky share changes over time according to the state of a hidden economy. As usual, standard filtering theory is used to transform a financial model with hidden information into one with complete information, where a martingale approach is applied to discuss the optimal asset allocation problem. Using a martingale representation coupled with stochastic flows of diffeomorphisms for the filtering equation, the integrand in the martingale representation is identified which gives rise to an optimal portfolio strategy under some differentiability conditions.
Egolf, T. A.; Landgrebe, A. J.
1982-01-01
A user's manual is provided which includes the technical approach for the Prescribed Wake Rotor Inflow and Flow Field Prediction Analysis. The analysis is used to provide the rotor wake induced velocities at the rotor blades for use in blade airloads and response analyses and to provide induced velocities at arbitrary field points such as at a tail surface. This analysis calculates the distribution of rotor wake induced velocities based on a prescribed wake model. Section operating conditions are prescribed from blade motion and controls determined by a separate blade response analysis. The analysis represents each blade by a segmented lifting line, and the rotor wake by discrete segmented trailing vortex filaments. Blade loading and circulation distributions are calculated based on blade element strip theory including the local induced velocity predicted by the numerical integration of the Biot-Savart Law applied to the vortex wake model.
International Nuclear Information System (INIS)
Hung, P.C.; Irwin, G.; Kee, R.; McLoone, S.
2005-01-01
Thermocouples are one of the most popular devices for temperature measurement due to their robustness, ease of manufacture and installation, and low cost. However, when used in certain harsh environments, for example, in combustion systems and engine exhausts, large wire diameters are required, and consequently the measurement bandwidth is reduced. This article discusses a software compensation technique to address the loss of high frequency fluctuations based on measurements from two thermocouples. In particular, a difference equation (DE) approach is proposed and compared with existing methods both in simulation and on experimental test rig data with constant flow velocity. It is found that the DE algorithm, combined with the use of generalized total least squares for parameter identification, provides better performance in terms of time constant estimation without any a priori assumption on the time constant ratios of the thermocouples
A finite difference, multipoint flux numerical approach to flow in porous media: Numerical examples
Osman, Hossam Omar
2012-06-17
It is clear that none of the current available numerical schemes which may be adopted to solve transport phenomena in porous media fulfill all the required robustness conditions. That is while the finite difference methods are the simplest of all, they face several difficulties in complex geometries and anisotropic media. On the other hand, while finite element methods are well suited to complex geometries and can deal with anisotropic media, they are more involved in coding and usually require more execution time. Therefore, in this work we try to combine some features of the finite element technique, namely its ability to work with anisotropic media with the finite difference approach. We reduce the multipoint flux, mixed finite element technique through some quadrature rules to an equivalent cell-centered finite difference approximation. We show examples on using this technique to single-phase flow in anisotropic porous media.
An LES-PBE-PDF approach for modeling particle formation in turbulent reacting flows
Sewerin, Fabian; Rigopoulos, Stelios
2017-10-01
Many chemical and environmental processes involve the formation of a polydispersed particulate phase in a turbulent carrier flow. Frequently, the immersed particles are characterized by an intrinsic property such as the particle size, and the distribution of this property across a sample population is taken as an indicator for the quality of the particulate product or its environmental impact. In the present article, we propose a comprehensive model and an efficient numerical solution scheme for predicting the evolution of the property distribution associated with a polydispersed particulate phase forming in a turbulent reacting flow. Here, the particulate phase is described in terms of the particle number density whose evolution in both physical and particle property space is governed by the population balance equation (PBE). Based on the concept of large eddy simulation (LES), we augment the existing LES-transported probability density function (PDF) approach for fluid phase scalars by the particle number density and obtain a modeled evolution equation for the filtered PDF associated with the instantaneous fluid composition and particle property distribution. This LES-PBE-PDF approach allows us to predict the LES-filtered fluid composition and particle property distribution at each spatial location and point in time without any restriction on the chemical or particle formation kinetics. In view of a numerical solution, we apply the method of Eulerian stochastic fields, invoking an explicit adaptive grid technique in order to discretize the stochastic field equation for the number density in particle property space. In this way, sharp moving features of the particle property distribution can be accurately resolved at a significantly reduced computational cost. As a test case, we consider the condensation of an aerosol in a developed turbulent mixing layer. Our investigation not only demonstrates the predictive capabilities of the LES-PBE-PDF model but also
Relaxation of entangled model H-shaped polymers a SANS investigation
Heinrich, M; Richter, D; Straube, E; Wiedenmann, A
2002-01-01
This study is related to the understanding of rheology of long-chain branched polymers. A model compound for long-chain branching (H-shaped architecture) was investigated in elongational flow as a function of time after a step strain to lambda=2. The experiments were performed in a strain rig with temperature and strain-rate control. The structure factor was measured after specific relaxation times intimately connected to the microscopic hierarchy of the polymer structure. The correlation hole effect and the quenched disorder in the scattering were described in a random phase approximation approach. This approach, already used for permanent rubber-elastic networks, has been modified to permit the observation of strain locally along the faster-relaxing arms. The data roughly follow the time scale of linear-shear rheology from which shift factors were derived. They confirm that bridge and arm relaxations can be treated in a decoupled, hierarchical way in time, although details of the analysis remain unsolved. (...
Nezlobin, David; Pariente, Sarah; Lavee, Hanoch; Sachs, Eyal
2017-04-01
Source-sink systems are very common in hydrology; in particular, some land cover types often generate runoff (e.g. embedded rocks, bare soil) , while other obstruct it (e.g. vegetation, cracked soil). Surface runoff coefficients of patchy slopes/plots covered by runoff generating and obstructing covers (e.g., bare soil and vegetation) depend critically on the percentage cover (i.e. sources/sinks abundance) and decrease strongly with observation scale. The classic mathematical percolation theory provides a powerful apparatus for describing the runoff connectivity on patchy hillslopes, but it ignores strong effect of the overland flow directionality. To overcome this and other difficulties, modified percolation theory approaches can be considered, such as straight percolation (for the planar slopes), quasi-straight percolation and models with limited obstruction. These approaches may explain both the observed critical dependence of runoff coefficients on percentage cover and their scale decrease in systems with strong flow directionality (e.g. planar slopes). The contributing area increases sharply when the runoff generating percentage cover approaches the straight percolation threshold. This explains the strong increase of the surface runoff and erosion for relatively low values (normally less than 35%) of the obstructing cover (e.g., vegetation). Combinatorial models of urns with restricted occupancy can be applied for the analytic evaluation of meaningful straight percolation quantities, such as NOGA's (Non-Obstructed Generating Area) expected value and straight percolation probability. It is shown that the nature of the cover-related runoff scale decrease is combinatorial - the probability for the generated runoff to avoid obstruction in unit area decreases with scale for the non-trivial percentage cover values. The magnitude of the scale effect is found to be a skewed non-monotonous function of the percentage cover. It is shown that the cover-related scale
Liu, Shun; Xu, Jinglei; Yu, Kaikai
2017-06-01
This paper proposes an improved approach for extraction of pressure fields from velocity data, such as obtained by particle image velocimetry (PIV), especially for steady compressible flows with strong shocks. The principle of this approach is derived from Navier-Stokes equations, assuming adiabatic condition and neglecting viscosity of flow field boundaries measured by PIV. The computing method is based on MacCormack's technique in computational fluid dynamics. Thus, this approach is called the MacCormack method. Moreover, the MacCormack method is compared with several approaches proposed in previous literature, including the isentropic method, the spatial integration and the Poisson method. The effects of velocity error level and PIV spatial resolution on these approaches are also quantified by using artificial velocity data containing shock waves. The results demonstrate that the MacCormack method has higher reconstruction accuracy than other approaches, and its advantages become more remarkable with shock strengthening. Furthermore, the performance of the MacCormack method is also validated by using synthetic PIV images with an oblique shock wave, confirming the feasibility and advantage of this approach in real PIV experiments. This work is highly significant for the studies on aerospace engineering, especially the outer flow fields of supersonic aircraft and the internal flow fields of ramjets.
Dielectric relaxation studies of dilute solutions of amides
Energy Technology Data Exchange (ETDEWEB)
Malathi, M.; Sabesan, R.; Krishnan, S
2003-11-15
The dielectric constants and dielectric losses of formamide, acetamide, N-methyl acetamide, acetanilide and N,N-dimethyl acetamide in dilute solutions of 1,4-dioxan/benzene have been measured at 308 K using 9.37 GHz, dielectric relaxation set up. The relaxation time for the over all rotation {tau}{sub (1)} and that for the group rotation {tau}{sub (2)} of (the molecules were determined using Higasi's method. The activation energies for the processes of dielectric relaxation and viscous flow were determined by using Eyring's rate theory. From relaxation time behaviour of amides in non-polar solvent, solute-solvent and solute-solute type of molecular association is proposed.
In silico approaches to study mass and energy flows in microbial consortia: a syntrophic case study
Directory of Open Access Journals (Sweden)
Mallette Natasha
2009-12-01
Full Text Available Abstract Background Three methods were developed for the application of stoichiometry-based network analysis approaches including elementary mode analysis to the study of mass and energy flows in microbial communities. Each has distinct advantages and disadvantages suitable for analyzing systems with different degrees of complexity and a priori knowledge. These approaches were tested and compared using data from the thermophilic, phototrophic mat communities from Octopus and Mushroom Springs in Yellowstone National Park (USA. The models were based on three distinct microbial guilds: oxygenic phototrophs, filamentous anoxygenic phototrophs, and sulfate-reducing bacteria. Two phases, day and night, were modeled to account for differences in the sources of mass and energy and the routes available for their exchange. Results The in silico models were used to explore fundamental questions in ecology including the prediction of and explanation for measured relative abundances of primary producers in the mat, theoretical tradeoffs between overall productivity and the generation of toxic by-products, and the relative robustness of various guild interactions. Conclusion The three modeling approaches represent a flexible toolbox for creating cellular metabolic networks to study microbial communities on scales ranging from cells to ecosystems. A comparison of the three methods highlights considerations for selecting the one most appropriate for a given microbial system. For instance, communities represented only by metagenomic data can be modeled using the pooled method which analyzes a community's total metabolic potential without attempting to partition enzymes to different organisms. Systems with extensive a priori information on microbial guilds can be represented using the compartmentalized technique, employing distinct control volumes to separate guild-appropriate enzymes and metabolites. If the complexity of a compartmentalized network creates an
DEFF Research Database (Denmark)
Habib, Komal; Schibye, Peter Klausen; Vestbø, Andreas Peter
2014-01-01
for considerable size and weight reduction in modern applications. This study aims to explore the current and future potential of secondary supply of neodymium and dysprosium from recycling of NdFeB magnets. For this purpose, Material Flow Analysis (MFA) has been carried out to perform the detailed mapping...
Kuniansky, Eve L.
2016-09-22
been developed that incorporate the submerged conduits as a one-dimensional pipe network within the aquifer rather than as discrete, extremely transmissive features in a porous-equivalent medium; these submerged conduit models are usually referred to as hybrid models and may include the capability to simulate both laminar and turbulent flow in the one-dimensional pipe network. Comparisons of the application of a porous-equivalent media model with and without turbulence (MODFLOW-Conduit Flow Process mode 2 and basic MODFLOW, respectively) and a hybrid (MODFLOW-Conduit Flow Process mode 1) model to the Woodville Karst Plain near Tallahassee, Florida, indicated that for annual, monthly, or seasonal average hydrologic conditions, all methods met calibration criteria (matched observed groundwater levels and average flows). Thus, the increased effort required, such as the collection of data on conduit location, to develop a hybrid model and its increased computational burden, is not necessary for simulation of average hydrologic conditions (non-laminar flow effects on simulated head and spring discharge were minimal). However, simulation of a large storm event in the Woodville Karst Plain with daily stress periods indicated that turbulence is important for matching daily springflow hydrographs. Thus, if matching streamflow hydrographs over a storm event is required, the simulation of non-laminar flow and the location of conduits are required. The main challenge in application of the methods and approaches for developing hybrid models relates to the difficulty of mapping conduit networks or having high-quality datasets to calibrate these models. Additionally, hybrid models have long simulation times, which can preclude the use of parameter estimation for calibration. Simulation of contaminant transport that does not account for preferential flow through conduits or extremely permeable zones in any approach is ill-advised. Simulation results in other karst aquifers or other
Energy Technology Data Exchange (ETDEWEB)
Guadalupe Maldonado, S.
2014-07-01
Pressurized water reactors (PWR) used for power generation are operated at elevated temperatures (280-300 °C) and under higher pressure (120-150 bar). In addition to these harsh environmental conditions some components of the PWR assemblies are subject to mechanical loading (sliding, vibration and impacts) leading to undesirable and hardly controllable material degradation phenomena. In such situations wear is determined by the complex interplay (tribocorrosion) between mechanical, material and physical-chemical phenomena. Tribocorrosion in PWR conditions is at present little understood and models need to be developed in order to predict component lifetime over several decades. The goal of this project, carried out in collaboration with the French company AREVA NP, is to develop a predictive model based on the mechanistic understanding of tribocorrosion of specific PWR components (stainless steel control assemblies, stellite grippers). The approach taken here is to describe degradation in terms of electro-chemical and mechanical material flows (third body concept of tribology) from the metal into the friction film (i.e. the oxidized film forming during rubbing on the metal surface) and from the friction film into the environment instead of simple mass loss considerations. The project involves the establishment of mechanistic models for describing the single flows based on ad-hoc tribocorrosion measurements operating at low temperature. The overall behaviour at high temperature and pressure in investigated using a dedicated tribometer (Aurore) including electrochemical control of the contact during rubbing. Physical laws describing the individual flows according to defined mechanisms and as a function of defined physical parameters were identified based on the obtained experimental results and from literature data. The physical laws were converted into mass flow rates and solved as differential equation system by considering the mass balance in compartments
Corruption and illicit financial flows: The limits and possibilities of current approaches
Reed, Quentin; Fontana, Alessandra
2011-01-01
This paper attempts to clarify the links between illicit financial flows and corruption, and how corruption may be tackled by stemming such flows. For this purpose, it clarifies the terminology surrounding illicit flows, describes the impact of such flows, outlines the techniques used to launder them (with a particular focus on laundering of the proceeds of corruption), and critically analyses existing policies designed to tackle illicit flows. This paper contributes to the regulatory de...
Non-monotonic behaviour in relaxation dynamics of image restoration
International Nuclear Information System (INIS)
Ozeki, Tomoko; Okada, Masato
2003-01-01
We have investigated the relaxation dynamics of image restoration through a Bayesian approach. The relaxation dynamics is much faster at zero temperature than at the Nishimori temperature where the pixel-wise error rate is minimized in equilibrium. At low temperature, we observed non-monotonic development of the overlap. We suggest that the optimal performance is realized through premature termination in the relaxation processes in the case of the infinite-range model. We also performed Markov chain Monte Carlo simulations to clarify the underlying mechanism of non-trivial behaviour at low temperature by checking the local field distributions of each pixel
Viscoelasticity, nonlinear shear start-up, and relaxation of entangled star polymers
Snijkers, Frank
2013-07-23
We report on a detailed rheological investigation of well-defined symmetric entangled polymer stars of low functionality with varying number of arms, molar mass of the arms, and solvent content. Emphasis is placed on the response of the stars in simple shear, during start-up, and for relaxation upon flow cessation. To reduce experimental artifacts associated with edge fracture (primarily) and wall slip, we employ a homemade cone-partitioned plate fixture which was successfully implemented in recent studies. Reliable data for these highly entangled stars could be obtained for Weissenberg numbers below 300. The appearance of a stress overshoot during start-up with a corresponding strain approaching a value of 2 suggests that in the investigated shear regime the stars orient but do not stretch. This is corroborated by the fact that the empirical Cox-Merx rule appears to be validated, within experimental error. On the other hand, the (shear) rate dependent steady shear viscosity data exhibit a slope smaller than the convective constraint release slope of -1 (for linear polymers) for the investigated range of rates. The broadness of the stress overshoot reflects the broad linear relaxation spectrum of the stars. The initial stress relaxation rate, reflecting the initial loss of entanglements due to the action of convective constraint release in steady shear flow, increases with Weissenberg number. More importantly, when compared against the relevant rates for comb polymers with relatively short arms, the latter are slower at larger Weissenberg numbers. At long times, the relaxation data are consistent with the linear viscoelastic data on these systems. © 2013 American Chemical Society.
Estimating construction and demolition debris generation using a materials flow analysis approach.
Cochran, K M; Townsend, T G
2010-11-01
The magnitude and composition of a region's construction and demolition (C&D) debris should be understood when developing rules, policies and strategies for managing this segment of the solid waste stream. In the US, several national estimates have been conducted using a weight-per-construction-area approximation; national estimates using alternative procedures such as those used for other segments of the solid waste stream have not been reported for C&D debris. This paper presents an evaluation of a materials flow analysis (MFA) approach for estimating C&D debris generation and composition for a large region (the US). The consumption of construction materials in the US and typical waste factors used for construction materials purchasing were used to estimate the mass of solid waste generated as a result of construction activities. Debris from demolition activities was predicted from various historical construction materials consumption data and estimates of average service lives of the materials. The MFA approach estimated that approximately 610-78 × 10(6)Mg of C&D debris was generated in 2002. This predicted mass exceeds previous estimates using other C&D debris predictive methodologies and reflects the large waste stream that exists. Copyright © 2010 Elsevier Ltd. All rights reserved.
Directory of Open Access Journals (Sweden)
Xiangmin Guan
2015-01-01
Full Text Available Considering reducing the airspace congestion and the flight delay simultaneously, this paper formulates the airway network flow assignment (ANFA problem as a multiobjective optimization model and presents a new multiobjective optimization framework to solve it. Firstly, an effective multi-island parallel evolution algorithm with multiple evolution populations is employed to improve the optimization capability. Secondly, the nondominated sorting genetic algorithm II is applied for each population. In addition, a cooperative coevolution algorithm is adapted to divide the ANFA problem into several low-dimensional biobjective optimization problems which are easier to deal with. Finally, in order to maintain the diversity of solutions and to avoid prematurity, a dynamic adjustment operator based on solution congestion degree is specifically designed for the ANFA problem. Simulation results using the real traffic data from China air route network and daily flight plans demonstrate that the proposed approach can improve the solution quality effectively, showing superiority to the existing approaches such as the multiobjective genetic algorithm, the well-known multiobjective evolutionary algorithm based on decomposition, and a cooperative coevolution multiobjective algorithm as well as other parallel evolution algorithms with different migration topology.
Abrantes, João R. C. B.; Moruzzi, Rodrigo B.; Silveira, Alexandre; de Lima, João L. M. P.
2018-02-01
The accurate measurement of shallow flow velocities is crucial to understand and model the dynamics of sediment and pollutant transport by overland flow. In this study, a novel triple-tracer approach was used to re-evaluate and compare the traditional and well established dye and salt tracer techniques with the more recent thermal tracer technique in estimating shallow flow velocities. For this purpose a triple tracer (i.e. dyed-salted-heated water) was used. Optical and infrared video cameras and an electrical conductivity sensor were used to detect the tracers in the flow. Leading edge and centroid velocities of the tracers were measured and the correction factors used to determine the actual mean flow velocities from tracer measured velocities were compared and investigated. Experiments were carried out for different flow discharges (32-1813 ml s-1) on smooth acrylic, sand, stones and synthetic grass bed surfaces with 0.8, 4.4 and 13.2% slopes. The results showed that thermal tracers can be used to estimate shallow flow velocities, since the three techniques yielded very similar results without significant differences between them. The main advantages of the thermal tracer were that the movement of the tracer along the measuring section was more easily visible than it was in the real image videos and that it was possible to measure space-averaged flow velocities instead of only one velocity value, with the salt tracer. The correction factors used to determine the actual mean velocity of overland flow varied directly with Reynolds and Froude numbers, flow velocity and slope and inversely with flow depth and bed roughness. In shallow flows, velocity estimation using tracers entails considerable uncertainty and caution must be taken with these measurements, especially in field studies where these variables vary appreciably in space and time.
Relaxed memory models: an operational approach
Boudol , Gérard; Petri , Gustavo
2009-01-01
International audience; Memory models define an interface between programs written in some language and their implementation, determining which behaviour the memory (and thus a program) is allowed to have in a given model. A minimal guarantee memory models should provide to the programmer is that well-synchronized, that is, data-race free code has a standard semantics. Traditionally, memory models are defined axiomatically, setting constraints on the order in which memory operations are allow...
Mirus, Benjamin B.; Nimmo, J.R.
2013-01-01
The impact of preferential flow on recharge and contaminant transport poses a considerable challenge to water-resources management. Typical hydrologic models require extensive site characterization, but can underestimate fluxes when preferential flow is significant. A recently developed source-responsive model incorporates film-flow theory with conservation of mass to estimate unsaturated-zone preferential fluxes with readily available data. The term source-responsive describes the sensitivity of preferential flow in response to water availability at the source of input. We present the first rigorous tests of a parsimonious formulation for simulating water table fluctuations using two case studies, both in arid regions with thick unsaturated zones of fractured volcanic rock. Diffuse flow theory cannot adequately capture the observed water table responses at both sites; the source-responsive model is a viable alternative. We treat the active area fraction of preferential flow paths as a scaled function of water inputs at the land surface then calibrate the macropore density to fit observed water table rises. Unlike previous applications, we allow the characteristic film-flow velocity to vary, reflecting the lag time between source and deep water table responses. Analysis of model performance and parameter sensitivity for the two case studies underscores the importance of identifying thresholds for initiation of film flow in unsaturated rocks, and suggests that this parsimonious approach is potentially of great practical value.
DEFF Research Database (Denmark)
Parraguez, Pedro; Eppinger, Steven D.; Maier, Anja
2015-01-01
The pattern of information flow through the network of interdependent design activities is thought to be an important determinant of engineering design process results. A previously unexplored aspect of such patterns relates to the temporal dynamics of information transfer between activities...... design process and thus support theory-building toward the evolution of information flows through systems engineering stages. Implications include guidance on how to analyze and predict information flows as well as better planning of information flows in engineering design projects according...
Relaxed states of tokamak plasmas
International Nuclear Information System (INIS)
Kucinski, M.Y.; Okano, V.
1993-01-01
The relaxed states of tokamak plasmas are studied. It is assumed that the plasma relaxes to a quasi-steady state which is characterized by a minimum entropy production rate, compatible with a number of prescribed conditions and pressure balance. A poloidal current arises naturally due to the anisotropic resistivity. The minimum entropy production theory is applied, assuming the pressure equilibrium as fundamental constraint on the final state. (L.C.J.A.)
Negative magnetic relaxation in superconductors
Directory of Open Access Journals (Sweden)
Krasnoperov E.P.
2013-01-01
Full Text Available It was observed that the trapped magnetic moment of HTS tablets or annuli increases in time (negative relaxation if they are not completely magnetized by a pulsed magnetic field. It is shown, in the framework of the Bean critical-state model, that the radial temperature gradient appearing in tablets or annuli during a pulsed field magnetization can explain the negative magnetic relaxation in the superconductor.
Relaxation effects in ferrous complexes
International Nuclear Information System (INIS)
Nicolini, C.; Mathieu, J.P.; Chappert, J.
1976-01-01
The slow relaxation mechanism of the Fe 2+ ion in the tri-fluorinated TF(acac) and hexafluorinated HF(acac) complexes of Fe(II) acetylacetonate was investigated. The 300K and 77K Moessbauer spectra for TF(acac) consist in a slightly asymmetric quadrupole doublet. On the contrary, at 4.2K the higher energy line is strongly widened; that is typical of a slowing down in the electron relaxation frequency [fr
International Nuclear Information System (INIS)
Bletry, M.; Guyot, P.; Brechet, Y.; Blandin, J.J.; Soubeyroux, J.L.
2007-01-01
The homogeneous deformation of a zirconium-based bulk metallic glass is investigated in the glass transition range. Compression and stress-relaxation tests have been conducted. The stress-strain curves are modeled in the framework of the free volume theory, including transient phenomena (overshoot and undershoot). This approach allows several physical parameters (activation volume, flow defect creation and relaxation coefficient) to be determined from a mechanical experiment. This model is able to rationalize the dependency of stress overshoot on relaxation time. It is shown that, due to the relationship between flow defect concentration and free volume model, it is impossible to determine the equilibrium flow defect concentration. However, the relative variation of flow defect is always the same, and all the model parameters depend on the equilibrium flow defect concentration. The methodology presented in this paper should, in the future, allow the consistency of the free volume model to be assessed
Mass transfer effect of the stalk contraction-relaxation cycle of Vorticella convallaria
Zhou, Jiazhong; Admiraal, David; Ryu, Sangjin
2014-11-01
Vorticella convallaria is a genus of protozoa living in freshwater. Its stalk contracts and coil pulling the cell body towards the substrate at a remarkable speed, and then relaxes to its extended state much more slowly than the contraction. However, the reason for Vorticella's stalk contraction is still unknown. It is presumed that water flow induced by the stalk contraction-relaxation cycle may augment mass transfer near the substrate. We investigated this hypothesis using an experimental model with particle tracking velocimetry and a computational fluid dynamics model. In both approaches, Vorticella was modeled as a solid sphere translating perpendicular to a solid surface in water. After having been validated by the experimental model and verified by grid convergence index test, the computational model simulated water flow during the cycle based on the measured time course of stalk length changes of Vorticella. Based on the simulated flow field, we calculated trajectories of particles near the model Vorticella, and then evaluated the mass transfer effect of Vorticella's stalk contraction based on the particles' motion. We acknowlege support from Laymann Seed Grant of the University of Nebraska-Lincoln.
Nuclear spin-lattice relaxation in carbon nanostructures
Energy Technology Data Exchange (ETDEWEB)
Panich, A.M., E-mail: pan@bgu.ac.i [Department of Physics, Ben-Gurion University of the Negev, P.O. Box 653, Beer Sheva 84105 (Israel); Sergeev, N.A. [Institute of Physics, University of Szczecin, 70-451 Szczecin (Poland)
2010-04-15
Interpretation of nuclear spin-lattice relaxation data in the carbon nanostructures is usually based on the analysis of fluctuations of dipole-dipole interactions of nuclear spins and anisotropic electron-nuclear interactions responsible for chemical shielding, which are caused by molecular dynamics. However, many nanocarbon systems such as fullerene and nanotube derivatives, nanodiamonds and carbon onions reveal noticeable amount of paramagnetic defects with unpaired electrons originating from dangling bonds. The interaction between nuclear and electron spins strongly influences the nuclear spin-lattice relaxation, but usually is not taken into account, thus the relaxation data are not correctly interpreted. Here we report on the temperature dependent NMR spectra and spin-lattice relaxation measurements of intercalated fullerenes C{sub 60}(MF{sub 6}){sub 2} (M=As and Sb), where nuclear relaxation is caused by both molecular rotation and interaction between nuclei and unpaired electron spins. We present a detailed theoretical analysis of the spin-lattice relaxation data taking into account both these contributions. Good agreement between the experimental data and calculations is obtained. The developed approach would be useful in interpreting the NMR relaxation data in different nanostructures and their intercalation compounds.
Habib, Komal; Schibye, Peter Klausen; Vestbø, Andreas Peter; Dall, Ole; Wenzel, Henrik
2014-10-21
Neodymium-iron-boron (NdFeB) magnets have become highly desirable for modern hi-tech applications. These magnets, in general, contain two key rare earth elements (REEs), i.e., neodymium (Nd) and dysprosium (Dy), which are responsible for the very high strength of these magnets, allowing for considerable size and weight reduction in modern applications. This study aims to explore the current and future potential of a secondary supply of neodymium and dysprosium from recycling of NdFeB magnets. For this purpose, material flow analysis (MFA) has been carried out to perform the detailed mapping of stocks and flows of NdFeB magnets in Denmark. A novel element of this study is the value added to the traditionally practiced MFAs at national and/or global levels by complementing them with a comprehensive sampling and elemental analysis of NdFeB magnets, taken out from a sample of 157 different products representing 18 various product types. The results show that the current amount of neodymium and dysprosium in NdFeB magnets present in the Danish waste stream is only 3 and 0.2 Mg, respectively. However, this number is estimated to increase to 175 Mg of neodymium and 11.4 Mg of dysprosium by 2035. Nevertheless, efficient recovery of these elements from a very diverse electronic waste stream remains a logistic and economic challenge.
Scenario approach for the seasonal forecast of Kharif flows from the Upper Indus Basin
Fraz Ismail, Muhammad; Bogacki, Wolfgang
2018-02-01
Snow and glacial melt runoff are the major sources of water contribution from the high mountainous terrain of the Indus River upstream of the Tarbela reservoir. A reliable forecast of seasonal water availability for the Kharif cropping season (April-September) can pave the way towards better water management and a subsequent boost in the agro-economy of Pakistan. The use of degree-day models in conjunction with satellite-based remote-sensing data for the forecasting of seasonal snow and ice melt runoff has proved to be a suitable approach for data-scarce regions. In the present research, the Snowmelt Runoff Model (SRM) has not only been enhanced by incorporating the glacier (G) component but also applied for the forecast of seasonal water availability from the Upper Indus Basin (UIB). Excel-based SRM+G takes account of separate degree-day factors for snow and glacier melt processes. All-year simulation runs with SRM+G for the period 2003-2014 result in an average flow component distribution of 53, 21, and 26 % for snow, glacier, and rain, respectively. The UIB has been divided into Upper and Lower parts because of the different climatic conditions in the Tibetan Plateau. The scenario approach for seasonal forecasting, which like the Ensemble Streamflow Prediction method uses historic meteorology as model forcings, has proven to be adequate for long-term water availability forecasts. The accuracy of the forecast with a mean absolute percentage error (MAPE) of 9.5 % could be slightly improved compared to two existing operational forecasts for the UIB, and the bias could be reduced to -2.0 %. However, the association between forecasts and observations as well as the skill in predicting extreme conditions is rather weak for all three models, which motivates further research on the selection of a subset of ensemble members according to forecasted seasonal anomalies.
International Nuclear Information System (INIS)
Chou, Yi-Sin; Hsu, Ning-Yih; Jeng, King-Tsai; Chen, Kuan-Hsiang; Yen, Shi-Chern
2016-01-01
Highlights: • This is the first to apply ultrasonic sensing technique to monitor SOC of VRB. • Ultrasound velocity is affected by concentration and temperature of a solution. • The ultrasonic sensing is applicable to both positive and negative sides of VRB. • An empirical model equation fits the results of this two-component system well. • The SOC of a VRB can be properly measured using ultrasonic sensing. - Abstract: A novel ultrasonic velocity sensing approach is proposed and investigated to monitor the state of charge (SOC) of a vanadium redox flow battery (VRB, or VRFB). The positive electrode is designated as the energy storage capacity-limiting one so that the molar ratio of the V"5"+ ion in the positive electrolyte solution determines the SOC of a VRB. The tested single-cell VRB is connected to an ultrasonic sensor and charged/discharged almost to its two extremes at a constant current of 2 A under various operating temperatures. It is found that the ultrasound velocity exhibits distinct variations in accordance with changes of vanadium ion compositions in the positive electrolyte solution as the SOC of the VRB varies. The SOC obtained can be depicted in a 3D plot in terms of ultrasound velocity and operating temperature. An empirical model equation is proposed and found to fit the experimental results of both charging and discharging stages quite well. The advantages of this SOC sensing approach are that it is totally independent of VRB operations and can be readily applied to both sides of the electrodes. It is expected to develop into a dependable method for accurate and real-time monitoring of SOC for VRB.
International Nuclear Information System (INIS)
Ramazani, A.; Mukherjee, K.; Quade, H.; Prahl, U.; Bleck, W.
2013-01-01
A microstructure-based approach by means of representative volume elements (RVEs) is employed to evaluate the flow curve of DP steels using virtual tensile tests. Microstructures with different martensite fractions and morphologies are studied in two- and three-dimensional approaches. Micro sections of DP microstructures with various amounts of martensite have been converted to 2D RVEs, while 3D RVEs were constructed statistically with randomly distributed phases. A dislocation-based model is used to describe the flow curve of each ferrite and martensite phase separately as a function of carbon partitioning and microstructural features. Numerical tensile tests of RVE were carried out using the ABAQUS/Standard code to predict the flow behaviour of DP steels. It is observed that 2D plane strain modelling gives an underpredicted flow curve for DP steels, while the 3D modelling gives a quantitatively reasonable description of flow curve in comparison to the experimental data. In this work, a von Mises stress correlation factor σ 3D /σ 2D has been identified to compare the predicted flow curves of these two dimensionalities showing a third order polynomial relation with respect to martensite fraction and a second order polynomial relation with respect to equivalent plastic strain, respectively. The quantification of this polynomial correlation factor is performed based on laboratory-annealed DP600 chemistry with varying martensite content and it is validated for industrially produced DP qualities with various chemistry, strength level and martensite fraction.
Thermal relaxation of molecular oxygen in collisions with nitrogen atoms
Energy Technology Data Exchange (ETDEWEB)
Andrienko, Daniil A., E-mail: daniila@umich.edu; Boyd, Iain D. [Department of Aerospace Engineering, University of Michigan, 1320 Beal Ave., Ann Arbor, Michigan 48108 (United States)
2016-07-07
Investigation of O{sub 2}–N collisions is performed by means of the quasi-classical trajectory method on the two lowest ab initio potential energy surfaces at temperatures relevant to hypersonic flows. A complete set of bound–bound and bound–free transition rates is obtained for each precollisional rovibrational state. Special attention is paid to the vibrational and rotational relaxations of oxygen as a result of chemically non-reactive interaction with nitrogen atoms. The vibrational relaxation of oxygen partially occurs via the formation of an intermediate NO{sub 2} complex. The efficient energy randomization results in rapid vibrational relaxation at low temperatures, compared to other molecular systems with a purely repulsive potential. The vibrational relaxation time, computed by means of master equation studies, is nearly an order of magnitude lower than the relaxation time in N{sub 2}–O collisions. The rotational nonequilibrium starts to play a significant effect at translational temperatures above 8000 K. The present work provides convenient relations for the vibrational and rotational relaxation times as well as for the quasi-steady dissociation rate coefficient and thus fills a gap in data due to a lack of experimental measurements for this system.
Space station electrical power distribution analysis using a load flow approach
Emanuel, Ervin M.
1987-01-01
The space station's electrical power system will evolve and grow in a manner much similar to the present terrestrial electrical power system utilities. The initial baseline reference configuration will contain more than 50 nodes or busses, inverters, transformers, overcurrent protection devices, distribution lines, solar arrays, and/or solar dynamic power generating sources. The system is designed to manage and distribute 75 KW of power single phase or three phase at 20 KHz, and grow to a level of 300 KW steady state, and must be capable of operating at a peak of 450 KW for 5 to 10 min. In order to plan far into the future and keep pace with load growth, a load flow power system analysis approach must be developed and utilized. This method is a well known energy assessment and management tool that is widely used throughout the Electrical Power Utility Industry. The results of a comprehensive evaluation and assessment of an Electrical Distribution System Analysis Program (EDSA) is discussed. Its potential use as an analysis and design tool for the 20 KHz space station electrical power system is addressed.
Modeling Mixed Bicycle Traffic Flow: A Comparative Study on the Cellular Automata Approach
Directory of Open Access Journals (Sweden)
Dan Zhou
2015-01-01
Full Text Available Simulation, as a powerful tool for evaluating transportation systems, has been widely used in transportation planning, management, and operations. Most of the simulation models are focused on motorized vehicles, and the modeling of nonmotorized vehicles is ignored. The cellular automata (CA model is a very important simulation approach and is widely used for motorized vehicle traffic. The Nagel-Schreckenberg (NS CA model and the multivalue CA (M-CA model are two categories of CA model that have been used in previous studies on bicycle traffic flow. This paper improves on these two CA models and also compares their characteristics. It introduces a two-lane NS CA model and M-CA model for both regular bicycles (RBs and electric bicycles (EBs. In the research for this paper, many cases, featuring different values for the slowing down probability, lane-changing probability, and proportion of EBs, were simulated, while the fundamental diagrams and capacities of the proposed models were analyzed and compared between the two models. Field data were collected for the evaluation of the two models. The results show that the M-CA model exhibits more stable performance than the two-lane NS model and provides results that are closer to real bicycle traffic.
Post-CHF heat transfer: a non-equilibrium, relaxation model
International Nuclear Information System (INIS)
Jones, O.C. Jr.; Zuber, N.
1977-01-01
Existing phenomenological models of heat transfer in the non-equilibrium, liquid-deficient, dispersed flow regime can sometimes predict the thermal behavior fairly well but are quite complex, requiring coupled simultaneous differential equations to describe the axial gradients of mass and energy along with those of droplet acceleration and size. In addition, empirical relations are required to express the droplet breakup and increased effective heat transfer due to holdup. This report describes the development of a different approach to the problem. It is shown that the non-equilibrium component of the total energy can be expressed as a first order, inhomogeneous relaxation equation in terms of one variable coefficient termed the Superheat Relaxation number. A demonstration is provided to show that this relaxation number can be correlated using local variables in such a manner to allow the single non-equilibrium equation to accurately calculate the effects of mass velocity and heat flux along with tube length, diameter, and critical quality for equilibrium qualities from 0.13 to over 3.0
International Nuclear Information System (INIS)
Stosic, Z.V.; Stevanovic, V.D.
2001-01-01
A methodology for the simulation and analysis of one-phase and two-phase coolant flows around one or a row of spacers is presented. It is based on the multidimensional two-fluid mass, momentum and energy balance equations and application of adequate turbulence models. Necessary closure laws for interfacial transfer processes are presented. The stated general approach enables simulation and analyses of reactor coolant flow around spacers on different scale levels of the rod bundle geometry: detailed modelling of coolant flow around spacers and investigation of the influence of spacer's geometry on the coolant thermal-hydraulics, as well as prediction of global thermal-hydraulic parameters within the whole rod bundle with the investigation of the influence of rows of spacers on the bulk thermal-hydraulic processes. Sample problems are included illustrating these different modelling approaches. (author)
Chen, Chung-Yang; Hong, Ya-Chun; Chen, Pei-Chi
2014-01-01
Software development relies heavily on teamwork; determining how to streamline this collaborative development is an essential training subject in computer and software engineering education. A team process known as the meetings-flow (MF) approach has recently been introduced in software capstone projects in engineering programs at various…
DEFF Research Database (Denmark)
Shuai, Hang; Ai, Xiaomeng; Wen, Jinyu
2017-01-01
This paper proposes a hybrid approximate dynamic programming (ADP) approach for the multiple time-period optimal power flow in integrated gas and power systems. ADP successively solves Bellman's equation to make decisions according to the current state of the system. So, the updated near future...
DEFF Research Database (Denmark)
Obro, Nina Friesgaard; Madsen, Hans O.; Ryder, Lars Peter
2011-01-01
defined cell populations with subsequent analyses of leukemia-associated cytogenetic and molecular marker. The approaches described here optimize the use of the same tube of unfixed, antibody-stained BM cells for flow-sorting of small cell populations and subsequent exploratory FISH and PCR-based analyses....
Crisanti, A; Leuzzi, L; Paoluzzi, M
2011-09-01
The interrelation of dynamic processes active on separated time-scales in glasses and viscous liquids is investigated using a model displaying two time-scale bifurcations both between fast and secondary relaxation and between secondary and structural relaxation. The study of the dynamics allows for predictions on the system relaxation above the temperature of dynamic arrest in the mean-field approximation, that are compared with the outcomes of the equations of motion directly derived within the Mode Coupling Theory (MCT) for under-cooled viscous liquids. By varying the external thermodynamic parameters, a wide range of phenomenology can be represented, from a very clear separation of structural and secondary peak in the susceptibility loss to excess wing structures.
A Primal-Dual Approach for a Total Variation Wasserstein Flow
Benning, Martin; Calatroni, Luca; Dü ring, Bertram; Schö nlieb, Carola-Bibiane
2013-01-01
We consider a nonlinear fourth-order diffusion equation that arises in denoising of image densities. We propose an implicit time-stepping scheme that employs a primal-dual method for computing the subgradient of the total variation seminorm. The constraint on the dual variable is relaxed by adding a penalty term, depending on a parameter that determines the weight of the penalisation. The paper is furnished with some numerical examples showing the denoising properties of the model considered. © 2013 Springer-Verlag.
Study of blood flow in several benchmark micro-channels using a two-fluid approach
Wu, Wei-Tao; Yang, Fang; Antaki, James F.; Aubry, Nadine; Massoudi, Mehrdad
2015-01-01
It is known that in a vessel whose characteristic dimension (e.g., its diameter) is in the range of 20 to 500 microns, blood behaves as a non-Newtonian fluid, exhibiting complex phenomena, such as shear-thinning, stress relaxation, and also multi-component behaviors, such as the Fahraeus effect, plasma-skimming, etc. For describing these non-Newtonian and multi-component characteristics of blood, using the framework of mixture theory, a two-fluid model is applied, where the plasma is treated ...
Ber analysis of the box relaxation for BPSK signal recovery
Thrampoulidis, Christos; Abbasi, Ehsan; Xu, Weiyu; Hassibi, Babak
2016-01-01
We study the problem of recovering an n-dimensional BPSK signal from m linear noise-corrupted measurements using the box relaxation method which relaxes the discrete set {±1}n to the convex set [-1,1]n to obtain a convex optimization algorithm followed by hard thresholding. When the noise and measurement matrix have iid standard normal entries, we obtain an exact expression for the bit-wise probability of error Pe in the limit of n and m growing and m/n fixed. At high SNR our result shows that the Pe of box relaxation is within 3dB of the matched filter bound (MFB) for square systems, and that it approaches the (MFB) as m grows large compared to n. Our results also indicate that as m, n → ∞, for any fixed set of size k, the error events of the corresponding k bits in the box relaxation method are independent.
Ber analysis of the box relaxation for BPSK signal recovery
Thrampoulidis, Christos
2016-06-24
We study the problem of recovering an n-dimensional BPSK signal from m linear noise-corrupted measurements using the box relaxation method which relaxes the discrete set {±1}n to the convex set [-1,1]n to obtain a convex optimization algorithm followed by hard thresholding. When the noise and measurement matrix have iid standard normal entries, we obtain an exact expression for the bit-wise probability of error Pe in the limit of n and m growing and m/n fixed. At high SNR our result shows that the Pe of box relaxation is within 3dB of the matched filter bound (MFB) for square systems, and that it approaches the (MFB) as m grows large compared to n. Our results also indicate that as m, n → ∞, for any fixed set of size k, the error events of the corresponding k bits in the box relaxation method are independent.
Theoretical model of intravascular paramagnetic tracers effect on tissue relaxation
DEFF Research Database (Denmark)
Kjølby, Birgitte Fuglsang; Østergaard, Leif; Kiselev, Valerij G
2006-01-01
The concentration of MRI tracers cannot be measured directly by MRI and is commonly evaluated indirectly using their relaxation effect. This study develops a comprehensive theoretical model to describe the transverse relaxation in perfused tissue caused by intravascular tracers. The model takes...... into account a number of individual compartments. The signal dephasing is simulated in a semianalytical way by embedding Monte Carlo simulations in the framework of analytical theory. This approach yields a tool for fast, realistic simulation of the change in the transverse relaxation. The results indicate...... with bulk blood. The enhancement of relaxation in tissue is due to the contrast in magnetic susceptibility between blood vessels and parenchyma induced by the presence of paramagnetic tracer. Beyond the perfusion measurements, the results can be applied to quantitation of functional MRI and to vessel size...
^{129} Xe NMR Relaxation-Based Macromolecular Sensing
Energy Technology Data Exchange (ETDEWEB)
Gomes, Muller D. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division; Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; Dao, Phuong [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division; Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; Jeong, Keunhong [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division; Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; Slack, Clancy C. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division; Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; Vassiliou, Christophoros C. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; Finbloom, Joel A. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; Francis, Matthew B. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division; Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; Wemmer, David E. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Physical Biosciences Division; Pines, Alexander [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division; Univ. of California, Berkeley, CA (United States). Dept. of Chemistry
2016-07-29
A ^{129}Xe NMR relaxation-based sensing approach is reported on that exploits changes in the bulk xenon relaxation rate induced by slowed tumbling of a cryptophane-based sensor upon target binding. The amplification afforded by detection of the bulk dissolved xenon allows sensitive detection of targets. The sensor comprises a xenon-binding cryptophane cage, a target interaction element, and a metal chelating agent. Xenon associated with the target-bound cryptophane cage is rapidly relaxed and then detected after exchange with the bulk. Here we show that large macromolecular targets increase the rotational correlation time of xenon, increasing its relaxation rate. Upon binding of a biotin-containing sensor to avidin at 1.5 μM concentration, the free xenon T_{2} is reduced by a factor of 4.
Relaxation and kinetics in scalar field theories
International Nuclear Information System (INIS)
Boyanovsky, D.; Lawrie, I.D.; Lee, D.
1996-01-01
A new approach to the dynamics of relaxation and kinetics of thermalization in a scalar field theory is presented that incorporates the relevant time scales through the resummation of hard thermal loops. An alternative derivation of the kinetic equations for the open-quote open-quote quasiparticle close-quote close-quote distribution functions is obtained that allows a clear understanding of the different open-quote open-quote coarse-graining close-quote close-quote approximations usually involved in a kinetic description. This method leads to a systematic perturbative expansion to obtain the kinetic equations including hard thermal loop resummation and to an improvement including renormalization, off-shell effects, and contributions that change chemical equilibrium on short time scales. As a by-product of these methods we establish the equivalence between the relaxation time scale in the linearized equation of motion of the quasiparticles and the thermalization time scale of the quasiparticle distribution function in the open-quote open-quote relaxation time approximation close-quote close-quote including hard thermal loop effects. Hard thermal loop resummation dramatically modifies the scattering rate for long wavelength modes as compared to the usual (semi)classical estimate. Relaxation and kinetics are studied both in the unbroken and broken symmetry phases of the theory. The broken symmetry phase also provides the setting to obtain the contribution to the kinetic equations from processes that involve decay of a heavy scalar into light scalar particles in the medium. copyright 1996 The American Physical Society
Energy Technology Data Exchange (ETDEWEB)
Hollingsworth, Jennifer A. [Los Alamos National Laboratory; Palaniappan, Kumaranand [Los Alamos National Laboratory; Laocharoensuk, Rawiwan [National Science and Technology Center, Thailand; Smith, Nickolaus A. [Los Alamos National Laboratory; Dickerson, Robert M. [Los Alamos National Laboratory; Casson, Joanna L. [Los Alamos National Laboratory; Baldwin, Jon K. [Los Alamos National Laboratory
2012-06-07
Semiconductor nanowires (SC-NWs) have potential applications in diverse technologies from nanoelectronics and photonics to energy harvesting and storage due to their quantum-confined opto-electronic properties coupled with their highly anisotropic shape. Here, we explore new approaches to an important solution-based growth method known as solution-liquid-solid (SLS) growth. In SLS, molecular precursors are reacted in the presence of low-melting metal nanoparticles that serve as molten fluxes to catalyze the growth of the SC-NWs. The mechanism of growth is assumed to be similar to that of vapor-liquid-solid (VLS) growth, with the clear distinctions of being conducted in solution in the presence of coordinating ligands and at relatively lower temperatures (<300 C). The resultant SC-NWs are soluble in common organic solvents and solution processable, offering advantages such as simplified processing, scale-up, ultra-small diameters for quantum-confinement effects, and flexible choice of materials from group III-V to groups II-VI, IV-VI, as well as truly ternary I-III-VI semiconductors as we recently demonstrates. Despite these advantages of SLS growth, VLS offers several clear opportunities not allowed by conventional SLS. Namely, VLS allows sequential addition of precursors for facile synthesis of complex axial heterostructures. In addition, growth proceeds relatively slowly compared to SLS, allowing clear assessments of growth kinetics. In order to retain the materials and processing flexibility afforded by SLS, but add the elements of controlled growth afforded by VLS, we transformed SLS into a flow based method by adapting it to synthesis in a microfluidic system. By this new method - so-called 'flow-SLS' (FSLS) - we have now demonstrated unprecedented fabrication of multi-segmented SC-NWs, e.g., 8-segmented CdSe/ZnSe defined by either compositionally abrupt or alloyed interfaces as a function of growth conditions. In addition, we have studied growth
Parametric distribution approach for flow availability in small hydro potential analysis
Abdullah, Samizee; Basri, Mohd Juhari Mat; Jamaluddin, Zahrul Zamri; Azrulhisham, Engku Ahmad; Othman, Jamel
2016-10-01
Small hydro system is one of the important sources of renewable energy and it has been recognized worldwide as clean energy sources. Small hydropower generation system uses the potential energy in flowing water to produce electricity is often questionable due to inconsistent and intermittent of power generated. Potential analysis of small hydro system which is mainly dependent on the availability of water requires the knowledge of water flow or stream flow distribution. This paper presented the possibility of applying Pearson system for stream flow availability distribution approximation in the small hydro system. By considering the stochastic nature of stream flow, the Pearson parametric distribution approximation was computed based on the significant characteristic of Pearson system applying direct correlation between the first four statistical moments of the distribution. The advantage of applying various statistical moments in small hydro potential analysis will have the ability to analyze the variation shapes of stream flow distribution.
Energy Technology Data Exchange (ETDEWEB)
Guillemaud, V
2007-03-15
This thesis is devoted to the modelling and numerical simulation of liquid-vapor flows. In order to describe these phase transition flows, a two-fluid two-pressure approach is considered. This description of the liquid-vapor mixing is associated to the seven-equation model introduced by Baer and Nunziato. This work investigates the properties of this model in order to simulate the phase transition flows occurring in nuclear engineering. First, a theoretical thermodynamic framework is constructed to describe the liquid-vapor mixing. Provided with this framework, various modelling choices are suggested for the interaction terms between the phases. These closure laws comply with an entropy inequality. The mathematical properties of this model are thereafter examined. The convective part is associated to a nonconservative hyperbolic system. First, we focus on the definition of its weak solutions. Several flow regimes for the two-phase mixing derive from this analysis. Such regimes for the two-phase flows are analogous to the torrential and fluvial regimes for the shallow-water equations. Furthermore, we establish the linear and nonlinear stabilities of the liquid-vapor equilibrium. Finally, the implementation of a turbulence model and the introduction of a reconstruction process for the interfacial area are investigated in order to refine the description of the interfacial transfers. Using a fractional step approach, a Finite Volume method is at last constructed to simulate this model. First, various nonconservative adaptations of standard Riemann solvers are developed to approach the convective part. Unlike the classic nonconservative framework, these schemes converge towards the same solution. Furthermore, a new relaxation scheme is proposed to approach the interfacial transfers. Provided with these schemes, the whole numerical method preserves the liquid-vapor equilibria. Using this numerical method, a careful comparison between the one- and two-pressure two
Fluid-elastic instability in a confined annular flow: an experimental and analytical approach
Energy Technology Data Exchange (ETDEWEB)
Porcher, G.; Langre, E. de
1996-12-31
Self excitation of slender structures under axial flow have been reported in a large variety of local flow configurations. This paper reports the result of a research program, both experimental and analytical, aimed at the result of the basic phenomena leading to such instabilities. A cylindrical body with a diffuser is put in a confined annular flow of water. A case of flutter is observed and analysed with a classical potential flow method and with a friction based model. Closed-form solutions are proposed and the origin of the flutter instability is discussed. (authors). 25 refs., 6 figs., 5 tabs.
Petrou, Zisis I.; Xian, Yang; Tian, YingLi
2018-04-01
Estimation of sea ice motion at fine scales is important for a number of regional and local level applications, including modeling of sea ice distribution, ocean-atmosphere and climate dynamics, as well as safe navigation and sea operations. In this study, we propose an optical flow and super-resolution approach to accurately estimate motion from remote sensing images at a higher spatial resolution than the original data. First, an external example learning-based super-resolution method is applied on the original images to generate higher resolution versions. Then, an optical flow approach is applied on the higher resolution images, identifying sparse correspondences and interpolating them to extract a dense motion vector field with continuous values and subpixel accuracies. Our proposed approach is successfully evaluated on passive microwave, optical, and Synthetic Aperture Radar data, proving appropriate for multi-sensor applications and different spatial resolutions. The approach estimates motion with similar or higher accuracy than the original data, while increasing the spatial resolution of up to eight times. In addition, the adopted optical flow component outperforms a state-of-the-art pattern matching method. Overall, the proposed approach results in accurate motion vectors with unprecedented spatial resolutions of up to 1.5 km for passive microwave data covering the entire Arctic and 20 m for radar data, and proves promising for numerous scientific and operational applications.
Digital growth of thick N-polar InGaN films on relaxed InGaN pseudosubstrates
Lund, Cory; Hestroffer, Karine; Hatui, Nirupam; Nakamura, Shuji; DenBaars, Steven P.; Mishra, Umesh K.; Keller, Stacia
2017-11-01
Smooth relaxed N-polar InGaN films were grown by metal-organic CVD (MOCVD) on N-polar InGaN pseudosubstrates (PSs) using a novel digital approach consisting of a constant In precursor flow with the pulsed injection of H2 carrier gas. InGaN layers grown on PSs exhibited an In composition of about 50% higher than those of the layers grown on N-polar GaN templates, assuming the in-plane lattice constant of the relaxed PSs, corresponding to In0.11Ga0.89N. Additionally, the luminescence recorded from InGaN layers grown on PSs at 490 nm was twice as intense as that obtained from the layers deposited on coloaded GaN-on-sapphire templates, which emitted at 430 nm.
STRUCTURAL STRESS RELAXATION IN STAINLESS INSTABILITY STEEL
Directory of Open Access Journals (Sweden)
S. Lyabuk
2017-06-01
Full Text Available The approach to the description of conditions of martensitic transformation in austenitic steel is advanced. Transformation induced hardening is the result of Le Chatelier principle in instability alloys. The phase transformation in austenitic instability stainless steel is the cause of reduction of grain refining and increase of strength. It was experimentally shown that physical-mechanical characteristics of the prepared materials were defined by the structure and inhomogeneous distribution of the hardening phase within a grain. The reasons for high thermal stability of inverse austenitic were established. The factors determining the inverse austenitic relaxation resistibility and resources for its increasing were revealed.
Anisotropic hydrodynamics for conformal Gubser flow
Energy Technology Data Exchange (ETDEWEB)
Strickland, Michael; Nopoush, Mohammad [Kent State University, Kent OH 44242 (United States); Ryblewski, Radoslaw [The H. Niewodniczański Institute of Nuclear Physics, Polish Academy of Sciences, PL-31342 Kraków (Poland)
2016-12-15
In this proceedings contribution, we review the exact solution of the anisotropic hydrodynamics equations for a system subject to Gubser flow. For this purpose, we use the leading-order anisotropic hydrodynamics equations which assume that the distribution function is ellipsoidally symmetric in local-rest-frame momentum. We then prove that the SO(3){sub q} symmetry in de Sitter space constrains the anisotropy tensor to be of spheroidal form with only one independent anisotropy parameter remaining. As a consequence, the exact solution reduces to the problem of solving two coupled non-linear differential equations. We show that, in the limit that the relaxation time goes to zero, one obtains Gubser's ideal hydrodynamic solution and, in the limit that the relaxation time goes to infinity, one obtains the exact free streaming solution obtained originally by Denicol et al. For finite relaxation time, we solve the equations numerically and compare to the exact solution of the relaxation-time-approximation Boltzmann equation subject to Gubser flow. Using this as our standard, we find that anisotropic hydrodynamics describes the spatio-temporal evolution of the system better than all currently known dissipative hydrodynamics approaches.
Anisotropic hydrodynamics for conformal Gubser flow
International Nuclear Information System (INIS)
Strickland, Michael; Nopoush, Mohammad; Ryblewski, Radoslaw
2016-01-01
In this proceedings contribution, we review the exact solution of the anisotropic hydrodynamics equations for a system subject to Gubser flow. For this purpose, we use the leading-order anisotropic hydrodynamics equations which assume that the distribution function is ellipsoidally symmetric in local-rest-frame momentum. We then prove that the SO(3)_q symmetry in de Sitter space constrains the anisotropy tensor to be of spheroidal form with only one independent anisotropy parameter remaining. As a consequence, the exact solution reduces to the problem of solving two coupled non-linear differential equations. We show that, in the limit that the relaxation time goes to zero, one obtains Gubser's ideal hydrodynamic solution and, in the limit that the relaxation time goes to infinity, one obtains the exact free streaming solution obtained originally by Denicol et al. For finite relaxation time, we solve the equations numerically and compare to the exact solution of the relaxation-time-approximation Boltzmann equation subject to Gubser flow. Using this as our standard, we find that anisotropic hydrodynamics describes the spatio-temporal evolution of the system better than all currently known dissipative hydrodynamics approaches.
Approaches to Modeling Coupled Flow and Reaction in a 2-D Cementation Experiment
Energy Technology Data Exchange (ETDEWEB)
Steefel, Carl; Cochepin, B.; Trotignon, L.; Bildstein, O.; Steefel, C.; Lagneau, V.; van der Lee, J.
2008-04-01
Porosity evolution at reactive interfaces is a key process that governs the evolution and performances of many engineered systems that have important applications in earth and environmental sciences. This is the case, for example, at the interface between cement structures and clays in deep geological nuclear waste disposals. Although in a different transport regime, similar questions arise for permeable reactive barriers used for biogeochemical remediation in surface environments. The COMEDIE project aims at investigating the coupling between transport, hydrodynamics and chemistry when significant variations of porosity occur. The present work focuses on a numerical benchmark used as a design exercise for the future COMEDIE-2D experiment. The use of reactive transport simulation tools like Hytec and Crunch provides predictions of the physico-chemical evolutions that are expected during the future experiments in laboratory. Focus is given in this paper on the evolution during the simulated experiment of precipitate, permeability and porosity fields. A first case is considered in which the porosity is constant. Results obtained with Crunch and Hytec are in relatively good agreement. Differences are attributable to the models of reactive surface area taken into account for dissolution/precipitation processes. Crunch and Hytec simulations taking into account porosity variations are then presented and compared. Results given by the two codes are in qualitative agreement, with differences attributable in part to the models of reactive surface area for dissolution/precipitation processes. As a consequence, the localization of secondary precipitates predicted by Crunch leads to lower local porosities than for predictions obtained by Hytec and thus to a stronger coupling between flow and chemistry. This benchmark highlights the importance of the surface area model employed to describe systems in which strong porosity variations occur as a result of dissolution
Foreign capital flows, exports and growth in Zambia. A Vecm Approach
Directory of Open Access Journals (Sweden)
Kunofiwa Tsaurai
2015-10-01
Full Text Available This study investigates the causality between FDI net inflows, exports and GDP using Vector Error Correction Model (VECM approach. The words foreign capital flows and FDI are used interchangeably in this study. The findings from the VECM estimation technique is six fold: (1 the study revealed a long run causality relationship running from exports and GDP towards FDI, (2 the study showed a non–significant long run causality relationship running from FDI and exports towards GDP and (3 the existence of a weak long run causality relationship running from FDI and GDP towards exports in Zambia. The study also found out that no short run causality relationship that runs from FDI and exports towards GDP, short run causality running from FDI and GDP towards exports does not exist and there is no short run causality relationship running from exports and GDP towards FDI. Contrary to the theory which says that FDI brings along with it a whole lot of advantages (FDI technological diffusion and spill over effects, the current study found that the impact of FDI in Zambia is not significant in the long run. This is possibly because certain host country locational characteristics that ensures that Zambia can benefit from FDI inflows are not in place or they might be in place but still not yet reached a certain minimum threshold levels. This might be an interesting area for further research. On the backdrop of the findings of this study, the author recommends that the Zambian authorities should formulate and implement export promotion strategies and economic growth enhancement initiatives in order to be able to attract more FDI.
Itu, Lucian; Rapaka, Saikiran; Passerini, Tiziano; Georgescu, Bogdan; Schwemmer, Chris; Schoebinger, Max; Flohr, Thomas; Sharma, Puneet; Comaniciu, Dorin
2016-07-01
Fractional flow reserve (FFR) is a functional index quantifying the severity of coronary artery lesions and is clinically obtained using an invasive, catheter-based measurement. Recently, physics-based models have shown great promise in being able to noninvasively estimate FFR from patient-specific anatomical information, e.g., obtained from computed tomography scans of the heart and the coronary arteries. However, these models have high computational demand, limiting their clinical adoption. In this paper, we present a machine-learning-based model for predicting FFR as an alternative to physics-based approaches. The model is trained on a large database of synthetically generated coronary anatomies, where the target values are computed using the physics-based model. The trained model predicts FFR at each point along the centerline of the coronary tree, and its performance was assessed by comparing the predictions against physics-based computations and against invasively measured FFR for 87 patients and 125 lesions in total. Correlation between machine-learning and physics-based predictions was excellent (0.9994, P machine-learning algorithm with a sensitivity of 81.6%, a specificity of 83.9%, and an accuracy of 83.2%. The correlation was 0.729 (P assessment of FFR. Average execution time went down from 196.3 ± 78.5 s for the CFD model to ∼2.4 ± 0.44 s for the machine-learning model on a workstation with 3.4-GHz Intel i7 8-core processor. Copyright © 2016 the American Physiological Society.
A Modified Cellular Automaton Approach for Mixed Bicycle Traffic Flow Modeling
Directory of Open Access Journals (Sweden)
Xiaonian Shan
2015-01-01
Full Text Available Several previous studies have used the Cellular Automaton (CA for the modeling of bicycle traffic flow. However, previous CA models have several limitations, resulting in differences between the simulated and the observed traffic flow features. The primary objective of this study is to propose a modified CA model for simulating the characteristics of mixed bicycle traffic flow. Field data were collected on physically separated bicycle path in Shanghai, China, and were used to calibrate the CA model using the genetic algorithm. Traffic flow features between simulations of several CA models and field observations were compared. The results showed that our modified CA model produced more accurate simulation for the fundamental diagram and the passing events in mixed bicycle traffic flow. Based on our model, the bicycle traffic flow features, including the fundamental diagram, the number of passing events, and the number of lane changes, were analyzed. We also analyzed the traffic flow features with different traffic densities, traffic components on different travel lanes. Results of the study can provide important information for understanding and simulating the operations of mixed bicycle traffic flow.
International Nuclear Information System (INIS)
Sahin, Ahmet Z.
2012-01-01
Highlights: ► The optimality in both heat and fluid flow systems has been investigated. ► A new thermodynamic property has been introduced. ► The second law of thermodynamics was extended to present the temheat balance that included the temheat destruction. ► The principle of temheat destruction minimization was introduced. ► It is shown that the rate of total temheat destruction is minimized in steady heat conduction and fluid flow problems. - Abstract: Heat transfer and fluid flow processes exhibit similarities as they occur naturally and are governed by the same type of differential equations. Natural phenomena occur always in an optimum way. In this paper, the natural optimality that exists in the heat transfer and fluid flow processes is investigated. In this regard, heat transfer and fluid flow problems are treated as optimization problems. We discovered a thermodynamic quantity that is optimized during the steady heat transfer and fluid flow processes. Consequently, a new thermodynamic property, the so called temheat, is introduced using the second law of thermodynamics and the definition of entropy. It is shown, through several examples, that overall temheat destruction is always minimized in steady heat and fluid flow processes. The principle of temheat destruction minimization that is based on the temheat balance equation provides a better insight to understand how the natural flow processes take place.
Real-Time and Resilient Intrusion Detection: A Flow-Based Approach
Hofstede, R.J.; Pras, Aiko
Due to the demanding performance requirements of packet-based monitoring solutions on network equipment, flow-based intrusion detection systems will play an increasingly important role in current high-speed networks. The required technologies are already available and widely deployed: NetFlow and
H.R. Barnard; C.B. Graham; W.J. van Verseveld; J.R. Brooks; B.J. Bond; J.J. McDonnell
2010-01-01
Mechanistic assessment of how transpiration influences subsurface flow is necessary to advance understanding of catchment hydrology. We conducted a 24-day, steady-state irrigation experiment to quantify the relationships among soil moisture, transpiration and hillslope subsurface flow. Our objectives were to: (1) examine the time lag between maximum transpiration and...
Margaris, Konstantinos N; Nepiyushchikh, Zhanna; Zawieja, David C; Moore, James; Black, Richard A
2016-02-01
We describe the development of an optical flow visualization method for resolving the flow velocity vector field in lymphatic vessels in vitro. The aim is to develop an experimental protocol for accurately estimating flow parameters, such as flow rate and shear stresses, with high spatial and temporal resolution. Previous studies in situ have relied on lymphocytes as tracers, but their low density resulted in a reduced spatial resolution whereas the assumption that the flow was fully developed in order to determine the flow parameters of interest may not be valid, especially in the vicinity of the valves, where the flow is undoubtedly more complex. To overcome these issues, we have applied the time-resolved microparticle image velocimetry (μ -PIV) technique, a well-established method that can provide increased spatial and temporal resolution that this transient flow demands. To that end, we have developed a custom light source, utilizing high-power light-emitting diodes, and associated control and image processing software. This paper reports the performance of the system and the results of a series of preliminary experiments performed on vessels isolated from rat mesenteries, demonstrating, for the first time, the successful application of the μ -PIV technique in these vessels.
International Nuclear Information System (INIS)
More, Ameya; Dutta, B.K.; Durgaprasad, P.V.; Arya, A.K.
2012-01-01
Fe-Cr based Ferritic/Martensitic (F/M) steels are the candidate structural materials for future fusion reactors. In this work, a multi-scale approach comprising atomistic Molecular Dynamics (MD) simulations and Discrete Dislocation Dynamics (DDD) simulations are used to model the effect of irradiation dose on the flow stress of F/M steels. At the atomic scale, molecular dynamics simulations are used to study the dislocation interaction with irradiation induced defects, i.e. voids and He bubbles. Whereas, the DDD simulations are used to estimate the change in flow stress of the material as a result of irradiation hardening. (author)
International Nuclear Information System (INIS)
Xu Baoxing; Chen Xi; Yue Zhufeng
2010-01-01
We present the possibility of extracting the strain rate sensitivity, activation volume and Helmholtz free energy (for dislocation activation) using just one indentation stress relaxation test, and the approach is demonstrated with polycrystalline copper. The Helmholtz free energy measured from indentation relaxation agrees well with that from the conventional compression relaxation test, which validates the proposed approach. From the indentation relaxation test, the measured indentation strain rate sensitivity exponent is found to be slightly larger, and the indentation activation volume much smaller, than their counterparts from the compression test. The results indicate the involvement of multiple dislocation mechanisms in the indentation test.
Liu, Richeng; Li, Bo; Jiang, Yujing; Yu, Liyuan
2018-01-01
Hydro-mechanical properties of rock fractures are core issues for many geoscience and geo-engineering practices. Previous experimental and numerical studies have revealed that shear processes could greatly enhance the permeability of single rock fractures, yet the shear effects on hydraulic properties of fractured rock masses have received little attention. In most previous fracture network models, single fractures are typically presumed to be formed by parallel plates and flow is presumed to obey the cubic law. However, related studies have suggested that the parallel plate model cannot realistically represent the surface characters of natural rock fractures, and the relationship between flow rate and pressure drop will no longer be linear at sufficiently large Reynolds numbers. In the present study, a numerical approach was established to assess the effects of shear on the hydraulic properties of 2-D discrete fracture networks (DFNs) in both linear and nonlinear regimes. DFNs considering fracture surface roughness and variation of aperture in space were generated using an originally developed code DFNGEN. Numerical simulations by solving Navier-Stokes equations were performed to simulate the fluid flow through these DFNs. A fracture that cuts through each model was sheared and by varying the shear and normal displacements, effects of shear on equivalent permeability and nonlinear flow characteristics of DFNs were estimated. The results show that the critical condition of quantifying the transition from a linear flow regime to a nonlinear flow regime is: 10-4 〈 J hydraulic gradient. When the fluid flow is in a linear regime (i.e., J reduce the equivalent permeability significantly in the orientation perpendicular to the sheared fracture as much as 53.86% when J = 1, shear displacement Ds = 7 mm, and normal displacement Dn = 1 mm. By fitting the calculated results, the mathematical expression for δ2 is established to help choose proper governing equations when
Benke, Arthur C
2018-03-31
The majority of food web studies are based on connectivity, top-down impacts, bottom-up flows, or trophic position (TP), and ecologists have argued for decades which is best. Rarely have any two been considered simultaneously. The present study uses a procedure that integrates the last three approaches based on taxon-specific secondary production and gut analyses. Ingestion flows are quantified to create a flow web and the same data are used to quantify TP for all taxa. An individual predator's impacts also are estimated using the ratio of its ingestion (I) of each prey to prey production (P) to create an I/P web. This procedure was applied to 41 invertebrate taxa inhabiting submerged woody habitat in a southeastern U.S. river. A complex flow web starting with five basal food resources had 462 flows >1 mg·m -2 ·yr -1 , providing far more information than a connectivity web. Total flows from basal resources to primary consumers/omnivores were dominated by allochthonous amorphous detritus and ranged from 1 to >50,000 mg·m -2 ·yr -1 . Most predator-prey flows were much lower (1,000 mg·m -2 ·yr -1 . The I/P web showed that 83% of individual predator impacts were weak (90%). Quantitative estimates of TP ranged from 2 to 3.7, contrasting sharply with seven integer-based trophic levels based on longest feeding chain. Traditional omnivores (TP = 2.4-2.9) played an important role by consuming more prey and exerting higher impacts on primary consumers than strict predators (TP ≥ 3). This study illustrates how simultaneous quantification of flow pathways, predator impacts, and TP together provide an integrated characterization of natural food webs. © 2018 by the Ecological Society of America.
Directory of Open Access Journals (Sweden)
Bruno Tardiole Kuehne
Full Text Available This paper proposes a system named AWSCS (Automatic Web Service Composition System to evaluate different approaches for automatic composition of Web services, based on QoS parameters that are measured at execution time. The AWSCS is a system to implement different approaches for automatic composition of Web services and also to execute the resulting flows from these approaches. Aiming at demonstrating the results of this paper, a scenario was developed, where empirical flows were built to demonstrate the operation of AWSCS, since algorithms for automatic composition are not readily available to test. The results allow us to study the behaviour of running composite Web services, when flows with the same functionality but different problem-solving strategies were compared. Furthermore, we observed that the influence of the load applied on the running system as the type of load submitted to the system is an important factor to define which approach for the Web service composition can achieve the best performance in production.
Study of blood flow in several benchmark micro-channels using a two-fluid approach.
Wu, Wei-Tao; Yang, Fang; Antaki, James F; Aubry, Nadine; Massoudi, Mehrdad
2015-10-01
It is known that in a vessel whose characteristic dimension (e.g., its diameter) is in the range of 20 to 500 microns, blood behaves as a non-Newtonian fluid, exhibiting complex phenomena, such as shear-thinning, stress relaxation, and also multi-component behaviors, such as the Fahraeus effect, plasma-skimming, etc. For describing these non-Newtonian and multi-component characteristics of blood, using the framework of mixture theory, a two-fluid model is applied, where the plasma is treated as a Newtonian fluid and the red blood cells (RBCs) are treated as shear-thinning fluid. A computational fluid dynamic (CFD) simulation incorporating the constitutive model was implemented using OpenFOAM® in which benchmark problems including a sudden expansion and various driven slots and crevices were studied numerically. The numerical results exhibited good agreement with the experimental observations with respect to both the velocity field and the volume fraction distribution of RBCs.
Tanaka, H.; Shiomi, Y.; Ma, K.-F.
2017-11-01
To understand the fault zone fluid flow-like structure, namely the ductile deformation structure, often observed in the geological field (e.g., Ramsay and Huber The techniques of modern structure geology, vol. 1: strain analysis, Academia Press, London, 1983; Hobbs and Ord Structure geology: the mechanics of deforming metamorphic rocks, Vol. I: principles, Elsevier, Amsterdam, 2015), we applied a theoretical approach to estimate the rate of deformation, the shear stress and the time to form a streak-line pattern in the boundary layer of viscous fluids. We model the dynamics of streak lines in laminar boundary layers for Newtonian and pseudoplastic fluids and compare the results to those obtained via laboratory experiments. The structure of deformed streak lines obtained using our model is consistent with experimental observations, indicating that our model is appropriate for understanding the shear rate, flow time and shear stress based on the profile of deformed streak lines in the boundary layer in Newtonian and pseudoplastic viscous materials. This study improves our understanding of the transportation processes in fluids and of the transformation processes in fluid-like materials. Further application of this model could facilitate understanding the shear stress and time history of the fluid flow-like structure of fault zones observed in the field.[Figure not available: see fulltext.
Energy Technology Data Exchange (ETDEWEB)
Johnston, Henry [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Wang, Cong [Colorado School of Mines; Winterfeld, Philip [Colorado School of Mines; Wu, Yu-Shu [Colorado School of Mines
2018-02-14
An efficient modeling approach is described for incorporating arbitrary 3D, discrete fractures, such as hydraulic fractures or faults, into modeling fracture-dominated fluid flow and heat transfer in fractured geothermal reservoirs. This technique allows 3D discrete fractures to be discretized independently from surrounding rock volume and inserted explicitly into a primary fracture/matrix grid, generated without including 3D discrete fractures in prior. An effective computational algorithm is developed to discretize these 3D discrete fractures and construct local connections between 3D fractures and fracture/matrix grid blocks of representing the surrounding rock volume. The constructed gridding information on 3D fractures is then added to the primary grid. This embedded fracture modeling approach can be directly implemented into a developed geothermal reservoir simulator via the integral finite difference (IFD) method or with TOUGH2 technology This embedded fracture modeling approach is very promising and computationally efficient to handle realistic 3D discrete fractures with complicated geometries, connections, and spatial distributions. Compared with other fracture modeling approaches, it avoids cumbersome 3D unstructured, local refining procedures, and increases computational efficiency by simplifying Jacobian matrix size and sparsity, while keeps sufficient accuracy. Several numeral simulations are present to demonstrate the utility and robustness of the proposed technique. Our numerical experiments show that this approach captures all the key patterns about fluid flow and heat transfer dominated by fractures in these cases. Thus, this approach is readily available to simulation of fractured geothermal reservoirs with both artificial and natural fractures.
Ötvös, Sándor B; Mándity, István M; Fülöp, Ferenc
2011-08-01
A simple and efficient flow-based technique is reported for the catalytic deuteration of several model nitrogen-containing heterocyclic compounds which are important building blocks of pharmacologically active materials. A continuous flow reactor was used in combination with on-demand pressure-controlled electrolytic D(2) production. The D(2) source was D(2)O, the consumption of which was very low. The experimental set-up allows the fine-tuning of pressure, temperature, and flow rate so as to determine the optimal conditions for the deuteration reactions. The described procedure lacks most of the drawbacks of the conventional batch deuteration techniques, and additionally is highly selective and reproducible.
New Li-Yau-Hamilton Inequalities for the Ricci Flow via the Space-Time Approach
Chow, Bennett; Knopf, Dan
2002-01-01
We generalize Hamilton's matrix Li-Yau-type Harnack estimate for the Ricci flow by considering the space of all LYH (Li-Yau-Hamilton) quadratics that arise as curvature tensors of space-time connections satisfying the Ricci flow with respect to the natural space-time degenerate metric. As a special case, we employ scaling arguments to derive a linear-type matrix LYH estimate. The new LYH quadratics obtained in this way are associated to the system of the Ricci flow coupled to a 1-form and a 2...
Fratto, Brian E; Katz, Evgeny
2015-05-18
Reversible logic gates, such as the double Feynman gate, Toffoli gate and Peres gate, with 3-input/3-output channels are realized using reactions biocatalyzed with enzymes and performed in flow systems. The flow devices are constructed using a modular approach, where each flow cell is modified with one enzyme that biocatalyzes one chemical reaction. The multi-step processes mimicking the reversible logic gates are organized by combining the biocatalytic cells in different networks. This work emphasizes logical but not physical reversibility of the constructed systems. Their advantages and disadvantages are discussed and potential use in biosensing systems, rather than in computing devices, is suggested. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Kierkegaard, Axel; Boij, Susann; Efraimsson, Gunilla
2010-02-01
Acoustic wave propagation in flow ducts is commonly modeled with time-domain non-linear Navier-Stokes equation methodologies. To reduce computational effort, investigations of a linearized approach in frequency domain are carried out. Calculations of sound wave propagation in a straight duct are presented with an orifice plate and a mean flow present. Results of transmission and reflections at the orifice are presented on a two-port scattering matrix form and are compared to measurements with good agreement. The wave propagation is modeled with a frequency domain linearized Navier-Stokes equation methodology. This methodology is found to be efficient for cases where the acoustic field does not alter the mean flow field, i.e., when whistling does not occur.
Relaxation dispersion in MRI induced by fictitious magnetic fields.
Liimatainen, Timo; Mangia, Silvia; Ling, Wen; Ellermann, Jutta; Sorce, Dennis J; Garwood, Michael; Michaeli, Shalom
2011-04-01
A new method entitled Relaxation Along a Fictitious Field (RAFF) was recently introduced for investigating relaxations in rotating frames of rank ≥ 2. RAFF generates a fictitious field (E) by applying frequency-swept pulses with sine and cosine amplitude and frequency modulation operating in a sub-adiabatic regime. In the present work, MRI contrast is created by varying the orientation of E, i.e. the angle ε between E and the z″ axis of the second rotating frame. When ε > 45°, the amplitude of the fictitious field E generated during RAFF is significantly larger than the RF field amplitude used for transmitting the sine/cosine pulses. Relaxation during RAFF was investigated using an invariant-trajectory approach and the Bloch-McConnell formalism. Dipole-dipole interactions between identical (like) spins and anisochronous exchange (e.g., exchange between spins with different chemical shifts) in the fast exchange regime were considered. Experimental verifications were performed in vivo in human and mouse brain. Theoretical and experimental results demonstrated that changes in ε induced a dispersion of the relaxation rate constants. The fastest relaxation was achieved at ε ≈ 56°, where the averaged contributions from transverse components during the pulse are maximal and the contribution from longitudinal components are minimal. RAFF relaxation dispersion was compared with the relaxation dispersion achieved with off-resonance spin lock T(₁ρ) experiments. As compared with the off-resonance spin lock T(₁ρ) method, a slower rotating frame relaxation rate was observed with RAFF, which under certain experimental conditions is desirable. Copyright © 2011 Elsevier Inc. All rights reserved.
Intra-assembly flow redistribution in LMFBRs: a simple computational approach
International Nuclear Information System (INIS)
Khatib-Rahbar, M.; Cazzoli, E.G.
1983-01-01
The liquid metal fast breeder reactor (LMFBR) core consists of fuel, blanket, control, and shielding assemblies packed in a hexagonal configuration. Radial blanket assemblies occupy peripheral locations in the reactor core and are characterized by steep power gradients, while inner blanket assemblies are located within the fuel assembly region and have higher power levels but flatter distributions. It is due to the presence of this radial power gradient that large sodium temperature distributions exist at full power operation. However, at low power, low flow natural convection conditions, a significant flow redistribution takes place leading to considerable radial temperature flattening. The purpose of the present study is to formulate a simple flow-regime dependent model supported by experimental data for prediction of sodium temperature flattening due to buoyancy-induced flow redistribution in LMFBR subassemblies with significant radial power gradient
An efficient numerical approach for transient simulation of multiphase flow behavior in centrifuges
Hammerich, Simon; Nirschl, Hermann
2016-01-01
The separation process of particles and liquids in centrifuge is a widely used operation in industry. In spite of the long term usage of centrifuges, the knowledge for a detailed characterization of the interaction of the macroscopic processes due the separation is lacking. Reason for this is the complex multiphase flow and the sediment built-up within the machines. The sediment shape influences the flow behavior. The shape is dependent of the rheological behavior of the sediment. Computation...
Using Cash Flows to Predict Bankruptcy of Chemical Companies: Case Study Approach
Siow, Hui Wen
2009-01-01
The intent of this study is to present an argument for the usefulness of cash flow information in bankruptcy prediction, and whether cash flow information provide a superior prediction of business failure over the conventional accrual accounting information. In addition, this dissertation also aim to analyze other important factors leading to bankruptcy, particularly contingent liabilities in which the obligations are not accrued and accounted for, nor are they considered in conventional bank...
Relaxation properties in classical diamagnetism
Carati, A.; Benfenati, F.; Galgani, L.
2011-06-01
It is an old result of Bohr that, according to classical statistical mechanics, at equilibrium a system of electrons in a static magnetic field presents no magnetization. Thus a magnetization can occur only in an out of equilibrium state, such as that produced through the Foucault currents when a magnetic field is switched on. It was suggested by Bohr that, after the establishment of such a nonequilibrium state, the system of electrons would quickly relax back to equilibrium. In the present paper, we study numerically the relaxation to equilibrium in a modified Bohr model, which is mathematically equivalent to a billiard with obstacles, immersed in a magnetic field that is adiabatically switched on. We show that it is not guaranteed that equilibrium is attained within the typical time scales of microscopic dynamics. Depending on the values of the parameters, one has a relaxation either to equilibrium or to a diamagnetic (presumably metastable) state. The analogy with the relaxation properties in the Fermi Pasta Ulam problem is also pointed out.
Onsager relaxation of toroidal plasmas
International Nuclear Information System (INIS)
Samain, A.; Nguyen, F.
1997-01-01
The slow relaxation of isolated toroidal plasmas towards their thermodynamical equilibrium is studied in an Onsager framework based on the entropy metric. The basic tool is a variational principle, equivalent to the kinetic equation, involving the profiles of density, temperature, electric potential, electric current. New minimization procedures are proposed to obtain entropy and entropy production rate functionals. (author)
Anisotropic spin relaxation in graphene
Tombros, N.; Tanabe, S.; Veligura, A.; Jozsa, C.; Popinciuc, M.; Jonkman, H. T.; van Wees, B. J.
2008-01-01
Spin relaxation in graphene is investigated in electrical graphene spin valve devices in the nonlocal geometry. Ferromagnetic electrodes with in-plane magnetizations inject spins parallel to the graphene layer. They are subject to Hanle spin precession under a magnetic field B applied perpendicular
Stochastic and Chaotic Relaxation Oscillations
Grasman, J.; Roerdink, J.B.T.M.
1988-01-01
For relaxation oscillators stochastic and chaotic dynamics are investigated. The effect of random perturbations upon the period is computed. For an extended system with additional state variables chaotic behavior can be expected. As an example, the Van der Pol oscillator is changed into a
Tensions relaxation in Zircaloy-4
International Nuclear Information System (INIS)
Cuniberti, A.M.; Picasso, A.C.
1990-01-01
Traction and stress relaxation studies were performed on polycrystalline Zry-4 at room temperature. The effect of loading velocity on the plastic behaviour of the material is discussed, analysing log σ vs. log dε/dt at different deformation levels. The contribution introduced by the testing machine was taken into account in data evaluation. (Author). 7 refs., 3 figs., 3 tabs
Dependence of Brownian and Néel relaxation times on magnetic field strength
International Nuclear Information System (INIS)
Deissler, Robert J.; Wu, Yong; Martens, Michael A.
2014-01-01
Purpose: In magnetic particle imaging (MPI) and magnetic particle spectroscopy (MPS) the relaxation time of the magnetization in response to externally applied magnetic fields is determined by the Brownian and Néel relaxation mechanisms. Here the authors investigate the dependence of the relaxation times on the magnetic field strength and the implications for MPI and MPS. Methods: The Fokker–Planck equation with Brownian relaxation and the Fokker–Planck equation with Néel relaxation are solved numerically for a time-varying externally applied magnetic field, including a step-function, a sinusoidally varying, and a linearly ramped magnetic field. For magnetic fields that are applied as a step function, an eigenvalue approach is used to directly calculate both the Brownian and Néel relaxation times for a range of magnetic field strengths. For Néel relaxation, the eigenvalue calculations are compared to Brown's high-barrier approximation formula. Results: The relaxation times due to the Brownian or Néel mechanisms depend on the magnitude of the applied magnetic field. In particular, the Néel relaxation time is sensitive to the magnetic field strength, and varies by many orders of magnitude for nanoparticle properties and magnetic field strengths relevant for MPI and MPS. Therefore, the well-known zero-field relaxation times underestimate the actual relaxation times and, in particular, can underestimate the Néel relaxation time by many orders of magnitude. When only Néel relaxation is present—if the particles are embedded in a solid for instance—the authors found that there can be a strong magnetization response to a sinusoidal driving field, even if the period is much less than the zero-field relaxation time. For a ferrofluid in which both Brownian and Néel relaxation are present, only one relaxation mechanism may dominate depending on the magnetic field strength, the driving frequency (or ramp time), and the phase of the magnetization relative to the
Directory of Open Access Journals (Sweden)
Marius Alexandru PANAIT
2014-06-01
Full Text Available The pulsating heated flows are traditionally a difficult subject to treat with conventional hot wire or film methods. Special factors that complicate matters are flow reversal and non linear flow effects of vortices and wire probe wake disturbances on the heat transfer to the hot film or wire sensor in heated pulsating flows. The presence of these strongly nonlinear and unknown terms leads to great difficulties in calibration of hot film probes in this particular regime. The paper analyses the current state of matters in the field and reports a series of solutions that have been practically tested in a case of a high speed pulsated heated flow. Normally such measurements are made in a non-contact fashion using a LDV system or various visualization techniques but there have been recent attempts to use a constant temperature hot wire anemometer system (CTA.To obtain meaningful calibration for hot wire films in hot pulsating flows, a comparison system on other principles (LDV was used, as well as a specially designed nozzle to replace the calibrator unit that could not be operated with heated fluid due to structural integrity reasons. The method as described below works well for the expected speed range that could be generated using the special nozzle.
Inhomogeneous MUSIG Model - a population balance approach for polydispersed bubbly flows
International Nuclear Information System (INIS)
Frank, T.; Zwart, P.J.; Shi, J.; Krepper, E.; Lucas, D.; Rohde, U.
2005-01-01
Many flow regimes in Nuclear Reactor Safety (NRS) Research are characterized by multiphase flows, with one phase being a continuous liquid and the other phase consisting of gas or vapour of the liquid phase. In the range of low to intermediate volume fraction of the gaseous phase the multiphase flow under consideration is a bubbly or slug flow, where the disperse phase is characterized by an evolving bubble size distribution due to bubble breakup and coalescence processes. The paper presents a generalized inhomogeneous Multiple Size Group (MUSIG) Model. Within this model the disperse gaseous phase is divided into N inhomogeneous velocity groups (phases) and each of these groups is subdivided into M bubble size classes. Bubble breakup and coalescence processes between all bubble size classes are taken into account by appropriate models. The derived inhomogeneous MUSIG model has been validated against experimental data from the TOPFLOW test facility at the Research Center Rossendorf (FZR). Comparisons of gas volume fraction and velocity profiles with TOPFLOW-074 test case data are provided, showing the applicability and accuracy of the model for polydispersed bubbly flow in large diameter vertical pipe flow. (author)
Integrated risk management in a commercial market-maker bank using the 'cash flow at risk' approach
Voloshyn, Ihor; Voloshyn, Mykyta
2013-01-01
In this article, on the basis of the "cash flow at risk" approach, the system of the integrated (credit, market, operational and liquidity risks) risk management in a market-maker commercial bank is developed. This system guarantees reaching profitability, liquidity and coverage of banking risks and thus allows the fullest protection of the interests of depositors, creditors and shareholders of the bank providing its sustainable development.
Directory of Open Access Journals (Sweden)
Shanfang Huang
2017-01-01
Full Text Available High thermal neutron fluxes are needed in some research reactors and for irradiation tests of materials. A High Flux Research Reactor (HFRR with an inverse flux trap-converter target structure is being developed by the Reactor Engineering Analysis Lab (REAL at Tsinghua University. This paper studies the safety of the HFRR core by full core flow and temperature calculations using the porous media approach. The thermal nonequilibrium model is used in the porous media energy equation to calculate coolant and fuel assembly temperatures separately. The calculation results show that the coolant temperature keeps increasing along the flow direction, while the fuel temperature increases first and decreases afterwards. As long as the inlet coolant mass flow rate is greater than 450 kg/s, the peak cladding temperatures in the fuel assemblies are lower than the local saturation temperatures and no boiling exists. The flow distribution in the core is homogeneous with a small flow rate variation less than 5% for different assemblies. A large recirculation zone is observed in the outlet region. Moreover, the porous media model is compared with the exact model and found to be much more efficient than a detailed simulation of all the core components.
Sleep, Stress & Relaxation: Rejuvenate Body & Mind
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Mills, Freya; Petterson, Susan; Norman, Guy
2018-01-01
Public health benefits are often a key political driver of urban sanitation investment in developing countries, however, pathogen flows are rarely taken systematically into account in sanitation investment choices. While several tools and approaches on sanitation and health risks have recently been developed, this research identified gaps in their ability to predict faecal pathogen flows, to relate exposure risks to the existing sanitation services, and to compare expected impacts of improvements. This paper outlines a conceptual approach that links faecal waste discharge patterns with potential pathogen exposure pathways to quantitatively compare urban sanitation improvement options. An illustrative application of the approach is presented, using a spreadsheet-based model to compare the relative effect on disability-adjusted life years of six sanitation improvement options for a hypothetical urban situation. The approach includes consideration of the persistence or removal of different pathogen classes in different environments; recognition of multiple interconnected sludge and effluent pathways, and of multiple potential sites for exposure; and use of quantitative microbial risk assessment to support prediction of relative health risks for each option. This research provides a step forward in applying current knowledge to better consider public health, alongside environmental and other objectives, in urban sanitation decision making. Further empirical research in specific locations is now required to refine the approach and address data gaps. PMID:29360775
Flow Visualization at Cryogenic Conditions Using a Modified Pressure Sensitive Paint Approach
Watkins, A. Neal; Goad, William K.; Obara, Clifford J.; Sprinkle, Danny R.; Campbell, Richard L.; Carter, Melissa B.; Pendergraft, Odis C., Jr.; Bell, James H.; Ingram, JoAnne L.; Oglesby, Donald M.
2005-01-01
A modification to the Pressure Sensitive Paint (PSP) method was used to visualize streamlines on a Blended Wing Body (BWB) model at full-scale flight Reynolds numbers. In order to achieve these conditions, the tests were carried out in the National Transonic Facility operating under cryogenic conditions in a nitrogen environment. Oxygen is required for conventional PSP measurements, and several tests have been successfully completed in nitrogen environments by injecting small amounts (typically < 3000 ppm) of oxygen into the flow. A similar technique was employed here, except that air was purged through pressure tap orifices already existent on the model surface, resulting in changes in the PSP wherever oxygen was present. The results agree quite well with predicted results obtained through computational fluid dynamics analysis (CFD), which show this to be a viable technique for visualizing flows without resorting to more invasive procedures such as oil flow or minitufts.
International Nuclear Information System (INIS)
Huang, Qiu; Peng, Qiyu; Huang, Bin; Cheryauka, Arvi; Gullberg, Grant T.
2008-01-01
The measurement of flow obtained using continuous wave Doppler ultrasound is formulated as a directional projection of a flow vector field. When a continuous ultrasound wave bounces against a flowing particle, a signal is backscattered. This signal obtains a Doppler frequency shift proportional to the speed of the particle along the ultrasound beam. This occurs for each particle along the beam, giving rise to a Doppler velocity spectrum. The first moment of the spectrum provides the directional projection of the flow along the ultrasound beam. Signals reflected from points further away from the detector will have lower amplitude than signals reflected from points closer to the detector. The effect is very much akin to that modeled by the attenuated Radon transform in emission computed tomography.A least-squares method was adopted to reconstruct a 2D vector field from directional projection measurements. Attenuated projections of only the longitudinal projections of the vector field were simulated. The components of the vector field were reconstructed using the gradient algorithm to minimize a least-squares criterion. This result was compared with the reconstruction of longitudinal projections of the vector field without attenuation. If attenuation is known, the algorithm was able to accurately reconstruct both components of the full vector field from only one set of directional projection measurements. A better reconstruction was obtained with attenuation than without attenuation implying that attenuation provides important information for the reconstruction of flow vector fields.This confirms previous work where we showed that knowledge of the attenuation distribution helps in the reconstruction of MRI diffusion tensor fields from fewer than the required measurements. In the application of ultrasound the attenuation distribution is obtained with pulse wave transmission computed tomography and flow information is obtained with continuous wave Doppler
Sawayama, K.; Kitamura, K.; Tsuji, T.; Fujimitsu, Y.
2017-12-01
The estimation of fluid flow and its distribution in the fracture is essential to evaluate subsurface fluid (e.g., geothermal water, ground water, oil and gas). Recently, fluid flow in the geothermal reservoir has been attracting attention to develop EGS (enhanced geothermal system) technique. To detect the fluid distribution under the ground, geophysical exploration such as seismic and electromagnetic methods have been broadly applied. For better interpretation of these exploration data, more detailed investigation about the effect of fluid on seismic and electric properties of fracture is required. In this study, we measured and calculated seismic and electric properties of a cracked rock to discuss the effect of water distribution and saturation on them as well as fluid flow. For the experimental observation, we developed the technique to measure electrical impedance, P-wave velocity and water saturation simultaneously during the fluid-flow test. The test has been conducted as follows; a cracked andesite core sample was filled with nitrogen gas (Pp = 10 MPa) under 20 MPa of confining pressure and then, brine (1wt.%-KCl, 1.75 S/m) was injected into the sample to replace the gas. During the test, water saturation, permeability, electrical impedance and P-wave velocity were measured. As a result of this experimental study, electrical impedance dramatically decreased from 105 to 103 Ω and P-wave velocity increased by 2% due to the brine injection. This remarkable change of the electrical impedance could be due to the replacement of pre-filled nitrogen gas to the brine in the broad fracture. After the brine injection, electrical impedance decreased with injection pressure by up to 40% while P-wave velocity was almost constant. This decrease of electrical impedance could be related to the flow to the narrow path (microcrack) which cannot be detected by P-wave velocity. These two types of fluid flow mechanism were also suggested from other parameters such as
Energy Technology Data Exchange (ETDEWEB)
Kurban, Adib Paulo Abdalla [PETROBRAS, Rio de Janeiro (Brazil). Centro de Pesquisas; Bannwart, Antonio Carlos [Universidade Estadual de Campinas, SP (Brazil). Faculdade de Engenharia Mecanica
1990-12-31
The fully developed laminar flow of two immiscible liquids with both different viscosities and densities through a horizontal round pipe is studied. The interface between the fluids as well as their flow fields are determined by the use of a variational principle: the so called viscous dissipation principle: The results foreseen by this paper are in agreement with the physical observation (e.g. Southern and Ballman) that the more viscous fluid is total or partially encapsulated by the less viscous one. (author) 8 refs., 4 figs.
Blood flow velocity measurements in chicken embryo vascular network via PIV approach
Kurochkin, Maxim A.; Stiukhina, Elena S.; Fedosov, Ivan V.; Tuchin, Valery V.
2018-04-01
A method for measuring of blood velocity in the native vasculature of a chick embryo by the method of micro anemometry from particle images (μPIV) is improved. A method for interrogation regions sorting by the mask of the vasculature is proposed. A method for sorting of the velocity field of capillary blood flow is implemented. The in vitro method was evaluated for accuracy in a glass phantom of a blood vessel with a diameter of 50 μm and in vivo on the bloodstream of a chicken embryo, by comparing the transverse profile of the blood velocity obtained by the PIV method with the theoretical Poiseuille laminar flow profile.
Energy Technology Data Exchange (ETDEWEB)
Kurban, Adib Paulo Abdalla [PETROBRAS, Rio de Janeiro (Brazil). Centro de Pesquisas; Bannwart, Antonio Carlos [Universidade Estadual de Campinas, SP (Brazil). Faculdade de Engenharia Mecanica
1991-12-31
The fully developed laminar flow of two immiscible liquids with both different viscosities and densities through a horizontal round pipe is studied. The interface between the fluids as well as their flow fields are determined by the use of a variational principle: the so called viscous dissipation principle: The results foreseen by this paper are in agreement with the physical observation (e.g. Southern and Ballman) that the more viscous fluid is total or partially encapsulated by the less viscous one. (author) 8 refs., 4 figs.
Energy Technology Data Exchange (ETDEWEB)
1987-08-01
The large eddy concept in turbulent modeling and techniques for direct simulation are discussed. A review of turbulence modeling is presented along with physical and numerical aspects and applications. A closure model for turbulent flows is presented and routes to chaos by quasi-periodicity are discussed. Theoretical aspects of transition to turbulence by space/time intermittency are covered. The application to interpretation of experimental results of fractal dimensions and connection of spatial temporal chaos are reviewed. Simulation of hydrodynamic flow by using cellular automata is discussed.
Elliptic Flow at Finite Shear Viscosity in a Kinetic Approach at RHIC
International Nuclear Information System (INIS)
Greco, V.; Colonna, M.; Di Toro, M.; Ferini, G.
2010-01-01
Within a covariant parton cascade, we discuss the impact of both finite shear viscosity η and freeze-out dynamics on the elliptic flow generated at RHIC. We find that the enhancement of η/s in the cross-over region of the QGP phase transition cannot be neglected in order to extract the information from the QGP phase. We also point out that the elliptic flow v 2 (p T ) for a fluid at η/s∼0.1-0.2 is consistent with the one needed by quark number scaling drawing a nice consistency between the nearly perfect fluid property of QGP and the coalescence process.
Study of blood flow in several benchmark micro-channels using a two-fluid approach
Wu, Wei-Tao; Yang, Fang; Antaki, James F.; Aubry, Nadine; Massoudi, Mehrdad
2015-01-01
It is known that in a vessel whose characteristic dimension (e.g., its diameter) is in the range of 20 to 500 microns, blood behaves as a non-Newtonian fluid, exhibiting complex phenomena, such as shear-thinning, stress relaxation, and also multi-component behaviors, such as the Fahraeus effect, plasma-skimming, etc. For describing these non-Newtonian and multi-component characteristics of blood, using the framework of mixture theory, a two-fluid model is applied, where the plasma is treated as a Newtonian fluid and the red blood cells (RBCs) are treated as shear-thinning fluid. A computational fluid dynamic (CFD) simulation incorporating the constitutive model was implemented using OpenFOAM® in which benchmark problems including a sudden expansion and various driven slots and crevices were studied numerically. The numerical results exhibited good agreement with the experimental observations with respect to both the velocity field and the volume fraction distribution of RBCs. PMID:26240438
Relaxation Techniques to Manage IBS Symptoms
... for 15–20 seconds and then begin again. Progressive Muscle Relaxation This method of relaxation focuses on ... helpful, please consider supporting IFFGD with a small tax- deductible donation. Make Donation Adapted from IFFGD Publication # ...
Relaxation as a Factor in Semantic Desensitization
Bechtel, James E.; McNamara, J. Regis
1975-01-01
Relaxation and semantic desensitization were used to alleviate the fear of phobic females. Results showed that semantic desensitization, alone or in combination with relaxation, failed to modify the evaluative meanings evoked by the feared object. (SE)
The feasibility of parameterizing four-state equilibria using relaxation dispersion measurements
International Nuclear Information System (INIS)
Li Pilong; Martins, Ilídio R. S.; Rosen, Michael K.
2011-01-01
Coupled equilibria play important roles in controlling information flow in biochemical systems, including allosteric molecules and multidomain proteins. In the simplest case, two equilibria are coupled to produce four interconverting states. In this study, we assessed the feasibility of determining the degree of coupling between two equilibria in a four-state system via relaxation dispersion measurements. A major bottleneck in this effort is the lack of efficient approaches to data analysis. To this end, we designed a strategy to efficiently evaluate the smoothness of the target function surface (TFS). Using this approach, we found that the TFS is very rough when fitting benchmark CPMG data to all adjustable variables of the four-state equilibria. After constraining a portion of the adjustable variables, which can often be achieved through independent biochemical manipulation of the system, the smoothness of TFS improves dramatically, although it is still insufficient to pinpoint the solution. The four-state equilibria can be finally solved with further incorporation of independent chemical shift information that is readily available. We also used Monte Carlo simulations to evaluate how well each adjustable parameter can be determined in a large kinetic and thermodynamic parameter space and how much improvement can be achieved in defining the parameters through additional measurements. The results show that in favorable conditions the combination of relaxation dispersion and biochemical manipulation allow the four-state equilibrium to be parameterized, and thus coupling strength between two processes to be determined.
Directory of Open Access Journals (Sweden)
Frank C G van Bussel
Full Text Available Flow-mediated dilation is aimed at normalization of local wall shear stress under varying blood flow conditions. Blood flow velocity and vessel diameter are continuous and opposing influences that modulate wall shear stress. We derived an index FMDv to quantify wall shear stress normalization performance by flow-mediated dilation in the brachial artery. In 22 fasting presumed healthy men, we first assessed intra- and inter-session reproducibilities of two indices pFMDv and mFMDv, which consider the relative peak and relative mean hyperemic change in flow velocity, respectively. Second, utilizing oral glucose loading, we evaluated the tracking performance of both FMDv indices, in comparison with existing indices [i.e., the relative peak diameter increase (%FMD, the peak to baseline diameter ratio (Dpeak/Dbase, and the relative peak diameter increase normalized to the full area under the curve of blood flow velocity with hyperemia (FMD/shearAUC or with area integrated to peak hyperemia (FMD/shearAUC_peak]. Inter-session and intra-session reproducibilities for pFMDv, mFMDv and %FMD were comparable (intra-class correlation coefficients within 0.521-0.677 range. Both pFMDv and mFMDv showed more clearly a reduction after glucose loading (reduction of ~45%, p≤0.001 than the other indices (% given are relative reductions: %FMD (~11%, p≥0.074; Dpeak/Dbase (~11%, p≥0.074; FMD/shearAUC_peak (~20%, p≥0.016 and FMD/shearAUC (~38%, p≤0.038. Further analysis indicated that wall shear stress normalization under normal (fasting conditions is already far from ideal (FMDv << 1, which (therefore does not materially change with glucose loading. Our approach might be useful in intervention studies to detect intrinsic changes in shear stress normalization performance in conduit arteries.
Treatment of Nightmares via Relaxation and Desensitization: A Controlled Evaluation.
Miller, William R.; DiPilato, Marina
1983-01-01
Investigated the role of relaxation training as a component of desensitization to nightmares in adults (N=32). Results showed an 80 percent reduction in nightmares reported by 20 clients, of whom 12 reported total elimination of symptoms at 25-week follow-up, suggesting the effectiveness of a behavioral approach in treating nightmares. (LLL)
Expedient Method for Samarium(II) Iodide Preparation Utilizing a Flow Approach
Czech Academy of Sciences Publication Activity Database
Voltrová, Svatava; Šrogl, Jiří
2013-01-01
Roč. 24, č. 3 (2013), s. 394-396 ISSN 0936-5214 R&D Projects: GA MŠk LH12013 Institutional support: RVO:61388963 Keywords : flow * samarium * iodide * reduction Subject RIV: CC - Organic Chemistry Impact factor: 2.463, year: 2013
Optimal Power Flow for resistive DC Network : A Port-Hamiltonian approach
Benedito, Ernest; del Puerto-Flores, D.; Doria-Cerezo, A.; Scherpen, Jacquelien M.A.; Dochain, Denis; Henrion, Didier; Peaucelle, Dimitri
This paper studies the optimal power flow problem for resistive DC networks. The gradient method algorithm is written in a port-Hamiltonian form and the stability of the resulting dynamics is studied. Stability conditions are provided for general cyclic networks and a solution, when these conditions
Plasmon-mediated energy relaxation in graphene
Energy Technology Data Exchange (ETDEWEB)
Ferry, D. K. [School of Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, Arizona 85287-5706 (United States); Somphonsane, R. [Department of Physics, King Mongkut' s Institute of Technology, Ladkrabang, Bangkok 10520 (Thailand); Ramamoorthy, H.; Bird, J. P. [Department of Electrical Engineering, University at Buffalo, the State University of New York, Buffalo, New York 14260-1500 (United States)
2015-12-28
Energy relaxation of hot carriers in graphene is studied at low temperatures, where the loss rate may differ significantly from that predicted for electron-phonon interactions. We show here that plasmons, important in the relaxation of energetic carriers in bulk semiconductors, can also provide a pathway for energy relaxation in transport experiments in graphene. We obtain a total loss rate to plasmons that results in energy relaxation times whose dependence on temperature and density closely matches that found experimentally.
Vibrational-rotational relaxation of the simplest hydrogen-containing molecules (review)
International Nuclear Information System (INIS)
Molevich, N.E.; Oraevskii, A.N.
1987-01-01
In connection with the development of chemical lasers much attention is now devoted to the study of kinetic processes is gaseous mixtures containing the hydrogen halides. Vibrational relaxation of molecules if primarily studied without specifying its relation to the rational levels. Rotational relaxation is regarded a priori as faster than vibrational relaxation, so that the population of the rotational levels is assumed to be in equilibrium. This approach to the relaxation of hydrogen halide molecules (and other diatomic hydrogen-containing molecules), however, is unable to explain satisfactorily the results of the papers discussed below. An analysis of the data obtained in these papers leads to the conclusion that the general picture of relaxation in diatomic hydrogen-containing molecules must be viewed as a unified process of vibrational and rotational relaxation. It is shown that those effects observed during vibrational relaxation of such molecules which are unusual from the standpoint of the theory of vibrational-translational relaxation are well explained in terms of intermolecular vibrational-rotational relaxation together with pure rotational relaxation
Intronati, Guido A; Tamborenea, Pablo I; Weinmann, Dietmar; Jalabert, Rodolfo A
2012-01-06
We identify the Dresselhaus spin-orbit coupling as the source of the dominant spin-relaxation mechanism in the impurity band of a wide class of n-doped zinc blende semiconductors. The Dresselhaus hopping terms are derived and incorporated into a tight-binding model of impurity sites, and they are shown to unexpectedly dominate the spin relaxation, leading to spin-relaxation times in good agreement with experimental values. This conclusion is drawn from two complementary approaches: an analytical diffusive-evolution calculation and a numerical finite-size scaling study of the spin-relaxation time.
Effect of the initial stage of annealing on modeling of enthalpy relaxation in a hyperquenched glass
DEFF Research Database (Denmark)
Zhang, Yanfei; Guo, Xiaoju; Yue, Yuanzheng
2013-01-01
One of the major challenges in glass relaxation study is to establish a universal model describing the enthalpy relaxation in both the hyperquenched glass (HQG) (i.e., far from equilibrium) and the partially annealed hyperquenched glass(AHQG). In particular, the detailed features of the enthalpy ...... proposed composite relaxation function [L. Hornboell, et al., Chem. Phys. Lett. 1-3 (2010) 37] is a reasonable approach for describing those features. In addition, our modeling results imply that the structural heterogeneity plays a crucial role in relaxation of HQG....
Nonlinear Relaxation in Population Dynamics
Cirone, Markus A.; de Pasquale, Ferdinando; Spagnolo, Bernardo
We analyze the nonlinear relaxation of a complex ecosystem composed of many interacting species. The ecological system is described by generalized Lotka-Volterra equations with a multiplicative noise. The transient dynamics is studied in the framework of the mean field theory and with random interaction between the species. We focus on the statistical properties of the asymptotic behaviour of the time integral of the ith population and on the distribution of the population and of the local field.
Structural relaxation: low temperature properties
International Nuclear Information System (INIS)
Cruz, F. de la
1984-01-01
We discuss the changes in transport and superconducting properties of amorphous Zr 70 Cu 30 , induced by thermal relaxation. The experimental results are used to investigate the relation between the microscopic parameters and the observed physical properties. It is shown that the density of eletronic states determines the shift Tc as well as the variation of the electrical resistivity. It is necessary to assume strong hybridization between s and d bands to understand the eletrodynamic response of the superconductor. (Author) [pt
The Effects of Suggestibility on Relaxation.
Rickard, Henry C.; And Others
1985-01-01
Selected undergraduates (N=32) on the basis of Creative Imagination Scale scores and randomly assigned high and low suggestibility subjects to progressive relaxation (PR) and suggestions of relaxation (SR) training modes. Results revealed a significant pre-post relaxation effect, and main efffects for both suggestibility and training mode. (NRB)
Martha, Cornelius T; Hoogendoorn, Jan-Carel; Irth, Hubertus; Niessen, Wilfried M A
2011-05-15
Current development in catalyst discovery includes combinatorial synthesis methods for the rapid generation of compound libraries combined with high-throughput performance-screening methods to determine the associated activities. Of these novel methodologies, mass spectrometry (MS) based flow chemistry methods are especially attractive due to the ability to combine sensitive detection of the formed reaction product with identification of introduced catalyst complexes. Recently, such a mass spectrometry based continuous-flow reaction detection system was utilized to screen silver-adducted ferrocenyl bidentate catalyst complexes for activity in a multicomponent synthesis of a substituted 2-imidazoline. Here, we determine the merits of different ionization approaches by studying the combination of sensitive detection of product formation in the continuous-flow system with the ability to simultaneous characterize the introduced [ferrocenyl bidentate+Ag](+) catalyst complexes. To this end, we study the ionization characteristics of electrospray ionization (ESI), atmospheric-pressure chemical ionization (APCI), no-discharge APCI, dual ESI/APCI, and dual APCI/no-discharge APCI. Finally, we investigated the application potential of the different ionization approaches by the investigation of ferrocenyl bidentate catalyst complex responses in different solvents. Copyright © 2011 Elsevier B.V. All rights reserved.
Directory of Open Access Journals (Sweden)
Wang Wei
2016-01-01
Full Text Available When searching for the optimum condenser cooling water flow in a thermal power plant with natural draft cooling towers, it is essential to evaluate the outlet water temperature of cooling towers when the cooling water flow and inlet water temperature change. However, the air outlet temperature and tower draft or inlet air velocity are strongly coupled for natural draft cooling towers. Traditional methods, such as trial and error method, graphic method and iterative methods are not simple and efficient enough to be used for plant practice. In this paper, we combine Merkel equation with draft equation, and develop the coupled description for performance evaluation of natural draft cooling towers. This model contains two inputs: the cooling water flow, the inlet cooling water temperature and two outputs: the outlet water temperature, the inlet air velocity, equivalent to tower draft. In this model, we furthermore put forward a soft-sensing algorithm to calculate the total drag coefficient instead of empirical correlations. Finally, we design an iterative approach to solve this coupling model, and illustrate three cases to prove that the coupling model and solving approach proposed in our paper are effective for cooling tower performance evaluation.
Xue, Jie; Gui, Dongwei; Lei, Jiaqiang; Sun, Huaiwei; Zeng, Fanjiang; Feng, Xinlong
2017-12-01
Agriculture and the eco-environment are increasingly competing for water. The extension of intensive farmland for ensuring food security has resulted in excessive water exploitation by agriculture. Consequently, this has led to a lack of water supply in natural ecosystems. This paper proposes a trade-off framework to coordinate the water-use conflict between agriculture and the eco-environment, based on economic compensation for irrigation stakeholders. A hybrid Bayesian network (HBN) is developed to implement the framework, including: (a) agricultural water shortage assessments after meeting environmental flows; (b) water-use tradeoff analysis between agricultural irrigation and environmental flows using the HBN; and (c) quantification of the agricultural economic compensation for different irrigation stakeholders. The constructed HBN is computed by dynamic discretization, which is a more robust and accurate propagation algorithm than general static discretization. A case study of the Qira oasis area in Northwest China demonstrates that the water trade-off based on economic compensation depends on the available water supply and environmental flows at different levels. Agricultural irrigation water extracted for grain crops should be preferentially guaranteed to ensure food security, in spite of higher economic compensation in other cash crops' irrigation for water coordination. Updating water-saving engineering and adopting drip irrigation technology in agricultural facilities after satisfying environmental flows would greatly relieve agricultural water shortage and save the economic compensation for different irrigation stakeholders. The approach in this study can be easily applied in water-stressed areas worldwide for dealing with water competition.
The RiverFish Approach to Business Process Modeling: Linking Business Steps to Control-Flow Patterns
Zuliane, Devanir; Oikawa, Marcio K.; Malkowski, Simon; Alcazar, José Perez; Ferreira, João Eduardo
Despite the recent advances in the area of Business Process Management (BPM), today’s business processes have largely been implemented without clearly defined conceptual modeling. This results in growing difficulties for identification, maintenance, and reuse of rules, processes, and control-flow patterns. To mitigate these problems in future implementations, we propose a new approach to business process modeling using conceptual schemas, which represent hierarchies of concepts for rules and processes shared among collaborating information systems. This methodology bridges the gap between conceptual model description and identification of actual control-flow patterns for workflow implementation. We identify modeling guidelines that are characterized by clear phase separation, step-by-step execution, and process building through diagrams and tables. The separation of business process modeling in seven mutually exclusive phases clearly delimits information technology from business expertise. The sequential execution of these phases leads to the step-by-step creation of complex control-flow graphs. The process model is refined through intuitive table and diagram generation in each phase. Not only does the rigorous application of our modeling framework minimize the impact of rule and process changes, but it also facilitates the identification and maintenance of control-flow patterns in BPM-based information system architectures.
Mager, R; Balzereit, C; Gust, K; Hüsch, T; Herrmann, T; Nagele, U; Haferkamp, A; Schilling, D
2016-05-01
Passive removal of stone fragments in the irrigation stream is one of the characteristics in continuous-flow PCNL instruments. So far the physical principle of this so-called vacuum cleaner effect has not been fully understood yet. The aim of the study was to empirically prove the existence of the vacuum cleaner effect and to develop a physical hypothesis and generate a mathematical model for this phenomenon. In an empiric approach, common low-pressure PCNL instruments and conventional PCNL sheaths were tested using an in vitro model. Flow characteristics were visualized by coloring of irrigation fluid. Influence of irrigation pressure, sheath diameter, sheath design, nephroscope design and position of the nephroscope was assessed. Experiments were digitally recorded for further slow-motion analysis to deduce a physical model. In each tested nephroscope design, we could observe the vacuum cleaner effect. Increase in irrigation pressure and reduction in cross section of sheath sustained the effect. Slow-motion analysis of colored flow revealed a synergism of two effects causing suction and transportation of the stone. For the first time, our model showed a flow reversal in the sheath as an integral part of the origin of the stone transportation during vacuum cleaner effect. The application of Bernoulli's equation provided the explanation of these effects and confirmed our experimental results. We widen the understanding of PCNL with a conclusive physical model, which explains fluid mechanics of the vacuum cleaner effect.
Relaxed Poisson cure rate models.
Rodrigues, Josemar; Cordeiro, Gauss M; Cancho, Vicente G; Balakrishnan, N
2016-03-01
The purpose of this article is to make the standard promotion cure rate model (Yakovlev and Tsodikov, ) more flexible by assuming that the number of lesions or altered cells after a treatment follows a fractional Poisson distribution (Laskin, ). It is proved that the well-known Mittag-Leffler relaxation function (Berberan-Santos, ) is a simple way to obtain a new cure rate model that is a compromise between the promotion and geometric cure rate models allowing for superdispersion. So, the relaxed cure rate model developed here can be considered as a natural and less restrictive extension of the popular Poisson cure rate model at the cost of an additional parameter, but a competitor to negative-binomial cure rate models (Rodrigues et al., ). Some mathematical properties of a proper relaxed Poisson density are explored. A simulation study and an illustration of the proposed cure rate model from the Bayesian point of view are finally presented. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Arresting relaxation in Pickering Emulsions
Atherton, Tim; Burke, Chris
2015-03-01
Pickering emulsions consist of droplets of one fluid dispersed in a host fluid and stabilized by colloidal particles absorbed at the fluid-fluid interface. Everyday materials such as crude oil and food products like salad dressing are examples of these materials. Particles can stabilize non spherical droplet shapes in these emulsions through the following sequence: first, an isolated droplet is deformed, e.g. by an electric field, increasing the surface area above the equilibrium value; additional particles are then adsorbed to the interface reducing the surface tension. The droplet is then allowed to relax toward a sphere. If more particles were adsorbed than can be accommodated by the surface area of the spherical ground state, relaxation of the droplet is arrested at some non-spherical shape. Because the energetic cost of removing adsorbed colloids exceeds the interfacial driving force, these configurations can remain stable over long timescales. In this presentation, we present a computational study of the ordering present in anisotropic droplets produced through the mechanism of arrested relaxation and discuss the interplay between the geometry of the droplet, the dynamical process that produced it, and the structure of the defects observed.
Vibrational relaxation in OCS mixtures
International Nuclear Information System (INIS)
Simpson, C.J.S.M.; Gait, P.D.; Simmie, J.M.
1976-01-01
Experimental measurements are reported of vibrational relaxation times which may be used to show whether there is near resonant vibration-rotation energy transfer between OCS and H 2 , D 2 or HD. Vibrational relaxation times have been measured in OCS and OCS mixtures over the temperature range 360 to 1000 K using a shock tube and a laser schlieren system. The effectiveness of the additives in reducing the relaxation time of OCS is in the order 4 He 3 He 2 2 and HD. Along this series the effect of an increase in temperature changes from the case of speeding up the rate with 4 He to retarding it with D 2 , HD and H 2 . There is no measurable difference in the effectiveness of n-D 2 and o-D 2 and little, or no, difference between n-H 2 and p-H 2 . Thus the experimental results do not give clear evidence for rotational-vibration energy transfer between hydrogen and OCS. This contrasts with the situation for CO 2 + H 2 mixtures. (author)
International Nuclear Information System (INIS)
Spies, G.O.; Lortz, D.; Kaiser, R.
2001-01-01
Taylor's theory of relaxed toroidal plasmas (states of lowest energy with fixed total magnetic helicity) is extended to include a vacuum between the plasma and the wall. In the extended variational problem, one prescribes, in addition to the helicity and the magnetic fluxes whose conservation follows from the perfect conductivity of the wall, the fluxes whose conservation follows from the assumption that the plasma-vacuum interface is also perfectly conducting (if the wall is a magnetic surface, then one has the toroidal and the poloidal flux in the vacuum). Vanishing of the first energy variation implies a pressureless free-boundary magnetohydrostatic equilibrium with a Beltrami magnetic field in the plasma, and in general with a surface current in the interface. Positivity of the second variation implies that the equilibrium is stable according to ideal magnetohydrodynamics, that it is a relaxed state according to Taylor's theory if the interface is replaced by a wall, and that the surface current is nonzero (at least if there are no closed magnetic field lines in the interface). The plane slab, with suitable boundary conditions to simulate a genuine torus, is investigated in detail. The relaxed state has the same double symmetry as the vessel if, and only if, the prescribed helicity is in an interval that depends on the prescribed fluxes. This interval is determined in the limit of a thin slab
Regularized Label Relaxation Linear Regression.
Fang, Xiaozhao; Xu, Yong; Li, Xuelong; Lai, Zhihui; Wong, Wai Keung; Fang, Bingwu
2018-04-01
Linear regression (LR) and some of its variants have been widely used for classification problems. Most of these methods assume that during the learning phase, the training samples can be exactly transformed into a strict binary label matrix, which has too little freedom to fit the labels adequately. To address this problem, in this paper, we propose a novel regularized label relaxation LR method, which has the following notable characteristics. First, the proposed method relaxes the strict binary label matrix into a slack variable matrix by introducing a nonnegative label relaxation matrix into LR, which provides more freedom to fit the labels and simultaneously enlarges the margins between different classes as much as possible. Second, the proposed method constructs the class compactness graph based on manifold learning and uses it as the regularization item to avoid the problem of overfitting. The class compactness graph is used to ensure that the samples sharing the same labels can be kept close after they are transformed. Two different algorithms, which are, respectively, based on -norm and -norm loss functions are devised. These two algorithms have compact closed-form solutions in each iteration so that they are easily implemented. Extensive experiments show that these two algorithms outperform the state-of-the-art algorithms in terms of the classification accuracy and running time.
Hydrogels with tunable stress relaxation regulate stem cell fate and activity
Chaudhuri, Ovijit; Gu, Luo; Klumpers, Darinka; Darnell, Max; Bencherif, Sidi A.; Weaver, James C.; Huebsch, Nathaniel; Lee, Hong-Pyo; Lippens, Evi; Duda, Georg N.; Mooney, David J.
2016-03-01
Natural extracellular matrices (ECMs) are viscoelastic and exhibit stress relaxation. However, hydrogels used as synthetic ECMs for three-dimensional (3D) culture are typically elastic. Here, we report a materials approach to tune the rate of stress relaxation of hydrogels for 3D culture, independently of the hydrogel's initial elastic modulus, degradation, and cell-adhesion-ligand density. We find that cell spreading, proliferation, and osteogenic differentiation of mesenchymal stem cells (MSCs) are all enhanced in cells cultured in gels with faster relaxation. Strikingly, MSCs form a mineralized, collagen-1-rich matrix similar to bone in rapidly relaxing hydrogels with an initial elastic modulus of 17 kPa. We also show that the effects of stress relaxation are mediated by adhesion-ligand binding, actomyosin contractility and mechanical clustering of adhesion ligands. Our findings highlight stress relaxation as a key characteristic of cell-ECM interactions and as an important design parameter of biomaterials for cell culture.
Multistage Spectral Relaxation Method for Solving the Hyperchaotic Complex Systems
Directory of Open Access Journals (Sweden)
Hassan Saberi Nik
2014-01-01
Full Text Available We present a pseudospectral method application for solving the hyperchaotic complex systems. The proposed method, called the multistage spectral relaxation method (MSRM is based on a technique of extending Gauss-Seidel type relaxation ideas to systems of nonlinear differential equations and using the Chebyshev pseudospectral methods to solve the resulting system on a sequence of multiple intervals. In this new application, the MSRM is used to solve famous hyperchaotic complex systems such as hyperchaotic complex Lorenz system and the complex permanent magnet synchronous motor. We compare this approach to the Runge-Kutta based ode45 solver to show that the MSRM gives accurate results.
Directory of Open Access Journals (Sweden)
Lezhnin Sergey
2017-01-01
Full Text Available The two-temperature model of the outflow from a vessel with initial supercritical parameters of medium has been realized. The model uses thermodynamic non-equilibrium relaxation approach to describe phase transitions. Based on a new asymptotic model for computing the relaxation time, the outflow of water with supercritical initial pressure and super- and subcritical temperatures has been calculated.
Temperature relaxation in collisional non equilibrium plasmas
Energy Technology Data Exchange (ETDEWEB)
Potapenko, I.F.; Bobylev, A.V.; Azevedo, C.A.; Assis, A.S. [Universidade do Estado, Rio de Janeiro, RJ (Brazil). Inst. de Fisica
1997-12-31
Full text. We study the relaxation of a space uniform plasma composed of electrons and one species of ions. To simplified the consideration, standard approach is usually accepted: the distribution functions are considered to be a Maxwellian with time dependent electron T{sub e}(t) and ion T{sub i}(t) temperatures. This approach imposes a severe restriction on the electron/ion distributions that could be very far from the equilibrium. In the present work the problem is investigated on the basis of the nonlinear kinetic Fokker - Planck equation, which is widely used for the description of collisional plasmas. This equation has many applications in plasma physics as an intrinsic part of physical models, both analytical and numerical. A new detailed description of this classical problem of the collisional plasma kinetic theory is given. A deeper examination of the problem shows that the unusual perturbation theory can not be used. The part of the perturbation of the electron distribution has the character of a boundary layer in the neighborhood of small velocities. In this work the boundary layer is thoroughly studied. The correct distribution electron function is given. Nonmonotonic character of the distribution relaxation in the tail region is observed. The corrected formula for temperature equalization is obtained. The comparison of the calculation results with the asymptotic approach is made. We should stress the important role of the completely conservative different scheme used here, which keeps the symmetric properties of the nonlinear exact equation. This allows us to make calculations without numerical error accumulations, except for machine errors. (author)
Grid Cell Relaxation Effects on the High Frequency Vibration Characteristics
International Nuclear Information System (INIS)
Ryu, Joo-Young; Eom, Kyong-Bo; Jeon, Sang-Youn; Kim, Jae-Ik
2015-01-01
The plate structure of the grid of fuel assembly is always exposed to serious vortex induced vibration. Also, High Frequency flow induced Vibration (HFV) is primarily generated by vortex-shedding effect. When it comes to grid design as a fuel assembly component, HFV should be considered in advance since it is one of the critical factors. Excessive HFV has a possibility of making degradation of the fuel reliability that is directly related to the fuel robustness and operating performance. KEPCO NF (KNF) has performed HFV tests with various grid designs. While studying the HFV characteristics through the HFV tests, it has been observed that HFV amplitudes show different levels according to grid cell relaxation. It means that the testing could give different interpretations due to the condition of grid cell. Since the amount of relaxation is different under operating conditions and environments in a reactor, test specimens should be modified as much as possible to the real state of the fuel. Therefore, in order to consider the grid cell relaxation effects on the HFV tests, it is important to use cell sized or non-cell sized grids. The main focus of this study is to find out how the HFV characteristics such as amplitude and frequency are affected by grid cell relaxation. Three cases of the grid cell sized specimen which is nickel alloy were prepared and tested. Through the comparison of the test results, it could be concluded that HFV amplitudes show decreasing trend according to the grid cell relaxation in the case of nickel alloy grid. It is also possible to expect the tendency of grid cell relaxation of a zirconium alloy grid based on test results
DEFF Research Database (Denmark)
Jabbaribehnam, Mirmasoud; Hattel, Jesper Henri
2016-01-01
Tape casting has been used to produce thin layers of ceramics that can be used as single layers or can be stacked and laminated into multilayered structures. Many startup products such as multilayered inductors, multilayered varistors, piezoelectrics, ceramic fuel cells and lithium ion battery...... components are dependent upon tape casting technology. One of the growing sciences in the processing of ceramics by tape casting is the use of fluid flow analysis to control and enhance the final tapes. The fluid dynamics analysis of the ceramic slurries during tape casting is an efficient mean to elucidate...... the physical parameters crucial to the process. A review of the development of the tape casting process with particular focus on modelling the material flow is presented and in this context the current status is examined and future potential discussed....
Directory of Open Access Journals (Sweden)
Chinmay A. Shukla
2017-05-01
Full Text Available The implementation of automation in the multistep flow synthesis is essential for transforming laboratory-scale chemistry into a reliable industrial process. In this review, we briefly introduce the role of automation based on its application in synthesis viz. auto sampling and inline monitoring, optimization and process control. Subsequently, we have critically reviewed a few multistep flow synthesis and suggested a possible control strategy to be implemented so that it helps to reliably transfer the laboratory-scale synthesis strategy to a pilot scale at its optimum conditions. Due to the vast literature in multistep synthesis, we have classified the literature and have identified the case studies based on few criteria viz. type of reaction, heating methods, processes involving in-line separation units, telescopic synthesis, processes involving in-line quenching and process with the smallest time scale of operation. This classification will cover the broader range in the multistep synthesis literature.
Flow modeling in a porous cylinder with regressing walls using semi analytical approach
Directory of Open Access Journals (Sweden)
M Azimi
2016-10-01
Full Text Available In this paper, the mathematical modeling of the flow in a porous cylinder with a focus on applications to solid rocket motors is presented. As usual, the cylindrical propellant grain of a solid rocket motor is modeled as a long tube with one end closed at the headwall, while the other remains open. The cylindrical wall is assumed to be permeable so as to simulate the propellant burning and normal gas injection. At first, the problem description and formulation are considered. The Navier-Stokes equations for the viscous flow in a porous cylinder with regressing walls are reduced to a nonlinear ODE by using a similarity transformation in time and space. Application of Differential Transformation Method (DTM as an approximate analytical method has been successfully applied. Finally the results have been presented for various cases.
International Nuclear Information System (INIS)
Sabir, O; Ahmad, Norhafizan; Nukman, Y; Tuan Ya, T M Y S
2013-01-01
This paper describes an innovative method for computing fluid solid interaction using Immersed boundary methods with two stage pressure-velocity corrections. The algorithm calculates the interactions between incompressible viscous flows and a solid shape in three-dimensional domain. The fractional step method is used to solve the Navier-Stokes equations in finite difference schemes. Most of IBMs are concern about exchange of the momentum between the Eulerian variables (fluid) and the Lagrangian nodes (solid). To address that concern, a new algorithm to correct the pressure and the velocity using Simplified Marker and Cell method is added. This scheme is applied on staggered grid to simulate the flow past a circular cylinder and study the effect of the new stage on calculations cost. To evaluate the accuracy of the computations the results are compared with the previous software results. The paper confirms the capacity of new algorithm for accurate and robust simulation of Fluid Solid Interaction with respect to pressure field
Learning Based Approach for Optimal Clustering of Distributed Program's Call Flow Graph
Abofathi, Yousef; Zarei, Bager; Parsa, Saeed
Optimal clustering of call flow graph for reaching maximum concurrency in execution of distributable components is one of the NP-Complete problems. Learning automatas (LAs) are search tools which are used for solving many NP-Complete problems. In this paper a learning based algorithm is proposed to optimal clustering of call flow graph and appropriate distributing of programs in network level. The algorithm uses learning feature of LAs to search in state space. It has been shown that the speed of reaching to solution increases remarkably using LA in search process, and it also prevents algorithm from being trapped in local minimums. Experimental results show the superiority of proposed algorithm over others.
Hydro-energy production and water works face to face with environmental flow approach in Romania
International Nuclear Information System (INIS)
Mihailescu, Neculai; Varduca, Aurel; Popescu, Liviu N.; Varduca, Ioana Cristina
2007-01-01
In order to achieve an equilibrium between the requirements of 'environmental flow' and other needs like energy in this case studies are presented in the paper concerning: (i) Iron Gate Hydroelectric Complex on the lower Danube river and (ii) Dambovita river complex hydrotehnical works within and downstream Bucharest. For the first case the most relevant impacts are related with: (i) nutrient 'pump' particular properties; (ii) contamination of sediments with heavy metals and other associated pollutants; (iii) decrease of solid (suspended matter) loads - hydromorphological alterations; (iv) cutting the fish migration and other related issues. In the second case study the environmental flow issues practically do not exist. The case of Dambovita river downstream Bucharest faces increased organic loads, nitrates and especially hazardous substances contamination. (authors)
Steady Stokes flow past dumbbell shaped axially symmetric body of revolution: An analytic approach
Directory of Open Access Journals (Sweden)
Srivastava Kumar Deepak
2012-01-01
Full Text Available In this paper, the problem of steady Stokes flow past dumbbell-shaped axially symmetric isolated body of revolution about its axis of symmetry is considered by utilizing a method (Datta and Srivastava, 1999 based on body geometry under the restrictions of continuously turning tangent on the boundary. The relationship between drag and moment is established in transverse flow situation. The closed form expression of Stokes drag is then calculated for dumbbell-shaped body in terms of geometric parameters b, c, d and a with the aid of this linear relation and the formula of torque obtained by (Chwang and Wu, part 1, 1974 with the use of singularity distribution along axis of symmetry. Drag coefficient and moment coefficient are defined in various forms in terms of dumbbell parameters. Their numerical values are calculated and depicted in respective graphs and compared with some known values.
Li, Peiwu; Zhang, Zhaowei; Zhang, Qi; Zhang, Ning; Zhang, Wen; Ding, Xiaoxia; Li, Ran
2012-08-01
Mycotoxin contamination in the food chain has caused serious health issues in humans and animals. Thus, a rapid on-site and lab-independent detection method for mycotoxins, such as aflatoxins (AFTs), is desirable. Microfluidic chip based immunosensor technology is one of the most promising methods for fast mycotoxin assays. In this review, we cover the major microfluidic immunosensors used for mycotoxin analysis, via flow-through (capillary electromigration) and lateral flow technology. Sample preparation from different matrices of agricultural products and foodstuffs is summarized. The choice of materials, fabrication strategies, and detection methods for microfluidic immunosensors are further discussed in detail. The sensors application in mycotoxin determination is also outlined. Finally, future challenges and opportunities are discussed. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Kunova, O. V.; Shoev, G. V.; Kudryavtsev, A. N.
2017-01-01
Nonequilibrium flows of a two-component oxygen mixture O2/O behind a shock wave are studied with due allowance for the state-to-state vibrational and chemical kinetics. The system of gas-dynamic equations is supplemented with kinetic equations including contributions of VT (TV)-exchange and dissociation processes. A method of the numerical solution of this system with the use of the ANSYS Fluent commercial software package is proposed, which is used in a combination with the authors' code that takes into account nonequilibrium kinetics. The computed results are compared with parameters obtained by solving the problem in the shock-fitting formulation. The vibrational temperature is compared with experimental data. The numerical tool proposed in the present paper is applied to study the flow around a cylinder.
Local instabilities in magnetized rotational flows: A short-wavelength approach
Kirillov, Oleg N.; Stefani, Frank; Fukumoto, Yasuhide
2014-01-01
We perform a local stability analysis of rotational flows in the presence of a constant vertical magnetic field and an azimuthal magnetic field with a general radial dependence. Employing the short-wavelength approximation we develop a unified framework for the investigation of the standard, the helical, and the azimuthal version of the magnetorotational instability, as well as of current-driven kink-type instabilities. Considering the viscous and resistive setup, our main focus is on the cas...
Cold flow simulation of an internal combustion engine with vertical valves using layering approach
Martinas, G.; Cupsa, O. S.; Stan, L. C.; Arsenie, A.
2015-11-01
Complying with emission requirements and fuel consumption efficiency are the points which drive any development of internal combustion engine. Refinement of the process of combustion and mixture formation, together with in-cylinder flow refinement, is a requirement, valves and piston bowl and intake exhaust port design optimization is essential. In order to reduce the time for design optimization cycle it is used Computational Fluid Dynamics (CFD). Being time consuming and highly costly caring out of experiment using flow bench testing this methods start to become less utilized. Air motion inside the intake manifold is one of the important factors, which govern the engine performance and emission of multi-cylinder diesel engines. Any cold flow study on IC is targeting the process of identifying and improving the fluid flow inside the ports and the combustion chamber. This is only the base for an optimization process targeting to increase the volume of air accessing the combustion space and to increase the turbulence of the air at the end of the compression stage. One of the first conclusions will be that the valve diameter is a fine tradeoff between the need for a bigger diameter involving a greater mass of air filling the cylinder, and the need of a smaller diameter in order to reduce the blind zone. Here there is room for optimization studies. The relative pressure indicates a suction effect coming from the moving piston. The more the shape of the inlet port is smoother and the diameter of the piston is bigger, the aerodynamic resistance of the geometry will be smaller so that the difference of inlet port pressure and the pressure near to piston face will be smaller. Here again there is enough room for more optimization studies.
Foodsheds in Virtual Water Flow Networks: A Spectral Graph Theory Approach
Directory of Open Access Journals (Sweden)
Nina Kshetry
2017-06-01
Full Text Available A foodshed is a geographic area from which a population derives its food supply, but a method to determine boundaries of foodsheds has not been formalized. Drawing on the food–water–energy nexus, we propose a formal network science definition of foodsheds by using data from virtual water flows, i.e., water that is virtually embedded in food. In particular, we use spectral graph partitioning for directed graphs. If foodsheds turn out to be geographically compact, it suggests the food system is local and therefore reduces energy and externality costs of food transport. Using our proposed method we compute foodshed boundaries at the global-scale, and at the national-scale in the case of two of the largest agricultural countries: India and the United States. Based on our determination of foodshed boundaries, we are able to better understand commodity flows and whether foodsheds are contiguous and compact, and other factors that impact environmental sustainability. The formal method we propose may be used more broadly to study commodity flows and their impact on environmental sustainability.
Numerical Modelling Approaches for Assessing Improvements to the Flow Circulation in a Small Lake
Directory of Open Access Journals (Sweden)
Cheng He
2011-01-01
Full Text Available Kamaniskeg Lake is a long, narrow, and deep small lake located in the northern part of Ontario, Canada. The goals of this paper were to examine various options to improve the water quality in the northern part of the lake by altering the local hydraulic flow conditions. Towards this end, a preliminary screening suggested that the flow circulation could be increased around a central island (Mask Island in the northern part of the lake by opening up an existing causeway connecting the mainland and central island. Three-dimensional (3D hydraulic and transport models were adopted in this paper to investigate the hydraulic conditions under various wind forces and causeway structures. The modelling results show that opening the causeway in a few places is unlikely to generate a large flow circulation around the central island. Full circulation only appears to be possible if the causeway is fully removed and a strong wind blows in a favourable direction. The possible reasons for existing water quality variations at the intake of a local WTP (water treatment plant are also explored in the paper.
Constant flow ventilation as a novel approach to elimination of respiratory artifact in MR imaging
International Nuclear Information System (INIS)
Shtern, F.; Kersh, R.; Lee, A.; Venegas, J.; Brady, T.J.
1988-01-01
This pilot study was performed to evaluate constant flow ventilation (CFV) as a method of respiratory artifact suppression in magnetic resonance (MR) imaging. In contrast to currently used methods of respiratory artifact suppression, CFV is able to provide adequate ventilation in the absence of any chest wall motion and thus obviates the need for respiratory gating. High-velocity jets of fresh gas delivered through two narrow (2-mm) intrabronchial cannulas promote gas exchange through airway turbulence and enhanced molecular diffusion. One mongrel dog (8.5 kg) was anesthetized with pentobarbital (35 mg/kg). For CFV, endobronchial cannulas were inserted with the aid of bronchoscopy and connected to a flow meter (flow rate, 500 mL/sec). Intrathoracic pressure was monitored via a pressure transducer connected to an air-filled intraesophageal balloon. Conventional ventilation (CV), with a tidal volume of 85 mL and ten breaths per minute, was provided through a cuffed endotracheal tube. After establishment of adequate ventilation (carbon dioxide pressure, 39), muscle paralysis was induced by succinylcholine at 0.1 mg/kg. T2-weighted [1,500/50 (repetition time msec/echo time msec), two excitations] gradient-echo and spin-echo images were obtained at 0.6T with both CV and CFV. MR images with CFV were free of respiratory motion artifact, which was present on all MR images with CV. This pilot study indicates that implementation of CFV results in elimination of respiratory motion artifact
Tumuklu, Ozgur; Levin, Deborah A.; Theofilis, Vassilis
2018-04-01
Shock-dominated hypersonic laminar flows over a double cone are investigated using time accurate direct simulation Monte Carlo combined with the residuals algorithm for unit Reynolds numbers gradually increasing from 9.35 × 104 to 3.74 × 105 m-1 at a Mach number of about 16. The main flow features, such as the strong bow-shock, location of the separation shock, the triple point, and the entire laminar separated region, show a time-dependent behavior. Although the separation shock angle is found to be similar for all Re numbers, the effects of Reynolds number on the structure and extent of the separation region are profound. As the Reynolds number is increased, larger pressure values in the under-expanded jet region due to strong shock interactions form more prominent λ-shocklets in the supersonic region between two contact surfaces. Likewise, the surface parameters, especially on the second cone surface, show a strong dependence on the Reynolds number, with skin friction, pressure, and surface heating rates increasing and velocity slip and temperature jump values decreasing for increasing Re number. A Kelvin-Helmholtz instability arising at the shear layer results in an unsteady flow for the highest Reynolds number. These findings suggest that consideration of experimental measurement times is important when it comes to determining the steady state surface parameters even for a relatively simple double cone geometry at moderately large Reynolds numbers.
Biomimetic approaches for green tribology: from the lotus effect to blood flow control
International Nuclear Information System (INIS)
Maani, Nazanin; Rayz, Vitaliy S; Nosonovsky, Michael
2015-01-01
The research in Green tribology combines several areas including biomimetic tribomaterials and surfaces for controlled adhesion. Biomimetic surfaces mimic living nature and thus they are eco-friendly. The most famous biomimetic surface effect is the Lotus effect (reduction of water adhesion to a solid surface due to micro/nanostructuring of the solid surface). Several extensions of the Lotus effect have been discussed in the literature including the oleophobicity (repelling organic liquids such as oils), underwater oleophobicity to reduce fouling, and the shark skin effect (flow drag reduction due to specially oriented micro-riblets). Here we suggest a potentially important application of micro/nanostructured surfaces in the biomedical area: the micro/nanostructure controlled adhesion in blood flow. Blood is a suspension, and its adhesion properties are different from those of water and oil. For many cardiovascular applications, it is desirable to reduce stagnation and clotting of blood. Therefore, both the underwater oleophobicuity and shark-skin effect can be used. We discuss how computational fluid dynamics models can be used to investigate the structure–property relationships of surface pattern-controlled blood flow adhesion. (paper)
International Nuclear Information System (INIS)
Nelson, R.W.; Jacobson, E.A.; Conbere, W.
1985-06-01
There is a growing awareness of the need to quantify uncertainty in groundwater flow and transport model results. Regulatory organizations are beginning to request the statistical distributions of predicted contaminant arrival to the biosphere, so that realistic confidence intervals can be obtained for the modeling results. To meet these needs, methods are being developed to quantify uncertainty in the subsurface flow and transport analysis sequence. A method for evaluating this uncertainty, described in this paper, considers uncertainty in material properties and was applied to an example field problem. Our analysis begins by using field measurements of transmissivity and hydraulic head in a regional, parameter estimation method to obtain a calibrated fluid flow model and a covariance matrix of the parameter estimation errors. The calibrated model and the covariance matrix are next used in a conditional simulation mode to generate a large number of 'head realizations.' The specific pore water velocity distribution for each realization is calculated from the effective porosity, the aquifer parameter realization, and the associated head values. Each velocity distribution is used to obtain a transport solution for a contaminant originating from the same source for all realizations. The results are the statistical distributions for the outflow arrival times. The confidence intervals for contamination reaching the biosphere are obtained from the outflow statistical distributions. 20 refs., 12 figs
Pattanayak, Santanu
2017-01-01
Deploy deep learning solutions in production with ease using TensorFlow. You'll also develop the mathematical understanding and intuition required to invent new deep learning architectures and solutions on your own. Pro Deep Learning with TensorFlow provides practical, hands-on expertise so you can learn deep learning from scratch and deploy meaningful deep learning solutions. This book will allow you to get up to speed quickly using TensorFlow and to optimize different deep learning architectures. All of the practical aspects of deep learning that are relevant in any industry are emphasized in this book. You will be able to use the prototypes demonstrated to build new deep learning applications. The code presented in the book is available in the form of iPython notebooks and scripts which allow you to try out examples and extend them in interesting ways. You will be equipped with the mathematical foundation and scientific knowledge to pursue research in this field and give back to the community.
A digital elevation analysis: Spatially distributed flow apportioning algorithm
Energy Technology Data Exchange (ETDEWEB)
Kim, Sang-Hyun; Kim, Kyung-Hyun [Pusan National University, Pusan(Korea); Jung, Sun-Hee [Korea Environment Institute, (Korea)
2001-06-30
A flow determination algorithm is proposed for the distributed hydrologic model. The advantages of a single flow direction scheme and multiple flow direction schemes are selectively considered to address the drawbacks of existing algorithms. A spatially varied flow apportioning factor is introduced in order to accommodate the accumulated area from upslope cells. The channel initiation threshold area(CIT) concept is expanded and integrated into the spatially distributed flow apportioning algorithm in order to delineate a realistic channel network. An application of a field example suggests that the linearly distributed flow apportioning scheme provides some advantages over existing approaches, such as the relaxation of over-dissipation problems near channel cells, the connectivity feature of river cells, the continuity of saturated areas and the negligence of the optimization of few parameters in existing algorithms. The effects of grid sizes are explored spatially as well as statistically. (author). 28 refs., 7 figs.
Holographic grating relaxation technique for soft matter science
Energy Technology Data Exchange (ETDEWEB)
Lesnichii, Vasilii, E-mail: vasilii.lesnichii@physchem.uni-freiburg.de [Institute of Physical Chemistry, Albertstraße 21, Institute of Macromolecular Chemistry, Stefan-Meier-Str. 31, Albert-Ludwigs Universität, Freiburg im Breisgau 79104 (Germany); ITMO University, Kronverksky prospekt 49, Saint-Petersburg 197101 (Russian Federation); Kiessling, Andy [Institute of Physical Chemistry, Albertstraße 21, Institute of Macromolecular Chemistry, Stefan-Meier-Str. 31, Albert-Ludwigs Universität, Freiburg im Breisgau 79104 (Germany); Current address: Illinois Institute of Technology, 10 West 33rd Street, Chicago,IL60616 (United States); Bartsch, Eckhard [Institute of Physical Chemistry, Albertstraße 21, Institute of Macromolecular Chemistry, Stefan-Meier-Str. 31, Albert-Ludwigs Universität, Freiburg im Breisgau 79104 (Germany); Veniaminov, Andrey, E-mail: veniaminov@phoi.ifmo.ru [ITMO University, Kronverksky prospekt 49, Saint-Petersburg 197101 (Russian Federation)
2016-06-17
The holographic grating relaxation technique also known as forced Rayleigh scattering consists basically in writing a holographic grating in the specimen of interest and monitoring its diffraction efficiency as a function of time, from which valuable information on mass or heat transfer and photoinduced transformations can be extracted. In a more detailed view, the shape of the relaxation curve and the relaxation rate as a function of the grating period were found to be affected by the architecture of diffusing species (molecular probes) that constitute the grating, as well as that of the environment they diffuse in, thus making it possible to access and study spatial heterogeneity of materials and different modes of e.g., polymer motion. Minimum displacements and spatial domains approachable by the technique are in nanometer range, well below spatial periods of holographic gratings. In the present paper, several cases of holographic relaxation in heterogeneous media and complex motions are exemplified. Nano- to micro-structures or inhomogeneities comparable in spatial scale with holographic gratings manifest themselves in relaxation experiments via non-exponential decay (stepwise or stretched), spatial-period-dependent apparent diffusion coefficient, or unusual dependence of diffusion coefficient on molecular volume of diffusing probes.
[Neurophysiologic and respiratory changes during the practice of relaxation technics].
Gallois, P
1984-01-01
A polygraphic study, of 40 minutes duration, among 10 subjects who practiced autogenic training (TA) and 10 subjects who practiced transcendental meditation (MT), compared to 10 control subjects, gave the following results: rarity of the number of sleeping episodes during relaxation, cardiac rhythm, significantly decreased in the TM group, increased stability of the E.D.G. during and after relaxation, respiratory rate decreased to a value of 33% of the initial rate, respiratory suspensions were frequent in the TM group, reaching a maximal duration of 50 seconds. The absence of compensatory hypercapnia and hyperpnea is an argument in favor of their central origin, lastly, the simple reaction time after relaxation is slightly decreased, whereas it is increased in the controls, this aerobic hypometabolic state, the stability of the autonomic nervous system and the maintenance of the vigilance, induced by deep relaxation, seems to be the opposite of the state which is induced by stress; therefore deep relaxation may play a role in a psycho-somatic approach to treating a variety of disease states.
Sandpile model for relaxation in complex systems
International Nuclear Information System (INIS)
Vazquez, A.; Sotolongo-Costa, O.; Brouers, F.
1997-10-01
The relaxation in complex systems is, in general, nonexponential. After an initial rapid decay the system relaxes slowly following a long time tail. In the present paper a sandpile moderation of the relaxation in complex systems is analysed. Complexity is introduced by a process of avalanches in the Bethe lattice and a feedback mechanism which leads to slower decay with increasing time. In this way, some features of relaxation in complex systems: long time tails relaxation, aging, and fractal distribution of characteristic times, are obtained by simple computer simulations. (author)
International Nuclear Information System (INIS)
Ko, Soon Heum; Kim, Na Yong; Nikitopoulos, Dimitris E.; Moldovan, Dorel; Jha, Shantenu
2014-01-01
Numerical approaches are presented to minimize the statistical errors inherently present due to finite sampling and the presence of thermal fluctuations in the molecular region of a hybrid computational fluid dynamics (CFD) - molecular dynamics (MD) flow solution. Near the fluid-solid interface the hybrid CFD-MD simulation approach provides a more accurate solution, especially in the presence of significant molecular-level phenomena, than the traditional continuum-based simulation techniques. It also involves less computational cost than the pure particle-based MD. Despite these advantages the hybrid CFD-MD methodology has been applied mostly in flow studies at high velocities, mainly because of the higher statistical errors associated with low velocities. As an alternative to the costly increase of the size of the MD region to decrease statistical errors, we investigate a few numerical approaches that reduce sampling noise of the solution at moderate-velocities. These methods are based on sampling of multiple simulation replicas and linear regression of multiple spatial/temporal samples. We discuss the advantages and disadvantages of each technique in the perspective of solution accuracy and computational cost.
von Larcher, Thomas; Blome, Therese; Klein, Rupert; Schneider, Reinhold; Wolf, Sebastian; Huber, Benjamin
2016-04-01
Handling high-dimensional data sets like they occur e.g. in turbulent flows or in multiscale behaviour of certain types in Geosciences are one of the big challenges in numerical analysis and scientific computing. A suitable solution is to represent those large data sets in an appropriate compact form. In this context, tensor product decomposition methods currently emerge as an important tool. One reason is that these methods often enable one to attack high-dimensional problems successfully, another that they allow for very compact representations of large data sets. We follow the novel Tensor-Train (TT) decomposition method to support the development of improved understanding of the multiscale behavior and the development of compact storage schemes for solutions of such problems. One long-term goal of the project is the construction of a self-consistent closure for Large Eddy Simulations (LES) of turbulent flows that explicitly exploits the tensor product approach's capability of capturing self-similar structures. Secondly, we focus on a mixed deterministic-stochastic subgrid scale modelling strategy currently under development for application in Finite Volume Large Eddy Simulation (LES) codes. Advanced methods of time series analysis for the databased construction of stochastic models with inherently non-stationary statistical properties and concepts of information theory based on a modified Akaike information criterion and on the Bayesian information criterion for the model discrimination are used to construct surrogate models for the non-resolved flux fluctuations. Vector-valued auto-regressive models with external influences form the basis for the modelling approach [1], [2], [4]. Here, we present the reconstruction capabilities of the two modeling approaches tested against 3D turbulent channel flow data computed by direct numerical simulation (DNS) for an incompressible, isothermal fluid at Reynolds number Reτ = 590 (computed by [3]). References [1] I
International Nuclear Information System (INIS)
Knoeri, Christof; Wäger, Patrick A.; Stamp, Anna; Althaus, Hans-Joerg; Weil, Marcel
2013-01-01
Emerging technologies such as information and communication-, photovoltaic- or battery technologies are expected to increase significantly the demand for scarce metals in the near future. The recently developed methods to evaluate the criticality of mineral raw materials typically provide a ‘snapshot’ of the criticality of a certain material at one point in time by using static indicators both for supply risk and for the impacts of supply restrictions. While allowing for insights into the mechanisms behind the criticality of raw materials, these methods cannot account for dynamic changes in products and/or activities over time. In this paper we propose a conceptual framework intended to overcome these limitations by including the dynamic interactions between different possible demand and supply configurations. The framework integrates an agent-based behaviour model, where demand emerges from individual agent decisions and interaction, into a dynamic material flow model, representing the materials' stocks and flows. Within the framework, the environmental implications of substitution decisions are evaluated by applying life-cycle assessment methodology. The approach makes a first step towards a dynamic criticality assessment and will enhance the understanding of industrial substitution decisions and environmental implications related to critical metals. We discuss the potential and limitation of such an approach in contrast to state-of-the-art methods and how it might lead to criticality assessments tailored to the specific circumstances of single industrial sectors or individual companies. - Highlights: ► Current criticality assessment methods provide a ‘snapshot’ at one point in time. ► They do not account for dynamic interactions between demand and supply. ► We propose a conceptual framework to overcomes these limitations. ► The framework integrates an agent-based behaviour model with a dynamic material flow model. ► The approach proposed makes
The relationships between suggestibility, influenceability, and relaxability.
Polczyk, Romuald; Frey, Olga; Szpitalak, Malwina
2013-01-01
This research explores the relationships between relaxability and various aspects of suggestibility and influenceability. The Jacobson Progressive Muscle Relaxation procedure was used to induce relaxation. Tests of direct suggestibility, relating to the susceptibility of overt suggestions, and indirect suggestibility, referring to indirect hidden influence, as well as self-description questionnaires on suggestibility and the tendency to comply were used. Thayer's Activation-Deactivation Adjective Check List, measuring various kinds of activation and used as a pre- and posttest, determined the efficacy of the relaxation procedure. Indirect, direct, and self-measured suggestibility proved to be positively related to the ability to relax, measured by Thayer's subscales relating to emotions. Compliance was not related to relaxability. The results are discussed in terms of the aspects of relaxation training connected with suggestibility.
Energy Technology Data Exchange (ETDEWEB)
Zoellner, Frank Gerrit [Computer Assisted Clinical Medicine, Faculty of Medicine Mannheim, Univ. of Heidelberg, Mannheim (Germany); Section for Radiology, Dept. of Surgical Sciences, Univ. of Bergen (Norway); Monssen, Jan Ankar [Dept. of Radiology, Haukeland Univ. Hospital, Bergen (Norway); Roervik, Jarie [Section for Radiology, Dept. of Surgical Sciences, Univ. of Bergen (Norway); Dept. of Radiology, Haukeland Univ. Hospital, Bergen (Norway); Lundervold, Arvid [Dept. of Radiology, Haukeland Univ. Hospital, Bergen (Norway); Dept. of Biomedicine, Univ. of Bergen (Norway); Schad, Lothar R. [Computer Assisted Clinical Medicine, Faculty of Medicine Mannheim, Univ. of Heidelberg, Mannheim (Germany)
2009-07-01
We present a clustering approach to segment the renal artery from 2D PC Cine MR images to measure arterial blood velocity and flow. Such information is important in grading renal artery stenosis and to support the decision on surgical interventions like percutaneous transluminal angioplasty. Results from 20 data sets (volunteers, 7 patients) show that the renal arteries could be extracted automatically and the corresponding velocity profiles were close (r = 0.977) to that obtained by manual delineations of the vessel areas. (orig.)
International Nuclear Information System (INIS)
Zoellner, Frank Gerrit; Monssen, Jan Ankar; Roervik, Jarie; Lundervold, Arvid; Schad, Lothar R.
2009-01-01
We present a clustering approach to segment the renal artery from 2D PC Cine MR images to measure arterial blood velocity and flow. Such information is important in grading renal artery stenosis and to support the decision on surgical interventions like percutaneous transluminal angioplasty. Results from 20 data sets (volunteers, 7 patients) show that the renal arteries could be extracted automatically and the corresponding velocity profiles were close (r = 0.977) to that obtained by manual delineations of the vessel areas. (orig.)
Macroinvertebrate short-term responses to flow variation and oxygen depletion: A mesocosm approach.
Calapez, Ana R; Branco, Paulo; Santos, José M; Ferreira, Teresa; Hein, Thomas; Brito, António G; Feio, Maria João
2017-12-01
In Mediterranean rivers, water scarcity is a key stressor with direct and indirect effects on other stressors, such as water quality decline and inherent oxygen depletion associated with pollutants inputs. Yet, predicting the responses of macroinvertebrates to these stressors combination is quite challenging due to the reduced available information, especially if biotic and abiotic seasonal variations are taken under consideration. This study focused on the response of macroinvertebrates by drift to single and combined effects of water scarcity and dissolved oxygen (DO) depletion over two seasons (winter and spring). A factorial design of two flow velocity levels - regular and low (vL) - with three levels of oxygen depletion - normoxia, medium depletion (dM) and higher depletion (dH) - was carried out in a 5-artificial channels system, in short-term experiments. Results showed that both stressors individually and together had a significant effect on macroinvertebrate drift ratio for both seasons. Single stressor effects showed that macroinvertebrate drift decreased with flow velocity reduction and increased with DO depletion, in both winter and spring experiments. Despite single stressors opposing effects in drift ratio, combined stressors interaction (vL×dM and vL×dH) induced a positive synergistic drift effect for both seasons, but only in winter the drift ratio was different between the levels of DO depletion. Stressors interaction in winter seemed to intensify drift response when reached lower oxygen saturation. Also, drift patterns were different between seasons for all treatments, which may depend on individual's life stage and seasonal behaviour. Water scarcity seems to exacerbate the oxygen depletion conditions resulting into a greater drifting of invertebrates. The potential effects of oxygen depletion should be evaluated when addressing the impacts of water scarcity on river ecosystems, since flow reductions will likely contribute to a higher oxygen
Mapakshi, N. K.; Chang, J.; Nakshatrala, K. B.
2018-04-01
Mathematical models for flow through porous media typically enjoy the so-called maximum principles, which place bounds on the pressure field. It is highly desirable to preserve these bounds on the pressure field in predictive numerical simulations, that is, one needs to satisfy discrete maximum principles (DMP). Unfortunately, many of the existing formulations for flow through porous media models do not satisfy DMP. This paper presents a robust, scalable numerical formulation based on variational inequalities (VI), to model non-linear flows through heterogeneous, anisotropic porous media without violating DMP. VI is an optimization technique that places bounds on the numerical solutions of partial differential equations. To crystallize the ideas, a modification to Darcy equations by taking into account pressure-dependent viscosity will be discretized using the lowest-order Raviart-Thomas (RT0) and Variational Multi-scale (VMS) finite element formulations. It will be shown that these formulations violate DMP, and, in fact, these violations increase with an increase in anisotropy. It will be shown that the proposed VI-based formulation provides a viable route to enforce DMP. Moreover, it will be shown that the proposed formulation is scalable, and can work with any numerical discretization and weak form. A series of numerical benchmark problems are solved to demonstrate the effects of heterogeneity, anisotropy and non-linearity on DMP violations under the two chosen formulations (RT0 and VMS), and that of non-linearity on solver convergence for the proposed VI-based formulation. Parallel scalability on modern computational platforms will be illustrated through strong-scaling studies, which will prove the efficiency of the proposed formulation in a parallel setting. Algorithmic scalability as the problem size is scaled up will be demonstrated through novel static-scaling studies. The performed static-scaling studies can serve as a guide for users to be able to select
Energy Technology Data Exchange (ETDEWEB)
Garcia-Valladares, O.; Santoyo, E. [Centro de Investigacion en Energia (UNAM), Privada Xochicalco s/n, Temixco, Mor. 62580 (Mexico); Sanchez-Upton, P. [Posgrado en Ingenieria (Energia), UNAM, Privada Xochicalco s/n, Temixco, Mor. 62580 (Mexico)
2006-07-15
One dimensional steady and transient numerical modeling for describing the heat and fluid dynamic transport inside geothermal wells has been conducted. The mass, momentum and energy governing equations were solved using a segregated numerical scheme. Discretized governing equations for the fluid flow were coupled and solved with a fully implicit step by step method. The mathematical formulation used suitable empirical correlations for estimating the convective heat transfer coefficients as well as the shear stress and the void fraction parameters. Heat conduction across the wellbore materials was solved by an implicit central difference numerical scheme using the tri-diagonal matrix algorithm (TDMA). The flow characteristics of producer geothermal wells (pressure, temperature, enthalpy, heat fluxes, etc.) at each depth node were computed. Analytical data reported in the literature were used to validate the numerical capability of the wellbore simulator developed for this study (GEOWELLS). This simulator, together with another computer code (ORKISZEWSKI), was applied for modeling the heat and fluid flow processes inside some wells drilled in Mexican geothermal fields. The simulated pressure and temperature profiles were statistically compared against stable measured field data (through the computation of the residual sum of squares and Chi-square). A good agreement between the simulated and measured profiles of pressure and temperature was consistently obtained, having the best matching results for the GEOWELLS predictions. An analysis of the sensitivity and uncertainty was finally conducted to estimate the confidence to be accorded the simulation results predicted by GEOWELLS. Matching the sensitivity to variations in some input parameters (e.g., pressure, temperature, enthalpy and void fraction) was examined. The void fraction was identified as one of the most important parameters that affect the GEOWELLS simulations for matching measured field data correctly
International Nuclear Information System (INIS)
Garcia-Valladares, O.; Sanchez-Upton, P.; Santoyo, E.
2006-01-01
One dimensional steady and transient numerical modeling for describing the heat and fluid dynamic transport inside geothermal wells has been conducted. The mass, momentum and energy governing equations were solved using a segregated numerical scheme. Discretized governing equations for the fluid flow were coupled and solved with a fully implicit step by step method. The mathematical formulation used suitable empirical correlations for estimating the convective heat transfer coefficients as well as the shear stress and the void fraction parameters. Heat conduction across the wellbore materials was solved by an implicit central difference numerical scheme using the tri-diagonal matrix algorithm (TDMA). The flow characteristics of producer geothermal wells (pressure, temperature, enthalpy, heat fluxes, etc.) at each depth node were computed. Analytical data reported in the literature were used to validate the numerical capability of the wellbore simulator developed for this study (GEOWELLS). This simulator, together with another computer code (ORKISZEWSKI), was applied for modeling the heat and fluid flow processes inside some wells drilled in Mexican geothermal fields. The simulated pressure and temperature profiles were statistically compared against stable measured field data (through the computation of the residual sum of squares and Chi-square). A good agreement between the simulated and measured profiles of pressure and temperature was consistently obtained, having the best matching results for the GEOWELLS predictions. An analysis of the sensitivity and uncertainty was finally conducted to estimate the confidence to be accorded the simulation results predicted by GEOWELLS. Matching the sensitivity to variations in some input parameters (e.g., pressure, temperature, enthalpy and void fraction) was examined. The void fraction was identified as one of the most important parameters that affect the GEOWELLS simulations for matching measured field data correctly
Zaccariello, Lucio; Cremiato, Raffaele; Mastellone, Maria Laura
2015-10-01
The main role of a waste management plan is to define which is the combination of waste management strategies and method needed to collect and manage the waste in such a way to ensure a given set of targets is reached. Objectives have to be sustainable and realistic, consistent with the environmental policies and regulations and monitored to verify the progressive achievement of the given targets. To get the aim, the setting up and quantification of indicators can allow the measurement of efficiency of a waste management system. The quantification of efficiency indicators requires the developing of a material flow analysis over the system boundary, from waste collection to secondary materials selling, processing and disposal. The material flow analysis has been carried out with reference to a case study for which a reliable, time- and site-specific database was available. The material flow analysis allowed the evaluation of the amount of materials sent to recycling, to landfilling and to waste-to-energy, by highlighting that the sorting of residual waste can further increase the secondary materials amount. The utilisation of energy recovery to treat the low-grade waste allows the maximisation of waste diversion from landfill with a low production of hazardous ash. A preliminary economic balance has been carried out to define the gate fee of the waste management system that was in the range of 84-145 € t(-1) without including the separate collection cost. The cost of door-by-door separate collection, designed to ensure the collection of five separate streams, resulted in 250 € t(-1) ±30%. © The Author(s) 2015.
International Nuclear Information System (INIS)
Cabrera, J.M.; Prado, J.M.
1997-01-01
The constitutive equations to model the hot flow behaviour of metallic materials in general, and of microalloyed steels in particular (see part 2 of this work) are established in this work. Special emphasis is done on the dynamic softening mechanisms, i.e., dynamic recovery and recrystallization phenomena. The equations developed are physic-based, not empirical, and the modelling allows an easy implementation in an analysis by numerical methods. The resulting equations are even able to predict the final grain size. (Author) 39 refs
An Optimal Homotopy Asymptotic Approach Applied to Nonlinear MHD Jeffery-Hamel Flow
Directory of Open Access Journals (Sweden)
Vasile Marinca
2011-01-01
Full Text Available A simple and effective procedure is employed to propose a new analytic approximate solution for nonlinear MHD Jeffery-Hamel flow. This technique called the Optimal Homotopy Asymptotic Method (OHAM does not depend upon any small/large parameters and provides us with a convenient way to control the convergence of the solution. The examples given in this paper lead to the conclusion that the accuracy of the obtained results is growing along with increasing the number of constants in the auxiliary function, which are determined using a computer technique. The results obtained through the proposed method are in very good agreement with the numerical results.
International Nuclear Information System (INIS)
Eguchi, Yuzuru
2005-07-01
The report is concerned with the evaluation of applicability of numerical modelling methods for the prediction of gas entrainment in an upper plenum of a sodium-cooled fast breeder reactor (FBR). Special attention was paid to applicability of variational multiscale (VMS) modelling in the context of the Finite Element Method. Two flow problems, which were experimentally shown to induce gas entrainment, are solved by a VMS code (MISTRAL). First, computing a benchmark problem of a gas entrainment swirl flow in a cylindrical vessel has led to the following results; (1) the VMS solution is able to resolve the precise vortex core structure more accurately than the non-VMS solution computed by Smart-fem. The circumferential velocity obtained from VMS computation rises almost double in comparison with the non-VMS solution, though it still underestimates the experimental values. (2) the half-value radius of the negative region of the second invariant of velocity gradient matches well between the VMS solution and non-VMS solution. (3) the negative/positive boundary of the second invariant of velocity gradient obtained from the VMS solution is closer to the vortex core radius observed in the experiment than that of the non-VMS solution, though the vortex dip length computed from the VMS result is shorter than the experimental value. Second, computing a benchmark problem of open channel flow with a square pillar and downstream suction pipe has led to the following results; (4) 2Δx-type spatial oscillation was observed due to lack of mesh subdivisions. (5) the distributional profile of the second invariant of velocity gradient is similar to that of the first problem (swirl flow in a cylindrical vessel), characterized by a strong negative region surrounded by a weak positive region. As a possible future plan, it may be necessary to analyze more precisely the features of unsteady vortices obtained in the second benchmark problem and to identify the difference (if any) from the
Thin-coating as an alternative approach to improve flow properties of ibuprofen powder
DEFF Research Database (Denmark)
Genina, Natalja; Räikkönen, Heikki; Ehlers, Henrik
2010-01-01
In the present study, thin-coating as a potential method for improving flow properties of cohesive ibuprofen powder was introduced. Briefly, the technique was based on the successive deposition of ultrasound-assisted fine polymer mist onto the surface of the powdered active pharmaceutical...... ingredient (API), producing individual particles with a hydrophilic thin-coat. A 0.15% m/V aqueous solution of hydroxypropyl methylcellulose (HPMC) was used. Particle size and surface analysis revealed a decrease in the cohesiveness of ibuprofen powder and an increase in the homogeneity of particle surfaces...
A Bee Colony Optimization Approach for Mixed Blocking Constraints Flow Shop Scheduling Problems
Directory of Open Access Journals (Sweden)
Mostafa Khorramizadeh
2015-01-01
Full Text Available The flow shop scheduling problems with mixed blocking constraints with minimization of makespan are investigated. The Taguchi orthogonal arrays and path relinking along with some efficient local search methods are used to develop a metaheuristic algorithm based on bee colony optimization. In order to compare the performance of the proposed algorithm, two well-known test problems are considered. Computational results show that the presented algorithm has comparative performance with well-known algorithms of the literature, especially for the large sized problems.
Effective transfer entropy approach to information flow between exchange rates and stock markets
International Nuclear Information System (INIS)
Sensoy, Ahmet; Sobaci, Cihat; Sensoy, Sadri; Alali, Fatih
2014-01-01
We investigate the strength and direction of information flow between exchange rates and stock prices in several emerging countries by the novel concept of effective transfer entropy (an alternative non-linear causality measure) with symbolic encoding methodology. Analysis shows that before the 2008 crisis, only low level interaction exists between these two variables and exchange rates dominate stock prices in general. During crisis, strong bidirectional interaction arises. In the post-crisis period, the strong interaction continues to exist and in general stock prices dominate exchange rates
Nicolleau, FCGA; Redondo, J-M
2012-01-01
This book contains a collection of the main contributions from the first five workshops held by Ercoftac Special Interest Group on Synthetic Turbulence Models (SIG42. It is intended as an illustration of the sig's activities and of the latest developments in the field. This volume investigates the use of Kinematic Simulation (KS) and other synthetic turbulence models for the particular application to environmental flows. This volume offers the best syntheses on the research status in KS, which is widely used in various domains, including Lagrangian aspects in turbulence mixing/stirring, partic
Relaxation of fibrils in blends with one viscoelastic component: Bulk and confined conditions
Cardinaels, R.M.; Moldenaers, P.
2010-01-01
Using a counter rotating parallel plate shear flow cell, shape relaxation of fibrils in a quiescent matrix is studied microscopically. Both the effects of geometrical confinement and component viscoelasticity are systematically explored. By applying a supercritical shear flow for varying amounts of
Compaction and relaxation of biofilms
Valladares Linares, R.
2015-06-18
Operation of membrane systems for water treatment can be seriously hampered by biofouling. A better characterization of biofilms in membrane systems and their impact on membrane performance may help to develop effective biofouling control strategies. The objective of this study was to determine the occurrence, extent and timescale of biofilm compaction and relaxation (decompaction), caused by permeate flux variations. The impact of permeate flux changes on biofilm thickness, structure and stiffness was investigated in situ and non-destructively with optical coherence tomography using membrane fouling monitors operated at a constant crossflow velocity of 0.1 m s−1 with permeate production. The permeate flux was varied sequentially from 20 to 60 and back to 20 L m−2 h−1. The study showed that the average biofilm thickness on the membrane decreased after elevating the permeate flux from 20 to 60 L m−2 h−1 while the biofilm thickness increased again after restoring the original flux of 20 L m−2 h−1, indicating the occurrence of biofilm compaction and relaxation. Within a few seconds after the flux change, the biofilm thickness was changed and stabilized, biofilm compaction occurred faster than the relaxation after restoring the original permeate flux. The initial biofilm parameters were not fully reinstated: the biofilm thickness was reduced by 21%, biofilm stiffness had increased and the hydraulic biofilm resistance was elevated by 16%. Biofilm thickness was related to the hydraulic biofilm resistance. Membrane performance losses are related to the biofilm thickness, density and morphology, which are influenced by (variations in) hydraulic conditions. A (temporarily) permeate flux increase caused biofilm compaction, together with membrane performance losses. The impact of biofilms on membrane performance can be influenced (increased and reduced) by operational parameters. The article shows that a (temporary) pressure increase leads to more
Longitudinal relaxation of initially straight flexible and stiff polymers
Dimitrakopoulos, Panagiotis; Dissanayake, Inuka
2004-11-01
The present talk considers the relaxation of a single flexible or stiff polymer chain from an initial straight configuration in a viscous solvent. This problem commonly arises when strong flows are turned off in both industrial and biological applications. The problem is also motivated by recent experiments with single biopolymer molecules relaxing after being fully extended by applied forces as well as by the recent development of micro-devices involving stretched tethered biopolymers. Our results are applicable to a wide array of synthetic polymers such as polyacrylamides, Kevlar and polyesters as well as biopolymers such as DNA, actin filaments, microtubules and MTV. In this talk we discuss the mechanism of the polymer relaxation as was revealed through Brownian Dynamics simulations covering a broad range of time scales and chain stiffness. After the short-time free diffusion, the chain's longitudinal reduction at early intermediate times is shown to constitute a universal behavior for any chain stiffness caused by a quasi-steady relaxation of tensions associated with the deforming action of the Brownian forces. Stiff chains are shown to exhibit a late intermediate-time longitudinal reduction associated with a relaxation of tensions affected by the deforming Brownian and the restoring bending forces. The longitudinal and transverse relaxations are shown to obey different laws, i.e. the chain relaxation is anisotropic at all times. In the talk, we show how from the knowledge of the relaxation mechanism, we can predict and explain the polymer properties including the polymer stress and the solution birefringence. In addition, a generalized stress-optic law is derived valid for any time and chain stiffness. All polymer properties which depend on the polymer length are shown to exhibit two intermediate-time behaviors with the early one to constitute a universal behavior for any chain stiffness. This work was supported in part by the Minta Martin Research Fund. The
A different approach on the onset of separation in the flow around a circular cylinder
Malamataris, Nikolaos; Sarris, I.; Pazis, D.; Liakos, A.
2016-11-01
The onset of separation in the flow around a cylinder is revisited with new insight. The goal of the research is to compute the smallest Reynolds number where the separation actual occurs rather than computing small eddies and extrapolating to the value of the Reynolds number where separation may occur. To this purpose, an accurate home made code is designed with Galerkin finite elements. The computational domain is chosen as the laboratory experiments by Taneda. It is found that in all six different choices of Taneda's diameters of the cylinders he used, separation is not observed for Re separation is computed in all of his six cases for Re = 6 . 14 . Images of this smallest eddy are shown for the first time where all characteristics of eddies are recognisable (vortex centre, separation length etc). The vorticity of the flow is computed along the cylinder surface and it is shown that, at separation, vorticity changes sign. Byproducts of this research is the computation of the drag coefficient for Reynolds numbers starting from 1 .10-5 up to 40. In addition, the separation angle (point where vorticity changes sign) is computed for 6 . 14 work done on that subject so far.
Ice Flows: A Game-based Learning approach to Science Communication
Le Brocq, Anne
2017-04-01
Game-based learning allows people to become immersed in an environment, and learn how the system functions and responds to change through playing a game. Science and gaming share a similar characteristic: they both involve learning and understanding the rules of the environment you are in, in order to achieve your objective. I will share experiences of developing and using the educational game "Ice Flows" for science communication. The game tasks the player with getting a penguin to its destination, through controlling the size of the ice sheet via ocean temperature and snowfall. Therefore, the game aims to educate the user about the environmental controls on the behaviour of the ice sheet, whilst they are enjoying playing a game with penguins. The game was funded by a NERC Large Grant entitled "Ice shelves in a warming world: Filchner Ice Shelf system, Antarctica", so uses data from the Weddell Sea sector of the West Antarctic Ice Sheet to generate unique levels. The game will be easily expandable to other regions of Antarctica and beyond, with the ultimate aim of giving a full understanding to the user of different ice flow regimes across the planet.
Spectral SP: A New Approach to Mapping Reservoir Flow and Permeability
Energy Technology Data Exchange (ETDEWEB)
Thomas, Donald M. [Univ. of Hawaii, Honolulu, HI (United States). Hawaii Inst. of Geophysics; Lienert, Barry R. [Univ. of Hawaii, Honolulu, HI (United States). Hawaii Inst. of Geophysics; Wallin, Erin L. [Univ. of Hawaii, Honolulu, HI (United States); Gasperikova, Erika [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
2014-05-27
Our objectives for the current project were to develop an innovative inversion and analysis procedure for magnetotelluric field data and time variable self-potentials that will enable us to map not only the subsurface resistivity structure of a geothermal prospect but to also delineate the permeability distribution within the field. Hence, the ultimate objective were to provide better targeting information for exploratory and development drilling of a geothermal prospect. Field data were collected and analyzed from the Kilauea Summit, Kilauea East Rift Zone, and the Humuula Saddle between Mauna Loa and Mauna Kea volcanoes. All of these areas were known or suspected to have geothermal activity of varying intensities. Our results provided evidence for significant long-term coordinated changes in spontaneous potential that could be associated with subsurface flows, significant interferences were encountered that arose from surface environmental changes (rainfall, temperature) that rendered it nearly impossible to unequivocally distinguish between deep fluid flow changes and environmental effects. Further, the analysis of the inferred spontaneous potential changes in the context of depth of the signals, and hence, permeability horizons, were unable to be completed in the time available.
Determination of mean pressure from PIV in compressible flows using the Reynolds-averaging approach
van Gent, Paul L.; van Oudheusden, Bas W.; Schrijer, Ferry F. J.
2018-03-01
The feasibility of computing the flow pressure on the basis of PIV velocity data has been demonstrated abundantly for low-speed conditions. The added complications occurring for high-speed compressible flows have, however, so far proved to be largely inhibitive for the accurate experimental determination of instantaneous pressure. Obtaining mean pressure may remain a worthwhile and realistic goal to pursue. In a previous study, a Reynolds-averaging procedure was developed for this, under the moderate-Mach-number assumption that density fluctuations can be neglected. The present communication addresses the accuracy of this assumption, and the consistency of its implementation, by evaluating of the relevance of the different contributions resulting from the Reynolds-averaging. The methodology involves a theoretical order-of-magnitude analysis, complemented with a quantitative assessment based on a simulated and a real PIV experiment. The assessments show that it is sufficient to account for spatial variations in the mean velocity and the Reynolds-stresses and that temporal and spatial density variations (fluctuations and gradients) are of secondary importance and comparable order-of-magnitude. This result permits to simplify the calculation of mean pressure from PIV velocity data and to validate the approximation of neglecting temporal and spatial density variations without having access to reference pressure data.
Directory of Open Access Journals (Sweden)
Alan Nader Ackel Ghani
2015-04-01
Full Text Available This article analyzes the credit constraints, using the cash flow sensitivity approach, of private and listed companies between 2007 and 2010. According to this approach, the econometric results show that the credit constraints are the same for either private or listed companies. This paper seeks to contribute to the literature because the study of credit constraints of private companies based on cash flow sensitivity in Brazil has been rare.
Garavaglia, Federico; Le Lay, Matthieu; Gottardi, Fréderic; Garçon, Rémy; Gailhard, Joël; Paquet, Emmanuel; Mathevet, Thibault
2017-08-01
Model intercomparison experiments are widely used to investigate and improve hydrological model performance. However, a study based only on runoff simulation is not sufficient to discriminate between different model structures. Hence, there is a need to improve hydrological models for specific streamflow signatures (e.g., low and high flow) and multi-variable predictions (e.g., soil moisture, snow and groundwater). This study assesses the impact of model structure on flow simulation and hydrological realism using three versions of a hydrological model called MORDOR: the historical lumped structure and a revisited formulation available in both lumped and semi-distributed structures. In particular, the main goal of this paper is to investigate the relative impact of model equations and spatial discretization on flow simulation, snowpack representation and evapotranspiration estimation. Comparison of the models is based on an extensive dataset composed of 50 catchments located in French mountainous regions. The evaluation framework is founded on a multi-criterion split-sample strategy. All models were calibrated using an automatic optimization method based on an efficient genetic algorithm. The evaluation framework is enriched by the assessment of snow and evapotranspiration modeling against in situ and satellite data. The results showed that the new model formulations perform significantly better than the initial one in terms of the various streamflow signatures, snow and evapotranspiration predictions. The semi-distributed approach provides better calibration-validation performance for the snow cover area, snow water equivalent and runoff simulation, especially for nival catchments.
DEFF Research Database (Denmark)
Kjølby, Birgitte Fuglsang; Østergaard, Leif; Kiselev, Valerij
Concentration of magnetic resonance imaging (MRI) contrast agents (CA) cannot be measured directly and is commonly determined indirectly using their relaxation effect. This requires knowledge of the relaxivity of the used CA. Quantitative perfusion studies involve measurement of CA concentration...... studies (3,4) as demonstrated in (5). It was previously found (6) that the perfusion measurements using dynamic susceptibility contrast inherently overestimate cerebral blood flow and volume. In view of the present result, this is attributed to the significant difference in the relaxivity of the CA...