Aeroelastic Response of Swept Aircraft Wings in a Compressible Flow Field

NASA Technical Reports Server (NTRS)

Marzocca, Piergiovanni; Librescu, Liviu; Silva, Walter A.

2000-01-01

The present study addresses the subcritical aeroelastic response of swept wings, in various flight speed regimes, to arbitrary time-dependent external excitations. The methodology based on the concept of indicial functions is carried out in time and frequency domains. As a result of this approach, the proper unsteady aerodynamic loads necessary to study the subcritical aeroelastic response of the open/closed loop aeroelastic systems, and of flutter instability, respectively are obtained. Validation of the aeroelastic model is provided, and applications to subcritical aeroelastic response to blast pressure signatures are illustrated. In this context, an original representation of the aeroelastic response in the phase-space is displayed, and pertinent conclusions on the implications of a number of selected parameters of the system are outlined.

Brittle to Semibrittle Transition in Quartz Sandstone: Energetics

NASA Astrophysics Data System (ADS)

Kanaya, Taka; Hirth, Greg

2018-01-01

Triaxial compression experiments were conducted on a quartz sandstone at effective pressures up to 175 MPa and temperatures up to 900°C. Our experiments show a transition from brittle faulting to semibrittle faulting with an increase in both pressure and temperature. The yield behavior of samples deformed in the semibrittle regime follows a compactant elliptical cap at low strain, but evolves to a dilatant Mohr-Coulomb relationship with continued compaction. Optical microscopy indicates that semibrittle deformation involves cataclastic flow through shear-enhanced compaction and grain crushing; however, transmission electron microscopy shows evidence for dislocation glide in limited portions of samples. To constrain the relative contribution of brittle and crystal plastic mechanisms, we estimate the partitioning of the inelastic work into the dissipation energy for microcracking, intergranular frictional slip, and dislocation glide. We conclude that semibrittle deformation is accommodated primarily by cataclastic mechanisms, with only a limited contribution from crystal plasticity. Mechanical data, acoustic emission records, and analysis of surface energy all indicate the activation of subcritical cracking at elevated temperature. Hence, we infer that the enhancement of subcritical cracking is responsible for the transition to semibrittle flow through promoting distributed grain-scale fractures and millimeter-scale shear bands. Subcritical cracking promotes the nucleation of microfractures at lower stresses, and the resulting decrease in flow stress retards the propagation of transgranular microfractures. Our study illuminates the important role of temperature on the micromechanics of the transition from brittle faulting to cataclastic flow in the Earth.

Comparing DNS and Experiments of Subcritical Flow Past an Isolated Surface Roughness Element

NASA Astrophysics Data System (ADS)

Doolittle, Charles; Goldstein, David

2009-11-01

Results are presented from computational and experimental studies of subcritical roughness within a Blasius boundary layer. This work stems from discrepancies presented by Stephani and Goldstein (AIAA Paper 2009-585) where DNS results did not agree with hot-wire measurements. The near wake regions of cylindrical surface roughness elements corresponding to roughness-based Reynolds numbers Rek of about 202 are of specific concern. Laser-Doppler anemometry and flow visualization in water, as well as the same spectral DNS code used by Stephani and Goldstein are used to obtain both quantitative and qualitative comparisons with previous results. Conclusions regarding previous studies will be presented alongside discussion of current work including grid resolution studies and an examination of vorticity dynamics.

Cryogenic fluid flow instabilities in heat exchangers

NASA Technical Reports Server (NTRS)

Fleming, R. B.; Staub, F. W.

1969-01-01

Analytical and experimental investigation determines the nature of oscillations and instabilities that occur in the flow of two-phase cryogenic fluids at both subcritical and supercritical pressures in heat exchangers. Test results with varying system parameters suggest certain design approaches with regard to heat exchanger geometry.

Axial-Flow Turbine Rotor Discharge-Flow Overexpansion and Limit-Loading Condition, Part I: Computational Fluid Dynamics (CFD) Investigation

NASA Technical Reports Server (NTRS)

Chen, Shu-Cheng S.

2017-01-01

A Computational Fluid Dynamic (CFD) investigation is conducted over a two-dimensional axial-flow turbine rotor blade row to study the phenomena of turbine rotor discharge flow overexpansion at subcritical, critical, and supercritical conditions. Quantitative data of the mean-flow Mach numbers, mean-flow angles, the tangential blade pressure forces, the mean-flow mass flux, and the flow-path total pressure loss coefficients, averaged or integrated across the two-dimensional computational domain encompassing two blade-passages, are obtained over a series of 14 inlet-total to exit-static pressure ratios, from 1.5 (un-choked; subcritical condition) to 10.0 (supercritical with excessively high pressure ratio.) Detailed flow features over the full domain-of-computation, such as the streamline patterns, Mach contours, pressure contours, blade surface pressure distributions, etc. are collected and displayed in this paper. A formal, quantitative definition of the limit loading condition based on the channel flow theory is proposed and explained. Contrary to the comments made in the historical works performed on this subject, about the deficiency of the theoretical methods applied in analyzing this phenomena, using modern CFD method for the study of this subject appears to be quite adequate and successful. This paper describes the CFD work and its findings.

Symmetry-breaking bifurcations and enhanced mixing in microfluidic cross-slots

NASA Astrophysics Data System (ADS)

Poole, Rob; Haward, Simon; Oliveira, Paulo; Alves, Manuel

2014-11-01

We investigate, both experimentally and numerically, a new subcritical bifurcation phenomenon for a Newtonian fluid flowing through three-dimensional cross-slot geometries. At low Reynolds numbers the flow remains steady and symmetric. For the case of square inlets and outlets, at a critical Reynolds number of approximately 40 (based on average velocity) a pitchfork bifurcation is observed beyond which the unstable symmetrical solution is replaced by a pair of steady asymmetric solutions. Sensitivity of this critical Reynolds number to the initial conditions of the simulation, resulting in a small degree of hysteresis, suggests a subcritical instability. At higher flowrates the flow becomes unsteady. The effects of channel aspect ratio are investigated on the critical conditions and excellent agreement is found between three-dimensional finite volume simulations and flow visualisation experiments in microfluidic channels. Finally we suggest this new flow bifurcation could be an effective method of enhancing mixing in microfluidic channels as significant increases in mixing quality are observed beyond the bifurcation. This enhancement occurs at flowrates more than a factor of two smaller than those observed in the well-known T-channel micromixer.

Stability limits of unsteady open capillary channel flow

NASA Astrophysics Data System (ADS)

Grah, Aleksander; Haake, Dennis; Rosendahl, Uwe; Klatte, J.?Rg; Dreyer, Michael E.

This paper is concerned with steady and unsteady flow rate limitations in open capillary channels under low-gravity conditions. Capillary channels are widely used in Space technology for liquid transportation and positioning, e.g. in fuel tanks and life support systems. The channel observed in this work consists of two parallel plates bounded by free liquid surfaces along the open sides. The capillary forces of the free surfaces prevent leaking of the liquid and gas ingestion into the flow.In the case of steady stable flow the capillary pressure balances the differential pressure between the liquid and the surrounding constant-pressure gas phase. Increasing the flow rate in small steps causes a decrease of the liquid pressure. A maximum steady flow rate is achieved when the flow rate exceeds a certain limit leading to a collapse of the free surfaces due to the choking effect. In the case of unsteady flow additional dynamic effects take place due to flow rate transition and liquid acceleration. The maximum flow rate is smaller than in the case of steady flow. On the other hand, the choking effect does not necessarily cause surface collapse and stable temporarily choked flow is possible under certain circumstances.To determine the limiting volumetric flow rate and stable flow dynamic properties, a new stability theory for both steady and unsteady flow is introduced. Subcritical and supercritical (choked) flow regimes are defined. Stability criteria are formulated for each flow type. The steady (subcritical) criterion corresponds to the speed index defined by the limiting longitudinal small-amplitude wave speed, similar to the Mach number. The unsteady (supercritical) criterion for choked flow is defined by a new characteristic number, the dynamic index. It is based on pressure balances and reaches unity at the stability limit.The unsteady model based on the Bernoulli equation and the mass balance equation is solved numerically for perfectly wetting incompressible liquids. The unsteady model and the stability theory are verified by comparison to results of a sounding rocket experiment (TEXUS 41) on capillary channel flows launched in December 2005 from ESRANGE in north Sweden. For a clear overview of subcritical, supercritical, and unstable flow, parametric studies and stability diagrams are shown and compared to experimental observations.

Ion-scale turbulence in MAST: anomalous transport, subcritical transitions, and comparison to BES measurements

NASA Astrophysics Data System (ADS)

van Wyk, F.; Highcock, E. G.; Field, A. R.; Roach, C. M.; Schekochihin, A. A.; Parra, F. I.; Dorland, W.

2017-11-01

We investigate the effect of varying the ion temperature gradient (ITG) and toroidal equilibrium scale sheared flow on ion-scale turbulence in the outer core of MAST by means of local gyrokinetic simulations. We show that nonlinear simulations reproduce the experimental ion heat flux and that the experimentally measured values of the ITG and the flow shear lie close to the turbulence threshold. We demonstrate that the system is subcritical in the presence of flow shear, i.e., the system is formally stable to small perturbations, but transitions to a turbulent state given a large enough initial perturbation. We propose that the transition to subcritical turbulence occurs via an intermediate state dominated by low number of coherent long-lived structures, close to threshold, which increase in number as the system is taken away from the threshold into the more strongly turbulent regime, until they fill the domain and a more conventional turbulence emerges. We show that the properties of turbulence are effectively functions of the distance to threshold, as quantified by the ion heat flux. We make quantitative comparisons of correlation lengths, times, and amplitudes between our simulations and experimental measurements using the MAST BES diagnostic. We find reasonable agreement of the correlation properties, most notably of the correlation time, for which significant discrepancies were found in previous numerical studies of MAST turbulence.

Preliminary research on flow rate and free surface of the accelerator driven subcritical system gravity-driven dense granular-flow target

PubMed Central

Li, Xiaodong; Wan, Jiangfeng; Zhang, Sheng; Lin, Ping; Zhang, Yanshi; Yang, Guanghui; Wang, Mengke; Duan, Wenshan; Sun, Jian’an

2017-01-01

A spallation target is one of the three core parts of the accelerator driven subcritical system (ADS), which has already been investigated for decades. Recently, a gravity-driven Dense Granular-flow Target (DGT) is proposed, which consists of a cylindrical hopper and an internal coaxial cylindrical beam pipe. The research on the flow rate and free surface are important for the design of the target whether in Heavy Liquid Metal (HLM) targets or the DGT. In this paper, the relations of flow rate and the geometry of the DGT are investigated. Simulations based on the discrete element method (DEM) implementing on Graphics Processing Units (GPUs) and experiments are both performed. It is found that the existence of an internal pipe doesn’t influence the flow rate when the distance from the bottom of the pipe to orifice is large enough even in a larger system. Meanwhile, snapshots of the free surface formed just below the beam pipe are given. It is observed that the free surface is stable over time. The entire research is meaningful for the design of DGT. PMID:29095910

Effects of Gravity on Supercritical Water Oxidation (SCWO) Processes

NASA Technical Reports Server (NTRS)

Hegde, Uday; Hicks, Michael

2013-01-01

The effects of gravity on the fluid mechanics of supercritical water jets are being studied at NASA to develop a better understanding of flow behaviors for purposes of advancing supercritical water oxidation (SCWO) technologies for applications in reduced gravity environments. These studies provide guidance for the development of future SCWO experiments in new experimental platforms that will extend the current operational range of the DECLIC (Device for the Study of Critical Liquids and Crystallization) Facility on board the International Space Station (ISS). The hydrodynamics of supercritical fluid jets is one of the basic unit processes of a SCWO reactor. These hydrodynamics are often complicated by significant changes in the thermo-physical properties that govern flow behavior (e.g., viscosity, thermal conductivity, specific heat, compressibility, etc), particularly when fluids transition from sub-critical to supercritical conditions. Experiments were conducted in a 150 ml reactor cell under constant pressure with water injections at various flow rates. Flow configurations included supercritical jets injected into either sub-critical or supercritical water. Profound gravitational influences were observed, particularly in the transition to turbulence, for the flow conditions under study. These results will be presented and the parameters of the flow that control jet behavior will be examined and discussed.

Preliminary research on flow rate and free surface of the accelerator driven subcritical system gravity-driven dense granular-flow target.

PubMed

Li, Xiaodong; Wan, Jiangfeng; Zhang, Sheng; Lin, Ping; Zhang, Yanshi; Yang, Guanghui; Wang, Mengke; Duan, Wenshan; Sun, Jian'an; Yang, Lei

2017-01-01

A spallation target is one of the three core parts of the accelerator driven subcritical system (ADS), which has already been investigated for decades. Recently, a gravity-driven Dense Granular-flow Target (DGT) is proposed, which consists of a cylindrical hopper and an internal coaxial cylindrical beam pipe. The research on the flow rate and free surface are important for the design of the target whether in Heavy Liquid Metal (HLM) targets or the DGT. In this paper, the relations of flow rate and the geometry of the DGT are investigated. Simulations based on the discrete element method (DEM) implementing on Graphics Processing Units (GPUs) and experiments are both performed. It is found that the existence of an internal pipe doesn't influence the flow rate when the distance from the bottom of the pipe to orifice is large enough even in a larger system. Meanwhile, snapshots of the free surface formed just below the beam pipe are given. It is observed that the free surface is stable over time. The entire research is meaningful for the design of DGT.

Solution of transonic flows by an integro-differential equation method

NASA Technical Reports Server (NTRS)

Ogana, W.

1978-01-01

Solutions of steady transonic flow past a two-dimensional airfoil are obtained from a singular integro-differential equation which involves a tangential derivative of the perturbation velocity potential. Subcritical flows are solved by taking central differences everywhere. For supercritical flows with shocks, central differences are taken in subsonic flow regions and backward differences in supersonic flow regions. The method is applied to a nonlifting parabolic-arc airfoil and to a lifting NACA 0012 airfoil. Results compare favorably with those of finite-difference schemes.

Calculation of transonic flows using an extended integral equation method

NASA Technical Reports Server (NTRS)

Nixon, D.

1976-01-01

An extended integral equation method for transonic flows is developed. In the extended integral equation method velocities in the flow field are calculated in addition to values on the aerofoil surface, in contrast with the less accurate 'standard' integral equation method in which only surface velocities are calculated. The results obtained for aerofoils in subcritical flow and in supercritical flow when shock waves are present compare satisfactorily with the results of recent finite difference methods.

Supercritical bedforms and sedimentary structures from field and core studies, Middle Eocene deep-marine base-of-slope environment, Ainsa Basin, Spanish Pyrenees

NASA Astrophysics Data System (ADS)

Cornard, Pauline; Pickering, Kevin

2017-04-01

In recent years, many researchers have focussed on supercritical- and subcritical-flow deposits using flume-tank experiments (e.g., Cartigny el al., 2011; Postma et al., 2014; Postma and Cartigny, 2014), or from direct observations on presently active deep-water systems (e.g., Hughes et al., 2012). Using outcrop and core examples from a base-of-slope environment in the Middle Eocene Ainsa Basin, Spanish Pyrenees, and with published experimental work, a range of deposits are interpreted as upper-flow regime sedimentary structures. This contribution focusses on the interpretation of several supercritical bedforms (antidunes and chutes-and-pools) observed on the field and upper-flow regime sedimentary structures recognized in cores. The spatial distribution of supercritical-flow deposits obtained from an analysis of field outcrops and core sedimentary logs are evaluated in relation to the depositional environment (channel axis, off-axis, margin and interfan). The frequency distributions of the bed thicknesses are also analysed in relation to supercritical versus subcritical bed-thickness distributions.

Mathematical Modeling of the Heat Transfer and Conditions of Ignition of a Turbulent Flow of a Reactive Gas

NASA Astrophysics Data System (ADS)

Matvienko, O. V.

2016-01-01

Results of investigations into the heat transfer and conditions of ignition of a turbulent flow of a chemically reactive gas have been presented. Approximation formulas have been obtained for determining the critical conditions of ignition of the turbulent flow, the length of the preflame zone, and the criterion of heat transfer in subcritical and supercritical reaction regimes.

Adaptive-Wall Wind-Tunnel Investigations

DTIC Science & Technology

1981-02-01

boundary condition for unconfined flow. In this way, theory and experiment are combined to minimize wall interference. The concept of an adaptive wall...should be noted that although shock waves extend to the walls, the exterior-flow calculation was based on subcritical-flow theory . Goodyer’s configuration...and v by aerodynamic probes. Both subsonic and transonic small- disturbance theory were used, as appropriate, to evaluate the functional rela

Simulations of the flow past a cylinder using an unsteady double wake model

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

Ramos-García, N.; Sarlak, H.; Andersen, S. J.

2016-06-08

In the present work, the in-house UnSteady Double Wake Model (USDWM) is used to simulate flows past a cylinder at subcritical, supercritical, and transcritical Reynolds numbers. The flow model is a two-dimensional panel method which uses the unsteady double wake technique to model flow separation and its dynamics. In the present work the separation location is obtained from experimental data and fixed in time. The highly unsteady flow field behind the cylinder is analyzed in detail, comparing the vortex shedding charactericts under the different flow conditions.

On the instability of a three-dimensional attachment-line boundary layer - Weakly nonlinear theory and a numerical approach

NASA Technical Reports Server (NTRS)

Hall, P.; Malik, M. R.

1986-01-01

The instability of a three-dimensional attachment-line boundary layer is considered in the nonlinear regime. Using weakly nonlinear theory, it is found that, apart from a small interval near the (linear) critical Reynolds number, finite-amplitude solutions bifurcate subcritically from the upper branch of the neutral curve. The time-dependent Navier-Stokes equations for the attachment-line flow have been solved using a Fourier-Chebyshev spectral method and the subcritical instability is found at wavenumbers that correspond to the upper branch. Both the theory and the numerical calculations show the existence of supercritical finite-amplitude (equilibrium) states near the lower branch which explains why the observed flow exhibits a preference for the lower branch modes. The effect of blowing and suction on nonlinear stability of the attachment-line boundary layer is also investigated.

On the instability of a 3-dimensional attachment line boundary layer: Weakly nonlinear theory and a numerical approach

NASA Technical Reports Server (NTRS)

Hall, P.; Malik, M. R.

1984-01-01

The instability of a three dimensional attachment line boundary layer is considered in the nonlinear regime. Using weakly nonlinear theory, it is found that, apart from a small interval near the (linear) critical Reynolds number, finite amplitude solutions bifurcate subcritically from the upper branch of the neutral curve. The time dependent Navier-Stokes equations for the attachment line flow have been solved using a Fourier-Chebyshev spectral method and the subcritical instability is found at wavenumbers that correspond to the upper branch. Both the theory and the numerical calculations show the existence of supercritical finite amplitude (equilibrium) states near the lower branch which explains why the observed flow exhibits a preference for the lower branch modes. The effect of blowing and suction on nonlinear stability of the attachment line boundary layer is also investigated.

Volterra Series Approach for Nonlinear Aeroelastic Response of 2-D Lifting Surfaces

NASA Technical Reports Server (NTRS)

Silva, Walter A.; Marzocca, Piergiovanni; Librescu, Liviu

2001-01-01

The problem of the determination of the subcritical aeroelastic response and flutter instability of nonlinear two-dimensional lifting surfaces in an incompressible flow-field via Volterra series approach is addressed. The related aeroelastic governing equations are based upon the inclusion of structural nonlinearities, of the linear unsteady aerodynamics and consideration of an arbitrary time-dependent external pressure pulse. Unsteady aeroelastic nonlinear kernels are determined, and based on these, frequency and time histories of the subcritical aeroelastic response are obtained, and in this context the influence of geometric nonlinearities is emphasized. Conclusions and results displaying the implications of the considered effects are supplied.

Supercritical convection, critical heat flux, and coking characteristics of propane

NASA Technical Reports Server (NTRS)

Rousar, D. C.; Gross, R. S.; Boyd, W. C.

1984-01-01

The heat transfer characteristics of propane at subcritical and supercritical pressure were experimentally evaluated using electrically heated Monel K-500 tubes. A design correlation for supercritical heat transfer coefficient was established using the approach previously applied to supercritical oxygen. Flow oscillations were observed and the onset of these oscillations at supercritical pressures was correlated with wall-to-bulk temperature ratio and velocity. The critical heat flux measured at subcritical pressure was correlated with the product of velocity and subcooling. Long duration tests at fixed heat flux conditions were conducted to evaluate coking on the coolant side tube wall and coking rates comparable to RP-1 were observed.

TNT and RDX degradation and extraction from contaminated soil using subcritical water.

PubMed

Islam, Mohammad Nazrul; Shin, Moon-Su; Jo, Young-Tae; Park, Jeong-Hun

2015-01-01

The use of explosives either for industrial or military operations have resulted in the environmental pollution, poses ecological and health hazard. In this work, a subcritical water extraction (SCWE) process at laboratory scale was used at varying water temperature (100-175 °C) and flow rate (0.5-1.5 mL min(-1)), to treat 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) contaminated soil, to reveal information with respect to the explosives removal (based on the analyses of soil residue after extraction), and degradation performance (based on the analyses of water extracts) of this process. Continuous flow subcritical water has been considered on removal of explosives to avoid the repartitioning of non-degraded compounds to the soil upon cooling which usually occurs in the batch system. In the SCWE experiments, near complete degradation of both TNT and RDX was observed at 175 °C based on analysis of water extracts and soil. Test results also indicated that TNT removal of >99% and a complete RDX removal were achieved by this process, when the operating conditions were 1 mL min(-1), and treatment time of 20 min, after the temperature reached 175 °C. HPLC-UV and ion chromatography analysis confirmed that the explosives underwent for degradation. The low concentration of explosives found in the process wastewater indicates that water recycling may be viable, to treat additional soil. Our results have shown in the remediation of explosives contaminated soil, the effectiveness of the continuous flow SCWE process. Copyright © 2014 Elsevier Ltd. All rights reserved.

A Green's function formulation for a nonlinear potential flow solution applicable to transonic flow

NASA Technical Reports Server (NTRS)

Baker, A. J.; Fox, C. H., Jr.

1977-01-01

Routine determination of inviscid subsonic flow fields about wing-body-tail configurations employing a Green's function approach for numerical solution of the perturbation velocity potential equation is successfully extended into the high subsonic subcritical flow regime and into the shock-free supersonic flow regime. A modified Green's function formulation, valid throughout a range of Mach numbers including transonic, that takes an explicit accounting of the intrinsic nonlinearity in the parent governing partial differential equations is developed. Some considerations pertinent to flow field predictions in the transonic flow regime are discussed.

Finite element analysis of inviscid subsonic boattail flow

NASA Technical Reports Server (NTRS)

Chima, R. V.; Gerhart, P. M.

1981-01-01

A finite element code for analysis of inviscid subsonic flows over arbitrary nonlifting planar or axisymmetric bodies is described. The code solves a novel primitive variable formulation of the coupled irrotationality and compressible continuity equations. Results for flow over a cylinder, a sphere, and a NACA 0012 airfoil verify the code. Computed subcritical flows over an axisymmetric boattailed afterbody compare well with finite difference results and experimental data. Interative coupling with an integral turbulent boundary layer code shows strong viscous effects on the inviscid flow. Improvements in code efficiency and extensions to transonic flows are discussed.

Finite amplitude instability of second-order fluids in plane Poiseuille flow.

NASA Technical Reports Server (NTRS)

Mcintire, L. V.; Lin, C. H.

1972-01-01

The hydrodynamic stability of plane Poiseuille flow of second-order fluids to finite amplitude disturbances is examined using the method of Stuart and Watson as extended by Reynolds and Potter. For slightly non-Newtonian fluids subcritical instabilities are predicted. No supercritical equilibrium states are expected if the entire spectrum of disturbance wavelengths is present. Possible implications with respect to the Toms phenomenon are discussed.

Dynamics of homogeneous shear turbulence: A key role of the nonlinear transverse cascade in the bypass concept.

PubMed

Mamatsashvili, G; Khujadze, G; Chagelishvili, G; Dong, S; Jiménez, J; Foysi, H

2016-08-01

To understand the mechanism of the self-sustenance of subcritical turbulence in spectrally stable (constant) shear flows, we performed direct numerical simulations of homogeneous shear turbulence for different aspect ratios of the flow domain with subsequent analysis of the dynamical processes in spectral or Fourier space. There are no exponentially growing modes in such flows and the turbulence is energetically supported only by the linear growth of Fourier harmonics of perturbations due to the shear flow non-normality. This non-normality-induced growth, also known as nonmodal growth, is anisotropic in spectral space, which, in turn, leads to anisotropy of nonlinear processes in this space. As a result, a transverse (angular) redistribution of harmonics in Fourier space is the main nonlinear process in these flows, rather than direct or inverse cascades. We refer to this type of nonlinear redistribution as the nonlinear transverse cascade. It is demonstrated that the turbulence is sustained by a subtle interplay between the linear nonmodal growth and the nonlinear transverse cascade. This course of events reliably exemplifies a well-known bypass scenario of subcritical turbulence in spectrally stable shear flows. These two basic processes mainly operate at large length scales, comparable to the domain size. Therefore, this central, small wave number area of Fourier space is crucial in the self-sustenance; we defined its size and labeled it as the vital area of turbulence. Outside the vital area, the nonmodal growth and the transverse cascade are of secondary importance: Fourier harmonics are transferred to dissipative scales by the nonlinear direct cascade. Although the cascades and the self-sustaining process of turbulence are qualitatively the same at different aspect ratios, the number of harmonics actively participating in this process (i.e., the harmonics whose energies grow more than 10% of the maximum spectral energy at least once during evolution) varies, but always remains quite large (equal to 36, 86, and 209) in the considered here three aspect ratios. This implies that the self-sustenance of subcritical turbulence cannot be described by low-order models.

Dynamics of homogeneous shear turbulence: A key role of the nonlinear transverse cascade in the bypass concept

NASA Astrophysics Data System (ADS)

Mamatsashvili, G.; Khujadze, G.; Chagelishvili, G.; Dong, S.; Jiménez, J.; Foysi, H.

2016-08-01

To understand the mechanism of the self-sustenance of subcritical turbulence in spectrally stable (constant) shear flows, we performed direct numerical simulations of homogeneous shear turbulence for different aspect ratios of the flow domain with subsequent analysis of the dynamical processes in spectral or Fourier space. There are no exponentially growing modes in such flows and the turbulence is energetically supported only by the linear growth of Fourier harmonics of perturbations due to the shear flow non-normality. This non-normality-induced growth, also known as nonmodal growth, is anisotropic in spectral space, which, in turn, leads to anisotropy of nonlinear processes in this space. As a result, a transverse (angular) redistribution of harmonics in Fourier space is the main nonlinear process in these flows, rather than direct or inverse cascades. We refer to this type of nonlinear redistribution as the nonlinear transverse cascade. It is demonstrated that the turbulence is sustained by a subtle interplay between the linear nonmodal growth and the nonlinear transverse cascade. This course of events reliably exemplifies a well-known bypass scenario of subcritical turbulence in spectrally stable shear flows. These two basic processes mainly operate at large length scales, comparable to the domain size. Therefore, this central, small wave number area of Fourier space is crucial in the self-sustenance; we defined its size and labeled it as the vital area of turbulence. Outside the vital area, the nonmodal growth and the transverse cascade are of secondary importance: Fourier harmonics are transferred to dissipative scales by the nonlinear direct cascade. Although the cascades and the self-sustaining process of turbulence are qualitatively the same at different aspect ratios, the number of harmonics actively participating in this process (i.e., the harmonics whose energies grow more than 10% of the maximum spectral energy at least once during evolution) varies, but always remains quite large (equal to 36, 86, and 209) in the considered here three aspect ratios. This implies that the self-sustenance of subcritical turbulence cannot be described by low-order models.

Aeroelastic Response of Nonlinear Wing Section By Functional Series Technique

NASA Technical Reports Server (NTRS)

Marzocca, Piergiovanni; Librescu, Liviu; Silva, Walter A.

2000-01-01

This paper addresses the problem of the determination of the subcritical aeroelastic response and flutter instability of nonlinear two-dimensional lifting surfaces in an incompressible flow-field via indicial functions and Volterra series approach. The related aeroelastic governing equations are based upon the inclusion of structural and damping nonlinearities in plunging and pitching, of the linear unsteady aerodynamics and consideration of an arbitrary time-dependent external pressure pulse. Unsteady aeroelastic nonlinear kernels are determined, and based on these, frequency and time histories of the subcritical aeroelastic response are obtained, and in this context the influence of the considered nonlinearities is emphasized. Conclusions and results displaying the implications of the considered effects are supplied.

Aeroelastic Response of Nonlinear Wing Section by Functional Series Technique

NASA Technical Reports Server (NTRS)

Silva, Walter A.; Marzocca, Piergiovanni

2001-01-01

This paper addresses the problem of the determination of the subcritical aeroelastic response and flutter instability of nonlinear two-dimensional lifting surfaces in an incompressible flow-field via indicial functions and Volterra series approach. The related aeroelastic governing equations are based upon the inclusion of structural and damping nonlinearities in plunging and pitching, of the linear unsteady aerodynamics and consideration of an arbitrary time-dependent external pressure pulse. Unsteady aeroelastic nonlinear kernels are determined, and based on these, frequency and time histories of the subcritical aeroelastic response are obtained, and in this context the influence of the considered nonlinearities is emphasized. Conclusions and results displaying the implications of the considered effects are supplied.

Some Operating Experience and Problems Encountered During Operation of a Free-jet Facility

NASA Technical Reports Server (NTRS)

Mcaulay, John E; Prince, William R

1957-01-01

During a free-jet investigation of a 28-inch ram-jet engine at a Mach number of 2.35, flow pulsation at the engine inlet were discovered which proved to have an effect on the engine performance and operational characteristics, particularly the engine rich blowout limits. This report discusses the finding of the flow pulsations, their elimination, and effect. Other facility characteristics, such as the establishment of flow simulation and the degree of subcritical operation of the diffuser, are also explained.

Instability mechanisms and transition scenarios of spiral turbulence in Taylor-Couette flow.

PubMed

Meseguer, Alvaro; Mellibovsky, Fernando; Avila, Marc; Marques, Francisco

2009-10-01

Alternating laminar and turbulent helical bands appearing in shear flows between counterrotating cylinders are accurately computed and the near-wall instability phenomena responsible for their generation identified. The computations show that this intermittent regime can only exist within large domains and that its spiral coherence is not dictated by endwall boundary conditions. A supercritical transition route, consisting of a progressive helical alignment of localized turbulent spots, is carefully studied. Subcritical routes disconnected from secondary laminar flows have also been identified.

Novel Method to Assess Arterial Insufficiency in Rodent Hindlimb

PubMed Central

Ziegler, Matthew A.; DiStasi, Matthew R.; Miller, Steven J.; Dalsing, Michael C.; Unthank, Joseph L.

2015-01-01

Background Lack of techniques to assess maximal blood flow capacity thwarts the use of rodent models of arterial insufficiency to evaluate therapies for intermittent claudication. We evaluated femoral vein outflow (VO) in combination with stimulated muscle contraction as a potential method to assess functional hindlimb arterial reserve and therapeutic efficacy in a rodent model of subcritical limb ischemia. Materials and methods VO was measured with perivascular flow probes at rest and during stimulated calf muscle contraction in young healthy rats (Wistar Kyoto, WKY; lean Zucker, LZR) and rats with cardiovascular risk factors (Spontaneously Hypertensive, SHR; Obese Zucker, OZR) with acute and/or chronic femoral arterial occlusion. Therapeutic efficacy was assessed by administration of Ramipril or Losartan to SHR after femoral artery excision. Results VO measurement in WKY demonstrated the utility of this method to assess hindlimb perfusion at rest and during calf muscle contraction. While application to diseased models (OZR, SHR) demonstrated normal resting perfusion compared to contralateral limbs, a significant reduction in reserve capacity was uncovered with muscle stimulation. Administration of Ramipril and Losartan demonstrated significant improvement in functional arterial reserve. Conclusion The results demonstrate that this novel method to assess distal limb perfusion in small rodents with subcritical limb ischemia is sufficient to unmask perfusion deficits not apparent at rest, detect impaired compensation in diseased animal models with risk factors, and assess therapeutic efficacy. The approach provides a significant advance in methods to investigate potential mechanisms and novel therapies for subcritical limb ischemia in pre-clinical rodent models. PMID:26850199

CFD Analysis and Design of Detailed Target Configurations for an Accelerator-Driven Subcritical System

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

Kraus, Adam; Merzari, Elia; Sofu, Tanju

2016-08-01

High-fidelity analysis has been utilized in the design of beam target options for an accelerator driven subcritical system. Designs featuring stacks of plates with square cross section have been investigated for both tungsten and uranium target materials. The presented work includes the first thermal-hydraulic simulations of the full, detailed target geometry. The innovative target cooling manifold design features many regions with complex flow features, including 90 bends and merging jets, which necessitate three-dimensional fluid simulations. These were performed using the commercial computational fluid dynamics code STAR-CCM+. Conjugate heat transfer was modeled between the plates, cladding, manifold structure, and fluid. Steady-statemore » simulations were performed but lacked good residual convergence. Unsteady simulations were then performed, which converged well and demonstrated that flow instability existed in the lower portion of the manifold. It was established that the flow instability had little effect on the peak plate temperatures, which were well below the melting point. The estimated plate surface temperatures and target region pressure were shown to provide sufficient margin to subcooled boiling for standard operating conditions. This demonstrated the safety of both potential target configurations during normal operation.« less

Production version of the extended NASA-Langley Vortex Lattice FORTRAN computer program. Volume 1: User's guide

NASA Technical Reports Server (NTRS)

Lamar, J. E.; Herbert, H. E.

1982-01-01

The latest production version, MARK IV, of the NASA-Langley vortex lattice computer program is summarized. All viable subcritical aerodynamic features of previous versions were retained. This version extends the previously documented program capabilities to four planforms, 400 panels, and enables the user to obtain vortex-flow aerodynamics on cambered planforms, flowfield properties off the configuration in attached flow, and planform longitudinal load distributions.

Models of fold-related hysteresis

NASA Astrophysics Data System (ADS)

Shtern, Vladimir

2018-05-01

Hysteresis is a strongly nonlinear physics phenomenon observed in many fluid mechanics flows. This paper composes evolution equations of the minimal nonlinearity and dimension which describe three hysteresis kinds related to a fold catastrophe formed by (i) two fold bifurcations, (ii) fold and transcritical bifurcations, and (iii) fold and subcritical bifurcations.

Mixing Under Transcritical Flow Conditions

DTIC Science & Technology

2011-03-01

between them. The signals were then sent to two amplifiers (Krohn-Hite model 7500 and a Trek model PZD2000A), one for each piezo-siren. The amplified...In Annual Research Briefs, pages 73–84. Center for Turbulence Research, NASA Ames/Stanford Univ., 1999. [61] C. Segal and SA Polikhov. Subcritical to

Accelerator driven sub-critical core

DOEpatents

McIntyre, Peter M; Sattarov, Akhdiyor

2015-03-17

Systems and methods for operating an accelerator driven sub-critical core. In one embodiment, a fission power generator includes a sub-critical core and a plurality of proton beam generators. Each of the proton beam generators is configured to concurrently provide a proton beam into a different area of the sub-critical core. Each proton beam scatters neutrons within the sub-critical core. The plurality of proton beam generators provides aggregate power to the sub-critical core, via the proton beams, to scatter neutrons sufficient to initiate fission in the sub-critical core.

Computational methods for aerodynamic design using numerical optimization

NASA Technical Reports Server (NTRS)

Peeters, M. F.

1983-01-01

Five methods to increase the computational efficiency of aerodynamic design using numerical optimization, by reducing the computer time required to perform gradient calculations, are examined. The most promising method consists of drastically reducing the size of the computational domain on which aerodynamic calculations are made during gradient calculations. Since a gradient calculation requires the solution of the flow about an airfoil whose geometry was slightly perturbed from a base airfoil, the flow about the base airfoil is used to determine boundary conditions on the reduced computational domain. This method worked well in subcritical flow.

Subcritical thermal convection of liquid metals in a rapidly rotating sphere

NASA Astrophysics Data System (ADS)

Cardin, P.; Schaeffer, N.; Guervilly, C.; Kaplan, E.

2017-12-01

Planetary cores consist of liquid metals (low Prandtl number Pr) that convect as the core cools. Here we study nonlinear convection in a rotating (low Ekman number Ek) planetary core using a fully 3D direct (down to Ek=10-7) and a quasi geostrophic (down to Ek=10-10) numerical simulations. Near the critical thermal forcing (Rayleigh number Ra), convection onsets as thermal Rossby waves, but as Ra increases, this state is superceded by one dominated by advection. At moderate rotation, these states (here called the weak branch and strong branch, respectively) are continuously connected. As the planetary core rotates faster, the continuous transition is replaced by hysteresis cycles and subcriticality until the weak branch disappears entirely and the strong branch onsets in a turbulent state at Ek<10-6 when Pr=0.01. Here the strong branch persists even as the thermal forcing decreases well below the linear onset of convection (Ra 0.4Racrit in this study for Ek=10-10 and Pr=0.01). We highlight the importance of the Reynolds stress, which is required for convection to persist below the linear onset. We further note the presence of a strong zonal flow that is nonetheless unimportant to the convective subcritical state. Our study suggests that, in the asymptotic regime of rapid rotation relevant for planetary interiors, thermal convection of liquid metals in a sphere onsets and shuts down through a subcritical bifurcation. This scenario may be relevant to explain the lunar and martian dynamo extinctions.

Birth of a hydraulic jump

NASA Astrophysics Data System (ADS)

Duchesne, Alexis; Bohr, Tomas; Andersen, Anders

2017-11-01

The hydraulic jump, i.e., the sharp transition between a supercritical and a subcritical free-surface flow, has been extensively studied in the past centuries. However, ever since Leonardo da Vinci asked it for the first time, an important question has been left unanswered: How does a hydraulic jump form? We present an experimental and theoretical study of the formation of stationary hydraulic jumps in centimeter wide channels. Two starting situations are considered: The channel is, respectively, empty or filled with liquid, the liquid level being fixed by the wetting properties and the boundary conditions. We then change the flow-rate abruptly from zero to a constant value. In an empty channel, we observe the formation of a stationary hydraulic jump in a two-stage process: First, the channel fills by the advancing liquid front, which undergoes a transition from supercritical to subcritical at some position in the channel. Later the influence of the downstream boundary conditions makes the jump move slowly upstream to its final position. In the pre-filled channel, the hydraulic jump forms at the injector edge and then moves downstream to its final position.

Multiple steady solutions in a driven cavity

NASA Astrophysics Data System (ADS)

Osman, Kahar; McHugh, John

2004-11-01

The symmetric driven cavity (Farias and McHugh, Phys. Fluids, 2002) in two and three dimensions is considered. Results are obtained via numerical computations of the Navier-Stokes equations, assuming constant density. The numerical algorithm is a splitting method, using finite differences. The forcing at the top is sinusoidal, and the forcing wavelength is allowed to vary in subsequent trials. The two dimensional results with 2, 4, and 6 oscillations in the forcing show a subcritical bifurcation to an asymmetric solution, with the Reynolds number as the important parameter. The symmetric solution is found to have vortex flow with streamlines that conform to the boundary shape. The asymmetric solution has vortex flow with streamlines that are approximately circular near the vortex center. Two dimensional results with 8 or more oscillations in the forcing show a supercritical bifurcation to an asymmetric solution. Three dimensional simulations show that the length ratios play a critical role, and the depth of the cavity must be large compared to the height in order to acheive the same subcritical bifurcation as with two dimensions.

Subcritical saturation of the magnetorotational instability through mean magnetic field generation

NASA Astrophysics Data System (ADS)

Xie, Jin-Han; Julien, Keith; Knobloch, Edgar

2018-03-01

The magnetorotational instability is widely believed to be responsible for outward angular momentum transport in astrophysical accretion discs. The efficiency of this transport depends on the amplitude of this instability in the saturated state. We employ an asymptotic expansion based on an explicit, astrophysically motivated time-scale separation between the orbital period, Alfvén crossing time and viscous or resistive dissipation time-scales, originally proposed by Knobloch and Julien, to formulate a semi-analytical description of the saturated state in an incompressible disc. In our approach a Keplerian shear flow is maintained by the central mass but the instability saturates via the generation of a mean vertical magnetic field. The theory assumes that the time-averaged angular momentum flux and the radial magnetic flux are constant and determines both self-consistently. The results predict that, depending on parameters, steady saturation may be supercritical or subcritical, and in the latter case that the upper (lower) solution branch is always stable (unstable). The angular momentum flux is always outward, consistent with the presence of accretion, and for fixed wavenumber peaks in the subcritical regime. The limit of infinite Reynolds number at large but finite magnetic Reynolds number is also discussed.

Patterned Roughness for Cross-flow Transition Control at Mach 6

NASA Astrophysics Data System (ADS)

Arndt, Alexander; Matlis, Eric; Semper, Michael; Corke, Thomas

2017-11-01

Experiments are performed to investigate patterned discrete roughness for transition control on a sharp right-circular cone at an angle of attack at Mach 6.0. The approach to transition control is based on exciting less-amplified (subcritical) stationary cross-flow (CF) modes that suppress the growth of the more-amplified (critical) CF modes, and thereby delay transition. The experiments were performed in the Air Force Academy Ludwieg Tube which is a conventional (noisy) design. The cone model is equipped with a motorized 3-D traversing mechanism that mounts on the support sting. The traversing mechanism held a closely-spaced pair of fast-response total pressure Pitot probes. The model utilized a removable tip to exchange between different tip-roughness conditions. Mean flow distortion x-development indicated that the transition Reynolds number increased by 25% with the addition of the subcritical roughness. The energy in traveling disturbances was centered in the band of most amplified traveling CF modes predicted by linear theory. The spatial pattern in the amplitude of the traveling CF modes indicated a nonlinear (sum and difference) interaction between the stationary and traveling CF modes that might explain differences in Retrans between noisy and quiet environments. Air Force Grant FA9550-15-1-0278.

Exact coherent structures in an asymptotically reduced description of parallel shear flows

NASA Astrophysics Data System (ADS)

Beaume, Cédric; Knobloch, Edgar; Chini, Gregory P.; Julien, Keith

2015-02-01

A reduced description of shear flows motivated by the Reynolds number scaling of lower-branch exact coherent states in plane Couette flow (Wang J, Gibson J and Waleffe F 2007 Phys. Rev. Lett. 98 204501) is constructed. Exact time-independent nonlinear solutions of the reduced equations corresponding to both lower and upper branch states are found for a sinusoidal, body-forced shear flow. The lower branch solution is characterized by fluctuations that vary slowly along the critical layer while the upper branch solutions display a bimodal structure and are more strongly focused on the critical layer. The reduced equations provide a rational framework for investigations of subcritical spatiotemporal patterns in parallel shear flows.

Experimental scaling law for the subcritical transition to turbulence in plane Poiseuille flow.

PubMed

Lemoult, Grégoire; Aider, Jean-Luc; Wesfreid, José Eduardo

2012-02-01

We present an experimental study of the transition to turbulence in a plane Poiseuille flow. Using a well-controlled perturbation, we analyze the flow by using extensive particle image velocimetry and flow visualization (using laser-induced fluorescence) measurements, and use the deformation of the mean velocity profile as a criterion to characterize the state of the flow. From a large parametric study, four different states are defined, depending on the values of the Reynolds number and the amplitude of the perturbation. We discuss the role of coherent structures, such as hairpin vortices, in the transition. We find that the minimal amplitude of the perturbation triggering transition scales asymptotically as Re(-1).

Homoclinic tangle on the edge of shear turbulence.

PubMed

van Veen, Lennaert; Kawahara, Genta

2011-09-09

Experiments and simulations lend mounting evidence for the edge state hypothesis on subcritical transition to turbulence, which asserts that simple states of fluid motion mediate between laminar and turbulent shear flow as their stable manifolds separate the two in state space. In this Letter we describe flows homoclinic to a time-periodic edge state that display the essential properties of turbulent bursting. During a burst, vortical structures and the associated energy dissipation are highly localized near the wall, in contrast with the familiar regeneration cycle.

Acoustic response of vortex breakdown modes in a coaxial isothermal unconfined swirling jet

NASA Astrophysics Data System (ADS)

Santhosh, R.; Basu, Saptarshi

2015-03-01

The present experimental work is concerned with the study of amplitude dependent acoustic response of an isothermal coaxial swirling jet. The excitation amplitude is increased in five distinct steps at the burner's Helmholtz resonator mode (i.e., 100 Hz). Two flow states are compared, namely, sub-critical and super-critical vortex breakdown (VB) that occur before and after the critical conical sheet breakdown, respectively. The geometric swirl number is varied in the range 2.14-4.03. Under the influence of external pulsing, global response characteristics are studied based on the topological changes observed in time-averaged 2D flow field. These are obtained from high resolution 2D PIV (particle image velocimetry) in the longitudinal-mid plane. PIV results also illustrate the changes in the normalized vortex core coordinates (rvcc/(rvcc)0 Hz, yvcc/(yvcc)0 Hz) of internal recirculation zone (IRZ). A strong forced response is observed at 100 Hz (excitation frequency) in the convectively unstable region which get amplified based on the magnitude of external forcing. The radial extent of this forced response region at a given excitation amplitude is represented by the acoustic response region (b). The topological placement of the responsive convectively unstable region is a function of both the intensity of imparted swirl (characterized by swirl number) and forcing amplitude. It is observed that for sub-critical VB mode, an increase in the excitation amplitude till a critical value shifts the vortex core centre (particularly, the vortex core moves downstream and radially outwards) leading to drastic fanning-out/widening of the IRZ. This is accompanied by ˜30% reduction in the recirculation velocity of the IRZ. It is also observed that b < R (R: radial distance from central axis to outer shear layer-OSL). At super-critical amplitudes, the sub-critical IRZ topology transits back (the vortex core retracts upstream and radially inwards) and finally undergoes a transverse shrinkage ((4vcc)/(rvcc) 0 Hz decreases by ˜20%) when b ≥ R. In contrast, the vortex core of super-critical breakdown mode consistently spreads radially outwards and is displaced further downstream. Finally, the IRZ fans-out at the threshold excitation amplitude. However, the acoustic response region b is still less than R. This is explained based on the characteristic geometric swirl number (SG) of the flow regimes. The super-critical flow mode with higher SG (hence, higher radial pressure drop due to rotational effect which scales as ΔP ˜ ρuθ2 and acts inwards towards the center line) compared to sub-critical state imposes a greater resistance to the radial outward spread of b. As a result, the acoustic energy supplied to the super-critical flow mode increases the degree of acoustic response at the pulsing frequency and energizes its harmonics (evident from power spectra). As a disturbance amplifier, the stronger convective instability mode within the flow structure of super-critical VB causes the topology to widen/fan-out severely at threshold excitation amplitude.

Effects of cylinder Reynolds number on the turbulent horseshoe vortex system and near wake of a surface-mounted circular cylinder

NASA Astrophysics Data System (ADS)

Kirkil, Gokhan; Constantinescu, George

2015-07-01

The turbulent horseshoe vortex (HV) system and the near-wake flow past a circular cylinder mounted on a flat bed in an open channel are investigated based on the results of eddy-resolving simulations and supporting flow visualizations. Of particular interest are the changes in the mean flow and turbulence statistics within the HV region as the necklace vortices wrap around the cylinder's base and the variation of the mean flow and turbulence statistics in the near wake, in between the channel bed and the free surface. While it is well known that the drag crisis induces important changes in the flow past infinitely long circular cylinders, the changes are less understood and more complex for the case of flow past a surface-mounted cylinder. This is because even at very high cylinder Reynolds numbers, ReD, the flow regime remains subcritical in the vicinity of the bed surface due to the reduction of the incoming flow velocity within the bottom boundary layer. The paper provides a detailed discussion of the changes in the flow physics between cylinder Reynolds numbers at which the flow in the upstream part of the separated shear layers (SSLs) is laminar (ReD = 16 000, subcritical flow regime) and Reynolds numbers at which the transition occurs inside the attached boundary layers away from the bed and the flow within the SSLs is turbulent (ReD = 5 ∗ 105, supercritical flow regime). The changes between the two regimes in the dynamics and level of coherence of the large-scale coherent structures (necklace vortices, vortex tubes shed in the SSLs and roller vortices shed in the wake) and their capacity to induce high-magnitude bed friction velocities in the mean and instantaneous flow fields and to amplify the near-bed turbulence are analyzed. Being able to quantitatively and qualitatively describe these changes is critical to understand Reynolds-number-induced scale effects on sediment erosion mechanisms around cylinders mounted on a loose bed, which is a problem of great practical relevance (e.g., for pier scour studies).

Rock fracture processes in chemically reactive environments

NASA Astrophysics Data System (ADS)

Eichhubl, P.

2015-12-01

Rock fracture is traditionally viewed as a brittle process involving damage nucleation and growth in a zone ahead of a larger fracture, resulting in fracture propagation once a threshold loading stress is exceeded. It is now increasingly recognized that coupled chemical-mechanical processes influence fracture growth in wide range of subsurface conditions that include igneous, metamorphic, and geothermal systems, and diagenetically reactive sedimentary systems with possible applications to hydrocarbon extraction and CO2 sequestration. Fracture processes aided or driven by chemical change can affect the onset of fracture, fracture shape and branching characteristics, and fracture network geometry, thus influencing mechanical strength and flow properties of rock systems. We are investigating two fundamental modes of chemical-mechanical interactions associated with fracture growth: 1. Fracture propagation may be aided by chemical dissolution or hydration reactions at the fracture tip allowing fracture propagation under subcritical stress loading conditions. We are evaluating effects of environmental conditions on critical (fracture toughness KIc) and subcritical (subcritical index) fracture properties using double torsion fracture mechanics tests on shale and sandstone. Depending on rock composition, the presence of reactive aqueous fluids can increase or decrease KIc and/or subcritical index. 2. Fracture may be concurrent with distributed dissolution-precipitation reactions in the hostrock beyond the immediate vicinity of the fracture tip. Reconstructing the fracture opening history recorded in crack-seal fracture cement of deeply buried sandstone we find that fracture length growth and fracture opening can be decoupled, with a phase of initial length growth followed by a phase of dominant fracture opening. This suggests that mechanical crack-tip failure processes, possibly aided by chemical crack-tip weakening, and distributed solution-precipitation creep in the hostrock can independently affect fracture opening displacement and thus fracture aperture profiles and aperture distribution.

Aeroelastic coupling of geometrically nonlinear structures and linear unsteady aerodynamics: Two formulations

NASA Astrophysics Data System (ADS)

Demasi, L.; Livne, E.

2009-07-01

Two different time domain formulations of integrating commonly used frequency-domain unsteady aerodynamic models based on a modal approach with full order finite element models for structures with geometric nonlinearities are presented. Both approaches are tailored to flight vehicle configurations where geometric stiffness effects are important but where deformations are moderate, flow is attached, and linear unsteady aerodynamic modeling is adequate, such as low aspect ratio wings or joined-wing and strut-braced wings at small to moderate angles of attack. Results obtained using the two approaches are compared using both planar and non-planar wing configurations. Sub-critical and post-flutter speeds are considered. It is demonstrated that the two methods lead to the same steady solution for the sub-critical case after the transients subside. It is also shown that the two methods predict the amplitude and frequency of limit cycle oscillation (when present) with the same accuracy.

A review of some Reynolds number effects related to bodies at high angles of attack

NASA Technical Reports Server (NTRS)

Polhamus, E. C.

1984-01-01

A review of some effects of Reynolds number on selected aerodynamic characteristics of two- and three-dimensional bodies of various cross sections in relation to fuselages at high angles of attack at subsonic and transonic speeds is presented. Emphasis is placed on the Reynolds number ranges above the subcritical and angles of attack where lee side vortex flow or unsteady wake type flows predominate. Lists of references, arranged in subject categories, are presented with emphasis on those which include data over a reasonable Reynolds number range. Selected Reynolds number data representative of various aerodynamic flows around bodies are presented and analyzed and some effects of these flows on fuselage aerodynamic parameters are discussed.

NASTRAN level 16 user's manual updates for aeroelastic analysis of bladed discs

NASA Technical Reports Server (NTRS)

Elchuri, V.; Gallo, A. M.

1980-01-01

The NASTRAN aeroelastic and flutter capability was extended to solve a class of problems associated with axial flow turbomachines. The capabilities of the program are briefly discussed. The aerodynamic data pertaining to the bladed disc sector, the associated aerodynamic modeling, the steady aerothermoelastic 'design/analysis' formulations, and the modal, flutter, and subcritical roots analyses are described. Sample problems and their solutions are included.

Target design optimization for an electron accelerator driven subcritical facility with circular and square beam profiles.

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

Gohar, M. Y. A; Sofu, T.; Zhong, Z.

2008-10-30

A subcritical facility driven by an electron accelerator is planned at the Kharkov Institute of Physics and Technology (KIPT) in Ukraine for medical isotope production, materials research, training, and education. The conceptual design of the facility is being pursued through collaborations between ANL and KIPT. As part of the design effort, the high-fidelity analyses of various target options are performed with formulations to reflect the realistic configuration and the three dimensional geometry of each design. This report summarizes the results of target design optimization studies for electron beams with two different beam profiles. The target design optimization is performed viamore » the sequential neutronic, thermal-hydraulic, and structural analyses for a comprehensive assessment of each configuration. First, a target CAD model is developed with proper emphasis on manufacturability to provide a basis for separate but consistent models for subsequent neutronic, thermal-hydraulic, and structural analyses. The optimizations are pursued for maximizing the neutron yield, streamlining the flow field to avoid hotspots, and minimizing the thermal stresses to increase the durability. In addition to general geometric modifications, the inlet/outlet channel configurations, target plate partitioning schemes, flow manipulations and rates, electron beam diameter/width options, and cladding material choices are included in the design optimizations. The electron beam interactions with the target assembly and the neutronic response of the subcritical facility are evaluated using the MCNPX code. the results for the electron beam energy deposition, neutron generation, and utilization in the subcritical pile are then used to characterize the axisymmetric heat generation profiles in the target assembly with explicit simulations of the beam tube, the coolant, the clad, and the target materials. Both tungsten and uranium are considered as target materials. Neutron spectra from tungsten and uranium are very similar allowing the use of either material in the subcritical assembly without changing its characteristics. However, the uranium target has a higher neutron yield, which increases the neutron flux of the subcritical assembly. Based on the considered dimensions and heat generation profiles, the commercial CFD software Star-CD is used for the thermal-hydraulic analysis of each target design to satisfy a set of thermal criteria, the most limiting of which being to maintain the water temperature 50 below the boiling point. It is found that the turbulence in the inlet channels dissipates quickly in narrow gaps between the target plates and, as a result, the heat transfer is limited by the laminar flow conditions. On average, 3-D CFD analyses of target assemblies agree well with 1-D calculations using RELAP (performed by KIPT). However, the recirculation and stagnation zones predicted with the CFD models prove the importance of a 3-D analysis to avoid the resulting hotspots. The calculated temperatures are subsequently used for the structural analysis of each target configuration to satisfy the other engineering design requirements. The thermo-structural calculations are performed mostly with NASTRAN and the results occasionally compared with the results from MARC. Both, NASTRAN and MARC are commercially available structural-mechanics analysis software. Although, a significant thermal gradient forms in target elements along the beam direction, the high thermal stresses are generally observed peripherally around the edge of thin target disks/plates. Due to its high thermal conductivity, temperatures and thermal stresses in tungsten target are estimated to be significantly lower than in uranium target. The deformations of the target disks/plates are found to be insignificant, which eliminate concerns for flow blockages in narrow coolant channels. Consistent with the specifications of the KIPT accelerator to be used in this facility, the electron beam power is 100-kW with electron energy in the range of 100 to 200 MeV. As expected, the 100 MeV electrons deposit their energy faster while the 200-MeV electrons spread their energy deposition further along the beam direction. However in that electron energy range, the energy deposition profiles near the beam window require very thin target plates/disks to limit the temperatures and thermal stresses.« less

Development of a Research Reactor Protocol for Neutron Multiplication Measurements

DOE PAGES

Arthur, Jennifer Ann; Bahran, Rian Mustafa; Hutchinson, Jesson D.; ...

2018-03-20

A new series of subcritical measurements has been conducted at the zero-power Walthousen Reactor Critical Facility (RCF) at Rensselaer Polytechnic Institute (RPI) using a 3He neutron multiplicity detector. The Critical and Subcritical 0-Power Experiment at Rensselaer (CaSPER) campaign establishes a protocol for advanced subcritical neutron multiplication measurements involving research reactors for validation of neutron multiplication inference techniques, Monte Carlo codes, and associated nuclear data. There has been increased attention and expanded efforts related to subcritical measurements and analyses, and this work provides yet another data set at known reactivity states that can be used in the validation of state-of-the-art Montemore » Carlo computer simulation tools. The diverse (mass, spatial, spectral) subcritical measurement configurations have been analyzed to produce parameters of interest such as singles rates, doubles rates, and leakage multiplication. MCNP ®6.2 was used to simulate the experiment and the resulting simulated data has been compared to the measured results. Comparison of the simulated and measured observables (singles rates, doubles rates, and leakage multiplication) show good agreement. This work builds upon the previous years of collaborative subcritical experiments and outlines a protocol for future subcritical neutron multiplication inference and subcriticality monitoring measurements on pool-type reactor systems.« less

Development of a Research Reactor Protocol for Neutron Multiplication Measurements

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

Arthur, Jennifer Ann; Bahran, Rian Mustafa; Hutchinson, Jesson D.

A new series of subcritical measurements has been conducted at the zero-power Walthousen Reactor Critical Facility (RCF) at Rensselaer Polytechnic Institute (RPI) using a 3He neutron multiplicity detector. The Critical and Subcritical 0-Power Experiment at Rensselaer (CaSPER) campaign establishes a protocol for advanced subcritical neutron multiplication measurements involving research reactors for validation of neutron multiplication inference techniques, Monte Carlo codes, and associated nuclear data. There has been increased attention and expanded efforts related to subcritical measurements and analyses, and this work provides yet another data set at known reactivity states that can be used in the validation of state-of-the-art Montemore » Carlo computer simulation tools. The diverse (mass, spatial, spectral) subcritical measurement configurations have been analyzed to produce parameters of interest such as singles rates, doubles rates, and leakage multiplication. MCNP ®6.2 was used to simulate the experiment and the resulting simulated data has been compared to the measured results. Comparison of the simulated and measured observables (singles rates, doubles rates, and leakage multiplication) show good agreement. This work builds upon the previous years of collaborative subcritical experiments and outlines a protocol for future subcritical neutron multiplication inference and subcriticality monitoring measurements on pool-type reactor systems.« less

Simultaneous dispersive liquid-liquid microextraction derivatisation and gas chromatography mass spectrometry analysis of subcritical water extracts of sweet and sour cherry stems.

PubMed

Švarc-Gajić, Jaroslava; Clavijo, Sabrina; Suárez, Ruth; Cvetanović, Aleksandra; Cerdà, Víctor

2018-03-01

Cherry stems have been used in traditional medicine mostly for the treatment of urinary tract infections. Extraction with subcritical water, according to its selectivity, efficiency and other aspects, differs substantially from conventional extraction techniques. The complexity of plant subcritical water extracts is due to the ability of subcritical water to extract different chemical classes of different physico-chemical properties and polarities in a single run. In this paper, dispersive liquid-liquid microextraction (DLLME) with simultaneous derivatisation was optimised for the analysis of complex subcritical water extracts of cherry stems to allow simple and rapid preparation prior to gas chromatography-mass spectrometry (GC-MS). After defining optimal extracting and dispersive solvents, the optimised method was used for the identification of compounds belonging to different chemical classes in a single analytical run. The developed sample preparation protocol enabled simultaneous extraction and derivatisation, as well as convenient coupling with GC-MS analysis, reducing the analysis time and number of steps. The applied analytical protocol allowed simple and rapid chemical screening of subcritical water extracts and was used for the comparison of subcritical water extracts of sweet and sour cherry stems. Graphical abstract DLLME GC MS analysis of cherry stem extracts obtained by subcritical water.

A fast approach to designing airfoils from given pressure distribution in compressible flows

NASA Technical Reports Server (NTRS)

Daripa, Prabir

1987-01-01

A new inverse method for aerodynamic design of airfols is presented for subcritical flows. The pressure distribution in this method can be prescribed as a function of the arc length of the as-yet unknown body. This inverse problem is shown to be mathematically equivalent to solving only one nonlinear boundary value problem subject to known Dirichlet data on the boundary. The solution to this problem determines the airfoil, the freestream Mach number, and the upstream flow direction. The existence of a solution to a given pressure distribution is discussed. The method is easy to implement and extremely efficient. A series of results for which comparisons are made with the known airfoils is presented.

Subcritical Transition in Channel Flows

NASA Astrophysics Data System (ADS)

Maestri, Joseph; Hall, Philip

2014-11-01

Exact-coherent structures, or colloquially non-linear solutions to the Navier-Stokes equations, have been the subject of great interest over the past decade due to their relevance in understanding the process of transition to turbulence in shear flows. Over the past few years the relationship between high Reynolds number vortex-wave interaction theory and such states has been elucidated in a number of papers and has provided a solid asymptotic framework to understand the so-called self-sustaining process that maintains such structures. In this talk, we will discuss this relationship before talking about recent work on solving the vortex-wave interaction equations using numerical techniques in order to propose laminar-flow control techniques.

Subcritical Thermal Convection of Liquid Metals in a Rapidly Rotating Sphere

NASA Astrophysics Data System (ADS)

Kaplan, E. J.; Schaeffer, N.; Vidal, J.; Cardin, P.

2017-09-01

Planetary cores consist of liquid metals (low Prandtl number Pr) that convect as the core cools. Here, we study nonlinear convection in a rotating (low Ekman number Ek) planetary core using a fully 3D direct numerical simulation. Near the critical thermal forcing (Rayleigh number Ra), convection onsets as thermal Rossby waves, but as Ra increases, this state is superseded by one dominated by advection. At moderate rotation, these states (here called the weak branch and strong branch, respectively) are smoothly connected. As the planetary core rotates faster, the smooth transition is replaced by hysteresis cycles and subcriticality until the weak branch disappears entirely and the strong branch onsets in a turbulent state at Ek <10-6. Here, the strong branch persists even as the thermal forcing drops well below the linear onset of convection (Ra =0.7 Racrit in this study). We highlight the importance of the Reynolds stress, which is required for convection to subsist below the linear onset. In addition, the Péclet number is consistently above 10 in the strong branch. We further note the presence of a strong zonal flow that is nonetheless unimportant to the convective state. Our study suggests that, in the asymptotic regime of rapid rotation relevant for planetary interiors, thermal convection of liquid metals in a sphere onsets through a subcritical bifurcation.

Analysis of the fluid flow and heat transfer in a thin liquid film in the presence and absence of gravity

NASA Technical Reports Server (NTRS)

Rahman, M. M.; Hankey, W. L.; Faghri, A.

1991-01-01

The hydrodynamic and thermal behavior of a thin liquid film flowing over a solid horizontal surface is analyzed for both plane and radially spreading flows. The situations where the gravitational force is completely absent and where it is significant are analyzed separately and their practical relevance to a micro-gravity environment is discussed. In the presence of gravity, in addition to Reynolds number, the Froude number of the film is found to be an important parameter that determines the supercritical and subcritical flow regimes and any associated hydraulic jump. A closed-form solution is possible under some flow situations, whereas others require numerical integration of ordinary differential equations. The approximate analytical results are found to compare well with the available two-dimensional numerical solutions.

Mathematical simulation of forced expiration.

PubMed

Elad, D; Kamm, R D; Shapiro, A H

1988-07-01

Flow limitation during forced expiration is simulated by a mathematical model. This model draws on the pressure-area law obtained in the accompanying paper, and the methods of analysis for one-dimensional flow in collapsible tubes developed by Shapiro (Trans. ASME J. Biomech. Eng. 99: 126-147, 1977). These methods represent an improvement over previous models in that 1) the effects of changing lung volume and of parenchymal-bronchial interdependence are simulated; 2) a more realistic representation of collapsed airways is employed; 3) a solution is obtained mouthward of the flow-limiting site by allowing for a smooth transition from sub- to supercritical flow speeds, then matching mouth pressure by imposing an elastic jump (an abrupt transition from super- to subcritical flow speeds) at the appropriate location; and 4) the effects of levels of effort (or vacuum pressure) in excess of those required to produce incipient flow limitation are examined, including the effects of potential physiological limitation.

Subcritical water extraction of lipids from wet algal biomass

DOEpatents

Deng, Shuguang; Reddy, Harvind K.; Schaub, Tanner; Holguin, Francisco Omar

2016-05-03

Methods of lipid extraction from biomass, in particular wet algae, through conventionally heated subcritical water, and microwave-assisted subcritical water. In one embodiment, fatty acid methyl esters from solids in a polar phase are further extracted to increase biofuel production.

A coupled CFD and wake model simulation of helicopter rotor in hover

NASA Astrophysics Data System (ADS)

Zhao, Qinghe; Li, Xiaodong

2018-03-01

The helicopter rotor wake plays a dominant role since it affects the flow field structure. It is very difficult to predict accurately of the flow-field. The numerical dissipation is so excessive that it eliminates the vortex structure. A hybrid method of CFD and prescribed wake model was constructed by applying the prescribed wake model as much as possible. The wake vortices were described as a single blade tip vortex in this study. The coupling model is used to simulate the flow field. Both non-lifting and lifting cases have been calculated with subcritical and supercritical tip Mach numbers. Surface pressure distributions are presented and compared with experimental data. The calculated results agree well with the experimental data.

Experimental Investigation of Shear Driven Liquid Films for Film Cooling Applications in Liquid Rocket Engines

DTIC Science & Technology

2012-12-01

6 1.1.1 Differences Between Hot-Fire at Subcritical Conditions and Cold Flow ........10 1.1.2 Differences at Supercritical Conditions...cooling. 1.1.2 Differences at Supercritical Conditions Liquid film cooling is expected to behave even more differently at supercritical conditions...phase will behave more like the mixing of two gases of dissimilar densities. Once enough heat is imparted into the supercritical fuel film, it

Subcritical Water Hydrolysis of Peptides: Amino Acid Side-Chain Modifications

NASA Astrophysics Data System (ADS)

Powell, Thomas; Bowra, Steve; Cooper, Helen J.

2017-09-01

Previously we have shown that subcritical water may be used as an alternative to enzymatic digestion in the proteolysis of proteins for bottom-up proteomics. Subcritical water hydrolysis of proteins was shown to result in protein sequence coverages greater than or equal to that obtained following digestion with trypsin; however, the percentage of peptide spectral matches for the samples treated with trypsin were consistently greater than for those treated with subcritical water. This observation suggests that in addition to cleavage of the peptide bond, subcritical water treatment results in other hydrolysis products, possibly due to modifications of amino acid side chains. Here, a model peptide comprising all common amino acid residues (VQSIKCADFLHYMENPTWGR) and two further model peptides (VCFQYMDRGDR and VQSIKADFLHYENPTWGR) were treated with subcritical water with the aim of probing any induced amino acid side-chain modifications. The hydrolysis products were analyzed by direct infusion electrospray tandem mass spectrometry, either collision-induced dissociation or electron transfer dissociation, and liquid chromatography collision-induced dissociation tandem mass spectrometry. The results show preferential oxidation of cysteine to sulfinic and sulfonic acid, and oxidation of methionine. In the absence of cysteine and methionine, oxidation of tryptophan was observed. In addition, water loss from aspartic acid and C-terminal amidation were observed in harsher subcritical water conditions. [Figure not available: see fulltext.

Research on unsteady transonic flow theory

NASA Technical Reports Server (NTRS)

Revell, J. D.

1973-01-01

A two-dimensional theory is considered for the unsteady flow disturbances caused by aeroelastic deformations of a thick wing at high subsonic freestream Mach numbers, having a single, internally embedded supercritical (locally supersonic) steady flow region adjacent to the low pressure side of the wing. The theory develops a matrix of unsteady aerodynamic influence coefficients (AICs) suitable as a strip theory for aeroelastic analysis of large aspect ratio thick wings of moderate sweep, typical of a wide class of current and future aircraft. The theory derives the linearized unsteady flow solutions separately for both the subcritical and supercritical regions. These solutions are coupled together to give the requisite (wing pressure-downwash) AICs by the intermediate step of defining flow disturbances on the sonic line, and at the shock wave; these intermediate quantities are then algebraically eliminated by expressing them in terms of the wing surface downwash.

Hydraulic jump and Bernoulli equation in nonlinear shallow water model

NASA Astrophysics Data System (ADS)

Sun, Wen-Yih

2018-06-01

A shallow water model was applied to study the hydraulic jump and Bernoulli equation across the jump. On a flat terrain, when a supercritical flow plunges into a subcritical flow, discontinuity develops on velocity and Bernoulli function across the jump. The shock generated by the obstacle may propagate downstream and upstream. The latter reflected from the inflow boundary, moves downstream and leaves the domain. Before the reflected wave reaching the obstacle, the short-term integration (i.e., quasi-steady) simulations agree with Houghton and Kasahara's results, which may have unphysical complex solutions. The quasi-steady flow is quickly disturbed by the reflected wave, finally, flow reaches steady and becomes critical without complex solutions. The results also indicate that Bernoulli function is discontinuous but the potential of mass flux remains constant across the jump. The latter can be used to predict velocity/height in a steady flow.

Beam Flutter and Energy Harvesting in Internal Flow

NASA Astrophysics Data System (ADS)

Tosi, Luis Phillipe; Colonius, Tim; Sherrit, Stewart; Lee, Hyeong Jae

2017-11-01

Aeroelastic flutter, largely studied for causing engineering failures, has more recently been used as a means of extracting energy from the flow. Particularly, flutter of a cantilever or an elastically mounted plate in a converging-diverging flow passage has shown promise as an energy harvesting concept for internal flow applications. The instability onset is observed as a function of throat velocity, internal wall geometry, fluid and structure material properties. To enable these devices, our work explores features of the fluid-structure coupled dynamics as a function of relevant nondimensional parameters. The flutter boundary is examined through stability analysis of a reduced order model, and corroborated with numerical simulations at low Reynolds number. Experiments for an energy harvester design are qualitatively compared to results from analytical and numerical work, suggesting a robust limit cycle ensues due to a subcritical Hopf bifurcation. Bosch Corporation.

Mechanical weathering and rock erosion by climate-dependent subcritical cracking

NASA Astrophysics Data System (ADS)

Eppes, Martha-Cary; Keanini, Russell

2017-06-01

This work constructs a fracture mechanics framework for conceptualizing mechanical rock breakdown and consequent regolith production and erosion on the surface of Earth and other terrestrial bodies. Here our analysis of fracture mechanics literature explicitly establishes for the first time that all mechanical weathering in most rock types likely progresses by climate-dependent subcritical cracking under virtually all Earth surface and near-surface environmental conditions. We substantiate and quantify this finding through development of physically based subcritical cracking and rock erosion models founded in well-vetted fracture mechanics and mechanical weathering, theory, and observation. The models show that subcritical cracking can culminate in significant rock fracture and erosion under commonly experienced environmental stress magnitudes that are significantly lower than rock critical strength. Our calculations also indicate that climate strongly influences subcritical cracking—and thus rock weathering rates—irrespective of the source of the stress (e.g., freezing, thermal cycling, and unloading). The climate dependence of subcritical cracking rates is due to the chemophysical processes acting to break bonds at crack tips experiencing these low stresses. We find that for any stress or combination of stresses lower than a rock's critical strength, linear increases in humidity lead to exponential acceleration of subcritical cracking and associated rock erosion. Our modeling also shows that these rates are sensitive to numerous other environment, rock, and mineral properties that are currently not well characterized. We propose that confining pressure from overlying soil or rock may serve to suppress subcritical cracking in near-surface environments. These results are applicable to all weathering processes.

Effect of water on critical and subcritical fracture properties of Woodford shale

NASA Astrophysics Data System (ADS)

Chen, Xiaofeng; Eichhubl, Peter; Olson, Jon E.

2017-04-01

Subcritical fracture behavior of shales under aqueous conditions is poorly characterized despite increased relevance to oil and gas resource development and seal integrity in waste disposal and subsurface carbon sequestration. We measured subcritical fracture properties of Woodford shale in ambient air, dry CO2 gas, and deionized water by using the double-torsion method. Compared to tests in ambient air, the presence of water reduces fracture toughness by 50%, subcritical index by 77%, and shear modulus by 27% and increases inelastic deformation. Comparison between test specimens coated with a hydrophobic agent and uncoated specimens demonstrates that the interaction of water with the bulk rock results in the reduction of fracture toughness and enhanced plastic effects, while water-rock interaction limited to the vicinity of the propagating fracture tip by a hydrophobic specimen coating lowers subcritical index and increases fracture velocity. The observed deviation of a rate-dependent subcritical index from the power law K-V relations for coated specimens tested in water is attributed to a time-dependent weakening process resulting from the interaction between water and clays in the vicinity of the fracture tip.

The calculation of steady non-linear transonic flow over finite wings with linear theory aerodynamics

NASA Technical Reports Server (NTRS)

Cunningham, A. M., Jr.

1976-01-01

The feasibility of calculating steady mean flow solutions for nonlinear transonic flow over finite wings with a linear theory aerodynamic computer program is studied. The methodology is based on independent solutions for upper and lower surface pressures that are coupled through the external flow fields. Two approaches for coupling the solutions are investigated which include the diaphragm and the edge singularity method. The final method is a combination of both where a line source along the wing leading edge is used to account for blunt nose airfoil effects; and the upper and lower surface flow fields are coupled through a diaphragm in the plane of the wing. An iterative solution is used to arrive at the nonuniform flow solution for both nonlifting and lifting cases. Final results for a swept tapered wing in subcritical flow show that the method converges in three iterations and gives excellent agreement with experiment at alpha = 0 deg and 2 deg. Recommendations are made for development of a procedure for routine application.

TAIR: A transonic airfoil analysis computer code

NASA Technical Reports Server (NTRS)

Dougherty, F. C.; Holst, T. L.; Grundy, K. L.; Thomas, S. D.

1981-01-01

The operation of the TAIR (Transonic AIRfoil) computer code, which uses a fast, fully implicit algorithm to solve the conservative full-potential equation for transonic flow fields about arbitrary airfoils, is described on two levels of sophistication: simplified operation and detailed operation. The program organization and theory are elaborated to simplify modification of TAIR for new applications. Examples with input and output are given for a wide range of cases, including incompressible, subcritical compressible, and transonic calculations.

Subcritical unity for the Argonaut reactor (in Portuguese)

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

Mongiovi, G.; Aghina, L.O.B.

1971-04-01

tubetype fuel elements aiming at the construction of a subcritical unit employing the internal thermal column of an Argonaut reactor as a source. The results confirmed the feasibility of the use of natural UO/sub 2/ for the proposed arrangement as long as one has a strong source or a subcritical unit diameter greater than 100 cm. (INIS)

Two-dimensional dynamics of elasto-inertial turbulence and its role in polymer drag reduction

NASA Astrophysics Data System (ADS)

Sid, S.; Terrapon, V. E.; Dubief, Y.

2018-02-01

The goal of the present study is threefold: (i) to demonstrate the two-dimensional nature of the elasto-inertial instability in elasto-inertial turbulence (EIT), (ii) to identify the role of the bidimensional instability in three-dimensional EIT flows, and (iii) to establish the role of the small elastic scales in the mechanism of self-sustained EIT. Direct numerical simulations of viscoelastic fluid flows are performed in both two- and three-dimensional straight periodic channels using the Peterlin finitely extensible nonlinear elastic model (FENE-P). The Reynolds number is set to Reτ=85 , which is subcritical for two-dimensional flows but beyond the transition for three-dimensional ones. The polymer properties selected correspond to those of typical dilute polymer solutions, and two moderate Weissenberg numbers, Wiτ=40 ,100 , are considered. The simulation results show that sustained turbulence can be observed in two-dimensional subcritical flows, confirming the existence of a bidimensional elasto-inertial instability. The same type of instability is also observed in three-dimensional simulations where both Newtonian and elasto-inertial turbulent structures coexist. Depending on the Wi number, one type of structure can dominate and drive the flow. For large Wi values, the elasto-inertial instability tends to prevail over the Newtonian turbulence. This statement is supported by (i) the absence of typical Newtonian near-wall vortices and (ii) strong similarities between two- and three-dimensional flows when considering larger Wi numbers. The role of small elastic scales is investigated by introducing global artificial diffusion (GAD) in the hyperbolic transport equation for polymers. The aim is to measure how the flow reacts when the smallest elastic scales are progressively filtered out. The study results show that the introduction of large polymer diffusion in the system strongly damps a significant part of the elastic scales that are necessary to feed turbulence, eventually leading to flow laminarization. A sufficiently high Schmidt number (weakly diffusive polymers) is necessary to allow self-sustained turbulence to settle. Although EIT can withstand a low amount of diffusion and remains in a nonlaminar chaotic state, adding a finite amount of GAD in the system can have an impact on the dynamics and lead to important quantitative changes, even for Schmidt numbers as large as 102. The use of GAD should therefore be avoided in viscoelastic flow simulations.

Some calculations of transonic potential flow for the NACA 64A006 airfoil with oscillating flap

NASA Technical Reports Server (NTRS)

Bennett, R. M.; Bland, S. R.

1978-01-01

A method for calculating the transonic flow over steady and oscillating airfoils was developed by Isogai. It solves the full potential equation with a semi-implicit, time-marching, finite difference technique. Steady flow solutions are obtained from time asymptotic solutions for a steady airfoil. Corresponding oscillatory solutions are obtained by initiating an oscillation and marching in time for several cycles until a converged periodic solution is achieved. In this paper the method is described in general terms, and results are compared with experimental data for both steady flow and for oscillations at several values of reduced frequency. Good agreement for static pressures is shown for subcritical speeds, with increasing deviation as Mach number is increased into the supercritical speed range. Fair agreement with experiment was obtained at high reduced frequencies with larger deviations at low reduced frequencies.

A qualitative view of cryogenic fluid injection into high speed flows

NASA Technical Reports Server (NTRS)

Hendricks, R. C.; Schlumberger, J.; Proctor, M.

1991-01-01

The injection of supercritical pressure, subcritical temperature fluids, into a 2-D, ambient, static temperature and static pressure supersonic tunnel and free jet supersonic nitrogen flow field was observed. Observed patterns with fluid air were the same as those observed for fluid nitrogen injected into the tunnel at 90 deg to the supersonic flow. The nominal injection pressure was of 6.9 MPa and tunnel Mach number was 2.7. When injected directly into and opposing the tunnel exhaust flow, the observed patterns with fluid air were similar to those observed for fluid nitrogen but appeared more diffusive. Cryogenic injection creates a high density region within the bow shock wake but the standoff distance remains unchanged from the gaseous value. However, as the temperature reaches a critical value, the shock faded and advanced into the supersonic stream. For both fluids, nitrogen and air, the phenomena was completely reversible.

Early stages of transition in viscosity-stratified channel flow

NASA Astrophysics Data System (ADS)

Govindarajan, Rama; Jose, Sharath; Brandt, Luca

2013-11-01

In parallel shear flows, it is well known that transition to turbulence usually occurs through a subcritical process. In this work we consider a flow through a channel across which there is a linear temperature variation. The temperature gradient leads to a viscosity variation across the channel. A large body of work has been done in the linear regime for this problem, and it has been seen that viscosity stratification can lead to considerable changes in stability and transient growth characteristics. Moreover contradictory effects of introducing a non uniform viscosity in the system have been reported. We conduct a linear stability analysis and direct numerical simulations (DNS) for this system. We show that the optimal initial structures in the viscosity-stratified case, unlike in unstratified flow, do not span the width of the channel, but are focussed near one wall. The nonlinear consequences of the localisation of the structures will be discussed.

Multiple Equilibria Associated with Response of the ITCZ to Seasonal SST Forcing

NASA Technical Reports Server (NTRS)

Chao, Winston C.

1998-01-01

Supported by numerical experiment results, the abrupt change of the location of the intertropical convergence zone (ITCZ), from the equatorial trough flow regime to the monsoon trough flow regime is interpreted as a subcritical instability. The existence of these multiple quasi-equilibria is due to the balance of two "forces" on the ITCZ: one toward the equator, due to the earth's rotation, has a nonlinear latitudinal dependence; and the other toward the latitude of the sea surface (or ground) temperature peak has a relatively linear latitudinal dependence. This work pivots on the finding that the ITCZ and Hadley circulation can still exist without the pole-to-equator gradient of radiative-convective equilibrium temperature.

Transition to spatiotemporal chaos in a two-dimensional hydrodynamic system.

PubMed

Pirat, Christophe; Naso, Aurore; Meunier, Jean-Louis; Maïssa, Philippe; Mathis, Christian

2005-04-08

We study the transition to spatiotemporal chaos in a two-dimensional hydrodynamic experiment where liquid columns take place in the gravity induced instability of a liquid film. The film is formed below a plane grid which is used as a porous media and is continuously supplied with a controlled flow rate. This system can be either ordered (on a hexagonal structure) or disordered depending on the flow rate. We observe, for the first time in an initially structured state, a subcritical transition to spatiotemporal disorder which arises through spatiotemporal intermittency. Statistics of numbers, creations, and fusions of columns are investigated. We exhibit a critical behavior close to the directed percolation one.

Droplet-turbulence interactions in subcritical and supercritical evaporating sprays

NASA Technical Reports Server (NTRS)

Santavicca, Domenic A.; Coy, Edward; Greenfield, Stuart; Song, Young-Hoon

1991-01-01

The objective of this research is to obtain an improved understanding of droplet turbulence interactions in vaporizing liquid sprays under conditions typical of those encountered in liquid fueled rocket engines. The interaction between liquid droplets and the surrounding turbulent gas flow affects droplet dispersion, droplet collisions, droplet vaporization and gas-phase, fuel-oxidant mixing, and therefore has a significant effect on the engine's combustion characteristics. An example of this is the role which droplet-turbulence interactions are believed to play in combustion instabilities. Despite their importance, droplet-turbulence interactions and their effect on liquid fueled rocket engine performance are not well understood. This is particularly true under supercritical conditions, where many conventional concepts, such as surface tension, no longer apply. Our limited understanding of droplet-turbulence interactions, under both subcritical conditions, represents a major limitation in our ability to design improved liquid previously unavailable information and valuable new insights which will directly impact the design of future liquid fueled rocket engines, as well as, allow for the development of significantly improved spray combustion models, making such models useful design tools.

Proximity-interference wake-induced vibration at subcritical Re: Mechanism analysis using a linear dynamic model

NASA Astrophysics Data System (ADS)

Li, Xintao; Zhang, Weiwei; Gao, Chuanqiang

2018-03-01

Wake-induced vibration (WIV) contains rich and complex phenomena due to the flow interference between cylinders. The aim of the present study is to gain physical insight into the intrinsic dynamics of WIV via linear stability analysis (LSA) of the fluid-structure interaction (FSI) system. A reduced-order-model-based linear dynamic model, combined with the direct computational fluid dynamics/computational structural dynamics simulation method, is adopted to investigate WIV in two identical tandem cylinders at low Re. The spacing ratio L/D, with L as the center-to-center distance and D as the diameter of cylinders, is selected as 2.0 to consider the effect of proximity flow interference. Results show that extensive WIV along with the vortex shedding could occur at subcritical Re conditions due to the instability of one coupled mode (i.e., coupled mode I, CM-I) of the FSI system. The eigenfrequency of CM-I transfers smoothly from close to the reduced natural frequency of structure to the eigenfrequency of uncoupled wake mode as the reduced velocity U* increases. Thus, CM-I characterizes as the structure mode (SM) at low U*, while it characterizes as the wake mode (WM) at large U*. Mode conversion of CM-I is the primary cause of the "frequency transition" phenomenon observed in WIV responses. Furthermore, LSA indicates that there exists a critical mass ratio mcr*, below which no upper instability boundary of CM-I exists (Uup p e r *→∞ ). The unbounded instability of CM-I ultimately leads to the "infinite WIV" phenomenon. The neutral stability boundaries for WIV in the (Re, U*) plane are determined through LSA. It is shown that the lowest Re possible for WIV regarding the present configuration is R el o w e s t≈34 . LSA accurately captures the dynamics of WIV at subcritical Re and reveals that it is essentially a fluid-elastic instability problem. This work lays a good foundation for the investigation of WIV at supercritical high Re and gives enlightenment to the understanding of more complex WIV phenomena therein.

Supercritical CO(2) and subcritical propane extraction of pungent paprika and quantification of carotenoids, tocopherols, and capsaicinoids.

PubMed

Gnayfeed, M H; Daood, H G; Illés, V; Biacs, P A

2001-06-01

Ground paprika (Capsicum annuum L.) was extracted with supercritical carbon dioxide (SC-CO(2)) and subcritical propane at different conditions of pressure and temperature to estimate the yield and variation in carotenoid, tocopherol, and capsaicinoid contents and composition. The yield of paprika extract was found to be affected by the extraction conditions with SC-CO(2) but fairly constant at different conditions with subcritical propane. The maximum yields of oleoresin were 7.9 and 8.1% of ground paprika by SC-CO(2) and subcritical propane, respectively. The quantitative distribution of carotenoids, tocopherols, and capsaicinoids between paprika extract and powder was influenced by extraction conditions. SC-CO(2) was inefficient in the extraction of diesters of xanthophylls even at 400 bar and 55 degrees C, whereas tocopherols and capsaicinoids were easy to extract at these conditions. Under mild conditions subcritical propane was superior to SC-CO(2) in the extraction of carotenoids and tocopherols but less efficient in the extraction of capsaicinoids.

Promotion or suppression of glucose isomerization in subcritical aqueous straight- and branched-chain alcohols.

PubMed

Gao, Da-Ming; Kobayashi, Takashi; Adachi, Shuji

2015-01-01

The influence of water-miscible alcohols (methanol, 1-propanol, 2-propanol, and t-butyl alcohol) on the isomerization of glucose to fructose and mannose was investigated under subcritical aqueous conditions (180-200 °C). Primary and secondary alcohols promoted the conversion and isomerization of glucose to afford fructose and mannose with high and low selectivity, respectively. On the other hand, the decomposition (side-reaction) of glucose was suppressed in the presence of the primary and secondary alcohols compared with that in subcritical water. The yield of fructose increased with increasing concentration of the primary and secondary alcohols, and the species of the primary and secondary alcohols tested had little effect on the isomerization behavior of glucose. In contrast, the isomerization of glucose was suppressed in subcritical aqueous t-butyl alcohol. Both the conversion of glucose and the yield of fructose decreased with increasing concentration of t-butyl alcohol. In addition, mannose was not detected in reactions using subcritical aqueous t-butyl alcohol.

Effects of supercritical environment on hydrocarbon-fuel injection

NASA Astrophysics Data System (ADS)

Shin, Bongchul; Kim, Dohun; Son, Min; Koo, Jaye

2017-04-01

In this study, the effects of environment conditions on decane were investigated. Decane was injected in subcritical and supercritical ambient conditions. The visualization chamber was pressurized to 1.68 MPa by using nitrogen gas at a temperature of 653 K for subcritical ambient conditions. For supercritical ambient conditions, the visualization chamber was pressurized to 2.52 MPa by using helium at a temperature of 653 K. The decane injection in the pressurized chamber was visualized via a shadowgraph technique and gradient images were obtained by a post processing method. A large variation in density gradient was observed at jet interface in the case of subcritical injection in subcritical ambient conditions. Conversely, for supercritical injection in supercritical ambient conditions, a small density gradient was observed at the jet interface. In a manner similar to that observed in other cases, supercritical injection in subcritical ambient conditions differed from supercritical ambient conditions such as sphere shape liquid. Additionally, there were changes in the interface, and the supercritical injection core width was thicker than that in the subcritical injection. Furthermore, in cases with the same injection conditions, the change in the supercritical ambient normalized core width was smaller than the change in the subcritical ambient normalized core width owing to high specific heat at the supercritical injection and small phase change at the interface. Therefore, the interface was affected by the changing ambient condition. Given that the effect of changing the thermodynamic properties of propellants could be essential for a variable thrust rocket engine, the effects of the ambient conditions were investigated experimentally.

A Proposal for a Subcritical Reactivity Meter based on Gandini and Salvatores' point kinetics equations for Multiplying Subcritical Systems

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

Pinto, Leticia N.; Dos Santos, Adimir

2015-07-01

Multiplying Subcritical Systems were for a long time poorly studied and its theoretical description remains with plenty open questions. Great interest on such systems arose partly due to the improvement of hybrid concepts, such as the Accelerator-Driven Systems (ADS). Along with the need for new technologies to be developed, further study and understanding of subcritical systems are essential also in more practical situations, such as in the case of a PWR criticalization in their physical startup tests. Point kinetics equations are fundamental to continuously monitor the reactivity behavior to a possible variation of external sources intensity. In this case, quicklymore » and accurately predicting power transients and reactivity becomes crucial. It is known that conventional Reactivity Meters cannot operate in subcritical levels nor describe the dynamics of multiplying systems in these conditions, by the very structure of the classical kinetic equations. Several theoretical models have been proposed to characterize the kinetics of such systems with special regard to the reactivity, as the one developed by Gandini and Salvatores among others. This work presents a discussion about the derivation of point kinetics equations for subcritical systems and the importance of considering the external source. From the point of view of the Gandini and Salvatores' point kinetics model and based on the experimental results provided by Lee and dos Santos, it was possible to develop an innovative approach. This article proposes an algorithm that describes the subcritical reactivity with external source, contributing to the advancement of studies in the field. (authors)« less

The flow of a thin liquid film on a stationary and rotating disk. I - Experimental analysis and flow visualization

NASA Technical Reports Server (NTRS)

Thomas, S.; Faghri, A.; Hankey, W.

1990-01-01

The mean thickness of a thin liquid film of deionized water with a free surface on a stationary and rotating horizontal disk has been measured with a nonobtrusive capacitance technique. The measurements were taken when the rotational speed was 0-300 RPM and the flow rate was 7.0-15.0 LPM. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. When the disk was stationary, a circular hydraulic jump was present on the disk. Surface waves were found in the supercritical and subcritical regions at all flow rates studied. When the rotational speed of the disk is low, a standing wave at the edge of the disk was present. As the rotational speed increased, the surface waves changed from the wavy-laminar region to a region in which the waves ran nearly radially across the disk on top of a thin substrate of fluid.

Wave number selection in the presence of noise: Experimental results

NASA Astrophysics Data System (ADS)

Zhilenko, Dmitry; Krivonosova, Olga; Gritsevich, Maria; Read, Peter

2018-05-01

In this study, we consider how the wave number selection in spherical Couette flow, in the transition to azimuthal waves after the first instability, occurs in the presence of noise. The outer sphere was held stationary, while the inner sphere rotational speed was increased linearly from a subcritical flow to a supercritical one. In a supercritical flow, one of two possible flow states, each with different azimuthal wave numbers, can appear depending upon the initial and final Reynolds numbers and the acceleration value. Noise perturbations were added by introducing small disturbances into the rotational speed signal. With an increasing noise amplitude, a change in the dominant wave number from m to m ± 1 was found to occur at the same initial and final Reynolds numbers and acceleration values. The flow velocity measurements were conducted by using laser Doppler anemometry. Using these results, the role of noise as well as the behaviour of the amplitudes of the competing modes in their stages of damping and growth were determined.

Toward high-efficiency and detailed Monte Carlo simulation study of the granular flow spallation target

NASA Astrophysics Data System (ADS)

Cai, Han-Jie; Zhang, Zhi-Lei; Fu, Fen; Li, Jian-Yang; Zhang, Xun-Chao; Zhang, Ya-Ling; Yan, Xue-Song; Lin, Ping; Xv, Jian-Ya; Yang, Lei

2018-02-01

The dense granular flow spallation target is a new target concept chosen for the Accelerator-Driven Subcritical (ADS) project in China. For the R&D of this kind of target concept, a dedicated Monte Carlo (MC) program named GMT was developed to perform the simulation study of the beam-target interaction. Owing to the complexities of the target geometry, the computational cost of the MC simulation of particle tracks is highly expensive. Thus, improvement of computational efficiency will be essential for the detailed MC simulation studies of the dense granular target. Here we present the special design of the GMT program and its high efficiency performance. In addition, the speedup potential of the GPU-accelerated spallation models is discussed.

Extraction of antioxidants from Chlorella sp. using subcritical water treatment

NASA Astrophysics Data System (ADS)

Zakaria, S. M.; Mustapa Kamal, S. M.; Harun, M. R.; Omar, R.; Siajam, S. I.

2017-06-01

Chlorella sp. microalgae is one of the main source of natural bioactive compounds used in the food and pharmaceutical industries. Subcritical water extraction is the technique that offers an efficient, non-toxic, and environmental-friendly method to obtain natural ingredients. In this work, the extracts of Chlorella sp. microalgae was evaluated in terms of: chemical composition, extraction (polysaccharides) yield and antioxidant activity, using subcritical water extraction. Extractions were performed at temperatures ranging from 100°C to 300°C. The results show that by using subcritical water, the highest yield of polysaccharides is 23.6 that obtained at 150°C. Analysis on the polysaccharides yield show that the contents were highly influenced by the extraction temperature. The individual antioxidant activity were evaluated by in vitro assay using a free radical method. In general, the antioxidant activity of the extracts obtained at different water temperatures was high, with values of 31.08-54.29 . The results indicated that extraction by subcritical water was effective and Chlorella sp. can be a useful source of natural antioxidants.

A Theoretical and Experimental Investigation of the Lift and Drag Characteristics of Hydrofoils at Subcritical and Supercritical Speeds

NASA Technical Reports Server (NTRS)

Wadlin, Kenneth L; Shuford, Charles L , Jr; Mcgehee, John R

1955-01-01

A theoretical and experimental investigation at subcavitation speeds was made of the effect of the free-water surface and rigid boundaries on the lift and drag of an aspect-ratio-10 hydrofoil at both subcritical and supercritical speeds and of an aspect ratio-4 hydrofoil at supercritical speeds. Approximate theoretical solutions for the effects of the free-water surface and rigid boundaries on drag at subcritical speeds are developed. An approximate theoretical solution for the effects of these boundaries on drag at subcritical speeds is also presented. The agreement between theory and experiment at both supercritical and subcritical speeds is satisfactory for engineering calculations of hydrofoil characteristics from aerodynamic data. The experimental investigation indicated no appreciable effect of the limiting speed of wave propagation on lift-curve slope or angle of zero lift. It also showed that the increase in drag as the critical speed is approached from the supercritical range is gradual. The result is contrary to the abrupt increase at the critical speed predicted by theory.

Subcritical n-hexane/isopropanol extraction of lipid from wet microalgal pastes of Scenedesmus obliquus.

PubMed

Bian, Xiaoyu; Jin, Wenbiao; Gu, Qiong; Zhou, Xu; Xi, Yuhe; Tu, Renjie; Han, Song-Fang; Xie, Guo-Jun; Gao, Shu-Hong; Wang, Qilin

2018-02-19

Subcritical co-solvents of n-hexane/isopropanol were primarily utilized to extract lipid from wet microalgal pastes of Scenedesmus obliquus. The effects of key operational parameters were investigated, and the optimal parameters were obtained: solvent ratio of n-hexane to isopropanol was 3:2 (V:V), phase ratio of co-solvents to microalgal biomass was 35:1 (mL:g), reactor stirring speed was 900 rpm, extraction time was 60 min. Additional pretreatment with acid, ultrasonic and microwave as well as enhanced subcritical pressure/heating treatments were also applied to further study their effects on lipid extraction. The results showed that the lipid recovery rate with acid pretreatment was 8.6 and 6.2% higher than ultrasonic and microwave pretreatment; the optimum enhanced subcritical condition was 55 °C with atmospheric pressure. Under optimal operating conditions, the lipid and FAME yield were 13.5 and 7.2%, which was 82.6 and 135.1% higher than the traditional method. The results indicated that the subcritical n-hexane/isopropanol extraction process had promising application potential.

Reaction kinetics of cellulose hydrolysis in subcritical and supercritical water

NASA Astrophysics Data System (ADS)

Olanrewaju, Kazeem Bode

The uncertainties in the continuous supply of fossil fuels from the crisis-ridden oil-rich region of the world is fast shifting focus on the need to utilize cellulosic biomass and develop more efficient technologies for its conversion to fuels and chemicals. One such technology is the rapid degradation of cellulose in supercritical water without the need for an enzyme or inorganic catalyst such as acid. This project focused on the study of reaction kinetics of cellulose hydrolysis in subcritical and supercritical water. Cellulose reactions at hydrothermal conditions can proceed via the homogeneous route involving dissolution and hydrolysis or the heterogeneous path of surface hydrolysis. The work is divided into three main parts. First, the detailed kinetic analysis of cellulose reactions in micro- and tubular reactors was conducted. Reaction kinetics models were applied, and kinetics parameters at both subcritical and supercritical conditions were evaluated. The second major task was the evaluation of yields of water soluble hydrolysates obtained from the hydrolysis of cellulose and starch in hydrothermal reactors. Lastly, changes in molecular weight distribution due to hydrothermolytic degradation of cellulose were investigated. These changes were also simulated based on different modes of scission, and the pattern generated from simulation was compared with the distribution pattern from experiments. For a better understanding of the reaction kinetics of cellulose in subcritical and supercritical water, a series of reactions was conducted in the microreactor. Hydrolysis of cellulose was performed at subcritical temperatures ranging from 270 to 340 °C (tau = 0.40--0.88 s). For the dissolution of cellulose, the reaction was conducted at supercritical temperatures ranging from 375 to 395 °C (tau = 0.27--0.44 s). The operating pressure for the reactions at both subcritical and supercritical conditions was 5000 psig. The results show that the rate-limiting step in converting cellulose to fermentable sugars in subcritical and supercritical water differs because of the difference in their activation energies. Cellulose and starch were both hydrolyzed in micro- and tubular reactors and at subcritical and supercritical conditions. Due to the difficulty involved in generating an aqueous based dissolved cellulose and having it reacted in subcritical water, dissolved starch was used instead. Better yield of water soluble hydrolysates, especially fermentable sugars, were observed from the hydrolysis of cellulose and dissolved starch in subcritical water than at supercritical conditions. The concluding phase of this project focuses on establishing the mode of scission of cellulose chains in the hydrothermal reactor. This was achieved by using the simulated degradation pattern generated based on different scission modes to fingerprint the degradation pattern obtained from experiment.

Nonlinear dead water resistance at subcritical speed

NASA Astrophysics Data System (ADS)

Grue, John

2015-08-01

The dead water resistance F 1 = /1 2 C d w ρ S U 2 (ρ fluid density, U ship speed, S wetted body surface, Cdw resistance coefficient) on a ship moving at subcritical speed along the upper layer of a two-layer fluid is calculated by a strongly nonlinear method assuming potential flow in each layer. The ship dimensions correspond to those of the Polar ship Fram. The ship draught, b0, is varied in the range 0.25h0-0.9h0 (h0 the upper layer depth). The calculations show that Cdw/(b0/h0)2 depends on the Froude number only, in the range close to critical speed, Fr = U/c0 ˜ 0.875-1.125 (c0 the linear internal long wave speed), irrespective of the ship draught. The function Cdw/(b0/h0)2 attains a maximum at subcritical Froude number depending on the draught. Maximum Cdw/(b0/h0)2 becomes 0.15 for Fr = 0.76, b0/h0 = 0.9, and 0.16 for Fr = 0.74, b0/h0 = 1, where the latter extrapolated value of the dead water resistance coefficient is about 60 times higher than the frictional drag coefficient and relevant for the historical dead water observations. The nonlinear Cdw significantly exceeds linear theory (Fr < 0.85). The ship generated waves have a wave height comparable to the upper layer depth. Calculations of three-dimensional wave patterns at critical speed compare well to available laboratory experiments. Upstream solitary waves are generated in a wave tank of finite width, when the layer depths differ, causing an oscillation of the force. In a wide ocean, a very wide wave system develops at critical speed. The force approaches a constant value for increasing time.

Computational Analyses of Pressurization in Cryogenic Tanks

NASA Technical Reports Server (NTRS)

Ahuja, Vineet; Hosangadi, Ashvin; Lee, Chun P.; Field, Robert E.; Ryan, Harry

2010-01-01

A comprehensive numerical framework utilizing multi-element unstructured CFD and rigorous real fluid property routines has been developed to carry out analyses of propellant tank and delivery systems at NASA SSC. Traditionally CFD modeling of pressurization and mixing in cryogenic tanks has been difficult primarily because the fluids in the tank co-exist in different sub-critical and supercritical states with largely varying properties that have to be accurately accounted for in order to predict the correct mixing and phase change between the ullage and the propellant. For example, during tank pressurization under some circumstances, rapid mixing of relatively warm pressurant gas with cryogenic propellant can lead to rapid densification of the gas and loss of pressure in the tank. This phenomenon can cause serious problems during testing because of the resulting decrease in propellant flow rate. With proper physical models implemented, CFD can model the coupling between the propellant and pressurant including heat transfer and phase change effects and accurately capture the complex physics in the evolving flowfields. This holds the promise of allowing the specification of operational conditions and procedures that could minimize the undesirable mixing and heat transfer inherent in propellant tank operation. In our modeling framework, we incorporated two different approaches to real fluids modeling: (a) the first approach is based on the HBMS model developed by Hirschfelder, Beuler, McGee and Sutton and (b) the second approach is based on a cubic equation of state developed by Soave, Redlich and Kwong (SRK). Both approaches cover fluid properties and property variation spanning sub-critical gas and liquid states as well as the supercritical states. Both models were rigorously tested and properties for common fluids such as oxygen, nitrogen, hydrogen etc were compared against NIST data in both the sub-critical as well as supercritical regimes.

On the Asymptotic Stability of Steady Flows with Nonzero Flux in Two-Dimensional Exterior Domains

NASA Astrophysics Data System (ADS)

Guillod, Julien

2017-05-01

The Navier-Stokes equations in a two-dimensional exterior domain are considered. The asymptotic stability of stationary solutions satisfying a general hypothesis is proven under any L 2-perturbation. In particular, the general hypothesis is valid if the steady solution is the sum of the critically decaying flux carrier with flux {| Φ | < 2 π} and a small subcritically decaying term. Under the central symmetry assumption, the general hypothesis is also proven for any critically decaying steady solutions under a suitable smallness condition.

Damage Mechanisms and Controlled Crack Propagation in a Hot Pressed Silicon Nitride Ceramic. Ph.D. Thesis - Northwestern Univ., 1993

NASA Technical Reports Server (NTRS)

Calomino, Anthony Martin

1994-01-01

The subcritical growth of cracks from pre-existing flaws in ceramics can severely affect the structural reliability of a material. The ability to directly observe subcritical crack growth and rigorously analyze its influence on fracture behavior is important for an accurate assessment of material performance. A Mode I fracture specimen and loading method has been developed which permits the observation of stable, subcritical crack extension in monolithic and toughened ceramics. The test specimen and procedure has demonstrated its ability to generate and stably propagate sharp, through-thickness cracks in brittle high modulus materials. Crack growth for an aluminum oxide ceramic was observed to be continuously stable throughout testing. Conversely, the fracture behavior of a silicon nitride ceramic exhibited crack growth as a series of subcritical extensions which are interrupted by dynamic propagation. Dynamic initiation and arrest fracture resistance measurements for the silicon nitride averaged 67 and 48 J/sq m, respectively. The dynamic initiation event was observed to be sudden and explosive. Increments of subcritical crack growth contributed to a 40 percent increase in fracture resistance before dynamic initiation. Subcritical crack growth visibly marked the fracture surface with an increase in surface roughness. Increments of subcritical crack growth loosen ceramic material near the fracture surface and the fracture debris is easily removed by a replication technique. Fracture debris is viewed as evidence that both crack bridging and subsurface microcracking may be some of the mechanisms contributing to the increase in fracture resistance. A Statistical Fracture Mechanics model specifically developed to address subcritical crack growth and fracture reliability is used together with a damaged zone of material at the crack tip to model experimental results. A Monte Carlo simulation of the actual experiments was used to establish a set of modeling input parameters. It was demonstrated that a single critical parameter does not characterize the conditions required for dynamic initiation. Experimental measurements for critical crack lengths, and the energy release rates exhibit significant scatter. The resulting output of the model produces good agreement with both the average values and scatter of experimental measurements.

Influence of non-adiabatic wall conditions on the cross-flow around a circular cylinder

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

Macha, J.M.; Shafa, K.S.

1984-02-01

The drag and heat transfer of a finite length circular cylinder in a cross-flow have been investigated in a wind tunnel at surface-to-freestream temperature ratios from 1.0 to 2.1 for freestream Reynolds numbers of 2.2 x 10/sup 5/ and 4.4 x 10/sup 5/. The measured surface pressures were integrated to determine the effect of cylinder temperature on the drag coefficient, and the average Nusselt number was calculated from the electrical power required to heat the cylinder. For the freestream Reynolds number of 4.4 x 10/sup 5/, the experimental data show that increasing the cylinder temperature caused a reverse-transition from supercriticalmore » to subcritical flow. As a result of the increased size of the low-velocity wake region, C /SUB D/ increased by 21 percent and Nu /SUB d/ decreased by 26 percent.« less

User's guide for a general purpose dam-break flood simulation model (K-634)

USGS Publications Warehouse

Land, Larry F.

1981-01-01

An existing computer program for simulating dam-break floods for forecast purposes has been modified with an emphasis on general purpose applications. The original model was formulated, developed and documented by the National Weather Service. This model is based on the complete flow equations and uses a nonlinear implicit finite-difference numerical method. The first phase of the simulation routes a flood wave through the reservoir and computes an outflow hydrograph which is the sum of the flow through the dam 's structures and the gradually developing breach. The second phase routes this outflow hydrograph through the stream which may be nonprismatic and have segments with subcritical or supercritical flow. The results are discharge and stage hydrographs at the dam as well as all of the computational nodes in the channel. From these hydrographs, peak discharge and stage profiles are tabulated. (USGS)

Hexagonal convection patterns and their evolutionary scenarios in electroconvection induced by a strong unipolar injection

NASA Astrophysics Data System (ADS)

Luo, Kang; Wu, Jian; Yi, Hong-Liang; Liu, Lin-Hua; Tan, He-Ping

2018-05-01

A regular hexagonal pattern of three-dimensional electroconvective flow induced by unipolar injection in dielectric liquids is numerically observed by solving the fully coupled governing equations using the lattice Boltzmann method. A small-amplitude perturbation in the form of a spatially periodic pattern of hexagonal cells is introduced initially. The transient development of convective cells that undergo a sequence of transitions agrees with the idea of flow seeking an optimal scale. Stable hexagonal convective cells and their subcritical bifurcation together with a hysteresis loop are clearly observed. In addition, the stability of the hexagonal flow pattern is analyzed in a wide range of relevant parameters, including the electric Rayleigh number T , nondimensional mobility M , and wave number k . It is found that centrally downflowing hexagonal cells, which are characterized by the central region being empty of charge, are preferred in the system.

Experimental investigation of flow characteristics around four square-cylinder arrays at subcritical Reynolds numbers

NASA Astrophysics Data System (ADS)

Liu, Mingyue; Xiao, Longfei; Yang, Lijun

2015-09-01

The Deep Draft Semi-Submersible (DDS) concepts are known for their favourable vertical motion performance. However, the DDS may experience critical Vortex-Induced Motion (VIM) stemming from the fluctuating forces on the columns. In order to investigate the current-induced excitation forces of VIM, an experimental study of flow characteristics around four square-section cylinders in a square configuration is presented. A number of column spacing ratios and array attack angles were considered to investigate the parametric influences. The results comprise flow patterns, drag and lift forces, as well as Strouhal numbers. It is shown that both the drag and lift forces acting on the cylinders are slightly different between the various L/D values, and the fluctuating forces peak at L/D = 4.14. The lift force of downstream cylinders reaches its maximum at around α = 15°. Furthermore, the flow around circular-section-cylinder arrays is also discussed in comparison with that of square cylinders.

Coherent substructure of turbulence near the stagnation zone of a bluff body

NASA Technical Reports Server (NTRS)

Sadeh, W. Z.; Brauer, H. J.

1980-01-01

The evolution of freestream turbulence in crossflow about a circular cylinder was studied in order to identify the existence of a coherent substructure which is the outcome of the amplification of freesteam turbulence by the stretching mechanism in diverging flow about a bluff body. Visualization of the flow events revealed the selective stretching of cross-vortex tubes and the emergence of an organized turbulent flow pattern near the cylinder stagnation zone. Significant amplification of the total turbulent energy of the streamwise fluctuating velocity was consistently monitored. Realization of selective amplification at scales larger than the neutral scale of the stagnation flow was indicated by the variation of the discrete streamwise turbulent energy. A most amplified scale, characteristic of the energy containing eddies within the coherent substructure and commensurate with the boundary-layer thickness, was detected. Penetration of the amplified turbulence into the cylinder boundary layer led to the retardation of separation and to a concurrent decrease in the drag coefficient at subcritical cylinder-diameter Reynolds numbers.

Twin tubular pinch effect in curving confined flows

PubMed Central

Clime, Liviu; Morton, Keith J.; Hoa, Xuyen D.; Veres, Teodor

2015-01-01

Colloidal suspensions of buoyancy neutral particles flowing in circular pipes focus into narrow distributions near the wall due to lateral migration effects associated with fluid inertia. In curving flows, these distributions are altered by Dean currents and the interplay between Reynolds and Dean numbers is used to predict equilibrium positions. Here, we propose a new description of inertial lateral migration in curving flows that expands current understanding of both focusing dynamics and equilibrium distributions. We find that at low Reynolds numbers, the ratio δ between lateral inertial migration and Dean forces scales simply with the particle radius, coil curvature and pipe radius as . A critical value δc = 0.148 of this parameter is identified along with two related inertial focusing mechanisms. In the regime below δc, coined subcritical, Dean forces generate permanently circulating, twinned annuli, each with intricate equilibrium particle distributions including eyes and trailing arms. At δ > δc (supercritical regime) inertial lateral migration forces are dominant and particles focus to a single stable equilibrium position. PMID:25927878

Hypersonic Viscous Flow Over Large Roughness Elements

NASA Technical Reports Server (NTRS)

Chang, Chau-Lyan; Choudhari, Meelan M.

2009-01-01

Viscous flow over discrete or distributed surface roughness has great implications for hypersonic flight due to aerothermodynamic considerations related to laminar-turbulent transition. Current prediction capability is greatly hampered by the limited knowledge base for such flows. To help fill that gap, numerical computations are used to investigate the intricate flow physics involved. An unstructured mesh, compressible Navier-Stokes code based on the space-time conservation element, solution element (CESE) method is used to perform time-accurate Navier-Stokes calculations for two roughness shapes investigated in wind tunnel experiments at NASA Langley Research Center. It was found through 2D parametric study that at subcritical Reynolds numbers of the boundary layers, absolute instability resulting in vortex shedding downstream, is likely to weaken at supersonic free-stream conditions. On the other hand, convective instability may be the dominant mechanism for supersonic boundary layers. Three-dimensional calculations for a rectangular or cylindrical roughness element at post-shock Mach numbers of 4.1 and 6.5 also confirm that no self-sustained vortex generation is present.

Periodic magnetorotational dynamo action as a prototype of nonlinear magnetic-field generation in shear flows.

PubMed

Herault, J; Rincon, F; Cossu, C; Lesur, G; Ogilvie, G I; Longaretti, P-Y

2011-09-01

The nature of dynamo action in shear flows prone to magnetohydrodynamc instabilities is investigated using the magnetorotational dynamo in Keplerian shear flow as a prototype problem. Using direct numerical simulations and Newton's method, we compute an exact time-periodic magnetorotational dynamo solution to three-dimensional dissipative incompressible magnetohydrodynamic equations with rotation and shear. We discuss the physical mechanism behind the cycle and show that it results from a combination of linear and nonlinear interactions between a large-scale axisymmetric toroidal magnetic field and nonaxisymmetric perturbations amplified by the magnetorotational instability. We demonstrate that this large-scale dynamo mechanism is overall intrinsically nonlinear and not reducible to the standard mean-field dynamo formalism. Our results therefore provide clear evidence for a generic nonlinear generation mechanism of time-dependent coherent large-scale magnetic fields in shear flows and call for new theoretical dynamo models. These findings may offer important clues to understanding the transitional and statistical properties of subcritical magnetorotational turbulence.

Automated startup of the MIT research reactor

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

Kwok, K.S.

1992-01-01

This summary describes the development, implementation, and testing of a generic method for performing automated startups of nuclear reactors described by space-independent kinetics under conditions of closed-loop digital control. The technique entails first obtaining a reliable estimate of the reactor's initial degree of subcriticality and then substituting that estimate into a model-based control law so as to permit a power increase from subcritical on a demanded trajectory. The estimation of subcriticality is accomplished by application of the perturbed reactivity method. The shutdown reactor is perturbed by the insertion of reactivity at a known rate. Observation of the resulting period permitsmore » determination of the initial degree of subcriticality. A major advantage to this method is that repeated estimates are obtained of the same quantity. Hence, statistical methods can be applied to improve the quality of the calculation.« less

Advanced electrical current measurements of microdischarges: evidence of sub-critical pulses and ion currents in barrier discharge in air

NASA Astrophysics Data System (ADS)

Synek, Petr; Zemánek, Miroslav; Kudrle, Vít; Hoder, Tomáš

2018-04-01

Electrical current measurements in corona or barrier microdischarges are a challenge as they require both high temporal resolution and a large dynamic range of the current probe used. In this article, we apply a simple self-assembled current probe and compare it to commercial ones. An analysis in the time and frequency domain is carried out. Moreover, an improved methodology is presented, enabling both temporal resolution in sub-nanosecond times and current sensitivity in the order of tens of micro-amperes. Combining this methodology with a high-tech oscilloscope and self-developed software, a unique statistical analysis of currents in volume barrier discharge driven in atmospheric-pressure air is made for over 80 consecutive periods of a 15 kHz applied voltage. We reveal the presence of repetitive sub-critical current pulses and conclude that these can be identified with the discharging of surface charge microdomains. Moreover, extremely low, long-lasting microsecond currents were detected which are caused by ion flow, and are analysed in detail. The statistical behaviour presented gives deeper insight into the discharge physics of these usually undetectable current signals.

Optimisation for subcritical fluid extraction of 17-methyltestosterone with 1,1,1,2-tetrafluoroethane for HPLC analysis.

PubMed

Han, Yuqian; Ma, Qinchuan; Lu, Jie; Xue, Yong; Xue, Changhu

2012-12-15

A simple, rapid and sensitive method was developed for determination of 17α-methyltestosterone in aquatic products by extraction with subcritical 1,1,1,2-tetrafluoroethane (R134a) extraction and high performance liquid chromatography (HPLC). Response surface methodology (RSM) was adopted to optimise extraction pressure, temperature and co-solvent volume. The optimum extraction conditions predicted within the experimental ranges were as follows: pressure 5 MPa, temperature 31°C, and co-solvent volume 3.35ml. The analysis was carried out on XDB-C(18) column (4.6 mm × 250 mm, 5 μm) with the mobile phase acetonitrile-water (55:45, v/v), flow rate 0.8 ml/min, temperature 30°C and wavelength 245 nm. Good linearity of detection was obtained for 17α-methyltestosterone between concentrations of 50-250 ng/ml, r(2)=0.999. The method was validated using samples fortified with 17α-methyltestosterone at levels of 10, 30 and 50 ng/g, the mean recovery exceeds 90%, and the RSD values were less than 10%. Crown Copyright © 2012. Published by Elsevier Ltd. All rights reserved.

Extinction times in the subcritical stochastic SIS logistic epidemic.

PubMed

Brightwell, Graham; House, Thomas; Luczak, Malwina

2018-01-31

Many real epidemics of an infectious disease are not straightforwardly super- or sub-critical, and the understanding of epidemic models that exhibit such complexity has been identified as a priority for theoretical work. We provide insights into the near-critical regime by considering the stochastic SIS logistic epidemic, a well-known birth-and-death chain used to model the spread of an epidemic within a population of a given size N. We study the behaviour of the process as the population size N tends to infinity. Our results cover the entire subcritical regime, including the "barely subcritical" regime, where the recovery rate exceeds the infection rate by an amount that tends to 0 as [Formula: see text] but more slowly than [Formula: see text]. We derive precise asymptotics for the distribution of the extinction time and the total number of cases throughout the subcritical regime, give a detailed description of the course of the epidemic, and compare to numerical results for a range of parameter values. We hypothesise that features of the course of the epidemic will be seen in a wide class of other epidemic models, and we use real data to provide some tentative and preliminary support for this theory.

A streamline curvature method for design of supercritical and subcritical airfoils

NASA Technical Reports Server (NTRS)

Barger, R. L.; Brooks, C. W., Jr.

1974-01-01

An airfoil design procedure, applicable to both subcritical and supercritical airfoils, is described. The method is based on the streamline curvature velocity equation. Several examples illustrating this method are presented and discussed.

Three-dimensional finite amplitude electroconvection in dielectric liquids

NASA Astrophysics Data System (ADS)

Luo, Kang; Wu, Jian; Yi, Hong-Liang; Tan, He-Ping

2018-02-01

Charge injection induced electroconvection in a dielectric liquid lying between two parallel plates is numerically simulated in three dimensions (3D) using a unified lattice Boltzmann method (LBM). Cellular flow patterns and their subcritical bifurcation phenomena of 3D electroconvection are numerically investigated for the first time. A unit conversion is also derived to connect the LBM system to the real physical system. The 3D LBM codes are validated by three carefully chosen cases and all results are found to be highly consistent with the analytical solutions or other numerical studies. For strong injection, the steady state roll, polygon, and square flow patterns are observed under different initial disturbances. Numerical results show that the hexagonal cell with the central region being empty of charge and centrally downward flow is preferred in symmetric systems under random initial disturbance. For weak injection, the numerical results show that the flow directly passes from the motionless state to turbulence once the system loses its linear stability. In addition, the numerically predicted linear and finite amplitude stability criteria of different flow patterns are discussed.

Geologic nozzles

USGS Publications Warehouse

Werner, Kieffer S.

1989-01-01

The importance of the low characteristic velocities of geologic fluids has not been widely recognized, and as a result, the importance of supercritical and supersonic flow in geological processes has generally been underestimated. The lateral blast at Mount St. Helens, Washington, propelled a gas heavily laden with dust into the atmosphere. Because of the low sound speed in this gas (about 100 m/s), the flow was internally supersonic. Old Faithful Geyser, Wyoming, is a converging-diverging nozzle in which liquid water refilling the conduit during the recharge cycle changes during eruption into a two-phase liquid-vapor mixture with a very low sound velocity. The high sound speed of liquid water determines the characteristics of harmonic tremor observed at the geyser during the recharge interval, whereas the low sound speed of the liquid-vapor mixture influences the fluid flow characteristics of the eruption. At the rapids of the Colorado River in the Grand Canyon, Arizona, the channel is constricted into the shape of a converging-diverging nozzle by the debris flows that enter from tributary canyons. Both subcritical and supercritical flow occur within the rapids. -from Author

Vectorized schemes for conical potential flow using the artificial density method

NASA Technical Reports Server (NTRS)

Bradley, P. F.; Dwoyer, D. L.; South, J. C., Jr.; Keen, J. M.

1984-01-01

A method is developed to determine solutions to the full-potential equation for steady supersonic conical flow using the artificial density method. Various update schemes used generally for transonic potential solutions are investigated. The schemes are compared for speed and robustness. All versions of the computer code have been vectorized and are currently running on the CYBER-203 computer. The update schemes are vectorized, where possible, either fully (explicit schemes) or partially (implicit schemes). Since each version of the code differs only by the update scheme and elements other than the update scheme are completely vectorizable, comparisons of computational effort and convergence rate among schemes are a measure of the specific scheme's performance. Results are presented for circular and elliptical cones at angle of attack for subcritical and supercritical crossflows.

High Fidelity Simulation of Transcritical Liquid Jet in Crossflow

NASA Astrophysics Data System (ADS)

Li, Xiaoyi; Soteriou, Marios

2017-11-01

Transcritical injection of liquid fuel occurs in many practical applications such as diesel, rocket and gas turbine engines. In these applications, the liquid fuel, with a supercritical pressure and a subcritical temperature, is introduced into an environment where both the pressure and temperature exceeds the critical point of the fuel. The convoluted physics of the transition from subcritical to supercritical conditions poses great challenges for both experimental and numerical investigations. In this work, numerical simulation of a binary system of a subcritical liquid injecting into a supercritical gaseous crossflow is performed. The spatially varying fluid thermodynamic and transport properties are evaluated using established cubic equation of state and extended corresponding state principles with established mixing rules. To efficiently account for the large spatial gradients in property variations, an adaptive mesh refinement technique is employed. The transcritical simulation results are compared with the predictions from the traditional subcritical jet atomization simulations.

New insights into membrane fouling in submerged MBR under sub-critical flux condition.

PubMed

Li, Jianfeng; Zhang, Xiuxiu; Cheng, Fangqin; Liu, Yu

2013-06-01

This study investigated the membrane fouling in MBRs under sub-critical flux condition. Results showed membrane fouling at subcritical flux evolved through a three-stage process: a slow linear increase in transmembrane pressure (TMP) (stage I), followed by an exponential increase in TMP (stage II), and finally a rapid linear TMP rise was observed at stage III. It was found that bound EPS would play a significant role in fouling development at stage I, while SMPs appeared to be the major contributor to self-accelerating fouling phenomena observed at stage II. At stage III, the entire membrane was covered by a cake layer of flocs, as the result, the fouling rate was likely determined by floc characteristics. This study offers new insights into the fouling development under sub-critical flux condition. Copyright © 2013 Elsevier Ltd. All rights reserved.

Production of rare sugars from common sugars in subcritical aqueous ethanol.

PubMed

Gao, Da-Ming; Kobayashi, Takashi; Adachi, Shuji

2015-05-15

A new isomerization reaction was developed to synthesize rare ketoses. D-tagatose, D-xylulose, and D-ribulose were obtained in the maximum yields of 24%, 38%, and 40%, respectively, from the corresponding aldoses, D-galactose, D-xylose, and D-ribose, by treating the aldoses with 80% (v/v) subcritical aqueous ethanol at 180°C. The maximum productivity of D-tagatose was ca. 80 g/(Lh). Increasing the concentration of ethanol significantly increased the isomerization of D-galactose. Variation in the reaction temperature did not significantly affect the production of D-tagatose from D-galactose. Subcritical aqueous ethanol converted both 2,3-threo and 2,3-erythro aldoses to the corresponding C-2 ketoses in high yields. Thus, the treatment of common aldoses in subcritical aqueous ethanol can be regarded as a new method to synthesize the corresponding rare sugars. Copyright © 2014 Elsevier Ltd. All rights reserved.

Ensuring the validity of calculated subcritical limits

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

Clark, H.K.

1977-01-01

The care taken at the Savannah River Laboratory and Plant to ensure the validity of calculated subcritical limits is described. Close attention is given to ANSI N16.1-1975, ''Validation of Calculational Methods for Nuclear Criticality Safety.'' The computer codes used for criticality safety computations, which are listed and are briefly described, have been placed in the SRL JOSHUA system to facilitate calculation and to reduce input errors. A driver module, KOKO, simplifies and standardizes input and links the codes together in various ways. For any criticality safety evaluation, correlations of the calculational methods are made with experiment to establish bias. Occasionallymore » subcritical experiments are performed expressly to provide benchmarks. Calculated subcritical limits contain an adequate but not excessive margin to allow for uncertainty in the bias. The final step in any criticality safety evaluation is the writing of a report describing the calculations and justifying the margin.« less

Influence of surrounding environment on subcritical crack growth in marble

NASA Astrophysics Data System (ADS)

Nara, Yoshitaka; Kashiwaya, Koki; Nishida, Yuki; , Toshinori, Ii

2017-06-01

Understanding subcritical crack growth in rock is essential for determining appropriate measures to ensure the long-term integrity of rock masses surrounding structures and for construction from rock material. In this study, subcritical crack growth in marble was investigated experimentally, focusing on the influence of the surrounding environment on the relationship between the crack velocity and stress intensity factor. The crack velocity increased with increasing temperature and/or relative humidity. In all cases, the crack velocity increased with increasing stress intensity factor. However, for Carrara marble (CM) in air, we observed a region in which the crack velocity still increased with temperature, but the increase in the crack velocity with increasing stress intensity factor was not significant. This is similar to Region II of subcritical crack growth observed in glass in air. Region II in glass is controlled by mass transport to the crack tip. In the case of rock, the transport of water to the crack tip is important. In general, Region II is not observed for subcritical crack growth in rock materials, because rocks contain water. Because the porosity of CM is very low, the amount of water contained in the marble is also very small. Therefore, our results imply that we observed Region II in CM. Because the crack velocity increased in both water and air with increasing temperature and humidity, we concluded that dry conditions at low temperature are desirable for the long-term integrity of a carbonate rock mass. Additionally, mass transport to the crack tip is an important process for subcritical crack growth in rock with low porosity.

Supercritical (and Subcritical) Fluid Behavior and Modeling: Drops, Streams, Shear and Mixing Layers, Jets and Sprays

NASA Technical Reports Server (NTRS)

Bellan, J.

1999-01-01

A critical review of recent investigations in the real of supercritical (and subcritical) fluid behavior is presented with the goal of obtaining a perspective on the peculiarities of high pressure observations.

77 FR 62539 - Dominion Nuclear Connecticut, Inc.; Millstone Power Station, Unit 2, Revocation of Exemption

Federal Register 2010, 2011, 2012, 2013, 2014

2012-10-15

... determined to be safely subcritical under the most adverse moderation conditions feasible by unborated water... 10 CFR 50.68 is to maintain spent fuel pools subcritical in an unborated, maximum moderation...

VIEW OF WATER SUPPLY TANK FOR THE PRESSURIZED SUBCRITICAL EXPERIMENT ...

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

VIEW OF WATER SUPPLY TANK FOR THE PRESSURIZED SUBCRITICAL EXPERIMENT (PSE), LOCATED IN STAIRWELL ADJACENT TO SP-SE ROOM, LEVEL -15’, LOOKING NORTH - Physics Assembly Laboratory, Area A/M, Savannah River Site, Aiken, Aiken County, SC

Transcritical flow of a stratified fluid over topography: analysis of the forced Gardner equation

NASA Astrophysics Data System (ADS)

Kamchatnov, A. M.; Kuo, Y.-H.; Lin, T.-C.; Horng, T.-L.; Gou, S.-C.; Clift, R.; El, G. A.; Grimshaw, R. H. J.

2013-12-01

Transcritical flow of a stratified fluid past a broad localised topographic obstacle is studied analytically in the framework of the forced extended Korteweg--de Vries (eKdV), or Gardner, equation. We consider both possible signs for the cubic nonlinear term in the Gardner equation corresponding to different fluid density stratification profiles. We identify the range of the input parameters: the oncoming flow speed (the Froude number) and the topographic amplitude, for which the obstacle supports a stationary localised hydraulic transition from the subcritical flow upstream to the supercritical flow downstream. Such a localised transcritical flow is resolved back into the equilibrium flow state away from the obstacle with the aid of unsteady coherent nonlinear wave structures propagating upstream and downstream. Along with the regular, cnoidal undular bores occurring in the analogous problem for the single-layer flow modeled by the forced KdV equation, the transcritical internal wave flows support a diverse family of upstream and downstream wave structures, including solibores, rarefaction waves, reversed and trigonometric undular bores, which we describe using the recent development of the nonlinear modulation theory for the (unforced) Gardner equation. The predictions of the developed analytic construction are confirmed by direct numerical simulations of the forced Gardner equation for a broad range of input parameters.

Effect of plate permeability on nonlinear stability of the asymptotic suction boundary layer.

PubMed

Wedin, Håkan; Cherubini, Stefania; Bottaro, Alessandro

2015-07-01

The nonlinear stability of the asymptotic suction boundary layer is studied numerically, searching for finite-amplitude solutions that bifurcate from the laminar flow state. By changing the boundary conditions for disturbances at the plate from the classical no-slip condition to more physically sound ones, the stability characteristics of the flow may change radically, both for the linearized as well as the nonlinear problem. The wall boundary condition takes into account the permeability K̂ of the plate; for very low permeability, it is acceptable to impose the classical boundary condition (K̂=0). This leads to a Reynolds number of approximately Re(c)=54400 for the onset of linearly unstable waves, and close to Re(g)=3200 for the emergence of nonlinear solutions [F. A. Milinazzo and P. G. Saffman, J. Fluid Mech. 160, 281 (1985); J. H. M. Fransson, Ph.D. thesis, Royal Institute of Technology, KTH, Sweden, 2003]. However, for larger values of the plate's permeability, the lower limit for the existence of linear and nonlinear solutions shifts to significantly lower Reynolds numbers. For the largest permeability studied here, the limit values of the Reynolds numbers reduce down to Re(c)=796 and Re(g)=294. For all cases studied, the solutions bifurcate subcritically toward lower Re, and this leads to the conjecture that they may be involved in the very first stages of a transition scenario similar to the classical route of the Blasius boundary layer initiated by Tollmien-Schlichting (TS) waves. The stability of these nonlinear solutions is also investigated, showing a low-frequency main unstable mode whose growth rate decreases with increasing permeability and with the Reynolds number, following a power law Re(-ρ), where the value of ρ depends on the permeability coefficient K̂. The nonlinear dynamics of the flow in the vicinity of the computed finite-amplitude solutions is finally investigated by direct numerical simulations, providing a viable scenario for subcritical transition due to TS waves.

Subcritical transition scenarios via linear and nonlinear localized optimal perturbations in plane Poiseuille flow

NASA Astrophysics Data System (ADS)

Farano, Mirko; Cherubini, Stefania; Robinet, Jean-Christophe; De Palma, Pietro

2016-12-01

Subcritical transition in plane Poiseuille flow is investigated by means of a Lagrange-multiplier direct-adjoint optimization procedure with the aim of finding localized three-dimensional perturbations optimally growing in a given time interval (target time). Space localization of these optimal perturbations (OPs) is achieved by choosing as objective function either a p-norm (with p\\gg 1) of the perturbation energy density in a linear framework; or the classical (1-norm) perturbation energy, including nonlinear effects. This work aims at analyzing the structure of linear and nonlinear localized OPs for Poiseuille flow, and comparing their transition thresholds and scenarios. The nonlinear optimization approach provides three types of solutions: a weakly nonlinear, a hairpin-like and a highly nonlinear optimal perturbation, depending on the value of the initial energy and the target time. The former shows localization only in the wall-normal direction, whereas the latter appears much more localized and breaks the spanwise symmetry found at lower target times. Both solutions show spanwise inclined vortices and large values of the streamwise component of velocity already at the initial time. On the other hand, p-norm optimal perturbations, although being strongly localized in space, keep a shape similar to linear 1-norm optimal perturbations, showing streamwise-aligned vortices characterized by low values of the streamwise velocity component. When used for initializing direct numerical simulations, in most of the cases nonlinear OPs provide the most efficient route to transition in terms of time to transition and initial energy, even when they are less localized in space than the p-norm OP. The p-norm OP follows a transition path similar to the oblique transition scenario, with slightly oscillating streaks which saturate and eventually experience secondary instability. On the other hand, the nonlinear OP rapidly forms large-amplitude bent streaks and skips the phases of streak saturation, providing a contemporary growth of all of the velocity components due to strong nonlinear coupling.

SELECTIVE EXTRACTION OF OXYGENATES FROM SAVORY AND PEPPERMINT USING SUBCRITICAL WATER. (R825394)

EPA Science Inventory

The yields of oxygenated and non-oxygenated flavour and fragrance compounds from savory (Satureja hortensis) and peppermint (Mentha piperita) were compared using subcritical water extraction, supercritical carbon dioxide extraction (SFE) and hydrodistillation. Extraction rates wi...

Systematic parameter study of dynamo bifurcations in geodynamo simulations

NASA Astrophysics Data System (ADS)

Petitdemange, Ludovic

2018-04-01

We investigate the nature of the dynamo bifurcation in a configuration applicable to the Earth's liquid outer core, i.e. in a rotating spherical shell with thermally driven motions with no-slip boundaries. Unlike in previous studies on dynamo bifurcations, the control parameters have been varied significantly in order to deduce general tendencies. Numerical studies on the stability domain of dipolar magnetic fields found a dichotomy between non-reversing dipole-dominated dynamos and the reversing non-dipole-dominated multipolar solutions. We show that, by considering weak initial fields, the above transition disappears and is replaced by a region of bistability for which dipolar and multipolar dynamos coexist. Such a result was also observed in models with free-slip boundaries in which the geostrophic zonal flow can develop and participate to the dynamo mechanism for non-dipolar fields. We show that a similar process develops in no-slip models when viscous effects are reduced sufficiently. The following three regimes are distinguished: (i) Close to the onset of convection (Rac) with only the most critical convective mode (wave number) being present, dynamos set in supercritically in the Ekman number regime explored here and are dipole-dominated. Larger critical magnetic Reynolds numbers indicate that they are particularly inefficient. (ii) in the range 3 < Ra /Rac 10) , the relative importance of zonal flows increases with Ra in non-magnetic models. The field topology depends on the magnitude of the initial magnetic field. The dipolar branch has a subcritical behavior whereas the multipolar branch has a supercritical behavior. By approaching more realistic parameters, the extension of this bistable regime increases. A hysteretic behavior questions the common interpretation for geomagnetic reversals. Far above the dynamo threshold (by increasing the magnetic Prandtl number), Lorentz forces contribute to the first order force balance, as predicted for planetary dynamos. When Ra is sufficiently high, dipolar fields affect significantly the flow speed, the flow structure and heat transfer which is reduced by the Lorentz force regardless of the field strength. This physical regime seems to be relevant for studying geomagnetic processes.

High Pressure, Transport Properties of Fluids: Theory and Data from Levitated Fluid-Drops at Combustion-Relevant Temperatures

NASA Technical Reports Server (NTRS)

Bellan, J.; Ohaska, K.

2001-01-01

The objective of this investigation is to derive a set of consistent mixing rules for calculating diffusivities and thermal diffusion factors over a thermodynamic regime encompassing the subcritical and supercritical ranges. These should serve for modeling purposes, and therefore for accurate simulations of high pressure phenomena such as fluid disintegration, turbulent flows and sprays. A particular consequence of this work will be the determination of effective Lewis numbers for supercritical conditions, thus enabling the examination of the relative importance of heat and mass transfer at supercritical pressures.

Flow control by combining radial pulsation and rotation of a cylinder in uniform flow

NASA Astrophysics Data System (ADS)

Oualli, H.; Hanchi, S.; Bouabdallah, A.; Gad-El-Hak, M.

2008-11-01

Flow visualizations and hot-wire measurements are carried out to study a circular cylinder undergoing simultaneous radial pulsation and rotation and placed in a uniform flow. The Reynolds number is in the range of 1,000--22,000, for which transition in the shear layers and near wake is expected. Our previous experimental and numerical investigations in this subcritical flow regime have established the existence of an important energy transfer mechanism from the mean flow to the fluctuations. Radial pulsations cause and enhance that energy transfer. Certain values of the amplitude and frequency of the pulsations lead to negative drag (i.e. thrust). The nonlinear interaction between the Magnus effect induced by the steady rotation of the cylinder and the near-wake modulated by the bluff body's pulsation leads to alteration of the omnipresent Kármán vortices and the possibility of optimizing the lift-to-drag ratio as well as the rates of heat and mass transfer. Other useful applications include the ability to enhance or suppress the turbulence intensity, and to avoid the potentially destructive lock-in phenomenon in the wake of bridges, electric cables and other structures.

Transonic Navier-Stokes wing solutions using a zonal approach. Part 2: High angle-of-attack simulation

NASA Technical Reports Server (NTRS)

Chaderjian, N. M.

1986-01-01

A computer code is under development whereby the thin-layer Reynolds-averaged Navier-Stokes equations are to be applied to realistic fighter-aircraft configurations. This transonic Navier-Stokes code (TNS) utilizes a zonal approach in order to treat complex geometries and satisfy in-core computer memory constraints. The zonal approach has been applied to isolated wing geometries in order to facilitate code development. Part 1 of this paper addresses the TNS finite-difference algorithm, zonal methodology, and code validation with experimental data. Part 2 of this paper addresses some numerical issues such as code robustness, efficiency, and accuracy at high angles of attack. Special free-stream-preserving metrics proved an effective way to treat H-mesh singularities over a large range of severe flow conditions, including strong leading-edge flow gradients, massive shock-induced separation, and stall. Furthermore, lift and drag coefficients have been computed for a wing up through CLmax. Numerical oil flow patterns and particle trajectories are presented both for subcritical and transonic flow. These flow simulations are rich with complex separated flow physics and demonstrate the efficiency and robustness of the zonal approach.

Role of Elasto-Inertial Turbulence in Polymer Drag Reduction

NASA Astrophysics Data System (ADS)

Dubief, Yves; Sid, Samir; Terrapon, Vincent

2017-11-01

Elasto-Inertial Turbulence (EIT) is a peculiar state of turbulence found in dilute polymer solutions flowing in parallel wall flows over a wide range of Reynolds numbers. At subcritical Reynolds numbers, appropriate boundary conditions trigger EIT, a self-sustaining cycle of energy transfers between thin sheets of stretched polymers and velocity perturbations, which translates into an increase of friction drag. For critical and supercritical Reynolds numbers, polymer additives may lead to significant drag reduction, bounded by the asymptotic state known as Maximum Drag Reduction (MDR). The present research investigates the role of EIT in the dynamics of critical and supercritical Reynolds number wall flows. Using high-fidelity direct numerical simulations of channel flows and the FENE-P model, we establish that (i) EIT is two-dimensional, (ii) the scales essential to the existence of EIT are sub-Kolmogorov, and (iii) EIT drives MDR at low and possibly moderate Reynolds number turbulent flows. These findings were validated in two different codes and using unprecedented resolutions for polymer flows. YD is grateful for the support of Binational Science Foundation. SS and VT acknowledges Fonds de la Recherche Scientifique (FNRS), MarieCurie Career Integration Grant and computing allocation from University of Liege and PRACE.

Summary on the depressurization from supercritical pressure conditions

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

Anderson, M.; Chen, Y.; Ammirable, L.

When a fluid discharges from a high pressure and temperature system, a 'choking' or critical condition occurs, and the flow rate becomes independent of the downstream pressure. During a postulated loss of coolant accident (LOCA) of a water reactor the break flow will be subject to this condition. An accurate estimation of the critical flow rate is important for the evaluation of the reactor safety, because this flow rate controls the loss of coolant inventory and energy from the system, and thus has a significant effect on the accident consequences[1]. In the design of safety systems for a super criticalmore » water reactor (SCWR), postulated LOCA transients are particularly important due to the lower coolant inventory compared to a typical PWR for the same power output. This lower coolant inventory would result in a faster transient response of the SCWR, and hence accurate prediction of the critical discharge is mandatory. Under potential two-phase conditions critical flow is dominated by the vapor content or quality of the vapor, which is closely related with the onset of vaporization and the interfacial interaction between phases [2]. This presents a major challenge for the estimation of the flow rate due to the lack of the knowledge of those processes, especially under the conditions of interest for the SCWR. According to the limited data of supercritical fluids, the critical flows at conditions above the pseudo-critical point seem to be fairly stable and consistent with the subcritical homogeneous equilibrium model (HEM) model predictions, while having a lower flow rate than those in the two-phase region. Thus the major difficulty in the prediction of the depressurization flow rates remains in the region where two phases co-exist at the top of the vapor dome. In this region, the flow rate is strongly affected by the nozzle geometry and tends to be unstable. Various models for this region have been developed with different assumptions, e.g. the HEM and Moody model [3], and the Henry-Fauske non-equilibrium model [4], and are currently used in subcritical pressure reactor safety design[5]. It appears that some of these models could be reasonably extended to above the thermodynamic pseudo-critical point. The more stable and lower discharge flow rates observed in conditions above the pseudo-critical point suggests that even though SCWR's have a smaller coolant inventory, the safety implications of a LOCA and the subsequent depressurization may not be as severe as expected, this however needs to be confirmed by a rigorous evaluation of the particular event and further evaluation of the critical flow rate. This paper will summarize activities on critical flow models, experimental data and numerical modeling during blowdown from supercritical pressure conditions under the International Atomic Energy Agency (IAEA) Coordinated Research Project (CRP) on 'Heat Transfer Behaviour and Thermo-hydraulics Code testing for SCWRs'. (authors)« less

Measuring and monitoring KIPT Neutron Source Facility Reactivity

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

Cao, Yan; Gohar, Yousry; Zhong, Zhaopeng

2015-08-01

Argonne National Laboratory (ANL) of USA and Kharkov Institute of Physics and Technology (KIPT) of Ukraine have been collaborating on developing and constructing a neutron source facility at Kharkov, Ukraine. The facility consists of an accelerator-driven subcritical system. The accelerator has a 100 kW electron beam using 100 MeV electrons. The subcritical assembly has k eff less than 0.98. To ensure the safe operation of this neutron source facility, the reactivity of the subcritical core has to be accurately determined and continuously monitored. A technique which combines the area-ratio method and the flux-to-current ratio method is purposed to determine themore » reactivity of the KIPT subcritical assembly at various conditions. In particular, the area-ratio method can determine the absolute reactivity of the subcritical assembly in units of dollars by performing pulsed-neutron experiments. It provides reference reactivities for the flux-to-current ratio method to track and monitor the reactivity deviations from the reference state while the facility is at other operation modes. Monte Carlo simulations are performed to simulate both methods using the numerical model of the KIPT subcritical assembly. It is found that the reactivities obtained from both the area-ratio method and the flux-to-current ratio method are spatially dependent on the neutron detector locations and types. Numerical simulations also suggest optimal neutron detector locations to minimize the spatial effects in the flux-to-current ratio method. The spatial correction factors are calculated using Monte Carlo methods for both measuring methods at the selected neutron detector locations. Monte Carlo simulations are also performed to verify the accuracy of the flux-to-current ratio method in monitoring the reactivity swing during a fuel burnup cycle.« less

The physics of sub-critical lattices in accelerator driven hybrid systems: The MUSE experiments in the MASURCA facility

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

Chauvin, J. P.; Lebrat, J. F.; Soule, R.

Since 1991, the CEA has studied the physics of hybrid systems, involving a sub-critical reactor coupled with an accelerator. These studies have provided information on the potential of hybrid systems to transmute actinides and, long lived fission products. The potential of such a system remains to be proven, specifically in terms of the physical understanding of the different phenomena involved and their modelling, as well as in terms of experimental validation of coupled systems, sub-critical environment/accelerator. This validation must be achieved through mock-up studies of the sub-critical environments coupled to a source of external neutrons. The MUSE-4 mock-up experiment ismore » planed at the MASURCA facility and will use an accelerator coupled to a tritium target. The great step between the generator used in the past and the accelerator will allow to increase the knowledge in hybrid physic and to decrease the experimental biases and the measurement uncertainties.« less

Simulation of Nonlinear Instabilities in an Attachment-Line Boundary Layer

NASA Technical Reports Server (NTRS)

Joslin, Ronald D.

1996-01-01

The linear and the nonlinear stability of disturbances that propagate along the attachment line of a three-dimensional boundary layer is considered. The spatially evolving disturbances in the boundary layer are computed by direct numerical simulation (DNS) of the unsteady, incompressible Navier-Stokes equations. Disturbances are introduced either by forcing at the in ow or by applying suction and blowing at the wall. Quasi-parallel linear stability theory and a nonparallel theory yield notably different stability characteristics for disturbances near the critical Reynolds number; the DNS results con rm the latter theory. Previously, a weakly nonlinear theory and computations revealed a high wave-number region of subcritical disturbance growth. More recent computations have failed to achieve this subcritical growth. The present computational results indicate the presence of subcritically growing disturbances; the results support the weakly nonlinear theory. Furthermore, an explanation is provided for the previous theoretical and computational discrepancy. In addition, the present results demonstrate that steady suction can be used to stabilize disturbances that otherwise grow subcritically along the attachment line.

Hamiltonian Analysis of Subcritical Stochastic Epidemic Dynamics

PubMed Central

2017-01-01

We extend a technique of approximation of the long-term behavior of a supercritical stochastic epidemic model, using the WKB approximation and a Hamiltonian phase space, to the subcritical case. The limiting behavior of the model and approximation are qualitatively different in the subcritical case, requiring a novel analysis of the limiting behavior of the Hamiltonian system away from its deterministic subsystem. This yields a novel, general technique of approximation of the quasistationary distribution of stochastic epidemic and birth-death models and may lead to techniques for analysis of these models beyond the quasistationary distribution. For a classic SIS model, the approximation found for the quasistationary distribution is very similar to published approximations but not identical. For a birth-death process without depletion of susceptibles, the approximation is exact. Dynamics on the phase plane similar to those predicted by the Hamiltonian analysis are demonstrated in cross-sectional data from trachoma treatment trials in Ethiopia, in which declining prevalences are consistent with subcritical epidemic dynamics. PMID:28932256

Subcritical fracture propagation in rocks: An examination using the methods of fracture mechanics and non-destructive testing. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Swanson, P. L.

1984-01-01

An experimental investigation of tensile rock fracture is presented with an emphasis on characterizing time dependent crack growth using the methods of fracture mechanics. Subcritical fracture experiments were performed in moist air on glass and five different rock types at crack velocities using the double torsion technique. The experimental results suggest that subcritical fracture resistance in polycrystals is dominated by microstructural effects. Evidence for gross violations of the assumptions of linear elastic fracture mechanics and double torsion theory was found in the tests on rocks. In an effort to obtain a better understanding of the physical breakdown processes associated with rock fracture, a series of nondestructive evaluation tests were performed during subcritical fracture experiments on glass and granite. Comparison of the observed process zone shape with that expected on the basis of a critical normal principal tensile stress criterion shows that the zone is much more elongated in the crack propagation direction than predicted by the continuum based microcracking model alone.

Exploring How Weathering Related Stresses and Subcritical Crack Growth May Influence the Size of Sediment Produced From Different Rock Types.

NASA Astrophysics Data System (ADS)

Eppes, M. C.; Hallet, B.; Hancock, G. S.; Mackenzie-Helnwein, P.; Keanini, R.

2016-12-01

The formation and diminution of rock debris, sediment and soil at and near Earth's surface is driven in large part by in situ, non-transport related, rock cracking. Given the relatively low magnitude stresses that arise in surface and near-surface settings, this production and diminution of granular material is likely strongly influenced and/or driven by subcritical crack growth (Eppes et al., 2016), cracking that occurs under stress loading conditions much lower than a rock's strength as typically measured in the laboratory under rapid loading. Despite a relatively sound understanding of subcritical crack growth through engineering and geophysical studies, its geomorphic and sedimentologic implications have only been minimally explored. Here, based on existing studies, we formulate several hypotheses to predict how weathering-induced stresses combined with the subcritical crack growth properties of rock may influence sediment size distribution. For example, subcritical crack growth velocity (v) can be described by v = CKIn where KI is the mode I (simple opening mode) stress intensity factor, a function of tensile stress at the crack tip and crack length; C is a rock- and environment-dependent constant; and n is material constant, the subcritical crack growth index. Fracture length and spacing in rock is strongly dependent on n, where higher n values result in fewer, more distally spaced cracks (e.g. Olsen, 1993). Thus, coarser sediment might be expected from rocks with higher n values. Weathering-related stresses such as thermal stresses and mineral hydration, however, can disproportionally stress boundaries between minerals with contrasting thermal or chemical properties and orientation, resulting in granular disintegration. Thus, rocks with properties favorable to inducing these stresses might produce sediment whose size is reflective of its constituent grains. We begin to test these hypotheses through a detailed examination of crack and rock characteristics in outcrops of granite, sandstone, and quartzite found in Shenandoah National Park, Virginia. Preliminary results reveal that many observed cracking characteristics are consistent with our hypotheses linking subcritical crack growth, weathering stresses and the production of different sized sediment from different rock types.

Formation of localized sand patterns downstream from a vertical cylinder under steady flows: Experimental and theoretical study.

PubMed

Auzerais, Anthony; Jarno, Armelle; Ezersky, Alexander; Marin, François

2016-11-01

The generation of localized, spatially periodic patterns on a sandy bottom is experimentally and theoretically studied. Tests are performed in a hydrodynamic flume where patterns are produced downstream from a vertical cylinder under a steady current. It is found that patterns appear as a result of a subcritical instability of the water-sand bottom interface. A dependence of the area shape occupied by the patterns on the flow velocity and the cylinder diameter is investigated. It is shown that the patterns' characteristics can be explained using the Swift-Hohenberg equation. Numerical simulations point out that for a correct description of the patterns, an additional term which takes into account the impact of vortices on the sandy bottom in the wake of a cylinder must be added in the Swift-Hohenberg equation.

ELUTION OF ORGANIC SOLUTES FROM DIFFERENT POLARITY SORBENTS USING SUBCRITICAL WATER. (R825394)

EPA Science Inventory

The intermolecular interactions between organic solutes and sorbent matrices under subcritical water conditions have been investigated at a pressure of 50 bar and temperatures ranging from 50 to 250°C. Both polar and nonpolar organics (chlorophenols, amines, n-alkanes...

SPH numerical investigation of the characteristics of an oscillating hydraulic jump at an abrupt drop

NASA Astrophysics Data System (ADS)

De Padova, Diana; Mossa, Michele; Sibilla, Stefano

2018-02-01

This paper shows the results of the smooth particle hydrodynamics (SPH) modelling of the hydraulic jump at an abrupt drop, where the transition from supercritical to subcritical flow is characterised by several flow patterns depending upon the inflow and tailwater conditions. SPH simulations are obtained by a pseudo-compressible XSPH scheme with pressure smoothing; turbulent stresses are represented either by an algebraic mixing-length model, or by a two-equation k- ɛ model. The numerical model is applied to analyse the occurrence of oscillatory flow conditions between two different jump types characterised by quasi-periodic oscillation, and the results are compared with experiments performed at the hydraulics laboratory of Bari Technical University. The purpose of this paper is to obtain a deeper understanding of the physical features of a flow which is in general difficult to be reproduced numerically, owing to its unstable character: in particular, vorticity and turbulent kinetic energy fields, velocity, water depth and pressure spectra downstream of the jump, and velocity and pressure cross-correlations can be computed and analysed.

Modeling of biomass fractionation in a lab-scale biorefinery: Solubilization of hemicellulose and cellulose from holm oak wood using subcritical water.

PubMed

Cabeza, A; Piqueras, C M; Sobrón, F; García-Serna, J

2016-01-01

Lignocellulose fractionation is a key biorefinery process that need to be understood. In this work, a comprehensive study on hydrothermal-fractionation of holm oak in a semi-continuous system was conducted. The aim was to develop a physicochemical model in order to reproduce the role of temperature and water flow over the products composition. The experiments involved two sets: at constant flow (6mL/min) and two different ranges of temperature (140-180 and 240-280°C) and at a constant temperature range (180-260°C) and different flows: 11.0, 15.0 and 27.9mL/min. From the results, temperature has main influence and flow effect was observed only if soluble compounds were produced. The kinetic model was validated against experimental data, reproducing the total organic carbon profile (e.g. deviation of 33%) and the physicochemical phenomena observed in the process. In the model, it was also considered the variations of molecular weight of each biopolymer, successfully reproducing the biomass cleaving. Copyright © 2015 Elsevier Ltd. All rights reserved.

Attachment-Line Heating in a Compressible Flow

NASA Astrophysics Data System (ADS)

Reed, Helen; Saric, William

2011-11-01

The attachment-line boundary layer on a swept wing can be subject to either an instability or contamination by wing-root turbulence. A model of the attachment-line boundary layer is first developed including compressibility and wall heating in a Falkner-Skan-Cooke class of 3-D boundary layers with Hartree parameter of 1.0. For cases otherwise subcritical to either contamination or instability, the destabilizing effect of leading-edge heating under a variety of sweep angles and flight conditions is demonstrated. The results correlate with the attachment-line Reynolds number. Because the required heating levels are reasonable and achievable to trip the flow over the wing to turbulent, one possible application of this work is in the establishing of a baseline turbulent flow (on demand) for the calibration of a laminar-flow-control health monitoring system. *Portion based on work under Framework Agreement between Airbus Americas and NIA, and opinions, findings, conclusions do not necessarily reflect views of Airbus or NIA. Support from AFOSR/NASA National Center for Hypersonic Research in Laminar-Turbulent Transition through Grant FA9550-09-1-0341 gratefully acknowledged.

Aerodynamic Modeling of Transonic Aircraft Using Vortex Lattice Coupled with Transonic Small Disturbance for Conceptual Design

NASA Technical Reports Server (NTRS)

Chaparro, Daniel; Fujiwara, Gustavo E. C.; Ting, Eric; Nguyen, Nhan

2016-01-01

The need to rapidly scan large design spaces during conceptual design calls for computationally inexpensive tools such as the vortex lattice method (VLM). Although some VLM tools, such as Vorview have been extended to model fully-supersonic flow, VLM solutions are typically limited to inviscid, subcritical flow regimes. Many transport aircraft operate at transonic speeds, which limits the applicability of VLM for such applications. This paper presents a novel approach to correct three-dimensional VLM through coupling of two-dimensional transonic small disturbance (TSD) solutions along the span of an aircraft wing in order to accurately predict transonic aerodynamic loading and wave drag for transport aircraft. The approach is extended to predict flow separation and capture the attenuation of aerodynamic forces due to boundary layer viscosity by coupling the TSD solver with an integral boundary layer (IBL) model. The modeling framework is applied to the NASA General Transport Model (GTM) integrated with a novel control surface known as the Variable Camber Continuous Trailing Edge Flap (VCCTEF).

Low Mass-Damping Vortex-Induced Vibrations of a Single Cylinder at Moderate Reynolds Number.

PubMed

Jus, Y; Longatte, E; Chassaing, J-C; Sagaut, P

2014-10-01

The feasibility and accuracy of large eddy simulation is investigated for the case of three-dimensional unsteady flows past an elastically mounted cylinder at moderate Reynolds number. Although these flow problems are unconfined, complex wake flow patterns may be observed depending on the elastic properties of the structure. An iterative procedure is used to solve the structural dynamic equation to be coupled with the Navier-Stokes system formulated in a pseudo-Eulerian way. A moving mesh method is involved to deform the computational domain according to the motion of the fluid structure interface. Numerical simulations of vortex-induced vibrations are performed for a freely vibrating cylinder at Reynolds number 3900 in the subcritical regime under two low mass-damping conditions. A detailed physical analysis is provided for a wide range of reduced velocities, and the typical three-branch response of the amplitude behavior usually reported in the experiments is exhibited and reproduced by numerical simulation.

Near-field flow structures about subcritical surface roughness

NASA Astrophysics Data System (ADS)

Doolittle, Charles J.; Drews, Scott D.; Goldstein, David B.

2014-12-01

Laminar flow over a periodic array of cylindrical surface roughness elements is simulated with an immersed boundary spectral method both to validate the method for subsequent studies and to examine how persistent streamwise vortices are introduced by a low Reynolds number roughness element. Direct comparisons are made with prior studies at a roughness-based Reynolds number Rek (=U(k) k/ν) of 205 and a diameter to spanwise spacing ratio d/λ of 1/3. Downstream velocity contours match present and past experiments very well. The shear layer developed over the top of the roughness element produces the downstream velocity deficit. Upstream of the roughness element, the vortex topology is found to be consistent with juncture flow experiments, creating three cores along the recirculation line. Streamtraces stemming from these upstream cores, however, have unexpectedly little effect on the downstream flowfield as lateral divergence of the boundary layer quickly dissipates their vorticity. Long physical relaxation time of the recirculating wake behind the roughness remains a prominent issue for simulating this type of flowfield.

Fast-response underwater TSP investigation of subcritical instabilities of a cylinder in crossflow

NASA Astrophysics Data System (ADS)

Capone, Alessandro; Klein, Christian; Di Felice, Fabio; Beifuss, Uwe; Miozzi, Massimo

2015-10-01

We investigate the classic cylinder in crossflow case to test the effectiveness of a fast-response underwater temperature-sensitive paint coating (TSP) in providing highly resolved spatial and time observations of the action of a flow over a bluff body surface. The flow is investigated at Reynolds number <190 k, before the onset of the drag-crisis state. The obtained TSP image sequences convey an accurate description of the evolution of the main features in the fluid-cylinder interaction, like the separation line position, the pattern of the large coherent structures acting on the cylinder's surface and the small-scale intermittent streamwise arrays of vortices. Ad hoc data management and features extraction techniques are proposed which allow extraction of quantitative data, such as separation line position and vortex-shedding frequency, and results are compared to the literature. Use of TSP for water applications introduces an interesting point of view about the fluid-body interactions by focusing directly on the effect of the flow on the model surface.

On the stability of a time dependent boundary layer

NASA Technical Reports Server (NTRS)

Otto, S. R.

1993-01-01

The aim of this article is to determine the stability characteristics of a Rayleigh layer, which is known to occur when the fluid above a flat plate has a velocity imparted to it (parallel to the plate). This situation is intrinsically unsteady, however, as a first approximation we consider the instantaneous stability of the flow. The Orr-Sommerfeld equation is found to govern fixed downstream wavelength linear perturbations to the basic flow profile. By the solution of this equation, we can determine the Reynolds numbers at which the flow is neutrally stable; this quasisteady approach is only formally applicable for infinite Reynolds numbers. We shall consider the large Reynolds number limit of the original problem and use a three deck mentality to determine the form of the modes. The results of the two calculations are compared, and the linear large Reynolds number analysis is extended to consider the effect of weak nonlinearity in order to determine whether the system is subcritical or supercritical.

Effects of Soy Protein Hydrolysates Prepared by Varying Subcritical Media on the Physicochemical Properties of Pork Patties

PubMed Central

Davaatseren, Munkhtugs

2016-01-01

This study investigated the effect of soy protein hydrolysates (SPH) prepared by varying subcritical media on the physicochemical properties of pork patties. For resource of SPH, two different soybean species (Glycine max Merr.) of Daewonkong (DWK) and Saedanbaek (SDB) were selected. SPH was prepared by subcritical processing at 190℃ and 25 MPa under three different of media (water, 20% ethanol and 50% ethanol). Solubility and free amino group content revealed that water was better to yield larger amount of SPH than ethanol/water mixtures, regardless of species. Molecular weight (Mw) distribution of SPH was also similar between two species, while slightly different Mw distribution was obtained by subcritical media. For pork patty application, 50% ethanol treatment showed clear red color comparing to control after 14 d of storage. In addition, ethanol treatment had better oxidative stability than control and water treatment based on thiobarbituric acid-reactive substances (TBARS) analysis. For eating quality, although 20% ethanol treatment in SDB showed slightly higher cooking loss than control, generally addition of SPH did not affect the water-binding properties and hardness of pork patties. Consequently, the present study indicated that 50% ethanol was the best subcritical media to produce SPH possessing antioxidant activity, and the SPH produced from DWK exhibited better antioxidant activity than that produced SDB. PMID:27499657

HB-EGF embedded in PGA/PLLA scaffolds via subcritical CO2 augments the production of tissue engineered intestine.

PubMed

Liu, Yanchun; Nelson, Tyler; Cromeens, Barrett; Rager, Terrence; Lannutti, John; Johnson, Jed; Besner, Gail E

2016-10-01

The ability to deliver sustained-release, biologically active growth factors through custom designed tissue engineering scaffolds at sites of tissue regeneration offers great therapeutic opportunity. Due to the short in vivo half-lives of most growth factors, it is challenging to deliver these proteins to sites of interest where they may be used before being degraded. The application of subcritical CO2 uses gas-phase CO2 at subcritical pressures ranging from 41 to 62 bar (595-913 PSI) which avoids foaming by reducing the amount of CO2 dissolved in the polymer and maintains completely reversible plasticization. In the current study, heparin-binding EGF-like growth factor (HB-EGF) was embedded into polyglycolic acid (PGA)/Poly-l-latic acid (PLLA) scaffolds via subcritical CO2 exposure for the production of tissue engineered intestine (TEI). PGA fiber morphology after subcritical CO2 exposure was examined by scanning electron microscopy (SEM) and the distribution of HB-EGF embedded in the scaffold fibers was detected by HB-EGF immunofluorescent staining. In vivo implantation of HB-EGF-embedded scaffolds confirmed significantly improved TEI structure as a result of local delivery of the trophic growth factor. These findings may be critical for the production of TEI in the treatment of patients with short bowel syndrome in the future. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effects of Soy Protein Hydrolysates Prepared by Varying Subcritical Media on the Physicochemical Properties of Pork Patties.

PubMed

Lee, Yun-Kyung; Ko, Bo-Bae; Davaatseren, Munkhtugs; Hong, Geun-Pyo

2016-01-01

This study investigated the effect of soy protein hydrolysates (SPH) prepared by varying subcritical media on the physicochemical properties of pork patties. For resource of SPH, two different soybean species (Glycine max Merr.) of Daewonkong (DWK) and Saedanbaek (SDB) were selected. SPH was prepared by subcritical processing at 190℃ and 25 MPa under three different of media (water, 20% ethanol and 50% ethanol). Solubility and free amino group content revealed that water was better to yield larger amount of SPH than ethanol/water mixtures, regardless of species. Molecular weight (Mw) distribution of SPH was also similar between two species, while slightly different Mw distribution was obtained by subcritical media. For pork patty application, 50% ethanol treatment showed clear red color comparing to control after 14 d of storage. In addition, ethanol treatment had better oxidative stability than control and water treatment based on thiobarbituric acid-reactive substances (TBARS) analysis. For eating quality, although 20% ethanol treatment in SDB showed slightly higher cooking loss than control, generally addition of SPH did not affect the water-binding properties and hardness of pork patties. Consequently, the present study indicated that 50% ethanol was the best subcritical media to produce SPH possessing antioxidant activity, and the SPH produced from DWK exhibited better antioxidant activity than that produced SDB.

Topographic control on the nascent Mediterranean outflow

NASA Astrophysics Data System (ADS)

Gasser, M.; Pelegrí, J. L.; Nash, J. D.; Peters, H.; García-Lafuente, J.

2011-12-01

Data collected during a 12-day cruise in July 2009 served to examine the structure of the nascent Mediterranean Outflow Water (MOW) immediately west of the Espartel Sill, the westernmost sill in the Strait of Gibraltar. The MOW is characterized by high salinities (>37.0 and reaching 38.3) and high velocities (exceeding 1 m s-1 at 100 m above the seafloor), and follows a submerged valley along a 30 km stretch, the natural western extension of the strait. It is approx. 150 m thick and 10 km wide, and experiences a substantial drop from 420 to 530 m over a distance of some 3 km between two relatively flat regions. Measurements indicate that the nascent MOW behaves as a gravity current with nearly maximal traveling speed; if this condition is maintained, then the maximum MOW velocity would decrease slowly with distance from the Espartel Sill, remaining significantly high until the gravity current excess density is only a small fraction of its original value. The sharp pycnocline between the Mediterranean and the overlying North Atlantic Central waters is dynamically unstable, particularly where the flow interacts with the 100 m decrease in bottom depth. Here, subcritical gradient Richardson numbers coincide with the development of large interfacial undulations and billows. The very energetic downslope flow is likely responsible for the development of a narrow V-shaped channel downstream of the seafloor drop along the axis of the submerged valley, this probably being the very first erosional scour produced by the nascent MOW. The coincidence of subcritical gradient Richardson numbers with relatively high turbidity values above the channel flanks suggests it may be undergoing upstream erosion.

Field evidence for control of quarrying by rock bridges in jointed bedrock

NASA Astrophysics Data System (ADS)

Hooyer, T. S.; Cohen, D. O.; Iverson, N. R.

2011-12-01

Quarrying is generally thought to be the most important mechanism by which glaciers erode bedrock. In quarrying models it is assumed that slow, subcritical, growth of pre-existing cracks rate-limits the process and occurs where there are large stress differences in the bed, such as near rock bumps where ice separates from the bed to form water-filled cavities. Owing to the direction of principal stresses in rocks associated with sliding and resultant cavity formation, models predict that quarrying will occur along cracks oriented perpendicular to the ice flow direction or parallel to zones of ice-bed contact. Preglacial cracks in rocks will tend to propagate mainly downward, and in sedimentary or some metamorphic rocks will merge with bedding planes, thereby helping to isolate rock blocks for dislodgement. In contrast to these model assumptions, new measurements of quarried surface orientations in the deglaciated forefield of nine glaciers in Switzerland and Canada indicate a strong correlation between orientations of pre-existing joints and quarried bedrock surfaces, independent of ice flow direction or ice-water contact lines. The strong correlation persists across all rock types, and rocks devoid of major joints lack quarried surfaces. We propose a new conceptual model of quarrying that idealizes the bedrock as a series of blocks separated by discontinuous preglacial joints containing intact rock bridges. Bridges concentrate stress differences caused by normal and shear forces acting at the rock surface. Failure of bridges is caused by slow subcritical crack growth enhanced by water pressure fluctuations. To lend credibility to this new model, we show field evidence of failed rock bridges in quarried surfaces and of rib marks on plumose structures that we interpret as arrest fracture fronts due to transient subglacial water-pressure fluctuations.

Complete degradation of Orange G by electrolysis in sub-critical water.

PubMed

Yuksel, Asli; Sasaki, Mitsuru; Goto, Motonobu

2011-06-15

Complete degradation of azo dye Orange G was studied using a 500 mL continuous flow reactor made of SUS 316 stainless steel. In this system, a titanium reactor wall acted as a cathode and a titanium plate-type electrode was used as an anode in a subcritical reaction medium. This hydrothermal electrolysis process provides an environmentally friendly route that does not use any organic solvents or catalysts to remove organic pollutants from wastewater. Reactions were carried out from 30 to 90 min residence times at a pressure of 7 MPa, and at different temperatures of 180-250°C by applying various direct currents ranging from 0.5 to 1A. Removal of dye from the product solution and conversion of TOC increased with increasing current value. Moreover, the effect of salt addition on degradation of Orange G and TOC conversion was investigated, because in real textile wastewater, many salts are also included together with dye. Addition of Na(2)CO(3) resulted in a massive degradation of the dye itself and complete mineralization of TOC, while NaCl and Na(2)SO(4) obstructed the removal of Orange G. Greater than 99% of Orange G was successfully removed from the product solution with a 98% TOC conversion. Copyright © 2011 Elsevier B.V. All rights reserved.

Subcritical water extraction of phenolic and antioxidant constituents from pistachio (Pistacia vera L.) hulls.

PubMed

Erşan, Sevcan; Güçlü Üstündağ, Özlem; Carle, Reinhold; Schweiggert, Ralf M

2018-07-01

Pistachio hulls, important by-products of pistachio processing, were extracted using an environmentally friendly process with subcritical water (SCW) at a pressure of 6.9 MPa in the range of 110 and 190 °C, and a flow rate of 4 ml/min. Detailed HPLC-DAD-ESI/MS n analyses allowed the identification of 49 phenolic compounds in the SCW extracts. Total gallotannin yields up to 33 g/kg were reached at 150-170 °C, where gallic acid (22.2 g/kg) and penta-O-galloyl-β-d-glucose (9.77 g/kg) levels were 13.2- and 10.6-fold higher than those in the aqueous methanol extracts. Flavonols were also effectively extracted at 110-150 °C (4.37-5.65 g/kg), while anacardic acid recovery was poor (1.13-2.77 g/kg). Accordingly, high amounts of anacardic acids (up to 50.7 g/kg) were retained in the extraction residue, revealing that SCW extraction allowed selective extraction of gallotannins and flavonols. Antioxidant capacities ranged from 0.68 to 1.20 mmol Trolox equivalents (TE)/g for SCW extracts increasing with temperature up 190 °C. Copyright © 2018 Elsevier Ltd. All rights reserved.

ARC Researchers at 2015 IMECE

Science.gov Websites

diagram which in turn provides a broader understanding of the system behavior in its post-bifurcation also the post-bifurcation regime in both supercritical and subcritical cases despite the fact that it supercritical or subcritical characteristics) without placing the system in the post-bifurcation regime is a

PILOT-SCALE SUBCRITICAL WATER REMEDIATION OF POLYCYCLIC AROMATIC HYDROCARBON- AND PESTICIDE-CONTAMINATED SOIL. (R825394)

EPA Science Inventory

Subcritical water (hot water under enough pressure to maintain the liquid
state) was used to remove polycyclic aromatic hydrocarbons (PAHs) and pesticides
from highly contaminated soils. Laboratory-scale (8 g of soil) experiments were
used to determine conditions f...

Elasto-Inertial Turbulence: From Subcritical Turbulence to Maximum Drag Reduction

NASA Astrophysics Data System (ADS)

Dubief, Yves; Sid, Samir; Egan, Raphael; Terrapon, Vincent

2015-11-01

Elasto Inertial Turbulence (EIT) is a turbulence state found so far in polymer solutions. Upon the appropriate initial perturbation, an autonomous regeneration cycle emerges between polymer dynamics, pressure and velocity fluctuations. This cycle is best explained by the Poisson equation derived from viscoelastic flow models such as FENE-P (used in this study). This presentation provides an overview of the structure of EIT in 2D channel flows for Reynolds numbers ranging from Reτ = 10 to 100 and for 3D simulations up to Ret au = 300 . For flows below the Newtonian critical Reynolds number, EIT increases the drag. For higher Reynolds numbers, EIT is surmised to be the energetic bound of Maximum Drag Reduction (MDR), the asymptotic state of drag reduction in polymer solutions. The very existence of EIT at low Reynolds numbers (Reτ < 60) highlights a backward energy transfer from the small scale polymer dynamics to larger flow scales. Similar dynamics is identified at higher Reynolds numbers, which could explain why polymer flows never become fully laminar. The authors acknowledge computational resources from CÉCI (F.R.S.-FNRS grant No.2.5020.11), the PRACE infrastructure, and the Vermont Advanced Computing Core.

Hypersonic Viscous Flow Over Large Roughness Elements

NASA Technical Reports Server (NTRS)

Chang, Chau-Lyan; Choudhari, Meelan M.

2009-01-01

Viscous flow over discrete or distributed surface roughness has great implications for hypersonic flight due to aerothermodynamic considerations related to laminar-turbulent transition. Current prediction capability is greatly hampered by the limited knowledge base for such flows. To help fill that gap, numerical computations are used to investigate the intricate flow physics involved. An unstructured mesh, compressible Navier-Stokes code based on the space-time conservation element, solution element (CESE) method is used to perform time-accurate Navier-Stokes calculations for two roughness shapes investigated in wind tunnel experiments at NASA Langley Research Center. It was found through 2D parametric study that at subcritical Reynolds numbers, spontaneous absolute instability accompanying by sustained vortex shedding downstream of the roughness is likely to take place at subsonic free-stream conditions. On the other hand, convective instability may be the dominant mechanism for supersonic boundary layers. Three-dimensional calculations for both a rectangular and a cylindrical roughness element at post-shock Mach numbers of 4.1 and 6.5 also confirm that no self-sustained vortex generation from the top face of the roughness is observed, despite the presence of flow unsteadiness for the smaller post-shock Mach number case.

Numerical solution of the Saint-Venant equations by an efficient hybrid finite-volume/finite-difference method

NASA Astrophysics Data System (ADS)

Lai, Wencong; Khan, Abdul A.

2018-04-01

A computationally efficient hybrid finite-volume/finite-difference method is proposed for the numerical solution of Saint-Venant equations in one-dimensional open channel flows. The method adopts a mass-conservative finite volume discretization for the continuity equation and a semi-implicit finite difference discretization for the dynamic-wave momentum equation. The spatial discretization of the convective flux term in the momentum equation employs an upwind scheme and the water-surface gradient term is discretized using three different schemes. The performance of the numerical method is investigated in terms of efficiency and accuracy using various examples, including steady flow over a bump, dam-break flow over wet and dry downstream channels, wetting and drying in a parabolic bowl, and dam-break floods in laboratory physical models. Numerical solutions from the hybrid method are compared with solutions from a finite volume method along with analytic solutions or experimental measurements. Comparisons demonstrates that the hybrid method is efficient, accurate, and robust in modeling various flow scenarios, including subcritical, supercritical, and transcritical flows. In this method, the QUICK scheme for the surface slope discretization is more accurate and less diffusive than the center difference and the weighted average schemes.

Hydraulic properties for interrill erosion on steep slopes using a portable rainfall simulator

NASA Astrophysics Data System (ADS)

Shin, Seung Sook; Hwang, Yoonhee; Deog Park, Sang; Yun, Minu; Park, Sangyeon

2017-04-01

The hydraulic parameters for sheet flow on steep slopes have been not frequently measured because the shallow flow depth and slow flow velocity are difficult to measure. In this study hydraulic values of sheet flow were analyzed to evaluate interrill erosion on steep slopes. A portable rainfall simulator was used to conduct interrill erosion test. The kinetic energy of rainfall simulator was obtained by disdrometer being capable of measuring the drop size distribution and velocity of falling raindrops. The sheet flow velocity was determined by the taken time for a dye transferring fixed points using video images. Surface runoff discharge and sediment yield increased with increase of rainfall intensity and kinetic energy and slope steepness. Especially sediment yield was strongly correlated with sheet flow velocity. The maximum velocity of sheet flow was 2.3cm/s under rainfall intensity of 126.8mm/h and slope steepness of 53.2%. The sheet flow was laminar and subcritical flow as the flow Reynolds number and Froude number are respectively the ranges of 10 22 and 0.05 0.25. The roughness coefficient (Manning's n) for sheet flow on steep slopes was relatively large compared to them on the gentle slope. Keywords: Sheet flow velocity; Rainfall simulator; Interrill erosion; Steep slope This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIP) (No. 2015R1C1A2A01055469).

SIMPLE METHOD FOR ESTIMATING POLYCHLORINATED BIPHENYL CONCENTRATIONS ON SOILS AND SEDIMENTS USING SUBCRITICAL WATER EXTRACTION COUPLED WITH SOLID-PHASE MICROEXTRACTION. (R825368)

EPA Science Inventory

A rapid method for estimating polychlorinated biphenyl (PCB) concentrations in contaminated soils and sediments has been developed by coupling static subcritical water extraction with solid-phase microextraction (SPME). Soil, water, and internal standards are placed in a seale...

SUBCRITICAL (HOT) WATER/ETHANOL EXTRACTION OF NONYLPHENOL POLYETHOXY CARBOXYLATES IN INDUSTRIAL AND MUNICIPAL SLUDGES. (R821195)

EPA Science Inventory

Subcritical (hot) water with ethanol as modifier was used
to extract nonylphenol polyethoxy carboxylates (NPECs)
with 1-4 ethoxy groups from sludge samples. Quantitative
recovery of native NPECs from sludge was accomplished
by extracting 0.25 g samples for 20 min w...

Impact of the neutron detector choice on Bell and Glasstone spatial correction factor for subcriticality measurement

NASA Astrophysics Data System (ADS)

Talamo, Alberto; Gohar, Y.; Cao, Y.; Zhong, Z.; Kiyavitskaya, H.; Bournos, V.; Fokov, Y.; Routkovskaya, C.

2012-03-01

In subcritical assemblies, the Bell and Glasstone spatial correction factor is used to correct the measured reactivity from different detector positions. In addition to the measuring position, several other parameters affect the correction factor: the detector material, the detector size, and the energy-angle distribution of source neutrons. The effective multiplication factor calculated by computer codes in criticality mode slightly differs from the average value obtained from the measurements in the different experimental channels of the subcritical assembly, which are corrected by the Bell and Glasstone spatial correction factor. Generally, this difference is due to (1) neutron counting errors; (2) geometrical imperfections, which are not simulated in the calculational model, and (3) quantities and distributions of material impurities, which are missing from the material definitions. This work examines these issues and it focuses on the detector choice and the calculation methodologies. The work investigated the YALINA Booster subcritical assembly of Belarus, which has been operated with three different fuel enrichments in the fast zone either: high (90%) and medium (36%), medium (36%), or low (21%) enriched uranium fuel.

Plutonium Critical Mass Curve Comparison to Mass at Upper Subcritical Limit (USL) Using Whisper

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

Alwin, Jennifer Louise; Zhang, Ning

Whisper is computational software designed to assist the nuclear criticality safety analyst with validation studies with the MCNP ® Monte Carlo radiation transport package. Standard approaches to validation rely on the selection of benchmarks based upon expert judgment. Whisper uses sensitivity/uncertainty (S/U) methods to select relevant benchmarks to a particular application or set of applications being analyzed. Using these benchmarks, Whisper computes a calculational margin. Whisper attempts to quantify the margin of subcriticality (MOS) from errors in software and uncertainties in nuclear data. The combination of the Whisper-derived calculational margin and MOS comprise the baseline upper subcritical limit (USL), tomore » which an additional margin may be applied by the nuclear criticality safety analyst as appropriate to ensure subcriticality. A series of critical mass curves for plutonium, similar to those found in Figure 31 of LA-10860-MS, have been generated using MCNP6.1.1 and the iterative parameter study software, WORM_Solver. The baseline USL for each of the data points of the curves was then computed using Whisper 1.1. The USL was then used to determine the equivalent mass for plutonium metal-water system. ANSI/ANS-8.1 states that it is acceptable to use handbook data, such as the data directly from the LA-10860-MS, as it is already considered validated (Section 4.3 4) “Use of subcritical limit data provided in ANSI/ANS standards or accepted reference publications does not require further validation.”). This paper attempts to take a novel approach to visualize traditional critical mass curves and allows comparison with the amount of mass for which the k eff is equal to the USL (calculational margin + margin of subcriticality). However, the intent is to plot the critical mass data along with USL, not to suggest that already accepted handbook data should have new and more rigorous requirements for validation.« less

Long-Time Behavior and Critical Limit of Subcritical SQG Equations in Scale-Invariant Sobolev Spaces

NASA Astrophysics Data System (ADS)

Coti Zelati, Michele

2018-02-01

We consider the subcritical SQG equation in its natural scale-invariant Sobolev space and prove the existence of a global attractor of optimal regularity. The proof is based on a new energy estimate in Sobolev spaces to bootstrap the regularity to the optimal level, derived by means of nonlinear lower bounds on the fractional Laplacian. This estimate appears to be new in the literature and allows a sharp use of the subcritical nature of the L^∞ bounds for this problem. As a by-product, we obtain attractors for weak solutions as well. Moreover, we study the critical limit of the attractors and prove their stability and upper semicontinuity with respect to the strength of the diffusion.

Comparing the new generation accelerator driven subcritical reactor system (ADS) to traditional critical reactors

NASA Astrophysics Data System (ADS)

Kemah, Elif; Akkaya, Recep; Tokgöz, Seyit Rıza

2017-02-01

In recent years, the accelerator driven subcritical reactors have taken great interest worldwide. The Accelerator Driven System (ADS) has been used to produce neutron in subcritical state by the external proton beam source. These reactors, which are hybrid systems, are important in production of clean and safe energy and conversion of radioactive waste. The ADS with the selection of reliability and robust target materials have been the new generation of fission reactors. In addition, in the ADS Reactors the problems of long-lived radioactive fission products and waste actinides encountered in the fission process of the reactor during incineration can be solved, and ADS has come to the forefront of thorium as fuel for the reactors.

Summer mistral at the exit of the Rhône valley

NASA Astrophysics Data System (ADS)

Drobinski, P.; Bastin, S.; Guenard, V.; Caccia, J. L.; Dabas, A. M.; Delville, P.; Protat, A.; Reitebuch, O.; Werner, C.

2005-01-01

The paper examines the three-dimensional structure and dynamics of the mistral at the Rhône valley exit on 28 June 2001. The mistral refers to a severe wind that develops along the Rhône valley in southern France. This summer mistral event was documented in the framework of the ESCOMPTE field experiment. The dynamical processes driving the circulation of the mistral in the Rhône valley and particularly wake formation and planetary boundary layer (PBL) inhomogeneity at the scale of Rhône valley delta are investigated. Several important data sources are used (airborne Doppler lidar, radiosondes and surface stations) as well as non-hydrostatic mesoscale simulations. This paper analyses experimentally, numerically and theoretically the mechanism of wake formation. It shows that the flow impinging on the Alpine range and the Massif Central becomes supercritical all along the ridge line, including the Rhône valley and continues to accelerate in the lee regions until a hydraulic jump occurs. It leads to the formation of wakes behind and close to the mountain peaks. Compared to the Massif Central wake, the origin of the western Alps wake is rather complicated. In this study, the observations and simulations suggest a combined wall separation/gravity wave breaking mechanism to explain the western Alps wake. Indeed, it is shown that in addition to the flow descending the western Alps slopes and experiencing a strong hydraulic jump, the point where the mistral flow separates from the eastern flank of the Rhône valley located at about 44°N is associated with a 'flank-shock' which is an oblique hydraulic jump (i.e.the downstream Froude number is supercritical). Wake formation in the lee of the Alps and the Massif Central causes large inhomogeneity of the PBL with differences between land and sea. In the Massif Central and western Alps wakes, the continental PBL is deeper (1.8 km) than in the mistral flow (1 km), which is consistent with a subcritical regime associated with enhanced turbulent mixing. The supercritical air flow, descending the Massif Central and Alps slopes and transitioning to subcritical flow, increases the near-surface air temperature due to the föhn effect. Over the Mediterranean, the surface heat fluxes are slightly negative (between-50 and 0 W m -2) and the main source of PBL turbulence is mechanical (wind shear). The PBL depth within the mistral flow does not vary over land (1 km), whereas the absence of convection but also of strong winds prevent PBL development over the sea in the wakes of the Massif Central and the Alps (PBL depth of about 0.5 km).

On the mechanism of elasto-inertial turbulence.

PubMed

Dubief, Yves; Terrapon, Vincent E; Soria, Julio

2013-11-01

Elasto-inertial turbulence (EIT) is a new state of turbulence found in inertial flows with polymer additives. The dynamics of turbulence generated and controlled by such additives is investigated from the perspective of the coupling between polymer dynamics and flow structures. Direct numerical simulations of channel flow with Reynolds numbers ranging from 1000 to 6000 (based on the bulk and the channel height) are used to study the formation and dynamics of elastic instabilities and their effects on the flow. The flow topology of EIT is found to differ significantly from Newtonian wall-turbulence. Structures identified by positive (rotational flow topology) and negative (extensional/compressional flow topology) second invariant Q a isosurfaces of the velocity gradient are cylindrical and aligned in the spanwise direction. Polymers are significantly stretched in sheet-like regions that extend in the streamwise direction with a small upward tilt. The Q a cylindrical structures emerge from the sheets of high polymer extension, in a mechanism of energy transfer from the fluctuations of the polymer stress work to the turbulent kinetic energy. At subcritical Reynolds numbers, EIT is observed at modest Weissenberg number ( Wi , ratio polymer relaxation time to viscous time scale). For supercritical Reynolds numbers, flows approach EIT at large Wi . EIT provides new insights on the nature of the asymptotic state of polymer drag reduction (maximum drag reduction), and explains the phenomenon of early turbulence, or onset of turbulence at lower Reynolds numbers than for Newtonian flows observed in some polymeric flows.

On the mechanism of elasto-inertial turbulence

NASA Astrophysics Data System (ADS)

Dubief, Yves; Terrapon, Vincent E.; Soria, Julio

2013-11-01

Elasto-inertial turbulence (EIT) is a new state of turbulence found in inertial flows with polymer additives. The dynamics of turbulence generated and controlled by such additives is investigated from the perspective of the coupling between polymer dynamics and flow structures. Direct numerical simulations of channel flow with Reynolds numbers ranging from 1000 to 6000 (based on the bulk and the channel height) are used to study the formation and dynamics of elastic instabilities and their effects on the flow. The flow topology of EIT is found to differ significantly from Newtonian wall-turbulence. Structures identified by positive (rotational flow topology) and negative (extensional/compressional flow topology) second invariant Qa isosurfaces of the velocity gradient are cylindrical and aligned in the spanwise direction. Polymers are significantly stretched in sheet-like regions that extend in the streamwise direction with a small upward tilt. The Qa cylindrical structures emerge from the sheets of high polymer extension, in a mechanism of energy transfer from the fluctuations of the polymer stress work to the turbulent kinetic energy. At subcritical Reynolds numbers, EIT is observed at modest Weissenberg number (Wi, ratio polymer relaxation time to viscous time scale). For supercritical Reynolds numbers, flows approach EIT at large Wi. EIT provides new insights on the nature of the asymptotic state of polymer drag reduction (maximum drag reduction), and explains the phenomenon of early turbulence, or onset of turbulence at lower Reynolds numbers than for Newtonian flows observed in some polymeric flows.

On the mechanism of elasto-inertial turbulence

PubMed Central

Dubief, Yves; Terrapon, Vincent E.; Soria, Julio

2013-01-01

Elasto-inertial turbulence (EIT) is a new state of turbulence found in inertial flows with polymer additives. The dynamics of turbulence generated and controlled by such additives is investigated from the perspective of the coupling between polymer dynamics and flow structures. Direct numerical simulations of channel flow with Reynolds numbers ranging from 1000 to 6000 (based on the bulk and the channel height) are used to study the formation and dynamics of elastic instabilities and their effects on the flow. The flow topology of EIT is found to differ significantly from Newtonian wall-turbulence. Structures identified by positive (rotational flow topology) and negative (extensional/compressional flow topology) second invariant Qa isosurfaces of the velocity gradient are cylindrical and aligned in the spanwise direction. Polymers are significantly stretched in sheet-like regions that extend in the streamwise direction with a small upward tilt. The Qa cylindrical structures emerge from the sheets of high polymer extension, in a mechanism of energy transfer from the fluctuations of the polymer stress work to the turbulent kinetic energy. At subcritical Reynolds numbers, EIT is observed at modest Weissenberg number (Wi, ratio polymer relaxation time to viscous time scale). For supercritical Reynolds numbers, flows approach EIT at large Wi. EIT provides new insights on the nature of the asymptotic state of polymer drag reduction (maximum drag reduction), and explains the phenomenon of early turbulence, or onset of turbulence at lower Reynolds numbers than for Newtonian flows observed in some polymeric flows. PMID:24170968

Asymmetrical, inversely graded, upstream-migrating cyclic steps in marine settings: Late Miocene-early Pliocene Fish Creek-Vallecito Basin, southern California

NASA Astrophysics Data System (ADS)

Gong, Chenglin; Chen, Liuqin; West, Logan

2017-10-01

Cyclic steps are ubiquitous in modern sedimentary environments, yet their recognition remains sparse in the rock record. Here, we interpret three sets of undulating backsets (1 to 3) recognized in the late Miocene-early Pliocene Latrania Formation in the Anza-Borrego Desert, the Fish Creek-Vallecito Basin, southern California, USA as the first cm- to dm-scale outcrop record of cyclic steps, based on asymmetrical cross-sections, upstream migration, and inversely graded laminae. Upstream migration and asymmetrical cross-sections of backsets and concomitant backset laminae are attributed to supercritical-to-subcritical flow transitions through weak hydraulic jumps, which are composed of: (i) thin (tens of centimetres) and slower (reported as flow velocities (Ū) of 0.45 to 1.45 m s- 1, with mean value of Ū = 0.89 m s- 1) subcritical (represented by internal Froude numbers (Fr) of 0.67 to 0.99, with mean value of Fr = 0.84) turbidity currents on the stoss sides, and (ii) thin (tens of centimetres) and faster (reported as Ū of 0.99 to 4.03 m s- 1, with mean value of Ū = 2.24 m s- 1) supercritical (represented by Fr of 1.84 to 3.07, with mean value of Fr = 2.42) turbidity flows on the lee sides. The inversely graded laminae in the troughs of backsets are 2 to 5 cm thick, and consist of two discrete divisions: (i) 1 to 2 cm thick, lower finer-grained divisions made up of parallel laminated siltstones, overlain by very fine- to fine-grained sandstones, and (ii) 2 to 3 cm thick, upper divisions composed of medium- to coarse-grained sandstones, with sporadic occurrence of subrounded pebbles. These inversely graded laminae are related to stratified, collisional and/or frictional traction carpets under conditions of high fall-out rates. Due to the poor preservation potential of cyclic steps, the rock record of cyclic steps is generally considered to be rare. The present outcrop-based study presents a detailed analysis of sedimentary facies, growth patterns, and flow dynamics of marine cyclic steps, thereby contributing to better understand architectural styles and lithological properties of cyclic steps in the geological record.

Effects of energetic coherent motions on the power and wake of an axial-flow turbine

NASA Astrophysics Data System (ADS)

Chamorro, L. P.; Hill, C.; Neary, V. S.; Gunawan, B.; Arndt, R. E. A.; Sotiropoulos, F.

2015-05-01

A laboratory experiment examined the effects of energetic coherent motions on the structure of the wake and power fluctuations generated by a model axial-flow hydrokinetic turbine. The model turbine was placed in an open-channel flow and operated under subcritical conditions. The incoming flow was locally perturbed with vertically oriented cylinders of various diameters. An array of three acoustic Doppler velocimeters aligned in the cross-stream direction and a torque transducer were used to collect high-resolution and synchronous measurements of the three-velocity components of the incoming and wake flow as well as the turbine power. A strong scale-to-scale interaction between the large-scale and broadband turbulence shed by the cylinders and the turbine power revealed how the turbulence structure modulates the turbine behavior. In particular, the response of the turbine to the distinctive von Kármán-type vortices shed from the cylinders highlighted this phenomenon. The mean and fluctuating characteristics of the turbine wake are shown to be very sensitive to the energetic motions present in the flow. Tip vortices were substantially dampened and the near-field mean wake recovery accelerated in the presence of energetic motions in the flow. Strong coherent motions are shown to be more effective than turbulence levels for triggering the break-up of the spiral structure of the tip-vortices.

Convergence of Defect-Correction and Multigrid Iterations for Inviscid Flows

NASA Technical Reports Server (NTRS)

Diskin, Boris; Thomas, James L.

2011-01-01

Convergence of multigrid and defect-correction iterations is comprehensively studied within different incompressible and compressible inviscid regimes on high-density grids. Good smoothing properties of the defect-correction relaxation have been shown using both a modified Fourier analysis and a more general idealized-coarse-grid analysis. Single-grid defect correction alone has some slowly converging iterations on grids of medium density. The convergence is especially slow for near-sonic flows and for very low compressible Mach numbers. Additionally, the fast asymptotic convergence seen on medium density grids deteriorates on high-density grids. Certain downstream-boundary modes are very slowly damped on high-density grids. Multigrid scheme accelerates convergence of the slow defect-correction iterations to the extent determined by the coarse-grid correction. The two-level asymptotic convergence rates are stable and significantly below one in most of the regions but slow convergence is noted for near-sonic and very low-Mach compressible flows. Multigrid solver has been applied to the NACA 0012 airfoil and to different flow regimes, such as near-tangency and stagnation. Certain convergence difficulties have been encountered within stagnation regions. Nonetheless, for the airfoil flow, with a sharp trailing-edge, residuals were fast converging for a subcritical flow on a sequence of grids. For supercritical flow, residuals converged slower on some intermediate grids than on the finest grid or the two coarsest grids.

Subcritical crack growth in soda-lime glass in combined mode I and mode II loading

NASA Technical Reports Server (NTRS)

Singh, Dileep; Shetty, Dinesh K.

1990-01-01

Subcritical crack growth under mixed-mode loading was studied in soda-lime glass. Pure mode I, combined mode I and mode II, and pure mode II loadings were achieved in precracked disk specimens by loading in diametral compression at selected angles with respect to the symmetric radial crack. Crack growth was monitored by measuring the resistance changes in a microcircuit grid consisting of parallel, electrically conducting grid lines deposited on the surface of the disk specimens by photolithography. Subcritical crack growth rates in pure mode I, pure mode II, and combined mode I and mode II loading could be described by an exponential relationship between crack growth rate and an effective crack driving force derived from a mode I-mode II fracture toughness envelope. The effective crack driving force was based on an empirical representation of the noncoplanar strain energy release rate. Stress intensities for kinked cracks were assessed using the method of caustics and an initial decrease and a subsequent increase in the subcritical crack growth rates of kinked cracks were shown to correlate with the variations of the mode I and the mode II stress intensities.

Characteristics of membrane fouling in submerged membrane bioreactor under sub-critical flux operation.

PubMed

Su, Y C; Huang, C P; Pan, Jill R; Lee, H C

2008-01-01

Recently, the membrane bioreactor (MBR) process has become one of the novel technologies to enhance the performance of biological treatment of wastewater. Membrane bioreactor process uses the membrane unit to replace a sediment tank, and this can greatly enhance treatment performance. However, membrane fouling in MBR restricts its widespread application because it leads to permeate flux decline, making more frequent membrane cleaning and replacement necessary, which then increases operating and maintenance costs. This study investigated the sludge characteristics in membrane fouling under sub-critical flux operation and also assessed the effect of shear stress on membrane fouling. Membrane fouling was slow under sub-critical flux operation. However, as filamentous microbes became dominant in the reactor, membrane fouling increased dramatically due to the increased viscosity and polysaccharides. A close link was found between membrane fouling and the amount of polysaccharides in soluble EPS. The predominant resistance was the cake resistance which could be minimized by increasing the shear stress. However, the resistance of colloids and solutes was not apparently reduced by increasing shear stress. Therefore, smaller particles such as macromolecules (e.g. polysaccharides) may play an important role in membrane fouling under sub-critical flux operation.

Effect of residence time on two-step liquefaction of rice straw in a CO2 atmosphere: Differences between subcritical water and supercritical ethanol.

PubMed

Yang, Tianhua; Wang, Jian; Li, Bingshuo; Kai, Xingping; Li, Rundong

2017-04-01

This study investigated the influence of temperature and residence time on liquefaction of rice straw in subcritical CO 2 -subcritical water (subCO 2 -subH 2 O) and in subcritical CO 2 -supercritical ethanol (subCO 2 -scEtOH), considering the final reaction temperatures (270-345°C) and residence times (15 and 30min). Residence time was identified as a crucial parameter in the subCO 2 -subH 2 O liquefaction, whereas residence time had a marginal influence on subCO 2 -scEtOH liquefaction. When reaction conditions were 320°C and 15min, solvents have weak impact on the quality of bio-oil, HHV 28.57MJ/kg and 28.62MJ/kg, respectively. There was an obvious difference between the subCO 2 -subH 2 O and subCO 2 -scEtOH liquefaction mechanisms. In subCO 2 -subH 2 O, CO 2 promoted the carbonyl reaction. In subCO 2 -scEtOH, supercritical ethanol have the function of donating hydrogen and promoting the reaction of hydroxyl-alkylation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Bifurcations and chaos in convection taking non-Fourier heat-flux

NASA Astrophysics Data System (ADS)

Layek, G. C.; Pati, N. C.

2017-11-01

In this Letter, we report the influences of thermal time-lag on the onset of convection, its bifurcations and chaos of a horizontal layer of Boussinesq fluid heated underneath taking non-Fourier Cattaneo-Christov hyperbolic model for heat propagation. A five-dimensional nonlinear system is obtained for a low-order Galerkin expansion, and it reduces to Lorenz system for Cattaneo number tending to zero. The linear stability agreed with existing results that depend on Cattaneo number C. It also gives a threshold Cattaneo number, CT, above which only oscillatory solutions can persist. The oscillatory solutions branch terminates at the subcritical steady branch with a heteroclinic loop connecting a pair of saddle points for subcritical steady-state solutions. For subcritical onset of convection two stable solutions coexist, that is, hysteresis phenomenon occurs at this stage. The steady solution undergoes a Hopf bifurcation and is of subcritical type for small value of C, while it becomes supercritical for moderate Cattaneo number. The system goes through period-doubling/noisy period-doubling transition to chaos depending on the control parameters. There after the system exhibits Shil'nikov chaos via homoclinic explosion. The complexity of spiral strange attractor is analyzed using fractal dimension and return map.

Benchmarking criticality analysis of TRIGA fuel storage racks.

PubMed

Robinson, Matthew Loren; DeBey, Timothy M; Higginbotham, Jack F

2017-01-01

A criticality analysis was benchmarked to sub-criticality measurements of the hexagonal fuel storage racks at the United States Geological Survey TRIGA MARK I reactor in Denver. These racks, which hold up to 19 fuel elements each, are arranged at 0.61m (2 feet) spacings around the outer edge of the reactor. A 3-dimensional model was created of the racks using MCNP5, and the model was verified experimentally by comparison to measured subcritical multiplication data collected in an approach to critical loading of two of the racks. The validated model was then used to show that in the extreme condition where the entire circumference of the pool was lined with racks loaded with used fuel the storage array is subcritical with a k value of about 0.71; well below the regulatory limit of 0.8. A model was also constructed of the rectangular 2×10 fuel storage array used in many other TRIGA reactors to validate the technique against the original TRIGA licensing sub-critical analysis performed in 1966. The fuel used in this study was standard 20% enriched (LEU) aluminum or stainless steel clad TRIGA fuel. Copyright © 2016. Published by Elsevier Ltd.

Thermophysical Properties of Pore-confined Supercritical CO2 by Vibrating Tube Densimetry

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

Gruszkiewicz, Miroslaw; Wesolowski, David J; Cole, David R

2011-01-01

Properties of fluids confined in pore systems are needed for modeling fluid flow, fluid-rock interactions, and changes in reservoir porosity. The properties of CO2-rich fluids are particularly relevant to geothermal heat mining using carbon dioxide instead of water. While manometric, volumetric, and gravimetric techniques have been used successfully to investigate adsorption of low-density subcritical vapors, the results have not been satisfactory at higher, liquid-like densities of supercritical fluids. Even if the requirements for high experimental accuracy in the neighborhood of the critical region were met, these methods are fundamentally unable to deliver the total adsorption capacity, since the properties (e.g.more » density) of the adsorbed phase are in general not known. In this work we utilize vibrating tube densimetry for the first time to measure the total amount of fluid contained within a mesoporous solid. The method is first demonstrated using propane at subcritical and supercritical temperatures between 35 C and 97 C confined in silica aerogel (density 0.2 g cm-3, porosity 90%) that was synthesized inside Hastelloy U-tubes. Sorption and desorption of carbon dioxide on the same solid was measured at 35 C at pressures to 120 bar (density to 0.767 g cm-3). The results show total adsorption increasing monotonically with increasing pressure, unlike excess adsorption isotherms which show a maximum close to the critical density.« less

Neutronics performance and activation calculation of dense tungsten granular target for China-ADS

NASA Astrophysics Data System (ADS)

Zhang, Yaling; Li, Jianyang; Zhang, Xunchao; Cai, Hanjie; Yan, Xuesong; Yu, Lin; Fu, Fen; Lin, Ping; Gao, Xiaofei; Zhang, Zhilei; Zhang, Yanshi; Yang, Lei

2017-11-01

Spallation target, which constitutes the physical and functional interface between the high power accelerator and the subcritical core, is one of the most important components in Accelerator Driven Subcritical System (ADS). In this paper, we investigated the neutronics performance, the radiation damage and the activation of dense tungsten granular flow spallation target by using the Monte Carlo programs GMT and FLUKA at the proton energy of 250 MeV with a beam current of 10 mA . First, the leaking neutron yield, leaking neutron energy spectrum and laterally leaking neutron distribution at several time nodes and with different target parameters are explored. After that, the displacement per atom (DPA) and the helium/hydrogen production for tungsten grains and structural materials with stainless steel 316L are estimated. Finally, the radioactivity, residual dose rate and afterheat of granular target are presented. Results indicate that granule diameter below 1 cm and the beam profile diameter have negligible impact on neutronics performance, while the target diameter and volume fraction of grain have notable influence. The maximum DPA for target vessel (beam tube) is about 1.0 (1.6) DPA/year in bare target, and increased to 2.6 (2.8) DPA/year in fission environment. Average DPA for tungsten grains is relatively low. The decline rate of radioactivity and afterheat with cooling time grows with the decrease of the irradiation time.

Subcritical crack growth phenomenon and fractography of barium titanate and barium titanate-based composite

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

Hwang, H.J.; Niihara, Koichi

1997-01-15

Subcritical crack growth (SCG), the propagation of surface and subsurface flaws under subcritical stress, i.e., any stress less than that necessary to catastrophically propagate the flaw, is a general phenomenon frequently observed in ceramics. Recently, electrical devices are miniaturized and used under quite severe atmospheres. Such environments often lead to the initiation and propagation of cracks due to the repeated electrical cycling, stresses by the mismatch in thermal expansion coefficient between devices and other constituents and thermal shock. In this study, the authors fabricated BaTiO{sub 3} and BaTiO{sub 3}-based composites containing nano-sized SiC particulates. The SCG phenomenon and fractography weremore » discussed based on the data obtained from indentation-induced-fracture (IIF) method.« less

Effects of cylinder Reynolds number on the turbulent horseshoe vortex system and near wake of a surface-mounted circular cylinder

NASA Astrophysics Data System (ADS)

Kirkil, Gokhan; Constantinescu, George

2014-11-01

The turbulent horseshoe vortex (HV) system and the near-wake flow past a circular cylinder mounted on a flat bed in an open channel are investigated based on results of eddy-resolving simulations and supporting flow visualizations. Of particular interest are the changes in the mean flow and turbulence statistics within the HV region as the necklace vortices wrap around the cylinder's base and the variation of the mean flow and turbulence statistics in the near wake, in between the channel bed and the free surface. While it is well known that the drag crisis induces important changes in the flow past infinitely-long circular cylinders, the changes are less understood and more complex for the case of flow past a surface-mounted cylinder. A detailed discussion of the changes in the flow physics between cylinder Reynolds numbers at which the flow in the upstream part of the separated shear layers (SSLs) is laminar (Re = 16,000, subcritical flow regime) and Reynolds numbers at which transition occurs inside the attached boundary layers away from the bed and the flow within the SSLs is turbulent (Re = 500,000, supercritical flow regime). The changes between the two regimes in the dynamics and level of coherence of the large-scale coherent structures (necklace vortices, vortex tubes shed in the SSLs and roller vortices shed in the wake) and their capacity to induce high-magnitude bed friction velocities in the mean and instantaneous flow fields and to amplify the near-bed turbulence are analyzed.

Forced Convection Boiling and Critical Heat Flux of Ethanol in Electrically Heated Tube Tests

NASA Technical Reports Server (NTRS)

Meyer, Michael L.; Linne, Diane L.; Rousar, Donald C.

1998-01-01

Electrically heated tube tests were conducted to characterize the critical heat flux (transition from nucleate to film boiling) of subcritical ethanol flowing at conditions relevant to the design of a regeneratively cooled rocket engine thrust chamber. The coolant was SDA-3C alcohol (95% ethyl alcohol, 5% isopropyl alcohol by weight), and tests were conducted over the following ranges of conditions: pressure from 144 to 703 psia, flow velocities from 9.7 to 77 ft/s, coolant subcooling from 33 to 362 F, and critical heat fluxes up to 8.7 BTU/in(exp 2)/sec. For the data taken near 200 psia, critical heat flux was correlated as a function of the product of velocity and fluid subcooling to within +/- 20%. For data taken at higher pressures, an additional pressure term is needed to correlate the critical heat flux. It was also shown that at the higher test pressures and/or flow rates, exceeding the critical heat flux did not result in wall burnout. This result may significantly increase the engine heat flux design envelope for higher pressure conditions.

Three-dimensional wave evolution on electrified falling films

NASA Astrophysics Data System (ADS)

Tomlin, Ruben; Papageorgiou, Demetrios; Pavliotis, Greg

2016-11-01

We consider the full three-dimensional model for a thin viscous liquid film completely wetting a flat infinite solid substrate at some non-zero angle to the horizontal, with an electric field normal to the substrate far from the flow. Thin film flows have applications in cooling processes. Many studies have shown that the presence of interfacial waves increases heat transfer by orders of magnitude due to film thinning and convection effects. A long-wave asymptotics procedure yields a Kuramoto-Sivashinsky equation with a non-local term to model the weakly nonlinear evolution of the interface dynamics for overlying film arrangements, with a restriction on the electric field strength. The non-local term is always linearly destabilising and produces growth rates proportional to the cube of the magnitude of the wavenumber vector. A sufficiently strong electric field is able promote non-trivial dynamics for subcritical Reynolds number flows where the flat interface is stable in the absence of an electric field. We present numerical simulations where we observe rich dynamical behavior with competing attractors, including "snaking" travelling waves and other fully three-dimensional wave formations. EPSRC studentship (RJT).

Numerical Modelling of Staged Combustion Aft-Injected Hybrid Rocket Motors

NASA Astrophysics Data System (ADS)

Nijsse, Jeff

The staged combustion aft-injected hybrid (SCAIH) rocket motor is a promising design for the future of hybrid rocket propulsion. Advances in computational fluid dynamics and scientific computing have made computational modelling an effective tool in hybrid rocket motor design and development. The focus of this thesis is the numerical modelling of the SCAIH rocket motor in a turbulent combustion, high-speed, reactive flow framework accounting for solid soot transport and radiative heat transfer. The SCAIH motor is modelled with a shear coaxial injector with liquid oxygen injected in the center at sub-critical conditions: 150 K and 150 m/s (Mach ≈ 0.9), and a gas-generator gas-solid mixture of one-third carbon soot by mass injected in the annual opening at 1175 K and 460 m/s (Mach ≈ 0.6). Flow conditions in the near injector region and the flame anchoring mechanism are of particular interest. Overall, the flow is shown to exhibit instabilities and the flame is shown to anchor directly on the injector faceplate with temperatures in excess of 2700 K.

Convective hydromagnetic instabilities of a power-law liquid saturating a porous medium: Flux conditions

NASA Astrophysics Data System (ADS)

Chahtour, C.; Ben Hamed, H.; Beji, H.; Guizani, A.; Alimi, W.

2018-01-01

We investigate how an external imposed magnetic field affects thermal instability in a horizontal shallow porous cavity saturated by a non-Newtonian power-law liquid. The magnetic field is assumed to be constant and parallel to the gravity. A uniform heat flux is applied to the horizontal walls of the layer while the vertical walls are adiabatic. We use linear stability analysis to find expressions for the critical Rayleigh number as a function of the power-law index and the intensity of the magnetic field. We use nonlinear parallel flow theory to find some explicit solutions of the problem, and we use finite difference numerical simulations to solve the full nonlinear equations. We show how the presence of magnetic field alters the known hydrodynamical result of Newtonian flows and power-law flows and how it causes the presence of subcritical finite amplitude convection for both pseudoplastic and dilatant fluids. We also show that in the limit of very strong magnetic field, the dissipation of energy by Joule effect dominates the dissipation of energy by shear stress and gives to the liquid an inviscid character.

Experimental Investigation of Vortex Structures in Wake of Hyperboloid-Shaped Model by Means of 2D Particle Image Velocimetry Measurement

NASA Astrophysics Data System (ADS)

Barraclough, V.; Novotný, J.; Šafařík, P.

2018-06-01

This paper deals with flow around a bluff body of hyperboloid shape. It consists of results gathered in the course of research by means of Particle Image Velocimetry (PIV). The experiments were carried out by means of low-frequency 2D PIV in a range of Reynolds numbers from 40000 to 50000. A hyperboloid-shaped model was measured in a wind tunnel with a modelled atmospheric boundary layer (and additionally, in a low-speed wind tunnel with low turbulence). The model was tested in a subcritical range of Reynolds numbers and various planes in a wake of the model were captured with the intention of getting an estimation of 3D flow structures. The tunnel with the modelled atmospheric boundary layer has a high rate of turbulence, so the influence of the turbulence of incoming flow on the wake could be outlined. The ratio of the height of the model to a thickness of the modelled boundary layer in the tunnel was 1/3, meaning the turbulence in the boundary layer strongly influenced the flow around the model; it suppresses the wake which leads to a lot shorter area of recirculation than low turbulence incoming flow would cause.

A novel porous Ffowcs-Williams and Hawkings acoustic methodology for complex geometries

NASA Astrophysics Data System (ADS)

Nitzkorski, Zane Lloyd

Predictive noise calculations from high Reynolds number flows in complex engineering geometry are becoming a possibility with the high performance computing resources that have become available in recent years. Increasing the applicability and reliability of solution methodologies have been two key challenges toward this goal. This dissertation develops a porous Ffowcs-Williams and Hawkings methodology that uses a novel endcap methodology, and can be applied to unstructured grids. The use of unstructured grids allows complex geometry to be represented while porous formulation eliminates difficulties with the choice of acoustic Green's function. Specifically, this dissertation (1) proposes and examines a novel endcap procedure to account for spurious noise, (2) uses the proposed methodology to investigate noise production from a range of subcritical Reynolds number circular cylinders, and (3) investigates a trailing edge geometry for noise production and to illustrate the generality of the Green's function. Porous acoustic analogies need an endcap scheme in order to prevent spurious noise due to truncation errors. A dynamic end cap methodology is proposed to account for spurious contributions to the far--field sound within the context of the Ffowcs--Williams and Hawkings (FW--H) acoustic analogy. The quadrupole source terms are correlated over multiple planes to obtain a convection velocity which is then used to determine a corrective convective flux at the FW--H porous surface. The proposed approach is first demonstrated for a convecting potential vortex. The correlation is investigated by examining it pass through multiple exit planes. It is then evaluated by computing the sound emitted by flow over a circular cylinder at Reynolds number of 150 and compared to other endcap methods, such as Shur et al. [1]. Insensitivity to end plane location and spacing and the effect of the dynamic convection velocity are computed. Subcritical Reynolds number circular cylinder flows are investigated at Re = 3900, 10000 and 89000 in order to evaluate the method and investigate the physical sources of noise production. The Re = 3900 case was chosen due to its highly validated flow-field and to serve as a basis of comparison. The Re = 10000 cylinder is used to validate the noise production at turbulent Reynolds numbers against other simulations. Finally the Re = 89000 simulations are used to compare to experiment serving as a rigorous test of the methods predictive ability. The proposed approach demonstrates better performance than other commonly used approaches with the added benefit of computational efficiency and the ability to query independent volumes. This gives the added benefit of discovering how much noise production is directly associated with volumetric noise contributions. These capabilities allow for a thorough investigation of the sources of noise production and a means to evaluate proposed theories. A physical description of the source of sound for subcritical Reynolds number cylinders is established. A 45° beveled trailing edge configuration is investigated due to its relevance to hydrofoil and propeller noise. This configuration also allows for the evaluation of the assumption associated with the free-space Green's function since the half-plane Green's function can be used to represent the solution to the wave equation for this geometry. Similar results for directivity and amplitudes of the two formulations confirm the flexibility of the porous surface implementation. Good agreement with experiment is obtained. The effect of boundary layer thickness is investigated. The noise produced in the upper half plane is significantly decreased for the thinner boundary layer while the noise production in the lower half plane is only slightly decreased.

Effects of subcritical crack growth on fracture toughness of ceramics assessed in chevron-notched three-point bend tests

NASA Technical Reports Server (NTRS)

Chao, L. Y.; Singh, D.; Shetty, D. K.

1988-01-01

A numerical computational study was carried out to assess the effects of subcritical crack growth on crack stability in the chevron-notched three-point bend specimens. A power-law relationship between the subcritical crack velocity and the applied stress intensity were used along with compliance and stress-intensity relationships for the chevron-notched bend specimen to calculate the load response under fixed deflection rate and a machine compliance. The results indicate that the maximum load during the test occurs at the same crack length for all the deflection rates; the maximum load, however, is dependent on the deflection rate for rates below the critical rate. The resulting dependence of the apparent fracture toughness on the deflection rate is compared to experimental results on soda-lime glass and polycrystalline alumina.

Global Solutions for the zero-energy Novikov–Veselov equation by inverse scattering

NASA Astrophysics Data System (ADS)

Music, Michael; Perry, Peter

2018-07-01

Using the inverse scattering method, we construct global solutions to the Novikov–Veselov equation for real-valued decaying initial data q 0 with the property that the associated Schrödinger operator is nonnegative. Such initial data are either critical (an arbitrarily small perturbation of the potential makes the operator nonpositive) or subcritical (sufficiently small perturbations of the potential preserve non-negativity of the operator). Previously, Lassas, Mueller, Siltanen and Stahel proved global existence for critical potentials, also called potentials of conductivity type. We extend their results to include the much larger class of subcritical potentials. We show that the subcritical potentials form an open set and that the critical potentials form the nowhere dense boundary of this open set. Our analysis draws on previous work of the first author and on ideas of Grinevich and Manakov.

Hydrolysis of polycarbonate in sub-critical water in fused silica capillary reactor with in situ Raman spectroscopy

USGS Publications Warehouse

Pan, Z.; Chou, I-Ming; Burruss, R.C.

2009-01-01

The advantages of using fused silica capillary reactor (FSCR) instead of conventional autoclave for studying chemical reactions at elevated pressure and temperature conditions were demonstrated in this study, including the allowance for visual observation under a microscope and in situ Raman spectroscopic characterization of polycarbonate and coexisting phases during hydrolysis in subcritical water.

Accelerator Reactor Coupling for Energy Production in Advanced Nuclear Fuel Cycles

DOE PAGES

Brown, Nicholas R.; Heidet, Florent; Haj Tahar, Malek

2016-01-01

This article is a review of several accelerator–reactor interface issues and nuclear fuel cycle applications of acceleratordriven subcritical systems. The systems considered here have the primary goal of energy production, but that goal is accomplished via a specific application in various proposed nuclear fuel cycles, such as breed-and-burn of fertile material or burning of transuranic material. Several basic principles are reviewed, starting from the proton beam window including the target, blanket, reactor core, and up to the fuel cycle. We focus on issues of interest, such as the impact of the energy required to run the accelerator and associated systemsmore » on the potential electricity delivered to the grid. Accelerator-driven systems feature many of the constraints and issues associated with critical reactors, with the added challenges of subcritical operation and coupling to an accelerator. Reliable accelerator operation and avoidance of beam trips are critically important. One interesting challenge is measurement of blanket subcriticality level during operation. We also review the potential benefits of accelerator-driven systems in various nuclear fuel cycle applications. Ultimately, accelerator-driven subcritical systems with the goal of transmutation of transuranic material have lower 100,000-year radioactivity than a critical fast reactor with recycling of uranium and plutonium.« less

Neutron Detector Signal Processing to Calculate the Effective Neutron Multiplication Factor of Subcritical Assemblies

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

Talamo, Alberto; Gohar, Yousry

2016-06-01

This report describes different methodologies to calculate the effective neutron multiplication factor of subcritical assemblies by processing the neutron detector signals using MATLAB scripts. The subcritical assembly can be driven either by a spontaneous fission neutron source (e.g. californium) or by a neutron source generated from the interactions of accelerated particles with target materials. In the latter case, when the particle accelerator operates in a pulsed mode, the signals are typically stored into two files. One file contains the time when neutron reactions occur and the other contains the times when the neutron pulses start. In both files, the timemore » is given by an integer representing the number of time bins since the start of the counting. These signal files are used to construct the neutron count distribution from a single neutron pulse. The built-in functions of MATLAB are used to calculate the effective neutron multiplication factor through the application of the prompt decay fitting or the area method to the neutron count distribution. If the subcritical assembly is driven by a spontaneous fission neutron source, then the effective multiplication factor can be evaluated either using the prompt neutron decay constant obtained from Rossi or Feynman distributions or the Modified Source Multiplication (MSM) method.« less

Accelerator–Reactor Coupling for Energy Production in Advanced Nuclear Fuel Cycles

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

Heidet, Florent; Brown, Nicholas R.; Haj Tahar, Malek

2015-01-01

This article is a review of several accelerator-reactor interface issues and nuclear fuel cycle applications of accelerator-driven subcritical systems. The systems considered here have the primary goal of energy production, but that goal is accomplished via a specific application in various proposed nuclear fuel cycles, such as breed-and-burn of fertile material or burning of transuranic material. Several basic principles are reviewed, starting from the proton beam window including the target, blanket, reactor core, and up to the fuel cycle. We focused on issues of interest, e.g. the impact of the energy required to run the accelerator and associated systems onmore » the potential electricity delivered to the grid. Accelerator-driven systems feature many of the constraints and issues associated with critical reactors, with the added challenges of subcritical operation and coupling to an accelerator. Reliable accelerator operation and avoidance of beam trips are a critically important. One interesting challenge is measurement of blanket subcriticality level during operation. We also reviewed the potential benefits of accelerator-driven systems in various nuclear fuel cycle applications. Ultimately, accelerator-driven subcritical systems with the goal of transmutation of transuranic material have lower 100,000-year radioactivity versus a critical fast reactor with recycle of uranium and plutonium.« less

Transmutation of uranium and thorium in the particle field of the Quinta sub-critical assembly

NASA Astrophysics Data System (ADS)

Hashemi-Nezhad, S. R.; Asquith, N. L.; Voronko, V. A.; Sotnikov, V. V.; Zhadan, Alina; Zhuk, I. V.; Potapenko, A.; Husak, Krystsina; Chilap, V.; Adam, J.; Baldin, A.; Berlev, A.; Furman, W.; Kadykov, M.; Khushvaktov, J.; Kudashkin, I.; Mar'in, I.; Paraipan, M.; Pronskih, V.; Solnyshkin, A.; Tyutyunnikov, S.

2018-03-01

The fission rates of natural uranium and thorium were measured in the particle field of Quinta, a 512 kg natural uranium target-blanket sub-critical assembly. The Quinta assembly was irradiated with deuterons of energy 4 GeV from the Nuclotron accelerator of the Joint Institute for Nuclear Research (JINR), Dubna, Russia. Fission rates of uranium and thorium were measured using Gamma spectroscopy and fission track techniques. The production rate of 239Np was also measured. The obtained experimental results were compared with Monte Carlo predictions using the MCNPX 2.7 code employing the physics and fission-evaporation models of INCL4-ABLA, CEM03.03 and LAQGSM03.03. Some of the neutronic characteristics of the Quinta are compared with the "Energy plus Transmutation (EpT)" subcritical assembly, which is composed of a lead target and natU blanket. This comparison clearly demonstrates the importance of target material, neutron moderator and reflector types on the performance of a spallation neutron driven subcritical system. As the dimensions of the Quinta are very close to those of an optimal multi-rod-uranium target, the experimental and Monte Carlo calculation results presented in this paper provide insights on the particle field within a uranium target as well as in Accelerator Driven Systems in general.

Accelerator-Reactor Coupling for Energy Production in Advanced Nuclear Fuel Cycles

NASA Astrophysics Data System (ADS)

Heidet, Florent; Brown, Nicholas R.; Haj Tahar, Malek

This article is a review of several accelerator-reactor interface issues and nuclear fuel cycle applications of accelerator-driven subcritical systems. The systems considered here have the primary goal of energy production, but that goal is accomplished via a specific application in various proposed nuclear fuel cycles, such as breed-and-burn of fertile material or burning of transuranic material. Several basic principles are reviewed, starting from the proton beam window including the target, blanket, reactor core, and up to the fuel cycle. We focus on issues of interest, such as the impact of the energy required to run the accelerator and associated systems on the potential electricity delivered to the grid. Accelerator-driven systems feature many of the constraints and issues associated with critical reactors, with the added challenges of subcritical operation and coupling to an accelerator. Reliable accelerator operation and avoidance of beam trips are critically important. One interesting challenge is measurement of blanket subcriticality level during operation. We also review the potential benefits of accelerator-driven systems in various nuclear fuel cycle applications. Ultimately, accelerator-driven subcritical systems with the goal of transmutation of transuranic material have lower 100,000-year radioactivity than a critical fast reactor with recycling of uranium and plutonium.

The enigmatic ultra-long run-out of seafloor density driven flows

NASA Astrophysics Data System (ADS)

Dorrell, R. M.

2017-12-01

Dilute, particulate-laden, density-driven flows - turbidity currents - are a predominant mechanism for transporting sediment from source to sink in deep marine environments. These flows sculpt channels on the seafloor and, as evidenced by a wealth of bathymetric data, can travel for >1000km, forming some of the largest sedimentary landforms on the planet. For turbidity currents to travel such large dsitances, sediment must be self-maintained in suspension, i.e., be in a state of autosuspension. It has been shown that such self-maintained sediment suspensions can only occur whilst inertial forces are greater than gravitational forces, entailing supercritical flow. This conclusion is paradoxical, as inertia dominated flows rapidly entrain fluid, thereby thickening and slowing to become subcritical. However, current theory can only truly be applied to the proximal upper slope regions of seafloor channels where incised flows are fully confined. This contrasts with the distal reaches of long run out turbidity current systems, where the flow is only partially confined through self-channelization. Here it is shown that overspill of partially confined flow has a significant effect on the hydro- and morphodynamics of turbidity current systems. A new model is derived that shows that channel overspill acts to negate the effects of ambient fluid entrainment: a dynamic balance that limits increases in flow depth and maintains supercritical flow throughout the channel. In the new model mass, momentum and energy conservation is modulated by flow overspill onto channel banks, necessarily requiring description of the vertical structure of the flow. Analysis of continuously stratified steady state flow dynamics shows that the integration of overspill and stratification is necessary to enable maintained autosuspension and thus predict the ultra-long run-out of turbidity currents.

Effect of thermodynamic disequilibrium on critical liquid-vapor flow conditions

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

Bilicki, Z.; Kestin, J.

1989-01-01

In this lecture we characterize the effect of absence of unconstrained thermodynamic equilibrium and onset of a metastable state on the adiabatic flow of a mixture of liquid and its vapor through a convergent-divergent nozzle. We study steady-state flows and emphasize the relations that are present when the flow is choked. In such cases, there exists a cross-section in which the flow is critical and in which the adiabatic wave of small amplitude is stationary. More precisely, the relaxation process which results from the lack of equilibrium causes the system to be dispersive. In such circumstances, the critical velocity ismore » equal to the frozen speed of sound, a/sub f/ corresponding to /omega/ /yields/ /infinity/. The relaxation process displaces the critical cross-section quite far downstream from the throat and places it in the divergent portion of the channel. We present the topological portrait of solutions in a suitably defined state-velocity space and discuss the potential appearance of normal and dispersed shock waves. In extreme cases, the singular point (usually a saddle) which enables the flow to become supercritical is displaced so far that it is located outside the exit. Then, the flow velocity is everywhere subcritical (w < a/sub f/) even though it may exceed the equilibrium speed of sound (w /approx gt/ a/sub e/) beyond a certain cross-section, and in spite of the presence of a throat. 10 refs., 4 figs.« less

The effect of channel height on bubble nucleation in superhydrophobic microchannels due to subcritical heating

NASA Astrophysics Data System (ADS)

Cowley, Adam; Maynes, Daniel; Crockett, Julie; Iverson, Brian

2017-11-01

This work experimentally investigates the effects of heating on laminar flow in high aspect ratio superhydrophobic (SH) microchannels. When water that is saturated with dissolved air is used, the unwetted cavities of the SH surfaces act as nucleation sites and air effervesces out of solution onto the surfaces. The microchannels consist of a rib/cavity structured SH surface, that is heated, and a glass surface that is utilized for flow visualization. Two channel heights of nominally 183 and 366 μm are considered. The friction factor-Reynolds product (fRe) is obtained via pressure drop and volumetric flow rate measurements and the temperature profile along the channel is obtained via thermocouples embedded in an aluminum block below the SH surface. Five surface types/configurations are investigated: smooth hydrophilic, smooth hydrophobic, SH with ribs perpendicular to the flow, SH with ribs parallel to the flow, and SH with both ribs parallel to the flow and sparse ribs perpendicular to the flow. Depending on the surface type/configuration, large bubbles can form and adversely affect fRe and lead to higher temperatures along the channel. Once bubbles grow large enough, they are expelled from the channel. The channel size greatly effects the residence time of the bubbles and consequently fRe and the channel temperature. This research was supported by the National Science Foundation (NSF) (Grant No. CBET-1235881) and the Utah NASA Space Grant Consortium (NASA Grant NNX15A124H).

Degradation of caffeic acid in subcritical water and online HPLC-DPPH assay of degradation products.

PubMed

Khuwijitjaru, Pramote; Suaylam, Boonyanuch; Adachi, Shuji

2014-02-26

Caffeic acid was subjected to degradation under subcritical water conditions within 160-240 °C and at a constant pressure of 5 MPa in a continuous tubular reactor. Caffeic acid degraded quickly at these temperatures; the main products identified by liquid chromatography-diode array detection/mass spectrometry were hydroxytyrosol, protocatechuic aldehyde, and 4-vinylcatechol. The reaction rates for the degradation of caffeic acid and the formation of products were evaluated. Online high-performance liquid chromatography/2,2-diphenyl-1-picryhydrazyl assay was used to determine the antioxidant activity of each product in the solution. It was found that the overall antioxidant activity of the treated solution did not change during the degradation process. This study showed a potential of formation of antioxidants from natural phenolic compounds under these subcritical water conditions, and this may lead to a discovering of novel antioxidants compounds during the extraction by this technique.

a Novel Catalyst for Reductive Dechlorination of Chlorobenzene in Subcritical Water:. Bifunctional Fe/ZrO2

NASA Astrophysics Data System (ADS)

Wei, Guang-Tao; Wei, Chao-Hai; He, Feng-Mei; Wu, Chao-Fei

Bifunctional Fe/ZrO2 was prepared by mechanical mixing method, and its bifunctional effect on reductive dechlorination of chlorobenzene in subcritical water was studied. Dechlorination efficiency increased with increasing iron content in catalyst and catalyst amount. Dechlorination efficiency slowed when the iron content in catalyst reached 30%; bifunctional catalyst of Fe/ZrO2 was more efficient in dechlorination of chlorobenzene than Fe alone. Catalyst of Fe (30%)/ZrO2 was characterized by means of X-ray diffraction (XRD), H2 temperature programmed desorption (H2-TPD), and N2 adsorption. The possible mechanism of dechlorination in subcritical water by this bifunctional catalyst was proposed. H+ produced in the water dissociation formed the highly reactive spillover hydrogen on the surface of catalyst, and then reacted with chlorobenzene adsorbed on the catalyst surface by ZrO2 to form benzene and chloride ions.

Green chiral HPLC study of the stability of Chiralcel OD under high temperature liquid chromatography and subcritical water conditions.

PubMed

Droux, S; Roy, M; Félix, G

2014-10-01

We report here the study of the stability under subcritical water conditions of one of the most popular polysaccharide chiral stationary phase (CSP): Chiralcel OD. This CSP was used under high temperature and reversed phase conditions with acetonitrile and 2-propanol as modifier, respectively. The evolution of selectivity and resolution was investigated both in normal and reversed mode conditions with five racemates after packing, heating at 150 °C and separations of some racemic compounds under different high temperatures and mobile phase conditions. The results show that after using at high temperature and subcritical water conditions the selectivity was only moderately affected while the resolution fell dramatically especially in reversed mode due to the creation of a void at the head of the columns which reflects the dissolution of the silica matrix. Copyright © 2014 Elsevier B.V. All rights reserved.

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

Gonnelli, E.; Diniz, R.; Dos Santos, A.

The presented work shows the preliminary results of an experimental procedure to overcome the helium-3 detectors shortage in the IPEN/MB-01 nuclear reactor and be feasible the study of the high subcritical states with less sensitivity detectors. The main principle was employing the input logic nuclear module which was possible to execute logic operations with the neutron signals. Though these signals was possible to construct the Auto Power Spectral Densities (APSD) and obtain the Prompt Neutron Constant Decay (α). Two different kinds of thermal neutron detectors were used ({sup 3}He and BF{sub 3}). The arrangement was initially constituted by one ofmore » each type detector and, posteriorly, for a more complete data acquisition, in groups of two detectors for all subcritical configurations. The experiment was carried out using the control banks (BC-1 and BC-2) insertion to achieve all the subcritical states studied in this work. (authors)« less

The mechanism of hydrothermal hydrolysis for glycyrrhizic acid into glycyrrhetinic acid and glycyrrhetinic acid 3-O-mono-β-D-glucuronide in subcritical water.

PubMed

Fan, Rui; Li, Nan; Xu, Honggao; Xiang, Jun; Wang, Lei; Gao, Yanxiang

2016-01-01

To improve the bioactivity and sweetness properties of glycyrrhizic acid (GL), the hydrothermal hydrolysis of GL into glycyrrhetinic acid (GA) and glycyrrhetinic acid 3-O-mono-β-D-glucuronide (GAMG) in subcritical water was investigated. The effects of temperature, time and their interaction on the conversion ratios were analyzed and the reactions were elaborated with kinetics and thermodynamics. The results showed that GL hydrothermal hydrolysis was significantly (P < 0.05) affected by reaction time and temperature, as well as their interaction, and could be fitted into first-order kinetics. The thermodynamic analysis indicated that the hydrolysis of GL was endergonic and non-spontaneous. The hydrolytic pathways were composed of complex consecutive and parallel reactions. It was concluded that subcritical water may be a potential medium for producing GAMG and GA. Copyright © 2015 Elsevier Ltd. All rights reserved.

A microfluidic sub-critical water extraction instrument

NASA Astrophysics Data System (ADS)

Sherrit, Stewart; Noell, Aaron C.; Fisher, Anita; Lee, Mike C.; Takano, Nobuyuki; Bao, Xiaoqi; Kutzer, Thomas C.; Grunthaner, Frank

2017-11-01

This article discusses a microfluidic subcritical water extraction (SCWE) chip for autonomous extraction of amino acids from astrobiologically interesting samples. The microfluidic instrument is composed of three major components. These include a mixing chamber where the soil sample is mixed and agitated with the solvent (water), a subcritical water extraction chamber where the sample is sealed with a freeze valve at the chip inlet after a vapor bubble is injected into the inlet channels to ensure the pressure in the chip is in equilibrium with the vapor pressure and the slurry is then heated to ≤200 °C in the SCWE chamber, and a filter or settling chamber where the slurry is pumped to after extraction. The extraction yield of the microfluidic SCWE chip process ranged from 50% compared to acid hydrolysis and 80%-100% compared to a benchtop microwave SCWE for low biomass samples.

Subcritical ethanol extraction of flavonoids from Moringa oleifera leaf and evaluation of antioxidant activity.

PubMed

Wang, Yongqiang; Gao, Yujie; Ding, Hui; Liu, Shejiang; Han, Xu; Gui, Jianzhou; Liu, Dan

2017-03-01

A large-scale process to extract flavonoids from Moringa oleifera leaf by subcritical ethanol was developed and HPLC-MS analysis was conducted to qualitatively identify the compounds in the extracts. To optimize the effects of process parameters on the yield of flavonoids, a Box-Behnken design combined with response surface methodology was conducted in the present work. The results indicated that the highest extraction yield of flavonoids by subcritical ethanol extraction could reach 2.60% using 70% ethanol at 126.6°C for 2.05h extraction. Under the optimized conditions, flavonoids yield was substantially improved by 26.7% compared with the traditional ethanol reflux method while the extraction time was only 2h, and obvious energy saving was observed. FRAP and DPPH assays showed that the extracts had strong antioxidant and free radical scavenging activities. Copyright © 2016 Elsevier Ltd. All rights reserved.

Theoretical prediction of thick wing and pylon-fuselage-fanpod-nacelle aerodynamic characteristics at subcritical speeds. Part 1: Theory and results

NASA Technical Reports Server (NTRS)

Tulinius, J. R.

1974-01-01

The theoretical development and the comparison of results with data of a thick wing and pylon-fuselage-fanpod-nacelle analysis are presented. The analysis utilizes potential flow theory to compute the surface velocities and pressures, section lift and center of pressure, and the total configuration lift, moment, and vortex drag. The skin friction drag is also estimated in the analysis. The perturbation velocities induced by the wing and pylon, fuselage and fanpod, and nacelle are represented by source and vortex lattices, quadrilateral vortices, and source frustums, respectively. The strengths of these singularities are solved for simultaneously including all interference effects. The wing and pylon planforms, twists, cambers, and thickness distributions, and the fuselage and fanpod geometries can be arbitrary in shape, provided the surface gradients are smooth. The flow through nacelle is assumed to be axisymmetric. An axisymmetric center engine hub can also be included. The pylon and nacelle can be attached to the wing, fuselage, or fanpod.

Diffuse interfacelets in transcritical flows of propellants into high-pressure combustors

NASA Astrophysics Data System (ADS)

Urzay, Javier; Jofre, Lluis

2017-11-01

Rocket engines and new generations of high-power jet engines and diesel engines oftentimes involve the injection of one or more reactants at subcritical temperatures into combustor environments at high pressures, and more particularly, at pressures higher than those corresponding to the critical points of the individual components of the mixture, which typically range from 13 to 50 bars for most propellants. This class of trajectories in the thermodynamic space has been traditionally referred to as transcritical. Under particular conditions often found in hydrocarbon-fueled chemical propulsion systems, and despite the prevailing high pressures, the flow in the combustor may contain regions close to the injector where a diffuse interface is formed in between the fuel and oxidizer streams that is sustained by surface-tension forces as a result of the elevation of the critical pressure of the mixture. This talk describes progress towards modeling these effects in the conservation equations. Funded by the US Department of Energy.

Ship wakes and spectrograms: mathematical modelling and experimental data for finite-depth flows

NASA Astrophysics Data System (ADS)

McCue, Scott; Pethiyagoda, Ravindra; Moroney, Timothy; Macfarlane, Gregor; Binns, Jonathan

2017-11-01

We are concerned with how properties of a ship wake can be extracted from surface height data collected at a single point as the ship travels past. The tool we use is a spectrogram, which is a heat map that visualises the time-dependent frequency spectrum of the surface height signal. In this talk, the focus will be on presenting the theoretical framework which involves an idealised mathematical model with a pressure distribution applied to the surface. A geometric argument based on linear water wave theory provides encouraging results for both subcritical and supercritical flow regimes. We then summarise some recent findings obtained by comparing our analysis to experimental data collected at the Australian Maritime College for various sailing speeds and hull shapes*. Our work has the potential to inform ship design, the detection of irregular vessels, and how coastal damage is attributed to specific vessels in shipping channels. We acknowledge support of the Australian Research Council via the Discovery Project DP140100933.

Unsteady aerodynamic modeling and active aeroelastic control

NASA Technical Reports Server (NTRS)

Edwards, J. W.

1977-01-01

Unsteady aerodynamic modeling techniques are developed and applied to the study of active control of elastic vehicles. The problem of active control of a supercritical flutter mode poses a definite design goal stability, and is treated in detail. The transfer functions relating the arbitrary airfoil motions to the airloads are derived from the Laplace transforms of the linearized airload expressions for incompressible two dimensional flow. The transfer function relating the motions to the circulatory part of these loads is recognized as the Theodorsen function extended to complex values of reduced frequency, and is termed the generalized Theodorsen function. Inversion of the Laplace transforms yields exact transient airloads and airfoil motions. Exact root loci of aeroelastic modes are calculated, providing quantitative information regarding subcritical and supercritical flutter conditions.

Studies on Materials for Heavy-Liquid-Metal-Cooled Reactors in Japan

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

Minoru Takahashi; Masayuki Igashira; Toru Obara

2002-07-01

Recent studies on materials for the development of lead-bismuth (Pb-Bi)-cooled fast reactors (FR) and accelerator-driven sub-critical systems (ADS) in Japan are reported. The measurement of the neutron cross section of Bi to produce {sup 210}Po, the removal experiment of Po contamination and steel corrosion test in Pb-Bi flow were performed in Tokyo Institute of Technology. A target material corrosion test was performed in the project of Transmutation Experimental Facility for ADS in Japan Atomic Energy Research Institute (JAERI). Steel corrosion test was started in Mitsui Engineering and Shipbuilding Co., LTD (MES). The feasibility study for FR cycle performed in Japanmore » Nuclear Cycle Institute (JNC) are described. (authors)« less

Harbingers and latecomers - the order of appearance of exact coherent structures in plane Poiseuille flow

NASA Astrophysics Data System (ADS)

Zammert, Stefan; Eckhardt, Bruno

2017-02-01

The transition to turbulence in plane Poiseuille flow (PPF) is connected with the presence of exact coherent structures. We here discuss a variety of different structures that are relevant for the transition, compare the critical Reynolds numbers and optimal wavelengths for their appearance, and explore the differences between flows operating at constant mass flux or at constant pressure drop. The Reynolds numbers quoted here are based on the mean flow velocity and refer to constant mass flux. Reynolds numbers based on constant pressure drop are always higher. The Tollmien-Schlichting (TS) waves bifurcate subcritically from the laminar profile at Re = 5772 at wavelength 6.16 and reach down to Re = 2610 at a different optimal wave length of 4.65. Their streamwise localised counter part bifurcates at the even lower value Re = 2334. Three-dimensional exact solutions appear at much lower Reynolds numbers. We describe one exact solutions that has a critical Reynolds number of 316. Streamwise localised versions of this state require higher Reynolds numbers, with the lowest bifurcation occurring near Re = 1018. The analysis shows that the various branches of TS-waves cannot be connected with transition observed near Re ≈ 1000 and that the exact coherent structures related to downstream vortices come in at lower Reynolds numbers and prepare for the transition.

Research on Supersonic Inlet Bleed

NASA Technical Reports Server (NTRS)

Davis, David O.; Vyas, Manan A.; Slater, John W.

2012-01-01

Phase I data results of the Fundamental Inlet Bleed Experiments project at NASA Glenn Research Center (GRC) are presented which include flow coefficient results for two single-hole boundary-layer bleed configurations. The bleed configurations tested are round holes at inclination angles of 90deg and 20deg both having length-to-diameter ratios of 2.0. Results were obtained at freestream Mach numbers of 1.33, 1.62, 1.98, 2.46, and 2.92 and unit Reynolds numbers of 0.984, 1.89, and 2.46 10(exp 7)/m. Approach boundary-layer data are presented for each flow condition and the flow coefficient results are compared to existing multi-hole data obtained under similar conditions. For the 90deg hole, the single and multi-hole distributions agree fairly well with the exception that under supercritical operation, the multi-hole data chokes at higher flow coefficient levels. This behavior is also observed for the 20deg hole but to a lesser extent. The 20deg hole also shows a markedly different characteristic at subcritical operation. Also presented are preliminary results of a Computational Fluid Dynamics (CFD) analysis of both configurations at the Mach 1.33 and a unit Reynolds number of 2.46 10(exp 7)/m. Comparison of the results shows the agreement to be very good.

Observations of instability, hysteresis, and oscillation in low-Reynolds-number flow past polymer gels.

PubMed

Eggert, Matthew D; Kumar, Satish

2004-10-01

We perform a set of experiments to study the nonlinear nature of an instability that arises in low-Reynolds-number flow past polymer gels. A layer of a viscous liquid is placed on a polydimethylsiloxane (PDMS) gel in a parallel-plate rheometer which is operated in stress-controlled mode. As the shear stress on the top plate increases, the apparent viscosity stays relatively constant until a transition stress where it sharply increases. If the stress is held at a level slightly above the transition stress, the apparent viscosity oscillates with time. If the stress is increased to a value above the transition stress and then decreased back to zero, the apparent viscosity shows hysteretic behavior. If the stress is instead decreased to a constant value and held there, the apparent viscosity is different from its pretransition value and exhibits sustained oscillations. This can happen even if the stress is held at values below the transition stress. Our observations suggest that the instability studied here is subcritical and leads to a flow that is oscillatory and far from viscometric. The phenomena reported here may be useful in applications such as microfluidics, membrane separations, and polymer processing. They may also provide insight into the rheological behavior of complex fluids that undergo flow-induced gelation.

Algebraic disturbances and their consequences in rotating channel flow transition

NASA Astrophysics Data System (ADS)

Jose, Sharath; Kuzhimparampil, Vishnu; Pier, Benoît.; Govindarajan, Rama

2017-08-01

It is now established that subcritical mechanisms play a crucial role in the transition to turbulence of nonrotating plane shear flows. The role of these mechanisms in rotating channel flow is examined here in the linear and nonlinear stages. Distinct patterns of behavior are found: the transient growth leading to nonlinearity at low rotation rates R o , a highly chaotic intermediate R o regime, a localized weak chaos at higher R o , and complete stabilization of transient disturbances at very high R o . At very low R o , the transient growth amplitudes are close to those for nonrotating flow, but Coriolis forces assert themselves by producing distinct asymmetry about the channel centreline. Nonlinear processes are then triggered, in a streak-breakdown mode of transition. The high R o regimes do not show these signatures; here the leading eigenmode emerges as dominant in the early stages. Elongated structures plastered close to one wall are seen at higher rotation rates. Rotation is shown to reduce nonnormality in the linear operator, in an indirect manifestation of Taylor-Proudman effects. Although the critical Reynolds for exponential growth of instabilities is known to vary a lot with rotation rate, we show that the energy critical Reynolds number is insensitive to rotation rate. It is hoped that these findings will motivate experimental verification and examination of other rotating flows in this light.

Visualization and flow boiling heat transfer of hydrocarbons in a horizontal tube

NASA Astrophysics Data System (ADS)

Yang, Zhuqiang; Bi, Qincheng; Guo, Yong; Liu, Zhaohui; Yan, Jianguo

2013-07-01

Visualizations of a specific hydrocarbon fuel in a horizontal tube with 2.0 mm inside diameter were investigated. The experiments were conducted at mass velocity of 213.4, 426.5 and 640.2 kg/ (m2ṡs), diabatic lengths of 140, 240 and 420 mm under the pressure from 2.0-2.7 MPa. In the sub-pressure conditions, bubbly, intermittent, stratified-wave, churn and annular flow patterns were observed. The frictional pressure drops were also measured to distinguish the patterns. The development of flow patterns and frictional pressure drop were positively related to the mass velocity and the heat flux. However, the diabatic length of the tube takes an important part in the process. The residence time of the fluid does not only affect the transition of the patterns but influence the composition of the fuel manifested by the fuel color and carbon deposit. The special observational phenomenon was obtained for the supercritical pressure fluid. The flow in the tube became fuzzier and pressure drop changed sharply near the pseudocritical point. The flow boiling heat transfer characteristics of the hydrocarbons were also discussed respectively. The curve of critical heat flux about onset of nucleate boiling was plotted with different mass velocities and diabatic tube lengths. And heat transfer characteristics of supercritical fuel were proved to be better than that in subcritical conditions.

The Origin of Inlet Buzz in a Mach 1.7 Low Boom Inlet Design

NASA Technical Reports Server (NTRS)

Anderson, Bernhard H.; Weir, Lois

2014-01-01

Supersonic inlets with external compression, having a good level performance at the critical operating point, exhibit a marked instability of the flow in some subcritical operation below a critical value of the capture mass flow ratio. This takes the form of severe oscillations of the shock system, commonly known as "buzz". The underlying purpose of this study is to indicate how Detached Eddy Simulation (DES) analysis of supersonic inlets will alter how we envision unsteady inlet aerodynamics, particularly inlet buzz. Presented in this paper is a discussion regarding the physical explanation underlying inlet buzz as indicated by DES analysis. It is the normal shock wave boundary layer separation along the spike surface which reduces the capture mass flow that is the controlling mechanism which determines the onset of inlet buzz, and it is the aerodynamic characteristics of a choked nozzle that provide the feedback mechanism that sustains the buzz cycle by imposing a fixed mean corrected inlet weight flow. Comparisons between the DES analysis of the Lockheed Martin Corporation (LMCO) N+2 inlet and schlieren photographs taken during the test of the Gulfstream Large Scale Low Boom (LSLB) inlet in the NASA 8x6 ft. Supersonic Wind Tunnel (SWT) show a strong similarity both in turbulent flow field structure and shock wave formation during the buzz cycle. This demonstrates the value of DES analysis for the design and understanding of supersonic inlets.

Droplet turbulence interactions under subcritical and supercritical conditions

NASA Technical Reports Server (NTRS)

Coy, E. B.; Greenfield, S. C.; Ondas, M. S.; Song, Y.-H.; Spegar, T. D.; Santavicca, D. A.

1993-01-01

The goal of this research is to experimentally characterize the behavior of droplets in vaporizing liquid sprays under conditions typical of those encountered in high pressure combustion systems such as liquid fueled rocket engines. Of particular interest are measurements of droplet drag, droplet heating, droplet vaporization, droplet distortion, and secondary droplet breakup, under both subcritical and supercritical conditions. The paper presents a brief description of the specific accomplishments which have been made over the past year.

Accelerated Stress Corrosion Crack Initiation of Alloys 600 and 690 in Hydrogenated Supercritical Water

NASA Astrophysics Data System (ADS)

Moss, Tyler; Was, Gary S.

2017-04-01

The objective of this study is to determine whether stress corrosion crack initiation of Alloys 600 and 690 occurs by the same mechanism in subcritical and supercritical water. Tensile bars of Alloys 690 and 600 were strained in constant extension rate tensile experiments in hydrogenated subcritical and supercritical water from 593 K to 723 K (320 °C to 450 °C), and the crack initiation behavior was characterized by high-resolution electron microscopy. Intergranular cracking was observed across the entire temperature range, and the morphology, structure, composition, and temperature dependence of initiated cracks in Alloy 690 were consistent between hydrogenated subcritical and supercritical water. Crack initiation of Alloy 600 followed an Arrhenius relationship and did not exhibit a discontinuity or change in slope after crossing the critical temperature. The measured activation energy was 121 ± 13 kJ/mol. Stress corrosion crack initiation in Alloy 690 was fit with a single activation energy of 92 ± 12 kJ/mol across the entire temperature range. Cracks were observed to propagate along grain boundaries adjacent to chromium-depleted metal, with Cr2O3 observed ahead of crack tips. All measures of the SCC behavior indicate that the mechanism for stress corrosion crack initiation of Alloy 600 and Alloy 690 is consistent between hydrogenated subcritical and supercritical water.

Experimental study of elliptical jet from supercritical to subcritical conditions using planar laser induced fluorescence

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

Muthukumaran, C. K.; Vaidyanathan, Aravind, E-mail: aravind7@iist.ac.in

2015-03-15

The study of fluid jet dynamics at supercritical conditions involves strong coupling between fluid dynamic and thermodynamic phenomena. Beyond the critical point, the liquid-vapor coexistence ceases to exist, and the fluid exists as a single phase known as supercritical fluid with its properties that are entirely different from liquids and gases. At the critical point, the liquids do not possess surface tension and latent heat of evaporation. Around the critical point, the fluid undergoes large changes in density and possesses thermodynamic anomaly like enhancement in thermal conductivity and specific heat. In the present work, the transition of the supercritical andmore » near-critical elliptical jet into subcritical as well as supercritical environment is investigated experimentally with nitrogen and helium as the surrounding environment. Under atmospheric condition, a liquid jet injected from the elliptical orifice exhibits axis switching phenomena. As the injection temperature increases, the axis switching length also increases. Beyond the critical temperature, the axis switching is not observed. The investigation also revealed that pressure plays a major role in determining the thermodynamic transition of the elliptical jet only for the case of supercritical jet injected into subcritical chamber conditions. At larger pressures, the supercritical jet undergoes disintegration and formation of droplets in the subcritical environment is observed. However, for supercritical jet injection into supercritical environment, the gas-gas like mixing behavior is observed.« less

Recovery of Palm Oil and Valuable Material from Oil Palm Empty Fruit Bunch by Sub-critical Water.

PubMed

Ahmad Kurnin, Nor Azrin; Shah Ismail, Mohd Halim; Yoshida, Hiroyuki; Izhar, Shamsul

2016-01-01

Oil palm empty fruit bunch (EFB) is one of the solid wastes produced in huge volume by palm oil mill. Whilst it still contains valuable oil, approximately 22.6 million tons is generated annually and treated as solid waste. In this work, sub-critical water (sub-cw) was used to extract oil, sugar and tar from spikelet of EFB. The spikelet was treated with sub-cw between 180-280°C and a reaction time of 2 and 5 minutes. The highest yield of oil was 0.075 g-oil/g-dry EFB, obtained at 240°C and reaction time of 5 minutes. Astonishingly, oil that was extracted through this method was 84.5% of that obtained through Soxhlet method using hexane. Yield of oil extracted was strongly affected by the reaction temperature and time. Higher reaction temperature induces the dielectric constant of water towards the non-polar properties of solvent; thus increases the oil extraction capability. Meanwhile, the highest yield of sugar was 0.20 g-sugar/g-dry EFB obtained at 220°C. At this temperature, the ion product of water is high enough to enable maximum sub-critical water hydrolysis reaction. This study showed that oil and other valuable material can be recovered using water at sub-critical condition, and most attractive without the use of harmful organic solvent.

Georgia Tech Studies of Sub-Critical Advanced Burner Reactors with a D-T Fusion Tokamak Neutron Source for the Transmutation of Spent Nuclear Fuel

NASA Astrophysics Data System (ADS)

Stacey, W. M.

2009-09-01

The possibility that a tokamak D-T fusion neutron source, based on ITER physics and technology, could be used to drive sub-critical, fast-spectrum nuclear reactors fueled with the transuranics (TRU) in spent nuclear fuel discharged from conventional nuclear reactors has been investigated at Georgia Tech in a series of studies which are summarized in this paper. It is found that sub-critical operation of such fast transmutation reactors is advantageous in allowing longer fuel residence time, hence greater TRU burnup between fuel reprocessing stages, and in allowing higher TRU loading without compromising safety, relative to what could be achieved in a similar critical transmutation reactor. The required plasma and fusion technology operating parameter range of the fusion neutron source is generally within the anticipated operational range of ITER. The implications of these results for fusion development policy, if they hold up under more extensive and detailed analysis, is that a D-T fusion tokamak neutron source for a sub-critical transmutation reactor, built on the basis of the ITER operating experience, could possibly be a logical next step after ITER on the path to fusion electrical power reactors. At the same time, such an application would allow fusion to contribute to meeting the nation's energy needs at an earlier stage by helping to close the fission reactor nuclear fuel cycle.

Th and U fuel photofission study by NTD for AD-MSR subcritical assembly

NASA Astrophysics Data System (ADS)

Sajo-Bohus, Laszlo; Greaves, Eduardo D.; Davila, Jesus; Barros, Haydn; Pino, Felix; Barrera, Maria T.; Farina, Fulvio

2015-07-01

During the last decade a considerable effort has been devoted for developing energy generating systems based on advanced nuclear technology within the design concepts of GEN-IV. Thorium base fuel systems such as accelerator driven nuclear reactors are one of the often mentioned attractive and affordable options. Several radiotherapy linear accelerators are on the market and due to their reliability, they could be employed as drivers for subcritical liquid fuel assemblies. Bremsstrahlung photons with energies above 5.5MeV, induce (γ,n) and (e,e'n) reactions in the W-target. Resulting gamma radiation and photo or fission neutrons may be absorbed in target materials such as thorium and uranium isotopes to induce sustained fission or nuclear transmutation in waste radioactive materials. Relevant photo driven and photo-fission reaction cross sections are important for actinides 232Th, 238U and 237Np in the radiotherapy machines energy range of 10-20 MV. In this study we employ passive nuclear track detectors (NTD) to determine fission rates and neutron production rates with the aim to establish the feasibility for gamma and photo-neutron driven subcritical assemblies. To cope with these objectives a 20 MV radiotherapy machine has been employed with a mixed fuel target. Results will support further development for a subcritical assembly employing a thorium containing liquid fuel. It is expected that acquired technological knowledge will contribute to the Venezuelan nuclear energy program.

An Analysis of the Pressures, Forces and Moments Induced by the Ground Vortex Generated by a Single Impinging Jet

NASA Technical Reports Server (NTRS)

Kuhn, Richard E.

1997-01-01

When a jet STOVL aircraft is in STOL operation the jets impinge on the ground and generate wall jets flowing radially outward from the points at which the jets impinge. When the forward flowing part of a wall jet meets the free stream flow it is rolled back on itself forming a parabolic shaped ground vortex. Positive pressures are induced on the lower surface of the configuration ahead of the ground vortex and suction pressures are induced over the ground vortex itself. In addition, the suction pressures induced aft of the jet out of ground effect are reduced and lifting pressures are induced on the upper surface. This study analyzes available pressure and force data and develops a method for estimating the forces and moments induced in ground effect. The method includes the effects of configuration variables, height and operating conditions, as well as the effects of the location, deflection and shape of the jet. However, it is limited to single jets at subcritical nozzle pressure ratios. An analysis of the effects of moving over the ground vs. tests over a fixed ground plane is included.

Force and Pressure Recovery Characteristics at Supersonic Speeds of a Conical Spike Inlet with a Bypass Discharging from the Top or Bottom of the Diffuser in an Axial Direction

NASA Technical Reports Server (NTRS)

Allen, J L; Beke, Andrew

1953-01-01

Force and pressure-recovery characteristics of a nacelle-type conical-spike inlet with a fixed-area bypass located in the top or bottom of the diffuser are presented for flight Mach numbers of 1.6, 1.8, and 2.0 for angles of attack from 0 degrees to 9 degrees. Top or bottom location of the bypass did not have significant effects on diffuser pressure-recovery, bypass mass-flow ratio, or drag coefficient over the range of angles of attack, flight Mach numbers, and stable engine mass-flow ratios investigated. A larger stable subcritical operating range was obtained with the bypass on the bottom at angles of attack from 3 degrees to 9 degrees at a flight Mach number of 2.0. At a flight Mach number of 2.0, the discharge of 14 percent of the critical mass flow of the inlet by means of a bypass increased the drag only one-fifth of the additive drag that would result for equivalent spillage behind an inlet normal shock without significant reductions in diffuser pressure recovery.

Observations of Traveling Crossflow Resonant Triad Interactions on a Swept Wing

NASA Technical Reports Server (NTRS)

Eppink, Jenna L.; Wlezien, Richard

2012-01-01

Experimental evidence indicates the presence of a triad resonance interaction between traveling crossflow modes in a swept wing flow. Results indicate that this interaction occurs when the stationary and traveling crossflow modes have similar and relatively low amplitudes (approx.1% to 6% of the total freestream velocity). The resonant interaction occurs at instability amplitudes well below those typically known to cause transition, yet transition is observed to occur just downstream of the resonance. In each case, two primary linearly unstable traveling crossflow modes are nonlinearly coupled to a higher frequency linearly stable mode at the sum of their frequencies. The higher-frequency mode is linearly stable and presumed to exist as a consequence of the interaction of the two primary modes. Autoand cross-bicoherence are used to determine the extent of phase-matching between the modes, and wavenumber matching confirms the triad resonant nature of the interaction. The bicoherence results indicate a spectral broadening mechanism and the potential path to early transition. The implications for laminar flow control in swept wing flows are significant. Even if stationary crossflow modes remain subcritical, traveling crossflow interactions can lead to early transition.

Experimental Study on Interference Effects of Two Tandem Cylinders Wrapped Around by Triple Helical Rods with Gap on Induced Drag

NASA Astrophysics Data System (ADS)

Prastianto, R. W.; Dwipayana, K. H.; Syahroni, N.; Pumbarino, B.

2018-03-01

This paper examines the results of laboratory experiments to investigate the effect of interference of two tandem cylinders covered by triple helical rods with gap to the induced drag force. Two identical rigid models are horizontally positioned with roll support on both ends of each cylinder. Uniform air flow in subcritical regime that correspond to Reynolds number (Re) of 1.6 × 104 ∼ 6.5 × 104 perpendicularly flowed to the models in the wind tunnel with three variations of the distance between the cylinders which are 1.75D, 3D and 5D. At Re = 4.2 × 104 the results show that the maximum shielding effects occur in the rear cylinder at the distance of 1.75D so the drag coefficient (CD) is reduced to 93.6% compared to single cylinder case. This shielding effect will weaken with increasing the distance between the cylinder. In contrast, the fluid flow interference effect on the front cylinder increases due to increasing of spacing between the two cylinders and still occurred at that spacing of 5D until CD reduction reached 10% of the single cylinder case.

Experimental river delta size set by multiple floods and backwater hydrodynamics.

PubMed

Ganti, Vamsi; Chadwick, Austin J; Hassenruck-Gudipati, Hima J; Fuller, Brian M; Lamb, Michael P

2016-05-01

River deltas worldwide are currently under threat of drowning and destruction by sea-level rise, subsidence, and oceanic storms, highlighting the need to quantify their growth processes. Deltas are built through construction of sediment lobes, and emerging theories suggest that the size of delta lobes scales with backwater hydrodynamics, but these ideas are difficult to test on natural deltas that evolve slowly. We show results of the first laboratory delta built through successive deposition of lobes that maintain a constant size. We show that the characteristic size of delta lobes emerges because of a preferential avulsion node-the location where the river course periodically and abruptly shifts-that remains fixed spatially relative to the prograding shoreline. The preferential avulsion node in our experiments is a consequence of multiple river floods and Froude-subcritical flows that produce persistent nonuniform flows and a peak in net channel deposition within the backwater zone of the coastal river. In contrast, experimental deltas without multiple floods produce flows with uniform velocities and delta lobes that lack a characteristic size. Results have broad applications to sustainable management of deltas and for decoding their stratigraphic record on Earth and Mars.

Experimental river delta size set by multiple floods and backwater hydrodynamics

PubMed Central

Ganti, Vamsi; Chadwick, Austin J.; Hassenruck-Gudipati, Hima J.; Fuller, Brian M.; Lamb, Michael P.

2016-01-01

River deltas worldwide are currently under threat of drowning and destruction by sea-level rise, subsidence, and oceanic storms, highlighting the need to quantify their growth processes. Deltas are built through construction of sediment lobes, and emerging theories suggest that the size of delta lobes scales with backwater hydrodynamics, but these ideas are difficult to test on natural deltas that evolve slowly. We show results of the first laboratory delta built through successive deposition of lobes that maintain a constant size. We show that the characteristic size of delta lobes emerges because of a preferential avulsion node—the location where the river course periodically and abruptly shifts—that remains fixed spatially relative to the prograding shoreline. The preferential avulsion node in our experiments is a consequence of multiple river floods and Froude-subcritical flows that produce persistent nonuniform flows and a peak in net channel deposition within the backwater zone of the coastal river. In contrast, experimental deltas without multiple floods produce flows with uniform velocities and delta lobes that lack a characteristic size. Results have broad applications to sustainable management of deltas and for decoding their stratigraphic record on Earth and Mars. PMID:27386534

Estimating turbidity current conditions from channel morphology: A Froude number approach

NASA Astrophysics Data System (ADS)

Sequeiros, Octavio E.

2012-04-01

There is a growing need across different disciplines to develop better predictive tools for flow conditions of density and turbidity currents. Apart from resorting to complex numerical modeling or expensive field measurements, little is known about how to estimate gravity flow parameters from scarce available data and how they relate to each other. This study presents a new method to estimate normal flow conditions of gravity flows from channel morphology based on an extensive data set of laboratory and field measurements. The compilation consists of 78 published works containing 1092 combined measurements of velocity and concentration of gravity flows dating as far back as the early 1950s. Because the available data do not span all ranges of the critical parameters, such as bottom slope, a validated Reynolds-averaged Navier-Stokes (RANS)κ-ɛnumerical model is used to cover the gaps. It is shown that gravity flows fall within a range of Froude numbers spanning 1 order of magnitude centered on unity, as opposed to rivers and open-channel flows which extend to a much wider range. It is also observed that the transition from subcritical to supercritical flow regime occurs around a slope of 1%, with a spread caused by parameters other than the bed slope, like friction and suspended sediment settling velocity. The method is based on a set of equations relating Froude number to bed slope, combined friction, suspended material, and other flow parameters. The applications range from quick estimations of gravity flow conditions to improved numerical modeling and back calculation of missing parameters. A real case scenario of turbidity current estimation from a submarine canyon off the Nigerian coast is provided as an example.

Duality in an asset exchange model for wealth distribution

NASA Astrophysics Data System (ADS)

Li, Jie; Boghosian, Bruce M.

2018-05-01

Asset exchange models are agent-based economic models with binary transactions. Previous investigations have augmented these models with mechanisms for wealth redistribution, quantified by a parameter χ, and for trading bias favoring wealthier agents, quantified by a parameter ζ. By deriving and analyzing a Fokker-Planck equation for a particular asset exchange model thus augmented, it has been shown that it exhibits a second-order phase transition at ζ / χ = 1, between regimes with and without partial wealth condensation. In the "subcritical" regime with ζ / χ < 1, all of the wealth is classically distributed; in the "supercritical" regime with ζ / χ > 1, a fraction 1 - χ / ζ of the wealth is condensed. Intuitively, one may associate the supercritical, wealth-condensed regime as reflecting the presence of "oligarchy," by which we mean that an infinitesimal fraction of the total agents hold a finite fraction of the total wealth in the continuum limit. In this paper, we further elucidate the phase behavior of this model - and hence of the generalized solutions of the Fokker-Planck equation that describes it - by demonstrating the existence of a remarkable symmetry between its supercritical and subcritical regimes in the steady-state. Noting that the replacement { ζ → χ , χ → ζ } , which clearly has the effect of inverting the order parameter ζ / χ, provides a one-to-one correspondence between the subcritical and supercritical states, we demonstrate that the wealth distribution of the subcritical state is identical to that of the corresponding supercritical state when the oligarchy is removed from the latter. We demonstrate this result analytically, both from the microscopic agent-level model and from its macroscopic Fokker-Planck description, as well as numerically. We argue that this symmetry is a kind of duality, analogous to the famous Kramers-Wannier duality between the subcritical and supercritical states of the Ising model, and to the Maldacena duality that underlies AdS/CFT theory.

On the finite element modeling of the asymmetric cracked rotor

NASA Astrophysics Data System (ADS)

AL-Shudeifat, Mohammad A.

2013-05-01

The advanced phase of the breathing crack in the heavy duty horizontal rotor system is expected to be dominated by the open crack state rather than the breathing state after a short period of operation. The reason for this scenario is the expected plastic deformation in crack location due to a large compression stress field appears during the continuous shaft rotation. Based on that, the finite element modeling of a cracked rotor system with a transverse open crack is addressed here. The cracked rotor with the open crack model behaves as an asymmetric shaft due to the presence of the transverse edge crack. Hence, the time-varying area moments of inertia of the cracked section are employed in formulating the periodic finite element stiffness matrix which yields a linear time-periodic system. The harmonic balance method (HB) is used for solving the finite element (FE) equations of motion for studying the dynamic behavior of the system. The behavior of the whirl orbits during the passage through the subcritical rotational speeds of the open crack model is compared to that for the breathing crack model. The presence of the open crack with the unbalance force was found only to excite the 1/2 and 1/3 of the backward critical whirling speed. The whirl orbits in the neighborhood of these subcritical speeds were found to have nearly similar behavior for both open and breathing crack models. While unlike the breathing crack model, the subcritical forward whirling speeds have not been observed for the open crack model in the response to the unbalance force. As a result, the behavior of the whirl orbits during the passage through the forward subcritical rotational speeds is found to be enough to distinguish the breathing crack from the open crack model. These whirl orbits with inner loops that appear in the neighborhood of the forward subcritical speeds are then a unique property for the breathing crack model.

How do subcritical cracking rates and styles influence rock erosion? A test case from the Blue Ridge Mountains of Virginia.

NASA Astrophysics Data System (ADS)

Eppes, M. C.; Hancock, G. S.; Dewers, T. A.; Chen, X.; Eichhubl, P.

2017-12-01

There is a disconnect between measured rates of rock erosion and regolith production and our understanding of the factors and processes that drive them. Here we examine the mechanical weathering (cracking) characteristics of natural, bare bedrock outcrops characterized by 10Be derived erosion rates that vary from 2 to 40 m/my in the Blue Ridge Mountains, VA. Observed erosion rate variance generally correlates with rock type; we seek to characterize and quantify to what extent the mechanical weathering properties of the different rock types drive erosion rates. We assert that subcritical cracking constitutes the primary mechanism by which the outcrops increase their porosity and subsequently weather and erode. We therefore hypothesize that rock parameters that control rates and styles of subcritical cracking set the outcrop erosion rates. For each outcrop, we measured crack characteristics along transects: for every crack >2 cm length, we measured its length, width, orientation, and weathering characteristics (rounded vs sharp edges); and we measured the thickness of all `steps' (spallation remnants) encountered in the transects. For most outcrops, we collected surface samples in order to characterize their mineralogy and microcracking characteristics through thin section analysis. For each rock type, we collected samples for which we measured fracture toughness, as well as the subcritical crack growth index under different moisture conditions. Preliminary analysis of the field crack data indicates that each rock type (granite, sandstone, quartzite) is characterized by unique macro- and micro-scale crack characteristics consistent with known generic subcritical cracking parameters for those rocks. Crack density and length correlate with erosion rates in faster eroding rock types, but not slowly eroding ones. Overall, we hope these data will help to shed light on the driving and limiting factors for the mechanical production of porosity in rock at and near Earth's surface.

Breaking rocks made easy: subcritical processes and tectonic predesign

NASA Astrophysics Data System (ADS)

Voigtlaender, Anne; Krautblatter, Michael

2017-04-01

In geomorphic studies, to change in landforms, e.g. by rock slope failure, fluvial or glacial erosion, a threshold is commonly assumed, which is crossed either by an increase in external driving or a decrease of internal resisting forces, respectively. If the threshold is crossed, bedrock breaks and slope fails, rivers incise and glaciers plug and sew their bed. Here we put forward a focus on the decrease of the resisting forces, as an increase in the driving forces, to match the strength of bedrock, is not that likely. We suggest that the degradation of resisting forces of bedrock can be better explained by subcritical processes like creep, fatigue and stress corrosion interplaying with tectonic predesign. Both concepts, subcritical processes and tectonic predesign have been issued in the last century, but have not been widely accepted nor have their assumptions been explicitly stressed in recent case studies. Moreover both concepts profit especially on scale issues if merged. Subcritical crack growth, includes different mechanisms promoting fractures well below the ultimate strength. Single infinitesimal but irreversible damage and deformations are induced in the material over time. They interact with inherent microstructural flaws and low applied stresses, limiting local strength and macroscopic behavior of bedrock. This reissues the concept of tectonic predesigned, as proposed by A.E. Scheidegger, which not only encompasses structural features that determine the routing of drainage patterns and shear planes, e.g. joints, faults and foliations, but also the (neo)tectonic stress-field and the (in-situ) strain state of bedrocks and mountains. Combining subcritical processes and tectonic predesign we can better explain, why and where we see a dissected, eroded and geomorphic divers' landscape. In this conceptual framework actual magnitudes of the driving forces are accounted for and so is the nature of the bedrock material, to better understand the trajectories of the forms we study, and break rocks easily.

The procedure and results of calculations of the equilibrium isotopic composition of a demonstration subcritical molten salt reactor

NASA Astrophysics Data System (ADS)

Nevinitsa, V. A.; Dudnikov, A. A.; Blandinskiy, V. Yu.; Balanin, A. L.; Alekseev, P. N.; Titarenko, Yu. E.; Batyaev, V. F.; Pavlov, K. V.; Titarenko, A. Yu.

2015-12-01

A subcritical molten salt reactor with an external neutron source is studied computationally as a facility for incineration and transmutation of minor actinides from spent nuclear fuel of reactors of VVER-1000 type and for producing 233U from 232Th. The reactor configuration is chosen, the requirements to be imposed on the external neutron source are formulated, and the equilibrium isotopic composition of heavy nuclides and the key parameters of the fuel cycle are calculated.

Thermal neutron streaming effects and WIMS analysis of the Penn State subcritical graphite pile

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

Feltus, M.A.; Zediak, C.S.; Jester, W.A.

1997-12-01

This analysis was performed on the Pennsylvania State University (PSU) subcritical reactor to find more accurate values for such nuclear parameters as the thermal fuel utilization factor, thermal diffusion length in the graphite, migration area, k{sub eff}, etc. The analysis involved using the Winfrith Integrated Multigroup Scheme (WIMS) code as well as various hand calculations to find and compare those parameters. The data found in this analysis will be used by future students in the Penn State laboratory courses.

A thermodynamic analysis of propagating subcritical cracks with cohesive zones

NASA Technical Reports Server (NTRS)

Allen, David H.

1993-01-01

The results of the so-called energetic approach to fracture with particular attention to the issue of energy dissipation due to crack propagation are applied to the case of a crack with cohesive zone. The thermodynamic admissibility of subcritical crack growth (SCG) is discussed together with some hypotheses that lead to the derivation of SCG laws. A two-phase cohesive zone model for discontinuous crack growth is presented and its thermodynamics analyzed, followed by an example of its possible application.

Efficient collective influence maximization in cascading processes with first-order transitions

PubMed Central

Pei, Sen; Teng, Xian; Shaman, Jeffrey; Morone, Flaviano; Makse, Hernán A.

2017-01-01

In many social and biological networks, the collective dynamics of the entire system can be shaped by a small set of influential units through a global cascading process, manifested by an abrupt first-order transition in dynamical behaviors. Despite its importance in applications, efficient identification of multiple influential spreaders in cascading processes still remains a challenging task for large-scale networks. Here we address this issue by exploring the collective influence in general threshold models of cascading process. Our analysis reveals that the importance of spreaders is fixed by the subcritical paths along which cascades propagate: the number of subcritical paths attached to each spreader determines its contribution to global cascades. The concept of subcritical path allows us to introduce a scalable algorithm for massively large-scale networks. Results in both synthetic random graphs and real networks show that the proposed method can achieve larger collective influence given the same number of seeds compared with other scalable heuristic approaches. PMID:28349988

Vacuum ultraviolet spectroscopy of the lowest-lying electronic state in subcritical and supercritical water

NASA Astrophysics Data System (ADS)

Marin, Timothy W.; Janik, Ireneusz; Bartels, David M.; Chipman, Daniel M.

2017-05-01

The nature and extent of hydrogen bonding in water has been scrutinized for decades, including how it manifests in optical properties. Here we report vacuum ultraviolet absorption spectra for the lowest-lying electronic state of subcritical and supercritical water. For subcritical water, the spectrum redshifts considerably with increasing temperature, demonstrating the gradual breakdown of the hydrogen-bond network. Tuning the density at 381 °C gives insight into the extent of hydrogen bonding in supercritical water. The known gas-phase spectrum, including its vibronic structure, is duplicated in the low-density limit. With increasing density, the spectrum blueshifts and the vibronic structure is quenched as the water monomer becomes electronically perturbed. Fits to the supercritical water spectra demonstrate consistency with dimer/trimer fractions calculated from the water virial equation of state and equilibrium constants. Using the known water dimer interaction potential, we estimate the critical distance between molecules (ca. 4.5 Å) needed to explain the vibronic structure quenching.

Unavoidable food supply chain waste: acid-free pectin extraction from mango peel via subcritical water.

PubMed

Xia, H; Matharu, A S

2017-09-21

Mango peel is the major by-product of mango processing, and compromises 7-24% of the total mango weight. In this study, pectin was extracted from mango peel waste by using subcritical water extraction (SWE) in the absence of mineral acid. A highest yield of 18.34% was achieved from the Kesar variety and the pectin was characterised using ATR-IR spectroscopy, TGA and 13 C solid-state NMR spectroscopy to confirm the structure. The degree of esterification (DE) of the pectin was analysed with both titrimetry and 13 C solid-state NMR spectroscopy, and a high DE (>70%) was observed for all three varieties (Keitt, Sindhri and Kesar). This is the first report on acid-free subcritical water extraction of pectin from mango peel, which provides a green route for the valorisation of mango peel waste and contributes to a source of biobased materials and chemicals for a sustainable 21 st century.

Separation of Active Compounds from Food by-Product (Cocoa Shell) Using Subcritical Water Extraction.

PubMed

Jokić, Stela; Gagić, Tanja; Knez, Željko; Šubarić, Drago; Škerget, Mojca

2018-06-11

Large amounts of residues are produced in the food industries. The waste shells from cocoa processing are usually burnt for fuel or used as a mulch in gardens to add nutrients to soil and to suppress weeds. The objectives of this work were: (a) to separate valuable compounds from cocoa shell by applying sustainable green separation process—subcritical water extraction (SWE); (b) identification and quantification of active compounds, sugars and sugar degradation products in obtained extracts using HPLC; (c) characterization of the antioxidant activity of extracts; (d) optimization of separation process using response surface methodology (RSM). Depending on applied extraction conditions, different concentration of theobromine, caffeine, theophylline, epicatechin, catechin, chlorogenic acid and gallic acid were determined in the extracts obtained by subcritical water. Furthermore, mannose, glucose, xylose, arabinose, rhamnose and fucose were detected as well as their important degradation products such as 5-hydroxymethylfurfural (5-HMF), furfural, levulinic acid, lactic acid and formic acid.

Vacuum ultraviolet spectroscopy of the lowest-lying electronic state in subcritical and supercritical water

DOE PAGES

Marin, Timothy W.; Janik, Ireneusz; Bartels, David M.; ...

2017-05-17

The nature and extent of hydrogen bonding in water has been scrutinized for decades, including how it manifests in optical properties. Here we report vacuum ultraviolet absorption spectra for the lowest-lying electronic state of subcritical and supercritical water. For subcritical water, the spectrum redshifts considerably with increasing temperature, demonstrating the gradual breakdown of the hydrogen-bond network. Tuning the density at 381°C gives insight into the extent of hydrogen bonding in supercritical water. The known gas-phase spectrum, including its vibronic structure, is duplicated in the low-density limit. With increasing density, the spectrum blueshifts and the vibronic structure is quenched as themore » water monomer becomes electronically perturbed. Fits to the supercritical water spectra demonstrate consistency with dimer/trimer fractions calculated from the water virial equation of state and equilibrium constants. As a result, using the known water dimer interaction potential, we estimate the critical distance between molecules (ca. 4.5 Å) needed to explain the vibronic structure quenching.« less

Efficient collective influence maximization in cascading processes with first-order transitions

NASA Astrophysics Data System (ADS)

Pei, Sen; Teng, Xian; Shaman, Jeffrey; Morone, Flaviano; Makse, Hernán A.

2017-03-01

In many social and biological networks, the collective dynamics of the entire system can be shaped by a small set of influential units through a global cascading process, manifested by an abrupt first-order transition in dynamical behaviors. Despite its importance in applications, efficient identification of multiple influential spreaders in cascading processes still remains a challenging task for large-scale networks. Here we address this issue by exploring the collective influence in general threshold models of cascading process. Our analysis reveals that the importance of spreaders is fixed by the subcritical paths along which cascades propagate: the number of subcritical paths attached to each spreader determines its contribution to global cascades. The concept of subcritical path allows us to introduce a scalable algorithm for massively large-scale networks. Results in both synthetic random graphs and real networks show that the proposed method can achieve larger collective influence given the same number of seeds compared with other scalable heuristic approaches.

Transverse single-file diffusion and enhanced longitudinal diffusion near a subcritical bifurcation

NASA Astrophysics Data System (ADS)

Dessup, Tommy; Coste, Christophe; Saint Jean, Michel

2018-05-01

A quasi-one-dimensional system of repelling particles undergoes a configurational phase transition when the transverse confining potential decreases. Below a threshold, it becomes energetically favorable for the system to adopt one of two staggered raw patterns, symmetric with respect to the system axis. This transition is a subcritical pitchfork bifurcation for short range interactions. As a consequence, the homogeneous zigzag pattern is unstable in a finite zigzag amplitude range [hC 1,hC 2] . We exhibit strong qualitative effects of the subcriticality on the thermal motions of the particles. When the zigzag amplitude is close enough to the limits hC 1 and hC 2, a transverse vibrational soft mode occurs which induces a strongly subdiffusive behavior of the transverse fluctuations, similar to single-file diffusion. On the contrary, the longitudinal fluctuations are enhanced, with a diffusion coefficient which is more than doubled. Conversely, a simple measurement of the thermal fluctuations allows a precise determination of the bifurcation thresholds.

Absolute reactivity calibration of accelerator-driven systems after RACE-T experiments

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

Jammes, C. C.; Imel, G. R.; Geslot, B.

2006-07-01

The RACE-T experiments that were held in november 2005 in the ENEA-Casaccia research center near Rome allowed us to improve our knowledge of the experimental techniques for absolute reactivity calibration at either startup or shutdown phases of accelerator-driven systems. Various experimental techniques for assessing a subcritical level were inter-compared through three different subcritical configurations SC0, SC2 and SC3, about -0.5, -3 and -6 dollars, respectively. The area-ratio method based of the use of a pulsed neutron source appears as the most performing. When the reactivity estimate is expressed in dollar unit, the uncertainties obtained with the area-ratio method were lessmore » than 1% for any subcritical configuration. The sensitivity to measurement location was about slightly more than 1% and always less than 4%. Finally, it is noteworthy that the source jerk technique using a transient caused by the pulsed neutron source shutdown provides results in good agreement with those obtained from the area-ratio technique. (authors)« less

Surface chemistry and corrosion behavior of Inconel 625 and 718 in subcritical, supercritical, and ultrasupercritical water

NASA Astrophysics Data System (ADS)

Rodriguez, David; Merwin, Augustus; Karmiol, Zachary; Chidambaram, Dev

2017-05-01

Corrosion behavior of Inconel 625 and 718 in subcritical, supercritical and ultrasupercritical water was studied as a function of temperature and time. The change in the chemistry of the as-received surface film on Inconel 625 and 718 after exposure to subcritical water at 325 °C and supercritical water at 425 °C and 527.5 °C for 2 h was studied. After exposure to 325 °C subcritical water, the CrO42- based film formed; however minor quantities of NiFexCr2-xO4 spinel compounds were observed. The oxide film formed on both alloys when exposed to supercritical water at 425 °C consisted of NiFexCr2-xO4 spinel. The surface films on both alloys were identified as NiFe2O4 when exposed to supercritical water at 527.5 °C. To characterize the fully developed oxide layer, studies were conducted at test solution temperatures of 527.5 and 600 °C. Samples were exposed to these temperatures for 24, 96, and 200 h. Surface chemistry was analyzed using X-ray diffraction, as well as Raman and X-ray photoelectron spectroscopies. Inconel 718 exhibited greater mass gain than Inconel 625 for all temperatures and exposure times. The differences in corrosion behavior of the two alloys are attributed to the lower content of chromium and increased iron content of Inconel 718 as compared to Inconel 625.

New breathing functions for the transverse breathing crack of the cracked rotor system: Approach for critical and subcritical harmonic analysis

NASA Astrophysics Data System (ADS)

Al-Shudeifat, Mohammad A.; Butcher, Eric A.

2011-01-01

The actual breathing mechanism of the transverse breathing crack in the cracked rotor system that appears due to the shaft weight is addressed here. As a result, the correct time-varying area moments of inertia for the cracked element cross-section during shaft rotation are also determined. Hence, two new breathing functions are identified to represent the actual breathing effect on the cracked element stiffness matrix. The new breathing functions are used in formulating the time-varying finite element stiffness matrix of the cracked element. The finite element equations of motion are then formulated for the cracked rotor system and solved via harmonic balance method for response, whirl orbits and the shift in the critical and subcritical speeds. The analytical results of this approach are compared with some previously published results obtained using approximate formulas for the breathing mechanism. The comparison shows that the previously used breathing function is a weak model for the breathing mechanism in the cracked rotor even for small crack depths. The new breathing functions give more accurate results for the dynamic behavior of the cracked rotor system for a wide range of the crack depths. The current approach is found to be efficient for crack detection since the critical and subcritical shaft speeds, the unique vibration signature in the neighborhood of the subcritical speeds and the sensitivity to the unbalance force direction all together can be utilized to detect the breathing crack before further damage occurs.

MYRRHA: A multipurpose nuclear research facility

NASA Astrophysics Data System (ADS)

Baeten, P.; Schyns, M.; Fernandez, Rafaël; De Bruyn, Didier; Van den Eynde, Gert

2014-12-01

MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) is a multipurpose research facility currently being developed at SCK•CEN. MYRRHA is based on the ADS (Accelerator Driven System) concept where a proton accelerator, a spallation target and a subcritical reactor are coupled. MYRRHA will demonstrate the ADS full concept by coupling these three components at a reasonable power level to allow operation feedback. As a flexible irradiation facility, the MYRRHA research facility will be able to work in both critical as subcritical modes. In this way, MYRRHA will allow fuel developments for innovative reactor systems, material developments for GEN IV and fusion reactors, and radioisotope production for medical and industrial applications. MYRRHA will be cooled by lead-bismuth eutectic and will play an important role in the development of the Pb-alloys technology needed for the LFR (Lead Fast Reactor) GEN IV concept. MYRRHA will also contribute to the study of partitioning and transmutation of high-level waste. Transmutation of minor actinides (MA) can be completed in an efficient way in fast neutron spectrum facilities, so both critical reactors and subcritical ADS are potential candidates as dedicated transmutation systems. However critical reactors heavily loaded with fuel containing large amounts of MA pose reactivity control problems, and thus safety problems. A subcritical ADS operates in a flexible and safe manner, even with a core loading containing a high amount of MA leading to a high transmutation rate. In this paper, the most recent developments in the design of the MYRRHA facility are presented.

Speed of sound measurements and mixing characterization of underexpanded fuel jets with supercritical reservoir condition using laser-induced thermal acoustics

NASA Astrophysics Data System (ADS)

Baab, S.; Förster, F. J.; Lamanna, G.; Weigand, B.

2016-11-01

The four-wave mixing technique laser-induced thermal acoustics was used to measure the local speed of sound in the farfield zone of extremely underexpanded jets. N-hexane at supercritical injection temperature and pressure (supercritical reservoir condition) was injected into quiescent subcritical nitrogen (with respect to the injectant). The technique's capability to quantify the nonisothermal, turbulent mixing zone of small-scale jets is demonstrated for the first time. Consistent radially resolved speed of sound profiles are presented for different axial positions and varying injection temperatures. Furthermore, an adiabatic mixing model based on nonideal thermodynamic properties is presented to extract mixture composition and temperature from the experimental speed of sound data. High fuel mass fractions of up to 94 % are found for the centerline at an axial distance of 55 diameters from the nozzle followed by a rapid decay in axial direction. This is attributed to a supercritical fuel state at the nozzle exit resulting in the injection of a high-density fluid. The obtained concentration data are complemented by existing measurements and collapsed in a similarity law. It allows for mixture prediction of underexpanded jets with supercritical reservoir condition provided that nonideal thermodynamic behavior is considered for the nozzle flow. Specifically, it is shown that the fuel concentration in the farfield zone is very sensitive to the thermodynamic state at the nozzle exit. Here, a transition from supercritical fluid to subcritical vapor state results in strongly varying fuel concentrations, which implies high impact on the mixture formation and, consequently, on the combustion characteristics.

Observations of Scour and Transport at Coastal Structures from the 2011 Tohoku Tsunami - Implications for Flow in Natural Terrain

NASA Astrophysics Data System (ADS)

Petroff, C. M.

2011-12-01

Before the March 11, 2011 Tohoku tsunami, many communities along the Japan coast had shore protection barriers, some designed specifically to provide protection from tsunamis and others for typhoon and storm surge protection. A vast number of these structures were overtopped, damaged or destroyed by the high inundation and currents generated in the tsunami. Observations are presented about scour features at man-made coastal structures in the Tohoku region as well as the hydraulic transport of debris from these structures. Along with providing lessons for structure design and maintenance, these observations have implications for hydraulic transport in natural terrain, not only at hard points such as rock outcrops but also at other features such as river mouths, barrier islands and coastal dunes. As an example, Photo 1 shows the overtopping flow at the seawall at Noda, in the Iwate prefecture. From the point of view of hydraulics the type of flow seen in the photo is more like that at an in-line weir or spillway than the wave conditions for which the structure was designed. On the lee or downstream side of such structures, the flow is supercritical resulting in a supercritical to subcritical transition near the landward toe of the seawall. High flow velocities along with increased pore pressure and overturning flow create very deep scour in these locations Such as the zone clearly seen in Photo 2 behind the seawall at the Sendai airport. It is anticipated that similar hydraulic conditions would occur for flow over a high coastal dune ridge where the ridge would act as a flow control point and locally high velocities on the landward side of the ridge would result in high erosion and scour. Other examples are given.

Slow sedimentary processes on-a-chip: experiments on porous flow effects on granular bed creep

NASA Astrophysics Data System (ADS)

Houssais, M.; Maldarelli, C.; Shattuck, M.; Morris, J. F.

2017-12-01

Steep soils dynamics is hard to catch. they exhibit very slow granular creep most of the time, and sometimes, mostly under or after rain, turn into a landslide, a very fast avalanche flow.The conditions of transition from soil creep to avalanching remains a lot non-understood, and Safe Factor law (empirical criteria, function of rain intensity and duration). On another side, in marine fast deposition environments, compaction drives vertical porous flow, which makes bed shear resistance change, and form over time bed size patterns (pipes, dishes) or mechanical heterogeneities.Capturing how the slow creep dynamics depends on the porous flow would allow for much more accurate landscape evolution modeling.We present here preliminary results of an experimental investigation of one the major triggering condition for soils destabilization: rain infiltration, and more generally porous flow through a tilted granular bed. In a quasi-2D microfluidics channel, a flat sediment bed made of spherical particles is prepared, in fully submerged condition. It is thereafter tilted (at slope under critical slope of avalanching) and simultaneously put under vertical weak porous flow (well under the critical flow of liquefaction regarding positive pressure gradients). The two control parameters are varied, and local particles concentration and motion are measured. Interestingly, although staying in the sub-critical creeping regime, we observe an acceleration of the bed deformation downward, as the porous flow and the bed slope are increased, until the criteria for avalanching is reached. Those results appear to present similitudes with the case of tilted dry sediment bed under controlled vibrations. Consequently it opens the discussion about a potential universal model of landslides triggering due to frequent seismological and rainstorm events.

The procedure and results of calculations of the equilibrium isotopic composition of a demonstration subcritical molten salt reactor

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

Nevinitsa, V. A., E-mail: Neviniza-VA@nrcki.ru; Dudnikov, A. A.; Blandinskiy, V. Yu.

2015-12-15

A subcritical molten salt reactor with an external neutron source is studied computationally as a facility for incineration and transmutation of minor actinides from spent nuclear fuel of reactors of VVER-1000 type and for producing {sup 233}U from {sup 232}Th. The reactor configuration is chosen, the requirements to be imposed on the external neutron source are formulated, and the equilibrium isotopic composition of heavy nuclides and the key parameters of the fuel cycle are calculated.

Evaluation of supercritical cryogen storage and transfer systems for future NASA missions

NASA Technical Reports Server (NTRS)

Arif, Hugh; Aydelott, John C.; Chato, David J.

1990-01-01

Conceptual designs of Space Transportation Vehicles (STV), and their orbital servicing facilities, that utilize supercritical, single phase, cryogenic propellant were established and compared with conventional subcritical, two phases, STV concepts. The analytical study was motivated by the desire to avoid fluid management problems associated with the storage, acquisition and transfer of subcritical liquid oxygen and hydrogen propellants in the low gravity environment of space. Although feasible, the supercritical concepts suffer from STV weight penalties and propellant resupply system power requirements which make the concepts impractical.

Evaluation of supercritical cryogen storage and transfer systems for future NASA missions

NASA Technical Reports Server (NTRS)

Arif, Hugh; Aydelott, John C.; Chato, David J.

1989-01-01

Conceptual designs of Space Transportation Vehicles (STV), and their orbital servicing facilities, that utilize supercritical, single phase, cryogenic propellants were established and compared with conventional subcritical, two phase, STV concepts. The analytical study was motivated by the desire to avoid fluid management problems associated with the storage, acquisition and transfer of subcritical liquid oxygen and hydrogen propellants in the low gravity environment of space. Although feasible, the supercritical concepts suffer from STV weight penalties and propellant resupply system power requirements which make the concepts impractical.

Orbital storage and supply of subcritical liquid nitrogen

NASA Technical Reports Server (NTRS)

Aydelott, John C.

1990-01-01

Subcritical cryogenic fluid management has long been recognized as an enabling technology for key propulsion applications, such as space transfer vehicles (STV) and the on-orbit cryogenic fuel depots which will provide STV servicing capability. The LeRC Cryogenic Fluids Technology Office (CFTO), under the sponsorship of OAST, has the responsibility of developing the required technology via a balanced program involving analytical modeling, ground based testing, and in-space experimentation. Topics covered in viewgraph form include: cryogenic management technologies; nitrogen storage and supply; cryogenic nitrogen cooling capability; and LN2 system demonstration technical objectives.

Subcritical flutter testing and system identification

NASA Technical Reports Server (NTRS)

Houbolt, J. C.

1974-01-01

Treatment is given of system response evaluation, especially in application to subcritical flight and wind tunnel flutter testing of aircraft. An evaluation is made of various existing techniques, in conjuction with a companion survey which reports theoretical and analog experiments made to study the identification of system response characteristics. Various input excitations are considered, and new techniques for analyzing response are explored, particularly in reference to the prevalent practical case where unwanted input noise is present, such as caused by gusts or wind tunnel turbulence. Further developments are also made of system parameter identification techniques.

Interdroplet attractive forces in AOT water-in-oil microemulsions formed in subcritical and supercritical solvents

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

Tingey, J.M.; Fulton, J.L.; Smith, R.D.

1990-03-08

The van der Waals attractive interactions between aqueous droplets in water-in-oil type microemulsions have been investigated for a range of continuous-phase solvents including the alkanes from methane to isooctane and the noble gases, krypton and xenon. Hamaker constants for water droplets with surfactant shells of the sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in subcritical and supercritical solvents were calculated by using Lifshitz theory and the resulting interaction potential calculations qualitatively account for many features of the phase behavior of these systems.

Water-tunnel study of transition flow around circular cylinders

NASA Technical Reports Server (NTRS)

Almosnino, D.; Mcalister, K. W.

1984-01-01

The recently reported phenomenon of asymmetric flow separation from a circular cylinder in the critical Reynolds number regime has been confirmed in a water-tunnel experiment. For the first time, an attempt was made to visualize the wake of the cylinder during the transition from subcritical to critical flow and to correlate the visualizations with lift and drag measurements. The occurrence of a dominant asymmetric-flow state was quite repeatable, both when increasing and decreasing the Reynolds number, resulting in a mean lift coefficient of C sub L approx 1.2 and a shift in the angle of the wake by about 12 deg. A distinctive step change in the drag and shedding frequency was also found to occur. A hysteresis was confirmed to exist in this region as the Reynolds number was cycled over the transition range. Both boundaries of the asymmetry appear to be supercritical bifurcations in the flow. The asymmetry was normally steady in the mean; however, there were instances when the direction of the asymmetry reversed and remained so for the duration of the Reynolds number sweep through this transition region. A second asymmetry was observed at a higher Reynolds number; however, the mean lift coefficient was much lower, and the direction of the asymmetry was not observed to reverse. Introducing a small local disturbance into the boundary layer was found to prevent the critical asymmetry from developing along the entire span of the cylinder.

Experiment on smooth, circular cylinders in cross-flow in the critical Reynolds number regime

NASA Astrophysics Data System (ADS)

Miau, J. J.; Tsai, H. W.; Lin, Y. J.; Tu, J. K.; Fang, C. H.; Chen, M. C.

2011-10-01

Experiments were conducted for 2D circular cylinders at Reynolds numbers in the range of 1.73 × 105-5.86 × 105. In the experiment, two circular cylinder models made of acrylic and stainless steel, respectively, were employed, which have similar dimensions but different surface roughness. Particular attention was paid to the unsteady flow behaviors inferred by the signals obtained from the pressure taps on the cylinder models and by a hot-wire probe in the near-wake region. At Reynolds numbers pertaining to the initial transition from the subcritical to the critical regimes, pronounced pressure fluctuations were measured on the surfaces of both cylinder models, which were attributed to the excursion of unsteady flow separation over a large circumferential region. At the Reynolds numbers almost reaching the one-bubble state, it was noted that the development of separation bubble might switch from one side to the other with time. Wavelet analysis of the pressure signals measured simultaneously at θ = ±90° further revealed that when no separation bubble was developed, the instantaneous vortex-shedding frequencies could be clearly resolved, about 0.2, in terms of the Strouhal number. The results of oil-film flow visualization on the stainless steel cylinder of the one-bubble and two-bubble states showed that the flow reattachment region downstream of a separation bubble appeared not uniform along the span of the model. Thus, the three dimensionality was quite evident.

Bifilm Defect Formation in Hydraulic Jump of Liquid Aluminum

NASA Astrophysics Data System (ADS)

Hsu, Fu-Yuan

2016-06-01

In aluminum gravity casting, as liquid aluminum fell through a vertical sprue and impacted on the horizontal flat surface, a phenomenon known as hydraulic jump ( i.e., flow transition from super-critical to sub-critical flows) was observed. As the jump was transformed, a reverse eddy motion on the surface of the jump was created. This motion entrained aluminum oxide film from the surface into aluminum melt. This folded film (so-called "bifilm" defect) was engulfed by the melt and caused its quality to deteriorate. To understand this phenomenon, aluminum casting experiments and computational modeling were conducted. In the casting experiment, a radius ( R j) to the point where the circular hydraulic jump occurred was measured. This is the circular region of `irregular surface feature', a rough oxidized surface texture near the center area of the castings. To quantify contents of the bifilm defects in the outer region of the jump, the samples in this region were sectioned and re-melted for doing re-melted reduced pressure test (re-melt RPT). An "area-normalized" bifilm index map was plotted to analyze bifilms' population in the samples. The flow transition in the hydraulic jump of liquid aluminum depended on three pressure heads: inertial, gravitational, and surface-tension pressures. A new theoretical equation containing surface tension for describing the flow transition of liquid metal was proposed.

Effect of the cross sectional aspect ratio on the flow past a twisted cylinder

NASA Astrophysics Data System (ADS)

Jung, Jae Hwan; Yoon, Hyun Sik

2013-11-01

The cross-flow around twisted cylinders of cross sectional aspect ratio (A/B) from 1 to 2.25 is investigated at a subcritical Reynolds number (Re) of 3000 using large eddy simulation (LES). The flow past a corresponding smooth and wavy cylinder is also calculated for comparison and validation against experimental data. The effect of twisted surface assessed in terms of the mean drag and root-mean-square (RMS) value of fluctuating lift. The shear layer of the twisted cylinder covering the recirculation region is more elongated than those of the smooth and the wavy cylinder. Successively, vortex shedding of the twisted cylinder is considerably suppressed, compared with those of the smooth and the wavy cylinder. The maximum drag reduction of up to 13% compared with a smooth cylinder is obtained at a certain cross sectional aspect ratio. The fluctuating lift coefficient of the twisted cylinder is also significantly suppressed. We found that the cross sectional cross sectional aspect ratio (A/B) plays an essential role in determining the vortical structures behind the twisted cylinder which has a significant effect on the reduction of the fluctuating lift and suppression of flow-induced vibration. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) through GCRC-SOP (No. 2011-0030013).

Supercritical sedimentary structures and bedforms and criteria for recognition in the field: insights from the Middle Eocene deep-marine Morillo and Guaso systems, Ainsa Basin, Spanish Pyrenees

NASA Astrophysics Data System (ADS)

Torley, John; Pickering, Kevin

2017-04-01

It has long been acknowledged that for most submarine slopes with gradients > 0.5, common to many deep-water environments, they should contain abundant evidence of supercritical flows and their deposits. However, it is common for deep-marine sands/sandstones to be routinely modelled using the Bouma (1962) sequence for turbidites. Recently, the importance of supercritical flows has been highlighted from seafloor observations, with numerical and physical experiments. Such experiments have produced previously unrecognised bedforms which fail to be interpreted adequately by Bouma's model, including antidunes, chutes-and-pools, and cyclic steps. Fieldwork in the Middle Eocene Ainsa Basin, Spanish Pyrenees, has been undertaken in the Morillo and Guaso systems of the Upper Hecho Group. Approximately 5,000 beds were measured and documented in detail, e.g., grain size, sedimentary structures, bedforms and facies. Collectively, this data can be used to understand supercritical versus subcritical flow. The relative importance of supercritical flow can then be compared and contrasted within individual ancient deep-marine systems. The Morillo System is relatively coarse-grained, compared with the Guaso System. The results of this research contribute to an improved understanding of the processes in deep-marine systems, and directly benefit the hydrocarbon industry by providing better constraints to predict deep-water reservoir composition and architecture.

The initial-value problem for viscous channel flows

NASA Technical Reports Server (NTRS)

Criminale, W. O.; Jackson, T. L.; Lasseigne, D. G.

1995-01-01

Plane viscous channel flows are perturbed and the ensuing initial-value problems are investigated in detail. Unlike traditional methods where traveling wave normal modes are assumed for solution, this works offers a means whereby completely arbitrary initial input can be specified without having to resort to eigenfunction expansions. The full temporal behavior, including both early time transients and the long time asymptotics, can be determined for any initial disturbance. Effects of three-dimensionality can be assessed. The bases for the analysis are: (a) linearization of the governing equations; (b) Fourier decomposition in the spanwise and streamwise directions of the flow; and (c) direct numerical integration of the resulting partial differential equations. All of the stability data that are known for such flows can be reproduced. Also, the optimal initial condition can be determined in a straight forward manner and such optimal conditions clearly reflect transient growth data that is easily determined by a rational choice of a basis for the initial conditions. Although there can be significant transient growth for subcritical values of the Reynolds number using this approach it does not appear possible that arbitrary initial conditions will lead to the exceptionally large transient amplitudes that have been determined by optimization of normal modes. The approach is general and can be applied to other classes of problems where only a finite discrete spectrum exists, such as the boundary layer for example.

An experimental investigation of the flow past a finite circular cylinder at a low subcritical Reynolds number

NASA Technical Reports Server (NTRS)

Budair, M.; Ayoub, A.; Karamcheti, K.

1981-01-01

Results of hot wire measurements made in the near wake at a Reynolds number of 9955 are reported. The measurements include the mean velocity profiles, root mean square values of the velocity fluctuations, frequency spectra, and velocity cross correlations. The mean velocity profiles were used to determine the wake width, whose variation in the downstream and spanwise directions was examined. It is observed that close to the cylinder, the wake is narrower toward the free end than it is away from it, while further downstream the wake is wider toward the tip than it is away from it. It is found that the flow over the span can be characterized by four regions: a tip region where vortex shedding occurs at a lower frequency than that prevalent for away from the tip; an intermediate region adjacent to the first one where a frequency component of a nonshedding character is present; a third region characterized by a gradually increasing shedding frequency with increasing distance from the tip; and a two dimensional region where the shedding frequency is constant.

Subcritical and supercritical fuel injection and mixing in single and binary species systems

NASA Astrophysics Data System (ADS)

Roy, Arnab

Subcritical and supercritical fluid injection using a single round injector into a quiescent atmosphere comprising single and binary species was investigated using optical diagnostics. Different disintegration and mixing modes are expected for the two cases. In the binary species case, the atmosphere comprised an inert gas of a different composition than that of the injected fluid. In single species case, the atmosphere consisted of the same species as that of the injected fluid. Density values were quantified and density gradient profiles were inferred from the experimental data. A novel method was applied for the detection of detailed structures throughout the entire jet center plane. Various combinations of injectant and chamber conditions were tested and a wide range of density ratios were covered. The subcritical cases demonstrated the importance of surface tension and inertial forces, while the supercritical cases showed no signs of surface tension and, in most situations, resembled the mixing characteristics of a gaseous jet injected into a gaseous environment. A comparison between the single and binary species systems has also been provided. A detailed laser calibration procedure was undertaken to account for the laser absorption through the gas and liquid phases and for fluorescence in the non-linear excitation regime for high laser pulse energy. Core lengths were measured for binary species cases and correlated with visualization results. An eigenvalue approach was taken to determine the location of maximum gradients for determining the core length. Jet divergence angles were also calculated and were found to increase with chamber-to-injectant density ratio for both systems. A model was proposed for the spreading angle dependence on density ratio for both single and binary species systems and was compared to existing theoretical studies and experimental work. Finally, a linear stability analysis was performed for the jet injected into both subcritical and supercritical atmospheres. The subcritical cases showed good correlation with previous and current experimental results. The supercritical solutions, which have not yet been solved earlier by researchers, are found here through an asymptotic solution of the dispersion equation for exceedingly high Weber numbers.

Numerical simulation of fluid flow and heat transfer in a thin liquid film over a stationary and rotating disk and comparison with experimental data

NASA Technical Reports Server (NTRS)

Faghri, Amir; Swanson, Theodore D.

1990-01-01

In the first section, improvements in the theoretical model and computational procedure for the prediction of film height and heat-transfer coefficient of the free surface flow of a radially-spreading thin liquid film adjacent to a flat horizontal surface of finite extent are presented. Flows in the presence and absence of gravity are considered. Theoretical results are compared to available experimental data with good agreement. In the presence of gravity, a hydraulic jump is present, isolating the flow into two regimes: supercritical upstream from the jump and subcritical downstream of it. In this situation, the effects of surface tension are important near the outer edge of the disk where the fluid experiences a free fall. A region of flow separation is present just downstream of the jump. In the absence of gravity, no hydraulic jump or separated flow region is present. The variation of the heat-transfer coefficient for flows in the presence and absence of gravity are also presented. In the second section, the results of a numerical simulation of the flow field and associated heat transfer coefficients are presented for the free surface flow of a thin liquid film adjacent to a horizontal rotating disk. The computation was performed for different flow rates and rotational velocities using a 3-D boundary-fitted coordinate system. Since the geometry of the free surface is unknown and dependent on flow rate, rate of rotation, and other parameters, an iterative procedure had to be used to ascertain its location. The computed film height agreed well with existing experimental measurements. The flow is found to be dominated by inertia near the entrance and close to the free surface and dominated by centrifugal force at larger radii and adjacent to the disk. The rotation enhances the heat transfer coefficient by a significant amount.

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

Youker, Amanda J.; Krebs, John F.; Quigley, Kevin J.

With funding from the National Nuclear Security Administrations Material Management and Minimization Office, Argonne National Laboratory (Argonne) is providing technical assistance to help accelerate the U.S. production of Mo-99 using a non-highly enriched uranium (non-HEU) source. A potential Mo-99 production pathway is by accelerator-initiated fissioning in a subcritical uranyl sulfate solution containing low enriched uranium (LEU). As part of the Argonne development effort, we are undertaking the AMORE (Argonne Molybdenum Research Experiment) project, which is essentially a pilot facility for all phases of Mo-99 production, recovery, and purification. Production of Mo-99 and other fission products in the subcritical target solutionmore » is initiated by putting an electron beam on a depleted uranium (DU) target; the fast neutrons produced in the DU target are thermalized and lead to fissioning of U-235. At the end of irradiation, Mo is recovered from the target solution and separated from uranium and most of the fission products by using a titania column. The Mo is stripped from the column with an alkaline solution. After acidification of the Mo product solution from the recovery column, the Mo is concentrated (and further purified) in a second titania column. The strip solution from the concentration column is then purified with the LEU Modified Cintichem process. A full description of the process can be found elsewhere [1–3]. The initial commissioning steps for the AMORE project include performing a Mo-99 spike test with pH 1 sulfuric acid in the target vessel without a beam on the target to demonstrate the initial Mo separation-and-recovery process, followed by the concentration column process. All glovebox operations were tested with cold solutions prior to performing the Mo-99 spike tests. Two Mo-99 spike tests with pH 1 sulfuric acid have been performed to date. Figure 1 shows the flow diagram for the remotely operated Mo-recovery system for the AMORE project. There are two separate pumps and flow paths for the acid and base operations. The system contains three sample ladders with eight sample loops per ladder for target mixing; column loading, including acid and water washes; and column stripping, including the final water wash.« less

Combustion of LOX with H2(sub g) under subcritical, critical, and supercritical conditions and experimental observation of dense spray and mixing of impinging jets

NASA Technical Reports Server (NTRS)

Kuo, Kenneth K.; Hsieh, W. H.; Yang, A. S.; Brown, J. J.; Cheung, F. B.; Woodward, R. D.; Kline, M. C.

1992-01-01

Progress made during the period of February 1 to October 15, 1992 is reported. The overall objective of Task 1 of the investigation is to achieve a better understanding of the combustion processes of liquid oxygen and gaseous hydrogen under subcritical, critical, and supercritical conditions. Specific objectives of the research program are: (1) to determine the evaporation- and burning-rate characteristics of LOX in hydrogen/helium environments under broad ranges of operating conditions; (2) to measure species concentration profile and surface temperature of LOX employing the gas chromatography and fine-wire thermocouples under non-reacting flow situations; (3) to perform a fugacity-based multicomponent thermodynamic phase equilibrium analysis for examining the high-pressure vapor-liquid equilibrium behavior at the liquid surface of LOX; (4) to formulate and solve a theoretical model for simulating the evaporation and combustion processes in a LOX/H2/He system; and (5) to validate the theoretical model with the measured experimental data. Task 2 of the investigation is described. Observation of a like-on-like injector element in the near-injector region performed in the previous phase of this project has identified the existence of a high Reynolds number regime in which the pre-impingement jets are fully turbulent and undergoing surface breakup. The new spray regime, which has not been observed by previous investigators, is characterized by the presence of many fine droplets and the disappearance of the well-defined liquid breakup wave pattern in the post-impingement region. It is speculated that a cavitating region may be present within the orifice so that it could induce strong turbulence, leading to an onset of atomization of the jets prior to impingement. To further investigate the dense spray behavior of the impinging jets in the high Reynolds number region, experiments were conducted using Plexiglas injector components for direct internal flow observation. The main objective is to determine under what conditions a cavitating region would form and whether or not the cavitation is reponsible for the development of the high Reynolds number spray regime. The procedure and major findings of the injector cavitation study are described.

Dune bedforms produced by dilute pyroclastic density currents from the August 2006 eruption of Tungurahua volcano, Ecuador.

PubMed

Douillet, Guilhem Amin; Pacheco, Daniel Alejandro; Kueppers, Ulrich; Letort, Jean; Tsang-Hin-Sun, Ève; Bustillos, Jorge; Hall, Minard; Ramón, Patricio; Dingwell, Donald B

A series of pyroclastic density currents were generated at Tungurahua volcano (Ecuador) during a period of heightened activity in August 2006. Dense pyroclastic flows were confined to valleys of the drainage network, while dilute pyroclastic density currents overflowed on interfluves where they deposited isolated bodies comprising dune bedforms of cross-stratified ash exposed on the surface. Here, the description, measurement, and classification of more than 300 dune bedforms are presented. Four types of dune bedforms are identified with respect to their shape, internal structure, and geometry (length, width, thickness, stoss and lee face angles, and stoss face length). (1) "Elongate dune bedforms" have smooth shapes and are longer (in the flow direction) than wide or thick. Internal stratification consists of stoss-constructional, thick lensoidal layers of massive and coarse-grained material, alternating with bedsets of fine laminae that deposit continuously on both stoss and lee sides forming aggrading structures with upstream migration of the crests. (2) "Transverse dune bedforms" show linear crests perpendicular to the flow direction, with equivalent lengths and widths. Internally, these bedforms exhibit finely stratified bedsets of aggrading ash laminae with upstream crest migration. Steep truncations of the bedsets are visible on the stoss side only. (3) "Lunate dune bedforms" display a barchanoidal shape and have stratification patterns similar to those of the transverse ones. Finally, (4) "two-dimensional dune bedforms" are much wider than long, exhibit linear crests and are organized into trains. Elongate dune bedforms are found exclusively in proximal deposition zones. Transverse, lunate, and two-dimensional dune bedforms are found in distal ash bodies. The type of dune bedform developed varies spatially within an ash body, transverse dune bedforms occurring primarily at the onset of deposition zones, transitioning to lunate dune bedforms in intermediate zones, and two-dimensional dune bedforms exclusively on the lateral and distal edges of the deposits. The latter are also found where flows moved upslope. Elongate dune bedforms were deposited from flows with both granular-based and tractional flow boundaries that possessed high capacity and competence. They may have formed in a subcritical context by the blocking of material on the stoss side. We do not interpret them as antidune or "chute-and-pool" structures. The dimensions and cross-stratification patterns of transverse dune bedforms are interpreted as resulting from low competence currents with a significant deposition rate, but we rule out their interpretation as "antidunes". A similar conclusion holds for lunate dune bedforms, whose curved shape results from a sedimentation rate dependent on the thickness of the bedform. Finally, two-dimensional dune bedforms were formed where lateral transport exceeds longitudinal transport; i.e., in areas where currents were able to spread laterally in low velocity zones. We suggest that the aggrading ash bedsets with upstream crest migration were formed under subcritical flow conditions where the tractional bedload transport was less important than the simultaneous fallout from suspension. This produced differential draping with no further reworking. We propose the name "regressive climbing dunes" for structures produced by this process. A rapid decrease in current velocity, possibly triggered by hydraulic jumps affecting the entire parent flows, is inferred to explain their deposition. This process can in principle hold for any kind of particulate density current.

Super- and sub-critical regions in shocks driven by radio-loud and radio-quiet CMEs

PubMed Central

Bemporad, Alessandro; Mancuso, Salvatore

2012-01-01

White-light coronagraphic images of Coronal Mass Ejections (CMEs) observed by SOHO/LASCO C2 have been used to estimate the density jump along the whole front of two CME-driven shocks. The two events are different in that the first one was a “radio-loud” fast CME, while the second one was a “radio quiet” slow CME. From the compression ratios inferred along the shock fronts, we estimated the Alfvén Mach numbers for the general case of an oblique shock. It turns out that the “radio-loud” CME shock is initially super-critical around the shock center, while later on the whole shock becomes sub-critical. On the contrary, the shock associated with the “radio-quiet” CME is sub-critical at all times. This suggests that CME-driven shocks could be efficient particle accelerators at the shock nose only at the initiation phases of the event, if and when the shock is super-critical, while at later times they lose their energy and the capability to accelerate high energetic particles. PMID:25685431

Subcritical and supercritical water oxidation of CELSS model wastes

NASA Technical Reports Server (NTRS)

Takahashi, Y.; Wydeven, T.; Koo, C.

1989-01-01

A mixture of ammonium hydroxide with acetic acid and a slurry of human feces, urine, and wipes were used as CELSS model wastes to be wet-oxidized at temperatures from 250 to 500 C, i.e. below and above the critical point of water (374 C and 218 kg/sq cm or 21.4 MPa). The effects of oxidation temperature ( 250-500 C) and residence time (0-120 mn) on carbon and nitrogen and on metal corrosion from the reactor material were studied. Almost all of the organic matter in the model wastes was oxidized in the temperature range from 400 to 500 C, above the critical conditions for water. In contrast, only a small portion of the organic matter was oxidized at subcritical conditions. A substantial amount of nitrogen remained in solution in the form of ammonia at temperatures ranging from 350 to 450 C suggesting that, around 400 C, organic carbon is completely oxidized and most of the nitrogen is retained in solution. The Hastelloy C-276 alloy reactor corroded during subcritical and supercritical water oxidation.

Pyrolysis of low density polyethylene waste in subcritical water optimized by response surface methodology.

PubMed

Wong, S L; Ngadi, N; Amin, N A S; Abdullah, T A T; Inuwa, I M

2016-01-01

Pyrolysis of low density polyethylene (LDPE) waste from local waste separation company in subcritical water was conducted to investigate the effect of reaction time, temperature, as well as the mass ratio of water to polymer on the liquid yield. The data obtained from the study were used to optimize the liquid yield using response surface methodology. The range of reaction temperature used was 162-338°C, while the reaction time ranged from 37 min to 143 min, and the ratio of water to polymer ranged from 1.9 to 7.1. It was found that pyrolysis of LDPE waste in subcritical water produced hydrogen, methane, carbon monoxide and carbon dioxide, while the liquid product contained alkanes and alkenes with 10-50 carbons atoms, as well as heptadecanone, dichloroacetic acid and heptadecyl ester. The optimized conditions were 152.3°C, reaction time of 1.2 min and ratio of water solution to polymer of 32.7, with the optimum liquid yield of 13.6 wt% and gases yield of 2.6 wt%.

Modeling new coal projects: supercritical or subcritical?

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

Carrino, A.J.; Jones, R.B.

Decisions made on new build coal-fired plants are driven by several factors - emissions, fuel logistics and electric transmission access all provide constraints. The crucial economic decision whether to build supercritical or subcritical units often depends on assumptions concerning the reliability/availability of each technology, the cost of on-fuel operations including maintenance, the generation efficiencies and the potential for emissions credits at some future value. Modeling the influence of these key factors requires analysis and documentation to assure the assets actually meet the projected financial performance. This article addresses some of the issue related to the trade-offs that have the potentialmore » to be driven by the supercritical/subcritical decision. Solomon Associates has been collecting cost, generation and reliability data on coal-fired power generation assets for approximately 10 years using a strict methodology and taxonomy to categorize and compare actual plant operations data. This database provides validated information not only on performance, but also on alternative performance scenarios, which can provide useful insights in the pro forma financial analysis and models of new plants. 1 ref., 1 fig., 3 tabs.« less

Study of an Acid-Free Technique for the Preparation of Glycyrrhetinic Acid from Ammonium Glycyrrhizinate in Subcritical Water.

PubMed

Lekar, Anna V; Borisenko, Sergey N; Vetrova, Elena V; Filonova, Olga V; Maksimenko, Elena V; Borisenko, Nikolai I; Minkin, Vladimir I

2015-11-01

The aim of this work was to study an application of a previously developed expedient acid-free technique for the preparation of glycyrrhetinic acid from ammonium glycyrrhizinate that requires no use of acids and toxic organic solvents. Subcritical water that serves as a reactant and a solvent was used in order to obtain glycyrrhetinic acid in good yields starting from ammonium glycyrrhizinate. It has been shown that variation of only one parameter of the process (temperature) allows alteration to thecomposition of the hydrolysis products. A new method was used for the synthesis of glycyrrhetinic acid (glycyrrhizic acid aglycone) and its monoglycoside. HPLC combined with mass spectrometry and NMR spectroscopy were used to determine the quantitative and qualitative compositions of the obtained products. The method developed for the production of glycyrrhetinic acid in subcritical water is environmentally friendly and faster than conventional hydrolysis methods that use acids and-expensive and toxic organic solvents. The proposed technique has a potential for the future development of inexpensive and environmentally friendly technologies for production of new pharmaceutical plant-based substances.

Recovery of Oil with Unsaturated Fatty Acids and Polyphenols from Chaenomelessinensis (Thouin) Koehne: Process Optimization of Pilot-Scale Subcritical Fluid Assisted Extraction.

PubMed

Zhu, Zhenzhou; Zhang, Rui; Zhan, Shaoying; He, Jingren; Barba, Francisco J; Cravotto, Giancarlo; Wu, Weizhong; Li, Shuyi

2017-10-22

The potential effects of three modern extraction technologies (cold-pressing, microwaves and subcritical fluids) on the recovery of oil from Chaenomelessinensis (Thouin) Koehne seeds have been evaluated and compared to those of conventional chemical extraction methods (Soxhlet extraction). This oil contains unsaturated fatty acids and polyphenols. Subcritical fluid extraction (SbFE) provided the highest yield-25.79 g oil/100 g dry seeds-of the three methods. Moreover, the fatty acid composition in the oil samples was analysed using gas chromatography-mass spectrometry. This analysis showed that the percentages of monounsaturated (46.61%), and polyunsaturated fatty acids (42.14%), after applying SbFE were higher than those obtained by Soxhlet, cold-pressing or microwave-assisted extraction. In addition, the oil obtained under optimized SbFE conditions (35 min extraction at 35 °C with four extraction cycles), showed significant polyphenol (527.36 mg GAE/kg oil), and flavonoid (15.32 mg RE/kg oil), content, had a good appearance and was of high quality.

Effect of SO2 concentration as an impurity on carbon steel corrosion under subcritical CO2 environment

NASA Astrophysics Data System (ADS)

Mahlobo, MGR; Premlall, K.; Olubambi, PA

2017-12-01

Carbon dioxide (CO2) is considered to be easier to transport over moderate distances when turned into supercritical state (dense phase) than at any other state. Because of this reason, the transportation of CO2 during carbon capture and storage requires CO2 to be at its supercritical state. CO2 temperature profile from different regions causes CO2 to deviate between supercritical and subcritical state (gas/liquid phase). In this study the influence of sulphur dioxide (SO2) on the corrosion of carbon steel was evaluated under different SO2 concentrations (0.5, 1.5 and 5%) in combination with subcritical CO2. Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Energy-Dispersive X-ray Spectroscopy (EDS) were used to characterize the CO2 corrosion product layer formed on the carbon steel surface. The weight loss results showed that corrosion rate increased with SO2 concentration with corrosion rate up to 7.45 mm/year while at 0% SO2 the corrosion rate was 0.067 mm/year.

Quasi-equilibrium size distribution of subcritical nuclei in amorphous phase change AgIn-Sb2Te

NASA Astrophysics Data System (ADS)

Darmawikarta, Kristof; Lee, Bong-Sub; Shelby, Robert M.; Raoux, Simone; Bishop, Stephen G.; Abelson, John R.

2013-07-01

We investigate the effect of low temperature annealing or of extended storage at room temperature on the subsequent nucleation behavior of amorphous AgIn-incorporated Sb2Te (AIST), a material for phase change memories. Time-resolved reflectivity measurements during pulsed laser crystallization reveal the rates of solid-phase transformation, while fluctuation transmission electron microscopy detects the nanoscale order in the amorphous phase prior to crystallization. The nanoscale order is postulated to consist of subcritical nuclei that coarsen upon annealing at temperatures ranging from 25 °C (for months) or 100 °C (for hours). Samples that have been annealed remain fully amorphous as evaluated by conventional diffraction experiments. Shorter nucleation times are consistently associated with the observation of increased nanoscale order. The effect of annealing is observed to saturate: there is no further reduction in nucleation time or increase in nanoscale order for annealing at 100 °C beyond three hours. This result supports the general prediction of classical nucleation theory that the size distribution of subcritical nuclei increases from the as-deposited state to a quasi-equilibrium.

Subcritical water extractor for Mars analog soil analysis.

PubMed

Amashukeli, Xenia; Grunthaner, Frank J; Patrick, Steven B; Yung, Pun To

2008-06-01

Abstract Technologies that enable rapid and efficient extraction of biomarker compounds from various solid matrices are a critical requirement for the successful implementation of in situ chemical analysis of the martian regolith. Here, we describe a portable subcritical water extractor that mimics multiple organic solvent polarities by tuning the dielectric constant of liquid water through adjustment of temperature and pressure. Soil samples, collected from the Yungay region of the Atacama Desert (martian regolith analogue) in the summer of 2005, were used to test the instrument's performance. The total organic carbon was extracted from the samples at concentrations of 0.2-55.4 parts per million. The extraction data were compared to the total organic carbon content in the bulk soil, which was determined via a standard analytical procedure. The instrument's performance was examined over the temperature range of 25-250 degrees C at a fixed pressure of 20.7 MPa. Under these conditions, water remains in a subcritical fluid state with a dielectric constant varying between approximately 80 (at 25 degrees C) and approximately 30 (at 250 degrees C).

High order statistical signatures from source-driven measurements of subcritical fissile systems

NASA Astrophysics Data System (ADS)

Mattingly, John Kelly

1998-11-01

This research focuses on the development and application of high order statistical analyses applied to measurements performed with subcritical fissile systems driven by an introduced neutron source. The signatures presented are derived from counting statistics of the introduced source and radiation detectors that observe the response of the fissile system. It is demonstrated that successively higher order counting statistics possess progressively higher sensitivity to reactivity. Consequently, these signatures are more sensitive to changes in the composition, fissile mass, and configuration of the fissile assembly. Furthermore, it is shown that these techniques are capable of distinguishing the response of the fissile system to the introduced source from its response to any internal or inherent sources. This ability combined with the enhanced sensitivity of higher order signatures indicates that these techniques will be of significant utility in a variety of applications. Potential applications include enhanced radiation signature identification of weapons components for nuclear disarmament and safeguards applications and augmented nondestructive analysis of spent nuclear fuel. In general, these techniques expand present capabilities in the analysis of subcritical measurements.

Process Development for Hydrothermal Liquefaction of Algae Feedstocks in a Continuous-Flow Reactor

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

Elliott, Douglas C.; Hart, Todd R.; Schmidt, Andrew J.

Wet algae slurries can be converted into an upgradeable biocrude by hydrothermal liquefaction (HTL). High levels of carbon conversion to gravity-separable biocrude product were accomplished at relatively low temperature (350 °C) in a continuous-flow, pressurized (sub-critical liquid water) environment (20 MPa). As opposed to earlier work in batch reactors reported by others, direct oil recovery was achieved without the use of a solvent and biomass trace components were removed by processing steps so that they did not cause process difficulties. High conversions were obtained even with high slurry concentrations of up to 35 wt% of dry solids. Catalytic hydrotreating wasmore » effectively applied for hydrodeoxygenation, hydrodenitrogenation, and hydrodesulfurization of the biocrude to form liquid hydrocarbon fuel. Catalytic hydrothermal gasification was effectively applied for HTL byproduct water cleanup and fuel gas production from water soluble organics, allowing the water to be considered for recycle of nutrients to the algae growth ponds. As a result, high conversion of algae to liquid hydrocarbon and gas products was found with low levels of organic contamination in the byproduct water. All three process steps were accomplished in bench-scale, continuous-flow reactor systems such that design data for process scale-up was generated.« less

A nonlinear approach to transition in subcritical plasmas with sheared flow

NASA Astrophysics Data System (ADS)

Pringle, Chris C. T.; McMillan, Ben F.; Teaca, Bogdan

2017-12-01

In many plasma systems, introducing a small background shear flow is enough to stabilize the system linearly. The nonlinear dynamics are much less sensitive to sheared flows than the average linear growth rates, and very small amplitude perturbations can lead to sustained turbulence. We explore the general problem of characterizing how and when the transition from near-laminar states to sustained turbulence occurs, with a model of the interchange instability being used as a concrete example. These questions are fundamentally nonlinear, and the answers must go beyond the linear transient amplification of small perturbations. Two methods that account for nonlinear interactions are therefore explored here. The first method explored is edge tracking, which identifies the boundary between the basins of attraction of the laminar and turbulent states. Here, the edge is found to be structured around an exact, localized, traveling wave solution that is qualitatively similar to avalanche-like bursts seen in the turbulent regime. The second method is an application of nonlinear, non-modal stability theory which allows us to identify the smallest disturbances which can trigger turbulence (the minimal seed for the problem) and hence to quantify how stable the laminar regime is. The results obtained from these fully nonlinear methods provide confidence in the derivation of a semi-analytic approximation for the minimal seed.

Numerical study on the aerodynamics of a golf ball and its comparison with a smooth sphere

NASA Astrophysics Data System (ADS)

Li, Jing; Tsubokura, Makoto; Tsunoda, Masaya

2014-11-01

The present study has numerically investigated the flow over a golf ball and a smooth sphere by conducting large-eddy simulation (LES) using hundreds of millions of unstructured elements. Simulations were conducted at various Reynolds numbers ranging from the subcritical to the supercritical regimes. Special attention was paid to the phenomenon of drag crisis as well as the effect of surface roughness on the drag crisis. The simulation result shows that the surface roughness introduced by the dimples of the golf ball causes a local instability of the flow around the ball and subsequently leads to a momentum transfer in the near-wall region inside the dimples. The flow with high momentum in the near-wall region travels further downstream, which consequently results in the drag crisis occurring at a relatively lower Reynolds number compared with that of the smooth sphere. Moreover, the Magnus effect resulting from the rotating motion of a sphere was also one of the main concerns in this study. The simulation result shows that lift forces are imposed on both the rotating smooth sphere and rotating golf ball. For most cases the lift force points to the positive direction, however, the negative lift force appears also under certain conditions.

Calculation of potential flow past non-lifting bodies at angle of attack using axial and surface singularity methods. M.S. Thesis. Contractor Report, 1 Jan. 1981 - 31 Aug. 1982

NASA Technical Reports Server (NTRS)

Shu, J. Y.

1983-01-01

Two different singularity methods have been utilized to calculate the potential flow past a three dimensional non-lifting body. Two separate FORTRAN computer programs have been developed to implement these theoretical models, which will in the future allow inclusion of the fuselage effect in a pair of existing subcritical wing design computer programs. The first method uses higher order axial singularity distributions to model axisymmetric bodies of revolution in an either axial or inclined uniform potential flow. Use of inset of the singularity line away from the body for blunt noses, and cosine-type element distributions have been applied to obtain the optimal results. Excellent agreement to five significant figures with the exact solution pressure coefficient value has been found for a series of ellipsoids at different angles of attack. Solutions obtained for other axisymmetric bodies compare well with available experimental data. The second method utilizes distributions of singularities on the body surface, in the form of a discrete vortex lattice. This program is capable of modeling arbitrary three dimensional non-lifting bodies. Much effort has been devoted to finding the optimal method of calculating the tangential velocity on the body surface, extending techniques previously developed by other workers.

A nonlinear model of flow in meandering submarine and subaerial channels

NASA Astrophysics Data System (ADS)

Imran, Jasim; Parker, Gary; Pirmez, Carlos

1999-12-01

A generalized model of flow in meandering subaqueous and subaerial channels is developed. The conservation equations of mass and momentum are depth/layer integrated, normalized, and represented as deviations from a straight base state. This allows the determination of integrable forms which can be solved at both linear and nonlinear levels. The effects of various flow and geometric parameters on the flow dynamics are studied. Although the model is not limited to any specific planform, this study focuses on sine-generated curves. In analysing the flow patterns, the turbidity current of the subaqueous case is simplified to a conservative density flow with water entrainment from above neglected. The subaqueous model thus formally corresponds to a subcritical or only mildly supercritical mud-rich turbidity current. By extension, however the analysis can be applied to a depositional or erosional current carrying sand that is changing only slowly in the streamwise direction. By bringing the subaqueous and subaerial cases into a common form, flow behaviour in the two environments can be compared under similar geometric and boundary conditions. A major difference between the two cases is the degree of superelevation of channel flow around bends, which is modest in the subaerial case but substantial in the subaqueous case. Another difference concerns Coriolis effects: some of the largest subaqueous meandering systems are so large that Coriolis effects can become important. The model is applied to meander bends on the youngest channel in the mid-fan region of the Amazon Fan and a mildly sinuous bend of the North-West Atlantic Mid-Ocean Channel. In the absence of specific data on the turbid flows that created the channel, the model can be used to make inferences about the flow, and in particular the range of values of flow velocity and sediment concentration that would allow the growth and downfan migration of meander bends.

Reductive dechlorination of polychlorinated biphenyls by zerovalent iron in subcritical water

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

Yak, H.K.; Wenclawiak, B.W.; Cheng, I.F.

1999-04-15

A method for remediation of PCB-contaminated soil and sediments is described that uses zerovalent iron as the dechlorination agent and subcritical water extraction (SWE) as the transporting medium. By using 100-mesh iron powder and SWE conditions of 250 C and 10 MPa on Aroclor 1260 for 1--8 h, the higher chlorine-substituted homologues were completely reduced to their lower substituted counterparts. The lower-substituted congeners were subsequently near-completely dechlorinated. The initial findings indicate that this technique may be a viable method for remediation of PCB-contaminated soil and sediments.

Criticality Safety Evaluation of the LLNL Inherently Safe Subcritical Assembly (ISSA)

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

Percher, Catherine

2012-06-19

The LLNL Nuclear Criticality Safety Division has developed a training center to illustrate criticality safety and reactor physics concepts through hands-on experimental training. The experimental assembly, the Inherently Safe Subcritical Assembly (ISSA), uses surplus highly enriched research reactor fuel configured in a water tank. The training activities will be conducted by LLNL following the requirements of an Integration Work Sheet (IWS) and associated Safety Plan. Students will be allowed to handle the fissile material under the supervision of LLNL instructors. This report provides the technical criticality safety basis for instructional operations with the ISSA experimental assembly.

High Chromium Cast Irons: Destabilized-Subcritical Secondary Carbide Precipitation and Its Effect on Hardness and Wear Properties

NASA Astrophysics Data System (ADS)

Guitar, María Agustina; Suárez, Sebastián; Prat, Orlando; Duarte Guigou, Martín; Gari, Valentina; Pereira, Gastón; Mücklich, Frank

2018-05-01

This work evaluates the effect of a destabilization treatment combined with a subcritical diffusion (SCD) and a subsequent quenching (Q) steps on precipitation of secondary carbides and their influence on the wear properties of HCCI (16%Cr). The destabilization of the austenite at high temperature leads to a final microstructure composed of eutectic and secondary carbides, with an M7C3 nature, embedded in a martensitic matrix. An improved wear resistance was observed in the SCD + Q samples in comparison with the Q one, which was attributed to the size of secondary carbides.

A useful observable for estimating keff in fast subcritical systems

NASA Astrophysics Data System (ADS)

Saracco, Paolo; Borreani, Walter; Chersola, Davide; Lomonaco, Guglielmo; Ricco, Gianni; Ripani, Marco

2017-09-01

The neutron multiplication factor keff is a key quantity to characterize subcritical neutron multiplying devices and for understanting their physical behaviour, being related to the fundamental eigenvalue of Boltzmann transport equation. Both the maximum available power - and all quantities related to it, like, e.g. the effectiveness in burning nuclear wastes - as well as reactor kinetics and dynamics depend on keff. Nevertheless, keff is not directly measurable and its determination results from the solution of an inverse problem: minimizing model dependence of the solution for keff then becomes a critical issue, relevant both for practical and theoretical reasons.

Viscous, resistive MHD stability computed by spectral techniques

NASA Technical Reports Server (NTRS)

Dahlburg, R. B.; Zang, T. A.; Montgomery, D.; Hussaini, M. Y.

1983-01-01

Expansions in Chebyshev polynomials are used to study the linear stability of one dimensional magnetohydrodynamic (MHD) quasi-equilibria, in the presence of finite resistivity and viscosity. The method is modeled on the one used by Orszag in accurate computation of solutions of the Orr-Sommerfeld equation. Two Reynolds like numbers involving Alfven speeds, length scales, kinematic viscosity, and magnetic diffusivity govern the stability boundaries, which are determined by the geometric mean of the two Reynolds like numbers. Marginal stability curves, growth rates versus Reynolds like numbers, and growth rates versus parallel wave numbers are exhibited. A numerical result which appears general is that instability was found to be associated with inflection points in the current profile, though no general analytical proof has emerged. It is possible that nonlinear subcritical three dimensional instabilities may exist, similar to those in Poiseuille and Couette flow.

Aerodynamic configuration development of the highly maneuverable aircraft technology remotely piloted research vehicle

NASA Technical Reports Server (NTRS)

Gingrich, P. B.; Child, R. D.; Panageas, G. N.

1977-01-01

The aerodynamic development of the highly maneuverable aircraft technology remotely piloted research vehicle (HiMAT/RPRV) from the conceptual design to the final configuration is presented. The design integrates several advanced concepts to achieve a high degree of transonic maneuverability, and was keyed to sustained maneuverability goals while other fighter typical performance characteristics were maintained. When tests of the baseline configuration indicated deficiencies in the technology integration and design techniques, the vehicle was reconfigured to satisfy the subcritical and supersonic requirements. Drag-due-to-lift levels only 5 percent higher than the optimum were obtained for the wind tunnel model at a lift coefficient of 1 for Mach numbers of up to 0.8. The transonic drag rise was progressively lowered with the application of nonlinear potential flow analyses coupled with experimental data.

The Effects of Crossflow on the Pressures and Lift Induced by the Fountain Generated Between Two Impinging Jets

NASA Technical Reports Server (NTRS)

Kuhn, Richard E.

1998-01-01

When a jet STOVL aircraft is hovering, or in a crossflow, while close to the ground wall jets flowing radially outward from the impingement points of the jets are generated. An upflow, or fountain, is generated where the wall jets from adjacent jets meet on the ground surface. The induced lift and suckdown generated by the impingement of the fountain on the lower surface of the configuration has been the subject of previous studies. This study analyzes the limited available pressure and force data on the effect of crossflow on the fountain induced lift and suckdown. The analysis includes the effects of jet spacing, height and operating conditions. However, it is limited to twin jet configurations of circular, vertical jets operating at subcritical nozzle pressure ratios over a fixed ground surface.

Unified Formulation of the Aeroelasticity of Swept Lifting Surfaces

NASA Technical Reports Server (NTRS)

Silva, Walter; Marzocca, Piergiovanni; Librescu, Liviu

2001-01-01

An unified approach for dealing with stability and aeroelastic response to time-dependent pressure pulses of swept wings in an incompressible flow is developed. To this end the indicial function concept in time and frequency domains, enabling one to derive the proper unsteady aerodynamic loads is used. Results regarding stability in the frequency and time domains, and subcritical aeroelastic response to arbitrary time-dependent external excitation obtained via the direct use of the unsteady aerodynamic derivatives for 3-D wings are supplied. Closed form expressions for unsteady aerodynamic derivatives using this unified approach have been derived and used to illustrate their application to flutter and aeroelastic response to blast and sonic-boom signatures. In this context, an original representation of the aeroelastic response in the phase space was presented and pertinent conclusions on the implications of some basic parameters have been outlined.

Experimental investigation on in-plane/out-of-plane vortex-induced vibrations of curved cylinder in parallel and perpendicular flows

NASA Astrophysics Data System (ADS)

Srinil, Narakorn; Ma, Bowen; Zhang, Licong

2018-05-01

This study is motivated by an industrial need to better understand the vortex-induced vibration (VIV) of a curved structure subject to current flows with varying directions whose data for model calibration and validation are lacking. In this paper, new experimental investigations on the two-degree-of-freedom in-plane/out-of-plane VIV of a rigid curved circular cylinder immersed in steady and uniform free-stream flows are presented. The principal objective is to examine how the approaching flow direction versus the cylinder curvature plane affects cross-flow and in-line VIV and the associated hydrodynamic properties. This is achieved by testing the curved cylinder in 3 different flow orientations comprising the parallel flows aligned with the curvature vertical plane in convex and concave configurations, and the flows perpendicular to the curvature plane. The case of varying flow velocities in a subcritical flow range with a maximum Reynolds number of about 50,000 is considered for the curved cylinder with a low mass ratio and damping ratio. Experimental results are presented and discussed in terms of the cylinder response amplitudes, inclination angles, mean displacements, motion trajectories, oscillation frequencies, hydrodynamic forces, relative phases, fluid excitation and added inertia coefficients. Comparisons with other experimental results of curved and straight cylinder VIV are also presented. The experiments highlight the important effects of cylinder curvature versus flow orientation on the combined cross-flow/in-line VIV. The maximum (minimum) responses occur in the perpendicular (convex) flow case whereas the extended lower-branch responses occur in the concave flow case. For perpendicular flows, some meaningful features are observed, including the appearances of cross-flow mean displacements and asymmetric eight-shaped motion trajectories due to multiple 2:1:1 resonances where two out-of-plane and one in-plane dominant frequencies are simultaneously excited. Overall VIV phenomena caused by the system asymmetry should be recognised in a prediction model and design codes to capture the combined effects of curved configuration and approaching flow direction.

The Effect of Backward-Facing Step Height on Instability Growth and Breakdown in Swept Wing Boundary-Layer Transition

NASA Technical Reports Server (NTRS)

Eppink, Jenna L.; Wlezien, Richard W.; King, Rudolph A.; Choudhari, Meelan

2015-01-01

A low-speed experiment was performed on a swept at plate model with an imposed pressure gradient to determine the effect of a backward-facing step on transition in a stationary-cross flow dominated flow. Detailed hot-wire boundary-layer measurements were performed for three backward-facing step heights of approximately 36, 45, and 49% of the boundary-layer thickness at the step. These step heights correspond to a subcritical, nearly-critical, and critical case. Three leading-edge roughness configurations were tested to determine the effect of stationary-cross flow amplitude on transition. The step caused a local increase in amplitude of the stationary cross flow for the two larger step height cases, but farther downstream the amplitude decreased and remained below the baseline amplitude. The smallest step caused a slight local decrease in amplitude of the primary stationary cross flow mode, but the amplitude collapsed back to the baseline case far downstream of the step. The effect of the step on the amplitude of the primary cross flow mode increased with step height, however, the stationary cross flow amplitudes remained low and thus, stationary cross flow was not solely responsible for transition. Unsteady disturbances were present downstream of the step for all three step heights, and the amplitudes increased with increasing step height. The only exception is that the lower frequency (traveling crossflow-like) disturbance was not present in the lowest step height case. Positive and negative spikes in instantaneous velocity began to occur for the two larger step height cases and then grew in number and amplitude downstream of reattachment, eventually leading to transition. The number and amplitude of spikes varied depending on the step height and cross flow amplitude. Despite the low amplitude of the disturbances in the intermediate step height case, breakdown began to occur intermittently and the flow underwent a long transition region.

Flow splitting in numerical simulations of oceanic dense-water outflows

NASA Astrophysics Data System (ADS)

Marques, Gustavo M.; Wells, Mathew G.; Padman, Laurie; Özgökmen, Tamay M.

2017-05-01

Flow splitting occurs when part of a gravity current becomes neutrally buoyant and separates from the bottom-trapped plume as an interflow. This phenomenon has been previously observed in laboratory experiments, small-scale water bodies (e.g., lakes) and numerical studies of small-scale systems. Here, the potential for flow splitting in oceanic gravity currents is investigated using high-resolution (Δx = Δz = 5 m) two-dimensional numerical simulations of gravity flows into linearly stratified environments. The model is configured to solve the non-hydrostatic Boussinesq equations without rotation. A set of experiments is conducted by varying the initial buoyancy number B0 =Q0N3 /g‧2 (where Q0 is the volume flux of the dense water flow per unit width, N is the ambient stratification and g‧ is the reduced gravity), the bottom slope (α) and the turbulent Prandtl number (Pr). Regardless of α or Pr, when B0 ≤ 0.002 the outflow always reaches the deep ocean forming an underflow. Similarly, when B0 ≥ 0.13 the outflow always equilibrates at intermediate depths, forming an interflow. However, when B0 ∼ 0.016, flow splitting always occurs when Pr ≥ 10, while interflows always occur for Pr = 1. An important characteristic of simulations that result in flow splitting is the development of Holmboe-like interfacial instabilities and flow transition from a supercritical condition, where the Froude number (Fr) is greater than one, to a slower and more uniform subcritical condition (Fr < 1). This transition is associated with an internal hydraulic jump and consequent mixing enhancement. Although our experiments do not take into account three-dimensionality and rotation, which are likely to influence mixing and the transition between flow regimes, a comparison between our results and oceanic observations suggests that flow splitting may occur in dense-water outflows with weak ambient stratification, such as Antarctic outflows.

Numerical Studies of Flow Past Two Side-by-Side Circular Cylinders

NASA Astrophysics Data System (ADS)

Shao, J.; Zhang, C.

Multiple circular cylindrical configurations are widely used in engineering applications. The fluid dynamics of the flow around two identical circular cylinders in side-by-side arrangement has been investigated by both experiments and numerical simulations. The center-to-center transverse pitch ratio T/D plays an important role in determining the flow features. It is observed that for 1 < T/D < 1.1 to 1.2, a single vortex street is formed; for 1.2< T/D < 2 to 2.2, bi-stable narrow and wide wakes are formed; for 2.7< T/D < 4 or 5, anti-phase or in-phase vortex streets are formed. In the current study, the vortex structures of turbulent flows past two slightly heated side-by-side circular cylinders are investigated employing the large eddy simulation (LES). Simulations are performed using a commercial CFD software, FLUENT. The Smagorinsky-Lilly subgrid-scale model is employed for the large eddy simulation. The Reynolds number based on free-stream velocity and cylinder diameter is 5 800, which is in the subcritical regime. The transverse pitch ratio T/D = 3 is investigated. Laminar boundary layer, transition in shear layer, flow separation, large vortex structures and flow interference in the wake are all involved in the flow. Such complex flow features make the current study a challenging task. Both flow field and temperature field are investigated. The calculated results are analyzed and compared with experimental data. The simulation results are qualitatively in accordance with experimental observations. Two anti-phase vortex streets are obtained by the large-eddy simulation, which agrees with the experimental observation. At this transverse pitch ratio, these two cylinders behave as independent, isolated single cylinder in cross flow. The time-averaged streamwise velocity and temperature at x/D=10 are in good agreement with the experimental data. Figure1 displays the instantaneous spanwise vorticity at the center plane.

New turbidity current model based on high-resolution monitoring of the longest flow ever measured

NASA Astrophysics Data System (ADS)

Azpiroz, Maria; Cartigny, Matthieu; Talling, Peter; Parsons, Daniel; Simmons, Steve; Clare, Michael; Sumner, Esther; Pope, Ed

2016-04-01

Turbidity currents transport large amounts of sediment from shallow waters towards deep ocean basins. Little is known about these flows, despite their potential hazard for damaging expensive and strategically important seafloor infrastructure. So far turbidity currents have been profiled in only 6 deep ocean locations worldwide. Our current knowledge of these flows is therefore mainly based on scaled-down experimental and computationally-limited numerical modelling. Here we present results from the monitoring of a one-week long turbidity current in the Congo Canyon that had a discharge close to that of the Mississippi River. Measurements taken every 5 seconds give the most detailed image yet of a turbidity current deep-water over an unprecedented duration. Our analysis reveals a different flow structure than that presented in previous models. Classical models display a thick front of the flow followed by a thinner and faster flow, which gives way to a short and quasi-steady body. Instead, we observe a thin frontal cell that outruns a thicker (~80 m), long and slower quasi-steady flow. In contrast to the previous model, where the thinner faster flow feeds sediment into the head, the Congo Canyon turbidity current shows a frontal cell that feeds sediment into, and at the same time outruns, the succeeding quasi-steady flow. As a result of the faster moving frontal cell, the flow should continuously stretch and grow in length while propagating down the system. Within the quasi-steady body, the flow switches between what appears to be two stable flow modes. One mode exhibits a fast and thin velocity profile whose maximum is a low distance from the seabed and resembles Froude-supercritical flow conditions, while the other mode is similar to Froude-subcritical flow conditions as the flow is thicker and slower. These first observations provide new insights into the behaviour of deep water long duration flows that differ from traditional models and provide an exciting chance to explore the full range of turbidity current behaviour in nature.

Coupled Model for CO2 Leaks from Geological Storage: Geomechanics, Fluid Flow and Phase Transitions

NASA Astrophysics Data System (ADS)

Gor, G.; Prevost, J.

2013-12-01

Deep saline aquifers are considered as a promising option for long-term storage of carbon dioxide. However, risk of CO2 leakage from the aquifers through faults, natural or induced fractures or abandoned wells cannot be disregarded. Therefore, modeling of various leakage scenarios is crucial when selecting a site for CO2 sequestration and choosing proper operational conditions. Carbon dioxide is injected into wells at supercritical conditions (t > 31.04 C, P > 73.82 bar), and these conditions are maintained in the deep aquifers (at 1-2 km depth) due to hydrostatic pressure and geothermal gradient. However, if CO2 and brine start to migrate from the aquifer upward, both pressure and temperature will decrease, and at the depth of 500-750 m, the conditions for CO2 will become subcritical. At subcritical conditions, CO2 starts boiling and the character of the flow changes dramatically due to appearance of the third (vapor) phase and latent heat effects. When modeling CO2 leaks, one needs to couple the multiphase flow in porous media with geomechanics. These capabilities are provided by Dynaflow, a finite element analysis program [1]; Dynaflow has already showed to be efficient for modeling caprock failure causing CO2 leaks [2, 3]. Currently we have extended the capabilities of Dynaflow with the phase transition module, based on two-phase and three-phase isenthalpic flash calculations [4]. We have also developed and implemented an efficient method for solving heat and mass transport with the phase transition using our flash module. Therefore, we have developed a robust tool for modeling CO2 leaks. In the talk we will give a brief overview of our method and illustrate it with the results of simulations for characteristic test cases. References: [1] J.H. Prevost, DYNAFLOW: A Nonlinear Transient Finite Element Analysis Program. Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ. http://www.princeton.edu/~dynaflow/ (last update 2013), 1981. [2] M. Preisig, J.H. Prevost, Coupled multi-phase thermo-poromechanical effects. Case study: CO2 injection at In Salah, Algeria, International Journal of Greenhouse Gas Control, 5 (2011) 1055-1064. [3] G.Y. Gor, T.R. Elliot, J.H. Prevost, Effects of thermal stresses on caprock integrity during CO2 storage, International Journal of Greenhouse Gas Control, 12 (2013) 300-309. [4] M.L. Michelsen, J.M. Mollerup, Thermodynamic Models: Fundamentals and Computational Aspects. 2nd Edition, Tie-Line Publications, 2007.

Major safety and operational concerns for fuel debris criticality control

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

Tonoike, K.; Sono, H.; Umeda, M.

2013-07-01

It can be seen from the criticality control viewpoint that the requirement divides the decommissioning work into two parts. One is the present condition where it is requested to prevent criticality and to monitor subcritical condition while the debris is untouched. The other is future work where the subcritical condition shall be ensured even if the debris condition is changed intentionally by raising water level, debris retrieval, etc. Repair of damages on the containment vessel (CV) walls is one of the most important objectives at present in the site. On completion of this task, it will become possible to raisemore » water levels in the CVs and to shield the extremely high radiation emitted from the debris but there is a dilemma: raising the water level in the CVs implies to bring the debris closer to criticality because of the role of water for slowing down neutrons. This may be solved if the coolant water will start circulating in closed loops, and if a sufficient concentration of soluble neutron poison (borated water for instance) will be introduced in the loop. It should be still noted that this solution has a risk of worsening corrosion of the CV walls. Design of the retrieval operation of debris should be proposed as early as possible, which must include a neutron poison concentration required to ensure that the debris chunk is subcritical. In parallel, the development of the measurement system to monitor subcritical condition of the debris chunk should be conducted in case the borated water cannot be used continuously. The system would be based on a neutron counter with a high sensitivity and an appropriate shield for gamma-rays, and the adequate statistical signal processing.« less

Internal hydrogen-induced subcritical crack growth in austenitic stainless steels

NASA Astrophysics Data System (ADS)

Huang, J. H.; Altstetter, C. J.

1991-11-01

The effects of small amounts of dissolved hydrogen on crack propagation were determined for two austenitic stainless steel alloys, AISI 301 and 310S. In order to have a uniform distribution of hydrogen in the alloys, they were cathodically charged at high temperature in a molten salt electrolyte. Sustained load tests were performed on fatigue precracked specimens in air at 0 ‡C, 25 ‡C, and 50 ‡C with hydrogen contents up to 41 wt ppm. The electrical potential drop method with optical calibration was used to continuously monitor the crack position. Log crack velocity vs stress intensity curves had definite thresholds for subcritical crack growth (SCG), but stage II was not always clearly delineated. In the unstable austenitic steel, AISI 301, the threshold stress intensity decreased with increasing hydrogen content or increasing temperature, but beyond about 10 wt ppm, it became insensitive to hydrogen concentration. At higher concentrations, stage II became less distinct. In the stable stainless steel, subcritical crack growth was observed only for a specimen containing 41 wt ppm hydrogen. Fractographic features were correlated with stress intensity, hydrogen content, and temperature. The fracture mode changed with temperature and hydrogen content. For unstable austenitic steel, low temperature and high hydrogen content favored intergranular fracture while microvoid coalescence dominated at a low hydrogen content. The interpretation of these phenomena is based on the tendency for stress-induced phase transformation, the different hydrogen diffusivity and solubility in ferrite and austenite, and outgassing from the crack tip. After comparing the embrittlement due to internal hydrogen with that in external hydrogen, it is concluded that the critical hydrogen distribution for the onset of subcritical crack growth is reached at a location that is very near the crack tip.

Subcritical and supercritical technology for the production of second generation bioethanol.

PubMed

Rostagno, Mauricio A; Prado, Juliana M; Mudhoo, Ackmez; Santos, Diego T; Forster-Carneiro, Tânia; Meireles, M Angela A

2015-01-01

There is increased interest in reducing our reliance on fossil fuels and increasing the share of renewable raw materials in our energy supply chain due to environmental and economic concerns. Ethanol is emerging as a potential alternative to liquid fuels due to its eco-friendly characteristics and relatively low production costs. As ethanol is currently produced from commodities also used for human and animal consumption, there is an urgent need of identifying renewable raw materials that do not pose a competitive problem. Lignocellulosic agricultural residues are an ideal choice since they can be effectively hydrolyzed to fermentable sugars and integrated in the context of a biorefinery without competing with the food supply chain. However, the conventional hydrolysis methods still have major issues that need to be addressed. These issues are related to the processing rate and generation of fermentation inhibitors, which can compromise the quality of the product and the cost of the process. As the knowledge of the processes taking place during hydrolysis of agricultural residues is increasing, new techniques are being exploited to overcome these drawbacks. This review gives an overview of the state-of-the-art of hydrolysis with subcritical and supercritical water in the context of reusing agricultural residues for the production of suitable substrates to be processed during the fermentative production of bioethanol. Presently, subcritical and/or supercritical water hydrolysis has been found to yield low sugar contents mainly due to concurrent competing degradation of sugars during the hydrothermal processes. In this line of thinking, the present review also revisits the recent applications and advances to provide an insight of future research trends to optimize on the subcritical and supercritical process kinetics.

An Assessment of the Detection of Highly Enriched Uranium and its Use in an Improvised Nuclear Device using the Monte Carlo Computer Code MCNP-5

NASA Astrophysics Data System (ADS)

Cochran, Thomas

2007-04-01

In 2002 and again in 2003, an investigative journalist unit at ABC News transported a 6.8 kilogram metallic slug of depleted uranium (DU) via shipping container from Istanbul, Turkey to Brooklyn, NY and from Jakarta, Indonesia to Long Beach, CA. Targeted inspection of these shipping containers by Department of Homeland Security (DHS) personnel, included the use of gamma-ray imaging, portal monitors and hand-held radiation detectors, did not uncover the hidden DU. Monte Carlo analysis of the gamma-ray intensity and spectrum of a DU slug and one consisting of highly-enriched uranium (HEU) showed that DU was a proper surrogate for testing the ability of DHS to detect the illicit transport of HEU. Our analysis using MCNP-5 illustrated the ease of fully shielding an HEU sample to avoid detection. The assembly of an Improvised Nuclear Device (IND) -- a crude atomic bomb -- from sub-critical pieces of HEU metal was then examined via Monte Carlo criticality calculations. Nuclear explosive yields of such an IND as a function of the speed of assembly of the sub-critical HEU components were derived. A comparison was made between the more rapid assembly of sub-critical pieces of HEU in the ``Little Boy'' (Hiroshima) weapon's gun barrel and gravity assembly (i.e., dropping one sub-critical piece of HEU on another from a specified height). Based on the difficulty of detection of HEU and the straightforward construction of an IND utilizing HEU, current U.S. government policy must be modified to more urgently prioritize elimination of and securing the global inventories of HEU.

Catalyst-free ethyl biodiesel production from rice bran under subcritical condition

NASA Astrophysics Data System (ADS)

Zullaikah, Siti; Afifudin, Riza; Amalia, Rizky

2015-12-01

In-situ ethyl biodiesel production from rice bran under subcritical water and ethanol with no catalyst was employed. This process is environmentally friendly and is very flexible in term of feedstock utilization since it can handle relatively high moisture and free fatty acids (FFAs) contents. In addition, the alcohol, i.e. bioethanol, is a non-toxic, biodegradable, and green raw material when produced from non-edible biomass residues, leading to a 100% renewable biodiesel. The fatty acid ethyl esters (FAEEs, ethyl biodiesel) are better than fatty acid methyl esters (FAMEs, methyl biodiesel) in terms of fuel properties, including cetane number, oxidation stability and cold flow properties. The influences of the operating variables such as reaction time (1 - 10 h), ethanol concentration (12.5 - 87.5%), and pressurizing gas (N2 and CO2) on the ethyl biodiesel yield and purity have been investigated systematically while the temperature and pressure were kept constant at 200 °C and 40 bar. The optimum results were obtained at 5 h reaction time and 75% ethanol concentration using CO2 as compressing gas. Ethyl biodiesel yield and purity of 58.78% and 61.35%, respectively, were obtained using rice bran with initial FFAs content of 37.64%. FFAs level was reduced to 14.22% with crude ethyl biodiesel recovery of 95.98%. Increasing the reaction time up to 10 h only increased the yield and purity by only about 3%. Under N2 atmosphere and at the same operating conditions (5h and 75% ethanol), ethyl biodiesel yield and purity decreased to 54.63% and 58.07%, respectively, while FFAs level was increased to 17.93% and crude ethyl biodiesel recovery decreased to 87.32%.

Concept of turbines for ultrasupercritical, supercritical, and subcritical steam conditions

NASA Astrophysics Data System (ADS)

Mikhailov, V. E.; Khomenok, L. A.; Pichugin, I. I.; Kovalev, I. A.; Bozhko, V. V.; Vladimirskii, O. A.; Zaitsev, I. V.; Kachuriner, Yu. Ya.; Nosovitskii, I. A.; Orlik, V. G.

2017-11-01

The article describes the design features of condensing turbines for ultrasupercritical initial steam conditions (USSC) and large-capacity cogeneration turbines for super- and subcritical steam conditions having increased steam extractions for district heating purposes. For improving the efficiency and reliability indicators of USSC turbines, it is proposed to use forced cooling of the head high-temperature thermally stressed parts of the high- and intermediate-pressure rotors, reaction-type blades of the high-pressure cylinder (HPC) and at least the first stages of the intermediate-pressure cylinder (IPC), the double-wall HPC casing with narrow flanges of its horizontal joints, a rigid HPC rotor, an extended system of regenerative steam extractions without using extractions from the HPC flow path, and the low-pressure cylinder's inner casing moving in accordance with the IPC thermal expansions. For cogeneration turbines, it is proposed to shift the upper district heating extraction (or its significant part) to the feedwater pump turbine, which will make it possible to improve the turbine plant efficiency and arrange both district heating extractions in the IPC. In addition, in the case of using a disengaging coupling or precision conical bolts in the coupling, this solution will make it possible to disconnect the LPC in shifting the turbine to operate in the cogeneration mode. The article points out the need to intensify turbine development efforts with the use of modern methods for improving their efficiency and reliability involving, in particular, the use of relatively short 3D blades, last stages fitted with longer rotor blades, evaporation techniques for removing moisture in the last-stage diaphragm, and LPC rotor blades with radial grooves on their leading edges.

Magnetorotational dynamo chimeras. The missing link to turbulent accretion disk dynamo models?

NASA Astrophysics Data System (ADS)

Riols, A.; Rincon, F.; Cossu, C.; Lesur, G.; Ogilvie, G. I.; Longaretti, P.-Y.

2017-02-01

In Keplerian accretion disks, turbulence and magnetic fields may be jointly excited through a subcritical dynamo mechanisminvolving magnetorotational instability (MRI). This dynamo may notably contribute to explaining the time-variability of various accreting systems, as high-resolution simulations of MRI dynamo turbulence exhibit statistical self-organization into large-scale cyclic dynamics. However, understanding the physics underlying these statistical states and assessing their exact astrophysical relevance is theoretically challenging. The study of simple periodic nonlinear MRI dynamo solutions has recently proven useful in this respect, and has highlighted the role of turbulent magnetic diffusion in the seeming impossibility of a dynamo at low magnetic Prandtl number (Pm), a common regime in disks. Arguably though, these simple laminar structures may not be fully representative of the complex, statistically self-organized states expected in astrophysical regimes. Here, we aim at closing this seeming discrepancy by reporting the numerical discovery of exactly periodic, yet semi-statistical "chimeral MRI dynamo states" which are the organized outcome of a succession of MRI-unstable, non-axisymmetric dynamical stages of different forms and amplitudes. Interestingly, these states, while reminiscent of the statistical complexity of turbulent simulations, involve the same physical principles as simpler laminar cycles, and their analysis further confirms the theory that subcritical turbulent magnetic diffusion impedes the sustainment of an MRI dynamo at low Pm. Overall, chimera dynamo cycles therefore offer an unprecedented dual physical and statistical perspective on dynamos in rotating shear flows, which may prove useful in devising more accurate, yet intuitive mean-field models of time-dependent turbulent disk dynamos. Movies associated to Fig. 1 are available at http://www.aanda.org

Ductile flow by water-assisted cataclasis

NASA Astrophysics Data System (ADS)

den Brok, Bas

2003-04-01

In the presence of water otherwise brittle materials may deform macroscopically ductile by water-assisted cataclastic creep. This is possible as long as (i) solubility is high enough, so that stress-corrosion can occur, and (ii) local stress is low enough, to that fracturing remains subcritical. Water-assisted cataclastic creep (WACC) may play an important role in the middle and lower continental crust where mineral solubilities are high and stresses low. WACC is a poorly understood deformation process. Experiments were performed on very soluble brittle salts (Na-chlorate; K-alum) to study microstructure development by WACC. The experiments were carried out at room temperature and atmospheric pressure in a small see-through vessel. In this way the cataclastic deformation process could be studied "in-situ" under the microscope. Crystals were loaded in the presence of saturated salt solution. It appeared that originally straight mineral surfaces were instable when kept under stress. Grooves (or channels) slowly developed in the surface by local dissolution. These grooves behave like so-called Grinfeld instabilities. They develop because the energy of a grooved surface under stress is lower than the energy of a straight surface under stress. The grooves may deepen and turn into subcritical cracks when local stress further increases. These cracks propagate slowly. They propagate parallel to sigma1 but also at an angle and even perpendicular to sigma1, often following crystallographically controlled directions. The fractures mostly change direction while propagating, locally making turns of more than 180 degrees. Irregular fracture fragments thus develop. The fractures may migrate sideways (as with grain bounday migration) probably by solution-redeposition driven by differences in stress between both sides of the fracture. Thus the shape of the fragments changes. The size of the fracture fragments seems to be controlled by the distance of the grooves, which decreases with increasing stress.

Strong cation exchange-type chiral stationary phase for enantioseparation of chiral amines in subcritical fluid chromatography.

PubMed

Wolrab, Denise; Kohout, Michal; Boras, Mario; Lindner, Wolfgang

2013-05-10

A new strong cation exchange type chiral stationary phase (SCX CSP) based on a syringic acid amide derivative of trans-(R, R)-2-aminocyclohexanesulfonic acid was applied to subcritical fluid chromatography (SFC) for separation of various chiral basic drugs and their analogues. Mobile phase systems consisting of aliphatic alcohols as polar modifiers and a broad range of amines with different substitution patterns and lipophilicity were employed to evaluate the impact on the SFC retention and selectivity characteristics. The observed results point to the existence of carbonic and carbamic acid salts formed as a consequence of reactions occurring between carbon dioxide, the alcoholic modifiers and the amine species present in the sub/supercritical fluid medium, respectively. Evidence is provided that these species are essential for affecting ion exchange between the strongly acidic chiral selector units and the basic analytes, following the well-established stoichiometric displacement mechanisms. Specific trends were observed when different types of amines were used as basic additives. While ammonia gave rise to the formation of the most strongly eluting carbonic and carbamic salt species, simple tertiary amines consistently provided superior levels of enantioselectivity. Furthermore, trends in the chiral SFC separation characteristics were investigated by the systematic variation of the modifier content and temperature. Different effects of additives are interpreted in terms of changes in the relative concentration of the transient ionic species contributing to analyte elution, with ammonia-derived carbamic salts being depleted at elevated temperatures by decomposition. Additionally, in an effort to optimize SFC enantiomer separation conditions for selected analytes, the impact of the type of the organic modifier, temperature, flow rate and active back pressure were also investigated. Copyright © 2013 Elsevier B.V. All rights reserved.

Gravitational effects on global hemodynamics in different postures: A closed-loop multiscale mathematical analysis

NASA Astrophysics Data System (ADS)

Zhang, Xiancheng; Noda, Shigeho; Himeno, Ryutaro; Liu, Hao

2017-06-01

We present a novel methodology and strategy to predict pressures and flow rates in the global cardiovascular network in different postures varying from supine to upright. A closed-loop, multiscale mathematical model of the entire cardiovascular system (CVS) is developed through an integration of one-dimensional (1D) modeling of the large systemic arteries and veins, and zero-dimensional (0D) lumped-parameter modeling of the heart, the cardiac-pulmonary circulation, the cardiac and venous valves, as well as the microcirculation. A versatile junction model is proposed and incorporated into the 1D model to cope with splitting and/or merging flows across a multibranched junction, which is validated to be capable of estimating both subcritical and supercritical flows while ensuring the mass conservation and total pressure continuity. To model gravitational effects on global hemodynamics during postural change, a robust venous valve model is further established for the 1D venous flows and distributed throughout the entire venous network with consideration of its anatomically realistic numbers and locations. The present integrated model is proven to enable reasonable prediction of pressure and flow rate waveforms associated with cardiopulmonary circulation, systemic circulation in arteries and veins, as well as microcirculation within normal physiological ranges, particularly in mean venous pressures, which well match the in vivo measurements. Applications of the cardiovascular model at different postures demonstrate that gravity exerts remarkable influence on arterial and venous pressures, venous returns and cardiac outputs whereas venous pressures below the heart level show a specific correlation between central venous and hydrostatic pressures in right atrium and veins.

Water velocity and the nature of critical flow in large rapids on the Colorado River, Utah

USGS Publications Warehouse

Magirl, Christopher S.; Gartner, Jeffrey W.; Smart, Graeme M.; Webb, Robert H.

2009-01-01

Rapids are an integral part of bedrock‐controlled rivers, influencing aquatic ecology, geomorphology, and recreational value. Flow measurements in rapids and high‐gradient rivers are uncommon because of technical difficulties associated with positioning and operating sufficiently robust instruments. In the current study, detailed velocity, water surface, and bathymetric data were collected within rapids on the Colorado River in eastern Utah. With the water surface survey, it was found that shoreline‐based water surface surveys may misrepresent the water surface slope along the centerline of a rapid. Flow velocities were measured with an ADCP and an electronic pitot‐static tube. Integrating multiple measurements, the ADCP returned velocity data from the entire water column, even in sections of high water velocity. The maximum mean velocity measured with the ADCP was 3.7 m/s. The pitot‐static tube, while capable of only point measurements, quantified velocity 0.39 m below the surface. The maximum mean velocity measured with the pitot tube was 5.2 m/s, with instantaneous velocities up to 6.5 m/s. Analysis of the data showed that flow was subcritical throughout all measured rapids with a maximum measured Froude number of 0.7 in the largest measured rapids. Froude numbers were highest at the entrance of a given rapid, then decreased below the first breaking waves. In the absence of detailed bathymetric and velocity data, the Froude number in the fastest‐flowing section of a rapid was estimated from near‐surface velocity and depth soundings alone.

Inward-Turning Streamline-Traced Inlet Design Method for Low-Boom, Low-Drag Applications

NASA Technical Reports Server (NTRS)

Otto, Samuel; Trefny, Charles J.; Slater, John W.

2015-01-01

A new design method for inward-turning, streamline-traced inlets is presented. Resulting designs are intended for moderate supersonic, low-drag, low-boom applications such as that required for NASA's proposed low-boom flight demonstration aircraft. A critical feature of these designs is the internal cowl lip angle that allows for little or no flow turning on the outer nacelle. Present methods using conical-flow Busemann parent flowfields have simply truncated, or otherwise modified the stream-traced contours to include this internal cowl angle. Such modifications disrupt the parent flowfield, reducing inlet performance and flow uniformity. The method presented herein merges a conical flowfield that includes a leading shock with a truncated Busemann flowfield in a manner that minimizes unwanted interactions. A leading internal cowl angle is now inherent in the parent flowfield, and inlet contours traced from this flowfield retain its high performance and good flow uniformity. CFD analysis of a candidate inlet design is presented that verifies the design technique, and reveals a starting issue with the basic geometry. A minor modification to the cowl lip region is shown to eliminate this phenomenon, thereby allowing starting and smooth transition to sub-critical operation as back-pressure is increased. An inlet critical-point total pressure recovery of 96 is achieved based on CFD results for a Mach 1.7 freestream design. Correction for boundary-layer displacement thickness, and sizing for a given engine airflow requirement are also discussed.

Spatially Developing Secondary Instabilities and Attachment Line Instability in Supersonic Boundary Layers

NASA Technical Reports Server (NTRS)

Li, Fei; Choudhari, Meelan M.

2008-01-01

This paper reports on progress towards developing a spatial stability code for compressible shear flows with two inhomogeneous directions, such as crossflow dominated swept-wing boundary layers and attachment line flows. Certain unique aspects of formulating a spatial, two-dimensional eigenvalue problem for the secondary instability of finite amplitude crossflow vortices are discussed. A primary test case used for parameter study corresponds to the low-speed, NLF-0415(b) airfoil configuration as tested in the ASU Unsteady Wind Tunnel, wherein a spanwise periodic array of roughness elements was placed near the leading edge in order to excite stationary crossflow modes with a specified fundamental wavelength. The two classes of flow conditions selected for this analysis include those for which the roughness array spacing corresponds to either the naturally dominant crossflow wavelength, or a subcritical wavelength that serves to reduce the growth of the naturally excited dominant crossflow modes. Numerical predictions are compared with the measured database, both as indirect validation for the spatial instability analysis and to provide a basis for comparison with a higher Reynolds number, supersonic swept-wing configuration. Application of the eigenvalue analysis to the supersonic configuration reveals that a broad spectrum of stationary crossflow modes can sustain sufficiently strong secondary instabilities as to potentially cause transition over this configuration. Implications of this finding for transition control in swept wing boundary layers are examined. Finally, extension of the spatial stability analysis to supersonic attachment line flows is also considered.

Numerical simulations of katabatic jumps in coats land, Antartica

NASA Astrophysics Data System (ADS)

Yu, Ye; Cai, Xiaoming; King, John C.; Renfrew, Ian A.

A non-hydrostatic numerical model, the Regional Atmospheric Modeling System (RAMS), has been used to investigate the development of katabatic jumps in Coats Land, Antarctica. In the control run with a 5 m s-1downslope directed initial wind, a katabatic jump develops near the foot of the idealized slope. The jump is manifested as a rapid deceleration of the downslope flow and a change from supercritical to subcritical flow, in a hydraulic sense, i.e., the Froude number (Fr) of the flow changes from Fr > 1 to Fr> 1. Results from sensitivity experiments show that an increase in the upstream flow rate strengthens the jump, while an increase in the downstream inversion-layer depth results in a retreat of the jump. Hydraulic theory and Bernoulli''s theorem have been used to explain the surface pressure change across the jump. It is found that hydraulic theory always underestimates the surface pressure change, while Bernoulli''s theorem provides a satisfactory estimation. An analysis of the downs balance for the katabatic jump indicates that the important forces are those related to the pressure gradient, advection and, to a lesser extent, the turbulent momentum divergence. The development of katabatic jumps can be divided into two phases. In phase I, the t gradient force is nearly balanced by advection, while in phase II, the pressure gradient force is counterbalanced by turbulent momentum divergence. The upslope pressure gradient force associated with a pool of cold air over the ice shelf facilitates the formation of the katabatic jump.

An analytic solution for periodic thermally-driven flows over an infinite slope

NASA Astrophysics Data System (ADS)

Zardi, Dino; Serafin, Stefano

2013-04-01

The flow generated along an infinite slope in an unperturbed stably stratified atmosphere at rest by a time periodic surface temperature forcing is examined. Following Defant (1949), a set of equations is derived which extends Prandtl's (1942) theory to allow for nonstationary conditions. Uniform boundary conditions are conducive to an along-slope parallel flow, governed by a periodically reversing local imbalance between along-slope advection and slope-normal fluxes of momentum and heat. Solutions include both a transient part and a subsequent periodic regime. The former can only be expressed in an integral form, whereas the latter is a combination of exponential and sine or cosine functions of time and height normal to the slope. Key parameters are the quantity Nα = N sinα (where α is the slope angle, and N is the Brunt-Väisälä frequency of the unperturbed atmosphere) and the angular frequency of the driving surface temperature cycle, ?. Three different flow regimes may occur, namely subcritical (Nα < ?), critical (Nα = ?) and supercritical (Nα > ?). The properties of the solutions in each regime are examined and discussed. The relationship between the present solutions and the earlier time-dependent slope flow model by Defant (1949) is also discussed. References Defant, F., 1949: Zur Theorie der Hangwinde, nebst Bemerkungen zur Theorie der Berg- und Talwinde. [A theory of slope winds, along with remarks on the theory of mountain winds and valley winds]. Arch. Meteor. Geophys. Bioclimatol., Ser. A, 1, 421-450 (Theoretical and Applied Climatology). [English translation: Whiteman, C.D., and E. Dreiseitl, 1984: Alpine meteorology: Translations of classic contributions by A. Wagner, E. Ekhart and F. Defant. PNL-5141 / ASCOT-84-3. Pacific Northwest Laboratory, Richland, Washington, 121 pp]. Prandtl, L., 1942: Strömungslehre [Flow Studies]. Vieweg und Sohn, Braunschweig, 382 pp.

Kinematic dynamo action in a network of screw motions; application to the core of a fast breeder reactor

NASA Astrophysics Data System (ADS)

Plunian, F.; Marty, P.; Alemany, A.

1999-03-01

Most of the studies concerning the dynamo effect are motivated by astrophysical and geophysical applications. The dynamo effect is also the subject of some experimental studies in fast breeder reactors (FBR) for they contain liquid sodium in motion with magnetic Reynolds numbers larger than unity. In this paper, we are concerned with the flow of sodium inside the core of an FBR, characterized by a strong helicity. The sodium in the core flows through a network of vertical cylinders. In each cylinder assembly, the flow can be approximated by a smooth upwards helical motion with no-slip conditions at the boundary. As the core contains a large number of assemblies, the global flow is considered to be two-dimensionally periodic. We investigate the self-excitation of a two-dimensionally periodic magnetic field using an instability analysis of the induction equation which leads to an eigenvalue problem. Advantage is taken of the flow symmetries to reduce the size of the problem. The growth rate of the magnetic field is found as a function of the flow pitch, the magnetic Reynolds number (Rm) and the vertical magnetic wavenumber (k). An [alpha]-effect is shown to operate for moderate values of Rm, supporting a mean magnetic field. The large-Rm limit is investigated numerically. It is found that [alpha]=O(Rm[minus sign]2/3), which can be explained through appropriate dynamo mechanisms. Either a smooth Ponomarenko or a Roberts type of dynamo is operating in each periodic cell, depending on k. The standard power regime of an industrial FPBR is found to be subcritical.

Fine-scale hydrodynamics influence the spatio-temporal distribution of harbour porpoises at a coastal hotspot

NASA Astrophysics Data System (ADS)

Jones, A. R.; Hosegood, P.; Wynn, R. B.; De Boer, M. N.; Butler-Cowdry, S.; Embling, C. B.

2014-11-01

The coastal Runnelstone Reef, off southwest Cornwall (UK), is characterised by complex topography and strong tidal flows and is a known high-density site for harbour porpoise (Phocoena phocoena); a European protected species. Using a multidisciplinary dataset including: porpoise sightings from a multi-year land-based survey, Acoustic Doppler Current Profiling (ADCP), vertical profiling of water properties and high-resolution bathymetry; we investigate how interactions between tidal flow and topography drive the fine-scale porpoise spatio-temporal distribution at the site. Porpoise sightings were distributed non-uniformly within the survey area with highest sighting density recorded in areas with steep slopes and moderate depths. Greater numbers of sightings were recorded during strong westward (ebbing) tidal flows compared to strong eastward (flooding) flows and slack water periods. ADCP and Conductivity Temperature Depth (CTD) data identified fine-scale hydrodynamic features, associated with cross-reef tidal flows in the sections of the survey area with the highest recorded densities of porpoises. We observed layered, vertically sheared flows that were susceptible to the generation of turbulence by shear instability. Additionally, the intense, oscillatory near surface currents led to hydraulically controlled flow that transitioned from subcritical to supercritical conditions; indicating that highly turbulent and energetic hydraulic jumps were generated along the eastern and western slopes of the reef. The depression and release of isopycnals in the lee of the reef during cross-reef flows revealed that the flow released lee waves during upslope currents at specific phases of the tidal cycle when the highest sighting rates were recorded. The results of this unique, fine-scale field study provide new insights into specific hydrodynamic features, produced through tidal forcing, that may be important for creating predictable foraging opportunities for porpoises at a local scale. Information on the functional mechanisms linking porpoise distribution to static and dynamic physical habitat variables is extremely valuable to the monitoring and management of the species within the context of European conservation policies and marine renewable energy infrastructure development.

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

Klein, Steven Karl; Determan, John C.

Dynamic System Simulation (DSS) models of fissile solution systems have been developed and verified against a variety of historical configurations. DSS techniques have been applied specifically to subcritical accelerator-driven systems using fissile solution fuels of uranium. Initial DSS models were developed in DESIRE, a specialized simulation scripting language. In order to tailor the DSS models to specifically meet needs of system designers they were converted to a Visual Studio implementation, and one of these subsequently to National Instrument’s LabVIEW for human factors engineering and operator training. Specific operational characteristics of subcritical accelerator-driven systems have been examined using a DSS modelmore » tailored to this particular class using fissile fuel.« less

Properties of extracts from defatted rice bran by its subcritical water treatment.

PubMed

Wiboonsirikul, Jintana; Kimura, Yukitaka; Kadota, Megumi; Morita, Hisahiro; Tsuno, Takuo; Adachi, Shuji

2007-10-17

Defatted rice bran was extracted with water and subcritical water at 50-250 degrees C for 5 min. The highest extract yield was achieved at 200 degrees C, at which the maximum amounts of protein and carbohydrate were also obtained. The total phenolic and furfural contents, radical scavenging activity, and antioxidative activity for the autoxidation of linoleic acid increased with increasing treatment temperature. The bran extracts exhibited emulsifying activity except for the extract prepared at 250 degrees C, which was concomitant with the disappearance of its high-molecular-mass substances. The extract prepared at 200 degrees C also had the highest emulsion-stabilizing activity.

Metal elution from Ni- and Fe-based alloy reactors under hydrothermal conditions.

PubMed

Faisal, Muhammad; Quitain, Armando T; Urano, Shin-Ya; Daimon, Hiroyuki; Fujie, Koichi

2004-05-20

Elution of metals from Ni- and Fe-based alloy (i.e. Inconel 625 and SUS 316) under hydrothermal conditions was investigated. Results showed that metals could be eluted even in a short contact time. At subcritical conditions, a significant amount of Cr was extracted from SUS 316, while only traces of Ni, Fe, Mo, and Mn were eluted. In contrast, Ni was removed in significant amounts compared to Cr when Inconel 625 was tested. Several factors including temperature and contact time were found to affect elution behavior. The presence of air in the fluid even promoted elution under subcritical conditions.

Cryogenic Orbital Nitrogen Experiment (CONE): Phase A/B design study

NASA Technical Reports Server (NTRS)

Bailey, William J.; Weiner, Stephen P.; Beekman, Douglas H.

1991-01-01

Subcritical cryogenic fluid management (CFM) has long been recognized as an enabling technology for future space missions. Subcritical liquid storage and supply are two of the five CFM technology areas that need to be studied in the low gravity on-orbit environment. The Cryogenic Orbital Nitrogen Experiment (CONE) is a LN2 cryogenic storage and supply system demonstration placed in orbit by the National Space Transportation System (NSTS) Orbiter and operated as an in-bay payload. In-space demonstration of CFM using LN2 with a few well defined areas of focus would provide the confidence level required to implement subcritical cryogen use and is the first step towards the more far reaching issue of cryogen transfer and tankage resupply. A conceptual approach for CONE was developed and an overview of the program is described including the following: (1) a description of the background and scope of the technology objectives; (2) a description of the payload design and operation; and (3) the justification for CONE relating to potential near term benefits and risk mitigation for future systems. Data and criteria is provided to correlate in-space performance with analytical and numerical modeling of CFM systems.

Graphite Recycling from Spent Lithium-Ion Batteries.

PubMed

Rothermel, Sergej; Evertz, Marco; Kasnatscheew, Johannes; Qi, Xin; Grützke, Martin; Winter, Martin; Nowak, Sascha

2016-12-20

The present work reports on challenges in utilization of spent lithium-ion batteries (LIBs)-an increasingly important aspect associated with a significantly rising demand for electric vehicles (EVs). In this context, the feasibility of anode recycling in combination with three different electrolyte extraction concepts is investigated. The first method is based on a thermal treatment of graphite without electrolyte recovery. The second method additionally utilizes a subcritical carbon-dioxide (subcritical CO 2 )-assisted electrolyte extraction prior to thermal treatment. And the final investigated approach uses supercritical carbon dioxide (scCO 2 ) as extractant, subsequently followed by the thermal treatment. It is demonstrated that the best performance of recycled graphite anodes can be achieved when electrolyte extraction is performed using subcritical CO 2 . Comparative studies reveal that, in the best case, the electrochemical performance of recycled graphite exceeds the benchmark consisting of a newly synthesized graphite anode. As essential efforts towards electrolyte extraction and cathode recycling have been made in the past, the electrochemical behavior of recycled graphite, demonstrating the best performance, is investigated in combination with a recycled LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Subcritical crack growth in SiNx thin-film barriers studied by electro-mechanical two-point bending

NASA Astrophysics Data System (ADS)

Guan, Qingling; Laven, Jozua; Bouten, Piet C. P.; de With, Gijsbertus

2013-06-01

Mechanical failure resulting from subcritical crack growth in the SiNx inorganic barrier layer applied on a flexible multilayer structure was studied by an electro-mechanical two-point bending method. A 10 nm conducting tin-doped indium oxide layer was sputtered as an electrical probe to monitor the subcritical crack growth in the 150 nm dielectric SiNx layer carried by a polyethylene naphthalate substrate. In the electro-mechanical two-point bending test, dynamic and static loads were applied to investigate the crack propagation in the barrier layer. As consequence of using two loading modes, the characteristic failure strain and failure time could be determined. The failure probability distribution of strain and lifetime under each loading condition was described by Weibull statistics. In this study, results from the tests in dynamic and static loading modes were linked by a power law description to determine the critical failure over a range of conditions. The fatigue parameter n from the power law reduces greatly from 70 to 31 upon correcting for internal strain. The testing method and analysis tool as described in the paper can be used to understand the limit of thin-film barriers in terms of their mechanical properties.

Neutron noise measurements at the Delphi subcritical assembly

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

Szieberth, M.; Klujber, G.; Kloosterman, J. L.

2012-07-01

The paper presents the results and evaluations of a comprehensive set of neutron noise measurements on the Delphi subcritical assembly of the Delft Univ. of Technology. The measurements investigated the effect of different source distributions (inherent spontaneous fission and {sup 252}Cf) and the position of the detectors applied (both radially and vertically). The evaluation of the measured data has been performed by the variance-to-mean ratio (VTMR, Feynman-{alpha}), the autocorrelation (ACF, Rossi-{alpha}) and the cross-correlation (CCF) methods. The values obtained for the prompt decay constant show a strong bias, which depends both on the detector position and on the source distribution.more » This is due to the presence of higher modes in the system. It has been observed that the {alpha} value fitted is higher when the detector is close to the boundary of the core or to the {sup 252}Cf point-source. The higher alpha-modes have also been observed by fitting functions describing two alpha-modes. The successful set of measurement also provides a good basis for further theoretical investigations including the Monte Carlo simulation of the noise measurements and the calculation of the alpha-modes in the Delphi subcritical assembly. (authors)« less

Theory and methods for measuring the effective multiplication constant in ADS

NASA Astrophysics Data System (ADS)

Rugama Saez, Yolanda

2001-10-01

In the thesis an absolute measurements technique for the subcriticality determination is presented. The ADS is a hybrid system where a subcritical system is fed by a proton accelerator. There are different proposals to define an ADS, one is to use plutonium and minor actinides from power plants waste as fuel to be transmuted into non radioactive isotopes (transmuter/burner, ATW). Another proposal is to use a Th232-U233 cycle (Energy Amplifier), being that thorium is an interesting and abundant fertile isotope. The development of accelerator driven systems (ADS) requires the development of methods to monitor and control the subcriticality of this kind of system without interfering with its normal operation mode. With this finality, we have applied noise analysis techniques that allow us to characterise the system when it is operating. The method presented in this thesis is based on the stochastic neutron and photon transport theory that can be implemented by presently available neutron/photon transport codes. In this work, first we analyse the stochastic transport theory which has been applied to define a parameter to determine the subcritical reactivity monitoring measurements. Finally we give the main limitations and recommendations for these subcritical monitoring methodology. As a result of the theoretical methodology, done in the first part of this thesis, a monitoring measurement technique has been developed and verified using two coupled Monte Carlo programs. The first one, LAHET, simulates the spallation collisions and the high energy transport and the other, MCNP-DSP, is used to estimate the counting statistics from a neutron/photon ray counter in a fissile system, as well as the transport for neutron with energies less than 20 MeV. From the coupling of both codes we developed the LAHET/MCNP-DSP code which, has the capability to simulate the total process in the ADS from the proton interaction to the signal detector processing. In these simulations, we compute the cross power spectral densities between pairs of detectors located inside the system which, is defined as the measured parameter. From the comparison of the theoretical predictions with the Monte Carlo simulations, we obtain some practical and simple methods to determine the system multiplication constant. (Abstract shortened by UMI.)

Development of new critical fluid-based processing methods for nutraceuticals and natural products

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

King, J. W.

2004-01-01

The development of new supercritical fluid processing technology as applied to nutraceuticals and natural products is no longer confined to using just supercritical fluid extraction (SFE) and supercritical carbon dioxide (SC-CO{sub 2}). Recently reported advances have been focused on modifying natural products and improving functionality of an end product using newer experimental techniques and fluid phases. In this presentation four focus areas will be emphasized: (1) control of particle size/morphology and encapsulation of the nutraceutical ingredients, (2) the use of combinatorial methodology to optimize critical fluid processing, (3) application of sub-critical water as a complementary medium for processing natural products,more » and (4) an assessment of the current state of products and processing which use critical fluid to produce nutraceutical and natural products for the food and cosmetic marketplace. Application of the various particle fomiation processes conducted in the presence of critical fluid media, such as: CPF, SAS, DELOS, RESS, PGSS, and GAS, can be used to produce particles of small and uniform distribution, having unique morphologies, that facilitate rapid dissolution or sustained release of many nutraceutical ingredients. These substances have included: therapeutic spices, phystosterols, vitamins, phospholpids, and carotenoids. Accelerating the development of critical fluid processing has been the application of combinatorial methodology to optimize extraction, fractionation, and/or reactions in near-, SC-, or subcritical fluid media. This is frequently accomplished by using sequential or multichannel automated instrumentation that was originally designed for analytical purposes. Several examples will be provided of rapidly assessing the extraction of anthocyanins with sub-critical water and the SFE of natural products. However, differences do exist in conducting experiments on the above instrumentation vs. scaled-up continuous processes, which will be noted. Sub-critical water is finding increase use as an extraction/fractionation or reaction medium. The literature reports applications for the extraction spices, natural antioxidants (rosemary, anthocyanins, etc.), and herbal components (tea and coffee ingredients), Our studies and the literature provide adequate correlations of solute solubility in sub-critical water as well as models for the kinetics of extraction in this medium. Finally, the current state of critical fluid technology as applied to natural products and nutraceuticals will be assessed; noting specific processes, organizations, and products that exist.« less

A model for simulation of flow in singular and interconnected channels

USGS Publications Warehouse

Schaffranek, Raymond W.; Baltzer, R.A.; Goldberg, D.E.

1981-01-01

A one-dimensional numerical model is presented for simulating the unsteady flow in singular riverine or estuarine reaches and in networks of reaches composed of interconnected channels. The model is both general and flexible in that it can be used to simulate a wide range of flow conditions for various channel configurations. The channel geometry of the network to be modeled should be sufficiently simple so as to lend itself to characterization in one spatial dimension. The flow must be substantially homogenous in density, and hydrostatic pressure must prevail everywhere in the network channels. The slope of each channel bottom ought to be mild and reasonably constant over its length so that the flow remains subcritical. The model accommodates tributary inflows and diversions and includes the effects of wind shear on the water surface as a forcing function in the flow equations. Water-surface elevations and flow discharges are computed at channel junctions, as well as at specified intermediate locations within the network channels. The one-dimensional branch-network flow model uses a four-point, implicit, finite-difference approximation of the unsteady-flow equations. The flow equations are linearized over a time step, and branch transformations are formulated that describe the relationship between the unknowns at the end points of the channels. The resultant matrix of branch-transformation equations and required boundary-condition equations is solved by Gaussian elimination using maximum pivot strategy. Five example applications of the flow model are illustrated. The applications cover such diverse conditions as a singular upland river reach in which unsteady flow results from hydropower regulations, coastal rivers composed of sequentially connected reaches subject to unsteady tide-driven flow, and a multiply connected network of channels whose flow is principally governed by wind tides and seiches in adjoining lakes. The report includes a listing of the FORTRAN IV computer program and a description of the input data requirements. Model supporting programs for the processing and input of initial and boundary-value data are identified, various model output formats are illustrated, and instructions are given to permit the production of graphical output using the line printer, electromechanical pen plotters, cathode-ray-tube display units, or microfilm recorders.

Incompressible boundary-layer stability analysis of LFC experimental data for sub-critical Mach numbers. M.S. Thesis

NASA Technical Reports Server (NTRS)

Berry, S. A.

1986-01-01

An incompressible boundary-layer stability analysis of Laminar Flow Control (LFC) experimental data was completed and the results are presented. This analysis was undertaken for three reasons: to study laminar boundary-layer stability on a modern swept LFC airfoil; to calculate incompressible design limits of linear stability theory as applied to a modern airfoil at high subsonic speeds; and to verify the use of linear stability theory as a design tool. The experimental data were taken from the slotted LFC experiment recently completed in the NASA Langley 8-Foot Transonic Pressure Tunnel. Linear stability theory was applied and the results were compared with transition data to arrive at correlated n-factors. Results of the analysis showed that for the configuration and cases studied, Tollmien-Schlichting (TS) amplification was the dominating disturbance influencing transition. For these cases, incompressible linear stability theory correlated with an n-factor for TS waves of approximately 10 at transition. The n-factor method correlated rather consistently to this value despite a number of non-ideal conditions which indicates the method is useful as a design tool for advanced laminar flow airfoils.

Elasto-inertial turbulence in straight pipes at low Reynolds numbers

NASA Astrophysics Data System (ADS)

Choueiri, George; Hof, Björn

2017-11-01

An early point of contention in the study of polymer drag reduction had been whether polymers delay transition to turbulence or cause it to occur at earlier Reynolds numbers (Re). Recent results have shown that at low polymer concentrations, the subcritical transition to Newtonian type turbulence (NTT) is delayed; however at higher concentrations an elastic instability is encountered which results in a distinct flow state dubbed elasto-inertial turbulence (EIT). Here transition is continuous, fluctuation and friction levels are considerably lower than those for NTT and flow structures are qualitatively different. Several factors can influence the necessary Re for transition to occur for a specific polymer concentration; these include the type of polymer, its molecular weight, the solution viscosity and the proximity of the wall boundaries. By controlling these factors, we have found that chaotic motions can be measured at Re of the order of 1 even in straight smooth pipes as opposed to curved microchannels where curved streamlines cause a purely elastic instability. Furthermore we found that low-Re EIT is closely connected to turbulence that exists on the maximum drag reduction asymptote for polymer solutions with Re several orders of magnitude higher.

Method for the prediction of the installation aerodynamics of a propfan at subsonic speeds: User manual

NASA Technical Reports Server (NTRS)

Chandrasekaran, B.

1986-01-01

This document is the user's guide for the method developed earlier for predicting the slipstream wing interaction at subsonic speeds. The analysis involves a subsonic panel code (HESS code) modified to handle the propeller onset flow. The propfan slipstream effects are superimposed on the normal flow boundary condition and are applied over the surface washed by the slipstream. The effects of the propeller slipstream are to increase the axial induced velocity, tangential velocity, and a total pressure rise in the wake of the propeller. Principles based on blade performance theory, momentum theory, and vortex theory were used to evaluate the slipstream effects. The code can be applied to any arbitrary three dimensional geometry, expressed in the form of HESS input format. The code can handle a propeller alone configuration or a propeller/nacelle/airframe configuration, operating up to high subcritical Mach numbers over a range of angles of attack. Inclusion of a viscous modelling is briefly outlined. Wind tunnel results/theory comparisons are included as examples for the application of the code to a generic supercritical wing/overwing Nacelle with a powered propfan. A sample input/output listing is provided.

Heat Transfer and Entropy Generation Analysis of an Intermediate Heat Exchanger in ADS

NASA Astrophysics Data System (ADS)

Wang, Yongwei; Huai, Xiulan

2018-04-01

The intermediate heat exchanger for enhancement heat transfer is the important equipment in the usage of nuclear energy. In the present work, heat transfer and entropy generation of an intermediate heat exchanger (IHX) in the accelerator driven subcritical system (ADS) are investigated experimentally. The variation of entropy generation number with performance parameters of the IHX is analyzed, and effects of inlet conditions of the IHX on entropy generation number and heat transfer are discussed. Compared with the results at two working conditions of the constant mass flow rates of liquid lead-bismuth eutectic (LBE) and helium gas, the total pumping power all tends to reduce with the decreasing entropy generation number, but the variations of the effectiveness, number of transfer units and thermal capacity rate ratio are inconsistent, and need to analyze respectively. With the increasing inlet mass flow rate or LBE inlet temperature, the entropy generation number increases and the heat transfer is enhanced, while the opposite trend occurs with the increasing helium gas inlet temperature. The further study is necessary for obtaining the optimized operation parameters of the IHX to minimize entropy generation and enhance heat transfer.

Measurement of the flow properties within a copper tube containing a deflagrating explosive

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

Hill, Larry G; Morris, John S; Jackson, Scott I

2009-01-01

We report on the propagation of deflagration waves in the high explosive (HE) PBX 9501 (95 wt % HMX, 5 wt% binder). Our test configuration, which we call the def1agration cylinder test (DFCT), is fashioned after the detonation cylinder test (DTCT) that is used to calibrate the JWL detonation product equation of state (EOS). In the DFCT, the HE is heated to a uniform slightly subcritical temperature, and is ignited at one end by a hot wire. For some configurations and initial conditions, we observe a quasi-steady wave that flares the tube into a funnel shape, stretching it to themore » point of rupture. This behavior is qualitatively like the DTCT, such that, by invoking certain additional approximations that we discuss, its behavior can be analyzed by the same methods. We employ an analysis proposed by G.I. Taylor to infer the pressure-volume curve for the burning, expanding flow. By comparing this result to the EOS of HMX product gas alone. we infer that only {approx}20 wt% of the HMX has burned at tube rupture. This result confirms pre-existing observations about the role of convective burning in HMX cookoff explosions.« less

Recovery of energy from geothermal brine and other hot water sources

DOEpatents

Wahl, III, Edward F.; Boucher, Frederic B.

1981-01-01

Process and system for recovery of energy from geothermal brines and other hot water sources, by direct contact heat exchange between the brine or hot water, and an immiscible working fluid, e.g. a hydrocarbon such as isobutane, in a heat exchange column, the brine or hot water therein flowing countercurrent to the flow of the working fluid. The column can be operated at subcritical, critical or above the critical pressure of the working fluid. Preferably, the column is provided with a plurality of sieve plates, and the heat exchange process and column, e.g. with respect to the design of such plates, number of plates employed, spacing between plates, area thereof, column diameter, and the like, are designed to achieve maximum throughput of brine or hot water and reduction in temperature differential at the respective stages or plates between the brine or hot water and the working fluid, and so minimize lost work and maximize efficiency, and minimize scale deposition from hot water containing fluid including salts, such as brine. Maximum throughput approximates minimum cost of electricity which can be produced by conversion of the recovered thermal energy to electrical energy.

Partial Hydrothermal Oxidation of High Molecular Weight Unsaturated Carboxylic Acids for Upgrading of Biodiesel Fuel

NASA Astrophysics Data System (ADS)

Kawasaki, K.; Jin, F.; Kishita, A.; Tohji, K.; Enomoto, H.

2007-03-01

With increasing environmental awareness and crude oil price, biodiesel fuel (BDF) is gaining recognition as a renewable fuel which may be used as an alternative diesel fuel without any modification to the engine. The cold flow and viscosity of BDF, however, is a major drawback that limited its use in cold area. In this study, therefore, we investigated that partial oxidation of high molecular weight unsaturated carboxylic acids in subcritical water, which major compositions in BDF, to upgrade biodiesel fuel. Oleic acid, (HOOC(CH2)7CH=CH(CH2)7CH3), was selected as a model compound of high molecular weight unsaturated carboxylic acids. All experiments were performed with a batch reactor made of SUS 316 with an internal volume of 5.7 cm3. Oleic acid was oxidized at 300 °C with oxygen supply varying from 1-10 %. Results showed that a large amount of carboxylic acids and aldehydes having 8-9 carbon atoms were formed. These experimental results suggest that the hydrothermal oxidative cleavage may mainly occur at double bonds and the cleavage of double bonds could improve the cold flow and viscosity of BDF.

Investigation of transonic region of high dynamic response encountered on an elastic supercritical wing

NASA Technical Reports Server (NTRS)

Seidel, David A.; Eckstrom, Clinton V.; Sandford, Maynard C.

1987-01-01

Unsteady aerodynamic data were measured on an aspect ratio 10.3 elastic supercritical wing while undergoing high dynamic response above Mach number of 0.90. These tests were conducted in the NASA Langley Transonic Dynamics Tunnel. A previous test of this wing predicted an unusual instability boundary based upon subcritical response data. During the present test no instability was found, but an angle of attack dependent narrow Mach number region of high dynamic wing response was observed over a wide range of dynamic pressures. The effect on dynamic wing response of wing angle of attack, static outboard control surface deflection and a lower surface spanwise fence located near the 60 percent local chordline was investigated. The driving mechanism of the dynamic wing response appears to be related to chordwise shock movement in conjunction with flow separation and reattachment on both the upper and lower surfaces.

Investigation of transonic region of high dynamic response encountered on an elastic supercritical wing

NASA Technical Reports Server (NTRS)

Seidel, David A.; Eckstrom, Clinton V.; Sandford, Maynard C.

1987-01-01

Unsteady aerodynamic data were measured on an aspect ratio 10.3 elastic supercritical wing while undergoing high dynamic response above a Mach number of 0.90. These tests were conducted in the NASA Langley Transonic Dynamics Tunnel. A previous test of this wing predicted an unusual instability boundary based on subcritical response data. During the present test no instability was found, but an angle of attack dependent narrow Mach number region of high dynamic wing response was observed over a wide range of dynamic pressures. The effect on dynamic wing response of wing angle of attack, static outbound control surface deflection and a lower surface spanwise fence located near the 60 percent local chordline was investigated. The driving mechanism of the dynamic wing response appears to be related to chordwise shock movement in conjunction with flow separation and reattachment on both the upper and lower surfaces.

Multilayer shallow water models with locally variable number of layers and semi-implicit time discretization

NASA Astrophysics Data System (ADS)

Bonaventura, Luca; Fernández-Nieto, Enrique D.; Garres-Díaz, José; Narbona-Reina, Gladys

2018-07-01

We propose an extension of the discretization approaches for multilayer shallow water models, aimed at making them more flexible and efficient for realistic applications to coastal flows. A novel discretization approach is proposed, in which the number of vertical layers and their distribution are allowed to change in different regions of the computational domain. Furthermore, semi-implicit schemes are employed for the time discretization, leading to a significant efficiency improvement for subcritical regimes. We show that, in the typical regimes in which the application of multilayer shallow water models is justified, the resulting discretization does not introduce any major spurious feature and allows again to reduce substantially the computational cost in areas with complex bathymetry. As an example of the potential of the proposed technique, an application to a sediment transport problem is presented, showing a remarkable improvement with respect to standard discretization approaches.

Large Eddy Simulation of Cryogenic Injection Processes at Supercritical Pressure

NASA Technical Reports Server (NTRS)

Oefelein, Joseph C.; Garcia, Roberto (Technical Monitor)

2002-01-01

This paper highlights results from the first of a series of hierarchical simulations aimed at assessing the modeling requirements for application of the large eddy simulation technique to cryogenic injection and combustion processes in liquid rocket engines. The focus is on liquid-oxygen-hydrogen coaxial injectors at a condition where the liquid-oxygen is injected at a subcritical temperature into a supercritical environment. For this situation a diffusion dominated mode of combustion occurs in the presence of exceedingly large thermophysical property gradients. Though continuous, these gradients approach the behavior of a contact discontinuity. Significant real gas effects and transport anomalies coexist locally in colder regions of the flow, with ideal gas and transport characteristics occurring within the flame zone. The current focal point is on the interfacial region between the liquid-oxygen core and the coaxial hydrogen jet where the flame anchors itself.

The investigation of degradation reaction of various saccharides in high temperature and high pressure water

NASA Astrophysics Data System (ADS)

Saito, T.; Noguchi, S.; Matsumoto, T.; Sasaki, M.; Goto, M.

2008-07-01

Recently, conversions of polysaccharides included in biomass resources have been studied in order to recover valuable chemicals. Degradation of polysaccharides has been attracted by many researchers, whereas by-products from secondary reactions of the materials have not been studied very well. For the purpose of understanding reaction behavior of various monosaccharides in high-temperature and high-pressure water regions, we investigated reaction pathway and kinetics through reaction experiments of degradation of saccharides in subcritical water. The experiment was conducted by using continuous flow-type micro-reactors. Glucose was used as the starting material. From the experimental results, the conversion of glucose increased with increasing the residence time. The yields of fructose and 1, 6-anhydro-β-D-glucose decreased with increasing the residence time. The yields of organic acids and some aldehydes increased with increasing the residence time.

An initial investigation into methods of computing transonic aerodynamic sensitivity coefficients

NASA Technical Reports Server (NTRS)

Carlson, Leland A.

1991-01-01

Continuing studies associated with the development of the quasi-analytical (QA) sensitivity method for three dimensional transonic flow about wings are presented. Furthermore, initial results using the quasi-analytical approach were obtained and compared to those computed using the finite difference (FD) approach. The basic goals achieved were: (1) carrying out various debugging operations pertaining to the quasi-analytical method; (2) addition of section design variables to the sensitivity equation in the form of multiple right hand sides; (3) reconfiguring the analysis/sensitivity package in order to facilitate the execution of analysis/FD/QA test cases; and (4) enhancing the display of output data to allow careful examination of the results and to permit various comparisons of sensitivity derivatives obtained using the FC/QA methods to be conducted easily and quickly. In addition to discussing the above goals, the results of executing subcritical and supercritical test cases are presented.

The Origin of Filamentary Star Forming Clouds in Magnetised Galaxies

NASA Astrophysics Data System (ADS)

Körtgen, Bastian; Banerjee, Robi; Pudritz, Ralph E.; Schmidt, Wolfram

2018-05-01

Observations show that galaxies and their interstellar media are pervaded by strong magnetic fields with energies in the diffuse component being at least comparable to the thermal and even as large or larger than the turbulent energy. Such strong magnetic fields prevent the formation of stars because patches of the interstellar medium are magnetically subcritical. Here we present the results from global numerical simulations of strongly magnetised and self-gravitating galactic discs, which show that the buoyancy of the magnetic field due to the Parker instability leads at first to the formation of giant filamentary regions. These filamentary structures become gravitationally unstable and fragment into ˜105M⊙ clouds that attract kpc long, coherent filamentary flows that build them into GMCs. Our results thus provide a solution to the long-standing problem of how the transition from sub- to supercritical regions in the interstellar medium proceeds.

Model of heap formation in vibrated gravitational suspensions.

PubMed

Ebata, Hiroyuki; Sano, Masaki

2015-11-01

In vertically vibrated dense suspensions, several localized structures have been discovered, such as heaps, stable holes, expanding holes, and replicating holes. Because an inclined free fluid surface is difficult to maintain because of gravitational pressure, the mechanism of those structures is not understood intuitively. In this paper, as a candidate for the driving mechanism, we focus on the boundary condition on a solid wall: the slip-nonslip switching boundary condition in synchronization with vertical vibration. By applying the lubrication approximation, we derived the time evolution equation of the fluid thickness from the Oldroyd-B fluid model. In our model we show that the initially flat fluid layer becomes unstable in a subcritical manner, and heaps and convectional flow appear. The obtained results are consistent with those observed experimentally. We also find that heaps climb a slope when the bottom is slightly inclined. We show that viscoelasticity enhances heap formation and climbing of a heap on the slope.

An uncertainty analysis of the flood-stage upstream from a bridge.

PubMed

Sowiński, M

2006-01-01

The paper begins with the formulation of the problem in the form of a general performance function. Next the Latin hypercube sampling (LHS) technique--a modified version of the Monte Carlo method is briefly described. The essential uncertainty analysis of the flood-stage upstream from a bridge starts with a description of the hydraulic model. This model concept is based on the HEC-RAS model developed for subcritical flow under a bridge without piers in which the energy equation is applied. The next section contains the characteristic of the basic variables including a specification of their statistics (means and variances). Next the problem of correlated variables is discussed and assumptions concerning correlation among basic variables are formulated. The analysis of results is based on LHS ranking lists obtained from the computer package UNCSAM. Results fot two examples are given: one for independent and the other for correlated variables.

Production of cellulose II from native cellulose by near- and supercritical water solubilization.

PubMed

Sasaki, Mitsuru; Adschiri, Tadafumi; Arai, Kunio

2003-08-27

We explored conditions for dissolving microcrystalline cellulose in high-temperature and high-pressure water without catalyst and in order to produce cellulose II in a rapid and selective manner. For understanding reactions of microcrystalline cellulose in subcritical and supercritical water, its solubilization treatment was conducted using a continuous-flow-type microreactor. It was found that cellulose could dissolve in near- and supercritical water at short treatment times of 0.02-0.4 s, resulting in the formation of cellulose II in relatively high yield after the treatment. Next, characteristics of the cellulose II obtained were investigated. As a result, it was confirmed that the relative crystallinity index and the degree of polymerization of the cellulose II were high values ranging from 80 to 60% and from 50 to 30%, respectively. From these findings, it was suggested that this method had high potential as an alternative technique for the conventional cellulose II production method.

Effect of Material Property Variations at Near Critical Thermodynamic Conditions on Pipe Flow Heat Transfer

NASA Astrophysics Data System (ADS)

Barney, Rebecca; Nourgaliev, Robert; Delplanque, Jean-Pierre; McCallen, Rose

2017-11-01

Heat transfer is quantified and contrasted for the Poiseuille flow of a fluid at both subcritical and supercritical thermodynamic conditions in a circular pipe subject to a uniform wall heat flux. The conditions considered are relevant to Supercritical Water Reactor (SCWR) applications. In the supercritical thermodynamic regime, a fluid can exhibit large density variations of density, thermal conductivity, and viscosity, which will affect flow and heat transfer characteristics significantly. An advanced equation of state for supercritical water was implemented in a 2D and 3D Arbitrary Lagrangian-Eurlerian multi-physics simulation tool called ALE3D developed at Lawrence Livermore National Laboratory. A newly developed, robust, high-order in space and time, fully implicit reconstructed discontinuous Galerkin (rDG) method is used to enable the numerical simulation of convective heat transfer with supercritical water. Results demonstrate the capability of this approach to accurately capture the non-linear behavior and enhanced heat transfer with supercritical water. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Information management release number LLNL-ABS-736004. Work is supported by the Integrated University Program Graduate Fellowship. Opinions, findings, conclusions or recommendations expressed are of the authors and do not necessarily reflect the views of DOE office of NE.

Comparing observations and morphodynamic numerical modeling of upper-flow-regime bedforms in fjords and outcrop

NASA Astrophysics Data System (ADS)

Hubbard, Stephen; Kostic, Svetlana; Englert, Rebecca; Coutts, Daniel; Covault, Jacob

2017-04-01

Recent bathymetric observations of fjord prodeltas in British Columbia, Canada, reveal evidence for multi-phase channel erosion and deposition. These processes are interpreted to be related to the upstream migration of upper-flow-regime bedforms, namely cyclic steps. We integrate data from high-resolution bathymetric surveys and monitoring to inform morphodynamic numerical models of turbidity currents and associated bedforms in the Squamish prodelta. These models are applied to the interpretation of upper-flow-regime bedforms, including cyclic steps, antidunes, and/or transitional bedforms, in Late Cretaceous submarine conduit strata of the Nanaimo Group at Gabriola Island, British Columbia. In the Squamish prodelta, as bedforms migrate, >90% of the deposits are reworked, making morphology- and facies-based recognition challenging. Sedimentary bodies are 5-30 m long, 0.5-2 m thick and <30 m wide. The Nanaimo Group comprises scour fills of similar scale composed of structureless sandstone, with laminated siltstone locally overlying basal erosion surfaces. Backset stratification is locally observed; packages of 2-4 backset beds, each of which are up to 60 cm thick and up to 15 m long (along dip), commonly share composite basal erosion surfaces. Numerous scour fills are recognized over thin sections (<4 m), indicating limited aggradation and preservation of the bedforms. Preliminary morphodynamic numerical modeling indicates that Squamish and Nanaimo bedforms could be transitional upper-flow-regime bedforms between cyclic steps and antidunes. It is likely that cyclic steps and related upper-flow-regime bedforms are common in strata deposited on high gradient submarine slopes. Evidence for updip-migrating cyclic step and related deposits inform a revised interpretation of a high gradient setting dominated by supercritical flow, or alternating supercritical and subcritical flow in the Nanaimo Group. Integrating direct observations, morphodynamic numerical modeling, and outcrop characterization better constrains fundamental processes that operate in deep-water depositional systems; our analyses aims to further deduce the stratigraphy and preservation potential of upper flow-regime bedforms.

Sensitivity analysis of urban flood flows to hydraulic controls

NASA Astrophysics Data System (ADS)

Chen, Shangzhi; Garambois, Pierre-André; Finaud-Guyot, Pascal; Dellinger, Guilhem; Terfous, Abdelali; Ghenaim, Abdallah

2017-04-01

Flooding represents one of the most significant natural hazards on each continent and particularly in highly populated areas. Improving the accuracy and robustness of prediction systems has become a priority. However, in situ measurements of floods remain difficult while a better understanding of flood flow spatiotemporal dynamics along with dataset for model validations appear essential. The present contribution is based on a unique experimental device at the scale 1/200, able to produce urban flooding with flood flows corresponding to frequent to rare return periods. The influence of 1D Saint Venant and 2D Shallow water model input parameters on simulated flows is assessed using global sensitivity analysis (GSA). The tested parameters are: global and local boundary conditions (water heights and discharge), spatially uniform or distributed friction coefficient and or porosity respectively tested in various ranges centered around their nominal values - calibrated thanks to accurate experimental data and related uncertainties. For various experimental configurations a variance decomposition method (ANOVA) is used to calculate spatially distributed Sobol' sensitivity indices (Si's). The sensitivity of water depth to input parameters on two main streets of the experimental device is presented here. Results show that the closer from the downstream boundary condition on water height, the higher the Sobol' index as predicted by hydraulic theory for subcritical flow, while interestingly the sensitivity to friction decreases. The sensitivity indices of all lateral inflows, representing crossroads in 1D, are also quantified in this study along with their asymptotic trends along flow distance. The relationship between lateral discharge magnitude and resulting sensitivity index of water depth is investigated. Concerning simulations with distributed friction coefficients, crossroad friction is shown to have much higher influence on upstream water depth profile than street friction coefficients. This methodology could be applied to any urban flood configuration in order to better understand flow dynamics and repartition but also guide model calibration in the light of flow controls.

(n,xn) cross section measurements for Y-89 foils used as detectors for high energy neutron measurements in the deeply subcritical assembly "QUINTA"

NASA Astrophysics Data System (ADS)

Bielewicz, Marcin; Kilim, Stanisław; Strugalska-Gola, Elżbieta; Szuta, Marcin; Wojciechowski, Andrzej; Tyutyunnikov, Sergey; Prokofiev, Alexander; Passoth, Elke

2017-09-01

Study of the deep subcritical systems (QUINTA) using relativistic beams is performed within the project "Energy and Transmutation of Radioactive Wastes" (E&T - RAW). The experiment assembly was irradiated by deuteron/proton beam (Dubna NUCLOTRON). We calculated the neutron energy spectrum inside the whole assembly by using threshold energy (n,xn) reactions in yttrium (Y-89) foils. There are almost no experimental cross section data for those reactions. New Y-89(n,xn) cross section measurements were carried out at The Svedberg laboratory (TSL) in Uppsala, Sweden in 2015. In this paper we present preliminary results of those experiments.

The Model 9977 Radioactive Material Packaging Primer

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

Abramczyk, G.

2015-10-09

The Model 9977 Packaging is a single containment drum style radioactive material (RAM) shipping container designed, tested and analyzed to meet the performance requirements of Title 10 the Code of Federal Regulations Part 71. A radioactive material shipping package, in combination with its contents, must perform three functions (please note that the performance criteria specified in the Code of Federal Regulations have alternate limits for normal operations and after accident conditions): Containment, the package must “contain” the radioactive material within it; Shielding, the packaging must limit its users and the public to radiation doses within specified limits; and Subcriticality, themore » package must maintain its radioactive material as subcritical« less

REACTOR CONTROL DEVICE

DOEpatents

Graham, R.H.

1962-09-01

A wholly mechanical compact control device is designed for automatically rendering the core of a fission reactor subcritical in response to core temperatures in excess of the design operating temperature limit. The control device comprises an expansible bellows interposed between the base of a channel in a reactor core and the inner end of a fuel cylinder therein which is normally resiliently urged inwardly. The bellows contains a working fluid which undergoes a liquid to vapor phase change at a temperature substantially equal to the design temperature limit. Hence, the bellows abruptiy expands at this limiting temperature to force the fuel cylinder outward and render the core subcritical. The control device is particularly applicable to aircraft propulsion reactor service. (AEC)

Simulation of Fast Neutronics in an Accelerator-Driven Sub-Critical Core

NASA Astrophysics Data System (ADS)

Gwyn Rosaire, C.; Sattarov, Akhdiyor; McIntyre, Peter; Tsvetkov, Pavel

2011-10-01

Accelerator-driven subcritical fission in a molten salt core (ADSMS) is being developed as a technology for green nuclear power. ADSMS burns its fertile fuel to completion, it cannot melt down, and it destroys long-lived minor actinides. The ADSMS core consists of a vessel filled with a molten salt eutectic of UCl3 and NaCl. The fast neutronics of ADSMS makes possible two unique benefits: isobreeding, a steady-state equilibrium in which ^238U is bred to ^239Pu and the ^239Pu fissions, and destruction of minor actinides, in which fission of the intermediary nuclides dominates of breeding. Results of simulations of the fast neutronics in the ADSMS core will be presented.

Experimental study of subcritical laboratory magnetized collisionless shocks using a laser-driven magnetic piston

NASA Astrophysics Data System (ADS)

Schaeffer, D. B.; Everson, E. T.; Bondarenko, A. S.; Clark, S. E.; Constantin, C. G.; Winske, D.; Gekelman, W.; Niemann, C.

2015-11-01

Recent experiments at the University of California, Los Angeles have successfully generated subcritical magnetized collisionless shocks, allowing new laboratory studies of shock formation relevant to space shocks. The characteristics of these shocks are compared with new data in which no shock or a pre-shock formed. The results are consistent with theory and 2D hybrid simulations and indicate that the observed shock or shock-like structures can be organized into distinct regimes by coupling strength. With additional experiments on the early time parameters of the laser plasma utilizing Thomson scattering, spectroscopy, and fast-gate filtered imaging, these regimes are found to be in good agreement with theoretical shock formation criteria.

Nonlinear analysis of a closed-loop tractor-semitrailer vehicle system with time delay

NASA Astrophysics Data System (ADS)

Liu, Zhaoheng; Hu, Kun; Chung, Kwok-wai

2016-08-01

In this paper, a nonlinear analysis is performed on a closed-loop system of articulated heavy vehicles with driver steering control. The nonlinearity arises from the nonlinear cubic tire force model. An integration method is employed to derive an analytical periodic solution of the system in the neighbourhood of the critical speed. The results show that excellent accuracy can be achieved for the calculation of periodic solutions arising from Hopf bifurcation of the vehicle motion. A criterion is obtained for detecting the Bautin bifurcation which separates branches of supercritical and subcritical Hopf bifurcations. The integration method is compared to the incremental harmonic balance method in both supercritical and subcritical scenarios.

Nature of flow and turbulence structure around an in-stream vertical plate in a shallow channel and the implications for sediment erosion

NASA Astrophysics Data System (ADS)

Kirkil, Gokhan; Constantinescu, George

2009-06-01

Detailed knowledge of the dynamics of large-scale turbulence structures is needed to understand the geomorphodynamic processes around in-stream obstacles present in rivers. Detached Eddy Simulation is used to study the flow past a high-aspect-ratio rectangular cylinder (plate) mounted on a flat-bed relatively shallow channel at a channel Reynolds number of 2.4 × 105. Similar to other flows past surface-mounted bluff bodies, the large amplification of the turbulence inside the horseshoe vortex system is because the core of the main necklace vortex is subject to large-scale bimodal oscillations. The presence of a sharp edge at the flanks of the obstruction fixes the position of the flow separation at all depths and induces the formation and shedding of very strong wake rollers over the whole channel depth. Compared with the case of a circular cylinder where the intensity of the rollers decays significantly in the near-bed region because the incoming flow velocity is not sufficient to force the wake to transition from subcritical to supercritical regime, in the case of a high-aspect-ratio rectangular cylinder the passage of the rollers was found to induce high bed-shear stresses at large distances (6-8 D) behind the obstruction. Also, the nondimensional values of the pressure root-mean-square fluctuations at the bed were found to be about 1 order of magnitude higher than the ones predicted for circular cylinders. Overall, this shows that the shape of the in-stream obstruction can greatly modify the dynamics of the large-scale coherent structures, the nature of their interactions, and ultimately, their capability to entrain and transport sediment particles and the speed at which the scour process evolves during its initial stages.

Fluid dynamics and low gravity effects of chemical vapor deposition

NASA Technical Reports Server (NTRS)

Nyce, Thomas A.; Rosenberger, Franz

1990-01-01

Based on the comparison between experimental data and numerical results for the growth of GaAs from TMGa, it was shown that 3D simulations are necessary to simulate rectangular CVD reactors even when operated under subcritical (Ra) conditions. The important points found are summarized in the three attached reprints. The experimental studies of mixed convection in horizontal channels have shown three regimes of high Ra (22,220) number flows. At Re = 18.5, the rolls develop very quickly, significantly modulating the axial velocity even before it reaches the beginning of the hot plate. A few centimeters downstream, the velocities become asymmetric about the vertical centerplane and at x = 12 cm, become unsteady. These asymmetries were predicted theoretically, but experimental evidence has not been published prior to this work. At Re = 36, the axial velocity is only slightly modified at x = 0. Although the flow remains steady and symmetric about the vertical centerplane, there is a small spatial oscillation in the velocities over the length of the channel. The period of this oscillation was around 5 cm. At Re = 54, the longitudinal rolls developed smoothly over a length of 30 cm, with no asymmetries, unsteadiness, or spatial oscillations. Comparison of numerical simulations of these flows to experiments has revealed the importance and difficulty of setting proper thermal boundary conditions on the sidewalls. Calculated flows and experimentally measured flows showed very similar profiles, but at different axial locations, with the rolls developing more rapidly in the experiments. This is directly attributable to partially conducting sidewalls of the apparatus being hotter in the entrance section than the adiabatic walls of the simulations. A thorough comparison of the experimental data and numerical results for a variety of sidewall boundary conditions is in preparation.

YALINA-booster subcritical assembly pulsed-neutron e xperiments: detector dead time and apatial corrections.

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

Cao, Y.; Gohar, Y.; Nuclear Engineering Division

In almost every detector counting system, a minimal dead time is required to record two successive events as two separated pulses. Due to the random nature of neutron interactions in the subcritical assembly, there is always some probability that a true neutron event will not be recorded because it occurs too close to the preceding event. These losses may become rather severe for counting systems with high counting rates, and should be corrected before any utilization of the experimental data. This report examines the dead time effects for the pulsed neutron experiments of the YALINA-Booster subcritical assembly. The nonparalyzable modelmore » is utilized to correct the experimental data due to dead time. Overall, the reactivity values are increased by 0.19$ and 0.32$ after the spatial corrections for the YALINA-Booster 36% and 21% configurations respectively. The differences of the reactivities obtained with He-3 long or short detectors at the same detector channel diminish after the dead time corrections of the experimental data for the 36% YALINA-Booster configuration. In addition, better agreements between reactivities obtained from different experimental data sets are also observed after the dead time corrections for the 21% YALINA-Booster configuration.« less

Disintegration of the agricultural by-product wheat bran under subcritical conditions.

PubMed

Reisinger, Michael; Tirpanalan, Özge; Pruksasri, Suwattana; Kneifel, Wolfgang; Novalin, Senad

2018-02-10

The disintegration of destarched wheat bran in water and sulfuric acid (pH 3) under subcritical conditions (275-300 °C) and at short reaction times (1-4 min) was investigated. A cascade process comprising a stepwise separation of the liquid was applied to reduce the formation of undesired degradation products. The highest degree of biomass disintegration (67% dry mass solubilization) was achieved by application of a cascade process at 275 °C (pH 3). Regarding the dissolution of carbohydrates (monomeric and oligomeric form), the total glucose yields remained below 60%, while the total xylose and arabinose yields were about 76% and 67%. Approximately 74% of the protein and 95% of the mineral fraction could be extracted. The application of the cascade process enabled a substantially reduced formation of degradation products. When operating hydrothermally and subcritically in order to avoid some problematic aspects of a biorefinery, an extensive disintegration and monomerization of wheat bran and its constituents remains difficult even under the tested conditions (300 °C, pH 3). However, the applied cascade process proved to be useful to increase the yields and to substantially reduce the formation of undesired degradation products. Despite this fact, increased water consumption has to be conceded. © 2018 Society of Chemical Industry. © 2018 Society of Chemical Industry.

Subcritical Water Technology for Enhanced Extraction of Biochemical Compounds from Chlorella vulgaris

PubMed Central

Awaluddin, S. A.; Thiruvenkadam, Selvakumar; Izhar, Shamsul; Hiroyuki, Yoshida; Danquah, Michael K.; Harun, Razif

2016-01-01

Subcritical water extraction (SWE) technology has been used for the extraction of active compounds from different biomass materials with low process cost, mild operating conditions, short process times, and environmental sustainability. With the limited application of the technology to microalgal biomass, this work investigates parametrically the potential of subcritical water for high-yield extraction of biochemicals such as carbohydrates and proteins from microalgal biomass. The SWE process was optimized using central composite design (CCD) under varying process conditions of temperature (180–374°C), extraction time (1–20 min), biomass particulate size (38–250 μm), and microalgal biomass loading (5–40 wt.%). Chlorella vulgaris used in this study shows high volatile matter (83.5 wt.%) and carbon content (47.11 wt.%), giving advantage as a feedstock for biofuel production. The results showed maximum total carbohydrate content and protein yields of 14.2 g/100 g and 31.2 g/100 g, respectively, achieved under the process conditions of 277°C, 5% of microalgal biomass loading, and 5 min extraction time. Statistical analysis revealed that, of all the parameters investigated, temperature is the most critical during SWE of microalgal biomass for protein and carbohydrate production. PMID:27366748

Subcritical water extraction of alkaloids in Sophora flavescens Ait. and determination by capillary electrophoresis with field-amplified sample stacking.

PubMed

Wang, Haiyan; Lu, Yuchao; Chen, Jie; Li, Junchao; Liu, Shuhui

2012-01-25

The extraction and determination of cytisine, sophocarpine, matrine, sophoridine and oxymatrine in Sophora flavescens Ait. were performed using subcritical water extraction and capillary electrophoresis with field-amplified sample stacking. The effects of extraction temperature, pressure, time and cycle number on the extraction yields were investigated systematically for accelerated solvent extraction with ethanol (ASE) and accelerated solvent extraction with water (subcritical water extraction, SWE). The extraction yields obtained using SWE, ASE, water ultrasonic extraction and chloroform soaking extraction methods were compared. The electrophoresis separation buffer was monosodium phosphate (pH 3.0; 110 mM)-isopropanol (85:15, v/v). The effect of phosphoric acid added to the sample matrix on the reproducibility of the peak heights of the analytes was also examined. Cytisine, sophoridine and oxymatrine showed good linearity (R(2)>0.999) within 0.125-4.0 μg/mL, and sophocarpine and matrine exhibited good linearity (R(2)>0.998) within 0.0625-2.0 μg/mL, with the detection limits in the range of 0.004-0.0013 μg/mL. The five alkaloid contents in medicinal plants from different sources and Sophora instant granule were determined and compared. Copyright © 2011 Elsevier B.V. All rights reserved.

Passive Safety Features Evaluation of KIPT Neutron Source Facility

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

Zhong, Zhaopeng; Gohar, Yousry

2016-06-01

Argonne National Laboratory (ANL) of the United States and Kharkov Institute of Physics and Technology (KIPT) of Ukraine have cooperated on the development, design, and construction of a neutron source facility. The facility was constructed at Kharkov, Ukraine and its commissioning process is underway. It will be used to conduct basic and applied nuclear research, produce medical isotopes, and train young nuclear specialists. The facility has an electron accelerator-driven subcritical assembly. The electron beam power is 100 kW using 100 MeV electrons. Tungsten or natural uranium is the target material for generating neutrons driving the subcritical assembly. The subcritical assemblymore » is composed of WWR-M2 - Russian fuel assemblies with U-235 enrichment of 19.7 wt%, surrounded by beryllium reflector assembles and graphite blocks. The subcritical assembly is seated in a water tank, which is a part of the primary cooling loop. During normal operation, the water coolant operates at room temperature and the total facility power is ~300 KW. The passive safety features of the facility are discussed in in this study. Monte Carlo computer code MCNPX was utilized in the analyses with ENDF/B-VII.0 nuclear data libraries. Negative reactivity temperature feedback was consistently observed, which is important for the facility safety performance. Due to the design of WWR-M2 fuel assemblies, slight water temperature increase and the corresponding water density decrease produce large reactivity drop, which offset the reactivity gain by mistakenly loading an additional fuel assembly. The increase of fuel temperature also causes sufficiently large reactivity decrease. This enhances the facility safety performance because fuel temperature increase provides prompt negative reactivity feedback. The reactivity variation due to an empty fuel position filled by water during the fuel loading process is examined. Also, the loading mistakes of removing beryllium reflector assemblies and replacing them with dummy assemblies were analyzed. In all these circumstances, the reactivity change results do not cause any safety concerns.« less

Thermodynamic Properties of the Inverse Evershed Flow at Its Downflow Points

NASA Astrophysics Data System (ADS)

Choudhary, D. P.; Beck, C.

2018-06-01

We used spectropolarimetric observations of a sunspot in the active region NOAA 11809 in the Ca II line at 854.2 nm taken with the SpectroPolarimeter for Optical and Infrared Regions at the Dunn Solar Telescope to infer thermodynamic parameters along 100 super-penumbral fibrils that harbor the inverse Evershed flow. The fibrils were identified in line-of-sight (LOS) velocity and line–core intensity maps. The chromospheric LOS velocity abruptly decreases from 3 to 15 km s‑1 to zero at the inner footpoints of the fibrils that are located from the mid penumbra to about 1.4 spot radii. The spectra often show multiple absorption components, indicating spatially or vertically unresolved structures. Synthetic spectra with a 100% fill factor of a flow channel in the upper atmosphere yield strongly asymmetric profiles but no multiple separate components. The line–core intensity always peaks slightly closer to the umbra than the LOS velocity. Using the CAlcium Inversion using a Spectral ARchive code, we find that the fibrils make an angle of 30°–60° to the local vertical away from the umbra. The temperature near the downflow points is enhanced by 200 K at log τ ∼ -2 and up to 2000 K at log τ ∼ (‑6) compared to the quiet Sun, without any signature in the low photosphere. Our results are consistent with a critical, i.e., sonic, or supersonic siphon flow along super-penumbral flux tubes in which accelerating plasma abruptly attains subcritical velocity through a standing shock in or near the penumbra.

Deviations of Atmospheric Coastal Flow from the Open-channel Hydraulics Analogy

NASA Astrophysics Data System (ADS)

Rahn, D. A.; Parish, T. R.; Juliano, T. W.

2017-12-01

Low-level atmospheric flow along the coast of California bears resemblance to open-channel engineering applications referred to as hydraulic flow. During the warm season, strong equatorward wind is common near the surface. A marked temperature inversion separates the cool, moist marine air and the warm, dry free troposphere aloft. The low-level flow is bounded laterally by the coastal topography. Given the high wind speed in the shallow marine layer, the flow is often supercritical (Fr > 1). Features resembling oblique compression jumps and expansion fans occur near concave and convex bends in the coastline and impact wind energy production, wind stress on the ocean surface, and propagation of electromagnetic waves by modifying the vertical refractivity gradient. An aircraft collected fine-scale measurements offshore of southern California to test how well the observed features conform to the single-layer hydraulic approximation. Although the open-channel framework captures major features of the flow as indicated by prior work, the detailed measurements reveal when the analogy breaks down. The assumption of a passive upper layer can be violated due to mesoscale pressure gradients aloft and lee troughing associated with offshore flow, which can enhance the thinning of the marine layer associated with the expansion fan. The sharp interface between layers can be eroded when Ri becomes low, Kelvin-Helmholtz instability develops, and the structure of the lower atmosphere is drastically altered. This is poorly simulated in operational weather forecast models due to their relatively coarse grid spacing. The layer associated with the expansion fan rarely keeps its identity into the Santa Barbara Channel. An increase of surface heat flux and vertical mixing as the flow moves over warmer sea surface temperatures in the channel rapidly erodes the layer. Only one flight captured a hydraulic jump between the supercritical flow in the expansion fan and the subcritical flow downstream, but its features correspond well to predicted values. The lack of hydraulic jumps on other days is likely due to the loss of layer identity before the jump can be realized.

Lateral and vertical facies relationships of bedforms deposited by aggrading supercritical flows: From cyclic steps to humpback dunes

NASA Astrophysics Data System (ADS)

Lang, Jörg; Winsemann, Jutta

2013-10-01

The preservation of bedforms related to supercritical flows and hydraulic jumps is commonly considered to be rare in the geologic record, although these bedforms are known from a variety of depositional environments. This field-based study presents a detailed analysis of the sedimentary facies and stacking pattern of deposits of cyclic steps, chutes-and-pools, antidunes and humpback dunes from three-dimensional outcrops. The well exposed Middle Pleistocene successions from northern Germany comprise glacilacustrine ice-contact subaqueous fan and glacial lake-outburst flood deposits. The studied successions give new insights into the depositional architecture of bedforms related to supercritical flows and may serve as an analogue for other high-energy depositional environments such as fluvial settings, coarse-grained deltas or turbidite systems. Deposits of cyclic steps occur within the glacial lake-outburst flood succession and are characterised by lenticular scours infilled by gently to steeply dipping backsets. Cyclic steps formed due to acceleration and flow thinning when the glacial lake-outburst flood spilled over a push-moraine ridge. These bedforms are commonly laterally and vertically truncated and alternate with deposits of chutes-and-pools and antidunes. The subaqueous fan successions are dominated by laterally extensive sinusoidal waveforms, which are interpreted as deposits of aggrading stationary antidunes, which require quasi-steady flows at the lower limit of the supercritical flow stage and high rates of sedimentation. Humpback dunes are characterised by downflow divergent cross-stratification, displaying differentiation into topsets, foresets and bottomsets, and are interpreted as deposited at the transition from subcritical to supercritical flow conditions or vice versa. Gradual lateral and vertical transitions between humpback dunes and antidune deposits are very common. The absence of planar-parallel stratification in all studied successions suggests that the formation of these bedforms is suppressed in flows characterised by hydraulic jumps under highly aggradational conditions. The large-scale lateral and vertical successions of bedforms are interpreted as representing the temporal and spatial evolution of the initial supercritical flows, which was strongly affected by the occurrence of hydraulic jumps. Small-scale facies changes and the formation of individual bedforms are interpreted as controlled by fluctuating discharge, bed topography and pulsating unstable flows.

Symmetry-Breaking Bifurcation in the Nonlinear Schrödinger Equation with Symmetric Potentials

NASA Astrophysics Data System (ADS)

Kirr, E.; Kevrekidis, P. G.; Pelinovsky, D. E.

2011-12-01

We consider the focusing (attractive) nonlinear Schrödinger (NLS) equation with an external, symmetric potential which vanishes at infinity and supports a linear bound state. We prove that the symmetric, nonlinear ground states must undergo a symmetry breaking bifurcation if the potential has a non-degenerate local maxima at zero. Under a generic assumption we show that the bifurcation is either a subcritical or supercritical pitchfork. In the particular case of double-well potentials with large separation, the power of nonlinearity determines the subcritical or supercritical character of the bifurcation. The results are obtained from a careful analysis of the spectral properties of the ground states at both small and large values for the corresponding eigenvalue parameter.

Vibration analysis of paper machine's asymmetric tube roll supported by spherical roller bearings

NASA Astrophysics Data System (ADS)

Heikkinen, Janne E.; Ghalamchi, Behnam; Viitala, Raine; Sopanen, Jussi; Juhanko, Jari; Mikkola, Aki; Kuosmanen, Petri

2018-05-01

This paper presents a simulation method that is used to study subcritical vibrations of a tube roll in a paper machine. This study employs asymmetric 3D beam elements based on the Timoshenko beam theory. An asymmetric beam model accounts for varying stiffness and mass distributions. Additionally, a detailed rolling element bearing model defines the excitations arising from the set of spherical roller bearings at both ends of the rotor. The results obtained from the simulation model are compared against the results from the measurements. The results indicate that the waviness of the bearing rolling surfaces contributes significantly to the subcritical vibrations while the asymmetric properties of the tube roll have only a fractional effect on the studied vibrations.

NCSP IER 422 CED-3b Documentation

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

Hutchinson, Jesson D.; Cutler, Theresa Elizabeth; Bahran, Rian Mustafa

2017-11-22

A Subcritical Copper-Reflected α-phase Plutonium (SCRαP) integral benchmark experiment has been designed and measured. In this experiment, multiplication is approximated using correlated neutron data from a detector system consisting of 3He tubes inside high density polyethylene (HDPE). Measurements were performed on various subcritical experimental configurations consisting of a weapons-grade plutonium sphere surrounded by different Cu thicknesses. In addition to the proposed base experimental configurations with Cu, additional configurations were performed with the plutonium ball nested in various thicknesses of interleaved HDPE spherical shells mixed in with the Cu shells. The HDPE is intended to provide fast neutron moderation and reflection,more » resulting in additional measurements with differing multiplication, spectra, and nuclear data sensitivity.« less

The asymptotic behavior in a reversible random coagulation-fragmentation polymerization process with sub-exponential decay

NASA Astrophysics Data System (ADS)

Dong, Siqun; Zhao, Dianli

2018-01-01

This paper studies the subcritical, near-critical and supercritical asymptotic behavior of a reversible random coagulation-fragmentation polymerization process as N → ∞, with the number of distinct ways to form a k-clusters from k units satisfying f(k) =(1 + o (1)) cr-ke-kαk-β, where 0 < α < 1 and β > 0. When the cluster size is small, its distribution is proved to converge to the Gaussian distribution. For the medium clusters, its distribution will converge to Poisson distribution in supercritical stage, and no large clusters exist in this stage. Furthermore, the largest length of polymers of size N is of order ln N in the subcritical stage under α ⩽ 1 / 2.

Simple go/no-go test for subcritical damage in body armor panels

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

Fisher, Jason; Chimenti, D. E.

2011-06-23

The development of a simple test for subcritical damage in body armor panels using pressure-sensitive dye-indicator film has been performed and demonstrated effective. Measurements have shown that static indicator levels are accurately reproduced in dynamic loading events. Impacts from hard blunt impactors instrumented with an accelerometer and embedded force transducer were studied. Reliable correlations between the indicator film and instrumented impact force are shown for a range of impact energies. Force and acceleration waveforms with corresponding indicator film results are presented for impact events onto damaged and undamaged panels. We find that panel damage can occur at impact levels farmore » below the National Institute of Justice acceptance test standard.« less

Surface Plasmon States in Inhomogeneous Media at Critical and Subcritical Metal Concentrations

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

Seal, Katyayani; Genov, Dentcho A.

Semicontinuous metal-dielectric films are composed of a wide range of metal clusters of various geometries—sizes as well as structures. This ensures that at any given wavelength of incident radiation, clusters exist in the film that will respond resonantly, akin to resonating nanoantennas, resulting in the broad optical response (absorption) that is a characteristic of semicontinuous films. The physics of the surface plasmon states that are supported by such systems is complex and can involve both localized and propagating plasmons. This chapter describes near-field experimental and numerical studies of the surface plasmon states in semicontinuous films at critical and subcritical metalmore » concentrations and evaluates the local field intensity statistics to discuss the interplay between various eigenmodes.« less

Existence of infinitely many stationary solutions of the L2-subcritical and critical NLSE on compact metric graphs

NASA Astrophysics Data System (ADS)

Dovetta, Simone

2018-04-01

We investigate the existence of stationary solutions for the nonlinear Schrödinger equation on compact metric graphs. In the L2-subcritical setting, we prove the existence of an infinite number of such solutions, for every value of the mass. In the critical regime, the existence of infinitely many solutions is established if the mass is lower than a threshold value, while global minimizers of the NLS energy exist if and only if the mass is lower or equal to the threshold. Moreover, the relation between this threshold and the topology of the graph is characterized. The investigation is based on variational techniques and some new versions of Gagliardo-Nirenberg inequalities.

Long-term cryogenic space storage system

NASA Technical Reports Server (NTRS)

Hopkins, R. A.; Chronic, W. L.

1973-01-01

Discussion of the design, fabrication and testing of a 225-cu ft spherical cryogenic storage system for long-term subcritical applications under zero-g conditions in storing subcritical cryogens for space vehicle propulsion systems. The insulation system design, the analytical methods used, and the correlation between the performance test results and analytical predictions are described. The best available multilayer insulation materials and state-of-the-art thermal protection concepts were applied in the design, providing a boiloff rate of 0.152 lb/hr, or 0.032% per day, and an overall heat flux of 0.066 Btu/sq ft hr based on a 200 sq ft surface area. A six to eighteen month cryogenic storage is provided by this system for space applications.

Molten salt considerations for accelerator-driven subcritical fission to close the nuclear fuel cycle

NASA Astrophysics Data System (ADS)

Sooby, Elizabeth; Adams, Marvin; Baty, Austin; Gerity, James; McIntyre, Peter; Melconian, Karie; Phongikaroon, Supathorn; Pogue, Nathaniel; Sattarov, Akhdiyor; Simpson, Michael; Tripathy, Prabhat; Tsevkov, Pavel

2013-04-01

The host salt selection, molecular modeling, physical chemistry, and processing chemistry are presented here for an accelerator-driven subcritical fission in a molten salt core (ADSMS). The core is fueled solely with the transuranics (TRU) and long-lived fission products (LFP) from used nuclear fuel. The neutronics and salt composition are optimized to destroy the transuranics by fission and the long-lived fission products by transmutation. The cores are driven by proton beams from a strong-focusing cyclotron stack. One such ADSMS system can destroy the transuranics in the used nuclear fuel produced by a 1GWe conventional reactor. It uniquely provides a method to close the nuclear fuel cycle for green nuclear energy.

Large-eddy simulations of unidirectional water flow over dunes

NASA Astrophysics Data System (ADS)

Grigoriadis, D. G. E.; Balaras, E.; Dimas, A. A.

2009-06-01

The unidirectional, subcritical flow over fixed dunes is studied numerically using large-eddy simulation, while the immersed boundary method is implemented to incorporate the bed geometry. Results are presented for a typical dune shape and two Reynolds numbers, Re = 17,500 and Re = 93,500, on the basis of bulk velocity and water depth. The numerical predictions of velocity statistics at the low Reynolds number are in very good agreement with available experimental data. A primary recirculation region develops downstream of the dune crest at both Reynolds numbers, while a secondary region develops at the toe of the dune crest only for the low Reynolds number. Downstream of the reattachment point, on the dune stoss, the turbulence intensity in the developing boundary layer is weaker than in comparable equilibrium boundary layers. Coherent vortical structures are identified using the fluctuating pressure field and the second invariant of the velocity gradient tensor. Vorticity is primarily generated at the dune crest in the form of spanwise "roller" structures. Roller structures dominate the flow dynamics near the crest, and are responsible for perturbing the boundary layer downstream of the reattachment point, which leads to the formation of "horseshoe" structures. Horseshoe structures dominate the near-wall dynamics after the reattachment point, do not rise to the free surface, and are distorted by the shear layer of the next crest. The occasional interaction between roller and horseshoe structures generates tube-like "kolk" structures, which rise to the free surface and persist for a long time before attenuating.

GUINEVERE experiment: Kinetic analysis of some reactivity measurement methods by deterministic and Monte Carlo codes

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

Bianchini, G.; Burgio, N.; Carta, M.

The GUINEVERE experiment (Generation of Uninterrupted Intense Neutrons at the lead Venus Reactor) is an experimental program in support of the ADS technology presently carried out at SCK-CEN in Mol (Belgium). In the experiment a modified lay-out of the original thermal VENUS critical facility is coupled to an accelerator, built by the French body CNRS in Grenoble, working in both continuous and pulsed mode and delivering 14 MeV neutrons by bombardment of deuterons on a tritium-target. The modified lay-out of the facility consists of a fast subcritical core made of 30% U-235 enriched metallic Uranium in a lead matrix. Severalmore » off-line and on-line reactivity measurement techniques will be investigated during the experimental campaign. This report is focused on the simulation by deterministic (ERANOS French code) and Monte Carlo (MCNPX US code) calculations of three reactivity measurement techniques, Slope ({alpha}-fitting), Area-ratio and Source-jerk, applied to a GUINEVERE subcritical configuration (namely SC1). The inferred reactivity, in dollar units, by the Area-ratio method shows an overall agreement between the two deterministic and Monte Carlo computational approaches, whereas the MCNPX Source-jerk results are affected by large uncertainties and allow only partial conclusions about the comparison. Finally, no particular spatial dependence of the results is observed in the case of the GUINEVERE SC1 subcritical configuration. (authors)« less

Experimental Dynamic Analysis of a Breathing Cracked Rotor

NASA Astrophysics Data System (ADS)

Guo, Chao-Zhong; Yan, Ji-Hong; Bergman, Lawrence A.

2017-09-01

Crack fault diagnostics plays a critical role for rotating machinery in the traditional and Industry 4.0 factory. In this paper, an experiment is set up to study the dynamic response of a rotor with a breathing crack as it passes through its 1/2, 1/3, 1/4 and 1/5 subcritical speeds. A cracked shaft is made by applying fatigue loads through a three-point bending apparatus and then placed in a rotor testbed. The vibration signals of the testbed during the coasting-up process are collected. Whirl orbit evolution at these subcritical speed zones is analyzed. The Fourier spectra obtained by FFT are used to investigate the internal frequencies corresponding to the typical orbit characteristics. The results show that the appearance of the inner loops and orientation change of whirl orbits in the experiment are agreed well with the theoretical results obtained previously. The presence of higher frequencies 2X, 3X, 4X and 5X in Fourier spectra reveals the causes of subharmonic resonances at these subcritical speed zones. The experimental investigation is more systematic and thorough than previously reported in the literature. The unique dynamic behavior of the orbits and frequency spectra are feasible features for practical crack diagnosis. This paper provides a critical technology support for the self-aware health management of rotating machinery in the Industry 4.0 factory.

Mn-Ce-Co complex oxide nanoparticles: hydrothermal synthesis and their catalytic subcritical oxidation of 4,4'-Dibromobiphenyl.

PubMed

Chen, Jinyang; Xu, Tianjiao; Ding, Junying; Ji, Yimei; Ni, Pei; Li, Zhilian

2012-10-15

In situ transformation of 4,4'-Dibromobiphenyl (4,4'-DBB) in water was observed with hydrothermal diamond anvil cell (HDAC) up to 633 K. It shows that 4,4'-DBB dissolves in water to form a homogenous phase at the temperature of 588 K and thus subcritical water oxidation of 4,4'-DBB higher than the temperature can be a homogenous phase. To accelerate the oxidative degradation, some Mn-Ce-Co complex oxide nanoparticles of about 100 nm were prepared by co-precipitation hydrothermal method. The nanoparticles show enough stability and catalytic activity for oxidative degradation of 4,4'-DBB in subcritical water. The catalytic activation increases with some Co doping and as for the complex oxides of Mn(1)Ce(1), Mn(0.9)Ce(1)Co(0.1), Mn(0.5)Ce(1)Co(0.5), Mn(0.1)Ce(1)Co(0.9), and Co(1)Ce(1), the Mn(0.9)Ce(1)Co(0.1) presents the best activation. The main intermediate products of degradation are benzoic acid and phenol. The apparent activation energy (E(a)) is 35.92 with 5% Mn(0.9)Ce(1)Co(0.1) as catalyst and 46.69 kJ/mol with no catalyst about the chemical oxygen demand (COD). Copyright © 2012 Elsevier B.V. All rights reserved.

Critical and subcritical damage monitoring of bonded composite repairs using innovative non-destructive techniques

NASA Astrophysics Data System (ADS)

Grammatikos, S. A.; Kordatos, E. Z.; Aggelis, D. G.; Matikas, T. E.; Paipetis, A. S.

2012-04-01

Infrared Thermography (IrT) has been shown to be capable of detecting and monitoring service induced damage of repair composite structures. Full-field imaging, along with portability are the primary benefits of the thermographic technique. On-line lock-in thermography has been reported to successfully monitor damage propagation or/and stress concentration in composite coupons, as mechanical stresses in structures induce heat concentration phenomena around flaws. During mechanical fatigue, cyclic loading plays the role of the heating source and this allows for critical and subcritical damage identification and monitoring using thermography. The Electrical Potential Change Technique (EPCT) is a new method for damage identification and monitoring during loading. The measurement of electrical potential changes at specific points of Carbon Fiber Reinforced Polymers (CFRPs) under load are reported to enable the monitoring of strain or/and damage accumulation. Along with the aforementioned techniques Finally, Acoustic Emission (AE) method is well known to provide information about the location and type of damage. Damage accumulation due to cyclic loading imposes differentiation of certain parameters of AE like duration and energy. Within the scope of this study, infrared thermography is employed along with AE and EPCT methods in order to assess the integrity of bonded repair patches on composite substrates and to monitor critical and subcritical damage induced by the mechanical loading. The combined methodologies were effective in identifying damage initiation and propagation of bonded composite repairs.

Role of geomechanically grown fractures on dispersive transport in heterogeneous geological formations.

PubMed

Nick, H M; Paluszny, A; Blunt, M J; Matthai, S K

2011-11-01

A second order in space accurate implicit scheme for time-dependent advection-dispersion equations and a discrete fracture propagation model are employed to model solute transport in porous media. We study the impact of the fractures on mass transport and dispersion. To model flow and transport, pressure and transport equations are integrated using a finite-element, node-centered finite-volume approach. Fracture geometries are incrementally developed from a random distributions of material flaws using an adoptive geomechanical finite-element model that also produces fracture aperture distributions. This quasistatic propagation assumes a linear elastic rock matrix, and crack propagation is governed by a subcritical crack growth failure criterion. Fracture propagation, intersection, and closure are handled geometrically. The flow and transport simulations are separately conducted for a range of fracture densities that are generated by the geomechanical finite-element model. These computations show that the most influential parameters for solute transport in fractured porous media are as follows: fracture density and fracture-matrix flux ratio that is influenced by matrix permeability. Using an equivalent fracture aperture size, computed on the basis of equivalent permeability of the system, we also obtain an acceptable prediction of the macrodispersion of poorly interconnected fracture networks. The results hold for fractures at relatively low density.

Unsteady streamflow simulation using a linear implicit finite-difference model

USGS Publications Warehouse

Land, Larry F.

1978-01-01

A computer program for simulating one-dimensional subcritical, gradually varied, unsteady flow in a stream has been developed and documented. Given upstream and downstream boundary conditions and channel geometry data, roughness coefficients, stage, and discharge can be calculated anywhere within the reach as a function of time. The program uses a linear implicit finite-difference technique that discritizes the partial differential equations. Then it arranges the coefficients of the continuity and momentum equations into a pentadiagonal matrix for solution. Because it is a reasonable compromise between computational accuracy, speed and ease of use,the technique is one of the most commonly used. The upstream boundary condition is a depth hydrograph. However, options also allow the boundary condition to be discharge or water-surface elevation. The downstream boundary condition is a depth which may be constant, self-setting, or unsteady. The reach may be divided into uneven increments and the cross sections may be nonprismatic and may vary from one to the other. Tributary and lateral inflow may enter the reach. The digital model will simulate such common problems as (1) flood waves, (2) releases from dams, and (3) channels where storage is a consideration. It may also supply the needed flow information for mass-transport simulation. (Woodard-USGS)

Aeroacoustic Simulations of Tandem Cylinders with Subcritical Spacing

NASA Technical Reports Server (NTRS)

Lockard, David P.; Choudhari, Meelan M.; Khorrami, Mehdi R.; Neuhart, Dan H.; Hutcheson, Florence V.; Brooks, Thomas F.; Stead, Daniel J.

2008-01-01

Tandem cylinders are being studied because they model a variety of component level interactions of landing gear. The present effort is directed at the case of two identical cylinders with their centroids separated in the streamwise direction by 1.435 diameters. Experiments in the Basic Aerodynamic Research Tunnel and Quiet Flow Facility at NASA Langley Research Center have provided an extensive experimental database of the nearfield flow and radiated noise. The measurements were conducted at a Mach number of 0.1285 and Reynolds number of 1.66x10(exp 5) based on the cylinder diameter. A trip was used on the upstream cylinder to insure a fully turbulent flow separation and, hence, to simulate a major aspect of high Reynolds number flow. The parallel computational effort uses the three-dimensional Navier-Stokes solver CFL3D with a hybrid, zonal turbulence model that turns off the turbulence production term everywhere except in a narrow ring surrounding solid surfaces. The experiments exhibited an asymmetry in the surface pressure that was persistent despite attempts to eliminate it through small changes in the configuration. To model the asymmetry, the simulations were run with the cylinder configuration at a nonzero but small angle of attack. The computed results and experiments are in general agreement that vortex shedding for the spacing studied herein is weak relative to that observed at supercritical spacings. Although the shedding was subdued in the simulations, it was still more prominent than in the experiments. Overall, the simulation comparisons with measured near-field data and the radiated acoustics are reasonable, especially if one is concerned with capturing the trends relative to larger cylinder spacings. However, the flow details of the 1.435 diameter spacing have not been captured in full even though very fine grid computations have been performed. Some of the discrepancy may be associated with the simulation s inexact representation of the experimental configuration, but numerical and flow modeling errors are also likely contributors to the observed differences.

Combustion of LOX with H2(sub g) under subcritical, critical, and supercritical conditions (Task 1) and experimental observation of dense spray and mixing of impinging jets (Task 2)

NASA Technical Reports Server (NTRS)

Kuo, K. K.; Hsieh, W. H.; Cheung, F. B.; Yang, A. S.; Brown, J. J.; Woodward, R. D.; Kline, M. C.; Burch, R. L.

1992-01-01

The objective was to achieve a better understanding of the combustion processes of liquid oxygen and gaseous hydrogen under broad range of pressure covering subcritical, critical, and supercritical conditions. The scope of the experimental work falls into the following areas: (1) design of the overall experimental setup; (2) modification of an existing windowed high pressure chamber; (3) design of the LOX feeding system; (4) provision of the safety features in the test rig design; (5) LOX cleanliness requirements; (6) cold shock testing; (7) implementation of data acquisition systems; (8) preliminary tests for system checkout; (9) modification of LOX feeding system; and (10) evaporation tests. Progress in each area is discussed.

Could giant basin-forming impacts have killed Martian dynamo?

PubMed Central

Kuang, W; Jiang, W; Roberts, J; Frey, H V

2014-01-01

The observed strong remanent crustal magnetization at the surface of Mars suggests an active dynamo in the past and ceased to exist around early to middle Noachian era, estimated by examining remagnetization strengths in extant and buried impact basins. We investigate whether the Martian dynamo could have been killed by these large basin-forming impacts, via numerical simulation of subcritical dynamos with impact-induced thermal heterogeneity across the core-mantle boundary. We find that subcritical dynamos are prone to the impacts centered on locations within 30° of the equator but can easily survive those at higher latitudes. Our results further suggest that magnetic timing places a strong constraint on postimpact polar reorientation, e.g., a minimum 16° polar reorientation is needed if Utopia is the dynamo killer. PMID:26074641

Could Giant Basin-Forming Impacts Have Killed Martian Dynamo?

NASA Technical Reports Server (NTRS)

Kuang, W.; Jiang, W.; Roberts, J.; Frey, H. V.

2014-01-01

The observed strong remanent crustal magnetization at the surface of Mars suggests an active dynamo in the past and ceased to exist around early to middle Noachian era, estimated by examining remagnetization strengths in extant and buried impact basins. We investigate whether the Martian dynamo could have been killed by these large basin-forming impacts, via numerical simulation of subcritical dynamos with impact-induced thermal heterogeneity across the core-mantle boundary. We find that subcritical dynamos are prone to the impacts centered on locations within 30 deg of the equator but can easily survive those at higher latitudes. Our results further suggest that magnetic timing places a strong constraint on postimpact polar reorientation, e.g., a minimum 16 deg polar reorientation is needed if Utopia is the dynamo killer.

Could giant basin-forming impacts have killed Martian dynamo?

PubMed

Kuang, W; Jiang, W; Roberts, J; Frey, H V

2014-11-28

The observed strong remanent crustal magnetization at the surface of Mars suggests an active dynamo in the past and ceased to exist around early to middle Noachian era, estimated by examining remagnetization strengths in extant and buried impact basins. We investigate whether the Martian dynamo could have been killed by these large basin-forming impacts, via numerical simulation of subcritical dynamos with impact-induced thermal heterogeneity across the core-mantle boundary. We find that subcritical dynamos are prone to the impacts centered on locations within 30° of the equator but can easily survive those at higher latitudes. Our results further suggest that magnetic timing places a strong constraint on postimpact polar reorientation, e.g., a minimum 16° polar reorientation is needed if Utopia is the dynamo killer.

Benzo(a)pyrene accumulation in soils of technogenic emission zone by subcritical water extraction method

NASA Astrophysics Data System (ADS)

Sushkova, Svetlana; Minkina, Tatiana; Kizilkaya, Ridvan; Mandzhieva, Saglara; Batukaev, Abdulmalik; Bauer, Tatiana; Gulser, Coskun

2016-04-01

The purpose of research is the assessment of main marker of polycyclic aromatic hydrocarbons contamination, benzo[a]pyrene (BaP) content in soils of emission zone of the power complex plant in soils with use of ecologically clean and effective subcritical water extraction method. Studies were conducted on the soils of monitoring plots subjected to Novocherkassk Power Plant emissions from burning coal. In 2000, monitoring plots were established at different distances from the NPS (1.0-20.0 km). Soil samples for the determination of soil properties and the contents of BaP were taken from a depth of 0-20 cm. The soil cover in the region under study consisted of ordinary chernozems, meadow-chernozemic soils, and alluvial meadow soils. This soil revealed the following physical and chemical properties: Corg-3.1-5.0%, pH-7.3-7.6, ECE-31.2-47.6 mmol(+)/100g; CaCO3-0.2-1.0%, the content of physical clay - 51-67% and clay - 3-37%. BaP extraction from soils was carried out by a subcritical water extraction method. Subcritical water extraction of BaP from soil samples was conducted in a specially developed extraction cartridge made of stainless steel and equipped with screw-on caps at both ends. It was also equipped with a manometer that included a valve for pressure release to maintain an internal pressure of 100 atm. The extraction cartridge containing a sample and water was placed into an oven connected to a temperature regulator under temperature 250oC and pressure 60 atm. The BaP concentration in the acetonitrile extract was determined by HPLC. The efficiency of BaP extraction from soil was determined using a matrix spike. The main accumulation of pollutant in 20 cm layer of soils is noted directly in affected zone on the plots situated at 1.2, 1.6, 5.0, 8.0 km from emission source in the direction of prevailing winds. The maximum quantity of a pollutant was founded in the soil of the plot located mostly close to a source of pollution in the direction of prevailing winds. Value from 2012 to 2013 reached to 316.5 mkg/kg in 5 cm soil layer and 217.8 mkg/kg in 5-20 cm soil layer that exceeded the BaP maximum concentration limit level in the soil up to 15 times. The maximum limited concentration of BaP in soil is 20 mkg/kg according Russian Federation legislation. Thus, a method of BaP determination in soils has been approved as based upon the subcritical water extraction under the optimum conditions. The efficiency of the given method involves the use of subcritical water as an environmentally friendly solvent, a shorter time for environmental analysis. BaP distribution and accumulation tendencies were investigated during the 2 years of monitoring researches in studied soils. The main factor of technogenic influence on the soil the investigated area are toxic emissions of a power complex plant from burning coal. Despite the environmental activities of in the enterprise, the impact of emissions on the environment location nearby today is still primary. This research was supported by projects of the Ministry of Education and Science of Russia, no. 5.885.2014/K and Grant of President of Russian Federation no. MK-6827.2015.4, RFBR no. 15-35-21134.

Stability analysis of BWR nuclear-coupled thermal-hyraulics using a simple model

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

Karve, A.A.; Rizwan-uddin; Dorning, J.J.

1995-09-01

A simple mathematical model is developed to describe the dynamics of the nuclear-coupled thermal-hydraulics in a boiling water reactor (BWR) core. The model, which incorporates the essential features of neutron kinetics, and single-phase and two-phase thermal-hydraulics, leads to simple dynamical system comprised of a set of nonlinear ordinary differential equations (ODEs). The stability boundary is determined and plotted in the inlet-subcooling-number (enthalpy)/external-reactivity operating parameter plane. The eigenvalues of the Jacobian matrix of the dynamical system also are calculated at various steady-states (fixed points); the results are consistent with those of the direct stability analysis and indicate that a Hopf bifurcationmore » occurs as the stability boundary in the operating parameter plane is crossed. Numerical simulations of the time-dependent, nonlinear ODEs are carried out for selected points in the operating parameter plane to obtain the actual damped and growing oscillations in the neutron number density, the channel inlet flow velocity, and the other phase variables. These indicate that the Hopf bifurcation is subcritical, hence, density wave oscillations with growing amplitude could result from a finite perturbation of the system even where the steady-state is stable. The power-flow map, frequently used by reactor operators during start-up and shut-down operation of a BWR, is mapped to the inlet-subcooling-number/neutron-density (operating-parameter/phase-variable) plane, and then related to the stability boundaries for different fixed inlet velocities corresponding to selected points on the flow-control line. The stability boundaries for different fixed inlet subcooling numbers corresponding to those selected points, are plotted in the neutron-density/inlet-velocity phase variable plane and then the points on the flow-control line are related to their respective stability boundaries in this plane.« less

Full-scale-wind-tunnel Tests of a 35 Degree Sweptback Wing Airplane with High-velocity Blowing over the Training-edge Flaps

NASA Technical Reports Server (NTRS)

Kelley, Mark W; Tolhurst, William H JR

1955-01-01

A wind-tunnel investigation was made to determine the effects of ejecting high-velocity air near the leading edge of plain trailing-edge flaps on a 35 degree sweptback wing. The tests were made with flap deflections from 45 degrees to 85 degrees and with pressure ratios across the flap nozzles from sub-critical up to 2.9. A limited study of the effects of nozzle location and configuration on the efficiency of the flap was made. Measurements of the lift, drag, and pitching moment were made for Reynolds numbers from 5.8 to 10.1x10(6). Measurements were also made of the weight rate of flow, pressure, and temperature of the air supplied to the flap nozzles.The results show that blowing on the deflected flap produced large flap lift increments. The amount of air required to prevent flow separation on the flap was significantly less than that estimated from published two-dimensional data. When the amount of air ejected over the flap was just sufficient to prevent flow separation, the lift increment obtained agreed well with linear inviscid fluid theory up to flap deflections of 60 degrees. The flap lift increment at 85 degrees flap deflection was about 80 percent of that predicted theoretically.With larger amounts of air blown over the flap, these lift increments could be significantly increased. It was found that the performance of the flap was relatively insensitive to the location of the flap nozzle, to spacers in the nozzle, and to flow disturbances such as those caused by leading-edge slats or discontinuities on the wing or flap surfaces. Analysis of the results indicated that installation of this system on an F-86 airplane is feasible.

Negative Magnus lift on a rotating sphere at around the critical Reynolds number

NASA Astrophysics Data System (ADS)

Muto, Masaya; Tsubokura, Makoto; Oshima, Nobuyuki

2012-01-01

Negative Magnus lift acting on a sphere rotating about the axis perpendicular to an incoming flow was investigated using large-eddy simulation at three Reynolds numbers of 1.0 × 104, 2.0 × 105, and 1.14 × 106. The numerical methods used were first validated on a non-rotating sphere, and the spatial resolution around the sphere was determined so as to reproduce the laminar separation, reattachment, and turbulent transition of the boundary layer observed in the vicinity of the critical Reynolds number. The rotating sphere exhibited a positive or negative Magnus effect depending on the Reynolds number and the imposed rotating speed. At Reynolds numbers in the subcritical or supercritical regimes, the direction of the Magnus lift force was independent of the rotational speed. In contrast, the lift force was negative in the critical regime when particular rotating speeds were imposed. This negative Magnus effect was investigated in the context of suppression or promotion of boundary layer transition around the separation point.

Development of MCAERO wing design panel method with interactive graphics module

NASA Technical Reports Server (NTRS)

Hawk, J. D.; Bristow, D. R.

1984-01-01

A reliable and efficient iterative method has been developed for designing wing section contours corresponding to a prescribed subcritical pressure distribution. The design process is initialized by using MCAERO (MCAIR 3-D Subsonic Potential Flow Analysis Code) to analyze a baseline configuration. A second program DMCAERO is then used to calculate a matrix containing the partial derivative of potential at each control point with respect to each unknown geometry parameter by applying a first-order expansion to the baseline equations in MCAERO. This matrix is calculated only once but is used in each iteration cycle to calculate the geometry perturbation and to analyze the perturbed geometry. The potential on the new geometry is calculated by linear extrapolation from the baseline solution. This extrapolated potential is converted to velocity by numerical differentiation, and velocity is converted to pressure by using Bernoulli's equation. There is an interactive graphics option which allows the user to graphically display the results of the design process and to interactively change either the geometry or the prescribed pressure distribution.

Memory effects, transient growth, and wave breakup in a model of paced atrium

NASA Astrophysics Data System (ADS)

Garzón, Alejandro; Grigoriev, Roman O.

2017-09-01

The mechanisms underlying cardiac fibrillation have been investigated for over a century, but we are still finding surprising results that change our view of this phenomenon. The present study focuses on the transition from normal rhythm to spiral wave chaos associated with a gradual increase in the pacing rate. While some of our findings are consistent with existing experimental, numerical, and theoretical studies of this problem, one result appears to contradict the accepted picture. Specifically we show that, in a two-dimensional model of paced homogeneous atrial tissue, transition from discordant alternans to conduction block, wave breakup, reentry, and spiral wave chaos is associated with the transient growth of finite amplitude disturbances rather than a conventional instability. It is mathematically very similar to subcritical, or bypass, transition from laminar fluid flow to turbulence, which allows many of the tools developed in the context of fluid turbulence to be used for improving our understanding of cardiac arrhythmias.

New Species of Fire Discovered: Fingering Flamelets Form a Dynamic Population

NASA Technical Reports Server (NTRS)

Olson, Sandra L.; Miller, Fletcher J.; Wichman, Indrek S.

2005-01-01

Poets and artists have long used fire as a metaphor for life. At the NASA Glenn Research Center, recent experiments in a subcritical Rayleigh number flow channel demonstrated that this analogy holds up surprisingly well when tools developed to characterize a biological population are applied to a class of fire that occurs in near-extinction, weakly convective environments (such as microgravity) or in vertically confined spaces (such as our apparatus). Under these conditions, the flame breaks into numerous 'flamelets" that form a Turing-type reaction-diffusion fingering pattern as they spread across the fuel. It is standard practice on U.S. spacecraft for the astronaut crew to turn off the ventilation to help extinguish a fire, both to eliminate the fresh oxygen supply and to reduce the distribution of the smoke. When crew members think that the fire is fully extinguished, they reactivate the ventilation system to clear the smoke. However, some flamelets can survive, and our experiments have demonstrated that flamelets quickly grow into a large fire when ventilation increases.

Symmetry breaking motion of a vortex pair in a driven cavity

NASA Astrophysics Data System (ADS)

McHugh, John; Osman, Kahar; Farias, Jason

2002-11-01

The two-dimensional driven cavity problem with an anti-symmetric sinusoidal forcing has been found to exhibit a subcritical symmetry breaking bifurcation (Farias and McHugh, Phys. Fluids, 2002). Equilibrium solutions are either a symmetric vortex pair or an asymmetric motion. The asymmetric motion is an asymmetric vortex pair at low Reynolds numbers, but merges into a three vortex motion at higher Reynolds numbers. The asymmetric solution is obtained by initiating the flow with a single vortex centered in the domain. Symmetric motion is obtained with no initial vortex, or weak initial vortex. The steady three-vortex motion occurs at a Reynolds number of approximately 3000, where the symmetric vortex pair has already gone through a Hopf bifurcation. Further two-dimensional results show that forcing with two full oscillations across the top of the cavity results in two steady vortex motions, depending on initial conditions. Three-dimensional results have even more steady solutions. The results are computational and theoretical.

Subcritical fracturing of shales under chemically reactive conditions

NASA Astrophysics Data System (ADS)

Chen, X.; Callahan, O. A.; Eichhubl, P.; Olson, J. E.

2016-12-01

Growth of opening-mode fractures under chemically reactive subsurface conditions is potentially relevant for seal integrity in subsurface CO2 storage and hazardous waste disposal. Using double-torsion load relaxation tests we determine mode-I fracture toughness (KIC), subcritical index (SCI), and the stress-intensity factor vs fracture velocity (K-V) behavior of Marcellus, Woodford, and Mancos shales. Samples are tested under ambient air and aqueous conditions with variable NaCl and KCl concentrations, variable pH, and temperatures of up to 70. Under ambient air condition, KIC determined from double torsion tests is 1.3, 0.6, and 1.1 MPam1/2 for Marcellus, Woodford, and Mancos shales, respectively. SCI under ambient air condition is between 55 and 90 for the shales tested. Tests in aqueous solutions show a significant drop of KIC compared to ambient air condition. For tests in deionized water, KIC reduction is 18.5% for Marcellus and 47.0% for Woodford. The presence of aqueous fluids also results in a reduction of the SCI up to 85% compared to ambient condition. K-V curves generally obey a power-law relation throughout the load-relaxation period. However, aqueous-based tests on samples result in K-V curves deviating from the power-law relation, with the SCI values gradually decreasing with time during the relaxation period. This non-power-law behavior is obvious in Woodford and Mancos, but negligible in Marcellus. We find that the shales interact with the aqueous solution both at the fracture tip and within the rock matrix during subcritical fracturing. For Marcellus shale, water mainly interacts with the fracture tip on both tests due to low matrix permeability and less reactive mineral composition. However, Woodford and Mancos react strongly with water causing significant sample degradation. The competition between degradation and fracture growth results in the time-dependent SCI: at lower fracture velocities, the tip interacts longer with the chemically altered area around the tip; at higher fracture velocities, the fracture propagates through the altered area before significant degradation. Our results display strong weakening effects of chemically reactive fluids on subcritical fracture properties with implications on subsurface storage seal performance.

Subcritical water extraction of organic matter from sedimentary rocks.

PubMed

Luong, Duy; Sephton, Mark A; Watson, Jonathan S

2015-06-16

Subcritical water extraction of organic matter containing sedimentary rocks at 300°C and 1500 psi produces extracts comparable to conventional solvent extraction. Subcritical water extraction of previously solvent extracted samples confirms that high molecular weight organic matter (kerogen) degradation is not occurring and that only low molecular weight organic matter (free compounds) are being accessed in analogy to solvent extraction procedures. The sedimentary rocks chosen for extraction span the classic geochemical organic matter types. A type I organic matter-containing sedimentary rock produces n-alkanes and isoprenoidal hydrocarbons at 300°C and 1500 psi that indicate an algal source for the organic matter. Extraction of a rock containing type II organic matter at the same temperature and pressure produces aliphatic hydrocarbons but also aromatic compounds reflecting the increased contributions from terrestrial organic matter in this sample. A type III organic matter-containing sample produces a range of non-polar and polar compounds including polycyclic aromatic hydrocarbons and oxygenated aromatic compounds at 300°C and 1500 psi reflecting a dominantly terrestrial origin for the organic materials. Although extraction at 300°C and 1500 psi produces extracts that are comparable to solvent extraction, lower temperature steps display differences related to organic solubility. The type I organic matter produces no products below 300°C and 1500 psi, reflecting its dominantly aliphatic character, while type II and type III organic matter contribute some polar components to the lower temperature steps, reflecting the chemical heterogeneity of their organic inventory. The separation of polar and non-polar organic compounds by using different temperatures provides the potential for selective extraction that may obviate the need for subsequent preparative chromatography steps. Our results indicate that subcritical water extraction can act as a suitable replacement for conventional solvent extraction of sedimentary rocks, but can also be used for any organic matter containing mineral matrix, including soils and recent sediments, and has the added benefit of tailored extraction for analytes of specific polarities. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

Bedforms formed by experimental supercritical density flows

NASA Astrophysics Data System (ADS)

Naruse, Hajime; Izumi, Norihiro; Yokokawa, Miwa; Muto, Tetsuji

2014-05-01

This study reveals characteristics and formative conditions of bedforms produced by saline density flows in supercritical flow conditions, especially focusing on the mechanism of the formation of plane bed. The motion of sediment particles forming bedforms was resolved by high-speed cameras (1/1000 frame/seconds). Experimental density flows were produced by mixtures of salt water (1.01-1.04 in density) and plastic particles (1.5 in specific density, 140 or 240 mm in diameter). Salt water and plastic particles are analogue materials of muddy water and sand particles in turbidity currents respectively. Acrylic flume (4.0 m long, 2.0 cm wide and 0.5 m deep) was submerged in an experimental tank (6.0 m long, 1.8 m wide and 1.2 m deep) that was filled by clear water. Features of bedforms were observed when the bed state in the flume reached equilibrium condition. The experimental conditions range 1.5-4.2 in densimetric Froude number and 0.2-0.8 in Shields dimensionless stress. We report the two major discoveries as a result of the flume experiments: (1) Plane bed under Froude-supercritical flows and (2) Geometrical characteristics of cyclic steps formed by density flows. (1) Plane bed was formed under the condition of supercritical flow regime. In previous studies, plane bed has been known to be formed by subcritical unidirectional flows (ca. 0.8 in Froude number). However, this study implies that plane bed can also be formed by supercritical conditions with high Shields dimensionless stress (>0.4) and very high Froude number (> 4.0). This discovery may suggest that previous estimations of paleo-hydraulic conditions of parallel lamination in turbidites should be reconsidered. The previous experimental studies and data from high-speed camera suggest that the region of plane bed formation coincides with the region of the sheet flow developments. The particle transport in sheet flow (thick bedload layer) induces transform of profile of flow shear stress, which may be related with the formation of the plane bed. (2) This study also revealed geometrical characteristics of cyclic steps. Cyclic step is a type of bedform that is frequently observed in flanks of submarine levees. This study proved that cyclic steps of density flows show different geometry to those formed by open channel flows. Cyclic steps formed by open channel flows have generally asymmetrical geometry in which lee side is short, whereas cyclic steps formed by density flows are relatively symmetrical and varies their morphology remarkably depending on flow conditions.

Operation and reactivity measurements of an accelerator driven subcritical TRIGA reactor

NASA Astrophysics Data System (ADS)

O'Kelly, David Sean

Experiments were performed at the Nuclear Engineering Teaching Laboratory (NETL) in 2005 and 2006 in which a 20 MeV linear electron accelerator operating as a photoneutron source was coupled to the TRIGA (Training, Research, Isotope production, General Atomics) Mark II research reactor at the University of Texas at Austin (UT) to simulate the operation and characteristics of a full-scale accelerator driven subcritical system (ADSS). The experimental program provided a relatively low-cost substitute for the higher power and complexity of internationally proposed systems utilizing proton accelerators and spallation neutron sources for an advanced ADSS that may be used for the burning of high-level radioactive waste. Various instrumentation methods that permitted ADSS neutron flux monitoring in high gamma radiation fields were successfully explored and the data was used to evaluate the Stochastic Pulsed Feynman method for reactivity monitoring.

Subcritical Hopf Bifurcation and Stochastic Resonance of Electrical Activities in Neuron under Electromagnetic Induction

PubMed Central

Fu, Yu-Xuan; Kang, Yan-Mei; Xie, Yong

2018-01-01

The FitzHugh–Nagumo model is improved to consider the effect of the electromagnetic induction on single neuron. On the basis of investigating the Hopf bifurcation behavior of the improved model, stochastic resonance in the stochastic version is captured near the bifurcation point. It is revealed that a weak harmonic oscillation in the electromagnetic disturbance can be amplified through stochastic resonance, and it is the cooperative effect of random transition between the resting state and the large amplitude oscillating state that results in the resonant phenomenon. Using the noise dependence of the mean of interburst intervals, we essentially suggest a biologically feasible clue for detecting weak signal by means of neuron model with subcritical Hopf bifurcation. These observations should be helpful in understanding the influence of the magnetic field to neural electrical activity. PMID:29467642

On the asymptotic behavior of a subcritical convection-diffusion equation with nonlocal diffusion

NASA Astrophysics Data System (ADS)

Cazacu, Cristian M.; Ignat, Liviu I.; Pazoto, Ademir F.

2017-08-01

In this paper we consider a subcritical model that involves nonlocal diffusion and a classical convective term. In spite of the nonlocal diffusion, we obtain an Oleinik type estimate similar to the case when the diffusion is local. First we prove that the entropy solution can be obtained by adding a small viscous term μ uxx and letting μ\\to 0 . Then, by using uniform Oleinik estimates for the viscous approximation we are able to prove the well-posedness of the entropy solutions with L 1-initial data. Using a scaling argument and hyperbolic estimates given by Oleinik’s inequality, we obtain the first term in the asymptotic behavior of the nonnegative solutions. Finally, the large time behavior of changing sign solutions is proved using the classical flux-entropy method and estimates for the nonlocal operator.

Effect of Subcritical Fluid Extraction on the High Quality of Headspace Oil from Jasminum sambac (L.) Aiton.

PubMed

Ye, Qiuping; Jin, Xinyi; Wei, Shiqin; Zheng, Gongyu; Li, Xinlei

2016-05-01

Subcritical fluid extraction (SFE), as a novel method, was applied to investigate the yield, quality, and sensory evaluation of headspace oil from Jasminum sambac (L.) Aiton in comparison with petroleum ether extraction (PEE). The results indicated that the yield of the headspace oil using SFE was significantly higher (P < 0.05) than when using PEE. SFE contributed to obtaining alcohols and ethers, prevented the thermal reaction of terpenes, and reduced α-caryophyllene and β-caryophyllene in the headspace oil. The contents of linalool (21.90%) and benzyl acetate (16.31%) were higher via SFE than PEE. In addition, the sensory evaluation of SFE was superior to PEE, indicating a fresh, jasmine-like odor and green-yellow color. Thus, SFE is an improved method for obtaining natural headspace oil from jasmine flowers.

Magnetic-Force-Assisted Straightening of Bent Mild Steel Strip by Laser Irradiation

NASA Astrophysics Data System (ADS)

Dutta, Polash P.; Kalita, Karuna; Dixit, Uday S.; Liao, Hengcheng

2017-12-01

This study proposes a technique to straighten bent metallic strips with magnetic-force-assisted laser irradiation. Experiments were conducted for three different types of mechanically-bent mild strips. The first type was bent strips without any heat treatment. The second type was stress-relieved and third type was subcritical-annealed bent strips. These strips were straightened following different schemes of laser irradiation sequence to understand the performance of straightening. A parametric study was conducted by varying laser power and scanning speed. Micro-hardness, tensile test, Charpy impact test and microstructure after straightening were also studied. Different scanning schemes provided different microstructures and mechanical properties. Any serious deterioration in the quality of straightened strips was not noticed. Overall, subcritical-annealed bent strips provided the best performance in straightening. The proposed straightening scheme has potential of becoming an industrial practice.

Subcritical crack growth and other time- and environment-dependent behavior in crustal rocks

NASA Technical Reports Server (NTRS)

Swanson, P. L.

1984-01-01

Stable crack growth strongly influences both the fracture strength of brittle rocks and some of the phenomena precursory to catastrophic failure. Quantification of the time and environment dependence of fracture propagation is attempted with the use of a fracture mechanics technique. Some of the difficulties encountered when applying techniques originally developed for simple synthetic materials to complex materials like rocks are examined. A picture of subcritical fracture propagation is developed that embraces the essential ingredients of the microstructure, a microcrack process zone, and the different roles that the environment plays. To do this, the results of (1) fracture mechanics experiments on five rock types, (2) optical and scanning electron microscopy, (3) studies of microstructural aspects of fracture in ceramics, and (4) exploratory tests examining the time-dependent response of rock to the application of water are examined.

Optimization of subcritical water extraction parameters of antioxidant polyphenols from sea buckthorn (Hippophaë rhamnoides L.) seed residue.

PubMed

Gong, Ying; Zhang, Xiaofei; He, Li; Yan, Qiuli; Yuan, Fang; Gao, Yanxiang

2015-03-01

Polyphenols was extracted with subcritical water from the sea buckthorn seed residue (after oil recovery), and the extraction parameters were optimized using response surface methodology (RSM). The independent processing variables were extraction temperature, extraction time and the ratio of water to solid. The optimal extraction parameters for the extracts with highest ABTS radical scavenging activity were 120 °C, 36 min and the water to solid ratio of 20, and the maximize antioxidant capacity value was 32.42 mmol Trolox equivalent (TE)/100 g. Under the optimal conditions, the yield of total phenolics, total flavonoids and proanthocyanidins was 36.62 mg gallic acid equivalents (GAE)/g, 19.98 mg rutin equivalent (RE)/g and 10.76 mg catechin equivalents (CE)/g, respectively.

An integrated green process: Subcritical water, enzymatic hydrolysis, and fermentation, for biohydrogen production from coconut husk.

PubMed

Muharja, Maktum; Junianti, Fitri; Ranggina, Dian; Nurtono, Tantular; Widjaja, Arief

2018-02-01

The objective of this work is to develop an integrated green process of subcritical water (SCW), enzymatic hydrolysis and fermentation of coconut husk (CCH) to biohydrogen. The maximum sugar yield was obtained at mild severity factor. This was confirmed by the degradation of hemicellulose, cellulose and lignin. The tendency of the changing of sugar yield as a result of increasing severity factor was opposite to the tendency of pH change. It was found that CO 2 gave a different tendency of severity factor compared to N 2 as the pressurizing gas. The result of SEM analysis confirmed the structural changes during SCW pretreatment. This study integrated three steps all of which are green processes which ensured an environmentally friendly process to produce a clean biohydrogen. Copyright © 2017 Elsevier Ltd. All rights reserved.

Subcritical Hopf Bifurcation and Stochastic Resonance of Electrical Activities in Neuron under Electromagnetic Induction.

PubMed

Fu, Yu-Xuan; Kang, Yan-Mei; Xie, Yong

2018-01-01

The FitzHugh-Nagumo model is improved to consider the effect of the electromagnetic induction on single neuron. On the basis of investigating the Hopf bifurcation behavior of the improved model, stochastic resonance in the stochastic version is captured near the bifurcation point. It is revealed that a weak harmonic oscillation in the electromagnetic disturbance can be amplified through stochastic resonance, and it is the cooperative effect of random transition between the resting state and the large amplitude oscillating state that results in the resonant phenomenon. Using the noise dependence of the mean of interburst intervals, we essentially suggest a biologically feasible clue for detecting weak signal by means of neuron model with subcritical Hopf bifurcation. These observations should be helpful in understanding the influence of the magnetic field to neural electrical activity.

Peel-and-Stick: Mechanism Study for Efficient Fabrication of Flexible/Transparent Thin-film Electronics

NASA Astrophysics Data System (ADS)

Lee, Chi Hwan; Kim, Jae-Han; Zou, Chenyu; Cho, In Sun; Weisse, Jeffery M.; Nemeth, William; Wang, Qi; van Duin, Adri C. T.; Kim, Taek-Soo; Zheng, Xiaolin

2013-10-01

Peel-and-stick process, or water-assisted transfer printing (WTP), represents an emerging process for transferring fully fabricated thin-film electronic devices with high yield and fidelity from a SiO2/Si wafer to various non-Si based substrates, including papers, plastics and polymers. This study illustrates that the fundamental working principle of the peel-and-stick process is based on the water-assisted subcritical debonding, for which water reduces the critical adhesion energy of metal-SiO2 interface by 70 ~ 80%, leading to clean and high quality transfer of thin-film electronic devices. Water-assisted subcritical debonding is applicable for a range of metal-SiO2 interfaces, enabling the peel-and-stick process as a general and tunable method for fabricating flexible/transparent thin-film electronic devices.

Polychlorinated biphenyls degradation in subcritical water

NASA Astrophysics Data System (ADS)

Doctor, Ninad; Yang, Larry; Yang, Yu

2017-08-01

In this work, the degradation of PCB-118, PCB-156, and PCB-180 congeners under subcritical conditions has been investigated. Stainless reaction vessels were used to carry out the heating of reaction mixtures. Liquid-liquid extraction of the reaction mixtures was conducted prior to GC analysis. Approximately 30% PCBs were degraded by 30% hydrogen peroxide after 24 hours of reaction time but without heating the mixtures. The percent degradation of PCBs was however improved to approximately 60% after heating the mixtures at 300 °C for an hour. In general, the PCB degradation efficiency was enhanced by increasing the reaction temperature from 300 and 350 °C. The percent degradation of PCBs was mostly improved by increasing the heating time from 1 hour to 6 hours. In addition, increasing the percentage of hydrogen peroxide significantly increases the rate of PCB destruction.

Peel-and-stick: mechanism study for efficient fabrication of flexible/transparent thin-film electronics.

PubMed

Lee, Chi Hwan; Kim, Jae-Han; Zou, Chenyu; Cho, In Sun; Weisse, Jeffery M; Nemeth, William; Wang, Qi; van Duin, Adri C T; Kim, Taek-Soo; Zheng, Xiaolin

2013-10-10

Peel-and-stick process, or water-assisted transfer printing (WTP), represents an emerging process for transferring fully fabricated thin-film electronic devices with high yield and fidelity from a SiO2/Si wafer to various non-Si based substrates, including papers, plastics and polymers. This study illustrates that the fundamental working principle of the peel-and-stick process is based on the water-assisted subcritical debonding, for which water reduces the critical adhesion energy of metal-SiO2 interface by 70 ~ 80%, leading to clean and high quality transfer of thin-film electronic devices. Water-assisted subcritical debonding is applicable for a range of metal-SiO2 interfaces, enabling the peel-and-stick process as a general and tunable method for fabricating flexible/transparent thin-film electronic devices.

Temperature effects on diffusion coefficient for 6-gingerol and 6-shogaol in subcritical water extraction

NASA Astrophysics Data System (ADS)

Ilia Anisa, Nor; Azian, Noor; Sharizan, Mohd; Iwai, Yoshio

2014-04-01

6-gingerol and 6-shogaol are the main constituents as anti-inflammatory or bioactive compounds from zingiber officinale Roscoe. These bioactive compounds have been proven for inflammatory disease, antioxidatives and anticancer. The effect of temperature on diffusion coefficient for 6-gingerol and 6-shogaol were studied in subcritical water extraction. The diffusion coefficient was determined by Fick's second law. By neglecting external mass transfer and solid particle in spherical form, a linear portion of Ln (1-(Ct/Co)) versus time was plotted in determining the diffusion coefficient. 6-gingerol obtained the higher yield at 130°C with diffusion coefficient of 8.582x10-11 m2/s whilst for 6-shogaol, the higher yield and diffusion coefficient at 170°C and 19.417 × 10-11 m2/s.

Medical Isotope Production Analyses In KIPT Neutron Source Facility

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

Talamo, Alberto; Gohar, Yousry

Medical isotope production analyses in Kharkov Institute of Physics and Technology (KIPT) neutron source facility were performed to include the details of the irradiation cassette and the self-shielding effect. An updated detailed model of the facility was used for the analyses. The facility consists of an accelerator-driven system (ADS), which has a subcritical assembly using low-enriched uranium fuel elements with a beryllium-graphite reflector. The beryllium assemblies of the reflector have the same outer geometry as the fuel elements, which permits loading the subcritical assembly with different number of fuel elements without impacting the reflector performance. The subcritical assembly is drivenmore » by an external neutron source generated from the interaction of 100-kW electron beam with a tungsten target. The facility construction was completed at the end of 2015, and it is planned to start the operation during the year of 2016. It is the first ADS in the world, which has a coolant system for removing the generated fission power. Argonne National Laboratory has developed the design concept and performed extensive design analyses for the facility including its utilization for the production of different radioactive medical isotopes. 99Mo is the parent isotope of 99mTc, which is the most commonly used medical radioactive isotope. Detailed analyses were performed to define the optimal sample irradiation location and the generated activity, for several radioactive medical isotopes, as a function of the irradiation time.« less

Diethylstilbestrol in fish tissue determined through subcritical fluid extraction and with GC-MS

NASA Astrophysics Data System (ADS)

Qiao, Qinghui; Shi, Nianrong; Feng, Xiaomei; Lu, Jie; Han, Yuqian; Xue, Changhu

2016-06-01

As the key point in sex hormone analysis, sample pre-treatment technology has attracted scientists' attention all over the world, and the development trend of sample preparation forwarded to faster and more efficient technologies. Taking economic and environmental concerns into account, subcritical fluid extraction as a faster and more efficient method has stood out as a sample pre-treatment technology. This new extraction technology can overcome the shortcomings of supercritical fluid and achieve higher extraction efficiency at relatively low pressures and temperatures. In this experiment, a simple, sensitive and efficient method has been developed for the determination of diethylstilbestrol (DES) in fish tissue using subcritical 1,1,1,2-tetrafluoroethane (R134a) extraction in combination with gas chromatography-mass spectrometry (GC-MS). After extraction, freezing-lipid filtration was utilized to remove fatty co-extract. Further purification steps were performed with C18 and NH2 solid phase extraction (SPE). Finally, the analyte was derived by heptafluorobutyric anhydride (HFBA), followed by GC-MS analysis. Response surface methodology (RSM) was employed to optimizing the extraction condition, and the optimized was as follows: extraction pressure, 4.3 MPa; extraction temperature, 26°C; amount of co-solvent volume, 4.7 mL. Under this condition, at a spiked level of 1, 5, 10 μg kg-1, the mean recovery of DES was more than 90% with relative standard deviations (RSDs) less than 10%. Finally, the developed method has been successfully used to analyzing the real samples.

The use of sub-critical water hydrolysis for the recovery of peptides and free amino acids from food processing wastes. Review of sources and main parameters.

PubMed

Marcet, Ismael; Álvarez, Carlos; Paredes, Benjamín; Díaz, Mario

2016-03-01

Food industry processing wastes are produced in enormous amounts every year, such wastes are usually disposed with the corresponding economical cost it implies, in the best scenario they can be used for pet food or composting. However new promising technologies and tools have been developed in the last years aimed at recovering valuable compounds from this type of materials. In particular, sub-critical water hydrolysis (SWH) has been revealed as an interesting way for recovering high added-value molecules, and its applications have been broadly referred in the bibliography. Special interest has been focused on recovering protein hydrolysates in form of peptides or amino acids, from both animal and vegetable wastes, by means of SWH. These recovered biomolecules have a capital importance in fields such as biotechnology research, nutraceuticals, and above all in food industry, where such products can be applied with very different objectives. Present work reviews the current state of art of using sub-critical water hydrolysis for protein recovering from food industry wastes. Key parameters as reaction time, temperature, amino acid degradation and kinetic constants have been discussed. Besides, the characteristics of the raw material and the type of products that can be obtained depending on the substrate have been reviewed. Finally, the application of these hydrolysates based on their functional properties and antioxidant activity is described. Copyright © 2016 Elsevier Ltd. All rights reserved.

Highly Selective and Considerable Subcritical Butane Extraction to Separate Abamectin in Green Tea.

PubMed

Zhang, Yating; Gu, Lingbiao; Wang, Fei; Kong, Lingjun; Pang, Huili; Qin, Guangyong

2017-06-01

We specially carried out the subcritical butane extraction to separate abamectin from tea leaves. Four parameters, such as extraction temperature, extraction time, number of extraction cycles, and solid-liquid ratio were studied and optimized through the response surface methodology with design matrix developed by Box-Behnken. Seventeen experiments with three various factors and three variable levels were employed to investigate the effect of these parameters on the extraction of abamectin. Besides, catechins, theanine, caffeine, and aroma components were determined by both high-performance liquid chromatography and gas chromatography-mass spectrometry to evaluate the tea quality before and after the extraction. The results showed that the extraction temperature was the uppermost parameter compared with others. The optimal extraction conditions selected as follows: extraction temperature, 42°C; number of extraction cycles and extraction time, 1 and 30 min, respectively; and solid-liquid ratio, 1:10. Based on the above study, the separation efficiency of abamectin was up to 93.95%. It is notable that there has a quite low loss rate, including the negligible damage of aroma components, the bits reduce of catechins within the range of 0.7%-13.1%, and a handful lessen of caffeine and theanine of 1.81% and 2.6%, respectively. The proposed method suggested subcritical butane possesses solubility for lipid-soluble pesticides, and since most of the pesticides are attached to the surfaces of tea, thus the as-applied method was successfully effective to separate abamectin because of the so practical and promising method.

Fatigue of Self-Healing Nanofiber-based Composites: Static Test and Subcritical Crack Propagation.

PubMed

Lee, Min Wook; Sett, Soumyadip; Yoon, Sam S; Yarin, Alexander L

2016-07-20

Here, we studied the self-healing of composite materials filled with epoxy-containing nanofibers. An initial incision in the middle of a composite sample stretched in a static fatigue test can result in either crack propagation or healing. In this study, crack evolution was observed in real time. A binary epoxy, which acted as a self-healing agent, was encapsulated in two separate types of interwoven nano/microfibers formed by dual-solution blowing, with the core containing either epoxy or hardener and the shell being formed from poly(vinylidene fluoride)/ poly(ethylene oxide) mixture. The core-shell fibers were encased in a poly(dimethylsiloxane) matrix. When the fibers were damaged by a growing crack in this fiber-reinforced composite material because of static stretching in the fatigue test, they broke and released the healing agent into the crack area. The epoxy used in this study was cured and solidified for approximately an hour at room temperature, which then conglutinated and healed the damaged location. The observations were made for at least several hours and in some cases up to several days. It was revealed that the presence of the healing agent (the epoxy) in the fibers successfully prevented the propagation of cracks in stretched samples subjected to the fatigue test. A theoretical analysis of subcritical cracks was performed, and it revealed a jumplike growth of subcritical cracks, which was in qualitative agreement with the experimental results.

Oxidation of Alloy 600 and Alloy 690: Experimentally Accelerated Study in Hydrogenated Supercritical Water

NASA Astrophysics Data System (ADS)

Moss, Tyler; Cao, Guoping; Was, Gary S.

2017-04-01

The objective of this study is to determine whether the oxidation of Alloys 600 and 690 in supercritical water occurs by the same mechanism in subcritical water. Coupons of Alloys 690 and 600 were exposed to hydrogenated subcritical and supercritical water from 633 K to 673 K (360 °C to 400 °C) and the oxidation behavior was observed. By all measures of oxide character and behavior, the oxidation process is the same above and below the supercritical line. Similar oxide morphologies, structures, and chemistries were observed for each alloy across the critical point, indicating that the oxidation mechanism is the same in both subcritical and supercritical water. Oxidation results in a multi-layer oxide structure composed of particles of NiO and NiFe2O4 formed by precipitation on the outer surface and a chromium-rich inner oxide layer formed by diffusion of oxygen to the metal-oxide interface. The inner oxide on Alloy 600 is less chromium rich than that observed on Alloy 690 and is accompanied by preferential oxidation of grain boundaries. The inner oxide on Alloy 690 initially forms by internal oxidation before a protective layer of chromium-rich MO is formed with Cr2O3 at the metal-oxide interface. Grain boundaries in Alloy 690 act as fast diffusion paths for chromium that forms a protective Cr2O3 layer at the surface, preventing grain boundary oxidation from occurring.

Preliminary neutronics design of china lead-alloy cooled demonstration reactor (CLEAR-III) for nuclear waste transmutation

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

Chen, Z.; Southwest Science and Technology Univ., No.350 Shushanhu Road, Shushan District, Hefei, Anhui, 230031; Chen, Y.

2012-07-01

China Lead-Alloy cooled Demonstration Reactor (CLEAR-III), which is the concept of lead-bismuth cooled accelerator driven sub-critical reactor for nuclear waste transmutation, was proposed and designed by FDS team in China. In this study, preliminary neutronics design studies have primarily focused on three important performance parameters including Transmutation Support Ratio (TSR), effective multiplication factor and blanket thermal power. The constraint parameters, such as power peaking factor and initial TRU loading, were also considered. In the specific design, uranium-free metallic dispersion fuel of (TRU-Zr)-Zr was used as one of the CLEAR-III fuel types and the ratio between MA and Pu was adjustedmore » to maximize transmutation ratio. In addition, three different fuel zones differing in the TRU fraction of the fuel were respectively employed for this subcritical reactor, and the zone sizes and TRU fractions were determined such that the linear powers of these zones were close to each other. The neutronics calculations and analyses were performed by using Multi-Functional 4D Neutronics Simulation System named VisualBUS and nuclear data library HENDL (Hybrid Evaluated Nuclear Data Library). In the preliminary design, the maximum TSRLLMA was {approx}11 and the blanket thermal power was {approx}1000 MW when the effective multiplication factor was 0.98. The results showed that good performance of transmutation could be achieved based on the subcritical reactor loaded with uranium-free fuel. (authors)« less

Initial instability of round liquid jet at subcritical and supercritical environments

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

Muthukumaran, C. K.; Vaidyanathan, Aravind, E-mail: aravind7@iist.ac.in

2016-07-15

In the present experimental work, the behavior of laminar liquid jet in its own vapor as well as supercritical fluid environment is conducted. Also the study of liquid jet injection into nitrogen (N{sub 2}) environment is carried out at supercritical conditions. It is expected that the injected liquid jet would undergo thermodynamic transition to the chamber condition and this would alter the behavior of the injected jet. Moreover at such conditions there is a strong dependence between thermodynamic and fluid dynamic processes. Thus the thermodynamic transition has its effect on the initial instability as well as the breakup nature ofmore » the injected liquid jet. In the present study, the interfacial disturbance wavelength, breakup characteristics, and mixing behavior are analysed for the fluoroketone liquid jet that is injected into N{sub 2} environment as well as into its own vapor at subcritical to supercritical conditions. It is observed that at subcritical chamber conditions, the injected liquid jet exhibits classical liquid jet characteristics with Rayleigh breakup at lower Weber number and Taylor breakup at higher Weber number for both N{sub 2} and its own environment. At supercritical chamber conditions with its own environment, the injected liquid jet undergoes sudden thermodynamic transition to chamber conditions and single phase mixing characteristics is observed. However, the supercritical chamber conditions with N{sub 2} as ambient fluid does not have significant effect on the thermodynamic transition of the injected liquid jet.« less

Tailoring of processing parameters for sintering microsphere-based scaffolds with dense-phase carbon dioxide

PubMed Central

Jeon, Ju Hyeong; Bhamidipati, Manjari; Sridharan, BanuPriya; Scurto, Aaron M.; Berkland, Cory J.; Detamore, Michael S.

2015-01-01

Microsphere-based polymeric tissue-engineered scaffolds offer the advantage of shape-specific constructs with excellent spatiotemporal control and interconnected porous structures. The use of these highly versatile scaffolds requires a method to sinter the discrete microspheres together into a cohesive network, typically with the use of heat or organic solvents. We previously introduced subcritical CO2 as a sintering method for microsphere-based scaffolds; here we further explored the effect of processing parameters. Gaseous or subcritical CO2 was used for making the scaffolds, and various pressures, ratios of lactic acid to glycolic acid in poly(lactic acid-co-glycolic acid), and amounts of NaCl particles were explored. By changing these parameters, scaffolds with different mechanical properties and morphologies were prepared. The preferred range of applied subcritical CO2 was 15–25 bar. Scaffolds prepared at 25 bar with lower lactic acid ratios and without NaCl particles had a higher stiffness, while the constructs made at 15 bar, lower glycolic acid content, and with salt granules had lower elastic moduli. Human umbilical cord mesenchymal stromal cells (hUCMSCs) seeded on the scaffolds demonstrated that cells penetrate the scaffolds and remain viable. Overall, the study demonstrated the dependence of the optimal CO2 sintering parameters on the polymer and conditions, and identified desirable CO2 processing parameters to employ in the sintering of microsphere-based scaffolds as a more benign alternative to heat-sintering or solvent-based sintering methods. PMID:23115065

Factors that affect the permeability of commercial hollow-fibre membranes in a submerged anaerobic MBR (HF-SAnMBR) system.

PubMed

Robles, A; Ruano, M V; Ribes, J; Ferrer, J

2013-03-01

A demonstration plant with two commercial HF ultrafiltration membrane modules (PURON(®), Koch Membrane Systems, PUR-PSH31) was operated with urban wastewater. The effect of the main operating variables on membrane performance at sub-critical and supra-critical filtration conditions was tested. The physical operating variables that affected membrane performance most were gas sparging intensity and back-flush (BF) frequency. Indeed, low gas sparging intensities (around 0.23 Nm(3) h(-1) m(-2)) and low BF frequencies (30-s back-flush for every 10 basic filtration-relaxation cycles) were enough to enable membranes to be operated sub-critically even when levels of mixed liquor total solids were high (up to 25 g L(-1)). On the other hand, significant gas sparging intensities and BF frequencies were required in order to maintain long-term operating at supra-critical filtration conditions. After operating for more than two years at sub-critical conditions (transmembrane flux between 9 and 13.3 LMH at gas sparging intensities of around 0.23 Nm(3) h(-1) m(-2) and MLTS levels from around 10-30 g L(-1)) no significant irreversible/irrecoverable fouling problems were detected (membrane permeability remained above 100 LMH bar(-1) and total filtration resistance remained below 10(13) m(-1)), therefore no chemical cleaning was conducted. Membrane performance was similar to the aerobic HF membranes operated in full-scale MBR plants. Copyright © 2012 Elsevier Ltd. All rights reserved.

Bedform response to flow variability

USGS Publications Warehouse

Nelson, J.M.; Logan, B.L.; Kinzel, P.J.; Shimizu, Y.; Giri, S.; Shreve, R.L.; McLean, S.R.

2011-01-01

Laboratory observations and computational results for the response of bedform fields to rapid variations in discharge are compared and discussed. The simple case considered here begins with a relatively low discharge over a flat bed on which bedforms are initiated, followed by a short high-flow period with double the original discharge, during which the morphology of the bedforms adjusts, followed in turn by a relatively long period of the original low discharge. For the grain size and hydraulic conditions selected, the Froude number remains subcritical during the experiment, and sediment moves predominantly as bedload. Observations show rapid development of quasi-two-dimensional bedforms during the initial period of low flow with increasing wavelength and height over the initial low-flow period. When the flow increases, the bedforms rapidly increase in wavelength and height, as expected from other empirical results. When the flow decreases back to the original discharge, the height of the bedforms quickly decreases in response, but the wavelength decreases much more slowly. Computational results using an unsteady two-dimensional flow model coupled to a disequilibrium bedload transport model for the same conditions simulate the formation and initial growth of the bedforms fairly accurately and also predict an increase in dimensions during the high-flow period. However, the computational model predicts a much slower rate of wavelength increase, and also performs less accurately during the final low-flow period, where the wavelength remains essentially constant, rather than decreasing. In addition, the numerical results show less variability in bedform wavelength and height than the measured values; the bedform shape is also somewhat different. Based on observations, these discrepancies may result from the simplified model for sediment particle step lengths used in the computational approach. Experiments show that the particle step length varies spatially and temporally over the bedforms during the evolution process. Assuming a constant value for the step length neglects the role of flow alterations in the bedload sediment-transport process, which appears to result in predicted bedform wavelength changes smaller than those observed. However, observations also suggest that three-dimensional effects play at least some role in the decrease of bedform wavelength, so incorporating better models for particle hop lengths alone may not be sufficient to improve model predictions. ?? 2011 John Wiley & Sons, Ltd.

Morphodynamics of Travertine Dam/Waterfall Growth due to the Interaction of Biological Activity, Water Flow and Limestone Emplacement

NASA Astrophysics Data System (ADS)

Izumi, N.; Parker, G.

2012-12-01

Plitvice Lakes in Croatia are characterized by a step-like train of lakes and waterfalls. The waterfalls are located at the crests of naturally-emplaced dams. The top of each dam grows upward at the rate of a few millimeters per year. It is thought that the upward growth of these dams is caused by the interaction of water flow and biological activity, resulting in the precipitation of dissolved limestone. Dam evolution is initiated by the growth of mosses that favor swift, shallow water. Bacteria that inhabit the roots of the moss excrete solid limestone (travertine) from the water. The limestone fossilizes the moss, and then more moss grows on top of the travertine deposit. In this way, the natural dam can grow over to 10 m high, impounding the water behind it to form a lake. We propose a simple model to explain the formation of natural limestone dams by the interaction between water flow and biologically-mediated travertine deposition. We assume for simplicity that light is the only factor determining the growth of moss, which is then colonized by travertine-emplacing bacteria. We also assume that the water is saturated with dissolved limestone, so that the process is not limited by limestone availability. Photosynthesis, and thus the growth rate of moss are crudely approximated as decreasing linearly with depth. We employ the shallow water equations to describe water flow over the dam. In order to obtain a profile of permanent form for a dam migrating upward and downstream at constant speed, we solve the problem in a moving coordinate system. When water flows over the dam, it is accelerated in the streamwise direction, and the water surface forms a backwater curve. The flow regime changes from Froude-subcritical to Froude-supercritical at a point slightly downstream of the crest of the dam. Farther downstream, the flow attains a threshold velocity beyond which moss is detached. This threshold point defines the downstream end of the active part of the dam. The analysis provides a first-order morphodynamic model of natural dam/waterfall evolution.

10 CFR 72.236 - Specific requirements for spent fuel storage cask approval and fabrication.

Code of Federal Regulations, 2013 CFR

2013-01-01

... maintained in a subcritical condition under credible conditions. (d) Radiation shielding and confinement... confinement of radioactive material under normal, off-normal, and credible accident conditions. (m) To the...

10 CFR 72.236 - Specific requirements for spent fuel storage cask approval and fabrication.

Code of Federal Regulations, 2012 CFR

2012-01-01

... maintained in a subcritical condition under credible conditions. (d) Radiation shielding and confinement... confinement of radioactive material under normal, off-normal, and credible accident conditions. (m) To the...

10 CFR 72.236 - Specific requirements for spent fuel storage cask approval and fabrication.

Code of Federal Regulations, 2010 CFR

2010-01-01

... maintained in a subcritical condition under credible conditions. (d) Radiation shielding and confinement... of radioactive material under normal, off-normal, and credible accident conditions. (m) To the extent...

10 CFR 72.236 - Specific requirements for spent fuel storage cask approval and fabrication.

Code of Federal Regulations, 2011 CFR

2011-01-01

... maintained in a subcritical condition under credible conditions. (d) Radiation shielding and confinement... of radioactive material under normal, off-normal, and credible accident conditions. (m) To the extent...

10 CFR 72.236 - Specific requirements for spent fuel storage cask approval and fabrication.

Code of Federal Regulations, 2014 CFR

2014-01-01

... maintained in a subcritical condition under credible conditions. (d) Radiation shielding and confinement... confinement of radioactive material under normal, off-normal, and credible accident conditions. (m) To the...

Dynamical Regimes and the Dynamo Bifurcation in Geodynamo Simulations

NASA Astrophysics Data System (ADS)

Petitdemange, L.

2017-12-01

We investigate the nature of the dynamo bifurcation in a configuration applicable to the Earth's liquid outer core : in a rotating spherical shell with thermally driven motions with no-slip boundaries. Unlike previous studies on dynamo bifurcations, the control parameters have been varied significantly in order to deduce general tendencies. Numerical studies on the stability domain of dipolar magnetic fields found a dichotomy between non-reversing dipole-dominated dynamos and the reversing non-dipole-dominated multipolar solutions. We show that, by considering weak initial fields, the above transition is replaced by a region of bistability for which dipolar and multipolar dynamos coexist. Such a result was also observed in models with free-slip boundaries in which the strong shear of geostrophic zonal flows can develop and gives rise to non-dipolar fields. We show that a similar process develops in no-slip models when viscous effects are reduced sufficiently.Close to the onset of convection (Rac), the axial dipole grows exponentially in the kinematic phase and saturation occurs by marginally changing the flow structure close to the dynamo threshold Rmc. The resulting bifurcation is then supercritical.In the range 3RacIf (Ra/Ra_c>10), important zonal flows develop in non-magnetic models with low viscosity. The field topology depends on the initial magnetic field. The dipolar branch has a subcritical behaviour whereas the multipolar branch is supercritical. By approaching more realistic parameters, the extension of this bistable regime increases (lower Rossby numbers). An hysteretic behaviour questions the common interpretation for geomagnetic reversals. Far above Rm_c$, the Lorentz force becomes dominant, as it is expected in planetary cores.

Study of an External Neutron Source for an Accelerator-Driven System using the PHITS Code

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

Sugawara, Takanori; Iwasaki, Tomohiko; Chiba, Takashi

A code system for the Accelerator Driven System (ADS) has been under development for analyzing dynamic behaviors of a subcritical core coupled with an accelerator. This code system named DSE (Dynamics calculation code system for a Subcritical system with an External neutron source) consists of an accelerator part and a reactor part. The accelerator part employs a database, which is calculated by using PHITS, for investigating the effect related to the accelerator such as the changes of beam energy, beam diameter, void generation, and target level. This analysis method using the database may introduce some errors into dynamics calculations sincemore » the neutron source data derived from the database has some errors in fitting or interpolating procedures. In this study, the effects of various events are investigated to confirm that the method based on the database is appropriate.« less

Green chiral HPLC enantiomeric separations using high temperature liquid chromatography and subcritical water on Chiralcel OD and Chiralpak AD.

PubMed

Droux, Serge; Félix, Guy

2011-01-01

We report here the application of subcritical water in chiral separations on two popular polysaccharide chiral stationary phases (CSPs): Chiralpak AD and Chiralcel OD. The behavior of these two CSPs was studied under reversed phase conditions at room temperature to discover the maximum percentage of water in the mobile phase, which provided the separation of enantiomers of flavanone and benzoin, respectively, in a reasonable time (i.e., less than 1 h). Then, the stability of Chiralpak AD and Chiralcel OD versus temperature was investigated and discussed. Chiralcel OD separation of flavanone racemate was obtained at 120 °C with water and 2-propanol (80/20) as the mobile phase, while benzoin racemate was separated in pure water at 160 °C. Separations of several racemates were also presented, and advantages and limitations of the technique were discussed. Copyright © 2011 Wiley Periodicals, Inc.

Methodology Developed for Modeling the Fatigue Crack Growth Behavior of Single-Crystal, Nickel-Base Superalloys

NASA Technical Reports Server (NTRS)

1996-01-01

Because of their superior high-temperature properties, gas generator turbine airfoils made of single-crystal, nickel-base superalloys are fast becoming the standard equipment on today's advanced, high-performance aerospace engines. The increased temperature capabilities of these airfoils has allowed for a significant increase in the operating temperatures in turbine sections, resulting in superior propulsion performance and greater efficiencies. However, the previously developed methodologies for life-prediction models are based on experience with polycrystalline alloys and may not be applicable to single-crystal alloys under certain operating conditions. One of the main areas where behavior differences between single-crystal and polycrystalline alloys are readily apparent is subcritical fatigue crack growth (FCG). The NASA Lewis Research Center's work in this area enables accurate prediction of the subcritical fatigue crack growth behavior in single-crystal, nickel-based superalloys at elevated temperatures.

Subcritical water liquefaction of oil palm fruit press fiber in the presence of sodium hydroxide: an optimisation study using response surface methodology.

PubMed

Mazaheri, Hossein; Lee, Keat Teong; Bhatia, Subhash; Mohamed, Abdul Rahman

2010-12-01

Thermal decomposition of oil palm fruit press fiber (FPF) into a liquid product (LP) was achieved using subcritical water treatment in the presence of sodium hydroxide in a high pressure batch reactor. This study uses experimental design and process optimisation tools to maximise the LP yield using response surface methodology (RSM) with central composite rotatable design (CCRD). The independent variables were temperature, residence time, particle size, specimen loading, and additive loading. The mathematical model that was developed fit the experimental results well for all of the response variables that were studied. The optimal conditions were found to be a temperature of 551 K, a residence time of 40 min, a particle size of 710-1000 microm, a specimen loading of 5 g, and a additive loading of 9 wt.% to achieve a LP yield of 76.16%. 2010 Elsevier Ltd. All rights reserved.

Fracture behavior of the Space Shuttle thermal protection system

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

Komine, A.; Kobayashi, A.S.

1983-09-01

Stable crack-growth and fracture-toughness experiments were conducted using precracked specimens machined from LI-900 reusable surface insulation (RSI) tiles of the Space Shuttle thermal protection system (TPS) at room temperature. Similar fracture experiments were conducted on fracture specimens with preexisting cracks at the interface of the tile and the strain isolation pad (SIP). Stable crack growth was not observed in the LI-900 tile fracture specimens which had a fracture toughness of 12.0 kPa sq rt of m. The intermittent subcritical crack growth at the tile-pad interface of the fracture specimens was attributed to successive local pull-outs due to tensile overload inmore » the LI-900 tile and cannot be characterized by linear elastic fracture mechanics. No subcritical interfacial crack growth was observed in the fracture specimens with densified LI-900 tiles where brittle fracture initiated at an interior point away from the densification. 11 references.« less

Subcritical ethylic biodiesel production from wet animal fat and vegetable oils: A net energy ratio analysis

DOE PAGES

Sales, Emerson A.; Ghirardi, Maria L.; Jorquera, Orlando

2016-08-23

Ethylic transesterification process for biodiesel production without any chemical or biochemical catalysts at different subcritical thermodynamic conditions was performed using wet animal fat, soybean and palm oils as feedstock. The results indicate that 2 h of reaction at 240 °C with pressures varying from 20 to 45 bar was sufficient to transform almost all lipid fraction of the samples to biodiesel, depending on the reactor dead volume and proportions between reactants. Conversions of 100%, 84% and 98.5% were obtained for animal fat, soybean oil and palm oil, respectively, in the presence of water, with a net energy ration values ofmore » 2.6, 2.1 and 2.5 respectively. Finally, these results indicate that the process is energetically favorable, and thus represents a cleaner technology with environmental advantages when compared to traditional esterification or transesterification processes.« less

Glycolipid class profiling by packed-column subcritical fluid chromatography.

PubMed

Deschamps, Frantz S; Lesellier, Eric; Bleton, Jean; Baillet, Arlette; Tchapla, Alain; Chaminade, Pierre

2004-06-18

The potential of packed-column subcritical fluid chromatography (SubFC) for the separation of lipid classes has been assessed in this study. Three polar stationary phases were checked: silica, diol, and poly(vinyl alcohol). Carbon dioxide (CO2) with methanol as modifier was used as mobile phase and detection performed by evaporative light scattering detection. The influence of methanol content, temperature, and pressure on the chromatographic behavior of sphingolipids and glycolipids were investigated. A complete separation of lipid classes from a crude wheat lipid extract was achieved using a modifier gradient from 10 to 40% methanol in carbon dioxide. Solute selectivity was improved using coupled silica and diol columns in series. Because the variation of eluotropic strength depending on the fluid density changes, a normalized separation factor product (NSP) was used to select the nature, the number and the order of the columns to reach the optimum glycolipid separation.

FINAL DESIGN REVIEW REPORT Subcritical Experiments Gen 2, 3-ft Confinement Vessel Weldment

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

Romero, Christopher

A Final Design Review (FDR) of the Subcritical Experiments (SCE) Gen 2, 3-ft. Confinement Vessel Weldment was held at Los Alamos National Laboratory (LANL) on September 14, 2017. The review was a focused review on changes only to the confinement vessel weldment (versus a system design review). The changes resulted from lessons-learned in fabricating and inspecting the current set of confinement vessels used for the SCE Program. The baseline 3-ft. confinement vessel weldment design has successfully been used (to date) for three (3) high explosive (HE) over-tests, two (2) fragment tests, and five (5) integral HE experiments. The design teammore » applied lessons learned from fabrication and inspection of these vessel weldments to enhance fit-up, weldability, inspection, and fitness for service evaluations. The review team consisted of five (5) independent subject matter experts with engineering design, analysis, testing, fabrication, and inspection experience. The« less

Nonlinear elastic behavior of sub-critically damaged body armor panel

NASA Astrophysics Data System (ADS)

Fisher, Jason T.; Chimenti, D. E.

2012-05-01

A simple go/no-go test for body armor panels using pressure-sensitive, dye-indicator film (PSF) has been shown to be statistically effective in revealing subcritical damage to body armor panels. Previous measurements have shown that static indicator levels are accurately reproduced in dynamic loading events. Further impact tests on armor worn by a human resuscitation dummy using instrumented masses with an attached accelerometer and embedded force transducer have been performed and analyzed. New impact tests have shown a reliable correlation between PSF indication (as digitized images) and impact force for a wide range of impactor energies and masses. Numerical evaluation of digital PSF images is presented and correlated with impact parameters. Relationships between impactor mass and energy, and corresponding measured force are shown. We will also report on comparisons between ballistic testing performed on panels damaged under various impact conditions and tests performed on undamaged panels.

U-238 fission and Pu-239 production in subcritical assembly

NASA Astrophysics Data System (ADS)

Grab, Magdalena; Wojciechowski, Andrzej

2018-04-01

The project touches upon an issue of U-238 fission reactions and Pu-239 production reactions in subcritical assembly. The experiment took place in November 2014 at the Dzhelepov Laboratory of Nuclear Problems (JINR, Dubna) using PHASOTRON.Data of this experiment were analyzed in Laboratory of Information Technologies (LIT). Four MCNPX models were considered for simulation: Bertini/Dresnen, Bertini/Abla, INCL4/Drensnen, INCL4/Abla. The main goal of the project was to compare the experimental data and simulation results. We obtain a good agreement of experimental data and computation results especially for detectors placed besides the assembly axis. In addition, the U-238 fission reactions are more probable to be observed in the region of a higher particle energy spectrum, located closer to the assembly axis and the particle beam as well and vice versa Pu-239 production reactions were dominant in the peripheral region of geometry.

Subcritical ethylic biodiesel production from wet animal fat and vegetable oils: A net energy ratio analysis

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

Sales, Emerson A.; Ghirardi, Maria L.; Jorquera, Orlando

Ethylic transesterification process for biodiesel production without any chemical or biochemical catalysts at different subcritical thermodynamic conditions was performed using wet animal fat, soybean and palm oils as feedstock. The results indicate that 2 h of reaction at 240 °C with pressures varying from 20 to 45 bar was sufficient to transform almost all lipid fraction of the samples to biodiesel, depending on the reactor dead volume and proportions between reactants. Conversions of 100%, 84% and 98.5% were obtained for animal fat, soybean oil and palm oil, respectively, in the presence of water, with a net energy ration values ofmore » 2.6, 2.1 and 2.5 respectively. Finally, these results indicate that the process is energetically favorable, and thus represents a cleaner technology with environmental advantages when compared to traditional esterification or transesterification processes.« less

Nonlinear instability of half-solitons on star graphs

NASA Astrophysics Data System (ADS)

Kairzhan, Adilbek; Pelinovsky, Dmitry E.

2018-06-01

We consider a half-soliton stationary state of the nonlinear Schrödinger equation with the power nonlinearity on a star graph consisting of N edges and a single vertex. For the subcritical power nonlinearity, the half-soliton state is a degenerate critical point of the action functional under the mass constraint such that the second variation is nonnegative. By using normal forms, we prove that the degenerate critical point is a saddle point, for which the small perturbations to the half-soliton state grow slowly in time resulting in the nonlinear instability of the half-soliton state. The result holds for any N ≥ 3 and arbitrary subcritical power nonlinearity. It gives a precise dynamical characterization of the previous result of Adami et al. (2012) [2], where the half-soliton state was shown to be a saddle point of the action functional under the mass constraint for N = 3 and for cubic nonlinearity.

A review on green trend for oil extraction using subcritical water technology and biodiesel production.

PubMed

Abdelmoez, Weal; Ashour, Eman; Naguib, Shahenaz M

2015-01-01

It became a global agenda to develop clean alternative fuels which were domestically available, environmentally acceptable and technically feasible. Thus, biodiesel was destined to make a substantial contribution to the future energy demands of the domestic and industrial economies. Utilization of the non edible vegetable oils as raw materials for biodiesel production had been handled frequently for the past few years. The oil content of these seeds could be extracted by different oil extraction methods, such as mechanical extraction, solvent extraction and by subcritical water extraction technology SWT. Among them, SWT represents a new promising green extraction method. Therefore this review covered the current used non edible oil seeds for biodiesel production as well as giving a sharp focus on the efficiency of using the SWT as a promising extraction method. In addition the advantages and the disadvantages of the different biodiesel production techniques would be covered.

Parametrization in models of subcritical glass fracture: Activation offset and concerted activation

NASA Astrophysics Data System (ADS)

Rodrigues, Bruno Poletto; Hühn, Carolin; Erlebach, Andreas; Mey, Dorothea; Sierka, Marek; Wondraczek, Lothar

2017-08-01

There are two established but fundamentally different empirical approaches to parametrize the rate of subcritical fracture in brittle materials. While both are relying on a thermally activated reaction of bond rupture, the difference lies in the way as to how the externally applied stresses affect the local energy landscape. In the consideration of inorganic glasses, the strain energy is typically taken as an off-set on the activation barrier. As an alternative interpretation, the system’s volumetric strain-energy is added to its thermal energy. Such an interpretation is consistent with the democratic fiber bundle model. Here, we test this approach of concerted activation against macroscopic data of bond cleavage activation energy, and also against ab initio quantum chemical simulation of the energy barrier for cracking in silica. The fact that both models are able to reproduce experimental observation to a remarkable degree highlights the importance of a holistic consideration towards non-empirical understanding.

Benchmark of ReaxFF force field for subcritical and supercritical water.

PubMed

Manzano, Hegoi; Zhang, Weiwei; Raju, Muralikrishna; Dolado, Jorge S; López-Arbeloa, Iñigo; van Duin, Adri C T

2018-06-21

Water in the subcritical and supercritical states has remarkable properties that make it an excellent solvent for oxidation of hazardous chemicals, waste separation, and green synthesis. Molecular simulations are a valuable complement to experiments in order to understand and improve the relevant sub- and super-critical reaction mechanisms. Since water molecules under these conditions can act not only as a solvent but also as a reactant, dissociative force fields are especially interesting to investigate these processes. In this work, we evaluate the capacity of the ReaxFF force field to reproduce the microstructure, hydrogen bonding, dielectric constant, diffusion, and proton transfer of sub- and super-critical water. Our results indicate that ReaxFF is able to simulate water properties in these states in very good quantitative agreement with the existing experimental data, with the exception of the static dielectric constant that is reproduced only qualitatively.

Safety and control of accelerator-driven subcritical systems

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

Rief, H.; Takahashi, H.

1995-10-01

To study control and safety of accelertor driven nuclear systems, a one point kinetic model was developed and programed. It deals with fast transients as a function of reactivity insertion. Doppler feedback, and the intensity of an external neutron source. The model allows for a simultaneous calculation of an equivalent critical reactor. It was validated by a comparison with a benchmark specified by the Nuclear Energy Agency Committee of Reactor Physics. Additional features are the possibility of inserting a linear or quadratic time dependent reactivity ramp which may account for gravity induced accidents like earthquakes, the possibility to shut downmore » the external neutron source by an exponential decay law of the form exp({minus}t/{tau}), and a graphical display of the power and reactivity changes. The calculations revealed that such boosters behave quite benignly even if they are only slightly subcritical.« less

Extracting organic matter on Mars: A comparison of methods involving subcritical water, surfactant solutions and organic solvents

NASA Astrophysics Data System (ADS)

Luong, Duy; Court, Richard W.; Sims, Mark R.; Cullen, David C.; Sephton, Mark A.

2014-09-01

The first step in many life detection protocols on Mars involves attempts to extract or isolate organic matter from its mineral matrix. A number of extraction options are available and include heat and solvent assisted methods. Recent operations on Mars indicate that heating samples can cause the loss or obfuscation of organic signals from target materials, raising the importance of solvent-based systems for future missions. Several solvent types are available (e.g. organic solvents, surfactant based solvents and subcritical water extraction) but a comparison of their efficiencies in Mars relevant materials is missing. We have spiked the well characterised Mars analogue material JSC Mars-1 with a number of representative organic standards. Extraction of the spiked JSC Mars-1 with the three solvent methods provides insights into the relative efficiency of these methods and indicates how they may be used on future Mars missions.

Membrane biofouling process correlated to the microbial community succession in an A/O MBR.

PubMed

Chen, Chun-Hong; Fu, Yuan; Gao, Da-Wen

2015-12-01

The microbial community succession of the biofouling layer in a submerged anoxic/oxic membrane biological reactor (A/O MBR) that fed with synthesized domestic wastewater was investigated under three different flux conditions without the changing of the nutrient load. The noticeable microbial community succession and its significant correlation with the metabolic products were observed under the subcritical flux condition. Under the supercritical flux condition, the microbial community shift was in a different pattern compared with that under the subcritical flux condition and it was affected by the increased permeable suction more than the metabolic products. The most abundant microorganisms in the foulants were β-proteobacteria and γ-proteobacteria which can reach more than 20% of the microbial community. However the microorganisms which had significant correlation with the metabolic products were in lower abundance. Copyright © 2015 Elsevier Ltd. All rights reserved.

Microdeformation and subcritical cracking in chalk

NASA Astrophysics Data System (ADS)

Bergsaker, Anne; Dysthe, Dag Kristian

2016-04-01

Deformation processes in chalks, both in relation to changing pore fluids and stress conditions has been of great interest as chalk is an important reservoir rock for both hydrocarbons and ground water. Lately it has also gained interest as a potential reservoir rock for captured CO2. Chalks are composed of large amounts of biogenic calcite grains, the skeletal debris of marine microorganisms. Its deformation is highly time and stress dependent, and governed by a transition from distributed to localized deformation at the onset of yield, affected by mechanisms such as subcritical crack growth and pore collapse. We present a microdeformation rig which makes use of thermal expansion as a means of subjecting small samples to strictly controlled tensile stresses. High resolution imaging provides resolutions down to 0.5 micrometers, enabling study of pore scale processes during slow deformation. Examples of localized and distributed deformation are presented.

The effect of an electric field on the morphological stability of the crystal-melt interface of a binary alloy. III - Weakly nonlinear theory

NASA Technical Reports Server (NTRS)

Wheeler, A. A.; Mcfadden, G. B.; Coriell, S. R.; Hurle, D. T. J.

1990-01-01

The effect of a constant electric current on the crystal-melt interface morphology during directional solidification at constant velocity of a binary alloy is considered. A linear temperature field is assumed, and thermoelectric effects and Joule heating are neglected; electromigration and differing electrical conductivities of crystal and melt are taken into account. A two-dimensional weakly nonlinear analysis is carried out to third order in the interface amplitude, resulting in a cubic amplitude equation that describes whether the bifurcation from the planar state is supercritical or subcritical. For wavelengths corresponding to the most dangerous mode of linear theory, the demarcation between supercritical and subcritical behavior is calculated as a function of processing conditions and material parameters. The bifurcation behavior is a sensitive function of the magnitude and direction of the electric current and of the electrical conductivity ratio.

Real part of refractive index measurement approach for absorbing liquid.

PubMed

Liu, Hao; Ye, Junwei; Yang, Kecheng; Xia, Min; Guo, Wenping; Li, Wei

2015-07-01

An algorithm based on use of a reflected refractometer to measure the real part of the refractive index (RI) for an absorbing liquid is presented. The absorption of liquid will blur the division between bright and dark regions on a Fresnel reflective curve. However, the reflective ratio at some incident angles that are less than the critical angle have little sensitivity to absorbability. Unlike common methods that extract RI from reflectivity in critical angle vicinity, the presented method acquires the real RI from reflective ratio at a subcritical angle. Supported by the theoretical analysis and experimental results on a reflected refractometer, we have achieved accuracy better than 3×10(-4) RIU on ink samples with absorption coefficient around 300  cm(-1). Additional tests on Alizarin yellow GG solutions prove that the subcritical algorithm is feasible and of high accuracy.

Third-Order Memristive Morris-Lecar Model of Barnacle Muscle Fiber

NASA Astrophysics Data System (ADS)

Rajamani, Vetriveeran; Sah, Maheshwar Pd.; Mannan, Zubaer Ibna; Kim, Hyongsuk; Chua, Leon

This paper presents a detailed analysis of various oscillatory behaviors observed in relation to the calcium and potassium ions in the third-order Morris-Lecar model of giant barnacle muscle fiber. Since, both the calcium and potassium ions exhibit all of the characteristics of memristor fingerprints, we claim that the time-varying calcium and potassium ions in the third-order Morris-Lecar model are actually time-invariant calcium and potassium memristors in the third-order memristive Morris-Lecar model. We confirmed the existence of a small unstable limit cycle oscillation in both the second-order and the third-order Morris-Lecar model by numerically calculating the basin of attraction of the asymptotically stable equilibrium point associated with two subcritical Hopf bifurcation points. We also describe a comprehensive analysis of the generation of oscillations in third-order memristive Morris-Lecar model via small-signal circuit analysis and a subcritical Hopf bifurcation phenomenon.

Conversion of a wet waste feedstock to biocrude by hydrothermal processing in a continuous-flow reactor: grape pomace

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

Elliott, Douglas C.; Schmidt, Andrew J.; Hart, Todd R.

Wet waste feedstocks present an apt opportunity for biomass conversion to fuels by hydrothermal processing. In this study, grape pomace slurries from two varieties, Montepulciano and cabernet sauvignon, have been converted into a biocrude by hydrothermal liquefaction (HTL) in a bench-scale, continuous-flow reactor system. Carbon conversion to gravity-separable biocrude product up to 56 % was accomplished at relatively low temperature (350 C) in a pressurized (sub-critical liquid water) environment (20 MPa) when using grape pomace feedstock slurry with a 16.8 wt% concentration of dry solids processed at a liquid hourly space velocity of 2.1 h-1. Direct oil recovery was achievedmore » without the use of a solvent and biomass trace mineral components were removed by processing steps so that they did not cause processing difficulties. In addition, catalytic hydrothermal gasification (CHG) was effectively applied for HTL byproduct water cleanup using a Ru on C catalyst in a fixed bed producing a gas composed of methane and carbon dioxide from water soluble organics. Conversion of 99.8% of the chemical oxygen demand (COD) left in the aqueous phase was demonstrated. As a result, high conversion of grape pomace to liquid and gas fuel products was found with residual organic contamination in byproduct water reduced to <150 mg/kg COD.« less

Comparison of Nitronic 50 and Stainless Steel 316 for use in Supercritical Water Environments

NASA Astrophysics Data System (ADS)

Karmiol, Zachary

Increased efficiency can greatly benefit any mode of power production. Many proposed coal, natural gas, and nuclear reactors attempt to realize this goal through the use of increased operating temperatures and pressures, and as such require materials capable of withstanding extreme conditions. One such design employs supercritical water, which in addition to high temperatures and pressures is also highly oxidizing. A critical understanding of both mechanical and oxidation characteristics of candidate materials are required to determine the viability of materials for these reactors. This work investigates two potential materials, austenitic stainless steels, namely, Nitronic-50 and stainless steel 316, for use in these conditions. The supercritical water loop at the University of Nevada, Reno allowed for the study of materials at both subcritical and supercritical conditions. The materials were investigated mechanically using slow strain rate tests under conditions ranging from an inert nitrogen atmosphere, to both subcritical and supercritical water, with the failed samples surface characterized by optical microscopy, scanning electron microscopy, and Raman spectroscopy. Electrochemical studies were performed via potentiodynamic polarization in subcritical water only, and characterized using Raman spectroscopy. The samples were also exposed to supercritical water, and characterized using Raman spectroscopy. Nitronic-50 was found to have superior mechanical characteristics to stainless steel 316. SS-316 was found to have a surface film consisting of iron oxides, while the surface film of N-50 consisted predominantly of nickel-iron spinel. The crack interior of the sample was different from the exterior, indicating that the time and temperature of the exposure might play a defining role in determining the chemistry of the film.

Studies on the stability of preservatives under subcritical water conditions.

PubMed

Kapalavavi, B; Marple, R; Gamsky, C; Yang, Y

2015-06-01

The goal of this work was to further validate the subcritical water chromatography (SBWC) methods for separation and analysis of preservatives through the evaluation of analyte stability in subcritical water. In this study, the degradation of preservatives was investigated at temperatures of 100-200°C using two different approaches. First, the peak areas obtained by SBWC at high temperatures were compared with those achieved using the traditional high-performance liquid chromatography (HPLC) at 25°C. In the second approach, several preservatives and water were loaded into a vessel and heated at high temperatures for 30 or 60 min. The heated mixtures were then analysed by GC/MS to determine the stability of preservatives. The t- and F-test on the results of the first approach reveal that the peak areas achieved by HPLC and SBWC are not significantly different at the 95% confidence level, meaning that the preservatives studied are stable during the high-temperature SBWC runs. Although the results of the second approach show approximately 10% degradation of preservatives into mainly p-hydroxybenzoic acid and phenol at 200°C, the preservatives studied are stable at 100 and 150°C. This is in good agreement with the validation results obtained by the first approach. The findings of this work confirm that SBWC methods at temperatures up to 150°C are reliable for separation and analysis of preservatives in cosmetic and other samples. © 2014 Society of Cosmetic Scientists and the Société Française de Cosmétologie.

Modelling the fear effect in predator-prey interactions.

PubMed

Wang, Xiaoying; Zanette, Liana; Zou, Xingfu

2016-11-01

A recent field manipulation on a terrestrial vertebrate showed that the fear of predators alone altered anti-predator defences to such an extent that it greatly reduced the reproduction of prey. Because fear can evidently affect the populations of terrestrial vertebrates, we proposed a predator-prey model incorporating the cost of fear into prey reproduction. Our mathematical analyses show that high levels of fear (or equivalently strong anti-predator responses) can stabilize the predator-prey system by excluding the existence of periodic solutions. However, relatively low levels of fear can induce multiple limit cycles via subcritical Hopf bifurcations, leading to a bi-stability phenomenon. Compared to classic predator-prey models which ignore the cost of fear where Hopf bifurcations are typically supercritical, Hopf bifurcations in our model can be both supercritical and subcritical by choosing different sets of parameters. We conducted numerical simulations to explore the relationships between fear effects and other biologically related parameters (e.g. birth/death rate of adult prey), which further demonstrate the impact that fear can have in predator-prey interactions. For example, we found that under the conditions of a Hopf bifurcation, an increase in the level of fear may alter the direction of Hopf bifurcation from supercritical to subcritical when the birth rate of prey increases accordingly. Our simulations also show that the prey is less sensitive in perceiving predation risk with increasing birth rate of prey or increasing death rate of predators, but demonstrate that animals will mount stronger anti-predator defences as the attack rate of predators increases.

Numerical results on noise-induced dynamics in the subthreshold regime for thermoacoustic systems

NASA Astrophysics Data System (ADS)

Gupta, Vikrant; Saurabh, Aditya; Paschereit, Christian Oliver; Kabiraj, Lipika

2017-03-01

Thermoacoustic instability is a serious issue in practical combustion systems. Such systems are inherently noisy, and hence the influence of noise on the dynamics of thermoacoustic instability is an aspect of practical importance. The present work is motivated by a recent report on the experimental observation of coherence resonance, or noise-induced coherence with a resonance-like dependence on the noise intensity as the system approaches the stability margin, for a prototypical premixed laminar flame combustor (Kabiraj et al., Phys. Rev. E, 4 (2015)). We numerically investigate representative thermoacoustic models for such noise-induced dynamics. Similar to the experiments, we study variation in system dynamics in response to variations in the noise intensity and in a critical control parameter as the systems approach their stability margins. The qualitative match identified between experimental results and observations in the representative models investigated here confirms that coherence resonance is a feature of thermoacoustic systems. We also extend the experimental results, which were limited to the case of subcritical Hopf bifurcation, to the case of supercritical Hopf bifurcation. We identify that the phenomenon has qualitative differences for the systems undergoing transition via subcritical and supercritical Hopf bifurcations. Two important practical implications are associated with the findings. Firstly, the increase in noise-induced coherence as the system approaches the onset of thermoacoustic instability can be considered as a precursor to the instability. Secondly, the dependence of noise-induced dynamics on the bifurcation type can be utilised to distinguish between subcritical and supercritical bifurcation prior to the onset of the instability.

Blending Novatein¯ thermoplastic protein with PLA for carbon dioxide assisted batch foaming

NASA Astrophysics Data System (ADS)

Walallavita, Anuradha; Verbeek, Casparus J. R.; Lay, Mark

2016-03-01

The convenience of polymeric foams has led to their widespread utilisation in everyday life. However, disposal of synthetic petroleum-derived foams has had a detrimental effect on the environment which needs to be addressed. This study uses a clean and sustainable approach to investigate the foaming capability of a blend of two biodegradable polymers, polylactic acid (PLA) and Novatein® Thermoplastic Protein (NTP). PLA, derived from corn starch, can successfully be foamed using a batch technique developed by the Biopolymer Network Ltd. NTP is a patented formulation of bloodmeal and chemical additives which can be extruded and injection moulded similar to other thermoplastics. However, foaming NTP is a new area of study and its interaction with blowing agents in the batch process is entirely unknown. Subcritical and supercritical carbon dioxide have been examined individually in two uniquely designed pressure vessels to foam various compositions of NTP-PLA blends. Foamed material were characterised in terms of expansion ratio, cell size, and cellular morphology in order to study how the composition of NTP-PLA affects foaming with carbon dioxide. It was found that blends with 5 wt. % NTP foamed using subcritical CO2 expanded up to 11 times due to heterogeneous nucleation. Morphology analysis using scanning electron microscopy showed that foams blown with supercritical CO2 had a finer cell structure with consistent cell size, whereas, foams blown with subcritical CO2 ranged in cell size and showed cell wall rupture. Ultimately, this research would contribute to the production of a biodegradable foam material to be used in packaging applications, thereby adding to the application potential of NTP.

YALINA facility a sub-critical Accelerator- Driven System (ADS) for nuclear energy research facility description and an overview of the research program (1997-2008).

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

Gohar, Y.; Smith, D. L.; Nuclear Engineering Division

2010-04-28

The YALINA facility is a zero-power, sub-critical assembly driven by a conventional neutron generator. It was conceived, constructed, and put into operation at the Radiation Physics and Chemistry Problems Institute of the National Academy of Sciences of Belarus located in Minsk-Sosny, Belarus. This facility was conceived for the purpose of investigating the static and dynamic neutronics properties of accelerator driven sub-critical systems, and to serve as a neutron source for investigating the properties of nuclear reactions, in particular transmutation reactions involving minor-actinide nuclei. This report provides a detailed description of this facility and documents the progress of research carried outmore » there during a period of approximately a decade since the facility was conceived and built until the end of 2008. During its history of development and operation to date (1997-2008), the YALINA facility has hosted several foreign groups that worked with the resident staff as collaborators. The participation of Argonne National Laboratory in the YALINA research programs commenced in 2005. For obvious reasons, special emphasis is placed in this report on the work at YALINA facility that has involved Argonne's participation. Attention is given here to the experimental program at YALINA facility as well as to analytical investigations aimed at validating codes and computational procedures and at providing a better understanding of the physics and operational behavior of the YALINA facility in particular, and ADS systems in general, during the period 1997-2008.« less

Evolution of Heat Flow with Age on the Southern Flank of the Costa Rica Rift

NASA Astrophysics Data System (ADS)

Kolandaivelu, K. P.; Harris, R. N.; Lowell, R. P.; Wilson, D. J.; Hobbs, R. W.

2017-12-01

Analysis of 67 new conductive heat flow measurements at five sites ranging between ≈ 1.6 and 5.7 Ma on the southern flank of the Costa Rica Rift yields insight into factors that influence hydrothermal circulation in young oceanic crust. The heat flow measurements were collocated with a high-resolution multi-channel seismic line, extending from the ridge axis to ODP hole 504B. The mean conductive heat flow, qobs, 80 mWm-2, is ≈ 25% of the mean lithospheric heat flux, qth, predicted by half-space conductive cooling model. The ratio qobs/qth varies significantly from site to site indicating that advective heat loss may be influenced by the presence of high-angle, ridge-ward dipping normal faults, surface topography, and sediment thickness, which vary significantly along the profile. The 1.6 Ma heat flow site, which is located between two outcrops separated by 2 km and has thin sediment cover, yields qobs/qth » 0.08. The advective heat loss indicates a mass flux of 3 x 10-5 kgm-2s-1 and upper crustal permeabilities of 4 x 10-11 and 3 x 10-9 m2 for 1000 m and 100 m aquifer thicknesses, respectively. At the 2.6 Ma site with 75 m sediment cover, qobs/qth » 0.18 and heat flow is uniformly low, except for one high value near a fault. At the 3.5 Ma site, qobs/qth » 0.15. The heat flow deficit results from outcrop to outcrop flow, but subcritical cellular convection driven by local basement topography produces small heat flow highs and lows superimposed on the overall trend. At the 4.5 Ma site, qobs/qth » 0.06. The heat flow distribution indicates that discharge occurs through a large, thinly-sedimented topographical high, where estimated mass flux is 3 x 10-5 kgm-2s-1. At the oldest site of 5.7 Ma, qobs/qth » 1, but some heat flow values greater than qth occur near sparsely-sedimented basement outcrops, suggesting redistribution of heat by subsurface convection controlled by basement topography, similar to ODP Hole 504B. That qobs/qth » 1 at a much younger age than indicated by global data suggests that basement burial under a thick sediment cover inhibits advective heat loss through the crust. These data were collected as part of a major interdisciplinary NERC and NSF-funded collaboration entitled: Oceanographic and Seismic Characterization of heat dissipation and alteration by hydrothermal fluids at an Axial Ridge (OSCAR).

Spacelab cryogenic propellant management experiment

NASA Technical Reports Server (NTRS)

Cady, E. C.

1976-01-01

The conceptual design of a Spacelab cryogen management experiment was performed to demonstrate toe desirability and feasibility of subcritical cryogenic fluid orbital storage and supply. A description of the experimental apparatus, definition of supporting requirements, procedures, data analysis, and a cost estimate are included.

Subtropical Dust Storms and Downslope Wind Events

NASA Astrophysics Data System (ADS)

Pokharel, Ashok Kumar; Kaplan, Michael L.; Fiedler, Stephanie

2017-10-01

We performed detailed mesoscale observational analyses and Weather Research and Forecasting (WRF) model simulations to study the terrain-induced downslope winds that generated dust-emitting winds at the beginning of three strong subtropical dust storms in three distinctly different regions of North Africa and the Arabian Peninsula. We revisit the Harmattan dust storm of 2 March 2004, the Saudi dust storm of 9 March 2009, and the Bodélé Depression dust storm of 8 December 2011 and use high-resolution WRF modeling to assess the dynamical processes during the onset of the storms in more depth. Our results highlight the generation of terrain-induced downslope winds in response to the transition of the atmospheric flow from a subcritical to supercritical state in all three cases. These events precede the unbalanced adjustment processes in the lee of the mountain ranges that produced larger-scale dust aerosol mobilization and transport. We see that only the higher-resolution data sets can resolve the mesoscale processes, which are mainly responsible for creating strong low-level terrain-induced downslope winds leading to the initial dust storms.

An experimental investigation of liquid methane convection and boiling in rocket engine cooling channels

NASA Astrophysics Data System (ADS)

Trujillo, Abraham Gerardo

In the past decades, interest in developing hydrocarbon-fueled rocket engines for deep spaceflight missions has continued to grow. In particular, liquid methane (LCH4) has been of interest due to the weight efficiency, storage, and handling advantages it offers over several currently used propellants. Deep space exploration requires reusable, long life rocket engines. Due to the high temperatures reached during combustion, the life of an engine is significantly impacted by the cooling system's efficiency. Regenerative (regen) cooling is presented as a viable alternative to common cooling methods such as film and dump cooling since it provides improved engine efficiency. Due to limited availability of experimental sub-critical liquid methane cooling data for regen engine design, there has been an interest in studying the heat transfer characteristics of the propellant. For this reason, recent experimental studies at the Center for Space Exploration Technology Research (cSETR) at the University of Texas at El Paso (UTEP) have focused on investigating the heat transfer characteristics of sub-critical CH4 flowing through sub-scale cooling channels. To conduct the experiments, the csETR developed a High Heat Flux Test Facility (HHFTF) where all the channels are heated using a conduction-based thermal concentrator. In this study, two smooth channels with cross sectional geometries of 1.8 mm x 4.1 mm and 3.2 mm x 3.2 mm were tested. In addition, three roughened channels all with a 3.2 mm x 3.2 mm square cross section were also tested. For the rectangular smooth channel, Reynolds numbers ranged between 68,000 and 131,000, while the Nusselt numbers were between 40 and 325. For the rough channels, Reynolds numbers ranged from 82,000 to 131,000, and Nusselt numbers were between 65 and 810. Sub-cooled film-boiling phenomena were confirmed for all the channels presented in this work. Film-boiling onset at Critical Heat Flux (CHF) was correlated to a Boiling Number (Bo) of approximately 0.1 for all channels. Convective Nusselt number follows predicted trends for Reynolds number with a wall temperature correction for both the boiling and non-boiling regimes.

The role of contact angle on unstable flow formation during infiltration and drainage in wettable porous media

NASA Astrophysics Data System (ADS)

Wallach, Rony; Margolis, Michal; Graber, Ellen R.

2013-10-01

The impact of contact angle on 2-D spatial and temporal water-content distribution during infiltration and drainage was experimentally studied. The 0.3-0.5 mm fraction of a quartz dune sand was treated and turned subcritically repellent (contact angle of 33°, 48°, 56°, and 75° for S33, S48, S56, and S75, respectively). The media were packed uniformly in transparent flow chambers and water was supplied to the surface as a point source at different rates (1-20 ml/min). A sequence of gray-value images was taken by CCD camera during infiltration and subsequent drainage; gray values were converted to volumetric water content by water volume balance. Narrow and long plumes with water accumulation behind the downward moving wetting front (tip) and negative water gradient above it (tail) developed in the S56 and S75 media during infiltration at lower water application rates. The plumes became bulbous with spatially uniform water-content distribution as water application rates increased. All plumes in these media propagated downward at a constant rate during infiltration and did not change their shape during drainage. In contrast, regular plume shapes were observed in the S33 and S48 media at all flow rates, and drainage profiles were nonmonotonic with a transition plane at the depth that water reached during infiltration. Given that the studied media have similar pore-size distributions, the conclusion is that imbibition hindered by the nonzero contact angle induced pressure buildup at the wetting front (dynamic water-entry value) that controlled the plume shape and internal water-content distribution during infiltration and drainage.

Spectral stability of shifted states on star graphs

NASA Astrophysics Data System (ADS)

Kairzhan, Adilbek; Pelinovsky, Dmitry E.

2018-03-01

We consider the nonlinear Schrödinger (NLS) equation with the subcritical power nonlinearity on a star graph consisting of N edges and a single vertex under generalized Kirchhoff boundary conditions. The stationary NLS equation may admit a family of solitary waves parameterized by a translational parameter, which we call the shifted states. The two main examples include (i) the star graph with even N under the classical Kirchhoff boundary conditions and (ii) the star graph with one incoming edge and N  -  1 outgoing edges under a single constraint on coefficients of the generalized Kirchhoff boundary conditions. We obtain the general counting results on the Morse index of the shifted states and apply them to the two examples. In the case of (i), we prove that the shifted states with even N ≥slant 4 are saddle points of the action functional which are spectrally unstable under the NLS flow. In the case of (ii), we prove that the shifted states with the monotone profiles in the N  -  1 edges are spectrally stable, whereas the shifted states with non-monotone profiles in the N  -  1 edges are spectrally unstable, the two families intersect at the half-soliton states which are spectrally stable but nonlinearly unstable under the NLS flow. Since the NLS equation on a star graph with shifted states can be reduced to the homogeneous NLS equation on an infinite line, the spectral instability of shifted states is due to the perturbations breaking this reduction. We give a simple argument suggesting that the spectrally stable shifted states in the case of (ii) are nonlinearly unstable under the NLS flow due to the perturbations breaking the reduction to the homogeneous NLS equation.

Design and optimization of a semicontinuous hot-cold extraction of polyphenols from grape pomace.

PubMed

Monrad, Jeana K; Srinivas, Keerthi; Howard, Luke R; King, Jerry W

2012-06-06

Grape pomace contains appreciable amounts of polyphenolic compounds such as anthocyanins and procyanidins which can be recovered for use as food supplements. The extraction of these polyphenols from the pomace is usually accomplished at slightly elevated temperatures, frequently employing hydroethanolic solvents. Due to governmental regulations and the cost involved in using ethanol as a solvent, as well as the loss in polyphenolics due to thermal degradation, improved extraction techniques are required. In this study, a semicontinuous extraction apparatus employing only water was developed to maximize the recovery of anthocyanins and procyanidins from red grape pomace (Vitis vinifera). Water is preheated prior to its entry to the extraction cell containing the grape pomace sample, where it is allowed to then flow continuously through the unheated extraction vessel prior to its collection at ambient conditions. Extraction variables that impacted the polyphenolic recovery included pomace moisture content (crude or dried), sample mass, water flow rate, and extraction temperature. A response surface method was used to analyze the results from the extraction, and the optimal conditions were found to be 140 °C and 9 mL/min water flow rate. These conditions can produce an extract containing 130 mg/100 g DW of anthocyanins and 2077 mg/100 g DW of procyanidins. Higher yields of polyphenolics were observed using crude (wet) rather than dried pomace, hence avoiding the need to dry the pomace prior to extraction. The described semicontinuous extraction method using only water as the extraction solvent under subcritical conditions allowed the efficient extraction of polyphenols from red grape pomace without the attendant loss of polyphenolic content due to having to heat the extraction vessel prior to commencement of extraction.

Low gravity phase separator

NASA Technical Reports Server (NTRS)

Smoot, G. F.; Pope, W. L.; Smith, L. (Inventor)

1977-01-01

An apparatus is described for phase separating a gas-liquid mixture as might exist in a subcritical cryogenic helium vessel for cooling a superconducting magnet at low gravity such as in planetary orbit, permitting conservation of the liquid and extended service life of the superconducting magnet.

Interactive Graphics Analysis for Aircraft Design

NASA Technical Reports Server (NTRS)

Townsend, J. C.

1983-01-01

Program uses higher-order far field drag minimization. Computer program WDES WDEM preliminary aerodynamic design tool for one or two interacting, subsonic lifting surfaces. Subcritical wing design code employs higher-order far-field drag minimization technique. Linearized aerodynamic theory used. Program written in FORTRAN IV.

Characterizing subcritical assemblies with time of flight fixed by energy estimation distributions

NASA Astrophysics Data System (ADS)

Monterial, Mateusz; Marleau, Peter; Pozzi, Sara

2018-04-01

We present the Time of Flight Fixed by Energy Estimation (TOFFEE) as a measure of the fission chain dynamics in subcritical assemblies. TOFFEE is the time between correlated gamma rays and neutrons, subtracted by the estimated travel time of the incident neutron from its proton recoil. The measured subcritical assembly was the BeRP ball, a 4.482 kg sphere of α-phase weapons grade plutonium metal, which came in five configurations: bare, 0.5, 1, and 1.5 in iron, and 1 in nickel closed fitting shell reflectors. We extend the measurement with MCNPX-PoliMi simulations of shells ranging up to 6 inches in thickness, and two new reflector materials: aluminum and tungsten. We also simulated the BeRP ball with different masses ranging from 1 to 8 kg. A two-region and single-region point kinetics models were used to model the behavior of the positive side of the TOFFEE distribution from 0 to 100 ns. The single region model of the bare cases gave positive linear correlations between estimated and expected neutron decay constants and leakage multiplications. The two-region model provided a way to estimate neutron multiplication for the reflected cases, which correlated positively with expected multiplication, but the nature of the correlation (sub or superlinear) changed between material types. Finally, we found that the areal density of the reflector shells had a linear correlation with the integral of the two-region model fit. Therefore, we expect that with knowledge of reflector composition, one could determine the shell thickness, or vice versa. Furthermore, up to a certain amount and thickness of the reflector, the two-region model provides a way of distinguishing bare and reflected plutonium assemblies.

Compact D-D Neutron Source-Driven Subcritical Multiplier and Beam-Shaping Assembly for Boron Neutron Capture Therapy

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

Francesco Ganda; Jasmina Vujic; Ehud Greenspan

2010-12-01

This work assesses the feasibility of using a small, safe, and inexpensive keff 0.98 subcritical fission assembly [subcritical neutron multiplier (SCM)] to amplify the treatment neutron beam intensity attainable from a compact deuterium-deuterium (D-D) fusion neutron source delivering [approximately]1012 n/s. The objective is to reduce the treatment time for deep-seated brain tumors to [approximately]1 h. The paper describes the optimal SCM design and two optimal beam-shaping assemblies (BSAs) - one designed to maximize the dose rate and the other designed to maximize the total dose that can be delivered to a deep-seated tumor. The neutron beam intensity amplification achieved withmore » the optimized SCM and BSA results in an increase in the treatment dose rate by a factor of 18: from 0.56 Gy/h without the SCM to 10.1 Gy/h. The entire SCM is encased in an aluminum structure. The total amount of 20% enriched uranium required for the SCM is 8.5 kg, and the cost (not including fabrication) is estimated to be less than $60,000. The SCM power level is estimated at 400 W when driven by a 1012 n/s D-D neutron source. This translates into consumption of only [approximately]0.6% of the initially loaded 235U atoms during 50 years of continuous operation and implies that the SCM could operate continuously for the entire lifetime of the facility without refueling. Cooling the SCM does not pose a challenge; it may be accomplished by natural circulation as the maximum heat flux is only 0.034 W/cm2.« less

Blending Novatein{sup ®} thermoplastic protein with PLA for carbon dioxide assisted batch foaming

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

Walallavita, Anuradha, E-mail: asw15@students.waikato.ac.nz; Verbeek, Casparus J. R., E-mail: jverbeek@waikato.ac.nz; Lay, Mark, E-mail: mclay@waikato.ac.nz

2016-03-09

The convenience of polymeric foams has led to their widespread utilisation in everyday life. However, disposal of synthetic petroleum-derived foams has had a detrimental effect on the environment which needs to be addressed. This study uses a clean and sustainable approach to investigate the foaming capability of a blend of two biodegradable polymers, polylactic acid (PLA) and Novatein® Thermoplastic Protein (NTP). PLA, derived from corn starch, can successfully be foamed using a batch technique developed by the Biopolymer Network Ltd. NTP is a patented formulation of bloodmeal and chemical additives which can be extruded and injection moulded similar to othermore » thermoplastics. However, foaming NTP is a new area of study and its interaction with blowing agents in the batch process is entirely unknown. Subcritical and supercritical carbon dioxide have been examined individually in two uniquely designed pressure vessels to foam various compositions of NTP-PLA blends. Foamed material were characterised in terms of expansion ratio, cell size, and cellular morphology in order to study how the composition of NTP-PLA affects foaming with carbon dioxide. It was found that blends with 5 wt. % NTP foamed using subcritical CO{sub 2} expanded up to 11 times due to heterogeneous nucleation. Morphology analysis using scanning electron microscopy showed that foams blown with supercritical CO{sub 2} had a finer cell structure with consistent cell size, whereas, foams blown with subcritical CO{sub 2} ranged in cell size and showed cell wall rupture. Ultimately, this research would contribute to the production of a biodegradable foam material to be used in packaging applications, thereby adding to the application potential of NTP.« less

Spike avalanches in vivo suggest a driven, slightly subcritical brain state

PubMed Central

Priesemann, Viola; Wibral, Michael; Valderrama, Mario; Pröpper, Robert; Le Van Quyen, Michel; Geisel, Theo; Triesch, Jochen; Nikolić, Danko; Munk, Matthias H. J.

2014-01-01

In self-organized critical (SOC) systems avalanche size distributions follow power-laws. Power-laws have also been observed for neural activity, and so it has been proposed that SOC underlies brain organization as well. Surprisingly, for spiking activity in vivo, evidence for SOC is still lacking. Therefore, we analyzed highly parallel spike recordings from awake rats and monkeys, anesthetized cats, and also local field potentials from humans. We compared these to spiking activity from two established critical models: the Bak-Tang-Wiesenfeld model, and a stochastic branching model. We found fundamental differences between the neural and the model activity. These differences could be overcome for both models through a combination of three modifications: (1) subsampling, (2) increasing the input to the model (this way eliminating the separation of time scales, which is fundamental to SOC and its avalanche definition), and (3) making the model slightly sub-critical. The match between the neural activity and the modified models held not only for the classical avalanche size distributions and estimated branching parameters, but also for two novel measures (mean avalanche size, and frequency of single spikes), and for the dependence of all these measures on the temporal bin size. Our results suggest that neural activity in vivo shows a mélange of avalanches, and not temporally separated ones, and that their global activity propagation can be approximated by the principle that one spike on average triggers a little less than one spike in the next step. This implies that neural activity does not reflect a SOC state but a slightly sub-critical regime without a separation of time scales. Potential advantages of this regime may be faster information processing, and a safety margin from super-criticality, which has been linked to epilepsy. PMID:25009473

Subcritical-Water Extraction of Organics from Solid Matrices

NASA Technical Reports Server (NTRS)

Amashukeli, Xenia; Grunthaner, Frank; Patrick, Steven; Kirby, James; Bickler, Donald; Willis, Peter; Pelletier, Christine; Bryson, Charles

2009-01-01

An apparatus for extracting organic compounds from soils, sands, and other solid matrix materials utilizes water at subcritical temperature and pressure as a solvent. The apparatus, called subcritical water extractor (SCWE), is a prototype of subsystems of future instrumentation systems to be used in searching for organic compounds as signs of past or present life on Mars. An aqueous solution generated by an apparatus like this one can be analyzed by any of a variety of established chromatographic or spectroscopic means to detect the dissolved organic compound( s). The apparatus can be used on Earth: indeed, in proof-of-concept experiments, SCWE was used to extract amino acids from soils of the Atacama Desert (Chile), which was chosen because the dryness and other relevant soil conditions there approximate those on Mars. The design of the apparatus is based partly on the fact that the relative permittivity (also known as the dielectric constant) of liquid water varies with temperature and pressure. At a temperature of 30 C and a pressure of 0.1 MPa, the relative permittivity of water is 79.6, due to the strong dipole-dipole electrostatic interactions between individual molecular dipoles. As the temperature increases, increasing thermal energy causes increasing disorientation of molecular dipoles, with a consequent decrease in relative permittivity. For example, water at a temperature of 325 C and pressure of 20 MPa has a relative permittivity of 17.5, which is similar to the relative permittivities of such nonpolar organic solvents as 1-butanol (17.8). In the operation of this apparatus, the temperature and pressure of water are adjusted so that the water can be used in place of commonly used organic solvents to extract compounds that have dissimilar physical and chemical properties.

Loss of stability of a railway wheel-set, subcritical or supercritical

NASA Astrophysics Data System (ADS)

Zhang, Tingting; Dai, Huanyun

2017-11-01

Most researches on railway vehicle stability analysis are focused on the codimension 1 (for short, codim 1) bifurcations like subcritical and supercritical Hopf bifurcation. The analysis of codim 1 bifurcation can be completed based on one bifurcation parameter. However, two bifurcation parameters should be considered to give a general view of the motion of the system when it undergoes a degenerate Hopf bifurcation. This kind of bifurcation named the generalised Hopf bifurcation belongs to the codimension 2 (for short, codim 2) bifurcations where two bifurcation parameters need to be taken into consideration. In this paper, we give a numerical analysis of the codim 2 bifurcations of a nonlinear railway wheel-set with the QR algorithm to calculate the eigenvalues of the linearised system incorporating the Golden Cut method and the shooting method to calculate the limit cycles around the Hopf bifurcation points. Here, we found the existence of a generalised Hopf bifurcation where a subcritical Hopf bifurcation turns into a supercritical one with the increase of the bifurcation parameters, which belong to the codim 2 bifurcations, in a nonlinear railway wheel-set model. Only the nonlinear wheel/rail interactive relationship has been taken into consideration in the lateral model that is formulated in this paper. The motion of the wheel-set has been investigated when the bifurcation parameters are perturbed in the neighbourhood of their critical parameters, and the influences of different parameters on critical values of the bifurcation parameters are also given. From the results, it can be seen that the bifurcation types of the wheel-set will change with a variation of the bifurcation parameters in the neighbourhood of their critical values.

Efficient stabilization and acceleration of numerical simulation of fluid flows by residual recombination

NASA Astrophysics Data System (ADS)

Citro, V.; Luchini, P.; Giannetti, F.; Auteri, F.

2017-09-01

The study of the stability of a dynamical system described by a set of partial differential equations (PDEs) requires the computation of unstable states as the control parameter exceeds its critical threshold. Unfortunately, the discretization of the governing equations, especially for fluid dynamic applications, often leads to very large discrete systems. As a consequence, matrix based methods, like for example the Newton-Raphson algorithm coupled with a direct inversion of the Jacobian matrix, lead to computational costs too large in terms of both memory and execution time. We present a novel iterative algorithm, inspired by Krylov-subspace methods, which is able to compute unstable steady states and/or accelerate the convergence to stable configurations. Our new algorithm is based on the minimization of the residual norm at each iteration step with a projection basis updated at each iteration rather than at periodic restarts like in the classical GMRES method. The algorithm is able to stabilize any dynamical system without increasing the computational time of the original numerical procedure used to solve the governing equations. Moreover, it can be easily inserted into a pre-existing relaxation (integration) procedure with a call to a single black-box subroutine. The procedure is discussed for problems of different sizes, ranging from a small two-dimensional system to a large three-dimensional problem involving the Navier-Stokes equations. We show that the proposed algorithm is able to improve the convergence of existing iterative schemes. In particular, the procedure is applied to the subcritical flow inside a lid-driven cavity. We also discuss the application of Boostconv to compute the unstable steady flow past a fixed circular cylinder (2D) and boundary-layer flow over a hemispherical roughness element (3D) for supercritical values of the Reynolds number. We show that Boostconv can be used effectively with any spatial discretization, be it a finite-difference, finite-volume, finite-element or spectral method.

10 CFR 810.3 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-01-01

... of neutrons used to effect SNM production in the “subcritical assembly.” Agreement for cooperation... International Atomic Energy Agency. Non-nuclear-weapon state is a country not recognized as a nuclear-weapon...-Proliferation of Nuclear Weapons. Nuclear reactor means an apparatus, other than a nuclear explosive device...

10 CFR 810.3 - Definitions.

Code of Federal Regulations, 2013 CFR

2013-01-01

... of neutrons used to effect SNM production in the “subcritical assembly.” Agreement for cooperation... International Atomic Energy Agency. Non-nuclear-weapon state is a country not recognized as a nuclear-weapon...-Proliferation of Nuclear Weapons. Nuclear reactor means an apparatus, other than a nuclear explosive device...

Model-based adaptive sliding mode control of the subcritical boiler-turbine system with uncertainties.

PubMed

Tian, Zhen; Yuan, Jingqi; Xu, Liang; Zhang, Xiang; Wang, Jingcheng

2018-05-25

As higher requirements are proposed for the load regulation and efficiency enhancement, the control performance of boiler-turbine systems has become much more important. In this paper, a novel robust control approach is proposed to improve the coordinated control performance for subcritical boiler-turbine units. To capture the key features of the boiler-turbine system, a nonlinear control-oriented model is established and validated with the history operation data of a 300 MW unit. To achieve system linearization and decoupling, an adaptive feedback linearization strategy is proposed, which could asymptotically eliminate the linearization error caused by the model uncertainties. Based on the linearized boiler-turbine system, a second-order sliding mode controller is designed with the super-twisting algorithm. Moreover, the closed-loop system is proved robustly stable with respect to uncertainties and disturbances. Simulation results are presented to illustrate the effectiveness of the proposed control scheme, which achieves excellent tracking performance, strong robustness and chattering reduction. Copyright © 2018. Published by Elsevier Ltd.

Catalytic upgrading of duckweed biocrude in subcritical water.

PubMed

Zhang, Caicai; Duan, Peigao; Xu, Yuping; Wang, Bing; Wang, Feng; Zhang, Lei

2014-08-01

Herein, a duckweed biocrude produced from the hydrothermal liquefaction of Lemna minor was treated in subcritical water with added H₂. Effects of several different commercially available materials such as Ru/C, Pd/C, Pt/C, Pt/γ-Al₂O₃, Pt/C-sulfide, Rh/γ-Al₂O₃, activated carbon, MoS₂, Mo₂C, Co-Mo/γ-Al₂O₃, and zeolite on the yields of product fractions and the deoxygenation, denitrogenation, and desulfurization of biocrude at 350°C were examined, respectively. All the materials showed catalytic activity for deoxygenation and desulfurization of the biocrude and only Ru/C showed activity for denitrogenation. Of those catalysts examined, Pt/C showed the best performance for deoxygenation. Among all the upgraded oils, the oil produced with Ru/C shows the lowest sulfur, the highest hydrocarbon content (25.6%), the highest energy recovery (85.5%), and the highest higher heating value (42.6 MJ/kg). The gaseous products were mainly unreacted H₂, CH₄, CO₂, and C₂H6. Copyright © 2014 Elsevier Ltd. All rights reserved.

Status of intense permanent magnet proton source for China-accelerator driven sub-critical system Linac.

PubMed

Wu, Q; Ma, H Y; Yang, Y; Sun, L T; Zhang, X Z; Zhang, Z M; Zhao, H Y; He, Y; Zhao, H W

2016-02-01

Two compact intense 2.45 GHz permanent magnet proton sources and their corresponding low energy beam transport (LEBT) system were developed successfully for China accelerator driven sub-critical system in 2014. Both the proton sources operate at 35 kV potential. The beams extracted from the ion source are transported by the LEBT, which is composed of two identical solenoids, to the 2.1 MeV Radio-Frequency Quadrupole (RFQ). In order to ensure the safety of the superconducting cavities during commissioning, an electrostatic-chopper has been designed and installed in the LEBT line that can chop the continuous wave beam into a pulsed one. The minimum width of the pulse is less than 10 μs and the fall/rise time of the chopper is about 20 ns. The performance of the proton source and the LEBT, such as beam current, beam profile, emittance and the impact to RFQ injection will be presented.

Status of intense permanent magnet proton source for China-accelerator driven sub-critical system Linac

NASA Astrophysics Data System (ADS)

Wu, Q.; Ma, H. Y.; Yang, Y.; Sun, L. T.; Zhang, X. Z.; Zhang, Z. M.; Zhao, H. Y.; He, Y.; Zhao, H. W.

2016-02-01

Two compact intense 2.45 GHz permanent magnet proton sources and their corresponding low energy beam transport (LEBT) system were developed successfully for China accelerator driven sub-critical system in 2014. Both the proton sources operate at 35 kV potential. The beams extracted from the ion source are transported by the LEBT, which is composed of two identical solenoids, to the 2.1 MeV Radio-Frequency Quadrupole (RFQ). In order to ensure the safety of the superconducting cavities during commissioning, an electrostatic-chopper has been designed and installed in the LEBT line that can chop the continuous wave beam into a pulsed one. The minimum width of the pulse is less than 10 μs and the fall/rise time of the chopper is about 20 ns. The performance of the proton source and the LEBT, such as beam current, beam profile, emittance and the impact to RFQ injection will be presented.

Comparison of Performance and Oxidation of Nitronic-50 and Stainless Steel 316 in Subcritical and Supercritical Water Environments

NASA Astrophysics Data System (ADS)

Karmiol, Zachary; Chidambaram, Dev

2016-05-01

This work investigates two austenitic stainless steels, Nitronic-50 and stainless steel 316, for use in both subcritical and supercritical water (SCW) conditions. The mechanical characteristics of the materials were investigated using slow strain rate testing in a SCW test loop under the following conditions: nitrogen at ambient temperature and pressure, liquid water at 473 K (200 °C) and 8 MPa, liquid water at 573 K (300 °C) and 15 MPa, and SCW at 698 K (425 °C) and 27 MPa. The surfaces of the failed samples were characterized using Raman spectroscopy, and X-ray photoelectron spectroscopy. Nitronic-50 was found to have superior mechanical strength characteristics at all conditions compared to stainless steel 316. At all elevated temperature conditions, stainless steel 316 was found to have a surface film consisting of iron oxides, while the surface film of Nitronic-50 predominantly consisted of nickel-iron spinel.

Critical thresholds in sea lice epidemics: evidence, sensitivity and subcritical estimation

PubMed Central

Frazer, L. Neil; Morton, Alexandra; Krkošek, Martin

2012-01-01

Host density thresholds are a fundamental component of the population dynamics of pathogens, but empirical evidence and estimates are lacking. We studied host density thresholds in the dynamics of ectoparasitic sea lice (Lepeophtheirus salmonis) on salmon farms. Empirical examples include a 1994 epidemic in Atlantic Canada and a 2001 epidemic in Pacific Canada. A mathematical model suggests dynamics of lice are governed by a stable endemic equilibrium until the critical host density threshold drops owing to environmental change, or is exceeded by stocking, causing epidemics that require rapid harvest or treatment. Sensitivity analysis of the critical threshold suggests variation in dependence on biotic parameters and high sensitivity to temperature and salinity. We provide a method for estimating the critical threshold from parasite abundances at subcritical host densities and estimate the critical threshold and transmission coefficient for the two epidemics. Host density thresholds may be a fundamental component of disease dynamics in coastal seas where salmon farming occurs. PMID:22217721

Improved design of subcritical and supercritical cascades using complex characteristics and boundary layer correction

NASA Technical Reports Server (NTRS)

Sanz, J. M.

1983-01-01

The method of complex characteristics and hodograph transformation for the design of shockless airfoils was extended to design supercritical cascades with high solidities and large inlet angles. This capability was achieved by introducing a conformal mapping of the hodograph domain onto an ellipse and expanding the solution in terms of Tchebycheff polynomials. A computer code was developd based on this idea. A number of airfoils designed with the code are presented. Various supercritical and subcritical compressor, turbine and propeller sections are shown. The lag-entrainment method for the calculation of a turbulent boundary layer was incorporated to the inviscid design code. The results of this calculation are shown for the airfoils described. The elliptic conformal transformation developed to map the hodograph domain onto an ellipse can be used to generate a conformal grid in the physical domain of a cascade of airfoils with open trailing edges with a single transformation. A grid generated with this transformation is shown for the Korn airfoil.

Optimization of a mirror-based neutron source using differential evolution algorithm

NASA Astrophysics Data System (ADS)

Yurov, D. V.; Prikhodko, V. V.

2016-12-01

This study is dedicated to the assessment of capabilities of gas-dynamic trap (GDT) and gas-dynamic multiple-mirror trap (GDMT) as potential neutron sources for subcritical hybrids. In mathematical terms the problem of the study has been formulated as determining the global maximum of fusion gain (Q pl), the latter represented as a function of trap parameters. A differential evolution method has been applied to perform the search. Considered in all calculations has been a configuration of the neutron source with 20 m long distance between the mirrors and 100 MW heating power. It is important to mention that the numerical study has also taken into account a number of constraints on plasma characteristics so as to provide physical credibility of searched-for trap configurations. According to the results obtained the traps considered have demonstrated fusion gain up to 0.2, depending on the constraints applied. This enables them to be used either as neutron sources within subcritical reactors for minor actinides incineration or as material-testing facilities.

Molecular modification of native coffee polysaccharide using subcritical water treatment: Structural characterization, antioxidant, and DNA protecting activities.

PubMed

Getachew, Adane Tilahun; Chun, Byung Soo

2017-06-01

Polysaccharides are an abundant resource in coffee beans and have proved to show numerous bioactivities. Despite their abundance, their activities are not always satisfactory mostly due to their structure and large molecular size. Molecular modifications of native polysaccharides can overcome this problem. In this study, we used a novel and green method to modify native coffee polysaccharides using subcritical water (SCW) treatment. The SCW treatment was used at the temperature of 180°C-220°C and pressure of 30-60bar. The molecular and structural modification of the polysaccharides was confirmed using several techniques such as FT-IR, UV spectroscopy, XRD, and TGA. The antioxidant activity of the modified polysaccharides was evaluated using several chemical and Saccharomyces cerevisiae-based high throughput assays. The modified polysaccharides showed high antioxidant activities in all tested assays. Moreover, the polysaccharides showed high DNA protection activities. Therefore, SCW could be employed as a green solvent for molecular modification of polysaccharides. Copyright © 2017 Elsevier B.V. All rights reserved.

Materials Testing for an Accelerator-Driven Subcritical Molten Salt Fission System: A look at the Materials Science of Molten Salt Corrosion

NASA Astrophysics Data System (ADS)

Sooby, Elizabeth; Balachandran, Shreyas; Foley, David; Hartwig, Karl; McIntyre, Peter; Phongikaroon, Supathorn; Pogue, Nathaniel; Simpson, Michael; Tripathy, Prabhat

2011-10-01

For an accelerator-driven subcritical molten salt fission core to survive its 50+ year fuel life, the primary vessel, heat exchanger, and various internal components must be made of materials that resist corrosion and radiation damage in a high-temperature environment, (500-800 C). An experimental study of the corrosion behavior of candidate metals in contact with molten salt is being conducted at the Center for Advanced Energy Studies. Initial experiments have been run on Nb, Ta, Ni, two zirconium alloys, Hastelloy-N, and a series of steel alloys to form a base line for corrosion in both chloride and bromide salt. Metal coupons were immersed in LiCl-KCl or LiBr-KBr at 700 C in an inert-atmosphere. Salt samples were extracted on a time schedule over a 24-hr period. The samples were analyzed using inductively coupled plasma-mass spectrometry to determine concentrations of metals from corrosion. Preliminary results will be presented.